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043607365	claims	1. In a radiation shield for use in installations containing sources of radiation, said radiation shield comprising a container formed of thin flexible material composed of woven or knitted threads, the improvement wherein said radiation shield further comprises means connecting opposing walls of said container to maintain the distance therebetween when said container is filled with a radiation attenuating liquid, said means being sufficiently flexible to permit opposing walls of said container to approach each other for storage when said container is not filled with a radiation attenuating liquid, said means comprising drop stitches, said drop stitches comprising an intersecting grid of threads which extend between said opposing walls and are interlaced with the threads which compose said opposing walls. 2. In a radiation shield for use in installations containing sources of radiation, said radiation shield comprising a container formed of thin flexible material, the improvement wherein said radiation shield further comprises means connecting opposing walls of said container to maintain the distance therebetween when said container is filled with a radiation attenuating liquid, said means being sufficiently flexible to permit opposing walls of said container to approach each other for storage when said container is not filled with a radiation attenuating liquid, said means comprising wing tabs, said wing tabs comprising plies of material which are initially joined to said opposing walls along a plurality of nodes, after which said plies are cut between the nodes, bent inwardly, and joined to a correspondingly inwardly bent ply segment from the opposing wall.
	description	The present invention concerns a method and a device for irradiating a target with a beam approaching target points and a control system for controlling the invention-based device. The irradiation of a target with a beam approaching different target points (beam scanning) is already known. For example, when irradiating tumors, particle beams, especially ion beams, in particular with protons, αparticles or carbon nuclei, are used. The beam approaches parts of the target area, the target points, in sequence, one after the other. Particle beams are especially advantageous for irradiating a target volume because towards their end they pass through a maximum in energy deposition (Bragg-Peak). In this way, it is possible to irradiate effectively even imbedded three-dimensional structures without causing a lot of damage to the imbedding surroundings. Often, three-dimensional target regions are irradiated in layers wherein the radiation energy determining the depth of penetration is selected to be constant (iso-energy layer). A generally known method is also the so-called volumetric scanning in which the successively approached target points are not necessarily assigned to individual (iso-energy) layers. Basically, the invention concerns also embodiments in which the beam is formed by electromagnetic waves. Furthermore, the invention concerns also embodiments for irradiating plane target regions. Scanning methods allow for irradiation that is adapted to the shape of the target by scanning with a beam. Distinctions are made between different scanning methods. In the so-called spot-scan method and the pixel-scan method, the particle beam lingers at each target point for a pre-determined time period and/or deposits at each target point a predetermined number of particles and is turned off when deflecting magnets (scanning magnets) are adjusted to a next target point. In so-called grid scanning, the particle beam lingers at each of several screen dots during a predetermined time period or deposits at each screen dot a predetermined number of particles. However, between the screen dots, the particle is not or not always turned off. The screen dots can differ from the target points, because the screen dots are usually indicated in the coordination system of the irradiation device, while the target points are usually observed in the coordination system of the target. In particular, the screen dots and the target points do not have to be mutually congruent, although this is preferred. To simplify matters, the points approached during grid scanning are subsequently not always described as screen dots, but also as target points. In so-called continuous scanning methods, the target points form connected lines, i.e., they form continuous (or quasi-continuous) amounts, wherein their number can be approximately countably infinite. In a continuous scanning method, the particle beam is continuously deflected, at least within a line or row in an iso-energy layer, and scans the target points without lingering at individual places. By means of a depth modulation device, it is also possible to carry out a continuous scanning method in which the depth of penetration is continuously modulated. Furthermore, so-called uniform scanning is known wherein a homogeneous dose deposition is achieved in a respective iso-energy layer in that once or even several times an equal particle number is deposited at all target points or along the scan paths. The succession of the target points, the path, can basically run within an iso-energy layer by deflecting the beam merely in its traveling direction, i.e., one- or two-dimensionally lateral. However, the beam can also run between iso-energy layers by changing the energy of the beam. It is basically known to measure the position of the beam or its three-dimensional position during the irradiation process. It is also known to measure the intensity of the beam, for example, as particle flux or applied particle number, during the irradiation process. To simplify matters, the term intensity is here used in a uniform manner for all respective parameters. The publication “Magnetic scanning system for heavy ion therapy”, Haberer et al, Nuclear Instruments and Methods in Physics Research A330 (1993) 296 ff. shows, for example, a multi-wire-proportional-chamber (MWPC) in order to measure the position of the beam during the irradiation process. Furthermore, the publication shows to measure the intensity of the beam and to use the results of the measurement for controlling irradiation (intensity control). For example, the beam is moved faster when the dose to be deposited per target point is relatively small and the beam intensity is high. The beam is moved correspondingly slower when the dose to be deposited per target point is relatively high and the beam intensity is low. In other words: The beam is directed to the respective next target point when the required particle number has been deposited at the preceding target point. Basically, it is also known among experts to use the measured position of the beam and its measured intensity for the purpose of making corrections during the irradiation process if differences from the reference values occur. If required, irradiation is even interrupted, for example, in the case of a greater variance from the reference value. So far, such interruptions are made several times per target point in order to achieve a high level of accuracy of measurements. This applies to the position of the beam, as well as to its intensity. In addition, it is possible to measure the beam width. To have sufficient time for the position measurements, it is known to adjust the beam intensity in such a way that the measurements can be made for each target point. Often, the beam intensity selected for this purpose is lower than can be provided by the accelerator. The present invention is based on the objective of providing an advantageous method and an advantageous device to irradiate a target with a beam approaching target points, as well as a control system to control the invention-based device. The objective is achieved by a method for irradiating a target with a beam approaching target points which involves the following steps: Measuring at least one of the parameters relating to the position of the beam and the intensity of the beam, changing the beam as a function of the at least one measured parameter, particularly as a function of a variance relating to the at least one measured parameter. The method is characterized in that the at least one measured parameter is measured at the most once per target point. The dependent claims specify preferred embodiments of the invention which are subsequently described in more detail. The invention is based on the observation that the measurement of the position of the beam and the measurement of the intensity of the beam require minimal time. Furthermore, it is based on the knowledge that the measuring cycles described above limit the scanning velocity. Especially when the beam intensity is adjusted in such a way that it is possible to perform several position measurements per target point, irradiation time as a whole can be quite long, in particular, if the target is approached with several scans (Rescanning, see below). Moreover, the relatively low intensity has a negative effect on the signal-to-noise ratio of the intensity measurement. It has also been determined that the accuracy regarding the beam position and/or the beam intensity or the knowledge of the beam width achieved through repeated measurements is not particularly necessary, for example, because the device is designed for a respective precise beam guidance, or because it is particularly error tolerant due to a special irradiation arrangement (Rescanning, see below). It is the idea of the invention to measure the parameters to be measured, i.e., the position of the beam and/or the intensity of the beam, at the most once per target point. The invention includes the case wherein merely one of the two parameters is measured at the most once per target point. In particular, it includes the cases wherein one of the two parameters is measured several times per target point, or not at all, or distributed over several target points, and the respective other parameter is measured merely once per target point. Current technology allows for intensity measurements that are considerably faster than position measurements. Correspondingly, in a referred embodiment, the position measurement is performed once per target point, while intensity measuring is performed several times per target point. It is especially preferred to determine the scanning velocity based on the measured intensity of the beam (Intensity control, see above) and, if necessary, to measure the intensity of the beam several times per target point, while the position of the beam is determined at the most once per target point. The position and/or intensity measurements can be used to determine a variance from predetermined values or reference values; in other words, to determine errors. Changes of the beam can be associated with such determinations. In the easiest case, irradiation is interrupted or even discontinued when the results of the position measurement and/or the results of the intensity measurement exceed a specific variance. In the context of the invention, it is also possible to correct the position and/or the intensity of the beam depending on the amount of the variance. It is especially preferred to use the measurement of one of the two parameters or even both parameters merely for monitoring the beam, and to interrupt irradiation in case a variance is exceeded. In a preferred embodiment, the measurements are not used for correcting the beam. For example, this can save time spent for correcting the adjustment of the scanning magnets (see example) during the process of irradiation. Besides irradiating people or animals, it is relevant to irradiate organic materials, particularly cells, or even to irradiate inorganic materials, such as plastic materials, for example, in the context of material research. It is preferable to use the method of grid scanning, it allows for a particularly fast scanning process. In the generally known method of multiple irradiation with a beam approaching different target points (rescanning), an intended dose is applied successively during one session with several scans which are separated by short breaks, if required. In the process, within the individual scans, several target points, not necessarily all of them, are irradiated in sequence. In the course of the session, usually a good portion of the target points, or all target points, and thus a good portion of the target area, or the target area as a whole are irradiated several times. The cumulative dose per target point to be applied during the session is distributed to the individual scans, for example, equally or, if required, with different amounts. Even the method of multiple irradiation can be performed in layers or volumetrically. Especially for rescanning, it is advantageous to use a high scanning velocity because the path to be covered per session when using several scans is clearly longer in comparison to depositing the entire dose in a single scan. Without the invention, the irradiation time as a whole can be too long, for example, because the irradiation process is too encumbering for a person to be irradiated. Immobilization becomes worse with time. The performance of the equipment is relatively low. Rescanning allows for the use of the invention even in equipments that work less accurate because inaccuracies in the beam position and in beam intensity are kept at a minimum by averaging the performance over several scans. When the method of multiple irradiation is coordinated respectively, it is not necessary to know the precise beam position or beam intensity during the process of irradiation. If intensity measurements can be performed faster than position measurements, it is recommended even in the context of rescanning to control the beam by means of its intensity and to perform position measurements at the most once per target point. If a moved target is irradiated, it is advantageous to use rescanning. This is the case because the movement of the target results in variances from the intended dose distribution. This can happen also as a result of interferences between the irradiation procedure and the movement of the target. If irradiation is performed with several scans, such dose errors can be averaged. In the context of particle therapy, such a moved target can involve a tumor in the vicinity of the lung of a person to be irradiated which is moved cyclically up and down because of breathing. Preferably, the at least one measured parameter is measured at the most once for at least two target points; even more preferably in the sequence mentioned at the most once for three target points, 10 target points or one line of target points. It is especially preferred to keep the number of measurements so low that the time required for the measurements no longer limits the scanning speed. For example, this can be the case with intensity-controlled irradiation when the time required for applying the predetermined dose in several target points exceeds the time for the position measurements of these target points. If a measurement for several target points is performed at the most once, and if the measurement requires more time than the irradiation of the individual target points, it results in an average value averaged over several target points. For example, in intensity-controlled irradiation, the beam intensity usually varies from target point to target point, resulting in an inhomogeneous distribution. In order to obtain a most meaningful average value, especially with respect to position measurements and, if necessary, measurements of the beam width, it can be advantageous to take into consideration also timing effects, such as detector performances, for example, the distribution of ionization in the detection gas. This can be especially helpful for a precise correction of the beam position during the irradiation process. In a preferred embodiment of the invention, the points in time of measurements for the at least one measured parameter are determined by the time that elapsed during the irradiation process. For example, each measurement of a respective parameter can be performed after the cycle of a fixed interval, ideally in the fastest possible succession, i.e., the shortest possible interval. With this method, the intervals of the measurements are respectively independent from approaching the target points. In other words: approaching the target points and the measurements of the beam position and/or beam intensity are performed in asynchronous manner. For example, it is possible to select different intervals for the position measurements and the intensity measurements. In such a case, the position measurements and the intensity measurements are also asynchronous in relation to each other. It can also be advantageous to control the irradiation by means of the intensity of the beam and to measure the position of the beam repeatedly each after a respective fixed time interval. Even in this case, the measurements of both parameters are asynchronous with respect to each other, and the measurement of the position of the beam is asynchronous with regard to approaching the target points. In order to apply a specific dose in a specific target point by means of time control, that is, when approaching the target points is determined by means of the elapsed time, a scanning velocity is selected for the beam that allows for expecting that the intended dose is applied at this point. When the beam lingers at a target point, it is directed to the next target point as soon as a specific time has elapsed which allows for expecting that the intended dose has been applied. However, such time control does not exclude that knowledge about the properties of a beam can be included. It is therefore preferred to take into consideration the extraction profile of the beam source. In fact, it is possible that in time the number of extracted particles greatly varies, depending on the source. Usually, the extraction profile for a specific source is known. For example, it can be determined prior to irradiation. In the simple case of a homogenous intended dose distribution, this means that a comparatively fast scanning speed is selected when according to the extraction profile the particle number is high. When according to the extraction profile the particle number is low, a comparatively slow scanning velocity is selected. If the intended dose distribution is not homogenous, this has to be also taken into consideration by means of weighting. If a medium beam intensity and a respective scanning velocity is assumed without taking the extraction profile into consideration, the scanning velocity has to be increased comparatively when according to the extraction profile the beam intensity is high, and the scanning velocity has to be reduced when according to the extraction profile the beam intensity is low. In this way, it is possible to reduce variances from the intended dose distribution. The particle amount to be applied can be maintained in a more precise manner. Some detector types, for example, multi-wire proportional chambers, can perform a position measurement faster with a beam having a small cross-section than with a beam having a larger cross-section. The cross-section of the beam increases in the direction of the target. Therefore, it is preferred to measure the beam position as far as possible in the direction of the source of the beam that the cross-section of the beam corresponds to at the most 80%, preferably 60%, of its cross-section directly before the target. Preferably, the width of the beam is determined by means of a separate module. In comparison to a solution wherein the width of the beam is determined with the same module with which the position of the beam is determined, it is possible to achieve a velocity advantage. For example, a module can correspond to a complete analysis and/or operation chain from the detector to the software. It can also involve a separate computer or a separate process on the computer, which can already be sufficient to determine the parameters mentioned separately from one another. The invention also involves a device for irradiating a target with a beam approaching target points, which beam has a measuring device for measuring at least one of the parameters relating to position of the beam and intensity of the beam, and having a sequence control system which is designed to change the beam as a function of the at least one measured parameter, particularly as a function of a variance relating to the at least one measured parameter. The irradiation device is characterized in that it is designed to measure the at least one measured parameter at the most once per target point. Such an irradiation device comprises also equipment for generating a beam, particularly for generating a particle beam or especially an ion beam. For example, beam generation equipment can involve an accelerator, particularly a synchrotron or cyclotron. When irradiation is performed by means of an ion beam, the irradiation device comprises also a scanning device, or scanner, which involves scanning magnets for deflecting the ion beam and/or depth modulation device. Position measurements can be performed by means of an MWPC, a strip ionization chamber, a measuring chamber based on scintillators or PET. The intensity can be measured by means of an ionization chamber (IC) or also with an MWPC, a pixel ionization chamber or also by means of a measuring chamber based on scintillators. Basically, sequence control systems for generic irradiation devices are known. For example, the above-mentioned publication by Haberer et al. describes one of them. Such sequence control systems typically have the function of controlling irradiation, particularly the scanning process, the maximum dose, making comparisons with a radiation plan and documentation. If necessary, the sequence control system interferes in the irradiation procedure (interlock), for example by means of an interruption or correction of the irradiation procedure when the beam fluctuates in its intensity, or in the case of other interferences. For example, the sequence control system can be implemented with the help of a computer or data processing system. It is possible to store in such a computer information regarding the energy distribution of the scans and the iso-energy layers, the target points, the screen dots, the intended dose per screen dot, the treatment plan and criteria for ending the irradiation process. One criterion for ending the irradiation process can involve reaching the intended dose per target point specified in the treatment plan. The criterion of reaching the intended dose can be fed back to the scanning device. It is recommended to document the intended dose per target point in a chart. A respective or at least comparable chart containing all parameters for the sequence control system can also be documented for each scan during the process of rescanning. The computer can be provided with several modules for each respective function. The data processing system can be provided with several computers for each respective function. Such functions involve, for example: scanner control, pulse control center (requests an ion beam), intensity measurement (at least one, preferably two per target point for increasing redundancy, provided at the most one position measurement has been made), position measurement (at least one, preferably two per target point for increasing redundancy, provided at the most one intensity measurement has been made), documentation. Typically, the beam parameters from the pulse control center, the scanner parameters and the results of the intensity and position measurements are documented. If the device has several equipments for intensity measuring and position measuring—this can be beneficial for increasing redundancy—it is preferred to connect these in series in order to increase the sampling rate of the measurements and thus reduce the period of measuring. For example, if the device has two equipments, respectively, for intensity measuring and position measuring, and if the respective equipments for intensity measuring and the equipments position measuring connected in series, the respective maximum sampling rate can possibly be doubled. These equipments can involve detectors, modules, computers or evaluation units in general. Preferably, the irradiation device is designed to perform the invention-based method in any of the preferred embodiments. The invention also involves a control system for controlling the irradiation device. In contrast to the irradiation device, the control system itself does not comprise a beam generation device. If the control system is used for controlling an irradiation device for irradiating humans or animals, it is also called a therapy control system (TCS). For example, the invention-based method can be performed by modifying the position measuring device, also called position measuring module (SAM; memory and readout module) which can be part of the control system. For this purpose, the control system receives an additional component or an existing module is replaced. Basically, it is necessary to adjust the control system to the sequence control system, it is possibly sufficient to adjust the control software. The preceding and the following description of the individual characteristics comprise the method, as well as the device and the control system without mentioning it in every single case. The individual characteristics disclosed here can be of significance also in combinations not shown in this invention. The irradiation device is designed to irradiate a target volume 102. For example, the target volume 102 involves a tumor situated near or in the lung of a person. The target volume 102 shown has a diameter of approximately 20 cm vertically to the beam direction. Alternatively, it can also involve a phantom, for example, based on water or Plexiglas, or any other material. The target volume moves cyclically up and down, which is indicated in FIG. 1 by the arrows above and below the target volume 102. The irradiation device comprises a synchrotron, a cyclotron or any other accelerator 104 for providing a particle beam 105, consisting, for example, of protons or 12C nuclei. Typically, such a beam has an expansion of one or several millimeters, approximately between 3 and 10 mm. In the target volume 102 layers are indicated which correspond to the depth of the Bragg-Peak for a specific particle energy (iso-energy layers). The scanning method selected here is called grid scanning. The irradiation device uses the particle beam 105 to approach screen dots that are schematically represented in the target volume 102 as black points. These screen dots are located in the target volume approximately 2 mm apart from each other. To simplify matters, a layer-by-layer approach of the screen dots is shown. Alternative, it is also possible to approach the screen dots in volumetric manner (not shown). The particle beam 105 can be laterally impacted by means of scanning magnets 106. These scanning magnets are dipole magnets 106 in this example. For a longitudinal impact (in beam direction) the irradiation device comprises a passive energy variation system for energy modulation, for example, in the form of a wedge-type system 108. The wedge-type system 108 has wedges, consisting, for example, of plastic material which are moved by means of a linear motor (not shown). Preferably, the wedge-type system 108 is used with volumetric scans. In layer-by-layer scanning, the energy is preferably changed my means of an accelerator or an energy modulation system installed before the scanning magnets 106. Furthermore, the irradiation device comprises a sequence control system 112, a scanner control 114, a particle counter 116 and a position detector 117. The particle counter 116 and the position detector 117 can also be placed at other positions, for example at the position of the particle counter 116. Here, the sequence control system 112 has the function of a control system. The particle counter 116 is an ionization chamber (IC) and functions as an intensity measuring device. The position detector 117 is a multi-wire-proportional-chamber (MWPC). The ionization chamber 116 requires 15 μs for an intensity measurement. The multi-wire-proportional-chamber required 150 μs for determining the position of the beam 105. The position of the beam can be measured almost directly before the target or approximately 1 m before the target. Alternatively, it is recommended to measure the position of the beam further in the direction of the beam source because there the beam diameter is smaller and therefore the position measurement can be performed faster. The position detector 117 can be arranged in such a way that the beam diameter amounts to at the most 50% of its value directly before the target. Two modules, respectively, for determining the intensity and for determining the position of the beam have been provided. Each of them is connected in series (not shown). Here it is possible to obtain a higher temporal resolution, for example, through “time-shift” measurements. To increase safety it is possible to provide redundancy through a comparison that takes the time-shifts into consideration. The particle counter 116 determines the number of particles in the particle beam 105 and transmits the results to the sequence control system 112. The sequence control system 112 is designed to control the accelerator 104, the scanning magnet 106 and the wedge-type system 108. For this purpose, the sequence control system 112 determines respective control parameters by taking into consideration the data received from the particle counter 116 and the position detector 117. The irradiation process is performed by means of several scans, using the method of rescanning. A selection can be made between approximately 5 and 10, preferably 15 to 20, or up to 30 scans. Typically, the target volume is divided in 50 layers. Typically, it takes 100 ms up to 1 s to completely approach a layer. When a volume is approached, the approach period ranges seconds. During the irradiation process, generally at the most one position measurement or at the most one intensity measurement per screen dot is performed, see FIG. 2. According to the invention, the following measures can be taken for determining the position or intensity of the beam: at the most one position measurement per screen dot, no intensity measurement; at the most one intensity measurement per screen dot, no position measurement; at the most one position measurement per screen dot, as well as one intensity measurement per screen dot; at the most one position measurement per screen dot, as well as several intensity measurements per screen dot; at the most one intensity measurement per screen dot, as well as several position measurements per screen dot; control of the irradiation procedure according to the intensity of the beam (intensity control). If necessary with several intensity measurements per screen dot, wherein the position of the beam is measured at the most once per screen dot; at the most one position measurement for three or 10 screen dots or even for one line of screen dots; at the most one intensity measurement for three or 10 screen dots or even for one line of screen dots; performance of intensity measurements and/or position measurements according to fixed intervals; shortest possible selection of intervals; intensity control of the irradiation process; fixed intervals for the position measurements; coordination of intervals, so that three or 10 screen dots or even one line of screen dots is approached in between the measurements; coordination of intervals so that the irradiation time is not increased by the measurements; averaging a measurement over several screen dots; taking into consideration the ionization in the detector gas for improving such an averaging process; timing of irradiation, wherein the positions are measured at the most once per screen dot; taking into consideration the extraction profile in such timing; measuring the beam position relatively near the beam source; the measurement of the width of the beam is performed with a separate module, decoupled from the location measurement; connecting measuring devices in series; FIG. 3 shows a selection. According to the invention, the following measures concerning possible changes of the beam resulting from a determination of the position or the intensity of the beam involve: interrupting the irradiation process if the measured position or the measured intensity considerably deviate from the respective intention; correcting the beam position if the measured position deviates slightly from its target value; FIG. 4 shows a selection. FIG. 5 shows a schematic extraction profile of the device for a krypton beam (shown in FIG. 1) having energy of 300 MeV/u. In addition to rise and fall, a real (synchrotron) profile would comprise also a plateau with fluctuations, a so-called “ripple”. It can be observed that the particle number (events) per extraction (spill) initially increases rapidly. after approximately half a second, it reaches a maximum, and after one second it basically dropped again to zero. When the approach of the screen dots is not controlled by means of the intensity of the beam, but in temporal manner, said extraction profile for determining the scan speed is taken into consideration. If the number of extracted particles is especially high, it is possible to select a fast scan speed; if it s low a slow scan speed is selected.
051026155	description	DETAILED DESCRIPTION Referring to FIG. 1, a container is provided for storing and transporting radioactive material, such as racks of irradiated fuel bundles 1, comprising a vessel 2 and a cap 3. Referring to FIG. 2, the vessel 2 has an upwardly open cavity 4 for accommodating radioactive material. The particular container illustrated has a vessel 2, cavity 4 and cap 3 of substantially rectangular transverse cross-section. The vessel 2 and cap 3 have rounded longitudinal edges. The vessel 2 has walls with a core 5 of radioactive shielding material enveloped and isolated within a continuous metal lining. The vessel's continuous metal lining comprises: an upwardly open internal liner 6; an external vessel liner 7; and a top vessel plate 8 (a plan view of which is shown in FIG. 5). The internal liner 6 has side and bottom walls, the inner surfaces of which define the cavity 4. The external liner 7 also has side and bottom walls which are spaced outward from the internal liner 6. Referring to FIGS. 2 and 5, the top vessel plate 8 has a central opening 9 defining the cavity 4. An inner portion of the top vessel plate 8 adjacent the central opening 9 is continuously welded to an upper portion of the internal liner 6. An outer portion of the top vessel plate 8 is continuously welded to an upper portion of the external vessel liner 7. The concrete shielding material 5 fills the internal space defined by the internal and external vessel liners 6 and 7 and the top vessel plate 8. The cap 3 covers the top surface of the vessel 2 sealing the cavity 4. The cap 3 also has a core 10 of concrete shielding material enveloped and isolated within a continuous metal lining. The lower outer peripheral edge of the cap 3 is continuously welded to the upper outer peripheral edge of the vessel 2. The continuous metal lining of the cap 3 comprises: a bottom cap plate 11; a top cap plate 12 spaced upward from the bottom plate; and an external cap liner 13. The external cap liner 13 has side walls, the top and bottom portions of which are continuously welded respectively to the outer portions of the top and bottom cap plates 11 and 12. The concrete shielding material fills the internal space defined by the bottom and top cap plates 11 and 12 and the external cap liner 13. The concrete shielding material of the vessel core 5 and cap core 10 is high density concrete having aggregates of magnetite or specularite preferably. Concrete mixtures also may be designed to impart desirable properties during disposal. Concrete is alkaline and therefore inhibits corrosion of steel liners and reinforcing bars. Ground water containing dissolved salts may penetrate the exterior liner. The alkaline concrete buffers such penetration of corrosive ions. The concrete may be reinforced or not depending upon design stresses. The continuous metal lining of the container is preferably of carbon steel plate due to its relatively low cost and wide availability in a variety of grades. The metal lining may be made of stainless steel, copper, titantium or other metal suitable for the corrosive environment anticipated particularly in a disposal site. The outer surfaces of the container may be coated with epoxy paint to facilitate concrete decontamination. The inner surfaces of the internal liner 6 may also be coated with epoxy paint to inhibit corrosion which clouds the water and impairs the loading operator's vision when the vessel 2 is loaded with concrete material underwater. A particular advantage of the invention is its ability to be loaded underwater such that the shielding material is not exposed to contaminated water and the exterior of the container may be easily decontaminated. The vessel 2 includes two diametrically opposing lifting lugs 14 attached to the outer side walls of the vessel 2 for lifting the vessel 2 and container. A spreader beam 18 suspended from an overhead crane may be used engaging the lugs 14 with mating trunnions 30 as shown in FIG. 2. The lugs 14 are anchored in the vessel's concrete core 5 using embedded studs 15 welded to a lug anchoring plate 16 which is itself welded to the external vessel liner 7. The cap 3 includes at least one lifting eyelet 17 attached to the top surface of the cap 3 for lifting the cap 3 with a crane. The lifting eyelets 17 are anchored in the cap's concrete core 10 using embedded studs 19 welded to an eyelet anchoring plate 20 which is itself welded to the top cap plate 12. Referring to FIGS. 2 and 4, in order to accurately and quickly position the cap 3 upon the vessel 2 prior to welding the cap 3 and vessel 2 together, aligning pins 21 and aligning sockets 22 are provided. The aligning pins 21 are connected to the top surface of the vessel as shown by welding to the top vessel plate 8. The aligning sockets 22 are recessed within the lower surface of the cap by welding adjacent a hole in the bottom cap plate 11. The aligning sockets 22 correspond to and mate with the aligning pins 21 to position and align the cap 3 upon the vessel 2. The container is particularly suited to be loaded with concrete material while immersed in the water of a short term storage pool. In addition to the continuous metal linings which envelope and isolate the concrete radioactive shielding cores, and the epoxy paint coatings described above, underwater loading is further facilitated by the provision of a drain, a vent and a gasket ring. Since the contaminated water, surrounding the radioactive material within the loaded cavity 4, adds to the risk of radioactive leakage and to the corrosion of the metal fuel racks 1, it is desirable to drain the contaminated water from the cavity 4 and to vacuum dry the cavity 4 and its contents prior to transporting the container to long term storage. A gasket ring 23 is positioned between the top surface of the vessel 2, embedded within a groove in the vessel top plate 8, and the lower surface of the cap 3, such that the gasket ring 23 engages the bottom cap plate 11. Referring to FIG. 5, the gasket ring 23 is positioned adjacent the central opening 9, in the top vessel plate 8, which defines the cavity 4. The gasket ring 23 is used as a temporary seal during the draining and drying of the cavity 4 to seal the cavity 4. Referring to FIGS. 2 and 3, a drain pipe 24 communicates between a lower portion of the cavity 4 and the exterior of the container. Drain control means, comprising first and second drain plugs 25 and 26, are housed within an enlarged outer portion of the drain pipe 24, for sealing the drain pipe 24 and for enabling fluid to pass between the cavity 4 and the exterior of the container. Referring to FIGS. 1 and 2, a vent pipe 27 communicates between an upper portion of the cavity 4 and the exterior of the container. In the particular embodiment shown the vent pipe 27 is embedded within the cap 3. Venting control means, comprising first and second vent plugs 28 and 29, are housed within an enlarged outer portion of the vent pipe 27, for sealing the vent pipe 27 and for enabling fluid to pass between the cavity 4 and the exterior of the container. The following sequence of operations is carried out in order to load the container with radioactive material and seal the container. The radioactive material, such as for example irradiated spent fuel bundles 1 are initially stored underwater in racks in the short term storage pools of a nuclear power station. When the radioactive material is to be transferred to another site for long term storage, a vessel 2 with its first and second drain plugs 25 and 26 installed is placed underwater in the short term storage pool by an overhead handling crane above the pool. The crane is fitted with a lifting beam 18 and the lifting beam trunnions are engaged with the lifting lugs 14 of the vessel 2 as shown in FIG. 2. The crane is then used to lift the racks of radioactive material and place them within the cavity 4 of the vessel 2 at all times maintaining the radioactive material underwater. The loaded vessel 2 is then lifted from the pool and placed on a platform adjacent the pool. The cap 2 is lifted by its lifting eyelets and placed upon the top surface of the vessel 3. The weight of the cap 3 compresses the gasket ring 23 to temporarily seal the cavity 4. Aligning pins 21 and mating aligning sockets guide the cap 3 into proper alignment upon the vessel 2. The outer surfaces of the container have previously been coated with epoxy paint to facilitate concrete decontamination. A mixture of water and cleaning solution (such as Alxonox/Alcojet) is used with long handled brushes to decontaminate the outer surfaces. A chemical cleaner may also be used to further decontaminate the container's outer surfaces. Vacuum pumps and conduits are then attached to the vent pipe 27 and drain pipe 24 after removal of the vent plugs 28 and 29 and drain plugs 25 and 26. The water from within the cavity 4 is drained away and returned to the pool. The vacuum pump is used to vacuum dry the cavity 4 and its contents via the vent pipe 27 and drain pipe 24 to prevent corrosion of the internal liner 6 and the racks supporting the irradiated fuel bundles. After drying the drain plugs 25 and 26 are replaced and the cavity is back filled with helium gas via the vent pipe 27. The vent plugs 28 and 29 are then replaced and the container is leak tested. Referring to FIG. 4, the lower outer peripheral edge of the cap 3 is continuously welded to the upper outer peripheral edge of the vessel 2. The weld shown in FIG. 4 is a full penetration butt weld preferably deposited by semiautomatic welding equipment. The cap 3 to vessel 2 weld is inspected by non-destructive methods. Upon completion of welding the decontaminated container is lifted by the lifting beam 18 and crane and placed upon a flatbed truck or rail car to be transported to its long term storage site. Trade-mark
	claims	1. A method for retaining ruthenium within a vitrified product obtained by a vitrification of a nitric acid aqueous solution stemming from a reprocessing of radioactive liquid effluents, the nitric acid aqueous solution comprising radionuclides including ruthenium, the vitrification comprising:a) calcining the nitric acid aqueous solution to form a calcine;b) mixing the calcine with a glass frit;c) heating the mixed calcine and glass frit until a molten mixture is obtained; andd) cooling the molten mixture to form the vitrified product in which the radionuclides including ruthenium are included;wherein the method comprises, before a), adding to the nitric acid aqueous solution a composition comprising a lignin, a lignocellulose, a salt thereof or a mixture thereof wherein the content of the lignin, the lignocellulose, the salt thereof or mixture thereof is more than 70% by mass based on the mass of the composition. 2. A method for manufacturing a vitrified product by vitrifying a nitric acid aqueous solution stemming from a reprocessing of radioactive liquid effluents, the nitric acid aqueous solution comprising radionuclides including ruthenium; the method successively comprising:a) adding to the nitric acid aqueous solution a composition comprising a lignin, a lignocellulose, a salt thereof or a mixture thereof wherein the content of the lignin, the lignocellulose, the salt thereof or mixture thereof is more than 70% by mass based on the mass of the composition;b) calcining the nitric acid aqueous solution, thereby obtaining a non-tacky calcine;c) mixing the non-tacky calcine with a glass frit;d) heating the mixed non-tacky calcine and glass frit until a molten mixture is obtained; ande) cooling the molten mixture to form a vitrified product in which the radionuclides including ruthenium are retained.
042235758	summary	BACKGROUND OF THE INVENTION This invention relates to tools for removing studs from a nuclear reactor vessel and particularly to such tools utilizing automated mechanisms and weight supporting devices. In nuclear reactors well known in the art, the reactor comprises a core of fuel assemblies having fuel elements containing nuclear fuel which produce heat in a commonly understood fashion. The core is disposed within a reactor vessel designed to contain radioactive material that has an inlet and an outlet for circulating a coolant such as water in heat transfer relationship with the fuel assemblies. A closure head is located on the top of the reactor vessel and is usually bolted thereto by a plurality of studs that extend through the closure head and into the reactor vessel so as to seal the radioactive material in the reactor vessel. The reactor coolant that has been circulated through the reactor vessel transfers the heat produced by the core to steam generating equipment for the production of heat in a conventional manner. After a period of reactor operation, the fuel assemblies in the core become depleted and must be replaced with fresh ones in a process generally referred to as refueling. During the refueling of the reactor it is necessary to remove the closure head so that the fuel assemblies of the core may be accessed. In order to remove the closure head, it is first necessary to remove the studs which hold the closure head to the reactor vessel. Of course, once the refueling operation has been completed the closure head must be again fastened to the reactor vessel by means of the studs that were removed. There are many methods known in the art for so removing these studs; however, those methods have disadvantages which render them unsatisfactory. One method known in the art for removing the studs from a reactor vessel closure head is to manually unscrew the studs by the use of strap wrenches. When the closure head studs have thus been unscrewed a lifting bolt may be attached to the closure head stud so that an overhead crane may lift and remove the closure head studs. Once the closure head studs have been removed, an overhead crane may be utilized to lift and remove the closure head so that access may be had to the fuel assemblies in the reactor core. After the refueling process has been completed, this process is reversed resulting in the closure head being bolted to the reactor vessel. While the process can be completed in this manner, it requires the use of several working personnel for approximately twenty hours. The length of time involved in such a process substantially delays the refueling process. Furthermore, because the working personnel must be stationed in a relatively high radiation exposure area during the stud removal and insertion process, additional personnel are needed in order to minimize the radiation exposure to any particular person. Therefore, what is needed is an apparatus that can quickly remove or insert the reactor closure head studs without damaging them. SUMMARY OF THE INVENTION Apparatus for removing or inserting studs of a nuclear reactor vessel closure head so that the closure head may be removed for refueling the nuclear reactor. The apparatus comprises a carriage having an engagement mechanism, a rotation mechanism, and a drive mechanism mounted thereon. The engagement mechanism firmly contacts the stud while the rotation mechanism and drive mechanism together cause the engagement mechanism and stud to rotate. In addition, a support device is associated with the carriage for supporting the carriage while the carriage is positioned near the stud and for supporting the weight of the stud while the stud is being manipulated so that the weight of the stud does not damage the threads of the reactor vessel.
	claims	1. A method comprising:receiving, by learning logic, historical metrics of a computing system being monitored;determining, by the learning logic, from the received historical metrics, forms of sub-functions that are included in an equation, wherein each sub-function represents a dependency between two components linked in a hierarchical structure representing the computing system being monitored;receiving, by state determination logic, metric values of the computing system being monitored;determining, by the state determination logic, states that minimize the equation composed of the sub-functions over the received metric values; anddetecting anomalous behavior of the computing system based on the determined states. 2. The method of claim 1 comprising:determining, by the learning logic, said forms of said sub-functions that minimize the description length of said equation over the received historical metrics. 3. The method of claim 2 comprising:selecting, by the learning logic, sub-functions d and h such that the description length represented by said equation is minimized over the received historical metrics;wherein sub-function di is a cost function associated with a component i in a base layer of the hierarchical structure representing the computing system being monitored; andwherein sub-function hk,i is a function associated with each component i of each intermediate layer k of the hierarchical structure representing the computing system, where said function hk,i is based on the state of the corresponding component i and the state of the component to which said corresponding component i is connected in a successive layer k+1 of the hierarchical structure. 4. The method of claim 3 further comprising:selecting, by the state determination logic, arguments of sub-functions h and d that minimize said description length for the received metric values. 5. The method of claim 1 wherein said equation comprises: DL = ∑ k = 1 K ⁢ ⁢ ∑ i = 1 n k ⁢ ⁢ h k , i ⁡ ( s k , s k + 1 ) + ∑ j = 1 n 1 ⁢ ⁢ d j ⁡ ( m j , s 1 ) ;wherein DL is description length;wherein the hierarchical structure comprises K layers, with a number, n1, of components in layer 1 that is equal to a number of metrics observed for the computing system; and a number, nk, of components in layer K is equal to one; and a number, nk, of components in layer k, where 1<k<K, is equal to the number of components in layer k;wherein each component, i, in layer 1 is associated with a function of form di(mi,s), where mi is an observed value of metric i and s is a state variable; andwherein each component, i, in each layer k is associated with a function of form hk,i(s,t), where s is a state of the component and t is a state of the component to which it is connected in layer k+1. 6. The method of claim 5 wherein each component in layer k, where 1<k<K, is connected to:(i) one or more components in layer k−1; and(ii) one and only one component in layer k+1. 7. The method of claim 5 wherein function di is a cost function whose value is high when a corresponding metric indicates abnormal behavior and is low when the corresponding metric indicates normal behavior. 8. The method of claim 1 comprising:determining, by the state determination logic, said states that minimize a description length for the received metric values. 9. A method comprising:receiving, by learning logic, historical metrics of a computing system being monitored;determining, by the learning logic, a corresponding function for determining a state of at least one component of the computing system, wherein the learning logic uses a hierarchical model of the computing system to determine the corresponding function;receiving, by state determination logic, at least one measured metric of the computing system being monitored; anddetermining, by the state determination logic, a state of the at least one component of the computing system based on the determined corresponding function for determining the state. 10. A method comprising:receiving, by learning logic, historical metrics of a computing system being monitored;determining, by the learning logic, a corresponding function for determining a state of at least one component of the computing system;receiving, by state determination logic, at least one measured metric of the computing system being monitored;determining, by the state determination logic, a state of the at least one component of the computing system based on the determined corresponding function for determining the state;wherein said determining said corresponding function comprises:determining, by said learning logic, forms of sub-functions that are included in a given equation, wherein each sub-function represents a dependency between two components linked in a hierarchical structure representing the computing system. 11. The method of claim 10 wherein said determining said state comprises:determining, by the state determination logic, said state that minimizes the equation composed of the sub-functions over the received at least one measured metric. 12. The method of claim 11 wherein said equation comprises: DL = ∑ k = 1 K ⁢ ⁢ ∑ i = 1 n k ⁢ ⁢ h k , i ⁡ ( s k , s k + 1 ) + ∑ j = 1 n 1 ⁢ ⁢ d j ⁡ ( m j , s 1 ) ;wherein DL is description length;wherein the hierarchical structure comprises K layers, with a number, n1, of components in layer 1 that is equal to a number of metrics observed for the computing system; and a number, nk, of components in layer K is equal to one; and a number, nk, of components in layer k, where 1<k<K, is equal to the number of components in layer k;wherein each component, i, in layer 1 is associated with a function of form di(mi,s), where mi is an observed value of metric i and s is a state variable; andwherein each component, i, in each layer k is associated with a function of form hk,i(s,t), where s is a state of the component and t is a state of the component to which it is connected in layer k+1. 13. The method of claim 9 further comprising:detecting anomalous behavior of the computing system based on the determined state. 14. A system comprising:a hierarchical model representing at least a portion of a computing system;learning logic operable to receive historical metrics of the computing system, and determine a corresponding function for determining a state of each component of the hierarchical model; andstate determination logic operable to receive at least one measured metric of the computing system, and determine a state of each component of the hierarchical model based on the determined corresponding function for determining the state. 15. The system of claim 14 wherein said corresponding function determined by said learning logic comprises forms of sub-functions that are included in a given equation, wherein each sub-function represents a dependency between two components linked in the hierarchical model. 16. The system of claim 15 wherein the state determination logic is operable to determine said states that minimize the given equation composed of the sub-functions over the received at least one measured metric. 17. The system of claim 16 wherein said given equation comprises: DL = ∑ k = 1 K ⁢ ⁢ ∑ i = 1 n k ⁢ ⁢ h k , i ⁡ ( s k , s k + 1 ) + ∑ j = 1 n 1 ⁢ ⁢ d j ⁡ ( m j , s 1 ) ;wherein DL is description length;wherein the hierarchical model comprises K layers, with a number, n1, of components in layer 1 that is equal to a number of metrics observed for the at least a portion of the computing system; and a number, nk, of components in layer K is equal to one; and a number, nk, of components in layer k, where 1<k<K, is equal to the number of components in layer k;wherein each component, i, in layer 1 is associated with a function of form di(mi,s), where mi, is an observed value of metric i and s is a state variable; andwherein each component, i, in each layer k is associated with a function of form hk,i(s,t), where S is a state of the component and t is a state of the component to which it is connected in layer k+1. 18. The system of claim 14 wherein said hierarchical model represents a distributed application implemented on the computing system. 19. The system of claim 14 wherein said hierarchical model comprises:a base layer that corresponds to components of the at least a portion of the computing system for which metrics are observed;one or more intermediate layers that correspond to system components that are dependent on one or more of the components of the base layer; andan apex layer that corresponds to the at least a portion of the computing system for which metrics are observed, which is dependent on the components of the preceding layers. 20. The system of claim 14 wherein said learning logic and said state determination logic comprise computer-executable software code stored to computer-readable medium which, when executed by a computer, causes the computer to perform their respective operations.
	summary
048805971	summary	BACKGROUND OF THE INVENTION This invention relates to nuclear fuel elements and, in particular, the provisions of fuel elements with a burnable poison coating in the form of a thin layer of a boron-containing alloy on the inside of a cladding tube. The burnable poison is deposited as an alloy using an electroless nickel-thallium-boron plating process that utilizes boron-containing reducing agents on the inside of a zirconium-alloy cladding tube. A nuclear fuel element of the type involved in the invention is part of a fuel assembly. Heretofore, typically, fuel assembly designs have employed fixed lattice burnable poison rods to control early-in-life reactivity and power peaking. These rods have become a necessary design feature for the fuel management of first cores of light water reactors as well as in schemes to achieve extended burnups and reduced radial neutron leakage. Such rods displace fuel rods within the assembly lattice which increases the core average linear heat generation rate and local peaking factors. Alternate approaches have been proposed that place burnable poison material inside the fuel rods so that much less fuel material is displaced, for example, as boride coatings on the UO.sub.2 pellets. Such coatings, however, while adhering when first applied, tend to spall off under the stresses of the irradiation environment in the nuclear reactor core, in part because of difficulty in matching the thermal expansion behavior of the coating to that of the fission material or UO.sub.2 pellet. Attempts to incorporate boron compounds as mixtures within the UO.sub.2 pellets have not been successful because of volatilization of boron species during high temperature fabrication processes and redistribution of the boron under irradiation. U.S. Pat. No. 3,625,821 discloses an electroplated inside tube coating of a matrix meta and boron compound of, for example, nickel, iron manganese or chrome. Boron nitride (BN), titanium boride (TiB.sub.2) and zirconium boride (ZiB.sub.2) are specifically named. Electroplating boron compounds onto the Zircaloy substrate, as described in U.S. Pat. No. 3,625,821, has been shown to cause the substrate to hydride. This pickup of hydrogen causes the material to embrittle effecting its physical properties. U.S. Pat. No. 4,695,476 shows vapor deposition of volatilized boron compounds on the inside of fuel rod cladding. For further background, see U.S. Pat. Nos. 3,925,151; 4,372,817; 4,560,575; 4,566,989; 4,582,676; 4,587,087; 4,587,088; and 4,636,404. SUMMARY OF THE INVENTION The invention involves an improved fuel element with a burnable poison coating which substantially overcomes problems of spalling and coating integrity because of the closely matched thermal expansion coefficients of the substrate and coating material and the action of fission sintering to enhance adhesion of the coating to the substrate. The invention includes coating a thin layer of a boron-containing alloy on the inside surface of the zirconium alloy cladding tube of the fuel rod. The preferred boron-containing alloy is an electroless nickel-thallium-boron plating or coating known in the art as SAE AMS 2433. It offers a unique combination of hardness, ductility and low coefficient of friction while not having any significant effect on tensile properties of the zirconium alloy cladding tube. The adhesion of the nickel-thallium-boron coating to the zirconium alloy cladding tube is dependent on tube preparation, i.e. minimizing surface contamination. The substrate material is compatible with the coating and adhesion is excellent. Therefore, the coating is less likely to deteriorate under irradiation than would similar coatings on the UO.sub.2 pellets. A suitable thin layer or coating of homogeneous amorphous nickel-thallium-boron on the inside surface of the cladding tube is applied by using a method of electroless plating, or chemical deposition using sodium borohydride reducing agents, on the inside of nuclear fuel rod cladding. The liquid process bath contains nickel, approximately 5 percent by weight boron, 2.5 to 6 percent by weight thallium, and the reducing agents. The boron percent by weight content and isotopic content, together, essentially determine the end product burnable poison characteristics. The boron is preferably initially enriched in the B.sup.10 isotope to a level in the range of 50 to 80 percent by weight, typically 50 percent. (However, both natural and enriched boron will work). Eagle-Picher Industries, Inc., Quapaw, Okla. 74363, enriches the boron by a process of fractional distillation. Boron trifluoride (BF.sub.3) dimethylether complex is dissociated in a fractional distillation column. B.sup.10 F.sub.3 -dimethylether reassociates more readily so that B.sup.11 concentrates in the vapor phase and B.sup.10 concentrates in the liquid phase. Any enrichment of B.sup.10 can be produced by the Eagle-Picher process.
	abstract	System and a method for electrically testing a semiconductor wafer, the method including: (a) scanning a charged particle beam along at least one scan line while maintaining an electrode located at a vicinity of the wafer at a first voltage that differs from a voltage level of a first scanned portion of the wafer, and collecting charged particles scattered from the first scanned portion; (b) scanning a charged particle beam along at least one other scan line while maintaining the electrode at a second voltage that differs from a voltage level of a second scanned portion such as to control a charging state of at least an area that comprises the first and second scanned portions; and (c) repeating the scanning stages until a predefined section of the wafer is scanned.
	claims	1. A system for registering a radiation image, comprising: a radiation pick-up device comprising a charge layer wherein electrical charges are generated dependent on radiation incident on said charge layer, an electrode layer allocated to said charge layer that is chargeable with high-voltage for triggering an electron-multiplying avalanche effect in said charge layer by producing a potential across said charge layer resulting from said high voltage, and a read-out device for reading out charges generated in said charge layer using an electron beam; a reset light source positioned for exposing said charge layer to reset said charge layer to a selected charge level; and a control device connected to said radiation pick-up device, said high voltage being supplied to said electrode layer by said control unit and said control unit varying said high voltage to vary a gain of said charge layer caused by said avalanche effect. 2. A system as claimed in claim 1 wherein said control unit varies said high voltage while radiation is incident on said charge layer. claim 1 3. A system as claimed in claim 2 wherein said control unit varies an amplitude of said high voltage dependent on a dose of said radiation incident on said charge layer. claim 2 4. A system as claimed in claim 1 wherein said electrode layer comprises a film disposed on a carrier. claim 1 5. A system as claimed in claim 4 wherein said carrier is comprised of glass. claim 4 6. A system as claimed in claim 4 wherein said electrode layer is printed on said carrier. claim 4 7. A system as claimed in claim 4 wherein said electrode layer comprises a plurality of substantially parallel layer strips spaced from each other. claim 4 8. A system as claimed in claim 1 wherein said read-out device is a flat emitter device. claim 1 9. A system as claimed in claim 8 wherein said flat emitter device comprises a plurality of electron emitter cathodes having deflection electrodes respectively allocated thereto. claim 8 10. A system as claimed in claim 8 wherein said flat emitter device comprises micro-structured electron emitter cathodes. claim 8 11. A system as claimed in claim 10 wherein said micro-structured electron emitter cathodes are arranged in a matrix. claim 10 12. A system as claimed in claim 10 wherein said micro-structured electron emitter cathodes are arranged in an array. claim 10 13. A system as claimed in claim 8 comprising a vacuum housing with fiat housing walls in which said radiation pick-up device is disposed, said housing walls having stabilization elements thereon. claim 8 14. A system as claimed in claim 13 wherein said stabilization elements comprise structural webs. claim 13 15. A system as claimed in claim 1 wherein said reset light source is connected to and is controlled by said control device. claim 1 16. A system as claimed in claim 15 wherein said control device operates said reset light source in a pulsed manner. claim 15
050892185	claims	1. A water cooled nuclear reactor comprising a pressure vessel, a reactor core, a primary water coolant circuit, a pressurizer, the reactor core and at least a portion of the primary water coolant circuit being located in a pressure vessel, the primary water coolant circuit being arranged to cool the reactor core, the pressurizer having a diaphragm and a pressurizer pressure vessel, the diaphragm being movable and being sealingly secured to the pressurizer pressure vessel to divide the pressurizer pressure vessel into a first water space and a second fluid space, the second fluid space being arranged to contain a gas, and at least one surge port means which communicates between the pressurizer and the primary water coolant circuit to connect the first space of the pressurizer with the primary water coolant circuit, the diaphragm being movable so as to allow changes in the volume or pressure of the water in the first space of the pressurizer and the primary water coolant circuit, sealing means interconnecting and securing the diaphragm to said pressurizer pressure vessel to form a seal and for allowing relative movement between said diaphragm and said pressurizer pressure vessel. 2. A water cooled nuclear reactor as claimed in claim 1 in which the reactor core, the primary water coolant circuit and the pressurizer are arranged as an integral unit enclosed by an integral pressure vessel, at least one casing being located in the integral pressure vessel to substantially divide the integral pressure vessel into a first chamber and a second chamber, the pressurizer being located in the first chamber, the reactor core and the primary water coolant circuit being located in the second chamber. 3. A water cooled nuclear reactor comprising a pressure vessel, a reactor core, a primary water coolant circuit, a pressurizer, the reactor core and at least a portion of the primary water coolant circuit being located in a pressure vessel, the primary water coolant circuit being arranged to cool the reactor core, the presurizer having a diaphragm and a pressurizer pressure vessel, the diaphragm being movable and being sealingly secured to the pressurizer pressure vessel to divide the pressurizer pressure vessel into a first water space and a second fluid space, the second fluid space being arranged to contain a gas, and at least one surge port means which communicates between the pressurizer and the primary water coolant circuit to connect the first space of the pressurizer with the primary water coolant circuit, the diaphragm being movable so a to allow changes in the volume or pressure of the water in the first space of the pressurizer and the primary water coolant circuit, the reactor core, the primary water coolant circuit and the pressurizer being arranged as an integral unit enclosed by an integral pressure vessel, at least one casing being located in the integral pressure vessel to substantially divide the integral pressure vessel into a first chamber and a second chamber, the pressurizer being located in the first chamber, the reactor core and the primary water coolant circuit being located in the second chamber. 4. A water cooled nuclear reactor as claimed in claim 2 in which the casing divides the pressure vessel into a first vertically upper chamber and a second vertically lower chamber. 5. A water cooled nuclear reactor as claimed in claim 4 in which the casing comprises an annular member which extends downwards from the peripheral region thereof, the annular member being sealingly secured to the pressure vessel to form an annular lower portion of the first water space. 6. A water cooled nuclear reactor as claimed in claim 2 or 3 in which the casing comprises an annular member which is sealingly secured to and extends downwards from the pressure vessel, the annular member having the at least one surge port means at its lower end. 7. A water cooled nuclear reactor as claimed in claim 1 or 3 in which the diaphragm is sealingly secured to the pressure vessel by bellow means. 8. A water cooled nuclear reactor as claimed in claim 6 in which the diaphragm is sealingly secured to the casing by bellow means. 9. A water cooled nuclear reactor as claimed in claim 1 or 3 in which the diaphragm is spring loaded. 10. A water cooled nuclear reactor as claimed in claim 6 in which the bellow means comprises a spring. 11. A water cooled nuclear reactor as claimed in claim 1 or 3 in which the diaphragm has damper means. 12. A water cooled nuclear reactor as claimed in claim 11 in which the diaphragm has at least one rod and piston, the casing having at least one cylinder, the at least one rod and piston being arranged to move coaxially within the cylinder to damp oscillations of the diaphragm. 13. A water cooled nuclear reactor as claimed in claim 7 in which the bellow means are arranged to expand with an increase in the volume or pressure of the water. 14. A water cooled nuclear reactor as claimed in claim 7 in which the bellow means are arranged to contract with an increase in the volume or pressure of the water. 15. A water cooled nuclear reactor as claimed in claim 2 or 3 in which the reactor core is arranged in the lower region of the second chamber, the primary water coolant circuit comprising a riser passage to convey relatively hot water to a heat exchanger, and a downcomer passage to convey relatively cool water from the heat exchanger to the reactor core. 16. A water cooled nuclear reactor as claimed in claim 15 in which the riser passage is defined by a hollow cylindrical member, the downcomer passage being defined between the hollow cylindrical member and the pressure vessel. 17. A water cooled nuclear reactor as claimed in claim 15 in which the heat exchanger is positioned in an upper region of the downcomer passage. 18. A water cooled nuclear reactor as claimed in claim 6 in which the reactor core is positioned in the lower region of the second chamber, the primary water coolant circuit comprising a riser passage defined by a hollow cylindrical member to convey relatively hot water to a heat exchanger, and a downcomer passage defined between the hollow cylindrical member and the pressure vessel to convey relatively cool water from the heat exchanger to the reactor core. 19. A water cooled nuclear reactor as claimed in claim 18 in which the casing is positioned coaxially with the hollow cylindrical member, the casing extending downwards from the pressure vessel into the hollow cylindrical member. 20. A water cooled nuclear reactor as claimed in claim 1 or 3 in which the pressure vessel has a vent to inter-connect the second fluid space with atmosphere. 21. A water cooled nuclear reactor as claimed in claim 20 in which the vent has a relief valve and the space between the diaphragm and the relief valve is filled with a predetermined mass of gas. 22. A water cooled nuclear reactor as claimed in claim 1 or 3 in which the diaphragm is an elastic membrane. 23. A pressurizer for a water cooled nuclear reactor comprising a pressure vessel, a diaphragm, the diaphragm being movable and being sealingly secured to the pressure vessel to divide the pressure vessel into a first space and a second space, sealing means being provided to interconnect and secure said diaphragm to the pressure vessel to form a seal and to allow relative movement between the diaphragm and the pressure vessel, the first space being arranged to interconnect with the water cooled nuclear reactor for the supply of water therebetween, the second space being arranged to contain a gas, the diaphragm being movable so as to allow changes in the volume or pressure of the water in the first space of the pressurizer and the water cooled nuclear reactor. 24. A pressurizer for a water cooled nuclear reactor comprising a pressure vessel, a diaphragm, the diaphragm being movable and being sealingly secured to the pressure vessel to divide the pressure vessel into a first space and a second space, the first space being arranged to interconnect with a water cooled nuclear reactor for the supply of water therebetween, the second space being arranged to contain gas, the diaphragm being movable so as to allow changes in the volume or pressure of the water in the first space of the pressurizer and the water cooled nuclear reactor, said diaphragm being sealingly secured to the pressure vessel by bellows means. 25. A pressurizer as claimed in claim 23 in which the diaphragm is sealingly secured to the pressure vessel by bellow means. 26. A pressurizer as claimed in claim 23 or 24 in which the diaphragm is spring loaded. 27. A pressurizer as claimed in claim 25 in which the bellow means comprises a spring. 28. A pressurizer as claimed in claim 23 or 24 in which the diaphragm has damper means. 29. A pressurizer as claimed in claim 25 in which the bellow means are arranged to expand with an increase in the volume or pressure of the water. 30. A pressurizer as claimed in claim 25 in which the bellow means are arranged to contract with an increase in the volume or pressure of the water. 31. A pressurizer as claimed in claim 23 or 24 in which the pressure vessel has a vent to interconnect the second space with atmosphere. 32. A pressurizer as claimed in claim 31 in which the vent has a relief valve. 33. A pressurizer as claimed in claim 23 or 24 in which the diaphragm is an elastic membrane.
	description	This patent claims priority to U.S. Provisional Patent Application Ser. No. 62/627,473, filed Feb. 7, 2018, entitled “X-Ray Detectors for Generating Digital Images,” U.S. Provisional Patent Application Ser. No. 62/627,469, filed Feb. 7, 2018, entitled “Systems and Methods for Digital X-Ray Imaging,” U.S. Provisional Patent Application Ser. No. 62/627,464, filed Feb. 7, 2018, entitled “Systems and Methods for Digital X-Ray Imaging,” and U.S. Provisional Patent Application Ser. No. 62/627,466, filed Feb. 7, 2018, entitled “Radiography Backscatter Shields and X-Ray Imaging Systems Including Backscatter Shields.” The entireties of U.S. Provisional Patent Application Ser. No. 62/627,473, U.S. Provisional Patent Application Ser. No. 62/627,469, U.S. Provisional Patent Application Ser. No. 62/627,464, and U.S. Provisional Patent Application Ser. No. 62/627,466 are incorporated herein by reference. This disclosure relates generally to radiography, and more particularly, to radiography backscatter shields and X-ray imaging systems including backscatter shields. Radiography backscatter shields and X-ray imaging systems including backscatter shields are disclosed, substantially as illustrated by and described in connection with at least one of the figures, as set forth more completely in the claims. The figures are not necessarily to scale. Wherever appropriate, similar or identical reference numerals are used to refer to similar or identical components. Disclosed example backscatter shielding devices for handheld X-ray imaging equipment reduce the radiation dosage to the operator caused by radiation scattering back from the scanned object. Disclosed backscatter shields include conforming shielding material to enable the backscatter shield to make close contact with the object to be radiographically scanned or tested. The contours of the shielding material may be tailored to the contours of the object being tested. In some examples, a backscatter shielding device includes a triggering device for a complementary switch on the imaging equipment. The triggering device, when detected by the switch, enables operation of the imaging equipment. Thus, disclosed examples ensure proper installation of the backscatter shielding device prior to use of the imaging equipment, which improves operator safety by reducing the radiation dose to the operator. As used herein, the term “real-time” refers to the actual time elapsed in the performance of a computation by a computing device, the result of the computation being required for the continuation of a physical process (i.e., no significant delays are introduced). For example, real-time display of captured images includes processing captured image data and displaying the resulting output images to create the perception to a user that the images are displayed immediately upon capture. As used herein, the term “portable” includes handheld (e.g., capable of being carried and operated by a single person) and/or wheeled (e.g., capable of being transported and operated while wheels are attached and/or placed on wheels). Disclosed example backscatter shielding devices include: a conforming backscatter shield configured to provide shielding from Compton scatter radiation when placed in contact with an object to be scanned; and a shield frame configured to couple the backscatter shield to an X-ray source. In some examples, the backscatter shield includes a first end and a second end having a contour corresponding to an outer surface of the object to be scanned. In some examples, the backscatter shield includes silicone blended with a shielding material. In some examples, the shielding material is at least one of bismuth, tungsten, lead or iron. In some examples, the X-ray shield includes a plate embedded within the backscatter shield, the plate configured to attach the backscatter shield to the shield frame. In some examples, the plate is configured to detachably attach the backscatter shield to the shield frame. In some examples, the shield frame includes an X-ray source attachment rail configured to mount the shield frame to the X-ray source, and a switch actuator configured to activate a switch in the X-ray source when the shield frame is fully mounted to the X-ray source. In some examples, the switch includes at least one of a mechanical switch, a capacitive sensor, an inductive sensor, a magnetic sensor, or an optical sensor. Disclosed example portable X-ray scanners, include: an X-ray detector configured to generate images based on incident X-ray radiation; an X-ray tube configured to output X-ray radiation; and a frame configured to: hold the X-ray detector; hold the X-ray tube such that the X-ray tube directs the X-ray radiation to the X-ray detector; and enable attachment of a Compton scatter shielding device to the frame. Some example portable X-ray scanners further include a switch configured to detect attachment of the shielding device to the frame and enable activation of the X-ray tube in response to detecting the attachment of the shielding device. Some examples further include a collimator configured to filter the output of the X-ray radiation, in which the switch is configured to detect attachment of the shielding device adjacent the collimator. In some examples, the switch includes a sensor configured to detect the presence of the shielding device. In some examples, the sensor iat least one of a mechanical switch, a capacitive sensor, an inductive sensor, a magnetic sensor, or an optical sensor. In some examples, the switch is configured to enable activation of the X-ray tube based on whether the X-ray tube is configured to use a tube voltage that satisfies a threshold tube voltage. In some examples, the threshold tube voltage is 70 kV, and the switch is configured to disable the X-ray tube when the X-ray tube is configured to use at least the threshold tube voltage and attachment of the shielding device to the frame is not detected. In some examples, the frame includes an attachment rail configured to hold the shielding device. Disclosed example portable X-ray scanners include: an X-ray detector configured to generate images based on incident X-ray radiation; an X-ray tube configured to output X-ray radiation; and a frame configured to: hold the X-ray detector; hold the X-ray tube such that the X-ray tube directs the X-ray radiation to the X-ray detector; and a backscatter shield configured to provide shielding from Compton scatter radiation when placed in contact with an object to be scanned. Disclosed example X-ray scanners further include a switch configured to detect attachment of the backscatter shield to the frame and enable activation of the X-ray tube in response to detecting the attachment of the backscatter shield. In some examples, the switch is configured to enable activation of the X-ray tube based on whether the X-ray tube is configured to use a tube voltage that satisfies a threshold tube voltage. In some examples, the threshold tube voltage is 70 kV, and the switch is configured to disable the X-ray tube when the X-ray tube is configured to use at least the threshold tube voltage and attachment of the shielding device to the frame is not detected. FIG. 1 is a perspective view of an example handheld X-ray imaging system 100 to generate and output digital images and/or video based on incident X-rays. The example handheld X-ray imaging system 100 may be used to perform non-destructive testing (NDT), medical scanning, security scanning, and/or any other scanning application. The system 100 of FIG. 1 includes a frame 102 that holds an X-ray generator 104 and an X-ray detector 106. In the example of FIG. 1, the frame 102 is C-shaped, such that the X-ray generator 104 directs X-ray radiation toward the X-ray detector 106. As described in more detail below, the frame 102 is positionable (e.g., held by an operator, supported by an external support structure and/or manipulated by the operator, etc.) around an object to be scanned with X-rays. The example frame 102 is constructed using carbon fiber and/or machined aluminum. The X-ray generator 104 is located on a first section 108 of the C-shaped frame 102 generates and outputs X-ray radiation, which traverses and/or scatters based on the state of the object under test. The X-ray detector 106 is located on a second section 110 of the frame 102 (e.g., opposite the first section 108) and receives incident radiation generated by the X-ray generator 104. The example frame 102 may be manipulated using one or more handles 112, 114. A first one of the handles 112 is an operator control handle, and enables an operator to both mechanically manipulate the frame 102 and control the operation of the handheld X-ray imaging system 100. A second one of the handles 114 is adjustable and may be secured to provide the operator with leverage to manipulate the frame 102. The example handle 114 may be oriented with multiple degrees of freedom and/or adjusted along a length of a central section 116 of the frame 102. During operation, the handheld X-ray imaging system 100 generates digital images (e.g., digital video and/or digital still images) from the X-ray radiation. The handheld X-ray imaging system 100 may store the digital images on one or more storage devices, display the digital images on a display device 118, and/or transmit the digital images to a remote receiver. The example display device 118 is attachable to the example frame 102 and/or may be oriented for viewing by the operator. The display device 118 may also be detached from the frame 102. When detached, the display device 118 receives the digital images (e.g., still images and/or video) via a wireless data connection. When attached, the display device 118 may receive the digital images via a wired connection and/or a wireless connection. A power supply 120, such as a detachable battery, is attached to the frame 102 and provides power to the X-ray generator 104, the X-ray detector 106, and/or other circuitry of the handheld X-ray imaging system 100. An example power supply 120 that may be used is a lithium-ion battery pack. The display device 118 may receive power from the power supply 120 and/or from another power source such as an internal battery of the display device 118. The example central section 116 of the frame 102 is coupled to the first section 108 via a joint 122 and to the second section 110 via a joint 124. The example joints 122, 124 are hollow to facilitate routing of cabling between the sections 108, 110, 116. The joints 122, 124 enable the first section 108 and the second section 110 to be folded toward the center section to further improve the compactness of the handheld X-ray imaging system 100 when not in use (e.g., during storage and/or travel). FIG. 2 is a block diagram of an example digital X-ray imaging system 200 that may be used to implement the handheld X-ray imaging system 100 of FIG. 1. The example digital X-ray imaging system 200 of FIG. 2 includes a frame 202 holding an X-ray generator 204, an X-ray detector 206, a computing device 208, a battery 210, one or more display device(s) 212, one or more operator input device(s) 214, and one or more handle(s) 216. The X-ray generator 204 includes an X-ray tube 218, a collimator 220, and a shield switch 222. The X-ray tube 218 generates X-rays when energized. In some examples, the X-ray tube 218 operates at voltages between 40 kV and 120 kV. In combination with a shielding device, X-ray tube voltages between 70 kV and 120 kV may be used while staying within acceptable X-ray dosage limits for the operator. Other voltage ranges may also be used. The collimator 220 filters the X-ray radiation output by the X-ray tube 218 to more narrowly direct the X-ray radiation at the X-ray detector 206 and any intervening objects. The collimator 220 reduces the X-ray dose to the operator of the system 200, reduces undesired X-ray energies to the detector 206 resulting from X-ray scattering, and/or improves the resulting digital image generated at the X-ray detector 206. The shield switch 222 selectively enables and/or disables the X-ray tube 218 based on whether a backscatter shielding device 224 is attached to the frame. The backscatter shielding device 224 reduces the dose to the operator holding the frame 202 by providing shielding between the collimator 220 and an object under test. The example backscatter shielding device 224 includes a switch trigger configured to trigger the shield switch 222 when properly installed. For example, the shield switch 222 may be a reed switch or similar magnetically-triggered switch, and the backscatter shielding device 224 includes a magnet. The reed switch and magnet are respectively positioned on the frame 202 and the backscatter shielding device 224 such that the magnet triggers the reed switch when the backscatter shielding device 224 is attached to the frame 202. The shield switch 222 may include any type of a capacitive sensor, an inductive sensor, a magnetic sensor, an optical sensor, and/or any other type of proximity sensor. The shield switch 222 is configured to disable the X-ray tube 218 when the backscatter shielding device 224 is not installed. The shield switch 222 may be implemented using, for example, hardware circuitry and/or via software executed by the computing device 208. In some examples, the computing device 208 may selectively override the shield switch 222 to permit operation of the X-ray tube 218 when the backscatter shielding device 224 is not installed. The override may be controlled by an administrator or other authorized user. The X-ray detector 206 of FIG. 2 generates digital images based on incident X-ray radiation (e.g., generated by the X-ray tube 218 and directed toward the X-ray detector 206 by the collimator 220). The example X-ray detector 206 includes a detector housing 226, which holds a scintillation screen 228, a reflector 230, and a digital imaging sensor 232. The scintillation screen 228, the reflector 230, and the digital imaging sensor 232 are components of a fluoroscopy detection system 234. The example fluoroscopy detection system 234 is configured so that the digital imaging sensor 232 (e.g., a camera, a sensor chip, etc.) receives the image indirectly via the scintillation screen 228 and the reflector 230. In other examples, the fluoroscopy detection system 234 includes a sensor panel (e.g., a CCD panel, a CMOS panel, etc.) configured to receive the X-rays directly, and to generate the digital images. In some other examples, the scintillation screen 228, may be replaced with a solid state panel that is coupled to the scintillation screen 228 and has pixels that correspond to portions of the scintillation screen 228. Example solid state panels may include CMOS X-ray panels and/or CCD X-ray panels. The computing device 208 controls the X-ray tube 218, receives digital images from the X-ray detector 206 (e.g., from the digital imaging sensor 232), and outputs the digital images to the display device 212. Additionally or alternatively, the computing device 208 may store digital images to a storage device. The computing device 208 may output the digital images as digital video to aid in real-time non-destructive testing and/or store digital still images. As mentioned above, the computing device 208 may provide the digital images to the display device(s) 212 via a wired connection or a wireless connection. To this end, the computing device 208 includes wireless communication circuitry. For example, the display device(s) 212 may be detachable from the frame 202 and held separately from the frame 202 while the computing device 208 wirelessly transmits the digital images to the display device(s) 212. The display device(s) 212 may include a smartphone, a tablet computer, a laptop computer, a wireless monitoring device, and/or any other type of display device equipped with wired and/or wireless communications circuitry to communicate with (e.g., receive digital images from) the computing device 208. In some examples, the computing device 208 adds data to the digital images to assist in subsequent analysis of the digital images. Example data includes a timestamp, a date stamp, geographic data, or a scanner inclination. The example computing device 208 adds the data to the images by adding metadata to the digital image file(s) and/or by superimposing a visual representation of the data onto a portion of the digital images. The operator input device(s) 214 enable the operator to configure and/or control the example digital X-ray imaging system 200. For example, the operator input device(s) 214 may provide input to the computing device 208, which controls operation and/or configures the settings of the digital X-ray imaging system 200. Example operator input device(s) 214 include a trigger (e.g., for controlling activation of the X-ray tube 218), buttons, switches, analog joysticks, thumbpads, trackballs, and/or any other type of user input device. The handle(s) 216 are attached to the frame 202 and enable physical control and manipulation of the frame 202, the X-ray generator 204, and the X-ray detector 206. In some examples, one or more of the operator input device(s) 214 are implemented on the handle(s) 216 to enable a user to both physically manipulate and control operation of the digital X-ray imaging system 200. FIG. 3A is a perspective view of an example backscatter shielding device 300 to provide shielding against backscatter during handheld radiography. The example backscatter shielding device 300 may implement the backscatter shielding device 224 in the system 200 of FIG. 2. FIG. 3B is a front elevation view of the backscatter shielding device 300. FIG. 3C is a left-side elevation view of the backscatter shielding device 300, and FIG. 3D is a right-side elevation view of the backscatter shield. FIG. 3E is a top plan view of the backscatter shielding device 300, and FIG. 3F is a bottom plan view of the backscatter shielding device 300. FIG. 3G is a rear elevation view of the backscatter shielding device 300. The example backscatter shielding device 300 includes a conforming backscatter shield 302 and a shield frame 304. The backscatter shield 302 provides shielding from Compton scatter radiation when placed in contact with an object to be scanned. The shield frame 304 couples the backscatter shield 302 to the X-ray source (e.g., to the frame 102 holding the X-ray generator 104). The example backscatter shield 302 of FIG. 3A-3G at least partially conforms to a surface of the object to be scanned (e.g., on a first end of the backscatter shield 302) and/or to a portion of the frame 102 when installed (e.g., on a second end of the backscatter shield 302). The conformance by the backscatter shield 302 improves the shielding by reducing or eliminating gaps between the object to be scanned and the shield 302. In the illustrated example, the backscatter shield 302 has a curved or contoured surface on the second end to conformably engage a corresponding curved or contoured surface of the object. To couple the shield frame 304 to the frame 102, the example shield frame 304 includes rail slides 306, which fit within respective rail slots of the frame 102. A spring-loaded plunger 308 enables the shield frame 304 to be secured to the frame 102. The shield frame 304 includes a switch actuator (e.g., a magnet) to indicate to the shield switch 222 (e.g., a reed switch) that the backscatter shielding device 300 is properly installed. The switch actuator may be positioned at any appropriate location, in or on the backscatter shield 302 and/or the frame 304, where the backscatter shield 302 or the shield frame 304 is adjacent the frame 102 in a fully installed position. The shield switch 222 and the switch actuator are installed in complementary locations in the frame 102 and the shield frame 304 and/or the backscatter shield 302. The example backscatter shield 302 of FIG. 3 includes silicone blended with a shielding material. The shielding material may include bismuth, tungsten, lead and/or iron, and/or any other radiation shielding material. The example silicone is a high-wear blend, such as silicone 940. To facilitate coupling of the backscatter shield 302 to the shield frame 304, the example backscatter shield 302 includes plates embedded within the backscatter shield 302. The plates may be screwed, bolted, or otherwise attached to the shield frame 304. Example screws 310 to couple the backscatter shield 302 to the shield frame 304 are illustrated. Additionally or alternatively, the backscatter shield 302 may be attached to the shield frame 304 via adhesives such as glue or epoxy. FIG. 4 illustrates the example backscatter shielding device 300 of FIG. 3 installed on the example handheld X-ray imaging system of FIG. 1. FIG. 5 illustrates the example handheld X-ray imaging system of FIG. 1, with the backscatter shielding device 300 of FIG. 3 installed, during imaging of an object under test 502 by directing X-rays 504 from the X-ray tube 218 to the X-ray detector 106. The backscatter shielding device 300 is installed on the frame 102 by sliding the rail slides 306 into corresponding rails on the frame 102, until a stop surface (e.g., the bottom of the shield frame 304) meets a stop surface on the frame 102. Other techniques of reliably positioning the backscatter shielding device 300 may be used. As mentioned above, the collimator 220 reduces X-ray radiation that is not directed at the X-ray detector 106, so the concentration of the X-ray radiation 504 that is not scattered by the object 502 is incident on the X-ray detector 106. The backscatter shielding device 300 conforms to the object 502 such that the backscatter shielding device 300 and the object 502 enclose and/or shield backscattered Compton scatter radiation. For example, the backscatter shield 302 conforms to the surface of the object 502, and the object contacts or nearly contacts the frame 102. The example backscatter shield 302 is positioned in the primary pathways for Compton scatter radiation to reach an operator, thereby substantially reducing the Compton scatter dose received by the operator and/or increasing the power that may be used to drive the X-ray tube 218. FIG. 6 illustrates another example backscatter shielding device 600 installed on the example handheld X-ray imaging system 100 of FIG. 1. The example backscatter shielding device 600 is substantially identical to the backscatter shielding device 300 of FIGS. 3A-3G, 4, and 5, except that the backscatter shielding device 600 is configured to more closely conform to flat objects than to curved objects as with the backscatter shielding device 300. To this end, the backscatter shielding device 600 includes an backscatter shield 602 and a shield frame 604. The shield frame 604 is identical to the example shield frame 304 and/or may be implemented as in any of the examples described above with reference to the shield frame 304. The backscatter shield 602 is also identical to the example backscatter shield 302, with the exception of the contour of the end making contact with the object. As mentioned above, the backscatter shield 602 has a flat contour to better conform to flat objects. FIG. 7 illustrates the example handheld X-ray imaging system 100 of FIG. 1, with the backscatter shield 600 of FIG. 6 installed, during imaging of another example object under test 702 by directing X-rays 704 from the X-ray tube 218 to the X-ray detector 106. FIG. 8 is a flowchart representative of example machine readable instructions 800 which may be executed by the example computing device 208 of FIG. 2 to perform digital X-ray imaging. The example machine readable instructions 800 of FIG. 8 are described below with reference to the digital X-ray imaging system 200 of FIG. 2, but may be performed by the digital X-ray imaging system 100 of FIG. 1. At block 802, the example computing device 208 initializes the X-ray detector 206. For example, the computing device 208 may verify that the X-ray detector 206 is in communication with the computing device 208 and/or is configured to capture digital images of X-ray radiation. At block 803, an operator of the digital X-ray imaging system 200 may position the frame 202 adjacent on object under test, such that the object under test is located between the X-ray detector 206 and the X-ray tube 218. At block 804, the computing device 208 determines whether a trigger is activated. For example, the computing device 208 may activate the X-ray tube 218 in response to activation of a trigger (e.g., a physical trigger, a button, a switch, etc.) by an operator. If the trigger has not been activated (block 804), control returns to block 804 to await activation of the trigger. When the trigger is activated (block 804), at block 805 the computing device 208 determines whether the X-ray tube voltage is at least a threshold voltage. An example threshold is 70 kV. For example, the X-ray tube voltage may be configured to be between 70 kV and 120 kV, in which case the computing device 208 requires the backscatter shielding device 224 to be detected (e.g., via the shield switch 222). If the X-ray tube voltage is at least the threshold (block 805), at block 806 the computing device 208 determines whether a backscatter shield is detected. For example, the computing device 208 may determine whether the backscatter shield (e.g., the backscatter shielding device 224, the backscatter shielding device 300, the backscatter shield 600) is installed using the shield switch 222. If the backscatter shield is not detected (block 806), at block 808 the computing device 208 disables the X-ray tube 218 and outputs a backscatter shield alert (e.g., via a visual and/or audible alarm, via the display device 212, etc.). Control then returns to block 804. If the backscatter shield is detected (block 806), or if the X-ray tube voltage is less than the threshold (block 805), at block 810 the X-ray tube 218 generates and outputs X-ray radiation. At block 812, the X-ray detector 106 (e.g., via the scintillation screen 228, the reflector 230, and the digital imaging sensor 232, and/or via a solid state panel coupled to a scintillator) captures digital image(s) (e.g., digital still images and/or digital video). The X-ray detector 106 provides the captured digital image(s) to the computing device 208. At block 814, the computing device 208 adds the auxiliary data to the digital image(s). Example auxiliary data includes a timestamp, a date stamp, geographic data, and/or an inclination of the frame 202, the X-ray detector 206, the X-ray tube 218, and/or any other component of the digital X-ray imaging system 200. At block 816, the computing device 208 outputs the digital image(s) to the display device(s) 218 (e.g., via a wired and/or wireless connection). In some examples, the computing device 208 outputs the digital image(s) to an external computing device such as a laptop, a smartphone, a server, a tablet computer, a personal computer, and/or any other type of external computing device. At block 818, the computing device 208 determines whether the digital image(s) are to be stored (e.g., in a storage device). If the digital image(s) are to be stored (block 818), at block 820 the example computing device 208 stores the image(s). The example computing device 208 may be configured to store the digital image(s) in one or more available storage devices, such as a removable storage device. After storing the image(s) (block 820), or if the digital image(s) are not to be stored (block 818), control returns to block 804. In some examples, blocks 810-820 may be iterated substantially continuously until the trigger is deactivated. FIG. 9 is a block diagram of an example computing system 900 that may be used to implement the computing device 208 of FIG. 2. The example computing system 900 may be implemented using a personal computer, a server, a smartphone, a laptop computer, a workstation, a tablet computer, and/or any other type of computing device. The example computing system 900 of FIG. 9 includes a processor 902. The example processor 902 may be any general purpose central processing unit (CPU) from any manufacturer. In some other examples, the processor 902 may include one or more specialized processing units, such as RISC processors with an ARM core, graphic processing units, digital signal processors, and/or system-on-chips (SoC). The processor 902 executes machine readable instructions 904 that may be stored locally at the processor (e.g., in an included cache or SoC), in a random access memory 906 (or other volatile memory), in a read only memory 908 (or other non-volatile memory such as FLASH memory), and/or in a mass storage device 910. The example mass storage device 910 may be a hard drive, a solid state storage drive, a hybrid drive, a RAID array, and/or any other mass data storage device. A bus 912 enables communications between the processor 902, the RAM 906, the ROM 908, the mass storage device 910, a network interface 914, and/or an input/output interface 916. The example network interface 914 includes hardware, firmware, and/or software to connect the computing system 900 to a communications network 918 such as the Internet. For example, the network interface 914 may include IEEE 902.X-compliant wireless and/or wired communications hardware for transmitting and/or receiving communications. The example I/O interface 916 of FIG. 9 includes hardware, firmware, and/or software to connect one or more input/output devices 920 to the processor 902 for providing input to the processor 902 and/or providing output from the processor 902. For example, the I/O interface 916 may include a graphics processing unit for interfacing with a display device, a universal serial bus port for interfacing with one or more USB-compliant devices, a FireWire, a field bus, and/or any other type of interface. Example I/O device(s) 920 may include a keyboard, a keypad, a mouse, a trackball, a pointing device, a microphone, an audio speaker, an optical media drive, a multi-touch touch screen, a gesture recognition interface, a display device (e.g., the display device(s) 118, 212) a magnetic media drive, and/or any other type of input and/or output device. The example computing system 900 may access a non-transitory machine readable medium 922 via the I/O interface 916 and/or the I/O device(s) 920. Examples of the machine readable medium 922 of FIG. 9 include optical discs (e.g., compact discs (CDs), digital versatile/video discs (DVDs), Blu-ray discs, etc.), magnetic media (e.g., floppy disks), portable storage media (e.g., portable flash drives, secure digital (SD) cards, etc.), and/or any other type of removable and/or installed machine readable media. Example wireless interfaces, protocols, and/or standards that may be supported and/or used by the network interface(s) 914 and/or the I/O interface(s) 916, such as to communicate with the display device(s) 212, include wireless personal area network (WPAN) protocols, such as Bluetooth (IEEE 802.15); near field communication (NFC) standards; wireless local area network (WLAN) protocols, such as WiFi (IEEE 802.11); cellular standards, such as 2 G/2 G+ (e.g., GSM/GPRS/EDGE, and IS-95 or cdmaOne) and/or 2 G/2 G+ (e.g., CDMA2000, UMTS, and HSPA); 4 G standards, such as WiMAX (IEEE 802.16) and LTE; Ultra-Wideband (UWB); etc. Example wired interfaces, protocols, and/or standards that may be supported and/or used by the network interface(s) 914 and/or the I/O interface(s) 916, such as to communicate with the display device(s) 212, include comprise Ethernet (IEEE 802.3), Fiber Distributed Data Interface (FDDI), Integrated Services Digital Network (ISDN), cable television and/or internet (ATSC, DVB-C, DOCSIS), Universal Serial Bus (USB) based interfaces, etc. The processor 202, the network interface(s) 914, and/or the I/O interface(s) 916, and/or the display device 212, may perform signal processing operations such as, for example, filtering, amplification, analog-to-digital conversion and/or digital-to-analog conversion, up-conversion/down-conversion of baseband signals, encoding/decoding, encryption/decryption, modulation/demodulation, and/or any other appropriate signal processing. The computing device 208 and/or the display device 212 may use one or more antennas for wireless communications and/or one or more wired port(s) for wired communications. The antenna(s) may be any type of antenna (e.g., directional antennas, omnidirectional antennas, multi-input multi-output (MIMO) antennas, etc.) suited for the frequencies, power levels, diversity, and/or other parameters required for the wireless interfaces and/or protocols used to communicate. The port(s) may include any type of connectors suited for the communications over wired interfaces/protocols supported by the computing device 208 and/or the display device 212. For example, the port(s) may include an Ethernet over twisted pair port, a USB port, an HDMI port, a passive optical network (PON) port, and/or any other suitable port for interfacing with a wired or optical cable. The present methods and systems may be realized in hardware, software, and/or a combination of hardware and software. The present methods and/or systems may be realized in a centralized fashion in at least one computing system, or in a distributed fashion where different elements are spread across several interconnected computing systems. Any kind of computing system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software may include a general-purpose computing system with a program or other code that, when being loaded and executed, controls the computing system such that it carries out the methods described herein. Another typical implementation may comprise an application specific integrated circuit or chip. Some implementations may comprise a non-transitory machine-readable (e.g., computer readable) medium (e.g., FLASH drive, optical disk, magnetic storage disk, or the like) having stored thereon one or more lines of code executable by a machine, thereby causing the machine to perform processes as described herein. As used herein, the term “non-transitory machine-readable medium” is defined to include all types of machine readable storage media and to exclude propagating signals. As utilized herein the terms “circuits” and “circuitry” refer to physical electronic components (i.e. hardware) and any software and/or firmware (“code”) which may configure the hardware, be executed by the hardware, and or otherwise be associated with the hardware. As used herein, for example, a particular processor and memory may comprise a first “circuit” when executing a first one or more lines of code and may comprise a second “circuit” when executing a second one or more lines of code. As utilized herein, “and/or” means any one or more of the items in the list joined by “and/or”. As an example, “x and/or y” means any element of the three-element set {(x), (y), (x, y)}. In other words, “x and/or y” means “one or both of x and y”. As another example, “x, y, and/or z” means any element of the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. In other words, “x, y and/or z” means “one or more of x, y and z”. As utilized herein, the term “exemplary” means serving as a non-limiting example, instance, or illustration. As utilized herein, the terms “e.g.,” and “for example” set off lists of one or more non-limiting examples, instances, or illustrations. As utilized herein, circuitry is “operable” to perform a function whenever the circuitry comprises the necessary hardware and code (if any is necessary) to perform the function, regardless of whether performance of the function is disabled or not enabled (e.g., by a user-configurable setting, factory trim, etc.). While the present method and/or system has been described with reference to certain implementations, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present method and/or system. For example, block and/or components of disclosed examples may be combined, divided, re-arranged, and/or otherwise modified. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. Therefore, the present method and/or system are not limited to the particular implementations disclosed. Instead, the present method and/or system will include all implementations falling within the scope of the appended claims, both literally and under the doctrine of equivalents.
	abstract	Methods are disclosed for calculating cumulative exposure energy from a microlithography reticle, especially a reticle used for charged-particle-beam (CPB) microlithography. The methods provide an accuracy of results at least as high as conventional methods, but the subject methods can be performed using substantially less calculation time, even for complex patterns. The pattern features contained within a region and/or one or more size parameters of the region are evaluated according to specified rules. The region also is subdivided according to the specified rules. Subdivision produces subregions that also are evaluated according to the rules to determine whether to subdivide further or to cease further subdivision. The result is a branching structure for the region, containing multiple levels of subregions arranged in an hierarchical manner. As a result, e.g., a subregion distant from a cumulative-energy evaluation point (and that has little effect on the distribution position of elements therein) can be left relatively large, whereas a subregion near the evaluation point has a relatively large effect on the distribution position of the elements therein and hence is relatively small. From the branching structure, cumulative energy is calculated from the constituent subregions.
	abstract	Embodiments of the invention are directed to a method for production of a nuclear fuel pellet by spark plasma sintering (SPS), wherein a fuel pellet with more than 80% TD or more than 90% TD is formed. The SPS can be performed with the imposition of a controlled uniaxial pressure applied at the maximum temperature of the processing to achieve a very high density, in excess of 95% TD, at temperatures of 850 to 1600° C. The formation of a fuel pellet can be carried out in one hour or less. In an embodiment of the invention, a nuclear fuel pellet comprises UO2 and a highly thermally conductive material, such as SiC or diamond.
048521426	claims	1. A filter for a gamma camera comprising a plate made from a homogeneous alloy comprising from about 85 to about 95 wt. % cadmium, from about 5 to about 15 wt. % copper and from 0 to about 3 wt. % of incidental impurities. 2. A filter as claimed in claim 1 which comprises from about 8 to about 12 wt. % copper. 3. A filter as claimed in claim 1 which comprises from about 88 to about 92 wt. % cadmium. 4. A filter as claimed in claim 1 which comprises approximately 90 wt. % cadmium and 10 wt. % copper. 5. A filter as claimed in claim 1 wherein the plate is a substantially circular plate having a diameter of 200 to 600 mm. 6. A filter as claimed in claim 1 wherein the thickness of the plate is from 0.3 to 0.8 mm. 7. A gamma camera comprising an array of photomultipliers a flat scintillating crystal in front of the photomultipliers an optically coupled thereto, a collimator in the form of a perforated metal plate in front of the crystal and spaced therefrom, a filter comprising a plate made from a homogeneous alloy comprising from about 85 to about 95 wt. % cadmium, from about 5 to about 15 wt. % copper and from 0 to about 3 wt. % of incidental impurities, said filter is located between the collimator and the crystal and circuitry associated with the photomultipliers to form an image from scintillations of the crystal caused by gamma emissions passing through the collimator. 8. A gamma camera as claimed in claim 7 wherein the scintillating crystal is a sodium iodide crystal. 9. A gamma camera as claimed in claim 7 wherein the collimator is made of lead. 10. A gamma camera as claimed in claim 7 wherein a shield of a heavy metal, is provided around the collimator, filter, crystal and photomultipliers. 11. A gamma camera as claimed in claim 10, wherein said heavy metal shield is made of tungsten.
	abstract	Packaging system for radioactive materials having: a vial with closure for accommodating the radioactive material; a first casing to be opened, enclosing the vial, and essentially made from a transparent material, which has a capture cross-section selected for shielding at least a part of the emitted radiation; and a second casing to be opened, made from a material with a high capture cross-section (Z) for essentially shielding the remaining radiation, the second casing enclosing the first casing.
049820982	claims	1. A speed compensated intensifying screen for X-ray radiography of the head, comprising a substrate, a layer of phosphor formed on said substrate, a protective film formed on said layer of phosphor, and a light-absorbing layer serving to absorb the light emitted from said layer of phosphor proportionately to the part of the human body subjected to radiography, which intensifying screen is characterized by the fact that said light-absorbing layer enables said layer of phosphor to create a plurality of regions differing in speed, said plurality of regions of speed substantially comprise a substantially elliptical region J of high speed located substantially in the central part relative to the longitudinal cross section of the head, a region L of low speed corresponding to the outside of the contour of the head, and a region K corresponding to the head except for said region J of high speed and possessing a magnitude of speed of said region L and the speed across each of the borderlines of said regions of speed is continuously varied. 2. The intensifying screen according to claim 1, wherein the speed in said region K is substantially continuously lowered radially from said region J of high speed to said region L of low speed. 3. The intensifying screen according to claim 2, wherein the magnitudes of speed of said plurality of regions of speed are such that where the magnitude of the speed of said region J of high speed is taken as 100, the magnitude of said region L of low speed is not more than 50. 4. The intensifying screen according to any of claims 1 through 3, wherein the ratio of change in speed across each of said plurality of regions of speed and/or in said region K is continuous so that the produced X-ray radiograph shows no visibly discernible line pattern. 5. The intensifying screen according to any of claims 1 through 3, wherein said light-absorbing layer is formed on said layer of phosphor, or within said layer of phosphor. 6. The intensifying screen according to any of claims 1 through 3, wherein said light-absorbing layer comprises a filmlike material and a layer formed on said filmlike material with a substance capable of absorbing the light emitted from the phosphor used. 7. A speed compensated intensifying screen for X-ray radiography of the upper and lower jaws and the periphery thereof, comprising a substrate, a layer of phosphor formed on said substrate, a protective film formed on said layer of phosphor, and a light-absorbing layer serving to absorb the light emitted from said layer of phosphor proportionately to the part of the human body subjected to radiography, which intensifying screen is characterized by the fact that said light-absorbing layer enables said layer of phosphor to create a plurality of regions differing in speed, said plurality of regions of speed substantially comprise a beltlike region M of high speed extending from the central part of one end to the central part of the other end and substantially corresponding to the position of the cervical vertebra and another region N and the speed across each of the borderlines between said plurality of regions of speed is continuously varied. 8. The intensifying screen according to claim 7, wherein said belt-like region M of high speed exists along the center line extending from the center of one major side to the center of the other major side in a width in the range of 5 to 40 mm on either side of said central line. 9. The intensifying screen according to claim 8, wherein the magnitudes of speed in said plurality of regions of speed are such that when the magnitude of speed in said belt-like region M of high speed is taken as 100, the magnitude of speed in the other region N is in the range of 40 to 80. 10. The intensifying screen according to any of claims 7 through 9, wherein the ratio of change in speed across each of said plurality of borderlines of speed is continuous so that the produced X-ray radiograph shows no visibly discernible line pattern. 11. The intensifying screen according to any of claims 7 through 9, wherein said light-absorbing layeris formed on said layer of phosphor, or within said layer of phosphor. 12. The intensifying screen according to any of claims 7 through 9, wherein said light-absorbing layer comprises a filmlike material and a layer formed on said filmlike material with a substrate capable of absorbing the light emitted from the phosphor used.
041705122	claims	1. A method of making a soft-x-ray mask of a composite sheet of x-ray transmissive plastic and another x-ray opaque patterned material comprising: applying said plastic in liquid form to a substrate, hardening said plastic to form an optically smooth polymer film of plastic whose thickness and composition is substantially transparent to soft-x-rays and which has a mechanical bond to said substrate, depositing photolithographically patternable soft x-ray opaque material on said hardened plastic to form a mechanical bond therewith and hence a composite material of said plastic and opaque material, patterning a region of said deposited material to form a mask of said x-ray opaque material on said plastic, adhesively attaching a mechanical support to said composite material to enclose said patterned region within said support, dissolving the entire said substrate to leave only the composite material as attached to said support, removing that portion of said composite material external to said mechanical support to provide a supported mask. said liquid form of plastic is polyimide plastic precursor, said hardening comprises heating said precursor to form a polyimide film, said substrate is a glass, said depositing of material on said polyimide film comprises vaporizing a metal and depositing the vapor on the film, said dissolving of the substrate comprises etching away said glass in hydrofluoric acid. said applying of the polyimide plastic precursor on the glass substrate comprises spinning said precursor and substrate to form a layer of liquid precursor of substantially uniform thickness. forming a pattern in said deposited metal by ion beam etching away selected portions of the metal. said mechanical support forms a liquid barrier to prevent said hydrofluoric acid from entering the region within said support, filling said support with a liquid prior to the etching step to prevent said acid from passing through said composite material during the etching. adhesively attaching a mask holder to said composite material to contain said pattern within said mask holder, said attachment being made before said substrate is etched away, and removing said attached mechanical support after said substrate is totally etched away to leave said composite material within and attached only to and supported by said mask holder. adhesively attaching a mask holder to the plastic nonpatterned side of said composite material to contain said pattern within said mask holder, said attachment being made after said substrate is etched away, and thereafter removing said attached mechanical support after said substrate is totally etched away to leave said composite material within and attached only to and supported by mask holder. said mechanical support comprises a first and second mechanical support each adhesively attached to said composite material, said second mechanical support forming a liquid tight enclosure around said first mechanical support, said first mechanical support being of a material which would be dissolved at the time that said substrate is being dissolved in the absence of being enclosed by said second mechanical support, and wherein said removing of the composite material comprises removing said second mechanical support and said composite material external to said first mechanical support. patterning of said x-ray opaque material includes removing said opaque material from the region of attachment of said mechanical support to result in said attachment of said mechanical support being to said plastic. applying said plastic in liquid form to a substrate, hardening said plastic to form an optically smooth polymer film of plastic of thickness and composition substantially transparent to soft-x-rays, said plastic having a mechanical bond to said substrate, depositing a photolithographically patternable soft-x-ray opaque material on said hardened plastic to form a mechanical bond therewith and hence a composite material of said plastic and opaque material, patterning a region of said deposited material to form a mask of said x-ray opaque material on said plastic, adhesively attaching a mechanical support to said composite material to enclose said patterned region within said support, selectively dissolving said substrate to leave only a portion of said substrate in the form of a ring attached to said plastic to support said composite material, said supporting substrate enclosing said patterned region within the region supported by said mechanical support, removing said composite material and mechanical support external to said substrate support ring to leave said substrate support ring attached to said film to provide a supported mask. said liquid form of plastic is polyimide plastic precursor, said hardening comprises heating said precursor to form a polyimide film, said substrate is a glass, said depositing of material on said polyimide film comprises vaporizing a metal and depositing the vapor on the film, said dissolving of the substrate comprises etching away said glass in hydrofluoric acid. said applying of the polyimide plastic precursor on the glass substrate comprises spinning said precursor and substrate to form a layer of liquid precursor of substantially uniform thickness. forming a pattern in said deposited metal by ion beam etching away selected portions of the metal. said mechanical support forms a liquid barrier to prevent said hydrofluoric acid from entering the region within said support, filling said support with a liquid prior to the etching step to prevent said acid from passing through said composite material during the etching. patterning of said x-ray opaque material includes removing said opaque material from the region of attachment of said mechanical support to result in said attachment of said mechanical support being to said plastic. 2. The method of claim 1 wherein: 3. The method of claim 2 wherein: 4. The method of claim 2 comprising in addition: 5. The method of claim 2 wherein: 6. The method of claim 2 wherein said polyimide film has a thickness between 0.05.mu. and 3.mu.. 7. The method of claim 1 comprising in addition: 8. The method of claim 1 comprising in addition: 9. The method of claim 1 wherein: 10. The method of claim 1 wherein said 11. The method of making a soft x-ray mask of composite sheet of x-ray transmissive plastic and an x-ray opaque material comprising: 12. The method of claim 11 wherein: 13. The method of claim 12 wherein said polyimide film has a thickness between 0.05.mu. and 3.mu.. 14. The method of claim 11 wherein: 15. The method of claim 11 comprising in addition: 16. The method of claim 11 wherein: 17. The method of claim 11 wherein said
046684654	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be described as applied to a rod position monitoring system for the pressurized water reactor (PWR) shown in FIG. 1 although it is to be understood that the invention has broader application to instrumentation generally for nuclear reactors, and even more broadly, to remote control and monitoring of other processes carried out in a hazardous environment inside a containment structure. The PWR 1 of FIG. 1 includes a nuclear reactor 3 enclosed within a containment building 5 which prevents the escape of most radiation generated by the reactor. The reactor 3 includes a reactor vessel 7 housing a core 9 of fissile material having hundreds of neutron absorbing rods 11 which control the reactivity of the core. These neutron absorbing rods 11 include: control rods which are moved in and out of the core to regulate the power level of the reactor, shutdown rods which are either all the way in when the reactor is shutdown or all the way out when it is at power, and part-length rods which can be used to regulate the axial distribution of power in the core 9. The neutron absorbing rods 11 are inserted in and retracted from the core by drive rods 13 with several neutron absorbing rods driven by a common drive rod 13 through a spider 15. The control rods and shutdown rods are further grouped into typically four banks each with the rods in each bank distributed symmetrically across the reactor core and with all of the rods in each bank driven in and out of the core in synchronism by their drive rods 13. The drive rods 13 are incrementally stepped into and out of the core 9 by a drive rod mechanism 17 such as the magnetic jack device disclosed in U.S. Pat. No. 3,158,766. As the drive rods 13 are lifted up by their respective drive rod mechanisms 17 they each advance upward into a separate housing 19 on top of the reactor vessel 7. A rod position detector 21 tracks the movement of the end of the drive rod within the housing to determine the position within the reactor core 9 of the associated neutron absorbing rods 11. Since the reactor vessel 7 forms one of the several barriers to the release of fissile material and since the rod housings form an extension of that barrier, no penetrations of the housings are permitted to determine the position of the drive rods. It is for this reason that it has been common practice to use various arrangements of electrical coils in the detectors 21 as described above. A separate detector 21 is provided for each drive rod 13 of which, as mentioned above, there are several scores in a typical PWR. The electrical signals generated by each detector 21 are sent to a data cabinet 23 over electrical leads 25. The data cabinet 23 is located within the containment building 5 but is separated from the reactor 3 by a "biological shield" 27 which reduces the radiation to which the electrical components within the cabinet 23 are exposed, thereby significantly extending their useful life. As will be more fully discussed below, these electrical components process the signals received from the detectors 21 and output them over serial data links 29 extending through the containment building wall to controller/interface equipment 31 in equipment room 33. The controller/interface equipment 31 processes the serial data received over the data links and sends the processed data over leads 35 to a display device and plant computer, identified collectively as 37, in the control room 39. The overall architecture of the rod position indicating system is illustrated in FIG. 2. In the system shown, one level of redundancy is used except that only one detector 21 and one set of interconnecting leads 25 are provided for each drive rod. Field history has shown these components to be sufficiently reliable to be used without backup in most applications. However, as will be more evident from the more detailed discussion below, the system architecture is also applicable to systems using redundant detector coils. The signals on leads 25 from each of the detectors 21 are applied to a separate encoder card 41 housed in the data cabinet 23 in the containment building. Each of the detector cards 41 has two identical circuits, labeled A and B in FIG. 2, which process the signals generated by the detector coils to produce redundant binary gray code representations of rod position. A key aspect of the invention is that the redundant information from the A and B circuits on the encoder cards 41 is distributed to each set of redundant components in the system. Thus, the encoder cards 41 include four separate fault isolating bus interfaces which feed the redundant binary rod position signals generated by the A and B circuits to each of two redundant, fully independent, byte parallel communications buses 43 and 45 physically provided on backplane cards in the data cabinet 23. Each of the communications buses 41 and 43 is controlled by a bus controller/serial output device 47 and 49 respectively mounted on its own printed circuit card in cabinet 23. Each bus controller/serial output card polls each redundant half of each encoder card 41 to collect and store all of the rod position data once per second. These devices also contain circuitry to monitor the local environment including temperature, power supply voltage, door "open" status, and self test. Each of the bus controller/serial output cards 47 and 49 has two redundant individually buffered serial data link outputs 29a and b and 29c and d respectively. On one bus controller/serial output card, 47 for instance, one data link, 29a, is the primary link to a display controller/interface 51, which forms part of the equipment 31 located in the equipment room 33, and the second data link, 29b, serves as a backup input for a plant computer interface 53 also located in the equipment room. The other bus controller/serial output card, 49, has one data link, 29c, which is the primary link to the plant computer interface 53 and a second, 29d, which is a backup to the display controller/interface 51. The data stored by the bus controller/serial output cards 47 and 49 is formatted into three blocks for transmission over each of the associated pairs of data links. The three blocks contain, respectively, all rod positions from the "A" portion of each of the encoder cards, all rod positions from the "B" portion of each of the encoder cards, and a fixed field and system status information. The data is transmitted using an asynchronous simplex byte count oriented protocol similar to DDCMP (digital data communications message protocol). The bus controller/serial output cards 47 and 49 each utilize a single chip microprocessor for control of all functions. As a result, the sequence of bus control and serial data link protocol can be easily modified for unique applications. A single bus monitor card 55 is provided to improve self test and fault diagnosis. When polled by the bus controller/serial output cards, 47 and 49, it provides complementary fixed binary codes in place of rod position signals. Proper receipt of those codes verifies the integrity of each bus and assists in the isolation of system faults to the board level before maintenance personnel enter the containment building. Alternatively, separate bus monitor cards can be provided at the remote end of each bus 43 and 45 to assure continuity of the entire bus. The fixed field block of data transmitted by each bus controller/serial output device provides a means for checking and isolating faults in the data links 29. The containment electronics in data cabinet 23 also includes fully redundant d-c power supplies that are individually distributed via the backplane and are diode auctioneered at the board level. The display controller/interface 51 and the plant computer interface 53, which comprise the controller/interface equipment 31 located in the equipment room 33, each receive data from the two bus controller/serial output cards 47 and 49 over serial data links 29a and d and 29c and b respectively. Only one serial data link is used by either subsystem at any give time. The source of the data is chosen manually by a toggle switch 57. Each subsystem 51, 53 receives the serially transmitted data and checks for transmission errors. They also check system status failures and compare the rod position from the redundant portions of each encoder card 41 as a reasonability check. Only one source, either "A" or "B", of data for each rod is used for control of display, alarm and plant computer interfaces. The selection of the set of redundant data to be used is made manually by a small hand-held portable terminal 59 which may be plugged as needed into the display controller/interface 51 or plant computer interface 53. The operator may choose that all rod position data be taken from the "A" side or the "B" side of each encoder card 41 or he may choose which side the data will be taken from on a rod by rod basis. Once the selection is made, the instructions are stored in non-volatile memory so that the system will automatically return to the previous operating mode following a power outage. The ability to manually select the source of the data, both from the bus controller/serial output cards and from the encoder cards, as well as the overall system architecture, insures maximum fault tolerance and recoverability for those few equipment failures that may occur. Each subsystem 51 and 53 processes its set of rod position data and controls it associated display devices. The display controller interface 51 formats the data for one of five display pages and produces an output compatible for driving a color cathode ray tube (CRT) monitor 61 in the main control board located in the control room 39. The operator interface is provided with four push buttons 63 also in the main control board to control system reset, alarm acknowledgement, rod position data page selection and system alarm page selection. The display controller interface 51 also provides two contact closure outputs to a control board annunciator system 65 for urgent and non-urgent alarms. The urgent alarm results from any of the many detectable system failures. Those system alarms are displayed on the CRT 61. The non-urgent alarms result from detectable misplacement of rods including rod deviation (rod to rod in a bank), rod on bottom, and rod off top. These alarms are also deisplayed on the CRT 61 as more fully described below. The plant computer interface 53 generates outputs suitable for use by the plant computer 67 located in the control room for generating on its CRT, displays similar to those presented on the CRT color monitor 61 thus providing the redundant representation of the rod positions. The plant computer also logs the rod position signals for record keeping purposes. FIGS. 3 and 4 illustrate a suitable rod position detector 21 for use with the invention. The detector depicted is the digital detector covered by commonly owned copending application Ser. No. 657,423 filed on Oct. 3, 1984. As illustrated, the drive rod 13 is longitudinally movable inside the tubular housing 19 and is preferably made of a material of high magnetic permeability such as steel, but could also be made of an electrically conductive material in which eddy currents can be induced by magnetic fields. Spaced along the travel path of the drive rod 13 at spaced intervals along the outside of the housing 19 are a number of electrical coils L.sub.1 through L.sub.20. As shown in FIG. 4, each of the coils L.sub.1 through L.sub.20 is energized by a low voltage, low frequency, for instance 12 volt 60 hertz, a-c power source. The magnetic fields generated by such a low frequency current in the coils penetrate the non-magnetic housing 13 and, where it is present, the drive rod 13. Since the drive rod is electrically conductive and/or preferably magnetically permeable, the impedance of each coil in succession changes as the end of the drive rod passes through it. Thus, by monitoring the sequential changes in the impedance of the coils, the movement of the rod can be tracked. Pairs of detector coils are connected in series across the a-c source 69 together with a pair of series connected resistors R.sub.1 and R.sub.2 which are located in the data cabinet 23. Leads 25a through 25j connect the common nodes 71 of each resistor pair with appropriate circuits on dedicated encoder card 41 in the data cabinet 23. Lead 73 connects the common node 75 between the resistors R.sub.1 and R.sub.2 with these same circuits which compare the voltage at node 75 with that at each of the nodes 71 of the coil pairs. With matched coils and resistors of equal value, no differential voltage is generated for coil pairs in which both coils or neither coil is penetrated by the rod 13, however, a differential voltage will be generated for those coil pairs in which one coil is penetrated by the rod 13 and one is not. As will be seen, the differential voltage between the node 74 and each node 71 generates one digit of a binary coded signal. By arranging the coils so that the end of the rod 13 penetrates a coil in a pair to the left and a pair to the right between passing through the two coils in a given pair, a unique multi-digit digital signal is generated by the detector. FIG. 5 illustrates the circuit on one of the encoder boards 41 which processes the signals from one of the detectors 21. The lead 25a through j from the detector coils are applied to the input side of a printed circuit board 77 through connector 79. Each of the leads 25a through 25j is split at a branch point 81 into two leads 25a' and a" through 25j' and j" with each of the leads 25a' through 25j' applied to one input of a differential amplifier 83A in a processing circuit 85A through an input resistor 87A, and with each of the leads 25a" through 25j" applied through an input resistor 87B to one input of a differential amplifier 83B in processing circuit 85B. In the case where a redundant coils were used, the signals from one set would be applied to the differential amplifiers 83A and those from the other set to the amplifiers 85B. The lead 73 from the common node 75 between the resistors R.sub.1 and R.sub.2, which are physically located on the printed circuit board 77, is applied to the other input of each of the differential amplifiers 83A and B through resistors 87A and B respectively. The differential a-c voltages produced by the amplifiers 83A and B are applied to discriminators 91A and B respectively where they are converted to d-c signals and compared with threshold levels to generate standard logic outputs, D.sub.0 through D.sub.9. Since there are only 20 coils in each detector, the 10 digit binary signals produced by the discriminators 91A and B are converted to 8 bit signals, D.sub.0 ' through D.sub.7 ', inconverters 93A and B respectively to be compatible with the 8 bit structure of the downstream components even though 5 digits would be sufficient to identify the location of the rod with respect to the 20 coils. The 8 bit binary signals D.sub.0 ' through D.sub.7 'produced by the processing circuits 85A and B are each applied through an interface 95 to each of the communications buses, BUS No. 1, 43, and BUS No. 2, 45. The leads 97a through 97h carrying the 8 bit signal from the A processing circuit are split into two leads each 97a' through h' and 97a" through h" for application to an A Data Bus Driver 99' and 99" associated with the No. 1 and No. 2 Buses 43 and 45 respectively. Similarly, the 8 bit signal from the converter 93B in the B processing circuit is applied over leads 101a through h which split into 101a' through 101h' and 101" through h' to B Data Bus Drivers 103' and 103". Each of the bus drivers 99', 99", 103' and 103" includes 8 CMOS gates 105 which selectively feed either the applied A or B data to each of the 8 bit buses 43 and 45 through leads 107 and 109 and connectors 111 and 113 respectively. A Bus 1 Address Decoder 115 receives a detector address signal DET ADD, and A/B DATA signal and an ENABLE signal from the BUS 1 through connector 111. These signals are generated by the bus controller/serial output No. 1, 47, to control the sequential transmission of data on communications Bus No. 1. The DET ADD signal identifies which board (i.e. which detector) is to place data on the bus, the A/B DATA signal determines which of the redundant sets of signals, A or B, is to be transmitted and the ENABLE signal implements the transfer. With the detector board shown in FIG. 5 addressed and A data selected, the ENABLE signal applies a pulse to each of the CMOS gates 105 in A Data Bus Driver 99' through lead 117 to apply the 8 bit digital position signal generated by processing circuit 85A to Bus No. 1. With the B data from this detector selected, an ENABLE signal applies a pulse through lead 119 to each of the CMOS gates (not shown) in B Data Bus Driver 103'. In like manner, the A data and B data are applied to BUS No. 2 by similar control signals generated by bus controller/serial output No. 2, 49, and applied to BUS 2 Address Decoder 121 which responds by pulsing the A Data Bus Driver 99" through lead 123 and the B Data Bus Driver 103" through lead 125 as commanded. The input impedance of the differential amplifiers 83A and B and the value of the input resistors 87A and B and 89A and B is very high while the impedance of the coils L.sub.1 to L.sub.20 and resistors R.sub.1 and R.sub.2 is low so that a failure in one of the processing circuits 85A or B is not propagated to the other through the inputs. Likewise, the input impedance of the CMOS gates 105 in the bus drivers 99', 99", 103' and 103" is very high as is the value of resistors 127', 127", 129' and 129" while the output impedance of the converters 93A and B is relatively low so that no faults are propagated through the outputs. The serial transmission of data through the communications buses, and data links as well as the digital storage of data in the bus controller/serial outputs preserve the isolation of the redundant detector signals. The primary function of the rod position indicating system is to provide plant operators with as much information as possible concerning the position of the rods in the reactor core. It was determined that this could best be done by preventing the information to the operator in the form of graphical displays on a color CRT rather than through individual analog or digital indicators. Redundant displays are made available by presenting the rod position information on the CRT of the plant computer 67 as well as the dedicated CRT 61 in the control room. Since all the pertinent data cannot be reasonably presented on one CRT display, a five page display 131 was developed. Three pages illustrate respectively, the positions of the control rods, shutdown rods and the part-length rods (where necessary). FIG. 6 illustrates the control rod display page 131A. The major field of the CRT is devoted to a bargraph representation 133 of rod position, while space is reserved at the bottom of each page for status messages 135. This arrangement provides the operator with information pertinent to abnormal conditions on the other pages while viewing the position data on a particular page. Rod position is displayed by bank. The customary convention of indicating rod position by the number of steps the rod has been withdrawn is utilized with a scale of 1 to 228 steps in 12 step increments shown. In keeping with this convention, the amount of withdrawal is shown on the bargraph in a prominent color such as yellow with the background shown in a less prominent color such as blue. The identification of the rod and the number of steps it is withdrawn is shown below the bar. Where no information or erroneous information is received, ERR appears in reverse video with a red background and no bar is shown as for the rod H10 in the A bank of control rods. The average value of the valid rod position signals is shown after the bank label, for instance "152" for the B bank. Four groups of status messages 135 are provided at the bottom of the page. The first indicates Rod Deviation. All of the rods in a bank should move simultaneously. Any deviations from this pattern should be brought to the operator's attention. FIG. 6 shows in the status message area that there are deviations in control rod banks B and D. Reference then to the bargraphs shows that rod B6 is only out 36 steps while the remainder of the rods in B bank are out 168 steps. Likewise, the Bank D bargraphs show that rod M8 is out 84 steps while all the other D bank control rods are on the bottom. When such a status message first appears, the bank label flashes in reverse video. When the message is acknowledged, the background appears solid. The second status message is identified as the "Rod on Bottom" signal. Normally, at power the control rods in all the banks will be out part way. The boron system is used to accommodate long term changes in load so that this condition prevails. Also, at power all the shutdown rods should be fully withdrawn. On the other hand, when the reactor is shutdown, all of the rods should be "on the bottom" or fully inserted. Thus, this message alerts the operator to an abnormal condition during operation and provides a quick reference during a reactor trip whether all the rods have been fully inserted. In FIG. 6, it can be seen that all of the rods in the D bank, except one which is out of place, are on the bottom indicating an abnormal condition in the control system which should be investigated. The third status message is "Rod Off Top" which is only pertinent as to the shutdown rods and indicates in FIG. 6 that rods in the A and C shutdown banks are not fully withdrawn as they should be with the reactor at power. If the operator wants more detailed information, he can page to the shutdown rod page which is presented in the simpler format to FIG. 6 to see in more detail from the bargraphs what the situation is. The part-length rod page for plants having such rods is much similar since there is only one bank of such rods and normally they are fully withdrawn under present control schemes. The fourth status message is the rod position indicating system alarm messages "RPI System Alarm". When the "See Alarm Page" message appears in reverse video, the operator should look to the remaining two pages which include the "System Status" page 131B of FIG. 7. This page shows thh status of system components by location. For the equipment room electronics, PROM and RAM memory check results are displayed. The valid check results are shown in blue while components which failed the test are shown in red. In the example shown, the number 2 PROM memory and number 6 RAM have failed their tests and are thus shown in red which also generates a "System Alarm" in the lower right-hand corner of this page and the "See Alarm Page" signal on the rod position pages. The "Number Of Main Loop Time-outs" count shown for the equipment room electronics is the number of times the dead man timer timed out since the last software reset. This number provides a measure of system integrity. The "Containment Electronics" section indicates the status of components in the cabinet 23 located inside the containment building. The items displayed are self-explanatory. The "Communication System" section provides information on the status of the data link which is supplying data to the redundant display being viewed. "The quick brown fox jumped over the lazy dog" is an example of the fixed field header message which is transmitted as an integrity check. The "Header Count" indicates how many times this message has been received correctly and the A and B counts indicate the number of times the A and B data have been received without an error. A system alarm is generated if any of the three counts exceeds the average of the counts. A maintenance page can also be provided which displays the raw data received on each rod and can be referred to for more detailed information in case of a system alarm. 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 arrangements 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.
	claims	1. A ceramic nuclear fuel pellet for a nuclear reactor, wherein the nuclear fuel pellet comprises a first fissile material of UB2, wherein the boron of the UB2 is enriched to have a concentration of the isotope 11B that is higher than for natural B, wherein the concentration of the isotope 11B is at least 85% by weight,wherein the nuclear fuel pellet further comprises at least one second fissile material, the at least one second fissile material comprises UN. 2. The ceramic nuclear fuel pellet according to claim 1, wherein the concentration of the isotope 11B is at least 90% by weight. 3. The ceramic nuclear fuel pellet according to claim 1, wherein the concentration of the isotope 11B is at least 95% by weight. 4. The ceramic nuclear fuel pellet according to claim 1, wherein the concentration of the isotope 11B is at approximately 100% by weight. 5. The ceramic nuclear fuel pellet according to claim 1, wherein the nuclear fuel pellet consists of UB2. 6. The ceramic nuclear fuel pellet according to claim 1, wherein the at least one second fissile material comprises one of an actinide nitride, an actinide silicide and an actinide oxide. 7. The ceramic nuclear fuel pellet according to claim 1, wherein the first fissile material and the at least one second fissile material are mixed in the nuclear fuel pellet. 8. The ceramic nuclear fuel pellet according to claim 1, wherein the nuclear fuel pellet is a sintered nuclear fuel pellet. 9. A fuel rod comprising a cladding tube and a plurality of nuclear fuel pellets according to claim 1. 10. The fuel rod according to claim 9, wherein the fuel rod comprises a plurality of absorbing pellets comprising UB2, in which the boron of the UB2 has a concentration of the isotope 10B that is higher than in the UB2 of the first fissile material of the nuclear fuel pellets. 11. The fuel rod according to claim 10, wherein the concentration of the isotope 10B in the UB2 of the absorbing pellets is at least 25, 30, 40, 50, 60, 70, 80, 90 or 100% by weight. 12. A fuel assembly comprising a plurality of fuel rods according to claim 9.
	abstract	A scintillator material according to one embodiment includes a polymer matrix; a primary dye in the polymer matrix, the primary dye being a fluorescent dye, the primary dye being present in an amount of 3 wt % or more; and at least one component in the polymer matrix, the component being selected from a group consisting of B, Li, Gd, a B-containing compound, a Li-containing compound and a Gd-containing compound, wherein the scintillator material exhibits an optical response signature for thermal neutrons that is different than an optical response signature for fast neutrons and gamma rays. A system according to one embodiment includes a scintillator material as disclosed herein and a photodetector for detecting the response of the material to fast neutron, thermal neutron and gamma ray irradiation.
	claims	1. A two-dimensional magneto-optical trap (MOT) device, comprising:an atom source;a bakeable ultra-high vacuum cell;a two dimensional quadrupole magnetic field;3+n pairs of counter-propagating trapping laser beams, wherein n is an integer larger than or equal to zero, the trapping laser beams comprising one pair of counter-propagating beams perpendicular to a magnetic field longitudinal symmetry axis, and the remaining 2+n pairs of counter-propagating beams, with no trapping laser beams on the magnetic field longitudinal symmetry axis; andat least one repumping laser beam. 2. The two-dimensional magneto-optical trap device of claim 1, wherein n=0, with one pair of counter-propagating beams perpendicular to the magnetic field longitudinal symmetry axis, and the remaining 2 pairs of counter-propagating beams having a target alignment of a 45 degree angle to the magnetic field longitudinal symmetry axis and perpendicular to the first pair of counter-propagating beams. 3. The two-dimensional magneto-optical trap device of claim 1, wherein said bakeable ultra-high vacuum cell comprises a glass cell chamber, a glass-to-metal transition tube, and a metal flange. 4. The two-dimensional magneto-optical trap device of claim 3, wherein said glass cell chamber has one of an octagonal shape or a rectangular shape. 5. The two-dimensional magneto-optical trap device of claim 1, wherein said two-dimensional quadrupole magnetic field has a zero field line along the magnetic field longitudinal symmetry axis and the magnetic field remains on continuously during an experiment while maintaining a ground state coherence time of up to 5 μs 6. The two-dimensional magneto-optical trap device of claim 1, wherein said two-dimensional quadrupole magnetic field has a zero field line along the magnetic field longitudinal symmetry axis and turning off the magnetic field results in obtaining a ground state coherence time of more than 5 μs. 7. The two-dimensional magneto-optical trap device of claim 1, wherein the two-dimensional quadrupole magnetic field is established with a three-dimensional single-wire magnetic coil, the coil comprising a single hollow-core wire or conductor without any interconnection, provided with a liquid cooling passage, wherein the single hollow-core wire or conductor has no interconnection and provides a continuous and smooth path for electricity and provides a liquid cooling passage. 8. A dark-line two-dimensional magneto-optical trap (MOT) device, comprising:an atom source;a bakeable ultra-high vacuum cell;a two dimensional quadrupole magnetic field;3+n pairs of counter-propagating trapping laser beams, wherein n is an integer larger than or equal to zero, the trapping laser beams comprising one pair of counter-propagating beams perpendicular to the symmetry axis, and the remaining 2+n pairs of counter-propagating beams aligned in a plane perpendicular to the first pair of counter-propagating beams; andtwo orthogonal repumping laser beams with a dark line crossover at center along the longitudinal axis. 9. The dark-line two-dimensional magneto-optical trap device of claim 8, wherein for the optimal trapping beam has a configuration with n=0, one pair of counter-propagating beams are perpendicular to the symmetry axis, and the remaining 2 pairs of counter propagating beams have a target alignment of a 45 degree angle to the longitudinal symmetry axis and perpendicular to the first pair of counter-propagating beams. 10. The dark-line two-dimensional magneto-optical trap device of claim 8, wherein said bakeable ultra-high vacuum cell comprises a glass cell chamber, a glass-to-metal transition tube, and a metal flange. 11. The dark-line two-dimensional magneto-optical trap device of claim 10, wherein said glass cell chamber has one of an octagonal shape or a rectangular shape. 12. The dark-line two-dimensional magneto-optical trap device of claim 8, wherein said two-dimensional quadrupole magnetic field has a zero field line along the symmetry axis and the magnetic field remains on continuously during an experiment while maintaining a ground state coherence time of up to 5 μs. 13. The dark-line two-dimensional magneto-optical trap device of claim 8, wherein said two-dimensional quadrupole magnetic field has a zero field line along the symmetry axis and turning off the magnetic field results in obtaining a ground state coherence time of more than 5 μs. 14. A method to produce a repumping laser dark line on the center of a dark-line two-dimensional magneto-optical trap (MOT), comprising:using a lens imaging system to image an opaque line to the longitudinal axis of the two dimensional magneto optical trap in each repumping beam. 15. The method of claim 14, wherein the overlap of the two line images creates a dark line volume in the longitudinal axis exhibiting an absence of repumping light.
	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, including any priority claims, 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 of U.S. patent application Ser. No. 12/658,649, 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 12 Feb. 2010 U.S. Pat. No. 7,912,171, which is currently an application of which a currently 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, continuation-in-part, or divisional of a parent application. Stephen G. Kunin, Benefit of Prior-Filed Application, USPTO Official Gazette Mar. 18, 2003. 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 has provided designation(s) of a relationship between the present application and its parent application(s) as set forth above, but expressly points out that such designation(s) 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 nuclear reactors, and systems, applications, and apparatuses related thereto. The following embodiments and aspects thereof are described and illustrated in conjunction with systems and methods which are meant to be exemplary and illustrative, not limiting in scope. Exemplary embodiments provide automated nuclear fission reactors and methods for their operation. Exemplary embodiments and aspects include, without limitation, re-use of nuclear fission fuel, alternate fuels and fuel geometries, modular fuel cores, fast fluid cooling, variable burn-up, programmable nuclear thermostats, fast flux irradiation, temperature-driven neutron absorption, low coolant temperature cores, refueling, and the like. In addition to the exemplary embodiments and aspects described above, further embodiments and aspects will become apparent by reference to the drawings and by study of the following detailed description. By way of overview, embodiments provide automated nuclear fission reactors and methods for their operation. Details of an exemplary reactor, exemplary core nucleonics, and operations, all given by way of non-limiting example, will be set forth first. Then, details will be set forth regarding several exemplary embodiments and aspects, such as without limitation re-use of nuclear fission fuel, alternate fuels and fuel geometries, modular fuel cores, fast fluid cooling, variable burn-up, programmable nuclear thermostats, fast flux irradiation, temperature-driven neutron absorption, low coolant temperature cores, refueling, and the like. Referring now to FIG. 1A, a nuclear fission reactor 10, given by way of example and not of limitation, acts as an exemplary host environment for embodiments and aspects described herein. While many embodiments of the reactor 10 are contemplated, a common feature among many contemplated embodiments of the reactor 10 is origination and propagation of a nuclear fission deflagration wave, or “burnfront”. Considerations Before discussing details of the reactor 10, some considerations behind embodiments of the reactor 10 will be given by way of overview but are not to be interpreted as limitations. Some embodiments of the reactor 10 reflect attainment of all of the considerations discussed below. On the other hand, some other embodiments of the reactor 10 reflect attainment of selected considerations, and need not accommodate all of the considerations discussed below. Portions of the following discussion includes 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 entire contents of which are hereby incorporated by reference. Nuclear fission fuels envisioned for use in embodiments of the reactor 10 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 be used in embodiments of the reactor 10. While embodiments of the reactor 10 contemplate long-term operation at full power on the order of around ⅓ century to around ½ century or longer, an aspect of some embodiments of the reactor 10 does not contemplate nuclear refueling (but instead contemplate burial in-place at ends-of-life) while some aspects of embodiments of the reactor 10 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, thereby mitigating possibilities for diversion to military uses and other issues. Other considerations behind embodiments of the reactor 10 include disposing in a manifestly safe manner long-lived radioactivity generated in the course of operation. It is envisioned that the reactor 10 may be able to mitigate damage due to operator error, casualties such as a loss of coolant accident (LOCA), or the like. In some aspects decommissioning may be effected in low-risk and inexpensive manner. As a result, some embodiments of the reactor 10 may entail underground siting, thereby addressing large, abrupt releases and small, steady-state releases of radioactivity into the biosphere. Some embodiments of the reactor 10 may entail minimizing operator controls, thereby automating those embodiments as much as practicable. In some embodiments, a life-cycle-oriented design is contemplated, wherein those embodiments of the reactor 10 can operate from startup to shutdown at end-of-life in as fully-automatic manner as practicable. Some embodiments of the reactor 10 lend themselves to modularized construction. Finally, some embodiments of the reactor 10 may be designed according to high power density. Some features of various embodiments of the reactor 10 result from some of the above considerations. For example, 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 entails use of a fast neutron spectrum. As another example, in some embodiments a negative temperature coefficient of reactivity (αT) is engineered-in to the reactor 10, such as via negative feedback on local reactivity implemented with strong absorbers of fast neutrons. As a further example, in some embodiments of the reactor 10 a distributed thermostat enables a propagating nuclear fission deflagration wave mode of nuclear fission fuel burn. This mode simultaneously 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 another example, in some embodiments of the reactor 10, multiple redundancy is provided in primary and secondary core cooling. Now that some of the considerations behind some of the embodiments of the reactor 10 have been set forth, further details regarding an exemplary embodiment of the reactor 10 will be explained. It is emphasized that the following description of an exemplary embodiment of the reactor 10 is given by way of non-limiting example only and not by way of limitation. As mentioned above, several embodiments of the reactor 10 are contemplated, as well as further aspects of the reactor 10. After details regarding an exemplary embodiment of the reactor 10 are discussed, other embodiments and aspects will also be discussed. Still referring to FIG. 1A, an exemplary embodiment of the reactor 10 includes a nuclear fission reactor core assembly 100 that is disposed within a reactor pressure vessel 12. Several embodiments and aspects of the nuclear fission reactor core assembly 100 are contemplated that will be discussed later. Some of the features that will be discussed later in detail regarding the nuclear fission reactor core assembly 100 include nuclear fission fuel materials and their respective nucleonics, fuel assemblies, fuel geometries, and initiation and propagation of nuclear fission deflagration waves. The reactor pressure vessel 12 suitably is any acceptable pressure vessel known in the art and may be made from any materials acceptable for use in reactor pressure vessels, such as without limitation stainless steel. Within the reactor pressure vessel 12, a neutron reflector (not shown) and a radiation shield (not shown) surround the nuclear fission reactor core assembly 100. In some embodiments, the reactor pressure vessel 12 is sited underground. In such cases, the reactor pressure vessel 12 can also function as a burial cask for the nuclear fission reactor core assembly 100. In these embodiments, the reactor pressure vessel 12 suitably is surrounded by a region (not shown) of isolation material, such as dry sand, for long-term environmental isolation. The region (not shown) of isolation material may have a size of around 100 m in diameter or so. However, in other embodiments, the reactor pressure vessel 12 is sited on or toward the Earth's surface. Reactor coolant loops 14 transfer heat from nuclear fission in the nuclear fission reactor core assembly 100 to application heat exchangers 16. The reactor coolant may be selected as desired for a particular application. In some embodiments, the reactor coolant suitably is helium (He) gas. In other embodiments, the reactor coolant suitably may be other pressurized inert gases, such as neon, argon, krypton, xenon, or other fluids such as water or gaseous or superfluidic carbon dioxide, or liquid metals, such as sodium or lead, or metal alloys, such as Pb—Bi, or organic coolants, such as polyphenyls, or fluorocarbons. The reactor coolant loops suitably may be made from tantalum (Ta), tungsten (W), aluminum (Al), steel or other ferrous or non-iron groups alloys or titanium or zirconium-based alloys, or from other metals and alloys, or from other structural materials or composites, as desired. In some embodiments, the application heat exchangers 16 may be steam generators that generate steam that is provided as a prime mover for rotating machinery, such as electrical turbine-generators 18 within an electrical generating station 20. In such a case, the nuclear fission reactor core assembly 100 suitably operates at a high operating pressure and temperature, such as above 1,000K or so and the steam generated in the steam generator may be superheated steam. In other embodiments, the application heat exchanger 16 may be any steam generator that generates steam at lower pressures and temperatures (that is, need not be not superheated steam) and the nuclear fission reactor core assembly 100 operates at temperatures less than around 550K. In these cases, the application heat exchangers 16 may provide process heat for applications such as desalination plants for seawater or for processing biomass by distillation into ethanol, or the like. Optional reactor coolant pumps 22 circulate reactor coolant through the nuclear fission reactor core assembly 100 and the application heat exchangers 16. Note that although the illustrative embodiment shows pumps and gravitationally driven circulation, other approaches may not utilize pumps, or circulatory structures or be otherwise similarly geometrically limited. The reactor coolant pumps 22 suitably are provided when the nuclear fission reactor core assembly 100 is sited approximately vertically coplanar with the application heat exchangers 16, such that thermal driving head is not generated. The reactor coolant pumps 22 may also be provided when the nuclear fission reactor core assembly 100 is sited underground. However, when the nuclear fission reactor core assembly 100 is sited underground or in any fashion so the nuclear fission reactor core assembly 100 is vertically spaced below the application heat exchangers 16, thermal driving head may be developed between the reactor coolant exiting the reactor pressure vessel 12 and the reactor coolant exiting the application heat exchangers 16 at a lower temperature than the reactor coolant exiting the reactor pressure vessel 12. When sufficient thermal driving head exists, the reactor coolant pumps 22 need not be provided in order to provide sufficient circulation of reactor coolant through the nuclear fission reactor core assembly 100 to remove heat from fission during operation at power. In some embodiments more than one reactor coolant loop 14 may be provided, thereby providing redundancy in the event of a casualty, such as a loss of coolant accident (LOCA) or a loss of flow accident (LOFA) or a primary-to-secondary leak or the like, to any one of the other reactor coolant loops 14. Each reactor coolant loop 14 is typically rated for full-power operation, though some applications may remove this constraint. In some embodiments, one-time closures 24, such as reactor coolant shutoff valves, are provided in lines of the reactor coolant system 14. In each reactor coolant loop 14 provided, a closure 24 is provided in an outlet line from the reactor pressure vessel 12 and in a return line to the reactor pressure vessel 12 from an outlet of the application heat exchanger 16. The one-time closures 24 are fast-acting closures that shut quickly under emergency conditions, such as detection of significant fission-product entrainment in reactor coolant). The one-time closures 24 are provided in addition to a redundant system of automatically-actuated conventional valves (not shown). Heat-dump heat exchangers 26 are provided for removal of after-life heat (decay heat). The heat-dump heat exchanger 26 includes a primary loop that is configured to circulate decay heat removal coolant through the nuclear fission reactor core assembly 100. The heat-dump heat exchanger 26 includes a secondary loop that is coupled to an engineered heat-dump heat pipe network (not shown). In some situations, for example, for redundancy purposes, more than one the heat-dump heat exchanger 26 may be provided. Each of the heat-dump heat exchangers 26 provided may be sited at a vertical distance above the nuclear fission reactor core assembly 100 so sufficient thermal driving head is provided to enable natural flow of decay heat removal coolant without need for decay heat removal coolant pumps. However, in some embodiments decay heat removal pumps (not shown) may be provided or, if provided, the reactor coolant pumps may be used for decay heat removal, where appropriate. Now that an overview of an exemplary embodiment of the reactor 10 has been given, other embodiments and aspects will be discussed. First, embodiments and aspects of the nuclear fission reactor core assembly 100 will be discussed. An overview of the nuclear fission reactor core assembly 100 and its nucleonics and propagation of a nuclear fission deflagration wave will be set forth first, followed by descriptions of exemplary embodiments and other aspects of the nuclear fission reactor core assembly 100. Given by way of overview and in general terms, structural components of the reactor core assembly 100 may be made of tantalum (Ta), tungsten (W), rhenium (Re), or carbon composite, ceramics, or the like. These materials are suitable because of the high temperatures at which the nuclear fission reactor core assembly 100 operates, and because of their creep resistance over the envisioned lifetime of full power operation, mechanical workability, and corrosion resistance. Structural components can be made from single materials, or from combinations of materials (e.g., coatings, alloys, multilayers, composites, and the like). In some embodiments, the reactor core assembly 100 operates at sufficiently lower temperatures so that other materials, such as aluminum (Al), steel, titanium (Ti) or the like can be used, alone or in combinations, for structural components. The nuclear fission reactor core assembly 100 includes a small 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. In some embodiments, uniform temperature throughout the nuclear fission reactor core assembly 100 is maintained by thermostating modules, described in detail later, which regulate local neutron flux and thereby control local power production. The nuclear fission reactor core assembly 100 suitably is a breeder for reasons of efficient nuclear fission fuel utilization and of minimization of requirements for isotopic enrichment. Further, and referring now to FIGS. 1B and 1C, the nuclear fission reactor core assembly 100 suitably utilizes a fast neutron spectrum because the high absorption cross-section of fission products for thermal neutrons does not permit utilization of more than about 1% of thorium or of the more abundant uranium isotope, U238, in uranium-fueled embodiments, without removal of fission products. In FIG. 1B, cross-sections for the dominant neutron-driven nuclear reactions of interest for the Th232-fueled embodiments are plotted over the neutron energy range 10−3-107 eV. It can be seen that losses to radiative capture on fission product nuclei dominate neutron economies at near-thermal (˜0.1 eV) energies, but are comparatively negligible above the resonance capture region (between ˜3-300 eV). Thus, operating with a fast neutron spectrum when attempting to realize a high-gain fertile-to-fissile breeder can help to preclude fuel recycling (that is, periodic or continuous removal of fission products). The radiative capture cross-sections for fission products shown are those for intermediate-Z nuclei resulting from fast neutron-induced fission that have undergone subsequent beta-decay to negligible extents. Those in the central portions of the burn-waves of embodiments of the nuclear fission reactor core assembly 100 will have undergone some decay and thus will have somewhat higher neutron avidity. However, parameter studies have indicated that core fuel-burning results may be insensitive to the precise degree of such decay. In FIG. 1C, cross-sections for the dominant neutron-driven nuclear reactions of primary interest for the Th232-fueled embodiments are plotted over the most interesting portion of the neutron energy range, between >104 and <106.5 eV, in the upper portion of FIG. 1C. The neutron spectrum of embodiments of the reactor 10 peaks in the ≧105 eV neutron energy region. The lower portion of FIG. 1C contains the ratio of these cross-sections vs. neutron energy to the cross-section for neutron radiative capture on Th232, the fertile-to-fissile breeding step (as the resulting Th233 swiftly beta-decays to Pa233, which then relatively slowly beta-decays to U233, analogously to the U239-Np239-Pu239 beta decay-chain upon neutron capture by U238). It can be seen that losses to radiative capture on fission products are comparatively negligible over the neutron energy range of interest, and furthermore that atom-fractions of a few tens of percent of high-performance structural material, such as Ta, will impose tolerable loads on the neutron economy in the nuclear fission reactor core assembly 100. These data also suggest that core-averaged fuel burn-up in excess of 50% can be realizable, and that fission product-to-fissile atom-ratios behind the nuclear fission deflagration wave when reactivity is finally driven negative by fission-product accumulation will be approximately 10:1. Origination and Propagation of Nuclear Fission Deflagration Wave Burnfront The nuclear fission deflagration wave within the nuclear fission reactor core assembly 100 will now be explained. Propagation of deflagration burning-waves through combustible materials can release power at a predictable level. Moreover, if the material configuration has the requisite time-invariant features, the ensuing power production may be at a steady level. Finally, if deflagration wave propagation-speed may be externally modulated in a practical manner, the energy release-rate and thus power production may be controlled as desired. For several reasons, steady-state nuclear fission detonation waves are not generally appropriate for power production, such as for electrical power generation and the like. Further, nuclear fission deflagration waves are rare in nature, due to having to prevent the initial nuclear fission fuel configuration from disassembling as a hydrodynamic consequence of energy release during the earliest phases of wave propagation. However, in embodiments of the nuclear fission reactor core assembly 100 a nuclear fission deflagration wave can be initiated and propagated in a sub-sonic manner in fissionable fuel whose pressure is substantially independent of its temperature, so that its hydrodynamics is substantially ‘clamped’. The nuclear fission deflagration wave's propagation speed within the nuclear fission reactor core assembly 100 can be controlled in a manner conducive to large-scale civilian power generation, such as in an electricity-producing reactor system like embodiments of the reactor 10. Nucleonics of the nuclear fission deflagration wave are explained below. Inducing nuclear fission of selected isotopes of the actinide elements—the fissile ones—by capture of neutrons of any energy permits the release of nuclear binding energy at any material temperature, including arbitrarily low ones. Release of more than a single neutron per neutron captured, on the average, by nuclear fission of substantially any actinide isotope admits the possibility-in-principle of a diverging neutron-mediated nuclear-fission chain reaction in such materials. Release of more than two neutrons for every neutron which is captured (over certain neutron-energy ranges, on the average) by nuclear fission by some actinide isotopes admits the possibility-in-principle of 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 of neutron-fissioning the nucleus of the newly-created fissile isotope in the course of a second neutron capture. Most really high-Z (Z≧90) nuclear species can be combusted 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 deflagration wave in the given material can be satisfied. Due to beta-decay in the process of converting a fertile nucleus to a fissile nucleus, the characteristic speed of wave advance is of the order of the ratio of the distance traveled by a neutron from its fission-birth to its radiative capture on a fertile nucleus to the half-life of the (longest-lived nucleus in the chain of) beta-decay leading from the fertile nucleus to the fissile one. Since 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, the characteristic wave-speed is 10−4-10−7 cm sec−1, or 10−13-10−14 of that of a nuclear detonation wave. Such a “glacial” speed-of-advance makes clear that the wave is that of a deflagration wave, not of a detonation wave. The deflagration wave propagates not only very slowly but very stably. If such a wave attempts to accelerate, its leading-edge counters ever-more-pure fertile material (which is quite lossy in a neutronic sense), for the concentration of fissile nuclei well ahead of the center of the wave becomes exponentially low, and thus the wave's leading-edge (referred to herein as a “burnfront”) stalls. Conversely, if the wave slows, however, 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 deflagration 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. The use of both naturally-occurring and man-made ones, such as U235 and Pu239, respectively, in initiating and propagating nuclear fission detonation waves is well-known. Consideration of pertinent neutron cross-sections (shown in FIGS. 1B and 1C) suggests that a nuclear fission deflagration wave can burn a large fraction of a core of naturally-occurring actinides, such as Th232 or U238, 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 capture events which result in fission (rather than merely γ-ray emission). The algebraic sign of the function α(ν-2) constitutes a necessary condition for the feasibility of nuclear fission deflagration 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 nuclear fission reactor core assembly 100. 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(ν2)/ν upper-bounds the fraction of total fission-born neutrons which may be lost to leakage, parasitic absorption, or geometric divergence during deflagration 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 (see FIG. 1C), 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 deflagration wave, neutron leakage may be effectively ignored for very large, “self-reflected” actinide configurations. Referring to FIG. 1C and analytic estimates of the extent of neutron moderation-by-scattering entirely on actinide nuclei, it will be appreciated that deflagration wave propagation can be established in sufficiently large configurations of the two types of actinides that are relatively abundant terrestrially: Th232 and U238, 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). Referring to FIG. 1B, it will be appreciated that fission product nuclei concentrations must significantly exceed fertile ones and fissile nuclear concentrations may be an order-of-magnitude less than the lesser of fission-product or fertile ones before it becomes quantitatively questionable. Consideration of pertinent neutron scattering cross-sections suggests that right circular cylindrical 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 U238-Th232. As an example, studies have indicated that circular cylinders of solid-density Th232 of 25 cm radius, overcoated with an annular shell of 15 cm of C12 (as graphite), may propagate nuclear fission deflagration waves with ≧70% burn-up of the Th232 initially present. Moreover, studies have indicated that replacing the Th232 with half-density U238 may yield similar results—albeit fertile isotope burn-up of ≧80% is realized (as would be expected from inspection of FIG. 1C). A basic condition on the ‘local’ geometry of the breeding-and-burning wave is that the flux history of neutrons excess to the local fissioning process in the core of the burn wave be quantitatively sufficient to at-least-reproduce the fissile atom density 1-2 mean-free-paths into the yet-unburned fuel, in a self-consistent sense. The ‘ash’ behind the burn-wave's peak is substantially ‘neutronically neutral’ in such an accounting scheme, 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's 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 deflagration 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 deflagration waves for arbitrarily great axial distances. However, propagation of nuclear fission deflagration 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 the nuclear fission reactor core 100 will be described later. Propagation of a nuclear fission deflagration wave has implications for embodiments of the nuclear fission reactor 10. As a first example, local material temperature feedback can be imposed on the local nuclear reaction rate at an acceptable expense in the deflagration wave's neutron economy. Such a large negative temperature coefficient of neutronic reactivity confers an ability to control the speed-of-advance of the deflagration 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 exemplary implementations of temperature feedback within embodiments of the nuclear fission reactor core assembly 100 will be discussed later. As a second example of implications of propagation of a nuclear fission deflagration wave on embodiments of the nuclear fission reactor 10, less than all of the total fission neutron production in the nuclear fission reactor 10 may be utilized. For example, the local material-temperature thermostating modules may use around 5-10% of the total fission neutron production in the nuclear fission reactor 10. Another ≦10% of the total fission neutron production in the nuclear fission reactor 10 may be lost to parasitic absorption in the relatively large quantities of high-performance, high temperature, structure materials (such as Ta, W, or Re) employed in structural components of the nuclear fission reactor 10. This loss occurs in order to realize ≧60% thermodynamic efficiency 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, as is indicated for Ta in FIGS. 1B and 1C. A final 5-10% of the total fission neutron production in the nuclear fission reactor 10 may be lost to parasitic absorption in fission products. As noted above, the neutron economy characteristically is sufficiently rich that approximately 0.7 of total fission neutron production is sufficient to sustain deflagration wave-propagation in the absence of leakage and rapid geometric divergence. This is in sharp contrast with (epi) thermal-neutron power reactors employing low-enrichment fuel, for which neutron-economy discipline in design and operation must be strict. As a third example of implications of propagation of a nuclear fission deflagration wave on embodiments of the nuclear fission reactor 10, high burn-ups (on the order of around 50% to around 80%) of initial actinide fuel-inventories which are characteristic of the nuclear fission deflagration waves permit high-efficiency utilization of as-mined fuel—moreover without a requirement for reprocessing. Referring now to FIGS. 1D-1H, features of the fuel-charge of embodiments of the nuclear fission reactor core assembly 100 are depicted at four equi-spaced times during the operational life of the reactor after origination of the nuclear fission deflagration wave (sometimes referred to herein as “nuclear fission ignition”) in a scenario in which full reactor power is continuously demanded over a ⅓ century time-interval. In the embodiment shown, two nuclear fission deflagration wavefronts propagate from an origination point 28 (near the center of the nuclear fission reactor core assembly 100) toward ends of the nuclear fission reactor core assembly 100. Corresponding positions of the leading edge of the nuclear fission deflagration wave-pair at various time-points after full ignition of the fuel-charge of the nuclear fission reactor core assembly 100 are indicated in FIG. 1D. FIGS. 1E, 1F, 1G, and 1G illustrate masses (in kg of total mass per cm of axial core-length) of various isotopic components in a set of representative near-axial zones and fuel specific power (in W/g) at the indicated axial position as ordinate-values versus axial position along an exemplary, non-limiting 10-meter-length of the fuel-charge as an abscissal value at approximate times after nuclear fission ignition of approximately 7.5 years, 15 years, 22.5 years, and 30 years, respectively. The central perturbation is due to the presence of the nuclear fission igniter module indicated by the origination point 28 (FIG. 1D). 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 deflagration wave. After the nuclear fission deflagration 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 also be noted that in the illustrated embodiments, differing actions of two slightly different types of thermostating units on the left and the right sides of the igniter module account for the corresponding slightly differing power production levels. Still referring to FIGS. 1D-1H, it can be seen that well behind the nuclear fission deflagration 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 (FIG. 1B), the “local neutronic reactivity” thereupon goes slightly negative, and both burning and breeding effectively cease—as will be appreciated from comparing FIGS. 1E, 1F, 1G, and 1H with each other, far behind the nuclear fission deflagration wave burnfront. In some embodiments of the nuclear fission reactor 10, all the nuclear fission fuel ever used in the reactor is installed during manufacture of the nuclear fission reactor core assembly 100, and no spent fuel is ever removed from the nuclear fission reactor core assembly 100, which is never accessed after nuclear fission ignition. However, in some other embodiments of the nuclear fission reactor 10, additional nuclear fission fuel is added to the nuclear fission reactor core assembly 100 after nuclear fission ignition. However, in some other embodiments of the nuclear fission reactor 10, spent fuel is removed from the reactor core assembly (and, in some embodiments, removal of spent fuel from the nuclear fission reactor core assembly 100 may be performed while the nuclear fission reactor 10 is operating at power). 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 deflagration wave sweeps over any given axial element of actinide ‘fuel,’ converting it into fission-product ‘ash.’ Launching of nuclear fission deflagration waves into Th232 or U238 fuel-charges is readily accomplished with ‘nuclear fission igniter modules’ enriched in fissile isotopes. Higher enrichments result in 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. Such modules may employ U235 in U238, in sufficiently low concentration as to be effectively non-detonatable in any quantity or configuration—such as ≦0%—in contrast, for example, to technically more optimal Pu239 in Th232. Quantities of U235 already excess to military stockpiles suffice for ≧104 such nuclear fission igniter modules, corresponding to a total inventory of nuclear fission power reactors sufficient to supply 10 billion people with kilowatt-per-capita electricity. While the illustrative nuclear fission igniter of the previously described embodiments included nuclear fission material configured to initiate propagation of the burning wavefront, in other approaches, the nuclear fission igniter may include other types of reactivity sources in addition to or in place of those previously described. For example, 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 deflagration wave reactor. Such “burning embers” may function as nuclear fission igniters, despite the presence of various amounts of fission products “ash”. For example, nuclear fission igniters may include neutron sources using 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 initiate the propagating fission wave. Now that nucleonics of the fuel charge and the nuclear fission deflagration wave have been discussed, further details regarding “nuclear fission ignition” and maintenance of the nuclear fission deflagration wave will be discussed. A centrally-positioned nuclear fission igniter moderately enriched in fissionable material, such as U235, has a neutron-absorbing material (such as a borohydride) removed from it (such as by operator-commanded electrical heating), and the nuclear fission igniter becomes neutronically critical. Local fuel temperature rises to a design set-point and is regulated thereafter by the local thermostating modules (discussed in detail later). Neutrons from the fast fission of U235 are mostly captured at first on local U238 or Th232. 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. The maximum (unregulated) reactivity of the nuclear fission reactor core assembly 100 slowly decreases in the first phase of the nuclear fission ignition process because, although the total fissile isotope inventory is increasing monotonically, this total inventory is becoming 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. A quasi-spherical annular shell then provides maximum specific power production. At this point, the fuel-charge of the nuclear fission reactor core assembly 100 is referred to as “ignited.” Now that the fuel-charge of the nuclear fission reactor core assembly 100 has been “ignited”, propagation of the nuclear fission deflagration wave, also referred to herein as “nuclear fission burning”, will now be discussed. 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 this surface, it naturally breaks into two spherical zonal surfaces, with one surface propagating in each of the two opposite directions along the axis of the cylinder. At this time-point, the full thermal power production potential of the core has been developed. This epoch is characterized as that of the launching of the two axially-propagating nuclear fission deflagration 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 one end, as desired for a particular application. 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 deflagration waves will 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 deflagration waves may be initiated and propagated. However, for sake of understanding, the discussion herein refers, without limitation, to propagation of two nuclear fission deflagration wave burnfronts. From this time forward through the break-out of the two waves when they reach the two opposite ends, the physics of nuclear power generation is effectively time-stationary in the frame of either wave, as illustrated in FIGS. 1E-1H. 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 demanded from the nuclear fission reactor core assembly 100 via the collective action on the nuclear fission deflagration wave's neutron budget of the thermostating modules (not shown). When more power is demanded from the reactor via lower-temperature coolant flowing into the core, 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. 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 of the thermostating modules—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, as illustrated in FIGS. 1E-1H. Thus, the core's neutronics 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). The primary function of the neutron reflector in such core designs is to drastically reduce the fast neutron fluence seen by the outer portions of the reactor, such as its radiation shield, structural supports, thermostating modules and outermost shell. Its incidental influence on the performance of the core is to improve the breeding efficiency and the specific power in the outermost portions of the fuel, though the value of this is primarily an enhancement of 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. Final, irreversible negation of the core's neutronic reactivity may be performed at any time by injection of neutronic poison into the coolant stream, via either the primary loops which extend to the application heat exchangers 16 (FIG. 1A) or the afterheat-dumping loops connecting the nuclear fission reactor 10 (FIG. 1A) to the heat dump heat exchangers 26 (FIG. 1A). For example, lightly loading the 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 the 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 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. Exemplary embodiments and aspects of the nuclear fission reactor core assembly 100 and exemplary nuclear fission fuel charges disposed therein will now be discussed. Referring now to FIG. 1I, the nuclear fission reactor core assembly 100 is suitable for use with a fast neutron spectrum nuclear fission reactor. It will be appreciated that the nuclear fission reactor core assembly 100 is shown schematically in FIG. 1I. As such, no geometric limitations are intended regarding shape of the nuclear fission reactor core assembly 100. As mentioned above, details were discussed for circular cylinders of natural uranium or thorium metal that may stably propagate nuclear fission deflagration waves for arbitrarily great axial distances. However, it is again emphasized that propagation of nuclear fission deflagration waves is not to be construed to be limited to circular cylinders or to metallic nuclear fission fuels, or to pure uranium or thorium nuclear fission fuel materials. To that end, additional embodiments of alternate geometries of the nuclear fission reactor core assembly 100 and fuel charges disposed therein will be described later. A neutron reflector/radiation shield 120 surrounds nuclear fission fuel 130. The nuclear fission fuel 130 is fissionable material, that is material appropriate for undergoing fission in a nuclear fission reactor, examples of which are actinide or transuranic elements. As discussed above, the fissionable material for the nuclear fission fuel 130 may include without limitation Th232 or U238. However, in other embodiments discussed below, other fissionable material may be used in the nuclear fission fuel 130. In some embodiments, the nuclear fission fuel 130 is contiguous. In other embodiments, the nuclear fission fuel 130 is non-contiguous. A nuclear fission igniter 110 acts within the nuclear fission fuel 130 for initiating a nuclear fission deflagration wave burnfront (not shown). The nuclear fission igniter 110 is made and operates according to principles and details discussed above. Therefore, details of construction and operation of the nuclear fission igniter 110 need not be repeated for sake of brevity. Referring now to FIG. 1J, after the nuclear fission fuel 130 (FIG. 1I) has been ignited by the nuclear fission igniter 110 (in a manner as discussed above), a propagating burnfront 140 (that is, a propagating nuclear fission deflagration wave burnfront, as discussed above) is initiated and propagates throughout the nuclear fission fuel 130 (FIG. 1I) a direction shown by an arrow 144. As discussed above, a region 150 of maximum reactivity is established around the propagating burnfront 140. The propagating burnfront 140 propagates through unburnt nuclear fission fuel 154 in the direction indicated by the arrow 144, leaving behind the propagating burnfront 140 burnt nuclear fission fuel 160 that includes fission products 164, such as isotopes of iodine, cesium, strontium, xenon, and/or barium (and referred to in the discussion above as “fission product ash”). In the context of burnt nuclear fission fuel and unburnt nuclear fission fuel, the term “burning” (as applied to nuclear fission fuel) means that at least some components of the nuclear fission fuel undergo neutron-mediated nuclear fission. In the context of propagating nuclear fission deflagration wave burnfronts, the terms “burning” and “burnt” also mean that at least some components of the nuclear fission fuel undergo “breeding”, whereby neutron absorption is followed by multi-second half-life beta-decay transmutation into one or more fissile isotopes, which then may or may not undergo neutron-mediated nuclear fission. Thus, the unburnt nuclear fission fuel 154 may be considered a first neutron environment having a first set of neutron environment parameters. Similarly, the burnt nuclear fission fuel 160 may be considered a second neutron environment having a second set of neutron environment parameters that are different than the first set of neutron environment parameters. The term “neutron environment” refers to the detailed neutron distribution, including its variation with respect to time, space, direction, and energy. The neutron environment includes the aggregate of multiple individual neutrons, each of which may occupy different locations at different times, and each of which may have different directions of motion and different energies. In some circumstances, a nuclear environment may be characterized by a reduced subset of these detailed properties. In one example, a reduced subset may include an aggregation of all neutrons within given space, time, direction, and energy ranges of specified time, space, direction, and energy values. In another example, some or all of the time, space, direction, or energy aggregations may incorporate value-dependent weighting functions. In another example, a reduced subset may include weighted aggregation over the full range of direction and energy values. In another example, the aggregation over energies may involve energy-dependent weighting by a specified energy function. Examples of such weighting functions include material and energy-dependent cross-sections, such as those for neutron absorption or fission. In some embodiments, only the propagating burnfront 140 is originated and propagated through the unburnt nuclear fission fuel 154. In such embodiments, the nuclear fission igniter 110 may be located as desired. For example, the nuclear fission igniter 110 may be located toward the center of the nuclear fission fuel 130 (FIG. 10. In other embodiments (not shown) the nuclear fission igniter 110 may be located toward an end of the nuclear fission fuel 130. In other embodiments, in addition to the propagating burnfront 140, a propagating burnfront 141 is originated and propagated through the other fuel 154 along a direction indicated by an arrow 145. A region 151 of maximum reactivity is established around the obligating burnfront 141. The propagating burnfront 141 leaves behind it the burnt nuclear fission fuel 160 and the fission products 164. Principles and details of origination and propagation of the propagating burnfront 141 are the same as that previously discussed for the propagating burnfront 140. Therefore, details of origination and propagation of the propagating burnfront 141 need not be provided for sake of brevity. Referring now to FIG. 2A, a nuclear fission reactor 200, such as a fast neutron spectrum nuclear fission reactor, includes nuclear fission fuel assemblies 210 disposed therein. The following discussion includes details of exemplary nuclear fission fuel assemblies 210 that may be used in the nuclear fission reactor 200. Other details regarding the nuclear fission reactor 200, including origination and propagation of a nuclear fission deflagration wave burnfront (that is, “burning” the nuclear fission fuel) are similar to those of the nuclear fission reactor 10 (FIG. 1A), and need not be repeated for sake of brevity. Referring now to FIG. 2B and given by way of non-limiting example, in one embodiment the nuclear fission fuel assembly 210 suitably includes a previously burnt nuclear fission fuel assembly 220. The previously burnt nuclear fission fuel assembly 220 is clad with cladding 224. The cladding 224 is the “original” cladding in which the previously burned nuclear fission fuel assembly 220 was clad. The term “previously burnt” means that at least some components of the nuclear fission fuel assembly have undergone neutron-mediated nuclear fission and that the isotopic composition of the nuclear fission fuel has been modified. That is, the nuclear fission fuel assembly has been put in a neutron spectrum or flux (either fast or slow), at least some components have undergone neutron-mediated nuclear fission and, as result, the isotopic composition of the nuclear fission fuel has been changed. Thus, a burnt nuclear fission fuel assembly 220 may have been previously burnt in any reactor, such as without limitation a light water reactor. It is intended that the previously burnt nuclear fission fuel assembly 220 can include without limitation any type of nuclear fissionable material whatsoever appropriate for undergoing fission in a nuclear fission reactor, such as actinide or transuranic elements like natural thorium, natural uranium, enriched uranium, or the like. In some other embodiments, the previously burnt nuclear fission fuel assembly 220 may not be clad with “original” cladding 224, but in these embodiments, the previously burnt nuclear fission fuel assembly 220 is chemically untreated subsequent to its previous burning in the nuclear fission reactor 200. Referring now to FIG. 2C, the previously burnt nuclear fission fuel assembly 220 and its “original” cladding 224 is clad with cladding 230. Thus, the previously burnt nuclear fission fuel assembly 220 is retained in its original cladding 224, and the cladding 230 is disposed around an exterior of the cladding 224. The cladding 230 can accommodate swelling. For example, when the previously burnt nuclear fission fuel assembly 220 was burnt in a light water reactor, the cladding 224 was sufficient to contain swelling at approximately 3% burn-up of the previously burnt nuclear fission fuel assembly 220. In one nonlimiting example, the cladding 230 contacts the cladding 224 at azimuthally, symmetric, cylindrical faces around the cladding 224. Such an arrangement enables removal of heat through the contacting faces while allowing at least one half of the cladding 224 to expand into void spaces between the cladding 224 and the cladding 230. In some embodiments, the cladding 230 is made up of cladding sections (not shown) that are configured to help accommodate swelling into the void spaces, as described above. In other embodiments, the cladding 230 may be provided as a barrier, such as a tube, provided between an exterior of the cladding 224 and reactor coolant (not shown). In some other embodiments, the previously burned nuclear fission fuel assembly 220 is burnt in the nuclear fission reactor 200 as the nuclear fission fuel assembly 210. That is, the previously burnt nuclear fission fuel assembly 220 may not be clad with the cladding 230. This embodiment envisions burning the previously burnt nuclear fission fuel assembly 220, such as one that was burnt in a light water reactor, or in a fast neutron spectrum nuclear fission reactor, or in any other form of nuclear fission reactor and either (a) tolerating or planning to accept possible failure of the cladding 224 due to swell or, (b) burning the previously burnt nuclear fission fuel assembly 220 in the fast neutron spectrum nuclear fission reactor 200 to levels significantly less than isotopic depletion (in which case swelling may be of acceptable magnitude). Referring now to FIGS. 3A, 3B, 3C, and 3D, alternate nuclear fission fuel geometries of nuclear fission fuel structures 310, 320, 330, and 340, respectively, are discussed. Each of the nuclear fission fuel structures 310, 320, 330, and 340 includes a nuclear fission igniter 300, and a propagating nuclear fission deflagration wave 302 is propagated in a direction indicated by an arrow 304. In a spherical nuclear fission fuel structure 310 (FIG. 3A), the nuclear fission igniter 300 is disposed toward a center of the spherical nuclear fission fuel structure 310. The propagating burnfront 302 propagates radially outward from the nuclear fission igniter 300, as indicated by the arrows 304. In a parallelepiped nuclear fission fuel structure 320, the nuclear fission igniter 300 is disposed as desired. As discussed above, two propagating burnfronts 302 may be originated and propagated toward ends of the parallelepiped nuclear fission fuel structure 320 along directions indicated by the arrows 304. Alternately, the nuclear fission igniter 300 may be disposed toward an end of the parallelepiped nuclear fission fuel structure 320, in which case one propagating burnfront 302 is originated and propagates toward the other end of the parallelepiped nuclear fission fuel structure 320 along the direction indicated by the arrow 304. In a toroidal nuclear fission fuel structure 330 (FIG. 3C), the nuclear fission igniter 300 is disposed as desired. Two propagating burnfronts 302 may be originated and propagated away from the nuclear fission igniter 300 and toward each other along directions indicated by the arrows 304. In such a case, the toroidal nuclear fission fuel structure 330 may be considered to be “burnt” when the propagating burnfronts 302 meet, and propagation of the propagating burnfront 302 may stop. Alternately, only one propagating burnfront 302 is originated and propagates around the toroidal nuclear fission fuel structure 330 along the direction indicated by the arrow 304. In such a case, the toroidal nuclear fission fuel structure 330 may be considered to be “burnt” when the propagating burnfront 302 returns to the site of the nuclear fission igniter 300, and propagation of the propagating burnfront 302 may stop or may be re-started. In another embodiment, the propagating burnfront 302 is “restarted” due to the removal or decay of fission products during the burnfront's propagation around the toroid. In another embodiment, the propagating burnfront 302 is “restarted” due to control of neutron modifying structures, as discussed later. In another embodiment, the toroidal nuclear fission fuel structure 330 is not a “geometric” toroid, but a “logical” toroid, with a more general reentrant structure. As mentioned above, nuclear fission deflagration propagating wave burnfronts can be initiated and propagated in nuclear fission fuels having any shape as desired. For example, in an irregularly-shaped nuclear fission fuel structure 340, the nuclear fission igniter 300 can be located as desired. Propagating burnfronts 302 are initiated and propagate along directions indicated by the arrows 304 as desired for a particular application. In one approach, thermal management may be adjusted to provide thermal control appropriate for any changes in operational parameters, such as revised neutronic action of the previously burnt or modified nuclear fission fuel or other parameter changes, that may result from removal of ash, addition of fuels, or from other parameters of re-burning. In these exemplary geometries, the nuclear fission ignitor 300 may be any of the varieties of nuclear fission ignitor previously discussed. The indicated nuclear fission ignitor 300 is the site at which nuclear fission ignition occurs, but for some embodiments (e.g., electrical neutron sources) additional components of the nuclear fission ignitor may exist, and may reside in different physical locations. Referring now to FIG. 4, a nuclear fission fuel structure 400 includes a nuclear fission igniter 410 and non-contiguous segments 420 of nuclear fission fuel material. The behavior of a nuclear fission deflagration wave with non-contiguous segments 420 of nuclear fission fuel material is similar to that previously discussed for contiguous nuclear fission fuel material; it is crucial only that the non-contiguous segments 420 be in “neutronic” contact, not physical contact. Referring now to FIG. 5, a modular nuclear fission fuel core 500 includes a neutron reflector/radiation shield 510 and modular nuclear fission fuel assemblies 520. The modular nuclear fission fuel assemblies 520 are placed as desired within the fuel assembly receptacles 530. The modular nuclear fission fuel core 500 may be operated in any number of ways. For example, all of the fuel assembly receptacles 530 in the modular nuclear fission fuel core 500 may be fully populated with modular nuclear fission fuel assemblies 520 prior to initial operation (e.g., prior to initial origination and propagation of a nuclear fission deflagration propagating wave burnfront within and through the modular nuclear fission fuel assemblies 520). As another example, after a nuclear fission deflagration wave burnfront has completely propagated through modular nuclear fission fuel assemblies 520, such “burnt” modular nuclear fission fuel assemblies 520 may be removed from their respective fuel assembly receptacles 530 and replaced with unused modular nuclear fission fuel assemblies 540, as desired; this emplacement is indicated by the arrow 544. A nuclear fission deflagration wave burnfront can be initiated in the unused modular nuclear fission fuel assemblies 540, thereby enabling continued or extended operation of the modular nuclear fission fuel core 500 as desired. As another example, the modular nuclear fission fuel core 500 need not be fully populated with modular nuclear fission fuel assemblies 520 prior to initial operation. For example, less than all of the fuel assembly receptacles 530 can be populated with modular nuclear fission fuel assemblies 520. In such a case, the number of modular nuclear fission fuel assemblies 520 that are placed within the modular nuclear fission fuel core 500 can be determined based upon power demand, such as electrical loading in watts, that will be placed upon the modular nuclear fission fuel core 500. A nuclear fission deflagration wave burnfront is originated and propagated through the modular nuclear fission fuel assemblies 520 as previously described. In one approach, thermal management may be adjusted to provide thermal control appropriate to maintain the inserted fuel assembly receptacles 530 at appropriate temperatures. As another example, the modular nuclear fission fuel core 500 again need not be fully populated with modular nuclear fission fuel assemblies 520 prior to initial operation. The number of modular nuclear fission fuel assemblies 520 provided may be determined based upon a number of modular nuclear fission fuel assemblies 520 that are available or for other reasons. A nuclear fission deflagration wave burnfront is originated and propagates through the modular nuclear fission fuel assemblies 520. As the nuclear fission deflagration wave burnfront approaches unpopulated fuel assembly receptacles 530, the unpopulated fuel assembly receptacles 530 can be populated with modular nuclear fission fuel assemblies 520, such as on a “just-in-time” basis; this emplacement is indicated by the arrow 544. Thus, continued or extended operation of the modular nuclear fission fuel core 500 can be enabled without initially fueling the entire modular nuclear fission fuel core 500 with modular nuclear fission fuel assemblies 520. It will be appreciated that the concept of modularity can be extended. For example, in other embodiments, a modular nuclear fission reactor can be populated with any number of nuclear fission reactor cores in the same manner that the modular nuclear fission fuel core 500 can be populated with any number of modular nuclear fission fuel assemblies 520. To that end, the modular nuclear fission reactor can be analogized to the modular nuclear fission fuel core 500 and nuclear fission reactor cores can be analogized to the modular nuclear fission fuel assemblies 520. The several contemplated modes of operation discussed above for the modular nuclear fission fuel core 500 thus apply by analogy to a modular nuclear fission reactor. Applications of modular designs are shown in FIGS. 6A-6C. Referring to FIG. 6A, a nuclear fission facility 600 includes a fast neutron spectrum nuclear fission core assembly 610 that is operationally coupled to an operational sub system 620 (such as without limitation an electrical power generating facility) via a core-subsystem coupling 630 (such as without limitation a reactor coolant system such as a primary loop and, if desired, a secondary loop including a steam generator). Referring now to FIG. 6B, another fast neutron spectrum nuclear fission core assembly 610 may be emplaced within the nuclear fission facility 600. The additional fast neutron spectrum nuclear fission core assembly 610 is operationally coupled to another operational sub system 620 by another core-subsystem coupling 630: The operational sub system's 620 are coupled to each other via a subsystem-subsystem coupling 640. A subsystem-subsystem coupling 640 can provide prime mover or other energy transfer medium between the operational sub systems 620. To that end, energy produced by any one of the nuclear core assemblies 610 can be transferred to any operational sub system 620 as desired. Referring now to FIG. 6C, a third fast neutron spectrum nuclear fission core assembly 610, and associated operational sub system 620, and core-subsystem coupling 630 have been placed in the nuclear fission facility 600. Again, as described above, energy produced by any one of the fast neutron spectrum nuclear fission core assemblies 610 can be transferred to any operational sub system 620 as desired. In other embodiments, this linking process can be more general than discussed above, so that, the nuclear fission facility 600 may consist of a number N of fast neutron spectrum nuclear fission core assemblies 610, and a same or different number M of operational subsystems 620. It will be appreciated, that the individual nuclear fast neutron spectrum nuclear fission core assemblies 610 need not be identical to each other, nor need the operational sub systems 620 be identical to each other. Similarly, the core-subsystem couplings 630 need not be identical to each other, nor do the subsystem-subsystem couplings 640 need be identical to each other. In addition to the operational sub system 620 embodiment discussed above, other embodiments of operational sub system 620 include, without limitation, reactor coolant systems, electrical nuclear fission ignitors, afterlife heat-dumps, reactor site facilities (such as basing and security), and the like. Referring now to FIG. 7, heat energy can be extracted from a nuclear fission reactor core according to another embodiment. In a nuclear fission reactor 700, a nuclear fission deflagration wave burnfront is initiated and propagated in a burning wavefront heat generating region 720, in a manner as described above. Heat absorbing material 710, such as a condensed phase density fluid (e.g., water, liquid metals, terphenyls, polyphenyls, fluorocarbons, FLIBE (2LiF—BeF2) and the like) flows through the region 720 as indicated by an arrow 750, and heat is transferred from the propagating burnfront fission to the heat absorbing material 710. In some fast fission spectrum nuclear reactors, the heat absorbing material 710 is chosen to be a nuclear inert material (such as He4) so as to minimally perturb the neutron spectrum. In some embodiments of the nuclear fission reactor 700, the neutron content is sufficiently robust, so that a non-nuclear-inert heat absorbing material 710 may be acceptably utilized. The heat absorbing material 710 flows to a heat extraction region 730 that is substantially out of thermal contact with the burning wavefront heat generating region 720. The energy 740 is extracted from the heat absorbing material 710 at the heat extraction region 730. The heat absorbing material 710 can reside in either a liquid state, a multiphase state, or a substantially gaseous state upon extraction of the heat energy 740 in the heat extraction region 730. Referring now to FIG. 8, in some embodiments a nuclear fission deflagration wave burnfront can be driven into areas of nuclear fission fuel as desired, thereby enabling a variable nuclear fission fuel burn-up. In a propagating burnfront nuclear fission reactor 800, a nuclear fission deflagration wave burnfront 810 is initiated and propagated as described above. Actively controllable neutron modifying structures 830 can direct or move the burnfront 810 in directions indicated by areas 820. In one embodiment, the actively controllable neutron modifying structures 830 insert neutron absorbers, such as without limitation Li6, B10, or Gd, into nuclear fission fuel behind the burnfront 810, thereby driving down or lowering neutronic reactivity of fuel that is presently being burned by the burnfront 810 relative to neutronic reactivity of fuel ahead of the burnfront 810, thereby speeding up the propagation rate of the nuclear fission deflagration wave. In another embodiment, the actively controllable neutron modifying structures 830 insert neutron absorbers into nuclear fission fuel ahead of the burnfront 810, thereby slowing down the propagation of the nuclear fission deflagration wave. In other embodiments the actively controllable neutron modifying structures 830 insert neutron absorbers into nuclear fission fuel within or to the side of the burnfront 810, thereby changing the effective size of the burnfront 810. In another embodiment, the actively controllable neutron modifying structures 830 insert neutron moderators, such as without limitation hydrocarbons or Li7, thereby modifying the neutron energy spectrum, and thereby changing the neutronic reactivity of nuclear fission fuel that is presently being burned by the burnfront 810 relative to neutronic reactivity of nuclear fission fuel ahead of or behind the burnfront 810. In some situations, an effect of the neutron moderators is associated with detailed changes in the neutron energy spectrum (e.g., hitting or missing cross-section resonances), while in other cases the effects are associated with lowering the mean neutron energy of the neutron environment (e.g., downshifting from “fast” neutron energies to epithermal or thermal neutron energies). In yet other situations, an effect of the neutron moderators is to deflect neutrons to or away from selected locations. In some embodiments, one of the aforementioned effects of neutron moderators is of primary importance, while in other embodiments, multiple effects are of comparable design significance. In another embodiment, the actively controllable neutron modifying structures 830 contain both neutron absorbers and neutron moderators; in one nonlimiting example, the location of neutron absorbing material relative to that of neutron moderating material is changed to affect control (e.g., by masking or unmasking absorbers, or by spectral-shifting to increase or decrease the absorption of absorbers), in another nonlimiting example, control is affected by changing the amounts of neutron absorbing material and/or neutron moderating material. The burnfront 810 can be directed as desired according to selected propagation parameters. For example, propagation parameters can include a propagation direction or orientation of the burnfront 810, a propagation rate of the burnfront 810, power demand parameters such the heat generation density, cross-sectional dimensions of a burning region through which the burnfront 810 is to the propagated (such as an axial or lateral dimension of the burning region relative to an axis of propagation of the burnfront 810), or the like. For example, the propagation parameters may be selected so as to control the spatial or temporal location of the burnfront 810, so as to avoid failed or malfunctioning control elements (e.g., neutron modifying structures or thermostats), or the like. Referring now to FIGS. 9A and 9B, a nuclear fission reactor can be controlled with programmable thermostats, thereby enabling the temperature of the reactor's fuel-charge to be varied over time responsive to changes in operating parameters. Temperature profiles 940 are determined as a function of position through a fuel-charge of a nuclear fission reactor 900. An operating temperature profile 942 of operating temperatures throughout the nuclear fission reactor 900 is established responsive to a first set of operating parameters, such as predicted power draw, thermal creep of structural materials, etc. At other times, or in other circumstances, the operating parameters may be revised. To that end, a revised operating temperature profile 944 of revised operating temperatures throughout the nuclear fission reactor 900 is established. The nuclear fission reactor 900 includes programmable temperature responsive neutron modifying structures 930. The programmable temperature responsive neutron modifying structures 930 (an example of which is described in detail later) introduce and remove neutron absorbing or neutron moderating material into and from the fuel-charge of a nuclear fission reactor 900. A nuclear fission deflagration wave burnfront 910 is initiated and propagated in a fuel-charge of the nuclear fission reactor 900. Responsive to the revised operating temperature profile 944, the programmable temperature responsive neutron modifying structures 930 introduce neutron absorbing or moderating material into the fuel-charge of the nuclear fission reactor 900 to lower operating temperature in the nuclear fission reactor 900 or remove neutron absorbing or moderating material from the fuel-charge of the nuclear fission reactor 900 in order to raise operating temperature of the nuclear fission reactor 900. It will be appreciated, that operating temperature profiles are only one example of control parameters which can be used to determine the control settings of programmable temperature responsive neutron modifying structures 930, which are in such cases responsive to the selected control parameters, not necessarily to the temperature. Nonlimiting examples of other control parameters which can be used to determine the control settings of programmable temperature responsive neutron modifying structures 930 include power levels, neutron levels, neutron spectrum, neutron absorption, fuel burnup levels, and the like. In one example, the neutron modifying structures 930 are used to control fuel burnup levels to relatively low (e.g., <50%) levels in order to achieve high-rate “breeding” of nuclear fission fuel for use in other nuclear fission reactors, or to enhance suitability of the burnt nuclear fission fuel for subsequent re-propagation of a nuclear fission deflagration wave in a propagating nuclear fission deflagration wave reactor. Different control parameters can be used at different times, or in different portions of the reactor. It will be appreciated that the various neutron modifying methods discussed previously in the context of neutron modifying structures can also be utilized in programmable temperature responsive neutron modifying structures 930, including without limitation, the use of neutron absorbers, neutron moderators, combinations of neutron absorbers and/or neutron moderators, variable geometry neutron modifiers, and the like. According to other embodiments and referring now to FIGS. 10A and 10B, material can be nuclearly processed. As shown in FIG. 10A, nuclearly processable material 1020 (that has a set of non-irradiated properties) is placed in a propagating nuclear fission deflagration wave reactor 1000. A nuclear fission deflagration wave propagating burnfront 1030 is originated and propagated along a direction indicated by arrows 1040 as described above. The material 1020 is placed in neutronic coupling with a region of maximized reactivity 1010, that is the material is neutron irradiated, as the nuclear fission deflagration wave propagating burnfront 1030 propagates through or in the vicinity of the material 1020, thereby irradiating the material 1020 and conferring upon the material 1020 a desired set of modified properties. In one embodiment, the neutron irradiation of material 1020 may be controlled by the duration and/or extent of the nuclear fission deflagration wave propagating burnfront 1030. In another embodiment, the neutron irradiation of material 1020 may be controlled by control of the neutron environment (e.g., the neutron energy spectrum for Np237 processing) via neutron modifying structures. In another embodiment, the propagating nuclear fission deflagration wave reactor 1000 may be operated in a “safe” sub-critical manner, relying upon an external source of neutrons to sustain the propagating burnfront 1030, while using a portion of the fission-generated neutrons for nuclear processing of the material 1020. In some embodiments, the material 1020 may be present before nuclear fission ignition occurs within the propagating nuclear fission deflagration wave reactor 1000, while in other embodiments the material 1020 may be added after nuclear fission ignition. In some embodiments, the material 1020 is removed from the propagating nuclear fission deflagration wave reactor 1000, while in other embodiments it remains in place. Alternately and as shown in FIG. 10B, a nuclear fission deflagration wave propagating burnfront 1030 is initiated and propagated in a propagating nuclear fission deflagration wave reactor 1000 along a direction indicated by arrows 1040. Material 1050 having a set of non-irradiated properties is loaded into the propagating nuclear fission deflagration wave reactor 1000. As indicated generally at 1052, the material 1050 in transported into physical proximity and neutronic coupling with a region of maximized reactivity as the nuclear fission deflagration wave propagating burnfront 1030 passes through the material 1050. The material 1050 remains in neutronic coupling for a sufficient time interval to convert the material 1050 into material 1056 having a desired set of modified properties. Upon the material 1050 having thus been converted into the material 1056, the material 1056 may be physically transported out of the reactor 1000 as generally indicated at 1054. The removal 1054 can take place either during operation of the propagating nuclear fission deflagration wave reactor 1000 or afterward it has been “shut-off”, and can be performed in either a continuous, sequential, or batch process. In one example, the nuclearly processed material 1056 may be subsequently used as nuclear fission fuel in another nuclear fission reactor, such as without limitation LWRs or propagating nuclear fission deflagration wave reactors. In another nonlimiting example, the nuclearly processed material 1056 may be subsequently used within the nuclear fission ignitor of a propagating nuclear fission deflagration wave reactor. In one approach, thermal management may be adjusted to provide thermal control appropriate for any changes in operational parameters, as appropriate for the revised materials or structures. According to further embodiments, temperature-driven neutron absorption can be used to control a nuclear fission reactor, thereby “engineering-in” an inherently-stable negative temperature coefficient of reactivity (αT). Referring now to FIG. 11A, a nuclear fission reactor 1100 is instrumented with temperature detectors 1110, such as without limitation thermocouples. In this embodiment. the nuclear fission reactor 1100 suitably can be any type of fission reactor whatsoever. To that end, the nuclear fission reactor 1100 can be a thermal neutron spectrum nuclear fission reactor or a fast neutron spectrum nuclear fission reactor, as desired for a particular application. The temperature detectors detect local temperature in the nuclear fission reactor 1100 and generate a signal 1114 indicative of a detected local temperature. The signal 1114 is transmitted to a control system 1120 in any acceptable manner, such as without limitation, fluid coupling, electrical coupling, optical coupling, radiofrequency transmission, acoustic coupling, magnetic coupling, or the like. Responsive to the signal 1114 indicative of the detected local temperature, the control system 1120 determines an appropriate correction (positive or negative) to local neutronic reactivity in the nuclear fission reactor 1100 to return the nuclear fission reactor 1100 to desired operating parameters (such as desired local temperatures for full reactor power). To that end, the control system 1120 generates a control signal 1124 indicative of a desired correction to local neutronic reactivity. The control signal 1124 is transmitted to a dispenser 1130 of neutron absorbing material. The signal 1124 suitably is transmitted in the same manner as the signal 1114. The neutron absorbing material suitably is any neutron absorbing material as desired for a particular application, such as without limitation Li6, B10, or Gd. The dispenser 1130 suitably is any reservoir and dispensing mechanism acceptable for a desired application, and may, for example, have the reservoir located remotely (e.g., outside the neutron reflector of the nuclear fission reactor 1100) from the dispensing mechanism 1130. The dispenser 1130 dispenses the neutron absorbing material within the nuclear fission reactor core responsive to the control signal 1124, thereby altering the local neutronic reactivity. Referring now to FIG. 11B and given by way of non-limiting example, exemplary thermal control may be established with a neutron absorbing fluid. A thermally coupled fluid containing structure 1140 contains a fluid in thermal communication with a local region of the nuclear fission reactor 1100. The fluid in the structure 1140 expands or contracts responsive to local temperature fluctuations. Expansion and/or contraction of the fluid is operatively communicated to a force coupling structure 1150, such as without limitation a piston, located external to the nuclear fission reactor 1100. A resultant force communicated by the force coupling structure 1150 is exerted on neutron absorbing fluid in a neutron absorbing fluid containing structure 1160. The neutron absorbing fluid is dispensed accordingly from the structure 1160, thereby altering the local neutronic reactivity. In another example, a neutron moderating fluid may be used instead of, or in addition to, the neutron absorbing fluid. The neutron moderating fluid changes the neutron energy spectrum and lowers the mean neutron energy of the local neutron environment, thereby driving down or lowering neutronic reactivity of nuclear fission fuel within the nuclear fission reactor 1100. In another example, the neutron absorbing fluid and/or the neutron modifying fluid may have a multiple phase composition (e.g., solid pellets within a liquid). FIG. 11C illustrates details of an exemplary implementation of the arrangement shown in FIG. 11B. Referring now to FIG. 11C, fuel power density in a nuclear fission reactor 1100′ is continuously regulated by the collective action of a distributed set of independently-acting thermostating modules, over very large variations in neutron flux, significant variations in neutron spectrum, large changes in fuel composition and order-of-magnitude changes in power demand on the reactor. This action provides a large negative temperature coefficient of reactivity just above the design-temperature of the nuclear fission reactor 1100′. Located throughout the fuel-charge in the nuclear fission reactor 1100′ in a 3-D lattice (which can form either a uniform or a non-uniform array) whose local spacing is roughly a mean free path of a median-energy-for-fission neutron (or may be reduced for redundancy purposes), each of these modules includes a pair of compartments 1140′ and 1160′, each one of which is fed by a capillary tube. The small thermostat-bulb compartment 1160′ located in the nuclear fission fuel contains a thermally sensitive material, such as without limitation, Li7, whose neutron absorption cross-section may be low for neutron energies of interest, while the relatively large compartment 1140′ positioned in a different location (e.g., on the wall of a coolant tube) may contain variable amounts of a neutron absorbing material, such as without limitation, Li6, which has a comparatively large neutron absorption cross-section. Lithium melts at 453 K and 1-bar-boils at 1615 K, and therefore is a liquid across typical operating temperature ranges of the nuclear fission reactor 1100′. As the fuel temperature rises, the thermally sensitive material contained in the thermostat-bulb 1160′ expands, and a small fraction of it is expelled (approximately 10−3, for a 100K temperature change in Li7), potentially under kilobar pressure, into the capillary tube which terminates on the bottom of a cylinder-and-piston assembly 1150′ located remotely (e.g., outside of the radiation shield) and physically lower than the neutron absorbing material's intra-core compartment 1140′ (in the event that gravitational forces are to be utilized). There the modest volume of high-pressure thermally sensitive material drives a swept-volume-multiplying piston in the assembly 1150′ which pushes a potentially three order-of-magnitude larger volume of neutron absorbing material through a core-threading capillary tube into an intra-core compartment proximate to the thermostat-bulb which is driving the flow. There the neutron absorbing material, whose spatial configuration is immaterial as long as its smallest dimension is less than a neutron mean free path, acts to absorptively depress the local neutron flux, thereby reducing the local fuel power density. When the local fuel temperature drops, neutron absorbing material returns to the cylinder-and-piston assembly 1150′ (e.g., under action of a gravitational pressure-head), thereby returning the thermally sensitive material to the thermostat-bulb 1160′ whose now-lower thermomechanical pressure permits it to be received. It will be appreciated that operation of thermostating modules does not rely upon the specific fluids (Li6 and Li7) discussed in the above exemplary implementation. In one exemplary embodiment, the thermally sensitive material may be chemically, not just isotopically, different from the neutron absorbing material. In another exemplary embodiment, the thermally sensitive material may be isotopically the same as the neutron absorbing material, with the differential neutron absorbing properties due to a difference in volume of neutronically exposed material, not a difference in material composition. Referring now to FIG. 12, in another embodiment a propagating nuclear fission deflagration wave reactor 1200 operates at core temperatures significantly lower than core temperatures of nuclear fission reactors of other embodiments. While nuclear fission reactors of other embodiments may operate at core temperatures in the order of around 1,000K or so, (e.g., to enhance electrical power conversion efficiency) the propagating nuclear fission deflagration wave reactor 1200 operates at core temperatures of less than around 550K, and some embodiments operate at core temperatures of between around 400K and around 500K. Reactor coolant 1210 transfers heat from nuclear fission in the propagating nuclear fission deflagration wave reactor 1200. In turn thermal energy 1220 is transferred from the reactor coolant 1210 to a thermally driven application. Given by way of non-limiting examples, exemplary thermally driven applications include desalinating seawater, processing biomass into ethanol, space-heating, and the like. In another embodiment, a propagating nuclear fission deflagration wave reactor 1200 may operate at core temperatures above 550K, and utilize thermal energy 1220 from the reactor coolant 1210 for thermally driven applications instead of or in addition to, electrical power generation applications. Given by way of non-limiting examples, exemplary thermally driven applications include thermolysis of water, thermal hydrocarbon processing, and the like. Referring now to FIG. 13, in another embodiment nuclear fission fuel can be removed after it has been burned. A nuclear fission deflagration wave propagating burnfront 1310 is initiated and propagated in a modular nuclear fission reactor core 1300 along a direction indicated by arrows 1320 toward modules 1340 of nuclear fission fuel material, thereby establishing a region 1330 of maximized reactivity as discussed above. As discussed above, the modules 1340 of nuclear fission fuel material may be considered “burnt” after the propagating burnfront 1310 has propagated the region 1330 of maximized reactivity through the module 1340 of nuclear fission fuel material. That is, the modules 1340 of nuclear fission fuel material “behind” the region 1330 of maximized reactivity may be considered “burnt”. Any desired number of the “burnt” modules 1340 of nuclear fission fuel material (behind the region 1330 of maximized reactivity) are removed, as generally indicated at 1350. As generally indicated at 1360, nuclear fission fuel material has been removed from the nuclear fission reactor core 1300. Referring now to FIGS. 14A and 14B, according to other embodiments nuclear fission fuel can be re-burned in place without reprocessing. As shown in FIG. 14A, a propagating nuclear fission deflagration wave reactor 1400 includes regions 1410 and 1420. A nuclear fission deflagration wave burnfront 1430 is initiated and propagated through the region 1410 toward the region 1420. The nuclear fission deflagration wave burnfront 1430 propagates through the region 1420 as a nuclear fission deflagration wave burnfront 1440. After the nuclear fission deflagration wave burnfront 1440 propagates into region 1420, and either before or after it reaches an end of the propagating nuclear fission deflagration wave reactor 1400, the nuclear fission deflagration wave burnfront 1440 is redirected or re-initiated and retraces a path of propagation away from the end of the propagating nuclear fission deflagration wave reactor 1400 back toward the region 1410. The nuclear fission deflagration wave burnfront 1440 propagates through the region 1410 as a nuclear fission deflagration wave burnfront 1450 away from the region 1420 toward an end of the propagating nuclear fission deflagration wave reactor 1400. The nuclear fission fuel in regions 1410 and 1420 is different during the repropagation of nuclear fission deflagration wave burnfronts 1440 and 1450 than it was during the previous propagation of nuclear fission deflagration wave burnfronts 1430 and 1440, due to changes in the amounts of fissile isotopes and the amounts of fission product “ash”. The neutron environment may differ during propagation and repropagation due to the above differences in the nuclear fission fuel, as well as other factors, such as without limitation, possible changes in the control of neutron modifying structures, thermal heat extraction levels, or the like. As shown in FIG. 14B (and as briefly mentioned in reference to FIG. 3C), the geometry of an embodiment of the propagating nuclear fission deflagration wave reactor 1400 forms a closed loop, such as an approximately toroidal shape. In this exemplary embodiment, the propagating nuclear fission deflagration wave reactor 1400 includes the regions 1410 and 1420 and a third region 1460 different from the regions 1410 and 1420. The nuclear fission deflagration wave burnfront 1430 is initiated and propagated through the region 1410 toward the region 1420. The nuclear fission deflagration wave burnfront 1430 propagates through the region 1420 as the nuclear fission deflagration wave burnfront 1440. The nuclear fission deflagration wave burnfront 1440 propagates through the region 1460 as a nuclear fission deflagration wave burnfront 1470. When the nuclear fission deflagration wave burnfronts 1430, 1440, and 1470 have propagated completely through the regions 1410, 1420, and 1460, respectively, nuclear fission fuel material in the regions 1410, 1420, and 1460 can be considered “burnt”. After the nuclear fission fuel material has been burnt, the nuclear fission deflagration wave burnfront 1430 is re-initiated and propagates through the region 1410 as a nuclear fission deflagration wave burnfront 1450. The re-initiation in region 1410 may occur without limitation, through the action of a nuclear fission igniter, such as discussed earlier, or may occur as a result of the decay and/or removal of nuclear fission products from the nuclear fission fuel material in region 1410, or may occur as the result of other sources of neutrons or fissile material, or may occur due to control of neutron modifying structures, as discussed previously. In another exemplary embodiment, the nuclear fission deflagration wave may potentially propagate in a plurality of directions. One or more propagation paths may be established, and may thereafter split into one or more separate propagation paths. The splitting of propagation paths may be accomplished without limitation by such methods as the configuration of the nuclear fission fuel material, the action of neutron modifying structures as discussed earlier, or the like. Propagation paths may be distinct, or may be reentrant. Nuclear fission fuel material may be burnt once, never, or multiple times. Repropagation of a nuclear fission deflagration wave multiple times through a region of nuclear fission fuel material may involve either the same or a different propagation direction. While some of the embodiments described previously illustrate nuclear fission fuel cores of substantially constant chemical and/or isotropic materials, in some approaches nuclear fission fuel cores of nonuniform material may be used. For example, in some approaches nuclear fission fuel cores may include regions having different percentages of uranium and thorium. In other approaches, nuclear fission fuel cores may include regions of different actinide or transuranic isotopes, such as without limitation different isotopes of thorium or different isotopes of uranium. In addition, mixtures of such different combinations may also be appropriate. For example, mixtures of thorium and of different uranium isotope ratios may provide different burning rates, temperatures, propagation features, localization, or other features. In other approaches, the nuclear fission fuel cores may include mixtures of “breedable” isotopes (such as Th232 or U238) along with other fissionable actinide or transuranic elements, such as without limitation, uranium, plutonium, americium, or the like. Additionally, such variations in chemicals, isotopes, cross sections, densities, or other aspects of the fuel or may vary radially, axially or in a variety of other spatial manners. For example, such variations may be defined according to anticipated variations in energy demand, aging, or other anticipated variations. In one aspect, where growth of energy demand in a region would be reasonably anticipated, it may be useful to define the fuel or materials to correlate to an expected increased demand of the region. In still another aspect, such variations may be implemented according to other approaches described herein. For example, the variations may be defined after initiation of burning using the modular approach is described herein or the multipath approaches described herein. In other approaches, movement of portions of the material may produce the appropriate material concentrations, positioning, ratios, or other characteristics. While the embodiments above have illustrated propagating nuclear fission deflagration wavefronts in fixed or variable fuel cores, in one aspect, propagating nuclear fission deflagration wavefronts may remain substantially spatially fixed while the fuel core or portions of the fuel core move relative to the wavefront. In one such approach, movement of the nuclear fission fuel core to maintain substantially localized positioning of the propagating nuclear fission deflagration wavefront can stabilize, optimize, or otherwise control thermal coupling to a cooling or heat transfer system. Or, in another aspect, controlled positioning of the propagating nuclear fission deflagration wavefront by physically displacing the nuclear fission fuel can simplify or reduce constraints upon other aspects of the nuclear fission reactor, such as the cooling system, neutron shielding, or other aspects of neutron density control. While a number of exemplary embodiments and aspects have been illustrated and discussed above, those of skill in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, and sub-combinations as are within their true spirit and scope.
	summary
	claims	1. A system for performing an operation with x-rays, comprising: a source for generating the x-rays; and a polycrystalline surface region having crystal spacings suitable for reflecting a plurality of x-rays at the same Bragg angle along said region and transmitting the reflected x-rays to a reference position. 2. The system of claim 1 wherein the polycrystalline surface region is a barrel-shaped reflecting lens positionable to focus the x-rays about a point. claim 1 3. The system of claim 1 including a detector for measuring electron emissions when a work piece is located at the reference position. claim 1 4. The system of claim 1 wherein the polycrystalline surface region has a curved plane fiber texture orientation. claim 1 5. A method of performing an operation with x-rays, comprising: and providing x-rays to a polycrystalline surface region having crystal spacings suitable for reflecting a plurality of x-rays at the same Bragg angle along said region and transmitting the reflected x-rays to a reference position; positioning a sample between the surface region and the reference position so that x-rays are transmitted through the sample. 6. The method of claim 5 further including positioning a mask between the surface region and the sample to transmit a portion of the x-ray intensity striking the mask to the sample. claim 5 7. The method of claim 5 wherein the reference position is a surface, further including the step of positioning a detector at the reference position to provide information indicative of an image of the sample. claim 5 8. The method of claim 5 wherein the detector comprises a photographic film plate. claim 5 9. A method of performing an operation with x-rays, comprising: providing x-rays to a polycrystalline surface region having crystal spacings suitable for reflecting a plurality of x-rays at the same Bragg angle along said region and transmitting the reflected x-rays to a reference position; and positioning a sample at the reference position so that x-rays strike the sample. 10. The method of claim 9 wherein the x-rays perform on the sample one or more operations from the set consisting of cutting, welding, hardening, modifying mechanical properties, melting, alloying, cladding, texturing, and machining. claim 9
	summary
	claims	1. A method of magnetic field generation with an atomic sensor, the method comprising:laser cooling a sample of atoms in a chamber; andtrapping the sample of atoms in a magneto-optical trap within the chamber by applying an atom trapping field across the sample of atoms using at least one pair of electro-permanent magnet units;wherein each electro-permanent magnet unit of the at least one pair of electro-permanent magnet units comprises:a first magnetic ring of a first magnetic material;a second magnetic ring of a second magnetic material; anda coil of magnet wire that is wrapped around one or both of the first magnetic ring and the second magnetic ring;wherein applying an atom trapping magnetic field across the sample of atoms further comprises applying a first pulse of current having a first duration and amplitude to the coil of magnetic wire, wherein the applied first pulse of current also switches each electro permanent magnet unit of the at least one pair of electro-permanent magnet units from an off state to an on state by switching a magnetic polarity of the second magnetic ring without switching a polarity of the first magnetic ring. 2. The method of claim 1, further comprising:performing an atomic interrogation scheme on the sample of atoms while momentarily de-energizing the atom trapping magnetic field across the sample of atoms. 3. The method of claim 1, wherein the sample of atoms comprises one of atomic Rubidium (Rb), Cesium (Cs), atomic Calcium (Ca) or atomic Ytterbium (Yb). 4. The method of claim 1, wherein in the off state, a first magnetic field of the first magnetic ring and a second magnetic field of the second magnetic ring are oppositely polarized in order to offset each other, andwherein, in the on state, the first magnetic field of the first magnetic ring and the second magnetic field of the second magnetic ring are similarly polarized in order to add to each other. 5. The method of claim 1, the first magnetic material having a first magnetic hardness sufficient to not change polarity in response to the first pulse of current; andthe second magnetic material having a second magnetic hardness that is less than the magnetic hardness of the first magnetic material such that the second magnetic material will change its polarity in response to the first pulse of current, but wherein the second magnetic material has a hardness that is sufficient in order to not change polarity in response to the first magnetic pulse of current applied to the first magnetic ring. 6. The method of claim 1, wherein the least one pair of electro-permanent magnet units comprises a first electro-permanent magnet unit having a first center ring hole and a second electro-permanent magnet unit having a second center ring hole;wherein the laser cooling further comprises:launching a first laser beam provided by a first laser source through the first center ring hole towards the second center ring hole, andlaunching a second laser beam provided by a second laser source through the second center ring hole towards the first center ring hold, wherein the first laser beam and the second laser beam are collinear with one another and intersect at the magneto-optical trap. 7. The method of claim 1, wherein laser cooling further comprises applying a first laser beam and a second laser beam into the magneto-optical trap with each laser beam being aligned to an axis of an anti-Helmholtz magnetic field. 8. The method of claim 1, further comprising:probing the sample of atoms in order to measure a net magnetic field; andcalibrating at least a first electro-permanent magnet unit of the at least one pair of electro-permanent magnet units based on the net magnetic field measured by the probing. 9. The method of claim 8, wherein the first electro-permanent magnet unit further comprising: at least one shim coil; and wherein calibrating at least the first electro-permanent magnet unit comprises controlling a feedback current to the at least one shim coil based on the net magnetic field measured by the probing. 10. A cold atom sensor, the cold atom sensor comprising:a vacuum chamber having a sample of atoms sealed within the vacuum chamber;at least one pair of electro-permanent magnet units arranged across the vacuum chamber, the least one pair of electro-permanent magnet units comprising a first electro-permanent magnet unit having a first center ring hole and a second electro-permanent magnet unit having a second center ring hole;a first laser source configured to launch a first laser beam through the first center ring hole and towards the second center ring hole, and a second laser source configured to launch a second laser beam through the second center ring hole and towards the first center ring hold, wherein the first laser beam and the second laser beam are collinear;wherein the first laser source and the second laser source are configured to laser cool the sample of atoms when the first laser beam and the second laser beam are energized and the first electro-permanent magnet unit and the second electro-permanent magnet unit are configured to produce an atom trapping magnetic field that holds the sample of atoms in an magneto-optical trap;wherein each electro-permanent magnet unit of the at least one pair of electro-permanent magnet units comprises:a first magnetic ring of a first magnetic material;a second magnetic ring of a second magnetic material; anda coil of magnet wire that is wrapped around one or both of the first magnetic ring and the second magnetic ring;wherein the at least one pair of electro-permanent magnet units are configured to produce the atom trapping magnetic field across the sample of atoms by applying a first pulse of current having a first duration and amplitude to the coil of magnetic wire, wherein the applied first pulse of current also switches each electro-permanent magnet unit of the at least one pair of electro-permanent magnet units from an off state to an on state by switching a magnetic polarity of the second magnetic ring without switching a polarity of the first magnetic ring. 11. The cold atom sensor of claim 10, wherein the cold atom sensor is configured to perform an atomic interrogation on the sample of atoms while momentarily de-energizing the atom trapping magnetic field across the sample of atoms by switching a polarity of the second magnetic ring. 12. The cold atom sensor of claim 10, wherein when switched to an off state, a first magnetic field of the first magnetic ring and a second magnetic field of the second magnetic ring are oppositely polarized in order to offset each other, andwherein when switched to an on state, the first magnetic field of the first magnetic ring and the second magnetic field of the second magnetic ring are similarly polarized in order to add to each other. 13. The cold atom sensor of claim 10, the first magnetic material having first magnetic hardness sufficient to not change polarity in response to the first pulse of current; andthe second magnetic material having a second magnetic hardness that is less than the magnetic hardness of the first magnetic material such that the second magnetic material will change its polarity in response to the first pulse of current, but wherein the second magnetic material has a hardness that is sufficient hi order to not change polarity in response to the first magnetic pulse of current applied to the first magnetic ring. 14. The cold atom sensor of now, wherein the first laser beam and the second laser beam are each aligned to an axis of the atom trapping magnetic field. 15. The cold atom sensor of claim 10, wherein the sample of atoms comprise one of atomic Rubidium (Rb), Cesium (Cs), atomic Calcium (Ca) or atomic Ytterbium (Yb). 16. The cold atom sensor of claim 10, further comprising: an atom characterization function configured to probe the sample of atoms in order to measure a net magnetic field; andwherein the atom characterization function is configured to calibrate at least a first electro-permanent magnet unit of the at least one pair of electro-permanent magnet units based on the net magnetic field measured by the probing performed by the atom characterization function. 17. The cold atom sensor of claim 16, wherein the at least one of the pair of electro-permanent magnet units comprises a shim coil; andwherein the atom characterization function is configured to control a feedback current supplied to the at least one shim coil based on the net magnetic field measured by the probing performed by the atom characterization function. 18. The cold atom sensor of claim 10, wherein the at least one pair of electro-permanent magnet units comprise: a first pair of electro-permanent magnet units producing a first anti-Helmholtz magnetic field gradient across the magneto-optical trap.
	description	1) Field of the Invention The present invention relates to a technology for sealing a radioactive-material container. 2) Description of the Related Art When a nuclear fuel assembly is at the end of a nuclear fuel cycle, finishes the combustion, and is not useful any longer, the nuclear fuel is called a recycle fuel assembly. The recycle fuel assembly is cooled at a cooling pit of a nuclear power plant for about 10 years because the recycle fuel assembly contains highly radioactive materials such as fission product (FP) and requires thermal cooling. Then, the recycle fuel assembly is contained in a radioactive-material container, conveyed to a reprocessing facility, and stored. Because the radioactive-material container contains highly radioactive materials, the radioactive-material container must be sealed with a strict care while the radioactive-material container is stored for about 40 years to 60 years. FIG. 20 is a cross section for illustrating a sealing structure of a conventional radioactive-material container. In a conventional radioactive-material container 600, a primary lid 607 and a secondary lid 608 are fixed using bolts 610, 611 on a flange member 606. From a viewpoint of maintaining a sealing function over a long period of time, metal gaskets 618, 619, which have a heat resistance, a corrosion resistance, and a high durability, are used to seal a space between the primary lid 607 and the flange member 606 and a space between the secondary lid 608 and the flange member 606. That is, using the metal gaskets 618, 619, the recycle fuel stored in the radioactive-material container 600 is sealed. FIGS. 21A, 21B are enlarged views for illustrating the metal gaskets 618, 619 and a sealing part of the radioactive-material container 600. A sealing part between the primary lid 607 and the flange member 606 and a sealing part between the secondary lid 608 and the flange member 606 has the same sealing structure. A metal groove 625 is formed by machining and the metal gaskets 618, 619 with a double-ring structure are used. In the metal gasket 618 or the metal gasket 619, inner covers 622a, 622b respectively cover coil springs 621a, 621b so as to form two rings, and an outer cover 623 covers the rings. The coil springs 621 and the inner covers 622 are made of Inconel (a registered trademark, a nickel alloy containing 16% chromium and 7% iron), which is corrosion resistant and oxidation resistant at high temperature, and the outer cover 623 is made of aluminum (the reference symbol with a subscript is represented by the reference symbol without the subscript, and the same is applied hereinafter). The metal gasket 618 (619), shown in FIG. 21A, has not been used yet. The metal gasket 618 (619), shown in FIG. 21B, is tightened and transformed by fixing the secondary lid 608, a body 601, and the like, and exerts a sealing function. The metal gasket 618 (619) is fixed to the gasket groove 625 using a bolt hole arranged in the outer cover 623. As the metal gasket 618 (619), “TRYBACK” from NIPPON VALQUA INDUSTRIES, LTD. or “Helicoflex” from Cefilac in France, which are often used in radioactive-material container for nuclear power, may be used. A time-and-temperature dependence of both a plastic-deformation ratio and a sealing performance of a metal gasket can be represented by Larson-Miller Parameter (LMP), and the details are disclosed in the documents: KATO, ITO, AND MIEDA, Development of method of verifying the long-term sealing performance of spent fuel storage casks, Journal of the Atomic Energy Society of Japan, 1996, Vol. 38, No. 6, pages 95 to 101. Generally, a long-term sealing performance of a metal gasket is verified by acquiring LMP of sealing-maintenance limit and estimating the limit time at a predetermined temperature. The radioactive-material container 600, which contains the recycle fuel assembly, is stored in the storage facility for a long time of several decades. At this time, the recycle fuel gives out a decay heat, therefore, the metal gaskets 618, 619 is used in the environment at about 120 degrees at the beginning. Then, the temperature gradually goes down during the storage period of several decades, and at the end of the storage period, the metal gaskets 618, 619 is used in the environment at about 60 degrees. The outer covers 623 of the metal gaskets 618, 619 are made of aluminum, and for aluminum, the temperature range described above is corresponding to a range between a temperature where a high-temperature creep occurs and a temperature where a low-temperature creep occurs. Therefore, even though the metal gaskets 618, 619 have the sufficient sealing performance in the early stage, the stress relaxation is caused by a creep deformation and the sealing performance may go down after the metal gaskets 618, 619 are used in a high-temperature environment for a long time. Moreover, though the metal gaskets 618, 619 can maintain the sealing under the applied stress of a few megapascals (MPa), the outer cover 623 creeps easily when the high stress is applied and the outer cover 623 is stressed strongly. Currently, to maintain a desired sealing performance for several decades, a high material (such as gold and silver), which does not creep easily, is used to the metal gasket, or a metal gasket with a large diameter, which enables maintaining a sealing function even when a creep occurs, is used. A process of containing the recycle fuel assembly in the radioactive-material container 600 needs to be conducted in a pool. After setting the metal gasket 618 in the radioactive-material container 600 sunk in the pool and lifting up the radioactive-material container 600 from the pool, it is necessary to remove water around the metal gasket 618 by vacuum drying. However, an interspace in the sealing part is small, and in some cases, it takes a long time to completely remove the water inside the metal gasket 618. Japanese Utility Model Laid-Open Publication No. H5-75154 p. 1 FIGS. 1 and 2 discloses a structure that ensures a sealing performance of a metal gasket by forming a cover of solid lubricant between an outer cover and an inner cover. However, such a structure has a problem that, in case the water enters inside the metal gasket accidentally during the process conducted in the pool, it takes a very long time to remove the water completely. It is an object of the present invention to solve at least the above problems in the conventional technology. The radioactive-material container according to one aspect of the present invention includes a container body that shields nuclear radiation, which includes a cavity that stores a basket containing a recycle fuel assembly; a lid that covers the cavity; and a metal gasket that includes a sealing area that makes a physical contact with the container body and the lid. The sealing area has a specific shape that disperses tightening stress acting on the metal gasket for a sealing. The radioactive-material container according to another aspect of the present invention includes a container body that shields nuclear radiation, which includes a cavity that stores a basket containing a recycle fuel assembly; a lid that covers the cavity; and a metal gasket that maintains a sealing inside the cavity, arranged between the container body and the lid. The metal gasket includes at least one coil spring in circular shape, an inner cover that covers the at least one coil spring, and an outer cover that covers the inner cover. The metal gasket according to still another aspect of the present invention includes a coil spring in circular shape, an inner cover that covers the coil spring, and an outer cover that covers the inner cover. A hole for draining water is arranged in the inner cover. The metal gasket according to still another aspect of the present invention includes a coil spring in circular shape, an inner cover that covers the coil spring, and an outer cover that covers the inner cover. A portion of the inner cover on a side of smaller hoop-diameter is exposed along a hoop diameter of the outer cover, and the hole for draining water is arranged in the portion. The metal gasket according to still another aspect of the present invention includes a first coil spring with a first hoop-diameter and a second coil spring with a second hoop-diameter in circular shape, the first hoop-diameter different from the second hoop-diameter; a first inner cover that covers the first coil spring and a second inner cover that covers the second coil spring; and an outer cover that covers the first inner cover and the second inner cover, linking the first coil spring and the second coil spring to form a double ring. A portion of the inner cover on a side of smaller hoop-diameter is exposed along a hoop diameter of the outer cover, and the hole for draining water is arranged in the portion. The metal gasket according to still another aspect of the present invention includes a spring that is formed by forming a plate material to be circular and have substantially circular cross-section and overlapping both ends of the plate material, and an outer cover that covers the spring. A hole for draining water is arranged in the spring. The method of manufacturing a metal gasket according to still another aspect of the present invention includes making a hole for draining water in a plate material, the plate material; forming a coil spring in circular shape; forming an inner cover by winding the plate material around the coil spring; and winding an outer cover around the inner cover. The method of manufacturing a metal gasket according tot still another aspect of the present invention includes making a hole for draining water in a plate material; forming a coil spring in circular shape; forming an inner cover by winding the plate material around the coil spring; and winding an outer cover around the inner cover in such a manner that the hole for draining water is exposed. The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. Exemplary embodiments of a radioactive-material container, a metal gasket for sealing the radioactive-material container, and a method of manufacturing the metal gasket according to the present invention will be explained below in detail with reference to the accompanying diagrams. The present invention is not limited to the following embodiments, and the components of the following embodiments include components that a person skilled in the art assumes easily or substantially same components. An applicable scope of a metal gasket according to the present invention is not especially limited, and, for example, the metal gasket may be applied to a sealing part of a radioactive-material container, and a sealing part of a reactor container. The metal gasket is suited to an application that requires maintaining the sealing performance for decades in the comparatively-high-temperature environment, more especially a radioactive-material container that contains the recycle fuel assembly, is conveyed, and stores the recycle fuel assembly for a long period of time. FIG. 1 is a schematic for illustrating a sealing structure 101 of a radioactive-material container according to a first embodiment of the present invention. FIG. 2A is a cross section of a metal gasket 202 according to the first embodiment of the present invention, and FIG. 2B is a cross section of a metal gasket 203 according to the first embodiment of the present invention. The sealing structure 101 is characterized in using a metal gasket 201 with a flat surface for the sealing. The flat surface corresponds to a sealing area 50s1 of an outer cover 501. The metal gasket 201 is so-called double-ring type, and includes coil springs 30a1, 30b1, inner covers 40a1, 40b1, and an outer cover 501. In the metal gasket 201, the coil springs 30a1, 30b1 have the different hoop-diameters Df, are arranged concentrically, and covered with the outer cover 501. However, a metal gasket applied to the present invention is not limited to such a double-ring type, but may be applied to the metal gasket 203, which is so called single-ring type. In the metal gasket 203, an inner cover 403 covers a spring coil 303 while an outer cover 503 covers the inner cover 403. The same is applied to the following embodiments, and the inner cover 40 may be removed. Regarding the hoop diameter, the diameter of the circular metal gasket 20, the diameter of the circular coil spring 30, the diameter of the circular inner cover 40, or the diameter of the circular outer cover 50 are called a hoop diameter. FIG. 19 is a cross section of a radioactive-material container 500 according to the first embodiment of the present invention. The radioactive-material container 500 includes a body 501, which is made of stainless or carbon steel, an external cylinder 502, which composes an external surface of the radioactive-material container 500, a resin 503, which is a polymeric material that contains hydrogen and fills a space between the body 501 and the external cylinder 502, a bottom plate 505, which is welded to the bottom of the body 501 and in which a resin 504 is enclosed, a primary lid 507 and a secondary lid 508, which are arranged on a flange member 506. The flange member 506 is formed so as to unite with the body 501. A basket 513 that contains the recycle fuel assembly is arranged inside a cavity 509 of the body 501. The primary lid 507 and the secondary lid 508 are fixed using bolts 510, 511 on the flange member 506, and a resin 512 is enclosed in the secondary lid 508. The basket 513 is composed of a plurality of cells formed of boron/aluminum composite. The cavity 509 is filled with negative-pressure helium gas while a space between the primary lid 507 and the secondary lid 508 is positive pressured. Therefore, a pressure barrier is formed between the inside and the outside of the radioactive-material container 500. A hole 514 is arranged in the secondary lid 508 to measure the pressure of a space between the primary lid 507 and the secondary lid 508, and a pressure sensor 515 is arranged on an outlet of the hole 514. A valve 516 is arranged in the primary lid 507 to replace the gas inside the radioactive-material container 500, and covered with a valve cover 517. To seal a gap between the primary lid 507 and the body 501 or a gap between the secondary lid 508 and the body 501, the metal gasket 20 according to the first embodiment of the present invention is used. As shown in FIG. 1, the sealing structure 101 is, for example, arranged between the secondary lid 508 and the flange member 506 of the body 501. A sealing structure and a metal gasket according to the present invention may be applied to the space between the primary lid 507 and the flange member 506 of the body 501 (the same is applied hereinafter). In metal gasket 201, the inner cover 40a1 covers the coil spring 30a1 so as to form an inner hoop 701, the inner cover 40b1 covers the coil spring 30b1 so as to form an outer hoop 801, and the outer cover 501 covers the inner hoop 701 and the outer hoop 801. The metal gasket 201 has the hoop diameter Df of approximately 2 meters (m) (the hoop diameter Df corresponds to a distance from a center C of the body 501 to the metal gasket 201), the inner hoop 701 and the outer hoop 801 have the sectional diameter D of approximately 5.5 millimeters (mm), the outer cover 501 has the thickness of 0.4 mm, and the inner covers 40a1, 40b1 have the thickness of 0.2 mm. As a material of the outer cover 50, a soft metal, such as aluminum, silver, copper, and nickel, is used to ensure the seal performance. As a material of the inner cover 40 and the coil spring 30, a nickel alloy, such as Inconel (a registered trademark), which is corrosion resistant and oxidation resistant at high temperature, is used to maintain elasticity in a high-temperature environment. Nimonic (a registered trademark), which has a high Co content, or the like may be used to improve the durability at higher temperature. Although the inner covers 40a1, 40b1 are used in the metal gasket 201, the inner covers 40a1, 40b1 are not always necessary and may be used if needed. It is preferable to arrange the inner covers 40a1, 40b1 when the outer cover 501 is made of a soft metal such as aluminum. By arranging the inner covers 40a1, 40b1, the repulsive force of the coil springs 30a1, 30b1 can be transmitted to the outer cover 501 more uniformly, and the stress-concentration that occurs locally in the outer cover 501 can be decreased as much as possible. Consequently, the creep deformation to be described later can be decreased. The sealing areas 50s are formed on the outer cover 50 to have a flat surface as shown in FIGS. 2A and 2B, and make a contact with the secondary lid 508 and the like to perform the sealing. Such sealing areas 50s enable decreasing the tightening-stress relaxation caused by the creep deformation of the outer cover 50, and the details will be described later. As a material of the secondary lid 508, the primary lid 507, and the body 501, stainless steel or carbon steel is used to block off the radiation and maintain the mechanical strength. On the other hand, as a material of the outer cover 50, a soft metal such as aluminum or silver is used to exert the sealing performance. Therefore, when the secondary lid 508, the primary lid 507, and the body 501 make a contact with the outer cover 50, a contact between the different metals causes a voltage potential difference between the metal gasket 20 and the secondary lid 508 or the like, the galvanic corrosion occurs in the metal gasket 20, and the air tight is broken. To prevent the galvanic corrosion, SUS317 or SUS625, which contains molybdenum, is used as a material of the secondary lid 508 and the body 501. SUS317 and SUS625 have a good weldability and are generally suited to an application that has a lot of parts to be welded, such as a radioactive-material container. SUS314, SUS316, SUS326, and SUS345 may be used as an alternative to SUS317 and SUS625. Instead of making the secondary lid 508 and the body 501 of SUS317 or the like, a sealing surface 90 may be made on the secondary lid 508 and the body 501 so as to have a bulge portion using the same material. Another way to prevent the galvanic corrosion of the secondary lid 508 and the body 501, aluminum may be used as a material of the outer cover 50. Aluminum has the higher corrosion potential than SUS317 or SUS 625, which is a material of the secondary lid 508 and the body 501 and contains molybdenum. When the outer cover 50 is made of aluminum, the outer cover 50 is corroded more easily than the secondary lid 508 and the body 501. However the outer cover 50 can be replaced more easily than the secondary lid 508 and the body 501, so that the secondary lid 508 and the body 501 can be protected from the galvanic corrosion. FIGS. 3A and 3B are views for explaining the coil spring 30 of the metal gasket 20 according to the first embodiment of the present invention. A coil spring 304 is formed by closely winding a wire material, which is made of Inconel (a registered trademark), Nimonic (a registered trademark), or the like. If the wire material is not wound closely, when the sealing is performed and the metal gasket 20 is squashed, the coil spring 30 can not push back the inner cover 40 and the outer cover 50 with a uniform force, and the desired sealing-performance can not be exerted in long-time usage (see FIG. 2). Generally, to gain the seal pressure in the metal gasket 20, the flexural rigidity of the coil spring 30 needs to be increased by using the coil spring 30 with the large wire diameter d. When the wire diameter d of the coil spring 30 gets larger, it gets harder to wind the wire and the winding diameter D1 of the coil spring 30 gets larger. Consequently, the cross-sectional diameter D of the metal gasket 20, which needs to sustain a high seal-pressure, gets larger in comparison with that of a metal gasket that provides to a low seal-pressure. The flexural rigidity of the coil spring 30 indicates how hard to transform the coil spring 30 to the radial direction when force P is acted on the coil spring 30 to the radial direction (the same is applied hereinafter). The metal gasket 20, which is used in the radioactive-material container, is required to have a sealing performance that can be exerted for several decades. At the beginning, the metal gasket 20 is used in the environment at about 120 degrees, because the recycle fuel assembly contained in the radioactive-material container gives out a decay heat. While the recycle fuel assembly is contained for several decades, the temperature where the metal gasket 20 is used goes down gradually and reaches around 60 degrees finally. In such an environment, the outer cover 50 creeps depending on a kind of a material of the outer cover 50. Especially, in case the outer cover 50 is made of the aluminum with a comparatively-low melting point, the creep deformation becomes a problem. The relation between the stress that acts on the metal gasket 20 and the strain of the metal gasket 20 is shown in FIG. 4. When the secondary lid 508 or the like is tightened, a predetermined tightening stress σ0 acts on the metal gasket 20, and an initial strain ε 0 occurs. The initial strain ε 0 corresponds to the sum of a plastic strain ε p and an elastic strain εe(t=0). When a creep strain εc occurs after a certain time, the tightening stress σ0 relaxes and the elastic strain εe thereby decreases. When a certain time t passes after the tightening is performed, the tightening stress σ decreases to the tightening stress at corresponding to the increment of the creep strain εc. This phenomenon is called the stress-relaxation phenomenon of the metal gasket 20. When the stress that acts on the metal gasket 20 goes below an airtight critical stress σc, shown in FIG. 4, the air tight is broken by the different pressure between the inside and the outside of the radioactive-material container 500. If the tightening stress σ0 is removed just after the tightening stress σ0 acts on the metal gasket 20, the elastic strain εe is removed, and the strain of the metal gasket 20 thereby corresponds to the plastic strain εp. Therefore, the air tight is broken at a point R0. However, if the long time passes after the tightening stress σ0 acts on the metal gasket 20, the tightening stress decreases to the tightening stress at as described above. At this time, if the tightening stress is relieved, the strain of the metal gasket 20 corresponds to the sum of the plastic strain εp and the creep strain εc, and the air tight is broken at a point R1. This is because the initial elastic strain εe (t=0) decreases corresponding to the increment of the creep strain εc. The airtight critical stress of the metal gasket 20 is represented by σc, therefore, in case it is right after the metal gasket 20 is tightened, the air tight is broken when the strain of the metal gasket 20 decreases to ε1. On the other hand, in case a long time has passed, the air tight is broken when the strain of the metal gasket 20 decreases to ε2. Compared to the former case, the latter case shows that the air tight is broken with less strain, namely with less displacement. In order to maintain the sealing performance of the radioactive-material container 500 in the long-term storage and improve the reliability, the stress-relaxation phenomenon of the metal gasket 20 needs to be analyzed thoroughly. The present inventors studied on stress-relaxation phenomenon of the metal gasket 20 earnestly, and found the following items. First, the stress-relaxation phenomenon occurs when the elastic displacement of the coil spring 30 is relieved by the creep deformation of the material that composes the outer cover 50. The springback of the metal gasket 20 that deteriorates is determined by the flexural rigidity of the coil spring 30 plastically-deformed. Even after the long-term storage, the flexural rigidity of the coil spring 30 plastically-deformed is small enough to ignore a change of the characteristics in comparison with the flexural rigidity of the coil spring 30 when the metal gasket 20 is new, and can be considered to have no change in comparison with the outer cover 50. In other words, it is not required to consider the deterioration of the coil spring 30's material, such as Inconel and Nimonic, in considering the stress-relaxation phenomenon of the metal gasket 20. In order to maintain the sealing performance of the radioactive-material container 500 in the long-term storage and improve the reliability, the following tactics are useful. The first tactic is decreasing the creep deformation of the metal gasket 20. If the creep deformation can be decreased, the tightening stress σ0 decreases less after the long time passes. The second tactic is increasing an amount of the springback of the metal gasket 20 as much as possible after the long time passes. If the amount of the springback can be increased, the secondary lid 508 is allowed to have a larger displacement, which is produced till the tightening stress a reaches the airtight critical stress σc. Therefore, the sufficient margin is obtained when the secondary lid 508 or the like is misaligned by the fall or the like. A method of increasing the amount of springback (hereinafter, the springback amount) will be explained. The relation between a load that acts on the metal gasket and a displacement of the metal gasket is shown in FIG. 5. A dotted line indicates data of a conventional metal gasket 520 (see FIG. 7A), and a solid line indicates data of the metal gasket 20 according to the present invention. An analysis result, shown in FIG. 5, is based on an extrapolation method using LMP, and the temperature conditions are that the initial temperature is 120 degrees and the temperature goes down to 60 degrees for 60 years based on the collinear approximation. The temperature conditions are configured to meet the temperature conditions of the long-term storage in the radioactive-material container that is used actually. The extrapolation method using LMP is preferable in such an analysis, because in the extrapolation method, the stress relaxation is estimated to be on the safe side, namely to be large. The metal gasket 20 according to the present invention is configured to have a flexural rigidity that corresponds to approximately 50% of the flexural rigidity of the conventional metal gasket 520 by using the coil spring 30 with the wire diameter d thinner than that in the conventional metal gasket 520. The cross-sectional diameter D of the metal gasket 20 is same as that the conventional metal gasket 520. Preferably, the flexural rigidity of the metal gasket 20 is within the range from 30% of the flexural rigidity of the conventional metal gasket 520 to 80% thereof. In such a range, the effect of increasing the springback amount can be acquired while ensuring a certain degree of flexural rigidity. Moreover, the range from 30% of the flexural rigidity of the conventional metal gasket 520 to 60% thereof is more preferable. The metal gasket 20 according to the present invention is configured to have an initial tightening amount larger than that of the conventional metal gasket 520. Therefore, the initial stress (the tightening stress) σ0 acting on the conventional metal gasket 520 and that acting on the metal gasket 20 become equal, and the metal gasket 20 and the conventional metal gasket 520 have the same amount of the stress relaxation when a certain time passes. The tightening stress when a certain time passes is indicated by σt. If the tightening stress σ0 is gradually relieved when a certain time passes, the metal gasket gradually returns to the original form, and the displacement δ comes close to zero. The displacement δ when the tightening stress Σ reaches the airtight critical stress σc corresponds to the airtight critical displacement δc of the metal gasket. The metal gasket 20 according to the present invention is configured to have a flexural rigidity smaller than that of the conventional metal gasket 520, therefore, a change σ/δ of the tightening stress σ0 to the displacement δ of the metal gasket is more gradual in the metal gasket 20 than in the conventional metal gasket 520. Consequently, corresponding to the relaxation of the tightening stress σ, the metal gasket 20 is displaced more largely than conventional. That is, if the tightening stress σ acting on the metal gasket 20 is equal to that acting on the conventional metal gasket 520, the metal gasket 20 has the larger springback amount, and thereby has the larger airtight critical displacement δc. Therefore, even if the larger misalignment occurs in the metal gasket 20 than in the conventional metal gasket 520, the air tight of the radioactive-material container 500 can be maintained. Consequently, the radioactive-material container 500 can be safely transported even after the long-term storage while exerting the stable sealing performance. Particularly, the springback amount δ20 of the metal gasket 20 according to the present invention is about 0.20 mm while the springback amount δ520 of the conventional metal gasket 520 is about 0.01 mm to 0.02 mm. Like this, the springback amount δ20 is about 10 times to 20 times as large as the springback amount δ520. When the metal gasket is used to seal the radioactive-material container, the metal gasket is required to have the springback amount of about 0.05 mm, and the metal gasket 20 can satisfy this value. Consequently, the metal gasket 20 archives having the sufficient reliability when the radioactive-material container contains the recycle fuel assembly for several decades although the conventional metal gasket 520 fails. From the above explanation, the decrease of the flexural rigidity of the coil spring 30 increases the springback amount. However, too much decrease of the flexural rigidity increases the deformation amount of the metal gasket 20, and therefore, is not preferable. The evaluation results of the springback amount of the metal gasket after the long-term storage are shown in tables 1 to 3. These evaluations are conducted based on the an extrapolation method using LMP, and the temperature conditions are that the initial temperature is 120 degrees and the temperature goes down to 60 degrees for 60 years based on the collinear approximation. The symbol “◯” is shown when the metal gasket has the springback amount required for sealing the radioactive-material container. TABLE 1the sectional diameter D of the metal gasket = 5.6 mmwire diameter d0.300.350.400.500.530.55evaluationΔ∘∘∘Δxresult TABLE 2the sectional diameter D of the metal gasket = 12.0 mmwire diameter d0.500.600.700.800.850.90evaluation∘∘∘∘Δxresult TABLE 3d/D (d: wire diameter of the metal gasket; D: the sectional diameter ofthe metal gasket)d/D0.010.020.040.060.080.090.10evaluation resultΔ∘∘∘∘Δx The table 1 shows that, in case the sectional diameter D of the metal gasket 20 is 5.6 mm, the springback amount is favorable when the wire diameter d is between 0.35 mm and 0.50 mm. The table 2 shows that, in case the sectional diameter D of the metal gasket 20 is 12.00 mm, the springback amount is favorable when the wire diameter d is 0.80 mm or less. In the table 3, the ratio d/D of the wire diameter d of the coil spring 30 to the sectional diameter D of the metal gasket 20 is shown by arranging the evaluation results. The table 3 shows that the springback amount is favorable when the ratio d/D is within a range from 0.02 to 0.08. From the above results, the wire diameter d of the coil spring 30 (see FIGS. 3A and 3B) is preferably within a range from 0.35 mm to 0.80 mm, and more preferably within a range from 0.35 mm to 0.50 mm. When the sectional diameter D of the metal gasket 20 (see FIG. 2) is too small, the springback amount can not be ensured without increasing the tightening amount corresponding to the sectional diameter D. Blindly decreasing the sectional diameter D of the metal gasket 20 may break the air tight conducted by the metal gasket 20, and therefore, is not allowed. On the other hand, when the sectional diameter D of the metal gasket 20 is too large, the required flexural rigidity can not be ensured with the wire diameter d described above. Therefore, the sectional diameter D of the metal gasket 20 is preferably from 5.0 mm to 12.0 mm. The ratio d/D of the wire diameter d of the coil spring 30 to the sectional diameter D of the metal gasket 20 is preferably from 0.02 to 0.08. In the conventional metal gasket 520, when the conventional metal gasket 520 has the sectional diameter D within a range from 5.0 mm to 6.0 mm, the coil spring with the wire diameter of 0.55 mm or more is used, and the sealing pressure is 50 Mpa or more. In the metal gasket with the sectional diameter D within a range from 5.0 mm to 12.0 mm, if the coil spring with the wire diameter d within a range from 0.35 mm to 0.80 mm is used, the sealing pressure is less than 50 MPa. The sealing pressure in the radioactive-material container is about 1.0 MPa at most. Therefore, in the metal gasket with the sectional diameter D within a range from 5.0 mm to 12.0 mm, if the coil spring with the wire diameter d within a range from 0.35 mm to 0.80 mm is used, the stress produced in the outer cover be decreased without escaping the pressure, and the creep of the outer cover 50 accompanying the long-term usage can be decreased. A tactic of decreasing the creep deformation of the metal gasket 20 will be explained. FIGS. 6A to 6C are cross sections for illustrating the metal gasket 20 according to the present invention. FIGS. 7A to 7C are cross sections for illustrating the conventional metal gasket 520. In the conventional metal gasket 520, as shown in FIG. 7B, the cross sections of sealing areas 550s, where an outer cover 550 makes a physical contact with the body 501 or the secondary lid 508, draws an arc, and the sealing areas 550s are deformed by the tightening stress. Consequently, as shown in FIG. 7C, the stress acts on the sealing area 550s nonuniformly. Moreover, the flexural rigidity of a coil spring 530 is large needlessly, therefore, the large stress occurs at the center of the sealing part. Consequently, the action of relaxing the stress distribution is caused and the creep deformation is promoted. In the metal gasket 205 according to the present invention, as shown in FIG. 6A, a sealing area 50s5, where an outer cover 505 makes a physical contact with the secondary lid 508 or the like, is formed to have a flat surface in advance. Consequently, as shown in FIG. 6B, when the metal gasket 205 is compressed by the tightening stress, the stress distribution at the sealing area 50s5 is dispersed and become more uniform than conventional. In other word, if the tightening stress acts on an area 50y5, which is assumed to be an area except the sealing area 50s5, the stress distribution at the sealing area 50s5 is more uniform than that at the area 50y5. Compared to the conventional metal gasket 520, the action of uniforming the stress distribution works more at the sealing area 50s4, and the creep deformation of the outer cover 505 can be more gradual. Consequently, the creep deformation of the outer cover 505 can be smaller than conventional and the stress-relaxation phenomenon ascribable to the creep deformation can be inhibited. Moreover, the sealing area 50s5 is formed to have a flat surface, and such a shape has the lager section modulus in comparison with when the sealing area 550s draws an arc. Moreover, by forming the sealing area 50s5 to have a flat surface, the sealing area 50s5 of the outer cover 505, which creeps easily, has the thickness thinner than that in the conventional metal gasket 520 (see FIGS. 7A to 7C). Therefore, the absolute amount of the creep deformation is decreased, and the decrease of the recovery amount of the metal gasket 205 is inhibited corresponding to the decrease of the absolute amount of the creep deformation. Owning to these actions, the metal gasket 205 can bear the larger tightening stress that acts in a direction perpendicular to the sealing area 50s5 than the conventional metal gasket 520 with a non-flat sealing area 550s. Therefore, in the metal gasket 205, even if coil springs 30a5, 30b5 with the thinner wire diameter d are used, the outer cover 505 can support the larger load than conventional. Consequently, the springback amount can be increased, and the higher safety can be obtained even in the long-term storage. FIGS. 8A and 8B are views for illustrating other shapes to disperse the stress at the sealing area. As described above, in the metal gasket 20 according to the present invention, a sealing area 50s of an outer cover 50 is formed to have a flat surface to disperse the tightening stress for the sealing. To disperse the tightening stress for the sealing, as shown in FIG. 8A, a step 50d6 may be formed along the circumferential direction of a metal gasket 206 at an intersection of the flat surface corresponding to the sealing area 50s6 and an area 50y6. If the sealing area 50s5 is simply formed to have a flat surface as shown in FIG. 6B, the stress concentration occurs at the intersection of the sealing area 50s5 and the area 50y5. Therefore, a step 50d6 is formed at the intersection in advance, by cutting out the intersection, to decrease the stress concentration. Although a corner 50dc6 of the step 50d6 has an angular shape, the step 50d6 may be curved. In this manner, the stress concentration at the corner 50dc6 can be decreased. Even if the sealing area 50s is formed to have a flat surface, some parts are highly stressed depending on a facon. Therefore, at such a part, a groove 50x7 may be arranged along the circumferential direction of a metal gasket 207 to decrease the stress concentration. The number and the size of the groove 50x7 can be determined properly depending on the occurrence status of the stress concentration. The occurrence status of the stress concentration can be analyzed based on the finite element method or the like. In this manner, the stress concentration that occurs in an outer cover 507 of the metal gasket 207 can be uniformed, therefore, the progress of the creep deformation can be inhibited and the sealing performance can be maintained in the long-term storage. FIGS. 9A and 9B are views for illustrating another example to disperse the stress at the sealing area. As shown in FIG. 9A, a coil spring 30x8 is formed to have a flat surface on the side of a sealing area 50s8, and an outer cover 508 is formed to have a flat surface on the side of the sealing area 50s8. In this manner, the coil spring 30x8 presses the sealing area 50s8 of the outer cover 508 uniformly, therefore, the sealing area 50s8 has the more uniform stress distribution. The coil spring 30x8 may be manufactured as shown in FIG. 9B. The steps are: winding a wire rod 30y8 around a jig 30z8, doing the annealing so that the wire rod 30y8 has the shape of the jig 30z8, and manufacturing the coil spring 30x8 by a heat treatment. The jig 30z8 is a pillar that has a substantially elliptical cross-section and two flat surfaces on the side. The coil spring 30x8 has the smaller flexural rigidity than the coil spring with a circular cross-section. Consequently, the coil spring 30x8 needs to have the thicker wire diameter than the coil spring 304 with a circular cross-section (see FIGS. 3A and 3B). A plurality of micro-convexoconcaves 829 may be formed in a gasket-groove surface 90a1 and an opposed surface 90b1, which correspond to sealing surfaces 90, in the present invention as shown in FIG. 10. FIG. 10 is an enlarged view for illustrating the micro-convexoconcaves 829 formed in the gasket-groove surface 90a1 or the like. The maximum roughness Rmax of the micro-convexoconcave 829 is preferably from 2 μm to 20 μm. If the maximum roughness Rmax is less than 2 μm, a metal gasket 209 slides. If the maximum roughness Rmax is more than 20 μm, an outer cover 509 of the metal gasket 209 does not bite into the micro-convexoconcaves 829 completely and the sealing performance becomes insufficient. The average roughness Ra of the micro-convexoconcave 829 is preferably from 0.6 μm to 3.2 μm. If the metal gasket 209 is pressed when the micro-convexoconcaves 829 are formed, the micro-convexoconcaves 829 bite into the outer cover 509 (an anchoring behavior) and conform to the surface of the outer cover 509 as shown in FIG. 10. Consequently, the favorable sealing can be obtained (at a sealing area 50s9). At a convex part, the surface pressure increases, therefore, the higher sealing performance is obtained. In case the radioactive-material container 500 falls during the transport and the secondary lid 508 moves radially (namely, to the direction of an arrow A in FIG. 1), the metal gasket 209 does not slide because the outer cover 509 bites into the micro-convexoconcaves 829, and the metal gasket 209 behaves so as to wholly move to the moving direction of the lid (namely, to the direction of an arrow E in FIG. 1) while the outer cover 509 rotates (to the direction of an arrow B) and is deformed. At this time, the outer cover 509 bites into the micro-convexoconcaves 829 that the outer cover 509 has not bitten, and forms a new sealing area Sn. In this manner, even if the secondary lid 508 moves radially, the metal gasket 209 does not break the sealing, and the sealing performance can be maintained. Therefore, the radioactive-material container 500 can be conveyed without replacing the metal gasket 209 by a rubber O ring. Moreover, when the radioactive-material container 500 is stored for a long time, a plastic flow is caused by the tightening stress that acts on the metal gasket 20, and the decrease of the contact-surface pressure causes the decrease of the sealing performance. However, in this sealing structure, the plastic flow of the surface of the outer cover 509 is inhibited to some degree by forming the micro-convexoconcaves 829, and therefore, the secondary effect of preventing the decrease of the contact-surface pressure can be obtained. When the maximum roughness Rmax of the micro-convexoconcaves 829 is larger, the secondary effect is more effective. Micro-convexoconcaves 82 may be formed on the sealing surface 90 so that an upper edge 82u9 of the micro-convexoconcave 829 appears periodically. The upper edge 82a9 and the like may be formed based on a processing method such as a serration method. By using the serration method, the upper edge 82u9 is formed independently and the leakage path is not formed, therefore, the sealing performance can be maintained for a long time. Moreover, in case the upper edges 82u9 and lower edges 82l9 are formed, the values described above can be applied to the maximum roughness Rmax and the average roughness Ra. From a viewpoint of effectively inhibiting the metal gasket 209 from sliding while biting into the outer cover 509 and ensuring the sealing performance, in case the metal gasket 209 with the external diameter of about 6 mm to 12 mm is used, a pitch pm of the upper edge 82u9 is preferably from 0.1 mm to 2.0 mm, and more preferably, from 0.1 mm to 0.8 mm. From the same viewpoint, in case the metal gasket 209 with the external diameter of about 5 mm to 6 mm is used, the pitch pm is preferably from 0.1 mm to 0.5 mm, and more preferably, from 0.1 mm to 0.2 mm. When the pitch pm is within such a range, the sufficient sealing performance can be ensured while inhibiting the metal gasket 20 from sliding. Moreover, a sufficient number of the upper edges 82u9 bite into the sealing area 50s9 of the outer cover 509, therefore, the seal dimension increases. In this manner, the tightening load of the metal gasket 209 can be received dispersively, therefore, the creep deformation in the long-term storage can be inhibited. Obviously, the sealing structure described above can be applied to the space between the primary lid 507 (see FIG. 20) and the body 501 (the same is applied hereinafter). The configuration of the metal gasket 20 according to the first embodiment is especially suited to a case where the outer cover 50 is made of aluminum, tin, or the like, which have a comparatively-low melting point and whose creep deformation becomes a problem at the operating temperature in the radioactive-material container. The configuration may be applied to a case where the outer cover 50 is made of silver, gold, nickel, or the like, which have a comparatively-high melting point and whose creep deformation does not become a problem at the operating temperature in the radioactive-material container, as well. In the latter case, by making the spring coil thin simultaneously, the springback amount becomes 10 times to 20 times as large as the conventional springback amount, therefore, the margin during the transport of the radioactive-material container gets larger than conventional (the same is applied herein after). FIGS. 11A to 11D are views for illustrating a metal gasket 21 according to a first modification of the first embodiment. The metal gasket 21 and the metal gasket 20 of the radioactive-material container according to the first embodiment have substantially same configuration. However, the difference is that, in the metal gasket 21, two circular coil springs 31 with the different hoop-diameters are arranged concentrically, and the coil springs 31 have the different spring diameters. The other configuration is the same as the configuration in the first embodiment, therefore the explanation is omitted and the same reference symbol is applied to the same component. A metal gasket 211, shown in FIG. 11A, is so-called a double-ring type and includes coil springs 31a1, 31b1 that have the different diameters and are respectively covered with inner covers 41a1, 41b1. As shown in FIG. 11B, when a metal gasket 212 is arranged between the body 501 and the secondary lid 508, some parts, on the side of a coil spring 31b2, of an outer cover 512 makes a physical contact with the body 501 and the like first, because the coil spring 31b2 has the larger diameter than a coil spring 31a2. The secondary lid 508 is fixed to the body 501 temporarily in this state. Generally, in view of safety, the recycle fuel assembly is contained in the radioactive-material container while the radioactive-material container is sunk in the storage pool filled with water. Therefore, before the transport and the long-term storage, the water is removed by vacuum drying or the other drying means. In the metal gasket 212, water left inside a groove 92 of the metal gasket 212 (hereinafter, a gasket groove 92) evaporates and goes out from the side of the coil spring 31a2 during the vacuum drying, because the coil spring 31a1 has the smaller diameter and the sealing is not performed on the side of the coil spring 31a2. After completing the vacuum drying, the body 501 and the secondary lid 508 are tightened fully. In this manner, in the metal gasket 212, potential for corrosion can be minimized by fully removing the water inside the gasket groove 91 and the metal gasket 212. Consequently, reliability of the sealing performance improves even in the long-term storage. In FIG. 11B, the coil spring 31a2 with the smaller spring diameter is arranged on the cavity side, and in this case, there is an advantage when the vacuum drying is performed from the cavity side. A coil spring 31a3 with the smaller spring diameter may be arranged on the outer side as shown in FIG. 11C. In this case, the water can be removed effectively when the vacuum drying is performed from the side of the bolt hole, which fixes the secondary lid 508 or the like. In a metal gasket 214 shown in FIG. 11D, an outer cover 514 covers coil springs 31a4, 31b4 wholly, a spacer 614 is arranged between the coil springs 31a4, 31b4, and ends 5114 are sealed by welding or the other means for joining. In the metal gasket 214, the drying described above can be promoted by having the coil springs 31a4, 31b4 with the different diameters. Moreover, the metal gasket 214 can stop water from seeping inside. Consequently, compared to the metal gasket 211 shown in FIG. 11A, the drying can be performed faster in the metal gasket 214 as well. The spacer 614 is used to restrain the deformation of the outer cover 514, and a piece of pure aluminum or the like, or a coil spring may be used. The first modification can be applied to the primary lid and the embodiments below. FIG. 12A is a view for illustrating a metal gasket according to a second modification according to the first embodiment. For convenience in the explanation, the metal gasket 520 used in the conventional radioactive-material container is shown in FIG. 12B. A metal gasket 22 has substantially same configuration as the metal gasket 20 according to the first embodiment, however, the difference is that the metal gasket 22 includes a coil spring 32. In the coil spring 32, a curvature diameter r1 at a sealing area 52s is lager than a curvature diameter r2 at an area 52y, which is an area except the sealing area 52s. Another difference is that an internal element, which includes the coil spring 32 and an inner cover 42 covered with an outer cover 52, is formed to have substantially elliptical cross-section in advance. The other configuration is the same as the configuration in the first embodiment, therefore the explanation is omitted and the same reference symbol is applied to the same component. As shown in FIG. 12B, in the conventional metal gasket 520, an internal element 520e, which includes the inner cover 540 and the coil spring 530 covered with the inner cover 40, has substantially circular cross-section. Therefore, the flexural rigidity of the spring is high, and the sealing performance, which corresponds to dozens of megapascals, is obtained. However, as described above, when the flexural rigidity of the coil spring 530 is high, the springback amount can not be increased compared to when the flexural rigidity is small (see FIG. 5). Moreover, the outer cover 550 has been stressed for the long time of several decades, therefore, the outer cover 550 is burned out, and the restoring force weakens. Consequently, there are potentials of decreasing the sealing performance and decreasing the springback amount. In the metal gasket 22 according to the second modification, an internal element 22e, which includes the inner cover 42 and the coil spring 32 covered with the inner cover 42, is formed to have substantially elliptical cross-section in advance. Therefore, the flexural rigidity of the spring can be decreased compared to when the cross section is substantially circular. Consequently, the sufficient springback amount can be ensured. Even if the larger gap is produced in the metal gasket 22 than the conventional metal gasket 520, the safer transport can be performed because the air tight of the radioactive-material container can be maintained. Moreover, compared to the conventional metal gasket 520, the coil spring 32 make a contact with a sealing area 52s with the larger dimension, and therefore, the stress that acts on the outer cover 52 can be decreased more than conventional. Consequently, the creep deformation of the outer cover 52 is inhibited, the stress-relaxation phenomenon decreases, and the reliability in the long-term storage improves. In the metal gasket 22, the flexural rigidity of the coil spring 32 is smaller than conventional, therefore, the sealing pressure is lower than conventional. However, the metal gasket 22 is used to seal the radioactive-material container, and required to have the required sealing performance so that the positive pressure in the radioactive-material container 500 is at most about 1.0 MPa. Consequently, the sufficient sealing performance can be ensured with the sealing pressure of the metal gasket 22. The configuration of the metal gasket and the configuration of the radioactive-material container, which are explained in the first embodiment and the modifications, can be applied to a second embodiment or later. FIGS. 13A to 13D are views for illustrating a sealing structure in a radioactive-material container according to the second embodiment of the present invention. A radioactive-material container according to the second embodiment has substantially same configuration as the radioactive-material container according to the first embodiment. However, the difference is the metal gasket used in the radioactive-material container. A metal gasket according to the second embodiment is so-called double-ring type, and in the metal gasket, both ends of an outer cover are joined so as to unify coil springs, which have the different hoop-diameters and are arranged concentrically, while the outer cover covers the coil springs. The other configuration is the same as the configuration in the first embodiment, therefore the explanation is omitted and the same reference symbol is applied to the same component. In a metal gasket 23, which is so-called double-ring type, two coil springs 33 with the different diameters are arranged concentrically, two inner covers 43 cover the coil springs 33, the outer cover 53 covers the inner covers 43, and ends 53t of the outer cover 53 are jointed at a joint 53b. The ends 53t are jointed by welding or a friction bonding. It is preferable to perform the welding by a laser welding or an electron beam welding, because a caul does not need to be set at the joint 53b. As shown in FIG. 13A, ends 53ta1, 53tb1 may be jointed at a joint 53t1 arranged between coil springs 33a1, 33b1 with the different hoop diameter Df. In FIG. 13C, ends of an outer cover 533 is butted and jointed at a joint 53b3. The ends 53ta1, 53tb1 may be jointed in a manner shown in FIG. 13C. As shown in FIG. 13B, ends 53ta2, 53tb2 may be jointed at a side 33y2 of a coil springs 33b2, or a side of a coil springs 33a2 (not shown). Moreover, as shown in FIG. 13D, a spacer 634 is arranged inside an outer cover 534, and ends of the outer cover 534 and the spacer 634 may be jointed one another at a joint 53b4. Only the ends of the outer cover 534 may be jointed while using the spacer 634 as a backup for the joining. If the spacer 634 is used as a backup for the joining, the ends of the outer cover 534 can be jointed easily. The spacer 634 may be made of pure aluminum or the like. Moreover, at a space between the coil springs 33 shown in FIG. 13A or FIG. 13B, a spring, which has the slightly smaller external diameter than the coil springs 33, may be arranged to restrain the deformation of the outer cover 53 as alternative to the spacer 634. By using such a spring, the metal gasket 23 can be manufactured more easily in comparison with the case of using pure aluminum or the like. Moreover, using such a spring is preferable because the outer cover 53 is not stressed excessively by adjusting the repulsive force of the coil spring to the proper value. FIGS. 14A to 14C are views for illustrating a metal gasket, which is partially-open and double-ring type, and a metal gasket according to the second embodiment of the present invention. As shown in FIG. 14A, in a metal gasket 2010, which is partially-open and double-ring type, a sealing area 50sa10 and a sealing area 50sb10, which are sealing areas on the secondary lid 508 side, are connected via an outer cover 5010. Therefore, if the outer cover 5010 tries to creep to a radial direction X of the metal gasket 2010, the creep deformation is restrained. In this manner, the creep deformation of the outer cover 5010 is inhibited on the sides of the sealing areas 50sa10, 50sb10, and the stress relaxation of the metal gasket 2010 is restrained corresponding to the inhibition of the creep deformation. On the other hand, on the body 501 side, a sealing area 50sA10 and a sealing area 50sB10 are not connected via the outer cover 5010. Therefore, if the outer cover 5010 tries to creep to a radial direction X of the metal gasket 2010, nothing restrains the creep deformation. Therefore, compared to the secondary lid 508 side, the outer cover 5010 creeps more on the body 501 side, and the stress relaxation of the metal gasket 2010 increases corresponding to the creep deformation. However, as shown in FIG. 14B, in a metal gasket 235 according to the present invention, coil springs 33a5, 33b5 with the different hoop-diameters Df are arranged concentrically and covered with inner covers 43a5, 43b5 respectively, the inner covers 43a5, 43b5 are covered with an outer cover 535, and ends 53ta5, 53tb5 of the outer cover 535 are jointed. Therefore, at any sealing part on the secondary-lid 508 side and on the body 501 side, sealing areas 53sa5, 53sA5, 53sb5, 53sB5 are connected via the outer cover 535. Accordingly, the creep deformation of the outer cover 535 is restrained at any sealing areas 53s on the secondary-lid 508 side and on the body 501 side, namely the sealing areas 53sa5, 53sA5, 53sb5, 53sB5. Consequently, the stress-relaxation phenomenon accompanying the creep deformation is inhibited, the sealing performance is maintained even in the long-term storage, and the transport can be performed safely. Moreover, because the ends 53ta5, 53tb5 of the outer cover 535 are jointed by a friction bonding or other means for joining, the air tight can be maintained inside the metal gasket 235. Generally, in view of safety, the recycle fuel assembly is contained in the radioactive-material container while the radioactive-material container is sunk in the storage pool filled with water. Therefore, after the radioactive-material container is pulled out of the pool and the water is removed, the radioactive-material container is dried by vacuum drying or the other drying means. Then, the radioactive-material container is transported and stored for a long period of time. At this time, in the metal gasket 520 (see FIG. 7A), which is partially-open and double-ring type, it takes a long time to completely remove the water seeping inside by the vacuum drying because the insufficient drying may cause a corrosion. However, in the metal gasket 235, the water does not seep inside, therefore, time for the vacuum drying can be reduced significantly, there disappears the potential of the corrosion caused by the water left inside, and the higher reliability can be obtained in the long-term storage. As shown in FIG. 14C, ends 53ta6, 53tb6 of an outer cover 536 may be jointed after arranging a spacer 636 between coil springs 33a6, 33b6, which are arranged concentrically, covered with inner covers 43a6, 43b6 respectively, and have the different hoop-diameters. In this manner, the outer cover 536 can be supported by the spacer 636, therefore, the deformation of the outer cover 536 can be inhibited, and the ends 53ta6, 53tb6 can be jointed easily. As shown in FIG. 14C, to inhibit the deformation of the outer cover 536 when the tightening load is applied on the outer cover 536, the spacer 636 may be formed to have a height h as high as the diameter of the inner cover 436. In this manner, the deformation of the outer cover 536 can be inhibited when the outer cover 536 is tightened, therefore, the creep deformation of the outer cover 536 can be inhibited more, and the reliability in the long-term storage increases. The spacer 636 may have a shape so as to be easily deformed by the tightening stress of the metal gasket 236 without a needlessly high tightening-stress. As described above, instead of using the spacer 636, a spring that has the slightly smaller diameter than the coil spring 33 may be used. In the same way as the first embodiment, the sealing areas 53s of the metal gasket 23 may be formed to have a flat surface, and a step may be formed along the circumferential direction of the metal gasket 23 at the intersection of the sealing area and an area except the sealing area. In this manner, the stress concentration at the sealing areas 53s can be uniformed more, therefore, the creep deformation at the sealing areas 53s can be inhibited more. Consequently, the higher reliability can be obtained in the long-term storage. The second embodiment according to the present invention hereto has been explained. The configuration of the metal gasket and the configuration of the radioactive-material container, which are explained in the second embodiment, can be applied to a third embodiment or later. FIGS. 15A and 15B are views for illustrating a spring of a metal gasket according to the third embodiment of the present invention. A radioactive-material container according to the third embodiment and the radioactive-material container according to the first embodiment have substantially same configuration. However, the difference is that the metal gasket according to the third embodiment uses a coil spring that has a wire rod with substantially rectangular cross-section. The other configuration is the same as the configuration in the first embodiment, therefore the explanation is omitted and the same reference symbol is applied to the same component. As shown in FIG. 15A, a coil spring 341 used in a metal gasket 241 has a wire rod with a rectangular cross-section. Therefore, the coil spring 341 makes a contact with an inner cover 441 with the lager dimension in comparison with a coil spring with a circular cross-section, and a repulsive force of the coil spring 341 can be transmitted to the inner cover 441 and an outer cover 541 more uniformly. Consequently, the stress distribution of the outer cover 541 can be more uniformed, so that the inner cover 441, which contains a reaction force of the coil spring 341, may be removed or may have the thinner thickness, and moreover, the stress-relaxation phenomenon, ascribable to the creep deformation, of the metal gasket 241 can be decreased. Therefore, the sealing performance can be maintained even in the long-term storage. If the coil spring with a circular cross-section and the coil spring 341 with a rectangular cross-section have the same section modulus, the coil spring 341 has the thinner width b of the wire rod, and a pitch p can be smaller. Therefore, if the coil spring with a circular cross-section and the coil spring 341 have the same flexural rigidity, the winding number of the coil spring 341 can be increased, and the repulsive force of the coil spring 341 can be transmitted to the outer cover 541 more uniformly. As just described, when the coil spring 341 with a rectangular cross-section is used, the stress-relaxation phenomenon can be inhibited more in the metal gasket 241 than the coil spring with substantially circular cross-section. Moreover, the pitch p can be decreased, therefore, the coil spring 341 can have the smaller initial gradient θp=0, which is a gradient when the tightening stress does not act, than the coil spring with a circular cross-section. Consequently, the repulsive force of the coil spring 341 can be used more effectively. If the coil spring with a circular cross-section and the coil spring 341 with a rectangular cross-section have the same section modulus, the stress, which is caused in the coil spring by the tightening stress of the metal gasket, can be decreased more in the coil spring 341. Moreover, unlike the coil spring with a circular cross-section, the adjacent wire rods make a contact with each other via a surface 34a1 in the coil spring 341. In this manner, the stress that the tightening stress P produces on the surface 34a1 can be decreased more than in the coil spring with a circular cross-section. Consequently, a gradient Op, which is made by the tightening stress P, can be decreased more than in the coil spring with a circular cross-section, and the torsion stress, which acts on the wire rod of the coil spring 341, can be decreased. When the coil spring 341 with a rectangular cross-section is used, these actions provide the higher-and-longterm reliability of the coil spring 341. The third embodiment according to the present invention hereto has been explained. The configuration of the metal gasket and the configuration of the radioactive-material container, which are explained in the second embodiment, can be applied to a fourth embodiment or later. FIGS. 16A to 16D are partial cross-sections for illustrating a sealing structure of a radioactive-material container according to the fourth embodiment. The sealing structure of the radioactive-material container according to the fourth embodiment is characterized in that a metal gasket is made to be waterproof. Generally, in view of safety, the recycle fuel assembly is contained in the radioactive-material container while the radioactive-material container is sunk in the storage pool filled with water. Therefore, before the transport and the long-term storage, the water is removed by vacuum drying or the other drying means. In the partially-open-and-double-ring-type metal gasket and the single-ring-type metal gasket, the water that seeps inside could not be removed completely, or it takes a long time to perform the vacuum drying. The incomplete drying may cause the corrosion of the metal gasket. In FIG. 16A, as a waterproofing, a sealing agent 6411 is used to fill in an interspace inside an outer cover 5011 of a metal gasket 2011. This waterproofing prevents the water from seeping inside the metal gasket 2011 while containing the recycle fuel assembly. Moreover, arranging the drying agent inside coil springs 30a11, 30b11 is effective in keeping the inside of the coil springs 30a11, 30b11 dry. As shown in FIG. 16B, in a metal gasket 2012, which is double-ring type, a sealing agent 6412 may be used to fill in a space formed between two rings of the metal gasket 2012. In this manner, even if the metal gasket 2012 is tightened and deformed, a resin follows the deformation easily. Therefore, this manner increases the waterproofing property, and is preferable. Such a water proofing stops the water from seeping inside the metal gasket 2012, the corrosion of the metal gasket 2012 is not caused by the water. Consequently, the high sealing performance can be maintained even in the long-term storage. As the sealing agent 64, a silicone-rubber sealing agent is preferable because of waterproofing property, durability, and property of following a deformation. An example of the sealing agent 64 is “KE103” from Shin-Etsu Chemical Co., Ltd. As shown in FIG. 16C, a water-repellent agent 6513 may be applied to an interspace inside an outer cover 5013 of a metal gasket 2013. A part where the water-repellent agent 6513 is applied repels water, therefore, the water is easily removed by vacuum drying. Using both the sealing agent 64 and the water-repellent agent 65 provides the higher effect of waterproof. The water-repellent finishing may be performed on the metal gasket 2013 entirely, and such manner is preferable because the water can be removed more easily. Examples of the water-repellent agent 65 are a silicone water-repellent-agent, a fluorine water-repellent-agent, and a silane-coupling water-repellent-agent. Moreover, as a surfactant, before the sealing, alcohol such as ethanol, methanol, and isopropyl alcohol, or the other organic agents may be used to fill in a metal gasket 2014, or may be applied sufficiently. These organic agents prevent the water from seeping inside the metal gasket 2012 while the process of containing the recycle fuel assembly is performed under the water. These organic agents have a low melting-point, and completely evaporate in the vacuum drying, therefore, the water does not remain inside the metal gasket 2014. This manner also enables removing the water that remains, therefore, the corrosion of the metal gasket 2014 can be inhibited even in the long-term storage, and the reliability of the storage increases. As shown in FIG. 16D, the drying of the internal space may be promoted by arranging a drying agent 6614 in an enclosed space 20i14 of a metal gasket 2014. This manner enables drying the water that enters into the metal gasket 2014 accidentally, therefore, the corrosion of the metal gasket 2014 can be inhibited even in the long-term storage, and the reliability of the storage increases. Examples of the drying agent 66 are a silicon-dioxide drying-agent, a clay drying-agent, which are a physical absorption type, and a quicklime drying-agent, which is a chemical absorption type. On the surface of the outer cover 50 of the metal gasket 20, a metal film, an oxide film, and other anti-corrosive agent may be formed. In this manner, the anti-corrosive agent inhibits the corrosion of the outer cover 50 even if the water remains, and therefore, the reliability of the sealing performance in the long-term storage increases. The anti-corrosive film may be formed not only on the outer cover 50 but also the entire of the metal gasket 20. In this manner, the inner cover 40 and the coil spring 30 are protected from the corrosion as well. The anti-corrosive film is formed by a wet process like an alumite treatment, or by a method of evaporating a metal with a high corrosion-resistance, such as Ti, Cr, and Ag, to the outer cover 50 and the metal gasket 20 using an ion-plating method. Especially, an ion-plating method is preferable, because the anti-corrosive film can be formed after the outer cover 50 covers the inner cover 40 so as to form the metal gasket 20, and there is flexibility in the formation. FIGS. 17A to 17C are views for illustrating metal gaskets according to a first modification of the fourth embodiment. The metal gaskets are characterized in that including a hole for draining water (hereinafter, a water-draining hole). In a modification shown in FIG. 17A, water-draining holes 67a1, 67b1 are respectively arranged in coil spring 35a1, 35b1, and used to remove the water, which enters into the coil springs 35a1, 35b1, in the vacuum drying. In a modification shown in FIG. 17B, a water-draining hole 682 is arranged in an outer cover 552 and between coil springs 35a2, 35b2. The water-draining hole 682 enables removing the water that remains between the secondary lid 508 and the outer cover 552 of a metal gasket 252. As shown in FIG. 17C, a water-draining hole 683 is arranged in an outer cover 553 and between coil springs 35a3, 35b3, and moreover, the outer cover 553 may be curved so as to arrange an interspace between the outer cover 553 and the secondary lid 508. In this manner, the interspace between the outer cover 553 and the secondary lid 508 becomes larger, therefore, the effect of the surface tension of water decreases, and the drainage performance increases. Where and how many the water-draining holes 67, 68 are arranged may be changed properly based on the specification of the metal gasket 25. In the metal gaskets 25, the water that remains inside the metal gaskets 25 is easily removed from the water-draining holes 67, 68 in the vacuum drying, therefore, the drying can be performed more easily, and the corrosion of the metal gaskets 25 can be inhibited even in the long-term storage. FIGS. 18A and 18B are views for illustrating metal gaskets according to a second modification of the fourth embodiment. A metal gasket 261, shown in FIG. 18A, is characterized in that an outer cover 561 covers two internal elements and ends 56ta1, 56tb1 of the outer cover 561 are jointed with the outer cover 561. One internal element includes an inner cover 46a1 and a coil spring 36a1 covered with the inner cover 46a1 while another internal element includes an inner cover 46b1 and a coil spring 36b1 covered with the inner cover 46b1. In this manner, the internal elements are sealed at each joint, and the water does not seep inside the metal gasket 261. Therefore, the water does not cause the corrosion of the metal gasket 261, and the high sealing-performance can be maintained even in the long-term storage. The ends 56ta1, 56tb1 and the outer cover 561 may be jointed using means for welding such as a laser welding and an electron beam welding. If ends 56ta2, 56tb2 of an outer cover 562 and the outer cover 562 are jointed at one joint as shown in FIG. 18B, only the process for one joint is required, and the efficiency of the process improves. The fourth embodiment and the modifications can be applied to the conventional metal gasket 520 (see FIG. 7A). FIG. 22 is a view for illustrating a sealing structure in a radioactive-material container according to a fifth embodiment of the present invention. FIGS. 23A and 23B are cross sections of metal gaskets according to the fifth embodiment of the present invention. A metal gasket 2015 in a sealing structure 1015 of the radioactive-material container according to the fifth embodiment is characterized in that a first water-draining hole 10115 is arranged in an inner cover 40b15 and a second water-draining hole 10215 is arranged in an inner cover 40a15. In the metal gasket 2015, which is so-called a double-ring type, coil springs 30a15, 30b15 with the different hoop-diameters Df are arranged concentrically, and covered with an outer cover 5015. However, a metal gasket to which the present invention can be applied is not limited to a double-ring type metal gasket but may be applied to a metal gasket 2017, shown in FIG. 23B, that includes an outer cover 5017 with a flat upper part, and the single-ring type metal gasket 203 shown in FIG. 2B. As shown in FIG. 22, the sealing structure 1015 is arranged between the secondary lid 508 and the flange member 506 of the body 501. Needless to say, the sealing structure and the metal gasket, which are according to the present invention, can be applied to the space between the primary lid 507 and the body 501 (the same is applied hereinafter). As shown in FIG. 23A, in a metal gasket 2016, inner covers 40a16, 40b16 respectively covers coil springs 30a16, 30b16 so as to form an inner ring 7016 and an outer ring 8016, and an outer cover 5016 covers the inner ring 7016 and the outer ring 8016. A first water-draining hole 10116 is arranged in the inner cover 40b16 so as to face the center C of the body 501, and where the first water-draining hole 10116 is arranged is not covered with the outer cover 5016. A second water-draining hole 10216 is arranged in the inner cover 40a16 so as to face the center C of the body 501. Where the first water-draining hole 10116 is arranged in the inner cover 40b16 is not covered with the outer cover 5016, because it requires arranging the first water-draining hole 10116 only in the inner cover 40b16. After the first water-draining hole 10116 is arranged in the inner cover 40b16, the inner cover 40b16 is formed to be circular so as to wind and cover the coil spring 30b16. Similarly, after the second water-draining hole 10216 is arranged in the inner cover 40a16, the inner cover 40a16 is formed to be circular so as to wind and cover the coil spring 30a16. Functions of the first water-draining hole 101 and the second water-draining hole 102 will be explained with reference to FIG. 23A (the same is applied to the metal gasket 2015, shown in FIG. 22, and the metal gasket 2017, shown in FIG. 23B). A recycle fuel assembly is contained in the radioactive-material container 500 while the radioactive-material container 500 is sunk in the pool, and after the radioactive-material container 500 is pulled out from the pool, the water is removed from the radioactive-material container 500 by vacuum drying. When the radioactive-material container 500 is sunk in the pool, the water seeps inside the coil spring 30a16. Especially, when the inner cover 40a16 has an opening 40s16 that faces the inside of the metal gasket 2016, the water seeps inside the coil spring 30a16 easily. Like in the outer ring 8016, even if the inner cover 40b16 does not have an opening, the water seeps through a gap between the outer cover 5016 and the inner cover 40b16 and collects inside the 30b16. When the water is removed from the radioactive-material container 500, the water that seeps inside the coil spring 30b16 goes outside from the first water-draining hole 10116, and the water that seeps inside the coil spring 30a16 goes outside from the opening 40s16 of the inner cover 40a16. At this time, the water that remains between the inner cover 40a16 and the outer cover 5016 moves to the inside of the coil spring 30a16 through the second water-draining hole 10216 and goes out to an interspace between the inner ring 7016 and the outer ring 8016 through the 40s16. It is not required to arrange a water-draining hole on the opening 40s16 side of the inner cover 40a16. However, for example, in case that the opening 40s16 is arranged close to a bridge 50a16 of the outer cover 5016 and the water easily remains owing to the shape, it is preferable to arrange a water-draining hole on the opening 40s16 side of the inner cover 40a16. In manufacturing the metal gasket 2016, the first water-draining hole 10116 and the second water-draining hole 10216 should be carefully made without damaging the coil springs 30b16, 30a16. Therefore, the first water-draining hole 10116 and the second water-draining hole 10216 are made in the inner covers 40b16, 40a16 respectively, and then, the inner covers 40b16, 40a16 are respectively wound around the coil springs 30b16, 30a16. In this manner, the first water-draining hole 10116 and the second water-draining hole 10216 can be easily made in the inner covers 40b16, 40a16 respectively without damaging the coil springs 30b16, 30a16. In the embodiment above described, the first water-draining hole 10116 of the inner cover 40b16 is arranged so as to face the center C of the body 501 (that is, the first water-draining hole 101 is arranged along a line L, which connects the center of the outer ring 8016 and the center of the inner ring 7016), because it is hard to remove the water through the first water-draining hole 10116 if the first water-draining hole 10116 faces obliquely downward and is covered with the sealing surface. Preferably, the first water-draining hole 10116 is arranged so as to face the center C of the body 501 and within a range of +45 degrees against the line L. FIGS. 24A and 24B are cross sections of metal gaskets according to a sixth embodiment of the present invention. As shown in FIG. 24A, in a metal gasket 271, inner covers 210a1, 210b1 are formed to be circular and the inner covers 210a1, 210b1 with the different hoop-diameters are arranged concentrically. An outer cover 2201 covers the inner covers 210a1, 210b1 so as to have a double-ring shape entirely. The present invention is not limited to the double-ring-type metal-gasket like the metal gasket 271, but may be applied to the so-called single-ring-type metal-gasket like a metal gasket 272 shown in FIG. 24B. In the metal gasket 272, an inner cover 2102 is covered with an outer cover 2202. A material of the outer covers 220 is the same as explained in the first embodiment. In the sixth embodiment, the inner covers 210 function as a spring, therefore, the inner covers 210 are made of a material that is same as the material of the coil spring explained in the first embodiment. The inner covers 210a1, 210b1 of the metal gasket 271 are formed to be circular while overlapping ends of the inner cover 210a1 and overlapping ends of the inner cover 210b1. When a compression is caused by the sealing, overlaps 210sa1, 210sb1 slide and the diameters of the inner covers 210a1, 210b1 get smaller as a whole. The diameters of the inner covers 210a1, 210b1 get smaller, but the contact surfaces with the inner covers 210a1, 210b1 do not get larger. Therefore, the sealing can be performed surely. A lot of first water-draining holes 2301 are made in the inner cover 210b1. In the inner covers 210a1, a lot of second water-draining holes 2311 and third water-draining holes 2321 are made along a circumferential direction. The water-draining holes 2301, 2311, 2321 are used to let out the water that seeps inside the inner covers 210a1, 210b1. The first water-draining holes 2301 is arranged at substantially middle height of the inner cover 210b1, and so as to face the center C of the body 501. The reason is if, for example, the first water-draining hole 2301 is arranged downward and interferes with the outer cover 2201, another water-draining hole needs to be made in the outer cover 2201. Moreover, if the first water-draining hole 2301 is arranged near the sealing surface, the water easily seeps between the outer cover 2201 and the sealing surface, and it is hard to remove the water. Preferably, the first water-draining hole 2301 is arranged within a range of ±45 degrees against the line L, which indicates the direction to face the center C of the body 501. On the other hand, in the inner cover 210a1, the overlap 210sa1 is arranged inside the metal gasket 271, therefore, the third water-draining hole 2321 needs to be arranged so that the third water-draining hole 2321 is not covered when the sealing causes the compression and the overlap 210sa1 slides. Moreover, to decrease the water that remains between the inner cover 210a1 and the outer cover 220a1 as much as possible, preferably, the second water-draining hole 2311 is arranged in the inner cover 210a1 at substantially middle height of the inner cover 210a1 so as to faces the center C of body 501. The metal gasket 272, shown in FIG. 24B, is formed to be circular after building up the plate-shaped inner cover 2102 on the plate-shaped outer cover 2202. Then, a first water-draining hole 2332 is made at substantially middle height of the inner cover 2102. In this case, the inner cover 2102 is not exposed to the outside, therefore, a second water-draining hole 2342 is made so as to penetrate the inner cover 2102 and the outer cover 2102. The water that remains between the outer cover 2202 and the inner cover 2102 is moved to the inside of the inner cover 2102 through the first water-draining hole 2332, and removed to the outside of the metal gasket 272 through the second water-draining hole 2342. As explained in the above, according to the present invention, at lease any one of the followings can be achieved: ensuring the sufficient sealing performance even in the long-term usage by minimizing the deterioration of the metal gasket, exerting the sufficient sealing performance for the whole period of the long-term storage by surely removing the water inside the metal gasket in the vacuum drying; and reducing the time for the vacuum drying. Moreover, according to the present invention, the sufficient sealing performance can be exerted for a long period of time by removing the water inside the metal gasket. Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.
	abstract	In operation to obtain an optimal observation condition in a review system, the number of trial reviews can be reduced to improve efficiency of the operation. For a defect review conducted by the review system, a recipe parameter management system stores, as recipe parameter setting history in a recipe parameter setting history database (DB), a recipe parameter setting values of recipe parameters set when the defect review is conducted, the number of trial reviews carried out until the recipe parameter setting values are set, and defect images obtained when the defect review is conducted. The apparatus displays, on a terminal, histograms and the numbers of trial reviews generated based on the recipe parameter setting history data stored in the recipe parameter setting history database (DB). Hence, the operator can easily obtain data regarding the recipe parameter setting in the past.
061756067	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1a shows a boiling water fuel assembly 1 which comprises a long tubular container, of rectangular cross section, referred to as fuel channel 2. The fuel channel 2 is open at both ends so as to form a continuous flow passage through which the coolant of the reactor flows. The fuel assembly 1 comprises a large number of equally long tubular fuel rods 3, arranged in parallel in a bundle, in which pellets 4 of a nuclear fuel are arranged. The fuel rods 3 are arranged spaced from each other in four orthogonal sub-bundles by means of a cruciform support means 8 (see also FIG. 1b). The respective sub-bundle of fuel rods 3 is retained at the top by a top tie plate 5 and at the bottom by a bottom tie plate 6. The fuel rods 3 in the respective sub-bundle are kept spaced apart from each other by means of spacers 7 and are prevented from bending or vibrating when the reactor is in operation. The spacer 7 according to the invention may, of course, also be used in a boiling water reactor which lacks the cruciform support means 8 and instead is provided with, for example, one or more water tubes. At the lower part of the fuel assembly 1, a transition piece 9 is arranged. The task of the transition piece 9 is to guide coolant, flowing upwards through the core (not shown) of the nuclear reactor, to the fuel assembly 1 for cooling of the fuel rods 3 arranged therein. The transition piece 9 is arranged in the core in an opening in a so-called assembly supporting plate (not shown). Further, a bottom support 10 is arranged in the transition piece 9. The bottom tie plate 6 with the lower ends of the fuel rods 3 is arranged at least partly immersed into the bottom support 10. The bottom support 10 is provided with a plurality of through-holes 11 forming a filter. FIG. 2 shows the bottom support 10 in more detail. The bottom support 10 is substantially formed as a parallelepiped with a substantially square flat side. The direction of flow of the coolant is indicated by an arrow F. The parallelepiped is provided with a downstream and an upstream flat side 12, 13 and four narrow sides 14. The flat sides 12, 13 and the narrow sides 14 surround a cavity and form a parallelepiped. The downstream flat side 12 is formed with four openings 12a, where each opening 12a is adapted to receive the lower end of a sub-bundle. The holes are arranged in the upstream flat side 13 forming a filter through which the coolant F is forced to pass before it reaches the fuel rods arranged in the fuel bundle or in the fuel bundles. The holes 11 are substantially formed straight. Further, the bottom support 10 is provided with a passage opening 16 for passage of coolant to the cruciform support means 8. The cruciform support means 8 is formed as a channel for conducting non-boiling coolant up through the fuel assembly 1. Any foreign matter passing with the coolant through the fuel assembly does not run the risk of adhering to any unsuitable place therein. The embodiment of the invention shown in FIG. 3 is provided with so-called bypass holes 15. The bypass holes 15 are arranged in the upstream flat side 13 and at the respective corners of the bottom support 10. The bypass holes 15 have a substantially triangular shape. By arranging bypass holes 15 in the corners of the bottom support 10, it is ensured that coolant may always pass through the bottom support 10. In the event that the filter should be clogged by foreign matter, coolant flow is thus allowed to pass through the bypass holes 15. The bypass holes 15 are arranged such that the coolant flowing upwards through the fuel assembly 1 is forced to change its direction to be able to pass them (see the arrows F in FIG. 4). By this redirection of the coolant flow, any foreign matter is efficiently prevented from accompanying the coolant flow F up through the fuel assembly 1. The foreign matter which is possibly oriented such that it may pass with the coolant flow through the bypass holes 15 substantially maintains its orientation when the coolant flow F is forced to change its direction to be able to pass up through the bottom tie plate 6 to the fuel rods 3. Since the direction of the possible foreign matter is substantially maintained, the foreign matter will adhere to the bottom tie plate 6 and be prevented from passing up to the fuel bundle. The upstream flat side 13 of the bottom support 10 is shown in more detail in FIG. 3. FIG. 3 shows the filtering part of the bottom support 10 in a view from below. The filtering part, like the fuel assembly in its entirety, is divided into four parts. In principle, a filtering part is arranged below the respective sub-bundle of fuel rods 3. In the example shown, the through-holes 11 are arranged in rows, which are substantially parallel with an opening edge at the respective bypass hole 15. Further, the filter in the embodiment chosen in FIG. 3 is provided with a plurality of long and narrow grooves 17 (see also FIGS. 4-6). The grooves 17 are oriented so as to be arranged substantially parallel to an opening edge 15a of the respective bypass holes 15. By arranging grooves 17 in this way, an orientation of the possible foreign matter reaching the bottom support 10 is achieved, such that this foreign matter is prevented from being conducted out towards and through the bypass holes 15. The grooves 17 may, of course, also be oriented such that they are parallel to the respective narrow sides 14. The embodiment with grooves 17 also prevents clogging of the filter in that any foreign matter, which is arranged towards the upstream edge of the filter, does not make tight contact but there is a certain distance between the respective foreign matter and the filter, whereby coolant, possibly with a certain reorientation, is allowed to pass by the captured foreign matter. In FIG. 4, this is illustrated by foreign matter, drawn into the figure and marked with reference numeral 18. A space is thus formed between the foreign matter 18 and the bottom of the groove 17. The grooves 17 in the embodiments shown in FIGS. 3-6 have an additional function, namely, to form edges against which any foreign matter accompanying the coolant may be broken. The foreign matter which is broken when it reaches the surface provided with grooves 17 primarily consists of oxide flakes which have become detached from the fuel rods 3 and have accompanied the coolant. These oxide flakes do not give rise to any abrasion but may to some extent stop up and obstruct the flow passage if they have a size which is larger than the diameter of the holes 11 in the filter. Further, FIG. 4 shows that that part of the bottom support 10, in which the trough-holes 11 are arranged, is relatively thick. This provides for a stable design of the filter and ensures that vibrations, caused by the flow of the coolant therethrough, are avoided. In the embodiment shown in FIG. 4, the bottom support 10 downstream of the filter is formed with a flange 10a. The flange 10a has a substantially triangular shape which corresponds to the shape of the respective bypass holes 15. The flange 10a is arranged at a level between the upstream and downstream flat sides 12, 13 and above the opening of the respective bypass hole 15. The task of the flange 10a is to guide the coolant flow F, which has passed through the bypass hole 15, into the central parts of the bottom support 10 and then allow the flow to pass upwards through the bottom tie plate 6. The embodiment chosen, shown in FIG. 4, also shows the open structure in the bottom tie plate 6. The through-holes 6a in the bottom tie plate 6 have a diameter which compensates for the increased pressure drop which is caused by the filter. FIG. 5 shows an embodiment which corresponds to that shown in FIG. 4 apart from the fact that the bottom support is not provided with a flange 10a for guiding the coolant flow F. FIG. 6 shows an alternative embodiment of the invention, in which an additional level with a second filtering member (see reference numeral 19) is arranged in the bottom support 10. This second filtering member is, in the example shown, formed as a plate 20 with through-holes 21. The through-holes 21 preferably have their centre axis somewhat displaced in relation to the centre axis of the through-holes 11 arranged in the upstream flat side 13. The plate 20 is preferably provided with a centrally arranged opening for passage of coolant to the passage opening 16. FIG. 7 shows an alternative embodiment of a transition piece 9. The bottom support 10 is arranged as an integral part of the transition piece 9. The filter in its turn is made as an integral part of the bottom support 10. In the embodiment shown, the filter is provided with through-holes 11 and grooves 17 in a manner corresponding to that shown in FIG. 3.
	claims	1. A thermal conduction element (20) for a package holding radiological protection means (22) for transporting and/or storing radioactive materials, the element (20) comprising:an internal part (30) in contact with a lateral body (14) of the package;an external part (34) forming a portion of an external envelope (24) of said package; andan intermediate part (32) connecting the internal part to the external part,wherein the internal, external and intermediate parts are integrally formed from copper and one of the alloys thereof, andwherein steel connection areas (36) are positioned at two opposite ends of said external part (34), each of the steel connection areas (36) being welded to a steel connection area positioned on an external part of an adjacent thermal conduction element, the welded steel connection areas being configured to connect the external part (34) of the thermal conduction element (20) to external parts of adjacent thermal conduction elements. 2. The thermal conduction element according to claim 1, wherein each connection area (36) is produced from carbon steel or stainless steel. 3. The thermal conduction element according to claim 1, further comprising a transverse section roughly in the shape of a U or S. 4. The thermal conduction element according to claim 1, wherein each steel connection area (36) extends over a circumferential length (l) lying between 5% and 15% of the circumferential length (L) of its associated external part. 5. A package (2) holding radiological protection means (22) (2) for transporting and/or storing radioactive materials, further comprising a plurality of thermal conduction elements (20) corresponding to the thermal conduction element (20) and the adjacent thermal conduction elements of claim 1. 6. The package according to claim 5, wherein any adjacent two of the thermal conduction elements (20) define a cavity (50) housing the radiological protection means (22). 7. A method for manufacturing a package (2) holding radiological protection means (22) for transporting and/or storing radioactive materials, the package (2) comprising a lateral body 14) and a plurality of thermal conduction elements (20), each of the thermal conduction elements (20) comprising an internal part (30), an external part (34), and an intermediate part (32), the internal part (30) being in contact with the lateral body (14) of the package (2), the external part (34) forming a portion of an external envelope (24) of said package (2), the intermediate part (32) connecting the internal part (30) to the external part (34), the internal, external, and intermediate parts being integrally formed from copper and one of the alloys thereof, where steel connection areas (36) are positioned at two opposite ends of said external part (34), each of the steel connection areas (36) being welded to a steel connection area positioned on an external part of an adjacent one of the thermal conduction elements, the welded steel connection areas being configured to connect the external part (34) of the thermal conduction element (20) to external parts of adjacent ones of the thermal conduction elements, the method comprising pouring a radiological protection material into one of two of the thermal conduction elements (20a) defining a cavity (50) in which the radiological protection means (22) is to be housed, the pouring being carried out with the one thermal conduction element (20a) being assembled on the package (2). 8. The method according to claim 7, further comprising successively assembling the other one of the two of the thermal conduction elements (20b). 9. The method according to claim 8, wherein said cavities (50) are filled successively, one by one, with said package oriented horizontally and by introducing the radiological protection material from above. 10. The method according to claim 9, wherein the pouring of the radiological protection material takes place directly in said one of said two of the thermal conduction elements (20a) defining the cavity in which said radiological protection means (22) is being housed. 11. The method according to claim 9, wherein the pouring of the radiological protection material takes place through at least one orifice (70) provided on a tool (72) mounted above said one of said two of the thermal conduction elements (20a) defining the cavity (50) in which said radiological protection means (22) is housed, the other one of said two of the thermal conduction elements (20b) being assembled on the package after the removal of said tool (72). 12. The method according to claim 10, wherein the pouring of the radiological protection material takes place through at least one orifice (70) provided on the intermediate part (32) of said other one of said two of the thermal conduction elements (20b), mounted temporarily above said one of said two of the thermal conduction elements (20a) defining the cavity (50) in which said means (22) is housed, the other of said two of the thermal conduction elements (20b) then being removed and then reassembled definitively on the package. 13. The method according to claim 12, wherein welding of the steel connection areas (36) in pairs is carried out after the radiological protection means (22) of the package has been poured in the cavity (50) respectively associated with the thermal conduction elements (20) on which the pairs of the steel connection areas (36) are disposed.
052992420	abstract	A nuclear reactor control system is provided in a nuclear reactor having a core operating in the fast neutron energy spectrum where criticality control is achieved by neutron leakage. The control system includes dual annular, rotatable reflector rings. There are two reflector rings: an inner reflector ring and an outer reflector ring. The reflectors are concentrically assembled, surround the reactor core, and each reflector ring includes a plurality of openings. The openings in each ring are capable of being aligned or non-aligned with each other. Independent driving means for each of the annular reflector rings is provided so that reactor criticality can be initiated and controlled by rotation of either reflector ring such that the extent of alignment of the openings in each ring controls the reflection of neutrons from the core.
043552366	description	DETAILED DESCRIPTION OF THE INVENTION The invention will be described with respect to quadrupole magnets, however it will be readily appreciated by those skilled in the art that it is equally applicable to other multipole magnets, particularly higher order multipole magnets where the number of poles is an even positive integer. In accord with the present invention, with reference to the figures, an adjustable strength permanent multipole magnet 10 comprises a plurality of segments of REC material 20 arranged in a ring so that each segment has a predetermined easy axis orientation. The arrows in each REC segment 20', 20", indicate the direction of the easy axis throughout that segment. Particularly, with reference to FIGS. 2A and 2B, the radial symmetry line of a segment forms an angle .theta. with the x-axis and the direction of the easy axis forms an angle .alpha. with the symmetry line. Then for the embodiments illustrated, EQU .alpha.=2.theta. (1) For a segmented ring quadrupole with M trapezoidal pieces made of "perfect" REC material, the pole tip field is given by: ##EQU1## where .mu..sub.o is the permeability of free space, H.sub.c is the coercive magnetic force of the material, r.sub.i is the inner radius of the ring and r.sub.o is the outer radius of the ring. For M.fwdarw..infin., i.e. a quadrupole with continuously varying easy axes, Equation (2) becomes: ##EQU2## Two important theoretical parameters to consider for a segmented ring quadrupole are: (1) the decrease in the quadrupole strength due to the non-continuous easy axis orientation and (2) the order and magnitude of the harmonic multipole field errors introduced by the geometrical shape effects of the pieces. When M=16, Equation (2) gives the result that the pole tip field is reduced by only 6.3% compared to the continuous easy axis orientation. The nth order harmonic multipole error fields which are excited in a symmetrical array of M identically shaped (not necessarily trapezoidal) and rotationally symmetric pieces are: EQU n=2+kM; k=1, 2, 3 (4) i.e., for M=16 the first multipole error is n=18, the 36-pole. The magnitude of the 36-pole for the specific case of 16 trapezoidal pieces with r.sub.i /r.sub.o =1.1/3.0 is 6.8% of the quadrupole field at 100% aperture or 0.2% at 80% aperture. This error may be eliminated by a suitable thickness shim between the trapezoidal pieces in which case the first theoretical error would be of order 34, the 68-pole. For multipole magnets of order N, i.e. for the general case of a multiple segment 2N pole magnet, the above equations become ##EQU3## Although any anisotropic material can be used, rare earth cobalt and ceramic ferrite materials are preferred and samarium cobalt is particularly preferred. FIG. 1 illustrates one embodiment of the invention wherein an adjustable permanent quadrupole magnet 10 is made having four axial layers 12a, 12b, 12c, 12d. Each axial layer is a ring of sixteen rectangular-shaped segments 20 of REC material having its easy axis as illustrated by the arrows. The REC segments 20 are assembled into a circular configuration for each layer, such as 12a, by inserting them in ring 14a, which is held in annulus 11a by retainer ring 13a. Conveniently each axial layer, such as 12a, has a tab, such as 25a, for assisting angular displacement with respect to an adjacent layer, such as 12b. For convenience the shape of the individual segment magnet pieces 20" can be modified for example as illustrated in FIG. 3, to reduce the width of the pieces and accommodate a retainer spline 14' to position the segments. In FIG. 1 alternating axial layers are shown displaced in opposite angular directions to vary the aperture field strength. For instance layers 12a and 12c are rotatably displaced in one direction while layers 12b and 12d are displaced relatively in the other direction. In order to reduce beam coupling effects when using the adjustable strength quadrupole of this invention, it is preferred, for a four layer quadrupole, to displace the two inner layers in one direction and the two outer layers in the opposite direction. Theorectical analysis indicates that a five layer adjustable strength quadrupole can completely eliminate coupling effects on a charged particle beam. Quadrupoles in accord with this invention can be made, for example, from Hicorex 90B, a SmCo.sub.5 compound which has nominal properties of B.sub.r =8.7 Kilogauss, H.sub.c =8.2 Kilo-oersteds, H.sub.ci >15 Kilo-oersteds, where H.sub.ci is the intrinsic coercivity, and a recoil permeability of 1.05. First a block of the SmCo.sub.5 material is magnetically aligned and pressed, and then sintered. This block with approximate dimension of 2 by 2 by 1/2 inches has the easy axis angle aligned parallel to a 2 inch dimension and the pressing direction is parallel to the 1/2 inch dimension. At present this block is the largest piece of SmCo.sub.5 being manufactured in large quantity. Rectangular shaped pieces (or segments when arranged in the ring to form the quadrupole) are then cut out of this block, with the cutting directions parallel, perpendicular and at 45.degree. to the easy axis orientation so as to provide three easy axis angles. Next, the pieces are finish ground to the required dimensions and then given a further heat treatment to enhance the coercivity. Finally, the pieces are magnetized in an external field of the specified polarity. Individual blocks can also be made for each piece in the pressing, easy axis alignment, and sintering stage. In this case, the three easy axis angles are provided by rotating the die relative to the alignment magnetic field. The final stage of manufacture is to measure the effective magnetic dipole moment per unit volume of each piece. This measurement is made with an apparatus, consisting of a Helmholtz coil pair with a mechanism for positioning and rotating the pieces in the center of the coil pair, and an integrating voltmeter connected to the coils. A magnet piece is inserted in the positioning mechanism with its easy axis parallel to the axis of the coil system, the integrator is zeroed, and then the piece is quickly rotated by 180.degree.. The integrated induced voltage in the coil pair is proportional to the dipole strength of the piece. This measurement also includes the effect of misalignment of the easy axis angle, since the integrated signal is also proportional to the alignment of the dipole axis with the coil axis. It would be possible to measure the easy axis angle alignment relative to the axis of the piece with this apparatus, using a modified procedure. The significance of this data is that it provides a measure of the variation of the "strength" of the pieces due to manufacturing variables. This information gives essentially one point (open magnetic circuit) on the B-H curve, averaged over the piece. When building permanent magnet quadrupoles it is desirable to minimize the low order harmonic errors and especially the n=3 sextupole error. In contrast to electromagnet quadrupoles where it is simple to provide equal excitation of each pole, the permanent magnet material variables are difficult to control and somewhat tedious to measure. Therefore, in the assembly procedure it is highly desirable to select well matched pieces in terms of "strength" for each magnet assembly. This will help assure the equal "excitation" of each pole. FIG. 1 illustrates a four layer adjustable quadrupole of the invention where successive layers have been rotated alternately by plus and minus 221/2.degree.. The axial integral through such a multilayer quadrupole is a quadrupole field with a reduced strength proportional to the cosine of twice the rotation angle. The machanical design of such a quadrupole requires that the magnet pieces in each layer be clamped independently and that bearings be provided for precise radial and axial alignment during the rotation. The axial force between the layers must also be supported, because this force changes from maximum repulsion to maximum attraction during a plus and minus 45.degree. rotation of two adjacent layers. A preferred configuration consists of four 1/2" thick layers where the first and last layers are rotated by a positive angle and the middle two layers are rotated by the same angle in the opposite direction as illustrated in FIGS. 4 and 5. For example, in this case when the rotation angle is 20.degree., a 23% reduction in the integrated quadrupole strength is obtained. For this quadrupole the emittance growth has been evaluated for a typical beam and found to be less than 1%. FIGS. 4 and 5 illustrate a preferred adjustable strength quadrupole assembly 50 in accord with the invention having adjustment means for varying the aperture field strength. The adjustment means comprises a threaded rod 58 connected to three lever arms 54a, 54b and 54d. A lever arm is connected to each of the outside layers, 52a and 52d, and the third lever arm is connected to the middle two layers 52b and 52c. When the rod is moved inwardly toward the quadrupole the lever arms cause the outer layers to rotate in one direction while the two inner layers rotate an equal distance in the opposite direction. This rotation causes a reduction in the aperture field strength in proportion to the distance moved by the rod. The length of arms 54 (a, b and d), for example the distance from pivot point A to C, is equal to the distance from the axial center 0 of the quadrupole to point A. The geometry of the assembly is depicted in FIG. 6 wherein the length of the arms 54 is "L". For an angular rotation .DELTA..theta.=.theta..sub.2 -.theta..sub.1, the pivot point, 25a' or 25b', is displaced a distance .DELTA.y=y.sub.1 -y.sub.2 by the rod moving from A to B a distance 2 .DELTA.y. In this system both the quadrupole strength and the distance moved by the rod are proportional to cos .theta.. The field strength can thus be adjusted in an approximately linear manner. The adjustable strength multipole permanent magnets of this invention are particularly useful for focusing the particle beam produced by accelerators. For example, a proton linear accelerator of the Alvarez type is conventionally designed in most respects. A machine that will accelerate protons to 45 MeV and that will produce a very high beam current of up to 5 m-amperes requires injection into the drift tube linac at 750 KeV from a Cockcroft-Walton high voltage accelerator and the accelerating electric fields in the gaps between drift tubes in the linac tank are produced by a high power radio frequency system resonating at 201 M Hz. However, instead of using electromagnet quadrupoles in the beam transport lines for beam focusing, the adjustable strength quadrupole magnets described herein are used in accord with a further aspect of this invention. A characteristic of the quadrupoles of this invention that enables important advantages for beam transport line design. Because no space is required for a coil or cooling, the quadrupole is much more compact, for instance. This fact was used to advantage in laying out the space requirement for the focusing magnets in the beam transport lines. Another significant advantage of focusing charged particle beams in accord with this invention is that no electrical power is required to operate the magnets. Thus economic advantages can be realized in the operation of beam transport lines. This invention has been described in detail along with the preferred embodiments thereof. However, it will be appreciated that those skilled in the art upon reading this disclosure may make modification and improvements within this spirit and scope of the disclosure.
043550002	abstract	In a nuclear fuel reactor well, storage pool or the like, a lightweight, removable pneumatic action sealing means is disclosed for providing a leak-tight seal between the walls of said well and an access gate. The sealing means comprises a lightweight metallic beam structure removably supported by the gate and arranged between the gate and portions of the adjacent wall. Inflatable sealing members are mounted on the lightweight beam structure and are operable when the gate is in a locked position to expand between the gate and wall, thereby forming a leak-tight seal. The beam structure includes connector flanges so that a hoisting apparatus may be attached to the lightweight structure to lift the entire sealing means from the gate for repair, maintenance or replacement.
054065941	abstract	The described injection system includes: a pneumatic system operating with hydrogen or helium and formed of one or more two-stage or multi-stage propulsion systems provided with special control or cutoff valves, the relative feeding circuits, and one or more decompression chambers, a cryogenic device formed of a Dewar flask containing liquid helium, a circuit for transferring and recovering the cooling fluid, and one or more conventional (in situ) or alternative cryostats provided each with one or more launching barrels in which the cryogenic pellets are solidified; a vacuum system comprising electrovalves, electropneumatic valves, rotating and turbomolecular pumps, and an equipment set for the automatic remote control of the whole system and for collecting and supplying diagnostic data to the central processing unit.
047553472	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS In the construction of dry storage cells shown in FIG. 1 there is a preparation chamber 1 and an adjacent clean chamber 2 constituting a transfer corridor. Within the corridor there is track 3 which supports a train of transfer containers or buckets 4 each containing a canister 5 for receiving irradiated nuclear fuel. The preparation chamber has two posting facilities each comprising a tubular port member 6 extending from the preparation chamber into the clean chamber, the port member being normally closed by a removable closure plug 7 adjacent the preparation chamber. The other end of the port member 6 has opening 6a for embracing the body of a closed canister 5. The closure plug 7 carries a retractable retention means in the form of a grab 8, with a linear actuator 21, within the tubular port member for gripping and withdrawing the canister closure into the tubular port member. The grab has a hood 9 for sealably masking the outer surface of the canister closure designated 10. In one alternative construction the retention means is a vacuum operable gripping device and in a second a1ternative construction is a magnetically operated gripping device. In use the opening 6a of the tubular port member 6 seals about a canister 5 positioned immediately below and grab 8 with hood 9 is lowered within the tubular port member sealably to mask the canister closure 10. The grab is then engaged with the closure 10 and retracted to lift the closure clear of the canister. A grab (not shown) within the preparation chamber withdraws the closure plug 7 with a grab 8, hood 9 and a canister closure 10 into the preparation chamber the canister thereby forming an extension of the preparation chamber. Irradiated nuclear fuel, which may be in the form of a string of fuel elements, is then transferred into the canister whereupon the plug 7 with grab 8, hood 9 and canister closure 10 is restored to the tubular port member. The grab can then be extended to replace the closure 10 on the canister 5 whereupon the canister is retracted from the facility and removed for securing the closure by welding and checking for contamination of the external surfaces. In greater detail, the buckets 4 are carried in a bogie 11 and are sequentially positioned below a selected one of the facilities. As shown in FIG. 2 the plug 7 is secured to the port opening of the preparation chamber by clamps 12 and 13 and seals 14, 15, 16 are provided to ensure that contaminated surfaces of the port are not exposed to the clean chamber. The bucket situated below the facility is then raised by a jack 17 (FIG. 1) to engage the opening 6a with the canister carried in the bucket. A seal designated 18 is provided to seal the canister closure with the hood 9 and a seal designated 19 to seal the canister to the port member 6 following which the interspace bounded by the seals 16, 18 and 19 is vacuum tested by way of a connection 20 to check the efficiency of the seals. The seal 16 is then released and, as described hereinbefore, the grab 8 and linear actuator 21 remove the closure 10 from the canister whereupon the clamps 12 can be released and the assembly of plug 7, actuator 21, grab 8, hood 9 and closure 10 withdrawn into the preparation chamber. Irradiated fuel is then posted into the canister and the plug, actuator, grab, hood and closure assembly, replaced. After replacement the clamp 12 is re-engaged and the closure 10 is replaced on the canister by the actuator, seal 16 re-engaged and vacuum tested. The interspace is decontaminated by gas purges and seals 18, 19 released whereupon the bucket and canister is lowered into the transfer bogie and the canister subsequently transported to a closure welding facility. FIG. 3 illustrates an additional facility for handling defective canisters which may be required to be disposed of in the preparation chamber 1. Defective canisters are returned to the facility within a bucket 4 having a closure 22 fitted so that contamination is contained within the bucket. The procedure for with drawing the defective canister into the preparation chamber is generally similar to the foregoing procedure for withdrawing a canister closure into the fuel preparation chamber. The facility provides a second tubular port member 23 integral with the barrier wall between the preparation chamber 1 and the clean chamber 2 and extending co-axially into the clean chamber. The tubular port member 6 has an extension 24 and there are seals 25, 26, 27 similar to those designated 16, 18, 19 and a vacuum connection 28. The seals 18, 19, 26, 27 are of hollow section and are connectable to a vacuum source by selector valves (not shown). In their normal state the seals can embrace the canister 5 and container 4 in sealing manner but on connection to the vacuum source the seals are retracted into their housings to release the canister and container so that linear movement of the canister and container can take place out of contact with the seals. In an alternative construction the seals are arranged to sealingly embrace the canister and container when they are expanded by gas pressure and are retracted from contact at atmospheric pressure. In operation the posting port is sealed by seals 14, 15, 16 and 25 to ensure that contaminated surfaces of the port are not exposed to the clean chamber and the plug 7 is secured by clamps 12, 13. The bucket is raised by the jack 17 to engage the seals 26, 27 and vacuum tests made. The seal 25 is then released and the closure removal grab with its actuator 21 then withdraw the closure 22 into the first tubular port member 6 and after releasing the clamps 13 the assembly of tubular member 6, actuator 21, grab 8 and closure 22 can be lifted into the fuel preparation chamber. The canister 5 is then withdrawn into the preparation chamber from the bucket 4 and the assembly replaced in the outer sleeve 23. After replacement the clamp 13 is re-engaged and closure 22 is replaced on the bucket by the actuator 21. Seal 25 is re-engaged and vacuum tested. The interspace is decontaminated as previously described and the bucket subsequently transported for further decontamination.
	abstract	A radiation source assembly and a connector press used in producing such assemblies. In the radiation source assembly, each of the cap connector and the female connector is provided with internal round threads on its pigtail fitting hole, thus engaging with the large-diameter coil of the pigtail at the internal round threads through a thread engagement prior to a compression process of the press. The assembly also allows a person to know whether both ends of the pigtail fully reach desired points within the two connectors, thus securing a precise compressing target portion during a compression process of the press. The inserted lengths of the pigtail relative to the two connectors are maximize accomplishing a desired linearity of the assembly. In the assembly, a target biasing spring is provided on the capsule lid and allows the disc targets within the source capsule to effectively maintain a desired condition as point sources regardless of the number of targets. The connector press of this invention accomplishes a desired compression locking of the source capsule to the pigtail by simultaneously compressing the capsule at regularly and angularly spaced points through a multi-point compressing process, thus accomplishing a desired linearity of the radiation source assembly.
056082231	description	BEST MODE FOR PRACTICING THE INVENTION Below, an ion implantation device constituting one embodiment of the present invention will be described with reference to the attached figures. Referring to FIG. 1, the ion implantation device of this embodiment has a guide chamber 12 which guides an ion beam 10 from an ion source (not shown in the figures), and a treatment chamber 13 in which the ion beam 10 from the guide chamber 12 is implanted into semiconductor wafers. A disk 15 constructed according to the present invention (described in detail later) is installed inside the treatment chamber 13 shown in the figures. This disk 15 is caused to rotate at a high speed about a rotating shaft (installed at the center of said disk 15) by a high speed scanning driving mechanism 16. As a result of this rotation, the semiconductor wafers positioned around the circumference of the disk 15 are scanned at a high speed; furthermore, said wafers are also scanned at a low speed in the vertical direction in FIG. 1. Accordingly, a low-speed scanning driving mechanism 17 is installed so that the individual semiconductor wafers can also be scanned at a low speed in the radial direction from the axis of rotation. Here, a mechanism whose low-speed scanning operation can be controlled is used as the aforementioned low-speed scanning driving mechanism; meanwhile, the driving mechanism used for high-speed scanning may be an ordinary driving mechanism. A beam current measuring device 20 is positioned behind the disk 15 installed in the treatment chamber 13 (i.e., on the opposite side of said disk from the side irradiated by the ion beam), and the charge of the ion beam passing through the disk 15 is measured by this beam current measuring device 20. Since this beam current measuring device 20 may consist of a commonly used device, a detailed description of said device 20 is omitted here. The abovementioned beam current measuring device 20 is connected to a control part 22; this control part 22 performs predetermined calculations based on the charge detected, and controls the scanning speed of the low-speed scanning driving mechanism 17 so that ions are uniformly implanted. Referring now to FIG. 2 as well, a multiple number of semiconductor wafer attachment parts 151-167 used for wafer attachment, i.e., 17 wafer attachment parts in the case of this embodiment (hereafter referred to collectively as 15n, are installed around the outside circumference of the disk 15 in the present embodiment, and respective semiconductor wafers are placed on each of these attachment parts 15n. Furthermore, the central part 15a of the disk 15 and the semiconductor wafer attachment parts 15n, are connected by bridge parts 15b which have a narrower width than the semiconductor wafer attachment parts 15n, so that the area of the disk 15 that is exposed to the ion beam is reduced. Furthermore, in the example shown in the figures, the spacing between the semiconductor wafer attachment parts 151, 152 is set so that it is wider than the respective spacings between the other attachment parts (e.g. 152, 153). This means that the spacing between the semiconductor wafers attached to the attachment parts 151, 152 is wider than the respective spacings between the semiconductor wafers attached to the other attachment parts. Here, the conditions other than the aforementioned spacing, i.e. the wafer size and method of support, etc. are the same for all of the wafer attachment parts. In the case of a disk 15 constructed as described above, the bridge parts 15b are extremely narrow; accordingly, the area exposed to the ion beam is small, so that contamination caused by exposure of the disk 15 to the ion beam can be greatly reduced. Meanwhile, the angle between the center of the attachment part 151 and the center of the attachment part 152 can be expressed as A+B, where A is the angle between the center of the attachment part 152 and the center of the adjacent attachment part 153, and B is the angle of a space between the attachment parts 151, 152. In this case, assuming that the center of the ion beam is located at a distance of R from the center of the disk 15, the area indicated by shading in FIG. 2 is irradiated by the ion beam. Accordingly, the charge measured by the beam current measuring device 20 installed on the downstream side of the disk 15 while the center of the ion beam passes from the center position 1 of the attachment part 151 to the center position 2 of the attachment part 152 is measured as the charge of the ion beam passing through the gap (i.e., the spacing) between the attachment parts 151, 152. Here, the charge measured by the beam current measuring device 20 is designated as QA+B. Next, when the charge occurring while the center of the ion beam passes from the center position 2 of the attachment part 152 to the center position 3 of the attachment part 153 is similarly measured by the beam current measuring device 120, said charge is measured as the charge passing through the gap that defines the spacing of the attachment parts 152, 153. The charge measured in this case is designated as QA. It is seen that the charge of the beam passing through the fan-shaped portion with an angle of B can be determined by calculating QA+B-QA under the conditions described above. This means that changes in the ion beam current during ion implantation can be detected; consequently, the charge of the ions implanted into the semiconductor wafers 25 attached to the respective attachment parts 15n can be maintained at a substantially constant level by controlling the speed of movement of the disk 15 in the radial direction, i.e., the scanning speed, in accordance with the aforementioned changes. More concretely, where V is the aforementioned speed of movement in the radial direction, said movement speed V can be expressed as V=K(QA+B-QA)/R (here, K is a proportionality constant). If the movement speed V is calculated by the control part 22 (shown in FIG. 1) using this formula, and the low-speed scanning driving mechanism is controlled in accordance with the result obtained, ions can be uniformly implanted. It is sufficient if the abovementioned charge measurement and control action are performed for each revolution of the disk. In such a case, any discrepancies in timing are cancelled. Referring to FIG. 3, the disk 15 in a modification of the embodiment shown in FIG. 1 differs from the disk shown in FIG. 2 in that the center part 15a' of the disk and the attachment parts 15n are connected by rectangular bridge parts 15b'. As in FIG. 2, two of the attachment parts installed in specified positions (attachment parts 151, 152 in FIG. 3) are positioned with a spacing of angle B; as a result, the angle between the center positions of these specified attachment parts 151, 152 can be expressed as A+B, and thus different from the angle A between the center positions of the other attachment parts. In this case, as in the case of FIG. 2, the portion of the disk 15 that is exposed to the ion beam can be minimized; furthermore, the speed of movement of the disk 15 in the radial direction, i.e., the scanning speed, can be adjusted in accordance with changes in the ion beam current so that ions are uniformly implanted into the semiconductor wafers attached to the attachment parts 15n. Referring to FIG. 4, the disk in another embodiment of the present invention is constructed so that adjacent attachment parts 15n are separated from each other by notches (i.e.,valleys) 30, with a stipulated spacing between each pair of adjacent attachment parts 15n. Here, the spacing between attachment parts 15n is substantially the same as the spacing between the semiconductor wafers. In this example, the bridge parts 15b" which connect the attachment parts 15n with the central part 15a" of the disk have a tapered shape which becomes slightly wider toward the central part 15a" of the disk. In FIG. 4, the angular spacing determined by the notch between the attachment parts 151, 152 is set at B1, and the angular spacing determined by the notch between the attachment parts 159, 160 is set at B2. Meanwhile, the angular spacing between the remaining attachment parts is set at a value which is smaller than the aforementioned angular spacings B1, B2. Furthermore, in a case where the angle between the center position of the attachment part 152 and the center position of the adjacent attachment part 153 is set at A1, and the angle between the center position of the attachment part 160 and the center position of the adjacent attachment part 161 is set to A2, the angle between the attachment parts 151, 152 can be expressed as A1+B1, and the angle between the attachment parts 159, 160 can be expressed as A2+B2. In this case, as in the case of FIG. 2, the charges for the angles (A1+B1) and (A2+B2) can be expressed as the ion beam charges QA1+B1 and QA2+B2 passing through the respective notches. Accordingly, the scanning speed V at various locations in the radial direction can be expressed as follows (in a case where the ion beam is located at a position of radius R): EQU V+K(QAN+BN-QAN)/R (eq 1.) (Here, N indicates 1 or 2) As is also clear from the above equation, two or more notches with different angular spacings may be formed. Furthermore, the mean value of the charge may be used for the control of the scanning speed V. Referring to FIG. 5, the disk 15 in still another embodiment of the present invention has wide notches in four places, and has tapered bridge parts 15b that widen outward in the radial direction from the central part of the disk. Furthermore, these bridge parts 15b are formed as integral units with the attachment parts 15n, and semiconductor wafers 25 are placed on said attachment parts 15n. Here, the spacings between the centers of the attachment parts adjacent to the respective wide notches are expressed by the angles A1, A2, A3 and A4. Assuming that the four notches have respective angles of B1, B2, B3, and B4, the spacings between the centers of the respective attachment parts located on either side of the wide notches can be expressed by the angles (A1+B1), (A2+B2), (A3+B3) and (A4+B4). The aforementioned equation 1 is also valid in this example; accordingly, ions can be uniformly implanted into the semiconductor wafers 25 by controlling the scanning speed V. Referring to FIG. 6, a wide notch which has an angle of B, and ordinary notches which have angles smaller than that of the wide notch, are formed in the disk 15 of still another embodiment of the present invention. In this case, the scanning speed V can be controlled using the following equation (where A is the angle between the semiconductor wafers on either side of the ordinary notches, A+B is the angle between the semiconductor wafers on either side of the wide notch, and QA(R-.DELTA.R), QA(R+.DELTA.R) and QA+B(R) are the charges passing through the respective notches); EQU V=K(QA+B(R)-(QA(R-.DELTA.R)+QA(R+.DELTA.R))/2)/R (Eq 2.) As is clear from Equation 2 as well, the shift (.DELTA.R) in the radial position caused by low-speed scanning (which is ordinarily ignored) can be considered by subtracting the mean value of the charges passing through adjacent notches from the charge passing through the wide notch, so that ions can be implanted into the respective semiconductor wafers 25 more accurately. FIGS. 7A and 7B illustrate the construction of a clamping part used to support the semiconductor wafers on the disks of the respective embodiments of the present invention described above. As is clear from FIG. 7A, a first clamp 41 which supports the semiconductor wafer 25 against the centrifugal force caused by rotation is installed only the outer circumference of each attachment part, and second and third clamps 42, 43 are installed on the inner circumference. Here, the second and third clamps 42, 43 have the same structure; accordingly, on the second clamp 42 will be described below. As is shown in FIG. 7B, the first clamp 41 has a rotation shaft 411 which is fastened to the attachment part 15n, and a fastening pawl 412 which extends upward from the rotating shaft 411. This fastening pawl 412 contacts the circumference of the semiconductor wafer 25, and supports the wafer 25 so that said wafer 25 is not pushed outward by centrifugal force. Furthermore, the portion of the first clamp 41 that extends downward is fastened to the attachment part by a compression spring 413, so that said spring 413 drives the first clamp 41 in the clockwise direction in FIG. 7B. Moreover, a weight 414 is attached to the portion of the first clamp 41 that extends horizontally, and a stopper 415 is installed in front of the weight 414. Meanwhile, in the case of the second clamp 42, there is no need to consider the effects of centrifugal force. Accordingly, this clamp 42 has a simplified structure compared to that of the first clamp 41. Here, said clamp 42 is equipped with a moveable member 422 which can rotate about a rotating shaft 421 supported on the attachment part 15n, and an arm 424 which is attached to the attachment part 15n by a compression spring 423. A stopper 425 is installed at the inside edge part of the arm 424; this stopper 425 prevents the arm 424 from pivoting into an undesired position when no wafer 25 is attached. The semiconductor wafer 25 is retained from the sides by the first through third clamps constructed as described above, so that said semiconductor wafer 25 is clamped to the surface of the attachment part 15n. In the present invention, a disk which allows a plurality of wafers to be positioned at a prescribed spacing around the circumference of said disk is constructed so that there is at least one place on said disk where the spacing between wafers in different from the spacing elsewhere. As a result, the area of the disk that is exposed to the ion beam is reduced, and contamination caused by undesired sputtering can be prevented. Furthermore, fluctuations in the ion beam current are detected from the ion beam charges passing through the aforementioned areas with different spacing, and the rate of low-speed scanning is controlled in accordance with these detection results, so that ions can be uniformly implanted into the semiconductor wafers.
	claims	1. A vapor powered apparatus for generating electric power, comprising:a liquid chamber configured to contain a working fluid;a first heat exchanger, in fluid communication with the liquid chamber and a spent nuclear fuel rod storage system, configured to transfer heat from fluid coming from spent nuclear fuel rods to working fluid coming from the liquid chamber, wherein the transferred heat vaporizes at least a portion of the working fluid to provide a working pressure of the vaporized working fluid;a pressure motor, in fluid communication with the heat exchanger, configured to convert the working pressure of the vaporized working fluid into mechanical motion for a power generator operatively connected to the pressure motor;a vapor chamber configured to capture the vaporized working fluid exiting the pressure motor;a second heat exchanger configured to use working fluid from the liquid chamber to condense the captured vaporized working fluid, returning the condensed working fluid back to the liquid chamber, wherein at least one of the second heat exchanger and the liquid chamber is configured such that heat is able to transfer from the working fluid to a cooling source outside of the vapor powered apparatus; andan exchanger fluid system within the liquid chamber configured to provide the working fluid to the second heat exchanger from a bottom portion of a pool of working liquid in the liquid chamber. 2. The vapor powered apparatus of claim 1, wherein the working liquid has a boiling point of 150 degrees F. or less. 3. The vapor powered apparatus of claim 1, wherein the working fluid comprises Methoxy-nonafluorobutane, CF3CF2C(O)CF(CF3)2, or Dodecafluoro-2-methylpentan-3-one. 4. The vapor powered apparatus of claim 1, further comprising the generator. 5. The vapor powered apparatus of claim 1, wherein the working fluid becomes colder when maintained at a determined depth in the pool of working fluid in the liquid chamber. 6. A vapor powered apparatus for generating electric power, comprising:a liquid chamber configured to contain a working fluid;a first heat exchanger, in fluid communication with the liquid chamber, configured to transfer heat from fluid coming from a heating source to working fluid coming from the liquid chamber, wherein the transferred heat vaporizes at least a portion of the working fluid to provide a working pressure of the vaporized working fluid;a pressure motor, in fluid communication with the heat exchanger, configured to convert the working pressure of the vaporized working fluid into mechanical motion for a power generator operatively connected to the pressure motor;a vapor chamber configured to capture the vaporized working fluid exiting the pressure motor;a second heat exchanger configured to use working fluid from the liquid chamber to condense the captured vaporized working fluid, returning the condensed working fluid back to the liquid chamber; andan exchanger fluid system configured to provide the working fluid to the second heat exchanger from a bottom portion of a pool of working liquid in the liquid chamber, wherein the exchanger fluid system comprises:a conduit entry point at the bottom portion of the pool of working fluid in the liquid chamber; andan outside conduit that provides fluid communication between the conduit entry point and the second heat exchanger, wherein at least a portion of the outside conduit is outside of the liquid and vapor chambers, and wherein the outside conduit comprises a coil or increased surface area portion that is lower than the conduit entry point. 7. The vapor powered apparatus of claim 6, wherein the working fluid and the coil or increased surface area portion is arranged to cause condensation of air onto the coil or increased surface area portion. 8. The vapor powered apparatus of claim 6, wherein the working liquid has a boiling point of 150 degrees F. or less. 9. The vapor powered apparatus of claim 6, wherein the working fluid comprises Methoxy-nonafluorobutane, CF3CF2C(O)CF(CF3)2, or Dodecafluoro-2-methylpentan-3-one. 10. The vapor powered apparatus of claim 6, wherein the working fluid becomes colder when maintained at a determined depth in the pool of working fluid in the liquid chamber. 11. The vapor powered apparatus of claim 1, further comprising a thermostatically controlled valve system that manages and stabilizes the fluid coming from the spent nuclear fuel rods at the appropriate temperature required to power the power generator. 12. The vapor powered apparatus of claim 6, wherein the first heat exchanger is in fluid communication with a spent nuclear fuel rod storage system.
	abstract	A boiling water reactor is chemically decontaminated by circulating a decontamination solution through reactor recirculation loops and the annulus region of a reactor pressure vessel that surrounds the central core region while bypassing the central core region. The decontamination solution may also be circulated between the annulus region and a lower internals region while bypassing the central core region. The solution dissolves or breaks down metal oxide layers on the surfaces of the boiling water reactor. The metal oxide layers in the central core region and the activated metal ions contained in these layers, which do not substantially contribute to personnel exposure, are not released and, therefore, do not need to be removed from the solution.
	abstract	The invention relates to a device for applying laser radiation (13) to the outside of a rotationally symmetric component (11), comprising a plurality of lenses (10), which are designed and/or arranged in such a way that the axis of symmetry (12) of the component (11) lies at the focal point of each of the lenses (10).
	abstract	An improved method for substrate micromachining. Preferred embodiments of the present invention provide improved methods for the utilization of charged particle beam masking and laser ablation. A combination of the advantages of charged particle beam mask fabrication and ultra short pulse laser ablation are used to significantly reduce substrate processing time and improve lateral resolution and aspect ratio of features machined by laser ablation to preferably smaller than the diffraction limit of the machining laser.
	claims	1. A system for removing a part-length fuel rod from a fuel bundle, the fuel bundle residing in a spent fuel pool of a nuclear reactor plant, comprising:a fuel prep machine configured to be placed in the spent fuel pool for supporting the fuel bundle thereon,a rod grapple tool having a first end configured to be handled by an operator above the fuel pool in the plant and a second end configured to be inserted from a top end of the fuel bundle and down to a desired elevation of the fuel bundle to retrieve the part-length fuel rod within the fuel bundle, while the fuel bundle is supported by the fuel prep machine,the second end having a gripper configured to grip the part-length fuel rod,the gripper having a protective, removable guide pin with a tapered, rounded-end tip portion, the guide pin configured to attach to a distal end of the gripper to prevent the rod grapple tool from damaging components of the fuel bundle as the rod grapple tool is inserted into the fuel bundle, anda guide pin retrieval tool sized and configured to be inserted into a side of the fuel bundle and remove the guide pin from the distal end of the gripper, when the rod grapple tool has been inserted into the fuel bundle and the guide pin and gripper are positioned over the part-length fuel rod, to permit the gripper to be securely attached to an upper end plug of the part-length fuel rod to extract the part-length fuel rod from the fuel bundle. 2. The system of claim 1, wherein the guide pin retrieval tool includes:a handling pole,an extension element having a first end connected to the handling pole and including two sets of vertically-spaced semicircular ridges at a second end thereof, anda tongue attached to the extension element second end,wherein the two sets of vertically-spaced semicircular ridges are configured to mate flush against sides of adjacent fuel rods as the tongue is inserted into the side of the fuel bundle. 3. The system of claim 2, wherein the two sets of vertically-spaced semicircular ridges are configured to maintain the guide pin retrieval tool parallel with the side of the fuel bundle. 4. The system of claim 2, wherein the tongue has a mating aperture which is configured to fit over the tip portion of the guide pin to mate with a mating portion of the guide pin for releasing the guide pin from the rod grapple tool so as to expose the gripper. 5. The system of claim 4, wherein the two sets of vertically-spaced semicircular ridges maintain alignment of the tongue level with the fuel bundle to facilitate engagement of the mating aperture of the tongue with the mating portion of the guide pin. 6. The system of claim 2, wherein the tongue is located between the two sets of vertically-spaced semicircular ridges. 7. The system of claim 2, wherein the tongue is provided with varying lengths to ensure that the tongue is capable of reaching varying depths within the fuel bundle. 8. The system of claim 1, wherein the rod grapple tool is configured to provide a flush fit between the gripper and the guide pin, and between the gripper and the upper end plug of the part-length fuel rod. 9. The system of claim 2, wherein the handling pole includes an offset along the length of the handling pole.
	description	The preferred embodiments of the present invention are hereinafter described with reference to the accompanying drawings. FIG. 1 shows the structure of a magnetic energy filter in accordance with the present invention. FIGS. 2(a) to 2(f) are diagrams illustrating fundamental trajectories based on the results of a simulation of the magnetic energy filter in accordance with the present invention. FIG. 2(a) illustrates the trajectory of an electron beam forming an electron microscope image projected onto an entrance window plane. The electron beam creating a focused electron microscope image on the entrance window plane forms four crossover points in total and then forms a focused electron microscope image on the exit split plane again. FIG. 2(b) illustrates the trajectory of the electron beam having certain (two) energies within electron beams passing through the entrance window. The electron beams passing through the entrance window are focused three times and undergo a fourth focusing action on the exit slit plane. If electron beams have different energies, they draw different trajectories and are focused at different locations on the exit slit plane. Therefore, only an electron beam having a desired energy can be selected with an exit slit. FIG. 2(c) illustrates the trajectory xxcex1 (x alpha) of the electron beam forming a microscope image, the trajectory being parallel to the magnetic polepiece plane. FIG. 2(d) illustrates the trajectory yxcex2 (y beta) of the electron beam forming a microscope image, the trajectory being in the same direction as the direction of the magnetic field. FIG. 2(e) indicates the trajectory xxcex3 (x gamma) of an electron beam with a desired energy parallel to the magnetic polepiece plane, as well as the magnitude of dispersion x"khgr" (x chi) along the optical axis. FIG. 2(f) indicates the trajectory yxcex4 (y delta) of an electron beam having a desired energy in the direction of the magnetic field. Referring to FIG. 1, there are shown magnets M1-M4, an entrance window I, and an exit slit S. The trajectory of an electron beam in the geometry of FIG. 1 is described below. The electron beam impinges in the direction of the optical axis indicated by the arrow. The beam forms a crossover point (focused point) on the plane of the entrance window I and then hits a filter. The electron beam passed through the entrance window I enters the magnetic field of magnet M1 having a deflection angle of xcfx861. The beam is deflected through xcfx861. In the figure, the beam is shown to be deflected in a clockwise direction. The beam then exits from the field and undergoes a first focusing action from the filter. Then, the beam enters the magnet M2 having a deflection angle of xcfx862 and is deflected through xcfx862 in the reverse direction. In the figure, the beam is shown to be deflected in a counterclockwise direction. The beam then leaves the magnet M2 and passes across a point O at which a straight axis intersects the trajectory of the electron beam. The beam undergoes a second focusing action near this point O. After passing across the point O, the beam enters the magnet M3 that is located on the opposite side of the straight axis and has a deflection angle of xcfx863. In this magnet, the beam is deflected through xcfx863 in a clockwise direction and exits from the magnet, where xcfx863=xe2x88x92xcfx862. Then, the beam undergoes a third focusing action. The beam going out of the magnet M3 passes into the magnet M4 having a deflection angle of xcfx864, where xcfx864=xe2x88x92xcfx861 In this magnet, the beam is deflected through xcfx864 in a counterclockwise direction and exits from the magnet. The electron beam leaving the magnet M4 reaches the exit slit and undergoes a fourth focusing action on the exit slit plane. Under this condition, the electron beam is dispersed sufficiently because of variations in energy. Accordingly, the electron beam having only the desired energy passes through the exit slit and leaves the filter. The point O located midway between the magnets M2 and M3 is referred to as the midpoint. An axis that passes through this point and is vertical to the plane of the paper gives a two-fold rotational symmetry axis or a two-fold rotation axis for the selected electron beam path through the filter. That is, the physical structure of the filter gives a two-fold rotational symmetry around the axis passing through the point O (with the exception of the polarities of the magnets explained hereafter). In the magnetic energy filter in accordance with the present invention, magnets are located on opposite sides of the straight axis as described above. Furthermore, they are arranged with two-fold rotational symmetry. Compared with conventional filters, such as an OMEGA filter and an ALPHA filter where magnets are placed on only one side of a straight axis, the beam path can be elongated and the sum of the absolute values of the beam deflection angles can be increased without increasing the distance between the entrance and the exit of the filter, i.e., the distance D between the entrance window I and the exit slit S. Therefore, the magnetic energy filter designed as described above in accordance with the present invention is more compact than the prior art OMEGA filter. In the geometry of FIG. 1, the beam deflection angles are assumed to be 110xc2x0, xe2x88x92250xc2x0, 250xc2x0, and xe2x88x92110xc2x0 in this order from the entrance side. The sum of the absolute values of the deflection angles is 720xc2x0, which is twice that of the deflection angle of the ALPHA filter. In the case of the prior art OMEGA filter, the limit values of practical deflection angles of the four magnets are assumed to be 125xc2x0, xe2x88x92125xc2x0, xe2x88x92125xc2x0, and 125xc2x0 in this order. The sum of the absolute values of the deflection angles is 500xc2x0, which is 1.4 times as large as the conventional value. Where the energy filter proposed heretofore is made up of four magnetic fields M1, M2, M3, and M4, the magnetic fields M2 and M3 located on the opposite sides of the symmetry plane are identical in polarity. In a magnetic energy filter (hereinafter referred to as the S filter) in accordance with the present invention, the magnetic fields M2 and M3 located on the opposite sides of the rotational symmetry axis are opposite in polarity. In the example of FIGS. 1 and 2, the sum of the absolute values of the deflection angles is 720xc2x0. In the S filter where the magnetic fields 1 and 2 are opposite in polarity, if the sum of the absolute values of the deflection angles is set greater than 540xc2x0, the beam path can be elongated and the sum of the absolute values of the beam deflection angles can be increased without increasing the distance between the entrance and exit of the filter, i.e., the distance D between the entrance window I and the exit slit S. Hence, the purpose of the present invention is achieved. Another important characteristic is the number of times that the trajectory xxcex3 crosses the optical axis. Generally, it can be thought that as the number of times that trajectory xxcex3 crosses the optical axis indicating the center trajectory in the filter increases, greater dispersion takes place. The number of times the trajectory xxcex3 in the prior art OMEGA filter crosses the optical axis indicating the center trajectory in the filter is three, as indicated by the arrows in FIGS. 7(b) and 8(b) for both types A and B of FIGS. 5 and 6, respectively. On the other hand, in the filter in accordance with the present invention, the number of times is four as indicated by the arrows in FIG. 2(e). FIG. 3 is a diagram showing a magnetic energy filter in accordance with another embodiment of the present invention. This filter has magnets M5-M8, an entrance window I, and an exit slit S. In FIG. 3, the magnets M5 and M6 are both on the entrance side, i.e., on the side of the entrance window. The magnetic fields produced by these magnets M5 and M6 produce the same direction of beam deflection. The direction of beam deflection affected by the magnets M7 and M8 on the exit side, i.e., on the side of the exit slit, is opposite to the direction of beam deflection affected by the magnets M5 and M6 on the incident side where the entrance window is present. That is, these magnets are arranged with two-fold rotational symmetry. In particular, the magnets M5 and M6 have beam deflection angles of xcfx865 and xcfx866, respectively, while the magnets M7 and M8 have deflection angles of xcfx867(=xe2x88x92xcfx866) and xcfx868(=xe2x88x92xcfx865), respectively. This filter is referred to as the 8-shaped filter. In this 8-shaped filter, the sum of the absolute values of the beam deflection angles is approximately 720xc2x0. Supplementary, it can be said that the magnetic energy filter shown in FIG. 1 and built in accordance with the present invention is one modified form of an OMEGA filter and that the magnetic energy filter shown in FIG. 3 and built in accordance with the present invention is one modified form of an ALPHA filter. It is to be understood that the present invention is not limited to the embodiments described above. For instance, in the above-described embodiments, OMEGA and ALPHA filters are modified, and magnets are arranged on the opposite sides of a straight axis with two-fold rotational symmetry. Different types of magnets may be placed on the opposite sides of a straight axis. For example, a modification of an OMEGA filter, such as an S-filter, and a modification of an ALPHA filter may be placed on the opposite sides of a straight axis. Furthermore, in the embodiments described above, the filter is made up of four magnets such as M1-M4 or M5-M8. In summary, a magnetic energy filter is made of four magnetic fields. For example, each of some, or all of the magnets M2 and M3 shown in FIG. 1 and the magnets M6 and M7 shown in FIG. 3 may be split into two. For example, the magnet M2 may be split into two parts M2xe2x88x921 and M2xe2x88x922. That is, if one magnet is split into two and a drift space is inserted between them, the structure remains substantially unchanged. As can be understood from the description provided thus far, the present invention provides a magnetic energy filter which has four magnetic fields to deflect the trajectory of an electron beam from the entrance window plane to the exit slit plane, the energy filter having the following features. The number of the magnetic fields is at least four. The magnetic fields located on the opposite sides of a rotational symmetry axis are opposite in polarity, the rotational symmetry axis being located midway between the second and third magnetic fields. Deflecting magnets are mounted on the opposite sides of a straight axis. The sum of the absolute values of beam deflection angles of the magnetic fields is in excess of 540xc2x0 or is about 720xc2x0. Consequently, the beam path length and the sum of the absolute values of the deflection angles can be increased compared with the prior art OMEGA filter and ALPHA filter. In addition, the distance between the entrance window and the exit slit is shortened, thus making the energy filter more compact. Having thus described our invention with the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.
	description	Managing the operation of multiple wells in a well field of an aquifer is a difficult task. Competing environmental, equipment, and energy costs factor in to each operation decision for each well. However, it is difficult to predict how the wells will interact with each other, and with wells of other well fields that may draw from the same aquifer. Further, it is difficult to predict how the aquifer itself will respond to variations in well pumping operations at different locations in the well field. It is also difficult to predict how pumps will perform under changing aquifer conditions. To address these difficulties, much reliance has been placed on the knowledge acquired by well operators who have manually operated the pumps of a particular well field over years of changing aquifer conditions. While these approaches may have sufficed in the past, overreliance on human judgment can produce inefficiencies in operation, increased energy and equipment costs, and even damage to the aquifer. The inventors have recognized that data driven approaches to managing aquifer operation are needed to complement the judgment of human well operators. Systems and methods for managing aquifer operation are provided. One example method includes receiving at an analysis computing device, one or more water measurements from a plurality of sites in an aquifer. The water measurements are received at a plurality of time points, and a site includes one or more groundwater extraction wells. The method may further include calculating well operational data for at least one groundwater extraction well based on the water measurements, wherein the well operational data includes a well efficiency over a time period. Further, the method may include receiving an aquifer objective input via a graphical user interface presented on the analysis computing device, and generating a pump operation signal based on the well operational data and the aquifer objective input. This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure. FIG. 1 is a schematic view of an exemplary system 100 for managing aquifer operation. The system 100 includes an analysis computing device 102 in communication with site 1 104, site 2 106, and site N 108 of an aquifer 110. The system 100 may be in communication with any number of sites. The sites 104, 106, 108 may include one or more groundwater extraction wells (e.g., a pump 112), and/or one or more observation wells, and may further include an associated pump sensor 114 (e.g., for observation) and pump controller 116 (e.g., for adjusting pump operation). In some examples, a groundwater extraction well is designated as an observation well, as will be described later. The analysis computing device 102 is configured to receive aquifer data 118 including one or more water measurements from a plurality of sites 104, 106, 108 over a time interval. The analysis computing device 102 can then perform analyses on the aquifer data (e.g., water measurements) 118, for example by an analysis program 120 located in a mass storage 122 of the analysis computing device 102. As some examples, water measurements can include water flow, water pressure, and/or water level. Aquifer data 118 and analyzed aquifer data 136 (e.g., well operational data, modeled data) may be output from the analysis program 120, and/or stored in an analysis program data store 121, for later retrieval and downstream processing by the analysis program 120 and/or other applications such as a geographical rendering system, etc. Thus, a pump operation signal 138 can be sent to a display 126 and/or sites in the aquifer 110, as will be described with more detail with respect to FIG. 2. The system 100 also includes a graphical user interface (GUI) 124 presented on a display 126 associated with the analysis computing device 102. The graphical user interface 124 may itself include a well hydraulics module 128 and a hydrogeology module 130. Accordingly, the well hydraulics module 128 may graphically present hydraulics data, and the hydrogeology module 130 may graphically present hydrogeological data. It may be appreciated that the GUI 124 and the modules contained therein may also textually and otherwise present preprocessed aquifer data 118 and analyzed aquifer data 136. The GUI 124 may receive operator input 132 via an input device 134, which may be a keyboard, mouse, touch screen, etc., and send the operator input 132 to the analysis program 120 of the analysis computing device 102. The GUI 124 can also display aquifer data 118 received from the analysis computing device 102, and display analyzed aquifer data 136 received from the analysis computing device 102. Furthermore, the GUI 124 may display a pump operation signal 138 received from the analysis program 120 of the analysis computing device 102. In some examples, the pump operation signal 138 may include a pump operation advisory message 140, which can be displayed. In one specific example, a plurality of advisory messages of varying priority levels, such as a high, medium, and low priority, may be indicated by numbers, colors (red, yellow, and green), etc. on the GUI. These advisory messages 140 may advise a well operator regarding operation of a pump or site exceeding a performance threshold set by operator input 132 or otherwise stored within the analysis program 120. For example, if a pump is operating below a threshold efficiency, or an aquifer is drawn below a threshold level, then an advisory message indicating this information may be displayed. It may be appreciated that the display 126 associated with the analysis computing device 102 may be located outside of the analysis computing device 102, and/or integrated with the analysis computing device 102. Each of a plurality of modules (142, 144, 146, 150, 152, 154), contained in hydraulics module 128 and the hydrogeology module 130, and described in detail below, may display analysis options to an operator, and may also allow the operator to interact with the GUI 124. Referring now to the hydraulics module 128, it may include modules associated with well operational data. For example, an efficiency module 142, a specific capacity module 144, and an entrance velocity module 146. Specifically, the efficiency module 142 may be configured to receive efficiency operator input including one or more selected groundwater extraction wells and a time interval. The efficiency module 142 may send a well operational data request (e.g., a data request 148) to the analysis computing device 102, and receive well operational data (which is a form of analyzed aquifer data 136) from the analysis computing device 102 in response. Thus, the efficiency module 142 can display the well operational data, and/or send the well operational data into a data storage for future analysis of well operational data at another time interval. The well operational data may include well efficiency, aquifer-water pressure loss, well-water pressure loss, specific capacity, entrance velocity, and one or more critical water levels for the one or more selected groundwater extraction wells, for example. The critical water levels may be, for example, a water level at which cavitation on the pump impeller occurs, or a level at which the pump intake runs dry, for example. Well efficiency of one or more selected groundwater extraction wells can be calculated over a time interval at the analysis computing device 102, by calculating an intermediate well efficiency, executing an interference evaluation of at least one additional groundwater extraction well with the selected groundwater extraction well(s), and modifying the intermediate well efficiency based on the interference evaluation from the at least one additional groundwater extraction well. By doing this, the well efficiency can more closely represent actual well efficiency absent any interference effects that may be occurring between sites. Calculation of well operational data will be described in more detail with respect to FIG. 2. Another module included in the well hydraulics module 128 of the GUI 124 is the specific capacity module 144. The specific capacity module 144 may receive specific capacity operator input including one or more selected groundwater extraction wells for the analysis, a static water level, an interference water level, and a pumping water level. The specific capacity module 144 can send specific capacity operator input to the analysis program 120 of the analysis computing device 102, and also send a data request 148 for a calculated specific capacity. At the analysis computing device, a specific capacity of one or more groundwater extraction wells can be calculated over a time interval by calculating an intermediate specific capacity, executing an interference evaluation of at least one additional groundwater extraction well, and modifying the intermediate well efficiency based on the interference evaluation of the at least two groundwater extraction wells. By including an interference evaluation with a specific capacity calculation, the groundwater extraction wells' specific capacity can more closely represent actual well specific capacity, absent any interference effects that may be occurring due to operation of one or more additional groundwater extraction well operating simultaneously. Thus, the specific capacity module 144 can receive a calculated specific capacity (which is a form of analyzed aquifer data 136) for the one or more selected groundwater extraction wells from the analysis computing device 102 in response to the data request 148. Accordingly, the specific capacity module 144 can display the calculated specific capacity for the one or more selected groundwater extraction wells, and/or send the calculated specific capacity data into data storage for future analysis of groundwater extraction well specific capacity for another time interval. A third module, the entrance velocity module 146, may be included in the well hydraulics module 128. The entrance velocity module 146 may be configured to receive entrance velocity operator input including one or more selected groundwater extraction wells and selected groundwater extraction well parameters. The entrance velocity module 146 can also send an entrance velocity request (e.g., data request 148) to the analysis computing device 102, and receive an entrance velocity (e.g., analyzed aquifer data 136) for the one or more selected groundwater extraction wells, from the analysis computing device 102. Accordingly, the entrance velocity module 146 can display the entrance velocity for the one or more selected groundwater extraction wells, and/or send the entrance velocity data into data storage for future analysis of entrance velocity for another time interval. An advisory message may be displayed that indicates to a well operator that the entrance velocity exceeds a predetermined threshold, and a recommendation may be displayed to lower the pumping rate. A selector may be presented to the well operator to proceed and take the recommended action of lowering the pumping rate, for example. Turning now to the hydrogeology module 130 of the GUI 124, it may include one or more geostatistical modeling modules configured to display aquifer-water pressure data including elevation units, and apply one or more geostatistical models to the aquifer-water pressure data. The geostatistical modeling module may be a potentiometric surface module 150, a water-flow modeling module 152, an aquifer-extraction hydraulic-parameters analysis module 153 and/or an interference evaluation module 154. It may be appreciated that the geostatistical models described herein may also be applied to other water measurements. The potentiometric surface module 150 may receive potentiometric surface operator input including a plurality of sites (e.g., observation wells), and a time interval. Further, a desired geostatistical interpolation method including a linear-log kriging method, an inverse-distance weighted method, a spline method (e.g., cubic spline), a universal kriging method, and/or an ordinary kriging method can be received as potentiometric surface operator input at the potentiometric surface module 150. Thus, the potentiometric surface module 150 can send the potentiometric surface operator input to the analysis computing device 102, receive a potentiometric surface model from the analysis computing device 102 based on the potentiometric surface operator input, and display the potentiometric surface model in a geographic rendering system in two or three dimensional form, for example. The geographic rendering system may be incorporated into GUI 124, or may be a separate geographic information system (GIS) application executed on the analysis computing device 102, for example. Turning now to the water-flow modeling module 152 of the hydrogeology module 130, it is configured to receive water-flow modeling operator input including one or more of a selected groundwater extraction well, a location of water-flow traces, a number of water-flow traces, and a starting point for each water-flow trace from the GUI 124. In one example, these water-flow traces are particle tracking traces. The water-flow modeling module 152 may also receive an aquifer transmissivity input from one or more of the graphical user interface and the analysis computing device, and send the water-flow modeling operator input and the aquifer transmissivity input to the analysis computing device 102. In response, the water-flow modeling module 152 can receive a groundwater extraction well capture zone analysis in the analyzed aquifer data 136, from the analysis computing device 102. The groundwater extraction well capture zone analysis can include modeled water-flow traces for the one or more selected groundwater extraction wells based on the water-flow modeling operator input and the water transmissivity input. Further, the water-flow modeling module 152 may display the modeled water-flow traces, wherein the modeled water-flow traces are computed based on an interpolated pressure field, the water-flow modeling operator input, and the water transmissivity input, as some examples. The interference evaluation module 154 is yet another geostatistical modeling module which may be presented in the hydrogeology module 130 of the GUI 124. The interference evaluation module 154 may receive interference operator input including at least two groundwater extraction wells, and send the interference operator input to the analysis computing device 102. In response, the interference evaluation module 154 can receive an interference evaluation from the analysis computing device 102 based on the interference operator input, and graphically display the interference evaluation. Further, the interference evaluation data can be stored in the mass storage 122 for future analysis. It may be appreciated that additional terminals, such as a remote access terminal 156 can be connected to the analysis computing device 102, and can operate similarly to the analysis computing device 102, in that it can display the graphical user interface to a user over a computer network. That is, the remote access terminal 156 can receive aquifer data from the aquifer, and operator input, aquifer data, and analyzed aquifer data from the analysis computing device 102. Further, the GUI 124 can display aquifer data via the remote access terminal 156. Further still, the GUI 124 can display analyzed aquifer data received from the remote access terminal 156, and display a pump operation advisory message 140 via the remote access terminal. A remote access terminal may be an additional computing device, a display screen, a router, etc., and may be connected over a computer network (e.g., LAN or WAN such as the Internet). With regard to the hardware employed in system 100, the analysis program 120 and other programs of analysis computing device 102 may be stored in the mass storage 122 and executed on a processor 158 using portions of memory 160 and may further be configured to communicate with software programs on other computing devices, such as the remote access terminal 156 across one or more computer networks, and the input device 134 via input/output interface 162. Display 126 may also be configured to receive display output from the analysis program 120 via the input/output interface 162. It will further be appreciated that the analysis computing device 102 may be a single computing device or server, or multiple distributed computing devices and/or servers interoperating across one or more computer networks, and the components of the analysis program 120 may be implemented on these distributed devices. Turning now to FIG. 2, a flowchart illustrates a method 200 for managing aquifer operation. At 202, the method includes receiving, at an analysis computing device, one or more water measurements from a plurality of sites in an aquifer. The water measurements may be continuously or periodically monitored, being received at an analysis computing device, at a plurality of time points. In one example, the plurality of time points may be a plurality of time points collected according to a predetermined schedule (e.g., three times a day at specified hours, seven days a week, etc.) such that the water measurements are continuously monitored. In another example, the plurality of time points may include a series of water measurements collected in response to a change in one or more water measurements exceeding an associated threshold. For example, it may be desirable to monitor the water measurements of a site more frequently if there is a change in one or more aquifer conditions, such as: a water level above a level threshold, a water pressure above a pressure threshold, an electrical conductivity above a conductivity threshold, a water temperature above a temperature threshold, and a vibration parameter above a vibration threshold. Further still, there may be low thresholds for which values below the low thresholds trigger a collection of water measurements for a plurality of time points. It may be appreciated that water measurements may be collected responsive to predefined changes in aquifer conditions as described above, in addition to being collected at a predetermined schedule. At 204, the method 200 includes calculating well operational data for at least one groundwater extraction well based on the water measurements. Calculating the well operational data may optionally include executing, at 206, a well hydraulic interference evaluation of at least two groundwater extraction wells, based on geographic reference coordinates. Calculating the well hydraulic interference evaluation at 206 may include calculating an interference measurement based on a number of operator inputs received from the graphical user interface, as will be discussed with reference to FIG. 3. Well operational data can include well efficiency, aquifer-water pressure loss, and/or well-water pressure loss, among other measures of well performance. Thus, calculating well operational data may include calculating well efficiency at 208 for each groundwater extraction well based on associated interference evaluations and a number of efficiency operator inputs received at a graphical user interface associated with the analysis computing device. Likewise, the calculating of the well operational data may include calculating aquifer-water pressure loss and/or well-water pressure loss at 210, for a plurality of sites. As mentioned above, the well operational data may be calculated over a time period, such as a number of seconds, minutes, days, weeks, etc. After calculating the well operational data at 204, it will be appreciated the results of the calculation may be stored in an analysis program data store for later retrieval and downstream processing. At 211, analyzed aquifer data can be graphically displayed, as measurements over a time interval, to inform an operator of current aquifer operation parameters and measurements compared to historical aquifer operation parameters and measurements. In some examples, the analyzed aquifer data is displayed prior to setting or changing an aquifer objective input, and prior to generating a pump operation signal at 212 or sending a pump operation signal at 214, as described below. At 212, the method 200 includes receiving an aquifer objective input from, or via, a graphical user interface presented on an analysis computing device. An aquifer objective input may be an optimal energy consumption, an optimal groundwater elevation for each groundwater extraction well, an optimal pressure reading for each groundwater extraction well, an optimal water pumping volume, a site contamination avoidance for a selected site and/or a groundwater contamination removal for the aquifer. These aquifer objective inputs can be pre-set upon configuration of the system, and can further be pre-set for a particular groundwater extraction well or a group of groundwater extraction wells. It may also be appreciated that aquifer objective inputs can be adjusted at 212, or when aquifer objective inputs are changed by the operator. At 214, the method includes generating a pump operation signal, based on the well operational data and the aquifer objective input. The method 200 may further include sending the pump operation signal to the GUI for display at 216. The pump operation signal may include a pump operation advisory message to inform an operator of a recommended pump procedure, and may indicate preferable actions for the operator to carry out. For example, the recommended pump procedure may include a recommended well operation, and/or a well service procedure including one or more of a well cleaning and a pump impeller servicing. The advisory message may also inform a well operator of operating conditions exceeding established operating thresholds, as discussed above. The method 200 may alternatively or additionally include adjusting operation of at least one groundwater extraction well based on the pump operation signal, at 218. For example, at 218, a pump rate of the at least one groundwater extraction well may be adjusted when the well efficiency of the at least one groundwater extraction well is below a predetermined low threshold. Where step 218 is carried out, the associated pump operation signal may be an adjusting signal for carrying out said adjusting. It may further be appreciated that adjusting the operation of groundwater extraction wells may include shutting off and/or turning on one or more groundwater extraction wells. Furthermore, said adjusting may occur in real-time, during collection of aquifer data. The adjusting at 218 may be carried out programmatically according to predetermined rules programmed into analysis program 120, or may require an “opt-in” authorization by the well operator to be carried out. Further a combination of programmatic adjustment and operator authorized adjustment (e.g., a semi-automated adjustment) may be employed depending on a determined criticality level of the adjusting operation, so that only the most critical operations require operator authorization. Referring now to FIG. 3, a screen of an exemplary GUI 124 for carrying out the method 200, for example, is illustrated. A well hydraulics module 128 is graphically presented and may allow an operator to select one of the efficiency module 142, the specific capacity module 144, and the entrance velocity module 146 by traversal of a cursor, for example. Similarly, the hydrogeology module 130 is graphically presented and can allow the operator to select from a number of geostatistical modeling modules, such as the potentiometric surface module 150, the water-flow modeling module (e.g., “capture zone”) 152, an aquifer-extraction hydraulic-parameters analysis module 153, and the interference evaluation module 154. FIG. 3 specifically illustrates a GUI wherein the efficiency module 142 is selected. Upon selection of the efficiency module 142, a well efficiency pane 302 is presented (as indicated by the left-most, dotted arrow). The well efficiency pane 302 is configured to receive efficiency operator input, such as a well 304, a groundwater elevation 306, one or more flow rate parameters 308, a start date 310 and end date 312 to define a date range, and an analysis method 314, via operator input at various input fields. Upon traversal of a “Display graph” button 316, a graphing pane 318 may be presented in the same screen, in this example. In another example, the graphing pane 318 may be presented in a new window or screen. The presentation of said graphing pane 318 is indicated by the right-most, dotted arrow. In graphing pane 318, a well efficiency graph 320 and one or more of aquifer data and analyzed aquifer data parameters may also be presented, as a plurality of measurements over a time period. For example, parameter #1 322 may be a well efficiency, parameter #2 324 may be an aquifer-water pressure loss, parameter #N 326 may be a well-water pressure loss. Other parameters that may be displayed include groundwater elevation, location identifier, time and/or date range of the data associated with the graph, etc. It may be appreciated that each of the modules contained in the well hydraulics module 128 and hydrogeology module 130 may be selectable by an operator, and upon selection, one or more associated panes may be presented to the operator for receiving operator input and presenting aquifer data and analyzed aquifer data. Interactive graphs may be displayed, such that an operator may further specify data points of interest as operator input to the system, via selection of data points of a graph by traversal of a mouse, for example. Referring now to FIG. 4, a screen is illustrated wherein the specific capacity module 144 has been selected. Accordingly, a specific capacity pane is presented with various input fields, for receiving operator input. Upon selection of a “Graph data” button, a specific capacity graph pane may be presented in the same screen, or in another example, in a separate screen. A specific capacity graph contained therein may be interactive, such that a user can select data points from the graph as operator input. A specific capacity formula pane contained below the specific capacity graph is also configured to receive operator input via input fields. Data can be saved by traversal of the “Save” button. FIGS. 5a and 5b illustrate exemplary pump operation advisory messages as color ranges associated with a quality of pump operation. As discussed earlier, pump operation advisory messages of varying priority levels, such as a high, medium, and low priority, may be indicated by colors (red, yellow, and green), etc. Specifically, FIG. 5a illustrates a graph of well efficiency, with a well loss exponent on the y-axis over a selectable or default period of time (e.g., 60 days) on the x-axis. In some cases, the period of time may end at the current moment, as shown, enabling an operator to view current conditions as well as a recent history. In the depicted graph, when the well loss exponent is small, well loss is low and operation is in a green zone, where operation in the green zone is associated with pump operation of good efficiency. Toward the center of the x-axis, the well loss exponent increases and enters a yellow zone, associated with pump operation of fair efficiency. Toward day 60, which may be now, the well loss exponent enters a red zone associated with poor pump operation. It will be appreciated that each zone of operation carries with it corresponding lower and upper thresholds used to determine whether the pump operation parameter, in this case well efficiency, is within the zone. Thus, when such a well efficiency graph is presented with the pump operation color ranges, it can be easily understood that a pump service or an adjustment to pump operation may be desirable when pump operation is in a yellow or red zone. In some examples, an additional pump advisory message indicating a desired operator action may be presented. In the depicted embodiment of FIG. 5a, a pump advisory message indicating a current pump operation status (specific capacity in red zone), as well as a recommended action is displayed. A selector, labeled “adjust” in FIG. 5a, may also be displayed to enable the user to choose to undertake the recommended action, e.g., adjust pump operation range to a recommended parameter. Similarly, FIG. 5b illustrates specific capacity as a percentage of initial specific capacity on the y-axis over a selectable or default period of time (e.g., 60 days) on the x-axis. In this example, the specific capacity decreases non-linearly, passing from a green zone, through a yellow zone to a red zone. When specific capacity is high relative to an initial value, pump operation is good and thus in the green zone. When specific capacity is low relative to an initial value, pump operation is poor and is thus in the red zone. Accordingly, from this graph, it can be easily understood by an operator that a pump service or an adjustment to pump operation may be necessary when pump operation is in a yellow or red zone. In some examples, an additional pump advisory message indicating a desired operator action may be presented. Like in FIG. 5a, in FIG. 5b, a pump advisory message is displayed indicating that the specific capacity is currently in the red zone. The pump advisory message may include a recommended action, such as adjust pump operation range to a recommended parameter. A selector also may be displayed to enable the user to take the recommended action. It may be appreciated that an operator may request graphs such as the graphs of FIGS. 5a and 5b, and/or such graphs may be presented automatically when well operational data exceeds a predetermined threshold (e.g., well loss exponent entering a red zone, specific capacity entering a yellow zone). Referring now to FIG. 6, a schematic view of a screen where the entrance velocity module 146 has been selected is illustrated. Here, an entrance velocity calculator pane is presented, with various input fields for receiving operator (e.g., user) input (e.g., well diameter, screen length, slot size, wire width, etc.). Upon traversal of a “Go” button, various output parameters (e.g., total surface area, open area ratio, total open area, entrance velocity, etc.) are calculated and displayed in the entrance velocity calculator pane. FIG. 7 shows a schematic view where the potentiometric surface module 150 of the hydrogeology module 130 has been selected. Upon selection of the potentiometric surface module 150, a potentiometric surface pane is presented, as indicated by the left-most, dotted arrow. Various input fields are provided in the potentiometric surface pane for operator input (e.g., location group, ground water parameters, medium, interpolation method, options, interval, start date, end date, etc.) Upon traversal of a “Get data” button, a potentiometric surface viewer pane may be presented in the same screen or a different screen. The potentiometric surface viewer may include a graph and/or video indicating two-dimensional or 3-dimensional changes in the potentiometric surface. The location of sites (illustrated as small dark circles) in the aquifer may be displayed in the graph and/or video. Further, potentiometric surface map information is calculated upon traversal of the “Get data” button, such that values of various water measurements of corresponding wells and dates can be viewed in the potentiometric surface viewer pane. FIGS. 8a and 8b illustrate two exemplary potentiometric surface graphs where contour lines delineate areas associated with differing drawdown values. For example, FIG. 8a illustrates groundwater flow when none of the wells (shown as dark circles) are pumping water. In contrast, FIG. 8b illustrates groundwater flow when well #1 is turned on. It can be appreciated that drawdown may become great at the center of well #1, in such a case. In some examples, an extreme drawdown situation (i.e., when the drawdown is determined to be greater than a predetermined threshold) may be graphically indicated, for example by hatching or changes in color of a region of a potentiometric surface graph, as shown by the hatched ellipse of FIG. 8b. In such a case, a pump advisory message may be automatically presented to an operator, as shown. The pump advisory message may include a message indicating an operational status of the pump (e.g., excessive drawdown is occurring), and may also include a recommended action, such as turn off pump. Further, a selector may be provided to enable the user to take the recommended action. It will be appreciated that drawdown graphs can be presented as still images, and/or as videos, such that the drawdown can be visualized over a specified interval, and/or in real-time. Graphs such as those of FIGS. 8a and 8b may be presented responsive to a request by an operator and/or automatically when drawdown, or other water measurements exceed predetermined thresholds. FIG. 9 shows a schematic view where the water-flow modeling module (“groundwater extraction well capture zone”) 150 of the hydrogeology module 130 has been selected. Here, a groundwater extraction well capture zone analysis pane is presented, including a capture zone graph. The capture zone analysis pane also may include an input parameter section with various input fields for receiving operator input. Upon traversal of a “Calculate stagnation point” button, one or more stagnation point values for one or more capture zones may be calculated. Further, various output parameters are calculated and displayed under the output parameter section. Upon traversal of a “Rotate” button, the capture zone graph may be rotated to fit a direction of water flow. FIG. 10 shows a schematic view where an aquifer-extraction hydraulic-parameters analysis module 153 of the hydrogeology module 130 has been selected. A aquifer-extraction hydraulic-parameters analysis pane may be presented to the user, with various input fields by which a user can select groundwater extraction wells to be included in the analysis, as well as a time interval for analysis. Upon traversal of a “Begin” button, a aquifer-extraction hydraulic-parameters analysis graph pane may be presented, in this example. An operator may interact with a drawdown graph included therein to select a portion of the drawdown graph for use as an operator input for the analysis of the drawdown data. Further, the operator may edit parameters, such as the drawdown start and a drawdown end, and traverse a “Recalculate button” to trigger a recalculation of drawdown values. Finally, FIG. 11 shows a schematic view where the interference evaluation module 154 of the hydrogeology module has been selected. Upon selection, an interference evaluation pane is presented, in this example. Here, an operator can fill in various input fields, including set-up parameters, pumping location, observation well location (e.g., a groundwater extraction well at which the interference evaluation is being performed), and start and end times for analysis of well interference. Traversal of a “Next” button will cause a well interference pair graph to be presented, in the same screen or in a different screen. In the well interference pair graph, two sub-graphs are presented. These two graphs illustrate, respectively, groundwater elevation and a flow rate for the two or more selected wells. In this example, it can be observed from the flow rate graph that when well 2 is turned on, the groundwater elevation decreases for both well 1 and well 2. Thus, an operator can visually comprehend the effects of operating a first well on a second well, using this graphical user interface. Further, a drawdown parameter can be calculated, automatically, semi-automatically, or manually by operator input in input fields, as indicated by the formula located underneath the flow rate graph. It will be understood that the above described systems and methods may also be applied to aquifers with pumping stations that pump water into the aquifer to change the hydrogeologic conditions of the aquifer. Therefore, any of the extraction wells discussed herein may be equipped with intake and outflow capabilities. For example, in the potentiometric surface graph of FIG. 8b, the system may be configured to determine ground water pressure at the point of injection and determine whether such pressure exceeds a predetermined threshold. An advisory message may indicate this to the operator, and include a recommended action, such as maintaining the well to remove siltation of the well screen. A selector may be provided to take the recommended action and reverse water flow to remove siltation from the well screen, for example. It will be appreciated that the computing devices described herein may be any suitable computing device configured to execute the programs described herein. For example, the computing devices may be a mainframe computer, personal computer, laptop computer, portable data assistant (PDA), computer-enabled wireless telephone, networked computing device, or other suitable computing device, and may be connected to each other via computer networks, such as the Internet. These computing devices typically include a processor and associated volatile and non-volatile memory, and are configured to execute programs stored in non-volatile memory using portions of volatile memory and the processor. As used herein, the term “program” refers to software or firmware components that may be executed by, or utilized by, one or more computing devices described herein, and is meant to encompass individual or groups of executable files, data files, libraries, drivers, scripts, database records, etc. It will be appreciated that computer-readable media may be provided having program instructions stored thereon, which upon execution by a computing device, cause the computing device to execute the methods described above and cause operation of the systems described above. It should be understood that the embodiments herein are illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.
	summary
	claims	1. A radioactive carbon containment process, comprising a step of containing said radioactive carbon in a mixed carbonate of formula AB(CO3)(n+m)/2, the sintering temperature of which is below the decarbonation temperature of the mixed carbonate and the hardness of which is greater than or equal to 4 on the Mohs scale, in which A and B are different and chosen from the group consisting of alkali metals, alkaline-earth metals and rare earths, and in which n and m are positive integers such that the charge of AB(CO3)(n+m)/2 is neutral. 2. The radioactive carbon containment process as claimed in claim 1, in which A and B are different and chosen from the group consisting of Na, K, Ca, Ba, Mg and Sr. 3. The radioactive carbon containment process as claimed in claim 1, in which the mixed carbonate is BaCa(CO3)2. 4. The radioactive carbon containment process as claimed in claim 1, in which the mixed carbonate is sintered for the containment of the radioactive carbon. 5. The radioactive carbon containment process as claimed in claim 1, in which the radioactive carbon comes from a gaseous effluent of an irradiated nuclear fuel reprocessing plant. 6. A radio carbon containment process, comprising the following steps:a) mixing CO2 having a radioactive carbon to be contained, or a simple carbonate of an alkali, alkaline-earth or rare-earth metal having a radioactive carbon to be contained, with an aqueous solution of a mixture of ACln and BClm or with an aqueous solution of a mixture of A(OH)n and B(OH)m in order to obtain a precipitate of AB(CO3)(n+m)/2 where A and B are different and chosen from the group consisting of alkali metals, alkaline-earth metals, alkaline-earth metals and rare earths, and n and m are positive integers such that the charge of Aln, BClm, A(OH)n and B(OH)m is neutral;b) recovering the AB(CO3)2 precipitate obtained in step a) in powder form;c) optionally rinsing said powder; andd) pressing the powder and sintering it at a sintering temperature below the decarbonation temperature of the synthesized mixed carbonates in order to obtain sintered pellets of mixed carbonates of formula AB(CO3)(n+m)/2, the hardness of which is greater than or equal to 4 on the Mohs scale, and containing the radioactive carbon in the sintered pellets of mixed carbonates. 7. The process as claimed in claim 6, in which A and B are different and chosen from the group consisting of Na, K, Ca, Ba, Mg and Sr. 8. The process as claimed in claim 6, in which the mixed carbonate is BaCa(CO3)2. 9. The process as claimed in claim 6, in which the pressing is carried out at a pressure ranging from 10 to 20 MPa, and the sintering at said temperature for 1 to 3 hours. 10. The Process as claimed in claim 6, in which the pressing is carried out at a pressure of 14 to 16 MPa, and the sintering at a temperature of 550° C. to 600° C. for 1 hour 45 minutes to 2 hours 30 minutes. 11. The process as claimed in claim 6, in which the simple carbonate is obtained by trapping the radioactive carbon, in CO2 form, in accordance with a process chosen from the group consisting of a double alkali process, a direct hydroxide reaction process and a gas/solid process. 12. The process as claimed in claim 6, in which the CO2 having a radioactive carbon to be contained, or a simple carbonate of an alkali, alkaline-earth or rare-earth metal having a radioactive carbon to be contained, comes from an effluent of an irradiated nuclear fuel reprocessing plant.
	abstract	A system and method for removing spent fuel assemblies from a fuel building and transporting them to on-site facilities. A cask transporter is moved into the fuel building with an empty spent fuel storage cask, spent fuel assemblies are loaded into spent fuel storage cask, the cask is sealed, and the cask transporter moves the loaded spent fuel storage cask to a handling area for final disposal. Components of the system include a penetration cover, a lifting mechanism, a control system, a valve system, and the cask transporter.
	claims	1. A method of decontaminating naturally occurring radioactive material (NORM) from downhole equipment, the method comprising:circulating a wetting agent through an isolated region of a wellbore comprising NORM-contaminated production equipment such that the NORM-contaminated production equipment is rendered water wet;chemically treating the NORM-contaminated production equipment by injecting, after circulation of the wetting agent, one or more NORM dissolving chemicals into the isolated region of a wellbore such that a bypass string delivers a NORM dissolver of the one or more NORM dissolving chemicals to an appropriate location with the wellbore or one or more chemical injection mandrels inject the NORM dissolver into the wellbore at the appropriate location, and the appropriate location is dependent on a location of NORM-contaminated production equipment within the wellbore; andremoving the NORM contaminants from the production equipment;wherein the method further comprises:running a first gamma log before the injecting;running a second gamma log after the injecting; andverifying whether NORM has been removed. 2. The method of claim 1, further comprising:isolating the NORM-contaminated production equipment from other regions of the wellbore. 3. The method of claim 2, wherein the isolation of the NORM-contaminated production equipment is achievable by at least one packer. 4. The method of claim 2, wherein the isolation of the NORM-contaminated production equipment is achievable by at least one of a cement plug, a polymeric plug, and a gel plug. 5. The method of any of claim 1, further comprising:flushing a fluid through the isolated region prior to circulation of the wetting agent. 6. The method of any of claim 1, further comprising:flushing diesel through the isolated region after removal of the NORM contaminants. 7. The method of claim 1, wherein the NORM dissolver comprises at least one chelating agent. 8. The method of claim 1, wherein the NORM-contaminated production equipment comprises an artificial lift. 9. The method of claim 8, wherein the NORM-contaminated production equipment comprises an electric submersible pump. 10. The method of claim 8, wherein the NORM-contaminated production equipment comprises a gas lift. 11. The method of claim 1, wherein the NORM-contaminated production equipment comprises at least one valve. 12. The method of claim 1, wherein the NORM-contaminated production equipment comprises a packer. 13. The method of claim 1, wherein the NORM-contaminated production equipment comprises a cable. 14. The method of claim 1, wherein the NORM-contaminated production equipment comprises monitoring equipment. 15. The method of claim 1, further comprising:resuming production of hydrocarbons using the production equipment. 16. A method of decontaminating naturally occurring radioactive material (NORM) from downhole equipment, the method comprising:isolating NORM-contaminated production equipment from other regions of a wellbore;flushing diesel through the isolated region;injecting a wetting agent into the isolated region to render the NORM-contaminated production equipment water wet;chemically treating the NORM-contaminated production equipment by injecting, after injection of the wetting agent, one or more NORM dissolving chemicals into the isolated region such that a bypass string delivers a NORM dissolver of the one or more NORM dissolving chemicals to an appropriate location with the wellbore or one or more chemical injection mandrels inject the NORM dissolver into the wellbore at the appropriate location, and the appropriate location is dependent on a location of NORM-contaminated production equipment within the wellbore; andremoving the NORM contaminants from the production equipment;wherein the method further comprises:running a first gamma log before the injecting of the one or more NORM dissolving chemicals;running a second gamma log after the injecting of the one or more NORM dissolving chemicals; andverifying whether NORM has been removed. 17. The method of claim 16, further comprising:resuming production of hydrocarbons using the production equipment. 18. A method of decontaminating naturally occurring radioactive material (NORM) from downhole equipment, the method comprising:running a first gamma log;chemically treating the NORM-contaminated production equipment by injecting one or more NORM dissolving chemicals into an isolated region of a wellbore in which NORM-contaminated production equipment is located such that a bypass string delivers a NORM dissolver of the one or more NORM dissolving chemicals to an appropriate location with the wellbore or one or more chemical injection mandrels inject the NORM dissolver into the wellbore at the appropriate location, and the appropriate location is dependent on the location of NORM-contaminated production equipment within the wellbore;removing the NORM contaminants from the production equipment;running a second gamma log; andverifying whether NORM has been removed based on the first gamma log and the second gamma log.
044029039	summary	BACKGROUND OF THE INVENTION The present invention relates to control systems which operate with redundant logic channels, and more particularly where these redundant channels are to be physically and electrically independent. Such redundant control systems are employed in nuclear power plants as safety control systems for continued safe operation. It has been the practice to use photoelectric devices to maintain the physical and electrical insulation between the redundant channels, as is taught by U.S. Pat. No. 3,888,772, owned by the assignee of the present invention. Earlier systems interconnected the separate logic channels with either relays or transformers to provide the isolation. Electro-optical devices are well known in which a birefringent crystal is modulated by an applied electric field to vary the light transmission characteristic of the crystal. These devices have been used as electrically controlled switches as described in representative U.S. Pat. Nos. 3,069,973; 3,027,806; and 3,531,179. SUMMARY OF THE INVENTION The present invention utilizes a plurality of electro-optical modulators as coupling means for redundant logic channels while maintaining physical and electrical independence of the logic channels. Fiber optic cable linking means are provided between a system light source and detector, and the plurality of optical logic units which include the electro-optic modulators. Separate operating system sensors are connected to the respective optical logic units and provide operating system condition or parameter indicative signals, which provide the modulation signal for the electro-optic modulators, and to thereby control the light transmission characteristics of these modulators. In the particular embodiment the light intensity passed by the separate electro-optical modulatable member of the separate optical logic units is varied and controlled as a function of the operating system sensor generated signals. These sensors generate signals as a function predetermined system operating condition, and the signal is applied to modulate the light transmissivity through the separate redundant logic channels.
	abstract	A soft X-ray reduction projection exposure system includes a light source for generating a soft X-ray beam of a wavelength of a 4 through 20 nm band; a reflecting mask on which a desired pattern is formed; an illumination optical system for irradiating the reflecting mask with the soft X-ray beam; a reduction projection optical system for imaging the pattern of the reflecting mask on a wafer; and a controlling section for controlling a partial pressure of a gas of a carbon compound to be 1.33xc3x9710xe2x88x928 Pa or less in at least one of a first region where the illumination optical system is disposed, a second region where the reflecting mask is disposed and a third region where the reduction projection optical system is disposed.
040000397	claims	1. A fuel element for a high temperature reactor comprising a structural graphite block and a fuel zone comprising a graphite matrix containing embedded, coated fissile material particles, said fuel zone being removable from the structural graphite after burnup of the fissile material so that the fuel element can be filled with new fuel and again inserted in the reactor, said graphite matrix having sufficient strength to bind the embedded coated fuel particles which strength is at least 50 kg/cm.sup.2 less than the binding strength of the structural graphite whereby by the action of force said matrix can be easily split up without destroying the fuel particles. 2. A fuel element according to claim 1 wherein the matrix consists essentially of a carbon filler and binder coke, the amount of coke being less than 10. 3. A fuel element according to claim 2 wherein the carbon of the matrix is natural graphite. 4. A process of separating the structural graphite block from the fuel zone of a fuel element for a high temperature reactor, said fuel element comprising a structural graphite block having bore-holes therein and a fuel zone comprising a graphite matrix containing embedded, coated fissile material particles, said fuel zone being compressed into the bore-holes of the structural graphite block and being removable from the structured graphite after burnup of the fissile material so that the fuel element can be filled with new fuel embedded in graphite matrix by compressing it and again inserted in the reactor, said graphite matrix having sufficient strength to bind the embedded coated fuel particles which strength is at least 50 kg/cm.sup.2 less than the binding strength of the structural graphite, said process comprising disintegrating the matrix with a force insufficient to damage the structural graphite. 5. A process according to claim 4 wherein the disintegration is accomplished mechanically. 6. A process according to claim 4 wherein the disintegration is accomplished by erosion. 7. A process according to claim 4 wherein the disintegration is accomplished ultrasonically. 8. A process according to claim 4 including the steps of refilling the bore-holes in the structural graphite block after removal of the disintegrated matrix with lightly precompressed fuel inserts and then finishing the compressing of the fuel inserts in the structural graphite block. 9. A fuel element according to claim 1 wherein the binding strength of the graphite matrix is 50 to 350 kg/cm.sup.2 less than the binding strength of the structural graphite. 10. A process according to claim 4 wherein the binding strength of the graphite matrix is 50 to 350 kg/cm.sup.2 less than the binding strength of the structural graphite.
060318899	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic cross sectional view of an acoustic delay line of a beam line according to an embodiment of the invention. This acoustic delay line is used, for example, in place of the vacuum duct 57 of the X-ray exposure system shown in FIG. 9. At the downstream of the mirror box 54 shown in FIG. 9, a vacuum duct 57 is connected, at the downstream of which a beam line large-diameter outer tube unit 1 is connected. An inner tube 2 is installed inside of the large-diameter outer tube unit 1. The inner tube 2 is used as an envelope of an optical path of radiated light. A radiated light output frame 3 is coupled to the tip of the inner tube 2 on the downstream side thereof. A flange 5 mounted at the downstream end of the large-diameter outer tube unit 1 and the radiated light output frame 3 are hermetically sealed by a vacuum bellows 4. Drivers 6.sub.1 and 6.sub.2 are mounted on the lower wall of the large-diameter outer tube unit 1 at opposite end portions. The drivers 6.sub.1 and 6.sub.2 drive the inner tube 2 in a vertical direction while supporting it. The inner tube 2 is driven synchronously with a pivotal motion of the mirror 55 (FIG. 9) to establish an optical path of radiated light. A plurality of partition plates 7 are disposed inside of the large-diameter outer tube unit 1 at a predetermined pitch along the axial direction. Each of these partition plates 7 is formed with an opening 7' at the central area of the plate, the opening 7' having a size not to obstruct the up/down motion of the inner tube 2. These juxtaposed partition plates 7 are coupled together by coupling bolts 8. A plurality of partition plates 9 are formed on the outer circumference of the inner tube 2 at positions corresponding to the partition plates 7. Each pair of the partition plates 7 and 9 is preferably disposed at a gap of 1 mm or smaller. The partition plates 7 and 9 divide the inner space of the large-diameter outer tube unit 1 into a plurality of partitioned spaces 10. A number of holes 2' are formed in the upper and lower walls of the inner tube 2 to communicate each partitioned space with the inner space of the inner tube 2. Although the number, size and shape of holes 2' is optional, it is preferable to set the total opening area of holes 2' in one partitioned space 10 larger than the opening area of the inner tube 2 in the cross section vertical to the center axis of the tube 2, and it is more preferable to set the former ten times larger than the latter. The inside of the large-diameter outer tube unit 1 is evacuated via a vacuum exhaust port D formed in the wall of the large-diameter outer tube unit 1 at generally the central partitioned space 10. The detailed structure of the beam line of this embodiment will be described with reference to FIGS. 2 to 4. FIG. 2 is a vertical cross sectional view of the beam line, taken along the center axis of the beam line, and FIGS. 3 and 4 are cross sectional views taken along respective one-dot chain lines A--A and B--B shown in FIG. 2. Each of the drivers 6.sub.1 and 6.sub.2 for the inner tube 2 is constituted of: a bearing case 13 with an internal linear guide bearing 12; a guide shaft 15 having a fork at its one end; a linear actuator 16 fixed to the bearing case 13; a coupling plate 17 for coupling the movable part of the actuator 16 and the guide shaft 15; and a vacuum bellows 18. The vacuum bellows 18 is coupled between the one end of the guide shaft 15 and the bearing case 13 to retain the vacuum degree of the inside of the large-diameter outer tube unit 1. The bearing cases 13 of the drivers 6.sub.1 and 6.sub.2 are mounted on flanges 11.sub.1 and 11.sub.2 provided at the lower wall of the large-diameter outer tube unit 1. Coupling plates 19 are fixed to the forks 14 of the inner tube 2. Each coupling plate 19 and corresponding fork 14 are coupled together by a pin 20. The radiated light output frame 3 has a disk-like shape, and a rectangular or arc-shaped window matching a cross section of a radiated light flux is formed in the frame 3 at its central area. The window is hermetically sealed with a beryllium thin film 21 which is welded or soldered to the output frame 3. The output frame 3 is coupled to the flange 5 of the large-diameter outer tube unit 1 via the vacuum bellows 4 and flanges 3' and 5'. As shown in FIGS. 3 and 4, the cross section of the inner tube 2 has a shape covering the radiated light flux. As shown in FIG. 2, one end of the inner tube 2 is mounted on a flange 3" of the radiated light output frame 3, and the other end thereof protrudes from the large-diameter outer tube unit into the upstream vacuum duct 5. The drivers 6.sub.1 and 6.sub.2 drive the inner tube 2 in the vertical direction and receive a force in the horizontal direction generated by a pressure difference between the atmospheric pressure applied to the radiated light output frame 3 and the vacuum pressure in the large-diameter outer tube unit 1. The drivers 6.sub.1 and 6.sub.2 are driven by a signal supplied from a synchronizing means 81, synchronously with the operation of the driver 56 shown in FIG. 9. As shown in FIG. 4, for the convenience of assembly, each partition plate 7 of the large-diameter outer tube unit 1 is divided into upper and lower pieces which are coupled together by coupling plates 22 with screws. After the inner tube 2 and partition plates 9 are assembled integrally, they are assembled in the large-diameter outer tube unit 1. A sensor head 23 of a vacuum gauge is mounted on the flange 5. The sensor head 23 measures the vacuum degree in the large-diameter outer tube unit 1 and supplies the measured data to the controller 80 (FIG. 9). The controller 80 monitors a change in the vacuum degree, and when the beryllium thin film is broken, it operates to actuate the high speed shutter valve 66 and shutter valve 65 (FIG. 9) at the upstream positions. It is therefore possible to prevent gas from entering the inside of the synchrotron. The size of the large-diameter outer tube unit constituting the acoustic delay line is about 400 mm in outer diameter and about 2 m in length. In the large-diameter outer tube unit 1 shown in FIG. 1, the two adjacent partitioned spaces 10 communicate with each other via the holes 2' formed in the upper and lower walls of the inner tube 2 and via the internal space of the inner tube 2. If the total opening area of holes 2' in one partitioned space 10 is ten times or more of the cross sectional area of the inner space of the inner tube 2, a resistance applied to the gas flowing between the inner space of the inner tube 2 and its partitioned space 10 is sufficiently small as compared to a resistance applied to the gas flowing through the inner space of the inner tube 2 along its axial direction. Therefore, the structure shown in FIG. 1 can be considered as substantially equivalent to the structure that the two adjacent partitioned spaces 10 communicate with each other via a hole having a cross sectional area of the inner space of the inner tube 2. If the inner tube 2 is not used, the partition plates 9 cannot be mounted so that the two adjacent partitioned spaces 10 communicate with each other via the opening 7'. The cross sectional area of the inner space of the inner tube 2 is smaller than the area of the opening 7'. Therefore, the resistance of the gas flowing in the axial direction increases, and a transport speed of the gas flowing in the large-diameter outer tube unit 1 in its axial direction can be lowered. Next, another embodiment will be described with reference to FIGS. 5 to 8. In the system shown in FIG. 1, the inside of the large-diameter outer tube unit 1 is divided into a plurality of partitioned spaces 10 by the partition plates 7 and 9 superposed at a small gap, and each pair of adjacent partitioned spaces 10 communicates via the inner space of the inner tube 2 and the holes 2' formed in the upper and lower walls of the inner tube 2. It takes, therefore, a long time to evacuate the gas in each partitioned space from the vacuum exhaust port D and obtain a predetermined vacuum degree, when the inside of the large-diameter outer tube unit 1 is evacuated at the initial running stage. FIG. 5 is a schematic cross sectional view of a large-diameter outer tube unit capable of increasing an evacuation speed, according to another embodiment. When the inside of the large-diameter outer tube unit 1 is to be evacuated, the partition plates 7 are driven by a driver 30 to move them in the axial direction of the large-diameter outer tube unit and broaden a gap between the partition plates 7 and 9. In this manner, the evacuation speed can be increased. The detailed structure of the large-diameter outer tube unit of this embodiment will be described with reference to FIGS. 6 to 8. FIG. 6 is a vertical cross sectional view of the large-diameter outer tube unit 1 taken along the center axis of the unit 1, and FIG. 7 is a cross sectional view taken along one-dot chain line C--C of FIG. 6. As shown in FIG. 6, the partition plates 7 are coupled together by a bolt 8. Two brackets 31 are mounted on the lower portion of each partition plate 7. Each bracket 31 has a roller 32 mounted rotatively. FIG. 8 is a perspective view showing the bracket 31 and roller 32. As shown in FIG. 7, the roller 32 becomes in contact with the inner circumference of the large-diameter outer tube unit 1 to movably support the partition plate in the axial direction. As the roller 32 rolls on the inner circumference of the large-diameter outer tube unit 1, the partition plate 7 can move in the axial direction. The driver 30 for moving the partition plates 7 has a similar structure to those of the drivers 6.sub.1 and 6.sub.2 of the inner tube 2 of the first embodiment. Specifically, the driver 30 is constituted of: a bearing case 35 with an internal linear guide bearing 34; a linear actuator 36 fixed to the bearing case 35; a coupling shaft 37 coupled to the outermost partition plate 7; a vacuum bellows 38 for vacuum sealing the space between the coupling shaft 37 and bearing case 35; and a coupling plate 39 for coupling the actuator 36 and coupling shaft 37. The bearing case 35 of the driver 30 is mounted on a flange 5' of the large-diameter outer tube unit 1. The linear actuator 36 has a function of making the motion of the partition plates stop at opposite ends of a motion stroke and a function of generating an electric interlock signal, which indicates the operating status of the beam line. In operation, prior to evacuating the inside of the large-diameter outer tube unit 1, the linear actuator 36 is driven to move the coupling shaft to the left as viewed in FIG. 6. The partition plates 7 therefore move to the left and a space to a corresponding partition plate 9 mounted on the outer circumference of the inner tube 2 is broadened as shown in FIG. 5. In this state, the gas in the large-diameter outer tube unit 1 is discharged from the vacuum exhaust port D, so that the vacuum degree of the inside of the large-diameter outer tube unit 1 can be set to an operating value in short time. After the vacuum degree of the inside of the large-diameter outer tube unit 1 is set to the operating value, the linear actuator 36 is again driven to move the coupling shaft to the right as viewed in FIG. 5 and set each partition plate 7 near to the corresponding partition plate 9. In a state that the partition plate is set near to the corresponding partition plate 9 to such an extent as shown in FIG. 1, an exposure process starts. In the above embodiments, since the inner tube 2 used as an envelope of a light beam flux is swung up and down by the drivers 6.sub.1 and 6.sub.2 synchronously with the up/down scan of the X-ray mirror, the opening of the radiated light output frame 3 can be made narrow. Accordingly, as compared to a conventional large opening, the strength of the beryllium thin film 21 is increased so that breakage thereof can be prevented. Even if the beryllium thin film 21 is broken, there is an increased flow resistance of gas because the cross sectional area of the passage from the opening of the radiated light output frame 3 directly to the upstream is made-small. Furthermore, the gas enters each partitioned space 10 from the holes 2' whose total area is larger than the cross sectional area of the passage, and the gas is trapped by the partitioned space 10, so that the essential function of an acoustic delay line can be provided sufficiently. Accordingly, a time taken to reach the high speed shutter valve can be prolonged, and the gas can be prevented from entering the inside of the synchrotron 50 (FIG. 9). In the embodiments shown in FIGS. 1 and 5, the movable partitions 9 are supported by the inner tube 2. In place of the inner tube 2, a solid support member may be used for supporting the movable partitions 9. FIG. 10 is a schematic cross sectional view of a beam line in which movable partition plates 9 are supported by a solid support member 2a. The support member 2a may be only the upper portion, lower portion, or side portion of the inner tube 2 shown in FIG. 4. With this arrangement, the same advantageous effects as the embodiment shown in FIG. 1 can be expected. The present invention has been described in connection with the preferred embodiments. The invention is not limited only to the above embodiments. It is apparent that various modifications, improvements, combinations, and the like can be made by those skilled in the art.
	summary
	abstract	The present invention relates to a top nozzle for a nuclear fuel assembly that has a two-stage elastic section such that a pushing force against the axial movement of the nuclear fuel assembly under normal conditions is optimized and at the same time a suppressing force against a drastic uplifting force of the nuclear fuel assembly under transient conditions is strengthened, and that lowers the elastic coefficients of the springs operating under normal conditions more than those of existing coil springs, thereby providing an optimal pushing force against the nuclear fuel assembly.
	description	This application is a U.S. National Stage Filing under 35 U.S.C. 371 from International Application No. PCT/CN2016/089770, filed on Jul. 12, 2016, and published as WO2017/076057 on May 11, 2017, which application claims the benefit of Chinese Patent Application No. 201510751171.2, filed on Nov. 6, 2015 in the State Intellectual Property Office of China, the disclosures of each of which are incorporated herein by reference in their entirety. Embodiments of the present invention relate to a ray beam guiding device and a ray inspection apparatus having the ray beam guiding device. In existing ray inspection apparatus, an X-ray machine or accelerator is used to generate an X-ray which has a certain emitting solid angle. In order to make the X-ray form a fan-shape ray beam for a scanning inspection, it is often required to take several collimations through slit. In this case, a large amount of scattering rays will be generated in collimators and slit devices, leading to a large loading dose in surroundings. In order to avoid this case from occurring, a ray beam guiding box is usually mounted between a plurality of collimators in the inspection apparatus, so that the scattering rays are trapped and absorbed in the ray beam guiding box, thereby reducing a burden on environmental protection. Since the scattering rays are in disorder, a homogenized and conservative design is generally employed for the ray beam guiding box in order to enable the scattering rays at weak protection positions such as ends or the like to be blocked and absorbed sufficiently, thereby increasing the weight of the ray beam guiding box and the manufacturing cost, and incurring an inconvenient installation, transportation and the like. To this end, in order to address one or more aspects of the above problems, the present disclosure provides an improved ray beam guiding device and a ray inspection apparatus having the ray beam guiding device, in which a fin plate is mounted in a collimator to shield and absorb scattering rays, which is favorable for reducing a thickness of a wall of a ray beam guiding box and reducing an entire weight of the ray beam guiding box. According to one embodiment of the present invention, there is provided a ray beam guiding device for guiding ray beams in a ray inspection apparatus, the ray beam guiding device being provided in a housing of the ray inspection apparatus, two ends of the ray beam guiding device being connected to a front collimator and a rear collimator respectively, the ray beam guiding device comprising a plurality of guiding walls and a guiding cavity surrounded by the guiding walls, wherein the guiding walls are formed of a first material which is capable of absorbing rays or the first material is coated on an inside of the guiding wall, and the guiding cavity has a central axis extending along a direction from the rear collimator to the front collimator, and wherein the ray beam guiding device further comprises at least one fin plate provided in the guiding cavity of the device, the at least one fin plate being configured for blocking and/or absorbing scattered rays. In one embodiment, the ray beam guiding device comprises a rear fin portion provided in an end of the rear collimator located in the guiding cavity, the rear fin portion comprising at least one fin plate. In one embodiment, the ray beam guiding device comprises a front fin portion provided in an end of the front collimator located in the guiding cavity, the front fin portion comprising at least one fin plate. In one embodiment, the fin plate is sized such that most of the scattered rays through the front collimator and/or the rear collimator are blocked by the fin plate. In one embodiment, the fin plate is formed of a second material which is capable of absorbing rays or the second material is coated on a side of the fin plate facing towards the central axis of the guiding cavity, for absorbing the scattered rays through the front collimator and/or the rear collimator. In one embodiment, each fin plate comprises a first portion connected to the front collimator and/or the rear collimator and a second portion extending parallel to the central axis of the guiding cavity. In one embodiment, the front fin portion and/or the rear fin portion comprise a first fin plate and a second fin plate, respectively, and the first fin plate and the second fin plate are symmetrical with respect to the central axis of the guiding cavity. In one embodiment, the front fin portion or the rear fin portion consists of one fin plate located in one side of the central axis of the guiding cavity. In one embodiment, the first material and the second material are the same material. According to another embodiment of the present invention, there is provided a ray inspection apparatus, comprising: a ray source configured to generate rays; a rear collimator configured to process the rays generated by the ray source into a ray beam with a specific shape; a front collimator configured to divide the ray beam penetrating an object to be inspected into a plurality of ray beams; a detector; a ray beam guiding device according to any one of the above embodiments; wherein the ray beam guiding device is arranged between the front collimator and the rear collimator. In solutions of the embodiments of the present invention, the design of the interior of the ray beam guiding device is improved by adding a fin plate on the front and/or rear collimators, so that a large portion of scattered rays from the collimator and the slit device are absorbed by the fin plate, and a small portion of the scattered rays which are not absorbed by the fin plate or the ray scattered by the fin plate in turn will either not be easy to leak due to a large incident angle or not be easy to penetrate the ray beam guiding device due to a low energy of the double scattered ray when the ray strikes on the wall of the ray beam guiding device. Thus, the entire wall thickness of the ray beam guiding device may be reduced, the weight thereof may be reduced and cost performance for environmental protection may be increased. Embodiments of the present invention will be described in detail with reference to drawings, the same elements are denoted by like reference numerals throughout the descriptions. The embodiments described herein are explanatory and illustrative and shall not be construed to limit the present invention. According to a general concept of the present invention, there is provided a ray beam guiding device for guiding a ray beam in a ray inspection apparatus. The ray beam guiding device is provided in a housing of the ray inspection apparatus, and two ends of the ray beam guiding device are connected to a front collimator and a rear collimator, respectively. The ray beam guiding device comprises a plurality of guiding walls and a guiding cavity surrounded by the guiding walls. The guiding wall is formed of a first material which is capable of absorbing rays or the first material is coated on an inside of the guiding wall, and the guiding cavity has a central axis extending in a direction from the rear collimator to the front collimator, and the ray beam guiding device further comprises at least one fin plate provided in the guiding cavity of the ray beam guiding device. In the following detailed description, for easy of explanation, many specific details are described to provide a throughout understanding of the disclosed embodiments. Obviously, one or more embodiments can be implemented without these specific details. In other circumstances, well-known structures and devices are schematically illustrated for simplifying the drawings. FIG. 1 is a schematic view of a ray inspection apparatus. As shown in FIG. 1, the ray inspection apparatus comprises a ray source 1, a rear collimator 2, a ray beam guiding device 3, a front collimator 4 and a detector 5. The ray source 1 may include an X-ray source, a gamma ray source, a neutron source or the like. As an example, the ray source 1 in the embodiment is an X-ray machine or an accelerator which emits an X-ray with a certain emitting solid angle and has a target spot 11. The ray, such as X-ray, emitted from the ray source 1, is processed by the rear collimator 2 next to the ray source 1 into a ray beam with a specific shape, such as a fan shape, a conical shape or the like, according to a specific requirement of a user. The ray beam penetrating an object to be inspected is divided by the front collimator 4 into a plurality of thin ray beams. The detector may be an area-array detector or a linear-array detector. In the illustrated embodiment, the ray beam emitted from the X-ray machine 1 passes through the rear collimator 2 and the front collimator 4 to form a fan-shaped beam which is located in one plane with the linear-array detector 5 behind a channel. Further, a ray beam guiding device 3 is provided between the rear collimator 2 and the front collimator 4, for blocking and absorbing scattered rays from the front and rear collimators and/or a slit device, thereby reducing a radiation protective burden of the housing. In the embodiment, the ray beam guiding device is formed as a form of ray beam guiding box. Further, FIG. 2 is a schematic view of a ray beam guiding device according to an embodiment of the present invention. As shown in FIG. 2, the ray beam guiding device 3 is provided in a housing of the ray inspection apparatus, and two ends of the ray beam guiding device 3 are connected to the front collimator 4 and the rear collimator 2, respectively. The ray beam guiding device 3 comprises a plurality of guiding walls 31 and a guiding cavity 32 surrounded by the guiding walls 31. The guiding wall 31 is formed of a first material which is capable of absorbing rays. In one embodiment, the first material may be coated on an inside of the guiding wall 31, and the first material may be a material with high density, such as Pb. As shown in FIG. 2, the guiding cavity 32 has a central axis 33 extending along a direction from the rear collimator 2 to the front collimator 4, and the central axis 33 may pass through slits of the rear collimator 2 and the front collimator 4, extending in a lateral direction as shown in FIG. 2. The ray beam guiding device 3 further comprises at least one fin plate provided in the guiding cavity 32 of the device 3. The at least one fin plate is not necessary to be designed to have a large length and thickness, but may be designed so that a large portion of scattered rays from the collimators and the slit device are absorbed by the fin plate, while a small portion of the scattered rays which are not absorbed by the fin plate or rays scattered by the fin plate in turn will either not be easy to leak due to a large incident angle or not be easy to penetrate the ray beam guiding device due to a low power of the double scattered ray when the rays strike on the wall of the ray beam guiding device. In other words, the fin plate is sized so that most of the scattered rays through the front collimator and/or the rear collimator are blocked by the fin plate. In the embodiment illustrated in FIG. 2, the ray beam guiding device 3 comprises a rear fin portion 6 at the rear collimator 2 and a front fin portion 7 at the front collimator 4. FIGS. 3 and 4 are enlarged views showing the rear fin portion 6 and the front fin portion 7, respectively. As shown in FIG. 3, the rear fin portion 6 comprises a first fin plate 61 and a second fin plate 62. The first fin plate 61 comprises a first portion 611 connected to the rear collimator 2 and a second portion 612 extending parallel to the central axis 33 of the guiding cavity. The second fin plate 62 comprises a first portion 621 connected to the rear collimator 2 and a second portion 622 extending parallel to the central axis 33 of the guiding cavity. Specifically, the first portion 611 of the first fin plate 61 and the first portion 621 of the second fin plate 62 are secured onto one end of the rear collimator 2 via screws, respectively. Similarly, as shown in FIG. 4, the front fin portion 7 comprises a first fin plate 71 and a second fin plate 72. The first fin plate 71 comprises a first portion 711 connected to the front collimator 4 and a second portion 712 extending parallel to the central axis 33 of the guiding cavity. The second fin plate 72 comprises a first portion 721 connected to the front collimator 4 and a second portion 722 extending parallel to the central axis 33 of the guiding cavity. Specifically, the first portion 711 of the first fin plate 71 and the first portion 721 of the second fin plate 72 are secured onto one end of the front collimator 4 via screws, respectively. The fin plates 61, 71, 62 and 72 each may be sized so that most of the scattered rays through the front collimator 4 and/or the rear collimator 2 are blocked by the respective fin plates. In the illustrated embodiment, the first fin plates 61, 71 and the second fin plates 62, 72 are symmetrical with respect to the central axis 33 of the guiding cavity, respectively. In one embodiment, the dimensions (including length, thickness, etc.) of the fin plates 61, 71, 62, 72 may be different from each other. Further, the fin plates each may be formed of a second material which is capable of absorbing rays, or the second material is coated on a side of each of the fin plates facing towards the central axis 33 of the guiding cavity, for absorbing the scattered rays through the front collimator 4 and/or the rear collimator 2. For easy of manufacturing, the second material may be the same as the first material. For example, the fin plates each may be formed of a material with high density (such as Pb), or the fin plates each may be formed of stainless steel and then a Pb layer may be coated on the stainless steel plate by means of adhesion or the like. As shown, scattered rays 9 of an initial ray beam 8 through the slit device of the rear collimator 2 are blocked and/or absorbed by the fin plates 61, 71. Rays 9′, which are not blocked or absorbed, or are scattered by the fin plate in turn, have a large incident angle and a low energy when they reach the ray beam guiding box 3, so that the leakage dose is very low after they penetrate the ray beam guiding box 3. Similarly, when the initial ray beam 8 reaches the front collimator 4, most of the initial ray beam is blocked and scattered by the front collimator 4 while a small portion of the initial ray beam radiates through the slit, then most of the scattered rays are blocked and/or absorbed by the fin plates 71, 72. Rays 9′, which are not blocked or absorbed, or are scattered by the fin plate in turn, have a large incident angle and a low energy when they reach the ray beam guiding box 3, so that the leakage dose is very low after they penetrate the ray beam guiding box 3. Thus, an effective suppression and absorption to the scattered rays is increased, an entire thickness and a weight of the ray beam guiding box is reduced, and a manufacturing cost as well as installation and transportation difficulty are reduced. In the illustrated embodiment, the ray beam guiding device comprises two fin portions, i.e. the front fin portion and the rear fin portion, and the front fin portion and the rear fin portion each comprises two fin plates positioned at upper and lower sides of the central axis 33 respectively. However, in another embodiment, the ray beam guiding device may comprise only one fin portion/fin plate at one side of the ray beam guiding device, and the fin portion may also comprise only one fin plate positioned at one side of the central axis 33 of the guiding cavity. The purpose, technical solutions and advantages of the present invention are further explained in detail from the above specific embodiments. It should be appreciated that the above description is only used as the specific embodiments of the present invention and is not used to limit the present invention. Any modification, substitute and change thereto without departing from the principle and spirit of the present invention shall be included in the scope of present invention.
	summary
045256292	claims	1. A deflective focusing system for a charged particle beam comprising: a magnetic lens for focusing a charged particle beam; a plurality of rings made of magnetic material arranged substantially concentric with said magnetic lens inside of said magnetic lens, said rings being arranged dividedly in the direction of the central axis of said magnetic lens so as to form a predetermined magnetic focusing field distribution; and a one-stage electrostatic deflector having a plurality of deflection electrodes which are divided in a circumferential direction of said magnetic lens, are arranged substatially concentric with said magnetic lens inside of said magnetic lens and are extended in the direction of said central axis so as to form a predetermined electrostatic deflection field distribution, the charged particle beam passing through said concentrically arranged deflection electrodes to be deflected in accordance with a voltage applied to said deflection electrodes. 2. A deflective focusing system for a charged particle beam as claimed in claim 1, further comprising ring-like grounding electrodes which are disposed substantially concentric with said magnetic lens on the object and image plane sides of said electrostatic deflector along the passage of said charged particle beam. 3. A deflective focusing system for a charged particle beam as claimed in claim 2, wherein ring-like spacers made of non-magnetic material and having substantially the same diameter as said ring are inserted between said rings, so that the magnetic focusing field distribution is adjusted by the thicknesses of said rings in the direction of said central axis and the thicknesses of said ring-like spacers. 4. A deflective focusing system for a charged particle beam as claimed in claim 2 or 3, wherein a gap for adjusting the electrostatic deflection field is provided between said ring-like grounding electrodes and said electrostatic deflector, so that said electrostatic deflection field distribution is adjusted in accordance with the length of said gap. 5. A deflective focusing system for a charged particle beam as claimed in claim 4, wherein the inner diameter of said ring-like grounding electrode is more reduced than the inner diameter of said deflection electrode to have an abrupt fringe in the field distribution. 6. A deflective focusing system for a charged particle beam as claimed in claim 4, wherein said electrostatic deflector has the end portion on said image plane side shifted from the end portion of said ring on said image plane side toward said object plane side in the direction of said central axis. 7. A deflective focusing system for a charged particle beam as claimed in claim 2, wherein said electrostatic deflector has the inner diameter substantially equal to that of said ring-like grounding electrode. 8. A deflective focusing system for a charged particle beam as claimed in claim 7, further comprising a case having a first room, which is formed by said case and a sealing member made of nonmagnetic material, for accommodating the coil of said magnetic lens, a second room, which is formed by said sealing member, said electrostatic deflector and said grounding electrodes, for accommodating said rings, and a third room whose boundary is defined by said electrostatic deflector and said grounding electrodes and through which said charged particle beam passes, said sealing member sealing said second room vacuum-tightly and fixing said rings at predetermined positions. 9. A deflective focusing system for a charged particle beam as claimed in claim 8, wherein said case has a flange extended inwardly to cover said ring-like grounding electrode disposed on said object plane side of said electrostatic deflector. 10. A deflective focusing system for a charged particle beam as claimed in claim 2, wherein said ring-like grounding electrode on said image plane side has a flange for supporting said electrostatic deflector. 11. A deflective focusing system for a charged particle beam as claimed in claim 6, wherein a stigmator coil is wound on the periphery of a portion of said electrostatic deflector which is protruded from said rings toward said object plane side. 12. A deflective focusing system for a charged particle beam as claimed in claim 11, wherein a dynamic focusing coil is wound around said stigmator coil. 13. A deflective focusing system for a charged particle beam as claimed in claim 1 or 2, further comprising a shielding electrode around the outer periphery of said electrostatic deflector. 14. A deflective focusing system for a charged particle beam as claimed in claim 2, wherein said electrostatic deflector has the end portion on said image plane side shifted from the end portion of said ring on said image plane side toward said object plane side in the direction of said central axis. 15. A deflective focusing system for a charged particle beam as claimed in claim 14, wherein a stigmator coil is wound on the periphery of a portion of said electrostatic deflector which is protruded from said rings toward said object plane side. 16. A deflective focusing system for a charged particle beam as claimed in claim 15, wherein a dynamic focusing coil is wound around said stigmator coil.
	description	The present invention relates to an electron beam sterilizer which sterilizes vessels being conveyed by irradiation with an electron beam. An electron beam sterilizer which sterilizes vessels being conveyed by irradiation with an electron beam is known in the art (see Japanese Laid-Open Patent Application No. 11-137645 or No. 11-1212, for example). “Electron beam sterilizer for empty plastic vessels” according to the invention disclosed in the first cited Application comprises a feeder mechanism which feeds empty plastic vessels, a turning mechanism, an electron beam irradiation mechanism, and a discharge mechanism which discharges empty plastic vessels subjected to the electron beam irradiation. The purpose of the turning mechanism is to secure empty plastic vessels fed from the feeder mechanism by applying a vacuum suction thereto and to cause a turning motion and a revolving motion about individual axes of the empty plastic vessels while they are secured, and the turning mechanism comprises a plurality of turntables on which the empty plastic vessels are secured and a turntable drive. The electron beam irradiation mechanism sterilizes the empty plastic vessels by irradiating them with the electron beam from the inner periphery of and in synchronism with the turning mechanism. In the arrangement of the cited invention, the electron beam irradiation mechanism includes electron beam irradiators which are equal in number to the number of turntables disposed on the turning orbit of the turning mechanism. “Sterilizer for vessels utilizing electron beam” disclosed in the second sited Application comprises an electron beam generator disposed in a vertical position within a sterilization processing chamber, and vessel conveying means extending from the inlet to the outlet of the sterilization processing chamber. There is disposed revolution imparting means which causes a vessel to revolve at a location in front of the electron beam generator. According to the sterilizer shown in the second citation, vessels proceed through the sterilization processing chamber on vessel conveying means (air conveyor), and are subject to a revolution as they reach the revolution imparting means. Vessels which are conveyed while revolving pass an irradiation window of the electron beam generator while revolving about their axes. Vessels which are successively conveyed in this manner are sterilized by irradiation with the electron beam as they pass in front of the irradiation window while being imparted with a revolution by the revolution imparting means, and are subsequently discharged out of the sterilization processing chamber. In the arrangement of the invention disclosed in the first cited Application, there is a need for the provision of as many electron beam irradiators as the number of the turntables on which the vessels are secured, leading to a problem that the arrangement is expensive and bulky as a whole. By contrast, in the arrangement of the invention disclosed in the second cited Application, the electron beam irradiator is provided at a single location, but the revolution is imparted to the vessels for irradiating the electron beam around the full periphery of the vessels. The arrangement that the vessels are caused to revolve in the course of the air conveyance leads to a problem that a high speed operation is inhibited. Accordingly, it is an object of the present invention to provide an electron beam sterilizer which enables a sterilization around the full periphery of vessels with a single electron beam irradiator to simplify the arrangement and to achieve a cost reduction while allowing a high speed operation to be achieved. Above object is accomplished by providing an electron beam sterilizer which sterilizes vessels being conveyed by irradiation with an electron beam and which comprise vessel holder means including a pair of holders which carry two vessels in vertical alignment, transfer means on which a plurality of vessel holder means are mounted at an equal interval and are cyclically transferred, inversion means for inverting the vessel holder means by rotating it about an axis parallel to a direction in which the transfer means advances, and an electron beam irradiator capable of irradiating the electron beam across the upper and the lower end of the two vessels which are carried in vertical alignment by the vessel holder means, the arrangement being such that a transfer path of the transfer means extends from a vessel feed position to a vessel discharge position and includes an inversion interval where the inversion means inverts the vessel holder means and an upright transfer interval where the vessels in vertical alignment are transferred in an upright position, the electron beam irradiator having an electron beam irradiation position which is chosen within the upright transfer interval, the vessels which are fed through the vessel feed position being discharged at the vessel discharge position after passing through the electron beam irradiation position and the inversion interval twice. Several embodiments of the present invention shown in the drawings will now be described. Vessels 4 such as PET bottles (see FIGS. 2-5 which will be described later) which are conveyed by an air conveyor 2, representing vessel feed means, are carried by grippers 8 (see FIG. 4) of a feed gripper wheel 6 and are rotatively conveyed to be fed to an electron beam sterilizer 10 (a feed position where vessels 4 are fed from the feed gripper wheel 6 to the electron beam sterilizer 10 is indicated by a character A in FIG. 1). The electron beam sterilizer 10 comprises a plurality of vessel holder means 14 which are mounted around the outer periphery of a revolving body (transfer means) 12 at an equal circumferential spacing, and vessels 4 which are fed from the feed gripper wheel 6 are carried by the vessel holder means 14. As the revolving body 12 rotates, the vessel holder means 14 are rotatively transferred, thus rotatively conveying the vessels 4 which are carried thereby. Inversion means 16 which inverts the vessel holder means 14 which carries the vessels 4 is provided on a path of conveyance of the vessels 4, and accordingly, a vessel 4 which is fed in an erect position (where a mouth 4a of the vessel 4 is directed upward) can be inverted by the inversion means 16 to its inverted position. Subsequently, after the vessel 4 is rotatively conveyed in its inverted position, it is inverted again into the erect position by the inversion means 16, and then delivered to a gripper 20 of a discharge gripper wheel 18 (see FIG. 5) to be discharged and fed to a succeeding downstream step by an air conveyor 22. In this embodiment, a vessel 4 is handed from the gripper 8 of the feed gripper wheel 6 to the vessel holder means 14 of the electron beam sterilizer 10 at a vessel feed position (indicated by position A in FIG. 1), inverted twice during substantially two revolutions of the revolving body 12, and handed to the gripper 20 of the discharge gripper wheel 18 at a vessel discharge position (indicated by position B in FIG. 1) to be discharged by the air conveyor 22. The electron beam sterilizer 10 comprises an irradiation unit 24 which is disposed toward the outer periphery of the sterilizer at a location which is slightly downstream of the vessel feed position A as viewed in the direction in which the vessel 4 is conveyed (see FIGS. 1 and 3). As will be described later, the vessel holder means 14 includes a pair of upper and lower vessel holders 26, 26, and the irradiation unit 24 has a sufficient length which permits the pair of upper and lower vessels 4 which are carried in upright position by the pair of vessel holders 26 to be simultaneously irradiated by the electron beam. The arrangement of the electron beam sterilizer 10 will now be described in detail with reference to FIGS. 1 to 5. A plurality of vessel holder means 14 are disposed around the outer periphery of the revolving body 12 (not entirely shown) at an equal circumferential spacing. As shown in FIG. 2, channel-shaped mounting members 50 are mounted around the outer periphery of the revolving body 12 at an equal circumferential spacing and horizontally secured with an opening 50a of the mounting member directed radially outward of the revolving body 12, and the vessel holder means 14 are mounted on each of the plurality of mounting members 50. Each vessel holder means 14 includes a pair of vessel holders 26, 26. While the vessel holder means 14 used in this embodiment is constructed in the similar manner as the vessel holder means disclosed in Japanese Laid-Open Patent Application No. 2003-192095 filed by the present applicant, it may also be constructed in a different manner. In the present embodiment, each of the pair of vessel holders 26, 26 are constructed in the identical manner, and accordingly, corresponding parts are designated by like characters. A pair of parallel leaf springs (support plates) 56 which are centrally secured to the opposite ends of a rod 54 are rotatably supported in the opening 50a of the mounting member 50. As mentioned previously, the mounting member 50 is fixedly mounted around the outer periphery of the revolving body 12 so as to be directed in the radial direction, and accordingly, the rod 54 which is supported across the opening 50a is directed in the tangential direction of the revolving body 12. In addition, a pair of springs 58 are connected across the both leaf springs 56 on the opposite sides of the rod 54 to urge the ends 56a of the both leaf springs 56 toward each other normally. In addition, a pair of holding plates 60 which oppose each other are mounted on the respective ends 56a (upper and lower end as viewed in FIG. 2) of the pair of leaf springs 56, and define the vessel holders 26, 26. The opposing faces of the holding plates 60 are each centrally formed with an arcuate concave surface 60a which abuts against a neck of the vessel 4 (which is a portion 4c disposed below a flange 4b) and are each formed with guide surfaces 60b which extend outwardly to be further spaced from each other at locations which are disposed on the opposite sides of the concave surface 6Oa. The holding plates 60 on the opposite sides which define the vessel holders 26, 26 are secured to the ends 56a of the pair of leaf springs 56 and are attracted toward each other by the springs 58, whereby the vessel 4 is carried as the portion 4c located below the flange 4b moves between the guide surfaces 60b of the holding plates 60 which are then disposed on the opposite sides to urge the holding plates 60 away from each other to allow the portion 4c to be snapped into the space formed by the arcuate concave surfaces 60a of the holding plates 60, which are then caused to spring back under the resilience of the springs 58. It will be seen that because the guide surfaces 60b are formed on each holding plate 60 on the opposite sides of the arcuate concave surface 60a, an access into the space defined between the opposing arcurate concave surfaces 60a can be achieved through the guide surfaces 60b on either side. The leaf springs 56, the springs 58 and the vessel holders 26, 26 formed by a set of holding plates 60 constitute together the vessel holder means 14. In this embodiment, the vessel holder means 14 is constructed such that the vessel holders 26, 26 are disposed at positions which are symmetrical with respect to the center axis of the central rod 54 or an axis O1 which is disposed tangentially of the revolving body 12 to allow two vessels 4 to be carried in vertical alignment. An engaging member 64 which is formed in its opposite ends with U-shaped recesses 64a adapted to engage a guide rail 62, which will be described later, is secured to the central portion of the rod 54 as viewed in the length direction thereof. As illustrated in FIGS. 2 to 5, the engaging member 64 is mounted as skewed with respect to the leaf springs 56 located on the opposite sides. On the other hand, a guide rail 62 is disposed adjacent to and around the outer periphery of the revolving body 12 for engaging the U-shaped recess 64a in the engaging member 64 to rotate the vessel holder means 14 through about 180° about the axis O1 of the rod 54 so as to interchange upper and lower ones of the pair of vessel holders 26, 26 as the revolving body 12 revolves. The guide rail 62 constitutes the inversion means 16. As illustrated in FIGS. 4 and 5, it is supported by guide rail support means 63a mounted on a stationary stanchion 63 which is disposed externally of the revolving body 12 so as to avoid an interference with the vessels 4 or the vessel holder means 14. The distal end 62a (see FIGS. 1 and 2) of the guide rail 62 which is positioned over the feed gripper wheel 6 (which is located to the left as viewed in FIG. 4) engages the U-shaped recess 64a in the engaging member 64 at the vessel feed position A (see FIGS. 1 and 4) where the vessels 4 are fed from the feed gripper wheel 6 to the electron beam sterilizer 10. Toward the vessel discharge position B where the vessels 4 are discharged from the electron beam sterilizer 10 to the discharge gripper wheel 18, the guide rail 62 gradually increases its elevation and enters inside the revolving body 12 and then gradually decreases its elevation. In other words, the location of the guide rail 62 is twisted around the position of the rod 54 to rotate through 180°. The vessel holder means 14 and the vessels 4 shown in broken lines in FIG. 4 indicate their conditions in the course of such inversion. As mentioned previously, when the position is changed through 180°, the two vessels 4 assume completely interchanged positions as far as upper and lower vessels are concerned. In the present embodiment, a path section from a position C which is located downstream of the electron beam irradiation position E where the electron beam irradiation means 24 is disposed to a position D which is located one-half perimeter ahead in FIG. 1 represents an inversion interval where the guide rail 62 causes an inversion of the vessel holder means 14 and the two vessels 4 which are carried by the holders 26, 26. Along a path section from the vessel discharge position B to the vessel feed position A, only the upper vessel holder 26 carries the vessel 4. Accordingly, a path section from the position D where the inversion interval ends to the vessel discharge position B and from the vessel feed position A to the position C where the inversion interval begins represents an upright transfer interval where two vessels carried in vertical alignment are transferred while their axes are maintained in the vertical direction. The guide rail 62 and the engaging member 64 of the vessel holder means 14 define the inversion means 16 which causes an inversion of the vessel holder means 14 by rotating it about the tangential axis O1 of the revolving body 12. The operation of the electron beam sterilizer 10 constructed in the manner mentioned above will now be described. Vessels 4 which are conveyed in suspended form by the vessel feed means (air conveyor) 2 are carried by the gripper 8 of the feed gripper wheel 6 to be rotatively conveyed. In the present embodiment, the gripper 8 of the feed gripper wheel 6 carries a portion 4d of the vessel 4 which is located above the flange 4b formed around the neck of the vessel (see FIG. 4). As the vessel 4 carried by the gripper 8 of the feed gripper wheel 6 approaches the feed position A to the electron beam sterilizer 10, the portion 4c of the vessel 4 which is disposed below the flange 4b is inserted between the opposing holding plates 60 of one of the pair of upper and lower vessel holders 26, 26 which is then disposed downward (see the lower vessel holder 26 shown in FIG. 4 indicating the vessel feed position A) of the vessel holder means 14 mounted on the channel-shaped mounting members 50 which are secured to the revolving body 12 (transfer means of the electron beam sterilizer 10) at an equal circumferential spacing. It is to be noted that the pair of vessel holders 26, 26 are disposed in vertical alignment as shown in FIG. 4 at the feed position A from the feed gripper wheel 6 to the electron beam sterilizer 10. Since the both holding plates 60 are secured to the leaf springs 56 and are attracted toward each other by the springs 58, the vessel 4 carried by the gripper 8 of the feed gripper wheel 6 passes between the guide surfaces 60b of the both holding plates 60 by spreading them apart to be fitted between the arcuate concave portions 60a. At the start of the operation of the electron beam sterilizer 10, only the lower holder 26 shown in FIG. 4 carries the vessel 4. On the other hand, the engaging member 64 which is integral with the vessel holder means 14 has its downwardly directed U-shaped recess 64a engaged with the distal end 62a of the guide rail 62. At this point in time, the upwardly directed U-shaped recess 64a is engaged by the distal end 62b of the guide rail 62 (see FIGS. 1 and 4). As the feed gripper wheel 6 and the revolving body 12 of the electron beam sterilizer 10 both rotate and the gripper 8 and the vessel holder 26 of the vessel holder means 14 move away from each other, the vessel 4 is disengaged from the gripper 8 of the feed gripper wheel 6 and is carried by the vessel holder 26 to be rotatively conveyed as the revolving body 12 of the electron beam sterilizer 10 revolves. It will be noted that a path section short of the inversion start position C which is located downstream of the vessel feed position A to the electron beam sterilizer 10 represents the upright transfer interval, and the electron beam irradiation position E is chosen to be within this interval. The irradiation unit 24 of the electron beam irradiator is disposed so as to correspond to the electron beam irradiation position E and is directed radially inward of the revolving body 12 which forms the electron beam sterilizer 10 (see FIGS. 1 and 3), thus irradiating the electron beam across the upper and the lower end of the passing vessel 4. During this irradiation (the first irradiation with respect to the vessel 4), nearly one-half of the surface of the vessel 4 carried by the lower holder 26 of the vessel holder means 14 which is directed radially outward of the revolving body 12 is sterilized (specifically, hatched portion of the vessel 4 carried by the lower holder 26 as shown in FIG. 3 is sterilized). As the revolving body 12 continues to rotate, the vessel holder means 14 passes the frontage of the irradiation unit 24, and when it enters the inversion interval C-D, the U-shaped recess 64a in the engaging member 64 moves upward and radially inward in conformity to the configuration of the guide rail 62, whereby the vessel holder means 14 is rotated to interchange the two vessel holders 26, 26 as far as the upper and the lower one are concerned. When the two vessel holders 26, 26 rotate through 180° and are interchanged as far as the upper and the lower holder are concerned, the vessel which is carried by one of the vessel holders located downward as viewed in FIG. 4 is inverted from its lower, erect position to an upper inverted position. During the time the vessel holder means 14 passes through the inversion interval C-D, the upper and the lower holder 26, 26 rotate through 180° about the rod 54, whereby the vessel which was previously carried by the lower holder 26 to maintain an erect position now assumes a completely inverted position (see the upper vessel 4 shown in FIG. 5). Subsequently, the revolving body 12 of the electron beam sterilizer 10 further rotates to reach the vessel discharge position B. The discharge gripper wheel 18 including a gripper 20 is disposed at the vessel discharge position B, but this gripper 20 is located at an elevation to grip the vessel 4 carried by the lower holder 26, and at the present moment which immediately follows the start of the operation, the lower vessel hold 26 carries no vessel 4, and accordingly, the vessel holder means 14 passes through the discharge position B without any effect. When the vessel holder means 14 again reaches the vessel feed position A, the gripper 8 of the feed gripper wheel 6 which receives the vessel 4 from the air conveyor 2 to convey it rotatively acts to hand the next vessel 4 to the empty holder 26 of the vessel holder means 14 which now assumes a lower position. At this point, the vessel holder means 14 is in a condition such that the upper and the lower vessel holder 26, 26 each carries the vessel 4. At this time, the two vessels 4 are disposed in vertical alignment with the vessel 4 carried by the lower holder 26 assuming an erect position where the mouth faces upward and the vessel 4 carried by the upper holder 26 assuming an inverted position where the mouth faces downward, as shown in FIG. 4. The vessel holder means 14 carrying the two vessels 4 in vertical alignment reaches the electron beam irradiation position E where the irradiation unit 24 of the electron beam irradiator is disposed to be subject to the irradiation of the electron beam. The vessel 4 which has been subjected to be irradiation of the electron beam by the irradiation unit 24 during the previous run is now inverted about the rod 54 which is directed in the tangential direction of the revolving body 12 during the inversion interval C-D, and accordingly, the irradiated portion now assumes a position located to the right, as viewed in FIG. 3. Thus, the vessel 4 which passes the electron beam irradiation position E for the second time (or the upper vessel 4 as viewed in FIG. 3) is oriented such that the portion which has not been subject to the irradiation of the electron beam during the previous run (or the portion disposed to the left as viewed in FIG. 3) is directed toward the electron beam irradiator 24, and thus, this remaining portion of this vessel 4 and one-half of the vessel 4 carried by the lower vessel holder 26 which is located toward the electron beam irradiator 24 are subject to the irradiation of the electron beam which takes place across the upper and the lower end of these two vessels 4 to be sterilized. It will be seen that the vessel 4 which is carried by the upper vessel holder 26 is subject to the irradiation of the electron beam two times, namely, when it is located downward and when it is inverted and then located upward, and thus it follows that the entire outer peripheral surface has been sterilized. After passing through the electron beam irradiation position E, the vessel holder means 14 undergoes the upright transfer interval which extends from the vessel feed position A to the inversion start position C, and then the inversion interval C-D again, whereby the inversion takes place in accordance with the locus of the guide rail 62. Specifically, the holder 26 which assumed the upper position moves to its lower position while the holder 26 which assumed a lower position moves to its upper position, the vessel having its entire surface sterilized is carried in its lower, erect position while the vessel 4 having one-half surface which is located radially outward of the revolving body 12 assumes an inverted position with the sterilized surface directed radially inward. When the vessel holder means 14 passes through the inversion interval C-D and comes to the vessel discharge position B, the vessel 4 carried by the lower vessel holder 26 is now carried by the gripper 20 of the discharge gripper wheel 18 to be taken out of the vessel holder 26 and then rotatively conveyed to be discharged onto the air conveyor 22. The vessel holder means 14 travels while only the upper vessel holder 26 carries the vessel 4 in a path section from the vessel discharge position B to the vessel feed position A, where the vessel 4 is handed to the lower vessel holder 26 from the gripper 8 of the feed gripper wheel 6. In this manner, the single vessel 4 is conveyed so that it passes through the electron beam irradiation position E and the inversion interval twice as the revolving body 12 of the electron beam sterilizer 10 revolves, and is subject to the irradiation of the electron beam by passing the frontage of the irradiation unit 24 of the electron beam irradiator under two conditions that it is carried by the lower vessel holder 26 in an erect position and carried by the upper vessel holder 26 of the vessel holder means 14 in an inverted position. As a consequence, only the single electron beam irradiator 24 is provided, the entire outer peripheral surface of the vessel 4 can be completely sterilized while it is continuously conveyed. In addition, this allows a reduction in the size and the cost of the sterilizer while enabling a high speed operation. It is to be noted that while the electron beam irradiation position E is located between the vessel feed position A and the inversion start position C, it is not limited to such position, but may be chosen to be located within the upright transfer interval from the position D where the inversion interval ends to the vessel discharge position B. FIG. 6 is a longitudinal section of an electron beam sterilizer according to a second embodiment, taken at an electron beam irradiation position E where an electron beam irradiator is disposed, in a manner corresponding to FIG. 3 for the first embodiment. This embodiment differs from the first embodiment only in respect of the construction of the vessel holder means and is similar in other respects. Accordingly, only the difference will be described, and remaining parts will not be described while using similar characters for the remaining parts. Vessel holder means 114 of this embodiment comprises vessel holders 126, 126 formed by vacuum tables and connected to the opposite ends of a pair of parallel support plates 156 which are centrally secured to the opposite ends of a rod 154. The external surfaces of the both vacuum tables 126, 126 are formed with depressions 126a, 126a which substantially conform to the configuration of the bottom surface of vessels 4, 4 to be carried. The depressions 126a, 126a are centrally formed with vacuum openings 126b, 126b which are connected to a vacuum source, not shown. In this embodiment, the vessel feed means (conveyor) which conveys the vessels 4 is a top chain conveyor on which the vessels 4 are upstanding while they are conveyed, and the vessels are fed to the electron beam sterilizer 10 through a star wheel. The vessel carrying surfaces of the conveyor and the star wheel are substantially aligned with the upper surface of the vacuum table 126 of the vessel holder means 114, which represents the upper vessel holder, and the vessels 4 are fed to and discharged from the upper vacuum table 126. The vessels 4 which are conveyed by the conveyor are handed through the feed star wheel to the upper vacuum table 126 of the vessel holder means 114 contained in the electron beam sterilizer 10. The vessel 4 which is placed on the vacuum table 126a is carried by a suction applied through the vacuum opening 126b. When the vessel holder means 114 reaches the electron beam irradiation position E located in front of an irradiation unit 24 of the electron beam irradiator while carrying the vessel 4 on the upper vacuum table 126, the vessel 4 is subject to the irradiation of the electron beam which is directed from the radially outside of the revolving body 12, whereby substantially one-half of the external surface is sterilized. A hatched part of the vessel 4 carried by the upper vacuum table 126 as shown in FIG. 6 represents a portion which is sterilized by the irradiation with the electron beam. When the vessel holder means 114 travels rotatively as the revolving body 12 revolves and enters an inversion interval C-D to be inverted in the similar manner as in the first embodiment. In this embodiment, the vessel 4 which is externally fed is carried by the upper vacuum table 126, and accordingly, when it is inverted, it is then conveyed in its inverted position by having its bottom surface sucked by the lower vacuum table 126. When it passes through the inversion interval C-D, then the discharge position B to reach the feed position A, the next succeeding vessel 4 is fed to the vacuum table 126 which then assumes the upper position. Subsequently when the vessel holder means 114 reaches the electron beam irradiation position E located in front of the irradiation unit 24 of the electron beam irradiator, the surfaces of the vessels 4 which are carried by the upper and the lower vacuum table 126, 126 which are located toward the irradiation unit 24 are sterilized by irradiation with the electron beam. The vessel 4 carried by the lower vacuum table 126 is subject to the second irradiation while the vessel 4 carried by the upper vacuum table 126 is subject to the first irradiation of the electron beam (hatched portions of the two upper and lower vessels 4 shown in FIG. 6 represent portions which are irradiated with the electron beam). In the second embodiment also, the vessels 4 are subject to the inversion about the tangential axis of the revolving body 12 (or the center axis of the rod 154) and are subject to the irradiation with the electron beam from the electron beam irradiator 24 twice at their upper and lower positions in the similar manner as in the first embodiment, whereby the entire outer peripheral surfaces of the vessels 4 can be sterilized while they are continuously conveyed. In the electron beam sterilizer 10 according to each of the embodiments described above, vessel holder means 14, 114 are provided around the revolving body 12 at an equal circumferential spacing to convey rotatively the vessels 4 which are carried by the vessel holder means 14, 114 as the revolving body 12 revolves to perform the inversion of the vessels 4 and the irradiation with the electron beam. However, the transfer means which cyclically performs the transfer of the vessel holder means 14, 114 which carry the vessels 4 is not limited to one which causes a rotating movement along a circular path around the revolving body 12, but may be chosen to achieve a cyclic transfer along any given path. FIG. 7 is a plan view showing an overall arrangement of an electron beam sterilizer 210 according to a third embodiment where a plurality of vessel holder means (not shown) are provided at an equal interval on a chain 274 which is disposed to extend around an upstream circular sprocket 270 and a downstream circular sprocket 272, each vessel holder means carrying two vessels in vertical alignment which are subject to an inversion between upper and lower positions during the time they are cyclically transferred around the both sprocket 270, 272. An electron beam irradiator 224 is disposed on a linear path on which the vessels are conveyed, and an electron beam irradiation position E where the electron beam irradiator 224 is disposed is chosen to be within an upright transfer interval where vessel holder means carrying two vessels in vertical alignment are transferred. An inversion interval where the vessel holder means are inverted is chosen to be anywhere other than the electron beam irradiation position E. The location of the inversion interval may be on a linear conveying part between the both sprockets 270, 272, or may be in an interval where they are rotatively transferred around the sprockets 270, 272. When the inversion interval is chosen to be on the linear path between the sprockets 270, 272, the vessel holder means are rotated about an axis which is parallel to the direction in which the chain advances. When the inversion means is disposed in an interval where the vessels are rotatively transferred around the sprockets 270, 272, the vessel holder means are rotated about an axis which is tangential of the sprockets (revolving bodies) 270, 272, in the similar manner as in the first embodiment. The axis which is tangential to the revolving body is implied by the axis which is parallel to the travelling direction. The inversion means which causes an inversion of the two vessels between upper and lower positions may comprise the guide rail and the engaging member provided on the vessel holder means as in the first embodiment, but may also be constructed otherwise. In this embodiment, vessels which are conveyed by a vessel conveying conveyor 202 are separated into a given interval by an in-feed screw 276, handed to a feed wheel 206 and then fed to an electron beam sterilizer 210. The electron beam sterilizer 210 includes vessel holder means which convey vessels carried by a pair of upper and lower vessel holders. When passing the electron beam irradiation position E, the vessel is subject to the irradiation of the electron beam in its upright position twice, namely, when it assumes a lower position and when it assumes an upper position. Vessels which are carried by the vessel holders and conveyed substantially twice along the circulating path to be subject to the irradiation with the electron beam twice are then handed to a discharge wheel 218 to be discharged from the electron beam sterilizer 210 and then conveyed by a conveyor 222 to a succeeding step. In this embodiment also, the electron beam irradiator 224 disposed at a single location allows the full periphery of the vessel to be sterilized in the similar manner as in the described embodiments, allowing a simplification of the construction of the sterilizer. FIG. 8 is a schematic view showing an arrangement of an electron beam sterilizer 310 according to a fourth embodiment. In this embodiment, a transfer path for the vessel holder means which carry the vessels is different from each of the described embodiments, but in other respects, the arrangement is similar to the previous embodiments, and therefore will not be described. In this embodiment, a sprocket 380 of a large diameter is disposed in opposing relationship with a feed wheel 306 and a discharge wheel 318, and a chain 386 is disposed around the sprocket 380 and two sprockets 382 and 384 of a reduced diameter, and the vessels carried by the two vessel holders of the vessel holder means are cyclically conveyed around the three sprockets 380, 382 and 384. An electron beam irradiator 324 is disposed in an interval between the two sprockets 382, 384 of a reduced diameter where the vessels are linearly conveyed. The electron beam irradiation position E where the irradiation of the vessels with the electron beam takes place by the electron beam irradiator 324 is located in an upright transfer interval where the two vessels carried by the vessel holder means are disposed in an upright position and in vertical alignment, and an inversion interval where an inversion of the vessel holder means between upper and lower positions is chosen at a location other than the electron beam irradiation position E. The inversion interval may be chosen in a linear conveying part where the vessels are linearly conveyed between the sprockets 380, 382, 384, or may be chosen in an interval where the vessels are rotatively conveyed around the sprockets 380, 382, 384. Alternatively, the inversion interval may be chosen to include both the linear conveying path and the rotatively conveying path. In this embodiment also, similar effects and functions are achieved as in the previous embodiments.
	summary
	description	The present disclosure generally relates to a multi-leaf collimator, and more particularly to systems and methods for adjusting a multi-leaf collimator. Radiation therapy has been widely employed in cancer treatment in which ionizing radiation is guided towards a treatment region (e.g., a tumor) of an object. In radiation therapy, high-energy electromagnetic radiation beams and/or particles are delivered for killing or inhibiting the growth of undesired tissue. Generally, it is desirable to delimit the radiation rays so that the radiation dose is maximized in the treatment region and minimized in the healthy tissue of the object. A multi-leaf collimator (MLC) plays an important role in delimiting the radiation rays. An MLC can have a plurality of leaf pairs. Leaves and/or a drive mechanism of the MLC may become damaged by a collision between opposing leaf ends, and thus, care needs to be taken to avoid collisions between opposing leaf ends. To this end, a minimum gap may be maintained between opposing leaves when the leaves move. However, this gap may be undesirable for radiation treatment, because the dose passing through the gap may reach the tissue, resulting in an actual dose higher than planned. Therefore, it is desirable to provide methods and systems for adjusting the MLC of a radiation delivery device, and/or reducing or eliminating an effect of radiation leakage through a leaf gap in radiation with MLC. In one aspect of the present disclosure, a method for adjusting a multi-leaf collimator (MLC) in a treatment process is provided. The MLC may include a plurality of cross-layer leaf pairs each of which includes a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves. The method may be implemented on at least one machine each of which has at least one processor and at least one storage device. The method may include: for each of at least one of the plurality of cross-layer leaf pairs, determining, according to a treatment plan, an effective cross-layer leaf gap to be formed between the first leaf in the first layer and the second leaf in the second layer; causing at least one of the first leaf or the second leaf to move to form the effective cross-layer leaf gap; and causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer. A size of the in-layer leaf gap may be no less than a threshold. In some embodiments, for the each cross-layer leaf pair, the causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer may include: comparing a size of the effective cross-layer leaf gap with 0. In some embodiments, for the each cross-layer leaf pair, the causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer may further include: in response to determining that the size of the effective cross-layer leaf gap is equal to 0, comparing the size of the in-layer leaf gap with the threshold; and in response to determining that the size of the in-layer leaf gap is less than the threshold, causing the in-layer leaf gap to be adjusted to no less than the threshold, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, for the each cross-layer leaf pair, the causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer may further include: in response to determining that the size of the effective cross-layer leaf gap is equal to 0, comparing the size of the in-layer leaf gap with the threshold; and in response to determining that the size of the in-layer leaf gap is less than the threshold, causing the in-layer leaf gap to be adjusted to no less than the threshold and no larger than a second threshold, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, for the each cross-layer leaf pair, the causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer may further include: in response to determining that the size of the effective cross-layer leaf gap is larger than 0, comparing the size of the effective cross-layer leaf gap with the threshold; and in response to determining that the size of the effective cross-layer leaf gap is no larger than the threshold, causing the in-layer leaf gap to be adjusted to no less than the threshold, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, for the each cross-layer leaf pair, the causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer may further include: in response to determining that the size of the effective cross-layer leaf gap is larger than 0, comparing the size of the effective cross-layer leaf gap with the threshold; and in response to determining that the size of the effective cross-layer leaf gap is larger than the threshold, causing the in-layer leaf gap to be adjusted to no less than the effective cross-layer leaf gap, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, for the each cross-layer leaf pair, the causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer may further include: in response to determining that the size of the effective cross-layer leaf gap is larger than 0, comparing the size of the effective cross-layer leaf gap with the threshold; and in response to determining that the size of the effective cross-layer leaf gap is no larger than the threshold, causing the in-layer leaf gap to be adjusted to no less than the threshold and no larger than a second threshold, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, for the each cross-layer leaf pair, the causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer may further include: in response to determining that the size of the effective cross-layer leaf gap is larger than 0, comparing the size of the effective cross-layer leaf gap with the threshold and a second threshold; and in response to determining that the size of the effective cross-layer leaf gap is larger than the threshold but no larger than the second threshold, causing the in-layer leaf gap to be adjusted to no less than the effective cross-layer leaf gap and no larger than the second threshold, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, for the each cross-layer leaf pair, the causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer may further include: in response to determining that the size of the effective cross-layer leaf gap is larger than 0, comparing the size of the effective cross-layer leaf gap with a second threshold; and in response to determining that the size of the effective cross-layer leaf gap is larger than the second threshold, causing the in-layer leaf gap to be adjusted to no less than the effective cross-layer leaf gap, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, the method may further include: causing, based on the effective cross-layer leaf gap, a second in-layer leaf gap to be formed between the second leaf and an opposing second leaf that form a second in-layer leaf pair in the second layer. In some embodiments, the causing, based on the effective cross-layer leaf gap, a second in-layer leaf gap to be formed between the second leaf and an opposing second leaf that form a second in-layer leaf pair in the second layer may include: in response to determining that the size of the effective cross-layer leaf gap is larger than 0, comparing the size of the effective cross-layer leaf gap with the threshold; in response to determining that the size of the effective cross-layer leaf gap is no larger than the threshold, causing the second in-layer leaf gap to be adjusted to no less than the threshold, by causing the opposing second leaf of the second in-layer leaf pair in the second layer to move relative to the second leaf; and causing the in-layer leaf gap to be adjusted to no less than the threshold, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, the causing, based on the effective cross-layer leaf gap, a second in-layer leaf gap to be formed between the second leaf and an opposing second leaf that form a second in-layer leaf pair in the second layer may include: in response to determining that the size of the effective cross-layer leaf gap is larger than 0, comparing the size of the effective cross-layer leaf gap with the threshold; in response to determining that the size of the effective cross-layer leaf gap is larger than the threshold, causing the second in-layer leaf gap to be adjusted to no less than the effective cross-layer leaf gap, by causing the opposing second leaf of the second in-layer leaf pair in the second layer to move relative to the second leaf; and causing the in-layer leaf gap to be adjusted to no less than the effective cross-layer leaf gap, by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf. In some embodiments, the method may further include: for the each cross-layer leaf pair, causing at least one of the in-layer leaf pair in the first layer or the second in-layer leaf pair in the second layer to be adjusted before or during the treatment process by: causing, based on at least one of the in-layer leaf gap or the second in-layer leaf gap, the in-layer leaf pair in the first layer and the second in-layer leaf pair in the second layer to be adjusted synchronously. In some embodiments, the method may further include: for the each cross-layer leaf pair, causing the in-layer leaf pair in the first layer to be adjusted before or during the treatment process. In some embodiments, the threshold may be larger than 0. In some embodiments, the threshold may be within a range from 0.1 to 2 millimeters. In some embodiments, the threshold may be within a range from 0.2 to 0.5 millimeters. In some embodiments, in response to determining that the size of the effective cross-layer leaf gap is equal to 0, the in-layer leaf gap may be no larger than a second threshold. In some embodiments, the second threshold may be within a range from 2 to 3 millimeters. In another aspect of the present disclosure, a system for adjusting a multi-leaf collimator (MLC) in a treatment process is provided. The MLC may include a plurality of cross-layer leaf pairs each of which includes a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves, The system may include: a drive mechanism configured to drive the plurality of cross-layer leaf pairs to move; and a controller. The controller may be configured to: for each of at least one of the plurality of cross-layer leaf pairs, determining, according to a treatment plan, an effective cross-layer leaf gap to be formed between the first leaf in the first layer and the second leaf in the second layer; causing at least one of the first leaf or the second leaf to move to form the effective cross-layer leaf gap; and causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer. A size of the in-layer leaf gap may be no less than a threshold. In another aspect of the present disclosure, a system for adjusting a multi-leaf collimator (MLC) in a treatment process is provided. The MLC may include a plurality of cross-layer leaf pairs each of which includes a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves. The system may include: at least one storage device storing a set of instructions; and at least one processor in communication with the storage device, wherein when executing the set of instructions, the at least one processor may be configured to cause the system to perform operations. The operations may include: for each of at least one of the plurality of cross-layer leaf pairs, determining, according to a treatment plan, an effective cross-layer leaf gap to be formed between the first leaf in the first layer and the second leaf in the second layer; causing at least one of the first leaf or the second leaf to move to form the effective cross-layer leaf gap; and causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer. A size of the in-layer leaf gap may be no less than a threshold. In another aspect of the present disclosure, a non-transitory computer readable medium storing instructions is provided. The instructions, when executed by at least one processor, may cause the at least one processor to implement a method comprising: for each of at least one of the plurality of cross-layer leaf pairs, determining, according to a treatment plan, an effective cross-layer leaf gap to be formed between the first leaf in the first layer and the second leaf in the second layer; causing at least one of the first leaf or the second leaf to move to form the effective cross-layer leaf gap; and causing, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer. A size of the in-layer leaf gap may be no less than a threshold. In another aspect of the present disclosure, a system is provided. The system may include a multi-leaf collimator (MLC). The MLC may include a plurality of cross-layer leaf pairs each of which includes a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves. For each of at least one of the plurality of cross-layer leaf pairs, an effective cross-layer leaf gap may be formed between the first leaf in the first layer and the second leaf in the second layer; an in-layer leaf gap may be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer; and a size of the in-layer leaf gap may be no less than the effective cross-layer leaf gap. In some embodiments, the size of the in-layer leaf gap may be no less than a first threshold and no larger than a second threshold. In some embodiments, the size of the in-layer leaf gap may be determined based on a random value. In some embodiments, the size of the in-layer leaf gap may have a fixed value when a size of the effective cross-layer leaf gap is 0. In some embodiments, the size of the in-layer leaf gap may be equal to a sum of a fixed value and a size of the effective cross-layer leaf gap. In some embodiments, the size of the in-layer leaf gap may be equal to a size of the effective cross-layer leaf gap when the size of the effective cross-layer leaf gap is no less than a third threshold. Additional features will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The features of the present disclosure may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed examples discussed below. In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant disclosure. However, it should be apparent to those skilled in the art that the present disclosure may be practiced without such details. In other instances, well-known methods, procedures, systems, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present disclosure. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is not limited to the embodiments shown, but to be accorded the widest scope consistent with the claims. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise,” “comprises,” and/or “comprising,” “include,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that the term “object” and “subject” may be used interchangeably as a reference to a thing that undergoes a treatment and/or an imaging procedure in a radiation system of the present disclosure. It will be understood that the term “system,” “engine,” “unit,” “module,” and/or “block” used herein are one method to distinguish different components, elements, parts, section or assembly of different level in ascending order. However, the terms may be displaced by another expression if they achieve the same purpose. Generally, the word “module,” “unit,” or “block,” as used herein, refers to logic embodied in hardware or firmware, or to a collection of software instructions. A module, a unit, or a block described herein may be implemented as software and/or hardware and may be stored in any type of non-transitory computer-readable medium or another storage device. In some embodiments, a software module/unit/block may be compiled and linked into an executable program. It will be appreciated that software modules can be callable from other modules/units/blocks or themselves, and/or may be invoked in response to detected events or interrupts. Software modules/units/blocks configured for execution on computing devices (e.g., processor 210 as illustrated in FIG. 2) may be provided on a computer-readable medium, such as a compact disc, a digital video disc, a flash drive, a magnetic disc, or any other tangible medium, or as a digital download (and can be originally stored in a compressed or installable format that needs installation, decompression, or decryption prior to execution). Such software code may be stored, partially or fully, on a storage device of the executing computing device, for execution by the computing device. Software instructions may be embedded in firmware, such as an EPROM. It will be further appreciated that hardware modules/units/blocks may be included in connected logic components, such as gates and flip-flops, and/or can be included of programmable units, such as programmable gate arrays or processors. The modules/units/blocks or computing device functionality described herein may be implemented as software modules/units/blocks but may be represented in hardware or firmware. In general, the modules/units/blocks described herein refer to logical modules/units/blocks that may be combined with other modules/units/blocks or divided into sub-modules/sub-units/sub-blocks despite their physical organization or storage. The description may apply to a system, an engine, or a portion thereof. It will be understood that when a unit, engine, module or block is referred to as being “on,” “connected to,” or “coupled to,” another unit, engine, module, or block, it may be directly on, connected or coupled to, or communicate with the other unit, engine, module, or block, or an intervening unit, engine, module, or block may be present, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. These and other features, and characteristics of the present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, may become more apparent upon consideration of the following description with reference to the accompanying drawings, all of which form a part of this disclosure. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended to limit the scope of the present disclosure. It is understood that the drawings are not to scale. The flowcharts used in the present disclosure illustrate operations that systems implement according to some embodiments of the present disclosure. It is to be expressly understood, the operations of the flowcharts may be implemented not in order. Conversely, the operations may be implemented in inverted order, or synchronously. Moreover, one or more other operations may be added to the flowcharts. One or more operations may be removed from the flowcharts. The present disclosure relates to systems and methods for adjusting a multi-leaf collimator (MLC) of a radiation delivery device, and/or reducing or eliminating an effect of radiation leakage through a leaf gap in radiation with MLC. When leaves in an MLC move, the leaves or a drive mechanism of the MLC may become damaged by a collision between opposing leaf ends, and thus, care needs to be taken to avoid collisions between opposing leaf ends. To this end, a minimum gap may be maintained between opposing leaves in a same layer when the leaves move. However, this gap may be undesirable for radiation treatment, because it can allow a dose higher than planned to be delivered to the tissue underneath the gap. According to some embodiments of the present disclosure, a multi-layer MLC (e.g., a dual layer MLC) may be used. When leaves move while the beam is on, the leaves may be configured such that the leaf pairs in both layers of the multi-layer MLC have a larger in-layer leaf gap (than a prescribed gap determined according to a treatment plan) in order to avoid collision. Additionally, the gaps in different layers of the multi-layer MLC may be offset from each other such that an effective cross-layer leaf gap can be much smaller (e.g., 0), thereby reducing or eliminating the effect of leaf gap leakage through each layer. The MLC may include a plurality of cross-layer leaf pairs each of which includes a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves. For each of at least one of the plurality of cross-layer leaf pairs, an effective cross-layer leaf gap to be formed between the first leaf in the first layer and the second leaf in the second layer may be determined according to a treatment plan. At least one of the first leaf or the second leaf may be caused to move to form the effective cross-layer leaf gap. An in-layer leaf gap may be caused to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer. In some embodiments, a size of the in-layer leaf gap may be no less than a threshold. The threshold may correspond to a minimum size of the in-layer leaf gap. According to embodiments of the present disclosure, in the multi-layer MLC, in-layer leaf gaps may be employed to avoid or reduce the risk of collisions between opposing leaf ends, while effective cross-layer leaf gaps may be employed to avoid or reduce radiation leakage through the multi-layer MLC. Moreover, because the risk of collision can increase with a movement speed of the leaves, a reduced danger of collision may allow for a faster movement speed of the leaves, thereby reducing the time for the treatment, facilitating a treatment planning process (e.g., by reducing the impact of motion during a session of radiation delivery), and reducing the difficulty in radiation therapy. FIG. 1 is a schematic diagram illustrating an exemplary radiotherapy system according to some embodiments of the present disclosure. As shown in FIG. 1, the radiotherapy system 100 may include a radiation delivery device 110, a network 120, one or more terminals 130, a processing device 140, and a storage device 150. In some embodiments, the terminal(s) 130 may be used as upper computer(s) (or host computer(s)), while the processing device 140 may be used as a lower computer (or a slave computer). The components in the radiotherapy system 100 may be connected in one or more of various ways. Merely by way of example, the radiation delivery device 110 may be connected to the processing device 140 directly (e.g., via optical fiber (e.g., a peripheral component interconnect express (PCI-E) cable)). As another example, the radiation delivery device 110 may be connected to the processing device 140 through the network 120 as indicated by the bi-directional arrow in dotted lines linking the radiation delivery device 110 and the network 120. As still another example, the storage device 150 may be connected to the processing device 140 directly or through the network 120. As still another example, the terminal 130 may be connected to the processing device 140 directly (as indicated by the bi-directional arrow in dotted lines linking the terminal 130 and the processing device 140) or through the network 120. In some embodiments, the radiation delivery device 110 may be a radiotherapy (RT) device. In some embodiments, the RT device may deliver one or more radiation beams to a treatment region (e.g., a tumor) of an object (e.g., a patient) for causing an alleviation of the object's symptom. In some embodiments, the RT device may be a conformal radiation therapy device, an image guided radiation therapy (IGRT) device, an intensity modulated radiation therapy (IMRT) device, an intensity modulated arc therapy (IMAT) device, or the like. In some embodiments, the RT device may include a linear accelerator (also referred to as “linac”). The linac may generate and emit a radiation beam (e.g., an X-ray beam) from a treatment head. The radiation beam may pass through one or more collimators (e.g., an MLC)) forming certain shapes, and enter into the object. In some embodiments, the radiation beam may include electrons, photons, or other types of radiation. In some embodiments, the energy of the radiation beam may be in the megavoltage range (e.g., >1 MeV), and may therefore be referred to as a megavoltage beam. The treatment head may be coupled to a gantry. The gantry may rotate, for example, clockwise or counter-clockwise around a gantry rotation axis. In some embodiments, the treatment head may rotate along with the gantry. In some embodiments, the RT device may further include a table configured to support the object during radiation treatment. In some embodiments, the radiation delivery device 110 may further include one or more MLCs (not shown in FIG. 1). The MLC(s) may be configured to collimate radiation beam(s) of the radiation delivery device 110 and/or define the beam shape(s) thereof. In some embodiments, the MLC may include a plurality of leaves. The plurality of leaves may form an aperture. The aperture may define or modify the shape of the beam that is delivered to the object. In some embodiments, one or more leaves of the MLC may be moved according to a treatment plan. In some embodiments, the shape of the aperture may be changed according to a desired segment shape of the treatment plan. In some embodiments, the treatment plan may be generated by a treatment planning system (TPS) associated with the radiotherapy system 100. In some embodiments, the radiation delivery device 110 may further include a drive mechanism (not shown in FIG. 1) configured to drive the leaves to move. In some embodiments, the drive mechanism may include one or more driving circuits (not shown in FIG. 1). In some embodiments, a driving circuit may generate driving signal(s) to drive the leaves of the MLC to move towards target position(s) during treatment. In some embodiments, the driving circuits may be set in the radiation delivery device 110, and may communicate with the processing device 140 via the connection between the radiation delivery device 110 and the processing device 140. For example, the processing device 140 may provide (or send) a control signal to the drive circuit, and accordingly, the drive circuit may generate a driving signal to cause, e.g., one or more actuators to drive the leaves to move towards the target position(s). In some embodiments, the radiation delivery device 110 may further include one or more actuators configured to actuate the leaves to move. In some embodiments, an actuator may actuate the leaves to move according to a driving signal. In some embodiments, each leaf may be actuated by an actuator. Exemplary actuators may include motors, compressed gas loaded in one or more cylinders, a magnetic drive, etc. In the following descriptions, motors are described for illustration purpose; it should be noted that any other type of actuators can be used to actuate the leaves to move when using the driving methods and systems of the present disclosure. In some embodiments, the radiation delivery device 110 may further include one or more position detection devices (not shown in FIG. 1). A position detection device may be configured to detect a current position of a leaf, and/or a current velocity of the leaf directly or indirectly. In some embodiments, the position detection device may detect a displacement of the leaf, and the current position of the leaf may be determined based on the displacement of the leaf and an initial position of the leaf, and accordingly, the current velocity of the leaf may be determined based on the displacement of the leaf and a time for the leaf movement. Exemplary position detection device(s) may include a magnetic displacement sensor (e.g., a Hall effect sensor), a grating displacement sensor, an encoder (e.g., an encoder mounted on an actuator (e.g., a motor, a cylinder, or the like)), a potentiometer (e.g., a potentiometer mounted on a motor), or the like, or any combination thereof. In some embodiments, a leaf may have two corresponding position detection devices. For example, the leaf may have a magnetic displacement sensor and a potentiometer. The displacements of the leaf detected by the two position detection devices may be used to determine whether the leaf movement is abnormal. In some embodiments, the leaves may be configured in one or more layers. For example, the leaves may be configured in two layers, and a cross-layer leaf pair may include a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves. In some embodiments, the current position of a leaf and/or the current velocity of the leaf may be transmitted to the processing device 140 (e.g., the control module 804) to generate control signal(s). In some embodiments, the processing device 140 may control a leaf to move based on the current position of the leaf and/or the current velocity of the leaf. In some embodiments, the current position of a leaf and/or the current velocity of the leaf may be further transmitted to the terminal(s) 130 for display. In some embodiments, the object to be treated or scanned (also referred to as imaged) may include a body, substance, or the like, or any combination thereof. In some embodiments, the object may include a specific portion of a body, such as a head, a thorax, an abdomen, or the like, or any combination thereof. In some embodiments, the object may include a specific organ, such as a breast, an esophagus, a trachea, a bronchus, a stomach, a gallbladder, a small intestine, a colon, a bladder, a ureter, a uterus, a fallopian tube, etc. The network 120 may include any suitable network that can facilitate exchange of information and/or data for the radiotherapy system 100. In some embodiments, one or more components of the radiotherapy system 100 (e.g., the radiation delivery device 110, the terminal(s) 130, the processing device 140, the storage device 150, etc.) may communicate information and/or data with one or more other components of the radiotherapy system 100 via the network 120. For example, the processing device 140 may obtain data corresponding to the leaves of the MLC from the radiation delivery device 110 via the network 120. As another example, the processing device 140 may obtain user instructions from the terminal(s) 130 via the network 120. The network 120 may be and/or include a public network (e.g., the Internet), a private network (e.g., a local area network (LAN), a wide area network (WAN)), etc.), a wired network (e.g., an Ethernet network), a wireless network (e.g., an 802.11 network, a Wi-Fi network, etc.), a cellular network (e.g., a Long Term Evolution (LTE) network), a frame relay network, a virtual private network (“VPN”), a satellite network, a telephone network, routers, hubs, switches, server computers, and/or any combination thereof. Merely by way of example, the network 120 may include a cable network, a wireline network, a fiber-optic network, a telecommunications network, an intranet, a wireless local area network (WLAN), a metropolitan area network (MAN), a public telephone switched network (PSTN), a Bluetooth™ network, a ZigBee™ network, a near field communication (NFC) network, or the like, or any combination thereof. In some embodiments, the network 120 may include one or more network access points. For example, the network 120 may include wired and/or wireless network access points such as base stations and/or internet exchange points through which one or more components of the radiotherapy system 100 may be connected to the network 120 to exchange data and/or information. The terminal(s) 130 may enable interactions between a user and the radiotherapy system 100. The terminal(s) 130 may include a mobile device 131, a tablet computer 132, a laptop computer 133, or the like, or any combination thereof. In some embodiments, the mobile device 131 may include a smart home device, a wearable device, a mobile device, a virtual reality device, an augmented reality device, or the like, or any combination thereof. Merely by way of example, the terminal 130 may include a mobile device as illustrated in FIG. 3. In some embodiments, the smart home device may include a smart lighting device, a control device of an intelligent electrical apparatus, a smart monitoring device, a smart television, a smart video camera, an interphone, or the like, or any combination thereof. In some embodiments, the wearable device may include a bracelet, a footgear, eyeglasses, a helmet, a watch, clothing, a backpack, a smart accessory, or the like, or any combination thereof. In some embodiments, the mobile device may include a mobile phone, a personal digital assistant (PDA), a gaming device, a navigation device, a point of sale (POS) device, a laptop, a tablet computer, a desktop, or the like, or any combination thereof. In some embodiments, the virtual reality device and/or the augmented reality device may include a virtual reality helmet, virtual reality glasses, a virtual reality patch, an augmented reality helmet, augmented reality glasses, an augmented reality patch, or the like, or any combination thereof. For example, the virtual reality device and/or the augmented reality device may include a Google Glass™, an Oculus Rift™, a Hololens™, a Gear VR™, etc. In some embodiments, the terminal(s) 130 may be part of the processing device 140. In some embodiments, the terminal(s) 130 may remotely operate the radiation delivery device 110. In some embodiments, the terminal(s) 130 may operate the radiation delivery device 110 via a wireless connection. In some embodiments, the terminal(s) 130 may receive information and/or instructions inputted by a user, and send the received information and/or instructions to the radiation delivery device 110 or the processing device 140 via the network 120. In some embodiments, the terminal(s) 130 may receive data and/or information from the processing device 140. In some embodiments, the terminal(s) 130 may be part of the processing device 140. In some embodiments, the terminal(s) 130 may be omitted. In some embodiments, the terminal(s) 130 may include a control handle, a control box, a console, etc. In some embodiments, a user may choose, through the terminal(s) 130 to enable or disable the performance of the leaves illustrated in FIG. 9. The processing device 140 may process data and/or information obtained from the radiation delivery device 110, the terminal 130, and/or the storage device 150. For example, the processing device 140 may determine an effective cross-layer leaf gap to be formed between a first leaf in a first layer and a second leaf opposingly located in a second layer, according to the treatment plan. As another example, the processing device 140 may cause at least one of the first leaf or the second leaf to move to form the effective cross-layer leaf gap. As a further example, the processing device 140 may cause an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer based on the effective cross-layer leaf gap. In some embodiments, the processing device 140 may be a computer, a user console, a single server or a server group, etc. The server group may be centralized or distributed. In some embodiments, the processing device 140 may be local or remote. For example, the processing device 140 may access information and/or data stored in the radiation delivery device 110, the terminal 130, and/or the storage device 150 via the network 120. As another example, the processing device 140 may be directly connected to the radiation delivery device 110, the terminal 130, and/or the storage device 150 to access stored information and/or data. In some embodiments, the processing device 140 may be implemented on a cloud platform. Merely by way of example, the cloud platform may include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like, or any combination thereof. In some embodiments, the processing device 140 may be implemented by a computing device 200 having one or more components as illustrated in FIG. 2. In some embodiments, components of the radiotherapy system 100 (e.g., the radiation delivery device 110, the terminal 130, the processing device 140) may communicate with each other in a treatment process. For example, before the treatment process starts, the terminal 130 may send instruction(s) or information related to prescribed position(s) of a leaf to the processing device 140. The processing device 140 may determine a plurality of cross-layer leaf pairs each of which includes a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves. As another example, before one or more treatment fractions start, an effective cross-layer leaf gap to be formed between the first leaf in the first layer and the second leaf in the second layer may be determined by the processing device 140, and/or stored in the terminal 130. As a further example, during the treatment process, the radiation delivery device 110 may transmit the current positions of the cross-layer leaf pairs to the processing device 140, and the processing device 140 may cause at least one of the first leaf or the second leaf to move to form the effective cross-layer leaf gap. As still a further example, the processing device 140 may transmit the current positions of the cross-layer leaf pairs to the terminal 130 for display. The storage device 150 may store data, instructions, and/or any other information. In some embodiments, the storage device 150 may store data obtained from the radiation delivery device 110, the terminal 130 and/or the processing device 140. For example, the storage device 150 may store a treatment plan, parameters related to motion statuses of the leaves (e.g., a current position, an offset), or the like. In some embodiments, the storage device 150 may store data and/or instructions that the processing device 140 may execute or use to perform exemplary methods described in the present disclosure. In some embodiments, the storage device 150 may include a mass storage device, a removable storage device, a volatile read-and-write memory, a read-only memory (ROM), or the like, or any combination thereof. Exemplary mass storage devices may include a magnetic disk, an optical disk, a solid-state drive, etc. Exemplary removable storage devices may include a flash drive, a floppy disk, an optical disk, a memory card, a zip disk, a magnetic tape, etc. Exemplary volatile read-and-write memory may include a random access memory (RAM). Exemplary RAM may include a dynamic RAM (DRAM), a double date rate synchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristor RAM (T-RAM), and a zero-capacitor RAM (Z-RAM), etc. Exemplary ROM may include a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a compact disk ROM (CD-ROM), and a digital versatile disk ROM, etc. In some embodiments, the storage device 150 may be implemented on a cloud platform. Merely by way of example, the cloud platform may include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like, or any combination thereof. In some embodiments, the storage device 150 may be connected to the network 120 to communicate with one or more other components in the radiotherapy system 100 (e.g., the processing device 140, the terminal 130, etc.). One or more components in the radiotherapy system 100 may access the data or instructions stored in the storage device 150 via the network 120. In some embodiments, the storage device 150 may be directly connected to or communicate with one or more other components in the radiotherapy system 100 (e.g., the processing device 140, the terminal 130, etc.). In some embodiments, the storage device 150 may be part of the processing device 140. In some embodiments, the processing device 140 may be connected to or communicate with the radiation delivery device 110 via the network 120, or at the backend of the processing device 140. FIG. 2 is a schematic diagram illustrating exemplary hardware and/or software components of an exemplary computing device on which the processing device 140 may be implemented according to some embodiments of the present disclosure. As illustrated in FIG. 2, the computing device 200 may include a processor 210, a storage 220, an input/output (I/O) 230, and a communication port 240. The processor 210 may execute computer instructions (e.g., program code) and perform functions of the processing device 140 in accordance with techniques described herein. The computer instructions may include, for example, routines, programs, objects, components, data structures, procedures, modules, and functions, which perform particular functions described herein. For example, the processor 210 may process data obtained from the radiation delivery device 110, the terminal 130, the storage device 150, and/or any other component of the radiotherapy system 100. In some embodiments, the processor 210 may determine a plurality of cross-layer leaf pairs, each of which includes a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves. As illustrated in FIG. 5, a cross-layer leaf pair may include a first leaf located in a first layer of leaves and a second leaf opposingly located in a second layer of leaves, in which the first leaf and the second leaf have a same position on the Y-axis direction. In some embodiments, the processor 210 may determine an effective cross-layer leaf gap to be formed between the first leaf in the first layer and the second leaf in the second layer according to the treatment plan. In some embodiments, the processor 210 may cause at least one of the first leaf or the second leaf to move to form the effective cross-layer leaf gap. In some embodiments, the processor 210 may cause an in-layer leaf gap to be formed between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer based on the effective cross-layer leaf gap. In some embodiments, the processor 210 may include one or more hardware processors, such as a microcontroller, a microprocessor, a reduced instruction set computer (RISC), an application specific integrated circuits (ASICs), an application-specific instruction-set processor (ASIP), a central processing unit (CPU), a graphics processing unit (GPU), a physics processing unit (PPU), a microcontroller unit, a digital signal processor (DSP), a field programmable gate array (FPGA), an advanced RISC machine (ARM), a programmable logic device (PLD), any circuit or processor capable of executing one or more functions, or the like, or any combinations thereof. Merely for illustration, only one processor is described in the computing device 200. However, it should be noted that the computing device 200 in the present disclosure may also include multiple processors, thus operations and/or method steps that are performed by one processor as described in the present disclosure may also be jointly or separately performed by the multiple processors. For example, if in the present disclosure the processor of the computing device 200 executes both operation A and operation B, it should be understood that operation A and operation B may also be performed by two or more different processors jointly or separately in the computing device 200 (e.g., a first processor executes operation A and a second processor executes operation B, or the first and second processors jointly execute operations A and B). The storage 220 may store data/information obtained from the radiation delivery device 110, the terminal 130, the storage device 150, and/or any other component of the radiotherapy system 100. In some embodiments, the storage 220 may include a mass storage device, a removable storage device, a volatile read-and-write memory, a read-only memory (ROM), or the like, or any combination thereof. For example, the mass storage may include a magnetic disk, an optical disk, a solid-state drive, etc. The removable storage may include a flash drive, a floppy disk, an optical disk, a memory card, a zip disk, a magnetic tape, etc. The volatile read-and-write memory may include a random access memory (RAM). The RAM may include a dynamic RAM (DRAM), a double date rate synchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristor RAM (T-RAM), and a zero-capacitor RAM (Z-RAM), etc. The ROM may include a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a compact disk ROM (CD-ROM), and a digital versatile disk ROM, etc. In some embodiments, the storage 220 may store one or more programs and/or instructions to perform exemplary methods described in the present disclosure. For example, the storage 220 may store a program for driving the leaves of the MLC. The I/O 230 may input and/or output signals, data, information, etc. In some embodiments, the I/O 230 may enable a user interaction with the processing device 140. In some embodiments, the I/O 230 may include an input device and an output device. Examples of the input device may include a keyboard, a mouse, a touch screen, a microphone, or the like, or a combination thereof. Examples of the output device may include a display device, a loudspeaker, a printer, a projector, or the like, or a combination thereof. Examples of the display device may include a liquid crystal display (LCD), a light-emitting diode (LED)-based display, a flat panel display, a curved screen, a television device, a cathode ray tube (CRT), a touch screen, or the like, or a combination thereof. The communication port 240 may be connected to a network (e.g., the network 120) to facilitate data communications. The communication port 240 may establish connections between the processing device 140 and the radiation delivery device 110, the terminal 130, and/or the storage device 150. The connection may be a wired connection, a wireless connection, any other communication connection that can enable data transmission and/or reception, and/or any combination of these connections. The wired connection may include, for example, an electrical cable, an optical cable, a telephone wire, or the like, or any combination thereof. The wireless connection may include, for example, a Bluetooth™ link, a Wi-Fi™ link, a WiMax™ link, a WLAN link, a ZigBee link, a mobile network link (e.g., 3G, 4G, 5G, etc.), or the like, or a combination thereof. In some embodiments, the communication port 240 may be and/or include a standardized communication port, such as RS232, RS485, etc. In some embodiments, the communication port 240 may be a specially designed communication port. For example, the communication port 240 may be designed in accordance with the digital imaging and communications in medicine (DICOM) protocol. FIG. 3 is a schematic diagram illustrating exemplary hardware and/or software components of an exemplary mobile device 300 on which the terminal 130 may be implemented according to some embodiments of the present disclosure. As illustrated in FIG. 3, the mobile device 300 may include a communication platform 310, a display 320, a graphics processing unit (GPU) 330, a central processing unit (CPU) 340, an I/O 350, a memory 360, and a storage 390. In some embodiments, any other suitable component, including but not limited to a system bus or a controller (not shown), may also be included in the mobile device 300. In some embodiments, a mobile operating system 370 (e.g., iOS™, Android™, Windows Phone™, Harmony OS, etc.) and one or more applications 380 may be loaded into the memory 360 from the storage 390 in order to be executed by the CPU 340. The applications 380 may include a browser or any other suitable mobile apps for receiving and rendering information relating to image processing or other information from the processing device 140. User interactions with the information stream may be achieved via the I/O 350 and provided to the processing device 140 and/or other components of the radiotherapy system 100 via the network 120. In some embodiments, a user may input parameters to the radiotherapy system 100, via the mobile device 300. In order to implement various modules, units and their functions described above, a computer hardware platform may be used as hardware platforms of one or more elements (e.g., the processing device 140 and/or other components of the radiotherapy system 100 described in FIG. 1). Since these hardware elements, operating systems and program languages are common; it may be assumed that persons skilled in the art may be familiar with these techniques and they may be able to provide information needed in the imaging according to the techniques described in the present disclosure. A computer with the user interface may be used as a personal computer (PC), or other types of workstations or terminal devices. After being properly programmed, a computer with the user interface may be used as a server. It may be considered that those skilled in the art may also be familiar with such structures, programs, or general operations of this type of computing device. FIG. 4 is a schematic diagram illustrating a portion of an exemplary MLC according to some embodiments of the present disclosure. Although only one bank of leaves are shown in FIG. 4 for illustration purposes, it should be noted that the MLC 400 may include two or more banks of leaves. For example, the MLC 400 may include two opposing banks arranged in a same layer (i.e., a same plane, or same level). As another example, the MLC 400 may include two layers of leaves (i.e., two sets of leaves in two different planes, e.g., one on top of another), and each layer may include two opposing banks. As shown in FIG. 4, the MLC 400 may include a plurality of leaves 410, a rail box 440, one or more drive mechanisms 430, and a housing 420. In some embodiments, the housing 420 may be configured to accommodate the plurality of leaves 410, the drive mechanism(s) 430, etc. In some embodiments, the housing 420 may connect with the rail box 440. In some embodiments, the plurality of leaves 410 may be movable along a plurality of rails disposed on the rail box 440. In some embodiments, at least some leaves 410 of the plurality of leaves may be movable in a direction parallel to each another. In some embodiments, at least some of the leaves 410 may be configured to move synchronously while the radiation delivery is off. The plurality of leaves 410 may be configured to shield a portion of radiation beams and form an aperture to allow a portion of the radiation beams to pass through. The portion of the radiation beams passing through the aperture may reach a treatment region of an object to perform the radiation therapy. In some embodiments, the processing device 140 may control at least one leaf 410 of the MLC 400 to move into one or more positions to modify the shape of the aperture according to one or more parameters associated with the MLC 400 (e.g., a segment shape defined by the shape of the aperture formed by the MLC 400). The parameter(s) may be pre-determined by the processing device 140, or may be determined according to a specific condition as the specific condition occurs. Exemplary conditions may include that a scanner image of the object indicates that a position or shape of the treatment region to be treated is changed. In some embodiments, the parameter(s) may be preset in the treatment plan. The drive mechanism(s) 430 may be configured to actuate one or more of the leaves 410 to move. In some embodiments, the drive mechanism(s) 430 may facilitate the movement of the leaves 410 such that the MLC 400 can translate the leaves 410 between a first aperture shape and a second aperture shape. In some embodiments, each leaf 410 may be capable of translating between a first position and a second position (e.g., from an open position to a closed position, from a closed position to an open position). In some embodiments, each leaf 410 may be actuated to move independently or separately from other leaves 410 of the MLC 400. In some embodiments, two or more leaves 410 may be actuated to move synchronously. In some embodiments, the drive mechanism(s) 430 may include a fluid-power drive mechanism, a spring-based drive mechanism, an electric-charge-based drive mechanism, a magnetic drive mechanism, a pneumatic drive mechanism, or the like, or a combination thereof. In some embodiments, the drive mechanism(s) 430 may include a plurality of driving motors. In some embodiments, the drive mechanism 430 may include a drive screw operably coupled to a driving motor to transmit a driving force generated by the driving motor to a corresponding leaf. The drive mechanism(s) 430 may move each leaf of the MLC 400 individually and/or independently, or may move two or more leaves together. In some embodiments, the MLC 400 may include a plurality of the leaves 410, for example, 12, 15, 16, 24, 25, 31, 32, 36, 48, 50, 64, 72, 75, 100, 101, 120, 128, 135, etc. Merely by way of example, the MLC 400 may include 64 leaves. In some embodiments, each leaf 410 of the MLC 400 may have a width of about 1 mm to about 10 mm (e.g., about 2 mm). In some embodiments, the travel length of each leaf may be from about 0.25 cm to about 3 cm (e.g., about 1 cm). The smaller the travel range of the leaves 410 of the MLC 400 is, the more precise an aperture defined by the MLC 400 may be, and the more precisely the radiation may be delivered. However, in some embodiments, reducing leaf travel length and/or width may prolong patient treatment time. The size and shape of the leaves 410 may be at least partially determined by the geometry of a gantry, the width of the radiation beam, the distance to the radiation source (or the distance from the MLC to the target object), the target MLC penumbra, and/or the desired “resolution” at which radiation is to be applied (e.g., leaf width, number (or count) of leaves). The depth (or height) of the leaves 410 may be sufficiently thick to impede the transmission of the radiation beam when the leaves 410 are in the closed position. The depth of a leaf 410 may be the dimension of the leaf 410 along the Z-axis direction as illustrated in FIG. 4. In some embodiments, the speed of a leaf movement may be increased by increasing the speed of the drive mechanism(s) 430. Alternatively or additionally, the MLC 400 may optionally use ball screws with a relatively wide screw pitch. In some embodiments, only a portion of the leaves 410 that shield the radiation beam may have a high atomic number material (e.g., tungsten), while the peripheral support structure(s) of the leaves 410 may include one or more lighter-weight materials. In some embodiments, a portion of a leaf 410 may be made of a substantially-radiation-impermeable material (e.g., tungsten), while the remaining portion of the leaf 410 may be made of one or more other materials (e.g., a material that is less dense and/or lighter than the substantially-radiation-impermeable material, such as stainless steel or titanium). In some embodiments, the portion of the leaf 410 made of a substantially-radiation-impermeable material may also be referred to as a substantially-radiation-impermeable portion of the leaf 410. In some embodiments, removing or hollowing out one or more regions of the leaf 410 may help to reduce the weight of the leaf 410 with little or no impact on the ability of the leaf 410 to impede radiation transmission. For example, a first section of the substantially-radiation-impermeable portion of the leaf 410 that is in the radiation path may be substantially solid, while a second section of the substantially-radiation-impermeable portion of the leaf 410 that is not in the radiation path may have one or more hollow regions. In some embodiments, as shown in FIG. 4, the X-axis direction may refer to the longitudinal moving direction (as indicated by the arrow A) of the leaves of the MLC, the Y-axis direction may refer to the arrangement direction of adjacent leaves in a same bank of the MLC, and the Z-axis direction may be perpendicular to the X-axis direction and the Y-axis direction. In some embodiments, the X-axis direction and the Y-axis direction may be traverse to the beam direction. It should be noted that the X-axis direction, and/or Y-axis direction in the present disclosure are defined relative to the MLC. If the MLC rotates with the gantry, the actual direction of the X-axis direction, and/or Y-axis direction relative to the radiation delivery device 110 may change with the rotation of the MLC. It should be noted that only one layer of leaves 410 are presented in FIG. 4 merely for the purposes of illustration. In some embodiments, the plurality of leaves 410 may be arranged in two or more layers. For example, the MLC 400 may include two layers, each of which includes two opposing banks. The two opposing banks of each layer may include a plurality of leaves that form a plurality of in-layer leaf pairs in the each layer. An in-layer leaf pair may include two leaves that are arranged in the two opposing banks, respectively, and are longitudinally movable relative to each other (e.g., along the X-axis direction as illustrated in FIG. 4). In some embodiments, the longitudinal moving direction may be traverse to a beam direction (e.g., along the Z-axis direction as illustrated in FIG. 4). In some embodiments, one leaf of an in-layer leaf pair in a bank may be longitudinally movable relative to the other leaf of the pair in the opposing bank. In some embodiments, in a monolayer MLC, a portion of the in-layer leaf pairs may form an aperture shape according to the treatment plan, while other in-layer leaf pairs that are not a portion of the in-layer leaf pairs forming the aperture shape may be closed and form one or more closed in-layer leaf pairs. The closed in-layer leaf pair(s) may be configured to block at least a portion of the radiation beam impinging thereon. According to some embodiments of the present disclosure, the MLC may include a plurality of layers of leaves. Merely by way of example, the MLC may include two layers of leaves. For illustration purposes, the descriptions below are provided with reference to a dual layer MLC. It is understood that this is not intended to be limiting. An MLC according to the systems and methods described herein may include more than two layers of leaves. A dual layer MLC may include two layers of leaves (e.g., a first layer and a second layer), and each layer may include two opposing banks. In some embodiments, each layer of the dual layer MLC may have a similar structure to the monolayer MLC. In some embodiments, the first layer of leaves may overlap with (or be aligned with) the second layer of leaves. In some embodiments, the first layer of leaves may be set on top of the second layer of leaves. Alternatively, the second layer of leaves may be set on top of the first layer of leaves. In some embodiments, the dual layer MLC may include a plurality of cross-layer leaf pairs. A cross-layer leaf pair may include a first leaf located in the first layer of leaves and a second leaf opposingly located in the second layer of leaves. In some embodiments, at least a portion of the cross-layer leaf pairs may form an aperture according to the treatment plan, while other cross-layer leaf pairs that are not a portion of the cross-layer leaf pairs forming the aperture may be closed and form one or more closed cross-layer leaf pairs. In some embodiments, each of the cross-layer leaf pairs forming the aperture may have a corresponding effective cross-layer leaf gap according to the treatment plan. The effective cross-layer leaf gap between the first leaf and the second leaf may be formed or defined by one end of the first leaf facing an opposing first leaf in the first layer and one end of the second leaf facing an opposing second leaf in the second layer. In some embodiments, the effective cross-layer leaf gap of a cross-layer leaf pair that forms the aperture (or a portion thereof) may be larger than 0 (e.g., the effective cross-layer leaf gap G5 shown in FIG. 7). In some embodiments, the effective cross-layer leaf gap for a closed cross-layer leaf pair may be substantially 0 (e.g., the effective cross-layer leaf gap G1 shown in FIG. 5, the effective cross-layer leaf gap G4 shown in FIG. 6). More descriptions of the effective cross-layer leaf gap may be found elsewhere in the present disclosure (e.g., FIGS. 5-7 and descriptions thereof). In some embodiments, an in-layer leaf gap may exist between the leaves of a closed in-layer leaf pair where the leaves meet to avoid collision between leaves of a closed in-layer leaf pair. In some embodiments, at least a portion of the radiation beam impinging on the closed in-layer leaf pair may leak through the in-layer leaf gap. Using a dual layer MLC configuration, the in-layer leaf gaps in different layers may be offset with each other so that at least a portion of radiation the in-layer leaf gap in the first layer may be block by the leaf that is located in the second layer and underneath the in-layer leaf gap and the leakage through each of the in-layer leaf gaps can be reduced or eliminated. Therefore, the in-layer leaf gaps can be enlarged to avoid collisions of the in-layer leaf pairs (e.g., the closed in-layer leaf pairs). In some embodiments, for the dual layer MLC, the plurality of leaves 410 in different layers (e.g., the first layer and the second layer) may be caused to move synchronously or asynchronously. For example, the first layer of leaves may be caused to move simultaneously with the second layer of leaves. As another example, the first layer of leaves may be caused to move before the second layer of leaves. As a further example, cross-layer leaf pairs forming effective cross-layer leaf gaps (or the aperture shape) may be caused to move before other leaves. More descriptions of the movement of the plurality of leaves 410 in the first layer and in the second layer may be found elsewhere in the present disclosure (e.g., FIGS. 5-7, and the description thereof). In some embodiments, the speed of a leaf movement may be increased by increasing the speed of the drive mechanism(s) 430. For the dual layer MLC with offset in-layer leaf gaps, because of the allowance of a relatively large in-layer leaf gap, the speed of the leaf movement may be faster, so that the adjusting time of the MLC can be reduced, and the efficiency of treatment delivery can be improved. In some embodiments, the terms of “length,” “width,” “height,” “side,” and “end” of a leaf may be used in the description of the MLC. The “length” of a leaf as used herein may refer to a leaf dimension (e.g., in the X-axis direction) that is parallel to the leaf moving direction. The “width” of a leaf may refer to a dimension of the leaf (e.g., in the Y-axis direction) that is traverse to the leaf moving direction and the direction of the radiation beam. The “height” of a leaf may refer to a dimension of the leaf (e.g., in the Z-axis direction) substantially along the radiation beam direction. The “side” of a leaf may refer to a surface of the leaf (e.g., in the XZ plane) facing a neighboring leaf in a same bank. The “end” of a leaf may refer to a surface of the leaf (e.g., in the YZ plane) at an end of the leaf along the length of the leaf. In some embodiments, the leaves of the dual layer MLC exemplified in FIGS. 5-7 may have an rectangular shape. It should be noted that the rectangular cubes in FIGS. 5-7 are merely provided for the purposes of illustration, and not intended to limit the scope of the leaf in the present disclosure. In some embodiments, the leaves in the MLC may have a substantially same cross-section (e.g., a cross-section in the YZ plane). For example, the leaves in the MLC may have a same trapezoidal cross-section. The cross-section of the leaves may have other shapes including, for example, a rectangular shape, a tilted trapezoid shape, or a trapezoid with stepped or wavy ends, or the like. In some embodiments, the pattern of cross-sections of the leaves may alternate, such as trapezoid, rectangle, trapezoid, rectangle, and so on. In some embodiments, the leaf ends may be flat. In some embodiments, the neighboring leaf side surfaces may form a gap or spacing ranging from approximately 10 to 100 micrometers to facilitate relative movement between the leaves. In some embodiments, the leaf side gaps may be substantially the same. In some embodiments, the leaf end may be round, flat, or in one of various other configurations. The arrows R shown in FIGS. 5-7 illustrate the direction of radiation beams. A radiation beam may be emitted from a radiation source. A radiation beam may include a plurality of radiation beam lets. In some embodiments, the radiation beam lets of a radiation beam may be (substantially) parallel to each other. In some embodiments, the radiation beamlets of a radiation beam may be unparallel to each other. In some embodiments, the solid arrows may indicate the radiation beam delivered from a radiation source to the leaves 501a, 501b, 502a, 502b, 601a, 601b, 602a, 602b, 701a, 701b, 702a, and 702b. The radiation beam may include a particle beam, a photon beam, an ultrasound beam (e.g., a high intensity focused ultrasound beam), or the like, or a combination thereof. The particle beam may include a stream of neutrons, protons, electrons, heavy ions, or the like, or a combination thereof. The photon beam may include an X-ray beam, a γ-ray beam, an α-ray beam, a β-ray beam, an ultraviolet beam, a laser beam, or the like, or a combination thereof. It should be noted that the incidence direction of the radiation beam perpendicular to the XY-plane in FIGS. 5-7 is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For example, in some embodiments, the incidence direction of the radiation beam may form a certain angle with the XY-plane, such as 15°, 30°, 45°, 60°, 75°, or the like. FIG. 5 is a schematic diagram illustrating an exemplary effective cross-layer leaf gap and exemplary in-layer leaf gaps according to some embodiments of the present disclosure. FIG. 6 is a schematic diagram illustrating another exemplary effective cross-layer leaf gap and exemplary in-layer leaf gaps according to some embodiments of the present disclosure. FIG. 7 is a schematic diagram illustrating another exemplary effective cross-layer leaf gap and exemplary in-layer leaf gaps according to some embodiments of the present disclosure. Although only two in-layer leaf pairs and only one cross-layer leaf pair of a dual layer MLC are shown in FIGS. 5-7 for illustration purposes, it should be noted that the dual layer MLC may include one or more in-layer leaf pairs and one or more cross-layer leaf pairs illustrated in FIGS. 5-7. As shown in FIGS. 5-7, the dual layer MLC may include two layers of leaves (e.g., the first layer and the second layer). For illustration purposes, the first layer is set on top of the second layer. In some embodiments, the second layer may be set one top of the first layer. As shown in FIG. 5, the first layer may include a first leaf 501b and an opposing first leaf 501a that form an in-layer leaf pair in the first layer, and the second layer may include a second leaf 502a and an opposing second leaf 502b that form an in-layer leaf pair in the second layer. In some embodiments, the first leaf 501b, the opposing first leaf 501a, the second leaf 502a, and the opposing second leaf 502b may be set in different banks, respectively. In some embodiments, the first leaf 501b and the opposing second leaf 502b may be set in a same bank, and the second leaf 502a and the opposing first leaf 501a may be set in a same bank. As shown in FIG. 6, the first layer may include a first leaf 601b and an opposing first leaf 601a that form an in-layer leaf pair in the first layer, and the second layer may include a second leaf 602a and an opposing second leaf 602b that form an in-layer leaf pair in the second layer. In some embodiments, the first leaf 601b, the opposing first leaf 601a, the second leaf 602a, and the opposing second leaf 602b may be set in different banks, respectively. In some embodiments, the first leaf 601b and the opposing second leaf 602b may be set in a same bank, and the second leaf 602a and the opposing first leaf 601a may be set in a same bank. As shown in FIG. 7, the first layer may include a first leaf 701b and an opposing first leaf 701a that form an in-layer leaf pair in the first layer, and the second layer may include a second leaf 702a and an opposing second leaf 702b that form an in-layer leaf pair in the second layer. In some embodiments, the first leaf 701b, the opposing first leaf 701a, the second leaf 702a, and the opposing second leaf 702b may be set in different banks, respectively. In some embodiments, the first leaf 701b and the opposing second leaf 702b may be set in a same bank, and the second leaf 702a and the opposing first leaf 701a may be set in a same bank. An effective cross-layer leaf gap may be formed between a cross-layer leaf pair (i.e., a first leaf located in the first layer and a second leaf opposingly located in the second layer (e.g., the first leaf 501b in the first layer and the second leaf 502a in the second layer as illustrated in FIG. 5, the first leaf 601b in the first layer and the second leaf 602a in the second layer as illustrated in FIG. 6, the first leaf 701b in the first layer and the second leaf 702a in the second layer as illustrated in FIG. 7)). It should be noted that the effective cross-layer leaf gap between the first leaf and the second leaf (e.g., between the first leaf 501b and the second leaf 502a, between the first leaf 601b and the second leaf 602a, between the first leaf 701b and the second leaf 702a) is merely provided for the purposes of illustration, and not intended to limit the scope of the leaf in the present disclosure. For example, the effective cross-layer leaf gap may be formed between the opposing first leaf in the first layer and the opposing second leaf in the second layer (e.g., between the opposing first leaf 501a and the opposing second leaf 502b, between the opposing first leaf 601a and the opposing second leaf 602b, between the opposing first leaf 701a and the opposing second leaf 702b). It should be noted that the effective cross-layer leaf gap may refer to a relatively small leaf gap formed between two opposing cross-layer leaf pairs, or an effective gap that radiation beams can pass through the two opposing cross-layer leaf pairs. For example, a first cross-layer leaf gap may be formed between a first leaf located in the first layer and a second leaf opposingly located in the second layer, and a second cross-layer leaf gap may be formed between the opposing first leaf in the first layer and the opposing second leaf in the second layer. If the first cross-layer leaf gap is smaller than the second cross-layer leaf gap (i.e., radiation beams can pass through the first cross-layer leaf gap), then the first cross-layer leaf gap may be designated as the effective cross-layer leaf gap. If the second cross-layer leaf gap is smaller than the first cross-layer leaf gap (i.e., radiation beams can pass through the second cross-layer leaf gap), then the second cross-layer leaf gap may be designated as the effective cross-layer leaf gap. Specifically, as shown in FIG. 5, the effective cross-layer leaf gap G1 may be formed or defined by one end 503 of the first leaf 501b facing the opposing first leaf 501a in the first layer and one end 504 of the second leaf 502a facing the opposing second leaf 502b in the second layer. As shown in FIG. 6, the effective cross-layer leaf gap G4 may be formed or defined by one end 603 of the first leaf 601b facing the opposing first leaf 601a in the first layer and one end 604 of the second leaf 602a facing the opposing second leaf 602b in the second layer. As shown in FIG. 7, the effective cross-layer leaf gap G5 may be formed or defined by one end 703 of the first leaf 701b facing the opposing first leaf 701a in the first layer and one end 704 of the second leaf 702a facing the opposing second leaf 702b in the second layer. In some embodiments, the effective cross-layer leaf gap between a cross-layer leaf pair may form an aperture shape (or a portion thereof) prescribed by a treatment planning system. In some embodiments, a size of the effective cross-layer leaf gap may be determined according to a treatment plan generated by the treatment planning system. In some embodiments, the position of the aperture (i.e., the position(s) of the cross-layer leaf pair(s)) may be determined according to the treatment plan. In some embodiments, different positions may correspond to different effective cross-layer leaf gaps. In some embodiments, different positions may correspond to a same effective cross-layer leaf gap. In some embodiments, during or before radiation delivery, cross-layer leaf pair(s) may need to be moved to prescribed position(s), and effective cross-layer leaf gap(s) therebetween may need to be adjusted to prescribed size(s). In some embodiments, the position of a cross-layer leaf pair may be described in terms of a position of a portion of the cross-layer leaf pair (e.g., an end of the first leaf of the cross-layer leaf pair, an end of the second leaf of the cross-layer leaf pair, a centroid of the first leaf, a centroid of the second leaf, a center of the effective cross-layer leaf gap between the cross-layer leaf pair, etc.). In some embodiments (e.g., in a static radiation therapy), the leaves of cross-layer leaf pair(s) may be moved to prescribed position(s) first (e.g., to form in-layer leave gap(s)), and then the effective cross-layer leaf gap(s) therebetween may be adjusted to prescribed size(s) by adjusting the position(s) of at least one leaf of the cross-layer leaf pair(s). In some embodiments (e.g., in a static radiation therapy), the effective cross-layer leaf gap(s) may be adjusted to prescribed size(s) first by adjusting the position(s) of at least one leaf of the cross-layer leaf pair(s), and then one or more leaves of the cross-layer leaf pair(s) may be moved to prescribed position(s). In some embodiments (e.g., in a dynamic radiation therapy), the movement of the cross-layer leaf pair(s) toward prescribed position(s) and the adjustment of the effective cross-layer leaf gap(s) to prescribed size(s) may be performed simultaneously or synchronously. In some embodiments, an effective cross-layer leaf gap may be adjusted to a prescribed size by causing the first leaf and/or the second leaf to move to form the effective cross-layer leaf gap. It should be noted that the descriptions of the effective cross-layer leaf gap(s) and the adjustment of the effective cross-layer leaf gap(s) in the present disclosure are not intended to limit the scope of the MLC in the present disclosure. In some embodiments, according to the treatment plan, at certain positions (e.g., non-treatment regions (e.g., an organ at risk (OAR))) and/or in certain treatment fractions (or treatment sessions), no radiation beam (or beamlet) may need to be delivered through a certain cross-layer leaf pair. Accordingly, the effective cross-layer leaf gap of the certain cross-layer leaf pair may be prescribed as 0, i.e., the size of the effective cross-layer leaf gap is 0. In some embodiments, if the effective cross-layer leaf gap is prescribed as 0, one end of the first leaf in the first layer and one end of the second leaf in the second layer that form or define the effective cross-layer leaf gap may align with each other (e.g., along the Z-axis direction). For example, as shown in FIG. 5, the effective cross-layer leaf gap G1 is prescribed as 0, and thus, the end 503 of the first leaf 501b and the end 504 of the second leaf 502a may be aligned with each other along the Z-axis direction. In some embodiments, if the effective cross-layer leaf gap is prescribed as 0, one end of the first leaf in the first layer and one end of the second leaf in the second layer that form or define the effective cross-layer leaf gap may at least partially overlap with each other (e.g., along the X-axis direction). For example, as shown in FIG. 6, the effective cross-layer leaf gap G4 is prescribed as 0, and thus, the end 603 of the first leaf 601b and the end 604 of the second leaf 602a may at least partially overlap with each other along the X-axis direction. It should be noted that in FIG. 6, even though the absolute distance between the end 603 and the end 604 in the X-axis direction is larger than 0, the effective cross-layer leaf gap G4 is still considered 0 since the overlapping configuration of the first leaf 601b and the second leaf 602a along the X-axis direction can impede the transmission of the radiation beam (or beam let). In the present disclosure, if an effective cross-layer leaf gap is prescribed as 0 (either the effective cross-layer leaf gap G1 in FIG. 5, or the effective cross-layer leaf gap G4 in FIG. 6), it may refer that the cross-layer leaf pair that forms the effective cross-layer leaf gap is closed. If an effective cross-layer leaf gap is prescribed as larger than 0 (e.g., the effective cross-layer leaf gap G5 in FIG. 7), it may refer that the cross-layer leaf pair that forms the effective cross-layer leaf gap is open. In some embodiments, according to the treatment plan, at certain positions (e.g., treatment regions) and/or in certain treatment fractions (or treatment sessions), a radiation beam (or beam let) of a certain dose may need to be delivered through a certain cross-layer leaf pair. Accordingly, the effective cross-layer leaf gap of the certain cross-layer leaf pair may be prescribed as larger than 0, i.e., the size of the effective cross-layer leaf gap is larger than 0. The size of the effective cross-layer leaf gap may be determined according to the treatment plane. For example, as shown in FIG. 7, the effective cross-layer leaf gap G5 is prescribed as larger than 0, and thus, the end 703 of the first leaf 701b and the end 704 of the second leaf 702a may be spaced apart along the X-axis direction to allow a prescribed radiation beam (or beam let) to pass through. An in-layer leaf gap may be formed between an in-layer leaf pair (i.e., a first leaf located in the first layer and an opposing first leaf in the first layer, or a second leaf located in the second layer and an opposing second leaf in the second layer). The in-layer leaf gap between the first leaf and the opposing first leaf may be formed or defined by one end of the first leaf facing the opposing first leaf and one end of the opposing first leaf facing the first leaf. The in-layer leaf gap between the second leaf and the opposing second leaf may be formed or defined by one end of the second leaf facing the opposing second leaf and one end of the opposing second leaf facing the second leaf. Specifically, as shown in FIG. 5, the in-layer leaf gap G2 may be formed or defined by one end 503 of the first leaf 501b facing the opposing first leaf 501a in the first layer and one end 505 of the opposing first leaf 501a facing the first leaf 501b. The in-layer leaf gap G3 may be formed or defined by one end 504 of the second leaf 502a facing the opposing second leaf 502b in the second layer and one end 506 of the opposing second leaf 502b facing the second leaf 502a. As shown in FIG. 6, the in-layer leaf gap G′2 may be formed or defined by one end 603 of the first leaf 601b facing the opposing first leaf 601a in the first layer and one end 605 of the opposing first leaf 601a facing the first leaf 601b. The in-layer leaf gap G′3 may be formed or defined by one end 604 of the second leaf 602a facing the opposing second leaf 602b in the second layer and one end 606 of the opposing second leaf 602b facing the second leaf 602a. As shown in FIG. 7, the in-layer leaf gap G″2 may be formed or defined by one end 703 of the first leaf 701b facing the opposing first leaf 701a in the first layer and one end 705 of the opposing first leaf 701a facing the first leaf 701b. The in-layer leaf gap G″3 may be formed or defined by one end 704 of the second leaf 702a facing the opposing second leaf 702b in the second layer and one end 706 of the opposing second leaf 702b facing the second leaf 702a. In some embodiments, the in-layer leaf gap(s) may be adjusted according to the effective cross-layer leaf gap(s). When the effective cross-layer leaf gap is prescribed as 0 (i.e., no radiation beam (or beam let) may need to be delivered through the first leaf, the opposing first leaf, the second leaf, and the opposing second leaf), the first leaf and the second leaf that form the effective cross-layer leaf gap may be adjusted to achieve the prescribed size (i.e., 0), as shown in FIGS. 5-6. In some embodiments, the adjustment of the first leaf and the second leaf as shown in FIGS. 5-6 may reduce or prevent the passage of the radiation beam (or beamlet) through the effective cross-layer leaf gap. Therefore, theoretically, the opposing first leaf can be positioned anywhere in the X-axis direction as long as the opposing first leaf does not exceed the position of the first leaf. Similarly, the opposing second leaf can be positioned anywhere in the X-axis direction as long as the opposing second leaf does not exceed the position of the second leaf. For example, the opposing first leaf may be positioned close to the first leaf (i.e., the in-layer leaf gap therebetween may be substantially 0). As another example, the opposing first leaf may be positioned a certain distance apart from the first leaf (i.e., the in-layer leaf gap therebetween may be larger than 0 (e.g., the gaps G2, G3, G′2, and/or G′3 may be larger than 0)). It should be noted that if two opposing leaves in a same layer are close to each other, a collision of the two opposing leaves may occur when the two opposing leaves move (especially in dynamic radiation therapy, e.g., the opposing leaves move simultaneously), thereby damaging the opposing leaves and/or the drive mechanism(s). Therefore, the first leaf and the opposing first leaf (and/or the second leaf and the opposing second leaf) may be spaced apart by at least a certain distance (e.g., a first safe distance). The first safe distance may be a minimum distance (between two opposing leaves in a same layer when the opposing leaves are moved) to avoid collisions. The first safe distance may be regarded as a first threshold. For example, the gaps G2, G3, G′2, and/or G′3 may be set larger than the first threshold. The first threshold may be set according to a default setting of the radiotherapy system 100 or preset by a user or operator via the terminals 130. In some embodiments, the configuration of the leaves in the first layer and/or the leaves in the second layer may allow a relatively small amount of radiation leakage. For example, as shown in FIG. 5, the configuration of the second leaf 502a (e.g., the height of the second leaf 502a may be relatively small, the second leaf 502a may be made of a lighter-weight material, or the like) may allow a relatively small amount of radiation leakage when the radiation beam are delivered through the in-layer leaf gap G2. Therefore, in some embodiments, the size(s) of the in-layer leaf gap(s) may be set no larger than a second threshold. The second threshold may be a second safe distance between two opposing leaves in a same layer to avoid excessive radiation leakage through the first layer and/or the second layer. The second threshold may be set according to a default setting of the radiotherapy system 100 or preset by a user or operator via the terminals 130. The second threshold may be larger than the first threshold. When the effective cross-layer leaf gap is prescribed as larger than 0 (i.e., a radiation beam (or beam let) of a certain dose may need to be delivered through the effective cross-layer leaf gap), the first leaf and the second leaf that form the effective cross-layer leaf gap may be adjusted to achieve the prescribed size, as shown in FIG. 7. As illustrated above, the in-layer leaf gap(s) may need to satisfy the first threshold and/or the second threshold. In addition, the in-layer leaf gap(s) should not affect or change the effective cross-layer leaf gap(s). For example, as shown in FIG. 7, the opposing first leaf 701a and/or the opposing second leaf 702b should not protrude into the effective cross-layer leaf gap G5, otherwise the effective cross-layer leaf gap G5 may be narrowed or eliminated and may not satisfy the prescribed effective cross-layer leaf gap. That is, the in-layer leaf gap G″2 (and/or the in-layer leaf gap G″3) may be no less than the effective cross-layer leaf gap G5. It should be noted that the above descriptions of the effective cross-layer leaf gap(s) and in-layer leaf gap(s) in FIGS. 5-7 are merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. For example, the MLC may include three layers of leaves, four layers of leaves, etc. More descriptions of the adjustment of the effective cross-layer leaf gap(s) and in-layer leaf gap(s) may be found elsewhere in the present disclosure (e.g., FIG. 9 and descriptions thereof). FIG. 8 is a block diagram illustrating an exemplary processing device 140 according to some embodiments of the present disclosure. The processing device 140 may include a determination module 802 and a control module 804. At least a portion of the processing device 140 may be implemented on a computing device as illustrated in FIG. 2 or a mobile device as illustrated in FIG. 3. In some embodiments, the determination module 802 may be configured to determine one or more effective cross-layer leaf gaps. In some embodiments, the determination module 802 may determine the effective cross-layer leaf gap(s) according to a treatment plan or a portion thereof. In some embodiments, the determination module 802 may determine the effective cross-layer leaf gap(s) at one time point in the entire treatment plan or at different time points in the entire treatment plan. More description of the determination of effective cross-layer leaf gap may be found elsewhere in the present disclosure (e.g., FIG. 9 and descriptions thereof). In some embodiments, the control module 804 may be configured to cause one or more leaves to move to form one or more effective cross-layer leaf gaps. In some embodiments, the control module 804 may be configured to cause a first leaf and/or a second leaf to move to form a (prescribed) effective cross-layer leaf gap. In some embodiments, during or before radiation delivery (e.g., of a treatment fraction), the control module 804 may cause one or more leaves of the cross-layer leaf pair to move to prescribed position(s) to form the effective cross-layer leaf gap. More description of the forming of the effective cross-layer leaf gap may be found elsewhere in the present disclosure (e.g., FIG. 9 and descriptions thereof). In some embodiments, the control module 804 may be configured to cause one or more leaves to move to form one or more in-layer leaf gaps. In some embodiments, the control module 804 may be configured to cause, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed or adjusted between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer. Additionally or alternatively, the control module 804 may cause, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed or adjusted between the second leaf and an opposing second leaf that form an in-layer leaf pair in the second layer. In some embodiments, the control module 804 may cause the first in-layer leaf pair in the first layer (and/or the second in-layer leaf pair in the second layer) to be adjusted, based on the first in-layer leaf gap (and/or the second in-layer leaf gap), before or during the treatment process. The control module 804 may cause the first in-layer leaf pair in the first layer and the second in-layer leaf pair in the second layer to be adjusted synchronously or asynchronously (e.g., alternately). More description of the forming or adjustment of the in-layer leaf gap may be found elsewhere in the present disclosure (e.g., FIG. 9 and descriptions thereof). It should be noted that the above description of the processing device 140 is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. For example, the control module 804 may be divided into two units, and the effective cross-layer leaf gap(s) and the in-layer leaf gap(s) may be controlled respectively. FIG. 9 is a flowchart illustrating an exemplary process for adjusting a cross-layer leaf pair of an MLC according to some embodiments of the present disclosure. Various leaves of cross-layer leaf pairs of the MLC may be adjusted according to the process. In some embodiments, one or more operations of process 900 illustrated in FIG. 9 may be performed by the processing device 140 (e.g., the control module 804). In some embodiments, one or more operations of process 900 may be implemented in the radiotherapy system 100 illustrated in FIG. 1. For example, the process 900 may be stored in the storage device 150 and/or the storage 220 in the form of instructions (e.g., an application), and invoked and/or executed by the processing device 140 (e.g., the processor 210 of the computing device 200 as illustrated in FIG. 2, the CPU 340 of the mobile device 300 as illustrated in FIG. 3, one or more modules of the processing device 140 as illustrated in FIG. 8, or the like). As another example, a portion of the process 900 may be implemented on the radiation delivery device 110. The operations of the illustrated process presented below are intended to be illustrative. In some embodiments, the process 900 may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. Additionally, the order in which the operations of the process 900 as illustrated in FIG. 9 and described below is not intended to be limiting. In 902, the processing device 140 (e.g., the determination module 802) may determine an effective cross-layer leaf gap. In some embodiments, the effective cross-layer leaf gap may be formed between a cross-layer leaf pair (e.g., a first leaf in a first layer and a second leaf opposingly located in a second layer of a dual layer MLC (e.g., the effective cross-layer leaf gaps G1, G4, and G5 illustrated in FIGS. 5-7)). More descriptions of the effective cross-layer leaf gap may be found elsewhere in the present disclosure (e.g., FIGS. 5-7 and descriptions thereof). In some embodiments, the effective cross-layer leaf gap may be determined (or prescribed) according to a treatment plan or a portion thereof. In some embodiments, before a treatment process of an object starts, a treatment plan may be generated by a treatment planning system (TPS) associated with the radiotherapy system 100. In some embodiments, the treatment plan may include information associated with the treatment process including, for example, one or more radiation parameters, a treatment dose, or the like, or a combination thereof. The radiation parameters may include radiation beam properties (e.g., a beam shape of range, an aperture shape, an intensity, a radiation direction, or the like), positions and/or directions of an object to be treated, geometric properties of the MLC, or the like. In some embodiments, a treatment process may include one or more treatment fractions (or treatment sessions). In some embodiments, after the treatment plan is generated, a user may verify and/or adjust the treatment plan to avoid potential safety hazards and/or reduce the overall duration of a treatment process. In some embodiments, the user may include a doctor, a radiation therapist, a dosimetrist, a radiation oncologist, a radiation specialist, or the like. In some embodiments, a same cross-layer leaf pair may have different effective cross-layer leaf gaps in different positions or different treatment fractions. Although the treatment plan may be determined before the treatment process, the effective cross-layer leaf gap(s) may be determined before the treatment process or during the treatment process. In some embodiments, the effective cross-layer leaf gap(s) may be determined at one time point in the entire treatment process. Alternatively, the effective cross-layer leaf gap(s) may be determined at different time points in the entire treatment process. For example, after the treatment plan is generated and before the treatment process starts, the effective cross-layer leaf gap(s) in one or more treatment fractions may be already known according to the treatment plan, and then, the effective cross-layer leaf gap(s) in each of the one or more treatment fractions of the entire treatment process may be determined at one time. As another example, during the treatment process (e.g., before each treatment fraction), one or more effective cross-layer leaf gaps may be determined for an upcoming treatment fraction. In some embodiments, one or more first effective cross-layer leaf gaps of the same cross-layer leaf pair may be identified for a first treatment fraction before the first treatment fraction starts; one or more second effective cross-layer leaf gaps of the same cross-layer leaf pair may be determined for a second treatment fraction after the first treatment fraction is finished but before the second treatment fraction starts. It should be noted that in some embodiments, the effective cross-layer leaf gap of a cross-layer leaf pair may be equal to 0 throughout the treatment process. For example, a cross-layer leaf pair may be closed throughout the treatment process. In some embodiments, the effective cross-layer leaf gap of a cross-layer leaf pair may be equal to 0 for one or more treatment fractions. For example, the cross-layer leaf pair may be open in a previous treatment fraction, and may be closed in a next treatment fraction. As another example, the cross-layer leaf pair may be closed in a previous treatment fraction, and may be open in a next treatment fraction. In some embodiments, the effective cross-layer leaf gap of a cross-layer leaf pair may be larger than 0 throughout the treatment process. For example, the cross-layer leaf pair may be open throughout the treatment process. In some embodiments, the effective cross-layer leaf gap(s) may change from treatment fraction to treatment fraction. In some embodiments, in a dynamic radiation therapy, the effective cross-layer leaf gap may change dynamically. In 904, the processing device 140 (e.g., the control module 804) may cause the first leaf and/or the second leaf to move to form the (prescribed) effective cross-layer leaf gap. In some embodiments, the radiation therapy may be static. That is, the cross-layer leaf pair that form the effective cross-layer leaf gap may be static during beam delivery. In some embodiments, the first leaf and/or the second leaf in the cross-layer leaf pair may be caused to move (according to the treatment plan) to form the effective cross-layer leaf gap before the beam delivery. In some embodiments, the radiation therapy may be dynamic. That is, the first leaf and/or the second leaf in the cross-layer leaf pair that forms the effective cross-layer leaf gap may be moved during beam delivery. In some embodiments, the size of the prescribed effective cross-layer leaf gap may be compared with 0. If the prescribed effective cross-layer leaf gap is equal to 0, the first leaf and/or the second leaf may be caused to move, so that one end of the first leaf is aligned with an opposing end of the second leaf (as illustrated in FIG. 5), or the first leaf at least partially overlaps the second leaf (as illustrated in FIG. 6). If the prescribed effective cross-layer leaf gap is larger than 0, the first leaf and/or the second leaf may be caused to move so that one end of the first leaf and an opposing end of the second leaf are spaced apart by a certain distance (i.e., the size of the prescribed effective cross-layer leaf gap) (as illustrated in FIG. 7). In some embodiments, the position of the cross-layer leaf pair may be determined (or prescribed) according to the treatment plan. In some embodiments, different positions may correspond to different effective cross-layer leaf gaps. In some embodiments, different positions may correspond to a same effective cross-layer leaf gap. In some embodiments, during or before radiation delivery (e.g., of a treatment fraction), the cross-layer leaf pair may be caused to move to prescribed position(s). In some embodiments (e.g., in a static radiation therapy), the cross-layer leaf pair may be caused to move to prescribed position(s) first, and then the effective cross-layer leaf gap therebetween may be adjusted to prescribed size(s). In some embodiments (e.g., in a static radiation therapy), the effective cross-layer leaf gap may be adjusted to prescribed size(s) first, and then the cross-layer leaf pair may be caused to move to prescribed position(s). In some embodiments (e.g., in a dynamic radiation therapy), the movement of the cross-layer leaf pair toward prescribed position(s) and the adjustment of the effective cross-layer leaf gap to prescribed size(s) may be performed simultaneously or synchronously. For example, the first leaf and the second leaf of the cross-layer leaf pair may be caused to move simultaneously toward corresponding prescribed positions, respectively, such that when (or before) the first leaf and the second leaf reach corresponding prescribed positions, the effective cross-layer leaf gap therebetween has the prescribed size. In 906, the processing device 140 (e.g., the control module 804) may cause, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed or adjusted between the first leaf and an opposing first leaf that form an in-layer leaf pair in the first layer. Additionally or alternatively, in some embodiments, the processing device 140 (e.g., the control module 804) may cause, based on the effective cross-layer leaf gap, an in-layer leaf gap to be formed or adjusted between the second leaf and an opposing second leaf that form an in-layer leaf pair in the second layer. An in-layer leaf pair in the first layer may also be referred to as a first in-layer leaf pair. An in-layer leaf pair in the second layer may also be referred to as a second in-layer leaf pair. More descriptions of the in-layer leaf gap may be found elsewhere in the present disclosure (e.g., FIGS. 5-7 and descriptions thereof). In some embodiments, the radiation therapy may be static, and accordingly, at least one leaf in an in-layer leaf pair may be caused to be adjusted or moved to form the in-layer leaf gap before one or more treatment fractions (or beam deliveries). In some embodiments, the radiation therapy may be dynamic, and accordingly, the at least one leaf in the in-layer leaf pair may be caused to be adjusted or moved dynamically to form the in-layer leaf gap during one or more treatment fractions (or beam deliveries). In some embodiments, the in-layer leaf gap between the first leaf and the opposing first leaf may be caused to be formed or adjusted by causing the opposing first leaf to move relative to the first leaf (e.g., before or during the treatment process). Similarly, the in-layer leaf gap between the second leaf and the opposing second leaf may be caused to be formed or adjusted by causing the opposing second leaf to move relative to the second leaf (e.g., before or during the treatment process). In some embodiments, the processing device 140 (e.g., the control module 804) may cause a first in-layer leaf pair (or each in-layer leaf pair) in the first layer to be adjusted before or during the treatment process. In some embodiments, the processing device 140 (e.g., the control module 804) may cause a second in-layer leaf pair (or each of at least some in-layer leaf pairs) in the second layer to be adjusted before or during the treatment process. In some embodiments, an in-layer leaf pair may be adjusted by causing one or both of the leaves of the in-layer leaf pair to be moved or adjusted to form an in-layer leaf gap. In some embodiments, operation 906 may be performed before, after, or simultaneously with operation 904. That is, the adjustment (or forming) of the in-layer leaf gap (in the first layer and/or the second layer) may be performed before, after, or simultaneously with the adjustment (or forming) of the effective cross-layer leaf gap. For example, in a static radiation therapy, the in-layer leaf pair (e.g., the first in-layer leaf pair and/or the second in-layer leaf pair) may be adjusted first, and then the cross-layer leaf pair may be adjusted. As another example, in a static radiation therapy, the cross-layer leaf pair may be adjusted first, and then the in-layer leaf pair (e.g., the first in-layer leaf pair and/or the second in-layer leaf pair) may be adjusted. As a further example, the in-layer leaf pair and the cross-layer leaf pair may be adjusted simultaneously, such that when (or before) the first leaf and the second leaf reach corresponding prescribed positions, the effective cross-layer leaf gap therebetween has a prescribed size, the in-layer leaf gap between the first leaf and the opposing first leaf is formed, and/or the in-layer leaf gap between the second leaf and the opposing second leaf is formed. In some embodiments, in-layer leaf gaps of different in-layer leaf pairs (in a same layer or different layers) may be adjusted (i.e., in-layer leaf gaps may be caused to be formed between different in-layer leaf pairs) synchronously. In some embodiments, in-layer leaf gaps of different in-layer leaf pairs may be adjusted asynchronously. The sizes of in-layer leaf gaps of different in-layer leaf pairs may be the same or different. In some embodiments, the in-layer leaf gap may be caused to be formed or adjusted based on the effective cross-layer leaf gap. In some embodiments, the size of the effective cross-layer leaf gap may be compared with 0, and a current size of the in-layer leaf gap may be compared with a threshold (e.g., the first threshold). In some embodiments, the first threshold may be larger than 0. In some embodiments, the first threshold may be within a range from 0.1 to 2 millimeters (such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or the like). Merely by way of example, the first threshold may be within a range from 0.2 to 0.5 millimeters. If the size of the effective cross-layer leaf gap is equal to 0, and the current size of the in-layer leaf gap is less than the first threshold, the in-layer leaf gap between the first leaf and the opposing first leaf (also be referred to as the first in-layer leaf gap) may be caused to be adjusted to no less than the first threshold (e.g., by causing the opposing first leaf to move relative to the first leaf). For example, as shown in FIGS. 5-6, if the size of the effective cross-layer leaf gap (e.g., G1 in FIG. 5, or G4 in FIG. 6) is equal to 0, or the first leaf and/or the second leaf are caused to move to form the effective cross-layer leaf gap (i.e., 0), the current size of the first in-layer leaf gap (e.g., G2 in FIG. 5, or G′2 in FIG. 6) in the first layer may be compared with the first threshold. If the current size of the first in-layer leaf gap (e.g., G2 in FIG. 5, or G′2 in FIG. 6) is less than the first threshold, the first in-layer leaf gap may be caused to be adjusted to no less than the first threshold, e.g., by causing the opposing first leaf (e.g., the opposing first leaf 501a in FIG. 5, or the opposing first leaf 601a in FIG. 6) of the first in-layer leaf pair in the first layer to move relative to the first leaf (e.g., the first leaf 501b in FIG. 5, or the first leaf 601b in FIG. 6). As another example, as shown in FIGS. 5-6, if the size of the effective cross-layer leaf gap (e.g., G1 in FIG. 5, or G4 in FIG. 6) is equal to 0, or the first leaf and/or the second leaf are caused to move to form the effective cross-layer leaf gap (i.e., 0), the current size of the second in-layer leaf gap (e.g., G3 in FIG. 5, or G′3 in FIG. 6) in the second layer may be compared with the first threshold. If the current size of the second in-layer leaf gap (e.g., G3 in FIG. 5, or G′3 in FIG. 6) is less than the first threshold, the second in-layer leaf gap may be caused to be adjusted to no less than the first threshold, e.g., by causing the opposing second leaf (e.g., the opposing second leaf 502b in FIG. 5, or the opposing second leaf 602b in FIG. 6) of the second in-layer leaf pair in the second layer to move relative to the second leaf (e.g., the second leaf 502a in FIG. 5, or the second leaf 602a in FIG. 6). In some embodiments, the size of the effective cross-layer leaf gap may be compared with 0, and a current size of the in-layer leaf gap may be compared with two thresholds (e.g., the first threshold as illustrated above, and the second threshold as described in FIGS. 5-7). In some embodiments, the second threshold may be within a range from 2 to 3 millimeters (such as 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, or the like). The second threshold may be larger than the first threshold. If the size of the effective cross-layer leaf gap is equal to 0, and the current size of the in-layer leaf gap is less than the first threshold, the in-layer leaf gap between the first leaf and the opposing first leaf (also be referred to as the first in-layer leaf gap) may be caused to be adjusted to no less than the first threshold and no larger than the second threshold (e.g., by causing the opposing first leaf to move relative to the first leaf). If the size of the effective cross-layer leaf gap is equal to 0, and the current size of the in-layer leaf gap is larger than the second threshold, the in-layer leaf gap between the first leaf and the opposing first leaf (also be referred to as the first in-layer leaf gap) may be caused to be adjusted to no less than the first threshold and no larger than the second threshold (e.g., by causing the opposing first leaf to move relative to the first leaf). For example, as shown in FIGS. 5-6, if the size of the effective cross-layer leaf gap (e.g., G1 in FIG. 5, or G4 in FIG. 6) is equal to 0, or the first leaf and/or the second leaf are caused to move to form the effective cross-layer leaf gap (i.e., 0), the current size of the first in-layer leaf gap (e.g., G2 in FIG. 5, or G′2 in FIG. 6) in the first layer may be compared with the first threshold. If the current size of the first in-layer leaf gap (e.g., G2 in FIG. 5, or G′2 in FIG. 6) is less than the first threshold or larger than the second threshold, the first in-layer leaf gap may be caused to be adjusted to no less than the first threshold and no larger than the second threshold, e.g., by causing the opposing first leaf (e.g., the opposing first leaf 501a in FIG. 5, or the opposing first leaf 601a in FIG. 6) of the first in-layer leaf pair in the first layer to move relative to the first leaf (e.g., the first leaf 501b in FIG. 5, or the first leaf 601b in FIG. 6). Similarly, if the size of the effective cross-layer leaf gap is equal to 0, and the current size of the second in-layer leaf gap between the second leaf and the opposing second leaf in the second layer is less than the first threshold or larger than the second threshold, then the second in-layer leaf gap may be adjusted to no less than the first threshold and no larger than the second threshold. In some embodiments, if the size of the effective cross-layer leaf gap is larger than 0, then the size of the effective cross-layer leaf gap may be compared with the first threshold. If the effective cross-layer leaf gap is no larger than the first threshold, then the in-layer leaf gap between the first leaf and the opposing first leaf (also be referred to as the first in-layer leaf gap) may be caused to be adjusted to no less than the first threshold (e.g., by causing the opposing first leaf to move relative to the first leaf). For example, as shown in FIG. 7, if the size of the effective cross-layer leaf gap (e.g., G5 in FIG. 7) is larger than 0, or the first leaf and/or the second leaf are caused to move to form the effective cross-layer leaf gap G5, then the size of the effective cross-layer leaf gap (e.g., G5 in FIG. 7) may be compared with the first threshold. If the size of the effective cross-layer leaf gap (e.g., G5 in FIG. 7) is no larger than the first threshold, then the first in-layer leaf gap may be caused to be adjusted to no less than the first threshold, e.g., by causing the opposing first leaf (e.g., the opposing first leaf 701a in FIG. 7) of the first in-layer leaf pair in the first layer to move relative to the first leaf (e.g., the first leaf 701b in FIG. 7). Similarly, if the size of the effective cross-layer leaf gap is larger than 0 and no larger than the first threshold, then the second in-layer leaf gap between the second leaf and the opposing second leaf in the second layer may be adjusted to no less than the first threshold (e.g., by causing the opposing second leaf to move relative to the second leaf). Therefore, radiation beam (or beam let) of prescribed dose can be delivered through the effective cross-layer leaf gap, and collisions between in-layer leaf pairs can be avoided. In some embodiments, if the size of the effective cross-layer leaf gap is larger than 0 and no larger than the first threshold, then the first in-layer leaf gap (and/or the second in-layer leaf gap) may be adjusted to no less than the first threshold and no larger than the second threshold, e.g., by causing the opposing first leaf of the in-layer leaf pair in the first layer to move relative to the first leaf (and/or by causing the opposing second leaf of the in-layer leaf pair in the second layer to move relative to the second leaf). Therefore, radiation beam (or beam let) of prescribed dose can be delivered through the effective cross-layer leaf gap, collisions between in-layer leaf pairs can be avoided, and excessive radiation leakage through the in-layer leaf gap can be avoided. In some embodiments, if the size of the effective cross-layer leaf gap is larger than 0, then the size of the effective cross-layer leaf gap may be compared with the first threshold. If the effective cross-layer leaf gap is larger than the first threshold, then the in-layer leaf gap between the first leaf and the opposing first leaf (also be referred to as the first in-layer leaf gap) may be caused to be adjusted to no less than the effective cross-layer leaf gap (e.g., by causing the opposing first leaf to move relative to the first leaf). For example, as shown in FIG. 7, if the size of the effective cross-layer leaf gap (e.g., G5 in FIG. 7) is larger than 0, or the first leaf and/or the second leaf are caused to move to form the effective cross-layer leaf gap G5, then the size of the effective cross-layer leaf gap (e.g., G5 in FIG. 7) may be compared with the first threshold. If the size of the effective cross-layer leaf gap (e.g., G5 in FIG. 7) is larger than the first threshold, then the first in-layer leaf gap may be caused to be adjusted to no less than the effective cross-layer leaf gap, e.g., by causing the opposing first leaf (e.g., the opposing first leaf 701a in FIG. 7) of the first in-layer leaf pair in the first layer to move relative to the first leaf (e.g., the first leaf 701b in FIG. 7). Similarly, if the size of the effective cross-layer leaf gap is larger than 0 and further larger than the first threshold, then the second in-layer leaf gap between the second leaf and the opposing second leaf in the second layer may be adjusted to no less than the effective cross-layer leaf gap (e.g., by causing the opposing second leaf to move relative to the second leaf). Therefore, the opposing first leaf (or the opposing second leaf) does not protrude into the effective cross-layer leaf gap, radiation beam (or beam let) of prescribed dose can be delivered through the effective cross-layer leaf gap, and collisions between in-layer leaf pairs can be avoided. In some embodiments, if the size of the effective cross-layer leaf gap is larger than 0, then the size of the effective cross-layer leaf gap may be compared with the first threshold and the second threshold. If the effective cross-layer leaf gap is larger than the first threshold but no larger than the second threshold, then the in-layer leaf gap between the first leaf and the opposing first leaf (also be referred to as the first in-layer leaf gap) may be caused to be adjusted to no less than the effective cross-layer leaf gap and no larger than the second threshold (e.g., by causing the opposing first leaf to move relative to the first leaf). Similarly, if the size of the effective cross-layer leaf gap is larger than the first threshold but no larger than the second threshold, then the second in-layer leaf gap between the second leaf and the opposing second leaf in the second layer may be adjusted to no less than the effective cross-layer leaf gap and no larger than the second threshold (e.g., by causing the opposing second leaf to move relative to the second leaf). Therefore, the opposing first leaf (or the opposing second leaf) does not protrude into the effective cross-layer leaf gap, radiation beam (or beam let) of prescribed dose can be delivered through the effective cross-layer leaf gap, collisions between in-layer leaf pairs can be avoided, and excessive radiation leakage through the in-layer leaf gap can be avoided. In some embodiments, if the size of the effective cross-layer leaf gap is larger than the second threshold, then the in-layer leaf gap between the first leaf and the opposing first leaf (also be referred to as the first in-layer leaf gap) may be caused to be adjusted to no less than the effective cross-layer leaf gap (e.g., by causing the opposing first leaf to move relative to the first leaf). Similarly, if the size of the effective cross-layer leaf gap is larger than the second threshold, then the second in-layer leaf gap between the second leaf and the opposing second leaf in the second layer may be adjusted to no less than the effective cross-layer leaf gap (e.g., by causing the opposing second leaf to move relative to the second leaf). Therefore, the opposing first leaf (or the opposing second leaf) does not protrude into the effective cross-layer leaf gap, radiation beam (or beam let) of prescribed dose can be delivered through the effective cross-layer leaf gap, collisions between in-layer leaf pairs can be avoided, and excessive radiation leakage through the in-layer leaf gap can be avoided. In some embodiments, the processing device 140 (e.g., the control module 804) may cause the first in-layer leaf pair in the first layer (and/or the second in-layer leaf pair in the second layer) to be adjusted, based on the first in-layer leaf gap (and/or the second in-layer leaf gap), before or during the treatment process. In some embodiments, during the movement of the first in-layer leaf pair (or the second in-layer leaf pair), the first in-layer leaf gap (or the second in-layer leaf gap) may remain unchanged or be changed dynamically. The processing device 140 (e.g., the control module 804) may cause the first in-layer leaf pair in the first layer and the second in-layer leaf pair in the second layer to be adjusted synchronously or asynchronously (e.g., alternately). In some embodiments, in a treatment process, one or more leaves of cross-layer leaf pairs and/or one or more leaves of in-layer leaf pairs of the MLC may be adjusted or moved. In some embodiments, an effective cross-layer leaf gap may be formed between the first leaf in the first layer and the second leaf in the second layer. In some embodiments, an in-layer leaf gap may be formed between the first leaf and the opposing first leaf that form an in-layer leaf pair in the first layer. In some embodiments, the size of the in-layer leaf gap may be no less than the size of the effective cross-layer leaf gap. In some embodiments, the size of the in-layer leaf gap may be no less than the first threshold and no larger than the second threshold. In some embodiments, the size of the in-layer leaf gap may be determined based on a random value. For example, the size of the in-layer leaf gap may have a random value. In some embodiments, the size of the in-layer leaf gap may have a fixed value when the size of the effective cross-layer leaf gap is 0. In some embodiments, the size of the in-layer leaf gap may be equal to a sum of a fixed value and the size of the effective cross-layer leaf gap. In some embodiments, the size of the in-layer leaf gap may be equal to the size of the effective cross-layer leaf gap when the size of the effective cross-layer leaf gap is no less than a third threshold. In some embodiments, the third threshold may be larger than 0. In some embodiments, the third threshold may be no less than the first threshold and/or no larger than the second threshold. In some embodiments, the third threshold may be larger than the second threshold. It should be noted that the above descriptions of the process 900 are merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skill in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, at least one in-layer leaf pair or cross-layer leaf pair of the leaves in the MLC may be caused to move according to the process 900. In some embodiments, two or more in-layer leaf pairs or cross-layer leaf pairs of the MLC may be moved according to the process 900 synchronously or alternately. In some embodiments, the process 900 may be repeated to form two or more effective cross-layer leaf gaps for a same cross-layer leaf pair (or form two or more in-layer leaf gaps for a same in-layer leaf pair) for a radiation treatment. Having thus described the basic concepts, it may be rather apparent to those skilled in the art after reading this detailed disclosure that the foregoing detailed disclosure is intended to be presented by way of example only and is not limiting. Various alterations, improvements, and modifications may occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested by this disclosure and are within the spirit and scope of the exemplary embodiments of this disclosure. Moreover, certain terminology has been used to describe embodiments of the present disclosure. For example, the terms “one embodiment,” “an embodiment,” and/or “some embodiments” mean that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the present disclosure. Further, it will be appreciated by one skilled in the art, aspects of the present disclosure may be illustrated and described herein in any of a number of patentable classes or context including any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof. Accordingly, aspects of the present disclosure may be implemented entirely hardware, entirely software (including firmware, resident software, micro-code, etc.) or combining software and hardware implementation that may all generally be referred to herein as a “unit,” “module,” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer-readable media having computer readable program code embodied thereon. A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including electromagnetic, optical, or the like, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that may communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including wireless, wireline, optical fiber cable, RF, or the like, or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present disclosure may be written in a combination of one or more programming languages, including an object-oriented programming language such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB. NET, Python or the like, conventional procedural programming languages, such as the “C” programming language, Visual Basic, Fortran 2103, Perl, COBOL 2102, PHP, ABAP, dynamic programming languages such as Python, Ruby, and Groovy, or other programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider) or in a cloud computing environment or offered as a service such as a Software as a Service (SaaS). Furthermore, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations, therefore, is not intended to limit the claimed processes and methods to any order except as may be specified in the claims. Although the above disclosure discusses through various examples what is currently considered to be a variety of useful embodiments of the disclosure, it is to be understood that such detail is solely for that purpose and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover modifications and equivalent arrangements that are within the spirit and scope of the disclosed embodiments. For example, although the implementation of various components described above may be embodied in a hardware device, it may also be implemented as a software-only solution, for example, an installation on an existing server or mobile device. Similarly, it should be appreciated that in the foregoing description of embodiments of the present disclosure, various features are sometimes grouped in a single embodiment, figure, or descriptions thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive embodiments. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, inventive embodiments lie in less than all features of a single foregoing disclosed embodiment. In some embodiments, the numbers expressing quantities or properties used to describe and claim certain embodiments of the application are to be understood as being modified in some instances by the term “about,” “approximate,” or “substantially.” For example, “about,” “approximate,” or “substantially” may indicate ±20% variation of the value it describes, unless otherwise stated. Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. Each of the patents, patent applications, publications of patent applications, and other material, such as articles, books, specifications, publications, documents, things, and/or the like, referenced herein is hereby incorporated herein by this reference in its entirety for all purposes, excepting any prosecution file history associated with same, any of same that is inconsistent with or in conflict with the present document, or any of same that may have a limiting affect as to the broadest scope of the claims now or later associated with the present document. By way of example, should there be any inconsistency or conflict between the description, definition, and/or the use of a term associated with any of the incorporated material and that associated with the present document, the description, definition, and/or the use of the term in the present document shall prevail. In closing, it is to be understood that the embodiments of the application disclosed herein are illustrative of the principles of the embodiments of the application. Other modifications that may be employed may be within the scope of the application. Thus, by way of example, but not of limitation, alternative configurations of the embodiments of the application may be utilized in accordance with the teachings herein. Accordingly, embodiments of the present application are not limited to that precisely as shown and described.
	abstract	A 2D collimator is disclosed for a radiation detector. In at least one embodiment, the 2D collimator includes 2D collimator modules arranged in series, wherein adjacent 2D collimator modules are glued together to establish a fixed mechanical connection to facing module sides, and wherein, on their free-remaining side, the outer 2D collimator modules have a retaining element for mounting the 2D collimator opposite a detector mechanism. A method for manufacturing such a 2D collimator is also disclosed.
	summary
051805499	description	DETAILED DESCRIPTION OF THE INVENTION In the following description, like references characters designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. Referring now to the drawings, and particularly to FIG. 1, there is shown a fuel assembly, generally designated by the numeral 10, having a double enclosure top nozzle subassembly 12 constructed in accordance with the principles of the present invention. In addition to the top nozzle subassembly 12, the fuel assembly 10 basically includes a bottom nozzle 14 for supporting the fuel assembly on the lower core support plate (not shown) in the core region of a nuclear reactor (not shown) and a number of longitudinally extending control rod guide tubes or thimbles 16 projecting upwardly from the bottom nozzle 14 and attached at their upper and lower ends to the top nozzle subassembly 12 and bottom nozzle 14. Further, an organized array of fuel rods 18 are held in spaced relationship to one another by a number of transverse grids 20 spaced along the fuel assembly length and attached to the guide thimbles 16. An instrumentation tube 22 is located at the center of the fuel assembly 10. The top nozzle subassembly 12, bottom nozzle 14 and guide thimbles 16 together form an integral assembly capable of being conventionally handled without damaging the assembly parts. Referring to FIGS. 1 and 2, the double enclosure top nozzle subassembly 12 of the present invention has a construction which permits improved utilization of space for accommodating greater thermal growth of fuel rods 18 of the fuel assembly 10 and higher fuel rod burnup. At the same time, the top nozzle subassembly 12 continues to allow the use of a conventional handling system for installing and removing the fuel assembly 10 in and from the reactor core. Basically, the top nozzle subassembly 12 includes an upper structure 24, a lower structure 26, interengaging means 28 on the lower and upper peripheral edges of the respective upper and lower structures 24, 26, and a plurality of resiliently-yieldable biasing devices 30 disposed between the upper and lower structures 24 26. As shown alone and in greater detail in FIGS. 2-11, the upper structure 24 of the top nozzle subassembly 12 is composed of a top plate 32 and an outer sidewall enclosure 34 rigidly connected to and depending from the top plate 32. Referring to FIGS. 3-8, the top plate 32 is generally rectangular in configuration having four sides 32A defining four corners 32B. The top plate 32 includes an annular body 36 and an annular rim 38 integrally attached to and projecting outwardly from an upper outer peripheral edge of the body 36. The body 36 has an inner peripheral edge defining a large central opening 40. Two diagonal ones of the corner 32B of the top plate body 36 each has a hole 42 defined therethrough which permit insertion of components of the fuel assembly handling system (not shown) for engaging the underside surface 32C of the top plate 32 in order to lift the fuel assembly 10 in installing and removing it from the core. One of the other corners 32B has a hole 44 which provides a reference for properly orientating the fuel assembly 10 in the core. The annular rim 38 on the body 36 of the top plate 32 defines an annular cavity 46 surrounding the annular body 36 below an outer peripheral edge of the top plate 32 defined by the rim 38. The annular cavity 46 receives an upper peripheral edge portion 34A of outer sidewall enclosure 34. The top plate 32 also has a plurality of indentations 48 defined in spaced relation from one another along the periphery and underside surface 32C of the annular body 36 of the top plate 32. The indentations 48 face outwardly and downwardly of the annular body 36. Portions of the annular body 36 between the indentations 48 form downwardly protruding tabs 50 along the periphery of the body 36 for attaching the upper peripheral edge 34A of the outer sidewall enclosure 34 to the top plate 32. Referring to FIGS. 9 and 10, the outer sidewall enclosure 34 of the upper structure 24 is composed of four generally planar vertical wall portions 34B rigidly interconnected together at their opposite vertical edges to define the outer enclosure 34 in a generally square box-like configuration. As shown in FIGS. 19-22, a series of aligned holes 52, 54 are formed in the annular body 36 below the rim 38 and in the upper peripheral edge portion 34A of the outer sidewall enclosure 34. Pins 56 are inserted through the aligned holes 52, 54 for securing the outer sidewall enclosure 34 and the annular body 36 together. The holes 52 in the annular body 36 can either extend partially into the body 36 as shown in FIG. 20 and complete through the body 36 as shown in FIG. 21. As shown alone and in greater detail in FIGS. 12-15, the lower structure 26 of the top nozzle subassembly 12 is composed of a lower adapter plate 58 and an inner sidewall enclosure 60 rigidly connected to and upstanding from the lower adapter plate 58. Referring to FIG. 15, the lower adapter plate 58 is generally rectangular in configuration having four sides 58A defining four corners 58B. The lower adapter plate 58 is formed of a plurality of cross-laced ligaments or bars 62 defining a plurality of coolant flow openings 64 of oblong shapes. Also, a plurality of circular through holes 66 corresponding in number and pattern to that of the guide thimbles 16 are provided through the adapter plate 58. The through holes 66 are of sufficient dimensional size to permit the adapter plate 58 to be installed over the upper ends of the guide thimbles 16. Referring to FIGS. 12 and 13, the inner sidewall enclosure 60 of the lower structure 26 is composed of four generally planar vertical wall portions 60A rigidly interconnected together at their opposite vertical edges to define the inner enclosure 60 in a generally square box-like configuration and integrally connected at their lower edges to the periphery of the lower adapter plate 58. The inner sidewall enclosure 60 has a plurality of upper edge portions 60B spaced apart by notches 68 defined between the upper edge portions 60B. The alternating upper edge portions 60B and the notches 68 of the inner sidewall enclosure 60 of the lower structure 26 are capable of mating respectively with the alternating indentations 48 and tabs 50 of the annular body 36 of the top plate 32 of the upper structure 24 when the top nozzle subassembly 12 is in the compressed condition, as depicted in FIG. 18. Thus, the lower adapter plate 58 of the lower structure 26 is disposed below the top plate 32 of the upper structure 24 with the inner sidewall enclosure 60 being disposed within the outer sidewall enclosure 34. Further, the inner and outer sidewall enclosures 60, 34 are movable in sliding contacting relationship relative to one another so as to permit movement of the top plate 32 toward and away from the lower adapter plate 58 and thereby the top nozzle subassembly 12 between compressed condition of FIG. 18 and the expanded condition of FIG. 17. Referring to FIGS. 1, 9-14 and 16-22, the interengaging means 28 on respective upper and lower peripheral edge portions 60B, 34A of the inner and outer sidewall enclosures 60, 34 define stops which limit the movement of the top plate 32 and lower adapter plate 58 away from each other so as to retain the outer and inner sidewall enclosures 34, 60 in the sliding contacting relationship with one another. In addition, the interengaging means 28 define sliding contact surfaces between the outer and inner sidewall enclosures 34, 60. The interengaging means 28 on the respective upper and lower structures 24, 26 include an inwardly-projecting continuous annular flange 70 on the lower peripheral edge of the outer sidewall enclosure 34, and an outwardly-projecting interrupted annular flange 72 on the upper edge portion of the inner sidewall enclosure 60. The inwardly-projecting flange 70 defines a contact surface 70A engaged with an exterior surface 60C of the inner sidewall enclosure 60. The outwardly-projecting flange 72 defines a contact surface 72A engaged with an interior surface 34C of the outer sidewall enclosure 34. As seen in FIGS. 1, 16, 17 and 19-22, the flanges 70, 72 provide the stops by overlapping with one another so as to prevent the outer and inner enclosures 34, 60 from pulling apart. Referring to FIGS. 1 and 16-18, there is illustrated the resiliently-yieldable biasing devices 30 disposed within the outer and inner sidewall enclosures 34, 60 and extending between and engaging the top plate 32 and the lower adapter plate 58. The devices 30 are composed of resiliently and yieldable flexible material, such as a metal material, and are movable between compressed and expanded states, as shown in FIGS. 17 and 16, in response respectively to application and removal of a hold-down force on the upper structure 24 in the direction of the lower structure 26 for respectively permitting and causing movement of the top nozzle subassembly 12 between compressed and expanded conditions. More particularly, preferably the biasing devices 30 are a plurality of leaf springs 74 arranged in separate stacks thereof and disposed between the top plate 32 and the lower adapter plate 58 and flexible between expanded and compressed states. The lower adapter plate 58 has a depression 76 formed in a topside surface 58C of the lower adapter plate along each of the sides 58A and approximately midway between the corners 58B thereof. The top plate 32 has a pair of elongated guide grooves 78 defined in the underside surface 32C of the top plate 32 along each of the sides 32A and adjacent the corners 32B thereof. The leaf springs 74 each has a generally U-shaped configuration composed of a lower bight portion 74A and upper end portions 74B connected to and extending upwardly from the lower bight portion 74A. Each leaf spring 74 is seated at the lower bight portion 74A within one of the depressions 76 of the lower adapter plate 58 and at the opposite upper end portions 74B within the guide grooves 78 of the top plate 32. It should be realized, however, that other forms of the biasing devices 30 can be used, such as elongated coil springs. The coil springs would be mounted between the top plate 32 and the lower adapter plate 58 in the same way as illustrated and described in the patent application cross-referenced above, the disclosure of which is incorporated herein by reference. FIGS. 16 and 17 depict successive stages in the assembly of the double enclosure top nozzle subassembly 12. FIG. 16 shows the top nozzle subassembly 12 after the leaf springs 74 have been installed in the telescoping outer and inner enclosures 34, 60, but before the top plate 32 is applied and secured to the outer enclosure 34. FIG. 17 shows the top nozzle subassembly 12 after the top plate 32 and pins 56 has been installed to secure the top plate to the upper peripheral edge portion 34A of the outer enclosure 34. FIGS. 19-21 depict successive stages in the installation and securement of the top plate 32 and pins 56 to the upper peripheral edge portion 34A of the outer enclosure 34. In summary, FIG. 17 shows the top nozzle subassembly 12 in an expanded condition, whereas FIG. 18 shows it in a compressed condition. In both conditions of the top nozzle subassembly 12, the lower adapter plate 58 is stationarily secured in the same position on the upper ends of the guide thimbles 16 in a conventional manner by locking tubes 80. By way of example, the lower adapter plate 58 is disposed approximately 1 inch to 1.5 inches higher above the upper ends of the fuel rods 18 than is a conventional adapter plate heretofore. Also, the inner sidewall enclosure 58 is slidably movably mounted within the interior of the outer sidewall enclosure 34. The overlapping flanges 70, 72 provide stops which prevent separation of the upper structure 24 from the lower structure 26. To place the top nozzle subassembly 12 in the expanded condition seen in FIG. 17, the upper core support plate (not shown) is removed from imposing a downward bearing contact force upon the top plate 32 of the upper structure 24 of the top nozzle subassembly. The leaf springs 74 are thus allowed to assume their unflexed, or expanded, states in which they force the upper structure 24 away from the lower structure 26 to the limit defined by engagement between the flanges 70, 72. The lower adapter plate 58 and top plate 32 are now spaced their maximum distance apart and provide sufficient space between them for insertion of the components of the fuel assembly handling system through the corner holes 42 in the top plate 32. To place the top nozzle subassembly 12 in the compressed condition seen in FIG. 18, the upper core support plate is installed upon the top plate 32 of the upper structure 24 of the top nozzle subassembly so as to reimpose the downward bearing contact force thereon. The top plate 32 is thus moved downward toward the lower adapter plate 58 forcing the leaf springs 60 to their flexed, or compressed, states and slidably moving the outer sidewall enclosure 34 downwardly along and relative to the inner sidewall enclosure 60 and moving the flanges 70, 72 away from one another. The space between the top plate 32 and the adapter plate 58 is now reduced below that needed for insertion of the components of the fuel assembly handling system. This does not matter since the fuel assembly is never handled by the system while it is in the core with the upper core support plate placed on the top nozzle subassembly. Thus, the extra or "dead" space previously existing between the top plate 32 and adapter plate 58 has now been eliminated and is instead now being utilized by the higher mounting position of the adapter plate 58 on the guide thimbles 16 permitting greater distance between the adapter plate 58 and upper ends of the fuel rods 18 for increased thermal growth and greater burnup of the fuel rods in the core. Later when the fuel assembly 10 is to be handled, the upper core plate is removed and the leaf springs 74 moves the upper structure 24 upward to its position in FIG. 17 returning the top plate 32 and adapter plate 58 to their maximum spacing for providing the necessary space therebetween for the fuel assembly handling system components. The lower peripheral edge portion of the upper structure 24 does not move downwardly past the lower adapter plate 58 and so any possible fretting of the fuel rods 18 is eliminated. The central opening 40 of the top plate 32 accommodates passage of control rods (not shown) into the guide thimbles 16 in a conventional manner. The leaf springs 74 transmit the necessary hold-down force from the upper core plate directly to the adapter plate 58. It will be noted also that the telescoping outer and inner sidewall enclosures 34, 60 of the upper and lower structures 24, 26 completely enclose the leaf springs 74 in both expanded and compressed conditions of the top nozzle subassembly 12, thus protecting and shielding the springs from imposition of lateral forces thereon by coolant flow. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.
	abstract	A system and a method for injecting hydrogen into Boiling Water Reactor (BWR) reactor support systems in operation during reactor startup and/or shutdown to mitigate Inter-Granular Stress Corrosion Cracking (IGSCC). The system may provide hydrogen at variable pressures (including relatively higher pressures) that match changing operating pressures of the reactor supports systems as the reactor cycles through startup and shutdown modes.
	description	This is a divisional application of application Ser. No. 10/898,181 filed Jul. 26, 2004 now U.S. Pat. No. 7,203,263, the entire contents of which are hereby incorporated by reference. 1. Field of the Invention This invention relates generally to nuclear reactors and more particularly, to assemblies and methods for coupling core spray line assemblies within such reactors in a repair. 2. Description of Related Art A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud or shroud typically surrounds the core and is supported by a shroud support structure. Boiling water reactors have numerous piping systems, and such piping systems may be utilized, for example, to transport water throughout the RPV. For example, core spray piping may be used to deliver water from outside the RPV to core spargers inside the RPV and to cool the core. The core spray piping may be coupled to a thermal sleeve which may be slip fit into a RPV nozzle safe end. Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds which are exposed to high temperature water. The reactor components may be subject to a variety of stresses. These stresses may be associated with, for example, differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other stress sources, such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can influence the susceptibility of metal in a component to SCC. Reactor internal piping, such as thermal sleeves and core spray lines, may occasionally require replacement as a result of failure due to SCC. Replacing the core spray piping typically may include removing the core thermal sleeve from the RPV nozzle safe end. In the event a safe end requires replacement, the reactor must be shut down for maintenance and drained to an elevation below that of the safe end. The safe end is then removed and a replacement safe end is welded to the RPV nozzle. Thereafter, a replacement core spray line (external to the reactor) may be welded to the replacement safe end. Replacing a safe end is typically time consuming and costly, since such replacement generally requires a lengthy reactor outage of several days to a week or more. It would be desirable to provide an assembly which facilitates replacing core spray lines without removing the reactor pressure vessel safe end. It also would be desirable to provide such an assembly which is easily removed and installed without the necessity of welding. An exemplary embodiment of the present invention is directed to a core spray T-box attachment assembly for a core spray nozzle. The assembly may include a primary cruciform wedge and a secondary cruciform wedge in contact with the primary cruciform wedge to form a cruciform wedge subassembly adapted for insertion within a bore of the core spray nozzle to sealingly engage an interior converging portion of a safe end of the core spray nozzle. The assembly may include a spider in contact with the cruciform wedge subassembly, and a draw bolt for engaging an axial bore of a center portion of the cruciform wedge subassembly and the spider to the T-box. Another exemplary embodiment of the present invention is directed to a method of replacing a subassembly (having a T-box and thermal sleeve) within a core spray nozzle of a nuclear reactor. The method may include removing the T-box and thermal sleeve and machining the safe end. Replacement hardware may be inserted therein. The replacement hardware may be configured to create a seal against a converging inner surface of the safe end of a core spray nozzle. Another exemplary embodiment of the present invention is directed to an attachment assembly. The attachment assembly may include a hollow wedge having a plurality of parts. Each part may be configured to contact a first surface, the attachment assembly may also include a first component configured to pull each of the plurality of parts in a first direction against the first surface; and a second component configured to push against a second surface in a second direction, while pulling the first component in the first direction. FIG. 1 is a top plan view of a boiling water nuclear reactor pressure vessel (RPV) 10. RPV 10 includes a vessel wall 12 and a shroud 14 which surrounds the reactor core (not shown) of RPV 10. An annulus 16 may be formed between vessel wall 12 and shroud 14. The space inside annulus 16 may be limited, as most reactor support piping may be located within annulus 16. In the event of a reactor plant casualty, such as a loss of coolant accident, cooling water is delivered to the reactor core through core spray distribution header pipes 18 and 20, which are connected to respective downcomer pipes 22 and 24. Downcomer pipes 22 and 24 are connected to shroud 14 through respective lower T-boxes 26 and 28, which are attached to shroud 14 and internal spargers 30. FIG. 2 is a top sectional view of a T-box attachment assembly in accordance with an exemplary embodiment of the invention. Distribution header pipes 18 and 20 may diverge from an upper T-box attachment assembly 32. Particularly, T-box attachment assembly 32 may include, in one example, a T-box housing 34 having first, second, and third ends 36, 38 and 40 as shown in FIG. 2. First end 36 of T-box housing 34 is coupled to a safe end 42 of core spray nozzle 44 by a thermal sleeve 50 (shown in FIG. 2). Ends 38 and 40 are configured to be in substantial alignment and configured to couple to core spray distribution header pipes 18 and 20 respectively. Header pipes 18 and 20 are coupled to second and third ends 38 and 40 by pipe connectors 46 and 48 respectively. Pipe connectors 46 and 48 may be any pipe connectors known in the art, for example, ball flange connectors. FIG. 3 is a detailed view of a portion of the T-box attachment assembly in accordance with an exemplary embodiment of the invention. FIG. 4 is an exploded view of the T-box attachment assembly in accordance with an exemplary embodiment of the invention. Referring primarily to FIG. 3 (with occasional reference to FIG. 2), the T-box attachment assembly 32 includes in addition to T-box housing 34, a thermal sleeve 50, a spider 52, a cruciform wedge subassembly 53, a draw bolt 59, a draw bolt nut 58, and a nut keeper 60. First end 36 of T-box housing 34 is welded to a first end 62 of thermal sleeve 50. T-box housing 34 is configured to be positioned so that thermal sleeve 50 is located inside core spray nozzle 44 and is fitted to the inside of the spray nozzle safe end 42. For example, safe end 42 includes a safe end bore 68 extending through the safe end 42. Safe end bore 68 includes an inside surface 120 with a converging tapered portion 70 and a diverging tapered portion 71. A second end 72 of thermal sleeve 50 is positioned within core spray nozzle safe end 42. An inner surface of thermal sleeve 50 may include threads 114 at second end 72. T-box housing 34 may also include a cover opening (not shown for clarity) that is in substantial alignment with first end 36, and is configured to receive a T-box cover plate 82. Referring to FIG. 4, spider 52 may include a cylindrical shell that includes external threads 124 sized to threadedly engage internal threads 114 of thermal sleeve 50. Vanes extend from an inside surface of the spider shell to a spider center member. The spider 52 center member includes an axial spider bore 138 extending through the spider 52. The spider bore 138 may be sized to receive draw bolt 59. The spider 52 may include a tongue or groove to interface with a tongue or groove of the cruciform wedge subassembly 53 to form a tongue and groove joint 75, as generally shown in FIG. 3, for example. Cruciform wedge subassembly 53 may comprise a plurality of components. For example, the cruciform wedge subassembly 53 may include a primary cruciform wedge 54 and a secondary cruciform wedge 55. The primary cruciform wedge 54 may include a first support member 154a that extends between two web members 57 and a second support member 154b that also extends between two web members 57. The secondary cruciform wedge 55 may include a third support member 155a that extends between two web members 57 and a fourth support member 155b that also extends between two web members 57. The primary cruciform wedge 54 and the secondary cruciform wedge 55 may be joined to make the cruciform wedge subassembly 53. Cruciform wedge subassembly 53 includes a central member having a cruciform central member bore 136 extending, therethrough. The web members 57 of the primary cruciform wedge 54 and the secondary cruciform wedge 55 may be joined together to extend from the central member to form an “X” shaped configuration, for example. The support members 154a, 154b, 155a and 155b may be joined together to form a contiguous substantially circular support member. The support members 154a, 154b, 155a and 155b may be tapered to engage inside surface 120 of the nozzle safe end bore 68 tapered portion 70. The engagement of the support members 154a, 154b, 155a and 155b of the cruciform wedge subassembly 53 against the inside surface 120 of the nozzle safe end bore 68 tapered portion 70 may function as a mechanical seal to minimize leakage, for example. Additionally, the web members 57 are contoured to minimize flow resistance. Moreover, cruciform wedge subassembly 53 may include a tongue or groove to interface with a tongue or groove of the spider 52 to form the tongue and groove joint 75. Referring to FIG. 4, a draw bolt 59 may extend through the cruciform central member bore 136 and the spider bore 138. Draw bolt 59 may include a head portion 158 located at a first end. Head portion 158 may be larger than the diameter of the cruciform central member bore 136, and may be conical-shaped to substantially reduce or possibly minimize flow resistance. The conical shape is merely one example, other shapes which would reduce their resistance would be evident to those skilled in the art. A second end 56 of draw bolt 59 is threaded to threadedly engage draw bolt nut 58 (see also FIG. 2). An adjacent section of the draw bolt 59 may have a hexagonal contour that interfaces with a mating hexagonal shaped bore of nut keeper 60 to prevent draw bolt nut 58 from loosening. The nut keeper 60 may be crimped to the outer surface of the draw bolt nut 58, for example. Replacement To replace a core spray line in a nuclear reactor pressure vessel 10, the existing T-box/thermal sleeve combination is removed from the core spray nozzle safe end 42 by any suitable method. The T-box attachment assembly 32 may also be removed from core spray distribution header pipes 18 and 20 (also referred to as “core spray liner”) for example, by roll cutting, conventional underwater plasma arc cutting, and/or electric discharge machining (EDM). A new T-box attachment assembly 32 may be used to connect 18 and 20 to safe end 42 of core spray nozzle 44 by coupling first end 36 of T-box housing 34 to safe end 42 with thermal sleeve 50 and coupling ends 38 and 40 to core spray distribution header pipes 18 and 20. Spider 52 is attached to the second end 72 of thermal sleeve 50 by threadedly engaging spider external threads 124 with thermal sleeve internal threads 114. This threaded connection may provide for ease of fabrication and a means of adjusting the total length of the T-box attachment assembly 32. Once in place, the length of the T-box attachment assembly 32 maybe maintained by installing a dowel pin 168 in the spider 52 and thermal sleeve 50 to prevent relative rotation, as seen in FIG. 3, for example. Draw bolt 59 is then inserted through the cruciform central member bore 136 of the primary and secondary cruciform wedges 54, 55 and the spider bore 138 (not shown in FIG. 4 for reasons of clarity) with threaded end of draw bolt 59 extending away from safe end 42 and towards T-box housing 34. This may be accomplished by attaching a stainless steel cable or wire rope, of about 3 to 5 millimeters in diameter, (not shown) to the threaded end of bolt 59, and threading the cable through the cruciform central member bore 136 of the primary and secondary cruciform wedges 54, 55 and the spider bore 138 before inserting the primary and secondary cruciform wedges 54, 55 and draw bolt 59 into the safe end 42. The primary and secondary cruciform wedges 54, 55 and draw bolt 59 may then be inserted into safe end bore 68. The primary and secondary cruciform wedges 54 and 55 are sequentially inserted in an orientation that positions the axis of the cruciform central member bore 136 of the primary and secondary cruciform wedges 54, 55 perpendicular to the axis of the safe end bore 68 of nozzle safe end 42. Primary and secondary cruciform wedges 54, 55 are then tilted so as to move cruciform central member bore 136 into co-axial alignment with the safe end bore 68. The primary and secondary cruciform wedges may then be assembled to form the cruciform wedge subassembly 53 and support members 154a, 154b, 155a and 155b may be pulled to engage the tapered portion 70 of the safe end bore 68. After the cruciform wedge subassembly 53 has been oriented to its operational position, the wire may be pulled through the cruciform central member bore 136 of the cruciform wedge subassembly 53, which in turn pulls the threaded end of draw bolt 59 through cruciform central member bore 136 and the spider bore 138 into position. The head portion 158 of draw bolt 59 may then engage the cruciform wedge subassembly 53. Draw bolt 59 may be tensioned to fix the cruciform wedge subassembly 53 against the spider in tongue and groove 75. Draw bolt nut 58 is then tightened and nut keeper 60 may be crimped to draw bolt nut 58 to prevent loosening. Consequently, the cruciform wedge subassembly 53 may be pulled tight against the spider 52. Keeper 60 interfaces with the hexagonal section of draw bolt 59 to prevent rotation of the draw bolt nut 58 relative to draw bolt 59. The positioning of the cruciform wedge subassembly 53 and the manipulation of the draw bolt 59 may be accomplished through an access 90 in the T-box attachment assembly 32. T-box cover plate 82 is then inserted to cover the access 90. Core spray distribution header pipes 18 and 20 may then be coupled to ends 38 and 40 of the T-box housing 34. First end 36 may be welded to the first end 62 of the thermal sleeve 50, in order to couple first end 36 of the T-box housing 34 to safe end 42. Jack bolt clamp assemblies 25 may be attached to ends of the T-box attachment assembly 32 to complete the installation. The jack bolt clamp assemblies 25 may be adjusted to push against an inner surface of the vessel wall 12 in a first direction and pull, in a second direction, the T-box attachment assembly 32 toward the center of the RPV 10. While clamp assemblies 25 may be used to pull the T-box attachment assembly 32, a spreader or wedge may also be used to cause a similar pull to occur. This pulling action helps create a seal between the cruciform wedge subassembly 53 and the converging, inside surface 120 of the nozzle safe end bore 68 tapered portion 70, for example. The above described T-box attachment assembly 32 may facilitate replacing core spray distribution header pipes 18 and 20 without removing core spray nozzle safe end 42 or draining RPV 10. In addition T-box attachment assembly 32 may facilitate attaching core spray distribution header pipes 18 and 20 to safe end 42 without welding. While the invention has been described in terms of exemplary embodiments, those skilled in the art will e that the exemplary embodiments of the present invention practiced with modification within the spirit and scope of the claims.
051270293	summary	FIELD OF THE INVENTION AND RELATED ART This invention relates to an exposure apparatus using X-rays and, more particularly, to an X-ray exposure apparatus wherein an X-ray beam from a radiation source such as a synchrotron orbit radiation source (SOR source), for example, is made divergent and thus is expanded for exposure of a surface to be exposed. SOR source is a radiation source which emits sheet-like electromagnetic waves (X-rays and the like) having a large divergent angle in a horizontal direction but having a small divergent angle in a vertical direction. Because of small divergent angle in the vertical direction, if an X-ray beam from the SOR source is projected directly to a surface to be exposed, only a limited range of the surface with respect to the vertical direction can be illuminated. For this reason, in an X-ray exposure apparatus which uses a SOR source, it is necessary to take some measure for expanding the X-ray beam emitted from the SOR source in the vertical direction. As an example, a method has been proposed by R. P. Haelbick et al, "J. of Vac. Sci. Technol." B1(4), Oct.-Dec., 1983, pages 1262-1266, according to which a mirror is disposed between a SOR source and a surface to be exposed and the mirror is oscillated with an angle of a few miliradians to scan the whole surface to be exposed, with a slit-like X-ray beam from the SOR source. With this method, however, at a moment only a part of the surface to be exposed can be irradiated with the X-rays. This results in a possibility of local expansion of the surface to be exposed (e.g. a mask) which leads to distortion of a pattern of the mask to be transferred and thus causes a transfer error. Although such a problem may be solved if the period of oscillation of the mirror is made sufficiently short, in order to assure this it is necessary to use a large drive power. This is inconvenient. As another example of expanding the X-ray beam in the vertical direction, a method has been proposed by Warren D. Grobman, "Handbook on Synchrotron Radiation", Vol. 1, Chapter 13, page 1135, North-Holland Publishing Co., 1983, according to which a convex mirror is disposed between a SOR source and a surface to be exposed, so that with the reflection by the convex surface of the mirror the angle of divergence of the X-ray beam in the vertical direction is expanded. This method is free from the problem of local distortion of the pattern as described hereinbefore. However, there is another problem. That is, of the X-ray beam emitted from a SOR source, in a horizontal orbit plane (horizontal section), the X-rays having different emission angles have an intensity distribution which can be considered substantially uniform. However, in a plane (vertical section) perpendicular to the orbit plane, they have an intensity distribution like a Gaussian distribution. This means that there is a difference in intensity between a central part and a peripheral part of the X-ray beam. Therefore, if the X-ray beam is used for the exposure as it is, non-uniform exposure results. Thus, it can not properly be used in an exposure apparatus. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide an X-ray exposure apparatus having an improved mirror reflection system. In accordance with an aspect of the present invention, to achieve the above object, there is provided an X-ray exposure apparatus, comprising: an X-ray source; and directing means for directing an X-ray beam from said X-ray source to a surface to be exposed, said directing means including a mirror having a reflection surface of a curvature radius R with respect to a predetermined sectional plane, for reflecting the X-ray beam and for expanding the diameter thereof with respect to said sectional plane; wherein said mirror satisfies the following conditions: EQU R=(2d.sub.1 d.sub.2 .sigma.')/{[.DELTA.-(d.sub.1 +d.sub.2).sigma.'].multidot..alpha.} where d.sub.1 : the distance from the emission point of said X-ray source to the center of effective X-ray beam diameter on said reflection surface; PA0 d.sub.2 : the distance from the center of effective X-ray beam diameter on said reflection surface to the center of effective X-ray beam diameter on the surface to be exposed; PA0 .alpha.: the angle defined at the center of effective X-ray beam diameter on said reflection surface, between the X-ray beam and said reflection surface; PA0 .sigma.': a standard deviation of a distribution of intensities of X-rays having different emission angles at said sectional plane, at the gravity center wavelength of the X-ray beam from said X-ray source; PA0 .DELTA.: 0.43a.ltoreq.4.0a; and PA0 a: the length of the surface to be exposed, with respect to said sectional plane. PA0 d.sub.1 : the distance from the emission point of said X-ray source to the center of effective X-ray beam diameter on said reflection surface; PA0 d.sub.2 : the distance from the center of effective X-ray beam diameter on said reflection surface to the center of effective X-ray beam diameter on the surface to be exposed; PA0 .alpha.: the angle defined at the center of effective X-ray beam diameter on said reflection surface, between the X-ray beam and said reflection surface; PA0 .sigma.': a standard deviation of a distribution of intensities of X-rays having different angles of emission from said X-ray source, in a sectional plane perpendicular to a generating line of said mirror, at the gravity center wavelength of the X-ray beam from said X-ray source; PA0 .DELTA.: 0.43a.ltoreq..DELTA..ltoreq.4.0a; and PA0 a: the length of the surface to be exposed, with respect to a direction which is substantially perpendicular to the generating line of said mirror. PA0 d.sub.1 : the distance from the emission point of said X-ray source to the center of effective X-ray beam diameter on said reflection surface; PA0 d.sub.2 : the distance from the center of effective X-ray beam diameter on said reflection surface to the center of effective X-ray beam diameter on the mask; PA0 .alpha.: the angle defined at the center of effective X-ray beam diameter on said reflection surface, between the X-ray beam and said reflection surface; PA0 .sigma.': a standard deviation of a distribution of intensities of X-rays having different angles of emission from said X-ray source, in a sectional plane perpendicular to a generating line of said mirror, at the gravity center wavelength of the X-ray beam from said X-ray source; PA0 .DELTA.: 0.43a.ltoreq..DELTA..ltoreq.4.0a; and PA0 a: the length of an area for the pattern of the mask, with respect to a direction which is substantially perpendicular to the generating line of said mirror. In accordance with another aspect of the present invention, there is provided an X-ray exposure apparatus, comprising: an X-ray source; and directing means for directing an X-ray beam from said X-ray source to a surface to be exposed, said directing means including a mirror having a cylindrical surface of a curvature radius R, for reflecting the X-ray beam and for expanding the diameter thereof; wherein said mirror satisfies the following condition: EQU R=(2d.sub.1 d.sub.2 .sigma.')/{[.DELTA.-(d.sub.1 +d.sub.2).sigma.'].multidot..alpha.} where In accordance with a further aspect of the present invention, there is provided an X-ray exposure apparatus, comprising: means for supporting a mask; means for supporting a wafer; and directing means for directing an X-ray beam from an X-ray source to the wafer through the mask to thereby expose the wafer to a pattern of the mask, said directing means including a mirror having a cylindrical reflection surface of a curvature radius R, for reflecting the X-ray beam and for expanding the diameter thereof; wherein said mirror satisfies the following condition: R=(2d.sub.1 d.sub.2 .sigma.')/{[.DELTA.-(d.sub.1 +d.sub.2).sigma.'].multidot..alpha.} where In this Specification, the gravity center wavelength of an X-ray beam from an X-ray source means .lambda./ .sub. 0 which is given by the following equation: ##EQU1## where .lambda. is the wavelength, e(.lambda.) is the energy of the X-ray beam at the wavelength .lambda., and .lambda..sub.1 and .lambda..sub.2 are lower and upper limits of the wavelength region used for the exposure. In an X-ray exposure apparatus according to one preferred form of the present invention, the mirror of said directing means is set so as to satisfy the following condition: EQU R=(2d.sub.1 .multidot.d.sub.2)55 [.DELTA.'-(d.sub.1 +d.sub.2)].multidot..alpha.} where 4.3.times.10.sup.2 a.ltoreq..DELTA.'.ltoreq.4.0.times.10.sup.4 a. The reflection surface of a mirror usable in the present invention may have a well-known structure effective to reflect X-rays with a good efficiency. For example, it may have a multilayered film structure. The present invention can be applied effectively to an exposure apparatus for manufacture of semiconductor devices, for example, wherein the exposure is performed with X-rays from a SOR source. This is because: With the present invention, it is possible to reduce the non-uniformness in the intensity distribution of an X-ray beam from a SOR source. It is therefore possible to illuminate a mask having a semiconductor circuit pattern with X-rays of a desirable intensity distribution. As a result, the semiconductor circuit pattern of the mask can be transferred to a wafer very accurately. It is to be noted here that the present invention is applicable to various types of exposure apparatuses such as, for example, a contact type exposure apparatus wherein a mask is contacted to a wafer, a proximity type exposure apparatus wherein a mask is spaced from a wafer through a distance of a few microns to a few tens of microns, and a projection type exposure apparatus wherein a pattern of a mask is projected to a wafer through a projection system including mirrors. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
	claims	1. A method implemented on a computing device having at least one processor and at least one computer-readable storage medium for correcting position errors for a multi-leaf collimator (MLC), the MLC including a plurality of leaves to shape a radiation field, each of the plurality of leaves being associated with a driving component including a main encoder, the method comprising:determining a first position for each of the plurality of leaves, information associated with the first position including a first movement direction and a first angle, wherein a movement of the each of the plurality of leaves along the first movement direction is configured to move toward or away from a center of the radiation field;obtaining a first reference offset value associated with the first position of the each of the plurality of leaves from a pre-determined offset table;determining an offset value associated with the first position based on the first angle, the first movement direction, and the first reference offset value; anddetermining a target position of the each of the plurality of leaves based on the offset value. 2. The method of claim 1, wherein the determining a first position for each of the plurality of leaves includes:obtaining an angle of a gantry corresponding to the first position of the each of the plurality of leaves;obtaining an angle of a collimator corresponding to the first position of the each of the plurality of leaves, wherein the MLC is mounted in the collimator and rotates along with the collimator; anddetermining the first angle of the each of the plurality of leaves based on the angle of the gantry and the angle of the collimator. 3. The method of claim 1, wherein the determining a first position for each of the plurality of leaves includes:obtaining a first velocity relating to the driving component;in response to a determination that the first velocity relating to the driving component is lower than a first threshold, determining the first movement direction as a backward movement direction, the each of the plurality of leaves being configured to move away from the center of the radiation field along the backward movement direction; andin response to a determination that the first velocity relating to the driving component is greater than a second threshold, determining the first movement direction as a forward movement direction, the each of the plurality of leaves being configured to move toward the center of the radiation field along the forward movement direction. 4. The method of claim 1, wherein the determining a target position of the each of the plurality of leaves based on the offset value includes:subtracting the offset value from a preprogrammed position of the each of the plurality of leaves. 5. The method of claim 1, wherein the information associated with the first position includes a first main encoder value, the determining an offset value associated with the first position based on the first angle, the first movement direction, and the first reference offset value includes:obtaining a first main encoder value corresponding to the first position of the each of the plurality of leaves, the first main encoder value being acquired by the main encoder;obtaining a second main encoder value corresponding to a second position of the each of the plurality of leaves, the second main encoder value being acquired by the main encoder, and the second position being a position at where a movement direction of the each of the plurality of leaves changes from a second movement direction to the first movement direction; anddetermining the offset value associated with the first position based on the first movement direction, the first reference offset value, and a difference between the first main encoder value and the second main encoder value. 6. The method of claim 5, wherein the determining the offset value associated with the first position based on the first movement direction, the first reference offset value, and a difference between the first main encoder value and the second main encoder value includes:if the each of the plurality of leaves moves away from the center of the radiation field along the first movement direction, designating a minimum value among the first reference offset value and a sum of a second reference offset value associated with the second position and the difference between the first main encoder value and the second main encoder value as the offset value associated with the first position; andif the each of the plurality of leaves moves toward the center of the radiation field along the first movement direction, designating a maximum value among the first reference offset value and a sum of the second reference offset value associated with the second position and the difference between the first main encoder value and the second main encoder value as the offset value associated with the first position. 7. The method of claim 1, wherein the determining an offset value associated with the first position based on the first angle, the first movement direction, and the first reference offset value includes:if the each of the plurality of leaves moves toward the center of the radiation field along the first movement direction and the first angle is equal to 0 degrees, designating the offset value associated with the first position as 0. 8. The method of claim 1, wherein the determining a target position of the each of the plurality of leaves based on the offset value includes:obtaining a first main encoder value corresponding to a first position of each of the plurality of leaves acquired by the main encoder; andcorrecting the first main encoder value based on the offset value to obtain the target position of the each of the plurality of leaves. 9. The method of claim 8, wherein the correcting the first main encoder value based on the offset value includes:adding the offset value to the first main encoder value to obtain the target position of the each of the plurality of leaves. 10. A method implemented on a computing device having at least one processor and at least one computer-readable storage medium for correcting position errors for a multi-leaf collimator (MLC), the MLC including a plurality of leaves to shape a radiation field, each of the plurality of leaves being associated with a driving component including a main encoder, the method comprising:determining a first position for each of the plurality of leaves, information associated with the first position including a first movement phase, wherein a movement of the each of the plurality of leaves moves in the first movement phase is configured to move toward or away from a center of the radiation field;determining an offset value associated with the first position based on the first movement phase; anddetermining a target position of the each of the plurality of leaves based on the offset value;wherein the first movement phase associated with the first position of each of the plurality of leaves is determined based on a difference between a first measurement value and a second measurement value acquired by one of the main encoder and an auxiliary encoder in two adjacent sampling periods. 11. The method of claim 10, whereinthe first measurement value corresponds to the first position, the auxiliary encoder is associated with each of the plurality of leaves and configured to determine a position of each of the plurality of leaves; andthe first movement phase includes one of:a first phase in which the each of the plurality of leaves is moving toward the center of the radiation field;a second phase in which the each of the plurality of leaves is static relative to a carriage of the MLC and is directed to move away from the center of the radiation field;a third phase in which the each of the plurality of leaves is moving away from the center of the radiation field; anda fourth phase in which the each of the plurality of leaves is static relative to the carriage of the MLC and is directed to move toward the center of the radiation field. 12. The method of claim 11, wherein the determining an offset value associated with the first position based on the first movement phase includes:in response to a determination that the first movement phase is the second phase or the fourth phase, determining a reference offset value associated with a second position of the each of the plurality of leaves, the second position corresponding to a position at where a movement phase of the each of the plurality of leaves changes from a second movement phase to the first movement phase;obtaining a first main encoder value corresponding to the first position of the each of the plurality of leaves, the first main encoder value being acquired by the main encoder;obtaining a second main encoder value corresponding to the second position of the each of the plurality of leaves, the second main encoder value being acquired by the main encoder; anddetermining the offset value associated with the first position based on a difference between the first main encoder value and the second main encoder value and the reference offset value associated with the second position. 13. The method of claim 11, wherein the determining an offset value associated with the first position based on the first movement phase includes:in response to a determination that the first movement phase is the first phase or the third phase, the offset value associated with the first position is constant. 14. The method of claim 13, wherein the offset value associated with the first position is equal to a reference offset value associated with a second position at where a movement phase of the each of the plurality of leaves changes from a second movement phase to the first movement phase. 15. The method of claim 14, further comprising:determining whether an angle change value of the each of the plurality of leaves between the first position and the second position exceeds a preprogrammed threshold, the information associated with the first position including a first angle; andin response to a determination that the angle change value exceeds the preprogrammed threshold, correcting the offset value associated with the first position of the each of the plurality of leaves. 16. The method of claim 14, further comprising:obtaining a first main encoder value and a first auxiliary encoder value corresponding to the first position of the each of the plurality of leaves, the first main encoder value being acquired by the main encoder, the first auxiliary encoder value being acquired by the auxiliary encoder;obtaining a second main encoder value and a second auxiliary encoder value corresponding to the second position, the second main encoder value being acquired by the main encoder, the second auxiliary encoder value being acquired by the auxiliary encoder;determining a first difference between the first main encoder value and the second main encoder value;determining a second difference between the first auxiliary encoder value and the second auxiliary encoder value;determining whether the offset value associated with the first position needs to be corrected based on the first difference and the second difference; andcorrecting the offset value associated with the first position of the each of the plurality of leaves. 17. The method of claim 15, wherein the first angle of each of the plurality of leaves is determined by:obtaining an angle of a gantry corresponding to the first position of the each of the plurality of leaves;obtaining an angle of a collimator corresponding to the first position of the each of the plurality of leaves, wherein the MLC is mounted in the collimator and rotates along with the collimator; anddetermining the first angle of the each of the plurality of leaves based on the angle of the gantry and the angle of the collimator. 18. The method of claim 11, wherein the information of the first position includes a first angle, and if the first movement phase is the first phase and the first angle is equal to 0 degrees, the offset value associated with the first position is equal to 0. 19. The method of claim 10, wherein the determining a target position of the each of the plurality of leaves based on the offset value includes:subtracting the offset value from a preprogrammed position of the each of the plurality of leaves. 20. A system for correcting position errors for a multi-leaf collimator (MLC), the MLC including a plurality of leaves to shape a radiation field, each of the plurality of leaves being associated with a driving component including a main encoder, the system comprising:at least one storage device storing executable instructions, andat least one processor in communication with the at least one storage device, when executing the executable instructions, causing the system to:determine a first position for each of the plurality of leaves, information associated with the first position including a first movement direction and a first angle, wherein the each of the plurality of leaves moves toward or away from a center of the radiation field along the first movement direction;obtain a first reference offset value associated with the first position of the each of the plurality of leaves from a pre-determined offset table;determine an offset value associated with the first position based on the first angle, the first movement direction, and the first reference offset value; anddetermine a target position of the each of the plurality of leaves based on the offset value.
040452891	abstract	A nuclear reactor containment structure which includes a reinforced concrete shell, a hemispherical top dome, a steel liner, and a reinforced-concrete base slab supporting the concrete shell is constructed with a substantial proportion thereof below grade in an excavation made in solid rock with the concrete poured in contact with the rock and also includes a continuous, hollow, reinforced-concrete ring tunnel surrounding the concrete shell with its top at grade level, with one wall integral with the reinforced concrete shell, and with at least the base of the ring tunnel poured in contact with the rock.
	summary
063303019	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a diagrammatic view of the optical system 10 of the present invention. An x-ray beam 12 is generated by an x-ray source 14 that is directed towards an optic 16, such as an elliptical mirror, that focuses the x-ray beam 12. The optic 16 has a reflective surface which may be comprised of bent graphite, bent perfect crystal, a total reflection mirror, a mulitlayer Bragg reflector which may be depth or laterally graded, or any other x-ray reflective surface known in the art. The optic 16 directs the x-ray beam through a first slit (or pinhole) 18 and a second slit (or pinhole) 20 to form and define a coherent x-ray beam 21. Scattering and interference patterns or noise created by the first slit 18 are blocked by the second slit 20. The focal point 22 of the x-ray beam 21 is located between the second slit 20 and an x-ray detector 30. A sample chamber 24, containing a sample structure 26 to be analyzed, includes a third slit 28 to eliminate scattering and interference patterns created by the second slit 20. The x-ray beam 21 flux at the sample chamber 24 and the x-ray beam 21 size or incident area on the x-ray detector 30 depend on where the focal point 22 of the optic 16 is located. Flux passing through the second slit 20 and reaching the sample chamber 24 is the greatest when the focal point 22 of the optic 16 is positioned on the second slit 20, and the x-ray beam 21 size on the x-ray detector 30 is also the greatest in this situation. The x-ray beam 21 size on the x-ray detector 30 is the smallest if the focal point 22 of the optic 16 is positioned on or at the x-ray detector 30, therefore the resolution of a system using this focal point 22 position would be the greatest. However, the flux in this case would also be the smallest. Therefore, the position of the focal point 22 in the system is determined by the trade-off between intensity and resolution of x-rays incident on the x-ray detector 30. In certain cases, due to the intrinsic divergence of the x-ray beam 21, the resolution would reach its limit at certain positions of the focal point 22. Accordingly, moving the focal point 22 closer to x-ray detector 30 would not improve the resolution and would only reduce the flux. Thus, in this case, there would be no benefit to focus the x-ray beam 21 on the x-ray detector 30. Since the minimum accessible angle of the system is determined by the slit (pinhole) configuration, it is independent of the position of the focus. The first and second slits 18 and 20 of the optical system 10 determine the size and shape of the x-ray beam 21 and the third slit 28 blocks parasitic scattering. The x-ray beam 21, because of its focused nature, enables maximum flux to be concentrated on the sample structure 26. The x-ray detector 30 is able to detect the diffusion pattern created by the small angle scattering from the sample structure 26 because of the increased flux on the sample structure 26 and the elimination of divergence and scattering. The x-ray detector 30 is further equipped with a beam stopper 32 to prevent direct x-ray beam damage to the x-ray detector 30 and noise. The exact location of the focal point 22 between the second slit 20 and the x-ray detector 30 depends on the desired flux and resolution characteristics of the optical system 10. The optical system 10 of the present invention is preferably enclosed in a vacuum path or pre-flight beam pipe 27 to eliminate scattering and absorption caused by atmospheric gases and particles. The pre-flight beam pipe 27 is comprised of a number of individual pipes which may be mixed and matched to optimize and change the length of the system. The slits 18, 20, and 28 in the preferred embodiment, are formed as pinholes that are precision machined as round holes. Rounded pinholes create significant difficulty in alignment, especially when the sizes of the pinholes are small and multiple pinholes are used. The present invention includes a pinhole plate 34 having an alignment window 36 equipped with a triangle shaped nose 38 offset and aligned with a pinhole 40. During alignment of an x-ray beam, the x-ray beam is adjusted to enter and exit the alignment window 36. An x-ray detector is used as feedback to ensure that the x-ray beam is passing through the alignment window 36. The pinhole plate 34 is then moved manually or automatically in a vertical and horizontal fashion in the direction of the pinhole 40. If the x-ray detector does not detect the x-ray beam during an indexing of the alignment window 36 relative to the x-ray beam, the pinhole plate 34 will be moved to its last position and indexed in the opposite vertical or possibly horizontal direction. In this manner, the x-ray beam position is always known and the x-ray beam may be traversed to the vertex 37 of the triangle 38. The x-ray beam follows, in relative fashion, the cutout of the alignment window 36 until it reaches the vertex 37 of the triangle 38. At the vertex 37 of the triangle 38, movement will block or reduce the flux of the beam in both vertical directions and horizontal movement in the direction of the pinhole 40 will also block or reduce the beam. Accordingly, when such a condition is reached it is known that the beam is at the vertex 37 of the triangle 38. The pinhole 40 is a known fixed distance from the vertex 37 of the triangle 38. Thus, when the x-ray beam is found to be at the vertex 37 of the triangle 38, the pinhole plate 34 or x-ray beam may be precisely indexed this known distance to the pinhole 40, ensuring precise alignment of the pinhole 40 and the x-ray beam. Accordingly, the position of the x-ray beam will be known. In a first embodiment, the pinhole plate 34 is manually moved relative to the x-ray beam 21 using a precision x-ray table. The operator will read the x-ray detector 30 output and move the pinhole plate 34 accordingly. In alternate embodiments the operator will move the x-ray beam relative to the pinhole plate 34. In a second embodiment of the present invention, the pinhole plate 34 is moved using an automated servomotor or linear actuator system. The detector 30 feedback is transmitted to a computer which controls the x-y indexing of the x-ray beam or pinhole plate 34. In response to feedback from the detector 30, the computer will give the actuator system position commands to properly align the x-ray beam 21 and the pinhole plate 34. Referring to FIG. 3, an alternate embodiment of the pinhole plate 34' of the present invention is shown. The pinhole plate 34', as in the first embodiment 34, includes an alignment window 36' equipped with a triangle shaped nose 38' having a vertex 37'. A rotating aperture plate 42, having multiple apertures 44, rotates about a point 46 in the directions of arrow 48. The rotating aperture plate 42 allows multiple apertures 44 having various aperture diameters to be used in the present invention. Each aperture 44 may be indexed or rotated about point 46 to a position with a known offset from the vertex 37' of the triangle shaped nose 38'. The center of each aperture 44 in the rotating aperture plate 42 is the same radial distance from the point 46, allowing each aperture 44 to be correctly offset from the vertex 37' of the triangle shaped nose 38'. A rotary position feedback device such as an encoder or a manual latch may be used to precisely position the apertures 44 with respect to the vertex 37' of the triangle shaped nose 38'. It is to be understood that the invention is not limited to the exact construction illustrated and described above, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.
	abstract	A linkage mechanism of a scattered ray inhibition apparatus and a radiation field control apparatus is provided. The linkage mechanism includes a first timing belt, a second timing belt, and a transmission mechanism between the first timing belt and the second timing belt, wherein the scattered ray inhibition apparatus is mounted on the first timing belt, the radiation field control apparatus is mounted on the second timing belt, the transmission ratio of the transmission mechanism is equal to the ratio of the moving speed of the scattered ray inhibition apparatus to the moving speed of the radiation field control apparatus.
	summary
	summary
052895114	description	PREFERRED EMBODIMENTS OF THE INVENTION FIG. 1 shows a fast breeder reactor in which the present invention is applied to the primary sodium system. A reactor vessel 1, an intermediate heat exchanger 3, a primary sodium system pump 9 and a primary sodium system main piping 10 are all embedded and sealed in a solid sodium mass 20 solid at room temperature. High temperature liquid sodium serving as a coolant flows through the reactor vessel 1 and the piping 10. The liquid sodium coolant flowing out of the reactor vessel 1 returns to the primary sodium system pump 9 via the intermediate heat exchanger 3, and is recirculated again into the reactor vessel 1. The piping from the intermediate heat exchanger 3 to the primary sodium system pump 9 is not shown here since it is disposed in a part of the sodium mass 20 where the cutting plane of the section of this figure does not pass. In region 21 surrounding the reactor vessel 1, the pump 9 and the piping 10 through which the liquid sodium flows, the sodium stays in a molten state as its temperature is above its melting point. Although the solidified sodium mass 20 is contained in an outer container 22 with an upper cover 23, the outer container 22 does not need to have a great strength, but only needs to have water-tightness because the solidified sodium mass 20 itself has a sufficient strength. The space between the upper cover 23 and solid sodium mass 20 is filled with an inert gas. An inert gas inlet pipe 24 and a liquid sodium inlet pipe 25 are provided through the upper cover 23. A plurality of ventilation pipes 26 extend into the solid sodium mass 20 from the outside thereof in appropriate positions in the vicinity of the vessels (reactor vessel 1, intermediate heat exchanger 3 and pump 9) and the pipings (main piping 10 and pipings connecting the vessels). By controlling the temperature and velocity of ventilation air to be supplied to these ventilation pipes 26, the thickness of the molten sodium region 21 in the vicinity of the external of the vessels, and pipings can be maintained at a constant value despite transient changes in the temperature of liquid sodium flowing through the vessels and piping of the primary sodium system. Such an arrangement as described above enables the solid sodium mass 20 to actually form the coolant pressure boundary, so that the walls of the vessels and piping can be no more considered as a part of the coolant pressure boundary. Thus, the reactor vessel 1, the intermediate heat exchanger 3, the primary sodium system pump 9 and the like can be provided with sodium introducing orifices 27 through which liquid sodium can flow. By providing such sodium introducing orifices 27, both the inside and the outside of the primary sodium system can be filled with liquid sodium concurrently. That is, by supplying liquid sodium into the outer container 22 through the liquid sodium inlet pipe 25, it is filled with liquid sodium, and thereafter the reactor vessel 1, the intermediate heat exchanger 3, the primary sodium system pump 9, and further the piping 10 connecting therebetween are filled with liquid sodium through respective sodium introducing orifices 27. After the supplying of sodium is completed, by controlling the temperature and velocity of ventilation air to be supplied from the ventilation pipes 26, the liquid sodium in the region outside the primary sodium system can be solidified to create such a state as shown in FIG. 1. The sodium introducing orifices 27 may be formed in both the vessels and the piping. Further, the effects of a diffusion type cold trap can be produced by providing the sodium introducing orifices 27. Namely, impurities such as sodium oxide in the sodium coolant are transferred through the sodium introducing orifices 27 out of the primary sodium system into the molten sodium region 21 surrounding the primary sodium system, and are precipitated there in the lowest temperature portion, i.e., at the interface between the molten sodium region 21 and the solidified sodium mass 20. As can be understood from the foregoing, since the solid sodium mass surrounding the entire portion of the sodium coolant system forms the coolant pressure boundary, it is not necessary for the vessel walls or piping walls to ensure the integrity of the boundary. Therefore, it also is not necessary to install guard vessels around the respective vessels, or to dispose the main piping at higher locations. Further, it becomes possible to attach bellows to the main piping, as required. Still further, by providing sodium introducing orifices in the vessel walls and the piping walls which delimit the coolant pressure boundary, not only does it become easier to bury the sodium coolant system in the solid sodium mass, but it also becomes possible to transfer impurities in the coolant sodium to other regions outside the coolant system to allow them to precipitate there. This contributes to reducing the burden imposed on a coolant purifier system, or even allows the purifying system to be eliminated. Although the above description has been limited to the case where sodium is utilized as the liquid metal, the present invention can employ other liquid metal coolants which are solid at room temperature such as potassium, NaK, and lithium. Further, the liquid metal in the cooling system and the solid metal mass outside the cooling system may be of different kinds of metals as long as their compatibility can be maintained.
060834544	abstract	Uniform sized and shaped spheres are formed by applying a minute periodic disturbance to a low viscosity liquid material. Pressure forces the material through at least one orifice in a crucible as a steady laminar stream. The stream enters an enclosed controlled temperature solidification environment which contains at least one heat transfer medium. A charging means is applied to the stream as the stream exits the crucible and breaks into a plurality of spheres to deflect the spheres as they pass through an electric field. The enclosed controlled temperature solidification environment cools and substantially solidifies the spheres.
	description	The arrangement of components used in one embodiment of the system 10 is schematically illustrated in FIG. 1. A pulsed electron beam is generated by a conventional photocathode 2 and linear accelerator 3 and focused to a beam diameter of 50-200 microns using a focusing magnet M. The electron beam is then directed through an electron beam transport line into a small evacuated beam pipe containing a beam interaction zone IZ. A pulsed infrared (IR) beam 4 is simultaneously generated by a conventional tabletop laser 1 and directed into a vacuum chamber containing a beryllium mirror 6. The mirror 6 is oriented to target the IR beam directly toward the opposing electron beam so that they collide at the IZ. As the electrons collide with the IR photons, the IR photons are converted to a beam 9 of X-ray photons and leave the IZ on a path that is almost collinear with the electron beam path. In a preferred embodiment of the system 10, the X-ray photons generated by the system 10 first pass through optional beryllium window 7 to provide a transition from the evacuated beam pipe to ambient air. The X-ray beam can then optionally be directed at an array of graphite mosaic crystals 8. For example, the X-rays can then deflect off of the crystals 8 at relatively shallow angles into a beam transport pipe, for delivery into one or more patient examining or imaging rooms (not shown). The residual portion of the electron beam is carried out of the IZ and deflected by a permanent magnet PM into a conventional electron dump 11. Because of the novel pulse structure and operational parameters of this system 10, the dump 11 will have to dissipate very little power, on the order of 0.5 W. Accordingly, the dump 11 can be a simple conductive block, a 4-inch copper cube for example, with no auxiliary cooling needed. Preferably, the diameters of the colliding IR and electron beams will be substantially equal and as small as possible, to maximize the efficiency of production of X-ray photons using inverse Comptom scattering. In this regard, it is important that the opposing IR and electron beams be carefully aligned so that they impinge directly on each other, preferably producing a beam spot size at the collision point in the IZ of 25 to 100 microns in diameter. Accordingly, the system 10 includes a beam alignment tool that is mechanically inserted into the IZ during initial setup of the system 10 and during periodic calibration. An example of such a beam alignment tool 20 is shown in FIG. 3, combining an electron beam viewing screen 21, an IR viewing screen 22, and an alignment screen 23. The beams are brought into co-alignment, first by visualization of the transition radiation produced by the electron beam hitting a beryllium electron beam viewing screen 21 and secondly by focusing the IR beam onto an aluminum IR viewing screen 22. The electron beam and IR screens 21, 22 are machined from a single aluminum plug, so that their surfaces are at 90xc2x0 to one another and centered to the electron beam using actuators in the X, Y and Z directions. Both beams are observed through a common window. Both the electron beam and IR laser source 1 are pulsed. Preferably, the IR and electron beam pulses are closely synchronized to maximize efficiency and minimize background radiation. To obtain such synchronization and accurate timing of beam arrival at the IZ, a small amount of the IR beam from the laser 1 can be diverted at 5 and directed at the photocathode 2, thus triggering the electron emission pulse simultaneously with the IR pulse generated from the laser 1. Generally, the laser source 1 should be capable of generating a 3-10 ps pulse having an energy of 1 to 10 J, with a repetition rate of 1 to 10 Hz and a spectral width of less than 0.5%. Such a laser may be commercially available as an Alexandrite short pulse oscillator from Light Age, Inc., of Somerset, N.J., or, with lower repetition rates, a Nd:glass laser from Positive Light of San Jose, Calif. The electron beam source 2, 3 is adjusted to deliver 1 nC of charge in a single microbunch micropulse having a pulse length of 10 ps or less (or an electron beam brightness of 1012 A/m2xe2x80x94radian2 @ 500 A). Again, the electron beam pulse should be specified to correspond in time and duration to the IR beam pulse. An RF LINAC could be used as the electron beam source. The LINAC should be capable of supplying a beam energy in the range of 25 to 50 MeV, and a pulse charge of greater than 1 nC at a pulse length of less than 10 ps. The emittance of the LINAC should be less than 3 mm-mrad (rms), with a spot size diameter of 25 to 100 microns (90%), and a pointing stability that is small compared to the spot size. Accelerators capable of meeting these requirements are available from Advanced Energy Systems. Inc. of Medford, N.Y., as well as from other sources. Using the system 10 as described, short pulses (1 to 10 ps) of hard X-rays in the 10 to 50 keV range at high flux (109-1016 photons/10 ps pulse) can be produced. A time domain representation of a typical X-ray pulse generated by the system 10 is shown in FIG. 4. Time of Flight Imaging The fact that the X-rays of this system 10 are pulsed in bursts of a few picoseconds allows them to be used for time-of-flight (TOF) imaging,14 where data is collected by imaging only ballistic photons up to 180 ps from the initiation of the exposure and ignoring scatter exiting over many nanoseconds. This provides an additional improvement in visibility of six to nine times, and can improve conspicuity of lesions by ten times. In particular, the pulse structure makes gated time-of-flight X-ray imaging for the reduction of scatter in thick targets very simple. With a single X-ray bunch, the system 10 can be used in conjunction with a detector which can be abruptly gated off after the early photons arrive to filter out multiply scattered photons. It is much easier to make a detector which does this (by shorting out the high voltage bias on a microchannel plate, for example) than to make a detector which needs to be gated on and off repeatedly, as would be needed from a system for which more than one bunch of X-rays are needed to make an image. Phase Contrast Imaging The small effective spot size of the X-ray beam produced by this system 10 enables the performance of phase ontrast imaging using information traditionally discarded in conventional imaging.15 These improvements in imaging are not restricted to the breast but apply to any body part and to materials science as well. Beams having an energy of approximately 40-50 keV are achievable using small angles of reflection from mosaic crystals 8 and using high energy electrons. All of these techniques can be effected while reducing radiation dose to a patient and decreasing scatter due to the tunability of the beam and the limited bandwidth/narrow energy range delivered to the imaged part. Given the low atomic weights of the major constituents of the human body, there is little difference discernible between body tissues in absorption imaging, due to exceedingly small differences in the very low absorption coefficients of these atoms. However, 100 to 1000 times as much information can be obtained by using the phase information imparted to the beam as it traverses the patient. Therefore, phase imaging can use a silicon crystal as an analyzer separating X-ray photons diffracted by density changes at tissue interfaces, differences in tissue specific gravity, and even flowing blood, from those photons not diffracted at all. Stepped, slit-scanned images can be acquired at two locations simultaneously on the surface of the same multichannel plate/CCD detector used for the TOF imaging. The part to be imaged can be stepped through the beam and an image acquired for each step. The resultant images are summated into two separate (diffracted and non-diffracted images) and then subtracted from one another for difference phase images. The system 10 of this invention relies on inverse Compton scattering to produce the X-ray photons. The term inverse Compton scattering refers to photon scattering by an electron moving at relativistic speeds. Compton scattering is conventionally known as the process in which a photon scatters off an electron at rest, in which case the photon loses energy to the electron and its wavelength is lengthened. In inverse Compton scattering, the electron is moving and gives up energy to the photon. The basic concept of using inverse Compton scattering to produce X-ray photos is shown in FIG. 2. An incoming electron (el) from the linear accelerator xe2x80x9ccollides withxe2x80x9d the IR photon, converting it to an X-ray photon which follows a path almost collinear with the electron beam. The relative angles of the post-collision electron beam and X-ray beam are exaggerated on FIG. 2 for clarity. The inverse Compton scattering of a beam of low energy photons backwards by an anti-parallel beam of electrons can produce a narrow beam of high energy photons. In the case of scattering of the photon through 180xc2x0, its energy is increased by several orders of magnitude. The production rate of X-rays by inverse Compton scattering is governed by two factors: the probability of scattering an infrared photon by an electron, which depends on the cross section, and the intensities of the two beams, which is expressed as the luminosity of the beams. The first factor is obtained by integrating the differential cross section over the angular range of the narrow cone (xe2x88x920.005 rad) containing the high energy X-rays. The general solution of the photon-electron scattering yields the Klein-Nishina formulas, which, in the case that the photon energy in the electron rest frame is small compared to that of the electron rest mass, reduce to the Thomson scattering formulas. The electron velocity is relativistic, characterized by y=85, where y is the ratio of the electron""s energy to its mass. In a system where the shortest photon wavelengths are about 2xcexc, which correspond to an energy in the labaratory rest system of 0.52 eV, the photon energy in the electron rest system is small compared to mec2 of 0.511 MeV. The total Thomson cross section is given by σ r = 8 ⁢ π 3 ⁢ r e 2 where re, is the classical electron radius. Due to the relativistic electron motion, which has a Lorentz factor y=Ee/mec2, the scattering angle in the electron rest frame is related to the half-angle of the X-ray cone in the laboratory frame by xcex8s=2yxcex8c. The cross section for scattering into the forward cone is ∫ π π - θ ⁢ xe2x80x83 ⁢ s ⁢ η ⁢ xe2x80x83 ⁢ r e 2 ⁡ ( 1 + cos 2 ⁢ Θ s ) ⁢ xe2x80x83 ⁢ sin ⁢ xe2x80x83 ⁢ Θ s ⁢ ⅆ Θ s For a half-angle of 0.005 rad, the cross-section is 0.21 of the total Thomson cross section of 0.66 barn (=6.6xc3x9710xe2x88x9229m2). As seen by the electron, the photon energy is increased by a factor of 2y to xcx9c102 eV. This energy is so small compared to the electron rest mass that the Compton shift of wavelength is negligible. The photon is scattered nearly elastically through some angle xcex83. Near xcex83=180xc2x0 the energy of the scattered photon as seen in the laboratory system gains another factor of 2y, reaching a maximum of xcx9c17.9 keV. The second factor is the luminosity, which for colliding beams is L=Nexc3x97Nyxc3x97ƒ/A where Ne is the number of electrons per micropulse, Ny is the number of photons per micropulse, f the frequency of micropulses, and A the area of overlap of the two beams. The area can be calculated by integrating the product of the Gaussian distribution of the particles. If the two beams have the same size, the area is related to the width of the beams by A =xcfx80(2"sgr")2 For different radii, the area is A = 1 / 2 ⁢ η ⁢ ( r e 2 + r y 2 ) In a preferred embodiment of the system 10, the two beams are brought into co-alignment by an alignment tool 20 as shown in FIG. 3, first byvisualization of the transition radiation produced by the electron beam hitting a beryllium screen 21 and secondly by focusing the IR laser beam onto an aluminum screen 22. Both beams are observed through a common CaF window via a CCD TV camera with a remotely controlled and adjustable zoom/focus/iris lens. The alignment screen 23 assures centering of the device within the vacuum beamline pipe. Next the electron viewing screen 21 is used to delineate the location, size and shape of the electron beam from the transition radiation generated by the beam striking the screen. Lastly, the IR viewing screen 22 is used to steer the pointing lasers to the center of the electron beam. An X-ray detector consisting of two thin silicon surface-barrier detectors (not shown) can be used with the system 10. The detector is placed outside of the beamline on the optical table adjacent to a 0.010 inch beryllium window used as an exit port for the X-ray beam. These detectors are used as calorimeters which are separated by an aluminum absorber. The front detector sees both the intense high energy background radiation, plus the low energy X-rays produced by the inverse Compton scattering. The rear detector sees only the high energy background. Subtraction of one signal from the other using a balanced differential amplifier chain allowed for the separation of the signals and display of the X-ray signal as a time-resolved voltage overlying the timing signals generated by the electron beam and IR beam pulses. In one embodiment, there are approximately 1010 photons/pulse. In one embodiment of the invention, the wavelength of the X-ray pulse generated by the system 10 can be tuned by changing the energy level of the electrons emitted by the RF LINAC 3, by adjusting the RF source. The monochromaticity and narrow divergence angle of the X-ray beam produced by this system 10 not only enables the mosaic crystals to divert the beam to an imaging laboratory or patient treatment room, but also allows the redirection of the beam in a circular fashion creating CT images using conebeam backprojection algorithms. The time structure and the tunability make the system 10 attractive to the scientific community for exceedingly fast time-resolved studies of electronic, chemical and mechanical processes. The X-rays are not produced in a continuous spectrum, but are of very narrow bandwidth significantly reducing radiation dose to patients (from two to fifty times depending on the procedure being performed). Due to the small effective focal spot size, they can be used in phase contrast imaging, which delivers 100 to 1000 times the information than that obtained by the use of absorption imaging alone (the information used by radiologists for the last 100 years). The beam geometry is one of an area large enough to study large body parts, rather than the limited area visible at synchrotron facilities. The system is small enough to fit into a standard X-ray room and can be built to service several rooms at a time, reducing the amount of equipment needed by any radiology department. Harmonic Generation In another embodiment, the system 10 of this invention is also advantageous in its generation of harmonics. Referring again to FIG. 1, when the intensity of laser 1 is high enough, the number of X-ray photons generated on the second, third, and higher harmonics can become comparable to or greater than the number of photons on the fundamental. Increasing the beam intensity and/or decreasing the beam spot size at the IZ can affect the generation of harmonics to obtain a set of discrete monochromatic X-ray pulses at different energy levels. For example, for a 10 J pump laser pulse in 1 ps focused to a 20-micron diameter, the number of photons on the harmonics exceeds the number at the fundamental. The X-ray photons at the harmonics propagate in substantially the same direction as the fundamental. If the output of the laser 1 is operated to generate a pulse of 10 J in a 20 ps pulse, focused to a beam diameter of 50 microns, the number of X-ray photons on the second harmonic are approximately one percent of the number of X-ray photons on the fundamental. The presence of harmonics in the output of system offer several possible advantages, including: (1) Lower electron energy. For example, for 20 keV X-rays, operating on the fundamental requires the presence of 33 MeV electrons. However, operating on the third harmonic requires only 19 MeV electrons. This reduces the LIN-AC requirements and, in particular, the radiation shielding requirements. The desired harmonic could be selected at the output of the system by using a combination of conventional absorption filters and crystal reflectors (not shown). (2) Multiple wavelengths present in the harmonics could be used to produce images at several discrete wavelengths for image processing. (3) Multipass operation. After the laser beam has intersected the electron beam, it can be reflected with mirrors to intersect subsequent electron micropulses. These might be spaced at any subharmonic of the RF frequency of the accelerator, though several-nanosecond intervals would probably be most convenient. Multiple electron pulses could be formed by splitting the cathode drive laser pulse and delaying some pulses or by switching out several Pulses from the mode-locked oscillator/amplifier system. One pump laser pulse could be used several times, perhaps 10 times or more. Although the laser would intersect the electron beam from different directions, the X-rays would all propagate in the direction of the electron beam axis. Multipass operation would increase the total number of x-rays produced from a single laser pulse. Also, subsequent passes might be aligned at different angles to change the energy (but not the direction) of the x-rays. This might be useful for image processing, or might be used in scientific experiments to excite or probe a sample at different wavelengths at different times. The change in wavelengths could be used to separate successive x-ray pulses after they pass through the sample. Subsequent passes could be aligned to change the polarization of the x-rays. It is a unique feature of the Compton x-ray system that the x-rays are linearly polarized (or circularly polarized if the pump laser is circularly polarized). The change in polarization might have advantages for probing the system, improving images, or separating successive pulses. Multiple Pulse Mode In yet another embodiment. the system 10 is capable of producing two or more pulses in either closely spaced (picoseconds) or widely spaced (nanoseconds) groups. Optionally, pairs or groups of pulses can be generated to produce different X-ray energies. The system 10 can be operated in a closely-spaced, multiple pulse mode by splitting and re-combining the output of the laser 1 with a small time offset, resulting in the amplification of a pulse-pair. If this pulse pair is applied to the photocathode 2 and amplified into the interaction zone IZ, it can result in pairs of X-ray pulses separated by a few picoseconds to a few tens of picoseconds being generated. By taking advantage of the dependence of the electron beam energy on the phase of the electron bunch relative to the main radio frequency (RF) drive of the system, one could generate electron pulses of different energies which would result in X-ray pulses of different energies being produced. To produce widely spaced pulse groups, system 10 will be capable of producing trains of pulses separated by multiples of the basic RIF period (about 340 ps in the preferred embodiment), with a resultant large increase in X-ray production within a few nanosecond burst. This mode would be useful for many applications in which the extremely fast picosecond time structure is irrelevant, and for which generating a maximum number of X-rays within a few nanosecond window is desired. This can be achieved by first splitting the output pulse from laser 1 and recombining part of it into a pulse train to be fed to the photocathode 2 drive amplifier to produce a train of electron bunches separated by a multiple of the RF period. Then the main laser pulse which is passed through the interaction zone IZ would be re-collected after each pass through brought back and refocused into the IZ and re-collided with the next pulse in the electron bunch train. This would allow the system 10 to recycle the photons from the main drive laser 1 quite a few times to produce many more X-rays (possibly more than 10 times as many) in a nanosecond burst. Further, using appropriate gated detectors with this embodiment of the system 10, freeze-frame X-ray movies of processes on the nanosecond time scale could be obtained. Generation of Multiple X-ray Beams The system 10 can be used to generate multiple X-ray beams so that a single pulse will produce multiple images that would be needed, for example, for CT reconstruction. A beam reflection apparatus 30 for production of multiple beams from a single X-ray beam 9 from system 10 is shown on FIGS. 5 and 6. The incoming beam 9 is directed to a multifaceted pyramidal X-ray mirror 31 (made of either graphite crystal or a multilayer metal) having its apex 35 facing the beam 9. The mirror 31 splits the incoming beam 9 into a set of beams 36 that diverge at a small angle toward a corresponding set of off-axis reflectors 32. The split beams are then redirected at 37 back to the axis of the incoming beam 9 while crossing the original axis at different angles. Energy Scaling The system 10 as described can easily be scaled to produce X-rays of higher energy, while preserving the high fluxes available in the preferred embodiment. Since the energy of the emitted X-rays increases as the square of the electron beam energy (for X-ray energies much less than the electron-beam energy, i.e., less than many MeV), lengthening the LINAC will provide X-rays easily beyond the energy range used for the highest energy materials science work (a few hundred keV) and even into the gamma ray region (a few MeV) with very high fluxes. The embodiment of FIG. 1 uses a LINAC 3 approximately 2 m long, and should be able to provide X-rays beyond 60 keV. Using a 4-meter long LINAC 3, this would generate up to four times this energy, or 240 keV. Such an embodiment would result in a system 10 that is physically larger, and therefore would not be preferred for compact medical devices, but could be of benefit in materials radiography. As referred to above, the pulsed, tunable, monochromatic X-rays of the present invention can advantageously be used in performing mammography. More specifically, the present invention can be used to perform 3-D/volumetric monochromatic mammography without the use of breast compression. Acquisition of data using a cone-beam geometry inherent in the X-ray beam of this device and either rotation of a prone patient about the central axis of the breast, or the rotation of mosaic crystals in front of the patient, can be coupled with cone-beam backprojection algorithms for volumetric reconstruction of full 3-D images. The mosaic crystal geometry is described in greater detail in U.S. patent application Ser. No. 09/290,436, which is hereby incorporated herein by reference. Other available algorithms can also be used for 3-D reconstructions with this mosaic crystal geometry. In addition, monochromatic mammography can be combined with the administration of tumor-seeking drugs tagged with various atoms. The present invention can be tuned to the binding energy of the K shell electrons in the atom tags, thereby making the xe2x80x9cmarkedxe2x80x9d tumors more visible. The drugs can be administered either orally or intravenously. These same tumor-seeking agents can be used as an adjunct for brachytherapy treatment of invasive tumors in any body part. Once the drug has been administered, allowed to xe2x80x9cseekxe2x80x9d the tumor and accumulate there, it can be imaged with a beam tuned to the atom tag K-edge. Once it is located, it is additionally possible to concentrate the X-rays at that spot using X-ray optics. Thus tuned to the K-edge of the tag and made more intense by focusing, the X-rays will cause the K shell electrons to leave their orbits, in turn creating a cascade of photon emission in the atom in a very localized space of a few microns. This tends to restrict the effects predominately to the tumor itself Tumor-seeking drugs, of course, are not limited to use in breast malignancies, but can be used in colon, lung, and brain tumors, as well as other neoplasms. Since compression of the breast will not be used for most of these examinations, breast architecture is not distorted year-to-year or examination-to-examination. Computer Assisted Diagnosis can then be implemented to better/more accurately discern changes in the breast between examinations. The lack of breast compression reduces the discomfort/pain now commonplace with performance of the procedure. The same principles of tunability and K-edge enhancement can be used in plain film X-rays and CT examinations in the chest, extremities, bones, skull, spine, abdomen and kidneys, as well as many other objects to be imaged. Additionally, an analysis of the energies absorbed by the body and various organs at different energies imparts information as to the chemical composition of the part imaged. Since each point in an image is made up of the individual additive effects of the linear attenuations of each small volume of the tissue traversed by the beam, the final pattern of photon absorption is indicative of differing tissue makeup. This same principle can be applied to evaluating calcium deposits in the coronary arteries, carotid arteries or extremity arteries. Difference images, synthesized from images made at two or multiple different energies, will reveal much about the tissue composition. This can be done with both plain films and CTs. Arteriography of any body part can also benefit from this K-edge imaging. X-ray contrast agents could be used in much lower doses and used intravenously instead of requiring intra-arterial catheterization for delivery. The machine can be tuned to the K-edge of the metal atoms in the X-ray xe2x80x9cdyexe2x80x9d; which traditionally have used iodine (the K-edge of which is 33.2 keV). Even contrast agents not traditionally used in X-ray studies may be used in place of the traditional agents, such as those used in Magnetic Resonance Imaging, which contain gadolinium. By tuning to the K-edge of gadolinium (50.2 keV), instead of tuning to 33.2 keV (for iodine) one can reduce the radiation dose to the patient even further, since the body is more transparent to 50.2 keV photons than it is at 33.2 keV. Fewer photons will stop in the patient at the higher energy, thereby reducing radiation dose. By using lower doses of intravenous contrast, xe2x80x9ccatheter-lessxe2x80x9d coronary angiography is possible. Additionally, bronchography and examination of the very small peripheral airways can be performed using radiodense gases that are inhaled. The present invention can be tuned to the K-edge of the gas, allowing evaluation of both ventilation and perfusion of the peripheral airspaces, without the need for invasive intubation. Microscopic algorithms can be used to obtain information on extremely small airways where reactive airways diseases create their undesirable effects. Using conventional imaging techniques, these airways can not be imaged using even the best-known xe2x80x9chigh resolutionxe2x80x9d modes of imaging. The monochromaticity of the beam from the present invention, as well as its small effective focal spot size, make it extremely useful in the field of small animal imaging. Pharmaceutical firms, universities and proteomics firms can use the invention to longitudinally follow small animals over time to ascertain the long-term effects of drugs, disease states and alterations in the animals"" genes. Current technology delivers extremely high radiation doses to the animal during the acquisition of microscopic detail in the live animal. This raises radiation dose levels to lethal/near-lethal levels, even with only one study. In contract, the monochromatic nature of a beam from the present invention lowers radiation dose through several mechanisms, including the absence of soft X-rays in the beam, narrow bandwidth, lack of beam hardening, and pulsed X-ray delivery (i.e., no motion artifacts). The concept of using tumor-seeking agents applies in animals as well as humans, and can be extended to include the creation and use of other metabolically active compounds, as well as for use in gene specific sites with or without promoter and reporter genes to turn on or off some function of the cell or tissue in a telltale way. Because of the small effective focal spot and lateral coherence of a beam produced by the present invention, such a beam is ideal for use in phase contrast imaging, as referred to above. Absorption imaging requires something dense in an object to stop photons, leaving a xe2x80x9cshadowxe2x80x9d on the detector. That xe2x80x9cshadowgramxe2x80x9d is the standard absorption image used since the discovery of X-rays. Phase contrast, on the other hand, relies upon refractive and diffractive effects within the tissues and detection of the refracted/diffracted photons. Conventionally, synchrotrons are relied upon heavily to demonstrate phase contrast images, but are large, costly, unwieldy machines for this purpose. The present invention offers a more compact, affordable, practical source for this type of imaging. Phase contrast imaging has great potential value in mammography, soft tissue imaging in trauma and in other types of imaging as well. Because a beam produced by the present invention is so bright, tunable, and bandwidth adjustable, it is also an excellent source for use in the area of protein crystallography. xe2x80x9cAt homexe2x80x9d (i.e., local) devices consist of a large X-ray tube emitting 8.6 keV (the Cu k xcex1 line), and the appropriate beamline hardware and software. However, the information gleaned from the xe2x80x9chomexe2x80x9d devices is limited, and full determination of a protein crystallographic structure requires data that is currently acquired at synchrotrons (which are only available at a small number of locations). The present invention is capable of performing standard crystallography, Multiple Anomalous Dispersion, and Laue diffraction, which is performed at higher energies and with multiple energies simultaneously. With this new machine, this can all be done at the xe2x80x9chomexe2x80x9d lab, negating the necessity for travel to a synchrotron facility, as well as offering 24/7 access, thereby speeding the processes of discovery and testing of new proteins. Of course, the machine is not limited to protein crystallography, but can also be used for crystalline diffraction as well. Use of the present invention to perform non-destructive testing on fast moving/rotating/explosive/inaccessible objects is a natural extension of its ability to image in picoseconds. Moving turbines, rocket engines, reciprocating engines, wind tunnel targets, kinetic weapons, airline baggage and so forth are natural targets for this very rapid X-ray beam. The beam emitted from the present invention also undergoes very little divergence relative to a standard X-ray tube. Because of this, one can stand off at extended distances for imaging, by transmitting the beam through evacuated or helium filled pipes to the device/object to be imaged. The energy of this device is scalable to hundreds of keV for penetration of metal casings and thick composite structures. Studies with this machine can yield information while the imaged object is under full power/load/temperature. It can be used in both the transmission mode or by detecting backscatter from the object. It also could be useful for X-ray spectroscopy. FIG. 7 provides an exemplary embodiment of the invention that is consistent with FIG. 1. In FIG. 7, a pump continuous-wave, 9.5 W pump laser 705 is shown driving a mode-locked, Ti:Saph laser 704 running at a locking frequency of 81.6 MHz and coming from the master oscillator 724. The master oscillator 724 operates at the 35th subharmonic of the RF drive for a linear accelerator 711. Laser 704 seeds the pulse-stretcher/regenerative amplifier 703, which in turn is pumped by a pulsed, Q-switched laser 702 running at 480 Hz, i.e., the 8th harmonic of the power line frequency, to which the overall pulsing of the machine of FIG. 7 is locked. The beam from the amplifier 703 is split by splitter 723 into two components 719 and 720. Beam 719 passes through a series of progressively larger Nd:glass amplifiers 706, 707 and 708. The beam coming out of 708 is then passed to a pulse compressor 710, which reverses the effect of the stretching done in 703 to thereby produce a 10 ps pulse containing up to 10 J of energy. The beam from pulse compressor 710 is then turned into line with the electron beam from the Linac 711 by means of turning mirror 721. That beam then comes to a focus in the IZ region 713, where it collides with the electron beam to produce an X-ray pulse. Beam 720 from the splitter 723 is passed through a variable-time-delay device 709, known colloquially as a trombone. This provides the synchronization discussed above with respect to FIG. 1, whereby the electron beam and photon beam arrive at IZ 713 simultaneously. The beam from 709 is then amplified, re-compressed, and converted to the ultraviolet in the YLF laser subsystem 718, from which it goes into the electron gun 701 to drive the photocathode and create the electron beam. The accelerator starts with the 2856 MHz drive from the 35th harmonic converter 725, which is amplified by a high-power amplifier chain 726. High-power amplifier chain 726 consists of a travelling-wave-tube (TWT) preamplifier and a modulator/klystron subsystem (not shown). The output of this chain is split by an RF power splitter 727. One of the outputs 728 of the splitter 727 is sent to the electron gun 701. The other output is passed through a phase shifter 729. The output 730 of the phase shifter is used to drive the accelerator system 711. The electron beam from the accelerator 711 is focused by a superconducting solenoidal magnet 712 to collide with the high-power laser pulse at IZ 713. The spent electron beam is bent away from its initial trajectory by a dipole magnet 714 which directs it down a beamline toward the electron beam dump 717. Finally, the X-ray beam 716 produced at IZ 713 proceeds out of the vacuum system by passing through the beryllium mirror and window in the turning chamber 721. Thus, although there have been described particular embodiments of the present invention, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.
	claims	1. A radiation source configured to generate radiation, the radiation source comprising:a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site;a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site;a controller configured to control the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets; anda collector constructed and arranged to collect radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide, the collector being configured to reflect the radiation substantially along an optical axis of the radiation source,wherein the laser beam is directed to the plasma generation site through an aperture provided in the collector. 2. The radiation source of claim 1, wherein the stream of droplets are directed such that the stream of droplets has a component of movement along the optical axis of the radiation source pointing away from the collector. 3. The radiation source of claim 1, wherein the laser beam and the stream of droplets are directed such that the laser beam and the stream of droplets have a component of movement along the optical axis of the radiation source pointing away from the collector. 4. The radiation. source of claim 1, wherein the angle between the direction of movement of the stream of droplets and the direction of the laser beam is less than 85 °. 5. The radiation source of claim 1, wherein the angle between the direction of movement of the stream of droplets and the direction of the laser beam is less than 45 °. 6. The radiation source of claim 1, wherein the stream of droplets are directed to the plasma generation site through an aperture provided in the collector. 7. The radiation source of claim 1, wherein the radiation source is configured to generate EUV radiation. 8. The radiation source of claim 1, wherein the angle between the direction of movement of the stream of droplets and the direction of the laser beam is less than 90°. 9. A method of generating radiation, comprising:directing a stream of droplets of fuel from a fuel droplet generator to a plasma generation site;directing a laser beam generated by a single laser to the plasma generation site;controlling the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets;collecting radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide with a collector; andreflecting the radiation substantially along an optical axis of the radiation source,wherein the laser beam and/or the stream of droplets are directed to the plasma generation site through an aperture provided in the collector. 10. A radiation source configured to generate radiation, the radiation source comprising:a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site;a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site; anda controller configured to control the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets. 11. The radiation source of claim 10, wherein the direction of the laser beam and/or the stream of droplets is controlled to control the time taken for a droplet of the stream of droplets to pass through at least a part of the laser beam. 12. The radiation source of claim 10, wherein an angle between the stream of droplets and the direction of the laser beam is less than 90°. 13. The radiation source of claim 10, wherein the stream of droplets are directed to the plasma generation site through an aperture provided in the collector. 14. A method of generating radiation, the method comprising:directing a stream of droplets of fuel from a fuel droplet generator to a plasma generation site;directing a laser beam generated by a single laser to the plasma generation site; andcontrolling the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets. 15. A fuel droplet-laser beam collision time increasing apparatus arranged to generate radiation, the apparatus comprising:a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site;a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site, an angle between the direction of movement of the stream of droplets and the direction of the laser beam being less than about 90°; anda controller constructed and arranged to control the position or orientation of the fuel droplet generator and/or the laser to control the angle between the direction of movement of the stream of droplets and the direction of the laser beam. 16. A method of increasing the collision time between a droplet of fuel and at least a part of a laser beam, the collision resulting in the generation of radiation, the method comprising:directing a stream of droplets of fuel from a fuel droplet generator to a plasma generation site;directing a laser beam generated by a single laser to the plasma generation site, an angle between the stream of droplets and the direction of the laser beam being less than about 90°; andcontrolling the position or orientation of the fuel droplet generator and/or the laser to control the angle between the direction of movement of the stream of droplets and the direction of the laser beam. 17. A lithographic apparatus comprising:a radiation source configured to generate radiation, the radiation source comprisinga fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site,a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site,a controller configured to control the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets, anda collector constructed and arranged to collect radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide, the collector being configured to reflect the radiation substantially along an optical axis of the radiation source to an intermediate focus,wherein the laser beam is directed to the plasma generation site through an aperture provided in the collector;a support constructed and arranged to support a patterning device, the patterning device being configured to pattern radiation that passes through the intermediate focus; anda projection system constructed and arranged to project the patterned radiation onto a substrate. 18. A lithographic apparatus comprising:a radiation source configured to generate radiation, the radiation source comprising:a fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site;a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site; anda controller configured to control the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control the angle between the laser beam and the stream'of droplets;a support constructed and arranged to support a patterning device, the patterning device being configured to pattern radiation that passes from the radiation source and through an intermediate focus; anda projection system constructed and arranged to project the patterned radiation onto a substrate. 19. A lithographic apparatus comprising:a fuel droplet-laser beam collision time increasing apparatus arranged to generate radiation, the fuel droplet-laser beam collision time increasing apparatus comprisinga fuel droplet generator constructed and arranged to generate a stream of droplets of fuel that are directed to a plasma generation site,a laser constructed and arranged to generate a single laser beam that is directed to the plasma generation site, an angle between the direction of movement of the stream of droplets and the direction of the laser beam being less than about 90°, anda controller constructed and arranged to control the position or orientation of the fuel droplet generator and/or the laser to control the angle between the direction of movement of the stream of droplets and the direction of the laser beam;a support constructed and arranged to support a patterning device, the patterning device being configured to pattern radiation that passes from the fuel droplet-laser beam collision time increasing apparatus and through an intermediate focus; anda projection system constructed and arranged to project the patterned radiation onto a substrate. 20. A device manufacturing method comprising:generating radiation, said generating radiation comprisingdirecting a stream of droplets of fuel from a fuel droplet generator to a plasma generation site,directing a laser beam generated by a single laser to the plasma generation site,controlling the position or orientation of the fuel droplet generator and/or the laser to control the angle between the direction of movement of the stream of droplets and the direction of the laser beam,collecting radiation generated by a plasma formed at the plasma formation site when the beam of radiation and a droplet collide with a collector, andreflecting the radiation substantially along an optical axis of the radiation source,wherein the laser beam and/or the stream of droplets are directed to the plasma generation site through an aperture provided in the collector;patterning the radiation with a pattering device; andprojecting the patterned radiation onto a substrate. 21. A device manufacturing method comprising:generating radiation, said generating radiation comprisingdirecting a stream of droplets of fuel from a fuel droplet generator to a plasma generation site,directing a laser beam generated by a single laser to the plasma generation site, andcontrolling the position or orientation of the fuel droplet generator and/or the laser to control the direction of the laser beam and/or the direction of movement of the stream of droplets to control an angle between the laser beam and the stream of droplets;patterning the radiation with a pattering device; andprojecting the patterned radiation onto a substrate. 22. A device manufacturing method comprising:generating radiation by increasing the collision time between a droplet of fuel and at least a part of a laser beam, said increasing the collision time comprisingdirecting a stream of droplets of fuel from a fuel droplet generator to a plasma generation site,directing a laser beam generated by a single laser to the plasma generation site, an angle between the stream of droplets and the direction of the laser beam being less than about 90°, andcontrolling the position or orientation of the fuel droplet generator and/or the laser to control the angle, between the direction of movement of the stream of droplets and the direction of the laser beam;patterning the radiation with a patterning device; andprojecting the patterned radiation onto a substrate.
	claims	1. A method of improving nuclear reactor performance, comprising:implementing an operational solution generated for the nuclear reactor using an objective function including at least one of a spatially dependent and exposure dependent constraint accounting for a problem with operation of the nuclear reactor, the problem being an unintended change in reactor performance or configuration and capable of being represented by the at least one of the spatially dependent constraint and the exposure dependent constraint in the objective function, and the objective function producing a figure of merit for the operational solution. 2. The method of claim 1, wherein the constraint is a spatially dependent power distribution constraint. 3. The method of claim 2, wherein the spatially dependent power distribution constraint accounts for one or more leaking fuel rods. 4. The method of claim 2, wherein the spatially dependent power distribution constraint accounts for one or more corrosion-susceptible locations. 5. The method of claim 2, wherein the spatially dependent power distribution constraint accounts for degradation in reactor flow. 6. The method of claim 2, wherein the spatially dependent power distribution constraint accounts for degraded exit steam quality. 7. The method of claim 1, wherein the constraint is an exposure dependent constraint. 8. The method of claim 7, wherein the exposure dependent constraint accounts for exposure dependency of thermal limit. 9. The method of claim 7, wherein the exposure dependent constraint accounts for one or more parameters having exposure dependency when the nuclear reactor operates beyond an anticipated cycle length. 10. The method of claim 1, further comprising:modifying the constraint based on performance of the nuclear reactor following the implementing step; andrepeating the implementing step using the modified constraint. 11. A method of improving nuclear reactor performance, comprising:generating an operational solution for the nuclear reactor using an objective function including at least one of a spatially dependent and exposure dependent constraint accounting for a problem with operation of the nuclear reactor, the problem being an unintended change in reactor performance or configuration and capable of being represented by the at least one of the spatially dependent constraint and the exposure dependent constraint in the objective function, the objective function producing a figure of merit for the operational solution, andimplementing the operational solution. 12. The method of claim 11, wherein the constraint is a spatially dependent power distribution constraint. 13. The method of claim 12, wherein the spatially dependent power distribution constraint accounts for one or more leaking fuel rods. 14. The method of claim 12, wherein the spatially dependent power distribution constraint accounts for one or more corrosion-susceptible locations. 15. The method of claim 12, wherein the spatially dependent power distribution constraint accounts for degradation in reactor flow. 16. The method of claim 12, wherein the spatially dependent power distribution constraint accounts for degraded exit steam quality. 17. The method of claim 11, wherein the constraint is an exposure dependent constraint. 18. The method of claim 17, wherein the exposure dependent constraint accounts for exposure dependency of thermal limit. 19. The method of claim 17, wherein the exposure dependent constraint accounts for one or more parameters having exposure dependency when the nuclear reactor operates beyond an anticipated cycle length. 20. The method of claim 11, further comprising:developing the constraint; anddeveloping the objective function including the constraint. 21. The method of claim 20, wherein the developing the objective function step modifies a pre-existing objective function by adding the constraint to the objective function. 22. The method of claim 11, wherein the generating step is a constraint based optimization operation. 23. The method of claim 11, further comprising:modifying the constraint based on performance of the nuclear reactor following the implementation of the operational solution; and repeating the generating step using the modified constraint. 24. A method of improving nuclear reactor performance, comprising:generating an operational solution for the nuclear reactor using an objective function including a constraint tailored to a problem with operation of the nuclear reactor, the problem being an unintended change in reactor performance or configuration and capable of being represented by the at least one of the spatially dependent constraint and the exposure dependent constraint in the objective function, the objective function producing a figure of merit for the operational solution, andimplementing the operational solution.
	summary
	abstract	A target supply device includes a target supply device body including a nozzle having a through-hole through which a target material is discharged, a piezoelectric member having first and second surfaces and connected to the target supply device body at the first surface, the piezoelectric member being configured such that a distance between the first and second surfaces changes in according with an externally supplied electric signal, an elastic member having first and second ends and connected to the second surface of the piezoelectric member at the first end, the elastic member being configured such that a distance between the first and second ends extends or contract in accordance with an externally applied force, and a regulating member configured to regulate a distance between the second end of the elastic member and the target supply device body.
040424545	abstract	Si monocrystals of the n-type are produced by zone melting polycrystalline Si rods under conditions sufficient to produce monocrystal rods, measuring the specific conductivity of such monocrystal rods and subjecting such monocrystal rods to a controlled radiation by thermal neutrons based on the measured conductivity to produce a desired degree of n-conductivity in the ultimately attained rods.
	abstract	Filtering systems and methods remove debris from coolant in a nuclear reactor setting. One or more filters are installed outside coolant reservoirs specifically where coolant will flow toward the reservoir, such as during a transient or other coolant leak event. Useable filters permit coolant through-flow while catching, straining, diverting, or otherwise removing debris from the coolant without significant interference with the coolant flow.
	description	This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2007/052795, filed on Feb. 9, 2007, which in turn claims the benefit . of Japanese Application No. 2006-040110, filed on Feb. 17, 2006, the disclosures of which Applications are incorporated by reference herein. The present invention relates to a pattern inspecting/measuring method, a pattern inspecting/measuring apparatus and a computer program for performing inspection/critical dimension of a pattern and more particularly, to a method and apparatus for inspecting/measuring the shape or placement error concerning a pattern by comparing design data of the pattern with an actual pattern. It has been known to measure a circuit pattern of semiconductor device actually formed on a wafer by using a design data of the circuit pattern of semiconductor device. Since the design of the circuit pattern shows an ideal shape the circuit pattern of semiconductor device has primarily, the accuracy of patterning by a semiconductor fabrication process can be evaluated by comparing the design data with a pattern actually formed on the wafer. Recently, fineness of a semiconductor integrated circuit has been advancing and in the wake thereof, the performance of a semiconductor inspecting apparatus has been ameliorated. As one of the semiconductor inspecting apparatus as above, a CD-SEM (Critical Dimension Scanning Electron Microscope) is available. The CD-SEM is an apparatus in which the dimension of a pattern formed on a sample is measured on the basis of secondary electrons obtained by scanning an electron beam, a kind of charged-particle beam, on the sample. Patent Document 1 discloses that an amount of deformation of a pattern is detected by detecting a pattern edge of an inspection objective pattern with the help of the CD-SEM and by comparing it with a reference pattern. Secondary electrons obtained by scanning the electron beam on the sample sometimes differ in generation intensity and in distribution of generated secondary electrons depending on the direction of scanning of the electron beam and on the direction of a pattern edge of the inspection objective pattern. Patent Document 1 and Patent Document 2 propose that in order to mitigate the above inconvenience, the electron beam is constantly scanned vertically to the direction of an edge of the pattern to be measured. [Patent Document 1] JP-A-2004-163420 [Patent Document 2] JP-A-2005-116795 In some of up-to-date semiconductor integrated circuits, the fineness so advances as to make the pattern width amount to less than 32 nm. In order to control the pattern dimension as above, the pattern shape needs to be measured with an accuracy of sub-nanometer of 0.3 nm˜0.2 nm or less. To realize such a measurement accuracy, the differences in secondary electron generation intensity and distribution as well attributable to the differences in the electron beam scanning direction and in pattern edge direction cannot be neglected. Therefore, the Patent Document 1 and Patent Document 2 propose that the electron beam is always scanned vertically to the direction of the pattern edge of inspection objective pattern but they raise problems as below. The accuracy of control of scanning position and direction of the electron beam is limited and in some case, when the scanning direction is changed, the pattern edge detection position will change by 1 nm or more. Accordingly, with the electron beam managed to scan constantly vertically to the pattern edge of inspection objective pattern, an error will take place in pattern edge detection position depending on the scanning position and direction. The Patent Document 2 discloses a method of combining SEM images subject to different scanning directions but in-plane distortions of an SEM image differ with scanning direction and hence, all patterns within a field of view of the SEM image cannot be superposed with sufficiently high accuracies. The techniques disclosed in the Patent Documents 1 and 2, however, did not take countermeasures against errors in control of the scanning direction and position caused by changing the scanning direction and position of the electron beam as above. According to the present invention, to accomplish the above object, differences in generation intensity and distribution of secondary electrons attributable to differences in the scanning direction of an electron beam and the pattern edge direction as well are investigated in advance and put to a library and an actually acquired secondary electron signal is corrected by using the library, whereby the edge position of even a pattern edge not vertical to the scanning direction of the electron beam can be measured accurately. Further, by measuring a scanning error depending on the scanning position and direction of an electron beam in advance and superposing the error on a control signal during scanning of the electron beam, errors caused when the scanning direction and position of the electron beam are changed can be reduced and a pattern edge position can be measured sufficiently accurately. The principal advantage of the present invention is to provide sample dimension inspecting/measuring method and apparatus in which by reducing the error of measurement of a pattern edge position attributable to differences in the electron beam scanning direction and the pattern edge direction as well and by reducing the error of measurement of a pattern edge position due to errors of the scanning position and direction caused when the scanning direction of the electron beam is changed, edge positions in all directions of a fine pattern can be measured with high accuracies. The outline of a scanning electron microscope (hereinafter referred to as SEM) will be described hereunder by using FIG. 1. A voltage is applied across a cathode 1 and a first anode 2 by means of a high voltage control power supply 20 controlled by a control processor 30 and a primary electron beam 4 is extracted at a predetermined emission current from the cathode 1. Across the cathode 1 and a second anode 3, an accelerating voltage is applied by means of the high voltage control power supply 20 controlled by the control processor 30 and the primary electron beam 4 emitted from the cathode 1 is accelerated to proceed to a subsequent stage of lens system. The primary electron beam 4 is converged by a convergent lens 5 controlled in current by means of a lens control power supply 21 controlled by the control processor 30, is removed of its unwanted region by an aperture plate 8 and is then focused to a fine spot on a sample 10 with the help of a focusing lens 6 controlled in current by means of a lens control power supply 22 controlled by control processor 30 and an objective lens 7 controlled in current by means of an objective lens control power supply 23 controlled by the control processor 30. The objective lens 7 can take any of various types of in-lens, out-lens and Schnorchel type (semi-in-lens type). The retarding type of decelerating the primary electron beam by applying a negative voltage to the sample 10 may be employable. Further, each of the lenses may also be constructed of an electrostatic type lens having a plurality of electrodes applied with controlled voltages. The primary electron beam 4 is scanned two-dimensionally on the sample 10 with the help of a scanning coil 9 controlled in current by means of a scanning coil control power supply 24 controlled by the control processor 30. A secondary signal 12 of, for example, secondary electrons generated from the sample 10 under irradiation of the primary electron beam proceeds to above the objective lens 7 and thereafter separated from the primary electrons by means of an orthogonal electromagnetic field generation unit 11 for secondary signal separation so as to be detected by a secondary signal detector 13. The signal detected by the secondary signal detector 13 is amplified by a signal amplifier 14 and then transferred to an image memory 25 and displayed as a sample image on an image display unit 26. Two stages of deflection coils (aligner for objective lens) 16, which are controlled in current by means of an aligner control power supply 27 for objective lens controlled by the control processor 30, are arranged at the same position as the scanning coil 9 and the position along which the primary electrons 4 pass through the objective lens 7 can be controlled two-dimensionally. A stage 15 can move the sample 10 in at least two directions (X direction, Y direction) in a plane vertical to the primary electron beam, thereby ensuring that the scanning area of primary electrons 4 on the sample 10 can be changed. A pointing unit 31 can designate the position of a sample image displayed on the image display unit 26 to enable information of the sample image to be acquired. An input unit 32 can designate conditions of fetching of the image (scanning speed, number of accumulative images) and view field correction method and besides can designate delivery and storage of images. Address signals corresponding to memory positions of an image memory are generated in the control processor 30 or in a control computer 42 arranged separately, are subjected to analog conversion and are then supplied to the scanning coil control power supply 24. When the image memory has, for example, 512×512 pixels, the address signal in X direction is a digital signal repeating 0 to 512 and the address signal in Y direction is a digital signal repeating 0 to 512 which advances by plus 1 each time that the address signal in X direction starting from 0 reaches 512. These signals are converted into analog signals. The address of image memory 25 corresponds to the address of a deflection signal for scanning the electron beam and therefore, a two-dimensional image in an area of deflection of electron beam by means of the scanning coil 9 is recorded in the image memory. The signals inside the image memory 25 can be read out sequentially on time series basis by means of a read address generation circuit synchronized with a readout clock. A signal read out in correspondence with an address is converted into an analog signal that acts as a brightness modulation signal of the image display unit 26. The apparatus explained in the present example, has the function to form a line profile on the basis of detected secondary electrons or backscattering electrons. The line profile is formed on the basis of an amount of detected electrons or brightness information obtained when the primary electron beam 4 is scanned linearly or two-dimensionally on the sample 10 and the thus obtained line profile is used for dimension measurement and the like of, for example, a pattern formed on a semiconductor wafer. The control processor 30 is described in connection with FIG. 1 as being integral or so with the scanning electron microscope but this is in no way limitative and the process may be conducted with a processor provided separately from the scanning electron microscope column. In such a case, it is necessary that the detection signal detected by the secondary signal detector 13 be transmitted as an image to the control processor 30 and besides, a transmission medium for transmission of signals from the control processor 30 to the objective lens control power supply 23 and scanning coil control power supply 24 of the scanning electron microscope and an input/output terminal for input/output of the signals transmitted via the transmission medium be provided. Further, the present apparatus has the function to store in advance conditions for observation of, for example, plural points on the semiconductor wafer (measuring locations, optical conditions of scanning electron microscope and so on) as a recipe and conduct measurement and observation in accordance with the contents of the recipe. The control processor 30 also functions as an arithmetic unit during measurement of pattern dimensions. Also, a program for execution of a process to be described below may be registered in a memory medium and the program may be executed by a processor for supplying necessary signals to the scanning electron microscope and so on. Namely, an example to be explained below will be described by way of example of a program or a program product adoptable to a charged-particle beam apparatus capable of acquiring images such as the scanning electron microscope. Further, the control processor 30 may be connected with a design data management unit 33 adapted to store circuit pattern design data of semiconductor device expressed in a GDSII format or OASIS format and convert the design data into data necessary for control of the SEM. The design management unit 33 has the function to prepare a recipe for controlling the SEM on the basis of inputted design data. It also has the function to work the design data on the basis of a signal transmitted from the control processor 30. Further, a process to be described below may be executed by means of a processor provided in the design data management unit 33. Moreover, the scanning electron microscope may be controlled with a processor that is provided in the design management unit 33 to substitute for the control processor 30. In describing the present example, the design data management unit 33 will be described as being separate from the control processor 30 but this is not limitative and it may be integral with the control processor. Used as the sample 10 in the present example is a wafer on an excursion of fabrication of a semiconductor product. A resist pattern formed on the wafer through lithography process is used. As a comparative object, design data of a circuit pattern of semiconductor device from which the pattern originates is used. The design data of a circuit pattern of semiconductor device used herein indicates an ideal pattern when the semiconductor device circuit is formed on the wafer ultimately. In the following description, the inspection objective is the semiconductor wafer but this is not limitative so long as the design data and an object desired for evaluation are paired. For example, the following description is valid for a mask pattern formed on glass substrate used when exposure of a semiconductor pattern on a wafer is executed or for a pattern formed on a glass substrate such as a liquid crystal panel. The kind of design data of circuit pattern does not matter if the software for displaying the design data of circuit pattern can display its format form and can handle it as graphical data. With reference to the accompanying drawings, an example of measurement of an error in shape (hereinafter sometimes referred to as EPE (Edge Placement Error) measurement) between an edge portion of a pattern shown in an image acquired by an electron microscope (hereinafter sometimes referred to as SEM edge) and a pattern shape shown in design data (hereinafter sometimes referred to as design pattern) will be described. FIG. 3 illustrates a state in which an electron microscope image of an actual pattern 41 formed on a wafer (hereinafter referred sometimes to as an actual pattern) is superposed on a design pattern 40. This can be obtained by subjecting each of a binary-digitized template prepared from the design pattern 40 (S0001) and an SEM image actually acquired from the wafer to edge extraction (S0002) and smoothing (S0003) and then by subjecting them to a matching process (S0004) through the use of a normalizing function, as shown in FIG. 2. The EPE measurement is to measure an error in shape between the ideal pattern shape indicated by the design pattern 40 and the actual pattern 41 but as will be described with reference to FIG. 3, the actual pattern 41 is often formed while being constricted at a pattern tip portion 42 and rounded at a corner portion 43, for example. In an example as shown in FIG. 3, the pattern is sorted into 1) a tip portion of pattern (hereinafter referred to as tip portion 42), 2) a linear portion of pattern (hereinafter referred to as linear portion 44) and 3) a corner of pattern (hereinafter referred to as corner portion 43). The reason why this division is taken is that the tendency toward deformation and the amount of deformation will change with features of the pattern shape. The two-dimensional shape measurement is exactly to measure the whole of a pattern shape which changes variously in accordance with the features of the pattern shape. FIG. 3 is a diagram for explaining an instance where the EPE measurement 47 is carried out at all positions of SEM edges 45 detected from an SEM image but when the electron beam is scanned in a fixed direction, pattern edge positions cannot be measured with sub-nanometer precision in all directions because of the relation the direction of a pattern edge of the actual pattern 41 has to the scanning direction. Specifically, depending on different electron beam scanning directions 95 in relation to the direction of an edge of the actual pattern 41 on the wafer as shown in FIG. 4, different signal waveforms 96 of generated secondary electrons develop. Illustrated at (b) in FIG. 4 is a signal waveform of secondary electrons when the electron beam is scanned vertically to the edge of actual pattern 41 on the wafer, at (c) is a signal waveform of secondary electrons when scanning is in, for example, 45° direction and at (d) is a signal waveform of secondary electrons when scanning is in, for example, 30° direction. Further, the generation intensity and generation distribution of secondary electrons sometimes differ, as shown in FIG. 5, for the case where the electron beam (primary electron beam 4) is scanned from the outside (low intensity location) of actual pattern 41 to the inside (high intensity location) and for the case where the electron beam is scanned from the inside (high intensity location) to the outside (low intensity location). Illustrated at (b) in FIG. 5 is the instance where the electron beam is scanned from the outside (low intensity location) of actual pattern 41 on the wafer to the inside (high intensity location) and at (c) in FIG. 5 is the instance where the electron beam is scanned from the inside (high intensity location) of actual pattern 41 on the wafer to the outside (low intensity location). The differences in secondary electron signal waveforms have, as shown in FIG. 6, constant tendencies which depend on an angle the electron beam scanning direction makes to an actual pattern on the wafer. In the figure, 90° corresponds to the case where the electron beam is scanned from the outside (low intensity location) of actual pattern 41 on the wafer to the inside (high intensity location), 0° corresponds to the case where the electron beam is scanned horizontally to the edge of actual pattern 41 on the wafer and −90° corresponds to the case where the electron beam is scanned from the inside (high intensity location) of actual pattern 41 on the wafer to the outside (low intensity location). By using a dosage curve 97 of the intensity of secondary electrons and a dosage curve 97 of the half-width of the signal which are determined from graphs shown in FIG. 6, the signal waveform of secondary electrons at a desired angle can be corrected. For example, pursuant to equation (1), the signal intensity of secondary electrons can be corrected and pursuant to equation (2), the half-width of secondary electron signal waveform can be corrected.(signal intensity after correction)=(original signal intensity×f(θ) (1)(half-width after correction)=(original width)×g(θ) (2) In FIG. 7, a method of switching the scanning direction 95 of the electron beam in compliance with the EPE measurement direction. By using this method, identical signal waveforms of secondary electrons can be obtained even in respect of pattern edges in any directions. But, when the scanning direction of electron beam is changed as described previously, the scanning position will sometimes displace as shown in FIG. 8. In this example, the actual pattern 41 on SEM image when the electron beam scanning direction is 0° is indicated in solid curve, the actual pattern in the case of 180° is indicated in dotted curve and an error in the electron beam scanning direction between 0° and 180° directions is indicated by (ΔX, ΔY). While in this example only errors in X direction and Y direction are indicated, an error in rotational direction will possibly occur. Further, there is the possibility that these errors will differ with the distance or direction of the electron beam scanning position from the center axis of electron optical system. Accordingly, as shown in FIG. 9, errors in the scanning position and direction of the electron beam are measured in advance and by using the results, the control signal for the electron beam scan is corrected or after the scanning position and direction of the electron beam illustrated in FIG. 7 are corrected to correct (actual) position and direction, the pattern edge position is measured. It will be appreciated that a measure in FIG. 9 indicates a position of the electron beam from the center of electron optical system and an arrow shows an error in the electron beam scanning position at a position of interest. An example of measuring a pattern edge position by using secondary electron signal waveforms obtained through scanning of (one) electron beam at one position is shown in FIG. 4 but this is disadvantageous in that the S/N ratio of signal waveform is low and the accuracy of EPE measurement is insufficient. To the contrary, a method as shown in FIG. 10 is employable according to which by using a line profile 54 created by averaging and smoothing a plurality of secondary electron signal waveforms obtained through scanning of (plural) electron beams at plural positions, the pattern edge position is measured. Since the line profile 54 has a higher S/N than every one original secondary electron signal waveform, a correct pattern edge position can be measured accurately. By using the method as above, a correct contour of the actual pattern 41 can be detected with sub-nanometer accuracies. The line profile can be prepared 1) by extracting pieces of information of pixels inside an area of critical dimension box 53 (gradation information in gray scale) from image data of an SEM image of an inspection objective pattern and accumulating (averaging) and smoothing the information pieces in an edge search direction 57 or 2) by scanning an inspection objective area of critical dimension box 53 plural times with the electron beam in directions horizontal to the edge search direction 57 to obtain secondary electron signal waveforms and accumulating (averaging) and smoothing them. In FIG. 10, a constant threshold Th is set to the brightness value of line profile 54 and a position where the line profile 54 crosses the threshold Th is determined as a critical dimension edge 55 but putting this method aside, there are various methods for edge detection from the line profile 54 and this method is not limitative. In FIG. 10, the critical dimension box 53 is centered on a middle point 56 of SEM edge 45 so as to lie in a direction orthogonal to the design pattern 40 but this is not limitative as is clear from a description given with reference to FIG. 13. A process flow will be described specifically with reference to FIG. 11. Firstly, an instance where a profile is prepared by using information of pixels inside the critical dimension box 53 is shown at (a) in FIG. 11. Pieces of information of pixels of image data of an inspection objective pattern inside a critical dimension area (S0001) designated by the critical dimension box 53 are acquired (S0002). At that time, it is assumed that the direction of accumulation of the pieces of pixel information is vertical to the edge search direction 57. Next, the pixel information pieces are accumulated and smoothed to create a line profile 54 (S0003). Subsequently, a critical dimension edge 55 is detected from the line profile 54 (S0004). Finally, EPE measurement between a critical dimension edge 55 and the design pattern 40 is carried out (S0005). Next, an instance where a profile is prepared by scanning an area of critical dimension box 53 with the electron beam is shown at (b) in FIG. 11. The critical dimension area (S0001) designated by the critical dimension box 53 is scanned with the electron beam plural times (S0002). At that time, the scanning direction is assumed to be horizontal to the edge search direction 57. Subsequently, a line profile acquired by scanning the electron beam is prepared (S0003). Next, a critical dimension edge 55 is detected from the line profile 54 (S0004). Finally, EPE measurement between the critical dimension edge 55 and the design pattern 40 is carried out (S0005). Illustrated at (a) in FIG. 10 is an example where in the method of image processing such as Sobel filter, a portion of white band 46 of an SEM image at which the brightness is the highest is detected as the SEM edge 45. In this case, the SEM edge 45 is positioned very closely to the critical dimension edge 55 determined through the line profile but it erroneously differs from the critical dimension edge 55 by several nm and lacks accuracy for EPE measurement. Illustrated at (b) in FIG. 10 is an example where in the method of image processing such as Sobel filter, an inner side of the white band 46 is detected as the SEM edge 45. In this case, there is a large error between the SEM edge 45 and the position of critical dimension edge 55. Illustrated at (c) in FIG. 10 is an example where in the method of image processing such as Sobel filter, an inner edge 58 existing inside the actual pattern 41 is erroneously detected as an SEM edge of the pattern contour and with the inner edge 58 measured erroneously, a correct contour cannot be grasped. In any case shown in FIG. 10, a critical dimension edge 55 having sufficient precision for the EPE measurement can be detected by using the line profile 54. FIG. 12 illustrates examples of a method of placing the critical dimension box 53 indicative of an area for creating the line profile. Illustrated at (a) in FIG. 12 is an instance where the critical dimension box 53 is placed as being referenced to an SEM edge middle point 56 and lengths L1 and L2 of critical dimension box 53 in the edge search direction are set as being referenced to an SEM edge 45. The lengths L1 and L2 can be settled by setting specified values separately to these lengths, respectively, in expectation of an error in position between the SEM edge 45 and the critical dimension edge 55 but there is the possibility that an error in excess of the expectation will occur when the inner edge 58 is detected erroneously. In such a case, by making a crossing 59 of the edge search direction 57 and the design pattern 40 a point to which L2 is referenced as shown at (b) in FIG. 12, the critical dimension edge 55 can be grasped correctly. In the example shown at (b) in FIG. 12, the SEM edge 45 exists internally of a figure the design pattern 40 indicates but even in the case of external existence, processing can be executed similarly. Although not indicated in FIG. 12, a pattern shape estimating the edge search direction 57 and the actual pattern shape through simulation (hereinafter sometimes referred to as a simulation pattern) may be used by making the crossing with the edge search direction 57 a point to which L2 is referenced. Next, a width W of critical dimension box 53 as shown in FIG. 12 will be described. When the width W of critical dimension box 53 is increased, the number of pieces of image information to be accumulated during preparation of the line profile and the number of secondary electron signal waveforms increase and therefore, with the width W increased excessively, a local shape of a portion at which the shape changes greatly cannot be grasped. Then, the width W may be adjusted automatically in accordance with the length of the SEM edge 45. For example, by making the width W equal to the length of SEM edge 45, the width W of critical dimension box 53 can be narrowed automatically at a portion where the SEM edge 45 has a short length and changes in shape largely. Further, by setting to the width W upper and lower limit values (for example, an upper limit of 20 nm and a lower limit of 3 nm), the width W can be controlled within a constant range. Furthermore, in case the profile is formed by scanning the electron beam, the scanning density of the electron beam can be made to be constant by changing the number of lines of scan in accordance with the width W. Through this, such a damage caused by the electron beam as shrinkage of resist can remain intact irrespective of the length of the SEM edge. FIG. 13 is for explaining specified examples of edge search direction 57. Firstly, it is proposed that a direction in which the gradation of a gradation image obtained by painting up a pattern used as a reference and thereafter shading it off by means of, for example, a Gaussian filter changes is set as the edge search direction. For convenience of explanation, the SEM edge is used as the reference position for edge search as explained in connection with FIGS. 10 and 12 but this is not limitative. Illustrated at (a) in FIG. 13 is an example where the direction in which the gradation of a gradation image 60 prepared by painting up a design pattern 40 and thereafter shading it off with the Gaussian filter changes is set as the edge search direction 57. By using such a method, the edge search direction 57 can be set to a direction vertical to the design pattern 40 in connection with a linear shape portion and at a tip portion 42 and a corner of the pattern, the direction of accumulation of pieces of pixel information and the scanning direction of electron beam can be set in a radial direction commensurate with a change in shape. Illustrated at (b) in FIG. 13 is an example where a direction in which the gradation of a gradation image 60 prepared by painting up a pattern 61 obtained by deforming the design pattern 40 in expectation of a change in shape of the actual pattern and thereafter shading it off with the Gaussian filter changes is set as the edge search direction 57. In this example, in expectation that the tip portion 42 of the pattern will be shortened, the pattern 61 resulting from deforming the design pattern 40 is prepared. By using this method, in addition to the feature shown at (a) in FIG. 13, the direction of accumulation of pixel information and the scanning direction of electron beam which cope with a local difference in the change amount of pattern shape can be set. Illustrated at (c) in FIG. 13 is an example where a direction in which the gradation of a gradation image 60 prepared by painting up a polygon 62 connecting the SEM edges and thereafter shading it off with the Gaussian filter changes is set as the edge search direction 57. By using such a method, even in the event that the change amount of shape of the pattern exceeds an estimated level, the accumulation direction of pixel information and the scanning direction of electron beam which cope with a local difference in the amount of change in pattern shape can be set. Illustrated at (d) in FIG. 13 is an example where a direction in which the gradation of a gradation image 60 prepared by paining up a simulation pattern 63 and thereafter shading it off with the Gaussian filter changes is set as the edge search direction 57. In case the SEM edge exists at a position remote from the simulation pattern, calculation for making the SEM edge 45 commensurate with the simulation pattern 63 becomes complicated. In contrast thereto, by using the gradation image 60 obtained from the simulation pattern 63, the edge search direction 57 can be set easily no matter which position the SEM edge 45 exists at. In any of the instances at (a), (b), (c) and (d) in FIG. 13, the edge search direction 57 is so set as to direct from the outside to the inside of the pattern to which reference is made but the edge search may be conducted from the inside to the outside. For example, when the edge search is executed from dark to bright of the gradation of gradation image 60, the edge search direction 57 is so set as to be directed from the outside to the inside of a pattern to which reference is made if the pattern referenced to is painted up in color brighter than the background (for example, the background is in black and the inside of the reference pattern is in white). Conversely, when the pattern to be referenced to is painted up in darker than the background (for example, the background is in white and the inside of the reference pattern is in black), the edge search direction 57 can be set from the inside to the outside of the figure to be referenced to. FIG. 14 shows an influence the matching result has upon the EPE measurement values. In order to perform the EPE measurement, the relative positional relation between an SEM image and design data needs to be first settled. Then, through the process explained in connection with FIG. 2, pattern matching is carried out between a template prepared from the design data and an actual pattern. Illustrated at (a) in FIG. 15 is an instance where an SEM edge 45 is used for a process of pattern matching and a critical dimension edge 55 detected by using a line profile is used for EPE measurement. In case a bias occurs in errors in position between the SEM edge 45 used for matching and the critical dimension edge 55 used for the EPE measurement, the critical dimension values by the EPE measurement are also biased and the amount of deformation of the shape of the actual pattern cannot be grasped correctly. Accordingly, the present invention proposes that the pattern matching using as a reference an edge used during execution of the EPE measurement is carried out. Illustrated at (b) in FIG. 14 is a specified example where the critical dimension edge 55 is used for both the pattern matching and the EPE measurement. Since the critical dimension edge 55 is used for both the pattern matching and the EPE measurement as shown in this figure, the results of EPE measurement will not be biased if proper pattern matching is executed. The critical dimension edge 55 is used for both the pattern matching and the EPE measurement in the case indicated at (b) in FIG. 14 but similar results can be obtained even by using the SEM edge 45 for both the pattern matching and the EPE measurement. By using FIGS. 15 and 16, a specified embodiment of pattern matching using the critical dimension edge 55 will be described. Firstly, a gradation image of actual pattern 41 and a reference pattern (in the case of FIG. 15, a design pattern 40) with which the actual pattern is to be pattern-matched is prepared (S0001). Next, brightness values of the gradation image at individual positions of critical dimension edges 55 are recorded (S0002) and put together into a graph as shown at (c) in FIG. 15 (S0003). This graph is one for showing a variance of the number of edges with abscissa representing brightness value. When the result of pattern matching shows an ideal position as shown at (a) in FIG. 15, dispersions of brightness values of gradation image 60 at positions of individual critical dimension edges 55 are small and the graph exhibits a small variance σ1 as shown at (c) in FIG. 15. Conversely, when the results of pattern matching are biased as shown at (b) in FIG. 15, brightness values of gradation image 60 at the positions of individual critical dimension edges 55 disperse and as a result, the graph exhibits a large variance σ2 as shown at (d) in FIG. 15. By taking advantage of the principle as above, the variance of brightness values is evaluated (S0004) and positions at which the variance is minimized are selected as optimum matching positions (S0005). As described above, by evaluating the variance of brightness values of a gradation image of a reference pattern subject to pattern matching at the individual critical dimension edge positions, ideal pattern matching can be achieved. While in FIG. 15 the design data 40 is used as the reference pattern, the design pattern or simulation pattern reflecting the shape change estimation as explained in connection with FIG. 13 may be used. Further, the critical dimension edge 55 is used for pattern matching in FIG. 15 but alternatively, the SEM edge may be used. In addition, a method of correcting a rotational component during pattern matching will be described in detail. In the EPE measurement, accuracies of sub-nanometer are demanded and unless accurate pattern matching is carried out, the error in EPE measurement value increases. Especially, the pattern matching error of rotational component in a linear pattern as shown at (a) in FIG. 17 causes a large error in the EPE measurement value. To solve this problem, matching inclusive of correction of the error in rotational component needs to be carried out. The present example proposes, for the sake of correcting the rotational component, 1) a method of rotating the position (coordinates) of an edge used for EPE measurement ((b) in FIG. 17) and 2) a method of rotating the position (coordinates) of a pattern to which pattern matching is referenced is rotated ((c) in FIG. 17). 1) The method of rotating the position of an edge used for EPE measurement will be described in detail by making reference to (b) in FIG. 17 and FIG. 18. As shown at (b) in FIG. 17, coordinates (X1, Y1) of a critical dimension edge 55 detected under a condition not subjected to rotation (condition at (a) in FIG. 17) is corrected for rotation by angle θ by using equation of rotation as shown in equation (3) (S0001) and coordinates (X2, Y2) of a critical dimension edge 68 after rotation correction is obtained (S0002). ( X ⁢ ⁢ 2 Y ⁢ ⁢ 2 ) = ( cos ⁢ ⁢ θ sin ⁢ ⁢ θ - sin ⁢ ⁢ θ cos ⁢ ⁢ θ ) ⁢ ( X ⁢ ⁢ 1 Y ⁢ ⁢ 1 ) ( 3 ) Next, a variance of brightness values of individual critical dimension edges 68 after rotation correction is evaluated by using the method explained in connection with FIG. 15 (S0003˜S0006) and a position for optimum pattern matching is introduced (S0007). After the optimum matching result is obtained, EPE measurement between the critical dimension edge 68 after rotation correction and the reference pattern (here design pattern 40) is carried out (S0008). Here, selection of the optimum matching position effected by utilizing the rotation correction and its result is carried out once but in order to raise the accuracy further, the process may be repeated several times. 2) The method of rotating the position of a pattern to which pattern matching is referenced will be described in detail by making reference to (c) in FIG. 17 and FIG. 19. As shown at (c) in FIG. 17, coordinates of apices of a reference pattern (here design pattern 40) are rotated for correction by angle θ using the rotation expression as indicated by equation (3) (S0001) and a pattern of reference after rotation correction (here design pattern 69 after rotation correction) is obtained (S0002). Next, by using the reference pattern subjected to rotational correction, the variance of brightness values of the individual critical dimensions 55 is evaluated pursuant to the method explained in connection with FIG. 15 (S0003˜S0006) and an optimum pattern matching position is introduced (S0007). After the result of optimum matching is obtained, EPE measurement between the critical dimension edge 55 and the reference pattern subject to rotational correction (here, design pattern 69 subject to rotational correction) is carried out (S0008). The top feature of the methods of above 1) and 2) proposed in the present example resides in that the image data is not rotated and yet coordinate data is rotated. This ensures that fast processing can be executed and besides the error in EPE measurement accuracy attributable to errors in rounding pixels caused during rotation of the image data can be prevented from occurring. FIG. 20 is for explaining a method of obtaining cubical shape information of actual pattern 41 by changing the threshold at the time that a critical dimension edge 55 is detected through the use of a line profile 54. Illustrated at (a) and (b) in FIG. 20 are each the EPE measurement 47 of an actual pattern 41 having a sectional shape as shown at (e) in FIG. 20. When a threshold Th1 is set to the brightness value of line profile 54 as shown at (c) in FIG. 20, EPE measurement 47 using an SEM edge 55 is indicated as shown at (a) in FIG. 20. Contrary to this, when a threshold Th2 larger than the threshold Th1 is set to the brightness value of line profile 54 as shown at (d) in FIG. 20, EPE measurement 47 using an SEM edge 55 is indicated as shown at (b) in FIG. 20. As will be seen from comparison of the EPE measurement 47 at (a) in FIG. 20 with that at (b) in FIG. 20, contours at different heights of the actual pattern 41 can be grasped by changing the threshold during determination of the SEM edge 55 from the line profile 54. By using the information as above, the EPE measurement of the amount of cubical shape deformation of actual pattern 41 can be achieved. To add, only the two kinds of thresholds are used in this example but in the case of acquisition of more detailed cubical shape information, the threshold may be graded more finely in, for example, 10 steps. The EPE measurement adapted for the case where a semiconductor device is formed going through a plurality of layers will be described by using FIG. 21. FIG. 21 illustrates a semiconductor device to be observed through an SEM image has two layers of upper and lower layers but the existence of three or more layers may be involved. In a method for discriminating the EPE measurement of an upper layer from that of a lower layer, for an SEM edge extracted from an actual pattern, layer information of a design pattern with which the SEM edge is correspondent can be used. FIG. 21 shows an example where an SEM edge is made to be correspondent with a reference pattern lying in a direction vertical to the SEM edge (here, a design pattern). As shown in FIG. 21, an upper layer SEM edge 72 can be correspondent with an upper layer design pattern 70 and a lower SEM edge 77 can be correspondent with a lower layer design pattern 75. But, there is the possibility that the correspondence will become ambiguous at a portion 80 where an edge of the upper layer pattern overlaps that of the lower layer. Then, in the present example, a method will be proposed which sorts SEM edges according to individual layers by utilizing the difference in shape of a line profile prepared at individual positions of the SEM edges. Illustrated at (a) in FIG. 21 is a line profile 74 of an upper layer pattern edge and at (b) in FIG. 21 is a line profile 79 of a lower layer pattern edge. In this example, the brightness value of the line profile 79 of lower layer pattern edge is so exemplified as to be lower than that of the line profile 74 of upper layer pattern edge. In such a case, by setting a suitable threshold to the brightness value, the upper layer SEM edge 72 can be discriminated from the lower layer SEM edge 77. Further, like FIG. 21, FIG. 22 shows at (a) a line profile 74 of an upper layer pattern edge and at (b) a line profile 79 of a lower layer pattern edge. In this example, the brightness value of the upper layer line profile 74 has one peak whereas the brightness value of the lower layer line profile 79 has two peaks. In such a case, by examining the number of peaks in excess of an appropriate threshold Th set to the brightness value, the upper SEM edge 72 can be discriminated from the lower SEM edge 77. While in FIGS. 21 and 22 the difference in shape of line profile is determined by the threshold set to the line profile, the method for comparison of line profile shapes is not limited thereto. For example, line profile shapes per se may be compared to each other through normalized correlation. FIG. 23 shows an example of the output result of EPE measurement result. As shown in the figure, the output result includes 1) information 92 concerning the EPE measurement result, 2) information 93 of a reference pattern to which the EPE measurement is referenced and 3) results of evaluation of the EPE measurement. An EPE measurement information item contains measurement value of the EPE measurement, coordinates of a critical dimension edge from which the measurement value originates and coordinates of a correspondent reference pattern. A reference pattern information item contains the type of reference pattern (design pattern, simulation pattern or the like), layer information of the reference pattern (layer information, data type) and figure information (figure number, line segment number, line segment start point/end point coordinates, line segment direction). An evaluation result item contains sorting information of portions of a reference pattern made to be correspondent to during EPE measurement (linear portion, corner portion, tip portion and the like), standards of managing EPE measurement value (such as threshold for abnormality decision and so on) and importance degree of EPE measurement value (within specifications, outside specifications, fatal or not fatal). The sorting information of reference pattern will sometimes be contained in the reference pattern information. For example, when a specified layer number or data type is set to a figure collecting only Line portions, the reference pattern can be sorted by consulting it. Alternatively, the shape of reference pattern may be analyzed to prepare sorting information automatically. For example, it is possible that a line segment having a length exceeding a constant value is deemed as a linear portion, a portion remote by a constant distance from a portion at which line segments cross at right angles is deemed as a corner and a portion where two corners approach mutually and a linear portion having a length longer than a constant value connects is deemed as a tip portion. Furthermore, the managing standards can be set independently according to sorting of the reference pattern. For example, the managing standards for the corner portion can be mitigated as compared to those for the linear portion. Further, for the same linear portion, the managing standards may be set discriminatively on conditions (for example, the degree of importance a semiconductor circuit has). In the example of FIG. 23, the managing standards are set to −1.0˜1.0 nm in connection with a linear portion (Line-1) for which the standards are stringent, the managing standards are set to −3.0˜3.0 nm in connection with a linear portion (Line-2) for which the standards are tolerant and the managing standards are set to −15.0˜5.0 nm in connection with a corner for which the standards are more tolerant than those for the linear portion. In this manner, by storing various kinds of information having the relation to the EPE measurement in tabular form and by discriminatively displaying EPE measurement values in excess of the set managing standards to make them discernible from other measurement results, a pattern to be reevaluated may be clarified. In the case of the example of FIG. 23, by displaying a predetermined number or mark indicative of abnormality in an entry of importance categorized in the item of evaluation result of the EPE measurement, other measurement results are displayed discriminatively. More particularly, in the case of the EPE number 2, the EPE measurement value is −5.3 nm in relation to the managing standard lower limit −3.0 nm, indicating that the managing standards are exceeded, and therefore the degree of importance is set to 2 that is problematic. With this structure, the custodian can selectively evaluate only a portion exceeding the tolerable error and the efficiency of evaluation can be improved to advantage. In addition, although not shown in FIG. 23, EPE measurement values in individual different directions are averaged to obtain mean values and the means EPE values in the individual directions are examined as to whether to be biased, so that it can be decided whether either an actual pattern is displaced as a whole or only a part of the actual pattern is deformed in relation to a reference pattern. In other words, if only a part of the EPE measurement value is large, it is conceivable that only the area is deformed for any reasons. But, for example, if a mean EPE measurement value in a direction is largely minus and a mean EPE measurement value in the opposite direction is largely plus, there is the possibility that the pattern will be so formed as to make a large displacement in that direction.
	summary
	description	This application is the National Stage filing under 35 U.S.C. 371 of International Application No. PCT/KR2015/007635, filed on Jul. 22, 2015, which claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2014-0093457, filed on Jul. 23, 2014, the contents of which are all hereby incorporated by reference herein in their entirety. 1. Field of the Invention The present disclosure relates to a passive residual heat removal system used as one of emergency safety facilities and a nuclear power plant including the same. 2. Description of the Related Art A residual heat removal system is an emergency safety facility for removing sensible heat in a reactor coolant system and residual heat in a reactor core during an accident. In particular, the passive residual heat removal system removes sensible heat and residual heat in a passive manner using natural forces. For a coolant circulation method of the passive residual heat removal system, two methods such as 1) a method of directly circulating reactor primary coolant to cool a reactor (AP1000: U.S. Westinghouse) and 2) a method of circulating secondary coolant using a steam generator to cool a reactor (SMART reactor: Korea) are mostly used. In, addition, 3) a method of injecting primary coolant to a tank to directly condense it (CAREM: Argentina) is partially used. For a passive residual heat removal system to which a secondary coolant circulation method is applied, two types such as 2-1) a mode to which a pressurized makeup tank is applied and both directions of a steam line and a feedwater line of the passive residual heat removal system are isolated with an isolation valve during a normal operation (Korean Patent Application No. 10-2000-0067089), and 2-2) a mode to which gravity water head makeup tank is applied and only one direction of a feedwater line of the passive residual heat removal system is isolated with an isolation valve (IRIS: U.S. Westinghouse, SMART reactor: Korea) are used. Furthermore, for a method of cooling an outside of a heat exchanger (condensation heat exchanger), 1) a water-cooled method (AP1000) applied to most reactors, 2) a partially air-cooled method (WWER 1000: Russia), and 3) a water-air hybrid cooled method (IMR: Japan) have been used. A heat exchanger of the passive residual heat removal system performs a function of transferring heat received from a reactor to an outside (atmosphere) through an emergency cooling tank (heat sink) or the like, and condensation heat exchangers using a steam condensation phenomenon with an excellent heat transfer efficiency have been mostly used for a heat exchanger method. A steam generator performs a function of receiving heat in a reactor coolant system to produce steam, and supplying the steam to a turbine system. Furthermore, a secondary side of the steam generator is used as a supply source for producing steam in a passive residual heat removal system. The passive residual heat removal system performs a very important function for removing sensible heat and residual heat in a reactor during an accident. However, the passive residual heat removal system is generally known to exhibit a big difference in the cooling performance according to a coolant flow of the secondary side including the steam generator. In particular, a once-through type steam generator configured to receive feedwater to a tube side to produce superheated steam in the tube may exhibit a large different secondary water level in the steam generator according to a power operation state of the nuclear power plant. Furthermore, a flow of the passive residual heat removal system during an accident is affected by a time point at which the discharge of steam is suspended or the supply of feedwater is suspended by related signals (valve closed or pump stopped) during the accident. As described above, a coolant flow at a secondary side including the steam generator is affected by an initial water level of the steam generator and a time point at which steam discharge or feedwater is stopped, and the like, and if the coolant flow is unable to maintain an appropriate flow level, it is difficult to accomplish the target performance of the passive residual heat removal system. Furthermore, a gravity or pressurized makeup tank is provided in the passive residual heat removal system, and those makeup tanks is provided to make up a flow when the flow is insufficient. However, a conventional makeup tank is configured to supply a flow even when the flow is sufficient in a system, thus rather acting as a cause of deteriorating the performance of the passive residual heat removal system. Non-condensable gas in connection with the present disclosure performs the role of preventing flow and condensation in a heat exchanger such as a condensation heat exchanger to act as a cause of significantly deteriorating the performance of the heat exchanger. A patent associated with a vent system in a passive residual heat removal system associated therewith is disclosed in KR Laid-open Patent Publication No. 2001-0076565. In this patent, it is disclosed a line valve connected to a line subsequent to a main steam isolation valve from an upper portion of a condensation heat exchanger to remove non-condensable gas. However, the patent does not disclose a specific pressure drop scheme, and a connection line is provided subsequent to the main steam isolation valve, and as a result, if the isolation valve of the exhaust line is not closed when the passive residual heat removal system is operated during an accident, then there is a possibility in which the coolant of the passive residual heat removal system is lost through the exhaust line to cause a serious accident. On the other hand, a steam line of the passive residual heat removal system has a relatively large volume, and the passive residual heat removal system to which a method of opening the steam line is applied is operated in a state that the steam line is open during a normal operation. Accordingly, as the normal operation of a nuclear power plant continues, light non-condensable gas may be accumulated in the steam line. As a result, when an accident requiring the operation of the passive residual heat removal system occurs, the accumulated non-condensable gas may flow into the condensation heat exchanger to prevent steam condensation to cause the performance degradation of the condensation heat exchanger. In consideration of the effect, it is designed in such a way that a condensation heat exchanger capacity of the passive residual heat removal system is conservatively large. However, as a high pressure (for example, SMART reactor: 17 MPa) facility, the passive residual heat removal system has a problem of significantly increasing the cost due to an increase of capacity. Furthermore, as a high-temperature high-pressure facility, the reactor restricts rapid cooling to alleviate thermal shock other than a normal operation and a partially restrictive accident. Accordingly, there is a limit in designing that the capacity of the condensation heat exchanger is conservatively too large. An object of the present disclosure is to prevent the dysfunction of a makeup tank associated with a flow at a secondary side of a passive residual heat removal system and alleviate the performance degradation and prediction uncertainty of a condensation heat exchanger due to non-condensable gas to overcome the foregoing problems in the related art. Another object of the present disclosure is to propose a passive residual heat removal system provided with a makeup facility for performing a function of accommodating excess fluid and compensating for the lack of fluid in a passive residual heat removal system. Still another object of the present disclosure is to overcome a problem of causing the performance degradation of a passive residual heat removal system due to non-condensable gas accumulated in a line of the system. In order to accomplish one object of the present disclosure, according to a passive residual heat removal system in accordance with an embodiment of the present disclosure, there is provided 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 reactor coolant system and residual heat in a core during an accident, and the passive residual heat removal system may include a makeup facility configured to accommodate excess cooling fluid or supply makeup cooling fluid to maintain an amount of the cooling fluid within a preset range, wherein the makeup facility includes a makeup tank provided at a preset height between a lower inlet and an upper outlet of the steam generator to passively accommodate the excess cooling fluid or supply the makeup cooling fluid according to an amount of the cooling fluid; a first connection line connected to the main steam line and the makeup tank to form a flow path for flowing cooling fluid discharged from the steam generator to the main steam line through the makeup tank; and a second connection line connected to the makeup tank and the main feedwater line to form a supply flow path for supplying cooling fluid supplied from the makeup tank. According to an example associated with the present disclosure, an initial water level of the makeup tank may be set to either one of a first through a third water level, and the first water level may correspond 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, and the second water level may correspond 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, and the third water level may correspond 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. According to another example associated with the present disclosure, the first connection line may be 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. According to a still another example associated with the present disclosure, the makeup facility may further include a circulation line connected to the main steam line and the makeup tank to form a first circulation flow path to prevent non-condensable gas from being accumulated in the makeup tank along with the first connection line. The first connection line may be connected to the main steam line at a position closer to the steam generator than to the circulation line, and the circulation line may be connected to the main steam line at a position farther from the steam generator than the first connection line to form a flow of steam circulating through the first circulation flow path based on a phenomenon in which a pressure gradually decreases as being further away from the steam generator. The makeup facility may further include 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, and the first pressure drop structure may be provided at a connection portion of the circulation line and the main steam line to form a flow of steam circulating through the first circulation flow path so as to cause a local pressure drop. The makeup tank, the first connection line and the circulation line may be insulated by an insulator to limit the energy loss of steam passing through the first circulation flow path during the normal operation of a nuclear power plant. The passive residual heat removal system may include a condensation heat exchanger configured to discharge sensible heat in the reactor coolant system and residual heat in the 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 to form a flow path 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 to form a flow path for supplying cooling fluid discharged from the steam generator to the condensation heat exchanger; and a vent line connected to the steam line and the main steam line to form a second circulation flow path for preventing non-condensable gas from being accumulated in the makeup tank or the steam line. The passive residual heat removal system may further include an inflow structure configured to induce at least part of a flow of steam circulating through the first circulation flow path and second circulation flow path to a preset flow path, and the inflow structure may include 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; and a 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. The steam line may be connected to the main steam line at a position closer to the steam generator than to the vent line, and the vent line may be connected to the main steam line at a position farther from the steam generator than the steam line to form a flow of steam circulating through the second circulation flow path based on a principle in which a pressure gradually decreases as being further away from the steam generator. The passive residual heat removal system may further include 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, and the second pressure drop structure may be provided at an internal flow path of a connection portion of the vent line and the main steam line to form a flow of steam circulating through the second circulation flow path so as to cause a local pressure drop. An isolation valve that is open by related signals during an accident may be provided at the feedwater line to initiate the operation of the passive residual heat removal system, and the isolation valve may be provided in duplicate or in parallel or provided along with a check valve for preventing the backflow of feedwater from the main feedwater line, and the second connection line may be 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 to form a supply flow path of excess cooling fluid to the makeup tank. The feedwater line may be connected to the makeup tank to form a flow path for supplying cooling fluid discharged from the condensation heat exchanger to the makeup tank, and the second connection line may be connected to the main feedwater line to form a flow path for supplying cooling fluid received through the feedwater line to the steam generator, and the feedwater line may be connected to the main feedwater line through the makeup tank and the second connection line. The makeup facility further may include a flow resistance portion, and the flow resistance portion may include 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; and a 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. In order to accomplish the foregoing task, the present disclosure discloses a nuclear power plant having a passive residual heat removal system. The nuclear power plant may include 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 a steam generator through the main feedwater line and the main steam line to remove sensible heat in a reactor coolant system and residual heat in a core during an accident; and a makeup facility configured to accommodate excess cooling fluid or supply makeup cooling fluid to maintain an amount of the cooling fluid within a preset range, wherein the makeup facility includes a makeup tank provided at a preset height between a lower inlet and an upper outlet of the steam generator to passively accommodate the excess cooling fluid or supply the makeup cooling fluid according to a water level of the cooling fluid; a first connection line connected to the main steam line and the makeup tank to form a flow path for flowing cooling fluid discharged from the steam generator to the main steam line through the makeup tank; and a second connection line connected to the makeup tank and the main feedwater line to form a supply flow path for supplying cooling fluid supplied from the makeup tank. According to the present disclosure having the foregoing configuration, a makeup tank is provided at an appropriate position between a lower inlet and a upper outlet of a steam generator, and an upper portion of the makeup tank is filled with steam and a lower portion thereof is filled with makeup cooling fluid, when cooling fluid is excessive in a passive residual heat removal system, the makeup tank may accommodate excess cooling fluid, and on the contrary, when cooling fluid is insufficient in the passive residual heat removal system, the makeup tank may perform a buffer action for supplying makeup cooling fluid. Furthermore, according to the present disclosure, a steam line of the passive residual heat removal system and a circulation line of the makeup tank may be connected to a main steam line to continuously circulate a small amount of steam during the normal operation of a nuclear power plant. Accordingly, non-condensable gas may not be accumulated in the makeup tank, thereby preventing the performance degradation of a condensation heat exchanger due to non-condensable gas during the operation of the passive residual heat removal system. When a makeup facility according to the present disclosure is applied to a nuclear power plant, a water level of the steam generator may be maintained within an optimal range to allow the makeup tank to induce an optimal performance of the passive residual heat removal system during an accident. Furthermore, a leak flow rate of the passive residual heat removal system may be compensated by the makeup tank, thereby allowing the passive residual heat removal system to achieve an optimal performance. In addition, the present disclosure may remove non-condensable gas that can be accumulated in the passive residual heat removal system, thereby preventing the performance degradation of the condensation heat exchanger. Ultimately, the present disclosure may present a scheme capable of removing design uncertainty in the passive residual heat removal system and implementing an optimal performance to facilitate the performance prediction of the passive residual heat removal system. Accordingly, the prediction uncertainty of the passive residual heat removal system may decrease, thereby designing a condensation heat exchanger in an appropriate size and reducing the cost of a condensation heat exchanger facility. A excessive cooling problem of a nuclear power plant according to a conservative condensation heat exchanger design may be alleviated due to a supplicated performance prediction, thereby enhancing safety. Moreover, the design of a more sophisticated condensation heat exchanger may be allowed through the removal of the accumulation of non-condensable gas and the uncertainty of the water level to overcome design difficulties to allow the configuration of a safer passive residual heat removal system. Hereinafter, a nuclear power plant including a passive residual heat removal system associated with the present disclosure will be described in more detail with reference to the accompanying drawings. Even in different embodiments according to the present disclosure, the same or similar reference numerals are designated to the same or similar configurations, and the description thereof will be substituted by the earlier description. Unless clearly used otherwise, expressions in the singular number used in the present disclosure may include a plural meaning. In the specification, in case where it is mentioned that an element is “connected” to another element, it should be understood that an element may be directly connected to another element, but another element may exist therebetween. On the contrary, in case where it is mentioned that an element is “directly connected” to another element, it should be understood that any other element does not exist therebetween. It is mentioned to be “indirectly connected” when another element exists therebetween. FIG. 1 is a conceptual view illustrating a passive residual heat removal system 100a and a nuclear power plant 10a including the same associated with an embodiment of the present disclosure. The nuclear power plant 10a may include a reactor coolant system 11a, a core 12a, a steam generator 13a, a reactor coolant pump 14a, and a pressurizer 15a. In addition to the constituent elements illustrated in FIG. 1, the nuclear power plant 10a may include systems for a normal operation and various systems for securing safety. The reactor coolant system 11a is a coolant system for transferring and transporting thermal energy generated by fuel fission. An inside of the reactor coolant system 11a is filled with primary fluid. When an accident such as a loss of coolant accident occurs, primary fluid(steam) may be released from the reactor coolant system 11a, and a containment (not shown) prevents radioactive materials from being leaked to an outside. The steam generator 13a is located at a boundary between a primary system and a secondary system. A lower inlet of the steam generator 13a is connected to a main feedwater line 16a1, and an upper outlet of the steam generator 13a is connected to a main steam line 17a1. During a normal operation of the nuclear power plant 10a, working fluid is supplied to the steam generator 13a through the main feedwater line 16a1 from a feedwater system 16a. Feedwater becomes steam by receiving the heat of the core 12a from primary fluid while passing through the steam generator 13a. The steam is supplied from the steam generator 13a to a turbine system 17a. The reactor coolant pump 14a is provided to form a flow of primary fluid entering into the core 12a. The pressurizer 15a maintains a pressurized state exceeding a saturation pressure to suppress the boiling of coolant in the core 12a of a pressurized water reactor, and the pressurizer 15a controls a pressure of the reactor coolant system 11a. The passive residual heat removal system 100a is an emergency safety facility for removing sensible heat in the reactor coolant system 11a and residual heat in the core 12a during an accident, and in particular, remove sensible heat and residual heat in a passive manner using natural forces. The passive residual heat removal system 100a circulates cooling fluid to the steam generator 13a through the main feedwater line 16a1 and main steam line 17a1. The passive residual heat removal system 100a may include a condensation heat exchanger 110a, a feedwater line 140a, and a steam line 130a. The condensation heat exchanger 110a discharges sensible heat in the reactor coolant system 11a and residual heat in the core 12a received through the circulation of cooling fluid to an outside. The condensation heat exchanger 110a may be provided within the emergency cooling tank 120a, and coolant is filled into the emergency cooling tank 120a. Heat is exchanged between cooling fluid (vapor phase) and the coolant of the emergency cooling tank 120a in the condensation heat exchanger 110a. Heat is transferred to the coolant of the emergency cooling tank 120a from cooling fluid (vapor phase). The coolant of the emergency cooling tank 120a is evaporated as the temperature gradually increases. Steam formed by evaporating the coolant is discharged to an outside of the emergency cooling tank 120a. The passive residual heat removal system 100a may remove sensible heat in the reactor coolant system 11a and residual heat in the core 12a through the repetition of the process. The feedwater line 140a is connected to the condensation heat exchanger 110a and main feedwater line 16a1 to form a flow path for supplying cooling fluid to the steam generator 13a from the condensation heat exchanger 110a. An isolation valve 142a that is open by related signals during an accident is provided at the feedwater line 140a to initiate the operation of the passive residual heat removal system 100a. The isolation valve 142a is provided in duplicate or in parallel or provided along with a check valve 143a for preventing the backflow of feedwater from the main feedwater line 16a1. The isolation valve 142a is open by related signals when an accident occurs, and the check valve 143a is open by a flow of cooling fluid formed during an accident. In particular, referring to FIG. 1, the isolation valve 142a and check valve 143a are provided together at the feedwater line 140a. Furthermore, a flow resistance portion 141a for adjusting a flow of cooling fluid (liquid phase) supplied from the condensation heat exchanger 110a to the steam generator 13a may be provided at the feedwater line 140a. The flow resistance portion 141a described herein is referred to as a third flow resistance portion 141a to be distinguished from another flow resistance portion that will be described below. The third flow resistance portion 141a may include an orifice or venturi, for example. The third flow resistance portion 141a is provided at an internal flow path of the feedwater line 140a to form a flow resistance so as to adjust a flow of cooling fluid supplied to the steam generator 13a. The steam line 130a is connected to the main steam line 17a1 and condensation heat exchanger 110a to form a flow path for transferring cooling fluid (vapor phase) discharged from the steam generator 13a to the condensation heat exchanger 110a. Referring to FIG. 1, the steam line 130a may be branched from the main steam line 17a1 and connected to an upper portion of the condensation heat exchanger 110a. The condensation heat exchanger 110a, feedwater line 140a, main feedwater line 16a1, steam generator 13a, main steam line 17a1 and steam line 130a form a circulation flow path for circulating cooling fluid. The circulation flow path described herein is referred to as a third circulation flow path to be distinguished from another circulation flow path which will be described later. The cooling fluid receives sensible heat in the reactor coolant system 11a and residual heat in the core 12a while circulating through the third circulation flow path, and transfers heat from the condensation heat exchanger 110a to cooling water within the emergency cooling tank 120a. Due to the repetition of the process, the passive residual heat removal system 100a removes sensible heat in the reactor coolant system 11a and residual heat in the core 12a. As mentioned above as a problem in the background of the invention, the performance of the passive residual heat removal system 100a is affected by an amount of cooling fluid. Accordingly, it may be possible to maximize the performance of the passive residual heat removal system 100a when an amount of cooling fluid is maintained within an optimal range according to the characteristics of the passive residual heat removal system 100a of each nuclear power plant 10a. The present disclosure may include a makeup facility for deriving the maximum performance of the passive residual heat removal system 100a. The makeup facility may accommodate excess cooling fluid or supply makeup cooling fluid to maintain an amount of cooling fluid within a preset range. For the purpose of this, the makeup facility may include a makeup tank 160a, a first connection line 170a and a second connection line 180a. The makeup tank 160a is provided at a preset height between a lower inlet and an upper outlet of the steam generator 13a to passively accommodate excess cooling fluid or supply makeup cooling fluid according to an amount of the cooling fluid. When the passive residual heat removal system 100a is operated, the water levels and pressures of the makeup tank 160a, steam generator 13a and condensation heat exchanger 110a, respectively, may form an equilibrium. Furthermore, a change of temperature or pressure and a leakage according to the operation of the passive residual heat removal system 100a have an effect on an amount of cooling fluid. Accordingly, the installation height, water level and pressure of the makeup tank 160a are important factors for maintaining an amount of cooling fluid in an optimal range. An initial water level of the makeup tank 160a may be set to any one of a first through a third water level. The first through the third water level are referred to distinguish them from one another, but do not denote absolute values. The first water level corresponds to a level at which cooling fluid is fully filled in the makeup tank 160a to supply makeup cooling fluid when the water level of the steam generator 13a is less than the water level of the makeup tank 160a during an accident. The makeup tank 160a set to the first water level performs only a makeup function, and supplies makeup cooling fluid only when the water level of the steam generator 13a is less than that of the makeup tank 160a during an accident. The first water level may be applicable to a case where an amount of cooling fluid of the passive residual heat removal system 100a is insufficient in all conditions during an accident or a case of the nuclear power plant 10a having a characteristic capable of sufficiently performing the performance even though an amount of cooling fluid is somewhat large as a capacity of the condensation heat exchanger 110a is designed to be large enough. The second water level corresponds to a level at which cooling fluid is depleted in the makeup tank 160a to accommodate excess cooling fluid and afterward supply the accommodated cooling fluid as makeup cooling fluid during an accident. The makeup tank 160a set to the second water level may further accommodate excess cooling fluid when the excess cooling fluid is additionally generated during a continuous operation subsequent to an accident as well as an early stage of the accident of the passive residual heat removal system 100a. The second water level may be applicable to a case of the nuclear power plant 10a having a characteristic in which an amount of cooling fluid of the passive residual heat removal system 100a is excessive in all conditions during an accident. The 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 cooling fluid using initially stored cooling fluid as makeup cooling fluid during an accident. The makeup tank 160a set to the third water level may further accommodate excess cooling fluid when the excess cooling fluid is additionally generated during a continuous operation of the passive residual heat removal system 100a. The third water level may be applicable to a case of the nuclear power plant 10a having a characteristic in which a cooling fluid flow of the passive residual heat removal system 100a is insufficient as well as it is excessive according to a condition during an accident. An initial water level of the makeup tank 160a illustrated in FIG. 1 is set to the third water level. During a normal operation of the nuclear power plant 10a, the water level of the makeup tank 160a is maintained by a circulation flow due to the first connection line 170a and circulation line 190a. Furthermore, the makeup tank 160a accommodates excess cooling fluid during an accident, and supplies cooling fluid using initially stored cooling fluid as makeup cooling fluid. The makeup tank 160a is insulated by an insulator 161a to limit the energy loss of steam passing through the first circulation flow path during a normal operation of nuclear power plant 10a. When a case without the makeup tank 160a and a case with the makeup tank 160a are compared, a flow path of steam may increase and the energy loss of steam flowing into the turbine system 17a may increase due to the existence of the makeup tank 160a. In order to compensate this disadvantage, the insulator 161a is installed at an outer circumferential surface of the makeup tank 160a to reduce the energy loss of steam. The first connection line 170a is connected to the main steam line 17a1 and makeup tank 160a to form a flow path of flowing cooling fluid discharged from the steam generator 13a to the main steam line 17a1. Referring to FIG. 1, the first connection line 170a is branched from the main steam line 17a1 and connected to an upper portion of the makeup tank 160a. A manual valve 171a and a first flow resistance portion 172a may be provided at a flow path of the first connection line 170a. The manual valve 171a may be manually closed at a time point at which it should be isolated for the maintenance or the like of related facilities subsequent to being open during a normal operation. The first flow resistance portion 172a is provided at an internal flow path of the first connection line 170a to adjust a flow of cooling fluid introduced into the makeup tank 160a from the main steam line 17a1. The first connection line 170a is also insulated by an insulator 173a to limit the energy loss of steam flowing into the turbine system during a normal operation of the nuclear power plant 10a similarly to the makeup tank 160a. The second connection line 180a is connected to the makeup tank 160a and main feedwater line 16a1 to form a supply flow path for supplying cooling fluid supplied from the makeup tank 160a. Referring to FIG. 1, the second connection line 180a is branched from the feedwater line 140a and coupled to a lower portion of the makeup tank 160a. A second flow resistance portion 181a and a manual valve 182a may be provided at a flow path of the second connection line 180a. The second flow resistance portion 181a is provided within the second connection line 180a to adjust a flow of makeup cooling fluid supplied from the makeup tank 160a to the main feedwater line 16a1. The passive valve 182a may be manually closed at a time point at which it should be isolated for the maintenance or the like of related facilities subsequent to being open during a normal operation. The second connection line 180a may be connected to the feedwater line 140a at a position between the isolation valve 142a and the check valve 143a of the feedwater line 140a. The second connection line 180a is connected to the main feedwater line 16a1 through the feedwater line 140a. Accordingly, when makeup cooling fluid is supplied from the makeup tank 160a, the makeup cooling fluid is introduced into the feedwater line 140a through the second connection line 180a. When excess cooling fluid is introduced into the second connection line 180a, the excess cooling fluid is introduced into the makeup tank 160a through the feedwater line 140a and second connection line 180a. When makeup cooling fluid is supplied from the makeup tank 160a, the makeup cooling fluid and the cooling fluid from the condensation heat exchanger 110a through the feedwater line 140a join together, and then they are supplied to the main feedwater line 16a1. A makeup facility may further include a circulation line 190a and a pressure drop structure 191a. The circulation line 190a is connected to the main steam line 17a1 and makeup tank 160a to form a circulation loop for preventing the accumulation of non-condensable gas and maintaining the water level of the makeup tank 160a along with the first connection line 170a. The circulation line 190a is connected to a preset height of the makeup tank 160a. The circulation loop described herein is referred to as a first circulation loop to be distinguished from another circulation loop. The main steam line 17a1, first connection line 170a, makeup tank 160a and circulation line 190a form the first circulation loop. During a normal operation of the nuclear power plant 10a, non-condensable gas may be accumulated within the makeup tank 160a. However, when the first circulation loop is formed by the circulation line 190a and first connection line 170a connected to the makeup tank 160a, a small amount of steam or a small amount of cooling fluid (two phases of water and vapor) may be continuously circulated through the first circulation loop. As a result, it may be possible to prevent the accumulation of non-condensable gas and prevent the performance degradation of the condensation heat exchanger 110a due to the non-condensable gas along with the first connection line 170a. Furthermore, when the water level increases over a connection portion of the circulation line 190a, a small amount of cooling fluid may be discharged along the circulation line 190a to maintain a preset water level of the makeup tank 160a. An arrow shown in the drawing indicates a flow of fluid. A relatively large sized arrow indicates a relatively large flow, and a relatively small sized arrow indicates a relatively small flow. On the drawing, it is seen that a flow of steam or cooling fluid (water or two phases) circulating through the first circulation loop is much smaller than that of fluid flowing through the main steam line 17a1. The circulation line 190a is also insulated by an insulator 193a to limit the energy loss of steam flowing into the turbine system during a normal operation of the nuclear power plant 10a similarly to the makeup tank 160a, first connection line 170a. During a normal operation of the nuclear power plant 10a, the insulator 193a may limit the energy loss of steam circulating through the first connection line 170a, makeup tank 160a and circulation line 190a. A manual valve 192a and a flow resistance portion (not shown) are also provided at the circulation line 190a. The manual valve 192a may be manually closed at a time point at which it should be isolated for the maintenance or the like of related facilities subsequent to being open during a normal operation. Though not shown in the drawing, a flow resistance portion (not shown) may be provided at the circulation line 190a. The flow resistance portion may include an orifice or venturi that forms a flow resistance at an internal flow path of the circulation line 190a. The flow resistance portion is provided to suppress a large amount of flow (water or two phases of water and vapor) from being abruptly discharged and introduced into the turbine system 17a according to a variation of water level during a normal operation of the nuclear power plant 10a, and limit the circulation flow of steam to a design flow. The pressure drop structure 191a is 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. The pressure drop structure 191a described herein is referred to as a first pressure drop structure 191a to be distinguished from another pressure drop structure. The first pressure drop structure 191a is provided at a connection portion between the circulation line 190a and the main steam line 17a1 to form a flow of steam or cooling fluid (water or two phases) circulating through the first circulation loop so as to cause a local pressure drop. Since a pressure drop is locally induced at a position at which the first pressure drop structure 191a is provided, a circulation flow of steam or cooling fluid (water or two phases) may be formed by a pressure difference induced at the first circulation loop. The detailed description of the first pressure drop structure 191a will be described with reference to FIGS. 2 and 3. FIG. 2 is a conceptual view illustrating the detailed structure of portion “A” illustrated in FIG. 1. An upper outlet of the steam generator 13a (refer to FIG. 1) is connected to one end portion of the main steam line 17a1 (an end portion disposed when continuously extended to the left side of the main steam line 17a1 in FIG. 2), and the turbine system 17a (refer to FIG. 1) is connected to the other end portion of the main steam line 17a1 (an end portion disposed when continuously extended to the right side of the main steam line 17a1 in FIG. 2). The first pressure drop structure 191a may include an orifice or venturi provided at an internal flow path of the main steam line 17a1. The pressure drop structure 191a forms a flow resistance at an internal flow path of the main steam line 17a1, and at least part thereof is open not to block a flow path connected to the circulation line 190a. High-pressure steam flows into the main steam line 17a1. The speed increases while the high-pressure steam passes through the first pressure drop structure 191a. The first pressure drop structure 191a locally induces a drop of pressure. Accordingly, steam or cooling fluid within the circulation line 190a flows to a low pressure side, and the circulation flow of steam or cooling fluid is formed at the first circulation loop. FIG. 3 is a conceptual view illustrating another example of portion “A” illustrated in FIG. 1. An upper outlet of the steam generator 13a (refer to FIG. 1) is connected to one end portion of the main steam line 17a1 (an end portion disposed when continuously extended to the left side of the main steam line 17a1 in FIG. 2), and the turbine system 17a (refer to FIG. 1) is connected to the other end portion of the main steam line 17a1 (an end portion disposed when continuously extended to the right side of the main steam line 17a1 in FIG. 2). The first pressure drop structure 191a may be provided at the circulation line 190a. The first pressure drop structure 191a is provided at an end portion of the circulation line 190a, and protruded within the main steam line 17a1 and exposed at an inner flow path of the main steam line 17a1. Referring to FIG. 3, the first pressure drop structure 191a is configured to form a partially narrow flow path within the main steam line 17a1. The first pressure drop structure 191a is configured to form a flow path of steam or cooling fluid (fluid that has passed through the first circulation flow path) in a direction (a direction of flowing from the bottom to the top) crossing a flow direction (a direction of flowing from the left to the right) of high-pressure steam, and the steam or cooling fluid and the high-pressure steam join together. It may be configured to introduce steam or cooling fluid eve in an opposite direction (a direction of flowing from the top to the bottom) to the flow direction of steam or cooling fluid. The speed of high-pressure steam increases while passing through a narrow flow path formed by the pressure drop structure 191a. Furthermore, a pressure difference between different portions of the first circulation flow path is formed due to a local pressure drop induced by the first pressure drop structure 191a. Steam or cooling fluid may flow through the first circulation flow path due to the pressure difference. Hereinafter, an operation in case the nuclear power plant 10a including the passive residual heat removal system 100a illustrated in FIG. 1 is in a normal operation or an anticipated accident state will be described. FIG. 4 is a conceptual view illustrating a normal operation state of the nuclear power plant 10a including the passive residual heat removal system 100a illustrated in FIG. 1. During a normal operation of the nuclear power plant 10a, an isolation valve 17a2 provided at the main steam line 17a1 and an isolation valve 16a2 provided at the main feedwater line 16a1 are open. Feedwater is supplied from the feedwater system 16a to the steam generator 13a through the main feedwater line 16a1. The check valve 143a for allowing only a uni-directional flow to pass therethrough is provided at the feedwater line 140a. During a normal operation of the nuclear power plant 10a, an internal pressure of the main feedwater line 16a1 is higher than that of the feedwater line 140a, and thus the check valve 143a is not open. Accordingly, the check valve 143a may prevent feedwater from flowing backward from the main feedwater line 16a1 to the feedwater line 140a. Feedwater exchanges heat with primary fluid while passing through the steam generator 13a. The feedwater is heated to become steam by the heat of the core 12a received from primary fluid. Steam formed by heating feedwater is discharged through an upper outlet of the steam generator 13a, and supplied to the turbine system 17a through the main steam line 17a1. During a normal operation of the nuclear power plant 10a, the manual valve 171a, 192a provided at the first connection line 170a and circulation line 190a are open, respectively. Most of steam passing through the main steam line 17a1 is supplied to the turbine system 17a. A small amount of steam flowing through the main steam line 17a1 is supplied to the makeup tank 160a through the first connection line 170a, and discharged to the main steam line 17a1 through the circulation line 190a again. Actuating power that circulates steam is provided from a pressure difference formed by the first pressure drop structure 191a. non-condensable gas is prevented from being accumulated in the makeup tank 160a while a small amount of steam continuously circulates through the first connection line 170a and circulation line 190a connected to the makeup tank 160a. During a normal operation of the nuclear power plant 10a, the water level of the makeup tank 160a is maintained below a height at which the circulation line 190a is connected to makeup tank 160a. The water level formed above a connection height of the circulation line 190a is sprayed and discharged to the main steam line 17a1 through the circulation line 190a. FIG. 5 is a conceptual view illustrating a valve operation during an accident of the nuclear power plant 10a including the passive residual heat removal system 100a illustrated in FIG. 1. When an accident requiring the operation of the passive residual heat removal system 100a occurs in the nuclear power plant 10a, isolation valves 16a2, 17a2 provided at the main feedwater line 16a1 and main steam line 17a1 are closed by related signals. Accordingly, the supply of feedwater from the feedwater system 16a is stopped, and the supply of steam to the turbine system 17a is also stopped. When an accident requiring the operation of the passive residual heat removal system 100a occurs in the nuclear power plant 10a, the isolation valve 142a provided at the feedwater line 140a is open by relates signals. As the isolation valves 16a2, 17a2 provided at the main feedwater line 16a1 and main steam line 17a1 are closed and the isolation valve 142a provided at the feedwater line 140a is open, a flow path of fluid circulating through the steam generator 13a is changed to form a third circulation flow path connected to the condensation heat exchanger 110a, feedwater line 140a, main feedwater line 16a1, steam generator 13a, main steam line 17a1, steam line 130a and condensation heat exchanger 110a. As a result, the passive residual heat removal system 100a starts the operation. Cooling fluid (liquid phase) is supplied to the steam generator 13a while sequentially passing through the feedwater line 140a and main steam line 17a1, and the cooling fluid (liquid phase) is heated to become steam by receiving sensible heat in the reactor coolant system 11a and residual heat in the core 12a at the steam generator 13a. The cooling fluid (steam phase) is discharged to an upper outlet of the steam generator 13a, and transferred to the condensation heat exchanger 110a through the steam line 130a. The cooling fluid (steam phase) transfers heat to the coolant of the emergency cooling tank 120a from the condensation heat exchanger 110a and condenses. The cooling fluid that has transferred heat to the coolant of the emergency cooling tank 120a and condensed is supplied to the steam generator 13a again through the feedwater line 140a and main feedwater line 16a1. Sensible and residual heat in the reactor coolant system 11a can be removed by the circulation of the cooling fluid. Since the manual valve 182a provided at the second connection line 180a is open, part of cooling fluid supplied from the condensation heat exchanger 110a through the feedwater line 140a may flow to the makeup tank 160a through the second connection line 180a. Furthermore, the manual valve 171a provided at the first connection line 170a and the manual valve 192a provided at the circulation line 190a are also open, and thus part of steam generated by the evaporation of cooling fluid may be supplied to the makeup tank 160a through the first connection line 170a prior to flowing into the condensation heat exchanger 110a and then discharged to the main steam line 17a1 through the circulation line 190a again. However, since a flow of steam formed in the circulation line 190a during an accident is very small compared to that formed during a normal operation, the circulation line 190a during an accident cannot perform the non-condensable gas removal and a water level maintenance function of the makeup tank 160a, which is performed during a normal operation. Ps indicates a pressure of the steam generator 13a, and Hs indicates a water level of the steam generator 13a. Pm indicates a pressure of the makeup tank 160a, and Hm indicates a water level of the makeup tank 160a. Pc indicates a pressure of the condensation heat exchanger 110a, and Hc indicates a water level of the condensation heat exchanger 110a. At the time point of starting the operation of the passive residual heat removal system 100a, the pressure (Ps), water level (Hs) of the steam generator 13a, the pressure (Pm), water level (Hm) of the makeup tank 160a, and the pressure (Pc), water level (Hc) of the condensation heat exchanger 110a are not in an equilibrium state. FIG. 6 is a conceptual view illustrating a water level equilibrium state according to the progression of an accident in the nuclear power plant 10a including the passive residual heat removal system 100a illustrated in FIG. 1. When the operation of the passive residual heat removal system 100a starts and time passes, excess cooling fluid (excess cooling fluid at an upper portion higher than an initial water level of the makeup tank 160a, provided that a water level in consideration of pressure equilibrium) within cooling fluid circulating through the passive residual heat removal system 100a is returned to the makeup tank 160a. Furthermore, the pressure (Ps) and water level (Hs) of the steam generator 13a, the pressure (Pm) and water level (Hm) of the makeup tank 160a, and the pressure (Pc) and water level (Hc) of the condensation heat exchanger 110a form an equilibrium state. In a state that the operation of the passive residual heat removal system 100a continues, a large flow of cooling fluid does not occur. Furthermore, the makeup tank 160a, first connection line 170a and circulation line 190a are insulated by the insulator 161a, 173a, 193a (refer to FIG. 1), no significant heat loss occurs. As a result, the pressure (Ps) of the steam generator 13a and the pressure (Pm) of the makeup tank 160a are maintained at similar pressures and thus a water level in consideration of a loss of pressure and a change of density difference due to flow resistance is similarly maintained. FIG. 7 is a conceptual view for accommodating excess cooling fluid into a makeup tank according to the progression of an accident in the nuclear power plant 10a including the passive residual heat removal system 100a illustrated in FIG. 1. A temperature or pressure change according to the operation of the passive residual heat removal system 100a and a flow change of cooling fluid according to the leakage are accommodated in the makeup tank 160a. Excess cooling fluid is introduced into the makeup tank 160a to increase the water level of the makeup tank 160a. As a result, the pressure (Ps) and water level (Hs) of the steam generator 13a, the pressure (Pm) and water level (Hm) of the makeup tank 160a, and the pressure (Pc) and water level (Hc) of the condensation heat exchanger 110a form an equilibrium state. FIG. 8 is a conceptual view for supplying makeup cooling fluid from a makeup tank according to the progression of an accident in the nuclear power plant 10a including the passive residual heat removal system 100a illustrated in FIG. 1. When cooling fluid circulating through the second connection line 180a is insufficient, the makeup tank 160a supplies makeup cooling fluid to the steam generator 13a through the second connection line 180a. As a result, the pressure (Ps) and water level (Hs) of the steam generator 13a, the pressure (Pm) and water level (Hm) of the makeup tank 160a, and the pressure (Pc) and water level (Hc) of the condensation heat exchanger 110a continuously form an equilibrium state. During the operation of the passive residual heat removal system 100a for a long period of time, cooling fluid circulating through the passive residual heat removal system 100a may decrease due to a small amount of leakage. A decrease of cooling fluid may be checked through a water level measurement of the makeup tank 160a or the like. In this case, makeup water may be additionally injected into the passive residual heat removal system 100a to continuously maintain an appropriate water level. FIG. 9 is a conceptual view illustrating a modified example of the nuclear power plant 10b including the passive residual heat removal system 100b illustrated in FIG. 1. Isolation valves 142b, 144b may be provided in duplicate or in parallel (not shown) at a feedwater line 140b. Furthermore, a check valve 143b may be also provided at the feedwater line 140b along with the isolation valves 142b, 144b provided in duplicate. Furthermore, a second connection line 180b is connected to the feedwater line 140b at a position between two isolation valves 142b, 144b, and the second connection line 180b is connected to the a main feedwater line 16b1 through the feedwater line 140b. The remaining configuration will be substituted by the earlier description of FIG. 1. FIG. 10 is an another conceptual view illustrating a modified example of the nuclear power plant 10c including the passive residual heat removal system 100c illustrated in FIG. 1. Referring to FIG. 1 prior to examining FIG. 10, the first connection line 170a and steam line 130a are sequentially connected to the main steam line 17a1 in a direction of being further away from the steam generator 13a. The passive residual heat removal system 100c and nuclear power plant 10c illustrated in FIG. 10 have a different connection sequence from that of FIG. 1. Referring to FIG. 10, a first connection line 170c, a circulation line 190c and a steam line 130c are sequentially connected to a main steam line 17c1 in a direction of being further away from a steam generator 13c. If a connection sequence of FIG. 10 is referred to as a forward connection, then a connection sequence of FIG. 1 may be referred to as a backward connection. A configuration in which steam is introduced into a makeup tank 160c through a first connection line 170c, and returned to the main steam line 17c1 through a circulation line 190c will be substituted by the earlier description. Furthermore, due to this, it may be possible to prevent non-condensable gas from being accumulated in the makeup tank 160c and maintain a water level of the makeup tank 160c. FIG. 11 is a still another conceptual view illustrating a modified example of the nuclear power plant 10d including the passive residual heat removal system illustrated 100d in FIG. 1. The water level of the makeup tank 160d is set to a second water level. A cooling fluid flow of the passive residual heat removal system 100d during an accident may be different according to the design characteristics of the nuclear power plant 10d. The second water level corresponds to a level at which cooling fluid is depleted in the makeup tank 160d to accommodate excess cooling fluid and supply the accommodated cooling fluid as makeup cooling fluid during an accident. The makeup tank 160d set to the second water level may further accommodate excess cooling fluid when the excess cooling fluid is additionally generated during a continuous operation subsequent to an accident as well as an early stage of the accident of the passive residual heat removal system 100d. The second water level may be applicable to a case of the nuclear power plant 10d having a characteristic in which a cooling fluid flow of the passive residual heat removal system 100d is excessive in all conditions during an accident. A circulation line 190d is branched from a feedwater line 140d and connected to a main steam line 17d1. Accordingly, the circulation line 190d is connected to the makeup tank 160d through the feedwater line 140d. FIG. 12 is a yet still another conceptual view illustrating a modified example of the nuclear power plant 10e including the passive residual heat removal system 100e illustrated in FIG. 1. Referring to FIG. 12, the sequence of connecting a first connection line 170e and a circulation line 190e to a main steam line 17e1 corresponds to a forward connection described in FIG. 10. When the first connection line 170e and circulation line 190e are sequentially provided between the steam generator 13e and an isolation valve of the main steam line 17e1, and a flow resistance region 17e1′ is formed at the main steam line 17e1, a circulation flow may be formed using a pressure drop according to a line length of the main steam line 17e1. As located away from the steam generator 13e, a pressure of the main steam line 17e1 gradually decreases. Based on such a principle, when the first connection line 170e is connected to the main steam line 17e1 at a position closer to the steam generator 13e than to the circulation line 190e, and the circulation line 190e is connected to the main steam line 17e1 at a position farther from the steam generator 13e than the first connection line 170e, a circulation flow may be formed without a first pressure drop structure 191e. In particular, the flow resistance region 17e1′ may be formed between a connection portion of the first connection line 170e and a connection portion of the circulation line 190e in the main steam line 17e1 to induce the formation of a circulation flow. The flow resistance region 17e1′ may induce the flow of a small amount of steam to the first connection line 170e. FIG. 13 is a still yet another conceptual view illustrating a modified example of the nuclear power plant 10f including the passive residual heat removal system 100f illustrated in FIG. 1. A first connection line 170f and a circulation line 190f have a forward connection structure. The first connection line 170f, makeup tank 160f and circulation line 190f form a first circulation flow path. The passive residual heat removal system 100f may further include an inflow structure 174f configured to induce at least part of a flow steam or cooling fluid (water or two phases) circulating through the first circulation loop to a preset flow path. The inflow structure 174f may be provided at any position between a portion connected to a steam generator 13f and an installation portion of an isolation valve 17f2 in a main steam line 17f1 to induce a flow. The inflow structure described herein is referred to as a first inflow structure 174f to be distinguished from an inflow structure disposed at another place, and the inflow structure disposed at another place is referred to as a second inflow structure. The detailed structure of the first inflow structure 174f will be described with reference to FIGS. 14 and 15. FIG. 14 is a conceptual view illustrating the detailed structure of the inflow structure 174f illustrated in FIG. 13. A first inflow structure 174f′ is extended from the first connection line 170f and inserted into the main steam line 17f1 to induce at least part of steam flowing through the main steam line 17f1 to the first connection line 170f. An inlet of an internal flow path of the first inflow structure 174f′ faces steam flowing through the main steam line 17f1. Due to such a structure, a small amount of steam within steam flowing through the main steam line 17f1 flows to the side of the first connection line 170f. FIG. 15 is another conceptual view of the inflow structure 17f illustrated in FIG. 13. A first inflow structure 174f″ may be bent in a curved shape on the contrary to the first inflow structure 174f′ illustrated in FIG. 14. An inlet of the first inflow structure 174f″ faces a flow of steam flowing through the mode switching intention 17f1 at the front side, thereby efficiently inducing the flow of steam to the side of the first connection line 170f. FIG. 16 is a still another conceptual view illustrating a modified example of the nuclear power plant 10g including the passive residual heat removal system 100g illustrated in FIG. 1. A feedwater line 140g is connected to a makeup tank 160g to form a flow path for supplying cooling fluid discharged from a condensation heat exchanger 110g to the makeup tank 160g. The feedwater line 140g is connected to a main feedwater line 16g1 through the makeup tank 160g and second connection line 180g. A manual valve 145g is provided at the feedwater line 140g to be manually closed at a time point that requires maintenance. A check valve 183g is provided at a second connection line 180g to prevent feedwater from flowing backward from the main feedwater line 16g1 to the makeup tank 160g. The second connection line 180g is connected to the main feedwater line 16g1 to form a flow path for supplying cooling fluid stored therewithin and cooling fluid received through the feedwater line 140g to a steam generator 13g. According to the foregoing configuration, the passive residual heat removal system 100g is operated as a mechanism of collecting cooling fluid supplied from the condensation heat exchanger 110g to the makeup tank 160g and supplying the collected cooling fluid to the steam generator 13g again. FIG. 17 is a yet still another conceptual view illustrating a modified example of the nuclear power plant 10h including the passive residual heat removal system 100h illustrated in FIG. 1. Similarly to FIG. 16, in FIG. 17, a feedwater line 140h is connected to a main feedwater line 16h1 through a makeup tank 160h and a second connection line 180h. The feedwater line 140h is connected to the makeup tank 160h to form a flow path for supplying cooling fluid discharged from a condensation heat exchanger 110h to the makeup tank 160h. A check valve 183a and an isolation valve 184h may be respectively provided at the feedwater line 140h. The isolation valve 184h is open by related signals at a time point that requires the operation of the passive residual heat removal system 100h. The check valve 183h prevents feedwater from flowing backward from a main steam line 17h1 to the makeup tank 160h, and open by a flow of makeup cooling fluid when the makeup cooling fluid is supplied from the makeup tank 160h. FIG. 18 is a still another conceptual view illustrating a modified example of the nuclear power plant 10i including a passive residual heat removal system 100i illustrated in FIG. 1. Various shapes such as a spherical shape, a cylindrical shape, a rectangular shape both end portions of which are formed in a hemispherical shape or the like may be applicable to the shape of a makeup tank 160i. However, assuming that it is configured with the same volume, the shape of the makeup tank 160i with a low height and a large area is advantageous for minimizing a variation of the water level and maintaining an optimal water level of a steam generator 13i. In case where the makeup tank 160i in a rectangular shape is provided, it is more advantageous to have a lying-down shape. Referring to FIG. 18, the makeup tank 160i is formed in a shape in which both end portions thereof is formed in a hemispherical shape with a rectangular lying-down shape. FIG. 19 is a yet still another conceptual view illustrating a modified example of the nuclear power plant 10j including the passive residual heat removal system 100j illustrated in FIG. 1. A first connection line 170j may be connected to an appropriate position of a steam line 130j according to the convenience of the installation. The first connection line 170j is connected to a main steam line 17j1 through the steam line 130j to receive steam from the steam line 130j of the passive residual heat removal system 100j. The steam line 130j is branched from the main steam line 17j1, and the first connection line 170j is branched from the steam line 130j and connected to a makeup tank 160j. Steam flowing through the main steam line 17j1 is introduced into the steam line 130j, and the steam is introduced into the first connection line 170j again, and supplied to the makeup tank 160j through the first connection line 170j. The foregoing structure is formed for the purpose of forming a circulation flow of steam or cooling fluid in a first circulation loop to maintain a water level of the makeup tank 160j as well as prevent non-condensable gas from being accumulated in the makeup tank 160j. FIG. 20 is a conceptual view illustrating another passive residual heat removal system 200a and a nuclear power plant 20a including the same. The passive residual heat removal system 200a may further include a steam line 230a and a vent line 250a connected to a main steam line 27a1 to form a circulation loop for preventing non-condensable gas from being accumulated in a makeup tank 260a or steam line 230a and maintaining a water level of the makeup tank 260a. The circulation loop described herein is referred to as a second circulation loop to be distinguished from the foregoing first circulation loop. The vent line 250a is branched from the steam line 230a. Referring to FIG. 20, the vent line 250a is connected to the makeup tank 260a through a first connection line 270a, and connected to the main steam line 27a1 through the makeup tank 260a and a circulation line 290a. A small amount of steam flowing the main steam line 27a1 through the vent line 250a is introduced into the makeup tank 260a, and therefore it may be possible to prevent non-condensable gas from being accumulated in the makeup tank 260a through the process. The foregoing configuration is also used for the purpose of preventing non-condensable gas from being accumulated in the makeup tank 260a and steam line 230a. The circulation line 290a, vent line 250a and makeup tank 260a are integrated into one system. Steam flowing through the main steam line 27a1 is introduced into the steam line 230a, and a small amount of steam is supplied to the makeup tank 260a through the vent line 250a. The vent line 250a may be insulated by an insulator 251a to prevent the heat loss of steam during a normal operation of the nuclear power plant 20a. Steam supplied to the makeup tank 260a or cooling fluid in the makeup tank 260a is transferred to the main steam line 27a1 again through the circulation line 290a. Due to the foregoing configuration, it may be possible to prevent the accumulation of non-condensable gas and maintain a water level of the makeup tank 260a by a circulation flow formed at a first and a second circulation loop. The foregoing inflow structure 134f 134f′, 134f″ (refer to FIGS. 13 and 14) may be also applicable to the passive residual heat removal system 200a. The inflow structure 134f 134f′, 134f″ (refer to FIGS. 13 and 14) is provided within a portion shown as “B” on the drawing. The inflow structure described herein is referred to as a second inflow structure (not shown) to be distinguished from the foregoing inflow structure. The second inflow structure (not shown) is extended from the vent line 250a and inserted into the steam line 230a to induce at least part of steam flowing through the steam line 230a to the vent line 250a. An inlet of an internal flow path of the second inflow structure (not shown) faces steam flowing through the steam line 230a. The detailed structure of the second inflow structure (not shown) is illustrated with reference to FIGS. 14 and 15. Forming a flow of steam circulating through the second circulation flow path based on a principle in which a pressure gradually decreases as being further away from the steam generator 23a may be also applicable to the passive residual heat removal system 200a in FIG. 20. For example, on the contrary to the illustration of FIG. 20, the steam line 230a may be connected to the main steam line 27a1 at a position closer to the steam generator 23a than to the vent line 250a, and the vent line 250a may be connected to the main steam line 27a1 at a position farther from the steam generator 23a than the steam line 230a. Furthermore, a flow resistance region (not shown) may be formed between a connection portion of the steam line 230a and a connection portion of the vent line 250a in the main steam line 27a1. FIG. 21 is a conceptual view illustrating a modified example of the nuclear power plant 20b including the passive residual heat removal system 200b illustrated in FIG. 20. A first connection line 270b and a vent line 250b are formed as individual constituent elements. The passive residual heat removal system 200b may further include a second pressure drop structure 252b 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. Referring to FIG. 21, the second pressure drop structure 252b is provided along with a first pressure drop structure 291b. The second pressure drop structure 252b is provided at an internal flow path of a connection portion of the vent line 250b and the main steam line 27b1 to form a flow of steam circulating through the second circulation flow path to cause a local pressure drop. The detailed structure of the second pressure drop structure 252b is illustrated with reference to FIGS. 2 and 3. FIG. 22 is a still another conceptual view illustrating a passive residual heat removal system 300 and a nuclear power plant 30 including the same according to another embodiment of the present disclosure. Referring to FIG. 22, a makeup tank 360 is formed in a rectangular shape both end portions of which are formed in a hemispherical shape. Furthermore, a water level of the makeup tank 360 is determined as a first water level. The first water level corresponds to a level at which cooling fluid is fully filled in the makeup tank 360 to supply makeup cooling fluid when the water level of the steam generator 33a is less than the water level of the makeup tank 360 during an accident. The makeup tank 360 set to the first water level performs only a makeup function, and supplies makeup cooling fluid only when the water level of the steam generator 33a is less than that of the makeup tank 360 during an accident. The first water level may be applicable to a case where a flow of cooling fluid of the passive residual heat removal system 300 is insufficient in all conditions during an accident or a case of the nuclear power plant 30 having a characteristic capable of sufficiently performing the performance even though an amount of cooling fluid is somewhat large as a capacity of the condensation heat exchanger 310a is designed to be large enough. When the water level of the makeup tank 360 is determined as a first water level, it may be possible to remove the circulation line (not shown) described in another drawing in the above. The present disclosure illustrates only a case where a water-cooling condensation heat exchanger is applied thereto using an emergency cooling tank, but the present disclosure may be also applicable to a case where an air-cooling condensation heat exchanger is applied thereto by increasing the capacity of the condensation heat exchanger, and further applicable to a case where a water and air hybrid cooling condensation heat exchanger is applied thereto. The present disclosure may maintain an optimal amount of cooling fluid of the passive residual heat removal system, and the passive residual heat removal system may exhibit an optimal performance for a long period of time. Furthermore, the present disclosure may prevent non-condensable gas from being accumulated in the passive residual heat removal system. As a result, the present disclosure may enhance accuracy on the performance prediction of the passive residual heat removal system. In addition, the present disclosure may optimize a facility of the passive residual heat removal system to enhance economic efficiency, and alleviate the supercooling phenomenon of the nuclear power plant during an accident through an optimal design, and provide the safety enhancement of the nuclear power plant through the accuracy enhancement of performance prediction. The configurations and methods according to the above-described embodiments will not be applicable in a limited way to the foregoing passive residual heat removal system and a nuclear power plant including the same, and all or part of each embodiment may be selectively combined and configured to make various modifications thereto. 10a, 10b, 10c, 10d, 10e, 10f, 10g, 10h, 10i, 10j, 20a, 20b, 30: Nuclear power plant 100a, 100b, 100c, 100d, 100e, 100f, 100g, 100h, 100i, 100j, 200a, 200b, 300: Passive residual heat removal system 110a, 110b, 110c, 110d, 110e, 110f, 110g, 110h, 110i, 110j, 210a, 210b, 300: Condensation heat exchanger 120a, 120b, 120c, 120d, 120e, 120f, 120g, 120h, 120i, 120j, 220a, 220b, 320: Emergency cooling tank 130a, 130b, 130c, 130d, 130e, 130f, 130g, 130h, 130i, 130j, 230a, 230b, 330: Steam line 140a, 140b, 140c, 140d, 140e, 140f, 140g, 140h, 140i, 140j, 240a, 240b, 340: Feedwater line 250a, 250b: Vent line 160a, 160b, 160c, 160d, 160e, 160f, 160g, 160h, 160i, 160j, 260a, 260b, 360: Makeup tank 170a, 170b, 170c, 170d, 170e, 170f, 170g, 170h, 170i, 170j, 270a, 270b, 370: First connection line 180a, 180b, 180c, 180d, 180e, 180f, 180g, 180h, 180i, 180j, 280a, 280b, 380: Second connection line 190a, 190b, 190c, 190d, 190e, 190f, 190g, 190h, 190i, 190j, 290a, 290b: Circulation line The present disclosure may be used in the nuclear power plant industry including a passive residual heat removal system.
	description	This application is a Continuation of U.S. application Ser. No. 10/196,274 filed Jul. 17, 2002. This application claims priority to U.S. application Ser. No. 10/196,274 filed Jul. 17, 2002, which claims priority to Japanese Patent Application No. 2002-002002 filed on Jan. 9, 2002, the contents of which are hereby incorporated by reference into this application. 1. Field of the Invention The present invention relates to apparatus and methods for inspection of surfaces of samples such as semiconductor devices. 2. Description of the Related Art In manufacture of semiconductor devices, defects of circuit patterns formed on wafers are detected, for example, by comparison of images. For example, Japanese Patent Application Laid-Open No. 59-192943; J. Vac. Sci. Tech. B, Vol. 9, No. 6, pp. 3005-3009 (1991); J. Vac. Sci. Tech. B, Vol. 10, No. 6, pp. 2804-2808 (1992); SPIE Vol. 24, No. 39, pp. 174-183; and Japanese Patent Application Laid-Open No. 05-258703 disclose methods for pattern inspection by pattern comparison according to “SEM process” using a scanning point electron beam. These techniques are used for detection of defects each having a small size under the resolution limit of optical microscopes, such as minute etch residues or minute pattern defects and for detection of electric defects such as open defects of fine via-holes and contact holes. These techniques must yield pattern images at a very high speed in order to provide a practical inspection speed. To ensure a satisfactory signal to noise ratio (a S/N ratio) of the images obtained at a high speed, these techniques use a beam electric current higher hundred times or more (10 nA or more) that of conventional scanning electron microscope. Japanese Patent Application Laid-Open No. 7-249393, No. 10-197462, No. 2000-340160 and No. 11-108864 mention apparatus for high-speed inspection by means of a “projection process” in which a rectangular electron beam is applied to a semiconductor wafer, and images of back scattered electrons, secondary electrons or reflected electrons are formed with lenses. The reflected electrons are reflected without impingement on the wafer due to a formed retarding field for primary beam. Separately, a technique for obtaining an image of the outermost surface of a sample using a “mirror microscope” has been proposed (e.g., Rheinhold Godehardt, ADVANCES IN IMAGING AND ELECTRON PHYSICS, VOL. 94, p. 81-150). In this technique, a potential is applied to the sample to yield an electric field, and the electric field reflects an electron beam in the vicinity of the surface of the sample without impingement on the sample. However, all the conventional techniques for inspection using electron beams, such as the SEM process and the projection process using backs scattered electrons or secondary electrons, have the following problems. The SEM process uses an electron beam current higher than that in conventional scanning electron microscopes in order to form images having a satisfactory signal to noise ratio to be inspected. However, the SEM process cannot inspect a sample with a satisfactorily high speed (for a short time), since it two-shapeally scans the surface of the sample with a “point electron beam” formed by converging an electron beam to a point beam. In addition, the brightness of an electron source used and space charge effect limit increase in the electron beam current. For example, to yield a resolution of about 0.1 μm, the theoretical limit of the electron beam current is about several hundreds nanoamperes, and at most an electron beam current of about hundred nanoamperes is used in practice. A signal to noise ratio of an image is determined by the product of the time to acquire the image and the number of electrons used for the formation of the image, i.e., the magnitude of the electron beam current. To yield a sufficient signal to noise ratio of an image so as to operate image processing procedure successfully, it takes 100 seconds or longer to inspect an area of 1 cm2 on the surface of the sample when a 100-nA electron beam current 0.1 μm in size is used. In contrast, the projection process can illuminate the sample with a higher electron beam current at once than the SEM process and can yield images at once. Accordingly, the projection process may form images at a much higher speed than the SEM process. However, in the projection process, the secondary electrons are emitted at angles in a broad range and have energy in a broad distribution ranging from about 1 to 10 eV. To form an image of such electrons to thereby form a magnified image of the sample, the great majority of the second electrons must be cut off to yield a sufficient resolution. This can easily be understood from FIG. 6 in LSI Testing Symposium/1999 Proceedings, p. 142. This figure shows the relationship between the negative voltage applied to the sample to accelerate the secondary electrons emitted from the sample and the resolution in image formation of the secondary electrons and shows that the resolution is about 0.2 μm when the voltage applied to the sample is −5 kV. All the emitted secondary electrons are not always used for the image formation. For example, the calculation in the reference mentioned above uses a beam having an angle of aperture of less than or equal to 1.1 milliradian (mrad) in an image plane after passing through an objective lens. Secondary electrons each having an angle of aperture within this range occupy at most about 10% of the total secondary electrons. In the calculation, the energy distribution of the secondary electrons for use in image formation is assumed at 1 eV. However, secondary electrons actually emitted have a distribution range of energy of equal to or more than several electron volts or more, and some of them have energy of about 50 electron volts. Such secondary electrons having an energy distribution of at most 1 eV constitute only a fraction of secondary electrons having a broad energy distribution as described above. As thus described, when a high-current electron beam as a sheet beam is applied to form images at once, a sufficient signal to noise ratio of the image cannot significantly be obtained and the inspection time cannot sufficiently be shortened to an expected extent, since the ratio of electrons actually contributing to image formation is low. Likewise, in the projection process using back scattered electrons, electrons are emitted in an amount less by two orders of magnitude than the primary electron beam. Accordingly, the projection process using back scattered electrons cannot yield a high resolution and high speed in inspection concurrently as in the projection process using secondary electrons. In addition, this technique does not limit the direction of trajectory of the electron beam directed to the sample, illuminates the sample with the electron beam with a broad range of angles and thereby yields insufficient resolution of about submicron order and is insufficient in resolution to inspect current downsized semiconductor devices. Accordingly, an object of the present invention is to provide a method and apparatus for wafer pattern inspection for detecting defects of patterns formed on wafers with high resolution at a high speed. The above and other objects of the present invention can be achieved by the following configurations. Specifically, an electron beam not as a point beam but as a sheet beam (a two-shapeal electron beam) spreading two-shapeally is sequentially applied to plural illumination area (area fields) on a surface of a sample wafer. A negative potential is applied to the sample wafer. The negative potential is set at such a potential as to repel the great majority of electron beam in the vicinity of the outermost surface of the wafer and is, for example, a negative potential 0.5 to 5 V greater than that of an electron source (cathode). Then an image of the repelled electrons is formed. Hereinafter, such electrons which are repelled and turn back without impingement on the sample by action of an electric field are referred to as “drawn-back electrons” or “mirror electrons”. Magnified images of the respective plural illumination area are formed sequentially, are converted into electric image signals and are compared with one another. This configuration can detect pattern defects in the respective illumination area with high resolution at a high speed. Specifically, the present invention provides, in an aspect, a method for wafer pattern inspection. The method includes the steps of sequentially illuminating plural illumination area on a surface of a sample with a sheet electron beam, a negative voltage with reference to the potential of an electrode facing the surface of the sample being applied to the sample, the sheet electron beam two-dimensionally spreading in its plane profile upon application to the surface of the sample; forming an image of electrons constituting the electron beam upon an imaging device, the electrons not impinging with the surface of the sample but turning back in the vicinity of the surface of the sample; converting plural electron images corresponding to the plural illumination area to plural electron image signals, respectively, using the imaging device; and comparing the plural image signals with one another to thereby detect a pattern defect formed in the sample. In the method, the sheet electron beam is preferably applied to each of the plural illumination area in such a manner that the electrons constituting the sheet electron beam are approximately in parallel with one another in their traveling directions and are applied approximately vertically to the surface of the sample. In another aspect the present invention provides an apparatus for wafer pattern inspection. The apparatus includes a first electron optical system for sequentially illuminating plural illumination area on a surface of a sample with a sheet electron beam, the sheet electron beam being generated from an electron source and two-shapeally spreading in its plane profile upon application to the surface of the sample; a device for generating an electric field capable of repelling electrons constituting the electron beam in the vicinity of the outermost surface of the sample; a second electron optical system for forming images of electrons constituting the electron beam to thereby form magnified images of the plural illumination area, which electrons are repelled and turn back from the plural illumination area; an image signal detection device for converting plural magnified images corresponding to the plural illumination area to plural electric image signals, respectively; and an image signal processing device for comparing the plural image signals on the plural illumination area with one another to thereby detect a pattern defect formed in the sample. The present invention also relates to an apparatus for wafer pattern inspection. This apparatus includes an electron beam illumination system for illuminating plural illumination area on a surface of a sample with a sheet electron beam, the sheet electron beam being generated from an electron source and two-shapeally spreading in its plane profile upon application to the surface of the sample; a device for generating an electric field capable of repelling part or all of the electrons constituting the sheet electron beam in the vicinity of the surface of the sample without impingement on the surface of the sample; an imaging optical system for forming images of electrons constituting the electron beam which are repelled and turn back from the vicinity of the surface of the sample to thereby form magnified images of the plural illumination area; a sample stage for bearing and moving the sample so as to illuminate each of the plural illumination areas with the electron beam; an image signal detection device for converting plural electron images corresponding to the plural illumination area into plural electric image signals, respectively; and an image signal processing device for comparing the plural image signals with one another and for detecting the presence of a difference exceeding a predetermined threshold to thereby detect a pattern defect in each illumination field. The apparatus for wafer pattern inspection of the present invention may further comprise an electron optical system for obtaining a scanning electron microscopic image of the sample at a predetermined position in the moving direction of the sample stage. The first electron optical system or the electron beam illumination optical system may include an electron gun for generating the electron beam; a condenser lens for converging the electron beam emitted from the electron gun; and an objective lens arranged between the condenser lens and the sample, in which the condenser lens serves to position the focus of the electron beam in the vicinity of a focal plane of the objective lens on the electron source side, and the sheet electron beam may be applied to each of the plural illumination areas in such a manner that the electrons constituting the sheet electron beam are approximately in parallel with one another in their traveling directions and are applied approximately vertically to the surface of the sample. When an aperture electrode facing the sample plays a significant role as an electron lens, the focus of the electron beam may be positioned upon the focal plane of such an aperture lens by means of the objective lens. This configuration can yield a sheet electron beam, electrons constituting the sheet electron beam travel approximately in parallel and in a direction approximately perpendicular to the surface of the sample. The device for generating an electric field in the vicinity of the surface of the sample may be composed of a power supply for applying a predetermined negative potential to, for example, a conductive sample holder for holding the sample. When the sample is, for example, a semiconductor having an insulating film on its surface, the apparatus may further comprise a second electron gun and a pre-charge control system. The second electron gun is arranged at a distance from the optical axis of the electron beam for image formation, and the pre-charge control system applies electrons to the sample prior to image formation. The apparatus may further include a grid for applying a potential between the sample and the second electron gun, and a device for applying electrons to the sample using the second electron gun while controlling the potential applied to the grid. To inspect open defect of via-hole and contact hole, such as electrical shortings or break, of a pattern of a semiconductor sample, a potential difference between a normal pattern and a defective pattern formed by the preliminary illumination is detected to thereby detect a faulty pattern. However, when the defective pattern has a relatively low resistance, an accumulated charge escapes into the surroundings, and the potential difference between the normal pattern and defective pattern formed by the preliminary illumination cannot be maintained for a long time. In this case, the apparatus must further include a device for injecting electrons into the sample to thereby generate a potential difference between the normal pattern and the defective pattern and a device for applying electrons that do not impinge on the sample and form an image at approximately the same position approximately concurrently. To charge a faulty pattern and an insulating film pattern negatively, an electron beam having energy higher by eVn than the potential of the sample is applied to the sample, and an image is formed under a condition in which an insulator is charged at a negative potential of Vn and is stabilized. By this procedure, images can be obtained while the faulty pattern and the insulating film pattern are negatively charged. To charge the faulty pattern and the insulating film pattern positively, a beam for image acquisition and an electron beam or light ray for charging the sample positively may be applied at the same time or alternately. By setting the sample stage so as to move the sample continuously at an approximately constant speed, the defect can be inspected at a higher speed. In this configuration, the position of the sample stage must be monitored to control the electron beam to be applied to each illumination field on the sample surface for a predetermined time period. Specifically, the apparatus may preferably further include a stage-position measuring mechanism for real-time measurement of the position of the sample stage capable of continuously moving, in which the stage-position measuring mechanism determines a change in position with the continuous moving of the sample stage to feed back the measurement in position to an electron beam deflection mechanism of the first electron optical system to thereby ensure that the relative position between the electron beam and the sample moves in a predetermined direction at an approximately constant speed. The image signal detection device may project a magnified electron image formed by the second electron optical system or the imaging optical system on a phosphor screen to convert the same into an optical image and may form project the optical image onto an optical image detection device via an optical lens or an optical fiber. Alternatively, the magnified electron image formed by the optical system may be projected directly on an image detection element having sensitivity for electron. As the image detection element, a charge coupled device (CCD) or a device for integrating an optical signal input in a time delayed manner and outputting the integrated signal (time delayed integration sensor: TDI sensor). Detection signals from the image detection element may be read out by multiple channels in parallel. In addition and advantageously, the present invention provides an apparatus for wafer pattern inspection. The apparatus includes a first device for launching a sheet light ray with a desired incident energy into a sample, the sheet light ray being generated from a light source and two-dimensionally spreading in its plane profile upon application to the surface of the sample; a second device for applying a sheet electron beam in such a manner that the sheet electron beam is decelerated in the vicinity of the surface of the sample so that at least part of electrons constituting the electron beam are repelled and turn back from the vicinity of the surface of the sample without impingement on the surface of the sample; an electron optical system for forming an image of electrons constituting the electron beam upon an imaging device arranged on an extension of trajectories of the electrons, the electrons not coming into impingement on the surface of the sample but turning back from the vicinity of the surface of the sample; an image signal detection device for converting plural electron images corresponding to the plural illumination area to plural electric image signals, respectively, using the imaging device; and an image signal processing device for comparing the plural image signals with one another to thereby detect a defect formed in the sample. The present invention can thereby provide methods and apparatus for wafer pattern inspection which can image and detect fine pattern defects and electric defects such as open defects, shortings, and leakage on the surface of a sample such as a semiconductor device with a high sensitivity and high resolution at a high speed by using electron beams. The present invention will be illustrated in further detail with reference to several embodiments and attached drawings. FIG. 1 illustrates minimal essential components for the explanation of the operation principle of the present invention. An electron beam emitted from an electron source 1 is converged by a condenser lens 2 to form a crossover in the vicinity of a beam separator 3 in a front focal plane of an objective lens 6. The beam separator 3 deflects the electron beam to have an optical axis perpendicular to a wafer 7. The beam separator 3 only serves to deflect an electron beam incident from above. As the beam separator 3, an E×B deflector carrying an electric field and a magnetic field perpendicular to each other can be used, for example. The objective lens 6 converts the electron beam deflected by the beam separator 3 into a sheet electron beam uniform in a direction perpendicular to the surface of the sample (wafer) 7. A negative potential approximately equal to or slightly higher than an accelerating voltage of the electron beam is applied to the sample (wafer) 7 by a power supply 9 to thereby yield an electric field. The electric field corresponds to the shape of a semiconductor pattern formed or the charge thereof on a surface of the wafer 7. The great majority of the sheet electron beam is repelled by action of the electric field immediately before impingement on the wafer 7 and comes back upward with a direction and intensity corresponding to the pattern information of the wafer 7. The repelled electron beam is converged by the objective lens 6 and rises vertically, since the beam separator 3 does not deflect an electron beam coming from beneath. The electron beam then passes through an imaging lens to thereby form an image of the surface of the wafer 7 on an image detection unit 103. By this procedure, an image reflecting a change in local charge potential or a difference of the structure, such as projections and depressions, on the surface of the wafer 7 is formed. The image is converted into an electric signal and is transmitted to an image processing unit 104. To detect a defect of a semiconductor pattern formed on the wafer 7, the image processing unit 104 compares the obtained image with an image of an another part having the same pattern or compares the obtained image with an image of a defect-free portion obtained previously and stores a different portion as a defect in memory. The wafer 7 is placed on a stage (not shown), and the stage is continuously moved by a stage control system 30. The stage control system 30 and a beam control system 28 are linked to each other and continuously move an image acquisition filed while finely adjusting the position of the electron beam with the movement of the stage by action of a deflector (not shown). When the wafer 7 carries an insulator on its surface, the power supply 9 alone cannot determine the surface potential of the wafer 7. Accordingly, the apparatus further comprises a pre-charge control system 32 for charging the surface of the wafer to a desired potential. This device applies a voltage to a grid electrode in the proximity of the surface of the wafer 7 and applies the electron beam to the wafer 7 to thereby control the potential of the surface of the wafer 7. The operation principle and configuration of the pre-charge control system will be illustrated later. To charge the surface of the wafer 7 prior to inspection, the wafer 7 is passed underneath the pre-charge control system 32 to thereby charge inspection fields to a desired potential and is then passed directly below the objective lens 6 to form an image. An image of a defect of the wafer surface is formed under such conditions that the electron beam is repelled from the surface of the wafer 7 based on the following principle. FIG. 2 schematically illustrates an electron beams 201 which vertically enters an equipotential line 205 in the vicinity of the outermost surface of the wafer 7 and are repelled and turn back. The equipotential line 205 exhibits a nonuniform shape in a portion carrying a defect 202 on the surface of the wafer 7. The electron beam vertically entered there does not vertically turn back due to the nonuniform shape but turns back at an angle shown in the figure and enters a lens 204. The lens 204 is illustrated as one lens yielding an equivalent operation to those of the objective lens 6 and an imaging lens 11. When an image is formed on an imaging plane 203 by action of the lens 204, the electrons from the portion carrying the defect 202 are concentrated at a point of the imaging plane, and the point becomes brighter than the surroundings, as shown in FIG. 2. The image can serve to detect the presence and the location of the defect. FIG. 3 shows the result of a simulation of an equipotential line 314 in the vicinity of the surface of the wafer and a trajectory 302 of the electron beam according to the present invention. The cross section of a pattern includes conductive materials 312 (open squares) and insulating films 311 (diagonally shaded areas) each 70 nm in size. It is assumed in this procedure that a central conductive material 313 has a potential of 1 V and the other conductive materials 312 each have a potential of 0 V. In other words, it is assumed that the central conductive material 313 alone has insufficient conduction with a substrate and is thereby positively charged at a potential of 1 V with respect to the surroundings. The potential of the electron source is set at one electron volt (eV) higher than the potential of the wafer. Specifically, when the potential applied to the wafer is 0 V, the electron beam is reflected on an equipotential surface of +1 eV to form an imaging electron beam. FIG. 3 shows that a central pattern having a different potential disturbs equipotential lines, the disturbed equipotential lines strongly affect the electron beams, and the vertically incident electron beams are reflected at large angles. FIG. 4 shows simulation results of the density of electron beams repelled by the electric field and turned back from the surface of the wafer. As shown in “Structure” in the figure, arrayed squares in three rows and three columns represent conductive substances. It is assumed that a conductive substance at the center alone has a potential different from the surroundings by one volt. The trajectory of the electron beam in this case is calculated provided that the electron beam has an energy width (ΔE) of 2 eV, and the lower portions of FIG. 4 are plots of electrons turned back from the surface of the wafer. A highly dotted portion means a high electron density. The figure shows that the electrons are concentrated at the center to form a portion exhibiting a high electron density, indicating that a change of 1 V in the 70-nm fine pattern can be detected according to the principle shown in FIG. 2. In other words, an open defect of via-hole and contact hole can be detected according to the principle. One of the advantages of the present invention will be described in detail below. Specifically, the present invention can markedly improve an inspection speed as compared with the process of scanning a point electron beam (SEM process) or the process of projecting secondary electrons. In imaging devices using electron beams, the speed of image acquisition is ultimately limited and determined by a signal to noise ratio required for the image. The signal to noise ratio of the image is determined by the number of electrons used in formation of the image. The required signal to noise ratio is determined by the magnitude of image contrast caused by a defect to be detected. Specifically, when the contrast of the defect is defined as a signal C, the noise must be lower than the signal C. The noise N is defined by three sigmas (3σ) of the signal. The standard deviation sigma σis determined by the shot noise of the number of applied electrons and is the square root (√S) of the number S of electrons applied per pixel. Accordingly, the noise N is defined as 3√S. When the electron beam is brought into impingement on the wafer 7 to thereby detect secondary electrons formed as in the conventional technique, the process further includes a stochastic process of secondary electron emission from the sample. Accordingly, when the secondary electron emission is assumed to be a Poisson process, the noise N is expressed as (3√2) √S. When the defect contrast C is assumed at 5% of the average signal amount S, the defect contrast C equals 0.05 S, the noise N must be less than or equal to 0.05 S and the average signal amount S must be equal to or more than 7200. The inspection time T per square centimeter can be calculated according to the following equation based on this concept. T = ( 0.01 / x ) 2 · t = ( 1.6 ⁢ e ⁢ - ⁢ 19 · 0.01 2 · ( 3 ⁢ √ 2 ) 2 ) / ( I · η · C 2 · Pix 2 ) ( 1 ) wherein t=((1.6e-19·(3√2)2)/(I·η·q·C2))·(x2/Pix2) In the equation (1), t is the time within which the electron beam must reside at the same place in order to lower the noise than the contrast C. Specifically, the time t is the time for an electron beam probe to illuminate one pixel in the SEM process. The time t is the time for a beam to be directed to one point in the sheet beam illumination process. The time t is referred to as “shot time” hereinafter. In the equation (1), Pix is the required resolution; x is the length of one side of the sheet beam (it is the same with the pixel size, i.e. Pix, in the SEM process); I is the beam current; and η is the detect efficiency of electrons that can be used for image formation. In contrast, the process according to the present invention does not include a stochastic process caused by secondary electron emission, since the electron beam is repelled by the electric field without impingement on the surface of the wafer 7. Accordingly, “√2” in the equation (1) can be omitted in this process, and the inspection time T can be expressed according to the following equation (2): T = ( 0.01 / x ) 2 · t = ( 1.6 ⁢ e ⁢ - ⁢ 19 · 0.01 2 · ( 3 ) 2 ) / ( I · η · C 2 · Pix 2 ) ( 2 ) wherein t=((1.6e-19−(3)2)/(I·η·C2))·(x2/Pix2) The parameters η and C in the aforementioned processes will be estimated below. According to the SEM process, secondary electrons are emitted in an approximately equal number to the primer electrons constituting the irradiated electron beam, almost all of the emitted secondary electrons can be detected by a detector, and thereby η is approximately 1. According to the secondary electron projection process, a sheet electron beam is applied to the wafer 7 and images of generated secondary electrons are formed. In this process, only a limited number of emitted secondary electrons must contribute to image formation. If not, the resolution is deteriorated. This mechanism will be described in detail below with reference to FIGS. 5 and 6. FIG. 5 shows the relationship between the emission angle β of secondary electrons or back scattered electrons contributing image formation and the resolution of the image. The emission angle β corresponds to the aperture angle of electrons captured in the imaging system. The figure shows that, when an image is formed using secondary electrons having an emission angle of less than or equal to 100 mrad, the resolution is about 100 nm, for example. The calculation is performed on the condition that the electrons applied to the wafer have energy of 500 eV, the wafer surface is in a strong electric field of 5 kV/mm, and the secondary electrons have an energy width of 5 eV. Such secondary electrons have a broad energy distribution of equal to or more than 10 eV, but secondary electrons having an energy in a range of 2±2.5 eV alone are used in image formation. These secondary electrons occupy about a half of the total secondary electrons. As back scattered electrons, elastically scattered electrons alone are took into account, and these electrons are assumed to have an energy width of 1 eV. FIGS. 5 and 6 show that the secondary electrons must have an emission angle of 25 mrad to yield a resolution of 40 nm, for example and that the probability of scattering of the secondary electrons within the emission angle β of 25 mrad is about 0.1%. Assuming that the yield of the secondary electrons (the ratio of the number of the secondary electrons to the number of the primary electrons) is about 1, the parameter η in the secondary electron projection process is ½×0.001×1=0.0005. In the projection process using back scattered electrons, the emission angle β must be 80 mrad in order to yield a resolution of 40 nm, and the probability of occurrence of the back scattered electrons within the emission angle of 80 mrad is 0.2%, as shown in FIG. 6. The yield of the back scattered electrons (the ratio of the number of the back scattered electrons to the number of primary electrons) is about 0.02 to 0.03 at an illumination energy of 500 eV (refer to Image Formation in Low-Voltage Scanning Electron Microscopy, SPIE, Bellingham, p. 43, p 67, 1993). Accordingly, the parameter η in the back scattered electron projection process is as low as 0.002×0.025=e−5. In contrast, according to the present invention, the electron beam is repelled and turns back vertically upward on a flat wafer surface, and the aperture angle of the beam is equivalent to angle variation of the irradiated electron beam and is very low of about several milliradians. FIG. 7 is an explanatory diagram for further deepening the understanding of the above description. According to the secondary electron projection process, the secondary electrons are emitted into a vacuo and spread at an angle of 180 degrees from the sample as shown in the left hand of FIG. 7. In contrast, according to the present invention (mirror projection process), all the applied electrons move approximately right upward, and the applied electrons can effectively be utilized in image formation, as shown in the right hand of FIG. 7. When the surface of the wafer carries a protrusion or depression or a potential distribution, the electrons move upward at some angles from the vertical. In this case, the ratio of electrons directly contributing image formation decreases, but the change in angle itself contributes to the formation of image of the wafer surface to thereby increase the contrast. In other words, a decrease in η is equivalent to an increase in the contrast C and advantageously serves to detect the defect. The parameters η and C are linked to each other in the present invention, and C increases with a decreasing η. While depending on the types of the pattern and of the defect to be detected, it is assumed that a half of the total electrons can be detected as images in a defective portion, and the remained half contribute to increase the contrast. Accordingly, η and C are assumed as 0.5, respectively. Table 1 shows the summary of the above description, and FIG. 8 shows the relationship between the beam current and the inspection time. The relationship is estimated provided that Pix is 40 nm. Table 1 and FIG. 8 show that the process according to the present invention can inspect the sample in a significantly short time as compared with the conventional processes. TABLE 1Detect efficiencyηContrast CSEM1.05%Secondary electron projection5e−45%Back scattered electron projection5e−55%Mirror projection0.550% The configuration of an embodiment of the present invention will be illustrated in detail below. FIG. 9 illustrates the configuration of an inspection apparatus according to an embodiment of the present invention. The inspection apparatus according to the present embodiment roughly includes an electron optical system 101, a sample chamber 102, an image detection unit 103, an image processing unit 104 and a control unit 105. Each of these units will be described in detail below. Initially, the electron optical system 101 will be illustrated in detail. An accelerating power supply (electron-source power supply) 23 applies a high negative potential to an electron source 1. The electron source 1 emits an accelerated electron beam, the accelerated electron beam is converged by a condenser lens 2 and is applied to an aperture 4 having a rectangular opening. As the electron source 1, a Zr/O/W Schottky emitter that can stably yield a uniform sheet electron beam at a high current (e.g., 1.5 μA) having an energy width of 1.5 eV is used. A beam separator 3 deflects the electron beam to a direction of the wafer 7. The beam separator 3 serves to separate the optical paths of the incident electron beam from the electron source 1 and of the mirror electron beam from the sample. The condenser lens 2 forms a crossover on a focal plane of the objective lens 6. The aperture and the array of lenses are optimized so as to form an image of the aperture 4 on the surface of the wafer 7 by means of the objective lens 6. This configuration yields a sheet electron beam in a direction perpendicular to the surface of the wafer 7. The sheet electron beam has a shape analogous to that of the opening of the aperture 4. The electron beam comprises electrons having trajectories arrayed approximately in parallel with one another. The rectangular opening of the aperture 4 is, for example, of 100 μm square. The objective lens 6 reduces the electron beam to the half to thereby yield a sheet electron beam 50 μm square on the surface of the wafer 7. The sheet electron beam can be moved (or scanned) to a desired position on the surface of the wafer 7 by action of an illumination system deflector 5. If the front focal plane of the objective lens 6 does not completely agree with the crossover position, there is no problem as long as a shift between them is within a tolerance. The crossover ideally has a size of zero but has some limited size in actual due to aberration of the electron gun or condenser lens. Such a crossover having a size within a tolerance is acceptable. In an electron optical system in which the position of the crossover is accurately controlled and the aberration of the electron gun and the condenser lens is sufficiently minimized, the incident angle of the electron beam into the sample can have a minimized divergence of less than or equal to 0.5 mrad. The divergence of the incident angle is one of the factors that determine the resolution of a magnified image on the sample surface formed by the mirror electrons and is expressed by the following equation:r0=β2·Zm (3)wherein r0 is the resolution determined by the divergence of the incident angle; β is the maximum incident half angle; and Zm is the distance at which an electron field that repels the electrons is formed. In the present embodiment, β is 0.25 mrad and Zm is 5 mm. When these parameters are substituted into the equation (3), r0 is 0.3 nm, indicating that the divergence of the incident angle does not affect the resolution in the present embodiment. Accordingly, the beam current can be increased according to necessity. It is speculated that a defect of a semiconductor can satisfactorily be detected even when the resolution is around 30 nm. Based on this, when Zm is set at 5 mm, β up to 2.4 mrad can be accepted. In this case, the displacement between the front focal plane of the objective lens and the crossover, and the size of the crossover have significant allowances. The displacement of the crossover Δf can be expressed by the following equations:Δf=f·β/α (4)α=X/(2f) (5)wherein α is the aperture half angle of the beam on the front focal plane; f is the focal distance of the objective lens; Δf is the displacement of the crossover; and X is the radius of the sheet electron beam. The equations (4) and (5) indicate that the crossover displacement Δf up to about 10 mm can be accepted when the focal distance f of the objective lens is set at 10 mm and the size of the sheet electron beam X is set at 40 μm. The crossover displacement Δf of 10 mm is converted into a beam diameter on the front focal plane of about 40 μm. In all cases, a sufficient resolution can be obtained by positioning the crossover of the electron beam in the vicinity of the front focal plane of the objective lens. The beam separator 3 will be described in brief. The beam separator 3 deflects the electron beam emitted from the electron source 1 to a direction of the wafer 7 and deflects the mirror electron turned back from the wafer 7 not to a direction of the electron source 1 but to a direction of the imaging lens 11. A deflector utilizing a magnetic field can optimally be used as the deflector herein, since the direction of deflection by a magnetic field varies depending on the incident direction of electrons. In an optical system comprising the imaging lens and the objective lens 6 having optical axes in line with each other, an E×B deflector is used. The E×B deflector uses an electric field and a magnetic field orthogonal to each other, allows the mirror electron from beneath to travel in a straight line and deflects the electron beam incident from above alone. This embodiment will be illustrated later in detail as Second Embodiment with reference to FIG. 15. The power supply 9 applies a negative potential to the wafer 7 and the sample stage 8. The negative potential is slightly greater (has a slightly greater absolute value) than that of the electron source 1 and is preferably greater than that of the electron source 1 by 0.5 to 5 V. An excessively greater negative potential may deteriorate the resolution of the image. In contrast, an excessively small negative potential serves to form an image of trivial projections and depressions or a trivial change in potential with an excessively high contrast. In this case, a target defect cannot be detected. The negative potential decelerates the electron beam in front of the wafer 7, which electron beam is directed in a direction perpendicular to the surface of the wafer 7. The electron beam is drawn back upward by the electric field on the surface of the wafer 7. The repelled electron (mirror electron) carries the information on the surface of the wafer 7, as described above. The objective lens 6 makes a focus of the mirror electron, and the beam separator 3 deflects the mirror electron to a direction of an imaging system deflector 10 and the imaging lens 11. The deflected mirror electron enters the imaging lens 11 to form an image of the state of the surface of the wafer 7 as an electron image. The electron image is magnified and projected on a phosphor screen 15 by magnifying lenses 13 and 14 to thereby yield a fluorescent image (mirror electron image) reflecting the pattern or charge state of the surface of the wafer 7. To improve the contrast and resolution of the electron image, the apparatus can further comprise a contrast aperture 12 inserted into the crossover plane. The contrast aperture 12 removes electrons that are significantly outside the vertical direction after they are repelled by the electric field on the surface of the wafer 7 to thereby improve the resolution and contrast of the image. In the principle of imaging according to the present invention, the sensitivity and resolution of the image required for detection of a minute difference in charge of the wafer surface are determined by the energy width of the sheet electron beam. FIG. 10 shows the results of simulations of the energy widths and the contrasts, in which the same pattern as in FIG. 4 is taken as an example, and images are obtained at energy widths (ΔE) of the electron beam of 2 eV and 4 eV, respectively. The results show that an image obtained using an electron beam having an energy width of 4 eV exhibits no contrast on a portion having a different potential at the center of the pattern. In consideration of downsizing of semiconductor devices, the process must detect a difference of about 1 V in potential as a defect in fine patterns as shown in FIG. 10. Accordingly, the electron beam for use in the present invention should preferably have an energy width of less than or equal to 2 eV. In the process according to the present embodiment using the Zr/O/W Schottky emitter, the electron beam has an energy width of 1.5 eV and can be used without problems. If an electron source emitting an electron beam having a larger energy width, the energy width of the electron beam must be reduced to 2 eV or less between the emission of electron beam from the electron source and the ultimate image formation by arranging an energy filter on the optical path of the electron beam, for example. The energy filter is preferably placed between the electron source and the wafer 7, but it is also acceptable to subject the mirror electron from the wafer 7 to energy filtering to yield similar advantages. According to the present invention, the electron beam does not impinge on the wafer 7. Even if the wafer 7 carries an insulating film on its surface, the surface does not become charged in principle. Accordingly, if the wafer is inspected while carrying no charge, only shape defects in which the shapes are different from normal portions can be detected. However, in addition to such pattern defects, “electric defects” such as faulty electrical continuity (open defects of via-hole and contact hole), electrical shortings of components to be insulated, and a larger leak current than that in normal portions, should be detected in wafer pattern inspection. In conventional technologies using electron beams, such electrical defects are charged by application of an electron beam, forming a scanning electron microscopic (SEM) image exhibiting a difference in potential as a voltage contrast, and detecting the electrical defects based on the voltage contrast. To detect such electrical defects with high sensitivity, the apparatus according to the present embodiment further comprises a pre-charge control system which applies an electron beam dedicated to charge control to the wafer 7 prior to acquisition of images for inspection. By charging the wafer 7 to a predetermined potential with the pre-charge control system prior to inspection, electrical defects such as open defects of via-hole and contact hole, as well as shape defects, can be detected. The operation and configuration of the pre-charge control system will be illustrated below. FIG. 11 is an explanatory diagram of the operation principle of the pre-charge control system. An electron source 41 emits a high current electron beam from a plane having a measure of size (several hundreds micrometers to several tens millimeters). Such electron sources include, for example, an electron source comprising bundled carbon nanotubes, a tungsten filament thermal emitter, and a LaB6 emitter. An extract electrode 48 applies an extract voltage to an extract grid 42 to thereby allow the electron source 41 to emit an electron beam 43. The electron beam 43 passes through a control grid 44 and is applied to an insulating film 46. By this procedure, secondary electrons 45 are emitted. The secondary electrons 45 each have an energy of about 2 eV with reference to a potential of the surface of the insulating film 46. If the surface potential of the insulating film 46 is equivalent to that of a substrate 47, the electron beam 43 has an illumination energy equivalent to the voltage of an accelerating power supply 49. The voltage of the accelerating power supply 49 is set at such a level that a secondary electron is more than 1. The voltage may be set at 500 V in insulating film materials for use in typical semiconductor devices. By the above procedure, the surface of the insulating film 46 becomes positively charged, since the secondary electron yield is more than 1. A control power supply 50 is connected to the control grid 44 to apply an optional positive or negative voltage to the control grid 44. Accordingly, once the potential of the surface of the insulating film 46 becomes positive with reference to the set potential of the control grid 44 and the secondary electrons turn back toward the surface of the insulating film 46, positive charging of the surface of the insulating film 46 terminates. Thereafter, the surface of the insulating film 46 keeps a positive potential somewhat lower (about 2 V) than the potential of the control grid 44. Due to the energy of the secondary electron, the potential of the surface of the insulating film 46 does not become equal to that of the control grid 44. Based on the aforementioned principle, the potential of the surface of the insulating film 46 can be controlled by the potential of the control grid 44. FIG. 12 illustrates a configuration of a pre-charge control system using a carbon nanotube electron source. In this system, an electron source 41 is held in vacuo by an insulator 51 and serves to apply a potential. A control grid 44 faces a wafer 7, and an extract grid 42 extracts electrons from the electron source 41. FIG. 13 illustrates a configuration of a pre-charge control system using a LaB6 emitter. When such a LaB6 emitter is used in a microscope, a crossover is formed immediately after electron emission using a Wehnelt electrode. However, in this system, it is not required that the light source is small in size, and the system comprises an extract electrode 42′ instead. With reference to FIG. 9, the wafer 7 is placed on the sample stage 8 that is movable in two shapes (x and y directions) in the sample chamber 102. The power supply 9 applies such a negative potential to the wafer 7 that the great majority of the electron beam does not impinge on the wafer 7, as described above. The apparatus further comprises a stage-position measuring device 27 to determine the position of the sample stage 8 in real time accurately. The stage-position measuring device 27 is provided in order to acquire images while continuously moving the sample stage 8. A laser interferometer can be used as the stage-position measuring device 27, for example. To determine the height of the surface of the semiconductor sample (wafer) 7 accurately, the apparatus further comprises an optical sample-height gauge 26. In the sample-height gauge 26, for example, light is allowed to enter a field to be inspected on the surface of the wafer from a slanting direction, and the height of the surface of the wafer 7 is determined based on a change in position of the reflected light. The sample chamber 102 further comprises an optical microscope 31 for registration of inspection fields. Next, a stabilization time of the sample stage 8 will be described. If the sample stage 8 is moved in a step-and-repeat manner, the stabilization time of the sample stage 8 must be on the order of milliseconds. In this case, it takes much long time for the sample stage 8 to move even if the image signal to noise ratio is increased and the image acquisition time is shortened, and the inspection time cannot be shortened. Accordingly, the sample stage 8 moves continuously at an approximately constant speed in this embodiment. By this configuration, the stabilization time of the sample stage 8 does not limit the inspection time. However, the sample stage 8 thus continuously moves to thereby change the illumination position on the surface of the sample 7 even within one shot time which is a time required to form an image of one point. Accordingly, an illumination system deflector 5 makes the illumination electron beam follow the movement of the sample stage 8 in order to fix the illumination position during one shot. Likewise, the illumination point of the electron beam moves and an image 12 formed by the imaging lens 11 also moves relative to the electron optical system at rest with the movement of the sample stage 8. To avoid the movement of the image 12, the imaging system deflector 10 is operated so as to cooperate with the illumination system deflector 5. Next, the image detection unit 103 will be illustrated below. To detect images, the phosphor screen 15 for converting a magnified image of the mirror electron image 12 into an optical image is optically connected with an optical image detection device (e.g., a CCD) 17 via an optical fiber bundle 16. By this configuration, an optical image on the phosphor screen 15 is projected onto an active area of the optical image detection device 17. The optical fiber bundle 16 comprises bundled fine optical fibers in the same number with that of pixels. Alternatively, instead of the optical fiber bundle 16, an optical lens is used to project the optical image on the phosphor screen 15 onto the active area of the optical image detection device (CCD) 17. The phosphor screen 15 carries an electrode 300 and a transparent electrode 301 on both sides, respectively, and a high voltage is applied between the two electrodes in such a manner that the transparent electrode 301 becomes positive to avoid scattering of the electron beam. The optical image detection device (CCD) 17 converts the optical image formed on its active area into an electric image signal and produces an output of the signal. The outputted image signal is transmitted to the image processing unit 104 and undergoes image signal processing therein. Next, the read time of the image detection device (CCD) 17 will be described. According to the present embodiment, charges stored in the CCD 17 are read out from a 128-channel reader at a readout rate of 8 M line/second in a multichannel parallel readout manner. The number of pixels per channel per line is 8, and a readout time per line is 125 nanoseconds (nsec). Accordingly, a readout time per pixel is 125 nsec/8 pixel and is 16 nsec. In contrast, a process using readout from a CCD in one channel must read out at a very high speed and is not feasible. In the present embodiment, the reader of the image data from the CCD is divided into 128 channels, and the 128 channels read out the data in parallel concurrently. By this configuration, the readout time per pixel becomes 16 nsec which is sufficiently feasible. FIG. 14 schematically illustrates this configuration. The number of the readout channels of the image data from the CCD 17 is 128, and each of the 128 channels comprises 8 pixels×1024 lines. Accordingly, the readout time for one image data from the CCD 17 is about 125 microseconds (μsec). Specifically, the system can capture an image signal per one shot area within 125 μsec. If the pixel size is set at 50 nm and one shot area is set at 50 μm square, the inspection time per square centimeter of the surface area of the sample is 5 sec. According to the conventional processes, the inspection time per square centimeter of the surface area of the sample is about 400 sec provided that the pixel size is 50 nm. The process according to the present embodiment can inspect samples at a speed about 80 times higher than that in the conventional processes. According to the present embodiment, the inspection time is determined by the signal readout speed from the CCD 17. If a data readout process at a higher speed in a CCD is realized in future, the inspection will be possibly performed at a higher speed. The image processing unit 104 comprises image signal memory units 18 and 19, a computing unit 20 and a defect determination unit 21. The image signal memory units 18 and 19 store images of adjacent portions having the same pattern, and the computing unit 20 performs computations on the two images to thereby detect a point at which the two images are different. The defect determination unit 21 interprets the result as a defect and stores its coordinates in memory. The captured image signal is displayed in a monitor 22 as an image. A control computer 29 in the control unit 105 produces inputs and outputs of instructions and conditions of operations of individual units of the apparatus. The control computer 29 has been fed conditions such as an accelerating voltage upon generation of the electron beam, deflection width and deflection speed of the electron beam, a moving rate of the sample stage 8, and a capture timing of the image signal from the image detection device 17. Upon an instruction from the control computer 29, the beam control system 28 generates a correction signal based on signals from the stage-position measuring device 27 and the sample-height gauge 26 and transmits the correction signal to an objective lens power supply 25 and a scanning signal generator 24 so as to ensure the electron beam to be applied at a proper position always. The stage control system 30 controls the sample stage 8 upon an instruction from the control computer 29. Next, practical inspection procedures will be illustrated below. Initially, the procedure for alignment using the optical microscope 31 and the electron beam image will be described. The wafer 7 is placed on the wafer (sample) stage (X-Y-θ stage) 8 and is moved to beneath the optical microscope 31. An optical microscopic image of the surface of the wafer 7 is observed with a monitor 22, and an optional pattern, for example, at the center in an image area is stored in memory. In this case, the selected pattern must be a pattern that can be observed even on an electron beam image. Next, by rotating the wafer stage 8, the position of the wafer 7 is corrected so that the circuit pattern on the surface of the wafer 7 is in a direction parallel with or perpendicular to the direction of stage movement. Upon the rotation of the wafer stage 8 for correction, an optical image of an optional pattern in an optional chip of the circuit pattern on the surface of the wafer 7 at some stage position is captured and is displayed on the monitor 22, and an optional point in the image area is marked. Its optical image signal is then stored in the memory unit 18. Next, the wafer stage 7 is moved in the X direction or y direction at a length corresponding to several chips of the circuit pattern on the surface of the wafer 7, and an optical image of a new chip at a portion having the same pattern with that of the previous chip is captured and displayed on the monitor 22. A point corresponding to the previously marked point is also marked, and the new optical image signal is stored in the memory unit 19. Subsequently, the optical image signals stored in the memory units 18 and 19 are compared with each other and are subjected to calculation of a misregistration of the marked points in the two images in the computation unit 20. Based on the misregistration of the marked points and the stage travel between the two images, a rotation angle error of the wafer 7 is calculated, and the wafer stage 8 is rotated at an angle corresponding to the error to thereby correct the rotation angle. The rotation correction procedure is repeated several times to thereby control the rotation angle error below a predetermined level. Subsequently, the circuit pattern on the surface of the wafer 7 is observed with an optical microscopic image, and positions of chips and intervals between the chips (e.g., repeating pitch of a repeated pattern of a memory cell) on the wafer are determined previously, and the measurements are inputted to the control computer 29. A chip to be inspected on the surface of the wafer 7 and fields to be inspected in the chip are set on the optical microscopic image on the monitor 22. Such an optical microscopic image can be observed under a relatively low magnification. In addition, even when the circuit pattern on the surface of the wafer 7 is covered with a transparent film such as a silicon oxide film, the underlayer circuit pattern can be observed based on the optical microscopic image. Accordingly, a layout of the circuit pattern in the chip can easily be observed and the inspection fields can easily be set. S The wafer 7 is then moved to underneath the electron optical system, and an electron beam image of a field expected to include the inspection field set on the optical microscopic image is obtained. In this procedure, the inspection field should be included in one shot area. The wafer stage 8 is moved so that the pattern of the previously marked point is present in the same image area in the electron beam image with that in the optical microscopic image. This procedure can coordinate the electron beam illumination position with the optical microscopic observation position prior to inspection and can calibrate the image acquisition position. The same procedure as in the optical microscopic image is then performed on the electron beam image. This procedure can yield simple check and alignment of the observation position using the optical microscope and can adjust the electron beam illumination position. By using the electron beam image, the rotation can be corrected with further higher precision in addition to the rotation correction based on the optical microscopic image to some extent. Such an electron beam image has a higher resolution under a higher magnification than the optical microscopic image. In addition, by using the electron beam image, the inspection fields or the fields having the same pattern can be observed, checked and corrected with a high precision under a high magnification. However, when all or part of the surface of the semiconductor wafer 7 is covered with an insulator, a potential of the surface of the insulator is not equal to the potential of the substrate in some cases. The potential of the insulator surface must be controlled by the pre-charge control system 32 prior to the acquisition of the image in such cases. After the completion of setting of the inspection conditions, an electron beam image of part of the inspection field on the surface of the semiconductor wafer 7 is formed under the same condition with that in the actual inspection. Based on the electron beam image, information on brightness of the image depending on the material and shape of the inspection field and its variation range are calculated and are stored as a table in memory. In the subsequent inspection process, an image of a pattern in the inspection field is actually formed and detected, and whether or not the pattern is a defect is determined based on the stored table. A criteria on this determination has previously been set. After the completion of setting of the inspection field and defect determination criteria, an actual inspection is performed. Upon inspection, the sample stage 8 bearing the sample (semiconductor wafer) 7 thereon continuously moves in the X direction at a constant speed. During the movement, the electron beam is applied to one illumination field (an area field) on the surface of the wafer 7 during each one shot for a predetermined shot time (e.g., 50 μsec or more in the present embodiment). The electron beam is deflected and scanned following the continuous movement of the sample stage 8 by action of the illumination system deflector 5. The illumination field or illumination position of the electron beam is continuously monitored by the stage-position measuring device 27, the sample-height gauge 26 and other devices arranged on the sample stage 8. The monitored information is transmitted to the control computer 29 to thereby grasp misregistration in detail, and the misregistration is accurately corrected by the beam control system 28. These procedures can perform accurate registration for comparison and inspection of the patterns at a high speed with high precision. In addition, the height of the surface of the semiconductor wafer 7 is determined in real time by a means other than the electron beam, and the focal distances of the objective lens 6 for illumination of the electron beam and of the imaging lens 11 are corrected dynamically. Such other means than the electron beam include, for example, the optical height gauge 26 according to laser interferometry or according to measurement of a change in position of the reflected light. By this configuration, an electron beam image always focusing on the surface of the inspection field can be formed. Alternatively, the warpage of the wafer 7 has been determined prior to inspection, and the focal distances are corrected based on the measured data. In this case, there is no need of determining the height of the surface of the wafer 7 in the actual inspection. The electron beam is directed to the surface of the wafer 7, and a magnified optical image of a desired inspection field (area field) on the surface of the wafer 7 is formed by action of the mirror electrons. The magnified optical image is then converted into an electric image signal by action of the CCD 17, and the image signal is captured into the image processing unit 104 and is stored as an electron beam image signal in the memory unit 18 or 19. The electron beam image signal is on the area field corresponding to the electron beam illumination position that is supplied by the control unit 28 upon the instruction from the control computer 29. The patterns of adjacent chips A and B formed on the surface of the semiconductor wafer 7 and having the same design pattern are compared and inspected in the following manner. Initially, an electron beam image signal on an inspection field in the chip A is captured and is stored in the memory unit 18. Next, an image signal on an inspection field in the adjacent chip B corresponding to the inspection field in the chip A is captured, is stored in the memory unit 19 and, at the same time, is compared with the stored image signal in the memory unit 18. Subsequently, an image signal on a corresponding inspection field in an adjacent chip C is captured, is overwritten on the memory unit 18 and, at the same time, is compared with the stored image signal in the memory unit 19 on the inspection field in the chip B. By repeating this procedure, image signals on inspection fields in all the chips to be inspected are sequentially stored and are compared with one another. As an alternative embodiment, it is also acceptable that an electron beam image signal of an optional inspection field on a non-defective (defect-free) sample has been stored as a reference standard in the memory unit 18 prior to inspection. In this embodiment, the inspection field and inspection condition on the non-defective sample are inputted into the control computer 29 in advance, the non-defective sample is inspected based on the inputted data, and an image signal obtained on the desired inspection field is stored in the memory unit 18. Next, the wafer 7 to be inspected is placed on the sample stage 8 and is inspected in the same manner as above. An image signal acquired on an inspection field corresponding to the aforementioned inspection position is captured in the memory unit 19 and, at the same time, is compared with the image signal on the non-defective sample stored in the memory unit 18. By this procedure, the presence or absence of a pattern defect in the desired inspection field of the sample to be inspected is detected. As the standard reference (non-defective) sample, a wafer that is other than the sample to be inspected and has been verified to have no pattern defect can be used. Alternatively, a field (chip) which is on the surface of the sample to be inspected and has been verified to have no pattern defect can also be used. When patterns are formed on the surface of a semiconductor sample (wafer), misregistration (misalignment) between a lower pattern and an upper pattern overall the wafer may occur in some cases. In such cases, if patterns in the same wafer or in the same chip are compared for inspection, such a failure (a defect) occurring overall the wafer as above is overlooked and is not detected. However, according to the aforementioned embodiment, the image signal on a field that has been verified to have no defect is stored in memory and is then compared with the image signal of the inspection field, and even such a failure (a defect) occurring overall the wafer can be detected with high precision. The two image signals stored in the memory units 18 and 19 are captured into the computation unit 20, respectively. Based on the captured image signals, statistics, such as average and variance of image concentrations, and differences among adjacent pixels are calculated in the computation unit 20 under the defect criteria previously determined. The treated two image signals are transmitted to the defect determination unit 21 and are compared with each other to thereby extract difference signals between the two image signals. By comparing these difference signals with the defect criteria previously determined and stored, whether or not an image signal on a pattern field is defect is determined. The image signal on the pattern field determined as defect is distinguished from image signals on the other fields. The method and apparatus for inspection as described above can detect the presence of a pattern defect by forming images reflecting the potential and shapes of the surface of the wafer 7, and comparing and inspecting image signals on corresponding pattern fields. The method and apparatus can inspect samples at a much higher speed than the conventional inspection processes and apparatus using electron beams. According to First Embodiment, the area of an electron beam illumination field illuminated in one shot is significantly as large as of 50 μm square, and the magnified image of the semiconductor sample may have a deformed periphery or the beam current may not become satisfactorily uniform in density in the illumination field in some cases. When such image deformation or nonuniform current density occurs stationary, it can be corrected by changing the array of fiber wires of the optical fiber bundle 16 or by assigning weights to acquisition sensitivity or image processing of the image signals. However, if the image deformation and nonuniform current density vary with time, the techniques just mentioned above cannot remedy these problems. Accordingly, in the present embodiment, an illumination filed per shot is set at 5 μm square to thereby avoid deformation of image and nonuniformity in current density in the illumination field during one shot. The illumination electron beam current per shot is 1 μA. Provided that electron imaging efficiency η is 0.5, the irradiation time t of the electron beam per shot is 0.18 μsec as calculated according to the equation (1). After illuminating one illumination field (5 μm square) with the electron beam for a shot time of 0.18 μsec, the electron beam is moved to another adjacent illumination field (5 μm square) by action of the illumination system deflector 5. By directing the electron beam to be applied to one illumination field after another in this manner, the overall area of 100 μm in the X direction and 100 μm in the y direction is illuminated in a total of 400 shots (20×20 shots). In this procedure, a shot-to-shot magnified image is obtained on the CCD 17 at a position corresponding to the shot-to-shot electron beam illumination position, and the position of the magnified image on the CCD 17 moves with the movement of the electron beam illumination position caused by electron beam scanning, as shown in FIG. 15. As the CCD 17, a CCD of 1024×1024 pixels is used herein. One pixel on the CCD 17 is equivalent to an area 50 μm square on the surface of the wafer 7. Accordingly, an illumination field (5 μm square) per shot on the surface of the wafer 7 is equivalent to an area of 100×100 pixels on the active area of the CCD 17, which is equivalent to one hundredth of the total active area of the CCD 17. The overall active area of the CCD 17 is set so as to cover an area 50 μm square on the surface of the wafer 7. Accordingly, it takes 18 μsec (0.18 μsec×100 shots) to obtain a magnified image of the area 50 μm square on the surface of the wafer 7. Thus, the image of the field 50 μm square on the surface of the wafer 7 is formed on the CCD 17 over 18 μsec, and the image signals accumulated in the CCD 17 are stored as digital signals in the image memory unit 18. The wafer stage 8 must be moved by 50 μm in order to obtain image signals on another adjacent field on the surface of the wafer 7. In this embodiment, the wafer stage 8 continuously moves at a constant speed as in First Embodiment. To fix the relative position between the wafer stage 8 and the illumination electron beam so that as if the wafer stage 8 is still with respect to the illumination electron beam, the illumination electron beam is deflected and scanned by the illumination system deflector 5 so as to follow the movement of the wafer stage 8. This procedure avoids a waste of time caused by the movement and stopping of the wafer stage 8. To scan the illumination electron beam so as to follow the continuously moving wafer stage 8, a correction signal for deflection signal is calculated in the beam control system 28 with reference to the signals from the stage-position measuring device 27, and the correction signal for deflection signal is transmitted to the illumination system deflector 5 to thereby control the deflection of the illumination electron beam. In addition, corrections on deformation and positional drift of the magnified image of the sample formed by the electron beam are superimposed on the correction signal for deflection signal to thereby correct these parameters. Additionally, the imaging system deflector 10 is also cooperated with the illumination system deflector 5 so as to remove influences of the movement of the electron beam position following the wafer stage 8 on the position of the magnified image of the sample on the CCD 17. These configurations and procedures eliminate a waste of time caused by stage movement and can inspect the sample at a high speed with high precision. The subsequent procedures such as image processing for defect inspection are the same as in First Embodiment. By performing inspection according to the aforementioned procedures, the time T to form magnified images per square centimeter of the surface of the wafer 7 successively on the CCD 17 is 0.72 sec. In contrast, it takes 125 μsec to read one image (an image corresponding to an area 50 μm square on the surface of the wafer 7) from the CCD 17, and it takes 5 sec to read out image signals per square centimeter of the surface of the wafer 7 as in First Embodiment. The inspection time is a longer time between the time to form images or the time to readout the image signals, since image formation and image signal readout are performed in parallel in the CCD 17. In the present embodiment, the image signal readout time is longer than the image formation time and is 5 sec per square centimeter. Accordingly, the inspection time per square centimeter of the surface area of the sample is 5 sec. The above description has been made by taking the case wherein the electron beam illumination field per shot is fixed to a size of 5 μm square as an example. However, it is also acceptable that the size of the electron beam illumination field is varied depending on the pattern repetition pitch on the surface of the semiconductor wafer 7. The size of an electron beam illumination field per shot is set small in the present embodiment, as described above. Accordingly, even if some deformations occur in joint portions between illumination area, an equivalent deformation at an equivalent point in each illumination field occurs, and deformations in two images to be compared occur in equivalent manner to thereby avoid false detection caused by deformation. This configuration can inspect a pattern defect with high reliability. A time delayed integration CCD sensor is used as a device for converting images of the sample surface to electric signals in the present embodiment. This device is called as a TDI sensor and is generally used in optical inspection apparatus. The other configurations are the same as in Second Embodiment. A conceptual operation of the TDI sensor will be illustrated in detail below with reference to FIG. 16. The TDI sensor operates so that a charge formed according to the intensity of light received in each active field is moved along the line in the X direction and, concurrently, charges formed according to the intensity of received light at positions after movement are sequentially added. The accumulated charge is outputted to the outside as an electric signal at the time when the charge reaches the final line of the active area. By equalizing the speed of the charge in the x direction and that of the image on the active area in the X direction, signals obtained during the movement of the image on the sensor are integrated and are outputted. According to the present embodiment, by reading signals in 128 channels in parallel as in the CCD sensors in First and Second Embodiments, the reading speed is set at 4 M-line/sec. The TDI sensor used herein has an active field comprising 64 pixels in the X direction and 2048 pixels in the y direction. The lengths of one line in the x and y directions are equivalent to 50 nm and about 100 μm, respectively, on the wafer surface. In this procedure, images each 50 nm long and 100 μm wide are outputted at a speed of 4 M/sec., and thereby the wafer stage 8 continuously moves at a speed equivalent thereto (50 nm/250 nsec=200 mm/sec). The inspection field is moved in the X direction by moving the wafer stage 8 in this manner. One illumination field per shot is of 5 μm square, and the illumination field must be moved in the y direction by scanning of the electron beam, as shown in FIG. 16. Specifically, the electron beam must be scanned by 100 μm in the y direction during the movement of the wafer stage 8 in the x direction in one shot (5 μm). Provided that it takes 1.25 μsec for one shot, it takes 25 μsec to scan 100 mm (20 shots) in the y direction. The wafer stage 8 moves in the X direction at a speed of 200 mm/sec, and it takes 25 μsec for the wafer stage 8 to move in the X direction by one shot (5 μm). Thus, the time for the wafer stage 8 to move in the X direction by one shot (5 μm) is equalized with the time for the electron beam to scan in the y direction by 20 shots (100 μm) to thereby avoid a waste of time. According to this process, it takes a time 2×105 times the scanning time (25 μsec) per unit scanning field 5 μm in length and 100 μm in width to obtain an image equivalent to one square centimeter of the wafer surface area. The inspection time per square centimeter of the surface area of the wafer is therefore 5 sec. The moving speed of the wafer stage 8 determined by the signal output speed of the TDI sensor is 200 mm/sec in the present embodiment. Accordingly, the inspection field can sufficiently be moved in the X direction by the movement of the wafer stage 8. In addition, during this duration of time, the electron beam can be allowed to scan the inspection filed in the y direction sufficiently. In the present embodiment, the signal output speed of the TDI sensor determines the inspection speed, and the process can inspect the sample at a higher speed if the signal output speed is improved. The apparatus according the present embodiment uses an electron optical system that can obtain scanning electron microscopic (SEM) images. FIG. 17 shows the configuration of the apparatus. As an electron source 2010, a condenser lens 222 and a SEM objective lens 233, corresponding components constituting the electron optical system of scanning electron microscopes are employed as intact. A Zr/O/W Schottky emitter is used as the electron source 2010. Electrons are extracted from the electron source 2010, are deflected by a beam separator 303, are largely changed in angle by an electrostatic sector electrode electron defector 2050, are supplied to a beam separator 243 and vertically enter an objective lens 206. The resulting electron beam forms a crossover in the front focal plane of the objective lens 206 and is converted into a sheet electron beam by action of the objective lens 206. The electrons constituting the sheet electron beam are uniform in a direction perpendicular to the surface of a wafer 207. A voltage to be applied to the wafer 207, the arrangement of an aperture and other configurations are the same as in First Embodiment. One of the features of the present embodiment is that a scanning electron microscopic image can be observed with high resolution without taking the wafer 207 out of the apparatus. This is significantly advantageous when an image of a detected defect after wafer inspection should be observed in detail. Specifically, a scanning electron microscopic image at an optional position of the wafer 207 can be observed by allowing the electron beam to go straight without the operation of the beam separator 303, and moving the wafer 207 to beneath the optical axis of the SEM objective lens 233 by action of a wafer stage 208. FIG. 17 also illustrates an imaging lens 211, magnifying lenses 213 and 214, a SEM condenser lens 222, a beam control system 228, a pre-charge control system 232, a sample chamber 252, and an image detection unit 263. The aforementioned function according to the present embodiment can also be applied to pattern check of wafers prior to inspection, setting of inspection conditions, and alignment in addition to observation of detected defects. The apparatus and method according to the present embodiment comprise a means or device for applying two electron beams at approximately the same position at approximately the same time. One of the two electron beams is an electron beam that impinges on the sample to form a potential difference between a normal pattern and a defective pattern, and the other is an electron beam that is reflected without impingement on the sample and forms a mirror electron image. FIG. 18 illustrates the configuration of the apparatus. An electron beam is emitted from an electron source 1, is deflected into an optical axis direction perpendicular to a wafer 7 by action of a beam separator 3 and passes through an objective lens 6 to form a sheet incident electron beam 301. The electrons constituting the incident electron beam 301 are uniform in a direction perpendicular to the surface of the sample (wafer) 7. A sample power supply 9 applies a negative potential approximately equivalent to the voltage of the electron source 1. The sample power supply 9 can also set a potential difference between an aperture lens electrode 41 and the sample 7 to thereby vary an electric field between the aperture lens electrode 41 and the sample 7. The electric field between these components serves to decelerate the incident electron beam. For example, to detect a shape defect, the detection sensitivity of a shape defect can be increased by setting the electric field for deceleration at a higher level than normal cases. The incident electron beam 301 is rapidly decelerated between the aperture lens electrode 41 and the sample 7 and is absorbed by the sample 7 or changes in direction directly above the sample 7 to form a mirror electron beam 302 by action of an electric field. The electric field reflects the shape and charge of semiconductor patterns formed on the surface of the sample 7. When the sample 7 carries an insulator on its surface, the incident electron beam 301 is injected into the sample 7 to make the insulator charged, and an image is obtained. FIGS. 19(a), 19(b), 19(c) and 19(d) are sectional views illustrating a sample. In the sample, an insulating film (SiO2 film) 311 is formed on a silicon (Si) substrate 310 to form a wafer, and contact holes are formed on the wafer and are filled with tungsten (W) to form tungsten electrodes. The electrodes include normal electrodes 312 in conduction with the substrate 310 at a low resistance and a faulty electrode 313 at the center. The faulty electrode 313 is not in satisfactory conduction with the substrate 310 due to its high resistance caused by a residue of SiO2 at the bottom of the electrode 313. When an electron beam having a very low energy with a mean number of secondary electrons excited per incident electron of less than 1 is applied to an insulator, the insulator becomes negatively charged by accumulation of negative charges (electrons). For example, when an electron beam having an illumination energy of less than or equal to about 30 eV is applied to SiO2, the mean number of secondary electrons excited per incident electron is less than 1, and the SiO2 becomes negatively charged. FIG. 19(a) illustrates early stages of negative charging of the insulating film 311 in which an incident electron beam is applied thereto. The incident electron beam 301 applied to the sample 7 has an energy spread including an illumination energy eV0 at the early stages before the sample 7 becomes charged. In this procedure, the illumination energy is determined by the potential difference between the sample 7 and the electron source 1 and by the energy spread of the incident electron beam 301. By keeping application of the incident electron beam 301 to the sample 7, the negative charge of the insulating film increases until it repels the incident electron beam having a low energy, and is stabilized at a potential at which the number of electrons entering the insulating film 311 balances the number of electrons escaping from the insulating film 311 to surroundings. In the case where electrons accumulated in the insulating film 311 do not escape to surroundings, the insulating film 311 becomes negatively charged to a potential at which the incident electron beam 301 does not enter the insulating film 311. Likewise, the electrodes become charged to a potential at which the number of electrons entering becomes proportional to the number of electrons escaping from the electrodes to surroundings. Specifically, the normal electrodes 312 are in conduction with the substrate 310 at a low resistance, allow electrons injected thereinto to escape to the substrate 310, and thereby become little charged negatively. In contrast, the faulty electrode 313 has a high resistance to thereby prevent electrons to escape to surroundings and becomes negatively charged. With reference to FIG. 19(b), equipotential surfaces 314 reflect the potentials of these electrodes 312 and 313, and the insulating film 311. An equipotential surface 315 of V0 is formed approximately directly above the insulating film 311 and the faulty electrode 313 and reflects part of the incident electron beam 301 having an energy lower than energy V0. In contrast, the equipotential surface 315 of V0 is not formed approximately directly above the normal electrodes 312, and the incident electron beam 301 impinges on the normal electrodes 312. Accordingly, an image of the mirror electron beam 302 reflects a difference in dimensions (shapes) of equipotential surfaces approximately directly above the normal electrodes 312 and the faulty electrode 313. FIG. 21(a) is a schematic diagram of a mirror electron image obtained in the following manner. A sample comprises 70 nm×70 nm square plug patterns arrayed three columns wide and three rows deep including normal portions of 0 V, a faulty portion at the center of −1 V, and a SiO2 film of −2 V. An electron beam having an energy higher by about 1.2 V than the potential of the normal portions of 0 V is applied to the sample and is reflected to form the mirror electron image. In the normal portions, electrons impinge on the pattern and are absorbed, and the normal portions exhibit dark contrast patterns. In contrast, an open defect of via-hole and contact hole at a high resistance is negatively charged and repels the electrons without impingement to form an image, and the open defect can be detected as a bright contrast pattern. The charged potential of the insulator 311 depends on the energy eV0 of the incident electron beam 301 and can optionally be controlled by varying the energy of the incident electron beam 301. All the electrons of the incident electron beam 301 having an energy of eV1 with respect to the potential (0 V) of the substrate 310 of the sample are reflected upon the equipotential surface of 316 of V1, and the shape of the equipotential surface 316 greatly differs between the vicinity directly above the normal electrodes 312 and the vicinity directly above the faulty electrode 313. Accordingly, an image of the mirror electron beam 302 formed by reflecting the electrons of the incident electron beam 301 having an energy of eV1 can distinguish the normal electrodes 312 and the faulty electrode 313. The time to stabilize the potential of the insulating film is roughly estimated as follows. Assuming that this configuration is a parallel-plate capacitor comprising electrodes sandwiching an insulating film, the capacitance of the capacitor C is expressed by the following equation: C=ε0εS/D, wherein D is the thickness of the insulating film; S is the area of the electrodes; ε0 is the electric constant; εr is the dielectric constant of the insulating film. For example, when a current of 1 μA is applied to an insulating film having a thickness of 0.4 μm and a εr of 4 in an irradiation area of 20 μm square, it takes about 35 nsec for the insulating film to be charged at a voltage of 1 V, and the insulating film is charged and stabilized within a moment. In the cases where the insulating film is not charged and stabilized within a moment, an electron beam illumination field is set in front in the direction of inspection (direction of scanning) in an area larger then an image acquisition field to thereby apply the electron beam prior to the image acquisition, as shown in FIG. 20. Alternatively, when the electron beam illumination field is set in an area approximately equal to that of the image acquisition field, the image acquisition circuit is controlled so as to apply the electron beam to the image acquisition field and to acquire the image after the charge of the image acquisition field becomes stable. Secondary electrons are formed from the wafer 7 as a result of impingement of the incident electron beam 301 on the wafer (sample) 7, in addition to the mirror electron beam 302 which is reflected without impingement on the wafer 7. The angles of secondary electrons distribute as shown in FIG. 7. By downsizing the contrast aperture 12 arranged in the vicinity of the back focal plane of the objective lens 6, almost all the secondary electrons having an angular distribution as above can be absorbed by the contrast aperture 12 to thereby allow the electron beam which is reflected-without impingement on the sample 7 alone to form an image. To detect electrical defects, the moving direction of electrons in the pattern must also be controlled depending on the state of junction with the substrate 310. Accordingly, there is also a need to charge the insulating film 311 positively in addition to charge the same negatively. To charge the insulating film 311 positively, an electron beam having a mean number of secondary electrons excited per incident electron of more than 1 must be applied. FIG. 19C illustrates early stages of illumination of the electron beam to charge the insulating film 311 positively. Initially, an incident electron beam 310 having an energy of eVb with respect to the sample potential is applied to the sample 7. When Vb is set at 500 V, for example, the mean number of secondary electrons from the sample 7 excited per incident electron is more than 1, the insulating film 311 becomes positively charged, the positively charged insulating film 311 yields a potential barrier, the potential barrier turns back electrons to the sample, and the turned-back electrons stabilize the potential of the insulating film 311. Thus, the charging of the insulating film proceeds until the potential is stabilized. After the insulating film 311 and the faulty electrode 313 become positively charged, an electron beam having an energy of eVp which does not impinge on the insulator pattern is applied as shown in FIG. 19(d). By this procedure, deformation in potential of positively charged portions can be detected, since an equipotential surface 317 of Vp greatly varies between the vicinity directly abode the normal electrodes 312 and the vicinity directly above the faulty electrode 313. When the energy of the incident electron beam 301 is increased, the incident electron beam 301 impinges on the insulating film 311 prior to the pattern due to positive charge of the insulating film 311. If the incident electron beam 301 impinges on the insulating film 311, the positively charged potential of the insulating film 311 is reduced. The energy of the incident electron beam 301 applied to the sample 7 must be controlled so as to prevent the incident electron beam 301 from impinging on the insulating film 311. However, the potential of the positively charged insulating film 311 can be controlled by applying an electron beam for positive charging and an electron beam for image acquisition to the sample 7 concurrently. This is because the potential of the positively charged insulating film 311 is stabilized under such a condition that the injection of electrons into the insulating film 311 due to the impingement of the electron beam for image acquisition is in equilibrium with the flow of electrons from the insulating film 311 due to application of the electron beam for positive charging. FIG. 21(b) is a schematic diagram of a mirror electron image obtained in the following manner. Specifically, the sample comprises electrodes arrayed three columns wide and three rows deep. The normal electrodes 312, the faulty electrode 313 at the center and the insulating film 311 are charged at 0 V, +1 V and +2 V, respectively, and the incident electron beam 301 having an energy 1.9 V lower than the potential of the normal electrodes 312 of 0 V to form a mirror electron image. An equipotential surface formed between the sample 7 and the aperture lens 41 differs in shapes between the vicinity of the normal patterns and the vicinity of the faulty pattern by reflecting the potential difference between the normal electrodes 312 and the faulty electrode 313. The trajectories of electrons which are reflected without impingement on the sample 7 greatly depend on the shape of the equipotential surface at the position where they are reflected. Accordingly, the position of image formation largely differs between an electron beam reflected in the vicinity of the normal pattern and an electron beam reflected in the vicinity of the faulty pattern. With reference to FIG. 21(b), the object plane of a projection lens is set in the vicinity of the imaging plane of electrons reflected in the vicinity of the normal patterns, and the normal patterns yield bright contrast patterns. Alternatively, the object plane of the projection lens may be set in the vicinity of the imaging plane of electrons reflected in front of the faulty pattern, and in this case, an image shown in FIG. 21A is obtained, which is an inverted image relative to the image in FIG. 21(b). To perform the above procedures with one electron source, a relative potential between the sample power supply 9 and the electron source power supply (accelerating power supply) 23 may be periodically switched. Specifically, the voltage applied to the electron source power supply 23 or to the sample power supply 9 may be periodically switched. For example, the voltage applied to the electron source power supply 23 is periodically changed with reference to the voltage of the sample power supply 9, as shown in FIG. 22. Initially, the electron beam is moved to a predetermined inspection field using the sample stage 8 or the illumination system deflector 5, a voltage of +Vb, for example 500 V, for positively charging the sample 7 is applied from the electron source power supply 23 to the electron source 1 to apply the electron beam to the inspection field for a predetermined time to thereby charge the inspection field positively. Next, the voltage applied to the electron source power supply 23 is switched to the voltage for image acquisition of −Vp and is applied to the electron source 1. Thus, an electron beam having an energy lower by −eVp than the potential of the sample 7 is applied to the predetermined inspection field, and by repeating this procedure periodically on every inspection field, images can continuously be obtained while keeping the sample 7 positively charged. The apparatus according to the present embodiment further comprises an electron source for concurrently applying an electron beam having a mean number of secondary electrons excited per incident electron of more than 1, in addition to an electron source for applying an electron beam that turns back in front of the sample to form an image. By this configuration, the sample is positively charged and images are obtained concurrently. FIG. 23 illustrates the configuration of the apparatus. An electron source 1 has a potential slightly more positive than that of a wafer 7. An incident electron beam 301 emitted from the electron source 1 turns back directly above the wafer 7 to form a mirror electron beam 302. A second electron source 71 has a potential difference of about 500 V with respect to the wafer 7, and an electron beam 303 emitted from the second electron source 71 has an energy of 500 eV and is applied to the wafer 7. A magnetic prism 73 is covered with a shield electrode 74 floated at a potential of Vs. Accordingly, an electron beam entering the magnetic prism 73 is decelerated and is deflected by an energy of eVs. In contrast, en electron beam emitted from the magnetic prism 73 is accelerated by an energy of eVs. For example, the electron beam 301 emitted from the electron source 1 is decelerated to about 500 V immediately in front of the magnetic prism 73 and enters the magnetic prism 73. The electron beam 303 emitted from the second electron source 71 is decelerated to about 1000 V immediately in front of the magnetic prism 73 and enters the magnetic prism 73. When the magnetic flux density in the magnetic prism 73 is set at 5 gausses, the electron beam 301 and the electron beam 302 enter the same optical axes 304 in trajectories of cyclotron radii of 150 mm and about 210 mm, respectively. By this procedure, one inspection field can be illuminated with two electron beams having different energy concurrently. The mirror electron beam 302 turned back in the vicinity directly above the sample 7 enters the magnetic prism 703 and is deflected in the opposite direction to the incident electron beam and is projected via an intermediate lens 13 and a projection lens 14 onto a phosphor screen 15. With reference to FIG. 24, the apparatus according to the present embodiment includes a second electron source 71 and a second illumination lens 72. In this apparatus, an electron beam 303 is emitted from the second electron source 71 and impinges on a lower part of an aperture lens electrode 41 to yield elastically scattered electrons 304. The elastically scattered electrons 304 are then applied to a sample 7. If an energy component of the elastically scattered electrons 304 in the optical axis direction is larger than the energy reduced by action of the voltage applied between the aperture lens electrode 41 and the sample 7, the elastically scattered electrons 304 reach the sample surface. For example, when the elastically scattered electrons 304 have a peak in directional distribution at an angle of 30 degrees to the optical axis 402, the sample 7 can be charged positively by accelerating the electron beam 303 emitted from the second electron source 71 at a voltage of 1077 V. The voltage of 1077 V is 577 V higher than the voltage of 500 V applied between the aperture lens electrode 41 and the sample 7. The voltage of 577 V equals 500 V/cos 30°. The angle and position of the electron beam 303 brought into impingement on the lower part of the electrode 41 are set so that the electron beam 303 has approximately the same illumination position with the illumination electron beam 301 for imaging in consideration that the elastically scattered electrons 304 change their trajectories in the electric field for deceleration. The apparatus further includes an aligner 75 which is capable of inclining the beam and moving the beam position to thereby control the illumination position of the electron beam 303. With reference to FIG. 25, the apparatus according to the present embodiment includes a light source 251 as a means for charging a sample 7 to thereby apply a light ray 252 to the sample 7 concurrently with an electron beam. By applying a light ray having an energy larger than work functions of materials constituting the sample 7 to the sample 7, the sample 7 emits photoelectrons and is thereby positively charged. FIGS. 26(a) and 26(b) are sectional views of the sample 7 in which an insulating film (SiO2 film) 311 is formed on a silicon (Si) substrate 310 to form a wafer, and contact holes are formed on the wafer and are filled with tungsten (W) plugs. An open defect with a high resistance due to a residue of SiO2 is present at the bottom of a plug at the center. FIG. 26(a) illustrates early stages in which an incident electron beam is applied to allow an insulating film 311 to be positively charged. The potential of an electron source 1 is set at a positive potential +Vp with respect to the potential of the sample 7, an electron beam 301 emitted from the electron source 1 is decelerated between an aperture electrode 41 and the sample 7 and changes its direction in the vicinity directly above the sample 7 to form a mirror electron beam 302. The work function of SiO2 is about 9 eV. Accordingly, by applying ultraviolet rays having an energy higher than 9 eV as the light ray 252 concurrently, the insulating film 311 composed of SiO2 emits photoelectrons 305. Accordingly, the insulating film 311 becomes positively charged and an equipotential surface 314 in the vicinity directly above the insulating film 311 curves as shown in FIG. 26(b). When the insulating film 311 becomes further positively charged, part of the incident electron beam 301 reaches the insulating film 311, and the positively charged potential of the insulating film 311 is stabilized under such a condition that the amount of the photoelectrons emitted from the insulating film 311 becomes equal to the amount of the incident electron beam 301 reaching the insulating film 311. An image of the mirror electron beam 302 formed in this state includes a dark portion corresponding to the insulating film 311 and reflects the potential deformation in the vicinity of the insulating film 311. Thus, the resulting image exhibits a high contrast between the normal portions and the abnormal (faulty) portion. An optical axis 404 of the light ray 252 emitted from the light source 251 and an optical axis 402 of the illumination electron beam 301 are controlled so that the light ray 252 and the illumination electron beam 301 approximately coincide with each other on the sample 7. When the illumination field of the light ray 252 on the sample 7 is set larger than the illumination field of the illumination electron beam 301, and the stage is moved to acquire the image continuously, it is also accepted that the light ray 252 is applied to the sample 7 to thereby charge the sample 7 positively, and then the illumination electron beam 301 is applied to the sample 7. The photoelectrons 305 generated concurrently can be absorbed by a contrast aperture 12 arranged in the light path of the mirror electron beam 302 to thereby yield a mirror electron image with a high contrast. According to the present embodiment, two E×B deflectors and two spherical electrostatic prisms are used in combination as the beam separator 3 to thereby separate an incident electron beam from a mirror electron beam. FIG. 27 schematically illustrates the configuration of the apparatus according to the present embodiment. In this configuration, the mirror electron beam reflected from the sample is set so as to travel in a straight line in an E×B deflector 54. In addition, with respect to an incident electron beam 301, the aberrations of the illumination system and the imaging system can be reduced by operating the two E×B deflectors in the opposite directions and by operating the two electrostatic prisms in the opposite directions to thereby optimize conditions for the lenses to form images. Additionally, the imaging system and the illumination system can be arranged in a direction perpendicular to the stage to thereby minimize effects of, for example, mechanical vibration on the electron optical system. The configuration of this apparatus will be described in further detail below. When the mirror electron beam reflected from the sample enters the E×B deflector 54, the E×B deflector 54 operates so as to cancel the activities of a magnetic field and an electric field with each other to allow the mirror electron beam to travel in a straight line in the E×B deflector 54. In addition, by positioning an image point of the mirror electron beam in the vicinity of the E×B deflector 54, the lens aberration generated in the E×B deflector 54 is minimized. The incident electron beam 301 emitted from the electron source forms an image on an imaging point 403 on an optical axis 401 by action of a condenser lens, enters an E×B deflector 51 and is deflected at an angle of about 15 degrees. The deflected incident electron beam 301 enters an electrostatic prism 52, travels in a circular trajectory while rotating at a predetermined angle and is converged. The incident electron beam 301 exits the electrostatic prism 52, enters the electrostatic prism 53, rotates in the opposite direction and is converged. The incident electron beam 301 exits the electrostatic prism 53, enters the E×B deflector 54, is deflected at an angle of about 15 degrees in the opposite direction as in the E×B deflector 51, enters the optical axis 402 of the objective lens in the illumination system to thereby form an image at the image point 404. The aberration between the two electrostatic prisms can be corrected almost completely by controlling the distance between the electrostatic prism 52 and the image point 401 to be approximately equal to the distance between the electrostatic prism 53 and the image point 404 and by operating electrostatic prisms 52 and 53 in such a manner that the incident electron beam 301 exits the electrostatic prism 52 approximately in parallel and enters the electrostatic prism 53 approximately in parallel. For example, when the incident electron beam 301 having an incident energy of 10 keV enters the electrostatic prism 52 having a rotation angle of 200 degrees and a radius of 50 mm from a distance of about 170 mm corresponding to a distance between the electrostatic prism 52 and the condenser lens image point 403, the incident electron beam 301 becomes approximately parallel when it exits the electrostatic prism 52. Thereafter, the incident electron beam 301 enters the electrostatic prism 53, exits the same and converges at a symmetric point at a distance of about 170 mm from the electrostatic prism 53 corresponding to a distance between the electrostatic prism 53 and the image point 404. Under this condition, the aberrations between the electrostatic prism 52 and the electrostatic prism 53 cancel with each other and become approximately zero, and the incident electron beam 301 with a high intensity can be applied to the sample. A configuration according to the present embodiment includes a means for accurate inspection even if the height or inclination of the sample varies. A large-diameter wafer invites warpage and other deformation and thereby varies in its height and/or inclination largely in the wafer plane. Accordingly, the configuration for use herein should essentially have a means for avoiding image point variation even if the sample height changes, and a means for ensuring an incident electron beam enters the sample always vertically even if the sample inclination changes. FIG. 28 illustrates a control process for ensuring the incident electron beam 301 to enter the sample vertically even if the sample wafer inclines. Provided that the z direction is set as the optical axis and the sample surface is in a plane passing through the point z=0 and inclining at an angle of θ in the X direction in xyz rectangular coordinates, whereas the sample surface is in the xy plane where z=0 under normal β ≅ 2 3 ⁢ θ conditions, the z direction component Ez and X direction component Ex of a field intensity E are approximated at E and (1-z/L)E, respectively, wherein L is the distance between a sample 7 and an aperture lens electrode 41. By solving the equations of motion of electrons in the x and z directions, it is understood that the incident electron beam 301 enters the sample 7 approximately vertically whereas the incident electron beam 301 most approaches the sample 7 when the angle β of the incident electron beam 301 passing the aperture lens 41 approximately satisfies the following condition: In addition, the focal distance f of the aperture lens 41 can be approximated at 4L when the diameter of the aperture of the aperture lens 41 is sufficiently lower than L. The incident electron beam 301 entering the aperture lens 41 has only to be inclined at an angle of 2 sin θ under this condition. For example, the incident electron beam 301 can always be applied to the sample 7 vertically by arranging an aligner 42 between the objective lens 6 and the aperture lens 41 to ensure the incident electron beam 301 to incline at an angle of about 2θ when the sample inclines at an angle of θ in the X direction. The aligner 42 is preferably an electrostatic aligner so as to act upon the incident electron beam 301 and the mirror electron beam 302 in the same direction. The variation in sample height is corrected in the following manner. The focal distance f of the aperture lens 41 is approximated at 4L, and a virtual image of the mirror electron beam reflected from the sample is formed at a point L/3 below the sample. The object plane of the objective lens 6 coincides with the virtual image plane of the aperture lens 41. The virtual image plane of the aperture lens 41 changes with a change in sample height and thereby changes the object plane of the objective lens 6. Accordingly, the image can be controlled to always keep its sharpness even if the sample height varies, by calculating L from the sample height, calculating the virtual image plane of the aperture lens 41, i.e., the object plane of the objective lens 6, and controlling the lens excitation of the objective lens 6 so as to keep the image plane of the objective lens 6 constant. The height distribution of the semiconductor wafer 7 is determined prior to inspection upon several tens or more height measuring points using a height measuring means such as a height gauge 26. The inclination of a specific point of the sample can be obtained by dividing the difference in height between the specific point and an adjacent height measuring point by the distance between the two points. By averaging plural measurements on the inclination with adjacent plural height measuring points, the precision of the inclination measured can be improved. An inclination datum corresponding to an optional inspection point can be found by interpolation of the inclination data of the height measuring point. Upon actual inspection, the intensity (excitation) of the aligner 42 is controlled based on the data on the wafer inclination corresponding to the inspection position coordinates to thereby apply the incident electron beam 301 always vertically to the sample 7 within the wafer plane. While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the sprit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
	claims	1. A high-density storage rack for nuclear fuel assemblies comprising:a plurality of body parts each havinga basket cell configured to store a corresponding nuclear fuel assembly and having a generally square tube shape elongated in a height direction thereof, anda plurality of connection plates integrally connecting basket cells adjacent to each other and maintaining a predetermined distance therebetween;a base plate fixedly coupling an underside of each of the basket cells thereto and having a plurality of drain holes, each of the drain holes being formed in a circular shape at a position corresponding to a center portion of the basket cell;a plurality of cap parts each closing an upper end of a corresponding one of the plurality of body parts, wherein each of the plurality of cap parts comprisesa cap being a flat shape and closing an upper end of the basket cell,a crane adapter fixed to an upper surface of the cap,a round rod disposed at an underside of said cap, being a cylindrical shape as a whole and extending downwards from the cap, an upper end portion of the round rod passing through a center portion of the cap and being fixed directly to the crane adapter and a lower portion of the round rod suspending the nuclear fuel assembly therefrom, the round rod includinga lifting hook insertion hole formed at the lower portion of the round rod along a central axis of the round rod and having a circular shape closed in all directions by the round rod when taken from a bottom view,a lifting hook fixing pin hole passing straight through the lower portion of the round rod in a perpendicular direction to the central axis of the round rod and forming a cross-shape in combination with the lifting hook insertion hole, anda lifting hook suspending the nuclear fuel assembly therefrom, the lifting hook being inserted into the lifting hook insertion hole;a fixing groove formed in a bottom surface of the crane adapter in a vertical direction to the cap, anda bolt inserted into the fixing groove through the cap in the vertical direction to fix the crane adapter to the cap, wherein the bolt is disposed outside the center portion of the cap through which the round rod passes;a plurality of cap flanges each fixedly coupled to an upper end portion of the basket cell, wherein a lower part of each of the cap flanges surrounds an outer surface of the upper end portion of the basket cell along four edges of the basket cell, a middle part of said each of the cap flanges protrudes inwardly and directly contacts the top surface of the basket cell and a lower surface of the cap therebetween for preventing the cap from coming into contact with the top surface of the basket cell, thereby absorbing impact energy between the cap and the basket cell, and an upper part of said each of the cap flanges is formed to correspond to a shape of the cap for securely mounting the cap thereon in such a manner that an inner surface of the upper part of each of the cap flanges surrounds edges of the cap; anda plurality of bridge pier parts disposed on an underside of the base plate, each of the bridge pier parts supporting the load applied from the high-density storage rack and the nuclear fuel assemblies, when the nuclear fuel assemblies are stored in the high-density storage rack, and adjusting a horizontal level of the storage rack so as to place the storage rack at a horizontal state on a bottom surface of a storage tank when the storage rack is disposed in the storage tank, said each of the bridge pier parts includinga support nut coupled to the underside of the base plate and having a threaded hole thereinside such that the threaded hole directly communicates with an inside of the basket cell through corresponding one of the drain holes,a support bolt insertedly fastened to the threaded hole of the support nut and adjusting the height to allow the high-density storage rack to be placed at a horizontal level, the support bolt having a support bolt drain hole formed along a center axis of the support bolt, the support bolt drain hole being open to both sides of the support bolt, anda support plate coupled to the underside of the support bolt and distributing the load applied from the support bolt to the bottom surface of the storage tank,wherein the support bolt drain hole shares the center axis thereof with said corresponding one of the drain holes of the base plate and remains open to the both sides of the support hole at all times so as to discharge water generated in the basket cell to the outside through said corresponding one of the drain holes of the base plate and the support bolt drain hole. 2. The high-density storage rack for nuclear fuel assemblies according to claim 1, wherein each of the basket cells has a plurality of ventilation holes at upper portion and lower portion of basket cells, through which air flows inside and outside the basket cells. 3. The high-density storage rack for nuclear fuel assemblies according to claim 2, wherein the connection plates connecting the adjacent basket cells to each other are disposed alternately to each other. 4. The high-density storage rack for nuclear fuel assemblies according to claim 3, wherein the support bolt has a height adjuster disposed along the outer periphery of the lower portion thereof in such a manner as to adjust the height of the support bolt by contacting with a predetermined tool.
	description	An aspect of the present invention relates to a scintillator panel and a radiation detection device. A method for manufacturing a radiation detection device is described in Patent Document 1. In the method described in Patent Document 1, first, a mask is disposed at a front stage of photoelectric conversion elements arrayed on an element base, and a scintillator element is formed on the photoelectric conversion elements by vapor deposition of a scintillator material by use of the mask. Next, a light reflection material is applied or vapor-deposited to the whole of the element. At this time, grooves for separating the scintillator element are filled with the light reflection material. Then, light shielding processing is applied with aluminum foil or the like, to obtain a radiation detection device. Patent Document 1: Japanese Patent Application Laid-Open No. H9-325185 However, as the method described above, when grooves for separating a scintillator element are filled with a light reflection material (or a light absorbing material), to form a light shielding layer, a solvent or the like contained in the light reflection material (or the light absorbing material) may permeate among a plurality of columnar crystals composing the scintillator element in some cases. In such a case, the characteristics of the scintillator element having deliquescency may be degraded. In particular, in the case where the columnar crystals are made thicker (for example, its film thickness is approximately 500 μm), the gaps among the columnar crystals are likely to be widened, that has caused a problem. An aspect of the present invention has been achieved in consideration of such circumstances, and an object of the present invention is to provide a scintillator panel and a radiation detection device which are capable of preventing characteristic degradation associated with formation of a light shielding layer. In order to solve the above-described problem, a scintillator panel according to an aspect of the present invention, which is for converting radiation into scintillation light, the scintillator panel includes a substrate having a front surface and a back surface, a plurality of scintillator sections formed on the front surface of the substrate so as to be separate from one another, and having upper surfaces and side surfaces extending from the upper surfaces toward the front surface of the substrate, solvent permeation blocking film formed on the upper surfaces and the side surfaces of the scintillator sections so as to cover the upper surfaces and the side surfaces of the scintillator sections, and a light shielding layer formed on the solvent permeation blocking film, and for shielding scintillation light, and in the scintillator panel, the scintillator section is composed of a plurality of columnar crystals of a scintillator material, the solvent permeation blocking film is formed so as not to fill gaps between the side surfaces of the scintillator sections adjacent to one another, and the light shielding layer is formed on the solvent permeation blocking film on the side surfaces of the scintillator sections so as to fill the gaps. In this scintillator panel, the plurality of scintillator sections are formed on the substrate so as to be separate from one another, and the solvent permeation blocking film is formed on the side surfaces and the upper surfaces of the respective scintillator sections so as not to fill the gaps among those scintillator sections (among the side surfaces of the scintillator sections). Then, in this scintillator panel, the light shielding layer is formed on the solvent permeation blocking film so as to fill the gaps between the scintillator sections. Accordingly, at the time of forming the light shielding layer so as to fill the gaps between the scintillator sections with a predetermined material, a solvent or the like in the predetermined material does not permeate among the columnar crystals composing the scintillator sections. Therefore, in accordance with this scintillator panel, it is possible to prevent characteristic degradation associated with formation of a light shielding layer. In a scintillator panel according to an aspect of the present invention, the light shielding layer may be formed on the solvent permeation blocking film on the side surfaces of the scintillator sections, so as to cover the side surfaces of the scintillator sections. In this case, it is possible to securely confine scintillation light to each scintillator section. In a scintillator panel according to an aspect of the present invention, the light shielding layer may be further formed on the solvent permeation blocking film on the upper surfaces of the scintillator sections, so as to cover the upper surfaces of the scintillator sections. In this case, it is possible to securely confine scintillation light to each scintillator section. In a scintillator panel according to an aspect of the present invention, a plurality of convex portions projecting from the front surface in a direction from the back surface toward the front surface of the substrate, and concave portion defined by the convex portions may be formed on the substrate, and the scintillator sections may be respectively formed on upper surfaces of the convex portions. In this case, it is possible to form the scintillator sections so as to securely separate from one another. In a scintillator panel according to an aspect of the present invention, the solvent permeation blocking film may be further formed on side surfaces of the convex portions so as to cover the side surfaces of the convex portions. In this case, it is possible to securely prevent permeation of a solvent among the columnar crystals at the time of forming the light shielding layer. In a scintillator panel according to an aspect of the present invention, the solvent permeation blocking film may be further formed on a bottom surface of the concave portion so as to cover the bottom surface of the concave portion. In this case, not only is it possible to more securely prevent permeation of a solvent among the columnar crystals, but it is also easier to form the solvent permeation blocking film. Here, in order to solve the above-described problem, a radiation detection device according to an aspect of the present invention includes the scintillator panel described above, and the substrate is a sensor panel having a plurality of photoelectric conversion elements arrayed so as to be optically coupled to the scintillator sections. Because this radiation detection device includes the scintillator panel described above, it is possible to prevent characteristic degradation associated with formation of a light shielding layer. In accordance with an aspect of the present invention, it is possible to provide a scintillator panel and a radiation detection device which are capable of preventing characteristic degradation associated with formation of a light shielding layer. Hereinafter, a scintillator panel according to an embodiment will be described in detail with reference to the drawings. In addition, in the respective drawings, the same or the corresponding portions are denoted by the same reference signs, and overlapping descriptions thereof will be omitted. Scintillator panels according to the following embodiments are for converting incident radiation R such as X-rays into scintillation light such as visible light, and can be used as devices for radiation imaging, for example, in mammography equipment, chest examination equipment, CT devices, dental oral photographic apparatuses, radiation cameras, and the like. [First Embodiment] First, a scintillator panel according to a first embodiment will be described. FIG. 1 is a side view of the scintillator panel according to the first embodiment. FIG. 2 is a partial plan view of the scintillator panel shown in FIG. 2. As shown in FIGS. 1 and 2, the scintillator panel 1 includes a rectangular substrate 10. The substrate 10 has a front surface 10a and a back surface 10b facing each other. The substrate 10 has a concave-convex pattern Pa formed on the front surface 10a. As a material of the substrate 10, for example, metal such as Al or SUS (stainless steel), a resin film such as polyimide, polyethylene terephthalate, or polyethylene naphthalate, a carbon-based material such as amorphous carbon or carbon fiber reinforced plastic, an FOP (a Fiber Optic Plate: an optical device in which a large number of optical fibers with a diameter of several microns are bundled (for example, J5734 manufactured by Hamamatsu Photonics K.K.)), etc., may be used. As a material of the concave-convex pattern Pa, for example, a high-aspect resist such as epoxide resin (KMPR or SU-8 manufactured by Nippon Kayaku Co., Ltd., etc.), silicon, glass, or the like may be used. In particular, a material of the convex portions composing the concave-convex pattern Pa may be a material which is transmissive to scintillation light generated in a scintillator section 20 which will be described later. The concave-convex pattern Pa is formed from a plurality of convex portions 11 and a concave portion 12 defined by the convex portions 11. That is, the plurality of convex portions 11 and concave portion 12 are formed on the substrate 10. Each of the convex portions 11 projects from the front surface 10a along a direction toward the front surface 10a from the back surface 10b of the substrate 10 (here, an incident direction of the radiation R, and a direction perpendicular to the front surface 10a and the back surface 10b of the substrate 10). Each of the convex portions 11 is formed into a rectangular parallelepiped. The convex portions 11 are arrayed periodically in a two-dimensional array on the front surface 10a of the substrate 10. Accordingly, the concave portion 12 defined by the convex portions 11 is a groove showing rectangular lattice-shapes in planar view. With respect to the respective dimensions of this concave-convex pattern Pa, a width (groove width) W of the concave portion 12 may be set to approximately 35 μm in the case where a pitch (a cycle of forming the convex portions 11) P between the convex portions 11 is approximately 100 μm, the width W of the concave portion 12 may be set to approximately 20 μm to 40 μm in the case where the pitch P between the convex portions 11 is approximately 127 μm, and the width W of the concave portion 12 may be set to approximately 50 μm to 70 μm in the case where the pitch P between the convex portions 11 is approximately 200 μm. Further, a height H of the convex portion 11 may be set to approximately 2.5 μm to 50 μm. In particular, in the present embodiment, the pitch P between the convex portions 11 is approximately 127 μm, the width W of the concave portion 12 is approximately 45 μm, and the height H of the convex portion 11 is approximately 15 μm. The scintillator panel 1 includes a plurality of scintillator sections 20. The scintillator sections 20 are formed by a plurality of columnar crystals C standing in a forest-like manner, and there are gaps of approximately several μm among the columnar crystals C. The plurality of scintillator sections 20 are separated from one another. The scintillator sections 20 are respectively formed on upper surfaces 11a of the convex portions 11. Accordingly, the scintillator panel 1 includes the scintillator sections 20 the number of which corresponds to the number of the convex portions 11. The scintillator section 20 has an upper surface 20a, and side surfaces 20b extending from the upper surface 20a toward the front surface 10a of the substrate 10 so as to reach the upper surface 11a of the convex portion 11. The scintillator section 20 may be formed of a scintillator material forming columnar crystals such as CsI (cesium iodide), for example. The scintillator section 20 extends along the incident direction of the radiation R (a direction substantially vertical to the substrate 10) from the upper surface 11a of the convex portion 11. More specifically, the scintillator section 20 is composed of a plurality of columnar crystals C of a scintillator material extending along the incident direction of the radiation R from the upper surface 11a of the convex portion 11. The columnar crystal C composing the scintillator section 20 may show a tapered shape so as to expand its diameter with increasing distance from the upper surface 11a of the convex portion 11. In addition, a height (scintillator film thickness) T of the scintillator section 20 may be, for example, approximately 100 μm to 600 μm. In addition, by selecting a radiation (X-rays) transmissive base member as the substrate 10, it is possible to allow the radiation R to be incident from the back surface 10b of the substrate 10. Here, as described above, because the scintillator sections 20 are separated from one another, gaps 30 are formed between the side surfaces 20b of the scintillator sections 20 adjacent to one another. That is, the scintillator sections 20 are sectioned with the gaps 30, to be separate from one another. Then, the gaps 30 are greater in width than gaps among the plurality of columnar crystals C composing the scintillator sections 20. Here, the gap 30 extends from the upper end portion including the upper surface 20a of the scintillator section 20 (the end portion on the opposite side of the convex portion 11) up to the base end portion of the scintillator section 20 in contact with the upper surface 11a of the convex portion 11 (the end portion on the convex portion 11 side), and continues to the concave portion 12. Accordingly, a width of the gap 30 is, for example, approximately the width W of the concave portion 12. The gaps 30 are, as will be described later, filled with a solvent permeation blocking film 40 and a light shielding layer 50. The scintillator panel 1 includes the solvent permeation blocking film 40. The solvent permeation blocking film 40 is formed on the upper surfaces 20a and the side surfaces 20b of the scintillator sections 20 so as to cover the upper surfaces 20a and the side surfaces 20b of the scintillator sections 20. In particular, the solvent permeation blocking film 40 is formed so as not to fill the gaps 30 between the side surfaces 20b of the scintillator sections 20 adjacent to one another (that is, so as to keep the gaps 30). Accordingly, gaps 41 are formed between a portions of the solvent permeation blocking film 40 on the side surfaces 20b of the scintillator sections 20 adjacent to one another. The gap 41 extends from the upper end portion up to the base end portion of the scintillator section 20, and continues to the concave portion 12. Here, because a thickness FT of the solvent permeation blocking film 40 gradually increases in thickness from the base end portion toward the upper end portion of the scintillator section 20, a width of the gap 41 gradually decreases from the base end portion toward the upper end portion of the scintillator section 20. The thickness FT of the solvent permeation blocking film 40 is to an extent so as not to fill the gap 30 as described above, and may be set to, for example, approximately 1 μm to 5 μm, and may be set to approximately 2 μm to 3 μm. This solvent permeation blocking film 40 may be formed from, for example, (1) parylene (poly-para-xylene), (2) polyurea, (3) SiO2 or SiO, (4) SiN, (5) an organic or inorganic hybrid film of the above-described (1) to (4), (6) an Al2O3 layer or an MgF2 layer which is formed by an ALD (Atomic Layer Deposition) method, or the like. The scintillator panel 1 includes a light shielding layer 50. The light shielding layer 50 is a light reflection layer reflecting scintillation light generated in the scintillator section 20, or a light absorbing layer absorbing scintillation light generated in the scintillator section 20. That is, the light shielding layer 50 is for shielding scintillation light generated in a predetermined scintillator section 20, to confine the scintillation light to the predetermined scintillator section 20. For that, the light shielding layer 50 is formed on the solvent permeation blocking film 40 on the side surfaces 20b of the scintillator sections 20 so as to cover the side surfaces 20b of the scintillator sections 20. In particular, the light shielding layer 50 is formed so as to fill the gaps 30. More specifically, the light shielding layer 50 is formed so as to fill the gaps 41 defined in the gaps 30 by the solvent permeation blocking film 40. Further, the light shielding layer 50 is formed in the concave portion 12 as well so as to fill the concave portions 12. Further, the light shielding layer 50 is not formed on the solvent permeation blocking film 40 on the upper surfaces 20a of the scintillator sections 20. That is, the light shielding layer 50 is formed on the solvent permeation blocking film 40 so as to cover the whole of the respective scintillator sections 20 except the upper end portions of the scintillator sections 20 (in other words, the respective scintillator sections 20 are covered with the solvent permeation blocking film 40 at the upper end portions thereof and are exposed from the light shielding layer 50). This light shielding layer 50 may be composed of, for example, an ink, a coating material, or a paste containing organic pigment, inorganic pigment, or metallic pigment, or a metallic nano-ink containing metallic nanoparticles such as Ag, Pt, or Cu, or various types of dye compounds (hereinafter called “filling material”). Further, the light shielding layer 50 may be formed by forming a metallic film by an ALD method (Atomic Layer Deposition method), nonelectrolytic plating, or the like. In this way, provided that the light shielding layer 50 is fanned so as to cover the side surfaces 20b of the scintillator sections 20, it is possible to confine scintillation light generated in a predetermined scintillator section 20, to the predetermined scintillator section 20, which makes it possible to realize high brightness and high resolution. The scintillator panel 1 composed as described above can be manufactured, for example, as follows. That is, first, a base member for the substrate 10 is prepared, and a material of the concave-convex pattern Pa is applied onto the base member and dried to be formed thereon. Next, the concave-convex pattern Pa is formed on the base member by photolithograph, to fabricate the substrate 10 having the concave-convex pattern Pa in desired dimensions. Or, the concave-convex pattern Pa may be formed on the base member by screen-printing. Next, the scintillator sections 20 are formed on the respective upper surfaces 11a of the convex portions 11 of the substrate 10 by utilizing a vapor deposition method and/or a laser processing method, etc. By controlling the respective vapor deposition conditions (a degree of vacuum, a vapor deposition rate, a substrate heating temperature, an angle of vapor flow, and the like), it is possible to fonni the scintillator sections 20 as described above on the concave-convex pattern Pa. Next, the solvent permeation blocking film 40 is formed with a thickness so as not to fill the gaps 30 between the side surfaces 20b of the scintillator sections 20 adjacent to one another, on the upper surfaces 20a and the side surfaces 20b of the scintillator sections 20. The thickness FT of the solvent permeation blocking film 40 may be set to, for example, approximately 1 μm to 2 μm. Then, the light shielding layer 50 is formed on the solvent permeation blocking film 40. More specifically, the light shielding layer 50 is formed by applying the above-described filling material onto the solvent permeation blocking film 40 (that is, by filing the gaps 30 (gaps 41) with the filling material) under vacuum. The scintillator panel 1 is manufactured by the above-described processes. As described above, in the scintillator panel 1 according to the present embodiment, the plurality of scintillator sections 20 are formed on the substrate 10 so as to be separate from one another, and the solvent permeation blocking film 40 is formed on the side surfaces 20b and the upper surfaces 20a of the respective scintillator sections 20 so as not to fill the gaps 30 among those scintillator sections 20 (between the side surfaces 20b of the scintillator sections 20). Then, in the scintillator panel 1 according to the present embodiment, the light shielding layer 50 is formed on the solvent permeation blocking film 40. Accordingly, at the time of forming the light shielding layer 50 so as to fill the gaps 30 between the scintillator sections 20 with a filling material, because the scintillator sections 20 are covered with the solvent permeation blocking film 40, a solvent or the like in the filling material does not permeate among the columnar crystals C composing the scintillator sections 20. Therefore, in accordance with this scintillator panel 1 according to the present embodiment, it is possible to prevent characteristic degradation associated with formation of the light shielding layer 50. Further, if a solvent in the filling material permeates among the columnar crystals C composing the scintillator sections 20 at the time of forming the light shielding layer 50, the viscosity of the filling material is increased, and the gaps 30 may not be appropriately filled with the filling material in some cases. In accordance with the scintillator panel 1 according to the present embodiment, because it is prevented that a solvent in the filling material permeates among the columnar crystals C, such a problem is not caused in any case, and it is possible to appropriately fill the gaps 30 with the filling material. [Second Embodiment] Next, a scintillator panel according to a second embodiment will be described. FIG. 3 is a side view of the scintillator panel according to the second embodiment. As shown in FIG. 3, a scintillator panel 1A according to the present embodiment is, as compared with the scintillator panel 1 according to the first embodiment, different in the point that the scintillator panel 1A further includes a light shielding layer 60. The light shielding layer 60 is, in the same way as the light shielding layer 50, for shielding scintillation light, and is a light reflection layer reflecting scintillation light, or a light absorbing layer absorbing scintillation light. The light shielding layer 60 is formed on the solvent permeation blocking film 40 and the light shielding layer 50 so as to cover the solvent permeation blocking film 40 on the upper surfaces 20a of the scintillator sections 20 exposed form the light shielding layer 50 (that is, so as to cover the upper surfaces 20a of the scintillator sections 20). In addition, the light shielding layer 60 may be formed integrally with the light shielding layer 50, or may be formed separately from the light shielding layer 50. Further, the light shielding layer 50 may be formed from a material which is the same as that of the light shielding layer 50, or may be formed from a material different from that of the light shielding layer 50. This scintillator panel 1A may be manufactured such that, after the scintillator panel 1 is manufactured as described above, the filling material disposed on the solvent permeation blocking film 40 on the upper surfaces 20a of the scintillator sections 20 are removed, and thereafter a predetermined material (for example, the above-described filling material) is applied onto the solvent permeation blocking film 40 and the light shielding layer 50, to form the light shielding layer 60. In accordance with the scintillator panel 1A according to the present embodiment, in the same way as the scintillator panel 1 according to the first embodiment, it is possible to prevent permeation of a solvent or the like among the columnar crystals C at the time of forming the light shielding layers 50 and 60. Further, in accordance with the scintillator panel 1A according to the present embodiment, by further providing the light shielding layer 60, it is possible to securely confine scintillation light generated in a predetermined scintillator section 20, to the predetermined scintillator section 20. [Third Embodiment] Next, a scintillator panel according to a third embodiment will be described. FIG. 4 is a side view of the scintillator panel according to the third embodiment. As shown in FIG. 4, a scintillator panel 1B according to the present embodiment is, as compared with the scintillator panel 1 according to the first embodiment, different in the point that the scintillator panel 1B includes solvent permeation blocking film 40A in place of the solvent permeation blocking film 40. In addition, in the same way as the first embodiment, by selecting a radiation (X-rays) transmissive base member as the substrate 10, it is possible to allow the radiation R to be incident from the back surface 10b of the substrate 10. The solvent permeation blocking film 40A is formed on the upper surfaces 20a and the side surfaces 20b of the scintillator sections 20 and the side surfaces 11b of the convex portions 11 so as to cover the upper surfaces 20a and the side surfaces 20b of the scintillator sections 20 and the side surfaces 11 b of the convex portions 11. In particular, the solvent permeation blocking film 40A is formed so as not to fill the gaps 30 between the side surfaces 20b of the scintillator sections 20 adjacent to one another (that is, so as to keep the gaps 30). Further, the solvent permeation blocking film 40A is formed successively from the upper end portion of the scintillator section 20 up to the bottom surface 12a of the concave portion 12, and covers the boundary portion between the base end portion of the scintillator section 20 and the upper surface 11a of the convex portion 11. In the present embodiment, because a thickness FT of the solvent permeation blocking film 40A is substantially constant, a width of the gap 41 defined by the solvent permeation blocking film 40A as well is substantially constant. The thickness FT of the solvent permeation blocking film 40A may be set to, for example, approximately 1 μm to 5 μm, and may be set to approximately 2 μm to 3 μm. The solvent permeation blocking film 40A as described above may be formed from a material which is the same as that of the solvent permeation blocking film 40 according to the first embodiment by the same method. In the scintillator panel 1B according to the present embodiment, the solvent permeation blocking film 40A is formed, not only on the upper surface 20a and the side surfaces 20b of the scintillator section 20, but also on the side surfaces 11b of the convex portion 11. In particular, the solvent permeation blocking film 40A covers the boundary portion between the base end portion of the scintillator section 20 and the upper surface 1 la of the convex portion 11. Therefore, in accordance with the scintillator panel 1B according to the present embodiment, it is possible to securely prevent permeation of a solvent or the like among the columnar crystals C at the time of forming the light shielding layer 50. Further, the side surfaces 11 b of the convex portion 11 as well are covered with the solvent permeation blocking film 40A, thereby it is possible to prevent degradation of the convex portion 11 by a solvent component contained in the filling material. [Fourth Embodiment] Next, a scintillator panel according to a fourth embodiment will be described. FIG. 5 is a side view of the scintillator panel according to the fourth embodiment. As shown in FIG. 5, a scintillator panel 1C according to the present embodiment is, as compared with the scintillator panel 1B according to the third embodiment, different in the point that the scintillator panel 1C further includes a light shielding layer 60. In this way, in accordance with the scintillator panel 1C according to the present embodiment, in the same way as the scintillator panel 1B according to the third embodiment, it is possible to securely prevent permeation of a solvent or the like among the columnar crystals C, and in the same way as the scintillator panel 1B according to the second embodiment, it is possible to securely confine scintillation light. [Fifth Embodiment] Next, a scintillator panel according to a fifth embodiment will be described. FIG. 6 is a side view of the scintillator panel according to the fifth embodiment. As shown in FIG. 6, a scintillator panel 1D according to the present embodiment is, as compared with the scintillator panel 1B according to the third embodiment, different in the point that the scintillator panel 1D includes a solvent permeation blocking film 40D in place of the solvent permeation blocking film 40A. In addition, in the same way as the third embodiment, by selecting a radiation (X-rays) transmissive base member as the substrate 10, it is possible to allow the radiation R to be incident from the back surface 10b of the substrate 10. The solvent permeation blocking film 40D is formed on the upper surfaces 20a and the side surfaces 20b of the scintillator sections 20, the side surfaces 11b of the convex portions 11, and the bottom surface 12a of the concave portion 12, so as to cover the upper surfaces 20a and the side surfaces 20b of the scintillator sections 20, the side surfaces 11b of the convex portions 11, and the bottom surface 12a of the concave portion 12. In particular, the solvent permeation blocking film 40D is formed so as not to fill the gaps 30 between the side surfaces 20b of the scintillator sections 20 adjacent to one another (that is, so as to keep the gaps 30). In contrast with that the solvent permeation blocking film 40 and 40A are formed so as to be divided into a plurality of portions covering the respective scintillator sections 20, the solvent permeation blocking film 40D is integrally formed as a single portion. That is, the solvent permeation blocking film 40D is formed such that a portion covering a scintillator section 20 and its convex portion 11 and portions covering other scintillator sections 20 and their convex portions 11 are continued on the bottom surface 12a of the concave portion 12. In the present embodiment as well, because a thickness FT of the solvent permeation blocking film 40D is substantially constant, a width of the gap 41 defined by the solvent permeation blocking film 40D as well is substantially constant. The thickness FT of the solvent permeation blocking film 40D may be set to, for example, approximately 1 μm to 5 μm, and may be set to approximately 2 μm to 3 μm. The solvent permeation blocking film 4013 as described above may be formed from a material which is the same as that of the solvent permeation blocking film 40 in the first embodiment by the same method. In accordance with the scintillator panel 1D according to the present embodiment, the solvent permeation blocking film 40D is formed on the bottom surface 12a of the concave portion 12 as well. Therefore, it is possible to more securely prevent permeation of a solvent or the like among the columnar crystals C. Further, because the solvent permeation blocking film 40D is not divided into a plurality of portions, but integrally configured, it is easy to form the solvent permeation blocking film 40D. Further, the side surfaces 11b of the convex portions 11 as well are covered with the solvent permeation blocking film 40D, thereby it is possible to prevent degradation of the convex portions 11 by a solvent component contained in the filling material. Moreover, the front surface 10a of the substrate 10 (the bottom surface 12a of the concave portion 12) as well are covered with the solvent permeation blocking film 40D, thereby it is possible to protect the substrate 10 from a solvent component. [Sixth Embodiment] Next, a scintillator panel according to a sixth embodiment will be described. FIG. 7 is a side view of the scintillator panel according to the sixth embodiment. As shown in FIG. 7, a scintillator panel 1E according to the present embodiment is, as compared with the scintillator panel 1D according to the fifth embodiment, different in the point that the scintillator panel 1E further includes the light shielding layer 60. In this way, in accordance with the scintillator panel 1E according to the present embodiment, in the same way as the scintillator panel 1D according to the fifth embodiment, it is possible to more securely prevent permeation of a solvent or the like among the columnar crystals C, which makes it easy to form the solvent permeation blocking film 40D. Moreover, in accordance with the scintillator panel 1E according to the present embodiment, in the same way as the scintillator panel 1B according to the second embodiment, it is possible to securely confine scintillation light. The above-described embodiments have been described as an embodiment of a scintillator panel according to an aspect of the present invention. Accordingly, an aspect of the present invention is not limited to the above-described scintillator panels 1 to 1E. An aspect of the present invention makes it possible so as to arbitrarily change the above-described scintillator panels 1 to 1 E, or to be applied to another one within the range without changing the gist of the respective Claims. For example, the scintillator panels 1 to 1E according to the above-described embodiments may further include a moisture-proofing film. In such a case, in the scintillator panels 1 to 1E, the moisture-proofing film may be deposited-formed by parylene or the like on the solvent permeation blocking films 40, 40A, and 40D, the light shielding layer 50, and the light shielding layer 60 so as to cover the solvent permeation blocking films 40, 40A, and 40D, the light shielding layer 50, and the light shielding layer 60 (that is, so as to cover the whole of the scintillator sections 20). Provided that a moisture-proofing film is further provided in this way, the moisture resistance of the scintillator sections 20 is improved. Further, in the scintillator panels 1 to 1E according to the above-described embodiments, the scintillator sections 20 are to be formed on the convex portions 11 of the substrate 10. Meanwhile, a mode of formation of the scintillator sections 20 is not limited thereto, and for example, the scintillator sections 20 may be formed on the front surface of an arbitrary substrate on which convex portions are not formed. Moreover, in the above-described embodiments, the case where an aspect of the present invention is applied to a scintillator panel has been described. Meanwhile, an aspect of the present invention is applicable to a radiation detection device including the above-described scintillator panel or the like. In such a case, the radiation detection device includes any one of the above-described scintillator panels 1 to 1E, and the substrate 10 thereof may be a sensor panel including a plurality of photoelectric conversion elements arrayed so as to be optically coupled to the scintillator sections 20 (a TFT panel or a CMOS image sensor panel). In such a case, for example, the convex portions 11 respectively corresponding to the respective pixels of an TFT panel or a CMOS image sensor serving as the substrate 10 are formed, and the scintillator section 20 is formed thereon. A material and a method of forming the convex portions 11 are as described above. At that time, each of the convex portions 11 may be composed of a material transmissive to scintillation light generated in the scintillator section 20. In accordance with this radiation detection device, because the radiation detection device includes one of the above-described scintillator panels 1 to 1E, it is possible to suppress characteristic degradation associated with formation of the light shielding layer 50. Further, because the substrate 10 is a sensor panel including the photoelectric conversion elements, provided that the convex portions 11 are directly formed on the photoelectric conversion elements, to provide the scintillator sections 20, there is no need to paste together a scintillator panel and a sensor panel separately prepared. In accordance with an aspect of the present invention, it is possible to provide a scintillator panel and a radiation detection device which are capable of preventing characteristic degradation associated with formation of a light shielding layer. 1, 1A, 1B, 1C, 1D, 1E . . . scintillator panel, 10 . . . substrate (sensor panel), 10a . . . front surface, 10b . . . back surface, 11 . . . convex portion, 11a . . . upper surface, 11b . . . side surface, 12 . . . concave portion, 12a . . . bottom surface, 20 . . . scintillator section, 20a . . . upper surface, 20b . . . side surface, 30 . . . gap, 40, 40A, 40D . . . solvent permeation blocking film, 50 . . . light shielding layer, 60 . . . light shielding layer, C . . . columnar crystal, R . . . radiation.
	abstract	An example plasma confinement system includes an inner electrode having a rounded first end that is disposed on a longitudinal axis of the plasma confinement system and an outer electrode that at least partially surrounds the inner electrode. The outer electrode includes a solid conductive shell and an electrically conductive material disposed on the solid conductive shell and on the longitudinal axis of the plasma confinement system. The electrically conductive material has a melting point within a range of 170° C. to 800° C. at 1 atmosphere of pressure. Related plasma confinement systems and methods are also disclosed herein.
043751040	abstract	A device for sealing a gateway between interconnectable pools in a nuclear facility comprising a frame supporting a liquid impermeable sheet positioned in a U-shaped gateway between the pools. An inflatable tube carried in a channel in the periphery of the frame and adjoining the gateway provides a seal therebetween when inflated. A restraining arrangement on the bottom edge of the frame is releasably engagable with an adjacent portion of the gateway to restrict the movement of the frame in the U-shaped gateway upon inflation of the tube, thereby enhancing the seal. The impermeable sheet is formed of an elastomer and thus is conformable to a liquid permeable supportive wall upon application of liquid pressure to the side of the sheet opposite the wall.
	claims	1. An article comprising three major components, an adhesive, a filler, and a modifier, the article comprising primarily filler by volume, with the adhesive and any modifier agents filling the space between the filler particles, wherein the filler comprises Tungsten, Boron, Titanium, Gadolinium, Lead, Hafnium, Polyethylene, Aluminum or Gold; wherein the adhesives comprise epoxy, Bismalemide, or Cyanate Ester; and wherein the modifier includes fumed silica or alumina powder, that maximizes packing density of the fillers to provide optimal radiation shielding attenuation through proper filler particle size distribution (PSD) selection. 2. An article, according to claim 1, filled with high Hydrogen content filler, using polyethylene spheres. 3. An article according to claim 1, filled with multiple fillers to provide protection from radioactive species, such as X-rays and neutrons, using Tungsten and Gadolinium or Tungsten and Aluminum, or any combination of materials mentioned in claim 1. 4. An article according to claim 1, that provides radiation protection as an integral structure within a spacecraft. 5. An article according to claim 1, having filler particles of a preselected size in correspondence with a density corresponding to the particle size and wherein the article is cured to a preselected degree in correspondence with a preselected degree of rigidity. 6. An article according to claim 1, that employs novel processing techniques to optimize the shield density, via compaction and densification, through the use of a fugitive solvent, vibration, particle size distribution or a combination of these techniques. 7. An article according to claim 6, that combines Tungsten, between 50% and 100% of filler and Gadolinium, between 0% and 50% of filler by weight in optimal ratios to maximize radiation attenuation and shielding for black body X-ray and neutron radiation. 8. An article according to claim 4, that incorporates fumed silica, not to exceed 3% by weight, as a rheological additive, to assist in the homogeneous distribution of fillers during cure. 9. An article according to claim 4, that incorporates embedded sensors, including MEMS sensors, dosimeters, or other electronic devices to monitor an environment, for measurement of temperature, pressure and radiation exposure of the spacecraft.
	summary
	abstract	An apparatus and method for forming an alignment layer with uniform orientation is provided. An alignment layer-forming apparatus includes an ion source for generating ion beams and one or more masks disposed between the ion source and a substrate. The masks each have a reflective face directed to the substrate. The ion beams are reflected between the reflective face of each mask and a thin-film which is disposed on the substrate and which is processed into an alignment layer, whereby the alignment layer is formed with the ion beam finally applied to the thin-film. The orientation of a liquid crystal can be rendered uniform by varying the shape and/or arrangement of the reflective face of the mask. Hence, a liquid crystal display with no brightness or color non-uniformity can be manufactured.
	claims	1. An X-ray detector system for determining the contents of an item, the system comprising:an X-ray emitter configured for emitting X-ray radiation;a detector comprising a receiving surface, the detector configured to receive the X-ray radiation and to generate one or more intensity signals indicative of an intensity of the received X-ray radiation at each of a plurality of locations on the receiving surface;an X-ray penetration grid comprising a first grid structure comprising:at least one side oriented in a first primary direction;a first plurality of parallel grid members each having a first end and a second end; anda second plurality of parallel grid members each having a first end and a second end;wherein:the first end and the second end of each of the first plurality of parallel grid members intersect the at least one side at an angle such that the first plurality of parallel grid members are neither parallel nor perpendicular to the at least one side; andthe first end and the second end of each of the second plurality of parallel grid members intersect the at least one side at an angle such that the second plurality of parallel grid members are neither parallel nor perpendicular to the at least one side; anda conveying mechanism configured for conveying the item and the X-ray penetration grid in a second primary direction, said second primary direction being substantially the same as the first primary direction. 2. The X-ray detector system of claim 1, further comprising a user system comprising one or more memory and one or more processors, the user system configured to:receive, via the one or more processors, the one or more intensity signals; andcause, via a display device, display of the intensity signals. 3. The X-ray detector system of claim 2, wherein the displayed intensity signals further comprise:signals indicative of a current location of the item; andghost signals indicative of ghosted images extending at least substantially parallel to said second primary direction. 4. The X-ray detector system of claim 3, further configured to generate, via the one or more processors, one or more notifications indicating the presence of ghost signals. 5. The X-ray detector system of claim 1, wherein each of the first plurality of parallel grid members is continuous and each of the second plurality of parallel grid members is continuous. 6. The X-ray detector system of claim 1, wherein the angle at which the first end of each of the first plurality of parallel grid members intersects the perimeter is between 30 degrees and 55 degrees. 7. The X-ray detector system of claim 6, wherein the angle at which the first end of each of the first plurality of parallel grid members intersects the perimeter is 45 degrees. 8. The X-ray detector system of claim 1, wherein each of the second plurality of parallel grid members is discontinuous. 9. The X-ray detector system of claim 1, wherein:the first plurality of parallel grid members are spaced having at least substantially equivalent distances there-between; andthe second plurality of parallel grid members are spaced having at least substantially equivalent distances there-between. 10. The X-ray detector system of claim 1, wherein the first plurality of parallel grid members and second plurality of parallel grid members are radiopaque. 11. The X-ray detector system of claim 1, wherein a portion of the X-ray radiation passes through the item, and the portion of the X-ray radiation that passes through the item also passes through the X-ray penetration grid. 12. The X-ray detector system of claim 1, wherein the x-ray penetration grid further comprises a second grid structure comprising:at least one side oriented in a first primary direction;a third plurality of parallel grid members each having a first end and a second end; anda fourth plurality of parallel grid members each having a first end and a second end, wherein:the first end and the second end of each of the third plurality of parallel grid members intersect the at least one side of the second grid structure at an angle such that the third plurality of parallel grid members are neither parallel nor perpendicular to the at least one side of the second grid structure;the first end and the second end of each of the fourth plurality of parallel grid members intersect the at least one side of the second grid structure at an angle such that the fourth plurality of parallel grid members are neither parallel nor perpendicular to the at least one side of the second grid structure;the first grid structure lies in a first plane; andthe second grid structure lies in a second plane, the second plane being perpendicular to the first plane. 13. The X-ray detector system of claim 1, wherein a perimeter surrounds the X-ray penetration grid, the perimeter being defined, in part, by the at least one side. 14. A computer implemented method for scanning an item, the method comprising steps for:receiving, via a processor, one or more first intensity signals indicative of a first intensity of X-ray radiation received at each of a plurality of locations at a first scan time on a detector, wherein:the detector is configured to receive X-ray radiation from an X-ray emitter and to generate the one or more intensity signals indicative of an intensity of the received X-ray radiation at each of a plurality of locations on the receiving surface;the X-ray radiation is emitted from the X-ray emitter and at least a portion of the X-ray radiation passes through the item and an X-ray penetration grid before being received by the detector, wherein:the X-ray penetration grid comprises a first grid structure comprising:at least one side oriented in a first primary direction;a first plurality of parallel grid members each having a first end and a second end; anda second plurality of parallel grid members each having a first end and a second end;wherein:the first end and the second end of each of the first plurality of parallel grid members intersect the at least one side at an angle such that the first plurality of parallel grid members are neither parallel nor perpendicular to the at least one side; andthe first end and the second end of each of the second plurality of parallel grid members intersect the at least one side at an angle such that the second plurality of parallel grid members are neither parallel nor perpendicular to the at least one side; andthe item and the X-ray penetration grid are propelled in a second primary direction, said second primary direction being substantially the same as the first primary direction;causing, via a display device, display of the one or more first intensity signals;receiving, via the processor, one or more second intensity signals indicative of one or more ghosted images extending from an edge of the item; andidentifying, via the one or more processors, the presence of a radiation ghost based at least in part on the second intensity signals. 15. The computer implemented method for scanning an item of claim 14, wherein a first portion of the X-ray radiation passes through the item, and the first portion of the X-ray radiation that passes through the item also passes through the X-ray penetration grid. 16. The computer implemented method for scanning an item of claim 14, further comprising steps for generating, via the one or more processors, a notification indicating the item requires additional processing to determine the item's contents. 17. The computer implemented method for scanning an item of claim 14, wherein the angle at which the first end of each of the first plurality of parallel grid members intersects the perimeter is between 30 degrees and 55 degrees. 18. The computer implemented method for scanning an item of claim 14, wherein the first plurality of parallel grid members and second plurality of parallel grid members are radiopaque. 19. The computer implemented method for scanning an item of claim 14, wherein a portion of the X-ray radiation passes through the item, and the portion of the X-ray radiation that passes through the item also passes through the X-ray penetration grid. 20. The computer implemented method for scanning an item of claim 14, wherein:the x-ray penetration grid further comprises:a second grid structure comprising:at least one side oriented in a first primary direction;a third plurality of parallel grid members each having a first end and a second end; anda fourth plurality of parallel grid members each having a first end and a second end;wherein:the first end and the second end of each of the third plurality of parallel grid members intersect the at least one side of the second grid structure at an angle such that the third plurality of parallel grid members are neither parallel nor perpendicular to the at least one side of the second grid structure;the first end and the second end of each of the fourth plurality of parallel grid members intersect the at least one side of the second grid structure at an angle such that the fourth plurality of parallel grid members are neither parallel nor perpendicular to the at least one side of the second grid structure;the first grid structure lies in a first plane; andthe second grid structure lies in a second plane, the second plane being perpendicular to the first plane; anda second portion of the X-ray radiation passes through the item and the second grid structure before being received by the detector such that the second portion of the X-ray radiation does not pass through the first grid structure.
039719502	abstract	A mammographic compression and positioning device which is independent of the x-ray system utilized to produce images of an object being examined. A slide assembly is movable along a vertical post member which is adjustably secured to a base member. A compression paddle is coupled to the slide assembly and has a curved lower surface which, upon contacting the object, exerts a variable compressive force thereon. The position of the compression paddle is adjustable in a plurality of directions, allowing the paddle to be exactly positioned whereby an image of a selected object view may be obtained. The compression paddle is transparent enabling the user of the device to visualize the object being compressed and to take the steps necessary to provide initial image results which are satisfactory thereby reducing the number of reimages which normally would be required.
061887463	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS An inertial electrostatic confinement (IEC) particle generator is described in U.S. patent application Ser. No. 08/232,764 (Miley et al.) which was filed on Apr. 25, 1994 and is incorporated herein by reference. The inertial electrostatic confinement device disclosed therein includes a vacuum vessel which is held at ground potential and contains internally and concentric to the vessel, a wire grid which acts as a cathode. The cathode may be made from a variety of metals having structural strength and appropriate secondary electron and thermionic electron coefficients. The cathode wire grid is connected to a power source to provide a high negative potential (30 kV-70 Kv), while the vessel itself is conductive and maintained at a ground potential. Deuterium or a mixture of deuterium and tritium gas is introduced into the vessel. A voltage is applied to the cathode wire grid and the pressure is adjusted in order initiate a glow discharge. To maximize the neutron yield per unit power input while maximizing grid life-time by reducing collisions with a grid, operational conditions are used to create a "star" glow discharge mode. The glow discharge generates ions which are extracted from the discharge by the electric field created by the cathode grid. These ions are accelerated through the grid openings and focused at a spot in the center of the spherical device. The resulting high energy ions interact with the background gas (beam-background collisions) and themselves (beam-beam collisions) in a small volume around the center spot, resulting in a high rate of fusion reactions. The result is a neutron generator producing neutrons as one of the D-T fusion reaction products. Where the ejection rates are high, the ejected ions may provide a deep-self generated potential well that confines trapped beam ions, creating even higher reaction rates. The device may be modified by using a field gas mixture of deuterium and helium-3 to be a source of protons as well as neutrons. One geometrical form of the device is spherical and as seen in FIG. 1. This device is based upon the principle of an ion accelerator with a plasma target. In a neutron-generator embodiment, deuterium-deuterium fusion reactions takes place in the plasma target and produce energetic neutrons. The device acts as a simple spherical plasma diode, having a ground potential on the outer sphere and a negative potential on a nearly geometrically transparent inner spherical grid. The spherical inertial electrostatic confinement device 10 is illustrated in FIG. 1 where a conductive vacuum chamber 11 is connected to a ground potential at contact 17. The device has a cathode grid 12 which defines a small sphere within the chamber and has a grid design that provides a high geometric transparency. In operation, however, this grid design has an even higher effective transparency, due to the effect of a concentration of ions into a"microchannels", as subsequently described. A source of power 14 is connected by a high voltage feed through to the internal cathode grid 12. The voltage has a negative value, thereby providing a bias between the relatively positive walls of the vacuum chamber and the central grid area. Gas is introduced into the vacuum chamber 11 by a control valve 15 and is evacuated by a pump 18. Upon application of a potential to the cathode grid, under certain grid-voltage, gas pressure, gas type and grid-configuration conditions, high density ions and electron beams will form within the IEC device initiating a "star" mode of operation. In this mode, high density space charged neutralized ion beams are formed into microchannels that pass through the open spaces between the grid wires. As the ions avoid contact with the wires, this mode increases the effective grid transparency to a level above the geometric value. These microchannels significantly reduce grid bombardment and erosion and increase power efficiency. For conventional star mode operation, the grid and microchannel beams are symmetric so that a convergent high-density core develops. The inertial electrostatic confinement device serves as a valuable source of neutrons or protons. The spherical inertial electrostatic confinement (IEC) device has been used as a plasma fusion reactor. In a plasma fusion reactor, the energy production must compete with inevitable losses, and the role of the processes which result in such losses is crucial in determining the operating temperature of a plasma fusion reactor. Some energy losses can be minimized by a suitable choice of certain design parameters, but others are inherent in the reacting system; one of these is bremsstrahlung radiation. The efficiency of neutron production competes with the inevitable losses of bremsstrahlung radiation that are inherent in the reacting system. High intensity x-rays were measured in experiments Hirsch's x-ray measurement. Previously, the goal was to minimize the bremsstrahlung radiation by a suitable choice of certain design parameters. Affirmative use of this property can permit a device to serve as x-ray source. An IEC plasma x-ray source may have the general structure as seen in FIG. 2, wherein electrons are injected into the center of a spherical IEC device 400, formed from two spherical concentric electrodes. The inner electrode 401 (anode) made of a highly transparent grid (>90%, preferably >95%, transparency) is charged to a positive voltage, preferably in a range of 1 kV to 150 KV, relative to the outer grounded electrode 402 (cathode), at driving currents varying from 1 mA to 100 mA. The outer electrode is a hermedically sealed vacuum chamber that supports a pressure of less than 10.sup.-6 Torr. Electrons emanating from the cathode 402 are attracted to the anode 401, and pass through the anode (grid) many times before being captured by the grid. Due to spherical convergence, the injection of electrons constitute an accumulation of electrons that forms a dense electron cloud which then can be used to accelerate and heat ions. The electrons are injected by electron emitters 409 which are electrically heated to generate the electrons. There are at least two, preferably four to eight, such assemblies, and each assembly is comprised of an electron emitter and an electron extractor. The operation generates intense bremsstrahlung radiation in the spherical center due to the strong electron--electron interactions at a relativistic speed accelerated by the grid bias. The energy spectrum of the emitted x-rays shifts as the grid bias is changed. Notably, the bias on this configuration is opposite to that seen in FIG. 1, wherein the central grid is a cathode and the chamber 11 serves as an anode. As is well known, the plasma in a thermonuclear reactor consists of stripped nuclei of hydrogen isotopes together with electrons. From such a plasma, energy will inevitably be lost in the form of bremsstrahlung, that is, radiation emitted by charged particles, mainly the electrons, as a result of deflection by the Coulomb fields of other charged particles. An expression for the rate of electron-ion bremsstrahlung energy emission of the correct form L. Spitzer, USAEC Report NYO-6049 (1954), P. 9., but differing by a small numerical factor from the result obtained by a more rigorous procedure, can be derived from the classical expression for the rate P.sub.e at which energy is radiated by an accelerated electron, namely, ##EQU1## where e is the electron charge, c is the velocity of light, and a is the electron acceleration. The total power P.sub.br radiated as bremsstrahlung per unit volume has been calculated in a Maxwellian distribution of velocity among the electrons in a system containing a single ionic species of charge Z. S Glassston and R. H. Lovberg Controlled Thermonuclear Reactions, Van Nostrand Reinhold Company, 1960, Chapter 2. ##EQU2## where T.sub.e is the kinetic temperature of the electrons in a Maxwellian distribution, n.sub.e and n.sub.i are the density of electron and ion, respectively, m.sub.e is the electron rest mass, and h is Planck's constant. The classical expression for the rate of bremmstrahlung emission per unit volume per unit frequency interval in the frequency range from v to v+dv is ##EQU3## Upon integration over all frequencies, this expression leads to equation (2). For arbitrary electron and ion densities, the equation (3) expressed in terms of wave length, the relative values of Dp.lambda.,/d.lambda. have been plotted as a function of wave length in FIG. 4 (From C. T. Ulrey: Phys. Rev., 11:401 (1918), as cited on page 616, Evans, The Atomic Nucleus, McGraw-Hill, Inc., (1972). While this calculation was performed for a thick tungsten target, the shape of the spectra is expected to be quite similar to that obtained from the IED due to the similarity of the x-ray production mechanisms. To the left of the maximum for each curve, the energy emission as bremsstrahlung is dominated by the exponential term and decreases rapidly with decreasing wave length. The bremsstrahlung power distribution is calculated assuming a Maxwellian electron velocity distribution. For monoenergetic electron velocity, the distribution is expected to be narrower. At temperature below 50 kev, the bremsstrahlung from a plasma arises almost entirely from electron-ion interactions. At high temperatures, the production of bremsstrahlung due to electron--electron interactions, as distinct from those resulting from the electron-ion interactions, will be significant. Provided relativistic effects do not arise, there should be no electron--electron bremsttrahlung, but at high electron velocities such is not the case and appreciable losses can occur from this form of radiation. The following results will provide a general indication of the situation. At an electron kinetic temperature of 25 keV the ratio of electron--electron bremsstrahlung energy to that for electron-ion interaction is estimated to be 0.06, at 50 keV it is 0.13, and at 100 keV it is 0.34. C. F. Wandel, et al, Nuclear Instr., 4, 249 (1959). R. F. Post, Ann. Rev. Nuclear Sci, 9, 367 (1959). In the IEC configuration, under proper conditions of current-voltage-pressure, a virtual cathode can form. [G. Miley et al, Inertial-Electrostatic Confinement Neutron/Proton Source, AIP conf. proc. 299. Editors: M. Haines, A. Knight.] In that case, deceleration of the electrons as they approach the virtual cathode makes an additional contribution to the x-ray yield. [R. Eisberg, Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles, 2nd Ed., John Wiley and Sons, 1985.] This term can equal or dominate the electron/electron collisional contributions, depending of the height of the virtual cathode. Since electrons can lose their entire energy x-rays in this case, the effect generally causes a shift of the x-ray spectrum to higher energies. Experimental measures of the x-ray spectrum have been carried out using the experiment setup described in FIG. 2. Results are shown in FIG. 3. As expected, the data follows along a curve very similar to calculated spectra, previously shown in FIG. 4. The IEC spectrum in FIG. 3 was taken with the applied voltage set at 30 kV. The measured spectrum is somewhat broad having a 15 keV full-width at half-maximum (FWHM) for a spectrum ranging up to 230 kV (comparable to a 12 keV FWHM for E-30 keV in FIG. 4). The peak of the distribution can be shifted by varying the applied grid voltage to give a series of spectra similar to that of FIG. 4. For many experiments, a broad-range spectrum of this nature is quite useful. However, in some cases it may be desirable to employ a narrow band of x-ray energies. If so, a narrower spectrum or "band" can be selected by Bragg reflection from crystal surfaces, or by diffraction gratings, or by using other "conventional" x-ray optics techniques (J. B. Murphy et al., "Synchrotron radiation resources and condensers for projection x-ray lithography," Appl. Optics, vol. 32, no. 34, pp. 6920-6929 (Dec. 1, 1933); I. A. Artyukov et al., "On the efficiency of grazing incidence optics: the spiral collimator," in Short Wavelength Lasers and Their Applications, Nova Science Publishers, Inc., N.Y., pp. 299-310 (1992); H. Takenaka et al., "Heat resistance of Mo-based and W-based multilayer soft x-ray mirrors," in Laser Interaction and Rolation Plasma Phenomena, 12 International Conference, Osaka, Japan 1995, Part II, American Institute of Physics, pp. 808-813 (1992).) Such x-ray band selection is especially desirable in certain types of experiments or industrial applications where a narrow range of x-ray energies is desired. By using band selection techniques, the IEC voltage is first tuned to optimize the overall x-ray spectrum in the range desired. The x-ray band selector is then employed to further narrow the range of x-ray wavelengths striking the target or spectrum under treatment. This process is illustrated in FIG. 5. Assuming that x-rays in the wavelength range 0.45-0.55 nm are desired, the IEC voltage is first raised to 50 kV. This shifts the maximum intensity of the broad x-ray spectrum such that, as seen in the figure, the peak lies over the desired range. Then, an appropriate band selection technique (diffraction grating, etc.) is employed to select the 0.45-0.55 nm band. As observed from the figure, this procedure, adjusting the IEC x-ray spectrum followed by band selection, optimizes the x-ray intensity obtained in the desired range. If the IEC voltage had not been optimized, e.g., left at 30 kV or lower, the figure shows that the intensity in the desired band would be reduced by 50% or more. Otherwise, if a narrow wavelength of x-rays is not required, the tuned IEC x-ray can be used directly. Coupling of the band selection optics to the IEC x-ray source can be accomplished in a variety of ways. Two characteristic methods, illustrated in FIGS. 6a and 6b, differ by inserting the selection optics and target inside the IEC vacuum chamber 11, or using external optics 501 with x-rays extracted from the vacuum vessel through a thin, vacuum-tight, metallic x-ray window 502. FIG. 6a uses "conventional" x-ray diffraction optics 451 (C. V. Azaroff, X-ray Spectroscopy McGraw-Hill, N.Y., (1973).) for band selection. It and the target 452 are located in an expanded port 453 on the side of the IEC. The port 453 is connected through an opening 404 in the main vacuum vessel such that x-rays escape the IEC grid region and enter the optics system while the port volume is maintained under vacuum conditions through the main chamber pumping system. A double valve 455 arrangement on the end of the port allows convenient insertion and removal of targets/specimens without breaking the main chamber vacuum. This method has the advantage that the x-rays escaping the IEC are not attenuated by use of a vacuum window (such as in FIG. 6b), and the target can be maintained under vacuum conditions. On the other hand, insertion and removal of the target/speculum through the double gate valve system is a complication. If a slightly reduced x-ray intensity is tolerable, and if the target need not be maintained under vacuum, the external arrangement of FIG. 6b can be used. Here x-rays from the IEC chamber 11 escape through a low-Z metallic window 502. A low-Z material such as Be would be used to minimize x-ray attenuation which maintaining structural strength to hold vacuum conditions. Select glasses containing a minimum concentration of high-Z materials like lead could also be employed if visual observation into the chamber were desired. The two arrangements in FIG. 6 are considered typical examples. A number of variations in geometry, and selection optics, target/spectrum insertion/removal could be considered for specific applications. For example prisms also may be used. Other applications of the IEC x-ray source 601 involve x-ray imaging. Such techniques for using soft x-rays are well-known, e.g., I. H. Hutchinson, Principles of Plasma Diagnostics, Cambridge University Press, N.Y., (1987). A typical approach for adapting the IEC to this use is illustrated in FIG. 7. In this figure, the x-rays 600 are passed through a conventional pinhole camera system 604, the image being recorded on a detector 605 as shown or on photographic film. The subject 603 being photographed would be placed in the x-ray path in the appropriate position desired to obtain the focal length. The subject would be sufficiently thin that x-ray transmission through it would be possible. An x-ray window is used in the arrangement illustrated in analogy with FIG. 6b. However, if a vacuum arrangement is desired, a geometry similar to FIG. 6a could be employed. The foregoing characteristics of the bremsstrahlung effect in a plasma can be the basis for the proper selection of parameters in an IEC device such that a turnable x-ray source can be achieved. As seen in FIG. 2, in an IEC-SS system 400 electrons from electron emitters 409, which are heated by application of an electric current of 1A to 15A at a driving voltage of 5-15V, from a source 410, are accelerated 10's keV up to 100 keV by a spherical anode grid 401 that is disposed within a spherical vacuum confinement vessel 402, which also serves as a cathode. The spherical wire grid 401 is a self-supporting structure, free from internal supports, having a plurality of openings through which electrons may flow. The grid also may be formed of a plurality of vanes, joined together in a geometric pattern which provides a thin profile when viewed in a radial direction in order to achieve a high geometric transparency. Due to the spherical convergence, the energetic electrons 403 collide in the center of sphere 404. The interactions between the high energy electrons create intense x-rays. The x-ray spectra are dependent on the electron energy controlled by the grid bias 405. The x-rays are directed to a window 406 in a wall of the vessel and transmitted via a cylindrical passage 407 to a detector 408. Within the passage or at other convenient locations in the path of the X-rays, a means for narrowing the spectrum of the x-rays could be disposed. Such means could be a device using Bragg reflection from a crystal surface, diffraction gratings, prisms, or the like. The IEC-SS makes possible the generation of x-rays using relatively low-energy electrons. The IEC-SS has a number of potentially unique and attractive features which may serve a variety of applications. These features include compactness, relatively low cost, tunability, high photon energy operation. The relatively narrow natural line-width associated with the IEC-SS can provide less unusable radiation which could damage optics and target samples. In addition, by varying the electron pulse energy in an IEC-SS pulsed mode, chirped x-ray pulses may be generated. The pulse structure, tunability and high photon energy capability of the IEC-SS may provide an important tool for studying ultra-fast phenomena. Furthermore, the relatively low cost and compactness of a IEC-SS can make synchrotron light sources more readily available to users. Extended x-ray absorption fine structure (EXAFS), which is a powerful tool for structural determination in the materials, biomedical, and many other scientific fields, has been studied usually at synchrotron radiation (SR) facilities, so far. The development of instruments for EXAFS measurements in a laboratory is important because of their complementary usefulness for experiments with SR, especially when special sample preparation and/or quick feedback of the analysis are required. The problem with EXAFS measurements performed in a laboratory is mainly the degradation of spectrum caused by strong characteristic x-ray lines from the source. It is important to develop an x-ray source for dedicated use in EXAFS experiments. So far, the x-ray sources have been mostly used for x-ray diffractometry. Therefore, the electron gun is usually designed to operate at high tube voltage to provide strong characteristic x-rays. On the contrary, an EXAFS experiment requires intense continuum x-rays. The use of laboratory base IEC-SS may alleviate e this problem. One practical application of the e IEC-SS x-ray beam is to significantly enhance the imaging ability of low concentration of trace elements in the human body. Specifically, it could be used in digital differential angiography (DDA), a new medical x-ray diagnostic concept. P. R. Moran, et al, Physics Today, July (1983); also in "Optics Today," edited by J. N. Howard (AIP, New York, 1986), p. 308. This new technique is a differential x-ray absorption diagnostic procedure for imaging blood vessels. In conventional angiography, x-ray imaging of blood vessels is achieved by intravenously injecting an x-ray absorbing substance such as iodine. The available x-rays used for imaging are extremely broad band and large doses of both iodine and x-rays are required. A tunable x-ray beam, using a differential x-ray absorption technique, would be a very sensitive diagnostics tool for measuring low concentrations of iodine at a reduced radiation dose. Iodine has a K-edge absorption at a photon energy of .about.33 kev. In DDA, two x-ray beams are used: on at 33 kev (energy for peak absorption in iodine) and the other at .about.30 kev. The mass attenuation coefficients for these two photon energies differ by a factor of .about.8. The photon flush through the tissue is proportional to the exponent of the mass attenuation coefficient times the mass thickness of the tissue. Therefore, the difference between the 33 kev photon image and the 30 kev photon image is a direct and sensitive measure of the concentration of iodine, while the images of the bones and other tissues not containing the iodine is suppressed. This differential x-ray absorbing technique would use much lower concentrations of iodine injected "noninvasively" into the heart via the bloodstream. The imaging and subtraction of the two x-ray beams would be performed at the same time and, therefore, patient movement during the imaging process would not be a factor. While the present invention has been described in connection with several preferred embodiments, the invention is not limited thereto, and its scope is to be defined by the following claims.
	claims	1. A method of reducing corrosion of a material constituting a nuclear reactor structure, comprising the steps of:injecting, into nuclear reactor water, a solution or a suspension containing a substance generating an excitation current in a nuclear reactor having feed water and the nuclear reactor water, wherein a metal or a metallic compound forms the substance generating the excitation current under a condition in the nuclear reactor;depositing the substance generating an excitation current to a surface of the material of the nuclear reactor structure by an amount of more than 10 μg/cm2 and less than 200 μg/cm2, the substance being a conductive TiO2; andinjecting, into the nuclear reactor water, a further solution of hydrogen while controlling a hydrogen concentration in the feed water to be more than 0.2 ppm and less than 1.0 ppm to thereby control a corrosion potential,wherein the electrochemical corrosion potential is controlled in a range of −0.4 V vs. SHE to −0.1 V vs. SHE under a condition when no ultraviolet light is applied to the substance generating an excitation current. 2. The method of reducing corrosion of a material constituting a nuclear reactor structure according to claim 1, wherein the solution or the suspension is injected when the nuclear reactor is started up or when the nuclear reactor is shut down, and the further solution is hydrogen and is injected while the nuclear reactor is operated. 3. The method of reducing corrosion of a material constituting a nuclear reactor structure according to claim 1, wherein the hydrogen is added to the solution or the suspension in advance, and the solution or the suspension is injected in the reactor water while the nuclear reactor is operated. 4. The method of reducing corrosion of a material constituting a nuclear reactor structure according to claim 1, wherein the adhesion amount of the substance generating the excitation current on a surface of the nuclear reactor structural material is monitored, and the hydrogen concentration in a feed water is controlled in accordance with the adhesion amount.
06078640&	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a proximity unit-magnification X-ray exposure apparatus according to a first embodiment of the present invention. Denoted in FIG. 1 at 1 is a mask, and denoted at 2 is a thin plate (mask substrate) on which a membrane of the mask 1 is formed by deposition. Denoted at 3 is a mask magnification correcting mechanism of the type as disclosed in Japanese Published Patent Application, Publication No. 99095/1992, for example. Denoted at 4 is a mask abutment pin, and denoted at 5 is a mask chuck. Denoted at 6 is a semiconductor wafer, and denoted at 7 is a wafer chuck. Denoted at 8 is a wafer stage. Denoted at 9 is a reference mark for measurement of coordinates of an alignment mark on the mask 1. Denoted at 10 is a measuring system (pickup) for measurement of positional deviation, along a plane, between an alignment mark of the mask and an alignment mark of the wafer (hereinafter, "autoalignment measurement"), and for measurement of a gap between the mask and the wafer (hereinafter, "autofocus measurement"). The autoalignment (AA) measurement may be made in accordance with a method as disclosed in U.S. Pat. No. 5,327,221, for example, and the autofocus (AF) measurement may be made in accordance with a method as disclosed in U.S. Pat. No. 5,343,291, for example. Denoted at 11 is a controller for controlling the exposure apparatus. FIGS. 2A and 2B illustrate displacement of a mask pattern resulting from mask magnification correction. Now, a process of determining a stage drive pattern (drive locus) for a global alignment operation with the controller in accordance with the present invention will be explained. Initially, first time global autoalignment measurement and autofocus measurement are carried out. From the results of these measurements, the magnification of the pattern upon the wafer is calculated. If, from this result, the mask magnification correction is required, the magnification correcting mechanism 3 is used to change it. As shown in FIG. 2A or 2B, the mask pattern displaces by (.DELTA.x, .DELTA.y, .DELTA.z) as a result of mask magnification correction. For correction of this amount, global autoalignment measurement and autofocus measurement are repeated once again. On the basis of the results, a stage drive pattern is determined and wafer exposure is carried out. FIG. 3 illustrates this global alignment sequence (steps S01-S06), in a flow chart. With the global alignment sequence such as described above, displacement of a mask pattern resulting from mask magnification correction can be corrected and thus high precision pattern registration is assured. FIGS. 4A and 4B illustrate displacement of an alignment mark of a mask upon mask magnification correction, in a second embodiment of the present invention. Denoted in FIGS. 4A and 4B at 21-24 are alignment marks on a mask. In accordance with the second embodiment, for further increases of throughput as compared with the first embodiment, displacement of the pattern due to mask magnification correction is stored into the exposure apparatus beforehand in the form of a table. FIG. 5 illustrates the measurement sequence in the second embodiment, in the form of a flow chart. The operation according to this embodiment will be described below, with reference to FIGS. 1, 4A, 4B and 5. Table preparation and a storing procedure are carried out as below. First, the mask 1 is placed on the mask chuck 5. Then, the stage 8 is driven while executing autoalignment (AA) and autofocus (AF) measurement using the pickup 10, so that an alignment mark on the reference mark 9 is placed just below the mark 21 of the mask, with a predetermined gap thereto. The coordinates of the stage at this moment are stored into the controller 11. This procedure is repeated with respect to the marks 22-24 similarly, and the coordinates of the mask alignment marks 21-24 are determined. Subsequently, the mask magnification correcting mechanism 3 is actuated to change the magnification of the mask. After a predetermined magnification is set, the reference mark 9 is moved to the position of wafer alignment mark 21 coordinates as having been measured. Then, autoalignment and autofocus measurement is carried out, and the amount of mark displacement is measured. This procedure is repeated for the marks 22-24 similarly, and displacement amounts (.DELTA.x.sub.1, .DELTA.x.sub.2, .DELTA.y.sub.1, .DELTA.y.sub.2) of respective marks are measured. Also, a gap change .DELTA.z is measured. Then, from the displacement amounts of the four marks 21-24, the displacement amount (.DELTA.x, .DELTA.y) of the center of the mask is calculated. The above-described measurement procedure is carried out a predetermined number of times, for various magnifications, whereby a table of mask center displacement (.DELTA.x, .DELTA.y, .DELTA.z) with mask magnification is prepared. The resultant is stored into the controller 11. For the exposure procedure, first the wafer 6 is placed on and chucked by the wafer chuck 7 and, then, autoalignment and autofocus measurement for global alignment is performed. From the results, the position of a pattern already printed on the wafer and the magnification thereof are calculated. Here, while the stage drive pattern for the wafer exposure can be determined, displacement of the mask center resulting from the magnification correction is detected from the table and the stage drive pattern is corrected in accordance with the displacement. Subsequently, while moving the wafer stepwise in accordance with the corrected drive pattern, exposures of shot areas of the wafer are carried out (step-and-repeat exposure). After exposures of all shot areas on one wafer are completed, the exposed wafer is unloaded and the above-described exposure procedure is repeated to a subsequent wafer. With the preparation of a table for mask magnification and mask center displacement such as described above, the necessity of additional autoalignment and autofocus measurement after magnification correction is removed, such that the throughput is improved. In this embodiment, the mask magnification and mask center displacement are measured with the mask 1 being loaded in the exposure apparatus. However, a table may be prepared on the basis of measurement made by use of a device, separate from the exposure apparatus and, when the mask 1 is loaded into the exposure apparatus, mask data may be downloaded to the controller 1 as the mask inherent data. Substantially the same advantageous results are obtainable on that occasion, as a matter of course. For preparation of the table, the relationship between the magnification and the mask center displacement may be determined by simulation and a table may be prepared on the basis of it. Alternatively, the positions of printed patterns with mask magnification correction and without mask magnification correction, respectively, may be measured and the mask center displacements in these cases may be detected, for preparation of a table. Further, while the above-described embodiment has been explained with reference to an example wherein both autoalignment measurement and autofocus measurement are carried out, the present invention is applicable also to a case where only one of autoalignment measurement and autofocus measurement is carried out. Although the invention has been described with reference to a case of global alignment, it is similarly applicable to a case of die-by-die alignment. With the preparation of a table, the stage driving amount for alignment can be corrected on the basis of a pattern positional deviation amount, by which the alignment operation time can be reduced. Next, an embodiment of a device manufacturing method which uses an exposure apparatus or exposure method such as described above, will be explained. FIG. 6 is a flow chart of a procedure for the manufacture of microdevices such as semiconductor chips (e.g., ICs or LSIs), liquid crystal panels, CCDs, thin film magnetic heads or micro-machines, for example. Step 1 is a design process for designing a circuit of a semiconductor device. Step 2 is a process for making a mask on the basis of the circuit pattern design. Step 3 is a process for preparing a wafer by using a material such as silicon. Step 4 is a wafer process which is called a pre-process wherein, by using the so prepared mask and wafer, circuits are practically formed on the wafer through lithography. Step 5 subsequent to this is an assembling step which is called a post-process wherein the wafer having been processed by step 4 is formed into semiconductor chips. This step includes an assembling (dicing and bonding) process and a packaging (chip sealing) process. Step 6 is an inspection step wherein an operation check, a durability check and so on for the semiconductor devices provided by step 5, are carried out. With these processes, semiconductor devices are completed and they are shipped (step 7). FIG. 7 is a flow chart showing details of the wafer process. Step 11 is an oxidation process for oxidizing the surface of a wafer. Step 12 is a CVD process for forming an insulating film on the wafer surface. Step 13 is an electrode forming process for forming electrodes upon the wafer by vapor deposition. Step 14 is an ion implanting process for implanting ions to the wafer. Step 15 is a resist process for applying a resist (photosensitive material) to the wafer. Step 16 is an exposure process for printing, by exposure, the circuit pattern of the mask on the wafer through the exposure apparatus described above. Step 17 is a developing process for developing the exposed wafer. Step 18 is an etching process for removing portions other than the developed resist image. Step 19 is a resist separation process for separating the resist material remaining on the wafer after being subjected to the etching process. By repeating these processes, circuit patterns are superposedly formed on the wafer. With these processes, high density microdevices can be manufactured at lower cost. In accordance with the embodiments of the present invention as described above, an autoalignment or autofocus measured value or a stage driving amount is corrected on the basis of a mask pattern positional deviation amount produced by a mask magnification correcting mechanism of an X-ray exposure apparatus. Thus, even with the magnification correction, degradation of pattern registration precision can be prevented. A table for the mask magnification correction amount and pattern displacement amount due to the correction may be prepared in a controller of an exposure apparatus such that the amount of positional deviation resulting from mask magnification correction may be calculated by using the table and that an autoalignment or autofocus measured value or a stage driving amount may be then corrected. This eliminates the necessity of autoalignment or autofocus measurement for correction of positional deviation of a mask pattern, for every wafer, due to mask magnification correction. This enables an increase of throughput. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.
	claims	1. A traveling wave nuclear fission reactor, comprising:a nuclear reactor core;at least one nuclear fission reactor fuel assembly disposed in said reactor core, said nuclear fission reactor fuel assembly being configured to generate a burnfront emitting a neutron flux, having a burning parameter, and achieving a burnup value at or below a predetermined burnup value;a neutron flux monitoring system;one or more neutron absorber control rods disposable in the nuclear fission reactor fuel assembly;a controller configured to implement a control function responsive to the neutron flux monitoring system to selectively control an amount of the one or more neutron absorber control rods at a location relative to the burnfront for achieving the burnup value at or below the predetermined burnup value, including increasing an amount of the one or more neutron absorber control rods at a rear location behind the burnfront such that a burnup value at the burnfront increases and a burnup value behind the burnfront decreases; and a drive motor configured to dispose the one or more neutron absorber control rods in response to the controller implementing the control function. 2. The traveling wave nuclear fission reactor of claim 1, wherein the controller is configured to implement the control function responsive to the neutron flux monitoring system to selectively control the amount of the one or more neutron absorber control rods at the rear location behind the burnfront for achieving the burnup value at or below the predetermined burnup value. 3. The traveling wave nuclear fission reactor of claim 1, wherein said controller is capable controlling an amount of the one or more neutron absorber control rods for achieving neutron absorption at a plurality of locations relative to the burnfront and wherein a majority of the neutron absorption due to the one or more neutron absorber control rods being at a plurality of rear locations behind the burnfront. 4. The traveling wave nuclear fission reactor of claim 1, wherein said nuclear fission reactor fuel assembly is capable of controlling an amount of a neutron reflector at a location behind the burnfront for achieving the burnup value at or below the predetermined burnup value. 5. The traveling wave nuclear fission reactor of claim 4, wherein said nuclear fission reactor fuel assembly is capable of controlling the amount of a neutron reflector for achieving neutron reflection at a plurality of locations relative to the burnfront and wherein a majority of the neutron reflection due to the neutron reflector is at a plurality of locations behind the burnfront. 6. The traveling wave nuclear fission reactor of claim 1, further comprising a neutron emitter capable of being moved from a first location behind the burnfront to a second location behind the burnfront for achieving the burnup value at or below the predetermined burnup value. 7. The traveling wave nuclear fission reactor of claim 1, further comprising a neutron emitter capable of being moved from a first location behind the burnfront to a second location proximate to the burnfront for achieving the burnup value at or below the predetermined burnup value. 8. The traveling wave nuclear fission reactor of claim 1, further comprising a neutron emitter capable of being moved from a first location behind the burnfront to a second location in front of the burnfront for achieving the burnup value at or below the predetermined burnup value. 9. The traveling wave nuclear fission reactor of claim 1, wherein said nuclear fission reactor fuel assembly is capable of controlling radiation damage to one or more of a plurality of structural materials in response to controlling the burnup value in the traveling wave nuclear fission reactor. 10. The traveling wave nuclear fission reactor of claim 9, wherein said nuclear fission reactor fuel assembly is capable of controlling the radiation damage by achieving the radiation damage value at or below a predetermined radiation damage value. 11. The traveling wave nuclear fission reactor of claim 10, further comprising a neutron emitter capable of being moved from a first location behind the burnfront to a second location behind the burnfront for achieving the radiation damage value at or below the predetermined radiation damage value. 12. The traveling wave nuclear fission reactor of claim 10, further comprising a neutron emitter capable of being moved from a first location behind the burnfront to a second location proximate to the burnfront for achieving the radiation damage value at or below the predetermined radiation damage value. 13. The traveling wave nuclear fission reactor of claim 10, further comprising a neutron emitter capable of being moved from a first location behind the burnfront to a second location in front of the burnfront for achieving the radiation damage value at or below the predetermined radiation damage value. 14. The traveling wave nuclear fission reactor of claim 1, wherein said controller is configured to implement the control function responsive to the neutron flux monitoring system to selectively control the amount of the one or more neutron absorber control rods at the rear location behind the burnfront for achieving a radiation damage value at or below a predetermined radiation damage value. 15. The traveling wave nuclear fission reactor of claim 14, wherein said controller is configured to implement the control function responsive to the neutron flux monitoring system to selectively control the amount of the one or more neutron absorber control rods for achieving neutron absorption at a plurality of locations relative to the burnfront for obtaining the radiation damage value at or below a predetermined radiation damage value and wherein a majority of the neutron absorption due to the one or more neutron absorber control rods is at a plurality of locations behind the burnfront. 16. The traveling wave nuclear fission reactor of claim 1, wherein said nuclear fission reactor fuel assembly is capable of controlling an amount of a neutron reflector at a location behind the burnfront for achieving a radiation damage value at or below a predetermined radiation damage value. 17. The traveling wave nuclear fission reactor of claim 16, wherein said nuclear fission reactor fuel assembly is capable of controlling the amount of the neutron reflector for achieving neutron reflection at a plurality of locations relative to the burnfront for obtaining the radiation damage value at or below a predetermined radiation damage value and wherein a majority of the neutron reflection due to the neutron reflector is at a plurality of locations behind the burnfront. 18. The traveling wave nuclear fission reactor of claim 1, wherein said controller is configured to implement the control function responsive to the neutron flux monitoring system to selectively modulate the neutron flux at a first location relative to the burnfront for modulating the neutron flux emitted by the traveling wave nuclear fission reactor. 19. The traveling wave nuclear fission reactor of claim 1, wherein said controller is configured to implement the control function responsive to the neutron flux monitoring system to selectively modulate the neutron flux at the rear location behind the burnfront for modulating the neutron flux emitted by the traveling wave nuclear fission reactor. 20. The traveling wave nuclear fission reactor of claim 1, wherein said controller is configured to implement the control function responsive to the neutron flux monitoring system to selectively modulate the neutron flux at a plurality of locations relative to the burnfront and wherein an amount of modulation at the plurality of locations relative to the burnfront is governed by a spatial profile. 21. The traveling wave nuclear fission reactor of claim 20, wherein the spatial profile is symmetric with respect to the burnfront. 22. The traveling wave nuclear fission reactor of claim 20, wherein the spatial profile is asymmetric with respect to the burnfront. 23. The traveling wave nuclear fission reactor of claim 20, wherein the spatial profile indicates an amount of neutron absorber control rod insertion versus distance from a central location of the nuclear reactor core, the spatial profile has a slope having a steepest portion and wherein the steepest portion of the slope of the spatial profile occurs at a first location behind the burnfront. 24. The traveling wave nuclear fission reactor of claim 19, wherein the controller is configured to implement the control function responsive to the neutron flux monitoring system to selectively modulate the neutron flux at the location relative to the burnfront, so that a majority of the modulation of neutron flux occurs at a plurality of locations behind the burnfront. 25. The traveling wave nuclear fission reactor of claim 1, wherein the nuclear fission reactor fuel assembly is capable of selectively absorbing a portion of the neutron flux at the rear location relative to the burnfront. 26. The traveling wave nuclear fission reactor of claim 1, wherein the one or more neutron absorber control rods comprise a material chosen from lithium, silver, indium, cadmium, boron, cobalt, hafnium, dysprosium, gadolinium, samarium, erbium, europium and mixtures thereof. 27. The traveling wave nuclear fission reactor of claim 1, wherein the one or more neutron absorber control rods comprise a compound chosen from silver-indium-cadmium alloy, boron carbide, zirconium diboride, titanium diboride, hafnium diboride, gadolinium titanate, dysprosium titanate and mixtures thereof. 28. The traveling wave nuclear fission reactor of claim 1, wherein said controller is configured to implement the control function responsive to the neutron flux monitoring system to control an amount of a neutron interactive material at a location relative to the burnfront for selectively modulating the neutron flux emitted by the nuclear fission reactor fuel assembly. 29. The traveling wave nuclear fission reactor of claim 28, wherein the controller is configured to implement the control function responsive to the neutron flux monitoring system to control an amount of a neutron emitter at the location relative to the burnfront for controlling the amount of the neutron interactive material at the location relative to the burnfront. 30. The traveling wave nuclear fission reactor of claim 29, wherein the neutron emitter includes a fertile isotope. 31. The traveling wave nuclear fission reactor of claim 29, wherein the neutron emitter includes an element capable of undergoing beta decay to become a fissile isotope. 32. The traveling wave nuclear fission reactor of claim 28, wherein said nuclear fission reactor fuel assembly is capable of controlling an amount of a neutron reflector at the location relative to the burnfront for controlling the amount of the neutron interactive material at the location relative to the burnfront. 33. The travelling wave nuclear fission reactor of claim 1, wherein the control function includes decreasing an amount of the one or more neutron absorber control rods at a forward location in front of the burnfront such that the burnup value at the burnfront increases and the burnup value behind the burnfront decreases. 34. The travelling wave nuclear fission reactor of claim 1, wherein the controller is configured to implement a second control function responsive to the neutron flux monitoring system to selectively control an amount of the one or more neutron absorber control rods at a location relative to the burnfront, including decreasing an amount of the one or more neutron absorber control rods at the rear location behind the burnfront. 35. The travelling wave nuclear fission reactor of claim 34, wherein the second control function responsive to the neutron flux monitoring system further includes increasing an amount of the one or more neutron absorber control rods at a forward location in front of the burnfront such that a direction of movement of the burnfront reverses or speed of movement of the burnfront decreases. 36. The travelling wave nuclear fission reactor of claim 1, wherein increasing an amount of the one or more neutron absorber control rods at the rear location includes determining an amount of neutron absorber control rod insertion as a function of distance from a nuclear fission igniter of the travelling nuclear fission reactor.

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