Split (2)

train · 33.5k rows

patent_number stringlengths 0 9	section stringclasses 4 values	raw_text stringlengths 0 954k
	summary
	description	This patent application is a divisional patent application of U.S. patent application Ser. No. 13/282,260 filed on Oct. 26, 2011, now U.S. Pat. No. 8,833,054 and entitled “System, Method and Apparatus for Lean Combustion with Plasma from an Electrical Arc,”which is a continuation patent application of U.S. patent application Ser. No. 12/370,591 filed on Feb. 12, 2009, now U.S. Pat. No. 8,074,439, and entitled “System, Method and Apparatus for Lean Combustion with Plasma from an Electrical Arc,” which is a non-provisional patent application of U.S. provisional patent application Ser. No. 61/027,879 filed on Feb. 12, 2008 and entitled, “System, Method and Apparatus for Lean Combustion with Plasma from an Electrical Arc,” both of which are hereby incorporated by reference in their entirety. The present invention relates generally to gas turbine engines. More specifically, the present invention relates to a supersonic lean combustion plasma steam reforming turbine engine that will combust low BTU gas such as landfill gas, biogas, blast furnace gas, coke oven gas and syngas. Not Applicable. There are many problems associated with lean fuel combustion or low BTU gas combustion in gas turbine engines. With the successful flight of the X-43A, hypersonic flight has achieved several technological goals and entered a new era. With further developments, it will reach Technology Readiness Level. However, FAA and EPA emission regulations in addition to the cost of fossil-based aviation fuels have pushed the aviation community into research and development for highly efficient aircraft engines that work on alternative and/or renewable fuels. In particular, the land based gas turbine community has been conducting research for integrating coal gasification with a combined cycle turbine (“IGCC”). In any case, the combustion of the product from gasification of carbon containing matter—synthesis gas (“syngas”)—requires major modifications to current gas turbine engines. Because syngas has a low heating value (“LHV”) compared to natural gas, significantly more fuel must be injected in an IGCC turbine than a natural gas turbine. Therefore, the mass-flow—and thus the output power—of the gas turbine is much higher for an IGCC application. For the same reason, the gas turbine's output power is flat-rated to very high temperatures. Supersonic Combustion and Flame Holding Problem 1: Gas Turbine to Ramjet or Scramjet Operations High Bypass Fan Gas Turbines are the primary engines for transportation aircraft. Typical speeds are 893 km/h (482 kt) at altitude on aircraft such as the Boeing 777-300. Military aircraft use augmentors (“afterburners”) to achieve and sustain supersonic flight. Only the new F-22 raptor can sustain supersonic flight without the use of an augmentor. Air breathing ramjets or scramjets are required to achieve hypersonic flight using air. However, only one successful Scramjet has been flown since the beginning of aviation. The major problem with ramjets and scramjets can be traced back to the early problem of flame holding or preventing engine flame out. In addition, no matter which configuration is chosen for Hypersonic Flight a problem remains—transition from subsonic to supersonic and finally hypersonic flight will require several different engines. Problem 2: Lean Combustion or Low BTU Fuel Combustion Fuel-lean combustion can increase efficiency while lowering emissions. However, current combustors cannot hold a flame during lean combustion conditions. Likewise, low BTU fuel such as syngas is difficult to combust in current gas turbine engines. Ansaldo Energia (Genoa, Italy) has engineered a new gas turbine V94.2K2 that targets the low-Btu (3.5 MJ/Kg-7 MJ/Kg LHV) market. The K2 gas turbine builds on the design philosophy of Ansaldo Energia's V94.2K that can handle fuels with 8 MJ/Kg-13 MJ/Kg LHV. The K2 is intended for Chinese and Eastern European markets where the company sees a demand for power generation from industrial gases, such as Blast Furnace Gas (BFG) and Coke Oven Gas (COG). The Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL) for common hydrocarbon based fuels, such as diesel (0.6% to 7.5%), gasoline (1.4% to 7.6%), and natural gas (Methane—5.0% to 15%) is fairly limited in range. On the other hand, syngas a product of natural gas (methane) steam reforming or gasification of hydrocarbons, coal, biomass, etc. is composed of hydrogen and carbon monoxide. The LEL and UEL for hydrogen (4% to 75%) and carbon monoxide (12.5% to 74.0%) are much broader than the parent fuel such as methane. Thus, this allows syngas (hydrogen+carbon monoxide) to be burned in a lean mode. The problem with syngas is that it is not widely available. It must be generated onsite by steam reforming natural gas or gasification of carbonaceous matter such as hydrocarbons or biomass. Typical gasifiers are very large and extremely expensive. However, a small and inexpensive plasma gasifier, such as the ArcWhirl®, U.S. Pat. No. 7,422,695 issued on Sep. 9, 2008 to the present inventor coupled to an IC engine could achieve both lean burn and supersonic combustion by gasifying the fuel first then combusting it in a cyclone combustor that is driven by a turbocharger. Problem 3: Match Lit in Hurricane Supersonic combustion has been compared to keeping a match lit in a hurricane or tornado. All gas turbines slow the flow of compressed air to below supersonic velocities in order to maintain a flame. This is due to the inherit design of the flame-holding capabilities of the combustor for a given turbine. Move Match to Eye of Hurricane It is well known that speeds within a cyclone can easily attain supersonic velocities. For example, turbochargers and centrifugal compressors easily attain speeds of over 100,000 RPM. Likewise, the air circulating within a turbocharger would far exceed supersonic speeds. Thus, the present invention achieves supersonic combustion by utilizing the centripetal forces within a rotating air column, such as a cyclone or hurricane for energy transfer, while utilizing the void, commonly referred to as the eye or vortex, in order to keep the match lit in order to maintain ignition. Simply put, the match is moved from the whirling column of air known as the shear wall to the eye or center of the hurricane. Problem 4: Flame is Stretched Due to Whirl Flow & Melts Turbine Placing the igniter within the center of the combustor is common for many types of gas turbine engines. Allison's C-18 to C-20 series of gas turbine engines utilize a front mounted axial flow compressor that sweeps the compressed air to the combustor via externally mounted air conduits. If the combustor were redesigned such that the air tubes entered tangentially to the combustor housing, thus creating centrifugal flow within the redesigned cyclone or vortex combustor, then the igniter and fuel nozzle would be placed within the central void space or eye of a whirling mass of air. However, this would create a detrimental effect on the compressor turbine if operated at supersonic combustion utilizing an intense igniter such as a plasma torch. The intense heat within the centrally stretched out plasma flame would melt the center of the compressor turbine. Problem 5: Flame Out It is well known that lean combustion can achieve high efficiency while producing low emissions. However, attempting to achieve lean combustion within current internal combustion (“IC”) engine designs may lead to low reaction rates, flame extinction (“Flame Out”), instabilities, and mild heat release. Likewise, many IC engines are very sensitivity to fuel/air mixing. With the current push for sequestering carbon or utilizing renewable fuels, a need exists for a relatively inexpensive turbine engine design that can operate in a lean fuel combustion mode in addition to a supersonic combustion mode. If such a turbine could be easily coupled to a motor generator, high bypass fan or propeller, this would allow for rapid transition to renewable fuels for electrical generation, aviation, marine propulsion and thermal oxidation. The ability to transition from subsonic to supersonic then to hypersonic flight with the same engine would solve many problems with reaching space at an affordable payload rate. The ability to use the same air breathing supersonic combustion turbine as a steam plasma thruster in space solves the issues of carrying a large oxidizer payload. The present invention provides a supersonic lean fuel combustion plasma arc turbine that includes a plasma arc torch, a cyclone combustor and a turbocharger. The plasma arc torch includes a cylindrical vessel having a first end and a second end, a tangential inlet connected to or proximate to the first end, a tangential outlet connected to or proximate to the second end, an electrode housing connected to the first end of the cylindrical vessel such that a first electrode is (a) aligned with a longitudinal axis of the cylindrical vessel, and (b) extends into the cylindrical vessel, a hollow electrode nozzle connected to the second end of the cylindrical vessel such that the center line of the hollow electrode nozzle is aligned with the longitudinal axis of the cylindrical vessel, and wherein the tangential inlet and the tangential outlet create a vortex within the cylindrical vessel, and the first electrode and the hollow electrode nozzle create a plasma that discharges through the hollow electrode nozzle. The cyclone combustor is connected to a hollow electrode nozzle of the plasma arc torch. The cyclone combustor has a tangential entry, a tangential exit, and an exhaust outlet. The turbocharger has a turbine connected to a compressor via a shaft. The turbine entry is connected to the tangential exit of the cyclone combustor, and a compressor exit is connected to the tangential entry of the cyclone combustor. In addition, the present invention provides a plasma turbine thermal oxidizer that includes a plasma arc torch, a vessel housing at least one ceramic cyclone combustor, a first turbocharger and a second turbocharger. The plasma arc torch includes a cylindrical vessel having a first end and a second end, a tangential inlet connected to or proximate to the first end, a tangential outlet connected to or proximate to the second end, an electrode housing connected to the first end of the cylindrical vessel such that a first electrode is (a) aligned with a longitudinal axis of the cylindrical vessel, and (b) extends into the cylindrical vessel, a hollow electrode nozzle connected to the second end of the cylindrical vessel such that the center line of the hollow electrode nozzle is aligned with the longitudinal axis of the cylindrical vessel, and wherein the tangential inlet and the tangential outlet create a vortex within the cylindrical vessel, and the first electrode and the hollow electrode nozzle create a plasma that discharges through the hollow electrode nozzle. The vessel has an air intake, a discharge exhaust and houses at least one ceramic cyclone combustor connected to the hollow electrode nozzle. A first turbocharger has a first turbine entry, a first turbine exit, a first compressor entry and a first compressor exit, wherein the first turbine entry is connected to the discharge exhaust of the vessel and the compressor exit is attached to the tangential input of the plasma arc torch. A second turbocharger has a second turbine entry, a second turbine exit, a second compressor entry and a second compressor exit, wherein the second turbine entry is connected to the discharge exhaust of the vessel and the second compressor exit connected to an air intake of the vessel housing the ceramic cyclone combustor(s). The present invention also provides a plasma turbine air breathing and steam rocket that includes a plasma arc torch, a vessel housing at least one ceramic cyclone combustor, a recuperator encapsulating an exhaust nozzle connected to a discharge exhaust to the vessel housing the ceramic cyclone combustor(s), a first turbocompressor for compressing air, oxidant, or steam connected to the recuperator, a second turbocompressor for pressuring fuel connected to the tangential input of the plasma arc torch, a valve system and a secondary oxidant injection system. The plasma arc torch includes a cylindrical vessel having a first end and a second end, a tangential inlet connected to or proximate to the first end, a tangential outlet connected to or proximate to the second end, an electrode housing connected to the first end of the cylindrical vessel such that a first electrode is (a) aligned with a longitudinal axis of the cylindrical vessel, and (b) extends into the cylindrical vessel, a hollow electrode nozzle connected to the second end of the cylindrical vessel such that the center line of the hollow electrode nozzle is aligned with the longitudinal axis of the cylindrical vessel, and wherein the tangential inlet and the tangential outlet create a vortex within the cylindrical vessel, and the first electrode and the hollow electrode nozzle create a plasma that discharges through the hollow electrode nozzle. The vessel houses at least one ceramic cyclone combustor is connected to the hollow electrode nozzle. The valve system connects the tangential output of the plasma arc torch to the recuperator that converts the first turbocompressor into a vapor compressor pulling a suction on the recuperator while a water pump injects water into the recuperator and the compressed steam cools the ceramic cyclone combustor and enters into the cyclone and shifts the syngas to hydrogen and carbon dioxide while injecting a secondary oxidant into the nozzle, thus allowing the rocket to transition from air breathing to steam propulsion. The ceramic cyclone combustor is cooled with a preheated combustion air from the first turbocompressor which cooled the exhaust nozzle in the recuperator, an exhaust is scavenged to drive the first and second turbocompressors and a valve system means. Moreover, the present invention provides a method for supersonic lean fuel combustion by creating an electric arc, generating a whirl flow to confine a plasma from the electric arc, generating a combustion air whirl flow, extracting a rotational energy from one or more hot gases, recuperating energy from the hot gases, and utilizing the electrical arc for converting fuel to syngas while confining the plasma to the vortex of the whirling combustion air in order to maintain and hold a flame for supersonic combustion while coupled to a means for extracting rotational energy from the hot lean combustion exhaust gas while recuperating energy for preheating the fuel and combustion air. The present invention is described in detail below with reference to the accompanying drawings. While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. Now referring to FIG. 1, a plasma arc torch 100 in accordance with one embodiment of the present invention is shown. The plasma arc torch 100 is a modified version of the ARCWHIRL® device disclosed in U.S. Pat. No. 7,422,695 (which is hereby incorporated by reference in its entirety) that produces unexpected results. More specifically, by attaching a discharge volute 102 to the bottom of the vessel 104, closing off the vortex finder, replacing the bottom electrode with a hollow electrode nozzle 106, an electrical arc can be maintained while discharging plasma 108 through the hollow electrode nozzle 106 regardless of how much gas (e.g., air), fluid (e.g., water) or steam 110 is injected into plasma arc torch 100. In addition, when a valve (not shown) is connected to the discharge volute 102, the mass flow of plasma 108 discharged from the hollow electrode nozzle 106 can be controlled by throttling the valve (not shown) while adjusting the position of the first electrode 112 using the linear actuator 114. As a result, plasma arc torch 100 includes a cylindrical vessel 104 having a first end 116 and a second end 118. A tangential inlet 120 is connected to or proximate to the first end 116 and a tangential outlet 102 (discharge volute) is connected to or proximate to the second end 118. An electrode housing 122 is connected to the first end 116 of the cylindrical vessel 104 such that a first electrode 112 is aligned with the longitudinal axis 124 of the cylindrical vessel 104, extends into the cylindrical vessel 104, and can be moved along the longitudinal axis 124. Moreover, a linear actuator 114 is connected to the first electrode 112 to adjust the position of the first electrode 112 within the cylindrical vessel 104 along the longitudinal axis of the cylindrical vessel 124 as indicated by arrows 126. The hollow electrode nozzle 106 is connected to the second end 118 of the cylindrical vessel 104 such that the center line of the hollow electrode nozzle 106 is aligned with the longitudinal axis 124 of the cylindrical vessel 104. The shape of the hollow portion 128 of the hollow electrode nozzle 106 can be cylindrical or conical. Moreover, the hollow electrode nozzle 106 can extend to the second end 118 of the cylindrical vessel 104 or extend into the cylindrical vessel 104 as shown. As shown in FIG. 1, the tangential inlet 120 is volute attached to the first end 116 of the cylindrical vessel 104, the tangential outlet 102 is a volute attached to the second end 118 of the cylindrical vessel 104, the electrode housing 122 is connected to the inlet volute 120, and the hollow electrode nozzle 106 (cylindrical configuration) is connected to the discharge volute 102. Note that the plasma arc torch 100 is not shown to scale. A power supply 130 is electrically connected to the plasma arc torch 100 such that the first electrode 112 serves as the cathode and the hollow electrode nozzle 106 serves as the anode. The voltage, power and type of the power supply 130 is dependant upon the size, configuration and function of the plasma arc torch 100. A gas (e.g., air), fluid (e.g., water) or steam 110 is introduced into the tangential inlet 120 to form a vortex 132 within the cylindrical vessel 104 and exit through the tangential outlet 102 as discharge 134. The vortex 132 confines the plasma 108 within in the vessel 104 by the inertia (inertial confinement as opposed to magnetic confinement) caused by the angular momentum of the vortex, whirling, cyclonic or swirling flow of the gas (e.g., air), fluid (e.g., water) or steam 110 around the interior of the cylindrical vessel 104. During startup, the linear actuator 114 moves the first electrode 112 into contact with the hollow electrode nozzle 106 and then draws the first electrode 112 back to create an electrical arc which forms the plasma 108 that is discharged through the hollow electrode nozzle 106. During operation, the linear actuator 114 can adjust the position of the first electrode 112 to change the plasma 108 discharge or account for extended use of the first electrode 112. Referring now to FIG. 2, a diagram of a Supersonic Lean Combustion Plasma Turbine 200 in accordance with one embodiment of the present invention is shown. In order to gasify, crack, reform or pyrolyize fuel, the fuel 202 may be introduced into the system at one or more points: (a) introducing the fuel 202a into the plasma 108 directly through first electrode 112 wherein the first electrode 112 is hollow; (b) mixing (e.g., via an eductor) the fuel 202b with the gas (e.g., air), fluid (e.g., water) or steam 110 introduced into the tangential inlet 120 of the plasma arc torch 100; and (c) introducing (e.g., via an eductor) the fuel 202c into the plasma 108 plume exiting the hollow electrode nozzle 106. The plasma arch torch 100 is connected to a cyclone combustor 204 with a tangential entry 206 and tangential exit 208. The cyclone combustor 204 is connected to a turbocharger 210 via valve 212. Hot gases enter into a turbine 214 of the turbocharger 210. The turbine 214 rotates a compressor 216 by means of a shaft with a pinion 218. A compressor inlet valve 220 is connected to the compressor 216. Compressor inlet valve 220 eliminates the need for stators to impart a whirl flow to match the compressor wheel rotation direction. In addition, by utilizing a tapered reducer for the housing the velocity of the air 222 must increase in order to conserve angular momentum. By utilizing a plunger style stopper valve assembly 224 coupled to a linear actuator 226, the mass flow can be pinched or reduced while maintaining velocity. The physical separation of the compressor/turbine or turbocharger 210 from the combustor 204 allows for a radically different design for gas turbines, power plants and airframes. The turbocharger 210 can be located and oriented to maximize airflow while minimizing foreign object damage (FOD). In addition, the turbocharger 210 may be coupled to rotating unions and tubing in order to rotate or direct the exhaust from the turbine 214 for thrust vectoring. In order to maximize efficiency a first stage recuperator 228 is placed on the discharge exhaust from the turbine 214 and a second stage recuperator 230 is place on the discharge exhaust from the combustor 204 via a valve 232. Compressed air 234 enters into the first stage recuperator 228 and then into the second stage recuperator 230. The hot compressed air 236 then enters into the combustor 204 via a volute with tangential entry 206. More specifically, the compressor inlet valve 220 includes a volute with a tangential entry, a cone-shaped reducer connected to the volute, a linear actuator connected to the volute, and a cone-shaped stopper disposed within the cone-shaped reducer and operably connected to the linear actuator. A controller is connected to the linear actuator to adjust a gap between the cone-shaped stopper and the cone-shaped reducer to increase or decrease mass flow while maintaining whirl velocity to closely match compressor tip velocity. Although there are several variations and modes of operations a few brief examples will be given in order to quickly demonstrate the uniqueness as well as functionality of the Supersonic Lean Combustion Plasma Turbine 200. A vortex is formed within the plasma arc torch 100 using water, steam, fuel or any other fluid 110. The arc is struck and a plasma is discharged into the eye of the cyclone combustor 204. The plasma syngas plume entering into the cyclone combustor 204 is also the igniter. Since it is in the eye of the cyclone it will be extended along the longitudinal axis of the combustor 204 and into valve 232. By throttling valves 212 and 232 the turbine can be operated from a takeoff mode and transition to supersonic and hypersonic flight. The purpose of the pinion 218 on the turbocharger 210 in combination with separating the combustor 204 from the compressor 216 and turbine 214 allows for a unique and completely unobvious mode of operation. Referring now to FIG. 3, a diagram of a Supersonic Lean Combustion Plasma Turbine Motor Generator 300 in accordance with another embodiment of the present invention is shown. Two or more Plasma Turbines 200 (200a and 200b as shown) are coupled to a bull gear 302 in a locked-train fashion. The bull gear 302 drives a motor generator 306 via drive shaft 304. This configuration allows for operating in a very fuel efficient and cost effective means. The first Plasma Turbine 200a is started by using the motor to rotate the pinions in order to rotate the compressor. The cyclone valve's stopper is opened to allow air into the compressor. The second Plasma Turbine's 200b stopper is placed in a closed position in order to unload the compressor. This can also be accomplished by placing electrical clutches on the pinion. When air flow enters into the combustor, the plasma arc torch 100 is ignited with only water or steam flowing through it in the same rotational direction as the cyclone combustor. Once the plasma arc is stabilized fuel is flowed into the plasma arc torch 100 and gasified and synthesized into hydrogen and carbon monoxide. The hot syngas plasma flows into the cyclone combustor. It is ignited and lean combusted and flowed out of the combustor via the tangential exit. Valve is fully opened while valve is shut in order to maximize flow into the turbine. Valves and are then adjusted according to torque loading on the pinion in addition to turbine and compressor speed. By operating only one combustor at its maximum efficiency the generator can be operated as a spinning reserve. All utility companies within the US are required to maintain “Spinning Reserves.” In order to come up to full power additional Plasma Turbines can be started almost instantly with very little lag time. This annular Plasma Turbine configuration may have multiple bull gears on a single shaft with each bull gear consisting of multiple Plasma Turbines. Now referring to FIG. 4, a diagram of a Supersonic Lean Combustion Plasma Turbine High Bypass Fan 400 in accordance with another embodiment of the present invention is shown. Two or more Plasma Turbines 200 (200a and 200b as shown) are coupled to a bull gear 302 in a locked-train fashion. A high bypass fan 402 is attached to the shaft 304. Likewise, a small motor generator may be attached to the opposite end of the shaft for starting and inflight electrical needs. Once again the Plasma Turbine configuration allows for maximizing fuel efficiency while idling at the gate and taxing by operating only one Plasma Turbine attached to the bull gear. Prior to takeoff all Plasma Turbines are brought online to maximize thrust. After takeoff Plasma Turbines may be taken offline to maximize fuel efficiency during climbout and at cruise altitude and speed. When the pilot is ready to transition to supersonic flight the turbine inlet valve is slowly closed while the combustor valve is opened. The high bypass fan may be feathered in order to reduce speed of the bull gear or to reduce drag. Likewise an inlet cowling may be used to close air flow to the high bypass fan. Air flow into the combustor is directly due to speed of the aircraft. This is accomplished with an additional three way valve (not shown) connected to the combustor tangential entry. Thus, the combination of the plasma arc torch 100 and the cyclone combustor coupled to a unique exhaust valve allows for a true plasma turbine scramjet that can be operated in a supersonic lean fuel combustion mode. Referring to FIG. 5, a diagram of a Supersonic Lean Combustion Plasma Turbine Propeller in accordance with another embodiment of the present invention is shown, which is similar to the motor generator and high bypass fan, the system allows for a very unique marine turbine. In comparison, the US Navy's Spruance class destroyers were one of the first class of Naval ships to utilize high powered marinized aircraft turbines. Two GE LM-2500 Gas Turbine Engines were coupled to the port shaft via a bull gear and two GE LM-2500 Gas Turbine Engines were coupled to the starboard shaft via a bull gear. This gave the ship a total of 100,000 shaft horsepower. In order to operate in the most fuel efficient mode, only one engine was operated while the other engine was decoupled from the bull gear via a friction and spur gear type clutch. The other shaft was placed in a trail mode position and allowed to spin or rotate freely. If full power was needed the other 3 gas turbine engines required about 3 minutes to start in an emergency mode. There were two major problems associated with the LM-2500 coupled to a bull gear. First, when starting from a dead in the water position, the engineers had to conduct a dead shaft pickup. This required engaging the clutch and placing the friction brake on which held the power turbine. The turbine was started and hot gases flowed across a non-moving power turbine section. The brake was released and the power turbine rotated thus turning the bull gear. The variable pitched propeller was usually placed at zero pitch. Returning back to FIG. 5, the bull gear 302 with multiple Plasma Turbines 200 (200a and 200b are shown) may be attached to a drive shaft 304 that is connected to a propeller 502. However, this system can be greatly augmented with a motor generator (not shown) directly attached to the drive shaft 304. In fact, the propeller 502 can be eliminated and replaced with an all electric drive pod. Thus, FIG. 3 would be installed and simply would provide electrical power to the electric drive pod. Neither rotating a shaft for transportation and propulsion purposes nor rotating a large motor generator may be required from the Plasma Turbine System. Now referring to FIG. 6, a diagram of Plasma Turbine Thermal Oxidizer 600 in accordance with another embodiment of the present invention is shown. The plasma arc torch 100 is attached to a commonly available filter vessel 602 which houses a ceramic hydrocylone 604. Ceramic hydrocyclones 604 are available from CoorsTek and Natco. More specifically, the vessel 602 has an air intake 606, a discharge exhaust 608 and houses at least one ceramic cyclone combustor 604 connected to the hollow electrode nozzle of the plasma arc torch 100. A first turbocharger 610 has a first turbine entry 612, a first turbine exit 614, a first compressor entry 616 and a first compressor exit 618. A second turbocharger 602 has a second turbine entry 622, a second turbine exit 624, a second compressor entry 626 and a second compressor exit 628. The first turbine entry 612 and the second turbine entry 622 are connected to the discharge exhaust 608 of the vessel 602. A first recuperator 630 is connected to the first turbine exit 614, the first compressor exit 618 and the tangential input of the plasma arc torch 100 such that a compressed fuel from the first compressor exit 618 is heated by a first exhaust 632 from the first turbine exit 614 and enters the tangential input of the plasma arc torch 100. A second recuperator 634 connected to the second turbine exit 624, the second compressor exit 628 and the air intake 606 of the vessel 602 such that a compressed air from the second compressor exit 628 is heated by a second exhaust 636 from the second turbine exit 624 and enters the air intake 606 of the vessel 602. Many landfills as well as wastewater treatment plants produce a low BTU fuel referred to as biogas. Likewise, many industries produce a very low BTU offgas that must be thermally oxidized or incinerated. The plasma turbine thermal oxidizer achieves lean combustion by first gasifying the low BTU fuel in another low BTU fuel—syngas. However, since the syngas has a larger ignition range (LEL to UEL) it can be combusted at high flow rates without additional fuel. The system is operated in the following mode. The plasma arc torch 100 is turned on to establish an arc. Water or steam may be flowed in the plasma arc torch 100 to form the whirl or vortex flow. Air is flowed into a compressor through a recuperator and into the vessel. The air surrounds and cools the ceramic cyclone combustor. The air enters into the ceramic hydrocyclone tangentially then exits as a hot gas into the turbines. Once air flow is established the low BTU gas is flowed into a compressor then into a recuperator. The hot low BTU gas is flowed into the plasma arc torch 100 where it is steam reformed into syngas. Once again, the syngas plasma enters into apex valve of the ceramic cyclone combustor. The syngas is lean combusted and traverses to the turbine, recuperator and then exhausted for additional uses. In this system, the turbochargers may be installed with high speed alternators for providing electricity to operate the power supplies for the plasma arc torch 100. This system is especially useful at wastewater treatment plants (“WWTPs”). Biogas is often produced from digesters. Likewise, all WWTPs use air to aerate wastewater. Since the Plasma Turbine Thermal Oxidizer operates in a lean fuel combustion mode, there is ample oxygen left within the exhaust gas. This gas can be used for aerating wastewater. Likewise, plasma arc torch 100 can be used to disinfect water while steam reforming biogas. In addition, biosolids can be gasified with the plasma arc torch 100 to eliminate disposal problems and costs. Referring now to FIG. 7, a diagram of a Plasma Turbine Air Breathing & Steam Rocket with Recuperator 700 in accordance with another embodiment of the present invention is shown. The thermal oxidizer 600 of FIG. 6 can easily be converted into a rocket or process heater. A nozzle 702 and recuperator 704 are attached to the outlet 608 of the combustor 604. Air or an oxidant are flowed into the recuperator 704. The hot air or oxidant exits the recuperator 704 and enters into the vessel 602 and into the ceramic cyclone combustor 604. Fuel is pressurized via a turbocompressor 706 and enters into the plasma arc torch 100 where it is converted or cracked into syngas. The syngas plasma plume ejecting into the ceramic cyclone combustor 604 is controlled via a multi-position fuel recirculation valve 708. A portion of the fuel may flow into the nozzle 702 to increase thrust. In order to drive the turbines a portion of the hot exhaust gas is scavenged and flowed to the inlets of the fuel turbocompressor 706 and turbocharger 710. When used as an air breathing rocket, upon reaching altitudes where lean combustion cannot be sustained due a lack of oxygen molecules, in lieu of carrying an oxidant, the rocket would carry water. The water in pumped into the recuperator 704 to generate steam. The turbocharger 710 is valved such that it can pull a vacuum on the recuperator 704. The turbocharger 710 is then operated as a vapor compressor. The compressed steam is flowed in the vessel 602. The extremely hot syngas reacts with the steam in the ceramic cyclone combustor 604 for conversion to hydrogen and carbon dioxide via the water gas shift reaction. Since the water gas shift reaction is exothermic this will ensure that the steam remains in the vapor state. A small amount of liquid oxidizer may be added to combust the hydrogen. Finally, the present invention provides a method for supersonic lean fuel combustion by creating an electric arc, generating a whirl flow to confine a plasma from the electric arc, generating a combustion air whirl flow, extracting a rotational energy from one or more hot gases, recuperating energy from the hot gases, and utilizing the electrical arc for converting fuel to syngas while confining the plasma to the vortex of the whirling combustion air in order to maintain and hold a flame for supersonic combustion while coupled to a means for extracting rotational energy from the hot lean combustion exhaust gas while recuperating energy for preheating the fuel and combustion air. The foregoing description of the apparatus and methods of the invention in preferred and alternative embodiments and variations, and the foregoing examples of processes for which the invention may be beneficially used, are intended to be illustrative and not for purpose of limitation. The invention is susceptible to still further variations and alternative embodiments within the full scope of the invention, recited in the following claims.
	description	This application claims priority based on GB application number GB 0519926.0 filed Sep. 30, 2005, and GB application number GB 0519925.2 filed Sep. 30, 2005. This invention relates to an x-ray inspection system and related methods of inspecting articles using x-rays. There is an on-going need to inspect articles, whether this is the inspection of baggage in an airport, or other transport related situation, or in the output of a production process. For example, it is common in the food industry to inspect the actual content of the food in order to determine that the food content is as desired and does contain any foreign bodies such as stones, bone fragments, metal from the machines used in the production of the food, or the like. A typical x-ray inspection apparatus comprises a conveyor arranged to carry objects to be inspected through the apparatus. Within the apparatus there is an x-ray source with a collimator associated therewith arranged to produce a narrow irradiation zone extending across the conveyor. Beneath the conveyor there is provided a detector arranged to detect x-rays which have passed through an object, on the conveyor, passing through the irradiation zone. The detector generally comprises a linear array of photo-diodes, extending across the conveyor, adjacent the irradiation zone, The photo-diodes are generally provided in a series of modules, each of which contains a plurality of photo diodes. A phosphorescent strip is mounted above the photo-diodes within a module and x-rays which are incident upon the phosphorescent strip cause light to be emitted therefrom. The intensity of the light emitted from the phosphorescent strip is proportional to the amount of x-rays that are incident upon it and the light output is detected by the photo-diodes. Thus, the output from the photo-diodes can be used to give an indication of the amount of x-rays which are reaching the phosphorescent strip through the irradiation zone. The amount of x-rays reaching the phosphorescent strip will be dependent upon the nature of the object which is passing through the irradiation zone; denser materials such as bone, metal, stone and the like will absorb more x-rays that material such as meat, or other foodstuffs. Likewise, the absence of material, such as due to a void, will absorb less x-rays than meat or other foodstuff, Therefore, the amount of x-ray reaching the phosphorescent strip can be used to determine whether there is foreign matter in the product, or indeed whether there is an absence of matter. The output of the photo-diodes is commonly converted into a video display and/or processed in order to determine whether the object passing the irradiation zone meets predetermined criteria. Generally, the detector (e.g. the photo-diodes) is maintained in a fixed orientation and the object/product to be scanned is moved past the detector using a conveyor. Some applications in which such an x-ray inspection system might be used vary the speed of the conveyor. These applications include the monitoring of pharmaceutical or foodstuff packaging lines to ensure that the packaging is correctly filled with pharmaceutical/foodstuff; the monitoring of fluids or solids within a pipeline (e.g. soup and minced meat respectively); and other similar applications. Processing circuitry provided to process the output of the detector is generally calibrated to the speed at which the object to be scanned passes the detector. Therefore, if the speed of the conveyor is altered, the speed at which the object passes the detector alters, and the calibration of the processing circuitry becomes wrong. Many x-ray inspection systems function to automatically reject objects which do not meet predetermined criteria. Therefore, if the calibration is inaccurate, some objects may be rejected unnecessarily, or perhaps worse, some objects which should be rejected may not be. Thus respectively, objects could be wasted, or objects which are sub-standard may be allowed to proceed. According to a first aspect of the invention there is provided an x-ray inspection system arranged to inspect at least one object and comprising: a source of radiation; a detector, in use, capable of detecting the radiation passing through an irradiation zone and generating a periodic output of data therefrom; processing circuitry arranged to process the output generated by the detector; a speed determination means arranged, in use, to determine and output to the processing circuitry the speed at which an object passes the detector; wherein the processing circuitry is arranged to vary the period of the output of the detector according to the output from the speed determination means. According to a second aspect of the invention there is provided a method of monitoring a product comprising; measuring the speed at which the product passes through an irradiation zone in which x-rays generated by an x-ray source are incident; detecting the amount of x-rays that pass through the product using a detector adjacent the irradiation zone and having a periodic output; wherein the method comprises adjusting the period of the output according to the speed at which the object passes through the irradiation zone. According to a third aspect of the invention there is provided a computer readable medium containing instructions which when read by a processing circuitry cause that processing circuitry to provide the system of the first aspect of the invention. According to a fourth aspect of the invention there is provided a computer readable medium containing instructions which when read be a processing circuitry cause that processing circuitry to perform the method of the second or third aspects of the invention. The computer readable medium in any of the above aspects of the invention may be any of the following: a floppy disk; a CDROM; a DVD (including +R/+RW, −R/−RW, RAM); a hard disk; a memory (including memory sticks and the like); a tape; a transmitted signal (including an Internet download, an ftp transfer and the like); a wire; or the like. FIG. 1 is used to discuss an arrangement of a prior art x-ray inspection system which typically comprises a photo-diode array made up of discrete diodes arranged in a single row. A photo-diode array typically comprises 64 diodes and four of the diodes 10-16 in the array 8 are shown in FIG. 1. It will be readily appreciated by a person skilled in the art that the photo-diode array may comprise any number of photo-diodes wherein the number used will be determined by the application. FIG. 2 shows a general arrangement of an x-ray inspection system 198. This Figure is intended to put embodiments of the invention into context but may also be applicable to prior art systems. The system is intended to inspect objects to ensure that the inspected object is suitable and/or safe for its intended purpose. If the object were a foodstuff, or a pharmaceutical then the inspection may be to determine whether there are foreign bodies or voids therein, or an absence of product within the packaging. If the object is an item of baggage then the inspection may be to determine whether there banned goods in the baggage; for example to inspect baggage before an airline flight. The system comprises an x-ray source 200, providing a source of radiation, which is supplied from a high voltage power supply 202. The x-ray source is cooled by a cooler 204 to ensure that its temperature is maintained within an operating range. The power supply 202 and the cooler 204 are controlled by the processing circuitry within a controller 206 which is discussed hereinafter. The x-rays produced by the x-ray source 200 are collimated, in a known manner, to provide a thin beam of x-rays of generally a fan shape 208 (which shape can best be seen in FIG. 3) and typically having a width of roughly 1 mm. In FIG. 2 the fan shape is viewed from one side and is represented by a row of dots. A conveyor 210, having an upstream end 224 from which objects flow and a downstream end 226 to which objects flow, is provided and arranged to move an object 212 to be inspected through an irradiation zone 214 situated in a region below the x-ray source 200 and above an x-ray detector 216, which comprises a plurality of detector elements, each arranged to generate a periodic output. The conveyor 216 is shown in FIG. 2 as being a belt conveyor but could be any other suitable form of mechanism arranged to transfer objects 212 through the irradiation zone 214, such a Bandolier or web conveyor mechanisms or the like, It will be appreciated that if the direction of travel of the conveyor 210 is reversed then the upstream end 224 will become the downstream end 226 and visa versa. Some conveyor mechanisms may use packaging of the object as the conveyor (such as in packaging of pharmaceuticals). Other conveyor mechanisms may provide conduits for fluids such as soups, or the like. In such an embodiment the fluid is the object to be inspected. However, it is likely to still be desirable to inspect the content of objects carried by such transport mechanisms to ensure that the product is suitable and/or safe to be released. The detector 216 is arranged to output data indicative of the amount of x-rays incident thereupon. The x-rays emitted from the source 200 generally pass through the object 212 when it is in the irradiation zone 214, but are attenuated by the object 212 according to its composition, and are then detected by the x-ray detector 216. The amount of x-rays received at a point along the detector (i.e. into or out of the page as viewed in FIG. 2) give an indication of the composition of the object 212 at that point along the detector 216 at that point in time. As the object 212 (which may be a fluid, or packaging that should contain an object) is moved through the irradiation zone 214 by the conveyor 210 a two dimensional image of the object can be constructed from the data output from the detector 216. That is, the data output from the detector can be taken at predetermined intervals (typically roughly 1 ms) and stitched together to form an image after suitable processing In this embodiment, an output 218 from the detector 216 is processed by the processing circuitry of the controller 206 which generates a video display which is output to a display 220. In some embodiments, the controller 206 may also perform other processing on the data output from the detector 216, for example to determine whether the product being scanned should be rejected by making an output on an ‘Output reject mechanism’ 222. In such embodiments if the controller 206 determines that the object being scanned is below a predetermined standard (may be because it contains a foreign body above a predetermined size, it contains a void, a portion of the packaging is unfilled or the like) then it can cause a rejection mechanism to remove the object from the conveyor 210. Such rejection mechanisms are well known and will not be described further. In some embodiments, the display 220 may be omitted and the machine may perform automatic inspection of an object passing through the irradiation zone 214, During automatic inspection, if the controller 206 determines that a product falls outside acceptable criteria then the output to the reject mechanism 222 can be utilized to remove the product from the conveyor 210. The processing circuitry of the controller 206 typically comprises a processor such as an Intel™ Pentium™, AMD™ Athlon™, IBM™ PowerPC™, or other such processor. However, in other embodiments the processing circuitry may also comprise dedicated electronics as provided by one or more Application Specific Integrated Circuits (or the like). The processor is arranged to run code held in a memory accessible by the processor. The memory may or may not be provided within the system 198 and may be accessible over a network connection to the system 198. Further, it is likely that the memory comprises both a volatile portion (e.g. RAM) and a non-volatile portion (e.g. ROM, EPROM, a hard drive, or the like). The display 220 is typically a Liquid Crystal Display (LCD) but could be any other type of display such as a Cathode Ray Tube (CRT) display, a Light Emitting Polymer (LEP) display or the like. In FIG. 1, four detector elements 10, 12, 14, 16, are shown. A detector element would generally be a photo diode, The detector elements are provided in modules which are arranged to provide the detector. Typically a module would contain 64 photo diodes but this need not be the case and 32 and 128 diode modules are also known. It is possible that a module could contain any number of photo diodes. In one embodiment there are fourteen modules in the detector 216. However, other embodiments may have different numbers of detector modules which make up the detector 216. Indeed, the detector may not comprise modules. The number of modules is generally sufficient to provide detection across the width of the conveyor 210 which is used to transport objects 212 through the irradiation zone 214. Current embodiments generally have anywhere between roughly 4 and 20 modules, However, some embodiments have as many as 72 modules and it is conceivable that more detector or less modules could be employed. Therefore, in a system employing 72 modules, each having 64 detector elements therein, would employ 4608 detector elements (e.g. photo diodes). The image displayed on the display 220 is pixelated in nature as will be the corresponding image which is held in the memory of the processing circuitry of the controller 206 due to the digital nature of the electronics generally used. In an embodiment, when an image is processed, any object 212 on the conveyor 210 is assumed to have moved a predetermined distance in between samples taken of the outputs from the detector 216. Therefore, a fixed conveyor is speed is generally assumed. It is convenient that this speed is calculated to be length of the diodes in the direction of travel of the conveyor 210 multiplied by the scan rate:velocity=height (h)×scan rate. (1) Using the example of FIG. 1, the diodes have a height (h) in the direction of conveyor travel of 0.8 mm and the system has a scan rate of 1000 scan/s (i.e. a 1 ms period). Therefore, in the system of FIG. 1 an object would appear correctly on a display thereof (and within the memory) if the conveyor 210 were to be travelling at 0.8 mm×1000 scan/s—i.e. 800 mm a second. Halving the scan speed to 500 scans/s would reduce the speed of the conveyor to which the system is matched (i.e. require no correction) to 400 mm/sec. If such a fixed speed is assumed and the conveyor 210 travels at greater than this speed then the objects will appear, on the display 220, shorter than they should. Likewise, if the conveyor 210 travels at a lower speed then objects 212 will appear to be longer than they should. This can be problematic for processing performed by the controller 206 on the data output from the detector 216. For example, embodiments of the system may be arranged to process data output from the detector 216 in order to obtain a volume of an object (for example, a bar of chocolate, etc.), If the length of the bar were to vary because of the conveyor speed change then the volume would appear to fluctuate leading to the potential rejection of objects with an acceptable volume and/or the retention of objects with an unacceptable volume. Further, embodiments of the system may be used to determine whether foodstuffs (for example chocolates), pharmaceuticals, or the like, fill each cell of the packaging. A varying conveyor speed may lead to the controller 206 determining that a foodstuff, pharmaceutical, etc. is in a location which it does not actually occupy; i.e. it has been shifted. There now follows a discussion in relation to FIG. 4 which embodiments of the present invention may employ in order to correct processing of the data output from the detector 216 to the speed of the conveyor 210. Each of the detector elements is generally a photo-diode with which there is an associated scintillating layer of material (generally a strip of phosphorous). This is well known in the art. Further, the photo-diodes are generally reversed biased so that they function as a charged coupled device: as x-rays hit the scintillating layer light is generated; the generated light causes charge to be stored in the photo-diode; the magnitude of the charge on any one diode is read at a predetermined interval (as such the output from the detector is periodic); and after the level of charge is read the diode is reset so that the accumulated charge is removed therefrom, The level of charge, on any one photo-diode, read in this manner gives an indication of the amount of x-rays that were incident upon the scintillating material in a region above that photo-diode. Thus, photo-diodes in the detector 216 are reset at a regular intervals which are generally kept constant in order that the charge measured from the photo-diode is measured over a constant time period. FIG. 4a shows a suitable waveform 900 for resetting the photo-diodes in the detector. The waveform has a period T which comprises a low, reset, pulse 902 of period R which is used to reset the photo-diode and a high pulse of period C which allows charge to be accumulated on the diode, the period C may be thought of as a measurement pulse. The output from the detector is generally read at an end region of this measurement pulse before the detector is reset. It will be seen that the period T is substantially constant for the waveform 900 such that the edges of the reset pulse occur at a predetermined time. In order to accommodate a varying conveyor speed the skilled person may think that it would simply be a matter of altering the period T of the waveform 900 such that an object 212 on the conveyor moves a predetermined distance in between each reset pulse 902. However, there are complex calibration issues involved and if the period T is altered the system needs to be recalibrated in order to maintain the output of the detector 216 constant. This is not a practical solution particularly in applications of the system in which the speed of the conveyor 210 continuously varies. Such applications include the packaging of pharmaceuticals into blister packs comprising a plurality of blisters; the filling of continuously banded pouches of powder, or the like, monitoring fluids (such as soup) or pumped solids (such a minced meats) in a pipeline; and the like. In embodiments of the invention the processing performed on the data output from the detector 216 is compensated according to a method and apparatus which is described in relation to FIGS. 4a and 4b. It is assumed that the apparatus is largely as described in relation to FIG. 2 although the skilled person will appreciate how the teachings in relation to FIGS. 4a and 4b could be applied to apparatus of a different arrangement. In order to set up the method a determination is made of the maximum speed at which it will be desired to run the conveyor 210 and the controller 206 is configured to process data generated by the detector 216 appropriately. Part of this configuration is to set the periods T, C and R; the total period (T), the period in which charge is allowed to accumulate (C) and the reset period (R). In the method being described T and R vary whilst C remains constant. The period C is set during initial calibration of the system 198 and is calculated to give the required exposure of x-rays to the detector during the measurement period (i.e. period C). Once period, C has been set the periods T and R can be varied without affecting calibration of the system 198 since the detector will still be receiving the required exposure in each period of the output of the detector (e.g. period T). In an embodiment of the invention the period C is kept constant and the period R is varied as described below; therefore, the period T (i.e. the period of the output of the detector) also varies. Thus, in this embodiment the duration of the reset pulse applied to the detector is controlled. For example, the period C may typically be set to a period of roughly 1 ms although other values such as roughly any of the following may also be suitable: 100 μs, 500 μs, 1.5 ms, 5 ms, 10 ms or any value in between these values. As discussed above, in the period C of the waveform 900, charge accumulates on the photo-diodes within the detector 216. Calibration of the outputs of the individual photodiodes, the gain of the detector as a whole, and the like, requires that the period C remain constant. However, if the speed of the conveyor were to change then the speed of scanning of the data output from the detector needs to alter in order that the speed of the conveyor matches the scan speed according to the equation (1) above. Therefore, if the speed of the conveyor were to halve (e.g. from 800 mm/s to 400 mm/s) then the scan rate would also have to halve; that is the period T would have to double. In order to achieve this, the period R is increased in order to give the desired period T, keeping C constant (it is noted that R+C=T). Such an occurrence is shown in FIG. 4b. For example, assuming the 0.8 mm height h of FIG. 1, a conveyor velocity of 800 mm/s which would result in a scan speed of 1 m/s (i.e. 1000 scans/s) we could assume that C is 990 μs and R is 10 μs. Thus, the sum of R and C gives a period of 1 ms which is the required scan rate. If the speed of the conveyor were to slow to 400 mm/s the scan rate would halve (i.e. T becomes 2 ms) but C remains constant and therefore R becomes 1010 μs. Thus, controller 206 can accommodate a varying conveyor speed without the need to recalibrate the system. FIG. 4b shows an example in which the period T has been doubled when compared to FIG. 4a but in which the period C remains constant. Because when the system 198 is initially set up the maximum speed of the conveyor is determined, and the system set appropriately then the period T will never need to be decreased below this initial setting. Thus, as the conveyor 210 slows the period T is increased in proportion to the slowing of the conveyor 210. If the speed of the conveyor 210 subsequently increases then period T can be again be reduced. In order to achieve this the system 198 comprises a speed detector 228. The speed determination means 228 may be any suitable device such as an optical encoder, ferro magnetic coil, capacitive sensors, a switch (such as a micro switch, a reed switch or the like) or other device. Thus, in use the system 198 using a method as described with reference to FIG. 4 may be used for an application in which the speed of the conveyor 210 is periodically varied. In one particular example, the x-ray inspection system 198 is used to examine blister packs wherein each of the blisters in the package should have been filled with a capsule by the packaging process. If the controller 206 determines, by, processing the data output from the detector 210 that one or more blisters of the package do not contain a capsule then an output is made on the ‘Output reject mechanism’ 222 to reject that blister pack. The peak velocity of the conveyor 210 in this system is 60 m/s but the average velocity is 40 m/s. Thus, it is likely that a blister pack will be accelerating as it passes through the irradiation zone 214. The method of varying the period C described in relation to FIG. 4 allows the processing circuitry in the controller 206 to correctly process the data output from the detector 216 to identify whether each blister of the blister pack is full and avoid any of the problems discussed above.
	description	The present application is a continuation of patent application No. 11/549,851 entitled “CAMERA PLACED BEHIND A DISPLAY WITH A TRANSPARENT BACKLIGHT” filed on Oct. 16, 2006 at the USPTO, granted on Sep. 20, 2011 as U.S. Pat. No. 8,022,977, which in turn claimed the benefit of and priority to Indian Provisional Patent Application No. 1300/MUM/2005 entitled “A Combined Video Display and Camera System” and filed on Oct. 17, 2005. The present invention relates to electronic devices. More particularly, the invention relates to a combined video display and camera system. In video conferencing, two people communicate audio-visually. Each person is near a video conferencing terminal having a camera and a display. The camera captures the image of the person, which is transmitted to the distant person. The image of the distant person, is displayed on the display. Each person in the video conference is looking at his or her display to view the image of the other person. The camera is usually placed somewhere near the display. Since the person is looking at the display, the image captured by the camera is of the person looking away from the camera at the display. Each person is, thus unable to maintain eye contact. Absence of eye contact during a conversation greatly reduces the effectiveness of communication. Many prior art systems use a two-way mirror, also called a half silvered mirror or beam splitter. A two-way mirror simultaneously reflects some light and passes some light. FIG. 1 illustrates a prior art video conferencing system. A conferee 102 views the display 108 reflected in mirror 104 while the camera 106 captures images of the conferee 102. The image is captured from the same position that the conferee 102 is looking at. Teleprompters function this way. Another prior art video conferencing system uses a terminal equipped with a beamsplitter for reflecting an image generated by a video display so that only the reflection and not a direct view of the display is seen by the conferee. The camera is positioned behind the viewing side of the beamsplitter to capture the conferee's image through the beamsplitter. The direct view of the display is blocked by an image blocking film applied between the beamsplitter and the display. Blocking the direct view of the video display greatly improves teleconferencing by eliminating the distraction of simultaneously viewing both the video display and the reflection of the display. Prior art systems are quite bulky, especially when compared to modern display systems or modern teleconferencing systems. These systems waste a lot of energy, since a large amount of the energy radiated by the display is wasted since it goes through the two-way mirror. Many prior art systems compute a three-dimensional model of the conferee. Then the model is used to render an image of the conferee as if a camera were placed just behind the screen. The three-dimensional model is computed from multiple views of the conferee captured by cameras near the display, or by illuminating the conferee using light of a particular known pattern, and using the data pertaining to the illumination caused by the light. In another prior art system, the three-dimensional model is not computed, but the final virtual view from the direction of the display is estimated by visual flow interpolation techniques. All these methods are computationally expensive. Furthermore, they do not perfectly capture the required image, but just estimate it. Also, the closer the viewer is to the display, the larger the disparity between the images of the conferee captured by the various cameras, and the harder it is to compute an accurate three-dimensional model of the conferee. Also, such approximation models falter under improper lighting conditions and improper viewing conditions such as the presence of particulate matter or obstructions. A prior art method for achieving eye-contact in a video conferencing situation uses a camera placed directly in the line of sight between the conferee and the display. Though a correct image of the user may be captured this way, the visual obstruction of the camera is not comfortable to the conferee. An attachment mechanism removably secures the camera to a screen portion of a display screen such that the camera is disposed between the display screen and a person engaged in videoconferencing. The attachment mechanism can be a suction cup, strips of double-sided tape, or magnets. Magnetic force between the first and second magnets removably secures the camera to a screen portion of the flat panel display. Other prior art systems use projection systems and are bulky in nature. Furthermore, these systems do not offer complete isolation of the camera sensor from the light due to the display, causing unwanted glare. Also, in many situations flat panel displays are preferred to projection systems due to image quality reasons. A method and combined video display and camera system are disclosed. In one embodiment, the system comprises a first sheet and a second sheet oriented parallel to the first sheet, the second sheet including a light diffuser. A light source is placed along an edge of the second sheet, wherein the second sheet diffuses light generated by the light source. One or more cameras are placed behind the second sheet to capture an image through the second sheet and the first sheet. The above and other preferred features, including various details of implementation and combination of elements are more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular methods and systems described herein are shown by way of illustration only and not as limitations. As will be understood by those skilled in the art, the principles and features described herein may be employed in various and numerous embodiments without departing from the scope of the invention. A method and combined video display and camera system are disclosed. In one embodiment, the system comprises a first sheet and a second sheet oriented parallel to the first sheet, the second sheet including a light diffuser. A light source is placed along an edge of the second sheet, wherein the second sheet diffuses light generated by the light source. One or more cameras are placed behind the second sheet to capture an image through the second sheet and the first sheet. According to one embodiment, the present system and method captures images with a camera from almost the same location as a display is displaying another image. The system uses optical, electrical, electronic and optionally computational elements. One embodiment of the invention comprises a flat-panel screen which displays images picture by adjusting the optical transparency of its individual pixels. The display is illuminated using a backlight which diffuses light from a light source such that the light passes through the flat panel screen and the user sees the images. A camera captures an image of the user and his/her surroundings through the flat panel screen and backlight. An image correction system and method is employed on the captured image to reduce or eliminate the effects of displaying an image on a screen, backlight and illumination on the captured image. This corrected image is available at output 214. Almost all computers have displays, and many have web cams or other image capture mechanisms. The present system works as both of these, in a more compact form. Many present day mobile phones have both a display and a camera. Many mobile phones have a camera directed towards the viewer of the display of the mobile phone. The present system allows mobile phones to be more compact, and enable eye-to-eye teleconferencing in a mobile phone. In one embodiment, the system may be used for reading text while appearing to look straight at the camera. The present system allows energy conservation in such applications, saves studio space in traditional uses, and allows alternate uses such as web casting news or other programs from a personal computer, or reading text from the camera panel while shooting at an outdoor location. The present system may be used to conceal a camera behind a display or a patch of illumination, for surveillance purposes. For example, this could be used to place a camera inside the display of an automatic teller machine. The present system may also act as a mirror, by presenting the captured image on the display. The image may be flipped left-to-right to emulate a normal mirror, or it may not be flipped. FIG. 2 illustrates a block diagram of an exemplary combined camera and display system 299, according to one embodiment of the present invention. An image is displayed on a flat-panel screen 204. Flat panel screen 204 displays the picture by adjusting the optical transparency of its individual pixels. Screen 204 is illuminated using a backlight 206 which diffuses light from a light source 208 such that the light passes through the flat panel screen 204 to the user 200 who sees a picture. Camera 210 captures an image of the user 200 and his/her surroundings through screen 204 and backlight 206. An image correction system 212 is employed to reduce or eliminate the effects of the image displayed by the display 204 and backlight 206 on the image captured by the camera 210. The backlight 206 behind screen 204 scatters light into the camera 210 and interferes with its operation. The light scattered into the camera 210 is predictable and may be corrected with image correction system 212. A camera with high sensitivity and accuracy is used because the scattered light, may be more powerful than the light that is intended to be captured in the camera 210. The scattered light (being noise) decreases the signal-to-noise ratio of the captured image. System 299 displays images and captures images in separate periods of time, where the image display period and image capture period occurs in a rapidly alternating sequence. The frequency of alternating periods is so fast that the eye observing the screen does not perceive a flicker. The human eye cannot perceive flickers which occur at a rate faster than about 40 Hz. This principle is used in movies and cathode ray tube televisions. FIG. 3A illustrates a block diagram of an exemplary video system 300 when an image is displayed, according to one embodiment of the present invention. Light source 208 causes light to fall on the backlight panel 206. This light is scattered by the backlight panel 206. When the scattered light is viewed through the screen 204, the image displayed on the screen 204 is perceived. Camera 210 is not recording an image during this time period. FIG. 3B illustrates a block diagram of an exemplary video system 350 when an image is captured according to one embodiment of the present invention. Light source 208 is turned off, such that no light is scattered by the backlight panel 206. The camera 210 records an image 200 during this time through the screen 204 and the backlight panel 206. Since the light source 208 is turned off, no light used to display the image enters the camera 210, so the camera 210 gets a clear view of the captured object 200. The light source 208 cycles between off and on (or between light output and no light). This light source 208 may be a fluorescent light tube. Fluorescent lights have the ability to alternate quickly between outputting light and not outputting light. Fluorescent lights are used to light flat panel display backlights. These fluorescent lights cycle between the light and dark states at a rate as high as 1000 Hz. It is possible to vary the duty cycle of the light and dark states, (i.e. it is possible to electronically control what fraction of the total time the light source is in the light state, sourcing light into the backlight 206). In an alternate embodiment, the light source 208 is one or more LED light sources. The cycling between light and dark states is achieved by turning the LED light sources on and off in rapid succession. Incandescent lights are also a very good light source, but incandescent lights cannot switch between light and dark states very fast. Illumination from an incandescent light sources may be caused to alternate between light and dark by placing an obstruction between light source 208 and backlight 206. The obstruction switches at a high speed between transparent and opaque to cause the backlight 206 to glow and not glow. Such an obstruction may be a mechanical shutter, implemented as a rapidly opening and closing aperture or as a spinning disc with holes. Another system causing a periodic obstruction is an LCD panel which switches at a fast speed between opaque and transparent. Continuous light sources such as incandescent light are sometimes preferred in lighting systems because they produce a much more natural and even light spectrum. Other continuous systems such as arc lights produce a high power output. A light source and its driving electronic circuitry are arranged such that the fraction of time for which the light source is on is as small as possible. This allows for maximum time to be allotted to capturing the image with the camera 210, and thus increases the sensitivity of the camera 210. LED light sources exist which source a very high amount of light energy for a very small duty cycle. The camera 210 continuously switches between image recording mode and a mode wherein the light falling on the input aperture of the camera 210 has no effect on the camera 210, hereinafter referred to as non-recording mode. In one embodiment, this is achieved by using an obstruction near the input aperture of the camera 210 which alternates at a high frequency between transparent and opaque. If the camera 210 is an electronic camera, including a CCD camera or other such electronic device, another way of achieving an alternating obstruction is to use an electronic shutter. When electric potential is applied to the pixels of the image recording plane of the electronic camera 210, photons captured by the camera 210 are converted to electrons which are accumulated in physical spaces corresponding to each pixel of the picture. When this electric potential is removed, light falling on the recording plane has no effect. High frequency switching between recording and non-recording mode for an electronic camera 210 may be achieved by alternately applying and removing said electric potential. The time between application and removal of the electric potential is an exposure. After the electric potential is applied and removed, the amount of charge accumulated in each pixel position is recorded that serves as an electronic description of the image. In one embodiment, after each application and removal of the electric potential, the charge accumulated in each pixel is recorded, i.e. an image is captured per exposure. For very short exposures it may not be possible to accumulate enough photons in a single exposure to accurately estimate the intensities at each point. In such a case, a single image is recorded after many exposures. Thus, electric potential is applied and removed many times, causing the camera to switch between recording and non-recording mode many times. After a certain fixed number of exposures, the amount of charge accumulated at each pixel position is measured and recorded. Choosing the number of exposures after which an image is recorded achieves exposure control, i.e. controlling the total amount of time for which the pixels are exposed for the capturing of a single image. In an alternate embodiment, choosing the exposure time of each exposure achieves exposure control. Exposure control is a feature in cameras to achieve more control over the image recorded. Automatic exposure control is achieved by choosing the exposure time based upon the intensity of the previous image captured, or other light measurements. Cameras capture images at a fixed image rate. After the requisite number of exposures for the capture of an image occurs, the camera shutter is kept in non-recording mode until the next image is recorded. During this extended non-recording mode, the charge accumulated at each pixel position is recorded. Non-CCD cameras, non-electronic cameras and film based cameras may also be used. In the case of a film based camera, to achieve multiple exposures per image capture, the film frame is advanced after switching multiple times between recording and non-recording mode. This may require, similar to the case of the electronic camera, fast switching between the recording and non-recording mode, followed by an extended non-recording mode during which the film is advanced. Two serially placed apertures may be used—one for keeping the light of the backlight from entering the camera, and one to allow frame advance. The switching between light and dark of the light source 208 and the switching between recording and non-recording mode of the camera 210 are synchronized such that the camera 210 is in the recording mode only when the light source 208 is dark. Both the camera and light source are controlled by a single electronic oscillator and control circuit. In the case that the alternating apertures for the light source and camera are discs with holes, both the discs are driven by a single mechanical shaft. Alternatively, a single disc with holes is provided, and positions of the light source and camera are arranged such that either the light source is on or the camera is recording. A fluorescent or LED light source may be used together with an electronic camera and driving both of these devices using a single electronic circuit having a single oscillator controlling both these devices. According to one embodiment, a single electronic circuit having a single oscillator controls both the light source (either, fluorescent or LED) and the electronic camera. To further reduce costs, one may substitute a light source which can alternate between light and dark, but whose dark period is not a small fraction of the total time, but a large fraction of it. In this case, the synchronization mentioned above is adjusted such that a minimum possible light from the light source 208 enters the camera 210. In another embodiment, if the aperture of the camera 210 is very small, the illumination light entering the camera 210 may be of a tolerable limit, and its effects are nullified by the image correction system 212. Backlight 206 of the display 300 allows light incident at a particular angle to disperse in all directions. Light incident in other angles, though, is almost completely passed through the backlight without any change. FIG. 4 illustrates a block diagram of a light guide 400, according to one embodiment of the present invention. Core 404 of light guide 400 has a sparse distribution of light dispersing particles (core 404 may also be referred to as diffuser 404). The diffuser 404 is made of metallic, organic, or other powder or pigment, which reflects light incident on it. Alternately, diffuser 404 may be constituted of small transparent particles or bubbles, which disperse light by refraction, reflection at the boundary, by diffusion inside the particle, or by total internal reflection. The light from the primary light source 408 is dispersed over the entire surface of the light guide 400, and will exit both its large faces. Light guide 400 is primarily transparent and clear when viewed from one of its faces. Light is focused using a focusing reflector 410. FIG. 5 illustrates a diagram of an exemplary backlight, according to one embodiment of the present invention. Light from a light source 208 primarily falls on one edge of the middle layer 504 of backlight 208. An optical apparatus consisting of mirrors and lenses may be used so that the maximum amount of light from light source 208 enters the transparent sheet 504 at the required angle. An exemplary light ray 506 emanating from the light source 208 is depicted. This light ray suffers total internal reflection at the interface between the transparent sheet 504 and the other transparent sheet 510 of lower refractive index. The light ray will suffer further internal reflection and thus remain completely within transparent sheet 504. Thus, most of the light from the light source 208 is dispersed by backlight sheet 206. Also, since cladding sheets 502 and 506 are completely transparent, and middle sheet 504 is transparent with a very light concentration of dispersive particles backlight sheet 206 is almost completely transparent to light entering the large face of the sheet. Thus, the camera 210 views the backlight 206 as almost completely transparent. It is beneficial to use a non-uniform concentration of dispersive particles such that a uniform illumination is achieved. In the case of a single light source, the concentration of dispersive particles is lesser near the light source, and more at the other end of the middle sheet 504 of the backlight 206. The camera is placed behind a part of the backlight 206 which has lesser concentration of dispersive particles. Using non-uniform concentration, all the light due to the light source can be dispersed by the backlight. Image correction system 212 corrects defects in the image captured by camera 210 through the flat panel display 204 and backlight 206. The camera 210 is located very close to the flat panel display 204. A very few pixels of the flat panel display 204 affect the image captured by camera 210. Furthermore, the pixels of the flat panel display 204 are out of focus at the image capturing plane of the camera 210. The object to be captured by the camera 210, being further away, is in focus at the image capturing plane of the camera 210. The effect of the occlusion of the flat panel display 204 on any particular pixel of the image captured by camera 210 is a multiplicative change in intensity. The actual intensity at the particular pixel is multiplied by a function of the occluding pixels. Furthermore, since the occluding pixels are out of focus, more than one occluding pixel will contribute to the occlusion of each captured image pixel. The amount of occlusion suffered by each pixel of the captured image, henceforth called the occlusion map, has a specific relation to the occluding pixels on the flat panel display 204. In an embodiment, this relation is approximated as a linear relation that is evaluated by performing experiments whereby a single pixel on the screen 204 is opaque and all other pixels are transparent. The effect of a single screen pixel on the occlusion map is recorded. Knowing the occlusion map for each screen pixel, the occlusion map for any setting of values for the relevant screen pixels is evaluated. In an alternate embodiment, such linear relation is further characterized as a shift-invariant relation. Thus various fast convolution methods such as the methods based on the Fast Fourier Transform may be used to calculate the occlusion map from the values of the relevant screen pixels. Once the occlusion map is known, the occlusion suffered by each captured pixel is known, and the original value of the screen pixel is determined. There are many flat panel displays which have statically opaque elements, such as pixel boundaries and transistors. Statically opaque elements have a static additive effect on the occlusion map. The effect is estimated experimentally, by presenting the camera 210 with a flat intensity of light, and keeping all the screen pixels transparent. The known additive effect of statically opaque elements are added into the occlusion map to generate a composite occlusion map. The map reflects changes due to static as well as dynamic elements. The effect of the occlusion may then be nullified by dividing by the occlusion map. The defects introduced into the image captured by the camera 210 by the flat panel screen 204 are thus removed. There are two kinds of defects introduced by the backlight 206 into the image captured by the camera 210. The first of these defects is a slight dispersion of the light rays before the image is captured. In an alternative embodiment, to get a clear picture, the defect may be removed by standard deconvolution or linear system inversion. As a simple approximation, all the pixel values may be added to estimate the total dispersed light. The amount of this light, approximating the total light entering the camera 210 is further estimated to uniformly affect all pixels of the picture, and thus, a single uniform value is subtracted from each pixel. This improves the contrast of the captured picture by reducing the slight haze introduced by backlight 206. The second defect introduced by backlight 206 is dispersion of light from light source 208 into camera 210. Image correction system 212 corrects defects by subtracting the intensity at each pixel that is introduced by the scattering of the backlight. This is estimated per picture as a function of the time overlap between the display phase and capture phase. While the camera 210 is capturing the image, the image is occluded by the transparency setting of various screen pixels which are in front of the camera aperture. This occlusion causes darkness at the camera 210. Though the darkness can be overcome by amplification, the amplification causes an equivalent amplification in the noise including quantization noise, the stochastic nature of the photons falling on the pixel area, the stochastic nature of the photoelectric effect, thermal and electrical noise, and other similar causes of sensor noise. This decreases the accuracy and sensitivity of the captured image. In one embodiment of the invention, some or all of the screen pixels in the path of light to the camera 210 are made transparent during the time period when the light source 208 is in ‘off’ mode, i.e when the display is not lighted. The original transparency values of the pixels are restored before the light source 208 starts sourcing light again. If a new image is to be displayed on the screen 204, the pixels are now set to the new transparency values. Thus, in the time periods when an image is being displayed on the screen, the screen pixels are set to transparency values that result in the correct image being displayed, and in the time periods when an image is being captured by the camera, the screen pixels are set to a transparency value that cause more light to fall on the image plane of the camera 210. If screen 204 is a liquid crystal display (LCD), the changes in transparency are made by changing the charges stored at those pixel values. LCD pixels are slow to respond to changes in electric potential. Hence, the timing of these changes is accurately adjusted such that the maximum average transparency during the capture phase is possible. The frequency of switching between display and capture periods is kept slow enough to allow for the LCD pixels to switch to transparent and switch back to their original setting. Also, setting the duty cycle of the light source 208 such that a small fraction of the time is spent in the display period leaves more time for switching. Even if complete transparency is not achieved, the average transparency value achieved for a particular pixel during the capture period increases, thus causing an increase in the sensitivity of the camera. If complete transparency is achieved, the image correction system 212 has to compensate for static occlusion, which is a very simple algorithm. If complete transparency is not achieved, there is some effect of the screen pixel values on the occlusion map. This effect not only depends upon the screen pixel values themselves but also upon the time of exposure of the camera 210, and the average transparency of the particular pixel during the exposure. This is calculated by the image correction system 212 and the occlusion map is calculated from these changed pixel values. There are many methods of making a select set of pixels transparent on a flat-panel display, especially if the display is an LCD. For example, in matrix addressing, pixel values for a whole row of pixels are set at a time. An individual row is selected by a row enable wire that runs across the display. Multiple rows are made transparent in one operation by selecting multiple row enable wires. In systems using both row and column enables, a square area is selected to be made transparent in one operation by choosing the corresponding rows and columns to be enabled. Many LCD systems use a storage capacitor per pixel to store the charge which applies a given voltage across the liquid crystal pixel. Extra switching elements such as transistors may be used in the pixel to couple and decouple the liquid crystal from the charge stored in the capacitor. When the liquid crystal is decoupled from the charge, the pixel becomes transparent. Furthermore, coupling the liquid crystal to the capacitor causes the original transparency value to be restored. Usually, the voltage on one terminal of the storage capacitor or one end of the liquid crystal is varied, while the other end is kept constant. The voltage at the other end of the liquid crystal or storage capacitor is varied for the specified pixels or all pixels to turn the corresponding pixels transparent in a single operation without losing the voltages stored on the first end. When the voltage at the other end of the liquid crystal or storage capacitor is brought back to its original value, the original transparency values are restored. In another embodiment of the invention, whenever the display and camera are used together, as during a teleconference, the brightness of a particular pixel on the display is not allowed to drop below a particular transparency level. This is achieved with the driving circuit of the flat panel display, or in software by the computer attached to the display. This guarantees a minimum sensitivity for the captured picture. In yet another embodiment, the exposure time for obtaining a single image is varied to compensate for the loss of light due to occlusion. Such alteration of exposure time is usually controlled by the user, or by an automatic algorithm which adapts to the brightness level of the captured image. In one embodiment, the expected exposure time is multiplied by a factor derived from the advance knowledge of the average occlusion value that the captured image is going to suffer. The image correction system 212 corrects not only the defects due to the occlusion, but also due to the altered exposure time, the latter achieved by dividing by the same factor by which the actual exposure time is more than the expected exposure time, the division causing a reduction in the noise present in the image. FIG. 6A illustrates a diagram of an exemplary backlight 600 having a mirrored surface according to one embodiment of the present invention. Since the screen 204 is only on one side of the backlight 206, half the light energy will be wasted if special care is not taken. The non-display end of the backlight 600 is augmented with a mirror 602, such that the energy dispersed in the direction opposite to the display direction is reflected in the direction of the display. If the mirror 602 is a complete mirror, light will not pass through it into the camera 210. One way to overcome this problem is to use a partially silvered mirror. Though the energy efficiency of the backlight is improved, the image received by the camera 210 is attenuated, thus adversely affecting the sensitivity of the camera 210. FIG. 6B illustrates a diagram of an exemplary partially mirrored backlight 650, according to one embodiment of the present invention. A break 604 in the mirror may be provided for such that there is no obstruction to the camera 210. To compensate for the loss in brightness in the local region of the break 604 in the mirror 602, a higher concentration of light scattering particles is used in the light scattering sheet 504 near the break 604 in the mirror 602. In an alternative embodiment, to avoid a discrete appearance, both the reflectivity of the mirror 602 and the concentration of light scattering particles is varied continuously such that the mirror 602 is completely transparent in the region of the aperture of camera 210. The mirror 602 may produce highly specular reflections of objects on the other side of the display, which may make the display uncomfortable to view. This problem is overcome by making the mirror 602 a diffusing mirror, such that it has a glazed or brushed finish. In one embodiment, this is achieved by abrading the surface of transparent sheet 506 and depositing a metal on its surface. Alternatively, a light scattering sheet is used between mirror 602 and transparent sheet 506. FIG. 7A illustrates a diagram of an exemplary display 710 with a light diffuser 700, according to one embodiment of the present invention. Many standard flat panel backlighting systems use a light diffuser 700 between backlight 206 and flat panel screen 204. This is for the purpose of achieving even illumination, and to reduce specular reflections from the mirror of the backlight. Diffuser 700 ensures more even illumination in the presence of the break 604 in the mirror. In one embodiment, the diffuser 700 is made such that the outgoing light suffers a small deflection in comparison with the incoming light. Since the distance between diffuser 700 and camera 210 (not shown in figure) is small, the light does not scatter much. The scattering caused by diffuser 700 is in the form of a convolution, and the effects are nullified by the image correction system 212. FIG. 7B illustrates a diagram of an exemplary display 750 with a light diffuser 700, according to another embodiment of the present invention. Display 750 scatters the light emanating from the backlight 206 while ensuring that the view of the camera 210 is not obstructed. Diffuser section 702 of the diffuser 700 is made out of material such that it can be turned into a transparent material or a light scattering material. During the period when the light source 208 is off and the camera 210 is capturing an image, the diffuser section 702, which is directly in the line of sight of the camera 210, is turned transparent. During the period when the camera 210 is in non-recording mode and the light source 208 is turned on, the diffuser section 702 is turned into a material that scatters light. Many materials switch from scattering light to passing light with the application or removal of an electric field. These materials make use of various forms of liquid crystals. For uniformity of the diffuser 700, the remaining sections of diffuser 700 are made out of the same material that 702 is made out of. Furthermore, the sections of diffuser 700 and 702 may be a single segment of the material. In this case, the segment 702 is differentiated by the proximity of transparent electrodes which create a field across the segment such that the segment turns transparent. Thus, when the field is turned off, there is no detectable boundary between the diffuser 700 and the segment 702 which is also now a diffuser. It is frequently the case that the objects whose image is to be captured by the camera 210 are themselves illuminated by a regularly alternating external light source such as fluorescent light. Further, there is also the possibility of other displays within the field of view, these displays having their own frequencies of light emanation (both CRT and LCD displays exhibit this behavior). Such flickering light may cause a frequency aliasing effect when sampled through the high frequency capture periods of the camera 210. The effect of this aliasing on the captured images would be a low frequency oscillation in the illumination due to that particular light source. In one embodiment of the present invention, switching between capture and display periods is synchronized with the illumination due to the alternating light source, preferably such that the present system is in the capture period at the same time that the alternating external light source is illuminating the object whose image is to be captured. This eliminates the aliasing effect, and has the added benefit of a large amount of the illumination reaching the camera 210. Synchronization may be achieved by synching with the alternating mains power, which is usually driving the switching of the external light source, or by using a phase locked loop to lock into the frequency of the light source. The phase locked loop may use a photo-sensor or feedback from the camera 210 to achieve phase lock. In another embodiment, the switching frequency is a multiple of the frequency of switching of the external light source, or vice versa. In another embodiment, the aliasing effect is minimized by alternating between the capture and display periods at a very fast frequency compared to the frequency of switching the external light source off and on. Because of the higher sampling rate, the effect of aliasing is reduced. The residual aliasing effect causes a low frequency periodic change in the illumination of the captured image. Such periodic change is detected and cancelled out by the image correction system 212. The period of the frequency change is predicted by detecting the mains power frequency and subtracting the whole fraction of the switching frequency between the capture and display periods that are closest to it. To minimize flicker from high frequency light sources, the sequence of alternating between capture and display periods is randomized. The amount of time the system remains in each of the two phases of displaying an image and capturing an image is decided randomly based on some random or pseudorandom sequence of numbers. In many cases, the amount of time the light source 208 can remain on is limited. In such cases the randomization relates to the period between two flashes of light from light source 208. The random sequence is arranged such that the average illumination of the display is the chosen average illumination for the display, such that no flicker is perceived by the human eye considering the principle of persistence of vision, and each image being captured is exposed for the requisite time. The randomization in the sequence breaks up the symmetry of sampling and greatly reduces the effects of aliasing. The camera 210 is placed in a position closest to the expected location of the image of the remote conferee's eyes. Since the eyes of a human are located in the upper half of the head, and since usually head-and-shoulder images are most commonly transferred while video conferencing, the camera 210 is placed behind the upper part of the screen 204. In another embodiment, multiple cameras may be placed behind the screen. These may generate a stereoscopic or multiple-view image of the subject and surroundings. Alternately, views from various cameras could be transmitted to various conferees in a multi-party video conference. The image captured by the camera closest to the image of a particular remote conferee will be transferred to that particular conferee. This will simulate eye contact for the remote conferee only when the present conferee actually looks at that particular remote conferee. FIG. 8 illustrates a diagram of an exemplary display 800 with a camera 802, according to one embodiment of the present invention. To reduce the bulk of the camera unit 802, a first object lens 802 may be used, followed by a mirror or prism arrangement 804 which reflects light into such a direction such that the bulk can be more easily accommodated with the body of the remaining display unit 800. Light is focused by an object lens 802 through a mirror 804 onto light sensing plane 806, which may be a charge coupled device (CCD) or other device that measures the intensity of light at various spots. Such bulk reducing arrangements are useful in desktop display applications as well as smaller applications such as mobile phones. Since the camera 210 is an integral part of the video display unit, turning the camera in a different direction than the display is difficult. It may also be difficult to keep the display connected and yet disconnect the camera. To minimize the possibility of turning the camera on and capturing images unbeknownst to the user of the present invention, a simple electronic indication such as an LED indicator is provided on the front panel of the display whenever the camera starts capturing images. Many image display mechanisms and image capture mechanisms have a non-linear response. This causes the relation between occluding screen pixels and the occlusion mask to be non-linear, as well as the occlusion mask itself to be more complicated than a simple multiplier per pixel of the captured image. Though these relations are linear as far as the transparency values of the screen to the intensities at the camera pixels are concerned, the non-linear complications arise because the transparency of a screen pixel is not a linear function of the input pixel value, and because the pixel value recorded by the camera is not a linear function of the intensity incident at that pixel. To reduce or remove the non-linear effects, the image correction system 212 first operates on the captured image with the inverse of the non-linear function for the camera, to get a record pixel values which are linearly related to the intensities of light incident at those pixels. Also, before the occlusion map is calculated, the relevant pixels of the image to be displayed upon the screen are operated upon (computationally) by the same non-linear function as the non-linear function of the screen, to get an estimate of the transparency of each occluding pixel. The timing of the system is arranged such that the occluding screen pixels are not changing their transparency values during a particular image capture. This is achieved by synchronizing the display refresh cycle and the camera frame capture cycle. In the case that the transparency values of the occluding pixels change during the capture of a single image, the occlusion map calculated by the image correction system 212 is calculated as some function (a linear-combination), of the occlusion maps due to the first and the second setting of pixels on the screen. To display color images, color filters are used on individual pixels of the screen 204. To capture color images, color filters are applied to individual pixels of the camera 210. When viewed through a camera pixel of a particular color, pixels of different color than the color of the camera pixel seem much darker than pixels of the same color. This effect on perceived transparency of same and different colors is used in the calculation of the occlusion map by image correction system 212. A method and combined video display and camera system are disclosed. It is understood that the embodiments described herein are for the purpose of elucidation and should not be considered limiting the subject matter of the present patent. Various modifications, uses, substitutions, recombinations, improvements, methods of productions without departing from the scope or spirit of the present invention would be evident to a person skilled in the art.
	summary
	description	This invention pertains in general to hydrogen disposal systems and, more particularly, to hydrogen igniters and hydrogen recombiners for nuclear power plants. Conventional water-cooled nuclear reactors are designed to minimize the threat to the integrity of the containment due to a loss-of-coolant accident (“LOCA”). A LOCA can give rise to two distinct problems. First, a break in the reactor coolant circuit leads to the ejection of hot water and steam into the containment atmosphere. Unless systems are employed to remove heat from containment, the pressure and temperature within containment can rise beyond the design limits of the containment vessel. Second, in a severe LOCA involving not only loss of coolant but also failure to inject emergency coolant into the coolant system, the resulting increase in fuel temperature leads to a high temperature reaction between the residual steam in the primary system and the zirconium in the fuel sheathing. In serious cases, complete oxidation of the fuel sheathing may occur. The reaction is exothermic and produces hydrogen. The hydrogen produced from the reaction escapes along with steam from the break point in the primary system into containment atmosphere. In a severe accident, the mass; release rate of hydrogen can be in the order of a kilogram per second. Unless systems are employed to maintain hydrogen concentrations below self ignition limits, a potentially explosive gas mixture can be created in the reactor containment. New designs of water-cooled nuclear reactors avoid reliance on electrical supplies, service water and operator action in mitigating the effects of a LOCA. Such designs employ passive means to transferred heat from containment atmosphere through the containment walls in order to maintain containment pressure within design limits. For example, steel containment walls and external water cooling from elevated tanks are used to promote heat transfer. Heat from containment atmosphere is transferred to the containment walls by natural convection. Hot steam from the break mixes with air and rises to the top of containment and is cooled by contact with the cold containment wall. The cooler denser mixture falls and a process of natural circulation is begun wherein flow near the walls is down and flow in the central area is up. After the initial blow-down period, the pressure and temperature within containment increases until the rate of condensation of steam on the cold containment wall, and any other cool surfaces, equals the rate of steam discharge from the break. Conventional reactor design employs a variety of means to mitigate hydrogen build-up. Pre-inerting is one means and involves the generation of an oxygen-depleted atmosphere in containment before or during start-up for normal plant operation. An inert gas (usually nitrogen) is injected into containment to substitute for air that is simultaneously let out to ambient and to reduce the oxygen concentration below the level needed for hydrogen combustion. Pre-inerting is usually applied only to small containments in view of practical difficulties inherent in large designs. For mid- and larger containment designs, hydrogen igniters are commonly considered for hydrogen mitigation. Hydrogen igniters are conventionally distributed throughout containment, particularly in areas of likely high hydrogen concentration. Hydrogen igniters initiate combustion as soon as its concentration exceeds the ignition threshold, thereby removing the hydrogen by slow deflagration while distributing the energy release spatially and temporally. However, there is a risk in the use of hydrogen igniters that deflagration initiated at one location may propagate into a more sensitive region nearby (i.e., nearer to the release point of the hydrogen) or vent to flammable adjacent volumes (so called jet-ignition) and propagate more vigorously than expected. This may lead to transition from deflagration to detonation which can induce very high loads to the containment structure and equipment. An additional disadvantage to the method of intentional ignition is the unpredictability of the mixing behavior and the type of combustion that may result from intentional ignition of the mixture. This uncertainty has fueled the search for a method of removing hydrogen without deflagration. Further, igniters that rely on AC power could be unavailable in the event of a loss of electrical supply, battery powered igniters are limited to intermittent operation in view of the limited power available and catalytic igniters have limitations relating to the range of mixtures that can be ignited, their response time and their susceptibility to poisoning, fouling or mechanical damage. As a result, it is conventional practice to provide some other means of maintaining hydrogen concentrations below deflagration limits, and to rely on intentional ignition only if such other means are ineffective. One such other means is the use of hydrogen recombiners. Hydrogen recombiners combine hydrogen and oxygen to produce water, thereby reducing hydrogen concentration in containment. Catalytic recombiners, as opposed to thermal recombiners, are self-starting and do not require external power and, accordingly, can be used as part of a passive system. Although catalytic hydrogen recombiners have been proposed for use in containment, they have not been widely employed in practice due to a number of factors. It is conventional practice in large reactor designs to use containment atmosphere mixing to dilute hydrogen generated at the source of the break throughout containment. This is considered effective as the large containment volume is capable of diluting very large quantities of hydrogen before levels reach deflagration limits. This affords a reasonable period of time within which emergency action can be taken to deal with the LOCA. In order to operate effectively, hydrogen recombiners require a relatively high flow rate of air. The conventional use of natural circulation of containment atmosphere to effect containment cooling typically does not produce sufficiently high flow rates to render effective passive hydrogen recombiners to deal with large containment volumes. Also, due to the presence of machinery and spaces within containment, the natural convective flow patterns induced by a LOCA are exceedingly difficult to predict or model with the result that choosing optimum locations for passive hydrogen recombiners is an imprecise science at best. As a result, hydrogen recombiners are usually considered for placement in ventilation ducting through which a portion of the containment atmosphere is circulated by fans. This, of course, is not a passive system and is ineffective in the event of a loss of power to drive the circulation fans. Various methods have been proposed to improve the flow of air to recombiners. In DE 3035103, there is disclosed the use of vertical shafts and heating devices in the shafts to improve flow to recombiners by a chimney effect. While the shafts are effective to channel flow to the recombiners, the electric heaters used to generate the upward flow of air rely on external power. In addition, the large shafts present obvious physical difficulties in their integration with the equipment in containment. In view of their many limitations, hydrogen recombiners have found acceptance only for the routine removal of hydrogen produced from radiolysis and corrosion. For accident control applications, commercial reactors have not heretofore relied exclusively on hydrogen recombiners alone, but instead additionally provide for igniters and/or inerting. There is, therefore, a need to improve the conditions under which hydrogen can be removed by catalytic recombiners. This invention achieves the foregoing objective by providing a passive hydrogen recombiner and igniter comprising a substantially horizontal, metallic plate having an underside coated with a hydrogen recombination catalyst, supported in a peripheral housing having a first gaseous intake below the substantially horizontal, metallic plate and a first gaseous outlet around a periphery of the substantially horizontal, metallic plate. A second gaseous intake through the housing and through a first set of swirl vanes is provided substantially proximate to and in communication with an upper side of the substantially horizontal, metallic plate, with the first set of swirl vanes configured to create a vortex out of a second gas traversing the second gaseous intake. A second gaseous outlet is provided through an upper portion of the housing through which the vortex exits. A first passive igniter is supported proximate the first gaseous intake and a second passive igniter is supported proximate the second gaseous outlet. Preferably, the hydrogen recombination catalyst is either platinum or palladium or a combination thereof and the underside of the substantially horizontal, metallic plate includes downwardly projecting vanes covered with the hydrogen recombination catalyst, structured to direct a first gas entering the first gaseous intake to the first gaseous outlet. In one embodiment, the first gaseous outlet extends up through an interior of at least some of the first set of swirl vanes and exits outside the second gaseous outlet. Desirably, the first set of swirl vanes are structured to transfer heat from the first gas traveling through the swirl vanes to the second gas entering the second gaseous intake. Preferably, the first igniter is a platinum or palladium wire that is wound as a spring to increase its surface area and the second igniter is powered by the vortex. The second igniter may be a rotating device that accumulates charge, similar to a van de Graf generator, to create a spark as an ignition activation energy, a rotating device that drives an electric generator that charges a capacitor, which is structured to throw a spark once a particular voltage is reached, or a rotating device that drives a piezoelectric to create a spark. In another embodiment, the second gaseous outlet includes a cover spaced from the second gaseous outlet so the second gas can exhaust from under the cover. An upper side of the substantially horizontal, metallic plate may have a second set of swirl vanes attached to its surface and the second set of swirl vanes are configured to be co-directional with the vortex. The upper side of the substantially horizontal, metallic plate may also be substantially covered with a hydrogen recombination catalyst. The invention also contemplates a method of recombining and igniting hydrogen comprising the step of passively collecting a first gas, potentially having hydrogen as a component, through a first gaseous intake of a housing through which the first gas will be processed. The method directs the first gas from the first gaseous intake to an underside of a substantially horizontal, metallic plate coated with a hydrogen recombination catalyst, along an underside of the substantially horizontal, metallic plate to a first gas outlet at a periphery of the substantially horizontal, metallic plate. The method also passively collects a second gas, potentially having hydrogen as a component, through a second gaseous intake through the housing and through a first set of swirl vanes substantially proximate and in communication with an upper side of the substantially horizontal, metallic plate with the swirl vanes configured to create a vortex out of the second gas traversing the second gaseous intake. The method then exits the vortex at a second gaseous outlet through an upper portion of the housing and supports a first passive igniter at an entrance to the first gaseous intake and a second passive igniter proximate the second gaseous outlet. Preferably, the second igniter is powered from the vortex and may be a rotating device that accumulates a charge to create a spark as an ignition activation energy. Desirably, the method includes a cover spaced from the second gaseous outlet and includes the step of shielding the second igniter. As previously discussed, in a severe accident scenario at a nuclear power plant, hydrogen explosions within the containment are mitigated by i) PARs (Passive Autocatalytic Recombiners), which passively recombine hydrogen and oxygen from the air to form water vapor (employed generally in large, dry containments), ii) inerting the atmosphere (practically useful only in very small containments), and iii) electrically powered heating elements (active igniters), which heat up to a temperature above the ignition temperature of hydrogen at the lower flammability limit (used in ice condenser style containments, BWR Mark III containments and all containments of water cooled reactors licensed after Oct. 16, 2003). It is the objective of this invention to replace the active igniter technology. Current active igniters are essentially thermal glow plugs that are placed in strategic locations inside the containment where hydrogen is expected to form or accumulate. During an accident where offsite AC power is available, the back-up power is not needed and the igniters are reliable. In accident scenarios where offsite AC power is lost there are generally two independently powered groups of backups, each having approximately 33 igniters. One train has backup powered diesel generators, while the other train is powered by batteries. In some cases a redundant diesel generator or a portable generator is provided. If running on batteries, backup is generally designed for four hours of continuous power supply. The main concerns with current igniters are the extensive cabling they require, the difficulty with maintenance during outages and the need for external power to operate. Moreover, over time, these cables can get worn out and need to be replaced. Therefore, there is a need for passive, self-contained hydrogen igniters that do not rely on external power, associated wiring and controls. Unlike the current igniters, the system disclosed herein meets these criteria. Moreover, the apparatus disclosed herein do not require operator intervention to function. In the past there were passive igniter designs that employed a hydrogen recombination catalyst. There are a few critical challenges encountered in using such a passive igniter. First, the heat-up process of the igniter is slow due to the slow natural convective air flow through the catalyst. Second, as the reaction commences, water is formed on the catalyst surface which tends to inhibit the recombination reaction. As the reaction continues the steam that is generated from the exothermic reaction removes itself once the temperature of the plates rises and allows a higher velocity of air flow to strip away the water molecules. This velocity is reached once the plates reach temperatures higher than approximately 500° C. The passive igniter disclosed herein produces a hot surface by catalytic oxidation of hydrogen in air; naturally replenishes a continuous air flow across the catalytic surfaces; and naturally forms a vortex that has a high velocity (as compared to vertical buoyancy) to boost autocatalytic performance by improving mass transfer to and from the catalyst. All of these three factors allow faster heat-up of the passive igniter at lower concentrations of hydrogen compared to a passive igniter using a simple upward draft. The invention described herein shown in FIGS. 1-4 includes a substantially horizontal, metallic plate 14, and the bottom portion 16 of which is coated with a hydrogen recombination catalyst such as platinum or palladium or a mixture thereof. The plate, preferably, is made from a material having a high thermal conductivity. In the presence of hydrogen and air the bottom of the plate recombines the hydrogen on its surface, thus generating heat. Once the bottom 16 of the plate 14 gets heated, the top 18 also heats-up. As the top 18 of the plate 14 gets heated, the air above the top of the plate heats-up and the adjacent air rises due to its buoyancy. Colder air from the surroundings is drawn in to take its place. However, the passageway of the fresh inlet air around the plate is lined with radially spiraled vanes 28. These vane plates 28 force the inlet air to converge into a vortex 24, similar to a naturally occurring dust devil in a desert. This vortex 24 moves upwards and exits through the narrow chimney 22. An “igniter core” 26, is strategically placed in the mouth of the chimney 22. Similar to the bottom of the horizontal plate, the igniter core is also coated with hydrogen recombination catalyst. The high velocity of the vortex 24 ensures a high recombination reaction rate by 1) replenishing the catalyst with fresh reactants, and 2) by removing the water molecules (a byproduct of the catalytic reaction) from the catalyst surface. The horizontal plate 14, on the other hand, need not be heated to a high temperature. Past studies have shown that a very high velocity (8 to 10 m/s) vortex formation can be achieved with only a 100° C. temperature difference between a hot surface and the ambient air. Therefore, at lower hydrogen concentrations the horizontal plate 14 can generate a very high velocity (8 to 1 1 m/s) vortex compared to a vertical convection draft (0.5 to 1 m/s) requiring a temperature difference of at least greater than 200-500° C. The bottom 16 of the horizontal plate 14 needs to be exhausted through a passageway 30 in the housing 12 that does not obstruct the vortex flow 24. Therefore, the interior 32 of the guided fins or vanes 28 serves that purpose. The interior 32 of the guided vanes 28 forms a passageway for heated air from below the horizontal plate 14 to rise up and exit the apparatus as shown in FIG. 2. This also allows preheating of the vortex inlet air 20 as it flows along the exterior of the vanes 28. The bottom 16 of the horizontal plate 14 can have fins 34 to 1) allow a larger catalyst surface area, and 2) guide the hot air in a more hydrodynamically favorable path to the interior 32 of the guide fins 28 and exit the apparatus 10. Similarly, the top 18 of the horizontal plate 14 can be provided with fins 36, co-directional to the vortex flow, to allow better heat transfer to the air from the horizontal plate. Instead of fins 36, vertical pins, or flat plates, or other plate geometries can be employed to effectively transfer heat from the pins or plates to air, can be used. To enhance the heating of the vortex 24 the top 18 of the horizontal plate 14 can also be coated with a hydrogen recombination catalyst. FIGS. 1-4 show the preferred embodiment using the aforementioned principles. There is also a coiled spring igniter 38 at the mouth, i.e., lower air intake 42, of the preheater section 40 below the horizontal plate 14, which can also induce ignition to fresh air (with hydrogen) entering the intake 42. An alternate embodiment to the igniter 26 at the vortex exit 44 is to utilize a rotating mechanism to accumulate charge on a body (similar to a van de Graf generator) to create a spark as the ignition activation energy. In addition, a third set of vanes 36 can be formed on the upper surface 18 of the substantially horizontal, metallic plate 14 to force the buoyant, heated air layer to rotate as it rises, forming a columnar vortex that can be anchored and which draws in additional hot air to sustain itself to provide a new thermo-mechanical link between chemical energy and electrical energy. Additionally, the upper surface 18 of the substantially horizontal, metallic plate 14 and the third set of vanes 36 can be coated with the hydrogen recombination catalyst. Another alternate embodiment for the upper igniter 26 is to have the vortex 24 drive an electric generator that charges a capacitor, which will throw a spark once a particular voltage is reached. An additional, alternate embodiment for the upper igniter 26 is to have a rotating mechanism driven by the vortex 24, drive a piezoelectric device. One such rotating mechanism could be a shaft rotatably attached to the upper center of the substantially horizontal, metallic plate 14 with the shaft extending vertically with a vane extending radially from and spirally around the surface of the shaft. Thus, this invention provides a passive hydrogen igniter 10 that is self-actuating and self-sustaining. The buoyancy induced vortex 24 allows high velocity air to activate the igniter core, thus allowing igniter to reach auto ignition temperature faster and at lower concentrations. The igniter allows the vortex 24 to be formed by low plate temperature, thus allowing ignition at lower concentrations of hydrogen (above 4%, less than 8 mol % hydrogen in air). The guided fins 28 have dual functions: 1) the exterior surface guides inlet air to form the vortex; 2) the interior surface provides the passageway for the exhaust hot air from the bottom 16 of the substantially horizontal, metallic plate 14 recombination reaction; and 3) the interior hot air preheats the vortex inlet air 20, thus reducing time to ignition. The vortex 24 can run other electrical spark generators by using a vertical axis rotating vane, which is also self-driven. The spring igniter 38 can also cause ignition once the velocity in the preheater inlet 42 rises. The chimney hood 46 prevents exposure of the catalytic surfaces of the igniter core to containment spray, water, etc., while the other catalytic surfaces (lower fins 34 of the substantially horizontal, metallic plate 14 and the spring igniter 38) are protected by the design of the apparatus. A larger version of this design can be designed for dual functionality of existing PARs (passive autocatalytic recombiners), which are used to denature hydrogen over large quantities before it reaches the lower flammability limit (<4%) and active igniters, which ignites the excessive hydrogen before reaching an explosive level (>10%). PARs are generally slower and this embodiment can speed up the process and enhance plant safety for design basis and beyond design basis accidents. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
	summary
	claims	1. A dry filtered containment venting system for a nuclear reactor containment comprising:a housing; anda plurality of round and/or elongated aerosol filters inside the housing for removing contaminant aerosols from gas passing through the housing during venting of the containment,the housing including at least one inlet portion configured for directing gas into the plurality of aerosol filters during the venting of the containment and an outlet portion for gas filtered by the plurality of aerosol filters during the venting of the containment,the at least one inlet portion being arranged with respect to the plurality of aerosol filters such that, when a flow of gas through the outlet portion is closed off, gas flows through the at least one inlet portion to remove decay heat of the aerosols captured in the plurality of aerosol filters by at least one of convective, radiant and conductive heat transfer. 2. The dry filtered containment venting system as recited in claim 1 wherein the at least one inlet portion includes an inlet pipe and an inlet tubesheet, the outlet portion including an outlet pipe and an outlet tubesheet, the dry filtered containment venting system further comprising a plurality of tubes extending between the inlet tubesheet and the outlet tubesheet, each of the plurality of tubes including at least one of the aerosol filters positioned therein to capture contaminants within an airflow passing through the system. 3. The dry filtered containment venting system as recited in claim 2 wherein each of the plurality of tubes further includes a sieve positioned therein to capture contaminants within an airflow passing through the system. 4. The dry filtered containment venting system as recited in claim 2 wherein the plurality of tubes have a nominal diameter of approximately ten inches to approximately two inches. 5. The dry filtered containment venting system as recited in claim 2 wherein in at least one of the plurality of tubes, the aerosol filter is positioned in a spaced relationship with respect to the at least one tube, such that a gap is formed between an outer surface of the filter and an inner surface of the at least one tube and that the relative surface area of cold surface to hot surfaces for heat transfer is greater than 1. 6. The dry filter containment venting system as recited in claim 2 further comprising an iodine filter arranged between at least one of the aerosol filters and the outlet portion in a gas flow direction. 7. The dry filtered containment venting system as recited in claim 1 wherein the at least one inlet portion includes an inlet pipe and an inlet header, the outlet portion including an outlet pipe and an outlet header, the dry filtered containment venting system further comprising a plurality of tubes extending between the inlet header and the outlet header, each of the plurality of tubes including at least one of the aerosol filters positioned therein to capture contaminants within an airflow passing through the system. 8. The dry filtered containment venting system as recited in claim 7 wherein each of the plurality of tubes further includes a sieve positioned therein to capture contaminants within an airflow passing through the system. 9. The dry filtered containment venting system as recited in claim 7 wherein the plurality of tubes have a nominal diameter of approximately ten inches to approximately two inches. 10. The dry filtered containment venting system as recited in claim 7 wherein in at least one of the plurality of tubes, the filter is positioned in a spaced relationship with respect to the at least one tube, such that a gap is formed between an outer surface of the filter and an inner surface of the at least one tube and that the relative surface area of cold surface to hot surfaces for heat transfer is greater than 1. 11. The dry filtered containment venting system as recited in claim 1 wherein the at least one inlet portion includes:a lower inlet portion; andan upper inlet portion,the lower inlet portion arranged for directing gas upward into a lower section of the aerosol filters during the venting of the containment,the upper inlet portion arranged for directing gas downward into an upper section of the aerosol filters during the venting of the containment,the lower inlet portion and the upper inlet portion being arranged such that gas flows in through the lower inlet portion upward past the lower and upper sections of the aerosol filter and out past the upper inlet portion when a flow of gas through the outlet portion is closed off so as to allow a forced convective cooling of the decay heat of aerosols captured in the aerosol filters. 12. The dry filter containment venting system as recited in claim 11 wherein the aerosol filters each define a horizontally extending channel therein. 13. The dry filter containment venting system as recited in claim 12 wherein the aerosol filters are arranged with respect to the lower and upper inlet portions such that during venting of the containment gas streams enter both the lower and upper inlet portions and flow into the aerosol filters into the channels and then horizontally out of the outlet portion. 14. The dry filter containment venting system as recited in claim 13 further comprising an iodine filter horizontally between the aerosol filters and the outlet portion, the gas flowing into the channels passing through the iodine filter before flowing horizontally out of the outlet portion. 15. The dry filter containment venting system as recited in claim 14 wherein the iodine filter is a molecular sieve. 16. The dry filter containment venting system as recited in claim 14 wherein the lower inlet portion, the upper inlet portion and the at least one outlet portion are integral with the housing and form an integral structure configured for mounting in a wall of the nuclear reactor containment such that the lower inlet portion and the upper inlet portion are inside the containment and the least one outlet portion directs filtered gas out of the containment. 17. The dry filter containment venting system as recited in claim 12 wherein the aerosol filters are arranged with respect to the lower and upper inlet portions such that when a flow of gas through the outlet portion is closed off a gas stream enters the lower inlet portion and flows past the aerosol filters and upwardly out of the upper inlet portion. 18. The dry filter containment venting system as recited in claim 1 wherein the aerosol filters are round metal fiber filters. 19. The dry filter containment venting system as recited in claim 1 wherein the plurality of aerosol filters are each elongated and extend longitudinally between a longitudinal inlet end and a longitudinal outlet end, the plurality of aerosol filters being arranged such that gas filtered by the aerosol filters flows out the longitudinal outlet end of each of the aerosol filters and out the outlet portion when the outlet portion is open.
	description	This application is a continuation application of Ser. No. 10/720,251, filed Nov. 25, 2003 now U.S. Pat. No. 6,982,420, the disclosure of which is incorporated by reference in its entirety. The present invention relates to a transmission electron microscope and simple observation method using the same, particularly to a transmission electron microscope and simple observation method using the same capable of selecting a targeted sample from the field of view including the samples tilted in various angles. The sample observed by the transmission electron microscope is inclined in various directions with respect to the electron beam incoming direction. Accordingly, even in the samples having the same 3-dimensional structure, the transmission image may take on a hexagonal form or an octahedral form, depending on the state of inclination, as in the case of a virus particle having a regular dodecahedron. As described above, it requires experience and intuition of an observer and takes a lot of time to find out a sample having a particular form in a field of view where a great number of samples of different shapes are present. For a sample having a polyhedral structure, the profile of the transmission image varies according to the tilt angle of the sample. This makes it difficult to determine if a sample having bee found out has the desired profile. One of the ways to solve this problem is to observe the 3-dimensional structure of a sample. To observe the three-dimensional structure of a sample using a transmission electron microscope, a stereo-viewer is used to observe two stereoscopic photographs obtained by tilting the sample by a certain angle in the positive and negative directions. The Patent Document 1 describes the method of using a scanning electron microscope to determine the position of the targeted pattern according to the degree of similarity with a register pattern. The detected pattern position can be detected only from the positional relationship with the registered pattern. Further, all conditions for reproducing the image of the detected position including the observation conditions are detected using the position relationship (offset) with respect to the detected pattern. The perfect compatibility between the detected pattern and its position is not taken into account. When the sample once taken out is put back into the electron microscope to be searched again, the offset must be set again since the registered pattern by offset is set. Further, no consideration is given to the pattern when the sample is tilted. When the sample is rotated, there is a deviation in the positional relationship between the registered pattern and detected pattern. Accordingly, the offset registered in advanced becomes invalid. Patent Document 1: Japanese Patent Laid-Open Publication No. 09-245709 (1997) The aforementioned prior-art fails to give consideration to the work of finding out a targeted object where the apparent profile of the object varies according to the tilt angle of a sample. This has raised problems in the accuracy of sample searching. Namely, a stereoscopic pair is obtained by tilting the sample in the positive and negative directions with respect to optical axis, and is observed by a stereo-viewer, thereby observing the three dimensional structure of the object. This method has the defect of being too intuitive and is inferior in scientific precision. An attempt is often made to provide a schematic representation of the structure by line drawing. This method depends on manual work and is hence used only as supplementary means for grasping the three-dimensional structure. An object of the present invention is to provide a transmission electron microscope that permits accurate and efficient selection of a targeted object from the field of view including objects tilted in various angles, and reproduces the observation conditions for the targeted object whenever required. To achieve the aforementioned object, the present invention provides a sample observation method comprising a step of recognizing the image of an object in the transmission electron beam image of a sample by comparing it with a previously stored reference image. This sample observation method is characterized by further comprising the steps of specifying an object in the transmission electron beam image wherein multiple pairs of transmission electron beam images of multiple objects having a different tilt angle with respect to the optical axis are stored as the reference images for the objects; computing the correlation between the specified object image and the reference image; and displaying the result of computation. The sample observation method provided by the present invention comprises a step of recognizing the image of an object in the transmission electron beam image of a sample by comparing it with a previously stored reference image. This sample observation method is characterized by further comprising the steps of specifying an object in the transmission electron beam image wherein multiple images formed by polar coordinate conversion of transmission electron beam images of multiple objects are stored as the reference images; carrying out polar coordinate conversion of the image of the specified object; computing the correlation of the images between the specified object image having been subjected to polar coordinate conversion and the reference image; and displaying the result of computation. The electron beam transmission image of an object is preferred to be composed of a set of multiple electron beam transmission images of the object having different tilt angles with respect to optical axis. In this case, the image having been subjected to the polar coordinate conversion is prepared for each of multiple electron beam transmission images of the object having different tilt angles with respect to optical axis. The rotary fulcrum for polar coordinate conversion of the object image may be specified in the transmission electron beam images. The result of computing the correlation of the images can be displayed in terms of the degree of agreement between images. It can be displayed in various ways; by listing in the descending order of the degree of agreement; by displaying images according to class wherein the degree of agreement is classified into several classes having a certain range; and by listing such identifiers as image names and the degrees of agreement. The sample observation method for searching the same objects in multiple objects in the transmission electron beam images of a sample according to the present invention comprises steps of selecting multiple objects in the transmission electron beam images of a sample; carrying out polar coordinate conversion of each of the selected multiple object images; specifying one of the multiple objects; computing the correlation between the image of the specified object subsequent to polar coordinate conversion and the images of other objects subsequent polar coordinate conversion; and displaying the result of computation. It is preferred that the apparatus data items during transmission electron beam photographing of a sample be stored in the form associated with transmission electron images of the sample in a one-to-one relationship. This can be achieved, for example, by storing the transmission electron beam images of the sample as images in the TIFF format including the tag area and storing the apparatus data in the tag area. When this method is utilized, the apparatus data stored in the tag area can be set in the transmission electron microscope and the conditions for photographing the transmission electron beam images including the targeted object can be reproduced. The present invention ensures efficient and accurate searching of the targeted sample by selecting the specific object image based on the degree of agreement with the reference image and reproducing the observation conditions on the electron microscope automatically. The following describes the embodiments of the present invention with reference to drawings: FIG. 1 is a block diagram representing an example of the configuration of a transmission electron microscope according to the present invention; The electron beam 3 emitted from the electron gun 2 of the transmission electron microscope 1 is applied to a sample S held by a sample stage 5, by means of an irradiation lens 4. The electron beam image having passed through the sample S is magnified by the object lens 6 and magnifying lens system 7, and is projected in the TV camera 8. The TV camera 8 is equipped with a scintillator plate and image-capturing device such as a CCD. The electron beam image projected thereto is supplied to a TV camera controller 16 and is converted into the image signal. The image signal is sent to the monitor 17 and is displayed on the monitor 17 as an image. Further, the image signal outputted from the TV camera controller 16 is supplied to an administration controller 18 and is stored as image data. The bottom of the transmission electron microscope 1 is formed into a camera chamber 9 and a fluorescent screen 10 is arranged therein. The electron beam of a sample can be observed on the fluorescent screen 10 by causing the TV camera 8 to deviate from the optical axis of the electron beam 3 by a TV camera drive 19. The electron gun 2 is controlled by the electron gun controller 11, irradiation lens 4, object lens 6 and magnifying lens system 7 are controlled by an irradiation lens controller 12, an object lens controller 13 and a magnifying lens system controller 14, respectively. The sample stage 5 is controlled by a sample stage controller 15. These controllers 11 through 15 constitute an observation condition controller. The controllers 11 through 15 constituting an observation condition controller are connected to the administration controller 18 via a transmission line to allow exchange of data. The observation conditions can be set from the administration controller 18. The administration controller 18 is provided with a computer loaded with a certain program, and the input means 20 such as a keyboard is connected thereto. It generates the control data required for the control of controllers 11 through 15. The following describes the operation of the transmission electron microscope according to the present invention: The administration controller 18 takes charge of four types of processing; image recording, image recognition, image search and image calling. Image recording is the processing carried out when a desired sample is observed. Image recognition is the processing of making a decision on whether or not a desired object recorded by image recording is equal to the already stored image data (reference), or determining the data of reference image to which the desired object corresponds. Image search is the processing of finding out the reference object to which a desired object corresponds, or the object having the same profile as that of the desired object among multiple predetermined objects. Image calling is the processing of reproducing and observing the observation conditions for the searched object. In the preferred embodiment of the present invention, an image correlation is utilized to determine the similarity between the transmission image of the object in the samples and reference image. The following describes the outline of the phase-restricted correlation an example of the image correlation. Phase-restricted correlation is defined as one of the image computations modified in such a way that the amplitude component of the input image is replaced by the fixed value, in the computation process of correlation using the Fourier transform. (“Principle of phase-restricted correlation and its application”; by T. Kobayashi, Technical Report of Television Institute of Television Engineers of Japan. pp 1–6, No. 41, Vol. 20 (1996)). Only the phase spectrum is extracted out of the amplitude spectrum and phase spectrum obtained by the discrete Fourier transform of the image (transmission image), and the correlation image is obtained by inverse Fourier transform. When there are two transmission images f1(m, n) and f2(m, n), the discrete Fourier images F1(u, v) and F2(u, v) can be defined by the following equations, respectively. In this case, m=0, 1, 2, . . . , M−1: n=0, 1, 2, . . . N−1: u=0, 1, 2, . . . , M−1; v=0, 1, 2, . . . , N−1. A(u, v) and B(u, v) denote the amplitude spectrum, while θ(u, v) and φ(u, v) indicate the phase spectrum. [ Mathematical ⁢ ⁢ Formula ⁢ ⁢ 1 ] F ⁢ ⁢ 1 ⁢ ( u , v ) = ∑ m = 0 M - 1 ⁢ ∑ n = 0 N - 1 ⁢ f ⁢ ⁢ 1 ⁢ ( m , n ) ⁢ ⅇ - j2δ ⁡ ( mu M + mv N ) = A ⁡ ( n , v ) ⁢ ⅇ jθ ⁡ ( u , v ) ( 1 ) F ⁢ ⁢ 2 ⁢ ( u , v ) = ∑ m = 0 M - 1 ⁢ ∑ n = 0 N - 1 ⁢ f ⁢ ⁢ 2 ⁢ ( m , n ) ⁢ ⅇ - j2δ ⁡ ( mu M + mv N ) = B ⁡ ( n , v ) ⁢ ⅇ jϕ ⁡ ( u , v ) ( 2 ) In the phase-restricted correlation, the amplitude spectra A(u, v) and B(u, v) of F1(u, v) and F2(u, v) are used as fixed values; therefore, the images having only the phase information are obtained. Assuming that these phase images are F1′(u, v) and F2′(u, v), definition is given by Eq. (3) and (4): [Mathematical Formula 2]F1′(u,v)=ejθ(u,v) (3)F2(u,v)=ejθ(u,v) (4) The composite image H12(u, v) is obtained by multiplying the phase image F1′(u, v) by the complex conjugate of F2′(u, v). To be more specific, the phase difference is calculated for each pixel, as shown in Eq. 5. [ Mathematical ⁢ ⁢ Formula ⁢ ⁢ 3 ] H ⁢ ⁢ 12 ⁢ ( u , v ) = F ⁢ ⁢ 1 ′ ⁢ ( u , v ) ⁢ ( F ⁢ ⁢ 2 ′ ⁢ ( u , v ) ) * = ⅇ j ⁡ ( θ - ϕ ) ( 5 ) The correlative intensity image is obtained by inverse Fourier transform of the composite image, and is given by Eq. (6), provided that r=0, 1, 2, . . . M−1; s=0, 1, 2, . . . , N−1. [ Mathematical ⁢ ⁢ Formula ⁢ ⁢ 4 ] G ⁢ ⁢ 12 ⁢ ( r , s ) = ∑ m = 0 M - 1 ⁢ ∑ n = 0 N - 1 ⁢ ( H ⁢ ⁢ 12 ⁢ ( u , v ) ) ⁢ ⅇ j2δ ⁡ ( ur M + vs N ) = ∑ m = 0 M - 1 ⁢ ∑ n = 0 N - 1 ⁢ ( ⅇ j ⁡ ( θ - ϕ ) ) ⁢ ⅇ j2δ ⁡ ( ur M + vs N ) ( 6 ) The phase-restricted correlation is completely immune from image brightness. So the apparent thickness of the sample varies according to the tilt angle of the sample, and there is no need of readjusting the irradiation conditions, even if the irradiation conditions are changed. FIG. 2 is a diagram representing the spectrum of the correlative intensity image an example of the result of correlation obtained from phase-restricted correlation. FIG. 2(a) indicates the correlative intensity peak when similarity between two images is high. FIG. 2(b) indicates the correlative intensity peak when similarity between two images is not very high. As shown above, the similarity of images can be evaluated according to the height of the correlative intensity image peak. When images are perfectly equal to each other, the height of the autocorrelation peak is assumed as 100 or 1, and the relative peak height with respect to it can be expressed as the degree of agreement. The transmission image of the object as an item to be searched may be turning about optical axis with respect to the reference image. To find a correlation between the object image and reference image in this case, one can find a phase-restricted correlation between the object image having been subjected to polar coordinate conversion and reference image. FIG. 3 is a schematic view showing polar coordinate conversion. The coordinates (x, y) of the X-Y plane can be expressed by the following polar coordinates (r, θ): [Mathematical Formula 5]r=√{square root over (x2+y2)} (7)è=arc tan y/x (8) Let us consider the case where the objects of the same profile rotate about the origin on the X-Y plane. For example, consider the case where the rectangular object 31 whose apex was located at (r1, θ1) shown in FIG. 3(a) has rotated about the coordinate origin by angle α, as shown in FIG. 3(b). Then the apex (r1, θ1) of the rectangular object 31 is located at point (r1, θ1+α) for the rectangular object 32 having rotated by angle α. Similarly, a given point (r, θ) on the object 31 shown in FIG. 3(a) goes to the point (r, θ) of the object 32 having rotated, as shown in FIG. 3(b). The object before and after rotation is plotted on the two-dimensional coordinates where “r” is assigned on the vertical axis and θ on the horizontal axis. This will provide the objects 33 and 34 shown in FIG. 3(c). To be more specific, rotation about the origin in the X-Y plane is converted into the parallel motion in the θ direction in the two-dimensional coordinate system having undergone polar coordinate conversion. Therefore, when comparison is made between the images subjected to polar coordinate conversion, similarity between two images can be obtained without being affected by rotation about the origin on the X-Y plane. However, when the image on the X-Y plane is subjected to polar coordinate conversion so that it is converted to an image on the r-θ plane, the profile of the image on the r-θ plane varies according to where the origin is set. Accordingly, the origin when the transmission image of the object is subjected to polar coordinate conversion must be equal to the origin when the reference image is subjected to polar coordinate conversion. Thus, it is possible to specify a certain point in the image as a fulcrum so that “r” will be made constant by the transmission image of the object and reference image, and to captures an image having a certain size around it, whereby this image is subjected to polar coordinate conversion. For a digital image photographed by a CCD camera or the like, for example, the characteristic point of the image can be specified as an origin by manual operation by observing it on a monitor. FIG. 14 shows an example of extracting the characteristic point using an actual sample. The image is obtained by photographing the transmission electron beam image of a sample by a CCD camera. The transmission image of FIG. 14(a) is the reference image. The characteristic point of the transmission image is indicated by an arrow mark. This point is assumed as an origin of the polar coordinate, and conversion processing is applied. To capture the characteristic point, the image can be subjected to binarization. FIG. 15 is an example of binarization of the image shown in FIG. 14. The characteristic point extracted by binarization is indicated by an arrow mark. This can be used as an origin. FIG. 4 is a drawing an example of polar coordinate conversion where a point on the contour of an image on the X-Y plane is used as an origin. Consider the case where the rectangular object 41, where one apex was positioned at the origin on the X-Y plane as shown in FIG. 4(a), has rotated about the coordinate origin by angle β as shown in FIG. 4(b). The object before and after rotation is plotted on the two-dimensional coordinate where “r” is assigned to the vertical axis and the “θ” on the horizontal axis. This will provide images 43 and 44 having the same profile where they are moved in parallel displacement by angle β in the θ direction, shown in FIG. 4. The following describes the processing of image recording, image recognition, image search and image calling according to the present invention: The processing of image recording will be described first using the flowchart given in FIG. 5. An operator prepares a sample S to be observed, and operates a transmission electron microscope to set the observation conditions. Then the operator captures the enlarged image of a desired portion of the sample S using a TV camera 8. The operation in this case is carried out using input means 20 such as a keyboard. The operator enters the required control data into the electron gun controller 11, irradiation lens controller 12, object lens controller 13 and magnifying lens system controller 14 so that the desired acceleration voltage, scaling factor and observation mode can be obtained. Control data is also entered into the sample stage controller 15 and the sample stage 5 is operated in such a way that the desired portion of the sample 6 will be in the field of view. The above operations will provide the image on the desired portion (coordinate) of the sample S according to desired conditions. When the image of a desired portion of the sample S under desired conditions is obtained, the operator performs the operation required to record the image in the administration controller 18 (S11). The administration controller 18 memorizes the transmission image of the sample captured from the TV camera 8 into the memory and stores it therein (S13). The object image captured through the TV camera 8 may be stored after it has been converted into the data of TIFF format. In this case, it is also possible to make such arrangements that, in parallel with storage of image data in Step 13, the administration controller 18 captures the observation conditions as data from the controllers 11 through 15, and this data is stored in the tag area of the TIFF format as the tag data of the image data (S14). The observation conditions for storing the tag data into the tag area includes acceleration voltage, scaling factor, emission current, spot size, sample position coordinate, exposure time and the amount of exposure. The following describes the processing of registering the referenced image with reference to the flowchart given in FIG. 6: Multiple transmission images of an object previously captured by tilting in multiple directions, and an image obtained by polar coordinate conversion of the transmission image, as will be described later, can be used as reference images. Further, a reference image can be created from the object itself contained in the sample S. In this case as well, the transmission image with the sample tilted for the object to be searched from samples and the image obtained from the transmission image having been subjected to polar coordinate conversion are registered as reference images. When the tilt angle is zero degree without the sample state being tilted with respect to the optical axis, the transmission image of the object (reference image) is recorded (S21). Then the sample stage is tilted to record the transmission image of an object tilted at various angles (S22). After that, the reference image at a tilt angle of 0 degree and the reference image tilted at various angles are subjected to polar coordinate conversion, thereby obtaining an image (S23). Further, the image signal of the reference signal is converted into the TIFF format, and is stored in the administration controller 18 (S24). In parallel to the storage of the administration controller 18, the administration controller 18 captures the image observation condition as data from the controllers 11 through 15, and the captured data is stored as tag data of the image data in the tag area of TIFF format (S25). In the manner described above, the transmission image of the object tilted at various angles and the image obtained by polar coordinate conversion of such transmission image are used to create the image database of the reference image. FIG. 7 is a diagram showing an example of listing the transmission images used as reference images. In this figure, a virus is used as an object. The tilted transmission image of the object tilted at various angles with respect to the optical light and the image having been subjected to polar coordinate conversion are used as a database for the reference image. For example, the transmission images of virus A gained by tilting in a certain direction within the tilt angle of ±60 deg. in increments of 30 deg. are assumed as reference images Ra1, Ra2, Ra3, Ra4 and Ra5 of virus A. The transmission images gained by polar coordinate conversion of these images are registered as reference images RAa1, RAa2, RAa3, RAa4 and RAa5. A similar step is taken for virus B. Namely, the transmission images of virus B gained by tilting in a certain direction within the tilt angle of ±60 deg. in increments of 30 deg. are registered as reference images Rb1, Rb2, Rb3, Rb4 and Rb5 of virus B. The transmission images gained by polar coordinate conversion of these images are registered as reference images RAb1, RAb2, RAb3, RAb4 and RAb5 of virus B. Similarly for virus C, the transmission images of virus C gained by tilting in a certain direction within the tilt angle of ±60 deg. in increments of 30 deg. are assumed as reference images Rc1, Rc2, Rc3, Rc4 and Rc5 of virus C. The transmission images gained by polar coordinate conversion of these images are registered as reference images RAc1, RAc2, RAc3, RAc4 and RAc5. The following describes the processing of image recognition with reference to FIG. 8: Image recognition is the processing carried out to compare between the transmission image of a desired sample and reference image. The sample is observed (S31) and the transparent image of a desired area in the samples is recorded (S32). Images are obtained by polar coordinate conversion of an object in the transmission images (S33). The transmission images and images subsequent to polar coordinate conversion are stored (S34). After that, comparison is made between the transmission images of the desired object in the sample images and reference images (S35). Comparison can be made using the correlation of images as in the phase-restricted correlation method. It is preferred that the correlation be found among images subsequent to polar coordinate conversion, because it is not affected by the rotation of the object. The result of image correlation can be displayed to represent the degree of agreement among images (S36). The following describes the processing of image search: Image search is the processing of finding out the reference to which a desired object corresponds, or finding out a sample having the same profile as a desired object that is assumed as a reference. The scaling factor of the reference image and that of the image to be searched is preferred to be the same in principle. Should the scaling factor be changed, it is preferred that the scaling factor of the image be adjusted by ensuring that the observation condition for the reference image can be referenced in advance, when the sample image is recorded in the step of image recording. FIG. 9 is a flow chart representing the processing of image search. In image search, the image database of a reference image is selected (S41). This reference image contains the transmission image of the sample itself to be searched and its tilted transmission image. Based on the degree of agreement of images displayed after processing of image recognition, a reference image closely correlated with the desired sample is selected (S42) and the selected transmission image is displayed (S43). It is also possible to make such arrangements that the image of an object in the samples to be searched is correlated with the reference image, and the image is classified by comparison. Images be classified according to the database of the reference image; for example, the image of the object in the sample is the transmission image of virus A tilted by +30 deg. which is further rotated by 0 deg. by polar coordinate conversion. It is also possible to classify multiple samples, assuming a certain sample as a reference. It is also possible to find out a sample having the same profile as the reference sample from multiple samples by assuming a certain sample as a reference. Referring to FIG. 10, the following describes an example of searching the image: In the first plate, the transmission image of a desired object contained in the sample is captured and stored. Assume that the transmission image of the object shown in FIG. 10(a) is to be searched as a transmission image. An image is obtained by polar coordinate conversion of the transmission image of the object, and is also stored. Then the database of the reference image is selected. Let us assume here that the database of the reference images for viruses A, B and C given in FIG. 7 has been selected. The result of search is outputted as the list showing the result of image correlation (degree of agreement) with the reference image. FIGS. 10(b) and 10(c) are the diagrams representing the examples of the result of search processing. FIG. 10(b) shows an example of listing the results of correlation between the sample image and individual reference images stored in the database, where these results are ranked according to the degree of agreement in the descending order. FIG. 10(c) is an example of listing the results of correlation between images, for each reference image in the database. According to this example, it is highly possible that the object in the sample is virus B. FIG. 11 is an explanatory diagram representing an example of searching the same object as the reference image in the field of view for the sample containing multiple objects. In the first place, the field of view for the sample containing multiple objects are photographed and recorded, as shown in FIG. 11(a). Then multiple objects are selected from that field of view. When objects are selected, the objects can be enclosed by a frame having a certain size if the image is photographed by a CCD camera as illustrated in FIG. 11(b). The selected objects can be numbered as illustrated. In this example, six objects are selected. This is followed by the step of selecting the reference image to be searched, from the reference image database. Here the series of virus B given in FIG. 7 are specified as reference images, by way of an example. Then selected objects are correlated with reference images, and the results are indicated. As shown in FIG. 11(c), the result is displayed in terms of the degree of agreement between the objects selected from the sample and reference image. To display the result of search, it is also possible to make such arrangements that the degree of agreement is provided with a threshold value in advance, and only the results of research where the degree of agreement has exceeded the threshold value are outputted. In this example, the results of search indicate a high possibility that objects Nos. 002 and 003 in the sample are viruses B. It can be seen that there is also a high possibility of objects Nos. 006 and 001 being viruses B as well. FIG. 12 is an explanatory diagram representing an example of processing wherein an object having the same profile as that of the object is searched in the field of view for the sample containing multiple objects, with the object in the sample assumed as a reference. The field of view for the sample containing multiple objects are photographed and stored as shown in FIG. 12(a). Then a desired object sample is selected from the field of view. As shown in FIG. 12(b) the object is selected by enclosing the frame by a mouse. The selected object can be assigned with an appropriate number. Then one object out of multiple selected objects is used as a target object, and its transmission image and the image obtained by polar coordinate conversion of the transmission image are used as reference images. Correlation is established with the remaining objects having been selected. For the transmission images of the objects other than the target object, the image having been subjected to polar coordinate conversion is prepared and computation of image correlation is carried out between transmission images and between images having been subjected to polar coordinate conversion. As a result, the object having the same profile as that of the target object is found out. FIG. 12(d) shows an example of displaying the search result. In this example, the object having the same profile as that of the object No. 002 found out in the sample is searched in the sample. It can be seen that there is a high possibility that the object No. 003 is relevant. The illustrated example shows the case where the unmodified profile is used as a reference without the sample being tilted at multiple angles. It is also possible to tilt the sample at various angles and to record the transmission images of the object, as required, thereby using them as reference images, together with the images having been subjected to polar coordinate conversion. The following describes the processing of image calling with reference to FIG. 13: Image calling is the processing applied to reproduce the observation condition of the searched object for observation. The image data of the searched object is converted into the TIFF format and is stored in the administration controller 18. The image data of the TIFF format has the observation conditions of the image stored in the tag area. When a searched image is specified, the image data of the sample specified by the administration controller 18 is called up (S51). Then the administration controller 18 supplies this image to the monitor 17 so that the searched image stored is displayed on the monitor screen. Whenever required, the administration controller 18 calls up the tag data from this image data (S52), and supplies to the electron gun controller 11 and lens controllers 12 through 14, the control data representing the observation conditions such as acceleration voltage and scaling factor in the tag data (S53). This allows the sample stage 5 to move in such a way as to get the field of observation of the sample S specified by the tag data. Control is made to get the acceleration voltage, scaling factor, measurement mode (e.g. diffraction mode, high resolution mode, enhanced contrast mode or extra-low powered mode), thereby permitting observation of the same field of view as that of the recorded image (S54). According to this method, when the sample S contains objects tilted in various angles with respect to the direction of incoming electron beam, the reference image is compared with the projected image of the object, and the degree of agreement is evaluated quantitatively, whereby only the image tilted in a particular direction can be selected from the field of view. This ensures efficient image analysis. According to the prior art, an image is selected, for example, by the image pattern matching technique. However, the prior art does not use the arrangement of selecting the reference image to provide automatic selection of images based on the degree of agreement. Further, the image is not provided with observation conditions; therefore, even if an image has been selected, the observation conditions of the selected image cannot be reproduced for observation. In this case, the selected image cannot be recorded again under the same conditions, using a film and other recording medium, for example. According to the present invention, however, the image data is converted into the data of TIFF format and the observation conditions are stored in the tag area. This arrangement ensures observation conditions corresponding to the image at all times, and the corresponding observation conditions are obtained by mere calling of the image data at the same time. Further, there is little restriction on the amount of data to be stored. This provides a perfect reproduction of the observation conditions in an easy manner. The present invention ensures an accurate and efficient selection of a target object out of the objects tilted at various angles. Further, it allows a recorded object image to be displayed, and permits the observation conditions to be fed back to an electron microscope, thereby ensuring easy and faithful reproduction of a recorded image on the electron microscope.
	abstract	One embodiment relates to an apparatus of a dynamic pattern generator for reflection electron beam lithography. The apparatus includes a plurality of base electrodes in a two-dimensional array, an insulating border surrounding each base electrode so as to electrically isolate the base electrodes from each other; and a sidewall surrounding each base electrode. The sidewall comprises a plurality of stacked electrodes which are separated by insulating layers. In addition, the base electrodes are advantageously shaped so as to be concave. Furthermore, a conformal coating may be advantageously applied over the base electrodes and sidewalls. Another embodiment relates to an apparatus for reflection electron beam lithography. The apparatus includes a shadow mask configured to form an array of incident electron beamlets. The shadow mask comprises an array of holes which correspond one-to-one with an array of pixel pads of an electron reflective patterned structure. Other embodiments, aspects and features are disclosed.
	abstract	A method and apparatus for alignment and astigmatism correction for a scanning electron microscope can prevent an alignment or correction error attributable to the conditions of a particular specimen. First, a difference is determined between optimal values acquired from an automatic axis alignment result on a standard sample, and those obtained from each of a plurality automatic axis alignment results on a observation target sample. An optimal value is then adjusted using the standard sample, by use of the difference thus obtained. Correspondingly, an optimal stigmator value (astigmatism correction signal) is acquired by using the standard sample, and storing the optimal stigmator value as a default value. The optimal stigmator value and the default value depending on the height of an observation target sample pattern are added, and an astigmatism correction is performed on the basis of the resultant stigmator value.
	summary
	claims	1. An apparatus for positioning a tumor of a patient for treatment with positively charged particles, comprising:a patient positioning system, comprising:a rotatable platform configured to both support and rotate the patient during use;an upper body support affixed to said rotatable platform, wherein said upper body support comprises:a semi-upright patient support surface; anda motorized head positioning system;an upper support structure, said upper support structure configured to:co-rotate with said rotatable platform;hold a camera, both (1) said camera and (2) said upper support structure configured to rotate about an axis aligned with gravity during use; andhold a video display screen, said video display screen configured to co-rotate, about the axis aligned with gravity, with said upper support structure in view of a patient viewing position;means for recalling patient specific motor positions for:said motorized head positioning system; anda charged particle irradiation system comprising a charged particle beam path, said charged particle beam path passing within about six inches of said semi-upright patient support surface. 2. The apparatus of claim 1, wherein said charged particle beam path passes above a portion of said rotatable platform. 3. The apparatus of claim 2, wherein said rotatable platform further comprises:a lower support structure, said lower support structure holding a portion of said patient positioning system, said lower support structure indirectly supporting a back support, said back support comprising:a left side portion;a right side portion,a first distance between an upper end of said left side portion and an upper end of said right side portion; anda second distance between a lower end of said left side portion and a lower end of said right side portion, said first distance and said second distance comprising independently adjustable distances. 4. The apparatus of claim 1, further comprising:an X-ray generation source located within forty millimeters of the charged particle beam path, wherein said X-ray source maintains a single static position: (1) during use of said X-ray source and (2) during tumor treatment with the positively charged particles,wherein X-rays emitted from said X-ray source run substantially in parallel with the charged particle beam path. 5. The apparatus of claim 4, wherein said X-ray generation source comprises a tungsten anode. 6. The apparatus of claim 4, wherein use of said X-ray generation source occurs within thirty seconds of subsequent use of said charged particle irradiation system. 7. The apparatus of claim 1, wherein the positively charged particles travel along said charged particle beam path to the tumor of the patient. 8. The apparatus of claim 1, wherein said semi-upright patient support surface comprises an about vertical surface. 9. The apparatus of claim 1, wherein said semi-upright patient support surface is reclined from a vertical axis by less than about sixty-five degrees. 10. The apparatus of claim 1, wherein said patient positioning system further comprises:a motorized foot positioning system configured to adjust an angle of a foot of the patient independently of an angle of a torso of the patient. 11. The apparatus of claim 1, further comprising:means for recalling a historical position of the patient after the patient has departed from the apparatus for a period of at least hours. 12. The apparatus of claim 1, wherein said patient positioning system provides respiration instructions on said video screen, said respiration instructions generated using a respiration sensor configured to monitor the patient during use, said video screen configured to co-rotate with the patient about the axis aligned with gravity during use. 13. The apparatus of claim 1, wherein said patient positioning system reduces movement freedom of the tumor in terms of roll. 14. The apparatus of claim 1, said charged particle irradiation system further comprising a synchrotron, said synchrotron comprising:a center;straight sections;turning sections; andan extraction system comprising an extraction foil proximate the charged particle beam path, wherein said extraction system applies a radio-frequency field to the positively charged particles during use to alter the charged particle beam path through the extraction foil, said extraction foil positioned in the charged particle beam path prior to at least one Lambertson magnet about the charged particle beam path,wherein said charged particle beam path runs;about said center;through said straight sections; andthrough said turning sections,wherein each of said turning sections comprises a plurality of bending magnets,wherein said circulation beam path comprises a length of less than sixty meters, andwherein a number of said straight sections equals a number of said turning sections. 15. The apparatus of claim 1, wherein said charged particle irradiation system further comprises:horizontal position control of the positively charged particles;vertical position control of the positively charged particles; andan X-ray input signal, wherein said X-ray input signal comprises a signal generated by an X-ray source proximate said charged particle beam path,wherein said X-ray input signal is used in: setting position of said horizontal position and setting position of said vertical position. 16. A method for positioning a tumor of a patient for treatment with positively charged particles, comprising the steps of:positioning the patient with a patient positioning system, said patient positioning system comprising:a rotatable platform, wherein said rotatable platform comprises:a lower support structure, said lower support structure holding a portion of said patient positioning system;a rotatable upper support structure, said upper support structure:co-rotating with said rotatable platform;holding a camera, both (1) said camera and (2) said upper support structure co-rotating about an axis aligned with gravity; andholding a video display screen, said video screen co-rotating, about the axis aligned with gravity, with said upper support structure in view of a patient viewing position;an upper body support, wherein said upper body support comprises a semi-upright patient support surface; andirradiating the tumor of the patient with the positively charged particles from a charged particle system, said charged particle system comprising a charged particle beam path, said charge particle beam path passing within about six inches of said semi-upright patient support surface. 17. The method of claim 16, wherein the positively charged particles travel along said charged particle beam path and transmit through an extraction blade, said extraction blade consisting essentially of atoms comprising six or fewer protons per atom, to the tumor of the patient. 18. The method of claim 16, wherein said semi-upright patient support surface comprises an about vertical surface. 19. The method of claim 16, wherein said semi-upright patient support surface comprises a reclined position from a vertical axis of less than about sixty-five degrees. 20. The method of claim 16, further comprising the step of:said patient positioning system semi-restraining movement of the patient usinga motorized arm positioning system, said motorized arm positioning system directly connected to said rotatable upper support structure. 21. The method of claim 16, further comprising the step of:when the patient returns to the patient positioning system after a period of at least hours, recalling from a computer memory patient specific motor positions for any of:said motorized head positioning system;said motorized arm positioning system; andsaid motorized foot positioning system. 22. The method of claim 16, further comprising the steps of:after said step of positioning, collecting multi-field images of the tumor in the patient;developing a tumor irradiation plan;at least one day after said step of positioning, repositioning the tumor using said patient positioning system using any of the patient specific motor positions stored in said computer memory; andrepeating said step of irradiating. 23. The method of claim 16, further comprising the steps of:holding the patient with a rotatable platform, said rotatable platform holding at least a portion of said patient positioning system;rotating the patient on said rotatable platform; anddelivering the positively charged particles to the tumor of the patient from a synchrotron of said charged particle system during said step of rotating the patient. 24. The method of claim 16, further comprising the steps of:generating a respiration signal with a respiration sensor, said respiration signal corresponding to a breathing cycle of the patient;using data from the respiration sensor in a step of delivering a computer generated command to the patient; andtiming delivery of the positively charged particles to the tumor at a set point in said breathing cycle using said respiration signal. 25. The method of claim 16, further comprising the steps of:independently controlling:a horizontal position of the positively charged particles; anda vertical position of the positively charged particles;rotating the patient to at least ten rotation positions of a rotatable platform, said rotatable platform holding at least a portion of said patient positioning system; anddelivering the positively charged particles at a set point in a breathing cycle of the patient and in coordination with said step of rotating during said at least ten rotation positions of said rotatable platform. 26. The method of claim 16, further comprising the step of:rotating a rotatable platform through at least one hundred eighty degrees during an irradiation period of the patient, said rotatable platform holding at least a portion of said patient positioning system.
	description	The present invention relates to a nuclear fuel assembly top nozzle having an in-core instrument that is inserted through the top head of a nuclear reactor using an upper core plate guide pin. An in-core instrument (ICI) is a device for measuring the output of a nuclear reactor by measuring the density and temperature of neutron flux in a core of the nuclear reactor. In the related art, in-core instruments were inserted into a core through the bottom of a reactor vessel, but there was a problem that the substances in the core of a reactor may leak through the hole formed through the bottom of the reactor vessel. In order to solve this problem, all in-core instruments have been disposed close to a core through a hole at the top of a reactor vessel instead of the way of inserting them through the bottom of a reactor vessel. The in-core instruments that are inserted through the top head of a nuclear reactor may interfere with a control rod assembly that is inserted over a fuel rod disposed at the center of the nuclear reactor. 1. Korean Patent No. 10-0984018 (registered on Sep. 17, 2010) 2. Korean Patent Application Publication No. 10-2011-0103392 (published on Sep. 20, 2011) An object of the present invention is to provide a top nozzle having a structure that can guide an in-core instrument, which is supposed to be inserted through a top head of a nuclear reactor, within a predetermined path using a guide pin that aligns the top nozzle of a nuclear fuel assembly and the upper core plate of a nuclear reactor. In order to achieve the objects of the present invention, there is provided a nuclear reactor including: guide pins for aligning a top nozzle for a nuclear fuel assembly with an upper core plate of the nuclear reactor, in which guide holes are axially formed through the guide pins and in-core instruments are inserted through the guide holes. In the present invention, the guide pins may be inserted in aligning holes formed at corners of the top nozzle. Further, a guide pin for aligning a top nozzle for a nuclear assembly with an upper core plate of a nuclear reactor according to the present invention each have a guide hole axially formed therein for insertion of an in-core instrument. According to a nuclear reactor of the present invention, a guide hole is axially formed through guide pins for aligning a top nozzle for a nuclear fuel assembly with an upper core plate of the nuclear reactor and in-core instruments are inserted through the guide holes. Specific structures and functions stated in the following embodiments of the present invention are exemplified to illustrate embodiments according to the spirit of the present invention and the embodiments according to the spirit of the present invention can be achieved in various ways. Further, the present invention should not be construed as being limited to the following embodiments and should be construed as including all changes, equivalents, and replacements included in the spirit and scope of the present invention. Further, in the specification, terms including “first” and/or “second” may be used to describe various components, but the components are not limited to the terms. The terms are used to distinguish one component from another component, and for instance, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component without departing from the scope according to the spirit of the present invention. It should be understood that when one element is referred to as being “connected to” or “coupled to” another element, it may be connected directly to or coupled directly to another element or be connected to or coupled to another element, having the other element intervening therebetween. On the other hand, it is to be understood that when one element is referred to as being “connected directly to” or “contact directly with” another element, it may be connected to or coupled to another element without the other element intervening therebetween. Expressions for describing relationships between components, that is, “between”, “directly between”, “adjacent to”, and “directly adjacent to” should be construed in the same way. Hereinafter, embodiments of the present invention will be described hereafter in detail with reference to the accompanying drawings. Referring to FIGS. 1 and 2, a top nozzle 100 includes a rectangular fastening plate 110 to which a guide tube is fixed at the bottom and an enclosure 120 that protrudes upward along the edge of the fastening plate 110. Slabs 121 and 122 are disposed at the corners of the enclosure 120, in which two slabs 121 orthogonally facing each other have an aligning hole 121a and the other two slabs 122 orthogonally facing each other are provided as spring clamps each fixing a pressing spring unit 211a. In particular, guide pins 200 that are fixed in alignment with an upper core plate (not shown) of a nuclear reactor are inserted in the aligning holes 121a of the top nozzle 100, and preferably, the guide pins 200 each have a guide hole 210 axially formed to insert an in-core instrument 10. The upper ends of the guide pins 200 are coupled to the upper core plate of a nuclear reactor directly by nuts or indirectly through couplers. The guide pins 200 of the present invention that are coupled to the top nozzle 100 laterally fix a nuclear fuel assembly and guide an in-core instrument into instrumentation tubes of a nuclear fuel assembly. Accordingly, in-core instruments that are supposed to be inserted downward are inserted into the guide hole 210 of the guide pins 200 and guided to the core from an upper core plate when they are inserted into instrumentation tubes of a nuclear fuel assembly through the top nozzle 100 without straying out of a predetermined path. In particular, by using the guide pins 200 that are inserted in the aligning holes at the corners of the top nozzle 100, it is possible to insert in-core instruments without interference with a control rod assembly. It will be apparent to those skilled in the art that the foregoing present invention is not limited by the foregoing embodiments and the accompanying drawings, and various modifications and changes may be made without departing from the scope and spirit of the invention. <Description of the Reference Numerals in the Drawings> 10: In-core instrument100: Top nozzle200: Guide pin210: Guide hole
	claims	1. A device for producing electricity, comprising:a germanium substrate doped a first dopant type;a plurality of stacked material layers extending from the substrate, further comprising:a base layer doped the first dopant type;an emitter layer doped the second dopant type;a window layer having a lattice structure matched to the lattice structure of the emitter layer and doped the second dopant type; anda beta particle source for generating beta particles;wherein the plurality of stacked material layers further comprise an InAlP reflector layer doped the first dopant type and disposed between the substrate and the base layer. 2. The device of claim 1 wherein the plurality of stacked material layers further comprises a GaAs layer doped the first dopant type and disposed between the substrate and the base layer for serving as a nucleation layer or as a layer for establishing the crystal structure. 3. The device of claim 1 wherein the plurality of stacked material layers further comprise an intrinsic InGaP layer disposed between the base layer and the emitter layer. 4. The device of claim 1 further comprising a physical barrier for shielding edges of the plurality of stacked material layers from the beta particles. 5. A device for producing electricity, comprising:a germanium substrate doped a first dopant type;a plurality of stacked material layers extending from the substrate, further comprising:a base layer doped the first dopant type;an emitter layer doped the second dopant type;a window layer having a lattice structure matched to the lattice structure of the emitter layer and doped the second dopant type; anda beta particle source for generating beta particles;wherein the plurality of stacked material layers further comprise a GaAs cap layer doped the second dopant type and having a higher doping level than the emitter layer, the GaAs cap layer disposed between the window layer and the beta particle source. 6. The device of claim 5 wherein the bandgap of the window layer is greater than the band gap of the emitter layer. 7. The device of claim 5 wherein the first dopant type comprises a p dopant type and the second dopant type comprises an n dopant type or wherein the first dopant type comprises an n dopant type and the second dopant type comprises a p dopant type. 8. The device of claim 5 wherein a material of the window layer comprises one of InAlP, InAlGaP, ZnSe, AlAs, AlAsP, and a pseudomorphic layer. 9. The device of claim 5 wherein a material of the beta particle source comprises one of InAlP, AlGaP, and InGaP, tritium metal hydride and a polymer containing tritium. 10. The device of claim 5 wherein a material of the base layer comprises one of InGaP, In(AlGa)P, and InAlP and a material of the emitter layer comprises one of InGaP, In(AlGa)P, and InAlP. 11. A device for producing electricity, comprising:a germanium substrate doped a first dopant type;a plurality of stacked material layers extending from the substrate, further comprising:a base layer doped the first dopant type;an emitter layer doped the second dopant type;a window layer having a lattice structure matched to the lattice structure of the emitter layer and doped the second dopant type;a beta particle source for generating beta particles; anda housing, wherein the device is hermetically sealed within the housing. 12. A device for producing electricity, comprising:a germanium substrate doped a first dopant type;a plurality of stacked material layers extending from the substrate, further comprising:a base layer doped the first dopant type;an emitter layer doped the second dopant type;a window layer having a lattice structure matched to the lattice structure of the emitter layer and doped the second dopant type;a beta particle source for generating beta particles; anda first terminal comprising a contact ring disposed on a surface of the plurality of stacked material layers. 13. A device for producing electricity, comprising:a germanium substrate doped a first dopant type;a plurality of stacked material layers extending from the substrate, further comprising:a base layer doped the first dopant type;an emitter layer doped the second dopant type;a window layer having a lattice structure matched to the lattice structure of the emitter layer and doped the second dopant type; anda beta particle source for generating beta particles;wherein the substrate is doped a p dopant type, the base layer is doped an n dopant type and the emitter layer is doped the p dopant type, the device further comprising a p dopant type tunnel junction layer adjacent an n dopant type tunnel junction layer disposed between the substrate and the base layer with the p dopant type tunnel junction layer disposed closer to the substrate than the n dopant type tunnel junction layer. 14. A device for producing electricity, comprising:a germanium substrate doped a p dopant type;a plurality of stacked material layers extending from the substrate, further comprising:a GaAs first layer doped the p dopant type;an InGaP base layer doped the p dopant type;an InGaP emitter layer doped an n dopant type; andan InAlP window layer having a lattice structure matched to the lattice structure of the emitter layer and doped the n dopant type;a GaAs cap layer doped the n dopant type;an InAlP reflector layer doped the p dopant type and disposed between the substrate and the base layer; anda beta particle source for generating beta particles. 15. The device of claim 14 wherein the plurality of stacked material layers further comprise an intrinsic InGaP layer disposed between the base layer and the emitter layer. 16. The device of claim 14 wherein the GaAs first layer has a higher doping concentration than the base layer. 17. A device for producing electricity, comprising:a beta particle source layer for generating beta particles that travel in opposing directions from the beta particle source layer;a plurality of stacked material layers on each one of two opposing surfaces of the beta particle source layer;each of the plurality of stacked material layers comprising:a germanium substrate doped a first dopant type;a base layer doped the first dopant type;an emitter layer doped the second dopant type; anda window layer having a lattice structure matched to the lattice structure of the emitter layer. 18. The device of claim 17 wherein a material of the base layer comprises one of InGaP, In(AlGa)P, and InAlP and a material of the emitter layer comprises one of InGaP, In(AlGa)P, and InAlP.
	description	This application claims priority to German patent application DE 10 2018 201 250.4, filed on Jan. 26, 2018, the entire content of which is incorporated herein by reference. The invention relates to a variable stop apparatus and to a Computed-Tomography (CT) scanner comprising the variable stop apparatus. When measuring objects using computed tomography, scattered radiation is undesirable, because it increases the signal background and noise of the detector signals and furthermore produces undesired artefacts in the reconstructed images. The scattered radiation can be reduced if the computed tomography system is designed and/or operated such that only a limited, relevant solid angle range is illuminated with X-rays. If only relevant object details are irradiated, that is to say only those parts of which the image information is actually used, the image quality can be improved. In microfocus sources which are also operated at high power and therefore with focal spot sizes up to the millimeter range, the used ray angle is generally so large that only part of the X-ray beam is incident on the sensor surface of the detector and another part travels past the sensor surface or is incident next to the sensor surface. The reason for this is that the sensor surface would otherwise be illuminated inhomogeneously. In order to obtain sufficiently homogeneous illumination, it is typical to select used ray angles that are of a size such that the sensor surface is illuminated many times over. In a computed tomography system having a variable distance between X-ray source and detector, the used ray angle should, with a constant size of the sensor surface, be adapted to the distance to reduce scattered radiation. In this respect, two procedures are known from the related art. In the first procedure, a stop size, i.e., an aperture of the stop, which defines the used ray angle is selected to have a size such that the sensor surface of the detector is completely illuminated even in the case of the largest possible focal spot. The stop is here located at a fixed distance from the focal spot, independently of the size of the focal spot. The second procedure provides a window collimator, which is adjustable by a motor and which permits the setting of the size of the illuminated region in one or two direction(s) that extend transversely to the propagation direction of the radiation. The stop windows of the collimator are located in a common plane at a distance from the focal spot which is not adaptable to a change in the focal spot size. The sharpness of the imaging of the stop windows in the detector plane therefore depends on the stop size. Also known from medical technology, in which the radiation exposure of a patient is to be kept as small as possible, are so-called “multi-leaf” collimators. The latter consist of leaves that are adapted for individual recordings to the recording conditions. However, for automated actuation, a great number of independent actuators are used. It is an object of the invention to provide a variable stop apparatus and a CT-scanner with which scattered radiation can be reduced. The object is achieved by a variable stop apparatus and by a CT-scanner as disclosed herein. The invention is based on the finding that a stop size, i.e., an aperture of the stop, which is optimal with respect to a detector surface to be illuminated, and an optimum distance of the stop from the focal spot of the X-ray source exist for a focal spot size which is specified by specified measurement conditions such as, a power of the X-ray source. A larger stop should here ideally be positioned at a greater distance from the focal spot to produce a minimum unsharpness in the detector plane and to hereby in turn be able to keep the used ray angle as small as possible. Proposed in particular is a variable stop apparatus arranged between an X-ray source and an object to be measured in a CT-scanner, having a stop carrier that is pivotable about a pivot axis, wherein the stop carrier has at least two stops, and wherein the at least two stops are in each case able to be brought into a predetermined angular position by pivoting the stop carrier, and wherein at least two of the at least two stops are arranged at different longitudinal positions with respect to a longitudinal direction that is defined by the pivot axis. Owing to the ability to bring different stops, which are additionally arranged at different longitudinal positions, into the predetermined position, the stop apparatus is variable. In particular, the at least two stops are situated permanently at the same position relative to one another with respect to the stop carrier. Therefore, by pivoting the stop carrier, all stops are shifted at the same time about the pivot axis and maintain their angle distance with respect to one another. An arrangement of stops at different longitudinal positions with respect to a longitudinal direction that is defined by the pivot axis means in particular that the respective exit planes from which radiation exits during operation through said stops toward the detector are disposed in different planes which are transverse and in particular perpendicular to the pivot axis. In general, the exit plane of the stop is the plane that has the minimum opening cross section for the passage of radiation. If the stop has in the propagation direction of the radiation one or more longitudinal sections with an opening cross section of constant size, the exit plane is that plane which, during operation, is disposed at the greatest distance in the propagation direction of the radiation from the radiation source and thus closest to the object that is to be irradiated. Further provided is a CT-scanner including at least one exemplary embodiment of the variable stop apparatus, wherein the at least one variable stop apparatus is arranged such that the stop that is positioned at the predetermined angular position is located in the beam path between a focal spot of an X-ray source of the CT-scanner, and an object that is to be measured. The variable stop apparatus is therefore arranged such that, during operation of the CT-scanner, invasive radiation from the X-ray source passes in particular without absorption through the respective stop that is positioned at the predetermined angular position and enters the region in which the object that is to be measured is located. The radiation proportion that is not scattered or absorbed by the object can be detected by a detector of the CT-scanner. In particular, the pivot axis can coincide with an axis of symmetry of the, for example, conical X-ray beam or a central axis of the X-ray beam. A fundamental idea of the invention is to arrange a plurality of stops, i.e., at least two stops, at a pivotable stop carrier. Each of the plurality of stops can be brought into a predetermined angular position by way of a pivot movement of the stop carrier about the pivot axis. At this angular position, during operation, the respective stop is located in the beam path between a radiation source and an object that is to be measured in a CT-scanner, with the result that the radiation passes through the stop at the predetermined angular position and the used ray angle (i.e., the solid angle of the usable radiation) is determined by the stop. At least two of the plurality of stops are arranged at different longitudinal positions with respect to a longitudinal direction that is defined by the pivot axis. This allows not only for a stop to be brought into the beam path in a targeted fashion by pivoting the stop carrier, but also for the longitudinal position of the stop used during operation to be set, and thereby also for a distance between the X-ray source and the respectively used stop or for a position of the stop between the focal spot of the X-ray source and the X-ray detector to be set. The stop used can therefore be positioned at a suitable distance from the focal spot of the X-ray source. Compared to a linear movement of one of a plurality of available stops, which are connected to one another into a predetermined position, the invention has the advantage that less space is required. In particular, the stop carrier can have a disk, for example a circular disk, in which case the stop carrier has a stop wheel, since the disk can be referred to as a wheel. Located within the disk face are the apertures, which means that an X-ray beam can pass through the disk face when the X-ray beam is directed at the aperture. The disk consists of a material that absorbs X-rays and absorbs X-rays in particular with a high absorptance, with the result that it is substantially only the X-rays that pass through the respective aperture unimpeded that reach a region in which an object that is to be measured is located. The predetermined angular position into which the stops are able to be pivoted individually can optionally be one of a plurality of predetermined angular positions within a continuous region of angular positions. This makes it possible in particular to radiate X-rays into different partial regions in which an object that is to be investigated and measured can be situated. In other words, a specific stop can be used in different angular positions within the continuous region such that X-rays are irradiated onto the object that is to be investigated through the aperture of the stop. In one exemplary embodiment, provision is made for the at least two stops to have different stop shapes and/or stop dimensions. The terms stop shape and stop dimension relate to the shape or dimensions of the aperture of the stop. By selecting one of a plurality of different stop shapes, it is possible to ensure that only partial regions of a detector of the CT-scanner that correspond to the stop shape are illuminated and/or partial regions of an object to be measured that correspond to the stop shape are irradiated. The power of the X-ray source can generally be set continuously. At increased power of the X-ray source, in many cases the focal spot size of the X-ray source also increases. In accordance with the laws of geometric imaging, this focal spot size defines at a given magnification an unsharpness in the detector plane. Ideally, the unsharpness should here not be greater than a resolution of the detector, i.e., it should correspond to the size of a sensor element of the detector. That means that for a greater radiant flux density, the distance of the stop from the X-ray source should also be greater. Therefore, a distance of the used stop from the X-ray source that is as great as possible is always desired to minimize the unsharpness or the extent of a half shadow of the stop in the detector plane and also the used ray angle of the X-rays. In one exemplary embodiment, provision is therefore made for the longitudinal positions of the stops to be selected in dependence on a stop shape and/or on stop dimensions of the stops and/or on a focal spot size corresponding to the respective stop. With specified imaging conditions, a specified focal spot size and a specified stop shape and size, a longitudinal position of the stop can thus be selected. It is thus possible, with a given focal spot size, to select and/or set a suitable associated longitudinal position of the stop or of the stops and thus a distance between the X-ray source and the stop or a position of the stop between the focal spot of the X-ray source and the X-ray detector. In the case of a small focal spot size, the longitudinal position of the associated stop can be selected such that the distance between the X-ray source and the stop is correspondingly smaller than in the case of a large focal spot size. The longitudinal positions of the plurality of stops can be selected such that the distances required for the respectively provided focal spot sizes at which an acceptable unsharpness of the imaging is achieved are obtained. The at least two stops used generally differ in particular in pairs with respect to the stop dimensions and the longitudinal position, or the distance of the stop from the focal spot of the X-ray source, and optionally also with respect to the stop shape. However, it is also possible for the aperture sizes and/or the longitudinal positions of two stops to be the same, while the stop shapes differ. At least one stop, in particular having large stop dimensions (i.e., a large aperture), e.g., at a longitudinal position at a greater distance from the focal spot of the X-ray source than at least another stop of the apparatus, can be embodied in a hollow cylinder and/or tube having a radiation-absorbing wall. Thereby, the entry of scattered radiation from the outer periphery of the stop into the region of the object that is to be measured can be reduced. For this reason, provision is made in one exemplary embodiment for the stop carrier to include at least one tube, in particular a stop cylinder. This tube carries the stop. In particular, a longitudinal axis of the tube extends through the cavity of the tube, and, during operation of the stop apparatus, a stop is located within the tube at a longitudinal position with respect to the longitudinal axis that is at a distance from the object-side end of the tube. For example, the exit opening of the stop with reference to the longitudinal extent of the tube with respect to the longitudinal axis can have a distance from the object-side end that corresponds to at least a third and preferably at least half the longitudinal extent of the tube. In particular when the stop carrier includes a disk extending in a main plane, a cross-sectional area of the cavity of the tube can be congruent with a cutout in the disk which is correspondingly provided therefor. During operation of the apparatus, the longitudinal axis of the tube extends from the X-ray source away in the direction of the object that is to be measured and the detector, with the result that the X-ray beam can pass through the stop within the tube when this stop is arranged at the predetermined angular position. The radiant flux density of scattered radiation in the region of the object that is to be examined and on the detector is then reduced by the lateral surface of the tube and by the disk. Provision is made in one exemplary embodiment for the stop carrier to include at least two planes which are offset with respect to one another in the longitudinal direction, wherein the at least two planes extend in each case transversely to the pivot axis (in particular perpendicularly to the pivot axis and/or parallel with respect to a sensor surface of the detector), and wherein an exit opening of one of the stops is arranged in each of the planes. The planes which are offset with respect to one another can be used to ensure that the stops in the CT-scanner are located at different distances from a focal spot of an X-ray source. Provision is made in one exemplary embodiment for the variable stop apparatus to include a motor, wherein the motor is set up to drive the stop carrier and to hereby bring in each case one of the stops into the predetermined angular position. The motor is controlled by an associated controller, for example. The controller can here be set up to bring, after receiving a control signal, a stop corresponding to the control signal into the predetermined angular position by actuating the motor. The stop is movable into the predetermined angular position with a high degree of positioning accuracy. To this end, the motor controller can be combined with a high-resolution measurement system for measuring the position. In particular, the motor can exert a holding force that holds the stop in the predetermined angular position even in the case of expected external forces. Furthermore, the motor can be a stepper motor. The step width in this case is typically configured to have a given accuracy in the setting of the predetermined angular position. In a further exemplary embodiment, provision is made for the variable stop apparatus to have a filter arrangement that is arranged at a distance from the stop carrier. By pivoting the filter arrangement about a pivot axis, individual filters are able to be brought into a predetermined angular position, with the result that, during operation, an X-ray beam passes through the filter in its predetermined angular position and through an aperture of the stop in its predetermined angular position. The filter arrangement can in particular be a filter wheel (more particularly arranged parallel with respect to the stop carrier). The filter arrangement and the stop carrier can typically be able to be shifted about the same pivot axis. In more general terms, the pivot axes can extend parallel with respect to one another. In any case, both a filter and a desired stop of the stop apparatus can be moved into the beam path of the X-ray beam. The properties of the used beam can hereby be improved. In an exemplary embodiment, provision is furthermore made for a motor to be set up to drive both the stop carrier and the filter arrangement and in particular the filter wheel. Provision can be made here for example for the motor to drive only the stop carrier or the filter arrangement at a time. This can be effected for example using a correspondingly formed transmission with a clutch. It is then possible to deliberately select whether the filter arrangement or the stop carrier is to be driven. Using a single motor for both wheels, it is possible to save costs for material and installation space in the CT-scanner. A material thickness of the material used for forming the stop should not be arbitrarily thin, but is, for example, in the millimeter range to sufficiently block the radiation. The material is typically a highly absorbing material with respect to X-rays, such as a material including tungsten or lead or combinations thereof. For this reason, provision is made in one exemplary embodiment for a thickness of the stop carrier and of the at least two stops to have a minimum value. Here, the minimum value is determined on the basis of material parameters of the materials used and is dependent on the ability of the material to block X-rays and to ensure mechanical stability. Generally, the minimum value for the thickness will be the larger the higher the required positioning accuracy is, because a greater thickness ensures better stability of the stop carrier and of the stops. The variable stop apparatus can include further elements, such as a bearing, which supports the stop carrier, and/or a base or support, by way of which the stop carrier can be connected to a housing of the CT-scanner. The variable stop apparatus can furthermore include mechanical transmission devices such as a transmission, belts etc., which ensure that the stop carrier can be driven mechanically. In particular, a motor can drive the stop carrier via the transmission and/or a belt. For accurately determining the angular position of the stop carrier, the variable stop apparatus can furthermore have a mechanical or optical pulse generator. FIG. 1A shows a beam path in a CT-scanner for illustrating the generation of occurring scattered radiation 23. Illustrated schematically in the beam path from left to right are a focal spot 13 of an X-ray source, a small stop 4, an object 15 that is to be measured, and a detector 16 having a detector surface 17. The small stop 4 is disposed at a small distance 18 from the focal spot 13. FIG. 1A also illustrates a large distance 19 from the focal spot. In the arrangement illustrated in FIG. 1B, a large stop 5 is located at this large distance 19. In particular within the beam cone of a half shadow 21 of the stop 4 in accordance with FIG. 1A, disturbing scattered radiation 23 is produced, which is incident on the detector surface 17 and there results in undesired measurement artefacts. The size of the half shadow 21 and consequently the scattered radiation can be reduced by positioning the large stop 5, i.e., a stop having a larger aperture than the small stop 4, at the great distance 19 from the focal spot 13, which is greater than in FIG. 1A. This is shown schematically in FIG. 1B. Here, the large stop 5 is positioned at a large distance 19 from the focal spot 13 of the X-ray source. As a result, the size of the half shadow 21 decreases with the used beam 20 remaining the same. The region between the focal spot 13 and the detector 16 onto which radiation is directly incident is reduced. It is consequently also not possible in this region for any additional scattered radiation 23 to be produced which would then be partially incident on the detector 16 and would be detected by the detector 16. FIG. 2A shows a schematic illustration of an exemplary embodiment of the variable stop apparatus 1. The variable stop apparatus 1 includes a stop carrier 3 which is pivotable about a pivot axis 2, and, in the exemplary embodiment, takes the shape of a stop wheel. The pivotable stop carrier 3 carries two stops 4, 5 and/or forms two stops 4, 5. The stops 4, 5 in the exemplary embodiment differ with respect to the diameter of their circularly round aperture. The small stop 4 has a small aperture, while the large stop 5 has an aperture which is larger than the stop 4. The two stops 4, 5 can be brought individually into a predetermined angular position 6 by pivoting the stop carrier 3. The variable stop apparatus 1 is then arranged in a CT-scanner such that the pivotable stop carrier 3 and the predetermined angular position 6 are positioned and are oriented such that the stop 4, 5 which is arranged in each case at this predetermined angular position 6 is positioned in a beam path between a focal spot of an X-ray source and the object that is to be measured. Thereby, the small stop 4 or the large stop 5 can optionally be positioned in the beam path by pivoting the pivotable stop carrier 3. The variable stop apparatus 1 can include further elements. For example, the variable stop apparatus 1 can have a bearing 7 for supporting the pivotable stop carrier 3 and a holder 8, which accommodates the bearing 7 and hereby connects the pivotable stop carrier 3 to a housing of the CT-scanner. A motor 22 arranged on the holder 8 can serve to drive the pivotable stop carrier 3 and bring one of the stops 4, 5 into the predetermined angular position 6. FIG. 2B also shows the pivotable stop carrier 3. The stop 5 has a tube with an area (cross-sectional area of the cavity at the stop carrier 3) that is formed in a main plane of the stop carrier 3. The (in this case cylindrical) tube 9 forms the large stop 5, wherein an aperture of the large stop 5 is formed at a distal end of the tube 9 at the object-side end of the tube 9. The apertures of the stops 4, 5 are arranged at different longitudinal positions with respect to a longitudinal direction that is defined by the pivot axis 2, with the result that the respective exit planes from which radiation passing through said stops 4, 5 exits during operation in the direction of the X-ray detector are situated in different planes 10, 11 which are perpendicular to the pivot axis 2. The respective exit planes can thereby be positioned optimally between the focal spot of the X-ray source and the X-ray detector. A used ray profile of the X-rays can thereby be set in each case optimally for different operating conditions. FIGS. 3A and 3B explain the function of the variable stop apparatus 1 on the basis of two schematic illustrations of the variable stop apparatus 1 arranged in the beam path of a CT-scanner 12. Illustrated schematically in the beam path from left to right are a focal spot 13, 14 of an X-ray source, the variable stop apparatus 1, an object 15 that is to be measured, and a detector 16 having a detector surface 17. The variable stop apparatus 1 corresponds to the exemplary embodiment illustrated schematically in FIGS. 2A and 2B, which is to say it has a small stop 4 having a smaller aperture and a large stop 5 with a larger aperture and also a tube 9. The variable stop apparatus 1 is arranged in the beam path of the CT-scanner such that the stop 4, 5, which is positioned at the predetermined angular position of the stop carrier 3, is situated in the beam path. In FIG. 3A, the CT-scanner 12 is operated for example at low power of the X-ray source, that is to say with a small focal spot 13. As explained above, it is then expedient to use the small stop 4 having a small distance 18 from the focal spot 13 to optimally adapt the used ray profile. For this reason, the small stop 4 is brought into the predetermined angular position (which, in the illustration of the FIGS., is located at the uppermost vertex of the pivotable stop carrier 3) by pivoting the pivotable stop carrier 3 about the pivot axis 2. The aperture of the small stop 4 is then located in the beam path. The variable stop apparatus 1 is arranged in the beam path such, and a longitudinal position of the small stop 4 on the pivotable stop carrier 3 is such, that the small stop 4 is then positioned at a small distance 18 from the focal spot 13. At this small distance 18, the small stop 4 is positioned optimally with respect to the focal spot 13, with the result that the detector surface 17 is optimally illuminated by the used beam 20, and a half shadow 21 outside the detector surface 17 is small. Another situation is illustrated in FIG. 3B. Here, the CT-scanner is to be operated at a larger power of the X-ray source, that is to say with a large focal spot 14. Accordingly, when the large stop 5 is used, the large distance 19 from the large stop 5 to the large focal spot 14 is larger than the small distance 18 in the situation shown in FIG. 3A. This is achieved by rotating the pivotable stop carrier 3 about its pivot axis 2 until the large stop 5, the aperture of which is formed at the distal end of the tube 9, is pivoted into the predetermined angular position in the beam path. The large stop 5 is then positioned at the large distance 19 from the focal spot 14, with the result that the detector surface 17 is optimally illuminated by the used beam 20, and a half shadow 21 outside the detector surface 17 is small. A further exemplary embodiment of the variable stop apparatus 1 is depicted in FIGS. 4A and 4B. The exemplary embodiment in parts of its features corresponds to the exemplary embodiment shown in FIGS. 2A and 2B, but includes a total of eight stops 4, 5, 24. Six of the stops are designated each with the reference sign 24 to indicate that the number of stops can vary. For this reason, in another exemplary embodiment, only the stops 4, 5 and one or two further stops 24 are present, for example. The stops 4, 5, 24 are typically distributed uniformly over the circumferential direction, i.e., over the angle region around the pivot axis. Here, all stops 4, 5, 24 differ in terms of their stop shape and/or in terms of their stop dimensions, i.e., the associated apertures of the stops 4, 5, 24 differ in terms of shape and size. In this exemplary embodiment, a selection of eight different stops 4, 5, 24 can thus be provided, and by pivoting the stop carrier 3, the respectively desired stop 4, 5, 24 can be positioned at the predetermined angular position into the beam path between a X-ray source and an object. Typically, all stops are located here at different longitudinal positions with respect to the longitudinal direction that is defined by the pivot axis 2, with the result that the respective exit planes from which radiation passing through said stops 4, 5, 24 exits during operation in the direction of the X-ray detector are located in different planes 10, 11, which are perpendicular to the pivot axis 2 (FIG. 4B only shows the planes 10, 11 for the stops 4, 5). The longitudinal positions here are in each case selected such that the stops 4, 5, 24 are located at a desired distance or at a distance that corresponds to a focal spot size and stop size from the focal spot of the X-ray source (cf. FIG. 3A and FIG. 3B). Such a variable stop apparatus 1 has the advantage that a plurality of different stops 4, 5, 24 can be positioned flexibly at different distances from the focal spot or at different positions between the focal spot and the X-ray detector in the beam path. It is understood that the foregoing description is that of the exemplary embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. 1 Variable stop apparatus 2 Pivot axis 3 Stop carrier 4 Stop 5 Stop 6 Predetermined angular position 7 Bearing 8 Holder 9 Tube 10 Plane 11 Plane 12 CT-scanner 13 Focal spot 14 Focal spot 15 Object 16 Detector 17 Detector surface 18 Small distance 19 Large distance 20 Used beam 21 Half shadow 22 Motor 23 Scattered radiation 24 Further stop
	claims	1. A liquid metal cooled nuclear reactor comprising:a reactor vessel holding a reactor core and a coolant for the core;a containment surrounding an outside of the vessel;an air flow path configured to flow air around the containment to remove heat from the containment; andan injection unit configured to inject a filler in a gap between the vessel and the containment,wherein the injection unit further comprises:a liquid reservoir unit configured to reserve the filler;a connection path connecting the liquid reservoir unit and the gap; anda heater unit configured to heat the filler in the reservoir to keep the filler in a melted state. 2. The reactor according to claim 1, wherein the injection unit further comprises:a pressurization unit configured to pressurize the filler to lead the filler from the liquid reservoir unit to the gap,wherein the liquid reservoir unit is provided at a lower position than a bottom of the coolant. 3. The reactor according to claim 2, whereinthe pressurization unit has a piston, the piston moving horizontally or vertically from ends of the liquid reservoir unit toward an opening direction of the connection path in the liquid reservoir unit. 4. The reactor according to claim 1, wherein the injection unit includes a circulating path to cool down the filler having been heated in the gap. 5. The reactor according to claim 1, wherein:the injection unit further comprises a first flow-stopping valve for the filler arranged in the connection path; andthe liquid reservoir unit is provided to reserve the filler at a higher position than a top of the coolant. 6. The reactor according to claim 5, further comprising:a drain unit configured to drain the filler at a lower position of the gap than a bottom of the coolant. 7. The reactor according to claim 6, wherein the connection path connects to the gap via a pathway. 8. The reactor according to claim 6, further comprising a return path to return the filler in the drain unit to the liquid reservoir. 9. A heat removal method for a liquid metal cooled nuclear reactor including a reactor vessel holding a reactor core, a containment surrounding an outside of the reactor vessel, a liquid reservoir unit holding a filler, and a coolant for the reactor core, the method comprising:reserving the filler in the liquid reservoir unit;heating the filler in the liquid reservoir unit to keep a melted state;injecting the filler from the liquid reservoir unit into a gap between the reactor vessel and the containment; andflowing air around the containment to remove heat from the containment.
	description	The present application claims priority from Japanese Patent Application No. JP 2005-158282 filed on May 31, 2005, the content of which is hereby incorporated by reference into this application. The present invention relates to an electron microscope application apparatus and a sample inspection method. In particular, it relates to a technology effectively applied to an apparatus and a method for controlling a surface potential of a sample whose surface is covered with insulating material such as a semiconductor device or an insulating substrate and a measuring apparatus and a measuring method for a semiconductor device or an insulating substrate provided with a charge-control device. As a technology studied by the inventors of the present invention, for example, the following technologies are known in the field of an electron microscope application apparatus and a sample inspection method. Currently, in a manufacturing line for silicon devices, it is essential to inspect a wafer during a manufacturing process. This is because the inspection of a wafer during the manufacturing process can find the defect in an early stage and obtain the information for specifying a process causing the defect. By feeding back the inspection results to process conditions, the number of defects can be reduced, the number of chips obtained from one wafer can be increased, and yield can be improved. As an apparatus for inspecting a wafer to find defects in the wafer, an optical inspection apparatus and an electron beam inspection apparatus are principally used. The optical inspection apparatus is an optical microscope in principle and can find shape defects such as particles and pattern defects. However, minute shape defects and electrical defects which cannot be detected by the optical inspection apparatus have become problems due to the development in finer design rule. Therefore, attention has been paid to an electron beam inspection apparatus which can detect the defects which cannot be detected by the optical inspection apparatus, and the electron beam inspection apparatus has been developed in several makers. The detection of electrical defect in a silicon device by using the electron beam inspection apparatus is performed by charging a circuit pattern formed on a wafer surface and inspecting the contrast elicited by the charging. This process is called “voltage contrast method”, which is effective means for detecting electrical defect in a silicon device. In order to perform the inspection using the voltage contrast method with excellent reproducibility and high precision, it is necessary to control the charges of a circuit pattern to be inspected at high precision, and the improvement in control precision is directly linked to the improvement in detection precision for electrical defect. As a method for controlling the charges of a wafer surface, a method based on electron beam irradiation and a method based on ultraviolet light irradiation have been disclosed (for example, Japanese Unexamined Patent Publication No. 2002-524827 (Patent Document 1) and Japanese Patent Application Laid-Open Publication No. 11-121561 (Patent Document 2)). In both the methods, electron beam or ultraviolet light is irradiated onto an area larger than an area observed in the case of using an electron beam inspection apparatus and the charges are made uniform. Also, a method for removing the charges generated by the electron beam observation has been disclosed (for example, Japanese Patent Application Laid-Open Publication No. 2004-363085 (Patent Document 3)). In the Patent Document 3, charges of a sample are removed or made uniform by irradiating ultraviolet light onto metal so as to irradiate photoelectrons emitted by photoelectric effect onto the sample instead of directly irradiating ultraviolet light onto the sample. However, the following matters regarding the above technologies have been found through the examinations by the inventors of the present invention. For example, the Patent Document 3 discloses a method for removing the charges of a sample by irradiating ultraviolet light onto an electrode so as to absorb photoelectrons emitted from the electrode to the sample. In this method, however, there is a problem of a processing rate and control precision of the charges. First, regarding the processing rate, since an electrode from which photoelectrons are emitted is spaced away from a sample in the method disclosed in Patent Document 3, a ratio of photoelectrons which are not absorbed in the sample becomes high. Since a rate for removing the charges is proportional to the number of photoelectrons absorbed in the sample, it is necessary to consider a distance between the electrode and the sample in order to improve the processing rate. Also, regarding the controllability on charges, since a negative voltage for the sample is applied to the electrode in the Patent Document 3, a sample surface is charged up to the voltage applied to the electrode. When the charges on the sample surface are to be removed or the potential of the sample surface is to be reduced to 0 V, a mechanism for controlling the charges has to be additionally provided. Further, it is difficult to positively charge a sample in principle. Therefore, an object of the present invention is to provide a technology capable of controlling the charges of a sample in an electron microscope application apparatus and a sample inspection method. The above and other objects and novel characteristics of the present invention will be apparent from the description of this specification and the accompanying drawings. The typical ones of the inventions disclosed in this application will be briefly described as follows. In order to solve the problem described above, in an electron microscope application apparatus according to the present invention, an electrode for emitting photoelectrons is disposed just above a sample and in parallel thereto, and the electrode has a through-hole so that ultraviolet light can be irradiated on the sample through the electrode. Specifically, a metal plate which is formed in mesh or has one or plurality of holes is utilized as the electrode. By disposing the electrode just above the sample and in parallel thereto, electric field approximately perpendicular to the sample is generated when negative voltage is applied. Therefore, photoelectrons are efficiently absorbed to the sample. Also, by using an electrode having approximately the same size as the sample, charges on a whole surface of the sample can be removed collectively and evenly, and a time required for the process can be reduced. In the electron microscope application apparatus, it is possible to not only remove charges but also positively control the charges. When a sample is to be charged to a negative potential, an electrode potential is set to a negative potential relative to that of the sample and ultraviolet light is irradiated to the sample. Photoelectrons emitted from the electrode are pulled back to the sample due to electric field and then absorbed thereto. When the charges of the sample advance in a minus direction to reach the potential equivalent to that of the electrode, photoelectrons absorbed to the sample are balanced with photoelectrons emitted from the sample, and the charges are saturated. On the contrary, when a sample is to be charged to a positive potential, the electrode potential is set to a positive potential relative to that of the sample, and ultraviolet light is irradiated to the sample. The ultraviolet light is irradiated to the sample via the electrode and photoelectrons are emitted from the sample. Since photoelectrons are emitted, when the charges of the sample advance in a plus direction and the sample is charged to the potential equivalent to that of the electrode, photoelectrons emitted from the sample are balanced with photoelectrons absorbed to the sample, and the charges are saturated. Through the process described above, the charges of a sample can be controlled. The effects obtained by typical aspects of the present invention will be briefly described below. (1) By applying the present invention to a measuring apparatus based on charged particles, improvement in measurement precision and reproducibility can be achieved in the measuring apparatus. (2) By applying the present invention to an inspection apparatus for semiconductor based on charged particles, detection of electrical characteristic failure at high sensitivity can be achieved. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted. FIG. 1 is a diagram showing a structure of an electron microscope application apparatus according to a first embodiment of the present invention. First, one example of a structure of the electron microscope application apparatus according to the first embodiment will be described with reference to FIG. 1. The electron microscope application apparatus according to the first embodiment is, for example, an SEM type semiconductor pattern inspection apparatus. The inspection apparatus roughly includes an SEM chassis 10, a charge control chassis 6, a sample chamber 20, a sample preparation chamber 70, an SEM control unit 50, a charge control system unit 60, an inspection system control unit 90, an evacuating system unit 80, a stage control unit 40, and others, and it is assumed that the SEM chassis 10, the charge control chassis 6, the sample chamber 20, and the sample preparation chamber 70 are evacuated by the evacuating system unit 80. First, a basic structure of the SEM type semiconductor pattern inspection apparatus will be described. The SEM chassis 10 includes an electron source 11, a condenser lens A12, an aperture 13, a condenser lens B14, a detector 15, a deflector 16, an objective lens 17, a charge control electrode 18, and others. The sample chamber 20 includes a stage 23, an insulating material 22, a wafer holder 21, and a wafer 3, in which the wafer holder 21 and the wafer 3 are electrically insulated from the grounded stage 23 by the insulating material 22, and voltage can be externally applied to the wafer holder 21 and the wafer 3 by a retarding power source 42. Also, the stage 23 can move the wafer 3 and the wafer holder 21 in a vertical direction in a two-dimensional manner to the center axis of the SEM chassis 10, and the movement of the stage 23 is controlled by a stage controller 44 and a stage driving unit 43 in the stage control unit 40. The SEM control unit 50 includes an electron gun power source for SEM 51 and a lens control unit 52. Primary electrons emitted from the electron source 11 are adjusted to be focused on the wafer 3 through the condenser lens A12, the condenser lens B14, and the objective lens 17. At this time, energy of the primary electrons incident on the wafer 3 determined depending on a difference between a cathode voltage applied to the electron source 11 and a retarding voltage applied to the wafer 3, and the energy of primary electrons incident on the wafer 3 can be adjusted by changing the retarding voltage. Secondary electrons generated from the wafer 3 are accelerated and drawn into the detector 15. Note that, in order to form a scanned image, primary electrons are deflected by the deflector 16 so that they scan the wafer 3, secondary electrons taken in the detector 15 are converted to digital signal at an AD converter unit 31, and the digital signal is fed to an image processing unit 33 through an optical fiber 32. Then, a scanned image is formed in the image processing unit 33 as a map of secondary electron signals synchronized with scanning signals. In this case, it is assumed that the detector 15 and the AD converter unit 31 are floated to high voltage with positive polarity. In the image processing unit 33, equal pattern images at different places on the wafer 3 are compared with each other, and a defect portion on the wafer is extracted. Then, coordinate data of the extracted defect portion and an image thereof are stored as an inspection result. A user can check the inspection result as a defect distribution and the defect image in the wafer 3 through an image display unit 34 at any time. In the semiconductor pattern inspection apparatus disclosed here, the inspection system control unit 90 stores information about a pattern of a wafer to be inspected and a process for the inspection, inspection conditions, an area to be inspected, threshold values for defect detection, and the like, and it collectively manages and controls the whole apparatus so as to always perform an optimal inspection. In this manner, in the semiconductor pattern inspection apparatus, the inspection of a wafer can be performed and a failure of a semiconductor pattern can be monitored regardless of the presence of an operator. FIG. 2 is a diagram showing the structure of the charge control chassis 6 shown in FIG. 1 in detail, and FIG. 3 is a diagram showing another structure of the charge control chassis 6 shown in FIG. 1 in detail. As shown in FIG. 2, the charge control chassis 6 includes an ultraviolet light source 1, a charge control electrode 4, and others and is connected to the charge control system unit 60. The charge control electrode 4 is formed in a mesh (net-like) shape or a porous plate shape, in which a plurality of through-holes are formed. Operations of the charge control electrode 4 are collectively managed and controlled by the inspection system control unit 90 in which a voltage value of the charges, information about a flow of the charging process and the like are stored for each wafer to be inspected. The charge control system unit 60 includes a charge control device 61, a power source for ultraviolet light source 62, a power source for control electrode 63, and a charge monitor unit 64, and the charge control device 61 controls the power source for ultraviolet light source 62, the power source for control electrode 63, and the charge monitor unit 64 based on the information sent from the inspection system control unit 90. FIG. 2 shows the charge control chassis 6 and the charge control system unit 60 shown in FIG. 1 in an enlarged manner, and the charge control chassis 6 and the charge control system unit 60 include the ultraviolet light source 1, the sample chamber 20, the power source for ultraviolet light source 62, the power source for control electrode 63, the charge monitor unit 64, and others. The ultraviolet light source 1 is attached on the sample chamber 20, and it is arranged so as to irradiate the ultraviolet light to the wafer 3 through the charge control electrode 4. The power source for ultraviolet light source 62 is used to emit ultraviolet light from the ultraviolet light source 1. The power source for control electrode 63 is used for forming arbitrary electric field intensity including non electric field between the charge control electrode 4 and the wafer 3, and the charge monitor unit 64 has a function to monitor the absorption current flowing into the charge control electrode 4 and the wafer 3. The sample chamber 20 is composed of the wafer 3 and the wafer holder 21, and it is disposed on the sample stage 23. The sample stage 23 is to be controlled so that ultraviolet light irradiated from the ultraviolet light source 1 is irradiated on a whole surface of the sample. Also, the wafer 3 moves between a position just below the SEM chassis 10 and a position just below the charge control chassis 6 by means of the sample stage 23. The charges of the wafer 3 can be controlled based on a potential difference between the charge control electrode 4 disposed just above the wafer 3 and the wafer 3. FIG. 4 and FIG. 5 are explanatory diagrams showing a method for controlling the charges on a surface of a sample (wafer 3) in the electron microscope application apparatus according to the present embodiment. When a surface of the wafer 3 is to be positively charged, ultraviolet light is irradiated on the wafer 3 while applying positive bias (potential of the charge control electrode 4>potential of the wafer 3). Ultraviolet light is irradiated to the wafer 3 through the charge control electrode 4 and holes of the charge control electrode 4, and photoelectrons 2 are emitted from the wafer 3 and the charge control electrode 4. Since the photoelectrons 2 are pulled up in a direction toward the charge control electrode 4 due to electric field, the surface of the wafer 3 is put into a state where electrons lack, and thus, the surface of the wafer 3 is positively charged (FIG. 4). When the surface of the wafer 3 is to be negatively charged, ultraviolet light is irradiated to the wafer 3 while applying negative bias (potential of the charge control electrode 4<potential of the wafer 3). Ultraviolet light is irradiated to the wafer 3 through the charge control electrode 4 and holes of the charge control electrode 4, and photoelectrons 2 are emitted from the wafer 3 and the charge control electrode 4. In this case, since the photoelectrons 2 are pulled back in a direction toward the wafer 3 due to electric field unlike the case of the positive bias, the surface of the wafer 3 is put into a state of excessive electrons, and thus, the wafer 3 is negatively charged (FIG. 5). Also, by setting potentials of the wafer 3 and the charge control electrode 4 to be equal to each other, charges of the surface of the wafer 3 can be made approximately 0 V. The ultraviolet light source 1 used in the present embodiment has to be able to irradiate ultraviolet light having energy enough to emit photoelectrons from the charge control electrode 4 and the wafer 3. Material for the charge control electrode 4 is metal or compound having high quantum efficiency. Alternatively, it is also possible to deposit compound with high quantum efficiency on the charge control electrode 4. Since a work function of metal is about 4.5 eV though it depends on element, it is necessary to use ultraviolet light with a wavelength of 275 nm or shorter, and the wafer 3 can be negatively charged when using ultraviolet light in such a wavelength range. In general, the surface of the wafer 3 is generally covered with insulating material such as a silicon dioxide film or a silicon nitride film, and the work function of the material is 7 eV or more. Therefore, when the wafer 3 is to be positively charged, it is necessary to use ultraviolet light with a wavelength of 177 nm or shorter. Ultraviolet light with a wavelength shorter than the wavelength range degrades the characteristics of a semiconductor device in some cases. Such ultraviolet light is ultraviolet light with a wavelength range of 10 nm or shorter, that is, ultraviolet light in a range called “EUV (Extreme Ultraviolet). As shown in FIG. 3, therefore, a filter 5 shielding ultraviolet light with a wavelength range of 10 nm or shorter is interposed between the ultraviolet light source 1 and the wafer 3 so that degradation of the semiconductor device is prevented. In the structure of FIG. 3, the filter 5 is disposed between the ultraviolet light source 1 and the wafer 3. In the structure shown in FIG. 2, ultraviolet light is simultaneously irradiated to the charge control electrode 4 and the wafer 3. When the wafer 3 is to be positively charged, photoelectrons 2 emitted from the wafer 3 are pulled up by applying plus voltage relative to that of the wafer 3 to the charge control electrode 4 (FIG. 4). When charges of the charge control electrode 4 and the wafer 3 reach the same potential, electric field for pulling the photoelectrons 2 upward disappears. Therefore, the wafer 3 is not charged to a potential above the same potential. When the wafer 3 is to be negatively charged, photoelectrons 2 emitted from the charge control electrode 4 are pulled back to the wafer 3 by applying minus voltage relative to that of the wafer 3 to the charge control electrode 4 (FIG. 5). When charges of the charge control electrode 4 and the wafer 3 reach the same potential, electric field for pulling the photoelectrons 2 back disappears. Therefore, the wafer 3 is not charged to a potential below the same potential. Determination whether or not charge of the wafer 3 is saturated can be made by monitoring an absorption current of the wafer 3. As described above, when the charge potentials of the wafer 3 and the charge control electrode 4 become the same potential, the photoelectrons 2 are not pulled upward or are not pulled back. Therefore, the absorption current in the wafer 3 is reduced and current hardly flows. FIG. 6 is a graph showing a relationship between a potential difference between the charge control electrode 4 and a sample (wafer 3) and a sample absorption current in the electron microscope application apparatus according to the present embodiment. In the graph of FIG. 6, a horizontal axis indicates an absolute value of a difference between a charge control electrode voltage Vcc and a wafer charge potential Vw and a vertical axis indicates a wafer absorption current. As the difference between Vcc and Vw approaches zero, an absorption current decreases to become approximately zero. Therefore, determination whether or not the charge has been saturated is possible based on the absorption current in the wafer 3. Next, a sample inspection method in an electron beam appearance inspection apparatus will be described. First, a desired voltage is applied to the charge control electrode 4, ultraviolet light source 1 is turned ON, and a wafer 3 is moved below the charge control electrode 4. When a whole surface of the wafer 3 is to be charged, the stage 23 is controlled so that the whole surface of the wafer passes below the charge control electrode 4. FIG. 7 and FIG. 8 are diagrams showing the movement of the wafer in the sample inspection method according to the present embodiment. The movement of the wafer includes a method in which a wafer moves continuously at a fixed velocity and the charge of the whole surface of the wafer is controlled at once as shown in FIG. 8 and a method in which the wafer moves predetermined regions Pk (k=1 to n) on the wafer to stop as shown in FIG. 7. An example where charges of the wafer 3 are controlled according to the method described above is shown in FIG. 9. As is evident from FIG. 9, a voltage of the charge control electrode 4 and a potential of the wafer 3 (sample) are in a linear proportional relationship, and charge of the wafer 3 can be controlled. Also, SEM images of contact holes formed in a silicon dioxide film in respective charged states indicated by (a), (b), and (c) in FIG. 9 are shown in FIG. 10A, FIG. 10B, and FIG. 10C. FIG. 10A shows an SEM image when the wafer 3 is negatively charged, in which the contact holes are observed to be darker than the oxide film around them. Incidentally, round portions correspond to the contact holes and a portion around the contact holes corresponds to the oxide film. FIG. 10B shows an SEM image when the potential of the wafer 3 is approximately 0 V, namely, it is not charged, in which a contrast between the contact holes and the oxide film around them is observed to be low. FIG. 10C shows an SEM image when the wafer 3 is positively charged, in which the contact holes are observed to be brighter than the oxide film around the contact holes. Thus, SEM images having a contrast corresponding to the charged state of the wafer 3 can be observed, and it has been confirmed that the charge control method according to the present invention is effective. In this case, the silicon dioxide film has been described as an example, but similar effects can be obtained also when using other insulating material, for example, a silicon nitride film or resist. The charge control apparatus and method have been described with using the semiconductor pattern inspection apparatus as an example in the present embodiment. However, the electron microscope application apparatus and the sample inspection method according to the present invention can be applied to pattern size measurement of a semiconductor and a charge removing process in a semiconductor manufacturing process, and also, a sample to be processed in the electron microscope application apparatus and the sample inspection method according to the present invention is not limited to a semiconductor device and it may be any sample whose surface is formed from an insulating film. In the electron microscope application apparatus according to the first embodiment, charges of the sample surface can be controlled to both positive polarity and negative polarity by using the ultraviolet light source 1 and the charge control electrode 4. In the second embodiment, a method for collectively controlling the charge of the whole surface of the wafer by irradiating ultraviolet light to an area approximately equal to the area of the wafer 3 will be described. FIG. 11 is a diagram showing a structure of an electron microscope application apparatus according to the second embodiment, and FIG. 12 is a diagram showing a structure of a charge control chassis 6 shown in FIG. 11 in detail. FIG. 12 shows an example where the electron microscope application apparatus according to the present embodiment is mounted on a semiconductor pattern inspection apparatus. In this example, the ultraviolet light source 1 is mounted on a sample preparation chamber 70. Accordingly, in the semiconductor pattern inspection apparatus according to the second embodiment, after the process for controlling the charge is performed in the sample preparation chamber 70, a sample is transferred to the sample chamber 20 and then inspected therein. Also, the charge control system unit 60 includes the power source for ultraviolet light source 62 and the charge monitor unit 64, and operations thereof are collectively managed and controlled by the inspection system control unit 90 like the first embodiment. Since ultraviolet light is irradiated on a whole surface of a wafer in the second embodiment as shown in FIG. 12, it is possible to control the charges of the wafer whole surface collectively and evenly. Further, since charges can be controlled collectively, an irradiation time can be reduced, which is useful for throughput improvement. In the second embodiment, even if a wafer to be inspected has been already charged due to the process prior to the inspection performed in this inspection apparatus, the charges of the wafer can be removed in the sample preparation chamber 70. By removing the charges just prior to this inspection, a charged state of the wafer can be kept uniform. Therefore, the reproducibility in inspection can be improved. FIG. 13 is a diagram showing a structure of an electron microscope application apparatus according a third embodiment. FIG. 13 shows an example where the electron microscope application apparatus according to the present embodiment is mounted on a semiconductor pattern inspection apparatus. A charge control device shown in the third embodiment is an ultraviolet light source which is mountable to an existing apparatus, and similar effects can be realized by mounting this ultraviolet light source to another apparatus using charged particles. In FIG. 13, the ultraviolet light source 1 is attached below an objective lens 17, and it can irradiate ultraviolet light on an area approximately equal to an area to be inspected or an area including the area to be inspected and its vicinity. That is, the area to be inspected in the third embodiment is an area in which electrons emitted from the electron source 11 mounted on the SEM chassis 10 are focused to be irradiated on the wafer 3, and the ultraviolet light source 1 is attached so as to irradiate ultraviolet light to the area. Process for the inspection and charge control is collectively managed and controlled by the inspection system control unit 90 based upon inspection conditions and process conditions for charge control which are inputted by a user. In the inspection process, after a relay circuit 41 in the stage control unit 40 is switched to the retarding power source 42 and retarding voltage is applied to the wafer 3, an image on an area to be inspected is formed by using electrons emitted from the electron source 11. Note that, at this time, the ultraviolet light source 1 is controlled by the power source for ultraviolet light source 62 so that ultraviolet light emitted from the ultraviolet light source 1 does not block the image formation. On the other hand, in the process of charge control, the relay circuit 41 is switched to the charge monitor unit 64, and an absorption current flowing in the wafer 3 can be monitored in the process of charge control. Uniformity of the charges can be achieved by moving the stage 23 so that ultraviolet light emitted from the ultraviolet light source 1 is thoroughly irradiated on at least an area larger than the area to be inspected of the wafer 3 and performing this process at least once. Next, an example where charge control to a wafer is performed by using the ultraviolet light source 1 will be described with reference to FIG. 14. FIG. 14 schematically shows a portion near the wafer 3 in the electron microscope application apparatus shown in FIG. 13 in an enlarged manner, in which illustration of a portion of the SEM chassis 10 above the objective lens 17 is omitted. Ultraviolet light emitted from the ultraviolet light source 1 is obliquely irradiated onto an intersection point between the approximate central axis of the SEM chassis 10 and the wafer 3. The charge control electrode 18 can apply a voltage of a positive or negative polarity relative to the potential of the wafer 3 and can switch the polarity by a switch in the power source for control electrode 63. A surface of the wafer 3 can be adjusted to any voltage by the switching of the polarity. FIG. 15A and FIG. 15B are explanatory diagrams showing a charge control method in the electron microscope application apparatus according to the third embodiment. FIG. 15A shows a case where the wafer 3 is negatively charged and a negative voltage relative to the wafer 3 is applied to the charge control electrode 18. Broken lines indicate ultraviolet light 151 emitted from the ultraviolet light source 1, and the ultraviolet light 151 is assumed to be irradiated on the charge control electrode 18 and a portion approximately just below the same. Photoelectrons 2 emitted from the charge control electrode 18 are returned back to the wafer 3 by the negative voltage applied to the charge control electrode 18. In this manner, the wafer 3 is negatively charged. Also, FIG. 15B shows a case where the wafer 3 is positively charged, and a positive voltage relative to the wafer 3 is applied to the charge control electrode 18. In this case, since photoelectrons 2 emitted from the wafer 3 are pulled up to the charge control electrode 18, the wafer 3 is positively charged. Since the charge potential can be controlled by the charge control electrode as shown in the first embodiment, the potential does not exceed a desired charge potential. Process of charge control can be performed by simply mounting the structure shown in the third embodiment on an existing equipment. In the third embodiment, the pattern inspection apparatus has been described, but the principle of the present invention can be applied to not only the pattern inspection apparatus but also all apparatuses using charged particles. There is such a problem that a secondary electron trajectory is curved by the charges caused by electron beam scanning in the SEM and a correct sample shape cannot be observed. In the fourth embodiment, a technology for observing a correct sample shape by suppressing the charges will be described, in which ultraviolet light is intermittently irradiated during electron beam scanning with using the pattern inspection apparatus shown in the third embodiment. In the SEM, a real image of a sample is formed by scanning electron beam on the sample to detect secondary electrons. For example, when a sample shown in FIG. 16A is observed, an SEM image shown in FIG. 16C can be acquired. Note that FIG. 16A to FIG. 16C are diagrams showing semiconductor patterns in the fourth embodiment, and round portions correspond to contact holes. In the SEM, electron beam scans an observation area in a left-to-right direction and in an up-to-down direction. At this time, an area to which electron beam has been irradiated (irradiated area) and an area to which electron beam has not been irradiated (non-irradiated area) are present even within the observation area. When the irradiated area is charged, electric field is generated between the irradiated area and the non-irradiated area, and an SEM image with distorted pattern shape such as shown in FIG. 16B is observed. FIG. 17A and FIG. 17B are graphs showing a relationship in time between electron beam scanning and ultraviolet light irradiation in the fourth embodiment. An electron beam scanning method and an ultraviolet light irradiation method for suppressing the charges due to electron beam scanning will be described with reference to FIG. 17A and FIG. 17B. After electron beam scans from a left end of an observation area to a right end thereof, the electron beam is returned from the right end back to the left end. At this time, electron beam is not irradiated on a sample (FIG. 17A). Thus, ultraviolet light is irradiated during the time when electron beam is not irradiated, thereby removing the charges on the irradiated area (FIG. 17B). By repeating electron beam irradiation and ultraviolet light irradiation in this manner, a difference in charge between the irradiated area and the non-irradiated area is cancelled. Therefore, a normal SEM image shown in FIG. 16C can be acquired. In the fourth embodiment, the pattern inspection apparatus has been described, but the principle of the present invention can be applied to not only the pattern inspection apparatus but also all apparatuses using charged particles. In a fifth embodiment, a structure and a method of using the structure in the case where the electron microscope application apparatus according to the present invention is mounted on a critical dimension SEM will be described. FIG. 18 shows a critical dimension SEM equipped with the electron microscope application apparatus according to the present invention. The critical dimension SEM roughly includes an SEM chassis 10, a charge control chassis 6, a sample chamber 20, a sample preparation chamber 70, an SEM control unit 50, a charge control system unit 60, a critical dimension measuring system control unit 91, an evacuating system unit 80, a stage control unit 40, and others, in which the SEM chassis 10, the sample chamber 20, and the sample preparation chamber 70 are evacuated by the evacuating system unit 80. Primary electron beam emitted from a cathode by the voltage applied to the cathode and a first anode is accelerated by the voltage applied to a second anode and advances to a lens system of a latter stage. The primary electron beam is focused as a minute spot on a sample by a condenser lens A12 and the objective lens 17 controlled by the lens control unit 52, and it scans the sample in a two-dimensional manner by a two-staged deflection coil 19. Scanning signal of the deflection coil 19 is controlled by the critical dimension measuring system control unit 91 via the SEM control unit 50 in accordance with an observation magnification designated through an input device. In the structure of the apparatus, charge in a wafer surface is measured by using a voltage measuring probe 66 in the sample preparation chamber 70, and charges are removed in the sample chamber 20 based on the measurement result. By measuring a pattern size after removing the charges, measurement can be performed with high precision. FIG. 19 shows a case where the electron microscope application apparatus according to the present invention is mounted on the sample preparation chamber 70 of the critical dimension SEM. The degradation of a critical dimension measuring precision due to the charges can be prevented by measuring a charge distribution in a wafer surface in the sample preparation chamber 70 and performing the observation after setting optical conditions in accordance with the charge. However, the optical conditions cannot be sufficiently corrected depending on the magnitude of charge in some cases. Therefore, in such a case, observation is performed after the process of removing the charge of a wafer by using the electron microscope application apparatus according to the present invention. Since the process of removing the charge is performed, length measurement with excellent reproducibility which is not influenced by the charge can be provided. FIG. 20A and FIG. 20B are flowcharts showing a procedure for using a critical dimension SEM according to the fifth embodiment. FIG. 20A shows a sequence in the case where the charge is removed at each movement to a pattern to be measured critical dimension. As shown in FIG. 20A, first, a critical dimension measuring sequence starts (Step S201), and a charge distribution on a wafer is measured by a surface potential measurement (Step S202). Thereafter, movement to a position Pk where a pattern size is to be measured is conducted (Step S203) Then, the charge is removed based on a charge potential obtained by the surface potential measurement (Step S204). After the charge is removed, an SEM image is acquired (Step S205), and the image is stored (Step S206). Thereafter, if a pattern whose length is to be measured remains, the process from Step S203 to Step 206 is repeated (Step S208). If such a pattern does not remain, the critical dimension measuring sequence is terminated (Step S207). Next, FIG. 20B shows a sequence where a charge distribution is acquired prior to start of pattern length measurement and the length measurement is performed after the charge is removed. As shown in FIG. 20B, first, a critical dimension measuring sequence starts (Step S201), and a charge distribution on a wafer is measured by a surface potential measurement (Step S202). Thereafter, the charge on a whole surface of a wafer is removed (Step S204). After the charge is removed, movement to a position Pk where a pattern size is to be measured is conducted (Step S203), an SEM image is acquired (Step S205), and the image is stored (Step S206). Thereafter, if a pattern whose length is to be measured remains, the process from Step S204 to Step 206 is repeated (Step S208), but if such a pattern does not remain, the critical dimension measuring sequence is terminated (Step S207). As shown in the fifth embodiment, by irradiating ultraviolet light on a wafer in the sample preparation chamber 70, such an effect can be obtained that contamination hardly adheres to a wafer during the measurement using electron beams. Therefore, according to the electron microscope application apparatus and the sample inspection method of the embodiments, charges on a sample surface can be controlled rapidly and with high precision. Also, when the embodiments are applied to a measurement apparatus for a semiconductor wafer, the charges on a wafer surface can be always made uniform. Therefore, high precision measurement and high reproducibility can be realized. Further, when the embodiments are applied to an SEM type inspection apparatus, since a pattern formed on a wafer surface can be charged to a desired potential, electrical characteristic failure can be detected with high sensitivity. In the foregoing, the invention made by the inventors of the present invention has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments and various modifications and alterations can be made within the scope of the present invention. The present invention can be applied to a production and inspection equipment for industrial products such as semiconductor devices.
	abstract	A cylindrical gamma generator includes a coaxial RF-driven plasma ion source and target. A hydrogen plasma is produced by RF excitation in a cylindrical plasma ion generator using an RF antenna. A cylindrical gamma generating target is coaxial with the ion generator, separated by plasma and extraction electrodes which has many openings. The plasma generator emanates ions radially over 360° and the cylindrical target is thus irradiated by ions over its entire circumference. The plasma generator and target may be as long as desired.
06320925&	summary	BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to a spacer for a fuel assembly of a nuclear power station, in particular for a fuel assembly of a light water reactor. Spacers are used for fixing fuel rods in a fuel assembly. A spacer forms a matrix of intersecting webs and a base area covered by the spacer corresponds essentially to the cross sectional area of the fuel assembly. Each web has an assembly gap which is disposed at an intersection location with an intersecting web and receives the intersecting web. The webs which are guided in the assembly gaps and subsequently fixed, for example by welding, form cells having an essentially rectangular or square base area. The fuel rods, as well as guide tubes in the case of pressurized water fuel assemblies and possibly water rods in the case of boiling water fuel assemblies, project through the cells formed by the spacer and are held there. In other words, they are fixed in their position relative to the center axis of the fuel assembly. In certain circumstances, under the operating conditions in the core of the nuclear reactor, the spacers of a fuel assembly may undergo longitudinal expansion which may lead to an increase in the external dimensions of the spacers and consequently of the fuel assembly. In an extreme case, the result of the increase in the external dimensions may be that a fuel rod bundle formed by the spacer can no longer be removed from a fuel assembly box, for example in the case of a fuel assembly for a boiling water reactor. In the case of fuel assemblies of pressurized water reactors, the longitudinal expansion of the spacers is unusually high. The increase in the external dimensions may cause complications with the adjacent fuel assemblies during servicing work and during loading and unloading of the reactor core. SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a spacer for a fuel assembly of a nuclear power station, which overcomes the heretofore-mentioned disadvantages of the heretofore-known devices of this general type and which undergoes insignificant longitudinal expansion during an operating period. With the foregoing and other objects in view there is provided, in accordance with the invention, a spacer for a fuel assembly of a nuclear power station, comprising webs disposed in a grid defining intersection locations, each of the webs having a wall thickness and having an assembly gap receiving an intersecting web at one of the intersection locations; the assembly gap in each of the webs having regions through which parts of the other of the webs pass in the intersection location of two webs, at least two of the regions having different widths; and the assembly gap in each of the webs having a total length formed by the regions through which the parts of the other of the webs pass in the intersection location of two webs, at most a fraction of the total length having a width substantially corresponding to the wall thickness of the other of the webs. Therefore, the assembly gap has a width, at most over a fraction of its total length, which corresponds essentially to the wall thickness of the intersecting web, but in a remaining region is wider than the wall thickness of the intersecting web. The invention proceeds from the knowledge that, under normal operating conditions, the longitudinal expansion of a spacer may be caused by corrosion of the spacer. A corrosion layer may form on the web wall in the assembly gap, particularly at assembly gaps of a spacer web formed of a zirconium alloy, for example, a Zircalloy plate. In order to achieve a high accuracy of fit of the spacer composed of the webs, the assembly gaps have heretofore been dimensioned in such a way that their width corresponds essentially to the wall thickness of the intersecting web. With that structure of the spacer, there is the risk that the corrosion layers, which grow toward one another from the edges of the assembly gaps and from the surface of the inserted web, will meet one another before the end of the period of use. The corrosion layers then exert a solid pressure on the respective web which may lead to a lengthening of the web. Since each web has a multiplicity of assembly gaps with corrosion-endangered regions, the resulting total longitudinal expansion of the webs may become so great that the change in the external dimension of the spacer exceeds a critical value. Moreover, a varying longitudinal expansion of different webs may lead to the warping of individual webs and/or of parts of the spacer, thus adversely influencing the flow properties of the spacer. The invention proceeds, then, from the notion of reducing the solid pressure exerted on a web by the corrosion layers. According to the invention this is achieved, on one hand, in such a way that the assembly gaps of two webs which are provided at an intersection location with another web, have a width only over a fraction of their total length, through which parts of a web pass in each case, that corresponds to the wall thickness of the intersecting web. By virtue of the reduced bearing surface between the edges of the assembly gaps and the intersecting webs, the solid pressure on the web decreases, thus resulting in a considerable reduction in the undesirable longitudinal expansion of the web. The length of the regions in which the width of the assembly gap corresponds essentially to the wall thickness of the intersecting web is selected in such a way that the spacer matrix has a strength which is sufficient for subsequent machining steps, such as, for example, the welding of the webs at the intersection locations, and for the loads which occur under operating conditions. This affords the advantage of ensuring that, after the webs have been welded together, the assembly gaps do not have to be widened in an additional operation, for example by pickling or corroding, in order to reduce the solid pressure on the web which occurs as a result of corrosion. In accordance with another feature of the invention, each web has a recess on at least one side of each assembly gap, in the region of the narrowest cross section of the latter, wherein the recess is adjacent the assembly gap. This affords the advantage of permitting web deformation caused by corrosion in the region of the narrowest cross section of the assembly gap to be absorbed by the recess. The solid pressure on the remaining part of the web can thereby be further reduced. If the web is to have only minimal longitudinal expansion due to corrosion, without an additional recess, the width of the assembly gap is dimensioned, virtually over its entire length, to be greater than the wall thickness of the intersecting web. In order to acquire the necessary stability of the spacer matrix formed from the webs, the assembly gap has only a few (but at least three) support locations along its axis or principal extent, for example bearing points or bearing regions, at which the assembly gap touches the intersecting web. The support locations are disposed on both sides of each assembly gap, in such a way that the intersecting web is supported in each case on only one side over a sufficiently small area. The advantage of this is that a solid pressure may build up at the few support locations during the operating period and could partially deform the intersecting web transversely to its direction of principal extent, and consequently only some of the solid pressure contributes to the longitudinal expansion of the web. In accordance with a further feature of the invention, a further reduction in the solid pressure leading to longitudinal expansion is achieved through the use of apertures in the middle of the web. Preferably, each web has at least one aperture disposed on an assembly axis of each assembly gap. Advantageously, each assembly gap opens in each case into at least one of the apertures. Thus, corrosion-endangered locations in the web are cut out and, moreover, it becomes possible to have a sufficient cooling water stream for the regions of the spacer which are located in the vicinity of an intersection location, so that corrosion is retarded there. In accordance with an added feature of the invention, there are provided firm connections between the webs, through the use of which a stabilization of the spacer is achieved. Lengthening of the web is prevented by such a firm connection of the intersecting webs at a connection location, preferably through the use of a metallurgical connection, for example through the use of a weld spot in the intersection region. Moreover, metallurgical connections often undergo a lesser degree of corrosion than the untreated material. Such metallurgical connections may, for example, fill those regions in the assembly gap which would be particularly in danger of corrosion. In accordance with an additional feature of the invention, particularly in pressurized water reactors, it has proved particularly appropriate to have spacers with webs which contain at least two web plates bearing against one another at least in the region of an intersection location with an intersecting web. The common or combined thickness of these web plates at the intersection location corresponds to the wall thickness of the web. In the regions outside an intersection location, the web plates may be deformed and/or bent relative to one another so that, for example, flow ducts are obtained between them. In the case of spacers in fuel assemblies for pressurized water reactors, there is therefore a series of further locations, in addition to the assembly gaps, at which the webs or the web plates touch one another. There are, in part, regions in which the webs, in particular the web plates, bear against one another over a large area. For the reasons already explained with regard to the assembly gaps, these regions are likewise preferred regions for corrosion and/or for the formation of corrosion lenses and may cause deformation of the spacers. In accordance with yet another feature of the invention, consequently, in the case of the webs formed of a plurality of web plates, it is advantageous to connect the web plates which are located next to one another metallurgically to one another, in particular in the region of the intersection location of the webs. In accordance with yet a further feature of the invention, the web plates located next to one another are connected, preferably metallurgically connected, to the intersecting web at least at one connection location. The web plates may be connected to one another over a large area at least at one further connection location, preferably in a region in which they bear against one another. The latter is achieved, in particular, by welding at the locations at which the web plates bear against one another over a large area. This may be carried out, for example, when the webs are assembled to form the gridlike spacer. The web plates have expediently already been previously assembled to form webs. In accordance with yet an added feature of the invention, corrosion-endangered locations are avoided if each web is firmly connected, preferably metallurgically connected, to the other web virtually along the entire length of that part of each assembly gap having a width which corresponds essentially to the wall thickness of the other web. This results in long welds which are applied preferably along the narrower region or narrower regions of the assembly gaps by laser beam welding. With regard to the spatial conditions in the spacer, a longer run of the weld seam along the assembly gaps is possible as a result of laser beam welding, as compared with electron beam welding. Moreover, regions in danger of corrosion are those at which the webs and/or the web plates are bent. This relates, in particular, to regions with small bending radii. The cause of this is possibly the reduced cooling water stream in such regions, as compared with regions which have no bending radii. At those endangered locations and/or regions as well, for the reasons mentioned above, corrosion layers may exert a solid pressure on the respective web that may lead to a lengthening of the web. Making recesses, apertures or firm connections at such corrosion-endangered locations effectively prevents the longitudinal expansion of spacers, since a sufficient cooling water stream is ensured once again. In particular, such apertures may also be produced through the use of a bead or a groove. This preferably also relates to further apertures or recesses in the webs and/or web plates along an assembly axis of each assembly gap. In particular, this also relates to further connection locations which connect the web plates to one another, in particular metallurgically to one another, over a large area. In accordance with yet an additional feature of the invention, that part of a web which passes through an assembly gap of another web carries two elevations, between which the other web is held. These elevations fix the intersecting webs before they are firmly connected to one another, for example through the use of weld spots or weld seams. With the objects of the invention in view, there is also provided a spacer for a fuel assembly of a nuclear power station, comprising webs disposed in a grid defining intersection locations, each of the webs having an assembly gap receiving an intersecting web at one of the intersection locations; each assembly gap of each web including one region having a metallurgical connection of two webs in the intersection location of two webs; and each assembly gap of each web including another region in the intersection location of two webs through which part of the other web passes, the other region having a width sufficient to prevent two webs from touching. With the objects of the invention in view, there is additionally provided a spacer for a fuel assembly of a nuclear power station, comprising two mutually parallel first outer strips; two mutually parallel second outer strips perpendicularly to the first outer strips; first webs standing on edge, parallel to the first outer strips and having ends each engaging into and fixed to a respective one of the outer strips; second webs standing on edge, parallel to the second outer strips, intersecting the first webs and having ends each engaging into and fixed to a respective one of the outer strips; the first webs each having an upper edge and a lower edge, the upper edges running from one of the outer strips to another of the outer strips and each having an assembly gap at an intersection location with a respective one of the second webs, the assembly gap directed toward the lower edge and receiving part of an intersecting one of the second webs; the second webs each having an upper edge and a lower edge, the lower edges each having an assembly gap at an intersection location with a respective one of the first webs, the assembly gap directed toward the upper edge and receiving part of an intersecting one of the first webs; each of the assembly gaps closed at one of the edges of each of the webs by a metallurgical connection of one web with an intersecting web; and each of the assembly gaps having a region through which part of the intersecting web passes, the region wide enough to prevent two of the webs from touching. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a spacer for a fuel assembly of a nuclear power station, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
	abstract	A neutron spectrometer is provided by a series of substrates covered by a solid-state detector stacked on an absorbing layer. As many as 12 substrates that convert neutrons to protons are covered by a layer of absorbing material, acting as a proton absorber, with the detector placed within the layer to count protons passing through the absorbing layer. By using 12 detectors the range of neutron energies are covered. The flat embodiment of the neutron spectrometer is a chamber, a group of detectors each having an absorber layer, with each detector separated by gaps and arranged in an egg-crate-like structure within the chamber. Each absorber layer is constructed with a different thickness according to the minimum and maximum energies of neutrons in the spectrum. In this arrangement, each of the 12 surface facets provides a polyethylene substrate to convert neutrons to protons, covered by a layer of absorbing material, acting as a proton absorber, with the detector stacked on the absorbing layer to count protons passing through the absorbing layer.
	summary
048333344	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With a view to simplifying the description, the latter refers to a protective box formed from a monoblock cover fixed to base and formed by a single part, in which the element liable to be irradiated by X-rays is the box. The possible directions of the X-ray flux are represented by arrows F in FIGS. 1 to 3. As stated hereinbefore, the invention clearly has a much wider application. FIG. 1 diagrammatically shows in longitudinal section a box for protecting electronic circuits having a base 2, on which is fixed a cover 4, e.g. using screws 6. This box receives electronic circuits 8. In particular, these circuits can be fixed by any known means to bosses 10 provided for this purpose on the inner face of the box cover 4. In very diagrammatic manner as it does not form part of the object of the invention, the electronic circuits 8 are connected to electrical circuits outside the box by conductive tracks indicated at 12 and which e.g. pass through the box base 2. The specific shape of the box, as well as the fixing and connection of the electronic circuits located in the X-ray protection box are linked with the type of components used. These components can be encapsulated in boxes TO 5, TO 66, etc. According to the invention, cover 4 has a rigid structure 14 ensuring the mechanical protection of the electronic circuits. Structure 14 is formed from a thermosetting plastics material, such as bakelite, polyimide resin or silicones, reinforced by organic or non-organic fibres. Structure 14 is e.g. made from KINEL 5504 marketed by Rhone Poulenc, said material being a polyimide resin reinforced by long glass fibres arranged in a random manner. This rigid structure 14 is formed by moulding, either by injection, or by compression, said procedures being well known in the art. It can have a thickness of 2 mm. The protection against X-rays of the electronic circuits 8 located in the box is ensured with the aid of a layer material 16 in contact with the inner surface of the rigid structure 14 or, as shown in the drawing, in contact with the outer surface of the rigid structure. The X-ray protection material 16 covers all the outer surface of structure 14 liable to be irradiated by X-rays. In the case shown in FIG. 1, the material layer 16 covers the entire outer surface of structure 14, namely upper face 15 and side faces 17 of said structure. In order to ensure a good adhesion of the protective material 16 to rigid structure 14, the latter can have lots 18 formed during the molding of the rigid structure 14. These slots 18 are filled with X-ray protection material during the potting of the latter. The X-ray protection material 16 is e.g. formed from a tungsten powder representing 30% by volume of the finished product and which is regularly dispersed in a PA11 resin produced by ATOCHEM. This resin is a thermoplastic polyamide resin. The tungsten powder has an average grain size of 4 .mu.m, a dispersion of 2.5 and a purity of 99.9%. This protective material can be obtained by melting granules of PA11 resin, to which the tungsten powder is added. The premix obtained is introduced into a Werner ZSK30 extruder-granulator, in order to obtain mixture granules which can then be introduced into a mold already containing the rigid structure 14 to be covered by the X-ray protection material. The introduction of the mixture granules into the mold takes place by injection. The potting of the X-ray protection material is assured on rigid structure 14 heated in order to facilitate the adhesion of the X-ray material. The protective material obtained can have a thickness of 1.5 mm. The molding and potting respectively of rigid structure 14 and X-ray protection material 16 make it possible to directly obtain protective box covers with the requisite dimensions and accuracies without further machining being required. Moreover, these molding procedures are particularly advantageous from the financial and manufacturing time standpoints, because the runs of box covers to be produced make it possible to reduce the costs of specific tools for each box model. The X-ray protection material can also be constituted by a powder containing 6% by volume of tungsten and 24% by volume of uranium dioxide (UO.sub.2) embedded in PA11 resin. This material can have a thickness of 2 mm, in order to ensure effective filtering. In the same way, the PA11 polyamide resin can be replaced by a polyether block amide resin, such as that marketed under the trade name DINYL by Rhone-Poulenc. The resin of protective material 16 can also be bakelite or silicone. To avoid raising the electromagnetic level due to electron emission by the outer walls of the protective box during X-ray irradiation and in particular by the metal contained in the X-ray protection material 16, an anti-SGEMP material 20 forming the outer surface of cover 4 can be provided. In the case shown in FIG. 1, material 20 covers the entire X-ray protection material 16. It is made from beryllium so that, apart from the anti-SGEMP function, it provides the necessary protection of electronic circuits 8 against electromagnetic waves. The closing of the Faraday cage is obtained for the case described here by the presence of base 2 made from or covered by a good electricity conducting metal, such as nickel, silver, aluminium, beryllium or copper. Material 20 must have a thickness exceeding the free mean travel of the electrons emitted by the walls of the cover and also constitutes a covering for the final layer. In particular, in the case of an X-ray protection material covering the inner surface of the mechanical structure, the anti-SGEMP material advantageously constitutes the internal surface of the cover. It is possible to envisage the simultaneous use of an anti-SGEMP layer constituting the inner surface of the box and an anti-SGEMP layer constituting the outer surface of the box. FIG. 2 shows a second embodiment of the protective means according to the invention, in which the material used for preventing the emissivity effects of the walls of the case exposed to X-rays and in particular material 16 is made from a poor electricity conductor, such as carbon or boron. Under these conditions, the protection of integrated circuits 8 against electromagnetic waves is not assured. In order to assure this protection, the inner surface of the rigid structure 14 is completely covered with a good electricity conducting layer 22. In particular layer 22 is made from a metal, such as nickel or silver. Layer 22 has a thickness of approximately 0.1 mm. The other parts of the protective box and in particular cover 4 are unchanged compared with FIG. 1. FIG. 3 shows a third embodiment of the protective box according to the invention. This embodiment differs from that of FIG. 2 only in that the layer serving as the Faraday cage is positioned between the anti-SGEMP material layer 20a and the X-ray protection material layer 16. Layer 24 has a thickness of 0.1 mm and is in particular made from silver or nickel. As in the case of FIG. 1, the Faraday cage is closed by the presence of base 2 made from a metal or covered with a metal which is a good electricity conductor. In order to simplify the manufacture of the protective box according to the invention and ensure a good insulation of the electronic circuits 8 against electromagnetic waves, it is possible to provide a faradization layer 22-24 covering both the inner face of mechanical structure 14 (FIG. 2) and the outer surface of the X-ray protection material 16 (FIG. 3). This can be carried out by simply immersing the mechanical structure 14 coated with protective material 16 in a bath containing the metals to be deposited to serve as a Faraday cage (chemical deposition). It should be noted that the metal faradization layer cannot be applied to a silicone surface due to the poor adhesion of such a metal to such a resin. The description given hereinbefore has obviously been given in a non-limitative, illustrative manner and modifications are possible without passing beyond the scope of the invention. In particular, the X-ray protection material 16 may only cover the upper face 15 of the mechanical structure or only the side faces 17 thereof. In this case, the anti-SGEMP material 20 or 20a forming the outer surface of the box cover 4, covers all the X-ray material and that part of the rigid structure 14 not covered by X-ray protection material 16. Moreover, when the anti-SGEMP material is a poor electricity conductor, a faradization layer can be inserted between the anti-SGEMP layer 20a and those parts of the outer surface of structure 14 not covered by the X-ray protection material 16. The protective means according to the invention can be used wherever electronic circuits have to be protected against X-rays. This protection makes it possible to withstand severe surrounding climatic and mechanical conditions. In particular, the invention applies when minimum weight conditions are required. Thus, the protective box according to the invention makes it possible, in the case of an equivalent filtering efficiency to that of a solid material sheet covering a metal mechanical structure, permit gains as regards weight and overall dimensions, as well as a reduction in manufacturing costs. Thus, the protective box according to the invention can be advantageously used for producing very high performance electronic means on-board aircraft.
	description	The invention generally relates to a method for evaluating quantities relative to the distortion of a nuclear fuel assembly, in particular the bow and the twist of the assembly. Known from USH1262 is the use of a video surveillance camera or CCTV (closed-circuit television), hardened against radiation, for monitoring the bowing of fuel assemblies. The camera is placed in a sealed housing and is moved vertically, underwater, along the assemblies to be characterized. Such a monitoring method using an underwater camera is generally long to implement due to the volume and weight of the equipment to be installed, the remotely controlled movement of the camera along the fuel assembly, and the decontamination of the equipment after use. This monitoring is done for example when a nuclear reactor is stopped, in order to replace some of the nuclear fuel assemblies. All of the assemblies are taken out of the core of the reactor. The spent assemblies are evacuated and replaced with new assemblies. The other assemblies are reorganized inside the core. The assemblies can be subject to distortion monitoring before being evacuated or before being replaced in the core of the reactor. The main purpose of this monitoring is to obtain data on the behavior of the fuel assemblies under radiation. These checks are on the critical path when the reactor is stopped in order to replace part of the reactor's fuel. This, making the method for acquiring distortion data relative to the nuclear fuel assemblies simpler and faster to carry out makes it possible to shorten the period during which the reactor is stopped for reloading. In this context an object of the invention is to propose a method for evaluating at least one quantity relative to the distortion of a nuclear fuel assembly, that is easy to install and disassemble and faster to implement. The invention provides a method comprising the following steps: placing the nuclear fuel assembly in a volume of water bounded by a free upper surface; placing the camera outside the volume of water, above the free surface; taking at least one image of at least one lateral face of the nuclear fuel assembly; graphically analyzing the at least one image and deducing the at least one quantity relative to the distortion of the nuclear fuel assembly therefrom. The method can also have one or several of the features below, considered individually or according to all technically possible combinations: the entire lateral face of the nuclear fuel assembly appears in the image taken by the camera; the nuclear fuel assembly comprises a plurality of longitudinally elongated nuclear fuel rods and a plurality of grids for maintaining the nuclear fuel rods in position, distributed longitudinally along the nuclear fuel rods, the at least one quantity relative to the distortion of the nuclear fuel assembly being the respective shifts of the maintenance grids in a transverse plane perpendicular to the longitudinal direction; the camera has an optical axis forming an angle between 10° and 40° relative to the vertical at the time of the shot; the camera and the nuclear fuel assembly are spaced apart from each other when the image is taken by a distance between 1 meter and 4 meters in a horizontal plane; the nuclear fuel assembly comprises two end maintenance grids situated near opposite ends of the nuclear fuel rods, and a plurality of intermediate maintenance grids distributed between the two end maintenance grids, the step for graphic analysis comprises the following sub-steps: materializing, on the image, at least one substantially longitudinal reference line extending from one end grid to the other end grid; determining, on the image, the transverse shift of each intermediate grid relative to the at least one reference line; the maintenance grids or the fuel rods near the maintenance grids can have respective visual references substantially aligned longitudinally when said maintenance grids are not shifted transversely, the reference line passing through the visual references relative to the two end maintenance grids, the transverse shift of each intermediate maintenance grid being determined by estimating, on the image, the transverse shift between the visual reference relative to said intermediate maintenance grid and the reference line; at least one image is taken of each of two lateral faces perpendicular to each other of the nuclear fuel assembly, and the respective shifts of the maintenance grids are determined in two directions perpendicular to each other and perpendicular to the longitudinal direction; the nuclear fuel assembly comprises upper and lower caps, the quantity relative to the distortion of the nuclear fuel assembly being the rotation of the upper and lower caps relative to each other around the longitudinal direction; the camera presents an optical axis forming an angle between 1° and 10° relative to the vertical when the image is taken; the camera and the nuclear fuel assembly, when the image is taken, are spaced apart from each other by a distance smaller than 1 meter in a horizontal plane; the upper and lower caps have determined respective geometric lines normally parallel to each other when the upper and lower caps do not have any rotation relative to each other around the longitudinal direction, the step for graphic analysis of the image comprising the following sub-steps: determining, in the image, the two geometric lines; determining, in the image, the relative angle between the two geometric lines; the camera has a determined optical axis, a shielding widow being placed on the free surface and inserted on the optical axis of the camera. The method that will be described aims to determine the bow and the twist of nuclear fuel assemblies. As illustrated in a simplified manner in FIGS. 1 and 2, a nuclear fuel assembly 1 for a light water reactor includes a plurality of longitudinally elongated nuclear fuel rods 3, upper and lower caps 5 and 7, and grids 9 for maintaining the rods 3. The rods 3 contain nuclear fuel pellets. They are arranged parallel to each other, following a regular pattern, typically a square pitch pattern. The assembly 1 is generally parallelepiped and then has four lateral faces. The upper and lower caps 5 and 7 are positioned at the two ends of the assembly 1 and are secured to each other by a plurality of longitudinal tubes. These tubes are for example provided for the passage of the rods from the control cluster of the nuclear reactor. The grids 9 are rigidly fixed to the tubes securing the two caps 5 and 7. The grids 9, perpendicular to the longitudinal direction, have a square section. They are bounded by four lateral faces 11, perpendicular to each other. The inner space of the grids 9 is divided into a plurality of cells with a generally square-shaped section by an array of internal tabs. Each rod 3 is engaged in one of the cells. One of the grids 9a, called upper grid in the description that follows, is located near the upper cap 5, close to a longitudinal end of the rods 3. Another grid 9b, called lower grid in the description that follows, is located near the lower cap 7, close to the opposite longitudinal end of the rods 3. The other grids 9 are distributed evenly between the upper and lower grids along the rods 3. The nuclear fuel assemblies 1 are subjected, in the core of the reactor, to very substantial thermal and mechanical stresses. In the long term, these stresses can cause a distortion of the fuel assemblies, in particular distortion by bowing (FIG. 1) and distortion by twisting (FIG. 2). The assemblies 1 distorted by bowing assume a general bowed shape, in general a single curve (C-shaped distortion) or with two curves (S-shaped distortion), or even with three curves (M- or W-shaped distortion). The assemblies 1 have a deflection in a direction substantially perpendicular to the longitudinal direction of the assembly. The deflection is typically several millimeters and can go up to more than ten millimeters. As shown in FIG. 1, the shift is more pronounced for the intermediate grids located longitudinally at the center of the assembly when the assembly is C-shaped. These shifts are materialized by the deviations e1, e2 and e3 between the lateral faces 11 and an imaginary line 1 extending from the lower grid 9b to the upper grid 9a. The shift is more pronounced for the intermediate grids 9 located longitudinally in the upper half or in the lower half of the assembly when the assembly 1 is distorted in an “S” shape. Distortion by twisting, illustrated in FIG. 2, corresponds to twisting of the whole assembly 1 around a longitudinal axis materialized by a rotation of the upper 5 and lower 7 caps relative to each other. This twisting may or may not be accompanied by a shift of the two caps relative to each other in a transverse plane. As shown in FIG. 2, the caps 5 and 7 are perpendicular to the longitudinal direction of the square sections, and are laterally bounded by four faces 13 perpendicular to each other. Because of the relative rotation between the two caps, the respective lateral faces 13 of the caps are inclined relative to each other in top view. The method that will be described below aims to determine: the transverse shift of each of the intermediate grids 9 relative to the upper and lower grids 9a, 9b, in a transverse plane, along two directions that are perpendicular to each other; and the angle α (FIG. 2) of rotation around the longitudinal direction between the upper 5 and lower 7 caps. The shift of the grids 9 is measured along two directions perpendicular to two adjacent lateral faces of the assembly 1. The measurements of the shift of the grids 9 and relative rotation between the caps 5 and 7 are done, as shown in FIG. 3, on an assembly 1 arranged in a pool 12 of the nuclear reactor, for example the cooling pond of the combustible structure. The measuring device used comprises: a digital camera 15; a device 17 for maintaining and adjusting the position of the camera 15; a shielding window 19 placed on the free surface 20 of the water filling the pool 12; means 21 for maintaining the shielding window 19 in position; systems 23 able to control the camera 15 and process the images taken by said camera 15. The camera 15 is a digital camera whereof the resolution is approximately 10 million pixels. The camera 15 is placed above the surface 20 of the water in the pool 12. It is not submerged. The device 17 for maintaining the camera 15 in position is rigidly fixed to a coping 25 of the pool. It makes it possible to adjust the height of the camera 15 above the surface 20 of the water, as well as its position in a horizontal plane. Moreover, the lens of the camera 15 faces the bottom of the pool. The device 17 makes it possible to adjust the orientation of the optical axis of the camera 15, substantially in all directions oriented towards the bottom of the pool 12. The shielding window 19 is a circular shell made from a transparent material, for example transparent plastic such as Plexiglas®. It has a diameter of several tens of centimeters, for example 60 cm. The shielding window is placed on the surface 20 of the water, where it sinks slightly from its own weight. The bottom 27 of the shielding window 19 is positioned a few centimeters below the surface 20 of the water. The shielding window 19 also includes an upright edge 29 surrounding the bottom 27. The means 21 for maintaining the shielding window 19 in position for example include a rigid arm fixed to the coping 25 by one end and fixed to the shielding window 19 by its opposite end. This device and the slight sinking of the shielding window 19 under its own weight make it possible to avoid the oscillation (pitch, swell . . . ) of the shielding window under the effect of the waves that pass through the pool 12. The systems 23 for example comprise a microcomputer, connected to the camera 15 by a digital line 31. The microcomputer is capable of controlling the camera 15, and in particular triggering the shots. Moreover, the microcomputer is able to control the transfer of the digital files for each image from the camera 15 to an internal memory, and to display the images on a screen so as to verify the quality thereof. The systems 23 can comprise another microcomputer, equipped with graphic analysis means making it possible to determine the shift of the grids and the relative rotation of the caps 5, 7 from images taken by the camera 15. This computer can also be the same as the one that controls the camera 15. The measuring device can also include projectors 24 making it possible to light the assemblies 1 during the shots. The method for estimating the transverse shift of the grids 9 and the relative rotation of the caps 5 and 7 will be explained in detail below. During a first step, two series of shots are taken of the assembly to be characterized, one series to estimate the shift of the grids, and the other to estimate the rotation between caps. The assembly 1 to be characterized is grasped by a bridge crane, using a handling tool, and is brought to the position 33 (see FIG. 3) provided for measuring the shift of the grids. In that position, the upper cap 5 of the assembly 1 is situated about 3 meters below the surface of the water (FIG. 4). The camera 15 and the assembly 1, in a horizontal direction, are spaced apart from each other by a distance between 1 meter and 4 meters, preferably between 2 and 3 meters. The optical axis of the camera 15 is oriented downwards, and forms, with the vertical, an angle between 10° and 40°, preferably between 20° and 30°. A first lateral face of the assembly faces the camera 15. The orientation of the optical axis of the camera 15 and the horizontal distance between the assembly 1 and the camera 15 are chosen so that the entire lateral face of the assembly 1 facing the camera 15 appears in the images taken by the camera 15. Moreover, as shown by FIG. 4, the position of the shielding window 19 is adjusted so that the bottom 27 of the shielding window 19 is inserted on the optical path between the camera 15 and the lateral face of the assembly 1 to be photographed. While the images are taken, the assembly 1 remains suspended to the bridge crane by a handling tool 34. Before taking an image of the first lateral face of the assembly, one waits for the assembly to be stabilized in the position 33, and in particular for it no longer to be animated by a swinging movement at the end of the tool 34. Once the assembly is stabilized, an operator controls the camera 15 via the systems 23 to take an image of the first lateral face of the assembly 1. The operator then orders the transfer of the digital file of the image to the systems 23, and views the image on the microcomputer screen. If the quality of the image is satisfactory, the nuclear fuel assembly 1 is then pivoted a quarter-turn via a bridge crane, so as to turn a second lateral face of the nuclear fuel assembly 1 towards the camera 15. The assembly 1 remains at position 33. After the assembly is stabilized, the operator controls the camera 15 to take an image of the second lateral face of the fuel assembly 1. The same procedure can be repeated, until the camera 15 has taken at least one image of satisfactory quality of at least two adjacent lateral faces of the fuel assembly 1. The nuclear fuel assembly 1 to be characterized is then moved, using the bridge crane, to the position 35 (see FIG. 3) provided for taking images intended to evaluate the twist of the whole assembly around its longitudinal axis. In that position 35, the upper cap is located about 3 meters underwater. Following the horizontal direction, the distance between the camera 15 and the assembly 1 is between 50 cm and 1 m, and is for example 70 cm. The optical axis of the camera 15 forms an angle between 1° and 10° relative to the vertical, and is for example 5°. The shielding window 19 is again arranged in a position such that the bottom 27 is inserted on the optical path between the camera 15 and the nuclear fuel assembly 1 to be characterized. The horizontal distance between the camera 15 and the assembly 1, and the orientation of the optical axis, are chosen so that the entire lateral face of the assembly 1 facing the camera 15 appears in the images taken. The operator takes at least one image of at least one lateral face of the nuclear fuel assembly 1, after stabilizing the assembly 1. The corresponding digital file is transferred by the digital line 31 to the systems 23, and the operator checks the quality of the image(s) on the screen. During a second step, the digital files of the images taken are analyzed, in order to determine the shift of the grids and the relative rotation between the caps. This operation is done either on the systems 23 that control the camera 15, or on another microcomputer. Regarding the transverse shift of the grids, the procedure is as follows. First, an image of a first lateral face of the assembly is analyzed. As shown in FIG. 5, graphical analysis software is used to draw two longitudinal lines 37 and 39 on said face. Each of the lines 37 and 39 extends from the upper grid 9a to the lower grid 9b. The line 37 is located to the left of the first lateral face of the assembly, near the leftmost two fuel rods 3. Symmetrically, the line 39 is located to the right of the first lateral face, and passes near the rightmost two rods. More precisely, the operator calibrates an upper end of the straight line 37 on a reference of the lateral face 11 of the upper grid 9a or fuel rods 3 close to the left end of the upper grid 9a. According to the drawing of the grid and the visibility of the various components, this reference is for example the middle of the space separating the peripheral fuel rod 3 and the immediately adjacent rod 3, or the inner edge of the peripheral rod, or the hollow of the grid vane . . . . Likewise, the lower end of the line 37 is calibrated on the equivalent reference near the left end of the lower grid 9. The line 37 is rectilinear and extends continuously from the upper grid 9a to the lower grid 9b. The line 39 is drawn in the same way and is calibrated on the equivalent references located near the right end of the upper and lower grids 9 of the first lateral face. One then determines graphically, for each of the intermediate grids 9, the shift of the grid 9 to the right or left of the image relative to the line 37 and relative to the line 39. To that end, for each intermediate grid, the references 40 are used, for example as more particularly shown in FIG. 6 the ends of the inner tabs separating the cells in which the peripheral fuel rod 3 and the immediately adjacent fuel rod 3 are housed. These references, when the fuel assembly 1 is not distorted, are all longitudinally aligned with the corresponding references of the upper grid 9a and the lower grid 9b. In the present method, for each intermediate grid 9, the shift relative to line 37 of the reference 40 is determined. To that end, one counts, on the image of the first lateral face, the number of pixels separating the reference 40 from the line 37. Likewise, for each intermediate grid 9, one evaluates the number of pixels separating the line 39 from the equivalent reference located near the right end of the upper and lower grids 9a, 9b of the first lateral face. The distance between the lines 37 and 39 is also measured at each of the intermediate grids 9 and possibly at the upper and lower grids 9a, 9b, in number of pixels. For each type of nuclear fuel assembly 1, the theoretical distance between the two lines 37 and 39 is known. Thus, for a nuclear fuel assembly having a grid of 17 rods by 17 rods, the distance between the lines 37 and 39 is 189 mm, in the event the references 40 of FIG. 6 are used. Knowing, at each grid 9, the number of pixels separating the lines 37 and 39 and the theoretical width between the two lines, it is possible to calculating the width corresponding to each pixel. This width per pixel data makes it possible to convert, for each grid 9, the distances of the references 40 relative to the lines 37 and 39 measured in pixels, in distances estimated in millimeters. For each grid 9, the distance measured on the first lateral face of the assembly 1 corresponds to the average between the two distances estimated above, i.e. the distance relative to the line 37 and the distance relative to the line 39. The same procedure is repeated for an image of at least one other lateral face of the assembly, adjacent to the first. For each grid 9, the shift estimate done based on the images of the two opposite lateral faces makes it possible to estimate the shift along the direction parallel to said two faces. The relative rotation between the upper 5 and lower 7 caps is estimated using the procedure illustrated in FIGS. 7 and 8. For each image, the angle between the upper cap 5 and the horizontal of the image, and the angle between the lower cap 7 and the horizontal of the image, is estimated. The twist of the fuel assembly 1 between the upper cap 5 and the lower cap 7 is obtained by calculating the difference between the two angles estimated above. As shown in FIG. 8, a horizontal line 41 is first drawn immediately under the upper cap 5. Then, a line 43 is drawn on the face 13 of the upper cap 5 visible in the image. Typically, the line 43 is drawn along the lower edge of the face 13. The angle α1 is then measured between the lines 41 and 43. Secondly, a line 45 following the horizontal of the image is drawn near the lower cap 7. A line 47 is also drawn following a geometric line characteristic of the lower cap 7. The geometric lines 43 and 47 are chosen so that, in the absence of rotation between the upper 5 and lower 7 caps, the lines 43 and 47 are parallel to each other. For example, if the geometric line 43 corresponds to the lower edge of the upper cap 5, a line can be chosen for the geometric line 47 that passes through the edges of the two feet 49 of the lower cap 7 of the fuel assembly 1. In any case, a line is chosen for the line 47 that shows up clearly enough in the image. In certain images, the upper edge of the lower cap 7 is too blurry to make it possible to draw a precise geometric line. This edge could be used if the image was very clear. The angle α2 is then measured between the horizontal 45 and the geometric line 47. The rotation between the upper cap 5 and the lower cap 7 is calculated by calculating the difference between α1 and α2. Depending on the software used, it may not be necessary to draw the horizontal lines 41 and 45; some software in fact makes it possible to obtain the angle directly from a virtual line relative to the horizontal. The evaluation method described above has multiple advantages. According to a first aspect, the evaluation method includes a step consisting of placing the assembly to be characterized in a volume of water, a step consisting of placing a camera outside the volume of water, above the free surface of that volume of water, and taking at least one image of at least one lateral face of the nuclear fuel assembly, and a step for graphical analysis of the image. Because the camera is not submerged, but rather remains outside the water, it is quick to place. Likewise, the equipment making it possible to place and orient it is considerably simplified. The time needed to take the images is short, such that the handling bridge for the nuclear fuel assemblies is only immobilized for a short time. In the case where the checks are done during an unloading and reloading operation of the core of a nuclear reactor, the stop period of the reactor is shortened. The elements making it possible to maintain and orient the camera 15 are not submerged, and therefore do not have to undergo in-depth decontamination at the end of the operation. The camera is less exposed to radiation, and its lifespan is longer than that of a submerged camera moved along the assemblies to be characterized. Using a shielding window placed on the surface of the water, and inserted in the optical path of the camera, means that the images are not disrupted by the small waves spreading on the surface of the water. According to a second aspect of the invention, independent from the first, the invention relates to a method for evaluating a quantity characteristic of the bowing of a nuclear fuel assembly, the assembly including nuclear rods, two end maintenance grids located near opposite ends of the nuclear fuel rods, and a plurality of intermediate maintenance grids distributed between the two end maintenance grids, the method comprising: a step for taking an image of at least two lateral faces of the nuclear fuel assembly; for each face, a step for materialization, on the image, of at least one substantially longitudinal reference line extending from one end grid to the other end grid; a step for determining, on the image, the transverse shift of each intermediate grid relative to the reference line. This method can be used with a camera placed outside the volume of water, but also with a camera placed underwater. It has the advantage that it is not necessary, to evaluate the transverse shift of each grid, to use a plumb line arranged near the nuclear fuel assembly or a tape measure also arranged along the assembly. The method is particularly precise when two reference lines are drawn on the image, one to the right and the other to the left, the two lines having a known spacing. The use of existing visual references on the grids or on the rods and visible in the images, so as to estimate the shift relative to the reference lines, makes it possible to increase the precision of the method. In the method, the orientation of the optical axis of the camera and the spacing between the camera and the nuclear fuel assembly are chosen so that the entire lateral face of the assembly appears in the image. This makes it possible to increase the precision of the measurement. It would be possible to take two images, for example one of the upper portion and one of the lower portion of the nuclear fuel assembly. However, this would lead to less good precision for the shift estimates. According to a third aspect, independent of the first two, the invention relates to a method for evaluating a quantity characteristic of the twist of the fuel assembly estimated from the rotation of the upper and lower caps relative to each other around the longitudinal direction, comprising a step consisting of taking, with a camera, at least one lateral image of the nuclear fuel assembly, a step consisting of materializing, in the image, a geometric line of the upper cap and a geometric line of the lower cap, the two geometric lines normally being parallel to each other when the upper and lower caps do not have rotation relative to each other around the longitudinal direction, and a step consisting of determining, in the image, the relative angle between the two geometric lines. This method is particularly convenient, because it is possible to use images taken by a camera placed above the volume of water of the pool where the assembly to be characterized is placed. Orienting the optical axis of the camera along an angle between 1° and 10° relative to the vertical and placing the camera and the fuel assembly at a distance of less than 1 m in a horizontal plane, makes the entire lateral face of the fuel assembly appear in the image. The precision of the method is thus increased. The method described above can have multiple alternatives. To increase the precision of the method, it is possible not to limit oneself to the number of images strictly necessary to evaluate the lateral distortion of the fuel assembly 1 (a view of two adjacent lateral faces) and the twist of the whole assembly (a single image). It is for example possible to take a first image of each of the lateral faces of the assembly 1, then a second image of each of the faces of the assembly in each of positions 33 and 35 so as to minimize the risk of having a same image problem for one of the lateral faces of the assembly. It is also possible to take more than two images per face. The distortion is then evaluated by averaging the set of shifts estimated from each of the views clear enough to be graphically analyzed. Likewise, the twist is estimated from the set of values of the angle of rotation evaluated from each of the analyzed images. It is possible to photograph only one of the faces of the assembly, in which case the shift of the grids can only be estimated in one direction. It is also possible to photograph three or four faces. As indicated above, it is possible, for each lateral face of the assembly, to take several partial images and not one image covering the entirety of the lateral face. This is, however, detrimental to the precision of the evaluation of the shift of the maintenance grids or of the twist. To determine the shift of the lateral grids, it is possible to perform a graphic analysis by drawing a single line on the lateral face of the assembly. In that case, the estimate of the width of a pixel is done by calculation, taking a known dimension of the assembly as a reference, for example the total width of the grid. The angles between the optical axis of the camera and the vertical, and the distances between the assembly 1 and the camera, can be different from those mentioned above. They depend on the characteristics of the lens used in the camera and the dimensions of the fuel assembly to be characterized. To evaluate the shift between the grid and the longitudinal lines drawn on the lateral face of the fuel assembly, it is possible to use visual references other than those previously cited. It is for example possible to use the extreme edge of the grid, or even references placed specially on the grid to that end. Concerning the twist measurements, it is possible to use geometric lines other than those mentioned above. Thus, for the upper cap, it is possible to materialize a line corresponding to the upper edge of the cap. For the lower cap, it is possible to materialize a line corresponding to the upper edge of the cap or the lower edge of the cap. The camera can be a digital camera rather than a film camera. The description of the invention was done relative to a fuel assembly intended for a light water reactor of the pressurized water reactor type. The described method is also applicable to pressurized water reactors of the VVER type (Vodaa Vodiannee Energititscherski Reactor, in English Water Water Energy Reactor) for which the hexagonal grid of the fuel assembly requires that at least three images be taken to estimate the shift of the grids: one of each of three adjacent lateral faces of the assembly perpendicular to the longitudinal direction. It is also applicable to boiling water reactors (BWR), and more generally to any underwater monitoring of a fuel assembly for a nuclear reactor. The method described above makes it possible to estimate the shift of the grids in a transverse plane with a precision of about 2 mm in every direction. It also makes it possible to measure the twist of the assembly between the upper and lower caps with a precision of about 2°.
041347900	claims	1. In a nuclear reactor, structure for holding a fuel assembly in place on a core support plate, comprising: a. a horizontal core support plate; b. a plurality of fuel assembly alignment pins vertically and rigidly attached to said plate; c. said assembly, vertically disposed above said plate and having a substantially flat horizontal lower end fitting; d. a plurality of fuel assembly alignment posts extending vertically downward from said end fitting toward said plate, each of said posts being in close parallel proximity to one of said pins; e. spring means connected between each of a first set of at least one but less than all of said posts and a first set of said pins in respective close proximity therewith, for downwardly biasing said first set of posts relative to said first set of pins and for horizontally biasing each of said first set of posts away from each said respective pin in a direction and with a force sufficient to cause a second set of at least one of the remainder of said posts to firmly abut a second set of at least one of the remainder of said pins whereby a frictional resistance to vertical movement is achieved between said second set of posts and said second set of pins. a. said lower end fitting is square and has one of said posts extending from each corner thereof; b. said first set of posts consists of two non-diagonal posts; and c. the horizontal bias of said springs is in a direction along the diagonals of said end fitting. a. each of said fuel assembly alignment pins is substantially cylindrical and has a recessed region in the lower portion thereof; and, b. each of said cantilever springs has a latch formed at its lower end for engaging the recessed region in said pins, and each of said springs is attached at its upper end to the upper portion of one of said posts and is oriented downward such that the spring is deflectively loaded and said latch engages said recessed region when said four posts are in proper position relative to said plate. a. said latch on each of said springs comprises an upward-facing inclined surface; and b. said recessed region on each of said pins comprises a downward-facing inclined surface. 2. The structure of claim 1 wherein: 3. The structure of claim 2 wherein said spring means comprises a cantilever spring. 4. The structure of claim 3 wherein: 5. The structure of claim 4 further comprising means for additionally biasing said latch towards said recessed region. 6. The structure of claim 4 wherein: 7. The structure of claim 6 wherein said springs are attached to the sides of said first set of posts that face away from said pins that are in close proximity thereto when said four posts are in proper position relative to said plate. 8. The structure of claim 6 wherein said springs are attached to the sides of said first set of posts that face said pins that are in close proximity thereto when said four posts are in proper position relative to said plate. 9. The structure in claim 7 wherein each of said first set of posts has a cut-out passage through which said latch protrudes beyond the surface of said post that faces said pin.
	description	This application is a continuation of U.S. patent application Ser. No. 15/291,941 filed Oct. 12, 2016 entitled Radioabsorbent Assemblies, which claims benefit of and priority to U.S. Provisional Application Ser. No. 62/240,409 filed Oct. 12, 2015 entitled Radioabsorbent Assemblies, both of which are hereby incorporated herein by reference in their entireties. The present invention pertains to various embodiments of radiation shields to protect physicians and other health care workers present during procedures requiring real-time X-ray imaging. Radiation exposure during medical procedures requiring x-rays or other ionizing radiation is a major health concern for health care workers (HCW). Procedures requiring real-time imaging, such as percutaneous procedures, involve a patient on a table with an x-ray device mounted on a C-arm, known as an x-ray gantry. The radiation is emitted from a “tube” on the bottom of the C-arm and is directed upward through the bottom of the table and the patient. The physician and other attending HCWs are typically standing next to the table attending the patient and are subject to the radiation. Most of the radiation exposure to the HCWs emanate from x-ray photons that are reflected off of the patient's bones and other structures during the procedures. More specifically, the exposure to the HCWs from their waists down result from x-rays coming directly from the tube, as well as reflecting off of the table structure and the bones of the patient. Exposure to the HCWs from their waists up result from X-rays reflecting off of the bones of the patient and structures above the patient. Most are composed of an x-ray blocking material in the form of a hard, planar shield. These are attached to the ceiling or x-ray table. Some are flexible and some are clear. They are cumbersome, do not conform to the patient's anatomy (reducing effectiveness in blocking x-rays), do not facilitate surgical access to the body, and do not provide storage for tools or lighting. Additionally, these shields are heavy and often get in the way of adequate fluoroscopic visualization of the patient or key areas of the patient that require easy access or monitoring. The HCW has to move these heavy shields manually and also conform their bodies to visualize around the impediments caused by the existing devices. This is a major cause for musculoskeletal morbidity of the HCW resulting in chronic neck, back injuries. Consequently, it is common for the HCW to sacrifice radiation protection for better visualization as well as better ergonomics by moving the current shields out of the way or positioning them in a markedly sub-optimal protection position. Finally, it is not uncommon that the HCW forgets to move the shields for adequate protection. Other x-ray blocking shields have consisted of draping x-ray absorbing material (DXAM) over the patient during procedures. Because these draped materials lay on the patient, they need to be covered with sterile material or be disposed of after every use. This is cumbersome and, as a result, most of the draped material is made as a disposable item (disposable drape and x-ray barrier inside), increasing cost and toxic waste. Moreover, the draped polymer is heavy and uncomfortable for the patient because the patient supports the weight. Additionally, because the DXAM is positioned under the sterile drape that covers the patient, it is difficult to remove during the procedure should an emergency arise that requires more x-ray visualization. Another problem in protecting personnel from scatter x-ray exposure during medical procedures is that, when the x-ray source is below the patient, the x-ray is scattered off of the patient toward the floor. As a result, the legs and feet of personnel are heavily exposed to ionizing radiation. In addition, the x-ray tube housing can often leak substantial x-radiation, often of high energy. This also increases personnel exposure to high energy ionizing radiation. Current shielding for “below-the-table” radiation consists primarily of a radiation blocking barrier (called the table skirt) that hangs from the table. Since the table height is varied during the procedure, there is often a gap between the floor and the barrier. Additionally, these table skirts are usually hung on a lever arm from the foot end of the x-ray table. They do not cover the gap between the table and the floor from the mid abdomen to the head. As a result, personnel in the room stationed at the patient's head or side receive substantial radiation exposure. This is a particular risk for physicians performing procedures that require manipulation of catheters near the patient's head (such as subclavian or jugular vein access, subclavian artery access, or transesophageal ultrasound imaging). There is thus a need for a shielding system that allows a HCW access to a patient while protecting the HCW from radiation. The invention described herein provides several embodiments directed toward providing protection both below and above the waist as well as protecting HCWs located in various positions relative to the patient. The system of the invention includes a suite of shields and accessories that provide protection and convenience to HCWs working in x-ray imaging environments. The suite includes several components that extend from, or are attachable to a sled that carries a mattress and is attachable to an x-ray table. The radiation protection suite of the invention includes table shields, which extend below the table and protect the HCWs from the waist down. The suite also includes vertical flags that extend upwards and across the body of the patient. The suite further includes body shields, which extend upward from the sled and run along the sides of the patient. Wing shields are also included, which also extend upward along the sides of the patient. The wing shields are generally higher and more rigid than the body shields, providing more protection in high dosage areas. Finally, a tray is provided that extends horizontally across the body of the patient and provides both shielding as well as a work surface for the HCWs. In one aspect of the invention a “mini-sled” is provided. In particular, the shielding drape is connected actively or passively to a sled that holds a mattress on which the patient lies during the medical procedure. The sled has a bottom that lays on the x-ray table and two perpendicular sides, typically about 1-4 inches in height. A mattress lies within the U-shaped cavity of the sled. The sled can be the entire length of the mattress or shorter length. The table shield drape is positioned over the sled passively (by gravity) or actively attached. The active attachment can be reversible (such as by a zipper or hook and eye mechanism) or non-reversible (such as with a bonding agent). In one embodiment, attachment points for arm boards, shields or other devices protrude from the sled through the tray shield and attach to such devices. In the preferred embodiment, the arm boards rotate on the attachments to the sled, such that they can be flush to the sides of the sled in the down position, parallel to the x-ray table in the neutral position, or vertical above the sled in the up position. This allows stowage when transferring a patient off of the bed (down position), support of the patients arms during the procedure (neutral position), or clearance of the x-ray gantry when a lateral view is desired (up position). In addition, in the preferred embodiment, the arm boards pivot outward from the head-ward attachment, allowing the arm to abduct. This feature is important for optimal arm positioning for radial arterial catheterization. Turning now to FIGS. 3-9, there are shown embodiments of a table shield 100 of the invention. Table shield 100 prevents an HCW from radiation that is either reflected off of the various surfaces under the x-ray table, or directly from the x-ray tube. The table shield 100 is constructed of a flexible material such as vinyl fabric, that covers the patient procedure mat and table, where the sides of the material contain radiation blocking material. The surface of the table shield may be treated to retard the growth of infective agents such as bacteria (using silver impregnation, quanternary ammonium salts, or other agents). In another embodiment, an electrical heating element between the table shield layers can be activated, causing the surface temperature of the other table shield to rise to above 161 degrees Fahrenheit, thereby potentially providing a reduction in the number of infective agents. The table shield 100 generally includes a side table shield 102 and a cross table shield 120. The side table shield 102 is positioned over the sled 10 passively (by gravity) or actively attached. The active attachment can be reversible (such as by a zipper or hook and eye mechanism) or non-reversible (such as with a bonding agent). The cross table shield 120 contains radiation blocking material and is attached beneath the table to the sled sheath 19. The cross table shield 120 extends across the width of the table at a point relative to the patient that is below the areas desired to be viewed on x-ray. The side table shield 102 may include vertical slats or stays 104 that are curved or otherwise shaped to cause the shield to curve inwardly when hanging from the table, as seen in FIG. 4. The curved stays 104 reside in pockets 106 formed between the layers of the table shield 100. FIG. 4 illustrates the construction of the table shield 100. The table shield generally includes a covering 110 that forms one continuous loop joined at seam 112, which is positioned on the bottom of the shield 100 and aligned midline on the sled 10. From the seam 112, the bottom of the covering 110, which is herein referred to as an under layer 111, extends across a foam insert or mattress M in the sled 10 and down the side of the table T. The under layer 111 continues to a lower extent at which point it folds over itself and around the inner materials of the shield 100 and becomes the outer layer 113 as it continues back up and across the table, directly under the patient. The outer layer 113 then repeats this pattern on the other side of the table T, extending down to a lower extent, where it folds under and once again becomes the under layer 111, which is routed back up until it reaches the seam 112. Within the covering 110 is an x-ray blocking material 114 and several vertical stays 104, described above, which reside in pockets 106 and can be removed for storage. The stays 104 are shaped such that, when hanging from the table T, the offset geometric center of the stays 104 cause the lower edges of the side table shield 102 to curve inward. The importance of the inward curve of the stays 104 is best seen in FIGS. 5a and 5b. In FIG. 5a, the side table shields 102 hang naturally, curving inward at the bottom due to the shape of the stays 104. Shown is an x-ray tube X aimed directly up at the table T. The radiation, indicated by arrows R, emanates from the tube X but is blocked from hitting the feet of the operator by the inwardly curving side table shields 102. In FIG. 5b, the x-ray tube X is swung to the side at an oblique angle. The closer side shield 102 is passively moved to the side by the tube X. The stays 104 maintain enough rigidity so that the shield does not fold or sag into the imaging path of the tube X. In one embodiment, attachment points for arm boards, shields or other devices protrude from the sled through the table shield and attach to such devices. In the preferred embodiment, the arm boards rotate on the attachments to the sled, such that they can be flush to the sides of the sled in the down position, parallel to the x-ray table in the neutral position, or vertical above the sled in the up position. This allows stowage when transferring a patient off of the bed (down position), support of the patients arms during the procedure (neutral position), or clearance of the x-ray gantry when a lateral view is desired (up position). In addition, in the preferred embodiment, the arm boards pivot outward from the head-ward attachment, allowing the arm to abduct. This feature is important for radial arterial catheterization. Similarly, the cross-table shield 120, which shares a similar construction to side table shield 102, may have vertical stays. No curvature is necessary for the cross-table shield 120. The shield 120 is pivotally connected to the sled sheath 19, which extends down from the sled 10. As seen in FIG. 6, the pivotal connection between the sheath 19 and the cross-table shield 120 allows the shield 120 to be moved passively by the tube X. Referring now to FIGS. 7-9 a pattern 150 and steps for making one embodiment of the table shield 100 are provided. FIG. 7 provides the pattern 150 for the outer layer with dimensions given in centimeters. The pattern 150 can be broken up into four general sections, 180, 182, 184 and 186. Section 180 is the center section that is sized to extend across the width of an x-ray table T. As will be seen, no radiation protection is necessary for section 180, as the purpose of section 180 is to provide an anchor from which the other sections hang. Sections 182 and 184 will form the sides of the table shields 102. Section 186 will form a table shield 102 that will hang down vertically from the head of the patient. All of the shield sections 182, 184 and 186 contain radioabsorbant material as well as pockets 106 for stays. The pockets 106 of sections 182 and 184 will receive shaped stays while the pockets 106 of section 186 may receive vertical or shaped stays. The locations of the pockets 106 shown in the figures are suggestions but have yielded good results. The sections 106a, b and c represent additional fabric sewn onto the vinyl covering 110 to form the pockets 106. Triangular sections 152 and 154 form corner wraps that proved protection around the side edges of the shield 100, between sections 182 and 186, and between sections 184 and 186, when the side table shields 102 are hanging down. FIG. 8 shows the addition of the radiation blocking material 114. Notably, no radiation blocking material is placed where on the horizontal surface of the resulting shield 100 as this would block the patient from being imaged. Folds are then created at the intersections between the radiation blocking material 114 and the pocket sections 106a-c according to the folding arrows 160, 162 and 164. Folding results in the configuration shown in FIG. 9. Though the internal materials are illustrated in FIG. 9, one skilled in the art will realize that they are hidden by the layer 111 that results from folding and joining the edges to form seam 112. Another aspect of the invention provides a transverse flag shield with an element that attaches the flag to the sled, the patient's mattress, the table the patient lies on, a free standing device or to a wall or ceiling mount. The attachment mechanism has one or more rigid arms connected at an angle, such that an arm(s) are horizontal and extend from the Attachment mechanism. Below one of the arms is a radiation absorbing material configured in such a way as to conform to the patient's body. Above the same or another arm is a radio-absorbing material that can be reversibly displaced. For example, an x-ray camera can be positioned such that it passively pushes away only a portion of the upper part of the shield obstructing the camera to allow the camera to be positioned for a particular x-ray view. This passively minimizes the gap in x-ray blockage. One aspect of the invention provides a flag having elements to conform to patients' body habitus and other elements to flexibly and reversibly deform to accommodate other equipment in the environment of the operating room. Even though the upper unit of the flag shield is partially displaced, the lower functional unit is allowed to remain in place on the patient continuing to block radiation scatter from the patient's body while the upper unit bends away and conforms to the image intensifier. In addition, the flag shield can mate with the tray shield to seal the gap between the shields and prevent radiation leakage between the devices. In this way, the lower element of the flag shield conforms to the patient, the upper level of the shield conforms to the x-ray equipment movement, and the flag and table shield mate to each other, providing a complete blockage of x-radiation leakage. The elements of the flag may have vertical supports throughout. The supports contain a hinges or a spring apparatus to allow the flag to bend in the vertical plane. This allows the flag to conform to other radiation absorbing material, such as a tray of the invention, allowing the flag to form a shell around the patient to continue blocking the radiation scatter. Because the flag has elastic properties, when the image intensifier moves away from an interfering position, the flag returns to its initial position, preventing gaps in the shielding where radiation may be emitted towards the HCW. Another aspect provides a flag with asymmetric curves, which contour to a patient's body habitus, in the lower functional unit to maximize radiation protection to the HCW. This novel invention contrasts with current devices, which are pushed out of the way by the image intensifier or the HCW to prevent getting in the way of the HCW being able to work with catheters etc. The present invention, conversely, allows the lower portion of the flag to stay in place without moving away and also adds the ability of the upper functional unit to continue to offer radiation protection. This combination minimizes or eliminates the interference to the HCW work flow and allows them to continue their procedure uninterrupted. The connection between the flag shield and tray shield may be mechanical interference fit, detents, magnetic attraction or other means. In another embodiment, personnel scatter radiation exposure above the table is attenuated by attachment to the flexible table shield, or to the shield that covers the x-ray table, one or more radiation shields cover various body parts, but particularly the pelvis, chest and shoulder/neck areas. In one embodiment, rigid or flexible stays within the attached body shields keep the shield in an expanded state while allowing the shield to conform to the body contour. In one embodiment, the stays allow the shield to be folded easily (such as by rolling the shield perpendicular to the stays) and in a further embodiment, magnets within the stays help maintain the shield in a folded position. Since patient and procedure needs vary, the body shields can be reversibly detachable from the table shield using a variety of mechanisms, such as a zipper or hook and eyelet mechanism. The body shields may be used instead of, or in addition to, the wing shields. Another aspect of the invention, used in conjunction, or independently of, a tray is one or more vertical shields that extend upwardly from the table to a variable height. The shields aid in preventing radiation exposure to the HCW resulting from oblique or horizontal beams coming from deflecting surfaces, such as the patient's bones, the bottom of the tray, or other equipment, or radiation traveling directly from the tube at oblique angles due to the tube being positioned at oblique angles to the patient. The invention provides shields designed for placement at various locations relative to the patient. These shields move passively when pushed by the x-ray equipment and then return to their original position when the x-ray equipment moves away. Side shields, or “wings” attached to the arm board or sled extend vertically along the side of the patient, creating a wall of a desirable height between the HCW and the patient. The wing shields can be displaced passively by x-ray equipment. In one embodiment, the wing shields are attached to the patient arm board using a spring hinge. The wing shield is pushed away from the patient when the x-ray system is rotated to a lateral position (such as 45 degrees right anterior oblique) and returns to its upright position when the x-ray equipment is moved to an anterior-posterior position. The wing may have a number of shapes depending on the room and equipment. In one embodiment, the wing shield is curved from top to bottom, contains a clear window to observe the patient, and/or has deflector pieces that interact with the x-ray system to deflect the shield when the x-ray system approaches the wing shield from the headward or footward edges. One aspect of the invention provides a tray assembly as an alternative to a DXAM drape over the patient. The tray placed over a portion of the patient forms a radiation blocking workbench used by the physician during the procedure. The tray is generally horizontal and may curve downward on the end facing the operator. The tray is positioned across the patient's body near the vascular access site so that catheters and other tools may rest on a level surface rather than on the arm or legs of the patient. The tray is composed of a radio-opaque material that blocks x-radiation. The radio-opaque material absorbs x-ray photons emitting from the patient while the patient is undergoing an x-ray imaging procedure. The curve of the tray blocks radiation emitting from the side or legs of the patient. The operator radiation exposure is therefore reduced. The tray may be connected to an attachment apparatus that connects the device to a supporting structure (such as the mini-sled or a bed or x-ray table). The attachment apparatus is fastened to the sled, mattress or table that the patient lies on or to a side-rail attached to a supporting structure. A mechanism in the attachment apparatus allows the tray to rotate around the axis of the attachment apparatus, to flip up toward the attachment apparatus, and to tilt with one edge of the tray closer or farther away from the patient. The attachment mechanism itself can travel in a vertical up and down motion to move the tray above the patient and to lower the tray to the patient's body. This allows the tray to be positioned across and just above the patient easily, which allows the device to accommodate patients of different body shapes. It also allows for the tray to be removed up and out of the way quickly in case of emergency, and to allow for ease of patient transfer onto and off of the mattress. Another aspect of the invention provides a tray that is of a laminar construction with one or more layers of radio-opaque material and one or more layers of material with minimal x-ray absorption (such as carbon fiber). In another embodiment the tray is composed a clear x-ray absorbing material such as a clear plastic polymer with a high content of an x-ray absorbing material (such as boron, beryllium, barium). In another embodiment, the tray has attachments that do not absorb x-rays, such as a piece that connects to the attachment apparatus and the tray. In another embodiment, the tray has a forward edge that curves upward to more comfortably rest against the patients belly to further block radiation from the body. In addition, this edge can mate with the flag attachment, creating a radiation blocking seal between the two devices. The connection between the workbench shield and the flag shield can be passive or active (such as with magnets or using mechanical means). In another embodiment, the flag shield and the workbench shield can be permanently fixed and function at a single shield. In another embodiment, the tray is attached to a free standing device. One embodiment of the tray has cut outs to facilitate access to parts of the body, such as the femoral artery and vein, while minimizing x-ray transmission. In addition, radio-opaque flaps or barriers attached to the access sites can be opened and closed to allow access when the x-ray is off. In addition, ridges may be used near the access site to block x-ray photons that are directed at the operator's position. One aspect of the invention is a tray that has attachment devices to hold sterile surgical instruments, imaging devices, or supplies. These attachments allow the operator to have free hands for other tasks, such a puncturing an artery while the attachment holds an ultrasound probe to visualize the artery through the skin. In one embodiment, the attachments are connected to the tray underneath the sterile barrier or surgical drape and in another embodiment, the instruments are attached over a sterile barrier or surgical drape. These connections between the attachment and the tray may be mechanical (such as a clip under the drape) or magnetic (with the attachment containing a magnetic component that mates with a magnetic component within the tray under the drape). In one aspect of the invention, the tray also has indentations that provide storage areas for surgical devices and supplies, such as needles, guidewire attachments, gauze, suture, and sterile fluids. In addition, the tray has spring clips and other attachment devices to hold catheters and wires emanating from the body. This stabilizes the positions of the catheters or wires and frees-up the operator's hands. In one or more embodiments, a light may be attached to the tray illuminates the surgical area. The light may be controlled by a switch on the tray or by a remote device (such as a wireless device). The light can provide general lighting to the procedure area or a focused light on a particular area of interest. The lights are often dimmed in the x-ray imaging rooms and white light can interfere with the operators viewing of procedure monitors. In one embodiment, lights of different colors are used to provide lighting that optimizes the viewing of x-ray and vital sign monitors. In another embodiment, the tray, which is positioned over the body, is used to assist in a procedure by placing force on the body. During some types of surgical procedures, pressure needs to be applied to the body, for example, to stop bleeding or compress a hematoma. This can be challenging when the bleeding occurs next to the surgical site. The operator needs to be manipulating catheters or surgical devices and cannot press on the body at the same time. An assistant's hands in the field obstruct the operator's hands. A tray is provided with a balloon or active device under the tray can be inflated or activated to produce pressure on the body. When a balloon is employed, the balloon can be inflated by an electric pump, a manual pump operated by an assistant outside the sterile field, a manual pump pumped through the drape by the operator. Alternatively, a simple broad foot can be extended mechanically (such as a ratchet mechanism) down from the lower surface or side of the tray and mechanically locked into place. Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these 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. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements. The system of the invention includes a suite of shields and accessories that provide protection and convenience to HCWs working in x-ray imaging environments. The suite generally includes several components that extend from, or are attachable to a sled (body length) or mini-sled (torso length) that carries a mattress and is attachable to an x-ray table. The sled does not have radiation protection properties but acts as a foundation for the radiation protection suite, though all of the components of the suite are not necessarily attached to the sled. The radiation protection suite of the invention includes table shields, which extend below the table and protect the HCWs from the waist down. The suite also includes vertical flags that extend upwards and across the body of the patient. The suite further includes body shields, which extend upward from the sled and run along the sides of the patient. Wing shields are also included, which also extend upward along the sides of the patient. The wing shields are generally higher and more rigid than the body shields, providing more protection in high dosage areas. Finally, a tray is provided that extends horizontally across the body of the patient and provides both shielding as well as a work surface for the HCWs. The various components of the system are now detailed, with reference being made to the Figures. Referring now to FIGS. 1 and 2, an embodiment of a “mini-sled” 10 of the invention is provided. Generally, the sled 10 is a shallow, U-shaped frame that holds a mattress M on which the patient lies during the medical procedure. The sled 10 has a bottom 12 that lays on the x-ray table and two perpendicular sides 14, typically about 1-4 inches in height. The sled 10 can be the entire length of the mattress or shorter length. A pair of arm boards 16 are connected to the perpendicular sides 14 of the sled 10 with posts 18. A sheath 19 extends down under the sled 10 and is sized and shaped to receive a standard x-ray table T for securement thereto. Turning now to FIGS. 10-12, there is shown a patient P shrouded by a wing 200 on the side and transversely by a flag 210. Transverse shield or flag 210 includes an upper unit 212, a lower unit 214 and a lateral unit 216. The upper functional unit 212 has a degree of internal flexibility/elasticity and has a horizontal articulation 213 with the lower functional unit 214, as best shown in FIG. 12 in which arrows 220 and 222 show the articulating movement of upper unit 212 relative to lower unit 214. The flag 210 also has vertical articulation 215 with the lateral functional unit 216 as indicated by arrow 224. This articulation 213, 215 allows the upper unit 212 to freely move on a horizontal axis as well as have some elastic stretch when the equipment in the room such as an image intensifier pushes it to enable optimal imaging conditions. This the lower functional unit 214 is thus able to remain in place on the patient continuing to block radiation scatter from the patient's body while the upper unit 212 bends away and conforms to an image intensifier, for example. In addition, the flag 210 may have vertical supports throughout. The supports may contain a hinge or spring apparatus to allow the flag to bend in the vertical plane so that the flag 210 is able to conform to other radiation absorbing material, such as the wing 200, allowing the flag 210 continues to form a shell around the patient to continue blocking the radiation scatter. Because the flag 210 has elastic properties, when the image intensifier moves away from an interfering position, the flag 210 returns to its initial position, preventing gaps in the shielding where radiation may be emitted towards the HCW. As best seen in FIG. 11, the lower unit 214 includes bottom curves 230 that contour to a patient's body habitus in order to maximize radiation protection to the HCW. Similarly, the bottom of the lateral unit 216 includes a cutout 232 to contour to a patient's forearm. The upper, lower and lateral units 212, 214, 216 may be composed of multiple vertical strips of overlapping material to provide greater flexibility with positioning the barrier around objects. Additionally, the radioabsorbent barriers on the top or bottom of the flag can be composed of multiple overlapping material, such that an object displacing one piece of material would not displace the adjacent section. This would improve radiation protection. The flag units 212, 214, 216 can be constructed of radioabsorbent fully or partially transparent material or could have a radioabsorbent clear window (not shown) in portions to allow for optimal patient visualization. The flag 210 also can hold a patient instruction and or entertainment window where a screen could be placed. The flag 210 may be attached to the attachment mechanism 412 along with the tray 420. Alternatively, the flag 210 may be anchored to the mattress or patient table, to a separate free-standing mechanism, or to a wall or ceiling mount, with features that allow for rapid stowage. Like the tray 420, the flag 210 preferably has at least two, and more preferably three or more degrees of freedom. The wing 200, shown in FIG. 10, may be rigid or flexible and is a radioabsorbent wall that extends vertically along the side of the patient, and is height-adjustable to provide a desired level of protection between the HCW and the patient. Wing shields 200 are designed for placement at various locations relative to the patient. The wing shields 200 may be attached to the arm board or sled, and extend vertically along the side of the patient, creating a wall of a desirable height between the HCW and the patient. The wing shields can be displaced passively by x-ray equipment. In one embodiment, the wing shields are attached to the patient arm board using a spring hinge. The wing shield is pushed away from the patient when the x-ray system is rotated to a lateral position (such as 45 degrees right anterior oblique) and returns to its upright position when the x-ray equipment is moved to an anterior-posterior position. The wing may have a number of shapes depending on the room and equipment. In one embodiment, the wing shield is curved from top to bottom, contains a clear window to observe the patient, and/or has deflector pieces that deflect the shield when the x-ray system approaches the wing shield from the headward or footward edges. Referring now to FIG. 13 personnel scatter radiation exposure above the table is attenuated by attaching one or more flexible body shields 300 to the sled 10. to the flexible table shield, or to the shield that covers the x-ray table, one or more radiation shields cover various body parts, but particularly the pelvis, chest and shoulder/neck areas. In FIG. 13, there are shown three body shields 300—a shoulder and head shield 302, a chest and abdomen shield 310, and a pelvic and leg shield 320. The shoulder and head shield 302 extends from an edge of the sled 10 to an area approximating the chin of the patient where it is joined by the chest and abdomen shield 310. One or both of the shields 302 and 310 join to form a neck cutout 312, which provides easy access to the neck of the patient P. The chest and abdomen shield 310 extends to about waist level where it is joined by the pelvic and leg shield 320. The shield 320 has femoral artery cutouts 202 to align with the cutouts of the tray, if present, providing access to the femoral arteries. Some or all of the shields 300 may have horizontally aligned stays 330 that are constructed and arranged, with magnets for example, to maintain a stacked configuration, if desired, or to maintain a folded configuration, if desired. Thus, the height of the body shields 300 can be adjusted by simply folding the shields over at a desired location between stays 330. In one embodiment, rigid or flexible stays 330 keep the shield in an expanded state while allowing the shield to conform to the body contour. Since patient and procedure needs vary, the body shields can be reversibly detachable from the table shield using a variety of mechanisms, such as a zipper or hook and eyelet mechanism. FIGS. 14-20 show a tray 420 of the invention. The tray 420 is a generally horizontal tray that, in use, is positioned above the patient and provides a working surface for the physician while shielding the physician from radiation. The tray 420 may have cutouts 422 for accessing the femoral arteries of the patient. This obviates the need to move the tray when using a femoral navigation approach. The tray 420 may also include various features for holding tools securely, providing convenient access for the physician. For example, the tray 420 of FIG. 14 includes a well 424, which is a simple recess for securely containing tools. FIG. 15 shows an embodiment of tray 420 having several tool accommodations. In addition to providing two wells 424, one of which (424a) is used to hold needles and angioplasty wire knobs, and the other of which (424b) is used to hold gauze in a sterile saline solution, the tray 420 of FIG. 15 includes a light 426 for illuminating the tools, reducing eyestrain for the HCW and improving safety. Also shown are one or more clips 428, provided for attaching the catheters or wires that may be attached or inserted into the patient. The tray 420 is positioned over the patient with an attachment mechanism 412, such as a swing arm or boom. The attachment mechanism 412 provides at least two, preferably three or four degrees of freedom to the tray position, including adjustable height above the patient, horizontal rotation, horizontal translation, and vertical rotation or tilt. FIGS. 16a-d depict the adjustability provided by the attachment mechanism 412. FIG. 16a shows the relative positions of the tray 420, the operator O, and the patient P. The tray 420 is shown with femoral cutouts 422. Also shown is an arrows 430, indicating the ability of the tray 420 to be translated horizontally in the direction of the arrows 430. FIG. 16b shows the tray 420 rotated horizontally around a mast 414 of the attachment mechanism. Arrow 432 is provided to show the directions of rotation made available by the rotational connection of the tray 420 to the mast 414. FIG. 16c provides a side elevation of the tray 420 in a horizontal orientation. FIG. 16d shows the tray 420 being tilted in the direction of arrow 434. FIG. 17 shows an end elevation of the tray 420 placed over a patient P lying on a mattress M. An operator O is attending to the patient P. Three arrows, 432, 434, and 436 are shown to indicate the degrees of freedom for horizontal rotation, tilt, and vertical adjustment, respectively. FIG. 18 is a side elevation of a tray 420 showing that the tray 420 can be described as having two shielding components, a belly shield 421 and a side shield 423. Referring back to FIG. 17, the benefits of the belly shield 421 and side shield 423 are highlighted using radiation arrows R. The radiation arrows R emanate from the patient P but are blocked and absorbed both above, and to the side of, the patient P, thereby protecting operator O. It is not uncommon for the need to arise to put gentle pressure on the patient for various reasons. Pressing down on the patient during imaging necessarily exposes the HCW to even higher doses of radiation due to close proximity to the patient and also positioning him or herself above the patient to apply the pressure. FIGS. 19a and 19b show an embodiment of a tray 420 with a compression device 440 in the form of a balloon. The balloon 440 in FIG. 19a is shown as deflated and thus not applying pressure to the patient P. The balloon 440 in FIG. 19b is shown as inflated and thus applying pressure to the patient P. The rigidity of the tray 420 and the ability of the attachment mechanism to lock the position of the tray in place, provides a stationary force against which the balloon can act to apply pressure to the patient. FIG. 20 shows a plan view of a tray 420 that has adjustable sides 442 and 444. The sides 442 and 444 have a sliding connection to the rest of the tray 420 such that the width of the belly shield 421 may be adjusted to accommodate different patient sizes. The adjustability of the sides 442 and 444 is depicted by arrows 446 and 448, respectively. An experiment was conducted to test the efficacy of the system of the present invention. A standard anthropomorphic X-ray phantom was acquired from the US Department of Energy and placed on the table of a Toshiba® Infinix® C-arm radiographic system. The settings were as follows: 15 fr/sec fluoroscopy 70 keV tube voltage SID 100 cm 103-106 mA current Scatter radiation was measured, using a Fluke® Biomedical X2 Sensor System, at various locations, and at various heights, throughout the room, according to the map provided in FIG. 21. FIG. 21 shows that 6 locations were identified as corresponding to locations were HCWs would typically stand as follows: Position 1—Imaging Cardiologist Position 2—Right Heart Catheterization Cardiologist Position 3—Heart Biopsy Cardiologist Position 4—Femoral or Radial Access Angiography Cardiologist Position 5—Assistant Position 6—Nurse The graphs shown in FIGS. 22-27 each correspond to one of the positions 1-6 of FIG. 21. Measurements were taken at several heights, beginning at 1 cm from the floor and extending up to 20 cm at 1 cm intervals. Data was gathered for both a table using standard shielding as well as using the shielding of the present invention (represented in the table as “Maximal”). The results show a dramatic decrease in exposure at all six of the positions measured. Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.
	abstract	A nuclear fuel assembly having lateral support provided by a bimetallic spring that extends from a side of the fuel assembly under certain core conditions to pressure against an adjacent component and withdraws under other core conditions, such as shutdown, to enable the nuclear fuel assembly to be aligned or withdrawn from the core and repositioned.
	description	The present invention relates generally to a detector assembly, and, more particularly to a two piece collimator assembly with improved design flexibility. Computed tomography has been utilized for a wide variety of imaging applications. One such category of applications is comprised of medical imaging. Although it is known that computed tomography may take on a wide variety of configurations within the medical industry, it commonly is based on the transmission of low energy rays through a body structure. These low energy rays are subsequently received and processed to formulate an image, often three-dimensional, of the body structure that can by analyzed by clinicians as a diagnostic aid. The reception of the low energy rays, such as gamma rays or x-rays, is often accomplished through the use of a device referred to as a detector assembly. The detector assembly is typically comprised of a plurality of structures working in concert to receive and process the incoming energy rays after they have passed through the body structure. The detector assembly utilizes scintillator to absorb the photons and convert their energy into visible light. This allows the low energy rays received by the scintillator detector to be converted into useful information. Scintillator elements may come in a wide variety of forms and may be adapted to receive a wide variety of incoming rays. The light produced by the scintillator element is commonly processed by way of a device such as a light sensitive photodiode, which converts the light from the scintillator element into an electronic signal. In this fashion, the information from the scintillator detector can be easily transferred, converted, and processed by electronic modules to facilitate viewing and manipulation by clinicians. Imaging assemblies additionally include an element referred to as a collimator. A collimator is an element that commonly incorporates two fundamental functions. The collimator is used to reduce x-ray scatter as the x-rays approach the scintillator element. Scattered photons can cause noise and reduce resolution causing image artifacts. In addition, the collimator is commonly used as a shielding device for shielding the edges of the individual scintillator cells. This is necessary to prevent, X-rays from impinging on the edges of the scintillators causing non linearities and image artifacts, x-rays from damaging the reflector between scintillator elements, X-rays being transmitted through the gap between scintillator elements and impinging on the photo diode causing noise or X-rays being transmitted through the gap between scintillator elements and impinging on electronics located behind the detector causing damage to these sensitive electronic components. Thus present collimator designs commonly attempt to balance shielding and scatter reducing properties. Unfortunately, the design characteristics that make a collimator optimal for shielding the scintillator edges are not always compatible with the characteristics that make a collimator optimal for reducing x-ray scatter. Present collimator formation, therefore, often relies on a functional compromise between these two competing characteristics. Even when the physical characteristics necessary to perform each of these functions is not directly incompatible, their importance may vary by function. High manufacturing and assembly tolerances are often important for proper shielding functionality. These high tolerances, however, are not commonly required to reduce x-ray scatter. Therefore, by requiring the collimator assembly to be manufactured with tolerances suitable for shielding, the cost of the entire assembly is often increased. Approaches to resolving this balance of characteristics has lead some to modify other aspects of the detector assembly to accommodate existing collimator designs. These approaches include leaving large gaps between adjoining scintillator elements; use of x-ray absorbing layers between scintillator cells; and the use of organic reflector composites. In these approaches, however, the distance between scintillator elements tends to be large. This is often incompatible with the small cell and small gap requirements for the current generation of multi-slice CT systems. In addition, many existing systems do a poor job of attenuating scatter x-rays within the scintillator elements or to prevent X-rays from crossing over from one scintillator cell to an adjoining cell. Thus considerable room for improvement of existing designs and design approaches exists. It would, however, be highly desirable to have a detector assembly that could be simultaneously optimized for reducing scattering x-rays in addition to shielding scintillator elements. Similarly, it would be highly desirable to have a detector assembly suitable for use in modern high density imaging applications. An imaging detector assembly is provided comprising a detector array and a scintillator assembly positioned in communication with the detector array. The imaging detector assembly further includes a first collimator array optimized to shield the scintillator assembly. The first collimator array is mounted to the scintillator assembly. The imaging detector assembly further includes a second collimator array optimized to reduce x-ray scatter. The second collimator array is mounted independently from the first collimator array. Other features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. Referring now to FIGS. 1 and 2, which are illustrations of a computed tomography (CT) imaging system 10 for use with the detector assembly 18 of the present invention. Although a particular CT imaging system 10 has been illustrated, it should be understood that the detector assembly 18 of the present invention could be utilized in a wide variety of imaging systems. The CT imaging system 10 includes a scanner assembly 12 illustrated as a gantry assembly. The scanner assembly 12 includes an x-ray source 14 for projecting a beam of x-rays 16 toward a detector assembly 18 positioned opposite the x-ray source 14. The detector assembly 18 includes a plurality of detector elements 20, referred to as a detector array, which combine to sense the projected x-rays 16 that pass through an object, such as a medical patient 22. Each of the plurality of detector elements 20 produces an electrical signal that represents the intensity of an impinging x-ray beam and hence the attenuation of the beam 16 as it passes through the object of patient 22. Commonly, during a scan to acquire x-ray projection data, the scanner assembly 12 is rotated about the center of rotation 24. In one embodiment, illustrated in FIG. 2, detector elements 20 are arranged in one row such that projection data corresponding to a single image slice is acquired during a scan. In other embodiments, the detector elements 20 can be arranged in a plurality of parallel rows, such that projection data corresponding to a plurality of parallel slices can be acquired simultaneously during a scan. The rotation of the scanner assembly 12 and the operation of the x-ray source 14 are preferably governed by a control mechanism 26. The control mechanism 26 preferably includes an x-ray controller 29 that provides power and timing signals to the x-ray source 14 and a scanner motor controller 30 that controls the rotational speed and position of the scanner assembly 12. A data acquisition system (DAS) 32 in control mechanism 26 samples analog data from the detector elements 20, commonly a photodetector array, and converts the data to digital signals for subsequent processing. An image reconstructor 34 receives sampled and digitized x-ray data from DAS 32 and performs high speed image reconstruction. The reconstructed image is applied as an input to a computer 36 which stores the image in a mass storage device 38. The computer 36 also can receive commands and scanning parameters from an operator via console 40 that has a keyboard or similar input device. An associated display 42 allows the operator to observe the reconstructed image and other data from the computer 36. The operator supplied commands and parameters are used by computer 36 to provide control signals and information to the DAS 32, x-ray controller 29 , and scanner motor controller 30. In addition, the computer 36 operates a table motor controller 44 which controls a motorized table 46 to position patient 22 within the scanner assembly 12. Particularly, the table 46 moves portions of the patient 22 through the scanner opening 48. Each of the detector elements 20 of the detector assembly 18 produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. As illustrated in FIG. 3, the detector assembly 18 includes a scintillator assembly 50 including plurality of scintillator elements 52 each of which is associated with one of the detector elements 20. Scintillator elements 52 are known devices that, when struck by x-rays, convert at least a portion of the energy of the x-rays 16 into light 54 that can be detected by the detector elements 20, commonly photodetectors. The photodetectors 20, such as photodiodes or photocells, are commonly optically coupled, using an optical coupler 56, to the backs of the scintillator elements 52 and are utilized to generate electrical signals representative of the light output from the scintillator elements 50. The attenuation measurements from all detector elements 20 in the detector assembly 18 are acquired separately to produce a transmission profile. It should be understood that FIG. 3 illustrates a cross-section of the detector assembly 18 and is intended to be representative of both linear and multi-dimensional arrays of detectors. The present invention provides a unique approach to collimation of the incoming x-rays 16 by including a collimator assembly 60 comprised of a first collimator array 62 and a second collimator array 64. The use of such a two piece collimator assembly 60 allows each individual collimator array 62,64 to be specifically tailored and optimized for a single function rather than requiring a single collimator to balance differing performance requirements. To this end, the present invention includes a first collimator array 62 optimized to shield the scintillator array 50. Specifically, the first collimator array 62 is optimized to shield the scintillator element edges 66. Various methods of optimizing a collimator assembly to shield the scintillator array 50 would be obvious. The first collimator array 62 may be formed from a material highly suitable for shielding such as a high-Z, high atomic number material. The first collimator array 62 may have an increased first collimator width 68 (see FIG. 4) such as a width greater than said second collimator width 74. The first collimator height 70 is preferably minimal such that the first collimator array 62 retains a low profile and has little effect on x-ray scatter. The first collimator array 62 can be formed in a variety of fashions and materials. It can be formed from composite materials. It may be formed from cast materials. In one embodiment, it is contemplated that the first collimator array 62 can be formed with reduced manufacturing tolerances. In this fashions, the increased cost and manufacturing difficulty can be limited to the first collimator array 62 where such tolerances are beneficial. The first collimator array 62 may further be designed to optimize quantum detection efficiency QDE by providing minimal x-ray blockage (see FIG. 3). It is contemplated that the first collimator array 62 can be formed directly onto the scintillator array 50 to improve accuracy of placement. The first collimator array 62 can be cast directly onto the scintillator array 50 with a wide variety of materials such as loaded epoxies, lead, lead alloys, or composites. In other embodiments it is contemplated that the first collimator array 62 can be formed directly onto the scintillator array 50 (see FIG. 5) using a grid. This grid may include an etched grid, a grid formed by plunge electron discharge machining (EDM'ing), or a cross-wire grid. The low aspect ratio and direct fabrication allow a precise location of the first collimator array 62 in relation the scintillator elements 52 and reflector gaps 58 (Not shown in the figure). This allows less material to be used in the first collimator array 62, which in turn reduces x-ray blockage and increases QDE or lowers the patient dose. The present invention further includes a second collimator array 64 optimized to reduce x-ray scatter. It is contemplated that the second collimator array 64 be designed to have only minimal effect on shielding. In this fashion the second collimator array 64 can be directly tailored to the task of x-ray scatter reduction without impacting shielding. The second collimator array 64 is preferably manufactured and mounted independently from the first collimator array 62. This allows the manufacturing, materials, and assembly methods to remain independent. Although a mounting gap 71 between the first collimator array 62 and the second collimator array 64 is not required, one embodiment contemplates a gap of approximately one millimeter. The second collimator array 64 can be optimized to reduce scatter in a variety of fashions. A high aspect ratio, a second collimator height 72 maximized and a second collimator width 74 minimized (less than 200 microns), allows the second collimator array 64 to reduce scatter with minimal effect on shielding. The second collimator array 64 can be manufactured in a variety of fashions to optimize for reduction in scatter. The second collimator array 64 may be cast, formed from composites, use traditional plate technology, or adopt any other manufacturing technology. Since the second collimator array 64 is optimized solely for scatter reduction, the second collimator array 64 can be manufactured with much greater tolerances than are typically acceptable for shielding purposes. This allows a reduction in manufacturing time, complexity, and cost for the overall collimator assembly 60. In addition, since the second collimator array 64 can be manufactured without concern for engagement of the first collimator array 62, it can be designed to improve detector QDE and improve cell low signal performance. Finally, an added advantage of the present detector assembly 18 is that the second collimator array 64, due to independent mounting, can be easily removed such that the detector assembly can be installed into fourth generation imaging systems wherein x-rays 16 are received from a variety of angles (see FIG. 6). The present invention not only provides an improved approach and design for detector assemblies 18 in regards to improved collimation. The present design also allows for the use of higher performing scintillator assemblies 50. Since the first collimator array 62 can be directly tailored to shielding and can be mounted or formed directly onto the scintillator array 50, the amount of X-ray cross-talk within the individual scintillator elements 52 can be significantly reduced. If the scintillator elements 52 are separated only by thin film reflectors 76 then the x-ray shielded portion 77 of the scintillator element becomes an X-ray attenuator to shield X-rays 16 that are scattered in one scintillator cell 52 from crossing over from one scintillator cell 52 to an adjoining scintillator cell. By varying the first collimator width 68 of the first collimator array, the amount of X-ray shielding can be tailored to optimize the performance of the detector 10 or varying the amount of X-ray shielding from cell to cell. A reduction in X-ray cross talk will improve the spatial resolution of the CT system. By removing the necessity for x-ray blocking gaps or layers, the scintillator elements 52 can be positioned closer to each other and thereby improve resolution of the detector assembly 18. While particular embodiments of the invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.
	claims	1. A panel for attenuating radiation, the panel comprising: a layered structure comprising a laminate secured between layers of sheet metal, wherein said laminate comprises a flexible layer comprising polymeric material and metal, wherein said metal is for attenuating radiation, and a layer of foam secured to said layer of polymeric material containing metal, wherein said flexible layer is more flexible than said layer of foam. 2. The panel according to claim 1, wherein said layers of metal comprises a sheet of steel that is bonded to said layer of foam, so that said sheet of steel and said layer of foam are cooperative for at least partially supporting said layer of silicone containing metal. 3. The panel according to claim 1, wherein said polymeric material comprises silicone and said metal comprises at least one metal selected from the group consisting of tungsten and iron, and said silicone at least partially contains said metal. 4. The panel according to claim 3, wherein said metal is impregnated in said silicone. 5. The panel according to claim 1, wherein:said layer of foam is a first layer of foam;said laminate further comprises a second layer of foam;said flexible layer includes opposite first and second sides;said first side of said flexible layer is bonded to said first layer of foam; andsaid second side of said flexible layer is bonded to said second layer of foam. 6. The panel according to claim 5, wherein:said layers of metal comprises first and second sheets of steel;said first sheet of steel is bonded to said first layer of foam, so that said first sheet of steel and said first layer of foam are cooperative for at least partially supporting said layer of silicone containing metal; andsaid second sheet of steel is bonded to said second layer of foam, so that said second sheet of steel and said second layer of foam are cooperative for at least partially supporting said layer of silicone containing metal. 7. The panel according to claim 1, comprising a frame mounted to said layered structure for securing said layered structure, wherein:said layered structure comprises a top compound edge, a bottom compound edge, and side compound edges;said frame includes frame members, each of said frame members defines an elongate groove, and said grooves of said frame members are respectively in receipt of said top, bottom, and side compound edges of said layered structure; andsaid frame members are respectively secured to one another, so that said frame members cooperate to extend around said layered structure. 8. The panel according to claim 7, further comprising:a plurality of legs pivotably mounted to said frame for supporting said frame and said layered structure; anda plurality of wheels respectively mounted to said legs for supporting said legs, said frame and said layered structure, wherein said wheels are adapted for allowing the panel to be rolled across a surface.
	summary
	summary
045267421	description	DESCRIPTION OF PREFERRED EMBODIMENTS The nuclear reactor plant shown in FIGS. 1 and 2 comprises a pool 1 which is a substantially circular-cylindrical, hollow body made of prestressed concrete and dimensioned for an internal pressure of at least 15 bar, for example 70 bar. The pool 1 has a metallic lining 1' with an adjacent cooling tube system, embedded in the concrete of the pool, with a large number of cooling tubes 2. The pool 1, which is provided with a pool cover 1", encloses a pool space 3 which for the major part is filled with a neutron-absorbing liquid, in the form of borated water, and which houses a gas cushion 4, an inner tank 5, a reactor vessel 6 surrounded by the walls of the tank 5, heat exchange means in the form of three U-shaped steam generator elements 7, and a device 8 for the storage of spent fuel. The cooling system provided by the tubes 2 embedded in the concrete is intended to protect the pool walls from harmful heating. In addition, a cooler 128 is mounted in the pool and serves to cool the pool liquid to the desired temperature. The cooler 128 is arranged to be traversed by a cooling fluid, for example water, and is arranged with a predominant part of its total cooling surface in contact with the pool liquid. The cooling fluid is supplied to, and withdrawn from, the cooler via an inlet pipe 130 and a return pipe 129, respectively, these pipes being connected to a heat exchanger 131 located outside the pool. The reactor vessel 6 comprises a lower portion 6', an intermediate portion 6" and an upper portion 6"', which portions are joined together by flanged connection means. Within the lower portion 6' is a reactor core 9 with a plurality of vertical fuel assemblies 9' and vertical cooling channels. The core 9 is surrounded by a cylindrical casing 10 which is open at both ends. The casing 10 is provided at its upper end with an outwardly-directed flange which is positioned in a horizontal plane and the outer edge of which is attached to the upper edge of the lower portion 6' of the reactor vessel 6. This flange on the casing 10 is provided with a plurality of through-going circumferentially spaced-apart, circular holes, each of which is provided with an annular, elastically resilient sealing device 11. A tube 12, arranged coaxially with respect to the reactor vessel portion 6", has at its lower end a plurality of branches 13, each of which passes through a respective one of the sealing devices 11 into the space 14 between the lower reactor vessel portion 6' and the casing 10. The upper end of the tube 12 sealingly surrounds the lower, open end of a substantially hollow-cylindrical body 15, which is closed at its upper end. The body 15 surrounds a smaller, substantially hollow-cylindrical body 16, there being an annular space 15' between the bodies 15 and 16. The upper end of the body 16 is hydraulically connected to the inlet side of a circulating pump 17, the outlet side of which is hydraulically connected to the annular space 15'. The pump 17 is provided with a shunt circuit by arranging a hydraulic connection between the hollow cylinders 15 and 16 in the form of a shunt valve 34. During normal operation of the reactor, pump 17 provides a substantially constant flow of reactor cooling water through the core. The lower, otherwise closed, end of the body 16 is provided with three flexible inlet nozzles 18. The nozzles 18 pass in a pressure-tight manner through the cylindrical wall of the surrounding body 15 and are each detachably connected to a nozzle 18' at the wall of the upper reactor vessel portion 6"'. Each of the nozzles 18', in its turn, is flanged to an outlet nozzle 18" belonging to the primary circuit of a respective one of the three steam generator elements 7. Each of the steam generator elements 7 has, on its secondary side, an outlet conduit 34' for steam and a return conduit 35' for feed water. The hollow-cylindrical body 16 thus constitutes an inlet conduit which connects a heat exchanger, formed by the steam generator elements 7, with an inlet chamber of the reactor vessel 6, which inlet chamber comprises the space 15' between the bodies 15 and 16, the space 12' in the tube 12 and the space 14. The reactor vessel has an outlet chamber 19, which comprises the space defined between the tube 12, including the branches 13, and the reactor vessel portion 6" and the space which is defined between the upper reactor vessel portion 6"' and the hollow-cylindrical body 15. The upper reactor vessel portion 6"' has three outlet nozzles 29, each of which is connected by a respective outlet conduit 30 to an inlet opening of a respective one of the steam generator elements 7. The body 15 has an upper hollow-cylindrical portion 15", which passes through a central opening formed in the concrete cover 1" of the pool. The upper portion 15" is externally sealed in relation to the cover 1" by means of a bellows-shaped metallic body 20, which is welded between the upper portion 15" and a metallic ring cast into the concrete cover 1". A plurality of legs 21 welded to the portion 15" support a pump motor 22, which is connected to the pump 17 by a shaft which passes through a shaft seal 23 intended to seal against the pressure difference between the reactor pressure and atmospheric pressure. At the top of the pool 1 there is a gas cushion 4 in the form of trapped steam. The gas cushion 4 communicates with a steam boiler 24 which is provided with a pressure regulator (not shown). The interface between the gas cushion 4 and the pool liquid is designated by the numeral 25, and the interface between the gas cushion 4 and the water present in the reactor vessel 6 is designated by the numeral 26. As illustrated in FIG. 1 and mentioned previously, the portion of the reactor filled with cooling water has a vertical extension which constitutes a predominant part of the vertical extension of the reactor vessel 6. Annuli 27 and 28 of honeycomb material with thin vertical channels are arranged radially outside and radially inside the wall of the vessel portion 6"', respectively, these annuli extending along a vertical distance within which the interfaces 25, 26 may move. Each of the annuli 27 and 28 serves as a "gradient lock", that is, a means for obtaining a stable vertical temperature gradient in a vertical connecting member between a liquid disposed in one region and a relatively hotter fluid such as stem disposed in a higher region. As an alternative to such honeycomb material, the annuli 27, 28 may comprise a plurality of concentric hollow cylinders. In normal reactor operation, the difference in level between the interfaces 25 and 26 may be zero, or at any rate smaller than 30%, and preferably smaller than 20%, of the distance between the upper open end 28' of the reactor vessel portion 6"' and the upper edge of the reactor core; and the interface 25 may be higher than the interface 26, or inversely. The lower portion 14 of the space 12' is in hydraulic communication with a vertical inlet drum 33 via a plurality of nozzles 31 arranged at the bottom of the reactor portion 6' and a tube 32 connected to the nozzles 31. The drum 33 has an inlet opening 33' for pool liquid at its lower end. The inlet drum 33 is filled with honeycomb material and thus contains a gradient lock which, in principle, consists of a large number of thin parallel-connected, vertical tubes. Alternatively, a gas cushion may be used as the gradient lock. In the event of a shutdown of the reactor plant, for example an emergency shutdown, borated water from the pool flows in through the opening 33', and consequently this opening is referred to as the "lower shutdown opening" in the present specification. In a corresponding manner, the opening 28' at the upper end of both the reactor vessel and the annulus 28 is referred to as the "upper shutdown opening". The reactor vessel 6, the steam generator elements 7 and the intermediate connecting conduits are each provided externally with a heat-insulating layer 60, for example in the form of a water-filled metallic tissue, so that the mean temperature of the pool liquid during normal reactor operation is at least 50.degree. C., preferably at least 100.degree. C., lower than the temperature of the reactor cooling water flowing from the outlet chamber 19 of the reactor vessel. This means that the density of the reactor cooling water is considerably lower than the density of the pool liquid. Thus, the pressure exerted by a pool liquid column is higher than the pressure exerted by a cooling water column of the same height. In the reactor shown in FIGS. 1 and 2, the difference in level between the interface 26 and the lower end of the reactor core is so great that the pressure difference between a pool liquid column having a height equal to this difference in level and a cooling water column of the same height during normal reactor operation constitutes a predominant part of the pressure drop across the reactor core. In the reactor plant shown in FIGS. 1 and 2, the flow rate of cooling water flowing through the core is adjusted by means of the shunt valve 34 in such a way that the pressure drop across the reactor core during normal operation of the reactor is equal to the difference between a first pressure, corresponding to a pool liquid column from the interface 25 to a level approximately at the lower edge of the core, and a second pressure, corresponding to a cooling water column from the same level to the interface 26. The pressure difference, caused by the difference in density and the difference in height, if any, between the pool liquid column and the cooling water column of maximum height is somewhat greater than the pressure drop across the reactor core at the desired flow of cooling water. Thus, the vertical dimensions of the pool and the reactor are somewhat larger than is strictly required. Therefore, for the purpose of achieving balance between the above-mentioned pressure drop and the pressure difference between the two liquid columns, the lighter of the two liquid columns has been made somewhat longer than the other, which results in the pressure difference between the two columns becoming somewhat smaller than the value which would have been obtained if the interfaces 25 and 26 had had the same level. In the reactor shown, the difference between (a) the pressure exerted by a theoretical pool liquid column of the same height above the lower edge of the core as the cooling water column located in the outlet chamber 19, and (b) the pressure exerted by this cooling water column, constitutes more than 100% of the pressure drop across the reactor core during normal reactor operation, for example 110% of this pressure drop. For economic reasons this percentage should generally be smaller than 140% in a reactor plant according to the invention, since otherwise quite unacceptable vertical dimensions of the pool and the reactor vessel would be obtained. On the other hand, a reactor plant of the same kind as that shown in FIGS. 1 and 2 can be made with relatively small vertical dimensions of the pool and the reactor vessel, in which case the difference between the pressure exerted by a pool liquid column and the pressure exerted by a cooling water column of the same height is less than that required to balance the pressure drop across the reactor core during normal reactor operation. In order to achieve balance, the difference between the pressure exerted by the above-mentioned pool liquid column and the pressure exerted by the above-mentioned cooling water column is in such a case increased by making the pool liquid column longer than the cooling water column, that is, by arranging the interface 26 at a level which is lower than the interface 25. However, the cooling water column is always made so high that the difference between the pressure exerted by a pool liquid column of the same height and the pressure exerted by the cooling water column corresponds to a predominant portion such as more than 60% of the pressure drop across the reactor core during normal reactor operation, preferably more than 80% thereof. This usually means that the difference in height .DELTA.H, between the upper shutdown opening 28' and the lower shutdown opening 33' is greater than seven times the vertical dimension L of the core, and that the portion of the reactor vessel filled with cooling water has a vertical extension which constitutes a predominant part of the vertical extension of the reactor vessel. Since the reactor vessel 6 has a lower shutdown opening 33' where the pool liquid may flow in and an upper shutdown opening 28' where reactor cooling water may flow out into the pool, the reactor core is included not only in the primary cooling circuit of the reactor but also in a pneumatic-hydraulic shutdown circuit, in which the strongly borated water of the pool is included. In addition, the shutdown circuit includes the inlet drum 33 with its associated tube 32, the nozzles 31, the lower portion of the inlet chamber 12', the outlet chamber 19 and the gas cushion 4. In the shutdown circuit, the combination of a constantly hot water column located in the reactor vessel and a constantly cooler liquid column located outside the reactor vessel constitutes a flow-driving system. This system has a flow-driving capacity, that is, a driving pressure difference, which is substantially constant during the initial part of the shutdown process and substantially independent of the volume of liquid driven by the system, at least during the initial part of the shutdown process. In this specification, the expression "initial part of the shutdown process" is defined as the part of the shutdown process taking place from the first introduction of pool liquid into the reactor vessel to the stage when the amount of pool liquid introduced into the reactor vessel is equal to the volume of reactor coolant present below the top of the reactor core during normal reactor operation. During normal reactor operation, the above-mentioned pressure difference acting in the shutdown circuit is balanced by the pressure drop created across the reactor core due to the flow of coolant in the primary circuit, and no transport of pool liquid to the primary cooling circuit of the reactor takes place. If the flow of cooling water through the reactor is reduced because of a fault in the primary cooling circuit of the reactor, for example a faulty pump, a corresponding reduction of the pressure drop across the reactor core occurs, and this pressure drop is no longer able to balance that pressure difference which is tending to drive a flow of pool liquid through the shutdown circuit, and accordingly the pool liquid level rises in the inlet drum 33. If the reduction of the pressure drop across the core caused by the faulty pump is greater than the pressure that may be exerted by a cooling water column of the same height as the steam-filled portion of the outlet chamber 19, a flow of water will leave the reactor vessel via the upper shutdown opening 28', and an equally large flow of pool liquid will flow in through the lower shutdown opening 33'. This flow is relatively small in the case of small deviations from normal circulation in the primary cooling circuit of the reactor and relatively great in the case of large deviations, and it is driven by a pressure difference which acts in the shutdown circuit and which is caused by differences in height of pool and cooling water columns and by the difference in density between the liquid present in the pool and the relatively hotter water present in the reactor vessel. In the case of a considerable reduction of the water flowing through the primary cooling circuit, an emergency shutdown occurs which is primarily caused by a corresponding reduction of the pressure drop across the reactor core. In addition, the emergency shutdown is accelerated by the temperature of the reactor cooling water increasing, which results in an increase of the above-mentioned difference in density. If an emergency shutdown takes place, for example because the pump motor 22 stops, the reactor power will drop to a value which corresponds to the decay power even when the amount of water present in the core has received a boron content which is considerably smaller than the boron content in an equal amount of pool liquid, for example smaller than 50% of this boron content. As long as a considerable decay power is present, the difference in density between the liquid of the pool and the liquid of the reactor vessel will still be great enough to provide a flow-driving pressure difference in the shutdown circuit, at least for as long as a predominant part of the original liquid quantity remains in the pool. The pool is constructed with a pool liquid volume which is at least three times, preferably at least ten times, as great as the volume of the reactor vessel. An advantage with a reactor plant according to the invention is that, at increased reactor temperature, the shutdown circuit is able to release an emergency shutdown or a controlled action as a direct response to the temperature increase, whereas in the previously described known reactor such a reaction can only be obtained as an indirect reaction, namely in that the formation of steam bubbles at overtemperature results in increased hydraulic resistance, whereupon the shutdown circuit in its turn responds to insufficient water flow. If the water temperature in the outlet chamber 19 of the reactor vessel increases, the reduction in density caused by the temperature rise will be compensated for by a corresponding rise of the interface 26. If the water temperature exceeds a certain allowable value, which is below the boiling point at the prevailing reactor pressure, the interface 26 rises to the upper edge of the reactor vessel. An additional increase in temperature will result in the driving pressure difference of the shutdown circuit exceeding the pressure drop across the reactor core, so that pool liquid flows into the reactor vessel via the lower shutdown opening 33'. This flow will cease only if a temperature reduction occurs, for example because of the strongly borated pool liquid introduced into the reactor. On the other hand, if the temperature rise continues, the flow of pool liquid into the reactor vessel will increase. If a sudden temperature increase occurs in the reactor core, a considerable amount of steam may be generated in the cooling water, which results in a considerable increase of the hydraulic resistance in the core, and thus of the pressure drop across the core. In the reactor plant shown in FIGS. 1 and 2, the core and the reactor vessel are dimensioned in such a way that an increase of the flow-driving pressure difference due to density-decreasing steam bubbles appearing in the reactor vessel, is at least as great as the increase of the pressure drop across the reactor core caused by said steam generation. If, by mistake, the pool should be subjected to a greater pressure than that for which it is dimensioned, so that a crack occurs in the pool wall, the inner tank 5 can still be counted on to remain intact since this tank can never be subjected to a greater pressure than the static liquid pressure. The volume of the inner tank 5 constitutes at least 50%, preferably at least 70%, of the pool volume. During normal operation of a reactor according to the invention, the pressure in the pool is greater than 15 bar, preferably greater than 25 bar. In the reactor plant of FIGS. 1 and 2, and also in the embodiments described hereinafter, shimming is carried out with boric acid, and control rods in the normal sense are not required. Instead of this there is provided a shutdown device which is intended to supply the core with absorber bodies in the case of shutdown of the reactor for a long period and which is also effective as an additional emergency shutdown system. The shutdown device has a reservoir 36, arranged above the reactor vessel, which is composed of a large number of vertical reservoir tubes (not shown). Each reservoir tube comprises a large number of boron-steel balls. The reservoir 36 can be rotated around a vertical center line by means of a power transmitting device 37 passing through the pool cover 1". During reactor operation the balls are held in position in the reservoir by means of a perforated plate (not shown). On the lower side of the plate a plurality of distribution tubes 38 for the boron steel balls are arranged with their upper ends below a corresponding hole in the perforated plate. The lower ends of the distribution tubes 38 open above a corresponding fuel assembly 9'. Each hydraulic connection 18, 18', 18", 29, 30 between the reactor vessel 6 and the steam generator elements 7, is in its entirety arranged above a level which extends above the upper edge of the reactor core and the distance of which from said upper edge corresponds to at least 20%, preferably more than 35%, of the maximum liquid depth in the pool 1. If a leakage should occur between the primary side and the secondary side of any of the three steam generator elements 7, pool liquid may be forced out through the steam conduits 34' and the return conduits 35'. Since the above-mentioned hydraulic connections are arranged above the above-mentioned level, such a leakage can never cause the pool liquid to sink below this level. In the embodiment of the invention shown in FIGS. 1 and 2, there is an inherent pressure difference in the emergency shutdown circuit which gives a flow of pool liquid in the emergency shutdown circuit when the pressure drop across the core becomes smaller than this inherent pressure difference. Instead of achieving such an inherent pressure difference mainly by utilizing the difference in density between the pool liquid and the reactor water, a predominant part of the pressure difference in question can be generated with the aid of a special pump intended for this purpose, for example in the embodiment of the invention shown in FIG. 3, in which the items designated by the numerals 2, 60, 128, 129 and 130 are the same as the correspondingly designated items in FIG. 1. In the embodiment of the reactor plant shown in FIG. 3, the numeral 41 designates a pool made in the form of a substantially circular-cylindrical, hollow pressure vessel. The pool 41 is provided with a cover 72 and is filled with strongly borated water up to this cover. The pool comprises a reactor vessel 42, which encloses a reactor core 43. The reactor vessel 42 has an outlet chamber 44 and an inlet chamber 45, which together with the core 43, an outlet conduit 46, a heat exchanger in the form of a U-shaped steam generator element 47, a circulating pump 48, and an inlet conduit 49 are included in the primary cooling circuit of the reactor. The steam generator element 47 is of the same type as the element 7 of FIGS. 1 and 2. The uppermost portion of the outlet chamber 44 is defined by a bell-shaped body 50' attached to and surrounding the top of a long tubular portion. At its upper end the outlet chamber 44 is connected to a gas cushion 50 in the form of steam which is supplied to the body 50' by a pressurizer in the form of a steam boiler 24 via a pressurization tube 51, a substantially constant pressure of at least 15 bar thus being maintained in the gas cushion 50 and in the pool liquid. In addition to a space 45' located below the core, the inlet chamber 45 also comprises a side space 45", which at its lower end is provided with an inlet opening 52 for pool liquid and a gradient lock 53 in the form of a cylindrical body of honeycomb material with a plurality of vertical channels. The inlet opening 52 constitutes the lower shutdown opening. The upper shutdown opening is designated 28". The interface 25' between the gas cushion 50 and the pool liquid lies above the interface 26' between the gas cushion 50 and the reactor cooling water. The inlet conduit 49 has two branches 49' and 49", a predominant part of the water flow of the primary cooling circuit being supplied to the reactor core 43 via branch 49' and the side space 45". The branch 49' has a portion 54 of relatively small cross-section which is by-passed by a shunt circuit 55. This shunt circuit is provided with a regulating valve 56, by means of which the magnitude of the water flow supplied to the side space 45" can be regulated. The side space 45" is connected to the space 45' via a tube portion 57' in the form of a venturi tube which, together with a nozzle 57" formed at the end of the branch 49", forms a water jet pump 57. Instead of the jet pump 57, an auxiliary pump may be provided which is driven by a special motor, which is preferably interlocked with the motor connected to the pump 48 in such a way that it stops in the event of stoppage or a large reduction in speed of the latter motor. The reactor core 43, the outlet chamber 44, the gas cushion 50, the pool space, the inlet opening 52, the side space 45", the tube portion 57' and the space 45' form an emergency shutdown circuit, in which the water jet pump 57 provides a driving pressure difference. During normal reactor operation, the pressure drop across the reactor core 43 is balanced only to a very small extent by the pressure difference which corresponds to the difference in level between the interfaces 26' and 25' of the gas cushion 50. During normal reactor operation the pressure drop across the reactor core is balanced substantially by two pressure-generating systems, each system having the ability to maintain a flow-driving pressure substantially independently of the time integral of the flow. One of these systems is a self-circulating system having an inherent flow-driving pressure difference which in principle is due to the difference in density between the pool liquid and the relatively hotter water of the reactor vessel. The other pressure-generating system is constituted mainly by the water jet pump 57. Because of the water jet pump, it is possible to construct the pool and the reactor vessel with considerably smaller vertical dimensions than in the case of the plant shown in FIG. 1. In the case of an abnormal temperature increase in the reactor vessel, the difference in density between the pool liquid and the reactor coolant will be so great that pool liquid can flow in through the lower shutdown opening 52. The embodiment of the reactor plant shown in FIG. 4 differs from that shown in FIG. 3 in that the water jet pump 57 with associated equipment and the bell-shaped body 50' are omitted. In FIG. 4, the items designated by the numerals 2, 34', 35' 60 and 128 are the same as the correspondingly designated items in FIG. 1, and the items designated by the numerals 43, 45' and 49 are the same as the correspondingly designated items in FIG. 3. The numeral 41 designates a pool made in the form of a substantially circular-cylindrical, hollow pressure vessel. At its upper end the vessel 41 is formed with a substantially circular-cylindrical throat which is sealed in a pressure-tight manner by means of a pool cover 72. The pool is pressurized to a pressure of at least 15 bar by means of a steam boiler 24. A gas cushion 73 in the form of a space filled with steam is defined in the above-mentioned throat between the pool cover 72 and a space 74 containing cooling water. A relatively thin boundary layer, containing diluted boric acid solution, is situated mid-way between the lower and upper ends of a gradient lock 63 which is fitted into the above-mentioned throat and which comprises a plurality of thin, vertical channels. Upper and lower transducers 69 and 70, respectively, in the form of thermocouples, are arranged in the gradient lock 63, the vertical distance between these transducers being larger than the thickness of the above-mentioned boundary layer during normal reactor operation. In the operating state of the reactor plant, the transducer 69 is only in contact with liquid of the same, or approximately the same, temperature as the cooling water flowing out of the outlet chamber 44 of the reactor vessel, whereas the transducer 70 is only in contact with liquid having a temperature equal to, or approximately equal to, the mean temperature of the boric acid solution located in the pool. Upper and lower reference value generators 69' and 70', respectively, in the form of thermocouples, are arranged above and below the gradient lock 63. An outlet conduit 71 is hydraulically connected between a heat exchanger in the form of a steam generator element 47 and the outlet chamber. The outlet conduit 71, contrary to the corresponding conduits 30 and 46 in FIGS. 1 and 3, is not directly connected to the outlet chamber of the reactor vessel, but hydraulically connected to said chamber via the space 74 which is filled with reactor coolant and positioned between the above-mentioned boundary layer and the gas cushion 73. The reactor vessel 42' has an upper shutdown opening 75 and a lower shutdown opening 76. In the shutdown opening 76 there is fitted a circular-cylindrical gradient lock 64 comprising at least one body of honeycomb material. In the gradient lock there are arranged two, vertically spaced-apart transducers 61 and 62, in the form of thermocouples, and two reference generators 61' and 62', also in the form of thermocouples, are arranged respectively above and below the gradient lock. Signals from the transducers 61, 62, 61' and 62' are supplied to a control system (described in greater detail hereinafter) for position control of the boundary layer in the lower gradient lock 64, in such a manner that the boundary layer between the hot reactor coolant and the relatively cooler pool liquid, during normal operation, is retained in the region between the transducers 61 and 62. If the boundary layer tends to be displaced to too low a level, the speed of the circulating pump 48 is reduced, which results in the boundary layer being raised to a higher level, and vice versa. The reactor is provided with two outflow pipes 65 and 165 for pool liquid which are provided with outlet valves 65' and 165', respectively. The valves 65' and 165' are operated by controllable driving devices 115 and 115', respectively. The outflow pipe 65 has a lower inlet opening which is arranged in the lower part of the gradient lock 64 as well as an inlet opening 65" arranged in the upper pool space. The inlet opening 65" is preferably made with low resistance to steam flow and relatively greater hydraulic resistance. The purpose of the opening 65" is to let out steam in the case of a rupture in the pipe 65 outside the pool. The transducers 69, 70, 69' and 70' deliver signals to a regulating system, the duty of which is to ensure that the boundary layer in the upper gradient lock 63 lies between the transducers 69 and 70. Since no continuous outflow takes place from the reactor to the pool, the temperature in the upper part of the gradient look 63 will slowly decrease. When the temperature at the level at which the transducer 69 is located has fallen below a certain value, a level indicator, comprising the transducers 69', 69, 70, 70' and a microprocessor 102, sends a signal to a relay 118 via a signal converter 116 and a pulse generator device 117, with the result that the outlet valve 65' is closed, whereupon feed water supplied by pipes 67 (low borated) and 68 (high borated), which are connected to the primary system of the reactor via a common lead-in tube 66 passing through the wall of the pool 41, will tend to increase the volume of the reactor water. Since the pump 48 is controlled to maintain the boundary layer of the lower gradient lock 64 at a substantially constant level, an outflow of reactor water into the pool will take place in the upper gradient lock, i.e. hot reactor water replaces the cooler liquid in the upper part of the gradient lock 63 so that the transducer 69 again acquires a temperature corresponding to the desired position of the boundary layer. In order to avoid an increase of the water volume in the space 74, a volume of pool liquid, equal to that entering via the pipes 67 and 68, is taken out through the valve 165'. When the boundary layer in the upper gradient lock 63 has a normal position (between the transducers 69 and 70), the valve 65' is open and the valve 165' is closed. The flow supplied through the pipes 67 and 68, which are provided with valves 67' and 68', respectively, is equal to the outgoing flow through the valve 65'. It is generally not necessary to take any measure to prevent the boundary layer from sinking below the transducer 70. Because the lower end of the outflow pipe 65 is disposed in the gradient lock 64, a renewal of the liquid of the boundary layer in the lower gradient lock takes place continuously and a fairly constant characteristic of this boundary layer can be maintained. Due to this renewal and due to the activity of the automatic temperature control system, a small flow of reactor water leaves the primary circuit all the time. Since the lower inlet opening of the outflow pipe 65 is disposed in, or in the vicinity of, the lower shutdown opening, no significant part of this flow of reactor water is mixed with the pool liquid. Thus, if the reactor water for some reason should contain radioactive substances, a delivery of such substances to the pool liquid is substantially avoided. When a signal indicating too high a boundary layer in the upper gradient lock 63 is given, the valve 65' is shut and the valve 165' is opened. A quantity of reactor water supplied through the pipe 66 then forces the same quantity of pool liquid out of the pipe 165 with the result that the pool liquid level, and accordingly the boundary layer, falls. The signals from the transducers 61', 61, 62, 62' are supplied to a microprocessor 101 which operates according to the flow chart shown in FIG. 4a, where the respective signal values are designated T.sub.61', T.sub.61, T.sub.62, T.sub.62'. If the boundary layer in the lower gradient lock 64 rises to a level above the measuring point of the transducer 61, a positive pulse is given at the output of the microprocessor, i.e. U=1. If the boundary layer drops beneath the measuring point of the transducer 62, on the other hand, a negative pulse is delivered, i.e. U=-1. When the boundary layer lies between the measuring points of the transducers 61 and 62, no pulse is given, i.e. U=0. The output signals of the microprocessor are supplied to a digital integrator 103, the output value of which is supplied to a digital/analogue converter 104. The output side of the converter 104 is connected, via a change-over switch 106', to the control circuit of a controlled frequency converter 105, which is connected by its output to an asynchronous motor 48', which is mechanically connected to the circulating pump 48. The frequency of the frequency converter 105, and preferably also its voltage, varies in dependence on the supplied control voltage. In the case of manual control of the pump speed, the change-over switch 106' is put in its second position, the frequency converter 105 then receiving control voltage from a manually-controllable voltage source 106. When a reactor in accordance with the invention is shut-down, the primary circuit of the reactor contains an aqueous solution, the boron content of which greatly exceeds that which is required to prevent a chain reaction in the reactor, and the surrounding pool space is filled with an aqueous solution with approximately the same boron concentration. Start-up of the reactor is done by supplying clean water to the water located in the primary circuit, whereas the corresponding amount of borated water at the same time leaves the pool. The inlet pipes and the outflow pipes required for this purpose and for control purposes are shown in FIG. 4 only, but the corresponding piping is assumed to exist in the other embodimens of the invention shown in the drawings. In the embodiments shown in FIGS. 3 and 4 and also in the embodiments described hereinafter with reference to FIGS. 5 and 6, the lower or upper shutdown opening is provided with a device capable of absorbing an amount of gas in such a way that a gas lock is formed. Such a gas lock is not needed during normal operation but is very advantageous when start-up of a shut-down reactor is to be carried out. At the beginning of such a start-up, the pool is first pressurized with the aid of the boiler 24, and the circulation pump 48 is started and driven at a low speed. Deboration of the reactor cooling water then takes place by the supply of pure water to the primary circuit via the inlet pipe 66, while at the same time an equally large flow of borated water leaves the pool via the outflow pipe 65. With the aid of the above-mentioned gas lock, it is possible to avoid pool liquid flowing into the reactor vessel 42' at the stage when the temperature difference between reactor coolant and pool liquid is very small. Such a gas lock is shown in FIG. 4 b, which on a relatively large scale shows the lower circular-cylindrical portion of the reactor vessel 42' and an annular body 107 attached to said circular-cylindrical portion and comprising two coaxially arranged circular-cylindrical portions 120 and 121 which, together with an intermediate annular plane portion 121', form an open annular channel 122. A cup-shaped body 123 is arranged coaxially between the circular-cylindrical portions 120 and 121 and is hydraulically connected to the outflow conduit 65. A gas, for example nitrogen, is supplied to the channel 122 via a tube 124, so that a gas cushion is formed above the level 125 of the pool liquid. The gradient lock 64 comprises two circular discs 64' and 64" which are arranged in a circular cylindrical hollow cylinder with an intermediate gap 64"' Upon reactor start-up, the speed of the circulating pump 48 is gradually increased as the reactor coolant temperature rises. During normal operation, the reactor temperature is maintained at the desired value by means of an automatic control system provided for this purpose which, as shown in FIG. 4, includes a thermocouple 108, an analogue/digital converter 108', a desired-value setter 109 for the desired temperature of the core outlet water, a subtractor 110, a summator 111, a regulator 112, a driving device 113 for the valve 67' in the inlet pipe 67 which supplies pressurized water having a very low concentration of boric acid, if any, a driving device 114 for the valve 68' in the inlet pipe 68 which is connected to a pressure container (not shown) containing strongly borated water, and the driving device 115 for the valve 65'. The regulator 112 is of the PI type, that is, proportional and integrating. If the output signal of the regulator 112 is positive, which occurs at too low temperature in the outlet chamber 44, this signal is delivered to the driving device 113, the valve 67' thus being opened to admit weakly borated water; whereas, the control signal to the driving device 114 is very small--less than 10% of its maximum value. If, on the other hand, the output signal of the regulator is negative, the absolute value of the signal is given as a control signal to the driving device 114, whereupon the valve 68' opens and the control signal to the driving device 113 is very small--less than 10% of its maximum value. The fact that the summator 111 supplies a control signal to the driving device 115 which is greater than the very small ones mentioned above as soon as any of the devices 113 and 114 receives a control signal which is greater than zero, results in pool liquid leaving the pool via the outflow pipe 65 upon each supply of relatively pure or borated water via the lead-in tube 66. A condition for this to take place is that the contact member of the relay 118 is in the position shown in FIG. 4, which takes place as long as the boundary layer in the upper gradient lock 63 is not positioned above a certain allowable boundary layer region. As previously mentioned, the position of the boundary layer is controlled by means of a control device which, in addition to the relay 118, comprises the four transducers 69', 69, 70, 70', the microprocessor 102, the signal converter 116 and the pulse generator device 117. The microprocessor 102 is constructed and arranged in the same way as the microprocessor 101, and the flow chart shown in FIG. 4a applies to the microprocessor 102 if modified by replacing the output signals T.sub.61, T.sub.61', T.sub.62, T.sub.62' by the output signals from the transducers 69, 69', 70 and 70', respectively, and replacing the designations 61 and 62 used in the text by the designations 69 and 70, respectively. Upon an input signal 1, the signal converter 116 produces an output signal of 24 volts. In other cases, the output signal is zero. Each time the input signal of the pulse device 117 proceeds from 0 to 24 volts, a 24 volt pulse is produced on the output side of the pulse device, whereupon the two-position relay 118 assumes a contact position different from that shown for a time interval which is equal to the pulse length. The pulse has been released as a result of a rising boundary layer in the upper gradient lock. In the embodiment of the reactor plant shown in FIG. 5, the outlet chamber 44' of the reactor vessel 42 comprises a bell-shaped member 131 which is arranged in a coaxial relation with, and attached to, the uppermost end of a tubular portion of the outlet chamber. The bell-shaped member 131 surrounds an annular gradient lock 130. As in the case of the gradient lock 63 shown in FIG. 4, two vertically spaced-apart transducers (not shown), for example thermocouples, are arranged in the gradient lock 130. These transducers are included in a regulating system in the same way as the transducers 69 and 70 shown in FIG. 4. The upper end of the bellshaped member 131 is provided with a through-going pipe 132. During normal reactor operation, the mid-portion of the gradient lock 130 has a boundary layer between strongly borated pool water and weakly borated or pure reactor cooling water, the reactor cooling water filling the portion of the member 131 located above the boundary layer, and the pipe 132. As in the previously described embodiments, the pool is provided at the top with a narrow, substantially circular-cylindrical throat 133. In normal operation of the reactor plant there is a gas cushion 134 in the upper part of the throat 133, which is in communication with a steam boiler 24. The upper end of the tube 132 opens into the gas cushion 134. The outlet chamber 44' is connected to a heat exchanger in the form of a steam generator element 47 via an outlet tube 135, which is welded to the outlet chamber 44' below the upper gradient lock 130. In FIG. 5, the items designated by the numerals 2, 34', 35', 60 and 128 are the same as the corresponding designated items in FIG. 1, the items designated by the numerals 41, 43, 45', 48, 49 and 72 are the same as the correspondingly designated items in FIG. 3, and the items designated by the numerals 64 and 76 are the same as the correspondingly designated items in FIG. 4. The reactor plant shown in FIG. 6 has an upper gradient lock 130', corresponding to the gradient lock 130 shown in FIG. 5, and a bell-shaped body 131', corresponding to the bell-shaped body 131. The body 131' communicates via a pipe 132' with a gas cushion 134'. The portion of the body 131' located above the gradient lock 130' and the body 132' are, during normal operation of the reactor, filled with reactor cooling water. The boundary surface between the gas cushion 134' and the pool liquid lies in an extra gradient lock 136 which is arranged above the gradient lock 130'. The boundary layer between pool liquid and reactor cooling water lies in the mid-portion of the gradient lock 130'. An outlet conduit 137 opens out into the body 131' above the gradient lock 130'. In FIG. 6 the items designated by the numerals 2, 24, 34', 35', 60 and 128 are the same as the correspondingly designated items in FIG. 1, the items designated by the numerals 41, 42, 43, 45', 47, 48 and 49 are the same as the correspondingly designated items in FIG. 3, and the items designated by the numerals 64 and 76 are the same as the correspondingly designated items in FIG. 4. Although not shown in FIGS. 1, 3, 5 and 6, the reactor plants of these Figures are, of course, provided with an automatic control system for maintaining the reactor temperature at the desired value, which control system may be constructed in the same way as the control system described with reference to FIG. 4. The vertical distance, designated .DELTA.H, .DELTA.H', .DELTA.H", .DELTA.H"' and .DELTA.H"" in FIGS. 1, 3, 4, 5 and 6, respectively, between the upper shutdown opening and the lower shutdown opening is, in all cases, at least seven times, and preferably at least eight times, the vertical dimension L, L', L", L"' and L"", respectively, of the respective reactor core. In all cases, the steam boiler or other pressurizer 24 may be replaced by an electric heating element which is arranged in the pool liquid in the upper, throat portion of the pool. The coolers 128 shown in FIGS. 1, 4, 5 and 6 are only shown to suggest their cooling function. In practice they would be disposed in the uppermost portion of the pool, as shown in FIG. 3, in order to avoid emptying of the pool in the case of leakage. The reactor plants of FIGS. 1, 4, 5 and 6 may also be provided with an auxiliary pump having the same purpose as the pump 57 shown in FIG. 3. Preferably, several heat exchangers should be disposed in corresponding pockets in the "ceiling" of the pool body, each heat exchanger comprising a plurality of vertical cooling tubes. In that case each group of cooling tubes may advantageously be surrounded by a substantially hollow-cylindrical body and provided with an electrically driven pump, by means of which pool liquid is driven along the cooling tubes. Indication of a boundary layer between the pool liquid and the reactor water is--in the control equipment described above--carried out by means of a level indicator comprising a number of transducers in the form of thermoelements, thus taking advantage of the fact that the reactor water and the pool liquid are different as regards temperatures. However, since the two liquids are also different as regards other physical properties, it is possible to use transducers for these properties instead of the transducers described, for example transducers for electric resistivity, or transducers for refractive index. It is also possible to use a level indicator comprising a vertical resistance element arranged with its midpoint in the region of the normal boundary layer. The electrical resistance of this element indicates the height of the boundary layer. For example, the minimum resistance occurs when the element is totally surrounded by cold liquid.
046613064	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of the drawings and with regard to the particular embodiment depicted therein, there is shown a portion of the pressure vessel 10, a penetration 11 through the wall of the pressure vessel 10, a lower core support plate 12, a port 13 connected between penetration 11 and the core support plate 12, and a lower flow inlet nozzel 14 having a seal connector 15 flow connected to the core support plate 12. A portion of a typical fuel assembly 16 is also shown, a plurality of which comprises the core of the reactor. Penetration 11 includes a tubular or pipe member 20 which passes through the wall of the pressure vessel 10. A weld 21, around the circumference of tube 20, sealing connects tube 20 to pressure vessel 10. Such penetration of the pressure vessel 10 is well known in the art. A venturi orifice 22 is provided within tube 20 for purposes which will be more fully explained hereinafter. A bolted flange 23 is sealed and structurally welded to tube 20. Penetration 11 comprises one of a plurality of inlet penetrations or outlet penetrations to pressure vessel 10. A low neutron moderator fluid such as deuterium oxide is caused to flow within penetration 11 so as to displace a portion of the core coolant within the fuel assemblies 16 with a predetermined amount of deuterium oxide which amount is consistent with the need at that given time to harden the nuclear spectrum and effectuate the spectral shift. The control of the flow of the deuterium oxide is more completely described in copending U.S. patent application Ser. No. 626,942 entitled "Fluid Moderator Control System Fuel Assembly Seal Connector" by L. Veronesi, et al., filed on July 2, 1984 (W.E. No. 49,204) and assigned to Westinghoue Electric Corporation and accordingly will not be further explained herein except as it may apply to the instant invention. Port 13 flow connects penetration 11 with the flow channels in the core support plate 12. Port 13 comprises a lower substantially cylindrical member 24, an upper member 25, a bellows 26 connecting upper member 25 to lower member 24, and a skirt 27 surrounding bellows 26. As shown and described, port 13 is structurally connected at one end to flange 23 and at the other end to core support plate 12. Bellows 26 permits relative motion between upper member 25 and lower member 24 while maintaining a seal therebetween. Lower member 24 of port 13 includes a flange 28 which sealingly mates with flange 23 on penetration 11. A metal "o" ring seal 29 may be used to effectuate the seal between flanges 23 and 28. Bolts 30 structurally secure flange members 23 and 28. A flow channel 31 within lower member 24 is axially aligned with the flow channel 32 in penetration 11 and with the flow channel 33 in upper member 25. Flow channels 31, 32 and 33 provide flow communication for the deuterium oxide introduced and controlled by said fluid moderator control system to the core support plate 12. Upper member 25 of port 13 includes a lower cylindrical portion 34 which telescopically mates with the free upper end of member 24. One or more ring seals 35 which fit within circumferential grooves 36 in the free end 37 of member 24 provide a sliding seal between members 24 and 25. One end of bellows 26 is seal welded to the lower end 34 of member 25 while the other end of bellows 26 is seal welded to a cylindrical portion of member 24 in the vicinity of flange 24. In this manner, bellows 26 is given a length which provides for the differential thermal expansion between upper 25 and lower 24 members while minimizing any spring force exerted by bellows 26 resulting from such differential expansion. Skirt 27 may be secured at one end thereof to either upper member 25 or lower member 24. As shown, skirt 27 is welded to member 25. A tab 38 on the unsecured end of skirt 27 fits within a slot 39 in member 24 so as to limit the unrestrained motion between members 24 and 25 prior to assembly to the reactor and to prevent damage to telescoping portions of members 24 and 25. The control portion 40 of skirt 27 is slightly enlarged so as to fit closely within an opening 41 in guide plate 42 and to limit any lateral deflection of port 13 during reactor operation. A greater amount of clearance is provided between opening 41 and the main portions of skirt 27 to facilitate assembly of guide plate 42 over the plurality of ports 13 co-extending from the bottom of the reactor vessel 10. The upper end of member 25 provides for attachment of port 13 to the lower core support plate 12 and for ducting the flow of the low neutron moderating fluid from within flow channel 33 (which is in flow communication with port 13) to one or more horizontal flow channels within core support plate 12. As previously described, the lower end of member 25 comprises a cylindrical hollow tube 36 (with flow channel 33 comprising the hollow center of said cylindrical tube) which telescopically mates with a plunger upper end 37 of lower member 24 of port 13. Flow channel 33 terminates within the lower end 36 of member 25 at a position slightly below the lower surface of the core support plate 12. Slightly above the terminal end of flow channel 33, the cylindrical portion 36 of member 25 necks down to form shank 43 having a solid circular cross-sectional shape. The shank extends upwards toward the end 44 of member 25 where the cross-sectional diameter is enlarged and is axially drilled and internally tapped 45. A shoulder 46 is formed between the shank 43 and cylindrical tube 36. Shoulder 46 fits against the lower surface of the core support plate 12. Shank 43 and enlarged end 44 fit within an opening 47 in core support plate 12. A bolt 48 fitted through an opening 49 in the upper side of core support plate 12 threadingly engages with the enlarged upper end 44. Tightening bolt 48 causes shoulder 46 to firmly seat against the lower surface of the core support plate 12 and to effectuate a leakfree joint due to "o" ring seal 50 in groove 51 in shoulder 46. The opening 49 for bolt 48 is sealed by the use of another metallic "o" ring 52 provided within a groove 53 of cylindrical block 54 which is bolted by use of bolts 55 within the upper end of core support plate 12. In the manner provided, ports 13 may be assembled to the flanges 23 of penetrations 11 at the bottom of the pressure vessel 10 and then the reactor internals including the core support plate 12 may be lowered into position over the upper ends 44 of member 25. A tapered surface 56 also provided at end 44 facilitates such installation. Tightening of bolt 48 and installation of block 54 completes the assembly procedure. The flow of the low moderating fluid from within flow channel 33 to the core support plate 12 is, as mentioned above, provided for by the upper end of member 25. One or more holes 57 are drilled at an angle (relative to the axial center line of member 25) from the intersection of shank 43 and cylindrical tube 36 into the opening comprising flow channel 33. Holes 57 provide flow communication between channel 33 and the distribution or the core support plate ilet flow channel 58 formed by hole 47 in core support plate 12 and the necked-down portion or shank 43 of member 25. It being noted that "o" ring seals 50 and 52 effectively seal off distribution channel 58 except for the horizontal openings in lower core support plate 12. FIG. 2 shows in detail one method of distributing the flow of the low neutron moderating fluid within the lower core support plate 12 (from flow channels 58 to the seal connectors 15 of the fuel assemblies) and for returning the flow of said fluid from the seal connectors 15 back through the lower core support to flow channels 58. In this regard, it is to be noted that seal connectors 15 may act as flow inlet or flow outlet connectors depending upon their location with respect to flow nozzle 14. Further explanation of this aspect may be found in the above-referenced copending patent application by R. K. Gjertsen, et al. The core support plate is divided into four separate regions 61A, 61B, 61C and 61D. Each region is simultaneously supplied with the low neutron moderating fluid introduced through a corresponding flow channel 58 in the core support plate 12. Such an arrangement facilitates uniform flow to each fuel assembly and precludes large reactivity additions in the unlikely event of an inadvertent displacement of the low neutron moderating fluid with a high neutron moderator such as the light water reactor coolant. In order to provide the fuel assemblies within each region, 61A, 61B, 61C, 61D, with the low neutron moderator, a horizontal network of inlet and outlet flow channels is provided for each region 61A, 61B, 61C and 61D. For simplicity, the flow arrangement for region 61B only will be described. It will be noted, however, that the same arrangement is applicable to the other regions 61A, 61C and 61D, although not explained in detail. Still referring to FIGS. 1 through 4, region 61B may be classified as a center region. A single flow inlet channel 58' (FIG. 2) intersects a single main feed line 62B which is horizontally drilled at level 63-3. Branch feed lines 64B are also drilled horizontally at the same level as line 62B but at right angles to each other. In region 61B there are four branch feed lines 64B. A single main exit flow line 65B (intersecting with another channel 58') (FIG. 2) also services region 61B. Similarly, four branch exit flow lines 66B services region 61B, which flow lines intersect with lines 65B and are all at the same level 63-4 with each other. The main exit line 65B is at right angles to the four branch exit lines 66B. As can be seen in FIGS. 3 and 4, levels 63-3 and 63-4 are different. Thus, none of the main or branch inlet lines interfere with the main or branch exit lines. A vertical flow line 66B is provided at the intersection of each inlet seal connector of a fuel assembly and the branch feed lines 64B while lines 69B are provided at the intersection of each outlet seal connector of a fuel assembly and the exit branch lines 66B. The arrangement thus provides a complete flow path within region 61B from channel 58 to each inlet flow seal connector and from each exit flow seal connector back to a different flow channel 58. The inlet and outlet flow paths in regions 61A, 61C and 61D are similar to that described for regions 61B. Although there are two levels of flow lines (inlet and exit) for each region 61A-61D, the arrangement shown in FIGS. 1 through 4 requires a total of only four different levels. By way of clarification, flow level 63-1 services lines 62A, 62D, 64A and 64D; level 63-2 services lines 65A, 65D, 66A and 66D; level 63-3 services lines 62B, 62C, 64B and 64C; and, level 63-4 services lines 65B, 65C, 66B and 66C. In other words, each level services two functions for each of two flow regions. There are, of course, distinct advantages in minimizing the total number of flow line levels. It simplifies machining; it minimizes the possibility of interference with the main coolant flow channels through the lower core support plate 12. Other advantages will be apparent to one skilled in the art. All of the above-described horizontal flow lines may be gun drilled in the lower core support with the entrance or exit to the drilled hole sealed by a plug 70 fitted within the hole and seal welded 71 around its periphery as shown in FIG. 5. In the alternative, a method of horizontal flow distribution can be accomplished by attaching a piping manifold to either or both of the upper and lower surfaces of the lower core support plate 12. FIG. 6 depicts an alternate method to supply the low neutron moderating fluid to the lower core support plate distribution system shown in FIGS. 2 through 5. In this embodiment, the fluid is introduced into the reactor vessel 10 through top entry (as opposed to the bottom entry of FIG. 1). One or more penetrations 80 are welded to the pressure vessel in normal fashion. A flange 81 is welded to the internal diameter of the pressure vessel 10 at the location of penetration 80. A bellows 82, an elbow 83 and a bolted flange half 84 are connected to welded flange 81. The other half 85 of bolted flange is welded to a connecting pipe 86 which is in turn welded 87 to the upper flange of the lower barrel 88. Bellows 82 provides for differential thermal expansion between the reactor internals and the pressure vessel 10. Bolted flange halves 84 and 85 and connecting pipe 86 fit within an opening 89 in the flange 90 of the upper core support plate 91. The bolted flange 84 and 85 is provided to permit removal of elbow 83 if the lower internals are to be removed from the pressure vessel 10. A flow channel 92 is provided in flange 93 of the lower barrel 88. A pipe 94 welded thereto and connected at its lower end to the horizontal flow inlet channels in the lower core support plate 12, completes the flow distribution system. The flow channel shown in FIG. 6 may be used for fluid moderator inlet or outlet flow. Venturi 22 comprises an insert within penetration 20 to permit flow of the low neutron moderating fluid to the core of the reactor but restrict outward flow of the moderating fluid in the very unlikely event of a double failure of penetration 20 outside the pressure vessel 10 and one or more of the seal connectors 15. Venturi 22 is of a type which is well known in the art. The apparatus disclosed above has been described with regard to introducing a fluid such as deuterium oxide into the reactor core in order to effectuate spectral shift. The inventive apparatus is, of course, not intended to be limited to the flow of deuterium oxide. The flow of a suitable low moderating fluid may be used with the inventive apparatus. Additionally, the inventive apparatus contemplates the flow of a mixture of the low neutron moderating fluid in combination with the normal reactor coolant depending upon the degree of moderation required or desired at any time in accordance with the amount of excess reactivity then present in the core. The inventive apparatus even further contemplates the ultimate displacement of the low neutron moderating fluid with the normal reactor coolant during the later stages of core life when a maximum amount of moderation is required especially when a soft nuclear spectrum is desired. While the invention has been described, disclosed, illustrated and shown in certain terms or certain embodiments or modifications which it has assumed in practice, the scope of the invention is not intended to be nor should it be deemed to be limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.
	description	The disclosed and claimed concept relates generally to nuclear power generation equipment and, more particularly, to a hold-down spring apparatus usable with a fuel assembly of a nuclear reactor of a nuclear installation. Pressurized water nuclear reactors are well known in the relevant art. An exemplary pressurized water reactor is depicted generally in FIG. 1 and is described in greater detail below. The pressurized water reactor of FIG. 1 employs a set of hold-down springs that are depicted at the numeral 46 in FIG. 1, and another exemplary set of hold-down springs is depicted at the numeral 200 in FIG. 6. The hold-down spring pack provides a vertically downward force additional to gravity on the fuel apparatuses and is intended to retain the fuel apparatuses situated atop the lower core support plate and to resist the drag forces of the pressurized coolant fluid flow that is in an upward direction. As is generally understood in the relevant art, the pressurized cooling fluid is at its greatest density when the nuclear installation is in a cold condition, such as during startup or just prior to shut down, and the fluid drag forces in the vertically upward direction on the fuel apparatuses are therefore at their greatest when the nuclear reactor is cold. When the reactor is hot, the coolant is at a relatively lower density and thus causes relatively reduced vertically upward drag forces on the fuel apparatus. However, neutron bombardment of the fuel apparatuses, which are formed primarily of Zirconium alloy, causes the fuel apparatuses to grow in size. Moreover, the coefficient of thermal expansion of the Zirconium alloy from which the fuel apparatuses are made is less than that of the stainless steel from which the reactor containment is made. Furthermore, neutron bombardment of the spring pack relaxes the springs to have a reduced spring force. Chronologically, a cold condition exists at initial fuel installation, and cold hydraulic forces occur when the reactor is first started. This is followed by reduction in force due to a difference in hold-down force due to thermal expansion between fuel and core internals, and then hot hydraulic force, which is followed by irradiation induced effect during operation (i.e., growth of fuel structure, irradiation relaxation of spring force). It thus can be seen that complex factors are involved in the overall downward compressive load that is applied to the fuel apparatuses by the spring packs. As such, difficulty has been encountered in developing spring packs that will provide an appropriate level of downward force on the fuel apparatus at all times over the life of the components thereof. For instance, insufficient hold-down force leads to fuel assembly lift-off, which affects fuel behavior in normal and accidental conditions. Such fuel assembly lift-off could lead to fuel component damage including fuel rods, prevent RCCA insertion, etc. On the other hand, excessive hold-down force leads to fuel assembly distortion and may cause handling damage, increased water gaps and corresponding peaking factors. and IRI (Incomplete Rod Insertion). The hold-down force thus needs to be kept in a desirable range. Since this is difficult to achieve because of the complex loading issues mentioned above, improvements would be desirable. An improved spring apparatus in accordance with the disclosed and claimed concept is usable in a nuclear installation. In one embodiment, the spring apparatus includes a plurality of springs that are in a compressed state and that are compressively engaged with an upper core plate of a nuclear reactor when the reactor is in a cold condition. However, when the reactor is in a hot condition, a spring of the plurality of springs is in a free state wherein a free end of the spring is in an uncompressed state and is disengaged from the upper core plate. In another embodiment, the spring apparatus employs a support apparatus that is also in accordance with the disclosed and claimed concept and that includes one or more bumpers that engage the springs of a spring pack from the underside. Accordingly, an aspect of the disclosed and claimed concept is to provide an improved spring apparatus that is usable in a nuclear installation. Another aspect of the disclosed and claimed concept is to provide such a spring apparatus that includes a support apparatus having one or more bumpers that are situated generally between the springs and the fuel assembly and that compressively engage the springs that are situated above it to provide enhanced performance. Another aspect of the disclosed and claimed concept is to provide another such spring apparatus having a plurality of springs whose compressive engagement with an upper core plate of the nuclear reactor is based upon the temperature of a reactor. Accordingly, an aspect of the disclosed and claimed concept is to provide an improved support apparatus that is usable with a spring apparatus of a nuclear installation, the spring apparatus having a plurality of elongated springs that are stacked together one upon the other and that are affixed at an end thereof to a top nozzle of a fuel assembly of the nuclear installation, the plurality of springs at a location thereon that is spaced from the first end being engaged with an upper core plate of the nuclear installation, the plurality of springs engaged between the top nozzle and the upper core plate being deformed between a compressed state and another compressed state when the nuclear installation is operated between a cold condition and a hot condition. The support apparatus can be generally stated as including a support that is plate-like and that is structured to take the place of a spring of the plurality of springs that has been removed from the spring apparatus, the support further being structured to be stacked together with a number of remaining springs of the plurality of springs and to be affixed at an end thereof to the top nozzle, and an abutment apparatus that comprises a bumper that is affixed to the support and that is spaced a first distance from the first end, the bumper protruding a second distance away from a surface of the support in a direction generally toward the number of remaining springs and being structured to engage the number of remaining springs at a position on the number of remaining springs disposed between the end and the location during at least a portion of the deformation between the compressed state and the another compressed state. Another aspect of the disclosed and claimed concept is to provide an improved spring apparatus that is structured for use in a nuclear installation. The spring apparatus can be generally stated as including a number of elongated springs, a support apparatus comprising a plate-like support and an abutment apparatus that is situated on the support, the number of springs and the support being stacked together one upon the other and being structured to be affixed at an end thereof to a top nozzle of a fuel assembly of the nuclear installation, the number of springs at a location thereon that is spaced from the first end being structured to be engaged with an upper core plate of the nuclear installation, the number of springs engaged between the top nozzle and the upper core plate being deformed between a compressed state and another compressed state when the nuclear installation is operated between a cold condition and a hot condition, and the abutment apparatus comprising a bumper that is affixed to the support and that is spaced a first distance from the first end, the bumper protruding a second distance away from a surface of the support in a direction generally toward the number of springs and being structured to engage the number of springs at a position on the number of springs disposed between the end and the location during at least a portion of the deformation between the compressed state and the another compressed state. Another aspect of the disclosed and claimed concept is to provide an improved spring apparatus that is structured for use in a nuclear installation. The spring apparatus can be generally stated as including a plurality of elongated springs that are stacked together one upon the other and that are affixed at a first end thereof to a top nozzle of a fuel assembly of the nuclear installation, when the nuclear installation is in a cold condition, the plurality of springs being in a compressed state and each being compressively engaged at a location thereon that is spaced from the first end with an upper core plate of the nuclear installation, and when the nuclear installation is in a hot condition: a subset of the plurality of springs consisting of fewer than all of the plurality of springs being in another compressed state and each being compressively engaged with the upper core plate, and a spring of the plurality of springs being in a free state wherein a second end thereof opposite the first end is uncompressed and is disengaged from the upper core plate. Similar numerals refer to similar parts throughout the specification. An exemplary fuel assembly 10 mounted in a schematically depicted nuclear reactor 4 of a nuclear installation 6 is depicted generally in FIG. 1. One or more of the various components of the fuel assembly 10 and/or other components can be referred to as the internals 14 and 42 of the reactor 4. The fuel assembly 10 includes a bottom nozzle 12 that supports the fuel assembly 10 on a lower core support plate 14 in the core region of the nuclear reactor 4. The nuclear reactor 4 is a pressurized water reactor that includes a plurality of the fuel assemblies 10 disposed on the core support plate 14. In addition to the bottom nozzle 12, the structural skeleton of the fuel assembly 10 also includes a top nozzle 16 at its upper end and a number of elongated guide tubes or thimble tubes 18 which extend longitudinally between the bottom and top nozzles 12 and 16 and at opposite ends are connected therewith. The fuel assembly 10 further includes a plurality of transverse grids 20 axially spaced along and mounted to the thimble tubes 18 and an organized array of elongated fuel rods 22 transversely spaced and supported by the grids 20. Also, the exemplary fuel assembly 10 depicted in FIG. 1 includes an instrumentation tube 24 located in the center thereof that extends between the bottom and top nozzles 12 and 16. With such an arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conveniently handled without damaging the assembly parts. As mentioned above, the fuel rods 22 in the array thereof in the fuel assembly 10 are held in spaced relationship with one another by the grids 20 spaced along the length of the fuel assembly 10. Each fuel rod 22 includes a plurality of nuclear fuel pellets and is closed at its opposite ends by upper and lower end plugs 28 and 30. The fuel pellets are composed of fissile material and are responsible for creating the reactive power of the nuclear reactor 4. A liquid moderator/coolant such as water, or water containing boron, is pumped upwardly through a plurality of flow openings 32 in the lower core support plate 14 to the fuel assembly 10. Such flow is represented by a number of arrows that are indicated at the numerals 33A and 33B. As employed herein, the expression “a number of” and variations thereof shall refer broadly to any non-zero quantity, including a quantity of one. The bottom nozzle 12 of the fuel assembly 10 passes the coolant flow upwardly through the thimble tubes 18 and along the fuel rods 22 of the assembly in order to extract heat generated therein for the production of useful work. To control the fission process, a number of control rods 34 are reciprocally movable in the thimble tubes 18 located at predetermined positions in the fuel assembly 10. Specifically, a rod cluster control mechanism 36 positioned above the top nozzle 16 supports the control rods 34. The control mechanism 36 has an internally threaded cylindrical member 37 with a plurality of radially extending arms 38. Each arm 38 is interconnected to a control rod 34 such that the control mechanism 36 is operable to move the control rods 34 vertically in the thimble tubes 18 to thereby control the fission process in the fuel assembly 10, all in a well-known manner. The nuclear reactor 4 further includes an upper core support plate 42 that is situated opposite the lower core support plate 14 and between which the fuel assemblies 10 are situated. Each fuel assembly 10 includes a plurality of hold-down springs 46 which, as a general matter, are arranged in four spring packs, one of which is depicted in FIG. 1 as being at the front of the fuel assembly 10, i.e., the part facing the viewer, with the other spring packs not being shown but being situated at the left, right, and rear of the fuel assembly 10. When the upper core support plate 42 is situated atop the hold-down springs 46, the hold-down springs 46 are in an at least slightly compressed state and apply a compressive force to the fuel assembly 10 in the vertically downward direction from the perspective of FIG. 1. Such downward compressive force resists the fuel assembly 10 from being lifted off the lower core support plate 14 due to drag forces from the flow of coolant, as is indicated at the arrows 33A and 33B, acting on the fuel assembly 10. An improved spring apparatus 104 in accordance with a first embodiment of the disclosed and claimed concept is depicted in FIGS. 2-4. The spring apparatus 104 includes a plurality of springs that are indicated at the numerals 108, 112, and 116, and each of which is of an elongated plate-like configuration having a length and thickness that are depicted in FIGS. 2-4 and having a width into the plane of the page of FIGS. 2-4. The springs are formed of a material such as Alloy 718 or other appropriate material that is suited to the purpose. The springs 108, 112, and 116 are stacked, one upon the other, and are affixed to the top nozzle 16 of the fuel assembly 10. As can be understood from FIGS. 2-4, the spring 108 is situated atop the other springs 112 and 116, and it has a first end 120 that is secured in a mount 124 atop the fuel assembly 10, it being noted that the springs 112 and 116 are likewise secured to the fuel assembly 10 with the mount 124. The spring 108 additionally has a bend 128 formed therein, and the upper core plate 42 engages the spring 108 at an engagement location 132 thereon that is located on the bend 128. The bend 128 terminates at a ledge 136, and the spring 108 further includes a relatively narrower tail 140 that extends from the ledge 136 and includes a set of latching structures that are engaged with an interior surface of the top nozzle 16 of the fuel assembly 10. The spring 112 likewise includes a first end 148 that is secured to the mount 124. The spring 112 further includes a second end 152 opposite the first end 148 and has an opening 156 formed therein near the second end 152. The tail 140 is slidingly received in the opening 156. Furthermore, the spring 112 includes an engagement location 160 adjacent the opening 156 that engages the ledge 136 and thus is compressively engaged with the upper core plate 42 via the spring 108. In a similar fashion, the spring 116 has a first end 164 and a second end 168 opposite one another and further has an opening 172 formed therein near the second end 168 through which the tail 140 is slidingly received. Furthermore, the spring 116 has an engagement location 176 thereon situated adjacent the opening 172 that is engageable with the underside of the spring 112 and thus, via the spring 112 and the spring 108, is compressively engageable with the upper core plate 42, as is depicted in FIG. 4. As can be seen in FIGS. 2-4, the spring 116 can be said to have a first portion 180 that is engaged with the top nozzle 16 of the fuel assembly 10 and to have a second portion 184 opposite the first portion 180 and to further have a bend 188 situated between the first and second portions. In the depicted exemplary embodiment, the spring 116 is of a generally constant thickness, thereby minimizing the expense to form it. The first portion 180 can be said to be of a length 190. As a general matter, FIG. 2 depicts the spring apparatus 104 in a hot state of the nuclear reactor 4, and in such hot state the second end 168 of the spring 116 is spaced away from an underside the second end 152 of the spring 112 by a space 194. It thus can be seen that in the hot condition of FIG. 2, the spring 116 is in a free state wherein only its first end 164 is affixed to the top nozzle 16 of the fuel assembly 10 and wherein the second end 168 is disengaged from the upper core plate 42 and is unengaged with the top nozzle 16. That is, in the free state of FIG. 2 that corresponds with the hot condition of the nuclear reactor 4, the spring 116 is in an undeflected free state disengaged from the upper core plate 42 and with the second end 168 at most only being slidably engaged with the tail 140 that is received in the opening 172. On the other hand, FIG. 4 depicts the spring apparatus 104 when the nuclear reactor 4 is in a cold state, such as either at startup or immediately prior to shut down. In such a condition, it can be seen that the springs 108 and 112 remain compressively engaged with the upper core plate 42, but in the cold state of FIG. 4 the spring 116 is additionally compressively engaged with the upper core plate 42 by being compressively engaged with the undersurface of the spring 112 and by being, in turn, compressively engaged with the ledge 136 and thus the upper core plate 42. FIG. 3 represents a transition point between the hot condition of the reactor 4 of FIG. 2 and the cold condition of the reactor 4 of FIG. 4. FIG. 3 thus could be characterized as the point between the state in which the spring 116 is compressively engaged with the upper core plate 42 (as in FIG. 4) and the state in which the spring 116 is in its free state wherein it is in an uncompressed condition (as is indicated in FIG. 2). As can be understood from FIG. 5, a plurality of data points indicated at the numeral 198 are plotted for compressive force of the spring apparatus 104 versus deflection. Additionally, a plurality of load/deflection data points 196 are plotted for the hold-down springs 46 that are depicted in FIG. 1. As can be seen in FIG. 5, the data points 198 demonstrate slightly higher compressive forces for the spring apparatus 104 at the higher deflection values, which occur during the cold condition of the nuclear reactor 4 such as is depicted generally in FIG. 4. On the other hand, FIG. 5 demonstrates that the compressive forces indicated by the data points 198 are less than those of the data points 196 in the hot condition of the reactor 4, which would be in the range of approximately 0.500-1.250 inches of deflection. As mentioned above, the transition between cold operation and hot operation of the nuclear reactor 4 involves many complex factors that affect the compressive loading by the hold-down springs on the fuel assembly 10. Depending upon such factors, a given nuclear reactor may have compressive forces that are excessive during hot operation of the reactor and/or may have compressive forces that are undesirably low during cold operation of the reactor. The improved spring apparatus 104 would be advantageously implemented into such a reactor because, as can be seen in FIG. 5, implementation of the spring apparatus 104 results in reduced compressive forces during hot operation and slightly increased compressive forces during cold operation. It can further be understood that by varying the length 190 and the space 194, the various compressive performance characteristics of the spring 116 can be varied to provide specific load/deflection performance that is tailored to the particular needs of any given nuclear installation, of which the nuclear installation 6 is merely an example. By advantageously configuring the spring apparatus 104 such that the spring 116 is only compressively engaged with the upper core plate 42 at temperatures below that where the transition situation of FIG. 3 occurs, improved cold compressive performance can be obtained in conjunction with reduced hot temperature compressive forces. Other variations will be apparent. For instance, two springs or more may be engaged with the upper core plate 42 when the reactor 4 is cold but be disengaged therefrom when the reactor 4 is hot. Similarly, three or more springs could remain engaged with the upper core plate 42 when the reactor 4 is hot. Other examples can be envisioned. Another previously known spring pack is depicted generally in FIG. 6. FIG. 6 depicts a four-spring set of hold-down springs 200 that are similar to the hold-down springs 46 of FIG. 1, it being noted that the set of hold-down springs 200 of FIG. 6 includes four springs whereas the set of hold-down springs 46 includes only three springs. Three spring designs and four spring designs are well known in the relevant art, and it is understood that the advantageous teachings herein can be applied to either such configuration. An improved spring apparatus 204 in accordance with a second embodiment of the disclosed and claimed concept is depicted generally in FIGS. 7 and 8. The spring apparatus 204 is similar to the set of hold-down springs 200, except that a support apparatus 218 is provided in place of the bottom-most spring of the spring apparatus 204. That is, and as can be seen in FIG. 7, the spring apparatus 204 can be said to include a spring 208, a spring 212, and a spring 216, along with the support apparatus 218. The spring apparatus 204 potentially can be formed by removing the bottom-most spring from the set of hold-down springs 200 and replacing it with the support apparatus 218 in order to form the spring apparatus 204. Alternatively, the spring apparatus 204 can be formed by configuring the three springs 208, 212, and 216, together with the spring apparatus 218 to form the spring apparatus 204. The support apparatus 218 can be said to include a plate-like support 222 and an abutment apparatus 224 situated atop the support 222. In the depicted exemplary embodiment, the support apparatus 218 is co-formed as a single piece item by machining it from a block of stainless steel to form the support 222 with the abutment apparatus 224 situated thereon. In the depicted exemplary embodiment, the abutment apparatus 224 includes bumper 226 that is situated on the support 222. As can be seen in FIG. 7, the springs 208, 212, and 216 each have a first end 220A, 220B, and 220C, respectively, and the support 222 similarly has a first end 220D. The first ends 220A, 220B, 220C, and 220D are affixed with a mount 221 to the top nozzle 16 of the fuel assembly 10 (of FIG. 1). The springs 208, 212, and 216 are themselves similar to the hold-down springs 46, and in this regard it can be seen that the spring 208 is an elongated flat plate-like structure having a bend 228 opposite the first end 220A and having an engagement location 232 situated atop the bend 228. The bend 228 terminates in a ledge 236 from which extends a relatively narrower tail 240 which has latching structures opposite the bend 228 that engage an underside of the top nozzle 16 of the fuel assembly 10. The tail 240 is slidingly received through openings formed in the springs 212 and 216. As can be understood from FIG. 7, the bumper 226 is spaced a first distance 250 from the first end 220D of the support 222. The bumper 226 protrudes from the upper surface of the support 222 a second distance 254 in a direction generally away from the fuel assembly 10 and in a direction generally toward the spring 216. The bumper 226 engages the spring 216 at a position 258 thereon both in the hot condition of the nuclear reactor 4, such as is depicted generally in FIG. 7, as well as in the cold condition of the reactor 4, such as is depicted generally in FIG. 8. It is understood that the first and second distances 250 and 254 can be tailored in other embodiments such that the bumper 226 may be disengaged from the spring 216 at a given temperature of the nuclear reactor 4 or at a certain time during the lifetime of the components of the nuclear reactor 4, but in the depicted exemplary embodiment the bumper 226 is engaged with the spring 216 at all times. The size and shape of the bumper 226 can likewise be varied for such purposes. As can be understood from FIGS. 7 and 8, when the nuclear reactor 4 transitions from the hot condition of FIG. 7 to the cold condition of FIG. 8, the spring 216 compressively engages the bumper 226, and that the springs 212 and 208 likewise compressively engage the bumper 226 by compressively engaging one another and the spring 216. By spacing the bumper 226 from the first end 220D such that the bumper 226 engages the springs 208, 212, and 216 at the position 258 that is between the first ends 220A, 220B, and 220C and the opposite ends, the deflection characteristics of the spring apparatus 204 can be configured to be different than those of the set of hold-down springs 200. For example, FIG. 11 depicts a set of data points which are indicated generally at the numeral 296 of compressive load versus deflection for the set of hold-down springs 200. Likewise, another set of data points 298 represent load/deflection values for the improved spring apparatus 204. The improved spring apparatus 204 provides increased compressive load at each deflected value when compared with the deflection points 296 of the set of hold-down springs 200 of FIG. 6. The spring apparatus 204 thus would be advantageously employed in an application, such as the nuclear reactor 4, or other reactor, wherein greater compressive loading in both the hot condition and the cold condition of the reactor are desired. It is understood that the first and second distances 250 and 254 can be varied to provide whatever load/deflection characteristics are desired for a spring apparatus. For instance, it may be desirable to increase the first distance 250 while keeping the second distance 254 unchanged. Other variations will be apparent. An improved spring apparatus 304 in accordance with a third embodiment of the disclosed and claimed concept is depicted generally in FIGS. 9 and 10. The spring apparatus 304 is similar to the spring apparatus 204, except that the spring apparatus 304 includes an additional bumper. That is, the spring apparatus 304 includes three springs 308, 312, and 316, along with a support apparatus 318, and they are stacked one upon the other and are affixed at a first end to the top nozzle 16 of the fuel assembly 10. The support apparatus 318 includes a support 322 that is similar to the support 222 and further includes an abutment apparatus 324. The abutment apparatus 324 includes a bumper 326 and a bumper 327. In the depicted exemplary embodiment, the bumper 326 is spaced a first distance 350 from the first end 320 and protrudes a second distance 354 in the direction of the spring 316 from an upper surface of the support 322. The bumper 326 engages the spring 316 and thus also the springs 308 and 312, at a first position 358 on the spring 316. In the depicted exemplary embodiment, such engagement between the bumper 326 and the springs 308, 312, and 316 occurs in both the hot condition of the nuclear reactor 4, such as is depicted generally in FIG. 9, as well as in the cold condition of the nuclear reactor, as is depicted generally in FIG. 10. However, the bumper 327 is positioned another first distance 362 from the first end 20 and protrudes another second distance 366 from the upper surface of the support 322 in a direction generally toward the spring 316. The another first distance 362 is greater than the first distance 350, and the another second distance 366 is greater than the second distance 354, although this need not necessarily be the case in other embodiments. The bumper 327 engages the spring 316 and thus the springs 308 and 312, at another position 370 on the spring 316. As can be understood from FIGS. 9 and 10, the bumper 327 is disengaged from the springs 308, 312, and 316 in the hot position of FIG. 9, but becomes engaged with the springs 308, 312, and 316 as the springs 308, 312, and 316 transition from the hot position of FIG. 9 to the cold position of FIG. 10. The bumper 327 provides further compressive engagement with the springs 308, 312, and 316, thus further varying the load/deflection performance of the spring apparatus 304. As can further be seen in FIG. 11, another set of data points 399 represent the load/deflection characteristics of the improved spring apparatus 304. As can be seen from the data points 399, the spring apparatus 304 has higher compressive forces than the spring apparatus 204 during cold operation, such as in excess of approximately 1.4 inches of deflection, but has reduced compressive forces compared with the spring apparatus 204 during hot operation, such as from 0.25 to 1.4 inches of deflection. It thus can be seen that the spring apparatus 304 might desirably be implemented in an installation where improved cold condition compressive force is primarily what is desired, and possibly if slightly improved hot compressive forces are additionally desirable. FIG. 11 also indicates that the spring apparatus 204 might instead be desirably implemented in an application where improved hot and cold performance is desired. In this regard, it is understood that the first and second distances 350, 354, 362, and 366 can be varied depending upon the needs of the particular application to result in load/deflection performance curves and responses that are appropriate to the particular application. Other variation will be apparent. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
042736137	description	DESCRIPTION OF THE PREFERRED EMBODIMENT For purposes of example, the invention is described herein with respect to the heavy-water moderated power reactor following the design of the CAN-DU Plant at Douglas Point in Canada, or of its predecessor, the NPD-2 (Canadian Nuclear Power Demonstration) reactor completed in 1962. Both reactors are of the pressure-tube type utilizing heavy water at a pressure of about 1150 pounds per square inch as the moderator and coolant. The fuel is normal uranium dioxide jacketed in zirconium alloy supported in horizontal tubes of the same alloy. The coolant leaves the reactor at 277.degree. C. (530.degree. F.) and produces steam at about 230.degree. C. (446.degree. F.) in a heat exchanger. The NPD-2 reactor produced a gross electrical power output of 22 megawatts with a thermal efficiency of around 25%; whereas the CAN-DU plant produces over 100 megawatts of electrical power at a thermal efficiency of about 29%. FIG. 1 schematically illustrates the core in such a reactor. It includes a large tank or vessel, generally designated 2, pierced with a number of tubes 4, called calandria tubes. Each tube 4 includes a cluster of fuel rods 6 of fissile-material-containing elements, usually natural uranium, or in some instances, very slightly enriched uranium. The tank is filled with heavy water at ordinary pressure which fills the space between the tubes 4 and thereby serves as the moderator, remaining essentially at ordinary temperature. The tubes 4, enclosing the fuel rods 6, are filled with the coolant, also heavy water, under a pressure of 500 to 1500 pounds per square inch, the coolant flowing in the annular channels between the fuel rods 6 and the inner wall of the tubes. As more particularly shown in FIG. 2, there are 37 fuel rods 6 in each of the pressure tubes 4. Of these, 19 fuel rods occupy exterior positions in the cluster (these being indicated as rods 6e), and 18 fuel rods occupy interior positions in the cluster (these being indicated as rods 6i). Further details of the construction and operation of such reactors are readily available in the published literature, and therefore are not set forth herein. One characteristic of the above-type reactor is its ability to be refueled on-line, i.e., while the reactor is operating at full power. Another characteristic is that the exterior rods 6e are subject to a high thermal flux distribution, but to a low flux distribution of fast neutrons (i.e. neutrons above thermal); whereas the interior rods 6i are subject just to the opposite, namely to a low thermal flux distribution but to a high fast-neutron flux distribution. Both of the above characteristics are exploited by the present invention in order to operate the reactor so as to shift it from a uranium cycle to a thorium cycle, thereby decreasing both the consumption of natural uranium and the danger of a "run-away" should there be a loss of heavy water. The on-line refueling is effected by providing the fuel rods 6 within each pressure tube 4 in the form of a plurality of cluster segments, each as shown in FIG. 3. Each segment 9 includes a pair of circular end plates 10 having the rods 6 (both the exteriorly-positioned ones 6e and the interiorly-positioned ones 6i) in the form of segments extending between the end plates 10. The present practice in existing reactors of this type is to form the cluster segments 9 by welding the rod segments 6 to the end walls 10, to refuel the reactor by inserting a cluster segment of new fuel at the charge end and withdrawing a cluster segment of depleted fuel from the discharge end while the reactor is in normal operation, and to discard each cluster as it is removed from the discharge end. As distinguished from the existing reactors of this type, in the illustrated embodiment of the present invention the rod segments 6 are detachably carried by the end plates 10 to enable them to be conveniently removed and reattached in order to modify the cluster segments used for refueling the reactor at the charge end of the core. This permits the reactor to be operated in such a manner as to provide a gradual shift-over from a normal uranium cycle to a thorium cycle. The shift-over is effected by exploiting the above-mentioned characteristic of reactors of this type in which the fast-neutron flux distribution is highest at the interior fuel rods 6i and is lowest at the exterior fuel rods 6e, which flux distribution favors breeding in the interior fuel rods 6i and fuel burn-up in the external fuel rods 6e. Briefly, there is first inserted, at one end (e.g., the charge end) of the core, a cluster in which some of the interior rod segments (preferably the most interior ones) are of natural thorium; the remaining interior, as well as all the exterior, rod segments are of natural uranium as in the normal practice. There is only a small loss of reactivity since the thorium segments are in a position of low statistical weight. The thorium segments irradiated in the interior rod positions build up in multiplication factor to be about equivalent to natural uranium. The more irradiated thorium that is added, the higher will be the conversion ratio, and the faster will the fresh thorium be built up in multiplication factor. The above procedure is repeated for each refueling step until the rod segments at the discharge end of the interior positions have been irradiated sufficiently to be close to the maximum multiplication factor. In one example described below, each thorium segment is irradiated for ten refueling steps, and in a second example, it is irradiated for only two refueling steps. The irradiated thorium rod segments are then used for refueling the exterior positions of the cluster until they occupy all the exterior rod positions. As the thorium rod segments in the exterior rod positions are depleted, they are removed from the discharge end of the cluster and are used to refuel the interior positions of the cluster, while the irradiated thorium-containing segments are removed from the discharge end of the interior positions and are used to refuel the charge end of the exterior positions in the cluster. Whenever a thorium segment has reached its irradiation (metallurgical or reactivity) limit, or whenever the accumulation of fission products reduces the conversion ratio too much, fresh natural thorium segments can be introduced into the interior rod positions of the cluster and, when sufficiently irradiated, can then be used for refueling exterior rod positions as described above. It should be noted that considerable flexibility is provided in the above procedure for going over to the thorium cycle, depending on how well the nuclear parameters can be chosen. At any point, the change-over to the thorium cycle can be slowed down and some natural uranium introduced in lieu of natural thorium. It should also be noted that, since the conversion ratio will vary radially, each exterior rod position in successive charge clusters could receive irradiated thorium from a distribution over the interior of the entire calandria, so that all the external fuel rods would have approximately the same reactivity effect. The axial variation would not introduce any operational problems. By fuel management, in which certain of the calandria have more recently introduced thorium, greater burn-up can be achieved. The thorium fuel that is finally discharged from the reactor can be stored or buried until such time as it is economically and politically advantageous to extract the contained uranium-233 and fabricate it into fuel elements. Because of the low excess reactivity under which CAN-DU reactors are operated, the amount of fresh thorium which can be inserted into the reactor is small, and the transition to the thorium cycle will therefore take a number of years. This time period can be shortened by increasing the reactivity, for example by the use of "booster" rods composed of enriched uranium inserted into the moderator. The booster rods may be removed from the reactor when the transition to the thorium cycle is completed. In a standard CAN-DU reactor having 37 fuel rods 6 in each calandria tube 4, there is enough excess reactivity to replace only two natural uranium rods by thorium rods. The residence time of fuel in such a CAN-DU reactor is one year with about 7500 MWD/R average burn-up. In the two examples described below, the total length of the rod cluster in each calandria tube 4 is about 200 inches, and the length of each segment used for refueling is about 20 inches. Thus, one rod position can be completely converted in ten refueling steps by converting one segment of the rod position during each refueling step. EXAMPLE 1 Following is one example of a refueling procedure which could be used for converting the above standard CAN-DU reactor from a natural uranium loading to a thorium loading. This procedure is schematically illustrated in FIG. 4 and involves three phases, namely: Phase A, wherein thorium rod segments are irradiated in the interior rod positions of the cluster; Phase B, wherein the irradiated thorium rod segments are used for refueling the rod segments in all the exterior rod positions; and finally, Phase C, wherein the depleted thorium rod segments discharged from the exterior rod positions are used for refueling the remaining interior rod positions, thereby completing the transition to the thorium cycle. As mentioned earlier, both during Phase C and the subsequent operation of the reactor under an all-thorium cycle, fresh thorium segments may be used whenever necessary for refueling the interior rod positions, and after sufficiently irradiated, may then be used for refueling the exterior rod positions. Since, in this example, there is enough excess reactivity in the reactor to irradiate only two thorium rods, Phase A is divided into a number of subphases in each of which only a fraction (in this case two) of the interior rod positions are refueled with the thorium-containing rod segments. The number of subphases in Phase A would be sufficient to irradiate enough thorium-containing rod segments to refuel the rod segments of all the exterior rod positions of the cluster at each refueling step during the subsequent Phase B. This is schematically illustrated in FIG. 4, wherein Phase A is divided into a plurality of subphases, these being schematically indicated as Subphases A1, A2, it being appreciated that in this example there would be 10 such subphases in Phase A, as will be clear from the description below. Thus, as shown in FIG. 4, the first Subphase (A1) is started by refueling the charge end of a fraction (2 out of 18) of the interior rod positions (preferably the most interior ones) with natural thorium-containing segments. For simplification purposes, the diagram of FIG. 4 illustrates only 2 interior rod positions 6i to represent the actual 18 interior rod positions, and 2 exterior rod positions to represent the actual 19 exterior rod positions. Accordingly, whereas FIG. 4 illustrates a natural thorium-containing segment used for refueling only one interior rod position, it will be appreciated that this actually represents 2 interior rod positions; and whereas FIG. 4 illustrates a natural uranium-containing segment used for refueling only one interior rod position, it will be appreciated that this actually represents the remaining 16 interior rod positions. In this Subphase A1, all the exterior rod positions 6e are refueled with natural uranium-containing segments. Subphase A1 involves 10 refueling steps, taking one year to complete, at the end of which 2 thorium rods (schematically illustrated by only one rod position as explained above) will have been built up to the reactivity of natural uranium. Subphase A2 is then started in which the same interior rod positions are loaded with natural thorium at the charge end of the cluster, while the irradiated thorium segments are removed from the discharge end. Thus, at the end of Subphase A2 (end of the second year of operation), thorium-containing segments for two complete rods will have been irradiated and discharged. These are stored, and the process is repeated through nine additional subphases of Phase A (terminating at the end of the eleventh year of operation) at which time thorium-containing segments for 20 rods will have been irradiated and discharged. This completes Phase A and marks the start of Phase B in which, during each refueling step, the rod segments of all 19 of the exterior rod positions are refueled with thorium-containing segments irradiated during Phase A. Since there are 10 refuelings per year, each refueling involving the replacement of the 10 segments constituting a fuel rod, this Phase B takes one year, at the end of which (end of twelfth year) all the exterior rod positions will have been replaced by irradiated thorium-containing segments. Phase C begins at the start of the thirteenth year of operation, at which time all 19 of the exterior rod positions, but only 2 of the interior rod positions, are occupied by the thorium-containing segments, the remaining 16 interior positions still being occupied by uranium-containing segments. During this Phase C, the depleted thorium-containing segments removed from the discharge end of the exterior rod positions are used for refueling the charge end of the interior rod positions. In this example, one year is required for refueling two complete interior rod positions. Accordingly at the end of the thirteenth year of operation, 4 interior rod positions will have been refueled with thorium, and at the end of the twentieth year of operation, all 18 interior rod positions will have been refueled with thorium. It will be appreciated that during Phase C, the irradiated thorium-containing segments from the discharge end of the interior rod positions 6i are used for refueling the charge end of the exterior rod positions 6e. Accordingly, at the end of twenty years of operation, the transition to a thorium cycle in both the interior and exterior rod positions will have been completed. Whenever, during Phase C or the subsequent thorium cycle operation, a thorium segment has reached its irradiation (metallurgical or reactivity) limit, or whenever the accumulation of fission products reduces the conversion ratio too much, fresh natural thorium segments would be introduced into the interior rod positions of the cluster and, when irradiated sufficiently, would be placed in the exterior rod positions. In practice, the irradiated thorium-containing rod segments removed from the discharge end of the interior rod positions would be stored long enough for the protactinium to decay into uranium-233 before being introduced into the charge end of the exterior rod positions. This can be conveniently accomplished by introducing, following the completion of the above-described Phase A and before the start of Phase B, one additional refueling step to introduce a delay in the sequence of 36 days (one-tenth year) between refuelings, which is adequate time to permit the protactinium to decay before utilizing the irradiated thorium segments for refueling exterior rod positions in Phase B. EXAMPLE 2 Detailed calculations indicate that the initial build-up of uranium-233 in fresh natural thorium in interior rod positions is rapid, and therefore the procedure may be considerably shortened from that described in Example 1, wherein each thorium-containing rod segment is irradiated for a total of ten refueling periods (i.e., one year) by providing it at the charge end of the cluster, advancing it one position along the length of the cluster during each refueling step, and removing it from the discharge end for use in refueling the exterior rod positions in Phase B. Thus, in this Example 2, each thorium-containing rod segment may be irradiated for only two refueling steps, by providing it at one end of the cluster (either the charge end or the discharge end), retaining it in the same position in the cluster during the next refueling step, and then removing it from the same end (charge or discharge) of the cluster for later use in refueling the exterior rod positions in Phase B. One way of conveniently accomplishing this is to insert a cluster of uranium segments but including two thorium-containing segments in internal positions at the charge end of the core and, at the end of the first refueling step, to remove the thorium-containing segments and to replace them by fresh natural uranium segments. The cluster is then moved one position, thereby providing a vacant cluster position at the charge end of the core for the insertion of another cluster containing fresh natural uranium segments plus the two previously-removed thorium-containing segments. The thorium-containing rod segments may be similarly irradiated for two refueling steps in the last position at the discharge end of the cluster. After two thorium-containing rod segments have been irradiated for the two refueling periods, they may be removed and stored until a sufficient number have been prepared for use in refueling the exterior rod positions in the cluster during Phase B, as discussed above. It will thus be seen that, when compared to Example 1 above, the procedure set forth in this Example 2 substantially shortens Phase A during which a sufficient number of thorium-containing rod segments are irradiated in interior rod positions of the cluster to enable them to be used for refueling exterior rod positions in the cluster during Phase B. The remainder of the procedure in this Example 2 is otherwise the same as described above with respect to Example 1. As indicated above, each of the cluster segments 9 (FIG. 3) is constructed to facilitate the attachment and detachment of the rod segments 6 to the end plates 10 to permit the above-described refueling procedure. FIGS. 5a and 5b illustrate, for purposes of example only, one form of arrangement which could be used, in which one end of each of the rod segments 6 includes diametrically-opposed bayonet pins 20 each provided with an enlarged head 22, receivable within large holes 24 formed in end plate 10a, the holes being connected to narrow arcuate slots 26. The other end of each segment 6 is formed with a central threaded bore for receiving a threaded fastener 28 passing through an opening in the other end plate 10b. To attach a desired arrangement of rod segments 6 between the two end plates, it is only necessary to mount the bayonet pin end of all the rod segments to the respective end plate 10a by inserting the enlarged heads 22 of the bayonet pins 20 into the respective large holes 24 in the end plates 10 and rotating the rod segments along the narrow slots 26, and then to attach the other end plate 10b by the use of the threaded fasteners 28. FIG. 6 of the drawings illustrates a modification in the refueling procedure, in which modification booster rods 120 of enriched uranium are inserted into the heavy-water moderator 108 in order to shorten the time for the complete transition from the uranium cycle to the thorium cycle. By using such boosters, this transition time can be substantially shortened. This utilization of thorium can be enhanced by increasing the heavy-water content in the interior of the calandria pressure tubes 104 in order to increase the fast-neutron flux-capture therein, and thus hasten the build-up in uranium-233 content of the thorium in the fuel rods 106. About 25% increase in the heavy-water content of the interior would be feasible with only a 5% increase in the diameter of the calandria pressure tubes. The above contemplates that the thorium-containing rod segments 6i used for refueling the interior positions in Phase A consist of pure natural thorium. However, the conversion of sufficient thorium to uranium-233 to provide enough reactivity for reactor operation may be expedited by irradiating rods having thorium greatly diluted by beryllium. Such a rod construction is illustrated in FIG. 7, wherein it will be seen that it includes a cladding 130, e.g., of zirconium, loaded with thorium-oxide pellets 132 interspersed with a much larger number of beryllium-oxide pellets 134, so that the resonance integral of the thorium would be close to that of the infinite dilute value. In typical cases, about 10%-20% of the pellets would be of thorium-oxide. The absorption of the thorium would be greatly increased over that in all-thorium rods. On the other hand, the beryllium would serve to increase the reactivity effectiveness of the uranium fuel segments of the cluster, thus compensating for the increased absorption of the thorium. In fact, it may be possible to insert two or more of the beryllium-diluted rods near the center of each cluster. Furthermore, it would probably be necessary to irradiate the beryllium-diluted rods only during the time for a fuel cluster to advance by the distance of one fuel segment. This would also prevent over-heating. By using the bayonet-type fastening arrangement, e.g. as described with respect to FIGS. 5a and 5b, for the beryllium-diluted rods, they could be removed at the charge end and replaced by natural uranium when the associated pressure tube is opened for refueling. At the discharge end, when a cluster is pushed through to the final position, the central uranium rods could be replaced by the beryllium-diluted rods. When the irradiated rods are disassembled, the irradiated thorium-oxide pellets would be loaded into a rod so as to be interspersed with fresh natural thorium-oxide pellets to produce the desired enrichment. There would, of course, be some uneven heating, but this would probably not be serious in a distance as short as a segment. The beryllium-oxide pellets could be reprocessed as necessary to remove effects of irradiation and helium and lithium, and then re-used. FIG. 8 illustrates a further modification, as described in my co-pending U.S. patent application Ser. No. 929,078, filed July 28, 1978, wherein the thorium-containing rod segments may be made of pellets 192 of pressed powder or particles, each pellet having a central section 194 of natural uranium particles and an outer annular region 196 of thorium particles. For example, about 30% of the total pellet volume could be constituted of the natural uranium particles in the central section 194. In such an arrangement, the thorium would act to shield the uranium in the resonance region where most of the absorption of neutrons occurs, so that the uranium-238 will absorb relatively few neutrons. On the other hand, in the fast region where cross-sections are small, the thorium would have almost no shielding effect, and the uranium will have a proportionately fast fission factor, which is known to be relatively five times as great as for thorium. Accordingly, there will be a considerable amount of power generated from the thorium at the beginning of life due the natural uranium. On the other hand, little plutonium-239 will be formed in place of uranium-233; and moreover, that little will be more than compensated for by the improvement in the fast effect, so that the ultimate energy from the composite fuel rods will increase over that from pure thorium rods. Another advantage is that, if the fuel discharged from the reactor is ever reprocessed, the uranium will be a combination of U-233 and U-238, which will not be of any use for weapons. Many other variations, modifications and applications of the described embodiments of the invention will be apparent.
050900374	abstract	A CT apparatus reduces errors in projection data acquired in helical scanning. The imaged object moves concurrently along a translation axis and the x-ray beam is periodically translated with the imaged object so as to subtend a single predetermined volume element during the acquisition of one projection set of data for a first slice. The x-ray beam then returns to its starting position and tracks a second predetermined volume element within a next slice. The x-ray beam may be translated by moving the focal point or a collimator or a combination of both.
054019753	description	DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below. In the following description, a carbon atom cluster is abbreviated to "C.sub.n " in accordance with the number n of atoms contained therein on the unit structure. FIG. 1 is a view of a molecular structure of carbon atoms constructed according to the present invention. FIG. 1(A) is a top view of a toroidal molecule 100 which includes carbon atoms. The toroidal molecule 100 has an outer diameter of 2.26 nm and an inner diameter of 0.78 nm. The toroidal molecule 100 has a surface on which carbon atoms are bonded in a network manner. Accordingly, respective carbon atoms are located at the intersections of lines shown in FIG. 1(A). The structure shown as an example in FIG. 1 is constructed by 360 carbon atoms. FIG. 1(B) shows a crosssection 130 of the toroidal molecule 100. In FIG. 1(B), the right side of the crosssection shows an outer wall surface, and the left side of the crosssection shows an inner wall surface. FIG. 1(C) shows the outer wall surface 140 of the toroidal molecule 100, and FIG. 1(D) shows the inner wall surface 150 thereof. The toroidal molecule 100 has: ten sevenfold carbon rings 160 shown in FIG. 1(D) which are alternately arranged at upper and lower positions on the inner wall surface; ten fivefold carbon rings 110 shown in FIG. 1(C) which are alternately arranged at upper and lower positions on the outer wall surface in correspondence with the sevenfold carbon rings; and 160 sixfold carbon rings 120 having a structure similar to the graphite structure as shown in FIG. 1(A) which are arranged on positions of the surface other than those where the fivefold and sevenfold rings are arranged. Each sixfold ring 120 is shaped like a regular hexagon, and the nearest inter-bond distance is about 0.145 nm. The crosssection 130 of the torus of the molecule 100 is shaped like a circle. According to structure analysis by using a method of examining thermal stability of the structure on the assumption of presence of a potential between atoms on the basis of molecular dynamics, it is confirmed that the toroidal carbon molecule structure is stable even at a temperature of 2000.degree. K. Furthermore, cohesive energy is -7.4 eV per one atom at cryogenetic temperatures, which is the same value as the cohesive energy, -7.4 eV, per one atom in the graphite structure and as the cohesive energy, -7.4 eV, per one atom in a stable spheroidal molecule structure including 60 atoms and called "buckminsterfullerene". Accordingly, the toroidal molecule exists stably. By adjusting the number of sixfold carbon rings 120 other than the fivefold and sevenfold rings 110 and 160, a toroidal molecule of 120, 480, 1080, 1440 or 1920 carbon atoms can be constructed as well as the molecular structure shown in FIG. 1. The number N of atoms constituting one toroidal molecule is generally equal to a value obtained by multiplying 120 or 80 by 3.sup.n and further by 4.sup.m in which n and m represent integers being non-negative. In any case, the cohesive energy takes a value near to -7.4 eV, so that the toroidal molecule exists stably. According to a result of simulation, the relation between the inner radius of the torus and the number of atoms and the relation between the outer radius of the torus and the number of atoms are expressed in the curves 210 (inner radius) and 200 (outer radius) in FIG. 2, so that the respective radii increase as the number of atoms increases. Expansions in the same systems of C.sub.360 and C.sub.240 having 360 and 240 atoms among the respective numbers of atoms expressed in the axis of abscissa of FIG. 2 are shown in FIGS. 31 and 36. The respective numbers N of atoms constituting tori shown in FIGS. 31 and 36 are expressed by the following equations: EQU {C.sub.360 (FIG. 31)}N=120.times.(n.sup.2 +nm+m.sup.2) EQU {C.sub.240 (FIG. 36)}N=80.times.(n.sup.2 +nm+m.sup.2) in which n, m.gtoreq.0 (n=m.noteq.0). Further, as shown in FIGS. 35(A) and 35(B), toroidal molecules having various rotational (symmetrical) axes can be formed from C.sub.240 of FIG. 36 and from C.sub.360 in FIG. 31. The respective numbers N of atoms constituting the toroidal molecules shown in FIGS. 35(A) and 35(B) are expressed by the following equations: EQU {C.sub.360 (FIG. 35(A))}N=48.times.n EQU {C.sub.240 (FIG. 35(B))}N=72.times.n in which n=4, 5, 6, 7, 8. Each toroidal molecule shown in FIGS. 35(A) and 35(B) has rotation symmetry of 2n. That is, when each of the toroidal molecules is rotated by 180/n degrees, the structure thereof coincides with the original structure thereof. Similarly, as shown in FIG. 35(C), various rotation-symmetrical toroidal molecules can be formed from C.sub.540. The respective numbers N of atoms constituting respective toroidal molecules shown in FIG. 35(C) are expressed by the following equation: EQU {C.sub.540 (FIG. 35(C))}N=90.times.n in which n=4, 5, 6, 7, 8. Each toroidal molecule shown in FIG. 35(C) has rotation symmetry of n. That is, when the toroidal molecule is rotated by 360/n degrees, the structure thereof coincides with the original structure thereof. Even in the case where the number of carbon atoms is the same, molecular structures whose orientation of fivefold and sevenfold rings are different, can be formed. FIG. 37 shows such molecular structures whose orientation of fivefold and sevenfold rings in the torus are different, although those numbers of atoms are 240. In Pat.0 and Pat.1 of FIG. 37, one of the vertexes of each fivefold ring is oriented toward the center of the torus but Pat.0 and Pat.1 are different in the arrangement of sevenfold rings relative to fivefold rings. Similarly, in Pat.2 and Pat.3 of FIG. 37, one of the vertexes of each fivefold ring is oriented to be substantially perpendicular to a plane of FIG. 37 but Pat.2 and Pat.3 are different in the arrangement of sevenfold rings relative to fivefold rings. Interaction energy between carbon molecules, including toroidal molecules, is generally expressed by attraction potential being in inverse proportion to the sixth power of the distance between molecules. Interaction between atoms in each molecule is sufficiently strong. Accordingly, interaction between the molecules is sufficiently weaker than that between the atoms, so that the molecule is not decomposed because of other molecules near thereto. Thus, as shown in FIG. 3, structures 320, 330, 340 and 350 in which toroidal molecules are arranged one-dimensionally can be formed. The position of each of constituent atoms however changes by not larger than about 0.05 nm, because of the presence of near other molecules. Therefore, the bonding properties between the atoms in each molecule change more or less, so that potential energy changes in accordance with the change of the bonding properties. As a result, dynamic characteristics such as tensile strength, etc. and the energy band structure of electrons/holes change, so that electric characteristic changes. Particularly one-dimensional dynamic characteristics and electric characteristics can be controlled by arranging carbon molecules on a plane as shown in the arrangement 320 in FIG. 3 or by arranging carbon molecules to face ring-surfaces each other as shown in the arrangement 330 in FIG. 3. Alternatively, one-dimensional dynamic characteristics and electric characteristics can be modulated spatially by inserting a toroidal molecule vertically or obliquely in the arrangement 320 of carbon molecules on a plane, as shown in the arrangement 340 in FIG. 3. Furthermore, these characteristics can be controlled by forming a one-dimensional large molecule by a combination of the arrangements 320, 330 and 340 shown in FIG. 3. For example, a low dimensional structure such as a one- or two-dimensional structure can be formed by making buckminsterfullerene molecules adsorbed onto the surface (100) of Si. Because the local molecular arrangement of the toroidal molecules shown in FIG. 3 is similar to that of the buckminsterfullerene molecules, such a low dimensional structure can be formed of the toroidal molecules in the same manner as described above. That is, even in the case where impurities 390 are adsorbed onto a part of the toroidal molecules, as shown in the arrangement 350 in FIG. 3, the same change as in the arrangement 340 can be provided. Because the energy band structure of an impurity-adsorbed toroidal molecule with adsorbed atoms such as alkaline metal atoms, boron atoms, nitrogen atoms, etc. onto a toroidal molecule is different from that of a toroidal molecule constituted by only the carbon atoms, the dynamic characteristics of the impurity-adsorbed toroidal molecule and the electric characteristics thereof change according to the absorbed atoms so that the impurity-adsorbed toroidal molecule can act as a metal, an insulator or a semiconductor. By arranging such impurity toroidal molecules one-dimensionally and changing the arrangement thereof as described above, the characteristics of the whole system change. This can be applied to both the two-dimensional case and the three-dimensional case. Further, by removing a toroidal molecule from a position where the toroidal molecule is to be disposed or contrariwise by providing a toroidal molecule additionally, the dynamic characteristic and the electric characteristic can be changed spatially. Because also a molecular structure formed by combining a cylindrical carbon nano-tube with a toroidal molecule as shown in the carbon molecule 360 in FIG. 3 has cohesion energy substantially equal to that of buckminsterfullerene, the molecular structure can be formed easily. Similarly, a toroidal one-dimensional molecule 370 in which toroidal molecules are not connected by weak inter-molecular force but connected by inter-atom covalent bonding as shown in the one-dimensional molecule 370 in FIG. 3, and a torus-chain molecule 380 can be formed. The above-mentioned molecules 370 and 380 can be formed by radiating a laser beam onto a connection portion or applying arc discharge thereto after bringing a plurality of molecules close to one another. Although FIG. 3 shows the case where each of the molecules 370 and 380 is formed as one large molecule by combining three molecules strongly, it is a matter of course that a larger number of molecules can be combined in the same manner as described above. FIG. 4 shows an example in which toroidal carbon molecules 400 are arranged two-dimensionally. Because inter-molecular potential can be expressed by attraction potential being in inverse proportion to the sixth power of inter-molecular distance, a structure being stable against thermal fluctuation can be obtained if the respective toroidal molecules are arranged so that the respective centers of tori coincide with the vertexes of a triangle. As is obvious from comparison of the two-dimensional arrangement 410 of toroidal molecules shown in FIG. 4(A) with the two-dimensional arrangement 420 of toroidal molecules shown in FIG. 4(B), the coefficient of inter-molecular potential in the arrangement 420 is smaller than that in the arrangement 410. Accordingly, the inter-molecular distance in the arrangement 420 is smaller than that in the arrangement 410. Accordingly, the atomic density changes according to the arrangement of toroidal molecules as to whether the arrangement 410 is selected or whether the arrangement 420 is selected. Also in the arrangements shown in FIG. 4, two-dimensionally spread giant torus molecules or crystals such as the molecules 370 and 380 in FIG. 3 in which molecules are not connected by weak inter-molecular force but connected by strong inter-atom covalent bonding force can be formed by laser radiation or arc discharge. Because potential energy and the energy band structure of electrons/holes change in accordance with the above-mentioned two-dimensional structure, the dynamic characteristic and the electric characteristic are modulated spatially. Further, the dynamic characteristic and the electric characteristic can be changed spatially by removing a toroidal molecule from a position where the toroidal molecule is to be disposed or contrariwise by providing a toroidal molecule additionally. Further, because potential energy and the energy band structure of electrons/holes are changed if impurity toroidal molecules each formed by adsorbing atoms such as alkaline metal atoms, boron atoms, nitrogen atoms, etc. onto a toroidal molecule in the same manner as described above are arranged as a stratified formation and the method of the arrangement thereof is changed, the dynamic characteristic and the electric characteristic are modulated spatially. As shown in FIG. 5, buckminsterfullerene molecules or spheroidal carbon molecules 520 may be arranged in holes of two-dimensionally arranged toroidal carbon molecules 500, by using a probe 510, which is applied with a voltage or current, of a scanning tunneling microscope (hereinafter referred to as "STM") so that bit information in a hole-blocking state as shown in the state 540 and bit information in a hole-free state as shown in the state 530 are made to correspond to "1" and "0" respectively to make it possible to store information. As shown in the states 620 and 630 in FIG. 6, a part of toroidal molecules 500 instead of spheroidal atoms/molecules may be arranged vertically by using a probe 610 of a STM so that the state of absence of vertical molecules and the state of presence of vertical molecules are made to correspond to bit "1" and bit "0" respectively. As shown in FIG. 6, because the state of the arrangement of molecules is kept constant even at an ordinary temperature if molecules to be arranged are sufficiently large, information is stored in accordance with the state of the arrangement thereof. Writing and reading of information can be realized easily by using the STM. Further, the vertical toroidal molecules may be arranged two-dimensionally so that information can be stored in accordance with the orientation of the toroidal molecules. When, for example, the orientation of molecules in the state 630 and the orientation perpendicular thereto are made to correspond to "1" and "0" respectively, the energy required for writing and reading of information can be reduced. In the arrangement shown in the state 630 in FIG. 6, however, operation at a low temperature is required because the fluctuation of orientation caused by heat is large. As shown in FIG. 7, the spatial change of characteristics can be brought by partially arranging impurity-adsorbed toroidal molecules 710 or one-dimensional structures thereof into a two-dimensional arrangement 720 constituted by a plurality of toroidal molecules 700. In this case, the arrangement can be used in a wide space, so that the characteristics of the system can be modulated by ion implantation. As a method of the three-dimensional arrangement of toroidal molecules, there is a crystallization method in which two-dimensional structures each constituted by a plurality of toroidal carbon molecules 800 are combined as a stratified formation as shown in FIG. 8(A). Further, the characteristics of the system can be modulated by impurity-adsorbed molecules or ion implantation. On the other hand, as shown in the arrangement 810 in FIG. 8(B), the characteristics of the system can be changed spatially by arranging impurity-adsorbed toroidal molecules or layers 810 thereof as a stratified formation. Further, the characteristics of the system can be modulated by arranging the positions of toroidal molecules of different layers so that they overlap each other as shown in the arrangement 820 in FIG. 8(C) or by arranging the positions of toroidal molecules of different layers at a predetermined distance so that they are not overlap each other as shown in the arrangement 830 in FIG. 8(D). Further, a three-dimensional arrangement structure in which two-dimensional planes having the arrangements 410 and 420 shown in FIG. 4 are laminated alternately exists stably. Also in this case, a considerably hard three-dimensional crystal can be provided by not weak inter-molecular force but strong inter-atom covalent bonding force. As shown in FIG. 9, a spheroidal giant carbon molecule (cluster) 920 may be formed by collecting many toroidal molecules 900. In this case, the characteristics of the cluster can be changed continuously by changing of mixing impurity-adsorbed toroidal molecules 910 into the cluster 920. Further, a thin film or a structure being low in the number of dimensions can be formed by combining a plurality of such molecules 920. The dynamic characteristics and the electric characteristics can be controlled in accordance with the method of combination thereof. As the piles 930 and 940 of toroidal molecules shown in FIG. 9, three-dimensional structures can be formed by piling up a plurality of toroidal molecules different in size. Also in the case of three-dimensional structures, a crystal or a giant molecule in which toroidal molecules are connected by not weak inter-molecular force but strong inter-atom covalent bonding force can be realized by arc discharge or laser radiation. FIG. 10 shows an embodiment of a cluster of molecules formed by deforming toroidal molecules. Molecule structures 1000 and 1003 are molecules/crystals to form substrates. A spheroidal carbon molecule 1004 such as the sphere of buckminsterfullerene is adsorbed on the molecule structure 1000 to form a substrate, and a toroidal molecule 1002 having a hole to be just fitted to the sphere of buckminsterfullerene is adsorbed on the molecule structure 1003 to form the other substrate. As a result, the spheroidal molecule 1004 and the toroidal molecule 1002 are connected closely so that the substrates 1000 and 1003 constituted by molecules can be stuck and fixed to each other. Further, a key structure can be formed in a manner so that the toroidal molecule is halved and the separated molecules of the halved parts are fixed to molecules in directions opposite to each other to make a knot so-called Alexander's knot to thereby form a key structure as shown in the knot 1010 of toroidal molecules in FIG. 10. If a plurality of such key structures are used in combination as shown in the knot 1020 using toroidal molecules, a stronger key structure can be formed. As other molecular structures, a toroidal molecule 1030 having a knot formed at a hole and a molecule 1040 having a topological characteristic such as Klein's bottle being reversible can be formed. As shown in FIG. 11, a toroidal carbon molecule 1110 or a cluster 1130 of toroidal molecules on a substrate surface 1140 may be provided so that another atom/molecule can be adsorbed to the hole portion of the torus. In this case, a function such as an indicator for judging whether a rod-like molecule 1100 or 1120 is just fitted into the hole of the torus can be realized. This function can be used as an indicator. Because the change of the mechanical and electrical characteristics of the whole molecule 1110 or 1130 is caused by the shape change of the upper and lower portions of the rod molecule 1100 and 1120 inserted into the toroidal carbon molecules 1110 and 1130, the structure of FIG. 11 can serve as a pressure sensor by making the pressure change correspond to the shape change and further making the shape change correspond to the change of current-voltage characteristic. As shown in FIG. 12, a toroidal molecule 1210 can serve as a molecule-size capsule when the toroidal molecule 1210 or a cluster of toroidal molecules is provided so that an impurity molecule 1200 including atoms other than carbon can be adsorbed in the cylindrical ring of the molecule or the cluster 1210. That is, the cylinder of the toroidal molecule is opened locally by laser radiation, so that specific atoms/molecules are embedded in the inside of the toroidal molecule by an STM or the like. Thereafter, the toroidal molecule is moved to a certain place and the cylinder of the toroidal molecule is opened locally again by laser 1 radiation or the like, so that specific atoms/molecules are taken out. Further, in the case where a specific size toroidal molecule or a cluster of toroidal molecules can adsorb other atoms/molecules by directly taking the other atoms/molecules from the surface of the cylinder thereof into the inside thereof, the toroidal molecule 1210 can serve as a deodorizer. As shown in FIG. 13, a slender rod-like molecule 1320 such as a nanometer-scaled tube, i.e., a carbon nano-tube may be passed through holes of specific size toroidal molecules (or clusters) 1300 and 1310 to make it possible to provide a function of a rotor/wheel of a novel very fine molecular machine. When, for example, one molecule 1300 is rotated by a method as shown in FIG. 14, the rotation can be transmitted to the other toroidal molecule 1310 through the carbon nano-tube 1320 by inter-molecular force between each of the toroidal molecules 1300 and 1310 and the carbon molecule 1320. If the carbon nano-tube 1320 is replaced by a curved tube having arbitrary torsion, the motive power can be transmitted further in the direction of the axis of the carbon tube. As shown in FIG. 14, another slender axial molecule 1410, i.e., a very slender molecule such as a carbon nano-tube may be passed through a specific size toroidal molecule (or cluster) 1420 to make it possible to provide a rotor of a very fine molecular machine. The operating mechanism of the rotor of the very fine molecular machine will be described below in detail. When, for example, an electrostatic field is applied to the toroidal molecule 1420 clockwise by using eight electrodes 1430 shown in FIG. 14, the carbon molecule 1420 is polarized and rotates to follow the change in polarity of the electrodes. To raise the rotation efficiency, it is necessary to optimize the number of electrodes 1430 and the timing of the electric field change and to supply impurities to facilitate the polarization of the carbon molecule 1420. This can be achieved easily. For example, the rotation efficiency can be improved by changing the number of carbon atoms, that is, by changing the structure of the toroidal molecule so that fivefold rings 1400 contained in the toroidal molecule project from the outer wall surface of the toroidal molecule. Because the present invention uses a stable molecular structure, the structure can be determined substantially uniquely when the external condition with respect to the number of molecules is kept constant. Accordingly, the size of the structure can be made uniform in a very fine size range. When toroidal molecules different in size are produced by changing the number of atoms and are rotated in arrangement as shown in FIG. 15, gears of a very fine molecular machine can be provided. In FIG. 15, the shape of a portion of the toroidal molecule 1530 corresponding to teeth of a gear can be changed by changing the number of carbon atoms constituting the toroidal molecule 1530. Portions 1550 and 1560 each constituted by the one-dimensional arrangement 1520 of toroidal molecules are paths of propagation of light atom lean gas or light. In either case, particles of light atom lean gas or light collide with a gear in the incident side to transfer the momentum of the particles to the gear, so that the gear rotates. Alternately, one toroidal molecule receives rotation force directly from the carbon tube 1540 as an axis and rotates another adjacent toroidal molecule through teeth of the gear, so that rotational speed can be changed by using a difference in size between toroidal molecules. When specific size toroidal molecules (or clusters) are used in combination so that the energy band structure for electrons/holes is changed in accordance with the number of carbon atoms contained in each molecule (or cluster) to respond to light of a specific wavelength, an optical device for optically exciting/absorbing electrons can be formed. As shown in FIG. 16(A), the electron distribution in a toroidal molecule (or cluster) 1610 can be changed when the magnetic/electric field is changed in the vicinity of the hole of the torus by controlling the magnetic/electric field generated by lead wires, electrodes, or STM probes 1600 disposed in the vicinity of the toroidal molecule 1610. Thus, the toroidal carbon molecule 1610 can be made to serve as an electronic device. Particularly, when the magnetic field is supplied to pass through the hole of the torus, the toroidal molecule functions as an Aharonov-Bohm effect device. As a result, a quantum effect relation is obtained between resistance R and magnetic field intensity H as shown in the graph 1620 of FIG. 16(B). As shown in FIG. 17, the hole of a specific size toroidal molecule (or cluster) 1710 is blocked by another tubular or spheroidal molecule 1700. When a chemical/nuclear reaction is then brought by applying a neutron beam/gamma ray 1720 to the portion of the hole, the molecule 1700 which has blocked the hole is sprung out of the toroidal molecule 1710 at a predetermined speed 1730. Thus, such mechanism can be used as a launcher for giving kinetic energy to a molecule. As shown in FIG. 18, when a hole of a certain-size toroidal carbon molecule 1810 is narrowed rapidly by quenching the toroidal carbon molecule 1810 after a big tubular or spheroidal carbon molecule 1800 is inserted into the hole widened by heating the toroidal carbon molecule 1810, a function for chopping or crushing the molecule 1800 can be provided. As another chopping method, another molecule is inserted into the respective holes of two toroidal molecules arranged closely in parallel to each other, and then the two toroidal molecules are pulled in opposite directions by an STM or by the above-mentioned sticking method to make it possible to chop or crush (1820) the other molecule. Further, when a plurality of impurity toroidal 1 molecules in which impurities are enclosed are used in combination, a gyroscope can be provided. In this case, a carbon tube capable of passing through the hole of the toroidal molecule is used as the shaft of the gyroscope. Further, when the theory of a rotor shown in FIG. 14 is applied to the combination of a toroidal molecule and a carbon tube, a micro molecular top can be constructed. As shown in FIG. 19, a cylindrical carbon molecule 1900 constituting a torus can be provided by arranging sixfold rings 1910 of carbon atoms along an axis parallel to the center line of the cylinder, whereas a cylindrical carbon molecule 1920 having torsion can be provided by arranging such sixfold rings 1910 along an axis inclined with respect to the center line of the cylinder. Although the above description has been made upon the assumption that a toroidal molecule or a cluster of toroidal molecules is used, a helically-coiled carbon molecule can be formed by suitably changing the pressure, temperature, electric field, light, radiation, magnetic field or arc discharge current/voltage. In this case, a plurality of carbon atoms are so arranged that sevenfold rings each constituted by a plurality of carbon atoms are arranged in the inside of the helical coil while fivefold rings are arranged in the outside of the helical coil. Further, with respect to other carbon rings than the sevenfold and fivefold rings, when the arrangement of carbon atoms is distorted slightly after the carbon atoms are arranged so that the bonding length between atoms and the angle between atoms approach the bonding length of the graphitic structure of carbon and the angle (120 degrees) between atoms therein, a helically-coiled carbon molecule or a multiple helically-coiled carbon molecule (inclusive of a double helically-coiled carbon molecule) can be formed. In this case, a combination of an eightfold ring and some fivefold rings or a combination of a sevenfold ring and some sixfold rings may be arranged in the vicinity of the innermost wall surface of the helically-coiled carbon molecule. When the stability against temperature, of a helically-coiled molecular structure 2000 shown in FIG. 20 is examined by simulation upon the assumption of potential of atoms on the basis of molecular dynamics, the helically-coiled carbon molecular structure exists stably even at 2000K. Furthermore, cohesive energy at a very low temperature is about -7.3 eV per one atom, so that this molecular structure exists stably. Such helically-coiled structure can be provided by the steps of: chopping a toroidal molecule by using an STM or the like; moving up and down the chopped portions with respect to a plane of the toroidal molecule; and joining the toroidal molecule to another toroidal molecule processed in the same manner as described above. By using the thus produced helically-coiled molecular structure, a spring of a molecular machine can be formed. FIG. 32 shows various kinds of helically-coiled molecular structures different in the one-cycle axial length of the helical coil corresponding to the pitch of a spring. The helically-coiled molecular structures are expressed as Helix.sub.N in accordance with the number N of carbon atoms contained in one cyclic pitch of the molecular structure. As described above, Helix.sub.N can be obtained by the steps of: chopping a toroidal molecule C.sub.N ; slightly deforming the chopped portions as in the above description; and connecting the chopped portions. FIG. 32 shows Helix.sub.360, Helix.sub.540 and Helix.sub.1080 corresponding to C.sub.360, C.sub.540 and C.sub.1080 respectively. Even in the case where the number of carbon atoms is kept constant, the length of the helically-coiled molecular structure can be changed if the shape or arrangement of sevenfold rings contained in the inner wall surface of the helically-coiled molecular structure, i.e., an internal pattern is changed. FIG. 33 shows the change of the internal pattern with respect to the length of Helix.sub.360 shown in FIG. 32. In FIG. 33, the pattern 3300 is an internal pattern of a toroidal molecule in the case where the length of the helical coil is 0. In FIG. 33, the patterns 3301 and 3302 are internal patterns of Helix.sub.360 different in the length of the helical coil. The length of the helical coil in the pattern 3302 is larger than that in the pattern 3302. An angle of inclination of the cylinder portion of the helically-coiled molecular structure with respect to a plane perpendicular to the center axis of the helical coil is shown in the lower of each of the patterns 3301 and 3302 in FIG. 33. The original C.sub.360 is deformed by the angle, so that Helix.sub.360 is obtained. FIG. 34 shows helically-coiled molecular structures different in the pattern of the inner wall surface of Helix.sub.360 as shown in the pattern 3301 in FIG. 33. The pattern 3402 in FIG. 34 is the same as the pattern 3301 in FIG. 33. In the patterns 3400 and 3401 in FIG. 34, the inner wall surface is formed by using fivefold rings as well as sevenfold rings. In the pattern 3401 in FIG. 34, fivefold rings shown in the pattern 3400 in FIG. 34 are deformed considerably. FIG. 21 shows a double helically-coiled carbon molecule 2100. Similarly, a multiple helically-coiled structure can be formed. A knotted helically-coiled carbon molecule 2110 shown in FIG. 21 is also stable. In these molecular structures, diversity can be given to the characteristic of the multiple helical coil in accordance with the number of windings to be intertwined, the interval of torsion or the difference in defects/impurities contained in the inside. In the cylindrical carbon molecules shown in FIG. 19, the molecule 1900 in which sixfold rings are parallel to the axis of the cylinder and the molecule 1920 in which sixfold rings are inclined with respect to the axis of the cylinder are different from each other in the physical properties of the cylindrical carbon molecules. As shown in FIG. 22, when cylindrical molecules 2200 and 2240 are wound with helically-coiled molecules 2210 and 2250 respectively, the physical properties can be changed in accordance with the winding pitches 2220 and 2260. In this case, the structure of the helically-coiled molecule 2210 with respect to the cylindrical molecule 2200 can be controlled in accordance with the interval of torsion or the difference in defects or impurities contained in the inside. As shown in FIG. 23, the above-mentioned toroidal structure or helically-coiled structure can be constituted of small toroidal carbon molecules 2300. The state 2320 in which the thus constituted giant single ring structure 2310 is observed from above can be made to correspond to bit "0", while the stable state 2360 in which two rings facing to each other are formed so as to be dense when the giant double ring structure 2350 constituted by cylindrical carbon molecules 2340 shown in FIG. 23 is observed from above can be made to correspond to bit "1". Such control can be achieved easily when an electric field locally large in intensity is applied to the giant molecule by using an STM or the like. FIGS. 24, 25, 26 and 27 show super helical structures each containing a helical structure. FIG. 24 shows negatively and positively coiled super helical structures 2400 and 2410 in which opposite ends of a negatively or positively coiled helical coils are connected to each other through a part of a toroidal molecule, respectively. FIG. 25 shows negatively and positively coiled super helical carbon molecules 2500 and 2510 in which one part of a double helical coil obtained by winding two negatively or positively coiled helical coils on each other and connecting respective opposite ends thereof to each other is connected to another double helical coil obtained in the same manner as described above, respectively. FIG. 26 shows negatively and positively coiled super helical carbon molecules 2600 and 2601, in which respective opposite ends of two negative and positive helical coils are connected to each other after the helical coils are wound on each other, respectively. FIG. 27 shows negatively and positively coiled super helical carbon molecules 2700 and 2710, in which respective opposite ends of two negatively and positively coiled helical coils are connected to each other through deformed negatively or positively coiled helical coils, respectively. The helical structure in which the center axis is shaped like a straight line changes to any one of the positively and negatively coiled super helical structures 2400 to 2710 in accordance with environment such as the temperature, pressure, etc. and the presence/absence of molecule in the periphery. By using this property, a multivalue memory element can be formed. When a subsidiary normal vector perpendicular both to a tangent vector of the helical coil and to a main normal vector expressing the rate of the change of the tangent vector is determined, the helical coil in the case where the inner product of the subsidiary normal vector and a vector expressing the direction of the center axis of the helical coil is positive is defined as a positively coiled helical coil (counterclockwise) whereas the helical coil in the case where the inner product is negative is defined as a negatively coiled helical coil (clockwise). Further, information can be read/written by using a plurality of helically-coiled molecules to give torsion to one helical coil on the basis of another helical coil or to read the presence/absence of torsion of one helical coil on the basis of another helical coil. These helically-coiled molecules (or clusters) can be used for the purposes described above in the case of tori. Alternatively, as shown in FIGS. 28 and 29, solid structures may be formed by connecting half circles each constituting a part of a torus so that the structural change in accordance with the method of giving torsion can be made to correspond to one bit. In FIG. 28, solid structures 2801 and 2802 which are observed as a U-shape transversely are made to correspond to bit "0" while solid structures 2803 and 2804 which are observed as an 8-shape are made to correspond to bit "1". In FIG. 28, a bit train "0011" is expressed by four solid structures. In FIG. 29, another ring (torus) 2901 is passed through such a U-form solid structure 2900 as shown in FIG. 28 so that the state in which the torus is observed as a 1-shape transversely is made to correspond to bit "1" while the state in which the torus is observed as a "-"-shape or a 0-shape is made to correspond to bit "0". As shown in the broken line of FIG. 29, a further torus 2902 may be provided additionally so that a code correction or additional bit can be expressed. The movement of the torus or the change of the shape as shown in FIGS. 28 and 29 can be achieved by mechanical or electric force provided from the outside. A sensor can be formed by using the change of the positions of fivefold and sevenfold rings in accordance with the mechanical change of the above-mentioned structure such as the toroidal structure per se or the helical structure. That is, a sensor can be provided by observing the change of the shape directly with an STM or the like or by picking up the change of the shape as the voltage/current change through an STM. Further, if the positions of fivefold and sevenfold rings constituting the surface of the torus are changed preliminarily, the sectional shape of the torus can be changed as shown in FIG. 30 so that tori different in characteristic and structures such as helically-coiled structures can be obtained. For example, a structure such as a device, a sensor, etc. having a parameter range different from that of the above-mentioned structures can be provided by enclosing another atom in the center hole of the torus or in the tube of the torus or by connecting some structured materials thereto. FIG. 30 is a section of C.sub.240 and C.sub.360 seen from a plane passing the center axis of a torus. The section 3001 of C.sub.240 shown in the solid line and the section 3002 of C.sub.360 shown in the broken line are different from each other in the positions of fivefold rings. By adding atoms such as nitrogen atoms, boron atoms, etc. to the above-mentioned toroidal molecules, clusters thereof or helically-coiled molecules, by distorting or twisting rings by using a local temperature, stress, electrolysis, etc. or by generating defects through insertion/removal of carbon atoms, there are formed toroidal molecules, helically-coiled structures or clusters thereof different in the method of connection of rings. These are applied to the purposes described above in the case of tori constituted singly by carbon atoms. Further, by supplying an electric current to a molecular structure constituting a cylindrical surface after adding impurities to the molecular structure, a helically-coiled molecule can be used as a solenoid. Further, by gradually reducing the diameter of the cylindrical surface of the helically-coiled molecule, a molecular spring is formed. Furthermore, a telescopic structure of toroidal molecules can be formed by constructing a small toroidal molecule in the above-mentioned toroidal molecule. Finally, the method for constructing a toroidal molecule or a helically-coiled molecule will be described below. In a low-temperature state, a fivefold ring of a spheroidal carbon molecule is caught by a probe of an STM and pressed down to another fivefold ring in the symmetrical position with respect to the center of the sphere to form a toroidal molecule. Alternatively, the toroidal molecule can be realized by arranging carbon atoms one by one while supplying an electric/magnetic field. A structure in which these molecules contain impurities can be formed by pressing a spheroidal carbon molecule containing impurities by a probe of an STM. Alternatively, a structure in which these molecules contain impurities can be also achieved by arranging new molecules/atoms one by one on a toroidal molecule or helically-coiled molecule of pure carbon by using an STM. For constructing a toroidal molecule, a toroidal molecule is formed such that a plurality of sixfold rings each including six atoms are arranged in a torus form, while changing external physical force to be applied to the atoms. Then, the atoms arrangement in said toroidal molecule is changed such that first ones of the sixfold rings arranged on an outer wall surface of the toroidal molecule are replaced by first fivefold rings each including five atoms. The first sixfold rings are apart from each other. Also, the atoms arrangement in the toroidal molecule is changed such that second ones of the sixfold rings arranged on an inner wall surface of the toroidal molecule are replaced by second fivefold rings each including five atoms and sevenfold rings each including seven atoms. The second sixfold rings are apart from each other, and each of the first and second fivefold rings and the sevenfold rings is surrounded by the sixfold rings. Alternatively, for constructing a toroidal molecule, a toroidal molecule is formed such that a plurality of first sixfold rings each including six atoms are arranged in a torus form, while changing external physical force to be applied to the atoms. Then the atoms arrangement in the toroidal molecule is changed such that some of the first sixfold rings arranged on an outer wall surface of the toroidal molecule are replaced by second sixfold rings each including six atoms and having a size larger than that of each of the first sixfold rings. Also, the atoms arrangement in the toroidal molecule is changed such that some of the first sixfold rings arranged on an inner wall surface of the toroidal molecule are replaced by the second sixfold rings and third sixfold rings each including six atoms and having a size smaller than the size of each of said first sixfold rings. Each of the second and third sixfold rings is surrounded by the first sixfold rings. This is achieved by moving atoms one by one using the electric field created by the tip of a probe of a scanning microscope in the environment below 10.sup.-10 Torr. The other method is the discharge arc: Torus may be obtained as the small-length tubes in a carbon-arc chamber similar to that used for the C.sub.60 (fullarene) production. The vertical electrodes are installed in the center of the chamber. The anode is a graphitic carbon rod, and the cathode has a shallow dimple used to hollow a small piece of Fe (iron), Co (Cobalt) or/and Ni (Nickel), during evaporation. The evaporation chamber is filled with rare gas of 10 Torr to 500 Torr. The carbon discharge is started by flowing current of 95 to 200 A upon application of voltage of 20 V between the electrodes. The temperature of the chamber is controlled 300 degree to 1300 degree in Celsius. The rapid quenching laser is performed to weaken the crystal growth. The structures described above can be also achieved by using other stratified materials such as boron (B), phosphorus (P), tungsten (W), etc. than carbon. According to the present invention, novel topological properties which could not be given to conventional carbon can be given to carbon atoms so that the conventional method of use of carbon elements can be widened.
047298650	summary	BACKGROUND OF THE INVENTION This invention relates to improvements in nuclear power generation. The oil embargo of 1973 illustrated the vulnerability of the industrialized world to the interruption of its energy supply, and since that time considerable work and research have been done on alternate types of energy, particularly energies having an endless source of supply. One such source of energy is nuclear fission, which clearly has inherent disadvantages, such as long term radioactivity and the resulting negative public opinion. Design projects are now under way to test the practicality of generating power from the thermonuclear fusion of ions trapped by magnetic fields. Torus-shaped reactors have been built which seek to burn deuteruim-tritium mixtures. An alternative research project, a structure identified as a tandem mirror, comprises a device in which a plasma is confined by magnetic and electrostatic barriers at each end of a linear sequence of magnets. To date no device has demonstrated a particle containment adequate to provide a practical fusion reactor. Other disadvantages associated with the existing machines are extensive lithium blanket requirements and the problem of random, uncontrollable 14 MeV neutron emission. SUMMARY OF THE INVENTION According to the present invention and forming a primary objective thereof, a nuclear fusion reactor is provided that has a low contruction cost, that provides a unique plasma self-containment with relatively modest magnetic fields, that has a high output of energy, and that directs its high energy neutrons into lithium blankets of limited size while largely confining neutron damage to specific, easily replaceable structures. In carrying out these objectives, a metallic wave guide of rectangular cross section is positioned between super-conducting upper and lower extended electromagnets of horseshoe-type cross section, producing oppositely-directed vertical magnetic fields in close proximity through the continuous wave guide along its entire perimeter. Vertical particle containment is achieved through the use of very narrow and closely spaced ferromagnetic by-pass vanes, which produce a type of composite magnetic field composed of narrow, curving segments spaced between wider, weaker layers of vertical magnetic field across all four corners of the wave guide cross section along its entire perimeter, rather like double-edged razor blades embedded in a pound of cheese. These narrow, curving magnetic fields reverse the vertical components of horizontally oscillating plasma ions, and in conjunction with a horizontally resonating ionic wave actively damp the vertical components of the ionic oscillations, which together produce a highly effective type of plasma self-containment. High energy deuterons are injected into the wave guide from an accelerator, and being tangentially introduced, are caused to oscillate across the oppositely-directed magnetic field boundary in circular arc lengths with some specific intersection angle and at some specific frequency in accordance with the strength of the vertical magnetic fields. The injected deuterons spontaneously arrange themselves into two narrow, oppositely-phased groups, constituting a horizontally pulsating, self-bombarding wave, resonating along the continuous wave guide which has an effective perimeter equal to an odd number of half-wavelengths of the ionic oscillation frequency. Electrons from an incandescent wire are distributed through the plasma along the boundary between the vertical magnetic fields and move horizontally inward and outward within the resonating groups of ions under the influence of microwave frequency electric fields, and axially in the same manner because of the inductance of the rapidly converging and diverging ionic wave. The magnetic viscosity of the powerful magnetic fields forces the electrons to arrange themselves into systems of pulsating, parallel charges, producing highly organized microwave patterns which propagate within the narrow ionic wave and permit the electrons to ratchet their way rapidly across the magnetic field lines. The plasma ions absorb energy from the powerful microwave component of the resonating plasma pulsations, creating a circulating energy flow which lowers the electron temperature and reduces plasma radiation energy losses. The electrons also produce a transformer effect upon the plasma ions due to their inductance which selectively reduces each of the oscillating ions to the vicinity of the mean amplitude and energy level of that type of ion. More importantly, the powerfully organized plasma pulsations reincorporate each type of oscillating ions to beta-1 densities counter to the effects of coulomb scattering; largely because the resonating ionic wave develops a pulsating self-field which increases outwardly within each narrow group of ions and which continuously maintains its stability. A type of ionic bellows-action is developed in the plasma due to the extremely high density at its inner pulsation node which further reduces the electron temperature. The resonating plasma pulsations automatically adjust the various intersection angles between the oscillating ions and the oppositely-directed magnetic field boundary to maintain the resonant frequency in the existence of changing magnetic field strengths and ionic energy levels, which serves to automatically adjust the resonating ionic wave to the length of the wave guide. Deuterium and tritium neutral particle beams are injected tangentially along the magnetic field boundary, become ionized, and the particles arrange themselves at the proper amplitudes and intersection angles to allow them to become incorporated into the plasma pulsations. Energy is added to the plasma from external oscillators of the proper frequency through a system of equally spaced probes extending to the wave guide surface. The powerfully resonating plasma pulsations may be compared to a giant, nuclear-driven oscillator which produces a reverse-voltage counter to the external oscillator impulses and which increases with ionic density and energy levels. During an initial start-up procedure the external oscillator voltage is maintained above that of the pulsating plasma, energy flows into the wave guide, and the particle energy levels are maintained until an ignition density can be obtained. After ignition has been achieved the situation is reversed and energy is removed from the plasma through the external oscillators to maintain an optimal collision energy level for the narrow, beta-1 groups of head-on colliding tritons and deuterons at the plasma inner pulsation node. Replacement deuterium and tritium ions are introduced into the wave guide and are rapidly raised to their mean energy levels by the electron transformer effect and by the circulating microwave and ionic bellowsaction energies, while suprathermal alpha particles produced by fusion events are reduced to the mean energy level of the helium ash by the same process. Various types of alternate fusion reactions are briefly considered. The invention will be better understood and additional advantages will become apparent from the following description taken in connection with the accompanying drawings.
044980116	claims	1. A device for receiving, moving, and radiation shielding of vessels filled with expended reactor fuel elements, comprising a protective concrete container having a base; a cylindrical protective jacket, the inner diameter of which is somewhat greater than the diameter of the vessel holding the fuel elements to provide an annular space therebetween; a cover; lateral air inlet ducts at the lower rim of the jacket in communication with the atmosphere and said annular space; and lateral air outlet ducts in the region of the upper rim of the jacket below the cover in communication with the atmosphere and said annular space, characterized in that said base consists of a movable pallet separate from said jacket having a central platform for supporting said fuel element vessel, said jacket resting upon the margin of said base surrounding said platform, said base carries centering means to properly position said jacket on said base, and is supported by legs to permit underrun for lifting, said air outlet ducts have two inclined segments joined at an apex within the wall of said jacket, an inner segment opening into said annular space and an outer segment opening to the atmosphere, said inner segment being longer than and extending below said outer segment, said cover is in the form of a hood having a downwardly-turned flange spaced from and surrounding said jacket and extending below said outlet ducts.
	summary
	claims	1. A reflector assembly for a molten chloride fast reactor (MCFR) comprising:at least one reflector structure, wherein the at least one reflector structure is circumferentially arrangeable in a substantially cylindrical shape having a longitudinal axis that encapsulates a reactor core for containing nuclear fuel; andone or more tank sections disposed within the at least one reflector structure, wherein the one or more tank sections are configured to hold at least one reflector material to reflect fission born neutrons back to a center of the reactor core; anda support structure that holds the at least one reflector structure in the substantially cylindrical shape, wherein the support structure includes a top plate and a bottom plate, the at least one reflector structure disposed between the top plate and the bottom plate, wherein the support structure also includes a plurality of circumferentially spaced ribs that at least partially extend from the top plate along the longitudinal axis, and wherein the plurality of circumferentially spaced ribs also extend between an outer circumferential edge of the top plate and an inner circumferential edge of the top plate. 2. The reflector assembly of claim 1, wherein the at least one reflector structure forms a single tank section of the one or more tank sections. 3. The reflector assembly of claim 1, wherein the at least one reflector structure is monolithically formed with the one or more tank section defined therein. 4. The reflector assembly of claim 1, wherein the at least one reflector structure comprises two or more tank sections of the one or more tank sections, each of the two of more tank sections axially aligned along the longitudinal axis. 5. The reflector assembly of claim 4, wherein the at least one reflector structure comprises a plurality of reflector structures and each of the two or more tank sections are formed by individual and separable reflector structures of the plurality of reflector structures. 6. The reflector assembly of claim 1, wherein the one or more tank sections are formed by a grid pattern of a plurality of radial members and a plurality of circumferential members, each disposed within the at least one reflector structure. 7. The reflector assembly of claim 6, wherein the at least one reflector structure comprises two circumferential ends, and wherein the two circumferential ends comprise curved surfaces. 8. A reflector assembly for a molten fuel nuclear reactor comprising:a plurality of modular reflector structures disposed adjacent to one another and positioned circumferentially around a longitudinal axis to at least partially encapsulate a reactor core in a substantially cylindrical shape;at least one tank section disposed within each of the plurality of modular reflector structures;reflector material held within the at least one tank section configured to reflect fission born neutrons back to a center of the reactor core; anda support structure configured to hold the plurality of modular reflector structures in place within the molten fuel nuclear reactor, wherein the support structure includes a substantially cylindrical top plate and a substantially cylindrical bottom plate, the plurality of modular reflector structures disposed between the top plate and the bottom plate, wherein the support structure further includes a plurality of ribs extending from the substantially cylindrical top plate along the longitudinal axis, and wherein the plurality of circumferentially spaced ribs also extend in a radial direction from an outer circumferential surface of the plurality of modular reflector structures towards an inner circumferential surface of the plurality of modular reflector structures. 9. The reflector assembly of claim 8, wherein the reflector material comprises liquid lead. 10. The reflector assembly of claim 8, wherein the support structure further comprises one or more restraint hoops positioned around an outer perimeter of the plurality of modular reflector structures. 11. The reflector assembly of claim 8, wherein two ribs of the plurality of ribs at least partially form an exit flow channel from the reactor core. 12. The reflector assembly of claim 8, wherein the support structure further comprises a plurality of ribs extending between the substantially cylindrical top plate and the substantially cylindrical bottom plate. 13. The reflector assembly of claim 8, further comprising a flow guide disposed below the plurality of modular reflector structures, wherein the flow guide comprises a lower reflector.
056174560	summary	TECHNICAL FIELD The present invention relates to a fuel assembly, and more particularly to a fuel assembly which can be used in a boiling-water reactor to save the consumption of nuclear fuel substances. BACKGROUND ART In a conventional boiling-water reactor as is disclosed in Japanese Patent Laid-Open No. 121389/1979, the reactor core is loaded with a fuel assembly which has a pipe (hereinafter referred to as water rod) in which the cooling water only flows to decelerate the neutrons. Under the operation conditions of the conventional boiling-water reactor, the water rod exhibits an increased reactivity with the increase in the number of hydrogen atoms for uranium atoms, enabling the nuclear fuel substances loaded in the reactor core to be effectively utilized. In order to more effectively use the nuclear fuel substances, furthermore, it is recommended to change the number of hydrogen atoms in the reactor core as the nuclear fuel substances burn. Japanese Patent Laid-Open Nos. 125390/1982 and 125391/1989 teach one of the methods. That is, according to these patent publications, provision is made of slow neutron-absorbing water purge rods and intermediate neutron-absorbing water purge rods constituted by a stainless steel which has a larger reactivity value than that of the above water purge rods, and the amount of the cooling water in the reactor core is adjusted by controlling the amount for inserting the water purge rods in the reactor core. The water purge rods serve as means for changing the number of hydrogen atoms in the reactor core. The amount of the cooling water in the reactor core decreases with the increase in the amount for inserting the water purge rods in the reactor core, and the amount of the cooling water increases in the reactor core with the decrease in the amount of insertion. According to the above-mentioned method, water purge rods of different kinds must be newly provided and must be operated by drive means, requiring complex structure and cumbersome operation. Japanese Patent Laid-Open No. 38589/1986 discloses a fuel assembly which employs static means in order to solve the above-mentioned problems. According to this patent publication, the number of hydrogen atoms is changed by providing fuel rods having a low uranium 235 concentration in the water rod of fuel assembly, and by utilizing the change in the amount of voids in the water rod before and after uranium 235 of the fuel rods extinguishes. There is a method of adjusting the amount of the cooling water that flows in the reactor core without the need of newly providing operation means such as water purge rods. That is, the cooling water is permitted to flow in small amounts in the reactor core during the start of the fuel cycle, and is then permitted to flow in increased amounts as the fuel cycle proceeds halfway. Advantages will now be described in the case when the number of hydrogen atoms is changed in the reactor core accompanying the burn of the nuclear fuel substances. In the case of a typical fuel assembly used for boiling-water reactors, a higher burning degree can be obtained when the operation is carried out at a high void fraction (void fraction, 50%) during the period of a burning degree of 0 to 30 GWD/T and when the operation is carried out at a decreased void fraction (void fraction, 30%) during the period of a burning degree of 30 to 40 GWD/T than when the operation is carried out at a constant void fraction (e.g., at a void fraction of 30%). This is because, the neutrons have a high average speed and are easily absorbed by uranium 238 when the void fraction is high and the ratio of the number of hydrogen atoms to the number of uranium atoms is small, i.e., when the number of hydrogen atoms is small. The nuclear fuel substances used in the boiling-water reactor contains uranium 235 and uranium 238, uranium 235 occupying several per cent of the whole nuclear fuel substances and uranium 238 occupying most of the nuclear fuel substances. Among them, uranium 235 absorbs the neutrons and develops chiefly the nuclear fission, but uranium 238 develops nuclear fission very little. Therefore, the burn-up decreases if uranium 235 burns and decreases. Uranium 238, however, is converted into plutonium 239 when it absorbs neutrons of a large energy produced by the nuclear fission. Like uranium 235, however, plutonium 239 absorbs decelerated thermal neutrons to develop nuclear fission. The higher the void friction, the larger the energy of the neutrons and uranium 238 is converted into plutonium 239 at an increased ratio, while suppressing the nuclear fission of uranium 235 and plutonium 239. Therefore, the higher the void fraction, the slower the rate of reduction of the total amount of uranium 235 and plutonium 239. A high void fraction, however, causes the absolute value of reactivity to decrease. If the void fraction is maintained high, therefore, a minimum level is reached quickly at which the reactivity maintains the criticality compared with when the void fraction is low. Therefore, if the void fraction is lowered at that moment, the neutrons exhibit increased deceleration effect, whereby nuclear fission of uranium 235 and plutonium 239 increases, so that good reactivity is obtained compared with when the fuel substances are burned at a high void fraction that is maintained constant. This makes it possible to burn the core material contained in the nuclear fuel substances for an extended period of time before a minimum reactivity necessary for the criticality is reached. In the foregoing was mentioned the principle which is called spectrum shift operation for effectively utilizing the nuclear fuel substances by changing the void fraction accompanying the burn of the core material. Neither the method which provides static means in a simply constructed water rod nor the method which changes the number of hydrogen atoms in the reactor core by changing the amount of the cooling water (called reactor core flow rate) which flows through the reactor core, makes it possible to widely change the void fraction in the reactor core; i.e., these methods can only give small effect in the practical nuclear reactors. That is, the lower limit of the flow rate in the reactor core is determined by the thermal limit, and the upper limit is determined by the capacity of the circulation pump and the flow-induced vibration. Under the condition where the boiling-water reactor is producing a rated thermal output, therefore, it is allowed to change the void fraction only within a narrow range with the rated 100% flow rate in the reactor core as a center. For example, if the flow rate in the reactor core is allowed to change over a range of from 80 to 120%, then the void fraction can be changed by about 9%. Even with the structure in which a heat generating member (nuclear fuel substance) of which the calorific power decreases accompanying the burn, is placed in the water rod as disclosed in Japanese Patent Laid-Open No. 38589/1986, the void fraction in the water rod changes by about 30% at the greatest. The water in the water rod does not contribute to the cooling, and it is not allowed to much increase the sectional area of the water rod in the fuel assembly. If it is presumed that the sectional area of the water rod occupies 30% of the cooling water path in the fuel assembly, the effective void fraction change of 30% becomes 9% (30%.times.0.3) if it is regarded as the whole fuel assembly. Further, since a fuel rod having a low enrichment is used as a heat generating member, the structure becomes complex and its production involves cumbersome operation. To achieve a wide range of void fraction change, the flow rate in the water rod should be changed extremely greatly or the calorific power of the nuclear fuel substance in the water rod should be changed greatly. In fact, however, the flow rate or the calorific power cannot be greatly changed without employing the moving portions. Provision of the moving portions, however, poses problems from the stadpoint of reliability and makes the mechanism complex. SUMMARY OF THE INVENTION The object of the present invention is to provide a fuel assembly which is simply constructed and which is capable of greatly changing the internal average void fraction. The aforementioned object is achieved by the provision of a resistance member at the lower end portion of the fuel assembly; a coolant ascending path in which the water rods have coolant inlet ports that are open in a region lower than the resistance member; and a coolant descending path which is communicated with the coolant ascending path and which has a coolant delivery port that is open in a region higher than the resistance member, in order to guide the coolant downwardly which is opposite to the direction in which the coolant flows in the coolant ascending path. As the flow rate of the coolant that passes through the reactor core decreases, the coolant ascending path of the water rod is filled with water vapor and as the flow rate of the coolant increases, the amount of water vapor decreases conspicuously in the coolant ascending path. Therefore, the reactivity can be increased toward the last period of fuel cycle.
	description	The present application is based on provisional application Ser. No. 61/234,342, filed Aug. 17, 2009, the entire contents of which are herein incorporated by reference. 1. Technical Field The present disclosure relates to load tests and, more specifically, to methods and systems for automatic identification of execution phases in load tests. 2. Discussion of Related Art Modern computer software may be designed to process multiple threads of execution in a parallel fashion. Multi-threaded applications, as they are called, may include multiple program threads that are each responsible for performing a small operation that contributes to the greater application. Multiple threads may be executed concurrently using multiple microprocessors or multiple microprocessor cores. Alternatively, a single processor may interleave the execution of multiple threads by switching between threads, for example, using time-division multiplexing and/or interrupts. Development of effective real-time applications requires that the available processing power not be excessively taxed or the computer system may be unable to keep up with the computational demands presented by the application. Where the application is multi-threaded and a large number of threads may present for processing at substantially the same time, there is a particular concern that the computer system may be excessively taxed. Moreover, there is a concern that the threads should be scheduled so as to give priority for execution where required, but only where required. In addition, with multi-threaded systems, there is a concern that threads should be able to execute without being blocked by the absence of a signal or message. Accordingly, to gain insight into the manner in which computer programs tax system resources, load testing may be performed to monitor which threads are actively engaging the processor at any given time and to determine the extent to which the processor is being utilized. By examining the data collected during load testing, a programmer can gauge potential bottlenecks within the application execution so that the software may be improved to better distribute load and avoid overtaxing of the processor. However, as the complexity of computer programs advances, dozens or even hundreds of threads may all vie for limited processing resources. In such an event, data collected during load testing may be difficult to manually parse as there may be a great number of threads simultaneously driving processor utilization at any given time. A method for automatic identification of execution phases in load test data includes receiving load test data indicating processor utilization for a plurality of threads over a period of time. The period of time of the load test data is divided into a plurality of intervals. For each pair of proximate intervals of the plurality of intervals, it is determined whether a statistical characterization of thread-wise processor utilization for a first interval of the pair of intervals is statistically indistinguishable from a statistical characterization of thread-wise processor utilization for a second interval of the pair of intervals. The pair of proximate intervals is combined into a single interval when it is determined that the statistical characterization of processor utilization for the first interval is statistically indistinguishable from the statistical characterization of processor utilization for the second interval, for each of the plurality of threads. Each of the pair of proximate intervals is divided into subintervals when it is determined that the statistical characterization of processor utilization for the first interval is not statistically indistinguishable from the statistical characterization of processor utilization for the second interval, for at least one of the plurality of threads. One or more execution phases are automatically identified as occurring between proximate intervals that are not substantially equivalent. The processor may be a central processing unit (CPU). The thread-wise statistical characterization of processor utilization may be a mean CPU utilization for each of the plurality of threads. The thread-wise statistical characterization of processor utilization may be a standard deviation or variance of CPU utilization for each of the plurality of threads. Determining whether the mean CPU utilization for the first interval is statistically indistinguishable from the mean CPU utilization for the second interval may include performing a modified Student's T test. Determining whether the mean CPU utilization for the first interval is statistically indistinguishable from the mean CPU utilization for the second interval may include performing Welch's modification of Student's T test with unequal variances and unequal sample sizes. The period of time of the load test data may be initially divided into a plurality of intervals of equal duration prior to performance of the steps of combining and dividing. The process of dividing intervals into subintervals and comparing subintervals may be performed recursively up to a desired level of granularity. The determination as to whether the statistical characterization of thread-wise processor utilization of the pair of intervals is statistically indistinguishable may be performed using a predetermined confidence interval. The determination as to whether the statistical characterization of thread-wise processor utilization of the pair of intervals is statistically indistinguishable may be performed using multiple different confidence intervals, with each of the multiple different confidence intervals applied to calculating a statistical characterization of processor utilization for a different thread. The identified execution phases may be used to correlate execution phases with application code segments associated with the load test data to identify application code segments that are responsible for phases of relatively high thread-wise processor utilization. A method for automatic identification of bottlenecks in application code includes executing the application code and recording load test data indicating CPU utilization for a plurality of threads over a period of time. The period of time of the load test data is divided into a plurality of intervals. For each pair of proximate intervals of the plurality of intervals, it is determined whether a statistical characterization of thread-wise CPU utilization for a first interval of the pair of intervals is statistically indistinguishable from a statistical characterization of thread-wise CPU utilization for a second interval of the pair of intervals. The pair of proximate intervals is combined into a single interval when it is determined that the statistical characterization of CPU utilization for the first interval is statistically indistinguishable from the statistical characterization of CPU utilization for the second interval. Each of the pair of proximate intervals is divided into subintervals when it is determined that the statistical characterization of CPU utilization for the first interval is not statistically indistinguishable from the statistical characterization of CPU utilization for the second interval. One or more execution phases are automatically identified as occurring between proximate intervals that are not substantially equivalent. The identified execution phases are used to correlate execution phases with segments of the application code associated with the load test data to identify segments of the application code that are responsible for phases of relatively high thread-wise CPU utilization. It may be determined that the statistical characterization of CPU utilization for the first interval is statistically indistinguishable from the statistical characterization of CPU utilization for the second interval when the statistical characterization is statistically indistinguishable for every thread of the plurality of threads. It may be determined that the statistical characterization of CPU utilization for the first interval is not statistically indistinguishable from the statistical characterization of CPU utilization for the second interval when the statistical characterization is not statistically indistinguishable for at least one thread of the plurality of threads. The thread-wise statistical characterization of CPU utilization may be a mean CPU utilization for each of the plurality of threads. The thread-wise statistical characterization of CPU utilization may be a standard deviation or variance of CPU utilization for each of the plurality of threads. Determining whether the mean CPU utilization for the first interval is statistically indistinguishable from the mean CPU utilization for the second interval may include performing a modified Student's T test. Determining whether the mean CPU utilization for the first interval is statistically indistinguishable from the mean CPU utilization for the second interval may include performing Welch's modification of Student's T test with unequal variances and unequal sample sizes. A computer system includes a processor and a non-transitory, tangible, program storage medium, readable by the computer system, embodying a program of instructions executable by the processor to perform method steps for automatic identification of execution phases in load test data. The method includes receiving load test data indicating CPU utilization for a plurality of threads over a period of time, dividing the period of time of the load test data into a plurality of intervals, for each pair of proximate intervals of the plurality of intervals, determining whether a statistical characterization of thread-wise CPU utilization for a first interval of the pair of intervals is statistically indistinguishable from a statistical characterization of thread-wise CPU utilization for a second interval of the pair of intervals based on performing Welch's modification of Student's T test with unequal variances and unequal sample sizes, combining the pair of proximate intervals into a single interval when it is determined that the statistical characterization of CPU utilization for the first interval is statistically indistinguishable from the statistical characterization of CPU utilization for the second interval, for each of the plurality of threads, and dividing each of the pair of proximate intervals into subintervals when it is determined that the statistical characterization of CPU utilization for the first interval is not statistically indistinguishable from the statistical characterization of CPU utilization for the second interval, for at least one of the plurality of threads. One or more execution phases are automatically identified as occurring between proximate intervals that are not substantially equivalent. The determination as to whether the statistical characterization of thread-wise CPU utilization of the pair of intervals is statistically indistinguishable may be performed using multiple different confidence intervals, with each of the multiple different confidence intervals applied to calculating a statistical characterization of processor utilization for a different thread. The identified execution phases may be used to correlate execution phases with application code segments associated with the load test data to identify application code segments that are responsible for phases of relatively high thread-wise CPU utilization. In describing exemplary embodiments of the present disclosure illustrated in the drawings, specific terminology is employed for sake of clarity. However, the present disclosure is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents which operate in a similar manner. Exemplary embodiments of the present invention seek to automatically parse data collected during load testing of a computer system executing a multi-threaded application so that processor utilization of the application may be simply and accurately understood. Processor utilization, as used herein, may refer to the extent o which a microprocessor such as a CPU is taxed. For example, where time division multiplexing is used, full utilization may be defined as the CPU actively processing data at every time slice while half utilization may be defined as the CPU actively processing data at one out of every two time slices, etc. The processor need not be limited to a general purpose CPU and may be, for example, a graphical processing unit (GPU), digital signal processor, or another specialized microprocessor device. Where an instance of thread execution takes less time than the duration of a time slice, the utilization of the thread may be considered to be the sum of the durations of the execution instances divided by the length of the time interval during which the measurements are taken. An instance of thread execution may take less time than the duration of a slice for one of several reasons, for example, thread termination, encountering a wait semaphore operation that causes it to sleep or otherwise suspend execution, execution of I/O, or preemption by a thread of higher priority, Exemplary embodiments of the present invention may involve automatic identification of one or more phases of application execution. Each phase may represent a recognizable change in processor utilization. In this context, processor utilization may be understood not only as a utilization level from 0%, representing an idle processor, to 100% representing constant utilization, but also, processor utilization may be characterized by a level of processor utilization attributable to each of a set of threads being processed at substantially the same time. Thus one phase may be characterized as a period of time in which the processor is engaged in executing thread H1 and H2, each at a high level of utilization, and another phase may be characterized as a period of time in which the processor is no longer engaged in executing thread H1, is engaged in executing thread H2 only at a low level of utilization, and is also engaged in executing threads H3 and H4 each at a moderate level of execution. Thus distinct phases may be identified as having distinct processor utilization characteristics with respect to the set of threads being executed. Phases may occur, for example, because one thread changes its behavior or because a profile of multiple threads changes behavior. Where there are many threads, it may be useful to know where the boundary point between phases is located so that one may determine what is happening at that moment in application execution, for example, by cross-referencing phase times with time stamps in event logs. Alternatively, or additionally, determined phase boundaries may be cross-referenced with known execution paths for messages that are passed from one thread to the next so that the effect of these messages on processor utilization may be understood. FIG. 1 is a simplified illustration of load testing data corresponding to the example discussed above. As can be seen in this figure, four threads H1 to H4 contribute to processor utilization to different extents over time. Examination of the illustration may thus reveal that there is a first phase “Phase 1” between times t1 and t2 in which the processor is engaged in executing thread H1 and H2, each at a high level of utilization and there is a second phase “Phase 2” between times t2 and t3 in which the processor is no longer engaged in executing thread H1, is engaged in executing thread H2 at a low level of utilization, and is also engaged in executing threads H3 and H4 each at a moderate level of execution. By analyzing processor performance in terms of distinct phases, programmers may cross-reference phase-boundary times against e stamps in system event logs so that it can be determined what actions had transpired to implement the phase boundary. Then, information pertaining to phases of excessive processor utilization may be used to streamline the program to reduce excessive utilization. While phases may be manually identified in the case illustrated in FIG. 1, where there are dozens, hundreds, or more threads vying for processor utilization, manual identification of phases may not be possible. This is because large number of threads in the system under study (for example, about 100) may make accurate visual identification of all but the most obvious phase changes very difficult. FIG. 2 is an illustration of a complex set of load test data in which there are a relatively large number of threads being executed. Here, the computer application under test is an alarm monitoring application with multiple detection devices. In the event of conditions that may give rise to an alarm, a great number of zones may be in alarm at substantially the same time and accordingly, there exists a possibility for a burst of dozens if not hundreds of messages from one or more detection devices scattered over a broad area to contribute to the substantially simultaneous demand for execution by a large number threads. Because of the large number of threads, it is difficult to manually differentiate between distinct phases. Exemplary embodiments of the present invention, however, are not limited to the case in which processor utilization is captured with respect to alarm monitoring. Exemplary embodiments of the present invention may be applied to analyzing any load test data where load is bursty, such as network management systems, systems that monitor production lines such as printing presses, and the like. Accordingly, exemplary embodiments of the present invention seek to automatically identify execution phases from within load test data where there may be a relatively large number of threads to assess the performance of the system and to isolate system bottlenecks. FIG. 3 is a flow chart illustrating an approach for automatic identification of phases within load test data according to an exemplary embodiment of the present invention. First, load test data may be received (Step S11). Load test data may be acquired by running background monitoring software to capture processor utilization and active threads over time. This monitoring software may be passive in nature and as such should not affect processor utilization or performance. For example, in the system under study, a scheduler may be equipped with a tracer that non-invasively captures the start and stop times of every thread execution and the reason why the particular thread ceded control of the processor. These reasons may include, for example, waiting at a semaphore, preemption by a higher priority thread, timer interrupts upon completion of time slices, and completion of execution. The scheduler traces may also show the entire sequence of how much of the time is spent handling interrupts of various types. Examining the evolution of thread scheduler traces can yield insights into ways to reduce the total amount of time needed to process all the messages by facilitating the identification of processing hot spots. While much of this collected data may be useful in analyzing and improving the system under test, the load test data may at a minimum include an indication to the rate of processor utilization over time as well as the extent to which each active thread contributes to processor utilization. While any data format may be suitable, the disclosure herein may refer to the received load test data in terms of threads h (i,t), wherein i represents the thread number, which may be a positive integer from 1 to n, which is the maximum number of threads and t represents time. The load test data may thus include processor utilization data represented as u (i,t). Thus, for a given thread i and at a time t, u indicates processor utilization. Processor utilization may be expressed as a value between 0, representing idleness, and 1, representing full utilization. Accordingly, 0≦u(i,t)≦1. Next, the total time period may be divided into a set of contiguous time intervals (k) of equal duration (Step S12). Thus, the first time interval may extend from t=0 to t=k, the second time interval may extend from t=k to t=k+1, the third time interval may extend from time t=k+1 to t=k+2, etc. Each time interval may be thought of as a possible phase as exemplary embodiments of the present invention seek to adjust the composition of these time intervals through a sequence of combining and splitting of intervals until the recomposed time intervals accurately represent distinct phases of processor utilization. Similarity may then be measured between proximate pairs of intervals (Step S13). For example, the first time interval k may be compared to the second time interval k+1 and the second time interval k+1 may be compared to the third time interval k+2, etc. The comparisons seek to determine whether there is an identifiable difference between processor utilization in the first time interval of the pair and the second time interval of the pair. Statistical methods may be used to implement these comparisons. These comparisons need not be overly complex and in particular, they may be computationally simple as all that may need to be ascertained is whether there is a likely change of phase from the first time interval of the pair to the second time interval of the pair. According to exemplary embodiment of the present invention, successive intervals may be said to be dissimilar where the distributions of running threads h(i,t) is substantially different over the successive time intervals or the processor utilization u(i,t) is substantially different over the successive time intervals. For example if the set of invoked threads differs from one interval to the next, there may be at least one index j such that h (j, k)=0 and h (j, k)≠0. Alternatively, or additionally, similarity may be measured by comparing an average number of times that thread switching has occurred within the intervals being compared. This average number of thread switches may be measured as a number over a given time interval length, because, as described in detail below, intervals may be of different lengths. In such a case, a threshold may be established to differentiate between similar and dissimilar intervals. This threshold may be set as, for example, an order of magnitude difference or a difference by a factor of at least 1.5 times, although other suitable thresholds may be used. Here the profile of thread executions h (j, k) may be assumed to follow a multinomial distribution in each interval and as such, similarity between intervals may be obtained by comparing multinomial al distribution characteristics. FIG. 4 is a graph illustrating an approach for determining if proximate intervals are sufficiently similar according to an exemplary embodiment of the present invention. Here, the graph illustrates a time frame from 0 seconds to 40 seconds. The time frame is divided into two equal and proximate intervals A and B where A spans the time between 0 and 20 seconds and B spans the time between 20 and 40 seconds. A goodness-of-fit test may be employed on the measure of processor utilization within interval A as compared to the processor utilization within interval B. As the goodness-of-fit test may reveal that the two intervals are not substantially equivalent, it may be determined that a preliminary phase boundary exists between the two intervals. Accordingly, similarity of intervals may be established by determining whether the proximate intervals are statistically the same. Exemplary embodiments of the present invention may define statistical sameness as the event where the empirical distribution of a set of values in one interval is not significantly different from the corresponding empirical distribution in the next interval. Statistical difference could be determined, for example, by performance of a goodness-to-fit test or using empirical distribution functions rather than complex digital signal processing methods such as Kalman filters, which may assume normality and possibly linearity, or Fourier transform and related methods. Accordingly, exemplary embodiments of the present invention may utilize a distribution-free testing approach for the identification of segments of phased behavior. Alternatively, exemplary embodiments of the present invention may utilize image processing approaches to distinguish between similar and dissimilar intervals. Such images may first generate a plot of thread-specific processor utilization as a function of time, such as the plot illustrated in FIG. 2 and then visually search for one or more phases within the plotted data, for example, using trained classifiers or other image recognition techniques. For example, a plot may be generated in which the time axis is oriented as the horizontal and a processor performance metric is oriented as the vertical axis, then distinct vertical segments of the image may be identified by characterizing the positional and quantitative distributions of dots of different colors representing distinct threads of execution. Each pair of proximate intervals that are determined to be similar may then be combined to form a single larger interval (Step S14). By combining similar adjacent intervals, later computational expense may be saved by reducing the number of intervals that are handled. Exemplary embodiments of the present invention may thus combine proximate intervals when it is determined that no boundary between phases occurs between the pair of intervals. This process may be referred to herein as interval merging. Next, an interval bisection process may be performed (Steps S15-S19). In interval bisection, proximate intervals that are determined to be sufficiently different may each be split into two equally sized sub-intervals and the process of comparison and splitting may be recursively performed to hone in on the point where the change in processor utilization characteristics occurs. Splitting may be performed up until a desired level of granularity. The desired level of granularity may be set such that it is small enough to accurately place the phase boundaries such that correlation between program elements may be gauged but not so small that the computational burden becomes unnecessarily high. For example, the finest level of granularity may be set as somewhere between 20 seconds and a 100th of a second, but in particular, 5 seconds, 2 seconds, 1 second, ½ second, or ¼ second. FIG. 5 shows metacode for implementing bisection according to an exemplary embodiment of the present invention. The bisection approach may begin with a determination as to whether proximate intervals, for example, (k,k+1) and (k+1,k+2) are sufficiently similar (Step S15). If they are sufficiently similar (Yes, Step S19), then the next set of intervals may be compared, for example, (k,k+2) and (k,k+3). If, however, they are not sufficiently similar (No, Step S15), then it determined whether the interval may be further divisible (Step S16). Divisibility may be based, for example, on whether the existing intervals are larger than the level of finest granularity so that once finest granularity has been achieved, no further divisions are performed. However, if the intervals are divisible (Yes, Step S16) then each of the intervals being compared, here (k,k+1) and (k+1,k+2), may be split into subintervals (Step S17). Splitting of the intervals may be performed, for example, by equally dividing the interval into two subintervals. For example, (k,k+1) may be divided into (k,k+½) and (k+½,k+1), and (k+1,k+2) may be divided into (k+1,k+1½) and (k+1½,k+2). After the two dissimilar intervals have each been split (Step S17), the comparison and splitting process may be recursively performed with respect to the subintervals (Step S15). For example, (k,k+½) and (k+½,k+1) may be compared, (k+½,k+1) and (k+1,k+1½) may be compared, and (k+1,k+1½) and (k+1½,k+2) may be compared. Additionally, (k+1½,k+2) may be compared with the next interval (k+2,k+3). Accordingly, the change that is detectable between (k,k+1) and (k+1,k+2) may be found within one or more of the various subinterval comparisons. For example, it may be detected between (k+½,k+1) and (k+1,k+1½). In such a case, these two subintervals may be recursively split and compared provided that the maximum level of granularity has not been achieved. For example, these intervals may be split into the subintervals (k+½, k+¾), (k+¾, k+1), (k+1, k+1¼), and (k+1¼, k+1½). Now assuming that after comparisons of these sub intervals it is determined that the difference is found between (k+½, k+¾), and assuming that this represents the finest desired level of granularity (No, Step S16 the phase change is recorded as occurring between these two subintervals (Step S18). After the phase boundary has been recorded, the recursive process steps back and the next set of subintervals are compared, for example, (k+1, k+2) and (k+2, k+3). The process may end when all intervals have been compared, and where necessary, appropriately subdivided. Exemplary embodiments of the present invention may also intermix the steps of combining sufficiently similar intervals and recursively splitting dissimilar intervals so that split intervals may be recombined where no difference has been detected therebetween. FIG. 6 is a graph illustrating interval bisection according to an exemplary embodiment of the present invention. The taller vertical line 61 may represent original interval delineation at the 20 second mark, for example, as shown in FIG. 4. However, after it is determined that intervals A and B of FIG. 4 are not equivalent, each interval may be divided, for example, into a first subinterval between 0 and 10, a second subinterval between 10 and 20, a third subinterval between 20 and 30 and a fourth subinterval between 30 and 40. Subsequent processing, as described above, may lead to the determination that there is a detectable difference between the first and second subinterval, but no detectable difference between the second and third or third and fourth subintervals. Accordingly, the second, third, and fourth subintervals may be combined and the phase boundary may be recorded at the shorter vertical line 62. Accordingly, the original intervals may thus be refined to identify distinct phases. As indicated above, exemplary embodiments of the present invention are not limited to the use of the goodness-to-fit test in determining statistical difference. Exemplary embodiments of the present invention may utilize other statistical approaches and tests for determining whether processor usage is similar or dissimilar between proximate time intervals. For example, to determine where phase boundary occurs, significant change points within the data may be identified. These change points may be defined in terms of CPU utilization for each of the plurality of threads rather than total CPU utilization as discussed in detail above. Thus, thread-by-thread CPU utilization may be compared between proximate time intervals to determine if the intervals are distinct. For the purposes of the present disclosure, it may be sufficient that CPU utilization for even just a single thread has changed in order to identify a boundary between intervals. This may be because a statistically significant change to one thread can be meaningful in determining that a change has occurred in the way the program is being executed and this change, when correlated to increased overall CPU utilization may be indicative of a bottleneck. However, in order to statistically compare thread-by-thread CPU utilization between proximate intervals, a statistical measure may be used to characterize each interval. A mean and/or standard deviation (or variance) of thread-by-thread CPU utilization may serve as a suitable statistical characterization of each interval. To find change points, exemplary embodiments of the present invention may examine the average values of processor utilization in the successive contiguous intervals, and use a statistical. This may be accomplished, for example, by applying a Student's t test of the equality of means during adjacent intervals to the average processor utilizations of each thread. For this t test, a null hypothesis may be defined as proximate intervals having the same mean, a characteristic that may indicate that proximate intervals are functionally equivalent and may be merged into a single interval. A rejection of the null hypothesis may then be that t cannot be established with statistical significance, within a predetermined measure of confidence (α), that the proximate intervals have the same mean. In this event, a phase boundary may be recorded as existing between the proximate intervals. Thus, two adjacent intervals may be assigned to the same phase if the average processor utilization of corresponding threads are not significantly different from one interval to the next. Rather than comparing an average processor utilization, or another performance measure, observed in adjacent intervals directly, each interval may be divided into smaller intervals of equal length. This splitting may provide samples from which the mean and variance may be computed over each interval. These statistics may be used as inputs to t tests of the equality of means. The t test may be used because the means and variances in each interval are unknown. This may be performed for each thread. If the difference for at least one thread is significant, a phase change may be recorded. Because successive statistical tests may result in merging or splitting of intervals, adjacent intervals may have different lengths. For example, if the configured subinterval length is 1 second, the left interval is 10 seconds long, and the adjacent interval to the right is 20 seconds long, the number of samples in the two intervals may be 10 and 20 respectively. Thus, the sample sizes in the intervals may be different. This difference may be overcome by utilizing Welch's approximate method of computing the T statistic used to test for the equality of means of each interval. This technique, also referred to as Welch's t test is an adaptation of Student's t-test that may be used with two samples having possibly unequal variances. Thus, Welch's t test is an approximate solution to the Behrens-Fisher problem. Welch's t test may entail computing an estimate of the variance used in the t statistic, as well as an estimate of the number of degrees of freedom of the statistic to compensate for the inequality of the sizes of the two samples. The approximate estimator of the standard deviation of the difference in means may be given by: S X _ 1 - X _ 2 ≈ S 1 2 n 1 + S 2 2 n 2 ( 1 ) where Si2 denotes the unbiased estimator of the variance of observations from the ith interval, and ni denotes the corresponding sample size. The statistic uses for the t test may be: t ≈ X 1 - X 2 S X 1 - X 2 ( 2 ) where Xi denotes the mean of the observations in the ith interval. The number of degrees of freedom used in the t test is given by: df ≈ ( S 1 2 / n 1 + S 2 2 / n 2 ) 2 ( S 1 2 / n 1 ) 2 n 1 - 1 + ( S 2 2 / n 2 ) 2 n 2 - 1 ( 3 ) If df is not an integer, an approximate critical value of the T distribution may be obtained by interpolating critical values for the nearest integers above and below df for the desired α value. The resulting 100(1−α)% confidence interval for the difference of means may be given by: X 1 - X 2 ± t df , 1 - α 2 ⁡ [ S 1 2 n 1 + S 2 2 n 2 ] 1 2 ( 4 ) Accordingly, Welch's t test may be used with the t-distribution to test the null hypothesis that the two population's means are equal using a two-tailed test. Here, the null hypothesis may be that two proximate subintervals share a mean, which may be understood as the two proximate subintervals are equivalent. A rejection of the null hypothesis may thus be understood as the two proximate subintervals not sharing a mean and thus a difference in phase may be inferred. Although an inference may be made as to whether the average value of a performance measure, such as thread-by-thread mean CPU utilization, is the same in each interval at a chosen level of confidence, the same level of confidence might not be applicable to a complete set of performance measures. This problem may be viewed as an instance of the multiple comparison or Bonferroni problem. Bonferroni's inequality states that the probability that all N confidence intervals will simultaneously contain their respective true measures decreases as N increases. However, as change in CPU utilization by one thread may be a sufficient indicator that something meaningful has occurred in the system, full application of Boneferroni's inequality may not be necessary. Accordingly, use of the same confidence interval may be sufficient for the purposes of the present disclosure, however, various different confidence intervals may also be used. Exemplary embodiments of the present invention may utilize a succession matrix to track the flow of threads. The succession matrix may contain information about which threads tend to execute after which other threads. This data may be viewed either as the fraction (or percent) of successions attributable to each thread, or as the number of successions. Formally, for the ith of N threads, if Sij denotes the number of times thread j executes after thread i, and Fij denotes the fraction successions of thread i due to thread j, then F ij = S ij ∑ k = 1 N ⁢ S ik ,where 1≦i and j≦N. Thus, Fij may show the number of times that the different threads are executed during the run. Using this information in connection with previously generated utilization information may show a user which threads are taking up a lot of CPU utilization time while not being called very often. This may be a possible indicator of a performance bottleneck. If a thread is executed infrequently and requires a great deal of CPU utilization, then the thread may correspond to inefficient code. Graphs depicting the succession matrix may be helpful in determining how many times a particular thread is executed. FIG. 7 is a graph depicting a succession matrix according to an exemplary embodiment of the present invention. The succession matrix graph may illustrate along an x-axis, a seeded thread, which may be a first-occurring thread. Along a y-axis may be a successor thread. At each intersection, the frequency with which the successor thread follows the seed thread may be represented along a z-axis. The full set of threads may be represented as both seed threads and successor threads and thus at the x-axis/y-axis diagonals, where the same thread name is both seed and successor, the z-axis may indicate the frequency with which the given threads follows itself. FIG. 8 shows an example of a computer system which may implement a method and system of the present disclosure. The system and method of the present disclosure may be implemented in the form of a software application running on a computer system, for example, a mainframe, personal computer (PC), handheld computer, server, etc. The software application may be stored on a recording media locally accessible by the computer system and accessible via a hard wired or wireless connection to a network, for example, a local area network, or the Internet. The computer system referred to generally as system 1000 may include, for example, a central processing unit (CPU) 1001, random access memory (RAM) 1004, a printer interface 1010, a display unit 1011, a local area network (LAN) data transmission controller 1005, a LAN interface 1006, a network controller 1003, an internal bus 1002, and one or more input devices 1009, for example, a keyboard, mouse etc. As shown, the system 1000 may be connected to a data storage device, for example, a hard disk, 1008 via a link 1007. Exemplary embodiments described herein are illustrative, and many variations can be introduced without departing from the spirit of the disclosure or from the scope of the appended claims. For example, elements and/or features of different exemplary embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.
059237244	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The FIGURE shows an inventive X-ray diagnostic installation for the implementation of the inventive method. An X-ray source 2 driven via a high-voltage generator 1 and emits an X-ray beam 3 that penetrates a subject 4 and strikes a detector 5, for example a matrix detector or an image intensifier. The detector 5 is followed by a signal processing chain including a computer 6 for image generation and output and a display 7, for example a monitor. A filter arrangement 8 that effect a pre-filtering of the X-rays is arranged in the X-ray beam of the X-ray source 2. The filter arrangement 8 can, for example, be one or more wedge filters. A number of such filters can be provided in the filter arrangement 8 in order to allow an optimally exact matching to the current conditions. For implementing the inventive method, the X-ray diagnostic installation first is operated to produce a fluoroscopic exposure, the subject 4 being transirradiated with low-dose X-radiation during the course thereof in order to obtain information about the positioning of the subject 4 and about the exposure quality on the basis of the exposure. The X-rays attenuated by the subject 4 strike the detector 5 and are converted therein into radiation-dependent signals that are supplied to the computer 6. This computer 6 contains (or has access to) a memory 9 in which the signals obtained during the course of the first exposure are stored. After processing the supplied signals in the computer 6, the fluoroscopic image is supplied as an output to the display 7. With reference to the output fluoroscopic image, the operator can now determine whether there are over-exposure regions that are to be compensated with the filter arrangement 8. When this is the case, the filter arrangement 8 is placed into the beam path 3 dependent on the position of the over-exposure regions recognizable at the display 7. A position sensor 10 for recognizing the position of the filter arrangement 8 are allocated to the filter arrangement 8, the position of the filter arrangement 8 relative to the detector 7, and thus relative to the image visible at the display 7, being automatically determined therewith. The introduction of the filter arrangement 8 thereby occurs without the production of X-rays. In order to then generate the fluoroscopic image which would (will) exist after introduction of the filter arrangement 8, a number of processing parameters are supplied to the computer 6, particularly the operating parameters of the high-voltage generator 1 that serve as criterion for the quality of the emitted X-radiation. Further, the position data of the filter arrangement 8 identified by the position sensor 10 are supplied to the computer 6, (arrow b). Two tables T1 and T2 that are accessible by the computer 6 (arrows c, d) are also allocated to the computer 6. The table T1 contains absorption values of the filters of the filter arrangement 8 dependent on the operating voltage of the X-ray source 2. This makes it possible to determine the appertaining absorption value for every source operating voltage. This absorption value is specific to each filter, i.e. it takes into account the required filter data such as, for example, the material of the filter, the geometry of the filter, etc. By contrast, correction values, that serve for taking signal variations and fluctuations which occur within the computer 6 into consideration, are stored in table T2. Dependent on the nature of the computer 6 and of the display 7 employed, of course, different influences on the signal processing occur that in turn influence the respective signals which are produced. The calculation of the expected image with the filter arrangement in the X-ray beam ensues pixel-by-pixel. Only the picture elements that are "affected" by the filter arrangement 8, i.e. whose signal would change if a further fluoroscopic exposure were made with the filter arrangement 8 in the beam path 3, are taken into consideration in the processing. These picture elements are known from the knowledge of the position of the filter arrangement 8 obtained from the position sensor 10. These picture elements are now calculated as follows in terms of their gray scale values, this calculation ensuing for every individual picture element: First, the calculation of the filter attenuation S.sub.Image ensues in two steps: 1. Attenuation of the detector entry dose S.sub.Dose : PA0 2. Attenuation of the gray scale value S.sub.Image : S.sub.Dose =value from absorption table T1 dependent on the source voltage. PA1 S.sub.Image =S.sub.Dose .times.correction value from table T2. PA1 G.sub.Calculate =G.sub.Transirradiation -S.sub.Image The image attenuation S.sub.Image obtained in this way is subsequently subtracted from the respective gray scale value in order to obtain the calculated gray scale value: The calculation for the next picture element ensues after determination of the calculated gray scale value G.sub.Calculate until all picture elements in the overexposed region are processed. Subsequently, the computational gray scale values are operated on the other, non-processed gray scale values of the regions that are not overexposed (and thus not covered by the filter arrangement 8) in order to obtain the overall calculated image, which is subsequently supplied as an output. With reference thereto, the operator can then recognize and if necessary correct the pre-filtering which ensues due to the manual introduction of the filter arrangement 8. When such a correction is required, then the filter arrangement 8 is correspondingly shifted, and a new generation of the calculated image ensues due to the renewed position acquisition. In this case, the computer 6 accesses the first fluoroscopic image signals stored in the memory 9 and produces the new calculated image based thereon. Although various minor modifications might be suggested by those skilled in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come with the scope of my contribution to the art.
	abstract	An X-ray CT apparatus includes a plurality of X-ray tubes, a plurality of X-ray detectors corresponding to the plurality of X-ray tubes, respectively, a support mechanism which supports the X-ray tubes and the X-ray detectors to allow the X-ray tubes and the X-ray detectors to rotate about a single rotation axis, a reconstruction unit which reconstructs image data on the basis of outputs from the X-ray detectors, and a plurality of filters which are respectively provided for the plurality of X-ray tubes and each have a characteristic in which an X-ray path length changes along a curve approximate to an inverted Gaussian curve from the rotation center to the two ends of an X-ray beam.
060699302	claims	1. A passive containment cooling system for a nuclear reactor, the nuclear reactor including a wetwell, a drywell, and a vacuum breaker positioned between the wetwell and the drywell, said system comprising: at least one condenser; at least one vent line having a first end, a second end, and a passage extending between said first and second ends, said vent line first end coupled to said at least one condenser, said vent line second end extending into the wetwell; and at least one branch having a first end, a second end, and a passage extending between said branch first and said branch second ends, said branch first end coupled to said vent line so that said branch passage is in communication with said vent line passage, said branch second end coupled to the vacuum breaker. coupling a first end of the vent line branch to the vent line; and coupling a second end of the vent line branch to the vacuum breaker. 2. A passive containment cooling system in accordance with claim 1 wherein said vent line further comprises an intermediate portion between said first vent line end and said second vent line end, and wherein said branch first end is coupled to said vent line intermediate portion. 3. A passive containment cooling system in accordance with claim 1 wherein said branch second end is coupled to the vacuum breaker so that said branch slopes substantially downwardly from said branch second end to said branch first end. 4. A passive containment cooling system in accordance with claim 1 comprising at least two vent lines, one of said at least two vent lines coupled to at least one other of said at least two vent lines. 5. A passive containment cooling system in accordance with claim 1 wherein the wetwell includes a suppression pool, said vent line second end is submerged in the suppression pool, and wherein said system further comprises a vent bypass line extending between said vent line and the wetwell. 6. A passive containment cooling system in accordance with claim 5 wherein said vent bypass line comprises a first end and a second end, said vent bypass line first end coupled to said vent line adjacent said vent line second end, said vent bypass second end comprising a valve. 7. A passive containment cooling system in accordance with claim 5 wherein the nuclear reactor further includes a Gravity Driven Cooling System including a pool of coolant, wherein a connecting element extends between an air space above the pool of coolant and an air space above the suppression pool, and wherein said vent bypass line extends between said vent line and the pool of coolant. 8. A method for removing noncondensibles from a passive containment cooling system of a nuclear reactor utilizing a vent line branch, the nuclear reactor including a wetwell, a drywell, and a vacuum breaker positioned between the wetwell and the drywell, the passive containment cooling system including a condenser and a vent line, the vent line having a first end coupled to the condenser and having a second end positioned in the wetwell, said method comprising the steps of: 9. A method in accordance with claim 8 comprising the step of coupling the first end of the vent line so that the vent line branch slopes substantially downwardly from the second end of the vent line branch to the first end of the vent line branch. 10. A method in accordance with claim 8 comprising the step of coupling the first end of the vent line branch to the vent line adjacent the second end of the vent line. 11. A method in accordance with claim 8 wherein the passive containment cooling system includes at least two vent lines, and wherein said method further comprises the step of coupling at least one of the vent lines to at least one other of the vent lines. 12. A method in accordance with claim 8 wherein the wetwell includes a suppression pool and the vent line second end is submerged in the suppression pool, and wherein said method further comprises the step of extending a vent bypass line between the vent line and the wetwell. 13. A method in accordance with claim 8 wherein the nuclear reactor further includes a Gravity Driven Cooling System including a pool of coolant, wherein a connecting element extends between an air space above the pool of coolant and an air space above the suppression pool, and wherein said method further comprises the step of extending the vent bypass line between said vent line and the pool of coolant.
	description	This patent application claims the benefit of priority under 35 U.S.C. § 119 from Korean Patent Application No. 10-2019-0135740 filed on Oct. 29, 2019, the contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to a nuclear fuel rod including a burnable absorber. 2. Description of the Related Art Nuclear power plants refer to power plants in which electricity is produced from nuclear energy released from a nuclear reaction. Commercial nuclear power plants based on a nuclear fission chain reaction are classified, according to methods for slowing down neutrons and the neutron energy thereby, into pressurized water reactors (PWRs), pressurized heavy water reactors (PHWRs), boiling water reactors (BWRs), and fast reactors (FRs). The basic principle of a nuclear fission chain reaction is repetitive process that a fissile material such as uranium 235 (U-235) absorbs a single neutron and then emits approximately 2.5 neutrons which cause other fission reactions with other fissile materials. A fission reaction releases energy in form of kinetic energy of the neutrons and fission products, gamma rays, etc. Inside a nuclear reactor in a nuclear power plant, the numbers of neutrons released from nuclear fissions are artificially adjusted to control nuclear fission chain reactions as desired. If the amount of neutrons generated by the nuclear fission reactions is more than, less than, or equal to the amount of lost neutrons, these states are respectively defined as “supercritical”, “subcritical”, or “critical” state. The physical numerical value that indicates the extent of such nuclear fission chain reaction is referred to as “reactivity”. When the reactivity is positive, the reactor is in a “supercritical” state, when the reactivity is negative, the reactor is in a “subcritical” state, and when the reactivity is zero, the reactor is in a “critical” state, respectively. In a general light water reactor (LWR), a uranium-based fissile material in which a certain portion of uranium 235 is enriched is processed into a pellet form, and is charged into a nuclear reactor in a form of a bundle of nuclear fuel assemblies (FAs). Nuclear reactors are each operated for the design life thereof in a manner in which for every constant fuel cycle, a portion of burned nuclear FAs is extracted and new nuclear FAs are charged. When a nuclear reactor is operated without any reactivity control at the beginning of cycle (BOC) after a new nuclear fuel is charged, the nuclear reactor assumes a “supercritical” state, and the reactivity value at this point is defined as “excess reactivity”. The “excess reactivity” is generally the highest at an early stage of the nuclear reactor fuel cycle, is gradually decreased as the nuclear fuel is burnt, and approaches a “critical” state at the end of cycle. In an actual operation of a nuclear reactor, it is desirable during the fuel cycle to adjust the “excess reactivity” and artificially maintain the reactor in “critical state”. In a general nuclear reactor, the excess reactivity is adjusted by mechanical insertion or extraction of a control rod composed of neutron-absorbing materials. However, when the excess reactivity is large, the mechanical movement of the control rod should be increased, so that not only the uncertainty of reactivity adjustment increases, but also the risk of accident may increase. Thus, in a general nuclear reactor, the excess reactivity is lowered using another method, and then an additional reactivity control is carried out using a control rod. One of well-known methods is a method of adding borated water to a coolant. However, in this method, in order to neutralize the coolant's pH decreased by the borated water, LiOH is further added to the coolant. Consequently, not only a large amount of tritium is generated while LiOH and neutrons react, but also the moderator temperature coefficient (MTC), which is one of the inherent safety factors of a nuclear reactor, becomes less negative when the borated water is added to the coolant and may also be a positive value in a severe case. Thus, this method not only requires a complicated utility for controlling the concentration of the borated water but also deteriorates the inherent safety of the nuclear reactor, and the borated water itself has a property of corroding the structural materials of the nuclear reactor. Thus, LWRs have been advanced in the direction of improving the inherent safety of the nuclear reactor, while aiming to enable an operation in a low-boron condition by introducing a concept of applying burnable absorber materials. The burnable absorber material converts into a material, which has very small neutron absorption probability after absorbing a neutron, and becomes incapable of functioning as a neutron absorber material as time elapses from the initial stage to the final stage of the nuclear reactor fuel cycle. The BA materials can be integrated with fuel in FAs. There are typical examples such as an integral fuel burnable absorber (IFBA) in which the outer portion of a fuel pellet is coated with a burnable absorber material, and a method in which a burnable absorber such as Gd2O3 or Er2O3 is used by being uniformly mixed with a nuclear fuel. Most of these existing methods have obvious limitations in building a very-low-boron or a soluble-boron-free condition because of having low design flexibility and being optimized so as to be capable of only a low-boron operation in a general LWR environment. Therefore, recently, Korea advanced institute of science and technology (KAIST) has proposed a centrally-shielded burnable absorber (CSBA) in which design flexibility is guaranteed by locating a burnable absorber (Gd2O3) inside a fuel pellet, and in a physical aspect, the excess reactivity can efficiently be adjusted during cycle period of a nuclear reactor because the burnable absorber is very slowly burnt by using a self-shielding phenomenon. Compared to concepts of existing burnable absorbers in environments of existing LWRs, the merit, in which a fuel pellet charged with the CSBA remains inside a nuclear fuel and the excess reactivity can be effectively adjusted, has been verified through various research results. In addition, it was verified that the excess reactivity could be optimized even in a multi-batch reactor core design by inserting the CSBA into all of fuel pellets and using different numbers of CSBA. Also, in an aspect of manufacturability, it was verified that fuel pellets into which the CSBA was inserted could be manufactured, and even in various temperature environments, the integrity of the nuclear fuel was guaranteed. Consequently, it was confirmed through the existing research on the CSBA that the concept of burnable absorbers using the self-shielding phenomenon could build a very-low-boron or soluble-boron-free operation environment of a nuclear reactor by efficiently adjusting the excess reactivity, and thus, the inherent safety of the nuclear reactor could be maximized. However, for all these merits, there are practical limitations, such as complicated management of nuclear FAs under a situation of using various numbers of CSBA, integrity of fuel pellets in which the CSBAs are inserted in a neutron irradiation environment, and applicability to an actual commercial nuclear reactor due to changes in existing nuclear pellet manufacturing methods. The present invention proposes a technology for applying a new burnable absorber which solve the aforementioned inherent limitations of existing burnable absorbers, and which are easily manufactured while having an excellent performance similar to the CSBA. As described above, with regard to existing PWRs, technologies for various burnable absorbers adapted to the characteristics of the reactors have already been developed and the performance thereof have been sufficiently verified. However, in order to build a very-low-boron or a soluble-boron-free operation environment capable of remarkably improving the inherent safety and economy of the present commercial nuclear reactors and to satisfy the requirements for future-type long-fuel-cycle PWRs and small and medium sized or modular reactors (SMRs), various existing burnable absorbers exhibit obvious limitations thereof, and thus, new-concept burnable absorbers are demanded so as to match the required characteristics. The requirements for specific future-type nuclear reactors may be summarized as simpler and more economical burnable absorbers, implementation of very-low-boron or soluble-boron-free operations, economical and safe long-fuel cycle operations for 24 months, achievement of ultra-long operations by slightly increasing the degree of U-235 enrichment which is approximately 4-5% at present, and the like. Thus, in an aspect of the present invention, there is provided a method of using a new burnable absorber, in which the excess reactivity of a nuclear reactor is effectively adjusted using a self-shielding phenomenon to minimize the disadvantages of existing burnable absorbers, and which may be applied to future-type LWRs and SMRs while improving the inherent safety and economic feasibility of commercial nuclear reactors. According to an aspect of the present invention, there is provided a nuclear fuel rod including at least one or more fuel pellets and a cladding tube surrounding the fuel pellets, the nuclear fuel rod including a burnable absorber inside the cladding tube, and the burnable absorber including a burnable absorber material and a cladding material surrounding the burnable absorber material. According to another aspect of the present invention, there is provided a nuclear fuel rod including at least one or more fuel pellets and a cladding tube surrounding the fuel pellets, the nuclear fuel rod having a structure in which the fuel pellets and disk-like burnable absorbers are alternately stacked, the burnable absorbers each including a disk-like burnable absorber material and a cladding material surrounding the burnable absorber material, and the fuel pellet having dishes on upper and lower portions thereof. In addition, in another aspect of the present invention, there is provided a method for manufacturing a nuclear fuel rod, the method including: preparing at least one or more burnable absorbers each including a burnable absorber material and a cladding material surrounding the burnable absorber material; and alternately stacking, in a cladding tube, at least one or more fuel pellets and the at least one or more burnable absorbers. Furthermore, there is provided a nuclear reactor including the nuclear fuel rod. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings in such a manner that the technical idea of the present invention may easily be carried out by a person with ordinary skill in the art to which the invention pertains. The present disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, portions unnecessary for describing the present disclosure will be omitted for clarity, and like the reference numerals in the drawings denote like elements throughout the specification. In this disclosure below, when one part (or element, device, etc.) is referred to as being ‘connected’ to another part (or element, device, etc.), it should be understood that the former can be ‘directly connected’ to the latter, or ‘electrically connected to the latter via an intervening part (or element, device, etc.). Throughout the specification of the present invention, when a member is “on” another member, this includes not only the case in which the member is in contact with another member, but also the case in which still another member is present between the two members. Furthermore, when it is described that one comprises (or includes or has) some elements, it should be understood that it may comprise (or include or has) only those elements, or it may comprise (or include or have) other elements as well as those elements if there is no specific limitation. The terms “approximately”, “substantially”, and the like, which are used through the specification of the present invention, will be used as a meaning of being close to or adjacent to a numerical value when an allowable manufacturing or material error is provided to the described inherent meaning and to help understanding the present invention, and the terms are used to prevent an unscrupulous conscientious infringer from illegal use of a described content in which accurate or absolute numerical value is described. The terms “step of (performing) . . . ” or “step of . . . ” used in the entire specification of the present disclosure does not mean “step for”. Throughout the specification of the present invention, the term “combination thereof” included in a Markush type statement means a combination of one or more selected from the group consisting of elements described in the Markush type statement, and means that one or more selected from the group consisting of the elements are included. In an aspect of the present invention, there is provided a nuclear fuel rod 10 including at least one or more fuel pellets 11 and a cladding tube 12 surrounding the fuel pellets, wherein the nuclear fuel rod 10 includes therein burnable absorbers 13, and the burnable absorbers 13 each include a burnable absorber material 13a and cladding materials 13b surrounding the burnable absorber material 13a. Here, the nuclear fuel rod 10 provided in an aspect of the present invention is illustrated by schematic views in FIGS. 2 and 3, and hereinafter, with reference to the schematic views in FIGS. 2 and 3, the nuclear fuel rod 10 provided in an aspect of the present invention will be described in detail. First, a self-shielding phenomenon inside the burnable absorber will be described below. A neutron infiltrating the burnable absorber material from the surface thereof firstly reacts with the burnable absorber material at the surface thereof, and converts the burnable absorber material into a material that does not absorb the neutron at the position. At this point, the number of neutrons decreases toward the inside of the burnable absorber material while the neutrons infiltrating from the surface gradually react with the burnable absorber material, and this is referred to as a self-shielding phenomenon. Due to such self-shielding phenomena, there is an effect of slowing down the burning of the entirety of the burnable absorber material while the probability of absorbing a neutron decreases inside the burnable absorber material. Consequently, an effect is provided in which the smaller the surface area of the burnable absorber having the same volume, the stronger the self-shielding, and thus, the burnable absorber is more slowly burnt. In an aspect of the present invention, a burnable absorber is provided which has a shape appropriately charged so as to be spatially separated from the nuclear fuel. In the newly provided nuclear fuel rod including a burnable absorber, the ratio of the volume to the surface area may be determined by freely setting the design of the burnable absorber, and thus, there is a merit in that the self-shielding effect which is a physical characteristic may be optimized. FIG. 1 illustrates a conceptual view of a general nuclear fuel rod 1, FIG. 2 illustrates a conceptual view of a nuclear fuel rod 10 according to an embodiment of the present invention, and FIG. 3 illustrates a conceptual view of a burnable absorber 13 according to an embodiment of the present invention. Referring to the conceptual view of FIG. 2, the nuclear fuel rod 10 provided in an aspect of the present invention may have a shape in which fuel pellets 11 and burnable absorbers 13 are formed inside a cladding tube 12, and the burnable absorbers are inserted between the fuel pellets 11. The fuel pellets each may have a general pellet shape. In a specific example, the burnable absorbers 13 each include a burnable absorber material 13a and cladding materials 13b surrounding the burnable absorber material 13a, and as illustrated in the conceptual view of FIG. 3, the burnable absorbers may favorably have a disk shape. The fact that the burnable absorbers have a disk shape may mean a burnable absorber formed by a disk-like burnable absorber material and cladding materials surrounding the disk-like burnable absorber material. The nuclear fuel rod 10 provided in an aspect of the present invention includes the burnable absorber including cladding materials surrounding the burnable absorber material, and the burnable absorber is formed by the burnable absorber material and the cladding materials, and thus, the nuclear fuel rod provides direct use possibility also to burnable absorber materials, such as gadolinium (Gd) having the relatively low melting point to adjust the excess reactivity during an operation of a nuclear reactor. The burnable absorber material is sealed with cladding materials having relatively low melting points, so that an effect may be expected in that even when the burnable absorber material is melted in an abnormal environment of the nuclear reactor, loss of the burnable absorber material is prevented by causing the burnable absorber material to remain inside the cladding material. In addition, cladding materials having superior thermal conductivity are applied to the burnable absorbers stacked between the nuclear pellets, so that there is an effect of lowering the highest temperature of the fuel pellets formed during an operation of the nuclear reactor such that heat generated in the fuel pellets are more efficiently transferred to a coolant via the burnable absorber. The burnable absorber material 13a may be gadolinium (Gd), Gd2O3, erbium (Er), Er2O3, boron carbide (B4C), and the like. The nuclear fuel rod 10 provided in an aspect of the present invention includes the burnable absorbers 13, so that gadolinium (Gd) or erbium (Er), which are difficult to apply in related arts, may also be applied as it is. Due to the design characteristics of not being in contact with the nuclear fuel, the burnable absorber materials serve as stable materials, and thus, there is no need to further add other materials in the application of the burnable absorber materials. Thus, materials such as Gd, Gd2O3, Er, Er2O3, and B4C may be a candidate group, and if necessary, specific isotopes of these burnable absorber materials may be enriched and used. Specifically, when applying B4C, it is expected to be more economical while exhibiting the similar performance to that of IFBA from Westinghouse, and when Er2O3 is applied by enriching Er-167 or the like, more effective applicability is expected due to reactivity penalty compared to the case of applying Er2O3 with Gd2O3. In addition, the cladding materials 13b may be an alloy including zirconium. In general, a raw material used for the raw materials of nuclear fuel rod cladding tubes may be used. Furthermore, the nuclear fuel rod 10 may have at least one or more burnable absorbers 13 located between at least two or more nuclear pellets 11. In a specific example, the fuel rod may have a structure, in which a disk-like burnable absorber is stacked on a fuel pellet, another nuclear pellet is stocked on the burnable absorber, and another burnable absorber is stacked on the another fuel pellet, that is, the fuel rod may have a structure in which a plurality of fuel pellets and a plurality of burnable absorbers are alternately stacked. The diameter of the burnable absorber 13 may be equal to the diameter of the fuel pellet 11. If the diameter of the burnable absorber is larger than the diameter of the fuel pellet, the burnable absorber cannot be charged into the cladding tube due to constraints of the cladding tube, and when the diameter of the burnable absorber is smaller than the diameter of the fuel pellet, the burnable absorber may move inside the cladding tube and thereby cause a mechanical problem. The thickness of the burnable absorber 13 may be the thickness of a shape including the burnable absorber materials 13a and the cladding materials 13b surrounding the burnable absorber materials, may be approximately 0.1-2.0 mm, approximately 0.5-1.8 mm, approximately 1.0-1.7 mm, or approximately 1.3-1.6 mm. When the thickness of the burnable absorber exceeds approximately 2.0 mm, there may be a limitation in that the height of the entire reactor core is excessively high. The thicknesses of the burnable absorber materials 13a and the cladding materials 13b of the burnable absorber 13 may be set on the basis of the thickness range of the burnable absorber. The self-shielding effect is adjusted by the ratio of the surface area and the volume, and the burnable absorber provided in an aspect of the present invention may optimize the self-shielding effect by flexibly adjusting the design of the burnable absorber material. The diameters of the burnable absorber material 13a may be a diameter of approximately 30-95%, approximately 40-95%, approximately 50-90%, approximately 65-93%, approximately 70-92%, approximately 80-90%, approximately 50-85%, approximately 50-75%, or approximately 60-70% of the diameter of the fuel pellets 11. In a specific example, as illustrated in FIG. 4, the radii of the burnable absorber material 13a may be represented by a in the burnable absorber 13, and a may be approximately 1-3 mm, approximately 1.5-2.5 mm, or 1.7-2.4 mm. In addition, the thicknesses of the absorber materials may be represented by b, and b may be 0.8-1.6 mm or 1.0-1.4 mm. In addition, the thickness of the burnable absorber may be represented by c, where c is greater than b, and c may be approximately greater than 0.8 mm and below 2.0 mm. In addition, the thickness d of the cladding materials may be approximately 0.05-0.2 mm, approximately 0.07-0.15 mm, or approximately 0.08-0.12 mm. In addition, a predetermined space may be formed between the burnable absorber and the nuclear pellets, the thickness of the predetermined space or gap may be represented by e, and e may be approximately 0.01-0.1 mm, or approximately 0.03-0.07 mm. In addition, the radii of the burnable absorber may be represented by f and be equal to the radii of the nuclear pellets, and f may be approximately 2-5 mm or approximately 3.5-4.5 mm. In still another example, the fuel pellets 12 may have dishes formed in upper and lower portions thereof in the nuclear fuel rod 10. The dishes are formed in the upper and lower surfaces of the fuel pellets, so that the fuel pellets may be prevented from being pushed due to a phenomenon in which the pellets are irradiated with neutrons and axially expanded. FIG. 6 illustrates a plan view of a nuclear fuel rod 10 according to another embodiment of the present invention, and specifically, the nuclear fuel rod 10 has a structure in which fuel pellets 11 and a disk-like burnable absorber 13 are alternately stacked, and the burnable absorber include a burnable absorber materials 13a and a cladding material 13b surrounding the burnable absorber material 13a, and the fuel pellets may have grooves 11a on the upper and lower portions thereof. The nuclear fuel rod provided according to an aspect of the present invention has a merit in that the shape of the burnable absorber is freely adjusted and the self-shielding effect may be efficiently used. In addition, there is a merit in that due to the design in which the burnable absorber is positioned between the fuel pellets, the highest temperature of the burnable absorber is formed to be relatively lower than the fuel pellets, and the possibility that the burnable absorber is melted, and there is a merit in that the melted burnable absorber is positioned inside the cladding tube even under the assumption of being melted. Furthermore, there is a merit in that the manufacturing process of the burnable absorber constituted by a disk-type simple structure is also relatively very easy, and there is merit in that the integrity of already well-known nuclear fuel may be ensured because the burnable absorber has the shape of being separated from the nuclear fuel and independently present. In addition, in another aspect of the present invention, there is provided a method for manufacturing a nuclear fuel rod, the method including: a step for preparing a burnable absorber including a burnable absorber material and a cladding material surrounding the burnable absorber material; and a step for alternately stacking in a cladding tube at least one or more fuel pellets and at least one or more burnable absorbers. The method for manufacturing a nuclear fuel rod to be provided in another aspect of the present invention provides an example of the method for manufacturing the above-mentioned nuclear fuel rod 10, and the components of the nuclear fuel rod 10 are the same as described above, and thus detailed description thereof will not be provided. Furthermore, in still another aspect of the present invention, a nuclear reactor including the nuclear fuel rod is provided. Hereinafter, the present invention will be described in detail through experimental examples. However, the experimental examples below are merely for description of the present invention, and the content of the present invention are not limited by the experimental examples below. As illustrated in FIG. 4, as the nuclear fuel rod of example 1 (DiBA), a nuclear fuel rod was designed in which a unit body was formed such that a burnable absorber was positioned on upper and lower portions of the fuel pellets between the fuel pellets. Here, a was approximately 0.22527 cm, b was approximately 0.12048 cm, c was approximately 0.14048 cm, d was approximately 0.01 cm, e was 0.005 cm, and f was approximately 0.40958 cm. Gd2O3 was applied as burnable absorber materials. In addition, CSBAs of related arts were designed as the nuclear fuel rod of comparative example 1 (3-ball CSBA) and the nuclear fuel rod of comparative example 2 (2-ball CSBA). Gadolinium was applied as burnable absorber materials. Furthermore, a nuclear fuel was designed in which uranium oxides have approximately 7 wt % of enrichment as a control group (No BA (7 wt % UO2)). This experiment was performed by using a computation code Serpent 2, which is capable of very accurate computational simulation based on probabilistic method on the basis of ENDF/B-VII.1 nuclear data library. With respect to 17×17 nuclear FAs from Westinghouse Co., the behavior of reactivity according to burnup was evaluated under all reflective boundary condition by using approximately 100,000 histories. The evaluation was performed on the assumption that the temperature of the nuclear fuel is approximately 600 K, and uncertainty at this point was evaluated as approximately 30 pcm with respect to the multiplication factor. FIG. 5 is a graph comparing the result of using gadolinium (Gd) as the burnable absorber in the design of FIG. 4 with the reactivity control performance of the existing gadolinia (Gd2O3) CSBA design. The size of the CSBA used in this case, that is, the radius of burnable absorber material, is optimized to be approximately 0.14 cm in case of two CSBAs (comparative example 2: 2-ball CSBA), and approximately 0.12 cm in case of three CSBAs (comparative example 1: 3-ball CSBA). After selecting the case (control group), in which a nuclear fuel with approximately 7% enrichment was used reflecting the requirement of a future-type long cycle period PWR and the SMR, for the problem of comparing the reactivity control performance, a single assembly was formed by fuel pellets to which the CSBA and DiBA were applied by using a Monte Carlo code, that is, a Serpent 2 code, and the reactivity evaluation was performed under all reflective boundary condition environment. When comparing with the result of existing CSBAs (comparative examples 1 and 2) in which spherical absorber materials capable of inherently maximizing the self-shielding effect to be determined by the ratio of surface area to volume, it was evaluated that the disk-type burnable absorber also had excellent performance in an aspect of reactivity control through optimization. Furthermore, gadolinium was applied to the nuclear fuel rod of the Example 1, so that the problem in related arts in which it was difficult to apply gadolinium could be solved. Meanwhile, even when applying Gd2O3 as a neutron absorber, a very similar result to the case of metallic Gd of FIG. 5 was obtained. Specific reactivity control performance will be described below. When burnable absorbers rapidly react in an initial stage of a cycle period and are burnt, the initial reactivity will be evaluated to be low. Subsequently, although still in the initial stage of the cycle period, the reactivity will rapidly increase due to the rapidly burnt burnable absorbers, in a form converging to the reactivity in case of no burnable absorber. The increased reactivity thereafter exhibits a decreasing shape until the final stage of the cycle period, and this phenomenon is an inherent characteristic appearing in a strong burnable absorber such as Gd, and is referred as reactivity swing. All burnable absorbers are designed so as to appropriately show the reactivity swing through design optimization, and the target may be to maintain nearly flat reactivity during the entire cycle period. In this aspect, when evaluating the reactivity swing in example 1 (DiBA) and comparative examples 1 and 2 (CSBA) shown in FIG. 5, it may be confirmed that while the burnable absorbers efficiently remain during the entire cycle period, flat reactivity is maintained such that the reactivity swing does not almost appear. Consequently, it can be said that when the same burnable absorbers are used, the CSBA and DiBA have almost similar reactivity control performance. As illustrated in FIG. 6, as the nuclear fuel rod of example 2 (DiBA), a nuclear fuel rod was designed in which a unit body was formed such that a burnable absorber was positioned on upper and lower portions of the fuel pellets between the fuel pellets. And the fuel pellet comprises dishes on upper and lower portions thereof. Here, a was approximately 0.12048 cm, b was approximately 0.22527 cm, c was approximately 0.14048 cm, d was approximately 0.01 cm, e was approximately 0.005 cm, and f was approximately 40,958 cm, the diameter of the groove was approximately 0.40100 cm, and the height of the groove was approximately 0.02500 cm. Gadolinium (Gd) was applied as burnable absorber materials. In order to prevent a phenomenon in which the nuclear fuel was irradiated with neutrons and is unevenly expanded, small dishes were formed in upper and lower portions of initial fuel pellets in the manufacturing process. In aspect of reactivity control, since very small amount of nuclear fuel was removed, nearly the same performance as the existing result was exhibited. However, since the influence on the temperature distribution in burnable absorbers inside a nuclear fuel rod exerted by the fuel pellets having such dishes cannot be ignored, the heat transfer evaluation was performed considering the dishes. With respect to the nuclear fuel rod of example 2 above, the heat transfer performance was analyzed by using a FEM-based COMSOL code, and the results thereof are illustrated in FIGS. 7 and 8. FIG. 7 illustrates radial temperature distributions from central regions of a fuel pellet and a burnable absorber, and FIG. 8 illustrates axial and radial temperature distributions of a nuclear fuel rod including burnable absorbers. As illustrated in FIGS. 7 and 8, it may be confirmed that even considering the heat transfer effect due to the dishes of the fuel pellets, a temperature gradient from the fuel pellets to the burnable absorbers is meaningfully formed. When compared with the case of no dishes, it was evaluated that the temperature at the highest point has a difference of approximately 50 K. As confirmable in FIGS. 7 and 8, in this evaluation, the highest temperature of the burnable absorbers is evaluated to be lower than the melting point of approximately 1,586 K of gadolinium (Gd) by approximately 600 K, so that there is no concern about the melting of the burnable absorbers in a normal environment. Even if, for some reasons, gadolinium (Gd) is melted, gadolinium (Gd) is melted while sealed together inside a cladding material, and there is a margin of approximately 500 K as long as a temperature is formed lower than the melting point of approximately 2,123 K of the cladding material. In addition, as may be found in the graph of FIG. 8, axial-direction heat transfer occurs via the burnable absorbers inside the fuel pellets. This shows that there is a merit in that the characteristics of a UO2 nuclear fuel having relatively low thermal conductivity may be supplemented by the burnable absorbers. The concept of burnable absorbers proposed in the present invention has a merit in that self-shielding effects may be efficiently used by freely adjusting the shapes of the burnable absorbers. In addition, there is a merit in that due to the design in which the burnable absorber is positioned between the fuel pellets, the highest temperature of the burnable absorber is formed to be relatively lower than the fuel pellets, and the possibility that the burnable absorber is melted is lowered, and there is a merit in that the melted burnable absorber is positioned inside the cladding material even under the assumption of being melted. Furthermore, there is a merit in that the manufacturing process of the burnable absorber constituted by a disk-type simple structure is also very easy, and there is merit in that the integrity of already well-known nuclear fuel may be ensured because the burnable absorber has the shape of being separated from the nuclear fuel and independently present. After positioning a nuclear fuel rod including burnable absorbers in a nuclear FA used in an actual commercial reactor core and performing a numerical analysis, it was confirmed that due to a self-shielding effect, an effect was exhibited which was comparable to or better than the performance of the existing CSBA which was very efficiently applied. In addition, after evaluating the performance of the nuclear fuel rod including burnable absorbers in an aspect of heat transfer, it was confirmed that the highest temperature of the burnable absorbers was relatively lowered remarkably due to the burnable absorbers present between the fuel pellets. This means that various materials may be considered as a burnable absorber for a nuclear fuel rod. Since the actual positions of the burnable absorbers are independent from those of the fuel pellets, there is a merit of having no problem in manufacturability and compatibility. Also in aspect of manufacturing equipment, it is determined to be economical to additionally position independent burnable absorbers by optimizing the heights of the fuel pellets, so that high applicability and feasibility are expected not only in actual PWRs but also in boiling water reactors. In particular, in case of a PWR, it is expected that water-soluble boron which causes various problems in large-scale commercial reactor is removed, and that the economic feasibility and safety are remarkably improved. In addition, it is expected that even in the SMR, spotlighted as a next-generation nuclear reactor, the reactor core design, operability, safety, and economic feasibility are drastically improved and the realization of a high-performance SMR will be made possible. A nuclear fuel rod provided in an aspect of the present invention introduces burnable absorbers having shapes appropriately charged to be separate from nuclear fuels, and the ratio of the surface area thereof to the volume thereof may be determined by freely setting the design of the burnable absorbers, and accordingly, the self-shielding effect which is a physical property may be optimized. In addition, burnable absorber materials and cladding materials are formed as the burnable absorbers, so that the possibility is provided in which the positions of the neutron absorbers are fixed, and even for metallic burnable absorber materials such as gadolinium (Gd) having relatively low meting point, the burnable absorbers can be directly used to adjust the excess reactivity during the operation of a nuclear reactor. The burnable absorber material is sealed with cladding materials having the relatively high melting point, so that an effect may be expected in that even when the burnable absorber material is melted in an abnormal environment of the nuclear reactor, loss of the burnable absorber material is prevented by causing the burnable absorber material to remain inside the cladding material. In addition, the cladding material having a superior thermal conductivity is applied to the burnable absorbers stacked between the nuclear pellets, so that there is an effect of lowering the highest temperature of the fuel pellets formed during the operation of the nuclear reactor such that heat generated in the fuel pellets are more efficiently transferred to a coolant via the burnable absorber. So far, the nuclear fuel rod including burnable absorbers provided in an aspect of the present invention has been described, but the present invention is not construed to be limited by the examples and drawings disclosed in the specification, and various modifications can be made, of course, by those skilled in the art within the technical concept of the present invention.
052456420	description	DETAILED DESCRIPTION OF THE INVENTION This invention consists of a chemical process for removing cobalt contaminated oxide films that form on the surfaces of metal structures providing the coolant water circuits of water cooled nuclear fission reactors, such as inner portions of pipes, conduits, vessels, tanks, chambers, etc. Cobalt derived from metal alloy materials utilized in nuclear reactor plants is known as a major source of radiation, and in turn is a health hazard to operating and maintenance personnel working about the nuclear reactor structures. Cobalt, particularly the cobalt-60 isotope, is carried in the coolant water throughout the nuclear reactor coolant circuit or system and becomes entrained and/or embedded in the mass of oxides commonly forming and accreting over the exposed metal surfaces of vessels, conduits, etc. of the coolant water circuit system. Reducing the presence of cobalt by replacing cobalt containing alloys with alloys free of cobalt to minimize its source is expensive and most often impractical. Chemical decontamination procedures for removing cobalt contaminated oxide films from inside surfaces of coolant water containing structures have been proposed whereby the hazardous radiation fields are substantially reduced through oxide film removal by chemical means. However, due to extremely high corrosion rates, the decontaminated surfaces rapidly pick up cobalt-60 from the circulating coolant water and retain it in the accreting body of oxides forming over exposed surfaces. Thus, radiation levels measured one cycle after decontamination are frequently as great as before decontamination. In accordance with this invention a chemical technique is provided which controls and/or minimizes contamination in water cooled nuclear fission reactor system following decontamination. By minimizing recontamination, the chemical method of this invention can be a more effective means of reducing radiation exposure of personnel in a nuclear reactor plant. The chemical measures of this invention entail a combination of conditions that reduce the soluble (ionic) Co-60 concentration in reactor coolant water and pre-oxidize the surface of the coolant water retaining system with a oxide film substantially free of Co-60. The means of the invention comprise adding a solution of an iron compound, including, but not limited to, freshly prepared insoluble species Fe(OH).sub.3, Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, or water soluble compounds ferrous oxalate and ferric citrate in amounts sufficient to maintain a soluble iron concentration in the coolant water of the coolant system at about 200 parts per billion (ppb). With these conditions, preferably augmented by elevated water temperatures, the soluble (ionic) Co-60 in the reactor coolant water is effectively scavenged. Moreover, while the soluble Co-60 concentration in the coolant water is reduced, the surfaces of the coolant water retaining system can be oxidized to form a substantially cobalt free, protective film following a cobalt purging. Preferred conditions for the practice of this invention comprise adequate Fe(OH).sub.3 addition to maintain the iron concentration of approximately 200 ppb with the coolant water at a temperature of at least about 230.degree. C. Generally optimum effects are obtained when these conditions of iron concentration and temperature are retained in the coolant water of the reactor coolant system over a period of at least about 500 hours. The elevated temperatures of the coolant water can be provided without nuclear fission produced heat in a pre-startup treatment by any suitable means or source, such as heat generated by recirculation pumps which drive the coolant water through the reactor coolant system. In a typical reactor pre-startup treatment procedure of this invention, apt amounts of ferric hydroxide in a slightly basic water solution are injected into the reactor coolant for attaining the iron concentration conditions of about 200 ppb. Coolant water temperature is maintained at least about 230.degree. C. Given these conditions, the soluble Co-60 in the coolant water can be reduced down to less than about one percent of the total Co-60 concentration in the reactor water. To foster oxidation of the surfaces of cooling water circuit system upon purging of Co-60 from the coolant water, the dissolved oxygen content in the reactor coolant water is maintained at about 200 to about 400 parts per billion (ppb). This can be provided by introducing oxigated water, such as control rod drive water or other sources, or injecting oxygen. Preferably the operation of pH adjustment with iron solution addition for Co-60 purging of the coolant water system, and oxygen level control is carried out as long as is practical before startup of the nuclear reactor, for example at least about 500 hours. Following starting up of the water cooled nuclear fission reactor, the iron content of the coolant water may be depleted rapidly, whereby a high iron solution injection rate can be appropriate or required to maintain the iron content at least about 50 to about 100 parts per billion. Then the nuclear reactor is operated under the given conditions for approximately 500 hours before the iron solution injection is terminated. At this state the iron content of the coolant water should be maintained at about 5 ppb. This be can achieved by means of feedwater quality control.
	claims	1. A detector assembly comprising:a collimator assembly comprising:a first collimator segment having a first left end and a first right end, said first collimator segment comprising:a plurality of x-ray blocking first segment longitudinal walls having a first segment depth, each of said plurality of first segment longitudinal walls including a first interlocking protrusion comprising less than an entire portion of said first segment depth, said plurality of first segment longitudinal walls configured to be planar to projected x-rays;a second collimator segment having a second left end and a second right end, said second collimator segment comprising:a plurality of x-ray blocking second segment longitudinal walls having a second segment depth, each of said plurality of second segment longitudinal walls including a second interlocking protrusion comprising less than an entire portion of said second segment depth, each of said second interlocking protrusions engaging one of said first interlocking protrusions to form a continuous sidewall segment; anda plurality of first latitudinal segments positioned between each of said plurality of first longitudinal walls such that a plurality of first collimator chambers is formed, each of said first collimator chambers having a first collimator width. 2. A detector assembly as described in claim 1, wherein said first interlocking protrusion comprises a block shaped protrusion. 3. A detector assembly as described in claim 1, wherein said first interlocking protrusion comprises a triangular shaped protrusion. 4. A detector assembly as described in claim 1, wherein said plurality of first segment longitudinal walls comprise cast tungsten. 5. A detector assembly as described in claim 1, wherein said plurality of first segment longitudinal walls comprise cast lead. 6. A detector assembly as described in claim 1, wherein each of said first interlocking protrusions comprises a first protrusion width, said first protrusion width less than or equal to said first collimator width. 7. A detector assembly as described in claim 1, wherein:said first collimator segment comprises a first collimator height;said first interlocking protrusion comprising a first protrusion height;said second interlocking protrusion comprising a second protrusion height; andsaid first protrusion height added to said second protrusion height equaling said first collimator height. 8. A detector assembly as described in claim 1, further comprising:a scintillator assembly in communication with said collimator assembly, said scintillator assembly having a scintillator longitudinal width, said scintillator longitudinal width smaller than a collimator assembly longitudinal width. 9. A detector assembly as described in claim 1, wherein said first collimator segment further comprises:a plurality of opposing interlocking protrusions each of which is formed on one of said a plurality of first segment longitudinal walls, each of said plurality of opposing interlocking protrusions positioned opposite one of said first interlocking protrusions, said opposing interlocking protrusion comprising only a portion of said first segment depth. 10. A detector assembly as described in claim 9, wherein each of said opposing interlocking protrusions creates a mirror negative to one of said first interlocking protrusions. 11. A detector assembly as described in claim 1, wherein said plurality of first collimator chambers forms a rectangular array. 12. A collimator assembly segment for mating to a second collimator segment comprising a plurality of second segment longitudinal walls having a second segment depth, each of the plurality of second segment longitudinal walls having a second interlocking protrusion having a second protrusion height comprising less than an entire portion of the second segment depth, comprising:a first collimator segment having a first left end and a first right end, said first collimator segment comprising:a plurality of x-ray blocking first segment longitudinal walls having a first segment depth, each of said plurality of first segment longitudinal walls including a first interlocking protrusion comprising less than an entire portion of said first segment depth, each of said first interlocking protrusions shaped to engage one of the second interlocking protrusions to form a continuous sidewall segment, said plurality of first segment longitudinal walls configured to be planar to projected x-rays; anda plurality of first latitudinal segments positioned between each of said plurality of first longitudinal walls such that a plurality of first collimator chambers is formed, each of said first collimator chambers having a first collimator width. 13. A collimator assembly segment as described in claim 12, further comprising:a plurality of first latitudinal segments positioned between each of said plurality of first longitudinal walls such that a plurality of first collimator chambers is formed, each of said first collimator chambers having a first collimator width. 14. A detector assembly as described in claim 13, wherein each of said first interlocking protrusions comprises a first protrusion width, said first protrusion width less than or equal to said first collimator width. 15. A detector assembly as described in claim 12, wherein:said first collimator segment comprises a first collimator height;said first interlocking protrusion comprising a first protrusion height;said first protrusion height added to the second protrusion height equaling said first collimator height. 16. A detector assembly as described in claim 12, wherein said first collimator segment further comprises:a plurality of opposing interlocking protrusions each of which is formed on one of said a plurality of first segment longitudinal walls, each of said plurality of opposing interlocking protrusions positioned opposite one of said first interlocking protrusions, said opposing interlocking protrusion comprising only a portion of said first segment depth. 17. A detector assembly as described in claim 16, wherein each of said opposing interlocking protrusions creates a mirror negative to one of said first interlocking protrusions. 18. A method of manufacturing a detector assembly with extended longitudinal depth comprising:casting a first collimator segment comprising a plurality of first segment longitudinal walls having a first segment depth, each of said plurality of first segment longitudinal walls including a first interlocking protrusion comprising less than an entire portion of said first segment depth;casting a second collimator segment comprising a plurality of second segment longitudinal walls having a second segment depth, each of said plurality of second segment longitudinal walls including a second interlocking protrusion comprising less than an entire portion of said second segment depth;engaging each of said second interlocking protrusions with one of said first interlocking protrusions to form a plurality of continuous sidewall segments. 19. A method of manufacturing a detector assembly, as described in claim 18 further comprising:casting a plurality of first latitudinal segments between each of said plurality of first longitudinal walls such that a plurality of first collimator chambers is formed, each of said first collimator chambers having a first collimator width; andcasting said first interlocking protrusions and said second interlocking protrusions such that said first interlocking protrusions and said second interlocking protrusions combine to match said first segment.
	summary
	abstract	Systems and methods for separation or isolation of technetium radioisotopes from aqueous solutions of radioactive or non-radioactive molybdate salts using a polyalkyl glycol-based cross-linked polyether polymer. Some embodiments can be used for the effective purification of radioactive technetium-99m produced from low specific activity 99Mo.
	abstract	A small-sized filter unit of a simple structure, as well as an X-ray tube unit and an X-ray imaging system both having the filter unit, are implemented. A filter unit in a first aspect of the present invention comprises a filter plate, the filter plate having a first filter, a second filter disposed in a first direction with respect to the first filter and a third filter disposed in a second direction having a predetermined angle from the first direction with respect to the first filter, a guide plate having a guide frame for movement of the filter plate in the first and second directions, and a drive device for moving the filter plate.
046831100	abstract	An apparatus for consolidating spent fuel rods from spent fuel assemblies includes a container with a bottom and front, back, and side walls. The container has a plurality of flutes positioned adjacent to the front wall, and the plurality of flutes defines a plurality of channels. The apparatus also includes a plurality of springs, which are mounted on a support. The springs bear against the flutes and the channels when no fuel rods have been inserted into the container and the support is located proximate the front wall. The springs assist in guiding a fuel rod into a preselected location in the container; the springs are capable of maintaining the fuel rod in the preselected location. Preferably, each spring is a resilient finger that extends outwardly from the support toward the front wall. The support may be a movable sheet. The apparatus advantageously includes a device for moving the support. Such a device may automatically position the support in response to control signals.
	claims	1. A basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising:a disk-like grate having a ring-like structure encompassing and supporting a gridwork of horizontal beams;the gridwork of beams comprising a first series of parallel beams, a second series of parallel beams and a third series of parallel beams;each of the first, second, and third series of parallel beams having a first end engaged with the ring-like structure and an opposite second end engaged with the ring-like structure;wherein the first, second and third series of parallel beams are arranged in the ring-like structure so as to intersect and form a plurality of cells of at least two different shapes. 2. The basket apparatus of claim 1 wherein the first, second and third series of parallel beams are arranged in the ring-like structure form a first set of cells of a first size having a first shape and a second set of cells of a second size smaller than the first size having a second shape. 3. The basket apparatus of claim 2 wherein the first set of cells are hexagonal shaped and the second set of shells are triangular shaped. 4. The basket apparatus of claim 1 wherein the first, second and third series of parallel beams are arranged in the ring-like structure so that: (i) the first and second series of parallel beams intersect with one another; (ii) the first and third series of parallel beams intersect with one another; and (iii) the third and second series of parallel beams intersect with one another. 5. The basket apparatus of claim 1 further comprising:a plurality of the disk-like grates arranged in a stacked and spaced orientation;spacers located between the disk-like grates, the spacers maintaining separation between the disk-like structures. 6. The basket apparatus of claim 1, wherein the first and second series of parallel beams are oriented perpendicularly to each other and the third series of parallel beams are oriented obliquely to the first and second series of parallel beams. 7. The basket apparatus of claim 1, wherein the first and second series of parallel beams intersect at a plurality of first intersection points, and the third series of parallel beams intersect the first and second series of parallel beams at a plurality of second intersection points which do not coincide with the first intersection points. 8. A basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising:a disk-like grate having a circular ring-like structure encompassing and supporting a gridwork of intersecting horizontal beams; andthe gridwork of beams forming a first set of cells having a first shape and a second set of cells having a second shape, wherein the first set of cells are larger than the second set of cells;wherein the second set of cells are interspersed between the first set of cells in interior portions of the gridwork. 9. The basket apparatus of claim 8 wherein the first set of cells are hexagonal shaped and the second set of cells are triangular shaped. 10. The basket apparatus of claim 9, further comprising a vertically elongated fuel tube positioned in each cell of the first set of hexagonal shaped cells and a vertically elongated poison rod positioned in each cell of the second set of triangular shaped cells. 11. The basket apparatus of claim 8, wherein:the gridwork of beams includes a first series of parallel beams, a second series of parallel beams, and a third series of parallel beams; andthe first and second series of parallel beams are oriented perpendicularly to each other and the third series of parallel beams are oriented obliquely to the first and second series of parallel beams. 12. The basket apparatus of claim 11, wherein the first and second series of parallel beams intersect at a plurality of first intersection points, and the third series of parallel beams intersect the first and second series of parallel beams at a plurality of second intersection points which do not coincide with the first intersection points. 13. A basket apparatus for supporting a plurality of spent nuclear fuel rods within a containment structure comprising:a plurality of vertically spaced part disk-like grates each having a circular structural ring defining a central opening and supporting a gridwork of intersecting horizontal beams each spanning across the opening;the gridwork of beams comprising a first series of parallel beams having a first angular orientation, a second series of parallel beams having a second angular orientation, and a third series of parallel beams having a third angular orientation, wherein the first, second, and third angular orientations are each different than the other;wherein the first, second and third series of parallel beams in each structural ring are arranged to intersect and form a first array of open cells having a first shape and first size, and a second array of open cells having a second shape and second size different than the first shape and first size of the open cells of the first array. 14. The basket apparatus of claim 13, wherein the first and second series of parallel beams are oriented perpendicularly to each other and the third series of parallel beams are oriented obliquely to the first and second series of parallel beams. 15. The basket apparatus of claim 14, wherein the first and second series of parallel beams intersect at a plurality of first intersection points, and the third series of parallel beams intersect the first and second series of parallel beams at a plurality of second intersection points which do not coincide with the first intersection points. 16. The basket apparatus of claim 13, wherein the first array of cells are hexagonal shaped and the second array of cells are triangular shaped. 17. The basket apparatus of claim 13, wherein the second array of cells are interspersed between the first array of cells in interior portions of the gridwork.
	summary
	description	The invention relates to a method for generating extreme ultraviolet radiation and soft x-ray radiation with a gas discharge operated on the left branch of the Paschen curve, in particular, for EUV lithography, wherein a discharge chamber of a predetermined gas pressure and two electrodes are used, wherein the electrodes have an opening, respectively, positioned on the same symmetry axis and, in the course of a voltage increase upon reaching a predetermined ignition voltage generate a plasma located in the area between their openings, which plasma is a source of the radiation to be generated, wherein an ignition of the plasma is realized by affecting the gas pressure and/or by triggering, and wherein, with the ignition of the plasma, an energy storage device supplies by means of the electrodes stored energy into the plasma. A method with the aforementioned method steps is known from DE-A-197 53 696. The method is carried out in a device comprising an electrode system forming the discharge chamber. By means of this electrode system, extreme ultraviolet radiation and soft x-ray radiation are generated that can be used, in particular, for EUV lithography. The electrode system is comprised of two electrodes, i.e., a cathode and an anode, each having an opening. The opening is essentially a hole, and both openings are positioned on a common axis of symmetry. The cathode is embodied as a hollow cathode, i.e., it has a cavity. This cavity is used in order to generate the electrical field in a predetermined way. In particular, the arrangement of the electrodes is such that the field lines in the area or the bore holes are sufficiently stretched so that the firing condition of above a certain voltage is fulfilled. The discharge chamber is filled with gas, and the gas pressure, at least in the area of the electrode system, is within the range of 1 Pa to 100 Pa. The geometry of the electrodes and the gas pressure are selected such that the desired ignition of the plasma is realized on the left branch of the Paschen curve and, as a result of this, no dielectric firing between the electrodes outside of the openings occurs. As a result of the ignition, a current-conducting plasma channel of axial-symmetrical shape results in the area of the openings of the electrodes. In addition, current is supplied by means of the energy storage device via this channel. The resulting Lorentz force constricts the plasma. As a result of this constriction effect and because of resistance heating, very high temperatures occur within the plasma and radiation of a very short wavelength is generated. The known device can produce EUV light in the wavelength range of 10–20 nm. In connection with the method it is important that a switching element between the electrode system and the energy storage device is principally not needed. Accordingly, a low-inductive and effective coupling of the electrically stored energy into the electrode system can be achieved. Poles energies of a few Joules are sufficient in order to trigger current pulses in the range of several kilo ampere up to several 10 kilo ampere. Triggering of the energy coupling into the discharge that is operated in a controlled fashion or by automatic firing is realized by adjustment to a predetermined ignition voltage. The ignition voltage is affected, for example, by the gas composition, the temperature, pre-ionization, electrical field distribution, and other parameters. It can be adjusted according to the Paschen curve by means of the gas pressure of the discharge vessel. The energy storage device must also be charged up to this ignition voltage in order to be able to supply in the case of ignition as much energy as possible into the plasma. The invention has the object to improve a method comprising the aforementioned method steps such that the radiation yield, i.e., particularly the yield of EUV light, for each pulse is improved as well as the pulse-to-pulse stability of a plurality of sequentially performed discharges that are utilized in the method performed with pulse operation for generating the EUV light. The aforementioned object is solved in that the ignition of the plasma is realized by using a predetermined ignition delay. Carrying out the method with ignition delay results in a prolongation of the generation of the conductive plasma. In this way, an improvement of the cylinder symmetry of the low-impedance starting plasma that is required for discharge is obtained, i.e., of that plasma that is generated in the area of the openings of the electrodes after reaching the ignition voltage. The ignition delay results accordingly in an improvement of the EUV yield/pulse and the pulse-to-pulse stability. In connection with the method in a range of pulse operation of 50 Hz to 500 Hz an increase of the EUV yield by approximately 10 percent has been observed when selecting an ignition delay of approximately 1 ms. For affecting the ignition delay, the method is carried out such that the ignition delay is reduced by increasing the gas pressure or is increased by reducing the gas pressure. Such changes of the gas pressure can be obtained particularly easily when the gas flows through the area of the electrode system, for example, in order to affect the repetition frequency, i.e, to thereby perform the method with increased pulse frequencies. In order to affect the ignition delay, the method can be performed such that the ignition is realized by triggering a triggering pulse which is supplied to a triggering electrode affecting the ignition area of the plasma. By the triggering action, the distribution of the charge carriers in the ignition area of the plasma is affected and in this way also the point in time at which the ignition effectively occurs. It is expedient to carry out the method such that the triggering action for achieving a predetermined ignition delay is carried out in combination with an application of a pressure interval of the gas pressure. In this case, the pressure as well as the point in time of triggering are adjusted because the discharge, even for a triggered operation, can be carried in a stable way, or if at all, only within a certain pressure interval. In the afore described connection of triggering, the method can be carried out such that triggering is employed together with a predetermined triggering delay. The ignition delay is increased accordingly. The introduction of stored energy into the discharge that is carried out by automatic firing is realized together with the firing, i.e., automatically with the ignition of the plasma, wherein it should be ensured in this connection that the energy storage device taking into consideration the pulse operation is charged before the ignition is carried out. It is therefore necessary to have available information in regard to the voltage increase and obtaining a predetermined ignition voltage. As a result of this, the method can be carried out such that the voltage increase and/or obtaining a predetermined ignition voltage is determined measuring-technologically and in that affecting the gas pressure and/or the triggering action is realized taking into account the measured results. When the regulating action is performed within the context of continuous control, the gas pressure or a triggering delay is employed as a parameter. In this way, the desired ignition delay can be achieved or monitored measuring-technologically. It is also possible to carry out the method such that the point in time of ignition is determined measuring-technologically. In this way it is possible to determine the time which elapses between the point of reaching the ignition voltage and the effective point in time of ignition; this time corresponds to the ignition delay. For performing the measuring-technologically determination of the point in time of ignition, the method can be performed such that the point in time of ignition is measured by means of a measurement of a voltage differential of the electrode voltage and/or by means of a measurement of a current differential of the electrode current. At the beginning of ignition, the voltage supplied to the electrodes changes abruptly and, likewise, the current flowing during discharge. The voltage collapses and the current increases; both can be reliably detected. The ignition delay can be controlled in that the time between reaching the predetermined ignition voltage and the point in time of ignition is measured and in that the gas pressure is adjusted based on the measured results in order to match the predetermined ignition delay. The time between reaching the predetermined ignition voltage and the point in time of ignition is measured, for example, analog by means of an integrator or digitally by means of a counter. The time is supplied to a governor as a measured parameter; the governor adjust accordingly the gas pressure in the sense of a stabilization of the ignition delay. A series of discharge processes can be averaged, i.e., across a certain number of pulses. A special method is characterized in that a measuring-technological determination of the voltage present at the electrodes is realized from the beginning of the voltage increase across a certain time interval that includes a presumed point in time of ignition, wherein, for the measuring-technological determination, preferably an ignition voltage integrator is used. The time interval therefore surpasses the duration that is required for the charging process or the voltage increase at the electrodes. As a result of this, information in regard to the ignition voltage and in regard to the ignition delay can be derived from the same signal. The ignition voltage integrator enables a variety of information based on the same measured signal. Moreover, the method can be modified such that a measuring-technological determination of the voltage present at the electrodes includes saving the reached ignition voltage value up to the point of beginning of the subsequent voltage increase. The saving action is realized, for example, by means of a sample-and-hold circuit. Expediently, the method can be carried out such that the charge state of the capacitor block connected directly to the electrodes as an energy storage device is monitored continuously during voltage increase and that, after reaching a predetermined ignition voltage, triggering is carried out, as needed with a predetermined triggering delay. Information in regard to the charge state of the capacitor block can be obtained and evaluated with a suitable electronic device. The information is the basis for enabling operation of the method according to the above described strategies wherein influence is exerted on the gas pressure and/or the triggering of a triggering pulse. In some high-voltage capacitors their capacitance depends greatly on the temperature. In such cases, care must be taken that the energy of the capacitor at the time of ignition is maintained constant. In this connection, it is not important to maintain a constant ignition voltage; instead, the predetermined ignition voltage must be corrected by performing a corrective computation. For such a corrective computation the temperature of the capacitor or the capacitance across the duration of the charge ramp or the supplied charge voltage can be measured in order to carry out a corresponding correction. A special method is characterized in that triggering is carried out by means of a triggering electrode acting on charge carriers of an intermediate electrode space in that its blocking potential provided relative to a cathode is reduced. In this way, a triggering pulse can be reached at a predetermined point in time in order to influence in this way the ignition delay. In regard to a high EUV light efficiency, the method can be carried out such that the energy storage device is charged until a predetermined ignition voltage has been reached while forgoing complete recombination of the plasma taking place after extinguishing of the plasma. In this way, especially the repetition frequency can be increased, wherein the energy storage device can be recharged within shorter time intervals. In this connection, it is also possible to allow a high-impedance plasma to burn between the electrodes in the time period between two plasma discharges provided for generating radiation. The high-impedance plasma results in improved conditions for a starting plasma of high current discharge. The supply of stored energy into a discharge operated by automatic firing is carried out at the time of firing, i.e., automatically with the ignition of the plasma. However, in this connection it must be taken into consideration that a discharge system without triggering has only a single firing point that is determined by the conditions of the Paschen curve. This point is not stable. When the electrode system is heated in particular within the discharge chamber, the firing will no longer take place at the same voltage. Moreover, firings will repeat themselves in fast sequence to thus generate radiation constantly. Between two firings the system requires a certain amount of time for recombination of the gas in the discharge chamber. During this time period, the gas returns, at least partially, into its initial state so that the energy storage device can again be recharged and the required voltage can be build up at its electrodes. As a result of this, the state of the system also depends on when the last firing has taken place, i.e., at which repetition frequency the generation of the radiation has been carried out. At a high repetition frequency, the working point positioned on the Paschen curve will be different than for a low repetition frequency. In practice, this means that the repetition frequency can be very limited because no stable working point can be found at all anymore. In connection with this, problems reside in that it is not possible to switch quickly enough from one repetition frequency to another and that even for a certain repetition frequency switching on and off cannot be carried out repeatedly. Switching on and switching off is particularly important when a lithography device is operated where between the exposure processes pauses are mandatory in order to be able to perform adjustments on the device. The invention therefore has additionally the object to improve a method for generating extreme ultraviolet radiation and soft x-ray radiation with a gas discharge operated on the left branch of the Paschen curve, in particular, for EUV lithography, wherein a discharge chamber of a predetermined gas pressure and two electrodes are used, wherein the electrodes have an opening, respectively, positioned on the same symmetry axis and, in the course of a voltage increase upon reaching a predetermined ignition voltage, generate a plasma located in the area between their openings, which plasma is a source of the radiation to be generated, wherein an ignition of the plasma is realized by triggering, and wherein with the ignition of the plasma an energy storage device supplies by means of the electrodes stored energy into the plasma, such that for a method performed by pulse operation for the generation of the EUV light a precise control of the pulses can be achieved, in particular, within a wide parameter field of the discharge processes, in order to improve in this way the radiation yield of the EUV light in the sense of the afore described object. This object is solved in that the ignition of the plasma is realized by a triggering electrode whose potential before beginning the triggering process is higher than that of one of the electrodes used as a cathode. By the triggering action, an influence is exerted onto the ignition conditions for the plasma. In particular, triggering affects the distribution of charge carriers in the ignition area of the plasma and thus also the point in time at which the ignition will effectively occur. In this connection, the potential of the triggering electrode before the beginning of the triggering process is higher than that of the cathode. As a result of this, an effect on the field generation in the discharge chamber is realized in such a way that no firing can occur. Firing is possible only when the potential that prevents firing is removed. In a special way, the method is carried out such that a voltage of the triggering electrode relative to the electrode that is used as a cathode, the voltage on both electrodes, and the gas pressure of the discharge chamber are adjusted such that upon supplying the triggering voltage ignition of the plasma will not occur and will occur only after switching off the triggering voltage. Switching off the triggering voltage enables such a generation of the electrical field in the discharge chamber that the firing conditions are fulfilled. The point in time of firing can be precisely determined by the triggering signal, i.e., by switching off the triggering voltage. It is important in this connection that the parameter range for a discharge can be significantly broadened. The pressure in the gas chamber, the spacing of the electrodes, and the voltage at the electrodes can be selected differently as a function of the triggering voltage. While the firing in the un-triggered case is determined only by a single point on the Paschen curve, in the triggered case large voltage ranges ΔU or pressure ranges ΔP can be determined in which, after the triggering pulse, firing occurs. It is possible to adjust the parameters such that the method is operated with repetition frequencies between >0 Hz and 100 kHz. Good results were found for repetition frequencies of 10 kHz. Moreover, it is possible to perform the method such that it is operated with long operating intervals that are adjustable by switching on and off; during the intervals a fixed repetition frequency is used. An operating interval begins with switching on and ends with switching off. During an operating interval, for example, one wafer is exposed in a partial area. The radiation which is responsible for exposure is carried out according to one of the above described methods, in particular, at a fixed repetition frequency. After completion of an operating interval, an adjustment of the exposure device and/or of the wafer can be realized in order to then repeat, after exposure of the same wafer or of a different wafer, the described method with a predetermined repetition frequency. The invention relates also to a device for generating extreme ultraviolet radiation and soft x-ray radiation with a gas discharge operated on the left branch of the Paschen curve, comprising a discharge chamber of a predetermined gas pressure and two electrodes, wherein the electrodes have an opening, respectively, positioned on the same symmetry axis and, in the course of a voltage increase upon reaching a predetermined ignition voltage generate a plasma located in the area between their openings, which plasma is a source of the radiation to be generated, comprising a triggering electrode in the space adjoining the first electrode for triggering an ignition of the plasma, in particular for performing the method described above. Such a device is to be improved in particular for performing the above described methods such that a high service life and excellent cooling action of the electrodes is ensured. The above described object is solved in that the triggering electrode is embodied as a wall which has at least over surface area portions thereof has a predetermined spacing from the opening of the first electrode. The configuration of the triggering electrode as a wall ensures also in the case of a temperature-caused and plasma-caused wear of material a long durability and its large surfaces can be cooled easily, which, in turn, is beneficial with regard to a long service life. At the same time, the arrangement of the triggering electrode at a predetermined spacing from the opening of the first electrode ensures that the shape of the electrical field required for the field generation is ensured by means of the first electrode. In the above sense it is advantageous to configure the device such that the first electrode is a hollow electrode and that the triggering electrode is a wall or wall section within the geometry of this hollow electrode. This provides a corresponding simplification of the electrode configuration. When the triggering electrode is configured as a back wall that is parallel to the hollow electrode and positioned opposite its opening, the simplification of the electrode configuration is particularly enhanced. In particular, with regard to the symmetry axis of the bores of the electrode symmetrical configurations of the electrode systems can be achieved. It is preferred that the triggering electrode has a through opening arranged on the symmetry axis. In this way, it can be prevented that particle radiation that occurs upon discharge and the connected pulsed currents of typically a few 10 ampere can flow undesirably via the triggering electrode to the electronic triggering device. For the configuration of a hollow electrode it is advantageous to configure the device such that the triggering electrode is cup-shaped and that a cup axis extending perpendicularly to the cup bottom coincides with the symmetry axis of the electrodes. A simplified configuration results when the triggering electrode is mounted by means of an insulating device on the first electrode. The insulating device makes it possible that the first electrode, on the one hand, and the triggering electrode, on the other hand, are maintained at different electrical potentials. The afore describe configuration of the device can be specified in that the first electrode has an annular collar that is concentric to its opening and adjoins the triggering electrode while overlapping the insulator or engages an annular recess of the triggering electrode while maintaining a potential-separating spacing in each case. In this way, vapor deposition and short-circuiting of the insulator can be prevented. The invention relates also to a device for generating extreme ultraviolet radiation and soft x-ray radiation with a gas discharge operated on the left branch of the Paschen curve, comprising a discharge chamber of a predetermined gas pressure and two electrodes, wherein the electrodes have an opening, respectively, positioned on the same symmetry axis and, in the course of a voltage increase upon reaching a predetermined ignition voltage, generate a plasma located in the area between their openings, which plasma is a source of the radiation to be generated, comprising a triggering electrode in the space adjoining the first electrode for triggering an ignition of the plasma, and comprising an energy storage device for supplying stored energy into the plasma via the electrodes, in particular for performing the afore described method. In such a device ionization can occur in the discharge chamber. The movable ions located in the electrical field impact on the triggering electrode and have generally a sufficiently great energy in order to knock secondary electrons out of the metallic surface of the electrodes. These electrons reach the anode because of the potential difference. As a result of this, between the anode and the triggering electrode a conducting channel can be formed without the desired firing having already occurred in the area of the openings of the electrodes. In this connection, a noticeable proportion of the energy storage device can be discharged by means of the triggering circuit; this entails the risk of destruction of such a circuit. Moreover, a problem can be caused in that the potential of the triggering electrode, as a result of the formation of a conducting channel, drops to the level of the anode so that relative to the cathode a higher voltage is generated. As a result of this, undesirable discharges between the cathode and the triggering electrode can occur which can also have a disruptive effect on the proper function of the device. Finally, an ion or particle beam can lead to at least a portion of the cathode being vaporized as a result of its high energy. This results in an undesirable wear and in deposits of vaporized particles on the surrounding surfaces. In contrast to this, the invention has the object to configure a device having the aforementioned features such that a high service life without disruptions of its function can be obtained. The aforementioned object is solved in that the triggering electrode is arranged outside of a particle beam being formed on the symmetry axis or has to shielding preventing the latter. When the triggering electrode is arranged outside of the particle beam forming along the symmetry axis, the particles or ions accelerated on this axis no longer impact on the triggering electrode. The afore described malfunctions are at least significantly reduced. The same holds true when the triggering electrode has a shielding which prevents the generation of a conducting channel between the triggering electrode and the anode. An advantageous configuration of the device is characterized in that the triggering electrode is arranged on the symmetry axis of the openings of the electrodes and in that an end face facing the openings is provided with an insulator as a shielding at least in the formation area of the particle beam. The arrangement of the triggering electrode on the symmetry axis can be such that a uniform influence on the field lines in the discharge chamber is safely achieved. The insulator provides the desired protection for the triggering electrode without distorting the field lines in the discharge chamber in a significant way. It is advantageous when the insulator is in the form of a layer that is applied onto the end face of the triggering electrode. The triggering electrode in this case is protected sufficiently with a minimal material expenditure. The device can also be configured such that the insulator is formed as a member that is sunk into the end face of the triggering electrode. In this case, the triggering electrode and the insulator are to be assembled with conventional mechanical manufacturing means. An advantageous configuration of the device can be characterized in that the insulator has a recess with a cross-section matched to that of the particle beam. A particle beam, in this case, can impact on the bottom of the recess. The resulting vaporization products deposit therefore mainly on the inner walls of the recess and therefore hardly disturb the other surfaces of the arrangement. When the recess of the insulator tapers conically, the energy of an ion beam is distributed onto a larger surface area and, in this way, the local thermal heating is reduced. Correspondingly fewer vaporization products are formed. A further possibility reside in configuring the device such that the triggering electrode is insulated completely eat least relative to the space which adjoins the first electrode. The manufacture of the triggering electrode for such a device can be influenced advantageously by a complete insulation or coating. Also, inhomogeneities in regard to the field formation or discharge formation on the metal surfaces of the triggering electrode in the transition area between insulated and non-insulated metal surfaces are eliminated. A disadvantage of a complete installation of the triggering electrode can be that under certain discharge conditions electrical charges will collect on the insulated surface and can effect shielding of the triggering potential. In order to prevent this, the device can be configured such that the shielding of the triggering electrode has a residual conductivity that dissipates surface charges but prevents a discharge-affecting current flow between the second electrode and the triggering electrode. In this case of a shielding that dissipates surface charges, it is advantageous to insulate the triggering electrode completely in order to prevent additional dissipation paths. When the triggering electrode is not to be positioned on the symmetry axis, it is preferred to configure the device such that the triggering electrode is a hollow cylinder surrounding the symmetry axis. In particular, the device can be configured such that a hollow-cylindrical triggering electrode has a bottom facing away from the two electrodes wherein the bottom is configured as an insulator or has a metal bottom that is connected to the potential of one of the electrodes and, for this purpose, is insulated relative to the triggering electrode. The insulator can then take over the functions of the afore described insulators, in particular, relative to a possible particle beam. When the bottom is a metal bottom, it can either be connected to the potential of the anode so that a conducting channel cannot result because of identical potentials; however, the metal bottom can also be connected to the potential of the cathode in order to remove produced charge carriers. Moreover, it is advantageous to configure the device such that the triggering electrode is an annular plate or at least an electrode pin which is/are mounted transversely to the symmetry axis of the electrodes in the first electrode. With the annular plate or with the electrode pin, the electrical field can be affected in the discharge chamber or in the space adjoining the triggering electrode in order to influence the discharge behavior of the device. In order to reach the afore described goal, the triggering electrode is mounted in an insulated way within the first electrode. The device is exposed during its function to significant heat development. It is therefore expedient to configure it such that the shielding is comprised of temperature-resistant insulation material. Because of the described heat development, it is also expedient to connect the shielding with the triggering electrode in a thermally well conducting way in order to dissipate heat. In order to intercept the predominant portion of the charge carriers that reached the shielding the area of the symmetry axis, the device is expediently configured such that the shielding has a diameter that corresponds at least to the diameter of the openings. FIG. 1 shows schematically the configuration of an electrode system arranged in a discharge chamber 10. The discharge chamber 10 is filled with a gas of a predetermined gas pressure and can be formed by suitably configured electrodes of the electrode system itself. The gas pressure is adjustable. The devices of the discharge vessel for adjusting the gas pressure and a configuration of the electrode system matched thereto is present but is not illustrated. Two electrodes 11, 12 are present. The electrode 12 is configured as an anode with a central opening 15 which conically widens starting at an intermediate electrode space 22. The electrode 11 is a cathode, in particular, a hollow cathode with a cavity 23 that is connected by means of an opening 14 of the cathode to the intermediate electrode space 22. The openings 14, 15 are aligned with one another and define an axis of symmetry 13 of the electrode system. The electrodes 11, 12 are insulated relative to one another. An insulator 29 serving for this purpose determines the electrode spacing. As a result of the described configuration, the electrode system is enabled to form field lines upon supplying an electrical high voltage in the range of, for example, several 10 kV, wherein the field lines, at least in the area of the intermediate electrode space 22, are straight and parallel to the axis of symmetry 13. When the voltage is increased starting from a predetermined low value in a pulsed fashion, there results a charge ramp or voltage increase 16 according to FIGS. 2, 3. Ionization processes occur that, as a result of the field strength conditions, are concentrated in the intermediate electrode space 22. For this purpose, the voltage increase 16 and the gas pressure are adjusted relative to one another such that, because of the ionization, a gas discharge on the left branch of the Paschen curve results where a plasma channel or its plasma is not generated by means of a single short-term electrode avalanche but in several steps by means of secondary ionization processes. As a result of this, the plasma distribution already in the starting phase is highly cylindrically symmetrical, as is illustrated in the schematic illustration of the plasma in FIG. 1. The resulting plasma 17 is a source for the radiation 17′ to be generated. It is understood that an ignition of the plasma 17 is possible only when an ignition voltage Uz has been reached. According to the invention, it is provided that an ignition delay 18 occurs. As a result of this, the point in time of ignition tz despite the presence of the ignition voltage Uz is correspondingly delayed. The magnitude of the ignition delay 18 is regulated by controlling the gas pressure. The magnitude of the ignition delay is within typical durations in the range of several microseconds up to a few milliseconds. The ignition delay results in a prolongation of the generation of the conductive plasma. In this way, an improvement of the cylinder symmetry of the plasma 17 is achieved. The plasma which is formed after the ignition delay can be referred to as a starting plasma. It can serve for energy introduction from an energy storage device during automatic firing operation. FIG. 1 shows the capacitor block 21 as an energy storage device; upon reaching the predetermined ignition voltage and ignition delay the energy storage device will discharge and, in this way, enables the introduction of current pulses within a two-digit kilo ampere range into the plasma. The resulting Lorentz forces of the magnetic field constrict the plasma so that a high luminance results and, in particular, extreme ultraviolet radiation and soft x-ray radiation are generated which in particular have the required wavelength for EUV lithography. Instead of influencing the ignition delay 18 by means of the gas pressure, in addition a triggering electrode can be used for affecting the ignition delay. By means of a triggering electrode 19 it can be achieved that, despite reaching a predetermined ignition voltage Uz, a firing for discharge between the electrode 11, 12 will not yet take place. A triggering delay 20, achievable with the triggering electrode 19 according to FIGS. 4, 5, is illustrated in FIG. 3. It is added to the ignition delay 18. Affecting the total ignition delay by means of a triggering delay 20 is particularly advantageous because it is possible to employ measuring technology in order to reach the precise point in time of ignition tz. This holds true for the case where the gas discharge operation is carried out with automated firing as well as where a switching element between the electrode system and the capacitor block is used. The switching element makes it possible to supply a voltage to the electrode system which is greater than the ignition voltage Uz required for the automatic firing operation. In the latter case, it is possible to work at higher gas pressures; this results in higher intensities of the emitted radiation. It is expedient to measure the ignition point, in particular, when by means of the, charge device a higher voltage is allowed at the electrode system than their predetermined ignition voltage. The voltage which is connected to the electrode system, i.e., the course of a voltage increase 16, can be detected, for example, by determining the temporal change of the voltage supplied to the electrodes 11, 12. Accordingly, a dU/dt measurement is carried out. It is also possible to carry out a dl/dt measurement, i.e., a detection of the temporal change of the discharge current. Current and voltage change suddenly upon reaching the ignition point tz. The time between reaching the predetermined ignition voltage Uz and the point in time of ignition can be measured, for example, in an analog fashion by means of an integrator or digitally by means of a counter. This time is supplied as a measured value to a controller which affects accordingly the gas pressure in the sense of stabilization of the ignition delay 18. This holds true also for the situation of application of a triggering delay 20. The measurement can be performed, for example, by means of an ignition voltage integrator which takes over processing of the measured value high voltage or voltage at the electrode system or the capacitor block which processing is upstream of the actual controller. In this connection, the ignition voltage integrator integrates the high-voltage supply to the electrodes 11, 12 that is divided down and registers their final value by means of a sample-and-hold until the next charge process. The integration process begins with the charging process, i.e., with the increase of the electrical voltage supplied to the electrodes 11, 12 and is continued for a duration that is determined by a timer. This duration is generally longer than the actual charging process so that in this way also the desired information with regard to the magnitude of the ignition delay can be determined. Additional non-linear members such as, for example, square-root law transfer elements, can be used in order to improve the transmission characteristic line. In this way, information with regard to the ignition delay are obtained as well as with regard to the ignition voltage, and this with the same measured signal. In contrast to a peak detector that determines the ignition voltage, the method is entirely unsusceptible with regard to disturbance peaks that can result, for example, from high-voltage generators. An electronic device is not required for the ignition point detection. If the method is carried out without triggering electrode, the ignition point tz can be determined only via the magnitude of the gas pressure. In a method with triggering electrode the afore described triggering delay can be used in order to determine the point of ignition, if needed, in combination with a selection of a suitable gas pressure. In this way, the charge state of the capacitor block 21 is determined by means of an electronic evaluation device, for example, by means of the above described ignition voltage integrator. Triggering by means of the triggering electrode results in that, despite reaching the ignition voltage Uz a plasma deformation causing the discharge of the capacitor block 21 will not yet take place. Only in the case of triggering ignition occurs, i.e., in the case of triggering a triggering pulse after the predetermined triggering delay 20. The controlling parameter can be also the gas pressure which, for example, is adjusted by means of an electronic inlet valve. When the maintenance voltage is not reached after a predetermined reading time, the gas pressure must be reduced. In the other situation, the gas pressure, when ignition does not occur, must be increased after the triggering pulse. A control parameter in this method employing a triggering electrode is in the end the ignition delay, i.e., the time between triggering the triggering pulse and the voltage collapse. The pressure is then adjusted such that the ignition delay is maintained constant within certain tolerances. The triggering delay 20 indicated in FIG. 3 is provided in an exemplary fashion relative to the point in time of reaching the predetermined ignition voltage Uz. In principle, any point in time can be selected prior to this and can be determined by a suitable electronic device; for example, the beginning of the charging process or reaching of a predetermined value of the charge voltage can be selected. In FIGS. 4, 5, for example, configurations of triggering electrodes are illustrated. The triggering electrodes 19 are adjacent to the cathode 11 on the side of the cathode facing away from the anode 12. In the illustrated embodiments, they are assembled by means of an insulator 26 together with the cathode 11, wherein means for holding together the electrode 11, the insulator 26, and the triggering electrode 19 are not illustrated. All embodiments of the triggering electrode have in common that, relative to the symmetry axis 13, they are symmetrically arranged. All embodiments have an axis that is aligned with the symmetry axis 13. In this connection, the triggering electrode 19 is configured as a wall or wall section. It is positioned at a predetermined spacing away from the opening 14 of the electrode 11. In this way, it can be achieved at the same time that the electrode 11 is configured as a hollow electrode, for example, as a hollow cathode. The triggering electrode 19 then forms essentially the back wall of the cathode. Such a back wall is the wall 29 in the embodiment of FIG. 4 and a cup bottom 19′ of the cup-shaped triggering electrode 19 in the embodiment of FIG. 5. The cup-shaped configuration of the triggering electrode 19 shows that it cannot only be the back wall of the electrode 11 but also the sidewall of the space 23 of this hollow electrode that is to be enclosed. It is also conceivable that the triggering electrode 19 is exclusively a sidewall section of an electrode 11 which is connected, by the way, to the electrode potential or the cathode potential. FIG. 4 illustrates that the triggering electrode 19 is provided with a through opening 24 which serves for passage of the particle beams that form in accordance with the electrode configuration primarily in the area of the symmetry axis. With such a penetration opening, loading of the electronic triggering device can be maintained within acceptable limits. The particle beams are received by the parts of the electrode system which are connected to the potential of the cathode. A through opening 24 can also be used in the case of FIG. 5. In FIG. 4, bores 24′ that are parallel to the through opening 24 are provided. The bores 24′ can be gas bores, i.e., for passage of gas in the sense of a gas inlet. The through opening 24 can also be used in the sense of such a gas passage or in the sense of a gas inlet. Both is particularly advantageous when the electrode system itself forms the discharge chamber 10. In the case of gas discharge projecting into the space 23, vapor deposition on the insulator 26 with metal vapor is to be expected. This could lead to shortcircuiting of the insulator 26. In order to shielding it against the occurring metal vapor, the electrode 11 is provided with an annular collar 27 which is arranged concentrically to the opening 14 and which overlaps the torus-shaped insulator 26. Moreover, the triggering electrode 19 is provided with an annular recess 28. The annular collar 27 engages the annular recess 28. In this way, a potential separating spacing is provided which, however, must be only small because of the usually minimal potential differences between the cathode 11 and the triggering electrode 19. The triggering electrodes according to FIGS. 4, 5 are possible also in connection with a hollow anode. In this case, the light of the plasma 17 would have to be decoupled from the electrode 11 or from the hollow cathode. However, it is advantageous to decouple the light at the anode, as illustrated in FIG. 1, and to operate the cathode with negative high voltage because, in this way, debris from sputtering and high frequency discharges are prevented better in the part of the electrode system facing an observer. The potential of the triggering electrode 19 is selected before triggering a triggering pulse and thus before triggering a low-impedance plasma discharge such that the charge carriers are removed from the hollow electrode or hollow cathode and the intermediate electrode space in the bore hole area. This is realized, for example, by supplying to the triggering electrode 19 a positive voltage of typically several 100 V relative to the cathode potential. A triggering pulse is triggered when the potential of the triggering electrode is reduced to that of the cathode or in that a negative potential is supplied to the triggering electrode 19. Typical constant time values for a change of the potential of the triggering electrode 19 are advantageously in the range of a few nanoseconds up to several 100 ns. In order to obtain high light efficiencies, it is desired to enable a repetition frequency of the discharges that is as high as possible, i.e., in the range of several kHz and preferably above 10 kHz. In this connection, the required resolidification or recombination times of the plasma set limits. These limits depend on the type of gas with which the method is operated. With regard to a high radiation efficiency in the EUV field, the application of xenon is of particular interest. When operating with pure xenon, the repetition frequencies above approximately 1 kHz for typical pulse energies in the range of 1 Joule up to 10 Joule in operation with automatic firing can hardly be reached. It is therefore desirable to perform measures for accelerating the resolidification. As one possibility the admixture of gases should be mentioned. A fast recombination of the plasma after discharge of the capacitor block can be achieved by admixing gases, for example, air, synthetic air, nitrogen, oxygen, or halogens. Moreover, the transport of charged particles away from the area of the openings 14, 15 can be enhanced by suitable gas flow. A flow with gas inlet via the cathode and/or via the intermediate electrode space and with gas evacuation via the anode, which according to FIG. 1 is the electrode facing the observer, is advantageous. With such a gas flow a pressure drop in the area of the anode or in the area of a hollow anode can be produced. By means of such pressure gradients it is possible to move the plasma 17 in order to achieve an increased transmission for the EUV radiation in the observation path up to the user. Further measures for increasing the repetition frequency can be performed in connection with the capacitor block 21. This is based on that the generation of the low-impedance plasma, depending on the conditions, takes up to several 100 microseconds. The capacitor block 21 can now be charged faster than the generation time of the low-impedance plasma. As a result of this, a complete recombination of the plasma can be forgone. It is moreover also possible to allow a high-impedance plasma to burn between two discharges in the area of the openings 14, 15; this results in better conditions for a starting plasma of the high current discharge. FIG. 6 shows schematically the configuration of an electrode system arranged within the discharge chamber 10. The discharge chamber 10 is filled with a gas having a predetermined gas pressure and can be formed by suitably designed electrodes of the electrode system itself. The gas pressure is adjustable. The devices for adjusting the gas pressure of the discharge vessel 10 and a configuration of the electrode system matched thereto are present but not illustrated. Two electrodes 11, 12 are present. The electrode 12 is an anode with a central opening 15 and widens conically starting at an intermediate electrode space 22. The electrode 11 is a cathode and is embodied as a hollow cathode with a cavity 23 connected by means of the opening 14 of the cathode to the intermediate electrode space 22. The openings 14, 15 are aligned and together form a symmetry axis 13 of the electrode system. The electrodes 11, 12 are insulated relative to one another. An insulator 29 serving for this purpose determines the electrode spacing. The electrode system is enabled as a result of the afore describe configuration to generate filed lines upon supplying an electrical high voltage in the range of, for example, several 10 kV; the field lines extended at least in the area of the intermediate electrode space 22 in straight lines in parallel to the axis of symmetry 13. When the voltage is increased starting from a predetermined low value in a pulsed fashion, a charge ramp or voltage increase results. This causes ionization processes which are concentrated because of the field strength conditions within the intermediate electrode space 22. For this purpose, the voltage increase and the gas pressure are adjusted relative to one another such that as a result of the ionization gas discharge on the left branch of the Paschen curve will result, wherein a plasma channel or its plasma is not generated by a single short-time electrode avalanche but in several steps by means of secondary ionization processes. As a result of this, the plasma distribution already in the starting phase is highly cylindrical-symmetrical, as schematically illustrated in FIG. 6. The generated plasma 17 is a source of the radiation 17′, an electron radiation, that is to be generated. The generated plasma can be referred to as a starting plasma. It can serve for energy coupling from an energy storage device for automatic firing operation. FIG. 6 shows a capacitor block 21 as an energy storage device which discharges after reaching the predetermined ignition voltage and, in this way, enables a supply of current pulses within a two-digit kilo ampere range into the plasma. The Lorentz forces of the magnetic field which are formed accordingly constrict the plasma so that a high light efficiency results and, in particular, extreme ultraviolet radiation and soft x-ray radiation are is generated having, in particular, the required wavelength for EUV lithography. The electrode system illustrated in FIG. 6 is provided with a triggering device in the area of the electrode 11. For this purpose, the electrode 11 has a triggering electrode 19 on the symmetry axis 13 that is secured by an insulator 26 in the bottom 30 of the electrode 11. The insulator 26 serves for providing a potential to the triggering electrode 19 that is different from that of the electrode 11. In this connection, the triggering electrode 19 has a parasite capacitance 31 relative to the electrode 11, measured parallel to a switch 32 with which both electrodes 19, 11 can be connected to the same potential. Conventionally, the electrode 12 is configured as an anode and is grounded, as illustrated. In contrast, the cathode is connected to a negative potential −V while the triggering electron 19 is connected to a potential −V+Vt. The potential of the triggering electrode before beginning the triggering process is thus somewhat higher than that of the electrode 11. For the purpose of triggering, a triggering pulse is triggered by closing the switch 32, and the potential of the triggering electrode 19 is dropped to that of the electrode 11. Typical constant time values for a change of the potential of the triggering electrode 19 are advantageously in the range of a few nanoseconds s up to several hundred nanoseconds. The electrode arrangement schematically illustrated in FIG. 6 is typically configured such that between the electrodes 11, 12 a spacing of 1 to 10 mm is present. The smallest passage of the openings 14, 15 is typically 1 to 10 mm. The volume of the space 23 in the electrode 11 configured as a hollow cathode is typically 1 to 10 ccm. The gas pressure is between 0.01 and 1 mbar. The electrode voltage is typically 3 to 30 kV, and the potential difference between the triggering electrode 19 and the electrode 11 is between 50 V and 1,000 V. Principally, the ignition voltage at which firing between the electrodes 11, 12 occurs and the pressure depend form one another in accordance with the curve illustrated in FIG. 7. FIG. 7 relates to the left branch of the Paschen curve. The left curve of FIG. 7 applies to the operation of un-triggered device. On this curve for V=0 6 there exists only a single firing point which is, for example, provided at a gas pressure of 7 Pa at approximately 8 kV. Other pressures in the space 23 have correspondingly different ignition voltages. The triggering voltage, i.e., the potential difference between the triggering electrode 19 and the electrode 1 can however also deviate from 0. In this case, Vt is not equal 0 but, for example, equal V1 or V2. As a result of this, with the suitable value of the triggering voltage Vt it can be achieved that the device can be operated with different parameters. For a predetermined voltage at the electrodes 11, 12 there is the possibility of pressure variations as illustrated in FIG. 7. In a similar way, for a certain pressure the voltage variations illustrated in FIG. 2 are possible. Correspondingly, also the point in time of firing can be determined precisely by means of the triggering signal without reaching a working area where the above described difficulties would occur. In particular, repetition frequency can be ensured as they are required for the necessary use, for example, in the range of 10 to 22 Hz. Also, operating intervals for certain fixed repetition frequencies are possible so that between the operating intervals the energy essentially required for generating the desired radiation can be saved. The stability of the working point is significantly improved. Triggering is achieved by the circuit illustrated in FIG. 6. The capacitor block 21 is charged in that the electrode 11 is connected to negative voltage while the electrode 12 is grounded. The connection of the two electrodes 11, 12 is realized by a low-inductive circuit via the capacitor block 21. A high-impedance circuit connects the triggering electrode 19 with the electrode 11 wherein the connection can be opened by the switch 32. In the open situation, a potential difference Vt relative to the electrode 11 is present at the triggering electrode 19. For this case, the voltages at the electrodes 11, 12 as well as the gas pressure of the intermediate electrode space or chamber 23 of the electrode 11 are adjusted such that upon supplying a triggering voltage Vt an ignition of the plasma 17 cannot take place. When the switch 32 is however closed, the potential difference Vt is eliminated and the triggering electrode 19 is supplied with the potential of the electrode 11; a protective resistor 33 protects the voltage source of the triggering voltage. When the switch 32 is open, it is however possible that between the triggering electrode 19 of FIG. 6 and the electrode 12, serving as an anode, a conducting channel with a corresponding particle beam is formed which discharges the energy of the capacitor block 21 and can also cause damage of the triggering circuit. In FIGS. 8 through 18 differently configured triggering electrodes in a schematically illustrated system of main electrodes 11, 12 are illustrated which can contribute to proper functioning of the device. FIGS. 8 to 18 show triggering electrodes 19 arranged coaxially to the symmetry axis 13 defined by the electrodes 11, 12 or their openings 14, 15. In this connection, the triggering electrodes 19 of FIGS. 8 through 13 are configured such that they have an end face 34 facing the opening 14. At least this end face 34 is provided with a shielding 35 that is designed differently, respectively. Each shielding 35 is at least so large that it matches the diameter of the openings 14, 15. The shielding 35 is thus present in the vicinity of the triggering electrode 19 in the generation area of the particle beam. In the case of FIG. 8, the shielding 35 is an insulator in the form of a layer applied to the end face 34 of the triggering electrode 19. In the case of FIG. 9, the shielding 35 is also embodied as an insulator but it is a member that is sunk into the end face 34 of the triggering electrode 39. The cross-section of this member is, for example, of a circular cylindrical shape in order to be inserted in a conventional way into a bore of the triggering electrode 19 which is machined into the end face 34. In FIG. 10 and in FIG. 11 the triggering electrode 19 is identical to that of FIG. 9. However, different shieldings 35 are inserted into its bore. The shielding 35 of FIG. 10 is again a cylindrical member that however has a coaxial recess 36 embodied as a blind bore. The diameter of the blind bore is matched to the diameter of the potential partial stream. The shielding 35 of FIG. 11 is provided with a recess 36 which conically tapers away from the openings 14, 15. A particle beam that is possibly formed impinges on the relatively large surfaces of the shielding 35 so that the beam energy is distributed onto a larger surface area which prevents local thermal heating. In both cases of FIGS. 10, 11, the recesses are suitable to receive the vaporization products caused by an impinging particle beam which particles can deposit on the inner walls of the recesses 36 and therefore do not disturb the other surfaces of the arrangement. The triggering electrode of FIGS. 12, 13 are characterized in that they are completely insulated by their shielding at least relative to the space 23 adjoining the first electrode 11. The shielding 35 is a coating which does not expose any surface area of the triggering electrode 19. As a result of this, no inhomogeneous electrical fields of any kind can occur which could to be caused by such exposed spaces. Under certain discharge conditions, however, it can occur that on the surface of this shielding 35 electrical charges will collect which can effect shielding of the triggering voltage. A shielding of the triggering voltage would result in a malfunction of the device. Such a shielding action can be prevented when the shielding 35 is provided with a residual conductivity that is large enough to neutralize built-up surface charges or to dissipate them. This residual conductivity is however not large enough to allow current flow between the electrode 12 and the triggering electrode 19 that significantly discharges the capacitor block 21. FIG. 13 shows such a shielding 35 with a suitable residual conductivity. In all afore described embodiments, the dimensions can be varied within wide limits. For example, the triggering electrode 19 can be configured as a thin wire which is coated expediently according to FIGS. 12, 13. The triggering electrodes 19 of FIGS. 14 to 16 are hollow-cylindrical. These triggering electrodes are arranged coaxially relative to the symmetry axis 13. As a result of their hollow cylindrical embodiment and the field generation, on the other hand, a particle beam formed in the area of the symmetry axis 13 cannot reach the triggering electrode 19 and cannot act thereon in a disturbing or destructive way. In FIG. 14 the triggering electrode 19 is closed off by a metallic bottom 37 that is supplied to ground potential and is insulated relative to the hollow cylindrical triggering electrode 19. Between the bottom 37 and the electrode 12 a particle beam cannot form because this electrode, as an anode, is also connected to ground potential. FIG. 16 shows a bottom 38 configured as an insulator and therefore has, relative to the particle beam, a similar effect as the shieldings described in connection with FIGS. 8 to 11. In FIG. 16 the bottom 39 of the hollow cylindrical triggering electrode 19 is configured as a mental electrode that is conductingly connected to the electrode 11, the cathode. Charge carriers of particle beams present on the symmetry axis are supplied by means of the metallic bottom 39 by a connecting line 40 to the electrode 12. The configurations of FIGS. 17 and 18 are alternative arrangements of FIG. 16. In all cases, charge particles on the symmetry axis 13 or in the space 23 are supplied to the electrode 11. In FIG. 17 the triggering electrode 19 is embodied as an annular plate. This annular plate is mounted transversely to the symmetry axis 13 of the electrode 11, 12 into the first electrode 11. The upper and lower halves thereof, illustrated in FIG. 17, are conductingly connected to by lines 41 illustrated in dashed lines and have thus the same potential. The arrangement of the triggering electrode 19 relative to the symmetry axis 13 is cylinder-symmetrical. This is no longer the case in the situation of FIG. 18. In this embodiment, with the exception of the line 41, the configuration can be the same as in FIG. 17 in a side view. The symmetry axis 13, however, is positioned perpendicularly in FIG. 18 relative to the plane of the illustration, and FIG. 18 shows two identically configured parts 19′ and 19″ of a triggering electrode that are arranged coaxially and transversely to the symmetry axis 13. The parts 19′, 19″ represent electrode pins. Instead of the two parts 19, 19′ the triggering electrode can also be comprised of several parts. The shieldings 35 employed in connection with the triggering electrodes 19 are comprised of temperature-resistant insulation materials, for example, Al2O3, quartz, or silicon carbide. All materials used for the shieldings 35 are connected to the triggering electrode 19 so as to provide excellent thermal conducting. Moreover, it is understood that the triggering electrode 19 or its parts 19′, 19″ are mounted in an insulated way in the first electrode 11. The insulations 42 illustrated in FIGS. 8 through 18 fulfill the same functions as the insulator 26 of FIG. 6. The insulation 42 is temperature-resistant, respectively.
	abstract	According to one general aspect there is a needle package apparatus that comprises a top portion and a bottom portion; a plurality of needle slots exact distance apart that allows to place a plurality of needles that contain radioactive seeds; a cylindrical coil that is inserted to the plurality of needle slots to hold said plurality of needles, wherein said cylindrical coil prevents the leakage of the radiation from the radioactive seeds; a set of hinges located at the end of said needle package within the outer most said plurality of needle slots; wherein the hinges can be bend to change the angle of said top portion of said needle package by a medical personnel to create a stand; and a single end enclosure located at the distal end of said cylindrical coil to provide an enclosed cylinder.
	abstract	An x-ray imaging system according to the present invention comprising a stepped scanning-beam x-ray source and a multi-detector array. The output of the multi-detector array is input to an image reconstruction engine which combines the outputs of the multiple detectors over selected steps of the x-ray beam to generate an x-ray image of the object. A collimating element, preferably in the form of a perforated grid containing an array of apertures, interposed between the x-ray source and an object to be x-rayed. A maneuverable positioner incorporating an x-ray sensitive marker allowing the determination of the precise position coordinates of the maneuverable positioner.
	description	This application claims priority of International Application No. PCT/EP2005/055521, filed Oct. 25, 2005 and German Application No. 10 2004 052 994.9, filed Nov. 3, 2004, the complete disclosures of which are hereby incorporated by reference. a) Field of the Invention The invention is directed to a multibeam modulator for a particle beam. In particular, the invention is directed to a multibeam modulator which generates a plurality of individual beams from a particle beam. The particle beam illuminates the multibeam modulator at least partially over its surface. The multibeam modulator comprises a plurality of aperture groups, each aperture group having a plurality of aperture row groups. The totality of all aperture rows defines a matrix of m×n cells, where m cells form a row and k openings are formed in each row. b) Description of the Related Art The invention is further directed to the use of a multibeam modulator for maskless structuring of a substrate. In particular, a plurality of individual beams are generated by the invention in that a particle beam illuminates the multibeam modulator at least partially over its surface. A plurality of aperture groups are formed in the multibeam modulator, each aperture group having a plurality of aperture row groups. The totality of all aperture rows defines a matrix of m×n cells, where m cells form a row and k openings are formed in each row. U.S. Pat. No. 4,153,843 discloses an exposure system with a plurality of beams. A two-dimensional array with a plurality of openings is provided in the beam path of an electron beam exposure system. The array is illuminated over its surface by the electron beam and is imaged in a reduced manner on a substrate. Only one individual aperture plate is provided generating the plurality of individual electron beams from the surface illumination. The individual openings are uniformly distributed over the aperture plate within a row. U.S. Patent Application US 2003/0155534 A1 discloses a maskless exposure system for particle beams. A plurality of aperture plates which are fitted one behind the other generate a plurality of individual beams from an electron beam. The uppermost two plates and the bottom plate have openings through which the electron beam passes. Each plate has a thickness of about 100 μm and the plates have a distance from one another of 100 μm to 1 mm. An array of correction lenses is arranged between the second plate and the bottom plate in front of the final aperture plate. The density of openings within a row is constant. U.S. Pat. No. 5,144,142 discloses a particle beam system containing an aperture plate for blanking corresponding partial beams. The individual aperture plate comprises m rows and n columns of openings which are arranged two-dimensionally on a substrate. A pair of deflecting electrodes is associated with each opening. Further, n×m-bit shift registers are provided on the substrate to supply the m pairs of deflecting electrodes with voltages corresponding to the pattern data. However, the aperture plate is formed only as an individual structural component part. Also, an inhomogeneous distribution of openings within a row is not suggested. U.S. Pat. No. 5,369,282 discloses a particle beam system which generates a plurality of partial beams from a flat electron beam by means of an aperture plate, the partial beams being imaged on a substrate. A plurality of openings are formed in the aperture plate. The openings are homogeneously distributed over the aperture plate. U.S. Pat. No. 5,430,304 discloses a particle beam system by which a plurality of partial beams are imaged on a substrate. There is also an aperture plate in which a plurality of switchable openings are formed. The openings are controlled by means of a corresponding quantity of shift registers. The distribution of the openings in the aperture plate is homogeneous. The article “Programmable Aperture Plate for Maskless High-Throughput Nanolithography” by Berry et al., J. Vac. Sci. Technol. B 15(6), November/December 1997, pages 2382 to 2386, discloses a programmable aperture array comprising 3000×3000 apertures which can be electronically triggered and activated individually to monitor or control the passage of the beam. The pattern to be written is introduced into the aperture plate system as a binary signal from one side and is pushed through to the other side. The aperture plate system comprises an aperture plate with the corresponding deflecting electrodes. The openings are distributed in a correspondingly uniform fashion. The publications cited above show multibeam modulators in the form of rows or arrays in which the triggering of each control element is carried out separately. However, because of the large quantity of leads, the number of beams operating in parallel is limited to about 1000 and enables only a moderate increase in productivity in spite of the extensive resources employed. For this reason, it was proposed to use uniform or homogeneous array structures with n rows and m columns in which the on/off information in each row is advanced from one of the m modulator elements to the next by integrated delay elements or shift registers. The time shifting of the pixel image from column to column is correlated with a scanning movement of all beams relative to the substrate so that it is possible to use all of the n×m beams in parallel, but only new data for the n modulators of the first column need be provided in every exposure cycle. The main defect in known implementations of this principle is the limiting to one bit (on/off) per exposure cycle and row, so that mandatory dosing steps, proximity corrections, and the like can only be realized to a limited extent through the use of a plurality of arrays. Known solutions for the blanking chip require a high storage density and lack flexibility. It is the primary object of the invention to provide multibeam modulators for a particle beam for the maskless transfer of a layout to a substrate which can be directly electronically controlled and in which the multibeam modulator can be configured with respect to the minimum storage requirement of the electronic circuit, with respect to the temporal and spatial homogenization of the entirety of the beam, and with respect to beam-optical factors. This object is met, in accordance with the invention, by a multibeam modulator which generates a plurality of individual beams from a particle beam. The particle beam illuminates the multibeam modulator at least partially over a surface thereof. The multibeam modulator comprises a plurality of aperture groups. Each aperture group is formed of aperture row groups in such a way that the totality of all aperture rows defines a matrix of m×n cells, wherein m cells form a row and k openings are formed in each row. The density of the openings within a row is inhomogeneously distributed. A further object of the invention is the use of the multibeam modulator for the maskless structuring of substrates, wherein the multibeam modulator can be configured with respect to the minimum storage requirement of the electronic circuit, with respect to the temporal and spatial homogenization of the entirety of the beam, and with respect to beam-optical factors. This object is met by a method of using a multibeam modulator for maskless structuring of substrates comprising the steps of generating a plurality of individual beams in that a particle beam illuminates the multibeam modulator at least partially over its surface, forming a plurality of aperture groups comprising aperture row groups in the multibeam modulator, defining the totality of aperture rows by a matrix of m×n cells, wherein m cells form a row and k openings are formed in each row, and inhomogeneously distributing the density of openings within a row. The invention has the advantage that it avoids the elaborate, cost-intensive steps of producing exposure masks. However, the time-serial writing principle reduces the productivity of the exposure compared to parallel structure transfer using masks. Therefore, a line of development for maskless exposure devices consists in multiplying the effective writing speed though a large quantity of partial beams operating in parallel. The partial beams are arranged in the form of an array and can be switched on and off individually by a special modulation element (controllable beam sources, blanker, mirror). The present inventive solution describes the construction of a multibeam modulator based on row-oriented shift registers and its concept of dose control. The multibeam modulator can be configured with respect to the minimum memory requirement of the electronic circuit, with respect to the temporal and spatial homogenization of the entirety of the beam, and with respect to beam-optical and thermal factors. Further, it relates to proposed solutions enabling error redundancy and dose correction through the ability to reconfigure the control. The multibeam modulator has the advantage that the density of openings within a row is distributed in an inhomogeneous manner. Extremes in the total current of all partial beams are prevented in this way. The openings within a row are equidistant, but the distance between the openings, expressed as a quantity of cells, is less than the quotient of the number of cells of a row and the number of openings within a row. It is advantageous when the number k of openings within a row is between 64 and 71 or a multiple thereof. The cells of the multibeam modulator have a square shape and the dimensioning of the cells corresponds to a pixel to be written on the target multiplied by the imaging scale of the downstream optics. All of the openings of a row together with the cells therebetween form an aperture row. A plurality of aperture rows lying in the same X interval and a selected Y interval are combined to form aperture row groups. The aperture row groups also combine to form aperture groups and are uniformly arranged on a chip of an aperture plate. The aperture groups are separated by webs on which no structuring is carried out. The subject matter of the invention is shown schematically in the drawings and is described with reference to the following figures. FIG. 1 shows an aperture plate 100 according to the prior art. In this aperture plate 100, n rows 101 with m cells and m columns 102 with n cells are formed. In each row 101, a determined quantity k of openings 103 is formed. The openings 103 are distributed within a row such that the density of the openings 103 within a row is identical. FIG. 2 shows a schematic view of the construction of a total system for maskless electron beam lithography. Although the following description is limited to electron beams, this should not be construed as a limitation of the invention. The invention is, of course, suited to all particle beams. An electron beam 31 is generated by an electron gun 30 and propagates in direction of an electron-optical axis 32. The electrons exiting from the electron gun 30 have a source crossover 310. Downstream of the electron gun 30 is a beam centering device 33 which orients the electron beam symmetrically around the optical axis 32. After the beam centering device, the electron beam 31 traverses a condenser system 10 which forms a parallel beam from the initially divergent electron beam 31. The beam that is shaped through the condenser system 10 has a diameter along which the intensity is homogeneously distributed. After the condenser system 10, a flat object 34 is provided. The flat object 34 is an aperture plate or an aperture plate system 50. The aperture plate system 50 is provided with a plurality of openings for generating many parallel beam bundles 36. A deflecting plate 35 having a plurality of beam deflecting units follows in the propagation direction of the beam bundles 36 in direction of the target 6. After the deflecting plate 35, there is an acceleration lens 39 which increases the energy of the electrons in the electron beam 31 and then generates a first intermediate image of the crossover 311 at the location of the aperture diaphragm 38. All of the individual crossovers of the partial beam bundles 36 are formed at virtually the same location, namely, at the diaphragm opening of the aperture diaphragm 38. The diameter of the opening of the aperture diaphragm 38 is so selected that virtually all electrons of the undeflected beam bundles 36 can pass through the aperture diaphragm 38. Individual beams 37 that have undergone an individual change in direction through the deflecting plate 35 are stopped at the aperture diaphragm 38 because their crossover intermediate image does not occur at the location of the aperture diaphragm opening. Continuing along the beam path, there now follows at least one magnetic lens 40 for imaging the aperture plate 34 on the target 6 in a reduced manner. In the present embodiment example, two magnetic lenses 40 are shown. A second intermediate image of the crossover 312 is formed during the imaging. Before the undeflected beam bundles 36 impinge on the target 6, e.g., a wafer, they traverse an objective lens 41. The objective lens 41 is outfitted with a plurality of elements. Two deflecting devices 45 and 46 are provided before and after a second crossover 312 of the electron beam 31. The deflecting devices 45 and 46 serve to deflect and determine the position of the electron beam 31 or the plurality of undeflected beam bundles 36 in the target 6. The two independently controllable deflecting systems 45 and 46 are advantageously used for separate optimal adjustment of slow and fast deflecting processes. Fast deflecting processes in the megahertz to gigahertz frequency range are required, for example, to maintain constant the position of the reduced aperture plate 34 on the steadily moving target 6 for the duration of an exposure step or exposure cycle by means of sawtooth-shaped deflections and, subsequently, to jump to the next exposure point within a very brief time. Since neighboring pixels are typically spaced by less than 100 nanometers, the fast deflecting system 46 is preferably constructed as an electrostatic system. A slow but highly accurate magnetic deflecting system 45 is preferably used to compensate for low-frequency positional deviations of the target 6 from the uniform movement in the range of several micrometers. Further, stigmators 44 are provided and are preferably constructed as multi-tiered magnetic coil systems to compensate for astigmatism and distortion caused by manufacturing tolerances and alignment errors in the optical column. The objective lens 41 has a scanning height measuring system 42 at the point of incidence of the electron beam on the target 6. The height measuring system 42 serves to detect unevenness in the target 6 (e.g., wafer) and height variations that can be caused by a displacing table. A detector 43 for the particles or electrons which are backscattered from the target 6 is located near the impingement point of the beam. This detector 43 serves to determine the position of marks on the target 6 for purposes of overlaying a plurality of exposure planes or for calibrating control elements of an exposure installation. Further, three pairs of correction lenses 23, 24, 25 are located in the lower region of the corpuscular beam device 2. The correction lenses 23, 24, 25 are used for dynamic correction of the focus, image field size and image field rotation during the exposure of the continuously moving target 6. The correction lens system 23, 24, 25 makes it possible to correct errors brought about by height variations in the target and by fluctuating space charges in the column area. FIG. 3 shows a schematic view of a device 50 for structuring a particle beam 31. It should be noted that the particle beam 31 is equated with an electron beam. The device 50 for structuring the particle beam 31 comprises a first aperture plate 51, a second aperture plate 52, a third aperture plate 53 and a fourth aperture plate 54. The particle beam impinging in direction of the optical axis 32 illuminates the first aperture plate 51 over a large surface. A plurality of openings 61 having a substantially square cross section are formed in the first aperture plate 51. The first aperture plate 51 is made of silicon and has a thickness 51D of about 20 μm to 100 μm. A second aperture plate 52 is arranged downstream of the first aperture plate 51. Openings 62 are likewise formed in the second aperture plate. The second aperture plate 52 is followed by a third aperture plate 53 in which a plurality of openings 63 are also provided. The third aperture plate 53 is followed by a fourth aperture plate 54 in which there are also a plurality of openings 64. All of the openings 61, 62, 63, 64 in the first aperture plate 51, second aperture plate 52, third aperture plate 53 and fourth aperture plate 54 have a square cross section. The opening 61 in the first aperture plate has a larger dimensioning 71 than the opening 62 in the second aperture plate 52. The aperture plate 52 following the first aperture plate 51 has a thickness 52D of a few micrometers and the openings 62 have a highly precise square cross section. By highly precise is meant in this connection that the cross section maintains a tolerance of less than 100 nm for the absolute dimensional accuracy in x and y, and the corner acuity and edge roughness likewise conform to a tolerance of less than 100 nm. The openings 62 in the second aperture plate 52 have a dimensioning 72 that is smaller than the dimensioning 71 of the opening 61 in the first aperture plate 51. A typical ratio for the dimensions of the openings 71:72 is 2 . . . 3 assuming absolute measurements of 6 . . . 3 μm for the opening 62. As was already mentioned, the first aperture plate 51 is illuminated over its surface by the incident electron beam 31 and generates a plurality of partial beams through its openings 61, the cross sections of these partial beams corresponding to the cross section of the openings 61 in the first aperture plate 51. The first aperture plate 51 serves not only to generate a plurality of partial beams, but also to remove excess heat generated by the incident electron beam 31. The partial beams generated by the first aperture plate 51 impinge on the second aperture plate 52, and the openings 62 in the second aperture plate 52 generate the partial beam 80 of defined shape required for the imaging. The partial beam 80 of defined shape impinges on the third aperture plate 53 in which the openings 63 that are formed likewise have a larger dimensioning 73 than the openings 62 in the second aperture plate 52. On its side remote of the incident particle beam 31, the third aperture plate 53 has a control circuit 55 which generates the signals required for the deflection of the partial beam 80 of defined shape. The third aperture plate 53 has a thickness 53D of approximately 20 μm to 100 μm. The fourth aperture plate 54 has a thickness 54D of approximately 20 μm to 100 μm. Also on the side of the third aperture plate 53 remote of the incident particle beam 31, a deflector 56 for the partial beam 80 of defined shape is associated with every opening 63. The third aperture plate 53 is followed by a fourth aperture plate 54 in which are likewise provided openings 64 having approximately the same dimensioning 74 as the openings 63 in the third aperture plate 53. The first aperture plate 51, the second aperture plate 52, the third aperture plate 53 and the fourth aperture plate 54 are arranged relative to one another in such a way that all openings 61, 62, 63, 64 are oriented along a center axis 81. FIG. 4 shows a first embodiment form of the aperture plate 400 according to the invention. The openings 403 in the aperture plate 400 are distributed based on the system according to the invention. There are n rows 401 with m cells and m columns 402 with n cells formed in the aperture plate 400. A determined quantity k of openings 403 is formed in each row 401. The openings 403 are distributed within a row in such a way that the density of the openings 403 is inhomogeneously distributed within a row 401. In the present embodiment example, the openings 403 are grouped within a row 401 in such a way that the distance between the openings 403 in a row 401 corresponds to two cells. The number of openings 403 in a row 401 is four. The number of cells within a row 401 is greater than the number of openings 403 approximately by a factor of at least 10. The four openings 403 are distributed in such a way that every third cell is an opening 403. The aperture row offset 404 is eighteen cells in X-direction, i.e., two aperture rows 406 lying next to one another in X-direction are offset in each instance by eighteen cells. An aperture row subgroup 407 comprises three aperture rows 406. Aperture row groups 408 are formed by a plurality of aperture row subgroups 407 adjoining one another in Y-direction. Aperture rows 406 lying next to one another in X-direction always belong to different aperture row groups and have a Y-offset of at least one cell. FIG. 5 shows a second embodiment form of the aperture plate 500 according to the invention. The openings 503 in the aperture plate 500 are distributed based on the system according to the invention. There are n rows 501 with m cells and m columns 502 with n cells formed in the aperture plate 500. A determined quantity k of openings 503 is formed in each row 501. The openings 503 are distributed within a row in such a way that the density of the openings 503 is inhomogeneously distributed within a row 501. In the present embodiment example, the openings 503 are grouped within a row 501 in such a way that the distance between the openings 503 in a row 501 is two cells. The number of openings 503 in a row 501 is four. The number of cells within a row 501 is greater than the number of openings 503 approximately by a factor of at least 10. The four openings 503 are distributed in such a way that every third cell is an opening 503. The aperture row offset 504 is fifteen cells in X-direction, i.e., every two adjacent aperture subgroups 505, 507 are offset in X-direction by fifteen cells. In the present embodiment example, a first aperture row subgroup 505 alternates with a second aperture row subgroup 507. Both the first aperture row subgroup 505 and the second aperture row subgroup 507 comprise three aperture rows 506. The first aperture row subgroup 505 is formed in such a way that the first row 501 of the first aperture row subgroup 505 starts with an opening 503. The second aperture row subgroup 507 is formed in such a way that the first row 501 starts at the third cell with an opening 503. The variant implementations described above are suggested on the basis of the proposed distribution of the openings 403, 503 and, consequently, also of the modulator elements, where all k modulator elements of every row 401, 501 are arranged directly one behind the other at the shortest possible distance of p-times the partial beam width (p=4 . . . 8) resulting in the shortest possible aperture row length. In each instance, p aperture row groups are arranged so as to be offset in X-direction, and the offset corresponds to an integral multiple of the partial beam width and is greater than the aperture row length. A repeated arrangement of aperture row subgroups 407 and 505, 507 offset orthogonal to the row direction results in aperture row groups making up the complete aperture array (see FIGS. 4 and 5). Since the dose information need only be held in abbreviated rows, namely, the aperture rows, the total storage density is reduced by the factor p. Further, the blurring of a determined pixel on the substrate that is caused by the superposition of various distortions to which the individual apertures of an aperture row are subject when imaging on the target is reduced due to the close proximity of all of the openings 403, 503 and consequently also of all of the modulator elements in every row 401, 501. It is also possible to correct residual distortion errors which can arise from fabrication, for example, and which have been determined. This likewise results in an improved lithographic resolution. The heart of the suggested device 50 is the aperture plate system, wherein deflectors or modulator elements (see FIG. 3) are associated with the openings 403, 503 when there is at least one active aperture plate 53. In this connection, the invention does not make use of a predetermined, uniform array of openings 403, 503 or deflectors. The density of the openings 403, 503 within a row 401, 501 is not uniformly distributed along the row 401, 501. The deflectors or modulator elements comprise n shift registers of length m. This results in a multibeam modulator that is dependent on the various physical and technical boundary conditions. FIG. 6 shows a schematic view of a complete active aperture plate 600 according to an embodiment, form. The size of a chip 601 on which the aperture plate 600 is realized is 33 mm×26 mm. Control electronics 602 are also provided on the chip 601. The aperture row groups 604 which are arranged on the aperture plate 600 in an X-line 605 are separated by webs 606. No structuring by aperture row groups is carried out in the webs 606. The six aperture row groups in every X-line 605 have a Y-offset of 1 to 5 cells relative to one another so that the openings of the aperture rows of every aperture row group are positioned in different rows. In the embodiment example shown in FIG. 6, the number k of openings in every aperture row is 64. The distance between two openings within a row is five cells or pitch distance p (p=6). The aperture row offset in X-direction X can be, e.g., X=384 W+6×j×W, where 6×j×W is the width of the web 606 between the aperture row groups 605 arranged in a line. W stands for the dimensioning of the openings or cells and j is a whole number. An aperture row group 604 can have, e.g., 64 aperture rows which are offset respectively by 6 W in Y-direction. Accordingly, all of the 60 aperture row groups 604 shown in the drawing together contain 3840 aperture rows with 64 openings, respectively. For reasons of efficient data transmission, it may be useful to increase the quantity of aperture rows, e.g., to 4096, which can be carried out by arranging additional aperture row groups or by increasing the quantity of aperture rows per aperture row group. Electric lines 609, shown schematically, connect the control electronics to the respective shift register of every aperture row which shifts the gray value information in a timed manner from cell to cell through the aperture row. FIG. 7 is a schematic view showing a complete active aperture plate 700 according to another embodiment form. The size of a chip 701 on which the aperture plate 700 is realized is 33 mm×26 mm. Control electronics (not shown) are provided on the chip 701 in a manner analogous to FIG. 6. The individual aperture row groups 704 are arranged on the chip 701 of the aperture plate 700 in such a way that the distance 707 between the individual aperture row groups 704 is reduced in the corner regions 705 of a rectangle 706 drawn around the arrangement of individual aperture row groups. No structuring by aperture row groups 704 is carried out in the spaces 707 between the aperture row groups 704. In the embodiment example shown in FIG. 7, the number k of openings in every aperture row is 64. The distance between two openings within a row is five cells or pitch distance p (p=6). The aperture row offset in X-direction X can be, e.g., X=384 W+6×j×W, where 6×j×W is the maximum distance 707 between the successive aperture row groups 704. An aperture row group 704 can have, e.g., 64 aperture rows which are offset respectively by 6 W in Y-direction. Accordingly, all of the sixty aperture row groups 704 shown in the drawing together contain 64 openings, respectively. FIG. 8 is a schematic view showing a complete active aperture plate 800 according to another embodiment form. The size of a chip 801 on which the aperture plate 800 is realized is 33 mm×26 mm. Control electronics (not shown) are provided on the chip 801 in a manner analogous to FIG. 6. The individual aperture row groups 804 are arranged on the chip 801 of the aperture plate 800 so as to be divided into a first aperture group 810, a second aperture group 820, and a third aperture group 830. The individual aperture row groups 804 of the first aperture group 810, second aperture group 820 and third aperture group 830 are arranged in such a way that the individual aperture row groups of every aperture group directly adjoin one another. The individual aperture groups 810, 820, 830 are separated from one another on the chip by unstructured areas 807. The second aperture group 820 is formed in such a way that four aperture row groups 804 are arranged around the center of symmetry 809 of the second aperture group 820. Four L-shaped arrangements 811 of aperture row groups adjoin the four central aperture row groups 804. The short legs of the Ls face outward. In the embodiment example shown in FIG. 8, the number k of openings in every aperture row is 64. The distance between two openings within a row is five cells or pitch distance p (p=6). An aperture row group 804 can have, e.g., 64 aperture rows which are offset by 6 W in Y-direction. FIG. 9 is a schematic view showing a complete active aperture plate 900 according to another embodiment form of the invention. The size of a chip 901 on which the aperture plate 900 is realized is 33 mm×26 mm. The chip 901 is formed symmetrically and has control electronics 908, respectively, at opposite sides. The individual aperture row groups 904 are arranged on the chip 901 of the aperture plate 900 in six aperture groups 910, 920, 930, 940, 950, 960. The shape of the arrangement of individual aperture groups 910, 920, 930, 940, 950, 960 is substantially linear. The individual aperture groups 910, 920, 930, 940, 950, 960 also have the same distance 907 from one another. The third and fourth aperture groups 930, 940 have a number H of linearly arranged aperture row groups 904. The second and fifth aperture groups 920, 950 have four aperture row groups 904 arranged in a square at the respective opposite ends of the linear arrangement of aperture groups 920, 950. The first and sixth aperture groups 910, 960 have a number H-4 of linearly arranged aperture row groups 904. In the embodiment example shown in FIG. 9, the number k of openings in every aperture row is 64. The distance between two openings within a row is five cells or pitch distance p (p=6). An aperture row group 904 can have, e.g., 64 aperture rows which are offset by 6 W in Y-direction. FIG. 10 is a schematic view showing a complete active aperture plate 1000 according to another embodiment form. The size of a chip 1001 on which the aperture plate 1000 is realized is 66 mm×52 mm. Control electronics 1005 are provided, respectively, at opposite sides on the chip 1001. The individual aperture row groups 1004 are arranged on the chip 1001 of the active aperture plate 1000 around a center of symmetry 1008. The area 1009 around the center of symmetry 1008 is free from any structuring. In the embodiment example shown in FIG. 10, the number k of openings in every aperture row is 128. The distance between two openings within a row is five cells or pitch distance p (p=6). An aperture row group 1004 can have, e.g., 128 aperture rows which are offset by 6 W in Y-direction. Accordingly, all of the sixty aperture row groups 1004 shown in the drawing together contain 7680 aperture rows with 128 openings, respectively. For reasons of efficient data transmission, it may be useful to increase the quantity of aperture rows, e.g., to 8192, which can be carried out by arranging additional aperture row groups or by increasing the quantity of aperture rows per aperture row group. FIG. 11 is a schematic view showing an active aperture plate 1100 according to another embodiment form. The size of a chip 1101 on which the aperture plate 1100 is realized is 66 mm×52 mm. Control electronics 1105 are provided, respectively, at opposite sides on the chip 1101. The individual aperture row groups 1104 are arranged on the chip 1101 of the aperture plate 1100 around a center of symmetry 1108. The area 1109 around the center of symmetry 1108 is free from any structuring. In the embodiment example shown in FIG. 11, the number k of openings in every aperture row is 128. The distance between two openings within a row is five cells or pitch distance p (p=6). An aperture row group 1104 can have, e.g., 128 aperture rows which are offset by 6 W in Y-direction. FIG. 12 is a schematic view showing an active aperture plate 1200 according to another embodiment form. The size of a chip 1201 on which the aperture plate 1200 is realized is 66 mm×52 mm. Control electronics 1205 are provided, respectively, at opposite sides on the chip 1201. The individual aperture row groups 1204 are arranged on the chip 1201 of the aperture plate 1200 around a center of symmetry 1208. The area 1209 around the center of symmetry 1208 is free from any structuring. In the embodiment example shown in FIG. 12, the number k of openings in every aperture row is 128. The distance between two openings within a row is five cells or pitch distance p (p=6). An aperture row group 1204 can have, e.g., 128 aperture rows which are offset by 6 W in Y-direction. Here also, the Y-offset of the six aperture row groups within an X-line 1206 is between 1 W and 5 W. Another important aspect in the selection of the position of the openings in the individual aperture plates and the position of the beginning of the aperture rows consists in minimizing imaging errors. It is known from conventional optics that these errors increase sharply as the radial distance of the partial beams from the beam axis increases. Therefore, the rectangular array structure notwithstanding, it is useful to choose a configuration of the aperture plate which substantially avoids partial beams in the corner areas as is shown in different ways in FIGS. 7, 8, 9, 10, 11 and 12 by way of example. Due to the fact that, in practice, a certain minimum distance must be maintained between the modulator elements and because, on the other hand, a compact construction is preferable for reasons of space and optical transparency of the arrangement, a basic variant consists in a uniform array arrangement such as is suggested in various publications. The control (supply of dose information) of every aperture row is carried out directly at the start of the aperture row so that the respective X-offset relative to the start of the row and relative to the actuating electronics is bridged by conductors. A few shift registers 1302 or other signal shaping circuitry 1304 can be connected therebetween (see FIG. 13) to ensure signal quality. The correct data reference can be produced electronically by correspondingly providing the dose data and time-delayed readout of the row information. The shift register array m×n corresponds to a pixel field of size m×n on the substrate or target 6. The data feed is effected out via lines 1301 having a bit width b. Likewise, every shift register stage must have a bit width b so that 2b different dose values D can be coded. By using the above-described scan in row direction, which proceeds exactly synchronous with the clock shift, it is possible to associate a pixel position on the substrate with every dose value D traversing a corresponding shift row. Since every aperture row has m shift positions, it is possible in theory to actuate m different modulator elements successively with each dose value D. These modulator elements must be arranged in such a way that the associated partial beams are imaged through the projection optics in timed sequence on one and the same substrate pixel—ideally, at regular intervals on a line, realistically, on a curved line which compensates for the distortions of the imaging optics. For reasons of space, it is impossible to arrange a modulator element in every row at every shift position; on the other hand, this is also unnecessary. In order to achieve the desired dose staggering, k (typically 64 . . . 512) identical modulator elements are sufficient: 2b−1≦k<m. This makes it possible to select k positions from m in every aperture row taking into account the relationship between the shift step and the beam position. This provides the foundation for the construction of a multibeam modulator based on a shift register array of n rows and m shift stages, wherein k modulator elements can be arranged electively at k of m positions in every row. In practical implementation, of course, all shift stages which would follow after the final modulator element in every row can be omitted because the dose value information is no longer needed. Also, the shift stages in front of the first modulator element of a row can be omitted when the data feed is carried out with an appropriate clock delay. Another advantage of the proposed invention consists in that not only is on/off information is shifted through the rows of the active aperture plate or modulator array, but also grayscale information with a bit width b (typically 6 . . . 8 bits). This offers multifold possibilities for controlling the modulator elements. FIG. 14 shows a suggestion in which a combinational logic circuit 1400 is associated with every modulator element 1401. By means of the signal at the output of the logic circuit 1400, it is decided whether the modulator element 1401 switches the partial beam on or off. Accordingly, it is decided based on the upcoming dose value D whether or not the partial beam is switched on at the time of the transfer clock MODTakt. For example, of the k logic circuits of the k modulator elements of a row, exactly one at D>0, one at D>1, etc. up to exactly one at D>k−1 can supply “partial beam on” as a result so that k dose values can be realized. Any other logical operations of the bits of D are possible. Due to the fact that the logic circuits can be selectively associated with the modulators of a row, it is possible to choose a variant which produces a laterally homogeneous beam distribution for all dose values. Further, it is suggested to provide all or some of the logic circuits with s internal storage cells so that the combinational logic becomes a sequential logic 1500 (depending on the prior history because it has a “memory”). The storage cells are used as an s-bit configuration storage which must be loaded prior to the exposure. When s<=b, the loading can be carried out in such a way that determined bits of the upcoming dose value D are taken over in the configuration when a configuration signal Config is activated (FIG. 15). Even with one configuration bit (s=1), it is possible to activate a determined modulator element (it participates in the control of the partial beam depending on its logic) or to deactivate a determined modulator element (modulator is always in the “off” state). Increasing s results in a great number of possibilities for varying the control logic, although this also increases expenditure on circuitry. The ability to reconfigure the modulator electronically gives rise to the following novel possibilities. Error redundancy is made possible so that, in the event of a failure of individual modulator elements, some modulator elements which were deliberately provided in the layout as reserves can simply be activated. Likewise, it is possible to adapt the exposure rows with respect to dose. This is carried out by adapting the number of active modulators, and variations in dosage between the exposure rows can accordingly be compensated (compensation of illumination inhomogeneities). FIG. 16 shows a modification of the geometry of the openings in the second aperture plate 52. The uniform, square openings 62 are not modified. When the openings are produced in the aperture plate, corners can be rounded to deform the cross section of the partial beam. This can be partly compensated by a defined pre-distortion of the geometry of the openings in the aperture plate 52. In this connection, FIG. 16 shows simple examples for modifying the geometry of the openings. In a first variant, the openings 1602 have a square cross section with an additional small opening 1604 formed at each corner of the square. The entire geometry of the cross section of the opening extends beyond the dimension of a cell of the aperture plate 52. In another possible modification of an opening 1606 in the aperture plate, the opening 1606 is a rectangle which is oriented diagonally with respect to a cell. Additional small rectangular openings 1608 are formed at the corners of the rectangle. As is shown in FIG. 16, the shape of the openings can change within a row. The above-mentioned ability to configure the modulator elements within an aperture row on the active aperture plate makes it possible, depending on the specific exposure task, to activate individual, particularly well-suited partial beam cross sections 1606 and deactivate other, less suitable partial beam cross sections. The rectangular beam cross sections, shown by way of example, which are rotated by 45° or 135° could help to reduce the edge roughness during the exposure of diagonal lines. Also, special partial beam cross sections can be introduced for optimizing the exposure of any curved structures or special structures. While the foregoing description and drawings represent the present invention, it will be obvious to those skilled in the art that various changes may be made therein without departing from the true spirit and scope of the present invention.
	description	This is a Continuation Application of PCT Application No. PCT/JP2005/005583, filed Mar. 25, 2005, which was published under PCT Article 21(2) in Japanese. This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-188360, filed Jun. 25, 2004, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to a probe apparatus including such as an atomic force microscope (AFM) and a scanning tunneling microscope (STM). 2. Description of the Related Art In recent years, a non-contact type atomic force microscope has rapidly advanced. This microscope vibrates a cantilever serving as a probe with self-excitation to detect a small shift of the resonance frequency caused due to a charge-transfer force between the cantilever and a sample, thereby enabling nanoscopic measurement of a surface electron state (see, e.g., U.S. Pat. No. 7,250,602. Since this microscope detects a frequency, the microscope has resistance to noise and can detect an fN (femto-Newton) level force since a frequency is detected. Therefore, a single atom as well as a small charged state that is not greater than a single charge can be readily detected. However, observation of an image with respect to a photoexcited electron transfer process is required by measuring a change in an electron state in a short time (e.g., nanoseconds) in addition to nanoscopic measurement of a surface electron state. Here, detecting a fast signal is attempted in the STM. But, since local charges diffuse to a conductor substrate, a time resolution of the STM cannot be exploited. Further, in the AFM, a single charge on an insulator can be detected by an electrostatic force. But, a scanning time is longer than 10 seconds, and it is approximately 0.1 second even in a special high-speed AFM. Therefore, a dynamic process cannot be tracked. In nature, a subtle stereoscopic nano-structure is configured, and it has been revealed that a nanoscopic spatial arrangement is decisively important in highly efficient photoexcited electron transfer that can be observed in photosynthesis. However, when analyzing these structures in a conventional technology, there is only an indirect method, such as comparing a kinetic study on a solution-based molecular population with a crystal structure analysis using an X-ray or radiation light. An object of the present invention is to provide a probe apparatus that can observe a change in an electron state (electron transfer) of a molecule (or an atom) excited by light irradiation with a high time resolution and a high spatial resolution. It is to be noted that realizing the following matters can be expected in the probe apparatus according to the present invention. 1) A relationship between an intermolecular distance or a molecular orientation and a charge-transfer rate is directly revealed from an image by observing an image of a photoexcited charge transfer process between donor and acceptor molecules. 2) Long-distance electron transfer between oxidizing and reducing sites through a protein in, e.g., photosynthesis are experimentally examined a relationship between a conformation of a protein molecule and inter-site electronic coupling. Means for Achieving the Object The invention pays attention synchronous process of the mechanical motion and the electronic process, and is characterized in that, in a probe apparatus that intermittently irradiates a sample with excitation light to observe the sample while subjecting a cantilever including a probe arranged to face a surface of the sample to self-excited vibration, the sample is irradiated with the excitation light at a predetermined timing when a distance between the probe and the sample is not greater than a predetermined distance. An embodiment according to the present invention will now be explained with reference to the accompanying drawings. In a non-contact atomic force microscope, an electron state on a sample surface can be measured as described above by measuring a displacement of a resonance frequency of a cantilever caused by weak force acting on a probe enables. Therefore, when the sample surface is scanned by using the probe, this resonance frequency always fluctuates. Under such conditions, it is apparent that a timing of light irradiation cannot be synchronized with a vibration (a motion) of the cantilever when a sample is irradiated with a photoexcitation laser beam at a predetermined repetition frequency. Thus, it is necessary to detect a stroke for each reciprocation concerning a vibration of the cantilever or a time concerning a single reciprocation (i.e., a period of the vibration) and configure a system that emits a photoexcitation laser beam in accordance with the detection. FIG. 1 is a view showing a schematic configuration of a probe apparatus according to the present invention. As a probe apparatus, a conductive cantilever 10 having a probe 10a is used. It is to be noted that, as shown in FIG. 1, a sample 20 is arranged at a position facing the probe 10a on a piezoscanner 21 to be movable in triaxial directions. Further, a bias 22 having a variable applied voltage can apply a desired voltage to the sample 20. It is to be noted that an embodiment of applying a bias to the sample will be explained in this specification, but the bias may be applied to the probe. The piezoscanner 21 is movable along an X-Y plane with an X-Y scanning signal, whereby a surface state at a desired position can be measured. As a result, the surface state can be observed while scanning the sample 20. Furthermore, the piezoscanner 21 is movable in a Z-direction by receiving a Z-signal from a Z-piezoscanner driver 23 which will be explained later in detail, and a distance between the sample 20 and the probe 10a is maintained constant by the Z-signal. A specific operation will be described with reference to FIG. 1. For example, the cantilever 10 that has received an energy by, e.g., noise starts vibration. A motion of this cantilever 10 is detected by an optical system including a light source 31 and a detector 32 formed of a four-divided photodiode (this optical system will be referred to as an “optical lever”), converted into an electric signal, and output to a preamplifier 40. A periodic signal output from the preamplifier 40 is output to a transfer unit 41 and a controller 51. A synchronization signal output to the phase shifter 41 is compensated in regard to delay in an electric measurement system. A signal output from the phase shifter 41 is converted into a rectangular wave signal in a waveform converter 42. The rectangular wave signal output from the waveform converter 42 is input to an attenuator 43 and a frequency demodulator 45. The attenuator 43 attenuates the input rectangular wave signal at a predetermined rate. The rectangular wave signal subjected to this attenuation is input to a piezoelectric element 30 of the cantilever 10, and the cantilever 10 controls to automatically continue vibration with a vibration amplitude. As a result, the cantilever 10 performs self-excited vibration. A signal concerning a vibration amplitude value of the cantilever 10 is output by the rectangular wave signal input to the frequency demodulator 45, and a difference from a reference signal is calculated in an error amplifier 46. An output signal from the error amplifier 46 is output to a non-illustrated display section (an output section) through a filter 47 as an uneven image signal. A signal from the filter 47 is also output to the Z-piezoscanner driver 23 to control a movement of the sample 20 in the Z-direction. Further, by changing an applied voltage from the bias 22 to control a potential difference between the probe 10a and the sample 20, a frequency shift in a local state with each set voltage is detected. The controller 51 controls an emission timing of irradiation light for excitation from a laser light source 50 based on a periodic signal output from the preamplifier 40 to the controller 51. A specific control method is as explained below. An output from the detector 32 constituting the optical lever is monitored to track a motion of the cantilever. An emission timing of a pulsed laser beam for excitation (which will be simply referred to as a “laser beam” hereinafter) is determined by using this output. The determining method of emission timing will now be described with reference to FIG. 2. FIG. 2 is a graph showing a relationship between a delay time of laser irradiation and a force applied to a cantilever (displacement of a frequency is actually measured) when a distance between the cantilever and a sample surface is closest. In FIG. 2, an abscissa axis represents a delay time from the closest position of the cantilever with respect to the sample surface to irradiation of a laser beam, and an ordinate axis represents displacement of a feedback. It is to be noted that the sample is a membrane of phthalocyanine formed on a silicon substrate. Measurement shown in FIG. 2 is carried out in a state where the cantilever is fixed at a certain position on the sample surface, but a resonance frequency of the cantilever always varies by scanning when a time-resolved image is obtained while scanning the sample. Therefore, when excitation light enters the optical lever of the probe apparatus, apparent frequency modulation is given thereto. Accordingly, ingress of the laser beam into the optical lever control system must be reduced as much as possible, and hence the following methods are considered. A first method is a method that excitation light is introduced to the sample surface at a very shallow angle of 1 to 2 degrees vertical to a laser beam in the optical lever system. With this configuration, stray light entering the four-divided photodiode as a detector of the optical lever system is scattered light alone from a narrow cantilever distal end. This method has a drawback that a sufficient intensity of excitation light is hardly obtained since the incidence angle is shallow. A second method is a method of vertically introducing light with respect to a sample using a transparent substrate from a back side of the substrate. When this method is used, the sample can be irradiated with excitation light having a sufficient intensity while avoiding an interference with the optical lever system. However, a drawback is that a study target is restricted to a sample using a transparent substrate, e.g., sapphire. Since the two light irradiation methods respectively have advantages/drawbacks, a sample stage that can realize both the methods is required. The first method of applying excitation light from a shallow angle requires an optical system that can precisely control an optical path. The second method of performing irradiation from the back side of the sample must adopt a cylindrical piezoelectric element having a hole formed at the center thereof to assure an optical path. A stage of the AFM satisfying these conditions must be newly designed. Thus, as shown in FIG. 2, a trigger is generated when the probe is at a predetermined position, this trigger is determined as a reference, and a laser beam is irradiated after a given delay time (i.e., the substantially closest position of the probe to the sample, and it is after approximately 4.7 microseconds in the example shown in FIG. 2). To irradiate the laser beam before the cantilever becomes closest position to the sample surface, a vibration period of a previous period of the cantilever (probe) is measured and a timing may be set with this period determined as a reference. It can be understood from the graph of FIG. 2 that an electrostatic force is detected when a position of the cantilever is synchronized with irradiation of the photoexcitation laser beam. This principle will now be described with reference to FIG. 3. As shown in FIG. 2, a vibration period of the cantilever is a microsecond order. However, a force caused by an interaction (i.e., a shift of a frequency) is detected only at the moment that the cantilever distal end is closed to the surface, and its duration of effective action is as short as approximately 10 ns. Thus, by synchronizing the moment that the cantilever is placed at the closest position to the sample with the pulse laser beam irradiation, both a time resolution of several-ten ns and an atomic level (i.e., nanometer order) spatial resolution is satisfied, and a transitional charge generated by light excitation can be measured. It is to be noted that the time resolution is approximately microseconds in this measurement because measurement is carried out with respect to a sample in which charges are generated on an entire thin film surface thereof. According to this configuration, since the pulse laser beam used for photoexcitation is completely synchronized with a motion of the cantilever, even if excitation light enters the optical lever system, since only amplitude thereof is changed without varying a frequency, a feedback of the atomic force microscope is not affected. Using the above-described probe apparatus can realize the following applications. 1) Imaging of Aging of a Surface State For example, it is known that an excitation triplet of 5, 10, 15, 20-tetra-p-N-methylpyridylporphinatozinc (ZnTMPyP) has a long life duration that reaches 1 ms even in an aqueous solution. Furthermore, benzoquinone (BQ) has an excellent capacity as an electron acceptor. Thus, BQ is dispersed and immobilized on a sapphire substrate surface, and a fine particle aggregate of ZnTMPyP is produced thereon by vapor deposition. In such a sample, a charged state obtained by photoexcitation is alleviated with time, and an electron is re-coupled with a hole. Controlling the dispersed state of BQ and a size of the ZnTMPyP aggregate can adjust electron transfer and a relaxation speed, and hence this system is optimum to effect imaging concerning aging of a surface state. Therefore, this system can be used to generate samples having various conditions, and a relationship between a topograph and photoexcited electron transfer can be directly revealed from an image. 2) Imaging of Charge Transfer in Antenna Type Giant Molecules In the antenna type giant molecules, since many molecules are cooperatively excited and energy transfer occurs toward a specific region, highly efficient electron transfer, a long-life charge separation state, and multiphoton excitation are achieved. Such an antenna effect is similar to an arrangement of a heme structure in a protein included in a photosynthesis bacteria, and hence it is very interesting. The probe apparatus according to the embodiment of the present invention can image electron transfer dynamics of a molecule having a flat antenna function. For example, such porphyrin 21 mer as shown in FIG. 4 will be considered. Here, when a porphyrin ring having no metal is arranged at the center and a porphyrin ring with a long excitation life such as zinc is arranged at the periphery thereof, charge transfer occurs with a very high efficiency after light irradiation, and a charge separation state is realized between the center and the periphery. Moreover, when an acceptor portion is arranged at the center of a porphyrin array having a one-dimensional array, it is expected that charge transfer that is dependent on polarization of excitation light can be observed. 3) Charge Separation of Diode Type Porphyrin under Electric Field Gradient A diode type molecule having a donor and an acceptor coupled with each other is an idea as a molecule rectifier proposed more than a quarter of a century ago, and it is a central concept of molecular-scale electronics. In the embodiment according to the present invention, a dipole type porphyrin molecule is placed in an intensive electric field gradient to enable direct measurement of a velocity of photoexcited electron transfer. Based on a Marcus theory, a velocity of electron transfer between a donor and an acceptor is subject to a re-orientational energy of a solvent molecule in a liquid solution. However, in a solid surface absorption state where no solvent molecule is present and transfer of a molecule is considerably restricted, how a distance or a difference in ionization potential between the donor and the acceptor affects a tunneling velocity is unknown. Since a molecule has many degrees of internal freedom and an electron state is discrete, fundamental measurement, e.g., confirming whether a simple theory like electron tunneling between metals can be applied can be directly performed. 4) Photoexcited Electron Transfer from hemoprotein, e.g., cytochrome c It is known that a protein, e.g., cytochrome c or azurin highly efficiently performs electron transport. Such a protein has an oxidizable/reducible metal-porphyrin skeleton at the center, and its periphery is covered with an insulative organic molecular layer. Considering this structure from an electronic viewpoint, this protein is positioned as an electronic component having a small capacity partitioned by double tunnel coupling, i.e., a nanosize indicative of a coulomb blockade. In a liquid solution, a photoexcited electron transfer velocity from porphyrin in the protein to an Ru complex coupled with the protein is systematically studied by a spectroscopic method. However, when the protein is fixed on a surface as a solid device, since a structure of the protein is distorted and a conformation change is also suppressed, whether it shows such electronic properties or not cannot be readily presumed. However, histidine tag (His) can be introduced to various positions in the protein by a gene manipulation (FIG. 5). Thus, when a self-assembled membrane is formed on a gold substrate and coupled with histidine by using a Ni complex that is selectively coupled with a self-assembled molecule, the protein can be fixed on the gold substrate with an arbitrary orientation and distance. When an actual time of photoexcited electron transfer of such a sample is measured by using the probe apparatus according to the embodiment of the present invention, a direction and/or a structure of the protein molecule can be directly associated with an electronic connection state between the protein and a metal electrode to be revealed. As described above, the probe apparatus according to this embodiment has a nanosecond or nano-scale resolution exceeding an application range of an existing probe apparatus, and can directly and experimentally solve a problem of a spatial arrangement in photoexcited electron transfer that is insoluble by an existing method. That is, according to the embodiment of the present invention, it is possible to directly observe, e.g., charge separation of an electron transfer protein or charge concentration of an antenna type molecular, e.g., giant porphyrin or planar dendrimer. A stereo effect of photoexcited electron transfer that is conventionally indirectly discussed can be directly examined in this manner. Further, photoexcited electron transfer can be studied from a stereoscopic viewpoint, and an effect of a spatial arrangement of an individual molecule can be directly imaged. In the natural world, electron transport with an extraordinarily high efficiency is realized, but a stereoscopic arrangement that takes on an essential importance can be found in a large fluctuation of a macro-molecular system. When this result is compared with a theory to be determined as a design manual for a artifical system, it is possible to naturally learn, and hence it is very significant. The present invention is not restricted to each foregoing embodiment, and various modifications can be carried out on an embodying stage without departing from the scope of the invention. For example, although the AFM is taken as the example of the probe apparatus in the foregoing embodiment, a technique of synchronizing interlocking of the probe with a transitional dynamic phenomenon can be applied to various kinds of general nano-probes as a method of realizing a time resolution. That is, synchronizing a vibration of the contiguous probe with occurrence/change of a physical amount allows the present invention to be applied to a wide range of scanning probe microscopes. Specifically, the present invention can be applied to, e.g., a time-resolved scanning near-field optical microscope (photochemistry/biochemistry), a time-resolved magnetic force microscope (an electromagnetic field response), or a time-resolved electrostatic force microscope (a transitional response of a nano-circuit). Furthermore, when the probe apparatus according to the embodiment of the present invention is combined with a pump probe method, it can be considered that measurement achieving both a single-molecule resolution and a time resolution that is approximately picoseconds is possible. Moreover, the present invention can be likewise applied to a system in which an optical fiber is subjected to self-excited vibration in place of the cantilever to intermittently emit a laser beam. In this case, bending of the optical fiber is detected based on an optical lever or optical interferometry like the AFM to carry out rough control, and an optical phenomenon of a sample (e.g., light from the sample) caused due to light from the optical fiber (e.g., near-field light) may be measured by using an optical device such as a microscope. Additionally, each foregoing embodiment includes inventions on various stages, and wide-ranging inventions can be extracted from appropriate combinations of a plurality of disclosed constituent requirements. Further, for example, even if some constituent requirements are deleted from all constituent requirements disclosed in each foregoing embodiment, the problem explained in the section “Problem to be solved by the Invention” can be solved, and a structure in which such constituent requirements are deleted can be extracted as an invention when the effect explained in “Effect of the Invention” is obtained. According to the present invention, a change in an electron state (electron transfer) of a molecule (or an atom) excited by light irradiation can be observed with a high time resolution and a high spatial resolution.
042499950	claims	1. A liquid-metal cooled nuclear reactor comprising an open-topped main vessel having a vertical axis and containing liquid metal, a reactor core, an inner vessel mounted and coaxial within the main vessel, and an inner vessel extension in the form of a transverse skew wall provided with a downwardly-bent edge joined to a structure connected to said main vessel, said skew wall being transversed by cylindrical sleeves providing a leak-tight passage for the bodies of pumps and heat exchangers disposed at intervals around the reactor core, a baffle extending above said skew wall and delimiting therewith a space containing a practically static volume of liquid metal which forms a thermal screen between hot liquid metal located within the inner vessel above said baffle and cold liquid metal located between the inner vessel and the main vessel beneath said skew wall. 2. A liquid-metal cooled reactor according to claim 1, wherein the skew wall has the shape of a portion of a torus of revolution about the axis of the main vessel and has an inner and an outer edge and is joined by means of conical walls to the inner vessel at its inner edge and to the structure which is connected to said main vessel at its outer edge. 3. A liquid-metal cooled reactor according to claim 1, wherein the baffle has a horizontal surface which rests freely on stationary bearing members and is provided on its internal and external peripheries as well as at the point of penetration by each cylindrical sleeve with a downwardly-extending side portion which is immersed in the liquid metal and traps a blanket layer of neutral gas beneath the horizontal surface of said baffle. 4. A liquid-metal cooled reactor according to claim 1 or 2, wherein the baffle is constituted by a single unit supported on the stationary bearing members by means of sliding contacts. 5. A liquid-metal cooled reactor according to claim 4, wherein the baffle is constituted by adjacent sectors in juxtaposed relation and provided successively with overlapping edges for ensuring continuity of the baffle, each sector being joined to one of the cylindrical sleeves through which a pump or heat exchanger is intended to pass. 6. A liquid-metal cooled reactor according to claim 4, wherein the baffle is provided with circumferential ribs. 7. A liquid-metal cooled reactor according to claim 1 or claim 2, wherein the baffle is self-supporting and inclined towards the axis of the main vessel, said baffle being provided with an extension in the form of a lateral and vertical bearing shell placed within the inner vessel. 8. A liquid-metal cooled reactor according to claim 7, wherein the baffle is provided at its periphery and around the sleeves with downwardly-directed side portions extending parallel to the axis of the main vessel to the bottom level of the baffle, said side portions delimiting a plurality of annular spaces with lower ends which open into the hot liquid metal located above the baffle and within the space containing the volume which forms a thermal screen. 9. A liquid-metal cooled reactor according to claim 7, wherein the baffle is provided at its periphery and around the sleeves with upwardly-directed side portions extending parallel to the axis of the main vessel, said side portions delimiting a plurality of annular spaces with upper ends which open into a gaseous atmosphere located above the hot liquid metal, orifices being also formed in the lower portion of the bearing shell which supports the baffle.
	abstract	A truss-reinforced spacer grid and a method of manufacturing the same are provided, in which truss members having a small diameter are woven to form a truss structure surrounded by an external plate, and the truss structure is joined to the external plate to thereby improve the strength of the mechanical structure. The truss-reinforced spacer grid includes a truss structure in which horizontal trusses formed by horizontally weaving a plurality of truss members are vertically disposed at regular intervals, and an external plate is joined with ends of the horizontal trusses and surrounds the truss structure.
	description	A subject-matter of the present invention is the production of products based on phosphate of thorium and/or of actinides which can be used for the conditioning and treatment of reactive waste, such as liquid effluents. More specifically, it relates to the preparation of precursor products of thorium phosphate/diphosphate of formula Th4(PO4)4P2O7 (TPD) or of formula Th4-xMx(PO4)4P2O7 in which M is a tetravalent actinide, such as Pa, U, Np and Pu. The document WO 96/30300 [1] disclosed several processes for the synthesis and characterization of thorium phosphate Th4(PO4)4P2O7 as conditioning matrix for the storage of nuclear waste. The syntheses relate to various media. For the syntheses which take place in a liquid medium, they report a mixture of aqueous solutions of chemicals (thorium salts, compounds comprising nuclear waste, acids, bases) which always results in concentrated solutions. A dry and amorphous residue is obtained from these concentrated solutions, mainly by evaporation of the volatile materials (water and acids, for example), which residue will result, by calcination at 850–1300° C., in the fully crystalline thorium phosphate/diphosphate Th4(PO4)4P2O7, which then has the properties required for good retention of the nuclear waste which is incorporated therein. In this process, the stage which consists in carrying out the evaporation of concentrated solutions is entirely achievable but under extreme conditions. This is because it concerns the evaporation of chemically highly aggressive solutions (acidic or basic) comprising very high levels of radioactivity. This route is therefore technically possible but difficult. A subject-matter of the present invention is specifically a process for the preparation of a product based on phosphate of thorium and/or of actinide(s) which can be easily converted to thorium phosphate/diphosphate without requiring a stage of evaporation of aggressive solutions. According to the invention, the process for the preparation of a product comprising a phosphate of at least one element M(IV) chosen from thorium(IV) and actinide(IV)s is characterized in that it comprises the following stages: a) mixing a solution comprising thorium(IV) and/or at least one actinide(IV) with a phosphoric acid solution in amounts such that the molar ratio PO 4 M ⁢ ⁢ ( IV ) where M(IV) represents the total concentration of thorium(IV) and/or actinide(IV)s, is from 1.4 to 2, preferably from 1.5 to 1.8, b) heating the mixture of the solutions in a closed container at a temperature of 50 to 250° C. to precipitate a product comprising a phosphate of at least one element M chosen from thorium(IV) and actinide(IV)s having a P/M molar ratio of 1.5, and c) separating the precipitated product from the solution. Thus, according to this process, the starting materials are exclusively acidic solutions having a substantially identical chemical composition to that described above, and a crystalline precursor is obtained by mild chemistry, that is to say by moderate heating of the mixture in a closed container, to avoid, this time, the evaporation and to promote the precipitation of this precursor. The latter will subsequently be easily separated, by settling, filtration or centrifuging at ambient temperature, from the solution which has given rise to it. This process thus avoids the stage of evaporation and the treatment of the gaseous effluents inherent in the process disclosed in WO 96/30300 [1]. This is particularly advantageous when the process is used for the treatment of liquid effluents as the need to evaporate radioactive acidic solutions and to treat the gaseous effluents resulting from the evaporation is thus avoided. According to the invention, the heating is carried out in a closed chamber at a moderate temperature (50 to 250° C.) for a variable period of time which depends on the temperature used and on the nature of M(IV). This period of time can range, for example, from 1 hour to 1 month, in order to obtain a finely crystalline solid which can be easily separated from the solution after the latter has been cooled. The heating time is an important parameter as it has a direct influence on the quality of the precipitate formed. For this heating, the mixture of the solutions of M(IV) and of phosphoric acid is introduced, for example, into a Teflon container with a screw cap which is highly leaktight. The container can be heated by any means, for example in an electric resistance oven, in a microwave oven, in a sand bath, in an oil bath or alternatively by using an infrared lamp or a stream of hot gas. According to one advantageous characteristic, the process for the invention furthermore comprises the following stages: d) washing with water the precipitated product thus separated, and e) drying the washed product, for example in an oven. The solutions comprising thorium and/or one or more actinides which can be used in this process can be prepared, for example, from salts, such as chlorides, bromides, nitrates, sulphates and oxalates. It is also possible to prepare them by any method which makes possible the introduction of actinide(IV)s ions into solution, for example by dissolution of the metal or of the oxide. The process described above can be used to prepare thorium phosphate/diphosphate of formula Th4(PO4)4P2O7 by using, in stage a), a solution comprising thorium and phosphoric acid and by subjecting the product based on thorium(IV) phosphate, separated by precipitation, to a heat treatment carried out at least partially at a temperature of 700 to 1300° C. It is also possible to use the process of the invention to prepare a solid solution of phosphates of thorium and of at least one tetravalent actinide by using, in stage a), a solution comprising thorium and at least one tetravalent actinide and phosphoric acid and by subjecting the product based on phosphates of thorium(IV) and of actinide(IV) (s) obtained to a heat treatment carried out at least partially at a temperature of 700 to 1300° C. For example, the heat treatment is carried out in two stages, a first precalcination stage carried out at a temperature of 300 to 500° C. for 1 to 5 h and a second calcination stage carried out at a temperature of 1100 to 1300° C. for 3 to 15 h. It is also possible to carry out a cold compacting of the powder before carrying out the heat treatment, in order to obtain a sintered product. Thus, the process of the invention makes it possible to obtain a sintered product under better conditions (temperature, duration, pressure) than in the case of the document [1], because of the better physicochemical properties (particle size, specific surface) of the precipitated product. It is thus possible to prepare solid solutions of phosphates corresponding to the formula:Th4-xMx(PO4)4P2O7in which M is an element chosen from Pa(IV), U(IV), Np(IV) and Pu(IV), and x satisfies the following conditions: x≦3.75 for Pa(IV) x≦3 for U(IV) x≦2.14 for Np(IV) x≦1.67 for Pu(IV). For the implementation of the process of the invention, it is possible to use, for example, as thorium solution, a solution of ThCl4 in hydrochloric acid or a solution of thorium nitrate in nitric acid. The ThCl4 solution can be obtained by dissolution of solid ThCl4 in a 0.5 to 2M hydrochloric acid solution, in order to obtain a 0.5 to 2M ThCl4 solution. The solution of thorium in a nitric acid medium can be obtained by dissolution of Th(NO3)4.5H2O in a 0.5 to 5M HNO3 solution, in order to obtain a 0.5 to 2M Th solution. When the actinide is uranium(IV), the uranium(IV) solution can be a solution of UCl4 in hydrochloric acid, for example obtained by dissolution of UCl4 in 0.5 to 6M HCl or by dissolution of uranium metal in 6M HCl, subsequently brought to the desired concentration, for example 0.5 to 1.5M in U, by dilution with deionized water. When the actinide is neptunium(IV), the neptunium(IV) solution can be a solution of neptunium in nitric acid, for example obtained by dissolution of solid NpO2 in 4 to 5M HNO3 and dilution with deionized water, in order to have a nitric acid concentration of 1 to 4M and an Np concentration of 0.1 to 0.3M. When the actinide is plutonium(IV), the plutonium solution can be a solution of plutonium in nitric acid, for example obtained by dissolution of PuO2 in a 4 to 5M nitric acid HNO3 solution and dilution with deionized water, in order to obtain a nitric acid concentration of 1 to 4M and a Pu concentration of 0.2 to 0.6M. Thus, the process of the invention makes it possible to prepare thorium phosphate/diphosphate when it is carried out with a thorium solution to which a phosphoric acid solution is added in the desired molar ratio. A gel is thus formed, which gel, in the closed container, is subsequently converted by heating to a precipitate formed of a crystalline powder. This powder can subsequently be converted to thorium phosphate/diphosphate (TPD) by heat treatment. The process of the invention can also be used to prepare an actinide phosphate, for example a uranium(IV) phosphate, by first of all forming a uranium phosphate precipitate which is subsequently converted by heat treatment to a phosphate with a different structure from that of thorium phosphate/diphosphate, corresponding to a polyphase system. For this preparation, use is made, in stage a), of a solution comprising uranium and phosphoric acid, and the precipitated product is subjected to a heat treatment carried out at least partially at a temperature of 700 to 1300° C. In this case, the acidic uranium solution must not comprise an oxidizing agent as, in the presence of an oxidizing agent, such as, for example, nitric acid, the tetravalent uranium is oxidized to hexavalent uranium in the form of the uranyl ion UO22+, which will not form a precipitate under the conditions of the process of the invention. The process can also be used to form solid solutions of tetravalent actinides starting from a mixture of acidic solutions comprising several actinide(IV)s and of phosphoric acid, which is subsequently subjected to heating in a closed container at a temperature of 50 to 250° C. to precipitate a product comprising actinide phosphates. When the starting material is a solution of thorium and of actinide(s), a very homogeneous powder composed of particles with a size of less than 3 μm is obtained by precipitation followed by heating in the closed chamber, which powder can be converted by heat treatment to a phosphate/diphosphate of thorium and of uranium(IV). It is also possible to include trivalent elements or other tetravalent elements in this phosphate/diphosphate of thorium and/or of tetravalent actinide(s) by coprecipitating the trivalent elements with the tetravalent elements during the heating in a closed chamber. At the end of the operation, a two-phase or polyphase system composed of phosphate/diphosphate of thorium and/or of tetravalent actinide(s), and of a phosphate comprising trivalent lanthanide elements, such as gadolinium and lanthanum, and/or trivalent actinide elements, such as americium and curium, is obtained. It is also possible to prepare, from the product based on phosphate of thorium(IV) and/or of actinide(IV) (s) obtained by precipitation following stages a) to c), a composite material including at least one actinide(III) and/or at least one lanthanide(III) in the phosphate form, such as monazite M(III)PO4, xenotime M(III)PO4 and brabantite M(II)xM′ (IV)xM″ (III)(2-2x) (PO4)2. This material can be prepared by dispersing a powder of the phosphate(s) formed beforehand in the precipitate of the product comprising a phosphate of thorium(IV) and/or of actinide(IV)(s) and by subsequently subjecting the combination to a heat treatment, optionally preceded by a compacting, carried out at least partially at a temperature of 700 to 1300° C. A further subject-matter of the invention is a process for the separation of uranium(VI), in the form of the uranyl ion UO22+, present in a solution with other cations, including thorium, according to which phosphoric acid is added to the solution in an amount such that the phosphoric acid/other cation molar ratio is from 1.4 to 2, the solution thus obtained is heated at a temperature of 50 to 250° C. in a closed container, in order to precipitate a product comprising the cations other than uranium, and the solution comprising uranium(VI) is recovered. This is because uranyl phosphate (UO2)3(PO4)2·5H2O, which is more soluble than phosphates of trivalent and tetravalent cations, such as, for example, actinides and lanthanides, may not precipitate under certain operating conditions. It is therefore possible to separate uranium from the other cations by varying the concentrations of the entities in solution and the acidity of the medium, so as to form a precipitate comprising the other cations and to leave the uranium in solution. A further subject-matter of the invention is a process for the decontamination of radioactive aqueous effluents which consist in precipitating a product based on thorium phosphate from the effluent by addition of thorium and then of phosphoric acid to the effluent in amounts such that the P/Th molar ratio is from 1.4 to 2 and in heating in a closed container at a temperature of 50 to 250° C. in order to precipitate a product comprising thorium phosphate from the effluent, thus entraining the contaminating radioactive cations. Other characteristics and advantages of the invention will become more clearly apparent on reading the description which follows of examples, of course given by way of illustration and without implied limitation, with reference to the appended drawings. a) Preparation of the Precursor A thorium solution is prepared by dissolving 4 g of solid ThCl4 in a 2M hydrochloric acid solution in a Teflon container to obtain a thorium concentration of 0.7M. A 5M phosphoric acid H3PO4 solution, obtained by diluting approximately 14M concentrated acid with deionized water, is gradually added to this solution with stirring to obtain a phosphoric acid/thorium molar ratio of 3/2 with an excess of phosphoric acid of 2%. Stirring is then halted and the container is closed and heated at a temperature of 150° C. on a sand bath for 21 days. The gel initially formed is converted under these conditions to a precipitate. The reaction which occurs results in the production of a crystalline thorium phosphate. The container is cooled and the precipitate is allowed to separate by settling until a clear supernatant is obtained. The supernatant is removed using a pipette and is replaced with deionized water. The combined mixture is suspended by stirring, the precipitate is then allowed to separate by settling and the operation is repeated until a supernatant is obtained with a pH in the region of that of the deionized water. The precipitate is then filtered off on a sintered glass funnel under vacuum and is then dried at 120° C. The X-ray diffraction diagram of the dried product is represented in FIG. 1. The infrared spectrum of the same product is represented in FIG. 2. If the diagram of FIG. 1 is compared with the diagram of the thorium phosphate/diphosphate (TPD) illustrated in FIG. 1 of WO 96/30300 [1], it is noticed that this product is different from the thorium phosphate/diphosphate; it is a precursor of the TPD. b) Preparation of the TPD The precursor obtained above can be converted to thorium phosphate/diphosphate by subjecting it first of all to a precalcination at 400° C. for 2 h and then to a calcination at a temperature of 1150° C. for 10 h. The characteristics of the calcined product clearly correspond to those of the thorium phosphate/diphosphate of the document [1]. a) Preparation of the Precursor The same procedure is followed as in Example 1. Thus, a uranium(IV) solution is first of all prepared by dissolution of 4 g of UCl4 in a 4M hydrochloric acid HCl solution in order to obtain a uranium concentration of 0.7M. This solution is mixed with a 5M phosphoric acid solution in the phosphoric acid/uranium(IV) molar ratio of 3/2 with an excess of 2% of phosphoric acid. The mixing is carried out in a container which is subsequently closed and which is heated, as in Example 1, at a temperature of 150° C. on a sand bath for 1 week. Under these conditions, the initial gel is converted by heating to a crystalline powder. The powder is separated, is washed and is then dried as in Example 1. The X-ray diffraction diagram of the product obtained is represented in FIG. 3. The infrared spectrum of this product is represented in FIG. 4. b) Preparation of the Uranium Phosphate The product obtained above is subjected to a precalcination and to a calcination as in Example 1 and a polyphase uranium phosphate system is thus obtained. Products based on protactinium(IV) phosphate, on neptunium(IV) phosphate or on plutonium(IV) phosphate can be prepared in the same way by using the same phosphoric acid/actinide(IV) molar ratio and by preparing the mixture from an acidic protactinium(IV), neptunium(IV) or plutonium(IV) solution. In this case, the preparation is carried out of a solution of thorium and of actinide(IV) in proportions which make it possible to obtain a phosphate/diphosphate of formula Th4-xMx(PO4)4P2O7 in which M represents the actinide(IV), with x exhibiting the following values: x≦3.75 for Pa(IV) x≦3 for U(IV) x≦2.14 for Np(IV) x≦1.67 for Pu(IV). The thorium solution obtained in Example 1 is mixed with an actinide solution, and mixing is carried out with a 5M phosphoric acid solution as in the preceding examples. The amounts of thorium, of actinide M and of phosphoric acid are such that the phosphoric acid/Th+M molar ratio is 3/2 with an excess of phosphoric acid of 2%. This mixture is subsequently subjected to heating in a closed container at a temperature of 150° C. on a sand bath for 1 week. The gel initially formed is converted to a powder. The powder is separated, is washed and is dried as in Example 1. The dried powder is very homogeneous and is composed of particles with a size of less than 3 μm. The corresponding specific surface is close to 10 m2/g, which confers a higher reactivity thereon. This high reactivity of the powder renders it highly advantageous for the conditioning of the radioactive actinides introduced into the thorium phosphate/diphosphate. This is because a powder is obtained which has better physicochemical properties than those of the powder obtained in the document [1]. The powder is subsequently subjected to a heat treatment at a temperature of 1250° C. for 10 h to form the solid solution of phosphate/diphosphate of thorium and of actinide(IV) of formula Th4-xMx(PO4)4P2O7. The specific surface of the powder significantly decreases for heat treatment temperatures greater than or equal to 800° C. Correspondingly, the size of the particles increases until it reaches 10 to 20 μm at 1250° C. If, prior to the heat treatment, the powder is compacted at 500 MPa, the density of the product reaches 95% of that calculated, after only 5 hours of heat treatment, which corresponds to approximately 5% of total porosity, approximately equally divided between open porosity and closed porosity. Furthermore, the specific surface of the pellets is between 750 and 1500 cm2/g, which makes it possible, during leaching tests, to reduce by a factor of approximately 6 the rate of dissolution of the solid with respect to that of the powder. In addition to the influence of the specific surface on the rate of leaching, studies undertaken confirm the very good physicochemical properties of confinement of the solid solution of phosphate/diphosphate of thorium and of tetravalent actinide, such as uranium(IV). Solutions of thorium (0.7M) and of uranium(IV) (0.6M) in a hydrochloric acid medium are mixed, as described in the preceding examples, so as to observe a Th/U molar ratio of 1.5, and then a 5M phosphoric acid solution is added in the PO4/(Th+U) molar ratio of 1.5. This mixture is placed in a closed container and is heated on a sand bath at 150° C. for 2 days. The crystalline precipitate of phosphate of thorium and of uranium(IV) thus obtained is filtered off, washed and then dried as described in Example 3. Beforehand, a gadolinium phosphate powder is prepared by precipitation (or evaporation to dryness), heated at 150° C., filtered off, dried, milled and then treated at 1250° C. for 10 hours. The GdPO4 powder then crystallizes in the monazite structure. It is homogeneous and single-phase and is characterized by a specific surface of 1 to 3 m2/g and a mean particle size of less than 2 μm, which confers a high reactivity thereon. This powder is dispersed in the phosphate of thorium and of uranium(IV) in the phosphate of thorium and of uranium(IV)/gadolinium phosphate ratio by mass of 70/30. The mixture is milled, compacted at 500 MPa and then treated at 1250° C. for 10 hours under an inert atmosphere (for example, under an argon atmosphere). After heat treatment at 1250° C., a dense sintered glass is thus obtained, formed of a solid solution of phosphate/diphosphate of thorium and of uranium(IV) of formula Th2.4U1.6(PO4)4P2O7 comprising, in dispersion, gadolinium phosphate GdPO4 with a structure of monazite type. The gadolinium (used as neutron poison) can be partially substituted by americium and/or curium, while the uranium(IV) can be substituted by neptunium(IV) and/or plutonium(IV), which then makes it possible to prepare composite samples simultaneously comprising trivalent and tetravalent actinides. The starting material is a solution comprising 0.1M thorium nitrate and 0.1M uranyl nitrate in 2M nitric acid, and a 5M phosphoric acid H3PO4 solution is added thereto in order to have a phosphoric acid/thorium stoichiometric ratio of 1.5 with 2% excess of phosphoric acid. A gel is thus formed, which gel includes the ions, and then the gel is heated in a closed container at a temperature of 150° C. until a precipitate is obtained which comprises the precursor of the thorium phosphate/diphosphate, whereas the uranyl ion remains in the supernatant. Uranium(VI) can thus be recovered by separation by settling, filtration and washing. If the solution comprises other divalent cations, such as Ca2+, Ba2+ and Sr2+, and other trivalent cations, such as La3+, Gd3+ and Ce3+, the latter are entrained with the thorium phosphate in the precipitate form whereas uranium(VI) remains in solution. It is the same if the solution comprises other tetravalent actinides, which will be entrained in the solid phase with the thorium. The same procedure can be followed for decontaminating radioactive liquid effluents. [1] WO 96/30300
	claims	1. An optical module, comprising:a first component;a second component;a supporting structure; andan anticollision device,wherein:the first component is supported by the supporting structure;the first component is arranged a distance from the second component to define a gap;the supporting structure is configured to define a path of relative movement of the first component;the first component is configured to move along the path of relative movement in a direction of approach relative to the second component under an influence of a defined mechanical disturbance;the optical module is configured so that, when the anticollision device is absent or inactive, a collision between a first collision region of the first component and a second collision region of the second component occurs;the anticollision device comprises a first anticollision unit on the first component and configured to produce a first field;the anticollision device comprises a second anticollision unit on the second component, assigned to the first anticollision unit and configured to produce a second field;the first and second anticollision units are configured so that, as the first component and the second component increasingly approach each other along the path of relative movement, the first field and the second field produce an increasing counter-force on the first component that counteracts the approach;the first anticollision unit and/or the second anticollision unit comprises a plurality of anticollision elements configured to produce partial fields; andthe anticollision elements are assigned to each other so that, during use, a superimposition of their partial fields produces a field of the anticollision unit with a field line density that decreases more sharply with increasing distance from the anticollision unit along the path of relative movement than a field line density of one of the partial fields. 2. The optical module of claim 1, wherein the optical module is configured so that, during use, at least one of the following holds:the field line density of the field of the anticollision unit decreases exponentially with the distance from the anticollision unit;the field line density of the field of the anticollision unit decreases with the distance from the anticollision unit by a power of from five to 21; andthe superimposition of the partial fields of the anticollision unit produces a real field which, in interaction with a predefined counter-field, produces a predefined counter-force on the first component only at a distance between the first collision region and the second collision region which is smaller than in a theoretical reference state, for which the amounts of the theoretical partial forces that are obtained in the direction of approach from the respective partial field without the superimposition of the partial fields are added together. 3. The optical module of claim 1, wherein the first anticollision unit comprises N first anticollision elements, the second anticollision unit comprises M second anticollision elements, and at least one of the following holds:N is equal to M;N and/or M is an even number;N equals 2 to 20; andM equals 2 to 20. 4. The optical module of claim 1, wherein the optical module is configured so that, during use, at least one of the following holds:the anticollision elements of at least one of the anticollision units, in their interior, define an inner field direction of the partial field with an inner polarity;the anticollision elements of the at least one anticollision unit are arranged in a substantially annular arrangement in a plane extending transversely; andthe anticollision elements of the at least one anticollision unit are arranged in a substantially annular arrangement in a plane perpendicular to the inner field direction of one of the anticollision elements. 5. The optical module of claim 4, wherein the optical module is configured so that, during use, at least one of the following holds:at least two anticollision elements of the at least one anticollision unit are arranged along a circumferential direction of the annular arrangement so that they have a substantially opposed inner polarity;the anticollision elements of the at least one anticollision unit, at least section wise along a circumferential direction of the annular arrangement, are arranged with alternating polarity of the inner field direction; andthe inner field directions of at least two anticollision elements of the at least one anticollision unit are substantially parallel. 6. The optical module of claim 1, wherein the optical module is configured so that, during use:in a state of rest without any influence of the mechanical disturbance, the first and second collision regions are at an at-rest distance along the direction of approach;the first and second anticollision units produce a negligible first counter-force on the first component;for the first and second collision regions, there is a predefined minimum distance along the direction of approach, below which the approach must not go under the effect of the mechanical disturbance and at which the first and second anticollision units produce a second counter-force on the first component; andfor the first and second collision regions, there is an intermediate distance along the direction of approach which is achieved under the effect of the mechanical disturbance, which lies between the at-rest distance and the minimum distance and at which the first and second anticollision units produce a third counter-force on the first component that is not negligible and has a magnitude between the first counter-force and the second counter-force. 7. The optical module of claim 6, wherein the optical module is configured so that, during use, at least one of the following holds:the minimum distance is 3% to 20% of the at-rest distance;the intermediate distance is 20% to 70% of the at-rest distance;the at-rest distance is 0.2 mm to 1.0 mm;the minimum distance is 0.015 mm to 0.1 mm; andthe intermediate distance is 0.2 mm to 0.02 mm. 8. The optical module of claim 7, wherein wherein the optical module is configured so that, during use, at least one of the following holds:the first counter-force is less than 3% to 20 of the second counter-force;the third counter-force is less than 20% to 70% of the second counter-force; andthe third counter-force is 350% to 750% of the first counter-force. 9. The optical module of claim 6, wherein wherein the optical module is configured so that, during use, at least one of the following holds:the first counter-force is less than 3% to 20 of the second counter-force;the third counter-force is less than 20% to 70% of the second counter-force; andthe third counter-force is 350% to 750% of the first counter-force. 10. The optical module of claim 1, wherein wherein the optical module is configured so that, during use:the path of relative movement, at every point, defines a distance between the first and second collision regions along the direction of approach;for the first and second components, a minimum distance of the first and second collision regions in the direction of approach is predefined, below which the approach must not go under the effect of the mechanical disturbance; andthe counter-force produced by the first and second anticollision units on the first component, which counteracts the approach caused by the mechanical disturbance, reduces a relative speed between the first and second collision regions along the direction of approach to a value of zero at the latest when the minimum distance is reached. 11. The optical module of claim 1, wherein the first anticollision unit is in the region of the first collision region, and the second anticollision unit is in the region of the second collision region. 12. The optical module of claim 11, wherein the third anticollision unit is in the region of the third collision region, and the fourth anticollision unit is in the region of the fourth collision region. 13. The optical module of claim 11, wherein the optical module is configured so that, during use:the further mechanical disturbance is different at least in its direction of effect from that of the mechanical disturbance; andthe supporting structure defines the further path of relative movement of the first component, which is different from the path of relative movement and on which the first component moves along a further direction of approach in relation to the second component under the influence of the further mechanical disturbance. 14. The optical module of claim 1, wherein the optical module is configured so that, during use:the anticollision device comprises a third anticollision unit located a distance from the first anticollision unit;the third anticollision unit is on the first component;the third anticollision unit produces a third field;the anticollision device comprises a fourth anticollision unit located a distance from the second anticollision unit;the fourth anticollision unit is on the second component;the fourth anticollision unit is is assigned to the third anticollision unit;the fourth anticollision produces a fourth field;when the anticollision device is absent or inactive, a collision between a third collision region of the first component and a fourth collision region of the second component occurs under the influence of the mechanical disturbance and/or a further mechanical disturbance; andthe third and fourth anticollision unit and the fourth anticollision units are configured so that, with an increasing approach of the third and fourth collision regions along the path of relative movement or along a further path of relative movement, the third and fourth fields produce an increasing further counter-force on the first component that counteracts the approach. 15. The optical module of claim 14, wherein the optical module is configured so that, during use:the third anticollision unit and/or the fourth anticollision unit comprises a plurality of further anticollision elements that produce further partial fields; andthe further anticollision elements are assigned to each other so that the superimposition of their further partial fields produces a further field of the anticollision unit with a field line density that decreases more sharply with increasing distance from the anticollision unit along the path of relative movement than a field line density of one of the further partial fields. 16. The optical module of claim 14, wherein the third anticollision unit is in the region of the third collision region, and the fourth anticollision unit is in the region of the fourth collision region. 17. The optical module of claim 14, wherein the optical module is configured so that, during use:the further mechanical disturbance is different at least in its direction of effect from that of the mechanical disturbance; andthe supporting structure defines the further path of relative movement of the first component, which is different from the path of relative movement and on which the first component moves along a further direction of approach in relation to the second component under the influence of the further mechanical disturbance. 18. The optical module of claim 1, wherein at least one of the following holds:during use, at least one of the anticollision elements of at least one of the anticollision units produces a magnetic partial field and/or an electric partial field; andat least one of the anticollision elements of at least one of the anticollision units comprises a permanent magnet. 19. An optical imaging device, comprising:an illumination device comprising a first optical element group;a projection device comprising a second optical element group; andan image device,wherein:the illumination device is configured to illuminate an object;the projection device is configured to project an image of the illuminated object onto the image device;the illumination device and/or the projection device comprises an optical module according to claim 1; andthe optical imaging device is a microlithography optical imaging device. 20. A method of using an optical device comprising an illumination device, a projection device and an image device, the method comprising:using the illumination device to illuminate an object; andusing the projection device to project the illuminated object onto the image device,wherein the illumination device and/or the projection device comprises an optical module according to claim 1.
053612922	description	DETAILED DESCRIPTION OF THE INVENTION This system may be configured in a variety of ways by varying the mirror configurations and in other ways as well. One of the primary advances herein is the ability to separate the light from a quasi point source into several equal arcs that are then superimposed on each other at the ring field radius, thus maximizing the collection efficiency of the condenser. The scope of this invention should not be limited to these specific embodiments but rather be defined by the claims. Both embodiments are designed to use a laser plasma source of soft x-rays that radiates at 14 nm. The diameter and height of the source is specified as about 150 .mu.m. The camera at the other end of the system images a 60 degree, 125 mm long by 5 mm wide ring field onto the wafer at 5.times. reduction. The entrance pupil is 3.6 m behind the reflective object mask, and the numerical aperture of the camera is n.a.=0.08. Turning to the first embodiment of this system, the illuminator or collecting mirrors are composed of five off-axis segments of an aspheric mirror, each 60 degrees wide, producing five beams which each cross over the system axis or centerline 11 as defined by the source and the center of the parent mirror. The parent aspheric mirror 10 images the "point" source 12 into a ring image 14 as shown in FIG. 1. Therefore, its cross-section in the r-z plane is elliptical with one of the foci at the plasma source and the other at the ring field radius. Each of the 60 degree mirror segments images the source into a 60 degree segment of the ring image. Four of the five segments are shown in FIG. 1. FIG. 2 shows both a side view and an isometric view of the beam from one segment 20 of the aspheric mirror, with the isometric view rotated relative to the side view about a line 25 passing through the area of the beam having a smallest beam cross section. It shows the shape of the collector mirror 20, the arc image 22, and the bow-tie-shaped minimum beam cross-section 24, which is located at the center of the axial line focus. This design gives uniform illumination and image quality along the length of the arc 22. The five beams need to be directed so that their 60 degree ring focus segments are all superimposed in the camera's 60 degree ring field. Furthermore, all five beams must be aimed through the camera's virtual entrance pupil 49. In this embodiment, four of the five beams are translated and rotated by individual sets of three Rhodium-covered grazing-incidence flat mirrors 41, 42 and 43 such that their images at the ring field radius fall onto that of the fifth beam, which was undeviated by the correcting mirrors. The correcting mirrors are arranged similarly to the reflecting surfaces in a conventional "K-prism." The three mirrors used here allow enough degrees of freedom to rotate and translate the ring focus segments so that they overlap at the ring field and pass the beams through the real entrance pupil without overlapping. FIG. 3 is an end view of the system showing the five beams in the plane of the entrance pupil of the camera in their narrowest, bow-tie forms, in their uncorrected positions in solid lines 30, 32, 33, 34, and 35 and in their translated and rotated positions 32', 33', 34' , and 35' as shown in dotted lines. As can be seen, the bottom beam passes through the real entrance pupil 36 uncorrected while the other four beams are corrected by the K-mirror sets aligned in the various individual planes defined by the bow-tie centers at their uncorrected positions and the bow-tie center of the uncorrected beam 30. The five beams in the narrow, bow-tie forms efficiently fill the entrance pupil 36 without overlapping. A superior configuration is for the centers of the five bow-ties to fall onto an ellipse within the pupil rather than a circle as will be discussed below. The overall layout of this embodiment for one beam can be seen in FIG. 4. The radiation is collected from the source 12 by one of the mirror segments 40. Its beam is then translated and rotated by the set of correcting K-mirrors 41, 42, and 43 and passed through the real entrance pupil 44 of the camera as shown. The beam is then reflected off the imaging mirror 45 and onto the reflective mask 46. The imaging mirror 45 here is shown as a reflecting sphere. Somewhat better efficiency can be achieved by use of another grazing-incidence mirror which will flip the beam out to the right rather than fold it back as shown here. In this manner the condenser system delivers the five overlapped ring field segments at the ring field radius 48 which falls onto the reflective mask 46. System efficiency is a function of the size of the source and the reflectivity of the mirrors. The collection efficiency depends on the Entendu of the whole optical system. The Entendu or Lagrange invariant derived from the theorum of conservation of energy and indicates that, for an unvignetted pencil of light, the product of image height and numerical aperture is the same at all image planes in the system. This leads to an equivalence between source parameters (diameter and collection angle) and camera parameters (ring field width and numerical aperture). If one were to illuminate the ring field with only one beam, one could use the entire numerical aperture for it. However, with five beams one can only use about one fifth of the entrance pupil area for each beam. Thus, the camera parameters together with the 150 .mu.m source size limit the beam collection angle to about 50 degrees in elevation (and by 5.times.60 degrees=300 degrees in azimuth). This results in a total collection efficiency of about 50%. The transmission efficiency of the beam lines depends on the reflectivity of the mirrors. At 14 nm, the theoretically perfect reflectivities are 56%, 82%, 65%, 82%, and 82%, where the first number is the average reflectivity of the aspheric collector, the next three are for the grazing-incidence flats at various tilt angles, and the last is for the reimaging sphere. The product of these ideal reflectivities is 20%, which means that theoretically, 10% of the soft x-rays from the source can be delivered to the mask. With real reflectivities, one can expect more on the order of 7% to be delivered. Each segment of the parent mirror is astigmatic, having different circumferential and tangential focal planes. The circumferential image is the on-axis line focus shown in FIG. 2. This line is centered in the real entrance pupil, essentially giving Kohler illumination along the ring field. The tangential image (in the r-z plane) is located at the ring field, giving critical illumination. In a normal, non-scanning system this would give intensity and image quality variations in the radial direction. However, the scanning integrates out these radial variations. Hence, one is left with the uniform image quality which can only be achieved with Kohler illumination in a non-scanned system. Partial coherence in the illumination affects the image quality. In an incoherently illuminated optical system, small features are attenuated due to the fall-off of the modulation transfer function (MTF). Partial conherence can be introduced into the illumination to counter this attenuation. This normally done by underfilling the entrance pupil in a system with Kohler illumination. Put a different way, the source (which is usually a disk) is imaged into the entrance pupil, and this image is smaller than the pupil by a factor of .sigma..apprxeq.0.6. This value of .sigma. is a reasonable compromise which amplifies the small features and does not add too much "ringing" to the larger features. The entrance pupil illumination for this embodiment is shown in FIG. 3. It is obviously not a disk; rather, it is five bow-tie beam cross-sections arranged in a circle. Although the imaging of this system has not been analyzed in detail, study has been made of a five point pattern where the points are symmetrically located on a circle. It is interesting that this illumination pattern creates an image almost identical to a disk with .sigma..apprxeq.0.5. This similarity between the disk and the five point pattern implies that the five-fold symmetry is a very serendipitous choice. In this embodiment, there are five line sources in the entrance pupil, rather than five points. If their centers were located symmetrically on a circle, there would be some variation in the effective .sigma. value for features oriented radially or circumferentially. However, these variations can be removed by locating the line sources on an ellipse rather than on a circle. Further investigations of the invention resulted in another embodiment 50 which is illustrated in side view in FIG. 5. Here all, 52 et al., but one of the aspheric mirror segments are aligned to transmit their beams in parallel to the system centerline 60. The one remaining mirror segment 51 is tilted down towards the centerline 60 as shown in order to divert its beam 57 away from the correcting mirrors 53 and 54 et al. used on the other four segments. This unrotated beam 57 is translated by its two mirror set 58 and 59 to get around the correcting mirror sets for the other four rotated beams. The three-mirror sets used for rotation and translation for the first embodiment are here replaced with steeply tilted roof mirror pairs 53 and 54, and corresponding other pairs for the other beams which are not shown in this view. They do the same job but remove one reflective surface from the system and fold the beam line back onto itself. If a spherical imaging mirror 56 is employed as shown, the beam line can be folded back once more, resulting in a fairly compact configuration. By replacing the three mirror set which has reflectivities of 81%, 61%, and 81% with a two mirror set with reflectivities of 81% and 68%, the system efficiency can be improved up to about 25% with only a slight loss in bandwidth. The two mirror set used for translation and rotation is configured with the first mirror 53 tilted about 10 degrees from grazing and the second mirror 54 being a near-normal multilayer with similarly employed sets being used for the other translated and rotated beams. The two together act as an off-axis roof mirror which will rotate the image in the same manner as the K-mirror set used above. The four beams that are rotated still pass through the position of the unrotated beam. The multilayer mirrors tilt each beam up slightly so they miss the collector mirrors as they are folded back. The fifth beam 57 is not rotated, so its aspheric mirror segment can be tilted down slightly as shown. Once the beams have interacted with their respective two-mirror sets, the beams are handled as in the first embodiment. As with the first embodiment, the five beams are superimposed at the ring field radius 63 onto the mask 62. Any tilt errors remaining in the system can be easily nulled. It is possible to make a number of modifications to the these two embodiments. For example one might rotate and translate all five beams at the risk of adding some complexity and loss to the system so long as all the beams still passed through a single real entrance pupil of the camera about one of the beams and ended up superimposed at the ring field radius. These and many other variations are possible. The true scope of the invention is to be found in the claims.
	summary
048658022	description	DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 therein is depicted a schematic of a power system for use in a substantially zero gravity environment, such as an orbiting satellite or a spacecraft. The system includes a reactor 12 for heating a primary coolant fluid, a conduit 14 and a pump, typically an electromagnetic pump 16, for inducing a flow of heated primary fluid to a heat exchanger 18. A conduit 20 provides for return of the primary fluid to reactor 12. A working fluid is passed in indirect heat exchange relationship with the primary fluid via conduits 22 and 24 which circulate the working fluid through a power conversion system 26. Power conversion system 26 converts the heat in the working fluid to electrical energy for use, for example, as the source of power for data acquisition and transmission devices on an oribiting satellite. The primary fluid flowing through reactor 12 may range in temperature by as much as 1,000K during normal operation. This temperature differential results in either thermal expansion or contraction of the fluid, thus it is essential there be provided means for accommodating such expansion and contraction. As depicted, this is accomplished by an accumulator 28 which is in fluid communication with conduit 20. It will be appreciated that the precise location is not critical and accumulator 28 could be placed in fluid communication with the primary fluid at any point in the system. Referring now to FIG. 2, therein is depicted in cross-section a schematic of accumulator 28. In the preferred embodiment shown, accumulator 28 comprises a closed vessel 30 provided at an end thereof with a conduit 32. Located within vessel 30 is a grid plate 34 which is surrounded by and in sealing engagement with the walls of vessel 30. Grid plate 34 is provided with a plurality of openings, one for each tube, for receiving and supporting a plurality of tube members 36. Each of tube members 36 is provided with an internal passageway which provides the sole means of fluid communication between a liquid zone 38 and a gas zone 40. The apparatus further includes a body of liquid in liquid zone 38 which extends at least partially into each of tubes 36 wherein it is contained by capillary action. The surface tension of the liquid forms a meniscus in each tube which acts as a gas-liquid interface 42 forming a barrier to the body of gas contained in gas zone 40 and an upper portion of each of tubes 36. Alternatively, the body of gas may be contained within each individual tube by sealing an end 37 of the tube 36. Given the direction and intent of the present invention the precise size of the passageways within each of tubes 36 is readily determinable by the artisan. For the containment of the liquid metal in a substantially zero gravity environment, tubes 36 will typically have an internal diameter within the range of from about 0.5 to 10 millimeters. In selecting the precise size, consideration must be given of course, to the acceleration forces to which the apparatus will be exposed during operation as well as the direction of such forces. In a similar manner, the length and nubmer of tubes will be determined by the volume of liquid which must be accommodated. In addition, in some instances, to assist the apparatus in withstanding higher acceleration loadings, a screen could be placed beneath grid member 34. When a screen is used, it will typically have a size of from about 30.times.30 to 500.times.500 mesh standard sieve size. The operation of the device depicted in FIG. 2 will be described with reference to a particularly preferred application, namely, accommodating the thermal expansion of a primary coolant for a nuclear reactor required to operate in a substantially zero gravity environment. Typically, the coolant for such a reactor will be a liquid metal such as sodium, potassium, lithium or a mixture of sodium and potassium. Conduit 32 is placed in fluid communication with the primary coolant loop. Upon thermal expansion of the coolant, it will flow into liquid zone 38 displacing that coolant previously there and compressing the gas in gas zone 40. Generally the gas will be one of more of the inert gases from group VIIIa of the Periodic Table of the Elements. The more common gases for such use are helium and xenon or mixtures thereof. When the reactor output power is reduced, the coolant temperature will decline and the volume of coolant contract. At that time, the gas in gas zone 40 will expand pushing the liquid back through conduit 32 and back into the system from which it was drawn. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.
048572640	abstract	A pressurized water reactor of an advanced design comprises, in vertically spaced relationship, a lower barrel assembly having lower and upper core plates, an inner barrel assembly and an axially removable calandria assembly having a lower calandria plate. A plurality of rod guides are cantilever-mounted in parallel axial relationship within the inner barrel assembly by rigidly mounting the lower ends thereof to the upper core plate. Axially extending sleeves affixed to the upper ends of the rod guides and telescopingly receive therein generally cylindrical supports which are affixed to and depend downwardly from the lower calandria plate and define alignment axes for the respectively associated rod guides. Axially extending leaf springs in each sleeve are normally biased radially inwardly and, in the assembled relationship of the calandria and inner barrel assemblies, resiliently and frictionally engage the respective cylindrical supports to maintain alignment and react both lateral and axial loads. Load pick-up surfaces of non-yielding sleeve portions react excessive loads directly into the lower calandria plate. Mating top end supports for RCC and WDRC rod guides permit dense packing of same, while internal openings of the top end supports permit telescoping movement of the corresponding rod clusters therethrough to permit ease of assembly and disassembly operations.
	claims	1. A nuclear reactor comprising:a generally cylindrical pressure vessel defining a cylinder axis;a nuclear reactor core disposed in the generally cylindrical pressure vessel;a central riser disposed coaxially inside the generally cylindrical pressure vessel, the central riser being hollow and having a bottom end proximate to the nuclear reactor core to receive primary coolant heated by the nuclear reactor core, the central riser having a top end distal from the nuclear reactor core; anda once-through steam generator (OTSG) comprising tubes arranged parallel with the cylinder axis in an annular volume defined between the central riser and the generally cylindrical pressure vessel, primary coolant discharged from the top end of the central riser flowing inside the tubes toward the nuclear reactor core, the OTSG further including a fluid flow volume having a feedwater inlet and a steam outlet wherein fluid injected into the fluid flow volume at the feedwater inlet and discharged from the fluid flow volume at the steam outlet flows outside the tubes in a direction generally opposite flow of primary coolant inside the tubes;wherein the nuclear reactor has an operating state in which fluid comprising feedwater injected into the fluid flow volume at the feedwater inlet is converted by heat transfer from primary coolant flowing inside the tubes into steam that is discharged from the fluid flow volume at the steam outlet; andwherein the tubes of the OTSG are secured in a support including a pair of tubesheets made of steel and the tubes are supported at their ends by the tubesheets,wherein the tubes comprise a material having a higher coefficient of thermal expansion than steel and are in axial tension in a non-operating state of the nuclear reactor in which the tubes of the OTSG are at a temperature of less than 100° C. and are in axial compression in the operating state. 2. The nuclear reactor as set forth in claim 1, wherein:in the operating state of the nuclear reactor the primary coolant flowing in the tubes of the OTSG is at a temperature of at least 500° C. 3. The nuclear reactor as set forth in claim 2, wherein the tubes of the OTSG are made of an austenitic nickel-chromium-based alloy and the tubes are secured in the tubesheets which are attached to the central riser and the pressure vessel, wherein the central riser and pressure vessel are made of a steel, and wherein the austenitic nickel-chromium-based alloy has a higher coefficient of thermal expansion than the steel. 4. The nuclear reactor as set forth in claim 1, wherein:the tubesheets are attached to the central riser and the pressure vessel wherein the central riser and the pressure vessel are made of steel; andends of the tubes are expanded to secure to the tubesheets whereby the tubes are under axial tension due to the Poisson effect. 5. An apparatus comprising:a pressurized water nuclear reactor (PWR) including a pressure vessel, a nuclear reactor core disposed in the pressure vessel, and a vertically oriented hollow central riser disposed above the nuclear reactor core inside the pressure vessel; anda once-through steam generator (OTSG) disposed in the pressure vessel of the PWR, the OTSG including vertical tubes having a higher coefficient of thermal expansion than steel arranged in an annular volume defined by the central riser and the pressure vessel and secured in a support made of steel, the OTSG further including a fluid flow volume surrounding the vertical tubes;wherein the PWR has an operating state in which primary coolant at a temperature of at least 500° C. flows in the tubes of the OTSG and in which feedwater injected into the fluid flow volume at a feedwater inlet is converted to steam by heat emanating from the primary coolant flowing inside the tubes of the OTSG, and the steam is discharged from the fluid flow volume at a steam outlet; andwherein the tubes of the OTSG are in axial tension in a non-operating state of the PWR in which the tubes of the OTSG are at a temperature of less than 100° C. and are in axial compression in the operating state. 6. The apparatus as set forth in claim 5, further comprising:a flow diverter disposed in the generally cylindrical pressure vessel above the central riser, the flow diverter having a flow-diverting surface facing a top of the central riser that is at least one of sloped and curved to redirect primary coolant discharged from the top of the central riser toward inlets of the tubes of the OTSG. 7. The apparatus as set forth in claim 6, wherein the flow diverter divides the pressure vessel into an upper integral pressurizer volume and a remaining lower interior volume, and in the operating state the upper integral pressurizer volume contains fluid at a temperature greater than a temperature of the primary coolant disposed in the remaining lower interior volume of the pressure vessel. 8. The apparatus as set forth in claim 5, wherein the pressure vessel is divided into an upper integral pressurizer volume and a remaining lower interior volume, and in the operating state the upper integral pressurizer volume contains fluid at a temperature greater than a temperature of the primary coolant disposed in the remaining lower interior volume of the pressure vessel. 9. The apparatus as set forth in claim 8, further comprising:neutron-absorbing control rods; anda control rod drive mechanism (CRDM) configured to controllably insert and withdraw the control rods into and out of the nuclear reactor core;wherein no portion of the CRDM is disposed in or passes though the integral pressurizer volume. 10. The apparatus as set forth in claim 5, wherein:in the operating state of the nuclear reactor the primary coolant flowing inside the tubes is at a higher pressure than the fluid in the fluid flow volume. 11. The apparatus as set forth in claim 5, wherein the tubes of the OTSG are prestressed to place the tubes in axial tension in the non-operating state of the PWR in which the tubes of the OTSG are at a temperature of less than 100° C. by operations including:mounting the tubes in the tubesheets by expanding the tube ends to secure them to the tubesheets, whereby axial tension is imparted to the tubes. 12. An apparatus comprising:a pressurized water nuclear reactor (PWR) including a pressure vessel, a nuclear reactor core disposed in the pressure vessel, and a vertically oriented hollow central riser disposed above the nuclear reactor core inside the pressure vessel;a once-through steam generator (OTSG) disposed in the pressure vessel of the PWR, the OTSG including vertical tubes having a higher coefficient of thermal expansion than steel arranged in an annular volume defined by the central riser and the pressure vessel and secured in a support made of steel, the OTSG further including a fluid flow volume surrounding the vertical tubes;neutron-absorbing control rods; anda control rod drive mechanism (CRDM) configured to controllably insert and withdraw the control rods into and out of the nuclear reactor core;wherein the PWR has an operating state in which primary coolant at a temperature of at least 500° C. flows in the tubes of the OTSG and in which feedwater injected into the fluid flow volume at a feedwater inlet is converted to steam by heat emanating from the primary coolant flowing inside the tubes of the OTSG, and the steam is discharged from the fluid flow volume at a steam outlet;wherein the tubes of the OTSG are in axial tension in a non-operating state of the PWR in which the tubes of the OTSG are at a temperature of less than 100° C. and are in axial compression in the operating state;wherein the pressure vessel is divided into an upper integral pressurizer volume and a remaining lower interior volume, and in the operating state the upper integral pressurizer volume contains fluid at a temperature greater than a temperature of the primary coolant disposed in the remaining lower interior volume of the pressure vessel; andwherein no portion of the CRDM is disposed in or passes though the integral pressurizer volume. 13. The apparatus as set forth in claim 12, further comprising:a flow diverter disposed in the generally cylindrical pressure vessel above the central riser, the flow diverter having a flow-diverting surface facing a top of the central riser that is at least one of sloped and curved to redirect primary coolant discharged from the top of the central riser toward inlets of the tubes of the OTSG. 14. The apparatus as set forth in claim 13, wherein the flow diverter divides the pressure vessel into an upper integral pressurizer volume and a remaining lower interior volume, and in the operating state the upper integral pressurizer volume contains fluid at a temperature greater than a temperature of the primary coolant disposed in the remaining lower interior volume of the pressure vessel.
047598999	claims	1. A nuclear reactor comprising: a closed vessel containing a pool of secondary coolant; a reactor core located within said pool, said core having an upper end and a lower end, and having a plurality of passages extending therebetween to enable upward flow of coolant through the core; an inlet conduit system for directing primary coolant to said lower end of said core, said inlet conduit system having one or more openings formed therein to enable fluid communication between said inlet conduit system and said pool; pumping means for effecting flow of said primary coolant into said inlet conduit system; an outlet conduit system located above said core for receiving coolant from said upper end of said core and carrying it to an exterior outlet pipe, said outlet conduit system having one or more openings therein to enable fluid communication between said outlet conduit system and said pool; and pressure reduction means for reducing fluid pressure in said inlet conduit system adjacent all of said one or more openings therein by locally increasing fluid velocity adjacent all of said one or more openings, thereby providing a balance between pressure within the inlet conduit system and pool pressure adjacent said one or more openings, substantially preventing flow of coolant through said openings in said inlet and outlet conduit system during operation of said pumping means; said pressure reduction means being responsive to variations in flow rate to enable forced flow of said primary coolant through said core at various rates selected independently of core reactivity without undesirable intermixing of primary and secondary coolant; whereby under normal operating conditions, coolant flows in a primary cooling circuit and flow through said openings is minimal, but in the event of failure of said coolant supply means, natural convection will cause secondary coolant from said pool to circulate through a secondary cooling circuit into said openings in said inlet conduit system, through said core, and out of said openings in said outlet conduit system. a closed vessel containing a pool of secondary coolant; a core located within said pool, said core having an upper end and a lower end, and having a plurality of passages extending therebetween to enable upward flow of coolant through the core; an inlet conduit system for directing primary coolant to said lower end of said core from an exterior coolant supply pipe, said inlet conduit system having one or more openings formed therein to enable fluid communication between said inlet conduit system and said pool; an outlet conduit system located above said core for receiving coolant from said upper end of said core and carrying it to an exterior outlet pipe, said outlet conduit system having one or more openings therein to enable fluid communication between said outlet conduit system and said pool; pumping means for forcing liquid coolant into said inlet conduit system; and means for locally increasing coolant velocity within said inlet conduit system all of adjacent said openings therein so as to balance pressure within said inlet conduit system adjacent said openings with pressure in said pool adjacent said openings; whereby under normal operating conditions, coolant flows in a primary cooling circuit which includes said exterior pipes and flow through said openings is minimal, but in the event of failure of said coolant supply means, natural convection will cause secondary coolant from said pool to circulate through a secondary cooling circuit into said openings in said inlet conduit system, through said core, and out of said openings in said outlet conduit system. a closed vessel containing a pool of secondary coolant; a core located within said pool, said core having an upper end and a lower end, and having a plurality of passages extending therebetween to enable upward flow of coolant through the core; an inlet conduit system for directing primary coolant to said lower end of said core from an exterior coolant supply pipe, said inlet conduit system having one or more openings formed therein to enable fluid communication between said inlet conduit system and said pool; an outlet conduit system located above said core for receiving coolant from said upper end of said core and carrying it to an exterior outlet pipe, said outlet conduit system having one or more openings therein to enable fluid communication between said outlet conduit system and said pool; pumping means for forcing liquid coolant into said inlet conduit system; and means for locally increasing coolant velocity within said inlet conduit system adjacent said openings therein so as to balance pressure within said inlet conduit system adjacent said openings with pressure in said pool adjacent said openings; whereby under normal operating conditions, coolant flows in a primary cooling circuit which includes said exterior pipes and flow through said openings is minimal, but in the event of failure of said coolant supply means, natural convection will cause secondary coolant from said pool to circulate through a secondary cooling circuit into said openings in said inlet conduit system, through said core, and out of said openings in said outlet conduit system; said means for locally increasing coolant velocity comprising one or more venturi throats; each of said openings in said inlet conduit system comprising an annular gap in one of said venturi throats; said nuclear reactor further comprising adjustable means for varying internal cross-sectional area in said one or more venturi throats; said adjustable means comprising one or more movable, generally conical obstructions. 2. A nuclear reactor in accordance with claim 1 further comprising means for cooling said pool of secondary coolant by natural convection. 3. A nuclear reactor comprising: 4. A reactor in accordance with claim 3 wherein said inlet conduit system includes a length of pipe having a minimum internal cross-sectional area adjacent said openings. 5. A nuclear reactor in accordance with claim 3 wherein said means for locally increasing coolant velocity comprises one or more venturi throats. 6. A nuclear reactor in accordance with claim 5 wherein each of said openings in said inlet conduit system comprises an annular gap in one of said venturi throats. 7. A nuclear reactor in accordance with claim 6 further comprising adjustable means for varying internal cross-sectional area in said one or more venturi throats. 8. A reactor in accordance with claim 7 wherein said adjustable means comprises one or more movable, generally conical obstructions. 9. A reactor in accordance with claim 3 further comprising means for cooling said pool. 10. A reactor in accordance with claim 9 wherein said means for cooling said pool includes a reservoir of tertiary coolant located outside of said vessel; a cooler for circulation of said tertiary coolant located within said vessel; and means for enabling circulation of said tertiary coolant between said reservoir and said cooler and through said cooler, and wherein said reservoir is located so as to enable circulation of coolant from said reservoir to said cooler by natural convection. 11. A reactor in accordance with claim 10 wherein said cooler is configured so that said tertiary coolant is heated as it flows through said cooler and travels upward as it is heated. 12. A nuclear reactor comprising:
055662170	summary	TECHNICAL FIELD The present invention relates to a spacer for nuclear fuel rods and particularly to a reduced height spacer having minimum spacer material with consequent minimum impact on fuel bundle performance. BACKGROUND In nuclear reactors, for example, a boiling water reactor, nuclear fuel rods are grouped together in an open-ended tubular flow channel, typically referred to as a fuel assembly or bundle. A plurality of fuel assemblies are positioned in the reactor core in a matrix and a coolant/moderator flows upwardly about the fuel rods for generating steam. Fuel rods are supported between upper and lower tie plates in side-by-side parallel arrays. Spacers are employed at predetermined elevations along the fuel bundle to restrain the fuel rods from bowing or vibrating during reactor operation. Typical spacers often include a plurality of ferrules arranged in side-by-side relation and secured, for example, by welding to one another to form the support matrix of the spacer for the nuclear fuel rods. Generally, each ferrule includes circumferentially spaced protuberances and a spring assembly along an opposite side of the ferrule from the protuberances for centering and biasing each fuel rod against the protuberances, thereby maintaining the fuel rods in fixed relation one to the other across the spacer. Generally, the role of a spacer in a fuel bundle is to position the fuel rods for peak performance and to protect the fuel rod assembly during possible loading events, such as handling and shipping. The spacer itself, however, constitutes an obstacle to bundle performance in that its cross-section interferes with the flow of water/moderator through the bundle. An ideal spacer would have minimal impact on bundle performance (thermal hydraulics, critical power), while still restraining the rods in their intended positions and protecting them. Consequently, an optimum spacer should have as little cross-section as possible, use a minimum amount of material and simultaneously meet structural requirements for positioning and protecting the fuel rods. DISCLOSURE OF THE INVENTION According to the present invention, there is provided a spacer which employs ferrules to capture and retain the nuclear fuel rods in the bundle in the intended array. Ferrules are employed because of their excellent structural integrity as compared with other possible cross-sectional shapes. By shortening the height of the ferrule in accordance with the present invention, the structural integrity of the ferrule is retained, while simultaneously, the magnitude of the material employed in the spacer is greatly reduced. A separate spring, also having a reduced quantity of material, is provided for each ferrule and along a side thereof opposite a pair of stops formed along the interior ferrule surface. The spring constitutes a leaf spring extending above and below the opposite edges of the ferrule and having upper and lower contact points for engaging the fuel rod and biasing it against the stops. A central portion of the spring extends in a central opening of the ferrule and projects in an opposite direction toward an adjacent ferrule. Thus, the adjacent ferrule, which is welded to the one ferrule, provides a reaction force for the spring so that the spring biases the fuel rod in the one ferrule against its stops. That is, the spring preloads the fuel rod in one ferrule by engaging it at locations above and below the opposite edges of the one ferrule and engaging the adjacent ferrule to provide a reaction force for the spring. This ferrule configuration thus meets the requirements for a spacer having minimum material and cross-section and the necessary structural requirements. In a preferred embodiment according to the present invention, there is provided a subassembly for a spacer useful in a nuclear fuel bundle for maintaining a matrix of a plurality of nuclear fuel rods passing through the spacer in spaced-apart relation, comprising first and second ferrules lying adjacent one another for receiving respective nuclear fuel rods, each ferrule having a pair of fuel rod contacting points along one side of the ferrule for abutting a fuel rod within the ferrule and an opening along a side of the ferrule opposite the one side, a spring including a spring body lying in a plane having opposite end portions projecting to one side of the plane, a central portion between the end portions projecting to the opposite side of the plane and openings on opposite sides of the central portion between the central portion and the end portions, the spring being disposed between the ferrules with the central portion in the central opening of the first ferrule and bearing against the second ferrule between the contacting points, portions of the first ferrule on opposite sides of the opening therethrough extending in respective openings of the spring, the end portions extending beyond opposite upper and lower edges of the first ferrule for bearing directly against a fuel rod passing through the first ferrule and biasing the fuel rod against the contacting points along the one side of the first ferrule. In a further preferred embodiment according to the present invention, there is provided a spacer for maintaining a matrix of nuclear fuel rods in spaced-apart relation between upper and lower tie plates, the spacer assembly comprising a matrix of adjacent ferrules for receiving the fuel rods in the spacer, each ferrule having a pair of fuel rod contacting points along one side thereof for abutting a fuel rod within the ferrule and having an opening along a side of the ferrule opposite the one side, a plurality of springs, each spring including a spring body lying in a plane having opposite end portions projecting to one side of the plane, a central portion between the end portions projecting to the opposite side of the plane and openings on opposite sides of the central portion and between the central portion and the end portions, each spring being disposed between an adjacent pair of the ferrules with the central portion in the central opening of one of the adjacent ferrules and portions of the one ferrule on opposite sides of the opening therethrough extending in respective openings of the spring. Accordingly, it is a primary object of the present invention to provide a novel and improved spacer for the nuclear fuel rods of a nuclear fuel bundle, affording improved performance by shortening the height of the spacer and minimizing its cross-section, hence reducing the spacer material while simultaneously providing the necessary structural integrity to maintain the fuel rods in position.
	abstract	The invention provides a system for preventing fluid exchange between the interior and exterior of containment enclosures such as process-, hazard-, and research-enclosure systems generally, gloveboxes, containment systems, isolation systems, confinement systems, cleanrooms, negative air systems, and positive air system areas while simultaneously providing material transfer into and out of the enclosures. The invention also provides a method for transporting material into or out of a containment structure.
	abstract	An x-ray optical system includes an x-ray source which emits x-rays, a first optical element which conditions the x-rays to form two beams and at least a second optical element which further conditions at least one of the two beams from the first optical element.
	claims	1. A mobile device for monitoring building environmental data, the mobile device comprising:(1) a touchpad screen for accepting user input and displaying screens;(2) a wireless network interface for connecting said mobile device to a cloud server over the Internet, wherein said cloud server adapted to receive performance data generated by detection devices from a remote thermostat over the Internet; and(3) a specialized application, wherein said specialized application adapted to:(i) execute on said mobile device;(ii) display a first screen on said touchpad screen, said first screen displaying a quick report button for providing quick reports;(iii) responsive to clicking said quick report button, request said cloud server over the Internet to provide quick reports conforming to a set of saved settings, said set of saved settings entered via said touchpad screen, wherein said set of saved settings indicates a facility, a frequency and a quick report type; and(iv) receive a first quick report from said cloud server over the Internet. 2. The mobile device of claim 1 wherein:(1) said facility is one of a basement, downstairs, family room, home office, kitchen or bedroom, wherein a first detection device is a sensor, a thermostat or a HVAC control disposed in said facility to collect performance data, wherein said performance data is at least one of system run time in minutes, heat run time in minutes, cooling time in minutes, fan run time in minutes, average heating temperature by degrees, average cooling temperature by degree, average outdoor temperature by degrees, average humidity level by percent humidity, highest indoor temperature by degrees, indoor temperature by degrees, highest outdoor temperature by degrees, lowest indoor temperature by degrees, highest humidity level by percent humidity and highest percent humidity by percent humidity, date, time, system mode, system state, room temperature, setpoint, fan state, outdoor temperature and humidity level;(2) said frequency is daily, weekly or monthly; and(3) said quick report type is summary, all or both. 3. The mobile device of claim 2 wherein said sensor is an indoor temperature sensor, an outdoor temperature sensor, an occupancy sensor, a humidity level sensor, a smoke sensor, or a carbon monoxide sensor. 4. The mobile device of claim 1 wherein said specialized application is adapted, to receive said first quick report via an e-mail service. 5. The mobile device of claim 1 wherein said specialized application is further adapted to display a performance data, report notification indicating a date in the future when the next performance data report will be generated, wherein said date is computed based on said frequency. 6. The mobile device of claim 1 wherein said specialized application is further adapted to:(1) display a facility selection screen;(2) responsive to a first user input to select said facility, select said, facility;(3) responsive to a second user input to select said frequency, select said frequency;(4) responsive to a third user input to select said quick report type, select said quick report type; and(4) over the Internet, request said cloud server to generate performance reports based on said facility, said frequency and said quick report type, wherein said cloud server saves said facility, said frequency and said quick report type.
	description	This application claims the benefit of U.S. Provisional Application No. 62/979,640 filed Feb. 21, 2020, which is incorporated herein by reference in its entirety. The present invention relates generally to systems and vessels for transporting and storing high level radioactive nuclear waste materials, and more particularly to a box-type cask in one embodiment for transport and storage of radioactive nuclear waste materials. The overpacks or casks used to store neutron activated metal and other radiated non-fissile high level radioactive waste, such as that resulting from operation nuclear power generation plants or other type facilities, is typically an open-top cylindrical structure with a bolted circular lid. Such a cask is inefficient to load all types of nuclear waste materials not limited to spent nuclear fuel into the cask. The radiation waste materials are often too large and/or may be irregular shaped for insertion through the narrow top access opening in such cylindrical casks which leads to the internal storage cavity. Further, the act of tightening the bolts once the cylindrical cask is packed with nuclear waste materials is a time consuming which exposes the workers to radiation dosage in proportion to the time needed to complete the tedious installation of the closure bolts. Accordingly, there remains a need for an improved nuclear waste storage cask that can accommodate a wide variety of waste materials, and which can further be closed and sealed in an expedient manner to reduce radiation exposure of operating personnel handling the cask. The present application provides a nuclear waste storage system comprising a radiation-shielded nuclear waste storage cask which overcomes the shortcomings of the foregoing cylindrical type storage casks described above for storing a wide variety of different nuclear waste materials. In one embodiment, a longitudinally elongated box-type cask is disclosed comprising an essentially rectangular body with rectilinear cross sectional internal storage cavity configured for holding nuclear waste material, and a matching rectangular closure lid. The elongated large top opening leading into the storage cavity extends for a majority of the longitudinal length of the cask. In contrast to the small circular opening at the top of cylindrical casks, the present rectangular opening allows large and irregular shaped radioactive metal pieces of waste material to be loaded inside the cask storage cavity in an efficient and expedient manner without undue handling by operating personnel, thereby reducing potential radiation dosage. In one embodiment, the closure lid be coupled and sealed to the cask body to close the top opening through a quick connect-disconnect joint that does not utilize any threaded fasteners. Instead, a slider locking mechanism comprising mechanically interlocking protrusions provided on peripheral portions of each of the lid and correspondingly cask body around the cask top opening is employed. While the lid remains stationary on the cask body, the locking protrusions on the lid are slideably relative to the locking protrusions on the cask body between locked and unlocked positions or states. The locking protrusions may be arrayed and spaced apart perimetrically around the lid and cask body. The locking protrusions may be wedge-shaped in one embodiment to produce a wedging-action when mutually engaged which effectively locks the lid to the cask body and seals the nuclear waste contents inside the cask. A gasket at the lid to cask body interface is compressed by the wedging-action to form a gas-tight seal of the cask storage cavity which completes the containment barrier. There is no exchange of air between the ambient environment and the storage cavity in one embodiment. The term “nuclear waste material” as used herein shall be broadly construed to mean any type or form of radioactive waste material which has been irradiated by a source of radiation. Such irradiation may occur in a nuclear power generation plant with nuclear reactor, or other types of facilities. As one non-limiting example, the radioactive nuclear waste materials may be associated with decommissioning or repair/maintenance of a nuclear facility, and may therefore include a wide variety of sizes and shapes of pieces of equipment (including parts of the reactor), structural components/members, parts, debris, scrap, or similar which have been irradiated and generate radiation. In one aspect, a cask for containing radioactive materials comprises: a cask body comprising an opening forming a passageway into an internal storage cavity of the cask; a closure lid configured to be detachably coupled to the cask body to enclose the opening; and a locking mechanism comprising at least one first locking member and at least one second locking member, the first and second locking members slideable relative to one another to alter the locking mechanism between: (1) a first state in which the closure lid can be removed from the cask body; and (2) a second state in which the first and second locking members engage one another to prevent the closure lid from being removed from the cask body. According to another aspect, a cask for containing radioactive materials comprises: a longitudinal axis; an axially elongated cask body defining a top opening forming an entrance to an internal storage cavity of non-cylindrical cross-sectional configuration, the cavity configured for holding radioactive waste materials; and a closure lid detachably coupled to the cask body at the top opening. According to another aspect, a method for locking a radioactive waste storage cask comprises: positioning a closure lid on a cask body over an opening leading into an internal storage cavity; inserting a peripheral array of first locking protrusions on the lid between and through a peripheral array of second locking protrusions disposed on the cask body around the opening; slideably moving the first locking protrusions beneath the second locking protrusions; and frictionally engaging the first locking protrusions with the second locking protrusions; wherein the lid cannot be removed from the cask body. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. All drawings are schematic and not necessarily to scale. Features shown numbered in certain figures which may appear un-numbered in other figures are the same features unless noted otherwise herein. A general reference herein to a figure by a whole number which includes related figures sharing the same whole number but with different alphabetical suffixes shall be construed as a reference to all of those figures unless expressly noted otherwise. The features and benefits of the invention are illustrated and described herein by reference to non-limiting exemplary (“example”) embodiments. This description of exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. Accordingly, the disclosure expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features. In the description of embodiments disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. As used throughout, any ranges disclosed herein are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. In addition, any references cited herein are hereby incorporated by reference in their entireties. In the event of a conflict in a definition in the present disclosure and that of a cited reference, the present disclosure controls. The terms “seal weld or welding” as may be used herein shall be construed according to its conventional meaning in the art to be a continuous weld which forms a gas-tight hermetically sealed joint between the parts joined by the weld. The term “sealed” as may be used herein shall be construed to mean a gas-tight hermetic seal. FIGS. 1-28 show various aspects of the nuclear waste transport and storage system. The system includes nuclear waste transfer and storage cask 100 (hereafter nuclear waste cask for brevity) which is usable transport and/or store high level nuclear waste materials. Cask 100 comprises an elongated rectilinear-shaped cask body 101 defining a longitudinal axis LA and the lower part of the containment barrier for the nuclear waste. The body 101 may have a rectangular cuboid configuration in one embodiment (as shown) comprising an axially elongated bottom wall 102, a parallel pair of longitudinal sidewalls 103 attached to the bottom wall, and a pair of lateral end walls 104 attached to opposite ends of the bottom wall between the sidewalls. The longitudinal sidewalls are attached to the longitudinal sides or edges of the bottom wall. End walls 104 are oriented transversely and perpendicularly to longitudinal axis LA and longitudinal sidewalls 103, and the longitudinal sidewalls are oriented parallel to the axis to form the box-like structure shown. In one embodiment, the sidewalls and end walls may be welded to each other and in turn to the bottom wall to form a weldment. Four corners 107 are formed at the intersection of the sidewalls 103 and end walls 104 which extend vertically along the height of the cask body 101. Bottom wall 102 has a flat top surface 102a and parallel opposing flat bottom surface 102b. The bottom wall is configured to be seated on a horizontal support surface such as a concrete pad. The interior and exterior surfaces of each of the longitudinal sidewalls 103 and end walls 104 may be generally flat and parallel to each other as well. Cask 100 may be used in horizontal position as shown when transporting and storing nuclear waste. In this case, the vertical direction is defined for convenience of reference as being transverse and perpendicular to the longitudinal axis LA. A lateral direction is defined for convenience of reference in the horizontal direction as being transverse and perpendicular to the longitudinal axis. The bottom wall 102, longitudinal sidewalls 103, and end walls 104 collectively define an internal storage cavity 105 configured for storing nuclear waste materials previously described herein. The bottom wall, longitudinal sidewalls, and end walls define and circumscribe an axially elongated top opening 106 forming an entrance to the cavity for loading nuclear waste materials therein. The longitudinally-extending top opening 106 extends for a substantial majority of the entire length of the cask body (less the thicknesses of the sidewalls and end walls). This provides a large opening which facilitates loading many different shapes and sizes nuclear waste materials into the cask 100. Longitudinal sidewalls 103 and lateral end walls 104 of the cask may each have a composite construction comprising a metallic inner containment plate 110 adjacent to the storage cavity 105 and a metallic outer radiation dose blocker plate 111 abutted thereto. Bottom wall 102 may similarly have a composite construction comprising a metallic inner containment plate 112 adjacent to the storage cavity and a metallic outer radiation dose blocker plate 113. In some embodiments, as shown, an intermediate dose blocker plate 114 may be sandwiched between the inner containment plate and outer dose blocker plate when needed to provide additional radiation shielding. In some non-limiting embodiments, the containment plates may be formed of steel alloy and the radiation dose blocker plates may be formed of a different steel material such as for example stainless steel for protection against corrosion by the exterior ambient environment. A suitable thickness of the containment and blocker plates may be used as needed to effectively reduce the radiation emitted from the cask to within regulatory compliant exterior levels for containment casks. As noted, the bottom wall and walls of cask 100 may have an all metal construction without use of concrete. However, in other possible embodiments, concrete and additional or other radiation shielding materials including boron-containing materials for neutron attenuation and various combinations thereof may be provided if additional radiation blocking is needed. The bottom wall and wall construction materials used therefore do not limit the invention. With continuing reference to FIGS. 1-28, cask 100 further includes a longitudinally elongated closure lid 200 which forms the upper containment barrier. Lid 200 may be of rectangular shape in one embodiment to match the rectangular cuboid configuration of the cask body 101 shown. Lid 200 has a length and width sufficient to form a complete closure of the top opening of the cask in order to fully enclose and seal the internal storage cavity 105 of the cask and nuclear waste materials. Lid 200 includes an outward facing top surface 201 and parallel bottom surface 202 facing cavity 105 of the cask body 101 when positioned thereon, parallel longitudinal sides 203 (i.e., long sides of the lid), parallel lateral ends 204 (i.e., short sides of the lid) extending between the longitudinal sides, and corners 205 (four as shown) at the intersection of the longitudinal sides and lateral ends. Top and bottom surfaces 201, 202 are the major surfaces of the lid having a greater surface area than other surfaces on the lid. Referring additionally to FIGS. 10-17B, closure lid 200 may have a composite construction comprising a metallic inner containment plate 206 at bottom located adjacent to the storage cavity 105 when the lid is position on the cask body 101, and a top metallic outer radiation dose blocker plate 207. Containment plate 206 defines bottom surface 202 of the lid and blocker plate 207 defines top surface 201. An insulation board 208 may be sandwiched between plates 206 and 207 for protection against fire event. In one embodiment, a peripheral lid spacer frame 209 may be attached to the bottom containment plate 206 of lid 200. Frame 209 has an open space-frame structure which extends perimetrically around the bottom surface 202 of the lid. The frame 209 may include an X-brace 209a extending through the interior space defined by the peripheral linear members of the frame to add structural reinforcement and bracing. When lid 200 is positioned on cask body 101, inner containment plate 206 and frame 209 are received completely into storage cavity 105 of the cask (see, e.g., FIGS. 10 and 11). A compressible gasket 220 may be disposed on the bottom surface 202 of the lid 200 to form a gas-tight seal at the interface between the lid and cask body. Gasket 220 has a continuous perimetrically extending shape which is complementary configured dimensionally to conform to and circumscribed the top end of the cask body 101 on all sides. Gasket 220 therefore extends perimetrically along the tops of the longitudinal sidewalls 103 and lateral end walls 104 of the cask to form an effective seal. Gasket 220 may be formed of any suitable compressible material, such as elastomeric materials in some embodiments. According to one aspect of the disclosure, a bolt-free cask locking mechanism provided to lock and seal lid 200 to cask body 101. FIGS. 10-18 and 22-28 in particular show various aspects of the bolt-free cask locking mechanism, which will now be further described in detail. Lid 200 and cask body 101 include a plurality of locking features which cooperate to form the locking mechanism. The cask locking mechanism may comprise a plurality of first locking protrusions 212 spaced apart on the lid which are selectively and mechanically interlockable with a plurality of second locking protrusions 214 spaced apart on the cask body to lock the lid to the cask body. First locking protrusions 212 are movable relative to the lid and cask body 101, whereas second locking protrusions 214 are fixed in position on and stationary with respect to the cask body. The locking features of the lid 200 comprises at least one first locking member 212a, which may be in the form of a linearly elongated locking bar 210 for locking the lid to the cask body (see, e.g., FIGS. 15B and 29-32). In one embodiment, a plurality of elongated locking bars 210 are arranged perimetrically around the outer peripheral portions of the lid on longitudinal sides 203 and lateral ends 204. First locking protrusions 212 are formed on and may be an integral unitary structural part of the locking bars in one embodiment being formed of single monolithic piece of cast or forged metal. In other possible less preferred but satisfactory embodiments, locking protrusions 212 may be discrete elements separately attached to the locking bars 210 via mechanical fasteners or welding. Locking bars 210 are slideably disposed in corresponding outward facing elongated linear guide channels 211 formed in the longitudinal sides and lateral ends of the lid 200. The locking bars are movable back and forth in opposing directions within the guide channels relative to the lid. Each locking bar 210 includes a plurality of the first locking protrusions 212 which project outwardly from the bar beyond the outward facing surfaces of the longitudinal sides 203 and lateral ends 204 of the lid. The linear array of locking protrusions 212 are spaced apart to form openings 213 between adjacent locking protrusions for passing the second locking protrusions 214 on the cask body 101 therethrough, as further described herein. The longitudinal sides 203 and lateral ends 204 of the lid 200 may each include at least one locking bar 210. In one preferred but non-limiting embodiment, as illustrated, the lateral ends 204 of the lid may include a pair of the locking bars 210 and the longitudinal sides 203 of the lid may similarly include a pair of locking bars. This forms a unique arrangement and interaction between the locking bars to maintain a locked position, as further described herein. The corresponding locking features of the bolt-free cask locking mechanism on cask body 101 include at least one second locking member 214a comprising the second locking protrusions 214. Locking member 214a may comprise upper portions of cask body 101 in which the second locking protrusions 214 and related features such as locking slot 216 described below are integrally formed with the cask body inside storage cavity 105. Locking protrusions 214 are fixedly disposed in linear arrays on the cask body adjacent to top ends of the longitudinal sidewalls 103 and lateral end walls 104 of the body and cask body top opening 106. The second locking protrusions 214 are therefore stationary and not movable relative to the cask body. The second locking protrusions 214 project inwardly into the nuclear waste storage cavity 105 from the interior surfaces of the longitudinal sidewalls 103 and lateral end walls 104 of the cask body. Second locking protrusions 214 therefore are arranged around the entire perimeter of the cask body to interface with the first locking protrusions 212 of lid 200. The linear array of second locking protrusions 214 are spaced apart to form openings 215 between adjacent locking protrusions for passing the first locking protrusions 212 on the lid therethrough. A linearly elongated locking slot 216 is formed and recessed into the cask body 101 immediately below the second locking protrusions 214 on each of the longitudinal sidewalls 103 and end walls 104 of the cask body. The locking slots 216 form continuous and uninterrupted inwardly open structures having a length which extends beneath at least all of the second locking protrusions on each of the longitudinal sidewalls 103 and lateral end walls 104 of the cask body as shown. Locking slots 216 therefore extend for a majority of the lengths/widths of the cask body longitudinal sidewalls and end walls. Locking slots 216 are in communication with the openings 215 between the second locking protrusions 214 to form an insertion pathway for the first locking protrusions 212 of lid 200 to enter the locking slots. In one preferred but non-limiting construction, the openings 215 between the second locking protrusions 214 and the elongated locking slots 216 may be formed as recesses machined into the cask body 101 by removing material from longitudinal sidewalls 103 and lateral end walls 104. The material remaining therefore leaves the second locking protrusions 214 in relief. Second locking protrusions 214 therefore in this case are formed as integral unitary and monolithic parts of the cask body material. In other possible constructions, however, the second locking protrusions 214 may be separate structures which are welded or otherwise fixedly attached to the cask body 101. In this latter possible construction, no locking slot 216 is formed but the cask locking mechanism may nonetheless still function satisfactorily to lock the lid to the cask body. In yet other possible constructions, the second locking protrusions 214 and locking slots 216 may be formed on linearly elongated closure bars of metal having the same composite construction as the longitudinal sidewalls 103 and end walls 104 previously described herein. The closure bars are in turn welded onto the tops of each longitudinal sidewalls and end walls to produce the same structure in the end as illustrated herein. With continuing reference to FIGS. 10-18 and 22-28, the first and second locking protrusions 212, 214 may be generally block-shaped structures having a rectangular configuration. In one preferred but non-limiting embodiment, the first and second locking protrusions may each be wedge-shaped defining locking wedges having at least one tapered locking surface 217 or 218. The locking protrusions may be configured and arranged such that the tapered locking surfaces 217 of the first locking protrusions 212 on lid 200 are each slideably engageable with one of the tapered locking surfaces 218 of a corresponding second locking protrusion 214 of the cask body 101. In one embodiment, the tapered locking surfaces 217 of the first locking protrusions 212 on lid 200 may be formed on a top surface thereof, and the tapered locking surfaces 218 of the second locking protrusions 214 on cask body 101 may be formed on a bottom surface thereof. When the first and second locking protrusions are engaged to lock the lid to the cask body, the tapered locking surfaces 217, 218 become slideably engaged forming a generally flat-to-flat interface therebetween. This creates a wedging-action which draws the lid 200 towards against the cask body 101 to fully compress the gasket 220 therebetween which forms a gas-tight seal of the cask internal storage cavity 105 and its nuclear waste material content. The tapered locking surfaces 217 and 218 preferably have the same taper angle A1 (see, e.g., FIG. 29) to form the generally flat-to-flat interface therebetween when mutually and frictionally engaged via the wedging action. Any suitable taper angle A1 may be used. In one representative but non-limiting examples, the taper angle A1 preferably may be between about 2 and 20 degrees. Other tapered angles may be used where appropriate. The locking bars 210 with first locking protrusions 212 on lid 200 thereon are slideably movable between a locked position or state (see, e.g. FIG. 17A) in which the first and second protrusions 212, 214 are mutually engaged to prevent removal of the lid 200 from the cask body 101 (see, e.g. FIG. 11), and an unlocked position or state (see, e.g. FIG. 17B) in which the first and second protrusions are disengaged to allow removal of the lid from the cask body in a vertical direction transverse to longitudinal axis LA of the cask. To move the locking bars 210 with sufficient applied force to frictionally interlock the first and second locking protrusions 212, 214, and to concomitantly minimize radiation dosage to operating personnel, a remote lid operating system may be provided. This system is operably coupled to each of the locking bars 210 and configured to advantageously move the locking bars 210 between the locked and unlocked positons from a remote radiation safe distance and area. This obviates the need for operators to manually operate the locking bars directly at the cask during the lid-to-cask body closure and locking process. In one embodiment, the remotely-operated lid operating system comprises a local actuator 240 mounted on the top surface 201 of lid 200 for and coupled to each of the locking bars 210. FIGS. 27 and 28 show actuators 240 in isolation and detail. Each actuator 240 is an assembly which may generally comprise a cylinder-piston assembly 241 including cylinder 245 and an extendible/retractable piston rod 242 slideably received inside the cylinder. The cylinder-piston assembly is fixedly attached to lid 200. Cylinder 245 may be fixedly mounted to the lid via a bolt 249 passing through a tubular proximal mounting end 242b as shown. Pistol rod 242 has a tubular distal working end 242a fixedly coupled to the locking bar 210 through an elongated operating slot 243 formed through the lid. The piston rod 242 is therefore moves the locking bar 210 in the manner described herein. In one embodiment, slot 243 may be formed in a lid insert plate 243a which in turn is mounted to the lid. A threaded bolt 249 may be used to couple the piston rod to the locking bar 210 via an intermediate block assembly comprising an upper mounting block 246 and lower mounting block 247. Upper block 246 may be formed as integral part of lid insert plate 243a in some embodiments. Piston rod 242 is fixedly bolted to upper mounting block 246. Upper mounting block 246 is fixedly mounted to lower mounting block 247 via a plurality of threaded fasteners 248 which extend through the upper mounting block and are threadably engaged with the locking bar 210 (see, e.g., FIG. 28). The mounting block assembly provides a robust coupling of the piston rods 242 to the locking bars 210 which can withstand the shear forces generated when the cylinder-piston assemblies 241 are actuated to drive the locking protrusions 212, 214 of the lid 200 and cask body 101 into locking engagement. The cylinder-piston assembly 241 may be either (1) hydraulically operated wherein the working fluid is oil, or (2) pneumatically operated wherein the working fluid is compressed air. Oil or air hoses are fluidly coupled to the cylinder-piston assemblies (not shown) and operated from a remote hydraulic or pneumatic control unit in a conventional manner which comprises an air compressor or hydraulic pump with appropriate valving depending on the type of system provided. When actuated, the locking bar actuators 240 function to slide the locking bars 210 between the locked and unlocked positions (FIGS. 17A and 17B) via extending or retracting the piston rod 242. It bears noting that the use of hydraulic or pneumatic means to move the locking bars 210 applies a greater force to the locking bars to form tight locking engagement via the wedging-action between the first and second locking protrusions of the lid and cask body than could be provided by manually actuating the locking bars 210. This advantage, coupled with avoiding exposure of operating personnel or workers to radiation dosage are notable benefits of the present remote lid operating system. Interaction between the locking protrusions 212, 214 and a related process/method for locking the nuclear waste cask 100 (i.e., lid 200 to cask body 101) are described farther below. The movement and functioning of the locking bars 210, however, is first further described. FIGS. 17A and 17B show the locked and unlocked positions of the locking bars 210 on lid 200. Retention features are provided as a safety mechanism which lock and retain the locking bars in the locked position to prevent the lid 200 from being unintentionally unlocked from the cask body 101, such as could potentially result from substantial force impacts occurring during transporting and handling the cask (e.g., lifting, lowering, or loading the cask onto a transport vehicle/vessel), or during a regulatory postulated cask drop event. In one embodiment, the locking bars 210 on the longitudinal sides 203 of lid 200 are moveable towards each other to form the unlocked position shown, and away from each other to form the locked position shown. Conversely, the locking bars 210 on the lateral ends 204 of the lid are moveable towards each other to form the locked position, and away from each other to form the unlocked position. This apparent dichotomy serves a purpose. When locking bars 210 on the lateral ends 204 of the lid are therefore positioned and abutted together in the locked position, terminal end portions 210a of the locking bars on the longitudinal sides 203 of the lid are positioned to overlap and engage/block the locking bars on the lateral ends 204 of the lid from being moved apart to the unlocked position (see, e.g., FIG. 17A). This forms a first locking bar retention feature which locks the lid lateral end locking bars 210 in the locked position. The second locking bar retention feature acts on the locking bars 210 on the longitudinal sides 203 of the lid 200 to lock the lid longitudinal side locking bars in the locked position. This retention feature comprises a locking handle assembly 230 slideably mounted on each of the longitudinal sidewalls 103 of the cask body 101 (see, e.g., FIGS. 17A-B, 19-21, and 23-26). Each locking handle assembly 230 includes an elongated proximal handle 231 configured for receiving an applied force generated by a user such as via grasping or a tool, a distal elongated locking block 233, and a securement bar 235. The locking block 233 is coupled to the handle 231 by one or more elongated coupling rods 232 of any suitable polygonal or non-polygonal cross-sectional shape. Preferably a pair of coupling rods 232 are provided. Securement bar 235 is fixedly attached to the exterior surface of the cask body longitudinal sidewalls 103 (e.g., welded) and has a proximal end 235a which is insertable through an aperture 236 in the handle 231. End 235a may project through aperture 236 when the handle assembly is fully inward and can be secured in place (e.g., FIG. 20 further described herein). The locking handle assemblies 230 are positioned on each longitudinal sidewall 103 of the cask body 101 to allow the locking block 233 to be manually and selectively moved into and out of the locking slots 216 on the cask body sidewalls. A windows 234 formed in each longitudinal sidewall 103 allows the locking block 233 to access the guide channels 216. More particularly, window 234 is formed in and extends completely through inner containment plate 110 of the longitudinal sidewalls 103 of the cask body. Locking block 233 is completely retractable from locking slot 216 into the containment plate 110 to allow insertion of first locking protrusions 212 on locking bars 210 into and slideably moved along the locking slot 216 beneath second locking protrusions 214 of the cask body. The outer radiation dose blocker plate 111 comprises a pair of holes 237 to permit the two coupling rods 232 to be coupled to locking block 233 located inside the blocker plate in window 234 of the inner containment plate 110 (see, e.g., FIG. 18). A pair of cylindrical mounting flange units 239 may be used to fixedly mount each locking handle assembly 230 to the dose blocker plate 111 on the longitudinal sidewalls 103 of cask body 101 (see, e.g., FIG. 20). Flange units 239 may be bolted/screwed or welded to the outer blocker plate 111. The flange units 239 further act as standoffs to limit the maximum inward projection of the locking block 233 into the locking slot 216 of the cask body. The coupling rods 232 are slideably inward/outward through the flange units to change position of the locking handle assemblies 230. The locking handle assemblies 230 are moveable via handles 231 between (1) an inward blocking position in which the locking blocks 233 project into the locking slots 216 of the cask body 101 beneath the second locking protrusions 214, and (2) an outward non-blocking position in which the locking blocks 233 are completely retracted from the locking slots. The non-blocking position allows locking bars 210 with first locking protrusions 212 thereon to enter and slide back and forth in the locking slots 216 between the locked and unlocked positions (both previously described herein) when the lid 200 is positioned on cask body 101. Once the locking bars are in the locked position, a gap G is formed between each pair of locking bars on the longitudinal sides 203 of the lid (see, e.g., FIGS. 12 and 17A). Moving the locking handle assemblies 230 to the inward blocking position locates the locking blocks 233 in and fills the gaps G on each longitudinal sidewall 103 of the cask body (within guide channels 211 of lid 200). The locking bars 210 therefore cannot be drawn back together to their unlocked position, thereby locking the locking bars in the locked position due to interference between the locking blocks 233 and locking bars. To move the locking bars 210 on longitudinal sidewalls 103 to the unlocked position, the locking blocks 233 are first withdrawn via handles 231 of the locking handle assemblies 230 to re-open gap G, thereby allowing the longitudinal sidewall locking bars to slide together again to the unlocked position. When each handle assembly 230 is in the inward blocking position, the securement end 235a of securement bar 235 is projected through apertures 236 in handles 231. Any suitable commercially-available cable-lock security tag or seal tag 238 as shown may be coupled through hole 235b in securement bar 235 to lock the handle assemblies in the inward blocking position. Should the cask 100 be impacted or dropped during handled, the lid 200 will remain locked to the cask body 101 since the handle assemblies 230 cannot be moved outward to unlock the lid. The security tag also provides visual indication that the lid is in the locked position to operating personnel. This is especially helpful in situations where the cask lid 200 may be loaded with radioactive materials and locked to the cask body 101 at one location, and then the cask is transported to a more remote receiving location. The crew at the receiving location can readily confirm the lid is in the locked position or state. A process or method for locking the nuclear waste storage cask 100 using the foregoing features will now be briefly described. FIGS. 29-32 are sequential views showing the relationship between the first and second locking protrusions 212, 214 during the lid mounting and cask locking process. The process or method generally includes first placing the locking bars 210 on longitudinal sidewalls 103 and lateral end walls 104 of lid 200 in their unlocked position and the locking blocks 233 on locking handle assemblies 230 in their non-blocking positions which retracts the locking blocks 233 from the locking slots 216 on the longitudinal sidewalls 103 of the cask body 101 (FIG. 17B). The locking bar actuators 240 or manual means may be used to perform the foregoing step. The locking bars 210 on longitudinal sides 203 of lid 200 are together, and locking bars on lateral ends 204 of the lid are spaced apart forming gap G therebetween as shown. The lid is positioned over and align with the cask body 101 wherein the lid first locking protrusions 212 are vertically aligned with the openings 215 between second locking protrusions 214 on the cask body (FIG. 29). Next, the closure lid 200 is lowered and positioned on top of the cask body 101 over the top opening 106. This step first vertically inserts the peripheral array of first locking protrusions 212 on locking bars 201 of lid 200 between the peripheral array of second locking protrusions 214 disposed on the cask body 101 around the top opening (FIG. 30). As the lid engages the top of the cask body 101, the first locking protrusions pass completely through the openings 215 between the second locking protrusions 214 and enter the horizontally elongated locking slots 216 in a position below the second locking protrusions (FIG. 31). In turn, the second locking protrusions 214 pass through openings 213 between the first locking protrusions 212 and become positioned above the first locking protrusions. The process or method continues with then sliding the locking bars 210 to their locked positions (FIGS. 17A and 31), which moves the first locking protrusions 212 beneath the second locking protrusions 214 in a horizontal locking plane oriented parallel to the bottom wall 102 and passing through the locking slots 216. This step may be performed by actuating the hydraulic or pneumatic cylinder-piston assembles 241 of the locking bar actuators 240 from a location remote from the cask to minimize radiation exposure of operating personnel. Sliding the locking bars 210 slideably and frictionally engages the first locking protrusions 212 of the lid with bottom surfaces of the second locking protrusions 214 of the cask body 101. Specifically, the tapered locking surfaces 217, 218 of the wedge-shaped locking protrusions 212, 214 become mutually locked in increasingly tightening frictional engagement via the wedging-action produced. This draws lid 200 downward with added force beyond the weight of the lid alone onto and against the cask body 101 to fully compress gasket 220 and seal the cask cavity 105. The gasket is now compressed further than when the lid 200 first engages the cask body before the cask locking mechanism is actuated to draw the lid farther downward. Now that the lid 200 is fully coupled to the cask body 101, the locking handle assemblies 230 may be moved to their inward blocking positions to insert the locking blocks 233 between each pair of locking bars 210 on the longitudinal sides 103 of the lid, thereby preventing sliding and unlocking of the longitudinal side locking bars (FIG. 17A). The handle assemblies therefore retain the locked positions of the locking bars on the cask longitudinal sidewalls 103, which in turn retains the locking bars on the cask end walls in the locked position as previously described herein. It bears noting that although the locking bars 210 with locking protrusions 212 are shown and described herein as being slideably mounted to the lid 200 and locking protrusions 214 are shown and described as being fixedly mounted to the cask body 101 in one embodiment, in other embodiment the arrangement may be reversed. Accordingly, the locking bars 210 may be slideably mounted to guide channels 211 formed in the cask body while the fixed locking protrusions 214 may instead be fixedly mounted to the closure lid. This alternate arrangement provides the same benefits and is operated in the same manner previously described herein. The locking bar hydraulic or pneumatic actuators 240 in turn would be mounted to the cask body for operating the locking bars 210. Although the cask locking mechanism with locking bars 210 and locking protrusions 212, 214 are shown and described herein as being applied to a box-shaped rectangular cuboid cask body and rectangular lid, the locking mechanism may be applied with equal benefit to a conventional cylindrical cask body and circular lid. The fixed second locking protrusions 214 may be arranged on either the cylindrical cask body or lid, and the locking bars 210 may be mounted on the other one of the cask body or lid. The locking bars and guide channels for the cylindrical cask application may be arcuately curved and operated via the hydraulic or pneumatic locking bar actuators 240 previously described herein if mounted on either the cask body or circular lid. Alternatively, both the locking protrusions 212, 214 may be fixedly mounted to the cylindrical cask body and lid, and the slideable locking bars may be omitted. In this case, the lid may simply be rotated relative to the cylindrical cask body to slideably and frictionally engage the wedge-shaped locking protrusions to form a breech lock type closure. The lid may be rotated via assistance form the hydraulic/pneumatic actuators. Based on the foregoing alternative embodiments of the cask locking mechanism and description already provided herein, it is well within the ambit of those skilled in the art to implement any of these options without undue experimentation. With general reference to FIGS. 1-10 and 21-23, an impact absorption system is provided to protect the cask 100 and containment barrier from undue damage should the cask be forcibly impacted or dropped during transport and handling. In one embodiment, each of the longitudinal sidewalls 103 and lateral end walls 104 of the cask body 101 comprises a plurality of outwardly protruding impact absorber bars 140 fixedly coupled thereto. The closure lid 200 and bottom surface 102 of the cask body may also include multiple impact absorber bars 140 fixedly coupled thereto. The bars 140 may be each configured and arranged in appropriate locations on and in a pattern appropriate to meet regulatory requirements (e.g., Nuclear Regulator Commission or NRC) for surviving a postulated cask impact/drop event. In one embodiment, the impact absorber bars 140 may be configured as rectangular blocks of suitable thickness and dimension for the intended purpose. The locking handle assemblies 230 on longitudinal sidewalls 103 of cask body 101 may each be protected between at least a pair of absorber bars 140 located proximately to the assembly on each side. These protective impact absorber bars have depth measured perpendicularly to the exterior surface of the cask body longitudinal sidewalls 103 such that the handle assemblies 230 do not protrude outwards beyond the bars. In one embodiment, the impact absorber bars 140 may be bolted to the cask body and lid (see, e.g., FIGS. 23-26). This allows the bars to be readily replaced if damaged during a cask drop/impact event. In other embodiments, the bars 140 maybe welded thereto. Each corner 107 of the cask body 101 and corners 205 of lid 200 may be protected by corner impact absorbers 141 fixedly coupled to corner regions. Sets of upper and lower corner impact absorber are provided to cover and shield the lid and adjacent upper corner regions of the cask body, and the bottom wall 102 and adjacent lower corner regions of the cask body, respectively. In one embodiment, the corner impact absorbers 141 may be assemblies comprising an inner corner bracket 142 and outer corner blocks 143 fixedly coupled thereto. Inner corner brackets 142 may be fixedly coupled to the cask body 101 at the lower corners of the body, and the lid and/or cask body at the upper corners. In one embodiment, the inner corner brackets 142 and corner blocks 143 may be fixedly coupled to and movable with lid 200 as shown herein. The inner corner brackets 142 have inward facing concave recesses configured to conform to the perpendicular and squared off corners of the cask body and lid. The outer corner blocks 143 have concave recesses configured to conform to the exterior shape of the inner corner brackets 142. The upper corner impact absorbers 141 extend vertically downwards from the lid over the upper corners of the cask body, and horizontally wrap longitudinally and laterally around the side regions of the corners on both the cask body 101 and lid 200. The upper corner impact absorbers also extend partially over the top of the lid at the corners. The lower corner impact absorbers 141 horizontally wrap longitudinal and laterally around the side regions of the corners on the cask body 101 and bottom wall 102, and partially underneath the bottom wall. In one embodiment, the inner corner brackets 142 and outer corner blocks 143 may be bolted or screwed together via threaded fasteners. The inner corner brackets 142 may in turn be bolted or screws to the cask body 101 and cask body and/or lid 200 vi threaded fasteners as applicable. To facilitate handling the cask 100, each of the longitudinal sidewalls 103 of cask body 101 may include a plurality of outwardly protruding lifting trunnions 150 fixedly attached thereto. Lifting trunnions 150 may be generally cylindrical in configuration and of the retractable type in one embodiment which are known in the art. The lid 200 in turn may include a plurality of lifting lugs 151 for handling the lid. Lugs 151 are fixedly attached to the lid. Lifting lugs may be generally cylindrical in configuration in one embodiment. Any suitable number of lifting trunnions and lugs may be provided as needed to safely lift and maneuver the cask body and lid. Other configurations and constructions of the lifting trunnions and lugs may be provided which are suitable for lifting and maneuvering the weight of cask body and lid in a stable manner. While the foregoing description and drawings represent some example systems, it will be understood that various additions, modifications, and substitutions may be made therein without departing from the spirit and scope and range of equivalents of the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, sizes, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. In addition, numerous variations in the methods/processes described herein may be made. One skilled in the art will further appreciate that the invention may be used with many modifications of structure, arrangement, proportions, sizes, materials, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims and equivalents thereof, and not limited to the foregoing description or embodiments. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.
	claims	1. A repair device for the underwater repair of a hole of a nuclear reactor part by remachining the hole, the repair device comprising:a holder;a cutting tool held by the holder and having at least one cutting tooth for remachining an inner surface of the hole, the cutting tool having a suction channel extending into the cutting tool between at least one inlet opening and at least one outlet opening;a drive shaft for rotating the cutting tool, the drive shaft being held by the holder; anda suction tube connected to the holder and fluidly connected to the outlet opening of the suction channel,wherein the cutting tool comprises a cutting part and a drive part connected to the drive shaft, the outlet opening emerging in a recess of the drive shaft, the drive shaft having at least one lateral opening for the passage of the fluid from the inside of the recess toward the outside, the suction channel being connected to the holder in register with the lateral opening to suction the fluid through the lateral opening. 2. A repair device for the underwater repair of a hole of a nuclear reactor part by remachining the hole, the repair device comprising:a holder;a cutting tool held by the holder and having at least one cutting tooth for remachining an inner surface of the hole, the cutting tool having a suction channel extending into the cutting tool between at least one inlet opening and at least one outlet opening;a drive shaft for rotating the cutting tool, the drive shaft being held by the holder; anda suction tube connected to the holder and fluidly connected to the outlet opening of the suction channel,wherein the cutting tooth comprises a portion for machining a circular cylindrical hole and a portion for machining a frustoconical bevel at the inlet of the circular cylindrical hole. 3. A repair device for the underwater repair of a hole of a nuclear reactor part by remachining the hole, the repair device comprising:a holder;a cutting tool held by the holder and having at least one cutting tooth for remachining an inner surface of the hole, the cutting tool having a suction channel extending into the cutting tool between at least one inlet opening and at least one outlet opening;a drive shaft for rotating the cutting tool, the drive shaft being held by the holder; anda suction tube connected to the holder and fluidly connected to the outlet opening of the suction channel,further comprising a stop surface configured to abut against the part in which the hole to be repaired is arranged in order to limit the travel of the cutting tool in the hole to be repaired. 4. The repair device according to claim 3, wherein the suction channel extending extends inside the cutting tool. 5. The repair device according to claim 3, wherein the cutting tool comprises a cutting part and a drive part connected to the drive shaft, the outlet opening emerging in a recess of the drive shaft, the drive shaft having at least one lateral opening for the passage of the fluid from the inside of the recess toward the outside, the suction channel being connected to the holder in register with the lateral opening to suction the fluid through the lateral opening. 6. The repair device according to claim 3, wherein the holder and the drive shaft comprise at least one rotational guiding assembly comprising a bearing provided on the holder and a complementary transmission shaft provided on the drive shaft. 7. The repair device according to claim 6, wherein the cutting tool comprises a cutting part and a drive part connected to the drive shaft, the outlet opening emerging in a recess of the drive shaft, the drive shaft having at least one lateral opening for the passage of the fluid from the inside of the recess toward the outside, the suction channel being connected to the holder in register with the lateral opening to suction the fluid through the lateral opening and wherein the holder and the drive shaft comprise two rotational guiding assemblies located, along the drive shaft, on either side of the or each lateral opening. 8. The repair device according to claim 6, wherein at least one rotational guiding assembly provides the sealing between the holder and the drive shaft. 9. The repair device according to claim 3, wherein the holder is a support tube, the cutting tool being arranged at one end of the holder, the drive shaft extending inside the holder between the ends of the holder. 10. The repair device according to claim 3, wherein the cutting tool extends along a longitudinal axis, the cutting tooth extending substantially rectilinearly along the longitudinal axis. 11. The repair device according to claim 3, wherein the inlet opening of the suction channel is arranged at a base of an undercut face of the cutting tooth. 12. The repair device according to claim 3, wherein the inlet opening of the suction channel is elongated along the cutting tooth. 13. The repair device according to claim 3, wherein the cutting tool is a reamer. 14. The repair device according to claim 3, wherein the cutting tooth comprises a portion for machining a circular cylindrical hole and a portion for machining a frustoconical bevel at the inlet of the circular cylindrical hole. 15. The repair device according to claim 3, wherein the cutting tool comprises, on a cutting part of the cutting tool bearing the cutting tooth, at least one flat offset on the circumference of the cutting part, relative to the cutting tooth. 16. The repair device according to claim 3, wherein the cutting tool is configured to produce a centering hole for a nuclear fuel assembly upper nozzle, a mistake-proofing hole for a nuclear fuel assembly upper nozzle, a centering hole for a nuclear fuel assembly lower nozzle, a hole for a lower core plate or a hole for an upper core plate.
	summary
046817298	description	DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 1 to 4, a metal container 10 adapted to have an internal pressure greater than atmospheric has an upper wall 11 to the inside of which is fixed a detector 12. A detector head 13 is mounted on structure 14 forming part of grab 17 and has a spring-loaded nose 15 for bearing against the wall 11 and ensuring that the head 13 is properly located with respect to the external surface 16 of the wall 11 opposite the detector 12. A grab or other means is shown schematically at 17 and is adapted to rotate the head through 360.degree. around the axis of the stationary container so that the wall 11 is swept by the head. As described with reference to FIG. 8, the grab 17 may form part of a container handling machine in a storage and monitoring facility. The detector unit 12 comprises a generally tubular member 18 having at one end an outward flange 19 welded to the inner surface 20 of the wall 11. This weld is not necessarily in an air-tight manner. The response time of the device could be improved by allowing natural convection to the thermal strip, and possibly by perforating the body 18. In some cases welding may not be possible as this would cause mechanical deterioration and possible failure of the thermal link by conduction from the weld along the bar 36. The internal surface 21 of the member 18 is stepped to provide an annular should 22 intermediate the ends of the member, the outer end of which has bolted thereto an annular protective cover 23 providing a central mouth or inlet aperture 24. The surface 21 is stepped also adjacent the plate 23 to provide another shoulder 25. A circular retaining plate 26 has its annular outer marginal portion in engagement with the shoulder 25. An axial tube 28 extends through the plate 26 having a flange 27 abutting the plate 26 and extends towards the wall 11 passing through a central aperture in an annular plate 29 which abuts the shoulder 22 and through a compression spring 30 which extends between the plate 26 and the plate 29 to hold the plate 29 against the shoulder 22. The tube 28 at its end nearer the wall 11 has a threaded portion of reduced section which engages in a central passage in the base 31 of a horseshoe permanent magnet 32 having arms 33 with ends 34 engaging surface 20. A nut 35 holds these parts together. The container and, in particular, the wall 11 may be fabricated from a ferromagnetic material such as mild steel in which case the wall 11 in effect acts as a keeper for the magnet 32. Alternatively the container may be fabricated from a magnetically characterless metal such as a stainless steel. In the latter case, a keeper may be provided if desired and, as shown in FIG. 3A, it may be secured to, or form part of, the tubular member 18, the keeper being depicted by reference numeral 70. Where the wall 11 acts as a keeper or where a keeper 70 is provided, direct contact between the poles of the magnet 32 and the keeper may be undesirable because of the affects of residual magnetism in the keeper and consequently some form of non-magnetic spacer (not shown) may be interposed between the magnet and the keeper. A bar 36 is fixed to surface 20 between arms 33 and its ends are received in notches 37 in the inner surface 21 at one end thereof (FIG. 4) to resist rotation. A thermal link 38 is fixed to the bar 36, extends along the tube 28 and is secured at its other end to a block 39 in the end of the tube 28 and having an end portion overlying the flange 27 so that in the datum position shown in FIG. 3 the spring 30 is compressed, plate 29 engages shouler 22 and plate 26 engages shoulder 25. If the thermal link 38 breaks, for example due to corrosion or a rise in temperature above the melting point of the material of the link, the spring 30 moves the plate 26 into engagement with cover plate 23 (see FIG. 2) thus moving the magnet 32 away from the wall 11. When the magnet 32 is in the FIG. 3 position, the magnetic field induced in the wall 11 and the external or stray magnetic field outside the wall 11 are greatest, and are greater than with the magnet 32 in the FIG. 2 position. This change of magnetic flux is detected by a detector head 13 and the magnetic flux may be displayed on a fluxmeter connected to the head 13. The fluxmeter may take the form of a voltmeter displaying a voltage directly proportional to the magnetic flux. The voltmeter may be of digital form ("magnet present" or "magnet absent") but in suitable circumstances an analogue voltage reading could be displayed so as to measure temperature directly. The container 10, or at least the wall 11, may be of diamagnetic, paramagnetic or ferromagnetic material. The magnet 32 can take various forms and configurations, eg a bar magnet or magnets. The bar magnet could be disposed parallel to the wall 11, or at right angles to the wall 11 with the outer end connected to the rod 28. The bar magnet can be disposed either perpendicular or parallel to the wall 11 depending on the desired characteristics. With the bar magnet parallel to the wall the effect is similar to the horse shoe magnet, whilst with the magnet perpendicular to the wall the pull-off force is reduced but the measured leakage flux is increased. Preferably the magnet has both of its poles presented towards the wall 11 as shown in the illustrated embodiment, the poles being spaced apart in the direction of scan by the detector head 13 which assists precise location of the magnet since the two poles will give rise to opposite flux changes as the detector head scans across the magnet 32. The detector head 13 responsive to the change in magnetic flux preferably comprises a Hall effect transducer, preferably incorporating a suhl effect semiconductor, which is responsive to the leakage flux outside the wall 11. FIG. 7 shows a suitable arrangement in which a linear Hall effect device 50 has an output on lines 51, 52, connected to a differential amplifier 53 which has an output on line 54 to an inverting amplifier 55 including a zeroing circuit and an output on line 56 leading to the fluxmeter (voltmeter). A battery power supply is used. FIG. 5 shows the voltage output on line 56 for differing distances of four different magnets from the surface 20, and FIG. 6 shows the voltage output on line 56 for varying distances of the Hall effect device 50 from the surface 16 with the respective magnet engaging the surface 20. Two detectors and associated detector heads could be used to reduce the risk of overall failure. To avoid dissimilar welds, the member 18 is of the same material as the container wall 11, eg mild steel. The container 10 may for example be a canister for fuel for a nuclear reactor. In one arrangement applicable to situations in which the container is fabricated from a magnetically soft material (such as mild steel) or where a separate keeper is employed as in FIG. 3A, the detector detects the unidirectional magnetic flux within the wall 11 by superimposing a time varying flux onto the unidirectional flux and measuring the resultant interaction. Ideally the resultant flux should be measured within the wall 11 but, since this is not practicable, it is proposed to measure the interaction in the secondary iron circuit by a use of a search coil. It is considered that this method will have greater sensitivity since it is measuring the flux in the wall directly rather than the associated leakage flux. The development of the alternative method may permit the device to be used as a temperature transducer as opposed to a temperature sensor. The interaction in wall 11 is due to the induced ac magnetic flux interacting with the steady state flux of the permanent magnet in a common limb of an iron circuit. It can be compared to the interaction of an alternating voltage and a dc voltage through a common branch of a circuit which can be theoretically analysed using the classical "superposition theorem". One possibility is shown in FIGS. 2 and 3, the detector head 13 is in the form of a coil 61 on one arm of a core 64 and energized from an AC source and producing an alternating magnetic field in wall 11, which field interacts with the magnetic field in the wall 11 from the magnet 32. A sensor or search coil 62, also would on core 64, responds to changes in magnetic field outside the wall 11 due to the interacting magnetic fields in the wall 11 and has an output connected to a detector unit 63. The output from the sensor coil 62 is an alternating voltage whose magnitude and wave shape are dependent on the magnitude of the unidirectional flux produced by the permanent magnet 32. There would be a secondary effect of a small induced voltage due to the movement of the permanent magnet. This is not considered to be of any significance because of its small magnitude and the fact that the detector may not necessarily be present at the moment of operation (e.g. the detector may be mounted on the grab of a crane). The detector unit 63 may comprise a sensitive AC voltage detector, an amplifier, a scaler, and a display device. Instead of a fusible or breakable thermal link, the parts 36, 39 may be connected by a bimetal component, eg. a strip or bellows, whose expansion on rise of temperature allows the plate 26 to move and with it the magnet 32. The example described uses a fusible thermal link in conjunction with the spring to reposition the permanent magnet. This has the fundamental feature that once it has operated it cannot be reset without replacing the fusible link. This can be an advantage or disadvantage depending on the application. Other, resettable, alternatives would utilise bimetallic strips, gas contained within a bellows, expansion and contraction of suitable metals or waxes (as in a combustion engine CW thermostat) to reposition the permanent magnet. Possible transducers would include future developments in materials science such as memory alloys operating at cryogenic temperature. The container shown in FIG. 1 is intended for the long term storage of nuclear fuel materials in the form of, for example, fast reactor fuel sub-assemblies. The sub-assembly is introduced into the container via opening 74, a valve and handling unit 76 is then welded to the container and the container is pressurised via the valve unit to a pressure above atmospheric pressure. The container can thereafter be loaded into a storage facility such as that shown in FIG. 8. The facility comprises a vault 77 in the form of an array of container channels 78 which may comprise steel tubes supported in a concrete structure and accessible via removable plugs 80 in a shield structure 82. A container handling machine 84 is provided above the shield structure 82 and is mounted on carriages 86, 88 moveable in mutually orthogonal directions 90, 92 to enable the grab 17 of the machine to be moved across the array. In FIG. 8, the machine is shown lowering a container 10 into a channel 78, the grab being engaged with the valve and handling unit 76. The grab 17 includes a sniffing device (not shown) as well as detector head 13, the sniffing device being operable to detect for example fission gas release via the valve unit 76. Thus, in use, the machine 84 may be used to periodically examine each container 10 stored in the vault by means of detector head 13 and for fission gas leakage. In an alternative embodiment, the container may be constituted by a transport vessel, known as a bucket, for use in transporting fuel sub-assemblies from the interior of the liquid metal cooled fast breeder reactor to a storage facility, the bucket being filled with liquid metal coolant, eg. sodium, to prevent excess temperatures arising. One or more detector heads, for example of the form shown in FIGS. 2 and 3, may be located along the path of travel of the buckets so that the internal temperature may be monitored at critical stages in the transfer procedure.
	abstract	An atomic power plant operation system for assisting the operation of an atomic power generation plant is provided with: an operation monitoring system which monitors and controls the operation of the atomic power generation plant; an abnormality indication monitoring system which, on the basis of an operation history of the atomic power generation plant, monitors an indication of abnormality in the atomic power generation plant; an abnormality diagnosis system which, on the basis of a result of abnormality indication that has been detected, makes an abnormality diagnosis for the atomic power generation plant; and a maintenance system for performing maintenance and management of the atomic power generation plant, wherein the systems are communicably connected, and the abnormality diagnosis system provides the maintenance system with the result of the abnormality diagnosis of the atomic power generation plant.
048209295	description	BEST MODE FOR CARRYING OUT THE INVENTION Referring to FIG. 1, there is shown a dynamic infrared simulation cell 10 in accordance with the present invention. Simulation cell 10 has a first conductive layer 12, a photoconductive layer 14, a second conductive layer 16, and an energy source 18. These elements combine to form a simplified embodiment of the present invention in which a light image of a scene is converted into an infrared image. First conductive layer 12 is ideally a thin film of transparent gold. This first conductive layer 12 may also be Nesa glass, or a plastic film with a conductive coating, i.e., gold-covered Mylar. While in the preferred embodiment of the present invention, conductive layer 12 should be transparent, it is also possible to configure layer 12 in certain other ways such that layer 12 will be transmissive only with regard to certain known energies. In other words, layer 12 may be configured so as to block out certain forms of light while permitting other forms of light to pass therethrough. A lead 20 of energy source 18 is electrically connected to first conductive layer 12. Photoconductive layer 14 is a layer of silicon material integrally affixed between first conductive layer 12 and second conductive layer 16. The thickness of the silicon layer 14 must be selected to maximize the efficiency of the cell 10. Basically, the thicker the silicon, the more it interacts with a given energy of exposing radiation and the more electron-hole pair a given quantity of radiation produces. Conversely, as the silicon layer is made thinner the electric field acting on these electron-hole pairs becomes stronger (the same potential over less distance). The optimum thickness of this photoconductive layer 14 will depend on the characteristics of the photoconductor and the energy level of the imaging radiation it is designed to sense. It must be noted here that although silicon would be the preferable photoconductive material, it is also possible to utilize other materials as the photoconductor of the present invention. Selenium or cadmium sulfide are two types of photoconductive material that could be used instead of silicon. The particular type of photoconductive material will depend on the characteristics of the light being sensed, on manufacturing capabilities, and a wide variety of other factors. Second conductive layer 16 is a comparatively large layer of a material having good heat sink properties. The purpose of second conductive layer 16 is to remove the heat as fast as possible from photoconductive layer 14. This may be accomplished by using copper or aluminum as the material for the layer. Alternatively, and described hereinafter, this may also be accomplished with other materials and incorporating a cooling system therein. However, for the purpose of this simplified embodiment, an aluminum layer 16 will suffice. Lead 22 of energy source 18 is electrically connected to second conductive layer 16. Energy source 18 is generally any source of direct current. Energy source 18 serves to impress voltage through this layered structure of cell 10. While direct current is shown in conjunction with the simplified embodiment of the present invention, it is also possible to use alternating current in combination with the layered arrangement of FIG. 3, to be described hereinafter. FIG. 2 is a schematical illustration of the operation of this simplified embodiment of the present invention. Initially, the simulation cell 10 is placed in darkened enclosure 24. A projected image 26 is directed onto the first conductive layer 12 of cell 10 by partially silvered mirror 28. Typically, the light of the projected image 26 should be blue light in order for the silicon of the photoconductive layer 14 to act as a photoconductor. Of course, other forms of light could be used in association with other types of photoconductive material. The projected image 26 passes through transparent conductive layer 12 onto photoconductive layer 14. This light then spatially modulates the resistance of the photoconductive layer 14. While this is occurring, the constant potential of energy source 18 is impressed across first conductive layer 12 and second conductive layer 16. As the resistance of photoconductive layer 14 spatially changes in response to the projected light image 26, current flows through that portion of photoconductive layer 14 in response to the local resistance of the photoconductive layer. In essence, photoconductive layer 14 acts as a variable resistor. The passing of an electrical current through an area of high resistivity produces greater heat in that area of the photoconductive layer than an area exhibiting less resistivity. Typically, photoconductors become more conductive and less resistive in the presence of light. The degree of conductivity is a function of the intensity of light. The present invention produces an infrared image by generating heat in these areas of the photoconductive layer that correspond inversely to the intensity of light acting on such areas. In other words, a "heat" image is generated which corresponds to the image directed to the photoconductive layer. The interaction of electrical current and light results in power being expended in the local area of photoconductive layer corresponding to the image projected onto that local area. The heat thus generated emits an infrared flux 30 that can be viewed by appropriate thermal imaging systems. If the light image 26 is spatially and temporally modulated, then the dynamic infrared simulation cell 10 will present an infrared representation of the scene of projected image 26 on the surface of photoconductive layer 14. This image projects through first conductive layer 12 and outward through optics 32 as an infrared representation of the projected image. White the simplified embodiment of FIGS. 1 and 2 would work, some problems could be encountered due to thermal diffusion within photoconductive layer 14. Such thermal diffusion would weaken spatial resolution since the image would appear smeared. In addition, temporal resolution would be worsened since the heat in the photoconductive layer would diffuse throughout the photoconductive layer instead of into the heat sink/second conductive layer 16. However, the present invention could be modified so as to provide good spatial and temporal resolution. A modification for resolution enhancement of the simplified embodiment, shown in FIGS. 1 and 2, is illustrated in FIGS. 5 and 6. As can be seen in FIG. 5, the photoconductive layer 40 is divided into a plurality of segments 42 of photoconductive material. Essentially, the photoconductive layer 40 is cross-hatched with cuts such that "islands" of silicon (or other photoconductive material) are formed. Each segment 42 is distinct and separate from other segments 42. Essentially, these segments 42 of photoconductive material are arranged so as to act as the pixels of a typical projected image. The segments 42 may be created by chemical etching or ion-beam etching. The segments 42 are suitably deposited onto second conductive layer 44. A dielectric material 46 having low thermal conductivity is deposited between the segments 42 of photoconductive material. In essence, the dielectric material 46 serves to isolate each of the segments 42 of photoconductive material from other segments of photoconductive material. As seen in FIG. 6, the top of the layer having the photoconductive material 42 and the dielectric material 46 is "milled" such that the surfaces of the materials are reasonably coplanar. First conductive layer 48 is then deposited onto this layer. As before, first conductive layer 48 is optically transparent to light. Leads 50 and 52 connect the first conductive layer 48 and the second conductive layer 44 to energy source 54. As seen in FIG. 4, first conductive layer 48 has a conductive band 56 extending about its outer edges. Conductive band 56 has leads 58, 60, 62, and 64 electrically connected to its sides. The reason for this conductive band is to avoid "hot spots" about the photoconductive layer as the current is carried through the layered structure. By delivering the current to the layered arrangement from all four sides, the current more evenly distributes about the photoconductive layer 40, thereby avoiding spatial distortion in the produced infrared image. The operation of this embodiment of the invention is similar to that of the simplified embodiment. As stated previously, the projected image is directed onto the photoconductive layer 40 through first conductive layer 48. Since photoconductive layer 40 is made up of segments 42 of photoconductive material, the image is imparted onto discrete pixels (in the form of the segments 42). Each of the segments 42 is a part of the resistance pattern in the silicon layer. Similarly, each of the segments/pixels 42 contains a portion of the overall heat image produced. The combination of the image contained on each pixel found in photoconductive layer 40 emits an infrared flux that can be viewed by a thermal imaging system. As opposed to the simplified embodiment stated previously, this embodiment delivers the infrared image without the loss of spatial and temporal resolution caused by thermal diffusion throughout the photoconductive layer. The dielectric material 46 prevents thermal diffusion between the segments 42 in the photoconductive layer. Thus, there is no "smearing" of the projected infrared image. Additionally, the dielectric material 46 contains the heat image to the individual segment of photoconductive material. This means that the heat sink/second conductive layer 44 rapidly removes the heat from each of the pixels. This causes this embodiment of the invention to have a high level of temporal resolution. Another embodiment of the present invention is shown in FIG. 3. This embodiment is particularly adapted to the use of alternating current as the energy source. Specifically, this embodiment comprises a first conductive layer 80, a dielectric layer 82, a segmented photoconductive layer 84, a second conductive layer 86, and an alternating current energy source 88. In this embodiment, the segmented structure of photoconductive layer 84 is similar to that as appears in FIG. 5. Specifically, photoconductive layer 84 is made up of a multiplicity of individual pixels of photoconductive material. These pixels of photoconductive material are deposited upon second conductive layer 86. As with the previous embodiment, dielectric material, similar to that found in layer 82, is used to fill in the areas between the individual pixels of photoconductive layer 84. This material serves to isolate the individual pixels, as described previously. Dielectric layer 82 is deposited over the segmented photoconductive layer 84. This dielectriclayer has high resistivity and high thermal resistance. This dielectric layer 82 is integrally affixed to the layer formed by segmented photoconductive layer 84 and the filler dielectric material 90. The dielectric layer 82 physically supports first conductive layer 80. Dielectric layer 82 should also be generally transparent so as to transmit imaging radiation to the photoconductive layer 84. First conductive layer 80 is integrally affixed to the top of dielectric layer 82. Leads 92 and 94 are electrically connected to first conductive layer 80 and second conductive layer 86, respectively. Leads 92 and 94 connect the layered structure of this embodiment with alternating current energy source 88. This embodiment must be operated as an AC unit since a capacitor has been formed by the use of the dielectric layer 82 between the energy source and the photoconductive layer. The operation of this embodiment of the invention will be similar to that as described before, except for the fact that an alternating current energy source is used in place of the direct energy source. In this alternative embodiment of the invention, the conductive band, as illustrated in FIG. 4, may be arranged about the edges of the first conductive layer 80. This should enhance the operation of the infrared simulation cell by distributing the energy evenly across the photoconductive layer. FIG. 6 is a representation of the operation of the present invention. In FIG. 6, the source of a projected image 100 directs the image through lens 102. The source of projected image 100 may be either a typical film and light projector unit or it may be a cathode ray tube or laser projection unit. In this invention, the image may be projected onto the infrared simulation cell by either the projection of a light image over the field of the photoconductive layer of the cell or it may be a modulated light beam directed to the photoconductive layer of the cell in a raster scanning pattern. The infrared simulation cell will function properly with either of these sources of projected image. The light image passes through lens 102 into the darkened enclosure 104. Lens 102 focuses the light image onto the surface of transparent conductive layer 106. The light image passes through transparent conductive layer 106 and interacts with photoconductive layer 108. Since photoconductive layer 108 is a layer of segments of photoconductive material, as represented in FIG. 5, the projected light image will be received by individual pixels of photoconductive material. The projected light image, in combination with the voltage impressed across conductive layers 106 and 110, spatially changes the current flowing through the photoconductive layer 108. The voltage is impressed across layers 106 and 110 by energy source 112. Once the projected light image is received by photoconductive layer 108, heat is generated on the individual photoconductive pixels in relation to the intensity of the projected image. Thus, an infrared flux is emitted by each pixel in photoconductive layer 108. The combination of the infrared flux from each pixel in photoconductive layer 108 produces an infrared image simulating the projected image. The infrared image on photoconductive layer 108 is projected through infrared projector lens 114. The infrared flux passing through lens 114 is collimated. The image passing from the simulation cell may be received and viewed by thermal imaging systems. These thermal imaging systems are found in current military and industrial usage. The present invention, in all of its embodiments, offers a number of advantages not found before in previous infrared simulation systems. First, temperature changes within each of the individual pixels of photoconductive material can be greater than 100.degree. centigrade. Such a large temperature change potential provides great infrared resolution. Secondly, this simulation cell can be operated under realtime conditions. This imaging system may receive and convert film operating at 30 frames per second or more. The reason for the above two qualities is the fact that the individual pixels of photoconductive material are very small and thermally isolated from one other such that any rapid temperature changes will quickly diffuse into the heat sink or the dielectric material. Each pixel may have a temperature variation greater than 100.degree. centigrade in combination with an image projected at more than 30 frames per second. Such technology is presently not available in simulation cells of the prior art. Another advantage of the dynamic infrared simulation cell of the present invention is that it can operate with little energy or power expenditure. In the prior art, large amounts of power were required to produce a simulated infrared image. The present invention does not require much power since less mass needs to be heated. Preliminary calculations show that only four milliwatts of power is required to produce a 100.degree. centigrade temperature change in an individual pixel of photoconductive material. Thus, only a few hundred watts of power would be required to operate a cell having a hundred thousand pixels of photoconductive material. These calculations assume a pixel size of 0.002 cm..times.0.001 cm. It should be remembered, of course, that these estimates are only rough calculations. Less power would be required if the individual photoconductive pixels are of smaller size or if the total number of pixels used is less. Still another advantage of the present invention is that an infrared image will be produced by the simulation cell even though the light directed onto the cell is very, very low. The photoconductive material is highly interactive with the light levels of the projected image. If amplification of the projected image is needed such that a "comparatively" bright thermal image is needed in relation to the intensity of the projected image, then the voltage applied across the conductive layers of the cell can be changed to account for these low light levels. Thus, the present invention offers the advantages of being able to receive low levels of projected light and to adjust the intensity of the projected infrared image as desired. The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the details of the illustrated apparatus may be made within the scope of the appended claims without departing from the true spirit of the invention. The present should only be limited by the appended claims and their legal equivalents.
	abstract	An apparatus includes a support and a radioactive source on the support. The radioactive source includes nuclei. An excitation element is coupled to the support. Upon activation of the excitation element, radiation emission from the radioactive source is reduced. The excitation element includes a vibration source. Excitation is transferred from nuclei of the radioactive source to nuclei of the support. The excitation transfer occurs in bulk from multiple nuclei of the radioactive source. The excitation transfer causes emissions from the support.
	abstract	An electron accelerator comprising a resonant cavity, an electron source, an RF system, and at least one magnet unit is provided. The resonant cavity further comprises a hollow closed conductor and the electron source is configured to radially inject a beam of electrons into the cavity. The RF system is configured to generate an electric field to accelerate the electrons along radial trajectories. The at least one magnet unit further comprises a deflecting magnet configured to generate a magnetic field that deflects an electron beam emerging out of the resonant cavity along a first radial trajectory and redirects the electron beam into the resonant cavity along a second radial trajectory. The resonant cavity further comprises a first half shell, a second half shell, and a central ring element.
062333003	abstract	A top guide to shroud head interface is described. In one embodiment, the interface includes a top guide that includes a flange that is configured to engage a corresponding flange of the shroud head. The top guide flange includes a plurality of frusto-conical shaped guide pins extending from the top surface of the flange. The shroud head flange includes a plurality of guide pin openings configured to align with the guide pins located on the top guide flange. Each guide pin opening includes a frusto-conical portion that extends through the flange from the bottom surface of the shroud head flange and has a slope equal to the slope of the frusto-conical pins. Each guide pin opening also includes a cylindrical portion that extends from the small base of the frusto-conical portion of the guide pin opening to the top surface of the shroud head flange. The diameter of the frusto-conical guide pin opening at the bottom surface of the shroud head flange is configured to be larger than the diameter of the frusto-conical guide pin immediately adjacent the top surface of the top guide flange. The frusto-conical guide pins and guide pin openings provide for suitable clearances between the guide pins and the guide pin openings to accommodate any flexing of the shroud head flange during installation.
	description	This application is a continuation-in-part of U.S. patent application Ser. No. 15/167,617 filed May 27, 2016, which is: a continuation-in-part of U.S. patent application Ser. No. 15/152,479 filed May 11, 2016, which: is a continuation-in-part of U.S. patent application Ser. No. 14/216,788 filed Mar. 17, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 13/087,096 filed Apr. 14, 2011, which claims benefit of U.S. provisional patent application No. 61/324,776 filed Apr. 16, 2010; and is a continuation-in-part of U.S. patent application Ser. No. 13/788,890 filed Mar. 7, 2013; is a continuation-in-part of U.S. patent application Ser. No. 14/952,817 filed Nov. 25, 2015, which is a continuation-in-part of U.S. patent application Ser. No. 14/293,861 filed Jun. 2, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 12/985,039 filed Jan. 5, 2011, which claims the benefit of U.S. provisional patent application No. 61/324,776, filed Apr. 16, 2010; is a continuation-in-part of U.S. patent application Ser. No. 14/860,577 filed Sep. 21, 2015, which is a continuation of U.S. patent application Ser. No. 14/223,289 filed Mar. 24, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 14/216,788 filed Mar. 17, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 12/985,039 filed Jan. 5, 2011, which claims the benefit of U.S. provisional patent application No. 61/324,776, filed Apr. 16, 2010; and is a continuation-in-part U.S. patent application Ser. No. 15/073,471 filed Mar. 17, 2016, which claims benefit of U.S. provisional patent application No. 62/304,839 filed Mar. 7, 2016, is a continuation-in-part of U.S. patent application Ser. No. 14/860,577 filed Sep. 21, 2015, which is a continuation of U.S. patent application Ser. No. 14/223,289 filed Mar. 24, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 14/216,788 filed Mar. 17, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 13/572,542 filed Aug. 10, 2012, which is a continuation-in-part of U.S. patent application Ser. No. 12/425,683 filed Apr. 17, 2009, which claims the benefit of U.S. provisional patent application No. 61/055,395 filed May 22, 2008, now U.S. Pat. No. 7,939,809 B2; all of which are incorporated herein in their entirety by this reference thereto. Field of the Invention This invention relates generally to imaging and/or treatment of solid cancers. More particularly, the invention relates to control of a charged particle beam state, such as charged particle position, direction, intensity, density, energy, and/or distribution and/or positioning control of a patient. Discussion of the Prior Art Cancer Treatment Proton therapy works by aiming energetic ionizing particles, such as protons accelerated with a particle accelerator, onto a target tumor. These particles damage the DNA of cells, ultimately causing their death. Cancerous cells, because of their high rate of division and their reduced ability to repair damaged DNA, are particularly vulnerable to attack on their DNA. Patents related to the current invention are summarized here. Proton Beam Therapy System F. Cole, et. al. of Loma Linda University Medical Center “Multi-Station Proton Beam Therapy System”, U.S. Pat. No. 4,870,287 (Sep. 26, 1989) describe a proton beam therapy system for selectively generating and transporting proton beams from a single proton source and accelerator to a selected treatment room of a plurality of patient treatment rooms. Imaging P. Adamee, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 7,274,018 (Sep. 25, 2007) and P. Adamee, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 7,045,781 (May 16, 2006) describe a charged particle beam apparatus configured for serial and/or parallel imaging of an object. K. Hiramoto, et. al. “Ion Beam Therapy System and its Couch Positioning System”, U.S. Pat. No. 7,193,227 (Mar. 20, 2007) describe an ion beam therapy system having an X-ray imaging system moving in conjunction with a rotating gantry. C. Maurer, et. al. “Apparatus and Method for Registration of Images to Physical Space Using a Weighted Combination of Points and Surfaces”, U.S. Pat. No. 6,560,354 (May 6, 2003) described a process of X-ray computed tomography registered to physical measurements taken on the patient's body, where different body parts are given different weights. Weights are used in an iterative registration process to determine a rigid body transformation process, where the transformation function is used to assist surgical or stereotactic procedures. M. Blair, et. al. “Proton Beam Digital Imaging System”, U.S. Pat. No. 5,825,845 (Oct. 20, 1998) describe a proton beam digital imaging system having an X-ray source that is movable into a treatment beam line that can produce an X-ray beam through a region of the body. By comparison of the relative positions of the center of the beam in the patient orientation image and the isocentre in the master prescription image with respect to selected monuments, the amount and direction of movement of the patient to make the best beam center correspond to the target isocentre is determined. S. Nishihara, et. al. “Therapeutic Apparatus”, U.S. Pat. No. 5,039,867 (Aug. 13, 1991) describe a method and apparatus for positioning a therapeutic beam in which a first distance is determined on the basis of a first image, a second distance is determined on the basis of a second image, and the patient is moved to a therapy beam irradiation position on the basis of the first and second distances. There exists in the art of charged particle irradiation therapy a need to know and/or control position, direction, energy, intensity, and/or cross-sectional area or shape of the charged particle beam relative to a patient position, where the controls are individualized to individual patients and/or individual tumor shapes. The invention comprises a motion control system used to control a charged particle beam shape and direction relative to a patient and/or imaging system. Elements and steps in the figures are illustrated for simplicity and clarity and have not necessarily been rendered according to any particular sequence. For example, steps that are performed concurrently or in different order are illustrated in the figures to help improve understanding of embodiments of the present invention. The invention relates generally to control of a charged particle beam shape and direction relative to a patient position and/or an imaging surface, such as a scintillation plate of a tomography system. In one embodiment, multiple linked control stations are used to control position of elements of a beam transport system, nozzle, and/or patient specific beam shaping element relative to a dynamically controlled patient position and/or an imaging surface, element, or system. In another embodiment, a tomography system is optionally used in combination with a charged particle cancer therapy system. Optionally and preferably, a common injector, accelerator, and beam transport system is used for both charged particle based tomographic imaging and charged particle cancer therapy. In one case, an output nozzle of the beam transport system is positioned with a gantry system while the gantry system and/or a patient support maintains a scintillation plate of the tomography system on the opposite side of the patient from the output nozzle. In another example, a charged particle state determination system, of a cancer therapy system or tomographic imaging system, uses one or more coated layers in conjunction with a scintillation detector or a tomographic imaging system at time of tumor and surrounding tissue sample mapping and/or at time of tumor treatment, such as to determine an input vector of the charged particle beam into a patient and/or an output vector of the charged particle beam from the patient. In another example, the charged particle tomography apparatus is used in combination with a charged particle cancer therapy system. For example, tomographic imaging of a cancerous tumor is performed using charged particles generated with an injector, accelerator, and guided with a delivery system. The cancer therapy system uses the same injector, accelerator, and guided delivery system in delivering charged particles to the cancerous tumor. For example, the tomography apparatus and cancer therapy system use a common raster beam method and apparatus for treatment of solid cancers. More particularly, the invention comprises a multi-axis and/or multi-field raster beam charged particle accelerator used in: (1) tomography and (2) cancer therapy. Optionally, the system independently controls patient translation position, patient rotation position, two-dimensional beam trajectory, delivered radiation beam energy, delivered radiation beam intensity, beam velocity, timing of charged particle delivery, and/or distribution of radiation striking healthy tissue. The system operates in conjunction with a negative ion beam source, synchrotron, patient positioning, imaging, and/or targeting method and apparatus to deliver an effective and uniform dose of radiation to a tumor while distributing radiation striking healthy tissue. In another embodiment, a treatment delivery control system (TDCS) or main controller is used to control multiple aspects of the cancer therapy system, including one or more of: an imaging system, such as a CT or PET; a positioner, such as a couch or patient interface module; an injector or injection system; a radio-frequency quadrupole system; a ring accelerator or synchrotron; an extraction system; an irradiation plan; and a display system. The TDCS is preferably a control system for automated cancer therapy once the patient is positioned. The TDCS integrates output of one or more of the below described cancer therapy system elements with inputs of one or more of the below described cancer therapy system elements. More generally, the TDCS controls or manages input and/or output of imaging, an irradiation plan, and charged particle delivery. In yet another embodiment, one or more trays are inserted into the positively charged particle beam path, such as at or near the exit port of a gantry nozzle in close proximity to the patient. Each tray holds an insert, such as a patient specific insert for controlling the energy, focus depth, and/or shape of the charged particle beam. Examples of inserts include a range shifter, a compensator, an aperture, a ridge filter, and a blank. Optionally and preferably, each tray communicates a held and positioned insert to a main controller of the charged particle cancer therapy system. The trays optionally hold one or more of the imaging sheets configured to emit light upon transmission of the charged particle beam through a corresponding localized position of the one or more imaging sheets. Charged Particle Beam Therapy Throughout this document, a charged particle beam therapy system, such as a proton beam, hydrogen ion beam, or carbon ion beam, is described. Herein, the charged particle beam therapy system is described using a proton beam. However, the aspects taught and described in terms of a proton beam are not intended to be limiting to that of a proton beam and are illustrative of a charged particle beam system, a positively charged beam system, and/or a multiply charged particle beam system, such as C4+ or C6+. Any of the techniques described herein are equally applicable to any charged particle beam system. Referring now to FIG. 1A, a charged particle beam system 100 is illustrated. The charged particle beam preferably comprises a number of subsystems including any of: a main controller 110; an injection system 120; a synchrotron 130 that typically includes: (1) an accelerator system 132 and (2) an internal or connected extraction system 134; a beam transport system 135; a scanning/targeting/delivery system 140; a patient interface module 150; a display system 160; and/or an imaging system 170. An exemplary method of use of the charged particle beam system 100 is provided. The main controller 110 controls one or more of the subsystems to accurately and precisely deliver protons to a tumor of a patient. For example, the main controller 110 obtains an image, such as a portion of a body and/or of a tumor, from the imaging system 170. The main controller 110 also obtains position and/or timing information from the patient interface module 150. The main controller 110 optionally controls the injection system 120 to inject a proton into a synchrotron 130. The synchrotron typically contains at least an accelerator system 132 and an extraction system 134. The main controller 110 preferably controls the proton beam within the accelerator system, such as by controlling speed, trajectory, and timing of the proton beam. The main controller then controls extraction of a proton beam from the accelerator through the extraction system 134. For example, the controller controls timing, energy, and/or intensity of the extracted beam. The controller 110 also preferably controls targeting of the proton beam through the scanning/targeting/delivery system 140 to the patient interface module 150. One or more components of the patient interface module 150, such as translational and rotational position of the patient, are preferably controlled by the main controller 110. Further, display elements of the display system 160 are preferably controlled via the main controller 110. Displays, such as display screens, are typically provided to one or more operators and/or to one or more patients. In one embodiment, the main controller 110 times the delivery of the proton beam from all systems, such that protons are delivered in an optimal therapeutic manner to the tumor of the patient. Herein, the main controller 110 refers to a single system controlling the charged particle beam system 100, to a single controller controlling a plurality of subsystems controlling the charged particle beam system 100, or to a plurality of individual controllers controlling one or more sub-systems of the charged particle beam system 100. Referring now to FIG. 12B, a first example of the internal pendant 1218 is provided. In this example, in place of and/or in conjunction with a particular button, such as a first button 1270 and/or a second button 1280, moving or selecting a particular element, processes are optionally described, displayed, and/or selected within a flow process control unit 1260 of the internal pendant 1218. For example, one or more display screens and/or printed elements describe a set of processes, such as a first process 1261, a second process 1263, a third process 1265, and a fourth process 1267 and are selected through a touch screen selection process or via a selection button, such as a corresponding first selector 1262, second selector 1264, third selector 1266, and fourth selector 1268. Referring now to FIG. 1B, an example of a charged particle cancer therapy system 100 is provided. A main controller receives input from one, two, three, or four of a respiration monitoring and/or controlling controller 180, a beam controller 185, a rotation controller 147, and/or a timing to a time period in a respiration cycle controller 148. The beam controller 185 preferably includes one or more or a beam energy controller 182, the beam intensity controller 340, a beam velocity controller 186, and/or a horizontal/vertical beam positioning controller 188. The main controller 110 controls any element of the injection system 120; the synchrotron 130; the scanning/targeting/delivery system 140; the patient interface module 150; the display system 160; and/or the imaging system 170. For example, the respiration monitoring/controlling controller 180 controls any element or method associated with the respiration of the patient; the beam controller 185 controls any of the elements controlling acceleration and/or extraction of the charged particle beam; the rotation controller 147 controls any element associated with rotation of the patient 830 or gantry; and the timing to a period in respiration cycle controller 148 controls any aspects affecting delivery time of the charged particle beam to the patient. As a further example, the beam controller 185 optionally controls any magnetic and/or electric field about any magnet in the charged particle cancer therapy system 100. One or more beam state sensors 190 sense position, direction, intensity, and/or energy of the charged particles at one or more positions in the charged particle beam path. A tomography system 700, described infra, is optionally used to monitor intensity and/or position of the charged particle beam. Referring now to FIG. 2, an illustrative exemplary embodiment of one version of the charged particle beam system 100 is provided. The number, position, and described type of components is illustrative and non-limiting in nature. In the illustrated embodiment, the injection system 120 or ion source or charged particle beam source generates protons. The injection system 120 optionally includes one or more of: a negative ion beam source, an ion beam focusing lens, and a tandem accelerator. The protons are delivered into a vacuum tube that runs into, through, and out of the synchrotron. The generated protons are delivered along an initial path 262. Focusing magnets 230, such as quadrupole magnets or injection quadrupole magnets, are used to focus the proton beam path. A quadrupole magnet is a focusing magnet. An injector bending magnet 232 bends the proton beam toward a plane of the synchrotron 130. The focused protons having an initial energy are introduced into an injector magnet 240, which is preferably an injection Lamberson magnet. Typically, the initial beam path 262 is along an axis off of, such as above, a circulating plane of the synchrotron 130. The injector bending magnet 232 and injector magnet 240 combine to move the protons into the synchrotron 130. Main bending magnets, dipole magnets, turning magnets, or circulating magnets 250 are used to turn the protons along a circulating beam path 264. A dipole magnet is a bending magnet. The main bending magnets 250 bend the initial beam path 262 into a circulating beam path 264. In this example, the main bending magnets 250 or circulating magnets are represented as four sets of four magnets to maintain the circulating beam path 264 into a stable circulating beam path. However, any number of magnets or sets of magnets are optionally used to move the protons around a single orbit in the circulation process. The protons pass through an accelerator 270. The accelerator accelerates the protons in the circulating beam path 264. As the protons are accelerated, the fields applied by the magnets are increased. Particularly, the speed of the protons achieved by the accelerator 270 are synchronized with magnetic fields of the main bending magnets 250 or circulating magnets to maintain stable circulation of the protons about a central point or region 280 of the synchrotron. At separate points in time the accelerator 270/main bending magnet 250 combination is used to accelerate and/or decelerate the circulating protons while maintaining the protons in the circulating path or orbit. An extraction element of an inflector/deflector system is used in combination with a Lamberson extraction magnet 292 to remove protons from their circulating beam path 264 within the synchrotron 130. One example of a deflector component is a Lamberson magnet. Typically the deflector moves the protons from the circulating plane to an axis off of the circulating plane, such as above the circulating plane. Extracted protons are preferably directed and/or focused using an extraction bending magnet 237 and extraction focusing magnets 235, such as quadrupole magnets along a positively charged particle beam transport path 268 in a beam transport system 135, such as a beam path or proton beam path, into the scanning/targeting/delivery system 140. Two components of a scanning system 140 or targeting system typically include a first axis control 142, such as a vertical control, and a second axis control 144, such as a horizontal control. In one embodiment, the first axis control 142 allows for about 100 mm of vertical or y-axis scanning of the proton beam 268 and the second axis control 144 allows for about 700 mm of horizontal or x-axis scanning of the proton beam 268. A nozzle system 146 is used for imaging the proton beam, for defining shape of the proton beam, and/or as a vacuum barrier between the low pressure beam path of the synchrotron and the atmosphere. Protons are delivered with control to the patient interface module 150 and to a tumor of a patient. All of the above listed elements are optional and may be used in various permutations and combinations. Proton Beam Extraction Referring now to FIG. 3, both: (1) an exemplary proton beam extraction system 300 from the synchrotron 130 and (2) a charged particle beam intensity control system 305 are illustrated. For clarity, FIG. 3 removes elements represented in FIG. 2, such as the turning magnets, which allows for greater clarity of presentation of the proton beam path as a function of time. Generally, protons are extracted from the synchrotron 130 by slowing the protons. As described, supra, the protons were initially accelerated in a circulating path, which is maintained with a plurality of main bending magnets 250. The circulating path is referred to herein as an original central beamline 264. The protons repeatedly cycle around a central point in the synchrotron 280. The proton path traverses through a radio frequency (RF) cavity system 310. To initiate extraction, an RF field is applied across a first blade 312 and a second blade 314, in the RF cavity system 310. The first blade 312 and second blade 314 are referred to herein as a first pair of blades. In the proton extraction process, an RF voltage is applied across the first pair of blades, where the first blade 312 of the first pair of blades is on one side of the circulating proton beam path 264 and the second blade 314 of the first pair of blades is on an opposite side of the circulating proton beam path 264. The applied RF field applies energy to the circulating charged-particle beam. The applied RF field alters the orbiting or circulating beam path slightly of the protons from the original central beamline 264 to an altered circulating beam path 265. Upon a second pass of the protons through the RF cavity system, the RF field further moves the protons off of the original proton beamline 264. For example, if the original beamline is considered as a circular path, then the altered beamline is slightly elliptical. The frequency of the applied RF field is timed to apply outward or inward movement to a given band of protons circulating in the synchrotron accelerator. Orbits of the protons are slightly more off axis compared to the original circulating beam path 264. Successive passes of the protons through the RF cavity system are forced further and further from the original central beamline 264 by altering the direction and/or intensity of the RF field with each successive pass of the proton beam through the RF field. Timing of application of the RF field and/or frequency of the RF field is related to the circulating charged particles circulation pathlength in the synchrotron 130 and the velocity of the charged particles so that the applied RF field has a period, with a peak-to-peak time period, equal to a period of time of beam circulation in the synchrotron 130 about the center 280 or an integer multiple of the time period of beam circulation about the center 280 of the synchrotron 130. Alternatively, the time period of beam circulation about the center 280 of the synchrotron 130 is an integer multiple of the RF period time. The RF period is optionally used to calculated the velocity of the charged particles, which relates directly to the energy of the circulating charged particles. The RF voltage is frequency modulated at a frequency about equal to the period of one proton cycling around the synchrotron for one revolution or at a frequency than is an integral multiplier of the period of one proton cycling about the synchrotron. The applied RF frequency modulated voltage excites a betatron oscillation. For example, the oscillation is a sine wave motion of the protons. The process of timing the RF field to a given proton beam within the RF cavity system is repeated thousands of times with each successive pass of the protons being moved approximately one micrometer further off of the original central beamline 264. For clarity, the approximately 1000 changing beam paths with each successive path of a given band of protons through the RF field are illustrated as the altered beam path 265. The RF time period is process is known, thus energy of the charged particles at time of hitting the extraction material or material 330, described infra, is known. With a sufficient sine wave betatron amplitude, the altered circulating beam path 265 touches and/or traverses a material 330, such as a foil or a sheet of foil. The foil is preferably a lightweight material, such as beryllium, a lithium hydride, a carbon sheet, or a material having low nuclear charge components. Herein, a material of low nuclear charge is a material composed of atoms consisting essentially of atoms having six or fewer protons. The foil is preferably about 10 to 150 microns thick, is more preferably about 30 to 100 microns thick, and is still more preferably about 40 to 60 microns thick. In one example, the foil is beryllium with a thickness of about 50 microns. When the protons traverse through the foil, energy of the protons is lost and the speed of the protons is reduced. Typically, a current is also generated, described infra. Protons moving at the slower speed travel in the synchrotron with a reduced radius of curvature 266 compared to either the original central beamline 264 or the altered circulating path 265. The reduced radius of curvature 266 path is also referred to herein as a path having a smaller diameter of trajectory or a path having protons with reduced energy. The reduced radius of curvature 266 is typically about two millimeters less than a radius of curvature of the last pass of the protons along the altered proton beam path 265. The thickness of the material 330 is optionally adjusted to create a change in the radius of curvature, such as about ½, 1, 2, 3, or 4 mm less than the last pass of the protons 265 or original radius of curvature 264. The reduction in velocity of the charged particles transmitting through the material 330 is calculable, such as by using the pathlength of the betatron oscillating charged particle beam through the material 330 and/or using the density of the material 330. Protons moving with the smaller radius of curvature travel between a second pair of blades. In one case, the second pair of blades is physically distinct and/or is separated from the first pair of blades. In a second case, one of the first pair of blades is also a member of the second pair of blades. For example, the second pair of blades is the second blade 314 and a third blade 316 in the RF cavity system 310. A high voltage DC signal, such as about 1 to 5 kV, is then applied across the second pair of blades, which directs the protons out of the synchrotron through an extraction magnet 292, such as a Lamberson extraction magnet, into a transport path 268. Control of acceleration of the charged particle beam path in the synchrotron with the accelerator and/or applied fields of the turning magnets in combination with the above described extraction system allows for control of the intensity of the extracted proton beam, where intensity is a proton flux per unit time or the number of protons extracted as a function of time. For example, when a current is measured beyond a threshold, the RF field modulation in the RF cavity system is terminated or reinitiated to establish a subsequent cycle of proton beam extraction. This process is repeated to yield many cycles of proton beam extraction from the synchrotron accelerator. In another embodiment, instead of moving the charged particles to the material 330, the material 330 is mechanically moved to the circulating charged particles. Particularly, the material 330 is mechanically or electromechanically translated into the path of the circulating charged particles to induce the extraction process, described supra. In this case, the velocity or energy of the circulating charged particle beam is calculable using the pathlength of the beam path about the center 280 of the synchrotron 130 and from the force applied by the bending magnets 250. In either case, because the extraction system does not depend on any change in magnetic field properties, it allows the synchrotron to continue to operate in acceleration or deceleration mode during the extraction process. Stated differently, the extraction process does not interfere with synchrotron acceleration. In stark contrast, traditional extraction systems introduce a new magnetic field, such as via a hexapole, during the extraction process. More particularly, traditional synchrotrons have a magnet, such as a hexapole magnet, that is off during an acceleration stage. During the extraction phase, the hexapole magnetic field is introduced to the circulating path of the synchrotron. The introduction of the magnetic field necessitates two distinct modes, an acceleration mode and an extraction mode, which are mutually exclusive in time. The herein described system allows for acceleration and/or deceleration of the proton during the extraction step and tumor treatment without the use of a newly introduced magnetic field, such as by a hexapole magnet. Charged Particle Beam Intensity Control Control of applied field, such as a radio-frequency (RF) field, frequency and magnitude in the RF cavity system 310 allows for intensity control of the extracted proton beam, where intensity is extracted proton flux per unit time or the number of protons extracted as a function of time. Still referring FIG. 3, the intensity control system 305 is further described. In this example, an intensity control feedback loop is added to the extraction system, described supra. When protons in the proton beam hit the material 330 electrons are given off from the material 330 resulting in a current. The resulting current is converted to a voltage and is used as part of an ion beam intensity monitoring system or as part of an ion beam feedback loop for controlling beam intensity. The voltage is optionally measured and sent to the main controller 110 or to an intensity controller subsystem 340, which is preferably in communication or under the direction of the main controller 110. More particularly, when protons in the charged particle beam path pass through the material 330, some of the protons lose a small fraction of their energy, such as about one-tenth of a percent, which results in a secondary electron. That is, protons in the charged particle beam push some electrons when passing through material 330 giving the electrons enough energy to cause secondary emission. The resulting electron flow results in a current or signal that is proportional to the number of protons going through the target or extraction material 330. The resulting current is preferably converted to voltage and amplified. The resulting signal is referred to as a measured intensity signal. The amplified signal or measured intensity signal resulting from the protons passing through the material 330 is optionally used in monitoring the intensity of the extracted protons and is preferably used in controlling the intensity of the extracted protons. For example, the measured intensity signal is compared to a goal signal, which is predetermined in an irradiation of the tumor plan. The difference between the measured intensity signal and the planned for goal signal is calculated. The difference is used as a control to the RF generator. Hence, the measured flow of current resulting from the protons passing through the material 330 is used as a control in the RF generator to increase or decrease the number of protons undergoing betatron oscillation and striking the material 330. Hence, the voltage determined off of the material 330 is used as a measure of the orbital path and is used as a feedback control to control the RF cavity system. In one example, the intensity controller subsystem 340 preferably additionally receives input from: (1) a detector 350, which provides a reading of the actual intensity of the proton beam and/or (2) an irradiation plan 360. The irradiation plan provides the desired intensity of the proton beam for each x, y, energy, and/or rotational position of the patient/tumor as a function of time. Thus, the intensity controller 340 receives the desired intensity from the irradiation plan 350, the actual intensity from the detector 350 and/or a measure of intensity from the material 330, and adjusts the amplitude and/or the duration of application of the applied radio-frequency field in the RF cavity system 310 to yield an intensity of the proton beam that matches the desired intensity from the irradiation plan 360. As described, supra, the protons striking the material 330 is a step in the extraction of the protons from the synchrotron 130. Hence, the measured intensity signal is used to change the number of protons per unit time being extracted, which is referred to as intensity of the proton beam. The intensity of the proton beam is thus under algorithm control. Further, the intensity of the proton beam is controlled separately from the velocity of the protons in the synchrotron 130. Hence, intensity of the protons extracted and the energy of the protons extracted are independently variable. Still further, the intensity of the extracted protons is controllably variable while scanning the charged particles beam in the tumor from one voxel to an adjacent voxel as a separate hexapole and separated time period from acceleration and/or treatment is not required, as described supra. For example, protons initially move at an equilibrium trajectory in the synchrotron 130. An RF field is used to excite or move the protons into a betatron oscillation. In one case, the frequency of the protons orbit is about 10 MHz. In one example, in about one millisecond or after about 10,000 orbits, the first protons hit an outer edge of the target material 130. The specific frequency is dependent upon the period of the orbit. Upon hitting the material 130, the protons push electrons through the foil to produce a current. The current is converted to voltage and amplified to yield a measured intensity signal. The measured intensity signal is used as a feedback input to control the applied RF magnitude or RF field. An energy beam sensor, described infra, is optionally used as a feedback control to the RF field frequency or RF field of the RF field extraction system 310 to dynamically control, modify, and/or alter the delivered charge particle beam energy, such as in a continuous pencil beam scanning system operating to treat tumor voxels without alternating between an extraction phase and a treatment phase. Preferably, the measured intensity signal is compared to a target signal and a measure of the difference between the measured intensity signal and target signal is used to adjust the applied RF field in the RF cavity system 310 in the extraction system to control the intensity of the protons in the extraction step. Stated again, the signal resulting from the protons striking and/or passing through the material 130 is used as an input in RF field modulation. An increase in the magnitude of the RF modulation results in protons hitting the foil or material 130 sooner. By increasing the RF, more protons are pushed into the foil, which results in an increased intensity, or more protons per unit time, of protons extracted from the synchrotron 130. In another example, a detector 350 external to the synchrotron 130 is used to determine the flux of protons extracted from the synchrotron and a signal from the external detector is used to alter the RF field, RF intensity, RF amplitude, and/or RF modulation in the RF cavity system 310. Here the external detector generates an external signal, which is used in a manner similar to the measured intensity signal, described in the preceding paragraphs. Preferably, an algorithm or irradiation plan 360 is used as an input to the intensity controller 340, which controls the RF field modulation by directing the RF signal in the betatron oscillation generation in the RF cavity system 310. The irradiation plan 360 preferably includes the desired intensity of the charged particle beam as a function of time and/or energy of the charged particle beam as a function of time, for each patient rotation position, and/or for each x-, y-position of the charged particle beam. In yet another example, when a current from material 330 resulting from protons passing through or hitting material is measured beyond a threshold, the RF field modulation in the RF cavity system is terminated or reinitiated to establish a subsequent cycle of proton beam extraction. This process is repeated to yield many cycles of proton beam extraction from the synchrotron accelerator. In still yet another embodiment, intensity modulation of the extracted proton beam is controlled by the main controller 110. The main controller 110 optionally and/or additionally controls timing of extraction of the charged particle beam and energy of the extracted proton beam. The benefits of the system include a multi-dimensional scanning system. Particularly, the system allows independence in: (1) energy of the protons extracted and (2) intensity of the protons extracted. That is, energy of the protons extracted is controlled by an energy control system and an intensity control system controls the intensity of the extracted protons. The energy control system and intensity control system are optionally independently controlled. Preferably, the main controller 110 controls the energy control system and the main controller 110 simultaneously controls the intensity control system to yield an extracted proton beam with controlled energy and controlled intensity where the controlled energy and controlled intensity are independently variable and/or continually available as a separate extraction phase and acceleration phase are not required, as described supra. Thus the irradiation spot hitting the tumor is under independent control of: time; energy; intensity; x-axis position, where the x-axis represents horizontal movement of the proton beam relative to the patient, and y-axis position, where the y-axis represents vertical movement of the proton beam relative to the patient. In addition, the patient is optionally independently translated and/or rotated relative to a translational axis of the proton beam at the same time. Beam Transport The beam transport system 135 is used to move the charged particles from the accelerator to the patient, such as via a nozzle in a gantry, described infra. Charged Particle Energy The beam transport system 135 optionally includes means for determining an energy of the charged particles in the charged particle beam. For example, an energy of the charged particle beam is determined via calculation, such as via equation 1, using knowledge of a magnet geometry and applied magnetic field to determine mass and/or energy. Referring now to equation 1, for a known magnet geometry, charge, q, and magnetic field, B, the Larmor radius, ρL, or magnet bend radius is defined as: ρ L = v ⊥ Ω c = 2 ⁢ Em qB ( eq . ⁢ 1 ) where: ν⊥ is the ion velocity perpendicular to the magnetic field, Ωc is the cyclotron frequency, q is the charge of the ion, B is the magnetic field, m is the mass of the charge particle, and E is the charged particle energy. Solving for the charged particle energy yields equation 2. E = ( ρ L ⁢ qB ) 2 2 ⁢ m ( eq . ⁢ 2 ) Thus, an energy of the charged particle in the charged particle beam in the beam transport system 135 is calculable from the know magnet geometry, known or measured magnetic field, charged particle mass, charged particle charge, and the known magnet bend radius, which is proportional to and/or equivalent to the Larmor radius. Nozzle After extraction from the synchrotron 130 and transport of the charged particle beam along the proton beam path 268 in the beam transport system 135, the charged particle beam exits through the nozzle system 146. In one example, the nozzle system includes a nozzle foil covering an end of the nozzle system 146 or a cross-sectional area within the nozzle system forming a vacuum seal. The nozzle system includes a nozzle that expands in x/y-cross-sectional area along the z-axis of the proton beam path 268 to allow the proton beam 268 to be scanned along the x-axis and y-axis by the vertical control element and horizontal control element, respectively. The nozzle foil is preferably mechanically supported by the outer edges of an exit port of the nozzle 146. An example of a nozzle foil is a sheet of about 0.1 inch thick aluminum foil. Generally, the nozzle foil separates atmosphere pressures on the patient side of the nozzle foil from the low pressure region, such as about 10−5 to 10−7 torr region, on the synchrotron 130 side of the nozzle foil. The low pressure region is maintained to reduce scattering of the circulating charged particle beam in the synchrotron. Herein, the exit foil of the nozzle is optionally the first sheet 760 of the charged particle beam state determination system 750, described infra. Charged Particle Control Referring now to FIG. 4A, FIG. 4B, FIG. 5, FIG. 6A, and FIG. 6B, a charged particle beam control system is described where one or more patient specific beam control assemblies are removably inserted into the charged particle beam path proximate the nozzle of the charged particle cancer therapy system 100, where the patient specific beam control assemblies adjust the beam energy, diameter, cross-sectional shape, focal point, and/or beam state of the charged particle beam to properly couple energy of the charged particle beam to the individual's specific tumor. Beam Control Tray Referring now to FIG. 4A and FIG. 4B, a beam control tray assembly 400 is illustrated in a top view and side view, respectively. The beam control tray assembly 400 optionally comprises any of a tray frame 410, a tray aperture 412, a tray handle 420, a tray connector/communicator 430, and means for holding a patient specific tray insert 510, described infra. Generally, the beam control tray assembly 400 is used to: (1) hold the patient specific tray insert 510 in a rigid location relative to the beam control tray 400, (2) electronically identify the held patient specific tray insert 510 to the main controller 110, and (3) removably insert the patient specific tray insert 510 into an accurate and precise fixed location relative to the charged particle beam, such as the proton beam path 268 at the nozzle of the charged particle cancer therapy system 100. For clarity of presentation and without loss of generality, the means for holding the patient specific tray insert 510 in the tray frame 410 of the beam control tray assembly 400 is illustrated as a set of recessed set screws 415. However, the means for holding the patient specific tray insert 510 relative to the rest of the beam control tray assembly 400 is optionally any mechanical and/or electromechanical positioning element, such as a latch, clamp, fastener, clip, slide, strap, or the like. Generally, the means for holding the patient specific tray insert 510 in the beam control tray 400 fixes the tray insert and tray frame relative to one another even when rotated along and/or around multiple axes, such as when attached to a charged particle cancer therapy system 100 dynamic gantry nozzle 610 or gantry nozzle, which is an optional element of the nozzle system 146, that moves in three-dimensional space relative to a fixed point in the beamline, proton beam path 268, and/or a given patient position. As illustrated in FIG. 4A and FIG. 4B, the recessed set screws 415 fix the patient specific tray insert 510 into the aperture 412 of the tray frame 410. The tray frame 410 is illustrated as circumferentially surrounding the patient specific tray insert 510, which aids in structural stability of the beam control tray assembly 400. However, generally the tray frame 410 is of any geometry that forms a stable beam control tray assembly 400. Still referring to FIG. 4A and now referring to FIG. 5 and FIG. 6A, the optional tray handle 420 is used to manually insert/retract the beam control tray assembly 400 into a receiving element of the gantry nozzle or dynamic gantry nozzle 610. While the beam control tray assembly 400 is optionally inserted into the charged particle beam path 268 at any point after extraction from the synchrotron 130, the beam control tray assembly 400 is preferably inserted into the positively charged particle beam proximate the dynamic gantry nozzle 610 as control of the beam shape is preferably done with little space for the beam shape to defocus before striking the tumor. Optionally, insertion and/or retraction of the beam control tray assembly 400 is semi-automated, such as in a manner of a digital-video disk player receiving a digital-video disk, with a selected auto load and/or a selected auto unload feature. Patient Specific Tray Insert Referring again to FIG. 5, a system of assembling trays 500 is described. The beam control tray assembly 400 optionally and preferably has interchangeable patient specific tray inserts 510, such as a range shifter insert 511, a patient specific ridge filter insert 512, an aperture insert 513, a compensator insert 514, or a blank insert 515. As described, supra, any of the range shifter insert 511, the patient specific ridge filter insert 512, the aperture insert 513, the compensator insert 514, or the blank insert 515 after insertion into the tray frame 410 are inserted as the beam control tray assembly 400 into the positively charged particle beam path 268, such as proximate the dynamic gantry nozzle 610. Still referring to FIG. 5, the patient specific tray inserts 510 are further described. The patient specific tray inserts comprise a combination of any of: (1) a standardized beam control insert and (2) a patient specific beam control insert. For example, the range shifter insert or 511 or compensator insert 514 used to control the depth of penetration of the charged particle beam into the patient is optionally: (a) a standard thickness of a beam slowing material, such as a first thickness of Lucite, (b) one member of a set of members of varying thicknesses and/or densities where each member of the set of members slows the charged particles in the beam path by a known amount, or (c) is a material with a density and thickness designed to slow the charged particles by a customized amount for the individual patient being treated, based on the depth of the individual's tumor in the tissue, the thickness of intervening tissue, and/or the density of intervening bone/tissue. Similarly, the ridge filter insert 512 used to change the focal point or shape of the beam as a function of depth is optionally: (1) selected from a set of ridge filters where different members of the set of ridge filters yield different focal depths or (2) customized for treatment of the individual's tumor based on position of the tumor in the tissue of the individual. Similarly, the aperture insert is: (1) optionally selected from a set of aperture shapes or (2) is a customized individual aperture insert 513 designed for the specific shape of the individual's tumor. The blank insert 515 is an open slot, but serves the purpose of identifying slot occupancy, as described infra. Slot Occupancy/Identification Referring again to FIG. 4A, FIG. 4B, and FIG. 5, occupancy and identification of the particular patient specific tray insert 510 into the beam control tray assembly 400 is described. Generally, the beam control tray assembly 400 optionally contains means for identifying, to the main controller 110 and/or a treatment delivery control system described infra, the specific patient tray insert 510 and its location in the charged particle beam path 268. First, the particular tray insert is optionally labeled and/or communicated to the beam control tray assembly 400 or directly to the main controller 110. Second, the beam control tray assembly 400 optionally communicates the tray type and/or tray insert to the main controller 110. In various embodiments, communication of the particular tray insert to the main controller 110 is performed: (1) directly from the tray insert, (2) from the tray insert 510 to the tray assembly 400 and subsequently to the main controller 110, and/or (3) directly from the tray assembly 400. Generally, communication is performed wirelessly and/or via an established electromechanical link. Identification is optionally performed using a radio-frequency identification label, use of a barcode, or the like, and/or via operator input. Examples are provided to further clarify identification of the patient specific tray insert 510 in a given beam control tray assembly 400 to the main controller. In a first example, one or more of the patient specific tray inserts 510, such as the range shifter insert 511, the patient specific ridge filter insert 512, the aperture insert 513, the compensator insert 514, or the blank insert 515 include an identifier 520 and/or and a first electromechanical identifier plug 530. The identifier 520 is optionally a label, a radio-frequency identification tag, a barcode, a 2-dimensional bar-code, a matrix-code, or the like. The first electromechanical identifier plug 530 optionally includes memory programmed with the particular patient specific tray insert information and a connector used to communicate the information to the beam control tray assembly 400 and/or to the main controller 110. As illustrated in FIG. 5, the first electromechanical identifier plug 530 affixed to the patient specific tray insert 510 plugs into a second electromechanical identifier plug, such as the tray connector/communicator 430, of the beam control tray assembly 400, which is described infra. In a second example, the beam control tray assembly 400 uses the second electromechanical identifier plug to send occupancy, position, and/or identification information related to the type of tray insert or the patient specific tray insert 510 associated with the beam control tray assembly to the main controller 110. For example, a first tray assembly is configured with a first tray insert and a second tray assembly is configured with a second tray insert. The first tray assembly sends information to the main controller 110 that the first tray assembly holds the first tray insert, such as a range shifter, and the second tray assembly sends information to the main controller 110 that the second tray assembly holds the second tray insert, such as an aperture. The second electromechanical identifier plug optionally contains programmable memory for the operator to input the specific tray insert type, a selection switch for the operator to select the tray insert type, and/or an electromechanical connection to the main controller. The second electromechanical identifier plug associated with the beam control tray assembly 400 is optionally used without use of the first electromechanical identifier plug 530 associated with the tray insert 510. In a third example, one type of tray connector/communicator 430 is used for each type of patient specific tray insert 510. For example, a first connector/communicator type is used for holding a range shifter insert 511, while a second, third, fourth, and fifth connector/communicator type is used for trays respectively holding a patient specific ridge filter insert 512, an aperture insert 513, a compensator insert 514, or a blank insert 515. In one case, the tray communicates tray type with the main controller. In a second case, the tray communicates patient specific tray insert information with the main controller, such as an aperture identifier custom built for the individual patient being treated. Tray Insertion/Coupling Referring now to FIG. 6A and FIG. 6B a beam control insertion process 600 is described. The beam control insertion process 600 comprises: (1) insertion of the beam control tray assembly 400 and the associated patient specific tray insert 510 into the charged particle beam path 268 and/or dynamic gantry nozzle 610, such as into a tray assembly receiver 620 and (2) an optional partial or total retraction of beam of the tray assembly receiver 620 into the dynamic gantry nozzle 610. Referring now to FIG. 6A, insertion of one or more of the beam control tray assemblies 400 and the associated patient specific tray inserts 510 into the dynamic gantry nozzle 610 is further described. In FIG. 6A, three beam control tray assemblies, of a possible n tray assemblies, are illustrated, a first tray assembly 402, a second tray assembly 404, and a third tray assembly 406, where n is a positive integer of 1, 2, 3, 4, 5 or more. As illustrated, the first tray assembly 402 slides into a first receiving slot 403, the second tray assembly 404 slides into a second receiving slot 405, and the third tray assembly 406 slides into a third receiving slot 407. Generally, any tray optionally inserts into any slot or tray types are limited to particular slots through use of a mechanical, physical, positional, and/or steric constraints, such as a first tray type configured for a first insert type having a first size and a second tray type configured for a second insert type having a second distinct size at least ten percent different from the first size. Still referring to FIG. 6A, identification of individual tray inserts inserted into individual receiving slots is further described. As illustrated, sliding the first tray assembly 402 into the first receiving slot 403 connects the associated electromechanical connector/communicator 430 of the first tray assembly 402 to a first receptor 626. The electromechanical connector/communicator 430 of the first tray assembly communicates tray insert information of the first beam control tray assembly to the main controller 110 via the first receptor 626. Similarly, sliding the second tray assembly 404 into the second receiving slot 405 connects the associated electromechanical connector/communicator 430 of the second tray assembly 404 into a second receptor 627, which links communication of the associated electromechanical connector/communicator 430 with the main controller 110 via the second receptor 627, while a third receptor 628 connects to the electromechanical connected placed into the third slot 407. The non-wireless/direct connection is preferred due to the high radiation levels within the treatment room and the high shielding of the treatment room, which both hinder wireless communication. The connection of the communicator and the receptor is optionally of any configuration and/or orientation. Tray Receiver Assembly Retraction Referring again to FIG. 6A and FIG. 6B, retraction of the tray receiver assembly 620 relative to a nozzle end 612 of the dynamic gantry nozzle 610 is described. The tray receiver assembly 620 comprises a framework to hold one or more of the beam control tray assemblies 400 in one or more slots, such as through use of a first tray receiver assembly side 622 through which the beam control tray assemblies 400 are inserted and/or through use of a second tray receiver assembly side 624 used as a backstop, as illustrated holding the plugin receptors configured to receive associated tray connector/communicators 430, such as the first, second, and third receptors 626, 627, 628. Optionally, the tray receiver assembly 620 retracts partially or completely into the dynamic gantry nozzle 610 using a retraction mechanism 660 configured to alternatingly retract and extend the tray receiver assembly 620 relative to a nozzle end 612 of the gantry nozzle 610, such as along a first retraction track 662 and a second retraction track 664 using one or more motors and computer control. Optionally the tray receiver assembly 620 is partially or fully retracted when moving the gantry, nozzle, and/or gantry nozzle 610 to avoid physical constraints of movement, such as potential collision with another object in the patient treatment room. For clarity of presentation and without loss of generality, several examples of loading patient specific tray inserts into tray assemblies with subsequent insertion into an positively charged particle beam path proximate a gantry nozzle 610 are provided. In a first example, a single beam control tray assembly 400 is used to control the charged particle beam 268 in the charged particle cancer therapy system 100. In this example, a patient specific range shifter insert 511, which is custom fabricated for a patient, is loaded into a patient specific tray insert 510 to form a first tray assembly 402, where the first tray assembly 402 is loaded into the third receptor 628, which is fully retracted into the gantry nozzle 610. In a second example, two beam control assemblies 400 are used to control the charged particle beam 268 in the charged particle cancer therapy system 100. In this example, a patient specific ridge filter 512 is loaded into a first tray assembly 402, which is loaded into the second receptor 627 and a patient specific aperture 513 is loaded into a second tray assembly 404, which is loaded into the first receptor 626 and the two associated tray connector/communicators 430 using the first receptor 626 and second receptor 627 communicate to the main controller 110 the patient specific tray inserts 510. The tray receiver assembly 620 is subsequently retracted one slot so that the patient specific ridge filter 512 and the patient specific aperture reside outside of and at the nozzle end 612 of the gantry nozzle 610. In a third example, three beam control tray assemblies 400 are used, such as a range shifter 511 in a first tray inserted into the first receiving slot 403, a compensator in a second tray inserted into the second receiving slot 405, and an aperture in a third tray inserted into the third receiving slot 407. Generally, any patient specific tray insert 510 is inserted into a tray frame 410 to form a beam control tray assembly 400 inserted into any slot of the tray receiver assembly 620 and the tray assembly is not retracted or retracted any distance into the gantry nozzle 610. Tomography/Beam State In one embodiment, the charged particle tomography apparatus is used to image a tumor in a patient. As current beam position determination/verification is used in both tomography and cancer therapy treatment, for clarity of presentation and without limitation beam state determination is also addressed in this section. However, beam state determination is optionally used separately and without tomography. In another example, the charged particle tomography apparatus is used in combination with a charged particle cancer therapy system using common elements. For example, tomographic imaging of a cancerous tumor is performed using charged particles generated with an injector, accelerator, and guided with a delivery system that are part of the cancer therapy system, described supra. In various examples, the tomography imaging system is optionally simultaneously operational with a charged particle cancer therapy system using common elements, allows tomographic imaging with rotation of the patient, is operational on a patient in an upright, semi-upright, and/or horizontal position, is simultaneously operational with X-ray imaging, and/or allows use of adaptive charged particle cancer therapy. Further, the common tomography and cancer therapy apparatus elements are optionally operational in a multi-axis and/or multi-field raster beam mode. In conventional medical X-ray tomography, a sectional image through a body is made by moving one or both of an X-ray source and the X-ray film in opposite directions during the exposure. By modifying the direction and extent of the movement, operators can select different focal planes, which contain the structures of interest. More modern variations of tomography involve gathering projection data from multiple directions by moving the X-ray source and feeding the data into a tomographic reconstruction software algorithm processed by a computer. Herein, in stark contrast to known methods, the radiation source is a charged particle, such as a proton ion beam or a carbon ion beam. A proton beam is used herein to describe the tomography system, but the description applies to a heavier ion beam, such as a carbon ion beam. Further, in stark contrast to known techniques, herein the radiation source is preferably stationary while the patient is rotated. Referring now to FIG. 7, an example of a tomography apparatus is described and an example of a beam state determination is described. In this example, the tomography system 700 uses elements in common with the charged particle beam system 100, including elements of one or more of the injection system 120, accelerator 130, targeting/delivery system 140, patient interface module 150, display system 160, and/or imaging system 170, such as the X-ray imaging system. One or more scintillation plates, such as a scintillating plastic, are used to measure energy, intensity, and/or position of the charged particle beam. For instance, a scintillation plate 710 is positioned behind the patient 730 relative to the targeting/delivery system 140 elements, which is optionally used to measure intensity and/or position of the charged particle beam after transmitting through the patient. Optionally, a second scintillation plate or a charged particle induced photon emitting sheet, described infra, is positioned prior to the patient 730 relative to the targeting/delivery system 140 elements, which is optionally used to measure incident intensity and/or position of the charged particle beam prior to transmitting through the patient. The charged particle beam system 100 as described has proven operation at up to and including 330 MeV, which is sufficient to send protons through the body and into contact with the scintillation material. Particularly, 250 MeV to 330 MeV are used to pass the beam through a standard sized patient with a standard sized pathlength, such as through the chest. The intensity or count of protons hitting the plate as a function of position is used to create an image. The velocity or energy of the proton hitting the scintillation plate is also used in creation of an image of the tumor 720 and/or an image of the patient 730. The patient 730 is rotated about the y-axis and a new image is collected. Preferably, a new image is collected with about every one degree of rotation of the patient resulting in about 360 images that are combined into a tomogram using tomographic reconstruction software. The tomographic reconstruction software uses overlapping rotationally varied images in the reconstruction. Optionally, a new image is collected at about every 2, 3, 4, 5, 10, 15, 30, or 45 degrees of rotation of the patient. In one embodiment, a tomogram or an individual tomogram section image is collected at about the same time as cancer therapy occurs using the charged particle beam system 100. For example, a tomogram is collected and cancer therapy is subsequently performed: without the patient moving from the positioning systems, such as in a semi-vertical partial immobilization system, a sitting partial immobilization system, or the a laying position. In a second example, an individual tomogram slice is collected using a first cycle of the accelerator 130 and using a following cycle of the accelerator 130, the tumor 720 is irradiated, such as within about 1, 2, 5, 10, 15 or 30 seconds. In a third case, about 2, 3, 4, or 5 tomogram slices are collected using 1, 2, 3, 4, or more rotation positions of the patient 730 within about 5, 10, 15, 30, or 60 seconds of subsequent tumor irradiation therapy. In another embodiment, the independent control of the tomographic imaging process and X-ray collection process allows simultaneous single and/or multi-field collection of X-ray images and tomographic images easing interpretation of multiple images. Indeed, the X-ray and tomographic images are optionally overlaid to from a hybrid X-ray/proton beam tomographic image as the patient 730 is optionally in the same position for each image. In still another embodiment, the tomogram is collected with the patient 730 in the about the same position as when the patient's tumor is treated using subsequent irradiation therapy. For some tumors, the patient being positioned in the same upright or semi-upright position allows the tumor 720 to be separated from surrounding organs or tissue of the patient 730 better than in a laying position. Positioning of the scintillation plate 710 behind the patient 730 allows the tomographic imaging to occur while the patient is in the same upright or semi-upright position. The use of common elements in the tomographic imaging and in the charged particle cancer therapy allows benefits of the cancer therapy, described supra, to optionally be used with the tomographic imaging, such as proton beam x-axis control, proton beam y-axis control, control of proton beam energy, control of proton beam intensity, timing control of beam delivery to the patient, rotation control of the patient, and control of patient translation all in a raster beam mode of proton energy delivery. The use of a single proton or cation beamline for both imaging and treatment facilitates eases patient setup, reduces alignment uncertainties, reduces beam sate uncertainties, and eases quality assurance. In yet still another embodiment, initially a three-dimensional tomographic proton based reference image is collected, such as with hundreds of individual rotation images of the tumor 720 and patient 730. Subsequently, just prior to proton treatment of the cancer, just a few 2-dimensional control tomographic images of the patient are collected, such as with a stationary patient or at just a few rotation positions, such as an image straight on to the patient, with the patient rotated about 45 degrees each way, and/or the patient rotated about 90 degrees each way about the y-axis. The individual control images are compared with the 3-dimensional reference image. An adaptive proton therapy is subsequently performed where: (1) the proton cancer therapy is not used for a given position based on the differences between the 3-dimensional reference image and one or more of the 2-dimensional control images and/or (2) the proton cancer therapy is modified in real time based on the differences between the 3-dimensional reference image and one or more of the 2-dimensional control images. Charged Particle State Determination/Verification/Photonic Monitoring Still referring to FIG. 7, the tomography system 700 is optionally used with a charged particle beam state determination system 750, optionally used as a charged particle verification system. The charged particle state determination system 750 optionally measures, determines, and/or verifies one of more of: (1) position of the charged particle beam, (2) direction of the charged particle beam, (3) intensity of the charged particle beam, (4) energy of the charged particle beam, and (5) a history of the charged particle beam. For clarity of presentation and without loss of generality, a description of the charged particle beam state determination system 750 is described and illustrated separately in FIG. 8 and FIG. 9A; however, as described herein elements of the charged particle beam state determination system 750 are optionally and preferably integrated into the nozzle system 146 and/or the tomography system 700 of the charged particle treatment system 100. More particularly, any element of the charged particle beam state determination system 750 is integrated into the nozzle system 146, the dynamic gantry nozzle 610, and/or tomography system 700, such as a surface of the scintillation plate 710 or a surface of a scintillation detector, plate, or system. The nozzle system 146 or the dynamic gantry nozzle 610 provides an outlet of the charged particle beam from the vacuum tube initiating at the injection system 120 and passing through the synchrotron 130 and beam transport system 135. Any plate, sheet, fluorophore, or detector of the charged particle beam state determination system is optionally integrated into the nozzle system 146. For example, an exit foil of the nozzle 610 is optionally a first sheet 760 of the charged particle beam state determination system 750 and a first coating 762 is optionally coated onto the exit foil, as illustrated in FIG. 7. Similarly, optionally a surface of the scintillation plate 710 is a support surface for a fourth coating 792, as illustrated in FIG. 7. The charged particle beam state determination system 750 is further described, infra. Referring now to FIG. 7, FIG. 8, and FIG. 9A, four sheets, a first sheet 760, a second sheet 770, a third sheet 780, and a fourth sheet 790 are used to illustrated detection sheets and/or photon emitting sheets upon transmittance of a charged particle beam. Each sheet is optionally coated with a photon emitter, such as a fluorophore, such as the first sheet 760 is optionally coated with a first coating 762. Without loss of generality and for clarity of presentation, the four sheets are each illustrated as units, where the light emitting layer is not illustrated. Thus, for example, the second sheet 770 optionally refers to a support sheet, a light emitting sheet, and/or a support sheet coated by a light emitting element. The four sheets are representative of n sheets, where n is a positive integer. Referring now to FIG. 7 and FIG. 8, the charged particle beam state verification system 750 is a system that allows for monitoring of the actual charged particle beam position in real-time without destruction of the charged particle beam. The charged particle beam state verification system 750 preferably includes a first position element or first beam verification layer, which is also referred to herein as a coating, luminescent, fluorescent, phosphorescent, radiance, or viewing layer. The first position element optionally and preferably includes a coating or thin layer substantially in contact with a sheet, such as an inside surface of the nozzle foil, where the inside surface is on the synchrotron side of the nozzle foil. Less preferably, the verification layer or coating layer is substantially in contact with an outer surface of the nozzle foil, where the outer surface is on the patient treatment side of the nozzle foil. Preferably, the nozzle foil provides a substrate surface for coating by the coating layer. Optionally, a binding layer is located between the coating layer and the nozzle foil, substrate, or support sheet. Optionally, the position element is placed anywhere in the charged particle beam path. Optionally, more than one position element on more than one sheet, respectively, is used in the charged particle beam path and is used to determine a state property of the charged particle beam, as described infra. Still referring to FIG. 7 and FIG. 8, the coating, referred to as a fluorophore, yields a measurable spectroscopic response, spatially viewable by a detector or camera, as a result of transmission by the proton beam. The coating is preferably a phosphor, but is optionally any material that is viewable or imaged by a detector where the material changes spectroscopically as a result of the charged particle beam hitting or transmitting through the coating or coating layer. A detector or camera views secondary photons emitted from the coating layer and determines a current position of the charged particle beam 269 or final treatment vector of the charged particle beam by the spectroscopic differences resulting from protons and/or charged particle beam passing through the coating layer. For example, the camera views a surface of the coating surface as the proton beam or positively charged cation beam is being scanned by the first axis control 142, vertical control, and the second axis control 144, horizontal control, beam position control elements during treatment of the tumor 720. The camera views the current position of the charged particle beam 269 as measured by spectroscopic response. The coating layer is preferably a phosphor or luminescent material that glows and/or emits photons for a short period of time, such as less than 5 seconds for a 50% intensity, as a result of excitation by the charged particle beam. The detector observes the temperature change and/or observe photons emitted from the charged particle beam traversed spot. Optionally, a plurality of cameras or detectors are used, where each detector views all or a portion of the coating layer. For example, two detectors are used where a first detector views a first half of the coating layer and the second detector views a second half of the coating layer. Preferably, at least a portion of the detector is mounted into the nozzle system to view the proton beam position after passing through the first axis and second axis controllers 142, 144. Preferably, the coating layer is positioned in the proton beam path 268 in a position prior to the protons striking the patient 730. Referring now to FIG. 1 and FIG. 7, the main controller 110, connected to the camera or detector output, optionally and preferably compares the final proton beam position 269 with the planned proton beam position and/or a calibration reference to determine if the actual proton beam position 269 is within tolerance. The charged particle beam state determination system 750 preferably is used in one or more phases, such as a calibration phase, a mapping phase, a beam position verification phase, a treatment phase, and a treatment plan modification phase. The calibration phase is used to correlate, as a function of x-, y-position of the glowing response the actual x-, y-position of the proton beam at the patient interface. During the treatment phase, the charged particle beam position is monitored and compared to the calibration and/or treatment plan to verify accurate proton delivery to the tumor 720 and/or as a charged particle beam shutoff safety indicator. Referring now to FIG. 10, the position verification system 172 and/or the treatment delivery control system 112, upon determination of a tumor shift, an unpredicted tumor distortion upon treatment, and/or a treatment anomaly optionally generates and or provides a recommended treatment change 1070. The treatment change 1070 is optionally sent out while the patient 730 is still in the treatment position, such as to a proximate physician or over the internet to a remote physician, for physician approval 1072, receipt of which allows continuation of the now modified and approved treatment plan. Referring still to FIG. 12B, a second example of the internal pendant 1218 is provided. In this example, one or more buttons or the like, such as the first button 1270, and/or one or more of the processes, such as the first process 1261, are customizable, such as to an often repeated set of steps and/or to steps particular to treatment of a given patient 730. The customizable element, such as the first button 1270, is optionally further setup, programmed, controlled, and/or limited via information received from the patient treatment module 1290. In this example, a button, or the like, operates as an emergency all stop button, which at the minimum shuts down the accelerator, redirects the charged particle beam to a beam stop separate from a path through the patient, or stops moving the patient 730. In place of and/or in conjunction with a particular button, such as the first button 1270 and/or the second button 1280, moving or selecting a particular element, processes are optionally described, displayed, and/or selected within a flow process control unit 1260 of the internal pendant 1218. For example, one or more display screens and/or printed elements describe a set of processes, such as a first process 1261, a second process 1263, a third process 1265, and a fourth process 1267 and are selected through a touch screen selection process or via a selection button, such as a corresponding first selector 1262, second selector 1264, third selector 1266, and fourth selector 1268. Referring still to FIG. 12B, as illustrated for clarity and without loss or generalization, the first process 1261 and/or a display screen thereof operable by the first selector 1262 selects, initiates, and/or processes a set of steps related to the beam control tray assembly 400. For instance, the first selector 1262, functioning as a tray button: (1) confirms presence a requested patient specific tray insert 510 in a requested tray assembly; (2) confirms presence of a request patient specific tray insert in a receiving slot of the control tray assembly; (3) retracts the beam control tray assembly 400 into the nozzle system 146; (4) confirms information using the electromechanical identifier plug, such as the first electromechanical identifier plug 530; (5) confirms information using the patient treatment module 1290; and/or (6) performs a set of commands and/or movements identified with the first selector 1262 and/or identified with the first process 1261. Similarly, the second process 1263, corresponding to a second process display screen and/or the second selector 1264; the third process 1265, corresponding to a third process display screen and/or the third selector 1266; and the fourth process 1267, corresponding to a fourth process display screen and/or the fourth selector 1268 control and/or activate a set of actions, movements, and/or commands related to positioning the patient 730, imaging the patient 730, and treating the patient 730, respectively. Still yet another embodiment includes any combination and/or permutation of any of the elements described herein. Herein, any number, such as 1, 2, 3, 4, 5, is optionally more than the number, less than the number, or within 1, 2, 5, 10, 20, or 50 percent of the number. The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the present invention in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or physical couplings between the various elements. Many alternative or additional functional relationships or physical connections may be present in a practical system. In the foregoing description, the invention has been described with reference to specific exemplary embodiments; however, it will be appreciated that various modifications and changes may be made without departing from the scope of the present invention as set forth herein. The description and figures are to be regarded in an illustrative manner, rather than a restrictive one and all such modifications are intended to be included within the scope of the present invention. Accordingly, the scope of the invention should be determined by the generic embodiments described herein and their legal equivalents rather than by merely the specific examples described above. For example, the steps recited in any method or process embodiment may be executed in any order and are not limited to the explicit order presented in the specific examples. Additionally, the components and/or elements recited in any apparatus embodiment may be assembled or otherwise operationally configured in a variety of permutations to produce substantially the same result as the present invention and are accordingly not limited to the specific configuration recited in the specific examples. Benefits, other advantages and solutions to problems have been described above with regard to particular embodiments; however, any benefit, advantage, solution to problems or any element that may cause any particular benefit, advantage or solution to occur or to become more pronounced are not to be construed as critical, required or essential features or components. As used herein, the terms “comprises”, “comprising”, or any variation thereof, are intended to reference a non-exclusive inclusion, such that a process, method, article, composition or apparatus that comprises a list of elements does not include only those elements recited, but may also include other elements not expressly listed or inherent to such process, method, article, composition or apparatus. Other combinations and/or modifications of the above-described structures, arrangements, applications, proportions, elements, materials or components used in the practice of the present invention, in addition to those not specifically recited, may be varied or otherwise particularly adapted to specific environments, manufacturing specifications, design parameters or other operating requirements without departing from the general principles of the same. Although the invention has been described herein with reference to certain preferred embodiments, one skilled in the art will readily appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the present invention. Accordingly, the invention should only be limited by the Claims included below. In a fourth example, the gantry comprises at least two imaging devices, where each imaging device moves with rotation of the gantry and where the two imaging devices view the patient 730 along two axes forming an angle of ninety degrees, in the range of eighty-five to ninety-five degrees, and/or in the range of seventy-five to one hundred five degrees. Pendant Referring still to FIG. 12A and referring now to FIG. 12B, a pendant system 1250, such as a system using the external pendant 1216 and/or internal pendent 1218 is described. In a first case, the external pendant 1216 and internal pendant 1218 have identical controls. In a second case, controls and/or functions of the external pendant 1216 intersect with controls and/or function of the internal pendant 1218. Particular processes and functions of the internal pendant 1218 are provided below, without loss of generality, to facilitate description of the external and internal pendants 1216, 1218. The internal pendant 1218 optionally comprises any number of input buttons, screens, tabs, switches, or the like. The pendant system 1250 is further described, infra.
046577238	abstract	A coolant arrangement is disclosed for magnetic coil turn assemblies in which cooling fluid is flowed through a supply header along the face of a coil turn and into coolant inlet openings positioned along the face of the coil turn beneath the supply header structure. Coolant is directed through coolant channels around the magnetic coil turn, and into outlet openings. The outlet openings are in fluid communication with a return header also positioned on a flat face of a magnetic coil turn. There is also disclosed a method and apparatus for passing coolant through adjacent coolant channels in a magnetic coil turn in opposite directions. The cooling means disclosed avoids creating hot spots in the vicinity of the coolant inlets and outlets and reduces stresses in the coil in the vicinity of the coolant inlets and outlets. It also provides for maintaining a uniform average temperature throughout the coil turn. In addition, the cooling structure disclosed simplifies fabrication of the coil and is compact in nature so as to create favorable hydraulic and thermal conditions in environments where space limitations are crucial.
	abstract	The present invention relates to an optical device and a method of in situ treating an optical component (2, 6, 13) reflecting EUV and/or soft X-ray radiation in said optical device, said optical component (2, 6, 13) being arranged in a vacuum chamber (14) of said optical device and comprising one or several reflecting surfaces (3) having a top layer of one or several surface materials. In the method, a source (1, 5) of said one or several surface materials is provided in said chamber (14) of said optical device and surface material from said source (1, 5) is deposited on said one or several reflecting surfaces (3) during operation and/or during operation-pauses of said optical device in order to cover or substitute deposited contaminant material and/or to compensate for ablated surface material.
	description	As shown in FIG. 1, an x-ray fluoroscopy analyzing system 10 includes a radiation generator or source, such as x-ray tube 12, that generates a beam of radiation along a first direction, such as a beam of x-rays 14. The x-rays 14 have a wavelength that ranges from 0.3-1.0 nm. The x-rays 14 generated from x-ray tube 12 are received by and interact with the object or sample 16 so that x-ray fluorescence radiation 18 is generated from the object 16. The x-rays 18 are directed through a slit 19 and received by a multilayer grating/mirror 20, which reflects only a zeroth order of diffraction of x-rays 22 of a particular wavelength, such as 0.71 nm. The x-rays 22 are then received by a detector system 24, such as a proportional counter detector. The detected radiation is then analyzed in a well known manner. As shown in FIG. 2, the multilayer grating/mirror 20 includes a multilayer structure 26 deposited on a substrate 28. The multilayer structure 26 is made out of alternating layers of materials with large and small atomic numbers. The material with large atomic number can be selected from the materials W, Ni, Fe, Mo, V, Cr and the material with small atomic numbers can be selected from the materials C, Si, B4C. For example, the multilayer structure 26 can be made out of alternating layers of W (10 xc3x85) and C (10 xc3x85) layers. Thus, the period, d, of the alternating W and C layers is 20 xc3x85. In this embodiment, the number of periods, d, of alternating W/C bi-layers in the multilayer structure 26 is 500. Note that the number of bi-layer depends on a spectral resolution/bandpass requirements. For 500 bi-layers, the bandpassxcex/xcex94xcexxcx9cN xcx9c500. The period of the multilayer depends on a required Bragg angle and typically ranges from 15 A to 100 A for different wavelengths. In addition, other materials and thicknesses for the layers of materials with large and small atomic numbers are possible depending on the specific needs for wavelength and Bragg angle. As shown in FIG. 2, a plurality of grooves 30 are formed randomly on the multilayer grating/mirror 20. The grooves 30 are positioned between lands 32 of the multilayer structure 26, wherein each land 32 has a width of approximately 1 micron and contains 500 periods of alternating W/Si bilayers. The starting points or positions xi of the lands 30 can be determined by a formula given below: xi=(di)+[ki(dxe2x88x92Wland)], xe2x80x83xe2x80x83(2) where d=effective period of the grating/mirror 20, i=1, 2, 3, . . . ,; Wland=width of land and ki=a random number from 0 to 1. Note that the widths of the lands and depths of the grooves are constant for the entire area of the grating. Furthermore, the lands are placed randomly inside each period according to the formula (2) above. One of the benefits of using a multilayer grating/mirror 20 with a random pattern of grooves is that all diffraction orders, except the zeroth order, are suppressed. In other words, only the direct beam is reflected by the grating/mirror 20. The suppression of diffraction orders is shown by analogy to the single layer random structure transmission grating diffraction intensity distribution shown in FIG. 4. Obviously, if a single layer transmission grating with a random structure suppresses multiple diffraction orders, then a multi-layer transmission grating with a random structure will also suppress multiple diffraction orders. In the above-described mode of randomizing the grating/mirror 20, the land widths and the grooves depths are selected so that a desired width of the peak of the rocking curve of the grating/mirror 20, which is the same as an energy bandpass or spectral resolution of the grating/mirror 20, is achieved. Thus, the ability to change the bandpass allows the spectral resolution to be adjusted to specific requirements and so as to optimize flux and resolution. While the above description constitutes the preferred embodiments of the present invention, it will be appreciated that the invention is susceptible of modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims. For example, the grating 20 can also be used as a monochromator.
054266793	summary	TECHNICAL FIELD OF THE INVENTION This invention relates to a strainer device for filtering water to an emergency cooling system in a nuclear power plant of the type comprising a reactor arranged in a containment whose bottom part forms a pool for water, the strainer device being placed in the pool and serving to filter water which, if required, is taken from the pool and supplied to nozzles in the emergency cooling system in order to cool the reactor core in the event of an inadmissible temperature rise therein, the strainer comprising at least one housing with one or several apertured strainer walls through which the water can be sucked from the outside and into the housing and thereafter be fed to the emergency cooling system via a tube conduit connected to the housing. BACKGROUND OF THE INVENTION Strainer devices of the above related sort can be divided into two main types, to wit a first type being equipped with means for back-flushing of the strainer housing, and a second type which completely lacks such means. The first mentioned strainer devices are advantageous from a safety point of view, as long as they permit a cleaning of the apertured strainer walls of the housing at locations where these walls would unintentionally be clogged or blocked by fibres or other impurities circulating in the containment. This is effected by feeding clean wash-water into the strainer housing through a special feeding conduit with a pumping unit being connected thereto, the latter being actuable when necessary. However, an important inconvenience of such strainer arrangements is that the pumping unit as well as the special wash-water conduit are costly to produce and install. Moreover, they require considerable space in the area outside the strainer housing. It is true that the other type of strainer arrangements, i.e., those which completely lack back-flushing means, are comparatively inexpensive and space-saving, but they are limited in regard to the safety aspect, since they stop functioning if the holes in the strainer walls become clogged. In case fibres cumulate on the outside of the apertured envelope surface on a strainer housing, the fibres will form a continuous, circumferential mat. With previously known strainer arrangements, considerable difficulties have been encountered when detaching this fibre mat in connection with a backflushing. The washwater which is brought to flow from the inside in a direction radially outwards through the perforations in the strainer wall, does not bring about any complete and immediate release of the fibre mat; initially the water flow merely stretches the mat during simultaneous breaking up of the fibre structure. The removal of the mat is thus accomplished in such a way that individual fibres are successively released and removed from the mat. It is only after considerable hydromechanical action that the mat starts getting weaker and is gradually divided into chunks that leave the strainer wall. In order to cope with these difficulties, it has recently been suggested to provide radially protruding wings on the outside of the strainer wall, which wings split a cumulated fibre mat into several, peripherally separate sections, each one of which easily detaches from the strainer wall in connection with a backflushing. This is disclosed in PCT/SE93/01042. According to preferred embodiments of the present invention, radially protruding wings of the above mentioned type are foreseen, which are thus known per se. SUMMARY OF THE INVENTION The present invention aims at obviating the above-mentioned inconveniences of prior-art strainer devices and providing a simple and inexpensive strainer device with strainer walls which are always kept clean without any necessity of back-flushing. Thus, a main object of the invention is to provide a strainer device with at least two separate strainer walls or strainer wall surfaces of which one is always automatically kept clean in order to reliably make possible a feeding of water from the water pool to an emergency cooling system as soon as the necessity arises. A further object of the present invention is to provide a strainer device having means for keeping the holes of the strainer walls clean or open, which means are arranged so as to be capable of being built in the strainer housing itself, while avoiding any form of space-demanding connection components in the area outside the strainer housing. Yet another object of the present invention is to provide a strainer device for filtering water to an emergency cooling system in a nuclear power plant of the type having a reactor arranged in a containment zone and wherein the containment zone has the portion adapted to form a water pool, and wherein the system includes a strainer device adapted to be placed in the pool of water and functioning to filter water, and wherein the strainer includes at least one housing with at least one apertured strainered wall through which water can be drawn from the outside through the apertures into the housing, and wherein water may be fed to an emergency cooling system via at least one conduit connected to the housing, the improvement comprising flexible shield means mounted between separate strainer walls or strainer wall surfaces, said shield means being positioned in a first position or condition when water is drawn through one of said separate strainer walls or surfaces in which first position said shield means is operable to interrupt a fluid connection with the other strainer wall and said conduit, said shield means being capable of assuming a second position in which there is provided an open connection between said second strainer wall and said conduit when said first strainer wall is blocked by impurities sufficient to create a low-pressure zone between the first strainer wall and said shield means, said low-pressure zone being effective to effect said shield means between said first and second positions. In case fibres cumulate on the outside of the apertured envelope surface on a strainer housing, the fibres will form a continuous, circumferential mat. With previously known strainer arrangements, considerable difficulties have been encountered when detaching this fibre mat in connection with a backflushing. The washwater which is brought to flow from the inside in a direction radially outwards through the perforations in the strainer wall, does not bring about any complete and immediate release of the fibre mat; initially the water flow merely stretches the mat during simultaneous breaking up of the fibre structure. The removal of the mat is thus accomplished in such a way that individual fibres are successively released and removed from the mat. It is only after considerable hydromechanical action that the mat starts getting weaker and is gradually divided into chunks that leave the strainer wall. In order to cope with these difficulties, it has recently been suggested to provide radially protruding wings on the outside of the strainer wall, which wings split a cumulated fibre mat into several, peripherally separate sections, each one of which easily detaches from the strainer wall in connection with a backflushing. This is disclosed in PCT/SE93/01042. According to preferred embodiments of the present invention, radially protruding wings of the above mentioned type are foreseen, which are thus known per se.
	abstract	A nuclear reactor cooling system with passive cooling capabilities operable during a loss-of-coolant accident (LOCA) without available electric power. The system includes a reactor vessel with nuclear fuel core located in a reactor well. An in-containment water storage tank is fluidly coupled to the reactor well and holds an inventory of cooling water. During a LOCA event, the tank floods the reactor well with water. Eventually, the water heated by decay heat from the reactor vaporizes producing steam. The steam flows to an in-containment heat exchanger and condenses. The condensate is returned to the reactor well in a closed flow loop system in which flow may circulate solely via gravity from changes in phase and density of the water. In one embodiment, the heat exchanger may be an array of heat dissipater ducts mounted on the wall of the inner containment vessel surrounded by a heat sink.
052157075	claims	1. In a nuclear reactor having a core, a core support plate, a flow distribution plate, an instrument guide thimble extending into the core from the flow distribution plate, in-core instrumentation means for monitoring reactor operations extendable through the core support plate and flow distribution plate into the guide thimble, and, means for reducing flow induced vibration of the instrumentation means comprising: an instrument shroud disposed between the core support plate and flow distribution plate and having a cup with first and second openings for passing the instrument means therethrough, the first opening disposed adjacent an opening in the flow distribution plate and being of sufficient diameter to allow fluid flow into the instrument guide thimble, the second opening disposed adjacent to the core support plate and being of sufficient diameter to allow fluid flow into the cup, the cup having passages for diverting part of the fluid flow received from the second opening away from the instrument guide thimble, and, one or more shroud arms extending radially from the cup for engaging a substantially parallel core structure, each shroud arm having means for engaging the adjacent core structure at an end thereof, said engaging means having a locking pad disposed at the end of each shroud arm and spring means extending resiliently from each pad for biasing the shroud into position, the shroud arms preventing movement of the shroud due to fluid flow. providing an instrument guide thimble shroud having a cup with first and second openings for passing the instrument means therethrough, the first opening disposed adjacent an opening in the flow distribution plate and being of sufficient diameter to allow fluid flow into the thimble tube, the second opening disposed adjacent to the core support plate and being of sufficient diameter to allow fluid flow into the cup, the cup having passages for diverting part of the fluid flow received from the second opening away from the instrument guide thimble, and, one or more shroud arms extending radially from the cup for engaging a substantially parallel core structure, each shroud arm having means for engaging the adjacent core structure, the engaging means having a locking pad disposed at the end of each shroud arm and spring means extending resiliently from each pad for biasing the shroud into position, the shroud arms preventing movement of the shroud due to fluid flow; placing the instrument thimble tube shroud between the fuel assembly flow distribution plate and the reactor support plate; and, placing an instrument guide thimble within the shroud. 2. The shroud of claim 1 wherein the cup has a cylindrical shape. 3. The shroud of claim 1 wherein the cup has an upper inwardly tapered surface with the passages located therein. 4. The shroud of claim 1 wherein four shroud arms extend from the cup. 5. The shroud of claim 1 wherein the spring means comprise a spring plate having one or more spring arms for biasing the shroud arms into position, recesses provided in the adjacent core structure for accepting the spring arms therein. 6. The shroud of claim 5 further comprising a retaining spring extending from the spring plate for locking the shroud arm in position. 7. The shroud of claim 5 wherein each spring arm has first and second sloped surfaces. 8. The shroud of claim 6 wherein the retaining spring has an angled surface and an angled locking tab extending therefrom. 9. The shroud of claim 1 wherein the shroud is composed of a material from the group consisting of stainless steel, zirconium, Zircaloy-2, Zircaloy-4, Inconel and nickel alloys. 10. The shroud of claim 1 wherein the shroud is composed of stainless steel. 11. A method for preventing damage to an instrument guide thimble in a nuclear reactor having a core, a core support plate, a flow distribution plate, an instrument guide thimble extending into the core from the flow distribution plate, in-core instrumentation means for monitoring reactor operations extendable through the core support plate and flow distribution plate into the guide thimble, and, means for reducing flow induced vibration of the instrumentation means, the method comprising:
054229200	summary	TECHNICAL FIELD The present invention relates to a method for estimating crystal grain sizes of uranium dioxide (UO.sub.2) sintered pellets to be used as nuclear fuel. In particular, it relates to a method for estimating crystal grain sizes of UO.sub.2 sintered pellets according to oxidation behavior of UO.sub.2 powder. BACKGROUND ART Such UO.sub.2 sintered pellets are tightly enclosed in coating tubes made of zircaloy, and are used as nuclear fuel. Recently, in order to make the life of the nuclear fuel to be long to enable continuous operation for a long period of light water reactors or fast breeder reactors, it is advanced to realize a high degree of combustion of nuclear fuel. When the nuclear fuel is allowed to have a high degree of combustion, the amount of fission products (FP) generated from nuclear fuel pellets is increased. Among the products, gaseous one such as radon (Rn) scarcely make solid solutions in the matrix of the nuclear fuel pellet, which diffuse into the crystal grain boundary and generate bubbles there. Swelling occurs due to the bubble formation, and the volume of the pellet increases to give stress to the coating tube. This makes a cause to generate a mechanical interaction (PCI, Pellet Clad Interaction) between the pellet and the coating tube. In addition, the FP gas diffused into the grain boundary is released to the exterior of the pellet later, which increases the internal pressure of the fuel rod to make a cause to decrease the thermal conductivity of the gap between the pellet and the; coating tube. In order to prevent the increase in PCI and the decrease in the thermal conductivity, it has been attempted that the nuclear fuel pellet is allowed to have a large grain size so as to enclose the FP gas in the pellet. This is based on the fact that although the generation of the FP gas itself cannot be suppressed, when the pellet is allowed to have a large grain size, for example, when the crystal grain size is made to be two-fold, the arriving distance to the grain boundary of the FP gas generated in the crystal grain becomes two-fold, and consequently the release speed of the FP gas becomes half. Until now, methods for increasing the crystal grain size of the UO.sub.2 sintered pellet have been disclosed in Unexamined Published Japanese Patent Application No. 2-242195/1990; Unexamined Published Japanese Patent Application No. 3-287096/1991; Unexamined Published Japanese Patent Application No. 4-70594/1992 and the like. According to these methods, nuclear fuel pellets having crystals of a large grain size of 20-120 .mu.m are obtained. In the prior art, not only for the nuclear fuel pellets produced by these methods as a matter of course, but also for nuclear fuel pellets produced by other methods, the crystal grain size has been mainly measured by a cross-sectional method defined in accordance with ASTM E-112. In this cross-sectional method, at first a produced UO.sub.2 sintered pellet is embedded in a synthetic resin, the pellet embedded in the resin is cut, and then its cross section is polished. Next, a wet etching treatment is performed to expose crystal grain boundaries of the pellet, and then the crystal grain boundaries are photographed by an optical microscope or the like. Next, in a state in which a scale line having a predetermined length is projected on a screen using a slide type projector, a photographed negative film is projected on the same screen so as to overlay a grain boundary texture to the scale line. The number of grains intersecting the scale line on the screen is measured at a plurality of places by sliding the negative film, and an average value of crystal grain sizes is determined according to the grain number. However, in the above-mentioned cross-sectional method, there is such an advantage that the crystal grain size of the UO.sub.2 sintered pellet is directly observed by the photographing with the optical microscope or the like, and a value relatively having a high accuracy is obtained, but on the contrary, it is necessary that every time when the measurement is performed, the UO.sub.2 powder is placed in a mold frame to conduct formation and calcination to make the sintered pellet, as well as complicated works for preparation of the measurement are required, and fine operation and observation must be performed. For example, when UO.sub.2 sintered pellets having large crystal grain sizes are produced for a high degree of combustion of nuclear fuel, in order to decrease the ratio of deficiency of the sintered pellets, it is necessary to perform judgment of the suitability of raw material powders for the sintered pellets beforehand. However, in the case of the conventional measurement method, there has been such a problem that relatively much time is consumed for this judgment, and consequently management cost for the raw material powder is raised. An object of the present invention is to provide a method for estimating crystal grain sizes of UO.sub.2 sintered pellets without actually producing UO.sub.2 sintered pellets. Another object of the present invention is to provide a method for estimating crystal grain sizes of nuclear fuel pellets in which when UO.sub.2 sintered pellets having large crystal grain sizes are produced for realizing a high degree of combustion of nuclear fuel, the judgment of suitability of raw material powders for the sintered pellets can be performed rapidly and economically. DISCLOSURE OF THE INVENTION In order to achieve the above-mentioned objects, a method for estimating crystal grain sizes of nuclear fuel pellets according to the present invention includes the following procedures as shown in FIG. 1. (a) heating a plurality types of UO.sub.2 powders of a predetermined amount at a predetermined temperature raising speed in dry air of a constant flow amount, thereby measuring weight change ratios occurring due to the oxidation of each of the UO.sub.2 powders; (b) determining for each kind of UO.sub.2 powders a temperature at which a composition of the powder arrives at from the UO.sub.2+x phase to the U.sub.3 O.sub.7 phase, on the basis of a change in the weight change ratios; (c) producing UO.sub.2 sintered pellets from the plurality types of UO.sub.2 powders in which the arrival temperatures are known; (d) measuring the crystal grain sizes of the plurality types of the sintered pellets produced in (c); (e) recognizing a correlation between the U.sub.3 O.sub.7 phase arrival temperature determined in (b) and the crystal grain size of the sintered pellet measured in (d); (f) determining a U.sub.3 O.sub.7 phase arrival temperature of a UO.sub.2 powder of a test sample under the same conditions as those in (a) and (b); and (g) estimating a crystal grain size of the UO.sub.2 powder of the test sample upon production into a sintered pellet, according to the U.sub.3 0.sub.7 phase arrival temperature determined in (f) and the correlation determined in (e). The above-mentioned procedures of (a) to (e) of the present invention are basic procedures for determining the correlation between the U.sub.3 O.sub.7 phase arrival temperature of the UO.sub.2 powder and the crystal grain size of the sintered pellet produced with the powder, and the above-mentioned procedures of (f) and (g) are procedures for estimating the crystal grain size of the sintered pellet produced from the UO.sub.2 powder of the test sample. Once when the above-mentioned basic procedures of (a) to (e) are established only the above-mentioned procedures (f) and (g) for estimating the crystal grain size of the sintered pellet of the UO.sub.2 powder of the test sample are performed repeatedly. At first, a predetermined amount of the UO.sub.2 powder is heated at a predetermined temperature raising speed while allowing a constant amount of dry air to flow, thereby it is oxidized by oxygen in the dry air. As the UO.sub.2 powder to be oxidized, in order to provide different values of U.sub.3 O.sub.7 phase arrival temperature described hereinafter as far as possible, a plurality types of powders having various average grain sizes are prepared. It is known that when the UO.sub.2 powder is oxidized under the above-mentioned condition, the powder changes from the UO.sub.2+x phase to the U.sub.3 O.sub.7 phase, which ultimately becomes the U.sub.3 O.sub.8 phase to be stabilized. The phase-change of the powder can be known from the change ratio of the powder weight, so that the weight change ratio of the powder is measured. This measurement is performed by means of a commonly used thermogravimetric analysis apparatus (thermobalance). The weight change ratio is determined by measuring an increment in weight per unit time because the temperature raising speed is constant. According to the value at which the weight change ratio changes, the temperature of the arrival from the UO.sub.2+x phase to the U.sub.3 O.sub.7 phase is determined. It is preferable that the arrival temperature is determined, after drawing an oxidation curve of the UO.sub.2 powder as shown in FIG. 2, from a inflection point P of the curve. In FIG. 2, the axis of ordinate is the weight change ratio, and the axis of abscissa is the oxidation temperature. The inflection point Q indicates the U.sub.3 O.sub.8 phase arrival temperature. Using raw materials of a plurality types of UO.sub.2 powders having different U.sub.3 O.sub.7 phase arrival temperatures, sintered pellets are produced respectively under the same condition by means of a known method. Concretely, the production is performed such that a lubricant is added to the UO.sub.2 powder to perform powder-pressing formation to provide a green pellet, next the lubricant is removed, and thereafter sintering is performed in a hydrogen gas flow at a specified temperature in a range of 1400.degree.-1800.degree. C. The crystal grain sizes of produced plurality types of UO.sub.2 sintered pellets are measured by means of the following method. At first the produced UO.sub.2 sintered pellet is embedded in a synthetic resin, the pellet embedded in the resin is cut, and thereafter its cross section is polished. Next, after the polishing, an etching treatment is performed to expose crystal grain boundaries, and the measurement is performed by the above-mentioned cross-sectional method using a negative film photographed by an optical microscope or the like. As the synthetic resin in which the UO.sub.2 sintered pellet is embedded, acrylic type, silicone type, vinyl type and the like can be exemplified, however, the acrylic type is preferable. The U.sub.3 O.sub.7 phase arrival temperatures of the UO.sub.2 powder before the production of the sintered pellets and the values of the crystal grain sizes determined by the above-mentioned cross-sectional method are plotted on a chart shown in FIG. 3, and a curve R, which indicates a correlation between the U.sub.3 O.sub.7 arrival temperature and the crystal grain size of the sintered pellet, is drawn. On the basis of the obtained correlation, a UO.sub.2 powder for which the crystal grain size is intended to be estimated is prepared. The UO.sub.2 powder as a test sample is heated under the same condition as that of (a) as described above so as to measure its weight change ratio, and using the same procedure as (b) as described above its U.sub.3 O.sub.7 phase arrival temperature is determined from its oxidation curve. The determined U.sub.3 O.sub.7 phase arrival temperature is attributed to the curve R showing the above-mentioned correlation, and the crystal grain size upon production into a sintered pellet of the UO.sub.2 powder of the test sample is estimated. Incidentally, in the present invention, the weight change ratio is used as a parameter for obtaining the oxidation curve of the UO.sub.2 powder, however, according to an oxidation curve using a parameter of a calorific value corresponding to chemical energy required during change of crystals of uranium oxide, it is also possible to determine the temperature of arrival from the UO.sub.2 powder to the U.sub.3 O.sub.7 phase.
051606941	abstract	Fusion reactor (36) based on the cusped geometry concept in which the problem of indefinite tight plasma containment with inherent stability and high compression of the contained plasma in the reaction zone (19) is solved by an electric potential pot (22) surrounding the reaction zone and having an ion source (37) at the upper potential pot edge (38).
	abstract	In a method for operating an x-ray device, an x-ray beam is generated at a focal spot of a rotary anode that is rotatable around a rotation axis, and the x-ray beam is gated with a slit-shaped diaphragm to produce a fan-shaped x-ray beam, that is moved through an examination region in the manner of a scan. To improve the image resolution, the fan-shaped x-ray beam can be moved over the examination region essentially in the direction of the rotational axis of the rotary anode by tilting the x-ray tube on the focal spot, with the x-ray tube being tilted on the focal spot so that the fan-shaped x-ray beam is always gated from the region of the overall emitted x-ray beam having the highest image resolution or the highest image definition in the movement through the examination region.
056688431	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the figures of the drawings, which are partly diagrammatic and/or slightly out of shape in order to emphasize specific features, and first, particularly, to FIG. 1 thereof, there is seen a fragmentary view of a storage cage 1 with a baseplate 3, on which a plurality of rectangular casings 4 stand. A fuel assembly 2 symbolized by a cuboid is located in one of the casings 4. The casings 4 are fastened, especially anchored, on the baseplate 3 by non-illustrated provisions. Further positions 11 for non-illustrated casings are represented by broken lines. The baseplate 3 has apertures 5 which lead into the casings 4 and which make it possible for cooling liquid, especially water, that was previously supplied to be capable of flowing off out of the casings 4 when the storage cage 1 is lifted out of a water-filled storage pond. Each casing 4 has an edge region with lateral slots 6 which allow a cooling gas to circulate in the storage cage 1 between the fuel assembly 2 and the casing 4 when the storage cage is located in a non-illustrated container for transport purposes. The casings 4 are connected to one another through the use of straps 12. A connection between a casing 4 and a strap 12 can be made, in particular, by welding. FIG. 2 shows two casings 4 each of which has a relatively complicated, essentially rectangular cross section and each of which is provided with a multiplicity of slots 6. In this case, the slots 6 are disposed in parallel rows on lateral surfaces of the casings 4 in the longitudinal direction. The shape of the casings 4 and the form, number and configuration of the slots 6 are to be matched to the properties of the fuel assemblies 2 which are to be stored in the casings 4. The form, configuration and number of the slots 6 must be determined in each individual instance, in particular with reference to the thermal heat capacity which emanates from the fuel assembly 2 to be stored in the respective casing 4, and with reference to the cooling which has to be provided accordingly for the relevant fuel assembly 2. FIG. 3 shows a storage cage 1 having a multiplicity of approximately rectangular casings 4 in an approximately cylindrical configuration which is itself shrouded by a supporting wall 7. The supporting wall 7 forms a load-bearing part with the non-illustrated baseplate which, in particular, carries the casings 4 and which is to absorb all of the loads to which the storage cage 1 is exposed. The supporting wall 7 has corners which project into the storage cage 1 and in which anchor plates 10 with bores 13 are mounted at the end. A plurality of storage cages 1 can be connected to one another at the anchor plates 10, and moreover a corresponding lifting appliance can engage on the anchor plates 10. Furthermore, it can be seen from FIG. 3 how the storage cage 1 can be introduced into a container 8. The container 8 belongs to a two-part configuration and is surrounded therein by a shielding jacket 14. The container 8 or an actual transport container receiving the container 8 can be sealingly closed, so that radioactive radiation or radioactive fission products emanating from the non-illustrated fuel assemblies disposed in the storage cage 1 cannot escape into the environment. In this particular case, the shielding jacket 14 forms an integral part of an actual transport container which is equipped for transporting fuel assemblies on public highways. FIG. 4 shows how a multiplicity (in this case five) of storage cages 1 can be stacked to form a storage rack for fuel assemblies. The illustrated storage cages 1 essentially correspond in their construction to the construction of the storage cage 1 according to FIG. 3, so that to that extent reference is made to FIG. 3. The storage cages 1 according to FIG. 4 merely each have a multiplicity of anchor plates 10 at each corner disposed one above the other. The storage cages 1 can thus be connected to one another to form a particularly stable rack or can be anchored particularly securely in an associated container. Four of the storage cages 1 are disposed next to one another on a rack plate 17, with the baseplates 3 of the storage cages 1 lying in one plane. The fifth storage cage 1 is placed on one of the four storage cages 1, so that the lowest layer of anchor plates 10 of the storage cage 1 placed on top is congruent with the uppermost layer of anchor plates 10 of the load-bearing storage cage. Anchor plates 10 that touch one another can thereby be fixedly connected to one another. FIG. 5 shows a casing 4 which is especially advantageously incorporated into a storage cage 1 according to the invention. In this case, the casing 4 belongs to a two-layer structure and forms its inner layer. An outer layer of the structure is provided by a supporting wall 7 associated with the casing 4 and connected directly thereto. A storage cage 1 having such casings 4, each of which has its own supporting wall 7, is particularly strong or robust and therefore particularly meets the requirements to be placed on the storage and transport of fuel assemblies 2. A special construction of a fuel assembly 2 is also illustrated in FIG. 5. The fuel assembly 2 has a frame part 9, in which fuel rods 15, each of which contains fissionable material, are fastened. The frame part 9 has spacers 16 on its outside, in order to position it in a stable manner in the casing 4 (or in the nuclear reactor as well). The storage cage of any of the structures described above permits the storage and transport of fuel assemblies from a nuclear reactor both under water in a conventional storage pond and under gas, in particular under blanket gas, in a container that is suitable for transport on public highways. The outlay involved in the transfer of the fuel assemblies is reduced substantially in comparison with the structures known heretofore.
	claims	1. An X-ray reflecting device comprising a plurality of X-ray reflecting elements, each of said X-ray reflecting elements comprising:a body composed of a silicon plate; anda plurality of slits formed in said body through an etching process in such a manner as to penetrate from a front surface to a back surface of said body, each of said slits having a wall surface serving as an X-ray reflecting surface,wherein said plurality of X-ray reflecting elements are stacked on each other in a vertical direction and arranged side-by-side in a horizontal direction in such a manner as to allow said slits in the respective X-ray reflecting elements to be located in a given positional relationship with each other. 2. An X-ray reflecting device comprising a plurality of X-ray reflecting elements, each of said X-ray reflecting elements comprising:a body composed of a silicon plate; anda plurality of slits formed in said body through an etching process in such a manner as to penetrate from a front surface to a back surface of said body, each of said slits having a wall surface serving as an X-ray reflecting surface,wherein said plurality of X-ray reflecting elements are arranged side-by-side along a hypothetical spherical surface in such a manner as to allow said slits in the respective X-ray reflecting elements to be located in a given positional relationship with each other. 3. An X-ray reflecting device comprising a plurality of stacked structures each formed by stacking a plural number of X-ray reflecting elements on each other in a vertical direction in such a manner as to allow slits in the X-ray reflecting elements to be located in a given positional relationship with each other, said plurality of stacked structures being arranged side-by-side along a hypothetical spherical surface, wherein each of said X-ray reflecting elements comprises:a body composed of a silicon plate; anda plurality of said slits formed in said body through an etching process in such a manner as to penetrate from a front surface to a back surface of said body, each of said slits having a wall surface serving as an X-ray reflecting surface. 4. An X-ray reflecting element comprising:a body composed of a metal plate; anda plurality of slits formed in said body through an X-ray LIGA process in such a manner as to penetrate from a front surface to a back surface of said body, each of said slits having a wall surface serving as an X-ray reflecting surface, wherein said X-ray reflecting surface has a surface roughness of 100 angstroms or less. 5. An X-ray reflecting element comprising:a body composed of a metal plate; anda plurality of slits formed in said body through an X-ray LIGA process in such a manner as to penetrate from a front surface to a back surface of said body, each of said slits having a wall surface serving as an X-ray reflecting surface, wherein said body includes fastening means for allowing a plural number of said X-ray reflecting elements to be fastened to each other. 6. An X-ray reflecting device comprising a plurality of X-ray reflecting elements, each of said X-ray reflecting elements comprising:a body composed of a metal plate; anda plurality of slits formed in said body through an X-ray LIGA process in such a manner as to penetrate from a front surface to a back surface of said body, each of said slits having a wall surface serving as an X-ray reflecting surface,wherein said plurality of X-ray reflecting elements are stacked on each other in a vertical direction and arranged side-by-side in a horizontal direction in such a manner as to allow said slits in the respective X-ray reflecting elements to be located in a given positional relationship with each other. 7. An X-ray reflecting device comprising a plurality of X-ray reflecting elements, each of said X-ray reflecting elements comprising:a body composed of a metal plate; anda plurality of slits formed in said body through an X-ray LIGA process in such a manner as to penetrate from a front surface to a back surface of said body, each of said slits having a wall surface serving as an X-ray reflecting surface,wherein said plurality of X-ray reflecting elements are arranged side-by-side along a hypothetical spherical surface in such a manner as to allow said slits in the respective X-ray reflecting elements to be located in a given positional relationship with each other. 8. An X-ray reflecting device comprising a plurality of stacked structures each formed by stacking a plural number of X-ray reflecting elements on each other in a vertical direction in such a manner as to allow slits in the respective X-ray reflecting elements to be located in a given positional relationship with each other, said plurality of stacked structures being arranged side-by-side along a hypothetical spherical surface, wherein each of said X-ray reflecting elements comprises:a body composed of a metal plate; anda plurality of slits formed in said body through an X-ray LIGA process in such a manner as to penetrate from a front surface to a back surface of said body, each of said slits having a wall surface serving as an X-ray reflecting surface.
	claims	1. A seal-welding method for a closed vessel containing radioactive substance, comprising:filling water into a substantially tubular vessel body closed at the bottom and having a top opening; placing radioactive substance in the vessel body and immersing the substance in the water; setting a lid in the top opening of the vessel body to close the top opening; evacuating the vessel body through a discharge hole formed in the lid and discharging steam generated in the vessel body to the outside, while charging air into the vessel body through the discharge hole; and welding a peripheral edge portion of the lid to the vessel body, thereby sealing the top opening of the vessel body, while discharging the steam to the outside through the discharge hole. 2. A seal-welding method for a closed vessel according to claim 1, wherein the lid has an outer peripheral portion adjacently opposed to the inner peripheral surface of the vessel body, the outer peripheral portion including a welding portion welded to the inner peripheral surface of the vessel body and a space portion located on the bottom side of the vessel body with respect to the welding portion, and a shield gas is filled into or run through the space portion to prevent the steam from getting into the welding portion, as the lid is welded. 3. A seal-welding method for a closed vessel according to claim 2, wherein the shield gas is an inert gas. 4. A seal-welding method for a closed vessel containing radioactive substance, comprising:filling water into a substantially tubular vessel body closed at the bottom and having a top opening; placing radioactive substance in the vessel body and immersing the substance in the water; setting a shielding plate in the upper end portion of the vessel body to close the top opening, and sealing a gap between the inner peripheral surface of the vessel body and the shielding plate by means of a seal member; setting a lid in the top opening of the vessel body to be lapped on the shielding plate, thereby closing the top opening; evacuating the vessel body through a discharge hole formed in the lid and the shielding plate and discharging steam generated in the vessel body to the outside, while charging air into the vessel body through the discharge hole; and welding the peripheral edge portion of the lid to the vessel body, thereby sealing the top opening of the vessel body, while discharging the steam to the outside through the discharge hole. 5. A seal-welding method for a closed vessel according to claim 3, wherein the lid has an outer peripheral portion adjacently opposed to the inner peripheral surface of the vessel body, the outer peripheral portion including a welding portion welded to the inner peripheral surface of the vessel body and a space portion located on the bottom side of the vessel body with respect to the welding portion, and a shield gas is filled into or run through the space portion to prevent the steam from getting into the welding portion, as the lid means is welded. 6. A seal-welding method for a closed vessel according to claim 5, wherein the shield gas is an inert gas. 7. An exhaust method for a closed vessel containing radioactive substance, comprising:filling water into a substantially tubular vessel body closed at the bottom and having a top opening; placing radioactive substance in the vessel body and immersing the substance in the water; setting a lid in the top opening of the vessel body to close the top opening; evacuating the vessel body through a discharge hole formed in the lid and discharging steam generated in the vessel body to the outside, while charging air into the vessel body through the discharge hole; welding a peripheral edge portion of the lid to the vessel body, thereby sealing the top opening of the vessel body, while discharging the steam to the outside through the discharge hole; passing a charging pipe through the discharge hole, the charging pipe having a charging port opening into the vessel body and a suction port opening to the outside of the vessel body; disposing an exhaust pipe in the charging pipe to form a double-pipe structure, the exhaust pipe having an exhaust port opening into the vessel body and an extending portion extending to the outside of the vessel body; and connecting a suction device to the extending portion of the exhaust pipe; evacuating the vessel body through the exhaust pipe; and charging the open air into the vessel body through the charging pipe. 8. An exhaust method according to claim 7, wherein the charging port of the charging pipe and the exhaust port of the exhaust pipe are trumpet-shaped and substantially coaxial with each other. 9. An exhaust method according to claim 7, further comprising:disposing a flow regulating portion in the charging pipe near the suction port; and regulating a quantity of air charged into the vessel body.
	abstract	A nuclear fuel assembly includes a fuel bundle resting on a lower tie plate. The lower tie plate includes a grid having raised bosses disposed in a rectilinear array for receiving the end plugs of the fuel rods and webs interconnecting the bosses. Between the raised bosses and the end plugs, there is disposed a filter plate having holes registering with the holes through the bosses for receiving the end plugs and apertures providing an approximate 40% open area through the filter plate. The webs of the tie plate grid are recessed from the upper edges of the bosses, facilitating flow through the apertures of the filter plate.
	abstract	Asteroid redirection and soft-landing systems are provided that use cosmic ray and muon-catalyzed micro-fusion. These systems include a micro-fusion propulsion system providing thrust for redirecting a small asteroid, as well as providing a particle cushion at a landing site for a soft-landing. The systems deploy deuterium-containing fuel material as a localized cloud interacting with incoming ambient cosmic rays to generate energetic fusion products. Dust or other particulate matter in the fuel material converts some cosmic rays into muons that also catalyze fusion. The fusion products provide thrusting upon the asteroid. The fusion products also aid deceleration of incoming asteroids to be mined for a soft landing upon a lunar or planetary surface.
	abstract	A two dimensional collimator assembly and method of manufacturing thereof is disclosed. The collimator assembly includes a wall structure constructed to form a two dimensional array of channels to collimate x-rays. The wall structure further includes a first portion positioned proximate the object to be scanned and configured to absorb scattered x-rays and a second portion formed integrally with the first portion and extending out from the first portion away from the object to be scanned. The first portion of the wall structure has a height greater than a height of the second portion of the wall structure. The second portion of the wall structure includes a reflective material coated thereon in each of the channels forming the two dimensional array of channels.
056195486	description	BEST MODE FOR CARRYING OUT THE INVENTION Referring to FIG. 2, an X-ray scattering system for measuring thin-film structures in accord with the present invention includes an X-ray source 31 producing an X-ray bundle 33 that comprises of a plurality of X-rays shown as 35a, 35b and 35c. An X-ray reflector/reflecting surface 37 is placed in the path of the X-ray bundle 33. The reflector 37 directs the X-ray bundle 33 onto a test sample 39, typically including a thin-film layer 41 disposed on a substrate 43, held in a fixed position by a stage 45. A detector 47 is positioned to sense X-rays reflected/scattered from the test sample 39 and produce signals corresponding to the intensity and an angle of reflection of the X-rays sensed. Referring also to FIG. 3, information corresponding to the intensity and the angle of reflection of the X-rays is received from the detector 47 by a processing unit 49 along line 51. X-ray source 31 may be an electron-impact X-ray tube, a high temperature plasma or a synchrotron accelerator. It is preferred, however, that the X-ray source 31 be a X-ray tube with a chromium anode such as the Rigaku 1.2 kW, 60 kV rotating x-ray tube. This type of x-ray tube typically produces an x-ray having a wavelength of 2.3 angstroms. To facilitate small-angle intensity measurements, some degree of monochromatization of the X-rays incident on the sample is necessary, particularly if the X-ray source 31 is a synchrotron accelerator. To that end, the X-ray reflector/reflecting surface 37 is typically a monochromator, defining two focal areas. The monochromator may be shaped as a toroid or an ellipsoid, each defining two focal points, or a cylindrical shape, defining a point focus and a line focus. It is preferred, however, that a Huber quartz J-G cylindrically curved single-crystal monochromator be employed and configured to satisfy the Guinier conditions. The diffraction of the incident bundle 33 of X-rays within the single-crystal monochromator isolates a narrow band of the spectrum when the Bragg condition for a particular wavelength is satisfied. The diffraction produces a monochromatic bundle 55 of X-rays, shown as 57a, 57b and 57c, which are directed onto the test sample 39. The monochromator is considered curved because the monochromator is cylindrically shaped. As the monochromator satisfies the Guinier conditions, the focal areas need not be equally spaced from the monochromator. It is preferred, however, that X-ray source 31 be positioned proximate to the point focus twelve centimeters from the monochromator 37, so that a maximum flux of X-rays produced by the source 31 impinge on the monochromator. Typically, all the X-rays produced by the source impinge on the monochromator. This greatly improves the X-ray flux directed toward the sample surface 39. The test sample 39 is positioned proximate to the line focus twenty-one centimeters from the monochromator 37. Referring to FIG. 4, the X-rays 35a, 35b and 35c, forming the incident bundle 33, diverge from the X-ray source 11 to simultaneously impinge upon the curved monochromator 37 at different spatial positions 59, 61 and 63, along the y axis. The monochromatic X-rays 57a, 57b and 57c produced by the curved monochromator 37 corresponding to incident X-rays 35a, 35b and 35c, respectively. The monochromatic X-rays 57a, 57b and 57c are directed to focus on a line in the x-z plane. Due to the X-rays 35a, 35b and 35c impinging on the monochromator at different spatial positions, the monochromator directs X-rays 57a, 57b and 57c to simultaneously impinge upon the thin-film layer 41 of the test sample 39 at differing angles of incidence, shown as .psi..sub.1, .psi..sub.2 and .psi..sub.3, respectively. Typically all the incident angles, shown as .psi..sub.1, .psi..sub.2 and .psi..sub.3, of X-rays are greater than a critical angle, .psi..sub.c. The critical angle .psi..sub.c is approximated as follows: EQU .psi..sub.c =0.203 .rho..sup.1/2 /h.orgate. where .psi..sub.c is defined in terms of radians, .rho. is the mass density of substrate 43 in units grams/cubic centimeter and hu is the X-ray energy in units of keV. It is critical that the X-rays are incident on the test sample 39 at angles greater than .psi..sub.c to produce interference fringes upon reflection, discussed more fully below with respect to FIG. 5. Referring also to FIG. 5, X-rays 65a, 65b and 65c reflected from the test sample 39 are shown corresponding to monochromatic X-rays 57a, 57b and 57c, respectively. The reflected rays 65a, 65b and 65c result from constructive and destructive interference of X-rays reflecting from thin-film surface 75 and thin-film/substrate interface 77. It can be seen that the angle of reflection .psi..sub.11, .psi..sub.22 and .psi..sub.33, correspond to X-rays 65a, 65b and 65c, respectively. The function between the angles of incidence and the angles of reflection is linear and can be described as follows: EQU .psi..sub.11 =.psi..sub.1 EQU .psi..sub.22 =.psi..sub.2 EQU .psi..sub.33 =.psi..sub.3 Given that the reflected X-rays 65a, 65b and 65c reflect from the test sample 39 at differing angles of reflection, the beams diverge with respect to one another and may be spatially resolved along the y axis, in a detector plane located transverse to the plane of the test sample 39. In this manner, X-rays, shown as 65a, 65b and 65c, will impinge upon the detector plane 67 at points 69, 71 and 73, respectively. Thus, it can be seen that X-rays impinging in the detector plane 67 can be identified as being uniquely associated with a particular angle of incidence. To take advantage of these properties, typically detector 47 is a position sensitive detector capable of resolving the X-rays reflecting from the test sample 39 along the one axis. Although FIG. 5 shows spatially resolving the X-rays along the y axis, both the detector 47 and monochromator may be rotated so that resolution is obtained along the x or z axis, as well. Any position sensitive detector may be employed, for example, photographic film. The preferred detector, however, is a solid-state device such as a Reticon R12048S self-scanning photo-diode array (SSPA) positioned at the detecting plane 67. L. N. Koppel, in "Direct X-Ray Response of Self-Scanning Photodiode Arrays", Advances in X-Ray Analysis, vol. 19 (1975), describes the implementation of SSPAs to measure the spatial distribution of X-rays. Also, a linear or area-sensitive charged-coupled device, a multiple-anode microchannel plate detector, or a photostimulated storage phosphor image detector may be employed in place of an SSPA. The detector 47 is positioned to receive a maximum flux of X-rays, as shown by 65a, 65b and 65c, reflected from the test sample 39. Typically, the detector 47 is positioned to receive all of the X-rays reflected from the test sample 34. The X-rays impinging at points 69, 71 and 73 are resolved as interference fringes resulting from constructive and destructive interference of X-rays reflected from the top surface 75 of the thin-film 34 and from the thin-film substrate interface 77. The detector 47 produces signals which are subsequently digitized and analyzed by circuitry associated with the detector 47. Referring again to FIG. 3, the electronic circuitry associated with the detector 47 is shown generally as pre-amplifier 81 and signal conditioning circuit 83. The electronic circuitry amplifies the signals from the detector 47, shapes the signal into energy proportional voltage pulses and selects the pulses corresponding to the desired photon energy, thereby suppressing noise and polychromatic radiation. The pulses are digitized and fed into the processor 49 which determines a reflectivity curve that may be depicted logarithmically as reflectivity (R) versus reflection angle (.psi.). The information determined by the processor may be stored on a magnetic media or it may be visualized on an analyzer, as shown by curve 85 in FIG. 6. The reflectivity curve 85 may be analyzed employing the least-squares refinement described by T. C. Huang and W. Parrish in "Characterization of Single- and Multiple-Layer", Advances in X-Ray Analysis, vol. 35, pp. 137-142 (1992) to determine a plurality of properties concerning the thin-film layer. As discussed by Huang and Parrish, the maxima 87 and/or minima 89 of the interference fringes are related to the thickness of the thin-film by the modified Bragg equation as follows: EQU sin.psi..sub.i.sup.2 =.psi..sub.c.sup.2 =(n.sub.i +.DELTA.n.sup.2).lambda..sup.2 4t.sup.2 where .psi..sub.i is the angle for the maximum or the minimum of the ith interference fringe, .psi..sub.c is the critical angle for total reflection, n.sub.i is an integer, and .DELTA.n equals 1/2 or 0 for a maximum and minimum, respectively. t is the thickness of the thin-film layer and .lambda. is the wavelength of the X-rays. From the data concerning the thickness, Huang and Parrish continue to describe how the density of the thin-film layer can be determined, as well as the smoothness of the thin-film surface and the thin-film substrate interface, mentioned above. With the above-described features of the claimed invention, a plurality of properties of a thin-film layer on a substrate may be simultaneously determined, including the thickness, density and smoothness of both the thin-film surface and the thin-film/substrate interface.

Subsets and Splits

No community queries yet

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