Split (2)

train · 33.5k rows

patent_number stringlengths 0 9	section stringclasses 4 values	raw_text stringlengths 0 954k
	summary
	summary
	abstract	A high energy photon source. A pair of plasma pinch electrodes are located in a vacuum chamber. A working gas which includes a noble buffer gas and an active gas chosen to provide a desired spectral line. A pulse power source provides electrical pulses at voltages high enough to create electrical discharge between the electrodes to produce very high temperature, high density plasma pinch in the working gas providing radiation at the spectral line of the active gas. An external reflection radiation collector-director collects radiation produced in the plasma pinches and directs the radiation in a desired direction. In a preferred embodiment the active gas is lithium and the buffer gas is helium and the radiation collector-director is coated with the material used for the electrodes. A good choice for the material is tungsten. In a second preferred embodiment the buffer gas is argon and lithium gas is produced by vaporization of solid or liquid lithium located in a hole along the axis of the central electrode of a coaxial electrode configuration. Other preferred embodiments utilize a conical nested debris collector upstream of the radiation collector-director.
056423896	claims	1. A light water reactor, comprising: a reactor pressure vessel having an interior, a core disposed in a lower half of said pressure vessel, fuel assemblies disposed in said core, a column of water covering said core and acting as a coolant and a moderator, said column having a level, the level being within an initial level range during normal operation; and a steam-space disposed geodetically above said column of water; a safety device passively operating without externally applied power for improving an inherent safety of said reactor pressure vessel; and at least two fluid lines connected between said safety device and the interior of said pressure vessel, at least one of said fluid lines communicating with said column of water during the normal operation and at least one of said fluid lines communicating with said steam space during the normal operation, said fluid lines having means for automatically transmitting an actuation criterion to said safety device, with at least a drop of the level in said pressure vessel to a value below the initial level range serving as the actuation criterion. said safety device is a switching vessel in the form of a pressure vessel with a fluid space and a gas cushion space, said switching vessel has heat exchanging pipes being submerged in the fluid space and having one end communicating with the steam space and another end communicating with the reactor water column during normal operation or when the initial level range is present; said switching vessel initiates condensation in said heat-exchanging pipes if a flow of steam occurs from the reactor interior into said heat exchanging pipes, when dropping below the initial level region of the reactor water; and including at least one main fitting initiating a reactor safety measure, and at least one pilot fitting connected to said at least one main fitting for actuating said at least one main fitting, an increase in pressure due to absorbed condensation heat in said switching vessel being used as a derived actuation criterion for passive actuation of said pilot and main fittings. a water reservoir containing water; said pressure vessel having a steam space; said safety device being an emergency condenser having heat exchanging pipes being disposed in the water of said water reservoir; an inlet pipe configuration interconnecting said emergency condenser and the steam space during normal operation of said reactor, and a drainage pipe configuration interconnecting said emergency condenser and a lower region of the reactor water column at a point above said reactor core; water or condensate in said heat exchanging pipes stagnates during normal operation, but reactor steam flows through said inlet pipe configuration into said heat exchanging pipes and condenses there if the level of the reactor water drops to another level below the initial level range, so that condensate flows back into said pressure vessel through said drainage pipe configuration. 2. The light water reactor according to claim 1, wherein: 3. The light water reactor according to claim 2, including control rods to be inserted into said core, said at least one of pilot and main fittings actuated when the derived actuation criterion has been fulfilled, actuating a reactor scram as a safety measure by quickly inserting said control rods in said core. 4. The light water reactor according to claim 2, including a live steam line, and wherein said main fitting is a live steam penetration fitting closing said live steam line as a safety measure. 5. The light water reactor according to claim 2, including a live steam line and control rods to be inserted into said core, said at least one of pilot and main fittings actuated when the derived actuation criterion has been fulfilled, include live steam penetration fittings, said pilot and main fittings actuate a closing of said live steam line as a safety measure and actuate a reactor scram as a safety measure by quickly inserting said control rods in said core. 6. The light water reactor according to claim 2, including a condensation chamber, and blow-off units connected to said at least one of pilot and main fittings being actuated when the derived actuation criterion has been fulfilled, said blow-off units blowing-off steam in said condensation chamber to depressurize said pressure vessel or a primary loop. 7. The light water reactor according to claim 1, including: 8. The light water reactor according to claim 7, including a condensation chamber below said water reservoir for blowing-off excess reactor steam. 9. The light water reactor according to claim 7, wherein said inlet pipe configuration has an inlet and a connection to said heat exchanging pipes and slopes downward from said inlet to said connection, and said drainage pipe configuration has a connection to said heat exchanging pipes and an outlet end and slopes downward from said connection to said outlet end. 10. The light water reactor according to claim 9, wherein said heat exchanging pipes have first and second pipe legs and a reversing bend and are essentially hairpin shaped with respective upward and downward slopes, said first pipe leg being connected to said inlet pipe configuration and said second pipe leg being connected to said drainage pipe configuration. 11. The light water reactor according to claim 7, wherein said drainage pipe configuration has a downwardly running, hairpin shaped pipe bend located on a section in a gap between said pressure vessel and said flooding reservoir, said bend forming a circulation block during normal operation.
	claims	1. Pressuriser for a pressurised water nuclear power station, comprisingan outer casing which delimits an inner space;a duct which is located away from the casing and extends beneath the casing;a tap which places the inner space of the casing in communication with the duct, this tap having a lower end being welded to the duct by means of a weld seam and an upper end which opens into the inner space;a weld protecting sleeve arranged inside the tap and which has a lower peripheral edge which is engaged in the duct, an annular space selectively filled with a primary liquid being defined radially between the sleeve and the tap and the duct, the sleeve bounding the annular space on the inside, the tap and the duct bounding the annular space on the outside;wherein the duct has inside the lower peripheral edge of the sleeve an inner volume; andwherein the annular space has at least one opening along at least a portion of the lower peripheral edge of the sleeve and is in fluidic communication through the at least one opening with the inner volume of the duct. 2. Pressuriser according to claim 1, wherein the annular space is open along the entire lower peripheral edge of the sleeve. 3. Pressuriser according to claim 1, wherein the tap defines an inner channel which places the duct and the inner space of the casing in communication, the pressuriser comprising a crown which is rigidly fixed to an inner side of the casing around the inner channel, the sleeve having an upper end portion which is fixed to the crown. 4. Pressuriser according to claim 3, wherein the crown and/or the upper end portion of the sleeve comprise(s) circulation holes which place the annular space in communication with the inner space of the casing. 5. Pressuriser according to claim 4, wherein a passage cross-section of the circulation holes is calibrated in order to limit a flow rate of primary liquid through the annular space to a maximum predetermined value. 6. Pressuriser according to claim 5, wherein a total passage cross-section of the circulation holes is between 0.5% and 2% of the passage cross-section of the inner channel of the tap. 7. Pressuriser according to claim 3, wherein the annular space has, along the lower peripheral edge of the sleeve, a passage cross-section of between 2% and 10% of the passage cross-section of the inner channel of the tap. 8. Pressuriser according to claim 3, wherein the sleeve is removably mounted on the crown. 9. Pressuriser according to claim 3, wherein it comprises a strainer which covers the inner channel of the tap and which is removably mounted on the crown. 10. Pressuriser according to claim 9, wherein the upper end portion of the sleeve is engaged between the strainer and the crown.
059354399	summary	FIELD OF THE INVENTION The present invention relates generally to the field of fluid recirculation systems incorporating suction strainers. More particularly, the present invention relates to internal core tube suction strainers for use with Emergency Core Cooling Systems of nuclear power plants. BACKGROUND OF THE INVENTION A critical function of Emergency Core Cooling Systems (ECCS) and other recirculation systems of nuclear power plants is to move fluids quickly and in large volumes to critical areas of the nuclear power plant in the event of accidents and emergencies. Integral to this critical function is the ability of strainers, filters, screens and other such devices associated with the systems to remove solids from the moving fluids while at the same time maintaining a sufficiently large volume of fluid flow. Suction strainers are used in suppression pools of Boiling Water Reactor (BWR) nuclear power plants to remove solids from the fluid stored in the suppression pools when the fluid is drawn into an Emergency Core Cooling System (ECCS) or other recirculation system. The goal is to have strained fluid substantially free from particulate matter, thereby minimizing pump degradation. In the United States and other countries, there are generally three different types of BWR nuclear power plants. The most common of these is the Mark I, followed by the Mark II and finally the Mark III. Each type of BWR nuclear power plant has a different suppression pool design. Generally speaking, the Mark I has a toroidal-shaped suppression pool, the Mark II has a simple circular tank, and the Mark III can best be described as a moat around the power plant. The differences in suppression pool design, as well as other plant design differences, have made the construction of a universally adaptable suction strainer unfeasible. Moreover, retrofitting upgraded suction strainers in existing BWR nuclear power plants is an extremely difficult task. A universal goal in the nuclear power plant field has been to increase the effective surface area of suction strainers so that the required volumetric flow rate of water can be delivered to the reactor following a loss of coolant accident (LOCA). A LOCA can result when a high pressure pipe ruptures with such great force that large quantities of debris from thermal insulation, coatings, concrete, and other sources can wash into the suppression pool, thereby clogging the suction strainer(s). As a result, the volumetric flow rate of cooling water delivered to the reactor can be drastically reduced which, in turn, can lead to reactor core overheating. The thrust of recent advancements in the suction strainer art has been directed toward designing suction strainers that can adequately filter such debris from the suppression pool fluid without becoming clogged (i.e., without leading to a reduction in ECCS pump volumetric flow rate). Following a LOCA, it is critical that the ECCS pumps can operate undegraded for extended periods of time. To achieve this result, large quantities of fluid, free from solids and other particulate matter, must reach the pumps. Recent advances have yielded suction strainers that can adequately filter debris from the fluid to limit pump degradation, but the goal of increasing the surface area of suction strainers so that greater volumes of water can be delivered to the reactor has been more difficult to achieve in some BWR plants. This is due to the second effect of a LOCA. The second effect of a LOCA in a BWR plant is the generation of post-LOCA hydrodynamic forces. Following a LOCA, high pressure steam is expelled from the reactor through structures known as downcomers which extend into the suppression pool. The resulting hydrodynamic forces created within the suppression pool place extreme loads upon any protruding structure within the pool, including suction strainers. While one function of the suppression pool is to condense this steam and thereby quickly dissipate these high pressures, significant hydrodynamic forces are still applied to the structural features and protrusions within the pool. In general, the greater the length and diameter of the suction strainer, the greater the resulting load on the strainer. For this reason, while it is easy to design a suction strainer having an increased surface area by increasing the overall length and diameter of the suction strainer, it is difficult to support such a strainer and, in many cases, to install such a strainer. Heretofore, various suction strainers have been employed for the general objective of filtering solids from the fluid stored within a suppression pool of a BWR nuclear power plant. One such suction strainer design is the cantilevered suction strainer. Such suction strainers typically extend into the suppression pool, are connected to the ECCS suction pipe at one of its ends, and simply cantilever off that suction pipe end. That is the only means of support. Due to the extreme loads which result from post-LOCA hydrodynamic forces and the limited load carrying capabilities of the ECCS pipe and pipe penetration (that portion of the suppression pool wall adapted to receive the ECCS pipe to place the ECCS pipe in fluid communication with the suppression pool), the overall length and diameter of the cantilevered suction strainer is limited. For a given strainer diameter, if the cantilevered suction strainer is too long, the torque applied to the suction strainer by the post-LOCA hydrodynamic forces can damage the suction pipe to which it is attached and/or the penetration through the suppression pool wall. An advancement in cantilevered suction strainer design is disclosed in U.S. Pat. No. 5,696,801. The suction strainer disclosed in this Application includes a filtering surface defined by a filtering structure that is attached to and built around an internal core tube. Reinforcing structural members extend outward radially from the internal core tube and provide support for the filtering structure. The external filtering structure is formed from a plurality of perforated plate assemblies positioned adjacent one another along the length of the core tube. The plate assemblies extend radially at alternating distances from the internal core tube thereby forming alternating protrusions and troughs. In this way, the surface area of the filtering surface is increased without increasing the overall length of the filtering structure. Openings in the internal core tube allow water from the suppression pool to be drawn through the filtering structure through perforations in the filtering surface. This configuration promotes controlled fluid in-flow along the suction strainer and substantially precludes the establishment of non-uniform localized entrance velocities through the filtering surface. The unique configuration of the external filtering structure enlarges the filtering surface area while minimizing the projected area of the suction strainer. Thus, more water can be drawn through this cantilevered suction strainer without increasing the overall distance this suction strainer extends into the suppression pool. While the overall filtering surface area of cantilevered suction strainers can now be increased, for a given strainer diameter, such suction strainers are still hampered by length limitations. Other advancements in the art have been made by Sulzer Thermtec. Sulzer Thermtec has designed an elongated simple cylindrical strainer that appears to use a rib-type cage to support a perforated plate. The perforated plate performs the straining function while the cage provides structural support for the plate. The strainer extends parallel to and along the wall of the suppression pool and is connected at one end to the suction pipe with a 90.degree. tee. There is no internal core tube. In order to withstand the extreme forces in the pool, the strainer is secured to the suppression pool wall at each of its ribs. Legs extending from each rib are apparently bolted or otherwise attached to the walls of the suppression pool. Again, installation can be time consuming and difficult, particularly if the suppression pool cannot be drained and if welding is required for strainer installation. Also, most BWR plants cannot accommodate a strainer diameter larger than 3 or 4 feet. While the suction strainers described above remove solids from the fluid stored within the suppression pools of BWR nuclear power plants, it appears that neither is capable of handling the LOCA generated debris, being installed within geometrically limited diameters, and being supported adequately. What is needed, therefore, but seemingly unavailable in the art, is a suction system that can (1) handle the postulated debris quantities, (2) be adequately supported and withstand LOCA generated forces, and (3) be installed without modifying the shell in the suppression pools of BWR nuclear power plants. Unlike a BWR nuclear power plant, a Pressure Water Reactor (PWR) nuclear power plant does not utilize a suppression pool. Rather, a PWR nuclear power plant, both light water and heavy water types, has a containment area which remains dry until an accident occurs. In conventional PWR nuclear power plants, an accident results in the containment area being partially flooded with water and the ECCS relying on a sump pump to circulate the water through the reactor. Typically, the water is filtered through a structurally protective trash rack and then through a finer debris screen to separate particulate matter from the water passed through the ECCS. The suction strainer of the type utilized in a BWR nuclear power plant is not typically found connected to a PWR's ECCS suction piping. Typically, the volume and rate of fluid (e.g., water) flow recirculating through the ECCS is dependent upon the size of the sump pit as well as the overall size of the inlet orifice and related trash rack and debris screen. Accordingly, the volumes and rates of fluid flow in a prior art PWR nuclear power plant were limited by the structural limitations of these sump structures and fixtures. What is needed, therefore, is a manner of retrofitting PWR nuclear plants to overcome the surface area limitations of configurations already existing and, thereby, maintain rates of fluid flow through the ECCS that is encumbered by LOCA generated debris. SUMMARY OF THE INVENTION Briefly described, the present invention comprises an improved suction system including, in the genus, a suction strainer and suction pipe assembly mounted to fluid delivery piping of an ECCS of a nuclear power plant or other such fluid delivery system, with the suction strainer being supported between two opposing ends, and in its species a plurality of alternate embodiments of end mounted suction strainers and suction pipe assemblies mounted to BWR suppression pool wall(s) or PWR containment area sumps through various support combinations. The present invention provides an improved suction strainer for use, in its preferred embodiments, in the suppression pools and/or containment areas of nuclear power plants which overcomes the design deficiencies of other suction strainers known in the art. While the discussion of the improved suction strainer and the suction system of this invention focuses heavily on its use and value in connection with BWR nuclear power plants, alternate embodiments of the strainer also have utility when employed with Pressurized Water Reactor (PWR) nuclear power plants of both the light water and heavy water type. Furthermore, it will be understood from these descriptions that the invention will find application in connection with nuclear reactor plants other than BWR and PWR plants, and in connection with other facilities having comparable fluid delivery systems. The suction system of this invention provides an inventive improvement to that suction strainer disclosed in U.S. Pat. No. 5,696,801, which patent is incorporated herein by this reference. The result is a novel method and apparatus for filtering solids and other particulate matter from the fluid (e.g. water) used in the emergency core cooling systems of nuclear power plants and other recirculation systems. The elongated suction strainer of the suction system of the present invention can be used to maintain design volumetric flow capacity through an Emergency Core Cooling System (ECCS) encumbered with LOCA generated debris, and other similarly encumbered recirculation systems. Several ECCS pumps can be connected to the same suction strainer via multiple suction pipes. If one pump fails, the other pumps will continue to draw fluid through a common suction strainer. The present suction system is also designed to be adaptable for use within the suppression pool of any type of existing BWR nuclear power plant, either the Mark I, Mark II or Mark III. Moreover, the suction system of the present invention can easily be adapted for use in other suppression pools for BWR nuclear power plants not yet designed. Alternate embodiments of the suction system of this invention are employable for use with both light water and heavy water pressurized water reactor (PWR) nuclear power plants, typically as part of a larger assembly/system which includes additional piping attached to and projecting from the sunken drain of the PWR. The flexibility of the present system will be further described in greater detail hereafter. These and other advantages which will be discussed more fully below, are attainable due to the novel construction of the suction system of the present invention. The suction strainer of the system is connected to the suction pipe of a recirculation system and removes solids from the fluid from, for example, a suppression pool of a BWR nuclear power plant. The strainer is constructed with an internal hollow core tube and an exterior filtering structure. The internal core tube is formed from a core wall which bounds a hollow core chamber. A plurality of fluid inlets spaced along the core wall place the chamber and suppression pool in fluid communication with each other. The exterior filtering structure is connected to and at least partially bounds the core wall and has a number of very small perforations passing therethrough. The filtering structure is further constructed from a plurality of plate assemblies spaced sequentially along and surrounding the core wall. When ECCS pumps in the recirculation system are activated, fluid from the suppression pool is drawn through the perforations in the exterior filtering structure, then through the fluid inlets in the core wall, and finally, into the core chamber. The strained fluid is then, for example, drawn through the suction pipe to the pump where it is either sprayed onto the reactor core and/or simply recirculated through a closed loop cooling system. The details regarding the structure of the suction strainer as hereinabove described are more fully set forth in U.S. Pat. No. 5,696,801, which has been incorporated herein by reference. This suction strainer structure is applicable to all of the embodiments of the suction system of this invention which will be described in more detail below. The core tube of the present invention has at least two functions. First, it acts as a suction flow control apparatus once fluid from, for example, the suppression pool or containment area has passed through the perforations in the exterior filtering structure. Second, and more pertinent with respect to the novelty of the present invention, the core tube is the primary structural support for the suction strainer of the present invention. Because of the rigidity of the core tube, the suction strainer can be constructed so that when the suction strainer is supported only at its two ends, it spans a length significantly longer than any other suction strainer known in the art. The suction strainer can be a unitary structure or it can be formed from several sections connected end-to-end in series along a common longitudinal axis. Regardless of how the suction strainer is formed, an elongated suction strainer results. When several suction strainer sections are used to create the elongated suction strainer, the adjacent ends of the suction strainer sections can be connected in several ways. In one embodiment of the present invention, each end of the core tube has a truncated core extension depending therefrom. The core tube extensions are, preferably, equipped with a typical pipe flange on the extension end that is remote from the core tube. Each flange is sized and shaped to abut the flange of an adjacent suction strainer core tube extension to facilitate connection of the suction strainer sections. Typically, the core tube extensions protrude away from the strainer plate assemblies a distance sufficient to permit connection of the flanges between the opposed plate assemblies of adjacent suction strainer sections. The flanges can be connected by welding or with any number of suitable devices such as, but not limited to, clamps, brackets, sleeves, bolts, or other fastening mechanisms. The flanges are also sized and shaped to be attached to flanges depending from the end of the suction pipe of the piping system of a BWR nuclear power plant or the ECCS pipe penetration in the suppression pool wall. The flange connections at the suction pipe are made in the same manner as other flange connections between suction strainer sections. When a suction pipe is connected to each end of the elongated suction strainer, the core tube provides support for the entire weight of the elongated suction strainer. When the elongated suction strainer is supported in this manner, the suction pipes and ECCS pipe penetration should be reinforced so that they can withstand the loads which will result from post-LOCA hydrodynamic forces. The flanges attached to the core tube extensions at the ends of the elongated suction strainer can also be secured to a cap that prevents access to the core chamber. These end caps are then fastened to existing structural supports within the suppression pool so that the loads from post-LOCA hydrodynamic forces are transferred from the strainer sections, through the structural supports, and to the suppression pool supports rather than directly to the suction pipes or their penetrations. When the elongated suction strainer is supported at both of its ends in this manner, the suction pipe connections can be made anywhere between the end caps. Generally speaking, the type of BWR/PWR nuclear power plant, the suppression pool (or containment area and sump pit) geometry and the ECCS pipe configuration will dictate how the suction pipe connections are made, the maximum length of the strainer sections used and the maximum length of the resulting elongated suction strainer employed. In certain BWR nuclear power plant suppression pools, the suction pipes are connected to a pipe fitting, such as an elbow or tee, located between an end of the elongated suction strainer and the structural support within the pool. In an alternate embodiment of the present invention the suction strainer sections are formed with flangeless core tube extensions. The suction strainer sections are aligned end-to-end along a common axis so that the core tube extensions of adjacent suction strainer sections are directly in line with and in contact with each other. The core tube extensions are then connected together with welds, brackets, clamps or other fastening devices. The suction pipe connections are then made in the same manner as described above with respect to the first embodiment of the present invention; the one difference being that the core tube extensions at the ends of the elongated suction strainer may not have flanges. Thus, these suction pipe connections will also be made using welds, brackets, clamps or other fastening devices. In another embodiment of the suction system of the present invention, the suction pipe connections to the elongated suction strainer are made at a 90.degree. angle with respect to the longitudinal axis extending through the internal core tube. To make this connection, a weld-o-let T-connection is used. The weld-o-let T-connection preferably has a core tube portion and a suction pipe portion. The core tube portion has a core wall surface that defines a bore therethrough. A plurality of apertures are spaced along a portion of the core wall surface. That portion of the core wall surface having apertures therethrough is bounded by a plurality of partial plate assemblies spaced sequentially along and eccentrically mounted on the core tube portion of the weld-o-let T-connection. The suction pipe portion includes a solid suction wall surface which forms the leg of the weld-o-let T-connection. The suction wall surface defines a channel for connecting the bore to the suction pipe. Typically, the suction pipe portion extends from the non-perforated area of the core wall surface. As a result of this novel weld-o-let T-connection arrangement, the T-connection is a part of the suction system. This novel arrangement allows for an increase in the suction strainer surface area while providing additional suction pipe connections to the elongated suction strainer. Because the weld-o-let T-connections are a part of the suction system, the suction pipe connections can be staggered along the entire length of the elongated suction strainer. The core tube portion of the T-connections provide additional support to the elongated suction strainer, thus the elongated suction strainer can be made even longer. Another advantage of this arrangement is that a number of suction pumps, can be connected to the same suction strainer using separate suction pipe connections. Thus, if one pump falters, the effect on the recirculation system is minimal. While the preceding disclosure focuses primarily on elongated suction strainers constructed from a plurality of suction strainer sections, a single elongated suction strainer, supported at its ends, is a viable alternative due to the structural support provided by the internal core tube. However, forming the elongated suction strainer from a plurality of suction strainer sections provides a number of practical advantages. First, because existing nuclear power plants are to be retrofitted with the suction system of the present invention, it will be more practical to install the system using a number of smaller suction strainer sections. Moreover, because there are different types of ECCS for different BWR/PWR nuclear power plants, using several suction strainer sections will provide more design options. Additionally, it is easier to transport suction strainer sections rather than a single elongated suction strainer. Thus, the costs associated with transportation and installation are reduced. Also, standardized castings can be used to create standard size suction strainer sections. These and other objects, features and advantages of the present invention will be more readily apparent from the following detailed description, read in conjunction with the accompanying drawings.
059819642	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of a typical X-ray procedure table 10 and an embodiment of the adjustable X-ray shield 100 according to the present invention attached thereto. During a catheter procedure, for example, the patient's head rests on the narrow portion 11 of the table 10, while the patient's feet lie toward the wide portion 12 of the table 10. The physician normally stands to the patient's right, near waist level. The shape of the table 10, it is to be understood, may vary from that shown in FIG. 1. The embodiment of the adjustable X-ray shield 100 shown in FIG. 1 includes an adjustable frame assembly 30 attached to the table 10, and a plurality of sheets of radio-opaque shielding material attached thereto, such as sheets 20, 21, 22 and 23 (best shown in FIG. 3). The sheets of radio-opaque material 20, 21, 22 and 23 may include lead or any material suitable for blocking or attenuating radiation of other wavelengths. The sheet of radio-opaque shielding material 20, according to an embodiment of the present invention, is adjustably disposed alongside the procedure table 10, from an adjustable distance above the surface of the table 10 to about the surface of the floor. The sheet of radio-opaque shielding material 22 is adjustably disposed across and above the surface of the table 10, at about the patient's waist level, as the patient (not shown) lays on the table 10. The sheet 22 may have a generally rectangular shape and may include a cutout portion to accommodate the patient's waist or legs. The sheet of radio-opaque shielding material 21 is disposed across the width of the table 10, generally at the level of the patient's waist on the table 10, and spans the distance from just underneath the table 10 to about the surface of the floor. According to the present invention, the sheets of radio-opaque shielding material 20, 21 and 22 at least partially surround the X-ray tube (not shown), which is generally located within the corner formed by the shields 20 and 21. Investigations into the sources of radiation during interventional procedures have revealed that some direct radiation may reach the physician as a result of a less than perfectly collimated X-ray source, and that substantial amounts of radiation are scattered by the table and the patient's body. A substantial portion of this scatter, it has been found, is directed back underneath the table, toward the physician's lower body. The sheet 21, according to the present invention, protects the physician from this X-ray scatter directed back underneath the table by substantially partitioning the X-ray tube from the physician. Another portion of radiation travels through the patient's body, and is scattered thereby, in all directions. It has further been found that, of this scatter, a substantial portion emerges through the patient's hip and thigh region, near the physician. This unexpected finding is addressed in the present invention by providing at least one sheet of radio-opaque material 22 across the patient's hips and waist, at an adjustable distance above the surface of the procedure table 10. The sheet 22, disposed across the width of the table 10, protects the physician from the scatter that originates from the patient's body. In this manner, the physician is further protected against harmful scatter, particularly scatter originating from the table itself and from the patient's body. FIG. 2 shows a side view of the adjustable frame assembly 30 of an embodiment of the adjustable X-ray shield according to the present invention, whereas FIG. 3 shows a perspective elevation view of the adjustable X-ray shield 100. Considering now FIGS. 2 and 3 collectively, the frame assembly 30 of the adjustable X-ray shield 100 includes a main support bar 1 mounted substantially vertically on the table 10 near the patient's waist level. The main support bar 1 extends both above the surface of the table 10 and underneath the table 10. A first transversal support bar 5 is attached to the main support bar 1 just below the table 10. The first transversal support bar 5 extends across the width of the table 10 or across a substantial portion thereof, as best shown in FIG. 3. A second transversal support bar 6 is pivotally mounted to the main support bar 1 above the surface of the table 10 and also extends across the width of the table 10 or a substantial portion thereof, as shown in FIGS. 2 and 3. A first longitudinal bar 7, shown in FIG. 3, is pivotally mounted to the main support bar 1 above the surface of the table 10 and extends along a portion of the length of the table 10 from the main support bar 1 to at least past the patient's chest. As shown in FIG. 3, the first longitudinal support bar 7 may include an articulated joint 32, thereby allowing the physician to swing a portion of the first longitudinal support bar 7 and any attached sheet of radio-opaque shielding material away from the table 10. The first transversal, the second transversal and the first longitudinal support bars 5, 6 and 7 may be made from metal such as stainless steel or aluminum, from a radiolucent material, such as carbon fiber or from a combination thereof. As shown in FIGS. 2 and 3, the second transversal and the first longitudinal bars 6, 7 are pivotally attached to the main support bar 1 by respective clevis joints 9, 8 having respective pivot pins (not shown). Tightening the pivot pins increases the friction in the levis joints 9, 8. The main support bar 1 includes an outer support tube 2 below the table 10, an upper support tube 3 above the table 10 and a telescoping support bar 4 slidingly mounted at least within the upper support tube 3. The telescoping support bar 4 allows the height of the second transversal and first longitudinal support bars 6, 7 and thus of the sheets 20, 22 and 23 to be adjusted above the surface of the table to accommodate the patient's body habitus and to provide optimal radiation attenuation. For applications in which shielding is desired for personnel positioned on the side of the table 10 opposite to the side closest to the first longitudinal support bar 7 (the patient's left side as he or she is laying on the procedure table 10), a second upper support assembly, similar to upper support assembly 3, may be attached to the outer support tube 16. A second longitudinal support bar may then be attached by a clevis joint to the second upper support assembly. When a sheet of radio-opaque shielding material similar to sheet 20 is attached to this second longitudinal support bar, additional shielding on the patient's left side will be obtained. The second upper support assembly, the second longitudinal support bar, the levis joint connecting the two, as well as the sheet of radio-opaque shielding material attached to the second longitudinal support bar are not shown, for clarity, as their structures are similar to their counterparts on the patient's right side. For applications in which it is anticipated that X-ray scatter will be a factor above the level of the second transversal and first longitudinal support bars 6, 7, additional shielding may be required. This may be achieved by means of a ceiling mounted transparent leaded acrylic shield with a 1 millimeter lead equivalency, which is available from, for example, Minex Engineering, Antioch, Calif. As shown in FIG. 2, the first transversal support bar 5 includes a telescoping extender bar 15, allowing the adjustable frame assembly 30 according to the present invention to accommodate procedure tables of varying widths. The X-ray shield according to the present invention may be integral to the procedure table 10. Alternatively, as shown in both FIGS. 2 and 3, the X-ray shield according to the present invention may be removably attached to the table 10 by means of a clamping assembly. Preferably, as in the embodiment shown in FIG. 2, the upper support tube 3 should be removable, allowing the clamping assembly to remain attached to the table 10 at all times, if the adjustable shield according to the present invention is not to be used for a particular case. The clamping assembly may include mounting pads 13 and 14, which mounting pads support the adjustable frame assembly 30 on the table 10. The mounting pads 13 and 14 are placed on opposite sides and across the width of the procedure table 10. The separation between the mounting pads 13 and 14 is adjustable by means of the telescoping extender bar 15 of the first transversal support bar 5. According to one embodiment of the present invention, the clamping assembly includes a bell crank mechanism attached to the first transversal support bar 5 underneath the table 10 to secure the adjustable frame assembly 30 to the table 10. As shown in FIG. 2, the bell crank mechanism may include a pair of rectangular blocks 17, 18 each of which is pivotally attached to one end of a pair of center pivots 24, 25, respectively. The pair of rectangular blocks 17, 18 may be made of hard plastic or from other suitably hard material. The pair of rectangular blocks 17, 18 may be attached to the pair of center pivots 24, 25 by a pair of screws, for example. Likewise, the pair of center pivots 24, 25 may also be pivotally attached to the first transversal support bar 5 by means of screws or other suitable fasteners. Attached to the other end of the center pivots 24, 25 are a pair of threaded cylinders 26, 27, respectively. The threaded cylinders 26, 27 include respective cylinder threads 28, 29. The threaded cylinders 26, 27 are inserted through a threaded bore within the outer support tube 16 and the outer support tube 2 of the main support tube 1. Turning the threaded cylinder heads 31, 32 of the threaded cylinders 26, 27, respectively, causes the rectangular blocks 17, 18 to act like cams on the undersurface of the table 10 and exert a force thereon. The table 10 is then squeezed between the two rectangular blocks 17, 18, catching respective edges of the underside of the table 10. The rectangular blocks 17, 18 also exert a force component toward the mounting pads 14 and 13, respectively, further securing the adjustable frame assembly 30 to the table 10. It is to be noted that the embodiment of the clamping assembly described herein and shown in the referenced figures is but one of many possible embodiments of such a clamping assembly. Indeed, any such clamping assembly that is effective in securing the adjustable frame assembly 30 to the table 10 may be implemented within the context of the present invention. Whichever clamping assembly is implemented, however, must attach the adjustable frame assembly 30 to the table 10 with sufficient strength to allow the frame assembly to securely and safely support the combined weight of at least the sheets of radio-opaque shielding material 20, 21, 22 and 23. As shown in FIG. 3, at least one sheet of radio-opaque shielding material, such as sheets 20, 21, 22 and 23, is attachable to the first transversal support bar 5, the second transversal support bar 6 and the first longitudinal support bar 7. For example, the second transversal support bar 6 may support not only the sheet 22 having the cutout portion therein, but also another sheet of radio-opaque shielding material 23 draped over the patient's pelvic and thigh areas to attenuate scatter therefrom. The sheet 23 may be a rectangular sheet of radio-opaque material and may be attached to the second transversal support 6 adjacently to the main support bar 1. Providing additional shielding, the sheet of radio-opaque material 21 is particularly effective in attenuating X-ray scatter originating from underneath the table, while affording the physician with unobstructed space in which to stand. Such sheet 21 is attached to the first transversal support bar 5 and spans substantially the width of the table 10 from just underneath the table 10 to the floor surface. As shown in FIG. 2, the sheets of radio-opaque shielding material may overlap one another, to provide overlapping coverage along at least the vertical axis of the main support bar 1. Moreover, overlapping coverage may also be indicated on the patient's left side, along the axis of the second upper assembly support bar attached to the outer support tube 16, if the patient's left side is to be shielded. This overlapping coverage provides additional shielding when, for example, the second transversal and the first longitudinal support bars 6, 7 are swung away from their depicted positions. Such repositioning of the radio-opaque sheets may be necessary when the imaging angle is changed during a procedure. Preferably, the sheets 20, 21, 22 and 23 have at least a 1 millimeter lead equivalency rating. The sheets 20, 21, 22 and 23 may be attached to their respective support bars 7, 5, and 6 by any suitable means. Preferably, such attachment means allow the sheets 20, 21, 22 and 23 to be removable from the adjustable frame assembly 30. For example, VELCRO.RTM. hook and loop fasteners may be utilized with good results. The adjustable X-ray shield according to the present invention, as described and illustrated herein, is believed to be highly effective in blocking a substantial portion of scatter from the procedure table 10 itself, as well as from the patient's body. Accordingly, the present invention may allow the physician to dispense with a high lead equivalency (heavy) lead apron, or to dispense with the lead apron altogether. However, to insure the safety of the physician and that of other personnel present in the operating room, it is prudent to monitor the effectiveness of the adjustable shield. Moreover, as the shield must often be reconfigured and moved to accommodate changes in position of the X-ray tube, such monitoring should preferably be substantially constant to insure that the shield is optimally configured at all times to protect the physician from X-ray or other radiation scatter. According to another embodiment of the adjustable shield according to the present invention, at least one of the sheets of radio-opaque shielding material 20, 21, 22 and 23 (as well as those on the patient's left side, if present) includes at least one radiation sensor, such as an X-ray sensor. FIG. 4 shows an embodiment of an adjustable radiation shield according to the present invention, wherein the sheets 20, 21, 22 and 23 include a plurality of X-ray sensors attached thereto. The plurality of X-ray sensors 40 of FIG. 4 form an array of sensors that are connected to a data processing and display device, such as a computer 50 and a display 51. The display 51 is preferably visible to the physician during the interventional procedure, to allow the physician to monitor, in real time, the efficacy and proper deployment of the adjustable shield according to the present invention. The array of sensors 40 may be connected to the data processing and display device via a communication link 45, which may include wires, or may be a wireless communication channel. A plurality of additional sensors 46 (only two of which are shown in FIG. 4) are provided, which may be strategically placed anywhere in the operating room, or may be worn on the physician's or other caregiver's person, to provide a direct reading of the amount of radiation the physician (or other personnel in the room) is receiving and/or has cumulatively received. One of these additional sensors 46 may also be attached to the patient's back or to the table, to measure the patient's entrance dose of X-ray radiation. Although the additional sensors 46 are shown, in FIG. 4, as being attached to the computer 50, they may alternatively be connected to and form an integral part of the array of sensors 40 instead. The sensors 40, 46 may be semiconductor X-ray sensors, such as CdZnTe radiation sensors, available from eV Products, Saxonburg, Pa. The sensors 40 may be attached to the sheets 20, 21, 22 and 23 or may be sewn therein. The data processing and display device preferably allows the physician to view, in real time, his or her instantaneous radiation dose, as well as his or her cumulative radiation dose. Entrance dose data from the sensor attached to the patient's back may also be displayed. Historical radiation data for the physician may be stored within the data processing device 50, and such data may be later accessed and thereafter updated by entering a physician ID code, for example. In this manner, an accurate and timely source of radiation dose data may be acquired and maintained for each physician using the adjustable X-ray shield according to the present invention. According to one embodiment, the display 51 may display a graphical representation of the shield and radiation level indicia adjacent thereto or superimposed thereon. Such indicia may include color, numerical data or other perceptible and intuitive indication of radiation levels. To acquire the relevant radiation data, the sensors 40, 46 may be periodically polled, may generate interrupt signals, or may utilize some other protocol, thereby allowing the data processing and display unit to process and display real time radiation scatter data. Utilizing this real time information, the physician may make timely adjustments to the adjustable shield of the present invention to insure that it is optimally positioned at all times during a procedure. In this manner, the physician forms part of a feedback loop, alternately adjusting the shield and observing the resultant changes in the readings of the sensors 40, 46 on the display 51. Appropriate data acquisition and rendering software should be loaded and running on the computer 50. Should the display unit 51 show that one or more of the semiconductor sensors 40, 46 are registering an unacceptable level of scatter, an alarm may sound and the physician may then make any appropriate adjustments to the shield during the procedure to minimize radiation exposure. While the foregoing detailed description has described several embodiments of this invention, it is to be understood that the above description is illustrative only and not limiting of the disclosed invention. For example, the clamping assembly described herein may be varied to suit the particular procedure table utilized. Other details of the frame assembly or sheets of radio-opaque material may vary from that described and illustrated herein, without, however, departing from the spirit and scope of the present invention. For example, a letter "J" shaped rigid support member may be slid under the patient's right thigh and a sheet of radio-opaque shielding material may be draped thereon, to further protect the physician from scatter directed orthogonally from the patient's thigh. A number of other modifications will no doubt occur to persons of skill in this art. All such modifications, however, should be deemed to fall within the scope of the present invention. Thus, the invention is to be limited only by the claims as set forth below.
	claims	1. A process of treating hydrogen gas liberated from the acid or alkaline dissolution of a metal, the process comprising a step of passing the liberated hydrogen gas through a reactor containing an oxidising agent for oxidation of the hydrogen gas into water, followed by a step of regenerating the oxidising agent, wherein the oxidising agent is diluted with an inert diluent. 2. A process according to claim 1, wherein a step of regenerating the oxidising agent is carried out after each oxidation step. 3. A process according to claim 1, wherein the oxidising agent comprises a metal oxide in bulk form or finely dispersed on the surface of an inert support. 4. A process according to claim 1, wherein the inert diluent comprises stainless steel pellets. 5. A process according to claim 1, wherein the oxidising agent comprises copper oxide. 6. A process according to claim 1, wherein the step of regenerating the oxidising agent comprises passing a gas containing oxygen through the reactor containing the oxidising agent to be regenerated. 7. A process according to claim 1, wherein the metal, the dissolution of which liberates hydrogen gas, comprises uranium. 8. A process according to claim 7, wherein the metal is a uranium-aluminium alloy. 9. A process according to claim 1, wherein the reactor is at least partially immersed in an alumina bath. 10. A process according to claim 1, wherein the alumina bath is supplied with one or more heating elements. 11. An apparatus for carrying out a process according to claim 1, the apparatus comprising a reactor containing an oxidising agent for the oxidation of hydrogen gas into water, wherein the reactor is at least partially immersed in an alumina bath. 12. An apparatus according to claim 11, wherein the alumina bath is supplied with one or more external heating elements. 13. An apparatus according to claim 11, wherein the oxidising agent comprises a metal oxide in bulk form or a metal oxide finely dispersed on the surface of an inert support. 14. An apparatus according to claim 11, wherein the oxidising agent is diluted with an inert diluent. 15. An apparatus according to claim 14, wherein the inert diluent comprises stainless steel pellets. 16. An apparatus according to claim 11, wherein the oxidising agent comprises copper oxide. 17. A process of treating hydrogen gas liberated from the acid or alkaline dissolution of a metal, the process comprising a step of passing the liberated hydrogen gas through a reactor containing an oxidising agent for oxidation of the hydrogen gas into water, wherein the oxidising agent comprises a metal oxide finely dispersed on an inert carrier and/or diluted with an inert diluent. 18. A process according to claim 17, further comprising a step of regenerating the oxidising agent. 19. A process according to claim 17, wherein the metal oxide comprises copper oxide.
	description	The present invention relates to a nuclear fuel assembly for a boiling water reactor comprising a base, a head, and a bundle of full length fuel rods and partial length fuel rods, said bundle extending upwardly and longitudinally from the base to the head, the nuclear fuel assembly comprising at least one clamp for longitudinally retaining a lower end of a partial length fuel rod with respect to the base. In a nuclear fuel assembly for a boiling water reactor (BWR in the following specification), the full length fuel rods (FLFR in the following specification) are received between the base and the head of the fuel assembly with a small longitudinal gap allowing the FLFRs to expand in their longitudinal direction during operation of the nuclear reactor. Usually, the upper ends of the FLFRs are retained by the head of the nuclear fuel assembly. The partial length fuel rods (PLFR in the following specification) are used in BWRs for reasons of thermohydraulic stability and neutron moderation. PLFRs extend upwardly from the base of the fuel assembly and stop at a distance from the fuel assembly's head. Usually, the length of the PLFRs is comprised between 25% and 75% of the length of the FLFRs. The fuel rods are positioned and held longitudinally and transversally by a plurality of spacer grids spaced along the fuel rods. These spacer grids allow for local and limited sliding movement of the fuel rods in the spacer grids to accommodate the expansion of the fuel rods under irradiation. Nevertheless, under specific operating conditions, the longitudinal holding force applied by the spacer grids to the bundle of fuel rods may not be sufficient to prevent a significant longitudinal displacement of PLFRs. Accordingly, in order to prevent the PLFRs from lifting-off during nuclear reactor operation, PLFRs are usually attached to the base of the fuel assembly. US-2008/0101528 discloses a fuel assembly. In this fuel assembly, the lower ends of the PLFRs are attached to the base through clamps which are integral with the base. However, such an arrangement requires specific machining to achieve adequate tolerances for the clamps. Therefore, while such an arrangement is satisfactory, it is still desirable to simplify its design and lower its price. An object of the invention is therefore to provide a fuel assembly which reduces the risk of lift-off of the PLFRs during operation of the nuclear reactor and which induces lower costs. To this end, the invention relates to a fuel assembly as defined above, wherein the clamp is an additional part fitted to the base, the clamp is at least partially received in a housing provided in the base, and the clamp is assembled to the base by mechanical engagement of complementary assemblies. According to specific embodiments, the fuel assembly may comprise one or several of the following features: the complementary assemblies comprise first and second assemblies, the first assembly being adapted to retain the clamp against an upward displacement of the clamp with respect to the base and the second assembly being adapted to retain the clamp against a downward displacement with respect to the base, the clamp is embedded in the housing, the housing is a through-hole extending from an upper surface of the base to a lower surface of the base, the clamp comprises support, adapted to contact a portion of the lower plug of the partial length fuel rod in order to hold the lower plug of the partial length fuel rod at a distance from the lower surface of the base, the support comprise support tabs, spaced angularly about a longitudinal axis of the clamp, each support tab comprising a free end extending inwards in the direction of the longitudinal axis of the clamp, the free ends of the support tabs delimiting an opening for receiving said portion of the lower plug of the partial length fuel rod, the second assembly comprise a lower support surface provided in the housing, the support tabs being supported longitudinally on the lower support surface (55), the first assembly comprise an abutting surface provided in the housing, and elastic assembly tabs, provided on the clamp and comprising free ends extending upwards, the abutting surface being adapted to engage with the free ends of the elastic assembly tabs, the clamp comprises elastic retaining tabs, spaced angularly about the longitudinal direction of the clamp and adapted to engage with a shoulder provided on the lower plug of the partial length fuel rod to prevent a disengagement of the partial length fuel rod from the base, the clamp comprises a body and the support tabs extend inwards from a lower edge of the body, and the retaining tabs and assembly tabs extend upwards from an upper edge of the body, the clamp only contacts the lower plug of the partial length fuel rods by the support tabs and of the retaining tabs, a radial clearance existing between an inner surface of the clamp and the peripheral surface of the lower plug of the partial length fuel rod in the portion of the partial length fuel rod extending between the support tabs and the retaining tabs, the complementary assemblies comprise a central substantially flat base of the clamp, supported on a bottom of the housing and an abutting surface provided in the housing, the abutting surface being adapted to engage with upper free ends of the clamp, the clamp comprises a constriction, which resiliently engages with the lower plug of the partial length fuel rod and is adapted to cooperate with a shoulder provided on the lower plug of the partial length fuel rod, the base comprises an anti-debris filter, assembled to the base, the anti-debris filter comprising parallel bars, the housing being provided in a bar, the clamp comprises a central portion fitted around the bar and free ends, extending into the housing and forming a constriction in said housing, and the assemblies comprise complementary portions of the bar and the central portion of the clamp providing a form fit between the bar and the clamp and the constriction resiliently engages with the lower plug of the partial length fuel rod and is adapted to cooperate with a shoulder provided on the lower plug of the partial length fuel rod. FIG. 1 shows a nuclear fuel assembly 1 for a boiling water reactor (BWR). This fuel assembly 1 extends along a vertical longitudinal direction L. Such a fuel assembly 1 is intended to be placed in a core of a nuclear reactor where coolant flows upwardly during operation of the nuclear reactor. The fuel assembly 1 conventionally comprises: a base 2 intended to rest on a lower plate of the core, a head 3, a bundle 4 of fuel rods, said bundle 4 extending longitudinally between the base 2 and the head 3, a water channel 5 placed inside the bundle 4 and connecting the base 2 to the head 3, a plurality of spacer grids 6 spaced apart along the longitudinal direction L and maintaining the bundle 4 longitudinally and transversally, a fuel channel 7 surrounding the bundle 4 and the base 2 and fixed to the head 3. Only a portion of the fuel channel 7 is shown on FIG. 1. The bundle 4 comprises full length fuel rods (FLFRs) 9 and partial length fuel rods (PLFRs) 11 not shown on FIG. 1. In the disclosed embodiment, the fuel assembly 1 comprises 20 PLFRs 11 and 92 FLFRs 9. However, these numbers may change from one embodiment to the other. Each FLFR 9 and PLFR 11 comprises a cladding containing nuclear fuel pellets and closed by upper and lower plugs. The FLFRs 9 are retained through their upper ends by the head 3 in a conventional way, e.g. by a grid with holes receiving pins provided on the upper plugs of the FLFRs 9. The FLFRs 9 extend downwardly from the head 3 up to the base 2 while maintaining a longitudinal gap between the lower ends of the FLFRs 9 and the base 2 to allow longitudinal expansion of the FLFRs 9 during operation of the nuclear reactor. The PLFRs 11 are shorter than the FLFRs 9. They extend upwardly from the base 2 and stop at a distance from the head 3. In some embodiments, the PLFRs 11 within the fuel assembly 1 may have different lengths. As shown on FIG. 2, the lower plug 13 of each PLFR 11 comprises a shank 15, extended downwardly by a converging portion 18. A shoulder 20 is provided on the lower plug 13 at the junction between the shank 15 and the converging portion 18. At the junction between the shank 15 and the converging portion 18, the diameter of the converging portion 18 is greater than the diameter of the shank 15. In the disclosed embodiment, the shank 15 is cylindrical and the converging portion 18 is substantially conical. The base 2 includes a debris filter. This debris filter has, for example, a first set of parallel transversal bars and a second set of parallel transversal bars 27. The bars 27 of the second set of parallel bars extend e.g. perpendicular with respect to the bars of the first set of bars. On the figures, only one bar 27 of the debris filter is shown. Housings 30, having a longitudinal axis B, are provided in the bars 27. Each housing 30 receives a clamp 33. Each clamp 33 is assembled to the base 2 by mechanical engagement of complementary assembly. The complementary assemblies comprise first assembly, adapted to retain the clamp 33 against an upward displacement with respect to the base 2 and second assembly, adapted to retain the clamp 33 against a downward displacement with respect to the base 2. The first and second assembly allow a functional axial clearance of the clamp 33 with respect to the base 2, to allow the installation of the clamp 33 in the base 2 during manufacturing. Each clamp 33 receives the lower plug 13 of a respective PLFR 11 and is adapted for longitudinally retaining the respective PLFR 11 on the base 2, in order to prevent its disengagement from the base 2. All the housings 30 and the respective clamps 33 they receive have generally similar shapes. Only one housing 30, the respective clamp 33 and their relationship with the respective PLFR 11 are disclosed hereinafter with respect to FIGS. 2 to 7. FIGS. 2 to 4 show a first embodiment, where the lower plug 13 of the PLFR 11 is free to move longitudinally between a seated position (left part of FIG. 2), in which it is longitudinally supported by supports provided on the clamp 33 and a pulled away position (right part of FIG. 2), in which it is longitudinally retained by retainers provided on the clamp 33. In the seated position, the supports prevent the PLFR 11 from moving further downwards, for example under the effect of gravity. In the pulled away position, the retainers prevent the PLFR 11 from moving further upwards, for example under the effect of the flow of coolant, and thus from becoming disengaged from the base 2. In the nuclear fuel assembly 1, the PLFR 11 is free to move upwards from the seated position to the pulled away position or downwards from the pulled away position to the seated position. During normal operation of the nuclear reactor, the PLFR 11 is in the pulled away position, due to the flow of coolant through the nuclear fuel assembly 1. While the seated and pulled away positions of the PLFR 11 are shown respectively on the left and right parts of FIG. 2 with respect to the first embodiment, the above mentioned features may apply to all other embodiments. In the first embodiment, the clamp 33 is embedded in the housing 30. The housing 30 is a through-hole, extending from an upper surface 36 of the base 2, e.g. an upper surface 36 of the respective bar 27 to a lower surface 39 of the base 2, e.g. a lower surface of the bar 27. Upper and lower through-hole edges 42, 44 are formed respectively at the intersections of the housing 30 with the upper and lower surfaces 36, 39 of the base 2. The lower plug 13 of the PLFR 11 does not protrude below the lower surface 39 of the base 2. In the first embodiment, the housing 30 is a stepped through-hole. It comprises, starting from the lower surface 39 of the base 2: a first, a second and a third housing section 45, 46, 47, e.g. cylindrical sections of increasing diameter, a fourth housing section 48, e.g. a cylindrical section having a diameter which is smaller than that of the third housing section 47, and a fifth housing section 49, e.g. a cylindrical section having a diameter that is greater than the diameter of the fourth housing section 48. A top surface of the third housing section 47 forms an abutting surface 51. The abutting surface 51 extends in a plane that is perpendicular to the longitudinal axis B of the housing 30. A bottom surface of the fifth housing section 49 forms an upper support surface 53. A bottom surface of the second housing section 46 forms a lower support surface 55. The upper and lower support surfaces 53, 55 are substantially perpendicular to the longitudinal axis B of the housing 30 and parallel to the abutting surface 51. The clamp 33 according to the first embodiment is shown in more detail on FIGS. 3 and 4. It comprises a hollow body 58, e.g. of circular cross-section, having a longitudinal axis A. The body 58 is received in the second and third housing sections 46, 47 of the housing 30. The outer diameter of the body 58 is smaller than or equal to the diameter of the second housing section 46. The body 58 is rigid. The inner diameter of the body 58 is greater than the diameter of the shank 15 of the lower plug 13. In this embodiment, the supports, adapted to prevent a downward displacement of the lower plug 13 of the PLFR 11 from its seated position, comprise support tabs 61. Each support tab 61 comprises a free end 62 which extends inwards from a lower edge 63 of the body 58 towards the longitudinal axis A of the body 58. The support tabs 61 are spaced angularly about the longitudinal axis A of the clamp 33. The support tabs 61 have a bent shape and comprise first and second portions 65, 67, connected by means of a bend 69. The first portion 65 has an upper end 71 attached to the lower edge 63 of the body 58. The first portion 65 extends downwards with respect to the lower edge 63 and inwards with respect to an outer peripheral surface 66 of the body 58. The second portion 67 extends upward and inward with respect to the bend 69. The end of the second portion 67 is the free end 62. In this embodiment, each support tab 61 is made one-piece. The support tabs 61 are rigid. In particular, they do not yield under the weight of the PLFR 11. The free ends 62 jointly form a discontinuous circumference partially delimiting an opening 75, adapted to allow a tip of the converging portion 18 of the PLFR 11 to pass through said opening 75 and protrude below said free ends 62 in the seated position of the PLFR 11. The diameter of the opening 75 is intermediate between the smallest and the largest diameters of the converging portion 18. Thus, the free ends 62 contact the converging portion 18 of the respective PLFR 11 in the seated position. They are adapted to jointly longitudinally support the PLFR 11 in the seated position. The diameter of the opening 75 is smaller than the diameter of the first housing section 45. The opening 75 formed by the free ends 62 is spaced longitudinally from the lower surface 39 of the base 2 in order to prevent the lower plug 13 from plugging the first housing section 45 of the housing 30. The clamp 33 may e.g. comprise four support tabs 61, e.g. regularly spaced about the longitudinal axis A of the clamp 33. As is shown on FIG. 2, a lower surface 77 of the bend 69 is supported on the lower support surface 55 provided in the housing 30. Thus, in the first embodiment, the second assembly comprises the lower surface 77 of the bend 69 and the lower support surface 55. In the first embodiment, the clamp 33 further comprises elastic assembly tabs 78. The assembly tabs 78 are spaced angularly with respect to the longitudinal axis A of the clamp 33. They extend upwards from an upper edge 81 of the body 58 of the clamp 33. In a resting configuration, the assembly tabs 78 extend outwards with respect to the outer peripheral surface 66 of the body 58. They are elastically deformable under the effect of a force applied to their outer surface 83 at least towards a configuration in which they are flush with the outer peripheral surface 66 of the body 58. All the assembly tabs 78 may be identical. The clamp 33 may e.g. comprise four assembly tabs 78, regularly spaced about the longitudinal axis A of the clamp 33. The length of the assembly tabs 78 is such that the assembly tabs 78 are entirely comprised in the third housing section 47 and such that their respective free ends 86 are adapted to longitudinally abut against the abutting surface 51 when the clamp 33 is received in the housing 30. Thus, the assembly tabs 78 and the abutting surface 51 form the first assembly, adapted to retain the clamp 33 against an upward displacement with respect to the base 2. During the mounting of the nuclear fuel assembly 1, the clamp 33 is inserted into the housing 30 from the upper surface 36 of the base 2. During the insertion of the clamp 33 into the housing 30, the assembly tabs 78 are elastically deformed inwards by the force exerted by a peripheral wall 88 of the fourth housing section 48. As soon as the free ends 86 have passed the fourth housing section 48, the assembly tabs 78 deform elastically outwards towards their resting configuration, until they abut against a peripheral wall 91 of the third housing section 47. When the lower surfaces 77 of the support tabs 61 are supported on the lower support surface 55 provided in the housing 30, the free ends 86 of the assembly tabs 78 are located below the abutting surface 51, in order to retain the clamp 33 against an upward displacement. The clamp 33 further comprises elastic retaining tabs 94, adapted to longitudinally retain the lower plug 13 of the respective PLFR 11, in order to prevent its disengagement from the bar 27 and thus from the base 2. The clamp 33 may e.g. comprise four elastic retaining tabs 94. The elastic retaining tabs 94 are spaced about the longitudinal axis A of the clamp 33. They extend upwards from the upper edge 81 of the body 58. In the illustrated embodiment, the retaining tabs 94 are identical. Each retaining tab 94 comprises a constriction 97. As shown on the right side of FIG. 2, the constrictions 97 of the retaining tabs 94 extend inwards, in the direction of the longitudinal axis A of the clamp 33, above the shoulder 20 provided on the lower plug 13 of the respective PLFR 11. The constrictions 97 jointly delimit an opening 100. When the PLFR 11 is in the pulled away position, the constrictions 97 are adapted to engage with the shoulder 20, in order to prevent an upward displacement of the PLFR 11 and thus a disengagement of the PLFR 11 from the base 2. In a resting configuration, the diameter of the e.g. essentially circular discontinuous circumference of the opening 100 is smaller than the diameter of the converging portion 18 of the respective PLFR 11 at the junction between the converging portion 18 and the shank 15. From the resting configuration, the retaining tabs 94 are elastically deformable radially outwards, under the effect of a force applied to an inner surface 102 of the constrictions 97. In one embodiment, the diameter of the opening 100 in the resting configuration is smaller than the diameter of the shank 15. This feature increases the friction between the lower plug 13 and the retaining tabs 94, and therefore increases the clamping force of the clamp 33. The elasticity of the retaining tabs 94 is adapted to allow an elastic radial deformation of the retaining tabs 94 away from their resting configuration when the PLFR 11 is intentionally inserted into or extracted out of the clamp 33, and so as to prevent an outward deformation of the retaining tabs 94 merely under the effect of an upward force exerted by the PLFR 11, more particularly by the shoulder 20, on the constrictions 97 during operation of the nuclear fuel assembly 1. In the first embodiment, each retaining tab 94 further comprises, above the constriction 97, a substantially planar portion 105, which extends outwards. In the nuclear fuel assembly 1, the substantially planar portion 105 extends along a plane that is substantially parallel to the plane of the upper support surface 53 provided in the housing 30. The substantially planar portion 105 is adapted to facilitate the deformation of the retaining tabs 94 away from their resting configuration during insertion of the PLFR 11 into the clamp 33. In the first embodiment, the assembly tabs 78 and the retaining tabs 94 alternate along the upper edge 81 of the body 58. In this nuclear fuel assembly 1, the risk of lift-off of the PLFRs 11 during operation of the nuclear reactor is reduced, since the lower plugs 13 of the PLFRs 11 are longitudinally retained on the base 2 by the cooperation of the shoulder 20 provided on the lower plug 13 with the elastic retaining tabs 94. The nuclear fuel assembly 1 induces lower costs, since the clamp 33 is simple to manufacture and can be assembled and secured to the base 2 in one operation, simply by mechanical engagement of complementary assemblies. The fact that the housing 30 is a through-hole allows for coolant to flow through the base 2 and along the lower plugs 13 of the PLFRs 11. This flow of coolant is useful to cool the lower plugs 13 of the PLFRs 11 and to avoid CRUD (Chalk River Unidentified Deposits) occurring during normal plant operation and which may interfere with the proper function of the clamp 33 during pull out and insertion of PLFR 11. FIG. 5 shows a clamp 33 according to a second embodiment. The second embodiment differs from the first embodiment by the cross-section of the body 58 and the shape of the retaining tabs 94. In the second embodiment, the body 58 has a polygonal cross-section, and in particular an octagonal cross-section. The body 58 comprises e.g. eight rectangular faces 110, extending along the longitudinal direction A of the clamp 33 from the lower edge 63 to the upper edge 81 of the body 58. Each retaining tab 94 and each assembly tab 78 extends upwards from a portion of the upper edge 81 of the body 58 corresponding to one of the rectangular faces 110 of the body 58. In this embodiment, the diameter of the circle in which the octagonal cross-section of the body 58 is inscribed is smaller than or equal to the diameter of the second housing section 46. Moreover, the retaining tabs 94 do not comprise the planar portion 105. The nuclear fuel assembly 1 according to the second embodiment is simpler to manufacture than the nuclear fuel assembly 1 according to the first embodiment, since it does not comprise the planar portion 105. In the first and the second embodiment, the clamp 33 may comprise a slit 112 (FIG. 5), adapted to facilitate the insertion of the clamp 33. The octagonal cross-section of the body 58 in the second embodiment can be used together with the slit 112 to expand the body 58 when the end plug 13 is inserted into the clamp 33 in order to further press the assembly tabs 78 against the peripheral walls of the housing 30. In the third embodiment shown on FIG. 6, each housing 30 comprises a recess 130 provided in the base 2, and more particularly in a respective bar 27. The recess 130 has a longitudinal axis B and opens upwardly in order to receive the respective PLFR 11. The housing 30 is delimited by a closed bottom 132, a peripheral wall 134 and a top 136. The peripheral wall 134 extends upwardly from the bottom 132. The top 136 extends inwardly, towards the longitudinal axis B of the housing 30, from a top edge 138 of the peripheral wall 134. The top 136 delimits an opening 141 having transverse dimensions smaller than the cross-section of the recess 130 defined by the peripheral wall 134, and greater than the transverse dimensions of the shank 15 and the converging portion 18 of the lower plug 13. A lower surface of the top 136 forms an abutting surface 143. The bottom 132 is e.g. substantially disk-shaped. The peripheral wall 134 has e.g. a cylindrical shape of substantially circular cross-section. The clamp 33 is received in the respective housing 30. It is embedded in the housing 30. The clamp 33 is substantially symmetrical with respect to the longitudinal axis B of the housing 30. It comprises a substantially flat base 145, extended upwardly by at least two legs 147, the legs being arranged at symmetrical positions with respect to the longitudinal axis A of the clamp 33. In the illustrated embodiment, the clamp 33 comprises two legs 147 and is substantially U-shaped. In this embodiment, the retainers comprise a constriction 150, provided at the top end of the clamp 33 and adapted to longitudinally retain the respective PLFR 11. The constriction 150 is formed by a substantially V-shaped fold 155, provided in a diametrically opposed location on each of the legs 147 of the clamp 33. The constriction 150 is adapted to engage the shoulder 20 provided on the lower plug 13, when the PLFR 11 is in its pulled away position, in order to prevent the PLFR 11 from moving further upwards, and thus to prevent a disengagement of the PLFR 11 from the base 2. Free ends 157 of the clamp 33 are adapted to abut against the abutting surface 143. The free ends 157 extend upwardly towards the top 136 and outwardly towards the peripheral wall 134 of the housing 30 from the constriction 150. The first assembly, adapted to retain the clamp 33 against an upward displacement with respect to the base 2 thus comprises the free ends 157 of the clamp 33 and the abutting surface 143 provided on the housing 30. The base 145 of the clamp 33 is supported on the bottom 132 of the housing 30. The base 145 and the bottom 132 thus form the second assembly, adapted to retain the clamp 33 against a downward displacement with respect to the housing 30. The PLFR 11 is mobile along the longitudinal direction between a seated position and a pulled away position. In the seated position of the PLFR 11, the retainer, provided on the clamp 33, in particular the constriction 150, is spaced longitudinally from the shoulder 20 provided on the PLFR 11. In the pulled-away position, the PLFR 11 has moved upwards along the longitudinal axis with respect to the seated position and the retainer engages the shoulder 20. During normal operation of the nuclear reactor, the PLFR 11 is in the pulled away position, under the effect of the flow of coolant. The clamp 33 is for example a spring made one-piece, in particular a sheet spring. The elastic retaining force of the clamp 33 is chosen so as to allow the intentional insertion or extraction of the lower plug 13 of the PLFR 11 into or from the housing 30, and to prevent a disengagement of the PLFR 11 from the clamp 33 merely under the effect of the upward force exerted by the shoulder 20 on the constriction 150. In the disclosed third embodiment, the housing 30 has a substantially circular shape. However, other shapes may be contemplated. In this embodiment, the housing 30 has a closed bottom 132. However, alternately, the housing 30 may be a through hole, an opening being provided in the bottom 132. The nuclear fuel assembly 1 according to the third embodiment of the invention reduces the risk of lift-off of the PLFRs during operation of the nuclear reactor, since the lower plugs 13 of at least some of the PLFRs 11 are longitudinally retained on the base 2 due to the cooperation between the constriction 150 of the clamp 33 and the shoulder 20 provided on the lower plug 13. This nuclear fuel assembly 1 also induces lower costs, since the clamp 33 can be easily assembled and secured to the base, simply by insertion into the housing 30. Moreover, the clamp 33 has a particular simple structure and is easy to manufacture. In one embodiment (not illustrated), the clamp 33 according to the second embodiment may be used in combination with the housing 30 according to the third embodiment of the invention. In this embodiment, the retaining tabs 94 and the assembly tabs 78 may have the same length. In the fourth embodiment shown on FIG. 7, each housing 30 comprises a stepped through-hole 160 having a longitudinal axis B, provided in the respective bar 27. The housing 30 delimits a first housing section 162, extended upwardly by a second housing section 164. The second housing section 164 has a bottom 166, e.g. of substantially annular shape, extended upwardly by a peripheral wall 168, e.g. of substantially cylindrical shape having a circular cross-section. The first housing section 162 has a peripheral wall 170, e.g. of substantially cylindrical shape having a circular cross-section. The first housing section 162 is open upwardly and downwardly. The transverse dimensions, e.g. the diameter of the first housing section 162 are smaller than the transverse dimensions, e.g. the diameter of the second housing section 164. In particular, the diameter of the first housing section 162 is approximately equal to the diameter of the tip of the converging portion 18 of the PLFR 11. In this embodiment, the first housing section 162 provides a passage for the coolant to flow through the bar 27 along the lower plug 13 of the PLFR 11. In the nuclear fuel assembly 1 according to this embodiment, the clamp 33 is symmetrical with respect to the longitudinal axis B of the housing 30. The clamp 33 is substantially U-shaped. It comprises a central portion, comprising a flat base 172, extended upwardly by two legs 174, and free ends 176. The central portion of the clamp 33 is fitted around the bar 27. The free ends 176 are bent inwards and form a constriction 179 in the housing 30. The free ends 176 are received in the housing 30. The constriction 179 is adapted to engage the annular shoulder 20 of the PLFR 11 in order to retain the PLFR 11 longitudinally on the base 2. In this embodiment, the first assembly comprises complementary portions of the bar 27 and the central portion of the clamp 33, these complementary portions providing a form fit between the bar 27 and the clamp 33, and the second assembly comprises the bend of the free ends 176 into the housing 30. The clamp 33 is for example a spring made one-piece, in particular a sheet spring. The elastic retaining force of the clamp 33 is chosen so as to allow the intentional insertion or extraction of the lower plug 13 of the PLFR 11 into or from the housing 30, and to prevent a disengagement of the PLFR 11 from the clamp 33 merely under the effect of the upward force exerted by the shoulder 20 on the constriction 179. In the disclosed fourth embodiment, the housing 30 has a substantially circular shape. However, other shapes may be contemplated. The nuclear fuel assembly 1 according to the fourth embodiment of the invention reduces the risk of lift-off of the PLFRs 11 during operation of the nuclear reactor, since the lower plugs 13 of at least some of the PLFRs 11 are longitudinally retained on the base due to the cooperation between the constriction 179 of the clamp 33 and the shoulder 20 provided on the lower plug 13. This nuclear fuel assembly 1 also induces lower costs, since the clamp 33 can be easily assembled and secured to the base 2, simply by fitting around the bar 27 and by engagement of the free ends into the housing 30. Moreover, the clamp 33 has a particular simple structure and is easy to manufacture. In all the described embodiments, the clamp 33 is preferably made of material with high yield strength such as Ni-based super-alloy such as Inconel®, or Fe-based super alloy or Ti alloy or even precipitation-hardened stainless-steel such as defined by AMS (Aerospace Material Specification) 5629 and 5643. Moreover, in all the described embodiments, the clamp 33 may be made one-piece. The nuclear fuel assembly 1 according to first, second, third and fourth embodiments allows the flow of coolant through the housing 30 and along the lower ends of the PLFRs 11. This flow of coolant cools the lower ends of the PLFRs 11, but it also rinses the housing 30 in particular in order to avoid CRUD (Chalk River Unidentified Deposits), which are likely to accumulate about the lower ends of the PLFRs in a boiling water reactor (BWR). As shown in the third embodiment, this feature is not necessarily present. In all the disclosed embodiments, the relationship between the base 2 and the PLFRs 11 can be implemented through other parts of the base 2 than the debris filter. Also, only some of the PLFRs 11 may be retained by clamps 33, other PLFRs 11 being retained by other known retainers.
	claims	1. In a continuous fueling nuclear fission reactor, the improvement comprising:determining an asymptotic core for the nuclear fission reactor; andproviding the nuclear fission reactor with a moderator-to-fuel ratio that is optimally moderated for the asymptotic core of the nuclear fission reactor, the moderator-to-fuel ratio allowing said nuclear fission reactor to be substantially continuously operated in an optimally moderated state. 2. The nuclear fission reactor of claim 1, wherein providing the nuclear fission reactor with a moderator-to-fuel ratio that is optimally moderated for the asymptotic core of the nuclear fission reactor comprises providing a fuel source that is optimally moderated for the asymptotic core of the nuclear fission reactor. 3. The nuclear fission reactor of claim 2, wherein providing a fuel source comprises providing a fuel source with a graphite moderator, said graphite moderator being present in an amount sufficient to allow said nuclear fission reactor to be substantially continuously operated in an optimally moderated state. 4. The nuclear fission reactor of claim 2, wherein providing a fuel source comprises providing a fuel source with a moderator selected from the group consisting of graphite, hydrogen, deuterium, and beryllium, said moderator being present in an amount sufficient to allow said nuclear fission reactor to be substantially continuously operated in an optimally moderated state. 5. A method for designing a continuous fueling nuclear fission reactor, comprising:a) specifying a continuous fueling reactor design, the reactor design including reactor parameters;b) specifying a fuel source design for a fuel source comprising a fuel pebble having a fueled zone and an unfueled zone, wherein specifying a fuel source design comprises determining a radius of an interface between the fueled zone and the unfueled zone of the fuel pebble comprising the fuel source;c) using the specified fuel source design and specified reactor design to determine an effective multiplication factor (keff) for an asymptotic core; andd) repeating (b) and (c) until an optimized fuel source design is developed that yields an asymptotic core with the highest value of the effective multiplication factor (keff); ande) selecting the optimized fuel source design as a fuel source to be used in the continuous fueling nuclear fission reactor so that the continuous fueling nuclear fission reactor can be substantially continuously operated in an optimally moderated state. 6. The method of claim 5, further comprising: verifying that the highest value of the effective multiplication factor (keff) is equal to 1.0 within a specified tolerance; and if the highest value of the effective multiplication factor (keff) is not about equal to one within said specified tolerance, repeating (a), (b), and (c) until the maximum value of the effective multiplication factor (keff) equal to 1.0 within said specified tolerance. 7. The method of claim 5, wherein determining the radius of the interface between the fueled zone and the unfueled zone establishes a number of fuel kernels to be provided in the fueled zone of the fuel pebble. 8. The method of claim 7, wherein the number of fuel kernels in the fueled zone is in a range of about 9,800 to about 10,000 fuel kernels. 9. The method of claim 5, wherein the radius of the interface between the fueled zone and the unfueled zone is in the range of about 2.3 to about 2.4 cm. 10. The method of claim 9, wherein the radius of the interface between the fueled zone and the unfueled zone is about 2.33 cm. 11. The method of claim 9, wherein the radius of the interface between the fueled zone and the unfueled zone is about 2.4 cm. 12. The method of claim 5, wherein said fuel source comprises a fuel pebble having a plurality of fuel kernels provided therein, and wherein determining a fuel source design comprises determining a number of said plurality of fuel kernels to be provided to said fuel pebble. 13. The method of claim 5, wherein said fuel source comprises a moderator, and wherein determining a fuel source design comprises determining an amount of moderator to be provided to said fuel source. 14. The method of claim 5, wherein said fuel source comprises a moderator, and wherein determining a fuel source design comprises determining a composition of moderator to be provided to said fuel source. 15. The method of claim 5, wherein the reactor parameters comprise one or more reactor parameters selected from the group consisting of reactor shape, reactor size, presence of reflectors, location of reflectors, composition of reflectors, size of reflectors, operating power level, refueling rate, fuel source re-circulation pattern, and burn-up cutoff for spent fuel. 16. The method of claim 5, wherein (c) comprises using PEBBED computer code or another code embodying the methods of the PEBBED code. 17. The method of claim 16, further comprising using COMBINE computer code in conjunction with the PEBBED code in an iterative process to determine the effective multiplication factor (keff) for the asymptotic core. 18. The method of claim 5, wherein (c) comprises:i) assigning an initial average burn-up level for the fuel source design;ii) calculating microscopic nuclear data corresponding to the initial average burn-up level;iii) using the microscopic nuclear data to determine corresponding nuclide data;iv) using the corresponding nuclide data to calculate revised microscopic nuclear data; andv) repeating (iii) and (iv) until the nuclide data converge. 19. The method of claim 18, further comprising repeating (iii) and (iv) until the microscopic nuclear data converge. 20. The method of claim 18, wherein said nuclide data comprise a nuclide number density and a nuclide distribution. 21. The method of claim 18, wherein (iii) further comprises using the microscopic nuclear data to determine a corresponding asymptotic loading and burn-up pattern. 22. A method for designing a continuous fueling nuclear fission reactor, comprising:a) specifying a continuous fueling reactor design;b) specifying a fuel source design for a fuel source comprising a fuel pebble having a fueled zone and an unfueled zone, wherein specifying a fuel source design comprises determining a radius of an interface between the fueled zone and the unfueled zone of the fuel pebble comprising the fuel source;c) using the specified reactor design and the specified fuel source design to determine a keff for the fuel source design;d) repeating (b) and (c) until an optimized fuel source design is developed having a keff that is about a maximum for the specified reactor design;e) verifying that the maximum value of keff is equal to one within a specified tolerance and if not equal to one within said tolerance, modifying the design specified in (a) and repeating (b), (c) and (d) until the maximum value of keff is one within the specified tolerance; andf) selecting as an optimal fuel source design the fuel source design having the keff that is about a maximum, the optimal fuel source design allowing said continuous fueling nuclear fission reactor to be substantially continuously operated in an optimally moderated state. 23. The method of claim 22, wherein determining the radius of the interface between the fueled zone and the unfueled zone establishes a number of fuel kernels to be provided in the fueled zone of the fuel pebble. 24. The method of claim 23, wherein the number of fuel kernels in the fueled zone is in a range of about 9,800 to about 10,000 fuel kernels. 25. The method of claim 22, wherein the radius of the interface between the fueled zone and the unfueled zone is in the range of about 2.3 to about 2.4 cm. 26. The method of claim 22 further comprising using PEBBED computer code in determining the keff for the fuel source design. 27. The method of claim 26, further comprising using COMBINE computer code in conjunction with the PEBBED code in an iterative process to determine the keff for the fuel source design. 28. The method of claim 22, wherein specifying an initial reactor design comprises specifying parameters selected from the group consisting of reactor shape, reactor size, presence of reflectors, location of reflectors, operating power level, refueling rate, fuel source re-circulation pattern, and burn-up cutoff for spent fuel. 29. A method for designing a continuous fueling nuclear fission reactor, comprising:a) specifying a continuous fueling reactor design, the reactor design including reactor parameters;b) specifying a fuel source design;c) using the specified fuel source design and specified reactor design to determine an effective multiplication factor (keff) for an asymptotic core; andd) repeating (b) and (c) until an optimized fuel source design is developed that yields an asymptotic core with the highest value of the effective multiplication factor (keff); ande) selecting the optimized fuel source design as a fuel source to be used in the continuous fueling nuclear fission reactor so that the continuous fueling nuclear fission reactor can be substantially continuously operated in an optimally moderated state. 30. A method for designing a continuous fueling nuclear fission reactor, comprising:a) specifying a continuous fueling reactor design;b) specifying a fuel source design;c) using the specified reactor design and the specified fuel source design to determine a keff for the fuel source design;d) repeating (b) and (c) until an optimized fuel source design is developed having a keff that is about a maximum for the specified reactor design;e) verifying that the maximum value of keff is equal to one within a specified tolerance and if not equal to one within said tolerance, modifying the design specified in (a) and repeating (b), (c) and (d) until the maximum value of keff is one within the specified tolerance; andf) selecting as an optimal fuel source design the fuel source design having the keff that is about a maximum, the optimal fuel source design allowing said continuous fueling nuclear fission reactor to be substantially continuously operated in an optimally moderated state.
	abstract	An electro-technical device, includes an input electrical connection supplied with an input signal and electrically isolated from an output electrical connection. A bar magnet is pivotally mounted on a pedicel between the input electrical connection and the output electrical connection. A pair of coils disposed on opposite sides of the bar magnet and each being supplied with an electronic signal from a sensor, the bar magnet being responsive to an electromagnetic filed generated by the pair of coils to cause the bar magnet to contact the input electrical connection and the output electrical connection and complete a circuit and send out a control signal.
	description	This application claims benefit of U.S. Provisional Application Ser. No. 60/808,559, filed on May 26, 2006, the contents of which are incorporated by reference herein. The present invention relates to safety management systems, and more particularly to managing information for implementing fire safety regulations in nuclear power plants. On Mar. 22, 1975, a fire at the Browns Ferry Nuclear Power Plant fundamentally changed the concept of fire protection and associated regulatory requirements for U.S. nuclear power plants. Plant workers were fixing leaks in the cable spreading room outside the reactor building. The workers used a candle to test seals for air leaks into the reactor building. The polyurethane foam seal, however, was not fire-rated. The flame from the candle ignited both the seal and the electrical cables that passed through it. By the time the fire was extinguished, it had burned for almost 7 hours. More than 1600 electrical cables were affected, 628 of which were important to plant safety. The fire damaged electrical power, control systems, and instrumentation cables and impaired cooling systems for the reactor. Operators could not monitor the plant normally and had to perform emergency repairs on systems needed to shut the reactor down safely. Investigations after the fire revealed deficiencies in the design of fire protection features at nuclear power plants and in the plant procedures for responding to a fire. Fire insurance companies, normally concerned with occupant safety and property protection, did not sufficiently consider nuclear safety issues. A fire in certain locations at a nuclear plant could cause redundant safety systems and components to fail, making it difficult to shut the reactor down safely. After the Browns Ferry fire, the Nuclear Regulatory Commission (NRC) revised its fire protection regulations to reduce the chances of a fire starting and the consequences should a fire occur. Under these regulations, each licensee is required to maintain the ability to shut down the reactor safely in the event of a fire. More specifically, the objectives of the regulations are to: (1) minimize the potential for fires and explosions, (2) rapidly detect, control, and extinguish fires that do occur; and (3) ensure that fire will not prevent operators from shutting down the reactor safely or increase the risk of significant radioactive releases to the environment. Nuclear power plants have begun to implement redundant methods of fire protection to keep fires from damaging plant safety systems. Some of these methods include fire barriers, fire detection systems, and fire suppression systems (such as sprinklers). If a required element of fire protection is not available, the licensee must compensate for it using ‘Compensatory Measures,’ which often include placing dedicated personnel on a fire watch. The NRC regularly inspects licensees' means of achieving and maintaining the safe shutdown of their reactors in the event of a fire. In addition, plant workers are required to obtain permits before performing work that could potentially affect the fire safety posture of a plant or fire area. These permits must be obtained before work is performed on barriers such as walls or doors, suppression systems such as sprinkler systems, detection systems such as smoke detectors, ‘Hot Work’ such as welding or the use of flame-based heaters, and the movement of Transient Combustibles such as fuel, paint or large amounts of flammable clothing. Existing techniques for complying with NRC fire protection requirements have a number of drawbacks. Perhaps most importantly, these techniques are mostly manually performed and paper-based. For example, work permits are created on paper and tracked in filing cabinets. Compensatory measures are calculated by hand, which proves to be tedious and prone to error. Some efforts have been made to improve fire risk management in nuclear power plants. These efforts involve the use of a database to track work permits. However, these databases are passive in nature, serving merely to store and output data. They are not equipped, for example, to perform rules-based decision-making, probabilistic risk assessments, compensatory measures calculations, or any other type of complex processing. Thus, even with these databases, the need for human intervention to review and approve the substance of the permits in view of prevailing NRC safety rules is significant. A need therefore exists for a system and method of providing information for managing risk in a power plant in a way that will ensure compliance with NRC and/or other fire safety requirements, which system and method may automatically be performed by a integrated rules-based processing engine that requires virtually no human intervention, that significantly reduces the time, cost, and efficiency of managing the plant, and which provides a more reliable safeguard against fire hazards. One objective of the present invention is to provide a system and method of providing information for managing risk in a power plant or other industrial facility. Another objective of the present invention is to implement the aforementioned system and method to inform or guide personnel in managing fire risks and other safety hazards in a nuclear power plant. Another objective of the present invention is to use an application program that takes a holistic approach to providing information for informing and guiding personnel in managing fire risks that may arise from certain work or activities to be performed in a nuclear power plant. Another objective of the present invention is to provide information of the aforementioned type which may be used by a fire marshal or plant control room personnel to make decisions including, for example, whether to approve work permits with or without the implementation of compensatory measures. Another objective of the present invention is to monitor, in real-time, the fire safety status of a nuclear power plant or other facility and to update the status when work that poses a risk is sought to be performed. Another objective of the present invention is to use a rules-based decision engine to perform a probabilistic risk assessment (PRA) analysis of permits for work that pose a fire risk in one or more areas of a nuclear power plant, which analysis may use PRA numbers to support an actual core damage frequency analysis in real time for the plant Another objective of one non-limiting embodiment of the present invention is to store impairments, hot work, transient combustible permit, and other safety-related information in a single database, which allows for holistic use of the information for performing a risk determination analysis and generating reports such as but not limited to NRC reports and trend analysis. Another objective of the present invention is to automatically calculate one or more compensatory measures to be used during the work described in a permit, which compensatory measures are calculated based on results of a probabilistic risk assessment analysis and which are intended to serve as a protection or safeguard against fire that may occur during the work period. Another objective of the present invention is to implement a rules-based processing architecture which uses integrated work permit processing to thereby offer a holistic approach to compensatory measures calculations. Another objective of the present invention is to provide a system and method which integrate permits processing for barrier impairments, suppression impairments, detection impairments, hot work, and transfer of combustible materials in a nuclear power plant, which system and method is preferably implemented using a single computer program which provides the ability to centrally control all aspects of an operational fire safety program. Another objective of the present invention is to provide a process for automatically generating and entering permits for work to be performed in a nuclear power plant, which process is implemented using a standard format which may be modified to meet the specific features of different power plants. These and other objectives and advantages of the present invention are achieved by providing a computed-implemented method of providing information for managing risk in a nuclear power plant, which method includes receiving an electronic request for a permit to perform work in a plant area, obtaining a first risk value corresponding the work identified in the permit; obtaining a second risk value relating to the work area identified in the permit; performing an assessment analysis using a rules engine to determine a level of fire risk posed by the work, the assessment analysis performed based on the first and second risk values; generating a risk score based a result of the assessment analysis; and generating electronic authorization for the permit based on the risk score. The present invention also provides a system for providing information for managing risk in a nuclear power plant. This system includes a terminal to enter information for generating an electronic request for a permit to perform work in the plant; a rules engine which performs a risk assessment analysis to determine a level of fire risk posed by the work, and to automatically determine one or more compensatory measures to provide protection against the level of fire risk; and a central processor to generate a risk score based the probabilistic assessment, and to generate electronic authorization for the permit based on the risk score. The system may also include a memory to store a set of rules defining a fire safety policy for the nuclear power plant, wherein the rules engine performs said probabilistic assessment by comparing the work requested in the permit to the set of rules, and wherein the risk score is generated based on said comparison. A more detailed description of the system and method of the present invention now follows. Fire protection rules and regulations promulgated by the NRC provide safety margins for nuclear power plants, by ensuring that systems needed to safely shut down the reactor will survive a fire. Early versions of these requirements were deterministic in nature (e.g., based on a bounding set of possible accidents) and did not take probabilistic risk assessments (PRAs) into consideration. Past rules and regulations also did not consider recent advances in performance-based methods such as fire modeling. The present invention represents a significant improvement in the art, in that it provides a system and method of providing information for managing risk in an industrial facility, e.g., a nuclear power plant. In accordance with one embodiment, the system and method uses a processing architecture that integrates and analyzes risk information, automatically computes compensatory measures, performs fire safety modeling, and implements a variety of rules-based decisions to ensure compliance with risk-informed and performance-based regulations relating to fire safety in the plant. Risk-informed regulations ensure that the safety significance of requirements is considered and that the burden of a requirement on licensees is appropriate to the safety level that it provides. Performance-based regulations rely on a required outcome rather than a prescriptive process or technique. By ensuring compliance with these regulations, rules compliance can be ensured of being performed faster, more efficiently, and more effectively compared with prior methods. In accordance with one embodiment, the system and method of the present invention continuously monitors, in real-time, the overall fire-safety status of a nuclear power plant. This is accomplished by taking into consideration the current status of each zone of the plant, as well as all or a predetermined number of plant security systems which include but are not limited to fire barriers, fire detection systems, and fire suppression systems. The system also takes into consideration compensatory measures that may have been or may required to be put into place, for example, as a result of a particular type of work to be performed in a specific area in the plant. FIG. 1 shows one way in which the system of the present invention may be configured from a hardware standpoint. In this embodiment, the system includes a central processing unit 1, a rules memory 2, a database system 3, an interface module 4, and a plurality of user terminals 5. The system may be located on-site at a predetermined location in the plant, or any of the components of the system may be remotely located from the plant, for example, at a central authority site. In the latter case, the different components of the system may be coupled by local or wide area networks, e.g., the Internet. The central processing unit 1 includes a processor 11, a rules-based decision engine 12, and a program memory 13 for storing control and management software. The processor executes the control and management software to perform the functions of the various embodiments of the invention. These functions include continuously monitoring the fire safety status of the plant, in real-time, based on information stored in its databases, received from sensor signals of plant detection systems, as well as other information and data to be described in greater detail below. In performing these management functions, the processor also interacts with the rules-based decision engine to generate a risk score and/or risk color for indicating the safety risk(s) in performing work in one or more areas of the plant and/or to provide an indication of the overall fire safety status of the plant. The rule-based decision engine may also compute compensatory measures, as needed, to ensure compliance with safety regulations of the NRC and/or those of another private or governmental agency. To ensure compliance, rules engine 12 interacts with memory modules 211 to 21n in the rules memory. Each module stores information on respective numbers of sets of rules, regulations, and standards for ensuring safe operation of the plant. Examples include those set forth in the following documents: (1) General Design Criterion 3, Fire Protection of Appendix A, “General Design Criteria for Nuclear Power Plants,” to “Domestic Licensing of Production and Utilization Facilities,” now codified at 10 CFR Part 50, (2) “Fire Protection Program for Nuclear Power Facilities Operating Prior to Jan. 1, 1979,” codified at 10 CFR Part 50, Appendix R, taking the exceptions set forth in 10 CFR 50.48(b) into consideration, (3) National Fire Protection Association (NFPA) Standard 805, “Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants,” (4) Nuclear Energy Institute guidance document [NEI 04-02] entitled “Guidance for Implementing a Risk-Informed, Performance-Based Fire Protection Program under 10 CFR 50.48(c),” available in ADAMS, ML051430573, (5) U.S. Nuclear Regulatory Commission (NRC) Regulatory Guide 1.205, “Risk-Informed, Performance-Based Fire Protection for Existing Light-Water Nuclear Power Plants, codified at Title 10, Section 50.48(c) of the Code of Federal Regulations, and/or (6) Appendix O, which is a term used to refer to other regulations including standard building codes for the community or state wherein the plant is located, and which therefore may represent the minimum set of rules that apply to fire safety for the plant. The contents of these documents and any supplement thereto are incorporated by reference herein. In order to implement the aforementioned regulations, the system and method of the present invention performs risk-based calculations for a wide variety of scenarios that might come up in operational practice. These calculations may be performed based on probabilistic risk assessments or default parameters pre-assigned to the work and the area in which the work is to be performed. The calculations are then relied on to compute a risk score indicative of the safety status of the overall plant and/or of a particular are of the plant. When work must be performed in a given area, or other situations arise that may alter current safety status, the system and method may modify the risk score or color accordingly. For example, for each fire area in a nuclear facility, the change in fire risk may be calculated if a suppression system, detection system, or barrier fails. The system and method may also calculate the affect of various levels of transient combustibles and the impact of various kinds of “Hot Work.” These complex calculations are then integrated mathematically by the rules-based engine to generate a revised risk score, which may be used to determine the level of risk mitigation required for the given scenario, e.g., work to be performed. The database system 3 may be a single database or a distributed network of databases, each dedicated to storing specific information on various aspects of the system. For example, the database system may store information identifying the different areas of each plant and the operations and particular performance requirements of each area. The database system may also store information identifying safety systems (including fire barriers, fire suppression systems, and detection systems) that are in place in each area of the plant. Additional information which may be stored include the existence of any impairments in the plant facility, currently approved work, a history of previous work, and scheduling conflicts that may exist for work projects planned in a common area. All of this information may be taken into consideration by the rules-based decision engine in monitoring fire safety status of the plant, computing compensatory measures, and probabilistic risk assessments (e.g., score/color) and fire safety modeling throughout the plant. Interface module 4 may receive information (e.g., wirelessly or through a network) from various areas or systems of the plant for storage in the database system. This information may also be used by the central processing unit in monitoring fire safety status and performing risk assessment. Communications between the central processing unit and, for example, the fire suppression and detection systems may be bidirectional, e.g., in addition to assessing risk the central processing unit (e.g., through the execution of control software by processor 13) may activate, deactivate, or otherwise alter operational features of the fire suppression and detection system in order to achieve optimal compliance with NRC regulations. The user terminals may be interspersed at predetermined locations throughout the plant facility, to allow convenient access by various authorized personnel. The terminals are coupled to the central processing unit by a network and are preferably interactive to allow real-time access to system information and reporting of unsafe plant conditions. In addition, the terminals may be used to automatically generate requests for permits for specific work in the plant, for example, through the use of a standardized set of forms which may be customized to each work request and/or for the particular requirements of each nuclear power plant. The terminals may also be used to determine the probable affect of changes in fire safety for proposed work projects, to receive automatically generated compensatory measures calculated by the rules-based decision engine, to assess the affect of a user-desired compensatory measures in terms of risk assessment, to perform various administrative and data entry functions, as well as to achieve other purposes as described in greater detail below. In addition to the foregoing features, the system management and control software may provide impairment, Hot Work, and Transient Combustible Permit (TCP) tracking. This approach improves the current state of the art by centralizing the approval process for obtaining permits into a single software program that can be accessed anywhere in the facility. Also, since the computer program is always aware of the fire safety status of the entire plant, workers would no longer need to spend time researching other work being performed in related areas before starting work or getting permits approved. To facilitate the use of these automated permits, the system software first creates standardized permits based on regulatory requirements, and/or the requirements of the nuclear insurance industry for reporting of fire safety relevant incidents. This capability represents a significant improvement, since the administrators of each plant have traditionally been required to design their own forms with information each thinks is most relevant. The approach taken by the management software of the present invention standardizes the forms used for obtaining work permits. In addition, to provide maximum flexibility across the user base, the forms are customizable in a way that allows the form labels on the screen to change from one plant to another without changing the overall functionality of the software. In accordance with one embodiment, this flexibility may be attained by keeping field labels in a data file separate from the code of the program. This enables different plants to name a given field with different names, while still using the same program code. This feature may also allow the software to be offered in languages other than English without modifying the functionality of the software. In addition, because the software is aware of all fire safety-related work being performed within the plant, the software is able to determine compensatory measures automatically, more quickly, and more accurately than the current manual processes. The use of a rules engine allows natural language rules to be used to customize the software for each nuclear facility without modifications to the underlying software code. These rules, for example, direct the system software to process each permit and determine the impact on overall plant fire safety. The software then displays this information in several ways. First, compensatory measures are calculated and displayed for the permit requestor, and then are placed within the permit itself for historical record. Then, a risk calculation is performed to determine the impact on risk for all plant fire areas for each permit or permit change. This risk calculation may be used to impact (e.g., change, modify, generate, or approve) the compensatory measures if this plant is using risk-informed fire safety management. Otherwise, the risk calculation is used to calculate an overall risk score or ‘risk color’ as defined by the Nuclear Regulatory Commission (NRC). The risk score/color is preferably displayed on a main screen of the program to inform software users of the current risk posture of the plant at any given time. In addition, changes in risk color can impact displays within the software, such as the level of human review requirement before commencement of work. The permit submission and approval process as implemented by the present invention will now be described. In accordance with one embodiment, the management and control software is implemented as a ‘semi-custom’ software implementation. According to this implementation, the software utilizes a large amount of information that is specific to each plant. This information includes information about the rooms, barriers, suppression systems, and detection systems in the plant. In addition, the software takes into consideration unique compensatory measures rules and unique risk calculations that are specific to each plant and each fire area in the plant. Information on the unique compensatory measures rules and risk calculations may be stored in database system 3, one or more memory modules 21, or another data storage unit which may or may not be internal to the central process unit. To allow the software to take these unique features into consideration without requiring a re-write of the software for each implementation, the software implements rules engine 12. The rules engine may incorporate natural language rules as a data input to the program. These rules describe the compensatory measures, rules for calculation of risk in each fire area, and the risk score or color to be applied to each risk result, as well as a variety of other features. In addition, infrastructure information on rooms and fire safety systems may be stored in a relational database (within or coupled to database system 3) in a manner that is accessible by the rules engine. Through the use of this semi-custom approach, administrative users of the software are able to describe the plant features and rules to the software in a way that allows the software to properly calculate fire safety status for the plant. When a permit is created in the system, the software calculates the compensatory measures and a risk score based on, for example, the probability of risks imposed by the nature of the work to be performed, the area of the plant in which the work is to be done, and the potential damage that could result in that area should a fire break out during work. The compensatory measures and risk score may then be used by the software to generate, based on rules, prior experiences, and other objective data programmed into the rules engine, an optimal set of fire safety protections and work guidelines that should be put into place as a safeguard against a fire during a time when the work is performed. As previously indicated, each work project to be performed has the potential of changing the safety status or risk score (or color) of the plant. Through the rules engine, the system may approve or deny a work permit based on this change. Minor Risk. If the change in risk posture of the plant is considered minor (e.g., under a predetermined score or risk tolerance reference), the software may automatically approve the work described in the permit and advise appropriate personnel of one or more compensatory measures considered optimal in guarding against the increased risk. The work to be performed in any particular area may affect operations or safety conditions in other areas. The present invention may take this into consideration by opting to perform a dynamic analysis, instead of a static analysis which only takes into consideration the risks imposed by work in the permit area. By performing a dynamic analysis, the system software may therefore, through the rules engine, update the risk in other areas of the plant which may be affected by work in the area identified in the permit. Further, the system software may update the overall plant risk for other users of the software, and the user may be allowed to print a copy of the approval or evidence if needed. Moderate Risk. If the work requested in the permit would have a moderate impact on the risk posture of the plant, the system software may direct a system administrator to have a shift supervisor or other appropriate person approve the permit before work is performed on continues. The system may also provide recommendations of compensatory measures that should be put into place during the work. These measures may be computed by the rules engine in view of the nature of the work to be performed, the type of compensatory measures that are available (for example, as indicated by information stored in the database system), and the specific types of rules to be satisfied as indicated in the one or more memory modules of the system memory. Once approval (on-line) is provided, the permit is accepted and work can commence. Serious Risk. If the work requested in the permit would create a significant degradation of the risk posture, then the system, through the rules engine, may automatically reject the permit. The rejection of the permit may be overridden only if authorization is obtained by specific personnel (e.g., fire safety personnel, fire marshal, high-ranking employees of the plant, etc.), who are given special rights within the system. If the permit rejection is overridden, the system may modify the fire safety risk status of the plant to ‘red’ risk status during the time when the work is being performed. A red risk status may also trigger the system to generate a visual cue on a main screen of the application for all users of the software. This holistic view of all related permits in the plant allows the system and method of the present invention to make automated assessments of fire safety that otherwise could not be performed by existing techniques. In addition, the use of PRA calculations to provide real-time risk assessments provides an automated solution to the need for complex risk assessments to support the new risk-informed safety rules. In other embodiments, PRA calculations are replaced by the use of default calculation parameters. The risk assessments performed by the present invention may also be carried out using a research-based analysis. For example, potential risks developed through computer models or an historical database of actual accidents may be programmed into the rules engine, to allow the engine to make a more informed decision as to what types of work in a plant facility may pose the greatest risk of danger. A risk-informed, research-based system may also provide the potential to improve overall plant safety, while reducing the cost of implementing wrong or on potentially unnecessary compensatory measures. To achieve the aforementioned level of performance, the management and control software may use ‘plug in’ calculations and PRA-based or default-based parameters for each fire area in the plant and each piece of fire safety related infrastructure. By providing an architectural approach that provides for the easy customization of PRA-based calculation of risk, the software is able to calculate in real-time what changes in risk are produced from the work described in a given permit. This risk calculation may then enable the calculation of compensatory measures based on the need for risk reduction, rather than through the use of the current prescriptive methodology. The risk results may also be reported back to the rules engine that calculates the risk score or color of each fire area and for the plant as a whole. FIG. 2 shows steps included in method for managing operations in a nuclear power plant to ensure compliance with fire safety requirements. The method initially includes configuring the system shown in FIG. 1 to manage operations of a specific power plant. (Block 121). While each power plant tends to have the same basic features, each may also be very different in terms of its layout and the fire safety requirements that are to be implemented throughout each area of the layout. Accordingly, the configuration step may first include adapting the management and control software of the system (e.g., as stored in memory 13) to the plant configuration. (Block 511). The specific rules and regulations that are to be observed in operating the plant are then stored into one or more memory modules 21 of the rules memory. (Block 512). These rules and regulations include those promulgated by the NRC and also preferably those set by the nuclear insurance industry. The database system is then filled with information identifying the fire safety systems and features located in each area of the plant. (Block 513). These include the overall plant safety system configuration, fire barrier information, fire suppression system information, detection system information and impairments as well as other information. Once the system has been properly configured, the fire safety status of each area of the plant is preliminarily determined. (Block 122). This involves determining the operations currently being performed in each plant area, including the work that is currently underway in each area, the threat to fire safety imposed by the work, and any compensatory measures that have been put into place to safeguard the areas in which they work is performed against fire damage. Through its rules engine, a probabilistic risk assessment is then performed by comparing existing conditions to the rules and regulations in the rules memory and/or historical or statistical risk information stored in the database. The result of this analysis is used to compute a risk score (or color) for the entire plant. (Block 123). Once the system has been initialized according to the aforementioned steps, work permits are ready to be generated, reviewed, and acted on. This includes generating and entering an electronic request for a permit to perform work in a certain area of the plant. (Block 124). The request may be generated by a worker or administrator filling out an electronic form on one of the user terminals. In filling out this form, the area in which the work is to be performed and the type of work to be performed is identified, as well as other information considered pertinent to allowing the system to assess the fire safety risks associated with the work. Upon receiving the electronic request, the rules engine performs an analysis to determine whether the type of work requested in allowed to be performed within the designated area. (Block 125). This analysis may include checking the work against the rules and regulations stored in the rules memory for compliance. If the work falls within the scope of work allowed by the rules and regulations in the rules memory, then the rules engine performs a probabilistic assessment of the level of risk associated with the work, not only in the immediate area of the plant in which the work is to be performed but also in other areas that may be affected by a fire in the work area. The probabilistic assessment may be based on the use of PRA values obtained from another source (e.g., the NRC) or default risk values. (Block 126). The rules engine then performs an analysis to determine whether compensatory measures are available to improve the assessed risk. (Block 127). The compensatory measures are automatically determined by the rules engine, for example, based on a variety of measures previously programmed into the system. Preferably, the rules engine may generate and display on the user terminal one or more optimal compensatory measures that are to be implemented during a time when the work is to be performed. The user may then be given an option by the system to select the compensatory measure(s) prior to granting of the permit. The risk assessment analysis is then used as a basis for generating a risk score (or color) indicative of the impact the work identified in the permit would have on the fire safety status of the plant. (Block 128). The risk score may be generated by taking the compensatory measures into consideration, or the score may be based only on the risk assessment analysis. The rules engine, then, makes a determination of whether to grant or reject the work permit based on the risk score. (Block 129). This may involve comparing the risk score to one or more predetermined score ranges that, for example, correspond to minor, moderate, and serious risks. Work permits that pose only a minor risk to fire safety may automatically be granted, while work permits that pose a serious risk may automatically be rejected. For work permits that pose a moderate risk, system software may direct a system administrator to have a shift supervisor or other appropriate person approve the permit before work is performed. A different set of rules for rejecting or granting work permits may be applied if desired. For example, the method of the present invention may be modified to grant work permits for serious risks, provided additional conditions are met or extraordinary compensatory measures are implemented. These additional conditions may involve whether the work is considered routine or not. Upon granting the permit, the rules engine may re-compute the fire safety status of the entire plant during the time the work described in the permit is being performed. (Block 130). For example, if the work poses a minor risk in a non-critical area of the plant, the fire safety status of the plant may be left unchanged. Conversely, if the risk posed by the work is serious and is scheduled to be performed in a critical area, the fire safety status of the plant may be revised to correspond to the severity of the risk score calculated for the work described in the permit. Once the work has been completed, the system is updated with information indicating the same. (Block 131). The central processing unit then re-computes the fire safety status (or color) of the plant in this post-work period. (Block 132). Thus, for example, the re-computed risk score may be indicative of a safer status of the plant in view of completion of the work. Examples of how the method of the present invention may be applied to specific types of work permits will now be given. Referring to FIG. 3, when requesting work to be performed on a fire barrier (e.g., door, wall, fire curtain, penetration seal, or fire damper), the following steps may be performed. First, barrier impairment information is entered into the system, so that the system has knowledge of characteristics relating to the barrier. (Block 31). A work permit is then electronically generated and entered (Block 32), and the system computes compensatory measures, if any, that may be used to safeguard work on the barrier. (Block 33). A risk assessment is then performed to determine the level of risk imposed by the work, taking the computed compensatory measures into consideration. (Block 34). The order of the last two steps may be switched if desired. If the impairment would leave the plant in a yellow or red risk status (indicative of, for example, a moderate risk or serious risk, respectively) and the risk is routine maintenance, the system may require a special approval of the work permit, e.g., the work permit must be approved by the fire marshal. (Block 35). Approval of this type may be given electronically, for example, by the fire marshal entering his userID and password into the system and then making an appropriate designation. The fire safety status of the plant may then be updated to reflect the risk imposed by the permit, and the work is then performed. (Block 36). Once the work has been performed, the barrier impairment may be closed out electronically in the system. (Block 37). This may be performed by having work personnel, an administrator, or a supervisor enter his or her userID and password into the system and then entering appropriate information to inform the decision that the work has now been completed. At this point, the central processing unit modifies the fire risk safety status of the plant, or work area, by re-calculating the risk score or color, e.g., the fire safety status of the plant may now be revised to green status. (Block 38). An analogous set of steps may be performed for work to be performed for servicing a detector or alarm panel. Work Permit for Fixing a Defective Suppression System Referring to FIG. 4, when requesting work to be performed to fix a defective fire suppression system (e.g., sprinkler, hydrant, halon, CO2, foam), the following steps may be performed. First, impairment information indicative of the defect is entered into the system. (Block 41). This may be performed electronically, for example, by a sensor detecting a malfunction and sending an alarm signal to the central processing unit through the interface module 4. Or, the defect may be spotted by a maintenance worker, who then enters an electronic record into the system indicative of the defect. Next, a work permit for correcting the defect is generated and entered into the system (Block 42), and the management and control software determines whether the impairment (defect) of the fire suppression system meets the criteria for insurance company notification. (Block 43). These criteria may be stored in a respective one of the memory modules 21, and the determination may be made by the rules engine operating based on the management and control software. Compensatory measures for safeguarding the work are then calculated (Block 44), and a risk assessment is performed to determine the level of risk imposed by the work, taking the compensatory measures into consideration (Block 45). If the impairment would leave the plant in a yellow or red risk status and the work is routine maintenance, the system may require a special approval of the work permit. (Block 46). Approval of this type may be given electronically, for example, by the fire marshal entering his userID and password into the system and then making an appropriate designation. The work is then performed. (Block 47). Once the work has been performed, the entry indicative of the suppression system impairment may be closed out in the system. (Block 48). This may be performed by having work personnel, an administrator, or a supervisor enter his or her userID and password into the system and then entering appropriate information to inform the decision that the work has now been completed. The central processing unit, then, modifies the fire risk safety status of the plant, or work area, by re-calculating the risk score or color. (Block 49). Referring to FIG. 5, when moving combustible or other hazardous materials, the following steps may be performed. First, impairment information indicative of the request to move the combustible materials is entered into the system. (Block 51). This may be performed, for example, by a user entering an electronic record into the system. Next, a work permit for moving the materials is entered into the system (Block 52). As in all cases, the work permit may be automatically generated by the system based on information input by the user. The work permit may be in standard form modified to be compatible with the particular requirements of the nuclear power plant. Once the work permit has been submitted, compensatory measures for safeguarding the move are then calculated. (Block 53). These measures may require the movers to have special fire-extinguishing equipment on hand, or the moving equipment may be required to be padded with fire-retardant material. Next, an assessment is performed to determine the level of risk imposed by the work, taking the compensatory measures into consideration The risk assessment may involve calculating the total BTUs associated with the combustible material. (Block 54). If the number of BTUs exceeds an allowable amount, a yellow or red status may be indicated. In this case, further compensatory measures may be required or the work permit may have to be approved by a high-ranking official, e.g., the fire marshal. (Block 55). The work permit is then approved, and the fire safety status of the plant is revised during a time when the materials are moved. (Block 56). Once the work has been performed, a record corresponding to the work permit is closed out in the system. (Block 57) and the central processing unit, then, modifies the fire risk safety status of the plant, or work area, by re-calculating the risk score or color (Block 58). Referring to FIG. 6, when requesting a permit for hot work (e.g., welding), the following steps may be performed. First, information indicative of the hot work to be performed is entered into the system. (Block 61). A permit is then electronically generated and entered into the system for performing the work. (Block 62). Once the work permit has been submitted, compensatory measures for safeguarding the hot work are calculated. These measures may require the duration of the hot work to be limited depending, for example, on the overall fire safety mode of the plant that exists at that time. (Block 63). The work area is inspected and status information is entered into the system. (Block 64). Additional compensatory measures are then calculated, if required. (Block 65). Next, an assessment is performed to determine the level of risk imposed by the work, taking the compensatory measures into consideration (Block 66). If the assessment indicates that the hot work would leave the plant in a yellow or red risk status, the system may require a special approval of the work permit. (Block 67). Approval of this type may be given electronically, for example, by the fire marshal entering his userID and password into the system and then making an appropriate designation. The fire safety status of the plant is then updated and the work is performed. (Block 68). Once the work has been completed, the permit entry for the hot work impairment is closed out in the system. The central processing unit, then, modifies the fire risk safety status of the plant, or work area, by re-calculating the risk score or color. An exemplary application of the system and method of the present invention to assessing fire safety risk will now be given. This application uses Key System Tables that cover the basic structure of data centrally managed by the system and which are used to determine compensatory measures and risk. The tables store infrastructure information on rooms and fire safety systems in those rooms, as well as additional information relevant to rejecting or granting permits for plant work. These tables are preferably stored in database system 3 as shown in FIG. 1. This section describes the tables that contain key fire safety infrastructure information about the plant and the relationships between the infrastructure information. One important attribute of these data is the object's criticality in fire safety prevention. This criticality is captured and expressed in terms of “Appendix R, A, or O” of the fire safety regulations. Alternatively, “high, medium, or low” can be easily adopted for those plants that do not use the guidelines in the aforementioned fire safety-related appendices. RoomObject. The RoomObject table is used to store information about a room or fire zone. This may include the name of the room, the number of BTUs of combustible material allowed in the room under various circumstances (with or without suppression available, and two limits that can be used differently by the rules for the plant), the current risk value for the room, and any other administrative information about the room which needs to be tracked. The RoomObject table is a central component in calculating compensatory measures and risk score. Infrastructure elements such as barriers and detectors are related to one or more rooms, and permitting processes for activities such as Hot Work or transient combustibles are related to one or more rooms. BarrierLookup. The BarrierLookup table contains a listing of all barriers (walls, doors, seals, etc.), including the name of the barrier, the sub-component type of the barrier (e.g. door, wall, structural steel), the criticality of this barrier for use by the rules (i.e. Appendix A, O, or R), and any administrative information about the barrier. The sub-component type helps to distinguish internal vs. external barriers since the rules use them differently. BarrierRoomLink. The BarrierRoomLink table links the barriers (from BarrierLookup) to the appropriate room or rooms (from RoomObject) each barrier protects. SuppressionLookup. The SuppressionLookup table contains a list of all suppression systems (sprinklers, fire hoses, etc.), including the name of the suppression, the subcomponent type of the suppression (e.g. sprinkler, fire hose), the criticality of this suppression for use by the rules (i.e. Appendix A, O, or R), and any administrative information about the suppression system. SuppressionRoomLink. The SuppressionRoomLink table links each suppression system to the room or rooms protected by that suppression system. SuppressionBackupLookup. The SuppressionBackupLookup table stores information about each suppression system and the suppression system(s) that acts as its backup, if any. The rules utilize the existence of a working backup suppression system in calculating Compensatory Measures and Risk score. DetectionLookup. The DetectionLookup table contains a list of all detectors (smoke detectors, temperature sensor, fire detectors, etc.), including the name of the detector, the subcomponent type of the detector (e.g. smoke detector), and any administrative information about the detection system. DetectionGroupLookup. The DetectionGroupLookup table tracks information about each group of detectors, including the criticality of the detection group for use by the rules (i.e. Appendix A, O, or R). A group of detectors will be used to protect a specific area of a plant, and there is information about each group that must be tracked. The most important datum for the calculation of the rules is the number of detectors that must be functioning in a particular group in order for the detectors to be considered as protecting that area. In many cases, one or two detectors can be down without impact to plant risk. The threshold for each detection group is contained within this table, and is used by the rules. DetectionGroupLink. The DetectionGroupLink table links the detectors to the detection group each one is in. DetectionGroupRoomLink. The DetectionGroupRoomLink table links the detection groups to the room or rooms each group protects. AlarmPanelLookup and AlarmPanelDetectionGroupLink. The AlarmPanelLookup table tracks the alarm panels in the plant, which in turn monitor various detection groups (via the AlarmPanelDetectionGroupLink table). When an alarm panel is impaired, all the detection groups associated with that panel are considered to be impaired. AlarmNodeLookup. The AlarmNodeLookup table tracks the alarm nodes, each of which controls one or more alarm panels. If an alarm node is impaired, then the associated alarm panels are considered to be impaired, which in turn causes all the associated detection groups to be considered impaired. FireWatchTypeLookup. The FireWatchTypeLookup table stores the different types of fire watches that a plant may decide to use as a Compensatory Measure. The rules link to this table using FireWatchTypeID. This allows a plant to easily customize and change the types of fire watches to be implemented by the plant. For example, one plant may decide to implement a 6 hour fire watch as opposed to an 8 hour fire watch that another plant may use. The types of fire watches are ranked in order of severity. If one of the fire safety mechanisms in the plant is not fully functional, then this is considered an impairment. For example, a malfunctioning smoke detector is considered a detector impairment. Information on impairments may be stored in three basic tables: ImpairmentBarrierObject, ImpairmentSuppressionObject, and ImpairmentDetectionObject. These tables store any information about the impairments that are desired to be tracked. Additionally, each impairment is related to one or more fire safety mechanisms in order to make rules-based calculations. The ImpairmentSuppressionObject table includes a field that links the impairment to the appropriate suppression system in the SuppressionLookup table. The ImpairmentDetectionLink table specifies all detectors affected by a detector impairment contained in the ImpairmentDetectionObject table. The ImpairmentBarrierLink table specifies all the barriers affected by the impairment in the ImpairmentBarrierObject table. The table structures for impairments and their related object are set up this way to allow a plant the flexibility to specify multiple impairments for a single mechanism, such as a barrier. This may be the case when a barrier needs to be removed on two distinct dates for two separate activities. When a new impairment is entered into the system, the rules engine examines other impairments related to that room and other affected and surrounding rooms. It is able to do this because suppression systems, barriers, and detection groups are linked to one or more rooms (as explained earlier). The criticality for that mechanism (Appendix A, O, or R) is examined as part of calculating the compensatory measures and risk score based on the existence of this new impairment and other impairments. Before a combustible material, such as gasoline, can be moved to certain locations in the plant, a Transient Combustible Permit (TCP) must be obtained that specifies each material and location for it. The overall goal for this is to reduce a buildup of materials in one area that may exceed a certain threshold for combustibility. The TCPermitObject table is used as the primary table to store information about TCPs, including the start date and duration for the storage of the material. The details for the TCP is a list of combustible materials being tracked by the permit, which can be found in the TCPLineItem table. A record in the TCPLineItem table contains a link to the TCP number in the TCPermitID field, and a link to the actual combustible item in the FlammableID field. In addition, the quantity is tracked in the Quantity field. When the total number of BTUs of combustible material is needed, the software will multiply the quantity from the TCPLineItem table by the BTUs/unit value contained in the FlammableBTUPerUnit field of the FlammableLookup table and either display that value or pass it to the rules engine for further calculations. The main TCPermitObject table contains basic information about the permit itself, including the affected room or fire zone in the RoomID field. The RoomID field in turn is a link to the RoomObject, where the information about the room is stored. This linkage is used by the software to look up the limit of BTUs of material allowed in the room, as well as to search for other TCPs already in the system. The rules engine will calculate and compare the total BTUs from the TCPs and compare this to the allowable limits. Impairments related to that room are used in the calculations. Based on these calculations, the application may advise that no more material should be allowed in the room, or that combustible material needs to be reduced immediately. Hot Work encompasses any activity that may inadvertently or accidently ignite a fire. Examples of Hot Work include welding, cutting, and placement of a portable heater. The HotWorkObject table is the primary table used to track information about Hot Work being performed in one of the rooms of the plant. The information tracked includes the room (in the RoomID field which links to the RoomObject table), the type of Hot Work (from the HotWorkTypeLookup table via the HotWorkTypeID field in the HotWorkHotWorkTypeLink table, linked to by the HotWorkID field), and the HotWorkStart and HotWorkEnd fields, which list the dates and times when the Hot Work is scheduled to begin and end. The level of ‘risk’ for the Hot Work is contained in HotWorkRiskID and is used by the rules to calculate Compensatory Measures and Risk score. During the execution of the rules, both for calculation of Compensatory Measures and for the risk assessment calculations, the software implemented by the rules engine uses the tables listed above as well as the following set of tables used specifically for the calculations. SpecRoomFireWatchTypeLink allows for certain rooms to have special rules about fire watches assigned in case of fire-safety component failures. This allows the application to capture ‘exceptions to the rules’ that may arise from specific human expertise and knowledge regarding the plant. Typically these exceptions are more stringent fire watches, and are stored and matched using the RoomID and the ComponentTypeID of the failure and then using the specified Fire WatchTypeID. The ComponentTypeID is used to indicate whether the special rule is to be applied to a barrier impairment, detector impairment, or suppression system impairment. The application will incorporate and calculate an appropriate Compensatory Measures and Risk score based on the exceptions that have been entered into this table whenever an impairment of the indicated type is entered. An entity relationship diagram showing how all of the tables, data, and information stored in the system are interrelated is set forth in FIGS. 7A-7E. The application performs a Rules Execution analysis using the rules-based decision engine. In the following description, examples are provided on how compensatory measures are calculated and risk assessments are performed to generate a risk score or color for a specific plant. These calculations and assessments are performed based on the data and information stored in the Key System Tables, as well as aggregate data from the various permitting processes to provide an integrated and comprehensive response. More specifically, in the examples, Compensatory Measures and Risk score are calculated under various circumstances, such as an impairment, Hot Work, or TCP. The details below will show that information from the plant infrastructure and permit process are integrated in these calculations. However, the rules shown in the scenarios below are merely illustrative for a specific plant and are completely customizable. The numeric values also are only illustrative and can be customized to whatever numbers are appropriate for a specific plant. Whenever an impairment is created, changed or closed, or a TCP or Hot Work permit is created, closed or changed, rules such as the ones below may be executed to determine the Compensatory Measures required, the updated Risk score, and the fire watches needed for each room. It is also important to note that in alternative embodiments, the system and method of the present invention may allow the exact calculation of risk to be completely changed based on that plant's Prescriptive Risk Assessment (PRA) as well as other factors. The ability to support PRA based calculations represents a significant advance for these plants. This application can incorporate the results of a PRA by including the risk calculations in the rules engine. Impaired Barrier1.If a room has an impaired barrier,1.1.and the barrier is Appendix R,1.1.1.and the barrier is an internal one,1.1.1.1. and the room has working detection,then add 3.0 to the risk score and set an hourly fire watch on the room.1.1.1.2.and the room has NO working detection,then add 3.0 to the risk score and set a continuous fire watch on the room.1.1.2.and the barrier is not an internal one,1.1.2.1.and there is NO working detection on either side of the barrier, then add 3.0to the risk score and set a continuous fire watch on the room.1.1.2.2.and there is working detection on at least one side, then add 3.0 to the risk score and set an hourly fire watch on the room.1.2.and the barrier is Appendix A,then add 2.8 to the risk score and set an hourly fire watch onthe room.1.3.and the barrier is Appendix O,then add 2.0 to the risk score and set an 8-hourly fire watch onthe room.Impaired Suppression System2.If a room has an impaired suppression system,2.1.and the suppression system is Appendix R,2.1.1.and the suppression system has no backup,then add 3.2 to the risk score, set an hourly fire watch onthe room, and issue a “plant shutdown in 24 hours” warning.2.1.2.and the suppression system has a backup,2.1.2.1.and the backup is impaired,then add 3.2 to the risk score, set an hourly fire watch on the room, and issue a “plant shutdown in 24 hours” warning.2.1.2.2.and the backup is not impaired,then add 3.2 to the risk score and set an hourly fire watch on the room.2.2.and the suppression system is Appendix A,2.2.1.and the room has a special fire watch rule,then add 3.0 to the risk score, and set the special firewatch on the room.2.2.2.and the room has no special fire watch rule,2.2.2.1.and the room has no working detection,then add 3.0 to the risk score, and set an hourlyfire watch on the room.2.2.2.2.and the room has working detection,then add 3.0 to the risk score.2.3.and the suppression system is Appendix O,then add 2.8 to the risk score and set an 8-hourly fire watch onthe room.Impaired Detection Group3.If a room has an impaired detection group or an alarm panel associatedwith that detection group is impaired,3.1.and the detection group is Appendix R,then add 2.5 to the risk score and set an hourly fire watch onthe room.3.2.and the detection group is Appendix A,3.2.1.and the room has a special fire watch rule,then add 2.3 to the risk score and set the special firewatch on the room.3.2.2. and the room has no special fire watch rule,3.2.2.1.and the room has a working suppression system,then add 2.3 to the risk score.3.2.2.2.and the room has no working suppression system,then add 2.3 to the risk score and set an hourly fire watch on the room.3.3.and the detection group is Appendix O,then add 2.0 to the risk score and set an 8-hourly fire watch onthe room.Transient Combustible Permits4.If a room has an impaired suppression system,4.1.and the total BTUs stored in the room (according to approvedand active TCP's) exceeds the higher no-suppression limit for the room, then add 3.2 to the risk score and issue the “no more BTUs allowed in room” message.4.2.and the total BTUs stored in the room exceeds the lower no-suppression limit for the room,then add 0.8 to the risk score and issue the “reduce BTUs inroom” message.5.Otherwise5.1. if the total BTUs stored in the room exceeds the higher with-suppression limit for the room,then add 3.2 to the risk score and issue the “no more BTUsallowed in room” message.5.2.if the total BTUs stored in the room exceeds the lower with-suppression limit for the room,then add 0.8 to the risk score and issue the “reduce BTUs inroom” message.Hot Work6.If a room has ongoing Hot Work,6.1.and the room has an impaired Appendix R, non-internal barrierwith no working detection on either side,6.1.1.and the Hot Work is level 4,then add 2.3 to the risk score, set a continuous fire watchon the room, and issue a “suspend Hot Work immediately”message.6.1.2.and the Hot Work is level 3,then add 2.1 to the risk score, set a continuous fire watchon the room, and issue a “suspend Hot Work immediately”message.6.1.3. and the Hot Work is level 2,then add 1.8 to the risk score, set a continuous fire watchon the room, and issue a “suspend Hot Work immediately”message.6.1.4.and the Hot Work is level 1,then add 1.0 to the risk score, set a continuous fire watchon the room, and issue a “suspend Hot Work immediately”message.6.2.and the room has an impaired Appendix R internal barrier with noworking detection in the room,6.2.1.and the Hot Work is level 4,then add 2.3 to the risk score, set a continuous fire watchon the room, and issue a “suspend Hot Work immediately”message.6.2.2.and the Hot Work is level 3,then add 2.1 to the risk score, set a continuous fire watchon the room, and issue a “suspend Hot Work immediately”message.6.2.3.and the Hot Work is level 2,then add 1.8 to the risk score, set a continuous fire watchon the room, and issue a “suspend Hot Work immediately”message.6.2.4.and the Hot Work is level 1,then add 1.0 to the risk score, set a continuous fire watchon the room, and issue a “suspend Hot Work immediately”message.6.3.and the room has any other sort of impairment other that the oneslisted immediately above,6.3.1.and the Hot Work is level 4,then add 2.3 to the risk score and set a continuous firewatch on the room.6.3.2. and the Hot Work is level 3,then add 2.1 to the risk score and set a continuous firewatch on the room.6.3.3.and the Hot Work is level 2,then add 1.8 to the risk score and set a continuous firewatch on the room.6.3.4.and the Hot Work is level 1,then add 1.0 to the risk score and set a continuous firewatch on the room.6.4. and the room has no impairments,6.4.1.and the Hot Work is level 4,then add 2.3 to the risk score and set an 8-hourly firewatch on the room.6.4.2.and the Hot Work is level 3,then add 2.1 to the risk score and set an 8-hourly firewatch on the room.6.4.3.and the Hot Work is level 2,then add 1.8 to the risk score and set an 8-hourly firewatch on the room.6.4.4.and the Hot Work is level 1,then add 1.0 to the risk score and set an 8-hourly firewatch on the room.Alarm Node Impairment7.If the room contains an alarm node that is not the master alarm node,7.1.and the master alarm node is impaired,then set an hourly fire watch on the room. Analyzing the risk of severe damage to the core of a nuclear power plant from various events may be referred to as the “core damage frequency.” The core damage frequency may be used to affect design issues in the plant, and further may be relied on to ensure that each design feature is built with a design goal of having no more than a 1-in-a-million chance of causing core damage. Each plant may periodically perform a ‘Prescriptive Risk Assessment’ (PRA) to come up with the core damage values. However, because of the complexity of the PRA calculations, they have not been implemented during operation of a nuclear plant to determine current risk in real time. That is, there has been a lot of work done to try to come up with a way to determine risk, but no satisfactory answer has come from this work, as each attempt, most notably research done by the Electric Power Research Institute, has focused on re-doing assessment calculations at the time of a significant event, which has turned out to be too complex to do or to comprehend. The system and method of the present invention performs a risk assessment in a way that solves this problem. In accordance with one embodiment, the present invention performs risk assessment based on default calculation parameters or probabilistic risk assessment (PRA) values. Preferably, this assessment is performed based on the key tables and rules execution analysis previously described. However, in alternative embodiments, the use of these tables and the rules execution analysis is not a necessity. FIG. 8 shows steps included in a method for performing a risk assessment using default calculation parameters. The method includes generating a simplified risk model which involves assigning a unique risk value to each area of the plant. (Block 81). The risk value may lie within a predetermined range of values, e.g., between 0 and 10. The risk value may be decided arbitrarily by a system designer, preferably with consideration towards the risk associated with each different fire area in the plant. Next, a risk value is assigned to each type of work expected to be performed in the plant. (Block 82). This work includes hot work, TCPs, or any other the other types of work previously mentioned. The risk values assigned to each work type may be decided arbitrarily by a system designer, with consideration towards the risk associated with each type of work. After these values have been assigned and stored, for example, in the database memory in association with the key tables, a risk score is generated for specific work identified in a work permit request based on the area in which the work is to be performed. The risk score is generated based on the risk values assigned to the type of work and work area identified in the permit. (Block 83). The risk score may be generated, for example, by multiplying the risk values or according to another predetermined equation. The resulting product may then be normalized. Once the risk score has been calculated, a risk color may be assigned to the risk score. (Block 84). The risk color (e.g., green, yellow, red) to be applied to risk scores between 0 and 10 may be determined beforehand by the system designer. The risk color is preferably displayed on a user terminal at this time. Once the risk score and color have been calculated, compensatory measures for the work and work area are calculated, for example, based on the specific type of risk imposed and the work area(s) affected. (Block 85). The compensatory measures may be computed by a series of steps based on rules stored in the rules memory. For example, for a hot work permit, if the hot work involved corresponds to level 2 hot work (e.g., a specific type of hot work based on the degree to which the area will be exposed by flame), then if the risk score is at a certain level the rules memory may store rules indicating that a specific compensatory measure must be used. This calculation ensures a reduction in the risk associated with the hot work should the permit be authorized by the system. In addition, the system software may identify all adjacent rooms and then determine, for example, if the barrier between the rooms is in tact, if the sprinklers and detection systems are working on both sides of the barrier, etc. Taking these additional factors into consideration, the system calculates one or more appropriate compensatory measures. Once the compensatory measures have been calculated, the rules-based decision engine determines whether to authorize the work permit, for example, based on whether the risk is minor, moderate, or serious. (Block 86). At this time, the risk scores for all areas adjacent to or affected by the area in which the work described in the permit is to be performed may be re-calculated. (Block 87). A merge operation is then performed which involves analyzing the risk score in all plant areas. (Block 88). The fire safety status of the entire plant may then be determined based on the results of the merge operation. (Block 89). The merge operation may involve, for example, determining which plant area has the highest risk score and then correlating the overall fire safety of the plant to that highest score. A risk color is then assigned to the risk score to indicate the fire safety status of the plant (Block 90), and the risk color is then displayed on a user terminal (Block 91). As an example of this method, a plant can choose as an initial implementation of the algorithm to treat each room the same and to not use PRA values. Each room would have a risk value of 1. Then the values for Suppression Failure, Detection Failure, Barrier Failure, TCP in excess of the limit, and Hot Work ongoing in the room would each be assigned values. A plant could decide for example that a Barrier Impairment in their case would have a risk value of 2 and that Detection Failure would have a risk value of 1.5. Then a Barrier Failure and a Detection Failure in the same room would incur a total Risk Score of 3.5. Further, the NRC established risk colors are then applied to the 0 to 10 scale. For the previous example, ‘Green’ could be assigned to risk scores of less than 1. ‘White’ could be assigned to risk scores of 1 to 3. ‘Yellow’ could be assigned to risk scores of 3-6. ‘Red’ could be assigned to risk scores of more than 6. This would mean that the previous example would create a risk color for this room of Yellow. The risk scores of each fire area in the plant are then analyzed, and the plant risk is equal to the highest risk score of any room in the plant. This risk score and/or color are presented to users of the software to display a calculation of the risk of the plant in real time. FIG. 9 shows steps included in a method for performing a risk assessment using PRA values. The initial two steps of this method involve obtaining PRA values for each area of the plant and each type of work expected to be performed in the plant. (Blocks 101 and 102). The remaining steps of the method (Blocks 103 to 111) may be analogous to those performed in Blocks 83 to 91 in FIG. 8, except that the risk score is computed based on the PRA values instead of default calculation parameters. The PRA values may be computed based on, for example, on statistical and historical information compiled by a government agency such as the NRC. In some applications, the use of PRA values instead of default values may yield a more accurate interpretation of the potential risk imposed by a permit and fire safety status of the plant. In the foregoing embodiment, the PRA numbers calculated for each fire area and each fire related event may be normalized to produce risk values for each fire area associated with the probability of an event in that room causing a core damage event. Each fire safety related event may then be given a fixed value associated with the change in likelihood that that event would cause to the core damage frequency. The calculation of the exact risk values may be performed externally and preferably once during an analysis phase. The software of the system then uses these values as described above to calculate in real time the probability of a core damage event and convert that number to a risk color to present to software users. By simplifying the calculations of the risk scores and providing a way to do this in real time, in a format that all end users not just senior physicists can understand, the software allows for better decision making by plant operations personnel. If this analysis were performed manually, mistakes would frequently be made as plant personnel would not fully comprehend the impact of a given action on risk to the whole plant. More specifically, frequently an event can impact large sections of a plant, and a human reviewer for requests to do maintenance or repairs may not realize all fire areas that are impacted. For example, a given sprinkler system may serve 6 or 7 different fire areas. In turn, risk is affected by each adjoining fire area when the sprinkler system is taken out of service. These adjoining fire areas may be above, below or to the side of the fire areas served by the sprinkler system being taken out of service. In turn, there may be other work going on in those fire areas, such as Hot Work, which was started based on the assumption that the given sprinkler system would limit the risk of fire spreading to nearby areas. Through the embodiments of the present invention described herein, the software-based decision process may identify significant risks that human reviewers would not catch or otherwise appreciate. The invention, therefore, will allow operations personnel to be more aware of the ramifications of approving work. Also, for simpler situations where no other work is going on in affected areas, the computer software can be delegated the ability to approve low risk work, saving costs for the plants. Also, currently fire watches are expensive to perform because they require experienced, trained personnel to observe all areas on designated fire watch routes. Because the fire watch evaluation is done by humans who may have incomplete information, the procedure for determining what type of fire may be required is intentionally extremely conservative. By having one computer system be aware of all fire safety related work in the entire plant, as well as being aware of all associated risk impacts, plants will be able to reduce the fire watch requirements, without increasing fire safety risk, allowing the plants to save money. According to one embodiment, the scores generated in accordance with the foregoing embodiments may be combined with score increments indicated in the rules execution analysis section to derive a final risk score and preferably a corresponding risk color. For example, the risk score for a certain work requested in a permit may be given an initial value (e.g., 0) and a score according to the rules execution analysis previously discussed may then be added based on various factors relating to the work, work environment, and/or work to be performed in adjacent areas of the plant, e.g, if a room has an impaired barrier, and the barrier is Appendix R, the barrier is an internal one, and the room has working detection, then add 3.0 to the risk score and set an hourly fire watch on the room. The values (e.g, 3.0) in the rules execution analysis may correspond to default parameter values. Alternatively, the risk score value may constitute a probabilistic assessment value generated, for example, based on statistical analyses. Once the risk score has been calculated, the score may be multiplied by a multiplication factor. This factor is preferably a numerical value selected to indicate an level of importance and/or severity of risk of the work to be performed and/or the place where the work is to be performed, as well as other factors. For example, the multiplication factor may be one value when a sprinkler head is to be replaced, but a much higher factor when hot work is to be performed. The numerical values may be arbitrarily assigned or generated on a statistical basis. According to this embodiment, the final risk score for work may be generated according to the following equation: risk score×multiplication factor=final risk score. In approving hot work according to a manual process, a separate permit approval process may be required for any work involving significant heat or flames, including such things as welding, or the use of a large heater. This permit would be required not only for the hot work itself, but also for the transient combustibles that must be used to produce the heat. In many plants, a welder must go from a building where the welder is based and receives his original work order, to an engineering building where he must calculate the amount of combustible material to be used and convert that to a btu calculation. Then, he must have an engineer or fire marshall check his calculation, check that the number of btus would be acceptable for fire area where the work is to be done, then approve the TCP permit. Then, the welder would go to a third building or office where a supervisor in the operations department would approve the Hot Work and advise the welder of precautions required for that particular welding in that particular room. Then, potentially, the welder might also have to visit the control room of the plant to get approval to proceed. The system and method of the present invention simplifies this process. In accordance with at least one embodiment, the welder in this case could use a computer terminal in his office to enter the Transient Combustible Permit. The software would automatically calculate the btu's for the welder, eliminating the need for human review of the calculation, and make the determination of whether the amount requested exceeded the limit. A permit could then be provided by the software as a result of the calculations if the number of btus was below some threshold established and entered into the software during setup. The software also allows for the establishment of the a second, lower limit of btus for each room, which allows a plant to set one limit of btus that the software can automatically allow, and a higher level which shows the plants regulatory basis, which should not be exceeded in any case. This allows low risk applications to be approved, but when the btus in a fire area get close to the limit, a fire marshall approval could be required. Once the welder gets the TCP from the software, the welder would then enter their Hot Work permit, which would give them permission to perform the welding itself. Again, the software would calculate risk based on anything else going on within that fire area and adjacent fire areas, then determine risk based on those calculation and determinations. Based on the end risk value, and compensatory measures procedures built into the rules engine, the software would first determine if the work was allowed (based on the risk value), then would determine the compensatory measures required by the work (based on the procedures information built into the rules). If approved, the software would issue the actual Hot Work Permit, to be displayed at the work site, which would contain the compensatory measures required for the work. These compensatory measures would include fire watches required, precautionary measures required for the specific type of welding to be done, as well any other things required to maintain proper fire safety in all affected areas. Then, the welder would only be required to notify the control of work to be done, and would be able to skip visits to the engineer for TCP calculations, and the operations department for Hot Work approval. In addition, the assessment of risk caused by the proposed work would be done more holistically than could be done by a human reviewer, reducing the potential for incorrect approval of the work. The following is a description of screens shots that may be generated by the system and method of the present invention using sample data. FIG. 10 shows a main screen that may be generated by the system. The main screen includes a menu of selectable options that correspond to various functions of the system previously discussed. These options include Barrier Impairment for allowing a user to enter barrier impairment information into the system database, Suppression Impairment for allowing a user to enter suppression system impairment information into the database, and Detection Impairment for allowing a user to enter detection system impairment information. The main menu may also include a Combustible Permit option for automatically generating a TCP based on information entered by a user, and a Hot Work permit option for automatically generating a corresponding Hot Work permit based on information entered by a user. Additional options may be included for generating fire and other types of reports. The aforementioned options may be provided in two context, Initiate and Modify. The main screen also preferably includes a risk score indicative of the current overall fire safety status of the plant. This risk score is preferably color coded (Red—high risk status, Yellow—moderate risk status, Green—low risk status). In alternative embodiments, the risk score may be indicated numerically or in other ways. FIG. 11 shows a screen containing barrier impairment information. In this screen, a list of barrier impairments in existence over a predetermined time frame are listed, along with information indicative of the status of each impairment, the date the impairment was entered into the system or last acted on, and the room in the plant facility in which the impairment exists. FIG. 12 shows a screen that is generated when one of the barrier impairments listed on the screen of FIG. 11 is selected. In FIG. 12, the example is shown where a barrier impairment in the form of a wall exists in Room 11 of the plant. This screen further provides component, work document number, and impairment risk level information associated with the Room 11 impairment, and a risk score (2.0) associated with the work to be done in correcting the impairment. The screen also shows the types of Compensatory Measures that are recommended to be employed during correction of the Risk Level 2.0 impairment, which in this case is an 8 hour fire watch pursuant to an Appendix O barrier failure. The screen shows a similar Risk Score and Compensatory Measure for a barrier impairment in room 15. The screen may also includes a comments window for recording specific details of the barrier impairment, a window indicating the person(s) to perform the Compensatory Measure, as well as other information. Additionally, the screen of FIG. 12 includes information identifying any fire suppression or detection systems that may be associated with the barrier or the room in which the barrier is located, information on whether any TCPs or Hot Work permits have been issued for this area of the plant. The status of these suppression and detection systems and the permits may also be indicated on this screen. An additional option (Get Compensatory Measures) is provided to allow a user to obtain additional Compensatory Measures calculated by the system software. FIG. 13 shows a screen containing suppression impairment information. In this screen, a list of suppression impairments in existence over a predetermined time frame are listed, along with information indicative of the status of each impairment, the date the impairment was entered into the system or last acted on, and the room in the plant facility in which the impairment exists. FIG. 13 shows a screen that is generated when one of the suppression impairments listed on the screen of FIG. 11 is selected. In FIG. 14, the example is shown where a suppression impairment in Room 51 of the plant exists. This screen further provides component, work document number, and impairment risk level information associated with the Room 51 impairment, and a risk score (2.8) associated with the work to be done in correcting the impairment. The screen also shows the type of Compensatory Measures that are recommended to be employed during correction of the Risk Level 2.8 impairment, which in this case is an 8 hour fire watch pursuant to an Appendix O barrier failure. The screen may also includes a comments window for recording specific details of the impairment (e.g., test), a window indicating the person(s) to perform the Compensatory Measure, as well as other information. Additionally, the screen of FIG. 14 includes information identifying any barrier or detection systems that may be included in the room in which the suppression system is located, information on whether any TCPs or Hot Work permits have been issued for this area of the plant. The status of these suppression and detection systems and the permits may also be indicated on this screen. An additional option (Get Compensatory Measures) is provided to allow a user to obtain additional Compensatory Measures calculated by the system software. FIG. 15 shows a screen containing detection impairment information. In this screen, a list of detection impairments in existence over a predetermined time frame are listed, along with information indicative of the status of each impairment, the date the impairment was entered into the system or last acted on, and the room in the plant facility in which the impairment exists. FIG. 16 shows a screen that is generated when one of the detection impairments listed on the screen of FIG. 15 is selected, or when it is desired to view all of the detection impairments in the plant. In FIG. 16, the example is shown where a detection impairment in Room 50 of the plant exists. This screen further provides work document number and impairment risk level information associated with the Room 50 impairment, and a risk score (3.0) associated with the work to be done in correcting the impairment. The screen also shows the type of Compensatory Measures that are recommended to be employed during correction of the Risk Level 3.0 impairment, which in this case is a continuous fire watch associated with an Appendix R barrier. The screen may also includes a comments window for recording specific details of the impairment (e.g., test). Additionally, the screen lists detection impairments that may exist in other rooms of the plant, the Risk score associated with each impairment, and the Compensatory Measure(s) used to safeguard work to be performed in correcting the impairment. FIG. 17 shows a screen that is generated in order to obtain authorization for a Transient Combustible permit for moving flammable materials in Room 30 of the plant. The screen includes shop and work document number information associated with the permit, as well as the expected duration the permit is to be in place. The screen also provides information describing the TC material to be moved and recommended loading techniques. In this portion of the screen, a window is provided to allow a user to designate the type of transient combustible material (e.g., wood, alcohol, acetylene) and its associated BTU rating, the amount of material to be moved, and the number of BTUs associated with that amount of material. The screen then shows a Risk score calculated by the rules engine, for example, in accordance with the Rules Execution section previously discussed, and the Compensatory Measure(s) that may be required, if any, in moving the material. Additionally, the screen may include information identifying any barrier, suppression, or detection systems that may be included in the room (e.g, Room 30) in which the combustible material is located, information on whether any TCPs or Hot Work permits have been issued for this area of the plant. FIG. 18 shows a screen that is generated to obtain a Hot Work permit. This screen identifies the room (Room 30) in which the hot work is to be performed, the type of hot work (e.g., open flame, arc welding, cutting, grinding) to be performed, and the time duration for completing the work. The screen also includes information indicating data obtained from an inspection of the work area. This data includes the condition of the equipment to be used in performing the hot work, whether the work area has fire suppression and detection systems, and whether the work area includes flammable or combustible materials as well as other information. The screen also shows the Risk score (2.3) computed by the rules engine for the hot work to be performed, and well as any Compensatory Measures that are to be implemented during and after the work is completed. The screen also includes a Close Out window, which is to be filled in once the work is performed. In accordance with one embodiment, each of the versions of the permit may be generated and governed by different ones of the foregoing screens. For example, create Barrier Impairment may create the barrier impairment form. This form may not directly be the work permit, but may be considered a pre-requisite to performing the work. The Create Hot Work permit screen may correspond to an actual work permit. The Create TCP screen allows the user to create a Transient Combustible Permit, which is a pre-requisite for carrying flammable materials into an area, but does not constitute the work permit for the associated work. The system and method may include the following additional features. Reporting a Fire. When a fire breaks out in the plant, information about the fire, suppression systems and detectors are entered into the system database. The information may be entered in real-time through the interface module and appropriate action may be automatically taken by the central processing unit. This action may include providing notification to fire-fighting authorities, automatic activation of the fire suppression systems in various areas throughout the plant, etc. A historical record of the fire and its causes and the extent of the resulting damage may then be stored in the database for future use in calculating new compensatory measures and/or for providing more accurate risk assessments when permits are submitted for future work. In one or more embodiments described herein, the work permits may be automatically and electronically generated by the system based on entered information concerning the work. Monitoring Fire Risk. In addition to monitoring the overall fire risk/safety status for the plant, the system and method of the present invention may monitor the fire safety status of various areas of the plant, e.g., on an area-by-area or even on a room-by-room basis within various buildings on the plant site. Users may then select different rooms or areas to obtain a real-time indication of the status of those rooms/areas, and to determine all associated impairments and permits that exist for those rooms/areas at any given time. Preferably, the system may generate a graphical representation of the plant layout colored coded to provide a visual indication of the status of each area/room of the plant. The fire safety status of each area may be used as a basis for generating the fire safety status of the overall plant. Fire Safety Reports. The system may also allow a user to select a specific type of report to be generated. These reports include ones indicative of barrier impairments, detection system impairments, and/or transient combustible permits (TCP) that exist throughout the plant. The reports may be generated based on search criteria entered by a user. The search criteria may include an effective start date and end date of work that was performed, status and report format. Fire Watch Routes. The system may also maintain and generate information on various fire watch routes that exist throughout the plant. The fire watch routes may be graphically depicted on a screen in selectable form. When a route is selected, the system may output fire safety information applicable to the route. Fire Safety System Data. The system may also create or update fire safety system data for the plant. This function may include adding or updating a user to the system and assigning certain rights and authorities to the user (e.g., the ability to approve permits for work that pose moderate or serious threat to safety), adding or updating roles to the system including assigning specific rights each role is to have, and selecting a data table or data item to edit or update. These function may be performed independently of one another if desired. While the aforementioned embodiments have been described particularly with respect to managing the operations of a nuclear power plant, those skilled in the art can appreciate that the system and method of the present invention may also be applied to managing the operations of other plants or facilities, not only with respect to protecting against fire risks but also other hazards such as toxic or chemical spills, mechanical failures, electrical shock or arcing, and cracks or defects in plant infrastructure just to name a few. The present invention may offer a number of advantages not currently available. For example, significant cost savings can be achieved by shortening the process for obtaining permission to do work, particularly for TCP and Hot Work permits, and for reducing the number and frequency of fire watches without increasing plant risk. This enables plants to more easily move from the current ‘prescriptive’ rules for fire safety to the new ‘Risk Informed’ regulations. This transition may be considered by the NRC to not only improve safety, but also save plants a lot of money by only doing compensatory measures that actually provide significant reductions to the risk of the plant, and allow the plant to reduce redundant or unnecessary precautions. The present invention also provides a real time assessment of risk for plant operations. Currently, no such assessment is available despite many prior attempts to solve the problem. By displaying risk color directly to all software users on the main screen of the application, plant operations have a fast, simple way to be aware of the plant status. The embodiments of the present invention described herein can be extended to provide the same risk determination for flood and radiation risk. These risk related activities are currently also conducted manually, and provide many of the same challenges as the fire safety risk determination. For example, when a penetration of a barrier is requested, different departments within a plant must determine the fire safety impact of a hole in a fire barrier, determine the potential for the penetration to create a flood risk (if the core overheats, it is flooded with water—you don't want that water to flood the entire plant; you also don't want normal sprinklers to flood adjacent rooms that may have important safety systems or human exit paths), and radiation risk if the wall is a radiation barrier. We should be able to claim generally that our method for holistic risk calculation includes risk calculation for radiation and flood risk determinations as well, and that the combination of any 2 within a single software application is also a new invention. Any reference in this specification to an “embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. Furthermore, for ease of understanding, certain functional blocks may have been delineated as separate blocks; however, these separately delineated blocks should not necessarily be construed as being in the order in which they are discussed or otherwise presented herein. For example, some blocks may be able to be performed in an alternative ordering, simultaneously, etc. Although the present invention has been described herein with reference to a number of illustrative embodiments, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this invention. More particularly, reasonable variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the foregoing disclosure, the drawings and the appended claims without departing from the spirit of the invention. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.
	summary
062360558	abstract	An article irradiation system includes a radiation source for scanning a target region with radiation; a conveyor system including a process conveyor positioned for transporting articles in a given direction through the target region; radiation shielding material defining a chamber containing the radiation source, the target region and a portion of the conveyor system; wherein the radiation source is disposed along an approximately horizontal axis inside a loop defined by a portion of the conveyor system and is adapted for scanning the articles being transported through the target region with radiation scanned in a plane transverse to the given direction of transport by the process conveyor; and an intermediate wall of radiation shielding material positioned within the loop and transverse to the approximately horizontal axis. The intermediate wall supports a ceiling of the chamber, inhibits photons emitted from a beam stop disposed in a given wall from impinging upon at least one other wall of the chamber and restricts flow throughout the chamber of ozone derived in the target region from the radiation source.
042742056	description	DESCRIPTION A measuring fixture 11 according to the invention is illustrated in FIG. 1 as mounted in operating position along a wall 12 in a pool by water 13. The main frame of the fixture is an elongated support beam 14 shown herein as an H beam. An upper bracket 16, attached to the beam 14 near its upper end, includes a pair of rearwardly extending arms 17 formed to hook over a ledge 18 of the pool wall 12 to thereby support the fixture 11 in suspension along the wall 12. Adjustable pads 15 provide verticality adjustment. A lower bracket 19, attached to the beam 14 at its lower end, includes a pair of side plates 21. Rearward extensions 22 abut the wall 12 to position the beam 14 substantially parallel with the wall 12. Forward extensions 23 and a cross plate 24 provide support for other components of the fixture as described hereinafter. Supported between lower bracket 19 and an intermediate bracket 26 is a straight edge member 27 which serves as an accurate measurement plane of reference and as a track for an instrument bearing carriage 28. As best shown in FIG. 2, straight edge 27 is supported at its lower end by lower bracket 21 with a pair of pivot pins 29, and it is held in position at its upper end by intermediate bracket 26 with a center pin 31 carrying a sliding, spherical bearing journalled in a flange 32 of bracket 26. This mounting arrangement allows the straight edge 27 freedom of thermal expansion and contraction and aids in preventing transmission thereto of deforming loads from other portions of the fixture. To further minimize thermal deformation, the straight edge 27 is formed with a series of relatively large, equally spaced holes 33 along its length. To minimize torsional distortion of the support beam 14 that would affect the straight edge 27, the portion of beam 14 between intermediate bracket 26 and the lower end of the beam is "boxed in" by a back plate 34 secured, as by welding, to the rear edges thereof. The part of the beam 14 above the intermediate bracket 26 is left unboxed. Thus any twisting of beam 14, as might occur for example from unevenness of the pool wall 12, takes place in the part of the beam above the intermediate bracket 26 whereby transmission of such deformation to the straight edge 27 is avoided. The component to be measured, shown in FIG. 1 in phantom view by dashed lines as a fuel assembly flow channel 36 is removably secured in a position generally parallel to the straight edge 27. The channel 36 is supported at its bottom end by a channel support member 37 and is positioned at its top end by a clamp arrangement 38 secured to the top end of straight edge 27. The clamp arrangement 38 includes a fixed arm 39 and a swinging arm 41, the swinging arm 41 being remotely operable by a hydraulic or pneumatic cylinder 40 in well-known manner. The fixed arm 39 is fitted with a pair of jack screws 42 for adjustment of the alignment of the top end of the channel with the plane of the tips of the measuring devices on carriage 28. The channel contacting faces of the swinging arm 41 and the jack screws may be fitted with material such as nylon to prevent scratching of the channel. The channel is supported at its bottom end by channel support member 37, in a manner which does not restrain the channel from rotational motion about is longitudinal axis. This is necessary for measurement of channel twist. As shown in FIG. 3, this feature is provided by a support socket 43 which is journalled to allow rotational motion thereof by an annular ball bearing 44 carried by a bearing plate 46 secured to a spacing sleeve 47 which, in turn, is secured to the cross plate 24 of the lower bracket 19. The subject measuring fixture is adapted to accommodate and measure empty channels or flow channels which are still mounted on fuel assemblies (as shown in previously mentioned U.S. Pat. No. 3,689,358). Therefore, the upper end of the bore of support socket 43 is appropriately shaped, as at 48, to receive and mate with the nose pieces of the fuel assemblies to be accommodated. To accommodate empty flow channels, an empty channel adapter 49 is provided. The lower end 51 of the channel adapter has the shape of a fuel assembly nose piece for fitting into the support socket 43. The upper end 52 of the channel adapter has a pyramid shape, or the like, for ease of fitting the square end of the empty channel thereover and the adapter is sized at 53 near the base of the pyramid portion to fix the position of the channel 36 on the channel adapter. It is noted that, as shown in FIG. 3, the cross plate 24 and the bearing plate 46 are formed with large holes 45 and 50, respectively, and the support socket 43 and the adapter 49 are formed with large through bores. This provides for water circulation through the component being measured which allows water that has become radioactive in the component to drain away thus reducing user exposure. It also provides a convection path to convey heat away from the measuring devices. Empty channels or fuel assemblies, as the case may be, can be placed in position or removed from the measuring fixture by any suitable lifting and maneuvering device such as an overhead or boom mounted hoist (not shown) which is typically available as an adjunct to a nuclear fuel storage pool. Such hoist arrangements are shown, for example, in copending patent application Ser. No. 747,824 filed Dec. 6, 1976, now U.S. Pat. No. 4,172,760. Attention is now directed to the instrument carriage 28 shown in FIG. 1 and with greater clarity in FIG. 4. As illustrated herein the carriage 28 which is mounted on the straight edge 27 by a system of rollers or wheels includes a T-shaped front plate 54 which serves as the main frame of the carriage. The front plate 54 is positioned with respect to and guided along the straight edge 27 by a plurality of guide rollers. These guide rollers include a first pair of spaced rollers 56(1) and 56(2) journalled to the T portion of plate 54 for engagement with the right-front face portion of straight edge 27, a second pair of spaced rollers 57 likewise journalled to the T portion of plate 54 but for engagement with the right side of straight edge 27, and a single roller 58 journalled near the left hand end of plate 54 for engagement with the left-front face portion of straight edge 27. A plurality of rollers 59 journalled in a stud-mounted, spring-loaded back plate 61 and a pair of rollers 62 journalled in a stud-mounted, spring-loaded side plate 63 provide pressure on the guide rollers and assure their engagement with straight edge 27. Secured to the right hand end of plate 54 is an arm 64 suitable for supporting a plurality of distance detectors or other measuring devices 66(1)-66(3) in appropriate position for engagement with the flow channel 36 to be measured. The devices 66(1)-66(3) may be, for example, linear variable differential transformers. Briefly, such a device comprises a linearly movable spring loaded plunger 67 extending from a housing. Movement of the plunger 67 changes the mutual inductance of a pair of coils within the housing. Thus the mutual inductance of the pair of coils can be measured and interpreted as a function of the linear position of the plunger. The plunger 67 is fitted at its outer end with a rounded, smooth-faced nose piece 69 for sliding engagement with the outer surface of the channel 36 to be measured. Suitable such distance detectors are available from Schaevitz Engineering, U.S. Route 130 and Union Avenue, Pennsauken, New Jersey as catalog item No. GCA-121-500-0624. The signals from detectors 66(1)-66(3) are transmitted via a cable 71 to a signal processing recording and display device 72 (FIG. 1). A suitable device 72 is available from Schaevitz Engineering as catalog item No. CAS-0653. To be noted is that the detectors 66(1)-66(3) are supported such that the direction of measurement is in the direction of the major cross section dimension of straight edge 27 and hence in the direction of maximum straight edge stiffness. As illustrated herein, the carriage 28 is manually movable along the length of straight edge 27 as follows: A roller chain 73 attached to the carriage 28 is engaged by a lower idler sprocket wheel 74 and by an upper driven sprocket wheel 76. Wheel 76 is driven from a hand wheel 77 through suitable shafting and a pair of right-angle gear boxes 78(1) and 78(2). A counter 79 registers the rotations of the hand wheel 76 and can be designed to indicate the position of the carriage 28 along the straight edge 27 in convenient units. Also, a toothed wheel 82 engaged by a spring-loaded ball detent can be keyed to the shaft of hand wheel 77 to provide incremental carriage positioning and prevent carriage drift. It is noted that the chain 73 is attached to the carriage 28 as nearly as feasible to the center of gravity thereof to minimize twisting forces on the carriage due to the lifting force. Also, a counterweight 80 may be fitted to chain 73 to balance the weight of the carriage 28. To provide reference readings to the processing device and to check linearity of the detectors, a calibration block 81 is secured to the bearing plate 46 of support member 37 as shown in FIG. 3. The block 81 is stepped to provide three reference planes for engagement with the distance detectors 66(1)-66(3). The center step can be, for example, a zero reference plane, the lower step a positive reference plane and the upper step a negative reference plane. Operation of the measuring fixture is as follows: A flow channel to be measured is placed on the support socket 43 and clamped in position by clamp arrangement 38 as previously described. Operation of handwheel 77 moves the carriage 28 along straight edge 27 and the detectors 66(1)-66(3) provide signals indicative of the profile of the center and outer tracks of their engagement with the adjacent side of the channel. From these profile traces, flatness, bow and twist of that side of the channel can be determined. The other sides of the channel similarly can be measured by release of clamp 38, rotation of the channel by ninety degrees and reengagement of the clamp. In an embodiment of the measuring fixture the straight edge 27 is about 2 inches (5.1 cm) thick, 8" (20.3 cm) wide and 14 feet (43 m) long. It is formed of carbon steel for machineability, accurately ground and electroless nickel plated for corrosion resistance. The holes 33 are about 5.5 inches (14 cm) diameter spaced about 7.5 (19.1 cm) center-to-center. The support beam 14 is an 8 inch (20.3 cm) H beam. This and other structural members of the fixture are preferably formed of aluminum to minimize the weight of the fixture for ease of portability.
	summary
047553510	description	DETAILED DESCRIPTION OF EMBODIMENT The apparatus shown in the drawings is part of a nuclear reactor including a nuclear fuel assembly 11. The assembly 11 includes a skeleton formed of an upper nozzle 13, a lower nozzle 15 and a plurality of spaced screens 17 formed of straps interlaced in the manner of an egg crate to define aligned pocket 19. The nozzles 13 and 15 and the screens 17 are formed into a rigid body by thimble tubes 20 which extend around their peripheries and are joined to the screens. Fuel rods 21 are held in aligned pockets by springs (not shown) mounted on the part of the strap (not shown) bounding each pocket and dimples (not shown) in the part of each opposite strap bounding the pocket (see Andrews No. Re. 30047). The fuel assembly 11 is interposed between an upper core-support plate 23 and a lower core-support plate 25. These core plates 23 and 25 are connected to the core barrel (not shown) of the reactor. The upper nozzle 13 is in the shape of a plate of generally rectangular transverse cross-sections having a bottom which has holes 29 for transmitting the coolant and also holes (not shown) through which control rods 31, suspended from a spider 33, penetrate. The upper nozzle 13 also has, diagonally disposed, upwardly extending feet 35 and 37. The feet 35 are provided with load pads 39. The feet 37 are provided with axial holes. The upper core plate 23 has alignment pins 41 which extend generally axially with the holes. The pins 41 are of sufficient length to accommodate the full anticipated upward and downward movement of the fuel assembly 11. The plate which constitutes the upper nozzle is thin and the feet 35 and 37 are short compared to the corresponding components of the prior-art nozzle (because the springs are eliminated). For this reason the fuel rods can be extended and are longer than the fuel rods in prior-art assemblies. The lower nozzle 15 (FIG. 2) has a top 43 of generally rectangular transverse cross section having holes 45 for transmitting the coolant. Diagonally opposite feet 47 and 49 extend downwardly from the top 43. Each foot 47 is a snubber including a cup-shaped cylinder 51 (FIGS. 3, 4) within which an inverted cup-shaped piston 53 is slidable. A sealing ring (O-ring) 55 is embedded in the outer sliding surface of the piston 53. A helical compression spring 57 is connected to the piston 53 and cylinder 51 in such manner that it exerts downward pressure on the cylinder 51. Each leg 49 has a cylindrical hole 59 (FIG. 5) into which an alignment pin 62 projecting from the lower core-support plate 17 extends generally coaxially. A retaining spring 63 is interposed between the inner surface of the hole 59 and the pin 61. The spring assures that while the pin 61 is slidable relative to the hole, the pin engages the hole snugly so that vibrations of the fuel assembly 11 from which the leg 49 depends, under transverse forces of the coolant, are suppressed. A like retaining spring (not shown) is interposed between each pin 41 of the upper core support and the hole in leg 37 of the upper nozzle 13. In the use of the fuel assembly 11 in a reactor, the fuel assembly is in the state shown in FIG. 1 in the quiescent conditioning of the reactor with the coolant pumps (not shown) not in operation. In this state the piston 53 is advanced into the cylinder 51 by the weight of the assembly. Since the pressure of the coolant is high, coolant has penetrated into the cylinder under the piston notwithstanding the sealing ring 55. The upper nozzle 13 in this state of the reactor is spaced from the upper core plate but the pins are inserted in the holes in leg 37 and the pins 61 in the holes 59. When the coolant pumps are turned on, the coolant flows upwardly through the lower core plate 25, the lower nozzle 15, the interior of the assembly 11, the upper nozzle 13 and the upper core plate 23. The fuel assembly 11 is raised by the force of the coolant and the loads pads 39 engage the lower surface of the core plate 23 under pressure. The reactive force on the spring 57 causes the cylinders 51 to move downwardly so that the snubbers 47 assume the state shown in FIG. 2. The spring 57 causes the cylinder 51 to engage the upper surface of the bottom core plate 25. The spring 57 is dimensioned so that the pressure exerted by the cylinder on the core plate 25 is the required pressure. The retaining springs 63 suppress vibration of the fuel assembly. While a preferred embodiment of this invention has been disclosed herein, many modifications thereof are feasible. This invention is not to be restricted except insofar as is necessitated by the spirit of the prior art.
055531091	abstract	Apparatus is provided for simulating a nuclear fuel rod bundle transient condition and includes a vessel for containing a coolant, a pair of heating elements disposed in the vessel and a power supply for supplying power over time to each of the heating elements. The power supply is independently controlled whereby a variable supply of power over time to each heating element is provided, thus simulating the variation in power output and axial flux shape in a nuclear fuel bundle as a function of time.
	abstract	The present invention relates to a method and portable apparatus which is used to detect substances, such as explosives and drugs, by neutron irradiation. The apparatus has a portable neutron generating probe and corresponding controllers and data collection computers. The probe emits neutrons in order to interrogate an object. The probe also contains gamma ray detectors for the collection of gamma rays from fast neutron, thermal neutron and neutron activation reactions. Data collected from these detectors is sent to the computer for data de-convolution then object identification in order to determine whether the object being interrogated contains explosives or illicit contraband.
	abstract	A jet pump beam is made of improved heat-treated precipitation-hardened nickel base alloy excellent in anti-stress corrosion cracking properties and high-temperature strength, and having high ductility and a high elastic modulus. A jet pump beam 27 made of improved heat-treated nickel base alloy is produced by preparing a precipitation-strengthened nickel base alloy material having a component composition containing by mass %, Ni: 50.0% to 55.0%, Cr: 17.0% to 21.0%, Nb+Ta: 4.75% to 5.50%, Mo: 2.8% to 3.3%, Ti: 0.65% to 1.15%, Al: 0.2% to 0.8%, C: 0.08% or less, Mn: 0.35% or less, Si: 0.35% or less, S: 0.015% or less, P: 0.03% or less, Cu: 0.30% or less, B: 0.006% or less, and Co: 1.0% or less, and Fe and inevitable impurities constituting a remaining part, subjecting the nickel base alloy material to solution heat treatment at a temperature of 1010° C. to 1090° C., and subjecting the nickel base alloy material to age-hardening heat treatment at a temperature of 694° C. to 714° C. for 5 to 7 hours after the solution heat treatment.
	description	This application is a continuation application of U.S. Ser. No. 10/413,210, filed Apr. 15, 2003, which is a divisional of U.S. Ser. No. 09/983,324, filed on Oct. 24, 2001, now U.S. Pat. No. 6,568,851 and is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-325920, filed Oct. 25, 2000, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to an X-ray CT scanner having a correcting function. 2. Description of the Related Art An X-ray CT scanner is an apparatus which generates tomogram data by reconstructing, by using a computer, projection data obtained by irradiating an object to be examined with X-rays from the circumference of the object. These X-ray CT scanners are classified into the following three types in accordance with differences between the forms of X-ray beams. The first one is a “fan-beam X-ray CT scanner” which radiates a fan-shaped X-ray beam from an X-ray tube. This fan-beam X-ray CT scanner acquires projection data by using an X-ray detector obtained by arranging about, e.g., 1,000 channels of detecting elements in a line. Projection data acquiring operation is repeated about 1,000 times while the X-ray tube rotates around an object to be examined. This fan-beam X-ray CT scanner is also called a “single-slice CT scanner” because data concerning a single slice are acquired. The second one is a so-called “multi-slice X-ray CT scanner” in which several X-ray detectors each obtained by arranging about 1,000 channels of detecting elements in a line are juxtaposed in a slice direction. A slightly thick X-ray beam is radiated in accordance with the width of these juxtaposed detectors. This multi-slice X-ray CT scanner is so called because data of several slices can be simultaneously acquired. The third one is a so-called “cone-beam X-ray CT scanner” in which a plurality of detecting elements each composed of a combination of, e.g., a scintillator and a photodiode are two-dimensionally arrayed. A conical or pyramidal X-ray beam is radiated in accordance with the width of these detecting elements in a slice direction. This cone-beam X-ray CT scanner is also called a volume X-ray CT scanner because volume data can be acquired at once. The research of a cone-beam X-ray CT scanner has been advanced primarily on a system using an image intensifier (I.I.) as an X-ray detector since late 1980s. For example, in “Volume CT of anthropomorphic using a radiation therapy simulator” (Michael D. Silver, Yasuo Saito et al.; SPIE 1651 197-211 (1992)), the results of scan of chest phantoms in an experimental system combining a turntable and an I.I. are discussed. Some cone-beam X-ray CT scanners are beginning to be put into practical use as apparatuses for obtaining the shapes of high-contrast objects such as bones and blood vessels in angiography. As described above, a cone-beam X-ray CT scanner has a wider divergent angle of an X-ray beam in a slice direction than in the other two types. In other words, the X-ray beam is thick on the rotation central axis. Since this increases the number of paths through which scattered rays reach detecting elements, the scattered ray amount increases. Scattered rays cause abuses, e.g., deteriorate the image contrast. This scattered ray increasing mechanism means that the scattered ray amount varies in accordance with a change in the beam thickness. An X-ray CT scanner usually performs sensitivity correction in order to equalize the sensitivities of detecting elements. For this purpose, calibration data files (calibration data) for sensitivity correction are acquired by using a phantom (pseudo model). Since scattered rays change in accordance with the beam thickness as described above, these calibration data files must also be selectively used in accordance with the beam thickness. This paradoxically means that the degree of freedom of beam thickness adjustment is limited by the types of calibration data files that the apparatus has. Assume, for example, that a calibration data file acquired by a beam thickness X1 and a calibration data file acquired by a beam thickness X2 (>X1) are prepared. In this case, no corresponding calibration data files are prepared for beam thicknesses other than X1 and X2. Therefore, no such beam thicknesses can be set except when the inclusion of a scattered ray error is permitted. It is an object of the present invention to provide an X-ray CT scanner capable of extending the degree of freedom of setting of an X-ray beam thickness. According to a certain aspect of the present invention, an X-ray CT scanner comprises an X-ray tube which irradiates an object to be examined with X rays, a variable X-ray limiting device which limits the beam thickness of the X rays, an X-ray detector which detects X rays transmitted through the object and has a plurality of detecting elements arrayed in a matrix manner, a storing unit which stores a plurality of calibration data files corresponding to a plurality of beam thicknesses, a correcting unit which corrects an output from the X-ray detector on the basis of at least one calibration data file read out from the storing unit, a reconstructing unit which reconstructs image data concerning the object on the basis of an output from the correcting unit, and a control unit which controls the variable X-ray limiting device to change the beam thickness of the X rays, independently of the plurality of beam thicknesses to which the plurality of calibration data files stored correspond. Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. An embodiment of the present invention will be described below with reference the accompanying drawing. FIG. 1 is a schematic view showing the arrangement of an X-ray CT scanner according to this embodiment. Referring to FIG. 1, an X-ray CT scanner 1 includes a frame 11 and a console 12. The frame 11 has a hollow portion 11a. Into this hollow portion 11a, a patient P placed on a table top 11b of a bed is inserted. An X-ray tube 111 and an X-ray detector 112 are arranged around the hollow portion 11a. The X-ray tube 111 and the X-ray detector 112 are mounted to oppose each other on a rotary ring 11c held to be rotatable around a rotation central axis RA perpendicular to the drawing surface. The X-ray tube 111 is connected to an X-ray generating unit 111a including a high-voltage power supply. The X-ray detector 112 includes a plurality of detecting elements each composed of, e.g., a scintillator and a photodiode. These detecting elements are arrayed in a matrix manner in two directions, i.e., a direction parallel to the rotation central axis RA, and a direction substantially perpendicular to the rotation central axis RA. Note that the direction parallel to the rotation central axis RA will be referred to as a “slice direction” hereinafter, and the direction substantially perpendicular to the rotation central axis RA will be referred to as a “channel direction” hereinafter. X-rays generated by the X-ray tube 111 irradiate the patient P as indicated by the broken lines in FIG. 1. X-rays transmitted through the patient P are converted into electric signals by the detecting elements of the X-ray detector 112 and acquired by a data acquisition system 122. A variable X-ray limiting device (also called a collimator) 111c is attached to an X-ray emission window of the X-ray tube 111. This variable X-ray limiting device 111c has a plurality of shielding plates to limit the beam thickness of X-rays generated from the X-ray tube 111 in the slice direction. These shielding plates are so supported as to be individually movable in the slice direction. The X-ray beam thickness can be varied by adjusting the spacings between these shielding plates. The collimator 111c is typically a multi-leaf collimator. This multi-leaf collimator has a plurality of plate-like leaves constructing two leaf pairs. The multi-leaf collimator can freely limit the beam thickness of X-rays by moving these plate-like leaves independently of each other, such that the leaves come close to or move away from each other in the longitudinal direction. The console 12 includes, e.g., a central control unit 121, an input device 127, and an image displaying unit 12D. The central control unit 121 controls the frame 11, the bed, the table top, and the like. The input device 127 is used by an operator to access this central control unit 121. The image displaying unit 12D displays reconstructed CT images (e.g., an axial image, multi-planar reconstruction image (MPR image), body surface image, and maximum intensity projection image (MIP image)). Of these devices, the input device 127 can be a pointing device such as a mouse or a track ball, and the image displaying unit 12D can be a CRT or the like. An operator inputs a command to the central control unit 121 via the input device 127. In accordance with this input command, the central control unit 121 reconstructs tomogram data on the basis of an output from the X-ray detector 112, and displays the data on the image displaying unit 12D. More specifically, the tomogram or the like is reconstructed by the flow of data, or processing, conceptually shown in FIG. 2, in the data acquisition system 122, a preprocessing unit 123, a memory 124, a reconstructing unit 125, and a data processing unit 126 shown in FIG. 1. The reconstructed image is displayed on the image displaying unit 12D. Referring to FIG. 2, the data acquisition system 122 receives a plurality of electric signals from a plurality of detecting elements of the X-ray detector 112. This data acquisition system 122 amplifies these electric signals and outputs the amplified electric signals as digital signals via an A/D converter. A digital signal before being subjected to preprocessing is called raw data. The preprocessing unit 123 corrects the raw data from the data acquisition system 122 on the basis of at least one calibration data file read out from a plurality of calibration data files stored in a storing unit 12M. This correction process includes, e.g., reference correction, water correction, and sensitivity correction. The data corrected by this preprocessing unit 123 is data immediately before reconstruction and is called “projection data”. The memory 124 stores this projection data. The reconstructing unit 125 receives the projection data from the memory 124. On the basis of this projection data, the reconstructing unit 125 reconstructs the distribution (called volume data or voxel data) of X-ray absorption coefficients in a three-dimensional region extending in the slice direction of the patient P, by using a three-dimensional image reconstructing algorithm represented by, e.g., a method called a Feldkamp method. In the above description, the projection data is once stored in the storing unit 124. In some cases, however, the projection data can be directly supplied from the preprocessing unit 123 to the reconstructing unit 125 without being stored in the memory 124. The volume data is supplied to the data processing unit 126 directly or after being once stored in the storing unit 12M. From this volume data, the data processing unit 126 generates image data for display, such as a tomogram of a desired cross section, a transmission image of a desired direction, or a so-called three-dimensional image capable of two-dimensionally expressing a stereoscopic structure. The image displaying unit 12D displays this image data for display in gray scale or in color. The image data for display and the volume data are stored in the storing unit 12M typically implemented by a hard disk drive. Note that the arrangement of the X-ray CT scanner 1 shown in FIG. 1 is merely an example. That is, in FIG. 1 the reconstructing unit 125 and the like are configured as the console 12 separately from the frame 11. However, the reconstructing unit 125 and the like can also be installed in the frame 11. It is also possible to install the data acquisition unit 122 in the frame 11, and the preprocessing unit 123 and subsequent units in the console 12. In this case, the transmission of electric signals from the former to the latter is performed using a non-contact data transmitting means (not shown). A sensitivity correction process by the preprocessing unit 123 will be described below with reference to flow charts shown in FIGS. 3 and 9. FIG. 3 shows a calibration data file acquisition process. Raw data is corrected on the basis of a calibration data file. This correction is the process of equalizing the sensitivities of the detecting elements of the X-ray detector 112. By this correction, the CT value of water and the CT value of air are standardized to “0” and “−1,000”, respectively. A calibration data file is generated from data acquired under the same “scan conditions” as actual examination by using a cylindrical model filled with water, i.e., a “water phantom”. The “scan conditions” include a field of view (FOV), an approximate diameter of the patient P, a tube voltage, a tube current, and the like. The field of view FOV is a region as an object of reconstruction, and is formed into a columnar shape around the rotation central axis RA. The size of this field of view FOV is defined by its radius and length. Generally, the beam thickness of X-rays is so determined that the X-rays cover the entire field of view FOV. The X-ray beam thickness is defined as the thickness of an X-ray bundle on the rotation central axis RA. This X-ray beam thickness is determined by the size of the field of view FOV. Conversely, when the X-ray beam thickness is determined, the size of the field of view FOV is determined accordingly. That is, the X-ray beam thickness and the size of the field of view FOV are parameters which define each other. In the following explanation, the term “X-ray beam thickness” is used, but this term can also be reread as the size of the field of view FOV. In step S1 of FIG. 3, a phantom is placed between the X-ray tube 111 and the X-ray detector 112, and this phantom is irradiated with X-rays limited to a specific beam thickness through the collimator 111c. In step S2, the X-rays transmitted through the phantom are detected by the detector 112, and data (phantom data files) are acquired. This phantom data file acquisition is repeated every predetermined cycle while the X-ray tube 111 rotates around the phantom. Consequently, a plurality of phantom data files are acquired in one-to-one correspondence with a plurality of points discretely arranged at fixed intervals on the rotational orbit along which the X-ray tube 111 rotates around the phantom. In step S3, the data processing unit 126 calculates a calibration data file from the acquired phantom data files. The method of this calculation can be an arbitrary one. For example, the average addition value is calculated for each channel from the acquired phantom data files. A set of these average addition values is a calibration data file. Noise can be reduced by this addition average. In step S4, the calibration data file thus calculated is stored in the storing unit 12M. The routine from S1 to S4 is repeated until a plurality of calibration data files are acquired in one-to-one correspondence with a plurality of predetermined beam thicknesses (step S5). FIG. 4 shows examples of a plurality of beam thicknesses previously determined to acquire a plurality of calibration data files. FIG. 5 is a plan view showing the X-ray detector 112 viewed from a point at which the X-ray tube 111 exists. FIG. 5 shows the relationship between the range of the X-ray detector 112 within which effective data is detected, i.e., the use region of the X-ray detector 112, and the beam thicknesses shown in FIG. 4. As shown in FIGS. 4 and 5, in the slice direction of the patient P, a total of six different beam thicknesses, i.e., a maximum beam thickness “LL” determined by the use region of the X-ray detector 112, and subsequent beam thicknesses “L”, “M”, “S”, “SS”, and “SSS”, are set at substantially equal spacings. That is, six calibration data files are acquired in one-to-one correspondence with these six different beam thicknesses. The X-ray detector 112 has a plurality of detecting elements 112a arranged in an m×n matrix manner in the two, slice and channel directions. A center-to-center distance between the detecting elements 112a adjacent in the channel direction is, e.g., 1 mm, the distance is defined as the distance on the rotation central axis RA. A center-to-center distance between the detecting elements 112a adjacent in the slice direction is designed to be 1 mm, the same value, the distance is defined as the distance on the rotation central axis RA. The maximum beam thickness LL is given by n×1 mm. In actual scanning, the beam thickness can be finely set in units of 1 mm from 1 mm to n×1 mm. Six different calibration data files are acquired for beam thicknesses, in this embodiment the six different, discrete beam thicknesses, fewer than the settable beam thicknesses. It is of course also possible to acquire calibration data files for all the settable beam thicknesses, but this is not practical. As is well known, the sensitivity of the detecting element 112a varies with time. Accordingly, calibration data files must be updated whenever the main power supply is turned on, or periodically. If the calibration data file acquiring operation is repeated for all the beam thicknesses whenever update is executed, the time of this updating operation is significantly increased. FIG. 6 shows the six different calibration data files obtained for the six different beam thicknesses. As shown in FIG. 6, the larger the beam thickness, the larger the value of calibration data. This is so because the amount of scattered rays increases as the region of the patient P to be irradiated with X rays increases in size. The scattered ray amount increases because, as shown in FIGS. 7A and 7B, the larger the beam thickness, the larger the number of incident paths of scattered rays SX (indicated by the broken lines in FIGS. 7A and 7B). FIGS. 8A and 8B schematically illustrate the relationship between the size (a radius R and a length L) of the field of view FOV and the scattered ray amount. As depicted in FIGS. 8A and 8B, the scattered ray amount changes in accordance with the size of the patient P. In FIGS. 8A and 8B, the section of the X-ray detector 112 is a rectangle. However, this is merely an example, and the section can also be a circular arc (FIG. 19). As described above, the six calibration data files corresponding to the six different beam thicknesses are acquired. FIG. 9 shows an actual scan procedure for the patient P. As in step T1, the beam thickness (or the size of FOV) is input in accordance with the purpose of examination from the input device 127. This beam thickness can be set to an arbitrary integral multiple of a unit length of 1 mm as the pitch of the detecting elements, regardless of the six different, discrete beam thicknesses to which the six calibration data files correspond. Letting Xmax denote the beam thickness defined by the use region in the X-ray detector 112, a beam thickness Xt settable in this case can be expressed by 0<Xt≦Xmax. That is, the settable beam thickness Xt is substantially “arbitrary” within the range having Xmax as the upper limit, although the set pitch described above is restricted. FIG. 10A shows a beam thickness setting window. The beam thickness setting window is displayed with a patient information window and a scan condition table window in a screen. Two types of cursors CA and CB are displayed on a scanogram in order to set a beam thickness. The cursor CA represents the centerline of the beam with respect to the slice direction. The two cursors CB represent two ends of the beam with respect to the slice direction. The operator manipulates a pointing device such as a mouse to move the cursor CA back and forth along the slice direction. This allows setting the beam center to a desired position. The operator manipulates the pointing device such as the mouse to one of the two cursors CB back and forth along the slice direction. The other cursor CB automatically moves upon movement of one cursor CB such that the distance between one cursor CB (one beam end) and the cursor CA (beam center) becomes equal to the distance between the other cursor CB (other beam end) and the cursor CA (beam center). This allows setting the beam thickness to a desired thickness. The numerical values in start/end position cells of a beam thickness column are changed automatically in accordance with the movements of the cursors CA and CB. Conversely the positions of cursors CA and CB are changed automatically in accordance with the newal of the numerical values. FIG. 10B shows another beam thickness setting window. The beam thickness setting window is displayed with a patient information window and a scan condition table window in a screen. According to this method, two cursors CB representing the two ends of a beam with respect to the slice direction are used in order to set a beam thickness. The operator manipulates the pointing device such as the mouse to move one cursor CB back and forth along the slice direction. The operator also manipulates the pointing device such as a mouse to move the other cursor CB back and forth along the slice direction. This allows setting the beam thickness to a desired thickness and the beam center to a desired position. Next, as in step T2, on the basis of at least one calibration data file corresponding to the set beam thickness, a “calibration data file for use” to be used to correct raw data of the patient P is generated. The method of generating this calibration data file for use will be described later. This “generation” process is performed by the central control unit 121 described earlier. In step T3, a slice aperture of the limiting device 111c shown in FIG. 4 is set such that the set beam thickness is obtained. As shown in steps T4 to T7, the patient P is irradiated with X-rays to acquire raw data, and the acquired raw data is corrected by the preprocessing unit 123. On the basis of projection data generated by the correction, the reconstructing unit 125 reconstructs volume data. From this volume data, the data processing unit 126 generates image data for display, such as a tomogram or a three-dimensional image. This image data for display is displayed on the image displaying unit 12D or stored in the storing unit 12M. The correction process (step T5 in FIG. 9) that the preprocessing unit 123 performs for the raw data from the data acquisition system 122 by using the calibration data file for use will be described in detail below. FIG. 11 shows an example of geometry during scanning of the patient P. The beam thickness is set as indicated by the thick line in FIG. 11. The set beam thickness does not match any of the six different beam thicknesses corresponding to the six calibration data files. In this example, the set beam thickness is intermediate between M and S. If no matching calibration data file exists, correction cannot be performed in conventional apparatuses. In the first place, beam thickness choices are limited to beam thicknesses corresponding to calibration data files. In this embodiment, however, a calibration data file for use which matches an actually set beam thickness is generated from at least one of the six different calibration data files described above (step T2 in FIG. 9). As the method of generating the calibration data file for use, five different methods from the first to fifth methods are provided. The central control unit 121 can be equipped with one or all of these five methods. In the latter case, these five methods are selectively used in accordance with a designation by an operator. The five different methods of generating a calibration data file for use will be explained below in turn. (First Method: Interpolation) This first method obtains the aforementioned calibration data file for use by interpolation from at least one calibration data file selected in accordance with the set beam thickness from the six different existing calibration data files described above. As shown in FIG. 6, the values of these six different calibration data files increase as the beam thickness increases under the influence of scattered rays. However, it is known that the relationship between the scattered ray amount and the beam thickness is substantially a proportional relationship. Therefore, linear interpolation using the beam thickness as a parameter can be performed for each corresponding detecting element of the X-ray detector 112. For example, if the set beam thickness is between the M- and S-regions as shown in FIG. 11, two-point interpolation is performed using calibration data files of the M- and S-regions, as indicated by the alternate long and short dashed line in FIG. 12, for those detecting elements (in a region SI in FIG. 11) of the X-ray detector 112 which are inside the S-region. For detecting elements (in a region MS in FIG. 11) between the M- and S-regions, extrapolation is performed using calibration data files of the L- and M-regions, since there is no calibration data file of the S-region. By these interpolating processes, a calibration data file AA1 for use as shown in FIG. 12 is obtained. In the present invention, as indicated by the alternate long and two short dashed line in FIG. 12, multi-point interpolation can also be performed instead of the two-point interpolation. That is, for detecting elements in the region SI described above, interpolation can be performed using three points on calibration data files of the L-, M-, and S-regions. For the region MS, interpolation can be performed using three points on calibration data files of the LL-, L-, and M-regions. Furthermore, in place of the above methods, interpolation can also be performed using all the six different calibration data files for, e.g., detecting elements in the region SI. In the multi-point interpolation as described above, the number of points to be used in interpolation can be properly determined from the relationship between the effect and the processing amount. Also, as described above, FIG. 12 shows examples of two-point interpolation and three-point interpolation. However, this simply means that the two methods are illustrated in one figure for the sake of convenience of explanation. In practice, therefore, the calibration data file AA1 for all beam thicknesses is generally obtained by two-point interpolation or three-point interpolation alone. It is, however, exceptionally possible in some cases to use two-point interpolation and three-point or multi-point interpolation at the same time. A case is, e.g., when it is desirable to acquire an image having higher accuracy in a portion near the ordinate in FIG. 12, i.e., in a central portion of the X-ray detector 112, than in other portions. In this case, it is possible to perform three-point interpolation near the ordinate and two-point interpolation in the other portions. The present invention has no intention to positively exclude these forms. Also, if the set beam thickness is present between the LL- and L-regions (a region L3) as shown in FIG. 13, it is impossible to obtain calibration data files at a plurality of points necessary for interpolation for obtaining a calibration data file AA2 for use. This basically makes interpolation impossible to perform. The simplest method in a case like this is to, e.g., use a calibration data file concerning the LL-region directly as a calibration data file for use. In the processing as described above, however, as shown in FIG. 13, a calibration data file concerning the beam thickness inside the L-region and a calibration data file concerning the beam thickness in the region L3 become discontinuous. This situation is not preferred because it may cause an artifact on the reconstructed image. In this method, therefore, the following method can be used instead of the above one. That is, as shown in FIG. 13, it is possible to use information contained in an edge portion of a calibration data file pertaining to the L-region, i.e., to use a differential coefficient, or to obtain an extrapolation point on the basis of an output value near the edge. In this manner, a calibration data file (to be referred to as an “extended calibration data file” hereinafter) EA which is extended to smoothly connect to the edge portion is formed. When two-point interpolation is performed using this extended calibration data file EA and a calibration data file of the LL-region, a calibration data file AA′ for use having higher accuracy is obtained. In this method, no such discontinuous portion as mentioned above is produced. This method of forming the extended calibration data file EA is generally applicable to a portion where the combination of calibration data files for use in interpolation changes, i.e., to an edge portion of each of the six different calibration data files. For example, when the two-point interpolation explained with reference to FIG. 12 is to be performed, the process in the region MS is done by performing extrapolation using calibration data files of the L- and M-regions in the above method. Instead, it is possible to form an extended calibration data file concerning a calibration data file of the M-region on the basis of an edge portion of this calibration data file, and perform two-point interpolation in the same manner as in the region SI. This method can suppress the generation of an artifact caused by a difference in a portion where these regions connect. (Second Method: Substitution) In this second method, one calibration data file selected by predetermined standards from the six different calibration data files described above is substituted as most appropriate for a calibration data file for the set beam thickness. That is, a previously acquired calibration data file is directly used without performing any interpolation unlike in the above first method. For example, if the set beam thickness is present between the M- and S-regions as shown in FIG. 11, a calibration data file of the M-region is selected and used as a calibration data file AA3 for use as shown in FIG. 14. Examples of standards for selecting one of the six different calibration data files are the following items. First, to effectively perform calibration, calibration data files are required for all detecting elements from which data is acquired by scanning. Therefore, a calibration data file obtained by a beam thickness smaller than when the patient P is scanned cannot be used. That is, in the above example, the data of the M-, L-, and LL-regions are used without using the calibration data file of the S-region. Second, the scattered ray amount changes in accordance with the beam thickness as described earlier. Hence, data obtained under conditions closest to the beam thickness when the patient P is scanned is suitable as a calibration data file to be selected. From the foregoing, it is most preferable to use that calibration data file pertaining to the smallest beam thickness, which is one of calibration data files pertaining to beam thicknesses larger than the beam thickness when the patient P is scanned. In the example shown in FIG. 14, a calibration data file of the M-region is used. Whether to use interpolation of the first method or substitution of the second method is suitably determined by taking account of the performance of the X-ray CT scanner 1 or the central control unit 121. Alternatively, the X-ray CT scanner 1 according to the present invention can hold both the above two processes such that either process can be practiced. In this case, an operator of the apparatus can appropriately select a desired process. Generally speaking, the interpolation process described above enhances the effect of reducing the number of calibration data files which must be acquired in advance in accordance with FIG. 3. On the other hand, the substitution process has an effect of making this interpolation process unnecessary. (Third Method: Processing Using Calibration Data File Edge Portion) This third method is characterized in that a calibration data file for use is prepared by using an edge portion of a calibration data file, or by using the method of forming the extended calibration data file EA by focusing attention on this edge portion, described in the first method. In the following explanation, a case in which the set beam thickness is present between the M- and S-regions as shown in FIG. 11 is taken as a representative example. Also, figures to be referred to in the following explanation are simplified by showing only calibration data files of the M- and S-regions. First, as a simple method, the extended calibration data file described above can be directly used as a calibration data file for use. That is, as shown in FIG. 15, an extended calibration data file EB based on an edge portion of a calibration data file of the S-region is formed. In addition, a calibration data file AA4 for use is prepared by connecting this extended calibration data file EB and the calibration data file of the S-region. This processing method is basically similar to the concept of the substitution process mentioned above. The difference is that a calibration data file of the M-region is used in the substitution process (FIG. 14), but a calibration data file of the S-region is basically used in this process. This is possible because the extended calibration data file EB is formed. As a simpler method, an existing calibration data file form (curve form) is directly used without forming any extended calibration data file, but caution is exercised on an edge portion. That is, as shown in FIG. 16, a calibration data file in the region MS is shifted down to meet the output value of a calibration data file of the S-region. A connecting point (≈edge portion) J between the shifted calibration data file (of the M-region) in the region MS and the calibration data file of the S-region is subjected to processing by which the two output values continue. This processing has no big difference from the concept of the process of obtaining an extended calibration data file. Note that as a calibration data file AA4 for use, only the corresponding region need be extracted. Still another method is to make the best use of the form of a calibration data file without “shifting” the calibration data file. For example, as shown in FIG. 17, a calibration data file (to be referred to as a “connecting calibration data file” hereinafter) CL is prepared which connects an edge portion of a calibration data file of the S-region to a calibration data file of the M-region. One end of this connecting calibration data file CL is smoothly connected to a portion J1 near the edge portion of the calibration data file of the S-region. The other end of the connecting calibration data file CL is smoothly connected to a portion J2 near the edge portion in a position where the calibration data file curve of the M-region intersects the boundary defining the S-region. Note that as a calibration data file AA6 for use, only the corresponding region is extracted similar to FIG. 16. The processing method as described above can prevent the generation of a discontinuous portion as explained with reference to FIG. 13 in the first method. Also, this third method does not use a calibration data file concerning a region larger than the set beam thickness, unlike in the substitution process of the second method. That is, for a lacking portion (the region MS in FIG. 15 or 17), the extended calibration data file EB is used (FIG. 15), a calibration data file concerning a region larger than the set beam thickness is used after being shifted (FIG. 16), or a calibration data file concerning a region larger than the set beam thickness is used while the connecting calibration data file CL is formed and used (FIG. 17). This makes it possible to use a calibration data file of a region smaller than the set beam thickness. The use of a calibration data file of a region smaller than the beam thickness is advantageous when, in the examples shown in FIGS. 15 to 17, the beam thickness is close to the size of the S-region and far from the size of the M-region. The reason requires no explanation. In the above second method, however, a calibration data file of the M-region is prepared as a calibration data file for use even in a case like this. The significance of this third method is confirmed in this respect. That is, from this viewpoint it is preferable to use a calibration data file pertaining to a beam thickness closest to the set beam thickness. To make the above operation effective, it is necessary to determine which of the six different beam thicknesses (=“LL” to “SSS”) corresponding to the six different existing calibration data files the set beam thickness is close to. This is done simply by comparing practical numerical values of the beam thicknesses, i.e., “LL” to “SSS”, corresponding to the six different existing calibration data files previously acquired, with a practical numerical value of the set beam thickness. Consequently, it is readily possible to determine which of “LL” to “SSS” the set beam thickness is close to. Alternatively, as shown in FIG. 18, it is also possible to perform processing which conceptually uses a graph in which the output from a certain detecting element of the X-ray detector 112 is plotted on the ordinate, and the beam thickness is plotted on the abscissa. In this graph, the sizes (=beam thicknesses) and the outputs of the S- and M-regions are already known by the calibration data file acquisition process shown in FIG. 3. Also, an appropriate number of outputs from the certain detecting element with respect to a beam thickness between the S- and M-regions are acquired beforehand. As a consequence, the graph shown in FIG. 18 can be formed. By referring to the output result obtained by the set beam thickness for the certain detecting element concerning this graph, whether the set beam thickness is close to the S- or M-region is determined (see arrows in FIG. 18). On the basis of this result, various processes explained in this third method are performed if the set beam thickness is close to the S-region, and the substitution process explained in the second method is performed if the set beam thickness is close to the M-region. That is, processing using a calibration data file concerning a beam thickness close to the set beam thickness can be performed. This processing using FIG. 18 is advantageous because, as shown in FIG. 18, the outputs of a plurality of regions do not strictly have a proportional relationship in some instances. That is, if the beam thickness and the output have a nonlinear relationship as shown in FIG. 18, it is difficult for the simple comparison described above to accurately determine which region the set beam thickness is close to. However, the processing herein mentioned makes this possible. Note that the graph shown in FIG. 18 is formed for a “certain detecting element”. However, the present invention is not limited to this example. For example, a graph as shown in FIG. 18 can also be formed for “several detecting elements (specific detecting elements) selected with high symmetry from the X-ray detector 112”, or for a “plurality of detecting elements (specific detecting elements) in the same channel”. In this third embodiment, the set beam thickness is present between the M- and S-regions. However, other cases (e.g., a case in which the set beam thickness is present between the L- and M-regions) can also be exactly similarly processed. In step T5 of FIG. 9, the calibration data files AA1 to AA6 for use acquired by the first to third methods as described above are subjected to actual correction for scan data. It is obvious that this correction process using the calibration data files AA1 to AA6 for use can appropriately correct the sensitivity of the X-ray detector 112. (Fourth Method: Scattered Ray Correction) This fourth method is characterized in that variously settable beam thicknesses can be corrected by applying a scattered ray correction process. As described previously, scattered rays are excessively detected X-ray components other than direct X rays. The larger the beam thickness and the larger the diameter of the patient P, the larger the amount of scattered rays (FIGS. 7A, 7B, 8A, and 8B). “Scattered ray correction” is the process of excluding such scattered rays from projection data, and obtaining projection data consisting substantially primarily of direct X rays. This scattered ray correction process can be performed by using, e.g., the preprocessing unit 123, the central control unit 121, or a dedicated arithmetic unit (to be referred to as a second correcting means hereinafter). As the scattered ray correction process of this fourth method, a method disclosed in, e.g., Jpn. Pat. No. 1631264 or Jpn. Pat. Appln. KOKAI Publication No. 11-89827 can be used. The scattered ray correction process disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 1631264 will be briefly described below. That is, as shown in FIG. 19, an X-ray diagnostic apparatus of this publication includes an X-ray shielding means XS. This X-ray shielding means XS is constructed by arranging X-ray shielding members such as lead pieces XSB at equal intervals on an X-ray transmitting member XSA obtained by shaping, e.g., acrylic resin into the form of a thin plate. This X-ray shielding means XS can move as indicated by arrows shown in FIG. 19, and can make X-rays emitted from an X-ray tube 111 shielded or unshielded with respect to an X-ray detector 112. Note that X-rays are, of course, shielded or unshielded at the positions of the lead pieces XSB. When this X-ray shielding means XS is positioned in the field of irradiation, the X-ray diagnostic apparatus can acquire X-ray shielded data. During the acquisition of this X-ray shielded data, no X-rays are directly incident on detecting elements corresponding to the positions of the lead pieces XSB. So, the resulting output (scattered ray data) reflects the presence of scattered rays. After that, therefore, on the basis of the relationship between the positions of the lead pieces XSB and the scattered ray data corresponding to the individual positions, the distribution (scattered ray intensity data) of scattered ray intensity on the entire surface (=all detecting elements) of the X-ray detector 112 can be calculated. According to the publication, this is done by data interpolation using a sampling function. By calculating a difference between the scattered ray intensity data thus obtained and original image data obtained by positioning the X-ray shielding means XS outside the irradiation field, projection data excluding the influence of scattered rays is obtained. The scattered ray correction process disclosed in Jpn. Pat. Appln. KOKAI Publication No. 11-89827 is substantially as follows. That is, as shown in FIG. 20, an X-ray CT scanner of this publication includes a channel-direction collimator CDC and a slice-direction collimator SDC on the front surface of an X-ray detector 112. The channel-direction collimator CDC prevents scattered rays in a channel direction from entering the X-ray detector 112. The slice-direction collimator SDC prevents scattered rays in a slice direction (parallel to the axial direction of the patient P) from entering the X-ray detector 112. Collimator plates CDC1 are densely arranged in the channel-direction collimator CDC. Collimator plates SDC1 are “sparsely” arranged in the slice-direction collimator SDC. In this X-ray CT scanner, as shown in FIGS. 21A and 21B, the action of the slice-direction collimator SDC (physically) removes scattered rays only in the positions of the collimator plates SDC1. Consequently, detecting elements A to D of the X-ray detector 112 immediately below these positions detect only direct X rays (see “dense hatched portions” in FIGS. 21A and 21B). Detecting elements X2 and X3, X6 and X7, X10 and X11, and X14 and X15 on the two sides of the detecting elements A, B, C, and D, respectively, detect X rays from which scattered rays are slightly removed but which still contain remaining scattered ray components. Remaining detecting elements X1, X4, X5, X8, X9, X12, X13, and X16 detect X rays (direct X rays+scattered rays) from which no scattered ray components are removed at all (in FIGS. 21A and 21B, “broken-line portions” indicate physically removed scattered rays, and “sparse hatched portions” indicate detected scattered rays). In the above publication, from the differences between these modes, the distribution of direct ray components is estimated on the basis of the outputs from the detecting elements A to D, and the distribution of direct ray components and scattered ray components is estimated on the basis of the outputs from the detecting elements X1, X4, X5, X8, X9, X12, X13, and X16 (FIGS. 21A and 21B). By subtracting the former from the latter, the distribution of only scattered rays on the front surface of the collimator can be obtained. By multiplying this scattered ray distribution by a previously calculated removal ratio, a scattered ray amount incident on each detecting element can be estimated. By subtracting the thus estimated scattered ray amount from actual scan data, projection data from which the influence of scattered rays is eliminated is obtained. The “removal ratio” is the ratio of the scattered ray amount removed when the slice-direction collimator SDC is present to the total scattered ray amount when this collimator SDC is absent. In this fourth method, the above scattered ray correction is first performed in the calibration data file acquisition process explained with reference to FIG. 3. Note that this calibration data file acquisition is performed only for a calibration data file concerning the maximum beam thickness determined by the size of the X-ray detector 112. That is, in the example shown in FIG. 4, only a calibration data file concerning the LL-region is acquired. Therefore, in the calibration data file acquisition process shown in FIG. 3, the processing in step S5 is omitted. The actual scan conditions, however, include not only the beam thickness but also conditions such as the tube voltage of the X-ray tube 111. Hence, although “only a calibration data file pertaining to the LL-region is acquired”, a necessary number of calibration data files must be acquired for the other parameters. That is, it is necessary to acquire, e.g., a “calibration data file for a tube voltage v [V] of the X-ray tube 111 when the beam thickness is the LL-region”, and a “calibration data file for a diameter d [m] of the patient P when the beam thickness is the LL-region”. In this example, however, as already mentioned above, only the beam thickness is taken into consideration as the scan condition. The timing at which scattered ray correction is performed for the acquired calibration data file of the LL-region is between steps S3 and S4 in FIG. 3. In this way, the scattered-ray-corrected calibration data file is stored (step S4 in FIG. 3). Subsequently, the actual patient scanning process explained with reference to FIG. 9 begins. As described previously, a beam thickness is freely set at a fine pitch (steps T1 and T3 in FIG. 9), and data of a minimum necessary region of the patient P is acquired. A calibration data file prepared in step T2 of FIG. 9, i.e., a calibration data file for use in this fourth method, is naturally the scattered-ray-corrected calibration data file concerning the LL-region. In step T5 of FIG. 9, the preprocessing unit 123 performs various correcting processes and scattered ray correction for the acquired patient scan data. Subsequently, the sensitivity of the X-ray detector 112 is corrected by using the scattered-ray-corrected data file (calibration data file for use) related to the LL-region on this scattered-ray-corrected scan data. In this processing, sensitivity correction is performed by using the data (the scattered-ray-corrected calibration data file and scan data) from which the influence of scattered rays is eliminated by scattered ray correction. This eliminates the problem of the difference between scattered ray amounts produced by the difference between the beam thickness when calibration data files are acquired and that when the patient is scanned. As a consequence, a highly accurate image having little artifact is obtained. In the above forth method, outlines of Jpn. Pat. No. 1631264 and Jpn. Pat. Appln. KOKAI Publication No. 11-89827 are explained as scattered ray correction processes. In the present invention, however, it is basically possible to use scattered ray correction based on any methods in addition to the above two scattered ray correction processes. In any case, the function and effect described above are achieved. (Fifth Method: Combined Use of Scattered Ray Correction and Correction Process Based on Several Different Calibration Data Files) This fifth method is characterized by combining the interpolation process, the substitution process, and the processing using a calibration data file edge portion described in the first, second, and third methods, with the scattered ray correction process described in the fourth method. In the following description, the combination of the interpolation process of the first method and the scattered ray correction process will be explained. In this fifth method, similar to the first method described above, a plurality of different calibration data files concerning a predetermined beam thickness are acquired. Each of these calibration data files is subjected to scattered ray correction in the same manner as in the fourth method, and stored (the processing shown in FIG. 3 including scattered ray correction is performed). The procedure shown in FIG. 9 then starts. In accordance with the scan condition (i.e., the “beam thickness” in this method) of the patient, the scattered-ray-corrected calibration data files are interpolated to estimate a calibration data file for use of patient scan data (see step T2 in FIG. 9 and the description in the first method). Scattered ray correction is also performed for the patient scan data as in the fourth embodiment. Sensitivity correction is performed for the thus obtained scattered-ray-corrected scan data by using the “calibration data file for use” based on the several different scattered-ray-corrected calibration data files estimated above (step T5 in FIG. 9). This processing can simplify the scattered ray correction process. That is, in this fifth method, the interpolation process in the first method and the scattered ray correction process in the fourth method, both of which are proven to be effective in appropriately correcting a variously settable beam thickness, are performed in combination. This can relatively alleviate the duties to be fulfilled by the scattered ray correction process. This simplification of the scattered ray correction process is sometimes necessary depending on, e.g., the scheme of scattered ray correction and the weight, time, and the like of the correction process. Also, in the above fifth method, a highly accurate image having little artifact is obtained for the same reason as above, even when the accuracy of scattered ray correction is low. As has been described above, when the various processes explained as the first to fifth methods are performed, an appropriate calibration data file for use for a variously settable beam thickness can be obtained only by acquiring one or several different calibration data files. Basically, therefore, accurate sensitivity correction can be performed whatever the beam thickness is set. Accordingly, in these methods, usable beam thicknesses are not limited unlike in conventional methods, so the beam thickness can be freely set. As a consequence, the patient P is not unnecessarily exposed to X rays. In the first to third methods and the fifth method, six different calibration data files from “LL” to “SSS” are prepared for predetermined beam thicknesses. However, the present invention is not restricted to this form. Basically, any number of different calibration data files can be prepared. Also, in the methods except for the first method in which interpolation is performed, the processing can be performed in principle only by acquiring a calibration data file for “one” beam thickness. Generally speaking, however, the first method can infinitely perform the processing for any beam thickness in principle, because interpolation is performed. Therefore, the number of calibration data files to be prepared can be small. In the second and third methods, however, it is preferable to prepare a larger number of calibration data files than in the first method. The present invention is most suitably applicable to a so-called cone-beam X-ray CT scanner. However, it is of course also possible to apply the present invention to a “multi-slice X-ray CT scanner” described in “2 Description of the Related Art”. Furthermore, it is favorable to apply the following modification to the form of practicing the “scattered ray correction processes” described in the fourth and fifth methods. (Determination of Propriety of Scattered Ray Correction Process) This scattered ray correction process is characterized in that whether to perform scattered ray correction, or the amount or intensity (intensity of the degree of correction) of scattered ray components to be actually subtracted, is determined in accordance with a difference between set beam thicknesses and the like, for the fourth and fifth methods using scattered ray correction. As already described several times, the scattered ray amount strongly depends upon the scan conditions, particularly the beam thickness and the diameter of the patient P; the larger the beam thickness and the larger the diameter of the patient P, the larger the scattered ray amount (FIGS. 7A, 7B, 8A, and 8B). Conversely speaking, the influence of scattered rays is not so large if the beam thickness or the patient size (equivalent to the imaging region of an axial section as a scan condition) is small. Accordingly, when the beam thickness or the patient size is used as a parameter, it is possible to determine whether to perform scattered ray correction, or to determine the amount or intensity of scattered ray components to be actually subtracted. More specifically, if the beam thickness or the patient size is large, the scattered ray amount increases, so scattered ray correction is performed or the amount of intensity of scattered ray components to be actually subtracted is increased. In contrast, if the beam thickness or the patient size is small, the scattered ray amount reduces, so no scattered ray correction is performed or the amount or intensity of scattered ray components to be actually subtracted is decreased. The “amount or intensity of scattered ray components to be actually subtracted” described above can be determined by multiplying so-called “raw” scattered ray components (“scattered ray intensity data” in Jpn. Pat. No. 1631264, and an “estimated scattered ray amount” calculated by removal ratio multiplication in Jpn. Pat. Appln. KOKAI Publication No. 11-89827), purely calculated or estimated, by an appropriate proportional coefficient a. As is evident from the above explanation, the proportional coefficient a can be 0<a<1 or a≧1. This processing can prevent the occurrence of abuses when scattered ray correction is performed although the necessity of the process is weak. “Abuses” herein mentioned simply include a prolonged operation time caused by the scattered ray correction process, and also mean a case as shown in FIG. 22. That is, when X-ray intensity as indicated by the broken line in FIG. 22 is detected, net X-ray data P1 can be obtained even if scattered ray components SDM extending at the bottom of this X-ray intensity are removed. However, when this X-ray intensity is as indicated by the solid line in FIG. 22, the amount of (the degree of contribution of) scattered rays is large relative to net X-ray data P2. Therefore, if the scattered ray components SDM are removed in this state, the net X-ray data P2 becomes almost “0”, and this makes it difficult, or impossible, to obtain the value of the data. This scattered ray correction process can eliminate such “abuses”. As described above, whether to perform the scattered ray correction process, or the amount of intensity of scattered ray components to be actually subtracted, is determined by using the above-mentioned parameter. This determination is preferably performed such that the degree of contribution of scattered ray components with respect to the whole X-ray data detected is about 5 to 10%. In the above description, whether to perform the scattered ray correction process is determined on the basis of the beam thickness “or” the patient size. However, the present invention is not limited to this form. For example, it is also possible to regard the beam thickness and the patient size as having an organic relationship. In this case, no scattered ray correction process is performed as long as both the beam thickness and the patient size are equal to or smaller than first and second predetermined values (these values have the nature of a watershed which determines whether to perform the scattered ray correction process). That is, in this processing, the scattered ray correction process is performed if the patient size is larger than the second predetermined value although the beam thickness is equal to or smaller than the first predetermined value. In short, the present invention can determine whether to perform the scattered ray correction process, or to determine the amount of intensity of scattered ray components to be actually subtracted, in accordance with the combination of the beam thickness and the patient size. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit and scope of the general inventive concept as defined by the appended claims and their equivalents.
	claims	1. A nuclear reactor for operative connection to a power conversion system, the reactor comprising:a containment vessel;a reactor core housed within the containment vessel;a neutron reflector spaced from the containment vessel and positioned between the core and the containment vessel;a liquid fuel comprised of a nuclear fission material dissolved in a molten salt enclosed within the core;a plurality of heat transfer pipes, each pipe having a first end and a second end, the first end being positioned within the reactor core for absorbing heat from the fuel;a heat exchanger external to the containment vessel, the heat exchanger receiving the second end of each heat transfer pipe for transferring heat from the core to the heat exchanger; andat least two reactor shut down systems that together act as redundant fail-safe systems comprising a first shut down system and, at least one second shut down system, wherein the first shut down system comprises:a rotatable member mechanism comprising:a plurality of rotatable members positioned within the neutron reflector and having a neutron absorber section and a non-absorber section; and,a rotating drive mechanism operatively connected by activation rods to each rotatable member for rotating the rotatable member to move the neutron absorber section to one of a first position facing the core and a second position facing away from the core, andthe second shut down system comprises one or both of a neutron absorber activation system and a melt-plug mechanism. 2. The nuclear reactor recited in claim 1 wherein the second shut down system is the melt-plug mechanism and comprises:an opening in the containment vessel;a chamber fluidly connected to the opening in the containment vessel;a melt plug to plug the opening in the containment vessel;the melt plug being made of a material that melts at a predetermined temperature deemed to be indicative of unsafe temperature conditions within the reactor core. 3. The nuclear reactor recited in claim 2 wherein the melt plug is made of an alloy and the predetermined temperature is between 650° C.−900° C. 4. The nuclear reactor recited in claim 2 further comprising:a barrier housing for holding the containment vessel; anda plurality of heat dissipation elements extending from the chamber into the barrier housing. 5. The nuclear reactor recited in claim 1 further comprising:a central axis extending through the core;wherein the second shut down system comprises the neutron absorber activation system comprising:a hollow tube defining a cavity and being positioned coaxially to the central axis and extending from an area above the core into the core;a gate separating a first portion of the hollow tube above the core from a second portion of the hollow tube within the core;a neutron absorber material housed in an unactivated position within the first portion of the hollow tube;an activation rod operatively connected to the gate;a release member for releasing the actuation rod from the unactivated position to move to an activated position, wherein in the activated position, the actuation rod opens the gate to release the neutron absorber material into the cavity within the second portion of the hollow tube in proximity to the fuel to absorb neutrons from the fuel sufficient to shut down the reactor. 6. The nuclear reactor recited in claim 5 wherein the neutron absorber shut down system further comprises:a guide positioned within the hollow tube coaxial to the central axis and defining a channel between the hollow tube and the guide for receiving the neutron absorber material upon release thereof in the activated position. 7. The nuclear reactor recited in claim 1 further comprising:a barrier housing for holding the containment vessel. 8. The nuclear reactor recited in claim 1 wherein at least one of the first and at least one second shut down systems is a passive system and at least one is an active system. 9. The nuclear reactor recited in claim 1, wherein the containment vessel has an interior and an exterior, further comprising:a plurality of cooling fins on the exterior of the containment vessel. 10. The nuclear reactor recited in claim 1, wherein the containment vessel has an interior and an exterior, further comprising:a lining on the interior of the containment vessel comprised of a fission gas absorbing material. 11. The nuclear reactor recited in claim 1 wherein the fuel comprises one or both of a uranium halide or a uranium oxyhalide, dissolved in one or more of a potassium, magnesium, or sodium salt. 12. The nuclear reactor recited in claim 1 wherein the contaimnent vessel is in the shape of a cylinder. 13. A nuclear reactor for operative connection to a power conversion system, the reactor comprising:a containment vessel;a reactor core housed within the containment vessel;a neutron reflector spaced froze the containment vessel and positioned between the core and the containment vessel;a livid fuel comprised of a nuclear fission material dissolved in a molten salt enclosed within the core;a plurality of heat transfer pipes, each pipe having a first end and a second end, the first end being positioned within the reactor core for absorbing heat from the fuel;a heat exchanger external to the containment vessel, the heat exchanger receiving the second end of each heat transfer pipe for transferring heat from the core to the heat exchanger; andat least three reactor shut down systems comprising a first shut down system, a second shut down system, and a third shut down system, the first shut down system comprising:a rotatable member mechanism comprising:a plurality of rotatable members positioned evenly within the neutron reflector, each rotatable member having a neutron absorber section and a non-absorber section; and,a rotating drive mechanism operatively connected to each rotatable member for rotating the rotatable member to move the neutron absorber section to one of a first position facing the core and a second position facing away from the core;the second shut down s stem comprising:a melt-plug mechanism comprising:an opening in the containment vessel;a chamber fluidly connected to the opening in the containment vessel;a first melt plug, to plug the opening in the containment vessel;the first melt plug being made of a material that melts at a predetermined melting temperature deemed to be indicative of unsafe temperature conditions within the reactor core; and the third shut down system comprising:a central axis extending through the core and a neutron absorber activation system comprisinga hollow tube defining a cavity and being positioned coaxially to the central axis and extending from an area above the core into the core;a gate separating a first portion of the hollow tube above the core from a second portion of the hollow tube within the core;a neutron absorber material housed in an unactivated position within the first portion of the hollow tube;an activation rod operatively connected to the gate;a release member for releasing the actuation rod from the unactivated position to move to an activated position, wherein in the activated position, the actuation rod opens the gate to release the neutron absorber material into the cavity within the second portion of the hollow tube in proximity to the fuel to absorb neutrons from the fuel sufficient to shut down the reactor. 14. The nuclear reactor recited in claim 13 further comprising:a passage through the neutron reflector from the reactor core to a space defined between the containment vessel and the neutron reflector;a second melt plug to plug the passage;the second melt plug being made of a material that melts at a predetermined melting temperature deemed to be indicative of unsafe temperature conditions within the reactor core. 15. The nuclear reactor recited in claim 14 further comprising:a heating element positioned proximate to at least one of the opening in the containment vessel for heating the first melt plug, to the predetermined melting temperature of the first melt plug and the passage for heating the second melt plug to the predetermined melting temperature of the second melt plug, anda heating element controller electrically connected to the heating element for manual activation of the heating element. 16. The nuclear reactor recited in claim 13 wherein the neutron absorber shutdown system further comprises:a guide positioned within the hollow tube coaxial to the central axis and defining a channel between the hollow tube and the guide for receiving the neutron absorber material upon release thereof in the activated position.
	abstract	A lock plate for a locking device of a jet pump beam, the locking device including a locking sleeve including a lower portion, may include a beam bolt opening sized to receive the locking sleeve, and a spring arm including plurality of spring a ratchet teeth sized to mesh with locking sleeve ratchet teeth included in the lower portion of the locking sleeve, the spring arm being structured such that the spring arm has both i) an engaged position where the locking sleeve is in the beam bolt opening and at least a portion of the capture feature overlaps vertically with an upper surface of the lower portion of the locking sleeve, and ii) a disengaged position where the locking sleeve is in the beam bolt opening and the capture feature does not overlap vertically with the upper surface.
	summary
	description	The present invention relates to a wafer scanning device which causes a wafer or other workpieces to be processed to linearly scan in a vacuum chamber, particularly to a wafer scanning device which moves a semiconductor wafer linearly against an ion beam for ion implantation. In an ion implanter, it is general to cause a wafer to scan (translate) in a reciprocating motion in the particular straight direction so that the every portion of the wafer surface can be uniformly implanted by ions. One of the conventional, general wafer scanning devices which makes a wafer scan in a reciprocating motion is described as follows referring to FIG. 13. FIG. 13 shows the inner structure of the vacuum chamber where a wafer holder and other components are placed. In the device of FIG. 13, a drive shaft 81a is connected to an arm 81 and another arm 82, which are used to cause a wafer holder 85 to linearly reciprocate. Following are the details of the device. The first arm 81 is hollow and has both a drive shaft 81a and a driven shaft 81b in it. The shafts 81a and 81b are connected with a belt 81c. The second arm 82 has a bar-shape and is connected to the driven shaft 81b at its base portion. When the drive shaft 81a in the first arm 81 is rotated by means of a drive source such as a motor (not illustrated), the driven shaft 81b rotates while revolving together with the first arm 81 to change the position and angle of the second arm 82. The top portion of the second arm 82 is connected to the slide member 83 which moves along the guide member 84. The slide member 83 is fixed with a wafer holder 85. Accordingly the wafer holder 85 can linearly move by the rotation of the drive shaft 81a. A similar device is also seen in the disclosure of Japanese publication of unexamined patent application No. H10-326590 (see FIG. 4 in the concerned gazette). In the scanning device of FIG. 13, the belt 81c transmits the motive power from the first arm 81 to the second arm 82, so the responsiveness with respect to the transmission is not sufficient. In other words, as the belt 81c expands and contracts easily and the moment of inertia of the arms 81 and 82 with respect to the scan motion is large, the scan speed might affect the accuracy of the control. In addition to it, due to the use of the belt 81c, the rigidity in the scan direction might not be secured and the natural vibration at low frequency tends to generate. Under the influence of that, it might be difficult to keep a uniform scanning speed. Instead of the device of FIG. 13, another type of wafer scanning device which has no belt is proposed in the above application No. H10-326590. But even the proposed device can not solve all the expected technical problems. There is no description on the proper means to solve the following problems: a problem with the arrangement of a motor or other transmission equipment, which might quite easily generate particles (dust generation) or outgas (molecular contaminants), in a vacuum chamber for processing a semiconductor wafer or the like; and a problem of how to tilt a wafer preferably in order to change the angle of ion implanting. Moreover, the equipment for transmission or drive being positioned in vacuum also has problems on lubrication, heat radiation (cooling) and the like. When the equipment for transmission or drive is installed in vacuum, conventionally, solid lubrication or special lubrication is necessary for lubrication and a circulation cooling device is needed for heat radiation or cooling. But the costs for the lubricant or equipment and the space for equipment need to be improved and an effort has been made to solve the problems. The present invention is made to solve the above-mentioned problems and its object is to provide a wafer scanning device which enhances the uniformity of scanning speed by improving the responsiveness with respect to the scanning speed control, optimizes the arrangement of a motor or the like, tilts a wafer in a proper manner, and has no problem of lubrication or heat radiation. A wafer scanning device of the present invention is a device which causes a wafer (or other workpieces to be processed) to scan in a vacuum chamber including: a holder which can hold a wafer; a linear translation structure which causes the holder to scan; a transmission mechanism and a motor which drive the linear translation structure; and an integrated (or integrally assembled) support frame which supports them (the holder, the linear translation structure and the motor); wherein the holder and the linear translation structure are installed in a vacuum chamber; the transmission mechanism includes a first transmission mechanism on a line of travel of the linear translation structure and a second transmission mechanism offset from said line of travel; and the second transmission mechanism offset from the line of travel and the motor are installed in the atmosphere. In the description above, “a linear translation structure” includes a ball screw, a sliding screw, a planetary roller screw, a rack-and-pinion, etc. and “a line of travel of the linear translation structure” means a linear line along the direction of the linear movement of the structure. A wafer scanning device of FIG. 5 is one of the embodiments of the present invention. The wall 2 of the vacuum chamber are integrally formed with the support frame 60. The holder 10 and the ball screw 20 are positioned in a vacuum area inside the wall 2; and the motor 50 is positioned in the atmosphere, outside the wall 2. Thus composed, the wafer scanning device has the following functional features: Since the linear translation structure like a ball screw, etc., linearly moves the wafer holder, the device shows high responsiveness with respect to the scanning speed control and excellent uniformity of the scanning speed. That is because the linear translation structure, such as a ball screw or the like, has no component to greatly extend and contract, unlike the belt 81c of the conventional device of FIG. 13, and further has high rigidity that prevents the generation of natural vibration at low frequency range. The motor, being placed not in vacuum but in the atmosphere, will not cause problems with particles or outgas generated from its sliding portion or the like. As a result, it is possible to employ a general type motor (at a low cost). Further, it is not necessary that the lubrication for the sliding portion of the motor or the like be a special type which is expensive. As the transmission mechanism offset from the line of travel is positioned in the atmosphere as well as the motor, the vacuum chamber includes only the linear translation structure and a few components on the line of travel of the linear translation structure. Thus the device has only few mechanisms or components that require a consideration on generation of the particles and outgas. Therefore the device has the advantage of being composed at low cost and of being easily lubricated. As both the wafer holder and the linear translation structure to linearly move (scan) the holder are placed in the vacuum area, if the holder and the linear translation structure are positioned in the proper relationship to each other and a proper tilting mechanism is installed to the linear translation structure, it becomes possible to tilt the wafer in a preferable manner. In other words, as shown in FIG. 7(b) for example, when the wafer A is tilted just by inclining the holder 10 while keeping the scan direction s constant, the distance from the wafer A to the ion beam irradiation source differs depending on the portion of the wafer A. On the contrary, as shown in FIG. 7(a), when the wafer A is tilted by inclining the holder 10 together with the scan direction s determined by the linear translation structure (that is, the path of travel of the holder 10), it is possible to remove the unevenness of the distance in the wafer A (and thus to unify the beam density). In order to realize the latter tilting (FIG. 7(a)), it is necessary that both the wafer holder and the linear translation structure which determines the path of scanning, be positioned in the vacuum area as described above. As the wafer holder, the linear translation structure and the motor are fixed to the integrated support frame, it is easy to tilt the wafer in the preferable manner as mentioned above. In the embodiment of FIG. 5, it might be difficult to tilt the wafer because the wall 2 of the vacuum chamber which is integrated with the support frame 60 can not move. But, as shown in FIG. 6, if the part 2a of the wall 2 is rotatably integrated with the support frame 60, it is easy to preferably tilt the wafer as mentioned above. The support frame is preferably supported on a side of the vacuum chamber in such a manner that the support frame can rotate about an axis in the vacuum chamber. The device of FIG. 2 or 6, for example, is one of the embodiments of such a device. In this device, the support frame, which holds the wafer holder, the linear translation structure and the motor, can rotate about an axis. Therefore it is possible to tilt the wafer in a preferable manner as shown in FIG. 7(a) for example. The present invention can further has the following features: the support frame is positioned in the vacuum chamber together with the holder, the linear translation structure, the transmission mechanism, and the motor; the support frame has a vacuum-tight cover which is open to the outside of the vacuum chamber (that is, to the atmosphere) via a ventilation pipe and provided with a seal member along the line of travel of the linear translation structure in order to isolate the interior of the vacuum chamber from the atmosphere; and (all of) the second transmission mechanism offset from the line of travel of the linear translation structure and the motor are placed in the vacuum-tight cover which is open to the atmosphere. FIGS. 1–4 show one of the embodiments of the device, too. Referring to FIG. 2, the support frame 60 is positioned inside the wall 2 of the vacuum chamber. The vacuum-tight cover 70 (the hatched part of FIG. 2) is open to the outside of the vacuum chamber via the ventilation pipe 71 and provided with the seal member 72 positioned between the motor 50 and the ball screw 20, in which the motor 50 is placed. Accordingly the whole of the scan driving group including a motor is positioned in the vacuum chamber, and that brings the advantages on composition and positioning of the scan driving group. That means that the scan driving group can be compactly composed and easily be attached to the device. In addition to it, by the use of the above-mentioned vacuum-tight cover, it is possible to use the motor under atmospheric pressure though the motor is installed in the vacuum chamber. That is because the vacuum-tight cover is airproof, provided with the above mentioned seal member insulating the vacuum area from the atmosphere, and open to the atmosphere via a ventilation pipe. When a motor is used under the atmospheric pressure, the problem of generation of the particles and outgas is removed. That makes it possible to employ a motor of general specifications. The support frame is preferably supported by a wall of the vacuum chamber via a hollow rotation shaft including the ventilation pipe in it (in such a manner that the support frame can rotate), and changes its angle (for tilting) by the rotation of the hollow rotation shaft. When the support frame is positioned in the vacuum chamber together with the holder, the linear translation structure and the motor, and further the vacuum-tight cover with the ventilation pipe is employed so that the motor can placed in the atmosphere, it might be taken into consideration that the support frame is installed rotatably and the ventilation pipe is composed by a flexible hose extended to the outside of the vacuum chamber from the interior of the vacuum-tight cover. However, a longer hose might be required and the various restrictions might be caused like that, for example, the hose be arranged not to prevent the support frame from changing its angle freely. That might make the device disadvantageously complex and large. On the other hand, if the support frame is installed via the hollow rotation shaft including the ventilation pipe in it as described in the former paragraph, the ventilation pipe can be included in the rotation shaft compactly and the support frame can smoothly change its angle. Accordingly the support frame can freely change its angle by rotating the rotation shaft, while the ventilation pipe stays in the rotation shaft and keep its shape without hanging or bending. The transmission mechanism preferably includes a transmission belt which connects the first transmission mechanism on the line of travel of the linear translation structure and the second transmission mechanism offset from the line of travel, and the transmission belt is installed in the vacuum-tight cover (that is, in the atmosphere). In such a device, the transmission belt, which easily generates particles or outgas as well as the motor, is positioned in the vacuum-tight cover. That prevents generation of particles or the like in the vacuum chamber and thus secures the preferable vacuum environment where a wafer is caused to scan. The wafer scanning device still further has the following features: a surface of the wafer held by the holder is parallel to the path of travel of the holder determined by the linear translation structure (for example, the direction of an axis of a ball screw); the support frame is arranged in such a manner that it can change its angle (namely the frame can incline or rotate) and can cause the holder to tilt (in a manner shown in FIG. 7(a), for example) with keeping that condition (that is, the surface of a wafer is parallel to the path of travel of the holder); and the center line for changing the angle of the support frame is in (or very closely to) a plane including the surface of the wafer held by the holder. Thus composed, the wafer scanning device is properly incline the linear translation structure while keeping the holder in an appropriate position to the linear translation structure, so the wafer is tilted in a preferable manner as earlier mentioned. In other words, during the scan, the distance from an irradiation source of an ion beam or the like to a wafer is always kept constant at every portion of the wafer, as a result, the unification of the beam density is achieved. Moreover, in such a device, the center line of the angle change of the support frame is in the plane including the surface of the wafer, therefore, when the holder and wafer tilt by changing the angle of the support frame, the distance from the beam irradiation source to the surface of the wafer is invariable. If, as shown in FIG. 7(c) for example, the center line of the change of angle (that is the center of tilting) Ot of the support frame is offset from the surface of the wafer, the position of the wafer to the direction of the beam irradiation changes due to tilting. On the contrary, as shown in FIG. 7(a), if the center line of the change of angle Ot is in the surface of the wafer, such a change never occur. Keeping the distance from the irradiation source of a beam or the like to the surface of the wafer constant brings the advantage of unifying the ion implantation density easily. The support frame is preferably provided with a belt and a pulley to transmit the drive power of the motor to the linear translation structure, and further provided with a linear guide member (including a linear track and a sliding component which can smoothly move along the track) to guide the movement of the holder. The use of the linear guide member makes the linear motion of the holder, which causes a wafer to scan, especially smooth. In addition, an output shaft of the motor is connected to the linear translation structure like a ball screw not directly but via the belt and the pulley, so it is possible to freely set the motor in the proper position to the linear translation structure. Accordingly, it is possible to compose the wafer scanning device which is compact in size and functions very smoothly, while meeting the restrictions of placing the motor in the atmosphere, for instance. In addition to it, the moment of inertia about the rotation of the linear translation structure (such as a ball screw) is very small compared to that of the arm of the embodiment of FIG. 13, so the possibility of expansion of the belt is too small to prevent the control of the scanning speed. However; it is desirable to enhance the rigidity of the transmission belt by shortening the belt for example. The seal to isolate the interior of the vacuum area from the atmosphere can be a magnetic fluid seal which is installed on a rotation shaft directly connected to the linear translation structure. What the rotation shaft directly connected to the linear translation structure means is a shaft connected to the portion near the end the bolt of the ball screw (that is, a cylindrical portion without a thread) or a shaft positioned close to the bolt and concentrically connected to it, for example. In this case, being provided with a magnetic fluid seal as a seal member to isolate the vacuum area from the atmosphere, the device generates fewer particles compared to the case using other sealing means. That reduces the inconvenience in the process or the work in vacuum, such as the ion implantation. Moreover, installation of such a seal member to the point quite close to the linear translation structure reduces mechanisms or components positioned in the vacuum area. A mechanism placed in vacuum has to be composed to generate fewer particles or outgas and generally requires a special lubrication being provided to its sliding portion or a sealed composition, which is special and expensive. Accordingly the use of fewer mechanisms in vacuum means that it is possible to compose a wafer scanning device of easy to use at a lower cost. In addition to it, the magnetic fluid seal, being provided to the rotation shaft, is hardly out of lubricant and has stable sealing function. The linear translation structure and other components, having a rolling surface or a sliding surface and installed in a vacuum chamber, are preferably assembled so that it is possible to exchange them as a unit. Regarding the device provided with a linear guide member, as mentioned above, it is preferable to assemble the linear guide member (including a rolling surface or a sliding surface as well) into the unit, too. In a mechanism or component like a ball screw which has a rolling surface or a sliding surface and is placed in a vacuum area, general lubrication means can not be applied to, because the rolling surface or the sliding surface has the problem of generating dusts or the like. As a result, the linear translation structure, etc., requires a special lubrication and special maintenance for it. In the wafer scanning device of the present invention, the components which need special treatment in vacuum are assembled in such a manner that they can be exchanged as a unit, so the maintenance for lubrication or the like is quit easily performed as follows: remove the unit from the wafer scanning device, then install the unit which has already received maintenance (or a new unit). Thus the function of the device including the scan driving group is kept smoothly. It is convenient for the next maintenance work if the component of the unit removed from the device, a screw ball for example, is exchanged with a new one or reprocessed one. It is also preferable in the device that the wafer fixed to the holder is caused to scan by means of the linear translation structure while an ion beam is irradiated to the wafer. In such a device, the ion beam irradiation to a semiconductor wafer is performed in a desirable manner and ion implantation to the wafer is properly executed. The wafer scanning device preferably has a first transmission coupling connected between the transmission mechanism and the motor to drive the linear translation structure. By the use of a transmission coupling as mentioned above the arrangement of the transmission mechanism and the motor is considerably free and it is easy to assemble and disassemble. In other words, unlike the case that the transmission mechanism and the motor are directly connected to each other, it is easy to freely determine the relative position between the shafts, for example, and smoothly assemble even if there are a few error margins between the shafts (disagreement between each center of the shafts). The linear translation structure, which causes the holder to scan, can be a ball screw positioned in the vacuum chamber. In general, the linear translation structure may be a sliding screw, a planetary roller screw or a rack-and-pinion, etc. as mentioned above. But, a ball screw has the advantages of moving smoothly and generating a fewer mechanical loss. It is also advantageous in respect of cost that a general-purpose ball screw is acceptable. Further a ball screw makes a better responsiveness to the speed control. Accordingly, with the ball screw installed as the linear translation structure, the device can execute the smooth scanning motion of the holder efficiently and accurately. A rolling surface (which moves as rolling) and a sliding surface (which moves as sliding) of the ball screw are preferably coated with a diamond-like carbon film (DLC film) and further covered by a baking film of fluorine oil (DFO coating). As for the device including the above-mentioned linear guide member, it is also preferable that is coated with a diamond-like carbon film and a baking film of fluorine oil (at its rolling surface and sliding surface). In such a device, as a ball screw placed in a vacuum area is coated with a diamond-like carbon film and a baking film of fluorine oil, quite few particles or outgas are generated and lubrication is kept stable for a long time. The diamond-like carbon film (DLC film) is a film of high-hardness carbon like a diamond, which is made by an ion plating method, etc. and has a lubricate plane due to its amorphous composition with a diamond bonding or graphite boding, so it has excellent property of low friction and of low abrasion. The baking film of fluorine oil (DFO coating) is a viscous and lubricant film which is made by baking fluorine oil, generates few dusts and has a medium property between dry and wet and also has high-durability. The ball screw can be a ball-retainer-embedded ball screw. Some ball screws have spacer balls of a smaller diameter as means to prevent collision between adjacent ball, however, the number of loaded ball is decreased and that might lower the durability. At that point, a ball-retainer-embedded ball screw can prevent collision between adjacent balls and increase the number of loaded ball, so it has the advantage in durability. When the ball screw has a good durability, the abrasion goes slow and the generation of particles or outgas decreases for a long time, and that is particularly desirable for driving a wafer to scan in vacuum. The ball screw is preferably connected to the transmission mechanism via a second transmission coupling. With using the second transmission coupling, the arrangement of the ball screw or the transmission mechanism becomes considerably free and assembling or decomposing becomes easy. In other words, unlike the case that the ball screw and the transmission mechanism are directly connected each other, the relative position between the shafts is easily and freely determined and it is also easy to smoothly assemble even if there is some error margin between the shafts (disagreement between each center of the shafts). The ball screw is preferably supported by the support frame via a radial bearing at its either end and further supported by the support frame via a pre-loaded thrust bearing (a pre-loaded bearing combining angular ball bearings, or other precision bearings) at its end closer to the transmission mechanism. The thrust bearing has a function to remove the play in the axial direction of the ball screw and that helps the wafer to accurately perform scanning motion. As the thrust bearing is placed near the end of the ball screw at closer side to the transmission mechanism, if the ball screw is lengthened by heat or the like, there is no problem on the connection with the transmission mechanism. The wafer scanning device preferably includes a fluid (such as cooling water) passage which cools the ball screw and is formed to run near the thrust bearing of the support frame. Since the fluid cools the ball screw and runs near the thrust bearing, the thrust bearing is cooled, too. Although, during scanning motion of the wafer, heat generates in the ball screw and the thrust bearing due to the rolling of the ball, the cooling passage formed in such a manner can remove the inconvenient of heating, despite in a vacuum area where heat is isolated. In other words, the proper cooling by fluid improves the life of each component and reduces the generation of particles and outgas. The wafer scanning device according to the present invention has the following effects: the wafer holder, with linearly moved by means of the linear translation structure like a ball screw etc., shows better responsiveness with respect to the scanning speed control and can scan at a constant speed; as the motor is placed in the atmosphere and there are only few mechanisms or components exposed in the vacuum chamber, the device is more easily lubricated at low cost; as both the wafer holder and the linear translation structure are placed in the vacuum area, it is possible to tilt the wafer in a preferable manner; as the whole scan driving group including a motor is positioned in the vacuum chamber, the scan driving group can be composed compact in size and provided to the device easily, additionally, the merit due to positioning the motor in the atmosphere remains; as the device is provided with the support frame installed via the hollow rotation shaft including the ventilation pipe in it, the ventilation pipe can be included in the rotation shaft compactly and the support frame can always change its angle smoothly; as the transmission belt is positioned in the vacuum-tight cover, the preferable vacuum environment is secured; the wafer is tilted, during the scan, in such a preferable manner that the distance from an irradiation source of an ion beam or the like to the wafer is always constant at every portion of the wafer, and thus the beam density to the wafer can be unified, and additionally the distance from an beam irradiation source to the surface of the wafer is not affected by tilting; the use of the linear guide member makes the linear motion of the holder considerably smooth and the use of the belt and the pulley makes it possible to freely set the motor in the proper position with respect to the linear translation structure; due to the function of a magnetic fluid seal, the generation of particles is restricted and thus the process or work in a vacuum area such as an ion implantation is performed advantageously, and moreover, as there are fewer mechanisms or components in the vacuum area, it is possible to compose a device of easy to handle at a low cost; as the components which needs special treatment in the vacuum are assembled in such a manner that they can be exchanged as a unit, maintenance work for keeping the function of lubrication is quit easily performed; ion beam irradiation and implantation to a semiconductor wafer is performed in a proper manner; as a transmission coupling is used, it is considerably free to arrange the transmission mechanism and the motor and it is easy to assemble and disassemble the device; as a ball screw is employed as the linear translation structure, the smooth and accurate scanning motion of the holder can be achieved efficiently; the use of a ball screw which is coated with a diamond-like carbon film and a baking film of fluorine oil restricts the generation of particles or outgas and keeps lubrication stable for a long time; the use of a ball-retainer-embedded ball screw enhances durability of the ball screw and produces a desirable vacuum environment where few particles or outgas are generated; the use of a transmission coupling makes the arrangement of the ball screw or the transmission mechanism almost free and makes it easy to assemble or disassemble the device; the use of a thrust bearing removes the play of the ball screw and achieves the accurate scanning motion of the wafer; and as the ball screw or the thrust bearing is cooled by fluid, the life of each component is postponed and the generation of particles or outgas is restricted, and that keeps the vacuum environment desirable. Referring to FIGS. 1–4 and FIG. 8, the first embodiment of the invention is hereafter described. The scan driving group 1 is, as shown in FIG. 8 and FIG. 1(a), positioned inside the wall 2 forming a vacuum chamber of the ion implanter and composes a wafer scanning device together with a tilt driving group (reference letter 3 of FIG. 4(b); includes a motor and other drive source and a transmission mechanism for the motive power). A wafer (reference letter A of FIG. 4) is held by a chuck plate 11 of a holder 10 which is moved by means of a ball screw 20 (see FIG. 1(b) or FIG. 2, etc.) and thus causes the wafer to scan against an ion beam (see FIG. 4). In general, while an ion beam scans with high frequency in a fixed direction (direction x), the wafer is moved to scan in the direction perpendicular to the beam (direction y; the longitudinal direction of the ball screw 20). The use of the ball screw 20 makes the wafer light in the scanning motion so the scanning motion is good in responsiveness and even in speed. The detailed description of the scan driving group 1 is as follows. As shown in FIG. 1, it includes the following chief functioning parts: the holder 10 of a wafer; the ball screw 20 that moves it to the scan direction (the above-mentioned direction y); a motor 50 that rotates the ball screw 20; and a support frame 60. The support frame 60 holds the holder10, the motor 50 and other composition equipment of the scan driving group 1 together. The support frame 60 is rotatably supported by the wall 2 and can tilt by the force of rotation drive generated from the tilt driving group (reference letter 3 of FIG. 4(b)). A support member 60′, which is part of the support frame 60, supports the axis connection of the motor 50. The ball screw 20 is; as shown in FIG. 2, supported by the support frame 60 via radial bearings 20a, 20b at its both sides. Also the ball screw 20 is supported by the support frame via a precision thrust bearing 20c at about its end closer to a belt 40 or other transmission mechanisms (the upstream of power transmission). The precision thrust bearing 20c, which is for example a pre-loaded bearing composed of angular ball bearings, prevents the ball screw 20 from playing in the axial direction. The holder 10 includes the chuck plate 11, a chuck body 12 and a slide plate 13, as shown in FIG. 1(a). The slide plate 13 is connected to a nut 21 of the ball screw 20. Referring to FIG. 1(b), linear guide members 30 are disposed in parallel to both sides of the ball screw 20 and provided with a slide member 31, which can move along the track of the members 30 and is connected to the slide plate 13 of the holder 10. The chuck plate 11 is positioned in such a manner that the surface of a wafer fixed to the plate 11 is parallel to the longitudinal direction of the ball screw 20. The motor 50 is placed in a manner that the output axis (reference letters 51a of FIG. 2) is in parallel to and just far from the bolt of the ball screw 20. The power from the motor 50 to the ball screw 20 is transmitted by transmission mechanisms such as a transmission rubber belt 40 (a timing belt with gear teeth), a driving pulley 41, a driven pulley 42 and a tension pulley 43, etc., as shown in FIG. 1(a) and FIG. 3. Some transmission mechanisms are on the line of travel of the ball screw 20 and the other are offset from the line. Being used in vacuum, the ball screw 20, the linear guide member 30 and other components are made to the special specifications for removing the problem of dusts or outgas generated from the portions where two elements contact and relatively move: they are coated with a diamond-like carbon film (DLC film) and a baking film of fluorine oil (DFO film) which are special means to enhance the lubrication performance and abrasion resistance. What the portions where two elements contact and relatively move means the surfaces of a thread of the ball screw 20 or the nut 21, steel balls of the ball screw 20, grooves or steel balls of the bearings 20a, 20b and 20c supporting the ball screw 20, the track of the linear guide member 30, and steel balls of the slide member 31, etc., where each element rolls and slides. In order to easily maintain and check such components made to special specifications and to easily enhance the lubrication performance and abrasion resistance again in case that the coatings are abraded and damaged, the ball screw 20 and the linear guide member 30, etc., (including the slide plate 13 and the pulley 42, etc.) are composed so as to be integrally removed from the scan driving group 1, as shown in FIG. 1(b). In other words, the components such as the ball screw 20 are assembled in a compact frame 63 which is removably connected to the support frame 60. The support frame 60 and equipment or components held by the support frame 60, such as the holder 10, the ball screw 20 and the motor 50, are arranged inside the wall 2 of the vacuum chamber as described above. But the illustrated scan driving group 1 is composed in such a manner that a lot of things including the motor 50 can be used in the atmosphere. That is because when the equipment or components are used in the atmosphere, the particles or outgas generated by them will not cause any problem. That also means it is possible to employ inexpensive equipment or components of a general specification. In order to use the motor 50 and the like in the atmosphere, they are composed as follows. Referring to FIG. 2 (and FIG. 3), the motor 50, the belt 40, the pulleys 41, 42, 43, short shafts 53, 22, and the like, are covered with a vacuum-tight cover 70 (the hatched part in FIG. 2), which is open to the atmosphere, the outside of the wall 2. The vacuum-tight cover 70 is a hollow body, which is composed of a plurality of boxy or cylindrical hollow components tightly connected by a packing or the like. the motor 50 is covered with a vacuum-tight cover 70′ having a ventilation pipe 71 which is fixed to the portion near the motor 50 and leads to the atmosphere. In the sealed space thus formed in the vacuum-tight cover 70, the followings are included as shown in FIG. 2: the motor 50; a coupling 52 connected to the output axis 51a of the motor 50; the short shaft 53 connected to the coupling 52; the belt 40 (these are hereafter called the transmission mechanism offset from the line of travel of the ball screw 20); the pulleys 41, 42, 43; the short shaft 22 fixed with the pulley 42; and bearings attached to them. A magnetic fluid seal 72 is provided between the vacuum-tight cover 70 and the peripheral surface of the short shaft 22. In order to rotatably support the whole of the scan driving group 1, the support frame 60 is integrated with a hollow rotation shaft 61 which is inserted in and supported by a support hole 2a of the wall 2. A seal member 2b (such as a magnetic fluid seal) is provided to the inserted portion of the shaft 61. By inserting the ventilation pipe 71 of the vacuum-tight cover 70 in the hollow rotation shaft 61 (and attached with a seal member at the inserted portion), the pipe 71 can lead to the atmosphere. Air can flow in and out between the interior of the vacuum-tight cover 70 and the outside of the wall 2 via the inside of the ventilation pipe71, where a power supply line, a control line, a signal line or the like can run, too. The above-mentioned tilt driving group (reference letter 3 of FIG. 4 transmits the rotation power to the hollow rotation shaft 61 and thus causes the whole of the scan driving group 1 to tilt together with the support frame 60. Since the seal 72 is provided between the vacuum-tight cover 70 and the short shaft 22, the things placed over it such as the coupling 23, the ball screw 20, the bearings 20a, 20b, 20c, the nut 21 and the linear guide member 30, etc., are exposed to the interior of the vacuum chamber. Out of consideration for it, the rolling surface or the sliding surface of the ball screw 20 and the linear guide member 30 is coated with a DLC film or a DFO film as mentioned above. In addition to it, a ball-retainer-embedded ball screw is adopted as the ball screw 20, which has a long life even in vacuum, special environment. The composition of the essential moving part of the scan driving group 1 is typically shown in FIGS. 4(a) and (b), which functions as the following a) and b), serving as a wafer scanning device in an ion implanter. a) When a wafer A is attached to the chuck plate 11 of the holder 10, the rotation of the ball screw 20 by the motor 50 causes the wafer A to move (scan) along the ball screw 20 (the longitudinal direction of its bolt) with the holder 10. As described above, an ion beam repeatedly scans in the direction x (perpendicular to the sheet surface of FIG. 4(a); the right and left directions of FIG. 4(b)) at the specific position and the ball screw 20 is positioned in the direction y, which is perpendicular to the moving direction of the irradiation point that is the intersection of the beam and the wafer A. The direction y is defined as a scan direction s of the wafer A. During the scan, the wafer A on the chuck plate 11 is fixed so that its surface is perpendicular to the direction of the ion beam seen along the center of the axis of the ball screw 20, as shown in FIG. 4(b). b) It is possible to change the angle of ion implantation against the surface of the wafer A (tilt angle) by inclining the whole of the scan driving group 1 via the support frame 60. As described above, the support frame 60 is supported by the wall 2 of the ion implanter via the hollow rotation shaft 61. Therefore when the shaft 61 rotates by means of the tilt driving group 3 positioned outside the wall 2, the support frame 60 changes its angular position about the axis of the shaft 61 according to the tilt direction t shown in FIG. 4(a). As the support frame 60 holds the whole of the scan driving group 1 including the ball screw 20, when the support frame 60 thus changes its angle, the holder 10 tilt with the ball screw 20, and that can change the angle of the wafer A and the scan direction s to the same degree. That is, the surface of the wafer A and the longitudinal direction of the ball screw 20 determining the scan direction s of the wafer A tilt to the direction t, while the both keep parallel to each other. In addition, the hollow rotation shaft 61 is properly positioned so that the center of the tilt is in the surface of the wafer A on the holder 10, therefore the surface of the wafer A does not only come close to nor only go far from the ion irradiation source with tilting. That means that the distance from the ion beam irradiation source to every spot of the wafer A is independently constant whatever the tilt angle of the wafer A is. FIGS. 5(a), 5(b) and 5(c) show the second embodiment of the present invention (third-angle drawings). The element used in common to the first embodiment of FIGS. 1–4 is put with the same reference letter and the detailed description of it is omitted. In a scan driving group 4, exemplary illustrated in FIG. 5, the support frame 60 which supports the ball screw 20 for moving the wafer A (the holder 10) is integrally attached to the wall 2 of the ion implanter, and the motor 50 which drives the ball screw 20 is positioned outside the wall 2, namely in the atmosphere. The motive power from the motor 50 is transmitted to the ball screw 20 via a rubber belt 40 and pulleys 41, 42 which are covered with a seal type cover 75 in the vacuum chamber. In addition, a seal member 76 is provided to the inside of the extended cover 75 near the end of the bolt of the ball screw 20 to which the driven pulley 42 is attached. Thus the cover 75 and the seal member 76 insulate the atmosphere, which reaches to the outside of the wall 2, from the vacuum area inside the wall 2. The seal member 76 can start to use a magnetic fluid seal in order to prevent dusts or the like from generating in the vacuum area. Also in the scan driving group 4 of FIG. 5, the wafer A scans with high responsiveness at highly stable speed based on the rigidity of the ball screw 20. In addition to it, because the motor 50, the belt 40, and the pulleys 41, 42 are positioned in the atmosphere, the dust generated by their moving portions causes no travel. Therefore, general type motors, belts and pulleys are advantageously available for them. FIG. 6 is a top view of another embodiment (a scan drive group 4′) which is an alternation of the scan drive group 4 of FIG. 5. In the embodiment of FIG. 5, the support frame 60 is integrally formed with the wall 2 of the vacuum chamber and difficult to rotate, therefore it is difficult to tilt the wafer A. But by partially alternating the composition as follows, it becomes possible to properly tilt the wafer A: for example in the scan driving group 4′ of FIG. 6, a part 2a of the wall 2, which is integrated with the support frame 60 (or the support frame 60 itself), is assembled to the other part of the wall 2 in such a manner that the part 2a can freely rotate. A circular support member 66 including a bearing and a seal (such as a magnetic fluid seal) is provided between the wall 2 and the part 2a of the wall 2. Also in the scan driving group 4′ of FIG. 6, there are merits with respect to the scan speed, responsiveness and the type of the motor 50, etc. Further, there is a merit due to the above-mentioned tilting: as the ball screw 20 determining the scan direction is caused to tilt together with the wafer A (the holder 10), the preferable tilt is achieved in a manner shown in FIG. 7. FIGS. 9(a) and 9(b) shows another embodiment of the wafer scanning device. The element put with the same reference letter as that in FIGS. 1–8 has the same function. As shown in FIGS. 9(a) and 9(b), the angle of the support frame 60 may be set (changed or fixed) by means of manual control using stopper or the like, not by means of a motor or the like. FIG. 10 is a sectional view showing another embodiment of the scan driving group 1 of the wafer scanning device. The ball screw 20, the bearing 20c or the like, which are placed in the vacuum chamber and hopelessly cooled by heat transfer via air, are cooled by the cooling water which runs through the cooling passage A and cooling passage B provided to the support frame 60 or the like, as illustrated in FIG. 10. When the load of the ball screw 20 or its bearing is large, it is preferable to cool them in such a manner. In FIG. 2 and FIG. 10, the element which is common to each other or has the same function with each other is put with the same reference letter (same in the following drawings). FIG. 11 is a sectional view showing still another embodiment of the scan driving group 1 of the wafer scanning device. The motive power generated by the motor which is placed outside of the vacuum chamber is transmitted to the ball screw 20 via a bevel gear. FIG. 12 is a sectional view showing still one more other embodiment of the scan driving group 1 of the wafer scanning device. The motive power generated by the motor placed outside of the vacuum chamber is transmitted to the ball screw 20 via a transmission belt. Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.
	abstract	A process for cleaning reusable canisters known as pigs which contain radioactive drugs and may contain residual radioactive material and other contaminants. Those pigs that are contaminated with radio-active material are removed from the cleaning process until they have decayed to the background radiation level, cleaned and disinfected. Within a very clean drug preparation area a radioactive drug is inserted into the pig and the pig is placed in a protective outer container. At a treatment site the outer container and pig are delivered to a clean treatment area where the pig is removed from the outer container and the drug is removed from the pig and utilized.
052456480	description	SUMMARY OF THE INVENTION It has now been discovered that the signal to noise ratio and spatial resolution of a computerized x-ray tomographic microscopy system can be improved by incorporating into the system an asymmetric channel cut x-ray image magnifier. Thus, in one aspect this invention pertains to a computerized x-ray tomographic microscopy system utilizing an asymmetric channel cut image magnifier. In another aspect it pertains to the magnifier itself. In a third aspect it pertains to an image magnification process for improving the signal to noise ratio and the spatial resolution of images generated in a computerized x-ray tomographic microscopy system. The system, in its broadest aspect, comprises: a) source means for providing a parallel x-ray beam, b) staging means for staging and sequentially rotating a sample to be positioned in the path of the beam, c) an x-ray image magnifier positioned in the path of the beam downstream from the sample, d) detecting means for detecting the beam after being passed through and magnified by the image magnifier, and e) computing means for analyzing values received from the detecting means, and converting the values into three-dimensional representations. The image magnification process comprises: a) providing a parallel x-ray beam, b) passing the beam through a sample as it is being rotated in a predetermined sequence, c) magnifying the beam after it has passed through the sample, d) detecting the beams after they have been magnified, and converting them into electronic values, and e) analyzing the electronic values and converting the values into three-dimensional representations. The asymmetric channel cut magnifier itself comprises: a monolithic crystal containing parallel lattice planes having a base with a substantially smooth upper surface, a first plate projecting vertically from said upper surface of said base having a smooth inwardly facing face, a second plate projecting vertically from said upper surface of said base having a smooth inwardly facing face, at least one of said plates being adjustable with respect to the other, said faces of said first and second plates being separated from and asymmetrical with respect to each other, and wherein the lattice planes in each of said plates are parallel to each other. DETAILED DESCRIPTION OF THE INVENTION To understand the present invention, knowledge of the principles of x-ray computerized tomography (CT) is helpful. The x-ray tomographic microscopy (XTM) system of the invention is grounded generally upon the same principles as are used in medical computed tomography. That is, the x-ray attenuation coefficient, .mu., at a point r.sub.x,y,z in a material can be determined from a finite set of x-ray attenuation measurements (projection data) taken at different angles. The projection data is the transmitted x-ray intensity reaching a position-sensitive detector after passing through the sample. This data, which is directly related to the materials microstructure, is given by ; EQU I=S(E) exp--.mu.(x,y,z,E)dl dE, (1) where S(E) is the energy spectrum of the x-ray source, and .mu.(x,y,z,E) is the energy-dependent attenuation coefficient at a single point on the projection. The integral is taken along a straight path dl through the sample. Because a synchrotron beam can be made nearly monochromatic with photon energy E.sub.o, the energy spectrum can be approximated by delta function, and Eq. (1) reduces to the familiar form of the Radon transform, EQU lN I.sub.o /I =.mu.(x,y,z,E.sub.o)dl. (2) Measurements of the attenuation through the sample as a function of angle are used to numerically invert Equation (2) to solve for .mu.(x,y,z,E.sub.o). The number of angular views considered sufficient for this invention (reconstruction) is approximated, using simple geometric arguments, by EQU R.DELTA..THETA.=W, (3) where R is the maximum outward extent of the sample from the center of rotation, .DELTA..THETA. is the suggested angular increment, and W is the projection width. A typical value for R with the XTM of the invention is 2 mm, and W is 5 .mu.m. The angular increment sufficient for the reconstruction, using these dimensions, is approximately 0.2.degree.. In practice, however, an increment of 0.5 to 1.0.degree. is usually used because of limited beam time. The system of this invention has several embodiments. One embodiment of the computerized axial tomography microscopy system of this invention is shown in FIG. 1. As shown, the system 10 comprises an x-ray source 12 which emits parallel beams of x-rays 14, 16. Sequentially positioned in the path of x-rays 14, 16 emanating from the source 12, is a monochromator 18, a collimator 20, a sample stage 22 carrying a sample, a two-stage asymmetric channel cut single crystal beam magnifier 24, a scintillator 26, a lens 28, and a charge coupled device 30. A controller 32 is electronically connected to the charge coupled device 30 for receiving signals therefrom. A computer 34 is electronically connected to the controller 32, and receives signals from it. The sample stage 22 also sends signals to the computer by electronic means. An incident beam flux monitor 36 is positioned adjacent the monochromator 18 and monitors the x-rays 14, 16 as they exit the monochromator 18. In operation, parallel beams 14, 16 from the x-ray source 12 is passed through the monochromator 18. This monochromator 18, a double crystal one, selects x-rays in a narrow energy range from the primary beam supplied by the source 12. The beam 14, 16 emitted from the monochromator 18 is passed through the collimator 20 which reduces scatter. From the collimator the beam is passed through a sample 38 positioned on the sample stage 22. From the sample 38, the beam 14, 16 is passed to the two-stage asymmetric channel cut x-ray image magnifier 24. The x-ray image magnifier 24 eliminates scattered x-rays and enlarges the image anywhere from 4 to 25 times, depending on its precise construction. From the magnifier 24, the beam 14, 16 is passed to the scintillator 26, which converts the x-rays to visible light, through the scintillator 26 to the lens 28, and from the lens 28 to the charge coupled device 30. The charge coupled device 30 records the intensity of the beam 14, 16 (now visable light), and this information is electronically passed to the controller 32 and on to the computer 34. The sample 38 is sequentially rotated by a stepper motor (not shown) attached to the stage 22. Light intensity values are recorded by the charge coupled device 30 and passed on to the computer 34 at each stage of rotation of the sample 38. The sample 38 is rotated through 180.degree.. The computer 34 integrates the data obtained and by suitable software programs converts two-dimensional data into three-dimensional images. Suitable software can be obtained from Lawrence Berkeley Laboratory, Berkeley, California, under the designation Donner Code. The two-stage asymmetric channel cut x-ray image magnifier 24 comprises two substantially identical single crystals 40, positioned in tandem, one of the crystals being rotated around the axis of the x-ray beams 14, 16 and 90.degree. relative to the other. As used herein, therefore, the term "two-stage" refers to two of such crystals 40 mounted in tandem. One of the crystals 40 is shown in detail in FIG. 2. Each single crystal 40 has internal lattice diffraction planes 42, sometimes referred to as Bragg reflecting planes, and comprises a horizontal base 44 which has first and second upright rectangular plates 46, 48 projecting vertically from the top surface thereof. The plates 46 and 48 are cut from the monolithic crystal 40, and have faces which are asymmetric with respect to one another. Plate 46 has an inwardly oriented face 50, a trapezoidal shaped end portion 52, a weak section 54, and a substantially rectangular shaped intermediate section 56. If desired, a piezoelectric device, not shown, can be attached to the weak section 54, in order that it can be bent in order to correctly align the Bragg reflecting planes 42 in each of the plates 46, 48. For Proper operation of the magnifier 24, it is essential that the reflecting planes 42 in each of the plates 46 and 48 be close to parallel. Plate 48 has an inwardly oriented face 58. The faces 50 and 58 are cut asymmetric with respect to the Bragg reflecting planes 42 of the crystal 40 such that the incident angles are not equal to the reflected angles. Beam 14, 16, after having passed through the sample 38 impinge upon the lattice planes 42 of plate 46, and is ultimately diffracted off the lattice planes 42 of plate 48. The net effect of the diffraction, as seen in FIG. 2, is to increase the magnification of the beam 14, 16 in a single plane by an amount proportional to the ratio of the sines of the reflection angle divided by the incident angle, and to keep the exit beam traveling in the same directicn as the incident beams to facilitate alignment. In the two-stage magnifier 24, two asymmetric channel cut crystals 40 are employed to magnify the image in both planes, i.e., vertical and horizontal. The second crystal is positioned 90.degree. relative to the first. The optics of the image magnifier crystal 40 are demonstrated schematically in FIG. 3. As shown, incoming parallel x-ray beam 14, 16 is diffracted from the lattice planes 42 in plate 46, travel to plate 48 and are subsequently diffracted from the lattice planes 42 in plate 48. In FIG. 4 is demonstrated the optics of an x-ray magnifier utilizing two asymmetric diffractions to obtain a two-dimensional magnification of images contained in an x-ray beam. In order to magnify an x-ray beam which contains structure information (such as one containing radiographic images), the beam is successively diffracted from two crystals 40. The plane of diffraction, defined as the plane containing the incoming beam and the normal to the diffracting plane (and also the outgoing beam), for each of the two asymmetric diffractions, must be perpendicular. Hence the first diffraction magnifies the beam horizontally and the second in a perpendicular direction. The crystal 40 is either Si or Ge, preferably Si. A preferred magnifier 24 is an asymmetrically cut Si (111) - Si (111) combination in a double crystal configuration. Other combinations which can be used so long as Bragg diffracting conditions are met, include Si (220) - Si (220), Si (400) - Si (400), Si (511) - Si (333), Si (333) - Si (333), Ge (111) - Ge (111), or Ge (220) - Ge (220). The preferred source of x-rays 12, is an electron storage ring generating synchrotron radiation, because synchrotron x-radiation is very bright, very intense and easily tunable. Most preferred is an electron storage ring like the one located at Stanford Synchrotron Radiation Laboratory (SSRL) and a beamline designated BL-X which is a 30-pole wiggler utilizing Nd-Fe-B magnet materials. The monochromator 18 is used to select certain energy wavelengths out of the x-ray beam in order to insure that maximum contrast is achieved. Suitable monochromators can be made by those skilled in the art, or can be obtained from the Bede Scientific Instruments Ltd., under the designation x-ray monochromators. The function of the monochromator is to select a band of x-rays being emitted from the source. X-rays having energy levels ranging from about 21/2 to about 60 KV can be used, but the preferred range is from about 5 to about 20 KV, most preferred about 15 KV. The use of higher levels of energy, i.e., 60 KV, would require changes in the monochromator 18. Thus, a germanium instead of silicon monochromator would be more efficient. The monochromator 18 is cooled by water running through the components thereof. Thus, the monochromator is also used to dissapate heat deposited on the crystal as a consequence of the x-rays impinging thereon. The monochromator 18 removes more than 90% of the heat generated by the x-ray beams. The monochromator must be cooled sufficiently that the rocking curve of the beams is in the range of a few arc-seconds. Thus, the x-ray wavelength must not drift. If desired, the monochromator 18 can be replaced by another single asymmetric channel cut image magnifier 24. This alternative embodiment is shown in FIG. 9 where the monochromator 18 (as shown in FIG. 1) is replaced by another magnifier 24. The advantage of this is that the beam is made even more parallel and of greater spatial extent and uniformity. The collimator 20 is a slit type, which allows x-rays 14, 16 emerging from the monochromator 18 to pass through. Because parasitic scatter is a source of blurring, the collimator 20 is located several cm from the sample. The collimator 20 is used to eliminate scatter x-rays from the beam, and to insure that the beams is projected through the sample 38. The collimator is not an essential component of the system, but it is preferred to use one. A suitable collimator is manufactured by the Huber Company, under the trade name Adjustable Slit Collimator. If the x-ray source 12 is one which emits parallel beam of x-rays having the desired energy levels, then it would also be possible to eliminate the monochromator 18 from the system. Thus, both the monochromator 18 and the collimator 20 are optional, but preferred components of the system. After being collimated, the parallel x-ray beam passes through a sample 38 positioned on a stage 22 which contains means for rotating the sample. The sample stage 22, which provides rotational and translational motion, can be positioned with an accuracy of 0.01.degree. in rotation and 0.1 um in translation. It must be stable within 2 arc-seconds and wobble-free. A suitable sample stage 22 can be obtained from the Klinger Company, and is sold under the designation Stepper Motor. After passing through the sample, the x-rays pass through the magnifier 24 previously described. The optical principles behind the magnifier are set forth in Rev. Sci. Instrum. 50 (1), January 1979, pps. 26-30, which article is incorporated herein by reference to the extent allowed by law. To summarize, the magnification (M) achieved is equal to the sine of the ratio of the outgoing angle to the incoming angle, i.e., EQU M=(sin .PHI..sub.out) / (sin .PHI..sub.in) For maximum performance to be achieved the Bragg planes 42 of the two vertically projecting plates must be close to parallel. The exact relative tilt is determined by the theory of dynamically diffracting perfect crystals (e.g. W. Zachariasen, "Theory of X-Ray Diffraction in Crystals", New York: Wiley 1945) as worked out by R. Nu.beta.hardt (PhD-Thesis University of Dortmund 1990).. For practical purposes it has been empirically determined that the outgoing .PHI..sub.out and incident .PHI..sub.in angles should be greater than 6.degree. and less than 45o The scintillator 26 is used to convert the x-rays to visable light. The scintillator should have flat surfaces polished to within one quarter wave, i.e., it should be optically polished and free of defects. The back side must have an anti-reflective coating on it. Any standard scintillator can be used for this purpose. A particularly useful one is a single crystal one sold by the Harshaw Company under the designation Cadmium Tungstate (CdWO.sub.4). The charge coupled device (CCD) 30 accepts the light from the scintillator 26 in parallel wave fashion. It should be of optical grade and cooled to prevent dark current build-up. It should have no more than 1 charge per second dark current, and its dynamic range should be greater than 1,000. With a wide slowly diverging x-ray beam each pixel of the charge coupled device 30 defines a pencil beam. The CCD pixels measure the intensity of the beam. A suitable CCD device can be obtained from the Photometrics Company, Model No. CH200. The controller 32 and computer 34 to which signals from the CCD device are passed are both standard items of commerce. The controller 32 can be purchased from the Photometrics Company under the name CC200, while the computer 34 is preferably a Micro Vax II, or III sold by DEC (Digital Equipment Corporation). Any other computer which performs the same function would be suitable. An alternative to the scintillator 26 used in the system above, is a high resolution phosphor screen. In this embodiment, the image formed on the phosphor screen is projected onto the CCD with an optical lens that has been coated with an anti-reflective film. Any other lens which provides suitable quality can be used. The beam flux monitor 36 is an optional component of the system of the invention. It is conventionally connected to a single channel analyzer, and simply is used to monitor and count the photons emanating from the beam. Suitable beam flux monitors can be obtained from the Kevex Corp. In the practice of the process of this invention, the energy level of the x-ray beam from the synchrotron radiation source can range from about 100 eV to about 100 KeVs, preferably from about 3 KeV to about 40 KeV, and more preferably from about 7 to about 25 KeV. Most preferred is a beam having an energy level of about 15-20 KeV. Another embodiment of the system of the invention is shown in FIG. 8. The system comprises a source of x-ray beams 60, a monochromator 62, a beam shutter 64, a sample stage 66, a magnifier 68, a fluorescent screen 70, an optical mirror 72, a set of lenses 74, a charge coupled device 76, monitor counters 78, 80, and 82, and a solid state detector 84. The charge coupled device 76 is connected to another apparatus, not shown, which analyses the data obtained and converts it into three-dimensional representations. This invention will be more fully understood by reference to the following detailed description. A 1.5.times.1.5.times.10-mm specimen of an Al/SiC composite was obtained and examined by means of the system of this invention using as an x-ray source the 31-pole wiggler beamline at the Stanford Synchrotron Radiation Laboratory (SSRL). An x-ray energy of 21 keV was selected for good sample transparency and x-ray contrast between SiC and Al. A set of 97 contiguous cross sections of the composite was examined with the system. FIG. 5(a) shows a single slice with a projection width and slice thickness of 5.6 .mu.m; the spatial resolution is much better than 10 .mu.. Data was collected with 5-s exposure times at 1.degree. intervals, a much smaller interval than that suggested by the use of Equation (3). This undersampling leads to some blurring of the image; nevertheless, the 32-.mu.m-diameter graphite cores and surrounding 140-.mu.m-diameter SiC sheaths are clearly visible. The slight mottling in FIG. 5(a) is caused by either the statistical noise in the image (2%) or actual variations in the materials composition. Cracks running longitudinally in the plane of the fiber plies are evident in FIG. 5(a). These cracks, which do not penetrate the fibers, are similar to those observed in polished sections of the composite [FIG. 5(b)] and may, therefore, be a result of processing. This material is fabricated by means of a plasma-spray technique and is consolidated at high temperatures. It is possible that mismatches in thermal-expansion coefficients may create residual stresses that open these cracks during cooling, or that the material is not being completely surface relief and plastic flow of the matrix during polishing have apparently obscured the interfacial cracks that are observed in FIG. 5(a). This result highlights one advantage of the process of the invention over conventional metallography. FIG. 6(a) is a planar cut through the same sample as in FIG. 5, but parallel to the fibers. In this ply, the fibers are regularly arranged, and few cracks are present. FIG. 6(b) is a similar plane taken through a ply that is heavily populated with cracks. FIG. 6 demonstrates that the cracks tend to run along the fiber-matrix interface and between nearest-neighbor fibers rather than across the plies of the composite. FIG. 7 is a view of a single fiber that shows the graphite core and SiC sheath surrounding it. The change in columnar SiC subgran size produced during the growth of the sheath is evident, as is the SCS-8 coating in the final few micrometers near the Al interface. The application of x-ray tomographic microscopy (XTM) to the study of two Aluminum composites, one with Al.sub.2 O.sub.3 whiskers only 2-4 .mu.m diameter (sample 1), the 2) is described below. As will be shown, using XTM enabled the imaging in sample 1 of the clustering of intermetallic precipitates. In sample 2 the individual fibers were resolved. Furthermore, by exploiting the elemental sensitivity of XTM, the precipitates of different intermetallic phases in the composite matrix and correlated them with structures seen on optical, back-scattered electron (BSE), and wavelength dispersive (WDS) micrographs were imaged. The power of XTM as a high-resolution and nondestructive 3-D imaging method sensitive to elemental distribution, density changes, and binding state fluctuations becomes evident from these results. Measurements on sample 1 were performed on the 1 pole wiggler beamline 10-2 of SPEAR at SSRL (Stanford) employing a pair of symmetrically cut (220) Silicon crystals as monochromator and a Peltier-cooled CCD detector. Sample 2 was investigated on the bending-magnet beamline of the Two-Axis-Diffractometer, U. Bonse and K. Fischer, Nucl. Instr. Meth. 190 (1981), 593, at DORIS of HASYLAB (Hamburg) employing a cryogenically cooled CCD and the crystal magnifier described below and shown in FIG. 8. Furthermore, a special Germanium monochromator combining an asymmetrically cut (511) crystal with a symmetric (333) crystal, U. Bonse et al, HASYLAB Jahresbericht (Desy, Hamburg, 1988), p. 395, was optionally used. While preserving the nondispersive double crystal setting, the choice of the homologous 5 reflections (511) and (333) provides different crystallographic orientations for the crystals so that the occurrence of Laue spots is minimized. The asymmetry of the first crystal increases the acceptance of radiation from the SR source and at the same time reduces the divergence of the beam incident on the sample which improves spatial resolution. While the wiggler beamline is superior with respect to intensity, the more elaborate monochromator at DORIS allows better control of vertial beam size and divergence and of harmonic content. A monochromator optimized for XTM is expected to produce a beam with <0.2 mrad divergence, 1 to 5 mm.sup.2 cross section, wide energy tunability at <0.02% bandwidth and total harmonic content less than 0.1%. Typical storage ring operation parameters were 3.3 GeV, 30 mA, 12 hours lifetime at SPEAR Harmonic suppression/selection of the FIG. 8 system is achieved by suitably detuning the component crystals of MC 62 with respect to each other. For this to function in a proper way, the first crystal of MC 62 is internally water-cooled , U. Bonse et al, HASYLAB Jahresbericht (DESY, Hamburg, 1986), p. 395, in order to maintain its undeformed perfect crystal state under the unavoidable heatload delivered to it by the primary beam. The energy dispersive solid state detector 84 is used for monitoring the harmonic content and for energy calibration. The sample S is mounted on a rotary stage 66 capable of 360 degrees rotation at 0.001 degree minimum increment. Typical angular increments between individual Projections varied from 0.25 to 3 degrees depending on the required spatial resolution. For taking empty-beam references, the sample is shifted out of the beam in a direction parallel to its rotation axis. When the primary beam is not stationary, it is necessary to have references taken frequently. In order not to spend too much time removing the sample and setting it back, a device was constructed capable of withdrawing it at a speed >4 cm/s. After the reference has been taken, the sample is placed back into the beam at the same speed. The original sample position is reproduced to better than 1 micron accuracy. This is an important feature in order not to deteriorate spatial resolution through uncontrolled positional changes of the sample between exposures. Presently available CCD detectors both are damaged when exposed to x-rays and become transparent at photon energies above 10 keV. Hence x-ray-to-light conversion by a fluorescent screen or by a single-crystal scintillator is necessary. The advantage in using a single-crystal is that scattering of light inside the scintillator is negligible whereas with a polycrystalline screen light scattering is an additional cause of limited spatial resolution. On the other hand, a fluorescent screen is usually 10 to 50 times more efficient than the single crystal scintillator. The conversion of x-rays to light allows the use of straightforward optical light magnification to lessen the resolution requirements imposed on the CCD. Problems of limited spatial resolution inherent in x-ray-to-light converters are overcome by employing x-ray-optical magnification, U. Bonse et al, HASYLAB Jahresbericht (DESY, Hamburg, 1988), p. 469, and U. Bonse et al, HASYLAB Jahresbericht (DESY, Hamburg, 1989), p. 557, provided by twofold asymmetric Bragg reflection, the principle of which is explained by FIG. 2. The crystal magnifier consists of a grooved crystal with walls oriented at opposite asymmetry with respect to the reflecting Bragg planes. A suitable crystal is one which uses 220 (440) reflections with x-rays of about 9 keV (18 keV) energy, respectively. With this crystal, linear x-ray optical magnification in the range of two- to tenfold is achieved, the actual magnitude depending on the energy of the radiation used. Two kinds of converters, a CdWO.sub.4 single crystal plate 0.5 mm thick and an Eu-doped Y.sub.2 O.sub.2 S fluorescent screen about 40 .mu.m thick have been used. While the fluorescent screen was - depending on photon energy--up to 15 times greater in fluorescence than the single crystal plate, the single crystal provided considerably better spatial resolution. Projection of the fluorescent light image onto the CCD is achieved by employing either a single standard photographic lens with 50 mm focal length or a pair of such standard lenses, one with 50 mm and the other with 20 mm focal length in telefocal geometry. With the pair of lenses, a light-optical magnification of 2.4 is obtained. With the single lens, a magnification up to about 8 is easily feasible although rarely needed. With a lens system which is custom manufactured to optimally image the screen onto the CCD, optical magnifications up to tenfold at spatial resolution of 2-3 .mu. can be achieved, although such resolution requires no image degradation in the scintillator screen. This is possible only below 10 keV photon energy. At higher energy the conversions of x-rays to visible light is stretched out over a depth range which is likely to exceed the depth of focus range of the lens. Combining the x-ray optical with the light optical method of enlarging the projections, an overall magnification of up to 100 between the sample and the CCD is possible. At this magnification, to detect in the sample a detail of 1 .mu.m size requires a CCD pixel size of less than 50 .mu., which is easily obtained with commercially available CCD's. On the other hand, the maximum magnification is likely to be difficult to work with and in many cases will limit the size of the field of view unduly. These considerations, when taken together, indicate that CCD pixel sizes of the order of 5 to 20 .mu.m are probably best for XTM, with larger formats being desirable for imaging wider fields of view. Accordingly, the CCD types shown in Table 1 have been employed. TABLE 1 ______________________________________ CCD Detectors Used for XTM Type Format Pixel Size ______________________________________ Thomson CSF TH7882CDA 384 .times. 576 23 .mu.m .times. 23 .mu.m Texas Instruments 4849 390 .times. 584 22 .mu.m .times. 22 .mu.m Kodak KAF-1400 1320 .times. 1035 6.8 .mu.m .times. 6.8 .mu.m ______________________________________ The CCD with the smallest pixel size provides the highest resolution. However, with this CCD the maximum number of electrons that can be stored in a single pixel is only 1/5 that for the other two CCD's. Hence the smaller pixel size implies an accordingly smaller dynamic range of about 5.times.10.sup.3. This is to be compared to about 5.times.10.sup.4 for the CCD's having larger pixels. Hence, whenever a high dynamic range combined with the use of small-pixel CCD's is required, multiple exposures per radiograph are unavoidable. At SSRL data readout and processing was performed on a Microvax II and a VaxStation 3200 equipped with total CPU memory of 32 Mb and total disk space of about 3 Gb. A typical run for sample 1 included 365 radiographs each 736 columns wide and 421 rows high on the KAF-1400 CCD, measured at 1 degree angular increments. Slightly more than half of the radiographs were references taken of the empty beam. With the wiggler source, employing 2.4x optical magnification and the above CCD, exposure times per radiograph ranged from 5 to 15 sec., with the longer exposure related to the beam decay during the scan. Allowing also for time spent on readouts and mechanical motions of the sample, a typical run required from 2 to 5 hours of beam time. Between runs, a quick reconstruction of a single slice was made for survey purposes, using reduced data sets of only 100 columns obtained by averaging. Complete data sets took roughly 20 min per reconstructed slice. All reconstructions were performed using the method of filtered back projections, G. T. Herman, "Image Reconstruction from Projections: The Fundamentals of Computerized Tomography". (Academic Press, New York, (1980) and R. H. Huesman et al, "Donner Algorithms for Reconstruction Tomography", (Lawrence Berkeley Laboratory, University of California, October, 1977). The minimum amount of data one has to cope with in XTM may be estimated as follows: Assume a sample of width W and height H which is imaged at spatial resolution .DELTA.. We shall require that the spatial resolution of the 3-D reconstruction is also .DELTA.. This requirement determines the number, N, and size (R rows times C columns) of the radiographs to be collected. The size is H/.DELTA. rows (each corresponding to one reconstruction slice in the 3-D output image) and W/.DELTA. columns (each representing the sums of the absorption along paths through the sample at a given distance from the rotation axis). We must take N=.pi.C/4 such radiographs at angular increments of 180/N degrees. The resulting data contains N.R.C voxels which require a minimum of N.R.C.B bytes of storage if B bytes are used to store each voxel. In practice, 20 to 100% more data is collected because of the need to collect reference and dark images in order to compensate beam instability, CCD background and CCD nonuniform pixel sensitivity. Each reconstruction slice uses at least N.C.B bytes of raw data to produce 4C2 bytes of real-valued output. Performing reconstructions for the entire 3-D volume produces 4R.C.sup.2 bytes to be dealt with during 3-D rendering. As an example, consider a cylindrical sample of 1 mm in diameter and 0.5 mm high which is imaged at 3 micron spatial resolution: Each radiograph will have 167 rows and 333 columns. Two hundred sixty-two radiographs must be taken with the sample rotated 0.7 degree between each exposure. The resulting data consists of about 1.5.times.10.sup.7 voxels. Assuming the use of the KAF-1400 CCD which collects 12 bits of data (a dynamic range of about 4.times.10.sup.3) stored in 2 bytes of memory, about 30 Mbytes of data must be stored. Each reconstruction slice uses about 174 kbytes of input to produce about 444 kbytes of output. Reconstruction of all the data produces about 74 Mbytes of output to be rendered into a 3-D image. The assumed definition of resolution reflects a very conservative point of view. It should not be confused with the detectability of smallest-size objects. It was found in practice, that objects considerably smaller than the defined resolution limit are detectable under conditions of good contrast The correct treatment of resolution must be based on the concept of modulation transfer function (MTF), R. K. Swank, Appl. Opt. 12 (1973), 1865, which correctly accounts for the inherent link between the smallest size of a detectable object and its contrast. It may also be pointed out that the amount of data to be measured and handled does not primarily depend on the spatial resolution but rather more simply on the 5 number of voxels which must be examined together with what dynamic range is required in the final image. On the other hand, given a fixed sample volume, the amount of data to be measured scales with the third power of 1/.epsilon., .epsilon. being the smallest distance to be resolved. Hence when going to higher resolutions it becomes more important to limit the sample volume to its absolute minimum. At the same time, especially when employing CCD's with smaller and hence many more pixels, it appears very important to develop faster on-chip readout techniques and to provide storage media of several tens of Gb capacity. For fast rendering of the reconstructed 3-D image, the data of all pixels have to reside in CPU memory. This means the size of the memory should be on the order of 80 Mb and more. In the following discussion of the XTM images of sample 1, we will refer to `cuts` and `slices` as illustrated in FIG. 10. As is seen, all voxels of a given slice are related to each other through the same reconstruction calculation. Voxels of different slices are completely independent from each other. In contrast to this, voxels of a given cut are reconstruction-related only if they belong to the same line, where line means a line normal to the rotation axis. It is important to keep these relationships in mind when discussing the possibility that artifacts are generated by the reconstruction algorithm. FIG. 11 shows the XTM image of slice S47 of sample 1 (FIG. 10) taken at 20 keV. The almost cylindrical shape of the sample is recognizable. Bright areas in the picture correspond to higher absorption caused by alloy-phases in the Al matrix. The phases contain elements with z-values larger than that of Al. At first sight, the regions of strong absorption seen in FIG. 11 appear to form a three-dimensional 25 network with an average mesh size of roughly 150 .mu.m. However, there is another net, less absorbing than the first one, and featuring a much smaller mesh size of about 15 .mu.m. From a closer inspection of FIG. 11 we find that the strongly absorbing regions are just clusters of meshes of small cell size, i.e., there is only the smaller net which, however, has nonuniform density. (Circles around the center of rotation seen at the lower left are artefacts due to defective pixels). FIG. 12 shows cuts C150, C200, C250, C350, C400, and C450, all taken at right angle to FIG. 11. The locations where these cuts have been made are indicated in FIG. 10 and also on the right side of FIG. 11 in order to see easily the correspondence of the top lines of each cut with the structure seen in FIG. 11. Evidently the structure is the same in both directions, meaning that the network has no noticeable texture. The aluminum matrix is type KS 1275 AlSi.sub.12 CuMgNi from Kolbenschmidt AG, Neckarsulm. Its stated overall composition is 11 to 13% Si, 0.8 to 1.5% Cu, <1.3% Ni, <0.7% Fe, <0.2% Ti, <0.3% Mn, 0.3% Zn, and the balance Al. The material is normally used for pistons of diesel engines. The fiber reinforcement improves the material strength at higher working temperatures. The elements present in the alloy phases have been identified by inspection of back-scattered electron-micrographs (BSE) and wavelength-dispersive spectrometer-maps (WDS), examples of which are shown in FIG. 13 and FIG. 14. On the BSE micrograph FIG. 13a there are three types of phases distinguished, `light`, `grey`, and `dark grey`, respectively. The different types are labeled 1, 2, and 3 in FIG. 13b in which the pertinent contours of FIG. 13a have been redrawn in order to facilitate the recognition of the different phase types. From WDS-maps like those shown in FIG. 14b, 14c, and 14d for Fe, Si, and O, respectively, and other WDS-maps including Ni and Mg, it is found that phase 1 (light) contains Ni, Fe, Si, and Cu. Phase 2 (grey) contains Si, Mg, Ni, Fe, and Cu. Phase 3 (dark grey) is made up mostly of Si. Furthermore, strong evidence is obtained from the BSE-micrographs and WDS-maps that all three phases interconnect to form a three-dimensional network with an average mesh size of about 15 .mu.m. This could correspond to the smaller net observed on the XTM micrographs FIGS. 11, 12, 15 and 16. The Al.sub.2 O.sub.3 fibers are seen as black spots on the BSE-micrographs in FIGS. 13a and 14a. They match perfectly with light spots on the Oxygen WDS-map shown in FIG. 14d. The fibers are also clearly seen in the optical micrograph of FIG. 17. Most Al.sub.2 O.sub.3 fibers are oriented normal to the plane of FIG. 17. The result of a determination of all the compositions, i.e., of the matrix, of the phases 1,2,3 and of the fibers performed by x-ray fluorescent analysis (XFA) is given in Table 2. Because of the smallness of the phase grains the amount of Al is overstated in Table 2. TABLE 2 __________________________________________________________________________ Approximate Composition of Sample 1 in Weight % (W %) and atomic % (A %) as Determined by Electron Microprobe Analysis Matrix Light Ph. Grey Ph. Dark Ph. Fiber Element W % A % W % A % W % A % W % A % W % A % __________________________________________________________________________ Oxygen -- -- -- -- -- -- -- -- 43 56 Magnesium .3 .4 -- -- 19.3 23 .3 .4 -- -- Aluminum 98 98 64 78 42 44 31 32 55 42 Silicon 1.6 1.5 1.7 2.0 27 27 68 67 1.9 1.4 Iron -- -- 7.5 4.4 2.1 1.1 -- -- -- -- Nickel -- -- 25.6 14.4 8.5 4.0 -- -- -- -- Copper -- -- 1.0 .6 1.1 .5 -- -- -- -- __________________________________________________________________________ Al-rich alloy systems including the elements listed in Table 2, i.e., Mg, Si, Fe, Ni, and Cu, are known, "Equilibrium Diagrams of Aluminum Alloy Systems", Aluminum Development Association, 33 Grosvenor Street, London, W1, U.K., The kynoch Press, Birminghan, 1961, to contain the intermetallic phases shown in Table 3. From the known structure of these phases we have calculated their densities as listed in column 3 of Table 3. Using TABLE 3 ______________________________________ Properties of Components of Al-rich Alloy Systems Containing Mg, Al, Si, Fe, Ni, and Cu Absorption Occurrence Component Structure Density 20 keV Phase [14] [15] [g/cm.sup.3 ] [l/cm] relat. 1 2 3 ______________________________________ Al 2.70 9.11 1 Si CF8 2.33 10.15 1.11 x Mg.sub.2 Si CF12 2.00 6.56 0.72 x Al.sub.3.2 Fe mC102 3.81 46.30 5.08 x x Al.sub.3 Ni oP16 3.98 61.88 6.79 x x Al.sub.3 Ni.sub.2 hP5 4.76 97.65 10.72 x Al.sub.2 Cu tI12 4.36 86.59 9.50 x ______________________________________ the elemental mass absorption coefficients of reference, E. F. Plechaty et al. "Tables and Graphs of Photom Interaction Cross Sections from 0.1 keV to 100 MeV derived from the LLNL Evaluated Nuclear Data Library," 1981, UCRL-50400, Vol. 6, Rev. 3, we determined the linear and relative absorption coefficients of all components (columns 4 and 5 of Table 3). Because of the low solubility of Si in Al and the presence of a considerable amount of Mg, m ost of the Si is present in the component Mg.sub.2 Si. Since there is not enough Mg to bind all of the Si, the rest is found as a separate component consisting of the element Si, which we believe is identical with our phase 3 seen in FIG. 13 and FIG. 14c. Considering the composition of phase 2 we find that it is very likely made up of Mg.sub.2 Si plus Al.sub.3 Ni and a small fraction of Al.sub.3.2 Fe. Similarly, we conclude that phase 1 consists of the last four components listed in Table 3. The important point is that, according to the values found in Table 3, the absorption is high for phase 1, medium for phase 2 and not much different from that of the Al matrix in the case of phase 3. Therefore, in XTM micrographs we expect to see essentially three main levels of contrast. This is in agreement with the observation if we interpret the bright regions to be mostly phase 1 and the less bright net structure to consist of phase 2. Because of its low contrast, phase 3 is not likely to be seen at all at these size scales. In order to illustrate the structure of phases in three dimensions further, we show in FIG. 15 a set of six neighboring slices (S79 to S84) and in FIG. 16 a set of six neighboring cuts (C288 to C293) of sample 1. The distance between the mid planes of the neighboring slices (cuts) is about 2.8 .mu.m. This value is the resolution as defined in section 2. For sample 1 it is given by the CCD pixel size (6.8 .mu.m) divided by the light optical magnification used (2.4). As is seen, the network structures change continuously when passing through the stack of neighboring XTM micrographs. Taking FIGS. 11, 12, 15, and 16 together, it becomes evident that the structures seen are a network consisting of intermetallic phases which extend in three dimensions, and which have a mesh size on the order of 15 .mu.m. We believe this is the first time such fine and interconnected structures have been visualized nondestructively and in 3-D. FIG. 18a is a XTM micrograph of sample 2 taken normal to its rotation axis by employing the Thomson CSF TH7882CDA CCD combined with a x-ray optical magnification of 5.8 and a light optical magnification of 2.04. Since, in sample 2, all fibers are oriented normal to the image plane, we interpret the dark dots as cuts through individual fibers. The fiber diameter of 15-20 .mu.m as well as the distribution of fibers is in agreement with the scanning electron micrograph FIG. 18b and also FIG. 19, which shows a single fiber at even higher spatial resolution. The resolution of the XTM picture, FIG. 18a, when calculated simply from the CCD pixel size (23 .mu.m) and the overall magnification (11.8x), should be 23/11.8 .about.2 .mu.m. The modulation transfer function (MTF) measured for this imaging system, U. Bonse et al, HASYLAB Jahresbericht (DESY, Hamburg, 1988), p.557, yields 80 line pairs/mm at 20% contrast, corresponding to about 6 .mu.m resolution. This is not far from what one would estimate just by looking at FIG. 18a. Furthermore, we should point out that the MTF accounts for the resolution with respect to directions parallel to the reconstructed slices, i.e., normal to the axis about which the sample is rotated (FIGS. 8 and 10) when the projections are measured. At right angles to this plane, i.e., parallel to the rotation axis, there is no x-ray optical magnification, which means that the resolution in this direction is expected to be poorer by a factor of 5.8. Hence the image is integrated normal to the image plane over a depth of roughly 12 .mu.m which accounts for an additional loss of resolution. It could be avoided by placing behind 68 in FIG. 8 a second crystal magnifier, diffracting at right angle with respect to the first one. With the second magnifier in the beam we estimate the intensity to drop by an order of magnitude. A single magnifying crystal, diffracting in a plane perpendicular to the axis of sample rotation, although directly enlarging each projection only in one dimension, causes the reconstructed image to become magnified in two dimensions. When the projections are measured, a very large number of one-dimensional magnifications of sample projections in different directions are made. The reconstruction algorithm transforms the multi-directional one-dimensional magnifications of projections into the two-dimensionally magnified final image Hence, a kind of `balance` between the amount of measured information and the amount of information contained in the reconstructed image is maintained. On the other hand, a crystal magnifier which is diffracting in a plane parallel to the sample's rotation axis, yields only a one-dimensional magnification of the reconstructed image. The observations also confirm our theoretical estimates of resolution for the case when x-ray optical magnification is employed. Moreover, from the foregoing, we obtain substantial support for our thesis that by combining the techniques of magnification with the high resolution CCD and using a wiggler SR source, it will be possible to really achieve 3-D resolution on the scale of 1 micron and better for the XTM system. A major advantage of the system of the invention over the pinhole or photodiode techniques is that all of the data for three-dimensional imaging can be acquired in parallel. Data-acquisition times have been reduced to a few hours. Also, the cooled CCD has a tremendous dynamic range (10.sup.3) and is not as subject to nonlinearities as photodiode arrays are. The system of the invention has a three-dimensional resolution of better than 10.mu.m. In addition, when elemental or phase-mapping details are desired, excellent chemical contrast can be obtained by recording data at two x-ray wavelengths (usually above and below a characteristic absorption edge) and performing image subtraction to enhance chemical or phase-specific information. Conventional CT technology typically uses a polychromatic beam from conventional tube sources, which effectively precludes quantitative chemical analysis. The foregoing description of preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications, as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
	abstract	An ultraviolet laser-generating device, for use in a defect inspection apparatus and a method thereof, etc., comprising: a laser ray source for irradiating and emitting a basic wave of laser ray therefrom; a wavelength converter device for receiving the basic wave of laser ray emitted from the laser ray source and for converting it into an ultraviolet laser ray composed of a multiplied high harmonic light of the basic wave of laser ray; and a container having an inlet window, upon which the basic wave of laser ray emitted from the laser ray source is incident upon, and an outlet window for emitting the ultraviolet laser ray composed of the multiplied high harmonic light of the basic wave of laser ray, and installing the wavelength converter device therein, wherein the container is hermetically sealed and is filled up with an inert gas, such as nitrogen or argon gas, therein.
	description	Referring first to FIGS. 1 and 2, in computed tomography, a patient (not shown) to be examined is positioned in a scan circle 102 of a computer tomography (CT) scanner 100, parallel with a z-axis, and between an x-ray source 104 and a rectangular detector array 106. The x-ray source then projects a beam of energy, or x-rays 108, through the patient, to the detector array. By rotating the x-ray source about the z-axis and relative to the patient, radiation is projected through a portion of the patient to the detector array from a many different directions around the patient. An image of the scanned portion of the patient then is constructed from data provided by the detector array. The scanner 100 of FIGS. 1 and 2 employs a collimator 10 for shaping the cross-section of the beam 108 into a rectangular shape that matches the rectangular detector array 106. The collimator 10 ensures that only a preferred row of the detector array 106 is irradiated by the beam 108 and so that a patient being scanned is not subjected to an unnecessary dose of x-rays. Referring also to FIG. 3, the collimator 10 includes a plate-like body 12 defining at least one elongated slit 14 for allowing the x-ray beam to pass through the slit and be shaped by the collimator. As shown, the collimator 10 can be provided with a plurality of slits 14 of varied, but uniform widths, and the collimator can be included as part of an assembly 110 that allows for the. selection of one of the collimator slits 14 such that a desired beam width can be produced by the collimator 10. Details of the assembly 110 are disclosed in co-pending U.S. patent application Ser. No. 09/552,141, filed Apr. 19, 2000, now U.S. Pat. No. 6,301,334 issued Oct. 9, 2001, which is assigned to the assignee of the present application and incorporated into the present application by reference. As shown in FIG. 3, the collimator 10 also includes various mounting apertures 16 formed in the plate-like body 12 for mounting the collimator to the assembly 110. Referring also to FIGS. 4 through 6, the collimator 10 also includes a coating 18 covering a predetermined portion of a top surface 20 of the plate-like body 12. The coating 18 surrounds the collimating slits 14 and is comprised of an x-ray attenuating or absorbing material such a tungsten carbide. The plate-like body 12 is made of a suitable noncorrosive, more easily machined material such as stainless steel, aluminum or brass. As an example of a preferred embodiment of a collimator 10 constructed in accordance with the present disclosure, the plate-like body 12 is provided with a thickness of about 60/100 of an inch, while the coating 18 is provided with a thickness of at least about 1 millimeter. Referring to FIG. 7, a preferred method of applying the coating 18 is through a thermal spray process. For tungsten carbide an appropriate method is a plasma thermal spray process, which is basically the spraying of molten or heat softened tungsten carbide onto the top surface of the plate-like body to provide the coating. As shown, tungsten carbide in the form of powder is injected into a very high temperature plasma flame, where it is rapidly heated and accelerated to a high velocity. The hot tungsten carbide impacts on the surface of the plate-like body 12 and rapidly cools to form the coating 18. This process carried out correctly is called a xe2x80x9ccold processxe2x80x9d as the temperature of the plate-like body 12 can be kept low during processing thereby avoiding damage, metallurgical changes and distortion to the body. The plasma gun comprises a copper anode and tungsten cathode, both of which are water cooled. Plasma gas (argon, nitrogen, hydrogen, helium) flows around the cathode and through the anode which is shaped as a constricting nozzle. The plasma is initiated by a high voltage discharge which causes localized ionization and a conductive path for a DC arc to form between cathode and anode. The resistance heating from the arc causes the gas to reach extreme temperatures, dissociate and ionize to form a plasma. The plasma exits the anode nozzle as a free or neutral plasma flame (plasma which does not carry electric current). When the plasma is stabilized ready for spraying the electric arc extends down the nozzle, instead of shorting out to the nearest edge of the anode nozzle. This stretching of the arc is due to a thermal pinch effect. Cold gas around the surface of the water cooled anode nozzle being electrically non-conductive constricts the plasma arc, raising its temperature and velocity. Tungsten carbide powder is then fed into the plasma flame most commonly via an external powder port mounted near the anode nozzle exit. The powder is so rapidly heated and accelerated that spray distances can be in the order of 25 to 150 mm. The plasma thermal spray process is most commonly used in normal atmospheric conditions. Plasma spraying has the advantage that it can spray very high melting point materials such as refractory metals like tungsten, and plasma sprayed coatings are generally much denser, stronger and cleaner than the other thermal spray processes. Referring to FIGS. 8A through 8D, a method according to the present disclosure of manufacturing the collimator 10 of FIG. 3 is progressively illustrated. As shown first in FIGS. 8A and 8B, the coating 18 is applied to a predetermined portion of the top surface 20 of the plate-like body 12 of the collimator 10. The collimating slits 14 are then machined through the coating 18 and the plate-like body 12 as illustrated in FIG. 8C. Preferably, wire electrical discharge machining (EDM) is used to machine the collimating slits 14. Wire EDM is a machining process for cutting metals using a thin wire electrode. Although not shown, electrical sparks between the metal collimator 10 and the thin wire electrode melts thin line-like portions of the coating 18 and the plate-like body 12 to form the collimating slits 14. Wire EDM is a preferred method since it can make high precision cuts on any conductive materials, can be as accurate as +/xe2x88x920.0001 inches, and is ideal for precision and delicate cuttingxe2x80x94as is required for x-ray collimating slits. Referring to FIG. 8D, after the collimating slits 14 are machined, the mounting apertures 16 are machined in the plate-like body 12 between an outer periphery 22 of the coating 18 and an outer periphery 24 of the body 12 using a less expensive method of machining. While this disclosure has been particularly shown and described with references to the collimator of FIGS. 3-8, it will be understood by those skilled in the art that various changes in form and in details may be made thereto without departing from the spirit and scope of the disclosure as defined by the appended claims. For example, the novel features of a collimator as disclosed herein can be applied to a collimator having a single collimating slit, a curved collimator, or a post-patient collimator. In addition, the coating can comprise a suitable material other than tungsten carbide for attenuating and absorbing x-rays, such as a lead alloy. And the method of applying the coating is not limited to a plasma thermal spray process.
	description	This application is a continuation of prior International Patent Application No. PCT/JP2007/056246, filed Mar. 26, 2007, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to an electron beam exposure apparatus and an electron beam exposure method. Particularly, it relates to a multi-column electron beam exposure apparatus and a multi-column electron beam exposure method which are suitable for exposing process with multiple column cells. 2. Description of the Prior Art In prior art electron beam exposure apparatuses, a variable rectangular opening or multiple stencil mask patterns are provided to a stencil mask, and a certain pattern of the opening or a certain stencil mask pattern is selected by beam deflection and is exposed and transferred onto a wafer. Although multiple mask patterns are prepared in an electron beam exposure apparatus of this type, the number of electron beams used for exposure is one, and only one mask pattern is transferred at one time. As such an exposure apparatus, for example, Japanese Patent Application Publication No. 2004-88071 discloses an electron beam exposure apparatus which performs partial batch exposure. In the partial batch exposure, one pattern area (for example, a 300×300 μm area) selected by beam deflection from multiple (for example, 100 pieces of) stencil patterns disposed on a mask is irradiated with a beam. The cross section of the beam is shaped into the shape of the stencil pattern. The beam which has passed through the mask is deflected back by a deflector at a later stage. The beam is reduced to a certain reduction percentage (for example, 1/60) decided according to a property of an electron optical system, and the pattern is transferred onto a wafer surface by using the beam. The area of the wafer surface irradiated at one time is 5×5 μm, for example. When the stencil patterns on the mask are appropriately prepared according to device patterns to be exposed, the necessary number of exposure shots is reduced significantly and throughput is improved accordingly, compared with a case where only the variable rectangular opening is used. Furthermore, a multi-column electron beam exposure apparatus has been proposed, in which multiple of such columns each made smaller in size (hereinafter, referred to as column cells) are collected and arranged in parallel on a wafer for exposing process (see T. Haraguchi, et al., J. Vac. Sci. Technol, B22 (2004) 985). Each of the column cells is equivalent to a column in a single-column electron beam exposure apparatus. However, since the exposing process is performed by the multi-columns as a whole arranged in parallel, exposure throughput can be increased by severalfold of the columns. As described above, improvement in throughput can be attained in the multi-column electron beam exposure apparatus. However, connection accuracy across exposure patterns is reduced at a boundary of irradiation areas of column cells. FIGS. 1A and 1B show an example in which a desired pattern is not obtained at a position across adjacent column cells. FIG. 1A shows a desired pattern 3 at a boundary between an irradiation area 1 of a first column cell and an irradiation area 2 of a second column cell. FIG. 1B shows an example of a pattern obtained as a result of exposure. The irradiation area 1 is exposed as a pattern 5, and the irradiation area 2 is exposed as a pattern 4. Accordingly, the obtained pattern differs from the desired exposure pattern 3. In this manner, there arises a case where the width of the exposure pattern varies from area to area and a desired exposure pattern may not be obtained. Moreover, a position to be exposed may shift, and the pattern may be separated at worst. There is no particular problem when a design is made not to expose a pattern continuing across column cells as mentioned above. However, when the design is made taking positions of multiple column cells into consideration, the design flexibility is markedly reduced. Accordingly, exposure of a pattern continuing across column cells is inevitable. Moreover, there is no particular problem, for example, when patterns to be drawn are wide and may be shifted at a connection position across column cells as long as the patterns are connected. However, when the patterns are narrow as in a case of a transistor gate, higher connection accuracy is demanded. The present invention has been made in consideration of the problems in the prior art. An object of the present invention is to provide a multi-column electron beam exposure apparatus and a multi-column electron beam exposure method which achieve improved connection accuracy of patterns across column cells in the multi-column electron beam exposure apparatus. The above-mentioned object is attained with a multi-column electron beam exposure apparatus including: a plurality of column cells; a wafer stage including an electron-beam-property detecting unit for measuring an electron beam property; and a controller for measuring beam properties of electron beams used in all the column cells by using the electron-beam-property detecting unit, and for adjusting the electron beams of the respective column cells so that the properties of the electron beams used in the column cells become approximately identical to one another. In the multi-column electron beam exposure apparatus according to this aspect, the electron beam property may be any of a beam position, a beam strength, and a beam shape of the electron beam to be emitted. Moreover, the electron-beam-property detecting unit may be a chip for calibration with a reference mark formed thereon or a Faraday cup. Moreover, in the multi-column electron beam exposure apparatus according to this aspect, one electron-beam-property detecting unit for measuring the electron beam property of a same kind may be provided on an edge portion of the wafer stage. The controller performs the following operations. Specifically, using one column cell among the plurality of column cells as a reference column cell, and using an electron beam of the reference column cell as a reference beam, the controller moves the electron-beam-property detecting unit to a predetermined position below each of all the column cells to measure the beam properties of the electron beams of the column cells. Then, the controller adjusts the electron beam of each column cell other than the reference column cell so that a difference between the property of the electron beam used in the column cell and the property of the reference beam becomes within a predetermined value. In the present invention, the beam property is adjusted so that the beam properties of the electron beams emitted in the plurality of column cells become approximately identical to each other. One column cell is selected among the plurality of column cells. By using the electron beam emitted from an electron gun of the column cell as the reference beam, the electron beams of the other column cells are adjusted so as to have a beam property approximated to the beam property of the reference beam. Thereby, the beam properties of the electron beams emitted in the plurality of column cells become approximately identical. Thus, it becomes possible to prevent shifting of an irradiation position or prevent variations of the pattern width, even when a pattern extending across column cells is exposed. Accordingly, precise pattern exposure is attained. Moreover, the multi-column electron beam exposure apparatus according to this aspect may include: n electron-beam-property detecting units Mk (1≦k≦n) provided on an edge portion of the wafer stage, the electron-beam-property detecting units Mk being for measuring the electron beam property of the same kind; n column cell groups Gk (1≦k≦n) each including a plurality of column cells; and at least one column cell being common to the column cell group Gk and a column cell group Gk+1. In the multi-column electron beam exposure apparatus, the controller performs the following operations. Specifically, using one column cell among the plurality of column cells as the reference column cell, and using the electron-beam-property detecting unit Mk, the controller measures a property of an electron beam of each column cell within a column cell group Gk including the reference column cell. Then, the controller adjusts a difference between the property of the electron beam of each column cell and the beam property of the electron beam of the reference column cell so that the difference becomes within a predetermined value. Subsequently, the controller measures a beam property of the electron beam of each column cell of the column cell group Gk+1 (1≦k≦n−1) by using an electron-beam-property detecting unit Mk+1 (1≦k≦n−1). Thereafter, the controller adjusts the beam property on the basis of the electron beam property of the common column cell. In the present invention, a plurality of electron-beam-property detecting devices (units) are used for detection of beam properties, of a same kind, of the electron beams of the plurality of column cells. Each electron-beam-property detecting device detects the beam properties of the electron beams of the column cell group which has a pre-determined number of the plurality of column cells. The column cell groups have a column cell in common, and the beam properties of the electron beams of the other column cells in the column cell group are detected and adjusted on the basis of the beam property of the electron beam of the common column cell. This makes the beam properties of the electron beams of all the column cells approximately identical. Even when a pattern extending across column cells is formed, the beam properties, such as the irradiation position, intensity, and the like of the electron beam, are identical among the column cells. Accordingly, improvement in the connection accuracy of the patterns is possible. Moreover, since the properties of the electron beams used in the plurality of column cells is measured using the electron-beam-property detecting device located at a position close to those column cells, a range of the wafer stage moves in order to measure the beam properties can be small. Accordingly, deterioration of moving accuracy of the wafer stage is prevented, and in addition, a large space provided for the wafer stage movement is no longer necessary, thereby attaining miniaturization of the apparatus. Furthermore, another aspect of the present invention provides a multi-column electron beam exposure method used for the multi-column electron beam exposure apparatus according to the above-mentioned aspect. The multi-column electron beam exposure method according to this aspect includes the steps of: selecting a column cell serving as a reference among the plurality of column cells; measuring a beam property of a reference beam by using an electron-beam-property detecting unit, the reference beam being an electron beam of the column cell serving as the reference; measuring a beam property of an electron beam used in a column cell other than the reference column cell by using the electron-beam-property detecting unit; adjusting a difference between the beam property of the reference beam and the beam property of the electron beam other than the reference beam, to be within a predetermined value; and performing exposing process, using the electron beams of all the column cells, the electron beams having beam properties approximately identical to each other. Hereinafter, embodiments of the present invention will be described with reference to the drawings. (1) First Embodiment Configuration of Multi-column Electron Beam Exposure Apparatus FIG. 2 is a schematic configuration diagram of a multi-column electron beam exposure apparatus according to the present embodiment. The multi-column electron beam exposure apparatus is mainly divided into an electron beam column 10 and a controller 20 which controls the electron beam column 10. The electron beam column 10 includes multiple (for example, 16) identical column cells 11 to form the entire column. Every column cell 11 has the same structure which will be described later. Below the column cells 11, a wafer stage 13 is disposed, on which, for example, a 300-mm wafer 12 is mounted. The controller 20 includes a high voltage power supply 21 for electron gun, a lens power supply 22, a digital controller 23, a stage drive controller 24, and a stage position sensor 25. The high voltage power supply 21 for electron gun supplies power for driving an electron gun of each column cell 11 within the electron beam column 10. The lens power supply 22 supplies power for driving an electromagnetic lens of each column cell 11 within the electron beam column 10. The digital controller 23 is an electrical circuit which controls each part of the column cell 11, and outputs a deflection output at a high speed, etc. Typically, the number of the digital controllers 23 corresponds to the number of the column cells 11. On the basis of positional information from the stage position sensor 25, the stage drive controller 24 moves the wafer stage 13 so that a desired position of the wafer 12 may be irradiated with an electron beam. Each of the above-mentioned parts 21 to 25 is controlled by an integrated control system 26 such as a workstation in an integrative manner. In the multi-column electron beam exposure apparatus mentioned above, every column cell 11 is formed of the same column unit. FIG. 3 is a schematic configuration diagram of each column cell 11 used for the multi-column electron beam exposure apparatus. Each column cell 11 is mainly divided into an exposure part 100 and a column cell controller 31 which controls the exposure part 100. The exposure part 100 is formed of an electron beam generation portion 130, a mask deflection portion 140, and a substrate deflection portion 150. In the electron beam generation portion 130, an electron beam EB generated from an electron gun 101 is converged by a first electromagnetic lens 102. Subsequently, the electron beam EB transmits through a rectangular aperture 103a in a mask 103 for beam shaping, so that the cross section of the electron beam EB is shaped into a rectangular shape. Next, the electron beam EB forms an image on an exposure mask 110 with a second electromagnetic lens 105 of the mask deflection portion 140. Then, the electron beam EB is deflected by first and second electrostatic deflectors 104 and 106 into a particular pattern S formed on the exposure mask 110, so that the cross sectional shape of the electron beam EB is shaped into the shape of the pattern S. Although the exposure mask 110 is fixed onto a mask stage 123, the mask stage 123 is movable horizontally. Thus, when the pattern S located in a portion outside a deflection range (beam deflection area) of the first and second electrostatic deflectors 104 and 106 is used, the pattern S comes into the beam deflection area by moving the mask stage 123. Third and fourth electromagnetic lenses 108 and 111 respectively arranged above and below the exposure mask 110 are adjusted their current amounts, thereby forming an image on a substrate by the electron beam EB. The electron beam EB which has passed through the exposure mask 110 is deflected back to an optical axis C by deflection action of third and fourth electrostatic deflectors 112 and 113. Subsequently, the size of the electron beam EB is reduced by a fifth electromagnetic lens 114. First and second correction coils 107 and 109 are provided in the mask deflection portion 140, and correct beam deflection aberration caused by the first to the fourth electrostatic deflectors 104, 106, 112, and 113. Then, the electron beam EB passes through an aperture 115a of a shield plate 115 which constitutes the substrate deflection portion 150, and is projected on a substrate by first and second projection electromagnetic lenses 116 and 121. Thereby, an image with the pattern of the exposure mask 110 is transferred onto the substrate at a predetermined reduction percentage, for example, a reduction percentage of 1/10. Fifth electrostatic deflector 119 and an electromagnetic deflector 120 are provided in the substrate deflection portion 150, and these deflectors 119 and 120 deflect the electron beam EB, so that the image with the pattern of the exposure mask 110 is projected to a predetermined position of the substrate. Furthermore, third and fourth correction coils 117 and 118 for correcting deflection aberration of the electron beam EB on the substrate are provided in the substrate deflection portion 150. The column cell controller 31 includes an electron gun controller 202, an electron optical system controller 203, a mask deflection controller 204, a mask stage controller 205, a blanking controller 206, and a substrate deflection controller 207. The electron gun controller 202 controls the electron gun 101 to control the acceleration voltage, beam radiation conditions, and the like of the electron beam EB. The electron optical system controller 203 controls current amounts applied to the electromagnetic lenses 102, 105, 108, 111, 114, 116, and 121, and the like, to thereby adjust the magnification, focal position, and the like of an electron optical system formed of these electromagnetic lenses. The blanking controller 206 deflects the electron beam EB generated before start of exposure onto the shield plate 115 by controlling a voltage applied to a blanking electrode 127, to thereby prevent irradiation of the substrate with the electron beam EB before the exposure. The substrate deflection controller 207 controls a voltage applied to the fifth electrostatic deflector 119 and a current amount applied to the electromagnetic deflector 120, so as to deflect the electron beam EB onto a predetermined position of the substrate. Each of the above-mentioned parts 202 to 207 is controlled by the integrated control system 26 such as a workstation in an integrative manner. FIG. 4 is a schematic diagram of the column cell controller 31 in the multi-column electron beam exposure apparatus. Each of the column cells 11 includes the column cell controller 31. Each column cell controller 31 is connected to the integrated control system 26 with a bus 34. The integrated control system 26 controls the entire multi-column electron beam exposure apparatus. Moreover, an integrated storage unit 33 is formed of, for example, a hard disk in which data such as exposure data needed in all the column cells is stored. The integrated storage unit 33 is also connected to the integrated control system 26 with the bus 34. FIG. 5 is a conceptual diagram of the entire exposure apparatus including four column cells C1, C2, C3, and C4. The column cells C1, C2, C3, and C4 are disposed in an array form of 2×2. The distances between C1 and C2, between C2 and C3, between C3 and C4, and between C4 and C1 are, for example, 75 mm. One wafer stage 13 is disposed below all the column cells Cl, C2, C3, and C4. An electron-beam-property detecting device 41 (for example, a calibration chip 41a and a Faraday cup 41b) is provided on an edge portion of the wafer stage 13. The electron-beam-property detecting device (also referred to as “electron-beam-property detecting unit”) 41 measures the properties of an electron beam in order to adjust the beam intensity and beam position of the electron beam. The wafer stage 13 is capable of measuring the position using the stage position sensor 25 such as a laser measuring device, and accurately moving the electron-beam-property detecting device 41 to a desired position. In the multi-column electron beam exposure apparatus thus formed, exposure data on a pattern to be exposed on the wafer placed on the wafer stage 13 is transferred from the integrated storage unit 33 to a column cell storage unit 35 (FIG. 4) of each column cell controller 31. When the transferred exposure data needs to be corrected, the exposure data is corrected in a correction unit 36 (FIG. 4) of each column cell controller 31. As a result, the same pattern is exposed to an exposure area on the wafer 12 assigned to each column cell 11. Next, description will be given on a process for adjusting the beam properties of electron beams used in multiple column cells to be approximately identical by using the electron-beam-property detecting device 41. FIG. 6 is a drawing showing an area of a specimen 43 irradiated with the electron beams of the four column cells. Reference numerals 43a to 43d denote an irradiation area of each column cell. For example, in the irradiation area 43d, exposing process is performed on each field from the left side of FIG. 6 in a sequence shown by an arrow 51. Similarly, in the irradiation area 43a, exposing process is performed in a sequence shown by an arrow 52. In such an exposing process, when a pattern extending across column cells is exposed, a phenomenon that connection accuracy of the pattern is worsened occurs, as shown in FIG. 1B. As this cause, it is conceivable that there is a difference in irradiation time of the electron beams in the vicinity of a boundary 53 between the irradiation area 43d and the irradiation area 43a, which results in a difference in positional accuracy and intensity of the electron beam used in each column cell. Thus, the present inventors come up with a possibility of improving the connection accuracy of the above-mentioned pattern extending across the column cells by equalizing the properties of the electron beams which are used in all the column cells. In the present embodiment, a beam position property, a beam intensity property, and a beam shape property are targeted. The beam position property is a property which shows whether a desired position is accurately irradiated with the beam to be emitted. The beam intensity property is a property which shows the intensity of the beam and shows the size of the beam current. The beam shape property is a property which shows whether the beam has a desired shape when the beam is shaped into, for example, a variable rectangular beam. Additionally, cases where the calibration chip 41a and the Faraday cup 41b are used as the electron-beam-property detecting device 41 are targeted. FIGS. 7A to 7C are drawings illustrating shift from a target position occurs when the target position is irradiated with an electron beam. The abscissas in FIGS. 7A to 7C show a position, and the ordinates show probability distribution of variation of the beam irradiated position. Moreover, a true position to be irradiated with the beam is set to an origin PO. As factors that the irradiation position of the electron beam is shifted, positional shift due to setting of the voltage or the like applied to the deflectors of the exposure apparatus, positional shift due to drift, and beam position fluctuation at the time of drawing are taken into consideration. FIG. 7B shows a predicted value of connection shift between the column cells when the column cells are independently aligned with the true position. In other words, it shows a predicted value of connection shift based on the true position. The irradiation positional shift of the first column cell is the same as that of FIG. 7A. Suppose that the irradiation position of the electron beam of the second column cell is moved to P3 from the true position PO due to deflection amount error, and further moved to P4 due to beam position drift at the time of drawing. Under this condition, FIG. 7B shows a case where the error is the largest between the first column cell and the second column cell. FIG. 7B is a drawing showing a predicted value of connection shift between the column cells when the column cells are independently aligned with the true position. In other words, shown is a predicted value of connection shift based on the true position. The irradiation positional shift of the first column cell is the same as that of FIG. 7A. Suppose that the irradiation position of the electron beam of the second column cell is moved to P3 from the true position PO due to deflection amount error, and further moved to P4 due to beam position drift at the time of drawing. At this time, FIG. 7B shows a case where the error is the largest between the first column cell and the second column cell. FIG. 7C is a drawing showing a predicted value of connection shift across the column cells when connection across the column cells is given priority in terms of adjustment. In other words, FIG. 7C is a drawing showing a predicted value of connection shift across the column cells based on a position irradiated in the first column cell. As shown in FIG. 7C, based on the position P2 irradiated with the electron beam of the first column cell, a position away from P2 by the distance of X3 is a position P5 due to deflection amount error of the electron beam of the second column cell, and a position further away from P5 by the distance of X4 is a position P6 due to beam position drift at the time of drawing. This case also shows a case where the error is the largest between the first column cell and the second column cell. Thus, considering the case where the error is at maximum when the pattern is connected across the column cells, the connection error across the columns is made smaller by adjusting the electron beam of another column cell on the basis of the electron beam of one column cell determined in advance than by separately adjusting the electron beam on the basis of the true position. For this reason, in the present embodiment, the beam properties of the electron beams in multiple column cells of the multi-column electron beam exposure apparatus are adjusted so that, using the electron beam in one column cell as a reference beam, the beam properties of the electron beams of other column cells may correspond to the beam property of the reference beam. Hereinafter, description will be given on a case where the beam properties of the electron beams of all the column cells are measured using one electron-beam-property detecting device 41, and the beam property of the same kind is adjusted in accordance with the reference beam. In the present embodiment, description will be made taking the following case as an example. Specifically, the beam position is measured by the calibration chip 41a and the beam position is corrected; then, the beam intensity is measured by the Faraday cup 41b and the beam intensity is corrected (see FIG. 5). A column cell to serve as the reference is selected (referred to as a column cell 1), and the electron beam emitted from the electron gun of the column cell 1 is used as a reference beam. The beam position property of the reference beam is calculated. A reference mark formed on the calibration chip 41a is used to detect the beam position property by a well-known method. Specifically, the wafer stage is moved so that a center of the reference mark may be located directly below an optical axis of each column cell, and a deflector is used to scan the electron beam so that the reference mark may be irradiated with the electron beam. A backscattered electron detector detects backscattered electron signals at the time of scanning, and the beam irradiation position is calculated by performing signal processing on the backscattered electron signals. In comparison with a position where the actual reference mark is disposed, the irradiation position of the electron beam is calculated and the beam position property is measured. When the beam is not deflected and is on the optical axis, an edge is detected at the same position as that of the edge of the reference mark. On the other hand, when the beam is shifted, the edge detection position is different from the position of the reference mark. In the present embodiment, the position shifted from the true position is set as a reference position, and this electron beam is set as the reference beam. Next, in order to measure the electron beam properties of the other column cells, the same reference mark as used in order to examine the property of the reference beam is used. The wafer stage is moved so that the reference mark may be located directly below the optical axis of each column cell. Similar to the case of measuring the reference beam, the electron beam of each column cell is scanned by the deflector, backscattered electron signals of the reference mark are acquired, and positional shift of the electron beam from the edge position is measured. A value for correcting a voltage amount applied to the fifth electrostatic deflector 119 of each column cell is calculated so that this positional shift may be approximated to the positional shift measured with the reference beam. A difference between the irradiation position of the electron beam of each column cell and the irradiation position of the reference beam is adjusted so that the difference can take a predetermined value, for example, several nm. As for the voltage applied to the electrostatic deflector having a 2-way electrode in an x direction and a y direction of the deflector which changes the irradiation position of the electron beam on the specimen, an input in the x direction is represented by a formula (1), and an input in the y direction is represented by a formula (2).X′=AX+BY+HxXY+Ox(t) (1)Y′=CX+DY+HyXY+Oy(t) (2) A voltage proportional to this value is applied to the electrode of the electrostatic deflector to deflect the electron beam. In the formulas, A, B, C, D, Hx, Hy, Ox, and Oy are adjustment coefficients. In order to make the above-mentioned positional shift within a value not more than the predetermined value, for example, Ox and Oy are adjusted in the voltage applied to the deflector so that the positional shift may be approximated to the position of the reference beam. These values are stored in each column cell storage unit 35, and the electron beam is deflected at a corrected voltage when the electron beam is irradiated in each column cell. The above-mentioned process is performed on the electron beams of all the column cells other than the reference column cell to make the beam position properties of all the electron beams approximately identical. Next, the electron beam intensities of the electron beams of all the column cells are made approximately identical. The intensity (current value) of the electron beam is measured by using the Faraday cup and measuring the current value of the electron beam with which the reference position is irradiated. In the present embodiment, measurement of the current value of the electron beam of each column cell is performed using one Faraday cup and an ammeter. In addition, the beam position property of the electron beam of each column cell is adjusted. When the position is not adjusted, only a part of the electron beam enters the Faraday cup in some cases. For that reason, the beam to be used is adjusted so that the same position can be irradiated with the beam. In order to measure the current value of the reference beam used in the reference column cell, the wafer stage is moved so that the Faraday cup 41b shown in FIG. 5 may be located directly below the optical axis of the reference column cell. Then, irradiation with the electron beam for a predetermined time is performed to measure the current value. Similar to the case of the beam position, an adjustment coefficient for the beam intensity is changed so that a difference from the beam intensity of the reference beam becomes less than a predetermined value, for example, less than 1 nA in a case of a rectangle of 100 nm×100 nm. For example, in a case of a variable rectangle, an electron beam having a cross section shaped into rectangle is aligned on a rectangular opening of a mask, and shaped into a rectangle having a width Sx and a length Sy. As for a voltage applied to the electrostatic deflector having a 2-way electrode in an x direction and a y direction at this time, an input in the x direction is represented by a formula (3), and an input in the y direction is represented by a formula (4).Sx′=ASx+BSy+HxSxSy+Ox(t) (3)Sy′=CSx+DSy+HySxSy+Oy(t) (4) In the above-mentioned formulas (3) and (4), the coefficients Ox, Oy, or the coefficients A to D are adjusted so that the beam intensity may be approximated to the reference beam intensity. Moreover, shot time of the beam may be adjusted to adjust the beam current in accordance with a reference value. These values are stored in each column cell storage unit 35, and upon actual exposure, exposing process is performed in accordance with this data. When there is an extremely large difference in beam intensity from that of the reference beam, drastic change of the shape of the variable rectangle causes a larger difference in the shape of the beam from that of the reference beam. Accordingly, a desired pattern shape may not be exposed. In this case, the adjustment coefficient is determined in consideration of both the beam intensity and the beam shape of the references. Moreover, the beam shape is measured by: scanning the electron beam in the same manner as measurement of the beam position; passing the electron beam on the reference mark to detect an edge; and detecting the length of the beam in the scanning direction on the basis of a distance between the edges of the reference mark and a distance between the detected edges. As described above, in the multi-column electron beam exposure apparatus of the present embodiment, the beam properties, of the same kind, of the electron beams used in the multiple column cells are detected using one electron-beam-property detecting device, and the beam properties of the electron beams of the other column cells are adjusted so as to be equivalent to the properties of one beam serving as the reference. For example, the multi-column electron beam exposure apparatus is configured so as to detect the irradiation position of the electron beam using the reference mark, a backscattered electron detector, etc. so that the irradiation positions of the electron beams can be relatively identical in all the column cells. Thereby, the beam properties of the electron beams used in all the column cells are made approximately identical. Since the beam properties, such as the irradiation position and intensity of the electron beam, are identical among the column cells, even when the pattern extending across the column cells is formed, improvement in the connection accuracy of the pattern is possible. Adjustment of the beam properties is performed at a predetermined time before start of exposure or during exposure. When the pattern extending across the column cells is fine and demands accuracy, the number of times of adjustment of the beam properties is increased even during exposure. When the number of times of adjustment of the beam properties is increased, the exposing process is interrupted in accordance with the number of times, and therefore, a process speed is slowed. However, the connection accuracy of pattern across the column cells may be reduced by reduction of adjustment of the beam properties, and the pattern may be disconnected at worst. Moreover, the accuracy of the pattern formed by then is not guaranteed, either. Accordingly, the exposing process may be again performed from the start, and the throughput may be more deteriorated than in the case where the exposing process is interrupted during exposure. It is also possible to detect the beam intensity from an amount of the backscattered electrons not only from the beam position by use of the reference mark on the calibration chip 41a. However, in order to accurately detect the beam intensity of the electron beam, use of the Faraday cup 41b is desirable. Moreover, the beam shape can be determined using the reference mark on the calibration chip 41a. Accordingly, the shape may be measured simultaneously with measurement of the beam position. While measurement of the beam intensity with the Faraday cup 41b has been described in the present embodiment, the beam position may be measured by a beam position detector including the Faraday cup 41b, or the beam shape may be measured by a beam shape detector including the Faraday cup 41b. By measuring the beam position property, the beam intensity property, and the beam shape property with the reference mark on the calibration chip 41a, the number of times of movement of the wafer stage 13 can be reduced, and the time for measurement can be shortened. The same effect is also obtained when the beam properties are measured using the Faraday cup 41b. In the description above, the beam properties of the other column cells are adjusted in accordance with the reference beam in the state that the reference beam is shifted from the true position. However, a beam corrected in accordance with the true position may be used as the reference beam. This allows beam irradiation at an ideal position. (Multi-column Electron Beam Exposure Method) Next, an exposure method in the above-mentioned multi-column electron beam exposure apparatus will be described. FIG. 8 is a flow chart illustrating a beam property adjustment process with the multi-column electron beam exposure apparatus according to the present embodiment. In the present embodiment, description will emphasize on a method for detecting the beam position among the beam properties using the reference mark to adjust the beam position property of each column cell. A reference column cell which irradiates an electron beam serving as a reference beam is determined in advance, and is designated as C1. First, at Step S11, the calibration chip 41a on the wafer stage 13 is moved to a position directly below the optical axis of the reference column cell C1. Next, at Step S12, the deflector of the column cell C1 scans the electron beam so that the electron beam can pass on the reference mark, thereby to acquire backscattered electron signals of the reference mark. These backscattered electron signals are acquired by detecting backscattered electrons attributed to the scanned electron beam with a backscattered electron detector. Next, at Step S13, the edge position is detected from the backscattered electron signals of the reference mark detected at Step S12. Next, at Step S14, the amount of shift between a position of an actual reference mark and the position of the reference mark obtained by scanning the electron beam is detected. This amount of shift is stored as a reference amount in the storage unit. Next, at Steps S15 to S17, the properties of the electron beams of the column cells other than the reference column cell are measured, and the properties are adjusted. At Step S15, the wafer stage is moved so that the reference mark may be located directly below the optical axis of one column cell among the other column cells. At subsequent Step S16, the beam position property of the electron beam of the one column cell is measured in the same manner as in the case of measurement of the reference beam. At subsequent Step S17, a difference between the beam position property and the reference beam position property is calculated, and the adjustment coefficient of the voltage applied to the electrostatic deflector is adjusted so that the difference may be a value not more than a predetermined value. The predetermined value is several nm, for example. The adjusted coefficient is stored in the storage unit 35 of each column cell. At subsequent Step S18, it is determined whether adjustment of the beam position property is completed with respect to the electron beams of all the column cells. When the adjustment for all of the column cells is not completed, the process returns to Step S15, and the beam property adjustment process is repeated. The exposing process is performed after the above-mentioned beam property adjustment process. (2) Second Embodiment In the first embodiment, the properties of the electron beams in all the column cells are measured using one electron-beam-property detecting device for the beam property of the same kind, and are adjusted so as to be approximated to the reference beam properties. Unlike the first embodiment, in the present embodiment, in order to approximate the electron beam properties of all the column cells to the reference beam properties, multiple electron-beam-property detecting devices are used. Note that a multi-column electron beam exposure apparatus used in the present embodiment has the same configuration as that of the first embodiment, and therefore description thereof will be omitted. Hereinafter, description will be given on a method for approximating the electron beam properties of all the column cells to the reference beam properties by using the multiple electron-beam-property detecting devices. FIG. 9 shows some of the column cells when there are multiple (for example, 16) column cells, which is an example of a case where two electron-beam-property detecting devices (M1, M2) are used for four column cells. The electron-beam-property detecting device M1 measures the beam properties of the electron beams used in the column cells C1 and C2, while the electron-beam-property detecting device M2 measures the beam properties of the electron beams used in the column cells C2, C3, and C4. Moreover, the column cell C1 is set as a reference column cell, and the electron beam used in the column cell C1 is set as a reference beam. A group of the column cells C1 and C2 is referred to as a column cell group G1, while a group of the column cells C2, C3, and C4 is referred to as a column cell group G2. Thus, the column cell groups G1 and G2 have the column cell C2 in common. In the column cell group G1, using the electron-beam-property detecting device M1, the beam properties of the electron beam used in the column cell C2 are adjusted so as to be approximated to the reference beam properties, as shown in the first embodiment. Next, using the electron-beam-property detecting device M2, measurement of the electron beam used in each column cell of the column cell group G2 and adjustment of the beam properties thereof are performed. In the column cell group G2, the beam serving as the reference is the beam of the column cell C2 common to the column cell groups G1 and G2. In the column cell group G1, the column cell C2 is adjusted so as to be approximated to the reference beam of the reference column cell C1. Accordingly, by using the column cell C2 as the reference within the column cell group G2, it is possible to approximate the electron beams of the other column cells to the reference beam. When a difference in the beam property between the column cell C1 and the column cell C2 is at the maximum value and a difference in the beam property between the column cell C2 and the column cell C3 is at the maximum value, the beam properties of the column cell C3 is twice the allowable error of the reference beam. In other words, when the difference is at the maximum within the column cell group, the error range is enlarged by a product of the number of the electron-beam-property detecting devices and the difference. For this reason, while this value is taken into consideration, the design is made so as to reduce the allowable error range. The above concrete example is generalized as follows. A column cell group is designated as Gk where 1≦k≦n. Reference symbol k denotes order of measuring the beam properties. At this time, a common column cell is included in adjacent column cell groups Gk and Gk+1. Reference symbol n is the number of electron-beam-property detecting devices M, and an electron-beam-property detecting device Mk measures the beam properties of the electron beams used in column cells which the column cell group Gk has. First, a column cell which uses an electron beam serving as a reference beam is selected, and set as a reference column cell C1. In each column cell within a column cell group G1 including the reference column cell, the beam properties are measured using an electron-beam-property detecting device M1. As a result of measurement of the beam properties, the electron beam properties of each column cell within the column cell group G1 is adjusted so as to be approximated to those of the reference beam of the column cell C1. This adjustment is performed in the same manner as in the method described in the first embodiment. Next, in each column cell within a column cell group G2, the beam properties are measured using an electron-beam-property detecting device M2. A column cell C12 common to the column cell group G1 and the column cell group G2 is adjusted in accordance with the reference beam of the reference column cell C1. When the electron beams of the column cells within the column cell group G2 are adjusted, the common column cell C12 is used as the reference, and the electron beams of the other column cells within the column cell group G2 are adjusted on the basis of the adjusted electron beam. In this manner, the beam properties are measured in all the electron beams of the column cell group Gk+1 (1≦k≦n−1) using an electron-beam-property detecting device Mk+1 (1≦k≦n−1), and the beam properties of all the electron beams of the column cell group Gk+1 are adjusted on the basis of the electron beam properties of the common column cell. As a result, the beam properties of all the column cells are within a range of (predetermined error)×n relative to the reference beam of the reference column cell C1. As described above, in the multi-column electron beam exposure apparatus according to the present embodiment, multiple electron-beam-property detecting devices are used for detection of the beam properties, of the same kind, of the electron beams used in multiple column cells. Each electron-beam-property detecting device detects the beam properties of the electron beams of the column cell group which has a pre-determined number of multiple column cells. The column cell groups have a cell in common, and the beam properties of the electron beams of the other column cells in the column cell group are detected and adjusted on the basis of the beam properties of the electron beam of the common column cell. This makes the beam properties of the electron beams used in all the column cells approximately identical. Thus, even when a pattern extending across the column cells is formed, the beam properties, such as the irradiation position, intensity, and the like of the electron beam, become identical among the column cells. Accordingly, improvement in the connection accuracy of the pattern is possible. Moreover, since the properties of the electron beams used in multiple column cells are measured using the electron-beam-property detecting device located at a position close to those column cells, the range of the wafer stage moved in order to measure the beam properties can be small. Accordingly, deterioration of moving accuracy of the wafer stage is prevented, and in addition, a large space for the wafer stage movement is not necessary, thereby attaining miniaturization of the apparatus. Note that, while the description has been made in the present embodiment in which the column cell group has 2 or 3 column cells, the number of the column cells may be 4 or larger. Thereby, the number of times of measurement of the beam properties is reduced while the movement range of the wafer stage is made smaller, and enlargement of the error is reduced. (Multi-column Electron Beam Exposure Method) Next, an exposure method in the above-mentioned multi-column electron beam exposure apparatus will be described. FIG. 10 is a flow chart illustrating a beam property adjustment process with the multi-column electron beam exposure apparatus according to the present embodiment. In the present embodiment, description will emphasize on a method for detecting the beam position among the beam properties using the reference mark to adjust the beam property of each column cell. First, at Step S20, an initial setting is performed. In the initial setting, a reference column cell which irradiates an electron beam used as a reference beam is determined, and column cell groups and electron-beam-property detecting devices used by the column cell groups are determined. Moreover, a column cell group G1 includes the reference column cell, each column cell group is designated as Gk where the initial value of k is set to 2. At subsequent Step S21, the beam position property of the reference beam is measured and recorded in the storage unit. The beam position property of the reference beam is measured as follows. The electron-beam-property detecting device M1 on the wafer stage is moved so as to be located directly below the optical axis of the reference column cell C1 of the column cell group G1. At subsequent Step S22, the deflector of the column cell C1 scans the electron beam so that the electron beam can pass on the reference mark on the electron-beam-property detecting device M1, thereby to acquire backscattered electron signals of the reference mark. These backscattered electron signals are acquired by performing signal processing on backscattered electrons attributed to the scanned electron beam, the backscattered electrons being detected with a backscattered electron detector. Then, the edge position is detected from an image of the detected reference mark. Subsequently, the amount of shift between a position of an actual reference mark and the position of the reference mark obtained by scanning the electron beam is detected. This amount of shift is stored as a reference amount in the storage unit. Next, at Step S23, the beam property of the electron beam used in each column cell other than the reference column cell within the column cell group G1 is measured using the electron-beam-property detecting device M1, and the electron beam is adjusted so as to be approximated to the property of the reference beam. Upon measurement of the property and adjustment of the property of the electron beam of the column cell other than the reference column cell, first, the wafer stage is moved so that the reference mark may be located directly below the optical axis of the other column cell. Then, the beam position property of the electron beam of the other column cell is measured in the same manner as in the case of the reference beam. A difference between the beam position property and the reference beam position property is calculated, and an adjustment coefficient of the voltage applied to the electrostatic deflector is adjusted so that the difference may be a value not more than a predetermined value. The adjusted coefficient is stored in the storage unit 35 of each column cell. Next, at Step S24, the beam property is detected in the next column cell group Gk using an electron-beam-property detecting device Mk. The beam property of each beam is measured in the same manner as at Step S22. Note that the column cell common to the column cell group Gk and a column cell group Gk−1 is irradiated with the electron beam adjusted to the reference beam property at Step S22. Next, at Step S25, the electron beams used in the column cells within the column cell group Gk are adjusted on the basis of the beam property of the electron beam used in the column cell common to the column cell group Gk and the column cell group Gk−1. At subsequent Step S26, it is determined whether adjustment of the beam property is completed in all the column cell groups. When the adjustment is not completed, k is incremented at Step S27. Then, the process returns to Step S24, and the adjustment process is continued. The exposing process is performed after the above-mentioned beam property adjustment process. As described above, in the multi-column electron beam exposure method of the present embodiment, the beam property is adjusted in accordance with the reference beam using multiple electron-beam-property detecting devices. Since such multiple electron-beam-property detecting devices are used, the movement range of the wafer stage becomes small compared with the case where only one electron-beam-property detecting device is used. Furthermore, it is possible to prevent deterioration of the moving accuracy and to prevent increase of a spatial area in the movement range for the wafer stage.
	claims	1. A nuclear reactor comprising:a vessel;a core provided in the vessel;at least one plate heat exchanger provided in the vessel;at least one secondary fluid supply duct for supplying a secondary fluid to the heat exchanger and a discharge secondary fluid duct for discharging the secondary fluid from the heat exchanger, the discharge secondary fluid duct extending through the vessel; andan attachment for attaching the heat exchanger to an area of the vessel through which the discharge secondary fluid duct extends,wherein the secondary fluid supply duct supplying the heat exchanger with secondary fluid includes an upstream crossing extending through the vessel, and a plurality of flexible ducts connecting the upstream crossing to the heat exchanger,wherein the heat exchanger includes at least one upstream secondary collector supplying the heat exchanger with secondary fluid, the upstream secondary collector and the upstream crossing being connected to each other by the flexible ducts. 2. The nuclear reactor as recited in claim 1 wherein the attachment bears at least 70% of the weight of the exchanger. 3. The nuclear reactor as recited in claim 1 wherein the heat exchanger has a secondary fluid outlet orifice, the secondary fluid discharge duct comprising a downstream crossing extending through the vessel and having an inner passage for the secondary fluid placed to coincide with the outlet orifice, the attachment comprising a plurality of attachers distributed around the inner passage and the outlet orifice. 4. The nuclear reactor as recited in claim 1 wherein the vessel has a substantially vertical central axis, the attachment attaching an upper end of the heat exchanger to the vessel. 5. The nuclear reactor as recited in claim 4 further comprising a guide device suitable for limiting the travel of a lower part of the heat exchanger in a horizontal plane, and allowing a movement of the lower part in the vertical direction relative to the vessel. 6. The nuclear reactor as recited in claim 1 wherein the attachment attaches the heat exchanger to the vessel such that the attachment is disassembleable. 7. The nuclear reactor as recited in claim 6 wherein the attachment includes a plurality of attachers attaching the heat exchanger to the vessel, the attachers disassembleable from outside the vessel. 8. The nuclear reactor as recited in claim 1 wherein the heat exchanger includes a plurality of plates stacked parallel to one another, the secondary fluid discharge duct passing through the vessel in a substantially radial direction relative to a central axis of the vessel, the plates being substantially perpendicular to the radial direction. 9. The nuclear reactor as recited in claim 1 wherein the heat exchanger includes a downstream secondary collector collecting the secondary fluid leaving the heat exchanger, the secondary fluid discharge duct and the downstream secondary collector being aligned with each other. 10. The nuclear reactor as recited in claim 9 wherein the heat exchanger includes a plurality of plates stacked parallel to one another and the downstream secondary collector extends through the plates. 11. The nuclear reactor as recited in claim 1 wherein the heat exchanger includes a plurality of plates stacked parallel to one another and the upstream secondary collector extends through the plates. 12. The nuclear reactor as recited in claim 1 wherein the heat exchanger includes a plurality of plates stacked parallel to one another and heat exchanger includes a plurality of primary channels delimited between the plates and traveled by the primary fluid, each primary channel having a main inlet and a main outlet, the heat exchanger having at least one hood delimiting a water tank in which the main inlets or the main outlets emerge. 13. The nuclear reactor as recited in claim 1 wherein the vessel includes a shroud and a cover attached on the shroud so as to be disassembleable, the heat exchanger being attached to the cover. 14. The nuclear reactor as recited in claim 1 further comprising absorbers for controlling the reactivity of the core, which are vertically movable relative to the core, the absorbers being situated above the core and the heat exchanger being situated above the absorbers. 15. The nuclear reactor as recited in claim 14 further comprising a maneuverer provided to maneuver the absorbers selectively, the maneuverer including actuators placed vertically above the heat exchangers and rods connecting the actuators to the absorbers, the nuclear reactor having several heat exchangers distributed around the rods. 16. The nuclear reactor as recited in claim 1 wherein the secondary fluid discharge duct includes a downstream crossing engaged in an orifice of the vessel, the attachment including a plurality of attachers attaching the heat exchanger to the vessel, the attachers and the downstream crossing being removable from the vessel from outside the vessel. 17. The nuclear reactor as recited in claim 16 further comprising a ring configured for keeping the heat exchanger suspended from the vessel after the downstream crossing is removed from the vessel. 18. The nuclear reactor as recited in claim 1 wherein the secondary fluid discharge duct includes a downstream crossing engaged in an orifice of the vessel, the attachment attaching the heat exchanger directly to the downstream crossing. 19. A nuclear reactor comprising:a vessel;a core provided in the vessel;at least one plate heat exchanger provided in the vessel;at least one secondary fluid supply duct for supplying a secondary fluid to the heat exchanger and a discharge secondary fluid duct for discharging the secondary fluid from the heat exchanger, the discharge secondary fluid duct extending through the vessel; andan attachment for attaching the heat exchanger to an area of the vessel through which the discharge secondary fluid duct extends,wherein the heat exchanger has a secondary fluid outlet orifice, the secondary fluid discharge duct comprising a downstream crossing extending through the vessel and having an inner passage for the secondary fluid placed to coincide with the outlet orifice, the attachment comprising a plurality of attachers distributed around the inner passage and the outlet orifice. 20. A nuclear reactor comprising:a vessel;a core provided in the vessel;at least one plate heat exchanger provided in the vessel;at least one secondary fluid supply duct for supplying a secondary fluid to the heat exchanger and a discharge secondary fluid duct for discharging the secondary fluid from the heat exchanger, the discharge secondary fluid duct extending through the vessel; andan attachment for attaching the heat exchanger to an area of the vessel through which the discharge secondary fluid duct extends,wherein the heat exchanger includes a downstream secondary collector collecting the secondary fluid leaving the heat exchanger, the secondary fluid discharge duct and the downstream secondary collector being aligned with each other,wherein the heat exchanger includes a plurality of plates stacked parallel to one another and the downstream secondary collector extends through the plates.
	abstract	A data processing device, comprising a plurality of emitter antennas arranged on a movable data acquisition device and adapted to emit electromagnetic radiation including data acquired by the movable data acquisition device, a plurality of receiver antennas each adapted to receive the electromagnetic radiation emitted by each of the plurality of emitter antennas, and a data processing unit coupled to the plurality of receiver antennas and adapted to extract the data acquired by the movable data acquisition device from the electromagnetic radiation received by the plurality of receiver antennas.
	description	This application is a divisional application of U.S. patent application Ser. No. 10/119,707, filed Apr. 11, 2002, now U.S. Pat. No. 6,834,098 which is a continuation of U.S. patent application Ser. No. 08/917,373, filed Aug. 26, 1997, which issued as U.S. Pat. No. 6,504,896 on Jan. 7, 2003. This invention relates to an X-ray illumination optical system and an X-ray reduction exposure apparatus using the same and, in another aspect, it relates to a device manufacturing method using such an X-ray reduction exposure apparatus. An X-ray reduction projection exposure process is used for the manufacture of microdevices such as semiconductor circuit devices, having fine patterns. In such a process, a mask having a circuit pattern formed thereon is illuminated with X-rays and an image of the pattern of the mask is projected, in a reduced scale, on the surface of a wafer. A resist on the wafer surface is sensitized, whereby the pattern is transferred and printed thereon. FIG. 12 is a schematic view of a known example of an X-ray reduction projection exposure apparatus, FIG. 13 is a schematic and perspective view of a reflection type integrator, and FIG. 14 is a schematic view for explaining an illumination region upon the surface of a mask. In these drawings, denoted at 1001 is a light emission point for X-rays, and denoted at 1002 is an X-ray beam. Denoted at 1004 is a first rotational parabolic surface mirror, and denoted at 1005 is a reflection type integrator. Denoted at 1006 is a second rotational parabolic surface mirror, and denoted at 1007 is a mask. Denoted at 1008 is a projection optical system, and denoted at 1009 is a wafer. Denoted at 1010 is a mask stage, and denoted at 1011 is a wafer stage. Denoted at 1012 is an arcuate aperture, and denoted at 1013 is a laser light source. Denoted at 1014 is a laser collecting optical system, and denoted at 1015 is an illumination region defined on the surface of the mask. Denoted at 1016 is an arcuate region within which the exposure is performed. An X-ray light source may comprise a laser plasma or an undulator. In the illumination optical system, X-rays from the light source are collected by means of the first rotational parabolic surface mirror 1004, and the collected X-ray beam is projected on the reflection type integrator 1005, whereby secondary light sources are formed. X-rays from these secondary light sources are collected by means of the second rotational parabolic surface mirror 1006, to illuminate the mask 1007. The mask 1007 comprises a multilayered film reflection mirror on which non-reflective portions are defined by use of an X-ray absorptive material, for example, whereby a transfer pattern is formed thereon. X-rays reflected by the mask 1007 are imaged by the projection optical system 1008 upon the surface of the wafer 1009. The projection optical system 1008 is designed so as to provide good imaging performance with respect to a narrow arcuate region off the optical axis. In order that the exposure is performed only by use of this narrow arcuate region, an aperture 1012 having an arcuate opening is disposed just before the wafer 1009. For the pattern transfer to the whole surface of the mask having a rectangular shape, the exposure process is performed while scanningly moving the mask 1007 and the wafer 1009 simultaneously. The reflection type integrator 1005 may comprise a fly's-eye mirror having a number of small spherical surfaces arrayed two-dimensionally, as is best seen in FIG. 13, which are adapted to define a number of secondary light sources. Here, if the spatial extension of the secondary light source group is d, the angular extension of X-rays emitted from each secondary light source is θ, and the focal length of the second parabolic surface mirror 1006 is f, then the size of the illumination region 1015 on the mask 1007 surface is f×θ and the angular extension of X-rays illuminating a single point on the mask is d/f. As a parameter which represents the characteristic of the illumination optical system, there is a coherence factor σ. If the mask-side numerical aperture of the projection optical system 1008 is NAp1, and the mask-side numerical aperture of the illumination optical system is NAi, the coherence factor can be defined as follows:σ=NAi/NAp1 The optimum value of σ is determined by the required resolution and contrast. Generally, if the factor σ is too small, an interference pattern appears at the edge portion of an image of a fine pattern as projected on the wafer 1009. If the factor σ is too large, the contrast of the projected image reduces. If σ is zero, it is called coherent illumination. Regarding the transfer function OTF of the optical system, a constant value will be shown up to a particular spatial frequency as can be given by NAp2/λ where NAp2 is the wafer-side numerical aperture of the projection optical system and λ is the wavelength of the X-ray beam. For a higher frequency above the particular frequency, it becomes equal to zero, and resolving is not attainable. If, on the other hand, σ is equal to 1, it is called incoherent illumination. The transfer function OTF reduces with an increase in the spatial frequency, but it does not become equal to zero unless a particular spatial frequency given by 2×NAp2/λ is reached. Thus, a more fine pattern can be resolved. In X-ray exposure, an optimum value of σ may be selected in accordance with the shape or size of a pattern to be transferred, or the characteristic of a resist process to be adopted. Usually, a value such as σ=0.1–1.0 may be set. There is a problem to be solved, in conventional X-ray reduction projection exposure apparatuses. That is, as shown in FIG. 14, the illumination region 1015 on the mask surface has a rectangular shape or an elliptical shape, including an arcuate region 1016 through which the exposure is actually made. Thus, the region outside the exposure region is illuminated with many X-rays. These X-rays are not contributable to the exposure process, and they are wasteful. The loss of X-ray light quantity is large and it leads to prolongation of the exposure time. Thus, the throughput is low. It is accordingly an object of the present invention to provide an X-ray reduction exposure apparatus and/or an X-ray illumination optical system therefor, by which the loss of light quantity can be very small, the exposure time can be shortened, and the throughput can be improved. It is another object of the present invention to provide a device manufacturing method based on such an X-ray reduction exposure apparatus. In accordance with an aspect of the present invention, there is provided an X-ray illumination optical system, comprising: a reflection type integrator having cylindrical surfaces, for reflecting an X-ray beam; and a concave mirror for reflecting the X-ray beam reflected by said integrator and for illuminating an object with the X-ray beam. The system my further comprise a second concave mirror for projecting a parallel X-ray beam onto said integrator. Said integrator may provide a secondary light source and said concave mirror may have a focal point which is disposed at the position of said secondary light source. Said concave mirror may have a reflection surface of a rotational parabolic shape. An axis of said cylindrical surface of said integrator and an axis of the X-ray beam impinging on said integrator may be placed on the same plane. There may be an illumination region defined on the object, having an arcuate shape. Said integrator may have a reflection surface on which a multilayered film is formed. The illumination of the object may substantially satisfy the conditions for Koehler illumination. The X-ray beam may comprise one of a beam emitted from a laser plasma X-ray source and a beam emitted from an undulator X-ray source. In accordance with another aspect of the present invention, there is provided an X-ray reduction exposure apparatus, comprising: an X-ray illumination optical system as discussed above, for illuminating a mask having a pattern; and an X-ray reduction projection optical system for projecting, in a reduced scale, the pattern of the mask, as illuminated, onto the surface of a wafer. The apparatus may further comprise scanning means for relatively scanningly moving the mask and the wafer relative to said X-ray reduction projection optical system, at a predetermined speed ratio. In accordance with a further aspect of the present invention, there is provided a method of manufacturing a device by use of an X-ray reduction exposure apparatus as described above. 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. FIG. 1 is a schematic and perspective view for explaining reflection of parallel light impinging on a reflection type integrator having convex cylindrical surfaces. FIG. 2 is a schematic and sectional view of the reflection type integrator having cylindrical surfaces. FIG. 3 is a schematic view for explaining reflection of X-rays at a cylindrical surface of a reflection type integrator having convex cylindrical surfaces. FIG. 4 is a schematic view for explaining an angular distribution of X-rays reflected by a cylindrical surface of a reflection type integrator having cylindrical surfaces. In these drawings, denoted at 5 is a reflection type integrator having convex cylindrical surfaces. An X-ray beam of substantially parallel light emitted from an X-ray light source is projected on the reflection type integrator 5 having a plurality of cylindrical surfaces, and secondary light sources are defined by this integrator. The X-rays emitted from these secondary light sources have an angular distribution of a conical surface shape. A reflector having a focal point placed at the secondary light source position reflects the X-rays to illuminate a mask. For explanation of the function of such a reflection type integrator having cylindrical surfaces, first the action of reflection light in a case where parallel light impinges on one cylindrical surface reflector will be described with reference to FIG. 3. As shown, parallel light is incident on one cylindrical surface at an angle θ with respect to a plane perpendicular to the central axis thereof. If the light ray vector of the projected parallel light isR1=(0, −cos θ, sin θ)and the vector of a normal to the reflection surface of the cylindrical surface isn=(−sin α, cos α, 0)then the light ray vector of the reflection light isR2=(cos θ×sin 2α, cos θ×cos 2α, sin θ).Here, if the light ray vector of the reflection light is plotted in a phase space, the result is a circle of a radius cos θ on an X-Y plane as shown in FIG. 4. That is, the reflection light is formed into divergent light of a conical surface shape, and the secondary light source is located at the position of an apex of this conical surface. If the cylindrical surface comprises a concave surface, the secondary light source is placed outside the reflection surface. If the cylindrical surface comprises a convex surface, the secondary light source is placed inside the reflection surface. Also, if the reflection surface is limitedly provided by a portion of a cylindrical surface and the central angle thereof is 2ø, then as shown in FIG. 4 the light ray vector of reflection light is arcuate with a central angle 4ø upon the X-Y plane. Next, a case wherein parallel light is projected on a reflection mirror provided by a portion of a cylindrical surface, wherein a reflection mirror having a focal length f and a focal point placed at the position of this secondary light source, and wherein a mask is placed at the position away from this reflection mirror by a distance f, will be considered. The light emitted from the secondary light source is divergent light and, after it is reflected by the reflection mirror of a focal length f, it is transformed into parallel light. The reflection light here is formed into a sheet beam of an arcuate sectional shape with a central angle 4ø, at a radius f×cos θ. Thus, only an arcuate region upon the mask, having a radius f×cos θand a central angle 4ø can be illuminated. While one cylindrical surface reflection mirror has been explained above, a cylindrical surface integrator such as shown in FIG. 1 will now be considered. That is, as shown, parallel light of a diameter D is projected on a reflection mirror of a wider area, having a number of cylindrical surfaces arrayed in parallel in a one-dimensional direction. If the reflection mirror and the mask are disposed in the same manner as in the foregoing example, the angular distribution of light reflected by the reflection mirror, with a number of cylindrical surfaces arrayed in parallel, is essentially the same as in the preceding case. Thus, an arcuate region on the mask with a radius f×cos θand a central angle 4ø is illuminated. Since the light which impinges on a single point on the mask comes from the whole illumination region on the reflection mirror provided by cylindrical surfaces arrayed in parallel, the angular extension of it is D/f. That is, the numerical aperture of the illumination optical system is D/(2f). If the mask-side numerical aperture of the projection optical system is NAp1, the coherence factor isσ=D/(2fNAp1).Therefore, in accordance with the thickness (size) of the parallel light, an optimum coherence factor σ can be set. Next, embodiments of the present invention which use a reflection type integrator with plural cylindrical surfaces will be explained with reference to some drawings. [Embodiment 1] FIG. 5 is a schematic view of an X-ray reduction projection exposure apparatus according to a first embodiment of the present invention. FIG. 6 is a schematic and perspective view of a reflection type integrator with convex cylindrical surfaces, usable in the first embodiment of the present invention. FIG. 7 is a schematic view for explaining an illumination region on the surface of a mask, in the first embodiment of the present invention. Denoted in these drawings at 1 is a light emission point for X-rays, and denoted at 2 is an X-ray beam. Denoted at 3 is a filter, and denoted at 4 is a first rotational parabolic surface mirror. Denoted at 5 is a reflection type convex cylindrical surface integrator, and denoted at 5 is a second rotational parabolic surface mirror. Denoted at 7 is a mask, and denoted at 8 is a projection optical system. Denoted at 9 is a wafer, and denoted at 10 is a mask stage. Denoted at 11 is a wafer stage, and denoted at 12 is an arcuate aperture. Denoted at 13 is a laser plasma X-ray light source, and denoted at 14 is a laser collecting optical system. Denoted at 15 is an illumination region on the mask surface, and denoted at 16 is an arcuate region through which the exposure is to be performed. Denoted at 17 is a vacuum chamber. The X-ray reduction projection exposure apparatus of the first embodiment of the present invention comprises a laser plasma X-ray light source 13, an illumination optical system 8, a wafer 9, stages 10 and 11 on which the mask or wafer is placed, an alignment mechanism for precisely aligning the positions of the mask and wafer, a vacuum chamber 17 for keeping the optical arrangement as a whole in a vacuum to prevent X-ray attenuation, and an evacuation device, for example. The illumination optical system comprises a first rotational parabolic surface mirror 4, a reflection type convex cylindrical surface integrator 5, and a second rotational parabolic surface mirror 6. The mask 7 comprises a multilayered film reflection mirror on which a transfer pattern is defined by a non-reflective portion, provided by an X-ray absorptive material. The X-ray beam as reflected by the mask 7 is imaged by the projection optical system 8 upon the wafer 9 surface. The projection optical system 7 is so designed that good imaging performance is provided within a narrow arcuate region off the axis. For example, with a reduction magnification of 1:5, good imaging performance is assured with respect to a region on the mask 7 surface at 200 mm off the axis, and to a region on the wafer 9 surface at 40 mm off the axis, with a width of 1 mm. In order that the exposure process is performed only by use of this narrow arcuate region, an aperture 12 having an arcuate opening is disposed just before the wafer 9. For transfer of the pattern on the whole surface of the mask 7 having a rectangnlar shape, the mask 7 and the wafer 9 are scanningly moved simultaneously, at a predetermined speed ratio. The projection optical system 8 has two multilayered film reflection mirrors, and it serves to project the pattern of the mask 7 onto the wafer 9 in a reduced scale. The reduction magnification corresponds to the scan speed ratio between the mask and the wafer. The projection optical system 8 comprises a telecentric system. The X-ray beam 2 emitted from the light emission point 1 of the laser plasma X-ray source 13 passes a shield filter 3 of the target, for prevention of particle scattering, and it is reflected by the first rotational parabolic surface mirror 4, whereby it is transformed into a parallel beam. This beam is then reflected by the reflection type integrator 5 with convex cylindrical surfaces, whereby a number of secondary light sources are produced. The X-rays from these secondary light sources are reflected by the second rotational parabolic surface mirror 6, and then illuminate the mask 7. Both of the distance from the secondary light source to the second rotational parabolic surface mirror 6 and the distance from the second parabolic surface mirror 6 to the mask 7 are equal to the focal length of the second rotational parabolic surface mirror. Thus, the conditions for Koehler illumination are satisfied. The reflection type convex cylindrical surface integrator 5 comprises a total reflection mirror having such a shape that a number of small convex cylindrical surfaces are arrayed one-dimensionally such as shown in FIG. 6. In the sectional shape of the integrator 5, each arcuate portion has a radius of 0.5 mm and a central angle of 30 deg. When parallel light impinges on it, on a plane inside the reflection surface at a distance of 0.25 mm, there is formed a virtual image of linear secondary light sources, arrayed in parallel, that is, of the laser plasma X-ray light source 13. In this embodiment, the parallel X-ray beam has a thickness of 20 mm, and the incidence angle of the parallel X-ray beam upon the integrator 5 is 85 deg. The second rotational parabolic surface mirror 6, having a focal length f=2300 mm, has its focal point disposed at the position of the secondary light sources, as the linear secondary light sources arrayed in parallel are defined on a plane spaced by 0.25 mm from the reflection surface when parallel light is projected on the integrator 5. Also, the mask 7 is disposed at a distance 2300 mm from the second rotational parabolic surface mirror 6. Light emitted from one point on the secondary light source is divergent light having an angular distribution like a conical surface. It is reflected by the second rotational parabolic surface mirror 6 having a focal length f=2300 mm, and it is transformed into parallel light. Then, as shown in FIG. 7, an arcuate region 16 on the mask 7 having a radius 2300 mm×cos 85(deg)−200 mm and a central angle 30 deg. ×2 =60 deg. is illuminated. Here, the numerical aperture of the illumination optical system is 20/(2×2300)=0.0043. If the numerical aperture of the projection optical system is 0.01 on the mask side and 0.05 on the wafer side, the coherence factor is 0.43. On the mask 7 surface, an arcuate region 16 of a radius 200 mm and a central angle 60 deg. is illuminated, and the pattern within this region is projected in a reduced scale onto the resist surface of the wafer 9. If the reduction magnification is 1:5, an arcuate region on the wafer 9 having a radius 40 mm and central angle 60 deg. is illuminated at once. With the scan of the mask 7 and the wafer 9, a square region of 40 mm square, for example, can be exposed with good precision. As described, this embodiment uses a reflection type convex cylindrical surface integrator 5 having a reflection surface provided by a number of small convex cylindrical surfaces arrayed one-dimensionally, by which the region on the mask 7 to be illuminated can be defined with an arcuate shape and, simultaneously, an optimum value for a coherence factor of the illuminate optical system can be set. Also, the shape of the illumination region 15 on the mask 7 surface is restricted to the vicinity of the arcuate region 16 with which the exposure process is performed actually. Wasteful illumination of X-rays to a wide area outside the exposure region, such as shown in FIG. 14, is prevented. Thus, the loss of light quantity is reduced, the exposure time can be shortened and throughput can be improved. [Embodiment 2] FIG. 8 is a schematic view of an X-ray reduction projection exposure apparatus according to a second embodiment of the present invention. FIG. 9 is a schematic and perspective view of a reflection type integrator with concave cylindrical surfaces, usable in the second embodiment of the present invention. Denoted in these drawings at 801 is an undulator X-ray light source, and denoted at 802 is an X-ray beam. Denoted at 803 is a concave surface mirror, and denoted at 804 is a first concave surface mirror. Denoted at 805 is a reflection type integrator with concave cylindrical surfaces, and denoted at 806 is a second concave surface mirror. Denoted at 807 is a mask, and denoted at 808 is a projection optical system. Denoted at 809 is a wafer. Denoted at 810 is a mask stage, and denoted at 811 is a wafer stage. Denoted at 812 is an arcuate aperture, and denoted at 817 is a vacuum chamber. The X-ray reduction projection exposure apparatus according to the second embodiment of the present invention comprises an undulator X-ray light source 801, an illumination optical system, a mask 807, a projection optical system 808, a wafer 809, stages 810 and 811 having the mask or wafer placed thereon, an alignment mechanism for precisely aligning the positions of the mask and wafer, a vacuum chamber for keeping the optical arrangement as a whole in a vacuum for preparation of X-ray attenuation, and an evacuation device, for example. The illumination optical system of this embodiment comprises an undulator X-ray light source 801, a convex surface mirror 803, a first concave surface mirror 804, a reflection type concave cylindrical surface integrator 805, and a second concave surface mirror 806. The mask 807 comprises a multilayered film reflection mirror on which a transfer pattern is defined by a non-reflective portion, provided by an X-ray absorptive material. The X-ray beam as reflected by the mask 807 is imaged by the projection optical system 808 upon the wafer 809 surface. The projection optical system 808 is so designed that good imaging performance is provided in a narrow arcuate region off the axis. In order that the exposure process is performed only by the use of this narrow arcuate region, an aperture 812 having an arcuate opening is disposed just before the wafer 809. For transfer of the pattern on the whole surface of the mask 807 having a rectangular shape, the mask 807 and the wafer 809 are scanningly moved simultaneously. The projection optical system 808 has three multilayered film reflection mirrors, and it serves to project the pattern of the mask 807 onto the wafer 809 in a reduced scale. The X-ray beam 802 emitted from the light emission point of the undulator X-ray light source 801 is a narrow and substantially parallel beam. It is reflected by the convex surface mirror 803 and the first concave surface mirror 804, whereby it is transformed into a thick parallel beam. This beam is reflected by the reflection type concave cylindrical surface integrator 805 of the structure that concave cylindrical surfaces with multilayered films for increased X-ray reflectivity are arrayed in parallel. By this, a number of secondary light sources are produced. Light emitted from a single point on the secondary light source is divergent light of a conical surface shape and, after being reflected by the second concave surface mirror 806, it is transformed into parallel light. Then, an arcuate region on the mask 807 is illuminated. As described above, this embodiment uses a reflection type concave cylindrical surface integrator 805 having a number of small concave cylindrical surfaces arrayed one-dimensionally, by which the region on the mask 807 to be illuminated can be made arcuate and, additionally, an optimum value for the coherence factor of the illumination optical system can be set. Also, the shape of the illumination region on the mask 807 surface is restricted to an arcuate region with which the exposure is to be done actually. Wasteful X-ray illumination to those areas outside the exposure region is prevented. Thus, the loss of light quantity is reduced, the exposure time can be shortened and the throughput can be improved. The X-ray illumination optical system and X-ray reduction exposure apparatus described above assure, with use of a reflection type integrator having a reflection mirror of a wide area provided by a number of cylindrical surfaces arrayed in parallel, illumination of only an arcuate region on a mask. Also, it enables setting the numerical aperture of the illumination system to provide an optimum coherent factor σ. The shape of the illumination region on the mask is restricted to an arcuate region with which the exposure is to be done actually, and wasteful X-ray illumination to those areas other than the exposure region is prevented. Thus, loss of light quantity is reduced, the exposure time can be shortened and the throughput can be enhanced. The reflection surface of the reflection type integrator may be provided with a multilayered film, to provide higher X-ray reflectivity. [Embodiment of A Device Manufacturing Method] Next, an embodiment of a device manufacturing method for producing semiconductor devices, for example, which uses an exposure apparatus such as described above, will be explained. FIG. 10 is a flow chart of a procedure for the manufacture of microdevices such as semiconductor chips (e.g., ICs or LSIs), liquid crystal panels and CCDs, 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. 11 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. 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.
056339046	summary	FIELD OF THE INVENTION This invention relates generally to the handling of spent nuclear materials and more particularly to the handling of spent nuclear fuel rods for transportation to storage areas, inspection areas, or for further treatment. BACKGROUND OF THE INVENTION The generation of power from nuclear materials has been well known in the art for many decades. The nuclear material, after a period of use for power generation, is incapable of generating the energy necessary and must be removed from its nuclear reactor. The major component of used nuclear material is spent nuclear fuel (SNF) rods. The transportation of such spent nuclear fuel rods has been a troubling problem over the decades and one that has not been solved entirely satisfactorily. Spent nuclear fuel has the characteristic of emitting high amounts of radiation which is damaging to living tissue, particularly in humans. To handle the spent nuclear fuel safely, the fuel must be shielded with appropriate radiation shielding materials. Shielding materials, in general, are of a dense nature. To shield the radiation emitted from the spent nuclear fuel, shielded casks are used to maintain the exterior radiation levels at a sufficiently low level to prevent harm to personnel or the environment. For transferring spent nuclear fuel to a transportation or storage cask, the current commercial industrial practice is an underwater or wet fuel transfer process which includes the step of submerging a cask into the nuclear fuel storage pool. Then, through the use of cranes and grappling hooks and the like, the spent nuclear fuel rods are transferred while still underwater into the submerged cask. The water acts as a radiation shield to protect personnel performing the transfer. The cask is then lifted from the storage pool, the interior of the cask is drained and dried, the outside is decontaminated and the cask is sealed. An alternate method for the transfer of spent nuclear fuel rods is dry transfer. The current dry transfer system utilizes a transfer container to handle the spent nuclear fuel rods. A stand is placed under water in the spent nuclear fuel storage pool and the spent nuclear fuel rods are transferred to a position within the stand while still under water. The transfer container is landed on the stand and the bottom of the transfer container is opened by operating a translating gate. Then, a single spent fuel rod is raised through the bottom of and into the transfer container. This process is repeated to load the transfer container. Then, the transfer container is sealed by closing a translating gate and the transfer container is transported to a discharge stand. The transfer container is seated on the discharge stand and the translating gate is operated to open the bottom of the transfer container. A single spent fuel rod is lowered out of the transfer container and into a transportation cask located in the discharge stand. This process is repeated until all the spent nuclear fuel rods are removed from the transfer container and placed into the cask. Such method is disclosed in commonly assigned U.S. Pat. No. 5,319,686 to Pizzano et al, which patent is incorporated in its entirety herein by reference. The wet fuel transfer process utilizes casks which are too large to be handled at many fuel storage sites because of constraints on existing lifting and handling resources. In addition, the wet fuel transfer process requires the exterior of the submerged cask to be cleaned or decontaminated to remove radioactive particles which increases the process time and the possible exposure of operating personnel to radiation and radioactive contamination. The current dry fuel transfer process requires personnel to be located atop the transfer container to manipulate fuel handling tools and the like. Consequently, to protect the personnel atop the container, the transfer container must provide adequate shielding of the radiation being emitted by the spent nuclear fuel rods. This in turn increases the weight of the transfer container and its exterior dimensions which prevents its use at some fuel storage sites with limited lifting and handling capabilities. Also, grapple actuating tools penetrate the transfer container which hinders containment of any potential radioactive off-gases in the transfer container. In addition, the transfer container is only capable of raising or lowering one spent nuclear fuel (SNF) rod at a time. During the raising process, the SNF rods are not constrained from lateral motion after they are removed from the loading stand and prior to entering the transfer container. Also, during the lowering process, the SNF rods are not constrained from lateral motion after they are lowered from the transfer container and prior to entering the storage or transportation container. SUMMARY OF THE INVENTION The dry fuel transfer system of the present invention allows the transfer of spent nuclear fuel rods in the dry condition, while using a remote means to control and operate the system. The use of a remote control allows a reduction in personnel and allows personnel to remain a safe distance from the transfer container and thereby reduces the amount of radiation shielding material required and the radiation dosage to operating personnel. Consequently, the weight and overall dimensions of the transfer container are reduced to allow use of the present invention at all fuel storage sites without modification to their existing lifting and handling apparatus. Also, the dry fuel transfer system of the present invention permits raising or lowering of a number of nuclear fuel rods simultaneously. This greatly reduces the process time and thereby the radiation exposure of personnel. In addition, the proposed system does not require the penetration of any fuel handling tools or the like, which enables the transfer container to be sealed easily. The remote operation of the transfer container only requires one operator. Also, the improved system of the present invention ensures that the SNF assemblies are constrained from lateral motion during all of the fuel handling movements.
	summary
	claims	1. An X-ray diagnostic apparatus comprising: an X-ray tube; an X-ray detector; a grid arranged on an image reception plane of said X-ray detector; an arm configured to support said X-ray tube and said X-ray detector in such a manner that a distance between said X-ray tube and said image reception plane of said X-ray detector can be changed; an arm support device configured to support said arm in such a manner that an angle of said arm can be changed; a storage device configured to store moire image data files including moire fringes by said grid in association with at least one of said distance and said angle; and a moire correction circuit configured to correct image data outputted from said X-ray detector based on moire image data file selectively read from said storage device in accordance with at least one of said distance and said angle. 2. The X-ray diagnostic apparatus according to claim 1 , wherein said X-ray detector is a flat panel type detector adopting a direct conversion system or an indirect conversion system. claim 1 3. The X-ray diagnostic apparatus according to claim 1 , further comprising a circuit configured to adjust the contrast or density of said moire image data selectively read from said storage device based on at least one of an X-ray tube voltage, an X-ray tube current of said X-ray tube, a gain of said X-ray detector and a radiography time. claim 1 4. The X-ray diagnostic apparatus according to claim 1 , further comprising a circuit configured to dissolve or reduce the displacement of said moire image data selective read from said storage device with respect to image data outputted from said X-ray detector. claim 1 5. The X-ray diagnostic apparatus according to claim 1 , wherein the moire image data files are obtained in a condition no top plate for mounting a patient is arranged between said X-ray tube and said X-ray detector. claim 1 6. The X-ray diagnostic apparatus according to claim 1 , further comprising a circuit configured to generate a new moire image data file from moire image data files read from said storage device by a distance-linear interpolation. claim 1 7. The X-ray diagnostic apparatus according to claim 1 , wherein when an examination radiography is effected with the grid being removed, said image data outputted from said X-ray detector substantially passes through said moire correction circuit. claim 1 8. An X-ray diagnostic apparatus comprising: an X-ray tube; an X-ray detector; a gird arranged on an image reception plane of said X-ray detector; an arm configured to support said X-ray tube and said X-ray detector in such a manner that a distance between said X-ray tube and said image reception plane of said X-ray detector can be changed; an arm support device configured to support said arm in such a manner that an angle of said arm can be changed; a moire correction data generation circuit configured to perform frequency analysis of image data outputted from said X-ray detector, specifies a spatial frequency corresponding to a moire pattern, and generates moire correction data based on said specified spatial frequency; and a moire correction circuit configured to correct image data outputted from said X-ray detector based on said generated moire correction data. 9. The X-ray diagnostic apparatus according to claim 8 , wherein the spatial frequency corresponding to the moire pattern is a peak frequency in an analyzed spatial frequency distribution. claim 8 10. The X-ray diagnostic apparatus according to claim 8 , wherein said moire correction data generation circuit generates moire correction data including a plurality of moire fringes having said specified spatial frequency. claim 8 11. The X-ray diagnostic apparatus according to claim 8 , wherein said moire correction data generation circuit generates a one dimensional original image signal from image data outputted from said X-ray detector and subjects said one dimensional original image signal to frequency analysis. claim 8 12. The X-ray diagnostic apparatus according to claim 8 , wherein said moire correction data generation circuit generates a plurality of one dimensional original image signals corresponding to a plurality of directions from image data outputted from said X-ray detector, individually performs frequency analysis of a plurality of said one dimensional original image signals, specifies a plurality of peak frequencies corresponding to said one dimensional original image signals respectively, and selects a highest peak frequency from a plurality of said peak frequencies. claim 8 13. The X-ray diagnostic apparatus according to claim 12 , wherein said moire correction data generation circuit generates moire correction data including a plurality of moire fringes having said selected highest peak frequency as a spatial frequency in a direction corresponding to said selected highest peak frequency. claim 12 14. The X-ray diagnostic apparatus according to claim 8 , wherein said X-ray detector is a flat panel type detector adopting a direct conversion system or an indirect conversion system. claim 8 15. An X-ray diagnostic apparatus comprising: an X-ray tube; an X-ray detector; a grid arranged on an image reception plane of said X-ray detector; an arm configured to support said X-ray tube and said X-ray detector in such a manner that a distance between said X-ray tube and said image reception plane of said X-ray detector can be changed; an arm support device configured to support said arm in such a manner that an angle of said arm can be changed; a frequency analysis circuit configured to subject image data outputted from said X-ray detector to frequency analysis and specify a spatial frequency corresponding to a moire pattern; and a moire correction circuit configured to attenuate a component of said specified spatial frequency included in image data outputted from said X-ray detector. 16. The X-ray diagnostic apparatus according to claim 15 , wherein the spatial frequency corresponding to the moire pattern is a peak frequency in an analyzed spatial frequency distribution. claim 15 17. The X-ray diagnostic apparatus according to claim 15 , wherein said frequency analysis circuit generates a one dimensional original image signal from image data outputted from said X-ray detector and subjects said one dimensional original image signal to frequency analysis. claim 15 18. The X-ray diagnostic apparatus according to claim 15 , wherein said frequency analysis circuit generates a plurality of one dimensional original image signals corresponding to a plurality of directions from image data outputted from said X-ray detector, individually subjects a plurality of said primary image signals to frequency analysis, specifies a plurality of peak frequencies, and selects a highest peak frequency from a plurality of said peak frequencies. claim 15 19. X-ray diagnostic apparatus according to claim 18 , wherein said moire correction circuit attenuates a spatial frequency component of said selected highest peak frequency in a direction corresponding to said selected highest peak frequency. claim 18 20. The X-ray diagnostic apparatus according to claim 15 , wherein said X-ray detector is a flat panel type detector adopting a direct conversion system or an indirect conversion system. claim 15 21. An X-ray diagnostic apparatus comprising: an X-ray tube; an X-ray detector; a grid arranged on an image reception plane of said X-ray detector; an arm configured to support said X-ray tube and said X-ray detector in such a manner that a distance between said X-ray tube and said image reception plane of said X-ray detector can be changed; a sensor configured to detect a distance between said X-ray tube and said image reception plane of said X-ray detector; an arm support device configured to support said arm in such a manner that an angle of said arm can be changed; a storage device configured to store moire image data when a distance between said X-ray tube and said image reception plane of said X-ray detector is a reference distance; a moire image enlargement circuit which is configured to enlarge said moire image data based on said distance detected by said sensor and said reference distance; and a moire correction circuit which corrects image data outputted from said X-ray detector based on said enlarged moire image data. 22. An X-ray diagnostic apparatus according to claim 21 , wherein said moire image enlargement circuit enlarges said moire image data in accordance with a magnification C 1 /C 0 represented by the following expression: claim 21 C 1 / C 0 =( Ppxe2x88x92Pg )/(( Pp/M 1 )xe2x88x92 Pg ) where C 0 is a pattern cycle of moire fringes corresponding to said reference distance; C 1 is a pattern cycle of moire fringes corresponding to said distance detected by said sensor; Pp is a pixel pitch of said X-ray detector; Pg is a grid plate projected image of said grid on said image reception plane of said detector corresponding to said reference distance; and M 1 is a ratio of a magnification of a grid projected image on said image reception plane of said detector with respect to said grid corresponding to said reference distance and a magnification of a grid projected image on said image reception plane of said detector with respect to said grid corresponding to said distance detected by said sensor. 23. The X-ray diagnostic apparatus according to claim 22 , wherein said moire image enlargement circuit calculates said ratio M 1 in accordance with the following expression: claim 22 M 1 =( S 1 /( S 1 xe2x88x92 D 0 ))/( S 0 /( S 0 xe2x88x92 D 0 )) where D 0 is a physical distance between said grid and said image reception plane of said detector; S 0 is said reference distance; and S 1 is a distance detected by said sensor. 24. The X-ray diagnostic apparatus according to claim 21 , wherein said X-ray detector is a flat panel type detector adopting a direct conversion system or an indirect conversion system. claim 21
	claims	1. An extreme ultraviolet light generation apparatus used in combination with a laser system, the apparatus comprising:a chamber provided with at least one inlet port for introducing a laser beam outputted from the laser system into the chamber;a target supply unit provided to the chamber for supplying a target material to a predetermined region inside the chamber, where the target material is irradiated with the laser beam;at least one optical element disposed inside the chamber;a magnetic field generation unit for generating a magnetic field around the predetermined region;an ion collection unit disposed in a direction of a line of magnetic force of the magnetic field for collection an ion which is generated when the target material is irradiated with the laser beam and flows along the line of magnetic force; anda gas introduction unit for introducing an etching gas into the chamber. 2. The extreme ultraviolet light generation apparatus of claim 1, further comprising:a pressure detector for detecting pressure inside the chamber;a mass flow meter for detecting a flow rate of the etching gas;a gas flow controller for controlling the flow rate of the etching gas such that a value detected by the mass flow meter is a value at which a desired etching rate is achieved;an exhaust unit for discharging gas inside the chamber; andan ion sensor disposed close to the at least one optical element for detecting an ion. 3. The extreme ultraviolet light generation apparatus of claim 2, wherein the pressure inside the chamber is approximately at or above 0.5 Pa and is approximately at or below 13 Pa. 4. The extreme ultraviolet light generation apparatus of claim 2, wherein the flow rate of the etching gas is approximately at or above 25 sccm and is approximately at or below 100 sccm. 5. The extreme ultraviolet light generation apparatus of claim 2, wherein the gas flow controller controls the flow rate of the etching gas introduced into the chamber from the gas introduction unit based at least on one of the pressure detected by the pressure detector and the value detected by the ion sensor. 6. The extreme ultraviolet light generation apparatus of claim 1, further comprising:a magnetic field intensity controller for controlling intensity of the magnetic field;a power source for supplying current to the magnetic field generation unit; andan ion sensor disposed close to the at least one optical element for detecting an ion. 7. The extreme ultraviolet light generation apparatus of claim 1, further comprising:a magnet sensor for detecting a magnetic flux density of the magnetic field;a magnetic field intensity controller for controlling intensity of the magnetic field;a power source for supplying current to the magnetic field generation unit; andan ion sensor disposed close to the at least one optical element for detecting an ion. 8. The extreme ultraviolet light generation apparatus of claim 6, wherein the magnetic flux density of the magnetic field is approximately at or above 0.35 tesla and is approximately at or below 2 tesla. 9. The extreme ultraviolet light generation apparatus of claim 7, wherein the magnetic flux density of the magnetic field is approximately at or above 0.35 tesla and is approximately at or below 2 tesla. 10. The extreme ultraviolet light generation apparatus of claim 7, wherein the magnetic field intensity controller controls current supplied to the magnetic field generation unit based at least on one of the magnetic flux density detected by the magnet sensor and the value detected by the ion sensor. 11. The extreme ultraviolet light generation apparatus of claim 1, whereinthe ion flowing along the line of magnetic force forms an ion flow having a predetermined diffusion width, andthe at least one optical element is disposed substantially off an edge of the ion flow. 12. The extreme ultraviolet light generation apparatus of claim 1, whereinthe ion flowing along the line of magnetic force forms an ion flow having a predetermined diffusion width, andthe target supply unit has a tip thereof disposed substantially off an edge of the ion flow. 13. The extreme ultraviolet light generation apparatus of claim 1, whereinthe ion flowing along the line of magnetic force forms an ion flow having a predetermined diffusion width, andthe gas introduction unit has a tip thereof disposed substantially off an edge of the ion flow. 14. The extreme ultraviolet light generation apparatus of claim 11, wherein the predetermined diffusion width is determined by intensity distribution of the magnetic field, the pressure inside the chamber, and energy of the ion. 15. The extreme ultraviolet light generation apparatus of claim 12, wherein the predetermined diffusion width is determined by intensity distribution of the magnetic field, the pressure inside the chamber, and energy of the ion. 16. The extreme ultraviolet light generation apparatus of claim 13, wherein the predetermined diffusion width is determined by intensity distribution of the magnetic field, the pressure inside the chamber, and energy of the ion. 17. The extreme ultraviolet light generation apparatus of claim 1, further comprising a free radical source for turning the etching gas into a free radical. 18. The extreme ultraviolet light generation apparatus of claim 1, wherein the etching gas is hydrogen gas. 19. The extreme ultraviolet light generation apparatus of claim 1, wherein the etching gas is hydrogen radical gas. 20. The extreme ultraviolet light generation apparatus of claim 1, wherein the at least one optical element is a collector mirror for collecting extreme ultraviolet light emitted as the target material is irradiated with the laser beam inside the chamber. 21. The extreme ultraviolet light generation apparatus of claim 20, whereinthe magnetic field generation unit includes a coil to which current is supplied and a magnetic core which extends toward the predetermined region from the coil, anda part of the magnetic core extends into an obscuration region of the extreme ultraviolet light collected by the collector mirror. 22. The extreme ultraviolet light generation apparatus of claim 21, wherein a coating film is formed on a surface of the magnetic core. 23. The extreme ultraviolet light generation apparatus of claim 21, whereinthe magnetic core is cylindrical with one end thereof being open, andthe ion collection unit is disposed at the other end of the magnetic core. 24. The extreme ultraviolet light generation apparatus of claim 23, wherein a coating film is formed on a surface of the ion collection unit. 25. The extreme ultraviolet light generation apparatus of claim 1, wherein the at least one optical element is a measuring unit for measuring extreme ultraviolet light emitted as the target material is irradiated with the laser beam inside the chamber.
	abstract	Methods, apparatuses, devices, and systems for creating, controlling, conducting, and optimizing fusion activities of nuclei. The controlled fusion activities cover a spectrum of reactions from aneutronic, fusion reactions that produce essentially no neutrons, to neutronic, fusion reactions that produce substantial numbers of neutrons.
	description	FIG. 1 shows schematically the first means of the detection apparatus of the invention. These consist of sensor means for sensing the garrma rays. (1) emitted by the source (2), a plurality of means for measuring the gamma-ray flux and means for analyzing the measured flux. The sensor means consist of a collimator (3) which has a scintillating crystal (4) on its rear face. Moreover, the plurality of means for measuring the flux of the gamma rays (1) are in the form of a multi-anode photomultiplier (5) having four anodes. To identify in which direction the radioactive source (2) lies with respect to the center of the detector, the collimator has: a central area (6) comprising a plurality of mutually parallel channels (7) perpendicular to the surface of said collimator; a peripheral area (8) comprising a plurality of divergent channels (9) which are at an angle with the channels (7) of the central area (6) which increases with their distance from said central area. As already mentioned the photomultiplier has four anodes defining four sectorsxe2x80x94North, South, East and Westxe2x80x94with respect to the center of the photomultiplier. Thus, the intensities measured by the various sectors of the photomultiplier are analyzed in the form of four points coded in terms of X and Y with respect to the center of the photomultiplier, thus determining the coordinates of the impacts detected in the four North, South, East and West registers. The apparatus also includes second means (not shown) capable of pin-pointing the radioactive emission source. These second means consist of mechanical means or imparting a movement to the apparatus and means capable of defining the central axis of the apparatus, especially in the form of a light ray. In this example, the detection apparatus is used to detect the sentinel node, labeled with 99 m technetium, especially within the context of breast cancer. During the intervention, the detection apparatus is placed a few centimeters above the region within which the radioactive node probably lies. In a first step, he means for analyzing the intensities measured by the photomultiplier process all of the signals output by the entire sensitive area of the crystal. What is obtained is a number of impacts on the four anodes, these being converted into electrical signals by the photomultiplier. These impacts are distributed within the fourxe2x80x94North, East, South and Westxe2x80x94registers, as shown in FIG. 3. The apparatus is moved by the mechanical means in the direction in which lies that sector whose activity or flux is greater than a minimum background noise threshold measured beforehand. Likewise, if two sectors have an activity greater than the background noise, the apparatus is moved in the direction intermediate between the two sectors until the measured fluxes are almost the same. If three or four sectors have a greater activity, the apparatus then processes only the impacts obtained in the central area of the crystal. To avoid having to reset the registers to zero at each movement of the apparatus, the setting-to-zero may take place at regular intervals, especially every two seconds. As already mentioned, the second step follows on automatically and is restricted to analyzing the central part of the crystal, thus making it possible to center the apparatus more precisely, but more slowly on the hot point, whatever the sources lying within the rest of the scan field. As long as the values of the North, East, South and West registers are unequal, the mechanical movement means are activated for movement in the direction of the sector corresponding to the register containing the maximum value. The four cardinal registers are reset to zero at shorter time intervals than in the initial phase. When the radioactive tissue or organ is in the center of the field, the values contained in the registers are equal to one another, which immobilizes the apparatus and generates a specific signal, for example an audible signal or a flashing light. However, it should be noted that the notion of equality between the register values, must take account of the fact that it results From the temporal accumulation of a number of radioactive disintegrations. These values are therefore subject to statistical fluctuations of the Poissonian type. It is therefore necessary to avoid any movement of the apparatus while it is in the central equilibrium position, and to define a difference threshold between the register below which it is probable that the equilibrium position has been achieved. For this purpose, a fifth register, denoted sigma, contains the sum of the four others. Once equilibrium has been achieved, the central axis of the detector is defined by a light beam of the laser type emitted by the systems (10, 11) shown in FIG. 1. The light beam indicates, on the surface of the skin or on the visible surface of the targeted tissues, the direction of provenance of the source, that is to say the direction in which the radioactive node lies. The system has the advantage of operating in real time, so that the light beam continuously indicates the direction in which the node lies, even in the case of possible displacement of the tissues pressed by the surgeon, for example when he makes an incision in the tissues, seals them, or changes the position of the retractors. As already mentioned, the apparatus of the invention can be applied to the detection of any tissue or organ fixing a radioactive source. This method of detection will be more particularly advantageous for the detection of sentinel nodes, especially within the context of breast cancers or The advantages of the invention are clearly apparent from the description. The ability of the apparatus to precisely locate a radioactive source, so as to minimize the surgical intervention, should in particular be noted.
	description	The present invention relates to a method of controlling grain boundary solubility of additives and a method of manufacturing a sintered nuclear fuel pellet using the same, and more particularly, to a method of controlling grain boundary solubility, wherein the compositional gradient of additives across the grain boundaries is maintained at a certain level by stepwise varying of an oxygen partial pressure during sintering of a uranium-based oxide green pellet mixed with one or more additives of a chromium (Cr)-compound, an aluminum (Al)-compound, and a yttrium (Y)-compound, and a method of manufacturing a sintered pellet having a large grain size using the same. Nuclear power plant uses heat generated by the nuclear fission of uranium. The nuclear fuel material currently in widest use is uranium oxide pellets. In a typical production process of the uranium oxide pellets, a lubricant is added to and mixed with a starting material of uranium oxide powder, and then pre-molded under a predetermined pressure, e.g., about 1 ton/cm2 to produce a slug. The slug is pulverized to obtain granules. Subsequently the lubricant is added to and mixed with the granules obtained and then compression-molded to form a compact, i.e., green pellets having a theoretical density (TD) of about 50%. The compact is sintered in a hydrogen-containing gas atmosphere to produce uranium oxide pellets. The uranium oxide pellets obtained as described above have a TD of about 95.5% and a grain size of 6 to 10 μm. Crystal grains of the nuclear fuel pellets are of an equiaxed polyhedron. Recently, nuclear fuel for high burn-up and long fuel cycle have been developed in order to enhance the economic operation of nuclear power plant and minimize the amount of spent nuclear fuel. A sintered nuclear fuel pellet having a large grain size can improve the integrity of a nuclear fuel rod under high burn-up conditions by preventing the external release of fission products having a gaseous phase or corrosiveness from the sintered fuel pellets. Also, deformation characteristics at high temperatures are improved when grain size increases. As a result, the safety of the nuclear fuel rod can be improved by effectively decreasing stress induced on a cladding by the sintered fuel pellets during an operation. For this reason, research has been conducted into manufacturing sintered uranium-based oxide pellets having a large grain size as sintered pellets used in a nuclear fuel rod for high burn-up or ultra high burn-up. Since grain growth is achieved by means of the transfer of materials through grain boundaries, it is important to increase a transfer rate of materials through grain boundaries during sintering in order to manufacture a sintered pellet having a large grain size. Methods of increasing a sintering temperature or using additive elements have been disclosed in order to increase a grain size during the manufacturing of a sintered nuclear fuel pellet. Methods of dissolving additive elements and forming a liquid phase having a fast diffusion rate at grain boundaries are disclosed for the using of the additive elements. The method of dissolving additive elements uses a phenomenon in which defects are formed when additive elements are dissolved in a uranium-based oxide and the transfer of materials is facilitated, such that a grain growth rate is increased. A method of sintering at low temperatures by dissolving surplus oxygen in UO2 is disclosed in U.S. Pat. No. 6,878,313 B2. In this patent, a process for decreasing a sintering temperature by increasing an oxygen partial pressure of a sintering gas to dissolve oxygen ions in UO2 lattices to form uranium (U) cation vacancies, and increasing a material transfer rate through the formed U cation vacancies is suggested. In addition, aluminum (Al), chromium (Cr), titanium (Ti), niobium (Nb), magnesium (Mg), vanadium (V), phosphorous (P), or silicon (Si) are known as additive elements. The additive elements are usually added in a range of a few ppm to a few tens of thousands of ppm, based on a weight ratio with respect to uranium cations in a sintered pellet, and the amounts of additive elements may differ according to the type of additive element. In the method of increasing a grain growth rate by forming defects through the dissolution of additives, an amount of additives has to be increased in order to obtain a defect concentration above a certain level. Also, defects in UO2 lattices formed by dissolution have a limitation of contributing to increase release rates of fission gases generated during irradiation in a reactor. That is, although a grain size is increased to suppress fission gas release, a suppressing effect on the fission gas release is offset due to an increase in a diffusion rate of fission product in the UO2 lattices. According to the results of studies by Killeen et al. [Journal of Nuclear Materials, 88 (1980), p. 177-184] and Kashibe et al. [Journal of Nuclear Materials, 254 (1998), p. 234-242], it is reported that Cr ions were dissolved in a UO2 pellet to exhibit a grain growth effect, but a suppressing effect on fission gas release was low due to an increase in a diffusion rate of a fission gas caused by defect formation in UO2 lattices. To overcome the foregoing limitation, methods for removing surplus oxygen by heat treating in a reducing atmosphere at a temperature lower than a sintering temperature or minimizing lattice defects by precipitating dissolved metal cations in a metal form are disclosed in U.S. Pat. Nos. 6,878,313 B2 and 6,221,286 B1, respectively. Technologies related to the methods of increasing a grain size by allowing additive elements to form a liquid phase at grain boundaries near a sintering temperature are reported. In U.S. Pat. No. 4,869,866, a technology for manufacturing sintered UO2 having an average grain size of 37 μm by sintering at 1640° C. for 7 hours after adding 0.5 wt % of an alumino-silicate additive is disclosed. According to this patent, it is reported that the alumino-silicate additive forms a liquid phase at grain boundaries near a sintering temperature and grain growth occurs by considerably accelerating material transfer through the liquid phase. Bourgeois et al. [Journal of Nuclear Materials, 297 (2001), p. 313-326] report that when an oxygen partial pressure of a sintering gas is controlled to a specific value during the manufacturing of Cr-added sintered UO2, a Cr-compound additive forms a liquid phase during sintering to greatly increase the grain size of the sintered UO2. U.S. Pat. No. 6,221,286 B1 suggests a process, in which a Cr2O3-added UO2 green pellet is sintered in an oxygen partial pressure interval where a liquid phase is formed, and then, dissolved Cr is precipitated into Cr metal particles by annealing at low temperatures and low oxygen partial pressures. In the case of a process using a liquid phase, a grain size is determined by an amount of a liquid phase formed at grain boundaries, and since a portion of additives is dissolved before reaching a liquid phase formation temperature or a portion of the liquid phase is dissolved in grain interiors during liquid phase sintering, a large amount of additives may be necessary to obtain grains of a desired size. For example, a detailed method of manufacturing a Cr-added sintered UO2 having a large grain size disclosed in U.S. Pat. No. 6,221,286 B1 is as follows. A sintered pellet is manufactured by sintering a Cr2O3-added uranium oxide green pellet at 1700° C. for 4 hours in a wet hydrogen gas atmosphere having a moisture/hydrogen gas ratio of 1.7%, and then, a sintered nuclear fuel pellet with precipitated Cr is manufactured by annealing the sintered pellet at 1300° C. for 5 hours in a dry hydrogen gas atmosphere having a moisture/hydrogen gas ratio of 0.05% or less. In the foregoing method, the added Cr2O3 maintains a Cr2O3 phase while the temperature of the green pellet is increased to near 1680° C., and dissolution occurs in a portion of the added Cr2O3. A portion of the Cr2O3, remaining without dissolution, contributes to grain growth by forming a liquid phase at 1680° C. or more. Thereafter, dissolved Cr is precipitated into Cr metal particles in a low temperature annealing process. Since a large amount of initially added Cr2O3 is dissolved before the forming of a liquid phase and only a portion contributes to grain growth, a large additive amount more than 1000 ppm is necessary. When a grain size of a uranium-based oxide is increased by using additives, it is necessary to minimize an amount of the additives for obtaining the same grain size if possible. The reason is that the additive elements increase diffusion rates of fission products by dissolving UO2 lattice as well as reducing neutron economic by lowering an amount of a U charge or absorbing neutrons. Therefore, developments of new technologies capable of significantly increasing a grain size as well as minimizing an amount of additives are necessary. A method, which improves a grain growth effect by maximizing an amount of a liquid phase existing at a sintering temperature through maximally suppressing dissolution of additives while the temperature of a green pellet is increased to the sintering temperature, is disclosed in Korean Patent No. 10-0964953. This patent is characterized in that an added Cr-compound is reduced to Cr at 1500° C. or less and a Cr phase is maintained. Thereafter, a process of sintering at 1650-1780° C. in a gas atmosphere having an oxygen potential of forming a Cr liquid phase is included. A sintered pellet manufactured by the foregoing process may have a larger grain size because an amount of a liquid phase formed during sintering based on the same addition amount is greater in comparison to a sintered pellet manufactured by the process suggested in U.S. Pat. No. 6,221,286 B1. However, the process suggested in Korean Patent No. 10-0964953 has a limitation in that the additive liquid phase formed is rapidly dissolved into UO2 lattices because oxygen partial pressure rapidly increases at a high sintering temperature. According to the results of a study by A. Leenaers et al. [Journal of Nuclear Materials, 317 (2003), p. 62-68], it is reported that the solubility of Cr ions in UO2 lattices rapidly increases when temperature and oxygen partial pressure increase at 1550° C. or more. Therefore, the process suggested in Korean Patent No. 10-0964953 has limitations in that duration time of liquid phases formed at grain boundaries is too short to completely contribute to grain growth, and more than a certain amount of additives is necessary. An aspect of the present invention provides a method of controlling solubility of additives dissolved at and near grain boundaries during sintering of a uranium-based oxide green pellet including additives with solubility in a uranium-based oxide varied according to an oxygen partial pressure of a sintering gas, and a method of manufacturing a sintered nuclear fuel pellet having a large grain size using the same. An aspect of the present invention provides a method of controlling a solubility of additive elements at and near grain boundaries, wherein the solubility of the additives at and near the grain boundaries is maintained at a certain level by stepwise varying of an oxygen partial pressure during isothermal sintering of a uranium-based oxide green pellet including an additive powder of elements. The oxygen partial pressure may be stepwisely increased during the isothermal sintering. According to another aspect of the present invention, there is provided a method of manufacturing a sintered nuclear fuel pellet having a large grain size including: mixing an additive powder and a uranium oxide powder to prepare an additive mixed uranium oxide powder; forming an additive mixed uranium oxide green pellet by using the mixed powder; heating the green pellet to an isothermal sintering temperature in an atmosphere control gas having an oxygen partial pressure corresponding to a minimum oxygen partial pressure of isothermal sintering or less; and changing a sintering gas atmosphere to perform the isothermal sintering such that an oxygen partial pressure is stepwise increased at the isothermal sintering temperature. An amount of additive cations with respect to about 1 g of uranium-based cations in the uranium oxide green pellet may be about 10-2000 μg. The additive powder may be a powder mixed with at least one or more of a chromium (Cr)-compound, an aluminum (Al)-compound, and a yttrium (Y)-compound. Also, the Cr-compound, the Al-compound, and the Y-compound may be at least one or more selected from the group consisting of oxides, nitrates, stearates, chlorides, and hydroxides. In the preparing of the additive mixed uranium oxide powder, a UO2-based powder may be a UO2 powder or a powder mixed with the UO2 powder and one or more of a PuO2 powder, a Gd2O3 powder, and a ThO2 powder. The atmosphere control gas may be a hydrogen gas or a mixed gas of a hydrogen gas and at least one or more gases selected from the group consisting of carbon dioxide, water vapor, and inert gases. When a method of manufacturing a sintered pellet according to the present invention is used, a decrease in a driving force for grain growth during sintering is minimized so that a sintered pellet having a larger grain size than a typical sintered pellet may be manufactured by using the same amount of additives. Also, release of fission products during irradiation in a reactor is prevented and deformation characteristics at high temperatures are improved by manufacturing a sintered pellet having a large grain size. Therefore, there is an effect of improving the integrity and safety of a nuclear fuel rod for high burn-up. Hereinafter, the present invention will be described in detail. Among sesquioxides containing trivalent cations, for example, Al2O3, Cr2O3, Y2O3, and Al2O3 have a similar tendency to one another, in which solubility in UO2 lattices increases as an oxygen partial pressure increases. Also, grain boundary solubility of the sesquioxides increases as an oxygen partial pressure increases. Since a grain boundary has more defects than a lattice, the grain boundary has a higher solubility limit than the lattice in a grain. Also, since a driving force of grain growth may become high when the concentration differences of additives between at a grain boundary and a lattice are large, the large difference between at a grain boundary and a lattice may be advantageous for grain growth. Therefore, when grain boundary solubility of additives at grain boundary to in grain is denoted to C and the grain boundary solubility of additives is denoted as B, a growth rate of grains becomes large in a condition where B and C are large at the same time. FIG. 1 is a schematic diagram illustrating a change of an additive concentration across a grain boundary in terms of an oxygen partial pressure of a sintering gas during isothermal sintering of a uranium-based oxide green pellet, which contains additives including sesquioxides, such as Cr2O3 and Y2O3 having solubility increased with increasing oxygen partial pressure. As shown in FIG. 1(b), when sintered at a low oxygen partial pressure, solubility of the additives is very low at a grain boundary as well as in an interior of a lattice. Since B is low, although C may be maintained at a certain level, a very small amount of the additives may participate in grain growth. Therefore, grain growth may be difficult in this case. As shown in FIG. 1(c), when an oxygen partial pressure of a sintering gas is increased, grain growth may be promoted to a certain extent because B becomes high. However, since C also becomes gradually low when the additives concentration at grain boundary soon reaches a solubility limit and lattice diffusion of additives occurs, a driving force for grain growth will be gradually decreased. This may be also confirmed in Korean Patent No. 10-0964953, in which grain growth is actively performed at an oxygen partial pressure of forming a liquid phase disclosed in a Cr-containing UO2 sintering process, because B and C are simultaneously high at the time of the forming of a liquid phase during sintering of Cr-containing UO2. However, the additives in liquid phase thereafter diffuse fast into the interiors of grains to thereby end grain growth. According to the present invention, it may be understood that B and C may always be maintained above particular values during sintering in order to maximize grain growth during sintering of a uranium-based oxide green pellet containing additives including sesquioxides such as Cr2O3 and Y2O3 having solubility increased with increasing oxygen partial pressure. The maintaining of B and C above the particular values may be achieved through a method of a stepwise increase of an oxygen partial pressure of a sintering gas during isothermal sintering. That is, grain boundary solubility increases as an oxygen partial pressure is gradually increased, and thus, an amount of additives, which is larger than an amount of additives diffused from grain boundaries to the interiors of grains, will be continuously supplied to the grain boundaries. Therefore, as shown in FIG. 1(a), since B and C are maintained at high values and a decrease in a driving force of grain growth during sintering may be minimized, a sintered pellet with a grain size larger than a typical sintered pellet may be manufactured when the same amount of additives is used. In summary, in the sintering of a uranium-based oxide green pellet including additive powder of elements, it is possible to maintain concentration and compositional gradient of the additive elements at and near grain boundaries at a certain level by the stepwise varying of an oxygen partial pressure during isothermal sintering. More particularly, it is possible to maintain a solubility gradient capable of manufacturing a sintered nuclear fuel pellet having a large grain size if an oxygen partial pressure during the isothermal sintering is always increased. Also, a sintered nuclear fuel pellet having a large grain size may be manufactured when the foregoing solubility controlling method is used, thereby enabling an improvement in the integrity of a nuclear fuel rod for high burn-up. Hereinafter, a method of manufacturing a sintered nuclear fuel pellet according to the present invention is described. Additive mixed uranium oxide powder is prepared, and then, uranium oxide green pellets with mixed additives are formed by using the foregoing mixed powder. Subsequently, the green pellets are heated to a sintering temperature in a gas atmosphere with a low oxygen partial pressure, and then, sintered nuclear fuel pellets having a large grain size are manufactured by sintering the pellets while varying the sintering gas atmosphere in order to increase an oxygen partial pressure at an isothermal sintering temperature in a stepwise manner. An additive content of the uranium oxide powder may be about 50-2000 μg/g based on a weight ratio (ΣMi/U) of additive cations or metal elements with respect to uranium of the uranium oxide powder. When a sintered nuclear fuel pellet is manufactured with manufacturing conditions according to the present invention, grains are grown while a solubility limit is gradually increased by controlling an oxygen partial pressure during sintering. Therefore, a sufficient grain growth effect may be obtained even when a very small amount of additives is used as above. The preparing of the additive mixed uranium oxide powder may be performed by a method of mixing or grinding the uranium oxide powder and additive powder. The forming of the green pellets may be performed by a method of putting the additive mixed uranium oxide powder in a forming mold and molding at a pressure of about 3-5 tons/cm2. Among sesquioxides containing trivalent cations, for example, Al2O3, Cr2O3, Y2O3, and Al2O3 have a similar tendency to one another, in which solubility in UO2 lattices increases as an oxygen partial pressure increases. Also, grain boundary solubility of the sesquioxides increases as an oxygen partial pressure increases, and the foregoing additive powder may have a relatively low neutron absorption cross-section. Therefore, the additive powder may be a powder mixed with at least one or more of a chromium (Cr)-compound, an aluminum (Al)-compound, and a yttrium (Y)-compound. The Cr-compound, the Al-compound, and the Y-compound may be at least one or more selected from the group consisting of oxides, nitrates, stearates, chlorides, and hydroxides. In the preparing of the additive mixed uranium oxide powders, UO2-based powder may be UO2 powder or a powder mixed with the UO2 powder and at least one or more of PuO2 powder, Gd2O3 powder, and ThO2 powder. In the sintering, an atmosphere control gas used to increase an oxygen partial pressure may be a hydrogen gas or a mixing gas of a hydrogen gas and at least one or more gases selected from the group consisting of carbon dioxide, water vapor, and inert gases. Hereinafter, the present invention will be described in more detail by means of Examples. The following Examples only exemplify the present invention, but the scope of the present invention is not limited thereto. About 1500 μg/g of Cr2O3 powder based on a Cr/U was added to UO2 powder and was wet ground, and then, Cr2O3 mixed UO2 powder was prepared by drying the ground powder. Cylindrical green pellets were manufactured by press molding the mixed powder at a pressure of about 3 tons/cm2. The green pellets were subjected to sintered pellet manufacturing processes of the following Table 1 and then, grain sizes were measured and presented in Table 1. The densities of sintered pellets were measured by Archimedes method. Thereafter, cross-sections of the pellets were polished to observe a pore structure, and also thermally etched to observe a grain structure. The grain size of the pellets was measured by a linear intersection method. Also, as an example of the present invention, a sintering process of Example 1 was presented in FIG. 2. In the sintering process of the foregoing green pellets, a hydrogen atmosphere having a low oxygen partial pressure at which Cr2O3 is reduced to Cr is maintained up to a sintering temperature of about 1700° C. The reason for this is to prevent the foregoing C value from being lowered during isothermal sintering by minimizing a dissolving rate of Cr ions in UO2 lattices. In the foregoing sintering process, a mixing ratio of CO2 in hydrogen is stepwise increased in order to stepwise increase an oxygen partial pressure of a sintering gas in an isothermal sintering range of about 1700° C. The foregoing B and C values are always maintained above a certain level of values when the mixing ratio is increased as above, thereby enabling an effect of maximizing grain growth to be obtained. Also, micrographs of grains in the respective Example and Comparative Examples were observed, and the results thereof were presented in FIGS. 3A and 3B. FIG. 3A is a micrograph of grains of Example 1, and (B-1), (B-2), (B-3), and (B-4) of FIG. 3B are micrographs of grains in Comparative Examples 1, 2, 3, and 4, respectively. TABLE 1GrainSintered pellet manufacturing processSizeExample 1Maintain for 1MaintainMaintainMaintainCool to room130 μm hour afterfor 2 hoursfor 2 hoursfor 2 hourstemperatureheating toat 0.3at 1at 1.6(300° C./h)1700° C. at avolume %volume %volume %rate ofof CO2/H2of CO2/H2of CO2/H2300° C./h ingas ratiogas ratiogas ratioan atmosphereof 0.05volume % orless of CO2/H2gas ratioComparativeMaintain for 6 hours after heating to 1700° C. at a rate of17 μmExample 1300° C./h at 0.3 volume % or less of moisture/H2 gas ratioComparativeMaintain for 4 hours after heating to 1700° C. at a rate of34 μmExample 2300° C./h at 1.0 volume % or less of moisture/H2 gas ratioComparativeMaintain for 4 hours after heating to 1700° C. at a rate of45 μmExample 3300° C./h at 1.6 volume % or less of moisture/H2 gas ratioComparativeHeating up to 1700° C. at aMaintain for 6 hours at62 μmExample 4rate of 300° C./h at 0.051.6 volume % of CO2/H2volume % or less of CO2/H2gas ratiogas ratio When grain sizes in Example 1 and Comparative Examples 1 to 4 in Table 1 are compared, it may be confirmed that the grain size of Example 1 is 130 μm, which is increased about 2-9 times in comparison to the grain sizes of Comparative Examples 1 to 4. Differences between Example 1 and Comparative Examples 1 to 4 may be easily confirmed through the micrographs of grain sizes in FIGS. 3A and 3B. Referring to (B-1) of FIG. 3B and Table 1, the grain size of Comparative Example 1 is 17 μm, which represents a smaller grain size of about 119 times or less than that of Example 1. It may be understood that Comparative Example 1 has the smallest grain size among the Comparative Examples. Referring to (B-2) of FIG. 3B and Table 1, the grain size of Comparative Example 2 is 34 μm, which represents a smaller grain size of about ⅕ times or less than that of Example 1. On the other hand, it may be confirmed that the grain size of Comparative Example 2 increased about 2 times in comparison to that of Example 1. Since a sintered pellet was manufactured under a moisture/hydrogen gas ratio condition of 1.0 volume % in Comparative Example 2 while the moisture/hydrogen gas ratio in Example 1 was 0.3 volume %, the solubility of Cr becomes high as an oxygen partial pressure increases. As a result, it is considered that a grain size increases due to a fast material transfer rate. Referring to (B-3) of FIG. 3B and Table 1, the grain size of Comparative Example 3 is 45 μm, which represents a smaller grain size of about ⅓ times or less than that of Example 1. On the other hand, the grain size of Comparative Example 3 increased by about 3 times in comparison to that of Example 1. The reason is that a Cr additive forms a liquid phase in a sintering gas atmosphere to increase a material transfer rate. Referring to (B-4) of FIG. 3B and Table 1, the grain size of Comparative Example 4 is 62 μm, which represents a smaller grain size of about ½ times or less than that of Example 1. On the other hand, the grain size of Comparative Example 4 increased about 3.5 times or more in comparison to that of Example 1. Even though Comparative Example 4 was performed for the purpose of increasing an amount of a liquid phase by maximally preventing Cr from dissolving in UO2 during heating to a sintering temperature, the liquid phase is dissolved fast into grain boundaries during sintering. As a result, the grain size of Comparative Example 4 is small in comparison to Example 1. Therefore, it may be understood that properly controlling a concentration of Cr dissolved at grain boundaries and a concentration of Cr dissolved in grains during sintering, as in Example 1, is very effective in increasing a grain size. About 500 μg/g of Cr2O3 powder based on a Cr/U was added to UO2 powder and was wet ground, and then, Cr2O3 mixed UO2 powder was prepared by drying the ground powder. Processes of manufacturing green pellets and sintered pellets by using the ground powder were performed using the same method as that of Example 1. Densities and grain sizes were measured, and micrographs of grains were observed and the result thereof was presented in FIG. 3C. The grain size of Example 2 was measured as 46 μm, which is similar to Comparative Example 3 having a grain size of 45 μm. When Example 2 and Comparative Example 3 are compared, about 500 μg/g of Cr2O3 powder was added in Example 2 while about 1500 μg/g of Cr2O3 powder was added in the case of Comparative Example 3. Therefore, it is confirmed that a similar grain size may be obtained by adding a small additive amount, i.e., about ⅓ of a typical additive amount, when a sintered pellet is manufactured by a manufacturing method according to the present invention. While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
	description	FIG. 1 is a sectional schematic view of a passive decay heat removal system 10 for a pool type liquid metal nuclear reactor 12. Nuclear reactor 12 includes a reactor primary vessel 14 consisting of a cylindrical tank positioned with the longitudinal axis extending vertically upward, and having an open upper end 16 attached to and covered by a shield deck 18. Reactor primary vessel 14 contains a pool of liquid metal coolant 20, such as sodium metal, with a heat producing core of fissionable fuel material 22 substantially submerged within liquid metal pool 20. The rate of fission of the fuel material is governed by neutron absorbing control rods (not shown) that move into and out of the fuel core 22. Reactor primary vessel 14 is enclosed within a concentrically surrounding containment vessel 24 in a spaced apart relationship. A space 26 between reactor primary vessel 14 and containment vessel 24 is sealed and is typically filled with a relatively inert gas such as nitrogen or argon. A baffle cylinder 28 concentrically encircles substantially the length of containment and reactor vessels 24 and 14 in spaced apart relation to an outer wall 30 of containment vessel 24. A guard vessel 32 concentrically surrounds baffle cylinder 28 in spaced apart relation to outer wall 34 of baffle cylinder 28. Baffle cylinder 28 extends downward between containment vessel 24 and guard vessel 32 substantially to a bottom portion of reactor primary vessel 14, with baffle cylinder terminating a short distance above the bottom 36 of guard vessel 32. Thus, baffle cylinder 28 provides for fluid communication below a lower end 38 between a space 40 intermediate guard vessel 34 and cylindrical baffle 28 and a space 42 intermediate baffle cylinder 28 and containment vessel 24. Guard vessel 32 includes a support skirt 44 which rests on base mat 46. Guard vessel 32 also includes an upper support flange 48. A plurality of shield deck support pillars 50 extend between upper support flange 48 and shield deck 18 which enable shield deck 18 to be supported by base mat 46 and guard vessel 32. Reactor 12 also includes an ambient air inlet conduit 52, in fluid communications with space 40, and an air outlet conduit 54, in fluid communications with space 42. Passive decay heat removal system 10 combines air inlet conduit 52, space 40, space 42 and air outlet conduit 54. Passive decay heat removal system 10 removes heat produced by reactor core 22. In operation, heat produced by reactor core 22 is conveyed outward from core 22 to reactor primary vessel 14 by the natural convection of liquid metal coolant 20. The heat is then transferred mainly by thermal radiation across inert gas containing space 26 to containment vessel 24. The heat is absorbed by air contained in space 42 which is in contact with containment vessel 24 and is carried along in an upward air flow resulting from the added heat inducing a natural draft within space 42 and outlet conduit 54. The natural draft causes fresh air to be drawn into inlet conduit 52, through spaces 40 and 42, and out through outlet duct 54. FIG. 2 is a sectional schematic view of a top entry loop (TEL) type liquid metal nuclear reactor 60 in accordance with one embodiment of the present invention. A TEL type reactor includes a group of separated primary coolant containing vessels with each performing a specific role or function. Specifically, reactor 60 includes a primary unit 62 containing a reactor core (not shown) for producing energy, a pump unit 64 for inducing circulation of the liquid metal coolant, and a heat exchanger unit 66 for transferring the produced heat carried by the primary liquid metal coolant to a non-radioactive secondary coolant used to generate steam to drive a turbine generator to produce electricity. Similar to reactor 12 described above, primary unit 62 includes a reactor primary vessel enclosed within a concentrically surrounding containment vessel 68 in a spaced apart relationship. A baffle cylinder 70 concentrically encircles substantially the length of containment vessel 68 in spaced apart relation. A guard vessel,72 concentrically surrounds baffle cylinder 70 in spaced apart relation. Spaces 74 and 76 are formed between guard vessel 72 and baffle cylinder 70 and between containment vessel 68 and baffle cylinder 70 respectively. Spaces 74 and 76 are in fluid communications with each other at a lower end 78 of baffle cylinder 70. Pump unit 64 and heat exchanger unit 66 have similar construction. Particularly, pump unit 64 includes a pump vessel enclosed in a pump containment vessel 80, a baffle cylinder 82 concentrically encircling the length of containment vessel 80 and a guard vessel 84 concentrically surrounding baffle cylinder 82 in spaced apart relation. Spaces 86 and 88 are formed between guard vessel 84 and baffle cylinder 82 and between containment vessel 80 and baffle cylinder 82 respectively. Spaces 86 and 88 are in fluid communications with each other at a lower end 90 of baffle cylinder 82. Heat exchanger unit 66 includes a heat exchanger vessel enclosed in a containment vessel 92, a baffle cylinder 94 concentrically encircling the length of containment vessel 92 and a guard vessel 96 concentrically surrounding baffle cylinder 94 in spaced apart relation. Spaces 98 and 100 are formed between guard vessel 96 and baffle cylinder 94, and between containment vessel 92 and baffle cylinder 94 respectively. Spaces 98 and 100 are in fluid communications with each other at a lower end 102 of baffle cylinder 94. Spaces 74, 86, and 98 are in fluid communications with each other at an upper end 104 of units 62, 64, and 66. Spaces 76, 88, and 100 are in fluid communications with each other at upper end 104 of units 62, 64, and 66. Primary coolant containing vessels 62, 64, and 66 are housed in a concrete reactor vault 106. Typically, concrete vault 106 is located substantially underground so that primary vessels 62, 64, and 66 are below ground level. Units 62, 64, and 66 are attached to and covered by a shield deck 108. Guard vessels 72, 84, and 96 include support skirts 109, 110, and 112 respectively which rest on seismically isolated base mat 114. Guard vessels 72, 84, and 96 are coupled to and support shield deck 108. Flow passages are provided in guard vessels 72, 84, and 96 to permit horizontal air flow in air inlet 116 and air outlet 118 plenums. Reactor units 62, 64, and 66 are connected by a plurality of top entry loops 115 which permit the flow of liquid metal coolant between units 62, 64, and 66. Reactor 60 also includes a plurality of ambient cooling air inlet conduits 116 (one shown) which are in fluid communications with spaces 74, 86, and 98, and a plurality of air outlet conduits 118 (one shown) which are in fluid communication with spaces 76, 88, and 100. Each ambient inlet conduit 116 and each air outlet conduit 118 is coupled to a regenerative air-to-air heat exchanger 120. Heat exchangers 120 transfers a portion of the heat carried by the air flowing through outlet conduits 118 to the ambient air flowing through inlet conduits 116 to raise the temperature of the inlet air so that the air is above the dew point. By maintaining the temperature of the cooling air above the dew point, any moisture carried by the air will not condense on the reactor components. Therefore, an essential element in the corrosion process, the electrolyte, is not present in the reactor decay heat removal system that includes inlet and outlet conduits 116 and 118, and spaces 74, 76, 86, 88, 98, and 100. Without an electrolyte present, the potential for corrosion is greatly reduced. Reactor 60 also includes a passive reactor vault cooling system to remove heat from reactor vault 106. A plurality of ambient air inlets 124 (one shown) are in fluid communications with a space 126 formed by concrete vault 106 and guard vessels 72, 84, and 96. Also a plurality of air outlets 128 (one shown) are in fluid communications with space 126. Air inlet conduits 124 direct ambient cooling air into space 126 where the air absorbs heat by contacting guard vessels 72, 84, and 96 and then removes the heat by exiting space 126 through air outlet conduits 128. Air inlet conduits 124 and air outlet conduits 128 are configured in a co-axial arrangement with each outlet conduit 128 positioned inside and co-axial with inlet conduit 124. Heat is transferred from the air flowing in outlet conduit 128 through an outlet conduit wall 129 to the ambient air flowing in inlet conduit 124 to raise the temperature of the incoming air above the dew point. Decay heat is removed from reactor 60 by a passive decay heat removal system 130 which includes air inlet conduits 116, spaces 74, 76, 86, 88, 98, and 100, air outlet conduits 118 and regenerative heat exchangers 120. Heat generated in primary unit 62 is transferred by thermal radiation to containment vessels 68, 80, and 92 from the liquid metal coolant circulating within primary coolant vessels 62, 64, and 66. The heat is absorbed by air contained in spaces 76, 88, and 100 which are in contact with containment vessels 68, 80, and 92 respectively and is carried along in an upward air flow resulting from the added heat inducing a natural draft within spaces 76, 88, and 100 and outlet conduits 118. The natural draft causes fresh air to be drawn into inlet conduits 116, through spaces 74, 86, 98, heated in spaces 76, 88, and 100, and out through outlet conduits 118. A portion of the heat carried in outlet conduits 118 is transferred to the incoming air in inlet conduits 116 by regenerative heat exchangers 120. Reactor vault 106 is similarly cooled by ambient air entering through vault inlet conduits 124 flowing through space 126 and exiting through vault outlet conduits 128. Incoming air is maintained above the dew point by the transfer of heat from outlet conduit 128 to inlet conduit 124 because of the co-axial arrangement of inlet and outlet conduits 124 and 128. In other embodiments, inlet and outlet conduits 114 and 116 can be in co-axial arrangement to transfer heat to the incoming air to raise its temperature above the dew point instead of using heat exchangers 120. Also vault inlet and outlet conduits 124 and 128 can pass through a regenerative heat exchanger rather than be in a co-axial arrangement to transfer heat to the incoming air. In the unlikely event of a double vessel leak, for example where both the reactor vessel and containment vessel 68 leak, air inlet damper 121 and air outlet damper 122 can be closed to prevent burning of the sodium coolant and prevent a radioactive release. In this event, decay heat is removed from reactor system 60 by reactor vault 106 air inlet 124 and air outlet 128. FIG. 3 is a sectional schematic view of a liquid metal nuclear reactor 150 and FIG. 4 is a top schematic view of liquid metal nuclear reactor 150 in accordance with another embodiment of the present invention. Reactor 150 is a pool type liquid metal reactor that includes a plurality of primary reactor units 152 and a plurality of corresponding steam generator units 154 coupled to primary units 152 by liquid metal circulating conduits 156. Primary units 152 and steam generator units 154 are located in a concrete vault 158. Similar to reactor 12 described above, reactor primary units 152 each include a primary reactor vessel enclosed within a concentrically surrounding containment vessel 160 in a spaced apart relationship. A baffle cylinder 162 concentrically encircles substantially the length of containment vessel 160 in spaced apart relation. A guard vessel 164 concentrically surrounds baffle cylinder 162 in spaced apart relation. Spaces 166 and 168 are formed between guard vessel 164 and baffle cylinder 162 and between containment vessel 160 and baffle cylinder 162 respectively. Spaces 166 and 168 are in fluid communications with each other at a lower end 170 of baffle cylinder 162. Reactor units 152 are attached to and covered by a shield deck 172. Guard vessels 164 includes a support skirt 174 which rests on seismically isolated base mat 176. Guard vessels 164 are coupled to and support shield deck 172. Reactor 150 also includes ambient air inlet conduit 173, in fluid communications with space 166, and an air outlet conduit 178, in fluid communications with space 168. Reactor 150 also includes a passive reactor vault cooling system to remove heat from the reactor vault 158. A plurality of ambient air inlet conduits 182 are in fluid communications with a space 184 formed by concrete vault 158 and guard vessels 164. Also a plurality of air outlet conduits 186 are in fluid communications with space 184. Air inlet conduits 182 direct ambient cooling air into space 184 where the air absorbs heat by contacting guard vessels 164 and then removes the heat by exiting space 184 through air outlet conduits 186. Air inlet conduits 182 and air outlet conduits 186 are configured in a co-axial arrangement with each outlet conduit 186 positioned inside and co-axial with a corresponding inlet conduit 182. Heat is transferred from the air flowing in outlet conduit 186 through an outlet conduit wall 188 to the ambient air flowing in inlet conduit 182 to raise the temperature of the incoming air above the dew point. In the event of a double vessel leak, decay heat removal is maintained by closing an inlet damper 175 and an outlet damper 177, located in inlet conduit 173 and outlet conduit 178 respectively, and permitting the reactor vault cooling system to remove the decay heat by convection from guard vessel 164, as described above. In an alternate embodiment, the liquid metal reactor does not include a third or guard vessel and decay heat is removed by air circulating through the space between the containment vessel and cylindrical baffle 28. The air inlets include regenerative heat exchangers as described above. The above describe liquid metal reactors 60 and 150 eliminate the potential for corrosion within the spaces and structures which guide outside air past the reactor containment vessels to transfer reactor core decay heat from reactors 60 and 150 to the ambient air outside reactors 60 and 150 by utilizing the removed heat to raise the temperature of the incoming air above the dew point. The heat is transferred by air-to-air heat exchangers 120 or by a co-axial arrangement of the air inlet and air outlet conduits in reactors 60 and 150. Also, in the event that both the reactor and containment vessels fail, decay heat will continue to be removed, and a radiological release from reactors 60 and 150 will be prevented by closing inlet dampers 121 and 175, and outlet dampers 122 and 177 respectively. Decay heat removal following such a double vessel leak is provided by the reactor vault cooling system which is designed to permit convective cooling of the guard vessel which has been filled with sodium due to the double vessel breach. A radiological release through the inlet and outlet conduits is prevented by closing the inlet and outlet dampers to seal the system and extinguish a possible sodium pool fire by preventing oxygen and water vapor from reaching the sodium pool. Also, reactors 60 and 150 provide a lower cost method of supporting the reactor deck from which the primary vessel(s) are hung. While the invention has been described and illustrated in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
	abstract	A storage basket for radioactive materials, defining housings parallel to each other and each extending along a housing axis parallel to a longitudinal central axis of the basket, the latter including: a plurality of transverse plates, traversed by a plurality of openings; a plurality of housing tubes arranged parallel to the longitudinal central axis of the basket. The housing tubes are arranged in alternation with the transverse plates along the axis, such that the inner lateral surface of each housing is defined, successively along this axis, at least by the inner surface of a first housing tube, the inner surface of one of the openings of a first transverse plate, and the inner surface of a second housing tube.
	claims	1. A method of raster scanning a sample on a continuously moving stage for charged-particle beam imaging said sample, comprising:line scanning a charged-particle beam across a surface of said sample repeatedly to form thereon at least one 2-dimensional line array composed of a plurality of scan lines lying adjacent to each other, each line array having a parallelogram shape with one of its parallel-edge pairs (or extension lines thereof) intersecting the axis of stage movement, the distance along the axis of stage movement between the intersection points being referred to as the image width,wherein when each line scan is to be performed, said charged-particle beam is shifted, along the stage-moving direction, by an extra predefined distance at least equal to a distance of said stage travel during a time period from the beginning of the first line scan of the first formed line array to the beginning of the current line scan to be performed of the current line array being formed, andwherein said at least one line array forms an image of said sample surface. 2. The method of claim 1, further comprising after said image is formed, directing said charged-particle beam to the beginning position of the first line scan of the next image to be formed. 3. The method of claim 2, wherein the moving speed of said stage is less than said image width divided by a time period from the beginning of the first line scan of the previous said image formed to the beginning of the first line scan of the next image to be formed. 4. The method of claim 2, wherein the moving speed of said stage is substantially equal to said image width divided by a time period from the beginning of the first line scan of the previous image formed to the beginning of the first line scan of the next image to be formed. 5. The method of claim 2, wherein the moving speed of said stage is greater than said image width divided by a time period from the beginning of the first line scan of the previous image formed to the beginning of the first line scan of the of the next image to be formed. 6. The method of claim 1, wherein lines of said parallel-edge pair (or extensions thereof) intersecting the axis of stage movement have a larger incident angle with the axis of stage movement than lines of the other parallel-edge pair of said parallelogram. 7. The method of claim 1, wherein the line-scan direction is parallel to the stage-moving direction. 8. The method of claim 1, wherein the line-scan direction is perpendicular to the stage-moving direction. 9. The method of claim 1, wherein the line-scan direction is at an angle with the stage-moving direction, said angle falling in a range of 0 to 180 degrees but excluding 0, 90 and 180 degrees. 10. The method of claim 1, further comprising repeatedly line scanning said charged-particle beam across a same position of line on said sample at least two times,wherein when each of said at least two line scans is to be performed, said charged-particle beam is shifted, along the stage-moving direction, by an extra predefined distance at least equal to a distance of said stage travel during a time period from the beginning of the first line scan of the first formed line array to the beginning of the current line scan to be performed of the current said line array being formed. 11. A charged-particle beam imaging system, comprising:a charged-particle beam provider for providing a focused charged-particle beam;a deflection module for scanning said charged-particle beam across a surface of a sample to be imaged;a moving stage whereupon said sample is secured for imaging; anda control module coupled with said stage and said deflection module for coordinating the motion of said stage and said charged-particle beam, such that said charged-particle beam is scanned across a surface of said sample repeatedly to form thereon at least one 2-dimensional line array composed of a plurality of scan lines lying adjacent to each other, each line array having a shape of a parallelogram with lines of one of its parallel-edge pairs or extensions thereof intersecting the axis of stage movement, thereby defining a width on the axis between the intersection points,wherein when each line scan is to be performed, said charged-particle beam is shifted, along the stage-moving direction, by an extra predefined distance at least equal to one said stage traveled during a time period from the beginning of the first line scan of the first formed said line array to the beginning of the current line scan to be performed of the current said line array being formed, andwherein said at least one line array forms an image of said sample surface. 12. The charged-particle beam imaging system of claim 11, wherein after said image is formed the system is configured to direct said charged-particle beam to the beginning position of the first line scan of the next image to be formed on said sample surface. 13. The charged-particle beam imaging system of claim 12, wherein the moving speed of said stage is less than said width divided by a time period from the beginning of the first line scan of the previous said image formed to the beginning of the first line scan of the next image to be formed. 14. The charged-particle beam imaging system of claim 12, wherein the moving speed of said stage is substantially equal to said width divided by a time period from the beginning of the first line scan of the previous said image formed to the beginning of the first line scan of the next image to be formed. 15. The charged-particle beam imaging system of claim 12, wherein the moving speed of said stage is greater than said width divided by a time period from the beginning of the first line scan of the previous said image formed to the beginning of the first line scan of the next image to be formed. 16. The charged-particle beam imaging system of claim 11, wherein the lines of said parallel-edge pair intersecting the axis have a larger incident angle with the axis than do lines of the other parallel-edge pair of said parallelogram. 17. The charged-particle beam imaging system of claim 11, wherein the line-scan direction is parallel to the stage-moving direction. 18. The charged-particle beam imaging system of claim 11, wherein the line-scan direction is perpendicular to the stage-moving direction. 19. The charged-particle beam imaging system of claim 11, wherein an angle between the line-scan direction and the stage-moving direction is in a range of 0 to 180 degrees but is not equal to 0, 90 or 180 degrees. 20. The charged-particle beam imaging system of claim 11, the system being configured to repeatedly line scan, at least two times, said charged-particle beam across a same position of line on said sample,wherein when each of said at least two line scans is to be performed, the system is configured to shift said charged-particle beam along the stage-moving direction by an extra predefined distance about equal to that traveled by said stage during a time period from the beginning of the first line scan of the first formed line array to the beginning of the current line scan to be performed of the current said line array being formed.
048428124	summary	BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to the removal of suspended solids from liquid streams and in particular to the removal of colloidal corrosion products from nuclear reactor coolant streams. In the operation of power plants, a maintenance problem exists due to the presence of corrosion products which form in the plant cooling system and which are then deposited on the surfaces of the cooling system. The problem is particularly acute in nuclear power plants wherein deposited primary cooling system corrosion products are a source of radiation exposure to operating and maintenance personnel and contribute to the high cost of maintenance of such power plants. The primary cooling system corrosion products are generally solids which are produced principally by the corrosion of the steam generator tubes and to a lesser extent by corrosion of the other stainless steel plant surfaces. The corrosion product components circulate with the primary coolant, both as a suspended or insoluble solid phase and to some extent as ions in solution. The solid phase particles deposit on the reactor core surface where they become irradiated. After being irradiated, the solid phase particles become resuspended in the primary coolant solution and are thereafter deposited on plant surfaces away from the core where the irradiated solid phase particles are the most important source of radiation exposure to personnel in the power plant. In a pressurized water reactor (PWR) nuclear power plant, both the primary and secondary coolant streams carry a burden of insoluble magnetic corrosion products. These corrosion products also carry a surface charge, generally dependent on the pH of the coolant and, at least in the smaller particle sizes, are subject to electrostatic attraction which causes particles to adhere to the surfaces of the system. The primary cooling system corrosion products are largely nickel ferrite and a nickel ferrite composition wherein cobalt, manganese and other elements have been substituted for part of the nickel. Substitution of chromium for ferric iron in the corrosion products has also been indicated. Such corrosion products have become colloquially known as crud. It has been recognized in the literature that by far the major source (i.e., 70 to 90%) of occupational radiation exposure to the operators and maintenance personnel of nuclear power plants is the gamma radiation emanating from deposits of irradiated corrosion products which are ubiquitously distributed on the primary coolant system surfaces. In this connection, reference is made to a publication of Beslu et al. (P. Beslu and G. Frejaville, Occupational Radiation Exposure at French Power Plants: Measure and Prediction, Nuclear Technology, Vol. 44, pp. 84-90 (June, 1979)) and to a publication of Troy et al. (M. Troy, S. Kang, G. T. Zirps and D. W. Koch, Effect of High-Temperature Filtration on PWR Plant Radiation Fields in the book "Decontamination and Decommissioning of Nuclear Facilities", M. M. Osterhout editor, Plenum Press, New York, (1980)). Such corrosion products, or crud, are released from surfaces, transported as small particles and colloids to and deposited on the reactor fuel elements where they are activated by the neutron flux. The crud is then resuspended and transported as particles back to the other system surfaces. The chemistry of the reactor coolant and the electric charge of the surfaces, both particle and plant, determine to a large extent the rate of deposition. Other effects such as hydraulic forces and solution phenomena contribute to this distribution. The latter are believed to play only a minor role in the overall process, a situation which was discussed in a publication of Kang et al. (S. Kang, Y. Solomon and M. Troy, Reactor Coolant High-Temperature Filtration Volume 2: Evaluation of Effectiveness in Reducing Occupational Radiation Exposure, Electric Power Research Institute (EPRI) Report NP-3372, Volume 2, Research Project 1445-2 (May, 1984)). Accordingly, it is known that these insoluble corrosion products known as crud have an important adverse effect on personnel safety and plant availability and their removal carries a strong economic incentive. The insoluble magnetic ferrite corrosion products carry a surface charge dependent on the pH of the coolant, see Moroto, et al. (A. J. G. Moroto, M. A. Blesa, S. I. Passagio, and A. E. Regazzoni, Colloidal Interactions on the Deposition of Magnetite Particles on the Fuel Elements Surface, Paper No. 36, Conference on Water Chemistry of Nuclear Reactor Systems, Bournemouth, England, (October, 1980)) and in the small particle sizes at least, are subject to electrostatic attraction which causes particles to adhere to the surfaces of the system. In particular the crud deposits on the fuel element cladding. The fuel elements generally have Zircalloy clad surfaces which are further coated with a thin layer of zirconia (ZrO.sub.2). The ZrO.sub.2 layer influences the deposition rate of the crud due to the natural attraction between the surface electrical charges of the crud and the ZrO.sub.2. Particles suspended in solution acquire surface charges as a consequence of surface hydrolysis reactions and adsorption of ions from the solution. Solution pH most generally controls the polarity and extent of the charge for oxide surfaces. As the particle dimensions become smaller, the surface charge becomes more and more important in determining the properties of the suspended particles. When the particle dimension decreases to between 10 and 100 .ANG., the suspended solid is referred to as a colloidal particle, and the surface charge becomes the most significant element in determining properties. The stability of suspended particles with respect to flocculation and coagulation or precipitation is determined by the surface charge. The particles move when placed in an electric field and this process is referred to as electrophoresis. The charged particles, as a consequence of their mobility in an applied electric field, may be removed from solution and collected or deposited on an electrode surface. This electrophoretic deposition process is the basis for a significant technology in the industrial coating field, e.g., in depositing thin films of insulating materials, polymer and paint coatings. The electrostatic forces can cause charged particles to adhere to surfaces. A procedure advanced for the removal of crud from nuclear reactor coolant streams by taking advantage of the magnetic properties of crud is set forth in U.S. Pat. No. 4,594,215, which issued on June 10, 1986 to the present applicants. The magnetic filter of the '215 patent is a successful crud collector; however, the dangers inherent in radiation exposure and the economics of nuclear reactors tend to encourage further searching for still more efficient procedures. The present invention provides such an improved system. SUMMARY OF THE INVENTION The improved system presented by the present invention provides a method for decreasing the rate of deposition of colloidal corrosion products from a nuclear reactor coolant onto internal reactor surfaces in contact with the coolant and having surface characteristics that attract such products. The method comprises forming a batch of particles that are suspensible in said coolant and which have active surfaces that possess surface characteristics that attract the crud. Such particles are suspended in the coolant providing a surface upon which the crud products may deposit. In nuclear reactor systems, the particularly vulnerable surfaces are those surfaces of the reactor which are coated with a layer of zirconium oxide. Accordingly, the present invention provides suspensible particles which have active zirconium dioxide surfaces. The particles may preferably be zirconium oxide particles and may be formed by processes comprising oxidizing a zirconium metal sponge, oxidizing a zirconium salt or oxidizing zirconium hydride. Suitable particles may be formed by vacuum sputtering zirconium oxide onto a particulate substrate of a different composition. In a particularly valuable form of the invention, the particulate substrate may have positive magnetic susceptibility and may comprise magnetite. Moreover, as mentioned above, the ferrite crud particles themselves are strongly magnetic. In a preferred form of the invention, the total surface area of the active surfaces should be larger than the area of the reactor surface to be protected, and the overall efficiency of the process is enhanced whenever the total surface area of the active surface provided by the suspended particles is at least about 20 times larger than the area of the reactor surfaces to be protected. The invention also provides a method for removing colloidal corrosion products from a nuclear reactor coolant. In this aspect of the invention, the method of the invention comprises forming a batch of particles that are suspensible in the coolant and which have surface characteristics that attract the crud products. The particles are suspended in the coolant whereby the crud products deposit on the surfaces of the particles. Thereafter, the particles with the crud products deposited thereon may be removed from the coolant. In one preferred form of the invention, the particles may have magnetic susceptibility and the removing step may comprise magnetically attracting such particles. In another preferred aspect of the invention, the removal step may comprise filtration of the coolant by more conventional means. Manifestly, the method may involve both magnetic attraction and filtration of the coolant stream.
059490845	description	DETAILED DESCRIPTION OF THE INVENTION Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus generally shown in FIG. 1 through FIG. 2. It will be appreciated that the apparatus may vary as to configuration and as to details of the parts without departing from the basic concepts as disclosed herein. Referring to FIG. 1, a radioactive material storage apparatus 10 in accordance with the present invention is generally shown. Apparatus 10 generally comprises an inner vessel 12, an outer casing 14, a particulate matrix 16, a cover 18 and impact limiters 20, 22. Inner vessel 12 forms a chamber 24 structured and configured to receive and contain radioactive material therein. Inner vessel 12 is preferably composed of a metallic material such as stainless steel or like material possessing structural rigidity, yield strength and the capability of effectively shielding photon radiation, such as gamma rays, that are emitted from radioactive material stored therein. An opening 26 on inner vessel 12 provides external access to chamber 24. Outer casing 14, which provides photon radiation shielding capability, is also preferably composed of a metallic material such as stainless steel or like material and surrounds inner vessel 12 such that a space 28 is defmed between the inner vessel 12 and the outer casing 14. Space 28, which is preferably annular, completely envelops chamber 24, with the distance between inner vessel 12 and outer casing 14 being generally uniform around chamber 24. Space 28 is filled with particulate matrix 16 which is a neutron attenuator and absorber. Outer casing 14 also serves as a protective covering for inner vessel 12. Cover 18 is placed over opening 26 and completely seals chamber 24. Cover 18 includes an outer wall 30, an inner wall 32 and a cavity 34 disposed between outer wall 30 and inner wall 32. Outer wall 30 and inner wall 32 are preferably stainless steel. Cavity 34 is also filled with particulate matrix 16 to provide neutron attenuation and absorption. Referring also to FIG. 2, particulate matrix 16 comprises a plurality of metallic particles 36 tightly packed together. Metallic particles 36 are typically composed of depleted uranium or lead and are preferably but not necessarily spherical as shown, however, the use of spherical particles assures a maximum packing density so that the thickness of space 28 can be minimized. The advantage gained by minimizing the thickness of space 28 is that heat generated by the radioactive contents stored within chamber 24 is more easily dissipated by thermal conduction. Depleted uranium and lead both have the capability of attenuating photon radiation from radioactive materials, but by themselves cannot absorb or attenuate neutrons. Therefore, the voids or interstices 38 present between metallic particles 36 is filled with a neutron absorbing material 40. Neutron absorbing material 40 provides both moderation and absorption of neutrons emitted from radioactive materials stored therein. Conventionally known hydrogenous and neutron poison materials are used to formulate neutron absorbing material 40. Preferably, neutron absorbing material 40 is an aggregate mixture composed primarily of calcium sulfate, boric acid and water. Approximately, two parts calcium sulfate is mixed with one part boric acid and one part water to form a pourable aggregate mixture containing the neutron moderator and absorber. The mixture is poured or injected into annular space 28 formed between the inner vessel 12 and the outer casing 14. Metallic particles 36 are then added to the mixture which settle to the bottom 42 of space 28 and begin filling up to the top 44 of space 28. Vibrating the mixture during filling is helpful for settling metallic particles 36 properly within space 28. The mixture containing the metallic particles 36 generally harden within an hour, thus forming particulate matrix 16 which shields against both photon and neutron penetration. The hydrogen present in the water is known to be a neutron moderator, which has the effect of slowing the neutrons as they pass through the water. Borated water, which contains boron, can also be used in the aggregate mixture. Since boron is a natural neutron absorber, borated water increases the ability of the aggregate mixture to absorb neutrons, in addition to its effectiveness as a gamma shield. The combination of hydrogen and boron within the mixture, therefore provides the neutron moderation and absorption. The use of particulate matrix 16 in space 28 eliminates the requirement for a separate neutron shield, and the thermal conductivity of apparatus 10 need not be degraded by the application of such a separate neutron shield. The packing efficiency of particulate matrix 16 is preferably approximately 62.5%. The density of neutron particulate matrix 16 using depleted uranium spheres is preferably approximately 60% of the weight of solid lead or approximately 7.09 g/cm.sup.3, and its photon shielding capabilities would be equivalent to that of lead occupying the same volume, however, the use of depleted uranium in particulate matrix 16 provides the added advantage of incorporating hydrogen atoms for neutron moderation and boron atoms for neutron absorption. The size of metallic particles 36 must be large enough to eliminate the possibility of pyrophoric ignition. The volume of metallic particles 36 is typically in a range between approximately 50% to 70% of the volume of particulate matrix 16. Preferably, the minimum diameter of the metallic particles 36 must be at least 0.5 mm, and the maximum diameter is selected so that the packing efficiency is maximized. Other factors determining maximum sphere diameter are the practically and availability of manufacturing methods and associated production costs. Particulate matrix 16 adds strength and stiffness to apparatus 10 while also providing an effective impact limiter. Kinetic energy due to physical impact on apparatus 10, which may occur during transportation of apparatus 10, would be dissipated by the crushing of particulate matrix 16 at the point of impact. Therefore, outer casing 12 only requires sufficient ductility and tensile strength to deform without rupturing. The addition of impact limiters 20, 22, which are typically fabricated from wood, provide further impact or shock absorption to apparatus 10. Retrieval and/or recycling of metallic particles 36 in particulate matrix 16 is possible using conventional techniques. For instance, particulate matrix 16 would be broken up into small pieces by mechanical agitation, such as vigorous shaking, air blasting or the like. Accordingly, it will be seen that this invention provides for a vessel which allows for storing and/or transporting radioactive materials, which minimizes space requirements due to its "thin wall" design, and which has metallic components that can be recycled using conventional techniques. Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of this invention should be determined by the appended claims and their legal equivalents.
	summary
053171411	claims	1. A method for alignment of a first object with a second object, comprising the steps of: (a) determining the location of a feature on a surface of said second object using a probe of a scanned probe microscope, said scanned probe microscope being distinct from said first object; (b) positioning said first object in preselected spatial relationship with respect to said located feature. (a) using a probe of a second scanned probe microscope in determining the location of a second feature on the surface of said second object; and (b) positioning said first object in preselected spatial relationship with respect to the second located feature, simultaneously with said step of positioning said first object with respect to the first located feature, thereby obtaining rotational and translational alignment of said first object to said second object. (a) determining the location of a first feature on a surface of said second object using a probe of a scanned probe microscope; and (b) determining the location of a first feature on the surface of said first object, and (c) positioning said first object in preselected spatial relationship with respect to said located first feature on said second object. (a) determining the location of a second feature on the surface of said second object using a probe of a scanned probe microscope; and (b) positioning said first object in preselected spatial relationship with respect to the second located feature, simultaneously with said step of positioning said first object, thereby obtaining rotational and translational alignment of said first object to said second object. (a) determining, employing one and only one probe of a scanned probe microscope, the position and orientation on the surface of the second object of an alignment mark having a shape such that its position and orientation can be determined; (b) comparing the determined position and orientation of the alignment mark with a stored position and orientation of the alignment mark; and (c) translating and rotating said second object relative to said first object to align said first object with said second object. (a) means, comprising one and only one probe of a scanned probe microscope, for determining the position and orientation on the surface of the second object of an alignment mark having a shape such that its orientation can be determined; (b) data processing apparatus adapted to compare the determined position and orientation of the alignment mark with a stored position and orientation of the alignment mark; and (c) means for translating and rotating said second object relative to said first object to align said first object with said second object. (a) scanning the surface of the second object using a probe of a scanned probe microscope until sufficient information is obtained regarding the scanned portion of the surface such that the scanned portion can be identified on a stored reference image of the surface whereby the position of said probe can be determined; and (b) comparing the determined position of the probe on the surface to a predetermined home position for the probe on the reference image. (a) means, comprising a probe of a scanned probe microscope, for obtaining an image of a portion of the surface of the second object; and (b) means for comparing the obtained image of the surface of the second object with a stored reference image, in order to determine the location of the probe on the surface relative to a predetermined home position for said probe. 2. A method as recited in claim 1, wherein said step of positioning comprises maintaining said first object in fixed spatial relationship with respect to said probe. 3. A method as recited in claim 2, wherein said probe is rigidly mounted on a forward side of said first object. 4. A method as recited in claim 3, wherein said probe comprises a probe of a scanning tunneling microscope, said location determining means further comprising a conductor in electrical contact with said probe and extending substantially to an edge of said forward side of said first object. 5. The method of claim 3, further comprising the step of, prior to said step (a), performing metrology on the forward side of said first object to determine the relative location of a reference feature on said first object and the probe. 6. The method of claim 5, wherein said step of performing metrology comprises scanning the forward side of said first object with a scanning electron microscope. 7. A method as recited in claim 1, further comprising the steps of: 8. A method as recited in claim 7, wherein said first probe and said second probe are rigidly attached to a forward face of said first object. 9. A method as recited in claim 8, wherein said first and second probes comprise probes of scanning tunneling microscopes. 10. A method for alignment of a first object with a second object, comprising the steps of: 11. A method as recited in claim 10, wherein said step of determining the location of a feature on a surface of said first object comprises employing a probe of a scanned probe microscope. 12. A method as recited in claim 11, wherein said probe comprises a probe of an atomic force microscope. 13. A method as recited in claim 10, further comprising the steps of: 14. A method as recited in claim 13, wherein said step of positioning further comprises using a probe of a third scanned probe microscope in determining the location of a second feature on a surface of said first object. 15. In the apparatus for performing optical lithography on a substrate, having an optical mask and a mask holder supporting the optical mask, the improvement comprising means, comprising a probe of a first scanned probe microscope, for determining the location of a feature on a surface of the substrate, further comprising a probe of a second scanned probe microscope, in known spatial relationship with respect to said probe of said first scanned probe microscope, for determining the location of a feature on said mask. 16. The improvement of claim 15, wherein said probe of said first scanned probe microscope and said probe of said second scanned probe microscope each depends from said holder. 17. A method for rotational and translational alignment of a first object with a second object, comprising the steps of: 18. The method of claim 17, wherein said probe is mounted on a surface of said first object. 19. The method of claim 17, wherein said first object is a mask. 20. The method of claim 17, wherein said second object is a wafer. 21. An apparatus for rotational and translational alignment of a first object with a second object, comprising: 22. The apparatus of claim 21, wherein said probe is mounted on a surface of said first object. 23. The apparatus of claim 21, wherein said first object is a mask. 24. The apparatus of claim 21, wherein said second object is a wafer. 25. A method for detecting misalignment between a first object and a second object, comprising the steps of: 26. The method of claim 25 wherein the second object is a mask, and the first object is a mask holder. 27. An apparatus for detecting misalignment between a first object and a second object, comprising: 28. The apparatus of claim 27, wherein said second object is a mask, and said first object is a mask holder.
	claims	1. A method of treating a plurality of features on a surface of a workpiece using a gas cluster ion beam, the method comprising:measuring an attribute of the features;correlating the attribute of each of the features with a spatial location on the surface to generate a spatial map;directing ionized clusters in the gas cluster ion beam toward the surface of the workpiece; andbased on the spatial map, modulating delivery of the gas cluster ion beam across the surface of the workpiece so that different features in different regions on the surface receive different doses of the ionized clusters. 2. The method of claim 1 wherein the attribute is a dimension of the features, and measuring the attribute of the features further comprises:measuring the dimension of each of the features; andassessing a non-uniformity of the dimension among the features to generate the spatial map. 3. The method of claim 2 wherein modulating delivery of the gas cluster ion beam further comprises:selecting the different doses to reduce the non-uniformity of the dimension among the features. 4. The method of claim 2 wherein the features are recesses extending into the surface, and modulating the delivery of the gas cluster ion beam further comprises:etching the recesses in the different regions of the surface by different amounts to reduce the non-uniformity of the dimension among the recesses. 5. The method of claim 2 wherein the features are recesses extending into the surface, and modulating the delivery of the gas cluster ion beam further comprises:depositing different amounts of a material inside the recesses in the different regions of the surface to reduce the non-uniformity of the dimension among the recesses. 6. The method of claim 2 wherein the features are three-dimensional bodies projecting from the surface, and modulating the delivery of the gas cluster ion beam further comprises:etching the three-dimensional bodies by different amounts in the different regions of the surface to reduce the non-uniformity of the dimension among the three-dimensional bodies. 7. The method of claim 2 wherein the features are three-dimensional bodies projecting from the surface, and modulating the delivery of the gas cluster ion beam further comprises:depositing different amounts of a material on the three-dimensional bodies in the different regions of the surface to reduce the non-uniformity of the dimension among the three-dimensional bodies. 8. A method of using a gas cluster ion beam, the method comprising:measuring an attribute of the features on a plurality of workpieces;correlating the attribute of each of the features with a spatial location on the surface to generate a spatial map;directing ionized clusters in the gas cluster ion beam toward the surface of another workpiece; andbased on the spatial map, modulating delivery of the gas cluster ion beam across the surface of the another workpiece so that different features in different regions on the surface of the another workpiece receive different doses of the ionized clusters. 9. The method of claim 8 wherein the attribute is an electrical property, and measuring the attribute of the features on the plurality of workpieces further comprises:assessing a non-uniformity of the electrical property among the features on the surface of each of the plurality of workpieces to generate the spatial map. 10. The method of claim 8 wherein the attribute is a dimension of the features, and measuring the attribute of the features further comprises:measuring the dimension of each of the features on the surface of each of the plurality of workpieces; andassessing a non-uniformity of the dimension among the features to generate the spatial map. 11. The method of claim 10 wherein modulating delivery of the gas cluster ion beam further comprises:selecting the different doses to reduce the non-uniformity of the dimension among the features on the surface of the another workpiece. 12. The method of claim 10 wherein the features are recesses extending into the surface of the plurality of workpieces and the another workpiece, and modulating the delivery of the gas cluster ion beam further comprises:etching the recesses in the different regions of the surface of the another workpiece by different amounts to reduce the non-uniformity of the dimension among the recesses. 13. The method of claim 10 wherein the features are recesses extending into the surface of the plurality of workpieces and the another workpiece, and modulating the delivery of the gas cluster ion beam further comprises:depositing different amounts of a material inside the recesses in the different regions of the surface of the another workpiece to reduce the non-uniformity of the dimension among the recesses. 14. The method of claim 10 wherein the features are three-dimensional bodies projecting from the surface of the plurality of workpieces and the another workpiece, and modulating the delivery of the gas cluster ion beam further comprises:etching the three-dimensional bodies in the different regions of the surface of the another workpiece by different amounts to reduce the non-uniformity of the dimension among the three-dimensional bodies. 15. The method of claim 10 wherein the features are three-dimensional bodies projecting from the surface of the plurality of workpieces and the another workpiece, and modulating the delivery of the gas cluster ion beam further comprises:depositing different amounts of a material on the three-dimensional bodies in the different regions of the surface of the another workpiece to reduce the non-uniformity of the dimension among the three-dimensional bodies.
	description	The present patent document is a §371 nationalization of PCT Application Serial Number PCT/EP2013/060186, filed May 16, 2013, designating the United States, which is hereby incorporated by reference in its entirety. This patent document also claims the benefit of DE 10 2012 210 487.9, filed on Jun. 21, 2012, which is also hereby incorporated by reference in its entirety. The present invention relates to a scintillator plate for detecting X-rays and to a method for producing a scintillator plate. Scintillator plates serve to convert X-ray or gamma radiation into visible light and are used in medical technology and for non-destructive material testing. Typically, scintillator plates include a substrate on which a scintillator layer is arranged. The material of a scintillator layer is suitable for absorbing high-energy photons of X-ray and gamma radiation and for re-emitting the energy of the high-energy photons in the form of a large number of low-energy photons, e.g., in the visible region (therefore referred to in the following as light photons). It is thereby possible to process the information of the X-ray or gamma radiation with common optical sensors. The two-dimensional detection of an image is possible when using a matrix of photodetectors, such as for example CCD sensors made of crystalline silicon or photodiode arrays made of amorphous silicon. In order to achieve a high resolution in the image, as many as possible of the light photons generated by a single high-energy photon are received by a single photodetector of the matrix in order to obtain the information concerning the spatial correlation. One of the scintillator materials used is caesium iodide (referred to below as CsI). A scintillator layer made of CsI is typically generated by vapor-deposition of CsI onto a substrate in a vacuum. The CsI tends, under suitable manufacturing conditions, to form columnar microstructures or needles, which are separate from one another and which grow upwardly away from the substrate. The microstructures typically have structure sizes in the lateral direction of the order of 10 μm. Due to the effect of total reflection, these microstructures are suitable for conducting a large part of the photons generated in the interior thereof along the microstructure, similarly to a light guide. Only light photons that meet the surface at too large an angle leave the respective microstructure and scatter in the wider surroundings. If the layer thickness of the scintillator layer is selected to be larger, the microstructures tend to grow together and to come into contact with one another. This effect arises, e.g., in layer thicknesses from 300 μm upward. At contact sites of this type, the conditions, in part, no longer exist for total reflection, so that additional light photons are scattered out of the microstructures. Such layer thicknesses are used, e.g., when X-ray or gamma radiation with relatively high energies is used because, with the increasing energy, the absorption in the CsI decreases. The scintillator layer is configured thicker in order to absorb the majority of the X-ray or gamma photons. Typical layer thicknesses may be between 500 μm and 2000 μm. At these layer thicknesses, the spatial resolving power is consequently significantly reduced due to the light photons emerging laterally from the microstructures. In order to counteract this effect, as described in the published application DE 10242006 A1, it has been attempted to structure the scintillator layer in a targeted manner. As mentioned above, however, from a thickness of 300 μm, said scintillator layer tends to grow together again, so that at greater layer thicknesses, the desired effect cannot be achieved. In published applications DE 4433132 A1 and DE 10116803 A1, there are described attempts to color the surface of the microstructures in order to absorb light photons emerging laterally from the microstructure. However, the coloration is not restricted to the surface, but also extends into the interior of the microstructures. A raised level of absorption of the light photons in the interior of the microstructure is also associated therewith, which leads to a reduction in the desired signal. The publication “Structured CsI (Tl) Scintillators for X-Ray Imaging Applications” by V. V. Nagarkar, IEEE Transactions on Nuclear Science, vol. 45, No. 3, June 1998, describes covering the microstructures with an optically absorptive protective layer. The patent specification EP 1 793 457 B1 describes covering the microstructures completely from the base to the tip with a light photon-absorbing covering material. A covering of this type has a refractive index close to that of caesium iodide and therefore restricts the total reflection to relatively flat incident angles to the border layer between the caesium iodide and the covering material, such that more light photons enter the covering material and are absorbed there. Protective layers made of parylene are known from the patent document U.S. Pat. No. 4,123,308 and the published application DE 19509438 A1. The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, the present embodiments may address a problem in scintillator plates that the contrast and/or the resolution decreases with increasing thickness of the scintillator layer. The present embodiments may provide a scintillator plate that has better contrast, greater conversion efficiency and/or a higher resolution with a comparable thickness of the scintillator layer. The present embodiments relate to a scintillator plate having a substrate, a scintillator layer and a protective layer. A method may be provided for producing a scintillator plate of this type. The method for producing a scintillator plate includes providing a substrate. A buffer layer is applied to the substrate. The application of a scintillator layer onto the substrate is provided. A protective layer is applied to the scintillator layer. The buffer layer and/or the protective layer is colored by tempering. Because the buffer layer and/or the protective layer is colored by tempering, there is no danger that coloring substances will enter the scintillator layer and reduce the efficiency of the scintillator layer through absorption of the propagating light photons there. However, due to the coloring, the protective layer has a raised absorption for scattered light photons. For example, if the light photons do not pass through the protective layer by the shortest route, the light photons propagate at an angle to the propagation direction of the generating gamma or X-ray photons and take a longer path in the protective layer. Thus, due to the absorption of these non-directed light photons, the contrast and the resolution of the scintillator plate is improved. In this way, a colored buffer layer reduces the number of light photons that leave the scintillator layer in the direction toward the substrate at an angle and fall, reflected back from the substrate, in the direction of a detector. Because these light photons are also diffusely distributed around the original generation site, the absorption of the light photons in the buffer layer also improves the resolution and the contrast of the scintillator plate. The scintillator plate includes a substrate, a buffer layer on a surface of the substrate, a scintillator layer arranged on the buffer layer, and a protective layer. The buffer layer and/or the protective layer include a proportion of carbonyl groups, such that the buffer layer and/or the protective layer have a yellowish coloration. Due to the yellowish coloration of the protective layer, the protective layer has a raised absorption for scattered light photons, e.g., if the light photons do not pass through the protective layer by the shortest route, but propagate at an angle to the propagation direction of the generating gamma or X-ray photon and take a longer path in the protective layer. Thus, due to the absorption of these non-directed photons, the contrast and the resolution of the scintillator plate are improved. In the same way, a colored buffer layer reduces the number of light photons that leave the scintillator layer in the direction toward the substrate at an angle and fall, reflected back from the substrate, in the direction of a detector. Because these light photons are also distributed diffusely around the original generation site, due to the absorption thereof, the resolution and the contrast of the scintillator plate are also improved. The yellow coloration of the buffer layer and/or of the protective layer due to the carbonyl groups may be generated, for example, by tempering in an oxygen-containing atmosphere. Such coloration effects may occur with carbonyl proportions of, for example, more than 5000 ppm, where the coloration and the raised oxygen content levels may be limited to regions of the layer. The coloration may be useful because absorption of light in the visible wavelength region is provided without the protective layer being changed by pigments or coloring agents. The carbonyl groups arise in the buffer layer or the protective layer itself and do not pass into the scintillator layer where the carbonyl groups would reduce the conversion efficiency thereof. The protective layer may be made of a parylene from the substance group of poly-p-xylylenes, in particular, one of parylene C, parylene N or parylene D. Parylene C, for example, may be deposited from a gaseous phase and does not require water or solvent for application. A water-impervious protective film is formed, which protects the scintillator layer against moisture. This is useful, e.g., for the hygroscopic caesium iodide. Furthermore, parylene C is capable of becoming deposited in interstices by condensation from the gaseous phase. In one embodiment of the method, the tempering is implemented in a temperature range from 190° C. to 240° C. in an oxygen-containing atmosphere. In the above-mentioned temperature range, the scintillator layer is stable, whereas suitable protective layers become colored at these temperatures and with a supply of oxygen. In one embodiment of the scintillator layer, the scintillator layer forms microstructures such that interstices form between the microstructures essentially perpendicularly to the surface of the scintillator plate toward the substrate. The microstructure with the interstices extending essentially perpendicularly from the surface of the scintillator plate toward the substrate conducts the light photons generated through conversion of the X-rays and gamma rays, via total reflection, to border surfaces of the microstructures within the scintillator layer, e.g., in the direction toward the surface of the scintillator plate. Due to the small dimensions of the microstructure in the direction parallel to the surface of the scintillator plate, the light photons generated within a microstructure are guided to an area that corresponds to the small dimensions of the microstructure. Because the protective layer, which extends into the interstices between the microstructures, has an appreciable absorption for light photons, the protective layer absorbs the light photons scattered from the microstructure with a high probability and thereby improves the contrast and the resolution of the scintillator plate. Because the protective layer extends only partially into the interstices between the microstructures, and because a region that adjoins the buffer layer remains free, the border surfaces of the microstructure in this region are not in contact with the protective layer. Because the refractive index of the material of the scintillator layer differs more strongly from the surroundings than from the material of the protective layer, the limiting angle for total reflection in the region in which the protective layer does not extend is greater. Therefore, in this region, a greater proportion of the light photons generated in the microstructure by the X-ray or gamma photons is reflected back into the microstructure at the border surface and is guided away from the substrate in the microstructure. In one embodiment of the method, the scintillator layer includes caesium iodide and is deposited onto the buffer layer. Caesium iodide is distinguished by a good efficiency level for the conversion of X-ray photons into light photons. Furthermore, caesium iodide tends, when deposited on the substrate, to arrange itself into needle-like microstructures perpendicularly to the surface of the substrate, the microstructures acting as light guides and guiding the majority of the light photons generated in the interior of the microstructures to the surface. In one embodiment of the scintillator plate, the scintillator plate has microstructures with interstices. The interstices extend essentially perpendicularly to the surface of the scintillator plate toward the substrate. The microstructure conducts the light photons generated through conversion of the X-rays and gamma rays, via total reflection at border surfaces of the microstructures within the scintillator layer, e.g., in the direction toward the surface of the scintillator plate. Due to the small dimensions of the microstructure in the direction parallel to the surface of the scintillator plate, the light photons generated within a microstructure are guided to an area that corresponds with the small dimensions of the microstructure. In one embodiment of the scintillator plate, the scintillator layer includes caesium iodide. Caesium iodide is distinguished by a good efficiency level for the conversion of X-ray photons into light photons. Furthermore, due to the self-organization thereof, caesium iodide tends to be arranged in needle-like microstructures that are oriented perpendicularly to the surface of the substrate. The buffer layer and/or the protective layer may include one of parylene C, parylene N or parylene D. A buffer layer or protective layer made of parylene C is impermeable to water and is configured to protect the microstructures of the scintillator layer against moisture, which may be useful, e.g., for the hygroscopic caesium iodide. Furthermore, parylene C is suitable, during deposition from the gaseous phase, also to extend into interstices in the substrate or between the microstructures. In one embodiment, the buffer layer and/or the protective layer of parylene includes a proportion of carbonyl groups of, for example, greater than 5000 ppm, which causes a yellowish coloration. The coloration and the raised oxygen content may be limited to regions of the layer. The coloration is useful because absorption of light in the visible wavelength region is provided without the buffer layer and/or the protective layer being changed by pigments or coloring agents. FIG. 1 is a cross-section through a scintillator plate 1 according to the prior art. The scintillator plate 1 has a substrate 10 on which a scintillator layer 20 is arranged. If the material of the scintillator layer 20 is caesium iodide, then when growing on the substrate 10, the material forms microstructures in the form of columns or needles that extend away from the substrate 10. The scintillator layer 20 is relatively thin, typically thinner than, for example, 300 μm, so that the individual columns or needles are separate from one another. Arranged on the scintillator layer 20 is a protective layer 30, which is intended to protect the scintillator layer 20 against environmental influences. Such environmental influences may be dirt, liquids, gases or moisture. FIG. 2 shows, by contrast, a scintillator plate 1 with a scintillator layer 20 made of caesium iodide, as is typical for a thickness of 1000 μm. The individual microstructures in the form of columns or needles tend, at this thickness, to come into contact with one another at contact sites 21. FIG. 3 shows, in a detail view of FIG. 2, how X-ray radiation incident in the scintillator layer 20 is converted into visible light and how this light spreads out. An X-ray photon 60 interacts, at a respective probability, with the electrons of the scintillator layer 20 (by absorption, Compton effect). Due to the changes caused thereby in the electron shells of atoms of the scintillator layer 20, photons 62, 63 are emitted by the atoms at energies in the visible light region. A portion of the light photons 62 impinges at a steep angle on outer border surfaces of the microstructures of the scintillator layer 10, so that these light photons 62 leave the microstructure. Another portion of the light photons 61 is incident on the outer border surface of the microstructure at an angle smaller than the angle for total reflection and is completely reflected back into the microstructure. These light photons 61 are therefore conducted by the microstructure along the microstructure as by a light guide. However, if the outer border surface is in contact with another microstructure, then a light photon 63 may also cross over into an adjacent microstructure. Both the light photons 62 that leave the microstructure as well as the light photons 63 that cross over into other microstructures leave the scintillator layer at a distance 64 from the microstructure in which the X-ray photon was converted. These light photons 62, 63 therefore worsen both the spatial resolution and the contrast of the image generated by the scintillator plate 1. FIG. 4 shows a cross-section through a scintillator plate 1 according to one embodiment. The scintillator plate 1 includes a substrate 10 onto which a buffer layer 11 is applied. Arranged thereon is the scintillator layer 20. The scintillator layer 20 is structured into microstructures between which interstices 22 extend from an upper side facing toward a photodetector 100 to the substrate 10. The interstices 22 extend essentially perpendicularly to the surface of the substrate 10. The protective layer 30 is applied to the upper side facing toward the photodetector 100 and extends into the interstices 22 between the microstructures of the scintillator layer 20. The protective layer 30 may extend into the interstices 22 whilst with thin layers the protective layer 30 extends as far as the buffer layer 11. The protective layer 30 may extend into the interstices 22 only part of the way from the upper side facing toward the photodetector 100 to the buffer layer 11. The protective layer 30 may extend from the upper layer up to 500 μm into the interstices 22. The protective layer 30 is colored so as to absorb visible light appreciably. The coloration relates both to a region of the protective layer 30 applied to the upper side facing toward the photodetector 100, as well as to a region of the protective layer 30 that extends into the interstices 22 between the microstructures of the scintillator layer 20. A significant to overwhelming proportion of light photons 62, 63 that leave the microstructures of the scintillator layer 20 are absorbed by the protective layer 30 within the dimensions of the scintillator layer 20. This may be, for example, a coloration in which at least 10% of the light is absorbed in a propagation distance of 1000 μm. However, the buffer layer 11 may also or only be colored. A colored buffer layer 11 reduces the number of light photons propagating in the direction of the substrate 10 and being reflected therefrom. Due to the angular distribution and the large distance that these light photons have to cover to the detector on the side of the scintillator plate 1 facing away from the substrate, the photons are distributed over a wide region. If, however, the light photons are absorbed in the colored buffer layer 11, the resolution and the contrast of the scintillator plate 1 increase accordingly. The coloration may be evoked, for example, by the formation of carbonyl groups in the buffer layer 11 and/or the protective layer 30, if these are made, for example, of parylene. The carbonyl groups are noticeable, e.g., due to a yellowish coloration, which may also become a brownish color tone. A possible route to creating the carbonyl groups is described in the method set forth below. For example, the coloration may be provided via a carbonyl proportion in the protective layer of more than 5000 ppm. The presence of the carbonyl groups in an infrared spectrum of parylene may also be shown through absorption at the wave number of 1700 cm−1. FIG. 5 shows a corresponding transmission spectrum 110 of a parylene layer before tempering and a transmission spectrum 120 following tempering. Shown on the y-axis is the transmission in percentage values. Shown on the x-axis is the wavelength of the infrared light in the form of the wave number. Shown in the spectrum 120 is an absorption peak 121 at a wave number of approximately 1700 cm−1, which is caused by the carbonyl groups and is not visible in the spectrum 110 before the tempering. In order to determine a relative concentration of the carbonyl groups, a ratio of the amplitude of the peak to the amplitude of an absorption line of the parylene, which is not changed by the tempering, may be taken. For this purpose, the absorption peak 112, 122 at the wave number of 820 cm−1 may be used, which represents an out-of-plane deformation oscillation of the C—H-bond in the aromatic ring of the parylene. A corresponding coloration occurs if a quotient of the relevant absorption at the absorption peak of the wave number 820 cm−1 due to the relative absorption at the absorption peak of the wave number 1700 cm−1 is smaller than 10. Arranged on the upper side of the scintillator layer 20 facing away from the substrate 10 and having the protective layer 30 is a photodetector 100. The photodetector 100 may be, for example, a 2-dimensional CCD matrix for recording a 2-dimensional X-ray image. The CCD matrix may have active elements made of crystalline semiconductors. A one-dimensional detector row may be moved over the scintillator plate 1 as the photodetector 100. Photodiode arrays made of amorphous silicon may be used as the photodetector 100. A maximum resolution is achieved when the dimensions of the individual detector elements 101 correspond to the cross section of the microstructures in the scintillator layer 20 on the upper side. Smaller detector elements do not result in a higher resolution because, in the total reflections of the light photons in the microstructure, the spatial information regarding the X-ray photon becomes lost in the microstructure. The substrate itself may be sufficiently thin and transparent or may be a fiber optic plate, so that the photodetector is arranged on the side of the substrate 10 facing away from the scintillator layer 20. With a suitable photodetector that undergoes the process steps for generating the scintillator layer 20 without significant worsening of the detection properties, the scintillator layer 20 may be applied directly, or on a layer 11, onto the photodetector. A method for manufacturing a scintillator plate 1 is now described. A suitable substrate 10 is provided. Essentially all materials having a sufficiently clean and even surface for the growth of a scintillator layer 20 are suitable as the substrate. At the same time, the substrate is transparent to X-ray radiation 60. For example, glass, aluminum or amorphous carbon may be used as the material for the substrate. A buffer layer 11 may be applied to one of the above-mentioned base materials of the substrate 10. The buffer layer 11 may be made of the same substances as the protective layer 30 and the substances are suitable, due to the particularly good properties thereof, both to protect a subsequent scintillator layer 20 against environmental influences and to form a suitable base for deposition of the scintillator layer, and are considered in greater detail below in relation to the protective layer 30. The buffer layer 11 may be colored with one of the methods described in relation to the protective layer 30. As stated above, the photodetector 100 may be used as the substrate 10. In a further act, a scintillator layer 20 is applied to the substrate 10. In one embodiment, caesium iodide serves as the scintillator material. Caesium iodide may be vapor-deposited under vacuum and becomes deposited on the substrate. During the deposition, the caesium iodide grows perpendicularly away from the surface of the substrate 10 in column-shaped or needle-shaped microstructures. As mentioned above in relation to the scintillator plate 10, these microstructures are useful for the imaging properties thereof. Furthermore, caesium iodide distinguishes itself, e.g., when doped with thallium, by an effective conversion of X-rays into visible light. Other materials are also possible, which are suitable for converting X-ray radiation into visible light. Even if these materials do not themselves tend toward microstructuring, such structuring may be possible using technical means. Structuring of this type, for example, may be possible via photolithographic methods of semiconductor technology. For example, Gd2O2S may be used. In a further act, a protective layer 30 is applied to the scintillator layer 20. For example, caesium iodide is hygroscopic and requires protection against contact with moisture. In one embodiment, parylene C, which belongs together with the other parylenes to the group of poly-p-xylylenes, is applied as the protective layer 30. The deposition of parylene C is implemented from a gaseous phase without solvent. The starting molecules polymerize to a protective layer 30 directly onto the surface of the scintillator layer 20. In this process, the individual gaseous starting molecules are also capable of penetrating into interstices 22 of the scintillator layer 20 and of forming a protective layer 30 there that also extends into the interstices 22. However, other materials may be used for the protective layer 30, provided the materials are tolerable with the respective materials of the scintillator layer 20 and are capable of forming into a protective layer extending into the interstices 22 between the microstructures. These materials may be, for example, other substances of the substance group of poly-p-xylylenes, such as parylene D or parylene N or also epoxy resins. In one embodiment of the method, in a further act, the protective layer 30 is colored by tempering. By heating the protective layer 30 to a temperature in a range between 190° C. and 240° C. in an oxygen-containing atmosphere, the protective layer of parylene C becomes colored yellowish to yellow-brownish, depending on the temperature and duration of the heat treatment. Below 190° C., the coloration occurs so slowly that practicable production is not possible. Above 240° C., the structural stability and therefore the protective effect of the protective layer of parylene C no longer exists. Through tempering given these conditions, oxidation of the parylene occurs, so that oxygen is included into the parylene layer as carbonyl groups, which leads to the desired yellowish or brownish coloration. In one embodiment, the proportion of carbonyl groups in the protective layer 30 or in portions of the protective layer 30 amounts to more than 5000 ppm. Due to the coloration achieved, light photons are absorbed in the interstices 22 and, as a result, as described above, the contrast and resolution are improved. Coloration through tempering may also be achieved with protective layers 30 other than those mentioned above made of parylene C. The process parameters of duration, temperature and atmosphere composition are dependent on the respective materials of the protective layer 30. A possible material for the protective layer 30 may be, for example, an epoxy resin. The protective layer 30 may be already colored when the layer is applied. This may be possible, for example, in the case of gas deposition, in that a further component is added during the creation of the protective layer 30, provided this does not color the scintillator layer 20 itself. The protective layer 30 may be colored following application, using a suitable coloring method. For example, the protective layer 30 may be exposed to a further gaseous component, provided this does not damage the scintillator layer 20. It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification. While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.
051075261	description	DESCRIPTION OF THE PREFERRED EMBODIMENT A microscope generally indicated at 10 constructed in accordance with the principles of the present invention includes a hollow housing or mounting tube 12 within which reflecting optics comprising a primary and secondary reflector 14, 16 are mounted. The primary reflector 14 comprises a normal incidence concave spherical primary mirror substrate 18 having a highly polished reflective surface with a multilayer coating 20 applied to the reflecting surface, while the secondary reflector 16 comprises a normal incidence spherical convex mirror substrate 22 having a highly polished reflective surface with a multilayer coating 24 identical to the coating 20 applied to the reflective surface of the secondary mirror, the substrates, surface finish and coatings hereinafter described in detail. The primary mirror substrate 18 is an annular member having a central aperture 26. The mirrors are mounted such that the radius of curvature R.sub.1 of the primary mirror and the radius of curvature R.sub.2 of the secondary mirror having a common center of curvature C located on the optical axis of the microscope, the optical axis passing through the center of the aperture 26. Thus, the radius of curvature of both spherical mirrors are concentric about the center of curvature C and the radiation after being reflected by the secondary mirror 22 converges through the aperture 26 to the focal plane where the image is formed, i.e., the image plane. The rear surfaces of both mirrors are planar or flat and the mirrors are mounted in respective mountings 28, 30. The primary mirror mounting 28 comprises a substantially hollow cylindrical annular mounting cell within which the mirror 18 is positioned with the flat rear surface and the periphery abutting the interior of the cell, the cell having a small flange 32 at the periphery of the mirror mounting end for constraining the mirror 18 within the cell. The end of the mounting cell 28 remote from the mirror is secured to the imaging end 34 of the mounting tube 12 by means of screws 36 or the like so that the primary mirror is fixed in position. The secondary mirror mounting 30 comprises a substantially hollow cylindrical member within which the secondary mirror is mounted with its flat surface and periphery abutting the interior of the cylindrical member and with the reflecting surface facing toward the image plane, the secondary mirror being held in the mounting by a peripheral flange 33 at the open end of the mounting. One or more, and preferably three or less, very thin rods 40 form a spider for positioning and holding the secondary mounting 30 and thus the secondary mirror 22 in proper position on the optical axis and offer minimal obstruction to the incoming radiation, the rods of the spider being secured to the interior of the mount tube 12 by conventional means such as adhesives or the like. The selection of the radii R.sub.1 and R.sub.2 of the mirrors 18, 22 together with the positioning of the specimen 42 stage end 44, as hereinafter described, provides the optical configuration of an aplanatic, two spherical mirror microscope constrained by the imposition of the Schwarzschild condition so as to prevent aberrations, i.e., R.sub.2 /R.sub.1 =1.5-R.sub.2 /Z.sub.0 .+-.(1.25-R.sub.2 /Z.sub.0).sup.1/2 wherein Z.sub.0 is the distance along the optical axis he center of curvature C to the specimen. The reflecting surfaces 20, 24 of the mirror substrates 18, 22 respectively as aforesaid are coated with identical precision multilayer coatings 20, 24. The mirror substrates 18, 20 must be polished to an ultra-smooth finish prior to the application of the multilayer coatings. In the preferred embodiment the mirror substrates 18, 20 are of Hemlite Grade Sapphire, a stable material capable of receiving an ultra-smooth surface finish, which is polished by Advanced Flow Polishing or Ion Polishing methods capable of producing ultra-smooth surfaces to an RMS surface smoothness of 0.5 to 3 angstroms. Other materials deemed suitable for the mirror substrates, but which do not yield as high a polished surface as has been achieved on Sapphire, are Fused Silica and Zerodur. These materials have lower coefficients of expansion than Sapphire and would be preferred for applications where the optics may be subjected to significant thermal loadings. In the preferred embodiment, the multilayer coating to be utilized on the mirror will be a Tungsten/Silicon multilayer with a 2D of 36 angstroms. This is well within the "water window" but of a significantly long wavelength that the required coatings can now be produced. The multilayer operates as a synthetic Bragg crystal, reflecting x-rays by diffraction in accordance with the Bragg relation: n(.lambda.)=2DSin(.phi.), where n is the order of diffraction, .lambda. is the wavelength at which peak reflectivity occurs, D is the sum of the thickness of each of the high-Z diffractor layers in the stack plus the thickness of each of the low-Z spacer layers of the coating, and .phi. is the angle at which the radiation strikes the surface of the multilayer. Since the preferred form of the microscope is designed to operate at normal incidence, sin (.phi.)=1 and the Bragg relation reduces to the case in which the wavelength at which peak reflectivity by first order diffraction occurs is equal to the 2D parameter of the multilayer coating. Consequently, for this preferred embodiment of the microscope, the peak reflectivity will occur at an x-ray wavelength of 36 angstroms. With an appropriately configured Tungsten/Silicon multilayer, bandpass can be made sufficiently narrow such that a multilayer situated to peak at 36 angstroms should have a transmission which is a very small fraction of one percent for wavelengths longer than 43.7 angstroms and shorter than 23.3 angstroms. The multilayer coatings 20, 24 of both the primary and secondary mirrors 18,22 respectively must be very precisely matched to the same wavelength or greatly reduced system reflection efficiency will result. For this reason, it is preferred that both mirrors be coated at the same time. By sizing the secondary mirror and the annulus or aperture 26 of the primary mirror appropriately, the secondary mirror may be mounted within the aperture in the center of the primary mirror during the application of the multilayer coating to ensure very accurate bandpass matching of the primary and secondary optics. Under ideal conditions, a Tungsten/Silicon multilayer should be capable of yielding a normal incidence reflection efficiency of five to ten percent or more in this wavelength regime. Alternately, different multilayer coatings such as WB.sub.4 C, Mo/Si, or other coatings may be utilized and other 2D spacings selected to operate at other wavelengths in the "water window." Any of these or other appropriate multilayer coatings capable of producing the required narrow biologically important wavelength may be utilized. Shorter wavelengths yield higher contrast but it is more difficult to produce coatings for them. The important characteristics to be sought in any such multilayer coating is high reflectivity at the selected narrow bandpass within the 23.3 to 43.7 angstroms defining the "water window" with very low reflectivity outside of this wavelength range. Other important features of the coating include long term stability and the ability of the coating to be applied to a highly curved substrate with excellent bandpass matching for the primary and secondary mirrors Although any system magnification within a wide range can be selected, it is preferred that the microscope have a magnification of 25.times. and the convex secondary mirror substrate preferably has a radius of curvature of 8 cm. These parameters of magnification and substrate curvatures are dictated by the current state-of-the-art for fabricating precision multilayer coatings of the required low 2D spacing on curved surfaces and the desire to maintain the overall system length at a reasonable value for convenient instrument implementation. At a magnification of 25.times., when the Schwarzchild condition is imposed, the primary mirror substrate 18 has a radius of curvature such that the resultant system length, i.e., the distance from the object plane to the image plane, can be maintained at less than two meters. Alternately, systems with higher or lower magnifications may be constructed with microscope magnifications in the range of 20.times. to 30.times.. High resultant image magnifications, i.e., several thousand diameters, can be achieved by enlarging images recorded on ultra-high resolution photo resists or photographic films which are currently available. It is expected that more compact systems and systems with higher magnifications will be developed as the methods and techniques for fabricating lower 2D multilayer coatings are developed by advanced magnetron sputtering, atomic layer or molecular beam epitaxy methods. The surface configurations of the concave spherical primary mirror substrate 18 and the convex spherical secondary mirror substrate 22 should be accurate to better than 1/20 wave when tested with visible light. Under these conditions the preferred form of the microscope should have a useful field of view in the order of 1 mm and spatial resolution of better than 100 angstroms over a reasonable field in the object plane. This will permit the instrument to spatially resolve larger molecules, as well as many other ultra-small carbon based structures to be observed within living cells. The microscope can also be applied to investigations of viruses, proteins and protein crystals and a vast array of other microscopic structures outside of living cells. Indeed, although the primary thrust of the present invention lies in its ability to observe with high contrast, carbon based structures in the "water window" the microscope will be quite capable of producing high resolution images of non-carbon based microstructures, such as chemicals and pharmaceuticals, microscopic specimens of minerals and metal alloys. High contrast images of microscopic carbon based structures in living cells and other specimens placed in the object plane of the microscope can be produced in ultra-high spatial resolution and recorded by a suitable detector placed in the image focal plane 46 of the microscope. The stage end 44 of the mount tube 12 includes an aperture 48 within which the specimen 42 is mounted. The specimen 42 is deposited on the surface of a pre-filter 50 mounted in a filter holder 52 affixed to a movable specimen stage 54 by means of screws 56 or the like. The specimen stage 54 may be driven by any of a number of piezoelectric translator devices 58 which are commercially available. The piezoelectric translator 58 is fastened to the stage end of the mount tube 12 by means of screws 60 or the like. For reasons hereinafter explained the piezoelectric translator should be capable of functioning under vacuum conditions and are connected by wiring 62 to an interface 64. Any of a number of commercially available piezoelectric 3-axis translation devices satisfying these criteria are available and would serve to permit remote focusing and permit different regions of the specimen mount to be centered upon the optical axis. To illuminate the specimen with x-rays either an x-ray source 66 having a filament 68 and a target 70 may be mounted adjacent the stage end of the microscope, the filament 68 being fed by wiring 72 to an appropriate interface 74, or other suitable high intensity x-ray sources such as laser plasma sources, emission produced in laser fusion experiments at the University of Rochester's OMEGA Facility or the Lawrence Livermore National Laboratory's NOVA Facility or Synchrotron storage rings may be utilized. In the case of the Synchrotron, mounting tube 12 would be mounted within a vacuum chamber attached to the Synchrotron beam line. In the preferred embodiment in order to detect the image at the image focal plane 46 a detector in the form of a photographic film 76 is fed from a standard film cassette 78 mounted in a camera body 80, the camera conventionally having an internal motor drive 82. A remote adapter 84 may be utilized connected through electrical wiring 86 to an interface 88 so that exposures and film advance can be remotely operated. Conventional 35 mm or 70 mm film cameras with internal drive are suitable, examples being the Cannon T-70 35 mm camera and the Pentax 645 70 mm camera, both of these cameras being capable of operating in a vacuum environment as hereinafter described. The camera 80 includes a conventional lens T-mount 90 to which an adapter interface 92 is connected, the interface also being connected to a flange 94 at one end of a camera mounting tube 96 by conventional means such as screws or the like (not illustrated). The other end of the camera mounting tube 96 includes a mounting flange 98 which is secured by screws or the like 100 to the image end 34 of the microscope mounting tube 12. The detector film 76 preferably comprises a photographic emulsion such as type 649 produced by Eastman Kodak Company of Rochester, New York without a gelatin overcoat and deposited upon an anti-static backing which is suitable for vacuum operation. X-Ray test measurements on this film have shown it to be sensitive to x-rays in the 23.3 to 43.7 angstrom wavelength range and have a measured spatial resolution in the order of 2000 line pairs per mm. This ultra-high resolution allows great enlargements of the resultant images produced photographically yielding effective magnifications of several thousand diameters. The aforesaid type 649 photographic film affords ultra-high spatial resolution, (although it has reduced sensitivity as compared to traditional emulsions such, as 101-07 or the newer XUV 100 Tabular Grain film), when used with Synchrotron beam or the very bright pulsed sources, such as emissions produced when the 24 beam of UV (3510 angstrom) light converge on the target and laser fusion OMEGA Facility. A water window imaging x-ray microscope designed for use with a laser fusion facility must not interfere with the laser beams which converge on the pellet which they implode. The microscope will actually be mounted into the spherical cavity on the laser fusion device when it is desired to perform studies of the fusion event itself, or to obtain maximum illumination on the specimen. A water window imaging microscope to be used with this type of source, must have a conical exterior structure such that the converging beams can reach the pellet (which is to be imploded to produce the the fusion reaction). Instruments placed within the spherical chamber of the OMEGA facility are not permitted to obstruct the laser beams. FIG. 3 shows a water window imaging x-ray microscope of a conical configuration for use with this facility. The camera (not shown) mounts to camera tube 296 at mount flange 294. The primary reflector 214 is mounted in primary mirror mounting cell 228 and is attached to imaging end baseplate 234 by means of screws (not shown). The filament wound graphite cone 212 forms the stable optical bench that establishes and maintains the separation and alignment of the secondary reflector 216 to the primary reflector 214. Graphite epoxy is used in the preferred embodiment because it can be made with near zero coefficient of expansion, and it is very strong and lightweight. The secondary reflector 216 is mounted on spiders 240. A filter mount cone 252, constructed in the preferred embodiment of low carbon stainless steel is mounted to the end of graphite cone 212 by screws (not shown). The specimen 242 is deposited on the surface of a filter 250 affixed to a specimen mount stage 254 attached to the end of filter mount cone 240 by means of screws or the like The reduced film sensitivity poses no problem even when extremely high time resolution images are desired since the x-ray pulse produced is so brilliant. If the specimen is illuminated at the energy level and burst times utilized at the OMEGA Facility, images can be recorded with a microscope according to the present invention as though the specimen was illuminated by an intense x-ray strobe light. With high repetition rate laser plasma sources successive frames recorded with successive pulses should permit time varying processes within a living cell to be captured in the images so that direct imaging of the most fundamental and crucial of all life processes, the actual replication of DNA molecules in situ and reveal the processes of information transfer via the messenger RNA. This may even permit multiple images recorded by successive rapid pulses from high intensity laser plasmas to record ultra-high resolution motion pictures of these life processes. The XUV 100 emulsion although offering higher sensitivity than the type 649 emulsion, has a lower spatial resolution in the order of approximately 200 line pairs per mm. and would be preferred where the higher sensitivity is required such as for small, self-contained systems designed to operate with lower intensity x-ray sources. Photographic film as the detector offers a vast information storage capability and spatial resolution capability that appear to far exceed other detector means. However, alternate two dimensional imaging detectors that may provide direct, real-time images without photographic processing may include position sensitive proportional counters, charge coupled devices (CCD's) or Multi-Anode Microchannel Array's. Referring again to FIG. 1, the normal incidence multilayer coated mirrors 18, 22 are also capable of effectively reflecting visible light radiation. Since this could constitute a highly undesirable source of photons upon the detector, particularly when synchrotron, laser plasmas and other sources which produce bright fluxes of visible light are used to illuminate the specimen being investigated by the microscope. Therefore, to remove unwanted radiation, one or more thin foil x-ray filters preferably are mounted in the optical path. Such filters not only remove unwanted visible light, but also further reduce the system transmission of photons at wavelengths which lie outside of the natural bandpass. Several chemical elements have suitable L and M series absorption edges for utilization in such filters. These include the L edges of vanadium, titanium and scandium, and the M edges of tin and indium. For a system designed for use with the OMEGA Facility, the filter 50 upon which the specimen is deposited may be a pre-filter comprising a five mm diameter foil of unsupported titanium of 1500 angstrom thickness, or fail supported upon a nickel mesh. The x-ray transmission of this filter is expected to exceed 60 percent. Also, immediately in front of the camera 80 is a camera x-ray filter 102, which in the preferred embodiment comprises a composite of 1500 angstroms of tin with 500 angstroms of aluminum also supported upon a nickel mesh, the x-ray transmission of this filter being expected to exceed 50 percent in the "water window" wavelength band. Since air becomes very absorptive of x-rays above 20 angstroms, in order to reduce such absorption which would reduce the flux from the source and weaken the intensity of the image reaching the detector with acceptable exposure times, the entire microscope apparatus should be placed in a vacuum. This is true whether or not the microscope is used in conjunction with a synchrotron facility or laser fusion facility such as OMEGA, or used with a self-contained x-ray source such as illustrated at 66. Accordingly, the apparatus as heretofore described should be mounted within a vacuum chamber 104 equipped with appropriate vacuum valves such as 106 connected to one or more vacuum pumps 108 to allow the system to be evacuated prior to operation. The vacuum drawn may be in the order of 10.sup.-3 or 10.sup.-4 torr, and preferably is 10.sup.-6 to 10.sup.-8 torr for use in conjunction with a synchrotron facility. The chamber 104 includes a camera access port and specimen stage access ports at respective ends of the chamber are provided and closed by respective vacuum plates 110, 112 connected in sealed relationship with the chamber 104 by means of bolts 114 or the like. For use with external sources of radiation, such as synchrotrons, vacuum plate 112 contains a port 160 that terminates in a standard varian conflat flange 170. A high vacuum gate valve 180 is mounted to flange 170 by varian screws 172. To achieve a good seal, conventional copper gaskets 194 are used at all mating surfaces in accordance with standard high vacuum practices. Many types of high vacuum gate valves are commercially available and a simple mechanical valve is herein depicted to illustrate the principle only. Gate valve 180 contains a gate 190 which can be opened and closed by rotating lever 192. Outer surface of gate valve 180 is configured as a standard high vacuum conflat flange 196. This flange serves as the mount surface for the purpose of mounting the microscope vacuum chamber 104 to the vacuum chamber which constitutes a part of the synchrotron beam line (not shown). A thin foil x-ray window 198 prevents contamination of the synchrotron beam line by residual gases in chamber 104. This is necessary since synchrotrons must operate at ultra-high vacuum. To prevent thin foil window 198 from rupturing, gate 190 is only opened after a good vacuum (less than 10.sup.-3 torr) is achieved in the microscope chamber 104 and the synchrotron beam line on the other side of the gate valve is under high vacuum. Obviously, prior to use with a synchrotron source, small internal source 66 must be removed or it would block the radiation from the synchrotron beam (not shown) The microscope housing 12 may be supported by V-blocks 116, 118 mounted on the base of the vacuum chamber 104 such that the microscope is at the appropriate level for receiving x-rays from the source. The interfaces 64, 74, and 88 feed the required voltage sources through the chamber while maintaining a tight seal to preclude loss of vacuum. Accordingly, a double reflection microscope transmitting x-rays in the "water window" x-ray band of 23.3 to 43.3 angstroms is disclosed which images on the detector carbon structures in the specimen in high contrast. X-Rays within that bandpass will be reflected by the coatings 20, 24 on the mirrors 18, 22, while x-rays outside of that bandpass will not be reflected. The ultra-smooth polished mirror substrates 18, 22 with the multilayer coatings focus and image the x-rays in the narrow bandpass onto the detector 76. Additionally, in order to avoid undesirable light radiation the thin foil x-ray filters 50 and 102 utilized at the specimen stage and the camera ensure that only transmission at the desired wavelengths is received by the detector. Accordingly, a high resolution microscope capable of operating in the "water window" is disclosed which opens new horizons to research in the area of microbiology. Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to the preferred embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.
	summary
051909901	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS An important component of the radiation shields of the present invention is the powder of non-radioactive non-toxic high atomic density metal or metal alloy spherical particles. The high atomic density of the metal or metal alloy is desirable because it correlates with high Z (electron density within the atom). Heavy metals or alloys of heavy metals which can be atomized to very small spherical particles are particularly preferred. The use of molten atomization processing of metals or metal alloys makes possible the formation of highly spherical powders of very small particle sizes of, e.g., 40 microns and less. In general, powders with average particle sizes of about 1 to about 100 .mu.m are preferred, with 40 microns or smaller particularly preferred. Lathe cut or ground powders become stiff and unformable at high packing densities due to physical interferences on the particle surfaces. The use of spherical particles makes possible very dense packing without the loss of material flow properties. The atomization process used for fabrication of the powder alloys is similar to techniques described by Ridder and Biancaniello (1988). This process uses high pressure inert gas atomization field kept under inert gas pressures in excess of 100 bar. The particle size and shape are controlled by the molten metal pressure at the nozzle, the metal flow rate, and the solidification field pressure. Particle sizes are determined by laser diffraction, which measures the forward scattering of laser light through the process powder-stream, and this information is used to control the atomization processing parameters. The particles are then separated and graded. Examples of metal alloy compositions which may be used to formulate the spherical particle filler include 60 wt % Sn-40 wt % Sb; 70 wt % Ag-30 wt % Cu eutectic, 95 wt % Sn-5 wt % Sb, 81.5 wt % Cu-9.5 wt % Al and 72 wt % Ag-18 wt % Cu. These proportions of various metals are illustrative only, and the proportions may of course vary. Alloys of lead, bismuth, tin and cadmium are other choices. Metal powders of these and similar alloys with high packing densities are believed to be capable of exhibiting shielding qualities similar to solid metals when dispersed in an elastomeric precursor. Mixtures of particles of more than one composition type may be employed if desired. The powder of spherical metal or metal alloy particles is then homogeneously mixed as a high concentration filler into the liquid component of pre-polymerized elastomeric resin which can be worked by hand or with hand tools and which is polymerizable to a semi-rigid state within a clinically acceptable time period. Very high volume fractions of these powders can be incorporated into a polymer matrix to form a moldable mass with high metal density. Specifically, once the metal powder has been processed, it is blended in varying proportions with elastomeric polymers to form mixtures which can be easily handled and processed into prosthetic appliances. Packing density of the metal particles is controlled by gap-graded blending of different particle sizes as is common to the optimization of filler configuration in composite dental materials (Bowen, 1964). The filled metal-polymer blends are formulated to give the maximum stopping power with minimal effects from electron scatter while maintaining working consistencies adequate for convenient fabrication using both direct and indirect techniques. The level of metal or metal alloy spherical particle filler present in the elastomeric resin is variable depending on the shielding requirements necessitated by the radiation therapy which is indicated. Preferably the filler level is at least about 50 weight %, and may be as much as about 95 weight %, of the composite. The elastomeric material should also be non-toxic under its conditions of use. The preferred elastomeric resins are, due to their ready availability, commercial addition-reaction polymerizable silicone impression materials. Silicones and vinyl polysiloxane compositions are suitable, for example. The polysiloxane materials rely on catalyzed addition reactions to initiate polymerization, which gives the greatest amount of control over the working and handling times. Especially preferred are vinyl polysiloxane impression materials such as Reprosil.TM., available from Caulk/Dentsply in a form such that two equal parts of base and catalyst are mixed together. Other examples of silicone and vinyl polysiloxane precursors which may be employed include Hydrosil.TM. (Caulk/Dentsply), Impergum.TM. (Premier), Extrude.TM. (Kerr), Express.TM. (3M), Cuttersil.TM. (Cutter), Absolute.TM. (Coe), Baysilex.TM. (Cutter) and Cinch-Vinyl.TM. (Parkell). Reprosil.TM. (Caulk/Dentsply) is a polysiloxane impression material available in three fluid viscosities (light, medium, and heavy) as well as a thicker putty consistency. The base component and catalyst component are supplied separately and mixed in equal volumes to initiate polymerization. Different proportions of metal powder are optimal for different therapeutic modalities, and depending on the type and amount of filler employed, the preferred viscosity of polysiloxane may vary. The metal alloy powder is blended using hand or mechanical spatulation with all three viscosities of the elastomer to form equal metal-fraction catalyst and base components of each. Materials may be selected which demonstrate a fluid viscosity capable of reproducing the detail of a standard test pattern utilized for testing detail reproduction (ADA Specification No. 3) for dental impression compound (Stanford et al., 1955) or which have the viscosity closest to impression putty which can be mixed by hand kneading. Modifications in viscosity may be achieved as needed, for example by the further addition of (1) filler in the form of metal powder, (2) colloidal silica powder, and/or (3) finely ground polymerized elastomer. Other additives may also be incorporated in the composite so long as they do not negate its usefulness for its intended purpose. The various components of the material for formulation of the shield may be packaged in a convenient kit, for example, with a putty component of metal powder in base resin, a putty component of metal powder in catalyst, a component of unfilled resin, and a component of adhesive. Once the metal powders of high atomic density are blended as fillers with elastomeric polymer precursors to yield materials that can be mixed and applied directly without the laboratory fabrication of molds or models, both extra-oral and intra-oral shielding appliances can be conveniently formulated. The appliances may be fabricated in a reasonable amount of time (e.g., less than 20 minutes) within the radiotherapy treatment setting without the assistance of dental laboratory support. For example, unfilled impression putty material may be mixed and rolled out to form a sheet of approximately 0.5 mm thickness. This sheet of material can then be adapted to the body contours by hand manipulation and allowed to set. Airways are established and eye and nose protection provided as needed with cotton according to techniques commonly used in the taking of facial impressions. A thin layer of impression tray adhesive may be applied if necessary to the set material. The metal-filled elastomer is then mixed and applied over the unfilled elastomer. Viscosity adjustments may be necessary to formulate a material which can be controlled adequately during this application. After curing, the stent is removed and the radiation treatment window cut into the mask wherever appropriate. The shield is then positioned on the patient so as to correctly locate the treatment window and shield periphery, and radiation therapy is conducted in accordance with the usual treatment regimen. An example of the fabrication of an intraoral appliance would be the mixing of a thick putty consistency of the filled composite material and directly introducing it into the treatment site using a dental impression tray or by hand finger molding. After polymerization the shield would be removed, shaped and trimmed with a knife, and additions and corrections made where necessary by the adding of additional filled composite. Regions of high backscatter could be attenuated by the addition of a thin layer of unfilled polymer. The completed appliance could be reused for the duration of treatment sessions and could benefit additionally as a positioning stent for beam targeting. One problem associated with the use of metal shielding devices is the formation of electron scatter when using gamma and x-ray sources. This secondary radiation is comprised of low energy electrons and positrons which have a very short range of 1 to 2 mm in tissue. This effect is observed around dental protheses such as gold crowns. Acute reactions have occurred in tissues immediately adjacent when these restorations are in the beam path. (Thambi et al., 1979). This secondary radiation can easily be absorbed in materials of low density such as wax (Thambi et al., 1979; Fleming and Rambach, 1983) or impression materials. Intraoral stents employing metal must be coated with a sufficient thickness of polymer so as to laminate the beam-blocking metal between layers of scatter-absorbing acrylic (Fleming and Rambach, 1983). The inventive materials with high metal volume may also require the addition of a layer of unfilled polymer to absorb the metal-induced scatter. Unfilled polymer of similar consistency and handling properties could be easy laminated to the inventive materials to absorb surface scatter. Tests using collimated gamma-ray beams from a .sup.60 Co teletherapy unit show that quickly formed composites made of a flexible resin with high concentrations of powdered spherical metal alloys provide effective custom-designed shielding, as well as diminished backscattered radiation to normal tissues. An example of a successful formulation is a mixture of 90% by weight AgCu alloy powder in a vinyl polysiloxane resin. This material is a moldable putty which upon polymerization forms a rigid elastomeric material that is capable of attenuating approximately 50% of a .sup.60 Co beam at a thickness of only 2 cm. Interleaved stacks of calibrated thin radiochromic film strips and soft-tissue-simulating plastic (polystyrene) layers gave a means of mapping three-dimensional profiles of dose distributions adjacent to the high-density shielding materials using a spectrophotometer equipped with a gel scanner. EXAMPLES I AND II A study was performed to document the degree of shielding afforded by different resin-metal combinations and the optimum thickness of coatings required to limit dose enhancement due to backscatter of secondary electrons. A commercially available vinyl polysiloxane (referred to henceforth as "PVS") impression material (Reprosil.TM., Caulk/Dentsply) mixed in two equal parts, base and catalyst, was used as the elastomeric binder in the formulation of the test material. Equal quantities by weight of base and catalyst components were separately mixed with constant weights of one of two powdered spherical metal alloys. The two alloys used were a 60/40 weight-ratio Sn-Sb and a 70/30 weight-ratio Ag-Cu eutectic, in the form of spherical alloy powders. The alloy powders each exhibited an average particle size of 30 m. The filled base and catalyst were combined and mixed by hand kneading for approximately one minute (the consistency was putty-like and maintained its form during setting). The mixed mass was then immediately compacted into a long plastic cylinder, 1 cm in diameter, and allowed to cure for 5 minutes, into a solid rod. The total working time was about 2 minutes and the setting time approximately 5 minutes. Sample disks were then cut from this rod in lengths ranging from 0.5 to 10 cm. In order to measure radiation absorbed doses in water, D.sub.water (equivalent to absorbed dose in soft tissue), a new thin-film dosimetry medium (called GafChromic.TM.) was used. M. Saylor, T. T. Tomargo, W. L. McLaughlin, H. M. Khan, D. F. Lewis, and R. D. Schenfele, "A Thin Film Recording Medium for Use in Foot Irradiation," In: Proceedings, 6th International Meeting on Radiation Processing, Ottawa, Canada, 1987, Radiat. Phys. Chem.; W. L. McLaughlin, Chen Yun-Dong, C. G. Soares, A. Miller, G. Van Dyk, and D. F. Lewis, "Sensitometry of a New Radiochromic Film Dosimeter Response to Gamma Radiation and Electron Beams," (submitted to Nuclear Instruments and Methods, 1989). This coated radiochromic film has a sensor coating thickness of 6 .mu.m on a film base of 100 .mu.m polyester plastic. The film changes from a colorless to a high-resolution blue image with two absorption polysiloxane peaks (.about.650 and .about.600 nm) due to irradiation, without need for development of the image. The useful dose range is approximately 50 to 1,000 Gy (gray (Gy), where 1 Gy=1 Jkg.sup.-1, and in terms of the older unit of absorbed dose, rad, 1 Gy=100 rad) for radiographic imaging and dosimetry when the spectrophotometer measures the radiation-induced increase in absorbance at 650 or 600 nm (near the major and minor absorption peaks, respectively) as a function of the dose. These functions .DELTA.A.sub.650 or .DELTA.A.sub.600 versus D.sub.water, are nearly linear over this dose range. M. Saylor, T. T. Tomargo, W. L. McLaughlin, H. M. Khan, D. F. Lewis, and R. D. Schenfele, "A Thin Film Recording Medium for Use in Foot Irradiation," In: Proceedings, 6th International Meeting on Radiation Processing, Ottawa, Canada, 1987, Radiat. Phys. Chem. A calibration curve for the GafChromic.TM. film was generated by recording the values of .DELTA.A.sub.650 versus scanning distance across adjacent square pieces of the film irradiated to the indicated series of doses, using the scanning spectrophotometer set at 650-nm wavelength (slit image with dimensions 0.05 mm by 3 mm). The spectrophotometric readings were made with unirradiated film in the reference beam. Film strips of various lengths, depending on the lateral dimensions required, were mechanically transported lengthwise past the slit image using a gel scanning attachment and aligned so that the long dimension of the slit was perpendicular to the direction of the film motion. A continuous record of A.sub.650 as a function of distance along the length of the film provided a record of the lateral dose distribution according to the calibration of .DELTA.A.sub.650 versus D.sub.water. For the depth-dose profile study, the test materials were 1-cm-thick unfilled PVS polymer, 1-cm-thick polystyrene, 1-cm-thick 80% Sn-Sb alloy powder in PVS, and 1- and 2-cm thick 80% and 90% Ag-Cu alloy powder in PVS. One specimen was fabricated from 80% Ag-Cu alloy powder in PVS, cut to 0.8-cm length, and covered on one side with 0.2-cm-thick polymer (PVS only) to shield against the backscatter of secondary electrons. Each of these cylinders was sandwiched end-on between two stacks of calibrated GafChromic.TM. dosimeter films. All films were irradiated with the 6-m sensor coating facing toward the specimen cylinder ends on both sides. The gamma-ray beam axis was perpendicular to the surfaces of the stacked films. A .sup.60 Co source of gamma radiation (mean energy 1.25 MeV) was used for the irradiations (nominal dose 100 Gy). A square collimator supplied a gamma-ray beam that was several centimeters larger than the lateral dimensions of the phantom. For the measurement of absorbed dose versus thickness of the shielding material on the forward scatter side, ten different thickness cylinders of 90% Ag-Cu alloy powder in PVS, ranging from 0.5 to 10 cm in length, were placed on the radiation source side of the upper dosimeter films. The 20.times.20 cm collimated gamma-ray beam axis was perpendicular to the surfaces of the dosimeter films. Intimate contact was maintained between the shielding material and the thin sensor films in plane-parallel geometry. The phantom assembly was exposed to the same source and dose used in the previously described experiment. Each dosimeter film was read spectrophotometrically in terms of absorbed dose, to water or soft tissue, as a function of distance over the length of the film strip. Since the response characteristics, radiation penetration, and scattering properties of the detector-polymer laminates were approximately the same as those of biological tissues (e.g., compact bone and striated muscle), the resulting three-dimensional dose distributions simulated those in living tissues on both the forward- and backscattering sides of the shielding composites. FIG. 1 shows the gamma-ray depth-dose distributions on forward- and backscatter sides of the test specimen-film interfaces, using four different test materials. Polystyrene spacers 0.5-cm thick, were interleaved between the eight most distant films on each side of the test materials to demonstrate the dose distributions as a function of depth in the plastic material away from the interface. Depth-dose distributions on both sides of the materials reached a plateau corresponding to conditions of electron equilibrium at a depth of approximately 0.3 g cm.sup.-2 from the material interface. The "dose enhancement factor" (defined as the ratio of the maximum dose in water or soft tissue close to a high atomic-number interface material) on the backscattered side of the interface for each material was: 1.7 for 1-cm-thick 90% Ag-Cu powder in PVS, 1.6 for 2-cm-thick 90% Ag-Cu powder in PVS, 1.1 for 1-cm-thick PVS without metal filler, and 1.0 for 1-cm-thick polystyrene. Comparisons of the equilibrium dose levels on the backscatter and forward-scatter sides of the figure indicate the degree of attenuation of the .sup.60 Co beam by the samples. FIG. 2 illustrates the forward- and backscatter depth-dose distributions at interfaces with 1 cm-thick polystyrene, 1-cm 80% Sn-Sb powder in PVS, 0.8-cm 80% Ag-Cu powder in PVS covered with 0.2-cm of unfilled PVS, 1-cm 80% Ag-Cu powder in PVS, and 1-cm-thick 90% Ag-Cu powder in PVS, when irradiated from one side by the gamma-ray beam to the total nominal dose of 100 Gy. The dose reached approximate equilibrium values for each material at distances greater than 0.3 g cm.sup.-2, the range of the most penetrating secondary electrons. The dose enhancement factors on the backscattered side of the composite interfaces were: 1.6 for 1-cm 80% Sn-Sb and 1-cm-thick 90% Ag-Cu, 1.1 for 0.8-cm-thick 80% Ag-Cu covered with a 0.2-cm unfilled polymer layer, and 1.7 for 1-cm-thick 90% Ag-Cu. The reduction in backscatter with the sample containing the 0.2-cm layer of unfilled polymer is due to the attenuation of the low-energy electron scatter within this layer. FIG. 3 illustrates the effect of shielding thickness in terms of the transmitted dose (Gy) versus thickness of 90% Ag-Cu powder in polysiloxane measured on the forward-scatter side of the composite shielding material. The reduction in transmitted dose is largely due to greater photon and secondary electron attenuation by the increasing thickness of denser absorbing materials. The half-dose thickness of this particular material was approximately 2 cm when exposed to .sup.60 Co gamma radiation. In x- and .gamma.-ray teletherapy, the forward- and backscattered doses in soft tissue adjacent to metallic or other high-density material exhibit a marked dose enhancement effect near the interface. This dose enhancement effect is much greater on the backscattering side of the interface and it increases with increasing density and atomic density of the scattering material. Forward scatter and attenuation contributions to the dose distributions are also dependent upon the distance from the interface and atomic density of interface material. In addition, the forward-scatter dose profile and degree of shielding vary with the thickness of the high atomic density interface material, due to greater photon attenuation by the thicker and denser absorbing materials. In general, the present experiments with .sup.60 Co gamma rays demonstrate that the "soft tissue" on the forward-scattering side of high atomic-number metal or metal-polymer composite is subjected to a significantly diminished radiation dose (as much as 50% lower) when the photon beam passes through the shielding layer containing Ag, Cu, Sn, Sb and polymer composites or combinations of these. A 90% Ag-Cu-PVS composite layer of 2-cm thickness provides shielding equivalent to approximately 1-cm of lead for .sup.60 Co gamma radiation, H. E. Johns, The Physics of Radiology, second edition (Springfield, Ill., Charles C. Thomas, 1961) p. 633, which is approximately one-half the dose that would be received without shielding. An important consideration to keep in mind is that the surface "soft tissues" would be overdosed by nearly a factor of two on the corresponding backscatter side, and therefore, the electron backscatter in the high atomic density prosthesis must be absorbed by a thin (2-3 mm) unfilled polymer layer. Thus, these metal-polymer composites are effective shielding materials when used with .sup.60 Co radiation teletherapy. EXAMPLE III An experiment was run utilizing addition silicone impression materials to absorb radiation scatter only, with no attempt to shield surrounding tissues from incident (incoming) radiation around metallic restorations. This experiment was performed on a patient receiving 6000 rads of fractionated 6 MeV x-ray therapy for a tumor of the mandible where the lower left first molar was restored with silver-palladium crown and was directly in the beam path. A soft tissue lesion had appeared after 12 treatments in the 24 treatment regimen and therapy was interrupted to allow for healing. During the final 12 treatments a commercially available impression putty (Express.TM., 3M) was mixed and formed into a quadrant bite block covering the metallic restoration and stabilizing the bite position. Dosimeters implanted into the impression material were used to measure dose directly adjacent to the teeth and 3 mm into the silicone material. Direct dose measurements demonstrated a dose enhancement of over 20% adjacent to the crown and complete attenuation of the enhancement 3 mm into the shielding material. There was no recurrence of tissue damage in this case. Several patients were treated after this first trial using this technique, and none suffered this kind of soft tissue damage. Thus, only a few millimeters of material of near-unit density are necessary to completely eliminate tissue damage due to localized scatter. Furthermore, this test demonstrated the convenience of using these autopolymerizing materials for this type of application. Fabrication of the shield required no laboratory support and was done in the radiotherapy treatment room in approximately ten minutes. The shielding stent was durable enough to be reused for the entire treatment regimen and was very amenable to utilization of the commonly used thermoluminescent detector (TLD) dosimetry. An added advantage was the stabilization of bite position allowing for more accurate and reproducible targeting of the treatment beam. EXAMPLE IV A spherically atomized powder of a tin-antimony (Sn-Sb) alloy was screened to grade the particle sizes to 40 micrometers and smaller. This powder was then blended individually into the base and catalyst components of a polysiloxane impression material (Reprosil.TM., Caulk/Dentsply), which had a light-body consistency, to yield mixtures which were 80% by weight alloy. The use of the spherical powder resulted in a material which still had a fluid consistency and could be easily formed. The base and catalyst mixtures were combined and formed into blocks of material which were later cut to specified thicknesses. Setting time was within normal limits for the impression material, and the final polymer exhibited elastic properties similar to original impression material. One-centimeter cubes were cut from the cured metal-filled polymer using a diamond wafering saw (Isomet.TM.), and similar cubes were cut from a sample of the unfilled impression material. A phantom was assembled utilizing the two kinds of samples and a control of polystyrene; dosimetry films were stacked on both sides of the materials to measure the depth-dose profile around them. The phantom was irradiated with 10 Gy (10,000 rad) of cobalt 60 gamma radiation and films were read on a scanning spectrophotometer. The resulting depth-dose profile indicated a surface backscatter similar to that experienced with metal interfaces. This indicates that the density of metal within the polymer was high enough to require an additional layer of low density polymer on the surface to absorb this short-range scatter. The total attenuated dose at the surface (primary beam plus secondary electrons) on the forward side of the Sn-Sb-filled material was approximately 70% of the polystyrene control dose and 80% of the dose level within the unfilled impression material. This represents a significant dose reduction considering the high energy of the 1.2 MeV cobalt beam which would normally be attenuated only 42% with 1 cm of the Lipowitz solid shielding alloy (Poole and Flaxman, 1986). It should be understood that the foregoing disclosure emphasizes certain specific embodiments of the invention and that all modifications or alternatives equivalent thereto are within the spirit or scope of the invention as set forth in the appended claims.
	description	This application claims the benefit of priority under 35 U.S.C. § 1.119 to Korean Patent Application No. 2005-66517 filed on Jul. 22, 2005, the entire contents of which is herein incorporated by reference. 1. Field of the Invention Example embodiments of the present invention relate to an analyzing chamber and a mass analyzer including the same. In particular, example embodiments of the present invention relate to an analyzing chamber including a leakage ion beam detector for detecting a leak in a guide protecting a sidewall of the chamber, and a mass analyzer including the same. 2. Description of the Related Art Generally, semiconductor devices are manufactured by a series of unit processes including, for example, a photolithography process, an etching process, a diffusion process, an ion implantation process, a polishing process, cleaning and drying processes, etc. One or more of the processes may be selectively and repeatedly performed on a semiconductor substrate such as a wafer, for example. Among the above unit processes, the ion implantation and the diffusion processes may affect the electrical characteristics of the wafer the most. In an ion implantation process, a sufficient energy to penetrate a surface of the wafer may be applied to a plurality of ions and the ions may be implanted into the surface of a wafer at a depth. A conventional ion implantation process may be used to facilitate density control of the impurities implanted into the wafer and to accurately control the implantation depth of the impurities. Accordingly, an ion implantation process may be widely used for manufacturing a highly integrated semiconductor device. FIG. 1 is a view schematically illustrating a structure of a conventional ion implanter. Referring to FIG. 1, a conventional ion implanter 90 may include an ion source unit 10, a beam line assembly 20, an end station unit 30, a driving unit 50 and a control unit 40. In the ion source unit 10, an impurity gas may be ionized into a plurality of impurity ions and a high energy may be applied to the impurity ions to generate an ion beam. The beam line assembly 20 may guide the ion beam from the ion source unit 10 to a destination through a predetermined path. The end station unit 30 may accurately position a target wafer, and the driving unit 50 may drive the target wafer. The control unit 40 may systematically control the ion source unit 10, the beam line assembly 20, the end station unit 30 and the driving unit 50. Each of the above units may be connected to the control unit through a data line 7 and a control line 8, for example. The beam line assembly 20 may include a mass analyzer 23, a gate valve 21, an ion accelerator 25 and a deflection unit 27. The mass analyzer 23 may extract ions from an ion beam passing through a magnetic field based on a mass/charge ratio of each ion. The gate valve 21 may be interposed between the ion source unit 10 and the mass analyzer 23 and may selectively allow a generated ion beam to travel into the mass analyzer 23. The ion accelerator 25 may accelerate the extracted ions from the mass analyzer 23, and the deflection unit 27 may substantially uniformly scan the accelerated ions onto the wafer. Impurity material may be supplied to the ion source unit 10 of the ion implanter 90 in a gaseous state and may be ionized into a plurality of charged particles. A high energy may be applied to the charged particles in the ion source unit 10 so that the charged particles leave the ion source unit 10 as an ion beam moving at a high velocity. Then, the gate valve 21 may be opened and desired ions may be selected in and pass through the mass analyzer 23. The desired ions may be implanted into a top surface of the wafer after traveling through the ion-accelerator 25 and the deflection unit 27. The wafer may be positioned in the end station unit 30. FIG. 2A is a perspective view illustrating a conventional mass analyzer shown in FIG. 1, and FIG. 2B is a plan view illustrating the conventional mass analyzer shown in FIG. 2A. Referring to FIGS. 2A and 2B, a conventional mass analyzer 23 may include an analyzing chamber 23a for changing the direction of travel of the ion beam irradiated thereto, a shielding section 23b for protecting a sidewall of the analyzing chamber 23a from the high-energy ion beam and a magnet (not shown) installed in the analyzing chamber 23a and generating a magnetic field for extracting ions from the ion beam. The analyzing chamber 23a may include an inlet I and an outlet E. The longitudinal direction of the inlet I may be different from the longitudinal direction of the outlet E. The ion beam may enter the analyzing chamber 23a through the inlet I and ions may be selected in the analyzing chamber 23a. Accordingly, only desired ions leave the analyzing chamber 23 through the outlet E in the longitudinal outlet direction, which may be different from the longitudinal inlet direction. In a conventional analyzing chamber 23a, the outlet longitudinal direction is perpendicular to the inlet longitudinal direction and thus, the conventional analyzing chamber 23a may have the shape of a capital letter ‘L’. Accordingly, in a conventional analyzing chamber 23a, the direction of travel of the ion beam may be perpendicularly changed in the analyzing chamber 23a. The shielding section 23b may be arranged on an inner sidewall of the analyzing chamber 23a and may prevent an ion beam from causing damage to the inner sidewall of the analyzing chamber 23a. The shielding section 23b may include a plurality of shield partitions, which may be individually inserted into a groove one by one such that all of the inner sidewall of the analyzing chamber 23a may be covered with the shielding section 23b. For example, the shielding section 23b may include graphite such as black lead, for example, so that the ion beam may be adsorbed onto the shielding section 23b. An ion beam entering the analyzing chamber 23a through the inlet I may be deflected, travel along an arc-shaped path R and leave the analyzing chamber 23a through the outlet E based on a direction of a magnetic field generated by the magnet. Some of the charged particles, each of which may have a mass smaller than that of the desired ions, may travel along a path L in the analyzing chamber 23 and thus, may be adsorbed onto the shielding section 23b. Further, other charged particles, each of which may have a mass greater than that of the desired ions, may travel along a path H in the analyzing chamber 23 and thus, may be adsorbed onto the shielding section 23b. Accordingly, only the desired ions leave the analyzing chamber 23a. Accordingly, as the conventional mass analyzer 23 is repeatedly operated, the graphite of the shielding section 23b may gradually wear away due to collisions with the ion beam and a hole may be generated on an inner surface of the shielding section 23b. As a result, the inner sidewall of the analyzing chamber 23 may be partially exposed through the hole, and the ion beam may be irradiated onto the inner sidewall of the analyzing chamber 23 and may cause damage to the inner sidewall of the analyzing chamber 23. The damage to the inner sidewall of the analyzing chamber 23 may deteriorate the vacuum degree of the analyzing chamber 23a so that the desired ions can no longer be accurately extracted from the damaged conventional mass analyzer 23. If the shield partitions are not accurately arranged on the inner sidewall of the analyzing chamber 23a and a chink 27 is generated between neighboring shield partitions, the inner sidewall of the analyzing chamber 23a may not be completely covered with the shield partitions and the inner sidewall of the analyzing chamber 23a may be exposed to an ion beam. Accordingly, damage 28 may be caused to the inner sidewall of the analyzing chamber 23. FIG. 3 is a view illustrating a chink between neighboring shield partitions in a conventional analyzing chamber, and FIG. 4 is a view illustrating damage to the inner sidewall of the analyzing chamber, which may be caused by an ion beam leaking through the chink shown in FIG. 3. Example embodiments of the present invention provide an analyzing chamber for detecting an ion beam leaking through a shielding section to reduce and/or prevent damage to the inner sidewall of the analyzing chamber. Example embodiments of the present invention provide a mass analyzer including a mass analyzer for detecting an ion beam leaking through of a shielding section to reduce and/or prevent damage to the inner sidewall of the analyzing chamber. An example embodiment of the present invention provides an analyzing chamber for a mass analyzer. The analyzing chamber may include a body, a shielding section and a detector. The body may include an inlet through which an ion beam enters the analyzing chamber, an outlet through which the ion beam leaves the analyzing chamber, and a space for a path along which the ion beam travels from the inlet to the outlet. The shielding section may be arranged on a sidewall defining the space of the body, and may reduce and/or prevent the ion beam traveling along a path in the body from causing damage to the sidewall of the body. The detector may be interposed between the sidewall of the body and the shielding section and may detect a leakage ion beam leaked through the shielding section from the space of the body. An example embodiment of the present invention provides a mass analyzer. The mass analyzer may include an analyzing chamber, a magnet and a power supply. The analyzing chamber may include a body having a space for a path along which an ion beam travels, a shielding section for preventing the ion beam traveling along a path from causing damage to a sidewall defining the space, and a detector for detecting a leakage ion beam leaked through the shielding section from the space. The magnet may generate a magnetic field in the analyzing chamber, and the power supply may supply electrical power to the analyzing chamber and the magnet. According to an example embodiment of the present invention, the shielding section may be installed along the inner sidewall of the analyzing chamber in one body so that damage caused by a leakage ion beam passing through an arrangement failure of the shielding section, such as a chink, for example, is sufficiently reduced and/or prevented. In addition, the detector may be interposed between the shielding section and the sidewall of the body of the analyzing chamber so that damage caused by a leakage ion beam passing through a hole due to the wearing out of the shielding section may be sufficiently reduced and/or prevented from reaching the sidewall of the body of the analyzing chamber. An example embodiment of the present invention provides a detector. The detector may include a pad, which may be interposed between a shielding section and sidewall of an analyzing chamber, for generating an electrical signal based on an intensity of an ion beam leaking through the shielding section. The invention is described more fully hereinafter with reference to the accompanying drawings, in which example embodiments of the present invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected to or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments of the present invention. Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components. Example embodiments of the present invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments of the present invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle will, typically, have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. FIG. 5A is a perspective view illustrating an analyzing chamber 500 for a mass analyzer according to an example embodiment of the present invention, and FIG. 5B is a plan view illustrating the analyzing chamber shown in FIG. 5A. Referring to FIGS. 5A and 5B, an analyzing chamber 500 of an example embodiment of the present invention may include a body 100, a shielding section 200 and a detector 300. The body 100 may provide a space for a path along which an ion beam may travel from an ion source unit. The shielding section 200 may reduce and/or prevent damage to the inner sidewall 140 in FIG. 6B of the body 100, which may be caused by the ion beam. The detector 300 may detect if an ion beam leaks through the shielding section 200. The body 100 may include an inlet 110 through which the ion beam may enter the analyzing chamber 500 in a first direction and an outlet 120 through which the ion beam may leave the analyzing chamber 500 in a second direction. The first direction may be different than the second direction. The inlet 110 may be connected to an ion source unit. An impurity gas may be supplied the ion source unit and may be ionized into high-energy charged particles, thereby generating an ion beam. As a result, the ion beam may enter into the body 100 of the analyzing chamber 500 through the inlet 110 from the ion source unit. According to an example embodiment of the present invention, the body 100 may include aluminum or an aluminum alloy, for example. The ion beam entering the body 100 through the inlet 110 may be deflected by a magnetic field in the analyzing chamber, may travel along an elliptical locus R in the body 100, and may leave the analyzing chamber 500 through the outlet 120. The locus of the ion beam may be varied in accordance with an intensity of the magnetic field so that desired charged particles having a desired mass leave the analyzing chamber 500, whereas other charged particles, each of which may have a mass smaller or greater than the desired charged particles, may be adsorbed onto the shielding section 200 arranged on an inner sidewall of the space of the body 100. In an example embodiment of the present invention, the space of the body 100 may be set to be a high vacuum degree for accurate analysis and/or extraction of a desired ion beam. Accordingly, the inlet 110 and the outlet 120 may be sufficiently closed from surroundings during operation of the analyzing chamber 500 to maintain the space of the body 100 under the high vacuum degree. According to an example embodiment of the present invention, the first direction of the inlet 110 may cross the second direction of the outlet 120 at an angle within a range of about 70° to about 90°. As such, the ion beam traveling in the first direction through the inlet 110 may be deflected at an angle within a range of about 70° to about 90°, to thereby leave the analyzing chamber 500 in the second direction through the outlet 120. Charged particles, which may have a mass greater than that of the desired ions, may travel along a path L in the space of the body 100 and thus, may be adsorbed onto a first portion of the shielding section 23b. Other charged particles, which may have a mass smaller than that of the desired ions, may travel along a path H in the space of the body 100 and thus, may be adsorbed onto a second portion of the shielding section 200. Accordingly, the desired ions, of which an atomic weight is appropriate for ion implantation, may leave the analyzing chamber 500. An ion beam includes a plurality of high-energy charged particles, so that repeated collisions of the ion beam with an inner sidewall 140 of the space of the body 100 may cause damage to the inner sidewall 140 of the space of the body 100 and may reduce the vacuum degree of the space of the body 100. At least in part due to the above reason, the shielding section 200 may be arranged on the inner sidewall 140 of the body 100 to reduce and/or prevent a direct collision of the ion beam with the sidewall 140 of the body 100. The shielding section 200 may include graphite including carbon (C), such as black lead, for example, so the high-energy charged particles may be sufficiently adsorbed onto the shielding section 200. That is, the adsorption of the shielding section 200 may reduce and/or prevent the direct collision of the ion beam against the sidewall 140 of the body 100 and thus, may reduce and/or prevent damage to the sidewall 140 of the body 100 caused by the ion beam in the analyzing chamber 100. According to an example embodiment of the present invention, the shielding section 200 may include a plurality of shield plates, which may be sequentially arranged on the sidewall 140 of the body 100. Accordingly, the plurality of shield plates may be arranged similar to a belt surrounding the space of the body 100. According to an example embodiment of the present invention, the body 100 may also include a guide line for guiding and/or arranging the shield plates. According to an example embodiment of the present invention, one or all of the plurality of shield plates may be easily replaced if one or more of the shield plates are damaged. FIG. 6A is a perspective view illustrating a shielding section 200 and a pad 300 for detecting the ion beam according to an example embodiment of the present invention, and FIG. 6B is a perspective view illustrating a sidewall 140 of a body 100 including the guide line 130 for arranging the shielding section 200. Referring to FIG. 6A, the shielding section 200 includes a plurality of shield plates, which may be shaped into a belt including a flexible material. For example, the shielding section 200 may include a plate 210 facing the sidewall 140 of the body 100 to protect the sidewall 140 of the body 100 from the ion beam and a pair of fixation portions 212 and 214, which may be used for fixing and/or arranging the plate 210 along the sidewall 140 of the body 100. The plate 210 may include black lead including carbon (C), for example, so that an ion beam traveling toward the sidewall 140 of the body 100 may be adsorbed onto the plate 210. Referring to FIG. 6B, the body 100 may also include a guide line 130, which may protrude from a surface of the sidewall 140, and guide the shield plate along the sidewall 140 of the body 100. According to an example embodiment of the present invention, the guide line 130 may include a pair of supports 130a and 130b formed on the guide line 130 in a body and protrude from top and bottom end portions of the guide line 130 towards each other into the space of the body 100. The shield plate 210 may be arranged from the inlet 110 to the outlet 120 along the guide line 130 and parallel with the sidewall 140 of the body 100 so that the sidewall 140 of the body 100 may be sufficiently protected from the ion beam. If the shield plate 210 is worn away due to repeated collisions with the ion beam and a hole is generated on the surface of the shield plate, the ion beam may leak through the hole and may cause damage to the sidewall 140 of the body 100. According to an example embodiment of the present invention, the shield plate 210 may be replaced, thereby reducing maintenance costs of the analyzing chamber 500. According to an example embodiment of the present invention, the guide line 130 and the fixation portions 212 and 214 may be relatively moveable with respect to each other to facilitate maintenance. While the example embodiment of the present invention illustrated in FIG. 6A shows a belt-shaped shielding plate, a plurality of shielding partitions or any other configurations known to one of ordinary skill in the art may also be utilized in place of or in conjunction with the belt-shaped shielding plate. If the shielding partitions are utilized in place of the belt-shaped shielding plate, a size of the partition may be varied in accordance with facilities of manipulation and installation of the analyzing chamber. According to an example embodiment of the present invention, an ion beam leaking through a hole on a surface of the shielding section 200 may be detected by the detector 300. The detector 300 may include a pad 310 and a signal line 320. The pad 310 may detect the ion beam leakage and may generate an electrical signal based on the intensity of the leakage ion beam. The signal line 320 may transfer the electrical signal. According to an example embodiment of the present invention, the pad 310 may be interposed between the shielding section 200 and the sidewall 140 of the body 100. Although the leakage ion beam may pass through the hole of the shielding section 200, the pad 310 detects the leakage ion beam and generates an electrical signal corresponding to the intensity of the leakage ion beam before the ion beam reaches the sidewall 140 of the body 100 according to an example embodiment of the present invention. The pad 310 may include a photodiode for generating an electrical signal corresponding to the intensity of the leakage ion beam. Accordingly, if the leakage ion beam reaches a surface of the photo diode, a plurality of electrons may be discharged in proportion to the intensity of the leakage ion beam based on a photoelectric effect. According to an example embodiment of the present invention, the pad 310 may be installed on the body 100 using various methods on the condition that the pad 310 is interposed between the shielding section 200 and the sidewall 140 of the body 100. For example, the pad 310 may enclose a whole surface of the sidewall 140 of the body 100, or may enclose a portion of the surface of the shielding section 200. According to an example embodiment of the present invention, the pad 310 may be detachably installed on the surface of the shielding section 200 so that the pad 310 may be easily detached from the shielding section 200 and replaced. According to an example embodiment of an analyzing chamber 500, the shielding section 200 may be formed in a belt shape so that leakage of ion beam through an arrangement defect, such as a chink of the shielding section, for example, may be reduced and/or prevented. In addition, the detector may be interposed between the shielding section and the sidewall of the body so that the leakage ion beam, which may result from the wearing out of the shielding section, may be detected in advance. FIG. 7 is a perspective view illustrating a mass analyzer 900 according to an example embodiment of the present invention including the analyzing chamber 500 shown in FIG. 5A. Referring to FIG. 7, the mass analyzer 900 may include an analyzing chamber 500, power supply 700 and a magnet 600. The analyzing chamber 500 may extract a desired ion beam from an incident ion beam in accordance with a mass of the charged particles of the ion beam. The magnet 600 may generate a magnetic field in the analyzing chamber 500, and a power supply 700 may supply electrical power to the analyzing chamber 500 and/or the magnet 600. According to an example embodiment of the present invention, the analyzing chamber 500 may include a body 100, a shielding section 200 and a detector 300. The body 100 may provide a space for a path along which the ion beam may travel from an ion source unit. The shielding section 200 may reduce and/or prevent damage to the inner sidewall 140 in FIG. 6B of the body 100 caused by the ion beam leakage. The detector 300 may detect a leakage ion beam, which has leaked through the shielding section 200. The analyzing chamber 500 may be substantially the same as described with reference to FIGS. 4A to 5B. Accordingly, a further detailed description of the analyzing chamber 500 is omitted herein for the sake of brevity. The body 100 may include an inlet 110 through which the ion beam may enter the analyzing chamber 500 in a first direction and an outlet 120 through which the ion beam may leave the analyzing chamber 500 in a second direction. The first direction may be different than the second direction. The ion beam entering into the body 100 through the inlet 110 may be deflected by a magnetic field within the analyzing chamber, may travel along a curved locus in the body 100, and may leave the analyzing chamber 500 through the outlet 120. According to an example embodiment of the present embodiment, the first direction of the inlet 110 may cross the second direction of the outlet 120 at an angle within a range of about 70° to about 90°. Accordingly, the ion beam traveling in the first direction through the inlet 110 may be deflected at the angle within a range of about 70° to about 90° to leave the analyzing chamber 500 through the outlet 120. The shielding section 200 may include a flexible material and at least one belt-shaped shield plate. The body 100 may also include a guide line 130 that may protrude from the sidewall 140 for guiding the shield plate. The shield plate may be arranged from the inlet 110 to the outlet 120 along the guide line 130 parallel with the sidewall 140 of the body 100 so that the sidewall 140 of the body 100 may be sufficiently protected from the ion beam. According to an example embodiment of the present invention, the shielding plate 200 may include black lead including carbon (C), for example. The detector 300 may include a pad 310 and a signal line 320. The pad 310 may detect the leakage of an ion beam through the shielding plate 200 and may generate an electrical signal in accordance with an intensity of the leakage ion beam. The signal line 320 may transfer the electrical signal. According to an example embodiment of the present invention, the pad 310 is interposed between the shielding section 200 and the sidewall 140 of the body 100. If the leakage ion beam passes through a hole in the shielding section 200, the pad 310 may detect the leakage ion beam and generate an electrical signal corresponding to the intensity of the leakage ion beam before the ion beam reaches the sidewall 140 of the body 100. According to an example embodiment of the present invention, the pad 310 may include a photodiode for generating an electrical signal corresponding to the intensity of the leakage ion beam. The signal line 320 may be connected to the power supply 700. According to an example embodiment of the present invention, if the leakage ion beam leaks through the shielding section 200 and is detected by the detector 300, the power supply 700 may cut off power to the analyzing chamber 500 and/or the magnet 600. According to an example embodiment of the present invention, the magnet 600 may generate a magnetic field in a direction perpendicular to a longitudinal direction of the analyzing chamber 500. The ion beam may be analyzed in accordance with a mass of each of the charged particles of the ion beam in the analyzing chamber 500 so that a desired ion beam may leave the analyzing chamber 500. That is, the desired ion beam may leave the analyzing chamber 500 at a constant velocity based on the mass of the charged particles and an intensity of the magnetic field. Charged particles, each of which may have a mass smaller or greater than that of the charged particles of the desired ion beam, may not escape from the analyzing chamber 500 and may be adsorbed onto the shielding section 200 in the analyzing chamber 500. According to an example embodiment of the present invention, the magnet 600 may include an electromagnet. In this case, the magnet 600 may be operated by the power supply 700 simultaneously with the analyzing chamber 500. However, according to an example embodiment of the present invention, the magnet 600 may also include a permanent magnet as long as the permanent magnet generates a sufficient intensity of a magnetic field. The sufficient intensity would be known to one of ordinary skill in the art. The power supply 700 may supply electrical power to the analyzing chamber 500 and/or the magnet 600 to operate the mass analyzer 900. The power supply 700 may include a controller (not shown), a control line (not shown) and a power source (not shown). The controller may control the power supplied to the analyzing chamber 500 and/or the magnet 600. The control line may transfer control signals between the controller and the power source. The signal line 320 of the detector 300 may be connected to the control line. As such, an electrical signal indicating the ion beam has leaked through the shielding section 200 may be transferred to the controller through the control line. If the electrical signal is transferred to the controller, the controller may deactivate the power supply to the analyzing chamber 500 so the ion beam no longer enters into the body 100 of the analyzing chamber 500. Accordingly, damage to the sidewall 140 of the body 100 of the analyzing chamber 500 due to the leakage ion beam in advance may be sufficiently reduced and/or prevented. The mass analyzer 900 according to an example embodiment of the present invention may be operated as follows. An impurity gas may be supplied to the ion source unit and a high energy may be applied to the impurity gas so that the impurity gas is ionized into a plurality of high-energy charged particles to generate an ion beam. The generated ion beam may enter the analyzing chamber 500 through the inlet 110 of the body 100. An intensity of a magnetic field due to the magnet 600, an intensity of an electrical field due to the ion beam and an initial velocity of the ion beam may be set to a value. The value may be a predetermined constant value according to an example embodiment of the present invention. In this case, force equilibrium may be maintained between an electric force and a magnetic force in the analyzing chamber 500 so that desired charged particles, each of which may have a mass satisfying the force equilibrium, leave the analyzing chamber 500. Other charged particles, each of which may have a mass incompatible with the force equilibrium, may collide with the shielding section 200 arranged on the sidewall 140 of the body 100 of the analyzing chamber 500. The shielding section 200 may include graphite such as black lead, for example, and thus, particles colliding with the shielding section 200 may chemically react with the graphite and disappear in the analyzing chamber 500. Repeated operation of the mass analyzer may increase the chemical reaction of the ion beam and the graphite so that the graphite may be gradually worn away, thereby generating a hole on a surface of the graphite. If the ion beam in the analyzing chamber 500 leaks through the hole in the shielding section 200, the leakage ion beam may be detected by the detector 300. The detector may transfer an electrical signal corresponding to the intensity of the leakage ion beam to the power supply 700. The controller may deactivate a power supply of the analyzing chamber 500 and/or magnet 600. Accordingly, the ion beam may no longer enter the analyzing chamber 500 and the magnetic field within the analyzing chamber 500 may disappear to reduce and/or prevent damage to the sidewall 140 of the body 100 of the analyzing chamber 500, which may be caused by the leakage ion beam. If the power supply to the analyzing chamber 500 is deactivated, the defective shielding section may be removed from the guide line 130 and a non-defective shielding section may be installed into the guide line 130 of the body 100 in place of the defective shielding section. According to an example embodiment of the present invention, the shielding section 200 may be installed along the inner sidewall 140 of the analyzing chamber in one body 100 so that damage due to an ion beam leaking through an arrangement failure of the shielding section 200, for example, a chink, may be sufficiently reduced and/or prevented. In addition, the detector 300 may be interposed between the shielding section 200 and the sidewall 140 of the body 100 of the analyzing chamber 500 so an ion beam leaking through a hole due to the wearing out of the shielding section 200 may be detected and action may be taken to reduce and/or prevent the leakage ion beam from causing damage to the sidewall 140 of the body 100 of the analyzing chamber 500. In addition, defects in the analyzing chamber may be reduced and/or prevented in advance according to an example embodiment of the present invention and the desired ions appropriate for an ion implantation process may be effectively extracted from the analyzing chamber 500. Although example embodiments of the present invention have been described, it is understood that the present invention should not be limited to these example embodiments. Instead, various changes and/or modifications can be made by one skilled in the art without departing from the spirit and scope of the present invention.
	abstract	A method of producing an isotope comprising directing electrons at a converting material coated with a coating material, the coating material having an atomic number of n, whereby interaction of the electrons with the converting material produces photons, and whereby the photons produced interact with the coating material to produce an isotope having an atomic number of nxe2x88x921. In preferred embodiments, the converting material is Tungsten, the coating material having an atomic number of n is Radium-226, and the isotope having an atomic number of nxe2x88x921 is Radium-225.
	summary
	summary
	description	This application claims priority under 35 U.S.C. 119(e)(1) based on Applicants Provisional U.S. Patent Application Ser. No. 60/622,741 filed Oct. 28, 2004 and titled “RADIATION PROTECTION SHIELD”. This invention concerns a radiation protective shield structure which can be made transportable and which can be set up at various work sites within or without a building at which sites workers could otherwise be exposed to harmful radiation during maintenance or inspection of equipment or installations or other operations. The available work time per individual worker in a high radiation area is a function of two factors, the actual radiation level measured in the work area and the amount of radiation dose that the worker can safely be exposed to. The time available for an individual to be in the radiation area is called the “stay time”. When the work to be accomplished requires a period of time greater than the “stay time”, an additional worker must be added. Where the radiation level is very high, the “stay time” may be reduced to minutes and many workers would be required. Before an individual can start the work assigned, a lengthy Rad Worker training program must be completed and also generally, a job specific training program. The training may take several days to make the individual available for a few minutes actual work. A principal object therefore of this invention is to provide a shield, preferably one which is transportable and readily adapted for overall size expansion, between the work area and a high radiation source of e.g., alpha, beta, gamma, mention, or the like. The lower radiation levels, resulting from the use of the shield, will allow a few individuals to accomplish the work that would have required a large number of workers without the shield. After work and/or inspections are complete, the shield can be partially or completely removed, or moved to another work site. The present invention in one of its preferred structural embodiments comprises a plurality of generally rectangular (includes square) panels each of which is of a designed thickness having an inner lead or other radiation attenuating core encased (canned) in a steel (usually stainless) shield and having a tracking axis, two or more rollers mounted on the bottom of each panel, a lower track mounted on a base such as the concrete floor of a building for rollably supporting said rollers for movement of each said panel along said lower track to a designated position, said lower track being longitudinally configured to allow said panels to be rolled to positions to isolate workers in a particular area from a source of harmful radiation, first guide rail means on said lower track for maintaining proper alignment of said rollers with said lower track, an upper track mounted on a rigid structure adjacent upper portions of said panels and having second guide rail means for laterally engaging in a guiding manner upper guide elements on said upper portions of said panels, said upper track having substantially the same longitudinal configuration (tracking axis) as said lower track. Referring to the drawings and claims herein, the present shield assembly or structure generally designated 20 consists basically of a lower track 22, an upper track 24 and support means 26 therefor, a lower track support means 28 and the shield panels 30. All structural components of the shield assembly are steel or stainless steel, and, of course are sufficiently strong to rollably support panels which may weigh several thousands of pounds. Also, in the various figures equivalent structures may be numbered the same. The lower track typically rests on the concrete floor 32 of a building and supports the shield structure and provides the path (tracking axis) which the shield panels will follow. The tracks 22 and 24 may be straight or have bends to guide the shield panels into the most advantageous position and 22 is provided with leveling means 34 if required. The upper track 24 follows the path of the lower track and is supported overhead by support means 26 and guides the upper end of the shield panels and holds the panels substantially vertical. The upper track 24 may have more than one elevation, as shown in FIG. 1 to accommodate plant work area interferences requiring different height and or size panels. Each panel is fitted with two or more wheels or rollers 36 which can be of any configuration to fit the shape of the lower track, e.g., flat or crowned or grooved or the like and can be fixedly axially or of the caster type as shown, e.g., in FIG. 5. Provision to steer the caster type wheels may be incorporated as shown in FIG. 25. The wheels may also be powered, preferably by electric motors. The panels are of an appropriate shielding thickness, height, width and of proper shield material for the project at hand and is selected from material such as lead or other radiation attenuating material including concrete and steel. If the shield material is lead, an outer shell of steel, carbon steel or stainless steel preferably is provided to cover and seal any exposed lead. The panels lap over each other at their edges 38 and 40 as shown in FIGS. 6 and 18 to prevent radiation from streaming though the joint. The panels also have lifting provisions such as winch cable hook eyes 45 at the top. A latch mechanism as shown in FIGS. 12 and 13 can be provided to connect panels to adjacent panels in their operative positions and locations. The panels can be painted a light reflecting color to enhance the lighting in the work area. The operational sequence of the invention is as follows: The lower track is moved into place. It is leveled and secured to the floor if necessary. The upper track is then positioned, supported and secured directly above the lower track with their tracking axes aligned. Next the first shield panel is positioned vertically and placed on the lower track. It is advanced until the upper guide rollers are engaged in the upper track. The first panel is then advanced down the track to the required position. Additional shield panels are added as required. The entire track may be loaded with shield panels to develop a shield wall. One or more panels may be placed on the track in an assembly to shield a specific area. The panel assembly may be repositioned on the track as required. When the shield panels are no longer required, the panels may be removed, followed by the upper and lower track assemblies. In a further embodiment of this invention, the upper and lower track assemblies would be attached to each other and appropriately braced to make the movable shield free standing as shown in FIGS. 2 and 19. Hoisting equipment for lifting the shield panels and placing them on the track could include overhead travelling electric hoists, chain falls, electric winches, fork lift or other such equipment, and where feasible could be incorporated into the shield system itself or could be an independent unit or part of the track assembly. Referring further to the drawings, in particular FIGS. 1, 8, 16, 17, 20 and 23, many industrial installations wherein radioactive equipment or materials generally designated 42 in FIG. 8 are located are provided with radiation protective enclosures such as concrete walls 44 to protect workers who might be in the vicinity. Where it becomes necessary to practically completely protectively enclose dangerous areas, the present invention is a very practical way to accomplish it. In doing so, the lower track 22 is laid out in the configuration required by the radiation source 42 and by the locations which the workers must be in to perform their tasks. Such a layout, once it is determined as to shape and length, can be done by bending a straight track, 22 and 24 to the desired curvature or by providing the tracks in sections which can be connected together by mechanical means or by welding. Likewise the most appropriate size and shape of wall mounting brackets such as 46 can be provided for clamping to wall 44 by screw clamps 48 (FIG. 23). In this regard, once the lower track is set in position and leveled by leveling bolts 34 or the like, the upper track 24 is moved laterally to a vertical position over 22 by a screw mechanism (vertical adjustment means) generally designated 50 (FIG. 20) and comprising a rod section 51 threaded into a tube section 52, wherein 51 is connected to a vertical swivel joint 54 on the top of track 24, and 52 is connected to a vertical swivel joint 56 on the bracket 46. One of 51 or 52 is non-rotatable and longitudinally fixedd in its swivel joint and the other is rotatable but also longitudinally fixed in its swivel joint to afford the pushing or pulling of the upper track to a vertical position by relative rotation between 51 and 52. Referring to FIGS. 16 and 17, a variation of the vertical adjustment means is shown as comprising a threaded rod 58 rotatably mounted in a bushing 60 affixed to the top of wall 44 and longitudinally fixed therein by lock collars 62. The rod is threaded through a bushing 64 affixed to the top of track 24. Rotation of the bolt head 66 by e.g., a ratchet wrench, will push or pull the upper track to its proper verticality. A slotted arm 68 can be provided on the upper track and a complementary slotted arm 70 can be provided on wall 44 to firmly set the verticality of the upper track by tightening nut 72 on bolt 73. Referring to FIGS. 2, 3 and 19, the stand along embodiment generally designated 74 comprises the same upper track, panels and lower track as in, e.g., FIG. 1, but does not require brackets or the like such as 46 for attaching the upper track to a structural portion of a building. In this embodiment of the present shield each side of the track base 23 is affixed to stabilizer arms 25 which are welded to the base or are affixed thereto by screws 27 or the like whereby the arms can be disassembled from the base. Opposing pairs of bracing 29 are affixed to arms 25 and to the upper track by welding or screws or the like, again to be able to disassemble the shield for easy transport thereof. Each foot portion 31 of arms 25 is provided with a leveling means such as bolt 33 threaded through the foot and adapted to firmly engage the floor and rigidly stabilize the shield assembly. In the placement of shield 74 wherein the shield sections are assembled, a preferred procedure for making it ready for use is to first level the lower track laterally and longitudinally by means of the leveling bolts 34 (FIG. 14) or other leveling means such as to posture the panels in a vertical plane 47. The leveling bolts 33 on the arms 25 are then adjusted in their screw sockets 35 to firmly engage the floor 32 and thus stabilize the entire shield assembly. Referring to FIG. 25, the caster housing 37 can be provided with a socket member 39 into which a steering rod 41 can be inserted and employed as a lever to rotate the caster housing and spindle 43 to steer the roller. Referring to the variation of FIG. 7, the guide rollers 55 are affixed to the tops 57 of the panels by an Allen type screw 59 passing through a thrust bearing 49 and having a shoulder 61 bearing on top 57 of the panel. In the variation of FIG. 24 the upper rail 24 in configured as a vertical plate and the guide rollers 55 are mounted for vertical rotation in roller housings 53 affixed to the tops 57 of the panels. Referring to FIG. 10, a variation of the lower track roller mounting is shown where the spindle 43 is rotatably mounted through a bore 75 in a bushing 76 and bears against a thrust bearing 77. A sleeve member 78 welded at 79 to the bottom 63 of the panel threadedly receives bushing 76. In the variation of FIG. 11, the spindle 43 is provided with an annular shoulder 80 for engaging thrust bearing 77. Screws 82 threaded through the bottom 63 of the panel slidably nest in an annular groove 83 in the spindle for retaining it in bore 84 up into 63. Sleeve bearing means 85 are preferably provided for the spindles. In FIGS. 12 and 13 a latch 65 is shown for tightly drawing the panels together edgewise after they have been properly positioned. The latch comprises at threaded shaft 67 having an eye segment 69 through which a shaft member 71 is slidably mounted and fixed to bearing members 86 welded to an edge portion of each panel. A bushing member 87 is provided with a bore 88 for slidably receiving shaft 67. A semi-sleeve member 89 is welded to an adjacent edge portion of each panel and is provided with a slot 90 for allowing pivoting of 67 around 71 and removal of bushing member 87 from 89. A thumb nut 91 is provided for tensioning 67 sufficiently to retain said panels in edgewise contact. Additional such latches placed where desired on the panels may, of course, be used. The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications will be effected with the spirit and scope of the invention.
051165660	abstract	An apparatus for refurbishing the ends of control rod drive (CRD) penetrations used in nuclear boiling water reactor systems where the rods are disposed in a grid of rows and columns with a known predetermined spacing therebetween. The apparatus is rapidly positioned for support on a pair of CRDs adjacent to a CRD to be refurbished, coaxially aligning the end mill with the CRD to be refurbished. The end mill is then brought into contact with the CRD to be refurbished. After the refurbishment process, the apparatus is rapidly removed and ready to be positioned on another pair of CRDs adjacent to another CRD to be refubished.
055641032	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, a storage tank for a contaminated, depleted ion exchange resin bead slurry feed is shown as 10. This slurry feed can contain from 5 weight % to 70 weight % solids and may originate at a nuclear reactor power plant, hospital or any other governmental or commercial operation where ion exchange beads are utilized to capture contaminants. The slurry feed could also originate in any facility to remove ionic and dissolved impurities in a liquid media, as in water filtration plants and the like. The method of this invention is particularly applicable to a slurry feed containing at least 10 volume % of depleted ion exchange resin beads, and is particularly advantageous for contents of 20 volume % to 70 volume % of resin beads based on total solids content. These beads have a particle size range from 300 micrometers to 1000 micrometers diameter. Most commonly, nuclear grade resin beads have an average particle size of about 400 to 600 micrometers diameter and we have found that they are of generally uniform spherical shape such that 50%, that is at least one half (1/2) of the number of the beads are within .+-.10% from the average particle size of the beads taken as a whole. Therefore, if the average diameter of the beads is 500 micrometers, at least one half of the beads will be in the range of 450 to 550 micrometers. The packing factor or efficiency for these beads was found to be not much more than 0.52--the same as a simple cubic pack, which resists volume reduction. By packing factor is meant the volume of the spheres divided by the cell volume enclosing the spheres and is a reflection of packing density. Body centered cubic lattices have packing factors of 0.68, face centered cubic lattices have packing factors of 0.74, and hexagonal close parked lattices have packing factors of 0.74. Other components of the slurry feed can include ion exchange resin powder, soil, and the like, all of which are easily compressible to volume reductions of 25 volume %. In ion exchange, a solid phase contains bound groups that carry an ionic charge, either positive or negative, in conjunction with free ions of opposite charge that can be displaced. Most ion exchangers currently in large-scale use are based on synthetic resins, for example polystyrene copolymerized with divinylbenzene (to provide the requisite amount of cross linking), and they are permeable only at molecular dimensions, except when a network of coarser pores is deliberately superimposed. Cation-exchange resins can contain bound sulfonic acid groups; less commonly, these groups are carboxylic, phosphonic, phosphinic, etc. Anionic resins can contain quaternary ammonium groups (strongly basic) or other amino groups (weakly basic). Of the two types, the cross linked cation exchange resins are more difficult to process in the grinding step of this invention. Useful resinous materials effective to attract metal cations generally have structures such as a sulfonated, polystyrene divinyl benzene (strong acid); carboxylic acrylics (weak acid); quaternary ammonium gels (strong base); or a polystyrene-polyamine (weak base). In addition, a chelating functionality group may be incorporated into the resin to produce a greater affinity for metals. Any ion exchange bead resin that can capture radionucleides; cationic materials having an atomic weight greater than 22, for example, Na, Mg, Al, Ca, Mn, Co, Ni, Rb, Sr, Zr, Mo, Pb; or anionic materials such as bicarbonate, carbonate, hydroxide, sulfate, chloride, nitrate, phosphate and silica, can benefit from the resin grinding of the invention to better insure volume reduction. Of particular interest as an ion exchange feed are those having nuclear grade properties, such as those sold under the Tradename PUROLITE NRW-100, NRW-600 and NRW-37, of strong acid/cation gel, strong base/anion gel, and mixed bed strong acid gel/strong base gel, respectively. The slurry feed 10, containing the ion exchange resin beads and other solid components is preferably filtered in gross filter 11, to remove any hard objects that could harm grinder blades, and then transferred through piping 12 by pump 13 to blending tank 14. The blending tank will also receive an amount of water to insure a somewhat consistent volume of resin beads into the grinder 16. There should be a steady amount of resin beads solids, rather than an erratic flow of dilute feed followed by very viscous feed so that grinding can be consistent. The blending tank is preferably agitated as by stirring to help provide a homogeneous slurry feed into the grinder. The blending tank volume can range from about 757 liters (200 gal.) to about 15,120 liters (4000 gal). The process can be run continuously, or as a batch operation where the feed is periodically fed from tank 10 to tank 14. Preferably, the concentration of resin beads into the grinder will vary from about 30 volume % to about 50 volume % as determined from a variety of factors, such as whether the beads are the harder to process cation type beads. The homogeneous slurry from the blending tank is then passed into bead grinder 16. Pump 17 is a variable speed positive displacement pump to ensure feedrate control. The grinder will be in an enclosure to contain and eliminate all potential for airborne contamination and will operate in a manner effective to provide a processed slurry with fractured ion exchange beads having a particle size distribution of from 10 micrometers to 1000 micrometers diameters, preferably from 100 micrometers to 300 micrometers diameter. Grinding the beads to below 10 micrometers would interfere with efficient dewatering. It is important that no more than 33% of the fractured beads in the processed slurry have a relatively similar diameter, that is no more than about one third (1/3) of the number of fractured beads are within .+-.10% of the average particle size of the fractured beads taken as a whole. Therefore, if the average ground particle size is 200 micrometers, not more than one third of the fractured beads will be in the range of 180 to 220 micrometers. Ideally there will be an even distribution within the preferred range between 100 micrometers and 300 micrometers, with, for example, 10% at 100 micrometers, 10% at 120 micrometers and so on, as this would allow close random packing, allowing packing factors from 0.62 to 0.93. Other components of the processed slurry will also be ground finer but that is of minor importance to this invention which is mainly concerned with providing a compressible particle size range for the normally incompressible ion exchange beads. The grinding means can be of any type with an adjustable gap or grinding setting that can handle both high and low solid slurries of plastic like materials in a continuous fashion. Once the beads are ground the water coating on the fractured particles still serves to cause repelling action between the particles and such water must now be removed. The dewatering system can be of any type but is preferably of the type which includes a shell for providing primary containment for the slurry compression means in the shell and surrounding the slurry for compressing fluid from the slurry, filter means disposed in the shell for containing the slurry and for filtering the fluid compressed from the slurry, and vacuum means connected to the filter means for suctioning the fluid from the filter means and for producing a pressure differential across the compression means and for collapsing the compression means about the filter means and the slurry for compressing the slurry. U.S. Pat. No. 5,143,615 (Roy et al.), herein incorporated by reference, can be referred to for a complete description if such a dewatering system. Compressing dewatering alone can allow about a 5 volume % reduction, but when used in conjunction with prior grinding, the total effect can be a 20 volume % reduction, or higher. After dewatering, the effective result of this invention will be an approximate 20 volume % reduction in the final waste volume or an approximate 20 weight % increase of spent bead resin in a standard waste container. The process provides: minimal material hold-up to reduce radiation exposure to operating personnel; a totally enclosed, liquid slurry grinding process which eliminates all potential for airborne contamination; a process capable of handling wide swings in process flow rate and slurry concentration as are typically seen in nuclear plant radwaste transfer systems; and a process which minimizes the generation of particles <10 micrometers which would interfere with efficient dewatering. Water or other fluid recovered in the dewatering process can be fed through line 20 for further processing. The compressed material, including dewatered, contaminated, depleted, fractured, ion exchange resin beads and other components, can be fed through line 22 to a suitable waste container system 24.
059006382	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an x-ray diagnostics installation 1 that, for example, is an x-ray aiming device. The x-ray aiming device is usually arranged over a support platform or bed for an examination subject, and has a radiation protection arrangement 2 disposed at least one side facing toward the patient support. This radiation protection arrangement 2 has at least one lead-rubber strap 3, preferably a number of lead-rubber straps 3, joined to one another but movably seated in a guide rail 5 via a carrier 4. Each lead-rubber strap 3 preferably is seated in its own carrier 4. When a number of carriers 4 are provided, it is advantageous to join them chain-like to one another via a connecting element 6. For example, a cable, a revolute joint or a flexible rod can be employed as each connecting element 6. The lead-rubber straps 3 are seated at the respective carrier 4 pivotable around a transverse axis 7 and, expediently, also pivotable around a rotational axis 8 oriented substantially perpendicularly relative to the axis 7. When, for example, the x-ray aiming device 1 is adjusted a vertical alignment, then the lead-rubber straps 3 are also moved toward the right, i.e., downward by the force of gravity, in the guide rail 5 via their carriers 4. In order to prevent an independent or unintentional movement of the lead-rubber straps 3 or at least to make this more difficult during such an adjustment of the x-ray aiming device, a brake arrangement 9 for the carrier 4 is inventively provided. In the embodiment shown in FIG. 2 the brake arrangement 9 is a friction brake whose brake lining 10 engages at the carrier 4 preferably loaded by a resilient element 11, for example a coil spring. According to a modification shown in FIG. 3, the brake arrangement 9 is implemented such that it engages the carrier 4. Structurally, a peg 12 can be provided for this purpose that engages into a recess at the carrier 4. Conversely, of course, a recess at the brake arrangement 9 can engage a peg of the carrier 4. If a number of carriers 4 are attached to one another chain-like, then the peg 12 can also engage between two carriers 4. To this end, the peg 12 can likewise be adjusted in the direction toward the carrier 4 by a resilient element 11. In another modification of the invention shown in FIG. 4, a brake arrangement 9 is provided at the carrier 4 at the end thereof, this brake arrangement 9, for example, being fashioned as a catch 14 engaging into a channel 13. The catch 14 is pivotable around an axis 15 and, loaded by a resilient element 16, engages in the channel 13. The locking can be released in all modifications of the invention by an unlocking mechanism 17. The unlocking mechanism 17 is preferably implemented as a lever arrangement so as to enable an easy cancellation of the interlock or brake. FIGS. 5 and 6 schematically show a carrier 104 with a lead-rubber strap 103, with a formed part 109 inventively provided at the carrier 104 which effects a diversion of a lead-rubber strap 103 when the radiation protection means is pivoted. As can be seen in FIG. 6, the formed part 109 is fashioned as a bead at a retainer part 110. The preferably annular bead of the formed part 109 surrounds a swiveling axis 111 and can be placed in the lead-rubber straps 103 or placed on them. In the modification of the radiation protection arrangement of the invention shown in FIG. 7, at least two lead-rubber straps 103 are pivotably seated in respective carriers 112. The carriers 112 allow the straps 103 to be are seated such that they are joined to one another in a first direction 113 and are aligned in a second direction 114. The first and second directions 113 and 114 describe an angle a relative to one another. If a number of carriers 112 for respective lead-rubber straps 103 are adjoined to one another in a chain-like manner, then lead-rubber straps 103 neighboring one another should at least partially overlap order to assure a reliable radiation protection. In FIGS. 8 and 9, a lead-rubber strap 201 is shown which can be adjustable along a guide rail, particularly in an x-ray aiming device. According to the invention, the lead-rubber straps 201 can be folded (FIGS. 9, 11, 13) from an extended, i.e., suspended condition (FIGS. 8, 10, 12) and can be fixed in the folded-over condition. A snap fastener 202 according to FIGS. 8 and 9 a hook and loop closure 203 according to FIGS. 10 and 11, a clip 204 according to FIGS. 12 and 13 or a magnet means (not shown) are suitable for the fixing. The fixing can be provided at the front side or back side and can be glued, welded or sewn to the lead-rubber strap 201. The opening that is produced by folding the lead-rubber strap 201 up can be set dependent on the position of the fixing means. A number of retaining positions can be provided at the lead-rubber strap 1, so that differently sized openings can be achieved. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
054188326	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a scanning radiography instrument 10 includes a polychromatic x-ray source 12 and a dual energy detector array 13, both of which are mounted on a common carriage 14 which extends on either side of a supine patient 16. The carriage 14 is automatically operated, as by stepping motors, so as to scan the patient 16 along a scanning axis 19. In studying the human vertebra, the scan is preferably taken from the side of the patient 16, so as to provide a lateral scan of the vertebra 20 of the patient 16. In studying the lungs, (not shown) the scan is preferably taken vertically so as to provide an anterior/posterior scan of the patient 16. The carriage 14 carrying the radiation source 12 and detector array 13 is connected to, and operates under the control of, a general purpose digital computer 18 which is specifically programmed for use in operating the instrument 10 and analyzing the data and including specialized algorithms for carrying out the calculations required by the present invention. In addition, the present invention includes a data acquisition system ("DAS") and a data storage device, both of which are not shown and may be included in the computer 18. The computer 18 also includes a display means 22 for outputting the data analysis. Referring also to FIG. 2, the x-ray source 12 employs a standard x-ray tube having an anode 26 emitting a cone beam 30 of x-rays having a broad range of energies. This cone beam 30 is shaped by means of a rectangular slit 32 into a fan beam 23 as is projected toward the patient 16. The fan beam 23 has a rectangular cross section as measured in a plane normal to the fan beam axis 24. The longer dimension of the rectangular cross-section of the fan beam 23, i.e., its length, defines the z-axis of a Cartesian coordinate system with the y-axis being aligned with the shorter axis of the rectangular cross section, i.e., its width, and the z-axis being parallel to the fan beam axis 24. Referring to FIGS. 1 and 3, the detector array 13 conforms generally to the cross-section of the fan beam 23 and is comprised of rectilinear rows and columns of detector elements 28 and 28'. The multiple rows of detector elements 28 and 28' span the width of the detector array 13 along the y axis whereas the columns of detector elements 28 span the length of the detector array 13 along the z axis. Each detector element 28, 28' has a z-axis length of approximately 0.5 mm and a y-axis width of approximately 0.5 mm. Although FIG. 3 shows a detector array 13 having only two columns 28 and 28', it should be understood that the invention may be used advantageously with detector arrays having greater than two columns. The multiple elements 28 or 28' of each row provide data points at different spatial locations for each position of the carriage 14 along the scanning axis 19 (or y-axis), thus permitting the acquisition of a two dimensional array of data points with scanning in only a single direction. The two rows provide measurements of the attenuated x-ray radiation within two different energy bands. One row of elements 28' incorporates a copper filter 29 on its surface facing the x-ray source 12 to be preferentially sensitive to high energy x-rays. The remaining row of detector elements 28 has no filter and is responsive to low energy x-rays. Each elements 28 or 28' is one cell of a charge coupled device responsive to light emitted by a surface coating of an x-ray scintillator such as is known in the art. Alternatively, the detector array may be constructed as a "sandwich" of different superimposed detector layers as taught by U.S. Pat. No. 4,626,688 issued Dec. 2, 1986 entitled: Split Energy Level Radiation Detector, and U.S. Pat. No. 5,138,167 issued Aug. 11, 1992 and entitled: Split Energy Radiation Detector, both hereby incorporated by reference. During the scanning of the patient 16, the analog output of the detector array 13 is sampled and digitized by the DAS so as to produce x-ray intensity values for each of the data elements 28 and 28' of the detector array at each spatial location of the scan, the values which may then be transmitted to the computer 18 which stores the data in a computer memory (not shown) or a mass storage device. The spatial locations of the stored values differ by the distance that the source 12 and the detector array 13 moves along the scanning axis 19 between the taking of each value. In the preferred embodiment, the instrument moves approximately 0.25 millimeters between the acquisition of each data point. At the completion of the scanning, the computer 18 arranges the values obtained in the scan in a matrix within its memory where pairs of values are associated with single spatial location, defined by the position of the carriage 14 when the data element was acquired. Specifically, the data from one column of the detector array 13 is matched to the later acquired data from the second column of the detector array so as to provide a set of matched data values for two energies over the two dimensional image plane. Referring still to FIG. 3, positioned above the detector array 13 toward the x-ray source is an aft slot 36 being a generally planar sheet 39 of radio opaque material such as lead positioned parallel to the y-z plane and normal to the fan beam axis 24 having a rectangular aperture 43 centered about the fan beam axis 24. The aperture is sized to be substantially equal in outline to the exposed face of the detector array 13 and so as to allow unobstructed passage of x-rays generally parallel to the fan beam axis 24 through the aperture 43 to strike the elements 28 and 28'. The width of the aperture along the y-axis is designated W. The aperture 43 is surrounded by a skirt of the same radio opaque material as that which forms the aperture 43 and extending parallel to the fan beam axis 24 away from the x-ray source 12 to create a rectangular wall 44 of same cross-section as aperture 43 and with a height along the z-axis of H. The height H compared to the width W of the aperture 43 along the y-axis determines the grid ratio for the aft slot 36 and in the preferred embodiment is approximately 8:1, the slot having a height H of eight centimeters and a width W of one centimeter. Within the rectangular wall 44 are a plurality of radiopaque lamellae 46 extending the width of the aperture 43 to form a grid 38. The lamellae of the grid 38 are approximately fifty micrometers thick and separated to provide 41 lamellae per centimeter of aft slot 36 as measured along the z axis. Thus, radiation passes through the patient 16, the aft slot 36 and grid 38 and is then received by the detector array 13. Referring again to FIG. 2, as the fan beam 23 passes through the patient 16, some of the x-rays are scattered and diverge from the fan beam axis 24 as scattered rays 34 and 42. Some of the scattered rays 34 continue through the patient 16 at an angle so as to miss the aft slot 36 and to strike the backstop 40 and be absorbed there. Thus rays 34 do not degrade the image data collected by the detector array 13. Similarly, the collimation of the cone beam 30 into a fan beam 23 eliminates scatter from x-rays outside of the fan beam 23 as would exist in conventional area radiography. Finally, the addition of the aft slot 36 provides a shielding from multiply scattered beams 42 which diverge from the fan beam 23 and then are re-scattered to be redirected toward the detector array 13 but at an angle to the fan beam axis 24. Nevertheless, the elimination of these latter multiply-scattered beams may be expected to be less significant than the elimination of scatter as a result of collimation of the cone beam 30 to a fan beam 23. The lamellae 46 do not stop scattered rays 34 or 42 but rather apparently reduce scatter from rays having components along the z-axis. As will be discussed further below, computer simulation has indicated that the scatter in this direction is surprisingly significant and thus the use of the grid 38 of lamellae 46 provides important scatter reduction even after that provided by the collimation of slit 32 and the collimation of aft slot 36 previously discussed. The lamellae 46 of the grid can potentially produce grid lines or streaks in the image if every given point in the image is not swept over in equal proportion by lamellae 46 and the space between lamellae 46. Referring also to FIG. 4a, the lamellae 46 are accordingly angled with respect to the width of the grid along the y-axis at an angle .theta. so as to prevent certain portions of the image from being disproportionately occluded by lamellae 46. The lamellae 46 are fixed with respect to the underlying detector elements 28 and 28', however the motion of both the detector elements 28 and the lamellae 46 with motion of the carriage 14 causes an effective sweeping of the lamellae 46 in the z-axis direction with respect to the formed image. The x-rays blocked by each lamellae 46 form a shadow path that extends by the projected length of the lamellae 46 on the z-axis. Thus, ideally, the projection of each lamellae 46 on the x-axis is such that the shadow paths of each lamellae 46 just abut in the image and neither overlap nor have gaps which would produce streaks of darker or lighter image. This condition of abutting shadow paths from the lamellae 46 requires that the angle of the lamellae .theta. and the spacing of the lamellae along the z-axis follow certain ratios. In particular, the value of .theta. is equal to ##EQU1## Where D', the grid repeat distance, is equal to D+d where D is the spacing between each lamellae 46, and d is the thickness of the lamellae 46 (both measured perpendicularly to the lamellae) and W is the slit width as described before. n is a positive integer which when greater than one allows overlapping of the lamellae shadows as projected on the z-axis as shown in FIG. 4(c), but such that the every other shadow abuts in a seamless manner also eliminating bright or dark streaks. As shown in FIG. 4(b), more than one lamellae 46 may cover each detector element 28, 28' with certain grid spacings D' and further the grid spacing need not be evenly divisible into the detector element spacing along each column of the detector array 13. For smaller values of D', generally the value of .theta. decreases. Referring now to FIGS. 1 and 5, each ray 27 of the fan beam 23 diverges about the fan beam axis 24 along the z-axis at an angle .phi. from the fan beam axis 24, thus for the end rows of the detector array 13, the rays 27 are not truly normal to the surface of the detector array 13. In order to eliminate unnecessary occluding of the fan beam 23 by the lamellae 46, the lamellae 46 are also canted with respect to the fan beam axis 24 by an angle of 90.degree.-.phi. so that they present their smallest possible cross-section to each ray of the fan beam 23. EXAMPLE 1 A computer simulation was performed of a scanning radiographic system geometry provided in Table I and a patient simulated with a 23 cm thick Lucite scattering phantom 35 cm long and 43 cm wide. TABLE I ______________________________________ focal spot to image distance 150 cm focal spot to slit distance 60 cm slit width 3.5 mm focal spot to slot distance 140 cm slot width 10 mm slot height 80 mm slot grid ratio 8:1 ______________________________________ The above system was simulated on a computer using a Monte Carlo methodology such as is described in the paper "Spectral Dependence of Glandular Tissue Dose in Screen-Film Mammography", by X. Wu, G. T. Barnes, D. M. Tucker in Radiology, 1991; 179:143-148 incorporated herein by reference. In this simulation, photon energies from 20 to 140 keV in ten key increments were employed. For each energy, photons transmitted by the slot were binned in 5 keV energy increments from 15 keV to the energy of the increment. The received photons were also separated by the cosine of their angle .alpha. from the z-axis (within the x-z plane). The cosine bin increments were 0, 0.1, 0.2, . . . , 0.9, 0.95 and 1. Cos .alpha.=1 corresponds to a photon of x-ray energy traveling parallel to its original direction substantially parallel to the fan beam axis and cos .alpha.=0 corresponds to a scattered photon traveling along the z-axis. For energies greater than 80 keV, the histories of 6.times.10.sup.6 photons incident on the Lucite scattering phantom were traced and for energies of less than or equal to 70 keV, the histories of 3.times.10.sup.6 were followed. The ratio of scattered rays to primary rays (S/P) received by the simulated detector was calculated by summing over all the cosine bins except for the cos .alpha.=1 bin which includes both unscattered and scattered photons and where only scattered photons were counted as determined by the collision history in the simulation. The results were weighted using a published 140 kVp x-ray spectrum with a 2.5 millimeter aluminum total filtration. The effect of the addition of a grid for each incident photon energy was calculated analytically from the Monte Carlo tracings by determining the grid transmission for each angular bin and each energy bin. These results in turn were weighted and summed for the above mentioned 140 keV spectrum. The results are summarized in table II. TABLE II ______________________________________ Technique S/P ______________________________________ normal radiography and 12:1 grid (lung) 0.400 normal radiography and 12:1 grid (mediastinum) 1.300 scanning with slot 0.125 scanning with slot and 8:1 grid 0.055 scanning with slot and 12:1 grid 0.054 ______________________________________ For the slot without the grid the scatter to primary x-ray energy fluence was 0.125. When an 8:1 grid was incorporated into the slot, this value is reduced to 0.055. Similarly, the S/P ratio for a 12:1 grid is 0.054. The estimated precision of the Monte Carlo results is 2%. The binning and other analytical approximations introduce a potential systematic error of 5%. The Monte Carlo code was carefully benchmarked and the systematic error introduced by this phase of the methodology is less than 8%. Thus, the overall accuracy of the results is estimated to be ten percent. The reduction in S/P ratio by use of a grid is a marked improvement over conventional techniques despite the low scatter to be expected in a scanning system. While this invention has been described with reference to particular embodiments and examples, other modifications and variations, will occur to those skilled in the art in view of the above teachings. For example, the area of the detector array need not be limited to the area of the opening of slot but may be a stationary plate type detector, such as a storage phosphor plate, for example, of much greater area. Further, the scanning need not move both the x-ray source and detector simultaneously or in a line. If equal magnification of the image in directions both along the slot and across the slot are desired, the x-ray source may be held stationary and the slot and grid may be moved substantially in an arc about the stationary focal spot. In order to apprise the public of the various embodiments that may fall within the scope of the invention, the following claims are made.
	description	This application is a continuation of PCT/JP2007/050190, filed on Jan. 11, 2007, which claims priority to Japanese Application No. JP2006-016159, filed on Jan. 25, 2006. The entire contents of these applications are incorporated herein by reference. The present invention relates to a charged-particle beam apparatus for emitting a charged-particle beam onto a sample to fabricate or observe the sample. Conventionally, there has been proposed a charged-particle beam apparatus for emitting a charged-particle beam onto a sample in a vacuum atmosphere to fabricate or observe a surface of the sample. FIG. 3 schematically shows a charged-particle beam apparatus 50 as described above. The charged-particle beam apparatus 50 includes a chamber 51 in which a sample S is placed, and a lens-barrel 52 for directing a charged-particle beam B onto the sample S placed in the chamber 51. The lens-barrel 52 includes a charged-particle supplier 53 having a charged-particle source 53a, a condenser lens 54 and an objective lens 55 each serving as an electrostatic lens to which a voltage can be applied. Moreover, the chamber 51 is provided with an evacuating means 56 capable of evacuating the chamber 51, and a gas supplier 57 capable of supplying a gas such as N2 into the chamber 51. In the charged-particle beam apparatus 50 described above, a voltage is applied to the objective lens 55 in such a manner that the evacuating means 56 creates a high vacuum atmosphere inside the chamber 51 and the lens-barrel 52. In this state, a charged particle drawn from the charged-particle source 53a of the charged-particle supplier 53 is accelerated, and then is emitted as a charged-particle beam B50. Then, the released charged-particle beam 50B is converged by electric fields formed by the condenser lens 54 and the objective lens 55, respectively, and is irradiated onto the sample S, so that a surface of the sample S is subjected to fabrication or observation. As described above, after the completion of fabrication or observation of the sample S, the sample S is transported to the outside through a sample transport opening (not shown). Herein, in each of the interior of the chamber 51 and the interior of the lens-barrel 52, a high vacuum atmosphere is created. Consequently, when the sample transport opening is open, a large amount of outside dust disadvantageously enters each interior in addition to outside air. In order to avoid such a disadvantage, the chamber 51 and the lens-barrel 52 are filled with a gas by the gas supplying means 57 at a nearly atmospheric pressure, and then the sample S is transported to the outside through the sample transport opening As an example of the charged-particle beam apparatus 50 described above, more specifically, there is a focused ion beam apparatus that emits an ion beam to a sample with the use of an ion source serving as a charged-particle source (refer to, e.g., Japanese Unexamined Patent Publication No. 2002-251976). The focused ion beam apparatus 50 described above has an advantage that an ion beam is emitted to a sample in order to etch a surface of the sample or an assist gas is supplied to the sample simultaneously with the emission of the ion beam, so that a deposition is formed on the surface of the sample. As another example, moreover, there is a scanning electron microscope that emits an electron beam, which has been drawn from an electron source serving as a charged-particle source and then has been accelerated, to a sample to observe a surface of the sample. With regard to these charged-particle beams, when a high voltage is applied to an electrostatic lens used as an objective lens, optical aberration becomes small. As a result, the charged-particle beam can be converged effectively. When the charged-particle beam is converged effectively as described above, the focused ion beam apparatus can fabricate the surface of the sample more precisely. On the other hand, the scanning electron microscope can obtain an observation image at a high resolution. Recently, a sample to be fabricated or observed tends to become finer. In order to fabricate and observe such a sample more precisely, therefore, there has been proposed a method of applying a higher voltage to an electrostatic lens to fabricate or observe the sample. However, the application of a higher voltage to the electrostatic lens causes the following problem. That is, when dust is attached to the electrostatic lens, even if the attached dust is in such a small amount as to not pose any problem in the conventional art, electric discharge occurs at the electrostatic lens. As described above, conventionally, when a sample is transported from the chamber to the outside, the gas supplying means supplies a gas to the chamber to prevent outside dust from entering the chamber. However, it is impossible to prevent the dust from entering completely. In addition, since dust is also attached to the sample, a small amount of dust always exists in the chamber. When the gas supplying means supplies the gas into the chamber to create a high vacuum atmosphere, such dust is stirred up together with the gas, and then is flown into the lens-barrel. Herein, the dust is attached to the objective lens, resulting in electric discharge. The present invention has been devised in view of the circumstances described above. An object of the present invention is to provide a charged-particle beam apparatus capable of preventing a small amount of dust from being attached to an electrostatic lens serving as an objective lens to apply a high voltage to the electrostatic lens. In order to solve the foregoing problems, the present invention offers the following configurations. The present invention provides a charged-particle beam apparatus including: a chamber having an interior evacuated by an intra-chamber evacuating means; and a lens-barrel emitting a charged-particle beam onto a sample placed in the chamber. Herein, the lens-barrel includes: a cylindrical body having a distal end at which an emission outlet is formed for communication with the chamber and from which the charged-particle beam is released; a charged-particle supplier housed at a side of a proximal end in an interior of the cylindrical body to release the charged-particle beam; and an objective lens housed at a side of a distal end in the interior of the cylindrical body and having an electrostatic lens generating an electric field by voltage application and converging the charged-particle beam released from the charged-particle supply part. In the cylindrical body of the lens-barrel, a gas supplying means supplying a gas into the cylindrical body is provided at a side of a proximal end of the objective lens. In the charged-particle beam apparatus according to the present invention, the chamber is filled with the gas in such a manner that the gas supplying means supplies the gas from the proximal end side of the objective lens in the cylindrical body. With this configuration, first, the gas raises an atmospheric pressure in the cylindrical body filled with the gas, and then is flown into the chamber through the emission outlet of the cylindrical body, so that the chamber is filled with the gas. More specifically, the gas supplied from the gas supplying means is flown into the chamber from the cylindrical body in which the electrostatic lens serving as the objective lens is housed. This configuration prevents a small amount of dust existing in the chamber from being stirred up and prevents the dust from being attached to the electrostatic lens. Therefore, even when a high voltage is applied to the electrostatic lens, no electric discharge occurs. The electrostatic lens can effectively converge the charged-particle beam released from the charged-particle supply part and, then, can emit the converged charged-particle beam to the sample put in the chamber. In the charged-particle beam apparatus described above, preferably, the gas supplying means includes: a gas supply pipe having a distal end provided at the proximal end side of the objective lens; a gas supplier connected to a proximal end of the gas supply pipe to supply the gas; and a gas supply valve controlling an open/close state of the gas supply pipe. In the charged-particle beam apparatus according to the present invention, when the gas supply valve is opened, the gas supplied from the gas supplier is released through the supply pipe toward the proximal end side of the objective lens at which the distal end of the supply pipe is provided. In the charged-particle beam apparatus described above, preferably, the gas supply pipe of the gas supplying means is provided with a filter removing dust mixed in the gas supplied from the gas supplier. In the charged-particle beam apparatus according to the present invention, the filter of the gas supply pipe can remove a small amount of dust mixed in the gas supplied from the gas supplier, leading to more reliable prevention of electric discharge at the electrostatic lens serving as the objective lens. In the charged-particle beam apparatus described above, preferably, in the gas supply pipe of the gas supplying means, at least the distal end arranged inside the cylindrical body is made of metal. In the charged-particle beam apparatus according to the present invention, the distal end of the gas supply pipe is made of metal. This configuration prevents the distal end of the gas supply pipe from being degassed in a high vacuum atmosphere and maintains the interior of the chamber and the interior of the cylindrical body at a high vacuum state. In the charged-particle beam apparatus described above, preferably, in the gas supply pipe of the gas supplying means, at least the distal end arranged inside the cylindrical body is subjected to vacuum baking. In the charged-particle beam apparatus according to the present invention, the distal end of the gas supply pipe is subjected to vacuum baking. This configuration prevents the distal end of the gas supply pipe from being degassed in the high vacuum atmosphere and maintains the interior of the chamber and the interior of the cylindrical body at the high vacuum state. Preferably, the charged-particle beam apparatus described above further includes: a cylindrical body valve interposed between the gas supplying means and the charged-particle supply part to control an open/close state of each of the distal end side and the proximal end side in the cylindrical body; and a supply part evacuating means provided at the proximal end side of the cylindrical body to maintain the proximal end side of the cylindrical body, in which the charged-particle supply part is housed, at an ultra high vacuum state which is higher than a vacuum state of the chamber. In the charged-particle beam apparatus according to the present invention, at the time when the gas is supplied by the gas supplying means, the cylindrical body valve is closed. This configuration prevents the gas from being flown into the proximal end side of the cylindrical body in which the charged-particle supplier is housed. This configuration evacuates the proximal end side of the cylindrical body with the use of the supply part evacuating means different from the intra-chamber evacuating means in the state that the cylindrical body valve is closed. Therefore, this configuration efficiently evacuates the chamber and the cylindrical body upon fabrication or observation of the sample and to maintain the proximal end side of the cylindrical body at the ultra-high vacuum state. After completion of the fabrication or observation, further, this configuration efficiently supplies the gas with the use of the gas supplying means within a gas supply area set so as to be minimum. In the charged-particle beam apparatus described above, preferably, the objective lens further has a magnetic field lens generating a magnetic field so as to superimpose the magnetic field on the electric field generated by the electrostatic lens and converging the charged-particle beam. In the charged-particle beam apparatus according to the present invention, the electrostatic lens generates the electric field, and the magnetic field lens generates the magnetic field so as to superimpose the magnetic field on the electric field. This configuration effectively converges the charged-particle beam. In the charged-particle beam apparatus according to the present invention, the gas supplying means for supplying the gas into the chamber and the cylindrical body of the lens-barrel is provided at the proximal end side with respect to the objective lens. This configuration prevents dust, no matter how small amount it is of, from being attached to the electrostatic lens serving as the objective lens. Therefore, this configuration prevents electric discharge occurring due to the small amount of dust even when a high voltage is applied to the electrostatic lens and effectively converges the charged-particle beam to be emitted to the sample. FIG. 1 shows a first embodiment according to the present invention. As shown in FIG. 1, a focused ion beam apparatus (FIB) 1 serving as a charged-particle beam apparatus emits an ion beam B1 serving as a charged-particle beam to a sample S to fabricate a surface of the sample S. For example, a wafer is placed in the apparatus as the sample S to prepare a sample for observation using a TEM (Transmission Electron Microscope). Moreover, a photomask in photolithography is used as the sample S in order to correct the photomask. Hereinafter, detailed description will be given of the focused ion beam apparatus 1 according to this embodiment. As shown in FIG. 1, the focused ion beam apparatus 1 includes a chamber 2 having an interior 2a in which a sample stage 2b is disposed, and a lens-barrel 3 emitting the ion beam B1 to the sample S placed on the sample stage 2b. The chamber 2 is provided with an intra-chamber evacuating means 4 evacuating the interior 2a of the chamber 2 to set the interior at a high vacuum atmosphere. The intra-chamber evacuating means 4 is a vacuum pump such as a rotary pump or a turbo pump, and can control an open/close state using an evacuation valve 4a. Moreover, the lens barrel 3 includes a cylindrical body 5 having a distal end 5a at which an emission outlet 6 is formed for communication with the chamber 2, and an ion supplier 7 serving as a charged-particle supplier housed at a side of a proximal end 5c in an interior 5b of the cylindrical body 5. The ion supplier 7 includes an ion source 8 for supplying an ion, draws the ion from the ion source 8 and accelerates the ion to release the ion beam B1. Examples of the ion from the ion source 8 may include a gallium ion (Ga+) and the like. In the interior 5b of the cylindrical body 5, moreover, an optical system 9 for converging the ion beam B1 released from the ion supplier 7 is provided at a side of a distal end with respect to the ion supplier 7. The optical system 9 includes a condenser lens 10 and an objective lens 11. The condenser lens 10 is disposed at the distal end side with respect to the ion supplier 7 to converge the ion beam B1 released from the ion supplier 7. On the other hand, the objective lens 11 is disposed at the further distal end side with respect to the condenser lens 10 to further converge the ion beam B1 converged by the condenser lens 10 and, then, to emit the converged ion beam B1 to a predetermined emission position of the sample S. The condenser lens 10 is formed by three electrodes each having a through hole 10a formed at a center thereof such that the ion beam B1 passes through the through holes 10a and, also, the objective lens 11 is formed by three electrodes each having a through hole 11a formed at a center thereof such that the ion beam B1 passes through the through holes 11a. Then, the intermediate electrode is changed in potential with respect to the remaining two electrodes, so that an electric field is generated inside each of the through hole 10a and the through hole 11a to converge the ion beam B1 passing therethrough. Although not shown in the figure, a blanking electrode, a deflection electrode or the like may further be provided as the optical system 9. As shown in FIG. 1, moreover, a gas supplying means 12 is provided at a side of a proximal end of the objective lens 11. The gas supplying means 12 includes a gas supply pipe 13 having a distal end 13a provided at the proximal end side of the objective lens 11, and a gas supplier 14 connected to a proximal end 13b of the gas supply pipe 13 to supply a gas G. The gas G is N2, for example. Preferably, the gas G is a dry gas made of an inert substance. In the gas supply pipe 13, the distal end 13a disposed on the interior 5b of the cylindrical body 5 is made of metal subjected to vacuum baking, and is electrically connected to the cylindrical body 5 at a potential identical with that of the cylindrical body 5. Herein, the term “vacuum baking” refers to a process of baking metal at a temperature of about 150° C. under a vacuum atmosphere in order to degas the material to be processed. In addition, the gas supply pipe 13 is provided with a gas supply valve 15 capable of controlling an open/close state of the gas supply pipe 13, and a filter 16 capable of removing dust mixed in the gas G supplied from the gas supplier 14. In the interior 5b of the cylindrical body 5, further, a cylindrical body valve 17 capable of controlling an open/close state of each of the distal end 5a side and the proximal end 5b side is provided between the distal end 13a of the gas supply pipe 13 and the condenser lens 10, and a supply part evacuating means 18 is provided at the proximal end 5c side so as to adjoin to the ion supplier 7. The supply part evacuating means 18 is an ion pump, for example, and can maintain the proximal end 5c, in which the ion supplier 7 is housed, in the interior 5b of the cylindrical body 5 at a degree of vacuum higher than the vacuum state in the chamber 2. Next, description will be given of action of the focused ion beam apparatus 1. As shown in FIG. 1, first, the sample S is placed on the sample stage 2b. Then, the interior 2a of the chamber 2 and the interior 5b of the cylindrical body 5 are evacuated so as to be set at the high vacuum atmosphere. That is, in a state that the cylindrical body valve 17 is closed, the intra-chamber evacuating means 4 evacuates the interior 2a of the chamber 2 and the distal end 5a side of the interior 5b of the cylindrical body 5. Further, the supply part evacuating means 18 evacuates the proximal end 5c side of the cylindrical body 5. As described above, when the cylindrical body valve 17 is closed, the evacuation by each of the intra-chamber evacuating means 4 and the supply part evacuating means 18 can be performed efficiently. Herein, the distal end 13a of the gas supply pipe 13 is made of metal subjected to vacuum baking. This configuration prevents degassing from the distal end 13a of the gas supply pipe 13 in the high vacuum atmosphere and maintains each of the interior 2a of the chamber 2 and the interior 5b of the cylindrical body 5 at a high vacuum state. In this state, then, the cylindrical body valve 17 is opened to start fabrication of the sample S with the use of the ion beam B1. That is, a voltage is applied to each of the condenser lens 10 and the objective lens 11 in the optical system 9 to generate an electric field at each of the through hole 10a and the through hole 11a. Then, the ion beam B1, which has been drawn from the ion source 8 of the ion supplier 7 and has been accelerated, is converged by the condenser lens 10 and, further, is converged by the objective lens 11. Thus, the converged ion beam B1 is emitted to the predetermined emission position of the sample S. A deflecting means (not shown) allows the converged ion beam B1 to scan the sample S to detect secondary charged particles (not shown). Thus, a user can observe the surface of the sample. In addition, the scanning of a predetermined area on the sample S allows fabrication of the sample S. After completion of the fabrication of the sample S, next, the sample S is transported to the outside from the chamber 2 through a sample transport opening (not shown). First, the cylindrical body valve 17 is closed and, further, each of the interior 2a of the chamber 2 and the interior 5b of the cylindrical body 5 is filled with the gas G by the gas supplying means 13 so as to be set at an atmospheric pressure, so that outside dust is prevented from entering the chamber 2 and the cylindrical body 5 through the sample transport opening. More specifically, the gas supply valve 15 of the gas supplying means 13 is opened in order to supply the gas G from the gas supplier 14 to the proximal end side of the objective lens 11 through the filter 16. In the interior 5b of the cylindrical body 5, then, the distal end 5a side with respect to the cylindrical valve 17 is filled with the gas G supplied as described above, so that an atmospheric pressure increases in the interior 5b of the cylindrical body 5. Further, the gas G is flown into the chamber 2 through the emission outlet 6 of the cylindrical body 5, so that the interior 2a of the chamber 2 is filled with the gas G. As described above, the gas G supplied from the gas supplying means 12 is flown toward the chamber 2 from the cylindrical body 5 in which an electrostatic lens serving as the objective lens 11 is housed. This configuration brings about the following advantage. That is, even when a small amount of dust exists in the interior 2a of the chamber 2, the gas prevents the dust from being stirred up. As a result, there is no possibility that the dust is attached to the electrostatic lens serving as the objective lens 11. As described above, the provision of the gas supplying means 12 at the proximal end side with respect to the objective lens 11 prevents electric discharge occurring at the electrostatic lens due to a small amount of dust. Therefore, a higher voltage is applied to the electrostatic lens serving as the objective lens 11, so that the ion beam B1 to be emitted to the sample S can be emitted to the sample S while being converged effectively. Thus, the sample S can be fabricated more precisely. In addition, the provision of the filter 16 at the gas supplying means 12 allows removal of a small amount of dust mixed in the gas G supplied from the gas supplier 14. This configuration prevents electric discharge from occurring at the electrostatic lens serving as the objective lens 11 more accurately. Further, the provision of the cylindrical body valve 17 and the supply part evacuating means 18 allows efficient evacuation of the interior 2a of the chamber 2 and the interior 5b of the cylindrical body 5 upon fabrication of the sample S. Moreover, upon supply of the gas G by the gas supplying means 12, the gas G is prevented from being flown into the proximal end 5c side of the cylindrical body 5 in which the ion supplier 7 is housed. Thus, a gas supply range is set at a minimum level in order to efficiently supply the gas. As shown in FIG. 1, a scanning electron microscope (SEM) 20 in which an electron supplier 21 corresponds to the charged-particle supplier may be a charged-particle beam according to a modification of this embodiment in such a manner that an electron source 22 is used in place of the ion source 8. In such a scanning electron microscope 20, similarly, a gas supplying means 12 is provided at a proximal end side with respect to an objective lens 11; therefore, a higher voltage can be applied to each of a condenser lens 10 and the objective lens 11. As a result, an electron beam B20 released from the electron supplier 21 can be emitted to a sample S while being converged effectively, so that an observation image at high resolution can be obtained. FIG. 2 shows a second embodiment according to the present invention. In this embodiment, members equal to those used in the foregoing embodiment are denoted by identical reference symbols; therefore, description thereof will not be given here. As shown in FIG. 2, a scanning electron microscope (SEM) 30 serving as a charged-particle beam apparatus includes, as an optical system 31, a condenser lens 32 and an objective lens 33. The condenser lens 32 has a coil 34 functioning as a magnetic field lens. On the other hand, the objective lens 33 has a coil 35 functioning as a magnetic field lens, and an electrode 36 functioning as an electrostatic lens inserted into the coil 35. In the condenser lens 32, an electric current is fed to the coil 34 to generate a magnetic field. In the objective lens 33, on the other hand, a voltage is applied to the electrode 36 to generate an electric field and an electric current is fed to the coil 35 to generate a magnetic field so as to superimpose the magnetic field on the electric field. That is, an electron beam B30 released from an electron supplier 21 is converged by generation of the magnetic field at the condenser lens 32. Further, the electric field and the magnetic field functioned in a superimposed manner at the objective lens 33 can converge the electron beam B30 serving as the charged-particle beam more effectively by combination with an advantage obtained in such a manner that a gas supplying means 12 is provided at a proximal end side of the objective lens 33. Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to these embodiments. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the present invention. In the foregoing embodiments, the focused ion beam apparatus and the scanning electron microscope are described as an example of the charged-particle beam apparatus; however, the present invention is not limited thereto. For example, the charged-particle beam apparatus according to the present invention may be an FIB/SEM system including both a lens-barrel for emission of an ion beam and a lens-barrel for emission of an electron beam. Advantages similar to those described above can be expected as long as the charged-particle beam apparatus according to the present invention is an apparatus that allows an electrostatic lens to converge at least a charged-particle beam obtained by acceleration of a charged particle. In the foregoing embodiments, moreover, the condenser lens and the objective lens are used as an optical system for converging a charged-particle beam; however, the present invention is not limited to this example. A configuration that an objective lens is attached to at least a distal end side of a cylindrical body of a lens-barrel is allowed to converge a charged-particle beam and, then, to emit the converged charged-particle beam to a predetermined emission position of a sample. In the charged-particle beam apparatus, the gas supplying means for supplying a gas into the chamber and the cylindrical body of the lens-barrel is provided at the proximal end side with respect to the objective lens; therefore, a small amount of dust can be prevented from being attached to the electrostatic lens serving as the objective lens. As a result, even when a high voltage is applied to the electrostatic lens, the charged-particle beam apparatus according to the present invention can prevent occurrence of electric discharge due to a small amount of dust and can effectively converge a charged-particle beam to be emitted to a sample.
	description	The present disclosure relates to a uranium dioxide (UO2) pellet for light water reactor nuclear fuel and a method of making the same. Nuclear power plant uses heat generated by nuclear fission of uranium, and an UO2 sintered pellet is generally used as nuclear fuel for nuclear power plant. The UO2 sintered pellet may be produced by sintering a green pellet. The UO2 sintered pellet produced by such an existing method has a density of about 96% TD (theoretical density) and a grain size of about 8-14 μm. Recently, high burnup nuclear fuels have been developed, which are burnt for a long time in order to increase economic efficiency of nuclear fuel and reduce an amount of spent fuel. As the burnup of nuclear fuel increases, a generation amount of fission products such as Xe, Kr, Cs and I increases. The increased fission product will increase stress in a cladding tube, which may deteriorate the safety of nuclear fuel. Accordingly, in order to overcome those limitations, fission product must be released from the pellet as little as possible. In addition, after Hukusima nuclear power plant accident, there are increasing demands for development of UO2 nuclear fuel pellets with an enhanced accident resistance to trap highly radioactive fission product as much as possible to prevent the release of fission products having a high level of radioactivity outside the environments. The fission product is the material generated during the fission caused after fissile materials (a typical example of such fissile materials is U-235) absorb thermal neutron. When fission occurs in UO2 nuclear fuel, one uranium atom is split into two fission products. Fission products can be classified into four groups in terms of their volatility and chemical activity: volatile fission product including fission gases, semi-volatile fission product, fission product that are low volatile, and non-volatile fission product. Among the four groups, volatile fission product (I and Cs) and fission gases (Xe and Kr), are most important in terms of fuel degradation and radiological consequence, because they have very strong chemical activity and are also easily released outside the fuel pellet and environment. Accordingly, the present disclosure provides a uranium dioxide nuclear fuel pellet having ceramic microcells arranged therein and a fabricating method thereof. An aspect of the invention provides a uranium dioxide nuclear fuel pellet, which may comprise: microcells defined by micro-partitions comprising a ceramic material; and uranium dioxide contained in the microcells, such that at least part of fission products would be trapped in the microcells upon fissioning. In the foregoing uranium dioxide nuclear fuel pellet, metallic particles may be dispersed in the uranium dioxide and configured to react with oxygen more easily than the uranium dioxide does. The ceramic material may have a chemical attraction with the fission products. The ceramic material may comprise at least one chemical compound selected from a group consisting of Si-compound, Ti-compound, Al-compound, Mg-compound, Mn-compound, Na-compound, Ca-compound and Ba-compound. An average size of the microcell may be about 50 μm to about 400 μm. Each of at least some of the microcells contains a single grain of the uranium oxide. The metallic particles may comprise Cr or Mo. An average size of the metallic particles may be about 0.3 μm to about 10 μm. Still in the foregoing uranium dioxide nuclear fuel pellet, one of the micro-partitions may be located between two immediately neighboring grains of the uranium oxide and contacts the two immediately neighboring grains of the uranium oxide. The micro-partition located between the two immediately neighboring grains of the uranium oxide may completely separate the two immediately neighboring grains of the uranium oxide not to contact each other. The micro-partition located between the two immediately neighboring grains of the uranium oxide may have a hole allowing the two immediately neighboring grains to contact each other. The micro-partitions of the ceramic material may have chemical attraction with fission products and configured to inhibit diffusion of the fission products at boundaries of the uranium oxide. The uranium dioxide may be filled in the microcells. Another aspect of the invention provides a method of making a uranium dioxide nuclear fuel pellet, which may comprise: providing a mixture of uranium dioxide powder and additive powder comprising a ceramic material; forming a pellet by compressing the powder mixture; and sintering the pellet at a temperature at which at least part of the additive powder is changed into liquid which permeates between grains of the uranium oxide thereby forming micro-partitions comprising the ceramic material defining microcells in which the uranium dioxide is contained. In the foregoing method, the additive powder may be one or more selected from a group consisting of Si-compound, Ti-compound, Al-compound, Mg-compound, Mn-compound, Na-compound, Ca-compound and Ba-compound. In the mixture, a ratio of the additive powder with respect to the uranium dioxide powder may be about 0.1% to about 8.0% by weight. The compound selected as the additive powder comprises at least one selected from the group consisting of oxide, nitride, sulfide, fluoride, chloride, stearate, carbonate, nitrate and phosphate. The liquidus temperature of the additive may be about 1200° C. to about 1800° C. And the sintering temperature may be about 1600° C. to about 1800° C. The pellet may be sintered under reducing gas atmosphere of a reducing gas which comprises a hydrogen-containing gas. The hydrogen-containing gas may comprise a mixture of a hydrogen gas and at least one selected from a group consisting of carbon dioxide, water vapor and inert gas. The ceramic material may have chemical attraction with the fission products. In an aspect of the invention, about 50 μm to about 400 μm (with respect to a 3-dimentional size) microcells formed of a ceramic material having a chemical attraction with fission products generated in the nuclear fuel pellet and the fission products are absorbed and trapped, such that the extraction of the fission product may be retrained in a normal operation condition and that the performance of the nuclear fuel may be enhanced by mitigating PCI. In addition, ceramic microcell UO2 pellet will enhance the retention ability of highly radioactive and corrosive fission products such as Cs and I, where all UO2 grains are enveloped by thin ceramic cell walls which act as chemical trap in an accident condition, without being released into the environment. In another aspect, metallic particles reactive with excess oxygen generated during the burnup may be further provided in the ceramic microcells. Together with the trapping of the fission products, the excess oxygen may be effectively controlled to slow down the diffusion rate of the fission products. Accordingly, the performance of the nuclear fuel can be enhanced more. In still another aspect, the ceramic microcells arranged in the nuclear fuel pellet may be formed of a ceramic material having a chemical attraction with the fission products or metallic particles reactive with the excess oxygen generated during the burnup are additionally arranged in the ceramic microcells. Together with the trapping of the fission products, the diffusion rate may be slowed down to make the fission products remain in the nuclear fuel pellet effectively. Accordingly, release of the fission products may be controlled according to a fabricating method of the UO2 nuclear fuel pellet. Additional advantages and features of the disclosure will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The aspects and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. To achieve these aspects and other advantages and in accordance with the purpose of the embodiments, as embodied and broadly described herein, a uranium dioxide nuclear fuel pellet includes ceramic microcells arranged in the nuclear fuel pellet to trap fission products. In another aspect of the present invention, a uranium dioxide nuclear fuel pellet includes ceramic microcells arranged in the nuclear fuel pellet to trap fission products; and metallic particles arranged in the ceramic microcells to trap excess oxygen. In a further aspect of the present invention, a fabricating method of a uranium dioxide nuclear fuel pellet comprising ceramic microcells arranged therein, the fabricating method includes steps of fabricating a powder mixture by mixing a uranium dioxide powder with an additive powder comprising a chemical attraction with fission products; fabricating a pellet by compressing the powder mixture; and sintering the pellet at about 1600° C. to about 1800° C. under a reducing gas atmosphere. The additive may be one or more selected from a group of Si-compound, Ti-compound, Al-compound, Mg-compound, Mn-compound, Na-compound, Ca-compound and Ba-compound. The embodiments have the following advantageous effects. Microcells having about 50 μm to about 400 μm (with respect to a 3-dimentional size) are formed of a ceramic material having a chemical attraction with fission products generated in the nuclear fuel pellet and the fission products are absorbed and trapped, such that the extraction of the fission product may be retrained in a normal operation condition and that the performance of the nuclear fuel may be enhanced by mitigating PCI. In addition, highly radioactive fission products including Cs and I can be trapped in the pellet in an accident condition. It is to be understood that both the foregoing general description and the following detailed description of the embodiments or arrangements are exemplary and explanatory and are intended to provide further explanation of the embodiments as claimed. Various embodiments of a fission product trapping pellet with ceramic microcells arranged therein and a fabricating method thereof will be described as follows, referring to the accompanying drawings. Reference will now be made in detail to the specific embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In uranium oxide pellets without any barriers or walls between grains, the fission product is produced within grains and diffused to grain boundary, and exists as bubbles. When the fission product reaches a predetermined amount, a bubble tunnel is formed along the grain boundary, and the fission product is released from the pellet through the bubble tunnel. As the grain size of the pellet increases, the diffusion distance of fission product to the grain boundary becomes longer. Therefore, the fission product remains within the pellet for a longer time, thus reducing a released amount of the fission product. Thus, high burnup nuclear fuel pellet may have an increased grain size. UO2 nuclear fuel pellet is inserted in a zirconium alloy unclear fuel cladding which is deformed inwardly during the burn-up and the nuclear fuel pellet is swollen outwardly by neutron irradiation, such that the nuclear fuel pellet and the cladding may contact with each other to generate stress. Especially, it is more likely to operate a nuclear fuel for an ultrahigh burnup level in an extreme situation such as a high power or a transition operation. When the output power is increased for a relatively short time, the temperature of the nuclear fuel pellet is increased and a predetermined pressure is applied to the fuel cladding by heat expansion. When high stress is applied to the fuel cladding at a high burnup level for a relatively short time, there might be damage on the fuel cladding. Accordingly, to reduce the pressure applied to the fuel cladding generated by the thermal expansion of the nuclear fuel pellet, a new pellet having an increased amount of initial deformation and an increased rate of creep deformation is developed and Pellet-Clade interaction (hereinafter, PCI) characteristics are enhanced. When the grain size of the pellet is increased, the movement distance of the fission product is increased, and may slow down the extraction of the fission products. Further, an additive may be provided to heighten the creep deformation rate of the fuel pellet such that the stress applied to a fuel cladding can be reduced effectively. FIG. 1 is a conceptual diagram illustrating microcells arranged in a uranium dioxide fission nuclear pellet according to the present invention. There may be provided a method of trapping a fission product in a nuclear pellet (UO2 pellet) having microcells arranged therein. FIG. 2 is a conceptual drawing of trapping a fission product by arranging the ceramic microcells in the uranium dioxide nuclear fuel pellet according to the present invention. Ceramic microcells having a chemical attraction with fission products are arranged in the uranium dioxide nuclear fuel pellet, such that extraction of fission products in a normal operational condition may be restrained and that PCI is mitigated, so as to enhance the performance of the nuclear fuel and to enable the nuclear fuel pellet to effectively trap radioactive fission products including Cs and I having a long half-life and a large amount enough to affect the environments out of fission products in an accident condition to prevent release of the radioactive fission products outside. The ceramic material used in forming the microcells arranged in the uranium nuclear fuel pellet may be a material having a chemical attraction with the fission products. Especially, such the ceramic material may be one or more chemical elements selected from a group configured of a Si-compound, a Ti-compound, an Al-compound, an Mg-compound, a Mn-compound, a Na-compound, a Ca-compound and a Ba-compound. The ceramic material has a chemical attraction with Cs and I having a large generation amount and a long half-life out of the fission products enough to affect the environments if they are extracted outside in an accident. Accordingly, the fission products including Cs and I generated during the irradiation reaches a wall of the cell, the material composing the cell wall absorbs and traps the fission products, to restrain the release of the fission products. In embodiments, the size of the microcell is within about 50 to about 400 μm. In embodiments, a suitable number of microcells can be formed with a small amount of an additive powder and when the average size of the microcell is in the range of about 50 to about 400 μm. The ceramic material content of the microcell is in a range of about 0.1% to about 8.0% with respect to the weight of the uranium dioxide. The content of the ceramic material is in the range of about 0.1% to about 8.0% that can form the appropriate microcells in the nuclear fuel pellet and maintain the appropriate amount of the uranium per unit volume of the nuclear fuel pellet. The ceramic material of the microcell is partially or entirely changed into liquid at about 1200 to about 1800° C. In embodiments, the ceramic material is changed into liquid below about 1800° C. that is the upper limit of the sintering temperature, to form the microcells during the sintering effectively and to set the nuclear fuel pellet not changed to liquid below about 1200° C. that is the upper limit temperature of the normal operation condition. As mentioned above, the ceramic material starting to be changed into liquid ceramic in the range of about 1200 to about 1800° C. is used and then the cell wall is softened, such that the initial deformation amount and the creep deformation rate may be increased enough to enhance PCI characteristics of the nuclear fuel pellet. The ceramic material compound may be one or more ones selected from a group configured of metal, oxide, sulfide, fluoride, chloride, stearate, carbonate, nitrate and phosphate. In addition, the ceramic microcells are formed per grain unit. FIG. 3 is a conceptual drawing of trapping excess oxygen and the fission product by additionally arranging metallic particles in the ceramic microcells arranged in the uranium dioxide nuclear fuel pellet according to the present invention. Referring to FIG. 3, the ceramic microcells are arranged and metallic particles capable of forming an oxide stably by reacting with the excess oxygen, prior to UO2, are additionally arranged in the uranium dioxide nuclear fuel pellet, only to absorb and trap the fission products. Together with that, the movement speed of the fission products is slowed down and the nuclear fuel pellet can have an enhanced nuclear fuel performance and stability. A metallic particle arranged in the microcell of the uranium diode nuclear fuel pellet reacts with the excess oxygen generated at a burnup level of about 70,000 MWD/MTU, prior to UO2, and the metallic particle absorbs and isolates the excess oxygen not to react with UO2. It is preferable that the metallic particle is Cr or Mo. An average size of the metallic particle may be about 0.3 to about 10 μm. The size of the metallic particle may be in the range of about 0.3 to about 10 μm that is the range capable of arranging an appropriate number of the particles per unit weight. Next, a fabricating method of the uranium dioxide nuclear fuel pellet having the ceramic microcells arranged therein according to the present invention will be described as follows. The fabricating method includes steps of fabricating powder mixture by mixing the uranium dioxide powder with the additive powder that consists of one or more elements selected from the group of the Si-compound, Ti-compound, Al-compound, Mg-compound, Mn-compound, Na-compound, Ca-compound and Ba-compound; fabricating a green pellet by compressing the powder mixture; and sintering the green pellet at about 1600 to about 1800° C. under the reducing gas atmosphere. According to one embodiment of the present invention, the compounds provided in the additive powder added in the powder mixture fabricating step may be at least one selected from the group of metal, oxide, nitride, sulfide, fluoride, chloride, stearate, carbonate, nitrate and phosphate. According to one embodiment of the present invention, the content of the additive is about 0.1 to about 8.0% of the overall weight in the powder mixture fabricating step. The limited content of the ceramic material is the range of about 0.1 to about 8.0% that can form the appropriate microcells in the nuclear fuel pellet and maintain the appropriate amount of the uranium per unit volume of the nuclear fuel pellet. According to one embodiment of the present invention, the selected additive may be partially or entirely changed into liquid below about 1800° C. that is the upper limit temperature of the typical sintering temperature and it may not start to be changed into liquid below about 1200° C. that is the upper limit of the normal operation condition. The liquid formed in the sintering may make the grain grow rapidly and the liquid is disposed along a boundary of the growing grain. Accordingly, the grain unit ceramic microcell having an appropriate size can be formed effectively and the nuclear fuel pellet may be maintained during the irradiation, with no liquid grain boundary. The size of the microcell is limited within about 50 to about 400 μm. In embodiments, a suitable number of microcells can be formed with a small amount of an additive powder and when the average size of the microcell is in the range of about 50 to about 400 μm. According to one embodiment of the present invention, the reducing gas atmosphere in the sintering step may be hydrogen-containing gas atmosphere. Especially, the hydrogen-containing gas may be a hydrogen-containing gas mixture formed of a hydrogen gas mixed with at least one selected from a group of carbon dioxide, vapor and inert gas or a hydrogen. Next, embodiments of the present invention will be described in detail as follows. Here, the embodiments which will be described as follows are examples of the present invention and the scope of the present invention is not limited by the embodiments. First Embodiment 1.0% of SiO2, TiO2 and Al2O3 powder with respect to UO2 powder is added to uranium dioxide (UO2) powder and they are mixed with each other by a mixer for 2 hours, to prepare the powder mixture. At this time, the weight ratio of the SiO2 powder, TiO2 powder and Al2O3 powder added at this time may be 35.86%, 37.08% and 27.06%. A green pellet is fabricated by compressing the powder mixture with 3 ton/cm2. The green pellet is heated at a heating rate of 300° C. per hour under hydrogen gas atmosphere, to make the temperature of the pellet reach 1720° C. The heated pellet is maintained for 4 hours and cooled to be a normal temperature at a rate of 300° C. per hour under the same atmosphere, such that the uranium dioxide unclear fuel pellet may be fabricated. The density of the fabricated nuclear fuel pellet is measured based on Archimedes' principle and a cross section of the nuclear fuel pellet having the density measured is polished like a mirror. After that, the size and structure of the microcell is observed. FIG. 4 is a drawing illustrating a phase diagram of SiO2—TiO2—Al2O3 according to a first embodiment of the present invention and shows a composition ratio selected according to the embodiment. The temperature of a liquidus line possessed by the selected additive is about 1650° C. It is measured that the density of the nuclear fuel pellet fabricated in the process mentioned above is 96.9% of TD and that an average size of the microcell is 87 μm. FIG. 5 is an optical micrograph image of a ceramic microcell structure of a uranium dioxide nuclear fuel pellet fabricated according to the first embodiment of the present invention. As shown in FIG. 5, the microcells are formed along the grain boundary. Second Embodiment 1.0% of SiO2, Al2O3 and MnO powder with respect to UO2 powder is added to uranium dioxide (UO2) powder and they are mixed with each other by a mixer for 2 hours, to prepare the powder mixture. At this time, the weight ratio of the SiO2 powder, Al2O3 powder and MnO powder added at this time may be 40.5%, 45.5% and 14.0%. The powder mixture is compressed and sintered in the same process mentioned in the first embodiment and the UO2 pellet is fabricated. It is measured that the density of the nuclear fuel pellet fabricated in the process mentioned above is 97.3% of TD and that an average size of the microcell is 96 μm. FIG. 6 is an optical micrograph image of a ceramic microcell structure of a uranium dioxide nuclear fuel pellet fabricated according to a second embodiment of the present invention. As shown in FIG. 6, the microcells are formed along the grain boundary. Third Embodiment 0.8% of TiO2 and MgO powder with respect to UO2 powder is added to uranium dioxide (UO2) powder and they are mixed with each other by a mixer for 2 hours, to prepare the powder mixture. At this time, the weight ratio of the TiO2 powder and MgO powder added at this time may be 70% and 30%. The powder mixture is compressed and sintered in the same process mentioned in the first embodiment and the UO2 pellet is fabricated. It is measured that the density of the nuclear fuel pellet fabricated in the process mentioned above is 97.2% of TD and that an average size of the microcell is 102 μm. FIG. 7 is an optical micrograph image of a ceramic microcell structure of a uranium dioxide nuclear fuel pellet fabricated to a third embodiment of the present invention. As shown in FIG. 6, the microcells are formed along the grain boundary. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.
	summary
	abstract	A holographic mask includes a plurality of pixels each imparting a calculated phase and/or amplitude change to the projection beam to provide an image that is parallel to the mask. The holographic mask is used displaced from the best object plane of the projection lens.
	description	The present application claims priority to Korean Patent Application No. 10-2017-0060134, filed May 15, 2017, the entire contents of which is incorporated herein for all purposes by this reference. The present invention relates generally to a technique for improving safety and reliability in a protection system, made up of a process protection system and a reactor protection system that performs safety functions of a nuclear power plant. More particularly, the present invention relates to a digital protection system for a nuclear power plant, which is capable of eliminating a single point vulnerability (SPV) and responding to a common cause failure (CCF) in an existing protection system, by applying two different and mutually independent controllers to the protection system and appropriately combining processing results of the two controllers. Nuclear power generation refers to generating electricity using heat energy generated by a fission chain reaction to heat steam which drives a turbine generator by boiling water. An enormous amount of power is generated as energy required to completely separate atomic nuclei into protons and neutrons which are emitted as free particles, and accordingly nuclear power generation is the most desirable power source capable for acquiring large amounts of energy using an extremely small amount of fuel. Most countries around the world produce electricity using nuclear power generation. However, in the case of the nuclear power generation, since using nuclear energy has many risks, numerous safety devices and highly trained operators are required. The protection system serves to monitor the status of a nuclear steam supply system (NSSS), and mitigates an effect of an accident by allowing the reactor to be shut down when a monitored process variable reaches a prescribed protection system setting. An SPV event is a component failure resulting in a reactor or turbine shutdown due to a fault present in a single component. A number of SPVs may be present in any existing operating nuclear power plant, and the number of SPVs may reach up to 70-90 in reactor protection systems of operating nuclear power plants built in the 1980s. The SPVs are caused by various analog devices that are non-multiplexed within the reactor protection system. A CCF event is a situation where a failure simultaneously occurs in multiple components and is due to a cause that is common to the multiple components. Performance of unique safety functions of the protection system may be seriously effected when a CCF occurs in a protection system. An example CCF that can be easily understood is the Y2K bug, or millennium bug, in 1999. This meant that, upon arrival of the year 2000, computers incapable of recognizing the year 2000 could malfunction. However, in the Y2K case, preparatory measures were taken to allow the problem to be removed in advance and finished to the point where only a few errors occurred in some fields. It is an object of the present invention to provide a digital protection system for a nuclear power plant, including a process protection system and a reactor protection system that are constituted with concurrent logic controllers and comparative logic controllers of different (contrasting) types from each other, in order to address problems of being vulnerable to the SPV and the CCF that may occur in existing protection systems of nuclear power plants. It is another object of the present invention to provide a digital protection system for a nuclear power plant, in which safety is improved through an improvement of a reactor shutdown function. It is another object of the present invention to provide a digital protection system for a nuclear power plant, in which reliability is improved through an elimination of component failure resulting in reactor failure due to a single fault. The technical problem to be solved by the present invention is not limited to the above-mentioned technical problems, and various technical problems can be included within the scope of what will be apparent to the ordinarily skilled person in the art from the following description. According to an aspect of the present invention, there is provided a digital protection system having at least two channels and at least two trains and may include a process protection system and a reactor protection system. The process protection system may have, in one channel, first and second comparative logic controllers of different types that are mutually independent of each other, the first and second comparative logic controllers each receiving process variables as inputs and each outputting comparison logic results. The reactor protection system may have, in one train, first and second concurrent logic controllers of different types that are mutually independent from each other, the first and second concurrent controllers each receiving the comparison logic results as inputs and each outputting concurrent logic results. The reactor protection system may include at least two initiation circuits, each initiation circuit including a series circuit in which a plurality of relays are connected in series and a parallel circuit in which a plurality of relays are connected in parallel, one of the series circuit relays being controlled by receiving one of the concurrent logic results as an input and one of the parallel circuit relays being controlled by receiving the other of the concurrent logic results as an input. The at least two channels may include a first channel, a second channel, a third channel, and a fourth channel, and the at least two trains may include a first train and a second train. The different types of comparative logic controllers may include an FPGA type and a PLC type. Preferably, the comparative logic controllers each transmit the comparison logic results only to concurrent logic controllers of one type. The process variables may include information indicative of at least one of a reactor coolant hot-tube temperature, a reactor coolant cold-tube temperature, a reactor coolant flow rate, a pressurizer pressure, a pressurizer water level, a neutron flux value, a containment building pressure, a steam generator water level, a steam pipe pressure, and a refueling water tank level. The comparison logic results may include one of a normal signal and an abnormal signal. The first concurrent logic controller may output the concurrent logic results based on the number of the comparison logic results and the number of the abnormal signals received from the first comparative logic controllers included in each channel, and the outputted concurrent logic results of the first concurrent logic controller may include a first output signal being input to one relay included in the series circuit and a second output signal being input to one relay included in the parallel circuit. The second concurrent logic controller may output the concurrent logic results based on the number of the comparison logic results and the number of the abnormal signals received from the second comparative logic controllers included in each channel, and the outputted concurrent logic results of the second comparative logic controllers may include a third output signal being input to one relay included in the series circuit and a fourth output signal being input to one relay included in the parallel circuit. Here, the first and second output signals have opposite logic values, and the third and fourth output signals have opposite logic values. The first concurrent logic controller may output the concurrent logic results when the received comparison logic results includes at least one abnormal signal, by outputting a first logic value to the series circuit and a second logic value to the parallel circuit, and the second concurrent logic controller may output the concurrent logic results when the received comparison logic results include at least one abnormal signal, by outputting the first logic value to the series circuit and the second logic value to the parallel circuit. Meanwhile, the first concurrent logic controller may outputs the concurrent logic results when the received comparison logic results includes at least one normal signal, by outputting a first logic value to the series circuit and a second logic value to the parallel circuit, and the second concurrent logic controller may output the concurrent logic results when the received comparison logic results include at least one normal signal, by outputting the first logic value to the series circuit and the second logic value to the parallel circuit. The digital protection system may further include an RTSS, which may include a first NO contact connected between a power supply and a central node; a second NO contact connected between the power supply and the central node; a third NO contact connected between the central node and a CEDM; and a fourth NO contact connected between the central node and the CEDM. When at least one of the first NO contact and the second NO contact is closed and at least one of the third NO contact and the fourth NO contact is closed, power may be supplied from a motor-generator set to the CEDM. On the other hand, when both the first NO contact and the second NO contact are open or both the third NO contact and the fourth NO contact are open, power supplied from a motor-generator set to the CEDM may be interrupted. Each initiation circuit may include a first series circuit for controlling the first NO contact according to an output signal from the concurrent logic controller; a first parallel circuit for controlling the second NO contact according to the output signal from the concurrent logic controller; a second parallel circuit for controlling the third NO contact according to the output signal from the concurrent logic controller; and a second series circuit for controlling the fourth NO contact according to the output signal from the concurrent logic controller. The first series circuit and the first parallel circuit may receive the output signals from the first concurrent logic controller and the second concurrent logic controller included in a first train of the at least two trains as inputs. The second series circuit and the second parallel circuit may receive the output signals from the first concurrent logic controller and the second concurrent logic controller included in a second train of the at least two trains as inputs. Each initiation circuit may further include a third circuit including a relay for controlling the second NO contact, the relay for controlling the second NO contact being controlled by the first parallel circuit; and a fourth circuit including a relay for controlling the third NO contact, the relay for controlling the third NO contact being controlled by the first parallel circuit. Here, the relays included in the third circuit and the fourth circuit are normally closed (NC) contacts. The first series circuit or the second series circuit may include two relays connected in series, the two series relays being respectively turned on/off according to the output signal from the concurrent logic controller. The first NO contact or the fourth NO contact may be closed when the two relays are both on, and the first NO contact or the fourth NO contact may be open when at least one of the two relays is off. The first parallel circuit or the second parallel circuit may include two relays connected in parallel, the two parallel relays being turned on/off according to the output signal from the concurrent logic controller. The relay included in the third circuit or the fourth circuit may be turned on when the relays included in the first parallel circuit or the second parallel circuit are all off, and the relays included in the third circuit or the fourth circuit may be turned off when at least one of the relays included in the first parallel circuit or the second parallel circuit is on. The digital protection system according to the present invention is a protection system made up of a process protection system and a reactor protection system that performs safety functions of a nuclear power plant. The digital protection system according to the present invention can prevent a nuclear power plant from being shut down in the case of a single fault (i.e., a single point vulnerability, or SPV), by eliminating a component failure resulting in a reactor shutdown due to an SPV fault condition present in existing devices. The digital protection system according to the present invention allows the protection system to be safely operated even in the case of a CCF, by applying multiplexing to the digital protection system itself. In addition, the digital protection system according to the present invention, considering diversity and independence of the protection system itself, includes comparative logic controllers and concurrent logic controllers of different (contrasting) types from each other to correspond to the CCF, thereby eliminating SPV shutdowns and effectively preparing for the case of a CCF shutdown. In addition, according to the digital protection system of the present invention, it is possible to perform the reactor safety function in the case of the CCF, which results in improving safety and reliability. In addition, according to the digital protection system of the present invention, it is possible to operate the power plant with zero SPVs and to improve maintenance conditions. Hereinafter, a digital protection system according to the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the above-described embodiments, and various changes and modifications may be made without departing from the scope of the present invention. In addition, the matters described in the attached drawings may be different from those actually implemented by the schematic drawings to easily describe the embodiments of the present invention. In the meantime, each component described below is only an example for implementing the present invention. Thus, in other implementations of the present invention, other components may be used without departing from the spirit and scope of the present invention. Also, the expression of “comprising” is intended to merely denote that such elements are present to be “inclusive”, and should not be understood as excluding any additional elements. Also, the expressions such as ‘first’, ‘second’, etc. are expressions used only for distinguishing a plurality of components, and do not limit the order or other features among the components. In the description of the embodiments, it is to be understood that forming each layer (film), area, pattern, or structure “on” or “under” a substrate, each layer (film), area, pad, or pattern includes: forming directly; or forming by interposing another layer therebetween. The criteria for “on” or “under” with respect to each layer are described with reference to the drawings. When a part is “connected” to another part, it includes not only “directly connected” but also “indirectly connected” by interposing another part therebetween. Also, when certain portion is referred to as “comprising” certain components, it means that it can include other components, and does not exclude other components unless specifically stated otherwise. FIG. 1 illustrates a SPV that may occur in the structure of a protection system according to a related art. Referring to FIG. 1, a single fault occurs in one train (Train A) of the reactor protection system to cause one reactor trip breaker (RTB) to be open, which may lead to a reactor shutdown. FIG. 2 compares the cabinet appearance of a reactor protection system according to the present invention with a reactor protection system of a related art. Referring to FIG. 2, since the existing reactor protection system is an analog system and each logic gate is configured in the form of a hardware card, each card must be connected via various hardwirings to transmit signals in order to implement concurrent logic in the reactor protection systems, whereby there are disadvantages in that cabinet size is increased, cabling is complicated, and maintenance is difficult. Meanwhile, in the case of the digital protection system according to the present invention, the concurrent logic of the protection system is implemented using software and operated on a CPU or a field programmable gate array (FPGA), whereby there are advantages in that the cabinet size is reduced, the cabling is simple, and the maintenance is easy. In order to prevent the occurrence of a CCF, the digital protection system of the present invention duplexes the controllers into different types and implements the existing analog protection system as a digital protection system, thereby facilitating maintenance. FIG. 3 illustrates a configuration of the digital protection system according to the present invention, and FIG. 4 more detailedly illustrates the configuration of FIG. 3, showing a process protection system and a reactor protection system included in the digital protection system. Referring to FIGS. 3 and 4, the digital protection system according to the present invention may include four channels 221, 222, 223, and 224 of the process protection system, and two trains 231 and 232 of the reactor protection systems. The four channels 221, 222, 223, and 224 of the process protection system may include the first comparison logic controllers 221-1 and 222-1 and the second comparison logic controllers 221-2 and 222-2 of different types and transmit the comparison logic results to the two trains 231 and 232 of the reactor protection system. Although FIG. 3 illustrates an embodiment in which the process protection system includes four channels, it is not limited thereto. The process protection system of the present invention may include at least two channels. More specifically, the comparative logic controllers 221-1, 222-1, 221-2, and 222-2 of the respective channels 221, 222, 223 and 224 in the process protection system generate comparison logic results based on various process variables collected from sensors 110, 120, 130, and 140 installed in the nuclear steam supply system 210. Also, the comparative logic controllers 221-1, 222-1, 221-2, and 222-2 may transmit the comparison logic results to the concurrent logic controller of each train 231 and 232 in the reactor protection system. The comparative logic controllers 221-1, 222-1, 221-2, and 222-2 of the respective channels receive signals from the sensors 110, 120, 130, and 140 that are multiplexed, thereby performing comparative logic algorithms independently of each other. For example, the comparative logic controller included in at least one channel of the process protection system may determine whether hot-tube temperature information that has been sensed has reached a predetermined protection system setting and, and based on the determination, may transmit a signal indicating whether or not an abnormality exists to respective trains 231 and 232 of the reactor protection system. Here, each channel of the process protection system is physically/electrically isolated and independently derives its own result signal for each channel. For example, in the case of 2/4 concurrent logic, the concurrent logic controller generates a reactor shutdown signal when an abnormal signal is output from the comparison logic controller in at least two channels of process variables quadplexed. Even if the process protection system is multiplexed with four channels in the present invention, the process variables may be triplexed or duplexed depending on type, in which signals may be assigned only to three channels of the process protection system and 2/3 concurrent logic is performed based on the comparison logic results received from these three channels in the reactor protection system to determine whether a reactor shutdown signal is generated or not in the case of triplexed process variables, and signals may be assigned to only two channels of the process protection system and 1/2 concurrent logic is performed in the reactor protection system to determine whether a reactor shutdown signal is generated or not in the case of a duplexed process variables. The concurrent logic is not limited to 1/2, 2/3, and 3/4, but the concurrent logic may be 2/2, 1/3, 3/3, 3/4, and so on. When the concurrent logic described herein is defined as n/m, any concurrent logic is possible provided that n is greater than or equal to m. Each channel of process protection system is configured with the first comparative logic controller and the second comparative logic controller of different types that are mutually independent. For example, the first comparative logic controller may be configured based on a FPGA, and the second comparative logic controller may be configured based on a programmable logic controller (PLC), in which two comparative logic controllers may be controlled independently of each other. Therefore, even if a CCF occurs in one controller, the other controller may perform the unique functions of the process protection system, thereby effectively coping with both of a SPV and a CCF. Here, the comparative logic controllers may each transmit the comparison logic results to all concurrent logic controllers of the same type. The first comparative logic controllers 221-1, 222-1, 223-1, and 224-1 and the second comparative logic controllers 221-2, 222-2, 223-2, and 224-2 of the process protection system are configured with different types, and the first concurrent logic controllers 231-1 and 232-1 and the second concurrent logic controllers 231-2 and 232-2 in the reactor protection system are also configured with different types. Therefore, an entire protection system, from the process protection system (comparative logic controllers) to the reactor protection system (concurrent logic controllers), is independently controlled only by a device of the same type so that two protection systems may be practically operated. For example, an FPGA-based device allows its controllers to be operated independently of a PLC-based device without being influenced by each other, whereby the protection system may perform the safety function even when a CCF occurs. Each of the trains 231 and 232 of the reactor protection system includes the first concurrent logic controllers 231-1 and 232-1 and the second concurrent logic controllers 231-2 and 232-2 of different types, performs concurrent logic according to the comparison logic result, and transmits the resulting control signal to a reactor trip switchgear system (to be described later), or RTSS, via an initiation circuit as described below. Here, the reactor protection system may include a first train 231 and a second train 232. The first train 231 may include a first concurrent logic controller 231-1, a second concurrent logic controller 231-2, a first train serial initiation circuit 231-3, and a first train parallel initiation circuit 231-4; and the second train 232 may include a first concurrent logic controller 232-1, a second concurrent logic controller 232-2, a second train parallel initiation circuit 232-3, and a second train serial initiation circuit 232-4. The concurrent logic controllers 231-1, 232-1, 231-2, and 232-2 of the reactor protection system receive the comparison logic results transmitted by the process protection system. Here, the comparison logic results are received from all multiplexed channels of the process protection system. More specifically, the concurrent logic controllers 231-1, 232-1, 231-2, and 232-2 are provided to perform concurrent logic according to the number of channel trips (abnormal signals) included in the received comparison logic results and to transmit the resulting signal, indicating whether or not to shut down the reactor, to an RTSS 240 via the initiation circuits 231-3, 232-3, 231-4, and 232-4. For example, when applying 2/4 logic for quadplexed process variables, it may be determined that the reactor status is abnormal when the comparison logic results include at least two abnormal signals. Therefore, when reactor status abnormality is detected in at least two channels among four channels of the process protection system, the digital protection system determines that the reactor status is abnormal and thus takes an action such as dropping a control rod. The RTSS 240 is provided such that the reactor is normally operated when a nuclear steam supply system 210 is normal and the reactor is shut down when the status of the nuclear steam supply system 210 is abnormal, according to the control signals transmitted by the initiation circuits 231-3, 232-3, 231-4, and 232-4 of each train of the reactor protection system. Here, the RTSS 240 may perform the safety function even if a single fault or a CCF occurs in the comparative logic controllers or the concurrent logic controllers. This is because the controllers in the reactor protection system are constituted with concurrent logic controllers of different types. Therefore, even if a CCF occurs in either concurrent logic controller, a control signal path is secured by the other concurrent logic controller. FIG. 5 is a representative view of the present invention, illustrating a detailed embodiment in which the digital protection system, the RTSS 240, a motor-generator (MG) set 241, and a control element drive mechanism (CEDM) 242 are associated. The MG set 241 may include a first MG set MG1 and a second MG set MG2. Here, controllers of the same type are shown in a box-bundled manner, to allow paths of the control signals to be clearly identified. According to the present invention, the digital protection system includes a process protection system and a reactor protection system. The process protection system has, in one channel, a first comparative logic controller and a second comparative logic controller. The first and second comparative logic controllers of the present invention are of different (i.e., contrasting) types that are mutually independent from each other, whereby the first and second comparative logic controllers independently receive process variables as inputs and independently output comparison logic results. Meanwhile, the reactor protection system has, in one train, a first concurrent logic controller and a second concurrent logic controller. The first and second concurrent controllers of the present invention are of different (i.e., contrasting) types that are mutually independent from each other, whereby the first and second concurrent controllers independently receive the comparison logic results (from the comparative logic controllers) as inputs and independently output concurrent logic results. The reactor protection system further includes at least two initiation circuits, each of which includes a series circuit in which a plurality of relays are connected in series and a parallel circuit in which a plurality of relays are connected in parallel. One of the series circuit relays is controlled (i.e., turned on/off) by receiving one of the concurrent logic results as an input, and one of the parallel circuit relays is controlled (i.e., turned on/off) by receiving the other of the concurrent logic results as an input. Here, the concurrent logic results are received (by the relays) from the concurrent logic controllers of different types. The channels of the process protection system include the first comparative logic controllers 221-1, 222-1, 223-1, and 224-1 and the second comparative logic controllers 221-2 and 222-2, 223-2, and 224-2 of different types that are mutually independent, respectively, and the first comparative logic controllers 221-1, 222-1, 223-1, and 224-1 and the second comparative logic controllers 221-2, 222-2, 223-2, and 224-2 outputs comparison logic results by receiving the process variables as an input, in which the process protection system has at least two channels. As shown in FIG. 5, the reactor protection system includes at least two channels. The channels may include the first comparative logic controllers 221-1, 222-1, 223-1, and 224-1 and the second comparative logic controllers 221-2, 222-2, 223-2, and 224-2 of different types that are mutually independent, respectively. The first comparative logic controllers 221-1, 222-1, 223-1, and 224-1 may be configured based on an FPGA, and the second comparative logic controllers 221-2, 222-2, 223-2, and 224-2 may be configured based on a programmable logic controller (PLC), in which two comparative logic controllers may be controlled to be mutually independent. The trains of the reactor protection system include the first concurrent logic controllers 231-1 and 232-1 and the second concurrent logic controllers 231-2 and 232-2 of different types that are mutually independent, respectively, and the first concurrent logic controllers 231-1 and 232-1 and the second concurrent logic controllers 231-2 and 232-2 outputs the concurrent logic results by receiving the comparison logic results as an input, in which the reactor protection system has at least two trains. As shown in FIG. 5, the reactor protection system includes at least two trains. The trains include the first concurrent logic controllers 231-1 and 232-1 and second concurrent logic controllers 231-2 and 232-2 of different types that are mutually independent, respectively. The first concurrent logic controllers 231-1 and 232-1 may be configured based on an FPGA, and the second concurrent logic controllers 231-2 and 232-2 may be configured based on a PLC, in which two comparative logic controllers may be controlled to be mutually independent. The digital protection system further includes at least two initiation circuits. Here, the initiation circuits 231-3 and 231-4 included in the first train includes a series circuit 251 in which a plurality of relays 251-1 and 251-2 are connected in series and a parallel circuit in which a plurality of relays 252-1 and 252-2 are connected in parallel, and the initiation circuits 232-3 and 232-4 included in the second train include a series circuit 254 in which a plurality of relays 254-1 and 254-2 are connected in series and a parallel circuit 253 in which a plurality of relays 253-1 and 253-2 are connected in parallel. The plurality of relays 251-1, 251-2, 254-1, and 254-2 included in the series circuits 251 and 254 are turned on/off by receiving the concurrent logic results from concurrent logic controllers of different types as an input, and the plurality of relays 252-1, 252-2, 253-1, and 253-2 included in the parallel circuits 252 and 253 are turned on/off by receiving the concurrent logic results from concurrent logic controllers of different type as an input. More specifically, the relay 251-1 included in the series circuit 251 is turned on/off by receiving a concurrent logic result AF-1 as an input, and the relay 251-2 included in the series circuit 251 is turned on/off by receiving a concurrent logic result AP-1 different from the concurrent logic result AF-1 as an input. The relay 254-1 included in the series circuit 254 is turned on/off by receiving a concurrent logic result BF-1 as an input, and the relay 254-2 included in the series circuit 254 is turned on/off by receiving a concurrent logic result BP-1 different from the concurrent logic result BF-1 as an input. The relay 252-1 included in the parallel circuit 252 is turned on/off by receiving a concurrent logic result AF-2 as an input, and the relay 252-2 included in the parallel circuit 252 is turned on/off by receiving a concurrent logic result AP-2 different from the concurrent logic result AF-2 as an input. The relay 253-1 included in the parallel circuit 253 is turned on/off by receiving a concurrent logic result BF-2 as an input and the relay 253-2 included in the parallel circuit 253 is turned on/off by receiving a concurrent logic result BP-2 different from the concurrent logic result BF-2 as an input. The process protection system is configured to include a first channel, a second channel, a third channel, and a fourth channel. The number of channels is not limited thereto, and may be one or more. The reactor protection system may include a first train (Train A) and a second train (Train B). The process protection system may include the first FPGA-based comparative logic controllers 221-1, 222-1, 223-1, and 224-1 and the second PLC-based comparative logic controllers 221-2, 222-2, 223-2, and 224-2. The comparative logic controllers each transmit the comparison logic results to all concurrent logic controllers of the same type. The reactor protection system includes the first FPGA-based concurrent logic controllers 231-1 and 232-1 and the second PLC-based concurrent logic controllers 231-2 and 232-2 of the same type. The first FPGA-based comparative logic controllers 221-1, 222-1, 223-1, and 224-1 transmit the comparison logic results to the first FPGA-based concurrent logic controllers 231-1 and 232-1 of the same type. The second PLC-based comparative logic controllers 221-2, 222-2, 223-2, and 224-2 transmit the comparison logic results to the second PLC-based concurrent logic controllers 231-2 and 232-2 of the same type. The process variables include at least one of reactor coolant hot tube and cold tube temperature information, pressurizer pressure information, pressurizer water level information, neutron flux information, reactor coolant flow rate information, containment building pressure information, steam generator water level information, steam pipe pressure information, and refueling water tank level information. The sensor described above transmits at least one of information included in the process variables to at least one channel of the process protection system. Each channel receives at least one of information included in the process variable, in which the number and type of process variables received by the first channel, the second channel, the third channel, and the fourth channel may be the same or different. The first concurrent logic controllers 231-1 and 232-1 receives the comparison logic results including normal signal or abnormal signal from the first comparative logic controllers 221-1, 222-1, 223-1, and 224-1 included in each channel of the process protection system, and the concurrent logic results are output based on the number of the comparison logic results and the number of abnormal signals, in which the concurrent logic results includes two different output signals, one output signal being input to one relay AF-1 or BF-1 included in the series circuit and the other output signal being input to one relay AF-2 or BF-2 included in the parallel circuit. The first comparative logic controllers 221-1, 222-1, 223-1, and 224-1 each compare the received process variable with settings to determine whether to output a normal signal or an abnormal signal. The first comparative logic controllers 221-1, 222-1, 223-1, and 224-1 each output as many comparison logic results as the number of process variables received. That is, if the first comparative logic controller 221-1 receives three process variables, it compares the three process variables with the respective settings to output three comparison logic results. The first concurrent logic controllers 231-1 and 232-1 output the concurrent logic results based on the number of comparison logic results of abnormal signals compared with the total number of comparison logic results received. In this case, the first concurrent logic controllers 231-1 and 232-1 perform n/m concurrent logic defined by the total number (m) of comparison logic results and the number (n) of comparison logic results of abnormal signals for each process variable, and output the concurrent logic results that is a reactor shutdown signal when the n/m concurrent logic defined above is satisfied for at least one process variable. Referring to FIG. 5, when the first concurrent logic controllers 231-1 and 232-1 output the concurrent logic results of the reactor shutdown signals, AF-1 is “0,” AF-2 is “1,” BF-1 is “0,” and BF-2 is “1.” The second concurrent logic controller receives the comparison logic results including normal signal or abnormal signal from the second comparative logic controller included in each channel of the process protection system and outputs the concurrent logic results based on the number of the comparison logic results and the number of abnormal signals, in which the concurrent logic results include two different output signals, one output signal being input to the other relay AP-1 or BP-1 included in the series circuit and the other output signal being input to the other relay AP-2 or BP-2. The second comparative logic controllers 221-2, 222-2, 223-2, and 224-2 compare the received process variables with settings to determine whether to output a normal signal or an abnormal signal. The second comparative logic controllers 221-2, 222-2, 223-2, and 224-2 each output as many comparison logic results as the number of received process variables. That is, when the second comparative logic controllers 221-2, 222-2, 223-2, and 224-2 receive three process variables, it compares the three process variables with each setting to output three comparison logic results. The second concurrent logic controllers 231-2 and 232-2 output the concurrent logic results based on the number of comparison logic results of abnormal signals compared with the total number of comparison logic results received. In this case, the second concurrent logic controllers 231-2 and 232-2 perform n/m concurrent logic defined by the total number (m) of comparison logic results and the number (n) of comparison logic results of abnormal signals for each process variable, and output the concurrent logic result that is a reactor shutdown signal when the n/m concurrent logic defined above is satisfied for at least one process variable. Referring to FIG. 5, when the second concurrent logic controllers 231-2 and 232-2 output the concurrent logic results of the reactor shutdown signals, AP-1 is “0,” AP-2 is “1,” BP-1 is “0,” and BP-2 is “1.” The first concurrent logic controllers 231-1 and 232-1 output the concurrent logic results when the comparison logic results include at least one abnormal signal, in which the output signals AF-1 and BF-1 of “0” among the concurrent logic results are input to one relay 251-1 and 254-1 included in each of the series circuits and the output signals AF-2 and BF-2 of “1” are input to one relay 252-1 and 253-1 included in each of the parallel circuits. The concurrent logic result means a reactor shutdown signal. The second concurrent logic controllers 231-2 and 232-2 output the concurrent logic results when the comparison logic result includes at least one abnormal signal, in which the output signals AP-1 and BP-1 of “0” among the concurrent logic results are input to one relay 251-2 and 254-2 included in each of the series circuits and the output signals AP-2 and BP-2 of “1” are input to one relay 252-2 and 253-2 included in each of the parallel circuits. The concurrent logic result means a reactor shutdown signal. The first concurrent logic controllers 231-1 and 232-1 output the concurrent logic results when the comparison logic result includes at least one normal signal, in which the output signals AF-1 and BF-1 of “1” among the concurrent logic results are input to one relay 251-1 and 254-1 included in each of the series circuits and the output signals AF-2 and BF-2 of “0” are input to one relay 252-1 and 253-1 included in each of the parallel circuits. The concurrent logic result means a reactor shutdown signal. The second concurrent logic controllers 231-2 and 232-2 output the concurrent logic results when the comparison logic result includes at least one normal signal, in which the output signals AF-1 and BF-1 of “1” among the concurrent logic results are input to the other relay 251-2, 254-2 included in each of the series circuits and the output signals AP-2 and BP-2 of “0” are input to the other relay 252-2 and 253-2 included in each of the parallel circuits. The concurrent logic result means a reactor shutdown signal. Here, in the case where the comparison logic result includes at least one abnormal signal, the output signals AF-1 and BF-1, which have of a logic value of “0” according to the embodiment, have a first logic value according to the present invention; conversely, the output signals AF-2 and BF-2, which have of a logic value of “1” according to the embodiment, have a second logic value according to the present invention. On the other hand, in the case where the comparison logic result includes at least one normal signal, the output signals AF-1 and BF-1, which have of a logic value of “1” according to the embodiment, have a first logic value according to the present invention; conversely, the output signals AF-2 and BF-2, which have of a logic value of “0” according to the embodiment, have a second logic value according to the present invention. In other words, the first and second logic values are opposite logic values. Also, concurrent logic results being input to a relay included in each of the series circuits, or to a relay included in each of the parallel circuits, means that the concurrent logic results are effectively input to the series circuits or the parallel circuits accordingly. The digital protection system further includes a RTSS 240, and the RTSS 240 is configured with four RTBs. The RTBs may include a first normally-open (NO) contact 243, a second NO contact 244, a third NO contact 245, and a fourth NO contact 246. The MG set 241 supplies driving power for operating a control element drive mechanism (CEDM) 242. In the case of the RTSS 240 of the present invention, the NO contacts 243, 244, 245, and 246 are located between the MG set 241 and the CEDM 242 and thus the power may be supplied to the CEDM 242 or may not be supplied to the CEDM 242 according to switching-on or switching-off of the NO contacts 243, 244, 245, and 246. More specifically, when at least one of the first NO contact or the second NO contact is closed and at least one of the third NO contact or the fourth NO contact is closed, the power is supplied to the CEDM 242. This is because the first NO contact and the second NO contact are connected in parallel to each other and the third NO contact and the fourth NO contact are connected in parallel to each other so that a ladder-shaped circuit may selectively supply the power to the CEDM 242 When both the first NO contact 243 and the second NO contact 244 are open, or both the third NO contact 245 and the fourth NO contact 246 are closed, the MG set 241 is provided to interrupt the power to the CEDM 242. The CEDM 242 may control the position of a control rod to control a nuclear reaction in a reactor. In addition, the CEDM 242 directly grabs the control rod with the power supplied from the MG set 241, to allow the control rod to be released and thus dropped via gravity when the power is interrupted by the RTSS 240. More specifically, the CEDM 242 is provided such that the control rod is dropped to cause the reactor to be shut down when the power supply is not applied, and the position of the control rod is maintained to allow the reactor to be normally operated when the power supply is applied. When the control rod is dropped, the reactor is immediately shut down, whereby it is possible to take a quick action when an abnormal reactor condition is detected. Since the RTSS 240 of the present invention has four RTBs, the RTBs being respectively configured with NO contacts 243, 244, 245, and 246, the protection system may be stably operated in conjunction with series circuits and parallel circuits even when a common failure component occurs. In the case of NO contact, a fixed contact and a movable contact are initially detached from each other, and the fixed contact and the movable contact come into contact with each other to allow current to flow when an external force is applied. In other words, when the force (for example, electromagnetic force) is generated from the outside, the NO contact is connected and thus changed from normally open state to a closed state. In the case of FIG. 5, the NO contacts 243, 244, 245, and 246 may be changed from the open state to the closed state due to an electromagnetic force generated in the coil when a current flows through the series circuit. In the case of a normal closed (NC) contact described above, the fixed contact and the movable contact are initially kept connected to each other, and are disconnected from each other to cause the current not to flow when the external force is applied. In other words, when the force (for example, electromagnetic force) is generated from the outside, the NC contact is disconnected and thus changed from a normally closed state to an open state. In the case of FIG. 5, the NC contact 255-1 of the relay included in the third circuit may be changed from the closed state to the open state due to the electromagnetic force generated in the coil when a current flows through the first parallel circuit. The first NO contact 243 is connected between the MG set 241 and a central node 247. The second NO contact 244 is connected between the MG set 241 and the central node 247. The third NO contact 245 is connected between the central node 247 and the CEDM 242. The fourth NO contact 246 is connected between the central node 247 and the CEDM 242. The digital protection system according to an embodiment of the present invention is provided such that the RTSS 240 receiving the operation result of each train of the reactor protection system is configured in a “ladder” shape, in order to protect the unique safety functions of the protection system and to apply a design of minimizing unnecessary reactor shutdown. Further, the RTSS 240 of the present invention may include a first series circuit 251, a first parallel circuit 252, a second parallel circuit 253, and a second series circuit 254. The series circuits 251 and 254 or the parallel circuits 252 and 253 may control such that the power may be to be supplied to the CEDM 242 by allowing the NO contacts 243, 244, 245, and 246 to be closed/open. The first parallel circuit and the second parallel circuit may indirectly control the NO contacts 244 and 245, respectively. As will be described later, the first parallel circuit controls the contact 255-1 of the relay included in the third circuit, in which the third circuit directly controls to open/close the second NO contact. The second parallel circuit controls the contact 256-1 of the relay included in the fourth circuit, in which the fourth circuit directly controls to open/close the third NO contact. To this end, the output signal from the concurrent logic controller includes the series circuit control signals AF-1, AP-1, BF-1, and BP-1 and the parallel circuit control signals AF-2, AP-2, BF-2, and BP-2, and the first concurrent logic controllers 231-1 and 232-1 or the second concurrent logic controllers 232-1 and 232-2 generates the series circuit control signals AF-1, AP-1, BF 1, and BP-1 and the parallel circuit control signals AF-2, AP-2, BF-2, and BP-2. For example, the output signal from the concurrent logic controller controls such that the series circuits 251 and 254 are turned on/off, and the NO contacts 243 and 246 connected to the series circuits 251 and 254 are repeatedly connected and disconnected according to on/off of the series circuits 251 and 254. The initiation circuit includes a first series circuit for controlling closing/opening of the first NO contact according to an output signal from the concurrent logic controller; a first parallel circuit controlling close/open of the second NO contact according to an output signal from the concurrent logic controller; a second parallel circuit for controlling closing/opening of the third NO contact according to an output signal from the concurrent logic controller; and a second series circuit for controlling closing/opening of the fourth NO contact according to an output signal from the concurrent logic controller. The first series circuit 251 may control closing/opening of the first NO contact 243 according to an output signal from the concurrent logic controller. The first parallel circuit 252 may control closing/opening of the second NO contact 244 according to the output signal from the concurrent logic controller. In detail, the first parallel circuit 252 may control closing/opening of the second NO contact 244 via the third circuit 255 according to the output signal from the concurrent logic controller. The second parallel circuit 253 may control closing/opening of the third NO contact 245 according to the output signal from the concurrent logic controller. In detail, the second parallel circuit 252 may control closing/opening of the third NO contact 245 via the fourth circuit 256 according to the output signal from the concurrent logic controller. The second series circuit 254 may control closing/opening of the fourth NO contact 246 according to the output signal from the concurrent logic controller. The first series circuit 251 and the first parallel circuit 252 receive the output signals AF-1, AF-2, AP-1, and AP-2 from the first concurrent logic controller 231-1 and the second concurrent logic controller 231-2 included in any one train. The second series circuit 253 and the first parallel circuit 254 receive the output signals BF-1, BF-2, BP-1, and BP-2 from the first concurrent logic controller 232-1 and the second concurrent logic controller 232-2 included in the other train. The initiation circuit includes a third circuit 255 including a relay 255-1 and controlling closing/opening of the second NO contact 244 according to on/off of the relay 255-1; and a fourth circuit 256 including a relay 256-1 and controlling closing/opening of the third NO contact 245 according to on/off of the relay 256-1, in which the first parallel circuit 252 controls on/off of the relay 255-1 included in the third circuit 255, and the second parallel circuit 253 controls on/off of the relay 256-1 included in the fourth circuit 256. The relays 255-1 and 256-1 that are included in the third circuit 255 and the fourth circuit 256 are NC contacts. Here, the first series circuit 251, the first parallel circuit 252, the second parallel circuit 253, and the second series circuit 254 all receive control signals from the concurrent logic controllers of different types. Since the series circuits or the parallel circuits constituting the initiation circuit of the present invention all receive the control signals from the concurrent logic controllers of different types, it is possible to secure reactor safety even though any one concurrent logic controller stops operating. More specifically, the first series circuit 251 or the second series circuit 254 includes two relays connected in series, and the relay is turned on/off according to the output signal from the concurrent logic controller, in which the first NO contact 243 or the fourth NO contact 246 is turned on when all the relays are on, and the first NO contact 243 or the fourth NO contact 246 is turned off when at least one of the relays is off. Considering the first series circuit 251 on features described above, the first series circuit 251 includes two relays 251-1 and 251-2 connected in series, in which the relays 251-1 and 251-2 are turned on/off by the output signal from the concurrent logic controller, the first NO contact 243 is turned on when all the relays 251-1 and 251-2 are on, and the first NO contact 243 is turned off when at least one of relays 251-1 and 251-2 is off. Considering the second series circuit 254 on the feature described above, the second series circuit 254 includes two relays 254-1 and 254-2 connected in series, in which the relays 254-1 and 254-2 are turned on/off by the output signal from the concurrent logic controller, the fourth NO contact 246 is turned on when all the relays 254-1 and 254-2 are on, and the fourth NO contact 246 is turned off when at least one of relays 254-1 and 254-2 are off. The relays in the series circuit are provided to receive the output signals from the different concurrent logic controllers. For example, when receiving a switch-on signal from the FPGA-based concurrent logic controller and the PLC-based concurrent logic controller, the first series circuit 251 turns on both relays, thereby causing the first contact 243 to be closed. On the contrary, due to characteristics of the series circuit, when the output signal from at least one of the FPGA-based concurrent logic controller or the PLC-based concurrent logic controller is switched off, the series circuit is turned off to cause the first NO contact 243 to be open. More specifically, the first parallel circuit 252 or the second parallel circuit 253 includes two relays connected in parallel, in which the relays are turned on/off by the output signals from the concurrent logic controllers, the relay included in the third circuit 255 or the fourth circuit 256 is turned on when all the relays are turned off, and the relay included in the third circuit 255 or the fourth circuit 256 is turned off when at least one of the relays is on. Considering the first parallel circuit 252 on the features described above, the first parallel circuit 252 includes two relays 252-1 and 252-2 connected in parallel, in which the relays 252-1 and 252-2 are turned on/off by the output signals from the concurrent logic controllers, the relay 255-1 included in the third NO circuit 255 is turned on when all the relays 252-1 and 252-2 are off, and the relay 255-1 included in the third circuit 255 is turned off when at least one of relays 252-1 and 252-2 is on. Considering the second parallel circuit 253 on the feature described above, the second parallel circuit 253 includes two relays 253-1 and 253-2 connected in series, in which the relays 253-1 and 253-2 are turned on/off by the output signals from the concurrent logic controllers, the relay 256-1 included in the fourth circuit 256 is turned on when all the relays 253-1 and 253-2 are off, and the relay 256-1 included in the fourth circuit 256 is turned off when at least one of relays 253-1 and 253-2 is on. As a result, when the relays included in the first parallel circuit 252 are all off, the relay included in the third circuit 255 is turned on to allow the second NO contact 244 to be closed. In addition, when the relays included in the second parallel circuit 253 are all off, the relay in the fourth circuit 256 is turned on to allow the third NO contact 245 to be closed. When at least one of the relays included in the first parallel circuit 252 is on, the relay included in the third circuit 255 is turned off to allow the second NO contact 244 to be open. In addition, when at least one of the relays included in the second parallel circuit 253 is on, the relay included in the fourth circuit 256 is turned off to allow the third NO contact 245 to be open. Here, the relays included in the third circuit 255 and the fourth circuit 256 are the NC contacts 255-1 and 256-1, respectively. The relays included in the parallel circuit are provided to receive control signals from the different concurrent logic controllers. For example, when the control signal (switched off) is received from the FPGA-based concurrent logic controller and the control signal (switched off) is received from the PLC-based concurrent logic controller, the first parallel circuit 252 turns off both relays, thereby allowing the second NO contact 244 to be open. On the contrary, due to characteristic of the parallel circuit, when at least one of the FPGA-based concurrent logic controller or PLC-based concurrent logic controller is switched on, the parallel circuit is closed to allow the second NO contact 244 to be open. Therefore, the digital protection system of the present invention is configured such that the power is supplied in the order of the MG set 241, the RTSS 240, and the CEDM 242, and the CEDM 242 drops the control rod to cause the reactor to be shut down when the power is not supplied to the CEDM 242 according to close/open state of the contacts in the RTSS 240. FIGS. 6A to 6N are views illustrating various embodiments in which the digital protection system of the present invention is provided to control a normal reactor operation or a reactor shutdown according to various failure types. Each configuration in FIGS. 6A to 6N is the same as that in FIG. 5. FIG. 6A illustrates operations of the initiation circuit of the present invention in the case of the power plant under a normal condition and a safety system under a normal condition. When the nuclear power plant is normal and the safety system is normal, the first NO contact 243 to the fourth NO contact 246 included in the initiation circuit of the present invention are all kept closed and the power is supplied to the CEDM 242. Therefore, the CEDM 242 does not drop the control rod to allow the reactor to be normally operated. FIG. 6B illustrates operations of the inventive initiation circuit in the case of the power plant under an abnormal condition and the safety system under a normal condition. When the nuclear power plant is abnormal and the safety system is normal, the first NO contact 243 to the fourth NO contact 246 included in the initiation circuit of the present invention are all kept open, and the power is not supplied to the CEDM 242. Therefore, the CEDM 242 drops the control rod to cause the reactor to be shut down. FIG. 6C illustrates operations of the initiation circuit of the present invention in the case of the power plant under a normal condition and the safety system under an abnormal condition. Although the nuclear power plant is normal, the PLC-based concurrent logic controller of the safety system may have the AP-2 signal and the BP-2 signal detected as an abnormal signal (switched on), rather than an original signal (switched off). Here, any one of two relays in the first parallel circuit and the second parallel circuit is turned on, so that the relays in the third series circuit and the fourth series circuit are turned off and the second NO contact and the third NO contact are kept open. However, since the first NO contact 243 and the fourth NO contact 246 controlled by the first series circuit and the second series circuit are still kept closed, the power is normally supplied to the CEDM 242 via the first NO contact 243 and the fourth NO contact 246, thereby allowing the reactor to be normally operated. FIG. 6D illustrates operations of the initiation circuit of the present invention in the case of the power plant under an abnormal condition and the safety system under a normal condition. It corresponds to the worst case where the nuclear power plant is abnormal and the safety system is also abnormal. In this case, since the nuclear power plant abnormally operates, the safety system must immediately drop the control rod to cause the reactor to be shut down. However, the safety system may not be able to drop the control rod properly due to a problem occurring in the safety system. However, the protective system of the present invention can solve this problem. For example, the PLC-based concurrent logic controller of the safety system may have the AP-1 signal and the BP-1 signal detected as an abnormal signal (switched on), rather than an original signal (switched off). At this time, since any one of two relays in the first series circuit 251 and the fourth circuit 256 is off, the first NO contact and the fourth NO contact 246 are kept open. Since two relays included in the first parallel circuit 252 and the second parallel circuit 253 are all on, the relay included in the third circuit 255 and the fourth circuit 256 are turned off. Therefore, since the first NO contact 243, the second NO contact 244, the third NO contact 245, and the fourth NO contact 246 are all kept open, the power is not supplied to the CEDM 242 to cause the control rod to be dropped and thus the reactor to be shut down. FIG. 6E illustrates operations of the initiation circuit of the present invention in the case of the power plant under a normal condition and the safety system under an abnormal condition. The AP-1 signal and the BP-1 signal in the PLC-based concurrent logic controller of the safety system may be detected as an abnormal signal (switched off), rather than an original signal (switched on). Here, since any one of the relays in the first series circuit 251 and the fourth circuit 256 is off, the first NO contact 243 and the fourth NO contact 246 are kept open. However, the relays in the third circuit 255 and the fourth circuit 256 controlled by the first parallel circuit 252 and the second parallel circuit 253 are kept on, whereby the second NO contact 244 and the third NO contact 245 are kept on. As a result, the power may be normally supplied to the CEDM 242 via the second NO contact 244 and the third contact 245. FIG. 6F illustrates operations of the initiation circuit of the present invention in the case of the power plant under an abnormal condition and the safety system under an abnormal condition. It corresponds to the worst case where the nuclear power plant is abnormal and the safety system is also abnormal. In this case, since the nuclear power plant is abnormal, the safety system should immediately drop the control rod, but the control rod may not be properly dropped due to a problem occurring in the safety system. However, the protective system of the present invention can solve this problem. For example, the PLC-based concurrent logic controller of the safety system may have the AP-2 signal and the BP-2 signal detected as an abnormal signal (switched off), rather than an original signal (switched on). Then, any one of two relays included in each of the first parallel circuit 252 and the second parallel circuit 253 is turned on, whereby the relays included in the third circuit 255 and the fourth circuit 256 are turned off. Therefore, since the first NO contact 243, the second NO contact 244, the third NO contact 245, and the fourth NO contact 246 are all kept open, the power is not supplied to the CEDM 242 to cause the control rod to be dropped and thus the reactor to be shut down. FIG. 6G illustrates operations of the initiation circuit of the present invention when a first in-cabinet power supply PW1 included in the first series circuit 251 is abnormal in the case of the power plant under a normal condition and the safety system under a normal condition. The relays included in the first series circuit 251 are all on, but no current is supplied from the first in-cabinet power supply PW1, whereby the first NO contact 243 is open. The relays included in the first parallel circuit 252 are all turned off, and thus relay included in the third circuit 255 is turned on. Therefore, the second NO contact 244 is closed. The relays included in the second parallel circuit 253 are all turned off, and thus the relay included in the fourth circuit 256 is turned on. Therefore, the third NO contact 245 is closed. The relays included in the second series circuit 254 are all turned on, and thus the fourth NO contact 246 is closed. The power may be normally supplied to the CEDM 242 via the second NO contact 244 and the third NO contact 245 or the fourth NO contact 246, thereby allowing the rector to be normally operated. FIG. 6H illustrates operations of the initiation circuit of the present invention when the first in-cabinet power supply PW1 included in the first series circuit 251 is abnormal in the case of the power plant under an abnormal condition and the safety system under a normal condition. The relays included in the first series circuit 251 are all off and no current is supplied from the first in-cabinet power supply PW1, whereby the first NO contact 243 is open. The relays included in the first parallel circuit 252 are all turned on and the relay included in the third circuit 255 is turned off. Therefore, the second NO contact 244 is open. The relays included in the second parallel circuit 253 are all turned on and the relay included in the fourth circuit 256 is turned off. Therefore, the third NO contact 245 is open. The relays included in the second series circuit 254 are all turned off, whereby the fourth NO contact 246 is open. The power is not supplied to the CEDM 242 and the control rod is dropped, thereby causing the reactor to be shut down. FIG. 6I illustrates operations of the initiation circuit of the present invention when the in-cabinet power supplies PW2 included in the first parallel circuit 252 and the third circuit 255 are all abnormal in the case of a the power plant under a normal condition and the safety system under a normal condition. The relays included in the first series circuit 251 are all turned on and thus the first NO contact 243 is closed. The relays included in the first parallel circuit 252 are all turned off, and thus the relay included in the third circuit 255 is turned on. However, since no current is supplied from a second in-cabinet power supply PW2, the second NO contact 244 is open. The relays included in the second parallel circuit 253 are all turned off and thus the relays included in the fourth circuit 256 are turned on. Therefore, the third NO contact 245 is closed. The relays included in the second series circuit 254 are all turned on and thus the fourth NO contact 246 is closed. The power may be normally supplied from the MG set 241 to the CEDM 242 via the first NO contact 243 and the third NO contact 245 or the fourth NO contact 246, thereby allowing the reactor to be normally operated. FIG. 6J illustrates operations of the initiation circuit of the present invention when the second in-cabinet power supply PW2 included in the first parallel circuit 252 and the third circuit 255 are abnormal in the case of the power plant under an abnormal condition and the safety system under a normal condition. The relays included in the first series circuit 251 are all off, and thus the first NO contact 243 is open. The relays included in the first parallel circuit 252 are all turned on, but no current is supplied from the second in-cabinet power supply PW2, whereby the relay included in the third circuit 255 is turned on. However, there is also no current supplied from the second in-cabinet power supply PW2 included in the third circuit 255, and thus the second NO contact 244 is open. The relays included in the second parallel circuit 253 are all turned on and thus the relay included in the fourth circuit 256 is turned off, whereby the third NO contact 245 is open. The relays included in the second series circuit 254 are all turned off and thus the fourth NO contact 246 is open. The power is not supplied to the CEDM 242, thereby causing the control rod to be dropped and the reactor to be shut down. FIG. 6K illustrates operations of the initiation circuit of the present invention when the first in-cabinet power supply PW1 included in the first series circuit 251 and the second in-cabinet power supplies PW2 included in the first parallel circuit 252 and the third circuit 255 are all abnormal in the case of the power plant under a normal condition and the safety system under a normal condition. The relays included in the first series circuit 251 are all on, but no current is supplied from the first in-cabinet power supply PW1, whereby the first NO contact 243 is open. The relays included in the first parallel circuit 252 are all turned off, and the relay included in the third circuit 255 is turned on. However, no current is supplied from the second in-cabinet power supply PW2 and thus the second NO contact 244 is open. The relays included in the second parallel circuit 253 are all turned off and thus the relay included in the fourth circuit 256 is turned on, whereby the third NO contact 245 is closed. The relays included in the second series circuit 254 are all turned on and thus the fourth NO contact 246 is closed. The power is not supplied to the CEDM 242, thereby causing the control rod to be dropped and the reactor to be shut down. FIG. 6I illustrates operations of the initiation circuit of the present invention when the first in-cabinet power supply PW1 included in the first series circuit 251 and the second in-cabinet power supplies PW2 included in the first parallel circuit 252 and the third circuit 255 are all abnormal in the case of the power plant under an abnormal condition and the safety system under a normal condition. The relays included in the first series circuit 251 are all off and the power is not supplied from the first in-cabinet power supply PW1, whereby the first NO contact 243 is open. The relays included in the first parallel circuit 252 are all turned on, but no current is supplied from the in-cabinet power supply PW2, whereby the relay included in the third circuit 255 is turned on. However, there is also no current supplied from the second in-cabinet power supply PW2 included in the third circuit 255, and thus the second NO contact 244 is open. The relays included in the second parallel circuit 253 are all turned on and the relay included in the fourth circuit 256 is turned off, whereby the third NO contact 245 is open. The relays included in the second series circuit 254 are all turned off, and thus the fourth NO contact 246 is open. The power is not supplied to the CEDM 242, thereby causing the control rod to be dropped and the reactor to be shut down. FIG. 6M illustrates operations of the initiation circuit of the present invention when the first in-cabinet power supply PW1 included in the first series circuit 251, the second in-cabinet power supplies PW2 included in the first parallel circuit 252 and the third circuit 255, the in-cabinet power supply PW3 included in the second series circuit 254, and the fourth in-cabinet power supplies PW4 included in the second parallel circuit 253 and the fourth circuit 256 are all abnormal in the case of the power plant under a normal condition and the safety system under a normal condition. The relays included in the first series circuit 251 are all on, but no current is supplied from the first in-cabinet power supply PW1, whereby the first NO contact 243 is open. The relays included in the first parallel circuit 252 are all turned off and thus the relay included in the third circuit 255 is turned on. However, no current is supplied from the second in-cabinet power supply PW2, and thus the second NO contact 244 is open. The relays included in the second parallel circuit 253 are all turned off, and the relay included in the fourth circuit 256 is turned on. However, since no current is supplied from a third in-cabinet power supply PW3, the third NO contact 245 is open. The relays included in the second series circuit 254 are all turned on, but no current is supplied from the fourth in-cabinet power supply PW4, whereby the fourth NO contact 246 is open. The power is not supplied to the CEDM 242, thereby causing the control rod to be dropped and the reactor to be shut down. FIG. 6N illustrates operations of the initiation circuit of the present invention when the first in-cabinet power supply PW1 included in the first series circuit 251, the second in-cabinet power supplies PW2 included in the first parallel circuit 252 and the third circuit 255, the third in-cabinet power supply PW3 included in the second series circuit 254, and the fourth in-cabinet power supplies PW4 included in the second parallel circuit 253 and the fourth circuit 256 are all abnormal in the case of the power plant under a normal condition and the safety system under a normal condition. The relays in the series circuit 251 are all off and no current is supplied from the first in-cabinet power supply PW1, whereby the first NO contact 243 is open. The relays are all turned on and no current is supplied from the second in-cabinet power supply PW2 in the first parallel circuit 252, whereby the relay included in the third circuit 255 is turned on. However, there is also no current supplied from the second in-cabinet power supply PW2 included in the third circuit 255, thereby causing the second NO contact 244 to be open. The relays in the second parallel circuit 253 are all turned on and no current is supplied from the third in-cabinet power supply PW3, whereby the relay included in the fourth circuit 256 is turned on. The third NO contact 245 is therefore open. The relays in the second series circuit 254 are all off and no current is supplied from a fourth in-cabinet power supply PW4, whereby the first NO contact 243 is open. The power is not supplied to the CEDM 242, thereby causing the control rod to be dropped and the reactor to be shut down. Referring to FIG. 6A to FIG. 6N, in an emergency where a control rod drop signal must be generated, even though a failure occurs in any one relay or contact of the safety system, the digital protection system of the present invention may control the CEDM by allowing the remaining relays and contacts to be compensated with each other, whereby the safety system of the nuclear power plant may be normally operated even in a situation of a SPV or a CCF, and therefore a normal reactor operation or reactor shutdown may be processed. The embodiments of the present invention described above are disclosed for the purpose of illustration, and the present invention is not limited thereto. Further, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention and such modifications and alterations are considered to be within the scope of the present invention.
	abstract	An improved retention and alignment system for nuclear fuel rods includes an upper nozzle plate and a lower nozzle plate, nuclear fuel rods, each having an upper end and a lower end and extending axially between the upper and lower nozzle plates, a first precision magnet incorporated onto the lower end of the fuel rod, and a plurality of second precision magnets incorporated onto the lower nozzle plate in positions confronting the first precision magnets on the fuel rods. Each first precision magnet has at least one of a magnetic north or south polarity and the second precision magnet has at least one of a magnetic south or north polarity opposite the polarity of the confronting first precision magnet to effect magnetic attraction between the confronting first and second precision magnets. Grids between the upper and lower nozzle plates form cells through which the fuel rods pass. Precision magnets of the same polarity may be positioned laterally along the fuel rods and grid walls in positions confronting each other to repel the fuel rods from the grid walls to maintain fuel rod alignment and prevent contact between the fuel rods and the grids.
060884193	claims	1. A corrosion resistant nuclear fuel element for a boiling water nuclear reactor comprising: an elongated hollow metallic tubular cladding for containing a nuclear fuel, the tubular cladding comprising an outer tubular layer having an outer wall and an inner wall and an inner portion disposed between the outer wall and the inner wall, the outer tubular layer formed from a metal selected from the group consisting of zirconium and a zirconium alloy having integrally incorporated a predetermined concentration of oxygen, said predetermined concentration of oxygen being a decreasing oxygen concentration gradient from the outer wall extending into the inner portion, so that when subject to corrosion zirconium hydrides preferentially precipitate in the inner portion and are inhibited from forming on the outer wall; a body of nuclear fuel material disposed in the tubular cladding; sealing means at both ends of the tubular cladding; and wherein the outer tubular layer is formed from Zircaloy 2. a body of nuclear fuel material disposed in the tubular cladding; sealing means at both ends of the tubular cladding; wherein the decreasing oxygen concentration gradient from the outer wall extending into the inner portion decreases from at least about 1600 ppm to less than about 1200 ppm; and wherein the outer tubular layer is formed from Zircaloy 2. a body of nuclear fuel material disposed in the tubular cladding; sealing means at both ends of the tubular cladding; and wherein the outer tubular layer is formed from Zircaloy 4. a body of nuclear fuel material disposed in the tubular cladding; sealing means at both ends of the tubular cladding; wherein the decreasing oxygen concentration gradient from the outer wall extending into the inner portion decreases from at least about 1600 ppm to less than about 1200 ppm; and wherein the outer tubular layer is formed from Zircaloy 4. an elongated hollow metallic tubular cladding for containing a nuclear fuel, the tubular cladding comprising: an outer tubular layer having an outer wall and an inner wall and an inner portion disposed between the outer wall and the inner wall, the outer tubular layer formed from a metal selected from the group consisting of zirconium and a zirconium alloy, the outer tubular layer having integrally incorporated a first predetermined concentration of oxygen; an inner tubular layer bonded to the inner wall of the outer tubular layer and formed from a metal comprising a zirconium alloy, the inner tubular layer having integrally incorporated a second predetermined concentration of oxygen, said second predetermined concentration of oxygen being less than said first predetermined concentration of oxygen so that when subject to corrosion, zirconium hydrides preferentially precipitate in the inner tubular layer and are inhibited from forming in the outer layer; a body of nuclear fuel material disposed in the tubular cladding; sealing means at both ends of the tubular cladding for hermetically sealing the metallic tubular cladding; wherein the tubular cladding further includes an innermost layer bonded to an inner wall of the inner layer; the innermost layer formed from a metal selected from the group consisting of zirconium and a zirconium alloy and having integrally incorporated a third predetermined concentration of oxygen; and wherein said first predetermined concentration of oxygen is at least about 1600 ppm and said third predetermined concentration of oxygen is at least about 1600 ppm. wherein the tubular cladding further includes an inner layer bonded to the inner wall of the outer layer; and wherein the inner layer is a metal comprising a zirconium alloy. 2. A corrosion resistant nuclear fuel element for a boiling water nuclear reactor comprising an elongated hollow metallic tubular cladding for containing a nuclear fuel, the tubular cladding comprising an outer tubular layer having an outer wall and an inner wall and an inner portion disposed between the outer wall and the inner wall, the outer tubular layer formed from a metal selected from the group consisting of zirconium and a zirconium alloy having integrally incorporated a predetermined concentration of oxygen, said predetermined concentration of oxygen being a decreasing oxygen concentration gradient from the outer wall extending into the inner portion, so that when subject to corrosion zirconium hydrides preferentially precipitate in the inner portion and are inhibited from forming on the outer wall; 3. A corrosion resistant nuclear fuel element for a boiling water nuclear reactor comprising an elongated hollow metallic tubular cladding for containing a nuclear fuel, the tubular cladding comprising an outer tubular layer having an outer wall and an inner wall and an inner portion disposed between the outer wall and the inner wall, the outer tubular layer formed from a metal selected from the group consisting of zirconium and a zirconium alloy having integrally incorporated a predetermined concentration of oxygen, said predetermined concentration of oxygen being a decreasing oxygen concentration gradient from the outer wall extending into the inner portion, so that when subject to corrosion zirconium hydrides preferentially precipitate in the inner portion and are inhibited from forming on the outer wall; 4. A corrosion resistant nuclear fuel element for a boiling water nuclear reactor comprising an elongated hollow metallic tubular cladding for containing a nuclear fuel, the tubular cladding comprising an outer tubular layer having an outer wall and an inner wall and an inner portion disposed between the outer wall and the inner wall, the outer tubular layer formed from a metal selected from the group consisting of zirconium and a zirconium alloy having integrally incorporated a predetermined concentration of oxygen, said predetermined concentration of oxygen being a decreasing oxygen concentration gradient from the outer wall extending into the inner portion, so that when subject to corrosion zirconium hydrides preferentially precipitate in the inner portion and are inhibited from forming on the outer wall; 5. A corrosion resistant nuclear fuel element for a boiling water nuclear reactor comprising; 6. The corrosion resistant nuclear fuel element as in claim 5 wherein said second predetermined concentration of oxygen is less than about 1200 ppm. 7. A corrosion resistant cladding tube for nuclear fuel for a boiling water nuclear reactor comprising an elongated hollow metallic tubular cladding for containing a nuclear fuel, the tubular cladding comprising an outer tubular layer having an outer wall and an inner wall and an inner portion disposed between the outer wall and the inner wall, the outer tubular layer formed from a metal selected from the group consisting of zirconium and a zirconium alloy having integrally incorporated a predetermined concentration of oxygen, said predetermined concentration of oxygen being a decreasing oxygen concentration gradient from the outer wall extending into the inner portion, so that when subject to corrosion zirconium hydrides preferentially precipitate in the inner portion and are inhibited from forming on the outer wall;
	claims	1. A substrate holder assembly for holding substrates to be exposed to an ion beam during implantation in an ion implanter, the substrate holder assembly comprising:a base rotatable about a first axis of rotation;at least two support arms extending substantially in parallel with said first axis of rotation from the base to ends provided with substrate holders;wherein rotation of the base allows the substrate holders to adopt designated positions, with the at least two support arms extending from points on the base displaced from the first axis of rotation by substantially equal distances and separated by a substantially equal separation angle such that rotation of the base through the separation angle causes the support arms to move between designated positions. 2. The substrate holder assembly of claim 1, wherein the at least two support arms are rotatable about their longitudinal axes. 3. The substrate holder assembly of claim 1, wherein the substrate holders are each provided with a support surface for supporting the substrate, the support surface being rotatable about its centre axis. 4. The substrate holder assembly of claim 3, wherein the support surface's centre axis is substantially normal to the support arm's longitudinal axis. 5. The substrate holder assembly of claim 1, wherein the at least two support arms are moveable along their longitudinal axes such that the distance of each substrate holder from the base may be varied. 6. An ion implanter comprising an ion source, optics operable to guide ions produced by the ion source along an ion beam path to a process chamber for implantation in a substrate, a substrate transfer mechanism, and the substrate holder assembly of claim 1 positioned to hold substrates in the process chamber such that the at least two support arms extend substantially normal to the ion beam path; and wherein a first of the designated positions corresponds to the substrate holder being disposed to face into the ion beam, and a second of the designated positions corresponds to the substrate holder being disposed to be clear of the ion beam path and to co-operate with the substrate transfer mechanism thereby allowing substrates to be placed on and removed from the substrate holder. 7. The ion implanter of claim 6, wherein the at least two support arms are rotatable about their longitudinal axes. 8. The ion implanter of claim 6, wherein the substrate holders are each provided with a support surface for supporting the substrate, the support surface being rotatable about its centre axis. 9. The ion implanter of claim 8, wherein the support surface's centre axis is substantially normal to the support arm's longitudinal axis. 10. The ion implanter of claim 6, wherein the at least two support arms are moveable along their longitudinal axes such that the distance of each substrate holder from the base may be varied. 11. The ion implanter of claim 10, wherein the base has an associated scanning unit that is operable to scan the support arm back and forth along its longitudinal axis. 12. The ion implanter of claim 11, wherein the scanning unit is operable to scan the support arm in a direction substantially normal to both the longitudinal axis of the support arm and the ion beam path. 13. The ion implanter of claim 12, wherein the scanning unit is operable to scan the support arm such that the ion beam traces a raster pattern across a substrate when held by the substrate holder.
	summary
	summary
052025667	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A typical computer is shown at 10 with its video display terminal (VDT) indicated at 12. In front of the VDT is the protective hood 14 of the present invention. The hood comprises a frame 16, which in the preferred embodiment is the hood enclosure 18 itself, although were the invention limited to protection from emitted radiation only without the glare-reduction function, the hood could be abbreviated greatly, leaving only the frame structure necessary to support the reflectors as described below, and as suggested by FIGS. 4 and 8. The enclosure 18 defines a pair of sidewalls 20 which are parallel and spaced adequately to fit alongside the left and right edges of the VDT, as shown in FIG. 2. The sidewalls of the VDT are held in place by means of a first reflector 21, which has an aluminum tray 22, which is pivotally mounted by its flanges at 26 by a bolt and nut combination 28 and 30 which permits rotation, but which can be locked at any particular position by tightening the bolts. The second reflector 32 is also pivotally adjustable with the same bolt-and-nut combination 28 and 30. The pivotal reflectors are adequate supported to hold the two sidewalls together. The hood is held to the VDT by means of a bail 36, which has inwardly-directed ends 38 which engage in any pair of bail holes 40 bored into the sidewalls of the hood as shown in FIGS. 1 and 5. The crossbar portion of the bail seats in a selected one of the three grooves 42 in the attachment or mounting block 44, which is securely held on to the top of the VDT by means of a double-sided adhesive coated foam slab 46. The action of the reflectors is as follows. Both reflectors are rotated into adjusted position such that the viewer sees the image approximately as indicated in FIG. 8. The aluminum tray 22 of the reflector 21 is also grounded AS INDICATED AT 48 to the VDT ground to short-circuit the electrical components of the EMF and help eliminate static. The tray also has a ferromagnetic screen 23 bonded to its upper surface, which is intended to shield the operator from the magnetic field component of the EMF from the VDT. On top of the ferromagnetic screen is a layer of lead foil 50, which will absorb most of the X-rays, reflecting some of them. On top of the foil shield is a reflective surface 24, which could be a chromed, polished glass surface or any other kind of highly reflective surface, which will pass most EMF and X-rays, and absorb some UV and reflect some. It is not critical that the first reflector 21 absorb all or most of the harmful radiation, as long as it doesn't transmit it. All radiation reflected from the first reflector is reflected to the second reflector 32, which is where the remaining separation occurs. The second reflector, unlike the first reflector 21, comprises a sheet of plastic such as polycarbonate or allyldiglycol carbonate, marketed as an eyeglass lens material under the trademark CR-39.TM., with a highly polished reflective surface darkened with an organic (non-metallic) dye such as black azo dye. The preferred embodiment is treated with a black azo dye to a very dark density so that 95% to 97% of visible light which passes across the surface into the material is absorbed, but visible light reflection is maximized. The surface of the second reflector reflects visible light in the range of 400-700 nanometers in wavelength, but passes through all other wavelengths, so that all high-frequency radiation such as UV and X-rays harmlessly pass through this reflector to be dissipated in the environment, away from the operator. This action is best shown in FIG. 8. In this figure, rays indicated at a are emitted from the VDT and impinge on the first reflector 21. At 21, the EMF is largely absorbed, and the UV and X-rays partially absorbed. Non-absorbed radiation, including substantially all of the visible spectrum, is reflected as rays b to the second reflector 32. At the second reflector, high-frequency, harmful radiation is passed through as rays d, and the visible image is reflected to the viewer, as indicated at c. As seen in both FIGS. 3 and 8, the harmful radiation from the VDT screen is intercepted by the reflector combination so that the worker's body is in the shadow of the reflectors and thus shielded. These figures show an exaggerated posture in which the operator appears to be looking up, but the reflectors would ordinarily be arranged so that the operator is looking straight ahead and assumes the same posture, looking straight ahead or somewhat downward as he or she would were the enclosure not there. It will be noted that the bail 36 is multiply adjustable in the grooves 42, and the first and second reflectors both pivot. In any event, the VDT has a general longitudinal or axial axis and the reflectors do not deflect the VDT image left or right of that axis, but only upwardly and rearwardly in a vertical plane by the first reflector, and forwardly in the same basic vertical plane, which is parallel to the longitudinal axis of the VDT, with the second reflector. The ray diagram of FIGS. 4 and 8 are diagrammatic only, but with the multiple adjustability of the unit, which has been tried on the job, for any known type of computer VDT, the reflector and the hood itself can be adjusted properly so that full screen viewing is possible without any substantial gaps which could pass radiation to the body. The eyes and body do not actually face the VDT directly. It should be noted that the upper and lower reflectors could be reversed in function, with the upper reflector receiving the light first and reflecting it to the lower reflector, but this arrangement tends to protect the eyes only, and is geometrically awkward, so that the illustrated embodiment works better. The hood 14, in addition to having the sidewalls 20 and the reflectors, is intended to virtually eliminate all glare by excluding ambient light from the screen of the VDT. This is accomplished in the preferred embodiment by means of a top wall 52 which slides forward and rearwardly in channels 54, and a rear wall 56 which slides up and down in rear wall channels 58. The rear wall is preferably provided with a plurality of adjustment slots 60 which seat the rear edge of the top wall 52 as shown in FIG. 5, so that the rear wall is adjustable to accommodate the positioning of the hood on any particular VDT. The combination of the top wall and rear wall, together with the sidewalls and the first reflector 24 effectively eliminate most ambient light from the VDT screen. All of the wall members are black and dull-finished to eliminate internal reflection. As described above, the first, lower reflector is made of a normal silvered glass or plastic pane and will partially transmit and partially reflect harmful radiation. The upper reflector, being made of highly polished polycarbonate or CR-39 tinted to a density of 92-97 percent with an organic pigment such as black azo dye, reflects only visible light. Although the bulk of glare and extraneous light is eliminated by the dark hood, there are other factors that must be considered when protecting the operator from glare-induced eye strain. First, not all of the glare is eliminated by the hood. Also, often there is light that could be coming from an angle (such as the light from ceiling fixtures) which tends to interfere with vision. This light causes the pupils to constant contract, straining the eyes. To counter this, a pair of eyeglasses 62 with lenses 64 having an annular gradient 66 is provided. These glasses, which could be either prescription or not, have a clear center which measures about 1 cm. to 2 cm., and outside of the center they have a steep gradient tint that may vary from full light transmission at the center to as little as 10% transmission at the edges. This configuration accommodates the optical facts of computer use, in which only the very central portion of the field of vision is used anyway, about a 15 degree solid angle. Light impinging on the eyes at greater angles serves to constrict the pupil without providing any useful visual information, resulting in the apparent dimming of the useful image. Therefore, glasses having a clear central portion wide enough to allow viewing the VDT screen but excluding other light enhances the image in conjunction with the beneficial effects of the darkened hood described above. A computer operator can sit in front of a VDT equipped with the hood disclosed herein, wearing the glasses described herein, for hours on end in many instances without reporting any eye discomfort whatsoever. The same operator, when the hood and glasses are removed, report eye distress within an hour or two if the operator has sensitive eyes. There is thus no doubt that the elimination of glare plays a major part in the reduction of eye strain complaints among workers, so that the double function of the disclosed system produces immediate advantages in addition to elimination or reduction of the as yet unknown deleterious effects of various electromagnetic rays which do not fall within the visible spectrum.
	claims	1. A method for decontamination of an object comprising:introducing and dispering or dissolving an object to be decontaminated, which is contaminated with radioactive materials, into an eluting solvent to separate the radioactive materials from the object to be decontaminated by dissolution of the radioactive materials into the eluting solvent, the object to be decontaminated comprising contaminated soil and contaminated water;separating the radioactive materials dissolved in the eluting solvent and the object to be decontaminated into solid and liquid;collecting the soil after said solid-liquid separation and from which the radioactive materials have been removed by elution:electrolyzing the separated liquid containing the eluting solvent and the contaminated water after said solid-liquid separation by introducing the separated liquid into an electrolysis tank provided with an anode and a cathode;depositing metal ions comprising the radioactive materials on the cathode;collecting hydrogen containing tritium generated by the electrolysis in the electrolysis tank; andconveying the hydrogen to outside the electrolysis tank and there trapping the hydrogen. 2. The decontamination method according to claim 1, wherein the electrolysis tank in which the electrolysis is performed is hermetically sealed. 3. The decontamination method according to claim 1, wherein oxygen is discharged from the electrolysis tank upon a pressure of the oxygen accumulated in the electrolysis tank reaching at least a predetermined value during electrolysis. 4. The decontamination method according to claim 1, further comprising arranging one or a plurality of deposition members, to which an electric current is supplied from the cathode, in proximity to the cathode, whereby the metal ions comprising the radioactive materials are deposited on the deposition members as well as on the cathode. 5. The decontamination method according to claim 1, wherein the separated liquid is introduced into an adsorption filter before being introduced to the electrolysis tank, and the metal ions comprising the radioactive materials are adsorbed by the adsorption filter. 6. The decontamination method according to claim 1, wherein the trapping of the hydrogen comprises charging the hydrogen into a gas cylinder for storage. 7. The decontamination method for soil according to claim 1, further comprising as a last step, storing the electrolysis tank, the anode, the cathode and any other apparatus contacted by the contaminated material without disturbing residual decontamination thereon. 8. The decontamination method according to claim 1, wherein the contaminated water comprises tritiated water. 9. The decontamination method according to claim 1, wherein the radioactive materials comprise radioactive cesium and tritium.
051868881	abstract	The device is constituted by a metal structure (10) resting on the bottom of the reactor pit (3) and submerged in a mass of water filling the lower portion of the reactor pit (3). The metal structure (10) comprises a central chimney (11), a recovery wall (12) constituted by juxtaposed dihedra (22) made from metal sheet, and a peripheral wall (13) fixed to the external edges of the dihedra (22) and providing water passages at the periphery of the reactor pit. When the molten core of the reactor spreads into the reactor pit, following an accident, the structure (10) ensures its recovery and prevents contact between the molten core and the bottom of the reactor pit. The molten core flows onto the wall (12) in such a manner as to constitute a layer of small thickness which is cooled over its upper surface and over its lower surface and which solidifies rapidly.
	summary
042648246	claims	1. Apparatus for imaging radiation sources, comprising a collimator having a multiplicity of portions transmissive of radiation from a said source, the transmissivities of said portions to radiation reaching the collimator from a given said source being different from portion-to-portion for a given orientation of said collimator, regardless of the distance of said source from said collimator means for varying said transmissivities over time, and means for detecting the radiation passing through each said portion for successive values of its transmissivity, wherein said collimator is a slit collimator, the slits of which are defined by spaced, radiation absorbing sheets, and adjacent pairs of said sheets are non-parallel to each other, diverging from each other in the direction away from said means for detecting so as to provide said multiplicity of transmissivities. 2. The apparatus of claim 1 wherein said sheets lie along planes intersecting in a common focal plane. 3. The apparatus of claim 2 wherein corresponding surfaces of each said pair of adjacent sheets have the same included angle. 4. The apparatus of claim 1 wherein the plane bisecting any given slit is parallel to a boundary plane of an adjacent slit, a boundary plane being defined as extending from the forward edge of one sheet to the rear edge of an adjacent sheet. 5. The apparatus of claims 1 or 4 wherein said means for varying said transmissivities comprises means for moving said collimator relative to said source. 6. The apparatus of claim 5 wherein said means for moving comprises means for rotating said collimator about an axis pointing toward the field of view of the collimator. 7. The apparatus of claim 2 wherein said means for varying said transmissivities comprises means for rotating said collimator about an axis perpendicular to said focal line and pointing toward the field of view of the collimator.
042886996	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a storage rack for the storage of fuel elements of nuclear reactors consisting of a sheet metal lattice arrangement constituting a plurality of abutting similar vertical storage cases or tubes having in general a rectangular cross section. In anyone of the cases of this storage rack a rod-shaped fuel element may be stored. 2. Description of the Prior Art Within or in the neighbourhood of the reactor building there are available storage pools for storing spent or new thermal reactor fuel elements during a long or only a short period. Therein the fuel elements are placed in racks below water in such an arrangement that the necessary heat dissipation is warranted and no nuclear chain reaction may occur. Generally for such a design there are included very broad margins with respect to the mutual distances between the elements. When the storage capacity of such pools has been exhausted and the transfer of the spent fuel elements to a regeneration plant is not yet possible a temporary solution is found by placing the rods closer to each other in the pool in which case however, much more attention should be given to warrant sufficient criticality margins for the ensemble. A possibility for reducing the mutual distance or the pitch with which the fuel elements are being placed is the inclusion in the construction of a so-called neutron poison, i.e. a material having a very high effective cross section value for the absorption of neutrons. Such a material is the boron isotope B.sup.10 that may be included as an alloying component in the stainless steel, mostly used for the manufacture of these racks. When utilising such a material for the manufacture of the storage racks as a whole or part thereof the possibility arises of a much smaller pitch of the fuel elements and consequently of a much more compact storage than in the conventional racks. From nuclear physic calculations it is apparent that dependent on the chosen construction, the geometry of the ensemble and the specific fuel element, there may be found an optimum ratio of the construction material and the surrounding water with respect to the fuel elements. In case of the storage racks of the above-mentioned type there exists therefore a certain interstice between the cases determining the final storage capacity. At the found optimum any further increase of the amount of boron, i.e. the increase of the thickness of the borated sheet steel of the cases does not lead to an increase of the absorption capacity and consequently not to a decrease of the water gap or the mutual distance between the elements; that is to say that when the "saturation value" of the boron content is reached a decrease of the mutual distance between the elements will bring the ensemble closer to the criticality. Hence the effective multiplication factor will more closely approach the limit value usually assumed at 0.95. In case of storage rack arrangements including a neutron poison the water gap between the fuel rods play an important role as a moderator for the neutrons leading to a relatively high peak of the neutron flux between the said cases. This "surge" of the neutron flux at the location of the gap and consequently also in the case walls of borated steel leads to an increased capture of neutrons and consequently to a decrease of the multiplication factor of the ensemble. Also in case of a rack not provided with a neutron poison a decrease of the mutual distance between the elements leads to an increase of the multiplication factor after all. In case of a given rack construction and given fuel elements a theoretical minimum distance or gap width constituted by metal and water should be maintained between the fuel elements in order to satisfy the criterion for the multiplication factor. However, theoretical gap widths may only be applied when the storage rack may be manufactured within very close tolerances. Up till now these storage racks have been made as a welded construction. Notwithstanding the use of welding jigs the accurate gage maintenance and the attainable straightness of the cases and other construction parts constituting the storage rack are limited by the deformations inherent to each welding process. Therefore in case of a welded construction the theoretically permissible minimum gap width has to be increased with additional safety margins in view of the necessary manufacture tolerances. SUMMARY OF THE INVENTION The invention now provides a storage rack of the above-mentioned type, the manufacture of which may be carried out within very close tolerances, whereby the minimum distance between the fuel elements will nearly not be affected by the manufacturing process. If for a certain fuel element having a length of for instance 4 m the width of the water gap may be for instance 25 mm, the tolerance in case of a welded construction with respect to the case walls will be .+-.3 mm. Due to both the adjoining cases the tolerance with respect to the water gap will consequently be .+-.6 mm or about 25%. In accordance with the present invention for fuel elements having the same length, these tolerances will be .+-.5 mm with respect to the case walls and 1 mm with respect to the water gap, this corresponding with 4%. In the storage rack according to the present invention the lattice arrangement has been constructed of a plurality of mutually substantially perpendicular sheet elements having sharply shaped contours, all sheet elements in one of the two perpendicular directions completely or partially traversing the lattice arrangement at a mutual distance substantially corresponding to the width of a storage case and all sheet elements in the other of the two perpendicular directions each extending only substantially over the width of one storage case, the latter narrow sheet elements at the opposite edges thereof having been provided with lugs fitting in accurately formed openings in the traversing sheet elements, said lugs having been immobilized by means of a keying, the arrangement being such that the long edges of the narrow sheet elements may be pressed tightly against the traversing sheet elements. In accordance with one preferred embodiment of the invention all storage cases within the lattice arrangement have been separated from each other by a wall consisting of two parallel sheet elements at a short distance from each other inclusive the interstice between these sheet elements, the said interstice housing the lugs and the keyings. The keyings may then be embodied in such a manner that of the narrow sheet elements constituting together a partition wall, the lugs have been provided at the same level, said lugs having been connected with each other by means of a connecting strip running parallel to the traversing sheet elements and that between this connecting strip and the opposite wall of the cooperating traversing sheet element a key has been pinched. The connecting strips between the lugs may be secured by welding. These welds are no such critical welds that these will cause a deformation of the rack construction. Moreover each lug may be provided with an opening having an edge running parallel to the wall of a cooperating traversing sheet element while a key may be pinched between this edge and the wall of the traversing sheet element. In general the lugs will consist of an extended part of the sheet elements and slidably fit into slots in the cooperating sheet elements. For securing after assembling, all keys may be welded to the traversing sheet elements, the connecting strips and the lugs, respectively. These welds are not critical either. Such securing may also be attained by deformation of the keys. In a rectangular lattice arrangement the storage cases at each of the four outer walls of the lattice may be enclosed by a traversing sheet element extending over the entire side wall, while the sheet elements of the side walls extending parallel to the narrow sheet elements have been provided with slots for slidably receiving lugs formed on the edges of the traversing sheet elements perpendicular thereto, which lugs may then be fastened by means of a keying as described above. For the present invention it is in particular of importance that there are manufactured sheet elements having very accurate contours and openings for the lugs, for instance with an accuracy up to 0.1 mm. Hereby and by the use of keyings instead of welding combined with bending there may be obtained particularly dimensionally stable constructions throughout the entire height and width of the storage rack. The said accuracy applies in particular to the longitudinal edges of the sheet elements. By the use of the lattice arrangement according to the present invention in combination with a particular locking construction for the top plate and the bottom plate of the lattice, wherein no welding joints are employed either, there is provided a storage rack having a very stable construction. The storage racks according to the present invention entail the further advantages of enabling a very accurate prefabrication of all sheet elements, an easy cleaning of all parts of the storage rack separately, this being a necessity for the storage of nuclear fuel elements. Further the absence of welds, always resulting in uncertain material properties, excludes all worries about structural changes when exposed to the ionising radiation of the fuel elements. By keyings a very accurate assembly is possible. For the maintenance of the structural shape of the arrangement there is no necessity to use expensive assembly jigs as are required when welding. The keyings and the special construction of the storage rack by means of traversing and narrow sheet elements furthermore open the possibility of a rapid and simple exchange of parts of the rack. Moreover separate parts of a rack may easily be controlled with respect to the cleanness thereof. There are no critical welding constructions whereby expensive weld controls may be omitted and possible faults are eliminated.
047822317	abstract	This invention relates to a standard component .sup.99m TC elution generator useful for medical purposes and consisting of prefabricated component parts. The main generator column of the device may be used both as an irradiation container and an elution container, enabling the user to supply activated or nonactivated parts. The main generator column made from by neutrns little activable materials serves first as reactor irradiation ampoule and after having been activated in the reactor by neutrons and after a simple adjustment serves directly as the generator column. It is filled with water insoluable molybdates or polymolybdates (with the molybdenum content in the range 10-40%), easily releasing .sup.99m Tc generated by radioactive decay of the mother .sup.99 Mo formed in it by neutron activation. This column filling serves originally as target material for reactor irradiations and afterwards it is directly used as the generator elution matrix. Accordingly, all components of the generator can be produced in a "ready-to-use" form and supplied as inactive material. When nonactivated parts are used, activation is performed on-site by a local reactor. The use of nonactivated parts is advantageous because they are more easily and more safely manufactured and transported. The invention further provides for efficient generation of .sup.99m TC radionuclides from medium neutron flux irradiation of molybdenum in a natural isotopic mixture.
	abstract	A detection head and collimator for a gamma camera. The detection head includes several elementary detectors with semiconductors adjacent to each other to form a detection plane. The collimator is placed in front of the detection plane and includes a number of ducts laid out in a repetition pattern. The shape of the elementary detectors and the repetition pattern are rectangular in the detection plane.
	description	This application claims the benefit of U.S. Provisional Application No. 61/777,026, filed Mar. 12, 2013, titled “REFUELING WATER STORAGE TANK (RWST) WITH TAILORED EMERGENCY CORE COOLING (ECC) FLOW”, and U.S. Provisional Application No. 61/794,206, filed Mar. 15, 2013, titled “PASSIVE TECHNIQUES FOR LONG-TERM REACTOR COOLING”, the disclosures of which are hereby incorporated by reference in their entirety. This invention was made with government support under Contract No. DE-NE0000583 awarded by the Department of Energy. The government has certain rights in the invention. The following relates to the nuclear power generation arts, nuclear reactor safety arts, nuclear reactor emergency core cooling (ECC) arts, and related arts. In a loss of coolant accident (LOCA), or other event in which a nuclear reactor is rapidly depressurized, the nuclear reactor core is to be kept immersed in water so as to provide for removal of decay heat and to prevent fuel rod clad damage and subsequent failure of the fuel rod as a fission product barrier. The system that provides for core cooling following a LOCA is the emergency core cooling system (ECC). The ECC design may incorporate passive features that can be actuated using stored energy and do not continue to use electric power after actuation. In this kind of passive ECC design, a refueling water storage tank (RWST) is typically located inside radiological containment to provide water for use during reactor refueling, and this RWST also serves as a water source for the ECC system. The RWST is located above the reactor core so that the passive ECC system can operate by gravity-driven water flow. The RWST is sized to provide sufficient water to operate the ECC system for a design-basis time period, e.g. 72 hours in some scenarios. Depressurization valves allow gravity-driven flow (or injection) of water from the RWST into the reactor. Boiling heat transfer removes decay heat generated in the fuel assemblies and the resulting steam is subsequently vented through depressurization lines. The required RWST volume can be computed based on the latent heat capacity of water (i.e., the amount of thermal energy that is removed per liter of liquid water converted to steam), the known reactor core decay heat output versus time, and the chosen design-basis time period for ECC operation starting with a fully-filled RWST. In one disclosed aspect, an apparatus comprises: a nuclear reactor comprising a pressure vessel containing a nuclear reactor core comprising fissile material; a refueling water storage tank (RWST); an injection line connected to drain water from the RWST to the pressure vessel; and a standpipe having a lower end in fluid communication with the injection line and having two or more orifices at different heights along the standpipe in fluid communication with the RWST. In some embodiments the standpipe is disposed in the RWST and has two or more orifices at different heights along the standpipe. In some embodiments the standpipe is disposed outside of the RWST and has two or more orifices at different heights along the standpipe connected with the RWST via cross-connection pipes. Some embodiments further comprise a float valve configured to regulate flow through one of the two or more orifices, the float valve including a float disposed in the standpipe. In some embodiments the standpipe including the two or more orifices is configured to tailor flow from the RWST to the pressure vessel to approximate an expected decay heat versus time profile. In another disclosed aspect, a method comprises depressurizing the pressure vessel of a nuclear reactor, and providing cooling of the nuclear reactor core by operations including draining water from a refueling water storage tank (RWST) into a standpipe and draining water from the standpipe into the depressurized pressure vessel. In some embodiments the draining of water from the RWST into the standpipe comprises draining water from the RWST into the standpipe through orifices at two or more different elevations along the drainpipe. In some embodiments the draining of water from the RWST into the standpipe comprises: draining water from the RWST into the standpipe through a first orifice along the drainpipe; draining water from the RWST into the standpipe through a second orifice along the drainpipe; and controlling the draining of water from the RWST into the standpipe through the second orifice using a float valve having its float disposed in the standpipe at an elevation that is lower than the elevation of the first orifice. In another disclosed aspect, an apparatus comprises a nuclear reactor comprising a pressure vessel containing a nuclear reactor core comprising fissile material, a refueling water storage tank (RWST), and a reactor core cooling system which comprises: a standpipe including a plurality of orifices in fluid communication with the RWST to drain water from the RWST into the standpipe; and an injection line configured to drain water from the standpipe to the pressure vessel. In some embodiments the RWST is not in fluid communication with the pressure vessel during operation of the reactor core cooling system except through the standpipe. In some embodiments the standpipe is disposed in the RWST. In some embodiments the standpipe is disposed outside of the RWST and the reactor core cooling system further includes cross-connection pipes connecting the plurality of orifices with the RWST. In some embodiments the reactor core cooling system further comprises a valve configured to control flow through one orifice of the plurality of orifices in fluid communication with the RWST based on water level in the standpipe. In some such embodiments the valve comprises a float valve having its float disposed in the standpipe. With reference to FIG. 1, a cutaway perspective view is shown of an illustrative small modular reactor (SMR) 10 with which the disclosed emergency core cooling (ECC) techniques with tailored passive flow from one or more refueling water storage tank (RWST) units 12 are suitably employed. The illustrative SMR unit 10 of FIG. 1 is of the pressurized water reactor (PWR) variety, and includes a pressure vessel 14 and one or more integral steam generators 16 disposed inside the pressure vessel 14 (that is, the illustrative SMR 10 is an integral PWR 10). The illustrative SMR 10 of FIG. 1 is merely an example, and more generally the disclosed ECC techniques with tailored passive flow from one or more RWSTs are suitably employed with substantially any type of light water nuclear reactor, including PWRs (both integral as shown, and PWR configurations employing external steam generators), boiling water reactors (BWRs), and so forth. The disclosed ECC techniques with tailored passive flow from one or more RWSTs are also not limited to small and/or modular nuclear reactors, but rather may also be employed with larger-scale and/or non-modular reactor units. The illustrative SMR 10 of FIG. 1 includes an integral pressurizer 18 defining an integral pressurizer volume 19 at the top of the pressure vessel 14; however, again, more generally the disclosed ECC techniques with tailored passive flow from one or more RWSTs are suitably employed with light water nuclear reactors including either integral or external pressurizers. In general, the nuclear reactor (such as the illustrative SMR 10 of FIG. 1) includes a pressure vessel 14 containing a nuclear reactor core 20 comprising fissile material such as 235U (typically in an alloy, composite, mixture, or other form) immersed in (primary) coolant water (more generally herein, simply “coolant” or “coolant water”). With the reactor core 20 immersed in coolant water, and when control rod drive mechanisms (CRDMs) 22 at least partially withdraw control rods made of neutron-absorbing material, a nuclear chain reaction is initiated in the nuclear reactor core which heats the (primary) coolant water. The illustrative CRDMs 22 are internal CRDMs, in which the CRDM unit including its motor 22m including both rotor and stator are disposed inside the pressure vessel 14, and guide frame supports 23 guide the portions of the control rods located above the core; in other embodiments, external CRDM units may be employed. In the illustrative integral PWR 10, a separate water flow (secondary coolant) enters and exits the steam generators 16 via feedwater inlet 24 and steam outlets 26, respectively. The secondary coolant flows through secondary coolant channels of the steam generator or generators 16, and is converted to steam by heat from the reactor core carried by the (primary) coolant water. The steam generator(s) 16 thus act as a heat sink for the nuclear reactor 10. In other reactor types, such heat sinking is obtained by a different mechanism. For example, in a PWR with external steam generators, the primary coolant is piped out of the pressure vessel to the external steam generator where it converts secondary coolant flow to steam. In a BWR, the primary coolant is boiled to form steam inside the pressure vessel and this primary coolant steam directly drives a turbine or other useful apparatus. The pressure vessel 14 of the illustrative integral PWR 10 includes a lower portion 30 housing the nuclear reactor core 20 and an upper portion 32 housing the steam generators 16, with a mid-flange 34 connecting the upper and lower portions of the pressure vessel. The primary coolant flow circuit inside the pressure vessel 14 is defined by a cylindrical central riser 36 extending upward above the reactor core 20 and a downcomer annulus 38 defined between the central cylindrical riser 36 and the pressure vessel 14. The flow may be driven by natural circulation (i.e. by primary coolant heated by the reactor core 20 rising through the central cylindrical riser 36, discharging at the top and flowing downward through the downcomer annulus 38), or may be assisted or driven by reactor coolant pumps (RCPs), such as illustrative RCPs including RCP casings 40 containing impellers driven by RCP motors 42. The RCPs may alternatively be located elsewhere along the primary coolant path, or omitted entirely in a natural circulation reactor. It is again noted that the illustrative SMR 10 is merely an illustrative example, and the disclosed ECC techniques are suitably employed with substantially any type of light water nuclear reactor. With continuing reference to FIG. 1, a diagrammatic sectional view is shown of the SMR 10 disposed in a radiological containment structure 50 (also referred to herein as “radiological containment” or simply “containment”) along with the refueling water storage tank (RWST) 12. While a single RWST 12 is illustrated, it is to be understood that two or more RWSTs may be disposed inside containment to provide redundancy and/or to provide a larger total volume of water. The RWST 12 serves multiple purposes. As the name implies, is provides water for use during routine refueling (that is, removal of spent fuel comprising the nuclear reactor core and its replacement with fresh fuel). The RWST 12 also serves as a water reserve for use during certain accident scenarios, such as a loss of heat sinking event in which the heat sinking via the steam generators 16 or other heat sinking pathway is interrupted causing the pressure and temperature in the reactor pressure vessel 14 to rise; or a loss of coolant accident (LOCA) in which a break occurs in a (relatively large-diameter) pipe or vessel penetration connected with the pressure vessel 14. FIG. 1 diagrammatically illustrates the response to a LOCA comprising a break from which steam 52 (possibly in the form of a two-phase steam/water mixture 52) escapes. In FIG. 1 such a LOCA is diagrammatically indicated as originating in the proximity of the integral pressurizer 18 at the top of the pressure vessel 14. The steam/water 52 that escapes from the pressure vessel 14 is contained by the radiological containment 50, and the released energy is ejected to an ultimate heat sink (UHS) 54 via a suitable transfer mechanism. In illustrative FIG. 1, this heat transfer is achieved (at least in part) by direct thermal contact between the UHS 54 which is located on top of and in thermal contact with the top of the containment 50. Additionally, a passive emergency core cooling (ECC) is activated, which depressurizes the reactor 10 using valves connected to the pressurizer 18 (in the illustrative example of FIG. 1, or elsewhere in other reactor design) to vent the pressure vessel to the RWST. This operation is diagrammatically indicated by steam path 60 carrying steam (or two-phase steam/water mixture) from the pressurizer 18 to sparge into the top of the RWST 12. Any excess pressure in the RWST 12 resulting from the venting of the pressure vessel to the RWST escapes via a steam vent 62 from the RWST. While depressurizing the reactor, water is initially injected into the reactor vessel from two, nitrogen pressurized, intermediate pressure injection tanks (IPIT, of which one illustrative IPIT 64 is shown in FIG. 1) to assure the reactor core 20 remains immersed in coolant water. The water from the IPIT 64 optionally includes boron or another neutron poison to facilitate rapid shutdown of the nuclear chain reaction. Once the reactor 10 is depressurized, water in the RWST 12 (or RWSTs, if two or more redundant RWST units are provided inside containment) drains into the reactor vessel 14 via an injection line 66 running from the RWST 12 to the reactor pressure vessel, thus refilling the vessel 14. (Note that in illustrative FIG. 1, a downstream portion of the injection line 66 also provides the input path for water from the IPIT 64, in which case there is suitable valving, provided to valve off the IPIT 64 after initial depressurization is complete. The valving is optionally passive, e.g. automatically closing when the pressure in the pressure vessel 14 falls below a setpoint. It is also contemplated to connect the IPIT with the reactor pressure vessel via a separate line from the injection line 66.) The water in the RWST(s) 12 provides long-term cooling for the reactor core 20. The ECC response to a loss of heat sinking event is similar, except that coolant is not lost via a LOCA break, but rather the loss of heat sinking causes the pressure in the pressure vessel 14 to rise above a threshold at which the ECC activates to depressurize the pressure vessel 14. The flow of water from the RWST(s) 12 refills the reactor vessel 14. In some calculations for a LOCA in an SMR similar to the illustrative SMR 10 of FIG. 1 employing two RWST units, the water level is calculated to drop to within 50 inches of the top of the reactor core 20, and the escaping primary coolant 52 comprising a mixture of water and steam flows out of the vessel 14 through the break in the pressurizer 18. Over a period of hours, the water level in the RWSTs 12 is calculated to drop, but the analysis shows that the water level in the reactor pressure vessel 14 remains high. Without being limited to any particular theory of operation, it is believed that this is due to a lower density of the water above the reactor core 20 due to saturated conditions and steam in the central riser 36. As a result, a significant amount of water flows out through the break (that is, the integrated volume flow 52 is high), causing the RWST 12 to drain more quickly than it otherwise would if all the water was converted to steam. In the design basis of the calculations, there is sufficient water in each RWST 12 to remove core decay heat for greater than 72 hours if all of the water is converted to steam. However, liquid water lost through the LOCA break removes only about 10% of the energy that would be removed if an equivalent water mass was converted to steam by the heat in the pressure vessel 14. Therefore, the water carried out of the break has an adverse impact on the decay heat removal capacity of the RWSTs 12. With reference to FIG. 2, excessive water carryover from the break can potentially reduce RWST heat removal capacity to less than the design basis of 72 hours. In the calculations reported in FIG. 2, the RWST 12 was drained of water in only about 48 hours, which is much less than the design basis of 72 hours. With reference to FIG. 3, one approach for improving RWST energy removal capacity while retaining passive operation might be to limit the flow of water from the RWST using an orifice (i.e. constriction, not shown) in the injection line running from the RWST to the reactor pressure vessel. Adding fluid flow resistance to the RWST injection line reduces flow potential and, thereby, reduces the carryover of water through the break. However, the orifice cannot be made so small that the flow at any time over the (design basis 72 hour) ECC operation decreases below a required flow sufficient to provide a minimum decay heat removal rate. FIG. 3 shows calculated results using this approach, assuming only one of (redundant) two RWSTs is performing the ECC operation. Initially, the driving head is high because of the high initial RWST level (assumed to start at the 82 foot level in these calculations) and the low water level in the reactor pressure vessel. As the pressure vessel fills, however, the driving head is reduced, lowering the flow. At this point, the flow from the RWST decreases almost linearly as seen in FIG. 3, resulting in an excessive flow for the first 50 hours. At that point, the RWST is essentially empty and cooling is lost, and the design goal of 72 hours is not achieved. With returning reference to FIG. 1 and with further reference to FIGS. 4 and 5 which show detail drawings of the RWST 12 and injection line 66 at the beginning of the ECC process (FIG. 4) and partway through the ECC process (FIG. 5), an approach that provides tailored passive ECC flow is described. The goal is to tailor the flow from the RWST 12 into the pressure vessel 14 as a function of time to approximately match the decay heat versus time profile. The approach uses a stand pipe 70 disposed in the RWST 12. The lower end of the standpipe 70 feeds into the injection line 66 running from the RWST 12 to the reactor pressure vessel 14 (see FIG. 1). The upper end of the standpipe 12 extends to a height that is a depth d1 below the initial (and hence highest) water level L0 of the RWST 12 (see FIG. 4). In the illustrative example shown in FIG. 1, the initial water level L0 also coincides with the top of the pressurizer 18—this is not required, but has the advantage of providing the maximum water head while avoiding the possibility of unpressurized liquid water from the RWST 12 overflowing from a vessel break at the top of the pressurizer 18. With particular reference to FIGS. 4 and 5, the standpipe 70 includes multiple orifices O0, O1, O2 each of which admits water into the standpipe 70 so long as the water level in the RWST 12 is above the orifice. In illustrative FIGS. 4 and 5, the orifices include: an orifice O0 which is the opening at the top of the standpipe 70 located at depth d1 below the initial water level L0 of the RWST 12; an orifice O1 located at a depth d2 below the initial water line L0; and an orifice O2 located at or near the bottom of the standpipe 70 and hence at the maximum depth dmax below the initial water level L0. Without loss of generality, the illustrative orifices O0, O1, O2 are thus located at respective depths d1, d2, dmax below the initial water level where d1<d2<dmax. All water draining from the RWST 12 to the pressure vessel 14 via the injection line 66 flows through the stand pipe 70. When the ECC begins operation, the water level is at the (highest) initial water level L0, as shown in FIG. 4, and so all three orifices O0, O1, O2 are below the water level. Thus, initially water flows through all three orifices O0, O1, O2 creating a high water flow. As RWST 12 is gradually depleted as the ECC operation continues, the water level decreases. Water flow through the upper orifice O0 decreases faster than through the lower orifice O1 which decreases faster than flow through the lowermost orifice O2 because the relative heads drop more quickly for the orifices located higher up along the standpipe 70. With particular reference to FIG. 5, once RWST water level drops below the top of the standpipe 70 (that is, drops a depth d1 from the initial water level L0 to a lower water level L1 see FIG. 5), there is no flow at all through the uppermost orifice O0. When the water level drops below the orifice O1 (that is, drops a depth d2 from the initial water level, not illustrated), there is no flow at all through orifice O1. Flow continues through the lowermost orifice O2 until the RWST 12 is substantially completely drained. With reference to FIG. 6, the flow profile through the standpipe 70 is illustrated for a calculated design. By suitable selection of the depths d0, d1 respective to the maximum depth dmax of the RWST 12, and optionally by also optimizing the sizes of the orifices O0, O1, O2, the flow as a function of time can be tailored to closely match the decay heat profile, so that the flow over the entire relevant time (namely a design basis of 72 hours for the design of FIG. 6) remains at or above the minimum required flow, while not draining the RWST 12 over the design-basis 72 hour interval. Indeed, the flow through the standpipe 70 in these calculations provided excess flow throughout the 72 hour ECC operation. The flow profile closely matches the required flow, allowing decay heat to be removed over a longer period of time. With reference to FIG. 7, the use of the standpipes 70 in the RWST 12 passively tailors the flow of water from the RWST 12 as a function of time to minimize the loss of water out of the pipe break. This allows a single RWST 12 to maintain water level inside the reactor vessel for a longer period of time. FIG. 7 shows the estimated RWST level, assuming only one tank is used and assuming no internal changes are made to the reactor to minimize water loss through the pipe break. With a tank bottom elevation (dmax) of 41 ft used in the calculations, there is still seven feet, or 22,400 gal of water in the RWST (single side) after 72 hours. By comparison, without using the standpipe 70 and using two RWST units (not just one RWST unit as in the simulation of FIG. 7), the RWST tanks are completely drained in only 48 hours. Illustrative FIGS. 4 and 5 employ a single standpipe 70 with three orifices O0, O1, O2. More generally, more than one standpipe can be used to provide redundancy and/or additional flow (with the lower-end outputs of the standpipes coupled in parallel with the injection line 66 leading to the pressure vessel 14). The skilled artisan can readily optimize the number of standpipes and the number, size, and locations of orifices. As few as two orifices can be employed (e.g., orifices O0 and O2 with the intermediate orifice O1 omitted; it is also contemplated for the uppermost orifice to be located on the side of the standpipe rather than being an open upper end of the standpipe as in illustrative O0). Additional orifices generally allows for more precise tailoring of the flow rate as a function of time. The orifices O0, O1, O2 need not be of the same size. The orifices optionally include screens to limit debris ingress into the standpipe, and the flow resistance of any such screens is suitably taken into account in the design. The orifices may also be configured as longitudinal slits whose long dimension is parallel with the axis of the standpipe—such slits can reduce the abruptness of the transient as the decreasing water level passes the orifice (e.g., as in the abrupt transition labeled in FIG. 6). Some reduced abruptness can also be achieved by additionally or alternatively tilting the standpipe away from the illustrated vertical orientation. Another parameter that can be adjusted to tailor the flow rate as a function of time is to vary the diameter of the standpipe over its height. With reference to FIG. 8, in a variant embodiment including a modified RWST 112 and a standpipe 170 that is located outside of the RWST 112. As shown in FIG. 8, the ECC system of FIG. 8 is in the same context as the ECC system of FIGS. 4 and 5, e.g. the ECC of FIG. 8 operates to provide tailored flow of water into the nuclear reactor 10 to provide core cooling and to ensure the reactor core 20 remains immersed in water during the decay heat removal. Toward this end, water flows from the RWST 112 through the standpipe 170 and into the pressure vessel 14 via the injection line 66. In illustrative FIG. 8, the injection line 66 again also serves as the injection line for the illustrative IPIT 64 (although as already mentioned in reference to FIG. 1, the IPIT could be connected via a separate injection line). The ECC system of FIG. 8 differs from that of FIGS. 4 and 5 in that the standpipe 170 is located outside of the RWST 112. (By contrast, in the embodiment of FIGS. 4 and 5 the standpipe 70 is disposed inside the RWST 12.) To flow water from the RWST 112 through the externally located standpipe 170, a plurality of cross-connection pipes P0, P1, P2 connect the RWST 112 and the standpipe 170 at the different depths d0, d1, dmax (compare with FIG. 4). The cross-connection pipes P0, P1, P2 thus serve the same role as the orifices O0, O1, O2 of the embodiment of FIGS. 4 and 5. The stand pipe 170 is designed to fill to the top of the RWST 112 (that is, to the initial level L0) during normal operation providing the maximum head during initial draining. As water leaves the RWST 112, the water level drops below the level d0 of the first cross-connection pipe P0, resulting in a rapid decrease in water level in the stand pipe. Makeup water to the standpipe 70 is controlled by the one or more orifices O0, O1, O2 at different elevations in the embodiment of FIGS. 4 and 5; analogously, in the embodiment of FIG. 8 makup water to the standpipe 170 is controlled by the one or more cross-connection pipes P0, P1, P2 at different elevations. In both cases, this produces a significantly lower elevation head forcing water into the reactor vessel 14 as the water level in the RWST 12, 112 falls below the level (i.e. elevation) of each successive orifice or cross-connection pipe. The result is the desired tailored flow of water from the RWST 12, 112 into the pressure vessel 14, with a large head initially to keep the initially hot core 20 cool and immersed in water, and a reduced head over time which is as appropriate as the reactor core 20 cools and requires reduced water injection to remove the steadily decreasing decay heat output and to keep the cooling reactor core immersed in water. The embodiment of FIG. 8 has certain advantages as compared with the embodiment of FIGS. 4 and 5. The external standpipe 170 is readily accessible to perform maintenance. Valves can also be incorporated into the cross-connection pipes (e.g., redundant parallel valves are shown in the deeper cross-connection pipes P1, P2 of FIG. 8) to facilitate isolation of the standpipe 170 for such maintenance. Such valves could also be used to tailor the head as a function of time to accommodate specific circumstances. For example, during a LOCA if it is found that the water flow from the RWST 112 to the pressure vessel 14 is too high (e.g., as evidenced by excessive liquid water flowing out the LOCA breakage), one or more of the valves on the cross-connection piping can be closed off to reduce the effective head. On the other hand, the embodiment of FIGS. 4 and 5 has certain advantages, including a more compact design (since the standpipe 70 is disposed inside the RWST 12) and elimination of the cross-connection the piping P0, P1, P2. If multiple standpipes 70 are provided inside the RWST 12 and connected in parallel with the injection line 66, then a real-time manual tailoring of the head similar to that achieved using the valves on the cross-connection pipes P1, P2 can be achieved by providing valves on the individual standpipe-to-injection line connections so as to isolate individual standpipes to modulate the effective head in real-time. With reference to FIGS. 9 and 10, another variant embodiment includes a modified RWST 212 and an external standpipe 270. This embodiment includes the topmost cross-connection pipe P0 as in the embodiment of FIG. 8; however, the lower two cross-connection pipes P1, P2 of the embodiment of FIG. 8 are replaced by a single cross-connection pipe PP whose flow is controlled by a float valve 300 having its float 302 disposed in the standpipe 270. Alternatively, another type of passive valve can be employed such as a spring-type valve. Operation of the ECC system of FIG. 9 starts similarly to that of FIG. 8—the topmost cross-connection pipe P0 allows the standpipe 270 to be filled to the same level (initially level L0) as the RWST 212. The cross-connection pipe PP is initially valved closed by the float valve 300 because the high water level raises the float 302 to close the float valve 300. This is indicated diagrammatically in FIG. 10 by the indicated buoyancy force Fw acting on the float 302, which raises a valve body 304 (via a connecting shaft 305) against a valve seat 306 to close the float valve 300. This situation holds until the flow into the pressure vessel 14 causes the water level in the RWST 212 to fall below the topmost cross-connection pipe P0 (that is, to fall by a distance d1). At that point, flow into the standpipe 270 via the topmost cross-connection pipe P0 stops, and the remaining water in the standpipe 270 rapidly flows out through the injection line 66 to the pressure vessel 14. This rapid decrease in water level in the standpipe 270 stops when the water level falls below the level of the float 302 so that the buoyancy force Fw is removed and the float 302 falls downward under gravity causing the valve body 304 to move away from the valve seat 306 so as to allow water flow 308 to flow from the RWST 212 through the lower cross-connection pipe PP into the standpipe 270. The equilibrium state corresponds to a water level just sufficient to provide enough buoyancy to the float 302 so that the inflow of water through the pipe PP and float valve 300 balances the outflow of water through the injection line 66 into the pressure vessel 14. This water level is at about the position of the float 302. Thus, the ECC system of FIGS. 9 and 10 provides a two-level head: a high head during the initial stage of core cooling that continues until the water level in the RWST 212 falls to the level of the topmost cross-connection pipe P0; followed after a brief transition as the bulk of the water in the standpipe 270 flows out by a lower head corresponding to water flow through the pipe PP and the (at least partly) open float valve 300. It is noted that FIG. 9 diagrammatically shows the float valve 300 in a functional form, by showing the valve 300 diagrammatically valving the cross-connection pipe PP, controlled by the float 302 in the standpipe 270. The physical layout of the float valve 300 can be different, as shown by the illustrative embodiment of the float valve 300 shown in FIG. 10, where the valve components 304, 305, 306 are actually disposed in the standpipe 270, but operate to control the inflow 308 of water from the cross-connection pipe PP into the standpipe 270 (and hence, functionally the valve of FIG. 10 valves flow through the cross-connection pipe PP as shown in the functional diagram of FIG. 9). If the cross-connection pipe PP and float valve 300 in its fully open position have sufficiently high flow rate, then the water level in the standpipe 270 of the system of FIG. 9 after falling below depth d1 is pinned to the elevation of the float 302, which can be made precise by limiting the maximum travel stroke of the float 302 by suitable mechanical stops. The pinning of the water level at the level of the float 302 is obtained because as the water level in the standpipe 370 rises above the level of the float 302 this closes the float valve 300 resulting in rapid draining of the standpipe 370 via injection line 66 until the water level falls back to the float level. Similarly, if the water level in the standpipe 370 falls below the level of the float 302 this opens the float valve 300 which allows rapid inflow of water from the RWST 312 (assuming low flow resistance) until the water level in the standpipe 370 rises to lift the float 302 and close the float valve 300. This pinning of the water level to the float level assumes the cross-connection pipe PP and valve 300 are designed for high flow rate, which reduces the likelihood of clogging due to debris or the like. By contrast, the water level in the standpipe in the embodiments of FIGS. 4-5 and of FIG. 8 is determined by both the elevations of the orifices O0, O1, O2 or the pipes P0, P1, P2, and by the flow resistances presented by these orifices or pipes. Those flow resistances cannot be made too low, otherwise the water level in the standpipe will closely track the water level in the RWST. The ECC system of FIG. 9 is a two-level system. However, a three-level ECC system can be provided by adding an additional float valve-controlled cross-connection pipe with its float at an elevation (i.e. depth) between the elevations of the topmost cross-connection pipe P0 and the float 302. A four-level or higher-level ECC system can be similarly constructed by adding additional pipe/float valve combinations for the different levels. At each level of the ECC system, the water level in the standpipe is pinned to the elevation of the highest-elevation float that lies below the current water level in the RWST. A float valve is feasible for this application because total head on the valve is typically relatively low (e.g., of order 20 psi in some contemplated embodiments) and low leakage rates through the float valve are acceptable when the float valve is closed. Water temperature is expected to remain below 250° F. making the float 302 relatively easy to design. For example, in some contemplated embodiments the float 302 comprises a closed-cell foam material disposed in a stainless steel liner. Such a flow advantageously is not susceptible to failure by float rupture. The float valve 300 is advantageously a passive device that obtains its operating power from the fluid (i.e. water) being controlled. Redundancy can be provided by including more than one standpipe 270, optionally with multiple redundant float valves in each standpipe (where two float valves are redundant if their floats are at the same elevation). With reference to FIG. 11, the use of a float valve to control flow can also be employed with internal standpipes 370 located inside of an RWST 312. In this case the inlets to the float valves 300 can be open to the ambient water in the RWST 312, i.e. there is no need for the pipe PP of the embodiment of FIGS. 9 and 10. Additionally, in this embodiment the functionality of the topmost cross-connection pipe P0 can be obtained by constructing the standpipes 370 with open top ends at the elevation corresponding to the elevation of the pipe P0. The illustrative ECC system of FIG. 11 is a two-level system similar to that of FIG. 9; however, FIG. 11 illustrates use of two float valves 300 in a single standpipe 370 so as to provide advantageous redundancy. Further redundancy is provided in the embodiment of FIG. 11 by partitioning the RWST 312 into two compartments, with a standpipe 370 in each section of the RWST 312. In an alternate design, the illustrated two standpipes 370 can be located in the same RWST without partitioning the RWST into multiple compartments. The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
059616792	description	DETAILED DESCRIPTION OF THE INVENTION The first set of steps, which converts waste feeds into a B.sub.2 O.sub.3 fusion melt inside a glass melter, can be operated as a batch, semibatch, or continuous process. The initial condition for the process is a glass melter filled with a special molten oxidation-dissolution (lead borate) glass, which preferably has a composition of two or more moles of lead oxide (PbO) per mole of B.sub.2 O.sub.3. The B.sub.2 O.sub.3 fusion-melt operations have three steps: (1) feed oxidation, dehalogenation, and oxide dissolution; (2) PbO removal; and (3) lead oxidation. These operations can be carried out sequentially in either a single vessel or in separate process vessels. The process is best described with reference to FIG. 1, which shows a preferred embodiment of the invention. A. Oxidation, Dehalogenation, and Oxide Dissolution of Feed Material Lead oxide and boron oxide are added to the melter to form a dissolution glass. Nuclear waste feeds are added directly to the melter. The ceramic and amorphous components in the feed that are exposed to the molten glass rapidly dissolve into the glass. Molten glasses will generally dissolve most oxides, but the glasses do not dissolve metals or organic material (organics). To dissolve these latter components into the glass, metals and organics must first be oxidized. The PbO in the glass is a strong oxidizing agent and oxidation occurs in situ within the glass melter. If the feed contains organics, the organics are oxidized to CO.sub.2, possibly CO, and steam (H.sub.2 O), and the by-product lead metal sinks to the bottom of the melter. The CO.sub.2, CO and steam exit the melter via the off-gas system. Metals (excluding the noble metals) are oxidized by the PbO in the glass to metal oxides and, subsequently, dissolve into the glass. The lead by-product then sinks to the bottom of the melter. Typical chemical reactions are: 2Al+3PbO.fwdarw.Al.sub.2 O.sub.3 +3Pb.arrow-down dbl. PA1 Pu+2PbO.fwdarw.PuO.sub.2 +2Pb.arrow-down dbl. PA1 C+2PbO.fwdarw.CO.sub.2 .arrow-down dbl.+2Pb.arrow-down dbl. PA1 Zr+2PbO.fwdarw.ZrO.sub.2 +2Pb.arrow-down dbl. PA1 (1) The borate fusion melt is highly soluble in acid. As the B.sub.2 O.sub.3 matrix dissolves, oxides that are soluble in nitric acid dissolve. PA1 (2) The lead-borate oxidation step destroys troubling organics and converts metals to oxides. Thus, the lead-borate processing avoids the need to use some of the nitric acid to oxidize the incoming feed materials to produce oxidized materials that are soluble in the nitric acid. For example, uranium must be fully oxidized to the +6 valence state to be highly soluble in nitric acid. Because oxidation of feeds with nitric acid usually generates large quantities of nitrogen oxides as a by-product, the pretreatment provided by the invention also reduces the size and complexity of the dissolver off-gas system. PA1 (3) The borate fusion melt process further reduces the amount of gas generated by the dissolver off-gas system because volatile materials that would have been released in the acid dissolver are released earlier during the lead-borate dissolution process. When processing spent nuclear fuels (SNF), these volatile materials include tritiated water, xenon, and krypton. PA1 (4) The borate fusion melt dehalogenation step eliminates troublesome halogens. These can interfere with separations and complicate engineering. Halogens mixed with nitric acid are highly corrosive and thus create major problems in terms of equipment corrosion. PA1 (1) The process recycles PbO and excess B.sub.2 O.sub.3 within the process. This feature minimizes final waste volumes and waste quantities. PA1 (2) The process converts some metal components in some feeds into inert, nitric-acid-washed oxides with minimum volumes and mass that are acceptable waste forms. Separation into a clean oxide minimizes the total volume and mass of this waste. The dissolution glass also oxidizes sulfur-containing components to sulfur oxides that exit via the off-gas system. It is to be understood that the dissolution glass of the invention oxidizes everything in the molten mixture except the noble metals. Rapid oxidation and dissolution are the results of the special characteristics of the PbO:B.sub.2 O.sub.3 dissolution glass. At operating temperatures (700-900.degree. C.), the PbO is a powerful oxidizer. However, some metals and other materials form protective oxide coatings. The B.sub.2 O.sub.3 is an effective dissolution agent for oxides. It is used in many welding fluxes and analytical procedures for rapid dissolution of oxides. The combination of the PbO and B.sub.2 O.sub.3 creates the oxidation-dissolution capabilities of this molten glass. The 2PbO:B.sub.2 O.sub.3 glass composition is chosen to maximize chemical reaction rates and maximize solubility of oxides in the melt. B. Separation of Halogens from Feed Materials in the Molten Dissolution Glass The process separates halogens within the feed during feed dissolution. Using as an example a feed containing chlorides, in the dissolution glass, chlorides in the feed will react with the PbO and form lead chlorides (PbCl.sub.2), which are volatile gases at glass melter temperatures and exit to the aqueous sodium hydroxide (NaOH) scrubber. In the scrubber, the PbCl.sub.2 reacts with the NaOH to yield insoluble lead hydroxide Pb(OH).sub.2 ! and soluble NaCl salt. The insoluble Pb(OH).sub.2 is recycled back to the melter, wherein it decomposes to PbO and steam. The aqueous NaCl stream is cleaned and discharged as a chemical waste. Other halogen-containing feeds behave similarly. The PbO should be present in at least a stoichiometric amount with respect to the halogens to achieve adequate removal of the halogens. C. Removal of Noble Metals from the Molten Dissolution Glass The noble metals are not oxidized by the PbO. During feed dissolution, the noble metals separate from the glass and dissolve into the lead metal. Noble metals are not soluble in glass but they are highly soluble in lead metal. The noble metals sink to the bottom of the melter in the lead. The noble metals can be separated from the lead by vacuum distillation of the lead or by several other demonstrated processes. Significant quantities of noble metals are found in some lead ores in which the noble metals remain with the lead metal during smelting operations. Consequently, multiple processes for noble metal separation from lead have been developed and deployed. D. Conversion of Molten Dissolution Glass to Borate Fusion Melt Carbon is added to the dissolution glass. This may be done in the same melter, or the xPbO:B.sub.2 O.sub.3 fusion melt (devoid of halogens) may be removed to a separate melter where carbon is then added. Carbon reduces the PbO to lead metal while gaseous CO.sub.2 is produced. All of the PbO is removed from the dissolution glass to produce a B.sub.2 O.sub.3 fusion melt, comprising metal oxides dissolved in B.sub.2 O.sub.3. During this step, it may be necessary to supply additional B.sub.2 O.sub.3, depending upon the feed material, to keep all materials in solution. The solubility limits of certain elements in the B.sub.2 O.sub.3 --PbO dissolution glass may be higher than in just the B.sub.2 O.sub.3 without the PbO. E. Reoxidation of the lead to PbO by Addition of Oxygen Lead is an oxygen carrier in the dissolution process. Oxygen is injected into the molten lead recovered from the lead-borate dissolution step and recovered from the conversion of the dissolution glass to a B.sub.2 O.sub.3 -fusion melt, as can be seen in FIG. 1. Lead is oxidized to PbO. The oxidation reaction is: EQU 2 Pb+O.sub.2 .fwdarw.2PbO The PbO is recycled and used to make the next batch of lead-borate dissolution glass. The option exists to oxidize the lead in the melter by adding O.sub.2 to the melter after removing the B.sub.2 O.sub.3 fusion melt. Because of the corrosive characteristics of the initial dissolution glass during the conversion of feeds to a B.sub.2 O.sub.3 fusion melt, these steps in the process are best carried out in a cold-wall melter in which cooling jackets in the walls produce a "skull" of solidified material that protects the walls from the contents of the melter. The melter(s) can be heated by fossil, induction, plasma arc, or electron-beam systems. Such systems are currently used to melt high-temperature materials (e.g., titanium and superalloys) and produce specialty glasses. F. Removal of B.sub.2 O.sub.3 Fusion Melt The resultant B.sub.2 O.sub.3 fusion melt is poured from the furnace and preferably allowed to solidify before the glassy B.sub.2 O.sub.3 solid is fed to the separations step. Formation of crystalline compounds during solidification is to be avoided because of their slower dissolution rates in nitric acid. The solubility of various oxides in B.sub.2 O.sub.3 -fusion melts is strongly dependent upon the temperature of the melt. With rapid cooling of the melt, higher loadings of oxides can remain dissolved in the B.sub.2 O.sub.3 while forming a solid glassy B.sub.2 O.sub.3 structure. This approach minimizes the B.sub.2 O.sub.3 in the solid and reduces the volume of feed sent to the separations step. With current technology used in research reactor fuel fabrication, the option exists for rapid cooling (up to 10.sup.6 K/sec) and atomization of melts with uniform particles with sizes as small as 50 to 100 microns. G. Recovery of Uranium, Plutonium and Rare Earth Elements Processing of the radioactive waste feed material into a B.sub.2 O.sub.3 fusion melt creates a solid, oxide feed that is optimized for recovering uranium, plutonium, and other elements when using acid-based separation processes such as PUREX and ion exchange. In the process of the invention, the boron oxide fusion melt is solidified, and then dissolved in nitric acid. Prior to the dissolving, boron oxide may be recovered from the fusion melt and recycled back to the glass melter to go into the dissolution glass/waste mixture. After dissolution of the fusion melt in nitric acid, rare earth elements, U, and Pu are recovered from the acid solution by one of several processes such as PUREX or ion exchange. H. Vitrification and Recycle of Boron Oxide The nitric acid-boric acid waste stream resulting after the separation of U, Pu, and rare earths is converted to a waste glass, e.g., borosilicate waste glass, using the traditional vitrification processes. The waste stream is fed to a glass melter simultaneously with glass frit (primarily SiO.sub.2). The nitrates are decomposed to oxides and then converted to glass. This is the standard industrial process for conversion of nitric acid wastes into a high quality waste glass. In some cases, there may be excess B.sub.2 O.sub.3 in the nitric acid-boric acid waste stream. In that event there are three options: 1) Direct Conversion to Glass The waste can be converted to glass using added glass frit to dilute the excess B.sub.2 O.sub.3 in the waste stream. 2) Mixing with Other Wastes The waste steam can be fed to a glass melter along with other waste streams. The nitric acid stream from the acid-borate dissolution step provides the necessary B.sub.2 O.sub.3 to make borosilicate glass for both waste streams. In contrast, the traditional nitric acid separation processes creates waste streams with no B.sub.2 O.sub.3 ; hence, B.sub.2 O.sub.3 must be added to these waste streams when they are being converted to borosilicate glass. In the United States, there are large facilities to convert nitrate wastes in storage (primarily high-level radioactive wastes) to glass for disposal. These facilities are likely sites for deployment of this invention to process miscellaneous wastes. At such sites, the quantities of nitric acid wastes from processing miscellaneous wastes would be small compared to nitrate wastes that are currently being converted to glass. The B.sub.2 O.sub.3 -rich nitric acid wastes could be simultaneously converted to glass along with existing wastes, and the B.sub.2 O.sub.3 -rich acid waste could provide some of the needed B.sub.2 O.sub.3 for the glass-conversion step. 3) Separation of B.sub.2 O.sub.3 From Waste Stream The B.sub.2 O.sub.3 can be separated from the acid waste stream, after removal of the U, Pu and/or rare earths, and recycled back to the front of the process. There are several options for separation of B.sub.2 O.sub.3 depending upon the purity desired for the B.sub.2 O.sub.3. The commercial borate industry has various separation techniques. In addition, borates are used in pressurized water reactors as a soluble neutron absorber. Multiple technologies have been developed to recover borates from the reactor aqueous coolant. System Configuration and Equipment The B.sub.2 O.sub.3 fusion-melt process steps can be configured as batch, semibatch, or continuous operation. The preferred option will depend upon the scale of operation and other factors. In a batch operation all of the major steps (except off-gas processing) are performed in a single vessel in a sequence of four steps over a period of time. At the start of the process, B.sub.2 O.sub.3 and PbO are added to the melter to form a dissolution glass. As waste feed is added to the melter, feed oxidation, dehalogenation, and oxide dissolution simultaneously occur in the molten mixture with buildup of lead metal at the bottom of the melter. After feed dissolution, carbon is added for conversion of the dissolution glass to a B.sub.2 O.sub.3 fusion melt. The B.sub.2 O.sub.3 fusion melt is poured from the melter and the molten lead metal is left in the bottom of the melter. The solidified B.sub.2 O.sub.3 fusion melt is sent to the separations process. A new batch of dissolution glass is made in the melter by oxidizing the lead metal with O.sub.2 and adding B.sub.2 O.sub.3 to the melter. The cycle is then repeated. There is off-line recovery of any noble metals that build up in the lead over time. In a semibatch or continuous operation, the lead metal is drained from the melter as it is produced and it is reoxidized off-line. FIG. 2 shows a schematic drawing of a vessel used for a continuous process. There are also continuous process options for large-scale operations. The separations and vitrification steps use existing equipment designs. The B.sub.2 O.sub.3 fusion melt step is preferably carried out in a cold-wall melter because of the corrosive characteristics of the initial dissolution glass. The dissolution glass will dissolve all materials except noble metals and the molten lead will dissolve noble metals. Cold-wall melters have cooling jackets in the wall to produce a "skull" of solidified material that protects the wall from the melter contents. Cold-wall melters are used industrially to melt high-temperature materials (e.g., titanium and superalloys) and to produce ultrapure materials (e.g., glass for fiber optics). Russia, France, and the United States are modifying such equipment for processing various radioactive wastes. Batch size may be as large as hundreds of kilograms for miscellaneous fissile materials (MFMs) with low fissile material concentrations. In Europe, cold-wall melters are currently being developed for throughputs of up to 800 kg/h. There are multiple heating methods available, known to those of skill in the art. The process of the invention produces a boron oxide fusion melt which provides a superior feed material to be used in an aqueous separations process, particularly to recover U, Pu, and rare earths from radioactive waste, industrial or other wastes. Some of the advantages of the process are: Further advantages include the minimization of waste generation. Some of the features which accomplish this are: Additionally, the process of the invention has the capability to recover key elements from the waste or convert the waste directly into borosilicate glass. The initial process steps produce a lead-borate dissolution glass. From this dissolution glass, a boron oxide fusion melt is produced that, in turn, allows recovery of valuable elements. Alternatively, the lead-borate dissolution glass can be turned into a borosilicate waste glass for direct disposal of the material as shown in FIG. 1 (the alternative end point). For some wastes, it will not be clear whether recovery of selected elements is required for waste management and/or is economically viable. Some feeds are complex, heterogeneous mixtures that are difficult and expensive to analyze. After such feeds are converted to a homogeneous lead-borate dissolution glass, simple analytical tests can determine the concentration of valuable elements in the glass. At such time, a decision can be made as to whether recovery of valuable elements is economically worthwhile. While preferred embodiments of the present invention have been illustrated and described, it will be understood that changes and modifications can be made therein without departing from the invention in broader aspects. Various features of the invention are defined in the following claims.
	description	The present application claims priority to U.S. Provisional Application No. 61/046,007, which is hereby incorporated by reference in its entirety. Collimators are used to focus energy and in some embodiments X-rays, UV light, infrared light, and visible light. Additionally gamma radiation or other energy sources can also be collimated. Previous collimators have only been able to collimate energy sources using channels or grooves, whose dimensions are in the millimeter range. Examples of collimators, whose design was such that the width of the irradiated strips was in the millimeter range are found in U.S. Pat. Nos. 1,476,048 and 5,771,270. Accordingly, there is still a need for collimators whose collimation channels are in the submicrometer range or in the micrometer range to produce energy fields in the submicrometer range or in the micrometer range. The present invention fulfills this need as well as others. In some embodiments, the present invention is directed to a collimator, a collimator holder and uses thereof including, but not limited to, apparatuses that include one or both components. In some embodiments the present invention comprises a collimator and/or a collimator holder. A collimator collimates an X-ray beam so that its width can be limited, which in some embodiments the width is limited to the micrometer range. In some embodiments, the collimator holder holds the collimator and optionally includes an alignment apparatus and specimen holder to align the collimator to the X-ray beam and to hold the specimen, respectively. In some embodiments, the present invention provides a collimator comprising at least one plate, wherein the plate comprises at least one groove, wherein the groove has a dimension that is in the submicrometer to micrometer range. In some embodiments the collimator can be used to allow a specimen to be exposed to an X-ray field or fields, wherein the X-ray field or fields smallest dimension is in the submicrometer to micrometer range. In some embodiments, the present invention provides an apparatus comprising a collimator holder and a collimator as described herein. The collimator works on the principle of differential X-ray absorption. As X-rays travel through matter, their intensity is attenuated by a negative exponential coefficient. Different materials have different attenuation coefficients making it possible to create X-ray masks by combining them. The X-ray collimator described herein provides just such an X-ray contrast in order to collimate X-rays into patterns with micron and even sub-micron dimensions. The collimator is designed, for example, for stripe irradiations, through stripe length and width may vary with application. Thus, in some embodiments, the collimator comprises a stack of flat x-ray absorbing chips, and some type of controlled spacer to separate them—producing paths along which x-rays can travel through the collimator stack. In some embodiments, the collimator comprises a stack of chips cut from standard Si, gallenium arsenide, and the like wafers used in microfabrication. The X-rays travel length-wise down the stack along the planes of contact between the chips. X-ray contrast is provided by at least one groove running the length of the top of each chip. As the top side of one chip is placed against the bottom of another chip within the stack, the grooves provide channels for X-rays to pass unimpeded along the length of the stack. X-rays not aligned with the grooves are absorbed by the Si, gallenium arsenide, and the like chips resulting in collimation. The wafers can be polished on both sides so as to provide smooth surfaces for stacking and close contact. One example of such a collimator and how it can work in some embodiments is shown in FIG. 1. The collimator can be constructed using any method that enables one to construct a collimator with grooves or channels in the submicrometer or micrometer range. In some embodiments the chips, which can be for example, but not limited to, Si chips, gallenium arsenide chips, and the like chips, used in the collimator are fabricated using standard microfabrication methods. In some embodiments, fabrication involves three steps: 1) Photolithography 2) Etching & 3) Dicing. For example, in photolithography a polymer mask is photodefined into long strips on a Si wafer or a wafer made up of another material, such as gallenium arsenide and the like. The regions covered by the polymer will be protected from etching and will form ridges. The uncovered regions will be exposed to etching and will form the grooves. A complete layer of polymer is applied to the underside of the wafer to protect that surface during etching. For example, in etching, the exposed surface of the wafer is attacked by chemical and/or physical means. The material is removed creating grooves. The depth of a groove and a channels that is formed when two chips are stacked (and hence the X-ray collimator line width) is defined by the amount of material etched. In some embodiments, the chips are coated with layers of Si02 or SiN by chemical vapor deposition (CVD). There are four advantages to using this technique. Firstly, these materials all have similar X-ray absorption coefficients. Second, CVD 10 processes produce thin films with a high degree of control over thickness ranging from tens of nanometers to several microns, and a high level of uniformity over a wafer's surface permitting many viable chips to be cut from one wafer. Thirdly, many etching systems exist offering a high degree of selectivity of Si02 or SiN over Si or gallenium arsenide resulting in groove-depth being controlled by film thickness rather than etching parameters. Finally, as CVD involves a gradual reaction of the Si or gallenium arsenide wafer itself the resulting films (the ridges and backsides of chips) and bottoms of the grooves (where the films are removed to expose Si or gallenium arsenide) are very smooth—ensuring good edge contrast within the collimator. The grooves can also be made by direct etching the surface of the Si or gallenium arsenide wafers themselves. For example, in dicing, the wafer can be sectioned into chips by sawing. In some embodiments, chips can be 1 to 2 cm wide and 1 to 2 cm high. However, the chips can be made in nearly any dimensions provided the chips will fit on a Si or gallenium arsenide wafer and are large enough to be diced and assembled. Following dicing, the chips can be inspected and any showing defects which might interfere with the function of the collimator can be removed. The remaining polymer from the protective photomask can then be removed by an organic solvent. The chips can be rinsed in a weaker solvent and then sonicated in de-ionized water to remove residual solvent and dust particles. The chips can be dried under an N2 stream, cleaned by an oxygen plasma, and then can be finally be assembled in the collimator holder. The collimators can be produced from double-side polished 4″ (100 mm) diameter Si wafers or other wafers, such as gallenium arsenide, though nearly any microfabrication-compatible substrates can be used. The wafers can be 380 μm thick with a variance of ±10 μm. The thickness of the CVD films (when used) defines the groove depth (and hence X-ray collimator linewidth) and can be between 500 nm and 10 μm or, in some embodiments, up to and including 50 μm. This thickness can be varied over a large range, for example, from 10's of nanometers to several tens of microns if desired. When direct etching of the wafer is used to produce the grooves instead of etching a CVD layer, the grooves can be made 10's of nanometers to hundreds of micrometers in depth. The groove width defines the collimator line length. In some embodiments, the groove width is not less than 50 μm to ensure a good probability of cutting across an entire cell spread on a surface (and irradiating its nucleus). The groove width can also be greater than 50 μm, including, but not limited to up to and including 3 mm wide. In some embodiments, the groove width can be 50-100, 50-500, 50-1000, 50-2000, or 50-3000 μm. Larger groove widths can leave the chips more prone to bending/deflection once subjected to a packing force inside the collimator holder. A greater number of ridges on a chip can reduce this bending but would require smaller groove widths. The dimensions of the final Si or gallium arsenide chips are defined by the dimensions of the collimator holder. In some embodiments, chips of 1 cm width and 1 or 2 cm length have been used quite conveniently, however they can be made in nearly any size. In addition to the sacrificial thin-film or direct etching methods presented above, there are various other ways by which collimators can be fabricated. Regarding the chips, nearly any x-ray absorbing material can be used so long as it is mechanically stable enough to be clamped. In some embodiments, the chips are those with uniform thickness and very flat surfaces. In addition to the chips presented here, other common semiconductor materials can be used for collimator because they actually attenuate x-rays to a higher degree than Si and can be micromachined as well. This includes, but is not limited to, the III-V semiconductors as well as other x-ray absorbing semiconducting compounds, such as, but not limited to, In, Ga, Ge, or combinations thereof. One such example is also, but not limited, to gallenium arsenide. These compounds are commonly used in microelectronics components specifically for x-ray applications (such as dosimeters and x-ray photography) for this very reason. Other materials which might conceivably be used as x-ray attenuating chips include ceramics and metallic plates though once again provided that they can be fabricated with a uniform thickness and possess uniform surfaces. In some embodiments, there are two methods of producing spacers for the collimators: additive and subtractive processes. In subtractive processes, material is removed from either a sacrificial layer or from the x-ray attenuating chips themselves by various means. As described above, the etching of grooves into thin-films (Si02 or SiN) used as sacrificial layers on the wafers and the etching of grooves into native surface, such as Si or gallenium arsenide. In addition to etching, other means of micromachining could also be used to produce grooves along which x-rays can travel. These include, but are not limited to, laser machining (laser ablation) and conventional machining—for which a series of controlled cuts would be made along the surfaces of the x-ray attenuators to serve as grooves. In additive processes, a spacer is basically built onto the x-ray attenuating chips and they are once again stacked. An example of such a process can be to use photoresist to structure spacers on one side of the chips. In this case, these polymeric spacers (ridges) are substantially transparent to x-rays as compared to the attenuating chips meaning that x-rays would be permitted to pass along the entire planes between the chips in the stack with minimal attenuation. In some embodiments, the collimator described herein can be used to collimate X-rays, it can also be used to collimate other energy waves, including, for example, UV, visible and infrared light waves. Changes in the energy waves collimated may require changes in dimensions and materials used. As described above, in some embodiments the collimator comprises silicon wafers with grooves, whose depth matches the desired width of the X-ray beam. The collimator is assembled by stacking silicon wafers and holding them against each other under pressure. In some embodiments, the collimator holder comprises two plates, which can be made out of, but not limited to, stainless steel or strong plastic or other suitable material) with the silicon wafers stacked between them. In some embodiments, the two plates can be incorporated within a larger holder that allows pressure to be exerted on the stack of silicon wafers using either screws or springs. By exerting pressure, one avoids the presence of air gaps between the silicon wafers and thus ensures that the width of the collimated X-ray beam corresponds to the depth of the grooves on the silicon wafers. In some embodiments, to ensure that no dust is trapped between the wafers (which would prevent the wafers from coming in close contact with each other) the silicon wafers can optionally be assembled into the holder, while being submerged in deionized water or ethanol. The pattern of the collimated X-ray beam will depend on the patterns present in the silicon wafers that are assembled to form the collimator. The design of the collimator can, for example, place constraints on the patterns that can be generated. However, in some embodiments, the range of patterns can be enhanced by irradiating the specimen, then moving the specimen in a specified way and irradiating it again. For example, the specimen can be irradiated once, then rotated by 90 degrees and then irradiated again, thus creating cross-like patterns. Alternatively the specimen may be translated by a few microns (for example, by 100 microns), creating patterns that are more dense than the patterns that can be achieved with 380 micron-thick silicon wafers. The dimensions of the silicon wafers and the dimensions of the depressions on their surface can make it difficult to align the collimator to the X-ray beam. For example, in some embodiments for wafers that are 2 cm high and have grooves that are 1 micrometer deep, the X-rays beams that can penetrate the collimator without being obstructed must conform to an angle range of approximately 0.0056 degrees (See FIG. 2). If the X-ray beam that was being collimated consisted of X-rays that were entirely parallel to each other, then the collimator with the dimensions of the embodiment described above (2 cm high wafers with 1 micrometer deep grooves) would have to be aligned to the X-ray beam with an accuracy of ±0.0056 degrees, which can be difficult. X-rays emitted by most X-ray sources are not entirely parallel and this provides some leeway in the alignment of the collimator to the X-ray source. Nevertheless, the leeway may not be great and for this purpose the collimator holder can, optionally, incorporate an alignment apparatus. There are many possible embodiments for alignment apparatuses. The basic principle is to allow the collimator holder to rotate along an axis that is perpendicular to the X-ray beam axis and also perpendicular to the shortest edge of the depression pattern in the silicon wafers (i.e. perpendicular to the depth of the groove). The rotation axis may pass through the center of the collimator or through its bottom edge or through other positions in space. In some embodiments, if the specimen to be irradiated is attached to the collimator holder and rotates with it, then the position of the rotation axis is not critical. In some embodiments, the rotation axis can be at the center of the X-ray beam, so that the distance of the collimator to the X-ray source does not change during alignment. In some embodiments, the collimator can be rotated manually or remotely using a motor. In either case, the collimator can be rotated until the dose rate of X-rays passing through the collimator, which can be measured with an X-ray dosimeter, is maximized. In some embodiments, another possibility that essentially eliminates the need for adjustment is to use the motorized version of the alignment apparatus and program a slow rotation of the collimator over an angle range from about −2 degrees to about +2 degrees relative to the X-ray beam. This ensures that the correct alignment of the collimator relative to the X-ray beam is attained at some point during the rotation. Accordingly, the X-ray dose that the specimen receives can be controlled by varying the speed of rotation with slower rotation speeds leading to higher X-ray doses. In some embodiments, the collimator holder can also optionally incorporate a specimen holder. If the alignment apparatus described above is also incorporated, then the specimen holder can rotate together with the collimator holder to ensure that the collimated X-rays always target the same area of the specimen during its rotation. In some embodiments, the specimen can be positioned to be as close as to the collimator as possible. However, because the X-rays passing through the collimator are essentially parallel to each other (with a divergence angle of about 0.0056 degrees for a collimator consisting of wafers that are 2 cm high and have 1 micrometer deep depressions), the specimen, in some embodiments, can be positioned at a distance of a few mm from the edge of the collimator. The design of the specimen holder will of course have to take into consideration the specimen that will be irradiated. In some embodiments, a microcollimator holder that includes a motorized alignment apparatus and a specimen holder is shown in FIG. 3 and FIG. 4. This example should not be considered limiting, since many different designs that achieve the same goals are possible. In some embodiments, the present invention provides for a collimator allowing a specimen to be exposed to an X-ray field, wherein the X-ray field is in the submicrometer to micrometer range, wherein said collimator is comprised of at least 2 plates made of X-ray absorbing material that are stacked against each other and wherein said plates have one or more grooves on their surfaces, through which X-rays can penetrate to produce the X-ray field or fields, whose smallest dimension is in the submicrometer to micrometer range. In some embodiments, the present invention provides a collimator for exposing a specimen to an X-ray field, wherein the X-ray field is in the submicrometer to micrometer range. In some embodiments, the collimator comprises a first structure and a second structure. In some embodiments, the structure is a plate. The shape of the plate can be any shape that allows the grooves to come in contact with a planar surface of another structure to form a channel. For example, the shape of the structure can be, but is not limited to a square, rectangular, circular, oval, hexagon, pentagon, or any other suitable geometric shape, and the like. In some embodiments, the collimator comprises a first plate having a first planar surface and a second planar surface, wherein the first planar surface comprises one or more grooves. In some embodiments, the collimator comprises a second plate having a first planar surface and a second planar surface, wherein the first planar surface on the second plate optionally comprises one or more grooves. In some embodiments, the present invention provides for a collimator wherein the first planar surface of the first plate is in contact with the second planar surface of the second plate such that the second plate covers over the one or more grooves on first plate. In some embodiments, the collimator comprises more than two structures, such as, but not limited to 3, 4, 5, 6, 7, 8, 9, or 10. In some embodiments, the collimator comprises less than 20 structures. In some embodiments, the structures that can be used in the collimator comprise a first planar and a second planar surface, wherein the first planar surface can comprise one or more grooves. In some embodiments, the structures are in contact with one another where the edges of the structures are flush or blunt with one another. In some embodiments, the structures in contact with one another are not flush or blunt with one another, wherein the edge of one plate overhangs the edge of another structure. In some embodiments, the collimator comprises plates through which X-rays 30 can penetrate to produce a X-ray field or fields, wherein plate comprises a groove having a smallest dimension that is in the submicrometer to micrometer range. In some embodiments, the plates comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1-10, I-20, 1-30 grooves. In some embodiments, the plates comprises less than 10 grooves. In some embodiments, the grooves are or are about 0.5-100, 0.5-50, 0.5-10, 0.5-2, 2-10, 2-50, 0.5, 1, 2, 10, or 50 micrometers in depth. In some embodiments, the grooves are or are about 0.5 micrometers to 3 millimeters in width. In some embodiments, however, the depth is the smaller than the width and in some embodiments, the width is smaller than the depth. In some embodiments, the channel or groove is perpendicular to one edge and/or parallel to another. In some embodiments, the channel or groove is straight. In some embodiments, the grooves are continuous through the structure such that when a channel is formed the channel extends through the structure and the channel is open on both ends. The length of the channel can be any length allowing for the collimation of the energy or light source as described herein. In some embodiments, the length of the channel is about 1-2 centimeters long, but can also be about 0.5 to 5 centimeters in length. In some embodiments, the collimator produces an X-ray field that is or is about 0.5-50 micrometers in one dimension and 0.5 micrometers to 3 millimeters in a second dimension. In some embodiments, the collimator produces an X-ray field that is or is about 0.5-10 micrometers in one dimension and 0.5 micrometers to 3 millimeters in a second dimension. In some embodiments, the collimator produces an X-ray field that is or is about 0.5-2 micrometers in one dimension and 0.5 micrometers to 3 millimeters in a second dimension. In some embodiments, when one or more plates are stacked the grooves will form a channel when contacted with a second plate that has a smooth surface. In some embodiments, the channels are or are about 0.5-50, 0.5-10, 0.5-2 micrometers in depth. In some embodiments, the channels are or are about 0.5 micrometers to 3 millimeters in width. In some embodiments, the collimator comprises or comprises at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 channels. In some embodiments, the collimator comprises or comprises about 1-10, 1-20, 1-30, 1-50 channels. In some embodiments, the collimator comprises at least 1 channel but not more than or not more than about 100, 200, or 300 channels. In some embodiments, the collimator comprises plates that are 1-230 centimeters long and/or 1-2 centimeter wide and/or 25-400 micrometers thick. In some embodiments, the said X-ray absorbing material is Silicon. In some embodiments, the X-ray absorbing material is a semiconducting material (such as, but not limited to, In, Ga, or Ge), a ceramic material, a metallic material, a semi-metal, an alloy, a glass or combinations thereof. In some embodiments, the structures are made of S or gallenium arsenidei or other semiconducting material (such as, but not limited to, In, Ga, or Ge), a ceramic material, a metallic material, a semi-metal, an alloy, a glass or combinations thereof. In some embodiments, the plates are coated with a Si02 surface layer. In some embodiments, the plates coated with a Si02 surface layer are etched resulting in grooves, through which the X-rays penetrate through the collimator. In some embodiments, the collimator comprises more than one plate with at least one groove and are stacked against each other to produce multiple X-ray fields. In some embodiments the collimator comprises or comprises about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 plates with at least one groove each. In some embodiments the collimator comprises 1-10, 1-20, 1-30, 1-100 plates with at least one groove each. In some embodiments, the present invention provides for an apparatus comprising a collimator holder and a collimator, wherein the holder comprises a first holder plate and a second holder plate. In some embodiments, the apparatus comprises a specimen holder. In some embodiments, the apparatus comprises a third and fourth holder plates that can exert pressure on the first and second plate so that the collimator can be put under pressure In some embodiments, the apparatus comprises an alignment apparatus. In some embodiments, the alignment apparatus rotates the holder along an axis that is perpendicular to an X-ray beam axis. In some embodiments, the alignment apparatus rotates the holder perpendicular to the shortest edge of the produced X-ray field. In some embodiments, the alignment apparatus comprises a motor. In some embodiments, the apparatus comprises an X-ray source, UV-source, infrared source, visible light source, or other radiation or light source. To demonstrate whether the collimator would perform as expected, we cultured human U20S osteosarcoma cells on a 12 mm diameter coverslip. Once the cells were almost confluent, we placed the coverslip on the cell plate of the collimator holder and attached the entire collimator to the X-ray tube of the XRAD320 irradiator (manufactured by Precision X-Ray, Inc., North Branford, Conn., USA). The cells were irradiated with a voltage setting of 20,000 Volts and current setting of 25 milliAmps for a total exposure time of 5 minutes. During this time the collimator holder rotated over a range of 5 degrees at a speed of 1 degree per minute. During this rotation the X-rays would be aligned with the collimator, leading to exposure of the cells. Immediately after irradiation the cells were returned to the tissue culture incubator. They were fixed one hour later and processed for immunofluorescence to detect 53BP1, as previously described (Schultz L B, Chehab N H, Malikzay A, Halazonetis T D. p53 binding protein 1 (53BP1) is an early participant in the cellular response to DNA double-strand breaks. J. Cell Biol. 2000; 151: 1381-90). 53BP1 is a protein that gets recruited to sites of DNA double-strand breaks; its intracellular localization can therefore serve as a marker of irradiated stripes Indeed, the immunofluorescence analysis indicated the presence of an irradiated stripe about 2 micrometers wide (FIG. 5). The collimator used in this example contained Si chips coated with a 2 micrometer Si02 thin-film, which was etched to produce grooves that were 2 micrometers deep and 1 mm wide. Microfabrication was performed using the 3 steps described herein: photolithography, etching and dicing, resulting in Si chips with dimensions of 1 cm×2 cm×380 micrometers. About 25 such Si chips were stacked and placed in a holder. The holder was part of an apparatus that included a motorized alignment module and a cell holder. A diagram of the entire apparatus, including the collimator is shown in FIGS. 3 and 4. The disclosures of each and every patent, patent application, publication, and accession number cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention. The appended claims are intended to be construed to include all such embodiments and equivalent variations.
050705199	summary	FIELD AND BACKGROUND OF THE INVENTION The invention relates to radiography and particularly to equalized radiography which improves diagnostic capabilities by locally varying the radiation incident on the object to expose denser parts to more radiation and thereby to image all parts well despite limitations in the dynamic range and other characteristics of the imaging medium. More specifically, the invention pertains to selective equalization radiography which improves image quality by equalizing different fields of the image differently. A special case is exposing the lung field uniformly while equalizing other fields. In conventional radiography, image quality and diagnostic value can be compromised when the object x-ray transmission variations exceed the limits of the imaging medium. For example, a good x-ray image of the lung field typically leaves the mediastinum and retrocardiac areas underexposed; if those areas are exposed well, then the lung field is overexposed. Equalization radiography can overcome such problems and can improve image quality and diagnostic value by varying the local x-ray exposure to compensate for local variations in the object's x-ray transmission. Such radiography is discussed in the commonly assigned Wang European Patent Application No. 86308224.4 and Aitkenhead and Gershman U.S. patent application Ser. No. 07/525,498 filed on May 18, 1990, as well as in Plewes U.S. Pat. No. 4,773,087 and U.S. patent application Ser. No. 07/242,644 filed Sept. 13, 1988. See, also, U.S. Pat. Nos. 4,675,893, 4,715,056, 4,677,652, and 4,741,012. All of the documents cited in this paragraph are hereby incorporated by reference in this specification. Further background material concerning the subject can be found in the documents made of record in the patents and applications cited in this paragraph. In an exemplary equalization system, an x-ray fan shaped beam scans the patient and a modulator locally controls the x-rays before they reach the patient in order to modulate the radiation differently as between different sectors of the fan shaped and as between different stages of the scanning movement. The degree and kind of local modulation are under the conrol of a feedback circuit which locally measures the x-rays in the fan shaped exiting the object. The goal of this local, time varying modulation is to equalize the image by reducing the difference in exposure as between different areas at the image plane. The modulator can use a row of modulator elements which are individually and selectively movable into the x-ray beam to vary it locally such as by varying the local attenuation, the local beam cross-section, and/or the local exposure time of the x-rays impinging on the object. An earlier proposal is discussed in Plewes, D. B., Computer Assisted Exposure In Scanned Film Radiography, Proceedings International Workshop On Physics and Engineering In Medical Imaging, March, 1982, pages 79-86. This proposal states at page 82, in connection with FIGS. 5 and 8, that while equalization may be helpful for nodule detection it may be detrimental for looking at diseases manifested by diffuse opacifications and for such a case the system feedback could be adjusted to maintain low spatial frequency over the lung field alone. The proposal shows in FIG. 5 a relationship setting forth a "conventional image" for the lung field and shows the result of a related experiment in FIG. 8. Other parts of the citation might be relevant as well. While equalized radiography can provide significant improvement in image quality and diagnostic value, it can also introduce some image artifacts, as noted for example in Plewes, D. B. and Vogelstein, E., Exposure Artifacts in Raster Scanned Equalization Radiography, Med. Phys. Vol. 11. pp. 158-165 (1984) and in Vlasbloem, et al., RADIOLOGY, Vol. 169, pages 29-34 (October 1988). See, also, Plewes, D. B. et al., Maximizing Film Contrast For Scanning Equalization Radiography, Medical Physics, Vol. 17, No. 3, May/June 1990, pages 357-361, as well as the documents cited therein. SUMMARY OF THE INVENTION An object of the invention is to improve equalization radiography. A more specific object is to reduce image artifacts in selected fields such as the lung field. A still more specific object is to improve equalization radiography by identifying and exposing selected fields without equalization or under different equalization. In an exemplary and non-limiting embodiment of the invention, first a low-intensity beam of penetrating radiation scans the object to identify a selected field (e.g., the lung field) and to derive other information for a second scan. Then, a higher-intensity beam scans while being modulated in a desired manner outside the selected field. In the selected field, the beam exposes the object substantially uniformly. This equalizes the image where desired but delivers constant exposure where preferred. As an alternative, the selected field can also be equalized, but differently from other fields. More specifically, in an exemplary embodiment an x-ray source/modulator assembly generates a fan shaped beam which is thin in the vertical direction and wide in the horizontal direction. In a first scan, the beam is set at a constant low intensity and sweeps vertically across the object while a detector/film assembly measures the object-attenuated beam to determine how to set various parameters for a second scan. In the second scan, a higher intensity beam of the same general shape sweeps vertically. However, this time its sectors are selectively and individually modulated to vary locally the exposure delivered to the object in order to equalize the exposure delivered to the image plane everywhere except at a selected field such as the lung field. The same technique can be used in accordance with the invention while scanning similar beams horizontally rather than vertically or in some other orientation. The terms "object" and "patient" are used interchangeably in this specification because the invention applies to imaging patients by equalizing everywhere else except at a selected field as well as to imaging inanimate objects in a similar manner.
	description	The present invention relates to a radiation phase-contrast imaging device capable of imaging an internal structure of an object utilizing a phase-contrast of radiation transmitted through the object. Conventionally, various devices have been conceived as a radiation imaging device for imaging an internal structure of an object by making radiation transmit through the object. A commonly-used radiation imaging device is configured to image a radiation projection image by irradiating radiation to an object to make the radiation transmit through the object. In such a projection image, shading appears depending on the ease of permeation of radiation, which represents the internal structure of the object. With such a radiation imaging device, only objects having a property capable of absorbing radiation to some extent can be imaged. For example, soft biological tissues hardly absorb radiation. Even if it is tried to image such a tissue with a general device, nothing is reflected in the projection image. When trying to image the internal structure of an object that does not absorb radiation as described above, there is a theoretical limit in a general radiation imaging device. Under the circumstances, a radiation phase-contrast imaging device that images an internal structure of an object utilizing a phase-contrast of transmitted radiation has been proposed. Such a device is configured to image an internal structure of an object using Talbot interference. Talbot interference will be described. From the radiation source 53 shown in FIG. 26, phase-aligned radiation is irradiated. When making the radiation transmit through the phase grating 55 which is in a streak form, the image of the phase grating 55 appears on the projection surface which is apart from the phase grating 55 by a predetermined distance (Talbot distance). This image is called self-image. The self-image is not just a projection image of the phase grating 55. The self-image occurs only at the position where the projection surface is separated from the phase grating 55 by the Talbot distance. The self-image is configured by the interference fringes caused by interference of light. The reason that the self-image of the phase grating 55 appears at the Talbot distance is that the phase of radiation generated from the radiation source 53 is aligned. When the phase of radiation is disturbed, the self-image appearing at the Talbot distance is also disturbed. The radiation phase-contrast imaging device is configured to image an internal structure of an object utilizing the self-image disturbance. It is assumed that an object is placed between the radiation source and the phase grating 55. Since this object hardly absorbs radiation, most of the radiation incident on the object exits to the phase grating 55 side. The radiation has not passed through the object completely as it is. The phase of the radiation changes while passing through the object. The radiation exited the object passes through the phase grating 55 with the phase changed. The observation of the radiation on the projection plane arranged at the Talbot distance shows disturbances in the self-image of the phase grating 55. The degree of disturbances of the self-image represents the radiation phase change. The specific magnitude of the phase change of the radiation that transmitted through the object changes depends on where the radiation has transmitted through the object. If the object has a homogeneous configuration, the change of the radiation phase remains the same no matter where the radiation transmits through the object. In general, however, an object has some internal structure. When making radiation transmit through such an object, the phase change does not remain the same. Therefore, when the phase change is known, the internal structure of the object can be grasped. The phase change can be known by observing the self-image of the phase grating 55 at the Talbot distance. In such an apparatus, how to observe the self-image becomes a problem. The self-image has the same streak pattern as the pattern of the phase grating 55. The streak pattern needs to be considerably finer to the extent that Talbot interference occurs. It is technically extremely difficult to image such a very fine pattern. This is because a detector equipped with extremely small detection elements is required for the self-image detection. Therefore, in some conventional configurations, there are configurations that give up detecting the self-image itself with detectors. That is, in a conventional configuration, as shown in FIG. 27, another grating (absorption grating 57) is set on a detection surface of a detector. The absorption grating 57 has a streak structure similar to the phase grating 55. Therefore, the self-image incident on the absorption grating 57 interferes with the absorption grating 57 to generate a moire. This moire has a pattern in which dark lines are arranged, and since the pitch between the dark lines is large, imaging can be sufficiently performed even if the size of the detection element is large. By detecting this moire, the self-image can be obtained indirectly (see, for example, Patent Document 1). [Patent Document 1] International Patent Laid-Open Publication No. 2009104560 However, the conventional radiation phase-contrast imaging device has the following problems. That is, also in the conventional radiation phase-contrast imaging device, it is difficult to manufacture it. Even with the configuration in which the absorption grating 57 is placed on the detection surface of the detector, it is difficult to realize a radiation phase-contrast imaging device. In order to assuredly generate a moire, the absorption grating 57 is required to have a high absorption rate. The pitch of the phase grating 55 of the absorption grating 57 needs to be narrow enough to interfere with the self-image. It is extremely difficult to produce such absorption grating 57. In order to increase the absorption rate of the absorption grating 57, a certain thickness will be required for the absorption grating 57. When the absorption grating 57 becomes thicker, it becomes difficult to obtain the precision of the grating arrangement. When the moire is observed with an absorption grating 57 with poor precision, the moire becomes distorted due to the disturbance of the absorption grating 57, which adversely affects the imaging of the internal structure of the object. Therefore, if there is a method of directly detecting the self-image without relying on the absorption grating 57, it is preferable. However, if the configuration not equipped with the absorption grating 57 is applied as described above, there is no choice but to configure to detect the self-image itself. Since there is a limit to miniaturize the detection element of the detector, it is difficult to directly detect the self-image in the first place. Under the circumstances, it is required to configure such that a self-image imaging method does not require the absorption grating 57 and the miniaturization of the detection element. The present invention has been made in view of such circumstances, and its object is to provide a radiation phase-contrast imaging device capable of assuredly imaging a self-image to image an internal structure of an object in detail. The present invention has the following configurations to solve the above-mentioned problems. That is, the radiation phase-contrast imaging device according to the present invention includes an imaging system; the imaging system being composed of a radiation source configured to irradiate radiation, a grating in which an absorber absorbing the radiation and extending in one direction is arranged in a direction perpendicular to the one direction, and a detection unit configured to detect a self-image of the grating generated by Talbot interference on a detection surface in which a detection element configured to detect the radiation is arranged in a matrix in a plane; and a position changing unit configured to change a relative position of the imaging system and an object such that a projection of the object moves linearly on the detection surface while keeping a positional relation of the radiation source, the grating, and the detection unit. (A) A longitudinal direction which is a direction along which the detection elements on the detection surface of the detection unit are arranged is inclined with respect to an extending direction of the absorber of the grating. [Functions/Effects] According to the present invention, a radiation phase-contract imaging device capable of generating a clearer projection image by extracting more information on the inside of the object as compared with a conventional device without miniaturizing the detection element can be provided. That is, according to the configuration of the present invention, the longitudinal direction of the detection surface is inclined with respect to the extending direction of the absorber. By configuring the detection unit and the grating as described above, the self-image of the phase grating appearing as a stripe pattern is reflected with the self-image inclined obliquely with respect to the detection surface. This state means that the position (phase) at which the stripe pattern of the self-image is reflected differs depending on the position of the detection surface. Therefore, according to the present invention, it is considered that the same effects as those obtainable when a plurality of images different in reflecting position (phase) to which the self-image is reflected are obtained can be realized. However, by this alone, the self-image phase for a specific region of the object M is fixed to one. Therefore, according to the configuration of the present invention, the imaging is performed while changing the relative position of the imaging system and the object M to perform the imaging of the self-image for different phases at the same place of the object M. By performing such imaging, it is possible to obtain the information on the inside of the object that cannot be obtained unless a phase grating in which the absorption lines are arranged at a high density and a detection unit in which the detection element is miniaturized are used without changing the configuration of the detection unit. Further, in the aforementioned radiation phase-contrast imaging device, it is more preferable that a lateral direction which is a direction along which the detection element on the detection surface of the detection unit be arranged be inclined with respect to an arrangement direction of the absorbers of the grating. [Functions/Effects] The aforementioned configuration is a more specific configuration of the present invention. When the lateral direction which is a direction along which a detection element on the detection surface of the detection unit is arranged is inclined with respect to the arrangement direction of the absorbers of the grating, the detection direction which is a direction along which the detection elements on the detection surface of the detection unit are arranged is assuredly inclined with respect to the extending direction of the absorber of the grating. Further, in the aforementioned radiation phase-contrast imaging device, it is more preferable that the detection surface of the detection unit include a rectangular region configured such that an array in which a stripe-shaped self-image of one cycle is reflected and the detection element is arranged in one row in the longitudinal direction is arranged in a lateral direction. [Function/Effects] The aforementioned configuration is a more specific configuration of the present invention. When the detection surface of the detection unit includes a rectangular region configured such that an array in which a stripe-shaped self-image of one cycle is reflected and the detection element is arranged in one row in the longitudinal direction is arranged in a lateral direction, the position (phase) at which the stripe pattern of the self-image is reflected can be assuredly changed depending on the position of the detection surface. Further, in the aforementioned radiation phase-contrast imaging device, it is more preferable that it further includes a radiation source controller configured to make the radiation source irradiate the radiation every time a projection of the object moves by an amount corresponding to one detection element on the detection surface. [Function/Effects] The aforementioned configuration is a more specific configuration of the present invention. By configuring such that the radiation source executes irradiation of radiation every time the position changing unit changes the relative position of the object with respect to the imaging system by an amount corresponding to one detection element, it is possible to more assuredly perform imaging of the self-image. Further, in the aforementioned radiation phase-contrast imaging device, it is more preferable that the grating include a region in which an absorber absorbing the radiation and extending in one direction is arranged in a direction perpendicular to the one direction, and a region in which an absorber absorbing the radiation and extending in an intersecting direction intersecting with the one direction are arranged in a direction perpendicular to the intersecting direction, and both the regions are arranged in a direction along which the projection of the object moves on the detection surface. [Functions/Effects] According to the aforementioned configuration, it is possible to image two patterns of self-images different in the extending direction of the dark line by merely performing scan imaging against the subject only once. According to the aforementioned configuration, it is possible to obtain more information on the internal structure of the object and generate a transparent image of the object. Further, it may be configured such that a radiation phase-contrast imaging device includes an imaging system; the imaging system is composed of a radiation source configured to irradiate radiation, a grating in which an absorber absorbing the radiation and extending in one direction is arranged in a direction perpendicular to the one direction, (S) a detection unit configured to detect a self-image of the grating generated by Talbot interference on a detection surface on which a detection element configured to detect the radiation is arranged in a matrix in a plane; and a position changing unit configured to change a relative position of the imaging system and an object such that a projection of the object moves linearly on the detection surface while keeping a positional relation of the radiation source, the grating, and the detection unit. (B) A longitudinal direction which is a direction along which the detection element on the detection surface of the detection unit is arranged coincides with an extending direction of the absorber of the grating and is inclined with respect to a moving direction of the projection of the object on the detection surface. [Functions/Effects] The aforementioned configuration shows another embodiment of the present invention. Even with the aforementioned configuration, a radiation phase-contract imaging device capable of generating a clearer projection image by extracting more information on the inside of the object as compared with a conventional device without miniaturizing the detection element can be provided. That is, according to the aforementioned configuration, the longitudinal direction of the detection unit is inclined with respect to the moving direction of the object relative to the imaging system. So, when the detection unit is observed from the moving direction, it looks that the detection elements are arranged at a pitch narrower than the width of one detection element. In addition to this point of view, the aforementioned configuration is configured to detect the radiation at a higher density by repeating the imaging while changing the relative position of the imaging system and the object. By performing such imaging, it is possible to obtain the information on the inside of the object that cannot be obtained unless a grating in which absorbers are arranged at a high density and a detection unit in which the detection element is miniaturized are used, without changing the configuration of the detection unit. Further, in the aforementioned radiation phase-contrast imaging device, it is more preferable that a lateral direction which is a direction along which the detection elements on the detection surface of the detection unit are arranged do not perpendicularly intersect with the moving direction of the projection of the object on the detection surface. [Function and Effects] In the aforementioned configuration is a more specific configuration of the present invention, when the lateral direction which is an arrangement direction that the detection elements on the detection surface of the detection unit are arranged does not perpendicularly intersect with the moving direction of the object with respect to the imaging system, the longitudinal direction of the detection surface is inclined with respect to the moving direction of the object relative to the imaging system. Further, in the aforementioned radiation phase-contrast imaging device, it is more preferable that on the detection surface of the detection unit, an oblique direction along which it advances by an amount corresponding to one detection element in a lateral direction as it advances from a given detection element in the longitudinal direction by an amount corresponding to three detection elements coincide with the moving direction of the projection of the object on the detection surface. [Function/Effects] The aforementioned configuration is a more specific configuration of the present invention. Provided that the moving direction of the object with respect to the imaging system coincides with the oblique direction in which it advances in the lateral direction by an amount corresponding to one detection element as it advances in the detection direction by an amount corresponding to three detection elements on the detection surface, when the detection unit is observed from the moving direction, it looks that the detection elements are arranged at equal intervals, so it is possible to obtain a self-image more assuredly. Further, in the aforementioned radiation phase-contrast imaging device, it is more preferable that it further include a radiation source controller configured to make the radiation source execute irradiation of the radiation every time the projection of the object on the detection surface moves by 1/101/2 times a width of one detection element. [Function/Effects] The aforementioned configuration is a more specific configuration of the present invention. By configuring such that the radiation source executes irradiation of radiation every time the position changing unit changes the relative position of the object with respect to the imaging system by 1/101/2 times a width of one detection element, it is possible to more assuredly perform the imaging of the self-image. Further, the following configuration exerts the same effects as those obtainable by the aforementioned radiation phase-contrast imaging device. That is, it may be configured such that a radiation phase-contrast imaging device includes: an imaging system; the imaging system is composed of a radiation source configured to irradiate radiation, a grating in which an absorber absorbing the radiation and extending in one direction is arranged in a direction perpendicular to the one direction, and (S1) a detection unit configured to detect a self-image of the grating generated by Talbot interference on a detection surface for detecting the radiation; and a position changing unit configured to change a relative position of the imaging system and an object such that a projection of the object moves linearly on the detection surface while keeping a positional relation of the radiation source, the grating, and the detection unit. (C) An array configured by detection elements arranged in a inclined direction which is a direction inclined with respect to a longitudinal direction is two-dimensionally arranged by being arranged in a lateral direction perpendicular to the longitudinal direction on the detection surface of the detection unit. (A0) The inclined direction is inclined with respect to an extending direction of the absorber of the grating. [Functions/Effects] Also with the aforementioned configuration, since the arrangement direction of the detection elements is inclined with respect to the extending direction of the absorber, the same effects as those obtainable by the aforementioned configuration can be obtained. According to the present invention, a radiation phase-contract imaging device capable of generating a clearer projection image by extracting more information on an inside of an object as compared with a conventional device without miniaturizing a detection element can be provided. That is, according to the configuration of the present invention, the longitudinal direction of the detection surface is inclined with respect to the extending direction of the absorber. So, the position (phase) at which the stripe pattern of the self-image is reflected assuredly differs depending on the position of the detection surface. Therefore, it is considered that the same effects as those obtainable when a plurality of self-images are obtained by performing plural imaging in which the self-images on the detection surface are different in reflecting position can be realized. However, by this alone, the self-image phase for a specific position of the object M is fixed to one. Therefore, according to the configuration of the present invention, the imaging is performed while changing the relative position of the imaging system and the object. Next, embodiments for carrying out the invention will be described with reference to each Example. The X-ray in Examples corresponds to the “radiation” of the present invention. The FPD in Examples is an abbreviation for a flat panel detector. The radiation phase-contrast imaging device of the present invention can image even an object M with less radiation absorption, and therefore it is suitable for a fluoroscopy of a substrate for industrial applications and a fluoroscopy of a breast, etc., for medical applications. A radiation phase-contrast imaging device according to the present invention will be described. FIG. 1 shows the overall configuration of an imaging device 1 according to the present invention. As shown in FIG. 1, the imaging device 1 includes a platform 2 on which an object M is placed, an X-ray source 3 provided above the platform 2 and configured to irradiate an X-ray beam spreading in a pyramidal shape, and an FPD 4 for detecting the X-ray generated from the X-ray source 3 and transmitted through the object M on the platform 2. A phase grating 5 for generating Talbot interference is provided at a position between the FPD 4 and the platform 2. The X-ray source 3 corresponds to the “radiation source” of the present invention, and the FPD 4 corresponds to the “detection unit” of the present invention. The phase grating 5 corresponds to the “grating” of the present invention. The imaging device 1 is a radiation imaging device utilizing Talbot interference. Therefore, the X-ray source 3 is configured to output a phase-aligned X-ray beam. The distance between the phase grating 5 and the FPD 4 is set to the Talbot distance. With this setting, the self-image of the phase grating 5 will appear on the detection surface of the FPD 4 that detects the X-ray. The self-image generation unit 11 generates the self-image of the phase grating 5 based on the output of the FPD 4. The generated self-image is output to the transparent image generation unit 12. The transparent image generation unit 12 generates a transparent image in which the phase-contrast of the X-ray generated in the object M is imaged based on the self-image of the phase grating 5. The imaging system moving mechanism 13 is configured to move the X-ray source 3, the FPD 4, and the phase grating 5 with respect to the platform 2 while maintaining the mutual positional relationship as shown in FIG. 2. With the imaging system moving mechanism 13, the X-ray source 3, the FPD 4, the phase grating 5 can move in a direction parallel to the platform 2. The imaging system moving mechanism 13 changes the relative position of the imaging system 3, 4, and 5 and the object M so that the projection of the object M linearly moves on the detection surface of the FPD 4 with the positional relationship among the X-ray source 3, the phase grating 5, and the FPD 4 maintained. The imaging system 3, 4, and 5 is composed of the X-ray source 3 which irradiates an X-ray, the phase grating 5 in which an absorption line 5a extending in one direction and absorbing the radiation is arranged in a direction perpendicular to the one direction, and the FPD 4 that detects the self-image of the phase grating 5 generated by the Talbot interference on the detection surface in which detection elements 4a detecting radiation are arranged in a matrix in a plane. Note that the absorption line 5a corresponds to the “absorber” of the present invention, and the imaging system moving mechanism 13 corresponds to the “position changing unit” of the present invention. In the case of Example 1, the change of the relative position of the object M with respect to the imaging system 3, 4, and 5 can be performed by moving the imaging system 3, 4, and 5 without moving the object M. The imaging system moving control unit 14 is provided for the purpose of controlling the imaging system moving mechanism 13. The imaging system moving control unit 14 is provided for the purpose of controlling the imaging system moving mechanism 13. During the imaging, the X-ray source control unit 6 controls the X-ray source 3 so as to repeatedly output an X-ray beam in a pulsed manner. Every time the X-ray source 3 outputs an X-ray beam, the FPD 4 detects the X-ray that transmitted through the object M on the platform 2 and the phase grating 5 and transfers the detection data to the self-image generation unit 11. In this way, the device of the present invention is configured to generate a self-image by continuously performing the X-ray imaging. The X-ray source control unit 6 corresponds to the “radiation source controller” of the present invention. The continuous X-ray imaging is realized by the cooperation of the X-ray source control unit 6 and the imaging system moving control unit 14. That is, by the cooperation of them, the operation of moving the imaging system 3, 4, and 5 by the movement amount corresponding to the width of one pixel of the detection element on the FPD 4 and the operation of irradiating the X-ray beam are repeated. Therefore, as the continuous imaging is continued, the projected position of the object M on the FPD 4 moves one by one pixel. As described above, the X-ray source control unit 6 according to Example 1 makes the X-ray source 3 irradiate the radiation every time the imaging system moving mechanism 13 moves the projection of the object M by an amount corresponding to one detection element on the detection surface. FIG. 3 illustrates the detection surface of the FPD 4. On the detection surface of the FPD 4, detection elements 4a each having a rectangular shape of 20 μm in length×20 μm in width are arranged in a matrix in a plane. The longitudinal direction of the detection element 4a coincides with the moving direction of the imaging system 3, 4, and 5 realized by the imaging system moving mechanism 13. The detection surface of the FPD 4 has a rectangular shape with the moving direction of the imaging system 3, 4, and 5 as the longitudinal direction and the direction perpendicular to the moving direction as the lateral direction. The detection surface has a width of 20 cm in the longitudinal direction and a width of 2 cm in the lateral direction. The size of the detection element and that of the detection surface can be changed arbitrarily. The FPD 4 is a direct conversion type X-ray detector. That is, the FPD 4 has a conversion layer for converting an X-ray into a pair of electron and hole (carrier pair). The carriers generated in the conversion layer are captured by and accumulated in each of the detection elements 4a. When a signal for outputting a carrier is sent to the detection element 4a, the detection element 4a outputs the accumulated carrier as a detection signal. The fineness of this detection element 4a is a main factor determining the spatial resolution of the FPD 4. The smaller the detection element 4a, the better the spatial resolution of the FPD 4, so that it is possible to detect a finer structure. FIG. 4 illustrates the phase grating 5. The phase grating 5 has such a shape that the projection of the X-ray beam is reflected on the entire region of the detection surface of the FPD 4. Therefore, in the same manner as in the detection surface of the FPD 4, the phase grating 5 has a rectangular shape with the moving direction of the imaging system 3, 4, and 5 as the longitudinal direction and a direction perpendicular to the moving direction as the lateral direction. The phase grating 5 has a plurality of absorption lines 5a absorbing an X-ray and extending linearly. The absorption line 5a is arranged at a predetermined pitch in a direction perpendicular to the extending direction thereof. The absorption line 5a is not extended in the moving direction of the imaging system 3, 4, and 5, but is inclined with respect to the moving direction. As described above, the longitudinal direction which is the arrangement direction of the detection elements 4a on the detection surface of the FPD 4 is inclined with respect to the extending direction of the absorption line 5a of the phase grating 5. In other words, the lateral direction which is the arrangement direction of the detection elements 4a on the detection surface of the FPD 4 is inclined with respect to the arrangement direction of the absorption lines 5a of the phase grating 5. FIG. 5 illustrates the state in which the projection of the phase grating 5 is reflected on the detection surface of the FPD 4. On the FPD 4, a plurality of dark lines S are reflected as a stripe pattern. This dark line S is not the projection itself of the absorption line 5a of the phase grating 5, but is the self-image of the phase grating 5 resulting from the Talbot interference. The self-image at this time is, intuitively speaking, formed by overlapping the interference fringes caused by the light interference. According to FIG. 5, it can be seen that the dark line S on the FPD 4 extends obliquely with respect to the arrangement of the detection elements 4a. The reason that the extending direction of the dark line S is directed as described above is that the absorption line 5a of the phase grating 5 is inclined with respect to the longitudinal direction of the FPD 4. Since the extending direction of the dark line S coincides with the extending direction of the absorption line 5a of the phase grating 5, the dark line S on the FPD 4 is obliquely reflected on the FPD 4. Further, according to FIG. 5, the pitch when the dark line S is arranged in the lateral direction corresponds to three detection elements. This pitch can be arbitrarily changed. Hereinafter, the following description will be made assuming that the dark line S is arranged in the lateral direction at a pitch of three pixels. FIG. 6 shows the relationship between the dark line S and the arrangement of the detection elements 4a in more detail. Attention is paid to the array in which the detection elements indicated by shading are arranged vertically in one line in FIG. 6. When observing this array from the top to the bottom, the followings can be found. That is, in the upper end portion of the array in FIG. 6, the dark line S is reflected. When observing the lower section of the array from there, the dark line S reflected in the array escapes toward the left side. When continuously observing the further lower section of the array, the array comes to a position sandwiched between adjacent dark lines S. At this time, the distance between the dark line S on the left side and the array and the distance between the dark line S on the right side and the array becomes equal. When further observing the lower section of the array, the dark line S which was on the right side of the array gradually approaches the array, and the dark line S is reflected at the lower end section of the array. In other words, when observing the array from the top to the bottom, in the first half section indicated by the arrow A on the right side of FIG. 6, the dark line S which was superimposed on the array moves away from the array, and in the latter half section indicated by the arrow B, the dark line S which was separated from the array is superimposed on the array. In other words, in the array, all of the state in which the dark line S is completely superimposed on the array, the state in which the dark line S is not at all superimposed on the array, and the state in which the intermediate state therebetween are realized. That is, the detection surface of the FPD 4 has an array in which one cycle of the stripe-shaped self-image is reflected and the detection elements 4a are arranged in one row in the longitudinal direction. The aforementioned phenomenon occurs not only in the array shown by the shading in FIG. 6 but also in all conceivable arrays on the FPD 4 in which the detection elements 4a are arranged vertically in one line. In other words, the detection surface of the FPD 4 is a rectangular region configured by arranging the aforementioned arrays in which one cycle of the self-image is reflected in the lateral direction. It may be configured such that the detection surface of the FPD 4 in Example 1 is extended so as to be longer than the aforementioned region so that the detection surface of the FPD 4 can reflect more than one cycle of the self-image. <The Reason That the Spatial Resolution is Improved Due to the Inclination of the Absorption Line 5a> Since the absorption line 5a of the phase grating 5 is inclined with respect to the moving direction of the imaging system 3, 4, and 5 and the arrangement of the detection elements like in the present invention, a transparent image high in spatial resolution can be obtained. This will be explained as follows. FIG. 7 shows a conventional radiation phase-contrast imaging device. In the conventional radiation phase-contrast imaging device, a movement of the imaging system 3, 4, and 5 with respect to the object M is not performed. As shown in the upper left side in FIG. 7, the dark line appearing on the detection surface of the FPD 4 extends along the arrangement of the detection elements. Each dark line is arranged at intervals wider than the width of one detection element. In FIG. 7, it is assumed that the interval between the adjacent dark lines is three times the width of the detection element. As for how the dark line appears on the detection surface, three types are conceivable depending on the positional relationship of the phase grating 5 with respect to the FPD 4. The three types include: Type 1 in which the dark line appears on the third column, the sixth column, the ninth column, . . . , of the detection element arrays, which are columns of multiples of 3, as shown on the left side of the upper row in FIG. 7; Type 2 in which the dark line appears on the second row, the fifth row, the eighth column, . . . , of the detection element arrays, which are columns of the number obtained by subtracting 1 from multiples of 3, as shown on the left side of the middle row in FIG. 7; and Type 3 in which the dark line appears in the first row, the fourth row, the seventh column, . . . , of the detection element arrays, which are columns of the number obtained by subtracting 2 from triples of 3, as shown on the left side of the middle row of FIG. 7. As shown on the right side in FIG. 7, the obtained self-images differ depending on the dark line appearance Types 1, 2, and 3 on the detection surface. That is, the position where the dark lines appears in the self-image differs depending on the Type. That the dark line is inclined with respect to the FPD 4 like in the present present means that the appearance of the dark line differs in the FPD 4. In the case shown on the left side of the upper row in FIG. 7, the column on which the dark line is to be appeared is fixed. This is because the dark line and the detection element column are arranged in parallel. This situation is also applied to the cases shown in the middle row and the bottom row in FIG. 7. However, when the dark line is inclined with respect to the FPD 4, the detection element column on which the dark line is to be appeared differs depending on the location of the FPD 4. That is, the type of appearance of the dark line on the FPD 4 is Type 1 in a certain place, Type 2 in another place, and Type 3 in still another place. The type of actual appearance of the dark line on the FPD 4 according to the present invention includes an intermediate type in addition to Types 1, 2, and 3. However, in order to briefly explain the effects of the present invention, the detection surface as shown on the left side in FIG. 8 will be considered. In the upper stage “a” of this detection surface, the appearance of the dark line is Type 1, and in the middle stage “b” of this detection surface, the appearance of the dark line is Type 2. In the lower stage “c” of the detection surface, the appearance of the dark line is Type 3. It is assumed that the upper stage, the middle stage, and the lower stage are arranged in the moving direction of the imaging system 3, 4, and 5. The self-image obtained by the detection surface as shown on the left side in FIG. 8 differs in the dark line appearance position depending on the position of the image as shown on the right side in FIG. 8. This is because that how the dark line appears on the detection surface is a mixture of three Types. FIG. 9 shows how the imaging system 3, 4, and 5 is moving during the imaging. As the imaging system 3, 4, and 5 is moved, the upper stage “a”, the middle stage “b”, and the lower stage “c” of the detection surface approach the object M in this order and moves away from the object M in this order. FIG. 10 shows the state that the upper stage “a”, the middle stage “b”, and the lower stage “c” pass through one end portion of the object M. On the left side in FIG. 10, one end portion of the object M is imaged at the upper stage “a” of the detection surface. In the center in FIG. 10, the one end portion of the object M is imaged at the middle stage “b” of the detection surface. On the right side in FIG. 10, the one end portion of the object M is imaged at the lower stage “c” of the detection surface. Thus, the one end portion of the object M is imaged in each of the three stages of the detection surface. By the way, the self-image shown on the right side in FIG. 7 contains more information on the internal structure of the object M as the dark lines S are closely arranged. The transparent image generation unit 12 acquires the inside state of the object based on how the dark line appearing in the self-image distorts and images it. Therefore, for example, if the number of the dark lines that appeared in the self-image is 4, the transparent image generation unit 12 has no choice but to retrieve the information on the inside of the subject by relying on the small number of dark lines. The transparent image obtained at this time will not become clear. In the conventional configuration, if three self-images shown on the right side in FIG. 7 can be separately acquired and these can be synthesized into one self-image as shown in FIG. 11, the density of the dark lines in the self-image is improved to twelve, which is three times. In this case, the transparent image generation unit 12 can refer to a larger number of dark lines, which makes it possible to retrieve the information on the inside of the subject. In this way, a much clearer transparent image can be obtained. According to the configuration of the present invention, it is possible to obtain the self-image in which the number of dark lines shown in FIG. 11 has been tripled by continuously performing the imaging while moving the imaging system 3, 4, and 5. That is, the self-image generation unit 11 generates a self-image based on the detection data output from the upper stage “a” of the detection surface with reference to the position of the FPD 4 and the position of the imaging system 3, 4, and 5. Similarly, the self-image generation unit 11 generates a self-image based on the detection data output from the middle stage “b” of the detection surface, and generates a self-image based on the detection data output from the lower stage “c” of the detection surface. In this way, the self-image generation unit 11 generates a plurality of self-images different in the dark mark reflection position. At this time, superimposing the three self-images generated by the self-image generation unit 11 results in the image shown in FIG. 11. How the dark lines actually appear in the FPD 4 according to the present present invention includes intermediate types other than Types 1, 2, and 3 described in FIG. 7. Therefore, the manner that the dark lines appear in the FPD 4 is not limited to three Types, and it also can be thought that there are more types. Based on this idea, it is also possible to configure the self-image generation unit 11 so as to generate self-images of more than the aforementioned three types. The transparent image generation unit 12 generates a transparent image based on a plurality of self-images generated by the self-image generation unit 11. This transparent image is a much clearer image reflecting the inside of the object. This is because the transparent image was generated based on much more information. In practice, the transparent image generation unit 12 can utilize a conventional configuration in which a self-image in which the dark lines are arranged at the pitch shown in FIG. 11 is converted into a transparent image. Provided that if the number of the dark lines configuring a self-image is increased, a clearer transparent image can be obtained, there naturally comes a thought that it is better to increase the number of absorption lines 5a in the phase grating 5. The left side in FIG. 12 shows the state in which, according to this idea, the absorption line 5a in the phase grating 5 is increased three times as compared with the case described in FIG. 7. In this case, the dark lines are placed one by one on all detection element rows. Even if it is tried to obtain a self-image in this state, since all the detection elements are the same in condition, only an image having the same pixel value on the entire surface is obtained as shown in the right side in FIG. 12 from the output of the FPD 4, resulting in no self-image. This is because the detection element is too large with respect to the pitch of the absorption line 5a. In other words, if it is attempted to detect the stripe pattern in which dark lines are arranged at a narrow pitch as shown on the left side in FIG. 12, it is required to further reduce the size of the detection element. There is a limit for the miniaturization of the detection element. However, according to the present invention, it is possible to obtain a self-image as if the absorption line 5a of the phase grating 5 were made three times finer without further reducing the detection element. The main control unit 21 shown in FIG. 1 is provided for the purpose of comprehensively controlling the respective units 6, 11, 12, and 14. This main control unit 21 is configured by a CPU, and realizes each unit by executing various programs. Further, these units may be divided into and executed by arithmetic units in charge of these units. Each unit can access the storage 27 as necessary. The console 25 is provided for the purpose of inputting an instruction of an operator. Further, the display 26 is provided for the purpose of displaying a transparent image. As described above, according to the present invention, an imaging device 1 capable of generating a clearer projection image by extracting more information on the inside of the object as compared with a conventional device without miniaturizing the detection element 4a can be provided. That is, according to the configuration of the present invention, the longitudinal direction of the detection surface of the FPD 4 is inclined with respect to the extending direction of the absorption line 5a in the phase grating 5. By configuring the FPD 4 and the phase grating 5 as described above, the self-image of the phase grating 5 appearing as a stripe pattern is reflected on the detection surface in a manner as to be obliquely inclined with respect to the detection surface. This state means that the position (phase) where the stripe pattern of the self-image is reflected differs depending on the position of the detection surface. Therefore, it can be considered that the configuration of Example 1 can realize the same effects as those obtainable when a plurality of self-images having different positions (phases) are obtained. However, by this alone, the self-image phase for a specific location of the object M is fixed to one. Therefore, according to the configuration of the present invention, imaging is performed while changing the relative position of the imaging system and the object M to perform the imaging of the self-image for different phases at the same place of the object M. By performing such imaging, it is possible to obtain the information on the inside of the object that cannot be obtained unless a phase grating 5 in which absorption lines 5a are arranged at a high density and an FPD 4 in which the detection element 4a is miniaturized are used, without changing the configuration of the FPD 4. Next, a configuration according to Example 2 will be described. The fundamental configuration of Example 2 is the same as that shown in FIG. 1, and therefore the description thereof will be omitted. There are four characteristic configurations in Example 2. One of them is the relationship between the moving direction of the imaging system 3, 4, and 5 and the arrangement of the detection elements 4a as shown in FIG. 13. On the detection surface of the FPD 4, detection elements 4a are arranged in a matrix in a plane. The imaging direction of the imaging system 3, 4, and 5 realized by the imaging system moving mechanism 13 is inclined with respect to the longitudinal direction of the detection elements 4a. That is, the moving direction of the imaging system 3, 4, and 5 is a direction along which the imaging system advances by three detection elements of the FPD 4 in the longitudinal direction as the imaging system advances by one detection element of the FPD 4 in the lateral direction. The second characteristic configuration in Example 2 is the relationship between the moving direction of the imaging system 3, 4, and 5 and the extending direction of the absorption line 5a of the phase grating 5. The phase grating 5 has a plurality of linear absorption lines 5a extending linearly and absorbing an X-ray. The absorption lines 5a are arranged at a predetermined pitch in a direction perpendicular to the extending direction thereof. The imaging direction of the imaging system 3, 4, and 5 realized by the imaging system moving mechanism 13 is inclined with respect to the extending direction of the absorption line 5a. That is, the longitudinal direction which is the arrangement direction of the detection elements 4a on the detection surface of the FPD 4 coincides with the extending direction of the absorption line 5a of the phase grating 5, and is inclined with respect to the moving direction of the projection of the object M on the detection surface of the FPD 4. In other words, the lateral direction which is the arrangement direction along which the detection elements 4a on the detection surface of the FPD 4 are arranged does not intersect at right angle with the moving direction of the projection of the object M on the detection surface of the FPD 4. More specifically, the moving direction of the imaging system 3, 4, and 5 is a direction in which it advances in the longitudinal direction by an amount corresponding to three detection elements as it advances in the lateral direction by an amount corresponding to one detection element of the FPD 4. FIG. 14 illustrates a phase grating 5 of Example 2. The phase grating 5 has a plurality of linear absorption lines 5a extending linearly and absorbing an X-ray. The absorption line 5a is arranged at a predetermined pitch in a direction perpendicular to the extending direction thereof. The absorption line 5a extends in the moving direction of the imaging system 3, 4, and 5, and is parallel to the longitudinal arrangement of the detection elements in the FPD 4. Thus, in other words, the absorption line 5a is inclined with respect to the moving direction of the object M relative to the imaging system. The inclination angle is the same as the angle between the longitudinal direction of the detection surface and the moving direction of the object M relative to the imaging system. FIG. 15 illustrates a state in which the projection of the phase grating 5 is reflected on the detection surface of the FPD 4. In the FPD 4, a plurality of dark lines S are reflected as a stripe pattern. This dark line S is not the projection itself of the absorption line 5a of the phase grating 5 but the self-image of the phase grating 5 resulting from the Talbot interference. The self-image at this time is, intuitively speaking, formed by overlapping the interference fringes caused by the light interference. According to FIG. 15, it is understood that the dark line S on the FPD 4 extends along the arrangement of the detection elements 4a. The reason that the extending direction of the dark line S is directed as described above is that the absorption line 5a of the phase grating 5 extends in the longitudinal direction of the FPD 4. Since the extending direction of the dark line S coincides with the extending direction of the absorption line 5a of the phase grating 5, the dark line S extending in the longitudinal direction on the FPD 4 is reflected. Further, according to FIG. 15, the pitch when the dark line S is arranged in the lateral direction corresponds to three detection elements. This pitch can be arbitrarily changed. Hereinafter, the following description will be made assuming that the dark line S is arranged in the lateral direction at a pitch of three pixels. The third characteristic configurations in Example 2 is the operation of the self-image generation unit 11. Hereinafter, the operation of the self-image generation unit 11 will be described in detail. For the sake of simplicity, as shown on the left side in FIG. 16, it is assumed that the FPD 4 has detection elements of 3 vertical×3 horizontal. The detection elements are distinguished as D1 to D9, respectively. The right side in FIG. 16 shows the center points d1 to d9 of the detection elements D1 to D9. The case will be considered in which these center points d1 to d9 are projected on a line segment K perpendicular to the moving direction of the imaging system 3, 4, and 5. Then, the mappings of the center points d1 to d9 are arranged at equal intervals without being overlapped each other. The reason that the mappings are arranged as described above is that the moving direction of the projection of the object M on the detection surface of the FPD 4 coincides with the direction in which it advances in the longitudinal direction by an amount corresponding to three detection elements as it advances in the lateral direction by an amount corresponding to one detection element of the FPD 4. The mappings are arranged on the line segment K at a pitch of 1/101/2 times (about 0.32 times) the width of one detection element. Therefore, the distance between adjacent mappings is smaller than the width of one detection element. Hereinafter, the length of 1/101/2 times the width of one detection element 1 will be referred to as one unit. It is assumed that the imaging system 3, 4, and 5 is moved in the moving direction. At this time, the center points d1 to d9 of the detection elements D1 to D9 moves on the individual line segments L1 to L9, respectively. The line segments L1 to L9 extend in the moving direction of the imaging system 3, 4, and 5. Considering that the mappings of the center points d1 to d9 are arranged at equal intervals on the line segment K, the line segments L1 to L9 are arranged at equal intervals (specifically, at intervals of 1 unit) in the lateral direction (the extending direction of the line segment K). The left side in FIG. 17 shows the state when the imaging system 3, 4, and 5 is in the initial position. At this time, the center point d1 of the detection element D1 is, of course, on the line segment L1. The position of the center point d1 at this time is assumed to be on the line segment L1 and the line segment K1 perpendicular to the line segment L1. From this state, it is assumed that the imaging system 3, 4, and 5 is moved in the moving direction one by one unit. The center in FIG. 17 shows the state when the imaging system 3, 4, and 5 is moved by one unit from the initial position. At this time, the center point d1 of the detection element D1 appears at a position moved by one unit from the initial position. The position of the center point d1 at this time is assumed to be on the line segment L1 and the line segment K2 perpendicular to the line segment L1. The right side in FIG. 17 shows the state when the imaging system 3, 4, and 5 is moved by two units from the initial position. At this time, the center point d1 of the detection element D1 appears at a position moved by two units from the initial position. The position of the center point d1 at this time is assumed to be on the line segment L1 and the line segment K3 perpendicular to the line segment L1. When observing the center in FIG. 17, it is understand that the center point d2 of the detection element D2 is positioned at the intersection of the line segment L2 and the line segment K1. Also, when observing the right side in FIG. 17, it is understand that the center point d2 of the detection element D2 is positioned at the intersection of the line segment L2 and the line segment K2. At the same time, it is understand that the center point d3 of the detection element D3 is positioned at the intersection of the line segment L3 and the line segment K1. In this manner, by moving the imaging system 3, 4, and 5 one by one unit in the moving direction, the center point d1 of the detection element D1 on the line segment L1 moves one by one unit. This situation is the same as in all detection elements. FIG. 18 shows the state when the imaging system 3, 4, and 5 is moved by eight units from the initial position. At this time, it is understand that the center point d9 of the detection element D9 is positioned at the intersection of the line segment L9 and the line segment K1. The self-image generation unit 11 operates assuming that the detection data detected by each detection element is the detection data at the center point of the detection element. For example, the self-image generation unit 11 assumes that the detection data output by the detection element D1 on the left side in FIG. 17 is the detection result of the X-ray at the intersection of the line segment K1 and the line segment L1. In the same manner, the self-image generation unit 11 assumes that the detection data output by the detection element D1 on the left side in FIG. 17 is the detection result of the X-ray at the intersection of the line segment K2 and the line segment L1 and that the detection data output by the detection element D2 is the detection result of the X-ray at the intersection of the line segment K1 and the line segment L2. Further, in the same manner, the self-image generation unit 11 assumes that the detection data output by the detection element D1 on the right side in FIG. 17 is the detection result of the X-ray at the intersection of the line segment K3 and the line segment L1 and that the detection data output by the detection element D2 is the detection result of the X-ray at the intersection of the line segment K2 and the line segment L2. And the self-image generation unit 11 assumes that the detection data output by the detection element D3 is the detection result of the X-ray at the intersection of the line segment K1 and the line segment L3. In FIG. 17 and FIG. 18, the intersection point where the black circle is placed indicates the intersection point at which the detection data is obtained at the current position of the FPD 4, and the intersection point where the white circle is placed indicates the intersection point where the detection data has already been acquired. The intersection points where no circles are placed are unknown intersection points whose detection data is unknown. In the example shown in FIGS. 17 and 18, since there are only nine detection elements, detection data can be obtained only for the nine line segments L1 to 9, but the actual FPD 4 has more detection elements, and therefore there are more line segments from which detection data can be obtained. As described above, the self-image generation unit 11 samples the detection results of the X-rays on the respective line segments L1 to L9 at one unit intervals based on the detection data repeatedly output from the FPD 4 while the imaging system 3, 4, and 5 is moved one by one unit. As a result, the self-image generation unit 11 can generate an image (self-image) in which the vertical size corresponds to one unit and the horizontal size corresponds to one unit. The self-image obtained at this time is higher in resolution than the conventional imaging method shown in the upper part in FIG. 7. In the conventional imaging method shown in the upper part in FIG. 7, only the image (self-image) whose longitudinal and lateral sizes each corresponds to the width of one detection element can be obtained. However, the self-image generation unit 11 according to Example 2 can generate an image (self-image) in which the length and width sizes each corresponds to 1/101/2 times (about 0.32 times) the width of one detection element. Therefore, according to the method of Example 2, the resolution of the self-image can be increased to 9/81/2 times (about 3.2 times) as compared with the conventional method. A clearer transparent image can be obtained when the resolution of the obtained self-image is higher. The fourth characteristic configuration in Example 2 is that the imaging system 3, 4, and 5 is moved one by one unit in the moving direction as described above. Also in Example 2, the continuous X-ray imaging is realized by the cooperation of the X-ray source control unit 6 and the imaging system moving control unit 14. That is, by the cooperation of both of them, the operation of moving the imaging system 3, 4, and 5 only by one unit and the operation of irradiating the X-ray beam are repeated. The X-ray source control unit 6 makes the X-ray source 3 irradiate the radiation every time the imaging system moving mechanism 13 moves the projection of the object M by 1/101/2 time the width of one detection element on the detection surface of the FPD 4. As described above, the aforementioned configuration shows another embodiment of the present invention. Also with the aforementioned configuration, the imaging device 1 capable of generating a clearer projection image by extracting more information on the inside of the object as compared with a conventional device, without miniaturizing the detection element 4a can be provided. That is, according to the aforementioned configuration, the longitudinal direction of the FPD 4 is inclined with respect to the moving direction of the object M relative to the imaging system. So, when observing the FPD 4 from the moving direction, it looks that the detection elements 4a are arranged at a pitch narrower than the width of one detection element 4a. In addition to this point of view, the aforementioned configuration repeats the imaging while changing the relative position of the imaging system and the object M to detect the radiation at higher density. By performing such imaging, it is possible to obtain the information on the inside of the object that cannot be obtained unless a phase grating 5 in which the absorption lines 5a are arranged at a high density and an FPD 4 in which the detection element 4a is miniaturized are used, without changing the configuration of the FPD 4. The present invention is not limited to the aforementioned configuration, and may be modified as follows. (1) According to the aforementioned Example, the imaging system moving mechanism 13 is configured to move the X-ray source 3 together with the FPD 4 and the phase grating 5, but the present invention is not limited thereto. It may be configured such that the relative position of the object M and the imaging system are changed by configuring the imaging system moving mechanism 13 so as to move the FPD 4 and the phase grating 5 by tracing the locus of a circular arc so as not to change the positional relationship between the X-ray source 3, the FPD 4, and the phase grating 5. Further, the relative position of the object M and the imaging system may be changed by moving the platform 2 without moving the imaging system 3, 4, and 5. (2) According to the aforementioned configuration, although the object M is placed between the X-ray source 3 and the phase grating 5, the present invention is not limited to the configuration. The platform 2 and the object M may be placed between the phase grating 5 and the FPD 4. (3) According to the aforementioned Example 1, although the extending direction of the absorption line 5a of the phase grating 5 is inclined in the same direction with respect to the longitudinal direction, the present invention is not limited to this configuration. As shown in FIG. 19, the phase grating 5 may be configured so as to have absorption lines 5a different in the inclination angle with respect to the longitudinal direction of the FPD 4. Such a phase grating 5 has two regions R1 and R2 arranged in the moving direction of the imaging system 3, 4, and 5. The absorption line 5a1 positioned in the region R1 obliquely extends from the upper right to the lower left, and the absorption line 5a2 positioned in the region R2 obliquely extends from the upper left to the lower right. As described above, the phase grating 5 of this modification has the region R1 in which an absorption line 5a absorbing an X-ray and extending in one direction is arranged in a direction perpendicular to the one direction and the region R2 in which an absorption line 5a extending in an intersecting direction which is a direction intersecting with the one direction is arranged in a direction perpendicular to the intersecting direction. The respective regions R1 and R2 are arranged in a direction along which the projection of the object M moves on the detection surface. By configuring the phase grating 5 as described above, it is possible to extract more information on the object M when performing the X-ray phase-contrast imaging. FIG. 20 shows the state in which the self-image of the phase grating 5 of the modified example is reflected on the FPD 4. On the upper side of the FPD 4, a stripe pattern in which the dark lines S1 extending diagonally from the upper right to the lower left are arranged in the lateral direction appears. On the lower side of the FPD 4, a stripe pattern in which the dark lines S2 extending diagonally from the upper left to the lower right are arranged in the lateral direction appears. These two stripe patterns configure the self-image of the phase grating 5. That is, the direction perpendicular to the dark line S1 appearing on the upper side of the self-image is a direction from the upper left to the lower right as shown by the arrow in the figure. The direction perpendicular to the dark line S2 appearing on the lower side of the self-image is a direction from the upper right to the lower left as shown by the arrow in the figure. The imaging device 1 images the internal structure of the object M utilizing the self-image disturbances of the phase grating 5. That is, the dark lines S1 and S2 configuring the self-image in FIG. 20 are distorted in directions perpendicular to the extending directions of the dark lines S1 and S2 due to the transmission of the object M. The imaging device 1 executes the imaging of the internal structure of the object M by observing the distortions. Therefore, when the self-image is generated using the phase grating 5 as described with reference to FIG. 4, the self-image shifts only in a direction perpendicular to the dark line S in FIG. 5 and does not shift in other directions. In the self-image using the phase grating 5, not all information on the internal structure of the object M can be retrieved. By imaging the self-image of the object M again using another phase grating 5 different in the extending direction of the dark line S, new information can be retrieved from the object M. According to the configuration of this modified example, it is possible to image two patterns of self-images different in extending direction of the dark line S by merely performing scan imaging for the subject only once. FIG. 21 illustrates this principle. As the imaging system 3, 4, and 5 moves, the regions R1 and R2 of the phase grating 5 approaches the object M in this order and move away from the object M in this order. FIG. 22 shows the state in which the regions R1 and R2 of the phase grating 5 pass through one end portion of the object M. On the left side in FIG. 22, the X-ray that passed through one end portion of the object M is incident on the region R1 of the phase grating 5. On the right side in FIG. 22, the X-ray that passed through one end portion of the object M is incident on the region R2 of the phase grating 5. In this way, the one end portion of the object M is imaged using two regions of the phase grating 5. That two regions of the phase grating 5 are used at the time of imaging is the same in other portions of the object M. In this manner, according to this modified example, two patterns of self-images different in extending direction of the dark line S are imaged by merely performing scan imaging for the subject only once. According to this modified example, more information on the internal structure of the object M can be obtained and a transparent image of the object M can be generated. (4) In the configuration of Example 1, it is configured that the FPD 4 having the detection surface in which the detection elements 4a are arranged in a matrix in a plane is provided and the extending direction of the absorption line 5a of the phase grating 5 is inclined with respect to the arrangement of the detection element 4, but the present invention is not limited to such configuration. Instead of such a configuration, in the present invention, the arrangement direction of the detection elements 4a may be inclined with respect to the absorption line 5a of the phase grating 5. FIG. 23 illustrates the configuration of this modified example. The FPD 4 according to the modified example is configured such that the detection elements 4a are arranged in the inclination direction “a” which is inclined with respect to the moving direction of the imaging system 3, 4, and 5 to constitute an array and that this array is arranged in the lateral direction perpendicular to the moving direction the imaging system 3, 4, and 5 so that the detection elements are arranged two-dimensionally. FIG. 23 illustrates the detection surface on which one of the arrays is represented by shading. In this manner, an array configured by arranging the detection elements 4a on the detection surface of the FPD 4 in the inclination direction “a” which is a direction inclined to the longitudinal direction is arranged in the lateral direction perpendicular to the longitudinal direction two-dimensionally. On the other hand, the phase grating 5 in this modified example has absorption lines 5a parallel to the moving direction of the imaging system 3, 4, and 5 as shown in FIG. 24. Therefore, the inclination direction “a” is inclined with respect to the extending direction of the absorption line 5a of the phase grating 5. FIG. 25 shows the state in which the self-image of the phase grating 5 is reflected on the FPD 4 of the modified example. Also with the configuration of this modified example, since the arrangement direction is inclined with respect to the extending direction of the absorption line 5a, the same effects as those obtainable by the configuration of Example 1 can be obtained. (5) The configuration of the regions R1 and R2 described in FIG. 19 is merely an example of a modified example. As a specific example of the configuration of the regions R1 and R2, as described with reference to FIG. 23, a configuration in which the arrangement of the detection elements of the FPD 4 is inclined with respect to the absorption line 5a can be adopted. As described above, the present invention is suitably applicable in the industrial field. 3: X-ray source (radiation source) 4a: detection element 4: FPD (detection unit) 5a: absorption line (absorber) 5: phase grating (grating) 6: X-ray source control unit (radiation source controller) 13: imaging system moving mechanism (position changing unit)
042386438	description	SUMMARY OF THE INVENTION The present invention has as its object to provide a novel multi engine propulsion system, capable of propelling a vehicle within the atsmosphere of earth and beyond and may be able to be used in a ship or ocean going transit and above the stratosphere it may exceed 3 M or 4 M or even 5 -Ms speed that is as the fusilage will allow. A propulsion system comprising A. a source of liquid water. PA1 B. a boiler (a sphere), means connected to said source of H.sub.2 O by line 1. for converting said water to steam by means of line 2 to deliver a nuclear reactor to the boiler. PA1 C. a reactor storage to hold 6 pellets or cores, made of a lead caseing for a shield, and line 2. to deliver one core at a time to the boiler. PA1 D. a diverter switch connected to said steam boiler by line 3, having a plurality of outputs. PA1 E. by line 4 of said outputs connected to the intake of a turbo-jet (E) wherein it is mixed with air and developes a directional thrust. PA1 F. The other said output (of steam) being connected to the input or intake of a ramjet (F) by line 5, wherein it is mixed with air and developes a directional thrust. PA1 G. By means of line 6 said steam also being connected to an electrical generator, means a magneto, so as to supply electricity to a storage battery by line 7. PA1 H. Said battery connected to Auxiliary Equipment by line 8. PA1 I. Auxiliary Equipment connected to storage battery by line 8. PA1 K. Rocket connected to storage battery by line 9. and line 10 connecting storage battery to Ion-jet.
	summary
	claims	1. An apparatus, comprising:a reactor core, a boom and a shield assembly supportively interposed between the reactor core and the boom;a heat pipe disposed in thermal communication with the reactor core;a thermoelectric power converter operably coupled to the heat pipe;struts supportively coupled to the heat pipe at opposite ends of the power converter; andhinge joints to rotatably couple the struts to the boom, at least one of the hinge joints being spring-loaded. 2. The apparatus according to claim 1, wherein the at least one spring loaded hinge joint biases the struts to resist rotation due to thermal expansion of the heat pipe, the apparatus further comprising an end stop to limit the rotation. 3. An apparatus, comprising:a reactor core, a boom and a shield assembly supportively interposed between the reactor core and the boom;a heat pipe disposed in thermal communication with the reactor core;two or more thermoelectric power converters operably coupled to the heat pipe;three or more struts supportively coupled to the heat pipe at opposite ends of each of the power converters; andhinge joints to rotatably couple the struts to the boom, at least one of the hinge joints being spring loaded. 4. The apparatus according to claim 3, wherein the heat pipe is plural in number and further comprising lateral support structures supportively coupled to adjacent struts. 5. The apparatus according to claim 3, wherein four power converters are operably coupled to the heat pipe and five struts are supportively coupled to the heat pipe at the opposite ends of each of the power converters. 6. The apparatus according to claim 3, wherein each strut comprises:an elongate member; anda flanged interface for receiving the heat pipe therethrough at an end of the elongate member. 7. The apparatus according to claim 6, wherein the elongate member comprises titanium. 8. The apparatus according to claim 6, wherein the flanged interface is tightly fit about the heat pipe. 9. The apparatus according to claim 6, wherein the flanged interface has a split cap bolted construction. 10. The apparatus according to claim 6, wherein the flanged interface comprises a titanium ball pivot joint with a zircon insert. 11. The apparatus according to claim 3, wherein the at least one spring loaded hinge joint biases the struts to resist rotation. 12. The apparatus according to claim 11, further comprising an end stop to limit the rotation. 13. A thermoelectric power converter support structure for an apparatus including a reactor core, a boom, a shield assembly supportively interposed between the reactor core and the boom and a heat pipe disposed in thermal communication with the reactor core on which two or more thermoelectric power converters are operably coupled, the support structure comprising:three or more struts supportively coupled to the heat pipe at opposite ends of each of the power converters; andhinge joints to rotatably couple the struts to the boom; at least one of the struts being spring loaded. 14. The support structure according to claim 13, wherein four power converters are operably coupled to the heat pipe and five struts are supportively coupled to the heat pipe at the opposite ends of each of the power converters. 15. The support structure according to claim 13, wherein each strut comprises:an elongate member; anda flanged interface for receiving the heat pipe therethrough at an end of the elongate member. 16. The support structure according to claim 15, wherein the elongate member comprises titanium. 17. The support structure according to claim 15, wherein the flanged interface is tightly fit about the heat pipe. 18. The support structure according to claim 15, wherein the flanged interface has a split cap bolted construction which captures a titanium ball pivot joint with a zircon insert. 19. The support structure according to claim 13, wherein the spring loaded hinge joint biases the struts to resist rotation. 20. The support structure according to claim 19, further comprising an end stop to limit the rotation.
	summary
	summary
051903334	description	DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIG. 1, there is illustrated a linkage in one environment of use. The linkage, indicated by the reference numeral 10 is attached to a tube 12 that serves as a frame to which linkage 10 can be mounted and positioned in the general vicinity of need. Depending from linkage 10 is an end effector, such as a gripper 14. Within tube 12 is an actuator such as an air cylinder 20 with an air hose 22 and a shaft or rod 24 moved by the injection of and release of air from air cylinder 20. Adjacent to air cylinder 20, on one side is stationary bracket 26; on the other side is a stopping bracket 28, the functions of which will be explained presently. Gripper 14 is illustrated as being operated by its own air cylinder 36 supplied by a separate air hose 38. However, other end effectors manipulated by other means may be deployed by linkage 10 equivalently. Linkage 10 has three links: a first link 44, a second link 46, and a third link 48. First link 44 has a first end 52 and a second end 54. Second link 46 has a first end 58 and a second end 60. Third link 48 has a first end 64 and a second end 66. As will be seen by comparing FIGS. 1 and 3, each link is doubled, in the preferred embodiment, for equalization of forces and stresses. First end 52 of first link 44 is pivotally attached to a bar 70 that is attached to rod 24. Second end 54 of first link 44 is pivotally attached to second link 46 at a point 72 between first end 58 and second end 60 of second link 46. First end 58 of second link 46 is pivotally attached to a stop 74 on the end of stopping bracket 28. Second end 60 of second link 46 is pivotally attached to the side of gripper 14 at 76. First end 64 of third link 48 is pivotally attached to stationary bracket 26, and second end 66 of third link 48 is pivotally attached to the end of gripper 14 at 78. When linkage 10 is holding gripper 14 in line with an axis 82, the arrangement presents a compact, small diameter device, suitable for inserting in narrow channels. In FIGS. 2 and 4, however, gripper 14 has been rotated about a second axis 84 perpendicular to axis 82 to invert gripper 14. The inversion is achieved by the pulling of rod 24 which in turn pulls first link 44. First link 44 pulls at 72 on second link 46 causing it to rotate about its first end 58. Third link 48 moves with gripper 14 and acts to prevent gripper 14 from swinging about second end 60 of second link 46 at 76 where it meets gripper 14. Third link 48 therefore serves a stabilizing function. Second link 46 affects the amount and direction of rotation of gripper 14. Second link 46 has a right angle bend as illustrated which divides the 180.degree. required for the inversion into two 90.degree. portions. The first portion is achieved by first end 58 of second link 46 as it moves from engagement with a first face 92 of stop 74 to a second face 94 90.degree. from first face 92. Meanwhile, second end 60 of second link 46 pivots with respect to side 76 from parallel to perpendicular to complete the inversion. It will be apparent to those skilled in the art that many changes and substitutions can be made to the preferred embodiment herein described without departing from the spirit and scope of the present invention. For example, the inversion does not have to be 180.degree. but can be less or a little more depending on such factors as the angle between first and second faces 92, 94 and the length of first link 44. The end effector can be a gripper, as referred to in the present description, or some other tool or manipulator or operative device such as a welding torch. Similarly, air cylinder 20 could be replaced by an hydraulic cylinder or electro-mechanical device, so long as it is capable of controlled motion of rod 24. The invention is, therefore, to be defined by the appended claims.
053533208	description	DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Illustrated schematically in FIG. 1 is an exemplary pressure vessel 10 containing a conventional boiling water reactor core 12 submerged in reactor water 14. Other conventional details inside the pressure vessel 10 are not illustrated for clarity of presentation. The pressure vessel 10 is conventionally disposed in a containment building 16 which includes among other things a conventional annular wetwell or suppression pool 18 which surrounds the pressure vessel 10 and is disposed at a suitable elevation above the reactor core 12. The suppression pool 18 contains water 20 which is used for various functions in the normal operation of the power plant. For example, a first supply pipe or line 22 is joined at one end to the suppression pool 18 and at an opposite end to a first inlet nozzle 24 on the pressure vessel 10 and includes a first valve 26 for controlling the flow of water 20 from the suppression pool 18 by gravity into the pressure vessel 10 in the event of loss of coolant accident (LOCA). In the event of a LOCA, the pressure vessel 10 is conventionally depressurized and the first valve 26 is opened for allowing gravity flow of the water 20 into the pressure vessel 10. During normal operation, the first valve 26 is closed and prevents flow through the first supply line 22. The exemplary embodiment illustrated in FIG. 1 is representative of a simplified boiling water reactor (SBWR) wherein the containment building 16 further includes a gravity-driven cooling system (GDCS) which has a GDCS pool 28 containing water 30 disposed at an elevation above both the suppression pool 18 and the reactor core 12. A second supply pipe or line 32 is joined at one end in flow communication with the GDCS pool 28 and at an opposite end to a second inlet nozzle 34 of the pressure vessel 10 disposed at an elevation above the first nozzle 24. Disposed in the second supply pipe 32 is a conventional second valve 36 which is selectively openable, before opening the first valve 26, for allowing the water 30 in the GDCS pool 28 to flow by gravity through the second supply pipe 32 and into the pressure vessel 10 through the second nozzle 34 following a LOCA condition. During normal operation, the second valve 36 is closed. Both the suppression pool 18 and the GDCS pool 28 are conventionally used to provide makeup water into the pressure vessel 10 in the event of a LOCA wherein the break occurs in any of the various pipes (not shown) leading to the pressure vessel 10 except, however, for a break in either of the first and second supply lines 22, 32 themselves. Since the normal level of water within the pressure vessel 10 is higher than the elevation of the first and second nozzles 24, 34, a leak in the supply lines 22, 32 between the nozzles 24, 34 and the respective valves 26, 36 will allow the reactor water 14 to escape from the vessel 10. However, in accordance with the present invention, each of the nozzles 24, 34 has a preferred configuration to provide a relatively low flow resistance and pressure drop in the normal, forward flow direction from the respective pools 18, 28 to the vessel 10, and a relatively large resistance to flow in the backflow direction from the pressure vessel 10 through the nozzles 24, 34. In this way, the nozzles 24, 34 allow gravity draining of the pools 18, 28 into the pressure vessel 10 following a LOCA without substantial flow resistance to provide makeup water into the vessel 10, but in the event of a LOCA created in the supply lines 22, 32 themselves, a substantial flow resistance is created for reducing leakage of the reactor water 14 from the pressure vessel 10 through the respective nozzles 24 or 34. Illustrated in cross-section in FIG. 2 is an exemplary embodiment of the second inlet nozzle 34 joined to the pressure vessel 10 and the second supply pipe 32 in accordance with one embodiment of the present invention. The first nozzle 24 is identical to the second nozzle 34 except for specific dimensions, with the description of the second nozzle 34 applying equally as well to the first nozzle 24. The nozzle 34 includes a tubular body 38 having a longitudinal or axial centerline axis 40 and a proximal end 42 adapted for being fixedly joined to the pressure vessel 10. In the exemplary embodiment illustrated in FIG. 2, the proximal end 42 has a larger diameter than that of the main body 38 and is conventionally welded into the wall of the pressure vessel 10. The body 38 also includes a distal end 44 adapted for being joined to the supply pipe 32, and in the exemplary embodiment illustrated in FIG. 2, the distal end 44 is cylindrical and conventionally welded to the cylindrical supply pipe 32. Extending completely axially through the body 38 is an annular or preferably circular flow channel or passage 46 which includes several portions in serial flow communication from the distal end 44 to the proximal end 42, all disposed coaxially about the centerline axis 40. The portions include an annular first port or inlet 48 at the distal end 44 which is disposed in flow communication with the supply pipe 32 when the distal end 44 is welded thereto. The first port 48 has a first inner diameter D.sub.1 which is constant for a suitable axial distance to provide a substantially constant flow area preferably equal to that of the supply pipe 32. The supply pipe 32 has an inner diameter D.sub.p which, therefore, is preferably substantially equal to the first inner diameter D.sub.1 of the first port 48. The flow passage 46 further includes a throat 50 spaced axially from the first port 48 which has a second inner diameter D.sub.2 which is less than the first inner diameter D.sub.1 to provide backflow resistance through the nozzle 34. A conical channel 52 extends axially from one end thereof at the throat 50 to an opposite end thereof adjacent the nozzle proximal end 42 and has an inner diameter D which increases axially from one end at the throat 50, i.e., D.sub.2, to a maximum or third inner diameter D.sub.3 at its opposite end. A second port or outlet 54 is disposed at the nozzle proximal end 42 and is joined in flow communication with the pressure vessel 10. Accordingly, in the event of a LOCA condition, forward flow of the water 30 from the GDCS pool 28 (see FIG. 1) occurs through the nozzle 34 illustrated in FIG. 2 from the supply pipe 32 at the right to the pressure vessel 10 at the left as represented by the flow arrow labeled 30. The water, therefore, flows through the throat 50 of decreased flow area, which causes flow resistance and a corresponding pressure drop, but then continues to flow through the conical channel 52 which in the forward flow direction to the left as illustrated in FIG. 2 is a diverging channel or diffuser having a preferred half-angle H selected for obtaining diffusion of the water 30 to maximize recovery of the pressure drop resulting from the throat 50 for improving the flow rate of the water 30 in the forward direction into the pressure vessel 10 without flow separation from the walls of the channel 52. However, in the event of a LOCA caused by a break in the supply pipe 32 upstream from the nozzle 34, the reactor water 14 will enter the second port 54 for flow outwardly from the vessel 10 through the nozzle 34 to the site of the break in the supply pipe 32. Since in this backflow direction to the right in FIG. 2, as represented by the phantom arrow labeled 14, the conical channel 52 is a converging channel, it provides increasing resistance to the discharge of the reactor water 14 therethrough, with the throat 50 and first port 48 providing additional pressure losses in the backflow. Although the throat 50 provides a smaller flow area than that of the supply pipe 32, the preferred configuration of the nozzle 34 provides more resistance to flow in the backflow direction from the nozzle 34 than in the forward flow direction into the nozzle 34. In this way, the GDCS pool 28 may be designed to provide a predetermined flow rate of water 30 through the nozzle 34 and into the pressure vessel 10 by gravity, but in the event of a backflow condition through the nozzle 34, resistance to leakage of the reactor water 14 therethrough is provided. In the preferred embodiment, the throat 50 has a substantially constant flow area for a predetermined axial throat length L.sub.t, with the second inner diameter D.sub.2 being the same for the entire length of the throat 50. The preferred length L.sub.t of the throat 50 is at least 10 cm so that the conventionally known homogeneous flow model may be used to calculate blowdown flow rates from the pressure vessel 10. Since the pressure vessel 10 is normally under relatively high pressure and contains steam therein in addition to the reactor water 14, discharge of the reactor water 14 from the vessel 10 through the nozzle 34 will cause the water 14 to flash boil and form steam bubbles. The throat 50 is so configured for ensuring the generation of an equilibrium saturated mixture of steam and water (homogeneous mixture) being discharged from the nozzle 34 into the supply pipe 32. Furthermore, the conical channel 52 is preferably straight with its sidewalls having linearly varying diameters between its two ends over its axial length L.sub.C. In this way, a substantially uniform rate of diffusion is provided in the forward flow direction of the water 30 from the first port 48 and out through the second port 54 for maximizing pressure recovery in the water 30. And, in the backflow direction from the second port 54 and out the first port 48, the decreasing flow area correspondingly increases the pressure drop and, therefore, resistance to flow of the reactor water 14 therethrough. Also in the preferred embodiment, the axial length L.sub.C of the conical channel 52 and the third inner diameter D.sub.3 at its largest end are selected to ensure that flow in the forward direction into the vessel 10 does not separate from the walls of the channel 52 to maximize pressure recovery. In order to further reduce pressure losses in the water 30 in the forward direction through the nozzle 34 into the vessel 10, the flow passage 46 further includes a first bellmouth 56 integrally joining the first port 48 to the throat 50 for providing a relatively smooth transition of decreasing flow area in the forward flow direction from the first port 48 to the throat 50. And, the flow passage 46 further includes a second bellmouth 58 integrally joining the conical channel 52 to the second port 54 to provide a relatively smooth discharge from the channel 52 into the vessel 10 with the second bellmouth 58 increasing in diameter in the forward flow direction from the channel 52 to the second port 54. In a preferred and exemplary embodiment of the present invention, the conical channel 52 has a half-angle H of about 3.8.degree. for the first nozzle 24 and 4.05.degree. for the second nozzle 34 for obtaining maximum pressure recovery from the forward flow of the water 20, 30, while still providing an effective.sup.amount of backflow resistance to the reactor water 14 through the nozzles 24, 34 in the event of a leak downstream therefrom. Accordingly, the nozzle 34 provides relatively low resistance to flow in the normal or inward flow direction with recovery of pressure through the diverging channel 52, while, in the reverse or outward direction from the nozzle 34, provides the necessary restriction in flow by a simple reduction in flow area and ensures a homogeneous bubbly mixture of reactor water 14 and flash steam to further increase backflow resistance. Referring again to FIG. 1, the first nozzle 24 is disposed at an elevation below the second nozzle 34 and is therefore subject to higher head pressure in the reactor water 14 in the vessel 10. The first nozzle 24 may be configured substantially identically to the second nozzle 34 illustrated in FIG. 2 except, however, the respective diameters of the flow passage 46 thereof are preferably made smaller than in the second nozzle 34 to further increase the backflow resistance against the higher driving pressure force of the reactor water 14 in the vessel 10. Since the nozzle 34 includes the throat 50, the nozzle 34 may be used if desired to measure the normal forward water flow through the nozzle 34 from the GDCS pool 28. A first conventional pressure sensor 60 may be preferably operatively mounted in the throat 50 for measuring the pressure, P.sub.1 therein. And, a second conventional pressure sensor 62 may be operatively joined to the pressure vessel 10 for measuring the pressure P.sub.2 therein, adjacent to the nozzle second port 54. The difference in pressure P.sub.1 -P.sub.2 may be determined in a conventional comparator 64 which is effective for providing a flow value proportional to the pressure differential. While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein, and it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention. Accordingly, what is desired to be secured by Letters Patent of the United States is the invention as defined and differentiated in the following claims:
052590135	summary	FIELD OF INVENTION This invention relates to apparatus and a method for using hard x-rays to obtain high resolution alteration of observed image dimensions (magnification or reduction) and, more particularly, to an apparatus and method for providing alteration of image dimensions in up to three dimensions employing asymmetric x-ray diffraction from flat, optically polished surfaces of two mutually orthogonal nearly perfect crystals and direct generation of, for example, magnified images by an x-ray sensitive CCD detector or direct generation of precisely reduced undistorted image patterns onto materials such as photo-resists on substrates. BACKGROUND OF THE PRIOR ART There are many scientific and engineering activities which require highly detailed and precise information concerning specific materials. These include: fabrication of novel microelectronic and photonic device materials designed on the atomic scale; rapid solidification of metals to obtain unusual strength, ductility and corrosion resistance; and production of improved ceramics and composite materials which typically are highly vulnerable to thermal and mechanical problems during processing. In these and other comparable activities, it is often essential to examine a specimen of a selected material at very high resolution, e.g. to detect lines of less than 1 micrometer width and/or to resolve lines as little as 1.2 micrometer apart. Such high resolution requires advances in the state of the art of x-ray imaging, as practiced in the techniques of radiography, tomography, and diffraction topography. Also, in many applications, including microcardiography and high resolution tomography, it is highly desirable to obtain three-dimensional imaging of the specimens. In fact, x-ray microtomography is a rapidly developing field for the detection of flaws and defects inside materials produced for industrial applications. For example, the structure of all materials as they are formed is often locally non-uniform over regions of the order of 1 micrometer. Inhomogeneities occurring in diffusion layers and grain boundaries, local compositional variations, regionally homogeneous strains (residual stresses) and inhomogeneous strains, etc., often alter the behavior of materials from their originally designed characteristics. Successful fabrication of tailored materials having structures not found in nature depends entirely on minute structural details and their influence on the properties and performance of the object fabricated therefrom. Similarly, in microelectronic devices, where different atoms are doped in mutually coherent layers, the thickness and shape of doped layers may change and may cause degradation of functional properties intended to be obtained by the designer. What is needed in such instances is a measurement technique to "see" what happens locally, and to pinpoint local events of significance with high spatial resolution. It is to such needs that the present invention is directed. The invention magnifies, in one or two dimensions, parallel projection monochromatic x-ray images. Such images are obtained, for example, by the techniques of radiography, tomography, and diffraction topography, when the specimen is irradiated with well collimated monochromatic x-rays. It should be understood that other materials, such as tissue samples from living beings and plants, also may be studied advantageously by high resolution viewing and adequate magnification to clarify significant details, e.g., the presence of abnormal cells or the like. What is needed, therefore, are apparatus and methods for significantly magnifying a view that is originally generated by the passage of short wave-length hard x-rays through a thin specimen of a selected material. For certain applications, using the same apparatus and method with obvious changes, the x-rays are reflected off a selected surface of a specimen to study its local topography with very high resolution. It is to such needs that the present invention is directed. The invention magnifies, in one or two dimensions, parallel projection monochromatic x-ray images. Such images are obtained, for example, by the techniques of radiography, tomography, and diffraction topography, when the specimen is irradiated with well collimated monochromatic x-rays. A paper titled "Improvement of Spatial Resolution of Monochromatic X-ray CT Using Synchrotron Radiation" by Sakamoto et al., Japanese Journal of Applied Physics, Volume 27, No. 1, January 1988, pp. 127-132, discloses an x-ray computer tomography technique using synchrotron radiation (SR) as an x-ray source to generate CT images of improved quality. A method is disclosed for improving the spatial resolution, involving the one-dimensional magnification of projection images using asymmetric diffraction. The disclosed method employs a scintillator covering the detector surface. The best spatial resolution obtained was about 15 to 20 micrometers, using a magnification factor of 9.0. The dispersal of visible light, generated by x-rays, in the scintillator appeared to degrade significantly the spatial resolution, as stated on page 130 of the same paper. There are numerous devices and systems known and commercially available for generating magnified images of very fine details in material samples. U.S. Pat. No. 4,672,651, to Horiba et al., discloses apparatus and a method in which respective cone-like beams of x-rays are projected from two different directions through a person's body, and the transmitted x-rays are analyzed to generate a projection image. A contrast medium is initially injected into the body to reach a part of the body which is of interest. A direct x-ray detector is used which can also convert a received signal into an optical image which can be directed into a TV camera. U.S. Pat. No. 4,635,197, to Vinegar et al., discloses a high-resolution tomographic imaging method, wherein a sample is scanned at many points in corresponding cross-sections which are separated by a distance less than the width of an x-ray beam of a CAT scanner. The measured density function thus obtained is deconvolved, with the beam width function for the CAT for each of the plurality of points, to thereby obtain the actual density function for the plurality of points. This information is directly used to generate an image of a sample which has a spatial resolution in the axial direction that is smaller than the width of the x-ray beam of the CAT. U.S. Pat. No. 5,012,498, to Cuzin et al., discloses an x-ray tomography device which enables the generation of an image at a plane identified transversely through an object. It comprises an x-ray source which supplies high energy pulses which traverse the object. Both the source of the x-rays and the detector are stationary, and the object is rotated. U.S. Pat. No. Re. 32,779, to Kruger, discloses a radiographic system employing multi-linear arrays of electronic radiation detectors of the CCD type. An x-ray source provides a diverging x-ray beam which passes through portions of a human body to be received first through an image intensifier and then passed through a lens or other focusing device. The transmitted-radiation is focused upon a multi-linear array which comprises a two-dimensional CCD detector. There clearly exists a need for a high resolution, one-, two- or three-dimensional magnification system and corresponding methods which permit magnifications of up to 200 times the original at resolutions enabling study of features less than 1 micrometer in size and for separation of adjacent features at close to the 1 micrometer level of precision. The present invention, as described more fully hereinafter, is believed to answer this need. Persons of ordinary skill in the art, upon understanding the present disclosure, are expected to consider obvious modifications of both the apparatus and the method disclosed herein. Such modifications and variations are intended to be comprehended within the scope of the invention described below in detail SUMMARY OF THE INVENTION Accordingly, it is a principal object of this invention to provide an apparatus for generating a highly magnified or demagnified image of fine structural details, at the micrometer or submicrometer level of resolution, within or on the surface of a specimen, by asymmetric dynamical x-ray diffraction. Because of the reciprocity theorem applicable to x-ray optics, the term "magnification" also implies the shrinkage of an image, that is "demagnification". This is so well known that this implication will not, hereafter, be mentioned explicitly. It is a further object of this invention to provide an apparatus and a method for generating highly magnified images of structural details at the micrometer level within or at the surface of a specimen, by asymmetric dynamical x-ray diffraction, preferably from a flat optically polished surface of a nearly-perfect crystal, using a monochromatic hard x-ray beam. It is an even further object of this invention to provide two-dimensional highly-magnified images of structural details at the micronmeter level in or at the surface of a specimen, by employing a parallel, hard, monochromatic x-ray beam, asymmetrically diffracting the same from optically flat polished surfaces of two nearly perfect crystals placed orthogonally to each other and directly converting the x-ray photons to electrical charges, without prior conversion to optical photons, to generate a high resolution two-dimensional and recordable magnified image. It is another related further object of this invention to provide apparatus and a method for x-ray phase contrast microscopy, in which the two-dimensionally magnified high resolution images of strain fields around flaws and defects in materials are generated in addition to the normal shape images of these flaws and defects, particularly when the initial x-ray beam containing the image of structural details is obtained from specimen materials under Bragg diffraction conditions. It is also a related further object of this invention to provide apparatus and a method for generating a three-dimensional, highly-magnified, high-resolution image of structural details of a specimen, using a parallel beam of hard, monochromatic, x-rays and direct conversion of information-bearing x-ray photons to visible photons. These and other related objects are realized by providing an apparatus comprising: means for applying a parallel first x-ray beam of predetermined energy and brilliance to a portion of the specimen, to thereby generate a parallel second x-ray beam which contains an initial image relating to the specimen; PA1 a first nearly perfect crystal formed to provide a first diffraction surface oriented to receive said second x-ray beam at a first angle of incidence to dynamically diffract the same and to thereby generate a parallel third x-ray beam containing a first one-dimensional magnification of said initial image, said third x-ray beam being reflected with respect to said first diffraction surface at a first angle of reflectance relative thereto; and PA1 x-ray sensitive detector means for receiving said third x-ray beam and directly generating therefrom an output corresponding to a first magnified image; PA1 monochromator means for monochromatizing said first x-ray beam prior to application thereof to said specimen; PA1 means for applying a parallel first x-ray beam of predetermined energy and brilliance to a portion of the specimen, to thereby generate a parallel second x-ray beam which contains an initial image relating to the specimen; PA1 a first nearly perfect crystal formed to provide a first diffraction surface oriented to receive said second x-ray beam at a first angle of incidence to dynamically diffract the same and to thereby generate a parallel third x-ray beam containing a first one-dimensional alteration of said initial image; said third x-ray beam being reflected with respect to said first diffraction surface at a first angle of reflectance relative thereto; PA1 a second nearly perfect crystal, similar to the first nearly perfect crystal, formed to provide a second diffraction surface oriented orthogonally with respect to said first diffraction surface and disposed to receive said third x-ray beam at a second angle of incidence to dynamically diffract the same and to reflect a parallel fourth x-ray beam containing a second one-dimensional alteration of said first dimensional alteration to the same degree, but orthogonally directed to said first dimensional alteration, the combined effect of both one-dimensional alterations being an undistorted two-dimensional alteration of said initial image, said fourth x-ray beam being reflected with respect to said second diffraction surface at a second angle of reflectance relative thereto; and PA1 x-ray sensitive detector means for receiving said fourth x-ray beam and directly generating therefrom an output corresponding to a two-dimensional second magnified image. PA1 means for applying a parallel first x-ray beam of predetermined energy and brilliance to a portion of the specimen, to thereby generate a parallel second x-ray beam which contains an initial image relating to the specimen; PA1 a first highly perfect crystal formed to provide a first diffraction surface oriented to receive said second x-ray beam at a first angle of incidence to dynamically diffract the same and to thereby generate a parallel third x-ray beam containing a first magnification of said initial image, said third x-ray beam being reflected with respect to said first diffraction surface at a first angle of reflectance relative thereto; PA1 a second nearly perfect crystal, similar to the first nearly perfect crystal, formed to provide a second diffraction surface oriented orthogonally with respect to said first diffraction surface and disposed to receive said third x-ray beam at a second angle of incidence to dynamically diffract the same and to reflect a parallel fourth x-ray beam containing a second one-dimensional alteration of said first one-dimensional alteration to the same degree, but orthogonally directed to said first one-dimensional alteration, the combined effect of both one-dimensional alterations being an undistorted two-dimensional alteration of said initial image, said fourth x-ray beam being reflected with respect to said second diffraction surface at a second angle of reflectance relative thereto; PA1 x-ray sensitive detector means for receiving said fourth x-ray beam and directly generating therefrom an output corresponding to a two-dimensional second magnified image; PA1 monochromator means for monochromatizing said first x-ray beam prior to application thereof to said specimen; PA1 disposition adjustment means for providing fine adjustments to the dispositions of said specimen relative to said first nearly perfect crystal, of said first nearly perfect crystal with respect to said second highly perfect crystal, and of said second highly perfect crystal relative to said detector means; PA1 computer means for controlling said adjustment means; PA1 means for rotating said specimen through a predetermined angle; and PA1 means for digitizing and processing data generated by said detector means in relation to a rotation of said specimen to develop a three-dimensionally magnified image of said specimen. PA1 applying a parallel first x-ray beam of predetermined energy and brilliance to a portion of the specimen to generate a parallel second x-ray beam which contains an initial image relating to the specimen; PA1 positioning a first highly-perfect crystal to orient a first diffraction surface thereof to receive said second x-ray beam at a first angle of incidence to dynamically diffract the same to generate a parallel third x-ray beam containing a first magnification of said initial image and reflecting said third x-ray beam with respect to said first diffraction surface and a first angle of reflectance relative thereto; PA1 disposing a second highly-perfect crystal to orient a second diffraction surface thereof orthogonally with respect to said first diffraction surface, said second diffraction surface being disposed to receive said third x-ray beam at a second angle of incidence to dynamically diffract the same and to reflect a parallel fourth x-ray beam containing a second magnification of said first magnification in a direction orthogonal to a direction of said first magnification, said fourth x-ray beam being reflected with respect to said second diffraction surface at a second angle of reflectance relative thereto; and PA1 receiving said fourth x-ray beam at an x-ray sensitive direct detecting means for generating therefrom an output corresponding to a two-dimensional second magnified image. In another aspect of the invention, there is provided a system for obtaining a two-dimensionally altered high-resolution image of a specimen, comprising: In yet another aspect of this invention, there is provided a system for generating a three-dimensionally magnified high-resolution image of a specimen, comprising: In another related aspect of this invention, there is provided a method for directly generating a two- or three-dimensionally magnified high-resolution image of a specimen, comprising the steps of:
	abstract	An integrated head assembly (100) is disclosed for a nuclear reactor. The preferred integrated head assembly includes a lift assembly (150) that supports the reactor vessel closure head (90) and integrated head assembly for removal, a separate support structure (202) supported by a ring beam (151) that sets atop the reactor vessel closure head, a shroud assembly (200), a seismic support system (300), a baffle assembly (500), a missile shield (400), and a CRDM cooling system. The CRDM cooling system draws cooling air into the baffle assembly, downwardly past the CRDMs (96), outwardly to upright air ducts (600), upwardly to an upper plenum (680), and out of the assembly through the air fans (190). In a second embodiment the integrated head assembly (1100) includes a missile shield (1400) and CRDM cooling system (1600) that permits access to individual CRDMs from above.
	abstract	A nuclear power plant comprising a casing which encloses a primary space, a reactor vessel arranged in the primary space, and a reactor core provided in the reactor vessel. The plant further comprises an upper space provided above the casing. The reactor core is separated from the upper space by means of an openable cover arrangement. The casing is designed in such a manner that the primary space is completely closed against the environment to at least the level corresponding to the most highly located part of the reactor core. The upper space is arranged to house a volume of a liquid sufficiently large to permit the filling of the primary space with the liquid to a level located above the most highly located part of the reactor core.
	description	The priority benefit of the Jun. 11, 2003 filing date of the U.S. Provisional Patent Application Ser. No. 60/477,334. titled “A Scanning Probe Microscope Using A Surface Drive Actuator To Position The Scanning Tip”, is hereby claimed. 1. Field of the Invention The present invention relates to a scanning probe microscope. In particular, the invention relates to an electrostatic surface actuator operatively coupled to a scanning probe tip of the scanning probe microscope. 2. Description of Related Art Scanning probe microscopes are known. For example, U.S. Pat. No. 4,724,318 to Binnig describes a method of imaging the surface of objects with atomic resolution. U.S. Pat. No. 6,005,251 to Alexander et al. describes a voice coil scanner for a scanning probe microscope, and U.S. Pat. No. 6,323,483 to Cleveland et al. describes a piezoelectric scanner for a scanning probe microscope. Known scanning probe microscopes use piezoelectric actuators to position the probe tip over the test surface, and such actuators transform the applied voltage into a displacement and are useful for ranges of motions from 100 μm down to 0.1 nm. Unfortunately, these piezoelectric actuators have limitations due to creep and resonant frequencies. When a voltage is applied, a piezoelectric actuator displaces to a corresponding position. The piezoelectric material “relaxes” at that position. When a second voltage is applied, the position corresponding to the second voltage exhibits a “memory” corresponding to the position when the initial voltage had been applied. This is referred to as hysteresis. The position of the piezoelectric actuator depends on the history of the applied voltage. When scanning a probe over a surface, the scan speed is limited by several factors such as tip wear, sample abrasion, cantilever response time, detector sensitivity, software acquisition times, external vibrations, available scanning speed, and the acceleration available to accelerate the tip normal to the surface, among others. Much progress has been made in many of these areas. For example, a research group demonstrated high frequency tips for data storage applications. See Reid et al. (5 MHz, 2N/m Piezoresistive Cantilevers with INCISIVE tips, 1997 International Conference on Solid State Sensors and Actuators, Chicago June 1997, pp. 447-450). However, the acceleration available to accelerate the tip is still extremely limited, being on the order of only several times the acceleration of gravity (g) for conventional scanning probes. When the piezoelectric actuator is used to displace a scanning microscope probe tip, the scan speed is limited. Operating at higher scan speeds results in the probe tip being driven more by mechanical resonance of the piezoelectric actuator than by the applied voltage. This limits the scan rate achievable with the piezoelectric actuator. The large mass of the piezoelectric actuator has a compounding effect when several actuation stages are stacked on each other. For some scanning probe microscopes, it is desirable to mount the z-actuator on an x-y stage. The large mass of the z actuator reduces the scan speed that the x-y stage can produce. The large mass of the z-actuator also implies that a large inverse reaction force is applied to the x-y stage when the probe is accelerated. Although Cleveland et al. (U.S. Pat. No. 6,323,483) and Bartzke et al. (U.S. Pat. No. 5,524,354) disclose a balanced piezoelectric actuator to reduce the inverse reaction force in which two parts of the actuator move in opposite directions, if applied to a z actuator of a scanning probe microscope, the use of a balanced piezoelectric actuator in this role would double the size and mass of the z actuator, further reducing the scanning speed that the x-y stage can provide. Furthermore, control of such actuators can be difficult and renders the overall scanning probe microscope more complex. Some attempts have been made to couple a scanning probe to a micromachined actuator. One approach proposed using a torsional micromachined element to allow fast out-of-plane positioning of either an AFM or STM tip. See Miller et al. (Scaling Torsional Cantilevers for Scanning Probe Microscope Arrays: Theory and Experiment, 1997 International Conference on Solid State Sensors and Actuators, Chicago June 1997, pp. 455-458). At present, scanning probe microscopes use many possible tips. As yet no group has demonstrated a micromachined structure that is capable of scanning standard tips. cl SUMMARY OF THE INVENTION The invention improves the state of the art by providing an electrostatic surface actuator operatively coupled to a scanning probe tip. The electrostatic surface actuator positions and drives the scanning probe tip over the test surface. This and other improvements are realized in a scanning probe microscope that includes a scanning probe tip and an electrostatic surface actuator operatively coupled to the scanning probe tip. The electrostatic surface actuator includes a movable member that has a first surface with a first plurality of electrodes disposed on the first surface and a stationary member that has a second surface with a second plurality of electrodes disposed on the second surface. The movable member is resiliently coupled to the stationary member so that the first and second surfaces are disposed in a confronting relationship and so that the movable member is capable of being displaced with respect to the stationary member in a first direction. The first and second pluralities of electrodes are configured to generate electrostatic forces in response to voltages applied to the first and second plurality of electrodes, the electrostatic forces being aligned to laterally displace the movable member in the first direction generally parallel to the first and second surfaces. The movable member is mechanically attached to the scanning probe tip such that the scanning probe tip is controllably positioned by displacement of the movable member. This and other improvements are alternatively realized with a method of scanning a sample using a surface electrostatic actuator and this method includes mounting, displacing and sensing. The mounting mounts a probe on a movable member of the surface electrostatic actuator. A surface of the movable member is generally disposed to face a surface of a stationary member of the surface electrostatic actuator. The displacing displaces the movable member relative to the stationary member in a direction generally parallel to the surface of the movable member to scan the probe over the sample. The sensing senses a property of the probe that is responsive to the scan of the probe over the sample. The inventor of the present application has concluded that a key limiting factor is the mass of the piezoelectric or magnetic actuator conventionally used to position the tip normal to the sample surface. While the cantilever and the probe tip may have a combined mass of only a few nanograms, the actuator used to position the probe tip has a mass of tens to hundreds of grams. Clearly, in positioning and accelerating the probe, most of the generated force is used to accelerate the actuator itself. It is desirable to have an actuator that more closely matches the mass of the tip. The present invention forms a scanning probe microscope using an electrostatic surface actuator operatively coupled to a scanning probe tip. The scanning probe tip can be an atomic force microscope tip (AFM tip), a magnetic force microscope tip (MFM tip), a scanning tunneling microscope tip (STM tip), a scanning field emission tip (SFM tip), electric force microscope tip (EFM), a scanning thermal microscope tip, and a scanning near-field optical microscope tip (SNOM tip) or any other scanning probe tip. An electrostatic surface actuator provides a large area onto which a probe tip can be adhered. The electrostatic surface actuator can position and drive the scanning probe tip over a large range of motion (100 μm) across the test surface. Moreover, since the electrostatic surface actuator has a high resonant frequency, the probe tip can be moved extremely precisely and accurately at high scan rates. FIG. 1 is a schematic section view of an exemplary scanning probe microscope 1 and its reference axes. Axes X, Y and Z provide three mutually orthogonal axes. Axis Z extends along the direction of movement of the translator of actuator 10 as discussed with respect to FIGS. 2-8. In FIG. 1, microscope 1 includes a base 2, two poles 3, a chuck assembly 4 onto which a sample to be measured is mounted, and a scanner 5 on to which the scanning probe 6 is mounted. The Z axis extends between the two poles 3 and through chuck assembly 4 and scanner 5. Other microscope arrangements (such as are described in U.S. Pat. No. 4,724,318 to Binnig, U.S. Pat. No. 6,005,251 to Alexander et al. and U.S. Pat. No. 6,323,483 to Cleveland et al.), incorporated herein by reference, are within the scope of the invention as discussed further herein. Furthermore, chuck assembly 4 may advantageously include an X, Y, Z adjustable stage for coarse positioning of the sample while scanner 5 executes fine positioning of the scanning probe in X, Y, Z axes. Alternatively, scanner 5 may advantageously include an X, Y, Z adjustable stage 29 (shown in FIG. 2) affixed to a pole for coarse positioning the fine adjustable scanner while chuck assembly 4 fixedly holds the sample. Alternatively, scanner 5 may advantageously include an X, Y adjustable stage affixed to a pole for course positioning the fine adjustable scanner while chuck assembly 4 fixedly holds the sample to an adjustable stage for course positioning of the sample in the Z direction (here defined to be along an axis between poles 3). Many different combinations of course adjustable stages and fine adjustable scanners, that are within the scope of the present invention, may be used in microscope 1. FIG. 2 is a section view, and FIG. 3 is a plan view, of a scanner 5 of the scanning probe microscope 1 according to one example of the present invention. In FIG. 2, scanner 5 of scanning probe microscope 1 includes the scanning probe 6 fixedly coupled to a fine scale Z actuator 10. Z actuator 10 is mounted to holding structure 17 with clamps or other means that fixedly hold a stationary surface of the Z actuator while allowing the free movement of the translating portion of the Z actuator. The clamps or other means that mount Z actuator 10 to holding structure 17 provide for electrical probe tips to contact electrical pads in a way that electrical signals are able to pass between holding structure 17 and actuator 10, or equivalent paths. Holding structure 17 is fixedly attached to a translator of a fine scale X actuator 18. The stator of the fine scale X actuator 18 is flexibly attached to the translator of the fine scale Y actuator 19. The stator of the fine scale Y actuator 19 is fixedly attached to rigid support 120. Fine scale X actuator 18, fine scale Y actuator 19 and rigid support 120 make a drive assembly 121. Although not shown in FIG. 2 or 3, electrical paths are provided to couple electrical signals from rigid support 120 to holding structure 17. Preferably, probe 6 is affixed to Z actuator 10 so that cantilever 8 (see FIG. 5) of probe 6 is disposed at a small angle with respect to the surface of a sample to be measured 27. The relative orientation of probe 6 and Z actuator 10 as well as the constituent parts of probe 6 are shown in more detail in FIG. 5. The small angle between cantilever 8 and the surface of the sample is for example, about 10 degrees, and provides clearance so that parts of probe tip 7) do not contact the surface 27 of sample 28 when the scanning probe microscope is in operation. A measurement system is attached to scanner 5 of scanning probe microscope 1. This measurement system serves to detect and measure the deflections of cantilever 8. The measurement system includes a first folding mirror 21 fixedly attached to the translator of fine scale Y actuator 19 and a second folding mirror 22 fixedly attached to the translator of fine scale X actuator 18. The measurement system also includes a laser diode and collimator 23 and a quadrant photo detector 26 (both out of the plane of the section view of FIG. 2, see FIG. 3). Laser diode and collimator 23 forms and reflects a light beam off first folding mirror 21 as an incident light beam 24. Incident light beam 24 reflects off second folding mirror 22, and back off of a reflective surface of cantilever 8 (see FIG. 5) of scanning probe 6, and from there off second folding mirror 22 as reflected light beam 25. Reflected light beam 25 reflects off first folding mirror 21 into quadrant photo detector 26. Other measurement systems are known and could be substituted for the measurement system described above. In particular, a piezoresistor can be incorporated into the base of the cantilever 8. Deflections of the cantilever would then cause changes in the resistance of the piezoresistor. Alternatively, an optical interferometer can be used to detect the position of the cantilever 8 relative to a reference surface. The position of the cantilever 8 could also be monitored by measuring the capacitance between cantilever 8 and a fixed surface. Other methods of measuring the position of cantilever 8 will be evident to one skilled in the art. FIG. 3 is a plan view of a two-dimensional fine scale actuator of scanner 5 capable of translating along both the X and Y axes as depicted in a section view in FIG. 2. Depicted are folding mirrors 21, 22, laser, collimator and quadrant photo detector 23, 26. In FIG. 3, the two-dimensional fine scale actuator is a piezoelectric driven two-dimensional actuator. Rigid structure 120 is fixedly coupled to one pole of the scanning probe microscope 1 (possibly through a large scale XY or XYZ or Z adjustable stage) while sample 27 is fixedly attached (possibly through an adjustable stage) to the other pole of the scanning probe microscope. The translator of the Y actuator 19 (on which folding mirror 21 is affixed) is flexibly coupled to rigid structure 120 through three main flexure structures 40 disposed roughly at three corners of the four corners of the translator of the Y actuator 19. These three flexure structures are structures similar to corresponding structures described in U.S. Pat. No. 6,215,222 to Hoen, titled Optical Cross-Connect Switch Using Electrostatic Surface Actuators, or equivalent. The translator of Y actuator 19 is coupled to a first end of a Y pivot arm 124 through a pivot flexure 306, and rigid structure 120 is coupled to a fulcrum of Y pivot arm 124 through another pivot flexure 304. Rigid structure 120 is fixedly attached to one end of a Y piezoelectric actuator 122, and the second end of Y pivot arm 124 is coupled through a pivot flexure 302 to the other end of Y piezoelectric actuator 122. The pivot flexures 302, 304, 306 accommodate modest rotational movement about axes normal to the XY plane, but are stiff to permit the piezoelectric actuator to push and pull on the second end of pivot arm 124 and permit first end of pivot arm 124 to push and pull on the translator of Y actuator 19. The translator of Y actuator 19 serves as a rigid structure for the X actuator 18. The translator of X actuator 18 is flexibly coupled to the translator of Y actuator 19 through three main flexure structures 41 disposed roughly at three corners of the four corners of the translator of X actuator 18, and folding mirror 22 is affixed to the translator of X actuator 18. The three main flexure structures coupling the X translator to the Y translator are substantially the same design as the three main flexure structures coupling the Y translator to rigid structure 120. These three flexure structures are structures similar to corresponding structures described in U.S. Pat. No. 6,215,222 to Hoen or equivalent. The translator of X actuator 18 is coupled to piezoelectric actuator 132 in a way substantially the same as the translator of Y actuator 19 is coupled to piezoelectric actuator 122. More specifically, the translator of X actuator 18 is coupled to a first end of an X pivot arm 134 through a pivot flexure, and the translator of Y actuator 19 is coupled to a fulcrum of X pivot arm 134 through another pivot flexure. The translator of Y actuator 19 is fixedly attached to one end of an X piezoelectric 132, and the second end of X pivot arm 134 is coupled through a pivot flexure to the other end of the X piezoelectric 132. These pivot flexures accommodate modest rotational movement about axes normal to the XY plane, but are stiff to permit the piezoelectric to push and pull on the second end of pivot arm 134 and permit the first end of pivot arm 134 to push and pull on the translator of X actuator 18. As can be seen in FIG. 3, there are two main flexure structures 40 on one side of the fulcrum at 304 and only one main flexure structure 40 on the other side of the fulcrum at 304. For Y pivot arm 124, the position along the movable translator 19 of the pivot flexure 306 at the first end of pivot arm 124 is adjusted to balance the spring forces of the main flexure structures 40. This ensures smooth translation without rotation. When all main flexure structures provide equal spring forces, it will be necessary to position the pivot flexure 306 at the first end of the pivot arm 124 closer to end of the translator where two main flexure structures 40 are formed to ensure smooth translation without rotation. The X pivot arm 134 design is analogous to the Y pivot arm design. For each of the X and Y pivot arms, the positions of the pivot flexure at the fulcrums, for example at 304, are adjusted to provide motion amplitude multiplication or mechanical advantage as required. An arrangement providing amplitude multiplication is illustrated. Many of the components of the two-dimensional fine scale actuator of scanner 5 shown in FIGS. 2 and 3 have the same thickness and can be made advantageously from a single plate of material. Common machining techniques such as wire electrical discharge machining (EDM) or laser machining can be used to form the X actuator 18, Y actuator 19, and their associated flexures 40, pivot arms and pivot flexures. Suitable materials for the scanner 5 include aluminum, high strength steel and other materials that have a large ratio between Youngs modulus and density. In operation, the X and Y scanner, depicted in FIGS. 2 and 3, scans holding structure 17 and actuator 10 over the sample 27. Actuator 10 adjusts to ensure that probe tip 7 is just in contact with the surface of sample 27 or just above the surface of sample 27 or is oscillating above the surface of sample 27 or is oscillating and contacting the surface of sample 27 or is in whatever other modality of scanning is required by the user. When probe tip 7 encounters a high spot on the surface of sample 27, cantilever 8 bends, and the reflective surface of cantilever 8 (on the opposite side from probe tip 7) reflects the reflected light beam 25 at a new angle in a first direction. Similarly, on irregular surfaces of sample, the cantilever can twist when the probe tip scans over the irregular surface and the light beam reflects in a second direction. The flexure of the cantilever, both bending and twisting, causes reflected light beam 25 to project on, and be detected by, quadrant photo detector 26 with an offset in the two directions proportional to the amount of bending and twisting. As described above, probe tip 7 is scanned over sample 27; however, it is the relative motion between probe tip 7 and sample 27 that is required. Scanning probe 6 could be fixedly mounted and sample 27 could be mounted on actuator 10 so that sample 27 is scanned over probe tip 7. Such a scanning sample microscope would require a corresponding adjustment of the measuring system to measure deflection of cantilever 8. Sample 27 is preferably mounted in a chuck on a stage movable in X, Y and Z directions to provide large scale movement and permit the X, Y and Z actuators to provide fine scanning movements. Here too, it is the relative motion between probe tip 7 and sample 27 that is required. Alternatively, a large scale X, Y, Z adjustable stage could be attached to the rigid structure 120 of the set of fine scale stages and provide large scale motion of the probe with respect to the sample. A preferred actuator technology for this application is an electrostatic surface actuator. Electrostatic surface actuators themselves have been described in a number of patents. In particular, Higuchi et al., Electrostatic Actuator, U.S. Pat. No. 5,378,954, Hoen et al., Electrostatic Actuator with Alternating Voltage Patterns, U.S. Pat. No. 5,986,381, and Hoen, Optical Cross-Connect Switch Using Electrostatic Surface Actuators, U.S. Pat. No. 6,215,222, all incorporated herein by reference. FIGS. 4-8 show details of an electrostatic surface actuator such as might be used as actuator 10 in FIGS. 2 and 3. FIG. 4 depicts a plan view of the actuator showing the location of section lines 5-5′ and 6-6′. FIG. 5 depicts the view of the section through section line 5-5′, and FIG. 6 depicts the view of the section through section line 6-6′. FIGS. 7 and 8 depict facing views of the stator and translator, respectively, of the electrostatic surface actuator. In FIG. 4, translator 34 is shown overlaying stator 36. Translator 34 is flexibly coupled to stator 36 through four flexure structures 42, two flexure structures coupled on each side of translator 34. In the exemplary embodiment shown, each flexure structure 42 includes four individual flexures 15. Eight translator supports 38 are affixed to the upper surface of the stator. The four individual flexures 15 of each of the flexure structures 40 are integrally formed with translator 34. Two central flexures 15 of each flexure structure 42 are integrally affixed at a first end to translator 34 and at a second end to rigid floating element 16. Each of the two outside flexures 15 of each flexure structure 42 is attached at a first end to a corresponding one of the eight translator supports 38 and at a second end to rigid floating element 16. The flexure structures allow the translator to move in one preferred direction relative to the stator, and although small motions are possible in the other two orthogonal directions, such orthogonal displacement is minimal. As a more specific example, the flexures 15 may have a thickness of 2 μm and a depth of 100 μm. Affixed to one end of the translator is scanning probe handle 9, cantilever 8 and probe tip 7. An alternative location on which to mount scanning probe 6 (e.g., scanning probe handle 9, cantilever 8 and probe tip 7) is mounting pad 30 on a top surface of the translator. FIG. 5 shows a cross-section through section line 5-5′ of electrostatic surface actuator 10 with a scanning probe 6 mounted on the actuator. Scanning probe 6 includes probe tip 7, cantilever 8 and handle 9. Handle 9 is called a “handle” since it is formed to be large enough to be able to be handled whereas cantilever 8 and probe tip 7 are of a size that is not easily handled. The surface 403 (also shown in FIG. 4) of cantilever 8 opposite probe tip 7 is reflective to work with the measurement system described with respect to FIGS. 2 and 3. It is possible, as in an alternative embodiment, to fabricate the cantilever and probe attached to the surface drive actuator without the handle. Electrostatic surface actuator 10 is typically formed of a stator assembly 37 and a translator assembly 39. The stator assembly includes a stator 36, translator support 12 formed on an outer perimeter of stator 36 and stator electrodes 56 formed on a more central portion of stator 36. The stator electrodes are either formed on an insulating stator or formed on surface 404 of insulating layer 408 formed on the stator (collectively referred to as insulatively spaced from the stator). The translator assembly includes a rigid frame 13 fixedly attached to translator support 12, a translator 34, flexures 15 (see FIGS. 4 and 6) coupled between rigid frame 13 and translator 34, and translator electrodes 58 (collectively, translator and stator electrodes are called driving electrodes) formed on a surface of translator 34 to be in a confronting relationship with stator electrodes 56. The translator electrodes are either formed on an insulating translator or formed on surface 402 of insulating layer 406 formed on the translator (collectively referred to as insulatively spaced from the translator). Since rigid frame 13, flexures 15 and translator 16 are formed to be very thin, handle 14 is advantageously formed on rigid frame 13 and translator 34 to provide a stronger structure and something to hold on to, if needed, when the translator assembly is attached to the stator assembly. It is possible, as in an alternative embodiment, to fabricate the rigid frame 13, flexures 15 and translator 16 without handle 14. In general, rigid frame 13, translator 34, flexures 15, and floating post 16 are usually formed from a silicon wafer using common micromachining techniques. Similarly, the stator can be fabricated using conventional integrated circuit techniques on a silicon wafer. As described in U.S. Pat. No. 5,986,381 to Hoen et al., or U.S. Pat. No. 6,215,222 to Hoen, changing the voltage on one of the stator electrodes steps the position to the translator. The translator can be moved in sub-nanometer sized steps, and in fact, moved in steps that are only a fractional part of a tenth of a nanometer. Because the translator sits in a steep potential well, the translator position is accurate and repeatable. Translator 34 is a movable member that has a first surface, and stator 36 is a stationary member that has a second surface. The movable member includes first electrodes disposed on the first surface, and the stationary member includes second electrodes disposed on the second surface (shown in FIGS. 7 and 8) located on the opposing surfaces of the translator and the stator. The movable member is resiliently coupled to the stationary member so that the first and second surfaces are disposed in a confronting relationship and so that the movable member is capable of being displaced along the Z direction with respect to the stationary member. When electrostatic surface actuator 10 is activated, the electrostatic forces created by applying voltages to the electrodes of the translator and the stator can be manipulated to laterally displace the translator with respect to the stator in the preferred direction. The displacement operation of the translator and the stator will be described below. The lateral movement of the translator moves the scanning probe tip that is adhered to translator 34 (e.g., an end of, or mounting pad 30 of, the translator 34). FIG. 6 shows a view of the section through section line 6-6′ of FIG. 4. FIG. 6 depicts stator 36 translator support 12, translator handle 14, rigid frame 13 and flexures 15. Translator 34 is out of the plane of the section depicted as FIG. 6 (see FIG. 4). In FIGS. 7 and 8, two sets of drive electrodes, electrodes 58 of the translator and stator electrodes 56, are shown. The drive electrodes 58 are located on the bottom surface of the translator 34, while the drive electrodes 56 are located on the upper surface of the stator 36. These drive electrodes generate the electrostatic forces that will displace the translator 34 in the Z direction. The generation of the electrostatic forces by the drive electrodes will be described below. Each drive electrode is a thin strip of conductive material that is parallel to the other drive electrodes in the set. In a preferred embodiment, a thin layer of insulating material is located between the translator electrodes and the translator 34. Similarly, another layer of insulating material is located between the stator electrodes and the stator 36. These insulating layers electrically isolate each electrode so that electrical charge on a particular electrode is not lost to another electrode via the stator or the translator. More specifically, a silicon oxide, silicon nitride, or aluminum nitride formed by plasma-enhanced chemical vapor deposition, sputter deposition, or low-pressure chemical vapor deposition is used to insulatively space the electrodes from the stator or translator. The stator or translator is generally formed from a slightly doped silicon wafer. The wafer can be either p or n doped. FIG. 7 shows the surface of stator 36 that faces translator 34. FIG. 8 shows the surface of translator 34 that faces stator 36. The translator electrodes are positioned in a mirror image of the stator electrodes. Therefore, the translator electrodes are disposed facing the stator electrodes in actuator 10. The electrostatic forces that laterally displace the translator 34 are generated by the translator electrodes and the stator electrodes. The electrostatic forces between the opposing electrodes are generated by applying different voltages to these electrodes. By varying the electrostatic forces between these drive electrodes, the translator 34 can be displaced in a predetermined direction. A repeat distance is defined by the distance between the center of a translator electrode held at a particular voltage and the center of the nearest translator electrode, respectively, held at approximately the same voltage. In a preferred embodiment, where every other translator electrode is held at the same voltage, the repeat distance is twice the center-to-center spacing of the translator electrodes, assuming that the spacing is constant. To ensure that the generated electrostatic forces will be optimal for laterally displacing the translator 34, it is desirable to keep the ratio of the repeat distance associated with the translator electrodes and the gap distance between the stator electrodes and the translator electrodes within a certain range. To minimize the forces in a direction transverse to the direction of movement in the one-dimensional actuator 10, it is desirable to keep the repeat distance divided by the distance between the stator electrodes and the translator electrodes below approximately sixteen. There are numerous ways to apply the voltages to the drive electrodes to generate and vary the electrostatic forces. An exemplary way to generate and vary the electrostatic forces between the drive electrodes to displace the translator 34 will now be described with reference to FIGS. 9, 10 and 11. In FIG. 9, cross-sectional segments of the translator 34 and the stator 36 are shown. The translator is illustrated with a number of translator electrodes 60, 62, 64, 66, 68, 70 and 72 that are electrically coupled to either a voltage source 74 or a voltage source 76 in an alternating fashion. The voltage source 74 provides a constant predetermined voltage (of, for example, positive five volts, but may advantageously range from, for example, 3 volts to 100 volts) to the electrodes 62, 66 and 70, while the voltage source 76 provides a constant voltage (of, for example, zero volts, but may advantageously range from, for example, 10 V to −100V) to electrodes 60, 64, 68 and 72. The stator 36 is illustrated with a number of stator electrodes 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108 and 110 that are coupled to a controller 112. The controller 112 selectively provides either zero volts or a predetermined voltage (e.g., positive five volts) to the stator electrodes 78-110. The translator electrodes 60-72 are spaced such that approximately six translator electrodes are situated for a specific length L, while approximately seven stator electrodes are situated for the same length L. Since the stator will remain stationary as the translator is laterally displaced, the left edge of the stator electrode 94 will be designated as a reference point Xref. Initially, in one example, the controller 112 applies five volts to stator electrodes 76, 80, 84, 86, 90, 94, 98, 100 and 104, as shown in FIG. 9. The electrodes that are supplied with five volts have been cross-hatched to ease identification. To displace translator 34 in the preferred direction, i.e. to the left, every seventh stator electrode is switched from the original voltage of zero or five volts to the other voltage of zero or five volts by the controller 112. In this exemplary manner, the stator electrodes 90 and 104 have been switched from five volts to zero volts, as shown in FIG. 10. This change causes a net electrostatic force on the translator 34, which incrementally displaces the translator 34 in the preferred direction. Next, every seventh stator electrode 78, 92 and 106 that is just right of the stator electrodes 90 and 104 that were previously switched are switched to further displace the translator in the preferred direction. The stator electrodes 78, 92 and 106 are switched from zero volts to five volts by the controller 112. The resulting voltage pattern is shown in FIG. 11. Similar to the previous change, this change in the voltage pattern of the stator electrodes 78-110 incrementally displaces the translator in the preferred direction. By continually switching the voltages for every seventh stator electrode in this fashion, the translator is further moved in the preferred direction. However, there is a limit to the total displacement of the translator from its original position due to the fact that the translator is physically coupled to the stator 36 by the flexures 40 and the translator supports 38. Returning to FIG. 9, it is possible to move the translator in smaller increments than that caused by the method described above. Instead of changing the voltage on electrodes 90 and 104 from five volts to zero volts, the voltage on these electrodes can be changed a fraction of five volts, causing the translator to move less than the increment shown between FIG. 9 and FIG. 10. Indeed, under many operating ranges, the position of the translator is linear with the voltage applied to the electrodes 90 and 104. Other configurations of drive electrodes and applied voltages are possible for applying lateral forces to the movable translator 34. The method of applying voltages described above is directly extendable to groups of electrodes in which the first set of electrodes is composed of groups of 2n electrodes and the second set of electrodes is composed of groups of 2n±1 electrodes. Similar to the above method, a spatially alternating pattern of voltages is applied to the first set of electrodes and a spatially alternating pattern of voltages is applied to the second set of electrodes. Because the second set of electrodes consists of groups of an odd number of electrodes, two electrodes in each group have the same voltage as one of their nearest neighbors. Similar to the above method, movement of the translator is induced by switching the voltage on the electrodes that have the same voltage as their nearest neighbor. Other electrostatic surface drives are also applicable to this invention. One example is described by Higuchi et al. in U.S. Pat. No. 5,448,124. In this case, the pitches of the first and second set of drive electrodes are similar and three-phase temporally alternating voltages are applied to both the first and second sets of drive electrodes. The position of the translator is controlled by varying the phase difference between the three phase signals applied to the first and second sets of electrodes. FIG. 12 is a top plan view of an alternative embodiment of a two-dimensional fine scale actuator 200 capable of translating along both the X and Y axes with respect to stator 236. A two-dimensional electrostatic surface actuator may be used in the present invention. The two-dimensional electrostatic surface actuator is easily generalized in light of the description above of the one-dimensional actuator 10. In FIG. 12, rigid structure 213 is flexibly coupled to Y translator 219 through four main flexure structures 40 (substantially similar to the flexure structures discussed with respect to FIGS. 4 and 6). In the embodiment of FIG. 12, Y translator 219 is electrostatically driven along the Y axis with a drive mechanism similar to the drive mechanism discussed with respect to FIGS. 4-11. Then, Y translator 219 serves as a rigid structure to which X translator 218 is flexibly coupled through four main flexures (substantially similar to the flexures discussed with respect to FIGS. 4 and 6). In the embodiment of FIG. 12, X translator 218 is electrostatically driven along the X axis with a drive mechanism similar to the drive mechanism discussed with respect to FIGS. 4-11. For the same level of performance, the electrostatically driven XY translators 218, 219 of FIG. 12 tend to be lighter than the corresponding piezoelectrically driven XY translators 18, 19 of FIG. 3. The lighter translators have a faster slew rate and can therefore scan at a faster rate. Furthermore, the electrostatic surface actuators do not have the memory or creep problems of piezoelectric actuators where the position of the piezoelectric actuator depends on the history of the applied voltage. In FIG. 13, scanner 5 (see FIG. 1 for the scanner's relationship to the microscope 1) includes linear piezoelectric actuator 210 and two-dimensional fine scale actuator 200 (see FIG. 12) shown schematically in FIG. 13 with scanning probe 6 attached to mounting pad 30 (see FIG. 12). Owing to the light weight and other properties of the electrostatic surface actuator 200, scanner 5 has improved scan rate performance over known similar scanners. In yet a further improvement to achieve even a faster slew rate, vibrations, that would normally result from the fast and sudden movement of scanning probe 6, are isolated with a structure of FIG. 14. When the structure of FIG. 14 is used as linear actuator 10 in the microscope of FIG. 1, two co-linear actuators 140, 150 are provided. Scanning probe 6 is mounted on mounting pad 30 of linear actuator 140, and a corresponding mass is mounted on mounting pad 130 of linear actuator 150. Alternatively, probe 6 may be mounted on mounting pad 130 and the corresponding mass may be mounted on mounting pad 30. Electrodes disposed between stator and translator of electrostatic surface actuators 140, 150 are configured so that when actuator 140 moves to the right, actuator 150 moves to the left, and vice versa. In this case actuator 150 does not help drive the probe, but it will reduce the inverse reaction force. Actuator 150 is loaded with a mass that matches the mass of probe 6 to better neutralize vibrations created by the motion actuator 140. In an alternative improvement to achieve a faster slew rate, vibrations are isolated with a structure of FIG. 15. The embodiment of FIG. 15 differs from the embodiment of FIG. 14 in that the embodiment of FIG. 15 includes two direction reversing structures, each direction reversing structure including pivot arm 142 and pivot flexures 144, 146 and 148 and are similar to the pivot arm structures 134 discussed above with respect to FIG. 3. The translator 140 of this embodiment of actuator 10 is coupled to a first end of the pivot arm 142 through pivot flexure 144, and a rigid structure 120 is coupled to a fulcrum of pivot arm 142 through pivot flexure 146. The second end of pivot arm 142 is coupled through pivot flexure 148 to the translator 150. In this way, when translator 140 moves left, translator 150 will move right, and vice versa. The pivot flexures accommodate modest rotational movement about axes normal to the XY plane, but are stiff to permit translator 140 to push and pull on the first end of pivot arm 142 and permit the second end of pivot arm 142 to pull and push on the translator 150. By using the direction reversing structures, the embodiment of FIG. 15 needs to have drive electrodes under only one of the translators 140, 150 thus simplifying the drive electronics. The embodiments of both FIGS. 14 and 15 use micromachined balanced actuators. By starting with a low mass electrostatic surface actuator, the embodiments of FIGS. 14 and 15 are able to achieve unsurpassed slew rates. Furthermore, the principles of vibration isolation of the electrostatic surface actuator of FIG. 14 or 15 can be equally well applied to the electrostatic surface actuators of the embodiment of FIG. 12. In some instances, it is desirable to operate Z actuator 10 in a humid or aqueous environment. Water, since it is a polar molecule, tends to shield the electrostatic potentials produced by the stator electrodes 56 and translator electrodes 58 and reduces the forces induced by the Z actuator 10. The embodiment 300 of FIG. 16 circumvents this problem by interposing a layer of dielectric fluid 310 between the translator 34 and stator 36. A suitable dielectric fluid is sold by the 3M company under the trade name FLUORINERT. Transformer oils are also suitable; one such oil is sold by the Shell Oil Corporation under the trade name DIALA Oil M. A further embodiment 350 for protecting the electrodes from a water environment is shown in FIG. 17. In this case, a hydrophobic dielectric film 355 is coated on parts of the Z actuator 10 exterior to the stator electrodes 56 and translator electrodes 58. Because the gaps between the surfaces are very small, ranging from 100 microns to 1 micron, liquid water cannot traverse these regions and satisfactory operation of the Z actuator is achieved. Furthermore, the principles of isolating the electrodes from an aqueous environment shown in FIGS. 16 and 17 can be equally well applied to the electrostatic surface actuators of FIGS. 12, 14, and 15. A method of scanning with a probe tip in accordance with the invention will be described with reference to FIG. 18. The method of scanning a sample uses a surface electrostatic actuator is illustrated in FIG. 18. Initially, at 161, a probe tip and an electrostatic surface actuator comprising a stator and a translator are provided. Then, at 162, a probe is mounted on a movable member of the surface electrostatic actuator. A surface of the movable member is generally disposed to face a surface of a stationary member of the surface electrostatic actuator. Then, at 164, the movable member is displaced in a direction generally parallel to the surface of the movable member. This scans the probe over the sample where the cantilever 8 flexes in response to the probe tip scanning over the surface. Additional responses of the tip are also possible depending on the method of scanning probe microscopy being used. For example, if the tip is a scanning tunneling microscope tip, then different currents will flow when a voltage is applied to cantilever 8. Alternatively, if the tip is a scanning thermal microscope tip, then the tip will exhibit increased or decreased heat loss in response to changes in the sample surface. Further responses of the tip will be apparent to one skilled in the art of scanning probe microscopy. At 166, a property (e.g., flexing, heat loss, differing currents, etc.) of the probe that is responsive to the scan of the probe over the sample is sensed. Conventionally, the displacement of the tip causes the flexure to bend and to change the position of a reflected beam of light. This method of sensing is shown in FIGS. 1 and 2. Another method of sensing the deflection of the tip is to detect a change of resistance of a piezoresistor that is incorporated on the flexure. Yet another method of sensing the deflection of the tip is to use a laser interferometer to detect deflections of the cantilever relative to a reference surface. As described above, the method of sensing could entail detecting a change in current flow through the tip or detecting a difference in heat loss through the tip. Having described preferred embodiments of a novel scanning probe microscope using a surface drive actuator to position a scanning tip (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope of the invention as defined by the appended claims.
	claims	1. A method of repairing a weld connection in a jet pump diffuser using a weld repair device including a lower ring section and an upper ring section, the method comprising:forming pockets in an exterior surface of the diffuser on opposite sides of the weld to be repaired;fitting a plurality of grippers into a corresponding plurality of aligned gripper slots in the lower ring section and the upper ring section, wherein at least one of the gripper slots and the grippers defines cam surfaces shaped to drive the grippers radially inward as the lower and upper ring sections are drawn toward each other;placing the lower ring section and the upper ring section around a circumference of the diffuser on opposite sides of the weld, respectively, with lugs on the grippers engaging the pockets; andtightening connector bolts secured between the lower ring section and the upper ring section to draw the lower and upper ring sections toward each other,wherein the step of forming pockets is practiced by selecting pocket locations above and below the weld that result in no relative differential expansion between the weld repair device and the jet pump diffuser. 2. A method of repairing a jet pump diffuser weld, the method comprising:forming pockets in an exterior surface of the diffuser on opposite sides of a weld to be repaired;fitting a lower ring section and an upper ring section entirely around a circumference of the diffuser on opposite sides of the weld to be repaired;forming a plurality of aligned gripper slots in intermittent positions in an inner circumference of the lower and upper ring sections;fitting a corresponding plurality of grippers into the gripper slots facing radially inward toward the diffuser;forming the grippers with double-tapered cam surfaces respectively engaging the lower ring section and the upper ring section, the double-tapered cam surfaces being tapered radially outward from axially distal ends of the grippers toward a central apex to drive the grippers radially inward as the lower and upper ring sections are drawn toward each other;providing the grippers with engaging lugs shaped to fit in the pockets formed on the opposite sides of the weld; andtightening a plurality of connector bolts secured between the lower ring section and the upper ring section to thereby draw the lower and upper ring sections toward each other. 3. A method according to claim 2, wherein the method is performed in situ in a shroud to vessel annulus in a boiling water nuclear reactor. 4. A method according to claim 2, wherein the forming step is practiced by electric discharge machining the diffuser exterior surface. 5. A method according to claim 4, further comprising polishing the diffuser exterior surface subjected to electric discharge machining. 6. A method according to claim 2, wherein the forming pockets step is practiced by forming pockets comprising multiple grooves. 7. A method according to claim 2, wherein the step of forming the gripper slots is practiced by forming the gripper slots with angled surfaces as the cam surfaces engaging the tapered surfaces of the grippers. 8. A method according to claim 2, wherein if the opposite sides of the weld in the diffuser exterior surface in which the pockets are formed are of different materials, the method further comprises selecting a material of the grippers such that its coefficient of thermal expansion falls between coefficients of thermal expansion of the different materials. 9. A method of repairing a jet pump diffuser weld, the method comprising:forming pockets in an exterior surface of the diffuser on opposite sides of a weld to be repaired;fitting a lower ring section and an upper ring section entirely around a circumference of the diffuser on opposite sides of the weld to be repaired;forming a plurality of aligned gripper slots in an inner circumference of the lower and upper ring sections;fitting a corresponding plurality of grippers into the gripper slots facing radially inward toward the diffuser;forming the grippers with double-tapered cam surfaces respectively engaging the lower ring section and the upper ring section, the double-tapered cam surfaces being tapered radially outward from axially distal ends of the grippers toward a central apex to drive the grippers radially inward as the lower and upper ring sections are drawn toward each other;providing the grippers with engaging lugs shaped to fit in the pockets formed on the opposite sides of the weld; andtightening a plurality of connector bolts secured between the lower ring section and the upper ring section to thereby draw the lower and upper ring sections toward each other,wherein the step of forming pockets is practiced by selecting pocket locations above and below the weld that result in no relative differential expansion between weld repair components and the diffuser. 10. A method of repairing a weld in a thin wall welded pipe, the method comprising:fitting a lower ring section and an upper ring section entirely around a circumference of the thin wall welded pipe on opposite sides of a weld to be repaired;fitting a plurality of grippers into aligned gripper slots formed intermittently in an inner circumference of the lower and upper ring sections, wherein the step of fitting the plurality of grippers is practiced such that the plurality of grippers face radially inward toward the thin wall welded pipe, wherein the grippers include double-tapered cam surfaces respectively engaging the lower ring section and the upper ring section, the double-tapered cam surfaces being tapered radially outward from axially distal ends of the grippers toward a central apex to drive the grippers radially inward as the lower and upper ring sections are drawn toward each other;securing a plurality of connector bolts between the lower ring section and the upper ring section; andtightening the connector bolts to draw the lower and upper ring sections toward each other. 11. A weld repair method according to claim 10, wherein the opposite sides of the weld comprise different materials, the method further comprising selecting a material of the grippers such that its coefficient of thermal expansion falls between coefficients of thermal expansion of the different materials. 12. A weld repair method according to claim 10, wherein the pipe on one side of the weld is cylindrical and on an opposite side of the weld is conical constituting a shape change, the method further comprising configuring the lower and upper ring sections and the grippers to accommodate the shape change. 13. A weld repair method according to claim 10, further comprising fitting engaging lugs of the grippers into pockets formed in an exterior surface of the thin wall welded pipe on the opposite sides of the weld.
	description	A unique characteristic of nuclear energy is that used fuel may be separated from other components and reused as new fuel. For instance, the nuclear materials contained in a spent rod from a nuclear power plant can be reprocessed and reused to produce new fuel rods. Practically all nuclear materials, including uranium and plutonium, can be reprocessed in this manner. Fuel elements, including fuel rods in nuclear reactors, become unusable not so much on account of actual depletion of the fissionable fuel values, but because of the accumulation within the element of fission products. These fission products can interfere with the neutron flux within the reactor. Consequently, fuel elements are withdrawn from the reactor long before the fuel values are anywhere near to being completely consumed. The withdrawn or used nuclear fuel (sometimes referred to as spent fuel rods) have significant fuel value. At the same time, it is desirable to recover the valuable by-products of reactor operation, the transmutation products such as plutonium, which is a fissionable fuel, and certain isotopes of the fission products which are useful in many different fields and have many different applications. Many research reactor fuel assemblies or fuel plates contain a nuclear material in combination with aluminum, such as a uranium-aluminum alloy or a uranium aluminide dispersed in a continuous aluminum phase. Aluminum is also widely used as a fuel element cladding material because it has a relatively low neutron absorption cross-section and has excellent physical and chemical properties. One type of aluminum used as a cladding material includes 1100 aluminum. Other alloys include 6061 and 6063. A conventional process for recovering nuclear materials from used nuclear fuel is a dissolution process during which the aluminum material is dissolved. In one embodiment, the process for recovering fissionable materials is an aqueous process during which the fuel elements are dissolved in an acidic solution. Fuel elements containing an aluminum-uranium alloy contained in aluminum cladding, for instance, may be dissolved in a mercury-catalyzed, nitric acid flowsheet. After the fuel is dissolved in the solution, the uranium can be recovered from the aluminum and fission products. The dissolution process must be carefully controlled to ensure that the used nuclear fuel dissolves at an acceptable rate without producing unacceptable amounts of off-gas. The off-gas generation rate during nuclear fuel dissolution changes depending upon many factors. Thus, the off-gas generation rate is never constant. Off-gases that are produced include nitrogen oxides, hydrogen gas, in addition to volatile fission product gases, such as krypton, xenon and iodine vapor. The mechanisms that impact off-gas concentrations and species that produce the above gases during the course of dissolution are complex and are not well understood. Spikes in the generation of off-gases, however, can produce significant amounts of hydrogen gas which may drift above safety levels in the processing plant. In the past, various processes have been proposed in order to control the generation of off-gases. For instance, U.S. Pat. No. 3,119,658 to Schulz, which is incorporated herein by reference, suggests that the rate of reactions during dissolution can be controlled by adding small amounts of nickelous nitrate or nickel II ion. The process proposed in the '658 patent, however, has had limited success. Consequently, a need exists for a method or process of decreasing the off-gas generation rate or hydrogen gas concentration in the off-gas during used nuclear fuel dissolution processes. Controlling the off-gas rate and/or the amount of hydrogen gas being produced can significantly increase throughput and efficiency. In general, the present disclosure is directed to a process for controlling the dissolution of aluminum in an acid bath. More particularly, the process of the present disclosure is directed to dissolving aluminum under controlled conditions in order to positively affect off-gas production during the process. For instance, in one embodiment, the rate at which hydrogen gas evolves during the process can be controlled and reduced. The process of the present disclosure can be used to reduce the rate at which hydrogen gas is created, reduce the amount of hydrogen gas concentration in the off-gas during the process, and/or reduce the total amount of hydrogen gas that is produced during the process. In one embodiment, the present disclosure is directed to a process for dissolving aluminum during the recovery of a nuclear fuel. The process includes the steps of contacting a material containing aluminum and a nuclear fuel with an acid in the presence of a metal catalyst and an iron source. The acid and metal catalyst dissolve the aluminum. In accordance with the present disclosure, the iron source is present in an amount sufficient to decrease hydrogen off-gas production during dissolution. For instance, in one embodiment, the iron source is present in an amount sufficient to decrease the rate at which hydrogen gas is produced during the process. For instance, in one embodiment, the hydrogen gas production rate is controlled using a purge gas such that the off-gas contains a hydrogen concentration of less than about 4% by volume at all times; although, a fraction of this concentration (e.g., 60%) is sometimes required as an additional safety constraint. In one embodiment, the acid, metal catalyst and iron source comprise a dissolution mixture or solution. The acid, for instance, may comprise nitric acid. The metal catalyst, on the other hand, may comprise mercury. In one embodiment, the initial nitric acid concentration in the dissolution solution can be from about 4 molar to about 15 molar, such as from about 5 molar to about 8 molar. The mercury concentration, on the other hand, can be from about 0.001 molar to about 0.02 molar. During the process, at least about 80%, such as at least about 90%, such as at least about 95% of the aluminum is dissolved. In one embodiment, for instance, substantially all of the aluminum is dissolved. After the aluminum is dissolved, the final nitric acid concentration is generally not less than about 0.5 molar. Various different iron sources may be used to supply iron ions during the process. The iron source, for instance, may comprise a ferrous metal or any suitable ferrous or ferric iron salt. In one embodiment, for instance, ferrous sulfamate or ferric nitrate may be added to the acid and metal catalyst. The iron source may be present in the dissolution solution at a concentration of up to and greater than about 1.0 g/L, such as greater than about 2.5 g/L, such as greater than about 4 g/L, such as greater than about 6 g/L, such as greater than about 8 The iron concentration is generally less than about 20 g/L, such as less than about 18 g/L, such as less than about 16 g/L, such as less than about 14 g/L, such as less than about 12 g/L, such as less than about 10 g/L. The amount of iron added during the process is generally proportional to the amount of metal catalyst in order to control off-gas production. For instance, the molar ratio between iron and the metal catalyst is generally greater than about 3:1, such as greater than about 5:1, such as greater than about 7:1, such as greater than about 9:1, such as greater than about 11:1. The iron to metal catalyst molar ratio is generally less than about 40:1, such less than about 30:1, such as less than about 20:1, such as less than about 18:1, such as less than about 15:1. In one embodiment, an amount of excess iron is added that is large enough to nearly stop or stop the reaction completely. In one embodiment, the nuclear fuel combined with the aluminum may comprise used or spent nuclear fuel. The nuclear fuel may comprise uranium, plutonium, or mixtures thereof. In one embodiment, the material being dissolved may comprise a research reactor fuel assembly or fuel plate containing an aluminum-uranium alloy or uranium aluminide dispersed in a continuous aluminum phase surrounded by an aluminum cladding. After the aluminum-containing fuel is dissolved during the process, the process can further include the step of separating the nuclear fuel from the aluminum. The nuclear fuel can then be collected and reused. For instance, the nuclear fuel can be used to produce new fuel elements or fuel rods. Other features and aspects of the present disclosure are discussed in greater detail below. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present disclosure. In general, the present disclosure is directed to a method for controlling the dissolution of a metal, particularly aluminum or alloys of aluminum, such as U—Al alloy, during a process for dissolving the metal. As will be explained in greater detail below, the method of the present disclosure can be used to control the rate at which the metal dissolves, can control the amount of gases produced during the dissolution process and/or can be used to reduce the amount of off-gases produced during the process. Although the teachings of the present disclosure can be used in numerous and diverse applications, in one embodiment, the method of the present disclosure is used to control off-gas production during the recycling of used nuclear fuel. Research reactor fuel assemblies or fuel plates are typically comprised of an aluminum cladding surrounding a nuclear fuel. The nuclear fuel may comprise uranium, plutonium, and mixtures thereof. In one embodiment, the research reactor fuel assemblies or fuel plates contains an aluminum-uranium alloy or uranium aluminide dispersed in a continuous aluminum phase contained in the aluminum cladding. Spent research reactor fuel assemblies or fuel plates still contain a significant amount of reusable nuclear fuel. In order to reuse the nuclear fuel, in one embodiment, the aluminum-containing fuel is dissolved in an acid in the presence of a metal catalyst which allows the nuclear fuel to be separated from the aluminum. In one embodiment, for instance, the recovery of fissionable materials comprises the dissolution of fuel assemblies in an acid bath. The acid bath contains a dissolution solution that is comprised of an acid and a metal catalyst. One or more fuel assemblies are slowly lowered into the dissolution solution while the solution is at an elevated temperature. In one embodiment, the acid bath contains nitric acid with a mercury catalyst to dissolve the aluminum/uranium and allow the recovery of the uranium from the aluminum and fission products. In the past, the dissolution process was carefully controlled to make sure that the fuel element dissolved at an acceptable rate while preventing excessive dissolution and off-gas generation. In particular, during the dissolution process, hydrogen gas is produced. For safety reasons, the rate at which hydrogen gas is produced should be controlled. The off-gas generation rate during fuel dissolution changes depending upon many factors. In general, the off-gas generation rate is fastest at low dissolved aluminum concentrations, which is typically when the process is initiated. Furthermore, the mechanisms that impact off-gas concentrations and species that produce gases such as nitrogen oxides and hydrogen during the course of the dissolution are complex and not well understood. Decreasing the off-gas generation rate or hydrogen concentration in the off-gas during fuel dissolution, and particularly during the initial phase of fuel dissolution, is desirable as it will allow for additional fuel assemblies to be simultaneously charged to a dissolver, which can dramatically improve efficiency. The present inventors discovered that iron (iron ions) can be used as an additive to control and slow the dissolution rate and/or control and slow the off-gas generation rates when fuel elements are dissolved using a mercury catalyzed acid solution. During the dissolution process, mercury ions are reduced to elemental mercury on the surface of the aluminum. An amalgamation of the aluminum with the mercury then forms on the surface which subsequently dissolves in a heated nitric acid solution, such as a boiling solution. The mercury is reoxidized by the nitric acid, which regenerates the mercury ions. The addition of iron has a remarkable and dramatic effect in reducing the effectiveness of the mercury catalyst. Controlling the iron concentration in conjunction with the mercury concentration thus allows for more control over the process. The addition of iron to the dissolution solution can provide numerous benefits. As described above, the presence of iron can be used to control the rate at which aluminum is dissolved and the rate at which off-gases are produced. Addition of iron can reduce the hydrogen concentration in the off-gas. Of particular advantage, the effectiveness of iron in reducing the dissolution rate and the off-gas rate is effective even in the presence of other impurities. In addition, the nuclear fuel can be separated from the dissolved iron and aluminum. In accordance with the present disclosure, any suitable iron source can be fed to the dissolution solution or acid bath in order to control the rate at which aluminum dissolves and/or the rate of off-gas generation, and particularly the rate of hydrogen gas generation. In general, any suitable iron source can be used that provides iron ions to the process without interfering with the process or producing any unwanted contaminants either in the dissolution solution or in the off-gas stream. In one embodiment, for instance, the iron source comprises elemental iron or an iron metal. Alternatively, an iron salt may be added. The iron salt may be a ferric salt or a ferrous salt. The iron salt, for instance, may comprise iron sulfamate or iron nitrate. Other iron salts that may be used in accordance with the present disclosure include iron fluoride, iron sulfate, iron phosphate, iron chloride, iron bromide, iron perchlorate, iron acetate, iron hydroxide, iron carbonate, etc., and mixtures thereof. The amount of the iron source that is added to the dissolution solution can depend on various factors. The amount, for instance, may depend upon the desired result, the concentration of the acid in the bath, and the concentration of the catalyst. In general, an iron source is added to the dissolution solution in an amount greater than about 1 g/L, such as greater than about 2 g/L, such as greater than about 3 g/L, such as greater than about 4 g/L, such as greater than about 5 g/L, such as greater than about 6 g/L, such as greater than about 7 g/L, such as greater than about 8 g/L. The iron source is added to the dissolution solution in an amount generally less than about 30 g/L, such as less than about 25 g/L, such as less than about 20 g/L, such as less than about 15 g/L, such as less than about 12 g/L. In one embodiment, the iron source is added to the dissolution solution in an amount based upon the amount of metal catalyst present. For example, the iron source may be added to the dissolution solution such that the molar ratio of iron to the metal catalyst (i.e. mercury concentration) can be generally greater than about 3:1, such as greater than about 6:1, such as greater than about 8:1, such as greater than about 10:1, such as greater than about 12:1, such as greater than about 14:1. The molar ratio of iron to metal catalyst is generally less than about 30:1, such as less than about 25:1, such as less than about 20:1, such as less than about 18:1, such as less than about 16:1, such as less than about 14:1. The amount of metal catalyst contained in the dissolution solution generally ranges from 0.001 to 0.02 molar. In general, the metal catalyst, such as mercury, is present in the dissolution solution in an amount greater than about 0.001 molar, such as greater than about 0.002 molar, such as greater than about 0.01 molar. The catalyst concentration is generally less than about 0.1 molar, such as less than about 0.08 molar, such as less than about 0.06 molar, such as less than about 0.04 molar, such as less than about 0.02 molar. The acid present in the dissolution solution comprises any suitable acid capable of dissolving the aluminum in the presence of the metal catalyst. In one embodiment, nitric acid is used. The nitric acid should be heated in the presence of the catalyst up to or near boiling. For instance, the nitric acid can be heated to within about 10° C. of its boiling point. Alternatively, the nitric acid may be heated near to or at its boiling point. As aluminum dissolves, the nitric acid is consumed during the process releasing off-gases, such as nitrogen oxides and hydrogen. In one embodiment, as the process proceeds, the molar concentration of nitric acid decreases. In one embodiment, the initial molar concentration of nitric acid in the dissolution solution prior to beginning the process is greater than about 3 molar, such as greater than about 5 molar, such as greater than about 7 molar, such as greater than about 9 molar. The initial nitric acid concentration is generally less than about 16 molar, such as less than about 15 molar, such as less than about 12 molar, such as less than about 10 molar, such as less than about 9 molar. In one embodiment, the initial concentration of the nitric acid is from about 5 molar to about 8 molar. The lowest or final concentration of nitric acid in the dissolution solution can depend upon various factors. In one embodiment, for instance, greater amounts of nitric acid can be added to the solution as the aluminum dissolves. In a batch process, however, the process will continue until virtually all of the aluminum has dissolved. In this embodiment, the final nitric acid concentration can be less than about 2 molar, such as less than about 1.5 molar, such as less than about 1 molar, such as no less than about 0.5 molar. During the process, at least 95%, such as at least 96%, such as at least 97%, such as at least 98%, such as even at least 99% of the aluminum is dissolved. By adding an iron source into the dissolution solution during the process, the rate at which the aluminum dissolves, the rate at which off-gases are produced, the rate at which hydrogen gas is produced, the total amount of off-gas produced, and/or the total amount of hydrogen gas that is produced during the process may be reduced. The iron source can be present during the entire process or may be added to the process at selective times. For instance, in one embodiment, an iron source may be present during initial dissolution of the metal or aluminum. In one embodiment, the iron source is used to decrease the rate at which hydrogen gas is produced by at least 10%, such as by at least 20%, such as by at least 30%, such as by at least 40%, such as even by at least 50%. The above reductions can also relate to the total amount of hydrogen gas produced and/or may relate to the peek hydrogen gas production rates and are in comparison to an identical process not containing the iron source. Ultimately, an off-gas stream using a purge gas can be produced that contains hydrogen gas in an amount less than 4% by volume, such as in an amount less than 3.8% by volume, such as in an amount less than about 3.6% by volume, such as in an amount less than about 3.4% by volume, such as in an amount less than about 3.2% by volume during the entire process. The process of the present disclosure is particularly well suited to processing used nuclear fuel. For instance, spent fuel assemblies or fuel plates can be lowered slowly into the dissolution solution for dissolving the aluminum and nuclear materials. After the fuel and cladding are dissolved, the aluminum can be separated from the nuclear fuel which may comprise uranium, plutonium, or mixtures thereof. By controlling the off-gas rate and particularly hydrogen gas production, greater amounts of the spent fuel assemblies or fuel plates may be processed simultaneously, dramatically improving the efficiency of the process. The present disclosure may be better understood with reference to the following examples. Single-impurity scoping experiments to determine the influence of individual contaminants on off-gas rate were initially performed using Al-1100 alloy coupons. A series of four Al-1100 coupons were cut to the approximate dimensions of 19×11×3 mm. A 1/16 inch hole was drilled into each coupon in order to fasten each coupon to the glass rods used to lower them into a dissolving nitric acid solution. The coupons were lightly sanded, washed with soap and water, and then weighed and measured. Each coupon weighed approximately 1.7 g and had a surface area of approximately 6 cm2. Each coupon was tied by Teflon™ string through the 1116 inch hole to a glass rod on the dissolver apparatus that was labeled with the coupon position number for coupon identification. A dissolver apparatus and off-gas collection system were assembled in a chemical hood. The dissolver apparatus contained a boiling flask with multiple ports, a condenser, an in-line gas sample glass bulb, and a water-submerged gas collection Tedlar™ bag. Glass rods were arranged to allow for attachment of alloy coupons and penetration of the lid of the boiling flask. Compressed O-ring fittings were present for subsequent sealing of the glass rods, allowing for dissolution of all 4 coupons without breaking the gas-sealed system by lowering each glass rod sequentially over the duration of the experiment. Removable glass bulbs were included in the assembly for sampling of the H2 concentration. Tedlar™ bag systems were used for measurement of the gas generation rate through water displacement in a graduated column. A second apparatus was placed in a radiological hood for conducting experiments with U—Al alloys. Experiment 1 was conducted using a dissolving solution of 7 M HNO3, 0.1 M KF, and 0.002 M Hg, and no contaminants. Nominally 150 mL of dissolving solution was weighed, added to a flask containing a Teflon™ stir bar, and then sealed. The dissolution vessel and off-gas collection system (including 8 sample glass bulbs) were leak checked by filling the system with Ar to inflate the Tedlar™ bag and observing a constant water column height over several minutes. The stir bar rotation was set at 325 rpm. The dissolving solution was then heated to 100° C. The off-gas system was vented to relieve pressure (to zero the off-gas collection system), and a stopwatch was started as the first of four Al-1100 coupons was lowered into the solution. To measure the gas generation rate, time versus water displacement was manually recorded until the coupon was visually observed to have dissolved completely. For each coupon dissolution, a gas sample was taken generally at 450 mL of off-gas volume (about half of total gas produced for each coupon) and a second sample was taken after the coupon had completely dissolved. The collected gas in the Tedlar™ bag was then purged, leaving residual gas in the remainder of the void space of the apparatus. The procedure was repeated for the dissolution of coupons 2 through 4, producing a total of 4 off-gas generation rate data sets (1 per coupon), and 8 gas samples (2 per coupon) for each experiment. Off-gas samples were analyzed for hydrogen concentration using gas chromatography. A 1 volume percent H2 standard was used for determining the response factor for H2. Experiment 2 was conducted in a manner analogous to Experiment 1 using a dissolving solution of 7 M HNO3, 0.1 M KF, and 0.002 M Hg, and an Fe contaminant (2.5 g/L). As shown in FIG. 1, the presence of even a small amount of Fe in the process reduced the rate of off-gas generation significantly when compared to the process with no Fe present. Another series of experiments were performed to determine the impact of Fe on off-gas generation rates for uranium-aluminum dissolution at higher concentrations of Hg. A series of four 30 wt % U—Al alloy coupons, cut to 20×12×3 mm with a mass of 1.6-2.1 g, were prepared as described in Example 1. Experiment 3 was conducted using a method analogous to that of Example 1 with a dissolving solution of 7 M HNO3, 0.1 M KF, 0.012 M Hg, and no Fe contamination. Hg was initially present in the solution, and the solution was heated to 100° C. before lowering the first coupon. The concentration of hydrogen in the off-gas was measured using gas chromatography. Experiment 4 was conducted using a dissolving solution of 7 M HNO3, 0.1 M KF, 0.012 M Hg, and no Fe contamination. Approximately 130 mL of dissolving solution was weighed and added to the dissolver flask containing a Teflon™ stir bar. The solution containing all components except Hg was then heated to 100° C. A syringe pump was then started to meter the Hg into the solution at the rate of 0.79 mL/min. The 10 mL Hg addition was completed during the first coupon dissolution, bringing the total concentration of Hg in the solution to 0.012 M. Off-gas generation rate and hydrogen concentration were measured in the manner described in Example 1. Experiments 5 and 6 were conducted in the same manner as Experiment 4. Experiment 5 used a dissolving solution of 7.0 M HNO3, 0.1 M K, 0.1 M F, and 2.5 g/L Fe. Experiment 6 used a dissolving solution of 7.0 M HNO3, 0.1 M K, 0.1 M F, and 10 g/L. Fe. For each experiment, four 30 wt % U—Al coupons were dissolved in a dissolving solution to which Hg solution was added at a rate of 0.79 mL/rein to achieve a concentration of 0.012 M Hg in the solution. Off-gas generation rate and hydrogen concentration were measured in the manner described in Example 1. Table 1 shows that Experiment 5 with 2.5 g/L Fe produced higher off-gas rates than did Experiment 6 with 10 g/L Fe. Table 2 demonstrates that Experiment 5 also produced higher concentrations of H2 gas during the course of the dissolution than did Experiment 6. TABLE 1Measured Peak Off-gas Rates and Al Concentrations for Experiments 5and 6 with 30 wt % U—Al Alloy.Experiment 5Experiment 62.5 g/L FeInitial10 g/L FeInitialPeak Off-gas[Al]Peak Off-gas[Al]Coupon No.(cm3/min/cm2)(M)(cm3/min/cm2)(M)Coupon 130.6025.20Coupon 233.30.4029.20.32Coupon 333.10.8016.40.67Coupon 419.01.1824.10.97All Coupons—1.55—1.31 TABLE 2Corrected H2 Gas Concentration Measurements for Experiments 5 and 6with 30 wt % U—Al Alloy.Experiment 5Experiment 62.5 g/L Fe10 g/L FeGas30% U—Al30% U—AlSampleH2 (vol %)H2 (Vol %)114.15.828.25.838.33.148.43.753.82.867.81.875.33.785.42.4 Similar results are shown in FIGS. 2 and 3. Experiments 5 and 6, which were conducted with dissolving solutions including Fe concentrations of 2.5 (minimum) and 10 g/L (maximum), respectively, demonstrated a significantly lower off-gas generation rate for uranium-aluminum dissolution than did Experiments 3 and 4, which were conducted with dissolving solutions without Fe (FIG. 2). Experiment 6, with a dissolving solution containing the maximum Fe concentration, demonstrated a significantly lower H2 concentration at all concentrations of dissolved Al than did either Experiments 3, 4, or 5 (FIG. 3). These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.
	summary
049901834	claims	1. In a process for producing steel in a ladle furnace comprising stirring the steel in a molten state by injecting inert gas in a lower part of the furnace and adding additives to the molten steel so as to modify the composition of the molten metal, the inert gas being gaseous argon injected at a rate of flow of at least 5 Nm.sup.3 /h so as to distribute said additives in a homogeneous manner, and in which a layer of slag is formed on the surface of the molten steel, the invention comprising simultaneously injecting liquid argon above the surface of the bath, in a region of intumescence of said slag layer, said injection of liquid argon being at a rate of flow equal to at least 1.5 1/min., said liquid argon being directed in a jet toward a central part of the intumescence such that the liquid argon so injected flows over substantially the whole of area of said intumescence, thereby reducing any increase in the nitrogen content of said steel, wherein the ratio of the flow of gaseous argon (expressed in Nm.sup.3) to the flow of liquid argon (express in Nm.sup.3) is between 0.01 and 0.11. 2. Process according to claim 1, wherein the rate of flow of said gaseous argon is between 5 and 40 Nm3/h. 3. Process according to claim 1, wherein the flow of said liquid argon is between 1.5 and 8 1/min. 4. Process according to claim 1, wherein the additive contains an element selected from the group consisting of calcium, magnesium and any other element having a high vapor pressure at usual temperatures of treatment of steel in a ladle. 5. Process according to claim 1, wherein the additive is silico-calcium. 6. Process according to claim 4, wherein the additive is incorporated in a wire introduced in the bath of molten metal at a rate of between 0.5 and 2 m/s. 7. Process according to claim 5, wherein the additive is incorporated in a wire introduced in the bath of molten metal at a rate of between 0.5 and 2 m/s. 8. Process according to claim 1, preceded by a step of transferring the steel to a ladle while protecting the surface of the molten steel with carbon dioxide in the form of snow. 9. Process according to claim 1, wherein the ladle furnace has a cover, said Process comprising starting the injection of the liquid argon at the latest when the ladle furnace is covered with said cover. 10. Process according to claim 9, comprising stopping the injection of liquid argon after having stopped said stirring.
052456420	claims	1. A method for controlling Co-60 radiation recontamination on the surfaces of structures providing a coolant water circuit of a boiling water nuclear fission reactor following decontamination, consisting essentially of: adding a solution of at least one iron compound selected from the group consisting of ferrous oxalate, ferric citrate, and freshly prepared Fe(OH).sub.3, Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 to coolant water of a water cooled nuclear fission reactor in amounts sufficient to maintain an iron concentration in the coolant water circulating through the coolant water circuit of the water cooled nuclear fission reactor at about 200 parts per billion. adding a solution of at least one iron compound selected from the group consisting of ferrous oxalate, ferric citrate, and freshly prepared Fe(OH).sub.3, Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 to coolant water of a water cooled nuclear fission reactor in amounts sufficient to maintain an iron concentration in the coolant water circulating through the coolant water circuit at about 200 parts per billion, and maintaining a dissolved oxygen content in the coolant water circulating through the coolant wataer circuit of the water cooled nuclear fission reactor at about 200 to about 400 parts per billion. adding a solution of at least one iron compound selected from the group consisting of ferrous oxalate, ferric citrate, and freshly prepared Fe(OH).sub.3, Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 to coolant water of a water cooled nuclear fission reactor in amounts sufficient to maintain an iron concentration in the coolant water circulating through the coolant water circuit at about 200 parts per billion, maintaining the coolant water circulating through the coolant water circuit at a temperature of at least about 230.degree. C., and continuing said pH adjustment, iron solution addition and temperature maintenance for a period of at least about 500 hours. 2. The method for controlling Co-60 radiation recontamination on the surface of structures providing a coolant water circuit of a boiling water nuclear fission reactor of claim 1, comprising maintaining the coolant water circulating through the coolant water circuit at a temperature of at least about 230.degree. C. 3. A method for controlling Co-60 radiation contamination on the surfaces of structures providing a coolant water circuit of a boiling water nuclear fission reactor, consisting essentially of the steps of: 4. The method for controlling Co-60 radiation recontamination on the surface of structures providing a coolant water circuit of a boiling water nuclear fission reactor of claim 3, comprising maintaining the coolant water circulating through the coolant water circuit at a temperature of at least about 230.degree. C. 5. The method for controlling Co-b 60 radiation recontamination on the surface of structures providing a coolant water circuit of a boiling water nuclear fission reactor of claim 3, comprising maintaining the induced pH and iron concentration condition of the circulating coolant water for a period of at least about 500 hours. 6. The method for controlling Co-60 radiation recontamination on the surface of structures providing a coolant water circuit of a boiling water nuclear fission reactor of claim 3, comprising applying the pH adjustment and iron concentration while the nuclear reactor is shut down, and continuing the treatment during subsequent fission operation of the water cooled nuclear reactor while maintaining an iron concentration in the circulating coolant water at about 50 to about 100 parts per billion. 7. A method for controlling Co-60 radiation contamination on the surfaces of structures providing a coolant water circuit of a boiling water nuclear fission reactor, consisting essentially of the steps of: 8. The method for controlling Co-60 radiation contamination on the surface of structures providing a coolant water circuit of a boiling water nuclear fission reactor of claim 7, comprising applying the pH adjustment, iron solution addition and temperature maintenance while the nuclear reactor fuel core is shut down, and continuing the said treatment steps during subsequent fission operation of the fuel core of the water cooled nuclear reactor while maintaining a lower iron concentration in the circulating coolant water of about 50 to about 100 parts per billion.

Subsets and Splits

No community queries yet

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