Split (2)

train · 33.5k rows

patent_number stringlengths 0 9	section stringclasses 4 values	raw_text stringlengths 0 954k
047730870	description	DETAILED DESCRIPTION Referring to the schematic diagram of FIG. 1, an x-ray beam 10 comes from a source which comprises an x-ray tube 12 powered by a grid tank 14. Beam 10 is initially cone-shaped or pyramid-shaped, but is collimated to a scanning beam 16 by a pre-patient collimator (fore collimator) 18 to scan a patient 20 in raster fashion. A post-patient collimator (aft collimator) 22 sweeps the patient in synchrony with the pre-patient collimator such that scanning beam 16 scans a film cassette 24 (or some other receptor) in a raster of overlapping scan lines. A post-patient detector 26 receives radiation which has passed through receptor 24, and its output is used by microcomputer 28 to control grid tank 14 through interface 30 such that scanning beam 16 is modulated in a desired manner to achieve a desired result, for example in terms of image quality, SN ratio and/or patient dosage. Referring to the partial view of FIG. 2, a rotating wheel collimator 17 is between x-ray source 12 and pre-patient (fore) collimator 18 to collimate the cone- (or pyramid-) shaped x-ray beam 10 from source 12 into a fan 11, which in turn is collimated by the linear slit of collimator 18 into raster scanning beam 16 which can be, as a nonlimiting example, of a rectangular section of about 3.5.times.3.5 cm at the plane of receptor 24. Post-receptor detector 26, used in the feedback loop, can move with scanning beam 16, both along the raster lines and from raster line to raster line (as in FIG. 1), or it can be as long as a raster line so that it only need move from raster line to raster line with scanning beam 16 (as in FIG. 2). In the type of an x-ray system illustrated in FIGS. 1 and 2, scanning beam 16 can be modulated by dynamically varying its velocity along a scan line (velocity modulation) or by pulsing it at a selected frequency and at selected pulse widths (pulse width modulation or PWM) or by dynamically modulating its intensity and/or hardness or by dynamically modulating its shape (e.g., cross-section) or by a combination of subcombination of the foregoing types of modulation. Some of those types of modulation are discussed in greater details in the publications authored or co-authored by Dr. Plewes, cited earlier and incorporated by reference. In accordance with one nonlimiting aspect of the invention, scanning beam 16 is modulated on the basis of post-patient measurements of both primary and scattered radiation through the use of a feedback loop to reduce variations in signal-to-noise ratio in the image. Referring to FIG. 3, the patient (not shown) is between pre-patient collimator assembly 32 and scanning image intensifier 34, and is scanned in a raster pattern of overlapping lines (actually strips) with scanning beam 16. Collimator assembly 32 comprises a rotating wheel collimator 17 and linear slit collimator 18. The entire unit comprised of x-ray tube 12, wheel 17 and collimator 18 rotates about axis 36 to move scanning beam 16 from one raster line to another. Scanning image intensifier 34 receives the post-patient part of scanning beam 16 and supplies some brightness gain relative to an unintensified phosphor, so as to preserve a large number of detected optical photons per absorbed x-ray photon after focusing through an optical system. In operation, x-ray beam 16 is scanned across the patient in overlapping raster lines and image intensifier 34 is scanned (moved relative to the patient) in synchronism, only in the direction transverse to the raster lines. During the scan, a video camera 38 views the portion of image intensifier 34 illuminated by scanning x-ray beam 16 through an objective lens 40 and a light amplifier 42. Camera 38 integrates the image on the photocathode of its video tube, which can be a Plumbicon. After the scan is complete, the charge pattern on the video tube photocathode can be read out in a slow scan, progressive mode to allow a spatial resolution of, e.g., 1024.times.1024 pixels. Referring to the detailed view of FIG. 4, where the components corresponding to those shown in FIG. 3 bear the same reference numerals, the output of image intensifier 34 appears on mirror 44 as a path 46 of the scanning beam, and is viewed through objective lens 40 and light amplifier 42. A beam splitter 46 sends a part to camera 38 and a part to a bi-directionally gimbaled mirror 50 through a lens 48. Mirror 50 sends the optical image to a second beam splitter 52, which splits it into a part directed to a photomultiplier tube D1 and a part directed to a photomultiplier tube D2. Apertures 54 and 56 placed in front of photomultiplier tubes D1 and D2, respectively, are used to select respective portions of the scanning beam. The aperture for detector D1 is set to include measurements only over the area of scanning x-ray beam 16, to serve as an approximate measure of primary post-patient radiation, but the aperture for detector D2 is positioned to detect radiation reaching image intensifier 34 slightly off-axis of scanning x-ray beam 16, to serve as an approximate measure of scattered post-patient radiation. Thus, the two photomultipliers D1 and D2 provide a simultaneous indication of post-patient primary radiation as well as post-patient scattered radiation. Gimbaled mirror 50, splitter 52 and photomultipliers D1 and D2 and their apertures, move in synchronism with the path 46 of scanning beam 16 on mirror 44. The geometry of the scanning apparatus illustrated in FIGS. 3 and 4 is such that the presence of scattered radiation is low relative to that of conventional chest radiography, and can result in a scatter/primary ratio of 0.6 for a 2 cm.sup.2 cross-section of scanning beam 16 with an absorber thickness of 20 cm. While this scatter contamination is not large, it still can reduce the detectability of low contrast details. In addition, the presence of optical scattering can add to x-ray scatter to degrade system contrast. This scatter represents a nonlinear contribution to projection data which can limit the use of some numerical processing techniques of interest to chest radiography. A point in case is the example of dual energy radiography, in which it is particularly desirable to avoid such nonlinear effects. The presence of scattered radiation in conventional imaging is known to degrade image contrast, and also is known to play a role in reducing the image signal/noise ratio. It is believed that the image signal/noise ratio for low contrast objects in the presence of scattered radiation can be approximated by: EQU S/N=[N.sub.0 ATn/(1+R)].sup.1/2 (1) where N.sub.0 is the incident photon fluence, T is the patient transmission, A is the pixel size, n is the detector quantum efficiency and R is the ratio of scattered to primary photons in the image. It should be noted that the scatter contribution a point in the image is the result of the total scatter over the image from all locations of the scanning beam. If a narrow scanning beam is used, scatter can be said to result from different positions of that beam along respective scan lines. Typically, the scatter field is a smooth, slowly varying distribution over the image field, so that scatter from different positions of the scanning beam along a given scan line tends to be roughly constant. Thus, the scatter measurement made by detector D2 for a given point in the image will tend to be approximately proportional to the scatter that would be contributed to that point from the other positions of the beam along that scan line. To get a measure of the scatter/primary ratio, the measurement from detector D2 should be normalized by that from detector D1. The result will only approximate the scatter/primary ratio, and can be scaled and calibrated to become a more accurate representation of the true scatter/primary ratio. Relationship (1) above indicates that the signal/noise ratio is related to patient transmission such that in a scatter-free situation beam equalization would operate to keep the signal/noise ratio approximately constant throughout the image. However, in the presence of scatter, equalization on the basis of patient transmission alone would not ensure a constant image signal/noise ratio. Accordingly, in accordance with this aspect of the invention, a post-patient scattered radiation measurement corresponding to R is used in the feedback characteristics of the system. In practical terms, variations in T typically are much larger than the variations in R. However, the equalization technique in accordance with this aspect of the invention allows the noise degrading effects of scatter to be reduced or eliminated by considering the value R in system feedback. Thus, by the independent measurements of approximate scatter contribution and the scatter plus primary contribution attainable from detectors D1 and D2 in FIG. 4, it is possible in accordance with this aspect of the invention to calculate a value of R during the course of the scan and to use this value in a modified feedback relation. This is illustrated schematically in FIG. 3, where the outputs of exposure detectors D1 and D2 are supplied to x-ray tube control feedback device 58 which in turn controls x-ray tube 12 to vary N.sub.0 (the incident photon fluence) in such a manner that the quantity S/N in equation (1) above remains substantially constant. In practice this can be implemented by a digital or an analog circuit arranged to derive the control signals needed to adjust N.sub.0 in a manner which will maintain S/N constant in the relationship described by equation (1) above. The effect of this is to modulate scanning x-ray beam 16 through a feedback loop on the basis of post-patient measurements of primary and scattered radiation to reduce variations in signal-to-noise ratio in the image. This modulation is dynamic, as it is done on the fly during the raster scan movement of scanning x-ray beam 16. In another aspect of the invention, the scatter measurements from detector D2, which looks only at the scatter measurement area shown in FIG. 4 below the scanning X-ray beam, can be used to generate an approximate scatter map, which can later be subtracted from the x-ray image, for example by using subtraction techniques such as used in digital subtraction radiography. This can give a good approximation of the correction needed to account for the nonlinear effect of scatter, although the noise due to scatter would still be present. If detector D2 looks only at the scatter measurement area below the scanning x-ray beam, as illustrated in FIG. 4, the gimbaled mirror arrangement is required only to scan the aperture for detector D2 in the scow scanning direction, i.e., from one scan line to another. As an alternative to using the scatter measurement area which is below the x-ray beam, the alternate scatter measurement areas which are in line with the x-ray beam can be used, as also illustrated in Fig. 4. In this case, the gimbaled mirror would need to track the fast motion of the x-ray beam along a scan line as well as the slow motion from one scan line to another. In this alternative, the aperture for detector D2 makes it look only at the illustrated alternate scatter measurement areas. Another aspect of the invention pertains to simulataneously and dynamically modulating the scanning x-ray beam in terms of both intensity and hardness to improve image quality. This can be done on the basis of intermittent post-patient beam measurements made at select positions of the beam relative to the patient and at a selected low beam intensity. For example, a very short pulse of low energy radiation and a very short pulse of high energy radiation can be used at each select position of scanning x-ray beam 16, the attenuation along the beam for that beam position can be found and then the best combination of intensity and spectrum for that beam position can be calculated and the x-ray tube can be energized accordingly. The choice of an optimum beam spectrum for a given beam position is dependent on the interplay of patient dose, scatter contamination, tissue thickness and the resultant subject contrast. In considering chest radiography in particular, conflicting conditions influence this choice. In principle, it is desirable to maintain as low a beam energy as permissible by patient dose over the thinner portions of the lung, where soft tissue pulmonary markings are present, and thereby increase their subject contrast. However, the structures of interest in the mediastinum are mainly bony detail of the spine, which is intrinsically a high subject contrast structure, so that a low energy beam is not necessary. Furthermore, the thicker areas of the mediastinum would be better served with a more penetrating beam of radiation, since the dose for adequate exposure at low energies would be prohibitively large. The choice of optimum spectrum is further complicated by the presence of ribs over the thin lung field. While using a low kilovoltage beam over the lung zone can increase soft tissue subject contrast, it will also increase rib contrast to an even greater extent because of its thin atomic number. Thus, the net effect is that while soft tissue contrast can be improved, the greater attenuation from the ribs may degrade the visualization of soft tissue structures that are projected behind these ribs. Thus, because of the variation in structure thickness and atomic number, the optimum choice of beam energy for chest radiography is at best a compromise. These considerations, plus a desire to maintain visualization through the thicker body portions, have resulted in conventional chest radiography being routinely done at moderately high (120-140 KVP) kilovoltages in spite of the loss of subject contrast for soft tissue. It is possible in accordance with the invention to vary the beam intensity and kilovoltage continuously over the anatomy to maintain an optimum beam kilovoltage and exposure for maximum soft tissue contrast throughout the entire anatomy. A relatively simple implementation can be to monitor post-patient radiation for each selected position of the scanning x-ray beam as a clue to the structure being imaged. This parameter can then be used to modulate beam kilovoltage in a predetermined fashion. Film intensity equalization, e.g., by the use of pulse width modulation as described in the papers cited earlier, can be done simultaneously to ensure maximum film contrast. This requires that for each x-ray pulse the duration and kilovoltage need to be controllable. A reasonable relation between patient transmission and kilovoltage is to use a low kilovoltage over the lung fields and continuously shift to a higher kilovoltage over the thicker body parts. By this means, both the intensity and kilovoltage of the scanning x-ray beam can be modulated over the patient to avoid the kilovoltage compromises that currently limit conventional chest radiography and increase soft tissue contrast beyond that of simple intensity-modulated techniques. By changing beam kilovoltage over the anatomy as just described, significant improvements in soft tissue contrast can be obtained. However, this relatively simple implementation of variable kilovoltage can show degraded contrast due to rib shadowing for reduced kilovoltage over the lung fields. In this method the ribs will be represented as local areas of moderately decreased transmission and will not be handled any differently from any other structural variation. However, if knowledge of the location of the ribs were available, the beam kilovoltage can be locally increased over the area of the ribs to avoid the undesirable consequences of rib shadowing. One approach to this problem in accordance with the invention is to use a two-scan approach: a pre-scan immediately followed by a second scan forming the desired image. The first scan obtains a low resolution transmission distribution of the patient. This can be done using very short pulses of radiation (e.g., 25 microseconds per pulse) that would not contribute significantly to patient dose and are inadequate to expose the film or other receptor. This transmission map can then be used to determine the position of the major structures such as the mediastinum, abdomen, heart and lung contours. In addition, using edge detection methods the positions of the ribs in the lung zones can be located. This information can then be used in the second, immediately following scan of the patient, which exposes the film or other receptor. Of course, the delay between the first and second scans, although of only a few seconds, can lead to registration problems because of patient movement. Accordingly, in accordance with another feature of the invention, these registration problems are reduced or eliminated by a dual energy method to locate the ribs in the lung field. In accordance with this aspect of the invention, two short pre-exposure pulses of widely different kilovoltage (e.g. 120 and 80 KVP) are used, followed by a longer pulse of a duration which exposes the receptor for that position of the scanning x-ray beam. The pre-exposure pulses are short enough to give only negligible receptor exposure, and are used to determine the projected density of bone and tissue, using dual energy algorithms similar to those discussed by Alvarez and Rutherford for dual energy CT and Brody for dual energy chest radiography applications using the techniques referred to in the earlier-cited literature. The kilovoltage for the imaging pulse can then be determined from the pre-exposure pulses while the duration of the imaging pulse (i.e., the integrated beam intensity) can be determined to equalize image density. By this dual energy means, the amount of bone at each selected position of the scanning x-ray beam can be measured during the scan, and a predetermined lookup table adjustments of beam kilovoltage can be made to minimize rib shadowing artifacts directly. Referring to FIGS. 5 and 6, at each selected position of scanning x-ray beam 16 along the raster scan lines, the x-ray tube is energized for a short, low energy pulse 60, immediately followed by a similarly short but higher energy pulse 62, follwed by an exposure pulse 64 of a variable duration determined as discussed in said articles authored or co-authored by Dr. Plewes, for uniform receptor exposure. The kilovoltage of exposure pulse 64 is determined on the basis of a continuous relation such as illustrated in FIG. 6, which shows the lines of constant kilovoltage of x-ray tube 12 as a function of bone and tissue density. Such a relation continuously raises the x-ray tube potential over areas of either large tissue thickness or lung rib areas and shift toward lower kilovoltages in regions of lung field where little bone is present. By the choice of this function the rate at which the tube kilovoltage is raised is a function of bone and tissue density is programmable. To accomplish independent control of the x-ray tube kilovoltage, a tetrode switching apparatus can be fitted to an x-ray tube high voltage generator. This device is a pair of voltage regulators for the cathode and anode lines in the secondary line of the x-ray generator high voltage transformer, and allows precise kilovoltage control. The same device is capable of switching the x-ray beam on and off as can alternately be accomplished with grid control. The tetrode switching apparatus thus can allow for simultaneous and dynamic pulse width and beam kilovoltage modulation of the scanning x-ray beam. A particular tetrode switch can control the tube kilovoltage between 50 and 140 KVP and pulse the x-ray beam at frequencies of up to in excess of 2,000 Hz. In the systems illustrated in FIGS. 2 and 3 the rotating wheel collimator 17 has apertures in the form of straight radial slits which, in combination with the aperture in the form of a linear slit in pre-patient collimator 18, scan x-ray beam 16 along successive, overlapping scan lines. In this geometry the scanning velocity of x-ray beam 16 along the receptor is not constant; the velocity decreases slowly from the extreme end of a scan line toward its center and then increases toward the other extremity of the scan line. This variation in velocity must be accounted for in modulating the scanning x-ray beam. In order to avoid increasing the complexity of the modulating technique because of such velocity variation, a linearly scanning aperture can be used, or the entire x-ray tube can be scanned with respect to the patient. This, however, introduces mechanical complications. Velocity variations can also be decreased by the use of a large wheel collimator with a relatively large number of aperture slots. This again introduces mechanical complications. In accordance with another aspect of the invention, the velocity of the scanning x-ray beam along a scan line is kept substantially constant through the use of a novel wheel collimator which is small in diameter and uses a uniquely curved aperture slit. As illustrated in FIG. 7, if a rotating wheel collimator 17 with a straight radial slit is used, for a fixed rotation rate the horizontal scanning x-ray beam velocity will be variable since the radius of the collimator slit projecting the beam increases as it moves toward the scan line limits. Thus, the velocity increases toward the scan line ends P1 and P3. However, when the wheel slit is curved as shown in FIG. 7, and restricts the scan line to be between P2 and P3, the curved slit causes the horizontal position of the scanning x-ray beam to fall progressively behind the corresponding position of the radial slit, thereby reducing the scanning x-ray beam velocity toward the point P3. A rotating wheel collimator 17 with a single spiral slit can scan the x-ray beam over a scan line in a single rotation. This spirally curved slit is shown in FIG. 8 at four different 90.degree. intervals as it intersects the pre-patient collimator 18. As the wheel collimator moves through successive 90.degree. increments, its intersection with the linear slit in collimator 18 moves the x-ray beam through constant linear intervals, indicating its constant velocity. FIG. 9 is another illustration of a rotating wheel collimator 17 with a spiral aperture slit 17a superimposed on the linear slit 18a of pre-patient collimator 18. FIG. 10 illustrates a variation, in which two counter rotating collimator wheels 17 having curved aperture slits 17a are used to scan x-ray beam 16 with respect to the linear aperture 18a of the pre-patient collimator. It should be noted that similar combinations of rotating wheel collimators with curved aperture slits and collimators with fixed linear slits can be used between the patient and the film or x-ray detector but, of course, would have to be proportionately larger in size than the pre-patient collimators, and would have to be synchronized with the pre-patient collimators so that the x-ray beam 16 passes through aligned apertures in the pre-patient and post-patient collimators before reaching the receptor. In the embodiments discussed above, a single scanning beam 16 is used to scan the patient in overlapping scan lines. This can expose the receptor for a typical chest x-ray in about 3-5 seconds, during which time some motion artifacts may become apparent. In order to reduce exposure time, a fan beam divided into a number of segments can be used, each segment in effect scanning its own scan line, and with a number of scan lines scanned simultaneously. This is illustrated in Fig. 11, where a number of segments, each represented by a respective square, scan along respective horizontal scan lines indicated by respective arrows. If velocity modulation is used, then each segment can be considered an individual scanning beam and can be individually velocity modulated, in the manner discussed for velocity modulation of single beam systems in said publications. If the pre-patient collimators producing the individually scanned segments of the fan beam are placed close to the x-ray focal spot, then their exposure profiles on the film or image intensifier will be blurred or overlapped, as illustrated in FIG. 12. If the segments are moving at the same speed across the patient, and the adjacent apertures for the segments are such that their edges are collinear, then the blur of adjacent scan lines will combine to produce a substantially uniform exposure, as illustrated in FIG. 12. However, if the beams are moving at different scan line velocities, then the receptor exposure from each scan line will differ, and the transition between adjacent scan lines will be rendered as a smooth gradation, as illustrated in FIG. 13. A conventional scatter rejection grid can be used in place of a rotating post-patient collimator in the system discussed in connection with FIGS. 11-13. If a fan beam is divided into three segments, in an exemplary test system, three pre-patient scanning apertures can be used, moved by small linear stepper motors. Each stepper motor is controlled for velocity modulation of the respective segment in the manner discussed for single beam systems in said prior publications authored or co-authored by Dr. Plewes. As an alternative to velocity modulation, simple attenuation of the respective beam segments can be used. Respective servomechanism can move respective wedge-shaped attenuators into and out of the respective segments of the fan beam to modulate the transmission through the wedge in a feedback scheme of the type discussed above for the case of a single scanning beam. As yet another alternative, the segments of the fan can be subjected to individual beam width modulation in a feedback arrangement of the type discussed above in the case of using a single scanning beam. For this, the cross-sectional shape and size of each segment of the fan beam can be individually modulated as the segment sweeps across the patient and receptor, in a feedback arrangement such that the segment becomes narrower (its cross-sectional area is less) over thin sections such as the lungs and wider (greater cross-sectional area) over thicker sections such as bone. The segments thus move at the same speed and side-by-side. The beam width modulation can be implemented, as earlier discussed, by individual shutters for the respective segments, which open more or less as the segment scans the patient, in a feedback arrangement using measurements of post-patient radiation in the manner earlier discussed. As yet another alternative, pulse width modulation can be used for the respective segments of the fan beam, in the manner discussed earlier for a single beam. In the feedback arrangements for the segments of the fan beam, it can be desirable to use a respective detector, or a respective pair of detectors, for each respective segments, in the manner detector 26 is used in FIG. 1 or detectors D1 and D2 are used in FIG. 4.
	description	The present application is related to and claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Related Applications”) (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Related Application(s)). All subject matter of the Related Applications and of any and all parent, grandparent, great-grandparent, etc. applications of the Related Applications is incorporated herein by reference to the extent such subject matter is not inconsistent herewith. For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of U.S. patent application Ser. No. 12/590,448, entitled METHODS AND SYSTEMS FOR MIGRATING FUEL ASSEMBLIES IN A NUCLEAR FISSION REACTOR, naming Roderick A. Hyde, Robert C. Petroski, Joshua C. Walter, Thomas Allan Weaver, Charles Whitmer, Lowell L. Wood, Jr., and George B. Zimmerman as inventors, filed Nov. 6, 2009, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. The United States Patent Office (USPTO) has published a notice to the effect that the USPTO's computer programs require that patent applicants reference both a serial number and indicate whether an application is a continuation or continuation-in-part. Stephen G. Kunin, Benefit of Prior-Filed Application, USPTO Official Gazette Mar. 18, 2003, available at http://www.uspto.gov/web/offices/com/sol/og/2003/week11/patbene.htm. The present Applicant Entity (hereinafter “Applicant”) has provided above a specific reference to the application(s) from which priority is being claimed as recited by statute. Applicant understands that the statute is unambiguous in its specific reference language and does not require either a serial number or any characterization, such as “continuation” or “continuation-in-part,” for claiming priority to U.S. patent applications. Notwithstanding the foregoing, Applicant understands that the USPTO's computer programs have certain data entry requirements, and hence Applicant is designating the present application as a continuation-in-part of its parent applications as set forth above, but expressly points out that such designations are not to be construed in any way as any type of commentary and/or admission as to whether or not the present application contains any new matter in addition to the matter of its parent application(s). The present application relates to methods and systems for migrating fuel assemblies in a nuclear fission reactor. Illustrative embodiments provide methods and systems for migrating fuel assemblies in a nuclear fission reactor, methods of operating a nuclear fission traveling wave reactor, methods of controlling a nuclear fission traveling wave reactor, systems for controlling a nuclear fission traveling wave reactor, computer software program products for controlling a nuclear fission traveling wave reactor, and nuclear fission traveling wave reactors with systems for migrating fuel assemblies. The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. Illustrative embodiments provide methods and systems for migrating fuel assemblies in a nuclear fission reactor, methods of operating a nuclear fission traveling wave reactor, methods of controlling a nuclear fission traveling wave reactor, systems for controlling a nuclear fission traveling wave reactor, computer software program products for controlling a nuclear fission traveling wave reactor, and nuclear fission traveling wave reactors with systems for migrating fuel assemblies. Before details are explained regarding the non-limiting embodiments set forth herein, a brief overview will be set forth regarding a nuclear fission traveling wave. While a nuclear fission traveling wave is also known as a nuclear fission deflagration wave, for sake of clarity reference will be made herein to a nuclear fission traveling wave. Portions of the following discussion include information excerpted from a paper entitled “Completely Automated Nuclear Power Reactors For Long-Term Operation: III. Enabling Technology For Large-Scale, Low-Risk, Affordable Nuclear Electricity” by Edward Teller, Muriel Ishikawa, Lowell Wood, Roderick Hyde, and John Nuckolls, presented at the July 2003 Workshop of the Aspen Global Change Institute, University of California Lawrence Livermore National Laboratory publication UCRL-JRNL-122708 (2003) (This paper was prepared for submittal to Energy, The International Journal, 30 Nov. 2003), the contents of which are hereby incorporated by reference. In a “wave” that moves through a core of a nuclear fission traveling wave reactor at speeds on the order of around a centimeter or so per year, fertile nuclear fission fuel material is bred into fissile nuclear fission fuel material, which then undergoes fission. Certain of the nuclear fission fuels envisioned for use in nuclear fission traveling wave reactors are typically widely available, such as without limitation uranium (natural, depleted, or enriched), thorium, plutonium, or even previously-burned nuclear fission fuel assemblies. Other, less widely available nuclear fission fuels, such as without limitation other actinide elements or isotopes thereof may also be used. Some nuclear fission traveling wave reactors contemplate long-term operation at full power on the order of around ⅓ century to around ½ century or longer. Some nuclear fission traveling wave reactors do not contemplate nuclear refueling (but instead contemplate burial in-place at end-of-life) while some other nuclear fission traveling wave reactors contemplate nuclear refueling—with some nuclear refueling occurring during shutdown and some nuclear refueling occurring during operation at power. It is also contemplated that nuclear fission fuel reprocessing may be avoided in some cases, thereby mitigating possibilities for diversion to military uses and other issues. Simultaneously accommodating desires to achieve ⅓-½ century (or longer) of operations at full power without nuclear refueling and to avoid nuclear fission fuel reprocessing may entail use of a fast neutron spectrum. Moreover, propagating a nuclear fission traveling wave permits a high average burn-up of non-enriched actinide fuels, such as natural uranium or thorium, and use of a comparatively small “nuclear fission igniter” region of moderate isotopic enrichment of nuclear fissionable materials in the core's fuel charge. As such, a nuclear fission traveling wave reactor core suitably can include a nuclear fission igniter and a larger nuclear fission deflagration burn-wave-propagating region. The nuclear fission deflagration burn-wave-propagating region suitably contains thorium or uranium fuel, and functions on the general principle of fast neutron spectrum fission breeding. A nuclear fission traveling wave reactor core suitably is a breeder for reasons of efficient nuclear fission fuel utilization and of minimization of requirements for isotopic enrichment. Further, a fast neutron spectrum suitably is used because the high absorption cross-section of fission products for thermal neutrons typically does not permit high fuel utilization of thorium or of the more abundant uranium isotope, 238U, in uranium-fueled embodiments, without removal of fission products. An illustrative nuclear fission traveling wave will now be explained. Propagation of deflagration burning-waves through nuclear fission fuel materials can release power at predictable levels. Moreover, if the material configuration has sufficiently time-invariant features such as configurations found in typical commercial power-producing nuclear reactors, then ensuing power production may be at a steady level. Finally, if traveling wave propagation-speed may be externally modulated in a practical manner, the energy release-rate and thus power production may be controlled as desired. Nucleonics of the nuclear fission traveling wave are explained below. Inducing nuclear fission of selected isotopes of the actinide elements—the fissile ones—by absorption of neutrons of any energy may permit the release of nuclear binding energy at any material temperature, including arbitrarily low ones. The neutrons that are absorbed by the fissile actinide element may be provided by the nuclear fission igniter. Release of more than a single neutron per neutron absorbed, on the average, by nuclear fission of substantially any actinide isotope can provide opportunity for a diverging neutron-mediated nuclear-fission chain reaction in such materials. Typically, the number of neutrons released per absorption is identified as η, where η=υσf/(σf−σc) with υ being the number of neutrons released per fission. Release of more than two neutrons for every neutron which is absorbed (over certain neutron-energy ranges, on the average) may permit first converting an atom of a non-fissile isotope to a fissile one (via neutron capture and subsequent beta-decay) by an initial neutron capture, and then additionally permit neutron-fissioning the nucleus of the newly-created fissile isotope in the course of a second neutron fission absorption. Most high-Z (Z≧90) nuclear species can be used as nuclear fission fuel material in a traveling wave reactor (or a breeder reactor) if, on the average, one neutron from a given nuclear fission event can be radiatively captured on a non-fissile-but-‘fertile’ nucleus which will then convert (such as via beta-decay) into a fissile nucleus and a second neutron from the same fission event can be captured on a fissile nucleus and, thereby, induce fission. In particular, if either of these arrangements is steady-state, then sufficient conditions for propagating a nuclear fission traveling wave in the given material can be satisfied. Due to beta-decay of intermediate isotopes in the process of converting a fertile nucleus to a fissile nucleus, the rate at which fissile material is made available for fissioning is limited. The characteristic speed of wave advance is, therefore, limited by the half-lives on the order of days or months. For example, a characteristic speed of wave advance may be on the order of the ratio of the distance traveled by a neutron from its fission-birth to its radiative capture on a fertile nucleus (that is, a mean free path) to the half-life of the (longest-lived nucleus in the chain of) beta-decay leading from the fertile nucleus to the fissile one. Such a characteristic fission neutron-transport distance in normal-density actinides is approximately 10 cm and the beta-decay half-life is 105-106 seconds for most cases of interest. Accordingly for some designs, the characteristic wave-speed is 10−4-10−7 cm sec−1. Such a relatively slow speed-of-advance indicates that the wave can be characterized as a traveling wave or a deflagration wave, rather than a detonation wave. If the traveling wave attempts to accelerate, its leading-edge counters ever-more-pure fertile material (which is relatively lossy in a neutronic sense), for the concentration of fissile nuclei well ahead of the center of the wave becomes exponentially low. Thus the wave's leading-edge (referred to herein as a “burnfront”) stalls or slows. Conversely, if the wave slows and the conversion ratio is maintained greater than one (that is, breeding rate is greater than fissioning rate), then the local concentration of fissile nuclei arising from continuing beta-decay increases, the local rates of fission and neutron production rise, and the wave's leading-edge, that is the burnfront, accelerates. Finally, if the heat associated with nuclear fission is removed sufficiently rapidly from all portions of the configuration of initially fertile matter in which the wave is propagating, the propagation may take place at an arbitrarily low material temperature—although the temperatures of both the neutrons and the fissioning nuclei may be around 1 MeV. Such conditions for initiating and propagating a nuclear fission traveling wave can be realized with readily available materials. While fissile isotopes of actinide elements are rare terrestrially, both absolutely and relative to fertile isotopes of these elements, fissile isotopes can be concentrated, enriched and synthesized. For example, the use of both naturally-occurring and man-made fissile isotopes, such as U233, 235U and 239Pu, respectively, in initiating nuclear fission chain reactions is well-known. Consideration of pertinent neutron cross-sections suggests that a nuclear fission traveling wave can burn a large fraction of a core of naturally-occurring actinides, such as 232Th or 238U, if the neutron spectrum in the wave is a ‘hard’ or ‘fast’ one. That is, if the neutrons which carry the chain reaction in the wave have energies which are not very small compared to the approximately 1 MeV at which they are evaporated from nascent fission fragments, then relatively large losses to the spacetime-local neutron economy can be avoided when the local mass-fraction of fission products becomes comparable to that of the fertile material (recalling that a single mole of fissile material fission-converts to two moles of fission-product nuclei). Even neutronic losses to typical neutron-reactor structural materials, such as Ta, which has desirable high-temperature properties, may become substantial at neutron energies ≦0.1 MeV. Another consideration is the (comparatively small) variation with incident neutron energy of the neutron multiplicity of fission, ν, and the fraction of all neutron absorption events which result in fission (rather than merely γ-ray emission from neutron capture), α. The algebraic sign of the function α(ν−2) constitutes a condition for the feasibility of nuclear fission traveling wave propagation in fertile material compared with the overall fissile isotopic mass budget, in the absence of neutron leakage from the core or parasitic absorptions (such as on fission products) within its body, for each of the fissile isotopes of the reactor core. The algebraic sign is generally positive for all fissile isotopes of interest, from fission neutron-energies of approximately 1 MeV down into the resonance capture region. The quantity α(ν−2)/ν upper-bounds the fraction of total fission-born neutrons which may be lost to leakage, parasitic absorption, or geometric divergence during traveling wave propagation. It is noted that this fraction is 0.15-0.30 for the major fissile isotopes over the range of neutron energies which prevails in all effectively unmoderated actinide isotopic configurations of practical interest (approximately 0.1-1.5 MeV). In contrast to the situation prevailing for neutrons of (epi-) thermal energy, in which the parasitic losses due to fission products dominate those of fertile-to-fissile conversion by 1-1.5 decimal orders-of-magnitude, fissile element generation by capture on fertile isotopes is favored over fission-product capture by 0.7-1.5 orders-of-magnitude over the neutron energy range 0.1-1.5 MeV. The former suggests that fertile-to-fissile conversion will be feasible only to the extent of 1.5-5% percent at-or-near thermal neutron energies, while the latter indicates that conversions in excess of 50% may be expected for near-fission energy neutron spectra. In considering conditions for propagation of a nuclear fission traveling wave, in some approaches neutron leakage may be effectively ignored for very large, “self-reflected” actinide configurations. It will be appreciated that traveling wave propagation can be established in sufficiently large configurations of the two types of actinides that are relatively abundant terrestrially: 232Th and 238U, the exclusive and the principal (that is, longest-lived) isotopic components of naturally-occurring thorium and uranium, respectively. Specifically, transport of fission neutrons in these actinide isotopes will likely result in either capture on a fertile isotopic nucleus or fission of a fissile one before neutron energy has decreased significantly below 0.1 MeV (and thereupon becomes susceptible with non-negligible likelihood to capture on a fission-product nucleus). It will be appreciated that fission product nuclei concentrations can approach or in some circumstances exceed fertile ones and fissile nuclear concentrations may be an order-of-magnitude less than the lesser of fission-product or fertile ones while remaining quantitatively substantially reliable. Consideration of pertinent neutron scattering cross-sections suggests that configurations of actinides which are sufficiently extensive to be effectively infinitely thick—that is, self-reflecting—to fission neutrons in their radial dimension will have density-radius products >>200 gm/cm2—that is, they will have radii >>10-20 cm of solid-density 238U-232Th. The breeding-and-burning wave provides sufficient excess neutrons to breed new fissile material 1-2 mean-free-paths into the yet-unburned fuel, effectively replacing the fissile fuel burnt in the wave. The ‘ash’ behind the burn-wave's peak is substantially ‘neutronically neutral’, since the neutronic reactivity of its fissile fraction is just balanced by the parasitic absorptions of structure and fission product inventories on top of leakage. If the fissile atom inventory in the wave's center and just in advance of it is time-stationary as the wave propagates, then it is doing so stably; if less, then the wave is ‘dying’, while if more, the wave may be said to be ‘accelerating.’ Thus, a nuclear fission traveling wave may be propagated and maintained in substantially steady-state conditions for long time intervals in configurations of naturally-occurring actinide isotopes. The above discussion has considered, by way of non-limiting example, circular cylinders of natural uranium or thorium metal of less than a meter or so diameter—and that may be substantially smaller in diameter if efficient neutron reflectors are employed—that may stably propagate nuclear fission traveling waves for arbitrarily great axial distances. However, propagation of nuclear fission traveling waves is not to be construed to be limited to circular cylinders, to symmetric geometries, or to singly-connected geometries. To that end, additional embodiments of alternate geometries of nuclear fission traveling wave reactor cores are described in U.S. patent application Ser. No. 11/605,943, entitled AUTOMATED NUCLEAR POWER REACTOR FOR LONG-TERM OPERATION, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006, the contents of which are hereby incorporated by reference. Propagation of a nuclear fission traveling wave has implications for embodiments of nuclear fission traveling wave reactors. As a first example, local material temperature feedback can be imposed on the local nuclear reaction rate at an acceptable expense in the traveling wave's neutron economy. Such a large negative temperature coefficient of neutronic reactivity confers an ability to control the speed-of-advance of the traveling wave. If very little thermal power is extracted from the burning fuel, its temperature rises and the temperature-dependent reactivity falls, and the nuclear fission rate at wave-center becomes correspondingly small and the wave's equation-of-time reflects only a very small axial rate-of-advance. Similarly, if the thermal power removal rate is large, the material temperature decreases and the neutronic reactivity rises, the intra-wave neutron economy becomes relatively undamped, and the wave advances axially relatively rapidly. Details regarding illustrative implementations of temperature feedback that may be incorporated within embodiments of reactor core assemblies are described in U.S. patent application Ser. No. 11/605,933, entitled CONTROLLABLE LONG TERM OPERATION OF A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006, the contents of which are hereby incorporated by reference. As a second example of implications of propagation of a nuclear fission traveling wave on embodiments of nuclear fission traveling wave reactors, less than all of the total fission neutron production in a nuclear fission traveling wave reactor may be utilized. For example, reactivity control systems, such as without limitation neutron-absorbing material in control rods or local material-temperature thermostating modules, may use around 5-10% of the total fission neutron production in the nuclear fission traveling wave reactor 10. Another ≦10% of the total fission neutron production in a nuclear fission traveling wave reactor may be lost to parasitic absorption in the high-performance, high temperature, structure materials (such as Ta, W, or Re) employed in structural components of the nuclear fission traveling wave reactor. This loss occurs in order to realize desired thermodynamic efficiencies in conversion to electricity and to gain high system safety figures-of-merit. The Zs of these materials, such as Ta, W and Re, are approximately 80% of that of the actinides, and thus their radiative capture cross-sections for high-energy neutrons are not particularly small compared to those of the actinides. A final 5-10% of the total fission neutron production in a nuclear fission traveling wave reactor may be lost to parasitic absorption in fission products. However, it may be expected that the spectrum may be similar to that of a sodium-cooled fast reactor in that parasitic absorption may account for only around a 1-2% loss. As noted above, the neutron economy characteristically is sufficiently rich that approximately 70% of total fission neutron production is sufficient to sustain traveling wave-propagation in the absence of leakage and rapid geometric divergence. As a third example of implications of propagation of a nuclear fission traveling wave on embodiments of nuclear fission traveling wave reactors, high burn-ups (on the order of up to around 20% to around 30% or, in some cases around 40% or 50% to as much as around 80%) of initial actinide fuel-inventories which are characteristic of the nuclear fission traveling waves can permit high-efficiency utilization of as-mined fuel—moreover without a requirement for reprocessing. It will be noted that the neutron flux from the most intensely burning region behind the burnfront breeds a fissile isotope-rich region at the burnfront's leading-edge, thereby serving to advance the nuclear fission traveling wave. After the nuclear fission traveling wave's burnfront has swept over a given mass of fuel, the fissile atom concentration continues to rise for as long as radiative capture of neutrons on available fertile nuclei is considerably more likely than on fission product nuclei, while ongoing fission generates an ever-greater mass of fission products. Nuclear power-production density peaks in this region of the fuel-charge, at any given moment. It will be appreciated that well behind the nuclear fission traveling wave's advancing burnfront, the concentration ratio of fission product nuclei (whose mass closely averages half that of a fissile nucleus) to fissile ones climbs to a value comparable to the ratio of the fissile fission to the fission product radiative capture cross-sections. The “local neutronic reactivity” thereupon approaches a negative value or, in some embodiments may become negative. Hence, both burning and breeding effectively cease. It will also be appreciated that in some embodiments, non-fissile neutron absorbing material, such as boron carbide, hafnium, or gadolinium may be added to ensure the “local neutronic reactivity” is negative. In some embodiments of nuclear fission traveling wave reactors, all the nuclear fission fuel ever used in the reactor is installed during manufacture of the reactor core assembly. Also, in some configurations no spent fuel is ever removed from the reactor core assembly. In one approach, such embodiments may allow operation without ever accessing the reactor core after nuclear fission ignition up to and perhaps after completion of propagation of the burnfront. In some other embodiments of nuclear fission traveling wave reactors, all the nuclear fission fuel ever used in the reactor is installed during manufacture of the reactor core assembly and in some configurations no spent fuel is ever removed from the reactor core assembly. However, and as will be explained below, at least some of the nuclear fission fuel may be migrated or shuffled between or among locations within a reactor core. Such migration or shuffling of at least some of the nuclear fission fuel may be performed to achieve objectives as discussed below. However, in some other embodiments of nuclear fission traveling wave reactors, additional nuclear fission fuel may be added to the reactor core assembly after nuclear fission ignition. In some other embodiments of nuclear fission traveling wave reactors, spent fuel may be removed from the reactor core assembly (and, in some embodiments, removal of spent fuel from the reactor core assembly may be performed while the nuclear fission traveling wave reactor is operating at power). Such illustrative refueling and defueling is explained in U.S. patent application Ser. No. 11/605,848, entitled METHOD AND SYSTEM FOR PROVIDING FUEL IN A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006, the contents of which are hereby incorporated by reference. Regardless of whether or not spent fuel is removed, pre-expansion of the as-loaded fuel permits higher-density actinides to be replaced with lower-density fission products without any overall volume changes in fuel elements, as the nuclear fission traveling wave sweeps over any given axial element of actinide ‘fuel,’ converting it into fission-product ‘ash.’ Given by way of overview, launching of nuclear fission traveling waves into 232Th or 238U fuel-charges can initiate with ‘nuclear fission igniter modules’, such as without limitation nuclear fission fuel assemblies that are enriched in fissile isotopes. Illustrative nuclear fission igniter modules and methods for launching nuclear fission traveling waves are discussed in detail in a co-pending U.S. patent application Ser. No. 12/069,908, entitled NUCLEAR FISSION IGNITER naming CHARLES E. AHLFELD, JOHN ROGERS GILLELAND, RODERICK A. HYDE, MURIEL Y. ISHIKAWA, DAVID G. MCALEES, NATHAN P. MYHRVOLD, CHARLES WHITMER, AND LOWELL L. WOOD, JR. as inventors, filed 12 Feb. 2008, the contents of which are hereby incorporated by reference. Higher enrichments can produce more compact modules, and minimum mass modules may employ moderator concentration gradients. In addition, nuclear fission igniter module design may be determined in part by non-technical considerations, such as resistance to materials diversion for military purposes in various scenarios. In other approaches, illustrative nuclear fission igniters may have other types of reactivity sources. For example, other nuclear fission igniters may include “burning embers”, e.g., nuclear fission fuel enriched in fissile isotopes via exposure to neutrons within a propagating nuclear fission traveling wave reactor. Such “burning embers” may function as nuclear fission igniters, despite the presence of various amounts of fission products “ash”. In other approaches to launching a nuclear fission traveling wave, nuclear fission igniter modules enriched in fissile isotopes may be used to supplement other neutron sources that use electrically driven sources of high energy ions (such as protons, deuterons, alpha particles, or the like) or electrons that may in turn produce neutrons. In one illustrative approach, a particle accelerator, such as a linear accelerator may be positioned to provide high energy protons to an intermediate material that may in turn provide such neutrons (e.g., through spallation). In another illustrative approach, a particle accelerator, such as a linear accelerator may be positioned to provide high energy electrons to an intermediate material that may in turn provide such neutrons (e.g., by electro-fission and/or photofission of high-Z elements). Alternatively, other known neutron emissive processes and structures, such as electrically induced fusion approaches, may provide neutrons (e.g., 14 Mev neutrons from D-T fusion) that may thereby be used in addition to nuclear fission igniter modules enriched in fissile isotopes to initiate the propagating fission wave. Now that nucleonics of the fuel charge and the nuclear fission traveling wave have been discussed, further details regarding “nuclear fission ignition” and maintenance of the nuclear fission traveling wave will be discussed. A centrally-positioned illustrative nuclear fission igniter moderately enriched in fissionable material, such as 235U or 239Pu, has a neutron-absorbing material (such as a borohydride or the like) removed from it (such as by operator-commanded electrical heating or by withdrawal of one or more control rods), and the nuclear fission igniter becomes neutronically critical. Local fuel temperature rises to a predetermined temperature and is regulated thereafter, such as by a reactor coolant system and/or a reactivity control system or local thermostating modules (discussed in detail in U.S. patent application Ser. No. 11/605,943, entitled AUTOMATED NUCLEAR POWER REACTOR FOR LONG-TERM OPERATION, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006, the contents of which are hereby incorporated by reference). Neutrons from the fast fission of 233U or 239Pu are mostly captured at first on local 238U or 232Th. It will be appreciated that uranium enrichment of the nuclear fission igniter may be reduced to levels not much greater than that of light water reactor (LWR) fuel by introduction into the nuclear fission igniter and the fuel region immediately surrounding it of a radial density gradient of a refractory moderator, such as graphite. High moderator density enables low-enrichment fuel to burn satisfactorily, while decreasing moderator density permits efficient fissile breeding to occur. Thus, optimum nuclear fission igniter design may involve trade-offs between proliferation robustness and the minimum latency from initial criticality to the availability of full-rated-power from the fully-ignited fuel-charge of the core. Lower nuclear fission igniter enrichments entail more breeding generations and thus impose longer latencies. In some embodiments, the peak reactivity of the reactor core assembly may slowly decrease in the first phase of the nuclear fission ignition process because, although the total fissile isotope inventory is increasing, the total inventory becomes more spatially dispersed. As a result of choice of initial fuel geometry, fuel enrichment versus position, and fuel density, it may be arranged for the maximum reactivity to still be slightly positive at the time-point at which its minimum value is attained. Soon thereafter, the maximum reactivity begins to increase rapidly toward its greatest value, corresponding to the fissile isotope inventory in the region of breeding substantially exceeding that remaining in the nuclear fission igniter. For many cases a quasi-spherical annular shell then provides maximum specific power production. At this point, the fuel-charge of the reactor core assembly can be referred to as “ignited.” Propagation of the nuclear fission traveling wave, which may also be referred to herein as “nuclear fission burning”, will now be discussed. In the previously described configuration, the spherically-diverging shell of maximum specific nuclear power production continues to advance radially from the nuclear fission igniter toward the outer surface of the fuel charge. When it reaches the outer surface, it typically breaks into two spherical zonal surfaces, with each surface propagating in a respective one of two opposite directions along the axis of the cylinder. At this time-point, the full thermal power production potential of the core may have been developed. This interval is characterized as that of the launching period of the two axially-propagating nuclear fission traveling wave burnfronts. In some embodiments the center of the core's fuel-charge is ignited, thus generating two oppositely-propagating waves. This arrangement doubles the mass and volume of the core in which power production occurs at any given time, and thus decreases by two-fold the core's peak specific power generation, thereby quantitatively minimizing thermal transport challenges. However, in other embodiments, the core's fuel charge is ignited at or near one end, as desired for a particular application. Such an approach may result in a single propagating wave in some configurations. In other embodiments, the core's fuel charge may be ignited in multiple sites. In yet other embodiments, the core's fuel charge is ignited at any 3-D location within the core as desired for a particular application. In some embodiments, two propagating nuclear fission traveling waves may be initiated and propagate away from a nuclear fission ignition site; however, depending upon geometry, nuclear fission fuel composition, the action of neutron modifying control structures, or other considerations, different numbers (e.g., one, three, or more) of nuclear fission traveling waves may be initiated and propagated. However, for sake of understanding and brevity, the discussion herein refers, without limitation, to propagation of two nuclear fission traveling wave burnfronts. From this time forward through the break-out of the two waves when they reach or approach the two opposite ends, the physics of nuclear power generation is typically effectively time-stationary in the frame of either wave. The speed of wave advance through the fuel is proportional to the local neutron flux, which in turn is linearly dependent on the thermal power drawn from the reactor core assembly via the collective action on the nuclear fission traveling wave's neutron budget of the neutron control system, In one approach, the neutron control system may be implemented with thermostating modules (not shown) as has been described in U.S. patent application Ser. No. 11/605,933, entitled CONTROLLABLE LONG TERM OPERATION OF A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, AND LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006, the contents of which are hereby incorporated by reference. In other approaches, the neutron control system may be implemented with one or more rods containing neutron-absorbing material and being movable with one or more control rod drive mechanisms. When more power is demanded from the reactor via lower-temperature coolant flowing into the core, in some embodiments the temperature of the two ends of the core (which in some embodiments are closest to the coolant inlets) decreases slightly below the thermostating modules' design set-point, a neutron absorber is thereby withdrawn from the corresponding sub-population of the core's thermostating modules, and the local neutron flux is permitted thereby to increase to bring the local thermal power production to the level which drives the local material temperature up to the set-point of the local thermostating modules. In some other embodiments, temperature control may be effected by shimming control rods as desired responsive to changes in monitored temperature. However, in the two burnfront embodiment this process is not effective in heating the coolant significantly until its two divided flows move into the two nuclear burn-fronts. These two portions of the core's fuel-charge—which are capable of producing significant levels of nuclear power when not suppressed by the neutron absorbers—then act to heat the coolant to the temperature specified by the design set-point of their modules, provided that the nuclear fission fuel temperature does not become excessive (and regardless of the temperature at which the coolant arrived in the core). The two coolant flows then move through the two sections of already-burned fuel centerward of the two burnfronts, removing residual nuclear fission and afterheat thermal power from them, both exiting the fuel-charge at its center. This arrangement encourages the propagation of the two burnfronts toward the two ends of the fuel-charge by “trimming” excess neutrons primarily from the trailing edge of each front. Thus, the core's neutronics in this configuration may be considered to be substantially self-regulated. For example, for cylindrical core embodiments, the core's nucleonics may be considered to be substantially self-regulating when the fuel density-radius product of the cylindrical core is ≧200 gm/cm2 (that is, 1-2 mean free paths for neutron-induced fission in a core of typical composition, for a reasonably fast neutron spectrum). One function of the neutron reflector in such core design may be to substantially reduce the fast neutron fluence seen by the outer portions of the reactor, such as its radiation shield, structural supports, outermost shell, and reactivity control system components such as without limitation control rods (when provided) or thermostating modules (when provided). The neutron reflector may also impact the performance of the core by increasing the breeding efficiency and the specific power in the outermost portions of the fuel. Such impact may enhance the reactor's economic efficiency. Outlying portions of the fuel-charge are not used at low overall energetic efficiency, but have isotopic burn-up levels comparable to those at the center of the fuel-charge. While the core's neutronics in the above-described configurations may be considered to be substantially self-regulated, other configurations may operate under control of a reactor control system that includes a suitable electronic controller having appropriate electrical circuitry and that may include a suitable electro-mechanical system, such as one or more rods containing neutron-absorbing material and being movable with one or more control rod drive mechanisms. Final, irreversible negation of the core's neutronic reactivity may be performed at any time by injection of neutronic poison into the coolant stream as desired. For example, lightly loading a coolant stream with a material such as BF3, possibly accompanied by a volatile reducing agent such as H2 if desired, may deposit metallic boron substantially uniformly over the inner walls of coolant-tubes threading through the reactor's core, via exponential acceleration of the otherwise slow chemical reaction 2BF3+3H2→2B+6HF by the high temperatures found therein. Boron, in turn, is a highly refractory metalloid, and will not typically migrate from its site of deposition. Substantially uniform presence of boron in the core in <100 kg quantities may negate the core's neutronic reactivity for indefinitely prolonged intervals without involving the use of powered mechanisms in the vicinity of the reactor. In a general sense, those skilled in the art will recognize that the various aspects described herein which can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, and/or any combination thereof can be viewed as being composed of various types of “electrical circuitry.” Consequently, as used herein “electrical circuitry” includes, but is not limited to, electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer configured by a computer program which at least partially carries out processes and/or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and/or devices described herein), electrical circuitry forming a memory device (e.g., forms of memory (e.g., random access, flash, read only, etc.)), and/or electrical circuitry forming a communications device (e.g., a modem, communications switch, optical-electrical equipment, etc.). Those having skill in the art will recognize that the subject matter described herein may be implemented in an analog or digital fashion or some combination thereof. In a general sense, those skilled in the art will recognize that the various embodiments described herein can be implemented, individually and/or collectively, by various types of electro-mechanical systems having a wide range of electrical components such as hardware, software, firmware, and/or virtually any combination thereof; and a wide range of components that may impart mechanical force or motion such as rigid bodies, spring or torsional bodies, hydraulics, electro-magnetically actuated devices, and/or virtually any combination thereof. Consequently, as used herein “electro-mechanical system” includes, but is not limited to, electrical circuitry operably coupled with a transducer (e.g., an actuator, a motor, a piezoelectric crystal, a Micro Electro Mechanical System (MEMS), etc.), electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer configured by a computer program which at least partially carries out processes and/or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and/or devices described herein), electrical circuitry forming a memory device (e.g., forms of memory (e.g., random access, flash, read only, etc.)), electrical circuitry forming a communications device (e.g., a modem, communications switch, optical-electrical equipment, etc.), and/or any non-electrical analog thereto, such as optical or other analogs. Those skilled in the art will also appreciate that examples of electro-mechanical systems include but are not limited to a variety of consumer electronics systems, medical devices, as well as other systems such as motorized transport systems, factory automation systems, security systems, and/or communication/computing systems. Those skilled in the art will recognize that electro-mechanical as used herein is not necessarily limited to a system that has both electrical and mechanical actuation except as context may dictate otherwise. Now that a brief overview has been set forth regarding initiation and propagation of a nuclear fission traveling wave, illustrative embodiments will now be explained by way of non-limiting examples. Following are a series of flowcharts depicting implementations. For ease of understanding, the flowcharts are organized such that the initial flowcharts present implementations via an example implementation and thereafter the following flowcharts present alternate implementations and/or expansions of the initial flowchart(s) as either sub-component operations or additional component operations building on one or more earlier-presented flowcharts. Those having skill in the art will appreciate that the style of presentation utilized herein (e.g., beginning with a presentation of a flowchart(s) presenting an example implementation and thereafter providing additions to and/or further details in subsequent flowcharts) generally allows for a rapid and easy understanding of the various process implementations. In addition, those skilled in the art will further appreciate that the style of presentation used herein also lends itself well to modular and/or object-oriented program design paradigms. Referring now to FIG. 1A and by way of overview, an illustrative method 10 is provided for operating a nuclear fission traveling wave reactor. Referring additionally to FIG. 1B, components of an illustrative nuclear fission traveling wave reactor core 12 of a nuclear fission traveling wave reactor are shown by way of example and not of limitation. Nuclear fission fuel subassemblies 14 are housed in a reactor core assembly 16. To aid in clarity, FIG. 1B may illustrate less than all of the nuclear fission fuel subassemblies 14 that may be housed in embodiments of the reactor core assembly 16. A frame of reference is defined within the reactor core assembly 16. In some embodiments, the frame of reference can be defined by an x-dimension, a y-dimension, and a z-dimension. In some other embodiments, the frame of reference can be defined by a radial dimension and an axial dimension. In some other embodiments, the frame of reference can include an axial dimension and a lateral dimension. In some embodiments, the nuclear fission fuel subassemblies 14 may be individual nuclear fission fuel elements, such as nuclear fission fuel rods, plates, spheres, or the like. In some other embodiments, the nuclear fission fuel subassemblies 14 may be nuclear fission fuel assemblies—that is, two or more individual nuclear fission fuel elements that are grouped into an assembly. Regardless of embodiment of the nuclear fission fuel subassemblies 14, nuclear fission fuel material contained within the nuclear fission fuel subassemblies 14 can be any suitable type of nuclear fission fuel material as described above. Still by way of overview, the method 10 starts at a block 18. At a block 20, a nuclear fission traveling wave burnfront 22 is propagated (as indicated by arrows 24) along first and second dimensions within the nuclear fission fuel subassemblies 14 in the reactor core assembly 16 of the nuclear fission traveling wave reactor core 12. At a block 26 selected ones of the nuclear fission fuel subassemblies 14 are controllably migrated along the first dimension from respective first locations toward respective second locations in a manner that defines a shape of the nuclear fission traveling wave burnfront 22 along the second dimension according to a selected set of dimensional constraints. The method 10 stops at a block 28. Illustrative details will now be explained by way of non-limiting examples. The nuclear fission fuel subassemblies 14 bear a spatial relationship to the dimensions that are designated as the first and second dimensions. For example, in some embodiments the nuclear fission fuel subassemblies 14 may be elongate along the second dimension. In some embodiments, the second dimension may be the y-dimension or an axial dimension. In some other embodiments, the second dimension may be the x-dimension, the z-dimension, or a lateral dimension. Moreover, in some embodiments the first dimension may be substantially orthogonal to an elongated axis of the nuclear fission subassemblies 14. In some embodiments, the first dimension and the second dimension may be substantially orthogonal to each other. Various dimensions may be designated as the first dimension and second dimension. For example, in some embodiments the first dimension may include a radial dimension and the second dimension may include an axial dimension. In some other embodiments the first dimension may include an axial dimension and the second dimension may include a radial dimension. In some embodiments the first dimension may include an axial dimension and the second dimension may include a lateral dimension. In some other embodiments the first dimension may include a lateral dimension and the second dimension may include an axial dimension. In a cylindrical core with assemblies elongated in the axial direction, such as typical commercial light water reactor configurations, the first dimension may be the radial dimension and the second dimension may be the axial dimension. In other reactor configurations, such as that of the CANDU heavy water reactors, the fuel assemblies are elongated in a first dimension and can be moved in a lateral or radial second dimension. As illustrated in FIG. 1B, locations within the reactor core 12 may be characterized as the first locations and the second locations according to various attributes. In general, a location may be considered to be a space in a vicinity of a region of the reactor core 12 around a nuclear fission fuel subassembly 14. A location may also be considered generally to be a space immediately surrounding any given area in the reactor core 12, or may be considered to be most of the reactor core 12. For example and referring additionally to FIG. 1C, in some embodiments the first locations may include outward locations 30 and the second locations may include inward locations 32. As illustrated in FIG. 1C, in some embodiments the inward locations 32 and outward locations 30 may be based on geometrical proximity to a central portion of the reactor core 12. In some other embodiments, the inward locations and the outward locations may be based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. In some other embodiments, the inward locations and the outward locations may be based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. Embodiments typical of a traveling wave reactor may have outward locations including locations outside, or in the direction of, a propagating wave while inward locations may include locations through which a nuclear fission traveling wave is propagating or has already propagated. Given by way of further examples and referring additionally to FIG. 1D, in some embodiments the first locations may include the inward locations 32 and the second locations may include the outward locations 30. As illustrated in FIG. 1D, in some embodiments the inward locations 32 and the outward locations 30 may be based on geometrical proximity to the central portion of the reactor core 12. In some other embodiments, the inward locations and the outward locations may be based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. In some other embodiments, the inward locations and the outward locations may be based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. In other embodiments, the inward and outward locations may be described in terms of the predominant nuclear reaction occurring in those regions. Given by way of non-limiting example, the inward location may be characterized by predominantly nuclear fission reactions while the outward location may be characterized by predominantly nuclear absorption reactions on fertile material. Regardless of characterization of the first locations and the second locations as either inward locations or outward locations, the first locations and the second locations may be characterized according to other attributes. For example, in some embodiments the first locations and the second locations may be located on opposite sides of a reference value along the first dimension. In some other embodiments the first locations and the second locations may include at least one attribute that is substantially equalized. For example, the at least one attribute that is substantially equalized may include geometrical proximity to a central region of the reactor core, neutron flux, reactivity, or the like. Given by way of non-limiting example and referring to FIG. 1E, selected ones of the nuclear fission fuel subassemblies (not shown for clarity) may be controllably migrated radially outwardly from respective inward locations 32 toward respective outward locations 30 in a manner that defines a shape of the nuclear fission traveling wave burnfront 22 axially according to a selected set of dimensional constraints. Given by way of illustration and not of limitation, axial changes in shape of the nuclear fission traveling wave burnfront 22 with radial movement of nuclear fission fuel subassemblies (not shown) are shown. A left pane illustrates an initial shape of the nuclear fission traveling wave burnfront 22. It will be appreciated that, for clarity purposes, only one-fourth of the perimeter of the nuclear fission traveling wave burnfront 22 is shown. In a center pane, a selected nuclear fission fuel subassembly (not shown) has been radially migrated from the inward location 32 to the outward location 30 after the selected nuclear fission fuel subassembly (not shown) has been burned for a desired time or according to a desired reactivity parameter (such as, without limitation, burnup). Reactivity has been moved radially outwardly from a peak that was radially located at the inward location 32 (as shown in the left pane) to the outward location 30 (as shown in the center pane). Over the life of the nuclear fission traveling wave reactor core 12, additional nuclear fission fuel subassemblies (not shown) may be radially migrated outwardly from the inward locations 32 to the outward locations 30. As a result of such additional outward migration, nuclear fission fuel subassemblies (not shown) at radially inward locations in the nuclear fission traveling wave reactor core 12 may be kept from burning more than nuclear fission fuel subassemblies (not shown) at radially outward locations in the nuclear fission traveling wave reactor core 12. As shown in the right pane, if a sufficient number of the nuclear fission fuel subassemblies are migrated radially outwardly as described above, then the shape of the nuclear fission traveling wave burnfront 22 may approximate a Bessel function. Also, if a sufficient number of the nuclear fission fuel subassemblies are migrated radially outwardly as described above, then all or substantially all of the nuclear fission fuel subassemblies in the nuclear fission traveling wave reactor core 12 may reach or approach their respective burn-up limits at around a same time. In such a case, use of the nuclear fission fuel subassemblies in the nuclear fission traveling wave reactor core 12 has been maximized. Given by way of another non-limiting example and referring to FIG. 1F, selected ones of the nuclear fission fuel subassemblies 14 may be controllably migrated radially outwardly from respective inward locations 32 toward respective outward locations 30 and other selected ones of the nuclear fission fuel subassemblies 14′ may be controllably migrated radially inwardly from the respective outward locations 30 to the respective inward locations 32 in a manner that defines a shape of the nuclear fission traveling wave burnfront 22 axially according to a selected set of dimensional constraints. That is, the selected nuclear fission fuel assemblies 14 and 14′ are interchanged between the inward locations 32 and the outward locations 30. Given by way of illustration and not of limitation, axial changes in shape of the nuclear fission traveling wave burnfront 22 with such interchanging radial movement of nuclear fission fuel subassemblies 14 and 14′ are shown. A left pane illustrates an initial shape of the nuclear fission traveling wave burnfront 22. In the left pane, the nuclear fission fuel assemblies 14 have more fissile content than do the nuclear fission fuel assemblies 14′. For example, the nuclear fission fuel subassemblies 14 may be part of an igniter assembly for the nuclear fission traveling wave reactor core 12. As another example, the nuclear fission fuel assemblies 14 may include fissile material that has been bred from fertile isotopic material as a result of absorption of fast spectrum neutrons in the nuclear fission traveling wave reactor core 12 and subsequent transmutation into fissile isotopes. By contrast, the nuclear fission fuel subassemblies 14′ have less fissile content than do the nuclear fission fuel subassemblies 14. In some cases, the nuclear fission fuel subassemblies 14′ may include more fertile isotopic content than do the nuclear fission fuel subassemblies 14. In such cases, the nuclear fission fuel subassemblies 14′ are more absorptive to fast spectrum neutrons than are the nuclear fission fuel subassemblies 14. In a right pane, the selected nuclear fission fuel subassembly 14 has been radially outwardly migrated from the inward location 32 to the outward location 30 and the selected nuclear fission fuel subassembly 14′ has been radially inwardly migrated from the outward location 30 to the inward location 32. After the interchanging of the nuclear fission fuel subassemblies 14 and 14′, the axial profile of the nuclear fission traveling wave burnfront 22 has been made more compact and more uniform compared to the axial profile of the nuclear fission traveling wave burnfront 22 before such interchanging (see the left pane). As a result, in some embodiments a substantially uniform profile or uniform profile may be achieved for the nuclear fission traveling wave burnfront 22. In some other embodiments it may not be desired to achieve a substantially uniform profile or uniform profile for the nuclear fission traveling wave burnfront 22. In such cases it may merely be desired to relocate fissile material or to relocate fertile isotopic material. In some other embodiments it may be desirable to extend the nuclear fission traveling wave burnfront 22 in the radial dimension. Referring additionally to FIG. 1G, the shape of the nuclear fission traveling wave burnfront 22 also may be defined in the radial dimension by migrating the nuclear fission fuel subassemblies 14 and 14′ in the radial dimension as discussed above with reference to FIG. 1F. The radial profile of the nuclear fission traveling wave burnfront 22 may be considered to represent neutron leakage current. The left and right panes of FIG. 1G show views along the axial dimension that correspond to the left and right panes, respectively, of FIG. 1F. Referring now to FIG. 1H, selected ones of the nuclear fission fuel subassemblies 14 may be controllably migrated laterally from respective first locations toward respective second locations in a manner that defines a shape of the nuclear fission traveling wave burnfront 22 radially according to a selected set of dimensional constraints. A left pane illustrates an initial shape of the nuclear fission traveling wave burnfront 22 viewed along the axial dimension. A selected nuclear fission fuel subassembly 14 is located at a first location z, r, φ1. In the example shown for illustration purposes, the nuclear fission fuel subassembly 14 contributes reactivity at the first location z, r, φ1 that may be determined, for any reason whatsoever, to be in excess of an amount of reactivity desired at the first location z, r, φ1. For example, the nuclear fission fuel subassembly 14 may be part of an igniter assembly for the nuclear fission traveling wave reactor core 12. As another example, the nuclear fission fuel assembly 14 may include fissile material that has been bred from fertile isotopic material as a result of absorption of fast spectrum neutrons in the nuclear fission traveling wave reactor core 12 and subsequent transmutation into fissile isotopes. As a result, the nuclear fission traveling wave burnfront 22 may be propagating too much in the radial direction at the first location z, r, φ1. As shown in the right pane, the selected nuclear fission fuel subassembly 14 has been laterally migrated along the lateral dimension φ from the first location z, r, φ1 to the second location z, r, φ2. It will be appreciated that the shape of the nuclear fission traveling wave burnfront 22 has been defined radially as a result of lateral migration of the selected nuclear fission fuel subassembly 14 from the first location z, r, φ1 to the second location z, r, φ2. Lateral migration of the selected nuclear fission fuel subassembly from the first location z, r, φ1 to the second location z, r, φ2 has removed fissile content from the first location z, r, φ1 and has added fissile content to the second location z, r, φ1. As shown in the right pane, the shape of the nuclear fission traveling wave burnfront 22 has been shortened along the radial dimension r in the vicinity of the first location z, r, φ1 and has been lengthened along the radial dimension r in the vicinity of the second location z, r, φ2. Controllably migrating selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 26 may entail one or more processes. For example and referring additionally to FIGS. 1I and 1J, in some embodiments controllably migrating selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 26 may include rotating at least one of the selected ones of the nuclear fission fuel subassemblies 14 at a block 34, as indicated by arrow 36 (FIG. 1J). It will be appreciated that rotating at least one of the selected ones of the nuclear fission fuel subassemblies 14 at the block 34 may be performed with any suitable in-core fuel handling system as desired. Furthermore, it may be desired to rotate the selected nuclear fission fuel subassemblies 14 in order to minimize or prevent deformation of reactor structural material, such as bowing of nuclear fission fuel subassemblies. As another example and referring additionally to FIGS. 1K and 1L, in some other embodiments controllably migrating selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 26 may include inverting at least one of the selected ones of the nuclear fission fuel subassemblies 14 at a block 38, as indicated by arrows 40 (FIG. 1L). It will be appreciated that inverting at least one of the selected ones of the nuclear fission fuel subassemblies 14 at the block 38 may be performed with any suitable in-core fuel handling system as desired. Inverting a nuclear fission fuel subassembly 14 can result in an inlet of the nuclear fission fuel subassembly 14 (prior to inversion) becoming an outlet of the nuclear fission fuel subassembly 14 (after inversion), and vice versa. Such an inversion can result in axially equalizing thermal stresses and/or radiation effects on the nuclear fission fuel subassembly 14 at the ends of the nuclear fission fuel subassembly 14. Any such radiation effects may be temperature related and/or may be related to variations in neutron flux at the axial ends of the nuclear fission reactor core 12. It will be appreciated that inversion of a nuclear fission fuel subassembly 14 results in both ends of the inverted nuclear fission fuel subassembly 14 migrating from a first location to a second location about the central point of inversion. However, in some cases, it may be desirable to alter the location of the assembly laterally as well. It will also be appreciated that any one or more dimensional constraints may be selected as desired for a particular application. For example, in some embodiments the selected set of dimensional constraints may include a predetermined maximum distance along the second dimension. In some other embodiments, the selected set of dimensional constraints may be a function of at least one burnfront criteria. For example, the burnfront criteria may include neutron flux. In some arrangements the neutron flux may be associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14. In some other embodiments the burnfront criteria may include neutron fluence. In some arrangements the neutron fluence may be associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14. In some other embodiments the burnfront criteria may include burnup. In some arrangements the burnup may be associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14. In such arrangements, it may be desirable to move the selected ones of the nuclear fission fuel subassemblies 14 from a first location having a first burn-up rate to a second location having a second burn-up rate. If the selected nuclear fission fuel subassembly 14 is nearing the end of its useful lifetime, then the first location may be a location that is characterized by a high burn-up rate and the second location may be a location that is characterized by a reduced burn-up rate (relative to the high burn-up rate at the first location) or a substantially zero value of burn-up rate. In embodiments where a nuclear fission fuel subassembly 14 is being bred-up, it may be desirable to move the nuclear fission fuel subassembly 14 from a first location having a low burn-up rate to a second location having a higher burn-up rate (relative to that of the first location). In some other embodiments the burnfront criteria may include burnfront location within at least one of the selected ones of the nuclear fission fuel subassemblies 14. Burnfront location may be characterized by features of the nuclear fission traveling wave reactor core 12 or nuclear fission fuel subassemblies 14 therein. Such features may include, but are not limited to, fission rate, breeding rate, power output, temperature, reactivity, and the like. It will be appreciated that controllably migrating selected ones of the nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations at the block 26 may be performed in any manner as desired for a particular application. For example and referring additionally to FIG. 1M (and as indicated in FIGS. 1C and 1D), in some embodiments controllably migrating selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 26 may include controllably migrating selected ones of the nuclear fission fuel subassemblies 14 radially along the first dimension from respective first locations toward respective second locations at a block 42. It will be appreciated that radial migration at the block 42 may be performed with any suitable in-core fuel handling system as desired. In some other embodiments and referring additionally to FIGS. 1N and 1O, controllably migrating selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 26 may include controllably migrating selected ones of the nuclear fission fuel subassemblies spirally along the first dimension from respective first locations toward respective second locations at a block 44, as indicated by arrow 46. It will be appreciated that spiral migration at the block 44 may be performed with any suitable in-core fuel handling system as desired. In some other embodiments and referring additionally to FIGS. 1P and 1Q, controllably migrating selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 26 may include controllably migrating selected ones of the nuclear fission fuel subassemblies 14 axially along the first dimension from respective first locations toward respective second locations at a block 48, as indicated by an arrow 50. It will be appreciated that axial migration at the block 48 may be performed with any suitable in-core fuel handling system as desired. It will be appreciated that the shape of the nuclear fission traveling wave burnfront 22 may be defined by any parameter associated with the nuclear fission traveling wave burnfront 22, such as without limitation neutron flux, neutron fluence, burnup, and/or reactivity (or any of their components). It will also be appreciated that the nuclear fission traveling wave burnfront 22 may have any shape as desired for a particular application. For example and referring additionally to FIG. 1R, in some embodiments the shape of the nuclear fission traveling wave burnfront 22 may be substantially spherical. In some other embodiments and referring additionally to FIG. 1S, the shape of the nuclear fission traveling wave burnfront 22 may substantially conform to a selected continuously curved surface. In some embodiments and referring additionally to FIG. 1T, the shape of the nuclear fission traveling wave burnfront 22 may be substantially rotationally symmetrical around the second dimension. In some other embodiments and referring additionally to FIGS. 1U and 1V, the shape of the nuclear fission traveling wave burnfront 22 may have substantial n-fold rotational symmetry around the second dimension. It is known by those skilled in the art that maintaining a substantially constant, ‘flat’, burn profile (such as a Bessel function) across a reactor core minimizes power peaking between nuclear fission fuel subassemblies within the core and enhances fuel utilization. In a traveling wave nuclear fission reactor, as described above, the burning region of the reactor tends to expand in size due to a high conversion ratio. The burning region is maintained with sufficient feed nuclear material, such as fertile isotopic material or fissile material, to maintain a high conversion ratio. It will be appreciated that in some reactor configurations, there are advantages to migrating nuclear fission fuel subassemblies as described above to maintain desired reactor burn-front characteristics. For example, migrating the nuclear fission fuel subassemblies radially into the burn region may act to supply either fertile isotopic material or fissile material to the reaction zone. Moving nuclear fission fuel subassemblies radially outward may serve to migrate nuclear fission fuel subassemblies having reached their burn-up limit out of an area of high neutronic activity. Radially outward movement may also serve to lower the power density of the burning region by spreading fissile, burnable, nuclear fission fuel material to previously non-burning regions. It will be appreciated that radial movement combined with spiral movement allows for a finer spatial increment of radial motion combined with azimuthal movement for yet further burnfront shaping. It will also be appreciated that, in some cases, nuclear fission fuel subassemblies may be exchanged (or interchanged) with nuclear fission fuel subassemblies in other locations. In such cases, fertile isotopic material may be exchanged from a fertile blanket region with well-burned material from the reactor burning region. In other cases, nuclear fission fuel material may be exchanged from directly-adjacent reactor core locations such that two or more nuclear fission fuel subassemblies trade locations. In some embodiments and referring additionally to FIG. 1W, the shape of the nuclear fission traveling wave burnfront 22 along the second dimension may be asymmetrical. In some arrangements, the shape of the nuclear fission traveling wave burnfront 22 may be rotationally asymmetrical around the second dimension. In some embodiments and referring additionally to FIG. 1X, the method 20 may also include initiating the nuclear fission traveling wave burnfront 22 with nuclear fission traveling wave igniter assemblies (not shown) at a block 52. Illustrative examples of initiation of a nuclear fission traveling wave with nuclear fission traveling wave igniter assemblies have been discussed above and need not be repeated. Referring additionally to FIG. 1Y, at a block 54 at least one of the nuclear fission traveling wave igniter assemblies may be removed prior to controllably migrating selected ones of the nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. Referring additionally to FIG. 1Z, in some embodiments, removing at least one of the nuclear fission traveling wave igniter assemblies at the block 54 prior to controllably migrating selected ones of the nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations may include, at a block 56, removing at least one of the nuclear fission traveling wave igniter assemblies from the second locations prior to controllably migrating selected ones of the nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. In some embodiments and referring additionally to FIG. 1AA, at a block 58 the nuclear fission traveling wave reactor is caused to become subcritical prior to controllably migrating selected ones of the nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. For example and referring additionally to FIG. 1AB, in some embodiments causing the nuclear fission traveling wave reactor to become subcritical at the block 58 may include inserting neutron absorbing material into the reactor core at a block 60. Referring additionally to FIG. 1AC, in some embodiments at a block 62 criticality may be re-established after controllably migrating selected ones of the nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. For example and referring additionally to FIG. 1AD, in some embodiments re-establishing criticality at the block 62 may include removing at least a portion of neutron absorbing material from the reactor core at a block 64. In some embodiments and referring additionally to FIG. 1AE, at a block 66 the nuclear fission traveling wave reactor may be shut down prior to controllably migrating selected ones of the nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. Referring additionally to FIG. 1AF, at a block 68 the nuclear fission traveling wave reactor may be re-started after controllably migrating selected ones of the nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. Referring now to FIG. 2A and FIG. 1B, an illustrative method 200 is provided for controlling a nuclear fission traveling wave reactor in which a nuclear fission traveling wave burnfront 22 is propagating along first and second dimensions. The method 200 starts at a block 202. At a block 204 a desired shape of the nuclear fission traveling wave burnfront 22 is determined along the second dimension within the nuclear fission fuel subassemblies 14 according to a selected set of dimensional constraints. At a block 206 a migration of selected ones of the nuclear fission fuel subassemblies 14 is determined along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. Referring additionally to FIG. 2B, in some embodiments at a block 210 an existing shape of the nuclear fission traveling wave burnfront 22 is determined. It will be appreciated that determining the existing shape of the nuclear fission traveling wave burnfront 22 at the block 210 may be performed as desired in relation to determining the desired shape of the nuclear fission traveling wave burnfront 22 at the block 204. In some embodiments determining the existing shape of the nuclear fission traveling wave burnfront 22 at the block 210 may be performed prior to determining the desired shape of the nuclear fission traveling wave burnfront 22 at the block 204. In some other embodiments determining the existing shape of the nuclear fission traveling wave burnfront 22 at the block 210 may be performed substantially simultaneously with determining the desired shape of the nuclear fission traveling wave burnfront 22 at the block 204. In some other embodiments determining the existing shape of the nuclear fission traveling wave burnfront 22 at the block 210 may be performed after determining the desired shape of the nuclear fission traveling wave burnfront 22 at the block 204. The desired shape may be determined as desired, including determination of fission rate, estimated burn-up, breeding rate, temperature distribution, power distribution, assembly operational history, and reactivity worth of the migrated nuclear fission fuel material within respective locations. It will be appreciated that the selected ones of the nuclear fission fuel subassemblies 14 may be migrated for any purpose as desired for a particular application, such as establishing the desired shape of the nuclear fission traveling wave burnfront 22 and/or maintaining the desired shape of the nuclear fission traveling wave burnfront 22. For example, in some embodiments and referring additionally to FIG. 2C, determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape at the block 206 may include determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner to establish the desired shape at a block 212. In some other embodiments and referring additionally to FIG. 2D, determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape may include determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner to maintain the desired shape at a block 214. It will be appreciated that it may be desirable to determine, among other things, a time when to perform desired migration. To that end and referring to FIG. 2E, in some embodiments at a block 216 a determination is made of a time when to migrate the selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. It will also be appreciated that the determination at the block 216 may be made at any point in performance of the method 200 as desired. In some embodiments the selected ones of the nuclear fission fuel subassemblies 14 may be migrated. Referring additionally to FIG. 2F, at a block 218 the selected ones of the nuclear fission fuel subassemblies 14 may be migrated along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. It will be appreciated that some aspects of the method 200 are similar to some of the aspects of the method 10 that have been explained above. These similar aspects will be mentioned but, for sake of brevity, their details need not be explained for an understanding. For example and referring additionally to FIG. 1B, in some embodiments the nuclear fission fuel subassemblies 14 may be elongate along the second dimension. The first dimension may be substantially orthogonal to an elongated axis of the nuclear fission subassemblies 14. The first dimension and the second dimension may be substantially orthogonal to each other. In further examples and still referring additionally to FIG. 1B, the first dimension may include a radial dimension and the second dimension may include an axial dimension. In some other examples, the first dimension may include an axial dimension and the second dimension may include a radial dimension. Nuclear fission reactors of any type may include nuclear fission fuel subassemblies that extend across the entire axial dimension with multiple nuclear fission fuel subassemblies extending across the radial dimension. A nuclear fission traveling wave may propagate along and axial dimension at a different rate than in the radial dimension depending on the power distribution and the divergence, in this case, of the nuclear fission traveling wave from inner regions to outer regions, particularly in cylindrical reactor core configurations. It is desirable in this case to perform radial migrations of nuclear fission fuel subassemblies to preserve wave shape and characteristics in the axial dimension. For example, propagation of the nuclear fission traveling wave to the axial extent of the reactor region will promote leakage of neutrons from the reactor core at the reactor core's axial ends. Such leakage, as described above, lessens the fertile-to-fissile conversion within the nuclear fission reactor. Nuclear fission fuel subassemblies with a burnfront that is expanding to undesired axial locations may be moved radially such that the nuclear fission fuel subassemblies are subjected to neutronic activity at locations within the nuclear fission fuel subassembly which reduce or limit further burnfront propagation to undesired locations. In other cases, it may be desirable to move nuclear fission fuel subassemblies radially based on nuclear fission traveling wave propagation in the axial dimension such that fissile material having been bred into the axial regions of the nuclear fission fuel subassembly may be used in other portions of the nuclear fission reactor core. At a given axial location, the burn-front may be made non-uniform in the radial dimension through controlled migration of nuclear fission fuel subassemblies such that, if desired, alternating zones of varying enrichment can be created. Placing high enrichment zones next to depleted or low enrichment zones increases neutron leakage from the high enrichment zone to the low enrichment zone, thereby facilitating conversion of the fertile isotopic material to fissile material. It will be appreciated that the above migrations may be performed to promote propagation in a first dimension while limiting propagation in a second dimension. In some further examples and still referring additionally to FIG. 1B, the first dimension may include an axial dimension and the second dimension may include a lateral dimension. In other examples, the first dimension may include a lateral dimension and the second dimension may include an axial dimension. As discussed above and referring additionally to FIG. 1C, the first locations may include the outward locations 30 and the second locations may include the inward locations 32. As also discussed above, the inward locations 32 and the outward locations 30 may be based on geometrical proximity to a central portion of the reactor core 12. The inward locations 32 and the outward locations 30 may also be based on neutron flux such that neutron flux at the inward locations 32 is greater than neutron flux at the outward locations 30. As discussed above, the inward locations 32 and the outward locations 30 may be based on reactivity such that keffective at the inward locations 32 is greater than keffective at the outward locations 30. In some embodiments and referring additionally to FIG. 1D, the first locations may include the inward locations 32 and the second locations may include the outward locations 30. The inward locations and the outward locations may be based on geometrical proximity to a central portion of the reactor core 12, and/or based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations, and/or based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. In some embodiments and as shown in FIG. 1B, the first locations and the second locations may be located on opposite sides of a reference value along the first dimension. As also shown in FIG. 1B, in some embodiments the first locations and the second locations may include at least one attribute that is substantially equalized. For example, the at least one attribute may include geometrical proximity to a central region of the reactor core 12, neutron flux, and/or reactivity. In some embodiments and referring additionally to FIG. 2G, determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 206 may include determining a rotation of at least one of the selected ones of the nuclear fission fuel subassemblies 14 at a block 220. In some embodiments and referring additionally to FIG. 2H, determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 206 may include determining an inversion of at least one of the selected ones of the nuclear fission fuel subassemblies 14 at a block 222. In some embodiments the selected set of dimensional constraints may include a predetermined maximum distance along the second dimension. In some other embodiments the selected set of dimensional constraints is a function of at least one burnfront criteria. For example, the burnfront criteria may include neutron flux, such as without limitation neutron flux that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14. As another example, the burnfront criteria may include neutron fluence, such as without limitation neutron fluence that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14. As another example, the burnfront criteria may include burnup, such as without limitation burnup that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14. In some other embodiments the burnfront criteria may include burnfront location within at least one of the selected ones of the nuclear fission fuel subassemblies 14. Referring additionally to FIG. 2I, in some embodiments determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 206 may include determining a radial migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at a block 224. In some embodiments and referring additionally to FIG. 2J, determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 206 may include determining a spiral migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at a block 226. In some other embodiments and referring additionally to FIG. 2K, determining a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations at the block 206 may include determining an axial translation of selected ones of the nuclear fission fuel subassemblies 14 at a block 228. Referring additionally to FIG. 2L, in some embodiments determining a desired shape of the nuclear fission traveling wave burnfront 22 at the block 204 may include determining a substantially spherical shape of the nuclear fission traveling wave burnfront 22 at a block 230. In some other embodiments and referring additionally to FIG. 2M, determining a desired shape of the nuclear fission traveling wave burnfront 22 along the second dimension at the block 204 may include determining a continuously curved surface shape of the nuclear fission traveling wave burnfront 22 at a block 232. In some other embodiments, the curved surface may be made such that the surface area of the burnfront is enhanced. In such embodiments, leakage of neutrons from burning zones to breeding zones is enhanced. The desired shape of the nuclear fission traveling wave burnfront 22 may be any shape. As discussed above, in various embodiments the desired shape of the nuclear fission traveling wave burnfront 22 may be substantially rotationally symmetrical around the second dimension; the desired shape of the nuclear fission traveling wave burnfront 22 may have substantial n-fold rotational symmetry around the second dimension; the desired shape of the nuclear fission traveling wave burnfront 22 may be asymmetrical; and/or the desired shape of the nuclear fission traveling wave burnfront 22 may be rotationally asymmetrical around the second dimension. In some other embodiments symmetrical shapes of n-fold symmetry may be transformed into separate burning zones within the nuclear fission traveling wave reactor core. For example, the burnfront can be transformed into lobes that can further be propagated into n- or less separate (that is, neutronically decoupled) burning regions (see FIG. 1V). Some embodiments may be provided as illustrative systems. For example and referring now to FIG. 3A, an illustrative system 300 is provided for determining migration of nuclear fission fuel subassemblies (not shown in FIG. 3A). Given by way of non-limiting example, the system 300 may provide a suitable system environment for performance of the method 200 (FIGS. 2A-2M). In some embodiments and referring additionally to FIG. 1B, for the nuclear fission traveling wave burnfront 22 propagating along the first and second dimensions, electrical circuitry 302 is configured to determine a desired shape of the nuclear fission traveling wave burnfront 22 along the second dimension within the nuclear fission fuel subassemblies 14 according to a selected set of dimensional constraints. Electrical circuitry 304 is configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. In a general sense, those skilled in the art will recognize that the various aspects described herein which can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, and/or any combination thereof can be viewed as being composed of various types of “electrical circuitry.” Consequently, as used herein “electrical circuitry” includes, but is not limited to, electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer configured by a computer program which at least partially carries out processes and/or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and/or devices described herein), electrical circuitry forming a memory device (e.g., forms of memory (e.g., random access, flash, read only, etc.)), and/or electrical circuitry forming a communications device (e.g., a modem, communications switch, optical-electrical equipment, etc.). Those having skill in the art will recognize that the subject matter described herein may be implemented in an analog or digital fashion or some combination thereof. Referring additionally to FIG. 3B, in an illustrative example the electrical circuitry 302 and/or the electrical circuitry 304 may be embodied as a computing system 306 (that also may be referred to as a host computer or system). In an illustrative embodiment a central processing unit (“CPU”) (or microprocessor) 308 is connected to a system bus 310. Random access main memory (“RAM”) 312 is coupled to the system bus 310 and provides the CPU 308 with access to memory storage 314 (which may be used for storage of data associated with one or more parameters of the nuclear fission traveling wave burnfront 22). When executing program instructions, the CPU 308 stores those process steps in the RAM 312 and executes the stored process steps out of the RAM 312. The computing system 306 may connect to a computer network (not shown) via a network interface 316 and through a network connection (not shown). One such network is the Internet that allows the computing system 306 to download applications, code, documents and other electronic information. Read only memory (“ROM”) 318 is provided to store invariant instruction sequences such as start-up instruction sequences or basic input/output operating system (BIOS) sequences. An Input/Output (“I/O”) device interface 320 allows the computing system 306 to connect to various input/output devices, for example, a keyboard, a pointing device (“mouse”), a monitor, printer, a modem, and the like. The I/O device interface 320 is shown as a single block for simplicity and may include several interfaces to interface with different types of I/O devices. It will be appreciated that embodiments are not limited to the architecture of the computing system 306 shown in FIG. 3B. Based on the type of applications/business environment, the computing system 306 may have more or fewer components. For example, the computing system 306 can be a set-top box, a lap-top computer, a notebook computer, a desktop system, or other types of systems. In various embodiments, portions of disclosed systems and methods include one or more computer program products. The computer program product includes a computer-readable storage medium, such as the non-volatile storage medium, and computer-readable program code portions, such as a series of computer instructions, embodied in the computer-readable storage medium. Typically, the computer program is stored and executed by a processing unit or a related memory device, such as the processing components depicted in FIG. 3B. In this regard, FIGS. 2A-2M and 3A-3C are flowcharts and block diagrams, respectively, of methods, systems, and program products according to various embodiments. It will be understood that each block of the flowcharts and block diagrams, and combinations of blocks in the flowcharts and block diagrams, can be implemented by computer program instructions. These computer program instructions may be loaded onto a computer or other programmable apparatus to produce a machine, such that the instructions which execute on the computer or other programmable apparatus create means for implementing the functions specified in the flowchart(s) or block diagram(s). These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart(s) or block diagram(s). The computer program instructions may also be loaded onto a computer or other programmable apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart(s) or block diagram(s). Accordingly, blocks of the flowchart or block diagram support combinations of means for performing the specified functions, combinations of steps for performing the specified functions, and program instruction means for performing the specified functions. It will also be understood that each block of the flowchart or block diagram and combinations of blocks in the flowchart(s) or block diagram(s) can be implemented by special purpose hardware-based computer systems which perform the specified functions or steps, or combinations of special purpose hardware and computer instructions. Referring additionally to FIG. 3C, in some embodiments the electrical circuitry 304 may be further configured to determine an existing shape of the nuclear fission traveling wave burnfront 22. For example, sensors 322 may be operatively coupled to the electrical circuitry 304 in signal communication via a suitable input interface 324. The sensors 322 may include any suitable sensor that measures a parameter of the nuclear fission traveling wave burnfront 22. For example, the sensors 322 may measure neutron flux, neutron fluence, burnup, and/or reactivity (or any of their components). As discussed above, embodiments of the system 300 and the electrical circuitry 302 and 304 may be configured to provide a suitable system environment for performance of the method 200 (FIGS. 2A-2M) regardless of whether computer program instructions are loaded onto a computer or other programmable apparatus to produce a machine such that the instructions which execute on the computer or other programmable apparatus create means for implementing the functions specified in the flowchart(s) or block diagram(s) or each block of the flowchart or block diagram and combinations of blocks in the flowchart(s) or block diagram(s) are implemented by special purpose hardware-based computer systems which perform the specified functions or steps, or combinations of special purpose hardware and computer instructions. Some features of embodiments of the system 300 will be discussed with reference additionally to FIGS. 1B-D, 1J, 1L, 1O, 1Q, 1R-1W, and 2A-2M. To that end, in some embodiments the electrical circuitry 304 may be further configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner to establish the desired shape. The electrical circuitry 304 may be further configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner to maintain the desired shape. The electrical circuitry 304 may be further configured to determine a time when to migrate the selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. As discussed above, in some embodiments the nuclear fission fuel subassemblies 14 may be elongate along the second dimension. As also discussed above, in some embodiments the first dimension may be substantially orthogonal to an elongated axis of the nuclear fission subassemblies 14. In some other embodiments, the first dimension and the second dimension may be substantially orthogonal to each other. In various embodiments the first dimension may include a radial dimension and the second dimension may include an axial dimension; the first dimension may include an axial dimension and the second dimension may include a radial dimension; the first dimension may include an axial dimension and the second dimension may include a lateral dimension; and/or the first dimension may include a lateral dimension and the second dimension may include an axial dimension. In some embodiments the first locations may include the outward locations 30 and the second locations may include the inward locations 32. The inward locations 32 and the outward locations 30 may be based on various attributes as desired, such as without limitation geometrical proximity to a central portion of the reactor core 12, neutron flux such that neutron flux at the inward locations 32 is greater than neutron flux at the outward locations 30, and/or reactivity such that keffective at the inward locations 32 is greater than keffective at the outward locations 30. In some other embodiments the first locations may include the inward locations 32 and the second locations may include the outward locations 30. The inward locations 32 and the outward locations 30 may be based on various attributes as desired, such as without limitation geometrical proximity to a central portion of the reactor core 12, neutron flux such that neutron flux at the inward locations 32 is greater than neutron flux at the outward locations 30, and/or reactivity such that keffective at the inward locations 32 is greater than keffective at the outward locations 30. In some embodiments the first locations and the second locations may be located on opposite sides of a reference value along the first dimension. In some other embodiments the first locations and the second locations may include at least one attribute that is substantially equalized. For example, the at least one attribute may include geometrical proximity to a central region of the reactor core 12, neutron flux, and/or reactivity. In some embodiments the electrical circuitry 304 may be further configured to determine rotation of at least one of the selected ones of the nuclear fission fuel subassemblies 14. In some other embodiments the electrical circuitry 304 may be further configured to determine inversion of at least one of the selected ones of the nuclear fission fuel subassemblies 14. As discussed above, in some embodiments the selected set of dimensional constraints may include a predetermined maximum distance along the second dimension. In some other embodiments the selected set of dimensional constraints may be a function of at least one burnfront criteria. For example, the burnfront criteria may include without limitation: neutron flux, such as neutron flux that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14; neutron fluence, such as neutron fluence that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14; and/or burnup, such as burnup that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14. In some embodiments the burnfront criteria may include burnfront location within at least one of the selected ones of the nuclear fission fuel subassemblies 14. In some embodiments the electrical circuitry 304 may be further configured to determine a radial migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations. The electrical circuitry 304 may be further configured to determine a spiral migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations. The electrical circuitry 304 may be further configured to determine an axial translation of selected ones of the nuclear fission fuel subassemblies 14. In some embodiments the electrical circuitry 302 may be further configured to determine a substantially spherical shape of the nuclear fission traveling wave burnfront 22. The electrical circuitry 302 may be further configured to determine a continuously curved surface shape of the nuclear fission traveling wave burnfront 22. In various embodiments the desired shape of the nuclear fission traveling wave burnfront 22 may be substantially rotationally symmetrical around the second dimension; may have substantial n-fold rotational symmetry around the second dimension; and/or may be asymmetrical, such as without limitation by being rotationally asymmetrical around the second dimension. As another example and referring now to FIG. 4A, another illustrative system 400 is provided for migrating nuclear fission fuel subassemblies (not shown in FIG. 3A). Given by way of non-limiting example, the system 400 may provide a suitable system environment for performance of the method 100 (FIGS. 1A-1AF). As such, the following discussion is made with additional reference to FIGS. 1A-1AF. In some embodiments, for the nuclear fission traveling wave burnfront 22 propagating along the first and second dimensions, electrical circuitry 402 is configured to determine a desired shape of the nuclear fission traveling wave burnfront 22 along the second dimension within the nuclear fission fuel subassemblies 14 according to a selected set of dimensional constraints. Electrical circuitry 404 is configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. A subassembly 405 is configured to migrate selected ones of the nuclear fission fuel subassemblies 14 responsive to the electrical circuitry 404. It will be appreciated that the electrical circuitry 402 and 404 may be similar to the electrical circuitry 302 and 304. In some cases, the electrical circuitry 402 and 404 may be the same as the electrical circuitry 302 and 304. To that end and for sake of brevity, details need not be repeated for an understanding. As a brief overview and referring additionally to FIG. 4B, in an illustrative example the electrical circuitry 402 and/or the electrical circuitry 404 may be embodied as a computing system 406 (that also may be referred to as a host computer or system). In an illustrative embodiment a central processing unit (“CPU”) (or microprocessor) 408 is connected to a system bus 410. Random access main memory (“RAM”) 412 is coupled to the system bus 410 and provides the CPU 408 with access to memory storage 414 (which may be used for storage of data associated with one or more parameters of the nuclear fission traveling wave burnfront 22). When executing program instructions, the CPU 408 stores those process steps in the RAM 412 and executes the stored process steps out of the RAM 412. The computing system 406 may connect to a computer network (not shown) via a network interface 416 and through a network connection (not shown). Read only memory (“ROM”) 418 is provided to store invariant instruction sequences such as start-up instruction sequences or basic input/output operating system (BIOS) sequences. An Input/Output (“I/O”) device interface 420 allows the computing system 406 to connect to various input/output devices, for example, a keyboard, a pointing device (“mouse”), a monitor, printer, a modem, and the like. It will be appreciated that embodiments are not limited to the architecture of the computing system 406 shown in FIG. 4B. The discussion of non-limitation regarding the computing system 306 (FIG. 3B) also applies to the computing system 406. In various embodiments, portions of disclosed systems and methods include one or more computer program products. The discussion above regarding computer program products related to the system 300 (FIG. 3A) also applies to the system 400. In this regard, FIGS. 1A, 1I, 1K, 1M-1N, 1P, and 1X-1AF and 4A-4C are flowcharts and block diagrams, respectively, of methods, systems, and program products according to various embodiments. It will be understood that each block of the flowcharts and block diagrams, and combinations of blocks in the flowcharts and block diagrams, can be implemented by computer program instructions. These computer program instructions may be loaded onto a computer or other programmable apparatus to produce a machine, such that the instructions which execute on the computer or other programmable apparatus create means for implementing the functions specified in the flowchart(s) or block diagram(s). These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart(s) or block diagram(s). The computer program instructions may also be loaded onto a computer or other programmable apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart(s) or block diagram(s). Accordingly, blocks of the flowchart or block diagram support combinations of means for performing the specified functions, combinations of steps for performing the specified functions, and program instruction means for performing the specified functions. It will also be understood that each block of the flowchart or block diagram and combinations of blocks in the flowchart(s) or block diagram(s) can be implemented by special purpose hardware-based computer systems which perform the specified functions or steps, or combinations of special purpose hardware and computer instructions. Referring additionally to FIG. 4C, in some embodiments the electrical circuitry 404 may be further configured to determine an existing shape of the nuclear fission traveling wave burnfront 22. For example, sensors 422 may be operatively coupled to the electrical circuitry 404 in signal communication via a suitable input interface 424. The electrical circuitry 404, sensors 422, and input interface 424 may be similar to (and in some cases may be the same as) the electrical circuitry 304, sensors 322, and input interface 324 (all FIG. 3C). Repetition of their details is not necessary for an understanding. As discussed above, embodiments of the system 400, the electrical circuitry 402 and 404, and the subassembly 405 may be configured to provide a suitable system environment for performance of the method 100 (FIGS. 1A, 1I, 1K, 1M-1N, 1P, and 1X-1AF) regardless of whether computer program instructions are loaded onto a computer or other programmable apparatus to produce a machine such that the instructions which execute on the computer or other programmable apparatus create means for implementing the functions specified in the flowchart(s) or block diagram(s) or each block of the flowchart or block diagram and combinations of blocks in the flowchart(s) or block diagram(s) are implemented by special purpose hardware-based computer systems which perform the specified functions or steps, or combinations of special purpose hardware and computer instructions. Some features of embodiments of the system 400 will be discussed with reference additionally to FIGS. 1A-1AF. In some embodiments and referring to FIG. 4C, the electrical circuitry 404 may be further configured to determine an existing shape of the nuclear fission traveling wave burnfront 22. Such a determination may be made in a similar or same manner by the electrical circuitry 304 (FIG. 3A) as described above. To that end, sensors 422 and an input interface 424 are similar or, in some cases, the same as the sensors 322 and the input interface 324 (all FIG. 3C). The sensors 422, input interface 424, and electrical circuitry 404 cooperate as discussed above for the sensors 322, input interface 324, and electrical circuitry 304 (all FIG. 3C). In some embodiments, the electrical circuitry 404 may be further configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner to establish the desired shape. In some other embodiments, the electrical circuitry 404 may be further configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner to maintain the desired shape. In some embodiments the electrical circuitry 404 may be further configured to determine a time when to migrate the selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. In some embodiments, the nuclear fission fuel subassemblies 14 may be elongate along the second dimension. The first dimension may be substantially orthogonal to an elongated axis of the nuclear fission subassemblies 14. The first dimension and the second dimension may be substantially orthogonal to each other. In various embodiments, the first dimension may include a radial dimension and the second dimension may includes an axial dimension; the first dimension may include an axial dimension and the second dimension may include a radial dimension; the first dimension may include an axial dimension and the second dimension may include a lateral dimension; and/or the first dimension may include a lateral dimension and the second dimension may include an axial dimension. In some embodiments the first locations may include the outward locations 30 and the second locations may include the inward locations 32. The inward locations 32 and the outward locations 30 may be based on: geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the inward locations 32 is greater than neutron flux at the outward locations 30; and/or reactivity such that keffective at the inward locations 32 is greater than keffective at the outward locations 30. In some other embodiments the first locations may include the inward locations 32 and the second locations include the outward locations 30. The inward locations and outward locations may be based on geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the inward locations 32 is greater than neutron flux at the outward locations 30; and/or reactivity such that keffective at the inward locations 32 is greater than keffective at the outward locations 30. In some embodiments the first locations and the second locations may be located on opposite sides of a reference value along the first dimension. In some other embodiments the first locations and the second locations may include at least one attribute that is substantially equalized. For example, the at least one attribute may include geometrical proximity to a central region of the reactor core 12; neutron flux; and/or reactivity. In various embodiments the electrical circuitry 404 may be further configured to determine rotation of at least one of the selected ones of the nuclear fission fuel subassemblies 14. The electrical circuitry 404 may be further configured to determine inversion of at least one of the selected ones of the nuclear fission fuel subassemblies 14. The subassembly 405 may include any suitable nuclear fuel handling apparatus known in the art, such as without limitation an in-core nuclear fuel handling apparatus. However, in some other embodiments the subassembly 405 may include an extra-core fuel handling apparatus. Regardless of form in which the subassembly 405 is embodied, in various embodiments the subassembly 405 may be further configured to radially migrate selected ones of the nuclear fission fuel subassemblies 14 from respective first locations toward respective second locations. The subassembly 405 may be further configured to spirally migrate selected ones of the nuclear fission fuel subassemblies 14 from respective first locations toward respective second locations. The subassembly 405 may be further configured to axially translate selected ones of the nuclear fission fuel subassemblies. In some embodiments the subassembly 405 may be further configured to rotate selected ones of the nuclear fission fuel subassemblies 14. In some other embodiments the subassembly 405 may be further configured to invert selected ones of the nuclear fission fuel subassemblies 14. Referring now to FIG. 5, in various embodiments an illustrative nuclear fission traveling wave reactor 500 may be provided. The nuclear fission traveling wave reactor 500 includes the nuclear fission traveling wave reactor core 12. As discussed above, the nuclear fission fuel subassemblies 14 are received in the nuclear fission traveling wave reactor core 12. Each of the nuclear fission fuel subassemblies 12 are configured to propagate the nuclear fission traveling wave burnfront 22 therein along first and second dimensions. The electrical circuitry 402 is configured to determine a desired shape of the nuclear fission traveling wave burnfront 22 along the second dimension within the nuclear fission fuel subassemblies 14 according to a selected set of dimensional constraints. The electrical circuitry 404 is configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. The subassembly 405 is configured to migrate selected ones of the nuclear fission fuel subassemblies 14 responsive to the electrical circuitry 404. Thus, the reactor 500 may be embodied as the reactor core 12, discussed above, in combination with and cooperating with the system 400, also discussed above. Because details have been set forth above regarding the reactor core 12 (and its components) and the system 400 (and its components), details need not be repeated for an understanding. As has been discussed above, in various embodiments the electrical circuitry 404 may be further configured to determine an existing shape of the nuclear fission traveling wave burnfront 22. The electrical circuitry 404 may be further configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner to establish the desired shape. The electrical circuitry 404 may be further configured to determine a migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner to maintain the desired shape. As discussed above, in some embodiments the electrical circuitry 404 may be further configured to determine a time when to migrate the selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. In some embodiments the nuclear fission fuel subassemblies 14 may be elongate along the second dimension. In some embodiments the first dimension may be substantially orthogonal to an elongated axis of the nuclear fission subassemblies 14. In some embodiments the first dimension and the second dimension may be substantially orthogonal to each other. In various embodiments, the first dimension may include a radial dimension and the second dimension may include an axial dimension; the first dimension may include an axial dimension and the second dimension may include a radial dimension; the first dimension may include an axial dimension and the second dimension may include a lateral dimension; and/or the first dimension may include a lateral dimension and the second dimension may include an axial dimension. In some embodiments the first locations may include the outward locations 30 and the second locations include the inward locations 32. The inward locations 32 and the outward locations 30 may be based on geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the inward locations 32 is greater than neutron flux at the outward locations 30; and/or reactivity such that keffective at the inward locations 32 is greater than keffective at the outward locations 30. In some other embodiments the first locations may include the inward locations 32 and the second locations may include the outward locations 30. The inward locations 32 and the outward locations 30 may be based on geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the inward locations 32 is greater than neutron flux at the outward locations 30; and/or reactivity such that keffective at the inward locations 32 is greater than keffective at the outward locations 30. In some embodiments the first locations and the second locations may be located on opposite sides of a reference value along the first dimension. In some embodiments the first locations and the second locations may include at least one attribute that is substantially equalized. The at least one attribute may include geometrical proximity to a central region of the reactor core 12; neutron flux; and/or reactivity. In various embodiments and as discussed above, the electrical circuitry 404 may be further configured to determine rotation of at least one of the selected ones of the nuclear fission fuel subassemblies 14 and/or further configured to determine inversion of at least one of the selected ones of the nuclear fission fuel subassemblies 14. In some embodiments the selected set of dimensional constraints may include a predetermined maximum distance along the second dimension. In some other embodiments the selected set of dimensional constraints may be a function of at least one burnfront criteria, such as without limitation: neutron flux, such as neutron flux that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14; neutron fluence, such as neutron fluence that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14; and/or burnup, such as burnup that is associated with at least one of the selected ones of the nuclear fission fuel subassemblies 14. In some other embodiments the burnfront criteria may include burnfront location within at least one of the selected ones of the nuclear fission fuel subassemblies 14. In various embodiments the electrical circuitry 404 may be further configured to determine a radial migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations. The electrical circuitry 404 may be further configured to determine a spiral migration of selected ones of the nuclear fission fuel subassemblies 14 along the first dimension from respective first locations toward respective second locations. The electrical circuitry 404 may be further configured to determine an axial translation of selected ones of the nuclear fission fuel subassemblies 14. In various embodiments the electrical circuitry 402 may be further configured to determine a substantially spherical shape of the nuclear fission traveling wave burnfront 22 and/or a continuously curved surface shape of the nuclear fission traveling wave burnfront 22. The desired shape of the nuclear fission traveling wave burnfront 22 may be substantially rotationally symmetrical around the second dimension; may have substantial n-fold rotational symmetry around the second dimension; and/or may be asymmetrical, such as rotationally asymmetrical around the second dimension. In some embodiments the subassembly 405 may include a nuclear fuel handling apparatus. As discussed above, the subassembly 405 may include any suitable nuclear fuel handling apparatus known in the art, such as without limitation an in-core nuclear fuel handling apparatus. However, in some other embodiments the subassembly 405 may include an extra-core fuel handling apparatus. As also discussed above, in various embodiments the subassembly 405 may be further configured to radially migrate selected ones of the nuclear fission fuel subassemblies 14 from respective first locations toward respective second locations. The subassembly 405 may be further configured to spirally migrate selected ones of the nuclear fission fuel subassemblies 14 from respective first locations toward respective second locations. The subassembly 405 may be further configured to axially translate selected ones of the nuclear fission fuel subassemblies 14. The subassembly 405 may be further configured to rotate selected ones of the nuclear fission fuel subassemblies 14. The subassembly 405 may be further configured to invert selected ones of the nuclear fission fuel subassemblies 14. Referring now to FIG. 6A, in some embodiments a method 600 is provided for operating a nuclear fission traveling wave reactor. The method 600 starts at a block 602. Referring additionally to FIG. 1B, at a block 604 at least one nuclear fission fuel assembly 14 is migrated outwardly from a first location in the nuclear fission traveling wave reactor core 12 to a second location in the nuclear fission traveling wave reactor core 12. The method 600 stops at a block 606. In some embodiments and referring additionally to FIG. 6B, at a block 608 the at least one nuclear fission fuel assembly 14 may be migrated inwardly from the second location. In various embodiments, the first locations and the second locations may be based on geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the first locations is greater than neutron flux at the second locations; and reactivity such that keffective at the first locations is greater than keffective at the second locations. Referring now to FIG. 7, in some embodiments a method 700 is provided for operating a nuclear fission traveling wave reactor. The method 700 starts at a block 702. Referring additionally to FIG. 1B, at a block 704 a migration is determined of at least one nuclear fission fuel assembly 14 in a first direction from a first location in a nuclear fission traveling wave reactor core 12 to a second location in the nuclear fission traveling wave reactor core 12. The second location is different from the first location. At a block 706 a migration is determined of the at least one nuclear fission fuel assembly 14 in a second direction from the second location. The second direction is different from the first direction. The method 700 stops at a block 708. In some embodiments, the first direction may be outwardly and the second direction may be inwardly. The first locations and the second locations may be based various attributes or parameters, such as without limitation: geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the first locations is greater than neutron flux at the second locations; and/or reactivity such that keffective at the first locations is greater than keffective at the second locations. In some other embodiments, the first direction may be inwardly and the second direction may be outwardly. The second locations and the first locations may be based on various attributes or parameters, such as without limitation: geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the second locations is greater than neutron flux at the first locations; and/or reactivity such that keffective at the second locations is greater than keffective at the first locations. Referring now to FIG. 8, in some embodiments a method 800 is provided for operating a nuclear fission traveling wave reactor. The method 800 starts at a block 802. Referring additionally to FIG. 1B, at a block 804 at least one nuclear fission fuel assembly 14 is migrated in a first direction from a first location in the nuclear fission traveling wave reactor core 12 to a second location in the nuclear fission traveling wave reactor core 12. The second location is different from the first location. At a block 806 a migration is determined of the at least one nuclear fission fuel assembly 14 in a second direction from the second location. The second direction is different from the first direction. The method 800 stops at a block 808. In some embodiments, the first direction may be outwardly and the second direction may be inwardly. The first locations and the second locations may be based various attributes or parameters, such as without limitation: geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the first locations is greater than neutron flux at the second locations; and/or reactivity such that keffective at the first locations is greater than keffective at the second locations. In some other embodiments, the first direction may be inwardly and the second direction may be outwardly. The second locations and the first locations may be based on various attributes or parameters, such as without limitation: geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the second locations is greater than neutron flux at the first locations; and/or reactivity such that keffective at the second locations is greater than keffective at the first locations. Referring now to FIG. 9, in some embodiments a method 900 is provided for operating a nuclear fission traveling wave reactor. The method 900 starts at a block 902. Referring additionally to FIG. 1B, at a block 904 at least one nuclear fission fuel assembly 14 is migrated in a first direction from a first location in the nuclear fission traveling wave reactor core 12 to a second location in the nuclear fission traveling wave reactor core 12. The second location is different from the first location. At a block 906 the at least one nuclear fission fuel assembly 14 is migrated in a second direction from the second location. The second direction is different from the first direction. The method 900 stops at a block 908. In some embodiments, the first direction may be outwardly and the second direction may be inwardly. The first locations and the second locations may be based various attributes or parameters, such as without limitation: geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the first locations is greater than neutron flux at the second locations; and/or reactivity such that keffective at the first locations is greater than keffective at the second locations. In some other embodiments, the first direction may be inwardly and the second direction may be outwardly. The second locations and the first locations may be based on various attributes or parameters, such as without limitation: geometrical proximity to a central portion of the reactor core 12; neutron flux such that neutron flux at the second locations is greater than neutron flux at the first locations; and/or reactivity such that keffective at the second locations is greater than keffective at the first locations. Referring now to FIG. 10A, in some embodiments a method 1000 is provided for operating a nuclear fission reactor. The method 1000 starts at a block 1002. At a block 1004 a predetermined burnup level is selected. At a block 1006 a migration is determined of selected ones of nuclear fission fuel assemblies in a nuclear fission reactor core in a manner to achieve a burnup level equalized toward the predetermined burnup level in substantially all of the nuclear fission fuel assemblies. The method 1000 stops at a block 1008. Referring additionally to FIG. 10B, in some embodiments at a block 1010 the selected ones of the nuclear fission fuel assemblies may be migrated in a nuclear fission reactor core in a manner responsive to the determined migration. Referring additionally to FIG. 10C, in some embodiments at a block 1012 removal may be determined of respective selected ones of the nuclear fission fuel assemblies when burnup level is equalized toward the predetermined burnup level. Referring additionally to FIG. 10D, in some embodiments at a block 1014 the selected ones of the nuclear fission fuel assemblies may be removed responsive to the determined removal. The present application uses formal outline headings for clarity of presentation. However, it is to be understood that the outline headings are for presentation purposes, and that different types of subject matter may be discussed throughout the application (e.g., device(s)/structure(s) may be described under process(es)/operations heading(s) and/or process(es)/operations may be discussed under structure(s)/process(es) headings; and/or descriptions of single topics may span two or more topic headings). Hence, the use of the formal outline headings is not intended to be in any way limiting. Those skilled in the art will appreciate that the foregoing specific exemplary processes and/or devices and/or technologies are representative of more general processes and/or devices and/or technologies taught elsewhere herein, such as in the claims filed herewith and/or elsewhere in the present application. Those having skill in the art will recognize that the state of the art has progressed to the point where there is little distinction left between hardware, software, and/or firmware implementations of aspects of systems; the use of hardware, software, and/or firmware is generally (but not always, in that in certain contexts the choice between hardware and software can become significant) a design choice representing cost vs. efficiency tradeoffs. Those having skill in the art will appreciate that there are various vehicles by which processes and/or systems and/or other technologies described herein can be effected (e.g., hardware, software, and/or firmware), and that the preferred vehicle will vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle; alternatively, if flexibility is paramount, the implementer may opt for a mainly software implementation; or, yet again alternatively, the implementer may opt for some combination of hardware, software, and/or firmware. Hence, there are several possible vehicles by which the processes and/or devices and/or other technologies described herein may be effected, none of which is inherently superior to the other in that any vehicle to be utilized is a choice dependent upon the context in which the vehicle will be deployed and the specific concerns (e.g., speed, flexibility, or predictability) of the implementer, any of which may vary. Those skilled in the art will recognize that optical aspects of implementations will typically employ optically-oriented hardware, software, and or firmware. In some implementations described herein, logic and similar implementations may include software or other control structures. Electronic circuitry, for example, may have one or more paths of electrical current constructed and arranged to implement various functions as described herein. In some implementations, one or more media may be configured to bear a device-detectable implementation when such media hold or transmit device detectable instructions operable to perform as described herein. In some variants, for example, implementations may include an update or modification of existing software or firmware, or of gate arrays or programmable hardware, such as by performing a reception of or a transmission of one or more instructions in relation to one or more operations described herein. Alternatively or additionally, in some variants, an implementation may include special-purpose hardware, software, firmware components, and/or general-purpose components executing or otherwise invoking special-purpose components. Specifications or other implementations may be transmitted by one or more instances of tangible transmission media as described herein, optionally by packet transmission or otherwise by passing through distributed media at various times. Alternatively or additionally, implementations may include executing a special-purpose instruction sequence or invoking circuitry for enabling, triggering, coordinating, requesting, or otherwise causing one or more occurrences of virtually any functional operations described herein. In some variants, operational or other logical descriptions herein may be expressed as source code and compiled or otherwise invoked as an executable instruction sequence. In some contexts, for example, implementations may be provided, in whole or in part, by source code, such as C++, or other code sequences. In other implementations, source or other code implementation, using commercially available and/or techniques in the art, may be compiled/implemented/translated/converted into a high-level descriptor language (e.g., initially implementing described technologies in C or C++ programming language and thereafter converting the programming language implementation into a logic-synthesizable language implementation, a hardware description language implementation, a hardware design simulation implementation, and/or other such similar mode(s) of expression). For example, some or all of a logical expression (e.g., computer programming language implementation) may be manifested as a Verilog-type hardware description (e.g., via Hardware Description Language (HDL) and/or Very High Speed Integrated Circuit Hardware Descriptor Language (VHDL)) or other circuitry model which may then be used to create a physical implementation having hardware (e.g., an Application Specific Integrated Circuit). Those skilled in the art will recognize how to obtain, configure, and optimize suitable transmission or computational elements, material supplies, actuators, or other structures in light of these teachings. The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, can be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein are capable of being distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., transmitter, receiver, transmission logic, reception logic, etc.), etc.). In a general sense, those skilled in the art will recognize that the various embodiments described herein can be implemented, individually and/or collectively, by various types of electro-mechanical systems having a wide range of electrical components such as hardware, software, firmware, and/or virtually any combination thereof; and a wide range of components that may impart mechanical force or motion such as rigid bodies, spring or torsional bodies, hydraulics, electro-magnetically actuated devices, and/or virtually any combination thereof. Consequently, as used herein “electro-mechanical system” includes, but is not limited to, electrical circuitry operably coupled with a transducer (e.g., an actuator, a motor, a piezoelectric crystal, a Micro Electro Mechanical System (MEMS), etc.), electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer configured by a computer program which at least partially carries out processes and/or devices described herein, or a microprocessor configured by a computer program which at least partially carries out processes and/or devices described herein), electrical circuitry forming a memory device (e.g., forms of memory (e.g., random access, flash, read only, etc.)), electrical circuitry forming a communications device (e.g., a modem, communications switch, optical-electrical equipment, etc.), and/or any non-electrical analog thereto, such as optical or other analogs. Those skilled in the art will also appreciate that examples of electro-mechanical systems include but are not limited to a variety of consumer electronics systems, medical devices, as well as other systems such as motorized transport systems, factory automation systems, security systems, and/or communication/computing systems. Those skilled in the art will recognize that electro-mechanical as used herein is not necessarily limited to a system that has both electrical and mechanical actuation except as context may dictate otherwise. All of the above U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in any Application Data Sheet, are incorporated herein by reference, to the extent not inconsistent herewith. One skilled in the art will recognize that the herein described components (e.g., operations), devices, objects, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken limiting. With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations are not expressly set forth herein for sake of clarity. The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components, and/or wirelessly interactable, and/or wirelessly interacting components, and/or logically interacting, and/or logically interactable components. While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that typically a disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase “A or B” will be typically understood to include the possibilities of “A” or “B” or “A and B.” With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those which are illustrated, or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
	abstract	A method for decontaminating a metal surface exposed to radioactive liquid or gas during operation of a nuclear facility comprises an oxidation step wherein a metal oxide layer on the metal surface is contacted with an aqueous oxidation solution comprising a permanganate oxidant for converting chromium into a Cr(VI) compound and dissolving the Cr(VI) compound in the oxidation solution; and a first cleaning step wherein the oxidation solution containing the Cr(VI) compound is directly passed over an anion exchange material and the Cr(VI) compound is immobilized on the anion exchange material. The method provides for substantial savings of radioactive waste and produces chelate-free waste.
	claims	1. A method for fabricating an x-ray collimator, comprising:identifying 3-dimensional structures and positions of the 3-dimensional structures in a collimator design;selecting a number of collimator layers;determining 2-dimensional shapes corresponding to the respective identified 3-dimensional structures for each layer;determining, in each collimator layer, positions of the 2-dimensional shapes corresponding to the respective identified 3-dimensional structures for each layer;forming apertures in at least one laminated layer to produce the selected number of collimator layers, each having apertures according to its respective determined 2-dimensional shapes at the respective determined positions;stacking the collimator layers in a position of alignment to form the identified 3-dimensional structures;attaching the stacked and aligned collimator layers to form a composite collimator structure with the identified 3-dimensional structures therein; andhoning the 3-dimensional structures within the composite collimator structure. 2. The method of claim 1, wherein the forming apertures in at least one laminated layer comprises:creating the collimator layers from as few as a single laminated layer by simultaneously forming a plurality of collimator layers at different sections of the as few as a single laminated layer, and extracting the plurality of collimator layers from its laminated layer. 3. The method of claim 1, wherein:the step of forming apertures in at least one laminated layer comprises photo-etching the at least one laminated layer to form the apertures. 4. The method of claim 1, wherein:the step of forming apertures in at least one laminated layer comprises punching the at least one laminated layer to form the apertures. 5. The method of claim 1, wherein:the step of forming apertures in at least one laminated layer comprises laser cutting the at least one laminated layer to form the apertures. 6. A method for fabricating an x-ray collimator, comprising:identifying 3-dimensional structures and positions of the 3-dimensional structures in a collimator design;selecting a number of collimator layers;determining 2-dimensional shapes corresponding to the respective identified 3-dimensional structures for each layer;determining, in each collimator layer, positions of the 2-dimensional shapes corresponding to the respective identified 3-dimensional structures for each layer;forming apertures in at least one laminated layer to produce the selected number of collimator layers, each having apertures according to its respective determined 2-dimensional shapes at the respective determined positions;stacking the collimator layers in a position of alignment to form the identified 3-dimensional structures; andattaching the stacked and aligned collimator layers to form a composite collimator structure with the identified 3-dimensional structures therein; andhoning the apertures of each collimator layer prior to stacking and attaching the collimator layers. 7. An x-ray collimator comprising:a plurality of collimator layers, each collimator layer corresponding to a respective cross-section of the x-ray collimator and each collimator layer having at least one aperture, the plurality of collimator layers stacked and attached to form a composite collimator structure wherein the apertures of the respective collimator layers are aligned to form 3-dimensional hollow pyramidal structures that direct x-rays generated by an x-ray source into x-ray beams. 8. The x-ray collimator of claim 7, wherein the plurality of collimator layers are made from thin laminated sheets. 9. The x-ray collimator of claim 7, wherein the plurality of collimator layers comprise Tungsten. 10. The x-ray collimator of claim 7, wherein at least one of the apertures of the collimator layers is honed. 11. The x-ray collimator of claim 7, wherein the 3-dimensional hollow pyramidal structures are fan beam apertures which collimate x-rays from the x-ray source into fan beams. 12. The x-ray collimator of claim 7, wherein the at least one of the apertures of the composite collimator structure has smooth meeting points between the layers so as to form a smooth surface through at least one of the 3-dimensional hollow pyramidal structures. 13. An x-ray collimator, comprising:a plurality of laminated layers having apertures therein, the plurality of laminated layers stacked and attached to form a composite collimator structure wherein the apertures of the respective laminated layers align to form 3-dimensional pyramidal apertures that direct x-rays generated by an x-ray source into x-ray beams. 14. The x-ray collimator of claim 13, wherein the at least one of the apertures of the composite collimator structure has smooth meeting points between the laminated layers so as to form a smooth surface through at least one of the 3-dimensional pyramidal apertures.
	description	1. Field This invention relates in general to spent nuclear fuel pools and, more particularly, to an emergency cooling system to maintain the safety of spent nuclear fuel pools. 2. Related Art Pressurized water nuclear reactors are typically refueled on an eighteen month cycle. During the refueling process, a portion of the irradiated fuel assemblies within the core are removed and replaced with fresh fuel assemblies which are relocated around the core. The removed spent fuel assemblies are typically transferred under water to a separate building that houses a spent fuel pool in which these radioactive fuel assemblies are stored. The water in the spent fuel pools is deep enough to shield radiation to an acceptable level and through convective cooling and recirculation prevents the fuel rods within the fuel assemblies from reaching temperatures that could breach the cladding of the fuel rods, which hermetically house the radioactive fuel material and fission products. Cooling continues at least until the decay heat within the fuel assemblies is brought down to a level where the temperature and radiation emissions of the assemblies is acceptable for dry storage. Until such time, the water in the spent fuel pools is actively cooled by pumping a portion of that coolant through heat exchangers to extract the heat. Current nuclear plants have acquired systems to effectively manage spent fuel cooling. However, certain emergency situations, such as a station blackout or an event causing the loss of an ultimate heat sink can lead to failure of the spent fuel pool cooling process. As a consequence, extensive temperature increase of the spent fuel pool inventory with the formation of steam can occur, and radioactive aerosols can possibly be released into the surrounding atmosphere. High concentrations of this radioactive aerosol and overheating of the air may lead to limited accessibility to the building and further impede emergency efforts. In an extremely unlikely event, such as where a catastrophic tsunami challenges plant systems beyond all reasonable predictions, such as occurred in Japan's Fukushima Daiichi Nuclear Power Plant, and where there is no cooling or inventory make-up for several days, the spent fuel pool may vaporize significant volumes of water and eventually dry up, posing the risk of fuel damage due to the inability to reject decay heat to a heat sink. Currently, a number of existing plants have a spray system incorporated on top of the spent fuel pool, which distributes water from an external water source to replenish water in the pool. However, the system requires a pump which requires power and manual start-up to carry out this operation. Accordingly, it is an object of this invention to provide a back-up spent fuel pool cooling system that does not require external power. Furthermore, it is an object of this invention to provide such a cooling system that will initiate cooling of the spent fuel pool passively upon the occurrence of a preselected event. Additionally, it is an object of this invention to provide such a cooling system that is relatively inexpensive and easy to implement. It is a further object of this invention to provide such a cooling system that is not going to hinder normal fuel pool operations, when the system is not in use. These and other objects are achieved with a spent nuclear fuel pool emergency cooling system that employs an evaporator/heat exchanger having an internal fluid path that extends in a generally planar direction, with the evaporator/heat exchanger being supported substantially vertically from a wall of a spent fuel pool. The hinged support connects a first side portion of the evaporated/heat exchanger to the wall of the spent fuel pool with the hinged support configured to rotate the evaporator/heat exchanger away from the wall and outward into the coolant within the spent fuel pool with a second side portion of the evaporator/heat exchanger, which is opposed from the first side portion, laterally spaced from the wall of the spent fuel pool. A temperature sensitive fusible link is connected between the wall and the second side portion of the evaporator/heat exchanger to maintain the exchanger in the substantially vertical position. The fusible link is responsive to a preselected change in an element of an environment of the spent fuel pool, to a pre-established level, to transfer the evaporator/heat exchanger to the position wherein the second side portion of the evaporator/heat exchanger is laterally spaced from the wall of the spent fuel pool. A dewar or a cryogen pipeline containing a supply of a cryogenic fluid is provided and is fluidly connected to the internal fluid path with an automatic valve for preventing the flow of cryogenic fluid from the dewar/cryogen supply to the internal fluid path until the evaporator/heat exchanger is substantially in the position wherein the second side portion of the evaporator/heat exchanger is laterally spaced from the wall of the spent fuel pool. Preferably, the position of the evaporator/heat exchanger wherein the second side portion is laterally spaced from the wall of the spent fuel pool places the evaporator/heat exchanger substantially in a horizontal position, where the heat exchanger is in contact with the spent fuel pool water. When the evaporator/heat exchanger is laterally spaced from the wall of the spent fuel pool, the automatic valve opens to allow the cryogenic fluid to collect heat from the spent fuel pool and expand itself into a gas through the internal fluid path wherein the gas exits the internal fluid path as a pressurized gaseous cryogenic fluid. In one embodiment, the pressurized gaseous cryogenic fluid is connected to a gas driven mechanical pump such as a gas operated double diaphragm pump which can be employed to passively supply make-up water to the spent fuel pool. In another embodiment, the pressurized gaseous cryogenic fluid is connected to a compressed gas turbo generator which can be employed to generate power to assist an air cooling system. The pressurized gaseous cryogenic fluid exiting the internal fluid path can also be conducted through a gas to air heat exchanger after driving the compressed gas turbo generator to collect heat from the surrounding air. Preferably, a check valve is in fluid communication with an inlet to the evaporator/heat exchanger to prevent the pressurized gaseous cryogenic fluid from flowing back into the dewar. Furthermore, the internal fluid path may be placed in fluid communication with a pressure regulating valve and/or pressure dampener to control the pressure of the gaseous cryogenic fluid in the internal fluid path. Desirably, aside from the evaporator/heat exchanger, substantially all of the plurality of components and instrumentation necessary for implementing the emergency cooling system can be supported on a readily transportable skid that can be back-fitted into existing plants. In one embodiment the gaseous cryogenic fluid is nitrogen. In another embodiment the gaseous cryogenic fluid is synthetic, breathable air (nitrogen and oxygen mixture) or another inert fluid. Preferably, the evaporator/heat exchanger has an inlet and an outlet to the internal fluid path and the internal fluid path extends in a serpentine pattern between the inlet and outlet desirably through a single plane. The shape of the heat exchanger tubing may be of other forms, with a large enough heat exchange area to flash the cryogenic fluid. In another embodiment, the heat exchanger can be in any shape or form, including finned tubes, to facilitate heat transfer. In still another embodiment, the evaporator/heat exchanger is supported substantially vertically upward from the wall of the spent fuel pool and drops away from the wall upon release of the fusible link, by gravity. This invention provides a system that can mitigate the decay heat removed from the used nuclear fuel assemblies in a spent fuel pool during a station blackout using the natural expansion forces of heating a cryogenic fluid. The term “cryogenic fluid” in this context is meant to include any fluid that is a liquid and has a boiling point at a temperature substantially below room temperature and the normal operating temperature of a spent fuel pool and that does not react with the substances that it comes in contact with in the system described hereafter, to adversely change its chemical composition. One embodiment includes the use of cryogenic nitrogen to achieve both water and space cooling and also utilizes the expanded gas to drive a make-up water pump to replenish spent fuel pool water and/or provide power to an air cooler system. The following describes three different embodiments incorporating this concept; two of which provide for spent fuel pool cooling alone while the third includes space cooling. The first embodiment utilizes an expanded cryogenic nitrogen gas to operate a compressed gas turbo generator to supply power to an electrical make-up water pump. The second embodiment uses the expanded nitrogen to operate a gas-operated double diaphragm pump to make up the lost water in a spent fuel pool. The third embodiment utilizes the expanded gas to drive an air blower for space cooling, in addition to operating a gas-operated operated double diaphragm pump as a make-up water source. These concepts are respectively shown in FIGS. 3, 4 and 5. By way of background, nitrogen is in its liquid state between the temperatures of −346 degrees and −325 degrees Fahrenheit (−198 Celsius) and is typically stored within highly insulated containers, i.e., dewars. This commodity is readily available commercially and is inexpensive. The system in accordance with this invention would include an on-site storage dewar 28 such as the one shown in FIGS. 3, 4 and 5. An additional embodiment for the storage dewar is for the dewar to be located on a skid, outside of the spent fuel pool building where it can be resupplied and refilled from an external source. The option of having the dewar on a skid inside the building is identified by reference character 28. The dewar 28 is connected to an evaporator/heat exchanger 12 with insulated piping and valves to transport the cryogen to the evaporator/heat exchanger. Gas-operated double diaphragm pumps such as the one identified by reference character 30 shown in FIGS. 3 and 5 are usually operated mechanically using a compressed gas, typically air. However, in this case the gas operated double diaphragm pumps are driven by flashed and heated cryogenic air or an inert gaseous cryogenic fluid, such as nitrogen. A gas operated double diaphragm pump is a positive displacement pump that utilizes a combination of the reciprocating action of a flexible diaphragm and valves on either side of the diaphragm to pump a fluid. Some gas-operated double diaphragm pumps operate at low head and low flow rates; however, others are capable of higher flow rates. Other advantages of the gas-operated double diaphragm pump are that it includes the ability to run dry and pump a wide range of fluids including slurries. Gas-operated double diaphragm pumps are able to achieve efficiencies as high as 97 percent. Usually such pumps are accompanied with pulse-dampeners, figuratively illustrated in FIG. 3 and denoted by reference character 38, to reduce a pulsating flow. An alternate embodiment to the gas-operated double diaphragm is to use a pump that can be driven by a cold pressurized gas. Another alternate embodiment is to use a compressed air driven power generator, such as a turbine. Gas-operated turbo generators are also common, but are generally driven by high temperature combustion gases. Such a system driven by a gaseous cryogenic fluid can produce electricity over long periods of time (depending on the size of the nitrogen supply tank) as a redundant, independent power generating system that can be of significant value during a station blackout. Accordingly, this invention presents a spent fuel pool emergency cooling system, which is capable of carrying out multi-functional efforts to mitigate the decay heat of a spent fuel pool for a long period of time without the need of external power or human intervention. The major components of this system are a cryogenic fluid storage tank or dewar, a gas-operated diaphragm pump and an evaporator/heat exchanger. Besides the evaporator/heat exchanger, most of the components and instrumentation can be situated on a relatively small skid. The system also has the capability of cooling the ambient air in the spent fuel pool area effectively without the need of a large heat exchanger. In addition to the aforementioned components, the system would need another heat exchanger (gas to air) and a pneumatic fan or an eductor (if liquid air is used) to provide this additional option for space cooling. One embodiment of the evaporator/heat exchanger 12 is shown in FIG. 1 and is designed such that it does not block or interfere with any regular operation in the spent fuel pool area. The evaporator/heat exchanger 12, in this embodiment, will be supported substantially in an upright position against the wall 24 of the spent fuel pool and will be lowered into the spent fuel pool only during an accident scenario. Preferably, the heat exchanger 12 is of a planar serpentine design as shown in FIG. 1, with an inlet 14 and an outlet 16. The evaporator/heat exchanger 12 is supported from the spent fuel pool wall 24 by hinged brackets 20 about which it can be rotated downward. The upper end is supported by a latch with a fusible link actuator 18 that may be extended from a handrail that surrounds portions of the spent fuel pool. During an accident, the evaporator/heat exchanger 12 can rotate down about the hinged brackets 20 by approximately 90 degrees. Preferably, the brackets 20 have a stop that prevents the evaporator/heat exchanger 12 from rotating substantially more than the 90 degree angle. The fusible latch 18 is preferably a temperature sensitive actuation device that passively opens its connection with the heat exchanger at a preselected temperature to allow the heat exchanger panel to be lowered onto the water surface by gravity. By the fusible link being passively actuated it is meant that no operator intervention or external power is required to implement the actuation. However, it should also be appreciated that other fusible links may be used, which are passively responsive to an element of the spent fuel pool environment to extend the evaporator/heat exchanger 12 into the spent fuel pool and/or turn on the cryogen supply to the inner tubes of the evaporator/heat exchanger. For example, the fusible link could be responsive to the level of coolant within the spent fuel pool to extend the evaporator/heat exchanger when the coolant level in the pool reached a preselected elevation or the fusible link could be responsive to a certain change in radiation level due to the reduced shielding resulting from a drop in the level of the spent fuel pool. This system can also be designed to have the evaporator/heat exchanger 12 submerged against the wall 24 of the spent fuel pool with the upper portion of the heat exchanger hinged against the sidewall of the spent fuel pool and the bottom of the evaporator/heat exchanger 12 tied against the wall with the fusible latch. In this latter embodiment the hinges 20 can be spring-loaded to permit the evaporator/heat exchanger to rotate upward when the fusible latch is activated at the preselected temperature. For this latter arrangement to be most effective, there has to be sufficient clearance between the evaporator/heat exchanger and the fixtures within the spent fuel pool. FIGS. 2a, b and c illustrate the actuation of the evaporator/heat exchanger 12. FIG. 2a shows the evaporator/heat exchanger 12 supported adjacent the spent fuel pool wall 24 and held in that position by the fusible latch 18 that extends between the top of the evaporator/heat exchanger and a handrail 26 that surrounds at least a portion of the edge of the spent fuel pool. FIG. 2b illustrates the actuation phase in which the fusible latch 18 releases the top of the evaporator/heat exchanger 12 that enables the evaporator/heat exchanger 12 to rotate downward under the force of gravity. FIG. 2c illustrates the cooling phase in which the evaporator/heat exchanger is submerged in the spent fuel pool. Cooling of the water around the evaporator/heat exchanger 12 causes a natural convection current to form that moves the cooler water towards the bottom of the pool and the hotter water up towards the heat exchanger. The system is designed to allow a cryogenic fluid such as liquid air or nitrogen to flow into the evaporator/heat exchanger when the latter is fully submerged in the spent fuel pool. The liquid air or nitrogen starts flowing through the tubes of the evaporator/heat exchanger, gains heat of vaporization and flashes to a gas. A check valve 52 in the inlet stream of the evaporator/heat exchanger prevents the pressurized gas from flowing back into the dewar or cryogenic storage vessel 28. Also, the pressure relief valve 54 in the evaporator/heat exchanger ensures the pressure does not exceed the design pressure of the evaporator/heat exchanger tubes. As the gas flows through the evaporator/heat exchanger it will also gain sensible heat and cool down the surface region of the spent fuel pool. Warmer and less dense water at the bottom of the pool will then rise up forcing the cooled water to displace to the bottom, initiating the natural convection cooling circulation in the spent fuel pool. The pressure regulating valve 54 assists the high pressure gaseous nitrogen to exit the outlet 16 of the evaporator/heat exchanger 12 and is fed to a make-up water pump 32 (FIGS. 3, 4 and 5) that can draw water from a storage tank 34 within the plant, from portable water trucks 36, or from an additional make-up water source located outside of the spent fuel pool building. The gas can be used to operate the make-up water pump 32 via two methods. The first is a gas-operated double diaphragm pump that will use pressurized gas to feed water to the spray system of the spent fuel pool as illustrated in FIG. 3. A pulse dampener 38 is provided to smooth out the peaks and valleys in the flow. The other method involves the use of pressurized gas to operate a small gas-powered turbo generator that will create electricity to operate an electrical pump 42 to feed water to the spent fuel pool spray system as shown in FIG. 4. It should also be appreciated that a mechanical pump could be connected to the shaft of a gas-powered turbine to provide a similar result. In the embodiment shown in FIG. 3, the gas from the evaporator/heat exchanger 12 is fed to a gas-operated double diaphragm pump 30 to draw water from a make-up water tank 34 or from water trucks 36 to feed the water to the spent fuel pool make-up line or spray system 46. That pump would require a low head and low flow rate (estimated to be approximately 35 gallons per minute), which is achievable using a gas-operated double diaphragm pump. The gas-operated double diaphragm pump may require a pulse dampener 38 to maintain a relatively smooth flow rate. The overall system is very compact and aside from the evaporator/heat exchanger, substantially all of the components necessary for implementing the emergency cooling system can be supported on a readily transportable skid 50 that can be back-fitted into existing plants to mitigate the overheating of a spent fuel pool during a station blackout or during loss of an ultimate heat sink. The embodiment illustrated in FIG. 4 has the capability to provide effective space cooling to cool down ambient air in the spent fuel pool area or other areas of a power plant. In this embodiment, the expanded gas from the evaporator/heat exchanger 12 flows into an air cooling heat exchanger 44 to extract heat from the ambient air. As seen in FIG. 4, a portion of the exit stream of the air cooling heat exchanger 44 is fed to a pneumatic fan 48 or an eductor (in the case when synthetic air is the fluid) attached to the air cooling heat exchanger 44 to enable forced convection to increase heat transfer between the air and the air cooling heat exchange tubes carrying cold gas. The forced convection by the pneumatic fan or eductor allows the air cooling heat exchanger 44 to be much smaller in size than a typical air cooler relying only on natural convection. This space cooler is compact, effective, and works without any external power. The space cooling feature can also be designed as a stand-alone system in a plant that requires emergency, passively activated air cooling during a station blackout or during normal operation. The space cooler makes the area more accessible to personnel to continue in other emergency efforts during a station blackout. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
	description	1. Field of the Invention The present invention relates to a charged particle lithography system, in particular to a maskless charged particle system, to a sensor therefore, in particular for determining charged particle beam properties, to a converter element therefore, as well as to a method of manufacturing the same. 2. Description of the Related Art Charged-particle beamlet lithography systems make use of a plurality of charged particle beamlets to transfer a pattern onto the surface of a target. The beamlets may write the pattern by being scanned over the target surface while their trajectory may be controllably blocked so as to create a beamlet that can be turned on or off. Blocking may be established by electrostatic deflection of beamlets on a blocking surface. Additionally, or alternatively, the size and shape of the beamlets may be adapted along the trajectory. Deflection, shaping and/or size adaptation may be executed by one or more electron optical components like for example an aperture array, an array of electrostatic deflectors and/or beamlet blankers. In order to transfer a pattern onto the target surface, the controllable blocking of beamlets in combination with their movement over the target surface is performed in accordance with modulation information. An example of a multiple charged-particle beamlet lithography system is described in U.S. Pat. No. 6,958,804, which disclosure is herewith incorporated by reference in its entirety. Such lithography systems can have very large numbers of beamlets, i.e. in the order of 10,000 or higher, for example 13,000. Future designs even envisage numbers in the order of 1,000,000 beamlets. It is a general aim for current electron beam lithography systems to be able to pattern a target surface in high-resolution, with some applications being capable of imaging patterns with a critical dimension of well below 100 nm feature sizes. For such multiple beamlet, high-resolution lithography systems to be commercially viable it is important that the position of each one of the charged particle beamlets is precisely known and controlled. Additionally, knowledge and control of spot size and shape and intensity of the beamlets at the target surface are also of importance. Due to various circumstances, such as manufacturing tolerances and thermal drift, such beamlet characteristics may however deviate from their expected and desired characteristics, which may render these deviating beamlets invalid for accurate patterning. Such deviations may include, among other things, a deviation in position, a deviation in spot size as exposed on the target surface and/or a deviation in beamlet intensity. Deviating beamlets may severely affect the quality of the pattern to be written. It is therefore desirable to detect these deviations so that corrective measures may be taken. In conventional lithography systems, the position of each beamlet is determined by frequent measurement of the beamlet position. With knowledge of the beamlet position the beamlet can be shifted to the correct position. For accurate writing it is beneficial to determine the beamlet position within a distance in the order of a few nanometers. Known beamlet position calibration methods generally comprise at least three steps: a measuring step in which the position of the beamlet is measured, a calculating step in which the measured position of the beamlet is compared to the desired expected position of that beamlet, and a compensation step in which the difference between the measured position and the desired position is compensated for. Compensation may be performed either in the software or in the hardware of the lithography system. In advanced charged particle beamlet lithography systems, besides position control, beamlet spot size control may be of equal importance. Desired specifications for spot size measurements include determination of beamlet spot sizes in the range of 30 nm to 150 nm; accuracy of spot size measurements with 3 sigma value smaller than 5 nm; and a reproducibility of such spot size measurements within a single sensor with 3 sigma value smaller than 5 nm. It is desirable to determine characteristics like beamlet position and/or beamlet spot size during operation of a lithography system to allow for early position and/or spot size calibration to improve the target surface patterning accuracy. In order to limit negative effects on throughput, i.e. the number of target surfaces that can be patterned within a predetermined period of time, it is desirable that the method of measuring the characteristics of the charged particle beamlets can be carried out within a limited period of time without sacrificing accuracy. A sensor for measuring properties of a large number of charged-particle beamlets, in particular for charged particle beamlets used in a lithography system, is described in US published patent application 2007/057204 assigned to the present applicant, the content of which is herewith incorporated by reference in its entirety. US 2007/057204 describes a sensor and method in which charged-particle beamlets are converted into light beams, using a converter element such as a fluorescent screen or a doped YAG material. Subsequently, the light beams are detected by an array of light sensitive detectors such as diodes, CCD or CMOS devices. A relatively fast measurement can be achieved by reading out a large number of light sensitive detectors in a single operation. Additionally the sensor structure, in particular the array of light detectors, enables a very small pitch of a multiplicity of beams to be measured without the necessity of unduly large structural measures in the region of the stage part of a lithography system. However, in view of the continuously increasing demands of the industry regarding small dimensions without loss of throughput, there remains a need to provide even more accurate devices and techniques for measurement of beamlet properties in lithography systems, particularly in lithography machines comprising a large number of charged-particle beamlets that are designed to offer a high throughput. It is an object of the present invention to provide a more accurate sensor is suitable for use in a charged particle lithography system with enhanced resolution performance. For this purpose, the present invention provides a charged particle beamlet lithography system for transferring a pattern to a surface of a target comprising a sensor for determining one or more characteristics of one or more charged particle beamlets, the sensor comprising a converter element for receiving charged particles and generating photons in response, the converter element comprising a surface for receiving one or more charged particle beamlets, the surface being provided with one or more cells for evaluating one or more individual beamlets, each cell comprising a predetermined blocking pattern of one or more charged particle blocking structures forming multiple knife edges at transitions between blocking and non-blocking regions along a predetermined beamlet scan trajectory over the converter element surface, wherein the converter element surface is covered with a coating layer substantially permeable for the charged particles and substantially impermeable for ambient light, and wherein the sensor further comprises an electrically conductive layer between the coating layer and the blocking structures. The coating layer allows the sensor to respond in a more uniform manner to the receipt of charged particles over a considerable area of the converter element surface, for example over an area of about 3×3 mm2. The coating layer removes local influences from ambient light, for example background radiation or the like. As a result, a plurality of beamlets may be sensed simultaneously with high resolution. Suitable materials for use in the coating layer include titanium (Ti) and aluminum (Al). The blocking structures generally comprise a heavy metal like tungsten (W), and providing such structures on top of a substrate generally includes one or more etching steps. The material being used for the electrically conductive layer preferably has a high selectivity for such etching steps. A suitable material that may be included in the material forming the electrically conductive layer is chromium (Cr). An advantage of using Cr is that it can be deposited in the same way as Ti, so that it can be applied without substantial amount of additional effort or difficulty. In an embodiment the invention relates to a method of manufacturing a converter element for selectively converting impinging charged particles into photons. The method comprises: providing a substrate comprising a conversion material for converting charged particles into photons; subsequently coating the substrate with a first layer comprising an electrically conductive material, a second layer comprising an etch stop material and a third layer comprising a third material; providing a resist layer on top of said third layer; patterning, and developing the resist layer so as to form a first predetermined pattern, and etching the developed resist layer until the third layer is exposed; coating the exposed third layer with a fourth layer comprising a further etch stop material; lifting of the developed resist such that the third layer is exposed in accordance with a second predetermined pattern, the second predetermined pattern being an inversion of the first predetermined pattern; etching the third layer in accordance with the second predetermined pattern until the second layer is exposed; etching the fourth layer as well as the second layer in accordance with the second predetermined pattern until the first layer is exposed. The following is a description of certain embodiments of the invention, given by way of example only and with reference to the drawings. FIG. 1 schematically shows the operation of a sensor for determining one or more characteristics of particle beams, in particular one or more characteristics of charged particle beamlets. The sensor comprises a converter element 1 and a photon receptor 5. The converter element is provided with a pattern comprising charged particle blocking regions 8 and charged particle transmissive regions 7, further referred to as non-blocking regions. The converter element 1 is arranged for receiving charged particles 2 and generating photons 3 in response. The photons 3 may be directed towards the photon receptor 5 by means of an optical system 11. The photon receptor 5 is communicatively coupled to a calculation unit, e.g. a computer 13 for determining one or more characteristics of the charged particles 2. The converter element 1 may take the form of a fluorescent element, for example a fluorescent screen, or a scintillating element, for example a substrate of a doped yttrium aluminum garnet (YAG) material. Hereafter, embodiments of the invention will be described in with a YAG-screen being used as converter element 1, where the YAG-screen may be referred to as YAG 1. The photon receptor 5 may include any suitable light sensitive detector, such as a plurality of diodes, charged coupled device (CCD) cameras or complementary metal-oxide semiconductor (CMOS) cameras. Hereafter, the photon receptor 5 may be referred to as camera 5. Additionally, although embodiments of the invention may be used for any type of (charged) particles or light beams 2, hereafter, embodiments of the invention will be discussed with reference to electrons. In electron beamlet devices where the beamlet size is in the nanometer range, for example electron microscopes, electron beam lithography apparatus, and electron beam pattern generators, direct observation of photons created by conversion by the converter element 1 is insufficient to enable determination of characteristics such as position of an electron beamlet as the resolution is limited by the wavelength of the converter element 1. To improve accuracy, an electron beamlet may be scanned across an electron blocking structure provided with sharp edges, further referred to as knife edges. An example of a sensor using a converter element provided with a knife edge is described in patent application US 2007/057204. FIG. 2A schematically shows a cross-section of a YAG 1 comprising an electron beamlet receiving surface provided with an electron blocking structure. The electron blocking structure comprises electron blocking regions provided with a layer 18 capable of blocking electrons. The blocking layer 18 may be a metal layer. A suitable metal for blocking electrons is tungsten. In between the blocking regions are non-blocking regions. An electron beam 22 impinging onto a non-blocking region of the electron blocking structure actually impinges onto the surface of the YAG 1 or a coating on the surface of the YAG. Within the portions for blocking electrons, besides the blocking layer 18 an additional layer 21 is present. The additional layer 21 serves the purpose of increasing the uniformity of the blocking layer 18. The additional layer 21 may be a metal layer. An example of a particularly suitable material for use in the additional layer 21 is chromium. The YAG 1 may be coated with a coating layer 20. The coating layer 20 may be a metal layer for blocking background radiation. The coating layer 20 is substantially permeable to charged particles on the one hand, while being substantially impermeable for ambient light on the other hand. For this reason, the thickness of the coating layer 20 is sufficient to establish both functions. Suitable materials for the coating layer 20 include aluminum and titanium. As mentioned earlier, in order to determine one or more characteristics of an electron beam 22, the electron beam 22 may be scanned over a blocking structure provided on the YAG 1 (in FIG. 2A in a direction denoted as X-direction). In response, photons generated within the YAG 1 may be detected by a camera. An exemplary result of such scanning and detection action is schematically depicted in FIG. 2B. FIG. 2B shows a graph representing intensity of light emitted by a converter element 1 as a function of x-position of an electron beam 22 over the surface of the converter element 1. A maximum response is observed when electron beam 22 is entirely positioned in a non-blocking region, and minimal light is generated if the electron beam 22 is positioned entirely on top of a blocking region. The crossing of a knife edge results in a steep change of light intensity. In some embodiments, in order to provide a robust processing of measurement results, intensity levels exceeding a higher threshold value Th, are provided as high level signal values to a processor. Similarly, detected intensity levels below a lower threshold value Tl may be provided as low level signal values. The use of threshold values Th, Tl may enable the use of digital processing. Upon scanning an electron beam in a predetermined direction, the electron beamlet may encounter two types of situations while crossing a knife edge. In a first situation, the beamlet experiences a transition from a blocking region to a non-blocking region. In a second situation, the beamlet experiences a transition from a non-blocking region to a blocking region. Knife edges being encountered during a transition that corresponds to the first situation may be referred to as knife edges of a first type. Similarly, knife edges being encountered during a transition that corresponds to the second situation may be referred to as knife edges of a second type. The type of knife edge is thus dependent on the scanning direction of the beamlet to be measured. If reference is made to “knife edges of similar type”, this means that all the knife edges involved either relate to knife edges of the first type or relate to knife edges of the second type. Knowledge of the knife edge pattern provided on the electron-receiving surface of the converter element surface allows for the determination of one or more characteristics of a beamlet. Characteristics that can be measured by using a sensor as described with reference to FIG. 1, and a knife edge pattern as described with reference to FIG. 2A, include beamlet position and beamlet spot size, where the spot size relates to the size of the electron beamlet on the surface of the converter element 1. For example, beamlet position can be measured by scanning the beamlet across the surface of the converter element in the x-direction and measuring the position at which the intensity of light emitted by a converter element changes from a maximum to a minimum value or from a minimum to a maximum value, as shown in FIG. 2B. For example, when the intensity changes from maximum to minimum value, this indicates that the beamlet is scanned over a knife edge transitioning from a non-blocking region to a blocking region in the x direction. However, there may be uncertainty as to which knife edge the beamlet is located at. The size of the beamlet can be determined, for example, by measuring the distance between the point at which the intensity begins to decrease from a maximum value and the point at which the intensity reaches a minimum value as the beamlet is scanned across a knife edge. This indicates the distance over which the beamlet is partly blocked and partly un-blocked. Similarly, the beamlet size can be determined by measuring the time between sensing a maximum intensity and sensing a minimum intensity as the beamlet is scanned across a knife edge, and multiplying by the scanning speed of the beamlet. These measurements can also be performed on the opposite knife edge, the beamlet moving from minimum to maximum intensity. Note that the measurement shown in FIG. 2B, and the discussion of beamlet position and beamlet size measurements relates to a beamlet having dimensions that are smaller than the widths of the blocking and non-blocking regions involved. These dimensions and widths are preferably taken along a direction parallel to the scan direction being used. In many applications, a single knife edge is not suitable to obtain beamlet characteristics with sufficient accuracy. In particular so-called line edge roughness (LER) of a knife edge may limit the accuracy of beamlet measurements. FIG. 2D schematically illustrates a problem related to LER. In FIG. 2D, a sensor is arranged to detect the intensity of a beamlet being moved across a knife edge 31 separating an electron blocking region 33 and an electron non-blocking region 34. The knife edge 31 is designed to have the orientation and shape as denoted by the dotted line 32. If the x-position of the beamlet is detected under the assumption that it follows a trajectory A across the knife edge 31 from the blocking region 33 towards the non-blocking region 34, while in reality the trajectory B is followed, the beamlet position in the scanning direction should be the same for both trajectories. After all, both trajectories cross the dotted line 32 at the same x-position. However, as can be readily seen in FIG. 2D, due to the line edge roughness of the knife edge 31, the measured x-position of the beamlet for trajectory A will be different than the measured x-position for trajectory B. In this example, determining the x-position based on the crossing of single knife edge 31 provides an inaccurate result. FIGS. 3A-3H schematically show different stages of a method of manufacturing a converter element, for example a converter element as discussed with reference to FIG. 2A. The converter element is arranged for selectively converting impinging charged particles into photons. First, as shown in FIG. 3A, a substrate 101 is provided for supporting further layers of the sensor. Throughout this description the combination of the substrate 101 and the structures applied thereon is referred to as converter element. The substrate 101 comprises a conversion material for converting charged particles into photons. Such conversion material may be a scintillating material. In particular for applications where electrons are used as charged particles, a suitable scintillating material may be a material comprising an yttrium aluminum garnet (YAG). Subsequently, as shown in FIG. 3B, a surface side of the substrate 101 arranged for reception of charged particles is coated with one or more layers, typically being metal layers. The layers comprise a first layer 103 comprising an electrically conductive material. The first layer 103 is substantially impermeable for ambient light, that is the layer is arranged for blocking background radiation. Such background light blocking layer enhances quality of the sensor by preventing background light from interfering with the light generated by the converter element. The first layer 103 is further substantially permeable for charged particle beamlets. For this reason, the first layer 103 generally has a thickness within the range of about 30 to about 80 nm. Suitable materials for the first metal include titanium and aluminum, Ti being preferred as less prone to oxidizing over time and hence more conducive to maintaining lasting surface uniformity of said layer. Additionally, the layers comprise a second layer 104 comprising a second material. The second material is an etch stop material that serves the purpose of stopping an etching process, preferably for both wet etching and dry etching processes. The use of the second layer can result in improved etching quality, in particular if the material has a high etch sensitivity. The second layer may be particularly useful for the realization of sharper edges. A suitable material for the second metal is chrome. The layers further comprise a third layer 105 comprising a third material. The third material serves the purpose of blocking charged particle beamlets. A suitable material for the third material is a material that blocks charged particles as well as ambient light while having a layer of limited thickness. A suitable material is tungsten, in which case a suitable thickness would lie within the range of 50 to 500 nm. Such thickness is thick enough to sufficiently block incoming charged particles. On the other hand, such thickness has a negligible influence on effects like defocus and edge roughness. On top of the number of layers 103, 104, 105, a resist layer 107 is provided. As schematically shown in FIG. 3C, the resist layer 107 may be a single resist layer or, alternatively, a double resist layer comprising an upper layer 107a, and a lower layer 107b respectively. Further reference will be made to a single resist layer 107. The resist layer 107 is then patterned in correspondence to a first predetermined pattern. After patterning, the resist layer 107 undergoes developing and etching steps in a fashion generally known in the art. The etching is performed until the third layer 105 is exposed. An exemplary end result of patterning, developing and etching the resist layer 107 is schematically shown in FIG. 3D. After etching, the exposed third layer 105 is coated with a fourth layer 109, for example by means of evaporation, as is schematically shown in FIG. 3E. Generally, the fourth layer 109 is a metal layer. The fourth layer 109 may serve as an etch stopping layer and may improve etching quality. The layer 109 may comprise the same material as used in the second layer 104, for example chrome. After deposition of the fourth layer 109, the developed resist is removed by lift off such that the third layer 105 is exposed in accordance with a second predetermined pattern, as schematically shown in FIG. 3F. The second predetermined pattern is an inversion of the first predetermined pattern. Subsequently, the exposed third layer 105 is etched in accordance with the second predetermined pattern until the second layer 104 is exposed. A schematic drawing of the converter element at this stage of the manufacturing process is shown in FIG. 3G. Finally, as schematically shown in FIG. 3H, the fourth layer 109 as well as the second layer 104 in accordance with the second predetermined pattern are removed, the latter one until the first layer 103 is exposed. Removal may be performed by techniques known in the art, for example etching. The resulting converter element is similar to the converter element described with reference to FIG. 2A. When the method of FIGS. 3A-3H would be used to manufacture the converter element of FIG. 2A, substrate 1 and layers 18, 20, and 21 in FIG. 2A correspond to substrate 101 and layers 105, 103, and 104 respectively. The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. Further modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention, which is defined in the accompanying claims.
043057870	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As may be seen in FIGS. 1 through 7, the rack is comprised of a series of self-supporting metal tubes 1 arranged in a staggered fashion with respect to each other. In the example described, each of the tubes is comprised of two steel L angle sections joined longitudinally along their outer edges. Each such section is provided in one of its flanges with a projection 2 which, once the tubular element is formed, lies opposite the other so as to define a like number of skegs which, once the rack is assembled, lie opposite the edges 3 of the adjacent tubes lacking such skegs. By welding the skegs 2 to the edges 3, the elements are joined to each other in such a fashion that a tubular hole of larger cross-sectional area than the tubular elements 1 is defined between each four tubular elements. The covering of protective material 5 is placed within the tubular holes 4 defined between each four tubular elements, so that the internal cross-sectional area defined by the covering is equal to the internal cross-sectional area of the tubular elements 1. With this construction, the spent radioactive fuel inserted into the tubular spaces 4 is protected by the protective covering 5. Similarly, the spent radioactive fuel stored in the tubular elements is protected by the protective coverings of the tubular holes surrounding each tubular element 1. The tubular elements 1 are self-supporting and when joined in the fashion explained above constitute a rigid spatial structure which does not require stiffening elements, it being sufficient to connect them to a base plate or structure which may in turn be provided with supports of a construction such as the one shown in FIG. 8. The supports consist of a sleeve 6, which fits within a stem 7 capable of sliding axially a given distance. This distance is jointly determined by the length of its narrower portion 8 and by the radial screw 9, which acts as a stop for the surfaces delimiting said portion 8. The stem 7 is provided outside the sleeve 6 with a wider portion 10 between which and the sleeve 6 is mounted a compression spring 11 which constantly pushes the stem downward. Furthermore, the lower end of the sleeve 7 may be provided with a head 12 having a spherical lower surface, which head fits into a bushing 13 which rests on the surface upon which the container is placed. the housing of the bushing 13 and the head 12, having a spherical lower surface, define a hinge joint permitting the free orientation of the bushing 13. This possibility of orientation and the spring 11 are together capable of absorbing irregularities in the ground or surface upon which the container is located. As shown in FIG. 2, the tubular elements 1 may consist of four duly welded plates, wherein one of the plates in each tubular element, referenced in the drawing with the number 14, is wider than the other three so as to define the projections 2 which are used for joining with the edges lacking such projections of the adjacent tubular elements. As in the case of FIG. 1, a tubular hole 4 whose cross-sectional area is larger than that of the tubular elements 1 is defined between each four elements; the protective covering 5 being located within said tubular holes 4. In the case of FIG. 3, the tubular elements 1 lack the longitudinal projections that define the skegs 2, said projections being obtained by welding along their longitudinal edges a longitudinal piece 15 at a 45.degree. angle and arranged in such a fashion that the two pieces 15 of the adjacent edges of each two consecutive tubular elements lie opposite each other as shown in the drawing and are joined to each other by means of a bolt 16 or a rivet. The two pieces 15 can be produced together with the tubular element 1 by extrusion, as is shown in FIG. 4, having the same orientation and being joined in the same fashion by means of bolts 16 or rivets. In the case of FIG. 5, the tubular elements 1 may be comprised, as in the case of FIG. 2, by four plates welded to each other through parts 17 interposed at a 45.degree. angle at their longitudinal corners and projecting outward so as to define the attachment skegs. The construction between the tubes may be effected, for example, by means of bolts 18 through tapped holes at a 45.degree. angle of various places of the parts 17. The same joining system is used in the case of FIGS. 6 and 7, with the difference that, in the case of FIG. 6, the projection 17 is part of one of the walls of the tubular element 1, and in the case of FIG. 7, the projections 17 are part of the entire tubular element 1 and are obtained, for example, by extrusion of said element. In all cases, the protective covering 5 is located inside the tubular hole defined between each four tubular elements 1. As can be seen, the construction of the tubular elements and the method of joining said elements to each other may be varied, provided no change is made in the essential characteristic of this construction, which is that the metal tubular elements 1 are self-supporting, that said tubular elements are arranged in a staggered fashion and are joined to each other along their longitudinal edges so as to form a rigid spatial structure, and that the protective covering is located only within the tubular holes defined by each four tubular elements 1. With reference to the second embodiment, as may be seen in FIGS. 9 through 12, the rack is comprised as in the preceding case by a series of self-supporting tubular elements 1, arranged in a staggered fashion with respect to each other, so as to delimit between each four tubes, a tubular space or hole 4 wherein will be located the element 5 bearing the encapsulated neutron-absorbing material. The tubular elements 1 may, for example, be welded to a bottom plate 19 which is in turn attached to a base plate 20 by means of, for example, bolts. As in the preceding case, the tubular spaces or holes 4 delimited between each four tubular elements 1 have a larger horizontal cross-sectional area than said tubular holes, precisely in order to receive the element 5 bearing the encapsulated neutron-absorbing material which will constitute the protection for the spent radioactive fuel rods that will be housed both within the tubular elements 1, and within the tubular holes 4. According to this invention, the tubular elements 1 are independent of each other throughout their length and each has a frame 21 attached to its upper end. The frames of the various tubes may be independent, as shown in FIGS. 9 through 12, each frame 21 having four vertical surfaces or faces 22 in the area adjacent to the four surrounding frames. The faces 22 opposite the adjacent frames 21 are parallel to each other, there being a slight void or gap between them, as may be seen in FIG. 9, whose right side shows the tubular elements with the frames attached to them while the left side of the figure shows the tubular elements in cross-section. The tubular elements 1 and the independent frames 21 together constitute a spatial structure of multiple elastic pillars capable of withstanding vibrations caused by, for example, earthquakes. According to another aspect of the invention, depicted in FIG. 13, an adjustable device intended to center the element 5 bearing the encapsulated neutron-absorbing material and to eliminate the gap between the upper part of said element and the surrounding tubes is provided between each tubular element 1 and its upper frame 21. This adjustable device is comprised of two plates 23 and 24 which are respectively depicted in FIGS. 14 and 15. These plates have surfaces, designated with the numbers 25 and 26, which face each other in a wedge-like fashion. The two plates are inserted back-to-back with respect to each other along the said surface between each tube 1 and the frame 5 of each element bearing the encapsulated neutron-absorbing material. The two plates are provided at the top with an elbow, designated with the number 27 in plate 23, and 28 in plate 24, as can be best seen in FIGS. 14 and 15. In order to facilitate the mutual attachment of the plates, the top of plate 23 is provided outside the region corresponding to the wedge surface 25 with a cut-out portion 29 into which the portion of the plate 24 lying above its wedge surface 26 fits. As can be seen in FIG. 13, the elbows 27 and 28 face toward the tubular element 1 and provide mutual support between them and on the upper outer edge of said tube. Adjustable support elements, consisting of bolts 30, making it possible to adjust the distance between the elbows 27 and 28, are arranged between the said elbows 27 and 28. The frame 21 of each tube is also provided with stop elements consisting of vertical through bolts 31. These elements are threaded through the frame of each tube, starting at the upper surface thereof and extending downward beyond said frame, so as to rest on the elbow 28 of the plate on the side of the element bearing the encapsulated neutron-absorbing material. These bolts 31 limit the vertical movement of the plates 23 and 24. According to the variant shown in FIG. 16, the frames 21 of the various tubes all comprise a single grid, so that the assembly of the tubes constitutes a spatial structure of multiple elastic bents. The system used to eliminate the gap between element 5 and the surrounding tubes may be the same as described with reference to FIGS. 13 through 15. In addition to the advantages derived from the construction discussed in the preceding embodiment, this construction achieves the further advantage that the rack is capable of withstanding the effects of earthquakes with low dynamic factors. As has already been mentioned, holes may be provided in the walls of the metal tubular elements 1 in order to reduce the weight of the assembly even further. Although only a preferred embodiment is specifically illustrated and described herein, it will be appreciated that many modifications and variations of the present invention are possible in light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.
048636827	description	DETAILED DESCRIPTION OF THE INVENTION This invention is particularly directed to a potential deficiency of susceptibility to irradiation degradation which may be encountered with chromium-nickel austenitic stainless steels comprising Type 304 and related high chromium-nickel alloys such as listed in Tables 5-4 on pages 5-12 and 5-13 of the 1958 edition of the Engineering Materials Handbook, edited by C. L. Mantell. These alloys comprise austenitic stainless steels of about 18 to 20 percent weight of chromium and about 9 to 11 percent weight of nickel, with up to a maximum of about 2 percent weight of manganese, and the balance iron with incidental impurities. This invention comprises a modified Type 304 austenitic stainless steel and a specific alloy composition including precise ratios of added alloying ingredients, as well as given limits on certain components of the standard austenitic stainless steel alloy. The alloy composition of this invention accordingly comprises the basic iron, chromium, nickel and manganese with the chromium in a percent weight of about 18 to 20, nickel in a percent weight of about 9 to 11 and manganese in a percent weight of about 1.5 to 2, with the balance iron and incidental impurities, except for the following fundamental alloying ingredients and requirements. The carbon component of the alloy is limited to a percent weight of 0.02 to about 0.04 percent weight. Also, a combination of niobium and tantalum is included together in a total of a minimum of 14 times the carbon percent weight, up to maximum of about 0.65 percent weight of the overall alloy, and with the niobium of the combination limited to a maximum of about 0.25 percent weight of the overall alloy. Thus, the tantalum of the combination can range up to about 0.4 percent weight of the overall alloy. Aside from the carbon content and the combination of niobium and tantalum in their given fundamental proportions, the other components of the alloy of this invention, including some incidental ingredients, comprises the following in approximate percent weight: ______________________________________ Iron Balance Chromium 18.0-20.0 Nickel 9.0-11.0 Manganese 1.5-2.0 Phosphorus 0.005 maximum Sulfur 0.004 maximum Silicon 0.03 maximum Nitrogen 0.03 maximum Aluminum 0.03 maximum Calcium 0.01 maximum Boron 0.003 maximum Cobalt 0.05 maximum ______________________________________ The foregoing specific austenitic stainless steel alloy composition, among other attributes, provides a high degree of resistance to stress corrosion cracking regardless of exposure to irradiation of high levels and/or over prolonged period, without incurring long term induced radioactivity. As such, the alloy composition of this invention is well suited for use in the manufacture of various components for service within and about nuclear fission reactors whereby it will retain its integrity and effectively perform over long periods of service regardless of the irradiation conditions. Moreover, the alloy composition of this invention additionally minimizes irradiation induced long term radioactivity whereby the safety and cost requirements for its disposal following termination of service are reduced, and of greatly shortened period. The following comprises an example of a preferred austenitic stainless steel alloy composition of this invention. ______________________________________ Alloy Ingredient Percent Weight ______________________________________ Carbon 0.033 Chromium 19.49 Nickel 9.34 Tantalum 0.40 Niobium 0.02 Sulfur 0.003 Phosphorus 0.001 Nitrogen 0.003 Silicon 0.03 Iron Balance ______________________________________ Physical Properties ______________________________________ Yield, KSI 40.0-47.0 Elongation, % 48-52 Grain Size (ASTM) 9.5 Hardness. R.sub.B ______________________________________
052375951	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference now to FIG. 1, wherein like numbers designated like components throughout all the several figures, the invention is an improved guide plate for use in the guide tubes used in a nuclear reactor 1. Such reactors 1 include a pressure vessel 3 having a removal closure head 5 which affords access to the upper internals assembly 6 contained therein. The pressure vessel 3 of the reactor 1 includes an inlet nozzle 7 for supplying a coolant, which may be water, to the interior of the reactor 1, and an outlet nozzle 9 for expelling coolant that has been heated by the reactor. The coolant expelled from the outlet nozzle 9 is circulated through a nuclear steam generator (not shown) which includes a system of heat exchanger tubes for converting non-radioactive water into steam which is ultimately used to drive electric generators. The bottom portion of the pressure vessel 3 includes a lower core barrel 11 defined between a foraminous lower core plate (not shown), and an apertured upper core plate 15. An array of nuclear fuel assemblies 17 is disposed between the lower and upper core plates 15. Each of these fuel assemblies 17 includes over 100 nuclear fuel rods 19, each of which is filled with fissionable uranium in the form of uranium dioxide The top portion of the pressure vessel 3 includes an upper core barrel 21 which is defined between the aforementioned upper core plate 15, and an upper support plate 23. A number of guide tubes 24 are bolted between the upper core plate 15 and upper support plate 23. These guide tubes 24 each have tubular walls 25 which may be either circular or square in cross-sectional shape which are provided with flow ports 26 at their bottom ends for facilitating a flow of coolant water from the inside to the outside of these tubes 24. The purpose of the guide tubes 24 is to slidingly guide a cluster of control rodlets 29 into and out of the fuel assemblies 17 in order to modulate the nuclear reaction occurring in the uranium contained within the individual fuel rods 19. Each of these control rodlets 29 is part of a rod cluster control assembly 27. This control assembly 27 includes a spider bracket 31 which interconnects the top ends of all the rodlets 29 together by means of bracket vanes 33. The manner in which the guide tubes 24 guide the individual control rodlets 29 of each rod cluster control assembly 27 is best understood with reference to FIGS. 2-5. At the bottom end of each of the guide tubes 24, where a precise alignment between the control rodlets 29 and various openings (not shown) in the fuel assembly 17 is the most critical, the guide tube 24 includes a guide sheath assembly 34 that is best seen in FIG. 3. In its interior, sheath assembly 34 includes a plurality of guide sheaths 35, each of which includes a pair of guide holes 36 interconnected by means of a slot 38. Each of the guide sheaths 35 is approximately 35 inches (88.9 cm) long, and operates to align the particular pair of rodlets 29 that it receives in much the same fashion that a sword aligns itself when inserted within its sheath, with the guide holes 36 each receiving an individual rodlet 29, and the slot 38 receiving the particular bracket vane 33 that inter-connects the rodlets 29. The guide sheath assembly 34 also includes a plurality of C-tubes 37 that slidably receive single rodlets on a single vane. The open spaces 39 between the guide sheaths 35 and C-tubes 37 conducts the axial flow of coolant flowing up from the fuel assemblies 17 below the upper core plate 15 to the middle and upper portions of the guide tube 24. At the middle and upper portions of the guide tube 24, alignment of the rodlets 29 is achieved by means of the lower guide plates 40 and upper guide plates 42 illustrated in FIGS. 4 and 5. A typical guide tube 24 includes between six and eight lower guide plates 40, and about four to six upper guide plates 42. In both the middle and upper sections of the guide tube 24, the guide plates 40,42 are spaced a little over twelve inches (30.48 cm) apart. Unlike the previously described guide sheath assembly 34, the plurality of spaced apart guide plates 40 and 42 do not envelope each of the rodlets 29 within a continuous sheath-like structure all along the longitudinal axis of the guide tube 24. But, while the discontinuity of the guidance afforded by these plates 40 and 42 does not allow them to guide the rodlet 29 quite as accurately as continuous guide sheaths 35, the guidance afforded by these plates 40 and 42 is accompanied by far less friction than the guidance afforded by such guide sheaths 35. The reduction in such frictional engagement more than compensates for any small loss in alignment ability by lengthening the life expectancy of the outer cladding of these rodlets 29, and further by reducing the minimum amount of time required to completely insert the rodlets 29 into their respective fuel assemblies 17. This "drop time" minimization aspect is an important one, as it results in the ability of the system operator to reduce or stop the nuclear reaction occurring within the fuel rods 19 of the fuel assembly 17 in the event of an emergency condition. With reference now to FIGS. 4, 5 and 6, each of the guide plates 40,42 includes a central orifice 44 for conducting coolant throughout the longitudinal axis of the guide tube 24. Like the previously described guide sheaths 35 of the guide sheath assembly 34, each plate 40 and 42 includes a plurality of guide holes pairs 46 interconnected between themselves and with the central orifice 44 by means of a slot 48, as well as single guide holes 47 which are similarly interconnected with the orifice 44 by means of a slot 48. To facilitate the receipt of the rodlets 29 into the guide holes 46,47, the upper and lower ends of each of the guide holes 46,47 preferably includes a bevel 50 as shown. Finally, each of the guide plates 40 and 42 include radial bores 52 for receiving pins (not shown) which affix the plate to the walls 25 of its respective guide tube 24. As may best be seen in FIG. 6, each of the guide plates 40,42 of the invention advantageously includes a plurality of vent openings in the form of vent holes 55a,b, and in the form of annular vent gaps 59 which, as will be explained in detail hereinafter, greatly reduce fretting and unwanted frictional engagement between the guide holes 46,47 in the plates 40 and 42, and the control rodlets 29. As is evident in FIG. 6, the vent holes 55a,b are each disposed between the slots 48 that interconnect the guide holes 46,47 with the central orifice 44. While more than one of such vent holes 55a,b could be provided between the various slots 48, only one such vent hole is preferred in order to simplify manufacturing. Each vent hole 55a,b that is positioned between any two adjacent slots 48 in the plate is preferably positioned adjacent to the midpoints of these slots 48, which is most effective position for these holes 55a,b to eliminate turbulence. Additionally, the diameter of these holes 55a,b is made as large as possible without jeopardizing the structural integrity of the plate 42. Because the lateral distance between adjacent slots 48 in the plate 42 varies, some of the vent holes 55a have a larger diameter than other of the vent holes 55b. To further assist each of these openings 55a,b in achieving their turbulence-minimizing function, both ends of each opening 55a,b is preferably chamfered in the manner illustrated in FIG. 6. In addition to vent holes 55a,b, each of the guide plates 40,42 of the invention also includes vent openings in the form of annular vent gaps 59. These gaps 59 are created by the provision of flanges 58 which, in the preferred embodiment, have a radial length of approximately 0.25 inches (0.635 cm) as measured from the center of the orifice 44. Four of these flanges 58 envelope the radial bores 52 into which the mounting pins are inserted that mount the plates 40,42 to the walls 25 of the guide tubes 24, while the other four flanges 58 are disposed between the first four flanges 58. While the vent gaps 59 in the preferred embodiment have a radial length (relative to the center of the orifice 44) of 0.25 inches (0.635 cm), gaps of as little as 0.125 inches (0.3175 cm) or smaller are within the purview of the invention. Additionally, while the radial length of the gaps 59 is shown to be substantially constant in the preferred embodiment, this radius may vary the only constraint being that the total cross-sectional area of any such vent gap 59 must be large enough to allow a flow around the edge of the plate 40 and 42 that is sufficient to significantly reduce the turbulence and pressure differential created just above the plate 40,42 by the flow of coolant through the orifice 44. To compensate for the reduction in shear strength caused by the provision of such vent openings in the plates 40,42, the thickness of these plates 40,42 is increased between 50 and 100 per cent. Accordingly, while the typical thickness of a prior art guide plate might be on the order of one inch (2.54 cm), the thickness of a guide plate 40,42 made in conformance with the invention is preferably between about 1.5 to 2.0 inches (3.81 to 5.08 cm). Finally, to further reduce frictional contact between the stainless steel or other metallic cladding that forms the outer surface of the rodlets 29, and the surface of the guide holes 46,47 in the guide plates 40,42, each of the guide holes 47,48 is preferably lined with a chrome plating 51. Such a chrome plating 51 not only renders the surfaces of these guide holes 46,47 smoother and harder; it further makes them even more corrosion resistant, which in turn helps keeps these inner surfaces smooth. This last feature is an important one, because even though the guide plates 40,42 are preferably fabricated from number 304 stainless steel, such stainless steel is not entirely corrosion proof in the relatively corrosive environment of a nuclear reactor hot, super heated water circulates over all metallic surfaces for periods of years. FIGS. 7 and 8 illustrate how the vent holes 55a,b and annular vent gaps 59 of the invention reduce turbulence. FIG. 7 illustrates a prior art guide plate 60 mounted in the walls 25 of a guide tube 24. As has been previously indicated, coolant in the form of water flows through the fuel assemblies 17 and through apertures (not shown) in the upper core plate 15 and axially through the guide tubes 24. When this coolant flow (indicated by the flow arrows) impinges the underside of a prior art guide plate 60 whose guide holes 46 are obstructed by the rodlets 29 of rod cluster control assembly 27, the flow of coolant is constricted through the opening afforded by the central orifice 44. As a result, a turbulent flow of coolant is generated around the upper surface of the prior art guide plate 60 from the interaction between the relatively rapidly moving coolant through the orifice 44 and the relatively quiescent coolant situated around the upper periphery of the plate 60. While the pressure differential generated between the quiescent coolant and the rapidly moving coolant through the orifice 44 generates a net radial vector 62 which tends to pull the rodlets 29 into engagement against their respective guide holes 46, the chaotic nature of the turbulence also creates a relatively smaller radially oriented pressure (indicated by the vector 64) so that the net result is a lateral vibration of the rodlets 29 accompanied by fretting and enhanced frictional engagement of the rodlets 29 against the guide holes 46. Over a period of time, such fretting and frictional engagement can damage and wear down the walls of the stainless steel cladding that surrounds the rodlets 29. In the preferred embodiment, the total cross-sectional area of the vent holes 55a,b is between about 50 and 60 per cent of the cross-sectional area of the central orifice 44. FIG. 8 illustrates how the vent openings in the improved guide plate 40,42 of the invention substantially prevents such turbulence from occurring. Specifically, these vent openings in the form of the vent holes 55a,b in combination with the annular vent gaps 59 allows the flow of coolant through the guide tube 24 to remain substantially parallel through the improved plate 40,42. The resulting, substantially parallel flow of coolant through the plate 40,42 eliminates much of the turbulence associated with a flow directed exclusively through the central orifice 44. Accordingly, the pressure differentials and lateral force vectors 62,64 associated with such turbulent flow are eliminated, and the rodlets 29 do not significantly fret against their respective guide holes 46, and moreover, do not frictionally engage against these holes as they are inserted into or withdrawn out of a fuel assembly 17. Finally, what small amount of frictional contact which may exist between these rodlets 29 and guide hole 46 can be even further minimized by the provision of the previously discussed chrome plating 51 in the guide holes 46,47 of the improved plates 40,42. In the preferred embodiment, the total cross-sectional area of all the vent gaps 59 is between 50 and 60 per cent of the orifice 44, so that the area of all of the vent openings 55a,b and 59 in the improved guide plate 40,42 of the invention is between 100 and 120 per cent of the central orifice 44. While the invention has been described with respect to a preferred embodiment, many variations in both the form and the dimensioning of the vent openings will become apparent to the person of ordinary skill in the art. All such variation in shape and dimensions of the vent openings are considered to be within the purview of this invention, which is constrained only by the claims appended hereto.
	abstract	In a process for estimating the concentration (C) of a chemical element in the primary coolant of a nuclear reactor, a dilution solution or a concentrated solution of said chemical element in a predetermined concentration (C*) is injected into the primary coolant within the reactor, and the reactor includes a sensor capable of measuring a quantity (Cm) representing the concentration of said chemical element. The process is an iterative process in which repeatedly in each time step k: a stage of acquiring quantities (qdk) and (qck) representing the injected flows of dilution solution and concentrated solution in step k, and a quantity (Cmk) representing the concentration measured by the sensor; a stage of calculating an estimated value (Cek+1) of the concentration of said chemical element in the primary coolant in step k+1 on the basis of representative quantities (qdk, qck, Cmk) acquired in stage k.
	description	The present invention relates generally to radiotherapy and irradiation systems, and particularly to modulating the intensity of a radiation beam by one or more attenuating leaves positioned in a radiation field. Medical equipment for radiation therapy treats tumorous tissue with high energy radiation. The dose and the placement of the dose must be accurately controlled to insure that the tumor receives sufficient radiation to be destroyed, and that damage to the surrounding and adjacent non-tumorous tissue, referred to as organs at risk (OAR), is minimized. Radiation therapy typically uses a radiation source that is external to the patient, typically either a radioisotope, such as cobalt-60, or a high energy x-ray source, such as a linear accelerator. The external source produces a collimated beam directed into the patient to the tumor site. However, external-source radiation therapy undesirably irradiates a significant volume of OAR in the path of the radiation beam along with the tumorous tissue. The adverse effect of irradiation of healthy tissue may be reduced, while maintaining a given dose of radiation in the tumorous tissue, by projecting the external radiation beam into the patient at a variety of gantry angles with the beams converging on the tumor site. This reduces the total dose to the healthy tissue during the entire treatment. The irradiation of healthy tissue also may be reduced by tightly collimating the radiation beam to the general cross section of the tumor taken perpendicular to the axis of the radiation beam. Numerous systems exist for producing such a circumferential collimation, such as systems with multileaf collimators. The multileaf collimator (MLC) may control the width and offset of the radiation beam as a function of gantry angle so that tumorous tissue may be accurately targeted. Collimation is just one way of shaping the radiation beam. Additionally or alternatively, the radiation beam may be spatially attenuated. Collimators control the outline of the radiation beam; attenuators control the intensity of the radiation beams that are beamed at the tissue. Phrased more technically, collimators block radiation so as to create a generally binary spatial intensity distribution (binary: passed or blocked), while attenuators or beam modulators, typically produce continuous spatial modulation of the beam intensity by selective attenuation. For example, intensity modulated radiotherapy (IMRT) is aimed at irradiating a target while protecting healthy tissue, especially organs-at-risk (OAR). Intensity modulation is implemented either by multileaf collimators or by attenuating modulators. A desired intensity map is approximated by segmentation: forming a sequence of aperture segments consecutively shaped by the MLC. Using inverse planning for radiotherapy treatment, the physician prescribes desired target dose and tolerances for sensitive structures, and optimization software explores a multitude of possibilities to determine machine settings so as to closely deliver the prescribed radiation dose. Irradiation is delivered from a discrete set of orientations or from a continuous arc. In order to modulate radiation beam intensity in a given field, the beam is conceptually partitioned into many small beam segments which are generically called pencil beams or beamlets. Beamlets are indexed by their respective positions in a radiation field and by the orientation of the beam relative to a patient. Dose distribution produced by a beamlet in the patient is calculated and/or measured. Optimizing IMRT amounts to selecting respective intensities of the beamlets, arranged as an intensity map, so as to achieve optimal accumulated dose distribution in the patient. Since separate irradiation of each beamlet is cumbersome, beamlets are grouped into field segments incorporating respectively uniform segment intensities. Successive irradiation of the segments approximates the optimized intensities prescribed by the intensity map. Direct methods optimize the field shape in addition to beamlets intensities, while delivery constraints may be incorporated in the optimization process. Collimators are configured to define a radiation field by blocking substantially all radiation outside the field aperture. Typically, a desired radiation field is produced by cascaded collimators. Primary, secondary and tertiary collimators are termed according to their respective proximity to the radiation source. A fixed-size stationary primary collimator defines the maximal field size. Secondary collimators are movable and are operable to generally produce rectangular fields of variable size and location. Finer field shaping is further accomplished by tertiary collimators, typically conical (sometimes called cylindrical) collimators of various diameters or multi-leaf collimators. Successive cascaded collimators overlap so as to prevent radiation from leaking between collimators. A multi-leaf collimator modifies field aperture by adjusting spaces between respective front-ends of opposing leaves. The produced field can be modified during irradiation or between irradiations. Respective rear-ends of MLC leaves overlap the secondary collimator (typically jaws). While collimators block radiation outside a field, beam intensity can be modulated by a physical modulator covering the whole field. Such a modulator incorporates spatially variable attenuating properties tailored to a specific intensity map. Simple modulators, e.g., a wedge, do not generally provide on their own IMRT with sufficient quality. The present invention seeks to provide a novel device and method for modulating intensity of a radiation beam in a radiation field by movable leaves configured to attenuate beam portions of the radiation field, as is described hereinbelow. In accordance with an embodiment of the present invention, a multi-leaf modulator is provided for use in a radiation system that emits a radiation beam in a radiation field, the modulator including a plurality of displaceable leaves configured to attenuate portions of the radiation beam in the radiation field, and means for displacing the leaves by radiolucent members attached to the leaves. The displacement is according to respective motion profiles derived from an optimized attenuation map so as to obtain a desired dose distribution. The attenuation of a leaf in a given location is proportional to the dwelling time of the leaf in that location or it is inversely proportional to the speed of the leaf in that location. It is noted that in the description, the members attached to the leaves are referred to as radiolucent. This term not only encompasses members that allow passage of the beam with substantially no attenuation, but also encompasses finite (small) attenuation, that is, significantly smaller than that of the leaf, such as no more than 10% of the leaf attenuation, more preferably no more than 5% of the leaf attenuation, and most preferably no more than 1% of the leaf attenuation. This small attenuation can be incorporated in the calculation of the leaf motion profile. There is thus provided in accordance with an embodiment of the present invention a modulator for use in a radiation system, the radiation system being capable of irradiating a target from a plurality of orientations, wherein the orientations are associated with directional radiation beams respectively collimated into radiation fields, including a plurality of displaceable radiation attenuating elements arranged in at least one row, the radiation attenuating elements being configured to attenuate portions of a radiation beam inside the radiation field according the position of the radiation attenuating elements, and wherein each radiation attenuating element is respectively attached to a substantially radiolucent member, and a driver operable to store motion profiles and to respectively drive the radiation attenuating elements in directions generally perpendicular to the radiation beam via the substantially radiolucent members, wherein the respective motions of the radiation attenuating elements are according to corresponding motion profiles, and wherein a motion profile relates position and/or velocity of the radiation attenuating elements to time and/or irradiation level. In one non-limiting embodiment, a collimator is operable to substantially block radiation outside a radiation field. In one non-limiting embodiment, a radiation source is operable to produce a radiation beam toward a target. In one non-limiting embodiment, a target positioner is provided for adjusting the relative position of the target and the radiation beam. In one non-limiting embodiment, a modulator positioner is provided for adjusting the relative position of the modulator and the radiation beam. In one non-limiting embodiment, an additional modulator is operable to modulate the radiation beam in the radiation field. In one non-limiting embodiment, a processor is in communication with the driver, wherein the processor is operable to derive attenuation maps associated with irradiating the target from respective orientations and to transform an attenuation map into motion profiles of the radiation attenuating elements, wherein the attenuation map provides attenuation levels related to the radiation attenuating elements in respective positions. Reference is now made to FIG. 1, which illustrates a radiation system 10 with a collimator system 12 (or for short, collimator 12), constructed and operative in accordance with a non-limiting embodiment of the present invention. In the non-limiting illustrated embodiment, radiation system 10 (e.g., a LINAC) includes a radiation source 14 that emits a radiation beam 16. The radiation source 14 and collimator 12 can be positioned in a gantry (not shown), as is well known in the art. Any radiation may be used, such as but not limited to, electron radiation or photon radiation (gamma radiation). As is known in the art, during treatment, beam 16 is trained on a target typically surrounding the isocenter of the gantry rotation. Imaging apparatus (not shown), such as a fluoroscope or ultrasound apparatus, for example, may be provided for imaging the target irradiated by radiation beam 16. The imaging apparatus may be used in conjunction with a closed loop, feedback control system (not shown) for controlling a relative position between the target and the radiation beam and for controlling the functioning of collimator 12. Collimator 12 is arranged to form an aperture 20 through which radiation beam 16 can pass. In one embodiment, collimator 12 is a single custom made radiation block shaped in accordance with previously acquired data of the tumor in the patient. In another embodiment of the present invention, collimator 12 may be a multileaf collimator including a plurality of movable radiation blocking leaves 18 arranged to form aperture 20. In general, although not limited by this, aperture 20 has a closed perimeter defined by the radiation block or by the leaves 18. Radiation system 10 is thus capable of irradiating a target from a plurality of orientations, wherein the orientations are associated with directional radiation beams 16 respectively collimated by collimator 12 into radiation fields. In accordance with an embodiment of the present invention, a multileaf modulator 21 is provided for use with radiation system 10. The multileaf modulator 21 includes one or more radiation attenuating elements 22, which are positioned to block a portion of radiation beam 16 that passes through a field of view of aperture 20. In the illustrated embodiment of FIG. 1, three radiation attenuating elements 22 are shown. FIG. 2 shows an alternative embodiment, wherein a plurality of radiation attenuating elements 22 are arranged to move along different planes substantially perpendicular to radiation beam 16. The radiation attenuating elements 22 may be a plurality of displaceable leaves arranged in at least one row. The leaves are configured to attenuate portions of radiation beam 16 inside the radiation field according the position of the leaves. Radiation attenuating element 22 is disposed on (attached to, joined to, or extending from) a substantially radiolucent member 24 that is made of a material that does not substantially block radiation beam 16. The one or more radiation attenuating elements 22 are moved by a driver 25 (e.g., linear actuator, step motor and others) to different positions in the field of view of aperture 20. In one embodiment, driver 25 stores motion profiles and respectively drives radiation attenuating elements 22 (also referred to as leaves 22) in directions generally perpendicular to the radiation beam 16 via the substantially radiolucent members 24. The respective motions of the leaves 22 are according to corresponding motion profiles; the motion profile relates position and/or velocity of the radiation attenuating element 22 to time and/or irradiation level. Radiation attenuating element 22 attenuates a portion of radiation beam 16 that passes through aperture 20, but other portions of radiation beam 16 outside of radiation attenuating element 22 pass substantially un-attenuated through aperture 20 and radiolucent member 24. (In the case of complete attenuation, radiation attenuating element 22 completely blocks the portion of radiation beam 16.) Thus, as seen in a plane 26 perpendicular to the beam direction, radiation passes all around radiation attenuating element 22 in aperture 20 but not at the position of radiation attenuating element 22. The shadow 27 of radiation attenuating element 22 is clearly seen on plane 26. In the illustrated embodiment, radiation attenuating element 22 and radiolucent member 24 are not coplanar with the one or more leaves 18. However, in another non-limiting embodiment shown in broken lines in FIG. 1, radiation attenuating element 22 and radiolucent member 24 may be coplanar with at least some of the leaves 18. The collimator may further include apparatus 28 for determining position and shape of the aperture (e.g., a camera). A target positioner 30 (such as a gantry) may be provided for adjusting the relative position of the target and radiation beam 16. A modulator positioner 32 may be provided for adjusting the relative position of the modulator 21 and radiation beam 16. For example, modulator 21 may be mounted on a precisely movable table. As another example, modulator positioner 32 may be the gantry. An additional modulator 34 (e.g., an additional attenuator) may be provided to modulate radiation beam 16 in the radiation field. A processor 36 may be in communication with driver 25. Processor 36 is operable to derive attenuation maps associated with irradiating the target from respective orientations and to transform an attenuation map into motion profiles of the radiation attenuating elements 22, wherein the attenuation map provides attenuation levels related to the radiation attenuating elements 22 in respective positions. Reference is now made to FIG. 3, which illustrates one non-limiting example of a method for performing IMRT, such as controlled by processor 36, in accordance with an embodiment of the present invention. The method includes irradiating a target from a plurality of orientations, wherein the orientations are associated with radiation beams respectively collimated into radiation fields. Respective intensity maps are optimized for the plurality of orientations. For each orientation, the corresponding field is segmented into segments, and for each segment, segment intensity and segment profiles are selected for the leaves of the multi-leaf modulator. A segment profile relates position and/or velocity of a leaf to time and/or irradiation level. The segment is irradiated by the segment intensity and the segment intensity is modulated according to the segment profiles. The method may further include optimizing the respective radiation fields associated with the orientations. For example, optimizing respective intensity maps may include minimizing a cost function subject to clinical and/or radiation delivery constraints. Segmenting the corresponding field into segments may include overlapping segments. Selecting segment intensity may be done by minimizing a cost function subject to clinical and/or radiation delivery constraints. The segment may be irradiated without turning the beam off following irradiation of another segment. The segment may be irradiated during a continuous adjustment of the relative orientation between the radiation beam and the target. The method may further include assigning various irradiation orientations to the segments prior to selecting segment intensity and segment profiles, such that each orientation is associated with one segment. The scope of the present invention includes both combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof which would occur to a person of skill in the art upon reading the foregoing description and which are not in the prior art.
044568274	description	DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, a transportation and/or storage container embodying this invention comprises mainly a thick-wall container body 12 of metallic material for containing therein and shielding gamma radiation of radioactive material. The material of the body 12 desirably is made of cast iron, preferably spherical graphite cast iron. The container body 12 preferably is cylindrical, is provided with the usual trunnion-like supporting projections 14 and has an open top and side walls 16 integral with a bottom 18 defining an interior cylindrical cavity 20 for the reception of radioactive material, e.g., spent nuclear fuel elements. The cavity 20 is provided with a corrosion resistant open-top lining 22 provided with a top peripheral flange 24 overlying the bottom 26 of a counterbore 28 in the open top of the container body 12. A thick gamma-radiation-shielding cover 30 for the lining 22 is fitted into the counterbore 28 in overlying engagement with the flange 24. Sealing means are provided between the lining cover 30 and the flange 24 adjacent the inner periphery of the latter, such as resilient sealing gaskets 32, e.g., O-rings, disposed in concentric annular grooves 34 in the underside of the cover. A container body or outside cover 36, preferably of the same material as the container body 12, overlies the lining cover 30 in an outer counterbore 38 in the top of the container body. This container body cover 36 may be secured in place by screws 40 engaged within threaded sockets 42 in the container body 12. Sealing means, such as resilient sealing gaskets 44, are interposed between the body cover 36 and the bottom 38 of the outer counterbore inwardly of the screws 40. The lining 22 is detachably fastened in the container body 12 by a circular array of countersunk headed screws 46 extending through the flange 24 into tapped sockets 48 in the container body. These sockets 48 are sealed against corrosion from the contents of the lining 22, and its cover 30, by the seals 32. The lining cover 30 is secured in place by a circular array of headed screws 50 which extend through the cover into tapped sockets 52 in the screws 46. Thus, the interior lining 22 and its cover 30 are secured to the body 12 independently of one another but in a manner which minimizes attachment space and assures against corrosion of the body 12 of the container by the contents of the lining. Preferably, the socketed screws 46 are made of corrosion resistant material. In actual practice, it has been found that the lining cover 30 may be secured in place by 24 M32 screws 50. In the event, the socketed screws 46 may be M48. With this arrangement, the cover screws 50 may be unscrewed readily without unscrewing the socketed lining screws 46. The head of each of the socketed screws 46 is shaped, as at 54, for engagement by a suitable wrench for easy screwing and unscrewing. Preferably a sealing gasket 56 is interposed between the under side of the head of the socketed screws 46 and the bottom of the corresponding countersink in the liner flange 24 to seal against admission of water into the tapped sockets 48 in the event the container is loaded with spent nuclear fuel elements while under water. The tapped sockets 52 in the screws 46 may have closed inner ends, as shown in the drawings, or such sockets may be replaced by open ended tapped bores. As shown in FIG. 1, the container body cover 36 preferably is provided with an aperture 58 having a removable sealing closure 60 which comprises a connection for monitoring the interspace between the two enclosures; an outer enclosure formed by the container body 12, the cavity 20 therein and its cover 36, and an inner enclosure formed by the lining 22 and its cover 30. Thus, it is possible, by way of the connection 58, to ascertain the integrity of the inner enclosure with a conventional search device for radioactive leakage without exposing an operator to radiation danger. Consequently, the container is suitable for intermediate storage of radioactive material which is to be reprocessed later. Referring now to FIGS. 3 and 4 of the drawings, the body 12 of the container, which preferably is cylindrical, is provided with a plurality of preferably equally-spaced exterior cooling ribs or fins 62 which may be arranged longitudinally, as shown, or circumferentially. These ribs 62 may be either cast integrally with the body 12 or welded thereto. Extending transversely to and between the ribs 62 and secured to the latter and to the exterior of the container body 12 are bridges or flanges 64 of a height less than that of the cooling ribs. These flanges 64 preferably are cast integrally with the body 12 and ribs 62, or they may be welded in place. The presence of the flanges 64 insures that in the event of the breaking off or cracking off of a cooling rib 62, the line of fracture of such rib is not located at its base but at a distance above such base. This minimizes the possibility that the breaking off or cracking off of a rib 62, which may occur in the event the container is dropped, will extend the fracture into the container body 12, i.e. insures against the continuation of such a crack into the container body. The safe distance of such a rib crack from the container body 12 itself can be insured by the judicious selection of relative heights of the flanges 64 and the ribs 62. Theoretical calculations, and also experiments, have shown that it is desirable to proportion the parts such that the height of the flanges 64 is no more than about two-thirds of the height of the cooling ribs 62 and that the spacing between flanges is no more than about ten times their height. In connection with the foregoing provision for inhibiting the extension of rib fracture cracks into the body 12 of the container, it has been found to be advantageous to provide notches 66 in the cooling ribs 62 in the area of intersection therewith of the flanges 64, as shown in FIG. 5. This construction even better insures against continuation of a rib crack into the body 12 of the container. The bottom of the notches 66 is no deeper than the tops of the flanges 64. Notches 66 of lesser depth are effective for their intended purpose, however, depending upon the specific design and material of the ribs 62 and flanges 64. Such notches 66 may be molded by a casting operation or formed by a machining operation. In a working example, a cast body container for irradiated nuclear fuel elements taken from a pressurized water reactor, the container having cast on longitudinal cooling ribs and circumferential flanges, may have flange spacing of the order of about 440 mm and a flange height of about 70 mm. The cooling ribs may have a height of about 240 mm with notches therein, at the location of intersection of the flanges, of a depth of the order of about 95 mm. With these dimensions, potential cracks in the container body 12, occasioned by damage to the cooling ribs, will be avoided. Connections also are made through the lining cover 30 to the interior of the lining 22. These include supply passages 68 through the cover 30, the outer end of each being provided with a removable closure 70. A rigid line, pipe or tube 72 is connected to the inner end of one of the passages 68 and depends to a location adjacent the bottom of the lining 11. The upper end of the tube 72 is inserted into the inner end of the passage 68 with a flange 74 on the tube determining the depth of insertion. A coil compression spring 76 is interposed between the lower end of the tube 72 and the lining bottom to retain the tube in place, as shown in FIGS. 1 and 6. Alternatively, the inner end of the passage 68 may terminate in an outwardly flaring cone 78 and the tube 72 may have an upper end complimentary to and fitting in the cone, as shown in FIG. 7. Neutron shielding material 80 desirably covers the cylindrical outer surface of the container body 12, preferably being disposed between the cooling ribs 62 in the spaces between the flanges 64 and the upper ends of ribs. It is particularly desirable to construct the neutron shielding material 80 in the form of molded bodies 82 to fit in such spaces, and even more desirable to form the bodies of several individual closely fitting parts 84 as shown in FIG. 10. Thus the neutron shielding 80 can be easily mounted, tested and serviced. The several parts 84 may have a variable shape, graduation and size, but should be fitted together into an ensemble which will shield stray neutrons. The molded bodies 82 preferably are held in place by engagement beneath lateral projections 86 on the cooling ribs 62, and may have a covering thereon (not shown) retained in place by such projections. Spring clips 88 having a folded or ridge-shaped resilient central portion 90 may be used effectively to retain multi-part molded bodies 84 in place, the ridge-like resilient portion 90 serving additionally as a minicooling rib. In a preferred embodiment, shown in FIG. 11, the multi-part molded body 82 may comprise a middle part 92 that is parabolic or cuniform in cross section and two identical parts 94 on the opposite sides of the middle part. The middle part 92 may be slightly oversize so that the force exerted thereon by the clip 88 will press the lateral parts 94 tightly against the outer surface of the body 12 and against the cooling ribs 62.
	abstract	A container for storing and/or transporting spent nuclear fuel. The container includes a body that defines an internal cavity that holds the spent nuclear fuel and an outer surface. The outer surface has holes formed therein into which trunnions are positioned. The container can be lifted by a lift yoke by coupling the lift yoke to the trunnions. The trunnions may include first and second components such that the first component is slidable in its axial direction relative to the second component when a force that exceeds a threshold acts on the second component. Thus, the second component may be slidable between a protruded state in which a portion of the second component protrudes from the outer surface of the body and a retracted state in which the second component does not protrude from the outer surface of the body.
	description	This application is a continuation of U.S. application Ser. No. 12/092,786 filed on May 6, 2008, issuing as U.S. Pat. No. 7,893,397. U.S. application Ser. No. 12/092,786 is a National Phase Entry of PCT Patent Application No. CA2006/001815 filed on Nov. 7, 2006, which claims the benefit of priority of U.S. Provisional Patent Application No. 60/733,812 filed on Nov. 7, 2005, which is incorporated herein by reference in its entirety. The present invention generally relates to charged particle beam systems. In particular, the present invention relates to a methods and apparatus for surface modification using charged particle beams. Focused Ion Beam (FIB) microscope systems have been produced commercially since the mid 1980's, and are now an integral part of rapidly bringing semiconductor devices to market. FIB systems produce a narrow, focused beam of charged particles, and scan this beam across a specimen in a raster fashion, similar to a cathode ray tube. Unlike the scanning electron microscope, whose charged particles are negatively charged electrons, FIB systems use charged atoms, hereinafter referred to as ions, to produce their beams. These ions are, in general, positively charged. These ion beams, when directed onto a semiconductor sample, will eject secondary electrons, secondary ions (i+ or i−), and neutral molecules and atoms from the exposed surface of the sample. By moving the beam across the sample and controlling various beam parameters such as beam current, spot size, pixel spacing, and dwell time, the FIB can be operated as an “atomic scale milling machine,” for selectively removing materials wherever the beam is placed. The dose, or amount of ions striking the sample surface, is generally a function of the beam current, duration of scan, and the area scanned. The ejected particles can be sensed by detectors, and then by correlating this sensed data with the known beam position as the incident beam interacts with the sample, an image can be produced and displayed for the operator. FIG. 1 is a schematic of a typical FIB system. FIB system 10 includes an evacuated envelope 11 having an upper neck portion 12 within which are located a liquid metal ion source 14 and a focusing column 16 including extractor electrodes and an electrostatic optical system. Ion beam 18 passes from source 14 through column 16 and between electrostatic deflection means schematically indicated at 20 toward sample 22, which comprises, for example, a semiconductor device positioned on movable X-Y stage 24 within lower chamber 26. An ion pump 28 is employed for evacuating neck portion 12. The chamber 26 is evacuated with turbomolecular and mechanical pumping system 30 under the control of vacuum controller 32. The vacuum system provides within chamber 26 a vacuum on the order of 1×10E-7 Torr. If an etch assisting, an etch retarding gas, a deposition precursor gas, or some other reactive or non-reactive gas is used, the chamber background pressure may rise, typically to about 5×10E-5 Torr. High voltage power supply 34 is connected to liquid metal ion source 14 and to appropriate electrodes in focusing column 16 and directing the ion beam. Deflection controller and amplifier 36, operated in accordance with a prescribed pattern provided by pattern generator 38, is coupled to deflection plates 20. A charged particle multiplier detector 40 detects secondary ion or electron emission for imaging, is connected to video circuit and amplifier 42, the latter supplying drive for video monitor 44 also receiving deflection signals from controller 36. A gas delivery nozzle 46 supplies the reactive or non-reactive gas to the surface of a material and preferably, in the path of the ion beam. A door 48 is provided for inserting sample 22 onto stage 24, which may be heated or cooled. Focused ion beam systems are commercially available from various companies, but the system shown in FIG. 1 represents one possible FIB system configuration. During any beam raster operation executed by FIB system 10, which includes imaging, milling, gas assisted etching or deposition, the FIB beam deflection software and hardware deflects the beam in a preset pattern across the surface, generally referred to as rastering. At each preset location, the beam is left to dwell for a given period of time before moving to the next point in the raster. At its simplest, a raster pass consists of deflecting the beam at fixed increments along one axis from a start point to an end point, dwelling for a fixed dwell time at each point. At the end of a line, the beam waits a fixed retrace time before moving an increment in a second axis. The beam may return to the start point in the first axis and begin again, or may begin “counting down” the first axis from the point it had just reached (depending on whether the raster type is raster (the former) or serpentine (the latter). This process continues until all increments in both axes have occurred, and the beam has dwelled at all points in the scan. It is well understood by those of skill in the art that FIB systems are used to perform microsurgery operations for executing design verification or to troubleshoot failed designs. This can involve physically “cutting” metal lines or selectively depositing metallic lines for shorting conductors together. As previously discussed, reactant materials such as gases, are directed at the surface of the material being processed. The reactant materials cooperate with the particle beam to enhance or modify the deposition or etching process being performed. For example, focused ion beams are used to etch conductive materials such as tungsten from the surface of semiconductor devices to repair or modify the circuitry of the semiconductor device. As a focused ion beam is directed to the surface of the semiconductor device, an etchant material is delivered to the surface of the semiconductor device. The focused ion beam and the etchant-type reactant material will cooperate to remove material, such as tungsten film, from the semiconductor device surface. In contrast to etching, a reactant-containing metal can be used for depositing a conductive material on the substrate surface, typically as wires and as connection pads. While FIB microsurgery is useful for semiconductor circuit design verification, the successful use of this tool relies on the precise control of the milling process. Current integrated circuits have multiple alternating layers of conducting material and insulating dielectrics, with many layers containing patterned areas. Hence the milling rate and effects of ion beam milling can vary vastly across the device. Unfortunately, a FIB operator is responsible for halting the milling process when a metal line of interest has been sufficiently exposed or completely cut, a process known as “endpointing”. Endpointing is done based on operator assessment of image or graphical information displayed on a user interface display of the FIB system. In most device modification operations, it is preferable to halt the milling process as soon as a particular layer is exposed. Imprecise endpointing can lead to erroneous analysis of the modified device. Older FIB systems operating on current state-of-the-art semiconductor devices do not provide image and graphical information with a sensitivity that is usable by the operator. This is due in part to the fact that older FIB systems will have imaging systems originally optimized for older generation semiconductor devices. In particular, as semiconductor device features continue to decrease in size from sub-micron to below 100 nm, it has become necessary to mill smaller and higher aspect ratio FIB vias with reduced ion beam current. This significantly reduces the number of secondary electrons and ions available for endpoint detection and imaging. In addition, FIB gas assisted etching introduces a gas delivery nozzle composed of conductive material. The proximity of the nozzle to the sample surface creates a shielding effect which reduces the secondary electron detection level. Particularly when performing circuit edit from the so-called front side of the device (accessing the circuitry from the side of the device furthest away from the silicon substrate, rather than through the substrate silicon as is done is so-called back side circuit edit), high beam currents are preferably not used due to the potential occurrence of electrostatic discharge (ESD) events, which can strike and damage the semiconductor circuit being worked on. By example, some FIB operations are limited on certain devices or even within regions of otherwise non problematic devices that are devoid of surface features, to the use of a 50 pA of beam current, otherwise the device charges up under the influence of the FIB beam, and an ESD event occurs, damaging the semiconductor device. Therefore, etch rates are slow and beam currents must be carefully controlled. U.S. Pat. No. 5,851,413 proposes the use of a partial chamber for increasing etch rates, particularly the etch rates of the silicon substrate during backside circuit edit. FIG. 2 is an illustration of a prior art partial chamber. The partial chamber 100 is to be used within FIB chamber 26, and includes a gas delivery tube 102 for providing a gas 103, a lower chamber 104 and an upper chamber 106. The lower chamber 104 and the upper chamber 106 have an interior passage, while the upper chamber 106 has a top aperture 108 and the lower chamber 106 has a bottom aperture 110. The upper chamber 106 is in communication with gas deliver tube 102. The top and bottom apertures 108 and 110 are concentric with each other and co-axial with the axis of the beam 112. It is noted that the beam can be either an ion beam or an electron beam. The two spaced apertures provide a path for the ion beam 112 to travel through the partial chamber 100 and to impact against the surface of a semiconductor chip 114. The partial chamber 100 is effective for concentrating a reactant gas in an area proximate to the surface to be worked on, thereby improving etching and deposition processes. Furthermore, since the gas provided by the gas delivery tube 102 is directed substantially perpendicular to the surface of the semiconductor chip 114, uniform topography can be obtained. This partial chamber is intended to speed up the removal rate of silicon by achieving a much higher pressure of XeF2 than the column could stand if it was in the main chamber. Use of the partial chamber is ideally used for backside edits, meaning etching through the bulk silicon and stopping near the device surface. However, the partial chamber is impractical for detailed etching from the backside since the pressure is typically too high, and after a while, spontaneous etching of the silicon will occur even in the absence of the beam. Using the partial chamber for etching the front side of a semiconductor device does not give an appreciable benefit versus using a standard gas nozzle in terms of etch rate. In fact, the partial chamber will reduce the signal available for detection, however use of such a chamber for etching the front side does have a benecificial effect in terms of reducing ESD, as will be discussed below. FIG. 3 is an illustration of an alternate partial chamber which addresses the problem of the partial chamber shown in FIG. 2. This type of partial chamber was coined a “cupola” nozzle and described in the paper titled “Gas Delivery and Virtual Process Chamber Concept for Gas Assisted Material Processing in Focused Ion Beam System”, by Valery Ray, presented at the 48th International Conference EIPBN 2004, in San Diego, Calif., USA. Partial chamber 200 includes a domed chamber 202 having an aperture 204 at its top, while being completely open at its bottom end 206 for passing through a beam 207. A gas delivery tube 208 provides a gas 210 to the domed chamber 202. Partial chamber 200 achieves at least the same effectiveness as partial chamber 100 of FIG. 2. A typical use of the partial chamber 200 is to enhance FIB etch rates. The advantage of partial chamber 200 is increased signal that can be detected. is subject to ESD events. In use, the partial chamber 200 is placed a few hundred micrometers above the surface of the silicon sample 212, where the base chamber pressure is approximately 1×10E-7 Torr. A reactive gas, such as XeF2, is delivered under high pressure into the partial chamber 200 until the full chamber pressure reaches approximately 8×10E-6 Torr. The ion beam is then passed through the partial chamber 200, the XeF2 gas, and onto the silicon device. This will greatly enhance the etch rate of the silicon when exposed to the ion beam and the XeF2 gas. Neither U.S. Pat. No. 5,851,413 or the paper by Valery Ray discuss or address the problem of ESD mitigation. It is, therefore, desirable to provide a method and system for improving front side etch rates in FIB systems while minimizing ESD events Significant advances have been made in the field of circuit editing involving the monitoring of secondary particles generated using ion beams impinging on a circuit or sample. However, many problems remain. One of these problems regards the low yield of detected secondary particles used in monitoring milling of integrated circuits (ICs) or of samples in general. The low yield of detected secondary particles leads to poor control of milling depths, and therefore of circuit editing precision. It is, therefore, desirable to provide a system and method for improving the yield of detected secondary particles. Another facet of ion beam circuit editing involves gas assisted editing of circuit or samples. Such gas assisted ion beam editing includes etching and deposition of materials on a sample in a gas environment. The physical and chemical processes at play during such etching and deposition of materials are usually temperature dependent. Thus, controlling the temperature of the portion of the circuit or sample being edited is therefore very important. However, most present techniques require that the temperature of the whole sample be changed by mounting the sample on a temperature control stage to change the temperature of the whole sample instead of only the portion being edited. This can be costly in terms of processing time and is subject to the highest temperature tolerable by the most heat vulnerable portion of the circuit or sample. Local heating of an edit portion of a circuit or sample can be achieved by the use of a laser. However, this requires special optics for the delivery and alignment of the laser, together with safety implements. It is therefore desirable to provide a system and method for heating the sample locally during gas assisted editing of the sample. Yet another facet of ion beam circuit editing or of circuit editing in general is that of the fabrication of ohmic contacts on circuits or samples. Attempts have been made at fabricating ohmic contacts by first performing ion beam deposition on an area of a sample and then driving a current through the sample, in the area of the ion beam deposited material. That approach has the disadvantage of providing undesired current to the part of the circuit the ohmic contact is being connected to, which can cause significant alteration and/or damage of that part of the circuit. It is therefore desirable to provide a method of fabricating ohmic contacts on an existing circuit that is not damaging to the circuit. It is an object of the present invention to obviate or mitigate at least one disadvantage of previous circuit edit techniques. In a first aspect, the present invention provides a method for charge neutralization of an ion beam. The method includes positioning a partial chamber over a sample within a main chamber; injecting a gas into the partial chamber; detecting a predetermined pressure of the main chamber, the predetermined pressure being effective for promoting charge neutralization in the partial chamber; and passing the ion beam through the partial chamber and onto the sample. According to embodiment of the present aspect, the predetermined pressure of the main chamber is about 8×10E-6 Torr, the a current of the ion beam is between 500 pA and 20 nA, the gas includes a non-reactive gas or a mixture of a non-reactive gas and a reactive gas. In a second aspect, the present invention provides method of controlling a yield of detected secondary particles at a detector, the secondary particles generated by charged particles impinging on a sample. The method includes forming a charged particle directing field, and positioning the charged particle directing field to change the yield of detected secondary particles at the detector. In an embodiment of the present aspect, positioning the charged particle directing field includes translating a field inducing circuit in at least one of a direction substantially parallel to a surface of the sample, and a direction substantially perpendicular to the surface of the sample. In a third aspect, the present invention provides a method of editing a sample. The method includes changing a temperature of an edit region of the sample by applying a temperature differential to the edit region by a probe held at a temperature different than a temperature of the sample, thereby changing a circuit edit property of the edit region relative to a remainder of the sample, and modifying the edit region. In a fourth aspect, the present invention provides a method of editing a circuit. The method includes providing an ion beam to an edit portion of the circuit; and contacting a heat source to the edit region. In a fifth aspect, the present invention provides a gas nozzle for delivering a gas to a sample. The gas nozzle includes a hollow body for receiving the gas, a frusto-conically shaped aperture extending through the hollow body for receiving at least one charged particle beam, and a gas outlet orifice concentric with the frusto-conically shaped aperture for delivering the gas from the hollow body to the sample. According to embodiments of the present aspect, the angle of the frusto-conically shaped aperture is at least an angle between two charged particle beams and the hollow body is shaped to form a gas reservoir around the gas outlet orifice. Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. Generally, the present invention provides an apparatus and method for using high beam currents in FIB circuit edit operations, without the generation of electrostatic discharge events. An internal partial chamber is disposed over the circuit to be worked on by the FIB. The partial chamber has top and bottom apertures for allowing the ion beam to pass through, and receives a gas through a gas delivery nozzle. A non-reactive gas, or a combination of a non-reactive gas and a reactive gas, is added to the FIB chamber via the partial chamber, until the chamber reaches a predetermined pressure. At the predetermined pressure, the gas pressure in the partial chamber will be much greater than that of the chamber, and will be sufficiently high such that the gas molecules will neutralize charging induced by the beam passing through the partial chamber. According to an embodiment of the invention, the partial chambers 100 or 200, can be used to neutralize charge induced by a high current ion beam. Partial chambers 100 and 200 are merely examples of chambers, or concentrators, which can be used for restricting the dissipation of the provided gas(es). However, any suitable type of chamber which can create a “micro environment” having a resulting pressure within being much closer to atmospheric pressure than the native high vacuum environment of the FIB chamber 26 can be used. Charge neutralization can be achieved by establishing a high pressure inside the partial chamber, thereby creating something analogous to a low vacuum or so-called environmental SEM, inside an otherwise “high vacuum” instrument that was not necessarily designed for low vacuum operation. More specifically, the partial chamber can be used with a non-reactive gas, such as nitrogen, at an even higher pressure than used in the enhanced etching example above. The total chamber pressure will climb somewhat, but the pressure inside the “micro environment” created by the partial chamber can reach a point where the non-reactive gas molecules will neutralize any charging that is induced by the ion beam. According to an embodiment of the present invention, the final FIB chamber pressure can be 10 times the pressure used in the prior art for gas-assisted etching or deposition. Therefore, much higher beam currents can be employed without damaging the silicon device by electrostatic discharge. By using higher beam currents, etching rates can be improved and circuit edit can be performed more quickly. Higher beam currents can also be employed during FIB nanomachining, for example during specimen preparation for failure analysis, where the goal is to remove a portion of the integrated circuit device to allow access to a particular site for investigation as to why a failure may have occurred. The use of the high pressure “micro environment” allows FIB nanomachining at higher beam currents, resulting in faster results, without the risk of an ESD event causing an artifact that could be mistaken for the failure being investigated. FIG. 4 is a flow chart illustrating the charge neutralization method, according to an embodiment of the present invention. The process begins at step 300, where the partial chamber is positioned over the sample to be worked on. At step 302, a non-reactive gas is injected into the partial chamber. It is presumed that the base chamber pressure is approximately 1×10E-7 Torr before non-reactive gas injection. At step 304, the FIB chamber pressure is detected at being a level which corresponds to the partial chamber pressure being sufficiently high to promote charge neutralization by the gas molecules. In a preferred embodiment, the FIB chamber should be at approximately 8×10E-6 Torr, resulting in a partial chamber pressure that is many times higher. Finally at step 306, the beam, either being a high current ion or electron beam, is passed through the partial chamber. Therefore, high beam currents can be used without risk of damaging the silicon device due to electrostatic discharge events, which are more likely to occur in the absence of the high pressure micro-environment provided by the partial chamber. In the present embodiment, the gas being injected at high pressure is 100% non-reactive gas. However, a mixture of non-reactive gas and reactive gas can be provided at high pressure to further enhance etching/deposition. In a preferred embodiment, the injected gas can be 10% reactive gas and 90% non-reactive gas, however any proportion can be used depending upon the desired amount of reactivity. An example mix can be N2 (non-reactive) and XeF2 (reactive). It is noted that both the reactive gas and the non-reactive gas molecules will provide charge neutralization at the high FIB chamber pressure that has been previously described. Accordingly, the proportion of gas can range between 100% reactive to 100% non-reactive, to tailor the amount of reactivity while achieving charge neutralization. It may be desirable that the proportion of gas can be varied, by means of external control, while the charged particle beam is incident on the target site, for example, 100% non-reactive gas can be used while the beam is being “tuned” on the sample, to provide charge neutralization without reaction, then the reactive gas can be introduced at the appropriate ratio when tuning is complete and a reaction is desired. According to an embodiment of the present invention, the reactive gas can be provided by one gas delivery tube connected to the partial chamber, while the non-reactive gas can be provided through a second gas delivery tube. Alternatively, the two gasses can be pre-mixed and provided through a single gas delivery tube. In this presently described embodiment, the same reaction rates as the prior art scheme described for FIG. 3 can be obtained, however the added benefit of charge neutralization due to the presence of the high pressure non-reactive/reactive gas allows for a much higher beam current to be employed, thereby increasing the speed at which a process can be completed. Experimentation with the partial chamber 100 has shown that at the high chamber pressure sufficient for promoting charge neutralization in the partial chamber, a beam current of up to 20 nA can be used without inflicting damage to the semiconductor device due to charging and ESD events. A preferable high current beam operating range lies between 500 pA and 5 nA, which is a 10 to 100 times improvement over the prior art beam current that can be used. One disadvantage of the partial chambers 100 and 200 shown in FIGS. 2 and 3 is the high presence of gas molecules in the path of low energy electrons ejected from the sample. In the 20 nA beam current case, the high gas pressure used to neutralize causes the beam to spread out somewhat, and the emitted secondaries are diffused so the endpoint detection becomes blurry as a result. Partially due to this (incoming blurring and secondaries) and partially due to the high gas flux, the hole being opened does not end up as flat as with the standard nozzles, having a tendency to be wider than the raster size and also more bowl shaped. A bowl shape is typically deeper in the center and less deep at the edges. Both partial chambers 100 and 200 are relatively high, resulting in a long flight path through high gas pressure. FIGS. 5a, 5b and 5c are schematics showing a novel gas nozzle according to an embodiment of the present invention. This novel gas nozzle design provides high gas flux at the sample surface, and includes a large escape angle for secondaries and reduced gas flux in the beam path between the column and the bottom of the nozzle. FIG. 5a is a planar view of a gas nozzle 400 according to an embodiment of the invention, while FIG. 5b shows a cross-sectional end view along line A-A and FIG. 15c shows a cross-sectional side view along line B-B. Gas nozzle 400 includes a hollow body 402 with a gas inlet 404 for receiving reactive and/or non-reactive gasses, and a frusto-conically shaped hole 406 extending through hollow body 402. Aperture 406 is defined by a top opening 408 having a first area and a bottom opening 410 having a second area, where the second area is smaller than the first area. For circuit edit operations for example, the second area can be about 200 um×200 um square. While the present embodiment uses circular shaped openings, any shaped opening can be used as long as it provides a uniform gas flow and is effective for providing a uniform field gradient if it was biased. The advantage of the slanted sidewalls extending to the bottom side of hollow body 402 provides a large escape angle for ejected secondaries to pass through from the sample and to the detector of the FIB apparatus. The bottom side of hollow body 402 includes a gas outlet orifice 412, shaped as a ring immediately adjacent to bottom opening 410 and a continuous bottom edge 414 of hollow body 402. Gas received from the inlet 404 is delivered to the sample through orifice 412. An advantage of the ring shape of gas outlet orifice 412 is that it provides a high degree of cylindrical symmetry to the gas flow. The angled side-walls allow the cone of light for an optical microscope objective or a Scwarzschild lens to enter/exit, as well as allowing two beams from two columns to both enter the target site. In a further embodiment, a gas guiding structure can be integrated into the bottom edge 414, such as an “O”-shaped ring. The ring can be configured as a sleeve extending from the bottom edge 414 and surrounding gas outlet aperture 412. The hollow body 402 has a reservoir volume formed by the capped end 416, beyond the gas outlet orifice 412. The arrows “turning around” in FIG. 5a illustrate the gas flow to the orifice 412. The openings in the hollow body 402 on either side of the a frusto-conically shaped hole 406, along the line A-A, are sufficiently large to allow essentially unimpeded gas flow past the a frusto-conically shaped hole 406, so the pressure on the gas input end 404 side and the closed capped end 416 is substantially the same. Those skilled in the art will understand that the geometric design parameters of nozzle 400 for meeting this critera can be determined using known techniques. Therefore, the gas flow out of the orifice 412 from all sides is constant. The desired result is to obtain a uniform gas flow that is even from all sides, maintaining a high, uniform gas flux at the surface of the sample without exposing the incoming primary particle to a long, high gas flux path. The angle of the frusto-conically shaped aperture 406 is at least the angle between two columns such that (a) a second charged particle beam from a so-called dual column instrument would also have line of site to the target area when the gas nozzle 400 is in place, and (b) the optical “cone” required to perform optical imaging on the sample is not compromised while the gas nozzle 400 is inserted. FIGS. 5d, 5e and 5f are schematics showing an alternate gas nozzle according to an embodiment of the present invention. This alternate gas nozzle 420 is similar to gas nozzle 400 shown in FIGS. 5a, 5b and 5c, and consists of the same numbered features previously described for gas nozzle 400. Gas nozzle 420 includes the following modifications to the design of gas nozzle 400. The bottom edge 422 is raised relative to the bottom of gas outlet aperture 412 and relative to the bottom edge 414 of gas nozzle 400. Alternatively, the conical wall of frusto-conically shaped aperture 406 can be extended past the bottom edge 422. By raising the bottom edge or extending the frusto-conically shaped aperture 406, clearance is provided such that the gas nozzle 420 will not come into contact with structures, such as bond wires, which may extend from the sample surface. Therefore, gas nozzle 420 can be positioned anywhere on a sample with high versatility. In yet a further alternate embodiment, the bottom edge 422 can be raised to the position shown by dashed lines 424 to achieve the same effect. While the illustrated hollow body 402 is shown as being parallel to an underlying sample, the hollow body 402 can be angled upwards and away from sample surfaces to further facilitate clearance of structures. Furthermore, a conical side-wall 426 can be added such that it is concentric with the conical wall of frusto-conically shaped aperture 406. Conical side-wall 426 and the conical wall of frusto-conically shaped aperture 406 cooperate to form a channel for guiding gas to the gas outlet aperture 412. Preferably, the channel will provide a uniformly directional flow of gas towards the sample. In the presently shown example, conical side-wall 426 is angled such that the distance from the conical wall of frusto-conically shaped aperture 406 is constant. In an alternate embodiment, the conical side-wall 426 can be angled such that the distance from the conical wall of frusto-conically shaped aperture 406 decreases as gas approaches the mouth of gas outlet aperture 412. In still another embodiment, a conical side-wall 426 can be added to the gas nozzle of FIGS. 5a to 5c. This cone shape is significant for apparatus such as a Credence Systems Corporation OptiFIB, which has a Schwarschild optical lens collinear with the ion column, as it allows unimpeded viewing of the sample surface. Furthermore, there is no optical distortion caused by standard nozzles inserted into the field of view of the lens. Preferably, the cone angle great enough that it does not impede the optical image or the line of site from a second column. Furthermore, the relatively large cone angle facilitates access to the sample through the use of a nanomanipulator, for example for probing the device. The nanomanipulator can also hold a detector or position a focusing element proximate to the target area while the gas nozzle 400 (or 420) is in place and in use. According further alternate embodiments, this nozzle can be shaped with the appropriate geometry and electrically biased to provide a concentric electric field, for providing a final deceleration of the electrons from a primary electron beam. For example, a 200 eV incident electron can be decelerated by a 150 V bias of the nozzle, to provide a 50 V landing energy while maintaining the improved properties of the higher energy electron though the bulk of its flight path. In order to counter re-absorption of secondary particles by the sample, the gas nozzle 400 and the sample can be biased, relative to the incoming electron, to slow down an electron and accelerate secondary electrons away from the surface and out to a detector. In further alternate embodiments, elements on the nozzle, alone or in combination with substrate biasing, can focus the secondary particles towards a detector. It is noted that the nozzle itself can be used as a detector by integrating detector elements, such as diodes to the bottom edge 422, in a way similar to the Nordlys II detector sold by HKL Technology. Alternately, the a portion of or the entire bottom edge 422 can be implemented as a detector. FIG. 6 illustrates the gas nozzle 400 of FIG. 5a positioned over a sample 430, with gas being provided through the hollow body 402 and applied to the surface of the sample 430 through the gas outlet orifice 412. A focused ion beam 432 can then be directed through the frusto-conically shaped aperture 406 and onto the sample 430. FIG. 7 shows an embodiment of a circuit editing apparatus 450 of the present invention. The apparatus 450 includes a base 510 onto which an integrated circuit (IC) or sample 500 can be mounted by any suitable means. An ion beam focusing column 16 produces an ion beam 18 used in milling a milling area 502 of the sample 500. Secondary particles 19 milled from the milling area 502 sputter away from the milling area 502 and are detected at detector 504, which can be coupled to any suitable circuitry for measuring, monitoring and/or visualizing the progress in milling the sample 500. Generally, the secondary particles 19 are not all detected by the detector 504. This is the result of various factors such as the mismatch in the solid angle into which the secondary particles 19 are sputtered and the detection solid angle of the detector 504. Other factors leading to a less than optimal detection yield of the secondary particles 19 include the natural tendency of the secondary particles 19 to return to the sample 500 and the presence of undesired electric and/or magnetic fields causing the secondary particles 19 to stray away from the detector 504. The present invention provides an increase in detected secondary particles 19 by introducing one or more electrostatic or electromagnetic fields (not shown) in the circuit editing apparatus 450. These fields can be provided by a charged particle directing field. In the following, the singular form of electromagnetic field inducing element (EFIE) is used but it is to be understood that it can include more than one EFIE. The additional EFIE can be fixed or variable and serve to alter the trajectory and/or the speed of the secondary particles 19. The additional EFIE field is such that its presence changes the yield of detection of secondary particles 19 at the detector 504. For the purpose of the description, the term electromagnetic field is to be understood as meaning either an electric field, a magnetic field, or a combined electric and magnetic field, and includes electrostatic elements, which those skilled in the art realize are more effective in guiding charged secondary particles more massive than electrons. The additional EFIE can be produced by any suitable EFIE element such as EFIE element 508, also referred to as an electromagnetic circuit. Element 508 is shown as a loop of conductive material held by a manipulator 506. Manufacturers of such manipulators, also referred to as nanomanipulators, includes Zyvex™ Corporation of Texas. The element 508 can also be a chamber of the same type as the partial chamber 200. The element 508 can produce an electric field when subjected to a voltage, a magnetic field when traversed by a current (or when composed of a permanent magnet, at least in part), or a combined electric and magnetic field when subjected to a current and a voltage. Although shown as a loop, the element 508 can be of any appropriate shape and include any suitable material. When only an electric field is required to be produced by the element 508, the shape of the element 508 need not be that of a loop. The shape of the element 508 can be variable in order to change the geometry and/or the strength of the EFIE produced by the element 508. For example, the loop defined by the element 508 can be made bigger or smaller by any suitable means such as, a manipulator 506 with expandable jaws. The EFIE produced by element 508 is controlled by an electromagnetic circuit controller 518, which is connected to the element 508 by any suitable means. Alternatively, the element 508 can be a constant field element such as, for example, a permanent magnet. Particularly suited for this are rare earth magnets that can provide relatively strong fields for small magnet size. Such permanents magnets can be located anywhere in the circuit editing apparatus such as, for example, on the base 510 The element 508 can be fixed in position inside the circuit editing apparatus 450 or can be movable within the circuit editing apparatus 450 as shown in Fig. A. The manipulator 506 to which the element 508 can provide fine motion in all axes and can be connected can be coupled to a rotational stage 516, a horizontal translational stage 512 and a vertical translational stage 514, or to any number and combinations of rotational and translational stages. As will be understood by a worker having ordinary skill in the art, any number of elements such as element 508 can be disposed in the circuit editing apparatus 400 to modify the yield of detection of secondary particles 19. The rotational stage 516 and the translational stages 512 and 514 can be controlled by any suitable controlling means, generally depicted as stage controls 520. The positioning of the element 508 to a specific location within the circuit editing apparatus 450 can be straightforward when the rotational stage 516 and the translational stages 512 and 514 include calibrated encoders. Otherwise, the positioning of the element 508 can be achieved through calibration or direct observation. Alternatively to providing an element 508 to create an electromagnetic field to increase the detection yield of secondary particles 19, it is also possible to provide a bias voltage to existing parts of the circuit editing apparatus 450. For example, it is possible to provide a bias voltage to parts of a gas delivery system (not shown), which is part of the circuit editing apparatus 450. The process of increasing the detection yield of secondary particles 19 can be automated. In this case, a signal from the detector 504 is provided to a processor (not shown) that controls the electromagnetic circuit controls 518 and the stage controls 520. The processor can include a computer program product with instructions to adjust the electromagnetic circuit controls 518 and the stage controls 520 until a pre-determined signal strength or signal condition is attained. Gas based chemistries can be used for gas assisted etching or deposition. Selectivity of this process, i.e. the ability to act on one material much more so than on another, is often very important. As the rate and quality of these processes can be controlled by moderating the surface adsorption rate and “sticking time” of the gas molecules, which typically is reduced as temperature is increased, and controlled by the thermal catalysis of these processes, which typically improves with temperature, controlling the temperature either locally or generally can be advantageous. FIG. 8 shows a system used in performing gas assisted ion beam editing of a circuit or sample, in accordance with the present invention. The sample 500 is fixed to the base 510 through any suitable means. An edit region 606 is subjected to a flow of gas 602 provided by a gas source 600. The edit region 606 is also subjected to the charged particle beam 18 provided by the charged particle beam focusing column 16. A heat region 604, which may be physically removed from the edit region 606, but in thermal contact with the edit region, is in contact with a heat source 608, which is secured by any suitable means to a positioner and heater 610. The positioner and heater 610 is controlled by heat and position controls 612. In operation, the heat source 608 is positioned and brought in contact with the heat region 604 of the sample, which is in thermal contact with the edit region 606. For example, the heat region 604 and the edit region 606 can be part of a same metal interconnect (not shown), the metal interconnect providing heat flow between the heat region 604 and the edit region 606. Any type of metal or heat conducting semi-conductor thermal connection, or any other suitable type of heat conductor, can be used. According to an alternate embodiment of the invention, localized cooling can be achieved using the previously described apparatus coupled with a cooling element or heat sink. The positioner and heater 610 can include any type of horizontal, vertical and rotational positioners. It can also include any type of heat source suitable for heating the heat source 608. The positioner and heater 610 can further include any type of temperature sensing means for measuring the temperature of heat source 608. An example of such a temperature sensing means is discussed below. For example, manipulators such as the manipulator 506 discussed above can be used as a local heating tool, through heating of a resistive element, such as a low doped silicon micro electro-mechanical system (MEMS) device, attached to the manipulator 506. In the case of a silicon “nano-tweezer” MEMS device, the device will open a known amount at a given temperature, thereby allowing direct measurement of the temperature of the “nano-tweezer” by straightforward measurement of the tweezer gap. Temperatures in excess of 400° C. can be reached, which provides an excellent temperature range (from room temperature to 400°) for optimizing the enhancement or retarding of gas related processes. For example, one could expose a number of metal interconnect lines using a gas that preferentially removes dielectric over metal, then switch to a gas that preferentially removes metal over dielectric, and touch a particular line with the heat source 608, retarding the removal rate of that line or enhancing the removal rate of that line, depending on the conditions. Of course, the shape of the heat source 608 can be varied and is not limited to the “tweezer” approach, and single point probes, dual point fixed width, flat probes and other shapes may be used depending on the circumstances and room for access. One skilled in the art will also realize that one type of tip can be attached to another to form the heat source, for example a needle formed from a refractory metal needle as tungsten can be affixed to the MEMS device outlined above so physical contact with the heat region 604 occurs through the tungsten needle, reducing the chance that alloying between the silicon MEMS device and the heat region 604 will occur. FIG. 9 shows the sample 500 receiving a charged particle beam from the charged particle column 16, the particle beam 18 impinging on the edit region 606 in the presence of a deposition gas 602. The heat source 608 may be at that time removed from the edit region 606. Once a sufficient number of charged particles have induced deposition on, the edit region 606, the charged particle beam 18 is removed from the edit region 606. The heat source 608 is then brought into contact with the edit region 606 by the heat and position controls 612 and heat is applied locally to the edit region 606. The heat applied to the edit region is used to anneal the deposited material and the edit region in order to improve the quality of the deposition and/or to form an ohmic contact between the deposited material and the edit region 606 of the sample 500, which could be, for example, doped silicon. The use of heat sources such as heat source 608, carefully engineered so that minimal current passes through the tip of the heat source to the device while still supplying sufficient heat to achieve the necessary reaction, be it an ohmic contact or some other result, such as a better quality deposition or removal of material, is preferable to the creating of heat by providing a current to flow through the circuit, which can damage the circuit. In an alternate embodiment, a focused x-ray source can be used for localized heating of a semiconductor device. While the presently discussed embodiments are described for localized heating, localized cooling can be achieved using the same apparatus. Hence, embodiments of the invention can include simultaneous local cooling and heating of different areas of a semiconductor device. The previously described method and apparatus for charge neutralization of an ion beam can be used in single column systems, ie a FIB system. However, dual column systems are available which can provide both an ion beam and an electron beam. Dual column systems combine FIB capabilities with scanning electron microscopy imaging capabilities. In such systems, charge neutralization can be achieved by using both beams concurrently and in proximity to each other. Therefore, one beam will effectively neutralize the other. Preferably, both columns are collinear, meaning that both ion and electron beams are positioned in the same axis. The sample can be heated or cooled in order to optimize gas adsorption so as to minimize gas pressure in the chamber so as to not interfere with low energy electrons flight. This technique lends itself to work in high aspect ratio holes as opposed to scanning probe. In the preceding description, for purposes of explanation, numerous details were set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the present invention. In other instances, well-known electrical structures and circuits are shown in block diagram form in order not to obscure the present invention. For example, specific details are not provided as to whether the embodiments of the invention described herein are implemented as a software routine, hardware circuit, firmware, or a combination thereof. The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.
046648755	abstract	A fixture for removing a top nozzle of a reconstitutable fuel assembly held in a fixed position within a work station includes a pair of guide openings in two diagonally opposed corners of its base to movably mount the base on a pair of upstanding guide members of the work station and on the top nozzle in alignment therewith. Also, the fixture includes a pair of hollow expandable split sleeves with wedge pins inserted therein which are operable to lock the fixture to the top nozzle. An arrangement of drive and driven gears connected with a plurality of reaction pins mounted on the base of the fixture are operable to move the fixture base with the top nozzle thereto away from the guide thimbles of the fuel assembly and thereby cause the top nozzle adapter plate to release its connection with the guide thimbles. However, prior to removing the top nozzle, a plurality of stop devices of the fixture are preset and operable for establishing a reference representing the distance between the fixture and work station so that the top nozzle can later be replaced at the same axial position on the fuel assembly it was at before removal.
	summary
	description	This application claims priority from U.S. Provisional Patent Application Ser. No. 60/648,147, filed Jan. 28, 2005, the disclosure of which is incorporated by reference in its entirety herein. 1. Field of the Invention The present invention relates to the field of positron emission tomography (PET). More particularly, this invention relates to a system and method for manually loading and remotely unloading a target disk into a proton beam. 2. Description of the Related Art Accelerators are commonly used to produce radionuclides for a variety of uses including Positron Emission Tomography (PET). PET is a noninvasive diagnostic imaging procedure that assesses the level of metabolic, biochemical, and functional activity and perfusion in various organ systems of the human body. PET provides information not available from traditional imaging technologies, such as Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) which depict changes in anatomy rather than changes in physiology. Physiological activity provides a much earlier detection measure for certain forms of disease, cancer in particular, than do anatomical changes over time. Typically, an accelerator produces radionuclides by accelerating a particle beam and bombarding a target material with the accelerated beam thereby producing radionuclides. The type of radionuclides produced are determined by the target material and particle beam used. Low or medium energy charged-particle accelerators typically produce radionuclides having a short half life. Radionuclides such as copper-64 or 64Cu have a longer half life than the conventional radionuclides typically used. Specifically, copper-64 is the cyclotron-produced PET isotope of copper. This isotope undergoes a special type of radioactive decay, whereby its nuclei emit positrons that travel only a few millimeters in tissue before colliding with electrons, converting their total mass into two photons of energy. The photons are displaced at 180 degrees from each other and can be detected simultaneously as “coincident” photons on opposite sides of the body. However, copper-64 is not easily producible as is shown in U.S. Pat. No. 6,011,825 which is incorporated herein in its entirety by reference. The production of copper-64 requires the irradiation of a solid target rather than a liquid or gaseous target that conventional accelerators are capable of handling. The combination of gold with plated enriched nickel can be used to produce copper-64. Other combinations of metals can also be used to provide copper-64. In addition, the combination of metals can take the form of pellets, foil or coin. There is a need for a target holder for loading and unloading a solid target to produce a radionuclide. There is also a need for a target holder that can accommodate a solid as well as a liquid and gas target cost effectively. There is a further need for a target holder that has a service position and an irradiation position An object of the present invention is to provide a solid target handling system for manually loading and remotely unloading a target disk into a proton beam. Another object of the present invention is to provide a target handling system that can efficiently and cost effectively accommodate a solid target, a liquid target and a gas target. An aspect of the present invention provides a system and method for a system for accommodating a solid target in an accelerator. The system and method includes a target changer having at least one port for accommodating the solid target, an insert for receiving the solid target in the target changer, a piston for providing a vacuum and a cooling system for the solid target, a cylinder for displacing the piston in one of three positions; and a bracket for securing the insert, piston and cylinder to the target changer. Another aspect of the present invention also provides a system and method for accommodating a solid target, a liquid target and a gaseous target mounted on an accelerator. The system and method provide a target changer having four ports, two of which are service positions, an insert for receiving the solid target in the target changer, a piston for providing a vacuum and a cooling system for the solid target, a cylinder for displacing the piston in one of three positions; and a bracket for securing the insert, piston and cylinder to the target changer in one of the ports. A further aspect of the present invention provides for the target changer being rotated from a first position to a second position, wherein the first position comprises a service/removal position and the second position comprises a beam position for irradiating the solid target. Throughout the figures, like symbols and numbers are used throughout. The solid target handling system 10 is configured with several criteria. First, the system 10 is received and operates in a conventional shield envelope (not shown). The system 10 is mounted to a conventional exiting target changer hub 24 as shown and described in U.S. Pat. No. 5,608,224 which is incorporated herein by reference in its entirety, and interfaces to an existing cooling arrangement. The hub 24 also mounts to an adjustable back plate for alignment to a beam. The beam has a range of about 5 MeV to about 25 MeV. Preferably, the beam has energies at about 11 MeV. FIGS. 1-4 show the above described components and assembly. More specifically, FIG. 1 illustrates a target changing system in accordance with an embodiment of the present invention. FIG. 2 illustrates an elevation view, in section, of the target assembly in accordance with an embodiment of the present invention. FIG. 3 illustrates the target changer 2 having four ports in accordance with an embodiment of the present invention. FIG. 4 illustrates various components of the target system in accordance with an embodiment of the present invention. The basic operation of the target changer interfaces with a conventional accelerator control system (not shown). The unloading of the system 10 is controlled by a remote controller (not shown), positioned outside the shield, with operational logic. The system 10 accommodates all conventional eclipse style targets in two ports, and accommodates a solid target in another two ports. The system 10 comprises a target changer 2, an insert 4, a piston 6, a shaft 22, a cylinder 8, a bracket 12 and a feed slot 14 as shown in FIG. 1. The insert 4 has an o-ring 16, a first opening 7, a second opening 9 and a cavity (not shown) providing a pass through between the first opening 7 and the second opening 9. The first and second openings of the insert 4 can be the same size; the first opening can be larger than the second opening or vice versa. The insert 4 also includes a slot 3. The slot 3 is positioned and arranged to allow a target to fall through from the feed slot 14. The piston 6 has a tab 5 and an o-ring 20. The feed slot 14 is located within the target changer 2. FIGS. 1, 2 and 3 together further show target changer 2 having a first port 26 for accommodating the insert 4, the piston 6, the shaft 22, the cylinder 8, and the bracket 12 all of which comprise subsystem 11. Target changer 2 also includes a third port 28 disposed about 180 degrees from the first port 26. It should be appreciated by those skilled in the art that the positions of the first port 26 and third position port 28 can vary from 180 degrees without departing from the scope of the present invention. For example, the first port 26 and the third port 28 can be 90 degrees apart without varying from the scope of the present invention. As shown in the combination of FIGS. 1-5, first port 26 is in the service/removal position. Third port 28 is in the beam position. The target changer 2 is rotated so that the first port 26 is displaced from a service position to a beam position. Second port 30 and fourth port 32 can accommodate conventional liquid and gas targets. In an embodiment of the present invention, target changer 2 comprises only first port 26 and third port 28. In another embodiment of the present invention, target changer 2 comprises a plurality of first ports 26 and a plurality of third ports 28. This will enable a plurality of solid targets to be accommodated and produce substantial amounts of radionuclides in a short amount of time. In operation, the solid target is manually loaded in the first port 26 or the service position of the target changer 2. The target extraction mechanism is then attached to the target via computer control. The target is then rotated into the beam position and bombarded for the desired time and current. The target is then rotated back to the service port and unloaded. The unloading process includes the following steps. First, the solid target is rotated to the service/removal position. The first port 26 vacuum line 40 is then vented. The cooling water valve 36 is closed, and then opened to drain. An air flush valve 42 is opened to remove all trapped water from the cooling lines. The target removal mechanism is initialized and the target is extracted from the insert 4. The target falls out of the device and to the floor of the accelerator pit aided by gravity. The fall is within a track (not shown) to control speed and location. The target changer 2 is then available to manually load another solid target. FIG. 4 illustrates an exemplary target 34. Target 34 is a solid target and preferably comprises a combination of enriched nickel and gold sufficient to provide copper-64. The piston 6 fits within the insert 4 and channels cooling water to the solid target via perforations 44 (See FIGS. 1, 4 and 6). The insert serves as the vacuum seal between the target and the accelerator. The piston has three positions within the insert. A load, extended and extraction position. The load position is such that the tab 5 on the piston extends into the slot 3 of the insert 4 preventing the target from continuing to fall out of the feed slot 14 where it exits the target changer. Specifically, the tab 5 (see mark up to FIG. 4) stops the target disk as it falls into the target changer 2 and positions the target in the center of the beam. In the extraction position the piston 6 is extracted in the insert 4. It should be appreciated by those skilled in the art that the extraction position can comprise a location where the piston 6 is still in the insert 4 but the tab 5 is not blocking feed slot 14. The three positions of the piston are controlled by a pneumatic cylinder 8 manufactured by Bimba. The cylinder is held in position by the bracket 12, which is connected to first port 26 via screws and precisely positions the cylinder 8 so that the stroke lengths are as needed. The displacement of shaft 22 which is connected to cylinder 8 at one end and piston 6 at a distant end causes piston 6 to move in a lateral direction. In an embodiment of the present invention, the system 10 is configured to accommodate a solid target having a range between 0.5 mm to 5 mm thickness and 10 mm to 35 mm in diameter. Preferably the target disk has 2 mm thickness and 25 mm diameter. The solid target preferably has a thermal conductivity greater than 2200 BTU-in/hr-Ft2-0F. In accordance with an embodiment of the present invention, system 10 operates in the following manner. When first port 26 is in the service position, the target 34 is dropped either manually or remotely into the feed slot 14 of the target changer 2. The feed slot 14 was formed via a rectangular slot that was burned into the target changer 2 via EDM. The feed slot 14 allows the target disk to fall by gravity into the insert 4. The target enters the insert 4 via the insert slot 3 and is prevented from passing through the insert 4 by the piston tab 5 because the piston 6 is in the load position. Air is removed via air inlet 40 compressing the target against the o-ring 16 of insert 4. The piston is placed in an extended position compressing the target against 0-ring 20 of the piston 6. The port 26 is rotated by the hub 24 from a service position to a beam position where the target is irradiated for a predetermined period by a beam having a predetermined energy. An exemplary predetermined time period can be 2 hours of 40 uA operation for the accelerator. In an embodiment of the present invention, the rotation can be clockwise. In another embodiment of the present invention, the rotation can be counter clockwise. Water is input via inlet 36 and the perforations 44 of the piston 6 to maintain the temperature of the target below a predetermined threshold temperature so that the target does not melt. Water is removed via outlet 38. The target changer 2 is rotated clockwise so that first port 26 is positioned to be in a removal position. In another embodiment of the present invention rather than continuing forward in a clockwise direction, the target changer 2 is rotated in a counter clockwise position. In the removal position, air is provided to port 26 via inlet 42, the piston 6 is placed in an extracted position causing the target to fall through slot 3 of the insert 4 via gravity out of the target changer 2 where the target is automatically unloaded and interfaces with a customer supplied transport system. The insert is designed to fit within the target changer. It functions to position the 25 mm diameter solid target in the larger target slot. It provides cooling water and vacuum seals. It also has integral tabs to strip the target disk from the piston during extraction. The beam position compresses the target disk between two face seal 0-rings for vacuum seal. The extract position pulls the piston back within the insert and allows the target disk to fall into the exit feed slot. The operation of the target assembly of the present invention is illustrated in FIG. 5. Target Cooling: The target disk is cooled by water jets normal to its non-beam side surface. The water is routed through the insert as indicated in FIG. 6. The target disk is cooled by conduction through the disk and convection from the disk into the cooling water. Conduction is calculated by Fouriers Law: q = KA ⁢ ⅆ t ⅆ l . Since the heat transmission is steady and the K and L are constant, this becomes: q = KA ⁢ ⁢ Δ ⁢ ⁢ T L ,where: q=heat input; K thermal conductivity of material; A=area of heat conduction; ΔT=(T2−T1); and L=thickness of target disk. In the instant case, where: q=10.5 MeV×60 uA=630 W=2150 btu/hr; K=2200 btu-in/hr-ft2-° F. (for gold); A=0.00136 ft2; and L=2 mm=0.079 in,then: ΔT=57° F. To estimate the value for “h”, the coefficient of heat transfer used in the following equations are used:H=Nu(Kwater)/L; Nu=0.228Re0.731Pr0.33 Re=VLρ/μ; andPr=Cpμ/Kwater,where: Nμ=Nusselt number; Re=Reynolds number; Pr=Prandlt number; Kwater=thermal conductivity of water=0.58 W/m K; L=length of flow=0.019 m; P=density of water=1000 kg/m3; M=viscosity of water=0.00114 kg/m-s; Cp=specific heat of water=4180 KJ/kg-K; and V=velocity of flow=4.3 m/s. From this, the results yield: Pr=8.2; Re=7.2×104; Nu=1627; and H=49,667 W/k=8741 btu/hr-ft2-° F. Convection is calculated by Newton's Law of Cooling for forced convection.q=hAΔTwhere: q=heat input; h=coefficient of heat transfer; A=area of heat convection; and ΔT=(Twall−Twater). In the instant case, where: q=10.5 MeV×60 uA=630 W=2150 btu/hr; h=8741 btu/hr-ft2-° F.; and A=0.00136 ft2,then: ΔT=180° F. The results show that where the temperature of the cooling water is 45° F., the temperature of the wall on the cooling water side is 225° F. and the temperature of the wall on the beam side is 282° F. While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.
	summary
	abstract	Provided are a water-blocking filler, the swelling properties of which do not decrease easily even when in contact with water containing calcium ions, and a filler for engineered multi-barriers with said water-blocking filler as the engineered multi-barrier filler. A water-blocking filler mainly comprising sodium bentonite obtained by mixing 30 weight % or less, in terms of inner percentage, of a pozzolan substance such as fly ash or silica fume with said bentonite, and a filler using said water-blocking filler that is used for engineered multi-barriers in radioactive waste disposal facilities.
047624027	claims	1. A system making it possible to obtain a selective reaction in photochemical processes on the basis of laser beams comprising: in a sealed enclosure, the substance whereof a species is to be extracted, said substance being in the form of a vapour flow, laser sources emitting towards said enclosure a beam S.sub.1 permitting a selective excitation of the species to be extracted and a beam S.sub.2 permitting a transformation of said excited species, wherein it comprises means for distributing the beams having: means for superimposing the beams S'.sub.1, S".sub.1, . . . S.sub.1.sup.(n) with n being an integer at least equal to 1, and for constituting several beams S.sub.1 introduced at several points through the vapour to be treated, means for introducing into the enclosure the resultant beams S.sub.1 and also beam S.sub.2 so as to make them colinear, whilst distinguishing them by one of their characteristics, said introduction means being periodically distributed on parallel arms defining the propagation directions of said beams in the enclosure. 2. A system according to claim 1, wherein it also comprises quarter-wave plates making it possible to obtain a circular polarization of beams S.sub.1 and S.sub.2, located upstream and downstream of the introduction means. 3. A system according to claim 1, wherein the means for introducing beams S.sub.1 and beam S.sub.2 into the enclosure are constituted by Glan prisms into which said beams are injected with two orthogonal polarizations and in directions which, following their passage into the prisms, can be colinear, each prism being located on an arm at the points where S.sub.1 is reintroduced into the enclosure. 4. A system according to claim 1, wherein it also comprises means for inverting the beams S.sub.1 and S.sub.2 along parallel arms. 5. A system according to claim 1, wherein the means for introducing beams S.sub.1 and beam S.sub.2 into the enclosure, in cavity operation, comprise a Glan prism at each end of an arm corresponding to a propagation direction of beams S.sub.1 and S.sub.2 into the vapour and on each of the arms in the enclosure, each of the beams S.sub.1 and S.sub.2 being introduced with the same polarization into one of the Glan prisms and in directions which, following their passage into said prisms, make it possible to have the same propagation direction, corresponding to an arm, but of the opposite sense. 6. A system according to claim 1, wherein, in cavity operation, it comprises means for reflecting the beams S.sub.1 and S.sub.2 on to themselves, said means comprising plane mirrors associated with Pockels cells, the assemblies constituted by the plane mirrors and Pockels cells being positioned symmetrically at each end of the arms and means for inverting beam S.sub.2 towards other arms, said means comprising a Pockels cell located on each arm. 7. A system according to claim 1, wherein the means for superimposing the beams S.sub.1 ', S".sub.1, . . . , S.sub.1.sup.(n) so as to form beams S.sub.1 incorporate a group of semitransparent plates having a reflection coefficient 0.5, which successively splits the different beams S'.sub.1, S".sub.1, . . . S.sub.1.sup.(n) into two, whilst superimposing the split beams in order to obtain the different beams S.sub.1 used in the system.
058621938	abstract	Methods for the production of radionuclides suitable for use in radiopharmaceuticals for diagnostic and therapeutic applications, and specifically, to the production of .sup.186 Re, .sup.188 Re and other radionuclides such as .sup.195m Pt and .sup.198 Au using an inorganic Szilard-Chalmers reaction. Thin-film and powdered .sup.185 or 187 Re.degree. metal targets, and .sup.185 or 187 Re oxide/metal oxide target compositions with rhenium in a lower, relatively reduced oxidation state are prepared. The thin-film rhenium targets are aged for at least about 24 hours and then irradiated with neutrons in the present of an oxidizing medium sufficient to form a product nuclide in the higher oxidized state of perrhenate, ReO.sub.4.sup.-. Significantly, the rate and/or extent of oxidation of target nuclides which do not react with a neutron is controlled. For example, oxidation of such non-bombarded target nuclides is minimized by irradiating under vacuum, controlling the amount of oxidizing agent present, cooling during irradiation, etc. The product nuclide is recovered by dissolving the perrhenate in a non-oxidizing solvent such as water or saline.
	description	The present application is a U.S. National Phase application of PCT/US2015/025585, filed on Apr. 13, 2015, claiming the benefit of U.S. Provisional Application No. 61/995,496, filed on Apr. 11, 2014, both of which are incorporated herein by reference in their entireties. The manufacture of radiovoltaic devices, generally. More particularly, the manufacture of radiovoltaic devices utilizing various techniques associated with the manufacture of integrated circuit devices combined with certain radioisotope activation techniques. By virtue of the tremendous benefits from micro/nanotechnology, implantable and portable devices/systems have become more and more prevalent. However, a major impediment for operating such devices/systems is lack of sustainable and reliable power sources in small scale. Chemical batteries and fuel cells are very bulky and heavy, and can offset the size advantage inherent in micro/nanofabrication technologies. Major disadvantages of using chemical based power sources are the low power density of the fuels as the size of the systems is reduced and the poor performance when they are designed to achieve longer lifetimes. In addition, the requirement of frequent recharging or refueling is an inconvenience and is not favorable for many applications including biomedical implants, space exploration, etc. Instead, solar cells can produce electrical power in a small package without refueling processes and operate in most environments where micro-scale power sources are desired. However, sun-light is always required. Various energy harvesters, which generate electrical power from stray energy like heat and vibration, are simply too weak and provide irregular levels of electric power. In contrast to the aforementioned power sources, nuclear or radioisotope batteries can provide long lasting power at very high energy density. Radioisotope batteries are devices which convert energy from the decay of radioisotopes into electrical power. These devices come in two varieties: direct conversion and indirect conversion. Direct conversion devices convert the radioactive energy directly to electrical energy via direct-charge generation in dielectrics via ionization or, more commonly, electron-hole pair generation in a semiconductor via excitation or ionization. Indirect conversion devices convert the radioactive energy into an intermediary form of energy, usually photonic or thermal, and convert the intermediary energy form to electricity. Indirect conversion is less efficient but tends to mitigate radiation damage to certain battery components. For any type of radiovoltaic, a radioisotope must be included, as its decay products supply the energy. Thus far, radiovoltaic batteries have been produced by fabricating a device for converting the decay product energy (e.g., semiconductor p-n junction) followed by attaching a radioisotope by hand or electroplating. With these methods, process control is naturally very poor. Radioactive waste is generated as a byproduct of fabrication and human handling of radioactive material is often necessary. Moreover, shortcomings of these cumbersome fabrication processes place strict limitations on the physical dimensions and mass production feasibility of radioisotope batteries. Likewise, the ability to integrate such devices directly into electronic circuitry is limited. The concept of voltaic cells powered by radioactive decay was first introduced in the late 1950s [1]. A radioisotope (typically a beta-emitter, but sometimes an alpha-emitter) emits radiation that energizes a semiconductor upon impact. When the semiconductor is energized, electron-hole pairs are generated and separated by a built-in electric field due to a p-n or Schottky junction. Betavoltaics and alphavoltaics are similar to solar cells except they use energy from radioactive decay instead of energy from the sun. Because radioactive decay is unaffected by temperature and pressure, a radioisotope micro-power source can operate for extended periods of time and in extreme environments. More importantly, because the energy change in radioactive decay is 104 to 106 times greater than that of a chemical reaction, the energy density (J/kg) of radioactive material is approximately 106 times greater than that of lithium ion batteries [2]. However, it is not easy to increase the capacity due to difficult handling and processing technologies for radioactive materials. Although nuclear batteries or radioisotope batteries or radiovoltaic batteries or atomic cells have been regarded as promising power sources, their adoption has been extremely limited. Additionally, although the radiovoltaic nuclear battery has been around for about 50 years, the structural design of nuclear batteries has gone relatively unchanged. Instead, nearly all efforts have focused on efficiency and/or lifetime improvement. Researchers have continually attempted to modify the topography of nuclear batteries to improve the directionality of harvesting, thereby increasing efficiency [3], [4]. In addition, radiation-resistant materials such as SiC and Se—S composites have been investigated for their ability to withstand damage to manufacture longer lasting batteries [5-8]. While efficiency continues to improve, the low total power density of nuclear batteries still limits them to niche applications. The current power density of nuclear batteries falls far short of the expectations imposed by the technology's reputation for extreme energy density. Consequently, the applications of nuclear batteries have shifted to almost exclusively micro-scale low consumption devices. In order to transition to widespread use, the issue of power density must be seriously addressed. While a number of conversion schemes have been developed and introduced thusfar, conventional types of the nuclear battery design have not changed. Specifically, individual cells on thick semiconductor substrates with external radioisotope thick-films are the norm. With this standard fabrication method, battery expansion can only be done laterally or by vertically combining multiple thick substrates. Lateral expansion is undesirable because the lateral dimensions of the device are almost always the largest, leaving little room to expand while still maintaining a small profile. Vertical expansion by combining multiple substrates quickly transitions from micro-scale to macro-scale where the substrates are typically about 300 μm thick. Bonding them together and electrically connecting them also introduces new levels of complexity and difficulty in design and processing. Thus, power density and expansion capabilities are greatly limited. In addition, nuclear battery fabrication is greatly encumbered by safety hazards and governmental regulations related to human handling of hazardous radioisotope materials. As a result, the fabrication of nuclear batteries remains very complicated, time consuming, and resistant to automation. To avoid hazards presented by vapor-deposition of radioisotopes, nuclear batteries are typically powered by external foils or electroplated thick-films. Introduction of these sources is carried out by hand, and is both hazardous and limiting. Governmental regulations, as well as in-house regulations by health physics committees limit the personnel who can perform these actions and the methods by which they can be done. In addition, attaching external sources to conversion devices is another challenge, and researchers often neglect to address this step [1], [3], and [5]-[8]. This would certainly have to be done by hand, and would be nearly impossible to accomplish on purely micro-scale levels. In addition, post-fabrication attachment of a radioisotope to the device also limits and complicates integration with other technologies. If nuclear batteries are to be truly integrated with other micro/nano technologies, new methods of fabrication and radioisotope loading must be considered. In view of the foregoing, a need still exists for a method of manufacturing radioisotope batteries that allow for one or more of the following: increased or total automation, decreased battery dimensions, improved precision, improved process control, improved safety, reduced or eliminated production of radioactive water, and improved integration with electronic circuitry. One embodiment of the present invention is directed to a method of producing an integrated circuit-type active radioisotope battery, the method comprising exposing at least a portion of an electronically functional, unactivated integrated circuit-type battery that is either on a substrate or comprises the substrate, wherein the unactivated integrated circuit-type battery comprises an unactivated cell that comprises: a conversion device for converting energy from decay products of a radioisotope into electrical energy capable of performing work; and a non-radioactive, transmutable material associated with the conversion device;to radiation to transmute at least a portion of the transmutable material to a radioisotope thereby producing an active cell, wherein the energy from the decay products of the radioisotope material are converted by the conversion device into electrical energy capable of performing work, and the integrated circuit-type active radioisotope battery. One embodiment of the present invention is directed to an integrated circuit-type active radioisotope battery produced by the method of the immediately preceding paragraph. One embodiment of the present invention is directed to an electronically functional, unactivated integrated circuit-type battery as described in the above-described method. One embodiment of the present invention is directed to an integrated circuit-type active radioisotope battery as described in the above-described method. One embodiment of the invention involves the use of micro- and nano-scaled fabrication techniques, usually associated with the production of integrated circuits (e.g., on silicon wafers), to fabricate an electronically functional but unactivated, radioisotope precursor-containing battery that is activated post-fabrication by irradiation. By fabricating the battery using non-radioactive materials, standard microfabrication techniques or virtually any other techniques may be used. Another embodiment is directed to unactivated integrated circuit-type radioisotope precursor-containing batteries. Yet another embodiment is directed to activate integrated circuit-type radioisotope batteries. Advantageously, the present invention may allow for one or more of the following benefits to be realized: increased or total automation, decreased battery dimensions, improved precision, improved process control, improved safety, reduced or eliminated production of radioactive hazardous waste, and improved integration with electronic circuitry. This means production-line processing, mass production, and concurrent processing with electronic circuitry are all possible. After the fabrication process is complete, non-radioactive material on the devices are “activated” by exposure to radiation, which transmutes stable isotopes in the devices into desired radioisotopes. The finished product will turn into a working radiovoltaic cell, which may or may not be already integrated into circuitry. Advantageously, the method allows for circumventing the hazards and complications associated with human handling of radioisotopes. Additionally, it is possible to decrease dimensions of radioisotope definition on substrates, and therefore allows radiovoltaics to be easily integrated with other electronic devices. The streamlined approach to deposition, along with the expanded dimensional capabilities allow for mass production of integrated radiovoltaic and electronic devices. Another advantage of post-fabrication activation is that it allows a variety of materials and techniques to be applicable. For example, film deposition techniques such as sputtering, evaporation, electroplating, electroless plating, and chemical vapor deposition may be used to incorporate various device materials, including transmutable materials, into the device. Further, the substrate itself may include transmutable materials. The transmutable (“radioisotope-to-be”) material(s) may be located/positioned/place essentially anywhere in the device. For example, the transmutable material(s) may be beneath, on-top of, or near the converting device or circuitry. Likewise, any shape is possible, as these layers may be patterned using standard photolithography, lift-off, or shadowmasks. Yet another advantage of the present method(s) is that multiple cells and/or multiple batteries may be fabricated and simultaneously activated. For example, many layers of transmutable material(s) may be sandwiched in between p-n, p-i-n, or Schottky junctions, as well as indirect conversion devices in a stacked or vertical manner. Radiation can then penetrate the entire structure, primarily activating the intended materials to generate radioisotopes, as seen in FIGS. 1 and 5. Method of Producing an Integrated Circuit-Type Active Radioisotope Battery In one embodiment, the method of producing an integrated circuit-type active radioisotope battery comprises exposing at least a portion of an electronically functional, unactivated integrated circuit-type battery that is either on a substrate or comprises the substrate, wherein the unactivated integrated circuit-type battery comprises an unactivated cell that comprises: a conversion device for converting energy from decay products of a radioisotope into electrical energy capable of performing work; and a non-radioactive, transmutable material associated with the conversion device;to radiation to transmute at least a portion of the transmutable material to a radioisotope thereby producing an active cell, wherein the energy from the decay products of the radioisotope material are converted by the conversion device into electrical energy capable of performing work, and the integrated circuit-type active radioisotope battery. In yet another embodiment, the method of producing an integrated circuit-type active radioisotope battery comprises exposing the above-described electronically functional, unactivated integrated circuit-type battery to radiation to transmute the transmutable material to a radioisotope thereby producing an active cell, wherein the energy from the decay products of the radioisotope material are converted by the conversion device into electrical energy capable of performing work, and the integrated circuit-type active radioisotope battery. Transmutable Material, Radiation, Radioisotope, and Decay Products In one embodiment, the transmutable material is selected from the group consisting of 63Cu, 64Ni, 62Ni, 6Li, 146Nd, 209Bi, 31P, 45Sc, 44Ca, 88Sr, 89Y, 148Sm, 150Sm, 203Tl, 204Hg, 110Pd, 109Ag, 124Sn, 59Co, and combinations thereof. Several sources for irradiation can be used with this method, including neutrons of any energy (cold, thermal, slow, fast, etc.) from a nuclear reactor, fusion system, or spallation neutron source, or ions from a particle accelerator (protons, deuterons, tritons, alpha particles, and combinations thereof. The resulting radioisotope is selected from the group consisting of 64Cu, 63Ni, 3H, 147Pm, 208Po, 210Po, 32P, 33P, 46Sc, 45Ca, 89Sr, 90Sr, 90Y, 151Sm, 204Tl, 148Eu, 148Gd, 110Ag, 111Ag, 124Sb, 125Sb, 60Co, and combinations thereof, and the decay products are a particles, β particles, γ rays, and combinations thereof. In another embodiment, the transmutable material and the radiation are selected to yield a β-emitting or an α-emitting radioisotope. In yet another embodiment, the transmutable material, the radiation, the radioisotope, and the decay products are selected from one or more of the reactions set forth in the following table: TransmutableDecayMaterial+Radiation→RadioisotopeProducts 63Cu+deuteron→ 64Cuβ particles,or neutronγ rays 64Ni+proton→ 64Cuβ particles,γ rays 62Ni+neutron→ 63Niβ particles 6Li+neutron→ 3Hβ particles146Nd+neutron→147Pmβ particles,(146Nd is transmuted toγ rays147Nd, which beta decaysto 147Pm)209Bi+neutron→210Poα particles,(209Bi is transmuted toγ rays210Bi, which beta decaysto 210Po)209Bi+proton→208Poα particles,γ rays 31P+neutron→ 32P, 33Pβ particles 45Sc+deuteron→ 46Scβ particles,or neutronγ rays 44Ca+deuteron→ 45Caβ particles,or neutronγ rays 88Sr+deuteron→ 89Sr, 90Srβ particles,or neutronγ rays 89Y+deuteron→ 90Yβ particles,γ rays150Sm+deuteron→151Smβ particles,or neutronγ rays203Tl+deuteron→204Tlβ particles204Hg+deuteron→204Tlβ particles209Bi+deuteron→208Po, 210Poα particles,γ rays148Sm+deuteron→148Euβ particles,γ rays,α particles148Sm+deuteron→148Gdα particles(148Sm is transmuted to148Eu, which beta decaysto 148Gd)110Pd+deuteron→110Ag, 111Agβ particles,or protonγ rays109Ag+deuteron→110Agβ particles,or neutronγ rays124Sn+Deuteron→124Sb, 125Sbβ particles,or protonγ rays 59Co+deuteron→ 60Coβ particles,or neutronγ rays As can be seen, the present invention allows for significant variability in the selection of transmutable material, radiation, radioisotope, and decay products. Additionally, the present invention allows for variability in selecting the location or locations of the transmutable material(s). For example, transmutable material may be located in a substrate and/or one or more layers, films, or deposits on a substrate. The variability is further exemplified by the following description of various particular embodiments. Film/Layer or Substrate Embodiments In another embodiment, the transmutable material is 63Cu present in natural copper and the radiation are selected to yield 64Cu a β-emitting radioisotope using accelerated deuterons. In another embodiment, 64Ni is transmuted into 64Cu using proton irradiation. Advantageously, the transmutable materials for yielding 64Cu may relatively easily and inexpensively deposited/formed using electroplated or electroless plating or provided as metal substrates. In another embodiment, the transmutable material is 62Ni, which may, for example, be deposited/formed in a layer/film of nickel enriched with 62Ni. The 62Ni is activated by exposure to neutron irradiation to result in radioactive 63Ni. Alternatively, the 62Ni may be provided as part of a metal substrate. In another embodiment, the desired radioisotope is 3H (tritium) and it is produced by irradiating lithium with neutrons or protons. Since tritium is a gas, practicality requires some sort of sealing. As such, in one such embodiment, a crystal matrix such as lithium fluoride or lithium niobate is used to partially seal the tritium thereby preventing it from escaping. Additionally, a sealant may be applied over the lithium compound source to prevent tritium gas from escaping after transmutation. For example, parylene thin films or common CVD materials such as silicon oxide, silicon nitride, and polysilicon may be used as sealants over lithium or lithium-compound substrates, films, or nanostructures before irradiation. Advantageously, lithium alloys may be inexpensively deposited/formed using electroplated or electroless plating. In another embodiment the radioisotope is 147Pm generated from neutron irradiation of 146Nd to transmute it into 147Nd, which rapidly beta decays to 147Pm. The 146Nd may, for example, present in the form of a layer/film enriched with 146Nd. Alternatively, the 146Nd may be present in a substrate. Powder or Liquid Embodiments In another embodiment, the transmutable materials are mixed into powder or liquid composition, preferably a semiconductor composition, before irradiation. For example, bismuth powder may be mixed with selenium and sulfur in a sealed device. Upon irradiation with neutrons, 209Bi will transmute to 210Bi, which will beta decay to 210Po. The result is a powder semiconductor device (liquid upon heating) containing radioisotope mixed therein. Many powder materials, including nanomaterials, may be transmuted in this way. In such an embodiment, it is preferable for the activation cross-section for the desired transmutation to exceed that of the operating semiconductor. Essentially any of the aforementioned transmutable materials may be included into a powder or liquid semiconductor in this manner. That said, this embodiment is particularly advantageous when the desired transmutable material is not readily deposited as a film or layer or incorporated into a substrate. For example, difficulties in depositing lithium make this powder/liquid embodiment an excellent option for transmuting lithium into tritium. Additionally, this powder/liquid embodiment also applies to incorporating transmutable material(s) into organic liquids, polymers, and gels. Dopant Embodiments of a Semiconductor Substrate or Layer In another embodiment, dopant(s) in a semiconductor is/are the transmutable material(s). For example, radioactive 32P and 33P are produced from neutron irradiation of the 31P present in phosphorus-doped silicon substrate or layer. Polymer Embodiments In another embodiment, one or more of the aforementioned transmutable materials are incorporated into a polymer matrix, which may, for example, be formed or deposited as a layer of the battery. Location of the Transmutable Material Relative the Conversion Device As indicated above, the non-radioactive, transmutable material is associated with the conversion device such that upon being activated/transmuted into the radioisotope, the decay products of the radioisotope contact/interact with the conversion device and their energies are converted into electrical energy capable of performing work. The present invention allows for significant variability in the locations/positions of the transmutable material and the conversion device. For example, in one embodiment, the transmutable material is located in a layer adjacent the conversion device. In another embodiment, the transmutable material is not adjacent to the conversion device but sufficiently near to allow for the decay products to travel to the conversion device and be converted to electrical energy. In yet another embodiment, the transmutable material is located in a substrate. In still another embodiment, the transmutable material is located in the conversion device. In yet another embodiment, the transmutable material may be located in one or more combinations of a layer adjacent and/or near the conversion device, the substrate, and/or the conversion device. Substrate As indicated above, the unactivated integrated circuit-type battery is either on a substrate or comprises the substrate (i.e., the substrate provides a battery function in addition to being the support or base). For example, in addition to being a support, the substrate may also act as, or be a component of, a semiconductor, an electrode, a p-n junction, a Schottky junction, and/or transmutable material. This, of course, also contributes to the high degree of variability that may be realized with the present invention. The substrate comprises a substrate material that is appropriate for the particular application. For example, the substrate material may be polycrystalline, a single crystalline, or amorphous. If the substrate is also providing a function such as being a semiconductor, it may be desirable for certain applications to select an amorphous material because they tend to be more resistant to being damaged by radiation. In one embodiment, the substrate component comprises a substrate material selected from the group consisting of glass, Si, plastic, and metals and alloys thereof, and combinations of the foregoing. In another embodiment, the substrate comprises a substrate material selected from the group consisting of a semiconductor material, metal dielectric material, and combinations thereof. In one embodiment, the semiconductor material is a large band gap semiconductor material. The large band gap semiconductor material may be selected from the group consisting of TiO2, Si, SiC, GaN, GaAs, ZnO, WO3, SnO2, SrTiO3, Fe2O3, CdS, ZnS, CdSe, GaP, MoS2, ZnS, ZrO2, and Ce2O3, and combinations thereof. Additionally, the semiconductor material may be polycrystalline. Alternatively, the semiconductor may be a single crystal. In another embodiment, the substrate is a doped or undoped single crystal silicon wafer. The single crystal silicon wafer may be of any appropriate size. For example, the single crystal silicon wafer may have a nominal thickness of 300 μm and a nominal diameter selected from the group consisting of 100 mm, 200 mm, 300 mm, and 450 mm. Conversion Device As indicated above, the conversion device is converting energy from decay products of a radioisotope into electrical energy capable of performing work. The present invention allows for customization of the particular conversion device depending upon the needs or specifications of the application. For example, the conversion device may be an indirect conversion device. Alternatively, the conversion device may be a direct conversion device. In fact, it is possible for the battery to comprise an indirect conversion device and a direct conversion device. Although allowing for variability, the present invention is particularly suited for direct conversion-type nuclear batteries. As such, in one embodiment, the conversion device is a direct conversion device that comprises a first electrode, a second electrode, and a rectifying junction-containing component between and in ohmic contact with the first and second electrodes. In particular, each of the first electrode and the second electrode comprises an ohmic metal or metalloid that is independently selected from the group consisting of Al, Ag, Ti, Ni, Au, Fe, Cr, Pt, Pb, Mo, Cu, and highly-doped silicon, alloys thereof, and combinations of the foregoing elements and/or alloys. Further, each of the first electrode and the second electrode have a thickness independently selected from a range of about 50 nm to about 10,000 nm. In one embodiment, the thicknesses of the first electrode and the second electrode layer are substantially the same (e.g., about 200 nm). Not only does the present invention allow for significant variability in the locations/positions of the transmutable material and the conversion device as indicated above, the present invention also allows for significant variability in the location of the transmutable material within the conversion device in such embodiments. For example, the transmutable material may be located in one or both electrode layers and/or the rectifying junction-containing component. Rectifying Junction-Containing Component In one embodiment, the conversion device is a direct conversion device comprising a rectifying junction-containing component. Said rectifying junction-containing component may comprise a semiconductor p-n rectifying junction or a Schottky rectifying junction. Semiconductor p-n Rectifying Junction In a particular p-n rectifying junction embodiment the direct conversion device comprises a semiconductor p-n rectifying junction formed by the contact of a p-doped Si layer and n-doped Si layer. The thicknesses of the doped layers may be any appropriate thickness but it is typically desirable for them to be sufficiently thin to allow electrons and holes to migrate to the adjacent electrodes thereby contributing to the electrical current to not be so thick as to result in significant recombination of electrons and holes. In general, the p-doped Si layer and the n-doped Si layer each have a thickness independently selected from a range of about 50 nm to about 10,000 nm. More typically, the thicknesses are selected from a range of about 100 nm to about 500 nm (e.g., 200 nm). In addition to n-type and p-type semiconductor material, the semiconductor material may also be selected from intrinsic semiconductor (i), n+-type semiconductor (n+), and p+-type semiconductor (p+). In view of this, particular combinations thereof that may be used for p-n rectifying junctions include n-p, n-i-p, n+-i-p+, and n+-n-i-p-p+. Schottky Rectifying Junction In one embodiment, the direct conversion device comprises a Schottky rectifying junction formed by the contact of a Schottky metal layer in rectifying contact with a Schottky semiconductor, wherein the Schottky semiconductor is either the substrate or a Schottky semiconductor layer. The thickness of a Schottky semiconductor layer is typically in a range of about 50 nm to about 10,000 nm. Likewise, the thickness of a Schottky metal layer is in a range of about 50 nm to about 10,000 nm. More typically, the thicknesses are selected from a range of about 100 nm to about 500 nm (e.g., 200 nm). In one embodiment, the Schottky metal is selected from the group consisting of Pt, Au, Pd, Fe, Co, Cr, Ni, Ag, Ti, Ru, Cu, Mo, Ir, and Rh, alloys thereof, and combinations of the foregoing metallic elements and/or alloys. Additionally, the Schottky semiconductor (layer or substrate) may be an n-type material, a p-type material, a n+-type material, and/or a p+-type material. In view of this, particular combinations thereof that may be used for Schottky rectifying junctions include n, p, p-p+, and n-n+. Shielding A transmutable layer may be placed on top of a converting device or circuitry to act as a shield for radiation-sensitive materials. If the transmutable layer is thick enough, it will absorb all of the radiation and prevent radiation damage to other parts of the device, as shown in FIG. 2. In addition to shielding circuitry or components from the activation radiation by the selection, thickness, and location of transmutable material, the unactivated integrated circuit-type battery may comprise shielding, which allows for transmission of the transmuting radiation but reduces or prevents transmission of the decay products of the radioisotope, and wherein the shielding is free or essentially free of a radioisotope and materials capable of transmuting to a long-lived radioisotope by the exposure to the radiation. Examples of materials suitable for such shielding include W, Au, Pb, Al, Rh, and combinations thereof. Typically, the shielding is of a thickness in a range of about 1000 nm to about 100,000. Additional Radiation Damage Controls Although amorphous thin-film junctions are not ideal, the use thereof as part conversion device may be advisable, depending on the application, because amorphous materials tend to be more resistant to radiation damage than crystalline materials. This would likely be best reserved to stacked cell embodiments such as depicted in FIG. 5 and described in more detail below. Additionally, radiation damage to components of the battery and/or associated circuitry may be reduced or eliminated through “selective irradiation,” which limits radiation exposure to selected portion(s) of the unactivated battery(ies). Selective irradiation may be accomplished, for example, by controlling the cross-sectional area of the radiation contacting the unactivated battery(ies) and/or controlling the trajectory of the radiation, and/or controlling the relative positions of the source of the radiation and the selected portion(s) of the unactivated battery(ies). One manner of accomplishing the foregoing is to use beam optics to focus on only the desired areas, as shown in FIG. 3. With charged or neutral particle radiation, a narrow radiation beam may be used, while the device is translated in the x & y directions to position the desired areas in the beam path. To focus and control a cyclotron beam, a simple solenoidal magnetic field may be used by, for example, placing two coils exterior to the beam drift tube on opposing sides. The coils provide a transverse magnetic field relative to the direction of the particle beam. The Lorentz force exerts a force orthogonal to both the beam direction and applied magnetic field. By varying the current drive to the coils, the applied magnetic field is varied, the Lorentz force is varied, and the beam may be swept in one dimension. By adding another set of coils, on an axis orthogonal to the first set of coils and the beam direction, a full two dimensional control of the beam is achieved across the irradiation surface of the target. In addition or as an alternative to the foregoing one or more shadowmasks may be placed between the radiation source and the unactivated battery(ies) to shield sensitive areas from the radiation as shown in FIG. 4. Still further, depending upon the application one may be able to activate the battery with thermal neutrons, which tend to be less damaging. Expanding Capacity As indicated, energy conversion from radiation requires semiconductors, metals and radioisotope layers, in which the built-in electric field in the semiconductors harvest electron-hole pairs generated by incident radiation, and power is extracted through metallic electrodes. To expand the capacity, multiple cells may be fabricated (using, for example, stacked layers) wherein the electrodes of each cell are connected in series or parallel. In addition to increasing the number of cells of a battery, the present invention allows for the multiple batteries to be connected (in series or parallel). Further, one or more batteries may be connected with one or more integrated circuits. Advantageously, the multiplicity of cells and/or batteries may be activated with a single irradiation. Further, as previously indicated, the present invention allows for utilizing known integrated circuit manufacturing techniques/methods/technologies which allow for thinner, more precise, smaller dimensional features, which contribute to more capacity and or increased efficiency. For example, using multiple semiconductor thin films rather than thick semiconductor substrates, is believed to contribute to higher conversion efficiency. In a radiovoltaic device, electron-hole pairs (EHPs) can be generated at any point inside the semiconductor, but must diffuse to the depletion region at the p-n or Schottky junction before being separated by the built-in electric field. In the case of a thick semiconductor substrate (approximately 300 μm), the length that EHPs must diffuse to reach the depletion region is often much longer than the average diffusion length, and the energy is simply lost when the electron-hole pair recombines before being separated. A battery with many thin-film semiconductors allows for electron-hole pairs to be generated within one average diffusion length of the depletion region. Plus, providing many layers of radioisotopes sandwiched between semiconductors allows for greater overall efficiency due to isotropic energy harvesting. In view of the foregoing, in one embodiment the unactivated integrated circuit-type battery comprises a multiplicity of unactivated cells that are activated by the exposure to the radiation. In another embodiment, the unactivated cells are essentially identical. In yet another embodiment, the unactivated integrated circuit-type battery is on the substrate and the multiplicity of unactivated cells are in a stacked arrangement. The unactivated cells may be connected in series, in parallel, or a combination thereof. Additionally, in one embodiment a multiplicity of batteries (single cell or multiple cell) usually on or comprising a shared substrate (e.g., silicon wafer) are activated while connected via the substrate simultaneously or sequentially. For example, at least portions of a multiplicity of unactivated batteries are exposed to the radiation to transmute at least portions of the transmutable materials associated with each unactivated cell of each unactivated battery to the radioisotopes thereby producing each active cell of each active radioisotope battery thereby yielding a multiplicity of active radioisotope batteries. The unactivated batteries may not be connected or connected in series, in parallel, or a combination thereof. Still further, each unactivated battery or collection of connected unactivated batteries is in electrical connection with one or more integrated circuits on the substrate and, upon being exposed to the radiation, the electrical energy capable of performing work from the active battery or collection of connected electrical batteries powers allows for operation of the one or more integrated circuits. In one embodiment, the one or more integrated circuits are shielded from the radiation by a layer comprising a transmutable material that absorbs all or substantially all of the radiation. Exemplary Embodiments of Fabrication Processes Process 1—Thin-Film p-n Junction on Transmutable Substrate A fabrication process for a thin-film p-n junction on transmutable substrate may comprise the following steps: a) Start with a substrate of the material which is to be transmuted (e.g., Ni, Cu, Li, Nd, etc.); b) Deposit a sealing layer on the substrate, if necessary (e.g., Parylene, silicon oxide, polysilicon, silicon nitride, etc.); c) Deposit an adhesion promoting layer on the substrate by, for example, sputtering or evaporation (e.g., Cr); d) Deposit an appropriate first ohmic contact (or electrode) layer for the following semiconductor material (e.g., p-type silicon), which may be, for example Pt, by evaporation or sputtering; e) Deposit an appropriate semiconductor material (e.g., p-type silicon) by, for example, sputtering; f) Deposit another appropriate semiconductor material (e.g., n-type silicon) by, for example, sputtering; g) Deposit a second ohmic contact (or electrode) layer appropriate for the preceding semiconductor material (e.g., n-type silicon), which may be, for example Al, by, for example, evaporation or sputtering; h) Pattern the foregoing assembly with photolithography as desired; and i) Transmute the transmutable material in the substrate using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Process 2—Thin-Film p-n Junction with Transmutable Film A fabrication process for a thin-film p-n junction with transmutable film may comprise the following steps: a) Start with an appropriate substrate (e.g., silicon wafer); b) Deposit an adhesion promoting layer (e.g. Cr) on the substrate by, for example, sputtering or evaporation; c) Deposit an appropriate first ohmic contact (or electrode) layer for the following semiconductor material (e.g., p-type silicon), which may be, for example Pt, by evaporation or sputtering; d) Deposit an appropriate semiconductor material (e.g., p-type silicon) by, for example, sputtering; e) Deposit another appropriate semiconductor material (e.g., n-type silicon) by, for example, sputtering; f) Deposit a second ohmic contact (or electrode) layer appropriate for the preceding semiconductor material (e.g., n-type silicon), which may be, for example Al, by, for example, evaporation or sputtering; g) Deposit an appropriate seed layer (e.g., Au, Pt, Cu, Ni, Nd) for electro- or electroless plating on the second ohmic contact layer by, for example, sputtering or evaporation; h) Pattern the foregoing assembly with photolithography as desired; i) Deposit a transmutable material layer (e.g., Cu, Ni, Nd, etc.) by electro- or electroless plating; and j) Transmute the transmutable material using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Process 3—Thin-Film Schottky Junction on Transmutable Substrate A fabrication process for a thin-film Schottky junction on transmutable substrate may comprise the following steps: a) Start with a substrate of the material which is to be transmuted (e.g., Ni, Cu, Li, Nd, etc.); b) Deposit an adhesion promoting layer on the substrate by, for example, sputtering or evaporation (e.g., Cr); c) Deposit an appropriate first ohmic contact (or electrode) layer for the following semiconductor material (e.g., p-type or n-type silicon), which may be, for example Pt, by, for example, evaporation or sputtering; d) Deposit an appropriate semiconductor material layer (e.g., p-type or n-type silicon) by, for example, sputtering; e) Deposit an appropriate rectifying metal layer (e.g., Al) on the semiconductor layer for Schottky contact by, for example, evaporation or sputtering; f) Pattern the foregoing assembly with photolithography as desired; and g) Transmute the transmutable material using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Process 4—Thin-Film Schottky Junction with Transmutable Film A fabrication process for a thin-film Schottky junction with transmutable film may comprise the following steps: a) Start with an appropriate substrate (e.g., silicon wafer); b) Deposit an adhesion promoting layer (e.g. Cr) on the substrate by, for example, sputtering or evaporation; c) Deposit an appropriate first ohmic contact (or electrode) layer for the following semiconductor material (e.g., p-type or n-type silicon), which may be, for example Pt, by evaporation or sputtering; d) Deposit an appropriate semiconductor material (e.g., p-type or n-type silicon) by, for example, sputtering; e) Deposit an appropriate rectifying metal layer (e.g., Al) on the semiconductor layer for Schottky contact by, for example, evaporation or sputtering; f) Deposit an appropriate seed layer (e.g., Au, Pt, Cu, Ni, Nd) for electro- or electroless plating on the second ohmic contact layer by, for example, sputtering or evaporation; g) Pattern the foregoing assembly with photolithography as desired; h) Deposit a transmutable material layer (e.g., Cu, Ni, Nd, etc.) by electro- or electroless plating; and i) Transmute the transmutable material using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Process 5—Stacked Thin-Film p-n Junction Device A fabrication process for a stacked thin-film p-n device may comprise the following steps: a) Start with an appropriate substrate (e.g., silicon wafer); b) Create a lift-off pattern for the radioisotope battery using, for example, photolithography; c) Deposit an adhesion promoting layer (e.g. Cr) on the substrate by, for example, sputtering or evaporation; d) Deposit an appropriate first ohmic contact (or electrode) layer for the following semiconductor material (e.g., p-type or n-type silicon), which may be, for example Pt, by evaporation or sputtering; e) Deposit an appropriate semiconductor material (e.g., p-type silicon) by, for example, sputtering; f) Deposit another appropriate semiconductor material (e.g., n-type silicon) by, for example, sputtering; g) Deposit a second ohmic contact (or electrode) layer appropriate for the preceding semiconductor material (e.g., n-type silicon), which may be, for example Al, by, for example, evaporation or sputtering; h) Deposit a transmutable material layer (e.g., Cu, Ni, Nd, etc.) by, for example sputtering or evaporation; i) Repeat steps c through h as desired to obtain multiple stacked devices; j) Remove the lift-off layer, leaving patterned material behind; and k) Transmute the transmutable material using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Process 6—Stacked Thin-Film Schottky Device A fabrication process for a stacked thin-film Schottky device may comprise the following steps: a) Start with an appropriate substrate (e.g., silicon wafer); b) Deposit an adhesion promoting layer (e.g. Cr) on the substrate by, for example, sputtering or evaporation; c) Deposit an appropriate first ohmic contact (or electrode) layer for the following semiconductor material (e.g., p-type or n-type silicon), which may be, for example Pt, by evaporation or sputtering; d) Deposit an appropriate semiconductor material (e.g., p-type or n-type silicon) by, for example, sputtering; e) Deposit an appropriate rectifying metal layer (e.g., Al) on the semiconductor layer for Schottky contact by, for example, evaporation or sputtering; f) Deposit a transmutable material layer (e.g., Cu, Ni, Nd, etc.) by, for example sputtering or evaporation; g) Repeat steps c through f as desired to obtain multiple stacked devices; h) Pattern the foregoing assembly with photolithography as desired; and i) Transmute the transmutable material using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Process 7—Bulk Semiconductor p-n Junction Device A fabrication process for a bulk semiconductor p-n junction with transmutable film may comprise the following steps: a) Start with an appropriate p-type or n-type substrate (e.g., p-type or n-type silicon wafer); b) Form an insulating layer on the substrate (e.g., thermal oxidation of the substrate to form a SiO2 layer); c) Pattern the insulating layer using, for example, photolithography, to form a masking layer; d) Form a layer of oppositely doped material on the unmasked areas of the substrate (e.g., using thermal diffusion or ion implantation to p-dope a region on an n-type silicon wafer or n-dope a region on p-type silicon wafer); e) Deposit an appropriate ohmic contact (or electrode) layer for the following semiconductor material (e.g., p-type or n-type silicon), which may be, for example Pt, by evaporation or sputtering; f) Deposit an appropriate seed layer (e.g., Au, Pt, Cu, Ni, Nd) for electro- or electroless plating on the ohmic contact layer by, for example, sputtering or evaporation; g) Pattern the foregoing metal layers with photolithography to match the previous masking pattern; h) Deposit a transmutable material layer (e.g., Cu, Ni, Nd, etc.) by electro- or electroless plating; and i) Transmute the transmutable material using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Process 8—Bulk Semiconductor Schottky Device A fabrication process for a bulk semiconductor Schottky junction with transmutable film may comprise the following steps: a) Start with an appropriate p-type or n-type substrate (e.g., p-type or n-type silicon wafer); b) Deposit an appropriate rectifying metal layer (e.g., Al) on the substrate for Schottky contact by, for example, evaporation or sputtering; c) Deposit an appropriate seed layer (e.g., Au, Pt, Cu, Ni, Nd) for electro- or electroless plating on the rectifying metal layer by, for example, sputtering or evaporation; d) Pattern the foregoing assembly with photolithography as desired; e) Deposit a transmutable material layer (e.g., Cu, Ni, Nd, etc.) by electro- or electroless plating; f) Deposit an appropriate ohmic contact (or electrode) layer for other side of the substrate; g) Pattern the ohmic contact layer with photolithography, aligned with the patterned Schottky areas on the front side of the substrate; and h) Transmute the transmutable material using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Process 9—Powder or Liquid Semiconductor p-n Junction or Schottky Device Referring to FIG. 10, a fabrication process for a p-n junction or Schottky device having a powder or liquid semiconductor may comprise the following steps: a) Start with two appropriate substrate (e.g., silicon wafer); b) Deposit an appropriate rectifying metal layer (e.g., Al) or semiconductor layer on one of the substrates by, for example, evaporation or sputtering; i. a rectifying metal will form a Schottky junction with the powder or liquid semiconductor; ii. a semiconductor can form a p-n junction with the powder or liquid semiconductor; c) Deposit an appropriate ohmic contact (or electrode) layer on the other substrate; d) If necessary, deposit a matrix or reservoir to retain the powder or liquid semiconductor material on one of the substrates, (e.g., a reservoir may be fabricated by milling a substrate); e) Placing a powder or liquid mixture comprising semiconductor material and transmutable material between the device-deposited substrates by, for example, manual loading, sol-gel deposition, or dip coating between; and f) Transmute the transmutable material using an appropriate/desired irradiation method (e.g., neutrons from nuclear reactor or spallation neutron source; or ions from ion beam). Monocrystalline silicon p-n junction wafers were manufactured according to the following steps: a) Cut a p-type silicon prime wafer to the size of 20.57 mm×20.57 mm using a Disco DAC550 dicing saw. This size is appropriate for placement in the cyclotron sample holder. b) The cut p-type silicon was cleaned. i. First the wafer was cleaned with acetone, methanol, and DI water, in succession (i.e., an AMD wash). ii. The AMD wash was followed by a ten minute boil in nitric acid at 90° C. to form a thin oxide layer. iii. A rinse with DI water is used to remove residual nitric acid solution. iv. A 20 second dip in a solution of hydrofluoric acid, 1:5—HF:H2O, removed the oxide layer. v. Removal of metallic surface contaminants was achieved by a 2 minute dip in solution of hydrochloric acid and hydrogen peroxide, 3:1:1—HCl:H2O:H2O2. vi. Removal of the newly formed surface oxide was achieved by a 30 second dip in hydrofluoric acid solution, 1:5—HF:H2O. vii. The cleaning process was completed with a rinse in DI water to eliminate residual hydrofluoric acid, and the sample is dried with N2. c) Thermal diffusion of phosphorus atoms into the silicon to form the p-n junction was performed. i. The thermal diffusion process started with allowing the spin-on-dopant (SOD) to acclimate to room temperature. The SOD was a phosphorous doped spin-on-glass product (P509) from Filmtronics. ii. 1 milliliter of SOD was dropped on the center of the wafer sample, and spun at 3000 rpm for 15 seconds. iii. The spin coating was followed by a pre-bake at 200° C. for 10 minutes. iv. The thermal diffusion occurred in a furnace set at 1000° C. for 1.5 hours, which drives the phosphorous atoms into the bulk silicon. This thermal diffusion process also produced a surface oxide layer, which must be removed prior to electrode deposition. v. A post-diffusion cleaning removed the surface oxide layer by dipping the wafer in buffered oxide etch (BOE) for 20 seconds. d) The p-n junction was completed by physical vapor deposition of electrodes on the device, aluminum was sputtered on the n-type silicon, and gold was sputtered on the p-type silicon. Embodiments of the devices were fabricated with thin-film silicon p-n junctions and crystalline Schottky junctions and activated electroplated copper films on top of these devices. The fabrications of silicon p-n and Schottky junctions were accomplished by sputter deposition from p-Si, n-Si, and/or metal targets. In particular, devices as depicted in FIG. 6 were made according to the above-described process 2 for making a thin-film p-n junction with transmutable film. Also, devices as depicted in FIG. 7 were made according to the above-described process 8 for making a bulk semiconductor Schottky device. The radioisotope (activated radionuclides) for both devices was 64Cu made by electroplating natural copper (69% 63Cu) and irradiating with 5.7 MeV deuterons from a cyclotron source. After irradiating approximately 10 μm of copper for 4 hours with approximately 40 μA beam current, a well-type radiation counter estimated the presence of approximately 1.37 mCi of 64Cu on top of a silicon thin-film p-n junction. The current-voltage (I-V) of the devices depicted in FIGS. 6 and 7 are shown in FIGS. 8 and 9, respectively. The nonlinear shapes of these I-V curves indicate a capability to harvest electron-hole pairs generated from incident radiation. In another experiment, approximately 100 μm of copper was used. Simulation results indicated that this thick copper would stop the deuteron beam before it reached the silicon, as was alluded to previously. In particular, it is possible to position a transmutable layer on top of a converting device or circuitry to act as a shield for radiation-sensitive materials. If the transmutable layer is thick enough, it will absorb all of the radiation and prevent radiation damage to other parts of the device, as shown in FIG. 2. After irradiation, a well-type radiation counter estimated the presence of approximately 1.5 mCi of 64Cu. The I-V characteristics of the device before and after irradiation did not show any evidence of radiation damage, implying that the deuteron beam did not penetrate into the converting silicon layers. It should be noted that the radioactivity estimated by the well-counter is likely an underestimate due to the system's poor efficiency and the anisotropy of the copper film. Additionally, fabrication of a working rectifying p-n junction on a parylene-sealed lithium substrate has been demonstrated. Parylene was deposited onto a pure lithium substrate for sealing. A silicon thin-film p-n junction was then fabricated on this sealed lithium substrate using the process described previously. A schematic of this device is shown in FIG. 11 and the I-V characteristics of the device are shown in FIG. 12. Having illustrated and described the principles of the present invention, it should be apparent to persons skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. Although the materials and methods of this invention have been described in terms of various embodiments and illustrative examples, it will be apparent to those of skill in the art that variations can be applied to the materials and methods described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims. [1] P. Rappaport, “The electron-voltaic effect in p-n junctions induced by beta-particle bombardment,” Physical Review, vol. 93, pp. 246-247, 1954. [2] C. J. Eiting, V. Krishnamoorthy, S. Rodgers, T. George, J. Brockman, and J. D. Robertson, “Demonstration of a Radiation Resistant, High Efficiency SIC Betavoltaic,” Applied Physics Letters 88, 064101-1-064101-3 (2006). [3] H. Guo and A. Lal, “Nanopower betavoltaic microbatteries,” 12th International Conference on Solid-State Sensors, Actuators and Microsystems, pp. 36-39, 2003. [4] R. Duggirala, et al., “3D silicon betavoltaics microfabricated using a self-aligned process for 5 milliwatt/cc average, 5 year lifetime microbatteries,” 14th International Conference on Solid-State Sensors, Actuators and Microsystems, pp. 279-282, 2007. [5] C. Eiting, et al., “Demonstration of a radiation resistant, high efficiency SiC betavoltaic,” Applied Physics Letters, vol. 88, p. 064101, 2006. [6] D. Y. Qiao, et al., “Demonstration of a 4H SiC Betavoltaic Nuclear Battery Based on Schottky Barrier Diode,” Chinese Physics Letters, vol. 25, pp. 3798-3800, 2008. [7] D. Y. Qiao, et al., “A Micro Nuclear Battery Based on SiC Schottky Barrier Diode,” Microelectromechanical Systems, Journal of, pp. 1-6, 2011. [8] M. Chandrashekhar, et al., “Demonstration of a 4H SiC betavoltaic cell,” Applied Physics Letters, vol. 88, p. 033506, 2006.
	claims	1. A method for altering the environment in a closed system which comprises emitting Terahertz radiation from Terahertz radiation treated water containing members of the group consisting of soluble inorganic salts and minerals that have been imprinted with Terahertz wavelengths of about 100 micrometers to 1 micrometer and frequencies from 300 GHz to 3 THz by means of a polarizing filter through which said polarized radiation containing Terahertz, spectrum radiation passes onto the water. 2. The method of claim 1 wherein the radiated water is in a transparent container. 3. The method of claim 1 wherein said closed system is an environmentally controlled chamber. 4. The method of claim 1 wherein said closed system contains food stuff. 5. The method of claim 1 wherein the source of Terahertz radiation is from the sun.
	abstract	The invention relates to a pressurised water nuclear reactor vessel, comprising: an outer casing which comprises at least one cylindrical shell and a dished bottom head, a core support plate, a vessel bottom head space being delimited between the support plate and the dished bottom head, the support plate being perforated with holes for circulation of the primary coolant which place the vessel bottom head space in communication with the core, a calming device which is arranged in the vessel bottom head space,wherein the calming device comprises at least one calming plate which is substantially perpendicular relative to the centre axis of the vessel and a plurality of calming holes, the calming holes being provided in the calming plate and being capable of calming the primary coolant by passing the fluid through the holes.
041394143	summary	BACKGROUND OF THE INVENTION The invention relates to shutdown mechanisms for nuclear reactors, and in particular to poison release mechanisms for reactors of the liquid metal type. It is known in the art of nuclear reactor control to use a multiplicity of small neutron absorbing masses, usually stainless steel spheres or the like, to rapidly shutdown (scram) the nuclear chain reaction on the occurrence of a severe accident. Because of the difficulties associated with resetting the masses after a scram, these prior art devices are usually provided in the nuclear reactor as a final safeguard against the most serious kinds of accidents, such as earthquakes or other events that might physically damage the regular shutdown system. Thus these devices have not been disclosed as having means for easily resetting the masses for renewed core operation, since it has been implicitly assumed that significant damage to the reactor has occurred, that repairs will be required, or that a prolonged testing period will be needed before operation can resume. During these prolonged outages, the prior art devices can be repaired or replaced, but they cannot be quickly reset if they scram inadvertently during normal operation or if they are actuated for test purposes. Examples of such prior art devices are described in U.S. Pat. Nos. 3,088,903 issued to A. Firth; 3,147,188 issued to R. H. Cambell; and 3,249,510 issued to A. J. Dohm, Jr. et al. SUMMARY OF THE INVENTION It is an object of the present invention to provide a scram system utilizing a multiplicity of neutron absorbing masses that can be used for routine scram incidents. It is a related object of the invention to provide for simple resetting of the scram device following a scram. It is a further object of the invention to provide a scram system that can be self-actuated from within the safety assembly for dropping a multiplicity of neutron absorbing masses into the reactor core. The present invention is an apparatus for holding, releasing and resetting a multiplicity of neutron absorbing balls within a safety assembly of a liquid metal nuclear reactor. Vertically hinged trap doors rest on the shoulders of a generally cylindrical release valve which is actuated either by the regular or self-actuated scram actuator. The doors and the valve shoulder provide a floor for the multiplicity of balls to be suspended above the reactor core during normal operation. When the actuator displaces the release valve, the doors lose their support and swing downward, permitting the poison balls to drop into the core. In the reset mode of operation, a platform at the bottom of the core is raised to lift the balls and swing the trap doors upward until the balls are above the door hinges. The release valve is reset to support the doors and the platform is lowered to the bottom of the safety assembly. The invention can be used as part of the regular scram system and is adaptable for use in conjunction with a variety of self-actuating scram devices used for backup scram control.
	summary
	summary
	summary
	claims	1. A grating for X-ray imaging, comprising:a grating structure including a first plurality of bar members and a second plurality of gaps; anda fixation structure arranged between the bar members to stabilize the grating bar members;wherein the bar members are extending in a length direction and in a height direction and are spaced from each other by one of the gaps in a spacing direction transverse to the height direction and to the length direction, wherein the gaps are arranged in a gap direction parallel to the length direction;wherein the fixation structure comprises at least one bridging web member that is provided between adjacent bar members of the plurality of bar members;wherein one bridging web member of the at least one bridging web member is longitudinal that extends in the gap direction and that is provided in an inclined manner in relation to the height direction, wherein an inclination is provided in the gap direction; andwherein the one bridging web member of the at least one bridging web member includes an inclined portion, the inclined portion of the one bridging web member extends along an inclined direction with a constant dimension in the spacing direction and the inclined direction is perpendicular to the spacing direction and is different from the height direction and the length direction. 2. The grating according to claim 1, wherein the at least one bridging web member and the bar members are made from the same material; and wherein the at least one bridging web member and the bar members are made as a one-piece structure. 3. The grating according to claim 1, wherein the bar members and the at least one bridging web member are made from structure material, and an X-ray absorbing material is arranged in the gaps; and wherein the structural material is less X-ray absorbing than the X-ray absorption material. 4. The grating according to claim 3, wherein the grating is an absorber grating, and the grating structure is made such that the gaps are filled with the X-ray absorbing material for X-ray absorption by the gaps; and wherein the bar members are provided to be less X-ray absorbing for X-ray radiation transmission in the bar members. 5. The grating according to claim 1, wherein the grating is an absorber grating, and the grating structure is made such that the bar members are made from X-ray absorbing material for X-ray absorption by the bar members, and the gaps are provided to be less X-ray absorbing for X-ray radiation transmission in the gaps. 6. The grating according to claim 1, wherein one bridging web member of the at least one bridging web member is arranged between the adjacent bar members such that the one bridging web member of the at least one bridging web member connects opposing portions of the bar members; and/orwherein the at least one bridging web member includes a plurality of bridging web members, and in a non-assembled state the plurality of bridging web members are arranged parallel to each other. 7. The grating according to claim 1, wherein, in an X-ray radiation viewing direction, across the height at least one first gap part and at least one web segment part are provided. 8. The grating according to claim 1, wherein one bridging web member of the at least one bridging web member is arranged such that, in an X-ray radiation viewing direction, a continuous degree of X-ray attenuation is provided along the gaps. 9. The grating according to claim 1, wherein one bridging web member of the at least one bridging web member extends in a continuous manner from an upper edge of the bar members to a lower edge of the bar members; and/orwherein the at least one bridging web member includes a plurality of bridging web members the plurality of bridging web members are arranged repeatedly in gap direction with a distance D over a gap height H; and wherein the plurality of bridging web members have an inclination ratio in relation to the height direction R of D/H. 10. The grating according to claim 1, wherein the at least one bridging web member includes a plurality of bridging web members, and the plurality of bridging web members are arranged at least as one of the following:as repeatedly arranged inclined web members with the same inclination angle;as inclined segments with the same inclination angle value, but with alternating inclination directions, which results in a zig-zag web pattern along the gap; andas repeatedly arranged inclined web segment portions that are provided in a crossing manner, which results in an X-type repeated web pattern. 11. The grating according to claim 1, wherein the grating is at least one of:an absorber grating for phase contrast and/or dark-field X-ray imaging; andan anti-scatter grid for X-ray imaging. 12. An X-ray imaging system, comprising:an X-ray source, an X-ray detector; anda grating according to claim 1 to be arranged in an X-ray radiation path between the X-ray source and the X-ray detector. 13. The X-ray imaging system according to claim 12, wherein the X-ray source provides the X-ray radiation towards the X-ray detector in an X-ray viewing direction; and wherein one bridging web member of the at least one bridging web member is provided in an inclined manner in relation to the X-ray viewing direction. 14. The X-ray imaging system according to claim 12, wherein a grating arrangement for phase contrast and/or dark-field X-ray imaging is provided;wherein at least partially coherent X-ray radiation is provided to radiate an object;wherein the grating arrangement comprises at least a phase grating and an analyzer grating; andwherein the grating is provided as an absorption grating forming:the analyzer grating; and/ora source grating to provide the at least partially coherent X-ray radiation. 15. A method for manufacturing a grating for X-ray imaging, comprising:generating a grating structure including a first plurality of bar members and a second plurality of gaps, wherein the bar members are extending in a length direction and in a height direction and are spaced from each other by one of the gaps in a spacing direction transverse to the height direction and to the length direction; andgenerating a fixation structure arranged between the bar members to stabilize the grating bar members, wherein the fixation structure comprises at least one bridging web member that is provided between adjacent bar members of the plurality of bar members, and wherein one bridging web member of the at least one bridging web member is longitudinal that extends in the direction of the gaps and that is provided in an inclined manner in relation to the height direction,wherein the one bridging web member of the at least one bridging web member includes an inclined portion, the inclined portion of the one bridging web member extends along an inclined direction with a constant dimension in the spacing direction, and the inclined direction is perpendicular to the spacing direction and is different from the height direction and the length direction.
	claims	1. A computer simulator implemented method of modeling a fissile system in a neutronics modeling method comprising:inputting, into the computer simulator, neutronics characteristics of at least one first geometric construct;inputting, into the computer simulator, an indication that the at least one first geometric construct completely fills a second geometric construct;performing, by the computer simulator, a criticality analysis of the fissile system including the first and second geometric constructs, the performing including defining at least one neutronic characteristic of the second geometric construct as if the second geometric construct were completely filled with a plurality of the first geometric constructs without inputting the at least one neutronic characteristic of the second geometric construct; andoutputting the criticality analysis of the fissile system including the first and the second geometric constructs. 2. The method of claim 1, wherein the second geometric construct is a region to be modeled in a neutronics modeling method. 3. The method of claim 1, wherein the first geometric construct includes a generally rectangular body having curved surfaces on the generally rectangular body. 4. The method of claim 3, wherein the curved surfaces are shaped as a portion of a surface of a cylinder or a sphere. 5. The method of claim 3, wherein the curved surfaces are shaped according to quadratic surface equations. 6. A method of claim 1, wherein the first geometric construct is formed by forming at least one interstitial region, the first geometric construct being formed by boundaries of the at least one interstitial region. 7. The method according to claim 6, wherein the boundaries of the at least one interstitial region are shaped such that the formed first geometric construct is cylindrical or spherical. 8. The method according to claim 7, wherein the boundaries of the at least one interstitial region are shaped such that the formed first geometric construct is shaped according to quadratic surface equations. 9. The method according to claim 1 further comprising:obtaining an effective neutron multiplication factor of a modeled system containing each geometric construct, wherein each geometric construct represents an object in a fissile system and has associated neutronic characteristics of the represented objects. 10. A computer simulator implemented method of modeling a fissile system in a neutronics modeling method comprising:inputting, into the computer simulator, neutronics characteristics of at least one first geometric construct;inputting, into the computer simulator, placement data of the at least one first geometric construct in a second geometric construct;performing, by the computer simulator, a criticality analysis of the fissile system including the first and second geometric constructs, the performing including defining at least one neutronic characteristic of the second geometric construct as if the second geometric construct contains the at least one first geometric construct based on the placement and neutronic characteristics of the at least one first geometric construct; andoutputting the criticality analysis of the fissile system including the first and the second geometric constructs. 11. The method of claim 10, further comprising:placing at least one of the second geometric construct into a third geometric construct; anddefining at least one neutronic characteristic of the third geometric construct as if the third geometric construct contains the at least one second geometric construct based on the placement and neutronic characteristics of the at least one second geometric construct. 12. The method of claim 11, wherein the steps of claim 11 are repeated N times with Nth geometric constructs so as to form a plurality of levels of embedded geometric constructs and wherein at least one neutronic characteristic of the Nth geometric construct is based on the placement and neutronic characteristics of each preceding level of geometric constructs and wherein N is a positive integer. 13. The method of claim 10, wherein a plurality of the first geometric constructs are placed into the second geometric construct and wherein each first geometric construct of the plurality of the first geometric constructs do not possess identical neutronic characteristics. 14. The method of claim 10, wherein a plurality of the first geometric constructs are placed into the second geometric construct and at least two first geometric constructs of the plurality of first geometric constructs spatially overlap and form an overlapping region within the second geometric construct. 15. The method of claim 10 further comprising:rotating the first geometric construct within the second geometric construct; anddefining at least one neutronic characteristic of the second geometric construct based on the placement and the rotation of the first geometric construct. 16. The method according to claim 11 further comprising:obtaining an effective neutron multiplication factor of a modeled system containing each geometric construct, wherein each geometric construct represents objects in a fissile system and have associated neutronic characteristics of the represented objects. 17. A computer simulator implemented method of modeling a fissile system in a neutronics modeling method comprising:inputting, into the computer simulator, neutronics characteristics of a first geometric construct;inputting, into the computer simulator, an indication that the at least one first geometric construct completely fills a second geometric construct;inputting, into the computer simulator, placement data of at least one second geometric construct in a third geometric construct;performing, by the computer simulator, a criticality analysis of the fissile system including the first, second, and third geometric constructs, the performing includingdefining at least one neutronic characteristic of the second geometric construct as if the second geometric construct were completely filled with a plurality of the first geometric constructs without inputting the at least one neutronic characteristic of the second geometric construct, anddefining at least one neutronic characteristic of the third geometric construct based on the placement and neutronic characteristics of the at least one second geometric construct; andoutputting the criticality analysis of the fissile system including the first, second, and third geometric constructs. 18. The method of claim 17, wherein a plurality of the second geometric constructs are placed into the third geometric construct and at least two second geometric constructs of the plurality of second geometric constructs spatially overlap and form an overlapping region within the third geometric construct. 19. The method of claim 18, wherein the at least two second geometric constructs do not possess identical neutronic characteristics. 20. The method of claim 19, wherein at least one neutronic characteristic of the overlapping region is defined exclusively by a corresponding neutronic characteristic of one second geometric construct of the at least two second geometric constructs forming the overlapping region. 21. The method of claim 20, wherein the one second geometric construct of the at least two second geometric constructs forming the overlapping region is chosen based on inherent priority of the one second geometric construct or user input.
	summary
039768880	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a high-flux thermal-neutron-nuclear reactor 11 is illustrated. The reactor is generally of the same type as the high flux isotope reactor (HFIR) at Oak Ridge which is more completely described in Proceeding of the Third International Conference on the Peaceful Uses of Atomic Energy, Vol. 7, Research and Testing Reactors, pp. 360-368 (United Nations, N.Y. 1965). As illustrated, the reactor includes a reactor vessel 13 with a coolant water inlet 15 and outlet 17. A barrier 16 at the top of the reactor is illustrated to separate components that would ordinarily be outside the reactor although not necessarily outside a shielded facility. The reactor core 19 includes a cylindrical beryllium reflector 21 surrounding reactor fuel elements 23 that are shaped as vertical curved plates. A control cylinder 20 containing neutron absorbing material is shown partially withdrawn from the bottom of core 19. The open central region, that is the flux trap 25, is filled with water which serves as a neutron moderator and extends the length of the core. For clarity in the drawing, the water is not shown, but it is well known that such is used as a moderator in the flux traps of reactors like the HFIR. It is in the flux trap region that high thermal-neutron flux are obtained. Within the flux trap 25 is illustrated a thermal neutron converter 31 that is a part of a materials testing device. The converter 31 is provided with an access tube 32 extending outside the reactor vessel 13 for installing and removing samples or other objects that are to be exposed to high flux of 14 MeV neutrons. Also included as a part of the test device is a conduit loop 33 containing a compressor 35 or other means for circulating a mixture of deuterium-tritium gas through the converter 31. The loop 33 is provided with a heat exchanger 37 including means for circulating a coolant 39 in indirect heat exchange relation with the deuterium-tritium gas. For example, a shell and tube or a concentric pipe type of heat exchanger bundle with suitable coolant pumps could be used for this purpose. Also illustrated is a helium separation facility 40 valved in parallel to conduit loop 33. Facility 40 would be employed periodically for removing helium gas produced along with adding makeup deuterium-tritium gas. The helium separation is carried out by a conventional process such as low temperature fractionation or other suitable process. Turning now to FIG. 2 where a more detailed illustration of the neutron converter 31 is presented. The converter is shown contained within a cylindrical shaped vessel 41 having an inlet 43 and an outlet (not shown in FIG. 2) for circulation of the deuterium-tritium gas mixture flowing within conduit loop 33 (FIG. 1). A plurality of thin-wall foils 45 containing fissionable materials are shown as concentric cylinders within vessel 41 surrounding a centrally disposed target support member 47. Member 47 is fixedly attached to a target material 49 or sample that is to be exposed to a high flux of approximately 14 MeV neutrons. In test applications where the target material is to be removed or replaced without disturbing the converter 31, the support member 47 will extend to an accessible location outside the reactor through tube 32 (FIG. 1). Although not shown suitable shielding and handling devices would be employed for changing samples. For tests in which the target is to be bombarded with only neutrons of approximately 14 MeV energy, a shield tube 51 is provided to enclose target 49 and block high-energy deuterons, tritons and fission fragments. Shield tube 51 will, of course, interconnect with access tube 32 (FIG. 1) at the upper end of converter 31. In most instances target 49 can be maintained at a sufficiently low temperature by the flow of deuterium-tritium gas through the converter device. Where additional cooling is needed, a separate coolant loop (not shown) could be provided within tubes 32 and 51. However, in applications where shield tube 51 is omitted the circulation of deuterium-tritium gas will be in direct contact with target 49 to provide effective cooling. It will be clear that other schemes for circulating the deuterium-tritium gas can also be provided within the scope of applicants' invention. For example, the return of gas from the heat exchanger 37 to the lower inlet 43 of converter device 31 could be passed through a separate channel within vessel 41, e.g. a centrally located, open-ended tube in place of shield tube 51 could be employed for both sample shielding and gas return along with providing coolant gas in contact with the target. Foils 45 are illustrated as cylindrical members with surfaces positioned transverse to the direction of thermal neutron flux. The cylindrical shape is a particularly suitable configuration for use in a flux trap with the reactor fuel 23 (FIG. 1) surrounding the neutron converter 31. This configuration establishes a flux of 14 MeV neutrons, from all circumferential directions, at the foil axis where the target material 49 is positioned. However, this is not to exclude other foil configurations such as flat or curved members in stacks or series alignment. The foils 45 are shown supported between upper 53 and lower 55 grid members, each having sufficient open area for passage of the deuterium-tritium gas flow. Vertical rods 57 connect the two grids 53 and 55 to consolidate the foils 45 into a cartridge. Where extremely thin foils are used, vertical ribs or grid type supports can be employed between the foils provided openings for gas flow are included. The foils are composed of a metal containing a fissionable material. For example, uranium metal enriched to contain a major portion, that is more than 50% by weight .sup.235 U could be employed for use in the illustrated embodiment. However, it is preferable that the .sup.235 U enrichment be as high as possible with the standard enrichment of 93% by weight .sup.235 U being a practical composition from which the foils can be provided. The foils are preferably sufficiently thin to facilitate release of fission fragments following thermal neutron induced fission. Foils of less than about 25 microns will function satisfactory but thicknesses of at least 8 microns will ordinarily be used for structure strength. To gain full benefit of the thermal neutron flux provided by the reactor, it is preferable that a sufficient number of foils be provided in series to be black to thermal neutrons between the thermal neutron source and the target. For 25 micron foils arranged in concentric cylinders at least about 7 to 10 foils should be employed. However, it will be understood that the number of foils required to block a thermal neutron flux will vary with the intensity of that flux and the thickness of the foils. The foils are spaced sufficiently far apart to provide space for deuterium-tritium gas flow. A sufficient space for gas is needed to allow fission fragments released from the foils to collide with and accelerate deuterons and tritons of the gas. Also, space for an adequate flow of gas to cool the foils and in some applications the target material is to be provided. As an example foil spacings of at least 3 millimeters, and to conserve space, foil spacings in a range of about 3 to 6 millimeters should be sufficient for most neutron converter devices as described herein. The deuterium-tritium gas pressure is preferably maintained at a high level, particularly between the foils 45 to provide high gas density and thereby increase the probability of collision between fission fragments and deuterons or tritons. Elevated gas pressures also decrease the average path length of a fission fragment to permit closer spacing of the foils 45. Practical gas pressures of about 10 to 100 atmospheres and even higher are contemplated in the neutron converter 31. However at very high pressures the disadvantages resulting from thick containment walls such as neutron flux attenuation, space considerations and other containment problems in the system will outweigh the gains attributable to increased gas density. In order to evaluate the performance of the neutron converter system, the following basic equation is presented: ##EQU1## where: A = N.sub.f n.sub.d n.sub.t K ##EQU2## Here X gives the number of 14 MeV neutrons produced by N.sub.f fission fragments of energy E.sub.o, mass M.sub.1, charge eZ.sub.1, striking particles (d or t) of mass M.sub.a, charge eZ.sub.a. The expression is summed over the four cases in which a light or heavy fragment strikes a deuteron or a triton. The other symbols are: n.sub.d, n.sub.t are atomic densities of deuterium and tritium, respectively, in the pressurized gas mixture; ##EQU3## where: Z is atomic number; e is electron charge; PA1 mc.sup.2 is the rest energy of an electron; PA1 Q is the initial energy of the recoiling particle; ##EQU4## E.sub.1 is the energy (variable) of a fission fragment as it slows down in the gas; ##EQU5## are the stopping powers respectively for the fragments and for the first recoil particle (energy loss per interval of path); and PA1 .sigma..sub.a (E.sub.a) = the cross section for either the reaction t(d,n).sup.4 He PA1 or d(t,n).sup.4 He. In terms of laboratory energies EQU .sigma.(E.sub.d) = .sigma. (2/3 E.sub.t). Values for cross sections of the reaction d(t,n).sup.4 He and the energy loss rates of both the recoil deuterium, tritium particles and of the fission fragments were taken from the literature. (See applicants' report ANCR-1134 cited above and incorporated by reference herein.) Through use of computer techniques the process of equation 1 was evaluated between fission fragment energies of 0.005 MeV and E.sub.o. The contributions from the four possible reactions are not equal. Assigning average kinetic energy and mass to each of the two fission fragments: .sup.n 14 MeV/.sup.n thermal .sup.ff light.fwdarw..sup.d accelerated .sup..sup.+t stationary .fwdarw. 0.67 .times. 10.sup..sup.-4 .sup.ff heavy.fwdarw..sup.d accelerated .sup..sup.+t stationary .fwdarw. 1.48 .times. 10.sup..sup.-4 .sup.ff light.fwdarw..sup.t accelerated .sup..sup.+d stationary .fwdarw. 0.44 .times. 10.sup..sup.-4 .sup.ff heavy.fwdarw..sup.t accelerated .sup..sup.+d stationary .fwdarw. 0.98 .times. 10.sup..sup.-4 TOTAL 3.57 .times. 10.sup..sup.-4 ______________________________________ where .sup.ff light are particles of less than 118 atomic weight and .sup.ff heavy are particles of more than 118 atomic weight. These models show that the heavy fragment accelerating deuterons produces the greatest number of 14 MeV neutrons. While the mass of the fission fragments cannot be changed appreciably in thermal neutron fission, it might be expected that adjusting the ratio by volume of deuterium as compared to tritium would increase the yield. However, in the practice of the present invention an equal mixture of deuterium and tritium is preferred to provide the maximum yield. This occurs even though the number of accelerated deuterons is increased by enriching the gas with deuterium because that increase is offset by a corresponding decrease in the number of target tritons thus decreasing the total yield. The total yield is decreased by about 4% with a 40-60 or 60-40 mixture as compared to a 50-50 mixture of deuterium and tritium. A converter system with a 50-50 volume ratio of deuterium and tritium employed within the flux trap of a reactor such as the HFIR where a thermal driving flux of 3 .times. 10.sup.15 n/cm.sup.2 -sec is available will provide an approximately 14 MeV neutron flux of about 10.sup.12 n/cm.sup.2 -sec. Various other reactors such as the ATR (Aerojet Nuclear Test Reactor at Idaho Falls) that have thermal neutron flux of about 10.sup.15 n/cm.sup.2 -sec could also be used with a slightly decreased 14 MeV neutron flux of about 3 .times. 10.sup.11 n/cm.sup.2 -sec. A comparison of the present converter system installed within the ATR with other neutron sources is presented below in Table II. The comparison with LAMPF is uncertain at this time because absolute flux calculations and confirming measurements were not complete. TABLE II __________________________________________________________________________ COMPARISON OF FISSION FRAGMENT DRIVEN SOURCE WITH OTHER NEUTRON SOURCES NEUTRON FLUX (n/cm.sup.2 sec) Total Fast >10 MeV >14 MeV >20 MeV __________________________________________________________________________ FISSION FRAGMENT DRIVEN d+t neutron source a) from reactor fast spectra (ATR) 1/3 .times. 10.sup.15 1/3 .times. 10.sup.12 5/3 .times. 10.sup.9 10.sup.7 b) from d+t 3 .times. 10.sup.11 3 .times. 10.sup.11 3 .times. 10.sup.11 0 TOTAL 1/3 .times. 10.sup.15 2/3 .times. 10.sup.12 3 .times. 10.sup.11 10.sup.7 FISSION SPECTRA (example) 10.sup.15 10.sup.12 5 .times. 10.sup.9 3 .times. 10.sup.7 LAMPF 10.sup.13 - 10.sup.14 .about.10% of total few % of total still relatively high EBR-II 3 .times. 10.sup.15 7.7 .times. 10.sup.11 3.5 .times. 10.sup.9 2.2 .times. 10.sup.7 LLL (rotating target) .about.10.sup.12 0 .about.10.sup.12 0 __________________________________________________________________________ As can be seen from table II, the neutrons at about 14 MeV produced by fission are an insignificant contribution in comparison with that obtained from the fission fragment driven deuterons and tritons. More importantly it is seen that thermal neutron converter driven by fission fragments produces 14 MeV neutron flux several orders of magnitude above most other sources. The LLL high intensity source is one of the few practical sources for materials testing that is capable of producing 14 MeV neutron flux at a competing level with the fission fragment driven device of the present invention. It can be seen that the present invention provides a method of efficiently converting a thermal neutron flux to a high-level 14 MeV neutron flux for use as a CTR materials test device. By selecting a reactor that can produce 3 .times. 10.sup.15 thermal neutrons/cm.sup.2 -sec, approximately 10.sup.12 n/cm.sup.2 -sec, 14 MeV neutron flux can be generated. In a year, fluences in excess of 10.sup.19 n/cm.sup.2 can be provided. A device of this type is relatively uncomplicated and can be assembled within existing high flux reactors to enable CTR materials testing to be carried out without a great deal of development work. This method and device are also appreciable improvements over previous techniques which rely on reactions involving lithium to generate high energy neutrons.
053176065	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention was made as a result of detailed investigation of JP-A-57-18097. In this consideration, the present inventors found that this prior art involves three problems. A first problem is that in the prior art, when the BWR plant condition deviates from the operational limit condition, only action that is taken is to block the recirculation flow rate control system as a means for adjusting the reactor power, and therefore, the condition of deviation from the operational limit condition continues for a relatively long time (time until an operation plan is made to return to within the operational limit condition and an operation is performed according to this plan). A second problem is that when the plant condition deviates from the operational limit condition, it is necessary to minimize the time for making an operation plan to return to within the above-mentioned limit condition, and this necessity increases the burden of the people who devise a plan. A third problem is that when the operational limit condition is exceeded, only blocking the recirculation flow rate control system does not rule out a possibility that the reactor characteristics shift naturally to undesirable state, resulting in a scram of the reactor (automatic stop of the reactor by lowering of all control rods). These problems with the BWR plant will be described with reference to FIGS. 1 and 2. FIG. 1 is the result of analysis of the operation of the BWR plant, in which while the reactor power rose from the condition A by an increase in the core flow rate (substantially proportional to the recirculation flow rate), the reactor power, for some reason, deviated from the normal operation range and assumed the condition B in the operation-prohibited range, and the recirculation flow rate control system is blocked (the increase in the core flow rate is interrupted and the flow rate is held). Even though the core flow rate was held constant under the reactor power condition B, when the concentration of xenon, a fission product, for example, lowers, the reactor power went up. Therefore, the reactor power rose naturally from the condition B to the condition C, leaving a possibility of occurrence of a scram of the reactor. FIG. 2 shows the results of analysis of the operation of the BWR plant, in which owing to the decrease of the core flow rate caused by stoppage of some of the recirculation pumps, the conditions A shifted to the condition B of the reactor power unstable region in the operation-prohibited region. In this unstable region, due to the low core flow rate with respect to the reactor power, the reactor power sometimes changes even if the core flow rate does not change. In consequence, there is a possibility that the condition B shifts to the condition C, resulting in a scram of the reactor. The present inventors studied various schemes to solve the problem mentioned above. As the result of this study, this invention was made. The automation system of a nuclear power generation plant according to an embodiment of this invention will be described with reference to the accompanying drawings. FIGS. 3 and 4 show the composition of this embodiment. This nuclear power plant automation system comprises BWR plants 1, supervisory monitor and control units 2, recirculation flow rate control units 31, control rod operation control units 32 for automatic operation of the control rods, and an operation plan unit for assisting in the formulation of operation plans. This operation plan unit 4 provides assistance, when necessary, in the formulation of operation plans not only for one BWR plant but also for a plurality of BWR plants, such as BWR plant No. 1 and No. 2 in this embodiment, for instance. A BWR plant comprises a reactor pressure vessel 1A, a core 1B contained in the reactor pressure vessel 1A, control rods 1C inserted into the core 1B, a control rod driving unit 1D to operate the control rods 1C, and recirculation pumps 1E to supply cooling water to the core 1B. Reference numeral 1F denotes a main steam pipe, and 1G denotes a feed water pump. The operation plan unit 4 has a function to assist in the formulation of operation plans to be used after an operation was performed according to an operation plan under abnormal condition as well as in the formulation of operation plans under normal plant condition (for BWR plant start operation, stop operation, load follow-up operation, rated power operation, control rod pattern adjusting operation, etc.) For example, the plant engineers prepare operation plans by using this unit 4. The central monitor and control panel 5 is used by the operators to monitor and control the plants. To be more specific, using this central monitor and control panel 5, the operators monitor and control the plants to perform an operation according to an operation plan al formulated by the operation plan unit 4. As the control units in this embodiment, there are provided feed water flow rate control units and turbine control units, both not shown, in addition to the recirculation flow rate control units 31 and the control rod operation control units 32. The recirculation flow rate control unit 31 receives input plant data c1 obtained by measurement, such as the recirculation pump speed, neutron flux, and core flow rate and outputs a control signal b1 to control the number of revolutions of the recirculation pumps 1E. The control rod operation control unit 32 receives measured plant data c2 such as the neutron flux, control rod position, and so on and outputs a control signal b2 to the control rod driving unit 1D to operate the control rods. The supervisory monitor and control unit 2 outputs a target value e1 of recirculation pump speed (or flow rate) to the recirculation flow rate control unit 31 and an operation command e2 for lifting/lowering of control rods to the control rod operation unit 32 to make plant data d1 including reactor power and generator power coincide with the power specified in the operation plan in order to achieve an operation of the BWR plant according to an operation plan al (a2 for No. 2 BWR plant). This supervisory monitor and control unit 2 includes a function to prevent a scram of the reactor by automatically applying an operation plan under abnormal condition when the plant condition deviates from a normal operation range in addition to control functions to achieve an operation according to the operation plan a1. Specifically, the supervisory monitor and control unit 2 stores a plurality of operation plans under abnormal condition, which are executed when any of plant data a1 obtained by measurement at the BWR plant No. 1 (process quantities such as generator power, reactor power, neutron flux, flow rate, temperature, and temperature change rate, and data on the condition of equipment, such as the pumps, valves, and control rods) deviates from the normal operation range. Those operation plans under abnormal condition are related to automatic actions which are taken under abnormal plant condition such as to decrease the reactor power by a predetermined range or to a predetermined level by a decrease of the core flow rate (substantially equal to the recirculation flow rate) and/or by lowering of the control rods. The supervisory monitor and control unit 2 decides whether or not to apply an operation plan under abnormal condition according to plant data d1. When a decision is made that an operation plan under abnormal condition should be applied, the supervisory monitor and control unit 2 switches from the normal operation plan al to an operation plan under abnormal condition corresponding to the current condition, and outputs commands e1 and e2 to put this operation plan under abnormal condition into operation. The recirculation flow rate control unit 31, in response to a command 1, reduces the rotating speed of the recirculation pumps 1E and decreases the core flow rate. The control rod operation control unit 32 controls the lowering of the control rods 1C into the core 1B according to a command e2. In the manner described, automatic actions are taken under abnormal plant condition such as reducing the reactor power. After the operation was done according to the plan under abnormal condition, the engineers prepare an operation plan to increase the reactor power to return to a pre-existent power level. The prepared operation plan a1 is input into the supervisory monitor and control unit 2. The operator decides when to start a BWR plant operation according to the newly prepared operation plan. A command to start an operation is transmitted by the central monitor and control unit 2 to the supervisory monitor and control unit 2. The supervisory monitor and control unit 2 controls the BWR plant No. 1 by switching from the operation plan under abnormal condition to the new plan made by the operation plan unit 4. In the BWR plant No. 2, the central monitor and control panel, supervisory monitor and control unit, recirculation flow rate control unit and control rod operation control unit have substantially the same functions as those of plant No. 1. Description will now be made in greater detail of the operation plan unit 4, the supervisory monitor and control unit 2, and the control units 31, 32. (1) Operation plan unit In this section, description will be made of examples of a plan making procedure, computer software and operation plan. As shown in FIG. 4, the operation plan unit 4 includes a computer 15, a keyboard as an input means, a display unit 17, and a storage device 18. (i) Procedure of making an operation plan The operation plan unit 4 stores in the storage device 18 a basic procedure (plan formulation control program) for making or revising a plan for reactor power change by control rod operation and adjustment of the recirculation flow rate 8 or the core flow rate). As shown in FIG. 5, this procedure includes steps 10 to 14. An operation plan prepared by the operation plan unit 4 is registered as a standard operation plan, when necessary, in the plan making knowledge base of the operation plan unit 4. The operation plan unit 4 partially modifies this standard operation plan and makes a new operation plan which is carried out after an operation plan under abnormal condition is serves the purpose. How to make a new operation plan which is executed after an operation plan under abnormal condition has been executed will be described in the following. (a) The standard operation plans registered in the storage device 18 are shown on the display unit 17. The engineer specifies a standard operation plan similar to a target operation plan (a load follow-up operation plan, for example). The specified standard operation plan is read from the storage device 18. Let us suppose a case in which the generator power is changed in the standard operation plan. The engineer inputs a desired change pattern of generator power that he specified by an input device (Step 10). (b) Then, a reactor power with thermal efficiency taken into consideration is calculated, the dynamic characteristic of xenon concentration is predicted (Step 11), and a draft of a new operation plan is prepared which is related to the adjustment methods of the core flow rate and the control rod pattern (Step 12). The prediction of the dynamic characteristic of the xenon concentration at Step 11 is done by a core one-point-approximated simulator stored in the plan making knowledge base to be described later. (c) In order to evaluate the core characteristics in an operation of the BWR plant according to a draft of a newly-prepared operation plan (changes with time of power, flow rate, control rod pattern, core thermal characteristic), the core characteristics are predicted by a core three-dimensional simulator (a core characteristics analysis program to be described later) (Step 13). (d) The three-dimensional characteristics of the core, obtained by analysis, are shown on the display unit 17. The displayed reactor power, core flow rate, control rod pattern, and the core thermal characteristics are evaluated. If the evaluation result shows that the limit condition is satisfied, the engineer inputs "YES", and if not, he inputs "NO" from the keyboard 16. If a prepared operation plan is unsatisfactory (i.e., "NO" is input), the decision made at Step 13A is "NO", and the process proceeds to Step 14. Whereupon, data required for revision of the operation plan is input from the keyboard 16, and the Steps from Step 12 on are executed. If the decision at Step 13A is "YES" (i.e., the draft operation plan is judged satisfactory), the operation plan making process is finished. If necessity arises to revise the operation plan during an operation for changing the reactor power, it is possible to revise the operation plan by omitting some of the processes mentioned above. (ii) Basic composition of the system As mentioned earlier, the hardware of the operation plan unit 4 comprises a computer 15 for inference for plan making and for analysis of the core characteristics, a display unit 17, which is a graphic display unit, a keyboard 16 for entering data, and an interface for connection with other devices, such as a mouse, a printer and a plotter. An example of software of the operation plan unit 4 is shown in FIG. 4. This unit 4 assists the operator in preparing and revising operation plans by using knowledge engineering methods and a simulator for simulation of reactor characteristics. The software comprises a plan making knowledge base, a plan making control program, an inference process program, a screen display program, and a core characteristics analysis program. The outline of software will be described as follows. The inference process program, knowledge data editing program and knowledge base framing, which are supported by a knowledge process system construction support tool, are used. 1 Plan making knowledge base The plan making knowledge base stores data and C-programs used with the inference process program, such as the plan making procedure, limit condition, standard operation plan, prepared operation plans, and a simple simulator for evaluation of core characteristics (core one-point-approximated simulator), prepared by using metarules, rules, frames, methods and C-language programs. (a) Metarule The plan making procedure is expressed using a pattern of "if . . . then . . . ", and thereby groups of rules to be used are decided. FIG. 6 shows an example of a metarule. In an actual process, rules are used which correspond to the events in the conditional sections of this metarule. The events such as "plan making" and "plan check" are registered from the rules. If events are not registered in the view note in the beginning of inference, a metarule whose if section has an event "start" is applied. Those metarules are used in the inference at Step 12 of FIG. 5. (b) Rule Knowledge by which to decide the timing of core flow rate adjustment and control rod operation and knowledge by which to modify the plan making condition by interactive processing is expressed by rules each composed of a pattern of "if . . . then. The rules are stored divided into a plurality of groups of rules. The "if" section of those rules is a conditional section, while the "then" section is a conclusion section. Of those groups of rules, a group of rules decided by a metarule at Step 12 of FIG. 5 are used. By using those rules, a decision is made whether the reactor power is changed by core flow rate adjustment or by control rod operation, whether or not the reactor power is kept constant by doing both core flow rate adjustment and control rod operation simultaneously, whether or not an achievable reactor power is obtained when the core flow rate and the control rod pattern disobey the limit condition, among other decisions, at specified times of the day (Step 12). FIG. 7 shows rules of groups of plan making rules. The first rule, "rule.sub.-- f.sub.-- 3" means that if "the kind of plan is a load follow-up plan and the reactor power (current power) is 65% or less at the time when a plan is made, and is in the course of rising (the current power is greater than the power at the previous specified time (previous power) and smaller than the power at the next specified time (subsequent power)", then, "an event that a control rod (CR) pattern is searched (CR search) is issued." FIG. 8 shows rules of a group of CR search rules. The rule.sub.-- cr.sub.-- 1 means that if "a memo of CR search [off] (a flag indicating that the calculation of CR search has not been started) has been registered in the private memo", then, "a method (procedure oriented process) of CR search of a frame of plan is started, a memo of CR search [on] is registered, and a memo of CR search [off] is erased." The rule.sub.-- cr.sub.-- 2 means that if "a memo of CR search has been registered and the control rod pattern at the current time is greater than the upper limit value", then, "an achievable power is searched (POWER search)." The rules of a group of plan check rules are used to check if all operation plans have been checked at a certain point in time. (c) Frame Data including the plan making conditions, standard operation plans, newly-prepared operation plans and data of the core characteristics data base are stored in the form of frame. The procedure oriented processes peculiar to the respective frames are expressed by programs in C language called methods. FIG. 9 shows an example of frame. The upper frame includes data related to the operation plan making conditions, wherein the upper limit of the core flow rate is 102% and the lower limit is 88%. The lower frame indicates data used in making operation plans, which includes the reactor power, core flow rate, control rod pattern, and data obtained by inference. In FIG. 9, the "flow rate" is "core flow rate", "CR" is "axial direction of control rods", and "power" is "reactor power." This frame stores data entered at Step 10 (e.g., a type of specified standard operation plan (e.g., a load follow-up plan) and data on reactor power according to a power-changed plan. FIG. 10 shows a frame which includes the results of planning such as the reactor power, core flow rate, control rod pattern at specified times. (d) Program This program executes general-purpose procedure-oriented processes such as a simulator for evaluation of core characteristics. The simulator for evaluation of the core characteristics is a core one-point-approximated simulator, which is a simplified simulator. Draft operation plans related to the reactor power, core flow rate, and control rod pattern are prepared by use of the core one-point-approximated simulator. The reason for using the above-mentioned simplified simulator is to avoid a problem that necessary rules amount to a very large number, if one tries to find values which are obtained quantitatively such as the core flow rate, control rod pattern and xenon concentration. When a core one-point-approximated simulator is used to determine the values of the reactor power P, the core flow rate F and the control rod pattern CR, the values of two variables are set and the remaining variables are determined. For example, an operation in which values of the reactor power P and the core flow rate F are set and the control rod pattern CR is found is referred to as a CR search. The values of MFLCPR as a core thermal characteristic (=limit value of minimum critical power rate MCPR/MCPR) and MFLPD (=maximum linear heat generation rating MLHGR/limit value of MLHGR) cannot be obtained with high accuracy unless they are calculated by the core three-dimensional characteristics analysis simulator (e.g., a core characteristics analysis program, for example). However, since these data are required as reference data when an approximation operation plan is made by using a core one-point-approximated simulator, a simplified formula obtained by statistical processing of data analyzed in advance is used. 2 Plan making control program This program controls the start and stop of the inference process and what screen images to show on the CRT, and has a procedure of FIG. 5. The plan making control program controls an inference process program, a screen display program, etc. by executing the procedure of FIG. 5. 3 Screen display program This program shows a prepared operation plan on the CRT and permits processing by interaction with the user. 4 Inference process program This program is provided by a knowledge process tool, and enables inference of the control rod pattern and the values of the core flow rate by using knowledge (rules) stored in the knowledge base. This inference process program is used particularly at Step 12 of the plan making control program. 5 Knowledge base editing program This program is provided by the knowledge process tool, and is used to edit, debug and compile the knowledge base. 6 Core characteristics analysis program This program analyzes the core three-dimensional characteristics, and outputs power distribution and core thermal characteristics. This core characteristics analysis program is used at Step 13 of FIG. 5. 7 Data editing program This program edits input data for analysis of core characteristics, and also edits results of analysis for display on the CRT. 8 Operation data input program This program inputs operation data of the BWR plant (plant data d1). Data is used to make and revise the operation plans. 9 Core characteristics data base This data base stores core characteristics analysis result obtained by the core characteristics program and operation data. (iii) Concrete examples of inference at Step 12 Referring to FIG. 11, description will now be made of an example of operation plan made by inference by using knowledge mentioned above. In this example, as shown at the upper right end (draft operation plan) of FIG. 11, a decision is made that the reactor power rises caused by lifting the control rods at time i when raising the reactor power by a load follow-up operation, and a control rod pattern (current CR value) is found (a pattern of control rods CR is searched). At Step 12, an inference process program is executed. The inference procedure of this program is as shown below. 1 Since an event "plan making" has been registered in the unit queue of the view note of the operation plan unit 4, a metarule having "plan making" at its "if" section is searched. As a result of this, a decision is made to apply a group of plan making rules. When inference is made at Step 12, if no event has been registered at the unit queue of the view note, rules of a group of condition setting rules specified in the "then" section of a metarule having "start" in its "if" section is applied. Of those rules, an event (e.g., plan making) set in the conditional section of a rule having, in its "if" section, information (e.g., revision of a standard operation plan) based on data input at Step 10 is registered in the view note. 2 The rule-f-3 of a group of plan making rules includes data related to operation plan making conditions registered in the frame, that is, data indicating that the kind of operation plan is a load follow-up plan, that the current power is 65% or less, and that the power is in the process of rising. Therefore, the conclusion section "CR search" of the rule.sub.-- f.sub.-- 3 is registered in the unit queue. 3 Since an event "CR search" has been registered in the unit queue, and according to a metarule having "CR search" in its "if" section, a decision is next made to apply a group of CR search rules. 4 The rule.sub.-- cr.sub.-- 1 of a group of CR search has in its "if" section a memo of CR search [off] registered in the private memo of the view note (a flag indicating that the calculation of CR search has not been started). Therefore, the "then" section of the rule.sub.-- cr.sub.-- 1 is executed. A method of "CR search" of the frame "plan" is started. This method calls research (i) which is a program in C language, calculates the control rod pattern and the core flow rate at time i, and stores the calculation result in a slot celled the current CR in the frame. In this manner, the control rod pattern and the core flow rate with respect to the power pattern specified at Step 10 are decided, and a draft operation plan of the reactor is prepared. This operation plan is evaluated as it goes through the core characteristics prediction at Step 13 and the decision at Step 14, and if this decision is "YES", the operation plan becomes an official one. The above-mentioned program is a core one-point-approximated simulator. (iv) An example of operation plan prepared An example of operation plan prepared by the operation plan unit 4 is an operation plan used to restart the BWR plant after the plant was stopped owing to lightning, for example. An example of CRT display screen by this operation plan is shown below. The power change pattern shows changes with time of the generator power and the reactor power. FIG. 12 shows an example of displayed power change pattern. In this example, a restart operation is started at time 20:00. The reactor is made to reach its critical level in about one hour, and the temperature and the pressure of the reactor are raised to the rated values in about one hour. Then, the reactor power is increased to the rated value in about six hours. FIG. 13 shows changes with time of the core flow rate and the control rod pattern to achieve the operation plan mentioned above. In FIG. 13, the values of the control rod pattern correspond to the reactor power when the core flow rate is at the rated value and the xenon concentration is in equilibrium, and comply with the value x in the so-called x% control rod pattern. The increase in the control rod pattern is caused by lifting the control rod pattern, while the decrease in the control rod pattern is caused by lowering the control rods. In this operation plan, the core flow rate shows decreases at times 4:00 and 7:00 and is likely to violate the limit condition. Therefore, with the reactor power maintained at a fixed level, the control rods are inserted (to decrease the values of the control rod pattern) and the core flow rate is increased. In other words, the core flow rate adjustment and the control rod operation are scheduled to be used at the same time. As shown in FIG. 14, the operation plan table includes the items of an operation plan such as the generator power, reactor power, control rod pattern, and the core flow rate, and also the core thermal characteristics at this time, such as MFLCPR and MFLPD. By looking at the CRT screen, the user can accurately grasp the changes in the quantities of state of the reactor. FIG. 15 shows an example of operation route showing the relation between the reactor power and the core flow rate. This diagram indicates that it is possible to abide by the limit condition without letting the relation between the power and the flow rate enter the operation-prohibited region. FIG. 16 shows an example of analysis result of the core characteristics according to this operation plan by using a three-dimensional simulator. This example shows the control rod lifting positions and the axial average power distribution, by which you can decide whether or not an operation which satisfies the limit condition is possible and see if there is any problem in the power distribution. An operation plan under normal condition which has been made by the operation plan unit 4 and for which no problem with the core characteristics has been confirmed by the three-dimensional simulator is input by the BWR plant operator into the supervisory monitor and control unit 2. This input may be done automatically. The result of simulation by the three-dimensional simulator is shown on the display unit 17. (2) Supervisory monitor and control unit FIG. 17 shows the composition of the supervisory monitor and control unit 2 and its relation with control units 31 and 32. An operation plan al prepared by the operation plan unit 4 is stored in the storage means 25 of the supervisory monitor and control unit 2. In order to achieve a reactor operation according to the operation plan a1, a normal-condition operation plan output section 21 outputs a control command m (a reactor power target value (or a generator power target value) and commands for power control by core flow rate adjustment, power control by control rod operation or power control by both) corresponding to the current plant condition to a reactor power control arithmetic section 24 through a control mode changeover section 23 when the plant condition is within the normal operation range and is normal. To make the reactor power (or the generator power) measured at the plant 1 coincide with a reactor power target value included in the control command m, the reactor power control arithmetic section 24 calculates and outputs a target value e1 of the recirculation pump speed and a command e2 for control rod operation (commands for lifting/lowering/operation interruption, etc.). The supervisory monitor and control unit 2 has a plurality of operation plans under abnormal condition, which will be described later, stored in storage means 26. The abnormal-condition operation plan output section 22 decides whether or not to apply an operation plan under abnormal condition by receiving plant data d1. The abnormal-condition operation plan output section 22 executes the procedure (Steps 27A to 27F) of FIG. 18, that is, selects an operation plan under abnormal condition (Step 27A) and decides whether or not to apply this plan (whether the plant condition deviates from the normal operation range) (Step 27B). When a decision is made that the operation plan under abnormal condition should be applied (i.e., the plant condition deviates from the normal operation range), the operation plan under abnormal condition is registered independently (Step 27C). At Step 27E, a decision is made whether or not an operation plan under abnormal condition, registered at Step 27C, is present. If there exists an operation plan under abnormal condition to be applied, the decision at Step 27E is "YES", the control mode changeover section 23 is switched to the abnormal-condition operation mode, and an operation plan under abnormal condition to be applied is output to the reactor power control arithmetic section 24 (Step 27E). By making a decision of whether or not to apply an operation plan under abnormal condition with a period of one second for example, when the plant condition deviates from the normal operation range, an automatic action for this condition can be taken instantly. A concrete example of an operation plan under abnormal condition will be described. FIGS. 19 to 21 show examples of operation plans under abnormal condition. Those operation plans are stored classified into groups of different operation modes, such as those in operation mode of reactor power of about 10% or more and those in reactor start operation mode with a reactor power of less than 10%. This obviates the need to make decisions of whether or not to apply operation plans under abnormal condition, which do not match the current plant condition in the least, so that time for decision can be reduced. An operation plan of No. 1 in FIG. 19 is for an automatic action to be taken when the operating point related to the reactor power and the reactor flow rate comes into the operation-prohibited range (i.e., the operation range is not abided by). As shown in FIG. 22, this operation plan is to interrupt the increase in reactor power when the operating point reaches the rod block line, decrease the core flow rate to reduce the reactor power by 10% when the rod block line is exceeded by more than predetermined value, and to insert the control rods to reduce the reactor power by another 10% when the operating point comes very close to the reactor scan line. An operation plan under abnormal condition of No. 2 in FIG. 19 is for an automatic action to be taken when the operating point related to the reactor power and the core flow rate comes into the unstable range, and inserts the control rods to reduce the reactor power to 25%. An operation plan of No. 3 in FIG. 19 is for an automatic action to be taken when a reactor feed water pump trips. This operation plan reduces the reactor power to at least 75% when the reactor power is 50% or more, one of the two turbine-driven feed water pumps trips, and a stand-by feed water pump starts to run, and reduces the reactor power to 50% when the stand-by feed water pump does not start. An operation plan under abnormal condition of No. 4 in FIG. 20 is for an automatic action to be taken when the core thermal characteristics are abnormal. No. 5 in FIG. 20 is an operation plan under abnormal condition for an automatic action to be taken when the power system frequency rises abnormally. No. 6 of FIG. 21 is an operation plan under abnormal condition for an automatic action to be taken when the value of the start region neutron monitor shows an abnormal rise. No. 7 of FIG. 21 is for an automatic action to be taken when the reactor temperature rise rate goes up abnormally. NO. 8 of FIG. 21 is an operation plan under abnormal condition for an abnormal increase of the value of the output region neutron monitor which occurs when the reactor is being started. Among those operation plans under abnormal condition are plans to automatically reduce reactor power by a predetermined range (e.g., 10%) to a predetermined level (e.g., 80%) (3) Operation of the automation system Description will be made of the operation of the automation system according to this embodiment when an operation plan under abnormal condition described above is applied. FIG. 23 shows an example of analysis result of the operation which is carried out when the operating point related to the reactor power and the core flow rate deviates from the normal operation range. This example corresponds to the prior art of FIG. 1. Let us suppose that in FIG. 23, when the reactor power was rising from the condition A to the condition B according to a normal operation plan al, the operating point deviated from the normal operation range (block line) and the operating point went into the operation-prohibited region for some reason. The supervisory monitor and control unit 2 executes the process of FIG. 18. More specifically, the abnormal-condition operation plan output section 22 decides whether or not to apply an operation plan under abnormal condition, and if the plan output section 22 finds it necessary, the control mode changeover section 23 switches the mode to the abnormal-condition operation mode. In an example of an operation under abnormal condition (as shown in FIG. 23), the reactor power control arithmetic section 24 automatically interrupts the rise of the reactor power (to be more precise, interrupts the increase in the core flow rate and the lifting of the control rods) according to the operation plan under abnormal condition of No. 1 in FIG. 19. If the deviation from the normal operation range becomes large and the operating point comes closer to the scram line, the reactor power is automatically decreased 10% by reducing the core flow rate. In other words, the plant condition automatically shifts from the condition B to the condition D within the normal operation range. When the plant condition becomes the condition D, the plant condition is not deviating from the normal operation range. Therefore, the abnormal-condition operation plan output section 22 switches the control mode changeover section 23 to the normal operation mode. Since an operation plan under normal condition which causes a change from the condition D to the condition F is not stored in the storage means 25, the condition D is maintained. Then, the operation plan unit 4, as described above, makes a new operation plan al to move the plant condition from the condition D after the operation plan under abnormal condition was executed, pass through the condition E and reaches the condition F. In compliance with this new operation plan, the reactor power control and arithmetic section 24 starts an operation to increase the reactor power to the condition F. The operation plan unit 4 may be said to make a new operation plan (to go back to the previous operation) to return from the finished condition of the operation according to an operation plan under abnormal condition to a normal operating condition before the plant condition deviated from the normal operation range. FIG. 24 shows the operation of an embodiment of this invention when the operating point of the BWR plant went into the unstable region. This example corresponds to the prior art of FIG. 2. In FIG. 24, if the plant condition moves from A to B for some reason, the BWR plant will be operated according to an operation plan under abnormal condition of No. 2 of FIG. 19. Specifically, the control rods are lowered, thereby automatically reducing the reactor power to 25%, so that the condition of the BWR plant moves to the condition D in the normal operation range. Thereafter, the operation plan unit 4 makes a new operation plan to move the plant condition from D to E, E to F, and F to G. According to this new operation plan, the reactor power is raised from D to G. Suppose that while the BWR plant is operated at 100% of the reactor power, one of the two feed water pumps tripped, and an event of the stand-by feed water pump's failure to start occurred. In this case, the second operation plan under abnormal condition of No. 3 in FIG. 19 is applied and the plant condition changes as shown in FIG. 25. If abnormality mentioned above occurs in the feed water pump, the reactor water level lowers, but the recirculation pump speed (or the core flow rate) is reduced and the reactor is decreased to 50%, so that the flow rate of steam generated by the reactor can be decreased. As a result, the reactor water level does not go down to a set value of scram and therefore, a scram of the reactor can be avoided. After automatic actions under abnormal condition mentioned above are finished, the feed water pump is investigated to find the cause of the abnormality and maintained. Then, the operation plan unit 4 makes a plan to bring the reactor power, for example, from about 50% to 100% of the rated value, at which the plant was operated previously. However, it is difficult to estimate time for the investigation and maintenance in advance. For this reason, it is difficult to make ready an accurate operation plan which conforms to the reactor power which changes with time. Therefore, it is necessary to make a plan for changing the reactor power by adjusting the core flow rate and controlling the control rods in accordance with the change in the xenon concentration of the reactor. FIGS. 26 and 27 show examples of new operation plans, which are used after an operation under abnormal condition was performed. New operation plans are made by the operation plan unit 4. In those plans, the reactor power was scheduled to be maintained at 100% of the rated power, but the reactor power dropped to 50% as shown in FIG. 25. To rectify this power drop, an operation plan was made to start to increase the reactor power and the generator power from time 24:00 and raise to the rated power at time 1:00. As shown in FIG. 27, changes with time of the core flow rate almost equal to the recirculation flow rate and the control rod pattern are not necessarily simple. In those new operation plans, the plant is scheduled to be operated at time 5:00 by carrying out an operation of jointly using the core flow rate adjustment and the control rod operation while the reactor power is maintained constant and performing an operation of conducting the core flow rate adjustment and the control rod operation separately at time other than the above-mentioned time. In order to achieve an efficient operation abiding by the operation standard, it is necessary to make appropriate operation plans as described. New operation plans al for normal condition, made by the operation plan unit 4 as described, are registered by the operator or the engineer in the storage means 25 of the supervisory monitor and control unit 2. And, the mode changeover section 23 switches the operation mode to the normal operation mode. Now, the BWR plant can be operated according to a new operation plan as shown in FIG. 26 or 27. According to an embodiment of this invention described above, various kinds of abnormality of the BWR plant can be dealt with automatically to avoid a scram of the reactor, thereby improving the operating rate of the BWR plant. Another effect of this invention is as follows. It is possible to efficiently make an operation plan to return to the pre-existent operating condition after an automatic operation has been done according to an operation plan under abnormal condition, and carry out the return operation plan in a short time. Therefore, it is possible to improve the BWR plant operating rate and operation reliability, alleviate the burden on the operators and engineers, and reduce the labor requirement for operation. In this embodiment, knowledge engineering methods are used in making and revising operation plans. Therefore, yet another effect is that adequate operation plans can be made and revised efficiently which are based on specialized knowledge about the formulation of operation plans. The values of the xenon concentration, core flow rate, control rod pattern, etc. are determined quantitatively by using both knowledge (rules) and a simplified core simulator. Therefore, the number of items of knowledge required is far smaller than the case where the values are determined quantitatively only by knowledge. In this embodiment, operation plans under abnormal condition, which are decided by the supervisory monitor and control unit 2 whether they are adopted or not, are limited in number according to the reactor conditions (to be more precise, operation modes). Therefore, this invention provides a still further effect that decision can be made in a short time. According to this embodiment, in addition to an operation of separately changing the core flow rate and the control rod positions, an operation of simultaneously changing these items (i.e., the core flow rate adjustment and the control rod operation are performed jointly) is performed. By this jointly-controlled operation, it is possible to carry out an operation of maintaining the reactor power at a constant level while abiding by the limit condition of the core flow rate. Therefore, the reactor power need not be reduced unnecessarily, so that this contributes to an improvement of the operating rate of the BWR plant. If the thermal characteristics of the core become abnormal by disobeying the operation standard, the reactor power is reduced automatically to bring the plant condition to a condition satisfying the operation standard. Consequently, the condition of disobeying the operation standard does not last for a long time, so that the plant can be operated safely. In an embodiment of this invention mentioned above, description centered on the start operation of the BWR plant, this invention can be applied to other operations, such as a stop operation, load follow-up operation, rated power operation, and control rod pattern adjusting operation. An embodiment of this invention which is applied to a load follow-up operation will now be described. FIGS. 28 and 31 show examples of load follow-up operation plans. FIG. 28 shows a power change pattern in a load follow-up operation, prepared by the operation plan unit 4. In this example, the generator power is reduced to 50% during the night from time 23:00 to 7:00, the power then is scheduled to be brought back to 100% of the rated value. FIG. 29 indicates an operation plan for changes with time of the core flow rate and the control rod pattern to achieve the above-mentioned power change pattern. In this operation plan, the core flow rate is adjusted according to changes in the reactor power and the xenon concentration. However, the reactor power cannot probably be controlled only by adjustment of the core flow rate (i.e., the limit condition for the core flow rate is disobeyed. So, the control rods are also operated. The decrease in the values of the control rod pattern corresponds to lowering of the control rods, while the increase in the values of the control rod pattern corresponds to lifting of the control rods. In this embodiment, the operation plan is arranged such that the plant is operated to maintain the reactor power at about 50% while the control rods are lifted and the core flow rate is decreased simultaneously at about time 7:00 and on the other hand, the plant is operated to maintain the reactor power at about 100% by lowering the control rods and increasing the core flow rate simultaneously at about time 10:00. FIG. 30 shows the power, core flow rate, control rod pattern, and the thermal characteristics of the core at specified times. The limit condition for MFLCPR and MFLPD, which are the thermal characteristics of the core is to maintain the value at 1.0 or less. This operation plan has enough allowances with regard to the limit condition. FIG. 31 shows the operation route in relation to the reactor power and the core flow rate, and indicates that the plant can be operated by complying with the operation standard without allowing the relation between the reactor power and the core flow rate to go into the operation-prohibited region. Normal operation plans made by the operation plan unit 4 as described are input by the operator or engineer of the BWR plant into the supervisory monitor and control unit 2. A load follow-up operation is almost the same as the reactor output operation mode in an start operation of the BWR plant described earlier. Therefore, an operation plan under abnormal condition is substantially the same as an operation plan under abnormal condition in the reactor power operation mode in FIGS. 19 and 20. Therefore, the operation of the supervisory monitor and control unit 2, the control units 31, 32, and the operation plan unit 4, which takes place when the plant condition deviates from the normal operation range in a load follow-up operation is substantially the same as in the plant start operation mode described above. The effects of this embodiment are the same as the effects of embodiments intended for the plant start operation described above. In the foregoing embodiments, description has been made of the cases in which there are provided a plurality of control units, such as a recirculation flow rate control unit, control rod control unit, feed water flow rate control unit, and turbine control unit. Those control units may be realized by a single control unit. In this case, the same effects can be obtained as in the embodiment of FIG. 3. The function of the supervisory monitor and control unit 2 may be realized by those control units. Also in this embodiment, the same effects can be obtained as in the embodiment of FIG. 3. As another embodiment of this invention, it is possible to apply this invention to a pressurized water reactor (PWR). In this embodiment, a control rod operation control unit is used in place of the recirculation flow rate control unit in a BWR plant, and a boron concentration control unit is used in place of the control rod operation control unit in a BWR plant. Still, by this embodiment, it is possible to automatically deal with various kinds of abnormality in the plant and thereby improve the operating rate of the plant. Furthermore, according to this embodiment, an operation plan to return to the previous operation is made after an operation plan under abnormal condition has been executed, and this return operation can be started in a short time, so that it is possible to improve the plant operating rate, lessen the burden on the operator and the engineer, and achieve labor savings in operation. Those effects are the same as in a BWR plant. In the foregoing embodiments, normal operation plans are made after the plant condition has become abnormal, but time for making and revising operation plans need not be limited to such a timing. In other words, the engineer at the site of the plant may, when necessary, prepare and revise normal operation plans on receipt of a command from the central load-dispatching office or according to monitor results of the plant condition. According to this invention, when the condition of a nuclear power generation plan deviates from the normal operation range, the reactor power can be reduced automatically by a predetermined value or to a predetermined level, thus preventing a scram of the plant. Therefore, the plant operating rate can be improved. On the other hand, an operation plan to return to the previous operating condition can be prepared efficiently and this return operation can be started in a short time. Therefore, the plant operating rate can be improved, the burden on the operator and the engineer can be lessened, and labor for operation can be reduced. When the core thermal characteristics or the like deviate from the normal operation range, the reactor power is decreased automatically, allowing the plant condition to move into to a condition satisfying the operation standard. Hence, the condition disobeying the operation standard does not last long, so that the plant can be operated safely.
043280714	summary	This invention relates to a device for guiding ducts assigned to a rotatable component. It is known that, in certain types of liquid-metal cooled fast nuclear reactors, the reactor vessel containing the core, the liquid metal coolant (usually consisting of sodium) as well as the primary pumps and primary heat exchangers in the integrated type is closed at the top by a concrete slab or shield roof. For operations involving loading and unloading of fuel assemblies constituting the reactor core, the shield roof is in fact fitted with a large rotating shield plug whose axis coincides with the axis of the reactor vessel and the axis of the reactor core, and a small shield plug rotatably mounted with respect to the large rotating plug about an axis which is displaced off-center with respect to the axis of said large rotating plug. Moreover, a so-called "core lid" structure is suspended beneath the small rotating shield plug in the immediate vicinity of the top face of the reactor core. Moreover, in order to check the correct operation of a fast reactor, it is known that provision is made for a very large number of measuring, control or monitoring instruments placed within the reactor core lid. These instruments consist of temperature and pressure sensors, instruments for measuring neutron flux, instruments for detection and location of can failures and so forth. As will readily be apparent, the complete assembly consisting of such sensors and instruments is connected to electric conductors for supplying current to these devices and for transmitting the data recorded by these latter. In addition, provision must also be made for tubes which supply these different devices with liquids or fluids of various types. In other words, a large number of these sheathed conductor cables or tubes must be assigned to the small rotating shield plug. This is the meaning which must be given to the term "duct" which will be employed in the following description and in the appended claims and which includes both cables and tubes. The problem which arises is clearly that of guiding said tubes between the small rotating shield plug and the recording or supply devices which are placed outside the reactor vessel but are therefore rigidly fixed to the stationary portion of the shield roof. In other words, the problem to be solved lies in the need to guide said cables and tubes which start from a fixed point and must arrive at one point of the small rotating shield plug. In point of fact, this small plug is rotatable with respect to the large plug which is in turn rotatable with respect to the shield roof. This problem is clearly made even more complex by the very large number of ducts involved (tubes or electric conductors) which result in a not-negligible degree of stiffness of the complete assembly. It is clearly necessary to guide these ducts while making it possible, without any attendant risk of damage, to subject them to the very large number of operations both of the small and large rotating shield plugs during refuelling operations. In the techniques of the prior art, supply of electric current and of fluid to devices attached to the small rotating shield plug was carried out by making use of a flexible cable connection. The systems employed consisted of circular hoods located above the rotating shield plugs and having approximately the same diameter as these latter. The cables or tubes were first connected to a stationary junction of the hood so as to form a large loop within the interior of this latter, then passed through a movable junction or a stationary junction connected to a movable portion of the hood. The cables extended vertically to connectors which were rigidly fixed to the small rotating plug. The loop provided the necessary slack to ensure that the movable junction was capable of following the combination of displacements of the small and large rotating plugs, thus maintaining the downwardly extending portion of the cables or supply tubes in a vertical position. The disadvantage of this solution lies in the fact that it is highly cumbersome and takes up a large volume above the seal plugs. This is a major drawback since the small and large rotating shield plugs are already obstructed by a large number of devices related to the operation of the nuclear reactor and replacement of a duct is consequently a matter of considerable difficulty. However, the field of application of the present invention is not limited in any sense to a nuclear reactor provided with two eccentric rotating shield plugs. The invention is generally applicable to the penetration of a bundle of cables through a rotating component, the other end of the cables being stationarily fixed with respect to the rotating component. In its application to fast reactors, this invention relates to a device which serves to guide cables and tubes assigned to the small rotating shield plug and makes it possible to free almost entirely the internal space located above the small and large rotating shield plugs. In all of its embodiments, the invention relates to a device which makes it possible to carry out tens of thousands of helical rotations of cables and tubes without producing any failure at angles of rotation of the rotating component of plus or minus 220.degree. with respect to the rest position. In order to obtain this result, the invention consists of a device for guiding ducts designed to pass through a movable component which is capable of rotational motion about a vertical axis. Said device essentially comprises means for supporting said ducts between a fixed point located externally of said component and a second point located on a vertical axis which coincides with the axis of rotation of said movable component and constitutes the extremity of the supporting means. The device further comprises means for guiding those portions of ducts which are placed between the extremity of said supporting means and the center of rotation of said movable component. Said guiding means are adapted to maintain said portions of ducts in uniformly spaced relation on a ruled surface of revolution about the axis of said movable component so that said portions of ducts thus form a bundle-type assembly. Means are further provided for securing the lower extremity of said guiding means to said movable component at the center of rotation thereof. As already mentioned, the invention is applicable in particular to nuclear reactors of the double rotating shield plug type. The stationary component in that case is the small rotating shield plug. Preferably, the means for supporting the cables or ducts consist of two articulated horizontal arms. In a first embodiment, the device essentially comprises a hanger rigidly fixed to said small shield plug and comprising a vertical column and a horizontal arm, the free extremity of said hanger arm being located on the axis of said small rotating shield plug. The device further comprises a first horizontal guiding arm articulated at one end with respect to a fixed point of the reactor, and an second horizontal guiding arm having one extremity which is pivotally attached to the free extremity of said first guiding arm. Means are provided for controlling the pivotal motion of the first arm with respect to the fixed point and the pivotal motion of the two guiding arms with respect to each other in such a manner as to ensure that the free extremity of said second guiding arm is caused to remain in the axis of said small rotating shield plug. The ducts aforesaid are fixed along said two guiding arms and along the horizontal arm of the hanger. Means are also provided for guiding portions of said ducts which are located between said hanger arm and said second guiding arm so as to maintain said portions of ducts in uniformly spaced relation on a ruled surface of revolution about the axis of said small rotating shield plug so that said portions of ducts thus form a bundle-type assembly. Preferably, the guiding means aforesaid consist of a plurality of circular plates forming a bottom guide-plate rigidly fixed to the extremity of the hanger arm, a top guide-plate rotationally coupled to the free extremity of the second guiding arm but capable of free vertical translational motion with respect to this latter, and at least one intermediate guide-plate. The portions of ducts aforesaid are fixed at uniform intervals on the periphery of said guide-plates. Means are provided for maintaining said guide-plates horizontal and centered on the axis of said small rotating shield plug. Provision is also made for means whereby the angle of rotation of the top guide-plate with respect to the bottom guide-plate at the time of pivotal motion of the guiding arms and of the rotating shield plugs is uniformly distributed between the guide-plates as a function of the vertical distances between said guide-plates, a degree of slack being left in the ducts between the top guide-plate and the second guiding arm. According to another distinctive feature, said top guide-plate is rigidly fixed to the extremity of the second guiding arm by means of a variable-length unit which exerts a constant force directed along the axis of said small rotating shield plug and provides a rotational coupling. Preferably, said unit is a jack having an operating rod disposed along the axis of said small rotating shield plug and rigidly fixed to said top guide-plate, the jack body being rigidly fixed to the extremity of said second guiding arm. According to another preferred distinctive feature, the guide-plates aforesaid are connected to each other by a plurality of cables having the same length, each cable being attached at the upper end thereof to the top guide-plate and at the lower end thereof to the bottom guide-plate, said cables being so arranged as to pass through the intermediate plates aforesaid and being fixed on these latter. In an improved embodiment, the hanger aforesaid is in turn capable of rotational motion about the vertical axis of its column by means of an actuating device. In this case, the device according to the invention is distinguished by the fact that said column is stationary and that said hanger arm is pivotally mounted at the upper extremity of said column, the portions of ducts which extend along said column being attached to the periphery of the second circular guide-plates which are similar to the first guide-plates, said second top guide-plate being rigidly fixed to said arm by means of resilient devices which produce a force in the vertical direction, a degree of slack being left in the ducts between said second top guide-plate and said hanger arm generating a vertically-directed force, with some slackness in the ducts between said second upper plate and said beam. In a first alternative embodiment, the hanger is dispensed with or, in other words, the bottom guide-plate is directly fixed on the small rotating shield plug and the center of the guide-plate corresponds to the axis of rotation of the small shield plug. In a second alternative embodiment, the guiding means consist of a vertical guiding mast rigidly fixed at the lower end to the center of the small rotating shield plug and at the upper end to the free extremity of the supporting means; a horizontal top guide-plate rotationally coupled to the free extremity of said supporting means but capable of free vertical translational motion and surrounding said mast; a horizontal bottom guide-plate surrounding said mast and rigidly fixed to the lower end of said mast; and at least one intermediate guide-plate surrounding said mast and capable of free translational motion in the direction of said mast, said intermediate guide-plate being partially free for rotational motion about said mast. Each guide-plate is provided at the periphery with uniformly spaced means for fixing the cables aforesaid. The intermediate guide-plate or each intermediate guide-plate is provided with means for limiting rotational displacement about the mast so as to ensure that the angle of rotation between the top guide-plate and the bottom guide-plate is uniformly distributed between the intermediate guide-plate or plates.
	summary
	abstract	Providing a roaster that operates at temperatures in the range of 800° Celsius to 2000° Celsius with inert, optional oxidizing and reducing gases to treat graphite contaminated with radionuclides including tritium, carbon-14, and chlorine-36. The combination of temperatures and gases allow for the removal of most to substantially all the carbon-14 within the graphite while substantially limiting gasifying the bulk graphite.
047754958	abstract	The process of the present invention comprises adding an alkaline earth metal hydroxide such as barium hydroxide to a radioactive liquid waste containing sodium sulfate as the main component to convert the latter into an insoluble alkaline earth metal salt such as barium sulfate, adding silicic acid to by-product sodium hydroxide to prepare water glass and solidifying the radioactive insoluble alkaline earth metal salt with the water glass. According to this process, exudation of radioactive substances from the solid can be prevented and the solid having a high durability can be obtained at a low cost.
053389417	claims	1. A method of making a radiation shielding container for irradiated nuclear-reactor fuel elements, comprising the steps of: (a) casting a spherulitic cast iron container body to form surfaces, said container body having a recessed seat for a cover and a cover is received in said seat, said surfaces having open pores in the cast iron; (b) coating said surfaces with particles of a metal or metal alloy selected from the group which consists of nickel, nickel-based alloys, and austenitic nickel/chromium stainless steels and of a particle size smaller in diameter than the diameter of said pores, thereby filling said pores with said particles; and (c) applying a laser beam upon said particles and said surfaces to at least partially fuse said particles to form a particle melt and bond said particles together and to said surfaces. 2. The method defined in claim 1 wherein said surfaces are coated with said particles in the form of a layer of powder producing a powder melt upon applying of the laser beam thereon to partially fuse said particles. 3. The method defined in claim 1 wherein said surfaces are coated with said particles in the form of a layer of powder producing a droplet melt upon applying of the laser beam thereon to partially fuse said particles. 4. The method defined in claim 1 wherein said particles are applied to said surfaces in at least one layer of a thickness up to about 200 micrometers. 5. The method defined in claim 4 wherein said layer is applied to said surface in a thickness of about 100 micrometers. 6. The method defined in claim 1 further comprising the step of mechanically abrading the surfaces before the coating thereof with said particles. 7. The method defined in claim 1 wherein said laser beam is applied on said surfaces with a back and forth movement fusing said particles to said surfaces. 8. The method defined in claim 7 wherein said particles are applied to said surfaces with a powder spray.
	claims	1. A nuclear fuel assembly for a boiling water reactor comprising:a base,a head, anda bundle of full length fuel rods and partial length fuel rods, the bundle extending upwardly and longitudinally from the base to the head,at least one clamp for longitudinally retaining a lower plug of a partial length fuel rod with respect to the base, the clamp being an additional part fitted to the base, the clamp being assembled to the base by mechanical engagement of complementary assemblies, the clamp being embedded in a housing provided in the base such that the clamp is entirely below an upper surface of the base and entirely above a lower surface of the base, the housing consisting of a hole formed in the base, the clamp being comprised in the hole, wherein the clamp comprises elastic retaining tabs, spaced angularly about a longitudinal axis of the clamp and adapted to engage with a shoulder provided on the lower plug of the partial length fuel rod to prevent a disengagement of the partial length fuel rod from the base. 2. The nuclear fuel assembly as recited in claim 1 wherein the complementary assemblies comprise a first assembly and a second assembly, the first assembly being adapted to retain the clamp against an upward displacement of the clamp with respect to the base and the second assembly being adapted to retain the clamp against a downward displacement with respect to the base. 3. The nuclear fuel assembly as recited in claim 2 wherein the housing is a through-hole extending from an upper surface of the base to a lower surface of the base. 4. The nuclear fuel assembly as recited in claim 3 wherein the clamp allows the flow of coolant through the housing and along the lower end of the partial length fuel rod. 5. The nuclear fuel assembly as recited in claim 3 wherein the clamp comprises a support adapted to contact a portion of the lower plug of the partial length fuel rod in order to hold the lower plug of the partial length fuel rod at a distance from the lower surface of the base. 6. The nuclear fuel assembly as recited in claim 5 wherein the support comprises support tabs, spaced angularly about a longitudinal axis of the clamp, each support tab comprising a free end extending inwards in the direction of the longitudinal axis of the clamp, the free ends of the support tabs delimiting an opening for receiving the portion of the lower plug of the partial length fuel rod. 7. The nuclear fuel assembly as recited in claim 6 wherein the second assembly comprises a lower support surface provided in the housing, the support tabs being supported longitudinally on the lower support surface. 8. The nuclear fuel assembly as recited in claim 6 wherein the first assembly comprises an abutting surface provided in the housing, and elastic assembly tabs provided on the clamp and comprising free ends extending upwards, the abutting surface being adapted to engage with the free ends of the elastic assembly tabs,wherein the clamp comprises elastic retaining tabs, spaced angularly about a longitudinal axis of the clamp and adapted to engage with a shoulder provided on the lower plug of the partial length fuel rod to prevent a disengagement of the partial length fuel rod from the base,wherein the clamp comprises a body and wherein the support tabs extend inwards from a lower edge of the body, and the retaining tabs and assembly tabs extend upwards from an upper edge of the body. 9. The nuclear fuel assembly as recited in claim 8 wherein in a seated position, in which the support prevents the partial length fuel rod from moving further downwards, the clamp only contacts the lower plug of the partial length fuel rods by the support tabs and of the retaining tabs, a radial clearance existing between an inner surface of the clamp and the peripheral surface of the lower plug of the partial length fuel rod in the portion of the partial length fuel rod extending between the support tabs and the retaining tabs. 10. The nuclear fuel assembly as recited in claim 2 wherein the first assembly comprises an abutting surface provided in the housing, and elastic assembly tabs provided on the clamp and comprising free ends extending upwards, the abutting surface being adapted to engage with the free ends of the elastic assembly tabs. 11. The nuclear fuel assembly as recited in claim 1 wherein the complementary assemblies comprise a central flat base of the clamp, supported on a bottom of the housing and an abutting surface provided in the housing, the abutting surface being adapted to engage with upper free ends of the clamp. 12. The nuclear fuel assembly as recited in claim 11 wherein the clamp comprises a constriction, which is resiliently biased to engage with the lower plug of the partial length fuel rod and is adapted to cooperate with a shoulder provided on the lower plug of the partial length fuel rod. 13. The nuclear fuel assembly as recited in claim 1 wherein the housing is a through-hole extending from an upper surface of the base to a lower surface of the base. 14. The nuclear fuel assembly as recited in claim 13 wherein the clamp allows the flow of coolant through the housing and along the lower end of the partial length fuel rod. 15. A nuclear fuel assembly for a boiling water reactor comprising:a base,a head, anda bundle of full length fuel rods and partial length fuel rods, the bundle extending upwardly and longitudinally from the base to the head,at least one clamp for longitudinally retaining a lower plug of a partial length fuel rod with respect to the base, the clamp being an additional part fitted to the base, the clamp being assembled to the base by mechanical engagement of complementary assemblies, the clamp being embedded in a housing provided in the base such that the clamp is entirely below an upper surface of the base and entirely above a lower surface of the base, the housing consisting of a hole formed in the base, the clamp being comprised in the hole,wherein the complementary assemblies comprise a first assembly and a second assembly, the first assembly being adapted to retain the clamp against an upward displacement of the clamp with respect to the base and the second assembly being adapted to retain the clamp against a downward displacement with respect to the base,wherein the housing is a through-hole extending from an upper surface of the base to a lower surface of the base,wherein the clamp comprises a support adapted to contact a portion of the lower plug of the partial length fuel rod in order to hold the lower plug of the partial length fuel rod at a distance from the lower surface of the base,wherein the support comprises support tabs, spaced angularly about a longitudinal axis of the clamp, each support tab comprising a free end extending inwards in the direction of the longitudinal axis of the clamp, the free ends of the support tabs delimiting an opening for receiving the portion of the lower plug of the partial length fuel rod,wherein the first assembly comprises an abutting surface provided in the housing, and elastic assembly tabs provided on the clamp and comprising free ends extending upwards, the abutting surface being adapted to engage with the free ends of the elastic assembly tabs,wherein the clamp comprises elastic retaining tabs, spaced angularly about a longitudinal axis of the clamp and adapted to engage with a shoulder provided on the lower plug of the partial length fuel rod to prevent a disengagement of the partial length fuel rod from the base,wherein the clamp comprises a body and wherein the support tabs extend inwards from a lower edge of the body, and the retaining tabs and assembly tabs extend upwards from an upper edge of the body. 16. The nuclear fuel assembly as recited in claim 15 wherein in a seated position, in which the support prevents the partial length fuel rod from moving further downwards, the clamp only contacts the lower plug of the partial length fuel rods by the support tabs and of the retaining tabs, a radial clearance existing between an inner surface of the clamp and the peripheral surface of the lower plug of the partial length fuel rod in the portion of the partial length fuel rod extending between the support tabs and the retaining tabs. 17. The nuclear fuel assembly as recited in claim 15 wherein the clamp allows the flow of coolant through the housing and along the lower end of the partial length fuel rod. 18. The nuclear fuel assembly as recited in claim 15 wherein the second assembly comprises a lower support surface provided in the housing, the support tabs being supported longitudinally on the lower support surface.
	summary
	summary
046831100	summary	BACKGROUND OF THE INVENTION The present invention relates, in general, to nuclear power plants. More particularly, the present invention pertains to an apparatus in which spent fuel rods from spent fuel assemblies may be consolidated for storage and to a method for consolidating spent fuel rods. In a nuclear power reactor, fuel rods are typically held in a fuel assembly by a grid structure, which positions the fuel rods so that they are spaced from one another. Once a fuel assembly has been sufficiently used in the nuclear reactor, it is removed from the nuclear reactor and usually stored in a fuel pool in the nuclear power plant. The spent fuel assembly is radioactive, emitting alpha, beta, and gamma radiation; consequently, it generates decay heat. The water in the fuel pool removes some decay heat through free circulation. The water in the fuel pool also provides some shielding from the radiation emitted by the spent fuel assemblies in the pool. The spent fuel assemblies are located with sufficient spacing between them to preclude criticality. Fuel pools in existing nuclear power plants were typically designed to accommodate spent fuel assemblies for interim storage only. The expectation was that reprocessing plants would be in service and that the spent fuel assemblies would be sent to such plants. However, such plants have not yet become operational. Furthermore, facilities for long-term storage of spent fuel assemblies on a large-scale basis are presently nonexistent. Accordingly, spent fuel assemblies are being stored in the fuel pools of nuclear power plants, and the available storage space in such pools is rapidly being consumed. In order to provide more storage space in their fuel pools, many nuclear power plants have installed, or intend to install, racks in their fuel pools that will permit the fuel assemblies to be stored closer together. These racks are typically equipped with sheets of shielding material located between the fuel assemblies. The sheets of shielding material enable the fuel assemblies to be stored closer together without becoming critical. Conventional fuel pool racks, however, generally have insufficient storage capacity to accommodate the spent fuel assemblies and rods that will accumulate during the lifetime of a nuclear power plant. Accordingly, a need exists for an uncomplicated, inexpensive apparatus in which spent fuel rods from spent fuel assemblies may be consolidated for storage after they have decayed sufficiently. Moreover, a need exists for a simple, efficient method for consolidating spent fuel rods. SUMMARY OF THE INVENTION The present invention satisfies the need for an uncomplicated, inexpensive apparatus in which spent fuel rods may be consolidated for storage and the need for a simple, efficient method for consolidating spent fuel rods. The present invention solves the problems associated with known devices and methods by providing an apparatus with a container having a front wall, a back wall, side walls connected between the front and back walls, and a bottom connected to the front, back, and side walls. The container also has a plurality of flutes positioned adjacent to the front wall. The plurality of flutes defines a plurality of channels. Springs bear against the flutes and channels when no fuel rods have been inserted into the container and the springs are located proximate the front wall. The springs are capable of maintaining a fuel rod in a preselected location in the container. The springs are mounted to a support, which is positioned within the container and which is movable between the front and back walls. Preferably, the springs are arranged in two or more rows, with the rows running between the side walls of the container. Each spring may be a resilient finger that extends outwardly from the support toward the front wall. The support may include a movable installation sheet, or it may include two or more plates. If the support includes two or more plates, the springs are advantageously arranged in two or more rows mounted on each of the plates. The flutes may be formed in the front wall; alternatively, the flutes may be formed in a stationary installation sheet that is positioned adjacent to the front wall. An apparatus according to the present invention may include a device for moving the support. Such a device may have two plates and a plurality of resilient elements connected between the two plates. One of the plates abuts the support, while the other of the plates is connected to a mechanism for adjusting its position. Such a mechanism may include a pantograph extension device. Furthermore, such a mechanism advantageously includes a control system for automatically adjusting the position of the second plate, and therefore the position of the support, in response to a control signal. An apparatus according to the present invention may include a plurality of resilient elements positioned between the support and the back wall instead of the device for moving the support. The resilient elements urge the support toward the front wall. The resilient elements may be wave-shaped springs, leaf springs, conical coil springs, or torsional springs. A further alternative to the device for moving the support is a device for producing a substantially constant force against the support means and urging the support means toward the front wall. An apparatus according to the present invention desirably includes a frame that is capable of holding the container and at least one fuel assembly. In addition, holes are advantageously formed in the bottom of the container and in the walls of the container at a level above the level of an inserted fuel rod. The holes permit inserted rods to be convectively cooled. Preferably, the holes in the bottom of the container are aligned with the interstitial channels defined by fuel rods inserted into the container. The container optionally includes a removable cover. The flutes and the channels of the container define a first row of locations along the front wall of the container. Accordingly, the container is packed by installing a first row of fuel rods in the first row of locations. The springs then bear against the first row of fuel rods and the flutes; the springs maintain the first row of fuel rods in position after the first row of fuel rods has been installed. The first row of fuel rods and the flutes define a second row of locations. Next, a second row of fuel rods is installed in the second row of locations. The springs then bear against the first row of fuel rods and the second row of fuel rods; the springs maintain the first and second rows of fuel rods in position after the second row of fuel rods has been installed. Preferably, fuel rods in the first row of fuel rods are in contact with the front wall, and fuel rods in the second row of fuel rods are in contact with fuel rods in the first row of fuel rods. Each row of fuel rods may be installed by inserting one fuel rod at a time into the container. In this manner, spent fuel rods from spent fuel assemblies may simply and efficiently be consolidated for storage.
058964290	claims	1. A method for inspecting a carbon hearth-wall liner inside a metal jacket of a furnace from outside the furnace, the carbon hearth-wall liner adapted to contain molten metal, comprising the following steps: directing photons of radiation into the hearth-wall liner; directing neutrons into the hearth-wall liner; measuring radiation emitted from the hearth-wall liner as a result of having directed the photons and the neutrons into the hearth-wall liner; and analyzing the measurements to determine the remaining thickness of the hearth-wall liner and the extent to which the molten metal has infiltrated the hearth-wall liner. directing photons of gamma radiation into the hearth-wall liner; using at least one radiation detector to measure radiation backscattered out of the hearth-wall liner and to measure gamma radiation produced as a result of pair production by the gamma radiation directed into the hearth-wall liner; and comparing the amount of backscattered radiation to the amount of radiation directed into the hearth-wall liner to estimate the thickness of the hearth-wall liner. directing neutrons into the hearth-wall liner; using a radiation detector to monitor for gamma radiation produced when the neutrons are absorbed; measuring the time elapsed between the neutrons being directed into the hearth-wall liner and the production of the gamma radiation; and using the measurements of elapsed time to estimate the amount of metal in the volume of the hearth-wall liner. directing electromagnetic radiation into the wall; directing neutrons into the wall; and measuring and analyzing radiation emitted from the wall as a result of having directed the electromagnetic radiation and the neutrons into the wall to evaluate the remaining thickness of the wall and to determine the extent to which the wall has been infiltrated by another material. a photon generator for generating photons of gamma radiation that are directed into the hearth-wall liner; a neutron generator for directing neutrons into the hearth-wall liner; at least one detector for detecting and measuring photons of radiation emitted from the hearth-wall liner as a result of having directed the radiation and the neutrons into the hearth-wall liner; and a computer for analyzing the measurements to determine the remaining thickness of the hearth-wall liner and the extent to which the molten metal has infiltrated the hearth-wall liner. 2. The method of claim 1, wherein the photons directed into the hearth-wall liner have an energy greater than a pair production threshold of 1.02 MeV. 3. The method of claim 2, wherein the radiation is emitted in photons and the analysis of the measurements further includes evaluating the number of photons emitted with an energy of approximately 511 keV. 4. The method of claim 2, wherein the radiation is emitted in photons and the analysis of the measurements further includes evaluating the number of photons emitted with an energy in a range between about 200 keV and about 511 keV. 5. The method of claim 2, wherein the radiation emitted from the hearth-wall liner is detected by a plurality of detectors and the determination of the remaining thickness of the hearth-wall liner further includes comparing the amount of radiation measured in each of the detectors. 6. The method of claim 2, wherein an electron accelerator triggers the emission of neutrons directed into the hearth-wall liner. 7. The method of claim 2, wherein the analysis of the measurements includes comparing the measurements with values predicted using a simulation program. 8. The method of claim 7, wherein the photons directed into the hearth-wall liner include bremsstrahlung radiation produced by an electron accelerator. 9. The method of claim 8, wherein the bremsstrahlung radiation has an energy of 3 to 8 MeV. 10. The method of claim 1, wherein the analysis of the measurements includes evaluating, as a function of time, emission of radiation produced by neutron absorption. 11. The method of claim 1, wherein the analysis of the measurements includes comparing the measurements with values predicted using a simulation program. 12. The method of claim 1, wherein the molten metal is iron. 13. A method for inspecting a carbon hearth-wall liner of a furnace from outside the furnace, the carbon hearth-wall liner containing molten metal, comprising the following steps: 14. The method of claim 13, wherein the gamma radiation directed into the hearth-wall liner has an energy greater than the pair production threshold of 1.02 MeV. 15. The method of claim 14, wherein the radiation emitted from the hearth-wall liner is detected by a plurality of detectors and the determination of the remaining thickness of the hearth-wall liner further includes comparing the amount of radiation measured in each of the detectors. 16. The method of claim 14, further including the step of comparing the measurements from the radiation detector to values predicted using a simulation program. 17. The method of claim 16, wherein the photons directed into the hearth-wall liner include bremsstrahlung radiation having an energy of 3 to 8 MeV. 18. The method of claim 13, wherein the metal is iron. 19. A method for inspecting a carbon hearth-wall liner of a furnace from outside the furnace, the carbon hearth-wall liner adapted to contain molten metal, comprising the following steps: 20. The method of claim 19, wherein the radiation emitted from the hearth-wall liner is detected by a plurality of detectors and the determination of the remaining thickness of the hearth-wall liner further includes comparing the amount of radiation measured in each of the detectors. 21. The method of claim 19, further including the step of comparing the measurements from the radiation detector to values predicted using a simulation program. 22. The method of claim 19, wherein the metal is iron. 23. A method for inspecting a wall comprising the following steps: 24. The method of claim 23, wherein the electromagnetic radiation directed into the wall has an energy greater than a pair production threshold of 1.02 MeV. 25. The method of claim 24, wherein the radiation is emitted in gamma-ray photons and the analysis of the emitted-radiation measurements further includes evaluating the number of photons emitted having an energy of approximately 511 keV. 26. The method of claim 24, wherein the radiation is emitted in photons and the analysis of the measurements further includes evaluating the number of photons emitted with an energy in a range between about 200 keV and about 511 keV. 27. The method of claim 24, wherein the radiation emitted from the wall is detected by a plurality of detectors and the determination of the remaining thickness of the wall further includes comparing the amount of radiation measured in each of the detectors. 28. The method of claim 24, wherein an electron accelerator triggers the emission of neutrons directed into the wall. 29. The method of claim 24, wherein the analysis of the emitted-radiation measurements includes comparing the emitted-radiation measurements with values predicted using a simulation program. 30. The method of claim 29, wherein the photons directed into the wall include bremsstrahlung radiation produced by an electron accelerator. 31. The method of claim 30, wherein the bremsstrahlung radiation has an energy of 3 to 8 MeV. 32. The method of claim 23, wherein the analysis of the emitted-radiation measurements includes evaluating, as a function of time, emission of gamma rays produced by neutron absorption. 33. The method of claim 32, wherein the analysis of the emitted-radiation measurements includes comparing the emitted-radiation measurements with values predicted using a simulation program. 34. An apparatus for inspecting a carbon hearth-wall liner inside a metal jacket of a furnace from outside the furnace, the carbon hearth-wall liner adapted to contain molten metal, comprising: 35. The apparatus of claim 34, wherein the radiation emitted from the hearth-wall liner is detected by a plurality of detectors. 36. The apparatus of claim 34, wherein the neutron generator comprises the photon generator and a neutron-emitting target. 37. The apparatus of claim 36, wherein the neutron-emitting target includes beryllium. 38. The apparatus of claim 34, wherein the photon generator is a linear accelerator capable of producing bremsstrahlung radiation. 39. The apparatus of claim 38, wherein the bremsstrahlung radiation has an energy of about 3 to about 8 MeV.
055090419	claims	1. An x-ray lithography method for irradiating an object to form a pattern thereon using an x-ray mask having a membrane, said membrane having an open membrane surface, comprising the step of passing x-ray radiation through said open membrane surface to irradiate said object wherein said open membrane surface is substantially uniformly exposed to said x-ray radiation and wherein said open membrane surface has an area substantially equal to said pattern. 2. The method of claim 1 wherein said object is a semiconductor wafer, said pattern corresponds to an integrated circuit disposed on said wafer, said integrated circuit has an area substantially equal to said area of said open membrane surface, and wherein said pattern is repetitively formed on said wafer to provide a plurality of integrated circuits. 3. The method of claim 1 wherein said pattern is formed in a resist layer disposed on said object. 4. The method of claim 1 wherein an intensity of said x-ray radiation impinging on said open membrane surface varies less than 5 percent over a full extent of said open membrane surface. 5. The method of claim 1 wherein a maximum tensile stress of said open membrane surface is less than 5.times.10.sup.9 dynes/cm.sup.2. 6. The method of claim 1 wherein a maximum tensile stress of said open membrane surface is less than 2.times.10.sup.9 dynes/cm.sup.2. 7. The method of claim 1 wherein a maximum displacement of a lithography mask pattern disposed on said membrane is less than about 5 nm after an exposure of said open membrane surface to said x-ray radiation of about 167 kJ/cm.sup.2. 8. The method of claim 7 wherein said membrane comprises silicon carbide. 9. The method of claim 1 wherein a maximum displacement of a lithography mask pattern disposed on said membrane is less than about 15 nm after an exposure of said open membrane surface to said x-ray radiation of about 500 kJ/cm.sup.2. 10. The method of claim 1 wherein an average stress change over said open membrane surface is less than about 6 percent from an initial pre-radiation state to a state after an exposure of said open membrane surface to said x-ray radiation of about 500 kJ/cm.sup.2. 11. An x-ray lithography method for irradiating a semiconductor wafer to form a repetitive pattern in a resist layer thereon for providing a plurality of integrated circuits from said wafer, comprising the steps of: (a) positioning an x-ray mask between an x-ray source and said semiconductor wafer, said x-ray mask comprising: (b) exposing said open membrane surface with substantially uniform x-ray radiation to irradiate said resist layer. 12. The method of claim 11 wherein said membrane is substantially overlying a full extent of said support wafer and said open membrane surface is defined by a portion of said membrane overlying said opening of said support wafer. 13. The method of claim 11 wherein said membrane comprises silicon carbide, boron-doped silicon, diamond, or silicon nitride. 14. The method of claim 13 wherein said support wafer comprises silcon. 15. The method of claim 14 wherein said membrane of said x-ray mask is disposed on a support ring comprising glass. 16. The method of claim 11 wherein a maximum displacement of said open membrane surface in one of an x or y direction is less than about 5 nm after an exposure of said open membrane surface to said x-ray radiation of about 167 kJ/cm.sup.2. 17. The method of claim 11 wherein a maximum displacement of said open membrane surface in one of an x or y direction is less than about 15 nm after an exposure of said open membrane surface to said x-ray radiation of about 500 kJ/cm.sup.2. 18. The method of claim 11 wherein said membrane has a thickness of about 2 microns.
	description	The present invention relates to an apparatus and method of generating radiation having a plurality of different wavelengths. The present invention also relates to an exposure apparatus and exposure method utilized in the manufacture of various types of devices, e.g., a semiconductor chip such as an IC or LSI, a display device such as a liquid crystal panel, a detection device such as a magnetic head, and an image sensing device such as a CCD. In recent years, as the packing density and operation speed of semiconductor integrated circuits increase, the pattern line width of the integrated circuits is decreased, and a higher-performance semiconductor fabricating method is sought for. Accordingly, as an exposure apparatus used for resist pattern formation in the lithography process of the semiconductor fabrication process, an exposure apparatus utilizing a short exposure wavelength of, e.g., extreme ultraviolet rays such as KrF laser (248 nm), ArF laser (193 nm), or F2 laser (157 nm), or of X-rays (0.2 to 1.5 nm) has been developed. In exposure using X-rays among these light beams, a proximity exposure method of moving an X-ray mask having a desired pattern to be close to a resist-coated wafer, and irradiating the wafer with X-rays through the X-ray mask, so that the mask pattern is transferred onto the wafer has been developed. In order to obtain high-intensity X-rays, an exposure method using synchrotron radiation is proposed. The technique has developed to such a degree that a pattern of 100 nm or less can be transferred. A synchrotron radiation source requires large-scale facilities. A profit cannot be expected unless device fabrication is performed by connecting ten or more exposure apparatuses to one light source. Hence, an exposure apparatus using a synchrotron radiation source is a system that is suitable for application to a highly demanded device such as a semiconductor memory. In recent years, a device using GaAs has been input into practical use as a communication device, and a large decrease in line width is required. Communication devices are produced in an amount less than that of semiconductor memories, and many types of communication devices are produced in small amounts. When an X-ray exposure system using synchrotron radiation as the light source is introduced to the fabrication of communication devices, it will probably make no profit. For this reason, an exposure apparatus using a compact X-ray source which generates high-intensity X-rays is used in actual communication device production. The light source ranges from one which is called a laser plasma beam source and generates a plasma by irradiating a target with a laser beam and uses X-rays generated by the plasma, to one which generates X-rays by generating a pinch plasma in a gas. These light sources are called point sources. According to a general arrangement, one exposure apparatus which transfers a pattern by aligning a mask and wafer is connected to one point source. FIG. 6 schematically shows an X-ray exposure apparatus using a conventional point source. Referring to FIG. 6, reference numeral 101 denotes an X-ray source unit for generating X-rays. In the X-ray source unit 101, a laser beam 121 is focused on a target 111 to irradiate it, in order to generate a plasma, thus generating X-rays 117. The X-rays 117 globally diverge from a light-emitting point 112. Some X-rays 117 are guided into a reduced-pressure He chamber 141 through an X-ray transmitting window 113. A mask 131 has a transfer pattern. A wafer 133 coated with a photosensitive agent is positioned at a position with a small gap of about 10 μm from the membrane by an alignment unit (not shown). The wafer 133 is irradiated with the X-rays 117 emerging from the light-emitting point 112, so the pattern is transferred onto the wafer 133. The wafer 133 is sequentially stepped by a wafer stage 132 and is exposed successively. In some cases, a collimator is installed midway along the X-ray path between the light-emitting point 112 and mask 131 and focuses and collimates the X-rays. The arrangement of the above conventional exposure apparatus will be detailed in further detail. The conventional exposure apparatus is mainly comprised of the X-ray source unit (to be also referred to as a light source unit hereinafter) 101 and a main body 102. The light source unit 101 is set on the main body 102. The target 111 is arranged in the light source unit 101, and is irradiated with the laser beam 121 to generate a plasma, thereby generating the X-rays 117. The laser beam 121 is generated by a laser beam generating unit 122 separately installed on the floor, and is focused on the target 111 to irradiated it through a laser beam optical system (not shown). The interior of the light source unit 101 is held at vacuum, and the main body 102 is set in a reduced-pressure He atmosphere by the reduced-pressure He chamber 141. The light source unit 101 and the main body 102 are isolated from each other by the Be-made X-ray transmitting window 113 with a thickness of several μm, so that the vacuum atmosphere will not be spoiled. Be has a high X-ray transmittance but does not transmit He, so Be is used to form an X-ray transmitting window. A bellows A (denoted by reference numerals 116) is set between the light source unit 101 and reduced-pressure He chamber 141 to isolate them from the outside. FIG. 7 shows the arrangement of the light source portion in detail. The target 111 for generating the X-rays forms a tape, and is held as it is wound around a tape roll 119. The tape-like target 111 fed from the tape roll 119 is taken up by a takeup section 120. The focused laser beam 121 irradiates the target 111, extending between the tape roll 119 and takeup section 120, by pulse emission, and the X-rays 117 are radially generated from the light-emitting point 112 at each pulse. Every time the laser pulse is irradiated, the target 111 is gradually fed out and taken up by the takeup section 120. The target 111 is made of Cu or the like. The main body 102 is set in the reduced-pressure He chamber 141, and is entirely maintained in the reduced-pressure He atmosphere by an He atmosphere creating unit (not shown). This is because attenuation of the X-rays can be suppressed and a high heat transfer efficiency can be maintained if the atmosphere where the X-rays as the exposure light pass is set to reduced-pressure He. The main body 102 is comprised of a mask stage (not shown) for holding and positioning the mask 131, the wafer stage 132 for holding, positioning, and stepping the wafer 133, a transfer system (not shown) for transferring the mask 131 and wafer 133, and a measurement system (not shown) for measuring the positions of the mask 131 and wafer 133 relative to each other. The entire portion of the main body 102 is installed on the floor through vibration damping units 136. A stage surface plate 134 is set on the vibration damping units 136, and the wafer stage 132 moves on it, so that exposure is performed successively. A main body frame 137 is set on the stage surface plate 134, and supports the mask stage (not shown), the mask 131, and the like. The vibration damping units 136 prevent the positioning precisions of the mask 131 and wafer 133 that require precise positioning from being decreased by vibration from the floor, so the main body 102 maintains a constant posture. Bellows B (denoted by reference numerals 142) are set between the reduced-pressure He chamber 141 and main body 102 so the reduced-pressure He atmosphere will not be spoiled when the posture of the main body 102 changes. In the conventional apparatus arrangement described above, the light source unit 101 uses one type of target 111 as the X-ray generating source. The spectral intensity of the emitted X-rays depends on the type of the target 111. FIG. 8A shows an example of transfer pattern intensity distribution on the wafer surface which is obtained when a Line & Space pattern is exposed with the conventional exposure apparatus. In this example, the small gap distance (exposure gap) between the mask and wafer is 10 μm. Ideally, the exposure apparatus resolves an image irrespective of the pattern, as shown in FIG. 8B. Factors that determine the image intensity distribution also include the material and thickness of the mask. As shown in FIG. 8A, with a 100-nm pattern, the intensity image is formed faithfully in accordance with the mask pattern. With a 70-nm Line & Space pattern, however, the image loses its shape, and the contrast decreases, so the image is not resolved. In other words, with the conventional X-ray generating source, since the exposure wavelength is a specific wavelength, depending on the mask pattern, the influence of diffraction becomes conspicuous, and sometimes the image cannot be resolved. In this example, the pattern loses its shape and the contrast decreases. Depending on the pattern, a positional error may occur. This problem may be avoided if the exposure gap is set to an appropriate amount. When the exposure gap changes, however, as the exposure light broadens, the positional error of the pattern to be transferred increases, and an overlaying error occurs. Therefore, this countermeasure cannot be used in practice. The present invention has been made in view of the above problems, and has as its object to provide a radiation generating apparatus, radiation generating method, exposure apparatus, and exposure method with which a plurality of different exposure wavelengths (spectra) are generated, and exposure wavelengths are selected or combined in accordance with the transfer pattern, so that a decrease in resolution can be suppressed. In order to solve the above problems and to achieve the above object, a radiation generating apparatus and radiation generating method according to the present invention comprise radiation generating means (step) for generating radiation having a plurality of different wavelengths, and wavelength selecting means (step) for selecting a wavelength of the radiation generated by the radiation generating means. Preferably, the radiation generating means (step) has plasma exciting means (step) and a plurality of different types of light-emitting portions (targets) plasma-excited by the plasma exciting means, and the wavelength selecting means has means for selecting and switching the light-emitting portions. Preferably, the plasma exciting means comprises laser exciting means. Preferably, the plurality of light-emitting portions are divided into a plurality of portions and arranged in a radial direction of a circular disk, and the wavelength selecting means has a driving portion for rotationally driving the disk. Preferably, the apparatus and method further comprise a synchronization control unit (step) for synchronizing a time when the plasma exciting means excites a plasma and a time when the wavelength selecting means selects and switches the light-emitting portions. Preferably, the apparatus further comprises a synchronization control unit for synchronizing a time when the plasma exciting means excites a plasma and a rotational angular position of the driving portion. More specifically, the radiation comprises X-rays. Preferably, the radiation generating apparatus or method is applied to an exposure apparatus or exposure method of projecting and transferring a pattern on a master onto a surface of a target exposure object by radiation exposure. In the exposure apparatus, the wavelength selecting unit acquires information on the pattern on the master, and selects a wavelength on the basis of wavelength information or wavelength distribution information contained in the acquired information. Preferably, the wavelength selecting unit selects a combination of a plurality of different wavelengths from the wavelength information. Desirably, the present invention is also applied to a semiconductor device manufacturing method comprising steps of installing manufacturing apparatuses for various processes including the exposure apparatus in a semiconductor manufacturing factory, and manufacturing a semiconductor device in a plurality of processes by using the manufacturing apparatuses. Preferably, the semiconductor device fabrication method further comprises steps of connecting the manufacturing apparatuses by a local area network, and communicating information about at least one of the manufacturing apparatuses between the local area network and an external network of the semiconductor manufacturing factory. Preferably, maintenance information of the manufacturing apparatus is acquired by data communication by accessing a database provided by a vendor or user of the exposure apparatus via the external network, or production is managed by data communication via the external network with a semiconductor manufacturing factory other than the semiconductor manufacturing factory. Furthermore, the present invention is also applied to a semiconductor manufacturing factory comprising manufacturing apparatuses for various processes including the exposure apparatus, a local area network for connecting the manufacturing apparatuses, and a gateway for allowing the local area network to access an external network of the factory, wherein information about at least one of the manufacturing apparatuses is communicated by connection to the external network. The present invention is also applied to a maintenance method for the exposure apparatus that is installed in a semiconductor manufacturing factory, comprising steps of causing a vendor or user of the exposure apparatus to provide a maintenance database connected to an external network of the semiconductor manufacturing factory, authenticating access from the semiconductor manufacturing factory to the maintenance database via the external network, and transmitting maintenance information accumulated in the maintenance database to the semiconductor manufacturing factory via the external network. Preferably, the exposure apparatus further comprises a display, a network interface, and a computer for executing communication software and enables communicating maintenance information of the exposure apparatus via a computer network. Preferably, the communication software is connected to an external network of a factory where the exposure apparatus is installed, provides on the display a user interface for accessing a maintenance database provided by a vendor or user of the exposure apparatus, and enables obtaining information from the database via the external network. As described above, according to the present invention, desired wavelengths or a combination thereof can be selected from a plurality of different wavelengths. Hence, an influence of diffraction depending on the mask pattern during exposure can be reduced to improve the resolution, so that a higher-precision transfer pattern can be obtained, and a smaller (higher-performance) semiconductor device can be manufactured. When wavelength information (spectrum data) contained in information on the mask pattern is used, the wavelength of the exposure light can be selected easily, so that operational mistakes can be decreased, and a decrease in yields can be prevented. Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention. The preferred embodiments of the present invention will be described with reference to the accompanying drawings. [Schematic Arrangement of Exposure Apparatus] The first embodiment to which the present invention is applied will be described with reference to FIG. 1. In the first embodiment, the present invention is applied to a proximity X-ray exposure apparatus using a point source as the light source. Referring to FIG. 1, the exposure apparatus of this embodiment is mainly comprised of a light source unit 1 and a main body 2. The X-ray source unit 1 is set on the main body 2. A circular disk-like target 14 is arranged in the X-ray source unit 1. A laser beam 21 is focused on the circular disk-like target 14 to irradiate it, thereby generating a plasma and then X-rays 17. The laser beam 21 is generated by a laser beam generating unit 22 separately installed on the floor, and irradiates the circular disk-like target 14 through a laser beam optical system (not shown). The interior of the light source unit 1 is held at vacuum, and the interior of the main body 2 is set in a reduced-pressure He atmosphere by a reduced-pressure He chamber 41. The light source unit 1 and the main body 2 are isolated from each other by a Be X-ray transmitting window 13 with a thickness of several μm, so that the vacuum atmosphere will not be spoiled. Be has a high X-ray transmittance but does not transmit He, so Be is used to form an X-ray transmitting window. A bellows A (denoted by reference numerals 16) is set between the X-ray source unit 1 and reduced-pressure He chamber 41 to isolate them from the outside. FIG. 2 shows the arrangement of the light source portion in detail. The circular disk-like target 14 for generating the X-rays has four types of quadrant first-, second-, third-, and fourth-wavelength light-emitting portions 14a, 14b, 14c, and 14d which are made of different materials and divided equiangularly (e.g., at 90°) in the radial direction. The laser beam 21 is emitted (pulse emission) by controlling the laser beam generating unit 22 with a pulse signal, and is focused on the circular disk-like target 14. The X-rays 17 are radially generated from the target 14 at each pulse emission. The target 14 is rotatably controlled by a rotational drive mechanism 15 in synchronism with pulse emission. As the rotational angle of the target 14 is controlled in synchronism with emission of the laser beam 21, the material (type) of the target 14 can be selected from the first-, second-, third-, and fourth-wavelength light-emitting portions 14a, 14b, 14c, and 14d. As the material of the target 14, a metal material such as Cu, W, or Fe is employed. The main body 2 comprises a mask stage (not shown) for holding and positioning a mask 31, a wafer stage 32 for holding, positioning, and stepping a wafer 33, a transfer system (not shown) for transferring the mask 31 and wafer 33, and a measurement system (not shown) for measuring the positions of the mask 31 and wafer 33 relative to each other. The main body 2 is installed in the reduced-pressure He chamber 41, and its interior is entirely maintained in a reduced-pressure He atmosphere by a He atmosphere generating unit (not shown). In this manner, when the atmosphere where the X-rays as the exposure light pass is set at the reduced-pressure He, the attenuation of the X-rays can be suppressed, and a high heat transfer efficiency can be maintained. The main body 2 is installed on the floor through vibration damping units 36. A stage surface plate 34 is set on the vibration damping units 36, and the wafer stage 32 holding the wafer 33 performs exposure while successively moving on the stage surface plate 34, so that the circuit pattern formed on the mask 31 is transferred onto the surface of the wafer 33. A main body frame 37 is set on the stage surface plate 34, and the mask stage (not shown), the mask 31, and the like are supported by the main body frame 37. The vibration damping units 36 prevent the positioning precisions of the mask and wafer that require precise positioning from being decreased by vibration from the floor, so the main body 2 maintains a constant posture. Bellows B (denoted by reference numerals 42) are set between the reduced-pressure He chamber 41 and main body 2 so the reduced-pressure He atmosphere will not be spoiled when the posture of the main body 2 changes. An exposure light wavelength selecting method of this embodiment will be described. As described above, the wavelength of the X-rays generated by the target 14 is determined by the material of the target irradiated with the laser beam 21. The target 14 of this embodiment generates four different types of wavelengths depending on the difference in material, i.e., a wavelength T1 from its first-wavelength light-emitting portion 14a, a wavelength T2 from its second-wavelength light-emitting portion 14b, a wavelength T3 from its third-wavelength light-emitting portion 14c, and a wavelength T4 from its fourth-wavelength light-emitting portion 14d. FIGS. 3A to 3C show the rotational angular position of the rotational drive mechanism 15 and pulse emission timing in wavelength selection control of irradiating, with the laser beam, either one of the first-, second-, third-, and fourth-wavelength light-emitting portions 14a, 14b, 14c, and 14d of the circular disk-like target 14. The laser beam 21 requires a high energy in order to excite the plasma and accordingly cannot be emitted continuously. Thus, the laser beam 21 is emitted in a pulse manner concentratedly during a short nsec-order period of time. FIG. 3A shows a control example in which the first-wavelength light-emitting portion 14a is irradiated with the laser beam 21 to generate X-rays 17 having the wavelength T1. The rotational angular position of the circular disk-like target 14 and the pulse emission period are synchronized, and pulse emission is performed at every rotational angle (0–90°) corresponding to the first-wavelength light-emitting portion 14a (alternatively, the target 14 is rotated in synchronism with pulse emission to irradiate the first-wavelength light-emitting portion 14a with the laser beam 21). Thus, the laser beam 21 irradiating the first-wavelength light-emitting portion 14a excites the plasma, so the first-wavelength light-emitting portion 14a generates X-rays having the wavelength T1. The timing of the angle sensor set in the rotational drive mechanism 15 with the trigger of the emission pulse is controlled by a central control unit 18, so the pulse emission timing and the rotational angular position of the target 14 are synchronized. When X-rays having the wavelength T2 are to be generated by the second-wavelength light-emitting portion 14b, as shown in FIG. 3B, pulse emission is performed at every rotational angle (90°–180°) corresponding to the second-wavelength light-emitting portion 14b (alternatively, the target 14 is rotated in synchronism with pulse emission to irradiate the second-wavelength light-emitting portion 14b with the laser beam 21). Thus, the laser beam 21 irradiating the second-wavelength light-emitting portion 14b excites the plasma, so the second-wavelength light-emitting portion 14b generates X-rays having the wavelength T2. As described above, when X-rays are to be generated by a single-wavelength light-emitting portion (when X-rays having a single wavelength are to be generated), the rotational angular position of the circular disk-like target 14 and the pulse emission timing need not be controlled to be synchronized. This X-ray generation can be realized also by fixing the rotational angular position of the target 14. Wavelength selection control that takes place when X-rays having a plurality of different wavelengths are to be generated will be described. FIG. 3C shows the relationship between the rotational angular position of the target 14 and the pulse emission timing when the X-rays having the wavelength T1 and the X-rays having the wavelength T3 are to be respectively generated by the first- and third-wavelength light-emitting portions 14a and 14c at a ratio of 1:1. For example, when the pulse emission period is maintained with no delay and the rotational speed of the target 14 is set to ½ that shown in FIG. 3A or 3B, X-rays having the wavelength T1 and X-rays having the wavelength T3 are generated at a ratio of 1:1. Then, the spectral distribution of the X-rays provided for exposure becomes broader, and an optimal wavelength distribution can be obtained for exposure with a specific pattern. According to another control example, the rotational drive mechanism 15 may be rotationally driven nonlinearly, so that the target can be selected at an arbitrary ratio. In the above control example, synchronization control of the pulse emission period and the rotational angular position by means of the rotational drive mechanism 15 is performed by the central control unit 18. Alternatively, the rotational angle of the circular disk-like target 14 may be controlled by the rotational drive mechanism 15 to match the pulse emission period. In the above embodiment, the central control unit 18 acquires various types of data concerning the mask used for performing exposure on the basis of mask data stored in the mask 31, and automatically selects the exposure wavelength in accordance with the exposure wavelength and wavelength distribution characteristics contained in the mask data, thus performing exposure. Therefore, input omission and input error can be decreased compared to a case wherein the operator selects the wavelength to match the mask pattern. The separation (period) of pulse emission depends on the performance of the laser beam source. When the present invention is applied to an exposure apparatus, the shorter the separation of pulse emission, the higher the exposure light intensity per unit time, so that the exposure time per shot is shortened and the throughput of the apparatus increases. On the other hand, if selection of the target type takes much time, a wasteful time occurs, and the throughput of the apparatus decreases. Therefore, according to this embodiment, pulse emission of the laser beam is always performed with the maximum period that the laser beam source allows, and target selection is controlled by changing the position (angle) of the target. In the above example, the respective-wavelength light-emitting portions are obtained by dividing the target 14 by four in accordance with the different materials. Even if the target 14 is divided by a number other than four, the resultant effect is not adversely affected at all. In the above description, the target 14 is driven only by rotation. If a driving portion for translating the target 14 is provided and accordingly the laser beam irradiation position by pulse emission is variable in the direction of the locus of movement, the laser beam irradiation position on the target 14 becomes variable, so that the service life of the target 14 can be prolonged. [Second Embodiment] FIG. 4 is a view showing the detailed arrangement of a target according to the second embodiment of the present invention. This target is applied to the X-ray exposure apparatus in the same manner as in the first embodiment. The schematic arrangement of the exposure apparatus is identical to that of the first embodiment, and a detailed description thereof will accordingly be omitted. The second embodiment is different from the first embodiment only in the shape of the target of a light source unit 1. Hence, only the target as the wavelength selecting portion of the light source unit will be described. Referring to FIG. 4, in a target 11, a fifth-wavelength light-emitting portion 23a (wavelength T5), sixth-wavelength light-emitting portion 23b (wavelength T6), and seventh-wavelength light-emitting portion 23c (wavelength T7) made of different materials form tapes, and align themselves as three rows in the widthwise direction. The respective-wavelength light-emitting portions 23a to 23c of the target 11 are held as they are wound around a tape roll 19. The tape-like target 11 fed from the tape roll 19 is taken up by a takeup section 20 on the other side. A focused laser beam 21 irradiates the target 11, extending between the tape roll 19 and takeup section 20, by pulse emission, and X-rays 17 are radially generated from a light-emitting point 12 at each pulse. Every time the laser pulse is irradiated, the target 11 is gradually fed out, and a new target surface appears and is taken up by the takeup section 20. The entire target unit is loaded in a driving unit (not shown) which drives in the vertical (widthwise) direction, and vertically moves the target 11 at each pulse, so that the target 11 to be irradiated with the laser beam 21 can be selected from the respective-wavelength light-emitting portions 23a to 23c. In the example of FIG. 4, X-rays are generated by irradiating the fifth- and sixth-wavelength light-emitting portions 23a and 23b with the laser beam at a ratio of 1:1. The X-rays from the fifth-wavelength light-emitting portion 23a and the X-rays from the sixth-wavelength light-emitting portion 23b are irradiated alternately at every other pulse. According to this embodiment, when the target is selected in accordance with the required X-ray wavelength, a desired X-way wavelength can be obtained, and an exposure wavelength optimal for the mask pattern can be used. Therefore, a pattern that cannot be resolved with a single target can be resolved by one exposure apparatus. The mask data has exposure wavelength data. This is the same as in the first embodiment. [Third Embodiment] FIG. 5 shows the arrangement of a target according to the third embodiment. In the third embodiment, the present invention is applied to a proximity X-ray exposure apparatus in the same manner as in the first embodiment. The arrangement of the entire exposure apparatus is identical to that of the first embodiment, and a detailed description thereof will accordingly be omitted. A description will be made only on the arrangement of a light source unit as a characteristic portion different from that of the first embodiment. According to the third embodiment, the light source unit generates X-rays on the following principle. Namely, liquefied gas (target) is sprayed, and is irradiated with a laser beam 21, so it is excited in a plasma state, thus generating X-rays. The light source unit is installed in a vacuum chamber in the same manner as in the first embodiment. The object corresponding to the target is liquefied gas, and is sprayed from first, second, or third nozzle 23, 24, or 25. An inert gas such as Xe or Ne is employed as the gas serving as the target (target gas). The inert gas adiabatically expands rapidly when it is sprayed from the nozzle. At this time, the inert gas is deprived of latent heat, so part of the sprayed target gas liquefies. In synchronism with the liquefaction timing, a laser beam is focused on the target gas to irradiate it, to excite the target gas in a plasma state. Thus, X-rays depending on the type (physical properties) of the target gas sprayed from the selected nozzle are generated. After generating the X-rays, the target gasifies instantaneously and is quickly discharged to the outside of the chamber by an exhaust system (not shown). Thus, the interior of the chamber is held at a constant vacuum degree. In this manner, when a target gas is selected and sprayed in accordance with a desired X-ray wavelength, the desired X-ray wavelength can be obtained, and X-rays having an exposure wavelength optimal for the mask pattern can be used. Therefore, even a mask pattern that cannot be resolved sufficiently with single-wavelength exposure light can be resolved by one exposure apparatus with an improved resolution. The nozzles are selected automatically in accordance with the exposure wavelength or wavelength distribution characteristics contained in the mask data stored in the mask 31, in the same manner as in the first embodiment. Then, exposure is performed with the selected nozzle. [Semiconductor Production System] A production system for a device of a semiconductor or the like (semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin-film magnetic head, a micromachine, or the like) using the exposure apparatus will be exemplified. The system performs maintenance services such as trouble shooting, periodic maintenance, and software distribution for manufacturing apparatuses installed in a semiconductor manufacturing factory by utilizing a computer network outside the manufacturing factory. FIG. 9 shows the overall system cut out at a given angle. In FIG. 9, reference numeral 1101 denotes an office of a vendor (apparatus supply manufacturer) which provides a semiconductor device manufacturing apparatus. Examples of the manufacturing apparatus are semiconductor manufacturing apparatuses for various processes used in a semiconductor manufacturing factory, such as pre-process apparatuses (lithography apparatus including an exposure apparatus, resist processing apparatus, and etching apparatus, an annealing apparatus, a film formation apparatus, a planarization apparatus, and the like) and post-process apparatuses (assembly apparatus, inspection apparatus, and the like). The office 1101 comprises a host management system 1108 which provides a maintenance database for the manufacturing apparatus, a plurality of operation terminal computers 1110, and a LAN (Local Area Network) 1109 which connects the host management system 1108 and computers 1110 to build an intranet or the like. The host management system 1108 has a gateway for connecting the LAN 1109 to the Internet 1105 serving as an external network of the office, and a security function for limiting external accesses. Reference numerals 1102 to 1104 denote manufacturing factories of the semiconductor manufacturer as users of manufacturing apparatuses. The manufacturing factories 1102 to 1104 may belong to different manufacturers or the same manufacturer (pre-process factory, post-process factory, and the like). Each of the factories 1102 to 1104 is equipped with a plurality of manufacturing apparatuses 1106, a LAN (Local Area Network) 1111 which connects these apparatuses 1106 to construct an intranet or the like, and a host management system 1107 serving as a monitoring apparatus which monitors the operation status of each manufacturing apparatus 1106. The host management system 1107 in each of the factories 1102 to 1104 has a gateway for connecting the LAN 1111 in the factory to the Internet 1105 serving as an external network of the factory. Each factory can access the host management system 1108 of the vendor 1101 from the LAN 1111 via the Internet 1105. The security function of the host management system 1108 typically permits only a limited user to access the host management system 1108. More specifically, the factory can notify the vendor via the Internet 1105 of status information (e.g., the symptom of a manufacturing apparatus in trouble) representing the operation status of each manufacturing apparatus 1106. Also, the vendor can transmit, to the factory, response information (e.g., information designating a remedy against the trouble, or remedy software or data) corresponding to the notification, or maintenance information such as the latest software or help information. Data communication between the factories 1102 to 1104 and the vendor 1101 and data communication via the LAN 1111 in each factory typically adopt a communication protocol (TCP/IP) generally used in the Internet. Instead of using the Internet as an external network of the factory, a high-security dedicated network (e.g., ISDN) which inhibits access of a third party can be adopted. The host management system is not limited to the one provided by the vendor. The user may construct a database and set the database on an external network, and the host management system may authorize access to the database from a plurality of user factories. FIG. 10 is a view showing the concept of the overall system of this embodiment that is cut out at a different angle from FIG. 9. In the above example, a plurality of user factories having manufacturing apparatuses and the management system of the manufacturing apparatus vendor are connected via an external network, and production management of each factory or information about at least one manufacturing apparatus is communicated via the external network. In the example of FIG. 10, a factory having a plurality of manufacturing apparatuses provided by a plurality of vendors and the management systems of the vendors for these manufacturing apparatuses are connected via the external network of the factory, and maintenance information about each manufacturing apparatus is communicated. In FIG. 10, reference numeral 1201 denotes a manufacturing factory of a manufacturing apparatus user (semiconductor device manufacturer). Manufacturing apparatuses for various processes, e.g., an exposure apparatus 1202, resist processing apparatus 1203, and film formation apparatus 1204 are installed in the manufacturing line of the factory. FIG. 10 shows only one manufacturing factory 1201, but a plurality of factories are networked in practice. The respective apparatuses in the factory are connected to each other by a LAN 1206 to build an intranet or the like, and a host management system 1205 manages the operation of the manufacturing line. The offices of vendors (apparatus supply manufacturers) such as an exposure apparatus manufacturer 1210, resist processing apparatus manufacturer 1220, and film formation apparatus manufacturer 1230 comprise host management systems 1211, 1221, and 1231 for executing remote maintenance for the supplied apparatuses. Each host management system has a maintenance database and a gateway for an external network, as described above. The host management system 1205 which manages the apparatuses in the manufacturing factory of the user, and the management systems 1211, 1221, and 1231 of the vendors for the respective apparatuses are connected via the Internet or dedicated network serving as an external network 1200. In this system, if a trouble occurs in any one of the manufacturing apparatuses along the manufacturing line, the operation of the manufacturing line stops. This trouble can be quickly solved by remote maintenance from the vendor of the apparatus in trouble via the Internet 1200. This can minimize the stop of the manufacturing line. Each manufacturing apparatus in the semiconductor manufacturing factory comprises a display, a network interface, and a computer which executes network access software and apparatus operating software that are stored in a storage device. The storage device is a built-in memory, hard disk, network file server, or the like. The network access software includes a dedicated or general-purpose web browser, and provides a user interface with a window as shown in FIG. 11 on the display. While referring to this window, the operator who manages manufacturing apparatuses in each factory inputs, into input fields on the windows, pieces of information such as the model of manufacturing apparatus 1401, serial number 1402, subject of trouble 1403, data of occurrence of trouble 1404, degree of urgency 1405, symptom 1406, remedy 1407, and progress 1408. The pieces of input information are transmitted to the maintenance database via the Internet, and appropriate maintenance information is sent back from the maintenance database and provided on the display. The user interface provided by the web browser realizes hyperlink functions 1410, 1411, and 1412, as shown in FIG. 11. This allows the operator to access more detailed information of each item, download the latest-version software to be used for a manufacturing apparatus from a software library provided by a vendor, and download an operation guide (help information) as a reference for the operator in the factory. The maintenance information provided by the maintenance database includes the above-described information that pertains to the present invention, and the software library also provides the latest software for realizing the present invention. A semiconductor device manufacturing process using the above-described production system will be explained. FIG. 12 shows the flow of the whole manufacturing process of a semiconductor device. In step S1 (circuit design), a semiconductor device circuit is designed. In step S2 (mask formation), a mask is formed based on the designed circuit pattern. In step S3 (wafer formation), a wafer is formed using a material such as silicon. In step S4 (wafer process) called a pre-process, an actual circuit is formed on the wafer by lithography using the prepared mask and wafer. Step S5 (assembly) called a post-process is the step of forming a semiconductor chip by using the wafer formed in step S4, and includes an assembly process (dicing and bonding) and packaging process (chip encapsulation). In step S6 (inspection), the semiconductor device manufactured in step S5 undergoes inspections such as an operation confirmation test and durability test. After these steps, the semiconductor device is completed and shipped (step S7). The pre-process and post-process are performed in separate dedicated factories, and each of the factories receives maintenance by the above-described remote maintenance system. Information for production management and apparatus maintenance is communicated between the pre-process factory and the post-process factory via the Internet or dedicated network. FIG. 13 shows the detailed flow of the wafer process. In step S11 (oxidation), the wafer surface is oxidized. In step S12 (CVD), an insulating film is formed on the wafer surface. In step S13 (electrode formation), an electrode is formed on the wafer by vapor deposition. In step S14 (ion implantation), ions are implanted in the wafer. In step S15 (resist processing), a photosensitive agent is applied to the wafer. In step S16 (exposure), the wafer is exposed to the circuit pattern of a mask by the above-mentioned exposure apparatus. In step S17 (developing), the exposed wafer is developed. In step S18 (etching), the resist is etched except the developed resist image. In step S19 (resist removal), an unnecessary resist after etching is removed. These steps are repeated to form multiple circuit patterns on the wafer. A manufacturing apparatus used in each step undergoes maintenance by the remote maintenance system, which prevents a trouble in advance. Even if a trouble occurs, the manufacturing apparatus can be quickly recovered. The semiconductor device productivity can be increased in comparison with the prior art. [Other Embodiment] The present invention is also achieved by supplying a software program (a wavelength selection method and exposure method according to the present invention) for realizing the functions of the above-described embodiments to a system or apparatus directly or from a remote place, and reading out and executing the supplied program codes by the computer of the system or apparatus. In this case, the software need not be a program as far as it has a program function. The present invention is therefore realized by program codes installed into the computer in order to realize functional processing of the present invention by the computer. That is, the claims of the present invention include a computer program for realizing functional processing of the present invention. In this case, the present invention can take any program form such as an object code, a program executed by an interpreter, or script data supplied to an OS as long as a program function is attained. A recording medium for supplying the program includes a floppy disk, hard disk, optical disk, magnetooptical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, and DVD (DVD-ROM and DVD-R). As another program supply method, the program can be supplied by connecting a client computer to an Internet homepage via the browser of the client computer, and downloading the computer program of the present invention or a compressed file containing an automatic installing function from the homepage to a recording medium such as a hard disk. The program can also be supplied by classifying program codes which constitute the program of the present invention into a plurality of files, and downloading the files from different homepages. That is, the claims of the present invention also incorporate a WWW server which allows a plurality of users to download the program files for realizing functional processing of the present invention by a computer. The present invention can also be realized by the following method. That is, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, and distributed to the user. A user who satisfies predetermined conditions is caused to download decryption key information from a homepage via the Internet. The user executes the encrypted program by using the key information, and installs the program in the computer. The functions of the above-described embodiments are realized when the computer executes a readout program. Also, the functions of the above-described embodiments are realized when an OS or the like running on a computer performs part or all of actual processing on the basis of the instructions of the program codes. The functions of the above-described embodiments are also realized when a program read out from a storage medium is written in the memory of a function expansion board inserted into a computer or the memory of a function expansion unit connected to the computer, and the CPU of the function expansion board or function expansion unit performs part or all of actual processing on the basis of the instructions of the program codes. The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to appraise the public of the scope of the present invention, the following claims are made.
	description	The electron beam exposure apparatus in the embodiment of the present invention has almost the same configuration as the conventional ones as shown in FIG. 1. FIG. 4 illustrates the block mask 21, the first through the fourth mask deflectors 16, 18, 23, and 25, and related drive circuits of the electron beam exposure apparatus. The CPU 41 reads out the drawing data stored in the magnetic tape 42 and the magnetic disc 43 via the bus 44, and sends out the data relating to the selection of a block mask, which is generated from the drawing data, to the exposure control portion 45. The CPU 41 also generates deflection data for the main deflector 31 and sub-deflector 32 and focus data for the focus coil 29, and sends them to each drive circuit, though an explanation is not provided here. The deflection position data relating to the block mask selection sent from the CPU 41 via the bus 44 is provided to the exposure control portion 45 via the interface 46. The lookup table 47 stores the signal values (output values) to be applied to the drive circuits of each mask deflector 16, 18, 23, and 25, and the deflector 17 according to the deflection position data. The exposure control portion 45 reads out the output value corresponding to the specified aperture pattern and sends it to the drive circuit 48 consisting of a D/A converter (DAC) and amplifier (AMP). The DAC/AMP circuit 48 generates an analog signal corresponding to the output value and applies it to the first through the fourth mask deflectors 16, 18, 23, and 25, and the deflector 17. A block mask is thus selected in the manner described above. In the present embodiment, the following measurement and adjustment are carried out after the abovementioned settings are completed. First of all, a block mask 21 in which all aperture patterns 61 include the adjusting aperture patterns as shown in FIGS. 5A through 5C is provided. Each adjusting aperture pattern has independent apertures of the same shape arranged along the opposite sides of the maximum aperture area 63. In FIG. 5A, for example, there are four rectangular apertures 71 to 74 arranged along each side of the maximum aperture area 63. The rectangular apertures 71 and 72 arranged along the opposite sides have the same shape and so do the apertures 73 and 74. In this case, the shapes of apertures 71 and 72 coincide with those of the apertures 73 and 74, respectively, after a rotation of 90 degrees. In FIG. 5B, there are four square apertures 75 to 78 in each corner of the maximum aperture area 63, and in FIG. 5C, there are five more square apertures 79 to 83 of the same shape, four at the middle of each side, and one in the center of the maximum aperture area 63, in addition to the apertures in FIG. 5B. The pattern shown in FIG. 5A is used here for explanation, though any pattern is possible. FIG. 6A illustrates the fine line 90 provided on the specimen (wafer) 1 to be used for measurement. A shifted (embossed or etched) pattern, in which the fine line 90 is made higher or lower than another part, is placed on the specimen 1. The fine line 90 has the line 90A that extends in the Y direction and the line 90B that extends in the X direction. When the specimen 1 that has a shifted pattern 90 as shown in FIG. 6A is scanned by the electron beam 10, the amount of the reflected electron while the electron beam traverses the pattern 90 increases and the increment can be detected by the reflected electron detector 33 shown in FIG. 1. An electron beam shaped into the adjusting aperture pattern in FIG. 5A is radiated onto the specimen after each line of the fine line 90 is adjusted to extend in the X and Y directions, respectively, as shown in FIG. 6B. At this time, the sides of the rectangular electron beam patterns 71xe2x80x2 to 74xe2x80x2 corresponding to the apertures 71 to 74 are adjusted so that they are parallel to the line 90A and line 90B, respectively. Then, the sub-deflector 32 is used to scan in the X and Y directions and the output of the reflected electron detector 33 is observed. FIGS. 7A and 7B illustrate examples of the variations in the detected signal when scanned in the X direction. FIG. 7A shows two high peaks corresponding to the patterns 71xe2x80x2 and 72xe2x80x2, and a low and wide peak corresponding to the patterns 73xe2x80x2 and 74xe2x80x2. The difference in height between the two peaks on both ends indicates the difference in intensity and it can be concluded that the position of the selected adjusting aperture pattern is different from that of the beam deflected by the mask deflector. Therefore, it is necessary to conduct the observation similarly with another adjusting value in the lookup table 47 in FIG. 4 until the two peaks have the same height as shown in FIG. 7B. At the same time, the value should be selected so that the height of the peaks is as high as possible. Similarly, the same adjustment is applied in the Y direction. The abovementioned adjustment will optimize the positions of the selected adjusting aperture pattern and the deflected beam. The optimum deflection for each aperture pattern can be obtained by applying the abovementioned adjustment to other adjusting aperture patterns of the block mask. In the manufacturing process of the electron beam exposure apparatus, a block mask 21 consisting only of adjusting aperture patterns is used to adjust the deflection position for each aperture pattern. Since the adjusted deflection amount may change with time, periodical checks and modifications are required. In this case, however, it is not necessary to check all the aperture patterns, instead, just taking measurement of only several central and peripheral aperture patterns and correcting the deviation using interpolation will do. The block mask 21 consisting only of adjusting aperture patterns can also be used for the abovementioned periodical checks and modifications. It is, however, necessary to change the block mask each time, making the work more troublesome. Therefore, it is advisable to use a block mask shown in FIG. 8. This block mask 21 has adjusting aperture patterns only at the aperture patterns 65 diagonally hatched and other aperture patterns are the normal ones that can be used with a normal optical exposure. If a block mask 21 like this is used, checks and adjustments can be conducted without replacement of the block mask 21. As explained above, the present invention can provide a precise amount of deflection of the mask deflector according to each aperture pattern because the difference in position between the beam deflected by the mask deflector and each aperture pattern is measured precisely. This not only realizes an exposure with high accuracy and without exposure variation, but also increases the efficiency by increasing the number of the aperture patterns formed on the block mask.
	description	1. Field of the Invention The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. 2. Background Art With high integration of a semiconductor device, a circuit pattern of the semiconductor device has been miniaturized. In order to form a micro circuit pattern in the semiconductor device, a high-precision original image pattern (i.e., reticle or mask) is required. It is known that an electron beam writing apparatus having excellent resolution is used to manufacture the original image pattern. In this type of electron beam writing apparatus, shot data is generated from write data in which the shape and position of each graphic pattern are defined. Main deflection data and sub deflection data are generated by a deflection controller in such a manner that each pattern contained in the shot data is written. The respective deflection data are DA-converted by a DAC amplifier (hereinafter abbreviated as “amp”). The so DA-converted signals are amplified and applied to a main deflector and a sub deflector, thereby writing each pattern onto a sample (refer to, for example, a patent document 1 (JP-A-2008-182073)). A conventional shot data generating method will be explained with reference to FIG. 13. As shown in FIG. 13, the shapes and positions of graphic patterns P1 and P2 are defined in write data D. In the conventional method, the graphic patterns P1 and P2 defined in the write data Dare divided into a plurality of subfield areas SF. Next, they are divided into graphics FG expressed in shot units within the respective subfield areas SF. Meanwhile, it is known that writing accuracy where a graphic is shot to the center of each subfield area SF and writing accuracy where a graphic is shot to the periphery of the subfield area SF, differ from each other. Multi-pass writing has been performed to enhance the writing accuracy. The multi-pass writing is a method for overlaying graphics written in plural independent passes on one another to write a target pattern. As the multi-pass writing, there are known a method for overlaying graphics written with each subfield area being shifted, on each other, a method for overlaying graphics written with each stripe area (see FIG. 2) being shifted, on each other, and a method for overlaying graphics written with both areas being shifted, on each other. FIG. 13 shows an example for generating shot data in two passes with subfield areas being shifted. In the example, subfield area division corresponding to the second pass is performed so as to differ from subfield area division corresponding to the first pass. In the conventional method, however, graphics FG subsequent to the subfield area divisions differ from one another at the first and second passes. Since shot division is performed on the graphics divided into the subfield areas, it is necessary to perform the shot division for every pass. Thus, since the shot division must be done by the number of passes, time is taken to generate shot data and writing throughput is hence degraded. Attention is paid to the rectangular graphic pattern P1 in the example illustrated in FIG. 13. The graphic pattern is shot-divided into 6×5=30 at the first pass, whereas the graphic pattern is shot-divided into 5×5=25 at the second pass. A problem arises in that when the number of shots differs for every pass in this way, a shot dividing method grows complicated. Further, a problem arises in that the number of shots increases depending on how to perform subfield division. In a normal electron beam writing apparatus, the estimation of the number of shots is performed as a pre-process prior to the generation of shot data, and writing time is estimated from the result of its estimation. Since the conventional shot division is based on the graphics subsequent to the subfield area division and grows very complicated as mentioned above, a huge amount of time is taken for arithmetic processing. Therefore, only a simple method can be adopted as the method for estimating the number of shots as the pre-process. As a result, a problem arises in that the shot dividing method at the pre-process stage and the shot dividing method at the shot data generation stage differ and the accuracy of estimation of the number of shots corresponding to the pre-process is degraded. The present invention has been made in view of the above problems. Namely, an object of the present invention is to provide a charged particle beam writing apparatus and a charged particle beam writing method capable of shortening the time necessary to generate shot data and improving writing throughput. Other objects and advantages of the present invention will become apparent from the following description. According to one aspect of the present invention, a charged particle beam writing apparatus for deflecting a charged particle beam by a main deflector and a sub deflector to write a pattern onto a sample, comprises a shot data generator for generating shot data from write data in which the shape and position of each graphic pattern are defined, and a deflection controller for generating deflection data for controlling the main deflector and the sub deflector from the shot data. The shot data generator comprises shot dividing means for dividing the graphic pattern defined in the write data into graphics expressed in shot units, and means for distributing the respective graphics divided by the shot dividing means to subfield areas capable of being deflected by the main deflector. According to another aspect of the present invention, in a charged particle beam writing method for writing each pattern onto a sample using a charged particle beam deflected by a main deflector and a sub deflector, shot data is generated from write data in which the shape and position of each graphic pattern are defined. Deflection data is generated for controlling the main deflector and the sub deflector from the shot data. The shot data generating step includes a shot dividing step for dividing the graphic pattern defined in the write data into a plurality of graphics expressed in shot units, and a distributing step for distributing the divided graphics to their corresponding subfield areas capable of being deflected by the main deflector. FIG. 1 is a conceptual diagram showing a configuration of an electron beam writing apparatus according to a first embodiment of the present invention. The electron beam writing apparatus shown in FIG. 1 is equipped with a writing section 100, which includes an electronic lens barrel 102. An illuminating lens 114 for applying an electron beam (electron beam accelerated at 50 kV, for example) 112 emitted from an electron gun 110 to a first shaping aperture 120 is disposed within the electronic lens barrel 102. The electron beam 112 is formed so as to assume a rectangle in its sectional shape by being penetrated through the first shaping aperture 120 having a rectangular opening. The so-shaped electron beam 112 is projected onto a second shaping aperture 126 by a projection lens 122. A molding or shaping deflector 124 is disposed concentrically with the electronic lens barrel 102 between the second shaping aperture 126 and the first shaping aperture 120. Since the degree of overlaying of a first shaping aperture image on an opening of the second shaping aperture 126 changes under control of the shaping deflector 124, the shape and size of the electron beam 112 can be controlled. A focal point of the electron beam 112 transmitted through the second shaping aperture 126 is focused on the surface of a sample 142 lying within a writing chamber 104 by an objective lens 128. The sample 142 is placed on an XY stage 140 continuously moved in an X direction (horizontal direction as viewed in the figure) and a Y direction (depth direction as viewed in the figure). The XY stage 140 is moved by a driver 230 and the amount of movement of the XY stage 140 is measured by a laser length measuring instrument 232, so that its position can be recognized. The sample 142 is, for example, a reticle or a mask in which a light-shielding film such as a chromium film and a resist film are stacked or laminated on a glass substrate. A main deflector 130 and a sub deflector 132 each corresponding to an object deflector are disposed concentrically with the electronic lens barrel 102 between the sample 142 and the second shaping aperture 126. A position where the electron beam 112 is applied onto the sample 142 is determined by the main deflector 130 and the sub deflector 132. When a writing process is executed at the electron beam writing apparatus, a pattern 11 to be written onto the sample 142 is divided into strip-like frame areas 12 as shown in FIG. 2. The respective frame areas 12 are written while the XY stage 140 is being continuously moved in the X direction and/or Y direction. Each frame area 12 is further divided into a plurality of subfield areas 13. The electron beam 112 shaped by the first and second shaping apertures 120 and 126 is deflected to write only a required part lying within the subfield area 13. Incidentally, the writing process is performed for every strip-like stripe area (shown with being hatched in FIG. 2) Sr different from the frame area 12. A two-stage object deflector comprised of the main deflector 130 and sub deflector 132 is used for deflection of the electron beam 112. The positioning of the subfield area 13 is performed by the main deflector 130, whereas the location of a pattern writing position within the subfield area 13 is performed by the sub deflector 132. The electron beam writing apparatus shown in FIG. 1 is equipped with a control section 200. The control section 200 is provided with a control computer 202 that performs various controls on the electron beam writing apparatus. The control computer 202 is connected with a storage device 204, which stores design data (CAD data) therein. The design data are data obtained by converting chip data into formats capable of being inputted to the electron beam writing apparatus by an unillustrated external device. A write data converter 206 converts the design data read from the storage device 204 to write data of a format inside the electron beam writing apparatus. The shape and position of each graphic pattern are defined in the write data. Incidentally, the format conversion of the design data to the write data may be performed by the external device. The post-format conversion write data is inputted to a pre-processor 208. The pre-processor 208 performs pre-processing such as a format check for the write data, an estimation of the number of shots, etc. The write data subjected to the pre-processing is inputted to a shot data generator 210. The shot data generator 210 has shot dividing means 212 for dividing graphic data defined in the write data into graphics expressed in shot units, and distributing means 214 for distributing the respective graphics divided by the shot dividing means 212 to their corresponding subfield areas while performing a process for developing position information described in the write data. The shot dividing means 212 temporarily stores the graphics divided in the shot units into a memory 216. The distributing means 214 reads each of the graphics stored in the memory 216 and distributes the read graphic to the subfield area. Shot data generated by the shot data generator 210 is inputted to a deflection controller 218. The deflection controller 218 generates shaping deflection data for control of the shaping deflector 124, main deflection data for control of the main deflector 130 and sub deflection data for control of the sub deflector 132 from the shot data. These shaping deflection data, main deflection data and sub deflection data are indication voltage signals of respective electrodes that configure the shaping deflector 124, main deflector 130 and sub deflector 132. The shaping deflection data generated at the deflection controller 218 is transmitted to a shaping deflection amplifier 220, the main deflection data is transmitted to a main deflection amplifier 222, and the sub deflection data is transmitted to a sub deflection amplifier 224, respectively. The shaping deflection data, the main deflection data and the sub deflection data are respectively DA-converted by the shaping deflection amplifier 220, the main deflection amplifier 222 and the sub deflection amplifier 224. The DA-converted signals are respectively amplified to be capable of driving the respective electrodes and then applied to the shaping deflector 124, the main deflector 130 and the sub deflector 132. Thus, the writing process is executed. A shot data generating method corresponding to a characterizing portion of the present invention will next be explained with reference to FIGS. 3 through 7. FIG. 3 is a flowchart showing a routine for generating shot data. When a shot data generation command is inputted from the control computer 202, the routine is started up by the shot data generator 210. According to the routine, it is discriminated whether a graphic pattern defined in an inputted write pattern has already been shot-divided at a previous pass (Step S10). It is discriminated at Step S10 whether the inputted graphic pattern is identical to the graphic pattern shot-divided at the previous pass. When it is determined at Step S10 referred to above that the graphic pattern has already been shot-divided at the previous pass (first pass), the routine proceeds to a process of Step S30 without executing a process of Step S20. Thus, the post-shot division graphics corresponding to the first pass stored in the memory 216 are used for processing of the following Step S30 subsequent to a second pass. On the other hand, when it is discriminated at Step S10 that the inputted graphic pattern is different from the graphic pattern shot-divided at the previous pass, i.e., when this time corresponds to shot division of a graphic pattern corresponding to the first time (first pass), the routine proceeds to the process of Step S20. At Step S20, the graphic pattern defined in the write data is divided into a plurality of graphics expressed in shot units. The divided graphics are stored in the memory 216. In an example shown in FIG. 4, a rectangular graphic pattern P1 is shot-divided into fifteen graphics FG (=5×3), and a triangular graphic pattern P2 is shot-divided into ten graphics FG. Since the shot division is performed before subfield area division on the basis of each graphic pattern defined in the write data unlike the conventional method, the shot dividing method can be simplified. That is, if the graphic pattern of the same shape is taken, the division of graphics is done by a unique method. Next, the respective graphics shot-divided at Step S20 referred to above are read from the memory 216 while a process for developing position information defined in a state of being compressed to write data is being performed, and then distributed to their corresponding subfield areas (Step S30). Since the graphic patterns per pass are identical where each pattern is drawn in multi-pass writing, the respective graphics shot-divided at the first pass can be used after the second pass. In an example shown in FIG. 7, distributions of graphics to subfield areas are rendered different from each other at first and second passes. When the pattern is written in the multi-pass writing in this way, the respective graphics stored in the memory 216 at the first pass can be used in the process of Step S30 executed after the second pass. Thus, the process of Step S20 becomes unnecessary after the second pass, the time necessary to generate the shot data is shortened and writing throughput can hence be improved. On the other hand, when one graphic subjected to shot division extends astride a plurality of subfield areas adjacent to one another, it goes out of a deflector's control region, thus resulting in the degradation of writing accuracy. It is thus necessary to assuredly contain or hold the shot-divided graphics into one subfield. Thus, in the present embodiment, subfield areas adjacent to one another are overlaid on one another by widths each greater than or equal to the maximum shot size as shown in FIG. 5A. An area hatched in FIG. 5A corresponds to one subfield area SF located in the center. The subfield area SF is superimposed on its adjacent each subfield area SF by the width of the maximum shot size a. The subfield areas SF are overlaid on each other in this way, so that the shot-divided graphics are always held within any one of the subfield areas. Incidentally, the width at which the subfield areas overlap each other is suitable for being set to the maximum shot size a in terms of the efficiency of the writing process. In the example shown in FIG. 5, when part of a graphic FG is located in an overlapped portion of each subfield area SF, the lower left corner of the graphic FG is taken as a standard part S as shown in FIG. 5B, and the corresponding graphic FG is distributed to either a subfield area SFa or SFb in which the standard part S is located, as shown in FIG. 5C. Incidentally, the standard part S at the distribution of each graphic FG to the corresponding subfield area SF may be set to the corner other than the lower left corner. With the center of gravity of each of the shot-divided graphics FG being taken as a standard part S as shown in FIG. 6, the graphics may be distributed to any one of subfield areas SF, based on the positions of the standard parts S. As shown in FIG. 6A, the overlay width of each subfield area SF is assumed to be a length equal to 4/3a times the maximum shot size a, and a line that separates its overlaid region into half is assumed to be a shot determination line L. As shown in FIG. 6B, graphics FG are distributed to either a subfield area SFa or SFb depending on whether the centers of gravity corresponding to standard parts S of the graphics FG are located on any subfield area side as viewed from the shot determination line L. It is next discriminated whether processing corresponding to one stripe has been ended (Step S40). When it is determined at Step S40 that the processing corresponding to one stripe has not been completed, the routine returns to the process of Step S10. On the other hand, the present routine is ended when the processing corresponding to one stripe is determined to have been ended. When distributing processing subsequent to a second pass exists in the next stripe area at this time, graphics shot-divided correspondingly are stored in the memory 216. In the present embodiment as described above, the graphic data defined in the write data is divided into the plural graphics expressed in the shot units, and thereafter the divided graphics are distributed to their corresponding subfield areas, thereby generating the shot data. Accordingly, the shot dividing method can be simplified as compared with the conventional method that performs the subfield division before the shot division. The conventional method that performs the subfield division before the shot division is accompanied by a problem in that when the boundary (referred to as “subfieldboundary” hereinafter) B between subfield areas exists as shown in FIG. 8A, the number of shots increases in a region R close to the subfield boundary B. On the other hand, according to the present embodiment, the number of shots is constant regardless of the presence or absence of subfield boundaries B as shown in FIG. 8B, and hence the number of shots can be prevented from increasing. Further, since the shot dividing method simplified in this way can be adopted upon execution of an estimation of the number of shots for pre-processing, it is possible to enhance the accuracy of an estimation of the number of shots conducted at the pre-processor 208, by extension, the accuracy of an estimation of a writing time. In the present embodiment, when the multi-pass writing is performed, the graphics shot-divided at the first pass are read from the memory 216 and used upon the distribution of the graphics to the subfield areas after the second pass, thereby making unnecessary the shot division subsequent to the second pass. Thus, since the time necessary for the shot division after the second pass can be reduced, the time taken to generate shot data can be shortened. It is thus possible to improve writing throughput. Further, when the multi-pass writing is performed with each subfield area being shifted within the same stripe area, the graphics shot-divided upon the generation of the shot data at the first pass are used for immediately-executed distribution to the subfield area at the second pass, thereby making it possible to erase the graphics stored in the memory 216 in a short time. There can thus be obtained an advantageous effect that the capacity of the memory 216 for storing the shot-divided graphics therein can be reduced. A second embodiment of the present invention will next be explained. FIG. 9 is a conceptual diagram showing a configuration of an electron beam writing apparatus according to the second embodiment of the present invention. The electron beam writing apparatus shown in FIG. 9 is different from the electron beam writing apparatus shown in FIG. 1 in that a shot data generator 210A further includes write data modifying means 213 in addition to shot dividing means 212 and distributing means 214. Since the electron beam writing apparatus shown in FIG. 9 is similar in other configuration to the electron beam writing apparatus shown in FIG. 1, the detailed description thereof will be omitted. The write data modifying means 213 performs a write data modifying process for causing the positions of respective graphics divided by the shot dividing means 212 to be moved on write data. The distributing means 214 distributes the respective graphics to their corresponding subfield areas, based on the positions of the graphics moved on the write data by the write data modifying means 213. The write data modifying process executed by the write data modifying means 213 will be explained with reference to FIGS. 10 through 12. A positional shift of an electron beam produced on a sample 142 of the electron beam writing apparatus will first be explained with reference to FIG. 10. In FIG. 10A, a position indicated by O is set as a reference point. In the example shown in FIG. 10, when an electron beam penetrated through a square opening of a first shaping aperture 120 is not deflected by a shaping deflector 124, it assumes an electron beam having an approximately square horizontal sectional shape and penetrates an opening 126a of a second shaping aperture 126. An approximately square pattern Pa is written in a predetermined position on the sample 142 shown in FIG. 10B by the electron beam 112a1 transmitted through the opening 126a. In the example shown in FIG. 10, when the electron beam penetrated through the opening of the first shaping aperture 120 is deflected by Δx1 to the plus side (right side in the figure) of an X axis and deflected by Δy1 to the plus side (upper side in the figure) of a Y axis by the shaping deflector 124, it assumes an electron beam having an approximately triangular horizontal sectional shape and penetrates an upper right portion 126a1 of the opening 126a of the second shaping aperture 126. Owing to the electron beam 112a2 penetrated through the upper right portion 126a1, an approximately triangular pattern Pb is written in a position shifted by Δx1′ from the position of the rectangular pattern Pa to the plus side of the X axis on the sample 142 and shifted by Δy1′ from the position thereof to the plus side of the Y axis on the sample 142. Similarly, owing to an electron beam 112a3 penetrated through an upper left portion 126a2 of the opening 126a of the second shaping aperture 126, an approximately triangular pattern Pc is written in a position shifted by Δx2′ from the position of the rectangular pattern Pa to the minus side of the X axis on the sample 142 and shifted by Δy2′ from the position thereof to the plus side of the Y axis on the sample 142. Other patterns Pd and Pe are also written in their corresponding positions shifted from the position of the rectangular pattern Pa on the sample 142. In order to cancel out the positional shifts Δx1′, Δx2′, . . . in the X-axis direction and the positional shifts Δy1′, Δy2′, . . . in the Y-axis direction, an offset process of a sub deflector 132 has conventionally been executed. In order to cancel out the positional shift Δx1′ in the X-axis direction, of the pattern Pb and the positional shift Δy1′ thereof in the Y-axis direction, both of which are shown in FIG. 10B by way of example, the electron beam is deflected to the minus side of the X-axis and the minus side of the Y axis by the sub deflector 132 as indicated by arrow in FIG. 11. Thus, as shown in FIG. 11, a pattern Pb′ is written in a target position (i.e., a position where the positional shifts Δx1′ and Δy1′ are canceled out) on the sample 142. Since, however, there is no other choice but to set the size of each subfield smaller than the size of a critical area or region (area in which the electron beam is deflectable at a maximum to the extent not to cause distortion or the like by the sub deflector 132) in such an offset process, writing throughput is in danger of being degraded. Thus, in the present embodiment, a write data modifying process is performed without carrying out the conventional offset process. A description will be made of an example in which approximately triangular patterns Pb1, Pb2, Pb3 and Pb4 located at the four corners of a critical area Aam shown in FIG. 12A are written. Incidentally, arrows shown in FIG. 12A respectively indicate positional shifts of an electron beam caused by its penetration portion of the second shaping aperture. As described with reference to FIGS. 10A and 10B, the positional shift Δx1′ in the X-axis direction and the positional shift Δy1′ in the Y-axis direction occur in the pattern Pb written by the electron beam 112a1. The write data modifying process for canceling out the positional shifts of these patterns Pb1, Pb2, Pb3 and Pb4 is performed by the write data modifying means 213. That is, the respective graphics subjected to the shot division are moved to the minus side of the X axis by the amount corresponding to the positional shift Δx1′ in the X-axis direction and moved to the minus side of the Y axis by the amount corresponding to the positional shift Δy1′ in the Y-axis direction on the write data. As a result, for example, shot-divided graphics FGb1, FGb2, FGb3 and FGb4 are moved to their corresponding positions of graphics FGb1′, FGb2′, FGb3′ and FGb4′ on write data. After the write data modifying process has been conducted as mentioned above, a plurality of graphics FGb1′, FGb2′, FGb3′ and FGb4′ contained in write data are respectively distributed to any of plural subfields by the distributing means 214. In an example illustrated in FIG. 12B, a graphic FGb1′ is distributed to its corresponding subfield SFm, a graphic FGb2′ is distributed to its corresponding subfield SF1, a graphic FGb3′ is distributed to its corresponding subfield SF1-1, and a graphic FGb4′ is distributed to its corresponding subfield SFm-1. In the present embodiment, the size of the subfield (SFm) can be made identical to the size of the critical area (Aam) as shown in FIG. 12. That is, it is not necessary to set the size of the subfield smaller than the size of the critical area. There can thus be obtained an advantageous effect that in addition to the advantageous effect obtained by the first embodiment, an improvement in throughput can be achieved as compared with the case where the conventional offset process is executed. Incidentally, the present invention is not limited to the above embodiments, but may be implemented by making various modifications thereto within the scope not departing from the gist of the present invention. Although the electron beam has been used in the above embodiments, for example, the present invention is not limited to it. The present invention is applicable even to the case where other charged particle beams such as an ion beam, etc. are used. Although in the present embodiment, the distribution of each graphic to the subfield area is performed after the shot division while the development process of each pattern position is being performed, the shot division may be carried out while performing the development process of each pattern position. The features and advantages of the present invention may be summarized as follows. In the first aspect of the present invention, each graphic pattern defined in write data is divided into a plurality of graphics expressed in shot units by shot dividing means. The divided graphics are distributed to their corresponding subfield areas by distributing means. According to the first aspect, since the graphic pattern of the write data is shot-divided without shot-dividing the graphics divided into the subfield areas, the shot division can be simplified. Thus, since the number of shots can be prevented from increasing and the time required to generate shot data can be shortened, writing throughput can be improved. In the second aspect of the present invention, each graphic pattern of write data is divided into a plurality of graphics expressed in shot units. The divided graphics are distributed to their corresponding subfield areas. According to the second aspect, since the graphic pattern defined in the write data is shot-divided without shot-dividing the graphics divided into the subfield areas, shot division can be simplified. Thus, since the number of shots can be prevented from increasing and the time necessary to generate shot data can be shortened, writing throughput can be improved. Thus, the shot division can be shared between a plurality of passes by applying the present invention to a case in which each pattern is written by multi-pass writing. Namely, since there is no need to perform the shot division by the number of passes and the shot division may be performed once, writing throughput can be enhanced. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. The entire disclosure of a Japanese Patent Application No. 2008-240340, filed on Sep. 19, 2008 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.
	summary
	claims	1. A passive residual heat removal system for circulating cooling fluid to a steam generator through a main feedwater line connected to a lower inlet of the steam generator and a main steam line connected to an upper outlet of the steam generator to remove sensible heat in a nuclear reactor coolant system and residual heat in a nuclear reactor core during an accident, the passive residual heat removal system comprising:a makeup facility configured to accommodate excess cooling fluid and supply makeup cooling fluid to maintain an amount of the cooling fluid within a preset range,wherein the lower inlet is at a first vertical height, and the upper outlet is at a second vertical height higher than the first vertical height,wherein the makeup facility comprises:a makeup tank vertically located between the first vertical height and the second vertical height to passively accommodate the excess cooling fluid and supply the makeup cooling fluid according to a water level of the cooling fluid in the makeup tank;a first connection line connected to the main steam line and the makeup tank for allowing cooling fluid to flow from the main steam line to the makeup tank; anda second connection line connected to the makeup tank and the main feedwater line for supplying the main feedwater line with cooling fluid supplied from the makeup tank. 2. The passive residual heat removal system of claim 1, wherein an initial water level of the makeup tank is set to either one of a first through a third water level, andthe first water level corresponds to a level at which the cooling fluid is fully filled in the makeup tank to supply the makeup cooling fluid when the water level of the steam generator is lower than the water level of the makeup tank during an accident, andthe second water level corresponds to a level at which cooling fluid is depleted in the makeup tank to accommodate the excess cooling fluid and supply the accommodated cooling fluid as the makeup cooling fluid during an accident, andthe third water level corresponds to a level formed at a height between the first water level and the second water level to accommodate the excess cooling fluid and supply the cooling fluid using initially stored cooling fluid as the makeup cooling fluid. 3. The passive residual heat removal system of claim 1, wherein the first connection line is connected to the main steam line through a steam line of the passive residual heat removal system to receive steam or the cooling fluid from the steam line. 4. The passive residual heat removal system of claim 1, wherein the makeup facility further comprises a circulation line having one end connected to the main steam line and having the other end connected to the makeup tank. 5. The passive residual heat removal system of claim 4, wherein the first connection line is connected to the main steam line at a position closer to the steam generator than to the circulation line, and the circulation line is connected to the main steam line at a position farther from the steam generator than the first connection line. 6. The passive residual heat removal system of claim 4, wherein the makeup facility further comprises a first pressure drop structure configured to locally cause a decrease of pressure based on a principle in which a pressure relatively decreases according to a speed increase of fluid, andthe first pressure drop structure is provided at a connection portion of the circulation line and the main steam line. 7. The passive residual heat removal system of claim 4, wherein the makeup tank, the first connection line and the circulation line are insulated by an insulator to limit the energy loss of steam passing through the makeup tank, the first connection line and the circulation line during the normal operation of a nuclear power plant. 8. The passive residual heat removal system of claim 4, wherein the passive residual heat removal system comprises:a condensation heat exchanger configured to discharge sensible heat in the nuclear reactor coolant system and residual heat in the nuclear reactor core received through the circulation of the cooling fluid to an outside;a feedwater line connected to the condensation heat exchanger and the main feedwater line for supplying the cooling fluid from the condensation heat exchanger to the steam generator;a steam line connected to the main steam line and the condensation heat exchanger for supplying cooling fluid discharged from the steam generator to the condensation heat exchanger; anda vent line connected to the steam line and the main steam line or connected to the steam line and the makeup tank for preventing non-condensable gas from being accumulated in the makeup tank or the steam line by allowing the cooling fluid flowing from the steam line to be supplied to the main steam line or the makeup tank. 9. The passive residual heat removal system of claim 8, wherein the passive residual heat removal system further comprises an inflow structure configured to induce at least part of a flow of steam, andthe inflow structure comprises at least one of:a first inflow structure extended from the first connection line and inserted into the main steam line to allow an inlet of an internal flow path to face steam flowing through the main steam line so as to induce at least part of steam flowing through the steam line to the first connection line; anda second inflow structure extended from the vent line and inserted into the steam line to allow an inlet of an internal flow path to face steam flowing through the steam line so as to induce at least part of steam flowing through the steam line to the vent line. 10. The passive residual heat removal system of claim 8, wherein the steam line is connected to the main steam line at a position closer to the steam generator than to the vent line, and the vent line is connected to the main steam line at a position farther from the steam generator than the steam line. 11. The passive residual heat removal system of claim 8, wherein the passive residual heat removal system further comprises a second pressure drop structure configured to locally cause a decrease of pressure based on a principle in which the pressure relatively decreases according to a speed increase of fluid, andthe second pressure drop structure is provided at an internal flow path of a connection portion of the vent line and the main steam line to cause a local pressure drop. 12. The passive residual heat removal system of claim 8, wherein an isolation valve that is open by related signals during an accident is provided at the feedwater line to initiate the operation of the passive residual heat removal system, andthe isolation valve is provided in duplicate or in parallel or provided along with a check valve for preventing the backflow of feedwater from the main feedwater line, andthe second connection line is connected to the feedwater line at a position between the two isolation valves provided in duplicate or between the isolation valve and the check valve, and connected to the main feedwater line through the feedwater line. 13. The passive residual heat removal system of claim 8, wherein the feedwater line is connected to the makeup tank for supplying cooling fluid discharged from the condensation heat exchanger to the makeup tank, and the second connection line is connected to the main feedwater line for supplying cooling fluid received through the feedwater line to the steam generator, and the feedwater line is connected to the main feedwater line through the makeup tank and the second connection line. 14. The passive residual heat removal system of claim 8, wherein the makeup facility further comprises a flow resistance portion, andthe flow resistance portion comprises at least one of:a first flow resistance portion provided at the first connection line to adjust a flow of cooling fluid introduced from the main steam line to the makeup tank;a second flow resistance portion provided at the second connection line to adjust a flow of makeup cooling fluid supplied from the makeup tank to the main feedwater line; anda third flow resistance portion provided at the feedwater line to adjust a flow of cooling fluid supplied from the condensation heat exchanger to the feedwater line. 15. A nuclear power plant, comprising:a steam generator provided at a boundary between a primary system and a secondary system;a main feedwater line connected to a lower inlet of the steam generator to supply feedwater from a feedwater system to the steam generator during a normal operation;a main steam line connected to an upper outlet of the steam generator to supply steam from the steam generator to a turbine system during a normal operation;a passive residual heat removal system configured to circulate cooling fluid to the steam generator through the main feedwater line and the main steam line to remove sensible heat in a nuclear reactor coolant system and residual heat in a nuclear reactor core during an accident; anda makeup facility configured to accommodate excess cooling fluid and supply makeup cooling fluid to maintain an amount of the cooling fluid within a preset range,wherein the lower inlet is at a first vertical height, and the upper outlet is at a second vertical height higher than the first vertical height,wherein the makeup facility comprises:a makeup tank vertically located between the first vertical height and the second vertical height to passively accommodate the excess cooling fluid and supply the makeup cooling fluid according to a water level of the cooling fluid in the makeup tank;a first connection line connected to the main steam line and the makeup tank for allowing cooling fluid to flow from the main steam line to the makeup tank; anda second connection line connected to the makeup tank and the main feedwater line for supplying the main feedwater line with cooling fluid supplied from the makeup tank.
041845145	summary	The invention relates to a valve system for actuation or de-actuation of a device, and more particularly to a valve system incorporating single failure protection logic. Valve systems for applications such as actuation or de-actuation of a control rod assembly of a nuclear reactor are known in the art. However, prior known valve systems for reactor scram applications have not incorporated the single failure criteria which protects against spurious action in case of a single failure, nor allowed for testing of the valves during normal operational conditions without either causing or preventing the safety action as required by the reactor protective systems. SUMMARY OF THE INVENTION The present invention provides a simple valve system, which incorporates single failure protection logic for a control rod system of a nuclear reactor, by means of three independent input signals combined in a function commonly known as two-out-of-three logic, which meets the above-mentioned single failure criteria while allowing testing of the actuating valves during normal operation of the reactor protective systems. Using the input signals as independent and redundant actuation/de-actuation signals, a single failure, or failure of the corresponding valve assembly or valve set, will neither prevent the desired action nor cause the undesired action of the associated mechanism. Therefore, it is an object of the invention to provide a valve system which incorporates a single failure protection logic. A further object of the invention is to provide a valve system which allows actuation or de-actuation of a device by means of three independent input signals combined in a function known as two-out-of-three logic. Another object of the invention is to provide a valve system wherein a single signal failure, or failure of the corresponding valve, will neither prevent the desired action nor cause the undesired action of an associated mechanism. Another object of the invention is to provide a valve system which allows testing of the system valves during normal operational conditions without either causing or preventing the action as required by the associated mechanism. Other objects of the invention will become readily apparent from the following descriptions and accompanying drawings.
	abstract	An optical arrangement, in particular a laser scanning microscope, having a light source, in particular a laser light source, and an interruption device (1) for a light beam (2) of the light source, is configured, in the interest of reliable operation, in such a way that means (3) for monitoring the functioning of the interruption device (1) are associated with the interruption device (1). The invention additionally concerns a shutter (5) for a light beam (2) of a light source, in particular a laser light source, which, again in the interest of reliable operation of an optical arrangement, is characterized by at least two movable components (6, 7) which are configured and arranged such that the mechanical momentum generated by a moving component (6) or by several moving components is compensated for by the motion of the other component (7) or components.
	abstract	A time point at which a predetermined period elapses since the start of use of a copying machine as a detection subject after factory shipment or repair is obtained. Pieces of set information, which are combinations of various types of information until the time point is reached are sequentially stored to construct a normal set information group. After the time point is reached, presence of abnormality in the copying machine is determined based on the normal set information group and the various types of information obtained.
	summary
053655559	description	DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Illustrated schematically in FIG. 1 is an exemplary boiling water reactor (BWR) plant conventionally including a reactor pressure vessel 10 disposed in a drywell 12 which in turn is disposed in a containment vessel 14, with a wetwell or suppression pool 16 contained therein. The vessel 10 conventionally includes a nuclear reactor core 18 and a steam separator assembly 20 disposed thereabove, with a steam dryer 22 disposed above the separator assembly 20. The vessel 10 is filled with water 24 to a normal or nominal level L.sub.n at an elevation suitably above the core 18 which is typically within the intermediate region of the steam separator assembly 20. The vessel 10 conventionally includes additional components such as, jet pumps 26 located in the annular downcomer region circumferentially surrounding the core 18 for circulating the water 24 upwardly through the core 18. The core heats the water for generating steam 24a which flows upwardly into the steam separator assembly 20. Moisture is removed from the steam 24a in the assembly 20, and additional moisture is removed therefrom in the dryer 22, as is conventionally known, prior to discharging the steam 24a from the vessel 10 through a conventional main steam nozzle 28. The vessel 10 also includes conventional feedwater nozzles 30 which channel relatively cold feedwater into the vessel 10, the feed water being discharged above the core 18, when required, from conventional spargers (not shown). During operation of the reactor illustrated in FIG. 1, the level L of the water 24 in the vessel 10 is maintained at the nominal level L.sub.n well above the core 18 and at the required location through the steam separator assembly 20. Since the water level L will vary during operation, it must be monitored so that the nominal level may be maintained as well as for providing a water level signal to various conventional safety systems which may be activated as required in the event of deviations of the water level from the nominal level L.sub.n. In accordance with the present invention, a system 32 is provided for measuring the water level L in the vessel 10 which, therefore, is a part thereof. The system 32 further includes a reference leg or pipe 34 containing a predetermined and substantially constant reference column of water therein having a first reference height H.sub.1, with a top or reference level L.sub.r disposed vertically above the nominal level L.sub.n of the reactor water 24 in the vessel 10. A first or narrow range (NR) variable leg or pipe 36 includes a first or upper pressure tap 36a disposed in flow communication with the vessel 10 at a predetermined first death or level D.sub.1 below the reference level L.sub.r and below the nominal level L.sub.n, and further includes a first upper port 36b preferably disposed below the first tap 36a. A first differential pressure monitor 38, also referred to as a level transmitter, is disposed in flow communication with the reference leg 34 and the first port 36b of the first leg 36 for determining differential pressure therebetween to indicate the level L of the water in the vessel 10 above the first tap 36a. The reference leg 34, the first variable leg 36, and the first monitor 38 are conventionally configured and function conventionally for monitoring and indicating the level L of the water 24 in the vessel 10 using the fundamental fluid hydrostatic relationship of the pressure gradient in a fluid at rest being directly proportional to its density, with the pressure difference in the fluid at corresponding elevations therein being interrelated. Accordingly, by measuring the differential pressure between a known constant column of water, i.e. in the reference leg 34, and the pressure in a varying column of water represented by the level L of the water 24 in the vessel 10 as measured at the first port 36b, an accurate indication of the level L in the vessel 10 may be determined in a conventional fashion. FIG. 2 illustrates in more particularity the system 32 which further includes a conventional, thermally insulated steam leg or pipe 40 having an inlet port or tap 40a disposed in flow communication with the vessel 10 above the first tap 36a and above the nominal level L.sub.n of the water 24, shown in phantom in FIG. 2. The steam leg 40 further includes an outlet port 40b which is preferably disposed above the inlet port 40a so that the steam leg 40 is inclined upwardly away from the vessel 10. A conventional cold condensing chamber 42 has an inlet disposed in flow communication with the steam leg outlet port 40b for receiving steam 24a therethrough from the vessel 10 to form condensate in the relatively cold chamber 42 for maintaining the reference level L.sub.r therein. The chamber 42 also includes an outlet at a bottom thereof disposed in flow communication with the reference leg 34 for discharging thereto the condensate formed in the condensing chamber 42. As the steam 24a condenses in the chamber 42 it will partially fill the chamber 42 until the water level reaches the steam leg outlet port 40b, with the excess condensate spilling from the chamber 42 downwardly by gravity through the steam leg 40 for return to the vessel 10. In this way, the column of water in the reference leg 34 is maintained substantially constant and provides the reference level L.sub.r. The reference leg 34, the cooperating steam leg 40, and the condensing chamber 42 are conventional in structure and in operation. Accurate measurement of the water level L in the vessel 10 requires that the column of water in the reference leg 34 be accurately maintained by the condensing chamber 42. However, it has been observed in some operating nuclear reactor plants, that upon depressurization of the vessel 10 under certain conditions, for example, below about 32 kg/cm.sup.2 g, that water level measurement may temporarily falsely read high as indicated above in the Background section. It has been discovered that this aberration appears to be caused by bubbles being buoyed upwardly from the reference leg 34 due to degassing of non-condensable gas dissolved in solution therein. The vessel 10 conventionally includes a non-condensable gas such as oxygen and hydrogen which over the course of time, for example, several months, flows through the steam leg 40 into the condensing chamber 42 wherein the concentration of non-condensable gas therein becomes relatively high and enters into solution into the water therein. Upon depressurization of the vessel 10, it is believed that the non-condensable gas begins to degas from the water in the reference leg 34, decreasing its effective density and thereby artificially reducing the effective height H.sub.1 thereof, and the reference level L.sub.r, which results in an artificially high water level reading from the first monitor 38 for example. In accordance with the present invention, a second variable leg or pipe 44 is provided below the first variable leg 36 and has a second, or lower, pressure tap 44a disposed in flow communication with the vessel 10 through the bottom skirt of one of the jet pumps 26, for example, at a predetermined second level or depth D.sub.2 below the reference level L.sub.r, below the nominal level L.sub.n, and below the first tap 36a. The second variable leg 44 further includes a second or lower port 44b disposed below the second tap 44a so that the second variable leg 44 is inclined downwardly away from the vessel 10. A second differential pressure monitor 46 is disposed in flow communication with the first leg 36 and the second port 44b of the second variable leg 44 in accordance with the present invention for determining differential pressure therebetween to indicate the level L of the water 24 in the vessel 10 between the first and second taps 36a, 44a when the water level falls below the first tap 36a to a lower level L.sub.1 shown in solid line in FIG. 2. The first leg 36 is inclined downwardly away from the vessel 10 for containing the reactor water 24 therein up to the first tap 36a to provide a predetermined second reference column of water having a second height H.sub.2 for the second monitor 46. The second monitor 46 is joined to the first variable leg 36 at any suitable location between the first tap 36a and first port 36b by an extension leg 36e thereof. But for the extension leg 36e joining the second monitor 46 to the first variable leg 36, both the second monitor 46 and the second variable leg 44 are conventional in configuration and function, with the second monitor 46 also being conventionally known as a fuel zone range (FZR) monitor 46 since the second tap 44a is disposed below the active fuel of the core 18, with the first tap 36a being disposed substantially above the top of the active fuel of the core 18. In this way, the water level L within the core 18 may be accurately measured. In a conventional water level measurement system, the second monitor 46 is not connected to the first variable leg 36, but is instead connected directly to the reference leg 34. The level measurement ranges of the first monitor 38 and the second monitor 46 are then suitably selected and calibrated for measuring the water level L in the vessel 10. Since both monitors 38 and 46 are joined to the common reference leg 34 in a conventional system, the spurious level measurement notch discussed above will occur in both monitors. However, in accordance with the present invention, by using the first variable leg 36 instead of the constant reference leg 34 with the second monitor 46, the notch problem will be reduced or eliminated. More specifically, since the notch problem appears to be caused by the degassing of non-condensable gas in the reference leg 34, using the first variable leg 36 instead will improve level measurement in the monitor 46. During normal operation when the normal level L.sub.n of the water 24 is maintained in the vessel 10 as illustrated in phantom line in FIG. 2, the first tap 36a is normally underwater, which prevents the non-condensable gas within the vessel 10 from accumulating in any portion of the first variable leg 36. This is in contrast to the reference leg 34 which communicates with the vessel 10 through the steam leg 40 and condensing chamber 42 which allow the non-condensable gas to accumulate in the chamber 42 over time and increase the concentration of the gas in the water contained in the reference leg 34. During abnormally low levels of the water 24 within the vessel 10 when the accuracy of its measurement is most important, the second monitor 46 in accordance with the present invention provides improved accuracy by using the first variable leg 36 instead of the reference leg 34. Once the level of the water 24 drops below the first tap 36a, the second monitor 46 may then be used to accurately indicate the water level L in the vessel 10 using the first variable leg 36 which is now filled with reactor water up to the first tap 36a with the predetermined water column height H.sub.2. Of course, by joining the second monitor 46 to the first variable leg 36 instead of the reference leg 34, the second monitor 46 is ineffective for measuring water level when the level is above the first tap 36a, in this case the water level being measured instead by the first monitor 38. The system 32 preferably also includes a third variable leg or pipe 48 having a third or middle pressure tap 48a disposed in flow communication with the vessel 10 at a predetermined third level or depth D.sub.3 below the reference level L.sub.r and below the first tap 36a, and above the second tap 44a, with the third leg 48 also including a third or middle port 48b which is disposed below the third tap 48a. A third differential pressure monitor 50 is disposed in flow communication with the reference leg 34 and the third port 48b of the third leg 48 for determining differential pressure therebetween to indicate level L of the water 24 in the vessel 10 above the third tap 48a. The third monitor 50 is joined to the reference leg 34 by an extension 34e thereof to provide a predetermined reference column of water having a height H.sub.3 for use as a reference for measuring water level in the vessel 10 down to the third tap 48a. The third variable leg 48 and the third monitor 50 are conventional in configuration and function, with the third monitor 50 also being conventionally referred to as a wide range (WR) monitor 50. In this way, the three monitors 38, 46, and 50 may be calibrated for use over different as well as overlapping vertical ranges. In the exemplary embodiment illustrated in FIG. 2, the first tap 36a is disposed adjacent to the steam separator assembly 20, at the bottom thereof for example, the third tap 48a is disposed adjacent the top of the core 18 and above the second tap 44a, which is disposed below the core 18. In this way, the first or NR monitor 38 indicates the water level L from the nominal level L.sub.n down to about the first tap 36a, the third or WR monitor 50 indicates the water level L from the nominal level L.sub.n down to about the third tap 48a, and the second or FZR monitor 46 indicates the water level L from about the first tap 36a down to about the second tap 44a when the level drops below the first tap 36a. This arrangement of the taps 36a, 44a, and 48a and the operating ranges of the three monitors 38, 46, and 50 is conventional except for joining the second monitor 46 to the first variable leg 36 through the extension 36e thereof instead of to the reference leg 34, such as the third monitor 50 joined thereto through the extension 34e. In this way, the three monitors 38, 46, and 50 may be conventionally used to monitor water level in the vessel 10 and control conventional safety systems as desired. Since the third monitor 50 uses the reference leg 34, the notch problem can still effect the accuracy of water level measurement therefrom. Accordingly, for those plants which require safety related low water level trips generated by the wide range third monitor 50, the system 32 may further include a fourth differential pressure monitor 52 disposed in flow communication between the first variable leg 36 and the third variable leg 48 for determining differential pressure therebetween to indicate level of the water in the vessel 10 between the first and third taps 36a, 48a when the water level falls below the first tap 36a. In this embodiment, the fourth monitor 52 is suitably joined through an extension 48e of the third variable leg 48 to provide a predetermined reference column of water having a height H.sub.4 up to the first tap 36a, and suitably joined to the first variable leg extension 36e. Although the fourth monitor 52 is unable to measure water level when it is above the first tap 36a, when the water level drops below the first tap 36a the reference column of water captured in the first variable leg 36 is used for the fourth monitor 52, as it is for the second monitor 46, for more accurately determining water level in the vessel 10. As shown in FIG. 2, the reference leg 34 and the variable legs 36, 44, and 48 are all preferably inclined downwardly away from the vessel 10 to allow any gas bubbles therein to escape by being buoyed upwardly for return to the vessel 10, with the first variable leg 36 also being inclined downwardly for capturing water therein to provide the reference column heights H.sub.2, H.sub.4 when the water level in the vessel 10 drops below the first tap 36a. If desired, the signals from the monitors 38 and 50 may be conventionally automatically analyzed by electronic means to detect the well known notching signature and provide an alarm for the plant operator. While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein, and it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims:
051805421	abstract	A container for material contaminated with a toxic substance or a radionuclide has a base with recesses. A highly absorbent cementitious material is disposed in the recesses for absorbing any liquid in the container. The cementitious material is made by mixing together a sodium bentonite clay slurry and a cement slurry at a water/solids ratio of about 1.5/1. Subsequent heating of the mixture removes capillary water without substantially dehydrating any hydrated cement.
	claims	1. A power generation system comprising:a reactor plant presenting a closed-system Brayton regenerated gas turbine cycle, said reactor plant having:a nuclear reactor heating a first working gas,a gas turbine receiving the heated first working gas from said nuclear reactor producing a mechanical output and an exhaust,a plurality of gas compressors, rotated by said gas turbine, and receiving said first working gas from said exhaust of said gas turbine pressurizing said first working gas and returning said first working gas to said nuclear reactor,a recuperator coupled between said gas compressors and said nuclear reactor preheating said first working gas directed into said nuclear reactor,a plurality of heat exchangers cooling said heated first working gas exhausted from said gas turbine prior to entry of said first working gas to said gas compressors, said heat exchangers being connected between said gas turbine and said gas compressors conveying said first working gas there through starting with said nuclear reactor, through said gas turbine, said recuperator, said heat exchangers, said gas compressors, said heat exchangers, said plurality of gas compressors, said recuperator and back to said nuclear reactor,an air compressor plant having a plurality of air compressors coupled to said gas turbine of said nuclear reactor raising a pressure of a second working gas, a plurality of heat exchangers coupled to said air compressors removing thermal energy from said second working gas prior to entry of said second working gas into said air compressors,a turbine plant having a combustion turbine employing fuel ignited in a combustor, said combustion turbine coupled to said compressors of said compressor plant receiving said second working gas therefrom, said combustion turbine and said air compressors of said compressor plant comprising an open-system Brayton combustion turbine cycle,a vapor addition unit having a vessel mixing compressed air from said compressor plant with heated water from said plurality of heat exchangers removing heat from said closed-system Brayton gas turbine cycle and said open-system Brayton combustion turbine cycle, thereby adding moisture by way of evaporation of said heated water into said compressed air of said compressor plant, and pumps circulating water removing heat from said open and closed system Brayton cycles, with said compressed air and vapor directed to said combustion turbine of said open-system Brayton combustion turbine cycle, said vapor with said combustion turbine forming a portion of a first Rankine steam cycle,a heat recovery unit having a plurality of heat exchangers removing thermal energy from combustion gas exhausted from said turbine plant combustion turbine creating steam, heating water for said vapor addition unit and heating said compressed air and said vapor prior to entry of said air vapor mixture to said combustion turbine of said turbine plant,a steam turbine using said steam generated by said heat recovery unit forming a second Rankine steam cycle, said second Rankine steam cycle and said open-system Brayton combustion turbine cycle comprising a combined cycle, andan electrical plant having a first electrical generator driven by said combustion turbine of said turbine plant and acting as a motor during plant startup, shut down and emergency cooling of said nuclear reactor, and a second electrical generator coupled to said steam turbine,whereas said power generating system provides an integrated coupled multi-cycle and multi-fuel system including said closed-system nuclear reactor heated Brayton regenerated gas turbine cycle coupled to said open-system Brayton regenerated combustion turbine cycle by way of said second working gas from said air compressor of said compressor plant of said open-system Brayton combustion turbine cycle, said second Rankine steam cycle coupled to said open-system Brayton combustion turbine cycle by way of said steam turbine using steam heated by waste heat exhausted from said combustion turbine and said first Rankine steam cycle coupled to said open-system Brayton combustion turbine cycle by way of said vapor addition unit coupled to a plurality of heat exchangers, employed throughout the power generating system, removing heat from said Brayton and Rankine cycles. 2. The power generation system set forth in claim 1 wherein said reactor plant further includes an accumulator controlling said closed and open system Brayton cycles, coupled between said gas compressor and said recuperator. 3. The power generation system set forth in claim 1 wherein said heat recovery unit further comprises duct burners coupled to said exhaust gas from said turbine plant combustion turbine. 4. The power generation system set forth in claim 1 wherein said turbine plant combustion turbine is cooled by the steam exhaust from said steam turbine. 5. The power generation system set forth in claim 1 wherein said turbine plant further comprises a steam accumulator coupled to the exhaust of said steam turbine. 6. The power generation system set forth in claim 1 further comprising a diesel and motor generator coupled to said reactor plant gas turbine and gas compressors, said diesel and motor generator providing emergency power and power generation system start-up. 7. The power generation system set forth in claim 1 further comprising a water recovery unit coupled to said turbine plant combustion turbine exhaust condensing water vapor in said combustion turbine exhaust for reuse. 8. The power generation system set forth in claim 7 wherein said condensed water vapor is neutralized minimizing corrosion of materials.
	description	This application claims priority of Provisional Application Ser. No. 60/276,670 filed Mar. 16, 2001. The United States Government has rights in this invention pursuant to Contract No. DE-AC03-76SF00098 between the United States Department of Energy and the University of California. The invention relates to neutron tubes or sources, and more particularly to neutron tubes or sources based on plasma ion generators, including compact neutron tubes or sources which generate a relatively high neutron flux using the D-D reaction. Conventional neutron tubes employ a Penning ion source and a single gap extractor. The target is a deuterium or tritium chemical embedded in a molybdenum or tungsten substrate. Neutron yield is limited by the ion source performance and beam size. The production of neutrons is limited by the beam current and power deposition on the target. In the conventional neutron tube, the extraction aperture and the target are limited to small areas, and so is the neutron output flux. Commercial neutron tubes have used the impact of deuterium on tritium (D-T) for neutron production. The deuterium-on-deuterium (D-D) reaction, with a cross section for production a hundred times lower, has not been able to provide the necessary neutron flux. It would be highly desirable and advantageous to make high flux D-D neutron sources feasible. This will greatly increase the lifetime of the neutron generator, which is unsatisfactory at present. For field applications, it would greatly reduce transport and operational safety concerns. For applications such as mine detection, where thermal neutrons are presently used, the use of the lower energy D-D neutrons (2.45 MeV rather than 14.1 MeV) also would decrease the size of the neutron moderator. High brightness or point neutron sources, i.e. sources in which the neutrons appear to be coming from a point source, are needed in radiography applications. To make a bright neutron source, the target dimensions must be small and the ion current impinging on the target must be high. In conventional neutron generators, the ion source can produce only low current density with low atomic deuterium ion species. Also, since the target dimensions of conventional sources are large, the neutron beam must be collimated to project back to a point source area. Therefore, a neutron source based on D-D reactions which has a high ion current impinging on a small target would be highly advantageous. Applications of a high brightness neutron source include neutron radiography; non-proliferation; mine detection; boron neutron capture therapy (BNCT); and material studies. A neutron generator design with a small target area and a high ion current incident on the target would be highly advantageous. The invention is a spherical neutron generator formed with a small spherical target and a spherical shell RF-driven plasma ion source surrounding the target. A deuterium (or deuterium and tritium) ion plasma is produced by RF excitation in a plasma ion generator using an RF antenna. The plasma generation region is a spherical shell between an outer chamber and an inner extraction electrode. A spherical neutron generating target is at the center of the ion generator and is separated therefrom by an extraction electrode which contains many holes. The target is a spherical ball of titanium which is biased negatively with respect to the extraction electrode. Ions passing through the holes in the extraction electrode are focused onto the target which produces neutrons by D-D or D-T reactions. The target is loaded with D or T by the impinging ion beam. This invention provides a high brightness neutron generator with a small target area and a high total ion current on the target, which thereby functions as a point neutron source. Because of the high ion current on the target area, the much safer D-D reaction can be used, eliminating any tritium from the source. The FIGURE shows a spherical neutron generator 10 of the invention, which has a small spherical neutron generating target (electrode) 12 inside a spherical shell plasma ion source 14. Neutron generator 10 has a spherical target 12 at its center, surrounded by plasma ion source 14. Plasma ion source 14 is formed in the spherical shell defined between outer vacuum chamber 16 and inner perforated extraction electrode 18. The principles of plasma ion sources are well known in the art. Preferably, ion source 14 is a magnetic cusp plasma ion source. Permanent magnets are arranged in a spaced apart relationship, on the outer surface of plasma ion generator 14, to from a magnetic cusp plasma ion source. The principles of magnetic cusp plasma ion sources are well known in the art. Conventional multicusp ion sources are illustrated by U.S. Pat. Nos. 4,793,961; 4,447,732; 5,198,677; 6,094,012, which are herein incorporated by reference. Ion source 14 includes at least one RF antenna (induction coil) 20 for producing an ion plasma from a gas which is introduced into ion source 14. The antenna(s) 20 are connected through a matching network 30 to an RF power supply 32. Preferably in the spherical shell there will be four RF antennas, one in each quadrant of the shell. For neutron generation the plasma is preferably a deuterium ion plasma but may also be a deuterium and tritium plasma. Ion source 14 also includes a spherically shaped extraction electrode 18 at its inner surface. Electrode 18 electrostatically controls the passage of ions from the plasma out of ion source 14. Electrode 18 contains many holes 22 on its circumference so that ions can be extracted from ion source 14 in many beamlets in all directions from the surface. Inside the surrounding ion source 14 is spherical target 12. Target 12 is the neutron generating element. Ions from plasma source 14 pass through holes 22 in electrode 18 and impinge on target 12, typically with energy of 120 keV to 150 keV, producing neutrons as the result of ion induced reactions. The target 12 is loaded with D (or D/T) atoms by the beam. Titanium is not required, but is preferred for target 12 since it improves the absorption of these atoms. Target 12 may have a titanium surface and may be a titanium sphere or a titanium coated copper sphere. In operation, target 12 is biased negatively, e.g.−120 kV, with respect to the extraction electrode 18, which is at ground potential. The bias voltage, from power supply 34, is applied to target 12 by high voltage feedthrough 24 which passes through ion source 14. Because of the spherical geometry, the equipotential surfaces between extraction electrode 18 and target 12 will also be spherical in shape and the electric field generated will focus the ions onto the target 12. A magnet 26 inside target 12 is used to suppress the secondary emission electrons generated on the target surface. Ion source 14 can generate a dense plasma with current density as high as about 1 A/cm2. Chamber cooling coils 28 may surround the chamber 16. The resulting neutron flux may reach 1016 n/s. Because of the high ion current, sufficient neutron flux can be generated from D-D reactions in this neutron generator, as well as by D-T reactions used in a conventional neutron tube, eliminating the need for radioactive tritium. The neutrons produced, 2.45 MeV for D-D or 14.1 MeV for D-T, will also go out radially from neutron generator 10 in all directions. Because of the small target size, neutron generator 10 acts as a point neutron source. The high brightness spherical neutron generator of the invention may be used for a wide variety of applications that require a point neutron source, including but not limited to neutron radiography; non-proliferation; mine detection; boron neutron capture therapy (BNCT); and material studies. Changes and modifications in the specifically described embodiments can be carried out without departing from the scope of the invention which is intended to be limited only by the scope of the appended claims.
	summary
	claims	1. A lithographic projection apparatus comprising:a radiation system for providing a beam of radiation;a support structure for supporting a patterning structure, the patterning structure serving to pattern the beam of radiation according to a desired pattern;a substrate table for holding a substrate; anda projection system for projecting the patterned beam onto a target portion of the substrate,wherein at least one of the radiation system and the projection system comprises at least one optical member and a piezoelectric actuator for positioning said optical member such that the piezoelectric actuator is constructed and arranged to position the optical member in two substantially orthogonal directions. 2. An apparatus according to claim 1, wherein said piezoelectric actuator is an inch-worm actuator. 3. An apparatus according to claim 1, wherein said piezoelectric actuator comprisestwo outer plates;an inner plate positioned between said two outer plates; andat least two piezoelectric stacks positioned on at least one side of said inner plate between said inner plate and one of said two outer plates;wherein said outer and inner plates are substantially parallel and said outer plates are biased towards each other by a compression structure. 4. An apparatus according to claim 3, wherein said piezoelectric stacks are secured to said one of said inner or outer plates. 5. An apparatus according to claim 3, wherein said piezoelectric stacks comprise a first layer of piezoelectric material capable of expanding/contracting in a first direction and, a second layer of piezoelectric material capable of expanding/contracting in a second direction, said first and second directions being substantially orthogonal to one another and at least one of said directions having a component in a direction perpendicular to the plane of said inner and outer plates. 6. An apparatus according to claim 5, further comprising a third layer of piezoelectric material capable of expanding/contracting in a third direction, said first, second and third directions all being substantially orthogonal to one another. 7. An apparatus according to claim 3, wherein said one of said two outer plates has a central cut-out through which a central pin attached to said inner plate at one end extends, and a connection between said central pin and said inner plate comprises a membrane-like portion located in a cut-out area of said inner plate and held by said inner plate at its outer circumference, wherein the central pin is connected to a central area of the membrane-like portion. 8. An apparatus according to claim 7, wherein said membrane-like portion comprises a plurality of spokes which extend from the central area to the outer circumference of the central pin. 9. An apparatus according to claim 8, wherein said membrane-like portion comprises a plurality of spokes which extend from the inner plate to a periphery edge of the central cut-out. 10. An apparatus according to claim 3, further comprising a further inner plate, said further inner plate having a central cut-out in which said inner plate is attached by a membrane-like portion. 11. An apparatus according to claim 1, wherein said optical member is supported by a mounting frame, the frame extending in a plane transverse to a path of radiation to or from the optical member and the frame thereby enclosing the optical member, wherein the optical member is connected to the frame and the frame is connected to at least one piezoelectric actuator. 12. An apparatus according to claim 11, wherein said frame comprises a plurality of struts which are connected at corners of the frame so as to form a frame structure with at least three corners and one of said at least one piezoelectric actuators is connected with each of said at least three corners.
	claims	1. A computer implemented method of determining whether to approve a work permit in a nuclear power plant, comprising:receiving an electronic permit request for a permit to perform work in an area of the plant;determining a quantitative fire risk value associated with the work identified in the permit request;comparing the determined fire risk value to a predetermined quantitative threshold fire risk value associated with the area in which the work will be performed; andgenerating automatic electronic authorization for the permit if the determined fire risk value does not exceed the threshold fire risk value. 2. The method of claim 1, further comprising determining, with one or more processors, at least one compensatory measure to provide protection against a fire risk posed by the work identified in the permit request. 3. The method of claim 2, wherein the step of electronically determining at least one compensatory measure comprises electronically checking the status of fire suppression equipment in and adjacent to the area of the plant in which the work listed in the permit request will occur. 4. The method of claim 2, wherein the step of electronically determining at least one compensatory measure comprises electronically checking the status of combustible transit permits that have been issued for plant areas adjacent to the area of the plant in which the work listed in the permit request will occur. 5. The method of claim 2, wherein the step of electronically determining at least one compensatory measure comprises electronically checking the status of hot work permits that have been issued for plant areas adjacent to the area of the plant in which the work listed in the permit request will occur. 6. The method of claim 2, wherein the step of electronically determining at least one compensatory measure comprises electronically checking the status of barriers in areas of the plant in and adjacent to the area of the plant in which the work listed in the permit request will occur. 7. The method of claim 2, further comprising generating and maintaining a database that lists the physical relationships between barriers, fire detection equipment and fire suppression equipment for different areas of the plant, and wherein the step of electronically determining at least one compensatory measure comprises electronically checking the locations of barriers, fire detection equipment and fire suppression equipment in areas of the plant that are in and adjacent to the area in which the work listed in the permit request will occur. 8. The method of claim 7, wherein the step of generating and maintaining the database also comprises storing the current status of the barriers, fire detection equipment and fire suppression equipment, and wherein the step of electronically determining at least one compensatory measure comprises electronically checking the current status of barriers, fire detection equipment and fire suppression equipment located in areas of the plant that are in and adjacent to the area in which the work listed in the permit request will occur. 9. The method of claim 8, wherein the step of electronically determining at least one compensatory measure further comprises electronically checking the current status of combustible transit permits and hot work permits that have been issued for areas of the plant that are in and adjacent to the area in which the work listed in the permit request will occur. 10. The method of claim 1, wherein the step of determining the quantitative fire risk value associated with the work identified in the work permit comprises:determining a work risk value associated with the work identified in the permit request;determining if any compensatory measures will be taken to reduce the risk of fire posed by the work identified in the permit request;determining a compensatory value representing an amount by which the work risk will be reduced by any compensatory measures that will be taken; anddetermining the quantitative fire risk value associated with the work identified in the permit request based on the determined work risk value and the determined compensatory value. 11. The method of claim 1, wherein the step of determining the quantitative fire risk value associated with the work identified in the permit request comprises considering conditions in areas adjacent to the area in which the work identified in the permit request will be performed. 12. The method of claim 11, wherein considering conditions in the areas adjacent to the area in which the work will be performed comprises considering the condition of fire suppression equipment in areas adjacent to the area in which the work will be performed. 13. The method of claim 11, wherein considering conditions in the areas adjacent to the area in which the work will be performed comprises considering the condition of fire detection equipment in areas adjacent to the area in which the work will be performed. 14. The method of claim 11, wherein considering conditions in the areas adjacent to the area in which the work will be performed comprises considering the condition of fire barriers between the area in which the work will be performed and areas adjacent to the area in which the work will be performed. 15. The method of claim 11, wherein considering conditions in the areas adjacent to the area in which the work will be performed comprises considering any hot work that is scheduled to be performed in areas adjacent to the area in which the work will be performed. 16. The method of claim 11, wherein considering conditions in the areas adjacent to the area in which the work will be performed comprises considering whether any combustible materials are currently being stored in areas adjacent to the area in which the work will be performed. 17. The method of claim 1, wherein the step of determining the quantitative fire risk value associated with the work identified in the permit request comprises determining a fire risk value based on a work risk value associated with the work identified in the permit request and an area risk value associated with the area in which the work will be performed. 18. The method of claim 1, wherein the step of determining the quantitative fire risk value associated with the work identified in the work permit request comprises considering the risk of impairment of alarm panels located in the area where the work identified in the permit request will be performed. 19. The method of claim 18, wherein the step of determining the quantitative fire risk value associated with the work identified in the work permit request further comprises considering the risk of impairment of alarm panels located in areas surrounding the area where the work identified in the permit request will be performed. 20. The method of claim 1, wherein the step of determining the quantitative fire risk value associated with the work identified in the permit request comprises determining an overall fire risk value, and wherein determining the overall fire risk value comprises:determining a work area risk value representative of the fire risk in the area where the work will be performed;determining surrounding area risk values for areas adjacent to the area where the work will be performed, wherein each surrounding area risk value is representative of the fire risk in a surrounding area which is associated with performance of the work identified in the permit request; anddetermining the overall fire risk value based on the work area risk value and the surrounding area risk values. 21. A computer implemented method of determining whether to approve a work permit in a nuclear power plant, comprising:receiving an electronic permit request for a permit to perform work in an area of the plant;recommending that the permit request be approved if a quantitative fire risk value posed by the work identified in the permit request does not exceed a predetermined threshold fire risk value associated with the area in which the work will be performed; andrecommending that the permit request be disapproved if a quantitative fire risk value posed by the work identified in the permit request exceeds the predetermined threshold fire risk value associated with the area in which the work will be performed. 22. The method of claim 21, wherein the step of recommending that the permit request be approved comprises:determining a quantitative fire risk value associated with the work identified in the permit request;comparing the determined fire risk value to the predetermined threshold fire risk value associated with the area in which the work will be performed; andrecommending that the permit request be approved if the determined fire risk value does not exceed the threshold fire risk value. 23. The method of claim 22, wherein the step of determining the fire risk value associated with the work identified in the work permit comprises:determining a quantitative work risk value associated with the work identified in the permit request;determining whether any compensatory measures will be taken to reduce the risk posed by the work identified in the permit request;determining a compensatory value representing an amount by which the quantitative work risk will be reduced by any compensatory measures that will be taken; anddetermining the quantitative fire risk value associated with the work identified in the permit request based on the determined work risk value and the determined compensatory value. 24. The method of claim 22, wherein the step of determining the fire risk value associated with the work identified in the permit request comprises determining a fire risk value based on a work risk value associated with the work identified in the permit request and an area risk value associated with the area in which the work will be performed. 25. The method of claim 2, wherein the step of electronically determining at least one compensatory measure comprises electronically checking the status of fire detection equipment in and adjacent to the area of the plant which the work listed in the permit request will occur.
051494957	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 a perspective view of a portion of a reactor core is provided. FIG. 1 depicts four fuel bundles 12, 14, 16, and 18, positioned as they would be in a nuclear reactor between a lower core plate 19 and an upper "top" guide 20. The fuel bundles 12, 16 are shown in partial cutaway view, without upper tie plates, exposing the interior of the bundles. A cruciform control rod 21 is depicted in a partially inserted position. Each of the four fuel bundles 12, 14, 16, and 18 contain 81 lattice positions in a regular square 9.times.9 array as defined, for example, at a top plate 22. As best seen in FIG. 3, the 81 lattice positions of the array are defined by imaginary lines 24, which are spaced apart by a distance or pitch 26. Each of the 81 lattice positions represents a potential site for a fuel rod. In each fuel bundle construction, certain of these sites are occupied by tie rods (not shown) for holding together top and bottom plates for structural purposes. Most of the lattice positions are substantially occupied by basic fuel rods 28. In most fuel bundle constructions, the fuel rods are tangentially separated by a space 32. As described above, this spacing of fuel rods is preferably maintained by means of spacer devices, described more fully below. Typically, in a boiling water reactor, using a 9.times.9 array, the pitch 26 equals about 11 mm and the spacing 32 equals about 3 mm. In the following, a new water-rod efficiency parameter is described, and water-rod efficiencies for a number of previous water rods are shown. Next, three particular water-rod configurations having a high water-rod efficiency, according to new efficiency parameters, are described. Finally, the way in which the water rods can be provided, and a manner in which they can joined to spacers, is described. According to the present invention, a water rod is provided which affords a desired amount of moderating effect without over moderating. Over-moderation means providing so much moderation that overall efficiency of the reactor is undesirably diminished because of absorption of thermal neutrons. It has been found that, for these purposes, a water rod should be configured to occupy greater than four lattice positions, preferably at least five lattice positions. The water rod should also occupy less than nine lattice positions, preferably about seven or fewer lattice positions. It has been found that by providing water rods occupying this range of lattice positions, the moderating effect of the water in the water rod is sufficient for providing a desirable increase in reactor efficiency without over-moderating the reaction. As described above, an indicator of efficiency is provided which is termed "water rod efficiency." This quantity has been found to be usefully provided by calculation as follows: ##EQU1## Referring now to FIG. 2, the net water rod cross-sectional area divided by the area of a single lattice position is shown as a function of the number of sacrificed lattice positions. TABLE 1 ______________________________________ Previous Device Number of or Sacrificed Point Present Invention Lattice Positions Shape Figure ______________________________________ 34 Previous Device 1 Round* -- 38 Previous Device 1 Round** -- 42 Previous Device 4 Round -- 48 Previous Device 4 Square -- 50 Previous Device 9 Square -- 46 Present Invention 7 Figure-8 9, 10 52 Present Invention 7 Peanut 3, 4 54 Present Invention 7 Rectangle 5, 6 56 Present Invention 5 Cruciform 7, 8 ______________________________________ diameter = fuel rod diameter *diameter > fuel rod diameter The water rod efficiency, defined by Equation No. 1 above, can be graphically seen in FIG. 2 as corresponding to the slope of a line connected to a point to the graph origin (0,0). Line 64, for example, depicts efficiencies of water rods configured as that shown for water rod 34. The efficiency for such configuration is about 0.33. Line 66 depicts the efficiency for water rods configured as water rod 38. The efficiency of such water rods is about 0.65. Line 68 depicts an efficiency of 100% or 1.0. As can be seen from FIG. 2, a number of previous water rod configurations, such as water rods of lines 64 and 66 have been limited to a water rod efficiency of less than about 0.6. For the understanding of the following graphical representation, reference will first be made to certain prior art water rod constructions. Specific points will be plotted on the graph so that the parameter of water rod efficiency can be evaluated in terms of the prior art. Thereafter, the designs herein developed with the help of this tool will be evaluated on the graphical representation. It will be shown that for water rods occupying more than four lattice positions but less than nine lattice positions that the graphical representation of FIG. 2 constitutes a valuable design tool. Consider the simplest prior example of a water rod. This water rod has the same shape and inner diameter of a fuel rod. Naturally, it occupies one lattice position and is round. In order to distribute the supplemental moderator throughout the bundle, ten evenly spaced rods are considered distributed in a 9.times.9 array. Assuming that one such water rod only is used, such a water rod displacement will appear at location 34 on the graphical representation of FIG. 2. Now take the same rod and multiply its location to a total number of 10 locations in the same array. Such a after rod distribution will be found to be at point 58 on the graphical representation of FIG. 2. The connection of the points 34 and 58 by a straight line through the origin of the graph is instructive. It will be found that intermediate numbers of water rods all adhering to the same configuration, will plot at the corresponding "Lattice Positions Sacrificed" location on line 64 of the graph. Consider the same round shape but expand the diameter of the water rod. Expansion of the water rod continues to and until the water rod reaches a maximum diameter without interfering with adjacent lattice position boundaries. Presuming that one such water rod is placed within a fuel bundle, the generation of the point 38 will be plotted. Expanding the total number of water rods to 10 in number, the point 60 will be generated. Connecting these two points by a straight line 66 extending through the origin of the graph as before defines further the efficiency of this water rod design. Further, it will be found that intermediate numbers of water rods all adhering to the same configuration, will plot at the corresponding "Lattice Positions Sacrificed" located on line 66 of the graph. We then have defined on FIG. 2, two lines 64 and 66 whose slope readily define relative boundaries of efficiencies for round prior art water rod and the maximum diameter of a water rod occupying single lattice positions. The plotting of two additional prior art water rod constructions can be instructive. Consider a round water rod. Have this water rod occupy four (4) lattice positions. Such a water rod will plot at point 42 on the graph. Now take the water rod shape and make the water rod section square instead of round. Further have the water rod occupy four lattice positions. Such a water rod will plot at point 48. Finally, take the same square shaped water rod. Continue to expand the dimension of the water rod until nine lattice positions are occupied. A plot of the point 50 will result. There is, however, a drawback to the configurations of the water rods of points 48 and 50. Water rod 48 has been found to occupy less than the desired number of lattice positions; water rod 50 has been found to occupy more than the number of desired lattice positions. It has been found that water rod configurations which occupy four or fewer lattice positions, and have been found to provide too little moderation for the desired efficient reaction in the bundle resident. Other configurations occupying nine or more lattice positions, and have been found to undesirable over-moderate the reaction or sacrifice too many fuel rods. Remembering that the slope of the lines connecting the point of origin (0,0) and a particular point on the graph of FIG. 2, it will be understood the two configurations of points 48 and 50 had highly desirable efficiencies. However, through either occupying too few lattice positions (four for point 48) or too many lattice positions (nine for point 50), respective under moderation or over moderation was present. Therefore, despite the apparent high efficiencies these designs of the prior art are not preferred. The present invention thus includes providing a water rod configuration which both efficiently uses the lattice positions that must be sacrificed, such as providing a water rod efficiency greater than about 0.6, preferably greater than about 0.7, and provides for efficiency of nuclear reactor operation by producing moderation in a desired range. Referring now to FIGS. 3 and 4, water rod 52 contains two topologically concave regions 74a and 74b. A topologically concave region is one in which there is at least one line segment connecting two points of the region which must pass outside of the boundary of the water rod 52. For example, taking points 100, 102, and connecting them by line 103, it can be seen line 103 passes outside of the water rod boundary. The water rod 52 occupies seven lattice positions, and is configured to define two round-cornered triangular regions 76a and 76b, continuously connected at their respective bases 78a and 78b by a constricted region 82. This constricted region 82 is defined by two inwardly-extending longitudinal projections 84a and 84b, as best seen in FIG. 4. As seen in FIG. 4, the inwardly extending longitudinal projections define two grooves 86a and 86b in the exterior of the water rod, which are configured to accommodate portions of fuel rods 87a, 87b. Referring now to FIGS. 5 and 6, a water rod 54 is provided, which is a topologically convex shape. A shape is topologically convex if a line segment connecting any two points does not pass outside the boundary of the water rod. For example, it can be seen that no two points connected by a line will cause the line to pass outside of the water rod. The cross-sectional region of the water rod 54 is substantially rectangular in shape. As best seen from FIG. 5, the water rod is substantially adjacent to a least ten fuel rods positioned in the fuel rod bundle. For this purpose, a fuel rod is adjacent if its lattice position has at least an edge in common with a displaced lattice on position. The water rod 54 occupies seven lattice positions. Turning now to FIGS. 7-8, a water rod 56 is shown, having four interiorly extending longitudinal projections 96a-96d which define therebetween four exteriorally projecting lobes 98a-98d. The interior extending projections 96a-96d define grooves 102a-102d which are configured to accommodate at least a portion of fuel rods 104a-104d within each. The water rod 56 occupies five lattice positions, and includes four topologically concave regions. Referring now to FIGS. 9-10, a water rod 46 is shown having two substantially circular portions. The water rod is substantially adjacent to at least ten fuel rods positioned in the fuel bundle. The water rod 46 occupies seven lattice positions. The water rod 46 can be conceptually viewed as two adjacent and contracting round tubes. In this view, each of the round tubes occupies three and one-half lattice positions. This is one advantage of providing tubes in closely adjacent positions, rather than in spaced-apart positions. If the ground tubes were isolated, each would occupy four lattice positions. By positioning two tubes adjacent to form a single "FIG. 8" water rod, only seven positions are occupied in total, for a savings of one lattice position. Plotting of the designs in the graphical representation of FIG. 2 can be instructive. First, it can be seen that the graphical plot of embodiment of FIGS. 3 and 4 plots at point 52 on the graph. This point yields an efficiency of over (0.91) and has the highest efficiency of the designs developed herein. Accordingly, it is preferred. Plotting of the design of FIGS. 5 and 6, plots at point 54 on the graph. This point yields a lower efficiency (0.77) than the design of FIGS. 3 and 4, but shows structurally a design that is easy to fabricate. This design is not as preferred as the embodiment of FIGS. 3 and 4, but is nevertheless highly advantageous. The four leaf or "clover" design of FIGS. 7 and 8 has high efficiency. It also includes occupation of 5 lattice positions, with the requisite range of lattice positions occupied to produce sufficient moderation. The efficiency of this design is (0.83). This design, because of its complexity of manufacture, is subordinate in preference to the design of FIGS. 3 and 4. Finally, the two adjacent round rods of FIGS. 9 and 10 exhibits high efficiency. It is noted, however, this design is truncated by a chord-presenting a difficulty of manufacture. This design has an efficiency of (0.76). As noted above, the water rods and fuel rods are maintained in a spaced-apart configuration using spacers. In previous configurations, such as circular and square configurations, some amount of rotation about the longitudinal axis of a water tube was possible without interfering with adjacent fuel rods. This characteristic was used to attach or latch a water rod to a spacer to prevent relative axial motion. In such method, a tab was provided on an exterior surface of the water tube. The water tube was moved longitudinally with respect to the spacer until the tab was aligned with, but offset from, an engaging or latching portion of the spacer. The tube was then rotated about its longitudinal axis to bring the tab into engagement with the engaging or latching portion of the spacer. The present invention includes providing a different method for maintaining the axial position of a water rod with respect to a spacer. Although this method can be used with a variety of water rods, it is especially useful when rotation of a water rod about its longitudinal axis is impractical or impossible. According to the present invention, a recess is defined on a portion of an exterior surface of a water rod. The recess can be defined by protrusions extending from the water rod, either integrally formed or attached by welding, brazing, adhering, and the like. The configuration of the water rod is such that the position of the recess with respect to the spacer can be changed by resilient deflection. In the preferred embodiment, the portion of the sidewall of the water tube adjacent to the recess has an amount of resilience. There is enough resilience that a portion of the sidewall near the recess can be inwardly deflected to effect movement of the recess portion. The resiliency also permits later springing back of the sidewall to substantially its original shape for engagement of the recess portion with a portion of the spacer. Referring now to FIGS. 11A-11C, protrusions 110 are integrally formed on an exterior surface of a water rod 112. The water rod protrusions 110 define a recess 114. The spacer 116 has a structure with a shape complementary to the recess. The water rod is axially slid with respect to a spacer assembly 116 until the protrusion 110 contacts at least a portion of the spacer assembly 116. Continuing axial movement of the water rod results in the water rod 112 being resiliently deflected, such as by engagement with a camming surface of the spacer assembly. This causes inward deflection of the sidewall of the water rod 112, as best seen in FIG. 11B. Further axial movement of the water rod with respect to the spacer assembly permits the recess 114 to become aligned with the engaging of the spacer assembly 116. Such engagement permits the water rod sidewall 112 to resiliently return to substantially its original position, as seen in FIG. 11C. The water rod 112 is thus in engaging or latching position with respect to the spacer, thereby maintaining the axial position of the spacer assembly 116 with respect to the water rod 112. Preferred circumferential positions for water rod protrusions are depicted in FIGS. 3, 5, and 7. In FIG. 3, a protrusions 120 is provided on the exterior surface of the water rod 52 in one of the grooves 86b. In FIG. 5 a protrusion 122 is provided on an exterior surface of one of the long sidewalls of a rectangular water rod 54. In FIG. 7 a protrusion 124 is provided in one of the grooves 102c of the water rod 56. The water rod depicted in FIG. 9 is preferably attached to spacer configurations by rotation around longitudinal axes of the round tubes, as described above. Although a number of possible water rod configurations are conceivable, only some configurations can be, in a practical sense, accurately and economically manufactured in the quantities needed. The water rod configurations 52, 54, 56, and 46 depicted in FIGS. 3, 5, 7 and 9, respectively, can be accurately and economically made in quantity. One method of manufacture involves beginning with conventionally-shaped, preferably thin-walled (e.g., 30-35 mils or about 0.75-0.85 mm), tubular bodies, such as circular or square cross-sectional bodies. The bodies are shaped as needed by cold-drawing through one or more dies to provide the desired configurations. The shaping can include the formation of grooves 86a, 86b, 102a-102d, lobes 98a-98d, or corners, as shown in FIGS. 3-8. The water rod 54 depicted in FIGS. 5-6 can also be made by joining, such as by welding, two U-shaped channels. The configurations depicted in FIGS. 3-10 have been found to represent viable configurations in the sense that they provide the desired efficiencies and moderation, and are manufacturable in a practical sense. The present invention includes a method of designing water rods to provide a water rod configuration which is practical and provides for a desired efficiency and desired moderation. Previous substantially empirical methods involved selecting a water rod configuration, typically without knowing the efficiency thereof. Many other reactor designs considerations are dependent upon the choice of water rod configuration. Thus, once a choice was made, redesign was so prohibitively expensive that the process often involved commitment to a design before the pertinent characteristics of the design could be empirically determined. In contrast, the present invention includes calculation of water rod efficiencies and lattice position displacements for two or more designs, and selecting a design using the calculated efficiencies and displacements. In this manner, water rods can be designed with knowledge of their efficiencies and displacements. The likelihood of later difficult and expensive redesign, dependent on the choice of water rod configuration, is, therefore, lessened. As will be apparent to those skilled in the art, a number of modifications and variations of the disclosed embodiments can also be practiced. Other cross-sectional configurations of water rods can be used, provided they produce a water rod efficiency greater than about 0.6, preferably greater than about 0.7, and produce the desired range of moderation. More than one water rod could be provided in a single fuel rod bundle, and different shapes of water rods can be provided in different bundles, although, preferably, the same shape is used in all bundles. Water rods can be provided which combine characteristics of various disclosed water rods. Because fuel for fuel rods a typically produced with a standard cross-sectional configuration, fuel rods are typically integral in that they either occupy all of a fuel rod position, as depicted in FIG. 2, or are entirely absent. However, it is also possible to provide an increased size axially or a changed-configuration of fuel rods to accommodate water rods of different shapes, with appropriate modifications to the calculation of efficiency, degree of moderation, and displaced flow area. Other methods of manufacture of water rods can be used, including casting, milling, rolling, hot-drawing, and the like. The attachment of a water rod to a spacer can be achieved by deflection of a tab without substantial sidewall deflection of a water rod, or by deflection of a portion of the spacer assembly without requiring deflection of the water rod, or some combination thereof. Although the description of the present invention has included a description of the preferred embodiments, other modifications and variations are included within the spirit and scope of the invention as limited only by the appended claims.
	abstract	A method of manufacturing a mask includes designing a second mask data pattern for forming a first mask data pattern, creating a first emulation pattern, which is determined from the second mask data pattern, using a first emulation, creating a second emulation pattern, which is determined from the first emulation pattern, using a second emulation, comparing a pattern, in which the first and second emulation patterns overlap, with the first mask data pattern, and manufacturing a mask layer, which corresponds to the second mask data pattern, according to results of the comparison.
044407181	description	DETAILED DESCRIPTION FIG. 1 shows the tank 1 of the nuclear reactor enclosing the core of this to the interior there penetrates the primary ramp 2 communicating with the loading-unloading lock 3 permitting the passage of the fuel assemblies from the priary ramp 2 to the secondary ramp 4 to bring the fuel assembly 5 into its intermediate storage position 5a at the base of the secondary ramp 4. The movable transfer device according to the invention enables the assembly 5 to be caused to pass from its intermediate storage position 5a to a position 5b inside a transfer module 7 in the evacuation position. The movable transfer device according to the invention further enables the module 7 to be disposed inside the transport truck 8 displaced on a rolling track 9 at the lower part of the structure of the reactor. The transfer device comprises a revolving platform 11 mounted for rotation about a vertical axis on a support 12 resting on the structure of the reactor above access shafts 14 and 15 formed in the structure of the reactor vertically in line with the storage position 5a for the fuel assemblies at the base of the secondary ramp 4 and vertically in line with the loading position for the transfer module. The platform 11 is mounted for rotation on the support 12 by means of a ball bearing 16, and a sealing device 17 enables the space situated below the platform and in communication with the shafts formed in the structure of the reactor to be isolated from the outside atmosphere. The platform 11 is pierced with apertures such as 19 and 20 visible in FIG. 1 and carries an assembly of devices visible in FIGS. 1 and 3. Each of these devices is placed straight above an aperture such as 19 and 20 traversing the platform 11 and bringing the device into communication with one of the vertical shafts 14 and 15 formed in the structure of the reactor, according to the position of the platform in relation to these vertical shafts. In fact, the displacement of the platform in rotation about its vertical axis of rotation enables the various apertures and the various devices to be brought successively into concordance with the vertical shafts 14 and 15. The devices carried by the platform 11 comprise a hopper 23 for the irradiated assemblies, a module winch 24, a hopper 25 for the new assemblies and a device 26 for opening and closing the modules. Moreover, an aperture is provided for the passage of a periscope 27 permitting the observation of the transported assemblies with a view to their identification and their orientation before introduction into the reactor. A motor device, not illustrated, enables the platform 11 to be caused to rotate about its axis to bring the various apertures corresponding to the devices 23,24,25,26 and 27 into coincidence with the upper portion of the shafts 14 and 15. At their upper portion, the shafts 14 and 15 are closed by valves 30 and 31, respectively, while the lower portion of the platform 11 carries connection devices such as 33 and 34 consisting of a device comprising a seal adapted to come into a connecting position on the upper face of the valve 30 or 31. In this manner, when the platform is in the position illustrated in FIG. 1, the hopper 23 for the irradiated assemblies and the module winch 24 being in position above the shafts 14 and 15 respectively, the connecting devices 33 and 34 permit a sealed connection between the interior of the hopper 23 or the interior of the housing of the winch 24 and the vertical shafts 14 and 15 disposed straight above the storage and evacuation positions for the assembly 5. The hopper for irradiated elements 23 consists of an internal tubular casing 35 covered by a protective casing 36 inside which there is disposed, in its upper portion, a winch 37 permitting the vertical displacement of the assembly 5 in the space constituted by the hopper and the shaft 14, when the valve 30 is open. Pincers 38 disposed at the end of the cable of the winch enable the fuel element 5 to be caught in the position 5a and raised inside the hopper 23, the height of which is adapted so that it can contain an assembly 5. The hopper for new assemblies 25 is identical to the hopper 23 except that it does not comprise a thick wall for protection against radiation similar to the thick wall 36. The module winch 24 is disposed inside a case 40, the thick wall of which permits insulation against radiation. Handling pincers 42 fixed to the end of the cable of the winch permit catching of the modules 7 for their displacement inside the shaft 15 into their loading position inside the transport truck 8. The modules 7 comprise a casing 43 of sufficient dimensions to contain a fuel assembly, closed by a stopper 44, the opening and closing of which may be effected by the tool associated with the device 26 for opening and closing the modules. The operation of the device according to the invention is as follows: Before effecting a transfer operation, the device is brought into its position of service in which the support 12 rests on the structure of the reactor in such a manner that the module winch is above the shaft 15. The support 12 is fixed to the structure of the reactor by means of movable fixing devices and the platform is brought into the position illustrated in FIG. 1 by means of its displacement device. Simultaneously, the module, which then contains a new assembly, is brought by the displacement truck 8 below the vertical passage 15 then into its position 7a where it is held in position by a locking device 45, by the module winch 24 and its gripping element 42. The module is then opened. The platform 11 is then turned through 90.degree. to bring the hopper 23 above the shaft 14 and the hopper 25 above the shaft 15. The new assembly contained in the module at 7a and the irradiated assembly placed in the position 5a are raised simultaneously in each of the hoppers. The platform 11 then turns through 180.degree. in such a manner as to bring the irradiated assembly straight above the shaft 15 and the new assembly straight above the shaft 14. The two assemblies are then lowered again, the irradiated assembly into the module at 7a and the new assembly at 5a. The latter can be replaced in the reactor by means of the ramps. A fresh rotation through 90.degree. of the platform 11 will bring the module winch back straight above the passage 14. The module is closed again. It can then be replaced, by means of this winch, in the truck 8 which will evacuate it from the reactor. The chain for handling the fuel assemblies illustrated in FIG. 2 is identical to the chain illustrated in FIGS. 1 and 3, except that a tank for the intermediate storage of the irradiated assemblies 51 is disposed in the vicinity of the tank 1 reactor for the storage of a large number of irradiated assemblies after their extraction from the core and their removal from the reactor tank for the decay of their radioactivity. The secondary ramp 4 leads into the storage tank 51, where a handling device 52 permits the extraction of the assembly 5 from the transport container 54 of the ramp 4 and the transport of the irradiated assembly 5 into a position 5c in the storage structure for the assemblies disposed inside the tank 51. The storage structure for the assemblies is fixed and the handling device 52 is installed on a rotating stopper 53 rigidly connected to a drive device for setting in rotation (not shown). In this manner, all the storage positions of this structure can be filled by means of the handling device 52 and the rotating stopper 53 of the device 51. A ramp 55 ends at its lower portion at the level of the storage structure for the irradiated assemblies. A storage case 56 is articulated to the end of this ramp. The assemblies 5 in the storage position 5c can be placed, by means of the handling tool 52, in the case 56 inside which they can be picked up by the gripping tool 38 of the winch 37 of the hopper for irradiated fuel assemblies 23. The transfer device according to the invention, disposed above the vertical shafts 57 and 58 communicating, respectively with the ramp 55 and with the loading position of the transfer carriage 8, can therefore effect the transfer of the irradiated fuel elements between the storage tank 51 and the module 7 in the position 7a in the passage 58. The other functions already described for the device illustrated in FIG. 1 can likewise be effected by the transfer device illustrated in FIG. 2. The storage tank 51 permits an intermediate storage of the assemblies, between their removal from the reactor tank and their transport by means of the module 7 and the truck 8, for a sufficiently long time for the radioactivity of these assemblies to decay by an important amount. Since the support 12 on which the platform 11 is disposed is movable in relation to the structure of the reactor, the whole of the transfer device can be transported from one place to another on the structure of the reactor at the level of shafts communicating with storage positions and evacuation positions for the fuel assemblies. In the case where a plurality of nuclear reactors are disposed on one and the same site, the transfer device can be used equally well on one or the other of the reactors. This shared use of the transfer device enables both the cost of construction of the nuclear reactors and the time elapsing between two successive uses of the transfer device to be reduced, which increases the reliability of the transfer chain for the assemblies. On the other hand, the transfer device according to the invention enables elimination of a complex assembly integrated with the structure of the reactor which increases its overall size and cost of construction. The invention is not limited to the forms of embodiment which have been described; on the contrary, it comprises all the modifications. Thus, while the device described is adapted to the case where the transfer of the fuel assemblies takes place inside modules which can be placed on transport trucks, it is equally possible to use it where such modules are not used. In such case, the platform might carry only one hopper for irradiated assemblies and one hopper for new assemblies, or even possibly a single hopper for the transfer of the assemblies. It is likewise possible to imagine other devices carried by the platform to effect handling or special work on the assemblies and their transport containers. In short, although the transfer device according to the invention is particularly well adapted to the case of an assembly of fast neutron nuclear reactors grouped on one and the same site, it is likewise possible to use it for the operation of an isolated fast neutron nuclear reactor.
	claims	1. A curved, monochromating diffractive optic for accepting and redirecting x-rays, comprising:at least two planar crystalline layers including a single continuous planar upper layer for accepting the x-rays, the layers each having an individual diffractive effect according to a similar material composition and differing crystalline orientation thereof. 2. The optic of claim 1, wherein the layers are bonded together using a material-on-insulator bonding technique. 3. The optic of claim 2, wherein the layers are silicon, and bonded together using a silicon-on-insulator bonding technique. 4. The optic of claim 3, wherein the optic is a doubly curved, point focusing, monochromating optic, and wherein each layer exhibits an x-ray diffractive property according to its crystalline orientation. 5. The optic of claim 1, wherein the layers are bonded together using an adhesive technique. 6. The optic of claim 1, wherein the optic is a doubly curved, point focusing, monochromating optic. 7. The optic of claim 1, wherein each layer exhibits an x-ray diffractive property according to its crystalline orientation. 8. A curved, monochromating diffractive optic for accepting and redirecting x-rays, comprising:at least two planar crystalline layers including a single continuous planar upper layer for accepting the x-rays, the layers each having an individual diffractive effect according to a different material composition and differing crystalline orientation thereof. 9. The optic of claim 8, wherein the layers are bonded together using a material-on-insulator bonding technique. 10. The optic of claim 9, wherein at least one of the layers is silicon, and bonded within the optic using a silicon-on-insulator bonding technique. 11. The optic of claim 10, wherein the optic is a doubly curved, point focusing, monochromating optic, and wherein each layer exhibits an x-ray diffractive property according to its crystalline orientation. 12. The optic of claim 8, wherein the layers are bonded together using an adhesive technique. 13. The optic of claim 8, wherein the optic is a doubly curved, point focusing, monochromating optic. 14. The optic of claim 8, wherein each layer exhibits an x-ray diffractive property according to its crystalline orientation. 15. A curved, monochromating diffractive optic for accepting and redirecting x-rays, comprising:at least two planar, crystalline layers including a single continuous planar upper layer for accenting the x-rays, the layers each having an individual diffractive effect according to different material compositions and having similar or differing crystalline orientations thereof. 16. The optic of claim 15, wherein the layers are bonded together using a material-on-insulator bonding technique. 17. The optic of claim 16, wherein the optic is a doubly curved, point focusing, monochromating optic, and wherein each layer exhibits an x-ray diffractive property according to its crystalline orientation. 18. The optic of claim 15, wherein the layers are bonded together using an adhesive technique. 19. The optic of claim 15, wherein the optic is a doubly curved, point focusing, monochromating optic. 20. The optic of claim 15, wherein each layer exhibits an x-ray diffractive property according to its crystalline orientation. 21. A method of forming a curved, monochromating diffractive optic for accepting and redirecting x-rays, comprising:using a material-on-insulator bonding technique to bond at least two planar material layers together, including a single continuous planar upper layer for accepting the x-rays, each of the at least two layers having an individual diffractive effect according to a pre-determined crystalline orientation, and similar or different material composition; andforming the at least two bonded layers into the curved, monochromating diffractive optic. 22. The method of claim 21, further comprising forming the at least two bonded layers into the curved optic using a mold. 23. The method of claim 21, wherein the curved optic is a doubly curved, point focusing, monochromating optic. 24. A method of forming a curved, monochromating diffractive optic for accepting and redirecting x-rays, comprising:using an adhesive bonding technique to bond at least two planar material layers together, including a single continuous planar upper layer for accepting the x-rays, each of the at least two layers having an individual diffractive effect according to a pre-determined crystalline orientation, and similar or different material composition; andforming the at least two bonded layers into the curved, monochromating diffractive optic. 25. The method of claim 24, further comprising forming the at least two bonded layers into the curved optic using a mold. 26. The method of claim 24, wherein the curved optic is a doubly curved, point focusing, monochromating optic.
	description	Several embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited to these embodiments. FIG. 1 is a block diagram of an X-ray CT apparatus, which is an embodiment of the present invention. The configuration of the apparatus represents an embodiment of the apparatus in accordance with the present invention. The operation of the apparatus represents an embodiment of the method in accordance with the present invention. As shown in FIG. 1, the apparatus comprises a scan gantry 2, an imaging table 4 and an operating console 6. The scan gantry 2 is an embodiment of the signal acquiring apparatus of the present invention. The scan gantry 2 has an X-ray tube 20. The X-ray tube 20 is an embodiment of the X-ray tube of the present invention. X-rays (not shown) emitted from the X-ray tube 20 are formed into, for example, a fan-shaped X-ray beam, i.e., a fan beam, by a collimator 22, and projected onto a detector array 24. The collimator 22 is an embodiment of the collimator of the present invention. The detector array 24 has a plurality of X-ray detector elements arranged in line as an array in the extent direction of the fan-shaped X-ray beam. The detector array 24 is an embodiment of the detector element array of the present invention. The configuration of the detector array 24 will be described in detail later. The X-ray tube 20, collimator 22 and detector array 24 together constitute an X-ray emitting/detecting apparatus, which will be described in detail later. The detector array 24 is connected with a data collecting section 26 for collecting data detected by the individual X-ray detector elements in the detector array 24. The emission of the X-rays from the X-ray tube 20 is controlled by an X-ray controller 28. The connection relationship between the X-ray tube 20 and the X-ray controller 28 is omitted in the drawing. The collimator 22 is controlled by a collimator controller 30. The connection relationship between the collimator 22 and the collimator controller 30 is omitted in the drawing. The above-described components from the X-ray tube 20 through the collimator controller 30 are mounted on a rotating section 34 of the scan gantry 2. The rotation of the rotating section 34 is controlled by a rotation controller 36. The connection relationship between the rotating section 34 and the rotation controller 36 is omitted in the drawing. The imaging table 4 is intended to carry an object to be imaged (not shown) into and out of an X-ray irradiation space in the scan gantry 2. The relationship between the object and the X-ray irradiation space will be described in detail later. The operating console 6 has a data processing apparatus 60, which is comprised of, for example, a computer. The data processing apparatus 60 is connected with a control interface 62, which is in turn connected with the scan gantry 2 and the imaging table 4. The data processing apparatus 60 controls the scan gantry 2 and the imaging table 4 via the control interface 62. The data collecting section 26, X-ray controller 28, collimator controller 30 and rotation controller 36 in the scan gantry 2 are controlled via the control interface 62. The individual connections between these sections and the control interface 62 are omitted in the drawing. The data processing apparatus 60 is also connected with a data collection buffer 64, which is in turn connected with the data collecting section 26 in the scan gantry 2. Data collected at the data collecting section 26 is input to the data processing apparatus 60 via the data collection buffer 64. The data processing apparatus 60 performs image reconstruction using signals of the transmitted X-rays for a plurality of views collected via the data collection buffer 64. The image reconstruction is performed using a filtered back projection technique, for example. The data processing apparatus 60 is an embodiment of the tomographic image producing apparatus of the present invention. The data processing apparatus 60 is also connected with a storage device 66 for storing several kinds of data, reconstructed images, programs for implementing the functions of the present apparatus, and so forth. The data processing apparatus 60 is moreover connected with a display device 68 that displays the reconstructed image and other information output from the data processing apparatus 60, and an operating device 70 that is operated by a user supplying several instructions and information to the data processing apparatus 60. The user interactively operates the present apparatus using the display device 68 and the operating device 70. FIG. 2 schematically shows a configuration of the detector array 24. As shown, the detector array 24 is a multi-channel X-ray detector having a plurality of X-ray detector elements 24(ik) arranged in an array. The plurality of the X-ray detector elements 24(ik) together form an X-ray impingement surface, curved as a cylindrical concavity. Reference symbol xe2x80x98ixe2x80x99 designates a channel index and xe2x80x98ixe2x80x99=1-1,000, for example. Reference symbol xe2x80x98kxe2x80x99 designates a row index and xe2x80x98kxe2x80x99=1, 2, for example. The X-ray detector elements 24(ik) that have the same row index xe2x80x98kxe2x80x99 together constitute a detector element row. The detector array 24 is not limited to having two rows, but may have more than two rows divided into two groups. Although the description will be made on an example the detector array 24 having two rows hereinbelow, the same holds for a detector array having more rows. A certain number of channels at the ends of the detector array 24 are reference channels 25 in each row. The reference channels 25 are situated outside a range of the object that is projected in imaging. Each X-ray detector element 24(ik) is formed of a combination of a scintillator and a photodiode, for example. It should be noted that the X-ray detector element 24(ik) is not limited thereto but may be a semiconductor X-ray detector element using cadmium telluride (CdTe) or the like, or an ionization chamber X-ray detector element using xenon (Xe) gas, for example. FIG. 3 illustrates a relationship among the X-ray tube 20, collimator 22 and detector array 24 in the X-ray emitting/detecting apparatus. FIG. 3(a) is a view from the front of the scan gantry 2 and (b) is a view from the side of the scan gantry 2. As shown, the X-rays emitted from the X-ray tube 20 are formed into a fan-shaped X-ray beam 400 by the collimator 22, and projected onto the detector array 24. In FIG. 3(a), the extent of the fan-shaped X-ray beam 400 is illustrated. The extent direction of the X-ray beam 400 is identical to the direction of the linear arrangement of the channels in the detector array 24. In FIG. 3(b), the thickness of the X-ray beam 400 is illustrated. The thickness direction of the X-ray beam 400 is identical to the direction of the side-by-side arrangement (k-direction) of the rows in the detector array 24. An object 8 placed on the imaging table 4 is carried into the X-ray irradiation space with the object""s body axis intersecting the fan surface of such an X-ray beam 400, as exemplarily shown in FIG. 4. The scan gantry 2 has a cylindrical structure containing therein the X-ray emitting/detecting apparatus. The X-ray irradiation space is formed in the internal space of the cylindrical structure of the scan gantry 2. An image of the object 8 sliced by the X-ray beam 400 is projected on the detector array 24. The X-rays after passing through the object 8 are detected by the detector array 24. The slice thickness xe2x80x98thxe2x80x99 of the X-ray beam 400 penetrating the object 8 is regulated by the openness of an aperture of the collimator 22. The X-ray emitting/detecting apparatus consisting of the X-ray tube 20, collimator 22 and detector array 24 rotates (or scans) around the body axis of the object 8 while maintaining their mutual relationships. Projection data for a plurality of (for example, ca. 1,000) views are collected per scan rotation. The collection of the projection data is performed by a system of the detector array 24, data collecting section 26 and data collection buffer 64. Based on projection data of two slices collected in the data collection buffer 64, tomographic image production, or image reconstruction, for the two slices is performed by the data processing apparatus 60. The image reconstruction is carried out such as by processing the projection data for, for example, 1,000 views obtained by one scan rotation by the filtered back projection technique. FIGS. 5 and 6 are schematic diagrams illustrating the X-ray beam 400 projected onto the detector array 24 in more detail. As shown in FIG. 5, the slice thickness xe2x80x98thxe2x80x99 of a projection image on the X-ray detectors 242 and 244 is reduced by shifting collimator blocks 220 and 222 in the collimator 22 in a direction such that the aperture is narrowed. Similarly, as shown in FIG. 6, the slice thickness xe2x80x98thxe2x80x99 is increased by moving the collimator blocks 220 and 222 in a direction such that the aperture is widened. Such regulation of the slice thickness is achieved by the collimator controller 30 under the direction of the data processing apparatus 60. Moreover, the impingement position on the detector array 24 in the k-direction is adjusted by simultaneously moving both the collimator blocks 220 and 224 defining the slice thickness xe2x80x98thxe2x80x99 in the k-direction while maintaining their relative positional relationship. The variation in the impingement position associated with the X-ray focus shift can thus be corrected and automatically controlled so that the X-ray beam 400 is always projected onto a constant position. The adjustment of the impingement position in the k-direction may be achieved by shifting the detector array 24 relative to the collimator 22 in the k-direction, as shown by broken arrow, instead of moving the collimator blocks 220 and 222. This allows the mechanism for the slice thickness adjustment and the mechanism for the impingement position control in the thickness direction to be separately provided, thereby allowing diversified control. On the other hand, if all such mechanisms are implemented by the collimator 22, the system for the control can be integrated and desired simplification of configuration can be fulfilled. It will be easily recognized that these two types of means may be combined to perform the impingement position adjustment. Such a function for automatically controlling the impingement position will be sometimes referred to as an auto collimator hereinbelow. FIG. 7 shows a block diagram of the present apparatus with respect to the auto collimator. An error of the impingement position of the X-ray beam 400 in the k-direction is detected by an error detecting section 101 as shown. The error detecting section 101 detects the impingement position error based on outputs from the reference channels 25 of the two rows in the detector array 24. The error detection is performed by using X-ray detected signals A and B of the X-ray beam 400 from the reference channels 25 of the two rows to calculate the error xe2x80x98exe2x80x99 from the following equation: e = A - B A + B . ( 1 ) An error measurement can thus be obtained independent of the magnitude of X-ray detected signals. The error detecting section 101 is implemented by a function of the data processing apparatus 60. The error detecting section 101 is an embodiment of the error detecting means of the present invention. It is also an embodiment of the error detecting apparatus of the present invention. The error detecting signal is input to a control section 103. The control section 103 then feedback-controls the collimator 22 so that the error xe2x80x98exe2x80x99 becomes zero. The control output from the control section 103 is proportional to the error xe2x80x98exe2x80x99, as exemplarily shown in FIG. 8. The slope of this input-output characteristic curve represents a proportional gain G for the control. The proportional gain will be sometimes referred to simply as the gain hereinbelow. When the error xe2x80x98exe2x80x99 becomes zero, the following equation holds: A=B.xe2x80x83xe2x80x83(2) That is, the X-ray beam 400 impinges equally upon the reference channels of the two rows. At this time, the X-ray beam 400 is projected equally divided between the two detector element rows in the detector array 24. The control section 103 is implemented by functions of the data processing apparatus 60 and the collimator controller 30. The control section 103 is an embodiment of the control means of the present invention. It is also an embodiment of the control apparatus of the present invention. The X-ray detected signals of the two detector element rows in the detector array 24 are collected at a signal acquiring section 107, and a tomographic image is produced at a tomographic image producing section 111 based on the collected signals. Thus, two tomographic images having equal slice thicknesses can be obtained. The signal acquiring section 107 is implemented by the data collecting section 26, rotation controller 36 and data collection buffer 64. The signal acquiring section 107 is an embodiment of the signal acquiring apparatus of the present invention. The tomographic image producing section 111 is implemented by a function of the data processing apparatus 60. The tomographic image producing section 111 is an embodiment of the tomographic image producing apparatus of the present invention. The gain of the control section 103 may be varied according to the error. Specifically, as exemplarily shown in FIG. 9, the gain is set to zero when \|e\|xe2x89xa6xcex11,xe2x80x83xe2x80x83(3) the gain is set to G1 (xe2x89xa00) when xcex11 less than \|e\|xe2x89xa6xcex12,xe2x80x83xe2x80x83(4) and the gain is set to G2 ( greater than G1) when \|e\| greater than xcex12.xe2x80x83xe2x80x83(5) In the above equations, xcex11 is an allowed value of the error. It is also a first gain switch point. xcex12 is a second gain switch point. Accordingly, the control is not performed when the error xe2x80x98exe2x80x99 is equal to or less than the allowed value xcex11, that is, a xe2x80x98neutral zonexe2x80x99 can be provided. The control can thereby be stabilized. When the error xe2x80x98exe2x80x99 is more than the allowed value xcex11 and is equal to or less than xcex12, the feedback control is performed with the gain G1 to draw the error xe2x80x98exe2x80x99 back to the allowed value. When the error xe2x80x98exe2x80x99 exceeds xcex12, the feedback is performed with the gain G2 larger than G1 to draw the error xe2x80x98exe2x80x99 back more rapidly than with the control with G1. By thus varying the gain according to the error, collimator control possessing both stability and rapidity can be achieved. It should be noted that the switching of the gain is not limited to three steps as shown in FIG. 9, but may have two steps or more than three steps. The error xe2x80x98exe2x80x99 contains high frequency components. The high frequency components are primarily caused by very small fluctuations of the focus position incident to the rotation of the anode in the X-ray tube. Since the rotation of the anode occurs at high speed, for example, at about 8,000-12,000 rpm, the fluctuations of the focus contain the high frequency components. Since such fluctuations are extraneous to the displacement of the X-ray focus incident to the temperature change, control effected to follow such fluctuations is meaningless, or rather may degrade the stability of the control. Therefore, the high frequency components are removed prior to inputting the error xe2x80x98exe2x80x99 to the control section 103 to further increase the stability of the control. FIG. 10 shows a block diagram of the present apparatus provided with such high frequency component removal. Similar portions in FIG. 10 to those shown in FIG. 7 are designated by similar reference numerals and explanation thereof will be omitted. As shown, a high frequency removing section 105 is situated between the error detecting section 101 and the control section 103. The high frequency removing section 105 removes the high frequency components in the error xe2x80x98exe2x80x99 input from the error detecting section 101 and inputs an error signal not containing the high frequency components to the control section 103. The high frequency removing section 105 is implemented by a function of the data processing apparatus 60. The high frequency removing section 105 is an embodiment of the high frequency component removing means of the present invention. It is also an embodiment of the high frequency component removing apparatus of the present invention. The high frequency component removal in the high frequency removing section 105 is achieved by, for example, determining the average of data obtained in time series. A moving average value of, for example, 16 time-series data values is employed as the average. The number of data values for the moving averaging is not limited to 16 but may be any other appropriate one. The data of the error xe2x80x98exe2x80x99 is obtained successively at the same timing as the view data. Therefore, the error xe2x80x98exe2x80x99 is moving-averaged for, for example, every 16 views. The moving averaging may be weighted by an appropriate weight instead of the simple moving averaging. Moreover, instead of the averaging, the removal of the high frequency components may be achieved by low-pass filtering of the data values of the time-series data. By thus removing the high frequency components contained in the error xe2x80x98exe2x80x99 by the high frequency removing section 105, the control of the impingement position can be stabilized. By stabilizing the impingement position, the slice thicknesses of two tomographic images become equal and stable, thus allowing images to be obtained with good quality. Although the present invention has been described with reference to the preferred embodiments, several changes and substitutions may be made on these embodiments by those ordinarily skilled in the art without departing from the scope of the present invention. Therefore, the scope of the present invention is intended to encompass not only the aforementioned embodiments but all embodiments pertaining to the appended claims. Many widely different embodiments of the invention may be configured without departing from the spirit and the scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.
	description	The present invention relates to a feed water pipe for a steam generator. Hitherto, there is a known feed water pipe which supplies cooling water into a steam generator such as a pressurized water reactor. In the feed water pipe, a thermal stratification phenomenon may occur due to vapor flowing into the pipe. The thermal stratification phenomenon is not desirable in that it causes a stress of a fatigue source. Further, when the vapor flowing into the pipe remains in the pipe after the supply of water is performed again, there is a possibility that water hammer occurs. The water hammer is not desirable in that it generates an impact on an inner pipe. Patent Literature 1 discloses a technique of a feed water pipe of a steam generator in which a weir is attached to an inner upper wall of a feed water pipe bent to raise a water supply ring. Patent Literature 2 discloses a technique of a water supply and discharge pipe structure of a steam generator with a body and a heat exchange pipe group provided inside the body in which a plurality of horizontal outlet ports are bored in an upper pipe wall of a horizontal water supply ring provided in the upper portion inside the body and communicating with a feed water pipe outside the body. Patent Literature 1: Japanese Utility Model Application Laid-open No. 61-121304 Patent Literature 2: Japanese Patent Application Laid-open No. 10-122502 There is room for examining how to suppress the thermal stratification and the water hammer inside the feed water pipe. It is an object of the invention to provide a feed water pipe for a steam generator capable of suppressing thermal stratification and suppressing water hammer inside a pipe. A feed water pipe for a steam generator of the present invention is characterized in that it includes: a generator internal pipe section that extends in the horizontal direction inside a steam generator and includes a pipe path through which cooling water supplied from the outside of the steam generator circulates; and a communication pipe section that is connected to the generator internal pipe section and is provided with a communication path which allows communication between the pipe path and a space outside the generator internal pipe section inside the steam generator, wherein one end of the communication path is connected to the pipe path at an upper end of a cross-section perpendicular to a flow direction of the cooling water in the pipe path and another end of the communication path is positioned lower than the one end of the communication path in a vertical direction, and wherein the one end side and the another end side of the communication path are connected at a position higher than the one end in the vertical direction. According to the feed water pipe for the steam generator, since the other end of the communication path is suppressed from being exposed to the gas layer and the vapor is suppressed from flowing into the pipe path, it is possible to suppress the water hammer inside the feed water pipe for the steam generator. It is preferable in the feed water pipe for the steam generator that another end of the communication path is positioned at or lower than a position of a lower end of the generator internal pipe section in the vertical direction. According to the feed water pipe for the steam generator, even when the water level inside the steam generator is lowered to the lower end of the generator internal pipe section, it is possible to suppress the other end of the communication path from being exposed to the gas layer. It is preferable in the feed water pipe for the steam generator that another end of the communication path is positioned lower than a target water level of the cooling water in the exterior space in the vertical direction. According to the feed water pipe for the steam generator, when the water level inside the steam generator is equal to or higher than the target water level, it is possible to suppress the other end of the communication path from being exposed to the gas layer. It is preferable in the feed water pipe for the steam generator that it further includes: an insertion pipe section that is inserted into a penetration hole penetrating an outer shell member of the steam generator and that extends in a horizontal direction, wherein the cooling water supplied from the outside of the steam generator flows into the pipe path through the insertion pipe section, and wherein the upper end of the cross-section perpendicular to the flow direction of the cooling water of the pipe path is positioned higher than an upper end of an inner wall surface of the insertion pipe section in the vertical direction. According to the feed water pipe for the steam generator, even when the vapor enters the pipe path, the vapor is suppressed from reaching the insertion pipe section. Further, even when the vapor flows from the exterior space into the pipe path, the vapor is suppressed from reaching the insertion pipe section. Further, when the cooling water is supplied from the outside of the steam generator to the insertion pipe section while the vapor remains in the insertion pipe section, the vapor inside the insertion pipe section immediately flows off. Accordingly, the thermal stratification in the insertion pipe section is suppressed. It is preferable in the feed water pipe for the steam generator that the another end of the communication path is positioned lower than the upper end of the inner wall surface of the insertion pipe section in the vertical direction. According to the feed water pipe for the steam generator, even when the water level inside the steam generator is lowered to the upper end of the inner wall surface of the insertion pipe section, it is possible to suppress the other end of the communication path from being exposed to the gas layer. It is preferable in the feed water pipe for the steam generator that a lower end of the pipe path is positioned upper than the upper end of the inner wall surface of the insertion pipe section in the vertical direction. According to the feed water pipe for the steam generator, even when the water level inside the steam generator is lowered to the lower end of the pipe path, it is possible to maintain a state where the insertion pipe section is filled with the cooling water. Accordingly, the vapor is suppressed from entering the insertion pipe section, and hence the thermal stratification in the insertion pipe section may be suppressed. According to the invention, it is possible to suppress the thermal stratification and the water hammer inside the pipe of the feed water pipe for the steam generator. Hereinafter, a feed water pipe for a steam generator according to embodiments of the invention will be described in detail by referring to the drawings. Furthermore, the invention is not limited to the embodiments. Further, the components in the embodiments below include a component which may be easily supposed by a person skilled in the art or a component which has substantially the same configuration. Referring to FIGS. 1 to 4, a first embodiment will be described. The embodiment relates to a feed water pipe for a steam generator. FIG. 1 is a schematic diagram illustrating a steam generator according to the embodiment, FIG. 2 is a cross-sectional view illustrating the feed water pipe for the steam generator according to the embodiment, and FIG. 3 is a cross-sectional view illustrating a main part of the feed water pipe for the steam generator according to the embodiment. FIG. 2 illustrates a cross-sectional diagram when the feed water pipe for the steam generator is viewed in the horizontal direction. A steam generator 1 is used in, for example, a pressurized water reactor (PWR). The pressurized water reactor uses light water as a nuclear reactor coolant and a neutron moderator. In the pressurized water reactor, hot and pressurized light water which is not boiled throughout an entire reactor core is sent as primary cooling water to the steam generator 1. The steam generator 1 transfers the heat of the hot and pressurized primary cooling water to secondary cooling water so as to generate vapor in the secondary cooling water. Then, the vapor rotates a turbine generator so as to generate power. As illustrated in FIG. 1, the steam generator 1 includes a body section 2 which extends in the up and down direction and forms a hermetic hollow cylindrical shape so that the diameter of the lower half portion is smaller than that of the upper half portion. The body section 2 is an outer shell member of the steam generator 1. A cylindrical tube bundle shroud 3 is provided inside the lower half portion of the body section 2 with a predetermined gap with respect to the inner wall surface of the body section 2. In the tube bundle shroud 3, the lower end thereof extends to a pipe plate 4 disposed at the lower side inside the lower half portion of the body section 2, and a predetermined gap is formed with respect to the upper surface of the pipe plate 4. A heat transfer pipe group 51 with a plurality of heat transfer pipes 5 formed in a reverse U-shape is provided inside the tube bundle shroud 3. Each heat transfer pipe 5 is disposed so that the U-shaped circular-arc portion faces the upside, where its end facing the downside is supported by the pipe plate 4 and its intermediate portion is supported by a plurality of pipe supporting plates 6. The pipe supporting plates 6 are provided with a plurality of penetration holes (not illustrated), and each heat transfer pipe 5 penetrates the penetration hole while the heat transfer pipe 5 is not fastened thereto. The lower end of the body section 2 is provided with a channel head 7. The inside of the channel head 7 is divided by a partition wall 8 into an inlet chamber 71 and an outlet chamber 72. One end of each heat transfer pipe 5 is connected to the inlet chamber 71, and the other end of each heat transfer pipe 5 is connected to the outlet chamber 72. Further, the inlet chamber 71 includes an inlet nozzle 711 which communicates with the outside of the channel head 7, and the outlet chamber 72 includes an outlet nozzle 721 which communicates with the outside of the channel head 7. Then, the inlet nozzle 711 is connected with a cooling water pipe (not illustrated) to which the primary cooling water is sent from the pressurized water reactor, and the outlet nozzle 721 is connected with a cooling water pipe (not illustrated) through which the primary cooling water subjected to the heat exchange is sent to the pressurized water reactor. The upper half portion of the body section 2 is provided with a steam-water separator 9 which separates steam into vapor and hot water and a moisture separator 10 which removes moisture of the separated vapor so as to obtain substantially dry vapor. A feed water pipe for a steam generator (hereinafter, simply referred to as a “feed water pipe”) 20 which supplies the secondary cooling water into the body section 2 from the outside is inserted to the outer periphery of the steam-water separator 9. Further, the upper end of the body section 2 is provided with a vapor discharge port 12. Further, a water supply path 13 is provided inside the lower half portion of the body section 2 so as to cause the secondary cooling water, which is supplied from the feed water pipe 20 into the body section 2, to flow down between the body section 2 and the tube bundle shroud 3 and to return at the pipe plate 4 so that the secondary cooling water rises along the heat transfer pipe group 51. Furthermore, the vapor discharge port 12 is connected with a vapor supply path (not illustrated) that sends the vapor to the turbine, and the feed water pipe 20 is connected with a cooling water pipe (not illustrated) that supplies the secondary cooling water in which the vapor used in the turbine is cooled by a condenser (not illustrated). In such a steam generator 1, the primary cooling water which is heated by the pressurized water reactor is sent to the inlet chamber 71, and reaches the outlet chamber 72 through the plurality of heat transfer pipes 5. Meanwhile, the secondary cooling water which is cooled by the condenser is sent to the feed water pipe 20, and is supplied to the body section 2 through the feed water pipe 20. In the embodiment, the secondary cooling water is simply referred to as “cooling water”. The cooling water supplied in to the body section 2 passes through the water supply path 13 and rises along the heat transfer pipe group 51. At this time, a heat exchange between the hot and pressurized primary cooling water and the secondary cooling water is performed inside the body section 2. Then, the cooled primary cooling water is returned from the outlet chamber 72 to the pressurized water reactor. Meanwhile, the secondary cooling water which exchanges heat with the hot and pressurized primary cooling water rises inside the body section 2, and is separated into vapor and hot water by the steam-water separator 9. Then, the separated vapor is sent to the turbine after its moisture is removed by the moisture separator 10. Here, there is a possibility that thermal stratification may occur inside the feed water pipe 20 such that the vapor and the cooling water are stratified or the high-temperature cooling water and the low-temperature cooling water are stratified. When the thermal stratification occurs, a stress which becomes a fatigue source is generated, and hence this is not desirable. Further, when the inflowing vapor remains inside the pipe after the supply of water is performed again, there is a possibility that the water hammer may occur. The water hammer is not desirable it that the water hammer applies an impact on the inner pipe. It is desirable to suppress the occurrence of the thermal stratification and the water hammer in the feed water pipe 20. As will be described in detail below, the feed water pipe 20 according to the embodiment includes a communication pipe section 25 (see FIG. 2) capable of suppressing the occurrence of the water hammer in the feed water pipe 20. The communication pipe section 25 is an outflow pipe through which the cooling water inside a pipe path 22a flows out toward a space 40 inside the steam generator 1. As illustrated in FIG. 3, the communication pipe section 25 is provided with a communication path 26 which causes the pipe path 22a of a generator internal pipe section 22 to communicate with the exterior space 40 of the generator internal pipe section 22. One end 26a of the communication path 26 is connected to the pipe path 22a, and the other end 26b thereof is opened toward the exterior space 40. The other end 26b of the communication path 26 is positioned at the lower side of one end 26a in the vertical direction. Thus, it is possible to suppress the other end 26b from being exposed to the gas layer even when the water level of the cooling water in the exterior space 40 decreases. Accordingly, it is possible to suppress the vapor from flowing into the pipe path 22a through the communication path 26. Accordingly, according to the feed water pipe 20 of the embodiment, the water hammer inside the feed water pipe 20 is suppressed. As illustrated in FIG. 2, the feed water pipe 20 includes an insertion pipe section 21, the generator internal pipe section 22, a connection pipe section 24, and the communication pipe section 25. The insertion pipe section 21, the generator internal pipe section 22, the connection pipe section 24, and the communication pipe section 25 are all tubular members having a circular cross-section. Each of the insertion pipe section 21, the generator internal pipe section 22, the connection pipe section 24, and the communication pipe section 25 is provided with a pipe path having a circular cross-section in the axial direction. The cooling water which is supplied from the outside of the steam generator 1 flows from the insertion pipe section 21 to the pipe path 22a of the generator internal pipe section 22 through the connection pipe section 24. The cooling water inside the pipe path 22a flows out to the space 40 inside the steam generator 1 through the communication pipe section 25. The body section 2 includes a nozzle 11. The nozzle 11 includes a protrusion portion 111 which protrudes outward in the radial direction of the body section 2. Further, the nozzle 11 is provided with a penetration hole 112 which penetrates the nozzle 11 in the axial direction of the protrusion portion 111. The penetration hole 112 penetrates the protrusion portion 111 in the radial direction of the body section 2. The insertion pipe section 21 is fitted to the penetration hole 112 from the inside of the body section 2 in the radial direction. The insertion pipe section 21 is fixed to the nozzle 11 by welding or the like while the outer peripheral surface of the insertion pipe section 21 faces the inner peripheral surface of the protrusion portion 111. That is, the insertion pipe section 21 is inserted into the penetration hole 112 which penetrates the body section 2 of the steam generator 1. The center axis of the nozzle 11, that is, the center axis of the penetration hole 112 is horizontal, and the insertion pipe section 21 extends in the horizontal direction so as to correspond thereto. Further, the insertion pipe section 21 extends in a linear shape, and the extension direction becomes the radial direction of the body section 2. The generator internal pipe section 22 is disposed inside the body section 2, that is, the steam generator 1. The generator internal pipe section 22 is formed in an annular shape, and is disposed horizontally. That is, the generator internal pipe section 22 extends in the circumferential direction of the body section 2 along an inner wall surface 2a of the body section 2. For example, the generator internal pipe section 22 may be disposed so that a center axis 50 of the body section 2 and the center axis of the annular shape exist on the same axis. The generator internal pipe section 22 is supported by the inner wall surface 2a of the body section 2 through a stay 14. The pipe path 22a, through which the cooling water supplied from the outside of the steam generator 1 circulates, is formed inside the generator internal pipe section 22. The pipe path 22a also extends in the horizontal direction so as to correspond to the generator internal pipe section 22 extending in the horizontal direction. That is, in the pipe path 22a, an upper end 22b of a cross-section perpendicular to the flow direction of the cooling water is present at the same vertical position in a cross-section of any axial position. Further, in the pipe path 22a, a lower end 22c of a cross-section perpendicular to the flow direction of the cooling water is present at the same vertical position in a cross-section of any axial position. In this way, the pipe path 22a is a pipe path which extends on the horizontal plane having the same center axis and has the same inner diameter. The connection pipe section 24 connects the insertion pipe section 21 to the generator internal pipe section 22. The connection pipe section 24 extends in the horizontal direction on the extension line of the insertion pipe section 21. In the connection pipe section 24, the end opposite to the connection side with respect to the insertion pipe section 21 is connected to the generator internal pipe section 22. The connection pipe section 24 becomes a branch pipe which is branched from the generator internal pipe section 22 outward in the radial direction of the body section 2. In the embodiment, the insertion pipe section 21, the connection pipe section 24, and the generator internal pipe section 22 are disposed so that the upper ends of the respective pipe paths exist at the same height position. That is, an upper end 21a of the inner wall surface (pipe path) of the insertion pipe section 21 in the connection portion between the insertion pipe section 21 and the connection pipe section 24, an upper end 24a of the pipe path of the connection pipe section 24, and the upper end 22b of the cross-section perpendicular to the flow direction of the cooling water in the pipe path 22a of the generator internal pipe section 22 are present at the same vertical height position. In other words, in the feed water pipe 20, the height position of the upper end in the cross-section perpendicular to the flow direction of the cooling water is the same at all positions of the feed water pipe 20. In this way, since the positions of the upper ends may be aligned, it is possible to suppress the vapor from remaining inside the feed water pipe 20. Furthermore, the center axis of the insertion pipe section 21, the center axis of the connection pipe section 24, and the center axis of the generator internal pipe section 22 may be present at the same vertical height position. The pipe diameter (inner diameter) of the connection pipe section 24 may be set to be equal to, for example, the pipe diameter of the insertion pipe section 21. Further, the pipe diameter of the generator internal pipe section 22 is set to be smaller than, for example, the pipe diameters of the insertion pipe section 21 and the connection pipe section 24. The generator internal pipe section 22 is connected with the communication pipe section 25. The communication pipe section 25 is formed in a reverse U-shape and a reverse J-shape. A plurality of the communication pipe sections 25 are arranged in the axial direction of the generator internal pipe section 22. The communication pipe sections 25 are arranged at the same interval, for example, in the axial direction of the generator internal pipe section 22. FIG. 3 is a cross-sectional view illustrating the generator internal pipe section 22 and the communication pipe section 25. FIG. 3 illustrates the cross-section perpendicular to the axial direction of the generator internal pipe section 22, that is, the cross-section perpendicular to the flow direction of the cooling water of the generator internal pipe section 22. As illustrated in FIG. 3, the communication pipe section 25 is provided with a pipe path 25a. The pipe path 25a serves as the communication path 26 that causes the exterior space 40 of the generator internal pipe section 22 to communicate with the pipe path 22a of the generator internal pipe section 22 inside the steam generator 1. The communication pipe section 25 includes a curved portion 251, a first straight pipe section 252, and a second straight pipe section 253. The curved portion 251 is formed in a reverse U-shape and is curved so that the center is positioned at the upside in relation to both ends in the vertical direction. The first straight pipe section 252 and the second straight pipe section 253 are respectively linear pipe sections, and extend in the vertical direction. The first straight pipe section 252 connects one end of the curved portion 251 to the generator internal pipe section 22 in the vertical direction. For example, the curved portion 251 may be directly connected to the generator internal pipe section 22 by removing the first straight pipe section 252. The first straight pipe section 252 is connected to the top portion of the generator internal pipe section 22, that is, the upper end of the cross-section perpendicular to the flow direction of the cooling water of the generator internal pipe section 22. A communication hole 22e which causes the pipe path 25a to communicate with the pipe path 22a is formed at the connection position between the generator internal pipe section 22 and the first straight pipe section 252. That is, the communication hole 22e serves as a part of the communication path 26 which causes the pipe path 22a to communicate with the exterior space 40. In the embodiment, the communication path 26 includes the pipe path 25a of the communication pipe section 25 and the communication hole 22e. In the embodiment, the diameter of the communication hole 22e is set to be equal to the diameter of the pipe path 25a of the communication pipe section 25. For example, a relation between the pipe diameter (inner diameter) of the communication pipe section 25 and the pipe diameter of the generator internal pipe section 22 may be set so that the sum of the cross-sectional area of the path of the communication pipe section 25 becomes equal to the cross-sectional area of the path of the generator internal pipe section 22. The second straight pipe section 253 is connected to the other end of the curved portion 251. The second straight pipe section 253 is positioned at the inside in the radial direction of the annular shape of the generator internal pipe section 22 in relation to the generator internal pipe section 22. The second straight pipe section 253 extends from the connection portion with respect to the curved portion 251 to the height position corresponding to the lower end of the generator internal pipe section 22 through the side portion of the generator internal pipe section 22. The curved portion 251 reverses the flow direction of the cooling water from the upward direction to the downward direction and ensures a gap between the first straight pipe section 252 and the second straight pipe section 253 so that the second straight pipe section 253 does not interfere with the generator internal pipe section 22. In the cross-section perpendicular to the axial direction of the generator internal pipe section 22, a region R1 existing in the generator internal pipe section 22 and a region R2 existing in the second straight pipe section 253 become different regions in the horizontal direction. In this way, an appropriate gap is ensured between the second straight pipe section 253 and the generator internal pipe section 22. When the cooling water is supplied from the outside of the steam generator 1 to the pipe path 22a, the cooling water inside the pipe path 22a flows out to the exterior space 40 through the communication path 26 by a hydraulic pressure. A lower end surface 253a of the second straight pipe section 253 becomes a horizontal surface. That is, the end opposite to the pipe path 22a in the communication path 26 is opened toward the lower side of the vertical direction. Thus, the cooling water flowing through the communication path 26 flows out toward the downside in the vertical direction. Since the top portion of the generator internal pipe section 22 is provided with the communication hole 22e, it is possible to suppress the vapor from remaining in the generator internal pipe section 22. Even when the vapor remains inside the generator internal pipe section 22, the vapor is discharged from the communication hole 22e to the outside of the generator internal pipe section 22 along with the outflow of the cooling water. Accordingly, it is possible to suppress the occurrence of the water hammer caused by the vapor remaining inside the generator internal pipe section 22. Further, since the communication pipe section 25 connected to the communication hole 22e is formed in a reverse J-shape which is curved upward in the vertical direction, it is possible to suppress the vapor from entering the generator internal pipe section 22 through the communication pipe section 25. The communication pipe section 25 extends upward in the vertical direction from the communication hole 22e, and is returned at the lower side of the curved portion 251 in the vertical direction. Accordingly, the communication path 26 extends upward in the vertical direction from one end 26a connected to the pipe path 22a, and is returned at the lower side of the curved portion 251 in the vertical direction. In this way, since the other end 26b of the communication path 26 is returned downward in the vertical direction, it is possible to suppress the other end 26b from being exposed to the gas layer. Since the exposure of the other end 26b is suppressed, it is possible to suppress the vapor from entering the pipe path 22a through the communication path 26. Further, since the height position of the outflow port of the communication path 26 is lowered in the feed water pipe 20 according to the embodiment, it is possible to suppress the vapor from entering the pipe path 22a. Specifically, in the communication path 26, the other end 26b is positioned at the downside in the vertical direction in relation to one end 26a connected to the pipe path 22a. In the description below, the other end 26b of the communication path 26 is referred to as the “outflow port 26b”. One end 26a of the communication path 26 is connected to the pipe path 22a at the upper end 22b of the cross-section perpendicular to the flow direction of the cooling water of the pipe path 22a, and the other end 26b of the communication path 26 is positioned at the downside in the vertical direction in relation to the upper end 22b. Thus, even when the water level of the cooling water in the exterior space 40 is lowered to the position of the upper end 22b of the pipe path 22a, the other end 26b of the communication path 26 is positioned below the water level of the cooling water. For this reason, it is possible to suppress the vapor of the exterior space 40 from flowing into the pipe path 22a through the communication path 26. Particularly, in the embodiment, the other end 26b of the communication path 26 is present at a position equal to or lower than the lower end of the generator internal pipe section 22 in the vertical direction. As illustrated in FIG. 3, the other end 26b of the communication path 26 is present at a position equal to or lower than a lower end 22f of the cross-section perpendicular to the flow direction of the cooling water in the generator internal pipe section 22, that is, a position equal to or lower than the lower end 22f of the outer peripheral surface of the generator internal pipe section 22 in the vertical direction. Accordingly, even when the water level of the cooling water of the exterior space 40 is lowered to the lower end 22f of the generator internal pipe section 22, it is possible to suppress the vapor of the exterior space 40 from flowing into the pipe path 22a through the communication path 26. Further, in the feed water pipe 20 according to the embodiment, even when the lower end surface 253a of the communication pipe section 25 is exposed to the gas layer, it is possible to suppress the vapor from entering the pipe path 22a of the generator internal pipe section 22. Since the communication pipe section 25 is formed in a shape which is curved upward in the vertical direction, the first straight pipe section 252 near one end 26a of the communication path 26 and the second straight pipe section 253 near the other end 26b are connected to each other at a position above one end 26a in the vertical direction. Since the curved portion 251 which connects the first straight pipe section 252 to the second straight pipe section 253 is positioned above one end 26a in the vertical direction, even when the vapor of the exterior space 40 enters the communication path 26 from the other end 26b, it is possible to suppress the vapor from entering one end 26a in relation to the curved portion 251. Further, in the feed water pipe 20 according to the embodiment, it is possible to suppress the cooling water inside the pipe path 22a from flowing to the outside when the supply of the cooling water is stopped. Since the communication hole 22e is formed at the top portion of the generator internal pipe section 22, it is possible to suppress the cooling water inside the generator internal pipe section 22 from flowing to the outside through the communication hole 22e when the supply of the cooling water is stopped. Further, the curved portion 251 which connects the first straight pipe section 252 to the second straight pipe section 253 is positioned at the upside in the vertical direction in relation to one end 26a. Accordingly, even when the cooling water inside the second straight pipe section 253 and the curved portion 251 flows out to the exterior space 40 in a case where the lower end surface 253a of the communication pipe section 25 is exposed to the gas layer, the cooling water remains in the first straight pipe section 252. Thus, it is possible to suppress the cooling water inside the pipe path 22a from flowing to the outside. In this way, in the feed water pipe 20 according to the embodiment, the vapor is suppressed from entering the pipe path 22a and the cooling water inside the pipe path 22a is suppressed from flowing to the outside when the supply of the cooling water from the outside is stopped. Accordingly, the water hammer inside the feed water pipe 20 is suppressed. The communication pipe section 25 of the embodiment is formed in a reverse J-shape, but the shape of the communication pipe section 25 is not limited thereto. Regardless of the shape of the communication pipe section 25 in the axial direction, it is possible to obtain the effect that suppresses the vapor from entering the pipe path 22a when the end opposite to the pipe path 22a is positioned at the downside in the vertical direction in relation to the end connected to the pipe path 22a in the communication path 26. In the embodiment, the lower end surface 253a of the second straight pipe section 253 is formed as a horizontal surface, but the invention is not limited thereto. For example, the lower end surface 253a, that is, the end surface opposite to the connection side with respect to the generator internal pipe section 22 in the communication pipe section 25 may be inclined with respect to the horizontal direction. In this case, the position of the other end 26b of the communication path 26 in the vertical direction may be set as, for example, the uppermost position of the other end 26b in the vertical direction. FIG. 4 is a diagram illustrating an example of the communication pipe section 25 with an inclined lower end surface. As illustrated in FIG. 4, when a lower end surface 253b of the communication pipe section 25 is inclined with respect to the horizontal plane, an upper end 26c of the other end 26b of the communication path 26 in the vertical direction may be represented as the position of the other end 26b in the vertical direction. That is, the upper end 26c as a portion which is first exposed to the gas layer in the other end 26b of the communication path 26 when the water level of the cooling water of the exterior space 40 is lowered may be positioned at the downside in relation to one end 26a of the communication path 26 or the lower end 22f of the generator internal pipe section 22 in the vertical direction. In the communication pipe section 25 of the embodiment, the outflow port 26b of the communication path 26 is positioned at the inside in the radial direction of the annular shape in relation to the generator internal pipe section 22. However, instead of this arrangement, the outflow port 26b may be positioned at the outside in the radial direction of the annular shape in relation to the generator internal pipe section 22. The generator internal pipe section 22 of the embodiment is formed in an annular shape, but the shape of the generator internal pipe section 22 is not limited thereto. A modified example of the first embodiment will be described. In the first embodiment, the position of the other end 26b of the communication path 26 in the vertical direction is defined based on the position of one end 26a of the communication path 26 or the lower end 22f of the generator internal pipe section 22. In the modified example, instead of this arrangement, the position of the other end 26b of the communication path 26 is defined in advance based on the target water level in the control of the water level of the cooling water of the exterior space 40. Furthermore, the target water level of the cooling water is defined depending on the control parameter of the nuclear plant with the steam generator 1. For example, the other end 26b of the communication path 26 may be set so as to be positioned at the downside in the vertical direction in relation to the lower limit defined in advance at the target water level of the cooling water. For example, when the target water level changes in accordance with the operation status of the nuclear plant, the other end 26b of the communication path 26 may be disposed at the downside in the vertical direction in relation to the lower limit of the target water level which may be set. In this way, even when the control target of the water level is set to any position in a predetermined selectable range, the other end 26b is suppressed from being exposed to the gas layer. Furthermore, a method of defining the position of the other end 26b of the communication path 26 based on the target water level of the cooling water is not limited thereto. For example, the position of the other end 26b may be defined so that the other end 26b is positioned at the downside in relation to the target water level in the normal operation state of the nuclear plant. Referring to FIG. 5, a second embodiment will be described. In the second embodiment, the same reference sign is given to the component having the same configuration as that of the above-described embodiment, and the description thereof will not be repeated. FIG. 5 is a cross-sectional view illustrating a feed water pipe for a steam generator according to the second embodiment. FIG. 5 illustrates a cross-sectional view when the feed water pipe for the steam generator is viewed in the horizontal direction as in FIG. 2. A feed water pipe 60 of the embodiment is different from the feed water pipe 20 of the first embodiment in that a generator internal pipe section 62 is disposed at the upside in the vertical direction in relation to the insertion pipe section 21. Thus, the thermal stratification inside the insertion pipe section 21 is effectively suppressed. The generator internal pipe section 62 is formed in an annular shape as in the generator internal pipe section 22 of the first embodiment, and is disposed horizontally inside the steam generator 1. Further, a pipe path 62a formed in the generator internal pipe section 62 extends in the horizontal direction as in the pipe path 22a of the first embodiment. In a case where the pipe diameter of the generator internal pipe section 62 is smaller than the pipe diameter of the insertion pipe section 21, a tapered portion 642 is formed in a connection pipe section 64 so as to correspond thereto. In the tapered portion 642, the pipe diameter of the connection pipe section 64 gradually decreases from the insertion pipe section 21 toward the generator internal pipe section 62. In accordance with a decrease in the pipe diameter, the pipe bottom of the tapered portion 642 is inclined upward in the vertical direction from the insertion pipe section 21 toward the generator internal pipe section 62. An upper end 62b of the cross-section perpendicular to the flow direction of the cooling water of the pipe path 62a is positioned at the upside in the vertical direction in relation to the upper end 21a of the inner wall surface of the insertion pipe section 21 at the connection portion between the insertion pipe section 21 and the connection pipe section 64. That is, the connection position between a communication path 66 and the pipe path 62a in the vertical direction is positioned at the upside in relation to the upper end 21a of the inner wall surface of the insertion pipe section 21. Accordingly, the connection pipe section 64 includes an inclined portion 641 of which the side near the generator internal pipe section 62 is positioned at the upside in relation to the side near the insertion pipe section 21 in the flow direction of the cooling water. In other words, the connection pipe section 64 is bent with respect to the insertion pipe section 21 so as to raise the generator internal pipe section 62. In this way, since the generator internal pipe section 62 is positioned at the upside in the vertical direction with respect to the insertion pipe section 21, the thermal stratification in the insertion pipe section 21 is suppressed. For example, even when the vapor enters the pipe path 62a of the generator internal pipe section 62, the vapor is suppressed from reaching the insertion pipe section 21. Further, in a case where the vapor of the exterior space 40 flows into the generator internal pipe section 62 through the communication path 66, the vapor is suppressed from reaching the insertion pipe section 21. Further, in a case where the cooling water is supplied from the outside of the steam generator 1 into the insertion pipe section 21 while the vapor remains inside the feed water pipe 60, the vapor inside the insertion pipe section 21 immediately flows off to the generator internal pipe section 62. Since the thermal stratification of the insertion pipe section 21 is suppressed, the feed water pipe 60 has an advantage that the thermal stress in the nozzle 11 is suppressed. Particularly, in the feed water pipe 60 of the embodiment, the pipe path 62a of the generator internal pipe section 62 and a pipe path 21b of the insertion pipe section 21 exist in different regions in the vertical direction, and the pipe path 62a is positioned at the upside in the vertical direction in relation to the pipe path 21b. In other words, a lower end 62c of the cross-section perpendicular to the flow direction of the cooling water of the pipe path 62a of the generator internal pipe section 62 is positioned at the upside in the vertical direction in relation to the upper end 21a of the inner wall surface of the insertion pipe section 21 at the connection portion between the insertion pipe section 21 and the connection pipe section 64. Thus, the thermal stratification in the insertion pipe section 21 is further reliably suppressed. For example, even when the water level of the cooling water of the exterior space 40 is lowered so that the water level of the cooling water is lowered to the lower end 62c of the pipe path 62a inside the generator internal pipe section 62, the pipe path 21b of the insertion pipe section 21 may be filled with the cooling water. Accordingly, it is possible to effectively suppress the vapor from entering the pipe path 21b. Further, in the embodiment, a communication pipe section 65 extends downward in the vertical direction so as to correspond to the structure in which the generator internal pipe section 62 is raised with respect to the insertion pipe section 21. The communication pipe section 65 is formed in a reverse J-shape as in the communication pipe section 25 of the first embodiment, and is provided with the communication path 66 which causes the pipe path 62a to communicate with the exterior space 40. One end 66a of the communication path 66 is connected to the upper end 62b of the cross-section perpendicular to the flow direction of the cooling water of the pipe path 62a. The other end 66b as the outflow port of the communication path 66 is positioned at the downside in the vertical direction in relation to the upper end 21a of the inner wall surface of the insertion pipe section 21 at the connection portion between the insertion pipe section 21 and the connection pipe section 64. Thus, since the other end 66b of the communication path 66 is not exposed to the gas layer even when the cooling water of the exterior space 40 decreases so that the upper end 21a of the inner wall surface of the insertion pipe section 21 is exposed, the vapor is suppressed from entering the generator internal pipe section 62. Furthermore, the position of the other end 66b of the communication path 66 in the vertical direction may be positioned at the lower side of, for example, a lower end 21c of the inner wall surface of the insertion pipe section 21. In this way, according to the feed water pipe 60 of the embodiment, the thermal stratification and the water hammer in the feed water pipe 60 may be suppressed. Particularly, the thermal stratification in the pipe path 21b of the insertion pipe section 21 may be effectively suppressed. Since the thermal stratification in the insertion pipe section 21 is suppressed, the thermal stress in the nozzle 11 is suppressed, and hence there is an advantage that the nozzle 11 is protected. The content described in the respective embodiments above may be performed by the appropriate combination thereof. As described above, the feed water pipe for the steam generator according to the invention may appropriately suppress the thermal stratification and the water hammer inside the pipe. 1 steam generator 2 body section 11 nozzle 20, 60 feed water pipe 21 insertion pipe section 22, 62 generator internal pipe section 22a, 62a pipe path 22e communication hole 24, 64 connection pipe section 25 communication pipe section 26, 66 communication path
	description	This is the U.S. National Stage of PCT/JP2015/078148 filed Oct. 5, 2015, which in turn claims priority to Japanese Application No. 2014-209570, filed Oct. 14, 2014, the entire contents of all applications are incorporated herein by reference in their entireties. The present invention relates to an electron beam sterilization apparatus for sterilizing, e.g., containers for foods and beverages or medical products by applying an electron beam. If a company handling containers for foods and beverages produces food poisoning due to insufficient sterilization of the containers, the company will significantly lose social credibility. Therefore, in advanced countries where safety of foods and beverages is essential, it is necessary to sterilize containers for foods and beverages securely. Devices currently used for secure sterilization of containers apply an electron beam to the containers. Although such devices permit secure sterilization of the containers, application of an electron beam to the containers may produce X-rays, which are radioactive and harmful to organisms. Therefore, there has been provided a structure for the above devices in which the X-rays are sufficiently blocked such that the X-rays produced are prevented from being leaked harmfully (see Patent Literature 1). As shown in FIG. 6 of Patent Literature 1, the structure disclosed in Patent Literature 1 includes a blocking member for blocking X-rays. The blocking member has a cylindrical shape and is mounted on a rotation table for conveying containers to a circular path. With this arrangement, the X-rays can be blocked sufficiently, as shown in FIG. 11 of Patent Literature 1. Patent Literature 1: International Publication No. WO 2013/058204. There have recently been demands for sterilization devices that apply electron beams to more containers in a shorter period of time, in other words, high speed sterilization devices. However, the sterilization devices disclosed in Patent Literature 1, which includes the blocking member mounted on the rotation table and has a large weight, cannot rotate the rotation table at a high speed and is not capable of increasing the speed. In addition, since the blocking member mounted on the rotation table has a large weight, the blocking member (having a cylindrical shape) needs to have a small diameter so as to stabilize the rotation of the rotation table. Therefore, as shown in FIG. 11 of Patent Literature 1, the sterilization device disclosed in Patent Literature 1 needs to have a large number of rotation tables having a blocking member mounted thereon so as to block the X-rays sufficiently, and thus also needs to have a large number of chambers for housing the rotation tables. Accordingly, the sterilization device of Patent Literature 1 has a large size due to a large number of rotation tables and chambers. One object of the present invention is to provide an electron beam sterilization apparatus that has a small size and operates at a high speed without harmful leakage of X-rays. To overcome the above problem, a first aspect of the present invention provides an electron beam sterilization apparatus for sterilizing a container by applying an electron beam while conveying the container, the apparatus comprising: a sterilization chamber including an electron beam application device for applying an electron beam to a container; and a blocking chamber for receiving the container from the sterilization chamber and blocking radioactive rays produced by application of the electron beam, wherein the blocking chamber includes an upstream opening and a downstream opening formed therein, the container being received from the sterilization chamber through the upstream opening and transferred to outside of the blocking chamber through the downstream opening, the blocking chamber includes: a retainer for retaining the container; a rotation table for conveying the container retained by the retainer in a circular path; and at least one blocking wall not in contact with the rotation table and configured to block the radioactive rays from the sterilization chamber, and the at least one blocking wall faces the upstream opening or the downstream opening and has a larger area than the upstream opening or the downstream opening facing thereto. A second aspect of the present invention provides the electron beam sterilization apparatus of the first aspect, wherein the retainer is attached to a periphery of the rotation table and configured to retain the container outside the periphery of the rotation table, and the at least one blocking wall is arranged within a region outward from the periphery of the rotation table to inside of a circular path in which the container is conveyed by the rotation table. Further, a third aspect of the present invention provides the electron beam sterilization apparatus of the first or second aspect, wherein the at least one blocking wall extends higher than upper ends of the upstream opening and the downstream opening. In addition, a fourth aspect of the present invention provides the electron beam sterilization apparatus of the first or second aspect, wherein the at least one blocking wall comprises an upstream blocking wall and a downstream blocking wall, the upstream blocking wall facing the upstream opening and having an area larger than the upstream opening, the downstream blocking wall facing the downstream opening and having an area larger than the downstream opening. A fifth aspect of the present invention provides the electron beam sterilization apparatus of the fourth aspect, wherein a ventilation space is formed between the upstream blocking wall and the downstream blocking wall. A sixth aspect of the present invention provides the electron beam sterilization apparatus of the fourth aspect, wherein the upstream blocking wall and the downstream blocking wall are positioned to block all straight lines connecting between the upstream opening and the downstream opening. A seventh aspect of the present invention provides the electron beam sterilization apparatus of the fourth aspect, wherein no straight lines extending through the upstream opening and an end of the upstream blocking wall intersect, in the blocking chamber, any straight lines extending through the downstream opening and an end of the downstream blocking wall. The above electron beam sterilization apparatus has a small size and operates at a high speed without harmful leakage of X-rays. An electron beam sterilization apparatus according to an embodiment of the present invention will be described below with reference to the accompanying drawings. Briefly, the electron beam sterilization apparatus may sterilize containers by applying an electron beam while conveying the containers. In the following description, a preform product P as shown in FIG. 1 is taken as an example of container. The preform product P may be a material prior to being formed into a plastic bottle B by blow molding and may have a test tube shape (having a U shape in a vertical section with an opened top end u). As shown in FIG. 2, the electron beam sterilization apparatus may schematically include five chambers. These five chambers may include, in the order from the upstream side of the path through which the preform products P are conveyed, a feed chamber 1 into which the preform products P are fed from outside, an outer-surface sterilization chamber 4 in which the outer surfaces of the preform products P are sterilized with electron beams, an inner-surface sterilization chamber 5 in which the inner surfaces of the preform products P are sterilized with electron beams, a blocking chamber 6 for preventing external leakage of X-rays (an example of radioactive rays) produced when the electron beams are applied to the preform products P, and a sorting chamber 9 in which preform products P that are insufficiently sterilized (hereinafter referred to simply as “defective products”) are ejected. These five chambers 1, 4, 5, 6, 9 may have a floor, walls, and a ceiling made of a material that blocks X-rays. The feed chamber 1 may include an input tube 11 for putting in the preform products P and an input star wheel 21 (an example of rotation conveyor plate) from which the preform products P put in through the input tube 11 are conveyed. The outer-surface sterilization chamber 4 may include an outer-surface sterilization unit 41 for receiving the preform products P from the input star wheel 21 and sterilizing the outer surfaces thereof with electron beams. The outer-surface sterilization unit 41 may include an oval path conveyor 42 and an outer-surface electron beam application device 45. The oval path conveyor 42 may be configured to convey in an oval path the preform products P received from the input star wheel 21, and the outer-surface electron beam application device 45 may be configured to apply an electron beam (having a substantially rectangular cross section) to outer surfaces of the preform products P being conveyed by the oval path conveyor 42. The oval path conveyor 42 may include two outer-surface sterilization star wheels 43 and an endless conveyor belt 44. One of the two outer-surface sterilization star wheels 43 may be positioned near one end of the outer-surface electron beam application device 45 and the other may be positioned near the other end of the same. The endless conveyor belt 44 may be stretched between the two outer-surface sterilization star wheels 43 and configured to convey the preform products P. The inner-surface sterilization chamber 5 may include a turn rotation table 51 and an inner-surface sterilization unit 52. The turn rotation table 51 may be configured to receive the preform products P from the oval path conveyor 42 and convey them in a circular path, and the inner-surface sterilization unit 52 may be configured to receive the preform products P from the turn rotation table 5 land sterilize the inner surfaces of the preform products P with electron beams. The inner-surface sterilization unit 52 may include an inner-surface sterilization rotation table 53, elevation devices (not shown), and inner-surface electron beam application devices (not shown) provided in the same number as the elevation devices. The inner-surface sterilization rotation table 53 may be configured to convey the preform products P in a circular path. The elevation devices may be provided on the inner-surface sterilization rotation table 53 at a pitch of a central angle (e.g., 18°, or 0.1 πrad) and configured to elevate and lower the preform products P. The inner-surface electron beam application devices may be positioned directly above the elevation devices and configured to apply electron beams (having a substantially circular cross section) to the inner surfaces of the preform products P. Each of the inner-surface electron beam application devices may be provided with a nozzle at its lower end, for emitting an electron beam downward. The inner-surface electron beam application devices may be positioned directly above the associated elevation devices and may be configured to move in the circular path at the same rotation speed as the elevation devices. The elevation devices may be configured to elevate the preform product P so as to insert the nozzle into an opening of the preform product P, and then lower the preform product P so as to pull the nozzle out of the opening of the preform product P. While the nozzle is out of the opening of the preform product P, the preform product P can be received from or transferred to other rotation tables 51, 71. The blocking chamber 6 may include a sterilized rotation table 71 and blocking walls 81. The sterilized rotation table 71 may be configured to receive preform products P from the inner-surface sterilization rotation table 53 and convey the preform products P in a circular path, and the blocking walls 81 may block the X-rays entering from the inner-surface sterilization chamber 5. The sorting chamber 9 may include a sorting rotation table 91 and an output rotation table 93. The sorting rotation table 91 may be configured to receive preform products P from the sterilized rotation table 71 and convey the preform products P in a circular path, while sorting the defective products from the others. The output rotation table 93 may be configured to receive the preform products P other than the defective products from the sorting rotation table 91 and convey them in a circular path, finally to output the preform products P. In the floor of the sorting chamber 9 below a part of the circular path of the sorting rotation table 91, there may be provided an outlet 92 through which defective products are ejected. When a preform product P being conveyed in the circular path is determined to be defective, the sorting rotation table 91 may drop the defective product from above the outlet 92. The output rotation table 93 may feed the preform products P other than the defective products to an external apparatus F (e.g., an apparatus for blow molding). The above-described rotation tables, that is, the turn rotation table 51, the inner-surface sterilization rotation table 53, the sterilized rotation table 71, the sorting rotation table 91, and the output rotation table 93, may be provided with grippers 74 (an example of retainers) for gripping the preform products P at a pitch of a central angle (e.g., 18°, or 0.1 πrad). At a position to receive a preform product P from the upstream side for conveying it in a circular path, the grippers 74 may grip a neck n (see FIG. 1) of the preform product P, and at the position to transfer the preform product P to the downstream side, the grippers 74 may release the preform product P. Thus, the preform product P can be transferred smoothly from the upstream side to the downstream side. The elevation devices provided for the inner-surface sterilization table 53 can elevate or lower the preform products P independently for the associated grippers 74. In the outer-surface sterilization chamber 4 and the inner-surface sterilization chamber 5, the electron beams may cause a chemical reaction of the air that produces ozone. Ozone may accumulate in the electron beam sterilization apparatus 10 to cause corrosion of the electron beam sterilization apparatus 10. Therefore, the electron beam sterilization apparatus 10 may include a ventilator (not shown) for discharging ozone by pressure difference. The blocking chamber 6 which constitutes the purport of the present invention will be described in detail with reference to FIGS. 3 to 5. As shown in FIGS. 3 to 5, the blocking chamber 6 may be partitioned with a partition wall 61 from the inner-surface sterilization chamber 5 and the sorting chamber 9 adjacent to the blocking chamber 6. The partition wall 61 may be made of a material that blocks X-rays. The partition wall 61 may have an upstream opening 62 and a downstream opening 63 formed therein. The upstream opening 62 may allow the preform products P to be transferred from the inner-surface sterilization rotation table 53 of the inner-surface sterilization chamber 5 to the sterilized rotation table 71, and the downstream opening 63 may allow the preform products P to be transferred from the sterilized rotation table 71 to the sorting rotation table 91 of the sorting chamber 9. The upstream opening 62 and the downstream opening 63 may have the minimum size that enables transfer of the preform products P, so as to prevent leakage of the X-rays. The sterilized rotation table 71 may include a circular plate 72 and a drive shaft 73. The circular plate 72 may serve as a table arranged substantially in a horizontal position, and as shown in FIG. 5, the drive shaft 73 may be configured to rotate the circular plate 72 around a vertical axis 7v (the central axis 7v of the circular plate 72). The lower end of the drive shaft 73 may be connected to a drive unit (not shown) provided below the floor of the blocking chamber 6, and the upper end of the drive shaft 73 may be connected to the circular plate 72. As shown in FIGS. 3 and 5, the grippers 74 provided on the sterilized rotation table 71 may include a connection plate 75, a suspending member 76, and a pair of grip arms 77. The connection plate 75 may extend from the top surface of the periphery of the sterilized rotation table 71 in an outward direction with respect to the central axis 7v. The suspending member 76 may extend downward from the outer end of the connection plate 75. The pair of grip arms 77 may be capable of gripping a preform product P outside the suspending member 76. With this arrangement of the grippers 74, the preform products P may be gripped outside and below the circular plate 72 of the sterilized rotation table 71. Therefore, the upstream opening 62 may also be below the circular plate 72 of the sterilized rotation table 71. As shown in FIGS. 4 and 5, the blocking walls 81 may include an upstream blocking wall 82 and a downstream blocking wall 83. The upstream blocking wall 82 may face the upstream opening 62 and have an area larger than the upstream opening 62, and the downstream blocking wall 83 may face the downstream opening 63 and have an area larger than the downstream opening 63. Both the upstream blocking wall 82 and the downstream blocking wall 83 may be positioned outside so as to be nearly in contact with the grippers 74. Therefore, as viewed in a plan view shown in FIG. 4, the upstream blocking wall 82 and the downstream blocking wall 83 may be arranged in an arc shape with the central axis 7v at the center thereof and extend so as to cover the upstream opening 62 and the downstream opening 63, respectively. Further, as shown in FIG. 5, the upstream blocking wall 82 and the downstream blocking wall 83 may have a height at least larger than those of the upstream opening 62 and the downstream opening 63, respectively, and may preferably be arranged to be nearly in contact with the grippers 74. The upstream blocking wall 82 and the downstream blocking wall 83 may not contact with the sterilized rotation table 71 as well as the grippers 74. As shown in FIG. 4, the upstream blocking wall 82 and the downstream blocking wall 83 may not be connected to each other and may be completely separate from each other. That is, there may be formed a space for passing a gas (ozone), or a ventilation space 84, between the upstream blocking wall 82 and the downstream blocking wall 83. The ventilation space 84 may preferably have such a shape and a size that a gas (ozone) can flow smoothly from the upstream opening 62 to the downstream opening 63 (and vice versa), that is, such a shape and a size that the gas (ozone) is less apt to accumulate in the blocking chamber 6. However, the upstream blocking wall 82 and the downstream blocking wall 83 may be arranged to completely interrupt the linear connection between the upstream opening 62 and the downstream opening 63. In other words, the upstream blocking wall 82 and the downstream blocking wall 83 may be positioned to interrupt all the straight lines connecting between the upstream opening 62 and the downstream opening 63. In addition, the upstream blocking wall 82 and the downstream blocking wall 83 may be positioned such that the straight line 2 extending through an end of the upstream opening 62 and an end of the upstream blocking wall 82 may not intersect, in the blocking chamber 6, the straight line 3 extending through an end of the downstream opening 63 and an end of the downstream blocking wall 83. In other words, no straight lines extending through the upstream opening 62 and an end of the upstream blocking wall 82 may intersect, in the blocking chamber 6, any straight lines extending through the downstream opening 63 and an end of the downstream blocking wall 83. In this arrangement, all the X-rays entering through the upstream opening 62 may be reflected three or more times by the blocking walls 81, the partition wall 61, and the like before reaching the downstream opening 63. The feed chamber 1 which constitutes another purport of the present invention will be described in detail with reference to FIGS. 6 to 7. As shown in FIG. 6, the input star wheel 21 may include a star wheel plate 22 and a drive shaft 23. The star wheel plate 22 may be disposed substantially in a horizontal position, and the drive shaft 23 may be configured to rotate the star wheel plate 22 around a vertical axis 1v (the central axis 1v of the star wheel plate 22). The lower end of the drive shaft 23 may be connected to a drive unit (not shown) provided below the floor of the feed chamber 1, and the upper end of the drive shaft 23 may be connected to the star wheel plate 22. A guide 13 may be connected to the input star wheel 21 so as to guide the preform products P sliding by the weight thereof through the input tube 11 to the upstream end of the star wheel plate 22. In addition, the input star wheel 21 may include a blocking unit 30 for blocking the X-rays entering from the outer-surface sterilization chamber 4. The blocking unit 30 may include a blocking short tube 31 (as an example of tubular blocking member) and a blocking roof 35. The blocking short tube 31 may be attached to the lower surface of the star wheel plate 22 and may cover the entire periphery of the drive shaft 23, and the blocking roof 35 may extend from above an opening of the input tube 11 at the downstream side thereof (hereinafter referred to simply as “the feed opening 12”) to near the upper surface of the star wheel plate 22. The blocking short tube 31 may prevent the X-rays entering from the outer-surface sterilization chamber 4 from reaching the lower half of the feed opening 12, and the blocking roof 35 may prevent the X-rays entering from the outer-surface sterilization chamber 4 from reaching the upper half of the feed opening 12. Therefore, the blocking short tube 31 and the blocking roof 35 may prevent the X-rays in the feed chamber 1 from leaking harmfully out of the electron beam sterilization apparatus 10 through the input tube 11. Further, the input tube 11 may be made of a material that blocks X-rays. The inclination angle and the length of the input tube 11 may be designed such that the upper end of the feed opening 12 (that is, the opening of the input tube 11 at the downstream side thereof) is lower than the lower end of the opening of the input tube 11 at the upstream side thereof. Therefore, the X-rays reaching the feed opening may be blocked by the input tube 11. In other words, the input tube 11 may prevent the X-rays in the feed chamber 1 from leaking out of the electron beam sterilization apparatus 10 harmfully. As shown in FIG. 7, the blocking short tube 31 may include an outer arcuate blocking plate 32 having a larger diameter and an inner arcuate blocking plate 33 having a smaller diameter. Both the outer arcuate blocking plate 32 and the inner arcuate blocking plate 33 may be centered at the central axis 1v of the star wheel plate 22 and may have a central angle of 180° or larger in a plan view, and the outer arcuate blocking plate 32 and the inner arcuate blocking plate 33 may overlap each other in the region w as viewed from the central axis 1v. The outer arcuate blocking plate 32 and the inner arcuate blocking plate 33 may not be connected to each other and may be completely separated from each other. That is, there may be formed a space for passing a gas (ozone), or a ventilation space 34, between the outer arcuate blocking plate 32 and the inner arcuate blocking plate 33. The ventilation space 34 may preferably have such a shape and a size that a gas (ozone) can flow smoothly from the outer-surface sterilization chamber 4 to the feed opening 12 (and vice versa), that is, such a shape and a size that the gas (ozone) is less apt to accumulate in the feed chamber 1. However, the inner arcuate blocking plate 33 may have such a large diameter as not to be in contact with the outer arcuate blocking plate 32, and the outer arcuate blocking plate 32 may have such a large diameter as to be nearly in contact with the preform products P. As shown in FIG. 6, the blocking roof 35 may include a horizontal portion 36 and a vertical portion 37. The horizontal portion 36 may project from above the feed opening 12 to above the input star wheel 21 substantially in a horizontal position, and the vertical portion 37 may suspend from the horizontal portion 36 toward the input star wheel 21. The lower end of the vertical portion 37 may be positioned so low as to be nearly in contact with the input star wheel 21 and the preform products P conveyed thereby. The operation of the electron beam sterilization apparatus 10 will be hereinafter described. As shown in FIG. 2, the preform products P fed into the feed chamber 1 may sequentially be conveyed to the outer-surface sterilization chamber 4, the inner-surface sterilization chamber 5, the blocking chamber 6, and the sorting chamber 9, and may then be fed to the external apparatus F from the sorting chamber 9. While being conveyed, the preform products P may have the outer surfaces thereof sterilized with the electron beams in the outer-surface sterilization chamber 4 and have the inner surfaces thereof sterilized with the electron beams in the inner-surface sterilization chamber 5. In the outer-surface sterilization chamber 4 and the inner-surface sterilization chamber 5, the electron beams may be applied to the preform products P for electron beam sterilization, and as a result, X-rays may be produced. Further, in the outer-surface sterilization chamber 4 and the inner-surface sterilization chamber 5, the electron beams may cause a chemical reaction of the air that undesirably produces ozone. The X-rays produced in the outer-surface sterilization chamber 4 and the inner-surface sterilization chamber 5 may enter the blocking chamber 6 and the feed chamber 1 adjacent thereto. The X-rays, which may possibly leak out of the electron beam sterilization apparatus 10, may be blocked in the blocking chamber 6 and the feed chamber 1 and prevented from leaking out harmfully. Meanwhile, the ozone gas produced in the outer-surface sterilization chamber 4 and the inner-surface sterilization chamber 5 may also enter the blocking chamber 6 and the feed chamber 1 having complex structures such as the blocking walls 81 and the blocking unit 30. However, since the ozone gas in the blocking chamber 6 and the feed chamber 1 may flow smoothly because of the ventilation spaces 84, 34, the ozone gas may be less apt to accumulate in the block chamber 6 and the feed chamber 1 and may be discharged from the electron beam sterilization apparatus 10 by the ventilator. The blocking chamber 6 and the feed chamber 1 will be hereinafter individually described. As shown in FIG. 4, the X-rays entering the blocking chamber 6 through the upstream opening 62 may be blocked by the blocking walls 81 and reflected by the blocking walls 81, the partition wall 61, and the like (the floor, walls, ceiling, etc. of the blocking chamber 6). As a result, the X-rays are attenuated. Because of the arrangement of the blocking walls 81 described above, all the X-rays entering through the upstream opening 62 may be reflected three or more times by the blocking walls 81, the partition wall 61, and the like before reaching the downstream opening 63, and thus may be attenuated to be harmless. As shown in FIGS. 2 and 6, the X-rays entering the feed chamber 1 from the outer-surface sterilization chamber 4 may be blocked by the blocking unit 30 and reflected by the blocking unit 30 and the like (the floor, walls, ceiling, etc. of the feed chamber 1). As a result, the X-rays are attenuated. Because of the arrangement of the blocking unit 30 described above, all the X-rays entering from the outer-surface sterilization chamber 4 may be reflected three or more times by the blocking unit 30 and the like before reaching the feed opening 12, and thus may be attenuated to be harmless. Thus, in the electron beam sterilization apparatus 10, the blocking walls 81 having a large weight may not be attached to the sterilized rotation table 71, and therefore, the sterilized rotation table 71 and other rotation tables 51, 53, 91, and 93 may be rotated at a high speed, thereby enabling high speed operation. In addition, the X-rays can be blocked sufficiently in the blocking chamber 6 and the feed chamber 1 alone, and therefore, the electron beam sterilization apparatus 10 may not need to include other chambers or structures for blocking the X-rays and thus can be downsized. Further, the electron beam sterilization apparatus 10, having fewer chambers, may tend to have less ozone gas accumulated therein, and thus can be prevented from corrosion. In addition, because of the ventilation spaces 34, 84, the electron beam sterilization apparatus 10 may tend to have less ozone gas accumulated therein, and thus can be prevented from corrosion. In the above description, the preform products P were taken as an example of container. The present invention can also be applied for plastic bottles B or other containers. In the above embodiment, the grippers 74 were taken as an example of retainer, but the present invention can use any other retainers that can retain the containers. Further, in the above embodiment, the blocking walls 81 may be positioned outside so as to be nearly in contact with the grippers 74. Therefore, the blocking walls 81 may be arranged within a region outward from the periphery of the sterilized rotation table 71. For example, the blocking walls 81 may be positioned under the portion of the connection plate 75 attached to the sterilized rotation table 71 (that is, in the periphery of the sterilized rotation table 71). In addition, the sorting chamber 9 of the above embodiment can include a blocking wall which was not described for the above embodiment. As shown in FIG. 8, the sorting chamber 9 may include a blocking wall 95 arranged such that the blocking wall 95 and the downstream blocking wall 83 are in line symmetry with respect to the partition wall 61 between the blocking chamber 6 and the sorting chamber 9. This arrangement may further facilitate sufficient blocking of the X-rays. It may also be possible that the downstream blocking wall 83 is omitted when the sorting chamber 9 includes the blocking wall 95. In addition, the inner-surface sterilization chamber 5 of the above embodiment can include a blocking wall which was not described for the above embodiment. As shown in FIG. 8, the inner-surface sterilization chamber 5 may include a blocking wall 55 arranged such that the blocking wall 55 and the upstream blocking wall 82 are in line symmetry with respect to the partition wall 61 between the inner-surface sterilization chamber 5 and the blocking chamber 6. This arrangement may further facilitate sufficient blocking of the X-rays. It may also be possible that the upstream blocking wall 82 is omitted when the inner-surface sterilization chamber 5 includes the blocking wall 55. In the above embodiment, the blocking short tube 31 may include an outer arcuate blocking plate 32 having a larger diameter and an inner arcuate blocking plate 33 having a smaller diameter. It may also be possible that, as shown in FIG. 9, the blocking short tube 31 includes arcuate blocking plates 32′, 33′ having the same diameter, as long as it has a ventilation space 34 and the overlapping region w. It may also be possible that the blocking short tube 31 includes three or more arcuate blocking plates, instead of two arcuate blocking plates. Alternatively, the blocking short tube 31 may have an integral structure, as long as it has a cutout serving as a ventilation space 34. The shape of the blocking walls 81 described for the above embodiment is not limitative. The blocking walls 81 need only to face the upstream opening 62 or the downstream opening 63 and have a larger area than the upstream opening 62 or the downstream opening 63 facing thereto. The suspending member 76 of the gripper 74, which was not described in detail for the above embodiment, may be made of a material that blocks X-rays. This arrangement may further facilitate sufficient blocking of the X-rays.
050227874	abstract	Disclosed is a method of returning geothermal gases discharged from geothermal plants to the underground together with waste water through a return well, characterized in that the apparent velocity of waste water V.sub.eo relative to the return well is equal to or more than 1 m/s and the range of the apparent velocity of waste water V.sub.eo and of an apparent velocity of the geothermal gases V.sub.go is regulated to satisfy the following equation: EQU V.sub.go <1.33V.sub.eo -0.41.
	abstract	A detector element is for detecting incident x-ray radiation. The detector element includes a scintillation layer for converting the x-ray radiation into scintillation light and a photoactive element for converting the scintillation light into an electric signal. The photoactive element includes a first photoactive absorption layer contacted by an electrode, and a second photoactive absorption layer contacted by a counter electrode. Here, the scintillation layer is arranged between the first photoactive absorption layer and the second photoactive absorption layer.
048790885	summary	BACKGROUND OF THE INVENTION By far, the majority of nuclear power reactors are water cooled and moderated reactors, utilizing enriched uranium dioxide as fuel. The core of the reactor is formed by elongated fuel rods which are grouped into bundles which are generally square in cross section. The rods have diameters usually in the range of one-fourth to one half inch and may be ten or twelve feet long. They are held parallel and closely spaced from each other. Each rod is formed of a jacket or "cladding" made of zirconium alloy or stainless steel, which is filled with the uranium dioxide. Most commonly, the uranium dioxide is in the form of pellets which are just enough smaller than the cladding to slide in conveniently. The uranium dioxide may, on the other hand, be in the form of microspheres or granules which are compacted within the cladding. The remainder of the space within the cladding is commonly filled with helium, which has a high thermal conductivity. The helium is frequently under higher than atomospheric pressure. During the operation of the reactor, holes may develop in the cladding due to stress, corrosion, wear, or defective welding to the end plugs which close the ends of the cladding tubes. If this happens, the helium and fission gases will escape into the cooling water of the reactor and the water will enter the cladding tubes. After a given fuel assembly has been exposed in the reactor for a given length of time, it is taken out, checked for defects, repaired if necessary, and either returned to the reactor or sent for reprocessing or permanent storage. If the assembly is to be returned to the reactor, it is almost essential that it be checked for defective fuel rods. These irradiated assemblies are highly radioactive and must be stored and inspected under water in order to remove heat caused by the decay of fission products as well as to protect persons working with them. It is therefore highly desirable to provide a method of testing fuel rods for leaks while they are assembled and underwater. One method of doing so is by ultrasonic testing. Such a method is disclosed in U.S. Pat. No. 4,313,791, granted Feb. 2, 1982 and assigned to the Babcock and Wilcox Company. In this method, a transducer emitting ultrasonic vibrations is placed against a fuel rod and an ultrasonic beam is transmitted into the rod by the transducer. The test is performed on a portion of the fuel rod which does not contain uranium dioxide. An analysis of the waves received by a pulse-echo system, reveals whether or not this portion of the rod is filled with water. It is disclosed as carried out at the lower plenum of a fuel rod and apparently would not be operative in a portion of a rod where uranium dioxide is present. A weakness of this method lies in the fact that many, probably most, fuel rods do not have a lower plenum. SUMMARY OF THE INVENTION We have devised an ultrasonic test for failed fuel rods which is an improvement on prior systems. According to out invention, a transducer is traversed through a fuel assembly, spaced from a row of rods which is to be checked. During the traverse, a series of ultrasonic pulses is emitted from the transducer in the form of a beam. When the beam strikes a fuel rod, it is reflected from the outer surface. If the beam is exactly normal to the surface, it will be reflected back into the tansducer to a maximum degree. By the use of well-known electrical systems, this gives rise to an electrical signal. This method is termed the "pulse-echo" technique. Not all of the ultrasonic beam is reflected at the outer surface, however. A portion continues in the tubing wall and strikes the inner surface of the cladding. In a perfect rod, this is in effect a metal-gas interface. No matter how close the fit between the tube and the uranium dioxide, the contact is not sufficient for efficient transfer of sound energy. Neither is the ultrasound transmitted by the helium gas to any substantial degree. There is, therefore, a reflection from the inner surface of the tubing as well as from the outer surface. In fact, the ultrasound is reflected back and forth between the inner and outer walls of the tubing, producing what is termed "wall ringing". This wall ringing is recorded by the electronic system referred to above. If the tube has filled with water, there will be a transfer of the ultrasonic energy from the tubing wall into the water, where it is effectively dispersed. This greatly attenuates the wall ringing. It is immaterial whether uranium dioxide is present or not. The "coupling" of the cladding to the water within the tube results in the attenuation of the wall ringing and so identifies a defective tube. More specifically, as the transducer is moved along a row of fuel rods, it continuously emits a series of ultrasonic pulses. Typically, the ultrasound has a frequency of 10-30 megahertz and the pulses have a repetition rate of 1-8 kilohertz. When it receives a maximum echo from the outer surface of a fuel rod, a signal is transmitted to a recording medium, e.g., a strip chart. This is done over a pre-selected period of time which may be termed a "time window". After a delay, which is chosen in accordance with the thickness and other characteristics of the cladding, the echo from the "wall ringing" is sampled during another "time window" and, if its amplitude is above a preselected threshold, a second signal is transmitted to the recording medium. Absence of this second signal indicates that water is present within the tube and that the latter is defective. Our invention also includes apparatus for effectively carrying out the method described above. The transducer is mounted on a probe which is so constructed as to provide the proper spacing between the tubes to be tested and the transducer, and also for the proper positioning of the transducer so that the beam will be perpendicular to the fuel rod axes. We have also provided an indexing system which permits the probe to be accurately and rapidly inserted into the fuel assembly while the latter is under water. This indexing system includes a plate having grooves which are parallel to the rows of fuel rods which are to be checked and which are spaced apart the same distance as the rows. A reciprocating system acting along those grooves moves the probe along the rows of fuel elements in the assembly. When the reciprocating element is retracted, a pressure medium autuomatically moves it to the next groove, and in this manner, the assembly can be checked very quickly. This indexing system is claimed in an application of Leo F. Van Swam and Quang D. Ho, Ser. No. 660,787, filed Oct. 15, 1984 and assigned to the assignee of this application, now U.S. Pat. No. 4,689,193, granted Aug. 25, 1987.
	summary
	summary
	summary
	summary
	claims	1. A radiation source assembly, comprising a source capsule enclosing a radiation source, a female connector connected to a male connector, and a pigtail connecting the source capsule and the female connector together, wherein a cap connector of said source capsule has first internal threads on its pigtail fitting hole, with said first internal threads having a profile corresponding to a large-diameter coil of said pigtail and engaging with the large-diameter coil of a first end of the pigtail through a thread engagement. 2. The radiation source assembly according to claim 1 , wherein said female connector has second internal threads on its pigtail fitting hole, with said second internal threads having a profile corresponding to said large-diameter coil of the pigtail and engaging with the large-diameter coil of a second end of the pigtail through a thread engagement. claim 1 3. The radiation source assembly according to claim 2 , wherein the number of each of said first and second internal threads is four or more. claim 2 4. The radiation source assembly according to claim 1 , wherein the number of said first internal threads is four or more. claim 1 5. A radiation source assembly, comprising: a capsule body receiving stacked radiation source disc targets; a capsule lid fitted into an open end of said capsule body and welded to said capsule body, thus sealing the capsule body; and a coil spring set within a spring seat hole of said capsule lid and adapted to normally bias the radiation source disc targets within the capsule body in a direction after the capsule lid is welded to the capsule body.
	claims	1. An X-ray apparatus comprisingan X-ray source configured for producing an X-ray beam and comprising a focus position;a detector configured for detecting X-radiation;a collimator arrangement comprising at least one collimator structure, positioned between the focus position and the detector;mechanics that move the collimator arrangement, the detector and the X-ray source along a curved scan trajectory travelling through an x-z plane and extending along a y-axis perpendicular to the x-z plane; anda control unit configured for controlling the mechanics to move the collimator arrangement, the detector and the X-ray source along the curved scan trajectory, wherein a curvature of the curved scan trajectory is adjustable. 2. The X-ray apparatus as claimed in claim 1, wherein the mechanics comprise:a base element;a moving element, to which the detector and/or the collimator arrangement and/or the X-ray source is connected and which is configured to move relative to the base element; anda guiding element configured for guiding the moving element along the curved scan trajectory. 3. The X-ray apparatus as claimed in claim 2, wherein the guiding element is rotatably connected to the base element and the moving element is rotatably connected to the guiding element. 4. The X-ray apparatus as claimed in claim 2, wherein the guiding element is curved. 5. The X-ray apparatus as claimed in claim 1, wherein the curvature of the curved scan trajectory is adjustable by adjustment of an effective length of the guiding and/or moving element. 6. The X-ray apparatus of claim 2, wherein the guiding element is configured as a parallelogram. 7. The X-ray apparatus of claim 5, further comprising a stepper motor that adjustably controls the effective length. 8. The X-ray apparatus of claim 1, further comprising an arm that connects the X-ray source, the detector, and the collimator arrangement to the mechanics. 9. The X-ray apparatus of claim 1, wherein the collimator arrangement, the detector, and the X-ray source cooperate to acquire X-radiation information at multiple locations along the curved scan trajectory from which imagery of a patient is created. 10. An X-ray apparatus comprisingan X-ray source configured for producing an X-ray beam and comprising a focus position;a detector configured for detecting X-radiation;a collimator arrangement comprising at least one collimator structure, positioned between the focus position and the detector;mechanics comprising: a base element; a moving element, to which the detector and/or the collimator arrangement and/or the X-ray source is connected and which is configured to move relative to the base element; and a guiding element configured for guiding the moving element along a, curved scan trajectory, the mechanics adapted to move the collimator arrangement, the detector and the X-ray source along the curved scan trajectory travelling through an x-z plane and extending along a y-axis perpendicular to the x-z plane, wherein a curvature of the curved scan trajectory is adjustable; anda control unit configured for controlling the mechanics to move the collimator arrangement, the detector and the X-ray source along the curved scan trajectory, wherein the guiding element is configured as a parallelogram. 11. The X-ray apparatus of claim 10, further comprising an arm that connects the X-ray source, the detector, and the collimator arrangement to the mechanics. 12. The X-ray apparatus of claim 11, wherein the collimator arrangement, the detector, and the X-ray source cooperate to acquire X-radiation information at multiple locations along the curved scan trajectory from which imagery of a patient is created.
	abstract	An extreme ultraviolet light generation apparatus may include a chamber causing a target substance to be turned into plasma with laser light, a light concentrating mirror concentrating extreme ultraviolet light generated by the turning of the target substance into plasma, a gas supply unit supplying gas into the chamber, a magnetic field generation unit generating a magnetic field including a magnetic field axis that crosses a light path of the extreme ultraviolet light, a first exhaust port arranged at a position through which the magnetic field axis passes in the chamber, a second exhaust port arranged at a position opposite to the light concentrating mirror in the chamber, and a gas exhaust amount adjustment unit adjusting a ratio between an exhaust amount of first exhaust gas exhausted from the first exhaust port and an exhaust amount of second exhaust gas exhausted from the second exhaust port.
	description	This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-216529, filed Nov. 4, 2016, the disclosures of which are expressly incorporated by reference herein. The present invention relates to a vehicle operation data collection system, a vehicle operation data collection apparatus, and a vehicle operation data collection method for collecting operation data of a vehicle suitable for detecting vehicle abnormality. In general, various kinds of sensors for monitoring an operation state of components are provided in main components (for example, an engine, wheels, or the like) which constitute a vehicle. Therefore, by monitoring the output values of the sensors, it is possible to detect malfunction or abnormality (hereinafter collectively referred to as vehicle abnormality) of the components. A statistical method is often used to detect such a vehicle abnormality. For example, when the output value of a specific sensor under a specific operation and environmental condition of a certain vehicle is greatly different from an average value of the output values of the same sensors under the same operation and environmental condition of another vehicle of the same vehicle type, it is considered that there is some abnormality in the “certain vehicle” mentioned above. Generally, in order to detect vehicle abnormality by the statistical method, it is necessary to collect output values (sensor data) of as many sensors as possible from as many vehicles as possible to a data center or the like over a considerable period of time. However, it is practically difficult to collect sensor data of all sensors in the vehicle from vehicles of any type, for example, traveling on the road to the data center, from the viewpoint of communication load, analysis load, and accumulation load. Therefore, when detecting vehicle abnormality by the statistical method, it is important to select and efficiently collect sensor data contributing to statistical process of abnormality detection as much as possible. In this specification, sensor data obtained from at least one sensor mounted in a running vehicle is referred to as vehicle operation data. JP-4107238-B2 discloses an example of an information center which receives information such as vehicle type, components, and point and instructs transmission of similar diagnostic information to components of vehicle of the same type running on the same point, in addition to abnormal diagnostic information (operation data) from a vehicle in which an abnormality is detected. In this example, the information center can analyze the cause of occurrence of the abnormality on the basis of the diagnostic information obtained from a plurality of vehicles under the same running environment. Therefore, analysis of the cause of occurrence of abnormality is facilitated. In order to detect the vehicle abnormality by the statistical method, it is necessary to collect the number of operation data sufficient for distinguishing between abnormality and normality in advance for each type of various abnormalities occurring in the vehicle. In general, it is relatively easy to collect a sufficient number of operation data for normal operation data or abnormal operation data with high occurrence frequency. In contrast, it is not always easy to collect abnormal operation data with low occurrence frequency. The information center disclosed in JP-4107238-B2 can efficiently collect operation data for analyzing the cause of occurrence of an abnormality detected in a certain vehicle from another vehicle. However, this does not mean that a large number of abnormal operation data required when trying to determine the normality/abnormality of the operation data using a statistical method, in particular, machine learning is obtained. Even if there are many normal operation data, when the abnormal operation data is small, it is not possible to improve the accuracy of determination of normality/abnormality. An object of the present invention is to provide a vehicle operation data collection apparatus, a vehicle operation data collection system, and a vehicle operation data collection method capable of efficiently collecting abnormal operation data in a vehicle. A vehicle operation data collection apparatus according to the present invention includes: a vehicle operation data accumulation unit which accumulates operation data of a vehicle acquired from the vehicle; a data excess and deficiency evaluation unit which evaluates excess or deficiency of operation data of the vehicle accumulated in the vehicle operation data accumulation unit for each of abnormality types, on the basis of accuracy information of classification obtained when classifying the abnormality types occurring in the vehicle by machine learning, using operation data of the vehicle accumulated in the vehicle operation data accumulation unit; a collection target vehicle extraction unit which extracts a vehicle suitable for acquiring data of an abnormality type evaluated as data deficiency by the data excess and deficiency evaluation unit from a database accumulating maintenance history information of the vehicle as a collection target vehicle; and a collection command distribution unit which distributes a collection command instructing collection of operation data to the extracted collection target vehicle. According to the present invention, there are provided a vehicle operation data collection apparatus, a vehicle operation data collection system, and a vehicle operation data collection method capable of efficiently collecting abnormal operation data in a vehicle. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the common constituent elements are denoted by the same reference numerals, and repeated descriptions will not be provided. FIG. 1 is a diagram illustrating an example of a configuration of a vehicle operation data collection system 1 including a vehicle operation data collection apparatus 10 according to an embodiment of the present invention. As illustrated in FIG. 1, the vehicle operation data collection system 1 is configured to include the vehicle operation data collection apparatus 10, and an in-vehicle terminal device 31 mounted on each of the plurality of vehicles 30 and connected to the vehicle operation data collection apparatus 10 to be wirelessly communicable via a communication base station 23. The vehicle operation data collection apparatus 10 is connected to an evaluator terminal 21 used by an evaluator who evaluates or analyzes abnormal operation data generated in the vehicle 30, and a maintenance person terminal 22 used by a maintenance person of the vehicle 30, via a dedicated communication line or a general purpose communication network. Here, various kinds of sensors for monitoring the operation state are attached to the main components such as an engine constituting the vehicle 30. Further, the vehicle 30 itself is provided with a thermometer, a camera, a global positioning system (GPS) position sensor, and the like for detecting the state of the outside world. Further, when receiving the operation data collection command transmitted from the vehicle operation data collection apparatus 10, the in-vehicle terminal device 31 collects the sensor data of the sensor instructed by the operation data collection command. Further, the collected sensor data is transmitted to the vehicle operation data collection apparatus 10 as the operation data of the vehicle 30. The vehicle operation data collection apparatus 10 includes blocks relating to the processing function, such as data excess and deficiency evaluation section 11, a collection target vehicle extraction section 12, a collection condition setting section 13, an evaluator terminal IF section 14, a vehicle communication section 15, and a maintenance person terminal IF section 16. Further, the vehicle operation data collection apparatus 10 includes blocks relating to storage functions, such as an analysis unit storage section 17, a vehicle operation history DB 18, and a vehicle maintenance history DB 19. Here, the data excess and deficiency evaluation section 11 includes an evaluation data generation section 111, a classification learning section 112, a learning result evaluation section 113, and the like as sub-blocks. Similarly, the evaluator terminal IF section 14 includes an analysis unit setting section 141, a collection condition display section 142, and the like as sub-blocks, and the vehicle communication section 15 includes an operation data reception unit 151, a collection command distribution section 152 and the like as sub-blocks. The vehicle operation data collection apparatus 10 having the above configuration is achieved by a single computer or a plurality of computers coupled to each other via a dedicated communication line or a general purpose communication network. In that case, the function of the block related to the processing function of the vehicle operation data collection apparatus 10 is embodied by the computer processing apparatus which executes a predetermined program stored in the storage device of the computer. Further, the block relating to the storage function is embodied as a storage region on the storage device of the computer. Subsequently, details of each block constituting the vehicle operation data collection apparatus 10 will be sequentially described with reference to the drawings of FIGS. 2A and 2B and the following drawings in addition to FIG. 1. The collection command distribution section 152 of the vehicle communication section 15 specifies the vehicle 30 and then distributes the operation data collection command which instructs the in-vehicle terminal device 31 mounted on the vehicle 30 to acquire the sensor data of the sensor included in the vehicle 30. Thus, for example, an operation data collection command such as “acquiring an opening degree sensor of an accelerator and sensor data of an engine tachometer at a sampling frequency of 1 Hz” is distributed to the in-vehicle terminal device 31 of the specific vehicle 30. The operation data reception unit 151 receives the operation data of the vehicle 30 transmitted from the in-vehicle terminal device 31 of the vehicle 30 in response to the distributed operation data collection command, and stores the received operation data as vehicle operation history data in the vehicle operation history DB (database) 18. FIG. 2A is a diagram illustrating an example of the configuration of the vehicle operation history data stored in the vehicle operation history DB 18, and FIG. 2B illustrates an example of the configuration of the operation data included in the vehicle operation history data. As illustrated in FIG. 2A, the vehicle operation history data includes data of items such as “data ID”, “acquisition date/time”, “acquisition position”, “vehicle ID”, “vehicle type”, “component configuration”, “sensor item”, “sampling frequency”, “operation data”, and “abnormality type”. Here, in the column of “data ID”, identification information added for uniquely identifying the vehicle operation history data of the row in the vehicle operation history DB 18 is stored. Further, in the columns of “acquisition date and time” and “acquisition position”, information of the date and time when the “operation data” of the relevant row was acquired, and the position information are stored. Further, the “acquisition position” may be information represented by the address name of the point or information represented by the latitude and longitude acquired by a GPS position sensor or the like. In the column of “vehicle ID”, identification information for uniquely identifying the vehicle 30 from which “operation data” of the relevant row is acquired is stored, and in the column of “vehicle type”, a model name or a type name of the vehicle 30 is stored. In the present embodiment, it is assumed that a unique vehicle ID is affixed in advance to all the vehicles 30 that are targets of the vehicle operation data collection system 1. In the column of “component configuration”, information on the component configuration of the vehicle 30 from which “operation data” of the relevant row is acquired is stored. For example, in the column of “component configuration”, the type of each component such as an engine or a braking device, the type of an injector attached to the engine, the type of each part attached to the component, and the like are stored. In the column of “sensor item”, the sensor name of the sensor that detects the “operation data” of the relevant row or the name of the output signal from the sensor, for example, information such as “accelerator opening degree” or “rotational speed of the engine” is stored. Further, in the column of “sampling frequency”, the sampling frequency when “operation data” of the relevant row is detected, for example, information such as “1 Hz” or “2 Hz” is stored. In the column of “operation data”, sensor data detected by a sensor specified by “sensor item” of the relevant row is stored. Since the “operation data” normally has a data structure of plural dimensions, as illustrated separately in FIG. 2B and the like, the data stored in the column of the “operation data” may be a file name that represents a region of the storage device in which “operation data” is stored. In the column of “abnormality type”, a value indicating that “operation data” in the relevant row is “normal” or “abnormal”, or a name of abnormality identification which identifies the “abnormality” in the case of the “abnormality” and the like are stored. Among the vehicle operation history data having the above configuration, data other than “data ID” and “abnormality type” are data included in the data transmitted from the in-vehicle terminal device 31 of the vehicle 30. On the other hand, the “data ID” is assigned when the operation data reception unit 151 receives the operation data transmitted from the in-vehicle terminal device 31 and accumulates the received operation data as vehicle operation history data in the vehicle operation history DB 18. Further, the column of “abnormality type” is blank when the vehicle operation history data is first accumulated in the vehicle operation history DB 18. Further, thereafter, if there is no repair or adjustment of the vehicle 30 at a repair shop or the like within a predetermined period (for example, three months), value of “normality” is filled in the column of “abnormality type” indicates. On the contrary, thereafter, when any repair or adjustment is performed on the vehicle 30 at a repair shop or the like, and the abnormality type can be clarified, the name of the clarified abnormality type is filled in the column of “abnormality type”. However, when the abnormality type cannot be clarified, the value of “abnormality” is simply filled in the column of “abnormality type”. Incidentally, filling of the value to “abnormality type” is performed by the maintenance person terminal IF section 16 on the basis of the data that is input by the maintenance person of the vehicle 30 via the maintenance person terminal 22. Subsequently, as illustrated in FIG. 2B, the operation data is configured to include, for example, data of items such as “data acquisition time”, “accelerator opening degree”, and “engine rotational speed”. Here, the time interval of time advance in the “data acquisition time” column is determined by the “sampling frequency” of the vehicle operation history data. Further, the names of the items such as “data acquisition time” and “accelerator opening degree” are determined by the data of the “sensor item” column of the vehicle operation history data. Therefore, the names of the items are not limited to “data acquisition time”, “accelerator opening degree”, and the like, but may include sensor names or output signal names of all sensors mounted on the vehicle 30 such as “camera image” and “laser radar distance”. FIG. 3 is a diagram illustrating an example of the configuration of the vehicle maintenance history data stored in the vehicle maintenance history DB 19. As illustrated in FIG. 3, the vehicle maintenance history data includes “maintenance date and time”, “maintenance base”, “maintenance staff”, “vehicle ID”, “cumulative maintenance cost”, “maintenance component”, “maintenance content”, “maintenance cost” and the like. Here, in the respective columns of “maintenance date and time”, “maintenance base”, and “maintenance staff”, the date and time when the maintenance (repair, adjustment, or the like) of the vehicle 30 specified by “vehicle ID” of the column is performed, the name of the repair shop, the name of the maintenance staff, and the like are stored. Further, in the column of “vehicle ID”, identification information for uniquely identifying the vehicle 30 subject to maintenance is stored, and in the column of “cumulative maintenance cost”, the cumulative amount of the maintenance cost after shipment of the vehicle 30 from the factory is stored. In the columns of “maintenance component”, “maintenance content”, and “maintenance cost”, the component name subjected to maintenance in the maintenance carried out at the “maintenance date and time” of the relevant row, information representing the contents of the maintenance work, and the cost required for maintenance thereof are stored, respectively. Each time maintenance of the vehicle 30 is performed, the vehicle maintenance history data is created by manipulating the maintenance person terminal 22 by a maintenance staff or the like who performed the maintenance work of the vehicle 30, and the vehicle maintenance history data is stored in the vehicle maintenance history DB 19 via the maintenance person terminal IF section 16. However, the column of “cumulative maintenance cost” does not require manipulation of the maintenance staff and is automatically added by process of the maintenance person terminal IF section 16. FIG. 4 is a diagram illustrating an example of a flow of entire processes in the vehicle operation data collection apparatus 10. By executing this process, the vehicle operation data collection apparatus 10 can efficiently collect the vehicle operation history data of the kind that is insufficient when the vehicle operation history data accumulated in the vehicle operation history DB 18 is used for abnormality detection of the vehicle 30 or classification of the detected abnormality. Further, hereinafter, the process illustrated in FIG. 4 is executed by the data excess and deficiency evaluation section 11, the collection target vehicle extraction section 12, the collection condition setting section 13, the collection command distribution section 152, and the like of the vehicle operation data collection apparatus 10. Further, this process is executed at a predetermined time period (for example, once a day) or when receiving an execution instruction that is input from the evaluator terminal 21. As illustrated in FIG. 4, the data excess and deficiency evaluation section 11 of the vehicle operation data collection apparatus 10 first selects one of the analysis units from the analysis unit storage section 17 (step S11). Here, the analysis unit means a combination (set) of data such as a vehicle type, a component configuration, a sensor item, and a sampling frequency, which are required to be specified at the time of individually analyzing abnormality of the vehicle 30. For example, when analyzing the abnormality of the engine of the vehicle type A, it is necessary to analyze a relation between the opening degree sensor of the accelerator and the rotational speed of the engine. In the data of the analysis unit in such a case, for example, the vehicle type is the vehicle type A, the component configuration is the accelerator and the engine, the sensor item is the accelerator opening degree and the rotational speed of the engine, and the sampling frequency is a value of a frequency such as 1 Hz or 2 Hz. Further, the evaluator who evaluates the abnormality of the vehicle 30 can freely set the analysis unit by manipulating the evaluator terminal 21. Further, the analysis unit set by the evaluator is written on the analysis unit storage section 17 via the analysis unit setting section 141 of the evaluator terminal IF section 14. Here, it is assumed that one or a plurality of analysis units set by the evaluator are stored in the analysis unit storage section 17 in advance. Next, the data excess and deficiency evaluation section 11 evaluates the excess or deficiency of the vehicle operation history data accumulated in the vehicle operation history DB 18 for each abnormality type related to the selected analysis unit (step S12). That is, the data excess and deficiency evaluation section 11 extracts the vehicle operation history data corresponding to the selected analysis unit from the vehicle operation history DB 18. Further, the extracted vehicle operation history data is classified by a plurality of abnormality types, for example, using a machine learning method, and it is evaluated whether or not the vehicle operation history data accumulated for each abnormality type reaches the accuracy that is sufficient for determining the abnormality type. As it will be described later, this evaluation is processed as a classification problem of machine learning, and the vehicle operation history data classified by the abnormality type in which an accuracy (correct answer rate) higher than a predetermined value is not obtained is determined that the number of data is insufficient. Here, the abnormality type refers to data expressed by two values (for example, “normal” or “abnormal” data) in the abnormality detection process, and refers to data (for example, an abnormality type name) expressed by a multivalued value of the number of types of assumed abnormalities in the abnormality classification process. For example, in the abnormality classification process, when three kinds of abnormality “abnormality A”, “abnormality B”, and “abnormality C” are assumed for a certain component, the abnormality type is expressed by three values of “abnormality A”, “abnormality B”, and “abnormal C”. Next, the collection target vehicle extraction section 12 extracts the vehicle 30 suitable for acquiring the vehicle operation history data classified by the abnormality type evaluated as data number insufficiency in step S12, on the basis of the vehicle maintenance history data accumulated in the vehicle maintenance history DB 19, and sets the vehicle 30 as a collection target vehicle (step S13). For example, in the abnormality detection process, when the normal vehicle operation history data is evaluated as insufficiency, a vehicle 30 in which the components corresponding to the component configuration of the analysis unit are immediately after maintenance or a vehicle 30 in which the cumulative maintenance cost is high is extracted as the collection target vehicle from the vehicle maintenance history DB 19. On the contrary, when abnormal vehicle operation history data is evaluated as insufficiency, a vehicle 30 in which components corresponding to the component configuration of the analysis unit are not maintained for a long period of time or a vehicle 30 with a low cumulative maintenance cost are extracted as a collection target vehicle from the vehicle maintenance history DB 19. Such a specification of extraction is based on ideas in which the maintenance of the vehicle 30 with the high cumulative maintenance cost is sufficiently performed from the usual time, and the maintenance of the vehicle 30 with the high cumulative maintenance cost is not sufficiently performed from the usual time. Further, even when the vehicle operation history data for each abnormality type classified by the abnormality classification process is evaluated as insufficiency, the vehicle 30 in which the components corresponding to the component configuration of the analysis unit are not maintained for a long period of time or the vehicle 30 with a low cumulative maintenance cost is extracted as the collection target vehicle from the vehicle maintenance history DB 19. Next, the collection condition setting section 13 sets operation data collection conditions which are transmitted to each of the extracted collection target vehicles (step S14). Here, the operation data collection condition refers to information which specifies “vehicle type”, “component configuration”, “sensor item”, and “sampling frequency” in each abnormality type evaluated as data number insufficiency in step S12. For example, the operation data collection condition is information such as “acquiring the rotational speed of the engine and the accelerator opening degree of the vehicle type A at a sampling frequency of 1 Hz”. Next, the collection condition setting section 13 determines whether or not the operation data collection condition is set for all the analysis units stored in the analysis unit storage section 17 (step S15). When the operation data collection condition is not set for all the analysis units (No in step S15), the process returns to step S11, and the processes after step S11 are repeatedly executed. On the other hand, when the operation data collection condition is set for ail the analysis units (Yes in step S15), if a plurality of operation data collection conditions is set for the same collection target vehicle, the collection condition setting section 13 integrates the operation data collection conditions (step S16). For example, when the collection of rotational speed of the engine is set for the same collection target vehicle in a certain analysis unit and the collection of the wheel speed is set in another analysis unit, the operation data collection condition can be gathered to the conditions for collecting both the rotational number of the engine and the wheel speed. Further, for example, when the collection of the wheel speed at 1 Hz cycle is set for the same collection target vehicle in a certain analysis unit and the collection of the wheel speed at 2 Hz cycle is set in another analysis unit, it is possible to gather these operation data collection conditions to the collection of the wheel speed at the cycle of 2 Hz. Next, the collection command distribution section 152 distributes the operation data collection command including the operation data collection condition set for each collection target vehicle to each collection target vehicle (step S17). Further, the operation data collection condition distributed to each collection target vehicle is displayed on the evaluator terminal 21 by the collection condition display section 142 in response to the request of the evaluator. Next, the details of the process of the data excess and deficiency evaluation section 11 in the step S12 will be described. As illustrated in FIG. 1, the data excess and deficiency evaluation section 11 includes an evaluation data generation section 111, a classification learning section 112, and a learning result evaluation section 113. The evaluation data generation section 111 generates data for performing the learning evaluation by the classification learning section 112. That is, the evaluation data generation section 111 executes processes of extraction of sensor items, determination of sampling frequency, and data loading for each analysis unit. Further, the analysis unit referred to here is information in which a sensor item or sampling frequency for each process of analysis, such as abnormality detection and abnormality classification, is associated with a vehicle type and a component to be analyzed such as “abnormality detection of vehicle type A”, and is stored in the analysis unit storage section 17 in advance. In the process of extracting the sensor item in the evaluation data generation section 111, the sensor item to be analyzed is selected, and in the process of selecting the sensor item, one or more sensor items are selected from the sensor item list predetermined for each component. Also, in the process of determining the sampling frequency, the sampling frequency at the time of analysis is selected from the frequency predetermined for each component in advance. These selections are performed by the evaluator who analyzes the abnormality of the vehicle 30 via the evaluator terminal 21 and the analysis unit setting section 141 of the evaluator terminal IF section 14. Further, in the data loading process, the evaluation data generation section 111 selects one of the analysis units stored in the analysis unit storage section 17, and loads the vehicle operation history data necessary for analyzing the abnormality related to the selected analysis unit from the vehicle operation history DB 18. That is, from the vehicle operation history DB 18, among the vehicle operation history data corresponding to “vehicle type” and “component configuration” of the analysis target, data of predetermined “sensor item” and “sampling frequency” can be extracted, and the vehicle operation history data having the correct answer value of “abnormality type” is read. Here, the correct answer value of the “abnormality type” refers to a value for each of normality, abnormality or abnormality type name that is set in the column of “abnormality type” of the vehicle operation history data (see FIG. 2A) by the maintenance person via the maintenance person terminal 22. For example, when the sensor item determined by the analysis unit in the case of the abnormality detection of the engine of the vehicle type A is the accelerator opening degree and the rotational speed of the engine, and the sampling frequency is 2 Hz, “vehicle type” is a vehicle type A, the engine and the accelerator are included in the “component configuration”, the accelerator opening degree and the rotational speed of the engine are included in “sensor item information”, and the vehicle operation history data having the “sampling frequency” of 2 Hz or more is loaded. Further, at this time, the vehicle operation history data in which the “abnormality type” is blank is not loaded. Also, when the analysis process is an abnormal classification, the vehicle operation history data in which “abnormality type” is “normal” is also not loaded. In this way, the evaluation data generation section 111 selects one or more sensor items and a set of one or more sampling frequencies for each of one or more analysis items, and extracts and loads the vehicle operation history data corresponding to the combinations from the vehicle operation history DB 18. The classification learning section 112 calculates the accuracy of classification in the abnormality detection and the abnormality classification for each of the vehicle operation history data of all the combinations loaded by the evaluation data generation section 111. In the present embodiment, an example of accuracy calculation using the machine learning will be described below. Abnormality detection of operation data can be handled as classification problem of two classes of normality and abnormality in the technique of machine learning, and the abnormality type number of the abnormality classification can be handled as classification problem of the class number. Therefore, in this case, it is considered to perform the abnormality detection and the abnormality classification, using a learning machine generally called “supervised learning classifier” such as support vector machine (hereinafter referred to as SVM). In this case, the vehicle operation history data extracted and loaded for each analysis item by the evaluation data generation section 111 is learned by the SVM, and the classes of normality/abnormality or abnormality type for each vehicle operation history data are classified. Thereafter, the class classified in this way is compared with the actual class, and the accuracy of classification is obtained on the basis of the result thereof. Further, the actual class mentioned here is a value in the column of “abnormality type” of the vehicle operation history data and information actually obtained as a result of maintenance. Also, the accuracy of classification refers to the ratio at which the class obtained by SVM (classifier) matches the actual class, and is often also called correct answer rate. Further, a method called cross validation is used for the accuracy evaluation of the classification using a classifier. As a method of cross validation, for example, there is a k-fold method. In the k-fold method, when dividing the data into k groups and classifying the class information of the i-th group, information of the group other than the i-th group is learned without learning data of the i-th group, and the data of the i-th group is classified. According to the cross validation, it is possible to evaluate the accuracy for data that has not been learned. Further, in case of the abnormality detection, it is also possible to use a classification method based on unsupervised learning. In this case, only the operation data of the normal class is learned by, for example, a mixed normal distribution. After that, the likelihood of unlearned data is calculated. When the likelihood is equal to or larger than a threshold value, it is classified into a normal class, and when the likelihood is lower than the threshold, it is classified into an abnormal class. Even when using the unsupervised learning method, accuracy evaluation can be performed using the cross validation. As described above, the classification learning section 112 classifies the vehicle operation history data loaded for each analysis unit into two classes of normality/abnormality or classes of a plurality of abnormality types, and obtains the accuracy of the classification of each class. The learning result evaluation section 113 performs the excess or deficiency determination of the vehicle operation history data based on the abnormality detection and the accuracy of the abnormality classification obtained by the learning section 112. That is, the learning result evaluation section 113 determines whether or not a predetermined condition is satisfied for each of the combination of one or more of the sensor items and the sampling frequencies for each analysis unit. Further, if the predetermined condition is satisfied, it is determined that a sufficient amount of the vehicle operation history data of the combination is accumulated. Further, if the predetermined condition is not satisfied, it is determined that the vehicle operation history data of the combination is insufficient. Here, the predetermined condition is, for example, a condition as to whether or not the number of data of each classified class is equal to or greater than a predetermined value, or a condition as to whether or not the accuracy of classification in each class is equal to or greater than a predetermined threshold. For example, when the number of data of each class is smaller than the threshold value, it is determined that the number of data itself is insufficient. When the accuracy of the class classified in the analysis unit is equal to or smaller than the threshold value, it is determined that the vehicle operation history data of the class with accuracy equal to or less than the threshold is insufficient. FIGS. 5A and 5B are diagrams illustrating an example of the learning result obtained by the classification learning section 112 (see FIG. 1) in a table format, FIG. 5A illustrates an example of a learning result in the case of the abnormality detection, and FIG. 5B is an example of the learning result in the case of the abnormality classification. Such a learning result is displayed on the evaluator terminal 21 via the evaluator terminal IF section 14 in accordance with the request of the evaluator. As illustrated in FIGS. 5A and 5B, the table of the learning result obtained by the classification learning section 112 includes the columns of “vehicle type, components”, “process”, “sensor item”, “sampling frequency”, “data number”, “correct answer rate” and the like. In the case of the abnormality detection process (FIG. 5A), the column of “correct answer rate” includes two columns of “normality” and “abnormality”, and in the case of the abnormality classification process (FIG. 5B), the column of “correct answer rate” includes the same number of columns as the number of abnormality types (number of classes) obtained in the abnormality classification process. Further, the correct answer rate mentioned here is an example of an index representing the accuracy of classification using the machine learning, and is given by the value acquired by dividing the number, in which the class classified by the classification learning section 112 matches the class obtained by actual maintenance, by the data number of the analysis target. Further, the correct answer rate is obtained for each class number of the classified classes. In this way, the learning result evaluation section 113 can obtain the accuracy of all class classifications for each analysis unit in which the vehicle type, components, and analysis process of the analysis target are all the same. Here, when the number of data of the normal or abnormal class is greater than the predetermined number of data and the correct answer rate in each class is higher than the predetermined threshold, the learning result evaluation section 113 determines that the operation data of the class is satisfied. Further, the operation data belonging to the normal or abnormal class is excluded from the operation data to be collected. On the other hand, when the number of data in the normal or abnormal class is smaller than the predetermined number of data and the correct answer rate in each class is lower than the predetermined threshold, the learning result evaluation section 113 determines that the operation data of the class is insufficient. Further, the operation data belonging to the normal or abnormal class is set as operation data to be collected. When receiving information on the analysis unit in which the operation data from the learning result evaluation section 113 is determined to be insufficient, the collection target vehicle extraction section 12 (see FIG. 1) extracts the vehicle maintenance history data having the corresponding vehicle type or the component configuration from the vehicle maintenance history DB 19. Furthermore, as described in step S13 of FIG. 4, when the collection target vehicle is the normal class, vehicles immediately after the maintenance of the components of the analysis unit or vehicles with the cumulative maintenance cost higher than the predetermined threshold are extracted as vehicles to be collected. Conversely, when the collection target is an abnormal class, vehicles in which the components of the analysis unit are not maintained for a certain period of time or vehicles with the cumulative maintenance cost lower than the predetermined threshold are extracted as vehicles to be collected. As described in steps S14 and S16 of FIG. 4 extracted for each analysis unit, the collection condition setting section 13 sets the operation data collection conditions for the collection target vehicle extracted for each analysis unit, and also integrates the operation data collection conditions when a plurality of operation data collection conditions is set for the same collection target vehicle. Further, as described in step S17 of FIG. 4, the collection command distribution section 152 distributes the operation data collection command including the operation data collection condition set for each collection target vehicle to each collection target vehicle. FIG. 6 is a diagram illustrating an example of the operation data collection condition display screen 50 displayed on the evaluator terminal 21 by the collection condition display section 142. As illustrated in FIG. 6, a vehicle type selection section 51, a component selection section 52, a collection situation and accuracy checking section 53, a collection command checking section 54, and the like are displayed on the operation data collection condition display screen 50. When checking the operation data collection condition in the operation data collection condition display screen 50, the analyzer can select the vehicle type and components to be checked, by the vehicle type selection section 51 and the component selection section 52, for example, from the pull-down displayed vehicle type or components. In the collection state and accuracy checking section 53, accuracy (correct answer rate) and excess and deficiency determination result for each analysis unit (sensor item, sampling frequency) for the vehicle type and components selected via the vehicle type selection section 51 and the component selection section 52 are displayed. Accordingly, the analyzer can check the analysis process, the sensor item, the sampling frequency, the number of data, the correct answer rate of each class, and the result of excess and deficiency determination for each analysis unit, by the display of the collection state and accuracy checking section 53. In the collection command checking section 54, the collection target vehicle, the sensor item and the sampling frequency are displayed. Here, as the collection target vehicle, the vehicle ID for individually specifying the vehicle 30 as a distribution target of the operation data collection command is displayed, and the total number of vehicles is displayed. Further, the sensor item and the sampling frequency are information directly forming the operation data collection command, which corresponds to an instruction “acquire the accelerator opening degree, the rotational speed of the engine, and the wheel speed at a sampling frequency of 2 Hz”. The analyzer can check the distributed operation data collection command which is transmitted to the collection target vehicle, by the display of the collection command checking section 54. Further, the analyzer can grasp on what type of vehicle 30 the operation data collection command is distributed, by the operation data collection condition display screen 50. As described above, in the embodiment of the present invention, the vehicle operation data collection apparatus 10 evaluates what kind of the vehicle operation history data of the abnormality type is insufficient for each analysis unit at the time of analyzing the vehicle abnormality, in the vehicle operation history data accumulated in the vehicle operation history DB 18. Next, the vehicle operation data collection apparatus 10 extracts the vehicle 30 determined that it is possible to efficiently acquire the vehicle operation history data of the abnormality type related to the analysis unit in which the vehicle operation history data is determined to be insufficient, from the vehicle maintenance history DB 19. Further, the vehicle operation data collection apparatus 10 distributes an operation data collection command for acquiring the vehicle operation history data of the abnormality type evaluated to be insufficient to the extracted vehicle 30, and acquires the vehicle operation history data from the vehicle 30, as a response thereof. Therefore, according to the embodiment, the vehicle operation data collection apparatus 10 can efficiently collect the vehicle operation history data of the abnormality type evaluated to be insufficient. In other words, it is possible to efficiently collect the vehicle operation data at the time of occurrence of the abnormality even for an abnormality having a low occurrence frequency. Furthermore, when the vehicle operation history data of the abnormality type evaluated to be insufficient is efficiently collected and the abnormality detection or the abnormality classification using the machine learning can be set to a predetermined accuracy (correct answer rate) or more, it is possible to reduce the work load of the abnormality detection and the abnormality classification of the maintenance person. As a result, in repair shops and the like of the vehicle 30, it is possible to expect effects such as reduction in man-hours for maintenance and cost reduction. The present invention is not limited to the above-described embodiments and modified examples, and various modified examples are included. For example, the above-described embodiments and modified examples have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. In addition, some of the configurations of certain embodiments and modified examples can be replaced with configurations of other embodiments and modified examples, and it is also possible to add the configuration of other embodiments and modified examples to the configuration of certain embodiments and modified examples. In addition, it is also possible to add, delete, or replace the configurations included in the other embodiments and modified examples with respect to some of the configurations of the embodiments and the modified examples.
048184683	description	DESCRIPTION OF THE SPECIFIC EMBODIMENTS A method is provided for efficient production of .sup.123 I from neat liquid XI, where X is alkali metal of atomic number 3-19, particularly sodium, or iodine. The target material is irradiated with high energy proton radiation in a predetermined energy range. The thickness of the target vessel in the radiation beam is controlled to provide a predetermined reduction in energy of the radiation beam. A gaseous stream of helium, optionally and preferably containing a small amount of naturally occurring xenon, is continuously swept through the target area, particularly across the target material surface. The target material is maintained at a temperature at or above the melting point of the target material and substantially below the boiling point of the target material. Depending upon the target material, the temperature will generally be from about 1.degree.-100.degree. C. above the melting point of the target material. The temperature of the target material is continuously monitored and controlled by means of the gaseous stream, the radiation beam and an external heater, if required. A shield is provided about the target to minimize convection currents and aid in the careful control of the temperature. Normally, the beam is swept across the target area at a rate which avoids excessive local beam heating and which provides continuous production of .sup.123 Xe. The target vessel is equipped with a reflux condenser which serves to return any entrained target material to the target vessel, as well as to cool the helium stream prior to its introduction into the collection assembly. The helium stream is then passed into an iodine scavenger which removes any iodine which has passed through the condenser. The helium stream is then directed to the collection and purification assembly. The target vessel normally has less than about one-half of its volume unfilled by the target material. For efficient production, a substantial portion (greater than about 25%) of the target material is in the irradiation beam. The irradiation zone comprises the target material in the target vessel both within and without the irradiation beam, the cross-section of the target material without the irradiation beam being not more than about 75% of the total cross-section of the target material in the target vessel. The collection and purification assembly comprises a plurality of spiral traps which are cooled to temperatures which allow substantially complete condensation and removal of .sup.123 Xe from the helium stream. Normally, all of the .sup.123 Xe will be collected in the first trap, the additional traps providing assurance that none of the radioactive xenon is lost. One or more collection and purification assemblies can be employed, so that irradiation of the target vessel is continuous until a sufficient quantity of .sup.123 Xe is collected. After a sufficient amount of .sup.123 Xe has been collected in the trap, the helium flow is stopped or switched to an alternate spiral collection trap and the original collection trap connected to a decay vessel which has been previously evacuated. By warming the collection trap, the .sup.123 Xe is efficiently transferred to the decay vessel which is cooled to a temperature below the boiling point of xenon. The decay vessel is then employed to allow the .sup.123 Xe to decay to .sup.123 I which may then be used in a variety of ways. The .sup.123 I which is obtained by the above procedure is substantially free of other undesirable radioisotopes. Desirably, the .sup.123 Xe may be allowed to decay in the presence of chlorine to form .sup.123 IC1, which can then be employed for radioiodination procedures. The target material will be either an alkali metal iodide, particularly sodium iodide, or mixtures of alkali metal iodides, e.g., NaI and LiI, or iodine of natural isotope distribution. Preferably, mixtures of iodides would provide the lowest melting point, e.g., eutectic mixtures. Usually, the target will be static, that is, a fixed target material will be irradiated until .sup.123 Xe is no longer efficiently produced. The target material will generally fill at least about one-half the volume of the target vessel and may occupy two-thirds or greater of the target vessel volume. The radiation beam will normally employ protons having energy in the range of about 60-70, preferably about 65MeV. The irradiation target will be of a sufficient thickness to provide about a 15-25Mevy, preferably about a 20MeV energy loss of the radiation beam through the target. With molten sodium iodide, a thickness of about 10.9 mm is desirable. The microamperage of the radiation beam will be greater than about 5 .mu.a and usually not exceed 25 .mu.a, being in the range of about 10-20 .mu.a or 0.6-1.2 .mu.A/cm.sup.2. The beam is normally swept over the target area, so as not to reside in any particular position for a time which would result in excessive heating. Therefore, the microamperage employed will be affected by the size of the beam spot, as well as the size of the target area subjected to the beam. Within these parameters, the microamperage will be chosen to optimize the yield of the desired radioisotope. Where sodium iodide is employed as the target material, the temperature of the sodium iodide will be maintained from about 650.degree.-720.degree. C., preferably 650.degree. to about 680.degree. C. With iodine as the target the temperature will be controlled in the range of about 100.degree.-130.degree. C., preferably about 100.degree.-110.degree. C. The helium stream will preferably have from about 0-0.2, preferably about 0.1 volume percent xenon. The xenon acts to aid in the efficient transfer of radioactive xenon from the target area and in the collection assembly. The temperature of the helium can be varied to aid in the temperature control of the target material. The rate at which the helium stream is passed through the target vessel will generally be 10-60 ml/min., more usually about 30 ml/min. The temperature of the helium stream is conveniently ambient temperature. The helium stream acts in combination with the liquid target material to rapidly and efficiently remove .sup.123 Xe from the irradiation zone. The irradiation beam involves greater than about 25% of the volume of the target material, so that the surface contacted by the helium stream is adjacent the radiation beam, normally being less than about 0.5" from the upper level of the irradiation beam. In a preferred embodiment, the helium stream is heated to the temperature of the target material, by having the helium conduit in the target vessel pass through the target material about the irradiation zone in a U-shaped form and then exit from the target material and direct the helium stream downwardly onto the target material surface. In addition, a baffle plate is provided beneath the exit from the target vessel which provides for a tortuous path for the helium stream from the surface of the target material to the exit from the target vessel. For further understanding of the invention, the drawings will now be considered. In FIG. 1 is depicted diagrammatically the target assembly 10. A target vessel 12 fitted with helium inlet tube 14 is situated in an aluminum target block 16. The target block has a carbon collimator 20 and an isolation foil 22, of stainless steel or aluminum of about 0.001 inch thickness. The carbon collimator 20 is retained in cooling block 24 which is equipped with helium inlet 26. A helium stream is introduced through helium inlet 26 and exits through helium outlet 30 so as to externally circulate around the target and minimize oxidation of the materials which might otherwise be prone to oxidation under the irradiation conditions while also providing cooling of the target. A Faraday cup 32 encloses the end of the aluminum target block 16. The aluminum target block 16 is fitted to a source of high energy radiation. The target vessel 12 holds the target material 34 in the radiation beam in the lower portion of the target vessel. At the top, the target vessel 12 is fitted with a condenser 36 which has upper cooling fluid inlet 40 and lower cooling fluid outlet 42, connected respectively to conduits 44 and 46. The condenser 36 may be packed with glass beads 50 to aid in the heat exchange between the cooling fluid and the helium stream. The helium stream exits the condenser and is directed by connecting conduit 52 to iodine scavenge vessel 54. The iodine scavenge vessel is conveniently a tube which can be packed with chemicals 58 which will react with the iodine and remove the iodine from the helium stream. Conveniently, a combination of silver nitrate and silver wire will remove substantially all or all of the iodine which has been entrained in the helium stream. From the iodine scavenging vessel, the helium stream is directed by means of conduit 56 to the purification and collection assembly. Conveniently, the conduit can be an inert, flexible tube, such as Teflon. The condenser 36 and scavenger 54 are contained within a hermetically sealed steel box 60 having a plexiglass window. The box 60 has an opening 62 for connection to a pump so as to maintain a mild negative pressure in the box. A plurality of openings are provided through which the various conduits are fitted for egress or ingress of the various streams. Conveniently, a helium conduit 64 is connected to the helium tube 14 through the steel box 60. The helium stream is then directed by means of conduit 56 to the collection and purification system as depicted in FIG. 2. The helium stream is passed through a first spiral trap 66, cooled in Dewar 70 with dry ice-acetone at a temperature of about -30.degree. to -40.degree. C. to further cool the helium stream to a temperature above the boiling point of xenon and to remove any materials which will condense at the indicated temperature. After the initial cooling, the helium stream is then directed through conduit 72 and solenoid control valve 74 to Tee-line 76. One leg of Tee-line 76 connects with spiral trap 80 which is cooled in liquid nitrogen (.about.-196.degree. C.) contained in Dewar 82. Spiral trap 80 serves to collect all, or substantially all, of the xenon in the helium stream, so that the radionuclide product is substantially completely isolated in the liquid nitrogen cooled spiral trap 80. The flow of the helium stream from spiral trap 80 is controlled by second solenoid valve 84. To ensure that no radioactive material is vented to the atmosphere, and that all of the radionuclide product is captured, a train of additional spiral traps cooled in liquid nitrogen can be employed. Usually one or two liquid nitrogen spiral traps in addition to the collection spiral trap 80 may be employed. In the Figure, two additional traps 86 and 90 are indicated which are cooled in liquid nitrogen. Solenoid valves 92 and 94 allow for transfer of radionuclide product from those traps to the product collection spiral trap 80. For example, if radio-nuclide has escaped from spiral trap 80 to spiral trap 86, spiral trap 80 can be cooled with liquid nitrogen and evacuated by a means which will be discussed, with both solenoid valves 84 and 92 closed. When the pressure in spiral trap 80 has been reduced to the desired level, valve 84 may be opened and spiral trap 86 slowly warmed, so that the radionuclide will transfer from spiral trap 86 to spiral trap 80. Valve 84 is then closed and vacuum distillation employed for purification of the product in spiral trap 80. The other leg of the Tee 76 is connected through valves 93 and 95 to decay vessel 96. Between valves 93 and 95 is cross-connector 100. One of the remaining arms of cross-connector 100 connects to vacuum gauge 102 through valve 104. The other arm connects through valve 106 and line 110 to pump 112. A copper trap 117 is provided in line 110 to protect the pump. All of the spiral traps are retained in a lead shielded glove box, which is not shown, having appropriate openings for the ingress and egress of the necessary lines. As indicated, the helium stream, containing the radionuclide xenon is directed through line 72, with the xenon being captured in spiral trap 80 and the helium stream continuing through a series of additional spiral traps and evacuated through flowmeter 114. The helium stream may be discarded, in which case it is contained in a vessel 119 to attend decay of C-11 and N-13 concomitant airborne radioactivity, or, preferably, reused with the xenon supplemented to provide the necessary amount of naturally occurring xenon in the helium stream for reuse in the target assembly. When a sufficient amount of product has been isolated in spiral trap 80, the first solenoid valve 74 is closed. The helium stream may then be directed to a second collection and purification system, whereby continuous irradiation and production of radionuclide is maintained in the target assembly. With solenoid valves 84 and 93 closed, and solenoid valves 104, 106 and 95 open, the decay vessel is evacuated to less than about 50.mu. Hg, preferably about 30.mu. Hg. The decay vessel is then cooled in liquid nitrogen, solenoid valves 104 and 106 closed, solenoid valves 74 and 84 remaining closed, and solenoid valve 95 opened. The spiral trap 80 is then allowed to warm slowly, which results in evaporation of the radionuclide xenon. Spiral trap 80 is opened to the low pressure system by opening solenoid valve 93 which results in an efficient xenon transfer to the decay vessel 96. When all of the radionuclide in spiral trap 80 has been transferred to the decay vessel, stopcock 116 is closed, sealing the decay vessel from the system. The decay vessel will then be allowed to stand for a few hours, usually about 6 hours, or can be transported to the place of use, while the .sup.123 Xe decays to .sup.123 I. In FIG. 3 a prototype target vessel 120 is depicted. The cross-section of the vessel in the beam direction will be chosen so as to give the desired energy reduction for the particles. Various materials may be used for the target vessel, depending upon the target material. Conveniently, stainless steel, tantalum or quartz may be employed, a stainless steel vessel having a window of 0.010 inch thickness being satisfactory with sodium iodide as the target material. The target area can be varied depending upon the capacity of the radiation beam. With a 10 .mu.a beam, a target area 7/8".times.11/2", with a 1/8" spot being swept across the area is found to be satisfactory. With a 20 .mu.a beam, a target area of 13/4".times.11/2" may be employed to enhance production of the radionuclide. Helium inlet tube 14 directs helium over the upper surface of the target material. Surrounding the container is a heat shield 132 having a housing 134 for a thermocouple 136. The heat shield can conveniently be of about 0.02 inches stainless steel and serves to minimize convective cooling and allow for improved temperature control. While not shown, it may be of advantage to introduce a heating element in the heat shield, so as to add the opportunity to heat the target container 122, should the irradiation beam provide insufficient heat. Flange 138 serves to position the helium inlet 14 and condenser connector tube 140, as well as provide a sealed connection between the container vessel 122 and the condenser 36. Plate 142 serves to position tubes 14 and 120 and ensure a hermetic seal with the vessel 122. It is observed that after a relatively extensive period of irradiation, usually 30 hours or more, the shape of the container vessel 142 will change, so that with a rectangular container the path length through the target material increases. In FIG. 4 is depicted a container vessel having a preferred configuration, with two parallel arcuate walls. The wall receiving the irradiation is conveniently 0.010 inches thick with the other walls the same or greater thickness, e.g., 0.020 inches. A non-corrosive stainless steel can be employed, e.g. 347, and the target vessel fabricated from the same thickness material with the wall receiving the proton radiation electrostripped to the desired thickness. The arc will circumscribe a minor chord of a circle. With the parallel concave and convex walls 144 and 146, the container vessel can be used for extended periods of time without a significant change in the radiation path length through the target material. The bowing approximately cancels out, as indicated by the broken lines in FIG. 4. In FIG. 5, an alternate preferred embodiment of a target vessel is depicted. The target vessel 150 is substantially filled by the target material 152. The beam area 154 covers a major portion of the target material 152 cross-section and due to diffusion, all of the target material will be irradiated during the irradiation. A helium conduit 156 has helium inlet 160. The helium conduit 156 follows the contours of the target vessel 150 adjacent the walls of the target vessel 150 defining a plane transverse to the irradiation beam. The helium conduit 156 terminates above the target material 152 and extends inwardly, with the exit 162 directing the helium stream downwardly onto the surface 164 of the target material. A baffle plate 166 is situated above the helium conduit exit 162 and below the target vessel exit 170 to aid in directing the helium stream across the target material surface 164. Condenser 172 is fitted into target vessel exit 170. By having the helium stream pass through the target material prior to exiting onto the target material surface, the helium stream can act as a coolant of the target material to control the target material temperature, while avoiding cooling of the surface below the melting point of the target material. The subject invention provides a large number of advantages over previously employed processes. High efficiency is obtained in the yield of the desired radionuclide based on the amperage of the radiation beam. The product is found to be radionuclidically pure except for extremely minor amounts (less than about 0.1%) of the undesired radioisotope .sup.125 I. The product is also found to be sterile and pyrogen free. By having a continuous process, losses of radioactive xenon which frequently result during batch processing because of the difficulty of sealing the target, are avoided. The continuous process reduces handling radiation hazard. Furthermore, as compared to earlier batch processing, the target can be continuously irradiated, so that interruption of the irradiation is substantially diminished. Targets properly sealed for irradiation must be opened carefully and such opening is frequently time consuming and efficient recovery of .sup.123 Xe difficult. During batch processing, the .sup.123 I resulting from .sup.123 Xe decay is frequently lost. During a two hour irradiaton, this loss can be about 25%. In the subject method .sup.123 Xe is collected about five minutes after production and only about 3% of the activity is lost. Experience with the subject apparatus and method has shown that on the average .sup.123 I can be produced at a rate of 18 mCi/.mu.Ahr. Since the target is operated at 20 a, the yield is 360 mCi/hr. This calculates out to a yield of 90% or better of the attainable yield. The use of .sup.127 I has many advantages over the use of other target materials, such as .sup.122 Te. One advantage is the substantial absence of undesirable radionuclide impurities. Another is that normal iodine is substantially less expensive than other target materials. Because of the expense of the target material, the target must be reused after irradiation and this results in a costly and hazardous procedure. Furthermore, the reprocessing frequently results in loss of the expensive target material and may introduce undesirable foreign material which can produce radioactive contaminants in subsequent irradiations, such as .sup.24 Na. The .sup.127 I targets are thicker than those used in the lower energy reactions, e.g., .sup.122 Te (d,n), .sup.123 I and it is much easier to maintain quality control of the radioisotopes which the subject process produces. Thin targets often produce radioactive contaminants because of the variability in the target thickness. With the use of iodine as compared to sodium iodide, there are additional advantages. There is a 20% increase in the yield of .sup.123 Xe per .mu.amp/hr, since the beam is not arrested by the sodium in sodium iodide. Furthermore, the release of xenon from the liquid iodine appears to be more efficient. The operating temperature is also lower and one avoids the build-up of radioactivity of radioactive isotopes of sodium, such as .sup.22 Na and .sup.24 Na. While the subject process has been described for the production of .sup.123 I, the process can also be used for the production of .sup.125 I by employing a lower proton energy in the range of about 20-40 MeV, particularly 32 MeV, whereby .sup.125 Xe is produced. The energy drop over the target vessel would be about 15-20 MeV. Since the beam exiting from the target vessel for the formation of .sup.123 Xe will have approximately the correct energy, by employing a second target vessel behind the first target vessel, both isotopes could be obtained simultaneously. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.
06014422&	summary	BACKGROUND OF THE INVENTION 1. Technical Field The present invention relates generally to the field of semi-conductor manufacturing and, more specifically, to a method for optimizing the use of x-ray lithography in conjunction with hybrid resists. 2. Background Art The need to remain cost and performance competitive in the production of semiconductor devices has caused continually increasing device density in integrated circuits. To facilitate the increase in device density, new technologies are constantly needed to allow the feature size of these semiconductor devices to be reduced. For the past 20 years, optical lithography has driven the device density and the industry has resorted to optical enhancements to allow increasing densities. As an example, some such enhancements include overexposing/overdeveloping, hard and soft phase shifts, phase edge masks, and edge shadowing. Unfortunately, the latest of such enhancements tend to offer only minor increases in density and the limit of optical enhancements appears inevitable in the near future. The same industry trend to increase device density is also causing a transition to x-ray lithography. X-rays are a desirable type of exposure radiation because the wavelength of x-rays (about 8 .ANG.) is smaller than the wavelength of ultra-violet radiation typically used to fabricate dense integrated circuits. The smaller wavelength allows for exposure of a resist through a mask having a smaller image than in optical lithography. However, certain aspects of x-ray lithography are insufficiently advanced to satisfy the current demand for increasing device density. In optical lithography, projection printing allows the mask image to be projected onto the resist at a reduced size to increase the possible device density. For example, a 4.times. reduction is typical. However, sufficient success has not been achieved in attempts to fabricate lenses for reducing the size of the x-ray mask image to a smaller aerial image. Accordingly, even though the potential exists for exposing a 0.05 .mu.m aerial image onto the resist using x-ray lithography, it requires a mask having a 0.05 .mu.m image. Producing such a mask within required tolerances can be a formidable task and constitutes the most significant disadvantage of x-ray lithography. In fact, the tolerances that are achieved in the x-ray mask dictate the tolerances that can be achieved in a product produced using x-ray lithography. The smaller images on a x-ray mask are more difficult to fabricate than the larger images on an optical mask because of the smaller image size and different materials. The smaller size requires electron beam lithography (EBL) to carve out the image and EBL has not yet advanced sufficiently to produce masks that take full advantage of the smaller wavelength. Further, instead of a chrome mask layer used in optical lithography, the nature of x-rays requires tungsten, gold, or other material with a high x-ray extinction coefficient that must also be much thicker than the typical chrome layer. Unfortunately, the high x-ray extinction materials are difficult to control within tolerance and the thickness increases the difficulty of mask fabrication. Also, x-ray lithography involves proximity printing the mask image onto the resist. Proximity printing simply means that the mask is in close proximity to, but not in contact with, the surface of the resist layer. The gap distance between the mask and the wafer is minimized to produce an aerial image through the mask with as high a contrast possible. That is, the gap distance is decreased so that the transition from zero intensity to full intensity occurs over a smaller area. Typical gap distances are between 10 and 50 .mu.m. The pitch, or combined width of an adjoining line and space in a semiconductor, can theoretically be very small when x-ray lithography is used, but the poor tolerance of the x-ray mask prevents the precise formation of reliable devices at x-ray pitch. Even though the possibility of x-ray pitch exists, abnormalities in the x-ray mask will yield abnormalities in lines and spaces sufficient to preclude fabricating reliable devices as small as allowed by the small x-ray wavelength. It would be an improvement in the art to provide a method for forming high tolerance devices with x-ray pitch. Such a method must yield few enough abnormalities in lines and spaces to provide performance of the final product within industry standards. Without a method for forming high tolerance devices at x-ray pitch, the value of x-ray lithography for increasing device density is seriously diminished and advancement in improving chip cost and performance may stagnate. DISCLOSURE OF INVENTION Accordingly, the present invention provides a method for defining high density features on semiconductor devices. The novel method uses hybrid resist and x-ray lithography to define these features. The method avoids the problems in accurately forming x-ray masks at the feature size dimensions by using the unique properties of hybrid resist to form spaces in the resist where an intermediate exposure occurs, in other words, to use an edge printing technique. These spaces have a dimension that is independent of the feature size of the mask and is smaller than the typical feature size of a conventional x-ray mask. Thus, the present invention is able to consistently form small, high tolerance features using x-ray lithography without requiring equally small and high tolerance mask shapes in the x-ray mask. The present invention method uses adjustments in the mask-wafer gap distance during x-ray exposure to form spaces in hybrid resist of a desirable dimension. In particular, the size of a space formed in hybrid resist is determined by the aerial image which, in turn, is varied by adjusting the gap distance during exposure. This can be used to provide accurate patterning of hybrid resist with different space widths. Additionally, this method can be used to compensate for process variations that would otherwise cause unwanted changes in space widths. Within a range of about 10-50 .mu.m as the mask-wafer gap distance, one can take advantage of the combined properties of x-ray and hybrid resist to increase the space width in the resist by increasing the gap distance between the mask and wafer. In this sense, the gap distance is not the problem, but rather the solution to the need for varying the hybrid resist space width and fine tuning to account for process variations. In addition, a x-ray hybrid resist yields high tolerance lines and spaces largely independent of a low tolerance x-ray mask. Only the transition from exposed resist to unexposed resist at the edge of the x-ray aerial image is involved in producing a corresponding space. The width of the space produced is generally not dependent on the size of the mask image. Thus, an x-ray mask image wherein the reticle opening is either too small or too large and causes a fatal defect in a typical resist might not yield such an effect in a hybrid resist. Accordingly, a space width in the hybrid resist can be selectively printed by varying the mask-wafer gap, allowing more versatile structures to be formed and adjustments to be made for process variations such as resist composition and ion implant levels. It is an advantage of the present invention that space width can be varied in the production of high tolerance spaces at x-ray pitch. It is an additional advantage that adjustments can be made in space dimensions at x-ray pitch to compensate for process variations. The foregoing and other advantages and features of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.
044619545	abstract	An ion-processing method and apparatus utilizing a slender tubular member having an open end and communicating with an inlet conduit. The tubular member is positioned to bring the open end in spaced juxtaposition with a workpiece across a small gap of a size of 10 and 1000 .mu.m in an evacuated an ionizable material is supplied into the slender tubular member through the inlet conduit for feeding it into the small gap through the open end. A power supply is provided to energize the supplied gas to form ions thereof and to apply an accelerating potential to the formed ions to propel them in a beam across the small gap to impinge upon a limited area of the surface of the workpiece juxtaposed with the open end of the slender tubular member. The pressure within the small gap, ranging between 10.sup.-4 and 10.sup.-1 Torr, is maintained in excess of the pressure of the surrounding the gap, ranging between 10.sup.-6 and 10.sup.-4 Torr.
	claims	1. An ultimate storage container assembly, comprising a gas-tight container, an arrangement of a plurality of spent fuel rods and spaces between said fuel rods, said arrangement being gas-tightly enclosed in said container, and a bulk fill selected from the group consisting of zeolite and activated charcoal embedding said spent fuel rods in said container, said bulk fill penetrating said spaces. 2. The container assembly according to claim 1 , which further comprises a fuel assembly enclosing said fuel rods and being penetrated by said bulk fill. claim 1 3. The container assembly according to claim 2 , wherein said container is dimensioned to house only a single said fuel assembly. claim 2 4. The container assembly according to claim 1 , wherein said bulk fill is formed of granulate material. claim 1 5. The container assembly according to claim 1 , which further comprises a further bulk fill selected from the group consisting of zeolite and activated charcoal surrounding said container. claim 1 6. The container assembly according to claim 1 , wherein said zeolite is A type zeolite. claim 1 7. The container assembly according to claim 6 , wherein said zeolite is formed from at least one substance selected from the group consisting of MgA, CaA, and SrA. claim 6 8. The container assembly according to claim 7 , wherein said zeolite is doped with silver. claim 7 9. The container assembly according to claim 6 , wherein said zeolite is doped with silver. claim 6 10. The container assembly according to claim 1 , wherein said zeolite is selected from the group consisting of chabazite and mordenite. claim 1 11. The container assembly according to claim 1 , which further comprises particles of at least one substance selected from the group consisting of metal grit, MnO 2 , Al 2 O 3 , MgO, SnO 2 , ZrO 2 , and silicate admixed with said bulk fill. claim 1 12. An ultimate storage container assembly, comprising a gas-tight container, an arrangement of a plurality of spent fuel rods and spaces therebetween, said arrangement being gas-tightly enclosed in said container, and a bulk fill selected from the group consisting of zeolite and activated charcoal embedding said spent fuel rods in said container and penetrating said spaces, said container being formed with steel walls and steel plates welded in gas-tight fashion to said steel walls.
	abstract
047524340	claims	1. In a control bar assembly for a nuclear reactor, said control bar assembly having a vertically movable elongate control bar and a drive mechanism for vertically positioning said bar, a coupling device for releasibly coupling said mechanism and said bar, having : an endmost pommel and a shoulder formed on said bar, said shoulder being formed at a vertical distance under said pommel and facing upwardly, a vertically movable gripping body included in said mechanism and having a plurality of resilient gripping fingers for locking engagement with said pommel; a sleeve included in said mechanism and vertically movable with respect to said gripping body between a first position where a downwardly directed endmost face of said sleeve is in abutment against said shoulder and a second position clear of said shoulder, when said gripping fingers are locked on said pommel; controllable means for moving said sleeve away from said first position toward said second position; and resilient prestressing means in said mechanism arranged to exert a force in said sleeve biasing said sleeve vertically away from the fingers so as to maintain said downwardly directed endmost face of the sleeve in firm abutment against the shoulder when the fingers are locked on the pommel. 2. The device according to claim 1, wherein said gripper body and said fingers are slidably mounted in the sleeve and said sleeve is formed with a recess allowing the fingers to spread apart and to release the pommel upon application of an external force overcoming the prestress of said prestressing spring. 3. The device according to claim 1, wherein said endmost face of the sleeve and said shoulder have a flaring shape for taking up lateral reactions and causing self centering during engagement of the sleeve on the pommel. 4. The device according to claim 1, wherein the gripper body has a central rod trasversing the whole of the mechanism and having a releasable abutment connection with a tubular rod situated at that end of the mechanism which is remote from said enmost face, the prestressing spring being compressed between said tubular rod and said sleeve. 5. The device according to claim 4, further comprising a tubular control rod fast with the sleeve and which cooperates with external longitudinal drive means, said tubular rod being located within and along said tubular control rod. 6. The device according to claim 2, wherein said sleeve is fast with a slide situated inside the gripper body and having a surface for abutting engagement with one end of the prestressing spring and the other end of the prestressing spring bears on a slider having a releasable abutment connection with the gripper body. 7. The device according to claim 6, wherein the abutment connection comprises locking cams disposed in the slider cooperating with an abutment sleeve fast with the gripper body and wherein a central rod is mounted in the slider for movement between a position in which it holds the cams in engagement against the sleeve and a position in which it allows the cams to retract. 8. The device according to claim 7, wherein the central rod is coaxial to a tube fast with the slider and to a tubular control rod fast with the gripper body and cooperating with longitudinal drive means. 9. The device according to claim 8, whereint he central rod is held in abutment against the tube through a stiffer spring by a less stiff spring and the central rod and the tube project outside the tubular control rod so as to allow the central rod and the tube to be moved with respect to each other with a tool, against the action of the return spring. 10. The device according to claim 1, wherein the sleeve comprises shoes for slidably guiding the sleeve along a fixed tubular guide placed in alignment with the control bar.
	description	This subject matter disclosed herein relates generally to imaging systems, and more particularly, to apertures for an x-ray collimator. Non-invasive imaging broadly encompasses techniques for generating images of the internal structures or regions of a person or object. One such imaging technique is known as x-ray computed tomography (CT). CT imaging systems measure the attenuation of x-ray beams that pass through the object from numerous angles (often referred to as projection data). Based upon these measurements, a computer is able to process and reconstruct images of the portions of the object responsible for the radiation attenuation. Collimators are used to filter a stream of rays from a source (such as an x-ray tube) so that the rays traveling in a desired direction or directions are allowed to pass through. The collimator may be made from a material that substantially blocks x-rays, with an aperture provided to allow a portion of the x-ray beams to pass through. For example, a system may include a source and a detector. For good image reconstruction, it is desirable that all or a given portion of a detector be uniformly covered by x-rays from the source. Certain CT systems use detectors that are generally rectangular in shape, but that curve with respect to a plane that is transverse to the x-ray beam. Use of a substantially planar collimator with a generally rectangular aperture profile to shape an x-ray beam to project on such a curved detector can result in undesirable beam projection coverage of the detector. The beam projection through the flat aperture results in a distortion (a different shape than that of the aperture) on a curved detector. This distortion reduces the dose efficiency of the system. This additional portion of the beam extending beyond the usable (or desired to be used) portion of the detector results in a patient being exposed to un-used x-rays, or an additional dose. Certain known CT systems have attempted to address this issue in various ways. For example, collimators that are curved along a length thereof instead of being substantially planar have been employed. These designs, however take up significantly more space than a substantially planar aperture, with space often being at a premium in CT systems (for example, space occupied by a collimator can be a limiting factor on size of bore). Also, for example, apertures with linear ramps extending from edge to center have been employed. While these linearly ramped apertures reduce the overdose when compared to rectilinear aperture shapes, linearly ramped apertures still result in un-used x-ray beam portions. Thus, presently known collimators occupy too much space, and/or result in an undesired overdose of x-ray exposure, and/or limit or inhibit functionality. In one embodiment, a collimator is provided. The collimator includes an x-ray blocking surface that comprises one or more generally flat plates defining an aperture edge of the aperture. The aperture edge includes a first end portion including a first end of the aperture edge, a second end portion including a second end of the aperture edge, and a central portion including a center of the aperture edge. The central portion is interposed between the first and second end portions. The first end portion of the aperture edge corresponds to a first end portion of a detector, the second end portion of the aperture edge corresponds to a second end portion of the detector, and the central portion of the aperture edge corresponds to a central portion of the detector. A profile of the aperture edge is discontinuous at a point between the first end of the aperture edge and the center of the aperture edge. In another embodiment, a system is provided. The system includes an x-ray source, a detector, and a collimator. The x-ray source provides an x-ray beam, and the detector receives a portion of the x-ray beam. The collimator is interposed between the detector and the x-ray source. The collimator includes an x-ray blocking surface that comprises one or more generally flat plates defining an aperture edge of the aperture. The x-ray blocking surface is configured so that the one or more generally flat plates prevent x-ray transmission and the aperture allows x-ray transmission therethrough, wherein a projection of the beam is projected proximate to the detector. The aperture edge includes a first end portion including a first end of the aperture edge, a second end portion including a second end of the aperture edge, and a central portion including a center of the aperture edge. The central portion is interposed between the first and second end portions. The first end portion of the aperture edge corresponds to a first end portion of a detector, the second end portion of the aperture edge corresponds to a second end portion of the detector, and the central portion of the aperture edge corresponds to a central portion of the detector. A profile of the aperture edge is discontinuous at a point between the first end of the aperture edge and the center of the aperture edge. In a further embodiment, a system is provided. The system includes an x-ray source, a detector, a collimator, and a processor. The x-ray source provides an x-ray beam, and the detector receives a portion of the x-ray beam. The collimator is interposed between the detector and the x-ray source. The collimator includes an x-ray blocking surface that comprises one or more generally flat plates defining an aperture edge of the aperture. The x-ray blocking surface is configured so that the one or more generally flat plates prevent x-ray transmission and the aperture allows x-ray transmission therethrough, wherein a projection of the beam is projected proximate to the detector. The aperture edge includes a first end portion including a first end of the aperture edge, a second end portion including a second end of the aperture edge, and a central portion including a center of the aperture edge, the central portion interposed between the first and second end portions. The first end portion of the aperture edge corresponds to a first end portion of the detector, the second end portion of the aperture edge corresponds to a second end portion of the detector, and the central portion of the aperture edge corresponds to a central portion of the detector. The central portion of the aperture edge is configured to provide a first beam projection portion substantially conforming with a profile of the central portion of the detector, and the first end portion of the aperture edge is configured to provide a second beam projection portion substantially differing with a profile of the first end portion of the detector. The processor is configured to reconstruct an image using information provided by the detector, wherein information provided by the central portion of the detector is processed in a first manner including reconstruction of an image and information provided by the first end portion of the detector is processed in a second manner including tracking processing. The foregoing summary, as well as the following detailed description of various embodiments, will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of the various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (e.g., processors or memories) may be implemented in a single piece of hardware (e.g., a general purpose signal processor or a block of random access memory, hard disk, or the like) or multiple pieces of hardware. Similarly, the programs may be stand alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings. Embodiments provide a generally planar aperture having an opening curvature tuned for a given system geometry. For example, the opening curvature in some embodiments has a greater width towards the ends of the aperture which projects a substantially straight line for a curved detector. Various embodiments provide a one-piece design having improved tolerance control and compactness. Certain embodiments may be used as a primary beam limiting aperture, while certain other embodiments may be used as a secondary aperture to reduce scatter. Various embodiments provide a relatively simple aperture edge shape, such as, for example, a radius, while certain other embodiments provide more complex geometries such as, for example, a series of differing edge profiles. For example, in certain embodiments, a complex aperture edge is provided which results in a linear projection in an imaging space and a non-linear projection outside of the imaging space. The non-linear projection outside of the imaging space may be used, for example, for tracking. A technical effect of various embodiments is to provide improved shaping of x-ray beams and/or improved x-ray dosage management and/or ease of manufacturing and/or customizable shaping and/or improved form factor (e.g. requiring less space). FIG. 1 is a simplified block diagram of a computed tomography (CT) imaging system 10 that is formed in accordance with various embodiments. The imaging system 10 may be utilized to acquire x-ray attenuation data at a variety of views around a volume undergoing imaging (e.g., a patient, package, manufactured part, and so forth). The imaging system 10 includes an x-ray source 12 that is configured to emit radiation, e.g., x-rays 14, through a volume containing a subject 16, e.g. a patient being imaged. In the embodiment shown in FIG. 1, the imaging system 10 includes a collimator 18. In operation, the emitted x-rays 14 pass through an opening, or aperture of the collimator 18 which limits the angular range associated with the x-rays 14 passing through the volume in one or more dimensions (certain apertures formed in accordance with various embodiments are discussed in more detail below). More specifically, the collimator 18 shapes the emitted x-rays 14, such as to a generally cone or generally fan shaped beam that passes into and through the imaging volume in which the subject or object of the imaging process, e.g., the subject 16, is positioned. In embodiments, the collimator 18 may be adjusted to accommodate different scan modes, such as to provide a narrow fan-shaped x-ray beam in a helical scan mode and a wider cone-shaped x-ray beam in an axial scan mode. The collimator 18 may be formed, for example, from a plate with an aperture formed therethrough. Optionally, the collimator 18 may be formed using two or more translating plates or shutters. The imaging system 10 also includes a filter 22 that is disposed between the x-ray source 12 and the collimator 18. In various embodiments, the filter 22 is a bowtie filter having a predetermined thickness and fabricated from a predetermined material. In operation, the x-rays 14 pass through the filter 22 which adjusts a frequency and/or an intensity characteristic of the emitted x-rays 14. The filter 22 may be a conventional bowtie filter or other X-ray beam shaping filter suitable for varying the intensity of the beam of x-rays 14 to compensate for different thicknesses of the subject 16 as seen from different angular positions of the x-ray source 12. In one embodiment, the thickness of the bowtie filter 22 may vary in the axial direction to compensate for the Heel effect. Optionally, a separate or additional filter having a thickness that varies in the axial direction may be provided in conjunction with the bowtie filter 22 to compensate for the Heel effect. In operation, the x-rays 14 pass through or around the subject 16 and impinge the detector 20. In the illustrated embodiment, the detector is shown curved along a direction generally transverse to the x-rays 14. The detector 20 includes a plurality of detector elements 24 that may be arranged in a single row or a plurality of rows to form an array of detector elements 24. The detector elements 24 generate electrical signals that represent the intensity of the incident x-rays 14. The electrical signals are acquired and processed to reconstruct images of one or more features or structures within the subject 16. In various embodiments, the imaging system 10 may also include an anti-scatter grid (not shown) to absorb or otherwise prevent x-ray photons that have been deflected or scattered in the imaging volume from impinging the detector 20. The anti-scatter grid may be a one-dimensional or two-dimensional grid and/or may include multiple sections, some of which are one-dimensional and some of which are two-dimensional. The imaging system 10 also includes an x-ray controller 26 that is configured to provide power and timing signals to the x-ray source 12. The imaging system 10 further includes a data acquisition system 28. In operation, the data acquisition system 28 receives data collected by readout electronics of the detector 20. The data acquisition system 28 may receive sampled analog signals from the detector 20 and convert the data to digital signals for subsequent processing by a processor 30. Optionally, the digital-to-analog conversion may be performed by circuitry provided on the detector 20. The processor 30 is programmed to perform functions described herein, and as used herein, the term processor is not limited to just integrated circuits referred to in the art as computers, but broadly refers to computers, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. FIG. 2 is a pictorial view of an imaging system 400 that is formed in accordance with various embodiments. FIG. 3 is a block schematic diagram of a portion of the imaging system 400 shown in FIG. 2. Although various embodiments are described in the context of an imaging system that includes a CT imaging system, it should be understood that other imaging systems capable of performing the functions described herein are contemplated as being used. The imaging system 300 is illustrated, and includes a CT imaging system 302. Optionally, modalities other than CT may be employed with the imaging system 300. For example, the imaging system 300 may be a standalone CT imaging system, an x-ray imaging system, and/or a CT system for a dedicated purpose such as extremity or breast scanning, and combinations thereof, among others. The imaging system 300 also may be a multi-modality imaging system. The CT imaging system 302 includes a gantry 310 that has the x-ray source 12 that projects a beam of x-rays 14 toward the detector array 20 on the opposite side of the gantry 310. The detector array 20 includes the plurality of detector elements 24 that are arranged in rows and channels that together sense the projected x-rays that pass through an object, such as the subject 306. The imaging system 300 also includes the computer 30 that receives the projection data from the detector array 20 and processes the projection data to reconstruct an image of the subject 306. In operation, operator supplied commands and parameters are used by the computer 30 to provide control signals and information to reposition a motorized table 322. More specifically, the motorized table 322 is utilized to move the subject 306 into and out of the gantry 310. Particularly, the table 322 moves at least a portion of the subject 306 through a gantry opening 324 that extends through the gantry 310. As discussed above, the detector 20 includes a plurality of detector elements 24. Each detector element 24 produces an electrical signal, or output, that represents the intensity of an impinging x-ray beam and hence allows estimation of the attenuation of the beam as it passes through the subject 306. During a scan to acquire the x-ray projection data, the gantry 310 and the components mounted thereon rotate about a center of rotation 340. FIG. 3 shows only a single row of detector elements 24 (i.e., a detector row). However, the multislice detector array 20 includes a plurality of parallel detector rows of detector elements 24 such that projection data corresponding to a plurality of slices can be acquired simultaneously during a scan. Rotation of the gantry 310 and the operation of the x-ray source 12 are governed by a control mechanism 342. The control mechanism 342 includes the x-ray controller 26 that provides power and timing signals to the x-ray source 12 and a gantry motor controller 346 that controls the rotational speed and position of the gantry 310. The data acquisition system (DAS) 28 in the control mechanism 342 samples analog data from detector elements 24 and converts the data to digital signals for subsequent processing. An image reconstructor 350 receives the sampled and digitized x-ray data from the DAS 28 and performs high-speed image reconstruction. The reconstructed images are input to the computer 30 that stores the image in a storage device 352. Optionally, the computer 30 may receive the sampled and digitized x-ray data from the DAS 28 and perform various methods described herein. The computer 30 also receives commands and scanning parameters from an operator via a console 360 that has a keyboard. An associated visual display unit 362 allows the operator to observe the reconstructed image and other data from computer. The operator supplied commands and parameters are used by the computer 30 to provide control signals and information to the DAS 28, the x-ray controller 26 and the gantry motor controller 346. In addition, the computer 30 operates a table motor controller 364 that controls the motorized table 322 to position the subject 306 in the gantry 310. Particularly, the table 322 moves at least a portion of the subject 306 through the gantry opening 324 as shown in FIG. 2. Referring again to FIG. 3, in one embodiment, the computer 30 includes a device 370, for example, a floppy disk drive, CD-ROM drive, DVD drive, magnetic optical disk (MOD) device, or any other digital device including a network connecting device such as an Ethernet device for reading instructions and/or data from a non-transitory computer-readable medium 372, such as a floppy disk, a CD-ROM, a DVD or an other digital source such as a network or the Internet, as well as yet to be developed digital means. In another embodiment, the computer 30 executes instructions stored in firmware (not shown). The computer 30 is programmed to perform functions described herein, and as used herein, the term computer is not limited to just those integrated circuits referred to in the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. In the exemplary embodiment, the x-ray source 12 and the detector array 20 are rotated with the gantry 310 within the imaging plane and around the subject 306 to be imaged such that the angle at which an x-ray beam 374 intersects the subject 306 constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array 20 at one gantry angle is referred to as a “view”. A “scan” of the subject 306 comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source 12 and the detector 20. In a CT scan, the projection data is processed to reconstruct an image that corresponds to a two dimensional slice taken through the subject 306. Exemplary embodiments of an imaging system are described above in detail. The imaging system components illustrated are not limited to the specific embodiments described herein, but rather, components of each imaging system may be utilized independently and separately from other components described herein. For example, the imaging system components described above may also be used in combination with other imaging systems. The collimator in such a system is used, for example, to help manage the dosage of x-rays received by a patient. For example, x-rays that pass through a patient, but are not projected onto a detector, or a portion of the detector used for imaging, may be considered an overdose. In systems utilizing a flat collimator with a rectilinear or linearly sloped aperture shape along with a detector that is curved with respect to a plane defined by the flat collimator, an overdose, or poor dose management, may result due to the geometry of the system. FIG. 4 illustrates a collimator system 100 and resulting overdose of x-rays. The collimator system 100 includes an x-ray source 102, a collimator 106 and a detector 140. A beam 104 emanating from the source 102 passes by the collimator 106 and projects generally toward the detector 140. In FIG. 4, the source 102 is modeled as a point source, however tube sources may be used. Further, a single collimator is shown. In embodiments, additional filters and/or collimators may be used. In FIG. 4, the collimator 106 is depicted as a single plate disposed on one side of the beam 104. A generally symmetric collimator plate may also be employed on an opposing side of the beam 104. While the detector 140 is curved along the x-direction of FIG. 4, the detector and projection of x-ray beam proximate to the detector 140 are illustrated as a horizontal projection. The detector 140 is generally rectangular in shape and includes a lateral side 142. The shape of the aperture defined by the collimator limits or defines the shape of the projection of the fan beam 104 onto and near the detector 140. For example, for a collimator 106 having a generally flat edge 128 (shown in phantom line in FIG. 4), the resulting beam projection, 130 (also shown in phantom line in FIG. 4) extends laterally past the lateral side 142 of the detector 140 as shown. The portion of the projection 130 extending past the lateral side 142 is generally considered an overdose of x-ray, as the patient is exposed to that portion, but the portion is not used by the system, for example, in reconstructing an image. Certain previously known systems have attempted to provide beam projections that reduce the overdose, and improve dose management. By reducing a width of the aperture at a center line of the aperture (and corresponding center line of the detector), the area of the portion or portions of the projection projecting beyond the detector may be reduced. For example, in FIG. 4, a sloped profile 118 (shown in dashed line) for the collimator is also shown. The resulting projection 120 (shown in dashed line) corresponding to profile 118 is closer to the lateral side 142 along the center line of the detector than the projection 130 resulting from a flat edge 128. The portions of the projection 120 extending beyond the detector also take up less area than those for the projection 130, resulting in better dose management. By bringing the peak of the sloped profile 118 laterally inward, the peak of the sloped profile may be located tangent to the detector projection line (a line extending from the source to the lateral edge of the detector at the detector center line). This is shown in FIG. 4 as a sloped profile 108 having a peak 109 located along the center line of the collimator 106 and projector 140. Projection 110 results from use of the sloped profile 108. The sloped profile 108 and the peak 109 are sized and configured so that the projection 110 does not extend substantially past the detector 140 at the center 144 of the lateral side 142 of the detector 140. If a similar sloped profile 108 were used on the opposing side of the beam 104, the resulting width of the projection 110 across the center line of the detector 140 (through the center 144 of the lateral side 142) would match the width of the detector in the z-direction. Thus, the beam width may be defined by the center of the aperture for a sloped profile such as sloped profile 108, or may be defined by the end points of the aperture for a flat aperture such as one having a generally flat edge 128. The above described aperture shapes are also discussed in connection with FIGS. 5a and 5b as well as FIGS. 6a and 6b. FIG. 5 depicts a collimator 500 with a generally flat, or rectilinear, aperture 502, and FIG. 6 depicts the resulting projection 560 of the aperture 502 on a detector that is curved along a direction substantially parallel to the collimator 500 (or transverse to a beam passing through the collimator 500). The collimator 500 is made of an appropriate material of sufficient width to allow for substantial prevention of the passage of x-rays through the solid portions of the collimator 500, and the aperture 502 is an opening extending through the thickness of the collimator 500 (into the page, in FIG. 5) configured to allow passage of x-rays. The aperture 502 is substantially rectilinear. The aperture has sides 504 that extend along the length of the aperture 502 and ends 506 that extend along width of the aperture 502. In FIG. 5, the sides 504 are flat, and are not sloped or angled with respect to corresponding sides of a rectilinear detector. FIG. 6 depicts the projection 560 resulting from passage of an x-ray beam through the aperture 502. The projection 560 is shown with respect to a detector 550. The detector 550 is rectilinear in shape, having sides 552 that extend along the length of the detector 550 and ends 554 that extend across the width of the detector 550. The width of the aperture 502 is configured so that the width of the projection 560 substantially matches the width of the detector 550 at the ends 554 of the detector. Thus, as discussed above, the projection 560 extends laterally beyond the detector 550, with a maximum distance of extension along the center line 570 of the detector 550. The projection 560 includes portions 556 that extend beyond the detector 550, representing excessive dosage of an x-ray. FIG. 7 depicts a collimator 600 with a tapered, aperture 602, and FIG. 8 depicts the resulting projection 660 of the aperture 602 on a detector that is curved along a direction substantially parallel to the collimator 600 (or transverse to a beam passing through the collimator 600). The collimator 600 is made of an appropriate material of sufficient width to allow for substantial prevention of the passage of x-rays through the solid portions of the collimator 600, and the aperture 602 is an opening extending through the thickness of the collimator 600 (into the page, in the sense of FIG. 6) configured to allow passage of x-rays. The aperture 602 includes an edge having a linear taper. The aperture 602 has lateral edges defined by end points 604 and center points 606. The edge tapers inward laterally and inward along the length of the aperture 602 from the end points 604 to the center points 606 along continuous sloped lines 608. Thus, the sides of the aperture 602 are not flat, and instead are sloped or angled with respect to corresponding sides of a rectilinear detector. FIG. 8 depicts the projection 660 resulting from passage of an x-ray beam through the aperture 602. The projection 660 is shown with respect to a detector 650. The detector 650 is rectilinear in shape, having sides 652 that extend along the length of the detector 650 and ends 654 that extend across the width of the detector 650. The width of the ends of the aperture 602 is configured so that the width of the projection 660 substantially matches the width of the detector 650 at the ends 654 of the detector at a given distance from the source, and the width between the center points 606 is configured so that the width of the projection 660 at the center line 670 substantially matches the width of the detector 650 at the given distance. Thus, as discussed above, the projection 660 extends laterally beyond the detector 650, and includes portions 656 that extend beyond the detector 650, representing excessive dosage of an x-ray. Various embodiments provide for improved dosage management by more closely correlating the shape of the projection, or beam projection, to a detector shape than is provided by, for example, the above described flat and/or linear taper profiles. For example, FIG. 9 depicts a collimator 700 with an aperture 702 including a plurality of points along a lateral edge that are tangent to a projection line of a detector, and FIG. 10 depicts the resulting projection 760 of the aperture 702 on a detector curved along a direction substantially parallel to the collimator 700 (or transverse to a beam passing through the collimator 700). FIG. 9 depicts a collimator 700 with an aperture 702 having an aperture edge 703, and FIG. 10 depicts the resulting projection 760 of the aperture 702 on a detector curved along a direction substantially parallel to the collimator 700 (or transverse to a beam passing through the collimator 700). The collimator 700 is made of an appropriate material of sufficient width to allow for substantial prevention of the passage of x-rays through the solid portions of the collimator 700, thereby providing an x-ray blocking surface, and the aperture 702 is an opening extending through the thickness of the collimator 700 (into the page, in the sense of FIG. 9) configured to allow passage of x-rays. The collimator 700 depicted in FIG. 9 is a substantially flat, or planar collimator. The collimator 700 may be made of a single plate with an aperture formed therethrough, or, as another example, the collimator 700 may include a plurality of blades, plates, or other portions that are positioned to provide a desired aperture. In some embodiments, the blades, plates or other portions may be articulable to provide for adjustability of, for example, aperture width. Further, in some embodiments, the collimator 700 may be one of a series of collimators that a beam passes through. For example, one collimator may be used to shape or direct a beam while other collimators are used to reduce scatter. The aperture shapes discussed herein may be used with one or more of such collimators used together in a system. The aperture edge 703 of the aperture 702 includes lateral edges that include end points 704, center points 708, and intermediate points 706. The end points 704 are located at the ends of the collimator 700, and the center points 708 are located along a center line of the collimator 700. The intermediate points 706 are located along the length of the lateral edges interposed between the end points 704 and the center points 708. Each of the end points 704, intermediate points 706, and center points 708 are configured, based on system geometry and configuration, so that, for a given distance of the beam source to the detector 750, each end point 704, intermediate point 706, and center point 708 will be tangent to the detector projection line (an individual ray passing by the point will land on the lateral edge of the detector at a corresponding length along a lateral edge of the detector). Thus, each of the end points 704, intermediate points 706, and center points 708 are configured so that the width of the projection 760 at a corresponding location along the length of the detector 750 substantially matches the width of the detector 750 at the corresponding location along the length of the detector 750. Each end point 704 is joined to an intermediate point 706 by a first line segment 710 that extends inwardly laterally along the length of the edge of the aperture 702. Also, each intermediate point 706 is joined to a center point 708 by a second line segment 712 that extends inwardly laterally along the length of the edge of the aperture 702. The slopes of the first line segment 710 and the second line segment 712 (or the angle between the first line segment 710 and the second line segment 712 and a lateral edge of the detector) are different. In FIG. 9, the aperture 702 includes two differently sloped, or discontinuous, line segments along the edge 703 between an end and the center of the collimator, and one intermediate peak point (a point at which the projection lies substantially at the edge of the detector) interposed between the center and the end of the aperture. In other embodiments, more line segments and peak points may be used. FIG. 10 depicts the projection 760 resulting from passage of an x-ray beam through the aperture 702. The projection 760 is shown with respect to a detector 750. The detector 750 is rectilinear in shape, having sides 752 that extend along the length of the detector 750 and ends 754 that extend across the width of the detector 750. As discussed above, the width of the aperture 702 is configured so that the width of the projection 760 substantially matches the width of the detector 650 at locations along the sides 752 of the detector 750 corresponding to the end points 704, intermediate points 706, and center points 708 of the aperture 702. For example, intermediate points 772, which correspond to intermediate points 706 of the aperture 702, are points at which the projection 760 is located substantially along a lateral edge of the detector 750. Similarly, center points 774, which correspond to center points 708 of the aperture 702, are points at which the projection 760 is located substantially along a lateral edge of the detector 750. The aperture 702 thus provides a plurality of points along a length of a detector where the projection does not extend substantially past an edge of a detector. The projection 760 extends laterally beyond the detector 750 at locations between the plurality of peak points, and includes portions 756 that extend beyond the detector 750. These portions are relatively smaller than the portions of the flat or linearly tapered apertures discussed above, thus reducing excessive dosage of an x-ray. Thus, some embodiments provide a substantially flat or planar collimator that provide a corresponding projection more closely approximating the surface of a curved rectilinear detector. Thus, various embodiments also provide reduced x-ray dosage when used with a curved detector. By breaking the edge of the aperture into increasingly shorter line segments interposed between points located along tangents to the projection of a detector edge, the portions of a resulting projection extending laterally beyond a detector may be even further reduced. As the line segments become infinitesimally small, the edge profile of the aperture becomes a curve. Thus, a curve of a given profile may be considered an ideal shape to produce a projection that substantially matches a rectilinear detector. FIG. 11 depicts a collimator 800 with a radiused aperture 802 having an aperture edge 803, and FIG. 12 depicts the resulting projection 860 of the aperture 802 on a detector that is curved along a direction substantially parallel to the collimator 800 (or transverse to a beam passing through the collimator 800). The collimator 800 is made of an appropriate material of sufficient width to allow for substantial prevention of the passage of x-rays through the solid portions of the collimator 800, and the aperture 802 is an opening extending through the thickness of the collimator 800 (into the page, in the sense of FIG. 11) configured to allow passage of x-rays. The aperture edge 803 of the aperture 802 includes opposed curved portions 804 that extend along the aperture edge 803 between the ends of the aperture 802. In the embodiment of FIGS. 8a and 8b, the aperture 802 is tuned or configured to provide a projection substantially conforming to a curved rectilinear detector for a given system geometry and configuration. Thus, for the given geometry and configuration, each point along the curved edge of the aperture 802 is substantially at a tangent to a ray from the source to an edge of the detector. As shown in FIG. 12, the detector 850 is rectilinear in shape, having sides 852 that extend along the length of the detector 850 and ends 854 that extend across the width of the detector 850. The projection 860 substantially matches the profile of the detector, reducing, minimizing, and/or eliminating excess x-ray dosage. In alternate embodiments, the aperture 802 may be tuned to cover only a given proportion of a detector. For example, in embodiments, only a portion of the detector surface area may be used for imaging. Thus, in embodiments, the aperture 802 may be tuned so that the resulting projection covers a desired portion, for example one-half, of a detector width. In other embodiments, the same collimator and aperture may be used for different applications requiring different imaging widths used by the detector. In such embodiments, the aperture may be tuned or configured for a given imaging width (for example, a more frequently used imaging width), and then adjusted as discussed above via, for example, movable plates, to provide alternate imaging widths. Or, as another example, the aperture may be tuned or configured for a width intermediate between two widths to provide more closely matched dosage management for both widths than if the aperture were tuned specifically for one of the widths. Thus, various embodiments provide for ideal or near ideal coverage of a given detector shape. In alternate embodiments, however, the aperture of a collimator may be configured to deviate from such ideal or near ideal coverage. For example, FIG. 13 illustrates a collimator 900 formed in accordance with an embodiment. The collimator 900 includes an aperture 902 having an aperture edge 903. In the embodiment of FIG. 9, the aperture 902 is tuned or configured so that a first portion of the resulting projection substantially matches the profile of a detector, and so that a second portion of the resulting projection substantially differs from the profile of the detector. FIG. 14 depicts the resulting projection 950 of the aperture 902 on a detector 952 that is curved along a direction substantially parallel to the collimator 900 (or transverse to a beam passing through the collimator 900). The collimator 900 is made of an appropriate material of sufficient width to allow for substantial prevention of the passage of x-rays through the solid portions of the collimator 900, and the aperture 902 is an opening extending through the thickness of the collimator 900 (into the page, in the sense of FIG. 13) configured to allow passage of x-rays. As shown in FIG. 13, the aperture edge 903 of the aperture 902 includes a central portion 908 interposed between end portions 906. The central portion 908 corresponds to a central portion of a detector, while the end portions 906 correspond to the end portions of a detector. The aperture 902 is configured to provide a beam projection substantially matching the profile of the detector over the central portion, but deviating from the profile over the end portions. In the illustrated embodiments, with the detector being substantially rectilinear and curved with respect to a plane generally parallel to a plane defined by the collimator 900, the central portion 908 of the aperture 912 comprises a curved portion 912. The curved portion 912 is tuned or configured to provide an ideal or near ideal projection for covering a detector having a given width (or for covering a given portion of a detector width). The curved portion 912 provides a substantially linear beam projection corresponding to the central portion of a corresponding rectilinear detector. The end portions 906 of the aperture 902 include a flat portion 910. As used herein in connection with aperture profiles, the term flat means generally parallel to a side or edge of a substantially rectilinear detector. The flat portion 910 joins the curved portion 912 at point 914, representing a discontinuity between the flat portion 910 and the curved portion 912 along the edge 903 of the aperture 902. The flat portion 910 is located laterally inwardly from the intersection of extensions of the curved portion 912 and an edge of the aperture 902 indicated at point 920. Thus, the aperture 902 is smaller in area than an aperture tuned to substantially match the profile of the detector over the length of the detector. The projection resulting from aperture 902 therefore covers less area than the detector profile. The flat portion 910 thus is configured to provide a beam projection that extends laterally inwardly from the substantially linear beam projection provided by the curved portion 912. FIG. 14 depicts the projection 950 resulting from the aperture 902 with respect to a substantially rectilinear detector 952. The detector 952 is rectilinear in shape, having sides 954 that extend along the length of the detector 952 and ends 956 that extend across the width of the detector 952. The projection 950 substantially matches the profile of the detector along a central portion 964 of the detector 952 corresponding to the central portion 908 of the aperture 902, thereby reducing, minimizing, and/or eliminating excess x-ray dosage while providing coverage of the available imaging space for the central portion 964. However, because of the configuration of the end portions 906 discussed above, the projection 950 does not extend across the full width of the detector 952 proximate to the end portions 960 of the detector 952. Instead, the detector 952 includes portions 970 that are not covered by the projection 950. For example, in embodiments, not all of the detector area may be utilized or required for imaging, and thus the entire detector area may not need to receive a portion of a beam. In certain embodiments, portions of the detector may be used for tracking purposes, for example, as discussed below, and the aperture may be tuned to provide improved tracking along one or more edges of a detector. Further, in alternate embodiments, different shapes, other than the flat portion, may be employed on one or more end portions of an aperture. For example, linear slopes, steps, or curves differing from a curved central portion may be included in alternate embodiments. In the embodiment of FIG. 13, the end portions are symmetric about the center of the aperture. In alternate embodiments, the end portions may be asymmetric. FIG. 15 illustrates a collimator 980 having an asymmetric aperture 982 having an aperture edge 983 formed in accordance with an embodiment. The illustrated embodiment is asymmetric about a center line 994 bisecting the length of the collimator 980. Additionally or alternatively, the aperture may be asymmetric about other axes as well, such as an axis bisecting the width of the collimator. The aperture edge 983 of the aperture 982 includes a first end 984 and a second end 988. A center portion 986 is interposed between the first end 984 and the second end 988. The center portion 986 includes a curved portion 992 that is tuned or configured to provide a projection substantially coinciding with a curved rectilinear detector profile. The curved portion 992 of the edge of the aperture 982 extends continuously through the center portion 986 as well as to the second end 988. However, the first end 984 includes a flat portion 990 of the edge 983 of the aperture 982, and the edge 983 of the aperture 982 is discontinuous where the flat portion 990 joins the curved portion 992 (see, e.g., discussion above regarding flat portion 910). For a detector having a curved rectilinear profile for which the aperture 982 was tuned or configured, the resulting projection of the aperture 982 would substantially coincide with the detector profile for the portion of the detector corresponding to the center portion 986 and the second end 988. However, for the portion of the detector corresponding to the first end 984 of the aperture 982, the resulting projection would not substantially coincide with the profile of the detector, instead resulting in portions of the detector not being covered by the projection (see, e.g., discussion above regarding portions 970). FIG. 16 illustrates a projection 1050 projected on a detector 1000 resulting from an aperture formed in accordance with an embodiment. For example, the detector 1000 is a curved rectilinear detector, and an aperture generally similar to the aperture 902 may be employed, with the aperture including a curved center portion configured to provide a projection substantially matching the profile of the detector 1000, and flat portions positioned at the ends of the aperture to provide a projection that does not substantially match the profile of the detector 1000 toward the ends of the detector 1000. The detector 1000 includes sides 1008 extending along the length of the detector 1000 and ends 1010 extending along the width of the detector 1000. The detector 1000 is generally rectilinear in shape, and is curved with respect to a plane transverse to the beam being projected on to the detector 1000. The detector includes a plurality of detector elements 1002 arranged in rows 1004 and channels 1006. As shown in FIG. 16, the detector 1000 includes portions defined by boundaries 1052 that are not covered by the projection. The boundaries 1052 are located proximate to the edges of the detector 1000. Thus, a subgroup of elements 1020 are defined that either are not exposed to the beam, or are only partially exposed to the beam, with only a portion of the element exposed to the beam. In embodiments, all or some of the subgroup of elements 1020 are used for tracking purposes. For example, during a scanning process, the focal point of the beam may move relative to the collimator and/or detector. By knowing the position of the detector as well as the position of the collimator, the focal point may be determined by the location of the beam projection on the detector. Also, by providing a projection that covers less than the entirety of the detector elements, the edge or boundary of the projection may be detected and tracked by the detector. For example, the movement of one or more of the boundaries 1052 may be tracked by one or more elements of the subgroup of elements 1020, with the information regarding the movement of the boundary used to determine the location and movement of the focal point. Thus, a flux of a beam on the detector may be detected and used to determine the position and movement of a focal point of the beam. By providing an aperture that provides a boundary 1052 with a higher order contour (such as a slope or a curve), increasingly precise information regarding movement of the focal point may be provided. Thus, the movement and/or the location of the focal point may be determined from information from the subgroup of elements 1020. In some embodiments, information from one group of detectors is processed by a processor to reconstruct an image, and information from the subgroup of elements 1020 is processed by the processor for tracking and to determine any necessary adjustments to system configuration or geometry. Thus, in embodiments, differently located detector elements are processed differently. In various embodiments, the imaging area may only require a portion of the available detector elements. In such embodiments, an aperture may be provided that provides a projection that substantially matches the desired imaging area for a portion of the detector, but that also expands beyond the desired imaging area and covers additional elements of the detector not used for imaging, with the additional elements used, for example, for tracking. In certain embodiments, the desired image area may be irregular in shape (e.g. not rectilinear), and an aperture formed in accordance with embodiments described herein may be utilized to provide an irregularly shaped projection. Further still, for example, in some embodiments the detector may be substantially flat instead of curved, and an aperture may be provided having a first, substantially flat edge over a first portion of the aperture to provide a beam that substantially matches the profile of the detector at a first corresponding detector portion, with the aperture having a second, differently shaped (for example curved) edge that shapes a beam portion that does not match the profile of the detector at a second corresponding detector portion. In other embodiments, the desired imaging area may be only a portion of detector, and the aperture may be tuned, configured, and/or adjusted to provide a beam covering the desired imaging area. Additionally or alternatively, some embodiments provide a system with interchangeable apertures that may be selected, or toggled between, for different applications. For example, collimators with differently sized apertures may be provided for differently sized imaging areas. As another example, one or more collimators may be provided that shape beams that substantially match a detector profile, along with one or more additional collimators that shape beams that do not substantially match a detector profile for at least a portion of the detector profile. As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional elements not having that property. Also as used herein, the phrase “reconstructing an image” is not intended to exclude embodiments of the present invention in which data representing an image is generated, but a viewable image is not. Therefore, as used herein the term “image” broadly refers to both viewable images and data representing a viewable image. However, many embodiments generate, or are configured to generate, at least one viewable image. As used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. In embodiments, the readable storage medium excludes signals. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program. It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. This written description uses examples to disclose the various embodiments of the invention, and also to enable any person skilled in the art to practice the various embodiments of the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the various embodiments of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if the examples have structural elements that do not differ from the literal language of the claims, or if the examples include equivalent structural elements with insubstantial differences from the literal languages of the claims.
	summary
	claims	1. A fast reactor having a reactivity control reflector comprising:a reactor vessel in which a coolant is accommodated;a reactor core in the reactor vessel dipped with the coolant;a core barrel surrounding the outside of the reactor core;a partition wall spaced apart from and parallel to the core barrel; anda reflector interposed between the core barrel and the partition wall, outside the reactor core, and surrounding only a portion of the reactor core so that the reflector moves around a periphery of the reactor core in a vertical direction to control reactivity of the reactor core, the reflector being cylindrically shaped,wherein the reflector has a lower neutron reflecting portion having a neutron reflection capability higher than that of the coolant and an upper cavity portion located above the lower neutron reflecting portion and having a neutron reflection capability lower than that of the coolant, and the upper cavity portion is composed of a plurality of hermetically-sealed vessels, andwherein the hermetically-sealed vessels are cylindrically shaped,wherein the upper cavity portion includes a frame assembly that surrounds peripheries of the hermetically-sealed vessels, supports the lower neutron reflecting portion and restrains the upper cavity portion in a horizontal direction,wherein the hermetically-sealed vessels are surrounded by supporting rods and are arranged side by side, stacked and accommodated in the frame assembly where the frame assembly includes a coupling member and the supporting rods. 2. The fast reactor having the reactivity control reflector according to claim 1, wherein the lower neutron reflecting portion comprises a plurality of laminated metal plates, and the laminated metal plates have a plurality of coolant flow paths in which the coolant flows. 3. The fast reactor having the reactivity control reflector according to claim 1, wherein the lower neutron reflecting portion comprises a plurality of laminated metal plates or SiC plates, and each of the laminated metal plates includes metal mainly composed of chromium-molybdenum steel, nickel steel, nickel or includes Inconel. 4. The fast reactor having the reactivity control reflector according to claim 1, wherein the lower neutron reflecting portion comprises a plurality of laminated metal plates or SiC plates to which a plurality of coolant flow paths, in which the coolant flows, are formed so as to communicate with each other. 5. The fast reactor having the reactivity control reflector according to claim 4, wherein a number of the plurality of coolant flow paths is larger on a reactor core side than on a reactor vessel side. 6. The fast reactor having the reactivity control reflector according to claim 1, wherein the reflector is arranged such that a plurality of pads are disposed around the upper and lower ends of the lower neutron reflecting portion and the upper cavity portion. 7. The fast reactor having the reactivity control reflector according to claim 1, wherein the hermetically-sealed vessels comprise convex portions or recessed portions formed to the upper and lower ends thereof, and horizontal movement of the hermetically-sealed vessels is configured to be restrained by connecting the hermetically-sealed vessels to each other in a columnar state by concave/convex engagement or engagement coupling through a framework. 8. The fast reactor having the reactivity control reflector according to claim 1, wherein upper and lower end plates are disposed to the hermetically-sealed vessels disposed to the upper cavity portion, the upper and lower end plates are integrally welded to the hermetically-sealed vessels, and the upper cavity portion is divided into a plurality of segments. 9. The fast reactor having the reactivity control reflector according to claim 1, wherein the reflector is arranged such that the upper cavity portion is formed on an extending line above a region of the lower neutron reflecting portion, and the hermetically-sealed vessels having a maximum diameter are disposed in a region of the upper cavity portion. 10. The fast reactor having the reactivity control reflector according to claim 1, wherein the reflector is arranged such that the hermetically-sealed vessels having a plurality of different diameters are disposed so that a volume occupied by the space in the hermetically-sealed vessels is 80% or more of an entire volume of the upper cavity portion. 11. The fast reactor having the reactivity control reflector according to claim 1, wherein the upper cavity portion is arranged such that the hermetically-sealed vessels are disposed in a horizontal direction so that influence on the core reactivity is reduced at a time of breaking any one of the hermetically-sealed vessels. 12. The fast reactor having the reactivity control reflector according to claim 1, further comprising a joint, configured to absorb thermal expansion, deformation and vibration, that couples the lower neutron reflecting portion to the upper cavity portion. 13. The fast reactor having the reactivity control reflector according to claim 1, further comprising a thermal expansion absorption element, attached to at least one of an upper portion and a lower portion of the upper cavity portion, configured to absorb thermal expansion in a vertical direction and absorb displacement of the hermetically-sealed vessels in the vertical direction. 14. The fast reactor having the reactivity control reflector according to claim 13, wherein the thermal expansion absorption element comprises one of a coil spring, a disk spring and a sheet spring.
	summary
	description	This invention was made with government support under DE-SC0002322 awarded by the US Department of Energy. The government has certain rights in the invention. The present invention relates to an apparatus for generating high-energy plasmas that can promote nuclear fusion, and in particular, to systems using magnetic mirror confinement and neutral beam injection, with additional radiofrequency power injection. High-temperature plasmas can be confined away from a physical container and avoiding damage to the container and possible plasma quenching, by a magnetic mirror confinement system. Such confinement systems may provide an axial magnetic field extending between two ends at which the magnetic flux lines converge. Plasma ions moving within this axial magnetic field spiral along the flux lines at the local cyclotron frequency and are “reflected” by an axial component of magnetic force acting on the spiraling ions. This reflecting magnetic force caused by the flux line convergence and concomitant increasing magnetic field strength is in the direction away from the convergence. Moreover, the reflecting force is proportional to the particle kinetic energy component which is perpendicular to the magnetic field. A similar reflecting force acts on the plasma electrons. Nuclear fusion can be promoted in a magnetic mirror confinement system by generating plasma with sufficiently high energy and density. One method of reaching this high-energy/density state injects electrically neutral particles (a neutral beam) through the magnetic containment field into the plasma where the neutral particles of the neutral beam are ionized, that is, split into plasma ions and electrons. The neutral beam has an initial energy above that necessary for fusion so that the resulting plasma ions maintain an energy suitable for fusion even with an expected collisional loss of energy of the plasma ions after introduction into the plasma. The plasma density and energy are determined by the loss rate of the fast ions injected by neutral beams which decreases with increasing beam energy; hence high energy ions are better confined than low energy ions. A neutral beam generating a sufficient flux of highly energetic particles at energies sufficient to maintain high fusion output in a magnetic mirror confinement system is difficult and costly from an energy standpoint. Currently, such an approach does not appear to be practical for net fusion energy generation. The present invention also injects a neutral beam injection into a magnetic mirror confinement but differs from the previous approaches by employing a low-energy neutral beam having far less energy than needed to produce significant fusion directly. Instead, after the neutral beam is ionized, the energy of those neutral beam sourced fast ions is boosted within the magnetic containment volume by using a radiofrequency electrical field. The difficulties of preferentially transferring radiofrequency energy to the fast-neutral beam ions rather than thermal ions is overcome by controlling the injection angle and energy of the neutral beam so that there is a well-defined “turning point” of the fast ions in the magnetic containment field. Tuning the radiofrequency waves to a multiple (i.e. a harmonic) of the cyclotron frequency at the turning point, preferentially energizes these neutral beam injected ions to fusion levels with only small expected wave damping effects on thermal ions. Specifically, then, in one embodiment, the invention provides an apparatus for producing high-energy plasma in a magnetic mirror containment field, the latter providing axially-extending magnetic flux lines converging at opposed first and second ends of a containment volume holding the plasma. A neutral beam generator directs a neutral beam of particles into the containment volume at a predetermined pitch angle with respect to the magnetic field and an energy range so that the particles disassociate into plasma ions at the same pitch angle within the containment volume and have a well-defined turning point. At the turning point, fast ions have purely perpendicular energy. A radiofrequency generator can then be used to produce an t electrical field to accelerate the beam-sourced ions to an energy sufficient for fusion of the plasma ions. It is thus a feature of at least one embodiment of the invention to provide a system for boosting the energy of the plasma ions after injection into the containment field, greatly increasing the efficiency of the neutral beam. The frequency of the electrical field may be functionally dependent on a cyclotron frequency at turning points for the plasma ions of the neutral beam in the magnetic mirror containment field. It is thus a feature of at least one embodiment of the invention to preferentially deposit energy in the plasma ions having a matching cyclotron frequency. In one embodiment, the frequency of the electrical field may be a harmonic of the cyclotron frequency at the turning point, greater than than the cyclotron frequency. It is thus a feature of at least one embodiment of the invention to exploit preferential transfer of radiofrequency electrical energy to resonant fast ions that occurs at higher cyclotron harmonics. The energy of the neutral beam is set so that more than 50 percent of the neutral beam particles are converted to plasma ions. It is thus a feature of at least one embodiment of the invention to permit the use of a lower energy neutral beam amenable to higher particle flux and thus capable of high plasma densities. The neutral beam may have an energy of less than 50,000 electron volts. It is thus a feature of at least one embodiment of the invention to allow setting the trade-off in the design of the neutral beam generator for high flux rates rather than high energies thereby improving ion fueling rates. The radiofrequency generator may boost the energy of the plasma ions from the neutral beam by more than 2 times. It is thus a feature of at least one embodiment of the invention to provide significant energy boosting of the plasma ions after injection. The radiofrequency generator may include an antenna positioned to be proximate to a reflection limit of the plasma ions and to generate a rotating electric vector perpendicular to the axis of the magnetic mirror containment field. It is thus a feature of at least one embodiment of the invention to optimize the antenna for energy deposition of the plasma ions. The angle of the neutral beam may be between 15° and 80° to the axis. It is thus a feature of at least one embodiment of the invention to provide a good trade-off between energy of the neutral beam and a turn-around point that isolates the neutral beam from thermal ions. The apparatus may further include a treatment volume at least partially surrounding the containment volume to receive high-energy neutrons therethrough and containing an element for transmutation into a different element. It is thus a feature of at least one embodiment of the invention to provide a system for treatment of materials with neutrons, for example, to create radiopharmaceuticals or to revitalize spent nuclear fuel. The neutral beam may be selected from the group consisting of deuterium and tritium and in some embodiments the system may use deuterium only with respect to the neutral beam and the gas in the containment volume. It is thus a feature of at least one embodiment of the invention to provide a system that can work with well-understood neutral beam materials and in some cases that can avoid the use of tritium in favor of deuterium. In one embodiment, the invention may be employed to create a fusion apparatus having a reaction volume holding a fusible material within a first axially-extending magnetic containment field. In this embodiment, a first and second plasma plug may flank the reaction volume along the axis, each plasma plug being the apparatus for producing high-energy plasma as described above, wherein plasma ions escaping from the first and second plasma plugs produce a fusion reaction in the reaction volume. It is thus a feature of at least one embodiment of the invention to provide an improved design for a fusion device for providing transmutation or power generation. These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. Referring now to FIG. 1, a high-energy plasma system 10 may provide a pressure vessel 12, for example, in the form of a sealed cylindrical shell of stainless steel or the like, extending along an axis 14 for receipt of a reaction gas, such as deuterium or tritium, through valve inlet assembly 13 from a pressure tank or the like (not shown). First and second electromagnetic coils 16a and 16 may be positioned within the pressure vessel 12 near the opposed ends of the pressure vessel 12 to define a containment volume 17 therebetween having a magnetic containment field 15. The electromagnetic coils 16 are oriented and separated to form a Helmholtz pair aligned along axis 14 for establishing an axial Bo field therebetween. In one embodiment, the electromagnetic coils 16 may be pancake coils providing spirals about axis 14 powered by an external, controllable DC power supply 18 of the type understood in the art. Positioned between the electromagnetic coils 16 but proximate to one electromagnetic coil 16b is a radiofrequency antenna 19 (shown in simplified form), for example, providing a circularly polarized radio field extending along axis 14 when driven by a radiofrequency generator 20. As is understood in the art, the polarized radio field provides an electrical vector 21 perpendicular to axis 14 rotating thereabout. Further discussion of loop antennas suitable for this purpose are found in T. H. Stix, “Fast Wave Heating of a Two-Component Plasma,” Nuclear Fusion 15, 737 (1975) and R. W. Harvey, M. G. McCoy, G. D. Kerbel, and S. C. Chiu, “ICRF Fusion Reactivity Enhancements in Tokamaks,” Nuclear Fusion 26, 43 (1986) hereby incorporated by reference. A treatment volume 22 may be located radially outside the pressure vessel 12, for example, in the form of a concentric outer cylindrical tank which may be filled with, for example, an aqueous material for transmutation by high-energy neutrons such as precursors to medical isotopes 99Mo (molybdenum 99), 131I (iodine 131), 133Xe (xenon 133), and 177Lu (lutetium 177) or which may support racks holding spent nuclear fuel rods being rejuvenated through transmutation by high-energy neutrons. A neutral beam generator 26 is positioned to inject a beam 28 of neutral particles 29 (that is non-ionized particles having zero net charge) at a pitch angle θ into the containment volume 17. The pitch angle θ is defined as an acute angle between an angle of the beam 28 and the axis 14. The neutral particles 29, for example, are atoms of deuterium or tritium introduced through a gas line 24 and ionized by a local plasma (not shown). These ions are accelerated in an accelerator chamber 27 having a successive set of electrically charged plates as is generally understood in the art. The ions then pass through a neutralizing gas cell 31 to produce neutral particles 29 by a charge exchange process to produce the neutral particles 29 of the beam 28. Referring now also to FIG. 2, the magnetic flux lines 30 generated by the coils 16 will produce a “bottle” shape expanding radially from the axis 14 at a midpoint between the coils 16 and contracting radially at the location of the coils 16. As is generally understood in the art, this configuration produces a mirror containment volume where randomly distributed “thermal” plasma ions of sufficient pitch angle 32 spiral around flux lines 30 between regions defined by turning points 34. These thermal plasma ions can be established in a variety of ways for example by using the radiofrequency antenna 19 (albeit at a low efficiency) or a separate heating system using high-frequency microwaves producing electron cyclotron resonance heating, as is understood in the art At the regions of the turning points 34, the thermal plasma ions 32 reverse direction caused by increasing axial components of the magnetic Lorentz force produced by the convergence of the flux lines 30. The frequency 35 of the spiraling about the flux lines 30 is termed the “cyclotron frequency” and is a function of the strength of the magnetic field 37 along axis 14, and for this reason the cyclotron frequency 35 generally increases toward the electromagnetic coils 16. For ions of equal mass and charge, the cyclotron frequencies will be nominally identical at a given location along the axis 14, independent of the velocities or energies of the ions; however, ions 32 of equal mass having different pitch angles will normally have different turning points 34. The velocity and hence the energy of the neutral particles 29 of the neutral beam 28 and the pitch angle θ of the neutral beam 28 are set so the majority, for example, greater than 50 percent, of the particles of the neutral beam 28 will be ionized into plasma ions 36 within the containment volume 17 before exiting the containment field. These plasma ions 36 at the same pitch angle, now having electrical charge, are captured by the magnetic flux lines 30 to increase the plasma density. In order to promote this entrapment of the majority of the neutral particles 29 of the neutral beam 28, the energy of the neutral beam 28 is limited to provide sufficient time-of-flight for the neutral particles 29 to be ionized. Generally, the desirable energy of the neutral beam 28 for ionization will be well below the kinetic energy required for substantial fusion, and typically less than 100 thousand electron volts or preferably less than 50,000 electron volts and more typically on the order of 15-25 keV. This is in contrast to prior art approaches which require neutral particles 29 with energies exceeding the energy necessary to promote fusion between the plasma ions 36 and typically having energies more than than one million electron volts for D-D fusion. By limiting the energy of the neutral beam 28, a trade-off may be affected in common neutron beam generators 26 to produce a higher flux density of neutral particles 29, also increasing the plasma density. Referring still to FIGS. 1 and 2, the pitch angle θ of the neutral beam 28 is selected to provide predetermined turning points 34′ along axis 14 for the resulting plasma ions 36 and thus to provide a corresponding predetermined cyclotron frequency 35 of the plasma ions 36 at the turning points 34′. This cyclotron frequency is used to set the frequency of the radiofrequency generator 20 as will be discussed below. In addition, the antenna 19 is placed proximate to one of the turnaround points 34′ to provide a maximum field strength in that region. Finally, within the energy levels for the neutral beam 28 that provide the desired capture of the neutral particles 29 within the containment volume 17, the energy of the neutral beam 28 is set to be as high as possible so that the radius of orbit of the of the plasma ions 36 produced by the neutral beam 28 (gyro-orbit 52) is higher than the average distribution gyro-orbit 52 of “thermal ions” 32, being ions not immediately derived from the neutral beam 28. While the inventors do not wish to be bound by a particular theory, the above-described: (a) setting of the cyclotron frequency of the radiofrequency generator 20 to a harmonic of the cyclotron frequency of the plasma ions 36 at the turning point 34′, (b) boosting of the energy of the plasma ions 36 above the average distribution of the thermal plasma ions 32, and (c) maximizing the electrical field strength at the turning point 34′, all work together to allow the radiofrequency generator 20 to preferentially boost the energy of the plasma ions 36 from the neutral beam 28 free from the damping effect of thermal plasma ions 32. In this regard, the setting of the radiofrequency generator 20 (per (a)) provides preferential coupling to the plasma ions 36 having a matching (e.g., a harmonically related) cyclotron frequency 35, in contrast to thermal plasma ions 32 having a range of different Doppler-shifted cyclotron frequencies and less effective coupling. The coupling may be proportional to the square of the Bessel function Bn-1(k⊥*v⊥/ωci) where: n is the resonant cyclotron harmonic number of the injected wave, k⊥ the perpendicular wave number, and ωci is the cyclotron frequency of the resonance ions. The quantity k⊥/ωci may may be ˜vA, the Alfven velocity of the ions (cf. T. H. Stix, “Fast Wave Heating of a Two-Component Plasma,” Nuclear Fusion 15, 737 (1975)). Given the dependence of the Bessel function on v⊥, the coupling is proportional to powers of the perpendicular velocity of the ions, and can be adjusted to preferentially damp on hot tail ions from the neutral beam and and on those diffused to higher energy by the radiofrequency waves. Further, by setting the frequency of the radiofrequency generator 20 according to the cyclotron frequency 35 at the turning point 34′, the influence of the electrical field from the radiofrequency generator 20 on the plasma ions 36 is increased because of the prolonged dwell time 50 of the plasma ions 36 at the turning point 34′ during their lowest axial velocity as they turn around. This is in contrast, for example, to thermal plasma ions 32 which move quickly through this zone to further turning points 34 or which do not reach as far as the turning point 34′. As noted above, by boosting the energy of the plasma ions 36 above the distribution of thermal plasma ions 32 (per (b)) and by setting the RF generator 20 to an RF frequency which is a high harmonic of the cyclotron frequency 35 of the plasma ions 36, higher energy plasma ions 36 having a higher radius of gyro-orbit 52 preferentially absorb power over the thermal plasma ions 32 having a lower gyro-orbit 52. In some embodiments, the RF frequency may be set to a range from 20 to 100 megahertz and/or to a harmonic n greater than n=2 and preferably n=4. Generally, the higher harmonics boost the relationship between energy absorption and gyro-orbit 52 according to increasing Bessel function numbers associated with those harmonics. Specifically, energy absorption will be proportional to Jn-1(k⊥ρ) where: Jn-1 is the Bessel coefficient for a given harmonic n, ρ is the radius of the particle's gyro-orbit 52 about the magnetic flux lines 30 which increases with energy by ρ = √ 2 ⁢ mE eB and k⊥ is a wave number of the plasma ions 36 being a property of the wave within the plasma and the polarization of the antenna 19 launching the wave. It will be appreciated that this effective preferential absorption of energy by the plasma ions 36 will be self-reinforcing as energy is absorbed and the gyro-orbit of the plasma ions 36 is increased. Finally, by placing a highest field strength of the antenna 19 near the turning point 34′, the plasma ions 36 are preferentially influenced. Generally, the magnetic containment field 15 will tend to lose some plasma ions 32 having low pitch angles through its ends. These particles are said to be in the “loss cone.” By boosting the population of the plasma ions 36 having a known pitch angle θ outside of the loss cone, increased plasma densities can be obtained. While the cyclotron frequency of the plasma ions 36 near the turning point 34′, and hence the desired setting of the frequency of the radiofrequency generator 20, is primarily a function of the vacuum magnetic field strength 37, it will shift slightly as a function of increasing plasma density/pressure. Accordingly, the invention contemplates that either or both of the DC power supply 18 or the RF frequency generator 20 may be adjusted during operation to maintain the above relationships which boost energy transfer to the plasma ions 36. In particular, this adjustment may be made via a closed-loop feedback control using a sensor 56 detecting plasma pressure, for example, using a diamagnetic loop, which will measure the decrease in magnetic field due to increased plasma pressure to ensure a matching of the excitation frequency of the RF generator 20 with the actual and dynamic cyclotron frequency 35 at the turnaround point 34′. To the extent that the cyclotron frequency is dictated by the total field (vacuum field from coil plus plasma diamagnetism); the invention also contemplates that no frequency change may be required but the location of the turning point will move closer to the electromagnetic mirror coil. Referring now to FIG. 3, this benefit of the present invention in providing high plasma densities makes it useful as part of a system where two high-energy plasma systems 10 may act as “plugs” to trap high-energy plasma ions in a larger scale neutron generator 60 for the purpose of transmutation (as discussed above) or fusion power generation. Such a design, for example, may make use of a tandem mirror scheme, for example, described at G. Dimov, V. Zakaidakov, and M. Kishinevski, Fiz. Plazmy 2 597 (1976), [Sov. J. Plasma], Phys 2, 326 (1976)] and T. K. Fowler and B. G. Logan, Comments on Plasma Physics and Controlled Fusion 2, 167 (1977) and hereby incorporated by reference. More specifically, in such a tandem mirror neutron generator 60, first and second high-energy plasma systems 10a and 10b are placed in opposition along axis 14 flanking a generator volume 62. Generally, the high-energy plasma systems 10 will have an axial length on the order of 2 meter whereas the generating volume 62 will be much larger, for example, on the order of 50 meters or more. The electromagnetic coils 16 of both of the high-energy plasma systems 10a and 10b are axially aligned to provide a same direction of polarization of the magnetic field along the common axis 14. As such, the flux lines 30 of the first high-energy plasma system 10a may continue through the volume 62 to the second high-energy plasma system 10b. Within the volume 62, the flux lines 30 are focused by an axially-extending solenoid coil 66 circling the axis 14 around the volume 62. For this purpose, the electromagnetic coils 16 may be superconducting magnets for example per D. Whyte, J. Minervini, B. LaBombard, E. Marmar, L. Bromberg, and M. Greenwald, “Smaller and sooner Exploiting high magnetic fields from new superconductors for a more attractive fusion energy development path,” Journal of Fusion Energy, 35, 41 (2016) also hereby incorporated by reference. A subset of thermal plasma ions 32, having a uniform distribution of pitch angles and having been boosted to higher energies by kinetic transfer from the plasma ions 36, may escape from the high-energy plasma systems 10 into the volume 62 containing a reactant gas, for example, deuterium or tritium, to promote fusion and the emission of neutrons 64 from the volume 62. The high pressure of the high-energy plasma systems 10 blocks the escape of high-energy plasma ions from the volume 62 to maintain the high densities for significant fusion. The volume 62 may be surrounded by a contained volume 22 which may include a heat exchanger liquid 68, for example, for receiving, through one or more heat exchangers, a working fluid 70 of a thermodynamic engine such as a turbine or the like, for example, for the generation of electrical power. Alternatively, the contained volume 22 may be used for the transmutation of materials to generate medical isotopes or to rejuvenate spent nuclear fuel as discussed above. The present application incorporates disclosure of US patent application 2019/0326029 entitled: Apparatus and Method for Generating Medical Isotopes, and US application 2013/0142296 entitled: Apparatus and method for generating medical isotopes which describe additional techniques for managing isotope transmutation including the use of neutron multiplier generators and other construction details and mechanisms for producing a neutral beam discussed above. Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.
050193210	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is in the field of fusion power generators, particularly those utilizing fusion reactors of the magnetic confinement type. 2. Description of the Prior Art Prior art concepts with regard to utilization of fusion energy for the economic production of power have been premised upon an ultimate design of a large scale reactor able to produce the desired power and lasting a sufficiently long time to justify the large capital investment required to build the reactor. The economics of a large capital investment with a long reactor lifetime have been carried over from the fission reactor field as an inherent basis in the design of economic fusion power plants. Consequently, plasma temperatures and densities have been parameterized to yield a maximum wall loading of the first wall (vacuum wall surrounding the plasma) consistent with durability of wall materials and a long replacement time which is economically acceptable. Typically, a maximum wall loading of 1-3 MW/m.sup.2 has been thought reasonable with a minimum replacement time of approximately five years. Consistent with the projected long life of the fusion reactor, the plasma core has traditionally been made large so as to allow large power output with low energy loadings on the first wall as well as for reasons of plasma confinement in the regimes of traditional interest. Furthermore, the plasma core has traditionally been surrounded directly with a thick material blanket region to absorb the plasma-generated neutron energy as well as to protect the large and expensive magnetic field windings surrounding the blanket. These large field windings, required to confine plasma in the plasma core, must be large enough to surround the plasma core. Traditionally, superconducting magnets have been utilized in order to reduce the power required to drive the magnetic coils, and the blanket thus served to remove the coils from the regime of high neutron fluxes and associated radiation damage to which the superconductors are susceptible. Such superconducting magnets have a limited magnetic field capability of between approximately 80 and 150 kilogauss. The maximum permissible density and temperature of the plasma is in turn dictated by the strength of the magnetic field possible which, because of the foregoing considerations has been limited to the maximum strength available from the superconducting magnets. Thus, traditional fusion device concepts have involved large plasma volumes, thick blankets of large volume, low first wall loadings, and the use of large, expensive superconducting magnets placed outside the regions of the blanket, plasma core, and any added auxiliary shielding. In utilizing large volume experimental reactors of the tokamak-type, and in the conceptual design of practical large volume toroidal reactors, ohmic heating inherently plays a negligible role in the process of raising the plasma temperatures to values of thermonuclear interests. This is true because the current density which can be induced in any toroidal plasma configuration is proportional to the magnetic field divided by the major radius of the torus. For the fields attainable by superconducting magnets and the dimensions of traditionally envisioned toroidal devices, the current density is insufficient to yield significant ohmic heating of the plasma. Thus, in both the experimental and conceptual designs large sources of energetic beams of neutral particles have been utilized to provide power to the plasma on the order of tens to hundreds of megawatts. Neutral beam injection techniques require the utilization of large access ports to the plasma through the surrounding magnetic structure thus adding to the cost and complexity of any practical fusion power plant. Additionally, in order to ensure proper beam penetration to the center of the plasma column, operation of neutral beam injection devices has been limited to plasma densities the order of 10.sup.14 /cm.sup.3. As experimental fusion devices, blankets have typically not been employed inasmuch as they are unnecessary to study many of the basic physical processes involved in the plasma such as plasma fusion ignition, confinement, plasma heating and fusion reaction studies. The tokamak has provided an experimental tool for testing the feasibility of plasma confinement and has been the subject of extensive experimentation, e.g., see "The Tokamak Approach in Fusion Research" by Bruno Coppi et al, Scientific American, July 1972, U.S. Pat. Nos. 3,778,343 and "Tokamak Experimental Power Reactor Conceptual Design", Vols. 1 and 2, ANL/CTR-76-3 (August 1976), all of which documents are incorporated herein by reference. One particular tokamak device, the Alcator, has been designed to achieve large plasma currents with high toroidal magnetic field strengths. Typically, plasma currents on the order of 100 kiloamps with field strengths up to 82 kilogauss have been obtained. In such experimental devices, plasmas with densities up to 9.times.10.sup.14 particles per cubic centimeter with temperatures up to 1 keV have been contained. However, the Alcator approach is not typical of the majority of prior art devices which have focused on toroidal devices of much lesser density, larger dimension, smaller magnetic fields and which require extensive auxiliary heating (generally by neutral beam injection) to strive for plasma ignition temperatures. The approach of a very high yield, high density and a small compact device such as the Alcator has been considered in the prior art as limited to merely academic interest for purposes of physics studies of plasma behavior but has not been considered of interest for future applications to practical fusion power production. Another experimental area that has been developed for the magnetic confinement of thermonuclear plasma is embodied in the stellarator concept. While in the tokamak, the confining magnetic field is partially produced by external coils and partially by the current induced in the plasma, in a stellarator, the confining field is produced only by external coils. Both the tokamak and the stellarator, however, may be considered forms of a toroidal plasma confinement device. SUMMARY OF THE INVENTION It is an object of the invention to overcome the disadvantages of the prior art by providing a controlled nuclear fusion device for power generation. Another object of the invention is to provide a modular fusion reactor system wherein a plurality of fusion power cores, each of relatively small size and low cost, are energized to provide a power system. Energy from the fusion power cores is absorbed in the core structure and within a surrounding blanket, and the cores themselves may be individually removed from the blanket and replaced by new cores as the cores deteriorate from high radiation flux damage. It is another object of this invention to provide a power generating system utilizing a plurality of fusion power cores, each of the toroidal-type and driven to ignition by ohmic heating techniques. In accordance with the principles of the invention, a fusion power device is provided and comprises a plasma containment means for containing a fusible plasma within a region and a blanket means which surrounds a substantial portion of the containment means. The plasma containment means is separable from the blanket means and may be replaced upon excessive radiation damage by a new or refabricated containment means. Means are also provided for feeding the fusible fuel into the containment means for forming the plasma. A power producing regime of temperature and density may be achieved using ohmic heating as effected, for example, by e-beam bombardment. Thermal energy extraction means are provided for extracting energy from the plasma containment means and/or the blanket means, and means are provided for converting the extracted thermal energy into mechanical and/or electrical energy. The disposable and/or recyclable characteristic of the considered fusion power core makes the remote handling and maintenance system for it considerably simpler and less expensive than those envisioned for a conventional large tokamak reactor where the removal and replacement of heavy and interconnected components is involved. The ability to place an easily accessible blanket at the outside of the fusion power core without the encumberance of a surrounding magnetic coil system makes it possible to adopt the simplest and least expensive system to breed Tritium. The absence of a need for easy access to the inside components of the fusion power core makes it possible to adopt a tight aspect ratio toroidal configuration. This feature which can also be coupled with the effects of adopted auxiliary heating systems that tend to produce well distributed plasma current densities, by enhancing the temperature at the outer edge of the plasma column, makes it possible to operate the plasma device with a relatively low safety margin against macroscopic instabilities. This is equivalent to a high degree of utilization of confining magnetic field. The small size and relatively low weight of the fusion core make it suitable to develop it, unlike the envisioned large size tokamaks, into one of the elements of a power plant to power or propel a ship, a space craft, or any other suitable type of vehicle. A choice of the appropriate structural materials of the fusion power core can be made with the objective to decrease their radio-activation to a minimum. For example, aluminum based metals can be considered for this purpose.
	claims	1. An X-ray diffractometer for obtaining X-ray diffraction angles of diffracted X-rays, comprising:an x-ray source configured to emit x-rays at a sample;an X-ray detector configured to detect diffracted X-rays diffracted at the sample angles about a center point of goniometer circles when x-rays are emitted at the sample; andan X-ray shield member provided with an X-ray passage port that is maintained on a center point of said goniometer circles,whereinthe X-rays diffracted at the sample so as to pass through the center point of the goniometer circles pass through the X-ray passage port, andthe X-rays diffracted at the sample so as to pass through areas other than the center point of the goniometer circles are shielded by the X-ray shield member. 2. The X-ray diffractometer according to claim 1, wherein the X-ray shield member is disposed in contact with the surface of the sample or near the surface of the sample. 3. The X-ray diffractometer according to claim 1, wherein the X-ray shield member is disposed in contact with the end face of the sample on the X-ray detector side, or near the end face of the sample on the X-ray detector side. 4. The X-ray diffractometer according to claim 1, wherein the X-ray passage port is a pinhole extending in the direction intersecting the sample, or a slit extending in the direction intersecting the sample. 5. The X-ray diffractometer according to claim 1, wherein the X-rays incident on the sample are line-focus X-rays, and the lengthwise direction of the line focus is the direction parallel to the surface of the sample. 6. The X-ray diffractometer according to claim 1, wherein X-rays are caused to be incident at a low angle with respect to the sample so that diffraction occurs on a lattice plane perpendicular to the surface of the sample. 7. The X-ray diffractometer according to claim 6, further comprising:an ω-rotation system for adjusting the incidence angle of X-rays on the sample;a φ-rotation system for rotating the sample in-plane;a 2θ-rotation system for moving the X-ray detector in the out-of-plane direction; anda 2θχ-rotation system for moving the X-ray detector in the in-plane direction;wherein the ω-rotation system, the φ-rotation system, the 2θ-rotation system, and the 2θχ-rotation system operate about the center point, as an origin, of the goniometer circles, which is a shared center point.
	claims	1. A method of determining a depth of penetration of an electron beam into a target material, the method comprising:providing an electron beam source;providing a layer of a detection material exhibiting a first sensitivity of a physical property in response to electron beam radiation;providing a layer of the target material of a first thickness in contact with the detection material and positioned proximate to the electron beam source, the target material exhibiting a second, reduced sensitivity of the physical property in response to electron beam radiation;directing electron beam radiation at a first energy into the target material; anddetecting a change in the physical property of the detection material to mark an observed electron beam penetration depth of the first thickness. 2. The method of claim 1 further comprising calculating a numerical power (n) of the Grunn Equation: Depth = 0.046 ⁢ ⁢ ( V acc ) n . ρ resulting based upon a density (ρ) of the target material, the first energy (Vacc), and the observed electron beam penetration depth (Depth). 3. The method of claim 2 further comprising:providing a second layer of the target material of a second thickness in contact with a second layer of the detection material and positioned proximate to the electron beam source;directing electron beam radiation of a second energy into the second target material layer;sensing a change in the physical property of the second detection material layer to reveal a second observed electron beam penetration depth of the second thickness; andconfirming the calculated numerical power (n) of the Grunn equation by fitting the target material density (ρ), the second energy (Vacc), and the second thickness (Depth). 4. The method of claim 1 wherein a changed thickness of the detection layer is sensed. 5. The method of claim 4 wherein the changed detection layer thickness is sensed utilizing spectroscopic ellipsometry. 6. The method of claim 1 wherein a changed composition of the detection layer is sensed. 7. The method of claim 1 wherein a change in one of a density, a mechanical property, a refractive index, and a dielectric constant of the detection layer is sensed. 8. The method of claim 1 wherein providing the target material comprises chemical vapor depositing a carbon-doped silicon oxide film. 9. The method of claim 8 wherein exposure of the target material to the electron beam liberates a porogen. 10. The method of claim 1 wherein providing the detection material comprises providing a carbon-doped silicon oxide film. 11. The method of claim 10 wherein exposure of the detection material to the electron beam reduces a carbon concentration in the detection material. 12. A method of predicting depth of penetration of an electron beam into a target material, the method comprising:providing a thickness of a target material layer in contact with a detection material layer and positioned proximate to the electron beam source, the target material exhibiting a second, reduced sensitivity of a physical property in response to electron beam radiation;successively irradiating the target material with electron beam radiation of increasing energies;identifying a threshold energy of the applied electron beam radiation resulting in a change of the physical property of the detection layer below a predetermined value;calculating a numerical power (n) of the Grunn Equation: Depth = 0.046 ⁢ ⁢ ( V acc ) n ρ based upon the density (ρ), the threshold energy (Vacc), and the thickness (Depth); andutilizing the Grunn Equation with the calculated numerical power (n) to predict a second depth of penetration into the target material of an electron beam of a second energy. 13. The method of claim 12 wherein at least one of a thickness, composition, density, mechanical property, refractive index, and dielectric constant of the detection layer is changed in the detection layer by the electron beam radiation. 14. The method of claim 12 wherein providing the target material comprises providing a carbon-doped silicon oxide film. 15. The method of claim 14 wherein providing the detection material comprises providing a different carbon doped silicon oxide film, and the predetermined value comprises a shrinkage of 2% or less of the different carbon doped silicon oxide film. 16. A composition for indicating depth of penetration of an electron beam, the composition comprising:a detection material exhibiting a first sensitivity of a physical property in response to an electron beam radiation exposure dosage; anda target material in contact with the detection material and positioned proximate to a source of electron beam radiation, the target material exhibiting a second, reduced sensitivity of the physical property in response to the electron beam radiation exposure dosage. 17. The composition of claim 16 wherein the detection material exhibits greater shrinkage than the target material in response to the exposure dosage. 18. The composition of claim 16 wherein the detection material comprises carbon doped silicon oxide. 19. The composition of claim 18 wherein the detection material exhibits a greater reduction in carbon content than the target material in response to the exposure dosage. 20. The composition of claim 18 wherein the detection material exhibits a greater reduction in dielectric constant than the target material in response to the exposure dosage. 21. A computer-readable storage medium having a computer-readable program embodied therein for directing operation of a host computer including a communications system, a processor, and a storage device, wherein the computer-readable program includes instructions for operating the host computer to calculate a numerical power n of a Grunn Equation in accordance with the following:receiving a thickness (Depth) of a target material in contact with a detection material and positioned proximate to the electron beam source, the target material exhibiting a reduced sensitivity of a physical property in response to electron beam radiation,receiving a density (ρ) of the target material,receiving a threshold energy of applied electron beam radiation (Vacc) resulting in a change of a physical property of a detection layer below a predetermined value; andcalculating a numerical power (n) of the Grunn Equation: Depth = 0.046 ⁢ ⁢ ( V acc ) n ρ based upon the density, the threshold energy, and the thickness. 22. The computer-readable storage medium of claim 21 further including instructions to utilize the calculated numerical power (n) to predict a second depth of penetration into the target material of an electron beam having a second energy.
	claims	1. An applicator means for x-ray radiation therapy for the irradiation of surfaces, having an applicator element for taking up a probe tip or a radiation source element of a radiation source means, is hereby characterized in that the applicator element for adjusting different beam characteristics has at least one element for influencing the beam, which is disposed in an exchangeable manner at/in the applicator element, that the element for influencing the beam is designed as a lens element or as a combination of lens elements, and that the lens element or the combination of lens elements is designed as an element or a combination of elements with a different mass distribution in one plane crosswise to the direction of expansion of the x-ray radiation. 2. The applicator means according to claim 1, further characterized in that the mass distribution of the lens element or of the combination of lens elements is adapted or is adaptable to the radiation characteristic of a radiation source means. 3. The applicator means according to claim 1, further characterized in that the lens element or the combination of lens elements and/or the applicator element has a round, or quadrangular, or octagonal shape, or has a shape adapted to a tumor. 4. The applicator means according to claim 1, further characterized in that the lens element or the combination of lens elements comprises one material or at least two different materials. 5. The applicator means according to claim 1, further characterized in that the lens element or the combination of lens elements has at least one positively curved surface and/or at least one neutral surface and/or at least one negatively curved surface. 6. The applicator means according to claim 1, further characterized in that the applicator element has a first end for positioning on the surface to be irradiated, and that element for influencing the beam is provided in the region of the first end of applicator element. 7. The applicator means according to claim 1, further characterized in that applicator element is designed as a cylinder, at least in regions. 8. A fastening means for fastening an applicator means for x-ray radiation therapy for the irradiation of surfaces, in particular, an applicator means according to claim 1, onto a surface to be treated, is characterized in that the fastening means has an uptake opening for taking up at least one region of applicator means, and that fastening means is designed as a fastening ring. 9. The fastening means according to claim 8, further characterized in that uptake opening has an inner contour, which corresponds to the outer contour of the region of applicator means that is to be taken up. 10. The fastening means according to claim 8, further characterized in that fastening means has at least one outwardly projecting fastening tab on at least one outer side. 11. The fastening means according to claim 10, further characterized in that at least one fastening tab has at least one fastening opening. 12. A radiation therapy device for the x-ray irradiation of surfaces, having a radiation source means and having an applicator means for taking up a probe tip or a radiation source element of the radiation source means, wherein the applicator element for adjusting different beam characteristics has at least one element for influencing the beam, which is disposed in an exchangeable manner at/in the applicator element, that the element for influencing the beam is designed as a lens element or as a combination of lens elements, and that the lens element or the combination of lens elements is designed as an element or a combination of elements with a different mass distribution in one plane crosswise to the direction of expansion of the x-ray radiation and/or having a fastening means according to claim 8 for attaching an applicator means for x-ray radiation therapy onto a surface to be treated. 13. The applicator means according to claim 1, further characterized in that the lens element or the combination of lens elements has a plane surface at its outer face.
	claims	1. System for producing electromagnetic radiation with enhancement from a drift tube containing a cylindrical Smith-Purcell structure, comprising:a) a magnetically insulated linear oscillator having a cylindrical resonant cavity containing a traveling wave electron gun and cooperating anode, and further containing a drift tube positioned between the traveling wave electron gun and the cooperating anode;b) the drift tube being formed of a hollow cylindrical conductive element that is positioned within said resonant cavity and that is electrically isolated from the traveling wave electron gun, wherein a cylindrical axis of the drift tube is coaxial with a main axis of the resonant cylindrical cavity in a region between said electron gun and said anode;c) the drift tube having an inner surface and a pair of ends; the hollow cylindrical conductive element being enhanced by containing a cylindrical Smith-Purcell grating surface formed on the inner surface of the drift tube; said grating surface comprising a reflection grating surface having a series of ridges spaced apart by respective grooves; said reflection grating surface extending for at least a majority of the length of the drift tube;d) the drift tube being adapted so that an electron beam, from the electron gun, passes through the inner space of the drift tube and interacts with the internal Smith-Purcell grating surface, so as to produce RF radiation by Smith-Purcell Effect; ande) the drift tube being further adapted so that spacing, face angle and shape of the Smith-Purcell grating surface, and an energy of the electron beam are determinants of the frequency of the RF radiation. 2. The system of claim 1, wherein the Smith-Purcell grating surface comprises an internal thread extending for at least a majority of length of the drift tube. 3. The system of claim 1, wherein each ridge of the reflection grating surface has a cross-section, taken along a plane passing through said cylindrical axis of the drift tube, comprising a triangle having one side parallel to said cylindrical axis.
052746860	summary	BACKGROUND OF THE INVENTION This invention relates generally to fuel rods and other components employed in nuclear reactors. More particularly, the present invention relates to fuel rod cladding tubes and other zirconium-alloy components. Fuel rods having outer cladding tubes are mounted in support grids of nuclear reactor fuel assemblies. Because of the harsh environment of the fuel assembly where the surrounding water temperature is typically 400.degree. C. and the water has a relatively high pressure, the cladding tube is susceptible to wear and corrosion. At the lower portions of the reactor assembly, the cladding tubes can also be exposed to debris fretting. In addition, severe wear forces can arise at the location of the grid support. Practitioners in this field are aware that a thin coating of zirconium nitride on a zirconium alloy tube, can dramatically improve wear and corrosion resistance. Such coatings can be applied by any one of a variety of techniques such as ion implantation or plasma spray as disclosed, for example, in U.S. Pat. No. 4,724,016 (Anthony) and U.S. Pat. No. 5,026,517 (Menken et al). More recent attempts include cathodic arc reactive deposition as disclosed in copending U.S. Ser. No. 514,870 (Bryan et al). These techniques, however, exhibit relative strengths and weaknesses, so that none has emerged as clearly superior. SUMMARY OF THE INVENTION An object of the present invention is to provide a new and improved wear and corrosion resistant coating for a cladding tube employed in a nuclear reactor. Another object of the invention is to provide a new and improved coating which may be applied to a zirconium-alloy nuclear cladding tube in an efficient and cost effective manner. A further objective of the invention is to provide a new and improved coating for a cladding tube which has enhanced resistance to debris fretting and corrosion and has an outer diameter which does not significantly increase the coolant flow resistance in the fuel assembly. It is a more specific object of the present invention to provide a cladding tube for a nuclear fuel assembly component, particularly a fuel rod, which has a thin film of zirconium nitride coating the outside surface. The zirconium nitride coating may be applied on a portion of the tube which will be located below or in the vicinity of a particular fuel assembly support grid, or on substantially the entire outside surface of the tube. A film having a thickness of approximately 5 microns is effective in resisting corrosion and wear of the cladding tube, which usually has a zirconium-alloy composition. The thin film of zirconium nitride is applied to the cladding tube by reactively depositing zirconium nitride on the surface of the cladding tube by an anodic arc plasma deposition process. The cladding tube is heated to a temperature in a range of approximately 300.degree. to 400.degree. C. in the presence of nitrogen. The anodic vacuum arc differs from the cathodic vacuum arc in that the arc is sustained by material evaporated from the anode, as opposed to the cathode. In the anodic vacuum arc, the cathode is either totally inactive without eroding cathode spots or has many rapidly moving spots on the cathode surface. All of the material that sustains the arc is emitted by the anode. Until recently, steady state arcs sustained by anodic material were only known for currents exceeding 400 A. In these high current arcs, anodic evaporation occurs in large luminous spots at the surface of the anode. High current anodic arcs were known predominantly in vacuum breakers where the aim of investigations was to minimize the erosion of the anode through elimination of the anodic arc. Several investigators have reported on the characteristics of low current microsecond-duration anode spots. In these experiments the arc was pulsed for approximately 10 .mu.sec at currents as low at 20A. Due to the short pulse length, very little material evaporation from the anode occurred and the usefulness of anodic evaporation for the deposition of coatings was not investigated. Recently, however, several investigators have found a new steady state mode of operation of the anodic vacuum arc at much lower currents, typically less than 100 A. In these low current anodic arcs the anode is tailored in order to enhance evaporation. The cathode is designed either for minimal erosion, by using a refractory material such as carbon or tungsten, or is manufactured of the same material as the anode. In either case the cathode is designed so as not to heat up appreciably. By tailoring the anode it has been possible to achieve rapid evaporation of the anode material without macroparticle inclusion that occurs in the cathodic arc. The anodic vacuum arc produces a metal vapor plasma that, unlike the fully ionized plasma of the cathodic arc, is only partially ionized (.about.20%). In the anodic arc, the ions are singly ionized and have a directed energy of approximately 5 eV while the electrons have a temperature of less than 1 eV. Near the anode, the density of the expanding plasma is approximately 1.times.10.sup.18 /cm.sup.3 while the neutral density is an order of magnitude higher. Coatings deposited with the low current anodic vacuum exhibit all of the desirable qualities of coatings deposited with plasma assisted deposition techniques, and cathodic arcs in specific, but do not suffer from many of the problems that these methods entail. In particular, the anodic arc rapidly produces coatings that are of a very high quality and do not suffer from macroparticle inclusion. Other advantages of the invention will become apparent from the drawings and the specification.
052020835	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The core 1 of a CANDU nuclear reactor has a number of fuel channels 2 extending through it with cooling water flowing from an inlet header 3 via pipe 12 through the channel 2 and via pipe 9 to outlet header 4. The normal flow of cooling water during operation of the reactor is from high temperature header 4 via pipe 10 through a steam generator 6 to main circulation pumps 5 which return the cooling water to low temperature header 3 and back to the reactor core. To prevent overheating of the reactor core when the steam generator cooling is lost due to an accident, a decay heat removal path is also connected between outlet header 4 and inlet header 3 to remove decay heat from the reactor core. Such decay heat removal paths are normally provided with a pump to circulate the coolant to a heat exchanger. However, pumps rely on electrical supplies. Instead the heat exchanger could be located, as in FIG. 1, at an elevation such that a natural convection flow will develop, precluding any reliance on electrical supplies. The decay heat cooling path consists of pipe 13 extending from high temperature header 4 to an inlet of a heat exchanger 8 in a large tank 7 of water which forms a heat sink. The outlet of heat exchanger 8 is connected to pipe 14 and through check valve 15 to low-temperature inlet header 3. The check valve 15 opposes the main pump head and prevents backflow through pipe 14, heat exchanger 8 and pipe 13 when the main pumps 5 are operating. The heat exchanger 8 is located at a higher level than the reactor headers 3 and 4 so that a natural convection flow can occur from header 4 to 3 when pump 5 is tripped. A further heat exchange coil 9 which is connected to service water by lines 16 and 17 can be provided on the other side of a partial divider 19 in tank 7 to remove heat from the water. However, the large tank 7 of water provides a heat sink for several days should service water, via pipes 16 and 17, be unavailable. In this type of system, when steam generator cooling is lost, the main pumps 5 would be tripped, and coolant from high temperature header 4 can start a natural convection circulation flow up pipe 13 down through heat exchanger 8 and via pipe 14 through check valve 15 to low temperature header 3. This natural circulation flow through the decay heat cooling path is of a sufficient size to remove decay heat from the shutdown reactor. However, in a CANDU reactor, the header to header pressure drop is close to zero and can even be in the wrong direction which creates problems in getting the natural circulation flow started in the decay heat cooling path. FIG. 2 shows an alternative system, according to the present invention, for inducing a natural circulation flow in the decay heat cooling path. The system contains the same elements as shown in FIG. 2 with the addition of a pump 20 in the coolant flow pipe 14 before the check valve 15. This pump 20 is normally running, along with main pumps 5, to provide a small flow through the decay heat cooling path. That small flow, from the high temperature header 4, is in the intended direction of the natural convection circulation flow and maintains a temperature difference within the decay heat removal path that provides a buoyancy force to immediately start a natural circulation flow in the decay heat cooling path if all the pumps 5 and 20 are shutdown. The inclusion of pump 20 in the circuit provides the additional advantage of a controllable flow in the shutdown cooling circuit when the steam generator is out of service for repairs. The decay heat cooling path pump 20 will need to have a head which matches that of the main pumps 5. The flow in the decay heat cooling path, during normal operation of the reactor, needs to be controlled so that it is as small as possible and at the same time maintains sufficient buoyancy force to start a natural circulation flow. This will avoid wasting thermal power from the reactor. As shown in FIG. 3 control valve 25 may be used to control the small flow in the decay heat cooling path but speed control of pump 20 is preferred since a flow control valve may stick. For greater reliability, it may be desirable as also shown in FIG. 3 to provide two decay heat cooling path pumps in parallel 20' and 20" each having its own check valve 15' and 15", respectively. If only a single pump 20 as in FIG. 2 were located in the decay heat cooling path and that pump stops, then the buoyancy force necessary to start a natural circulation flow would disappear as the hot leg of the decay heat cooling path cools down. The loss of a single decay heat cooling path pump may, as a result, necessitate tripping the reactor and main pumps before the hot leg cools down in order to ensure that a natural circulation flow is started in the decay heat cooling path. With two pumps 20' and 20" in parallel, the other pump can continue to maintain the low flow in the decay heat cooling path when one of them fails. A decay heat cooling path pump may be lost due to, for instance, shaft failure or a bearing seizure. Another reason for using two pumps in parallel is the resistance to a natural circulation flow that would be created by a seized pump if only one is used in the decay heat cooling path. An alternative means, to pump 20, of providing a small flow in the decay heat cooling path is to continuously bleed the flow from a location 21 through a valve 22 as shown in dotted lines in FIG. 2. Location 21 is positioned after the outlet from heat exchanger 8 and before check valve 15. This could then serve the dual purpose of supplying coolant for purification to purification unit 23 in which case the heat exchanger 8 would serve as a purification cooler. The flow could be returned to the heat transport system upstream of pump 5 to minimize the required pump head. Various modifications may be made to the preferred embodiments without departing from the spirit and scope of the invention as defined in the appended claims. For instance, although the preferred embodiments have been described with respect to a CANDU reactor, similar systems may be used in other types of nuclear reactors wherein a pump, or other means, would be operating during normal operation of the reactor to move a small flow from the primary cooling path through a decay heat cooling path and return that small flow to the primary cooling path, so as to permit a natural convection flow to be rapidly established, when required, in the decay heat cooling path.
	description	The disclosure herein relates to X-ray detectors, particularly relates to semiconductor X-ray detectors. X-ray detectors may be devices used to measure the flux, spatial distribution, spectrum or other properties of X-rays. X-ray detectors may be used for many applications. One important application is imaging. X-ray imaging is a radiography technique and can be used to reveal the internal structure of a non-uniformly composed and opaque object such as the human body. Early X-ray detectors for imaging include photographic plates and photographic films. A photographic plate may be a glass plate with a coating of light-sensitive emulsion. Although photographic plates were replaced by photographic films, they may still be used in special situations due to the superior quality they offer and their extreme stability. A photographic film may be a plastic film (e.g., a strip or sheet) with a coating of light-sensitive emulsion. In the 1980s, photostimulable phosphor plates (PSP plates) became available. A PSP plate may contain a phosphor material with color centers in its lattice. When the PSP plate is exposed to X-ray, electrons excited by X-ray are trapped in the color centers until they are stimulated by a laser beam scanning over the plate surface. As the plate is scanned by laser, trapped excited electrons give off light, which is collected by a photomultiplier tube. The collected light is converted into a digital image. In contrast to photographic plates and photographic films, PSP plates can be reused. Another kind of X-ray detectors are X-ray image intensifiers. Components of an X-ray image intensifier are usually sealed in a vacuum. In contrast to photographic plates, photographic films, and PSP plates, X-ray image intensifiers may produce real-time images, i.e., do not require post-exposure processing to produce images. X-ray first hits an input phosphor (e.g., cesium iodide) and is converted to visible light. The visible light then hits a photocathode (e.g., a thin metal layer containing cesium and antimony compounds) and causes emission of electrons. The number of emitted electrons is proportional to the intensity of the incident X-ray. The emitted electrons are projected, through electron optics, onto an output phosphor and cause the output phosphor to produce a visible-light image. Scintillators operate somewhat similarly to X-ray image intensifiers in that scintillators (e.g., sodium iodide) absorb X-ray and emit visible light, which can then be detected by a suitable image sensor for visible light. In scintillators, the visible light spreads and scatters in all directions and thus reduces spatial resolution. Reducing the scintillator thickness helps to improve the spatial resolution but also reduces absorption of X-ray. A scintillator thus has to strike a compromise between absorption efficiency and resolution. Semiconductor X-ray detectors largely overcome this problem by direct conversion of X-ray into electric signals. A semiconductor X-ray detector may include a semiconductor layer that absorbs X-ray in wavelengths of interest. When an X-ray photon is absorbed in the semiconductor layer, multiple charge carriers (e.g., electrons and holes) are generated and swept under an electric field towards electrical contacts on the semiconductor layer. Cumbersome heat management required in currently available semiconductor X-ray detectors (e.g., Medipix) can make a detector with a large area and a large number of pixels difficult or impossible to produce. Disclosed herein is an apparatus suitable for detecting x-ray, comprising: an X-ray absorption layer comprising an electrode; an electronics layer, the electronics layer comprising: a substrate having a first surface and a second surface, an electronics system in or on the substrate, an electric contact on the first surface, a via, and a redistribution layer (RDL) on the second surface; wherein the RDL comprises a transmission line; wherein the via extends from the first surface to the second surface; wherein the electrode is electrically connected to the electric contact; wherein the electronics system is electrically connected to the electric contact and the transmission line through the via. According to an embodiment, the substrate has a thickness of 200 μm or less. According to an embodiment, the electronics system comprises: a first voltage comparator configured to compare a voltage of the electrode to a first threshold; a second voltage comparator configured to compare the voltage to a second threshold; a counter configured to register a number of X-ray photons reaching the X-ray absorption layer; a controller; wherein the controller is configured to start a time delay from a time at which the first voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the first threshold; wherein the controller is configured to activate the second voltage comparator during the time delay; wherein the controller is configured to cause the number registered by the counter to increase by one, if the second voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the second threshold. According to an embodiment, the controller is configured to deactivate the first voltage comparator at a beginning of the time delay. According to an embodiment, the controller is configured to deactivate the second voltage comparator at expiration of the time delay or at a time when the second voltage comparator determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold, or a time in between. According to an embodiment, the apparatus further comprises a capacitor module electrically connected to the electrode, wherein the capacitor module is configured to collect charge carriers from the electrode. According to an embodiment, the controller is configured to activate the second voltage comparator at a beginning or expiration of the time delay. According to an embodiment, the apparatus further comprises a voltmeter, wherein the controller is configured to cause the voltmeter to measure the voltage upon expiration of the time delay. According to an embodiment, the controller is configured to determine an X-ray photon energy based on a value of the voltage measured upon expiration of the time delay. According to an embodiment, the controller is configured to connect the electrode to an electrical ground. According to an embodiment, a rate of change of the voltage is substantially zero at expiration of the time delay. According to an embodiment, a rate of change of the voltage is substantially non-zero at expiration of the time delay. According to an embodiment, the X-ray absorption layer comprises a diode. According to an embodiment, the X-ray absorption layer comprises silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. According to an embodiment, the apparatus does not comprise a scintillator. According to an embodiment, the apparatus comprises an array of pixels. Disclosed herein is a system comprising the apparatus disclosed herein and an X-ray source, wherein the system is configured to perform X-ray radiography on human chest or abdomen. Disclosed herein is a system comprising the apparatus disclosed herein and an X-ray source, wherein the system is configured to perform X-ray radiography on human mouth. Disclosed herein is a cargo scanning or non-intrusive inspection (NII) system, comprising the apparatus disclosed herein and an X-ray source, wherein the cargo scanning or non-intrusive inspection (NII) system is configured to form an image using backscattered X-ray. Disclosed herein is a cargo scanning or non-intrusive inspection (NII) system, comprising the apparatus disclosed herein and an X-ray source, wherein the cargo scanning or non-intrusive inspection (NII) system is configured to form an image using X-ray transmitted through an object inspected. Disclosed herein is a full-body scanner system comprising the apparatus disclosed herein and an X-ray source. Disclosed herein is an X-ray computed tomography (X-ray CT) system comprising the apparatus disclosed herein and an X-ray source. Disclosed herein is an electron microscope comprising the apparatus disclosed herein, an electron source and an electronic optical system. Disclosed herein is a system comprising the apparatus disclosed herein, wherein the system is an X-ray telescope, or an X-ray microscopy, or wherein the system is configured to perform mammography, industrial defect detection, microradiography, casting inspection, weld inspection, or digital subtraction angiography. Disclosed herein is a method comprising: obtaining an X-ray absorption layer comprising an electrode; obtaining an electronics layer, the electronics layer comprising: a substrate having a first surface and a second surface, an electronics system in or on the substrate, an electric contact on the first surface, a via, and a redistribution layer (RDL) on the second surface; bonding the X-ray absorption layer and the electronics layer such that the electrode is electrically connected to the electric contact; wherein the RDL comprises a transmission line; wherein the via extends from the first surface to the second surface; wherein the electronics system is electrically connected to the electric contact and the transmission line through the via. FIG. 1A schematically shows a semiconductor X-ray detector 100, according an embodiment. The semiconductor X-ray detector 100 may include an X-ray absorption layer 110 and an electronics layer 120 (e.g., an ASIC) for processing or analyzing electrical signals incident X-ray generates in the X-ray absorption layer 110. In an embodiment, the semiconductor X-ray detector 100 does not comprise a scintillator. The X-ray absorption layer 110 may include a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the X-ray energy of interest. The X-ray absorption layer 110 may include one or more diodes (e.g., p-i-n or p-n) formed by a first doped region 111, one or more discrete regions 114 of a second doped region 113. The second doped region 113 may be separated from the first doped region 111 by an optional the intrinsic region 112. The discrete portions 114 are separated from one another by the first doped region 111 or the intrinsic region 112. The first doped region 111 and the second doped region 113 have opposite types of doping (e.g., region 111 is p-type and region 113 is n-type, or region 111 is n-type and region 113 is p-type). In the example in FIG. 1A, each of the discrete regions 114 of the second doped region 113 forms a diode with the first doped region 111 and the optional intrinsic region 112. Namely, in the example in FIG. 1A, the X-ray absorption layer 110 has a plurality of diodes having the first doped region 111 as a shared electrode. The first doped region 111 may also have discrete portions. FIG. 1B shows a semiconductor X-ray detector 100, according an embodiment. The semiconductor X-ray detector 100 may include an X-ray absorption layer 110 and an electronics layer 120 (e.g., an ASIC) for processing or analyzing electrical signals incident X-ray generates in the X-ray absorption layer 110. In an embodiment, the semiconductor X-ray detector 100 does not comprise a scintillator. The X-ray absorption layer 110 may include a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the X-ray energy of interest. The X-ray absorption layer 110 may not include a diode but includes a resistor. When an X-ray photon hits the X-ray absorption layer 110 including diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. An X-ray photon may generate 10 to 100000 charge carriers. The charge carriers may drift to the electrodes of one of the diodes under an electric field. The field may be an external electric field. The electrical contact 119B may include discrete portions each of which is in electrical contact with the discrete regions 114. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single X-ray photon are not substantially shared by two different discrete regions 114 (“not substantially shared” here means less than 5%, less than 2% or less than 1% of these charge carriers flow to a different one of the discrete regions 114 than the rest of the charge carriers). In an embodiment, the charge carriers generated by a single X-ray photon can be shared by two different discrete regions 114. FIG. 2 shows an exemplary top view of a portion of the device 100 with a 4-by-4 array of discrete regions 114. Charge carriers generated by an X-ray photon incident around the footprint of one of these discrete regions 114 are not substantially shared with another of these discrete regions 114. The area around a discrete region 114 in which substantially all (more than 95%, more than 98% or more than 99% of) charge carriers generated by an X-ray photon incident therein flow to the discrete region 114 is called a pixel associated with the discrete region 114. Namely, less than 5%, less than 2% or less than 1% of these charge carriers flow beyond the pixel. By measuring the drift current flowing into each of the discrete regions 114, or the rate of change of the voltage of each of the discrete regions 114, the number of X-ray photons absorbed (which relates to the incident X-ray intensity) and/or the energies thereof in the pixels associated with the discrete regions 114 may be determined. Thus, the spatial distribution (e.g., an image) of incident X-ray intensity may be determined by individually measuring the drift current into each one of an array of discrete regions 114 or measuring the rate of change of the voltage of each one of an array of discrete regions 114. The pixels may be organized in any suitable array, such as, a square array, a triangular array and a honeycomb array. The pixels may have any suitable shape, such as, circular, triangular, square, rectangular, and hexangular. The pixels may be individually addressable. When an X-ray photon hits the X-ray absorption layer 110 including a resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. An X-ray photon may generate 10 to 100000 charge carriers. The charge carriers may drift to the electrical contacts 119A and 119B under an electric field. The field may be an external electric field. The electrical contact 119B includes discrete portions. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single X-ray photon are not substantially shared by two different discrete portions of the electrical contact 119B (“not substantially shared” here means less than 5%, less than 2% or less than 1% of these charge carriers flow to a different one of the discrete portions than the rest of the charge carriers). In an embodiment, the charge carriers generated by a single X-ray photon can be shared by two different discrete portions of the electrical contact 119B. Charge carriers generated by an X-ray photon incident around the footprint of one of these discrete portions of the electrical contact 119B are not substantially shared with another of these discrete portions of the electrical contact 119B. The area around a discrete portion of the electrical contact 119B in which substantially all (more than 95%, more than 98% or more than 99% of) charge carriers generated by an X-ray photon incident therein flow to the discrete portion of the electrical contact 119B is called a pixel associated with the discrete portion of the electrical contact 119B. Namely, less than 5%, less than 2% or less than 1% of these charge carriers flow beyond the pixel associated with the one discrete portion of the electrical contact 119B. By measuring the drift current flowing into each of the discrete portion of the electrical contact 119B, or the rate of change of the voltage of each of the discrete portions of the electrical contact 119B, the number of X-ray photons absorbed (which relates to the incident X-ray intensity) and/or the energies thereof in the pixels associated with of the discrete portions of the electrical contact 119B may be determined. Thus, the spatial distribution (e.g., an image) of incident X-ray intensity may be determined by individually measuring the drift current into each one of an array of discrete portions of the electrical contact 119B or measuring the rate of change of the voltage of each one of an array of discrete portions of the electrical contact 119B. The pixels may be organized in any suitable array, such as, a square array, a triangular array and a honeycomb array. The pixels may have any suitable shape, such as, circular, triangular, square, rectangular, and hexangular. The pixels may be individually addressable. The electronics layer 120 may include an electronic system 121 suitable for processing or interpreting signals generated by X-ray photons incident on the X-ray absorption layer 110. The electronic system 121 may include an analog circuitry such as a filter network, amplifiers, integrators, and comparators, or a digital circuitry such as a microprocessors, and memory. The electronic system 121 may include components shared by the pixels or components dedicated to a single pixel. For example, the electronic system 121 may include an amplifier dedicated to each pixel and a microprocessor shared among all the pixels. The electronic system 121 may be electrically connected to the pixels by vias 131. Space among the vias may be filled with a filler material 130, which may increase the mechanical stability of the connection of the electronics layer 120 to the X-ray absorption layer 110. Other bonding techniques are possible to connect the electronic system 121 to the pixels without using vias. FIG. 3A schematically shows the electronics layer 120 according to an embodiment. The electronic layer 120 comprises a substrate 122 having a first surface 124 and a second surface 128. A “surface” as used herein is not necessarily exposed, but can be buried wholly or partially. The electronic layer 120 comprises one or more electric contacts 125 on the first surface 124. The one or more electric contacts 125 may be configured to be electrically connected to one or more electrodes of the X-ray absorption layer 110. The electronics system 121 may be in or on the substrate 122. The electronic layer 120 comprises one or more vias 126 extending from the first surface 124 to the second surface 128. The electronic layer 120 comprises a redistribution layer (RDL) 123 on the second surface 128. The RDL 123 may comprise one or more transmission lines 127. The electronics system 121 is electrically connected to the electric contacts 125 and the transmission lines 127 through the vias 126. The RDL 123 is particularly useful when multiple chips each with an electronic layer 120 are arranged in an array to form a detector with a larger size, or when the electronic layer 120 is bigger than an area that can be exposed simultaneously in a photolithography process. The substrate 122 may be a thinned substrate. For example, the substrate may have at thickness of 750 microns or less, 200 microns or less, 100 microns or less, 50 microns or less, 20 microns or less, or 5 microns or less. The substrate 122 may be a silicon substrate or a substrate or other suitable semiconductor or insulator. The substrate 122 may be produced by grinding a thicker substrate to a desired thickness. The one or more electric contacts 125 may be a layer of metal or doped semiconductor. For example, the electric contacts 125 may be gold, copper, platinum, palladium, doped silicon, etc. The vias 126 pass through the substrate 122 and electrically connect electrical components (e.g., the electrical contacts 125) on the first surface 124 to electrical components (e.g., the RDL) on the second surface 128. The vias 126 may be used to provide electrical power and transmit signals to and from the electrical components in the detector 100. The vias 126 are sometimes referred to as “through-silicon vias” although they may be fabricated in substrates of materials other than silicon. The RDL 123 may comprise one or more transmission lines 127. The transmission lines 127 electrically connect electrical components (e.g., the vias 126) in the substrate 122 to bonding pads at other locations on the substrate 122. The transmission lines 127 may be electrically isolated from the substrate 122 except at certain vias 126 and certain bonding pads. The transmission lines 127 may be a material with small attenuation of X-ray, such as Al. The RDL 123 may redistribute electrical connections to more convenient locations. FIG. 3B schematically shows the electronics layer 120 according to an embodiment similar to the embodiment shown in FIG. 3A. Each of the electrical contacts 125 may have its dedicated controller 310. FIG. 3C schematically shows a top view of the electronics layer 120 according to an embodiment where a group of electrical contacts 125 share a peripheral circuit 319. The peripheral circuit 319 may be arranged on the first surface 124 in areas not occupied by other components (e.g., the group of electrical contacts 125, and the electronic system 121. If the electronics layer 120 is fabricated using photolithography, all or some of the electrical contacts 125 within an area exposed simultaneously may share one peripheral circuit 319. The peripheral circuit 319 may be connected to more than one transmission line 127 by more than one vias 126. FIG. 3D schematically shows a top view of the electronics layer 120 according to an embodiment, with a different arrangement of the peripheral circuit 319. The arrangement of the peripheral circuit 319 is not limited to these examples. The peripheral circuit 319 may have redundancy. Redundancy allows the semiconductor X-ray detector 100 not to be disabled due to a partial failure of the peripheral circuit 319. If one part of the peripheral circuit 319 fails, another part may be activated. For example, if multiple pixels share the same peripheral circuit 319, total failure of the peripheral circuit 319 will disable all these pixels and likely render the entire detector 100 inoperable. Having redundancy reduces the chance of total failure. The peripheral circuit 319 may be configured to perform various functions, such as multiplexing, input/output, providing power, data caching, etc. The peripheral circuit 319 is not necessarily arranged on the first surface. FIG. 3E schematically shows a cross-sectional view of the electronics layer 120 according to an embodiment where the peripheral circuit 319 is arranged on a surface 128 of a substrate 123A sandwiched between the substrate 122 and the RDL 123. The peripheral circuit 319 may be electrically connected to the electrical contacts 125 by a first group of vias 126A extending in the substrate 122 and electrically connected to the transmission lines 127 by a second group of vias 126B extending in the substrate 123A. Each of the electrical contacts 125 may have a dedicated vias 126A for connection to the peripheral circuit 319. The peripheral circuit 319 may be arranged on multiple surfaces. FIG. 4A schematically shows direct bonding between the X-ray absorption layer 110 and the electronic layer 120 at discrete portion of the electrical contact 119B and the electrical contacts 125. Direct bonding is a wafer bonding process without any additional intermediate layers (e.g., solder bumps). The bonding process is based on chemical bonds between two surfaces. Direct bonding may be at elevated temperature but not necessarily so. FIG. 4B schematically shows flip chip bonding between the X-ray absorption layer 110 and the electronic layer 120 at discrete portion of the electrical contact 119B and the electrical contacts 125. Flip chip bonding uses solder bumps 199 deposited onto contact pads (e.g., the electrodes of the X-ray absorption layer 110 or the electrical contacts 125). Either the X-ray absorption layer 110 or the electronic layer 120 is flipped over and the electrodes of the X-ray absorption layer 110 are aligned to the electrical contacts 125. The solder bumps 199 may be melted to solder the electrodes and the electrical contacts 125 together. Any void space among the solder bumps 199 may be filled with an insulating material. Other materials such as thermal copper or gold pillar bump may be used to achieve similar function as solder bumps. FIG. 5 schematically shows a bottom view of the RDL 123, with other components obstructing the view omitted. The transmission lines 127 can be seen to electrically connect to vias 126 and redistribute vias 126 to other locations. FIG. 6A shows that the electronics layer 120 as shown in FIG. 3A, FIG. 3B, FIG. 3C, FIG. 3D, or FIG. 3E allows stacking multiple semiconductor X-ray detectors 100 because the RDL 123 and the vias 126 facilitate routing of signal paths through multiple layers and because the electronic system 121 as described below may have low enough power consumption to eliminate bulky cooling mechanisms. The multiple semiconductor X-ray detectors 100 in the stack do not have to be identical. For example, the multiple semiconductor X-ray detectors 100 may differ in thickness, structure, or material. FIG. 6B schematically shows a top view of multiple semiconductor X-ray detectors 100 stacked. Each layer may have multiple detectors 100 tiled to cover a larger area. The tiled detectors 100 in one layer can be staggered relative to the tiled detectors 100 in another layer, which may eliminate gaps in which incident X-ray photons cannot be detected. According to an embodiment, the semiconductor X-ray detector 100 may be fabricated using a method including: obtaining an X-ray absorption layer comprising an electrode; obtaining an electronics layer, the electronics layer comprising: a substrate having a first surface and a second surface, an electronics system in or on the substrate, an electric contact on the first surface, a via, and a redistribution layer (RDL) on the second surface; bonding the X-ray absorption layer and the electronics layer such that the electrode is electrically connected to the electric contact; wherein the RDL comprises a transmission line; wherein the via extends from the first surface to the second surface; wherein the electronics system is electrically connected to the electric contact and the transmission line through the via. FIG. 7A and FIG. 7B each show a component diagram of the electronic system 121, according to an embodiment. The electronic system 121 may include a first voltage comparator 301, a second voltage comparator 302, a counter 320, a switch 305, a voltmeter 306 and a controller 310. The first voltage comparator 301 is configured to compare the voltage of an electrode of a diode 300 to a first threshold. The diode may be a diode formed by the first doped region 111, one of the discrete regions 114 of the second doped region 113, and the optional intrinsic region 112. Alternatively, the first voltage comparator 301 is configured to compare the voltage of an electrical contact (e.g., a discrete portion of electrical contact 119B) to a first threshold. The first voltage comparator 301 may be configured to monitor the voltage directly, or calculate the voltage by integrating an electric current flowing through the diode or electrical contact over a period of time. The first voltage comparator 301 may be controllably activated or deactivated by the controller 310. The first voltage comparator 301 may be a continuous comparator. Namely, the first voltage comparator 301 may be configured to be activated continuously, and monitor the voltage continuously. The first voltage comparator 301 configured as a continuous comparator reduces the chance that the system 121 misses signals generated by an incident X-ray photon. The first voltage comparator 301 configured as a continuous comparator is especially suitable when the incident X-ray intensity is relatively high. The first voltage comparator 301 may be a clocked comparator, which has the benefit of lower power consumption. The first voltage comparator 301 configured as a clocked comparator may cause the system 121 to miss signals generated by some incident X-ray photons. When the incident X-ray intensity is low, the chance of missing an incident X-ray photon is low because the time interval between two successive photons is relatively long. Therefore, the first voltage comparator 301 configured as a clocked comparator is especially suitable when the incident X-ray intensity is relatively low. The first threshold may be 5-10%, 10%-20%, 20-30%, 30-40% or 40-50% of the maximum voltage one incident X-ray photon may generate in the diode or the resistor. The maximum voltage may depend on the energy of the incident X-ray photon (i.e., the wavelength of the incident X-ray), the material of the X-ray absorption layer 110, and other factors. For example, the first threshold may be 50 mV, 100 mV, 150 mV, or 200 mV. The second voltage comparator 302 is configured to compare the voltage to a second threshold. The second voltage comparator 302 may be configured to monitor the voltage directly, or calculate the voltage by integrating an electric current flowing through the diode or the electrical contact over a period of time. The second voltage comparator 302 may be a continuous comparator. The second voltage comparator 302 may be controllably activate or deactivated by the controller 310. When the second voltage comparator 302 is deactivated, the power consumption of the second voltage comparator 302 may be less than 1%, less than 5%, less than 10% or less than 20% of the power consumption when the second voltage comparator 302 is activated. The absolute value of the second threshold is greater than the absolute value of the first threshold. As used herein, the term “absolute value” or “modulus” \|x\| of a real number x is the non-negative value of x without regard to its sign. Namely,  x  = { x , if ⁢ ⁢ x ≥ 0 - x , if ⁢ ⁢ x ≤ 0 . The second threshold may be 200%-300% of the first threshold. The second threshold may be at least 50% of the maximum voltage one incident X-ray photon may generate in the diode or resistor. For example, the second threshold may be 100 mV, 150 mV, 200 mV, 250 mV or 300 mV. The second voltage comparator 302 and the first voltage comparator 310 may be the same component. Namely, the system 121 may have one voltage comparator that can compare a voltage with two different thresholds at different times. The first voltage comparator 301 or the second voltage comparator 302 may include one or more op-amps or any other suitable circuitry. The first voltage comparator 301 or the second voltage comparator 302 may have a high speed to allow the system 121 to operate under a high flux of incident X-ray. However, having a high speed is often at the cost of power consumption. The counter 320 is configured to register a number of X-ray photons reaching the diode or resistor. The counter 320 may be a software component (e.g., a number stored in a computer memory) or a hardware component (e.g., a 4017 IC and a 7490 IC). The controller 310 may be a hardware component such as a microcontroller and a microprocessor. The controller 310 is configured to start a time delay from a time at which the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold (e.g., the absolute value of the voltage increases from below the absolute value of the first threshold to a value equal to or above the absolute value of the first threshold). The absolute value is used here because the voltage may be negative or positive, depending on whether the voltage of the cathode or the anode of the diode or which electrical contact is used. The controller 310 may be configured to keep deactivated the second voltage comparator 302, the counter 320 and any other circuits the operation of the first voltage comparator 301 does not require, before the time at which the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold. The time delay may expire before or after the voltage becomes stable, i.e., the rate of change of the voltage is substantially zero. The phase “the rate of change of the voltage is substantially zero” means that temporal change of the voltage is less than 0.1%/ns. The phase “the rate of change of the voltage is substantially non-zero” means that temporal change of the voltage is at least 0.1%/ns. The controller 310 may be configured to activate the second voltage comparator during (including the beginning and the expiration) the time delay. In an embodiment, the controller 310 is configured to activate the second voltage comparator at the beginning of the time delay. The term “activate” means causing the component to enter an operational state (e.g., by sending a signal such as a voltage pulse or a logic level, by providing power, etc.). The term “deactivate” means causing the component to enter a non-operational state (e.g., by sending a signal such as a voltage pulse or a logic level, by cut off power, etc.). The operational state may have higher power consumption (e.g., 10 times higher, 100 times higher, 1000 times higher) than the non-operational state. The controller 310 itself may be deactivated until the output of the first voltage comparator 301 activates the controller 310 when the absolute value of the voltage equals or exceeds the absolute value of the first threshold. The controller 310 may be configured to cause the number registered by the counter 320 to increase by one, if, during the time delay, the second voltage comparator 302 determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold. The controller 310 may be configured to cause the voltmeter 306 to measure the voltage upon expiration of the time delay. The controller 310 may be configured to connect the electrode to an electrical ground, so as to reset the voltage and discharge any charge carriers accumulated on the electrode. In an embodiment, the electrode is connected to an electrical ground after the expiration of the time delay. In an embodiment, the electrode is connected to an electrical ground for a finite reset time period. The controller 310 may connect the electrode to the electrical ground by controlling the switch 305. The switch may be a transistor such as a field-effect transistor (FET). In an embodiment, the system 121 has no analog filter network (e.g., a RC network). In an embodiment, the system 121 has no analog circuitry. The voltmeter 306 may feed the voltage it measures to the controller 310 as an analog or digital signal. The system 121 may include a capacitor module 309 electrically connected to the electrode of the diode 300 or which electrical contact, wherein the capacitor module is configured to collect charge carriers from the electrode. The capacitor module can include a capacitor in the feedback path of an amplifier. The amplifier configured as such is called a capacitive transimpedance amplifier (CTIA). CTIA has high dynamic range by keeping the amplifier from saturating and improves the signal-to-noise ratio by limiting the bandwidth in the signal path. Charge carriers from the electrode accumulate on the capacitor over a period of time (“integration period”) (e.g., as shown in FIG. 8, between to t0 t1, or t1-t2). After the integration period has expired, the capacitor voltage is sampled and then reset by a reset switch. The capacitor module can include a capacitor directly connected to the electrode. FIG. 8 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by charge carriers generated by an X-ray photon incident on the diode or the resistor, and a corresponding temporal change of the voltage of the electrode (lower curve). The voltage may be an integral of the electric current with respect to time. At time t0, the X-ray photon hits the diode or the resistor, charge carriers start being generated in the diode or the resistor, electric current starts to flow through the electrode of the diode or the resistor, and the absolute value of the voltage of the electrode or electrical contact starts to increase. At time t1, the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1, and the controller 310 starts the time delay TD1 and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD1. If the controller 310 is deactivated before t1, the controller 310 is activated at t1. During TD1, the controller 310 activates the second voltage comparator 302. The term “during” a time delay as used here means the beginning and the expiration (i.e., the end) and any time in between. For example, the controller 310 may activate the second voltage comparator 302 at the expiration of TD1. If during TD1, the second voltage comparator 302 determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold at time t2, the controller 310 causes the number registered by the counter 320 to increase by one. At time te, all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110. At time ts, the time delay TD1 expires. In the example of FIG. 8, time ts is after time te; namely TD1 expires after all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110. The rate of change of the voltage is thus substantially zero at ts. The controller 310 may be configured to deactivate the second voltage comparator 302 at expiration of TD1 or at t2, or any time in between. The controller 310 may be configured to cause the voltmeter 306 to measure the voltage upon expiration of the time delay TD1. In an embodiment, the controller 310 causes the voltmeter 306 to measure the voltage after the rate of change of the voltage becomes substantially zero after the expiration of the time delay TD1. The voltage at this moment is proportional to the amount of charge carriers generated by an X-ray photon, which relates to the energy of the X-ray photon. The controller 310 may be configured to determine the energy of the X-ray photon based on voltage the voltmeter 306 measures. One way to determine the energy is by binning the voltage. The counter 320 may have a sub-counter for each bin. When the controller 310 determines that the energy of the X-ray photon falls in a bin, the controller 310 may cause the number registered in the sub-counter for that bin to increase by one. Therefore, the system 121 may be able to detect an X-ray image and may be able to resolve X-ray photon energies of each X-ray photon. After TD1 expires, the controller 310 connects the electrode to an electric ground for a reset period RST to allow charge carriers accumulated on the electrode to flow to the ground and reset the voltage. After RST, the system 121 is ready to detect another incident X-ray photon. Implicitly, the rate of incident X-ray photons the system 121 can handle in the example of FIG. 8 is limited by 1/(TD1+RST). If the first voltage comparator 301 has been deactivated, the controller 310 can activate it at any time before RST expires. If the controller 310 has been deactivated, it may be activated before RST expires. FIG. 9 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by noise (e.g., dark current, background radiation, scattered X-rays, fluorescent X-rays, shared charges from adjacent pixels), and a corresponding temporal change of the voltage of the electrode (lower curve), in the system 121 operating in the way shown in FIG. 8. At time t0, the noise begins. If the noise is not large enough to cause the absolute value of the voltage to exceed the absolute value of V1, the controller 310 does not activate the second voltage comparator 302. If the noise is large enough to cause the absolute value of the voltage to exceed the absolute value of V1 at time t1 as determined by the first voltage comparator 301, the controller 310 starts the time delay TD1 and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD1. During TD1 (e.g., at expiration of TD1), the controller 310 activates the second voltage comparator 302. The noise is very unlikely large enough to cause the absolute value of the voltage to exceed the absolute value of V2 during TD1. Therefore, the controller 310 does not cause the number registered by the counter 320 to increase. At time te, the noise ends. At time ts, the time delay TD1 expires. The controller 310 may be configured to deactivate the second voltage comparator 302 at expiration of TD1. The controller 310 may be configured not to cause the voltmeter 306 to measure the voltage if the absolute value of the voltage does not exceed the absolute value of V2 during TD1. After TD1 expires, the controller 310 connects the electrode to an electric ground for a reset period RST to allow charge carriers accumulated on the electrode as a result of the noise to flow to the ground and reset the voltage. Therefore, the system 121 may be very effective in noise rejection. FIG. 10 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by charge carriers generated by an X-ray photon incident on the diode or the resistor, and a corresponding temporal change of the voltage of the electrode (lower curve), when the system 121 operates to detect incident X-ray photons at a rate higher than 1/(TD1+RST). The voltage may be an integral of the electric current with respect to time. At time t0, the X-ray photon hits the diode or the resistor, charge carriers start being generated in the diode or the resistor, electric current starts to flow through the electrode of the diode or the electrical contact of resistor, and the absolute value of the voltage of the electrode or the electrical contact starts to increase. At time t1, the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1, and the controller 310 starts a time delay TD2 shorter than TD1, and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD2. If the controller 310 is deactivated before t1, the controller 310 is activated at t1. During TD2 (e.g., at expiration of TD2), the controller 310 activates the second voltage comparator 302. If during TD2, the second voltage comparator 302 determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold at time t2, the controller 310 causes the number registered by the counter 320 to increase by one. At time te, all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110. At time th, the time delay TD2 expires. In the example of FIG. 10, time th is before time te; namely TD2 expires before all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110. The rate of change of the voltage is thus substantially non-zero at th. The controller 310 may be configured to deactivate the second voltage comparator 302 at expiration of TD2 or at t2, or any time in between. The controller 310 may be configured to extrapolate the voltage at te from the voltage as a function of time during TD2 and use the extrapolated voltage to determine the energy of the X-ray photon. After TD2 expires, the controller 310 connects the electrode to an electric ground for a reset period RST to allow charge carriers accumulated on the electrode to flow to the ground and reset the voltage. In an embodiment, RST expires before te. The rate of change of the voltage after RST may be substantially non-zero because all charge carriers generated by the X-ray photon have not drifted out of the X-ray absorption layer 110 upon expiration of RST before te. The rate of change of the voltage becomes substantially zero after te and the voltage stabilized to a residue voltage VR after te. In an embodiment, RST expires at or after te, and the rate of change of the voltage after RST may be substantially zero because all charge carriers generated by the X-ray photon drift out of the X-ray absorption layer 110 at te. After RST, the system 121 is ready to detect another incident X-ray photon. If the first voltage comparator 301 has been deactivated, the controller 310 can activate it at any time before RST expires. If the controller 310 has been deactivated, it may be activated before RST expires. FIG. 11 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by noise (e.g., dark current, background radiation, scattered X-rays, fluorescent X-rays, shared charges from adjacent pixels), and a corresponding temporal change of the voltage of the electrode (lower curve), in the system 121 operating in the way shown in FIG. 10. At time t0, the noise begins. If the noise is not large enough to cause the absolute value of the voltage to exceed the absolute value of V1, the controller 310 does not activate the second voltage comparator 302. If the noise is large enough to cause the absolute value of the voltage to exceed the absolute value of V1 at time t1 as determined by the first voltage comparator 301, the controller 310 starts the time delay TD2 and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD2. During TD2 (e.g., at expiration of TD2), the controller 310 activates the second voltage comparator 302. The noise is very unlikely large enough to cause the absolute value of the voltage to exceed the absolute value of V2 during TD2. Therefore, the controller 310 does not cause the number registered by the counter 320 to increase. At time te, the noise ends. At time th, the time delay TD2 expires. The controller 310 may be configured to deactivate the second voltage comparator 302 at expiration of TD2. After TD2 expires, the controller 310 connects the electrode to an electric ground for a reset period RST to allow charge carriers accumulated on the electrode as a result of the noise to flow to the ground and reset the voltage. Therefore, the system 121 may be very effective in noise rejection. FIG. 12 schematically shows a temporal change of the electric current flowing through the electrode (upper curve) caused by charge carriers generated by a series of X-ray photons incident on the diode or the resistor, and a corresponding temporal change of the voltage of the electrode (lower curve), in the system 121 operating in the way shown in FIG. 10 with RST expires before te. The voltage curve caused by charge carriers generated by each incident X-ray photon is offset by the residue voltage before that photon. The absolute value of the residue voltage successively increases with each incident photon. When the absolute value of the residue voltage exceeds V1 (see the dotted rectangle in FIG. 12), the controller starts the time delay TD2 and the controller 310 may deactivate the first voltage comparator 301 at the beginning of TD2. If no other X-ray photon incidence on the diode or the resistor during TD2, the controller connects the electrode to the electrical ground during the reset time period RST at the end of TD2, thereby resetting the residue voltage. The residue voltage thus does not cause an increase of the number registered by the counter 320. FIG. 13 schematically shows a system comprising the semiconductor X-ray detector 100 described herein. The system may be used for medical imaging such as chest X-ray radiography, abdominal X-ray radiography, etc. The system comprises an X-ray source 1201. X-ray emitted from the X-ray source 1201 penetrates an object 1202 (e.g., a human body part such as chest, limb, abdomen), is attenuated by different degrees by the internal structures of the object 1202 (e.g., bones, muscle, fat and organs, etc.), and is projected to the semiconductor X-ray detector 100. The semiconductor X-ray detector 100 forms an image by detecting the intensity distribution of the X-ray. FIG. 14 schematically shows a system comprising the semiconductor X-ray detector 100 described herein. The system may be used for medical imaging such as dental X-ray radiography. The system comprises an X-ray source 1301. X-ray emitted from the X-ray source 1301 penetrates an object 1302 that is part of a mammal (e.g., human) mouth. The object 1302 may include a maxilla bone, a palate bone, a tooth, the mandible, or the tongue. The X-ray is attenuated by different degrees by the different structures of the object 1302 and is projected to the semiconductor X-ray detector 100. The semiconductor X-ray detector 100 forms an image by detecting the intensity distribution of the X-ray. Teeth absorb X-ray more than dental caries, infections, periodontal ligament. The dosage of X-ray radiation received by a dental patient is typically small (around 0.150 mSv for a full mouth series). FIG. 15 schematically shows a cargo scanning or non-intrusive inspection (NII) system comprising the semiconductor X-ray detector 100 described herein. The system may be used for inspecting and identifying goods in transportation systems such as shipping containers, vehicles, ships, luggage, etc. The system comprises an X-ray source 1401. X-ray emitted from the X-ray source 1401 may backscatter from an object 1402 (e.g., shipping containers, vehicles, ships, etc.) and be projected to the semiconductor X-ray detector 100. Different internal structures of the object 1402 may backscatter X-ray differently. The semiconductor X-ray detector 100 forms an image by detecting the intensity distribution of the backscattered X-ray and/or energies of the backscattered X-ray photons. FIG. 16 schematically shows another cargo scanning or non-intrusive inspection (NII) system comprising the semiconductor X-ray detector 100 described herein. The system may be used for luggage screening at public transportation stations and airports. The system comprises an X-ray source 1501. X-ray emitted from the X-ray source 1501 may penetrate a piece of luggage 1502, be differently attenuated by the contents of the luggage, and projected to the semiconductor X-ray detector 100. The semiconductor X-ray detector 100 forms an image by detecting the intensity distribution of the transmitted X-ray. The system may reveal contents of luggage and identify items forbidden on public transportation, such as firearms, narcotics, edged weapons, flammables. FIG. 17 schematically shows a full-body scanner system comprising the semiconductor X-ray detector 100 described herein. The full-body scanner system may detect objects on a person's body for security screening purposes, without physically removing clothes or making physical contact. The full-body scanner system may be able to detect non-metal objects. The full-body scanner system comprises an X-ray source 1601. X-ray emitted from the X-ray source 1601 may backscatter from a human 1602 being screened and objects thereon, and be projected to the semiconductor X-ray detector 100. The objects and the human body may backscatter X-ray differently. The semiconductor X-ray detector 100 forms an image by detecting the intensity distribution of the backscattered X-ray. The semiconductor X-ray detector 100 and the X-ray source 1601 may be configured to scan the human in a linear or rotational direction. FIG. 18 schematically shows an X-ray computed tomography (X-ray CT) system. The X-ray CT system uses computer-processed X-rays to produce tomographic images (virtual “slices”) of specific areas of a scanned object. The tomographic images may be used for diagnostic and therapeutic purposes in various medical disciplines, or for flaw detection, failure analysis, metrology, assembly analysis and reverse engineering. The X-ray CT system comprises the semiconductor X-ray detector 100 described herein and an X-ray source 1701. The semiconductor X-ray detector 100 and the X-ray source 1701 may be configured to rotate synchronously along one or more circular or spiral paths. FIG. 19 schematically shows an electron microscope. The electron microscope comprises an electron source 1801 (also called an electron gun) that is configured to emit electrons. The electron source 1801 may have various emission mechanisms such as thermionic, photocathode, cold emission, or plasmas source. The emitted electrons pass through an electronic optical system 1803, which may be configured to shape, accelerate, or focus the electrons. The electrons then reach a sample 1802 and an image detector may form an image therefrom. The electron microscope may comprise the semiconductor X-ray detector 100 described herein, for performing energy-dispersive X-ray spectroscopy (EDS). EDS is an analytical technique used for the elemental analysis or chemical characterization of a sample. When the electrons incident on a sample, they cause emission of characteristic X-rays from the sample. The incident electrons may excite an electron in an inner shell of an atom in the sample, ejecting it from the shell while creating an electron hole where the electron was. An electron from an outer, higher-energy shell then fills the hole, and the difference in energy between the higher-energy shell and the lower energy shell may be released in the form of an X-ray. The number and energy of the X-rays emitted from the sample can be measured by the semiconductor X-ray detector 100. The semiconductor X-ray detector 100 described here may have other applications such as in an X-ray telescope, X-ray mammography, industrial X-ray defect detection, X-ray microscopy or microradiography, X-ray casting inspection, X-ray non-destructive testing, X-ray weld inspection, X-ray digital subtraction angiography, etc. It may be suitable to use this semiconductor X-ray detector 100 in place of a photographic plate, a photographic film, a PSP plate, an X-ray image intensifier, a scintillator, or another semiconductor X-ray detector. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
061756156	abstract	A collimator 100 for use in a radiation imaging system 10, and a method for making such collimators, are provided, wherein the collimator 100 is capable of collimating radiation in two orthogonal planes. The collimator in one embodiment includes a block 101 of radiation absorbing material having a plurality of focally aligned channels 102 extending therethrough; in a second embodiment, the collimator includes first and second collimation204, 212 sections having a respective first plurality of focally aligned plate sets 201 and a respective second plurality of focally aligned plate sets 203 disposed orthogonally to the first plurality of plate sets. The method for making the collimator includes generating a CAD drawing, generating from the CAD drawing one or more stereo-lithographic files, and using the stereo-lithographic files to control an electro-deposition machining machine which creates the channels in the block.
	description	This application is a U.S. National Stage Filing under 35 U.S.C. 371 from International Application No. PCT/US2013/043301, filed on 30 May 2013, which application is incorporated herein by reference in its entirety. The present invention relates generally to apparatus and methods of making measurements with respect to a drilling operation. Radioactive chemical neutron sources are widely used in thermal/epithermal neutron logging tools. These sources are statically mounted such that their output is constant and typically lacks the flexibility of pulsed neutron tools. Pulsed neutron tools employ timing gates to differentiate inelastic gamma and capture gamma rays, which are then used to determine rock properties. Typically, pulsed neutron tools in the industry use deuterium, tritium (D, T) neutron generators, which require charged particle accelerators. The usefulness of such measurements may be related to their complexity, to the precision or quality of the information and the presentation of the information derived from such measurements, and combinations thereof. The following detailed description refers to the accompanying drawings that show, by way of illustration and not limitation, various embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice these and other embodiments. Other embodiments may be utilized, and structural, logical, and electrical changes may be made to these embodiments. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The following detailed description is, therefore, not to be taken in a limiting sense. FIG. 1 shows an example embodiment of an apparatus having a pulsed neutron generator 105. The pulsed neutron generator 105 can comprise an emitter 110 and a neutron shield 115 having an aperture 120. The neutron shield 115 can be structured in an arrangement with the emitter 110 such that a chopper to neutrons emitted from the emitter 110 is operatively generated by the arrangement of the emitter 110 and the neutron shield 115. The emitter 110 can be realized as a chemical neutron emitter. The chemical neutron emitter may provide a constant source of neutrons. The chemical neutron emitter can include one or more radioactive isotopes. Control of the arrangement of the emitter 110 relative to the neutron shield 115 can make the combination of the emitter 110 and the neutron shield 115 operable as the pulsed neutron generator 105 from which a pulsed neutron beam is output. The neutron shield 115 can block neutrons from being output from the pulsed neutron generator 105 except through aperture 120. Movement of the emitter 110 and neutron shield 115 relative to each other provides a chopper function to a neutrons beam or a neutron beam emitted from the emitter 110. The relative movement can be provided by controlling movement of the emitter 110, the neutron shield 115, or combinations of the emitter 110 and the neutron shield 115. The control of the relative movement can be realized having a selected frequency of the relative movement. A number of different arrangements of the emitter 110 and the neutron shield 115 may be implemented to provide the relative movement to generate a chopper function to the neutrons generated by the emitter 110. FIG. 2 shows an example embodiment of a pulsed neutron generator 205 having a moving neutron shield design. The moving neutron shield design can include an emitter/neutron shield arrangement that can include an emitter 210 in a fixed position and a neutron shield 215 that is moveable, where the neutron shield 215 has an aperture 220. The pulsed neutron generator 205 can include a control unit 230 to move the neutron shield 215. The neutron shield 215 can be structured as a moveable shield such that the aperture 220 operatively aligns with the emitter 210 during a selected portion of movement of the neutron shield 215. The moveable motion of the neutron shield 215 can be a rotation around an axis structure 235 of a mounting platform 240. The neutron shield 215 can be positioned in a path of the neutrons emitted from the emitter 210. The neutron shield 215 can be structured as a rotatable shield such that the aperture 220 operatively aligns with the emitter 210 at one angular region in each rotation of the neutron shield 215. The aperture 220 can be arranged to operatively provide an output of the pulsed neutron generator 205. The output can be provided by the alignment of the emitter 210 and the aperture 220, where neutrons are blocked from output from the pulsed neutron generator 205 when the emitter 210 is not in alignment with the aperture 220. The neutron shield 215 may be controlled similar to an optical chopper. The emitter 210 can be realized as a chemical neutron emitter. The chemical neutron emitter may provide a constant source of neutrons. The chemical neutron emitter can include one or more radioactive isotopes. The chopping of the neutron beam can be controlled by the control unit 230. The control unit 230 can include circuitry structured to regulate motion of the neutron shield 215 at a selected frequency. In FIG. 2, regulation of motion by the control unit 230 is shown as a clockwise rotation to rotate the neutron shield 215. Motion can be attained as a counterclockwise rotation. Other motions of the neutron shield 215 can be controlled relative to the fixed emitter 210 to provide a chopping of the neutron beam output from the pulsed neutron generator 205. FIG. 3 shows an example embodiment of a pulsed neutron generator 305 having a moving emitter design. The moving emitter design can include an emitter/neutron shield arrangement that can include a neutron shield 315 in a fixed position, where the neutron shield 315 has an aperture 320, and an emitter 310 that is moveable. The pulsed neutron generator 305 can include a control unit 330 to move the emitter 310. The emitter 310 can be attached to a platform 340, where the platform 340 is moveable such that the emitter 310 is operatively aligned with the aperture 320 during a selected portion of movement of the platform 340. The aperture 320 can be arranged to operatively provide an output of the pulsed neutron generator 305. The moveable motion of the platform 340 can be a rotation around an axis structure 335 of platform 340. The neutron shield 315 can be positioned in a path of the neutrons emitted from the emitter 310. The platform 340 with the emitter 310 attached thereon can be structured as a rotatable platform such that the emitter 310 operatively aligns with the aperture 320 at one angular region in each rotation of the platform 340. The aperture 320 can be arranged to operatively provide an output of the pulsed neutron generator 305. The output can be provided by the alignment of the emitter 310 and the aperture 320, where neutrons are blocked from output from the pulsed neutron generator 305 when the emitter 210 is not in alignment with the aperture 320. The emitter 310 can be realized as a chemical neutron emitter. The chemical neutron emitter may provide a constant source of neutrons. The chemical neutron emitter can include one or more radioactive isotopes. The chopping of the neutron beam can be controlled by the control unit 330. The control unit 330 can include circuitry structured to regulate motion of the platform 340 at a selected frequency. In FIG. 3, regulation of motion by the control unit 330 is shown as a clockwise rotation to rotate the platform 340. Motion can be attained as a counterclockwise rotation. Other motions of the emitter 310 can be controlled relative to the fixed neutron shield 315 to provide a chopping of the neutron beam to output from the pulsed neutron generator 305. FIGS. 4A-4B show views of an example embodiment of a pulsed neutron generator 405 having a design of a moving neutron shield around an emitter. The design of a moving neutron shield around an emitter can include an emitter/neutron shield arrangement that can include an emitter 410 in a fixed position and a neutron shield 415 positioned to move around the emitter 410 such that an aperture 420 of the neutron shield 415 operatively aligns with the emitter 410 during a selected portion of the movement of the neutron shield 415 around the emitter 410. The neutron shield 415 can be structured to completely encircle the emitter 410. The pulsed neutron generator 405 can include a control unit 430 to move the neutron shield 415 around the emitter 410. The neutron shield 415 can be positioned to rotate around the emitter 410 such that the aperture 420 operatively aligns with the emitter 410 at one angular region in each rotation of the neutron shield 415 around the emitter 410. This rotation can be regulated by the control unit 430. The aperture 420 can be arranged to operatively provide an output of the pulsed neutron generator 405. The output can be provided by the alignment of the emitter 410 and the aperture 420, where neutrons are blocked from output from the pulsed neutron generator 405 when the emitter 410 is not in alignment with the aperture 420. The emitter 410 can be realized as a chemical neutron emitter. The chemical neutron emitter may provide a constant source of neutrons. The chemical neutron emitter can include one or more radioactive isotopes. The chopping of the neutron beam can be controlled by the control unit 430. The control unit 430 can include circuitry structured to regulate motion of the neutron shield 415 at a selected frequency. In FIGS. 4A-4B, regulation of motion by the control unit 430 is shown as a clockwise rotation to rotate the neutron shield 415. Motion can be attained as a counterclockwise rotation. Other motions of the neutron shield 415 can be controlled relative to the fixed emitter 410 at varying frequencies to provide a chopping of the neutron beam output from the pulsed neutron generator 405. The view in FIG. 4B shows use of an optional backstop 412. Backstop 412 can be used to direct neutrons from the emitter 410 in a specified direction. This arrangement may be used to avoid neutrons from passing through aperture 420 from reflections from within neutron shield 415 when the emitter 410 is not aligned with the aperture 420. With an emitter structured to emit neutrons in an omnidirectional manner, backstop 412 can provide a mechanism to effectively generate neutrons in a limited number of directions from the emitter. Other mechanisms may be used to set a direction of neutron flow from an emitter for alignment with an output of pulsed neutron generator 405. FIGS. 5A-5B show an example embodiment of an example pulsed neutron generator 505 having a design of a neutron shield positioned around a moving emitter. The design of a neutron shield positioned around a moving emitter can include an emitter/neutron shield arrangement that can include a neutron shield 515 in a fixed position and an emitter 510 attached to a platform 540 with the neutron shield 515 surrounding the emitter 510. The platform 540 can be moveable inside of the neutron shield 515 (within an entire surface of the neutron shield 515) such that the emitter 510 is operatively aligned with the aperture 520 during a selected portion of movement of the platform 540. The pulsed neutron generator 505 can include a control unit 430 to move the emitter 410 inside the neutron shield 515. The platform 540 with the emitter attached thereon can be rotatable inside of the neutron shield 515 such that the emitter 510 is operatively aligned with the aperture 520 at one angular region in each rotation of the platform 540. This rotation can be regulated by the control unit 530. The aperture 520 can be arranged to operatively provide an output of the pulsed neutron generator 505. The output can be provided by the alignment of the emitter 510 and the aperture 520, where neutrons are blocked from output from the pulsed neutron generator 505 when the emitter 510 is not in alignment with the aperture 520. The emitter 510 can be realized as a chemical neutron emitter. The chemical neutron emitter may provide a constant source of neutrons. The chemical neutron emitter can include one or more radioactive isotopes. The chopping of the neutron beam can be controlled by the control unit 530. The control unit 530 can include circuitry structured to regulate motion of the emitter 510 at a selected frequency. In FIGS. 5A-5B, regulation of motion by the control unit 530 is shown as a clockwise rotation to rotate the emitter 510. Motion can be attained as a counterclockwise rotation. Other motions of the emitter 510 can be controlled relative to the fixed neutron shield 515 at varying frequencies to provide a chopping of the neutron beam output from the pulsed neutron generator 505. The view in FIG. 5B shows use of an optional backstop 512. Backstop 512 can be used to direct neutrons from the emitter 510 in a specified direction. This arrangement may be used to avoid neutrons from passing through aperture 520 from reflections from within neutron shield 515 when the emitter 510 is not aligned with the aperture 520. With an emitter structured to emit neutrons in an omnidirectional manner, backstop 512 can provide a mechanism to effectively generate neutrons in a limited number of directions from the emitter. Other mechanisms may be used to set a direction of neutron flow from an emitter for alignment with an output of pulsed neutron generator 505. FIG. 6 shows an example embodiment of an example pulsed neutron generator 605 having a linearly moving neutron shield design. The linearly moving neutron shield design can include an emitter/neutron shield arrangement that can include an emitter 610 in a fixed position and an neutron shield 615 positioned in a path of neutrons emitted from the emitter 610, where the neutron shield 615 can be structured to move linearly across the path of the neutrons such that an aperture 620 of the neutron shield 615 operatively aligns with the emitter 610 at a position in the linear movement of the neutron shield 615. The pulsed neutron generator 605 can include a control unit 630 to move the neutron shield. The neutron shield 615 can be structured to oscillate linearly across the path of the neutrons such that the aperture 620 operatively aligns with the emitter 610 at a position in the linear oscillation of the neutron shield 615. The movement of the neutron shield 615 can be realized with the control unit 630 driving a platform 640 to which the neutron shield 615 can be attached. The aperture 620 can be arranged to operatively provide an output of the pulsed neutron generator 605. The output can be provided by the alignment of the emitter 610 and the aperture 620, where neutrons are blocked from output from the pulsed neutron generator 605 when the emitter 610 is not in alignment with the aperture 620. The emitter 610 can be realized as a chemical neutron emitter. The chemical neutron emitter may provide a constant source of neutrons. The chemical neutron emitter can include one or more radioactive isotopes. The chopping of the neutron beam can be controlled by the control unit 630. The control unit 630 can include circuitry structured to regulate motion of the neutron shield 615 at a selected frequency. Other motions of the neutron shield 615 can be controlled relative to the fixed emitter 610 at varying frequencies to provide a chopping of the neutron beam output from the pulsed neutron generator 605. FIG. 7 shows an example of a pulsed neutron generator 705 having a linearly moving emitter design. The linearly moving emitter design can include an emitter/neutron shield arrangement that can include a neutron shield 715 in a fixed position, where the neutron shield has an aperture 720, and an emitter 710 attached to a platform 740. The platform 740 can be structured to move in a linear direction such that the emitter 710 is operatively aligned with the aperture 720 at a position in the linear movement of the emitter 710. The pulsed neutron generator 705 can include a control unit 730 to move the emitter 710. The movement of the emitter 710 can be realized with the control unit 630 driving the platform 740 to which the emitter 710 can be attached. The platform 740 can be structured to oscillate in a linear direction such that the emitter 710 is operatively aligned with the aperture 720 at a position in the linear oscillation of the neutron shield 715. The aperture 720 can be arranged to operatively provide an output of the pulsed neutron generator 705. The output can be provided by the alignment of the emitter 710 and the aperture 720, where neutrons are blocked from output from the pulsed neutron generator 705 when the emitter 710 is not in alignment with the aperture 720. The emitter 710 can be realized as a chemical neutron emitter. The chemical neutron emitter may provide a constant source of neutrons. The chemical neutron emitter can include one or more radioactive isotopes. The chopping of the neutron beam can be controlled by the control unit 730. The control unit 730 can include circuitry structured to regulate motion of the emitter 710 at a selected frequency. Other motions of the emitter 710 can be controlled relative to the fixed neutron shield 715 at varying frequencies to provide a chopping of the neutron beam output from the pulsed neutron generator 705. FIG. 8 shows features of an embodiment of a method that includes providing a pulsed chemical neutron source. Such a pulsed chemical neutron source can be used in well logging applications. At 810, neutrons are generated from a chemical neutron emitter. Generating neutrons from the chemical neutron emitter can include generating neutrons using one or more radioactive isotopes. At 820, the neutrons are passed through a neutron shield or blocked by the neutron shield. The neutrons are passed through an aperture of the neutron shield when the chemical neutron emitter aligns with the aperture such that the neutrons are substantially blocked by the neutron shield when the chemical neutron emitter is unaligned with the aperture. At 830, movement of one or more of the chemical neutron emitter or the neutron shield is controlled. The control can be realized such that the aperture and the chemical neutron emitter operatively align with each other during a selected portion of the movement, generating pulses of neutrons output from the neutron shield. Controlling movement can include controlling movement of the neutron shield with the chemical neutron emitter fixed or controlling movement of the chemical neutron emitter with the neutron shield fixed. With the chemical neutron emitter or the neutron shield fixed, controlling the movement can include driving the respective movement by a rotational movement in a plane across a direction that aligns the chemical neutron emitter with the neutron shield. With the chemical neutron emitter or the neutron shield fixed, controlling the movement can include driving the respective movement by a rotational movement with the chemical neutron emitter surrounded by the neutron shield. With the chemical neutron emitter or the neutron shield fixed, controlling the movement can include driving the respective movement by a linear movement. The linear movement can include an oscillatory linear motion. Controlling movement can include controlling the movement with a selected frequency of the movement. Controlling movement can include controlling the movement with a selected variation of frequency of the movement. In various embodiments, methods using pulsed chemical neutron source can include generating pulsed neutrons in a borehole from an apparatus having a pulsed neutron generator structured according to an apparatus similar to or identical to apparatus disclosed herein or combinations thereof; analyzing signals in a processing unit from generating the pulsed neutrons in the borehole; and directing a drilling-based operation in response to analyzing the signals. The drilling-based operation can include, but is not limited to, storing parameters correlated to the formation in which the borehole is formed, generating data providing information on formation properties, generating a visual representation of formation properties, and other activities associated with well logging. In addition, a machine-readable storage device can have instructions stored thereon, which, when performed by a machine, cause the machine to perform operations, the operations comprising any of the features using a pulsed chemical neutron source discussed herein. Various components of a system operable to perform measurements using a pulsed chemical neutron source can be realized in combinations of hardware and software based implementations. These implementations may include a machine-readable storage device having machine-executable instructions, such as a computer-readable storage device having computer-executable instructions, to control the measurement system, store and implement parameters for measurements, store results, and communicate with other systems to provide data, analysis, or combinations of data and analysis. The instructions can include instructions to generate neutrons from a chemical neutron emitter; to pass the neutrons through an aperture of a neutron shield when the chemical neutron emitter aligns with the aperture such that the neutrons are substantially blocked by the neutron shield when the chemical neutron emitter is unaligned with the aperture; and to control movement of one or more of the chemical neutron emitter or the neutron shield such that the aperture and the chemical neutron emitter operatively align with each other during a selected portion of the movement, generating pulses of neutrons output from the neutron shield. The chemical neutron emitter can include one or more radioactive isotopes. Controlling movement can include controlling movement of the neutron shield with the chemical neutron emitter fixed or controlling movement of the chemical neutron emitter with the neutron shield fixed. Controlling the movement can include driving the respective movement by a rotational movement in a plane across a direction that aligns the chemical neutron emitter with the neutron shield. Controlling the movement can include driving the respective movement by a rotational movement with the chemical neutron emitter surrounded by the neutron shield. Controlling the movement can include driving the respective movement by a linear movement. The linear movement can include an oscillatory linear motion. Controlling movement can include controlling the movement with a selected frequency of the movement. Controlling movement can include controlling the movement with a selected variation of frequency of the movement. Examples of machine-readable storage devices include, but are not limited to, read only memory (ROM), random access memory (RAM), a magnetic disk storage device, an optical storage device, a flash memory, and other electronic, magnetic, and/or optical memory devices. FIG. 9 depicts a block diagram of features of an embodiment of an example system 900 operable to implement a pulsed chemical neutron source. The system 900 can include a pulsed neutron generator 905 having a chemical neutron emitter 910 and a neutron shield with aperture 915, where the chemical neutron emitter 910 and the neutron shield with aperture 915 can be structured with an arrangement similar to or identical to arrangements discussed herein or combinations thereof. The system 900 can include one or more processors 930, a user interface 962 operable with the one or more processors 930, a processing unit 945 operable with the user interface 962, where the one or more processors 930, the user interface 962, and the processing unit 945 can be structured to be operated according to any scheme similar to or identical to the schemes associated with controlling and regulating a pulsed neutron generator 905 as taught herein. In an embodiment, the processor(s) 930 can be realized as a single processor or a group of processors. Processors of the group of processors may operate independently depending on an assigned function. The processor(s) 930 can be used to control movement of one or more of the chemical neutron emitter 910 or the neutron shield with aperture 915 with respect to each other such that the aperture and the chemical neutron emitter 910 operatively align with each other during a selected portion of the respective movement generating neutrons through the aperture providing pulsed neutron output from the pulsed neutron generator 905. The chemical neutron emitter 910 can be configured such that neutrons can be output from the chemical neutron emitter 910 in a given direction for alignment. The system 900 can be arranged to perform various operations on data, acquired from probing using the pulsed neutron generator 905 operational downhole to make measurements with respect to formations, to provide processing thereof. The system 900 can be arranged as a distributed system and can include components in addition to the one or more processors 960, the user interface 962, and the processing unit 945. The system 900 can include electronic apparatus 950 having instrumentality to make measurements that provide data that can be operated in one format or another by the one or more processors 930, the user interface 962, and the processing unit 945 to present information regarding a formation. The electronic apparatus 950 can include sensors to receive signals in response to using the pulsed neutron generator 905. The electronic apparatus 950 can include timing circuitry operable with the mechanical mechanism associated with the chemical neutron emitter 910 and the neutron shield with the aperture 915 to provide a chopping function to neutrons emitted from the chemical neutron emitter 910 to generate pulsed neutrons from the aperture of the neutron shield. The electronic apparatus 950 can include drives and motors to control movement of the chemical neutron emitter 910, the neutron shield with aperture 915, or combination of the chemical neutron emitter 910 and the neutron shield with the aperture 915 in a manner identical to or similar to the mechanisms discussed herein. The motion of the chemical neutron emitter 910, the neutron shield with aperture 915, or combination of the chemical neutron emitter 910 and the neutron shield with aperture 915 can be regulated by the electronic apparatus 950 or other components of system to operate a selected frequency or variable frequencies. The system 900 can include a memory 935 and a communications unit 940. The processor(s) 930, the memory 935, and the communications unit 940 can be arranged to operate as a processing unit to control management of the pulsed neutron generator 905 and to perform operations on data signals collected from using the pulsed neutron generator 905. The memory 935 can include a database having information and other data such that the system 900 can operate on data generated from using the pulsed neutron generator 905. In an embodiment, the processing unit 945 can be distributed among the components of the system 900 including the electronic apparatus 950. The communications unit 940 can include downhole communications for communication to the surface at a well. Such downhole communications can include a telemetry system. The communications unit 940 may use combinations of wired communication technologies and wireless technologies at frequencies that do not interfere with on-going measurements. The communications unit 940 can allow for a portion or all of the data analysis to be conducted downhole with results provided to the user interface 962 for presentation on one or more display unit(s) 960 aboveground. However, the communications unit 940 can provide for data to be sent aboveground such that substantially all analysis is preformed aboveground. The communications unit 940 can allow for transmission of commands to the pulsed neutron generator 905 or drilling control downhole in response to signals provided by a user through the user interface 962, which allows interactive control of a drilling operation. The system 900 can also include a bus 937, where the bus 937 provides electrical conductivity among the components of the system 900. The bus 937 can include an address bus, a data bus, and a control bus, each independently configured. The bus 937 can be realized using a number of different communication mediums that allows for the distribution of components of the system 900. Use of the bus 937 can be regulated by the processor(s) 930. Bus 937 can include a network to transmit and receive signals including data signals and command and control signals. In various embodiments, the peripheral devices 955 can include additional storage memory and/or other control devices that may operate in conjunction with the processor(s) 930 and/or the memory 935. Display unit(s) 960 can be arranged with a screen display, as a distributed component on the surface, that can be used with instructions stored in the memory 935 to implement the user interface 962 to manage the operation of the pulsed neutron generator 905 and/or components distributed within the system 900. Such a user interface can be operated in conjunction with the communications unit 940 and the bus 937. The display unit(s) 960 can include a video screen, a printing device, or other structure to visually project information. The system 900 can include a number of selection devices 964 operable with the user interface 962 to provide user inputs to operate processing unit 945 or its equivalent. The selection device(s) 964 can include one or more of a touch screen or a computer mouse operable with the user interface 962 to provide user inputs to operate the processing unit 945. The system 900 can be compatible with a logging while drilling operation. The system 900 can be also compatible with a wireline operation. The system 900 can be arranged as a distributed system for a land-based drilling operation, a sea-based drilling operation, or a drilling operation having land-based and sea-based components. FIG. 10 depicts an embodiment of a system 1000 at a drilling site, where the system 1000 includes an apparatus operable to use a pulsed chemical neutron source with respect to a drilling operation. The system 1000 can include a tool 1005-1, 1005-2, or both 1005-1 and 1005-2 having a pulsed neutron generator including a chemical neutron emitter and a neutron shield with an aperture, where the chemical neutron emitter and the neutron shield with aperture structured with an arrangement similar to or identical to arrangements discussed herein or combinations thereof. The tools 1005-1 and 1005-2 can be structured to include a chemical neutron emitter/neutron shield architecture identical to or similar to chemical neutron emitter/neutron shield arrangements or combinations of such architectures discussed above. The tools 1005-1, 1005-2, or both 1005-1 and 1005-2 can be distributed among the components of system 1000. The system 1000 can include a drilling rig 1002 located at a surface 1004 of a well 1006 and a string of drill pipes, that is, drill string 1029, connected together so as to form a drilling string that is lowered through a rotary table 1007 into a wellbore or borehole 1012-1. The drilling rig 1002 can provide support for the drill string 1029. The drill string 1029 can operate to penetrate rotary table 1007 for drilling the borehole 1012-1 through subsurface formations 1014. The drill string 1029 can include a drill pipe 1018 and a bottom hole assembly 1020 located at the lower portion of the drill pipe 1018. The bottom hole assembly 1020 can include a drill collar 1016 and a drill bit 1026. The drill bit 1026 can operate to create the borehole 1012-1 by penetrating the surface 1004 and the subsurface formations 1014. The bottom hole assembly 1020 can include the tool 1005-1 attached to the drill collar 1016 to conduct measurements to determine formation parameters. The tool 1005-1 can be structured for an implementation as a measurements-while-drilling (MWD system such as a logging-while-drilling (LWD) system. The housing containing the tool 1005-1 can include electronics to initiate measurements using a pulsed chemical neutron source and to collect measurement signals in the measurement process. Such electronics can include a processing unit to provide analysis of formation parameters over a standard communication mechanism for operating in a well. Alternatively, electronics can include a communications interface to provide measurement signals collected by the tool 1005-1 to the surface over a standard communication mechanism for operating in a well, where these measurements signals can be analyzed at a processing unit at the surface to provide analysis of formation parameters. During drilling operations, the drill string 1029 can be rotated by the rotary table 1007. In addition to, or alternatively, the bottom hole assembly 1020 can also be rotated by a motor (e.g., a mud motor) that is located downhole. The drill collars 1016 can be used to add weight to the drill bit 1026. The drill collars 1016 also can stiffen the bottom hole assembly 1020 to allow the bottom hole assembly 1020 to transfer the added weight to the drill bit 1026, and in turn, assist the drill bit 1026 in penetrating the surface 1004 and the subsurface formations 1014. During drilling operations, a mud pump 1032 can pump drilling fluid (sometimes known by those of skill in the art as “drilling mud”) from a mud pit 1034 through a hose 1036 into the drill pipe 1018 and down to the drill bit 1026. The drilling fluid can flow out from the drill bit 1026 and be returned to the surface 1004 through an annular area 1040 between the drill pipe 1018 and the sides of the borehole 1012-1. The drilling fluid may then be returned to the mud pit 1034, where such fluid is filtered. In some embodiments, the drilling fluid can be used to cool the drill bit 1026, as well as to provide lubrication for the drill bit 1026 during drilling operations. Additionally, the drilling fluid may be used to remove subsurface formation cuttings created by operating the drill bit 1026. In various embodiments, the tool 1005-2 may be included in a tool body 1070 coupled to a logging cable 1074 such as, for example, for wireline applications. The tool body 1070 containing the tool 1005-2 can include electronics to initiate measurements using a pulsed chemical neutron source and to collect measurement signals in the measurement process. Such electronics can include a processing unit to provide analysis of formation parameters over a standard communication mechanism for operating in a well. Alternatively, electronics can include a communications interface to provide measurement signals collected by the tool 1005-1 to the surface over a standard communication mechanism for operating in a well, where these measurements signals can be analyzed at a processing unit at the surface to provide analysis of formation parameters. The logging cable 1074 may be realized as a wireline (multiple power and communication lines), a mono-cable (a single conductor), and/or a slick-line (no conductors for power or communications), or other appropriate structure for use in the borehole 1012. Though FIG. 10 depicts both an arrangement for wireline applications and an arrangement for LWD applications, the system 1000 may be also realized for one of the two applications. In various embodiments, a device can be implemented using a mechanical chopper-like mechanism with radioactive isotopes to function as a pulsed chemical neutron source. Such a source combined with a timing circuitry can be used on well logging tools. The device can utilize a chemical radioactive emitter, which has a lifespan depending upon the half-life of the radioisotope (from several to several hundreds of years), with a rugged mechanical design. Comparing to a neutron generator, the system complexity of the pulsed chemical neutron source can be simplified. In addition, the radioactive neutron emission may be less affected by environmental effects, such as temperature. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Various embodiments use permutations and/or combinations of embodiments described herein. It is to be understood that the above description is intended to be illustrative, and not restrictive, and that the phraseology or terminology employed herein is for the purpose of description. Combinations of the above embodiments and other embodiments will be apparent to those of skill in the art upon studying the above description.
	claims	1. A radiation protection equipment, comprising:a first protection sheet arranged on a periphery of a radiation source device and configured to shield radiation and to be foldable;a second protection sheet formed separately from the first protection sheet, arranged on a side of an operation table, and configured to shield radiation; anda third protection sheet formed separately from the first protection sheet and the second protection sheet, arranged on a periphery of a surgical field so as to expose the surgical field, and configured to shield the radiation. 2. A radiation protection equipment according to claim 1,wherein the third protection sheet includes at least two sheets that are combined so as to expose a rectangular region, andwherein the two sheets are formed separately from each other. 3. A radiation protection equipment according to claim 1,wherein the first protection sheet includes a first side surface sheet facing a first side surface of the radiation source device, a second side surface sheet facing a second side surface of the radiation source device, and a back surface sheet facing a back surface of the radiation source device, andwherein the first side surface sheet, the second side surface sheet, and the back surface sheet are formed separately from each other. 4. A radiation protection equipment according to claim 1, further comprising a sheet support part configured to support the first protection sheet or the third protection sheet. 5. A radiation protection equipment according to claim 4, wherein the sheet support part includes a first extension part extending in a horizontal direction, a second extension part continued from the first extension part and extending in a vertical direction, and a fixing part fixed to an operation table. 6. A radiation protection system, comprising: an imaging apparatus including a radiation source device and a detector; and the radiation protection equipment of claim 1. 7. A radiation protection equipment, comprising:a first protection member configured to shield radiation and including a first side surface member facing a first side surface of a radiation source device, a second side surface member facing a second side surface of the radiation source device, and a back surface member facing a back surface of the radiation source device; anda second protection member formed separately from the first protection member, arranged on a periphery of a surgical field so as to expose the surgical field, and configured to shield the radiation. 8. A radiation protection system, comprising:an imaging apparatus including a radiation source device and a detector; andthe radiation protection equipment of claim 7.

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.