patent_number
stringlengths 0
9
| section
stringclasses 4
values | raw_text
stringlengths 0
954k
|
|---|---|---|
summary | ||
047730870 | claims | 1. An x-ray machine comprising: a source of an x-ray beam; a scanner means to move the beam relative to a patient; an imaging device which has means to receive x-rays which have been attenuated by the patient during a succession of imaging intervals to form an x-ray image of the patient; a feedback system for deriving pre-exposure measurements of x-rays attenuated by the patient during a succession of feedback intervals which alternate with said imaging intervals for a single image of the patient and for causing the radiation during the imaging intervals to be modulated as a function of respective pre-exposure measurements, said feedback system comprising an x-ray detector receiving x-rays attenuated by the patient during said feedback intervals and a circuit which modulates the intensity and hardness of the beam during said imaging intervals on the basis of the x-rays attenuated by the patient and received by the detector during respective feedback intervals previous to said imaging intervals. a source of a fan-shaped beam of x-rays; a scanner means to move the beam relative to a patient in a direction transverse to the plane of the beam; means to divide said fan-shaped beam into a plurality of individual segments an imaging device which has means to receive x-rays which have been attenuated by the patient and forms an x-ray image therefrom; and a plurality of feedback loops, wherein each feedback loop includes a detector for x-rays attenuated by the patient and each feedback loop individually modulates a separate respective segment of the beam by selectively changing the velocity at which the respective beam segment moves relative to the patient. a source of an x-ray beam; a scanner means to move the x-ray beam relative to a patient; an imaging device which--has means to receive x-rays which have been attenuated--by the patient and forms an x-ray image of the patient; a feedback loop which separately measures primary and scattered radiation components of the x-rays attenuated by the patient and modulates the beam on the basis of measurements of the primary and scattered components selected to maintain a constant signal-to-noise ratio in the x-ray image. a source of an x-ray beam; a scanner which comprises means for moving the x-ray beam relative to a patient along straight raster lines, at constant velocity along a line, said means comprising a rotating pre-patient collimator having a curved slit aperture causing the beam to move relative to the patient along said straight raster lines and at constant velocity along each of said straight lines; and an imaging device which has means to receive the beam after attenuation thereof by the patient as a post-patient beam during a succession of imaging intervals to form an x-ray image of the patient: a feedback system having means for deriving pre-exposure measurements of the post-patient beam during a succession of feedback intervals which alternate with said imaging intervals for a single image of the patient and having means for causing the radiation during the imaging intervals to be modulated as a function of respective pre-exposure measurements. S/N =(N.sub.0 ATn / (1+R)) where T is the patient transmission, A is the pixel size of the x-ray image, n is the quantum efficiency of the imaging device forming the image and R is the ratio of scattered-to-primary photons in the image determined as a function of primary and scattered radiation measured by the feedback loop. scanning an x-ray beam relative to a patient; forming an x-ray image of the patient on the basis of the beam after attenuation thereof by the patient; separately measuring primary and scattered post-patient radiation and modulating the beam on the basis of post-patient measurements of primary and scattered radiation to maintain a desired signal-to-noise ratio distribution in the x-ray image. a source of a fan - shaped beam of x-rays; a scanner means to move the beam relative to a patient in a direction transverse to the plane of the beam; means to divide said fan-shaped beam into a plurality of individual segments; an imaging device which has means to receive x-rays which have been attenuated by the patient and forms an x-ray image therefrom; and a plurality of feedback loops, wherein each feedback loop includes a detector for x-rays attenuated by the patient and each feedback loop individually pulse width modulates a separate respective segment of the beam. 2. An x-ray machine comprising: 3. An x-ray machine comprising: 4. An x-ray machine comprising: 5. An x-ray machine as in claim 1 in which each imaging interval is preceded by two feedback intervals one of which is at a low energy relative to the other and each of which typically has a much shorter duration than the imaging interval. 6. An x-ray machine as in claim 5 in which each pair of feedback intervals is followed by an imaging interval of a duration determined as a function of x-rays attenuated by the patient and received by the feedback loop detector during the pair of feedback intervals. 7. An x-ray machine as in claim 6 in which each pair of feedback intervals is followed by an imaging interval and the beam hardness during the imaging interval is determined as a function of x-rays attenuated by the patient and received by the feedback loop detector during the pair of feedback intervals, wherein beam hardness is raised for high attenuation beam paths and is lowered for low attenuation beam paths during the imaging interval. 8. An x-ray machine as in claim 1 in which the x-ray beam source produces at least one short pulse of radiation during a feedback interval and then, during an imaging interval, a longer pulse of variable duration determined as a function of x-rays attenuated by the patient and received by the feedback loop detector during the short at least one pulse. 9. An x-ray machine as in claim 1 in which the x-ray beam source produces a short pulse of low energy radiation and a short pulse of high energy radiation during a feedback interval and then, during an imaging interval, a longer pulse of a duration determined as a function of x-rays attenuated by the patient and received by the feedback loop detector during the two short pulses. 10. An x-ray machine as in claim 1 in which said x-ray detector is separate from the imaging device which forms the x-ray image, and said x-ray detector scans relative to the patient in at least one dimension. 11. An x-ray machine as in claim 2 in which the separate segments of the fan-shaped beam overlap in part at an imaging plane of the imaging device. 12. An x-ray machine as in claim 3 in which the feedback loop comprises a primary detector which generates a primary signal related to the x-rays attenuated by the patient along the axis of the x-ray beam and a scatter detector which generates a scatter signal related to the x-rays attenuated by the patient off-axis of the x-ray beam. 13. An x-ray machine as in claim 12 in which the imaging device comprises an image intensifier scanned by the x-ray beam. 14. An x-ray machine as in claim 3 including means to vary the photon fluence N.sub.0 of the beam from the x-ray beam source incident on the patient so as to maintain the signal-to-noise ratio S/N substantially constant in accordance with the relationship: 15. An x-ray machine as in claim 4 in which the rotating prepatient collimator comprises a pair of rotating discs each having a spiral aperture slit, and including a second pre-patient collimator having a linear aperture slit, wherein the beam from the x-ray source passes through both the linear slit and one of the spiral slits before impinging on the patient. 16. A method comprising: 17. A method as in claim 16 including approximating said image in accordance with a selected measure of a spatial distribution parameter of the beam after attenuation thereof by the patient. 18. An x-ray machine comprising: |
description | The present application claims priority to Korean Patent Application No. 10-2016-0145468, filed Nov. 3, 2016, and Korean Patent Application No. 10-2017-0060134, filed on May 15, 2017, the disclosures of which are incorporated herein by reference in their entireties. Field Apparatuses and methods consistent with exemplary embodiments relate to improving safety (improving stopping function of a reactor) of a protection system for a nuclear power plant, and more specifically, to improving a stopping function of a reactor of the protection system in which duplexed controllers independent from each other are disposed, and operation processing results of the duplexed controllers are combined in a particular manner. Thus, single point vulnerability (SPV) of the protection system is removed, and response to a common cause failure (CCF) may be provided. Description of the Related Art Nuclear power plants refer to power plants that generate electricity by turning a turbine generator with steam that is generated by boiling water with energy generated through a nuclear fission chain reaction. In an atomic nucleus composed of protons and neutrons, enormous energy is released when the nucleus is divided into free particles. Nuclear power plants using the above feature correspond to an optimal power source capable of obtaining significant energy even with very small amounts of fuel. In many countries, nuclear power plants are used to produce electricity. However, in nuclear power plants, since the use of nuclear power is accompanied by a very high risk, it is necessary to control many safety devices and hire experts having advanced training. Protection systems perform functions of monitoring a state of a nuclear steam supply system (NSSS), stopping a nuclear reactor when monitored process parameters reach safety system preset values, and mitigating the effects of accidents. SPV refers to shutdown inducing elements of a nuclear reactor or a turbine due to a failure of a single device. Conventionally, places in which a number of SPVs occurs may exist within currently operating nuclear power plants. From among these, the number of SPVs of a reactor protection system of operating nuclear power plants built in the 1980s is about 70 to 90. These SPVs are caused by various analog equipment of the reactor protection system which is not multiplexed. CCFs refer to a situation where simultaneous failures occur in various devices due to a common cause. When a CCF occurs in the protection system, it may seriously affect the protection system's performance of safety functions. A representative example to easily understand CCF is Y2K (Millennium Bug) which was problematic in 1999. This refers to a phenomenon where it was determined that a computer may not recognize the year 2000 and thus may malfunction when that time occurs. However, in case of this problem, the cause of the problem was eliminated in advance through advance preparation, and only some errors occurred in some fields. Exemplary embodiments address at least the above problems and/or disadvantages and other disadvantages not described above. Also, the exemplary embodiments are not required to overcome the disadvantages described above, and may not overcome any of the problems described above. One or more exemplary embodiments provide solutions to the SPV and CCF problems occurring in the conventional nuclear power plant protection system. According to the exemplary embodiments, a digital protection system for a nuclear power plant is provided. The digital protection system may include a process protection system and a reactor protection system which are configured with coincidence logic controllers and bistable logic controllers that are different from each other. According to an aspect of an exemplary embodiment, there is provided a digital protection system including: a process protection system including at least two channels, each of the at least two channels including a first bistable logic controller and a second bistable logic controller which is independent and different from the first bistable logic controller, the first bistable logic controller and the second bistable logic controller receiving a process parameter and outputting bistable logic results based on the process parameter; and a reactor protection system including at least two trains, at least two initiation circuits, and a parallel circuit. Each of the two trains may include a first coincidence logic controller and a second coincidence logic controller which is independent and different from the first coincidence logic controller, the first coincidence logic controller and the second coincidence logic controller outputting coincidence logic results based on the bistable logic results. Each of the at least two initiation circuits may include a serial circuit in which a plurality of relays are serially connected. The parallel circuit may include a plurality of relays which are connected in parallel. The plurality of relays included in the serial circuit may be switched on or off based on the bistable logic results received from the first and second bistable logic controllers that are different from each other. The plurality of relays included in the parallel circuit may be switched on or off based on the coincidence logic results received from the first and second coincidence logic controllers different from each other. The process protection system may include a first channel, a second channel, a third channel, and a fourth channel. The reactor protection system may include a first train and a second train. The process protection system may include a first bistable logic controller based on a field programmable gate array (FPGA), and may include a second bistable logic controller based on a programmable logic controller (PLC). Each of the first and the second bistable logic controllers may transmit the bistable logic results to all coincidence logic controllers that have a same type of a logic structure. The process parameter may include at least one of temperature information about a high temperature pipe and a low temperature pipe of a reactor coolant, pressurizer pressure information, pressurizer water level information, neutron flux information, reactor coolant flow rate information, containment building pressure information, steam generator water level information, steam pipe pressure information, and refueling water tank water level information. The bistable logic results may include a first bistable logic result and a second bistable logic result, and the coincidence logic results may include a first coincidence logic result and a second coincidence logic result. The first coincidence logic controller may receive the first bistable logic result including a first normal signal or a first abnormal signal from the first bistable logic controller included in each of the channels, and may output the first coincidence logic result based on a number of the first bistable logic result and a number of the first abnormal signal. The first coincidence logic result may include a first output signal and a second output signal that is different from the first output signal. The first output signal may be input to a first relay of the plurality of relays included in the serial circuit. The second output signal may be input to a first relay of the plurality of relays included in the parallel circuit. The second coincidence logic controller may receive the second bistable logic result including a second normal signal or a second abnormal signal from the second bistable logic controller included in each of the channels, and may output the second coincidence logic result based on a number of the second bistable logic result and a number of the second abnormal signals. The second coincidence logic result may include a third output signal and a fourth output signal that is different from the third output signal, the third output signal may be input to a second relay of the plurality of relays included in the serial circuit, and the fourth output signal may be input to a second relay of the plurality of relays included in the parallel circuit. The first coincidence logic controller may output the first coincidence logic result in response to the first bistable logic result including at least one abnormal signal. An output signal being 0 of the first coincidence logic result may be input to the first relay of the plurality of relays included in the serial circuit, and an output signal being 1 of the first coincidence logic result may be input to the first relay of the plurality of relays included in the parallel circuit. The second coincidence logic controller may output a second coincidence logic result in response to the second bistable logic result including at least one abnormal signal, an output signal being 0 of the second coincidence logic result may be input to the second relay of the plurality of relays included in the serial circuit, and an output signal being 1 of the second coincidence logic result may be input to the second relay of the plurality of relays included in the parallel circuit. The first coincidence logic controller may output a coincidence logic result in response to the bistable logic results including at least one normal signal. An output signal being 1 of the coincidence logic result may be input to a first relay of the plurality of relays included in the serial circuit, and an output signal being 0 of the coincidence logic result may be input to a first relay of the plurality of relays included in the parallel circuit. The second coincidence logic controller may output a coincidence logic result in response to the bistable logic results including at least one normal signal, wherein an output signal being 1 of the coincidence logic result may be input to a second relay of the plurality of relays included in the serial circuit, and an output signal being 0 of the coincidence logic result may be input to a second relay of the plurality of relays included in the parallel circuit. The digital protection system may further include an reactor trip switchgear system (RTSS), wherein the RTSS may include: a first normally open (NO) contact point disposed between a power node and a central node; a second NO contact point disposed between the power node and the central node; a third NO contact point disposed between the central node and a control element drive mechanism (CEDM); and a fourth NO contact point disposed between the central node and the CEDM. When at least one of the first NO contact point and the second NO contact point is in a closed state and at least one of the third NO contact point and the fourth NO contact point is in a closed state, motor-generator set (MG-SET) power may be applied to the CEDM. When both of the first NO contact point and the second NO contact point are in opened states and both of the third NO contact point and the fourth NO contact point are in opened states, MG-SET power applied to the CEDM may be shut down. At least one of the initiation circuits may include: a first serial circuit configured to control a conduction state of the first NO contact point according to output signals of the coincidence logic controller; a first parallel circuit configured to control a conduction state of the second NO contact point according to output signals of the coincidence logic controller; a second parallel circuit configured to control a conduction state of the third NO contact point according to output signals of the coincidence logic controller; and a second serial circuit configured to control a conduction state of the fourth NO contact point according to output signals of the coincidence logic controller. The first serial circuit and the first parallel circuit may receive output signals from the first coincidence logic controller and the second coincidence logic controller that has a same logic structure as the first coincidence logic controller and included in any one of the at least two trains. The second parallel circuit and second serial circuit may receive output signals from the first coincidence logic controller and the second coincidence logic controller that has a same logic structure as the first coincidence logic controller and included another train of the at least two trains. At least one of the initiation circuits may include: a third circuit that includes a relay and is configured to switch on or off the relay included in the third circuit to control the conduction state of the second NO contact point; and a fourth circuit that includes a relay and is configured to switch on or off the relay included in the fourth circuit to control the conduction state of the third NO contact point, wherein the first parallel circuit may control to switch on or off the relay included in the third circuit, and the second parallel circuit may control to switch on or off the relay included in the fourth circuit. The relays included in the third circuit and the fourth circuit may be normally-closed (NC) contact points. The first serial circuit or the second serial circuit may include two relays that are serially connected, and the two relays may be switched on or off according to output signals of the coincidence logic controller. When all relays are switched on, the first NO contact point or the fourth NO contact point may be closed, or when at least one of the two relays is switched off, the first NO contact point or the fourth NO contact point may be opened. The first parallel circuit or the second parallel circuit may include two relays that are connected in parallel, and the two relays may be switched on or off according to output signals of the coincidence logic controller. When all relays included in the first parallel circuit or the second parallel circuit are switched off, the relay included in the third circuit or the fourth circuit may be switched on, or when at least one of the two relays included in the first parallel circuit or the second parallel circuit is switched on, the relay included in the third circuit or the fourth circuit may be switched off. Exemplary embodiments are described in greater detail below with reference to the accompanying drawings. In the following description, like drawing reference numerals are used for like elements, even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. However, it is apparent that the exemplary embodiments can be practiced without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the description with unnecessary detail. zed. The configuration units expressed in this specification are merely examples for implementing exemplary embodiment. Accordingly, other configuration units may be used in other implementations of the exemplary embodiment. Meanwhile, it will be understood that terms, such as ‘include’, in the specification are ‘open type’ expressions used to mean that there are corresponding components described in the specification and there is no intent to exclude existence or possibility of other components. Furthermore, it will be understood that terms, such as “first” or “second”, in the specification are used to discriminate one component from another component and do not restrict specific order between components or other characteristics. In the following description of the embodiments, it will be understood that, when a layer (film), a region, a pattern or a structure is referred to as being “on” or “under” a substrate, another layer (film), another region, another pad or other patterns, it can be “directly” or “indirectly” on the other layer (film), region, pattern or structure, or one or more intervening layers may also be present. Such a position of each layer is described with reference to accompanying drawings. When an element is mentioned to be “coupled” or “connected” to another element, this may mean that it is directly coupled or connected to the other element, but it is to be understood that yet another element may exist in-between. In addition, it will be understood that the terms “comprises”, “comprising”, “includes”, “including” when used in this specification, specify the presence of one or more other components, but do not preclude the presence or addition of one or more other components unless defined to the contrary. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. FIG. 1 illustrates single point vulnerability (SPV) that may occur in a structure of a related-art protection system. Referring to FIG. 1, a reactor may stop operating when one reactor trip breaker (RTB) is opened due to a single failure in a first train (Train A) of a reactor protection system. FIG. 2 illustrates a reactor protection system according to an exemplary embodiment, in comparison with a related-art reactor protection system. Referring to FIG. 2, since the related-art reactor protection system disposed in a cabinet operates in an analog method and each logic gate thereof is configured in a form of a hardware card, a number of hard-wired connections is required between respective cards for transmitting signals in order to implement coincidence logic. Thus, the size of the cabinet is increased, the cabling become complicated, and the maintenance of the cabinet becomes difficult. However, in the digital protection system according to an exemplary embodiment, coincidence logic of the protection system is implemented in software and executed in central processing units (CPUs) or field programmable gate arrays (FPGAs). Thus, the size of the cabinet is reduced, the cabling become simple, and the maintenance of the cabinet becomes easy. In the digital protection system according to the exemplary embodiment, in order to prevent a common case failure (CCF), duplexed controllers different from each other are used, and a digital protection system is implemented by digitalizing the related-art analog protection system. Thereby, the maintenance of the protection system becomes easy. FIG. 3 illustrates a configuration of a digital protection system according to an exemplary embodiment, and FIG. 4 illustrates configurations of process protection systems 221, 222, 223, and 224, and reactor protection systems 231 and 232 included in the digital protection system, according to an exemplary embodiment. Referring to FIGS. 3 and 4, in the digital protection system, the process protection system may include four channels 221, 222, 223, and 224, and the reactor protection system may include two trains 231 and 232. The four channels 221, 222, 223, and 224 of the process protection system may include respective first bistable logic controllers 221-1 and 222-1 and respective second bistable logic controllers 221-2 and 222-2 which are different from each other, and transmit bistable logic results to the two trains 231 and 232 of the reactor protection system. FIG. 3 shows an embodiment in that the process protection system includes four channels, but it is not limited thereto. The process protection system may include at least one channel. In detail, the bistable logic controllers 221-1, 222-1, 221-2, and 222-2 of the respective channels 221, 222, 223, and 224 of the process protection system generate bistable logic results based on various process parameters collected from sensors 110, 120, 130, and 140 that are installed in a nuclear steam supply system. In addition, the bistable logic controllers 221-1, 222-1, 221-2, and 222-2 may transmit the bistable logic results to coincidence logic controllers of the respective trains 231 and 232 of the reactor protection system. The bistable logic controllers 221-1, 222-1, 221-2, and 222-2 of the respective channels 221, 222, 223, and 224 may independently perform bistable logic algorithms by receiving signals from multiplexed sensors 110, 120, 130, and 140. For example, a bistable logic controller included in at least one channel of the process protection system determines whether or not temperature information of a high temperature pipe which is detected by a controller reaches a predetermined protection system setting value, and transmits a signal indicating whether or not the temperature is abnormal to the respective trains 231 and 232 of the reactor protection system. Herein, respective channels of the process protection system are physically/electrically separated from each other, and respective channels independently derive result signals thereof. For example, when a 2 of 4 (2 out of 4) coincidence logic is defined and bistable logic controllers of at least two channels output abnormal signals among four multiplexed process parameters, coincidence logic controllers generate reactor stopping signals. Although the process protection system is multiplexed in for channels, process parameters may be triplicated or duplicated depending on a type of process. In the triplicated process parameter, signals may be assigned to three channels of the process protection system, and the reactor protection system may perform a 2 of 3 (2 out of 3) coincidence logic based on bistable logic results received from the three channels, and determine whether or not to generate a reactor stopping signal. In the doubled process parameter, signals may be assigned to two channels of the process protection system, and the reactor protection system may perform a 1 of 2 (1 out of 2) coincidence logic based on bistable logic results received from the two channels, and determine whether or not to generate a reactor stopping signal. The coincidence logic is not limited to 1 of 2, 2 of 3, and 3 of 4 coincidence logic. The coincidence logic may be 2 of 2, 1 of 3, 3 of 3, 3 of 4, etc. When n of m coincidence logic is defined for the above described coincidence logic or for a later coincidence logic to be described, all coincidence logic in which the n is equal to or less than the m may be possible. The first bistable logic controllers and the second bistable logic controllers of the respective channels of the process protection system may be configured with types different and independent from each other. For example, the first bistable logic controller may be formed based on FPGA, the second bistable logic controller may be formed based on programmable logic controller (PLC), and the two bistable logic controllers may be independently controlled from each other. Accordingly, when a CCF occurs in one controller, a unique function of the process protection system may be performed in another controller since the two bistable logic controllers are configured with types different from each other. Thus, it may be possible to efficiently respond to SPV and a CCF. Herein, each bistable logic controller may transmit the bistable logic result to all coincidence logic controllers that are the same type. Since the first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 and the second bistable logic controllers 221-2, 222-2, 223-2 and 224-2 of the process protection system are configured with types different from each other, and the first coincidence logic controllers 231-1 and 232-1, and the second coincidence logic controllers 231-2 and 232-2 are also configured with types different from each other, two protection systems are actually operated by independently controlling the same types of devices in the entire interior, in other words, thoroughly from the process protection system (bistable logic controller) to the reactor protection system (coincidence logic controller), of the protection system. For example, since a device based on FPGA independently operates and is not affected by a device based on PLC, there is no effect on the protection system in performing safety functions when a CCF occurs. The respective trains 231 and 232 of the reactor protection system may include first coincidence logic controllers 231-1 and 232-1 and second coincidence logic controllers 231-2 and 232-2 which are configured with types different from each other, perform coincidence logic according to the bistable logic results, and transmit final control signals to an reactor trip switchgear system (RTSS) through an initiation circuit. Herein, the reactor protection system may include a first train 231 and a second train 232. The first train 231 may include a first coincidence logic controller 231-1, a second coincidence logic controller 231-2, a first train serial initiation circuit 231-3, and a first train parallel initiation circuit 231-4. The second train 232 may include a first coincidence logic controller 232-1, a second coincidence logic controller 232-2, a second train parallel initiation circuit 232-3, and a second train serial initiation circuit 232-4. The coincidence logic controllers 231-1, 232-1, 231-2, and 232-2 of the reactor protection system receive bistable logic results transmitted from the process protection system. Herein, the coincidence logic controllers 231-1, 232-1, 231-2, and 232-2 of the reactor protection system receive bistable logic results from all multiplexed channels of the process protection system. In detail, the coincidence logic controllers 231-1, 232-1, 231-2, and 232-2 perform coincidence logic according to a number of channel trips (abnormal signal) included in the bistable logic results, and transmit a final reactor stopping signal to the RTSS 240 through initiation circuits 231-3, 232-3, 231-4, and 232-4. For example, when a 2 of 4 coincidence logic is performed on four multiplexed process parameters and the bistable logic results include at least two abnormal signals, the reactor may be determined to be abnormal. Accordingly, when at least two channels among the four channels of the process protection system detect abnormality of the reactor, the digital protection system determines that the reactor is in an abnormal situation and takes actions such as dropping a control element. The RTSS 240 may normally operate the reactor when the nuclear steam supply system is in a normal state, and stop operating the reactor when the nuclear steam supply system is in an abnormal state according to control signals that are transmitted from the initiation circuits 231-3, 232-3, 231-4, and 232-4 of the respective trains of the reactor protection system. Herein, the RTSS 240 may perform safety functions even though a single failure or a CCF occurs in the bistable logic controller or in the coincidence logic controller. Since the controllers of the reactor protection system are configured with coincidence logic controllers of types different from each other, when a CCF occurs in one of the coincidence logic controllers, a control signal path associated with the CCF may be ensured by another coincidence logic controller. FIG. 5 shows a detailed exemplary embodiment of the digital protection system and the RTSS 240. Herein, FIG. 5 clearly shows a control signal path by grouping the controllers of the same type. The digital protection system includes: a process protection system that includes at least two channels, each channel including a first bistable logic controller and a second bistable logic controller which are different and independent from each other, the first bistable logic controller and the second bistable logic controller output bistable logic results by receiving input of process parameters; and a reactor protection system that includes at least two trains, each train including a first coincidence logic controller and a second coincidence logic controller which are different and independent from each other, the first coincidence logic controller and the second coincidence logic controller output coincidence logic results by receiving input of the bistable logic results. The reactor protection system further includes at least two initiation circuits, each initiation circuit including a serial circuit in which a plurality of relays are serially connected, and a parallel circuit in which a plurality of relays are connected in parallel. The plurality of relays included in the serial circuit is switched ON/OFF by receiving as input coincidence logic results of the coincidence logic controllers of types different from each other. The plurality of relays included in the parallel circuit is switched ON/OFF by receiving as input coincidence logic results of the coincidence logic controllers of types different from each other. Each channel of the process protection system includes first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 and second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 which are different and independent from each, and the first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 and the second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 output bistable logic results by receiving as input process parameters. The process protection system includes at least two channels. As shown in FIG. 5, the process protection system includes at least two channels. Each channel includes first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 and second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 which are different and independent from each other. The first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 may be formed based on FPGA, and the second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 may be formed based on PLC. The two types of bistable logic controllers may be independently controlled. Each train of the reactor protection system includes first coincidence logic controllers 231-1 and 232-1 and second coincidence logic controllers 231-2 and 232-2 which are different and independent from each other. The first coincidence logic controllers 231-1 and 232-1 and the second coincidence logic controllers 231-2 and 232-2 output coincidence logic results by receiving as input the bistable logic results. The reactor protection system includes at least two trains. As shown in FIG. 5, the reactor protection system includes at least two trains. Each train includes first coincidence logic controllers 231-1 and 232-1 and second coincidence logic controller 231-2 and 232-2 which are different and independent from each other. The first coincidence logic controllers 231-1 and 232-1 may be formed based on FPGA, and the second coincidence logic controllers 231-2 and 232-2 may be formed based on PLC. The two types of coincidence logic controllers may be independently controlled. The digital protection system further includes at least two initiation circuits. Initiation circuits 231-3 and 231-4 included in a first train include a serial circuit 251 in which a plurality of relays 251-1 and 251-2 is serially connected, and a parallel circuit 252 in which a plurality of relays 251-1 and 251-2 is connected in parallel. Initiation circuits 232-3, 232-4 included in a second train include a serial circuit 254 in which a plurality of relays 254-1 and 254-2 is serially connected, and a parallel circuit 253 in which a plurality of relays 253-1 and 253-2 is connected in parallel. The plurality of relays 251-1, 251-2, 254-1, and 254-2 included in the serial circuits 251 and 254 is switched ON/OFF by receiving as input coincidence logic results of coincidence logic controllers that are different from each other. The plurality of relays 252-1, 252-2, 253-1, and 253-2 included in the parallel circuits 252 and 253 is switched ON/OFF by receiving as input coincidence logic results of coincidence logic controllers that are different from each other. In detail, the relay 251-1 included in the serial circuit 251 is switched ON/OFF by receiving as input a coincidence logic result AF-1, and the relay 251-2 included in the serial circuit 251 is switched ON/OFF by receiving as input a coincidence logic result AP-1 that is different from the coincidence logic result AF-1. The relay 251-1 included in the serial circuit 251 is switched ON/OFF by receiving as input the coincidence logic result AF-1, and the relay 251-2 included in the serial circuit 251 is switched ON/OFF by receiving as input the coincidence logic result AP-1 that is different from the coincidence logic result AF-1. The relay 254-1 included in the serial circuit 254 is switched ON/OFF by receiving as input a coincidence logic result BF-1, and the relay 254-2 included in the serial circuit 254 is switched ON/OFF by receiving as input a coincidence logic result BP-1 that is different from the coincidence logic result BF-1. The relay 252-1 included in the parallel circuit 252 is switched ON/OFF by receiving as input a coincidence logic result AF-2, and the relay 252-2 included in the parallel circuit 252 is switched ON/OFF by receiving as input a coincidence logic result AP-2 that is different from the coincidence logic result AF-2. The relay 253-1 included in the parallel circuit 253 is switched ON/OFF by receiving as input a coincidence logic result BF-2, and the relay 253-2 included in the parallel circuit 253 is switched ON/OFF by receiving as input a coincidence logic result BP-2 that is different from the coincidence logic result BF-2. The process protection system includes a first channel, a second channel, a third channel, and a fourth channel. However, a number of the channels is not limited thereto, and may be at least one. The reactor protection system includes a first train (Train A) and a second train (Train B). The process protection system includes first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 that are based on FPGA, and second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 that are based on PLC. The bistable logic controllers transmit the bistable logic results to all coincidence logic controllers that are the same type. The reactor protection system includes first coincidence logic controllers 231-1 and 232-1 that are based on FPGA, and second coincidence logic controllers 231-2 and 232-2 that are based on PLC. The first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 that are based on FPGA transmit bistable logic results to the first coincidence logic controllers 231-1 and 232-1 that are based on the same FPGA The second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 that are based on PLC transmit bistable logic results to the second coincidence logic controllers 231-2 and 232-2 that are based on the same PLC. The process parameter includes at least one of temperature information about a high temperature pipe and a low temperature pipe of a reactor coolant, pressurizer pressure information, pressurizer water level information, neutron flux information, reactor coolant flow rate information, containment building pressure information, steam generator water level information, steam pipe pressure information, and refueling water tank water level information. The sensor that is described above transmits at least one piece of information included in the process parameter to at least one channel of the process protection system. A number of process parameters and a type thereof that are transmitted to a first channel, a second channel, a third channel, and a fourth channel may be the same or different so that each channel receives at least one piece of information included in the process parameter. The first coincidence logic controllers 231-1 and 232-1 receive bistable logic results including a normal signal or an abnormal signal from the first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 included in respective channels of the process protection system, and output coincidence logic results based on a number of bistable logic results and a number of abnormal signals, the respective coincidence logic results include two output signals that are different from each other. One of the two output signals is input to first relays 251-2 and 254-1 included in the serial circuit, and the other one of the two output signals is input to first relays 252-1 and 253-1 included in the parallel circuit. The first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 determine whether to output normal signals or abnormal signals by comparing the received process parameters and a preset value. The first bistable logic controllers 221-1, 222-1, 223-1, and 224-1 respectively output bistable logic results corresponding to a number of received process parameters. In other words, when the first bistable logic controller 221-1 receives three process parameters, the first bistable logic controller 221-1 outputs three bistable logic results by comparing the respective process parameters and a preset value. The first coincidence logic controllers 231-1 and 232-1 output coincidence logic results based on a number of all received bistable logic results and a number of bistable logic results that are abnormal signals. Herein, for respective process parameters, an n/m coincidence logic is defined by a number m of total bistable logic results and a number n of bistable logic results that are abnormal signals, and when the defined n/m coincidence logic satisfies at least one process parameter, the first coincidence logic controllers 231-1 and 232-1 output coincidence logic results which are reactor stopping signals by executing the n/m coincidence logic. Based on FIG. 5, when the first coincidence logic controllers 231-1 and 232-1 output coincidence logic results that are reactor stopping signals, AF-1 becomes ‘0’, AF-2 becomes ‘1’, BF-1 becomes ‘0’, and BF-2 becomes ‘1’. The second coincidence logic controller receives bistable logic results including a normal signal or an abnormal signal from the second bistable logic controllers included in respective channels, and outputs coincidence logic results based on a number of bistable logic results and a number of abnormal signals, the respective coincidence logic results including two output signals that are different from each other. One of the two output signals is input to second relays 251-2 and 254-2 included in the serial circuit, and the other one of the two output signals is input to second relays 252-2 and 253-2 included in the parallel circuit. The second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 determine whether to output normal signals or abnormal signals by comparing the received process parameters and a preset value. The second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 respectively output bistable logic results corresponding to a number of received process parameters. In other words, when the second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 receive three process parameters, the second bistable logic controllers 221-2, 222-2, 223-2, and 224-2 respectively output three bistable logic results by comparing the respective process parameters and a preset value. The second coincidence logic controllers 231-2 and 232-2 output coincidence logic results based on a number of total received bistable logic results and a number of bistable logic results that are abnormal signals. Herein, for respective process parameters, an n/m coincidence logic is defined by a number m of total bistable logic results and a number n of bistable logic results that are abnormal signals, and when the defined n/m coincidence logic satisfies at least one process parameter, the second coincidence logic controllers 231-2 and 232-2 output coincidence logic results that are reactor stopping signals by executing the n/m coincidence logic. Based on FIG. 5, when the second coincidence logic controllers 231-2 and 232-2 output coincidence logic results that are reactor stopping signals, AP-1 becomes ‘0’, AP-2 becomes ‘1’, BP-1 becomes ‘0’, and BP-2 becomes ‘1’. When at least one abnormal signal is included in the bistable logic results, the first coincidence logic controllers 231-1 and 232-1 output coincidence logic results. Output signals AF-1 and BF-1 of the coincidence logic results which are ‘0’ are input to first relays 251-1 and 254-1 included in the serial circuit, and output signals AF-2 and BF-2 of the coincidence logic results which are ‘1’ are input to first relays 252-1 and 253-1 included in the parallel circuit. The coincidence logic results are reactor stopping signals. When at least one abnormal signal is included in the bistable logic results, the second coincidence logic controllers 231-2 and 232-2 output coincidence logic results. Output signals AP-1 and BP-1 of the coincidence logic results which are ‘0’ are input to first relays 251-2 and 254-2 included in the serial circuit, and output signals AP-2 and BP-2 of the coincidence logic results which are ‘1’ are input to first relays 252-2 and 253-2 included in the parallel circuit. The coincidence logic results are reactor stopping signals. When at least one normal signal is included in the bistable logic results, the first coincidence logic controllers 231-1 and 232-1 output coincidence logic results. Output signals AF-1 and BF-1 of the coincidence logic results which are ‘1’ are input to first relays 251-1 and 254-1 included in the serial circuit, and output signals AF-2 and BF-2 of the coincidence logic results which are ‘0’ are input to first relays 252-1 and 253-1 included in the parallel circuit. The coincidence logic results are reactor operating signals. When at least one normal signal is included in the bistable logic results, the second coincidence logic controllers 231-2 and 232-2 output coincidence logic results. Output signals AF-1 and BF-1 of the coincidence logic results which are ‘1’ are input to second relays 251-2 and 254-2 included in the serial circuit, and output signals AP-2 and BP-2 of the coincidence logic results which are ‘0’ are input to second relays 252-2 and 253-2 included in the parallel circuit. The coincidence logic results are reactor operating signals. The digital protection system further includes an RTSS 240, the RTSS 240 is configured with 4 RTBs, and each RTB may include a first normally open (NO) contact point 243, a second NO contact point 244, a third NO contact point 245, and a fourth NO contact point 246. The first NO contact point 243, the second NO contact point 244, the first NO contact point 245, and the fourth NO contact point 246 may be implemented with switches which are open in the absence of force, and provide a path for the current when the switches are pressed. A motor-generator set (MG-SET) 241 supplies operating power to operate a control element drive mechanism (CEDM) 242. In the RTSS 240 according to an exemplary embodiment, when the NO contact points 243, 244, 245, and 246 are disposed between the MG-SET 241 and the CEDM 242, operating power of the MG-SET 241 may be supplied to the CEDM 242 according to whether the NO contact points 243, 244, 245, and 246 are switched ON/OFF. In detail, when at least one of the first NO contact point 243 and the second NO contact point 244 is in a closed state, and at least one of the third NO contact point 245 and the fourth NO contact point 246 is a closed state, the operating power of the MG-SET 241 is supplied to the CEDM 242. Since the first NO contact point 243 and the second NO contact point 244 are connected in parallel, and the third NO contact point 245 and the fourth NO contact point 246 are connected in parallel, a circuit having a shape of “” may selectively supply the operating power to the CEDM 242. When both of the first NO contact point 243 and the second NO contact point 244 are in opened states, or both of the third NO contact point 245 and the fourth NO contact point 246 are in opened states, the power of the MG-SET 241 supplied to the CEDM 242 is blocked. The CEDM 242 may adjust a position of a control element to control nuclear reactivity of the reactor. In addition, since the CEDM 242 directly holds the control element by using the operating power supplied from the MG-SET, the control element may be pulled down by gravity when the operating power supplied from the MG-SET 241 is blocked. In detail, when the operating power is not supplied, the CEDM 242 stops the reactor by dropping the control element, and when the operating power is supplied, the CEDM 242 normally operates the reactor by maintaining the position of the control element. Since when the control element is dropped, the reactor immediately stops operating, rapid response may be available when an abnormality occurs in the reactor. Since the RTSS according to an exemplary embodiment includes 4 RTBs, and each RTB is configured with NO contact points 243, 244, 245, and 246, the protection system may be stably operated by co-operations between the serial circuit and the parallel circuit when a common failure factor occurs. In case of the NO contact point, a fixed contact point and a driving contact point are separated from each other in an initial state. The fixed contact point and the driving contact point are connected to each other, and current flows therethrough when an external force is applied thereto. In other words, when an external force (for example, electromagnetic force) is applied in an original opened state, the fixed contact point and the driving contact point become a closed state by being connected to each other. In FIG. 5, when current flows in the serial circuit, the contact points 243, 244, 245, and 246 may become closed states from opened states by electromagnetic force generated in coils. In an normally-closed (NC) contact point that will be described later, a fixed contact point and a driving contact point are connected to each other in an initial state. The fixed contact point and the driving contact point are separated from each other when an external force is applied thereto, thus current does not flow therethrough. In other words, when an external force (for example, electromagnetic force) is applied in an original closed state, the fixed contact point and the driving contact point become an opened state by releasing the connection therebetween. In FIG. 5, an NC contact point 255-1 of a relay included in a third circuit may be changed from a closed state to an opened state due to electromagnetic force occurring in coils when current flows in a first parallel circuit. The first NO contact point 243 is disposed between the MG-SET 241 and a central node 247. The second NO contact point 244 is disposed between the MG-SET 241 and the central node 247. The third NO contact point 245 is disposed between the central node 247 and the CEDM 242. The fourth NO contact point 246 is disposed between the central node 247 and the CEDM 242. In order to apply a design that minimizes unnecessary stops of the reactor while unique safety functions of the protection system are maintained, the digital protection system according to the exemplary embodiment is configured to include an RTSS having a “”-shaped structure, and the RTSS receives a calculation result from each train of the reactor protection system. In addition, the RTSS according to an exemplary embodiment may include a first serial circuit 251, a first parallel circuit 252, a second parallel circuit 253, and a second serial circuit 254. The serial circuits 251 and 254 or the parallel circuits 252 and 253 may control to supply power to the CEDM by opening and closing the NO contact points 243, 244, 245, and 246. The first parallel circuit and the second parallel circuit may respectively and indirectly control the NO contact points 244 and 245. As it will be described later, the first parallel circuit 252 controls a contact point 255-1 of a relay included in the third circuit, and the third circuit directly controls to close/open the second NO contact point 244. The second parallel circuit 253 controls a contact point 256-1 of a relay included in a fourth circuit, and the fourth circuit directly controls to close/open the third NO contact point 245. For this, output signals of the coincidence logic controllers include serial circuit control signals AF-1, AP-1, BF-1, and BP-1, and parallel circuit control signals AF-2, AP-2, BF-2, and BP-2, the first coincidence logic controllers 231-1 and 232-1 or the second coincidence logic controllers 232-1 and 232-2 generate the serial circuit control signals AF-1, AP-1, BF-1, and BP-1, and the parallel circuit control signals AF-2, AP-2, BF-2, and BP-2. For example, output signals of the coincidence logic controllers control the serial circuits 251 and 254 to be switched ON/OFF, and the NO contact points 243 and 246 connected to serial circuits 251 and 254 may be repeatedly connected to each other or separated from each other according to switching ON/OFF of the serial circuits 251 and 254. The initiation circuit includes: a first serial circuit that controls to close/open the first NO contact point according to an output signal of the coincidence logic controller; a first parallel circuit that controls to close/open the second NO contact point according to an output signal of the coincidence logic controller; a second parallel circuit that controls to close/open the third NO contact point according to an output signal of the coincidence logic controller; and a second serial circuit that controls to close/open the fourth NO contact point according to an output signal of the coincidence logic controller. The first serial circuit 251 may control to close/open the first NO contact point 243 according to an output signal of the coincidence logic controller. The first parallel circuit 252 may control to close/open the second NO contact point 244 according to an output signal of the coincidence logic controller. In detail, the first parallel circuit 252 may control to close/open the second NO contact point 244 according to an output signal of the coincidence logic controller by using a third circuit 255. The second parallel circuit 253 may control to close/open the third NO contact point 245 according to an output signal of the coincidence logic controller. In detail, the second parallel circuit 253 may control to close/open the third NO contact point 245 according to an output signal of the coincidence logic controller by using a fourth circuit 256. The second serial circuit 254 may control to close/open the fourth NO contact point 246 according to an output signal of the coincidence logic controller. The first serial circuit 251 and the first parallel circuit 252 receive as input output signals AF-1, AF-2, AP-1, and AP-2 of the first coincidence logic controller 231-1 and the second coincidence logic controller 231-2 which are the same kind and are included in one train. For example, the first coincidence logic controller 231-1 and the second coincidence logic controller 231-2 may be implemented with FPGA to have the same logic structure. The second serial circuit 253 and the second parallel circuit 254 receive as input output signals BF-1, BF-2, BP-1, and BP-2 of the first coincidence logic controller 232-1 and the second coincidence logic controller 232-2 which are the same kind and which are included in other train. The initiation circuit includes the third circuit 255 that includes a relay 255-1 and controls to close/open to second NO contact point 244 according to switching ON/OFF of the relay 255-1, and the fourth circuit 256 that includes a relay 256-1 and controls to close/open the third NO contact point 245 according to switching ON/OFF of the relay 256-1. The first parallel circuit 252 controls to switch ON/OFF the relay 255-1 included in the third circuit 255, and the second parallel circuit 253 controls to switch ON/OFF the relay 256-1 included in the fourth circuit 256. The relays 255-1 and 256-1 included in the third circuit 255) and the fourth circuit 256 are NC contact points. Herein, the first serial circuit 251, the first parallel circuit 252, the second parallel circuit 253, and the second serial circuit 254 receive control signals from coincidence logic controllers that are different from each other. Since the serial circuits or the parallel circuits constituting the initiation circuit according to the exemplary embodiment receive control signals from coincidence logic controllers that are different from each other, safety of the reactor may be maintained even though any one of coincidence logic controllers stops operating. In detail, the first serial circuit 251 or the second serial circuit 254 includes two relays that are serially connected, the relays are switched ON/OFF by output signals of the coincidence logic controllers. When both relays are switched ON, the first NO contact point 243 or the fourth NO contact point 246 is switched ON. When at least one of the two relays is switched OFF, the first NO contact point 243 or the fourth NO contact point 246 is switched OFF. Describing the above features with the first serial circuit 251 described above, when the first serial circuit 251 includes the relays 251-1 and 251-2 that are serially connected, the relays 251-1 and 251-2 are switched ON/OFF according to an output signal of the coincidence logic controller. When both of the relays 251-1 and 251-2 are switched ON, the first NO contact point 243 is switched ON. When at least one of the relays 251-1 and 251-2 is switched OFF, the first NO contact point 243 is switched OFF. Describing the above features with the second serial circuit 254, the second serial circuit 254 includes the relays 254-1 and 254-2 that are serially connected, the relays 254-1 and 254-2 are switched ON/OFF according to an output signal of the coincidence logic controller. When both of the relays 254-1 and 254-2 are switched ON, the fourth NO contact point 246 is switched ON. When at least one of the relays 254-1 and 254-2 is switched OFF, the fourth NO contact point 246 is switched OFF. The relays included in a serial circuit receive output signals of coincidence logic controllers that are different from each other. For example, when switching ON signals are received from a coincidence logic controller based on FPGA and from a coincidence logic controller based on PLC, the first serial circuit 251 switches ON the two relays, thus the first NO contact point 243 becomes a closed state. Alternatively, according to the feature of the serial circuit, when at least one output signal of the coincidence logic controller based on FPGA or the coincidence logic controller based on PLC is a switching OFF signal, the serial circuit 251 is switched OFF, and the first NO contact point 243 becomes an opened state. In detail, when the first parallel circuit 252 or the second parallel circuit 253 includes two relays that are connected in parallel, the relays are switched ON/OFF according to an output signal of the coincidence logic controller. When both relays are switched OFF, the relay included in the third circuit 255 or the fourth circuit 256 is switched ON. When at least one of the two relays is switched ON, the relay included in the third circuit 255 or in the fourth circuit 256 is switched OFF. Describing the above features with the first parallel circuit 252, the first parallel circuit 252 includes two relays 252-1 and 252-2 that are connected in parallel, the relays 252-1 and 252-2 are switched ON/OFF according to an output signal of the coincidence logic controller. When both relays 252-1 and 252-2 are switched OFF, the relay 255-1 included in the third circuit 255 is switched ON. When at least one of the two relays 252-1 and 252-2 is switched ON, the relay 255-1 included in the third circuit 255 is switched OFF. Describing the above features with the second parallel circuit 253, the second parallel circuit 253 includes two relays 253-1 and 253-2, and the relays 253-1 and 253-2 are switched ON/OFF according to an output signal of the coincidence logic controller. When both relays 253-1 and 253-2 are switched OFF, the relay 256-1 included in the fourth circuit 256 is switched ON. When at least one of the two relays 253-1 and 253-2 is switched ON, the relay 256-1 included in the fourth circuit 256 is switched OFF. Accordingly, when all of the relays included in the first parallel circuit 252 are switched OFF, the relay included in the third circuit 255 is switched ON, thus the second NO contact point 244 becomes a closed state. In addition, when all of the relays included in the second parallel circuit 253 are switched OFF, the relay included in the fourth circuit 256 is switched ON, thus the third NO contact point 245 becomes a closed state. When at least one of the relays included in the first parallel circuit 252 is switched ON, the relay included in the third circuit 255 is switched OFF, thus the second NO contact point 244 becomes an opened state. In addition, when at least one of the relays included second parallel circuit 253 is switched ON, the relay included in the fourth circuit 256 is switched OFF, thus the third NO contact point 245 becomes an opened state. Herein, the relays included in the third circuit 255 and the fourth circuit 256 are NC contact points 255-1 and 256-1. The relays constituting the parallel circuit receive control signals from coincidence logic controllers that are different from each other. For example, when the relays receive a control signal (switching OFF) from a coincidence logic controller based on FPGA, and a control signal (switching OFF) from a coincidence logic controller based on PLC, the first parallel circuit 252 switches OFF the two relays thereof, thus the second NO contact point 244 becomes an opened state. Alternatively, according to the feature of the parallel circuit, when at least one of output signals of the coincidence logic controller based on FPGA and the coincidence logic controller based on PLC is a switching ON signal, the parallel circuit becomes a closes state, thus the second NO contact point 244 becomes an opened state. Accordingly, in the digital protection system according to an exemplary embodiment, power is supplied in the following sequence: MG-SET-RTSS-CEDM. The CEDM drops the control element to stop the reactor even though the power is not supplied to the CEDM according to closed/opened states of the contact points of the RTSS. FIGS. 6A to 6N illustrate various exemplary embodiments in which the digital protection system controls to normally operate or stop a rector according to various failure types. Each configuration in FIGS. 6A to 6N is the same as FIG. 5. FIG. 6A relates to an operation of an initiation circuit according to an exemplary embodiment, wherein a power plant and a protection system thereof are in normal states. When the power plant and the protection system thereof are in normal states, all of the first NO contact point 243 to the fourth NO contact point 246 included in the initiation circuit are maintained in closed states, and power is applied to the CEDM. Therefore, the CEDM does not drop the control element and the reactor normally operates. FIG. 6B relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant is an abnormal state and the protection system thereof is in a normal state. When the power plant is an abnormal state and the protection system thereof is in a normal state, all of the first NO contact point 243 to the fourth NO contact point 246 included in the initiation circuit are maintained in opened states, and the power is not applied to the CEDM. Therefore, the CEDM drops the control element and the reactor stops operating since the control element is dropped. FIG. 6C relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant is in a normal state and the protection system thereof is in an abnormal state. When the power plant is in a normal state and the protection system thereof is in an abnormal state, signals AP-2 and BP-2 of the coincidence logic controller based on a PLC of the protection system may show abnormal signals (switching ON) rather than original signals (switching OFF). Herein, since one of the two relays of the respective first parallel circuit and the second parallel circuit is switched ON, the relays of the third serial circuit and the fourth serial circuit are switched OFF, thus the second NO contact point and the third NO contact point are maintained in opened states. However, since the first NO contact point 243 and the fourth NO contact point 246 which are controlled by the first serial circuit and the second serial circuit are maintained in closed states, the power is normally applied to the CEDM by passing the first NO contact point 243 and the fourth NO contact point 246, thus the reactor normally operates. FIG. 6D relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant and the protection system thereof are in abnormal states. It corresponds to the worst case scenario wherein the power plant is in an abnormal state and the protection system thereof is also in an abnormal state. Herein, since the power plant is in an abnormal state, the protection system has to drop the control element to stop the reactor, and the protection system may not properly drop the control element as the protection system is also in an abnormal state. However, the protection system according to an exemplary embodiment may solve the above problem. For example, signals AP-1 and BP-1 of the coincidence logic controllers based on PLC of the protection system may show abnormal signals (switching ON) rather than original signals (switching OFF). Herein, since one of the two relays of the respective first serial circuit 251 and the fourth circuit 256 is switched OFF, the first NO contact point 243 and the fourth NO contact point 246 are maintained in opened states. Since the two relays respectively included in the first parallel circuit 252 and the second parallel circuit are switched ON, the relays respectively included in the third circuit 255 and the fourth circuit 256 are switched OFF. Therefore, the first NO contact point 243, the second NO contact point 244, the third NO contact point 245, and the fourth NO contact point 246 are maintained in opened states, thus the power is not supplied to the CEDM, and the reactor stops operating since the control element is dropped. FIG. 6E relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant is in a normal state and the protection system thereof is in abnormal state. Signals AP-1 and BP-1 of the coincidence logic controllers based on PLC of the protection system may show abnormal signals (switching OFF) rather than original signals (switching ON). Herein, since one of the two relays of the respective first serial circuit 251 and the fourth circuit 256 is switched OFF, the first NO contact point 243 and the fourth NO contact point are maintained in opened states. However, the relays respectively included in the third circuit 255 and the fourth circuit 256 which are controlled by the first parallel circuit 252 and the second parallel circuit 253 are maintained switched ON, and the second NO contact point 244 and the third NO contact point 245 are maintained in closed states. Accordingly, the power is normally applied to the CEDM by sequentially passing the second NO contact point 244 and the third NO contact point 245. FIG. 6F relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant and the protection system thereof are in abnormal states. It corresponds to the worst case scenario wherein the power plant is in an abnormal state and the protection system thereof is also in an abnormal state. Herein, since the power plant is in an abnormal state, the protection system has to drop the control element to stop the reactor, and the protection system may not properly drop the control element as the protection system is also in an abnormal state. However, the protection system according to an exemplary embodiment may solve the above problem. For example, signals AP-2 and BP-2 of the coincidence logic controllers based on PLC of the protection system may show abnormal signals (switching OFF) rather than original signals (switching ON). Herein, since one of the two relays of the respective first parallel circuit 252 and the second parallel circuit 253 is switched ON, the relays respectively included in third circuit 255 and the fourth circuit 256 are switched OFF. Therefore, the first NO contact point 243, the second NO contact point 244, the third NO contact point 245, and the fourth NO contact point 246 are maintained in opened states, the power is not supplied to the CEDM, and the reactor is stops operating since the control element is dropped. FIG. 6G relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant and the protections system are in normal states, and first cabinet internal power PW1 included in the first serial circuit 251 is in an abnormal state. As shown in FIG. 6G: all of the relays included in the first serial circuit 251 are switched ON, and the first NO contact point 243 becomes an opened state since current is not supplied from the first cabinet internal power PW1; all of the relays included in the first parallel circuit 252 are switched OFF, and the relay included in the third circuit 255 is switched ON. Accordingly, the second NO contact point 244 becomes a closed state. In addition, all of the relays included in the second parallel circuit 253 are switched OFF, and the relay included in the fourth circuit 256 is switched ON. Accordingly, the third NO contact point 245 becomes a closed state. In addition, all of the relays included in the second serial circuit 254 are switched ON, and the fourth NO contact point 246 becomes a closed state. The power is thus normally applied to the CEDM by sequentially passing the second NO contact point 244, and the third NO contact point 245 or the fourth NO contact point 246. Therefore, the reactor normally operates. FIG. 6H relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant is in an abnormal state, the protections system is in a normal state, and the first cabinet internal power PW1 included in the first serial circuit 251 is in an abnormal state. As shown in FIG. 6H: all of the relays included in the first serial circuit 251 are switched OFF, and the first NO contact point 243 becomes an opened state since current is not supplied from the first cabinet internal power PW1; and all of the relays included in the first parallel circuit 252 are switched ON, and the relay included in the third circuit 255 is switched OFF. Accordingly, the second NO contact point 244 becomes an opened state. In addition, all of the relays included in the second parallel circuit 253 are switched ON, and the relay included in fourth circuit 256 are switched OFF. Accordingly, the third NO contact point 245 becomes an opened state. In addition, all of the relays included in the second serial circuit 254 are switched OFF, and the fourth NO contact point 246 becomes an opened state. The power is thus not supplied to the CEDM, and the reactor stops operating since the control element is dropped. FIG. 6I relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant and the protections system are in normal states, and all of second cabinet internal powers PW2 included in the first parallel circuit 252 and the third circuit 255 are in abnormal states. As shown in FIG. 6I: all of the relays included in the first serial circuit 251 are switched ON, and the first NO contact point 243 becomes a closed state; and all of the relays included in the first parallel circuit 252 are switched OFF, and the relay included in the third circuit 255 is switched ON. However, the second NO contact point 244 becomes an opened state since current is not supplied from the second cabinet internal power PW2 included in the third circuit 255. In addition, all of the relays included in the second parallel circuit 253 are switched OFF, the relay included in the fourth circuit 256 is switched ON. Accordingly, the third NO contact point 245 becomes a closed state. In addition, all of the relays included in the second serial circuit 254 are switched ON, and the fourth NO contact point 246 becomes a closed state. The power is thus normally applied to the CEDM by sequentially passing the first NO contact point 243 and the third NO contact point 245 or the fourth NO contact point 246. Thus, the reactor normally operates. FIG. 6J relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant is in a normal state, the protections system is in a abnormal state, and all of the second cabinet internal powers PW2 included in the first parallel circuit 252 and the third circuit 255 are in abnormal states. As shown in FIG. 6J: all of the relays included in the first serial circuit 251 are switched OFF, and the first NO contact point 243 becomes an opened state; and all of the relays included in the first parallel circuit 252 are switched ON, and the relay included in the third circuit 255 is switched ON since current is not supplied from the second cabinet internal power PW2. However, the second NO contact point 244 becomes an opened state since current is not supplied from the second cabinet internal power PW2 included in the third circuit 255. In addition, all of the relays included in the second parallel circuit 253 are switched ON, and the relay included in the fourth circuit 256 is switched OFF. Accordingly, the third NO contact point 245 becomes an opened state. In addition, all of the relays included in the second serial circuit 254 are switched OFF, and the fourth NO contact point 246 becomes an opened state. The power is thus not supplied to the CEDM, and the reactor stops operating since the control element is dropped. FIG. 6K relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant and the protections system are in normal states, and all of the first cabinet internal power PW1 included in first serial circuit 251, and the second cabinet internal powers PW2 included in the first parallel circuit 252 and the third circuit 255 are in abnormal states. As shown in FIG. 6K: all of the relays included in the first serial circuit 251 are switched ON, and the first NO contact point 243 becomes an opened state since current is not supplied from the first cabinet internal power PW1; and all of the relays included in the first parallel circuit 252 are switched OFF, and the relay included in the third circuit 255 is switched ON. However, the second NO contact point 244 becomes an opened state since current is not supplied from the second cabinet internal power PW2 included in the third circuit 255. In addition, all of the relays included in the second parallel circuit 253 are switched OFF, and the relay included in the fourth circuit 256 is switched ON. Accordingly, the third NO contact point 245 becomes a closed state. In addition, all of the relays included in the second serial circuit 254 are switched ON, and the fourth NO contact point 246 becomes a closed state. The power is thus not supplied to the CEDM, and the reactor stops operating since the control element is dropped. FIG. 6L relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant is in an abnormal state, the protections system is in a normal state, and all of the first cabinet internal power PW1 included in first serial circuit 251, and the second cabinet internal powers PW2 included in the first parallel circuit 252 and the third circuit 255 are in abnormal states. As shown in FIG. 6L: all of the relays included in the first serial circuit 251 are switched OFF, and the first NO contact point 243 becomes an opened state since current is not supplied from the first cabinet internal power PW1; and all of the relays included in the first parallel circuit 252 are switched ON, and the relay included in the third circuit 255 is switched ON since current is not supplied from the second cabinet internal power PW2. However, the second NO contact point 244 becomes an opened state since current is not supplied to the second cabinet internal power PW2 included in the third circuit 255. In addition, all of the relays included in the second parallel circuit 253 are switched ON, and the relay included in the fourth circuit 256 is switched OFF. Accordingly, the third NO contact point 245 becomes an opened state. In addition, all of the relays included in the second serial circuit 254 are switched OFF, and the fourth NO contact point 246 becomes an opened state. The power is thus not supplied to the CEDM, and the reactor stops operating since the control element is dropped. FIG. 6M relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant and the protection system are in normal states, and all of the first cabinet internal power PW1 included in first serial circuit 251, the second cabinet internal powers PW2 included in the first parallel circuit 252 and the third circuit 255, third cabinet internal power PW3 included in the second serial circuit 254, and fourth cabinet internal powers PW4 included in the second parallel circuit 253 and the fourth circuit 256 are in abnormal states. As shown in FIG. 6M: all of the relays included in the first serial circuit 251 are switched ON, and the first NO contact point 243 becomes an opened state since current is not supplied from the first cabinet internal power PW1; and all of the relays included in the first parallel circuit 252 are switched OFF, and the relay included in the third circuit 255 is switched ON. However, the second NO contact point 244243 becomes an opened state since current is not supplied from the second cabinet internal power PW2. In addition, all of the relays included in the second parallel circuit 253 are switched OFF, and the relay included in the fourth circuit 256 is switched ON. However, the third NO contact point 245 becomes an opened state since current is not supplied from the third cabinet internal power PW3. In addition, all of the relays included in the second serial circuit 254 are switched ON, and the fourth NO contact point 246 becomes an opened state since current is not supplied from the fourth cabinet internal power PW4. The power is thus not supplied to the CEDM, and the reactor stops operating since the control element is dropped. FIG. 6N relates to an operation of the initiation circuit according to an exemplary embodiment, wherein the power plant is in an abnormal state, the protections system is in a normal state, and all of the first cabinet internal power PW1 included in first serial circuit 251, the second cabinet internal powers PW2 included in the first parallel circuit 252 and the third circuit 255, the third cabinet internal power PW3 included in the second serial circuit 254, and the fourth cabinet internal powers PW4 included in the second parallel circuit 253 and the fourth circuit 256 are in abnormal states. As shown in FIG. 6N: all of the relays included in the first serial circuit 251 are switched OFF, and the first NO contact point 243 becomes an opened state since current is not supplied from the first cabinet internal power PW1; and all of the relays included in the first parallel circuit 252 are switched ON, and the relay included in the third circuit 255 is switched ON since current is not supplied from the second cabinet internal power PW2. However, the second NO contact point 244 becomes an opened state since current is not supplied from the second cabinet internal power PW2 included in the third circuit 255. In addition, all of the relays included in the second parallel circuit 253 are switched ON, and the relay included in the fourth circuit 256 is switched ON since current is not supplied from the third cabinet internal power PW3. Accordingly, the third NO contact point 245 becomes an opened state. In addition, all of the relays included in the second serial circuit 254 are switched OFF, and the first NO contact point 243 becomes an opened state since current is not supplied from the fourth cabinet internal power PW4. The power is thus not supplied to the CEDM, and the reactor stops operating since the control element is dropped. Referring to FIGS. 6A to 6N, in an emergency situation wherein a control element dropping signal has to be generated, the digital protection system according to the exemplary embodiments controls the CEDM through mutual supplementation between remaining relays and contact points even though any one of the protection systems becomes in an abnormal state. Thus, the reactor may normally operate or stop operating since the protection system of the nuclear power plant normally operates in an event of SPV or CCF. The foregoing exemplary embodiments are merely exemplary and are not to be construed as limiting. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art. |
|
description | The present application is a continuation of U.S. patent application Ser. No. 10/090,470, filed Mar. 4, 2002 now U.S. Pat. No. 6,859,515. The Ser. No. 10/090,470 application is a continuation-in-part of U.S. patent application Ser. No. 09/705,662, which was filed on Nov. 3, 2000, and issued as U.S. Pat. No. 6,400,794, and which claimed priorities of: (a) International Application No. PCT/EP99/02999, filed May 4, 1999; (b) German Patent Application No. DE 199 03 807.4, filed Feb. 2, 1999; (c) German Patent Application No. DE 299 02 108.4, filed Feb. 8, 1999; and (d) German Patent Application No. DE 198 19 898.1, filed May 5, 1998. The invention concerns an illumination system for wavelength ≦193 nm, particularly for extreme ultraviolet (EUV) lithography, as well as a projection exposure apparatus with such an illumination system and a process for the production of microelectronic components with such a projection exposure apparatus. In order to reduce the structural widths for electronic components, particularly in the submicron range, it is necessary to reduce the wavelength of the light utilized for microlithography. Lithography with soft x-rays, so-called EUV lithography, is conceivable at wavelengths below 193 nm, for example. An illumination system suitable for EUV lithography will homogeneously, i.e., uniformly illuminate, with as few reflections as possible, a predetermined field for EUV lithography, particularly the annular field of an objective. Furthermore, the pupil of the objective should be illuminated up to a specific degree of filling, independent of the field, and the exit pupil of the illumination system should lie in the entrance pupil of the objective. An illumination system for a lithography device, which uses EUV radiation, has been made known from U.S. Pat. No. 5,339,246. For uniform illumination in the reticle plane and filling of the pupil, U.S. Pat. No. 5,339,246 proposes a condenser, which is constructed as a collector lens, and comprises at least four pairs of mirror facets, which are arranged symmetrically. A plasma light source is used as the light source. An illumination system with a plasma light source comprising a condenser mirror is shown in U.S. Pat. No. 5,737,137, in which an illumination of a mask or a reticle to be illuminated is achieved by means of spherical mirrors. U.S. Pat. No. 5,361,292 shows an illumination system, in which a plasma light source is provided and the point plasma light source is imaged by means of a condenser, which has at least three aspherical mirrors arranged off-center, in a ring-shaped illuminated surface. An illumination system has been made known from U.S. Pat. No. 5,581,605, in which a photon beam is spilt into a multiple number of secondary light sources by means of a plate with raster elements. A homogeneous or uniform illumination is achieved in this way in the reticle plane. The imaging of the reticle on the wafer to be exposed is produced by means of a conventional reducing optics. A gridded mirror with equally curved elements is provided precisely in the illuminating beam path. U.S. Pat. No. 5,677,939 shows an illumination system for EUV illumination devices, in which an annular field is homogeneously illuminated. In the EUV illumination system according to U.S. Pat. No. 5,677,939, the beams emitted from the EUV source are formed into a parallel beam of light, for example, by means of a mirror. In order to form a multiple number of secondary light sources, the parallel beam of light is guided onto a mirror with a plurality of cylinder raster elements. U.S. Pat. No. 5,677,939 also describes the use of synchrotron radiation sources, but of course, the light of the source is guided directly onto the mirror with cylinder raster elements, due to the parallel nature of the emitted synchrotron radiation, without optical elements situated therebetween. All embodiments shown in U.S. Pat. No. 5,677,939 operate in a parallel beam path. In addition, the facetted mirrors known from U.S. Pat. No. 5,677,939 contain facets with an optical effect and are arranged on a planar substrate. From U.S. Pat. No. 5,512,759 for an arc shaped-field projection system with a synchrotron radiation source an illumination system has been made known, which comprises a condenser system with a multiple number of convergent mirrors. The mirrors collect the radiation emitted by the synchrotron radiation source, to form an annular light beam, which corresponds to the annular field to be illuminated. Therefore, the annular field is illuminated very uniformly. The synchrotron radiation source has a beam divergence >100 mrads in the beam plane. U.S. Pat. No. 5,439,781 shows an illumination system with a synchrotron radiation source, in which the waveguide value, i.e., the Lagrange optical invariant, is adjusted by means of a scatter disk in the entrance pupil of the objective, whereby the scatter disk may have a plurality of pyramidal structures. The synchrotron radiation source in the case of U.S. Pat. No. 5,439,781 also has a beam divergence >100 mrads. The collector mirror for collecting the synchrotron radiation and bundling the same may itself be constructed with facets. The disclosure content of all of the previously named documents: U.S. Pat. No. 5,339,246 U.S. Pat. No. 5,737,137 U.S. Pat. No. 5,361,292 U.S. Pat. No. 5,581,605 U.S. Pat. No. 5,677,939 U.S. Pat. No. 5,512,759 U.S. Pat. No. 5,439,781is incorporated in the present application by reference. An object of the invention is to provide an illumination system that is constructed as simply as possible fulfilling the requirements for an exposure system for wavelengths ≦193 nm, particularly in the EUV region. In addition to a uniform illumination of the reticle, also the telecentricity requirements of a system for wavelengths ≦193 nm particularly should be fulfilled. Telecentricity is to be understood in the present application in that the entire system is telecentric at the wafer. This requires an adaptation of the exit pupil of the illumination system to the entrance pupil of the objective, which is finite for a reflective reticle. In the present application, the telecentricity requirement is fulfilled, if the divergence of the principal rays of the illumination system and objective in the reticle plane does not exceed a predetermined value, for example, ±4.0 mrads, preferably ±1.0 mrad, and the principal rays impinge on the wafer telecentrically. An embodiment of the present invention is an illumination system. The illumination system includes a light source for emitting light having a wavelength ≦193 nm, an optical system, and a radiation protection wall situated between the light source and the optical system. Another embodiment of the present invention is an illumination system having (a) a first optical subsystem that includes a light source for emitting a bundle of light having a wavelength ≦193 nm, and a mirror for receiving the bundle of light, (b) a second optical subsystem system for receiving the bundle of light from the first optical subsystem and illuminating a field in a field plane, and (c) a radiation protection wall situated between the first optical subsystem and the second optical subsystem. Yet another embodiment of the present invention is an illumination system for illuminating a field in a field plane. The illumination system has a first optical subsystem that includes a light source for providing light having a wavelength ≦193 nm, a second optical subsystem, and a free space between the first optical subsystem and the second optical subsystem. The second optical subsystem is situated in a path of the light from the first optical subsystem to the field plane. Typical EUV radiation sources are laser produced plasma sources, pinch plasma sources and synchrotron radiation sources. Synchrotron radiation sources are used in the EUV region as preferred light sources, with a beam divergence smaller than 5 mrads in the plane perpendicular to a predetermined plane. Synchrotron radiation is emitted, if relativistic electrons are deflected in a magnetic field. The synchrotron radiation is emitted tangentially to the path of the electrons. At the present time, one can distinguish three types of sources in the case of synchrotron radiation sources: (i) bending magnets (ii) wigglers (iii) undulators. With suitable dimensioning all above-mentioned synchrotron EUV radiation sources, provide EUV radiation, for example, of 13 or 11 nm with sufficient power for EUV lithography. Since the synchrotron radiation sources are characterized by a beam divergence that is smaller than 5 mrads, at least in one plane, advantageously the system comprises means for broadening the beam, for example, a collector system. In an advantageous embodiment, diverging mirrors or scanning mirrors, which are moved for illuminating a surface can be provided as means for broadening a beam. Since field and aperture of the light source are insufficient for filling or illuminating field and aperture in the reticle plane, the illumination system according to the invention contains at least one mirror with raster elements for producing a plurality of secondary light sources, which are distributed uniformly in the diaphragm plane. Since the geometric dimensions of the raster elements of the first mirror determines the form of the illuminated field in the reticle plane, field raster elements are formed preferably in a rectangular shape in the case of an arc-shaped scanning slit. The raster elements of the first mirror, which are also designated as field raster elements, are designed in such a way that their optical effect is to form images of the light source in the diaphragm plane, so-called secondary light sources. If the extension of the light source is small, for example, approximately point-like, as in the case of an undulator source, then the extension of each of the secondary light sources is also small, and all light rays approximately pass through one point. In each plane after the diaphragm plane then an image of the field raster elements is formed, whereby the magnification is given by the ratio of the distance diaphragm-reticle to the distance field raster element-diaphragm. The raster elements are tilted in such a way that the images of the field raster elements are superimposed at least partially in the reticle plane. The secondary light sources are advantageously imaged into the entrance pupil of the objective with a first optical element, e.g., a field mirror or a field lens, that forms an arc-shaped field. In the case of extended light sources, as, for example in case of a bending magnet, the secondary light sources are extended; therefore the images of the field raster elements in the reticle plane are not sharp. A sharp image can be achieved in such a system, if one provides a second mirror or lens with raster elements, i.e., a so-called double facetting, wherein the raster elements of the second mirror or lens, the so-called pupil raster elements, are located on, or nearby, the site of the secondary light sources. In systems with two mirrors with raster elements, the form of the raster elements of the second mirror, i.e., the pupil raster elements, is adapted to the shape of the secondary light sources and thus differs from the form of the first raster elements, i.e., the field raster elements. It is particularly preferred if the pupil raster elements are round, if the light source is also round in shape. It is particularly preferred that the first mirror with raster elements is illuminated in a round manner or rotation-symmetrically, since then a uniform distribution of the secondary light sources in the diaphragm plane can be achieved with an appropriate distribution. If the illumination of the first mirror is not round, but, for example, rectangular, then the desired round illumination of the entrance pupil of the objective is achieved by double facetting such a system. The first optical elements situated after the mirrors with raster elements serve for imaging the diaphragm plane of the illumination system in the entrance pupil of the projection objective and to form the arc-shaped field. Further, they serve for forming the illumination distribution according to the requirements of the exposure process. It is particularly preferred, that the optical elements comprise grazing-incidence mirrors with an angle of incidence ≦20°. In order to minimize the light losses associated with each reflection, it is advantageous if the number of field mirrors its kept small. Embodiments with at most two field mirrors are particularly preferred. A numerical example will be given below, from which it is obvious that increasing the waveguide value, i.e. the Lagrange optical invariant, for example, in the case of an undulator source is necessary. If one requires an aperture in the wafer plane of NAwafer=0.1–0.25, then this means an aperture in the reticle plane of NAreticle=0.025–0.0625 in the case of 4:1 systems. If the illumination system will illuminate this aperture homogeneously and independently of the field up to a filling degree of σ=0.6, then the EUV source must make available the following 2-dim waveguide value (LLW), i.e., the Lagrange optical invariant or etendu.LLWillumination=σ2LLWobj=0.149 mm2−0.928 mm2. The waveguide value LLW, i.e., the Lagrange optical invariant, is defined generally as follows: LLW=x·y·NA2+A·NA2, whereby A is the illuminated surface. In the reticle plane, A amounts to, e.g., 110 mm×6 mm. An undulator source will be considered as a light source for the EUV illumination system according to the invention, in a first form of embodiment. The waveguide value, i.e., the Lagrange optical invariant or etendu, for the undulator source, can be estimated according to a simplified model, assuming a homogeneous surface radiator with diameter Ø=1.0 mm and aperture NAundulator=0.001 with LLW = A · NA 2 A undulator = π · ( ∅ / 2 ) 2 = 0.785 mm 2 NA undulator = 0.001 so that LLWundulator=A·NA2=0.00000079 mm2=7.9e−07 mm2. As can be seen from this rough estimation, the waveguide value of the undulator source is disappearingly small in comparison to the required waveguide value. The waveguide value, i.e., the Lagrange optical invariant, can be increased by providing distributed secondary light sources to the necessary amount in the entrance pupil of the objective. For this purpose, the first mirror is designed with raster elements. The illumination of the entrance pupil of an objective is defined by the filling factor. The following applies: Filling factor: σ = r illumination R objective aperture wherein Robjective aperture is the radius of the entrance pupil of the objective, andrillumination is the radius of the illuminated area in the entrance pupil of the objective. With σ=1.0, the entrance pupil is completely filled; σ=0.6 corresponds to an underfilling. Since the partial pupils, i.e., the images of the secondary light sources in the entrance pupil of the objective, have sharp intensity peaks due to the small waveguide value of the undulator source, it is advantageous if these are smeared by means of “wobbling” field mirrors, whereby the field illumination should remain unaffected. Thus, it is advantageous to introduce a wobbling field mirror as close as possible to the reticle plane. An estimation for the angular region to be varied by the wobbling field mirror or by the periodically moving field mirror will be given below. If one assumes for the numerical aperture in the reticle plane NAret=0.025 and the angular distance ΔNA of the partial pupils amounts to approximately 0.005, due to the parceling, then the angular region to be varied should lie in the order of magnitude of approximately ±2.5 mrads. An example of a wobbling field mirror would be a toroidal mirror with a size of 160×170 mm as well as a local dynamic gradient of ±2 mrads in the x and y directions with a stability of ±0.1 mrad. A smearing can be achieved not only by means of movable so-called wobbling field mirrors, but also by dynamic deformation of the mirror surface. In order to achieve a high scanning uniformity, the use of active lenses or mirrors for the optical elements can be advantageous. Since the manufacture of field raster elements with a high aspect ratio of 20:1, for example, is difficult, in order to reduce the aspect ratio of field raster elements, it can be of advantage that these raster elements are of astigmatic shape. The secondary light sources are thus broken down into tangential and sagittal secondary sources, which lie in the tangential and sagittal diaphragm planes. Whereas the system for wavelengths in the EUV region, as described above, is designed purely reflectively, i.e., exclusively with mirror components, a use is also conceivable for 193-nm or 157-nm systems. In such a case, refractive components such as lenses are used. The systems described herein are particularly of interest for 193-nm or 157-nm systems, because they use only a few optical components and the optical elements have high absorptions at these wavelengths. It shall first be shown theoretically on the basis of FIGS. 1–20 how a system can be provided, which satisfies the requirements with respect to uniformity and telecentricity for any desired illumination distribution A in a plane with an illumination device according to the invention. The system shown is a system with field raster element and pupil raster element plates. In the art, a raster element plate is also known as a honeycomb plate. A principal diagram of the beam path of a refractive system with two raster element plates is illustrated in FIG. 1. The light from source 1 is collected by a collector lens 3 and transformed into a parallel or convergent light beam. Field raster elements 5 of the first raster element plate 7 decompose the light pencil and produce secondary light sources at the site of pupil raster elements 9. The field lens 12 images these secondary light sources in the exit pupil of the illumination system or the entrance pupil of the subsequent objective. Such an arrangement is characterized by an interlinked beam path of the field and pupil planes from the source up to the entrance pupil of the objective. For this the designation “Köhler illumination” is often selected, as defined, for example, in U.S. Pat. No. 5,677,939, whose disclosure is incorporated to the full extent in the present application by reference. The illumination system according to FIG. 1 will be considered segmentally below. Since the intersection of the light intensity and aperture distribution lies in the plane of the field raster elements, the system can be evaluated independently of the type of source and the collector mirror. The field and pupil imaging for the central pair of raster elements 20, 22 is shown in FIGS. 2A and 2B. The field raster element 20 is imaged on reticle 14 or the mask to be imaged by means of pupil raster element 22 and field lens 12. The geometric extension of field raster element 20 determines the shape of the illuminated field in reticle plane 14. The image scale is approximately given by the ratio of the distance between pupil raster element 22 and reticle 14 and the distance between field raster element 20 and pupil raster element 22. The optical effect of field raster element 20 is to form an image of light source 1, a secondary light source, at the site of pupil raster element 22. If the extension of the light source is small, for example, approximately point-like, then all light rays run through the centers of the pupil raster elements 22. In such a case, an illumination device can be produced, in which the pupil raster elements are dispensed with. As shown in FIG. 2B, field lens 12 images the secondary light sources in the entrance pupil 26 of an objective 24, e.g. a catoptic, katadioptic or all-reflective projection lens. If a field lens is introduced into the beam path, then the field imaging can be influenced in such a way that the image of the field raster elements is deformed by the control of the distortion. It is possible to deform a rectangle into a segment of a ring field, which is herein also referred to as, an annular field or an arc-shaped field. The image scale of the field raster element projection is thus not changed. The beam path of the light rays is shown in FIG. 3 for a special geometric form of a field raster element and a pupil raster element. The shape of field raster element 20 is a rectangle in the embodiment shown in FIG. 3. The aspect ratio of field raster element 20 thus corresponds to the ratio of the arc length to the annular width of the required annular field in the reticle plane. As shown in FIG. 4, the annular field is shaped by the field lens. As shown in FIG. 3, without the field lens, a rectangular field results in the reticle plane. In order to form annular field 30, as shown in FIG. 4, a grazing-incidence field mirror 32 is used. Under the constraint that the beam reflected by the reticle should not be directed back to the illumination system, one or two field mirrors 32 is (are) required, depending on the position of the entrance pupil of the objective. If the principal rays run divergently into the objective that is not shown, then one field mirror 32 is sufficient, as shown in FIG. 4. In the case of principal rays entering the projection objective convergently, two field mirrors are required. The second field mirror must rotate the orientation of the ring. Such a configuration is shown in FIG. 5. In the case of an illumination system in the EUV wavelength region, all components must be reflective ones. The present invention is suitable for use with wavelengths in a range of about 10 nm to 15 nm. Due to the high reflection losses for λ=10 nm–14 nm, it is advantageous that the number of reflections will be kept as small as possible. In the construction of the reflective system, the mutual vignetting of the beams must be taken into consideration. This can occur due to construction of the system in a zigzag beam path or by operation with obscuration. The process according to the invention for preparation of a design for an EUV illumination system with any illumination in a plane A will be described below as an example. The definitions necessary for the process according to the invention are shown in FIG. 6. First the beam path for the central pair of raster elements will be calculated. In a first step, the size of the field raster elements 5 of the field raster element plate 7 will be determined. As indicated previously, the aspect ratio (x/y) results for rectangular raster elements from the form of the arc-shaped field in the reticle plane. The size of the field is determined by the illuminated area A of the intensity distribution of the arbitrary light source in the plane of the field raster elements and the number N of field raster elements on the raster element plate, which in turn is given by the number of secondary light sources. The number of secondary light sources in turn results from the uniformity of the pupil illumination as well as the intermixing. The raster element surface AFRE of a field raster element can be expressed as follows with xFRE, yFRE:AFRE=xFRE·yFRE=(xfield/yfield)·y2FREwhereby xfield*yfield describe the magnitude of the rectangle, which establishes the annular field. Further, the following is valid for the number N of field raster elements:N=A/AFRE=A/[y2FRE·(xfield/yfield)]. From this, there results for the size of the individual field raster element:yFRE=√{square root over (A/[N·(xfield/yfield)])}andxFRE/yFRE=xfield/yfield The raster element size and the size of the rectangular field establish the imaging scale βFRE of the raster element imaging and thus the ratio of the distances d1 and d2.βFRE=xfield/yfield=z2/d1 The pre-given structural length L for the illumination system and the raster element imaging scale βFRE determine the absolute size of d1 and d2 and thus the position of the pupil raster element plate. The following is valid:d1=L/(1+βFRE)d2=d1·βFRE Then, d1 and d2 determine in turn the radius of the pupil raster elements. The following is valid: R FRE = 2 · z 1 · z 2 z 1 + z 2 In order to image the pupil raster elements in the entrance pupil of the objective and to remodel the rectangular field into an arc-shaped field, one or more field lenses, preferably in toroidal form, are introduced between pupil raster element and reticle. By introducing the field mirrors the previously given structural length is increased, since, among other things, the mirrors must maintain minimum distances in order to avoid vignetting. The positioning of the field raster elements depends on the intensity distribution in the plane of the field raster elements. The number N of field raster elements pre-given by the number of secondary light sources. The field raster elements are preferably arranged on the field raster element plate in such a way, that they cover the illuminated surface, without mutually vignetting. In order to position the pupil raster elements, the raster pattern of the secondary light sources in the entrance pupil of the objective is given in advance. The secondary light sources are imaged counter to the light direction by the field lens. The aperture stop plane of this projection is in the reticle plane. The images of the secondary light sources give the (x, y, z) position of the pupil raster elements. The tilt and rotation angles remain as degrees of freedom for producing the light path between field and pupil raster elements. If a pupil raster element is assigned to each field raster element in one configuration of the invention, then a light path is produced by tilting and rotating field and pupil raster elements. Thereby the light beams are deviated in such a way that the center rays all intersect the optical axis and reticle plane. The assignment of field and pupil raster elements can be made freely. One possibility for arrangement would be to assign spatially adjacent raster elements to one another. Thereby the deflection angles will be minimal. Another possibility consists of homogenizing the intensity distribution in the pupil plane. This is made, for example, if the intensity distribution in the plane of the field raster elements is non-homogeneous. If field and pupil raster elements have similar positions, the pattern is transferred to the pupil illumination. The intensity can be homogenized by intermixing. Advantageously the individual components of field raster element plate, pupil raster element plate, and field mirror of the illumination system are arranged in the beam path such that the beam course is as free of vignetting as possible. If such an arrangement has effects on the imaging, then the individual light channels and the field lenses must be re-optimized. Illumination systems for EUV lithography can be obtained with the previously described design process for any desired illumination A with two normal-incidence and one to two grazing-incidence reflections. These systems have the following properties: (i) a homogeneous illumination, for example, of an arc-shaped field (ii) a homogeneous and field-independent pupil illumination (iii) the combining of exit pupil of the illumination system and entrance pupil of the objective (iv) the adjustment of a pre-given structural length (v) the collection of the maximal possible waveguide value. Arrangements of field raster elements and pupil raster elements will be described below for one form of embodiment of the invention with field and pupil raster element plates. First, different arrangements of the field raster elements on the field raster element plate will be considered. The intensity distribution can be selected as desired. The depicted examples are limited to simple geometric shapes, such as circle, rectangle, and the coupling of several circles or rectangles. The intensity distribution will be homogeneous within the illuminated region or slowly varying. The aperture distribution will be independent of the field. In the case of circular illumination A of field raster element plate 100, field raster elements 102 may be arranged, for example, in columns and rows, as is shown in FIG. 7. Alternatively, the center points of the raster elements can be distributed uniformly by shifting the rows over the surface, as is shown in FIG. 8. The latter distribution is better adapted to a uniform distribution of the secondary light sources. A rectangular illumination A is shown in FIG. 9. A shifting of the rows, as shown in FIG. 10, leads to a more uniform distribution of the secondary light sources. These are arranged, however, according to the extension of the field raster element plate within a rectangle. In order to be able to distribute the secondary light sources in the circular diaphragm plane, a double facetting is provided. The pupil raster elements sit at the site of the secondary light sources. In the case of rectangular illumination, it is necessary to tilt the field raster elements in order to produce a light path between field and pupil raster elements, such that the beams impinge on the pupil raster elements, which are arranged, for example within a circle, and which also must be tilted. If the illumination A of field raster element plate 100 comprises several circles A1, A2, A3, A4, for example, by coupling of different beam paths of one or more sources, then with the same raster element size the intermixing is insufficient in the case of an arrangement of the raster elements in rows and columns according to FIG. 11. A more uniform illumination is obtained by shifting the raster element rows, as shown in FIG. 12. FIGS. 13 and 14 show the distribution of field raster elements 102 in case of combined illumination from individual rectangles A1, A2, A3, A4. Now, for example, arrangements of the pupil raster elements on the pupil raster element plate will be described. Two points of view are to be considered in arranging the pupil raster elements: 1. For minimizing the tilt angle of field and pupil raster elements for production the light path, it is advantageous to maintain the arrangement of the field raster elements. This is particularly advantageous with an approximately circular illumination of the field raster element plate. 2. For homogenous filling of the pupil, the secondary light sources should be uniformly distributed in the entrance pupil of the objective. This can be achieved by providing a uniform raster pattern of secondary light sources in the entrance pupil of the objective. These are imaged counter to the direction of light with the field lens in the plane of the pupil raster elements, and determine in this way will the ideal site of the pupil raster elements. If the field lens is free of distortion, then the distribution of the pupil raster elements corresponds to the distribution of the secondary light sources. However, since the field lens forms the arc-shaped field, distortion is purposely introduced. This does not involve rotation-symmetric cushion or semicircular distortion, but the bending of horizontal lines into arcs. The y-distance of the arcs remains constant in the ideal case. Real grazing-incidence field mirrors, however, also show an additional distortion in the y-direction. A raster 110 of secondary light sources 112 in the entrance pupil of the objective, which is also the exit pupil of the illumination system, is shown in FIG. 15, as it had been produced for distortion-free imaging. The arrangement of secondary light sources 112 corresponds precisely to the pre-given arrangement of the pupil raster elements. If the field lenses are utilized for arc-shaped field-formation as in FIG. 16, then secondary light sources 112 lie on arc 114. If the pupil raster elements of individual rows are placed on an arc, which compensate for the distortion, then one can place the secondary light sources again on a regular raster. If the field lens also produces distortion in the y-direction, the pupil is distorted in the y-direction, as shown in FIG. 17. The extent of the illuminated area onto field raster element plate is determined by the input illumination. The illumination of the pupil raster element plate is determined by the structural length and the aperture in the reticle plane. As described above in detail, the two surfaces must be fine-tuned to one another by rotation and tilting of the field and pupil raster elements. For illustration, the problems of this principle will be explained for refractive designs. The examples can be transferred directly, however, to reflective systems. Various configurations can be distinguished for a circular illumination of the field raster element plate, as shown below. If a converging effect is introduced by tilting the field raster elements, and a divergent effect is introduced by tilting the pupil raster elements, then the beam cross section can be reduced. The tilt angles of the individual raster elements are determined by tracing the center rays for each pair of raster elements. The center rays hit the corresponding raster elements in the center. The system acts like a telescope-system for the central rays, as shown in FIG. 18. How far the field raster elements must be tilted depends on the convergence of the impinging beam. If the convergence is adapted to the reduction of the beam cross section, the field raster elements can be introduced on a planar substrate without a tilting angle. A special case results if the convergence between field and pupil raster element plate corresponds to the aperture at the reticle, as shown in FIG. 19. No divergent effect must be introduced by the pupil raster elements, so they can be utilized without tilting. If the light source also possesses a very small waveguide value and the secondary light sources are nearly point-like, the pupil raster elements can be completely dispensed with. A magnification of the beam cross section is possible, if a diverging effect is introduced by tilting the field raster elements, and a collecting effect is introduced by tilting the pupil raster elements. For the central rays, the system operates as a retro-focus system, as shown in FIG. 20. If the divergence of the impinging radiation corresponds to the beam divergence between field and pupil raster elements, then the field raster elements can be used without tilting. Instead of the circular shape that has been described, rectangular or other shapes of illumination A of the field raster element plate are possible. The arrangements shown in FIGS. 21–56 described below show an embodiment of the invention for which undulators are used as synchrotron radiation light sources, without the invention being limited thereto. The radiation of the undulator light source can be described as a point light source with strongly directed radiation, for example, the divergence both in the horizontal as well as the vertical direction is less than 10 mrads. Therefore, all illuminating systems described below as examples have only one mirror or one lens with raster elements, without the invention being limited thereto. Undulator sources have in a predetermined plane in which a predetermined wavelength spectrum is irradiated, a beam divergence of <100 mrads, preferably <50 mrads. Therefore, collectors along the electron path for collecting the synchrotron radiation and bundling it, as described, for example, in U.S. Pat. No. 5,439,781 or U.S. Pat. No. 5,512,759 are not necessary for such sources. Three possible configurations of an illumination system with a light source, which is shown in this particular embodiment as an undulator source 200, without being limited thereto, and a mirror with raster elements, will be described below. Here: Type A describes an embodiment, in which the individual raster elements of the first mirror are individual tilted planar facets. Type B describes an embodiment, in which the individual raster elements are designed as raster elements with positive optical power in a convergent beam path. Type C describes an embodiment, in which the raster elements of the first mirror form one structural unit with the last optical element of the collector unit, which is a collective mirror or collective lens. An illumination system according to type A in a refractive form is shown for the definition of the parameters in FIGS. 21A and 21B. In an embodiment according to type A, the means for beam broadening comprises a diverging lens 206 or diverging mirror, without being limited thereto. The collecting effect for producing the secondary light sources is introduced by the collective mirror or collective lens 208 situated behind the diverging lens or diverging mirror 206. The means for beam broadening and the mirror or the lens with collecting effect form a so-called collector unit or a collecting system 210. If a mirror with raster elements is not present, the collective mirror would image source 200 in the diaphragm plane 212 of the illumination system. The secondary light source 216 is decomposed into a plurality of secondary light sources 218 by the mirror with raster elements 214 or the facetted mirror. The raster elements 214 can be formed as planar facets, since the secondary light sources or light sources in this form of embodiment are imaged in the diaphragm plane by means of the collector unit. The facets are tilted at angles with respect to one another or with respect to a plane of reference. The tilting angles of the planar facets are such that the center rays of the facets converge, i.e., intersect, at an optical axis 222 in the image plane 220. For the center rays, the facetted mirror or lens acts as a divergent mirror or lens. For illustration purposes, FIGS. 21A and 21B show the schematic structure based on a refractive, linearly constructed system. The facetted lens is not shown in FIG. 21A. The secondary light source 216 lies in the diaphragm plane. The facetted lens 214 is inserted in FIG. 21B. The arrangement of individual prisms in the refractive presentation corresponds to the tilt of the facets. An arrangement of the facetted mirror or lens in the convergent beam path according to type B as shown in FIGS. 22A and 22B is also possible. The collective mirror 208 is designed in such a way that the source 200 is imaged in the image plane 220 of the illumination system, as shown in FIG. 22A. The positive optical power of facets 214 is then designed such that secondary light sources 218 are produced in the diaphragm plane 212, as shown in FIG. 22B. In the embodiment of the invention according to type C, as shown in FIGS. 23A and 23B, the collective mirror or collective lens and the facetted mirror or lens are combined. In such a configuration, the collecting effect of the collector mirror is achieved by the individual tilts of the raster elements. The facets or raster elements are shown as a superimposition of prisms and a collective lens in the schematic presentation in FIGS. 23A and 23B. In a reflective embodiment, this would be realized with a plurality of tilted raster elements 224. As described before, illumination systems according to type C comprise at least a device for producing secondary light sources that includes at least a facetted mirror. The facetted mirror is divided into field raster elements. The field raster elements are tilted to have a converging effect to a diverging light beam, which impinges onto the facetted mirror. The field raster elements divide the impinging light bundle into a plurality of light bundles, where each light bundle is associated with a raster element and each light bundle has a center ray. The center ray of each light bundle is the ray traveling through the center of the corresponding field raster element. In this application a converging effect of the facetted mirror means that the center rays that travel divergent to the optical axis of the illumination system before being reflected by the facetted mirror, are reflected at the raster elements such that they travel convergent to the optical axis after being reflected by the facetted mirror. The optical axis of the illumination system is defined by the direct lines between the centers of the components of the illumination system. In a preferred embodiment at least two of the center rays of two different field raster elements intersect in the image plane, which means that they are collected in the image plane. Thus the images of the field raster elements in the image plane at least partially superimpose. FIG. 23C shows an enhancement of the illumination system of FIG. 23B that includes a plurality of pupil raster elements 221 on a pupil raster element plate. In this case, raster elements 224 are field raster elements. Pupil raster elements 221 are located at or nearby a site of secondary light sources 218. A first pupil raster element 221 receives and directs a first bundle of light from a first field raster element 224. A second pupil raster element 221 receives and directs second bundle of light from a second field raster element 224. The first pupil raster element 221 images the first field raster element 224 in an image plane 220, and the second pupil raster element 221 images the second field raster element 224 in image plane 220. Thus, there is a one-to-one correlation between field raster elements 224 and pupil raster elements 221. The following formulas describe the imaging by the field raster elements for the illumination arrangement according to types A–C: NA Ret = DU BL 2 d 5 ⇒ DU BL = 2 · d 5 · NA Ret DU BL x Wabe · d 4 + d 5 d 5 = 4.0 ⇒ x Wabe = DU BL 4.0 · d 5 d 4 + d 5 β Wabe = x Feld x Wabe = d 5 d 4 ⇒ β Wabe = x Feld x Wabe ⇒ d 4 = d 5 β Wabe wherein the abbreviations denote Wabe=field raster element=FRE DU=diameter Feld=field BL=diaphragm d5: measurement for the structural length NAret: aperture in the reticle plane. xFeld: x-extension of the field. DUBL: diameter of the diaphragm xWabe: x-extension of the raster element yWabe: y-extension of the raster element The number of field raster elements in a field raster element row corresponds to four (4) in the embodiment above. The number of raster elements is a measure for the number of secondary light sources, the uniformity of the field and the uniform illumination of the pupil. If the illumination systems shown in FIGS. 21A to 23B being examples for refractive systems are designed for 13-nm EUV radiation, then these systems must be reflective systems for 13-nm radiation with as few reflections as possible due to the high reflection losses. In a case where an undulator light source is used, a beam-broadening means, such as a divergent mirror or lens having negative optical power, is used. The divergent mirror can be combined with a collective mirror having positive optical power forming a collector unit for illuminating the mirror with raster elements. For an undulator source, the collector unit for 13-nm radiation can comprise a first grazing-incidence mirror or a scanning mirror, which broadens the beam bundle of radiation emitted by the undulator light source, and a second normal-incidence mirror, which forms a convergent beam bundle. The convergent beam bundle impinges onto the first mirror, which is divided into raster elements. In order to achieve an advantageous design in the case of 13-nm wavelength, due to the higher reflectivity, grazing-incidence mirrors (R≈80%) are preferred over normal-incidence mirrors (R≈65%). Advantageously, the distance d1 from the source to the first mirror should be at least d1=3000 mm. In the case of such an embodiment, a free space of 2000 mm should be maintained between the first mirror and the remaining optics for the radiation-protection wall. Alternatively to the arrangement with a first mirror in front of the radiation-protection wall and second mirror behind this wall, the first mirror can also be placed behind the radiation-protection wall with d1>5000 mm. It can be designed as a grazing-incidence or normal-incidence mirror. Advantageously, the undulator light source irradiates in the horizontal direction. The horizontally situated reticle is illuminated at a principal beam angle of at most 20°, preferably 10°, and most preferably 5.43°. A horizontal arrangement of reticle and wafer is necessary to avoid a bending of the optics in the gravitational field. Advantageously, two grazing-incidence field mirrors are used for forming the field, in order to illuminate the reticle with correct annular orientation and to deflect the light separated from the illumination system into the objective. The two grazing incidence mirrors are arranged between the first mirror, which is divided into raster elements, and the image plane of the illumination system. The reticle is situated in the image plane of the illumination system. Illumination systems according to types A and B are shown in FIG. 24 in schematic representation. The system according to types A and B comprises a divergent mirror 300, which is formed as a grazing-incidence toroidal mirror, which broadens the beam rays emitted by the light source, and a normal-incidence collector mirror 302, which illuminates the mirror with raster elements 304 in a round manner and projects the light source either in the diaphragm plane (type A) or in the reticle plane (type B). In type A and B-systems therefore a convergent light bundle impinges onto the facetted mirror. The reference number 304 designates the normal-incidence facetted mirror or mirror with raster elements. The field mirrors 306, 308 are formed as grazing-incidence field mirrors and form the field in the reticle plane. The system parameters can be designed such that the optical axis is tilted only around the x-axis (α-tilt). The meridional plane remains the same. The distances between the mirrors are adapted to the boundary conditions of the source. Such a type A system is described in detail below. Individually tilted planar facets are used as raster elements. The undulator source was assumed to be a homogeneous surface radiator with a diameter of 1.0 mm and NAundulator=0.001. The facet rows 310 were arranged in a displaced manner relative to one another for the uniform distribution of the secondary light sources in the diaphragm plane, as shown in FIG. 25. The circle 312 in FIG. 25 shows the illumination of the mirror with raster elements, which are planar facets 314 by the broadened undulator source 200. The arrangement of the mirrors relative to the coordinate system of the source, of the type A illumination system shown in FIGS. 26 to 33 is given in the following Table 1. TABLE 1Arrangement of the mirrors for type AComponentX [mm]Y [mm]Z [mm]α [°]β [°]γ [°]AOI [°]Source0.0000.0000.0000.0000.0000.0000.000—Divergent mirror0.0000.0005000.00080.0000.0000.00080.000g.i.Collecting mirror0.0001026.0607819.078−15.0000.000180.0005.000n.i.Mirror with field0.000878.4596981.991155.0000.0000.00015.000n.i.raster elementsDiaphragm0.0001007.0177135.200−40.0000.000180.0000.000—Field mirror 10.0001906.2318206.84238.8580.000180.00078.858g.i.Field mirror 20.0002039.0218276.60516.5730.0000.00078.857g.i.Reticle0.0002287.8998300.26390.000180.0000.0005.430n.i.EP objective0.00068.1588511.26390.0000.0000.0000.000—X, Y, Z: origin of the coordinates of the components.α, β, γ: rotation angle around the x-, y-, and z-axis. The angles are referred to the coordinate system of the source.AOI: angle of incidence of the optical axis at the componentsg.i./n.i.: grazing incidence/normal incidence. The z-axis of the reticle plane is at 90° relative to the z-axis of the source coordinate system. The z-distance between source 200 and divergent mirror 300 is 5000 mm in the system described below. For radiation-protection wall 316, a z-distance of 1900 mm is provided between collector mirror 300 and facetted mirror 304. The reticle plane 318 lies 2287.9 mm above the source. The design will now be described on the basis of FIGS. 26 to 33. FIG. 26 shows the entire system up to the entrance pupil 320 of the objective in the yz-section including source 200 and divergent mirror 300, collective mirror 302, planar facetted mirror 304, field mirrors 306, 308, reticle plane 318 and entrance pupil 320 of the objective. The center rays are indicated for the central field raster elements (0,0) and the two field raster elements with the greatest distance to the central field raster element. The beams intersect in reticle plane 318 and illuminate the entrance pupil 320 of the objective. FIG. 27 shows a part of the illumination system beginning with the divergent mirror 300. The beam deflection of the center rays due to the tilted facets on the facetted mirror 304 can be clearly seen. FIG. 28 shows a beam bundle traveling through the illumination system, which impinges onto the central raster element (0, 0) 322 of the first mirror. The collector mirror 302 produces the secondary light source 212 in the diaphragm plane. The field mirrors form the arc-shaped field and images the secondary light sources in the entrance pupil 320 of the objective. FIG. 29 shows the entire system with objective in yz-section, comprising: divergent mirror 300, collective mirror 302, mirror 304 with planar facets, field mirrors 306, 308, reticle plane 318 and 4-mirror projection objective 330. The beam bundle travels from the illumination system into the projection objective 330. As is apparent from FIG. 29, the illumination system and the projection objective are clearly separated. Projection objectives other than the 4-mirror projection objective are possible, for example, 5- or 6-mirror projection objectives. The illumination of the reticle situated in the image plane of an illumination system according to FIGS. 27 to 29 with a 30° annular field (r=211 mm; −3.0 mm<Δr<+3.0 mm) in a contour-line representation is shown in FIG. 30, r denotes the ring radius of the arc-shaped field shown in FIG. 30. The ring radius is the distance of the center of the arc-shaped field to the optical axis of the projection objective An intensity section parallel to the y-axis at x=0.0, 15 mm, 30 mm, and 45 mm is shown in FIG. 31. Since the secondary light sources have only minimal extension, an ideal step-like profile results. The width of the intensity profile increases at the edge of the field, due to the radius of the arc-shaped field and the non-optimal superimposition of the images of the raster elements of first mirror 304 in the image plane. In order to keep the scanning energy constant, the maximal intensity decreases to the same extent, by adjusting the intensity distribution in the image plane with one of the field mirrors 306. The integral scanning energy, i.e., the integration of the intensity along the scanning path, is a decisive factor in the lithography process. As shown in FIG. 32, the integral scanning energy is nearly homogeneous in the present embodiment. The integral scanning energy may be controlled by the design of the optical elements, such as field mirrors or field lenses. FIG. 33 shows the exit pupil illumination for a field point in the center of the arc-shaped field. Partial pupils 332, which are the images of the secondary light sources in the exit pupil, correspond to the raster element distribution on the first mirror. The maximal numerical aperture amounts to NAret=0.025. The numerical aperture of a partial pupil is negligibly small (NApartial pupil=2E−6) corresponding to the small Entendu of the undulator source. However, a complete filling of the pupil is achieved, when seen as an integral, due to the uniform distribution of the secondary light sources. By wobbling one of the field mirrors or by dynamically deforming the surface of one of the field mirrors the grid of the partial pupils in the exit pupil can be periodically shifted to get a complete filing of the pupil in a time average. An embodiment of the invention according to type B with a facetted mirror in a convergent beam path is shown in FIGS. 34 to 41. The light source is assumed to be similar to the light source described in the embodiment according to FIGS. 26 to 33. The facets or raster elements are arranged as in FIG. 25 and are formed in this embodiment as concave facets having a positive optical power, which are mounted on a planar support surface. The arrangement of the mirrors relative to the overall coordinate system of the source is shown in Table 2. TABLE 2Arrangement of the mirrors for type BComponentX [mm]Y [mm]Z [mm]α [°]β [°]γ [°]AOI [°]Source0.0000.0000.0000.0000.0000.0000.000—Divergent0.0000.0005000.00080.0000.0000.00080.000g.i.mirrorCollecting0.0001026.0607819.078−15.0000.000180.0005.000n.i.mirrorMirror with0.000913.1897178.953155.0000.0000.00015.000n.i.field rasterelementsDiaphragm0.0001041.7477332.162−40.0000.000180.0000.000—Field mirror 10.0001917.1878375.47138.8580.000180.00078.858g.i.Field mirror 20.0002049.9778445.23416.5730.0000.00078.857g.i.Reticle0.0002298.8558468.89290.000180.0000.0005.430n.i.EP objective0.00079.1148679.89290.0000.0000.0000.000—X, Y, Z origin of the coordinates of the components.α, β, γ: rotation angles around the x-, y-, and z-axis. The angles are referred to the coordinate system of the source.AOI: angle of incidence of the optical axis at the components.g.i./n.i.: grazing incidence/normal incidence. The z-axis of the reticle plane is at 90° relative to the z-axis of the source coordinate system. The z-distance between source 200 and collective mirror 302 is 5000 mm. For the radiation-protection wall (not shown), a z-distance between divergent mirror 300 and facetted mirror 304 of 2100 mm is provided. The reticle plane 318 lies 2298.9 mm above the source. FIG. 34 shows the entire system up to entrance pupil 320 of the objective in the yz-section, comprising: source 200, divergent mirror 300, convergent mirror 302, facetted mirror 304, field mirrors 306, 308, reticle plane 318, entrance pupil of objective 320. The center rays, which intersect each other in the reticle plane 318 and which are drawn up to the exit pupil 320, are indicated for the central field raster element (0,0) and the two field raster elements with the greatest distance to the central field raster element. The center rays in this application are the rays of the beam bundle traveling through the centers of the raster elements. Part of the illumination system beginning at the divergent mirror 300 is shown in FIG. 35. The center rays are not influenced by facetted mirror 304 since the facetted mirror 304 is made of concave raster elements attached to a planar mirror substrate without tilt angles. A beam bundle that impinges the central raster element (0,0) is depicted in FIG. 36. The positive optical power of the concave raster element produces the secondary light source in the diaphragm plane. The field mirrors 306, 308 form the arc-shaped field in the image plane 318 and image the secondary light sources situated in the diaphragm plane into the exit pupil 320 of the illumination system. FIG. 37 shows the entire system with objective in the yz-section, comprising: divergent mirror 300, collective mirror 302, facetted mirror 304, field mirrors 306, 308, reticle plane 318 and 4-mirror objective 330. As is apparent the facetted mirror 304 is situated in the convergent beam path, produced by collective mirror 302. The illumination of the reticle with the 30° annular field (r=211 mm; −3.0 mm<Δr<+3.0 mm) is shown in FIG. 38 as a contour-line representation. Here, r is the ring radius of the arc-shaped field, wherein a 30° segment from a ring is used. The ring radius r is the distance of the center of the arc-shaped field to the optical axis of the projection objective. FIG. 39 shows an intensity section parallel to the y-axis at x=0.0, 15 mm, 30 mm, and 45 mm. Since the secondary light sources have only minimal extension, an ideal step-like is formed at least in the center of the field. The width of the intensity profile increases at the edge of the field, due to the radius of the arc-shaped field and the non-optimal superimposition of the images of the first raster elements. The maximum intensity decreases with the broadening of the edges and the increased value of the half-width, so that the scanning energy remains constant. As FIG. 40 shows, the integral scanning energy of the presently described embodiment is nearly homogeneous. The exit pupil illumination of a field point in the center of the arc-shaped field is shown in FIG. 41. The following paragraph describes an illumination system with at least one device for producing secondary light sources comprising at least a first mirror, which is divided into raster elements, and one or more first optical elements, which are arranged between the device and an image plane of the illumination system. The first optical elements of the illumination system image the secondary light sources in an exit pupil of the illumination system. The raster elements are tilted to have a converging effect to a diverging light beam, which impinges onto the first mirror. An illumination system with these characteristics is designated as a type C system. In the embodiment described hereinafter the light source is a undulator light source, without being limited thereto. The undulator light source is taken as before as the point-like light source. The system according to type C comprises, in a first embodiment according to type C1, a first grazing-incidence collector mirror 400, which deflects radiation downward. Mirror 400 is a divergent mirror having negative optical power, which produces a diverging beam. The diverging beam impinges onto the facetted mirror 402, which reverses the radiation direction again towards the undulator source 200. In order to provide a solution that is free of vignetting, facetted mirror 402, which is divided into a plurality of facets or so called raster elements, introduces a tilt of the optical axis around the y-axis, the so-called β tilt. Therefore, the system axis runs beside the radiation-protection wall. In this application, the optical axis is defined as the connecting lines between the centers of the optical components. The origins of the local coordinate systems of the optical components of the illumination system are located in the centers of the optical components. For mirrors, the origin of the local coordinate system corresponds to the mirror vertex, and for the facetted mirror, to the center of the mirror plate on which the raster elements are mounted. FIG. 42 shows the lateral view in the y-z-plane of such a system and FIG. 43 shows the top view in the x-z-plane. The second embodiment, type C2, of a system according to type C is shown in FIG. 44. In the system according to type C2, the grazing-incidence mirror is replaced by a normal-incidence mirror 400. This has the consequence that the optical axis of the system again runs away from the undulator source after two reflections at mirror 400 and facetted mirror 402. The mirrors must then be tilted only around the x-axis, the so-called α-tilt. A tilt of the optical axis around the y-axis as in the case of type C1 is not necessary. Divergent mirror 400, having negative optical power for producing a diverging beam impinging onto the first mirror 402 with raster elements, is arranged outside the chamber comprising the light source in the case of type C2. Since the source radiation in the case of an undulator source is polarized nearly linearly in the horizontal direction, the optical axis can also be deflected nearby the Brewster angle. In FIGS. 45 to 54 a system according to type C1 is shown again, in more detail. The arrangement of the mirrors of this system shown in FIGS. 45 to 54 is given in Table 3. TABLE 3arrangement of the mirrors of a type C1-systemComponentX [mm]Y [mm]Z [mm]α [°]β [°]γ [°]AOI [°]Source0.0000.0000.0000.0000.0000.0000.000—Divergent mirror0.0000.0005000.000−80.0000.0000.00080.000g.i.Mirror with field0.000−1026.0607819.07831.0399.462179.08414.501n.i.raster elementsDiaphragm−63.666−897.5037679.723222.692−18.56216.3660.000—Field mirror 1−493.075−30.4126739.809138.466−18.880−15.99478.858g.i.Field mirror 2−531.728146.6416655.203−18.117203.471−7.42578.857g.i.Reticle−539.593345.7446637.988270.0000.00024.5545.430n.i.EP objective−627.274−1873.9976446.06990.0000.000155.4460.000—wherein the abbreviations denote:X, Y, Z: origin of the coordinates of the components.α, β, γ: rotation angle around the x-, y-, and z-axis. The angles are referred to the coordinate system of the sourceAOI: angle of incidence of the optical axis at the componentsg.i./n.i.: grazing incidence/normal incidence In this application normal incidence mirrors are mirrors with angles of incidence of the rays impinging the mirror surface smaller than 30° relative to the surface normal, and grazing incidence mirrors are mirrors with angles of incidence of rays impinging the mirror surface or φ>60° relative to the surface normal. The z-axis of the image plane in which the reticle is situated is at 90° relative to the z-axis of the source coordinate system. The z-distance between source and divergent mirror 400 amounts to 5000 mm. The facetted mirror 402 is rotated around the x and y axes such that the projection objective would not cross the illumination beam path. The facetted mirror 402 comprising a plurality of facets or so called raster elements lies −1026.1 mm in y-direction beneath the light source 200, and the reticle plane lies 345.79 mm in y-direction above the source. The design of type C1 given as an example will now be described in more detail on the basis of the figures. FIG. 45 shows the entire illumination system from the light source 200 up to the entrance pupil of the objective, which corresponds to the exit pupil 410 of the illumination system in the y-z section. The illumination system comprises a light source 200, a divergent mirror 400 having negative optical power, a facetted mirror 402 with a convergent effect to the divergent light beam impinging the facetted mirror, field mirrors 404, 406 and an image plane 408. Furthermore, the exit pupil 410, which corresponds to the entrance pupil of the objective, is shown. The center rays are shown for the central field raster element (0,0) and the two field raster elements on the field raster element plate with the greatest distance to central field raster element. According to the invention, by tilting each individual field raster element with respect to the surface of the facetted mirror 402 a convergent effect onto the divergent light beam formed, for example, by divergent mirror 400 impinging the facetted mirror 402, could be achieved. Due to the individual tilts the center rays of the different field raster elements of the facetted mirror 402 intersect each other in the image plane 408, where the reticle is situated. Thus, the images of the individual field raster elements are superimposed, at least partially, in the image plane. The exit pupil 410, which corresponds to the entrance pupil of the objective, is homogeneously illuminated. FIG. 46 shows a part of the illumination system beginning with the divergent mirror 400 in the y-z section. The depicted center rays are traveling divergent to the optical axis in front of the facetted mirror 402. They impinge at the facetted mirror 402 at the centers of the central field raster element and the two field raster elements with the greatest distance to the central field raster element. Due to the tilted field raster elements, the center rays are traveling convergent to the optical axis after reflection at the facetted mirror 402. They are deflected such that they intersect each other in the image plane 408. Therefore, the images of the raster elements are superimposed, at least partially, in the image plane 408. FIG. 47 shows the same part of the illumination system as FIG. 46, but in an x-z-section beginning with divergent mirror 400. The facetted mirror 402 also tilts the optical axis around the y-axis. Therefore, the objective can be situated away from the radiation protection wall. A beam bundle, which impinges on central raster element (0,0) of the facetted mirror is depicted in FIG. 48. The raster elements themselves have positive optical power to produce secondary light sources in the diaphragm plane. Field mirrors 404, 406 form the annular or arc-shaped field in the image plane and image the secondary light source 412 in the entrance pupil 410. FIG. 49 shows a projection exposure apparatus comprising an illumination system and a 4-mirror projection objective 430 in the y-z section. The illumination system comprises a divergent mirror 400 producing a divergent beam bundle impinging onto a facetted mirror 402 comprising a plurality of raster elements. The facetted mirror 402 has a convergent effect on the divergent beam bundle. Furthermore, the illumination system comprises field mirrors 404, 406, reticle plane 408 and 4-mirror objective 430. The beams running into the objective are separated from the illumination system. A part of the projection exposure apparatus is shown in the y-z section in FIG. 50. In this view, the separation of the projection beam path and the illumination beam path is clearly seen. FIG. 51 shows the illumination of the reticle with a 30° annular or arc-shaped field (r=211 mm; −3. mm<Δr<+3.0 mm) in contour-line representation. The different contour lines refer to lines with the same intensity in the image plane. As is apparent from this figure, the images of different field raster elements are superimposed, at least partially, in the image plane. FIG. 52 shows an intensity section of the illumination in the image plane parallel to the y-axis for x=0.0, 15 mm, 30 mm, and 45 mm of the C1-type system. FIG. 53 shows the integral scanning energy of the presently described embodiment, which is almost homogeneous. The illumination of the exit pupil of a type C1-system for the center field raster element is shown in FIG. 54. Partial pupils, which are the images of the secondary light sources in the exit pupil, correspond to the raster element distribution on the first mirror. The maximal numerical aperture amounts to NAret=0.025. The numerical aperture of a partial pupil is negligibly small (NApartial pupil=2E−6) corresponding to the small Entendu of the undulator source. However, a complete filling of the pupil is achieved, when seen as an integral, due to the uniform distribution of the secondary light sources. By wobbling one of the field mirrors, or by dynamically deforming the surface of one of the field mirrors, the grid of the partial pupils in the exit pupil can be periodically shifted to get a complete filing of the pupil in a time average. It is not necessary that the diaphragm plane is accessible, so one may also operate with a virtual diaphragm plane. For type C-systems, the raster elements of the facetted mirror must not have a positive optical power. They might be, for example, planar raster elements, which are easy to manufacture. In such a case, which is shown in FIG. 55, the divergent mirror 1002 having negative optical power produces a virtual secondary light source 1000, as shown in FIG. 55A. The divergent beam impinging on the facetted mirror is deflected in the embodiment shown by tilted planar raster elements such that the center rays associated with each raster element intersect each other in the image plane, where the reticle is situated on the optical axis. In a refractive embodiment, as shown in FIG. 55B, the tilted planar raster elements correspond to a plurality of prisms. In such an arrangement, a plurality of secondary light sources 1002 is produced in a virtual diaphragm plane. The following formulas describe relationship of the system parameters according to FIGS. 55A and B: NA Ret = DU BL 2 d 4 ⇒ DU BL = 2 · d 4 · NA Ret DU BL x Wabe · d 4 - d 3 d 4 = 4.0 ⇒ x Wabe = DU BL 4.0 · d 4 d 4 - d 3 β Wabe = x Feld x Wabe = d 4 d 3 ⇒ β Wabe = x Feld x Wabe ⇒ d 3 = d 4 β Wabe wherein: DU=diameter BL=diaphragm Wabe=raster element Feld=fieldwherein: d4: measurement for the structural length NAret: aperture in the reticle plane. The number of raster elements in a raster element row corresponds to four (4). This provides for the number of secondary light sources, the uniformity of the field, and the uniform illumination of the pupil. xField: x-extension of the field XWabe: x-extension of the raster element d1: distance between the primary light source and the divergent mirror d2: distance between the divergent mirror and the facetted mirror d3: distance between the virtual secondary light sources or the virtual diaphragm plane and the facetted mirror d4: distance between the virtual diaphragm plane and the image plane It is clear from the schematic representation according to FIGS. 55A–B that the distances d2 and d3 are approximately of equal magnitude for an undulator source with NAsource=0.001. Together with a structural length that can be realized, this will require, in practical terms, a normal-incidence collector mirror. The embodiment of FIGS. 55A and 55B is also an embodiment with a facetted mirror having a converging effect on a diverging beam bundle impinging this facetted mirror according to the invention. Advantageously, the raster elements in this embodiment can be planar. In order to smear the sharp intensity peaks as shown, for example, in FIG. 54, in the pupil and to effectively increase Entendu, the last field mirror can be designed as a moving mirror, a so-called wobbling field mirror, in all forms of embodiment of the invention. The movement of a wobbling field mirror primarily changes the positions of the partial pupils in the exit pupil and therefore causes a complete filling of the exit pupil in time average and has little influence on the field position since the wobbling mirror is arranged close to the image plane. In addition to a movement of the entire mirror, a periodic surface change of the last mirror is also conceivable in order to achieve this smearing of the sharp intensity peaks in the pupil. In order to reduce the raster element aspect ratio, the use of astigmatic facets is possible. The diaphragm plane is then split into sagittal and tangential diaphragm planes. The aspherical field mirrors image these two planes in the entrance pupil of the objective. The illumination distribution in the reticle plane can be influenced by the design of the field forming optical components, e.g., the filed mirrors or the field lenses. For example, the field forming optical components can be designed to achieve a uniform scanning energy. For the control of the scanning uniformity, in another configuration of the invention, one of the two field mirrors can be configured as an active mirror. The azimuthal distortion can be controlled by several actuator rows, which are arranged in the x-direction. FIGS. 56 to 58 show an enhancement of a type C1-illumination system, an example of which is shown in FIGS. 42 and 43. The enhanced system includes a light source 2012, a divergent mirror 2004, a field raster element plate 2002, a pupil raster element plate 2000, field mirrors 2006 and 2008, and an image plane 2010. The system also includes a radiation protection wall 2014. Light source 2012 is preferably an undulator light source, as described herein for other embodiments, but it is not limited thereto. Light source 2012 emits light that impinges divergent mirror 2004. Divergent mirror 2004 receives the light from light source 2012 and produces a divergent beam. The divergent beam travels in a light path from divergent mirror 2004 to field raster element plate 2002. Field raster element plate 2002, also known as a facetted mirror, includes a plurality of field raster elements. It receives the light from divergent mirror 2004 and directs the light to pupil raster element plate 2000. Pupil raster element plate 2000, also known as a facetted mirror, includes a plurality of pupil raster elements. The pupil raster elements are located at or nearby a site of secondary light sources. Pupil raster element plate 2000 receives the light from field raster element plate 2002 and directs it to field mirror 2006. The light travels from pupil raster element plate 2000 to field mirror 2006, and thereafter to field mirror 2008. Field mirror 2008 then directs the light to image plane 2010. A reticle (not shown) is situated in image plane 2010. If the illumination system of FIG. 56 is represented in only two-dimensions, e.g., the paper plane of FIG. 56, then the light path from divergent mirror 2004 to field raster element plate 2002 appears to cross the light path from pupil raster element plate 2000 to field mirror 2006. This crossing of the light path is also known as X-folding and provides for a very compact-sized illumination system. In contrast, FIG. 57 shows an Illumination system of type C1, in which the light path from divergent mirror 2004 to field raster element plate 2002 does not cross the light path from pupil raster element plate 2000 to field mirror 2006. FIG. 58 shows a detailed view of a field raster element plate and a pupil raster element plate in a system such as that illustrated in FIG. 56. As mentioned earlier, raster element plates are also known as facetted mirrors. The field raster element plate includes three field raster elements 2100.1, 2100.2, 2100.3. Each field raster element 2100.1, 2100.2, 2100.3 receives a divergent portion of light 2102.1, 2102.2, 2102.3, respectively, from a light source (not shown in FIG. 58). Each divergent portion of light 2102.1, 2102.2, 2102.3 has a center ray 2104.1, 2104.2, 2104.3, respectively. By tilting field raster elements about individual tilt angles a convergence of the diverging beam is achieved. For example, with respect to a plane 2106, field raster element 2100.1 situated parallel thereto, field raster element 2100.2 is tilted at an angle α1, and field raster element 2100.2 is tilted at an angle α2. Plane 2106, may represent, for example, a field raster element plate on which field raster elements 2100.1, 2100.2, 2100.3 are mounted. Due to the collecting effect of each field raster element 2100.1, 2100.2, 2100.3, secondary light sources 2106.1, 2106.2, 2106.3 are provided. A set of pupil raster elements 2108.1, 2108.2, 2108.3 are situated at or near the site of secondary light sources 2106.1, 2106.2, 2106.3. Pupil raster element 2108.1 receives and directs a first bundle of light from field raster element 2100.1. Pupil raster element 2108.2 receives and directs a second bundle of light from field raster element 2100.2. Pupil raster element 2108.1 images field raster element 2100.1 in an image plane (not shown in FIG. 58), and pupil raster element 2108.2 images field raster element 2100.2 in the image plane. Thus, there is a one-to-one correlation between the field raster elements and the pupil raster elements. Center rays 2104.1, 2104.2, 2104.3 from field raster elements 2100.1, 2100.2 and 2100.3 are received by pupil raster elements 2108.1, 2108.2 and 2108.3, respectively, and redirected so that they intersect in the image plane. This effect is achieved by tilting pupil raster elements 2108.1, 2108.2 and 2108.3 with respect to a plane 2110. For example, in FIG. 58, pupil raster element 2108.3 is shown to be situated parallel to plane 2110, whereas pupil raster elements 2108.1 and 2108.2 are tilted at angles β1 and β2, respectively, with respect to plane 2110. It should be understood that various alternatives and modifications of the present invention could be devised by those skilled in the art. The present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims. |
|
summary | ||
claims | 1. A method of suppressing deposition of radionuclides on components of a nuclear power plant comprising:connecting a pipe having a pump to piping of the nuclear power plant;removing contaminants including an oxide film deposited on an inner surface of the piping by chemical decontamination;forming a ferrite film on the inner surface of the piping by supplying a liquid, which is pressurized by the pump and has a temperature adjusted within 60° C. to 100° C. by a heating apparatus provided on the pipe and a pH adjusted to within 5.5 to 9.0, comprising iron (II) ions, and a chemical for oxidizing the iron (II) ions to iron (III) ions into the piping after connecting the pipe to the piping, and after the chemical decontamination; anddepositing noble metal on the ferrite film by supplying a solution including a noble metal to the piping through the pipe after formation of the ferrite film,wherein the steps of connecting the pipe, removing the contaminants, forming the ferrite film, and depositing the noble metal are carried out after the nuclear power plant is stopped and before starting the nuclear power plant. 2. The method of suppressing deposition of radionuclides on components of a nuclear power plant according to claim 1, further comprising circulating the liquid through a circulation loop formed by the pipe and the piping. |
|
046718982 | description | DISCLOSURE OF THE INVENTION It has now been found that in an unexpectedly simple way it is possible to reduce the volume of the spent ion exchange resin as well as to prepare a cement matrix wherein the radioactive nucleides are bound in a stable way. The process according to the invention is characterized by mixing the ion exchange resin partly with a salt, to liberate radioactive substances from the ion exchange resin, partly with an inorganic sorbent for the radioactive substances thus liberated, then drying and incinerating the mixture, and solidifying in cement the residue from the incineration. The salt may be added to the aqueous ion exchanger in a solid form or as an aqueous solution thereof. The salt is preferably added in such a quantity that the ion exchanger will be saturated. The cation of the salt should effectively elute active ions, such as Cs.sup.+ -ions, wich are sorbed on the ion exchanger. In order to obtain such an elution it is possible to utilize several common water-soluble salts, such as calcium nitrate or aluminium nitrate. However, according to the invention it is preferable to use water-soluble salts, the anions of which tend to liberate active nucleides, such as cobolt, zinc, through the formation of complexes, for instance salts of phosphoric acid, citric acid, tartaric acid, oxalic acid, formic acid, propionic acid. It has turned out that such complex-forming anions do not disturb the subsequent process steps, i.e. the incineration and cementation operations, and that said organic acids are eliminated in the incineration step. As cations of the salt calcium and aluminium are preferred. These salts are conducive to a favourable course of incineration. The explanation thereto seems to be that after their sorption on the ion exchanger the salts make said ion exchanger rather heavy, which facilitates the incineration. Furthermore, these salt reduce the tendency to an agglomeration of the ion exchange resin grains, which results in a larger contact surface towards the incineration air and a more rapid incineration. Salts of calcium and aluminium make the incineration residue more compatible with the cement matrix, and accordingly the solidification in cement will be facilitated. The inorganic sorbent should be added in such an amount that it completely sorbs the liberated radioactive nucleides. Preferably the sorbent has a particle size of 10-100 .mu.m. During the incineration operation the sorbent will retain radioactive nucleides, such as Cs-137, by converting them into stable compounds having low vapour pressures at high temperatures. Furthermore the sorbent imparts to the final product a good stability against leaching of radioactive nucleides from the cement matrix, which effect is especially pronounced for Cs-137. As said sorbent we prefere to utilize titanates or titanium hydroxide, zirconates or zirconium hydroxide or zirconium phosphate, aluminates or aluminium hydroxide, alumino silicates such as bentonite or a natural or synthetic zeolite, or a mixture of two or more of these sorbents. The ion exchange resin, the salt and the sorbent are preferably admixed at a temperature of 20.degree.-70.degree. C., and the aquous admixture is preferably dried at 90.degree.-120.degree. C. The dried admixture is preferably incinerated at 500.degree.-900.degree. C., preferably at about 800.degree. C., suitably in air that has been enriched to an oxygen content of 30-40% by volume. The residue from the incineration is mixed with cement and water. The water content of the mixture is preferably between 10 and 20% by weight. The precentage of the residue from the incineration should be at most 120% of the weight of the cement. In connection with the invention cement preferably means Portland cement, but also similar aqueous-hardening binders. The cement mixture is now cast in a mould, wherein it is allowed to harden, and the hardened body is allowed to dry. Our examinations show that the volume of the final or end product can be reduced up to 1/10 as compared to a direct solidification of a spent ion exchange resin in cement. It has also been found that the stability against leaching is increased at least ten times as compared to said direct cementation. EXAMPLE A spent radioactive organic ion exchange resin contained inter alia 10 kBq of Cs-137 per gram of resin. The resin had a dry solids content of 50% by weight and was of the mixed-bed type, the ratio of cationic exchanger:anionic exchanger being 1:1. 100 grams of said resin were mixed with 25 grams of calcium formate and 4 grams of bentonite. The mixture was dried at 110.degree. C. and incinerated at 700.degree. C. in air that had been enriched on oxygen. An incineration residue of 15 grams was then obtained. This was mixed with 15 grams of Portland cement and 6 grams of water and from the mixture there was cast a cube having a volume of 20 cm.sup.3. After said cube had hardened leaching tests showed that Cs-137 was leached at room temperature with a rate of about 10.sup.-5 g/cm.sup.2 .multidot.d. |
063317117 | abstract | In scanning lithography as used in the semiconductor industry, systematic variations in critical dimension feature size which depend on the substrate coordinates are compensated for in a lithography tool. This is done by determining (experimentally or theoretically) low frequency variations in the critical dimensions on the target caused by imperfections in the lithography tool and/or the resist and/or the process steps. These low frequency spatial errors are compensated for, after the primary scanning exposure using the original pattern data, by a secondary scanning exposure of the target using a weaker intensity and relatively larger diameter exposure beam. The secondary exposure is also carried out at a larger address size (address grid) than is the primary exposure so it is relatively fast in terms of throughput. Since the secondary exposure is additive to the more intense primary exposure, relative critical dimension control is provided in fine increments but with relatively minor adverse impact on throughput and thus fabrication cost. Thus the detected systematic variation defects are compensated for without requiring the primary exposure to be performed at a smaller address size. |
052251543 | description | DETAILED DESCRIPTION OF THE INVENTION A fuel structural member according to the invention will now be described with reference to FIG. 1. In a fuel cladding tube 11, an outer layer 16 in contact with reactor water is made of high corrosion resistance and high strength alloy, an inner surface layer 14 in contact with fuel pellet 12 is made of pure zirconium, and an intermediate layer 15 is made of alloy having a relatively high ductility, as shown in FIG. 1A, thereby performing the objects of the invention. In a spacer 2 and a channel box 3, a surface layers 26 in contact with the reactor water are made of high strength and high anti-corrosion alloy, and an intermediate layer 27 interposed between the surface layers is made of alloy having a high ductility to thereby perform the above-described objects, as shown in FIGS. 1B and 1C. It is most preferable to use, as the high strength and high alloy, a Zr-based alloy containing 0.5 to 2.2% Nb-0.5 to 1.5% Sn-0.1 to 0.8% Mo. Also, it is preferable to use, as the high ductility alloy, a Zr-based alloy containing 0.5 to 2.0% Sn-0.05 to 0.4% Fe-0.05 to 0.15% Cr-0.03 to 0.2% Ni, a Zr-based alloy containing 0.5 to 2.0% Sn-0.05 to 0.4% Fe-0.03 to 0.2% Ni, a Zr-based alloy containing 0.05 to 2.0% Sn-0.05 to 0.4% Fe-0.05 to 0.15% Cr-0.03 to 0.2% Ni-0.01 to 0.8% Mo, stainless steel or copper alloy. There can be used, as the high ductility alloy forming the intermediate layer, a stainless steel containing carbon, in an amount, by weight, of not more than 0.08%, and also containing, by weight, not more than 2.0% Mn, not more than 1.00% Si, 16.0 to 20.0% Cr, 8.00 to 14.00% Ni, not more than 3.00% Mo, and the balance Fe and incidental impurities. There can also be used, as the high ductility alloy forming the intermediate layer, a copper-based alloy consisting by weight of not more than 3.0% Pb, not more than 6.0% Fe, not more than 0.5% Zn, not more than 11.0% Al, not more than 2.0% Mn, not more than 33.0% Ni, and the balance Cu and incidental impurities. If a Zr-based alloy containing Nb-Sn-Mo and having preferably a tensile strength of 70 kgf/mm.sup.2 or more at room temperature is used in a surface in contact with the reactor water, it is possible to prevent the nodular corrosion and to increase the strength of the member. Furthermore, the degree of the hydrogen absorption of these alloys is small at about 1/5 of that of zircaloy-2 and zircaloy-4. It is thus possible to prevent the hydrogen embrittlement. If a high ductility alloy preferably with tensile strength of 45 to 60 kgf/mm.sup.2 at room temperature and with an elongation rate 25% or more is used as an intermediate layer interposed between the above-described high strength high anti-corrosion alloy which intermediate layer is out of contact with the fuel pellet, or as an intermediate layer interposed between a pure Zr liner layer, which preferably has a tensile strength of 30 to 40 kgf/mm.sup.2 and an elongation rate 30% or more, and the high strength high corrosion resistance alloy, the ductility of the member is enhanced, and in particular, the toughness of a member such as a spacer that is subjected to a impact load during the fuel handling is enhanced. The elongation rate is preferably 30% or more. As a material forming the intermediate layer, other than those described above, it is preferable to use copper alloy and stainless steel. The tensile strength of these materials at room temperature is shown in Table 1. TABLE 1 ______________________________________ tensile elon- Composition strength gation material (%) (kgf/mm.sup.2) (%) ______________________________________ copper 8% Al 8.0Al--92.0Cu 45.7 60 alloy bronze berylium 2.0Be--98.0Cu 48.5 35 copper nickel 66.0Ni--34.0Cu 53.9 42 copper AISI 304 -- 53.0 40 304L -- 49.0 40 347 -- 53.0 40 316 -- 53.0 40 316L -- 49.0 40 ______________________________________ Since the high strength high anti-corrosion alloy contains Nb, it is necessary to prevent the reduction in anti-corrosion property of welded portions. In order to satisfy this requirement, the alloy composition must meet the following relationship: EQU [Sn addition amount] (wt %).gtoreq.2.times.[Nb addition amount] (wt %) -3.0 In addition, the alloy should be heat-treated in the temperature range of 500.degree. to 700.degree. C. after welding. In particular, it is preferable to effect the heat treatment for heating the alloy for 1 to 30 hours in the temperature range of 530.degree. to 610.degree. C. The reasons therefor will be described below. The causes for the degradation in corrosion property of the weld zone and the heat-affected zone thereof are that a non-equilibrium phase in which a great amount of Nb exists in a solid-solution state is formed during a heating/cooling process in welding. The non-equilibrium phase is formed in such a manner that .beta. phase stable at a high temperature is formed in the weld zone and the heat-affected zone thereof and is quenched. The .beta. phase remains at the room temperature, or is not decomposed into an .alpha.-Zr phase and a .beta.-Nb precipitated phase stable at room temperature in the cooling process, and the .beta. phase is martensite-transformed into .omega. Zr phase. The corrosion property of this phase is extremely low, which causes the reduction in anti-corrosion property in weld zone. The purpose of the heat treatment after welding is to decompose the non-equilibrium phase into the .alpha.-Zr phase and the .beta.-Nb precipitated phase stable at room temperature. Also, the reason why the element of Sn is added to meet the above-described relationship is that Sn has an effect for preventing the generation of the non-equilibrium phase during the cooling process in welding and an effect for accelerating the decomposition of the non-equilibrium phase still remaining after welding. The reason why the upper limit of preferable temperature range is 610.degree. C. is that, if the alloy is heated above the upper limit, the .beta. phase will be again formed and the .beta. Nb phase that is finely precipitated in the .alpha. Zr phase to enhance the strength will be diffused into the .beta. phase to thereby remarkably reduce the strength. The reason why the lower limit of the preferable temperature range is 530.degree. C. is that the worked structure generated by cold working or the like is heated at 530.degree. C. or above so as to be recrystallized for enhancing the ductility of the material and for promoting the decomposition of the non-equilibrium phase remaining in the welded portions. The heating in the temperature range of 530.degree. to 610.degree. C. is performed for the purposes of preventing the crystalline particle of the high ductility alloy interposed between the high strength high anti-corrosion alloys from becoming coarse and of preventing superior ductility being degraded. It is preferable that a thickness of the high strength high anti-corrosion alloy be in the range of 5 to 20%. If the thickness is smaller than the lower limit, it would be very difficult to control the thickness during the manufacture. The upper limit thereof depends upon the necessary strength. More specifically, in a structural member having a thickness of, for example, 860 .mu.m, if the thickness of the innermost layer is less than 50 .mu.m, it is difficult to control the thickness during the manufacture. Also, the maximum value is 150 .mu.m in view of I.sub.2 SCC of the pure zirconium. Therefore, the thickness of the innermost layer is about 5.8 to 17.4% of the total thickness. Preferably, it is 5 to 20% thereof. On the other hand, from a view point of the anti-corrosion property and the strength, the thickness of the outermost layer is in the range of 100 to 480 .mu.m, that is, in the range of about 11.6 to 55.8% of the total thickness. It is preferable the range of the thickness of the outermost layer be 10 to 60%, and in particular, in case of a cladding tube, it is preferable that the thickness of the outermost layer be 15 to 30%, and as other requisite, it is preferable to make the thickness of a single layer be in the range of 20 to 35%. In case of the intermediate layer, the maximum and minimum values are varied depending upon the mechanical strength of the material to be used. An example of the maximum and minimum values in case of the intermediate layer of copper alloy or stainless steel is shown in Table 2. It is preferable to set the thickness of the intermediate layer in the range of 25 to 85%. In particular, in case of the cladding tube, it is preferable to set the intermediate layer thickness in the range of 50 to 70%, and in case of other members, it is preferable to set the intermediate layer thickness in the range of 35 to 60%. TABLE 2 ______________________________________ Max. (mm) Mini. (mm) (% regarding the (% regarding the total thickness) total thickness) ______________________________________ copper 8% Al 0.542 (about 63%) 0.23 (about 27%) alloy bronze berylium 0.580 (about 67%) " copper nickel 0.70 (about 81%) " copper AISI 304 0.68 (about 79%) " 304L 0.60 (about 69%) " 347 0.68 (about 79%) " 316 0.68 (about 79%) " 316L 0.60 (about 69%) " ______________________________________ The method for producing the above-described fuel structural member of three-layer structure will be described. Interfaces of the three-layer structure are preferably a metallurgically bonded faces. FIG. 6 is a view showing an example of a process for producing the fuel structural member according to the present invention. The integration is performed by the mutual diffusion of metal atoms between the materials at the time of hot rolling or hot extruding and intermediate annealing after cold rolling. When a stable phase such as an oxide film is formed on a surface of the material, this phase becomes a barrier against the mutual diffusion, resulting in inferior metallurgical bonding. Accordingly, any work that contaminate the surface must be avoided. After the surface is cleaned prior to the hot rolling or hot extruding, the materials forming the respective layers are overlapped with each other. At this time, end faces thereof are welded together to prevent air or the like from entering into the interior. When the welding work is performed in the atmosphere, there is a fear that an oxide layer is formed in the interface in welding. Therefore, it is preferable to perform the welding work under vacuum condition. The higher the hot extruding temperature or hot rolling temperature, the more the mutual diffusion between the materials will be accelerated. Thus, this is preferable for the metallurgical bonding. However, very coarse .beta. phase crystal grains will be caused in the temperature range exceeding 1,100.degree. C. This is undesirable. If the materials are heated up to the .alpha.+.beta. phase temperature or the .beta. phase temperature, the diffusion of alloy elements will be extremely accelerated. This is preferable for the metallurgical bonding. Accordingly, it is effective to insert after the hot working a step of heating the materials to the .alpha.+.beta. phase temperature or the .beta. phase temperature and then air- or water-cooling the materials. It is necessary that the water cooling rate be 8.degree. C./sec or more. If the cooling rate is lower than this limit, the precipitated phase will become coarse, to degrade the mechanical property. After this heat treatment, the cold rolling and annealing must be performed at least once. Since the ductility of the material cooled from the .alpha.+.beta. phase or the .beta. phase is low, it is necessary to grow new crystalline particles having no strain by heating the material above the recrystallization temperature after forming a working structure through the cold rolling. This treatment recovers the ductility. The invention is explained below in detail by use of embodiments. Embodiment 1 TABLE 3 ______________________________________ Alloy elements Kinds of (wt %) No. Material Sn Fe Ni Cr Nb O Zr ______________________________________ 1 Pure Zr -- 0.03 -- -- -- 0.06 99 2 Zircalloy 1.5 0.25 0.09 0.1 -- 0.11 bal 3 NSM alloy 1.0 -- -- -- 1.0 0.09 bal ______________________________________ TABLE 4 ______________________________________ Material .sigma.u (kg/mm.sup.2) .epsilon.l (%) ______________________________________ Pure Zr 35 34 Zircalloy-2 56 34 NSM alloy 80 20 ______________________________________ By using a vacuum arc melting method, there were produced a pure Zr ingot, a Zr-Sn-Fe-Ni-Cr alloy ingot, and a Zr-Sn-Nb-Mo alloy ingot. The alloy composition of each of the ingots is shown in Table 3, and the data of strength and elongation about each layer are shown in Table 4. Each of the ingots was forged at a temperature of 980.degree. to 1050.degree. C. (.beta. forging) and the forged billets were formed into billets having diameters different from each other. The forged billets were subjected to a heat-treatment (.beta. quenching) in which the billets were water-cooled after being held at 1000.degree. C. for one hour. After removing the surface oxide layer occurring on the .beta.-quenched billet materials by mechanical grinding, the billets were subjected to piercing so that the billets were provided with axial holes of diameters different each other. The inner diameter of the hole provided in the Zr-Sn-Fe-Nb-Mo alloy pierced cylindrical billet was approximately equal to the outer diameter of the hole provided in the Zr-Sn-Fe-Ni-Cr alloy pierced cylindrical billet, the latter being inserted in the former by use of a press. The outer diameter of the hole provided in the pure Zr billet was approximately equal to the inner diameter of the pierced Zr-Sn-Fe-Ni-Cr alloy billet, the pure Zr billet being inserted in the latter billet by use of the press so that the three billets were integrated. The inner diameter of the integrated billets was made to be 50 mm and the outer diameter thereof was made to be 150 mm, in which integrated billets the thickness of the Zr-Sn-Nb-Mo alloy was 10 mm, the thickness of the Zr-Sn-Fe-Ni alloy being 30 mm, and the thickness of the pure Zr being 10 mm. The boundary portions of the ends of the integrated billets were welded under a high vacuum not less than 1.times.10.sup.-4 Torr by an electron beam welding device. Then, the integrated billets were hot-extruded after being heated to 750.degree. C., with the result that there was produced a tube having an outer diameter of 64 mm and a thickness of 11 mm. Then, the tube was cold-rolled two times by use of pilger mills, so that there was obtained a tube having an outer diameter of 19.2 mm and a thickness of 1.9 mm. During the production of the tube, an intermediate annealing treatment was effected at 630.degree. C. in 2 hours after the first cold-rolling, then the tube was subjected to a heat-treatment (.alpha.+.beta. quenching) in which water was jetted onto the tube to effect the cooling thereof just after the tube passed a high frequency induction coil. After the heat-treatment, the tube was again rolled two times by the pilger mills to thereby obtain a tube having an outer diameter of 12.3 mm and a thickness of 0.86 mm, the intermediate annealing being effected at 590.degree. C. in 2 hours, and the final annealing was effected under vacuum at 570.degree. C. for 2 hours. In the resultant tube there was inserted uranium pellets, and then plugs were attached to both the ends of the tube, which plugs and the tube ends were joined by TIG welding under a He atmosphere of 3 atm, so that a fuel rod was obtained. The weld zones each defined by both the plug and the tube end was heated in a He atmosphere at 580.degree. C. and held in about 10 minutes, then being cooled. From both the weld zone and the center portion of the resultant fuel rod there were cut out test pieces, which were subjected to a corrosion test and a tensile test. The corrosion test was effected at a temperature of 500.degree. C. in steam of a pressure of 105 kgf/cm.sup.2 by holding them in 24 hours. Other test pieces were polished and etched to examine the thickness of each layer. As a result, it was found that the cross-sectional thickness of the pure Zr was 18% of the whole thickness of the fuel cladding tube, that the thickness of the Zr-Sn-Fe-Ni-Cr alloy layer is 62% thereof, and that the thickness of the Zr-Sn-Nb-Mo alloy layer is 20% thereof, that is, the thickness ratio of the layers was in proportion to the thickness ratio of the initial billets forming the integrated billets. As apparent from FIG. 7 showing the test results under steam, the anti-corrosion of the material of the invention was very high with respect to both the weld zone and the center portion of the fuel cladding tube in comparison with the comparative material. Further, neither nodular corrosion nor accelerated corrosion of white color occurred on the outer surface (Zr-Sn-Nb-Mo alloy layer) of the material of the invention, which outer surface was covered with a uniform oxide film of black color. On the other hand, in the comparative material, there were observed at both the weld zone and the center portion thereof much amount of nodular corrosion with respect to the test under steam. The remarkable difference in anti-corrosion occurring therebetween in the test under steam is attributed to the matter regarding whether or not the nodular corrosion occurred. In the tensile test, the tensile strength of the material of the invention was 63 kgf/mm.sup.2, the elongation thereof being 38%, so that the tensile strength of the material of the invention is higher by 5 to 8 kgf/mm.sup.2 than a conventional fuel cladding tube made of Zircalloy-2 and the elongation of the material of the invention is in the same degree in comparison therewith. Embodiment 2 TABLE 5 ______________________________________ Alloy elements Kinds of (wt %) No. Material Sn Fe Ni Cr Nb Mo Zr ______________________________________ 1 Zircalloy 1.0 0.3 0.1 0.05 -- -- bal 2 NSM 1.0 -- -- -- 2.0 0.2 bal ______________________________________ By use of a vacuum melting method, two kinds of alloys shown in Table 5 were melted to thereby provide ingots. The ingots were forged at a temperature of 980.degree. to 1050.degree. C. to provide slabs of 75 mm in thickness. The forged slabs was subjected to .beta. quenching in which the water cooling thereof was effected after holding the slabs at a temperature of 1000.degree. to 1050.degree. C. in 20 minutes. The alloy No. 1 shown in Table 5 was hot-rolled at a temperature of 600.degree. C. to have a thickness of 35 mm, the alloy No. 2 being hot-rolled at a temperature of 750.degree. C. to have a thickness of 20 mm. After the hot rollings thereof, the surfaces of both the alloys were finished by mechanical grinding. Then, the finished alloy No. 1 was sandwiched between two pieces of plates of the alloy No. 2. The end faces of the three pieces of plates, overlapping each other were integrated by electron beam welding, which integrated plates were hot-rolled two times at 780.degree. C. to provide a sheet having a thickness of 3 mm, which sheet was further cold-rolled to have a thickness of 2 mm and was subjected to an annealing treatment in which it was held at 650.degree. C. in 2 hours. After that, it was held at 870.degree. C. in 5 minutes and then cooled by jetting water onto both surfaces of the sheet. The sheet was further cold-rolled three times to provide a strip used for a spacer which strip had a thickness of 0.53 mm. Annealing was effected between adjacent two cold-rollings at 590.degree. C. in 1 hour, while the final annealing was effected at 570.degree. C. in 1 hour. From the strip there was formed a spacer band shown in FIG. 4B by punching, and it was subjected to a dimple working. Further, from the alloy ingots shown in Table 5 there were produced cylindrical billets. The billet of the alloy No. 1 (the intermediate layer billet) was sandwiched by the outer and inner two billets (the outer and inner surface layer billets) of the alloy No. 2 shown in Table 5, which outer surface layer billet of the alloy No. 2 had an outer diameter of 150 mm and a thickness of 15 mm, which intermediate layer billet had a thickness of 20 mm, and which inner surface layer billet had a thickness of 15 mm. The production process thereof was the same as the embodiment 1 with the exception of the size as shown above, that is, the end faces defined by those of the billets in a sandwich state was integrated by electron beam welding and then the integrated billets were hot-rolled at 750.degree. C. to provide a tube having an outer diameter of 64 mm and a thickness of 11 mm, which tube was rolled one time by a pilger mill to obtain a tube having an outer diameter of 34.9 mm and a thickness of 4.4 mm. The whole length of the tube was then subjected to a treatment in which it was heated to 870.degree. C. while passing a high frequency induction heating coil portion and water was jetted thereon to quench the tube at the position just under the heating portion. After the treatment, it was heat-treated at 600.degree. C. for 1 hour. Further, the cold working and intermediate annealing were alternately effected three times to obtain a tube having an outer diameter of 14 mm and a thickness of 0.6 mm, the temperature of which intermediate annealing was 590.degree. C. The tube was cut to obtain tube members each having a length of 25 mm, which members were plastically worked with a plate spring 28 being attached to each of the tube member so that the tube members was formed into a spacer ring 25 of such configuration as a fuel rod was able to be held in each of the tube members. A plurality of spacer rings were assembled to form a rounded cell type spacer lattice of 9.times.9 pieces, spacer band 22 being disposed around the outer periphery of the lattice and being spot-welded to thereby obtain a rounded type spacer. After the completion of the assembling thereof, the whole was heat-treated by holding it at 530.degree. C. for 10 hours. From the spacer there were cut out test pieces a part of which included a weld zone, the test pieces being subjected to a corrosion test in steam of 500.degree. C. After finishing the corrosion tests of both the material of the invention and comparative material (Zircalloy-2), results with respect to the increment of corrosion are shown in FIG. 8. According to the results of the corrosion test in steam, the material of the invention has very high anti-corrosion in comparison with the comparative material. Further, according to appearance observation of the test pieces which observation was effected after the finish of the corrosion test, the surface of the material of the invention was covered with a uniform oxide film of black color, and neither nodular corrosion nor accelerated corrosion of white color were observed on the surface thereof. On the other hand, much nodular corrosion was observed on the comparative material having been subjected to the corrosion test in steam. This remarkable difference therebetween with respect to anti-corrosion evaluated in steam was attributed to whether or not the nodular corrosion occurred. After the corrosion test, the content of hydrogen contained in the material of the invention was analyzed, so that the hydrogen absorption rate thereof was 3%. Also, a plate material made of the alloy No. 1 alone and another plate material made of the alloy No. 2 alone were subjected to a corrosion test in high temperature water, and the hydrogen absorption rates thereof were measured with the results that the hydrogen absorption rate of the alloy No. 1 was 35% while the hydrogen absorption rate of the alloy No. 2 was 3%. Thus, it was found that the hydrogen absorption rate of the structure members of the fuel assembly for nuclear reactor according to the invention is the same level as the alloy No. 2. Further, a plate of the alloy No. 2 alone provided with a notch was subjected to an impact test with the result that the absorption energy thereof was a low value of 3 kg.m/mm.sup.2, while the absorption energy of the plate of three-layer structure of the invention was 20 kg.m/mm.sup.2 which was a very improved value in comparison with the former. Thus, by forming the three-layer structure according to the invention, no nodular corrosion occurs, anti-corrosion being improved in a great degree, toughness being improved, and hydrogen absorption rate is lowered. Embodiment 3 Slabs of the same alloy compositions as in the Embodiment 2 were formed, being then integrated by electron beam welding, and were formed into a plate having a thickness of 75 mm by use of the same process as in the Embodiment 2, wherein the thickness of each alloy was the same value as in the case of the spacer band shown in the Embodiment 2. The plate was then hot-rolled at 780.degree. C. to have a thickness of 20 mm, the plate being again hot-rolled at 780.degree. C. after having been heat-treated at 650.degree. C. in 2 hours to thereby be formed into a sheet having a thickness of 3 mm. The sheet was cold-rolled into a thickness of 2.6 mm after having been held at 600.degree. C. in 2 hours. The final annealing was effected at 600.degree. C. in 2 hours. This sheet was bent to a channel shape, by use of which sheet there was produced a tube of a square cross section by TIG welding. After the welding, bead portions occurring in the welding were flattened by rolling. Thereafter, a mandrel made of a stainless steel was inserted in the interior of the tube of square cross-section, which tube was then held at 600.degree. C. in 2 hours. During this heat treatment, the square tube was plastically deformed in compliance with the shape of the mandrel because the linear expansion coefficient of the stainless steel is higher than that of the structural member, so that the square tube was formed to have a predetermined size. Test pieces were cut out from the weld zone of the channel box thus produced and were subjected to corrosion test, with the result that the same high anti-corrosion as in the Embodiments 1 and 2 was able to be confirmed. Also, it was confirmed that, by replacing the Zr-Sn-Fe-Ni-Cr alloy in these Embodiments by Zr-Sn-Fe-Ni-Cr-Mo alloy, there were able to obtain results similar to those of these Embodiments. According to the invention it is possible to prevent nodular corrosion from occurring and to prevent accelerated corrosion from occurring inherently in a weld zone of an alloy containing Nb. Further, in the invention it is also possible to reduce the hydrogen absorption rate into a degree of not more than 1/10 in comparison with that of the conventional Zircalloy shown in Table 5 and at the same time it is possible to enhance toughness against impact load. Thus, in the invention it is possible to greatly prolong the service life period of a fuel construction member disposed in a nuclear reactor, so that there can be obtained a fuel assembly for nuclear reactor and a member thereof both sufficiently compatible with a tendency to make the degree of burn-up of fuel higher. |
abstract | Provided is a micro-column electron beam apparatus including: a base; an electron lens bracket on which an electron lens module can be fixed, mounted in a central portion of the base; an electron beam source tip module vertically disposed on the electron lens module; a pan spring plate stage module that is mounted over the base, supports the electron beam source tip module at a central portion thereof, and includes a three-coupling pan spring plate portion including first through third spring units that are coupled to the electron beam source tip module in three directions on a plane perpendicular to the vertical axis, which vertically passes the center of the electron beam source tip module, to elastically support the electron beam source tip module in three directions; a first piezoelectric actuator coupled to the pan spring plate stage module to move the electron beam source tip module along a first axis perpendicular to the vertical axis; and a second piezoelectric actuator coupled to the pan spring plate stage module to move the electron beam source tip module along a second axis perpendicular to the vertical axis and the first axis. |
|
049838512 | abstract | A contact therapeutical apparatus for giving physical treatments such as magnetic and heat therapies by contacting the human body. The apparatus includes a heat generating portion inside a case body, and a far infrared radiating material is contained in the case body or a cover member covering the case body. The far infrared radiating material is exited by heat from the heat generating portion to radiate infrared rays and to heat inside the body sufficiently. There is provided a uniformalizing layer in the case body or cover member for distributing heat uniformly, and the far infrared radiating material is contained in the layer. Thereby, the uniform heating action by the infrared rays is obtained and the body can be warmed over in a wide area. |
043938990 | abstract | Apparatus for plugging a plurality of cylindrical holes provided at an inner peripheral wall of a cylindrical container comprises a plurality of plugs to be inserted into the plurality of holes for plugging the same, a support ring assembly having an outer diameter smaller than an inner diameter of the container, and a beam assembly for operating the support ring assembly and the plugs. The support ring assembly supports the plugs on an inner side of the container after the plugs have been inserted into the cylindrical holes, respectively. |
044141769 | summary | BACKGROUND OF THE INVENTION This invention relates to improved metal surfaces for the first wall and limiter in a plasma device and more particularly to metal surfaces with reduced loss of metal by erosion and particularly by sputtering during exposure to the plasma. In a second aspect of the invention, it relates to a metallic substrate containing an amount of the surface metal and providing a self-sustaining source of the surface metal. In a plasma device, plasma at an elevated temperature is magnetically confined within the first wall whose purpose is to limit the travel of particles escaping from the plasma. The limiter also serves to locate the plasma. During exposure to the hot plasma including bombardment by particles escaping from the plasma, surfaces of the first wall and limiter are subject to loss of material by erosion and particularly by sputtering. In the past, these surfaces have been constructed of metals such as stainless steel. Refractory materials such as ceramic and graphite coatings could also be useful. With ceramic materials, the extreme temperature changes may cause cracks to form and spallation to occur and therefore limit the effectiveness of the surface. Also, ceramic materials have limited value for removal of heat from the first wall and limiter and must therefore be applied as thin coatings over a metallic substrate. The failure of such coatings and clad layers could represent a serious materials problem for the development of plasma devices. With metal surfaces, the metal may be selected for its structural strength, resistance to corrosion, and ease of fabrication. However, metallic surfaces limit the effectiveness of the plasma device because they generate substantial amounts of sputtered neutral atoms which are not retained on the surface and contaminate the plasma. In addition, some metals selected for stuctural properties have a high atomic number and the presence of their atoms in the plasma reduces the energy available for the thermonuclear reactions. It has been suggested that the alkali and alkaline earth metals could be useful as components of the first wall and limiter. Since these metals are electropositive, they are potentially capable of providing a high secondary ion yield. However, these metals in the pure state do not possess the desired structural, fabricating, physical and chemical properties. In addition, a significant portion of the metal spattered from pure alkali metal surfaces in practice escapes as neutral atoms and not as secondary ions. As metal is lost from the surface, the useful life for operating of the plasma device is reduced because a new first wall or limiter or new surfaces for these metallic members must be installed. Accordingly, improvements in the first wall and limiter of the plasma devices are desired. One object of the invention is a first wall or limiter for a plasma device with a surface exhibiting reduced loss of metal by erosion and particularly by sputtering. A second object of the invention is a first wall or limiter for a plasma device with a surface exhibiting an improved secondary ion/neutral ratio. Another object of the invention is a first wall or limiter with means for replenishing metal on the surface exposed to plasma in a self-sustaining manner. Yet another object is a first wall or limiter with a surface coating of a low atomic number. An additional object of the invention is a first wall or limiter with reduced loss of structural metal. These and other objects will become apparent from the detailed description below. SUMMARY By the invention, a metallic member exposed to plasma in a plasma device is provided with a surface having reduced loss of metal by erosion and particularly by sputtering. Further, the member is constructed primarily of a metal having desired structural and fabrication features together with a surface having an improved secondary ion/neutral ratio. In addition, a substrate is provided with desired structural and fabrication properties together with properties which provide a source of the surface metal as it is depleted or lost from the surface. In the plasma device, the metallic member comprises a bulk portion or a metallic substrate composed of a first metal, and a thin surface layer composed of at least a major amount and advantageously a predominant amount in the order of at least 90 at.% of a second metal selected from the group consisting of alkali and alkaline earth metals and exhibiting a vapor pressure below the vapor pressure of the alkali or alkaline earth metal in its bulk form. Preferably, the surface layer consists essentially of the second metal with the surface layer being a monolayer and the atoms of the second metal in the surface being primarily bonded to atoms of the first metal. It is also preferred that the substrate include a portion of the second metal to serve as a source for replenishing metal on the surface lost during operation of the plasma device. The invention further includes a substrate containing a mixture of first and second metals, including an alloy or crystalline compound, with further characteristics which enhance its effectiveness as a source of the second metal. In one process or method whereby the substrate serves as a self-sustaining source of surface metal for maintaining the surface, the substrate is composed of first and second metals in an alloy with the metals being selected to satisfy the equation EQU H.sub.1,2 =.OMEGA.+1/2(H.sub.1,1 +H.sub.2,2) where .OMEGA..ltoreq.0 and H represents the enthalpy of sublimation for the alloy and the pure first and second metals. With the alloy having these characteristics, a structural member, such as the first wall, composed of the alloy is heated to an elevated temperature or subjected to another energy source such as particle radiation sufficient to cause atoms of the second metal to become segregated at the surface and to form a high concentration of the second metal in a monolayer at the surface with a sharp decrease in concentration in the next layer below the surface. Beyond the second layer, the concentration returns to the bulk concentration. As the surface metal is lost during operation of the plasma device, the segregation effect transfers atoms of the second metal to the surface layer to maintain the surface. When the composition of metals in the mixture forms an intermetallic compound, segregation of the second metal becomes limited. However, a second process or method becomes effective to maintain the surface during operation of the plasma device. Initially, the surface of the structural member will have atoms of both the first and second metals. During bombardment by particles from the plasma, atoms of both metals escape from the surface, with those of the first metal being primarily neutrals. Since those escaping atoms of the second metal which have ionic bonds leave as secondary ions, they are returned to the surface by the electrical and magnetic fields of the plasma device. Further, since the surface binding energy between atoms of the first and second metals is higher than the energy for like atoms of the second metal, returning atoms of the second metal will seek vacant sites on the surface and form a monolayer which in some instances need not be atomically smooth. |
047818859 | claims | 1. Nuclear reactor fuel assembly, comprising a fuel assembly top fitting having a square cross section, a fuel assembly base having a square cross section, an elongated fuel channel with a square cross section and channel walls, fuel rods containing nuclear fuel and an elongated prismatic water channel box both being disposed in said fuel channel in a spacing configuration defined by a lattice having mesh openings with sides parallel to said channel walls, said fuel rods being mutually spaced apart in said mesh openings, said water channel box having a cross section spanning more than one of said mesh openings, and said water channel box being spaced apart from said fuel channel by an interspace being completely filled with said mesh openings and said fuel rods disposed therein. 2. Nuclear reactor fuel assembly according to claim 1, wherein said water pipe is centrally disposed in said lattice. 3. Nuclear reactor fuel assembly according to claim 1, wherein said cross section of said water channel box is square. 4. Nuclear reactor fuel assembly according to claim 2, wherein said cross-section of said fuel channel has cross-section sides, said cross-section of said water channel box is square and has cross-sectional sides, said cross-sectional sides of said water channel box are each parallel to a respective cross-sectional side of said fuel channel, and said cross-sectional sides of said water channel box are each spaced apart from a respective one of said cross-sectional sides of said fuel channel by the same distance. 5. Nuclear reactor assembly according to claim 4, wherein said lattice has n.times.n mesh openings, where n.gtoreq.8, said cross section of said central water channel box spanning (n-6).times.(n-6) mesh openings leaving remaining mesh openings between said water channel box and said fuel channel being occupied solely by fuel rods. 6. Nuclear reactor fuel assembly, comprising an elongated fuel channel with a square cross section, fuel rods containing nuclear fuel being mutually spaced apart in an array in said fuel channel, each of said fuel rods being surrounded by a space with a substantially equal volume, and a prismatic water channel box having a cross section spanning more than one of said spaces, said water channel box and said fuel channel being mutually spaced apart defining a region therebetween being completely filled with said spaces and said fuel rods disposed therein. |
description | This application is a continuation application from U.S. patent application Ser. No. 15/385,024, filed Dec. 20, 2016, which claims priority to U.S. Provisional Patent Application No. 62/270,741, filed on Dec. 22, 2015, and to U.S. Provisional Patent Application No. 62/312,066, filed on Mar. 23, 2016, the disclosures of which are incorporated by reference. This disclosure relates in general to systems for efficiently and safely scanning luggage, packages, parcels, personal items, and the like, and, and, in particular, but not by way of limitation, to an electromagnetic radiation scanning system that includes shielding curtains with features to simplify manufacturing, assembly, and replacement of the shielding curtains. Electromagnetic radiation, for example X-ray radiation, is used to examine the contents of luggage and parcels prior to allowing such items to be taken on or loaded on transport vehicles or before allowing entry into buildings or other facilities. X-ray scanning machines continuously convey luggage, parcels, cargo, and personal items that are exposed to X-ray radiation that can penetrate the container and can be used to create an image of the contents of the container. Packages and luggage of all shapes and sizes are accommodated by the same scanning system. Radiation is contained within the scanning system by shielding curtains disposed at the entrance and exit of the scanning system. Conventional shielding curtains are fabricated in a laminated construction. Layers of material scrim, lead vinyl, lead rubber, and Teflon/nylon are fed from rolls and combined to becomes a layer of a thin sheet of material. The lead vinyl is sandwiched between Teflon/nylon layers. The continuous strip is wound on a spool and then cut into individual strips. The individual strips are then secured by one or two metal bars or attachment devices and arranged adjacent to each other such that a series of parallel individual strips hang in front of an entrance or exit of the scanning machine and collectively contain or deflect the X-rays within the machine, such that workers are not exposed to potentially harmful X-rays. The lead content of the strips is selected to block the radiation generated in a particular application. The layered construction of the curtain strips forms uniform thickness strips that are free of surface texture. Sandwiching the individual strips of layered construction between two generally flat bars forms the X-ray shielding curtain. Each of the bars includes a plurality of through holes. A fastener is received through the front bar, and extends through a hole formed through the layered strip, and through the rear bar or attachment bar located on the X-ray scanning system. The holes in the layered construction strips are generally formed after the strips are constructed but before the strips are sandwiched between the clamping bars. Misplacement or misalignment of an individual curtain strip with respect to an adjacent curtain strip may lead to unwanted radiation leakage through a curtain bank. An example scanning system is disclosed in U.S. Pat. No. 4,020,346, issued on Apr. 26, 1977, entitled “X-Ray Inspection Device and Method,” which is hereby incorporated by reference. The '346 patent discloses a scanning system with two banks of shielding arranged parallel to each other to block the entrance to the scanning system, and two banks of shielding curtains arranged parallel to each other to block the exit to the scanning system. However, scanning systems for different applications, such as pre-shipping parcel or cargo inspection may have greater strength radiation, and therefore may have additional banks of radiation shielding curtains positioned at the entrance and exit. Parcels, luggage, or personal items that are conveyed through the scanning system displace the strips of curtains. In certain applications, a light parcel may be required to simultaneously displace two or more banks of curtains. If the parcel is too light to displace multiple curtain banks, a back-up may occur on the system that must be addressed by a worker. As should be obvious, curtains with a greater stiffness are not as easily displaced as curtains that are more flexible. Also, friction between the curtains and the parcel must be overcome so the parcel can move through the scanning system. Finally, the layered construction strip curtains wear over time and use, which can lead to unwanted material, including lead, being rubbed off onto the luggage or parcels. Of course, worn shielding curtains need to be replaced. Embodiments herein disclose a shielding curtain that is configured to block through passage of electromagnetic radiation. The shielding curtain may be a flap portion of a larger shielding curtain or a single, unitary body that includes a single integrated mounting bead and a plurality of flaps. The shielding curtain is formed of a polymer material that has a uniformly dispersed particulate material. According to certain embodiments, the shielding curtain is molded from a composite polymer material that includes a thermosetting polymer material and the uniformly dispersed particulate material. Electromagnetic radiation emitted by an inspection system is blocked by the uniformly dispersed particulate material. A shielding curtain assembly includes a curtain suspending member with a slot that extends along a length of the curtain suspending member. A shielding curtain that blocks electromagnetic radiation is suspended by the curtain suspending member. The shielding curtain is formed of a polymer material, such as a thermosetting polymer, and a particulate filler material, such as Tungsten powder and/or Barium sulfate. According to certain embodiments, the shielding curtain includes a mounting bead that is received in the slot and a plurality of flaps that extend from the mounting bead. The mounting bead and the plurality of flaps may be a single, unitary body. Shielding curtains according to the present disclosure may be disposed at an entrance end or an exit end of an exposure station of an X-ray inspection system that emits electromagnetic radiation, for example X-ray radiation, to inspect the contents of luggage or shipping parcels. Each end of the inspection system may include multiple shielding curtains. Technical advantages of shielding curtains for electromagnetic radiation scanning systems according to the teachings of the present disclosure include mounting features that are directly molded into a unitary curtain with a plurality of flaps. The molded in mounting features facilitate easy installation, removal, and replacement of shielding curtains in existing inspection systems. In addition, the molded shielding curtains allow a surface texture of the flaps to be molded into the shielding curtain, which may reduce the coefficient of friction and/or the surface area of the shielding curtain that comes into contact with the package, parcel, or personal item to allow the item to more easily pass through the shielding curtain. Other technical advantages include the elimination of lead and replacement of lead containing curtains with a composite polymer material with a lead equivalency. The composite polymer material may be more flexible than conventional leaded layered construction curtains and may have a lower coefficient of friction. Lower frictional force and increased curtain flexibility results in increased throughput of packages, parcels, personal items, cargo, or luggage and also results in fewer jams or other stoppage of the inspection equipment. Other technical advantages will be readily apparent to one of ordinary skill in the art from the following figures, descriptions, and claims. Moreover, while specific advantages have been described above, various embodiments may include all, some, or none of the enumerated advantages. FIG. 1 is a perspective view of an electromagnetic radiation scanning system 10 according to the teachings of the present disclosure. The scanning system 10 may also be referred to as an inspection system. The electromagnetic radiation scanning system 10 includes a conveyor belt 12 that is supported by a support structure 14. The conveyor belt 12 conveys items 16 into an exposure station 18 where the items 16 are exposed to electromagnetic radiation that penetrates each item and provides an image of its contents. A worker views the image created by the penetrating electromagnetic radiation on a monitor 20 and can determine whether the item 16 should be further inspected. The item 16 may be luggage, a personal item, a package, or a parcel for shipping, or other container where an initial examination determines that the item is safe to transport or enter a facility and does not contain contraband. The item 16 may also be inspected to determine whether it contains items controlled by airport security regulations or other security protocol. For example the United States Transportation Security Administration may use an electromagnetic radiation scanning system 10 to inspect for explosive devices or other controlled items. The electromagnetic radiation may be in any suitable form for creating an image of the contents of a container. For example, the electromagnetic radiation may be x-rays, gamma rays, and the like. X-ray electromagnetic radiation is often used in scanning systems to inspect baggage and parcels. To protect individuals near the electromagnetic radiation scanning system 10, such as transportation, shipping, or security workers, the electromagnetic radiation should be contained within the exposure station 18. Therefore, the exposure station 18 is includes a material that is impenetrable by the particular emitted electromagnetic radiation. It is known to use lead to contain electromagnetic radiation, such as X-rays. The exposure station 18 includes an open entrance end 22 and exit end 24 that allow the conveyor belt 12 to continuously move the items 16 into and out of the exposure station 18. One or more shielding curtains 30 are disposed at the entrance end 22 and the exit end 24 of the exposure station 18 to block electromagnetic radiation from escaping into the ambient environment. In addition to blocking electromagnetic radiation, the shielding curtains are also configured to be displaced by the items 16 on the conveyor belt 12. Each shielding curtain 30 includes a plurality of flaps 32 that are displaced by the items 16. The shielding curtains 30 block the electromagnetic radiation from breaching the entrance end 22 and the exit end 22, but the flaps 32 of the shielding curtain 30 are flexible enough to be displaced by the items 16 moved by the conveyor belt 12. By displacing the flaps 32 of the shielding curtains 30 at the entrance end 22, the item 16 enters the exposure station 18 where it is safely exposed to electromagnetic radiation. After the exposure, the conveyor belt 12 moves the item 16 such that it displaces the flaps 32 of the shielding curtains 30 at the exit end 24 where the items 16 can be safely further handled. The shielding curtains 30 are coupled to the exposure station 18 such that they hang or are otherwise positioned to extend across and block the open entrance end 22 and the open exit end 24 of the exposure station 18. The shielding curtains 30 may be passive in that they hang and the item displaces the shielding curtain in order to pass through, or the shielding curtain 30 may be active in that mechanical actuation, usually automatic actuation, displaces the shielding curtain to allow items to pass. In certain embodiments, multiple shielding curtains 30 are disposed parallel to each other and each shielding curtain 30 must be traversed for an item 16 to be scanned by the system 10. This configuration further contains the electromagnetic radiation such that if the electromagnetic radiation escapes through an inner shielding curtain 30 that escaped electromagnetic radiation can be blocked by one or more outer shielding curtains 30. Any suitable number of shielding curtains may be positioned to block the entrance end 22 and the exit end 24. According to one embodiment, four to eight shielding curtains 30 are disposed parallel to each other at the entrance end 22 of the exposure station 18 and four to eight shielding curtains 30 are disposed at the exit end 24 of the exposure station 18. The slits 34 forming the individual flaps 32 of a shielding curtain 30 may be staggered with respect to adjacent shielding curtains 30 to further prevent the electromagnetic radiation from escaping the exposure station 18. According to alternate embodiments, the shielding curtain 30 may be mechanically actuated to open and close to allow the item 16 to pass through to a location where it can be exposed to electromagnetic radiation. Reference is now made to FIG. 2, which is a perspective view of a shielding curtain 31 according to the teachings of the present disclosure. The shielding curtain 31 is a single homogeneous, unitary body that is molded from a composite polymer material, as discussed in more detail below. According to one embodiment, the single, unitary body includes a plurality of flaps 32, as shown in FIG. 2. According to an alternate embodiment, the shielding curtain 31 may be formed from individually molded flaps that are molded from a composite polymer material. The shielding curtain 31 does not include molded-in mounting features. As such, the shielding curtain 31 may be mounted conventionally with fasteners received through the curtain and through a pair of clamping bars disposed on the front and the rear of the top edge of the shielding curtain 31. Certain advantages are obtained by molding the shielding curtain 31 including the plurality of flaps 32 or individual flaps 32 from a composite polymer material, as opposed to forming flaps using conventionally layered construction. For example, the composite polymer material may be more flexible than conventional leaded layered construction curtains and may have a lower coefficient of friction. Reference is made to FIGS. 3A and 3B, which are perspective views of a shielding curtain 30 with a molded-in mounting feature 36. The shielding curtain 30 may be a single, unitary body that includes a plurality of flaps, or it may be a single flap 32 with a portion of the molded-in mounting feature 36. The shielding curtain 30 includes an integrated mounting bead 36 as the molded-in mounting feature, and the shielding curtain 30 includes the plurality of flaps 32 extending from the mounting bead 36. The shielding curtain 30 and the shielding curtain 31 are each formed using a polymer fabrication process, such as injection molding, compression molding, casting, extrusion, and the like. The material that is molded or cast into the shielding curtain 30, 31 may be a composite polymer material, a lead vinyl material, or a lead rubber material. An exemplary composite polymer material includes a thermosetting polymer such as urethane and one or more heavy particulate filler, such as Tungsten powder, and/or one or more light particulate filler, such as Barium sulfate, and is sold under the trade name Brandonite. The filler material is in the form of particles or powder that is uniformly dispersed in the polymer material. Such composite polymer material is introduced into a mold as pellets or as liquid, and then formed into the desired flap or shielding curtain according to the teachings of the present disclosure. For example, a composite polymer material includes a filler material that includes either Tungsten powder or Barium sulfate or both materials in particle form that is uniformly dispersed in a urethane or other polymer. Other suitable polymers and particulate fillers are contemplated by the present disclosure. U.S. Pat. No. 8,487,029 to Wang and assigned to Globe Composite Solutions, Ltd., which is hereby incorporated by reference, describes materials and forming processes for composite polymer materials that result in a lead-free, non-toxic article that is particularly useful in radiation shielding applications. In addition, the composite polymer material is flexible to allow the item 16 to displace the flaps 32 of the shielding curtain 30, 31, while at the same time providing a barrier for the electromagnetic radiation. The shielding curtain 30, 31 formed of a composite polymer material may be compliant with the directive as to Restriction of Hazardous Substances (“RoHS”). The flaps 32 may be any thickness, for example, each flap 32 may be approximately 0.075 inches thick. Electromagnetic radiation shielding equivalency or lead equivalency corresponds to the thickness of the flaps 32 of the shielding curtain 30. For example, 1 millimeter in flap thickness corresponds to approximately 0.25 millimeters (0.010 inches) in lead equivalency. Certain embodiments of the shielding curtain 30, 31 have a uniform thickness of approximately 0.075 inches (1.9 millimeters), which corresponds to approximately 0.5 millimeters (0.020 inches) in lead equivalency. Accordingly, the shielding curtains 30, 31 can have any suitable thickness depending on the desired lead equivalency, provided that the flaps 32 remain flexible enough to be displaced by the items 16 as the items pass through the shielding curtain 30, 31. The mounting bead 36 is generally cylindrical or oblong and extends along the length of an upper edge of the shielding curtain 30. The flaps 32 are integral with the mounting bead 36 and hang from the mounting bead 36. According to an alternate embodiment, the mounting bead 36 may be molded around a reinforcing rod. Any suitable number of flaps 32 may extend from the mounting bead 36. For example, 10-16 flaps 32 or more may extend from the mounting bead 36. According to one embodiment, the mounting bead 36 and a pre-cut sheet extending from the mounting bead 36 is formed according to known polymer forming processes, such as molding, casting, or extrusion. The material formed may be a composite polymer material, a lead vinyl material, or a lead rubber material. Then, the sheet is cut to form a predetermined number of flaps 32 by cutting the slits 34 through the sheet such that the slits 34 extend from the bottom of the sheet to a location proximate the mounting bead 36, but the mounting bead 36 is not cut, such that the shielding curtain remains a single, unitary body. According to certain embodiments, the shielding curtain 30 is not cut into flaps 32. Rather, the shielding curtain 30 may be a single sheet extending from the mounting bead 36. The single sheet embodiment may be employed as an active shielding curtain, which may be useful shielding cargo that is exposed to electromagnetic radiation. In the active shielding curtain embodiment, the shielding curtain is automatically mechanically actuated to open and close to allow items to pass through. Returning to the multiple-flap embodiment, each slit 34 separates one flap 32 from an adjacent flap 32. The slits 34 may be made by an automated cutting system that is known in the machining art, such as a water jet, laser jet, cutting blade, and the like that automatically makes the flap forming slits 34 according to a software program. According to an alternate embodiment, a single flap 32 including a flap-sized mounting bead 36 may be formed, and then combined with other individually formed flaps 32 in an assembly according to the teachings of this disclosure to form a shielding curtain. With regard to the single, unitary body shielding curtain 30 with the plurality of flaps, either with or without (see FIG. 2) the mounting bead 36 or other molded-in mounting features (see FIGS. 6A-6C), a strain relief hole 38 may be formed at an upper end of the slit 34 proximate the upper edge of the shielding curtain 31 or the mounting bead 36. The strain relief holes 38 delimit each flap forming slit 34 and prevent the cut from propagating further toward the mounting bead 36 or the upper edge as the shielding curtain 30, 31 is flexed during use. The strain relief holes 38 may present a path for the electromagnetic radiation to breach a shielding curtain 30. Staggering the strain relief holes 38 in adjacent and/or successive shielding curtains 30 installed at the entrance end 22 or exit end 24 of the exposure station 18 helps prevent the electromagnetic radiation from escaping and entering the ambient environment. Additionally or in lieu of staggering the shielding curtains 30, the strain relief holes 38 may be aligned with a portion of the exposure station 18, which may prevent or reduce the electromagnetic radiation from passing through the strain relief holes 38. Reference is now made to FIGS. 4A and 4B, which are perspective views of an alternate flap configuration for the shielding curtain 31 without the mounting bead and for the shielding curtain 30, including the mounting bead 36 or other molded-in mounting feature. Each flap 32 of the shielding curtain may have a uniform thickness, as shown and described above with respect to FIGS. 2, 3A, and 3B, or a flap may have a varied or non-uniform thickness. A non-uniform thickness flap 40a is formed using the molding, casting, or extrusion processes of polymer forming and includes the mounting bead 36 or other molded-in mounting feature. And, a non-uniform thickness flap 40b does not include molded-in mounting features. Such non-uniform thickness flap 40a, 40b is an advantage over the layered strip flaps of conventional shielding curtains. The varied thickness in the flap may be implemented to provide varying lead equivalency for shielding against electromagnetic radiation. For example, the flap 40a, 40b may taper from a thicker, upper portion to a thinner, lower portion. A lower portion 42 of the varied thickness flap 40a, 40b may be thinner and have a lower lead equivalency and be less effective at blocking electromagnetic radiation than an upper portion 44. The upper portion 44 may have a greater thickness than the lower portion 42, and thus have a greater lead equivalency and be more effective in preventing electromagnetic radiation from penetrating the thicker portion of the flap 40a, 40b. Alternatively, the flap 40a, 40b may taper from a thicker, lower portion to a thinner, upper portion. The upper portion 42 of the varied thickness flap 40a, 40b may be thinner and have a lower lead equivalency and be less effective at blocking electromagnetic radiation than a lower portion 44. The lower portion 44 may have a greater thickness than the upper portion 42, and thus have a greater lead equivalency and be more effective in preventing electromagnetic radiation from penetrating the thicker portion of the flap 40a, 40b. By employing a varied or non-uniform thickness flap 40a, 40b shielding curtain, different zones may be made thicker to shield more effectively against the electromagnetic radiation than other zones. The different zones may be selected to accommodate the particular shielding application depending on an emission pattern and strength of the electromagnetic radiation. In addition, the electromagnetic radiation scanning system 10 may be equipped with different varied thickness flaps 40 shielding curtains at different locations at the entrance end 22 and/or the exit end 24 of the exposure station 18. According to an alternate embodiment, individual varied thickness flaps 40a, 40b may be formed by molding, casting, or extrusion of a composite polymer material, a lead vinyl material, or a lead rubber material and then subsequently assembled to form a shielding curtain. Reference is now made to FIGS. 5A-5C, which show various surfaces of the flaps 32 of a shielding curtain 30, 31 according to embodiments of the present disclosure. The surfaces of the flaps are the surfaces that are contacted by the items 16 moved by the conveyor belt 12 through the electromagnetic radiation scanning system 10. For example, as shown in FIG. 5A, a flap 32 may have a surface feature in the form of raised contact projections 46 that extend either parallel or perpendicular to the slits 34. In another embodiment shown in FIG. 5B, a raised contact feature may be in the form of a plurality of raised bosses or dome-shaped projections 48. According to yet another embodiment shown in FIG. 5C, the raised contact features are raised parallelepipeds 50. Each of the raised contact features, the raised strips 46, the raised dome-shaped projections 48, and the raised parallelepipeds 50 provide a contact surface area that is reduced from the overall surface area of the flap 32. In this manner, friction and drag between the conveyed item 16 displacing the flaps 32 and the flaps 32 is reduced and wear of the flaps 32 may also be reduced over conventional layered shielding curtains. The raised surface features described herein could also be depressions molded into the flaps 32 of the shielding curtain 30. The surface features of FIGS. 5A-5C may be employed with any of the shielding curtain or individual flap embodiments disclosed herein. Such surface features are formed by creating a mold with the negative of the desired surface feature, then molding the curtain or individual flap from the composite polymer material including the filler material that blocks electromagnetic radiation but remains flexible to be displaced by the items. Surface area reducing surface features are not easily formed in the fabrication process of conventional layered construction shielding curtains. The raised features may also be used to indicate the level of wear of the shielding curtains in use. Reference is now made to FIGS. 6A-6C, which are perspective views of portions of a shielding curtain 33 with various molded-in mounting features that may be used in lieu of the molded-in mounting bead depending on the particular curtain mounting features associated with the scanning system where original or replacement shielding curtains or original or replacement individual flaps are installed. Molded-in mounting features as shown and described with respect to FIGS. 6A-6C are included in the mold and created when the composite polymer material is formed by the mold. In this manner, few or no additional fabrication operations may be necessary for the shielding curtain or an individual flap to be mounted to a shielding curtain assembly that is ultimately installed in an electromagnetic radiation scanning system. FIG. 6A illustrates through holes 51 that have been molded into an upper portion of the shielding curtain 33. The through holes 51 may also be molded into individual flaps 32 of the shielding curtain. The through holes 51 may be any shape or size such that they correspond to the mounting features for the shielding curtain assembly or to allow for horizontal or vertical adjustment of the shielding curtains with respect to the specific mounting configuration. Protrusions 53 or bosses as shown in FIG. 6B may also be molded into the top portion of the shielding curtain 33 or individual flaps 32. The protrusions 53 may be any suitable size and shape that corresponds with mounting features or to allow for horizontal or vertical adjustment of the shielding curtains with respect to the specific mounting configuration for the particular scanning system. FIG. 6C illustrates molded-in mounting hardware 55. The mounting hardware 55 may be a generally elongated flat bar that extends through the shielding curtain 33. According to certain embodiments, the mounting hardware 55 extends such that it is exposed on each side of the shielding curtain 33 where an exposed mounting feature 57, such as a through hole, may be used to secure the shielding curtain 33 or to allow for horizontal or vertical adjustment of the shielding curtain with respect to the specific mounting configuration of the scanning system. The composite polymer material is bonded to the mounting hardware 55 because the liquid composite polymer material in the mold forms around the mounting hardware such that when the piece is taken out of the mold, the shielding curtain 33 or an individual flap 32 is bonded to the mounting hardware 55. According to an alternate embodiment, the shielding curtain 33 may not envelop or encapsulate all sides of the mounting hardware, but rather may be molded to be bonded to one front or rear surface of the mounting hardware 55. Other mounting hardware that may be molded into the shielding curtain or individual flaps include, but are not limited to, threaded inserts, fasteners, washers, bushings, pins, and the like. Reference is now made to FIG. 7, which is an exploded, perspective view of a shielding curtain assembly 52 according to the teachings of the present disclosure. The shielding curtain assembly 52 includes the shielding curtain 30 and a multi-piece curtain suspending member 54 that supports the shielding curtain 30. When assembled, the curtain suspending member 54 receives the mounting bead 36 of the shielding curtain 30. The multi-piece curtain suspending member 54 is received by a mounting channel 56 that is secured to the electromagnetic radiation scanning system 10. According to certain embodiments, the mounting channel 56 is accessible through at least one access door disposed on one or both sides or on the top of the scanning system 10. The mounting channel 56 may be the same as in conventional electromagnetic scanning systems so as to allow the shielding curtain assembly 52 of the present disclosure to be easily retrofit to existing and in-use scanning systems. The multi-piece curtain suspending member 54 includes a front bar 58a and a rear bar 58b, where front and rear refer generally to the direction of travel of the items 16 on the conveyor belt 12 that encounter the shielding curtain 30. Each of the front and rear bars 58a, 58b defines a generally semi-circular recess 60a, 60b disposed at a lower portion of each bar 58a, 58b. Disposed above the semicircular recess 60a, 60b on each bar 58a, 58b is a plurality of fastening holes 62a, 62b. When the bars 58a, 58b are abutted together, fasteners are received through the fastening holes 62a, 62b to join the bars 58a, 58b to form the multi-piece curtain suspending member 54, which includes a bead receiving slot 64. The shape of the bead receiving slot 64 corresponds to the shape of the mounting bead 36 on the shielding curtain 30 such that the mounting bead 36 is received by and supported by the bead receiving slot 64. Unlike conventional shielding curtains that are clamped between generally flat bars and secured therebetween by fasteners that penetrate the shielding curtain, no fasteners penetrate the mounting bead 36 or any other part of the shielding curtain 30. Rather, an upward facing portion 66 of the bead receiving slot 64 contacts an underside of the mounting bead 36 and the weight of the shielding curtain 30 is opposed by the upward facing portion 66 of the bead receiving slot 64 and the mounting bead 36 is held in the bead receiving slot 64. In this manner, the shielding curtain 30 is more easily initially assembled and replaced than conventional shielding curtains. The mounting bead 36 and the corresponding bead receiving slot 64 need not be cylindrical, and any suitable shape for the mounting bead 36 and the corresponding bead receiving slot 64 is contemplated by this disclosure, including, but not limited to cross-sections of the mounting bead having a shape generally in the form of square, rectangle, oval, triangle, and the like. In addition, the shielding curtain formed with a composite polymer material allows the installed shielding curtain 30 to be curved. The mounting bead 36 may likewise be curved or wavy along the length of the shielding curtain 30. According to an alternate embodiment, the flexibility of the molded composite polymer material allows the mounting bead 36 and the shielding curtain 30 to be generally straight, but when installed into a curved or wavy mounting slot, the curtain then has a curved or wavy configuration as it extends across the entrance end 22 or the exit end 24 of the exposure station 18. The flaps 32 of the shielding curtain 30 are received through an incomplete portion 68 of the generally circular slot 64 disposed at the bottom of the slot 64. The slot 64 also functions as a pivot for the collective flaps 32. Thus, the slot 64 and mounting bead 36 junction provides rotational freedom for the movement of the collective flaps 32 of the shielding curtain 30, which may reduce stresses on the shielding curtain 30 imparted as the items 16 displace and flex the flaps 32 of the shielding curtain 30. Such stress relief may result in a longer useful life of the shielding curtain 30. The joining of the front and rear bars 58a, 58b also forms a generally elongated outer rectangular shape that corresponds to the shape of the mounting channel 56 of the electromagnetic radiation scanning system 10. According to an alternate embodiment, an exterior of the front and/or rear bars 58a, 58b or other curtain suspending member may include any suitable mounting feature that corresponds to the scanning system. For example, one or both of the bars 58a, 58b may include an angle bar that includes through holes that correspond to tapped or non-tapped through holes on the scanning system. The front bar 58a and the rear bar 58b may each be a metal part where the generally semi-circular recesses 60a, 60b and the fastener holes 62a, 62b are machined into a blank piece of metal, for example a blank of steel or aluminum, to form the final front and rear bars 58a, 58b. In one example, a fastener hole 62a, 62b in either the front or rear bar 58a, 58b may be tapped to receive a threaded fastener. According to other embodiments, the front bar 58a and the rear bar 58b may be formed of various plastics or fiberglass and may include a bearing-type material and/or a lubricant proximate the slot to facilitate rotation of the mounting bead 36 within the slot 64, as described above. According to an alternate embodiment, the multi-piece curtain suspending member receives individual flaps 32 that are each formed with a mounting bead 36 with a shape that corresponds to the bead receiving slot 68. The individual flaps 32 are positioned to be adjacent to each other to minimize a distance between adjacent flaps 32 through which electromagnetic radiation may pass, yet each individual flap 32 is free to flex and be displaced separately such that the item can pass through the shielding curtain 30. The receiving slot 68 may also allow the shielding curtain 30 to move laterally more freely to act as a swinging hinge to permit items to pass through the shielding curtain 30 and enter or exit the exposure station 18. Reference is now made to FIG. 8, which is an exploded, perspective view of an alternate embodiment of a shielding curtain assembly 70. The curtain receiving assembly 70 includes a curtain receiving bar 72, which functions as a curtain suspending member, and the shielding curtain 30. The curtain receiving bar 72 is a single, unitary elongated member that includes an incomplete circular slot 74, similar to that described above with respect to the multi-piece curtain support 54 of FIG. 5. The incomplete circular slot 74 is sized and shaped to receive the mounting bead 36 of the shielding curtain 30 to allow the collective flaps 32 to be suspended to block the entrance end 22 or the exit end 24 of the radiation exposure station 18. The mounting bead 36 and the slot 74 may be any suitable shape as describe above with respect to the embodiment shown in FIG. 7. Unlike conventional shielding curtains that are clamped between generally flat bars and secured therebetween by fasteners that penetrate the shielding curtain, no fasteners penetrate the mounting bead 36 or any other part of the shielding curtain 30. Rather, an upward facing portion 76 of the incomplete circular slot 74 contacts and underside of the mounting bead 36 and the weight of the shielding curtain 30 is opposed by the upward facing portion 76 of the incomplete circular slot 74 and the mounting bead 36 is held in the incomplete circular slot 74. In this manner, the shielding curtain 30 is more easily initially assembled and replaced than conventional shielding curtains. The mounting bead 36 and the corresponding incomplete circular slot 74 need not be cylindrical, and any suitable shape for the mounting bead 36 and the corresponding slot 74 is contemplated by this disclosure, including, but not limited to cross-sections of the mounting bead having a shape generally in the form of square, rectangle, oval, triangle, and the like. The flaps 32 of the shielding curtain 30 are received through an incomplete portion 78 of the incomplete circular slot 74 disposed at the bottom of the slot 74. The slot 74 also functions as a pivot for the collective flaps 32. Thus, the slot 74 and mounting bead 36 junction provides rotational freedom for the movement of the collective flaps 32 of the shielding curtain 30, which may reduce stresses on the shielding curtain 30 imparted as the items 16 displace and flex the flaps 32 of the shielding curtain 30. Such stress relief may result in a longer useful life of the shielding curtain 30. The outer shape of the curtain receiving bar 72 is generally shaped in an elongated rectangular shape to correspond to the mounting channel 56 secured above and across the entrance end 22 and the exit end 24 of the exposure station 18. As described above, the mounting channel 56 may be similar to those found in existing and in-use electromagnetic radiation scanning systems, which facilitates retrofitting existing systems with replacement shielding curtain assemblies 70 according to the teachings of the present disclosure. According to certain embodiments, the curtain receiving bar 72 is an elongated, thin walled member that may be formed by extrusion of a polymer or metallic material, such as aluminum, a composite polymer material, a thermosetting polymer, or a thermoplastic polymer. According to other embodiments, the curtain receiving bar 72 is a metallic or polymer material formed by a different molding process other than extrusion, such as injection molding. The curtain receiving bar 72 may be any suitable length, for example it may have a length of between 35 inches and 50 inches, for example approximately 40 inches. The curtain receiving bar 72 may be extruded and/or cut to any suitable length to span across the entrance end 22 or exit end 24 of the exposure station 18 of the electromagnetic radiation scanning system 10. According to an alternate embodiment, the curtain receiving bar 72 receives individual flaps 32 that are each formed with a mounting bead 36 with a shape that corresponds to the incomplete circular slot 74. The individual flaps 32 are positioned to be adjacent to each other to minimize a distance between adjacent flaps 32 through which electromagnetic radiation may pass, yet each individual flap 32 is free to flex and be displaced separately such that the item can pass through the shielding curtain 30. Reference is now made to FIG. 9, which illustrates an alternate embodiment of a single-piece curtain receiving bar 80. The single-piece curtain receiving bar 80 has a different profile geometry than the curtain receiving bar 72 shown in FIG. 8. The curtain receiving bar 80 includes a pair of flanges 82 extending proximate a top portion of the curtain receiving bar 80. The flanges 82 are configured to receive a fastener to secure the curtain receiving bar 80 to the exposure station 18 of the electromagnetic radiation scanning system 10. Similar to the embodiment shown in FIG. 6, the curtain receiving bar 80 includes a bead receiving slot 84, and it is a generally thin-walled part formed by injection molding, pultrusion, or extrusion of a polymer or a metallic material. This disclosure contemplates any suitable extrusion profile that can be mounted to the electromagnetic radiation scanning system 10 and includes a bead receiving slot 84 that receives the mounting bead 36 of the shielding curtain 30. A single unitary body shielding curtain 30 with a mounting bead 36 or individual flaps 32 of a shielding curtain may be received and held in place by the single-piece curtain receiving bar 80, similar to the embodiments described above with respect to FIGS. 7 and 8. According to an alternate embodiment, a top portion of the curtain receiving bar may be open to allow the shielding curtain to be dropped in from above the curtain receiving bar such that the bead receiving slot supports and suspends the mounting bead 36 or other integrated mounting feature. In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as “left” and right”, “front” and “rear”, “above” and “below,” “top” and “bottom” and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms. In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive. Furthermore, invention(s) have been described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment. |
|
claims | 1. A unit spacer grid strap comprising:a plurality of first convexities protruding in one direction so as to be placed in contact with a nuclear fuel rod;a plurality of second convexities alternating with the first convexities, protruding in the other direction so as to be in contact with another nuclear fuel rod; anda plurality of joints, each of which connects the first convexity and the second convexity,wherein each of the first and second convexities includes:an intermediate support continuously connected with the joint between the first convexity and the second convexity;an upper support on a top edge of the unit spacer grip strap spaced apart from the intermediate support, and continuously connected with one of the two neighboring joints, the upper support having a shorter length than the intermediate support so that an end of the upper support is suspended in the space between the two neighboring joints; anda lower support on a bottom edge of the unit spacer grid strap spaced apart from the intermediate support, and continuously connected with the other of the two neighboring joints, the lower support having a shorter length than the intermediate support so that an end of the lower support is suspended in the space between the two neighboring joints. 2. The unit spacer grid strap as set forth in claim 1, wherein the upper support and the lower support have point symmetry with respect to a middle point of the intermediate support. 3. The unit spacer grid strap as set forth in claim 1, wherein at least one of the first and second convexities has a greater diameter than the others. 4. A spacer grid for nuclear fuel rods comprising:a plurality of unit spacer grids in a stacked configuration, each unit spacer grid including:a plurality of unit spacer grid straps disposed in a row at regular intervals, each having convexities alternating with each convexity on opposite sides of each strap at regular intervals, at least one of the convexities having a diameter greater than the others; anda plurality of fixing grid straps connected to respective opposite ends of the unit spacer grid straps so as to fix the unit spacer grid straps,each convexity is partitioned into an intermediate support, an upper support on a top edge of the unit spacer grid strap above the intermediate support, and a lower support on a lower edge of the unit spacer grid strap below the intermediate support;the upper support is configured so that one end thereof adjacent to the intermediate support is suspended in a space;the lower support is configured so that one end thereof adjacent to the intermediate support is suspended in the space,wherein the unit spacer grids are rotated in one direction at an angle of 90 or 180 degrees with respect to adjacent unit spacer grids in the stacked configuration. 5. The spacer grid for nuclear fuel rods as set forth in claim 4, wherein:the upper support and the lower support have point symmetry with respect to a middle point of the intermediate support. 6. The spacer grid for nuclear fuel rods as set forth in claim 4, wherein the stacked unit spacer grids are coupled by fixing rods inserted into respective four corners or middles of four faces thereof. |
|
051075261 | summary | BACKGROUND OF THE INVENTION This invention relates to x-ray microscopes and more particularly to a narrow bandpass high resolution x-ray microscope for imaging microscopic structures within biological specimens, the bandpass being in the water window wherein x-rays are absorbed by carbon and not absorbed by water within cells and tissues. The water window is the narrow x-ray band which lies between the K absorption edge of oxygen and the K absorption edge of carbon, the former being 23.3 angstroms and the latter being 43.7 angstroms. X-Rays of wavelength just below the K absorption edge of oxygen are highly absorbed by water, but at wavelengths just above the 23.3 angstrom K absorption edge, water is quite transparent. Similarly, carbon structures are very absorptive to wavelengths just below the carbon K absorption edge of 43.7 angstroms, but transparent at longer wavelengths. Because of these natural properties of the interactions of x-rays with matter, a microscope designed to produce images using x-rays of wavelength lying within the relatively narrow water window would provide a unique instrument ideally suited for ultra-high resolution studies of proteins, cell nuclei, chromosomes and gene structures, DNA and RNA molecules, mitochondria, viruses, cellular golgi apparatus and other carbon based structures within the aqueous environment of living or freshly killed cells. Such a microscope would take specific advantage of the nature and characteristics of x-ray absorption in the immediate vicinity of the K edges of the dominant components within living cells and tissues. It can thus be utilized for medical and microbiological research into the nature and characteristics of DNA and RNA molecules, genetic structures and investigations of proteins, protein crystals, viruses and a host of other microscopic carbon based structures. The value of a microscope permitting images of the important carbon constitutes of microscopic structures should be of immense value in many biological and medical research areas including DNA and RNA research, genetic research, gene splicing, genetic engineering, cancer and AIDS research. The prior art x-ray microscopes are broad bandpass systems. Thus, they are not capable of yielding high resolution, high contrast images of carbon structures within living cells since x-ray absorption within the water of the cell degrades the contrast and makes it impossible to obtain quality images of the small carbon based structures. These prior art microscopes have been fabricated based upon grazing incidence systems using the principle of the Kirkpatrick-Baez configuration and the Wolter (Hyperboloid-Ellipsoid) configurations. The single Wolter or crossed Kirkpatrick-Baez systems are typically made to operate at a low grazing angle of incidence, e.g., less than one degree and typically are effective reflectors of x-rays of wavelengths greater than 6 angstroms whether or not they are uncoated or coated with a high-Z diffractor material as gold, platinum or iridium Because they are broad bandpass systems an x-ray microscope of the prior art capable of reflecting radiations as short as 23.3 angstroms will also effectively reflect wavelengths much longer than 43.7 angstroms where carbon becomes transparent. Consequently, the prior art microscopes are not suited for research in the critical and relatively narrow band of the electromagnetic spectrum in which the properties of water and carbon, the components most important to living cells, play the dominant role in governing the achievable spatial resolution and contrast. An imaging microscope capable of having the narrow x-ray bandpass of the water window although invaluable to many biological and medical research areas is not known in the prior art. SUMMARY OF THE INVENTION Consequently, it is a primary object of the present invention to provide an x-ray microscope capable of imaging and producing ultra-high spatial resolution magnified images of microscopic carbon based structures. It is another object of the present invention to provide an imaging x-ray microscope having a narrow bandpass in the region of wavelengths in the water window. It is a further object of the present invention to provide an imaging x-ray microscope for optimizing contrast and maximizing spatial resolution of carbon based microstructures within the aqueous envelope common to living and freshly killed cells. Accordingly, the present invention provides a high resolution x-ray microscope for imaging microscopic structures within biological specimens, the microscope being configured particularly to take advantage of the nature and characteristics of x-ray absorption in the immediate vicinity of the K edges of the dominant components within living cells and tissues, e.g., carbon, water, hydrogen, oxygen and nitrogen. The microscope thus has an optical system including a highly polished primary and secondary mirror coated with identical multilayer coatings, the mirrors acting at normal incidence. The coatings are designed so as to have a high reflectivity in the narrow bandpass between 23.3 and 43.7 angstroms and having very low reflectivity outside of this wavelength range. In the specific form of the invention the reflecting mirror surfaces are spherical, the primary mirror being concave and the secondary mirror being convex, the mirrors having respective radii of curvature which are concentric about a common center of curvature on the optical axis of the microscopes extending from the object focal plane to the image focal plane. One or more foil x-ray filters may be mounted in the optical path to remove unwanted radiation resulting from certain x-ray sources. A specimen mounted on a filter at the object focal plane will be magnified and imaged in the narrow bandpass onto a detector such as a film at the image focal plane. In order to reduce x-ray absorption in air, the entire apparatus is mounted in a vacuum chamber. Thus, the invention relates to a microscope utilizing specially designed narrow bandpass multilayer coatings (which provide peak reflectivity in the water window) on optics and with thin composite metal foil x-ray filters with properly selected K or L series absorption edges chosen so as to effectively transmit x-rays w the water window and to very effectively reject UV and visible radiation wavelengths outside this important narrow bandpass. |
abstract | A method and apparatus for controlling implantation during vacuum fluctuations along a beam line. Vacuum fluctuations may be detected based on a detected beam current and/or may be compensated for without measuring pressure in an implantation chamber. A reference level for an ion beam current can determined and a difference between the reference value and the measured ion beam current can be used to control parameters of the ion implantation process, such as a wafer scan rate. The difference value can also be scaled to account for two types of charge exchanging collisions that result in a decrease in detected beam current. A first type of collision, a non-line of sight collision, causes a decrease in detected beam current, and also a decrease in the total dose delivered to a semiconductor wafer. A second type of collision, a line of sight collision, causes a decrease in detected beam current, but does not affect a total dose delivered to the wafer. Scaling of the difference can therefore be used to adjust a wafer scan rate that accounts for non-line of sight collisions. |
|
abstract | A mobile modular reactor, in particular, a graphite-moderated fission reactor, has an active core region and at least a portion of control region(s) that are located within an interior volume of a pressure vessel. Flow annulus features located in the flow annulus between an outer surface of the control rod/fuel rod and an inner surface of the cladding of the channel in which the rod is located stabilizes the flow annulus and maintains a reliable concentricity between the inner and outer claddings that envelope the flow annulus. Flow annulus features are equally circumferentially spaced at longitudinally separated locations and the flow annulus features at successive, longitudinally separated locations are rotationally offset relative to each other. For purposes of transportability, the pressure vessel is sized for mobile transport using a ship, train or truck, for example, by fitting within a shipping container. |
|
abstract | A nuclear reactor core comprising fissile material is surrounded by a core former. The core former comprises one or more single-piece annular rings wherein each single-piece annular ring comprises neutron-reflecting material. In some embodiments the core former comprises a stack of two or more such single-piece annular rings. In some embodiments the stack of single-piece annular rings is self-supporting. In some embodiments the stack of single-piece annular rings does not include welds or fasteners securing adjacent single-piece annular rings together. A core basket may contain the nuclear reactor core and the core former, and in some embodiments an annular gap is defined between the core former and the core basket. In some embodiments the core former does not include welds and does not include fasteners. |
|
summary | ||
description | This application is a continuation-in-part of U.S. application Ser. No. 13/961,125, filed Aug. 7, 2013, which is a continuation-in-part of U.S. application Ser. No. 11/601,498, filed Nov. 17, 2006, which claims the benefit under 35 USC 119(e) of Provisional Patent Application Ser. No. 60/737,931, filed Nov. 18, 2005, all of which are incorporated by reference herein in their entirety. The use of beta or alpha particles of radio-isotopic elements that are typically by-products of nuclear fission are used as a power source for the generation of electricity. Beta particles are a category of electrons emitted from a neutron of an atomic nucleus during its decay. Over a period, known as the isotope half life, a neutron of a decaying nucleus is converted into a proton, increasing by one the atomic number of the nucleus thereby increasing by one step in the periodic table an atom subject to such decay. The decay of the neutron may, in rare circumstances, result from a natural process. However, most such decay is the result of exposure of the nucleus to extreme conditions of heat and exposure to other sub-atomic particles, as often occur during nuclear fission. Such external conditions induce an instability into the basic quark structure of the neutron which normally consists of one so-called up or (u) quark and two so-called (d) or down quarks. In beta decay, the intra-nucleon electro-weak force W degrades one of the d quarks into an u quark creating, during the half life of the isotope, a structure of one d quark and two u quarks, that is, the quark structure of a proton. This causes the one step up in the periodic table of the atomic number of the affected nucleus. The modern theory of beta decay was developed in 1934 by Enrico Fermi, but was not experimentally proven until 1956 by T. D. Lee and C. N. Yang. This process, as now understood, can be expressed by a Feynman diagram showing one of the d quarks of the decaying neutron transformed by an electro-weak interaction W into an u quark, from which reaction is released one electron and one anti-neutrino. This additional particle is necessary to express beta decay in terms that do not violate the principles of conservation of energy and momentum in sub-atomic interactions. A neutron, if unassociated with a nucleus, will decay within a half life of about 600 seconds, but is stable if combined into a nucleus. When so combined with protons and other neutrons, it is governed by the nuclear strong force, and beta decay of the neutron would normally occur only over a period of many years, often centuries. When a neutron has fully decayed into a proton, a mass difference (decrease in energy of about 1.29 Mev) results, this representing the energy equivalent of the mass of the neutron which is lost during the above-described conversion of the d to an u quark. It has been shown that the beta decay electron carries away most of said energy difference in the form of kinetic energy and a strong magnetic field around the electron. The present invention seeks to make effective and efficient use of such high energy electrons resultant of neutron decay and the electro-weak interaction W within the quark structure of the neutron which causes the decay. Since the most accessible form of beta decay neutrons is that of the radio-isotopic by-products of nuclear fission, the instant invention may be appreciated in terms of a new use of these by-products, e.g., iron 55, nickel 63, strontium 90, tritium and others, as a power source or input, to a microwave-like radiation device known as a magnetron tube or simply a magnetron. The magnetron, as a source of microwaves, has existed since its discovery in the 1930s by Randall and Boot. The magnetron became a building block of what is now termed cavity magnetron microwave radar. The magnetron is also the basis of the standard microwave oven and may research applications. Methods and apparatus for the direct conversion of radiation of radio-isotopes including beta decay electrons, to electrical energy was first suggested in 1988 by the physicist Paul M. Brown, and is reflected in his U.S. Pat. No. 4,835,433, directed to a resonant circuit battery using a radio isotope inside a coil of a tank circuit. The invention of Brown sought to employ the so-called beta voltaic effect to access the electrical potential associated with energy in the magnetic field of high energy beta electrons. See <www.rexresearch.com/nucell/nucell.htm.> Isotopes which emit beta electrons occur within fuel rods of fission reactors and in the processing of uranium 238 and plutonium. Beta electrons are negatively charged and travel at a high velocity, approximately ¾ the speed of light (0.75 c), and exhibit an energy spectrum up to 0.782 MeV with a maximum at a lower level. Such spectrum varies between isotopes. In the nucleus of most naturally occurring elements, neutrons cannot decay because there is no available quark orbit for a decaying quark to occupy. As a result, most naturally-occurring nuclei are stable. However, when subjected to the high energy and extreme heat of nuclear fission, the d quark does decay, thus rendering the neutron unstable. When this occurs, the nucleus emits at least a beta electron and an anti-neutrino. Electrons emitted in this fashion thus exhibit exceedingly high levels of energy since they must possess sufficient energy and velocity to escape from the quark orbits of the decaying neutron of which they were a part. As has been determined by Brown and others, the magnetic energy associated with beta radiation electrons is several orders of magnitude greater than either the kinetic energy of those electrons or the static electric field energy of the same particles. As such, each emitted electron of a radio-isotope is associated with a powerful magnetic field which, if absorbed by a load, causes the field to collapse thus producing an EMF known as the beta voltaic effect. This field may however be used in a magnetron environment to produce a high energy rotating field and to induce microwaves, as is set forth below. One of the primary drawbacks to the use of nuclear power is the radioactive waste which results from its fission process. Much of the waste of the system is in the form of “spent” fuel rods which cannot efficiently sustain the fission reaction process in the reactor. After serving their useful lives, the spent fuel rods are removed from the reactor, but the fuel rods still possesses a significant amount of their original energy capability, particularly in the electro-weak force W that acts within the nucleons. Even after removal from the reactor, the fission process continues in the fuel rods and strong force (inter-nucleon) energy continues to be released, mainly in the form of kinetic energy which is subsequently converted to heat. Some of this energy will however affect the neutron nucleons, stimulating neutron decay which gives rise to the beta decay noted above. Thus, the fuel rods continue to produce energy as they undergo radioactive decay, meaning they are still “hot” in terms of hard radiation. The rods, therefore, must be isolated until they are no longer radioactive, which can take thousands of years or more. There are no final procedures for the storage of spent fuel rods and other radioactive material. That is, no steps are underway to make use of the massive amount of radioactive decay energy, including beta decay energy, that exists in radioactive materials, especially in spent fuel rods and plutonium by-products. Thus, there remains a need for a method of safely and efficiently utilizing the decay particles of radio-isotopes, both beta and alpha. Other attempts have been made to convert radioactive decay energy to electrical energy, however, none have proved commercially viable due to their complexity, minimal power generating capability, or lack of durability. For example, a solid-state device which seeks to employ the energy associated with alpha and beta particles at a Fermi junction is taught by U.S. Pat. No. 5,825,839 (1998) to Baskis. It teaches that the energy associated with alpha and beta particles are in a range of 1000 to nearly one million KV (1 MeV) per particle, that is, six to twelve orders of magnitude greater than the voltage of an electron at rest. Radio-isotopes as a power source in micromechanical, i.e., nano-structures, are addressed in U.S. Pat. No. 6,479,920 (2002) to Lal, et al. The primary deficiency of these devices has been degradation of the structures by long term exposure to the high kinetic energies of the beta electrons. As such, physical durability is a key design factor in building a commercially viable beta electron device which, preferably, would take the form of a battery that is size-scalable up or down as a function of application. Lindner (U.S. Pat. No. 2,517,120) teaches that the parameters of isotopes include a DC voltage and a form of energy that can be converted to a type of electrical current. He also teaches that such energy can be stored and that his design will repel emission when sufficiently charged. In addition, he teaches that isotopes have an impedance and how to calculate their impedance. Lindner however does not suggest that his emissions can be used to power a resonator of any type including those found in magnetrons, or that isotopes produce instantaneously accelerated electrons. In addition, what differentiates my invention is that the impedance of a cold isotope cathode affects the interaction space inside a magnetron and, more precisely affects the capacitance within that interaction space. This understanding is a critical aspect in designing a nuclear magnetron as taught herein. The cold cathode in this invention uses an isotope (isotopic cathode acting as the emitter of energy) that produces instantaneous or W force accelerated electrons and/or alpha-rays and should not be confused with hot cathodes, shown in the prior art, that produce thermionic electrons from heat that have to be accelerated using high external voltage, i.e., thermionic emissions. Such cold cathodes can and do release beta electrons, also referred to as beta rays, or beta particles. In the case of an isotopic cold cathode, they can produce alpha rays or particles. Beta rays and alpha rays however cannot both be used simultaneously. If a cold cathode did produce both types the invention would in fact cancel the effects needed from the cold cathode. The invention's isotopic cold cathode acts like an external power supply but in EM communication with the anode block of the inventive system. The concept of hot cathode devices and external power supply therefore do not apply to any aspect of this invention. This is an improvement in design of using high voltage cold cathode isotopes to produce a power source. No prior art known to the inventors sets forth a method or apparatus for the conversion of energy associated with the electro-weak force W, the beta voltaic effect or alpha particle emission thereof into high energy microwaves and, in turn, use of such microwaves as an input for the evaporation of liquid as an input to an electrical turbine generator or, alternatively, use of such a microwave magnetron output as an input to microwave DC generators known in the art. The present invention addresses this need. It is to be understood that each variety of isotope (singular cathode type) used this way produces an energy spectrum specific to that isotope. Such a magnetron system can be designed for a specific isotope but will need to be redesigned to operate with another isotope. This should not be confused with the standard linearly accelerated magnetron that uses high voltage to induce the acceleration of electrons typically from a neutral tungston cathode or other hot filament type cathode. The geometry of the emissions of these magnetron systems differ due to the linear accelerated electrons produced from a hot cathode using a heat source versus or the instantaneously accelerated electrons from a cold cathode using the W force of a nuclear isotope. It should also be noted that X-rays and gamma rays have little or no effect on magnetron type devices or how they operate. However, there exist types of isotopes produced or byproducts of X-rays or gamma rays having electron emissions that may be suitable for use with my cold cathode technology. In most cases, cold cathodes using isotopes will generate too much noise to be used in a standard type magnetron requiring a highly stable fixed frequency device with highly stable power output. Isotopes by nature produce an erratic form of emission or output making the isotopic nuclear magnetron, as taught herein, a noise type of device having permissible frequency fluctuations and changes in output power. But, in the invention, this does not affect the efficiency or production of energy needed to produce useful power. The publication of Cristea et al (IFA-FR-138-1975) teaches that there existed a lack of electrons available from his cold cathode in the year 1975 needed for an isotopic magnetron system to operate correctly. That is, such magnetron devices circa 1975 employed a “point contact” with small cathode areas while, although using beta electrons, could not supply a sufficient number of electrons to actually to operate a Cristea type device. Cristea further made assumptions about his device that, over time, have proven to be incorrect. That is, he did not understand the roles of the interaction space, resonators and resonator matching, or how a space-charge wheel in the interaction space would work. Nor did he fully understand magnetic arc moments for a magnetron and did not indicate the voltage range in which his device could work or with what isotopes. Cristea's solution would have turned an isotopic magnetron into a non-functioning device or into a neutron reactor that would transform the magnetic materials used in the magnetron into other elements, thus losing their magnetic properties and degrading the space-charge wheel that he clearly did not understand. Cristea's goal was to take a standard magnetron, not designed to work within the energy range of an isotope and flood the standard hot cathode with electrons to make it work. That is, his assumption regarding how to make a standard magnetron work with any kind of nuclear fuel is not correct, since in most nuclear fuels, the effect of strong force will overwhelm that of the weak force. Cristea also does not address any power limitations, constant current issues, noise or other magnetron design factors he might use for control of emission velocity of beta electrons. Cristea thus failed to understand critical issues of performance as addressed herein. Cristea IFA-FR-138-1975 also teaches that an isotopic magnetron will operate between a V1 and V2 voltage range. He, however, does not go into details as to how these ranges are set and operate. He also makes the assumption that his magnetron would work like a hot cathode magnetron. Cristea et al appears to lack understanding on how the resonator impedance operated at the time of his submission of the article and what needed to be taken into account. He assumed controlling electrons is the same in both a isotopic device and a hot cathode device. He was wrong in this assumption, and his results were of limited value due to his limited understanding of the underlying physics. He was correct, however, with the results he got from the device he used to do his testing. In his V1 voltage range, the lowest possible voltage of the magnetron, the operation range value is set by the magnetic field strength and the break over voltage point at which the magnetron will start to operate. His magnetrons looked like and operated like a Zener diode circuit with impedance (resistance) in them. See FIG. 31. His V2 point (the termination point of resonation). The V2 point is set by the upper values of the emission speed of the particles (voltage in his case). It is noted that the spacing between resonators must be large enough to handle the increased angular velocity of the space-charge wheel and still match all the strapping impedances of the resonators. The upper limit V2 is reached when the space-charge wheel rotates too fast for the resonators to work correctly, or that the space-charge wheel has too few electrons in it for the device to meet the minimal current for oscillation. It is noted that increasing the voltage in a standard hot cathode magnetron also increases the current at the same time. Therein, the current can go up in an exponential fashion in filament cathode magnetrons. This same statement is not true in the present magnetron since the isotopic cold cathode is constant current at all voltage levels. See FIG. 32. This is a major difference between the two types of devices. A. L. Vitter (U.S. Pat. No. 2,589,903) teaches that a magnetron can be tuned by a mechanical means, but the concentric grids thereof are at a plane above that between the cathode and anode block and therefore cannot affect, or can only minimally affect, beta electron or alpha ray emissions from the cathode to the anode. Vitter also teaches that by adding an external port one can change or pull the frequency of the magnetron. Vitter also indicates a magnetron can be modulated this way, but in fact only the impedance of the anode cavities can be regulated since circuitry and is external to the magnetron proper and only can bias the anode cavities, not the cathode. By using Vitter, one can compensate for frequency pull of isotope emission losses (cold cathode) over time or use isotopes in place of his method for adjusting the capacitance of an external cavity or port. Since the isotope loses power over an isotope's half-life, this is one way to compensate for frequency deviation from power loss in an isotopic cold cathode. Beta electrons and alpha-ray particles emitted by radio-isotopic, weak force, by-products of nuclear fission, such as nickel 63, or strontium 90 are used as a power source at a cold cathode of a magnetron system. Such particles include high speed, high energy electrons having a large EMF associated therewith. In the magnetron a radial electrical vector E, between the isotopic emitter and conduction block, interacts with an axial magnetic vector B vector to produce an ExB force vector that rotates the beta electrons or alpha-ray particles about the system axis. These emissions from a cold cathode derive from a small quantity of a radio-isotope within a set range of emission of beta electrons or alpha particles. Both however are not used by the same system. The angular velocity and geometry of a rotating field known as a space charge wheel (space-charge wheel) may be modulated by (1) an external RF input which, biases the cavities of a conduction block (2) and the use of circumferential biasing grids between the isotopic emitter and conduction block. In the magnetron is a polar array of resonant cavities within the conduction block into which the space-charge wheel induces LC values which excite the cavities, producing microwave resonance of electrons which may be used as an input to a power port for the direct or indirect generation of AC or DC power. This invention thus relates to a system of an electro magnetic oscillator tube with enhanced isotopes, having at least one layer, wherein each layer of said at least one layer comprises an axial sequence of a first magnet, a conduction block, and a second magnet of opposite polarity, an elongate axially disposed emitter of isotopic particles. The conduction block having an RF port, an opposite electrical polarity relative to said emitter of isotopic particles forming between said emitter of isotopic particles and said conduction block, and block disposed in a plane about said emitter of isotopic particles and having an interior radial periphery relative to said emitter of isotopic particles defining an interaction space. Further provided is a potential defining a radial electrical vector E. Additionally provided, is a coating of a carbon material on an inner periphery of said conduction block representing an outermost radius of an outermost space and thermal conduction paths within radii of said conduction block between said resonant cavities. Yet further provided is an outer periphery of said interaction space defining a polar array of resonant cavities in said conduction block separated from each other by surfaces in communication with said interaction space. Each of said resonant cavities having an LC value, wherein each resonant cavity generates a resonant frequency responsive to a particular annular motion and energy of isotopic particles of a cloud of electrons and isotopic particles also passing said surfaces and a plurality of entrances of said resonant cavities. Provided is the first magnet comprises an upper magnet outside and above said resonant cavity and said second magnet comprises a lower magnet of opposite polarity outside and below said resonant cavity, wherein said upper magnet and said lower magnet are in magnetic communication with said interaction space, and a plurality of electrically biased grids disposed concentrically about said emitter of isotopic particles within said interaction space to influence emission characteristic of electrons, within an energy spectrum of said isotopic particles to an integrity of said cloud of electrons and isotopic particles in said interaction space, shape thereof, and density of effective LC values at said resonant cavities, and a connection between selected groups of said resonant cavities at locations of like electrical polarity, wherein said connection comprises conductive strapping elements within said conduction block. The system also provides an assembly for conversion of microwave energy of said resonant cavities to a DC electrical output. It is an object of the invention to provide a safe and cost-effective means of conversion of isotopic electron emissions into useful electric energy. It is another object to provide a system for use of beta electron neutron decay as a power source for an electric generator or battery. It is a yet further object to provide a system of the above type having sufficient durability for use without maintenance during a period of at least two years. It is a further object to provide a system of a long-term power source that does not require continuous refueling, with numerous commercial and military applications within a variety of fields including aerospace and spacecraft design applications. A further object is to provide teaching of how to build an isotope powered magnetron that can be used to produce DC or AC power with conversion stage or stages added to the nuclear magnetron conversion stage or stages in the magnetron as needed. The DC converter stage can be used to power integrated circuit designs or power motor-generator AC devices for utility power. I show herein the design parameters that can be used relative to standard magnetron designs and how the operation of an isotopic magnetron differs therefrom. The above and yet other objects and advantages will become apparent from the hereinafter set forth Brief Description of the Drawings, Detailed Description of the Invention and claims appended herewith. With reference to FIG. 1, there is shown one form that an anode (conduction block) and cathode (emitter of isotopic particles) structure of traditional magnetron 10 may take. In this structure, an axially located a cold cathode 12 employs thermionic emission to release electrons 14, which travel outwardly in the direction of anode block 16 which includes anode cavities (resonant cavities) 27, interaction space 28 and anode poles 29. The otherwise natural radial paths of the electrons are deflected by a linear DC magnetic field 18 which is generated by upper and lower magnets 20 and 22 (see also FIG. 2) of polarity opposite each other. FIG. 2 is a vertical radial cross-sectional view of a typical magnetron which includes said cathode 12 and anode block 16. Cooling fins 24 typically extend integrally outwardly from an outer periphery 25 of the anode block. Also shown in FIG. 2 are interaction space 28, output antenna 40, vacuum power port 41, waveguide 42 and strap rings 30/32 more fully described below. It may be appreciated that electrons 14 would travel radially outwardly to anode poles 29 were it not for the transverse DC magnetic field 18 which deflects the emitted electrons to the left because the (ExB) cross-vector resultant from the interaction of the radial electric field of electrons with the transverse DC magnetic field 18. Thus, electrons 14 tend to sweep around annular interaction space 28 between the cathode 12 and poles 29 of the anode block 16. This circular motion is shown in FIG. 3 which also illustrates the radial geometry which an anode block 116 of a fin or stub type magnetron 100 may take. Therein, anode cavities 127 are formed between anode stubs 126, at the end of which are poles 129. These cavities are trapezoidal as opposed to the cavities 27 of the magnetron 10 (see FIG. 1) which are semi-circular in radial cross-section. FIG. 3 also shows rotating electron cloud pattern 128 and a RF port 44, later described. In the present invention, there is used a radio-isotope cathode (cold cathode) 112 which emits high energy electrons 15. An exploded view of magnetron 100 is shown in FIG. 4, which also shows DC magnets 120 and 122, and cavities 127. FIG. 5 is a vertical fragmentary radial view of the magnetron of FIG. 3, showing interaction space 128, stubs 126, DC magnets 120 and 122, vacuum RF port 141, cathode 112 and waveguide 42. In FIG. 6 is shown, in radial cross-sectional view, an actual magnetron of the type shown schematically in FIG. 3. Therein may be seen anode block 116, anode fins or stubs 126, trapezoidal anode cavities 127, the isotopic cathode 112, anode poles 129 and two sets of shorting straps 130 and 132, the function of which is explained below. Also shown in FIG. 6 is interaction space 128 between cathode 112, and anode stubs 126 and poles 129. In FIG. 16 is shown an assembly view of the magnetron 100 of FIG. 4. Shown therein are strips 160 of a non-conductive or dielectric material such as a polycarbonate, silicone, or the like. The structure thereof may be more fully appreciated with reference to the vertical cross-sectional view of FIG. 16A-16A in which interaction space 128 may also be seen (see also FIGS. 5 and 10). It may, from FIG. 16A, be appreciated that, in a given embodiment, the axial height of interaction space 128 may be very narrow while in other embodiments, such as those shown in FIGS. 4 and 5, it may be closer in dimension to the radius of the interaction space. Strapping 30/32 is shown in more detail in the hole-and-slot magnetron 200 shown in FIG. 7. As may be noted, positive poles 229 are tied to each other by inner strap 32 while negative poles 229.1 are tied to each other by strap 30. Strapping of respective pole pairs assures a desired phase relation of respective spokes 147 of the space-charge wheel 131 (see FIGS. 10 and 11) and uniformity of amplitude of each spoke. This facilitates the combining the power output of each cavity. Each strap 30 and 32 may then be connected to a power port output of the system. The effect of the rotation of electrons 15 is shown in the views of FIGS. 8 to 11. More particularly, the isotope input to the magnetron 100/200 is applied at center cathode 112 from which high speed (0.75 c), high-energy electrons 15 are released by neutron decay from the radioisotope. Nickel 63 may be employed because of its particular property of high rate of release of beta ray electrons, safety and reasonable cost. The inventive system thus employs a cold cathode requiring no external heat or power source. As noted above, beta rays are produced by the radioactive decay of neutrons of certain naturally occurring elements but, particularly, by man-made by-products of fission in nuclear power plants in the and production of plutonium. Nickel 63 gives off no alpha or gamma radiation, so that its use does not necessitate thick lead shielding or the like for safety purposes or alpha-specific shielding. As noted in the Background of the Invention, the magnetic energy given off by beta electrons possesses energy several orders of magnitude greater than either the kinetic energy or the direct electric charge of the electron, and far greater than that of electrons resultant of the thermionic emission of prior art magnetron cathodes. It is to be appreciated that any moving electrically charged particle, e.g., an electron, will behave like a current and thus yield a symmetric magnetic field in which energy is stored and thus carried by the particle. Absorption of such a charged particle causes its magnetic field to collapse the energy of which is considerable, as above noted. As set forth in U.S. Pat. No. 4,845,433 to Brown (see Background of the Invention above) an LC resonant tank circuit oscillation at a self-resonant frequency uses energy contributed by the beta voltaic effect, providing a resonant nuclear battery to convert beta electron energy into electricity. The within invention however employs the unique function of LC resonant microwave cavities of a magnetron which are more efficient and durable than the LC resonant tank circuit taught by Brown. This may be seen with reference to the description which follows: In FIG. 8 is shown an enlarged fragmentary view of the magnetron 10 of FIG. 1. Therein are shown anode block 16, anode cavities 27, anode stubs 26, and anode poles 29. Some of the electrons 15 emitted from the isotope cathode eventually reach anode pole 29 or become a part of a whirling cloud 131/231 of electrons, within the interaction space 128/228 (see FIGS. 10-11), having both radial and polar velocity components. In most cases, however, the polar component of momentum (produced by the above-referenced ExB vector) will predominate, causing the counterclockwise electron rotation shown in FIGS. 3, 10 and 11. With further reference to FIG. 8, electrons 15 will arrive from the cathode at a negatively charged region 34 of the anode pole 29 and, in so doing, will tend to “pump” the natural resonance frequency of the cavities 27 in two ways: Firstly, by forming a virtual capacitor across slot 46 between said negatively charged region 34 and a positively charged region 36 (which is induced upon the opposing side of the next anode pole 29). Opposing charge regions 34 and 36 at opposite sides of slots 46 of each anode cavity 27 thus yield a capacitive effect 35. (See FIG. 8) Concurrently, the difference in charge between regions 34 and 36 produces a current flow 38 around cavity 27 and, because of the geometry of this current flow, an inductive effect 37 transverse to cavity 27 is produced. Resultantly, the sweep/rotation of electron field 31 within interaction space 28 causes each cavity 27 to exhibit a resonance which is analogous to that of parallel resonant circuit, as shown in FIG. 9. Therein, the resonant frequency is expressed by the formula: f resonance ≈ 1 2 π 1 LC In the process of electron rotation, work is done on the electron charges because the axial magnetic field 18 of magnets 20 and 22 exerts force on electrons 15 which is perpendicular to their initial radial motion, thus causing them to be swept in the above noted annular motion by the (ExB) vector. In this manner, work is done upon the charges during their rotation. As the electrons sweep toward regions 34 of excess negative charge (see FIG. 8), a part of that charge is pushed around cavity 27, imparting both said inductive effect 37 and an oscillation which arises at the above-described natural frequency of the cavity. The driven oscillation of the charges past the anode cavities 27, regardless of their geometry, generates radiation of electromagnetic waves, typically in the microwave range, which are the output of every magnetron. In FIGS. 2, 3 and 10 are shown antennae 40/140 which provide said waves, through power port 41/141, to one or more waveguides 42 as described below. FIGS. 10-11 show counter clockwise electron wheels 131/231 (and space-charge wheel) of whirling electrons 15 as influenced by the above-described beta voltaic effect of isotope cathode 112 and the DC magnetic field between magnets 120 and 122. This forms a rotating pattern which, due to a property of the resonance cavities known as moding, produces a pattern which resembles spokes 147 of the space-charge wheel. The interaction of this rotating space-charge pattern with the configuration of the surfaces of anode poles and anode cavities produces a specific alternating current flow in the cavities of the anode. That is, as a spoke 147 of spinning electron pattern (space-charge wheel) 131/231 approaches an anode stub 126 (see FIGS. 3, 5, 6 10, and 11) a positive (+) charge is induced in that stub 126, or in pole 229 in FIGS. 7 and 11. As the electrons pass, the positive charge diminishes in one stub, a negative charge is induced in the next stub 126.1 or pole 229.1. (See FIGS. 10-11). Current is induced in the cavity because of the physical structure of the cavity 127, as above described with reference to FIG. 8, producing the high Q resonant inductive-capacitive (LC) circuit of FIG. 9 in each cavity. The parallel relationship between the L and C parameters of the resonant cavities is secured through the so-called even and odd strapping 130 and 132 (see FIGS. 6 and 7) of alternate anode stubs 126 of the magnetron. In other words, the formula for resonant frequency above set forth with reference to FIG. 9 indicates that, in a given application, resonant frequency may be modified through (1) changes in the strapping, relationship of the resonant cavities of the system and (2) changes in the geometry of the cavities 27/127 or their gaps 46/146, (3) rate of rotation of the field 131 and its shape (see FIGS. 10-11) and (4) energy density of the field. For example, cavities 27 of FIGS. 1 and 8 will have a smaller capacitance across its gap than will the cavities of the magnetron 100 shown in FIGS. 3 and 10. Similarly, so-called hole-and-slot magnetron 200 of the type shown in FIGS. 7 and 11 will have a yet smaller capacitance than magnetron 10 because of the minimal width of the gap 246 between anode poles 229. By increasing the diameter or surface area of the cavities 27/127/227, the inductive effect will increase. In other words, a rotating magnetic pattern 131/231 of greatly increased energy, as will occur in the use of isotopic cathode 112, would require that an effective inductance and capacitance of the magnetron be provided in a relationship inverse to each other if one wished to obtain the same resonant frequency output into waveguides 42 as would occur in a conventional microwave. This might be essential if one wished to obtain the same 2.455 MHz frequency output which is efficient in the evaporation of water. Also, the strength of DC magnets 30/32 would also require increase, as might the radius of the interaction space 28/128, due to the high energy of beta electron 15. An added significant factor in the behavior of rotating charge pattern (space-charge wheel) 131/231 (see FIGS. 10 and 11) is the effect of the introduction of an RF field into interaction space 28/128, from RF port 44. (See FIG. 3). In fact, in the absence of an introduced external RF field, most electrons would either congregate at an anode pole 229.1 as is shown by the path of electron (a) in FIG. 13 or would quickly return to the cathode 212 as is shown by the path of electrons (b) in FIG. 13. However, the presence of the RF field naturally modifies these paths to facilitate the shape and rate of rotation of space-charged wheel pattern 131/231 within the interaction space 128/228. (See FIGS. 10-11). In FIG. 13, it is noted that electron (a) spends much more time in the RF field than do electrons (b). Electrons (a) are thus retarded and, therefore, the force of the DC magnetic field on them is diminished. As a result, they can now move closer to the anode pole 229. Under proper conditions, by the time electrons (a) arrive from point 1 at point 2, the RF field has reversed polarity, meaning electrons (a) will again be in a position to give energy to the RF field by being retarded by it. The force on electron (a) diminishes once more, and another RF interaction of this type occurs, this time at point 3, provided that at all times the RF field reverses polarity polar each time these electrons arrives at a suitable interaction position. In this manner, such “favored” electrons spend considerable time in the interaction space 228, and are capable of orbiting the cold cathode 212 several times before eventually arriving at an anode pole 229. Electrons (b) undergo a totally different process. They are immediately accelerated by the RF field and, therefore, the force exerted upon them by the DC magnetic field increases. Electrons (b) thus return to the cathode even sooner than they would have in the absence of the RF field. They thus spend a much shorter time in the interaction space than electron (a). Although their interaction with the RE field takes as much energy from it as was supplied by electrons (a), there are far fewer interactions of the (b) type because these electrons are returned to the cathode after one, or possibly two, RF interactions. On the other hand, electrons (a) give up energy repeatedly. Therefore, more energy is given to the RF field than is taken from it, so that oscillations in the cavities 127/227 are sustained. The practical effect of electrons (b) is that they return to the cathode and tend to heat it. Electrons in a magnetron also tend to bunch, this known as the phase-focusing effect, without which favored electrons (a) would fall behind the phase change of the RF field across the anode gaps 246 or slots 146 (see FIG. 10), since such electrons are retarded at each interaction with the RF field. Electrons (c) (see FIG. 13) contribute some energy to the RF field, but do not give up as much as electrons (a) because the tangential component of the field is not as strong at that point. As a result, these electrons are initially less useful than electrons (a). Electrons (c) encounter not only a diminished tangential RF field but also a component of the radial RF field, as shown in FIGS. 11 and 13. This has the effect of accelerating the electron radially outwardly, forming arms 247 of pattern (space-charge wheel) 231 shown in FIG. 11. Immediately after this happens, the DC magnetic field exerts a stronger force on electrons (c) tending to bounce them back to the cathode 112 and also accelerating them in a counterclockwise direction. This, in turn, gives this electrons (c) a good chance of catching up with electrons (a). In a similar manner, electrons (d) (see FIG. 13) are retarded tangentially by the DC magnetic field and will therefore be overtaken by the favored electrons (a). Thus a bunching of electrons takes shape. If an electron slips backward or forward, it will quickly be returned to a correct position with respect to the RF field, by the phase-focusing effect above described. FIG. 11 shows the wheel-spokes or arms 247 in the cavity magnetron. In the case shown, these arms rotate counterclockwise with the correct velocity to keep up with the RF phase changes between adjoining anode poles 229 and 229.1, so that a continued interchange of energy takes place, with the RF field receiving much more than it gives. As above noted, the RF field changes polarity and, thus favored electrons (a), by the time they arrive opposite the next gap or slot 246, see a positive anode pole 229 above and to the right, and see negative anode pole 229.1 to the left. Should one wish to avoid the use of strapping or shorting rings 30/130 and 32/132 above described with reference to FIGS. 6 and 7, one may employ an anode block 300, shown in FIG. 14, in which alternating cavities 327 and 327.1 possess different radial dimensions. Therein larger cavities 327 are alternated with smaller cavities 327.1 to ensure that a suitable RF field is maintained in interaction space 328 and to avoid a phenomenon known as mode jumping. These differences in geometry between cavities 327 and 327.1 result in differences in resonant frequency that will be useful in tuning the magnetron of the present invention. Another method of modulating the behavior of the magnetron entails alternating a DC voltage on the anode block to affect the capacitative and inductive values of the cavities. Also a technique, known as frequency pushing, may be used to affect the orbital velocity of the rotating electron cloud above-described with reference to FIGS. 10 and 11. This can be useful in adjusting the resonant frequency emitted by the cavities since change in the orbital velocity of the electron cloud will change the LC values of the resonant cavities. Thusly a variable RF input will be useful in tuning the magnetron of the invention. As noted in FIGS. 2, 5, and 12, an antenna 40 provides electromagnetic communication from said strapping 30/32 of said cavities 27 into said power port 41 which feeds the energy resultant of excited fins/stubs 26/126 into waveguide 42. This microwave energy of the cavities is channeled through a plurality of waveguides 42 (see FIG. 15), one for each magnetron 10, employed in the present system. In one application, waveguides 42 provide the energy to a boiler 48 at 2.455 MHz which is highly efficient frequency for the heating and evaporation of water or liquid 52. This may then be used to power a turbine generator. It is to be noted that fluids other than water, such as a plasma, may be advantageously used in boiler 48, which may be suitable where more compact methods of power generation are required. Alternatively, a carbon load may be constructed, in lieu of boiler 48, to provide a concentration of heat from waveguides 42 to a local hot spot. Said anode cavities in combination with said waveguides 42 are highly efficient conductors of energy and are capable of transporting wattage high enough to constitute a substitute for fossil fuel and to create a steam input to a turbine generator having an advantageous power-to-weight and power-to-cost ratios. It is also noted that fluids other than air may be used within waveguides 42 where the chemistry of such fluids is more advantageous for transport of energy. Alternatively, and most likely, said waveguides, as well as the above-described magnetrons themselves, will be vacuum sealed to minimize molecular interference with the above-described use of the beta emitting radio-isotope as the cathode of the magnetron. It has been determined that nickel 63 or strontium 90, where available, constitutes the best and most efficient fuel for use in the magnetron in a commercial application, this due to the fact that it produces a high volume of very high speed electrons. Subject to the refinement of the various operating parameters of the magnetron, the system utilizes beta ray electrons and the substantial, historically untapped energy of the beta voltaic effect associated with the magnetic fields of such electrons. Where nickel 63 is unavailable, many other beta-emitting isotopes exist. See U.S. Pat. No. 5,825,839, referenced above, to Baskis. However, most of such other isotopes also emit alpha and/or gamma radiation. Therein, one may selectively shield or filter out the undesired radiation to leave emission only of the desired beta ray electrons discussed above. Therefore, either method, whether entailing the direct use of isotopes such as nickel 63, strontium 90 or iron 55, or the shielding out of other rays from numerous other isotopes, may be employed to achieve high volume, high speed beta electron emission. It is noted that the U.S. Department of Energy, in a project known as the Archimedes Separation Process, has developed a method for the separation, into discrete isotopes, of the constituent by-products of plutonium production. Using this process, nickel 63 and other isotopes may be cost-effectively extracted from rods of fission reactors and waste associated with production of plutonium. This technology is subject to U.S. Pat. Nos. 6,096,220 and 6,235,202 among others. As may be appreciated, many isotopes which are by-products of nuclear fission have been stored, without any viable commercial use, for many years. However, as above noted, the magnetic separation process developed by the U.S. Department of Energy has resulted in a method of separation, into discreet isotopes, of a constituent isotopes of plutonium production. Accordingly, large stock piles of many discreet isotopes exist e.g., nickel 63, and more material may be cost-effectively obtained through this process. It is to be appreciated that said waveguides 42, as in the case of said anode cavities 27, may assume various different geometries, depending upon application. Therein, frequency outputs of over 300 GHz have been obtained. The invention herein issues addresses deficiencies of the prior art important to isotopic fuel used in my nuclear magnetron, including design requirements for the isotopic cathode necessary to enable its use in the present system. By the year 2000, after many years of production of microwave oven magnetrons, cathode sizes had expanded many times. The modern magnetron can now house large amounts of isotope because it no longer uses point contact type magnetrons for high power applications. Thusly making a functional type isotope powered magnetron is now possible due to such improvements in cathode design of otherwise conventional microwave systems. In old style point contact magnetrons, small points of metal were used over the filament area limiting the cathodes to such small areas. By comparison, the modern non-point, contact magnetrons use doughnut magnets (see FIG. 4) as part of the magnetron which and allow for much larger cathode areas. As such, a gram or more of isotope could easily be used in non-point, contact isotope magnetron using other aspects of current designs, as is discussed below. Power Calculation The calculation of isotope power can be esoteric. The following provides, to of those skill in the art, a practical approach to deriving power from an isotope 812. Since a coulomb is approximately equal to about 6.24×1018 elementary charges, one ampere is approximately equivalent to about 6.24×1018 elementary charges, such as electrons, moving past a boundary in one second. This statement only applies to beta isotopes. An example of a Sr-90 isotope calculation of power for beta emission electrons 801 appears in FIG. 40. This isotope has 5.106×10 to the 12th power of elementary charges coming from it per second. We take 6.24×1018/5.106×10 to the 12th power=about 1,222,387. That is about 1/1,222,387 of an amp=about 8.18×10 to the −7th power of current in 1 second. To find power we know that the particles are averaged at 300,000 electron volts. 300,000 “volts”×8.18×10 to the −7th power “amps”=about 0.245 watts per second. volts×amps=power in watts per second. To change this to watt-hours, one must multiply by 3600 (60 seconds in a minute and 60 minutes in an hour). In the area of FIG. 40 electrical field 831 of the isotope produces about 0.245 watts per second. Changing this into a watt hour is 3600×0.245 watts=about 883.5 watts per hour. If we use the peak emission 540,000 volts the power in the isotope increases to about 1590.33 watts per hour. Note the large difference in watts per hour as the voltage range changes. Using one gram of isotope Sr-90 produces about 883.5 to about 1590.3 watts per hour of power for our nuclear magnetron, depending on how the isotopic cold cathode is designed and built. From this one can see that the energy around the isotope is far more than just the heat produced by the isotope alone. It should also be pointed out that in an isotopic magnetron a cold cathode acts as a constant current source. See FIG. 32. Standard magnetrons with hot cathodes are not current limiting and need some kind of current limiting added to them in the form of a pulse network driver or power supply current limiting. Constant current from an isotope is an added feature of isotopic magnetrons. Even though the isotope may vary in output in a general sense this still acts like constant current from an engineering point of view. We can see this current effect from how the equation above is expressed in “coulombs per second” versus how the isotope is expressed in limited “charges per second”. That is, the isotope behaves as a constant current source in a relative manner. This concept can be hard to grasp in electrical engineering terms and is not apparent. By understanding that the isotope acts as a constant current, isotopic magnetron design exhibits a smaller range of current fluxation and one need not be concerned with current limiting in most cases of the design. This develops the parameters of isotopes for cold cathodes that are needed for calculations in the inventive system. Also, isotopes by nature, may not be conductive or they may also act as an insulator even though they emit electrons. Isotopes also can act as a semiconductor. This may be a major issue with the design if it needs a power supply to start the operation of the isotope device. Again, designing an isotopic magnetron is not like building a standard magnetron using a known filament made of tungsten with a vacuum about it. One should not think of a cold cathode as a hot cathode since there are major differences between them. Tungston cathodes (hot cathodes) have a very low resistance whereas cold cathodes can exhibit anything from a low resistance to an insulator level of resistance which needs to be taken into account when designing an isotopic magnetron device. Counterintuitively, the fact that an isotopic cold cathode may have a low resistance does not allow extra current flow therein as in hot cathode system. The Bremsstrahlung effect is minimal in this device since the resonators of a magnetron convert the electron energy to microwave energy before most of the electrons hit the anode blocks or fall back to the concentric grids. See FIGS. 17-20. Only the cold cathode itself will have a high amount of radiation coming from it in the form of X-rays or gamma rays, meaning that appropriate shielding is necessary. Some of this occurs from fall back electrons from the space-charge wheel 131/231 (see FIGS. 10-11) to the cold cathode isotope 112/212. Some of this fall back can be mitigated with concentric grids in the system. See FIGS. 18 and 22. Power Conversion for an Isotopic Magnetron This invention provides power from high voltage isotopes and is not considered to be a frequency stable device for use in normal communication circuits such as receiver oscillators. However one might, under certain circumstances, be able to use it for this. Smith (U.S. Pat. No. 5,280,218) shows us why lack of noise is so important in a communications magnetron and how to reduce that noise from a hot theromic cathode. However, isotope noise does not diminish the production of power or RF output in an isotopic magnetron or the efficiency of the invention device. For simplicity, I use the terms anode or anode block and cathode or cold cathode, but, in most cases, no power supply is needed to actually run the device. That is, the RF signal is not needed to operate the magnetron. Like with all magnetrons, there are many electrical configurations that can control the energy flow from the isotope in starting and/or stopping the flow of particles or controlling the particle speed if needed. One can see in FIG. 23 that a magnetron with a beta (electron) emitter 412 uses a power supply 473 to start the device's operation. In FIG. 24 one can see that a power supply 475 of opposite polarity is provided for a magnetron with alpha emitter 412A. Respective switches 473/476 are provided. I note that the geometric trajectory of electrons of a cold cathode magnetron is different from that of a hot cathode magnetron and this must be considered when designing the device. See FIGS. 7-21. That is, hot cathode magnetrons use a “linear acceleration” or thermionic electron thus having an elongated arc type of path upon emission. As noted above, cold cathode magnetrons do not have “linear accelerated” electrons that this change the geometry of the electron being ejected from the cold cathode causing the invention (isotopic magnetron) to be designed different than standard hot cathode magnetrons. The same design principles can be used taking into account the arc differences in the ejected electrons from a cold cathode versus a hot cathode. This may seem minor at first but in fact it would cause the isotopic magnetron not to work correctly if not considered. From a technical point of view the terms anode and cathode come from tubes with a hot cathode or filament. One also has the word anode in a tube that implies that it will have some type of voltage impressed upon it. In the case of an isotopic magnetron, the anode may or may not have a voltage on it. And in the case of the cathode there may or may not be voltage impressed on it either. The isotopic magnetron is in fact a very different type of device from a standard cathode filament magnetron. In the inventive device current flow can only be measured from the particles coming from the isotope. An amp meter connected to the isotope and anode of the device would in fact produce an incorrect result. Herein lies a major difference between regular magnetrons using a power supply and magnetrons using an isotope. In some cases one will need a power supply only to start the nuclear magnetron since in production the magnets are added last. By adding magnets last the electrons from the isotopic cold cathode can cause a buildup of an electrical charge on the anode block of the device. If both the anode block and isotopic cold cathode have the same amount of charge the anode block will not allow electrons to flow toward it. By adding a power supply from the anode block to the isotopic cold cathode and applying a current you allow the excess charge on the anode block to be reduced and for the electrons to flow from the isotope to anode block. The voltage used must be about the same as the isotope produces or the voltage that the magnetron requires to start. These two start values can be quite different due to the impedance of the cold cathode isotope. Lindner (U.S. Pat. No. 2,517,120) teaches how to calculate an isotope's impedance. The power supply must be of sufficient current to at least match the isotope current used in the device. The same can be said for alpha particle isotopic cold cathode magnetron devices. The only difference is the power supply polarity must be reversed due to the nature of the isotope having a positive charge. See FIG. 24. The start time of the magnetron using a power supply may require several seconds to several minutes for the fields to form. But once started the device will continue to run until the flow of electrons from the isotope is stopped or the isotope runs out of electrons (an half life of the isotope or more). In most cases, once started you can remove the power supply from the device. Once the power supply is removed the majority of emitted electrons from the isotope are converted to RF or they become fall back electrons (see FIG. 13) that are removed by the concentric grids in the present magnetron. If the grids are absent in the device of the isotopic cold cathode it can be grounded to eliminate an excess of electrons falling back. (See FIG. 13) In most cases, the anode is isolated using an RF choke (inductor) but the electrical connection can be grounded once the device is started, allowing the anode block not to acquire a build-up of electrons that would stop emission from the cold cathode. The same can be said for an alpha particle device magnetron. If the device is sufficiently large with large amounts of isotope you may not need a power supply to start the device, but keeping the device turned-off may be a problem. In this case one may need concentric grids to absorb the electrons being given off by the isotope or to limit the interaction space velocity. See FIGS. 25-28, using a closable stop switches 477-480. Based on the information above, one should not consider the present device as a standard hot cathode magnetron. The concentric grids 462/463 in the interaction space of the invention patent are for power control of the isotope 12/412A to adjust its particle speed and velocity. See FIGS. 22, 29 and 30. This may also effect how the isotopic magnetron works with particular frequency inputs and power outputs. With a bias resistor 481 or 482 added to the grid or grids one can control some of the speed and flow of particles from the isotopic cold cathode. One should also note that a standard hot cathode magnetrons does not have concentric grids around the cathode, whether it is a point contact type or doughnut type magnetron. By definition a magnetron requires at least four resonators and a real space-charge wheel. Those with less than four resonators are nothing more than RF tubes and not considered a magnetron even if they use a magnet to control the flow or angle of electrons. In almost all cases one requires some kind of power grid 462/463 around the isotope to stop operation of the device if needed, as seen in FIGS. 17 and 18 and FIGS. 20-21. These grids stop or retard the flow of particles from the isotope or short the power of the isotope to ground or stop it from reaching the anode block. Or they may short the particles to the anode by bypassing the magnetic field in the magnetron. As a secondary function, the grids may also be made to limit the amount of secondary emission causing heating of the isotopic cold cathode from particle fall back. Magnetrons are primarily designed to work around a set of very narrow frequencies. They are, for the most part, not considered to be a wide band device. However, one can design them to work over many different frequencies, over a wide band but used only in a very small segment of frequencies in that band. In this invention are different types and styles of magnetrons used in standard operation modes but all of these devices, if converted to an isotopic cold cathode, would require modification for each type to work optimally. Computer programs today now can do most of such calculations. But one still must consider the geometry of the path of instant acceleration electrons (beta electrons) to make the device work optionally. The operational voltage range of the space-charge wheel 131/231/431 can vary from 1000 volts to nearly one million KV (1 MeV) per the particle range used by the space-charge wheel, as set by the design of the isotopic magnetron. See FIG. 17, showing an arms 447 of the space-charge wheel 431 turning. The impedance 485 of the arms is also represented in FIG. 32 which is an approximation of an electrical configuration equivalent of the present isotopic magnetron. One can see in FIG. 31 that a hot cathode device is different in operation and therefore has a different electrical equivalent circuit. Based on all information provided above it is apparent that an isotopic magnetron must be designed much differently from a hot cathode magnetron. The operation, to a large degree, of any magnetron device depends on how it is designed. Devices that operate at 20 KVa may operate as high as 50 KVa or as low as 10 KVa. A small or low voltage device may generally operate at 4 KVa but can function down to 1 KVa and up to 6 KVa. That is, these devices can be built for a large range of voltages. A 500 KVa device is not uncommon in magnetron design and is well suited for lower high voltage isotopes in the 100 KV to 500 KV range. Most pulsed magnetrons can be run in a CW mode (continuous wave) at reduced power. But, CW magnetrons cannot be run in pulse mode because, in most cases, the fields take too long to form. The microwave oven is a prime example of a CW magnetron that is designed without point contact magnets. This type of magnetron runs as a CW type magnetron with high power. Although X-rays are produced in some regular high voltage external powered magnetrons, extra caution should be taken in building a nuclear magnetron. Alpha Particle Systems Alpha particles in a cold cathode magnetron present other issues that are not generally apparent. Standard hot cathode magnetrons in fact can't produce alpha particles. The isotopic magnetron however can use and produce alpha particles but using a different isotope than for beta electrons. All things being equal in general design terms of a magnetron, the space-charge wheel of alpha particles will spin backwards or in the reverse direction of beta particles. See FIGS. 18 and 21 and elements 472/488 which show the arms 447A and rotation of the space-charge wheel 431A, and how it is reversed compared to FIGS. 17 and 20. The alpha particle is about 7300 times the mass of a beta particle and has 3.2×10{circumflex over ( )}-19 Coulombs of charge where as an electron has 1.60217657×10−19 coulombs of charge. That is an alpha particle, the mass and charge of about four protons, having the atomic weight of helium. This means that an alpha particle can and will produce about two times the power of a beta magnetron, based on the rate of emissions by the isotope and if the emission speed of the alpha particles were equal to that of beta particles for the same design parameters of the magnetron. The downside of use of alpha particles is they induce more damage to structures inside the magnetron because of their greater mass. But with present technology it is possible to use alpha particles in a nuclear magnetron that would work for many years. Note that Okress (U.S. Pat. No. 2,492,313) and La Rue (U.S. Pat. No. 2,922,075) show point contact type magnetrons. In a general sense, if a design requires substantial power from the device and in a point contact application, only alpha particle isotopes would be of use due to the small available size of the isotopic cold cathode area. This is not to say that beta isotopes could not be used in a point contact design, but for more power the alpha particles are a better choice. Cathode area and size is the main constraint to power in a nuclear magnetron. For example, Kato (EP Patent 2,237,304) teaches magnetrons using large cathode size elements in high power applications. Similar types of magnetrons are also useful with a nuclear isotope as a power source, although the frequency values may differ from a standard magnetron due to the isotopes used. In FIGS. 17 and 22 are shown further embodiments of a magnetron 400 which resembles the embodiment of magnetron 100 (see FIGS. 3, 4, 6 and 10) in that it is also a slot magnetron including, particularly, slots 426, cavities 427 therebetween, a radial cross-sectional geometry defined by housing 416, an isotope cathode 412, and interaction space 428. The embodiment of FIGS. 17 and 22 however differs from that of magnetron 100 in its use of concentric grids 462 and 463, more fully shown in the vertical axial cross-sectional view of FIG. 22. In this embodiment, a single grid 462 may be employed which projects upward from a dielectric or inert rigid surface 461. As another option, a second grid 465, technically a part of a composite first grid, projects downwardly from upper dielectric or inert surface 464 as a result of such an appropriately biased grid 462, which may include said upper grid 465 disposed at a like radius from cathode 412. The path of high energy electrons 15 may be confined to an opening 467 between the teeth of the upper and lower grid and, more importantly, the velocity of said electrons may be retarded for purposes of optimizing the curvature of circular rotation thereof within interaction space 428 and, as well, of reducing the energy of electrons 15 to a level which is more practical to use within magnetron 400, that is, that will cause less damage to the physical structure of the device than would unretarded electrons. Where an additional level or degree of control of electron path and velocity is considered necessary, a second concentric lower grid 463, may be employed and a similar, but downwardly projecting grid 466, may be added. In this embodiment, the interaction space is the annular region 428 which is outward of the outer biasing structure 463/466 but inward of stubs 426 of the magnetron. Further shown in FIG. 22 are upper and lower magnets 420 and 422 respectively. Design of Space-Charge Wheel The space-charge wheel 131/231/431 (see FIGS. 10, 11, and 17-21) is complex to design because it must take into account the interaction space 428, the isotope's impedance, the magnetic field strength and the number of resonators 427. Note that this wheel acts differently in some respects from that of the normal hot cathode magnetron due to the fact that the arc angle of the instantaneously accelerated beta electrons (or alpha particles) used in the space-charge wheel 431 causes the rotational speed to be different due to the nature of the acceleration of the electrons emitted from the isotope. The arcs of the emitted electrons 471 from an isotope change the wheel's speed rate since they are instantaneously accelerated electrons in a magnetic field. This may seem trivial but in fact may stop the nuclear magnetron from working if the spacing of the space-charge wheel spokes 447 and interaction space 428 are not taken in account. The wheel 131/231/431 may spin too fast for the resonators 427 and this relationship could stop them from working or may affect the amount of output power the isotopic magnetron can produce. The space-charge wheel speed can be controlled in several ways, the most obvious method being to add a non-ionizing fluid 483 to the interaction space 428 in the device to slow the wheel down as needed. FIG. 19 indicates fluid 483 added to the interaction space. This fluid can be pressurized to different levels inside the device to adjust its speed. The second method is by using a concentric grid system (FIG. 19, grids 462/463) in the device to slow down the particles' emission speeds. If using alpha particles verses beta particles, the added fluid will change the speed quite a bit as the alpha particles are 7300 times more massive. It is at the space-charge wheel's spokes 147/247/447 that the impedance matching for the resonators must take place. As with all resonators they have impedance and each spoke (singular) should match the impedance of each resonator 427. If one knows the quantity of beta electrons emitted by the isotope, one can approximate the total current. If one knows the number of spokes in the space-charge wheel of the device, one can divide that current into equal parts to match the number of spokes in the space-charge wheel 131/231/431. Since we know the isotope's voltage and/or speed of the electrons impacting the concentric grids, this gives us an approximate impedance for each spoke in the space-charge wheel (see FIGS. 17-22). The resonators in an isotopic magnetron will generally be very different in impedance from a standard hot cathode magnetron. This is due to the fact that hot cathodes generate huge numbers of electrons in a small area of the hot cathode, whereas isotopes in most cases generate much smaller numbers of more energetic electrons for the same amount of area used by a hot cathode. What can be said about the beta-electron space-charge wheel can also be said for the alpha particle space-charge wheel. With all things equal in design, the alpha space-charge wheel 431A will rotate backwards from the beta space-charge wheel because of the positive charge on the alpha particles. See FIGS. 18 and 21. With all other parameters equal, alpha particles will have different impedance spokes on its space-charge wheel 431A and require resonators that match that impedance due to the change in size of the particles and the amount of charge they have. Since its size is 7300 times larger, so is its charge. When addressing the space-charge wheel the concentric grids 462/463/466 (FIGS. 17 and 22) must be taken in account. Depending on the design, the concentric grids can interact with the space-charge wheel in two ways. The space-charge wheel can operate in the area from the isotope cathode to the anode block as part of the standard rotational interaction space 428 including the concentric grids. Or the space-charge wheel 431 can operate in the area from the outermost edge of the concentric grids to the anode block as seen in FIGS. 17 and 20, meaning that the space-charge wheel starts at the outside of the concentric grids and ends at the anode block 416. Only this part of the interaction space 428 is used for the space-charge wheel when the concentric grids are tightly spaced as to not allow the space-charge wheel to form beyond or behind the concentric grids, thus creating another embodiment of the isotopic magnetron because the operation of the space-charge wheel is then somewhat different in its position and rotation. Again, the space-charge wheel rotational speed will differ as will other parameters associated with it. Since no hot cathode magnetron has “concentric grids” this is a new embodiment of magnetron. Standard magnetrons with hot cathodes have a current flow that can be measured through the cathode. From an electrical engineering perspective, this is a closed loop current device producing RF energy at some frequency. See FIG. 21. The inventive isotopic magnetron is not a closed current loop and it would not be apparent that an isotope would work in this such case because of the lack of standard type tube current loop in the device. The fact that resonators have an oscillation current loop and convert the energy from the particles is why my device works as it does. In fact, the cold cathode (nuclear isotope) is what is known as a mass reduction emission, giving off beta electrons or alpha particles, but having no current loop like a standard hot filament tube. That is, the isotope's mass is reduced by the W force process as it emits quarks. This is a major difference between the two embodiments, an isotopic magnetron and a hot filament magnetron. Further, an isotope's half life will, at the end of its first half life, produce about half the amount of emissions as it does when it is new. This affects many parameters of the device, the space-charge wheel being one of them and this, in turn, affects the impedance of the resonators of the anode, all of which need to be addressed at the start of the design process for optimal results. The space-charge wheel's speed is generally determined by the voltage from the isotope that is applied in the interaction space of the magnetron. If the voltage from the isotope increases, the space-charge wheel's speed (angular velocity) will increase or, as the voltage goes down, the speed will decrease. At the same time the particles, or emissions, from the isotope will bunch up because of the resonators reaction to spinning fields of particles and the magnetic cross section of the field reacting with the resonators. See discussion of FIGS. 11 and 13 above. All this is standard magnetron theory of space-charge wheels at this time. When the space-charge wheel is running it also performs another function, that is, the bunching of particles produces an averaging effect of different speed particles. Lower voltage particles are somewhat speeded-up and higher speed particles are somewhat slowed-down. This effect occurs due to the interaction of the magnetic and static fields of the particles and their repelling of each other because of their like fields. This causes the bunching and averaging effects to happen as the space-charge wheel passes the anode poles 29/129/229 in the device. The interaction spaces in the isotopic magnetron can accommodate voltages between 1000 volts and 1 million volts (1 MEV) between the cathode, with or without concentric grids, and the anode block. It is the interaction space 428 where the space-charge wheel forms. See FIG. 17-21. However, this is just the breakover voltage range for the correct operation of the resonators 427 to function in the isotopic magnetron. See FIG. 32. An isotopic cathode may have even higher values of isotope voltage than is used in the space-charge wheel range, above, depending on if the cathode has any insulators or conductive coating on it. These coatings, or particle insulators, may retard or limit the voltage and/or slow the particles down coming from the isotope, which is desirable in may applications. The concentric grids may also slow down or adjust the impedance of the space-charge wheel as needed to make the magnetron function correctly. Since the magnets that are used with a magnetron are subject to variations, aging, and loss of field strength, one may also use the biasing of the concentric grids as an adjustment to the space-charge wheel 431 for correct operation as the magnetic field changes to help in changing the geometry of the moment arms of the particles. All magnetrons exhibit what is known as a threshold current V1. This is the current flow from the isotopic cold cathode, or a hot cathode, that allows the magnetron to operate without shutting off. This means one needs a threshold of charge or certain number of electrons/particles emitted by the isotope or hot cathode to define enough electrons to form a fully functional space-charge wheel and to make the resonators 427 operate correctly. This should be considered the V1 low voltage point of the magnetron. The space-charge wheel, if it were of alpha particles, would have the same design criteria applied to it even though they would turn in the opposite direction from beta electrons with all things being equal in the design. See FIGS. 18, 21 and 26. Because of the VI law point, a magnetron can operate without an RF impact to one or more anode cathode cavities at another location. Cristea (see Background of the Invention) assumes by adding more resonators you get more power. This, in fact, is a poor assumption. Adding more resonators in some cases will decrease the power from the device due to impedance factors in the space-charge wheel being changed and may even stop the device from working. Cristea was mistaken in this case and did not fully understand magnetron design nor did he mention space-charge wheels or how they work. The output port 41 is based on standard magnetron principles and its selection is based on frequency bandwidth and the internal design of the magnetron. See discussion of output port 41 and waveguides 42 above, per FIGS. 1-2. All circuits must have a closed current path. However, the isotopic magnetron defies this rule, making it more difficult to understand: isotopes (cold cathodes) do not have a current path as such. From a technical point of view the current path happens at the moment of decay of a quark of a beta or emission of a helium particle in an alpha isotope. There exist physical limitations on the size of a magnetron that can be built due to losses in the device that exist at microwave frequencies. This limits the interaction space and the mass of the isotope that can be used. The frequency of the device also has a bearing on its size. This however does not affect its power. There exist devices that are 6 to 15 inches high and at least and 8 inches wide that produce 50 Kw of CW power that are water cooled, in the 2.4 GHz band, using regular hot filament magnetrons. This is not to say that in the future with new materials that the interaction space could not become bigger in an isotopic nuclear magnetron device to allow for more power. That, the size and power of the magnetron of the inventive device is set by the engineering limits of its materials and frequency. Isotopic Cold Cathode Emissions Some assume that cold cathodes and hot cathodes emit electrons in the same way. This is not true and is one of the more interesting things about a cathode isotope. Its emissions can occur at any angle provided it is not emitting into the material holding the isotope and/or parts of the mounting for the isotope. Particles that do this are just losing energy and/or turn into X-rays, gamma-rays or secondary particles with less energy. This is why some may wonder why a cold cathode works. If one assumes that all angles around the isotope total 360 degrees, then the vector sum of emitted particles is also zero. This is the same result as if one were using a hot filament cathode in a standard magnetron which entails an assumption that all electrons come off a planar hot cathode in the form of parallel electrons. That is, only at the moment of acceleration do the electrons assume a field-defined trajectory toward the anode block. Until that point they do not have any path. One may want to place some mechanical restrictions on or about a cold cathode to help aim the emitted particles in a way to increase the efficiency of emission. This is not to say that the device would not work without aiming the particles, just that the efficiency of the inventive device can be improved. This too is very different from how a hot cathode magnetron works with its current-like flow of electrons from the cathode to the anode block. Hot cathodes produce a type of self-aligning flow of electrons because of the electrical charge (bias) at the anode and the fact that the electron starts from a neutral position in the hot cathode, is aimed at the anode block during its acceleration period, and is within a uni-directional E field. None of this self-aligning flow of particles occurs in a cold cathode magnetron. Therefor one may want to improve the particle emission by using mechanical means to enhance alignment flow of particles in such a device. I note that in both the isotopic magnetron and hot cathode magnetron, once the electrons are emitted and/or accelerated, the space-charge wheel disrupts the angular flow of particles. And in both cases, only the number of particles and the energy level (speed) of the particles matters in the basic design. Particles from a nuclear cold cathode that don't produce a backward flow to the space-charge wheel are better than ones that do. One might think that this would stop the cold cathode magnetron from working but in fact the magnetic field at the cathode always sends the majority of its particles in the correct direction at the time of emission. Some of this relates to the arc moment length. That is, the magnetic field will send the particles in a radial direction but subject to the ExB vector when the electrons are emitted from the isotopic cathode. By having the space-charge wheel form on the outside of the concentric grids one can eliminate any back flow problem of particles in the inventive device. Or one can design the isotopic cold cathode with mechanical limits (e.g., particles guides) to limit particles' back flow or preventing turning of the space-charge wheel in the reverse direction. One can see from the statement above that back flow particles can be mitigated with more anode pole surfaces in the design, as in a space-charge wheel. This is less of a problem with back flow particles because the space-charge wheel interacts with the back flow particles as it turns, producing an averaging effect as noted above. This inventive system is considered to be a power production device to convert high voltage electrons (beta or alpha rays) to usable RF (radio frequency) energy. See FIG. 41. By using RF one may produce voltages in the lower ranges that are good for powering integrated circuits. One can do this by attaching an RF to DC converter to a power port 941 of the magnetron or making it as part of the magnetron. One might also be able to use such high power RF for other uses such as part of a drive for ion drives for spacecraft. And other things set forth herein in other sections. The power conversion process for the RF to DC voltages takes the form of an RF transformer 990 with RF rectification by diode 992. Apparently impedance matching 942.1 and 942.2, 942.3 are provided at outputs of the transformer, e.g., microstrips or strip line. The RF is coupled to the port 941 of the isotopic magnetron and into the port of the RF transformer. The ratio of windings or elements in the RF transformer allows the RF to be changed to the desired operational voltage and rectified to a DC voltage set forth by the coupling ratio of the RF transformer. The RF rectifiers (RF diodes) 992 produce a high frequency rectified DC voltage 994 thus producing a voltage that is usable for integrated circuits. Associated filtering and voltage regulation control may also be required. All of the DC conversion preceding may be a part of, or integrated into, a magnetron. Or it could be external to the magnetron as a separate section or have several different power conversion sections attached to the port of the nuclear magnetron. One having microwave design experience would understand, and have knowledge of how, this process works as there are numerous types of designs for this. Again this is left to the engineer as to what will work best for one's design based on frequency, power and size based issues. I simply state and show some examples of this power conversion herein. Since RF energy has many uses that are too numerous to name I have set forth examples herein for some of those uses. In some cases where large power conversion may be required the Cyclotron Wave Converter, an example of which is set forth in the Journal of Radio-Electronics, No. 9, 1999, entitled “High Power Converter of Microwaves” would be a better option to produce higher current values and larger voltage ranges. The Cyclotron Wave Converter is a “single frequency” type of converter for RF energy and is not designed to convert wide band RF. From an engineering point of view the Cyclotron Wave Converter does not seam like a good match for the nuclear magnetron as a power converter because of the frequency shift and noise produced by the nuclear magnetron. But there are ways to lock the two devices to the same frequency. Farney (U.S. Pat. No. 5,084,651) teaches several different methods to lock a hot cathode magnetron to a frequency. By using Farney's method we would be able to lock the nuclear magnetron to a single frequency and applying these same methods to the Cyclotron Wave Converter, we also would be able to lock the Cyclotron Wave Converter. However, Farney says nothing about using his invention with an isotopic nuclear cold cathode in a magnetron or a Cyclotron Wave Converter. One also might link, or tie together, any number of isotopic magnetrons though a power combiner and run them all into a single Cyclotron Wave Converter for better efficiency or increased power. Again, the device would have to be frequency locked using Farney's or some other method. The Cyclotron Wave Converter locking method is not shown in this invention patent but the techniques are known in the art. Nuclear magnetron with Cyclotron Wave Converter. With reference to FIG. 33, there is shown a further embodiment 500 which comprises a Mayan pyramid-like structure having a number of discreet layers, each representing a separate magnetron and each consisting of the above-described three basic layers, namely, an upper magnet having a first magnetic polarity, an anode block, and a lower magnet of opposite magnetic polarity. Accordingly, each of the vertical layers of the embodiment of FIG. 33, denoted as layers 516A, 516B, 516C, 516D, 516E, and 516F are understood to include each of the above-described three basic layers of the inventive system, above described with reference to FIGS. 1-14. The embodiment 500 however differs in its use of a single cathode 512 which is shown as a single vertical rod in FIG. 33. This embodiment is also characterized by its use of a polar or horizontal slit in a grid which slit may repeat in a circular pattern about each of the constituent layers of FIGS. 16A-16A. In other words, slits 567 thru 572 each exhibit a different length or polar dimension, one purpose of which is to limit the integral of the energy of electrons that can escape through a given grid slit 567 thru 572 of a particular one of said layers 516A thru 516F. The rationale of this approach is to limit or control the total energy of a given group of emitted beta decay electrons to one which is suitable to the geometry and other operating parameters of the particular magnetron within each of said layers 516A thru 516F. Also, the energy of individual electrons which can escape through a given grid slit 567 to 572 is also affected by the strategy that the ExB vector will cause greater electron curvature (see FIG. 1) in the case of more energetic electrons. In view thereof, the topmost layer 516F and its corresponding small slit grid 572 would block more high energy electrons (because of their greater curvature) than would be the case at the other layers having larger slits. Conversely, where a cathode possesses an isotope which is weak in terms of either density of electron emission, position on the beta energy spectrum for that isotope, or in terms of mixture of the isotope with a non-isotope, for example for purposes of radiologic safety, then a layer 516A-E having a larger slit than slit 572 respectively, may be selected. It is to be appreciated that each of the individual layers of the embodiment of FIG. 33 may be produced or provided individually. It is however believed that applications exist in which it is more efficient to match a given anode geometry with a given emission velocity, density, energy integral, or E×B curvature, with the microwave outputs of different structures tied together to the intended load, rather than used individually. Shown in FIG. 34 is a further embodiment 600 of the present invention This embodiment, like that of FIG. 19, employs a common anode rod 612 upon which are stacked groups 601 of a lower magnet 620, an anode block 616A, and an opposing magnet 622. Each group 601 is separated from the next successive group by a magnetically insulating layer 623. In this embodiment, as with the other embodiments above described, a dielectric 660 may be inserted within either or both the interaction space of anode block 616A or the anode cavities 627 of the anode block. These dielectrics, wherever positioned, may be tunable, as is known in the art of dielectrics, as taught in U.S. Pat. Nos. 6,774,077 and 7,060,636. The significance of use of a dielectric (in this case could be some noble fluid or liquid under pressure, the commonly used fluid is argon fluid under pressure) in the interaction space is that the extreme velocity and momentum of the beta decay electrons may be mediated and more readily adapted in radius of rotation about the cathode within the interaction space to achieve objectives of improved life of the structure and, where the dielectric is used within the anode cavities, to tune the LC equivalent circuit (see FIG. 9) of the cavity resonators to produce microwaves of optimal frequency for a given application and for impedance matching to a wave guide or other system output. A simpler view is that slower electrons produce better efficiency in the resonators, where design constraints exist. This is an impedance type matching tool used to better match the resonators to the electrical characteristics of the emissions from the isotope. In FIG. 35 is shown a flattened polar sectional view, as indicated by curved arrows 24-35 in FIG. 34. FIG. 35 thereby shows that within a given segment 617 of anode block 616A may exist a plurality of cavities 627A-627E, each having an axis which is co-linear or parallel with the B vector of opposing magnet layers 620 and 622 (see FIG. 34). It is to be appreciated that said anode block 616A may be printed upon a flexible integrated circuit (IC) substrate as may be anode surfaces 629 between each of said anode cavities 627A-627E. After printing, the structure shown in FIG. 35, it is simply bent into the annular form, as reflected in all embodiments of the invention. In this process, dielectric material 660 may be disposed within the interior radius of the anode block 616A when it is bent about cathode rod 612, or printed on the IC substrate. In this embodiment, the properties of dielectric 660 may be electronically modulated through the use of circuit chip to optimize the above discussed characteristics of electron emission, density, curvature and effective LC parameters of the anode cavities 627. As may be noted in FIG. 36 single anode block 617A, whether in the context of the embodiment of FIG. 34 or in connection with any of the other embodiments above, may employ anode cavities of differing cross-sectional geometries, for example, the geometries of cavities 627A, 627F, 627G, and 627H. Such different geometries will of course produce significant differences in microwaves resultant from them and will also affect the rotation of the election cloud within the interaction space. FIG. 36 also shows anode surfaces 629A separating the respective anode cavities. FIGS. 37 and 38 show that the durability, that is, effective life of the magnetron in any of the embodiments of the invention may be improved through the deposition of a highly durable material, such as industrial diamond or carbon 670 or 672 respectively upon the surface of anode cavities 670 or 671 respectively, shown in FIGS. 37 and 38. The deposition of such surfaces of a non-reactive material including carbon, silicone, titanium, or composites thereof will considerably increase the effective life of the anode structure relative to the system of Brown and others. In other words, maintaining of the smooth surfaces and geometric integrity of the magnetron, once properly tuned, is an essential aspect of the practice of the present invention. With this aspect in mind one should understand that diamond would also change the impedance of the resonators and greatly improve the life of the device with only a couple molecule layers of diamond added to the devices resonators and interior walls that are exposed to the electron or alpha flow in the device. This would be a great improvement what would other wise be almost impossible to achieve with a standard industrial magnetron that is build with silver on copper or copper iron type magnetron. In using a diamond coating 670 OR 1070 (see FIG. 42) or coating of nanocarbons meeting high heat conductive factors, such as C60 buckyballs as part of the anode block in this way as part of the cavities 246 we can conduct heat from the magnetron 1001 at near the speed of sound, through diamond heat conduction path 1004, allowing for a small device to produce more power than it normally could because of the high rate of heat transfer that diamond allows for. This would be a benefit to builders of magnetrons that require better heat flow and reduction of the heat that is applied to the magnets allowing for better magnet life since high heat can reduce a magnet's strength or life over time. One should understand that diamond and types of man made carbons also can produce these high heat transfer effects. See FIG. 42. The magnetron, preferably, is also immersed in heat sink 1006, to assist the heat gradient out of the magnetron. In FIG. 39 is shown a schematic of a further embodiment 700 of the invention in which a polar array of antennae 727 are used as a functional equivalent of said anode cavities. Therein, a cathode 712 emits beta decay electrons 12 which, as in other embodiments, rotate within an interaction space 728. However, the resultant obtaining electron cloud induces the above-discussed LC values and excitation to antennae 727, as opposed to said cavities 27/127/227/327 of the other embodiments and induces positive and negative polarities. These polarities are strapped together by strapping means 730 and 732. Said antennae will resonate in like fashion to said cavities. Said strapping is used for purposes of phase lock, amplitude control and communication of output 725 to an optional power port, wave guides (not shown), and a power combiner 760. It is to be appreciated that the principles of the present invention are equally applicable to use with a cathode characterized by the emission of alpha or gamma particles, providing appropriate shielding exists in the case of gamma radiation. While there has been shown and described the preferred embodiment of the instant invention it is to be appreciated that the invention may be embodied otherwise than is herein specifically shown and described and that, within said embodiment, certain changes may be made in the form and arrangement of the parts without departing from the underlying ideas or principles of this invention as set forth. |
|
047042451 | abstract | Ability of ion adsorption apparatus such as a desalting unit, etc. as used in an atomic power plant is continuously monitored, and any deterioration in the ability is detected in advance by a method and an apparatus for monitoring a break in an ion adsorption apparatus by detecting a break point of the ion adsorption apparatus using ion exchange resin, thereby determining a timing for regenerating or exchanging the resin, which comprises making an ion species having a weaker selective adsortability to the ion exchange resin as a sampling ion species than that of a target ion species to be adsorbed and present in water to be treated, and detecting leakage of the sampling ion species at the downstream side of the adsorption apparatus, thereby determining the break point of the ion exchange resin. |
049869604 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is generally related to fuel elements for nuclear reactor cores and, in particular, to a holddown spring arrangement for securing fuel assemblies in the nuclear reactor core. 2. General Background Typically, a nuclear reactor for the generation of electrical power includes a core of fissionable material to heat a coolant flowing up therethrough. The fissionable material is enclosed in elongated fuel rods assembled in a square array called fuel assemblies. The fuel rods are held in spaced parallel relationship by a number of spacer grids distributed at intervals along the length of the assembly. The fuel assemblies are held in an array by core grid plates at the top and bottom and are provided with upper and lower end fittings for mating with the grid plates. Typically, hold down spring means is provided between the upper end fitting and the upper core grid plate. This is necessary to provide sufficient hold down force against hydraulic lift forces in the core generated by coolant flow. The springs also allow for axial dimensional growth of the fuel assembly due to either differential thermal expansion or irradiation induced material change. The problems of design, therefore, are in the ability to provide sufficient hold down force against hydraulic lift while allowing sufficient room for growth. Sufficient material strength and stiffness must be available within a limited volume area. The stiffness/volume efficiency of a spring becomes very important when used for nuclear fuel hold down. Known devices which address this problem include the following. U.S. Pat. No. 4,551,300 entitled "Nuclear Reactor Fuel Assembly End Fitting" discloses an end fitting having a plurality of rigid levers and elastic means in recesses in the end fitting which exert a restoring torque on corresponding levels. U.S. Pat. Nos. 4,072,562 and 4,072,564 disclose the use of torsion bars as hold down means. U.S. Pat. Nos. 4,671,924; 3,801,453; 4,427,624; 4,631,166; 4,420,457; and 4,560,532 disclose the use of leaf springs as hold down means. U.S. Pat. Re. Nos. 31,583; 3,475,273; 3,515,638; 3,600,276; 3,689,358; 3,770,583; 4,076,586; 4,078,969; 4,192,716; 4,208,249; 4,278,501; 4,534,933; 4,551,300; and 4,729,868 disclose the use of a variety of hold down devices including helical springs and are representative of the general state of the art. The known devices leave room for improvement. Leaf springs tend to be stroke limited and often must be ganged to achieve sufficient hold down force. As fuel assemblies are typically only eight inches square, there is generally inadequate dimension available to obtain sufficient flexure of the bar. Helical springs must be positioned to allow access of control rods and are fully exposed to coolant flow which subjects the springs to the dynamic stresses of flow induced vibration. Also, reconstitution of a fuel assembly utilizing the helical spring design is a relatively complex operation. SUMMARY OF THE INVENTION The present invention solves the aforementioned problems in a straightforward manner. What is provided is a two-piece upper end fitting with a spring design which overcomes the limitations of known devices. The lower portion of the upper end fitting is provided with a guide pin at each corner. The box portion of the upper end fitting is slidably received on the pins and retained thereon by suitable means. Hairpin shaped springs are positioned out of the coolant flow along the sides of the upper end fitting. |
040010783 | abstract | A nuclear reactor system is described in which flexible control rods are used to enable insertion of the control rods into guide holes in the core which are distributed over an area larger than the cross section of the control rod penetration in the reactor pressure vessel. Guide tubes extend from the penetration and fan out to the guide holes for guiding the control rods from the penetration to the guide holes. |
abstract | A neutron emitting assembly, which is useful in nuclear reactors and other industrial applications, is made of a major amount of beryllium encapsulating a minor amount of 252Cf, which can be placed in a capsule having end plugs and a holding spring. |
|
042016258 | description | ILLUSTRATIVE EXAMPLE A foil of vanadium measuring 20 by 20 mm in size and 0.25 mm thick was bombarded in a cyclotron with .sup.3 helium ions of 14 MeV energy at an intensity of 500 nA for 60 minutes with water cooling. Ten hours after the end of the irradiation, the vanadium foil was dissolved in 5 ml of 40% nitric acid. The solution was treated with 20 ml of a saturated potassium iodate solution and boiled until the color changed from green to yellow. The solution was allowed to cool, was brought to a pH value of 10 with sodium hydroxide solution and was immediately extracted with 40 ml of a 0.1 m solution of 8-hydroxychinolin in chloroform. The organic phase was washed with 20 ml of an aqueous solution set at pH=10 with sodium hydroxide. The organic phase contained only the desired .sup.52 manganese, while all the other radionuclides produced by the nuclear reaction remained in the aqueous phase. The yield of .sup.52 manganese amounted to 6 .mu.Ci per .mu.Ah(6.2.multidot.10.sup.7 s.sup.-1 /C). The chemical yield of the separation process described was from about 50 to 60% at 24 hours after the end of irridation. the radiochemical purity check carried out with a .gamma. spectrometer showed less than 0.1% .sup.54 manganese and 0.1% .sup.51 chromium, referred to the quantity of .sup.52 manganese produced. Contamination with .sup.54 manganese occurs in the nuclear reaction with the chromium contained in very small quantities in the target material. It amounts (at the start) to about 5.times.10.sup.-6 % per ppm of chromium. When a vanadium foil of technical quality with about 500 ppm of chromium is used, .sup.52 manganese is, accordingly, obtained with about 2.5.times.10.sup.-3 % of .sup.54 manganese impurity; whereas, from a very pure vanadium with 2 ppm chromium content, a product is produced that contains only 10.sup.-5 % of .sup.54 manganese. The .sup.52 manganese dissolved in chloroform as an oxinate complex is useful and easily available as a starting material for the preparation of radiochemical or radiopharmaceutical compositions. The manganese oxinate complex can, of course, be readily converted to provide some other manganese compound for uses of .sup.52 Mn in which the chloroform solvent medium is undesirable. Although the invention has been illustrated with reference to a particular illustrative example, it will be understood that variations and modifications of the illustrated example are possible within the inventive concept. |
claims | 1. An X ray computer tomography apparatus comprising:an X ray emitting unit which emits X rays;an X ray detection unit which is placed to face the X ray emitting unit and detects X rays incident to a detection surface; anda collimator unit which is placed on the X ray incident side of an X ray detector to remove scattered X rays and includes a plurality of collimator plates and a support unit, the plurality of collimator plates being arranged along a predetermined direction, and the support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein:the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further comprises a fourth support member which includes a plurality of fourth grooves for fitting of X ray emitting unit side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates. 2. An X ray computer tomography apparatus according to claim 1, wherein the support unit includes the third support members which are modularized. 3. An X ray computer tomography apparatus according to claim 2, wherein each of the third support members further includes a fifth groove which form the third groove for inserting the collimator plate between the neighboring the third support members when the third support members are arrayed along the predetermined direction. 4. An X ray computer tomography apparatus comprising:an X ray emitting unit which emits X rays;an X ray detection unit which is placed to face the X ray emitting unit and detects X rays incident to a detection surface; anda collimator unit which is placed on the X ray incident side of an X ray detector to remove scattered X rays and includes a plurality of collimator plates and a support unit, the plurality of collimator plates being arranged along a predetermined direction, and the support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein:the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further comprises a fourth support member which supports the plurality of the plates by pressing X-ray emitting unit side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates. 5. An X ray computer tomography apparatus according to claim 4, wherein the support unit includes the third support members which are modularized. 6. An X ray computer tomography apparatus according to claim 5, wherein each of the third support members further includes a fifth groove which form the third groove between the neighboring the third support members for inserting the collimator plate when the third support members are arrayed along the predetermined direction. 7. An X ray computer tomography apparatus according to claim 1, wherein each of the fourth support members further includes a fifth groove which form the fourth groove between the neighboring fourth support members for inserting the collimator plate when the third support members are arrayed along the predetermined direction. 8. An X ray computer tomography apparatus comprising:an X ray emitting unit which emits X rays;an X ray detection unit which is placed to face the X ray emitting unit and detects X rays incident to a detection surface; anda collimator unit which is placed on the X ray incident side of an X ray detector to remove scattered X rays and includes a plurality of collimator plates and a support unit, the plurality of collimator plates being arranged along a predetermined direction, and the support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein:the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further comprises a fourth support member which supports the plurality of the plates by pressing the X-ray emitting unit side peripheries of the collimator plates fitted in the first grooves and the second grooves, are modularized and are provided on the X ray emitting unit side of the plurality of collimator plates. 9. An X ray computer tomography apparatus comprising:an X ray emitting unit which emits X rays;an X ray detection unit which is placed to face the X ray emitting unit and detects X rays incident to a detection surface; anda collimator unit which is placed on the X ray incident side of an X ray detector to remove scattered X rays and includes a plurality of collimator plates and a support unit, the plurality of collimator plates being arranged along a predetermined direction, and the support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein:the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further includes:a fourth support member which includes a plurality of fourth grooves for fitting of the X-ray emitting unit side peripheries of the collimator plates fitted in the first grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates; anda fifth support member which includes a plurality of fifth grooves for fitting of the X-ray emitting unit side peripheries of the collimator plates fitted in the second grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates. 10. An X ray computer tomography apparatus comprising:an X ray emitting unit which emits X rays;an X ray detection unit which is placed to face the X ray emitting unit and detects X rays incident to a detection surface; anda collimator unit which is placed on the X ray incident side of an X ray detector to remove scattered X rays and includes a plurality of collimator plates and a support unit, the plurality of collimator plates being arranged along a predetermined direction, and the support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein:the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further includes:a fourth support member which supports the plurality of the plates by pressing the X-ray emitting unit side peripheries of the collimator plates fitted in the first grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates and along the first supporting member; anda fifth support member which supports the plurality of the plates by pressing the X-ray emitting unit side peripheries of the collimator plates fitted in the second grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates along the second supporting member. 11. An X ray computer tomography apparatus comprising:an X ray emitting unit which emits X rays;an X ray detection unit which is placed to face the X ray emitting unit and detects X rays incident to a detection surface; anda collimator unit which is placed on the X ray incident side of an X ray detector to remove scattered X rays and includes a plurality of collimator plates and a support unit, the plurality of collimator plates being arranged along a predetermined direction, and the support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein:the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;further comprising a fourth support unit which includes slits which support peripheries of the collimator plates on the X ray emitting unit side and allow the collimator plates fitted in the first grooves and the second grooves which face each other to pass through and is provided on the X ray emitting unit side of the collimator. 12. A collimator which is used for an X ray computer tomography apparatus comprising an X ray emitting unit which emits X rays and an X ray detection unit which is placed to face the X ray exposing unit and detects X rays striking a detection surface, and is provided on the detection surface side to remove scattered X rays, comprising:a plurality of collimator plates being arranged along a predetermined direction; anda support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further comprises a fourth support member which includes a plurality of fourth grooves for fitting of X ray emitting unit side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates. 13. A collimator which is used for an X ray computer tomography apparatus comprising an X ray emitting unit which emits X rays and an X ray detection unit which is placed to face the X ray exposing unit and detects X rays striking a detection surface, and is provided on the detection surface side to remove scattered X rays, comprising:a plurality of collimator plates being arranged along a predetermined direction; anda support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit includes the third support members which are modularized, and each of the third support members further includes a fourth groove which forms the third groove for inserting the collimator plate between the neighboring the third support members when the third support members are arrayed along the predetermined direction. 14. A collimator which is used for an X ray computer tomography apparatus comprising an X ray emitting unit which emits X rays and an X ray detection unit which is placed to face the X ray exposing unit and detects X rays striking a detection surface, and is provided on the detection surface side to remove scattered X rays, comprising:a plurality of collimator plates being arranged along a predetermined direction; anda support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further comprises a fourth support member which supports the plurality of the plates by pressing X-ray emitting unit side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates. 15. A collimator according to claim 14, wherein the support unit includes the third support members which are modularized. 16. A collimator according to claim 15, wherein each of the third support members further includes a fifth groove which form the third groove between the neighboring the third support members for inserting the collimator plate when the third support members are arrayed along the predetermined direction. 17. A collimator according to claim 12, wherein each of the fourth support members further includes a fifth groove which form the fourth groove between the neighboring third support members for inserting the collimator plate when the fourth support members are arrayed along the predetermined direction. 18. A collimator which is used for an X ray computer tomography apparatus comprising an X ray emitting unit which emits X rays and an X ray detection unit which is placed to face the X ray exposing unit and detects X rays striking a detection surface, and is provided on the detection surface side to remove scattered X rays, comprising:a plurality of collimator plates being arranged along a predetermined direction; anda support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further comprises a fourth support member which supports the plurality of the plates by pressing the X-ray emitting unit side peripheries of the collimator plates fitted in the first grooves and the second grooves, are modularized and are provided on the X ray emitting unit side of the plurality of collimator plates. 19. A collimator which is used for an X ray computer tomography apparatus comprising an X ray emitting unit which emits X rays and an X ray detection unit which is placed to face the X ray exposing unit and detects X rays striking a detection surface, and is provided on the detection surface side to remove scattered X rays, comprising:a plurality of collimator plates being arranged along a predetermined direction; anda support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further comprises:a fourth support member which includes a plurality of fifth grooves for fitting of the X-ray emitting unit side peripheries of the collimator plates fitted in the first grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates; anda fifth support member which includes a plurality of sixth grooves for fitting of the X-ray emitting unit side peripheries of the collimator plates fitted in the second grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates. 20. A collimator which is used for an X ray computer tomography apparatus comprising an X ray emitting unit which emits X rays and an X ray detection unit which is placed to face the X ray exposing unit and detects X rays striking a detection surface, and is provided on the detection surface side to remove scattered X rays, comprising:a plurality of collimator plates being arranged along a predetermined direction; anda support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;wherein the support unit further comprises:a fourth support member which supports the plurality of the plates by pressing the X-ray emitting unit side peripheries of the collimator plates fitted in the first grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates and along the first supporting member; anda fifth support member which supports the plurality of the plates by pressing the X-ray emitting unit side peripheries of the collimator plates fitted in the second grooves, and is provided on the X ray emitting unit side of the plurality of collimator plates along the second supporting member. 21. A collimator which is used for an X ray computer tomography apparatus comprising an X ray emitting unit which emits X rays and an X ray detection unit which is placed to face the X ray exposing unit and detects X rays striking a detection surface, and is provided on the detection surface side to remove scattered X rays, comprising:a plurality of collimator plates being arranged along a predetermined direction; anda support unit supporting each of the collimator plates along at least three sides thereof in such a manner that a surface of each of the collimator plates is substantially parallel to an X ray incident direction from the X ray emitting unit to the detection surface;wherein the support unit includes:a first support member which includes a plurality of first grooves provided along the predetermined direction, each of the first grooves being formed along the X ray incident direction;a second support member which is placed parallel to the first support unit and includes a plurality of second grooves provided along the predetermined direction so as to correspond to said plurality of first grooves, each of the second grooves being formed along the X ray incident direction; anda third support member which includes a plurality of third grooves for fitting of detection surface side peripheries of the collimator plates fitted in the first grooves and the second grooves, and is provided on the detection surface side of the plurality of collimator plates;further comprising a fourth support unit which includes slits which support peripheries of the collimator plates on the X ray emitting unit side and allow the collimator plates fitted in the first grooves and the second grooves which face each other to pass through and is provided on the X ray emitting unit side of the collimator. 22. An X ray computer tomography apparatus collimator manufacturing method of manufacturing a collimator which is used for an X ray computer tomography apparatus comprising an X ray emitting unit which emits X rays and an X ray detection unit which is placed to face the X ray emitting unit through a subject and detects X rays striking a detection surface, and is provided on the detection surface to remove scattered X rays, comprising:assembling, by using side surface members, a first support unit including a plurality of first grooves formed along an X ray incident direction from the X ray emitting unit to the detection surface and a second support unit including a plurality of second grooves formed along the X ray incident direction from the X ray emitting unit to the detection surface so as to correspond to said plurality of first grooves;fixing, to the detection surface side of the first support unit and second support unit, a third support unit including a plurality of third grooves for fitting of peripheries of the collimator plates fitted in the first grooves and the second grooves corresponding to each other which are located on the detection surface side;fixing the second support unit including slits which allow the collimator plates fitted in the first grooves and the second grooves which face each other to pass through the slits and support peripheries of the collimator plates which are on an X ray incident side to the X ray incident side of the first support unit and the second support unit;fitting collimator plates in the first grooves, the second grooves, and the third grooves upon making the collimator plates pass through the slits so as to support the collimator plates along at least three sides thereof; andbonding the collimator plates to the first grooves, the second grooves, the third grooves, and the slits which correspond to each other. |
|
claims | 1. An X-ray imaging apparatus comprising:a collimator including a plurality of blades to form a collimation area, wherein at least one blade of the plurality of blades is rotatable in a clockwise direction or in a counterclockwise direction;a display configured to display a guide image;an input device configured to receive n (n being an integer equal to or greater than three) number of input points with respect to the displayed guide image; andat least one processor configured to:set a polygon defined by the input points to a window area, and control the collimator to form a collimation area having a shape of the polygon defined by the input points, the collimator controlled to perform at least one movement of a rotational movement and a linear movement of at least one of the plurality of blades to place intersection points of the plurality of blades at locations of the input points, respectively, andcontrol the collimator to form a collimation area of a shape most similar to the polygon defined by the input points, in response to determining that the intersection points of the plurality of blades cannot be placed at the locations of the input points, respectively, by any of the at least one movement of the rotational movement and the linear movement of the at least one of the plurality of blades. 2. The X-ray imaging apparatus according to claim 1, wherein the at least one processor is configured to determine validity of the input points. 3. The X-ray imaging apparatus according to claim 2, wherein, in response to receiving an input point, the at least one processor is configured to determine validity of the input point, and if the at least one processor determines that the input point is invalid, the at least one processor is configured to display a result of that the input point is invalid through the display. 4. The X-ray imaging apparatus according to claim 2, wherein when a distance between a first input point and a second input point among the input points is less than a reference value, the at least one processor is configured to determine that an input point that is last input among the first input point and the second input point is invalid. 5. The X-ray imaging apparatus according to claim 2, wherein when at least three input points of the input points are located on a straight line, the at least one processor is configured to determine that an input point that is last input among the at least three input points is invalid. 6. The X-ray imaging apparatus according to claim 2, wherein when a figure defined by the input points has a concave shape, the at least one processor is configured to determine that an input point that is last input among the input points is invalid. 7. The X-ray imaging apparatus according to claim 6, wherein the at least one processor is configured to determine whether the figure defined by the input points has the concave shape based on whether an order in which a lastly input point among the input points is connected with previously input points is in a clockwise order or a counterclockwise order. 8. The X-ray imaging apparatus according to claim 2, wherein when the at least one processor determines that an input point among the input points is invalid, the input device is configured to receive a new input point that replaces the input point that is determined to be invalid. 9. The X-ray imaging apparatus according to claim 2, wherein when the at least one processor determines that all of the input points are valid, the at least one processor is configured to connect the input points to define the window area in a shape of the polygon. 10. The X-ray imaging apparatus according to claim 1, wherein the guide image includes at least one image among an X-ray image acquired by irradiating a low dose of X-rays on an object before main scanning, a camera image acquired by photographing the object with a camera, and a previously acquired X-ray image of the object. 11. The X-ray imaging apparatus according to claim 10, wherein when the at least one processor is configured to acquire an X-ray image corresponding to the collimation area of the shape most similar to the polygon defined by the input points, and to perform image processing on the acquired X-ray image. 12. The X-ray imaging apparatus according to claim 11, wherein the at least one processor is configured to perform the image processing in such a way to reduce brightness or definition of a remaining area except for the window area in the acquired X-ray image or to cut off the remaining area. 13. An X-ray imaging apparatus comprising:a collimator including a plurality of blades to form a collimation area, wherein at least one blade of the plurality of blades is rotatable in a clockwise direction or in a counterclockwise direction;a display configured to display a guide image;an input device configured to receive n number of a point for the guide image, the n number of the point input by a user, wherein n is an integer that is equal to or greater than 1; andat least one processor configured to set a circle defined by the n number of the point to a window area, to control the collimator to form a collimation area in a shape of a polygon including to the window area, and to perform image processing on an X-ray image acquired by X-rays passed through the collimation area to acquire an X-ray image corresponding to the window area,wherein, in response to determining that the collimator cannot form a collimation area having a shape of the circle defined by the n number of the point, the at least one processor is configured to control the collimator to form the collimation area in a shape of a square of which one side has a length equal to a diameter of the circle defined by the n number of the point. 14. The X-ray imaging apparatus according to claim 13, wherein when two points are input through the input device, the at least one processor is configured to set a circle whose diameter or radius is a straight line connecting the two points, to the window area. 15. The X-ray imaging apparatus according to claim 13, wherein when a point and a straight line starting from the point are input through the input device, the at least one processor is configured to set a circle whose center point is the point and whose radius is the straight line, to the window area. 16. The X-ray imaging apparatus according to claim 13, wherein when a point and a straight line starting from the point are input through the input device, the at least one processor is configured to set a circle whose diameter is the straight line, to the window area. 17. The X-ray imaging apparatus according to claim 13, wherein when a point is input through the input device, the at least one processor is configured to create a circle whose center point is the point input through the input device, and increase a radius of the circle in proportion to a time period for which the point is input. 18. The X-ray imaging apparatus according to claim 17, wherein the at least one processor is configured to set a circle having a radius acquired at time at which the point is no longer input, to the window area. 19. The X-ray imaging apparatus according to claim 13, wherein the plurality of blades are configured to perform at least one movement of a rotational movement and a linear movement. 20. The X-ray imaging apparatus according to claim 13, wherein the at least one processor is further configured to perform shutter processing on a remaining area in the acquired X-ray image except for an area occupied by the circle by the n number of the point or cut off the remaining area, to generate an X-ray image corresponding to the window area. 21. A method of controlling an X-ray imaging apparatus, comprising:displaying a guide image on a display;receiving n number of input points for the guide image from a user, wherein n is an integer that is equal to or greater than 3; andsetting a polygon defined by the n number of input points to a window area, and controlling a collimator including a plurality of blades to form a collimation area corresponding to the window area, wherein at least one blade of the plurality of blades is rotatable in a clockwise direction or in a counterclockwise direction,wherein the controlling the collimator comprises:controlling the collimator to form a collimation area having a shape of the polygon defined by the n number of input points, the collimator controlled to perform at least one movement of a rotational movement and a linear movement of at least one of the plurality of blades to place intersection points of the plurality of blades at locations of the n number of input points, respectively; andcontrolling the collimator to form a collimation area of a shape most similar to the polygon defined by the n number of input points, in response to determining that the intersection points of the plurality of blades cannot be placed at the locations of the n number of input points, respectively, by any of the at least one movement of the rotational movement and the linear movement of the at least one of the plurality of blades. 22. The method according to claim 21, wherein the controlling of the collimator to form the collimation area of the shape most similar to the polygon defined by the n number of input points comprises:acquiring an X-ray image corresponding to the collimation area of the shape most similar to the polygon defined by the n number of input points, andcontrolling the collimator to perform image processing on an acquired X-ray image. 23. A method of controlling an X-ray imaging apparatus, comprising:displaying a guide image on a display;receiving n number of a point for the guide image, the n number of the point input by a user, wherein n is an integer that is equal to or greater than 1; andsetting a circle defined by the n number of the point to a window area;controlling a collimator including a plurality of blades to form a collimation area in a shape of a polygon including the window area, wherein at least one blade of the plurality of blades is configured to be rotatable in a clockwise direction or in a counterclockwise direction;in response to determining that the collimator cannot form a collimation area having a shape of the circle defined by the n number of the point, controlling the collimator to form the collimation area in a shape of a square of which one side has a length equal to a diameter of the circle defined by the n number of the point; andperforming image processing on an X-ray image acquired by X-rays passed through the collimation area to acquire an X-ray image corresponding to the window area. 24. The method according to claim 23, wherein the performing the image processing comprises performing shutter processing on a remaining area in the acquired X-ray image except for an area occupied by the circle by the n number of the point or cutting off the remaining area, to generate an X-ray image corresponding to the window area. |
|
description | This application is a 35 U.S.C. § 111(a) continuation of PCT international application number PCT/US2016/035116 filed on May 31, 2016, incorporated herein by reference in its entirety, which claims priority to, and the benefit of, U.S. provisional patent application Ser. No. 62/169,498 filed on Jun. 1, 2015, incorporated herein by reference in its entirety. Priority is claimed to each of the foregoing applications. The above-referenced PCT international application was published as PCT International Publication No. WO 2016/196521 on Dec. 8, 2016, which publication is incorporated herein by reference in its entirety. This invention was made with Government support under EB014922, awarded by the National Institutes of Health. The Government has certain rights in the invention. Appendix A referenced herein is a computer program listing in a text file entitled “UC-2014-9AC-2-LA-US-appendix-A.txt” created on Nov. 28, 2017 and having a 18 kb file size. The computer program code, which exceeds 300 lines, is submitted as a computer program listing appendix through EFS-Web and is incorporated herein by reference in its entirety. A portion of the material in this patent document is subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C.F.R. § 1.14. This description pertains generally to medical imaging, and more particularly to X-ray computed tomography (CT) systems and methods. X-ray computed tomography (CT) is commonly used in clinical practice. Compared to Magnetic Resonance Imaging (MRI), CT has the advantages of fast imaging speed and fewer contraindications, however radiation is a major concern for patient safety and long term health. In particular, dynamic CT scans such as CT perfusion (CTP) and CT angiography (CTA) involve high radiation dose due to the X-ray source remaining continuously on during the scan period (e.g. one minute). Over recent years, several adverse events of CT radiation overdose have been reported by media, and radiation dose has become a public health concern. The standard CT scan involves continuous rotation of the X-ray source around the patient. According to the Nyquist criterion, a total of π/2*Xres (base resolution) projection views need to be acquired to form one CT image. For dynamic CT scans, the total number of X-ray projection views will be π/2*Xres*Nframe (number of temporal frames, typically 45-60 for CT), resulting in a high level of radiation dose. Accordingly, an object of the present disclosure is CT systems and methods to reduce radiation exposure. An aspect of the present description is low-dose CT imaging system and method that operates according to a pulsed X-ray emission scheme according to a predefined sequence of rotation angles of the X-ray source, along with image reconstruction algorithms to achieve high spatial and temporal resolution for CT scans. The systems and methods involve high speed switching (on the order of milliseconds) to generate pulsed exposure of X-ray radiation to the patient, reducing radiation dose by 4-8 folds or more compared to standard CT scans, without degrading image quality. The systems and methods of the present description allow for body CT perfusion scans that were previously not feasible due to the high radiation dose. In one embodiment, the system of the present description may include hardware and software components, wherein the hardware allows a user to adjust dose reduction via number of projections acquired and obtain projections at predefined sequences of angles that are optimized for the reconstruction software. Novel projection view sharing techniques may be implemented, as well as iterative and/or constrained reconstruction algorithms. Three representative sequences for rotation angles may include, but are not limited to 1) angle-bisect (or bit-reverse); 2) golden-ratio; and 3) pseudo-random schemes. Further aspects of the technology will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the technology without placing limitations thereon. FIG. 1 shows a side-view schematic diagram of a low-dose CT scanning system 10 according to the present disclosure. Low-dose CT scanning system 10 reduces the radiation dose of CT scans by controlling the X-ray source to be on intermittently (instead of continuously) at pre-specified rotation angles. The dynamic CT image series can then be reconstructed using algorithms that preserve high spatial and temporal resolutions as well as image quality comparable to those of standard scans. The CT scanning system 10 comprises a cylindrical enclosure 18 with a plurality of detectors 20 disposed circumferentially in a stationary ring along the inner wall of the X-ray enclosure 18. While a handful of detectors 20 are shown in the side view of FIG. 1, it is appreciated that any number of detectors 20 may be used incrementally along the circumference of the ring. Additionally, a number of rings or rows may be disposed axially down the tube 18. An X-ray source 12 is disposed in the enclosure 18 on a gantry 16 that rotates around the circumference of the inner wall of tube 18. FIG. 1 shows the X-ray source 12 in four orientations (e.g. starting from 12 o'clock to 3 o'clock) in FIG. 1. An X-ray pulse generator 15 is integrated with or attached to the X-ray source 12 to control the emission of X-rays from the source into the enclosure 18. Pulse generator 15 is shown in FIG. 1 as being disposed in front of X-ray source 12. However, it is appreciated that the pulse generator 15 may be implemented within X-ray source 12, as will be explained in further detail below. As seen in FIG. 1, a simplistic emission scenario is depicted wherein the pulse generator 15 is alternating between an off-state at 14a and an on-state at 14b. In the off-state 14a, no X-rays are emitted from the source 12. In the on state—14b, the pulse generator 15 allows X-rays 22 to be emitted into the enclosure 18, passing through the patient 30 for detection by one or more detectors 20 on the opposite wall of the enclosure 18. The pulse generator 15 may comprise different configurations having distinct principles of operation. In one embodiment, the pulse generator 15 comprises a mechanical shutter or lead shield that acts as blinds or a shutter that opens and closes at high speed (on the order of milliseconds) while the source 12 is continuously powered. The shutter is configured to restrict emission of X-rays 22 in the off-state 14a, and opens up to allow emission X-rays 22 in the on-state 14b. In an alternative embodiment, the pulse generator 15 operates via electromagnetic means using the modified X-ray source 80 shown in FIG. 5A and FIG. 5B, described in further detail below. FIG. 2 shows a high-level block diagram of hardware and software components used for the low-dose CT scanning system 50. From the hardware perspective, an existing CT scanner 52 is equipped with a pulse generator 15 for modulating the X-ray emission from the X-ray source 12 within in the scanner. It is appreciated that scanner 52 may be integrated with the pulse generator 15, either with a mechanical shutter built in to the source 12, or via electromagnetically pulsed operation via a modified CT X-ray source 12a/12b shown in FIG. 5A and FIG. 5B. On the software end, computer or server 60 may comprise image reconstruction software 64, synchronization control software 66 stored in memory 68 and operable on processor 62. Synchronization control software 66 contains instructions for operating pulse generator 15, in the form of shutter control commands 56 that control the timing of the pulsing of the X-rays, as will be described in further detail below. Image reconstruction software 64 comprises instructions for taking the output data 54 from the CT scanner 52 and reconstructing the data detected from the pulsed X-ray emission to generate a reconstructed image 70. Synchronization control software 66 is configured to control sequencing of the pulsing as the gantry 16 rotates the X-ray source 12 within the enclosure 18. In one embodiment illustrated in FIG. 3, synchronization control software 66 uses angle-bisect or bit-reverse sequence for the rotation angle at which X-ray exposure occurs. In the angle-bisect or bit-reverse scheme the full projection angles are acquired in an interleaved fashion (A, B, C, D). During the first gantry rotation, only one set of evenly distributed projection angles are acquired at position A (e.g. at 60° intervals). During subsequent gantry 16 rotations, projections that bisect the previous set of projections are acquired (position B intersects previous A positions, position C intersects A to B positions, and position D then intersects B to A positions) until the full projection angles are reached. FIG. 4A through FIG. 4C show various projection orders in accordance with other scanning methods that may be implemented in the control software 66 of the system 50. FIG. 4A shows a standard projection order based on a fixed increment (P=10), or 18° projection increments. FIG. 4B shows a projection order based on the Golden angle increment of 111.25°. In this configuration, the rotation angles of the X-ray source 12 are spaced by the golden angle (180°/1.618=111.25° which guarantees an optimal projection distribution for any arbitrary number of projections used in reconstruction. FIG. 4C shows a projection order based on the Tiny Golden angle increment of 23.62°. In this configuration, the rotation angles of the X-ray source 12 are spaced by the angle 23.62°, which guarantees an optimal projection distribution with the number of projections is greater than 7 for the shown angle increment. Pseudo-random schemes may also be implemented, which are optimized for modern sparse sampling techniques with constrained reconstruction, such as compressed sensing. Referring to FIG. 5A and FIG. 5B, high-speed power switching of the X-ray source 12 may be realized with a pulse generator 15 that operates via deflection of the electron beam off the tube anode using a magnetic field. FIG. 5A shows a schematic diagram of an exemplary pulsed X-ray CT tube 80 in a closed, non-illuminating mode 12a. In this configuration, the griddling electrode 84 is configured to have a high enough negative potential so as to prevent electron flow from the cathode 82, essentially forming an electromagnetic field-based shield or barrier 90 between cathode 82 and anode 86. Production of X-rays is stopped, allowing for pulsed distribution of X-rays into the enclosure 18. FIG. 5B shows a schematic diagram of the pulsed X-ray CT tube 80 in an open, illuminating mode 12b. In this mode, the griddling electrode 84 potential is modified to focus the electron beam 88 on to the anode 86, resulting in generation of the X-rays from the source 12b. To reconstruct the full set of dynamic CT images 70, image reconstruction software 64 may incorporate projection view sharing techniques such as K-space Weighted Image Contrast (KWIC). KWIC may be implemented for any of the angle-bisect scheme (FIG. 4A) Golden angle scheme (FIG. 4B) or Tiny Golden angle scheme (FIG. 4C) for projection acquisition rotation angles of the X-ray source. FIG. 6 shows a diagram of KWIC reconstruction of dynamic CT scanning with golden angle projections. Using KWIC, the central 2DFT space (similar to k-space in MRI), which determines the image contrast, is sampled by the projection views of the time frame of interest (Ti−1, Ti in FIG. 6), whereas the peripheral 2DFT space is filled by projection views of neighboring time frames (similar to view sharing). Therefore, both high spatial and temporal resolutions can be achieved for dynamic CT scans using KWIC for any of the Golden ratio, Tiny Golden ratio, and Bit-reverse schemes, as KWIC preserves undersampled CT image quality by proportionately increasing the number of encoded projections for more distant regions of the 2D Fourier Transform (FT) space. The image reconstruction software 64 employing KWIC is able to achieve a 10 fold reduction of radial projection views compared to standard techniques, which can be translated to 10 fold reduction of radiation dose for dynamic CT scans. Alternative reconstruction techniques may also include compressed sensing. Appendix A shows an example of software code for implementing the CT KWIC reconstruction algorithm, which provides an exemplary configuration of instructions that may be used for image reconstruction software 64. The aforementioned KWIC reconstruction techniques were applied on a FORBILD CT head phantom as well as a clinical CT perfusion data set, resulting in a simulated 4-8× dose reduction while preserving the image quality and quantification accuracy for perfusion parameters. FIG. 7A through FIG. 7D show dynamic, simulated CT phantoms of a 5 mm object (white dot) using standard filtered back projection (FBP) construction with full radiation dose with varying amounts of projections. FIG. 7E through FIG. 7H show dynamic, simulated CT phantoms of the same 5 mm object (white dot) using the CT-KWIC reconstruction with the same varying amounts of projections. The total number of projections per gantry rotation was reduced to obtain down to 12.5% of the original dose. The KWIC reconstruction algorithm preserves image quality that is lost to sampling artifacts in FBP. It is contemplated that even higher dose savings may be possible with refinements to the CT-KWIC reconstruction algorithm used for this demonstration. FIG. 8 shows a graph of clinical CT perfusion (CTP) signal curves of contrast uptake for KWIC at 50% dose, 25% dose, and fully sampled FBP. FIG. 9A and FIG. 9B show relative CBV (rCBV) maps reconstructed using FBP and KWIC, respectively. The temporal fidelity is preserved with up to 25% dose reduction using KWIC. The systems and methods of the present description are shown in a preferred configuration directed to dynamic CT. However, it is appreciated that systems and methods of the present description may be configured for implementation with other CT imaging modalities. The low-dose dynamic CT systems and methods described herein provide for precise CT imaging with substantially reduced dose to patients undergoing CT perfusion and angiographic exams. The low-dose dynamic CT systems and methods may be configured to allow patients to have multiple low dose CTP and CTA exams for more frequent and regular monitoring of their diseases, which could improve patient outcome. Such dose reductions may also allow for body perfusion (e.g. in the liver or kidneys) where it has previously been too high dose to be a viable diagnostic or study option. Embodiments of the present technology may be described with reference to flowchart illustrations of methods and systems according to embodiments of the technology, and/or algorithms, formulae, or other computational depictions, which may also be implemented as computer program products. In this regard, each block or step of a flowchart, and combinations of blocks (and/or steps) in a flowchart, algorithm, formula, or computational depiction can be implemented by various means, such as hardware, firmware, and/or software including one or more computer program instructions embodied in computer-readable program code logic. As will be appreciated, any such computer program instructions may be loaded onto a computer, including without limitation a general purpose computer or special purpose computer, or other programmable processing apparatus to produce a machine, such that the computer program instructions which execute on the computer or other programmable processing apparatus create means for implementing the functions specified in the block(s) of the flowchart(s). Accordingly, blocks of the flowcharts, algorithms, formulae, or computational depictions support combinations of means for performing the specified functions, combinations of steps for performing the specified functions, and computer program instructions, such as embodied in computer-readable program code logic means, for performing the specified functions. It will also be understood that each block of the flowchart illustrations, algorithms, formulae, or computational depictions and combinations thereof described herein, can be implemented by special purpose hardware-based computer systems which perform the specified functions or steps, or combinations of special purpose hardware and computer-readable program code logic means. Furthermore, these computer program instructions, such as embodied in computer-readable program code logic, may also be stored in a computer-readable memory that can direct a computer or other programmable processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the block(s) of the flowchart(s). The computer program instructions may also be loaded onto a computer or other programmable processing apparatus to cause a series of operational steps to be performed on the computer or other programmable processing apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable processing apparatus provide steps for implementing the functions specified in the block(s) of the flowchart(s), algorithm(s), formula(e), or computational depiction(s). It will further be appreciated that the terms “programming” or “program executable” as used herein refer to one or more instructions that can be executed by a processor to perform a function as described herein. The instructions can be embodied in software, in firmware, or in a combination of software and firmware. The instructions can be stored local to the device in non-transitory media, or can be stored remotely such as on a server, or all or a portion of the instructions can be stored locally and remotely. Instructions stored remotely can be downloaded (pushed) to the device by user initiation, or automatically based on one or more factors. It will further be appreciated that as used herein, that the terms processor, computer processor, central processing unit (CPU), and computer are used synonymously to denote a device capable of executing the instructions and communicating with input/output interfaces and/or peripheral devices. From the description herein, it will be appreciated that that the present disclosure encompasses multiple embodiments which include, but are not limited to, the following: 1. A system for low dose CT scanning of a subject, the system comprising: (a) a pulse generator configured to be coupled to an X-ray source of a CT scanner, the X-ray source being mounted on gantry so as to rotate within a cylindrical enclosure of the CT scanner; the pulse generator configured to periodically switch off emission of X-rays from the X-ray source into the cylindrical enclosure; and (b) application software coupled to the pulse generator; the application software comprising instructions to control timing of the pulse generator so as to intermittently expose a subject to X-rays from the X-ray source at pre-specified rotation angles of the gantry. 2. The system of any preceding embodiment: wherein the pulse generator comprises a mechanical shutter coupled to the x-ray source; wherein the shutter comprises an off-state to restrict X-rays from being emitted from the X-ray source and an on-state configured to allow X-rays to be emitted from the X-ray source into the enclosure; wherein the shutter is coupled to the application software to receive said instructions; and wherein the instructions comprise commands for timing the on-state of the shutter and resulting X-ray exposure at said pre-specified rotation angles of the gantry. 3. The system of any preceding embodiment: wherein the pulse generator comprises an off-state to restrict X-rays from being emitted from the X-ray pulse generator source and an on-state configured to allow X-rays to be emitted from the X-ray source into the enclosure; and wherein the pulse generator is coupled to the X-ray source to electromagnetic shield the X-ray source from emitting X-rays in the off-state; wherein the instructions comprise commands for timing the on-state of the pulse generator and resulting X-ray exposure at said pre-specified rotation angles of the gantry. 4. The system of any preceding embodiment: wherein the X-ray source comprises an anode, a cathode and a griddling electrode there between; and wherein the pulse generator is configured to modify a negative potential of the griddling electrode to form an electromagnetic field-based shield so as to prevent electron flow from the cathode the anode, thereby stopping emission of X-rays in the off-state. 5. The system of any preceding embodiment, wherein said pre-specified angles of rotation comprise a sequence of rotation angles selected from the group of rotation schemes consisting of: an angle-bisect scheme; a Golden-ratio scheme; or a Tiny Golden-ratio scheme. 6. The system of any preceding embodiment, further comprising: application software coupled to an output of the CT scanner for receiving pulsed images from the CT scanner, the pulsed images corresponding to exposures at said pre-specified rotation angles; the application software further configured for reconstructing each of said exposures to generate a reconstructed image. 7. The system of any preceding embodiment, wherein the reconstructed image is generated via a projection view sharing techniques. 8. The system of any preceding embodiment, wherein K-space Weighted Image Contrast (KWIC) is used to generate the reconstructed image. 9. An apparatus for lowering X-ray dose to a subject in a CT scanner, the CT scanner comprising an X-ray source being mounted on gantry so as to rotate within a cylindrical enclosure of the CT scanner, and a pulse generator coupled to the X-ray source to periodically switch off emission of X-rays from the X-ray source into the cylindrical enclosure, the apparatus comprising: (a) a computer processor coupled to the CT scanner; and (b) a non-transitory computer-readable memory storing instructions executable by the computer processor; (c) wherein said instructions, when executed by the computer processor, perform steps comprising: (i) controlling timing of the pulse generator so as to intermittently expose a subject to X-rays from the X-ray source at pre-specified rotation angles of the gantry; (ii) receiving pulsed images from the CT scanner, the pulsed images corresponding to exposures at said pre-specified rotation angles; and (iii) reconstructing each of said exposures to generate a reconstructed image. 10. The apparatus of any preceding embodiment: wherein the pulse generator comprises a mechanical shutter coupled to the x-ray source; wherein the shutter comprises an off-state to restrict X-rays from being emitted from the X-ray source and an on-state configured to allow X-rays to be emitted from the X-ray source into the enclosure; wherein the shutter is coupled to the application software to receive said instructions; and wherein the instructions comprise commands for timing the on-state of the shutter and resulting X-ray exposure at said pre-specified rotation angles of the gantry. 11. The apparatus of any preceding embodiment: wherein the pulse generator comprises an off-state to restrict X-rays from being emitted from the X-ray pulse generator source and an on-state configured to allow X-rays to be emitted from the X-ray source into the enclosure; wherein the pulse generator is coupled to the X-ray source to electromagnetic shield the X-ray source from emitting X-rays in the off-state; and wherein the instructions comprise commands for timing the on-state of the pulse generator and resulting X-ray exposure at said pre-specified rotation angles of the gantry. 12. The apparatus of any preceding embodiment: wherein the X-ray source comprises an anode, a cathode and a griddling electrode there between; and wherein the instructions are configured to modify a negative potential of the griddling electrode to form an electromagnetic field-based shield so as to prevent electron flow from the cathode the anode, thereby stopping emission of X-rays in the off-state. 13. The apparatus of any preceding embodiment, wherein said pre-specified angles of rotation comprise a sequence of rotation angles selected from the group of rotation schemes consisting of: an angle-bisect scheme; a Golden-ratio scheme; or a Tiny Golden-ratio scheme. 14. The apparatus of any preceding embodiment, wherein the reconstructed image is generated via a projection view sharing techniques. 15. The apparatus of any preceding embodiment, wherein K-space Weighted Image Contrast (KWIC) is used to generate the reconstructed image. 16. A low dose CT scanner for generating CT images of a subject, the CT scanner comprising: (a) an X-ray source disposed within a cylindrical enclosure; the cylindrical enclosure comprising a plurality of detectors configured to detect X-rays emitted from the X-ray source; the X-ray source mounted on a gantry so as to rotate within the cylindrical enclosure of the CT scanner; (b) a pulse generator coupled to the X-ray source; the pulse generator configured to periodically switch off emission of X-rays from the X-ray source into the cylindrical enclosure; and (c) application software coupled to the pulse generator; the application software comprising instructions to control timing of the pulse generator so as to intermittently expose a subject to X-rays from the X-ray source at pre-specified rotation angles of the gantry. 17. The CT scanner of any preceding embodiment: wherein the pulse generator comprises a mechanical shutter coupled to the x-ray source; wherein the shutter comprises an off-state to restrict X-rays from being emitted from the X-ray source and an on-state configured to allow X-rays to be emitted from the X-ray source into the enclosure; wherein the shutter is coupled to the application software to receive said instructions; and wherein the instructions comprise commands for timing the on-state of the shutter and resulting X-ray exposure at said pre-specified rotation angles of the gantry. 18. The CT scanner of any preceding embodiment: wherein the pulse generator comprises an off-state to restrict X-rays from being emitted from the X-ray pulse generator source and an on-state configured to allow X-rays to be emitted from the X-ray source into the enclosure; wherein the pulse generator is coupled to the X-ray source to electromagnetic shield the X-ray source from emitting X-rays in the off-state; and wherein the instructions comprise commands for timing the on-state of the pulse generator and resulting X-ray exposure at said pre-specified rotation angles of the gantry 19. The CT scanner of any preceding embodiment: wherein the X-ray source comprises an anode, a cathode and a griddling electrode there between; and wherein the pulse generator is configured to modify a negative potential of the griddling electrode to form an electromagnetic field-based shield so as to prevent electron flow from the cathode the anode, thereby stopping emission of X-rays in the off-state. 20. The CT scanner of any preceding embodiment, wherein said pre-specified angles of rotation comprise a sequence of rotation angles selected from the group of rotation schemes consisting of: an angle-bisect scheme; a Golden-ratio scheme; or a Tiny Golden-ratio scheme. 21. The CT scanner of any preceding embodiment, further comprising: application software coupled to the plurality of detectors for receiving pulsed images corresponding to exposures at said pre-specified rotation angles; the application software further configured for reconstructing each of said exposures to generate a reconstructed image. 22. The CT scanner of claim 21, wherein the reconstructed image is generated via a projection view sharing techniques. 23. The CT scanner of claim 22, wherein K-space Weighted Image Contrast (KWIC) is used to generate the reconstructed image. 24. A method for lowering X-ray dose to a subject in a CT scanner, the CT scanner comprising an X-ray source mounted on gantry so as to rotate within a cylindrical enclosure of the CT scanner and emit of X-rays into the cylindrical enclosure, the method comprising: (a) intermittently exposing a subject within the enclosure to X-rays from the X-ray source at pre-specified rotation angles of the gantry; (b) receiving pulsed images from the CT scanner, the pulsed images corresponding to exposures at said pre-specified rotation angles; and (c) reconstructing each of said exposures to generate a reconstructed image. 25. The method of any preceding embodiment: wherein the CT scanner comprises a mechanical shutter coupled to the x-ray source; wherein the shutter comprises an off-state to restrict X-rays from being emitted from the X-ray source and an on-state configured to allow X-rays to be emitted from the X-ray source into the enclosure; and wherein intermittently exposing a subject comprises timing the on-state of the shutter and resulting X-ray exposure at said pre-specified rotation angles of the gantry. 26. The method of any preceding embodiment: wherein the X-ray source comprises an electron beam being focused on an anode from a cathode to generate said X-rays; and wherein intermittently exposing a subject comprises deflecting the electron beam off the anode using a magnetic field, thereby restricting emission of X-rays from the X-ray source into the enclosure to control X-ray exposure to the subject only at said pre-specified rotation angles of the gantry. 27. The method of any preceding embodiment: wherein the X-ray source further comprises a griddling electrode between the anode and the cathode; and wherein deflecting the electron beam off the anode comprises generating sufficient negative potential within the griddling electrode to form an electromagnetic field-based shield so as to prevent electron flow from the cathode the anode, thereby stopping emission of X-rays for pre-specified rotation angles. 28. The method of any preceding embodiment, wherein said pre-specified angles of rotation comprise a sequence of rotation angles selected from the group of rotation schemes consisting of: an angle-bisect scheme; a Golden-ratio scheme; or a Tiny Golden-ratio scheme. 29. The method of any preceding embodiment, wherein the reconstructed image is generated via a projection view sharing techniques. 30. The method of any preceding embodiment, wherein K-space Weighted Image Contrast (KWIC) is used to generate the reconstructed image. Although the description herein contains many details, these should not be construed as limiting the scope of the disclosure but as merely providing illustrations of some of the presently preferred embodiments. Therefore, it will be appreciated that the scope of the disclosure fully encompasses other embodiments which may become obvious to those skilled in the art. In the claims, reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the disclosed embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed as a “means plus function” element unless the element is expressly recited using the phrase “means for”. No claim element herein is to be construed as a “step plus function” element unless the element is expressly recited using the phrase “step for”. |
|
summary | ||
summary | ||
claims | 1. An irradiation target handling system having an isotope production cable assembly comprising:a target holder drive cable (36) constructed to be compatible with conduits of an existing nuclear reactor moveable in-core detector system that conveys in-core detectors (12) from a detector drive unit (24) to and through instrument thimbles within a reactor core (14), the target holder drive cable having a remotely controlled one of a male or female coupling (58) on a leading end of the drive cable;a target holder drive cable drive motor unit (34) separate from and independent of the detector drive unit (24) on the existing nuclear reactor moveable in-core detector system and configured to drive the target holder drive cable (36) into and out of the core (14), wherein the target holder drive cable drive motor unit is structured to drive the target holder drive cable into and through the conduits, a first multipath selector (28) and a second multipath selector (30) on the existing nuclear reactor moveable in-core detector system;a specimen target holder (48) having another of the male or female coupling (60) on a trailing end of the specimen target holder with the another of the male or female coupling configured to mate with the one of the male or female coupling (58) on the leading end of the target holder drive cable (36); anda third multipath selector (40) structured to receive an input from an outlet path (52) on the second multipath selector (30) and provide a first output to a new specimen attachment location (42), a second output to an irradiated specimen offloading location (44) and a third output (54) to the core (14). 2. The irradiation target handling system of claim 1 wherein the specimen target holder (48) has a radial projection (76) extending from or through an outside wall of the specimen target holder into contact with an interior wall of an instrument thimble in the reactor core (14), into which the specimen target holder is driven by the target holder drive cable (36), which maintains an axial position of the specimen holder within the instrument thimble, when the specimen holder is detached from the drive cable. 3. The irradiation target handling system of claim 2 wherein the one of the male or female coupling (58) is configured to move the radial projection (76) away from the interior wall of the instrument thimble when coupled to the another of the male or female coupling (60) on the specimen target holder (48). 4. The irradiation target handling system of claim 1 including an axial positioning device (78) attached to the specimen target holder (48) for determining when the specimen target holder achieves a preselected axial position within an instrument thimble within the core (14), which the specimen target holder is driven into by the drive cable (36). 5. The irradiation target handling system of claim 4 wherein the instrument thimbles have a closed upper end and the axial positioning device is an axial projection (78) on a leading edge of the specimen target holder (48), the axial projection sized to contact an interior of the closed upper end of the instrument thimble into which the specimen target holder is driven. 6. The irradiation target handling system of claim 5 wherein the length of the axial projection (78) is a wire having an adjustable length. 7. The irradiation target handling system of claim 1 wherein the target holder drive cable (36) enters the conduits through a “Y” connection with one leg of the “Y” connected to the target holder drive cable drive motor unit (34) and a second leg of the “Y” connected to the detector drive unit (24). |
|
claims | 1. A computer-readable medium making computer display measurement results of a semiconductor wafer, based on electrons detected by a scanning electron microscope, the computer implementing steps, the steps comprising:obtaining information relating to a measurement value between an upper part of a layer which forms a part of the semiconductor wafer and a lower part of the layer; anddisplaying the information for each prescribed area on the semiconductor wafer. 2. The computer-readable medium according to claim 1,wherein a prescribed area is a chip of the semiconductor wafer or an area shot by an exposure apparatus. 3. The computer-readable medium according to claim 1,wherein the information of a measurement value is a displacement between a center of the upper part and the lower part of the layer. 4. The computer-readable medium according to claim 1,wherein the steps further comprise:categorizing the information into a plurality of levels, wherein the categorized levels are identified in the displaying steps. 5. The computer-readable medium according to claim 1,wherein the information for each prescribed area is displayed as a wafer map. 6. A computer-readable medium making computer display measurement results of a semiconductor wafer, based on electrons detected by a scanning electron microscope, the computer implementing steps, the steps comprising:obtaining information relating to displacement directions between an upper part of a layer which forms a part of the semiconductor wafer and a lower part of the layer; anddisplaying the information for each prescribed area on the semiconductor wafer. 7. The computer-readable medium according to claim 6,wherein the prescribed area is a chip of the semiconductor wafer or an area shot by an exposure apparatus. 8. The computer-readable medium according to claim 6,wherein the information is a displacement direction between a center of the upper part and the lower part of the layer. 9. The computer-readable medium according to claim 6,wherein the steps further comprise categorizing the information into a plurality of direction categories,wherein the categorized directions are identified in the displaying step. 10. The computer-readable medium according to claim 6,wherein the information for each prescribed area is displayed as a wafer map. 11. A computer-readable medium making computer display measurement results of a semiconductor wafer, based on electrons detected by a scanning electron microscope, the computer implementing steps, the steps comprising:obtaining information relating elliptically-shaped hole patterns on a semiconductor; anddisplaying the information for each prescribed area on the semiconductor wafer. 12. The computer-readable medium according to claim 11,wherein the prescribed area is a chip of the semiconductor wafer or an area shot by an exposure apparatus. 13. The computer-readable medium according to claim 11,wherein the steps further comprise:categorizing the information into a plurality of ranges relating to shape of the hole pattern,wherein the categorized ranges are identified in the displaying step. 14. The computer-readable medium according to claim 11,wherein the information is a degree of circularity, a ratio of the major and minor diameters, an absolute area value, and/or an area ratio of the inner and outer circles. 15. The computer-readable medium according to claim 11,wherein the information for each prescribed area is displayed as a wafer map. |
|
description | 1. Field of the Invention Embodiments of the invention relate to a transmission electron microscope (TEM) specimen and a method of manufacturing the specimen. More particularly, embodiments of the invention relate to a method of forming a dimple on a TEM specimen and a method of manufacturing the specimen. This application claims priority to Korean Patent Application No. 2004-85576, filed on Oct. 26, 2004, the subject matter of which is hereby incorporated by reference in its entirety. 2. Description of the Related Art In general, manufacturing a semiconductor device comprises several processes, such as a diffusion process, an oxidation process, a sputtering process, etc. These processes are performed repeatedly on a semiconductor substrate to stack layers on the substrate. A layer may be, for example, a metal layer such as an aluminum layer, a titanium layer, tungsten layer, etc., or an insulation layer such as a nitride layer, an oxide layer, etc. As semiconductor devices have become more highly integrated and their components have become increasingly smaller, the process of manufacturing a semiconductor device has become more complex. When any one of the layers formed on a semiconductor substrate is defective (e.g., abnormally formed), the semiconductor device will typically fail to operate properly. In such circumstances, it is necessary to accurately and effectively analyze the defective layer, or at least determine whether the layer is defective or not. A TEM is often used to analyze a potentially defective layer. Conventional TEMs focus an electron beam on a specimen under examination to analyze a potentially effective layer in the specimen. An image of the layer under examination is obtained from the irradiating electron beam. More particularly, an electron diffraction pattern is obtained as the irradiating electron beam is diffracted by the constituent components of the layer being examined. In this manner, the conventional TEM analyzes the crystalline structure of the layer based on the resulting electron diffraction pattern. To analyze a layer using a TEM, a suitable specimen must be properly prepared. There are many conventional methods and constituent processing steps involved in the preparation of a TEM specimen. Argon ion milling, chemical polishing, chemical etching, using a cleavage system, and electro polishing—all or individually applied to a specimen in accordance with the material properties of its stacked layers and the nature of the analysis point under examination—are typical method steps adapted to the preparation of a TEM specimen. Argon ion milling has been widely employed in the preparation of TEM specimens adapted to the examination of stacked layers formed on a semiconductor substrate and the interfaces between the stacked layers. As noted above, a TEM obtains information about a specimen from an image generated by the transmission of an accelerated electron beam through the specimen. Thus, the specimen must be relatively thin, at least in the portion being specifically examined by the electron beam. In addition, the specimen must be prepared without scratches or contaminants. Thus, various methods have been studied to effectively prepare TEM specimens. For example, one method of manufacturing a specimen for TEM examination is disclosed in Korean Patent No. 209658. According to the method disclosed in Korean Patent No. 209658, a rotational angle of the specimen is adjusted in accordance with a difference between average atomic weights for each of stacked layers or the difference between sputtering speeds used to fabricate each of the stacked layers. This ion milling process produces a specimen having a more uniform thickness, and may be completed in a relatively short time. Another method of manufacturing a planar wafer specimen for testing is also disclosed in Korean Patent No. 253320. According to the method disclosed in Korean Patent No. 253320, marks on the planar specimen are used (e.g., visualized) in order to analyze the cross sectional state and surface state of a specific region in the wafer specimen (e.g., a specific layer formed on the wafer as captured within the specimen). One conventional method of manufacturing a specimen comprises; a cutting process, a bonding process, a slicing process, a punching process, a grinding process, a dimpling process and an ion-milling process. In the cutting process, first and second preliminary specimens and first, second, third, and fourth dummy wafers are prepared. In the bonding process, a first face of the first preliminary specimen is formed on a first face of the second preliminary specimen. The first and second dummy wafers and the third and fourth dummy wafers are formed on second faces of the first and second preliminary specimens, respectively, to form a stacked specimen. The second faces of the first and second preliminary specimens are opposite the first faces of the first and second preliminary specimens, respectively. In the slicing process, the stacked specimen is cut using a diamond saw to form a rectangular specimen having a thickness of about 0.5 mm to about 1 mm. In the punching process, the rectangular specimen is punched to form a circular specimen having a diameter of about 3 mm. In the grinding process, both circular faces of the circular specimen are ground using a grinder or a polisher to form a final specimen having a thickness of no more than about 100 μm. In the dimpling process, a dimple is formed at a central portion of the final specimen so that the thickness of the central portion of the final specimen is no more than about 1 μm. In the ion-milling process, both sides of the final specimen are sputtered with argon ions to form a hole through the central portion of the final specimen, thereby completing the formation of the final specimen. The final specimen is held by a holder adapted for use with a TEM and is placed on a corresponding support. The hole of the final specimen is then visualized and analyzed. Figure (FIG.) 1 is a cross sectional view illustrating a conventional TEM specimen. Referring to FIG. 1, a first grinding region 20, a second grinding region 30, a third grinding region 40 and an ion-milling region 50 are formed concentrically around a central portion of a cross section of a specimen 10. Here, first grinding region 20 has a first diameter longer than a second diameter of second grinding region 30. The second diameter of second grinding region 30 is longer than a third diameter of third grinding region 40. Ion-milling region 50 has a fourth diameter shorter than the third diameter of third grinding region 40, and ion-milling region 50 is a hole used in observing specimen 10. A conventional method of forming a dimple on a preliminary specimen is described in relation to FIGS. 2 to 4. Referring to FIG. 2, a central portion of a cross section of a preliminary specimen 10′, formed by stacking wafers, is ground using a bronze wheel to form first circular grinding region 20 having the first diameter. Here, the formation of the first grinding region 20 is carried out until red light is observed in a transmission scope. Referring to FIG. 3, the central portion of preliminary specimen 10′ is ground using a coarse wheel to form second grinding region 30 having the second diameter. Second grinding region 30 is concentric with first grinding region 20. Here, the formation of second grinding region 30 is carried out until orange light is observed in the transmission scope. Referring to FIG. 4, the central portion of preliminary specimen 10′ is repeatedly ground using a fine wheel to form third grinding region 40 having the third diameter. Third grinding region 40 is concentric with first and second grinding regions 20 and 30. Here, the formation of third grinding region 40 is carried out until yellow light or white light is observed in the transmission scope. FIG. 5 is a transmission scope picture illustrating a conventional specimen having a dimple. Referring to FIG. 5, the red light serving as reference light in forming first grinding region 20 is exhibited in a first region I corresponding to an edge region of specimen 10. The yellow light serving as reference light in forming third grinding region 40 is exhibited in a third region III corresponding to a central region of specimen 10. The orange light serving as reference light in forming second grinding region 30 is exhibited in a second region II between first region I and third region III. To analyze the cross section of specimen 10 using a TEM, a central portion of third grinding region 40, which is the thinnest portion of preliminary specimen 10′, is aligned with a central portion of preliminary specimen 10′ in forming the dimple. Here, an analysis region of specimen 10 has an allowable diameter of about 30 μm to about 50 μm. However, when the central portion of third grinding region 40 is not aligned with the central portion of preliminary specimen 10′, the diameter of the analysis region of specimen 10 is smaller than the allowable diameter. Also, when hole 50 has a relatively large diameter, the analysis region in third grinding region 40 has a relatively small area. In one embodiment, the invention provides a TEM specimen comprising an analysis region comprising an analysis point, and a peripheral region enclosing the analysis region. The analysis region comprises a dimple region, and an ion-milling region, located at a central portion of the dimple region, comprising two separate holes having the analysis point between them. In another embodiment, the invention provides a method of manufacturing a TEM specimen comprising preparing a preliminary specimen, and forming a specimen by forming a dimple region on a surface portion of the preliminary specimen, and ion milling the preliminary specimen having the dimple region to form an ion-milling region comprising two separate holes having an analysis point between them. It will be understood that when an element or layer is referred to as being “on” another element or layer, it can be directly on the other element or layer, or intervening elements or layers may be present. FIG. 6 is a cross sectional view illustrating a TEM specimen in accordance with an exemplary embodiment of the invention. Referring to FIG. 6, a specimen 100 is in the shape of a disk, wherein the disk has a diameter of about 3 mm and a thickness of about 70 μm. An analysis region 106, formed on specimen 100, is centered at the center point of specimen 100. A peripheral region 108 corresponds to the entire region of specimen 100 surrounding analysis region 106. Peripheral region 108 is formed along an outer boundary of analysis region 106 and encloses analysis region 106. Analysis region 106 comprises a dimple region 109, and an ion-milling region 150 positioned at a central portion of dimple region 109. Dimple region 109 further comprises a first grinding region 120, a second grinding region 130 and a third grinding region 140. An analyzing direction is a direction from the analysis point toward the edge of a specimen or a preliminary specimen that is substantially parallel to the faces of the wafers used in the formation of the specimen or preliminary specimen. There are necessarily two analyzing directions, wherein a first analyzing direction is opposite a second analyzing direction. A line of analysis is a line that extends away from the analysis point of a specimen or a preliminary specimen in both of the analyzing directions. First grinding region 120 has a first area, a first length substantially along the line of analysis, and a first width smaller than the first length that is substantially perpendicular to the line of analysis. In this exemplary embodiment, first grinding region 120, as shown in FIG. 6, has an overlapping circular shape. As used herein, an overlapping circular shape is the shape of two partially overlapping circular shapes, as shown, for example, by first grinding region 120 of FIG. 6. The two overlapping circular shapes may overlap in the analyzing directions and/or with respect to the analysis point. Alternatively, first grinding region 120 may have an elliptical shape, having its major axis substantially along the line of analysis. First grinding region 120 may also have another shape, having a first length substantially along the line of analysis and a first width substantially perpendicular to the line of analysis. Second grinding region 130 has a second area smaller than the first area of first grinding region 120, a second length substantially along the line of analysis, and a second width smaller than the second length that is substantially perpendicular to the line of analysis. In this exemplary embodiment, second grinding region 130 has an elliptical shape. Alternatively, second grinding region 130 may have an overlapping circular shape. Third grinding region 140 has a third area smaller than the second area of second grinding region 130, a third length substantially along the line of analysis, and a third width smaller than the third length that is substantially perpendicular to the line of analysis. Here, the third length of third grinding region 140 may be about 50 μm to about 150 μm. In this exemplary embodiment, third grinding region 140 has an elliptical shape. Alternatively, third grinding region 140 may have an overlapping circular shape. Ion-milling region 150 comprises two separate holes that are within third grinding region 140 and have an analysis point between them. Specimen 100 is analyzed using the two holes. In accordance with this exemplary embodiment, specimen 100 has a relatively large analysis area. Hereinafter, a method of manufacturing specimen 100 will be described in detail. FIGS. 7 to 10 are flow charts illustrating a method of manufacturing specimen 100 of FIG. 6. FIG. 7 is a flow chart illustrating a method of manufacturing the specimen, FIG. 8 is a flow chart illustrating a method of forming a preliminary specimen, FIG. 9 is flow chart illustrating a method of forming a specimen from a preliminary specimen, and FIG. 10 is a flow chart illustrating a method of forming a dimple on a preliminary specimen. FIG. 11 is a picture illustrating a ground state of a specimen during formation of a dimple using a method that is in accordance with an exemplary embodiment of the invention. FIGS. 12 to 17 illustrate a method of manufacturing specimen 100 of FIG. 6. FIGS. 12 and 13 illustrate a method of forming the preliminary specimen, where FIG. 12 is a plain view and FIG. 13 is a cross sectional view. FIGS. 14 to 17 are cross sectional views illustrating a method of forming the specimen. Referring to FIG. 7, a method of manufacturing specimen 100 for the TEM comprises preparing a preliminary specimen 110 (300) and forming a specimen 100 (400) by grinding preliminary specimen 110. Hereinafter, preparing preliminary specimen 110 (300) will be described in detail. Referring to FIGS. 8 and 12, first and second separated specimens 101a and 101b, and first, second, third, and fourth dummy wafers 102a, 102b, 102c and 102d are formed through a cutting process (310). In particular, a patterned wafer, such as a semiconductor substrate on which a pattern to be analyzed is formed, is prepared. A cross section of the pattern on the semiconductor substrate is observed using an electron microscope to determine the analysis point of the pattern. The semiconductor substrate is then cut using a dicing saw to form first and second separated specimens 101a and 101b each having an area of about 4 mm×about 5 mm. In addition, wafers are cut to form first, second, third, and fourth dummy wafers 102a, 102b, 102c and 102d, each of which has an area substantially the same as that of first and second separated specimen 101a or 101b. Then, to form a stacked specimen 103, first and second dummy wafers 102a and 102b are formed on first separated specimen 101a, and third and fourth dummy wafers 102c and 102d are formed on second separated specimen 101b (320). In detail, a first face of first separated specimen 101a is formed on a first face of second separated specimen 10b. First and second dummy wafers 102a and 102b are each formed on a second face of first separated specimen 101a, which is opposite the first face of first separated specimen 101a, using a G1-epoxy resin. Third and fourth dummy wafers 102c and 102d are each formed on a second face of second separated specimen 101b, which is opposite the first face of second separated specimen 101b, using a G1-epoxy resin, thereby forming stacked specimen 103. Stacked specimen 103 is then compressed using a compressor to spread the G-epoxy resin widely and thinly. Next, stacked specimen 103 is heated to a temperature of about 145° C., thereby completing the construction of stacked specimen 103. Referring to FIGS. 8 and 13, stacked specimen 103 is sliced in a direction substantially perpendicular to the faces of the wafers using a diamond cutter to form a sliced specimen 104 (330) having a thickness of about 0.5 mm to about 1 mm. Sliced specimen 104 is then punched to form a circular specimen 105 (340) having a diameter of about 3 mm. Next, both circular faces of circular specimen 105 are ground, using a grinder or a polisher, to form preliminary specimen 110 (350) having a thickness of about 70 μm. Hereinafter, a method of forming specimen 100 from preliminary specimen 110 is described in detail. Referring to FIG. 7, forming specimen 100 (400) comprises, referring to FIG. 9, forming a dimple on preliminary specimen 110 (410), and then ion milling preliminary specimen 110 (420). Forming a dimple on preliminary specimen 110 (410) comprises, referring to FIGS. 10 and 14, forming the first grinding region (411). In particular, preliminary specimen 110 is ground in the analyzing directions from the analysis point to form first grinding region 120. First grinding region 120 has the first area, the first length substantially along the line of analysis, and the first width smaller than the first length that is substantially perpendicular to the line of analysis. In this exemplary embodiment, first grinding region 120 has an overlapping circular shape, as shown in FIG. 14. Alternatively, first grinding region 120 may have an elliptical shape having its major axis substantially along the line of analysis. Peripheral region 108 corresponds to the entire region of preliminary specimen 110 surrounding first grinding region 120. The thickness of preliminary specimen 110 at the dimple is not more than about 1 μm. This reduced thickness at the dimple is formed by polishing a cross section of the specimen using a chemical mechanical polishing (CMP) process. The process for forming the dimple is carried out using various abrasives in a series of steps. The abrasive used to form each grinding region may vary in accordance with the desired thickness of that grinding region. Preliminary specimen 110 is ground using a dual grinding wheel to form first grinding region 120 (411) having a thickness of about 10 μm to about 20 μm. The thickness of a grinding region, as used herein, means the thickness of the specimen or preliminary specimen at that grinding region, excluding the portion of that grinding region that contains other grinding regions or an ion-milling region. Here, when first grinding region 120 has a thickness of below about 10 μm, red light is observed in first grinding region 120 using a transmission scope. Thus, to form first grinding region 120, preliminary specimen 110 is ground until red light is observed. Referring to FIG. 11, the red light exhibited in an edge region IV of preliminary specimen 110 serves as a reference in forming first grinding region 120. The yellow light exhibited in a central region VI of preliminary specimen 110 serves as a reference in forming third grinding region 140. The orange light exhibited in an interface region V between edge region IV and central region VI serves as a reference in forming second grinding region 130. Since the process for forming first grinding region 120 is a fundamental process in forming the dimple, the process for forming first grinding region 120 need not be precise, and thus diamond particles may be used in forming first grinding region 120. The method of forming the dimple further comprises grinding first grinding region 120 to form second grinding region 130 (412). Referring to FIGS. 10 and 15, first grinding region 120 is ground with respect to the analysis point to form second grinding region 130 having an elliptical shape that has the second area smaller than the first area of first grinding region 120. The major axis of second grinding region 130 is substantially along the line of analysis of preliminary specimen 110. In this exemplary embodiment, first grinding region 120 is ground using an abrasive comprising about 80% by weight of diamond paste and about 20% by weight of aluminum oxide to form second grinding region 130 having a thickness of about 2 μm to about 3 μm. The abrasive used to form second grinding region 130 is different from that used to form first grinding region 120, since the thickness of second grinding region 130 is more precisely controlled than the thickness of first grinding region 120. When, in the process of grinding first grinding region 120, orange light is observed in fifth region V of FIG. 11 using a transmission scope, second grinding region 130 has a thickness of about 2 μm to about 3 μm. The process for forming second grinding region 130 is referred to as a coarse process. The process of forming second grinding region 130 is coarser than the process of forming third grinding region 140, and preliminary specimen 110 is planarized by the coarse process to expand an area to be analyzed by the TEM. The method of forming the dimple further comprises grinding second grinding region 130 to form third grinding region 140 (413). Referring to FIGS. 10 and 16, second grinding region 130 is ground with respect to the analysis point to form third grinding region 140 having an elliptical shape that has the third area smaller than the second area of second grinding region 130. The major axis of third grinding region 140 is substantially along the line of analysis of preliminary specimen 110. In this exemplary embodiment, second grinding region 130 is ground using an abrasive comprising aluminum oxide to form third grinding region 140 having a thickness of no more than about 1 μm. The abrasive used to form third grinding region 140 is different from that used to form second grinding region 130, since the thickness of third grinding region 140 is more precisely controlled than the thickness of second grinding region 130. When, in grinding second grinding region 130, yellow light or white light is observed in sixth region VI of FIG. 11 using a transmission scope, third grinding region 140 has a thickness of no more than about 1 μm. Here, to prepare the TEM specimen for analysis, a coarse surface of second grinding region 130 having fine scratches is minutely polished using aluminum oxide to form third grinding region 140 having the dimple. The major axis of third grinding region 140 has a length of about 50 μm to about 150 μm. First, second and third grinding regions 120, 130 and 140 together form dimple region 109. Referring to FIGS. 9 and 17, an ion-milling process is performed on preliminary specimen 110 to complete specimen 100 having ion-milling region 150 (420). In detail, third grinding region 140 is sputtered using argon ions to form two holes corresponding to ion-milling region 150. The holes are arranged along the line of analysis. As a result, dimple region 109 including first, second, and third grinding regions 120, 130, and 140 and ion-milling region 150 together form analysis region 106, thereby completing specimen 100. Specimen 100 is then placed on a table. Electrons are transmitted through the holes of ion milling region 150 to test specimen 100. Third grinding region 140 of specimen 100 is mainly observed. Analysis region 106 of specimen 100, in accordance with an exemplary embodiment, has a width of about 50 μm to about 150 μm, which is generally wider than the width of 30 μm to about 50 μm of the conventional specimen. A specimen in accordance with exemplary embodiments of the invention has a relatively large analysis region. Thus, even if the dimple region is not aligned with the center point of the specimen, or the holes have very large diameters, the specimen may still be readily analyzed. Although exemplary embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that modifications and variations can be made while remaining within the scope of the invention as set forth in the following claims. |
|
abstract | A diffracting x-ray optic for accepting and redirecting x-rays. The optic includes at least two layers, the layers having a similar or differing material composition and similar or differing crystalline orientation. Each of the layers exhibits a diffractive effect, and their collective effect provides a diffractive effect on the received x-rays. In one embodiment, the layers are silicon, and are bonded together using a silicon-on-insulator bonding technique. In another embodiment, an adhesive bonding technique may be used. The optic may be a curved, monochromating optic. |
|
050540416 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a gantry 20, representative of a "third generation" computed tomography scanner, includes an x-ray source 10 collimated by collimator 38 to project a fan beam of x-rays 22 through imaged object 12 to detector array 14. The x-ray source 10 and detector array 14 rotate on the gantry 20 as indicated by arrow 28, within an imaging plane 60, aligned with the x-y plane of a Cartesian coordinate system, and about the z-axis of that coordinate system. The detector array 14 is comprised of a number of detector elements 16, organized within the imaging plane 60, which together detect the projected image produced by the attenuated transmission of x-rays through the imaged object 12. The fan beam 22 emanates from a focal spot 26 in the x-ray source 10 and is directed along a fan beam axis 23 centered within the fan beam 22. The fan beam angle, measured along the broad face of the fan beam 22, is larger than the angle subtended by the imaged object 12 so that two peripheral beams 24 of the fan beam 22 are transmitted past the body without substantial attenuation. These peripheral beams 24 are received by peripheral detector elements 18 within the detector array 14. Referring to FIG. 2, uncollimated x-rays 19 radiating from the focal spot 26 in the x-ray source 10 (not shown in FIG. 2) are formed into a coarse fan beam 1 by primary aperture 40. The coarse fan beam 21 is collimated into fan beam 22 by means of collimator 38. Referring generally to FIGS. 2, 3(a) and 3(b), collimator 38 is comprised of a cylindrical x-ray absorbing mandrel 39 held within the coarse fan beam 21 on high precision bearings 42 allowing the mandrel 39 to rotate along its axis. The mandrel material is a sintered molybdenum to provide both good x-ray absorbing characteristics and randomly oriented residual stress ensuring dimensional stability after the necessary machining. A plurality of tapered slots 41 are cut through the mandrel's diameter by wire electro-discharge machining and extend along the length of the mandrel 39. The slots 41 are cut at varying angles about the mandrel's axis to permit rotation of the mandrel 39 by approximately 36.degree. to bring each such slot 41 into alignment with the coarse fan beam 21 so as to permit the passage of some rays of the coarse fan beam 21 through the slot 41 to form fan beam 22. Referring to FIG. 3(a) and 3(b), the tapered slots 41 are of varying width and hence the rotation of the mandrel 39 allows the width of the fan beam 22 to be varied between a narrow width (mm) as shown in FIG. 3(b) and wide width (10mm) as shown in FIG. 3(a). The fixed slots 41 ensure dimensional accuracy and repeatability of the fan beam 22. The tolerances on the narrowest slot 41 are +0.001 inches -0.000 inches with proportional tolerances on the larger slots 41. The slots 41 are tapered so that the entrance aperture 43 of each slot 41, when orientated with respect to the coarse fan beam 21, is wider than the exit aperture 5. The exit aperture 45 defines the width of the fan beam 2 and the extra width of the entrance aperture 43 prevents either edge of the entrance aperture 43 from blocking the coarse fan beam 21 during rotation of the mandrel 39 when such rotation is used to control the alignment of the fan beam axis 23 as will be discused in detail below. Referring again to FIG. 2, a stepping motor 48 is connected to one end of the mandrel 39 by coupling 50 that is stiff torsionally but flexible in other directions, and a low backlash brake 80 to be described further below. The stepping motor 48 is operated in the micro-step mode as is known in the art to provide a stepping increment of 50,800 steps per revolution. The stepper motor and controller are commercially available from Oriental Motor and compumotor, respectively. The remaining end of the mandrel 39 is attached to a position encoder 46 which allows accurate positioning of the mandrel by motor 48. The position encoder is of the incremental type, providing 20,000 pulses per revolution and a home or zero pulse used to determine absolute position. Fan beam angle shutters 44 at either ends of the mandrel 39 control the length of the fan beam 22. Referring to FIG. 4, the x-ray source 10 is comprised of a rotating anode 52 held within an evacuated glass tube (not shown) and supported by supporting structure including principally anode shaft 54 which is held on bearings 56 (one shown). The coarse fan beam 21 emanates from focal spot 26 at the surface of the anode 52. The coarse fan beam 21 is collimated by the collimator 38 to form a fan beam 22 as previously described. The plane containing the focal spot 26, the center line of the exit aperture 45, and the centerline of the detector array 14 along the z axis, and thus bisecting the fan beam 22 in the z axis direction, will be termed the "fan beam plane" 62. As previously described, the focal spot 26 may not be aligned with the imaging plane 60 either because of thermal drift of the anode 52 and its supporting structure or because of minor misalignment of the x-ray source 10 during assembly. Referring to FIG. 5, the anode 52 is shown displaced from the imaging plane 60 by misalignment distance 58. The effect of this misalignment is to displace focal spot position away from the imaging plane 60 and to move the the center of the fan beam exposure area 36 in the opposite direction. As a result of the movement of the focal spot 26, as shown in FIG. 5, the exposure area 36 is no longer centered within the imaging plane 60 and the fan beam plane 62 is no longer parallel with the imaging plane 60 but deviates by angle .phi.. Referring to FIG. 6, the collimator 38 may be rotated to restore the fan beam plane 62 to parallel with the imaging plane 60. This correction of the angle of the fan beam plane 62 will be termed "parallelism correction". Alternatively, referring to FIG. 7, the collimator 38 may be rotated so that the exposure area 36 will again be centered at within the imaging plane 60. Correction of the position of the of the fan beam exposure area 36 with respect to the detector 14 will be termed "z-axis offset correction". In summary, rotation of the collimator 38 may correct for misalignment of the fan beam plane 62 either to make it parallel with the imaging plane 60 or to bring the exposure area 36 into alignment on the detector array 14. As previously discussed, both of these corrections will reduce image artifacts. As discussed, various external forces act on the collimator 38 during the rotation of the gantry 20 shown in FIG. 1. The torque on the mandrel 39, exerted by these forces, is resisted by means of a low backlash brake 80 as shown in FIG. 2. Referring now to FIG. 8, the torque T.sub.s of the stepper motor 48 varies as a function of the angular displacement .alpha. of its shaft 78 around a step position .alpha..sub.o. The torque T.sub.s rises from zero torque at .alpha..sub.0 to positive values (representing counterclockwise torque) as one moves in a clockwise direction away from .alpha..sub.o, and the torque T.sub.s drops from zero torque to negative values (representing clockwise torque) as one moves in a counterclockwise direction away from .alpha..sub.o. This is typical of the torque characteristics of a positioning motor and reflects the positioning action of the motor around at .alpha..sub.o. Referring again to FIG. 1, the collimator mandrel 39 is disposed tangentially to the rotation 28 of the gantry 20 and hence experiences a steady centripetal acceleration and a rotating gravitational acceleration depending on the position and velocity of the gantry 20. The complex cross-section of mandrel 39 prevents it from being perfectly balanced under these varying accelerative forces and hence there exists a small but significant perturbation torque .+-.TP on the mandrel 39 during rotation of the gantry 20. Referring again to FIG. 8, when the stepping motor is energized this perturbation torque .+-.T.sub.p may move the mandrel by as much as .+-..alpha.p before it is resisted by the restoring torque T.sub.s of the stepping motor 48. Referring to FIG. 11, the effect of the perturbation torque .alpha.T.sub.P may be counteracted by means of the low backlash brake 80 comprised of a brake drum 82 affixed to, and coaxial with, the shaft 78 of the stepper motor 48 connected with the mandrel 39. A brake pad 84 attached to an arcuate brake shoe 86 is positioned in sliding contact with the circumference of the brake drum 82 so as to create a frictional countervailing braking torque T.sub.B. The brake shoe 86 is attached to a housing 88 by means of a flexible arm 90 of spring steel. The flexible arm 90 is orientated tangentially to the brake drum 82 to flex only in a radial direction and hence to be unyielding with respect to tangential forces imparted by the friction between the brake drum 82 and the brake lining 84. A biasing spring 92 serves to impart an inward radial force to the brake shoe 86 and brake pad 84 against the circumference of the brake drum 82 and hence to establish the frictional braking torque T.sub.F which may be adjusted by controlling the compression of biasing spring 92 and hence the force imparted by the biasing spring 92 on the brake shoe 86. Referring again to FIG. 9, the braking torque T.sub.B is essentially constant with angle .alpha. and equal to T.sub.F and always opposing the direction of rotation. The braking torque T.sub.B only counteracts the other torques and drops to zero when there is no motion. The braking torque T.sub.B creates the hysteresis curve of FIG. 9 where the torque curve T.sub.S is displaced by .+-.T.sub.F depending on the direction of rotation of shaft 78. With the braking torque T.sub.s, the stepping motor 48 will position its shaft at equilibrium point 100 or 100' removed from .alpha..sub.o depending on the direction which the stepping motor 48 approaches .alpha..sub.o. In the preferred embodiment, the stepper motor always turns in the counterclockwise direction (as viewed from the non-shaft side of the stepper motor) to ensure that its shaft 78 will always stop at equilibrium point 100. When the shaft 78 of the stepper motor 48 has reached position 100, the braking torque T.sub.B and the stepper motor torque T.sub.S are just balanced and the shaft 78 of the stepper motor 48 stops. Nevertheless, the shaft 78 is not immune from perturbation torque T.sub.P which may unbalance this equilibrium in either direction, even if T.sub.P is less than T.sub.F. This displacement is designated .alpha..sub.p ' and .alpha..sub.p " depending on the direction of perturbation. In general, the displacement .alpha..sub.p ' and .alpha..sub.P ", with the brake 80, will be less than the displacement .alpha..sub.p without the brake 80 as shown in FIG. 8. Referring to FIG. 9, once the stepper motor 48 has positioned its shaft 78 at point 100, the power to the stepper motor 48 is reduced to lessen the amount of the stepper motor restoring torque T.sub.s, for small displacement angles .alpha. of shaft 78, to T.sub.s ', where T.sub.s '<<T.sub.F for small angles .alpha.. This reduction of torque T.sub.s may be obtained by reducing the current flowing through the windings of the stepper motor 48 as is understood in the art. Now the braking torque T.sub.s provides a nearly constant resisting force to motion in either direction and will prevent motion of the shaft 78 from perturbing torques T.sub.P so long as -T.sub.F >T.sub.P >T.sub.F. Therefore, somewhat counterintuitively, the braking action is improved by reducing the stepper motor restoring torque T.sub.s to T.sub.s '. The stepper motor 48 is not shut off completely, however, so as to provide resistance to higher perturbation torques than T.sub.P and to prevent shifting of the mandrel 39 by large angles .alpha. . The above description has been that of a preferred embodiment of the present invention. It will occur to those who practice the art that many modifications may be made without departing from the spirit and scope of the invention. In order to apprise the public of the various embodiments that may fall within the scope of the invention, the following claims are made. |
claims | 1. A radiation protective material, comprising:at least one layer of fibrous material with composite filaments, wherein the filaments are structured in a regular pattern to form the radiation protective material, wherein the filaments comprises a radiopaque composite material including a radiopaque substance, wherein the radiopaque substance is mixed within the composite material and substantially evenly distributed within the composite material, wherein the radiopaque substance is substantially evenly distributed over the entire cross section of the filament, from a center to a surface of the filament, and said filaments are made of a mixture of the radiopaque substance and an organic polymer matrix, such that radiopaque substance is embedded within the organic polymer matrix, wherein the radiopaque substance comprises at least one metal in oxidized form, elemental form, as an alloy, or in salt form in combination with the organic polymer matrix, and wherein the organic polymer matrix comprises at least one of polyvinyl, polyolefin, and polyacetate;wherein the fibrous material is a woven regular pattern having 15-30 filaments per centimeter;wherein an amount of the radiopaque substance of the filaments is more than 25% by weight less than 90% by weight of the total weight of the filaments;wherein each filament forms a single filament yarn;wherein the fibrous material comprises a first group of filaments and a second group of filaments, wherein the filaments of the first group are arranged in parallel in a first plane with gaps in-between the filaments of the first group, and the filaments of the second group are arranged in parallel in a second plane with gaps in-between the filaments of the second group, and wherein gaps are provided to permit airflow between a filament of the first group and neighboring filaments of the second group, and wherein each filament of the second group has a diameter sized to partially overlap two filaments of the first group along the length of the filaments and to cover the gap between the two filaments of the first group,the filaments have a diameter in the range of 0.5 mm to 1.5 mm; andwherein said combination of woven regular pattern, filaments per centimeter, amount of radiopaque substance and filament diameter together provide said at least one layer with a radiopacity that permits penetration of not more than about 60% of X-ray radiation when exposed at 100 kV and 10 mAs charge in combination with a water-vapor resistance of up to 25 Ret. 2. The material according to claim 1, wherein:the at least one metal comprises at least one of actinium, antimony, barium, bismuth, bromine, cadmium, cerium, cesium, gold, iodine, indium, iridium, lanthanum, lead, mercury, molybdenum, osmium, platinum, pollonium, rhenium, rhodium, silver, strontium, tantalum, tellurium, thallium, thorium, tin, wolfram, and zirconium. 3. The material according to claim 1, wherein the fibrous material comprises a structure that allows for air to penetrate through the material, wherein the air permeability of a single layer of the radiation protective material is in the range of about 20 mm/s to 2000 mm/s, when measured using a pressured difference of 1 mbar. 4. The material according to claim 3, wherein the air permeability of a single layer of the radiation protective material is in the range of about 50 mm/s to 1500 mm/s, when measured using a pressure difference of 1 mbar. 5. The material according to claim 4, wherein the air permeability of a single layer of the radiation protective material is in the range of 100 mm/s to 750 mm/s, when measured using a pressure difference of 1 mbar. 6. The material according to claim 1, wherein at least one of a warp and a weft of the woven fibrous material comprises the radiopaque substance. 7. The material according to claim 6, wherein the weft comprises a filament made from recycled radiation protective garment, and the warp comprises non-radiation protective material. 8. The material according to claim 6, wherein the warp and the weft comprise the radiopaque substance. 9. A garment for use in radiation protection, wherein the garment comprises one or several layers of the radiation protective material of claim 1. 10. The garment according to claim 9, wherein the garment is a garment for medical applications. 11. The garment according to claim 10, wherein the garment is at least one of an apron, pant, jacket, vest, skirt, collar to protect the thyroid from radiation, sleeve, glove, trousers, coat, or cap. 12. The garment according to claim 10, wherein the garment comprises 1 to 10 layers of the radiation protective material. 13. The material according to claim 1, wherein a remaining part of the filament comprises an organic matrix including process additives and dye. 14. The material according to claim 1, wherein the filaments have a diameter in the range of 0.6 mm to 1 mm. 15. The material according to claim 1, wherein the material is an ionizing radiation protective material. 16. The material according to claim 1, wherein:the at least one metal comprises at least one of actinium, antimony, barium, bismuth, bromine, cadmium, cerium, cesium, gold, iodine, indium, iridium, lanthanum, lead, mercury, molybdenum, osmium, platinum, pollonium, rhenium, rhodium, silver, strontium, tantalum, tellurium, thallium, thorium, tin, wolfram, and zirconium. 17. The material according to claim 1, wherein said composite filaments are made of a mixture of the radiopaque substance and an organic polymer matrix, such that radiopaque substance is embedded within the organic polymer matrix. 18. The material according to claim 1, wherein said material has an electromagnetic radiation attenuation that is equivalent to a layer of metallic lead having a thickness of at least 0.10 mm. 19. The material according to claim 1, wherein the at least one metal comprises antimony. 20. The material according to claim 1, wherein the at least one metal comprises lead. 21. The material according to claim 1, wherein the at least one metal comprises wolfram. 22. A garment formed of plural said layers of radiation protective material according to claim 1, wherein said garment has a water-vapor resistance below 90 Ret and a radiopacity that permits penetration of not more than about 10% of X-ray radiation when exposed at 100 kV and 10 mAs charge. 23. The radiation protective material according to claim 1, further comprising at least six said layers, wherein said material has a radiopacity that permits penetration of not more than about 10% of X-ray radiation when exposed at 100 kV and 10 mAs charge. 24. A radiation protective material, comprising:at least one layer of fibrous material, said at least one layer comprising composite filaments with 15-30 filaments per centimeter and a filament diameter in the range of 0.5 mm to 1.5 mm, wherein the filaments are structured in a regular pattern to form the radiation protective material, wherein the fibrous material comprises a first group of filaments and a second group of filaments, wherein the filaments of the first group are arranged in parallel in a first plane with gaps in-between the filaments of the first group, and the filaments of the second group are arranged in parallel in a second plane with gaps in-between the filaments of the second group, and wherein gaps are provided to permit airflow between a filament of the first group and neighboring filaments of the second group, and wherein each filament of the second group has a diameter sized to partially overlap two filaments of the first group along the length of the filaments and to cover the gap between the two filaments of the first group, wherein the filaments comprise a radiopaque composite material including a radiopaque substance, wherein the radiopaque substance is substantially evenly distributed over the entire cross section of the filament, from a center to a surface of the filament, and said filaments are made of a mixture of the radiopaque substance and an organic polymer matrix, such that radiopaque substance is embedded within the organic polymer matrix, wherein the radiopaque substance comprises at least one metal in oxidized form, elemental form, as an alloy, or in salt form in combination with the organic polymer matrix;wherein said fibrous material, said filaments per centimeter, said filament diameter, said filament structure and said radiopaque composite material in combination provides said at least one layer with a radiopacity that permits penetration of not more than about 60% of X-ray radiation when exposed at 100 kV and 10 mAs charge and water-vapor resistance of up to 25 Ret. 25. The material according to claim 24, wherein the at least one metal comprises antimony. 26. The material according to claim 24, wherein the at least one metal comprises lead. 27. The material according to claim 24, wherein the at least one metal comprises wolfram. 28. The material according to claim 24, wherein the fibrous material comprises a structure that allows for air to penetrate through the material, wherein the air permeability of a single layer of the radiation protective material is in the range of about 20 mm/s to 2000 mm/s, when measured using a pressure difference of 1 mbar. 29. The material according to claim 28, wherein the air permeability of a single layer of the radiation protective material is in the range of about 50 mm/s to 1500 mm/s, when measured using a pressure difference of 1 mbar. 30. The material according to claim 24, wherein the fibrous material is a woven regular pattern. 31. The material according to claim 30, wherein the air permeability of a single layer of the radiation protective material is in the range of 100 mm/s to 750 mm/s, when measured using a pressure difference of 1 mbar. 32. The material according to claim 24, wherein an amount of the radiopaque substance of the filaments is more than 25% by weight less than 90% by weight of the total weight of the filaments. 33. The material according to claim 24, wherein the filaments have a diameter in the range of 0.6 mm to 1 mm. 34. A garment for use in radiation protection, wherein the garment comprises one or several layers of the radiation protective material of claim 24. 35. The garment according to claim 34, wherein the garment comprises 1 to 10 layers of the radiation protective material. 36. The material according to claim 24, wherein the at least one metal comprises barium sulfate. 37. A radiation protective material, comprising at least one layer of fibrous material with composite filaments structured in a regular pattern to form the at least one layer of radiation protective material, wherein:the filaments are woven in a regular pattern with structure that allows for air to penetrate through the material with an air permeability in a single layer in the range of about 20 mm/s to 2000 mm/s, when measured using a pressure difference of 1 mbar;the filaments are made of a mixture of at least one radiopaque metal in oxidized form, elemental form, as an alloy, or in salt form embedded within an organic polymer matrix,the at least one radiopaque metal comprises one of barium sulfate, antimony, lead or wolfram and is substantially evenly distributed over the entire cross section of the filaments, from a center to a surface of the filaments;the organic polymer matrix comprises at least one of copolymers of polyvinyl, polyolefin and polyester;an amount of radiopaque metal of the filaments is more than 25% by weight less than 90% by weight of the total weight of the filaments; andthe filaments have a diameter in the range of 0.5 mm to 1.5 mm, and a distribution comprising 15-30 of said composite filaments per centimeter per layer of said material;wherein the fibrous material comprises a first group of filaments and a second group of filaments, wherein the filaments of the first group are arranged in parallel in a first plane with gaps in-between the filaments of the first group, and the filaments of the second group are arranged in parallel in a second plane with gaps in-between the filaments of the second group, and wherein gaps are provided to permit airflow between a filament of the first group and neighboring filaments of the second group, and wherein each filament of the second group has a diameter sized to partially overlap two filaments of the first group along the length of the filaments and to cover the gap between the two filaments of the first group, andwherein said woven regular pattern, said mixture of at least one radiopaque material within the organic polymer matrix, said at least one radiopaque metal, and said filament diameter and distribution in combination provide said at least one layer with a radiopacity that permits penetration of not more than about 60% of X-ray radiation when exposed at 100 kV and 10 mAs charge. 38. The radiation protective material according to claim 37, wherein said at least one layer has a water-vapor resistance of up to 25 Ret. 39. The radiation protective material according to claim 37, further comprising at least six said layers, wherein said material has a radiopacity that permits penetration of not more than about 10% of X-ray radiation when exposed at 100 kV and 10 mAs charge. |
|
abstract | The invention relates to a device and a method for producing resist profiled elements. According to the invention, an electron beam lithography system is used to produce an electron beam, the axis of the beam being essentially perpendicular to a resist layer in which the resist profiled element is to be produced. The electron beam can be adjusted in terms of the electron surface dose in such a way that a non-orthogonal resist profiled element can be produced as a result of the irradiation by the electron beam. |
|
abstract | A method and system is presented for treating moving target regions in a patient's anatomy by creating radiosurgical lesions. The method includes determining a pulsating motion of a patient separately from a determining of a respiratory motion, and directing a radiosurgical beam, from a radiosurgical beam source, to a target in the patient based on the determining of the pulsating motion. Directing the radiosurgical beam to the target may include creating a lesion in the heart to inhibit atrial fibrillation. The method may further include determining the respiratory motion of the patient, and compensating for movement of the target, due to the respiratory motion and the pulsating motion of the patient, in the directing of the radiosurgical beam based on the determining of the respiratory motion and the determining of the pulsating motion. |
|
claims | 1. A technical system for determining the slide quality of a digital microscope slide, the system comprising:a computer readable storage medium for storing computer executable programmed modules;a processor communicatively coupled with the computer readable storage medium for executing programmed modules stored therein;a micro-analysis module stored in the computer readable storage medium and configured to:divide the digital microscope slide image into a plurality of regions;qualify at least a portion of said plurality of regions;analyze the qualified regions;generate a quantifiable value for each qualified region;generate a score map measurement for each qualified region based on the quantifiable values corresponding to the qualified regions; andgenerate a markup image based on the quantifiable values corresponding to the qualified regions. 2. The system of claim 1, further comprising a digital microscope slide acquisition module stored in the computer readable storage medium and configured to obtain a digital microscope slide image. 3. The system of claim 2, further comprising:a macro-analysis module stored in the computer readable storage medium and configured to:combine the score map measurements;perform artifact detection; andcompute a whole slide score in accordance with the combined score map measurements and detected artifacts. 4. A technical system comprising at least one processor communicatively coupled with at least one computer readable storage medium, wherein the processor is programmed to determine the slide quality of a digital microscope slide by:dividing the digital microscope slide image into a plurality of regions;qualifying a portion of said regions;analyzing the qualified regions;generating a quantifiable value for each qualified region;generating a markup image based on the quantifiable values corresponding to the qualified regions;generating a score map measurement for each qualified block based on the quantifiable values corresponding to the qualified regions. 5. The system of claim 4, wherein the processor is further programmed to determine the slide quality of a digital microscope slide by:combining the score map measurements;performing artifact detection; andcomputing a whole slide score in accordance with the combined score map measurements and detected artifacts. 6. A computer implemented method for determining the slide quality of a digital microscope slide, where one or more processors are programmed to perform steps comprising:micro-analyzing the digital microscope slide by:dividing the digital microscope slide image into a plurality of regions;qualifying a portion of the plurality of regions;analyzing the qualified regions;generating a quantifiable value for each qualified region;generating a score map measurement for each qualified region based on the quantifiable values corresponding to each region; andgenerating a markup image based on the quantifiable values corresponding to the qualified regions. 7. The computer implemented method of claim 6, further comprising:macro-analyzing the digital microscope slide by:combining the score map measurements;performing artifact detection; andcomputing a whole slide score. 8. A computer implemented method for scanning and determining the slide quality of a digital microscope slide, comprising:scanning a tissue specimen arranged on a microscope slide using a microscope slide scanner to generate a first digital microscope slide image;determining the slide quality of the first digital microscope slide image by performing steps comprising:micro-analyzing the first digital microscope slide image by:dividing the first digital microscope slide image into a plurality of regions;qualifying a portion of the plurality of regions;analyzing the qualified regions;generating a quantifiable value for each qualified region; andgenerating a markup image based on the quantifiable values corresponding to the plurality of qualified regions; andgenerating a second digital microscope slide image if the first digital microscope slide image is determined to be of poor quality. 9. The method of claim 8, wherein determining the slide quality of the first digital microscope slide image further comprises:macro-analyzing the first digital microscope slide image by:generating a score map measurement for each qualified region based on quantifiable values corresponding to each region;combining the score map measurements;performing artifact detection; andcomputing a whole slide score. 10. A computer implemented method for determining the slide quality of a digital microscope slide, where one or more processors are programmed to perform steps comprising:dividing the digital microscope slide image into a plurality of regions;dividing at least one of said plurality of regions into a plurality of blocks;determining a spatial frequency value for each block in said plurality of blocks;combining at least a portion of said spatial frequency values for said plurality of blocks into a block score;determining an image quality level for each of the respective plurality of blocks based upon an analysis of the block scores for each of the respective plurality of blocks;generating a score map comprising the block scores for said plurality of blocks; andcombining the score map measurements to compute a whole slide score. 11. The method of claim 10, wherein said at least a portion of said spatial frequency values for said plurality of blocks comprises only those spatial frequency values that exceed a predetermined value. 12. The method of claim 10, wherein each of said at least a portion of said spatial frequency values for said plurality of blocks is weighted. 13. The method of claim 12, wherein higher frequency values are weighted higher. 14. The method of claim 10, wherein the amount each of said plurality of blocks contributes to the block score is uniform. 15. The method of claim 10, wherein the amount each of said plurality of blocks contributes to the block score is determined by magnitude of the spatial frequency. |
|
abstract | A gas-cluster-jet generator with improved vacuum management techniques and apparatus is disclosed. The gas-cluster-jet generator comprises a substantially conically shaped vacuum chamber for housing the nozzle and jet exit portions of the gas-cluster-jet generator. A skimmer may be located at the narrow end of the conical chamber and a close-coupled vacuum pump is located at the wide end of the conical chamber. Support members for the nozzle are high conductivity “spider” supports that provide support rigidity while minimizing gas flow obstruction for high pumping speed. The conically shaped vacuum chamber redirects un-clustered gas in a direction opposite the direction of the gas-cluster-jet for efficient evacuation of the un-clustered gas. The nozzle and a skimmer may have fixed precision relative alignment, or may optionally have a nozzle aiming adjustment feature for aligning the gas-cluster-jet with the skimmer and downstream beamline components. Also disclosed are various configurations of gas-cluster ion-beam processing tools employing the improved gas-cluster-jet generator. |
|
description | This application is a continuation of U.S. application Ser. No. 12/354,823, filed Jan. 16, 2009 now U.S. Pat. No. 8,217,348, and which application claims priority from Japanese application serial no. JP2008-040818, filed on Feb. 22, 2008, the contents of which are hereby incorporated by reference into this application. The present invention relates to a method for evaluating and managing a resist pattern formed on a wafer in a semiconductor manufacturing process, and more particularly to a technique for measuring and evaluating the amount of film thickness reduction of a resist (a reduction in height of a resist pattern) using an electron microscope image of the resist pattern. Conventionally, a length-measuring scanning electron microscope (SEM) which is an electron microscope for the purpose of measuring a dimension of the pattern is widely used as a process management tool in a lithography process. The length-measuring SEM enables imaging at high magnification of a hundred thousand times to three hundred thousand times, and thus can measure the dimension of a fine pattern of the order of several tens of nanometers with an accuracy of 1 nanometer or less. The basic structure of the length-measuring SEM is disclosed in Tatsuhiko Higashiki, Ed. “Photolithography II—Measurement and Control—”, ED Research Co., Ltd., pp. 31-41 (2003). The lithography process involves transferring a circuit pattern onto a wafer by exposure and development of a resist, and etching along the resist pattern transferred. The length-measuring SEM is used to measure the dimension of the transferred resist pattern or the pattern etched. In particular, wiring patterns including a transistor gate wiring are subjected to strict dimensional control because the width of the pattern is strongly related to device performance. FIG. 2A shows sectional shapes of the patterns before etching, during etching, after etching in that order from left side thereof. The length-measuring SEM measures a resist pattern width W1, or a pattern width W2 after the etching. In a conventional lithography process, the resist pattern width W1 within the standard allows the pattern width W2 after the etching to be restrained within the standard. Thus, sufficient process management is available by monitoring measurement results of the widths W1 and W2. In order to satisfy the need for microfabrication of patterns, a high NA exposure technique has been developed for obtaining a resolution required for formation of a fine pattern. As a result, a margin for the exposure process becomes small, and a small variation of an exposure parameter, such as a dose amount or a focus position in exposure, leads to film thickness reduction of the resist pattern, that is, a decrease in height of the resist as compared to the case of the normal exposure. As shown in FIG. 2B, when a height of a pattern is low (h1<H1) even with the same pattern width before etching as that shown in FIG. 2A (w1=W1), a pattern width after the etching becomes smaller (w2<W2). During the etching, the thickness of the resist is gradually decreased. When the original pattern thickness is low, the resist pattern almost disappears during etching, and then a film of interest for process may be itself etched as shown in the center drawing in FIG. 2B. As mentioned above, the pattern width after the etching is directly related to the device performance. The condition which may cause the reduction in pattern width after the etching as shown in FIG. 2B is not appropriate. In order to introduce the high NA exposure technique, only measurement of the pattern width (W1, w1) is not sufficient in a resist pattern stage from a point of view of process management, and also a pattern height (H1, h1) is desired to be measured together with the width. Methods for measuring a pattern height can include measurement using an electron microscope for observation of a section of a wafer by dividing the wafer, and measurement using an atomic force microscope (AFM). The former needs dividing the wafer, which cannot be apparently applied to the normal in-line process management. The latter is not appropriate for use in monitoring the process which needs high throughput. The invention provides a system for achieving detection and measurement of film thickness reduction of a resist pattern with high throughput which can be applied to part of in-line process management. That is, the invention has been made by taking into consideration the following. When a resist pattern is formed under an exposure condition deviating from the normal exposure condition, the resist pattern has film thickness reduction together with some surface roughness (roughness) of the upper surface of the resist. Thus, the invention is adapted to calculate an index value of film thickness reduction of the resist pattern with respect to a resist pattern formed on the normal exposure condition by quantifying the degree of roughness of a part corresponding to the upper surface of the resist on an electron microscope image of the resist pattern. The invention not only calculates a film thickness reduction index value, but also estimates the amount of film thickness reduction of a resist pattern actually formed as compared to the resist pattern formed on the normal exposure condition by applying the calculated index value to a database previously stored for relating a film thickness reduction index value to an amount of film thickness reduction of a resist pattern. Further, the invention is adapted to make the database for relating the film thickness reduction index value to the amount of film thickness reduction of the resist pattern by calculating the index values from electron microscope images of the resist patterns formed under various exposure conditions, measuring the heights of the resist patterns by a height measuring device, and registering the relationship between the film thickness reduction index values and the results of measurement of the heights. That is, the invention provides an electron microscope system which includes electron beam image obtaining means for obtaining an image of a specimen having a resist pattern formed on a surface thereof using a scanning electron microscope, quantifying means for quantifying a feature of variations in brightness of the image at a desired area of the resist pattern by processing the obtained image, index value calculating means for calculating an index value for relating the feature of variations in brightness of the image quantified by the quantifying means to an amount of reduction from a reference value of a film thickness of the resist pattern, and display means for displaying information about the index value calculated by the index value calculating means on a screen. Further, the invention provides an electron microscope system which includes electron beam image obtaining means for obtaining an image of a specimen having a resist pattern formed on a surface thereof using a scanning electron microscope, quantifying means for quantifying a feature of variations in brightness of the image at a desired area of the resist pattern by processing the obtained image, index value calculating means for calculating an index value for relating the feature of variations in brightness of the image quantified by the quantifying means to an amount of reduction from a reference value of a film thickness of the resist pattern, estimation means for estimating the amount of reduction from the reference value of the film thickness of the resist pattern using the index value calculated by the index value calculating means, and display means for displaying information about the amount of reduction from the reference value of the film thickness of the resist pattern calculated by the estimation means on a screen. Further, the invention provides a method for evaluating film thickness reduction of a resist pattern using an electron microscope system which includes the steps of obtaining an image of a specimen having a resist pattern formed on a surface thereof using a scanning electron microscope, quantifying a feature of variations in brightness of the image at a desired area of the resist pattern by processing the obtained image, calculating an index value for relating the feature of variations in brightness of the image quantified to an amount of reduction from a reference value of a film thickness of the resist pattern, and displaying information about the index value calculated on a screen. Moreover, the invention provides a method for evaluating film thickness reduction of a resist pattern using an electron microscope system which includes the steps of obtaining an image of a specimen having a resist pattern formed on a surface thereof using a scanning electron microscope, quantifying a feature of variations in brightness of the image at a desired area of the resist pattern by processing the obtained image, calculating an index value for relating the feature of variations in brightness of the image quantified to an amount of reduction from a reference value of a film thickness of the resist pattern, estimating the amount of reduction from the reference value of the film thickness of the resist pattern using the calculated index value, and displaying information about the amount of reduction from a reference value of a film thickness of the resist pattern estimated on a screen. Accordingly, the invention can detect and measure the film thickness reduction using the image, which has been used by a conventional line width measurement method, and thus can monitor the film thickness reduction, which is a serious process failure, without reducing a throughput of the conventional process management. The invention is applied to extraction of conditions for the exposure process, that is, optimization of the dose amount and focus position thereby to enable more effective setting of a process window as compared to the use of only the conventional line width measurement result. These and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings. Now, a method for measuring film thickness reduction of a resist using an electron microscope according to the invention will be described below with reference to the accompanying drawings. (First Embodiment) The configuration of an SEM system associated with the measurement method of film thickness reduction of the resist using the electron microscope of the invention, and the entire flow of the method will be described below. Then, each step of the method will be described in detail, and further, the SEM system employing thereon the method will be described. [SEM System] FIG. 1A shows a configuration of the length-measuring SEM system having a function of measuring film thickness reduction according to the first embodiment. The length-measuring SEM system of this embodiment includes an SEM main unit 10, an image processing and whole controller 109, an arithmetic processor 110, and a database section 113, and is connected to a data server 116 via a network. The SEM main unit 10 includes an electron gun 101, an accelerating electrode 103 for accelerating an electron beam 102 emitted from the electron gun 101, a focusing lens 104, and a deflecting lens 105 for deflecting a track of the electron beam 102. The SEM main unit 10 also includes an objective lens 106 for controlling a position of focus of the electron beam 102 such that the focus position on which the electron beam 102 converges is positioned on a surface of a specimen 107 with a pattern formed thereon, and a detector 108 for detecting part of secondary electrons generated from the specimen 107 to which the electron beam 102 is applied. A detection signal of the detector 108 is fed to and processed by the image processing and whole controller 109 thereby to obtain an SEM image. The SEM image is processed in use by the arithmetic processor 110 with reference to information stored in the database section 113, and information regarding film thickness reduction is extracted. The result is fed to and stored in the data server 116 via a communication line. The specimen 107 is put on a table (not shown). The table (not shown) is controlled by the image processing and whole controller 109 such that a desired area on the specimen is positioned at an area for irradiation of the electron beam 102. The arithmetic processor 110 includes a film thickness reduction index value measuring section 111, a database verification section 112, a film thickness reduction amount estimating section 114, and an input and output section 115 with a display screen. [Entire Flow] FIG. 1B is an entire flowchart of measurement of film thickness reduction performed by the arithmetic processor 110. (Step S1): A resist pattern is imaged by the SEM 10, and a signal obtained by the imaging is processed by the image processing and whole controller 109 to obtain an SEM image of the specimen. (Step S2): An index value of film thickness reduction is calculated from the obtained image by a method to be described later. (Step S3): The film thickness reduction index value calculated is verified against a database 20 which registers a relationship between film thickness reduction index values and amounts of film thickness reduction of patterns actually formed based on a resist pattern formed under a normal exposure condition stored in the database section 113. A method for making the database 20 will be described later using FIG. 1C.(Step S4): The amount of film thickness reduction of the pattern actually formed according to the resist pattern formed under the normal exposure condition is estimated based on the result of verification. The verification result is displayed on a display screen of the input and output section 115. The entire of the film thickness reduction measurement has been described. Each step of the flow will be described below in detail. [Calculation of Film Thickness Reduction Index Value] Step S2 shown in FIG. 1B will be described below in detail. The film thickness reduction of the pattern actually formed based on the resist pattern formed under a normal exposure condition is caused by applying excessive light to a resist pattern portion to which the light should not be applied inherently, in particular, an upper portion of the resist pattern. The irradiation of the upper portion of the resist pattern with the excessive light may be caused by focus displacement in exposure, or by an increase in dose amount. Resist material commonly used has such properties that the more the amount of irradiated light, the larger the roughness of a surface (surface roughness). The film thickness reduction is caused by irradiating the resist pattern upper portion with the excessive light, which inevitably leads to roughness of the surface of the upper portion of the resist pattern. In the invention, this mechanism is used to quantify a change in roughness of the surface of the pattern upper portion on the SEM image together with the film thickness reduction, and the quantified change is used as a film thickness reduction index value. FIG. 3A shows an SEM image without film thickness reduction, and FIG. 3B shows an SEM image having film thickness reduction. In the SEM image, a flat portion is detected to be dark, and an inclined portion is detected to be bright by an inclined angle effect. The edge of the surface with roughness is detected to be bright in a streaky manner. As shown in FIG. 3A, a portion enclosed by a dotted line corresponds to the upper surface of the resist pattern. The reason for irregular bright areas shown in FIG. 3B is due to existence of the roughness as compared to the case shown in FIG. 3A. Now, methods for quantifying features on the image include the following examples. (A): A projected waveform on a Y axis of an area (an area enclosed by the dotted line shown in FIGS. 3A and 3B) corresponding to an upper portion of a pattern in an SEM image is generated (in FIG. 3C, a longitudinal axis SE intensity indicates the brightness of the SEM image, and a lateral axis Y indicates the position). The brightness variation of the projected waveform is represented by the standard deviation σ to be used as a roughness index value, that is, a resist film thickness reduction index value. As the roughness becomes larger, variations in brightness are increased, resulting in large standard deviation 6. FIG. 4B shows the projected waveforms on the Y axis for various amounts of film thickness reduction (as the reference number increases from (i) to (v), the amount of film thickness reduction becomes larger). As shown in the figure, as the amount of film thickness reduction becomes large, the index value takes a large one. According to this method, since a certain zone is projected to enable decreasing the influence of high frequency noise specific to the SEM by an averaging effect, the brightness variation due to the surface roughness can be detected with good sensitivity. The averaging processing is performed in the direction of width of a pattern line, which can reduce an influence of change in brightness due to a change in shape of the pattern other than the film thickness reduction. An area of the pattern in the longitudinal direction for generating the projected waveform is made longer, which can improve the high accuracy of the film thickness reduction index value. In graphs shown in (i) to (v) in FIG. 4B, the longitudinal axis and the lateral axis are the same as those shown in FIG. 3C, and a description thereof is omitted below.(B): A brightness histogram of an area corresponding to the pattern upper portion in the SEM image (enclosed by the dotted line shown in FIGS. 3A and 3B) is made (see FIG. 3D), and then the histogram is applied to a normal distribution. At that time, the σ value or the center of the normal distribution is used as a resist film thickness reduction index value. Specifically, the histogram is made by determining an appearance frequency for each brightness on the longitudinal axis from the projected waveform onto the Y axis determined by the above-mentioned method (A). The concept of this method is the same as that of the above method (A). This method involves qualifying by use of the feature that as the roughness becomes larger, the brightness variation is increased averagely toward the brighter level. FIG. 4C shows a histogram of each of various amounts of film thickness reduction (as the reference number increases from (i) to (v), the amount of film thickness reduction becomes large). Also, as the amount of film thickness reduction becomes larger, the index value takes a larger one. In the graphs shown in (i) to (v) in FIG. 4C, the longitudinal axis and the lateral axis are the same as those shown in FIG. 3D, and a description thereof is omitted below.(C): A projected waveform of the SEM image on the X axis is generated, and the minimum value of the center of the waveform (indicated by “min” shown in FIG. 3E) is set as the film thickness reduction index value. The edge having some surface roughness is detected to be bright in the streaky manner with increasing roughness. Thus, this method involves qualifying by use of the feature that as the roughness becomes larger, the brightness is increased averagely. FIG. 4D shows a projected waveform on the X axis of each of various amounts of film thickness reduction (as the reference number increases from (i) to (v), the amount of film thickness reduction becomes large). Also, as the amount of film thickness reduction becomes large, the index value takes a large one. This method advantageously has an excellent effect of reducing SEM noise by averaging over a wide area. This index value is apt to be influenced by a change in shape other than the film thickness roughness, in particular, together with the change in shape of the pattern top portion. Thus, the index value is effective for an object whose change in shape other than the film thickness reduction is small. In the graphs shown in (i) to (v) in FIG. 4D, the longitudinal axis and the lateral axis are the same as those shown in FIG. 3E, and a description thereof is omitted below.(D): A method for texture analysis can be applied as disclosed in Mikio Takagi and Haruhisa Shimoda, Ed. “Image Analysis handbook”, University of Tokyo Press, Function I, chapter 2 (1991). That is, a power spectrum of an area corresponding to the upper portion in the SEM image is determined, and the roughness of a texture is quantified from frequency properties. Alternatively, another method for quantifying the features of the image can involve combining some of the above various methods together. A further method can involve weighting and adding up various index values in use.[Method for Making Database 20] FIG. 1C shows a flowchart for making the database 20 stored in the database section 113. (Step S11): Samples with resist patterns formed under various exposure conditions are prepared for making the database 20. For example, a focus exposure matrix (FEM) wafer may preferably be used. The FEM wafer has the focus position and dose amount of one wafer changed as exposure conditions within a range in which these conditions can be varied.(Step S12): SEM images of the resist pattern samples prepared and formed under the various exposure conditions are obtained, and then film thickness reduction index values are calculated by any one of the methods (A) to (D) described in the above paragraph “Calculation of Film Thickness Reduction Index Value”.(Step S13): The height of the resist pattern of each same sample is measured by height measuring means, such as an atom force microscope (AFM), a scatterometry (lightwave scattering measurement), or observation of a pattern section using the SEM, thereby to determine the amount of film thickness reduction of the resist. Instead of actually measuring the height of the pattern, the height determined by calculating the sectional shape of the resist pattern under each of the various exposure conditions by an exposure simulation may be used.(Step S14): The relationship between the thus-obtained amount of film thickness reduction and the film thickness reduction index value is shown in the graph 21. As mentioned above, the larger the amount of film thickness reduction, the larger the film thickness reduction index value. In response to the result, an approximate function is calculated as the relationship between the amount of film thickness reduction and the film thickness reduction index value. At the same time, variations in amount of film thickness reduction respective to the film thickness reduction index value may be calculated. A look-up table format may be used in place of the approximate function.(Step S15): The approximate function calculated as the relationship between the amount of film thickness reduction and the film thickness reduction index value is stored in the database. The relationship of variations in amount of the film thickness reduction with respect to the calculated film thickness reduction index value is stored in the database.(Verification Against Database and Estimation of Amount of Film Thickness Reduction) Steps S3 and S4 shown in FIG. 1B will be described below in detail. In step S3 shown in FIG. 1B, an absolute value of the amount of film thickness reduction is estimated by substituting the index value calculated in step S2 into the approximate function calculated as the relationship between the amount of film thickness reduction and the film thickness reduction index value by the above database 20, or by referring to the look-up table based on the relationship between the amount of film thickness reduction and the film thickness reduction index value. The use of the index value calculated in step S2 can grasp an error of the above estimation result of the amount of film thickness reduction from the relationship of variations in amount of film thickness reduction with respect to the index value which relationship is stored in the database 20. [GUI] FIG. 5 shows an example of a graphic user interface (GUI) screen 500, which is one example of an input and output screen of the input and output section 115 of the SEM system in this embodiment. The GUI screen includes an input screen required to form and update the database 20 of the database section 113 for previously storing the relationship between the film thickness reduction amount and the film thickness reduction index value. The GUI screen 500 includes an input portion 501 for inputting a name of the database 20 to be newly registered or updated. The GUI screen 500 displays information selected from the database 20 according to the name input in the form of a data list 506 and a graph 507. The GUI screen 500 also includes a portion 502 for selecting a measurement recipe for obtaining a film thickness reduction index value for registration, and an image display area 504 for displaying an image 503 registered in the recipe selected. The GUI screen 500 further includes a portion 505 for selecting an area on the SEM image used for calculation of the film thickness reduction index value on the image 503 displayed. After inputting these items, a cursor (not shown) is moved to a button 508 for execution of the recipe and then a mouse (not shown) is clicked, whereby calculation of a film thickness reduction index value is performed based on the set conditions. Data about the film thickness reduction index value calculated is automatically updated, and then the data list 506 is also corrected. Further, data about the amount of film thickness reduction obtained by another device or means can be input into the data list 506 displayed on the screen 500. In order to store the input data in the database 20, an updating button 509 may be preferably clicked. This operation is performed to make the relationship between the amount of film thickness reduction and the film thickness reduction index value in the form of function, which is registered in the database 20. The input and output section 115 of the SEM system further displays a GUI screen 600 which includes a setting section for verification against the information in the database 20 and for estimation of the amount of film thickness reduction, and an output section for displaying the result. FIG. 6 shows an example of the GUI screen 600. In setting a measurement condition, the GUI screen 600 includes a portion 601 for selecting the database 20 for calculation of the film thickness reduction amount for reference, and a portion 602 for displaying an area for use in the film thickness reduction index value on the SEM image automatically obtained by the selection based on the information in the database. The GUI screen 600 further includes a portion (film thickness reduction evaluation image selector) 603 for selecting an image for evaluating the amount of film thickness reduction from the sets of images obtained, and an exertion button 604 for instructing calculation of the film thickness reduction index value for the selected image and for estimation of the amount of film thickness reduction. The GUI screen 600 also includes a portion 606 for displaying the selected image 605. The GUI screen 600 further includes a portion (a recipe selector for evaluation of film thickness reduction) 607 for selecting a measurement recipe, and an execution button 608 for calculation of the film thickness reduction index value and for estimation of the amount of film thickness reduction based on the recipe selected. The cursor (not shown) is moved to the execution button 608 on the screen 600 and then the mouse (not shown) is clicked, whereby calculation of a film thickness reduction index value and estimation of the amount of film thickness reduction are performed based on the set conditions. The result is displayed in the form of the graph 610 and the data list 609 together with estimated errors. As mentioned above, the invention can detect and measure the film thickness reduction using the image, which has been used by a conventional line width measurement method, and thus can monitor the film thickness reduction without reducing a throughput of the conventional process management. The invention may be applied to extraction of conditions for the exposure process, that is, optimization of the dose amount and focus position in exposure. The condition for preventing the occurrence of film thickness reduction is incorporated, which can set a more effective process window as compared to the use of only the conventional line width. (Second Embodiment) A second embodiment of the invention is shown in FIG. 7. In the first embodiment, the film thickness reduction index value is calculated from the SEM image (in step S2), and then is verified against the database (in step S3), whereby the absolute value of the film thickness reduction amount is estimated (in step S4), and the film thickness reduction index value and the amount of film thickness reduction are output. However, in the second embodiment, only the calculation of the film thickness reduction index value from the SEM image is performed (in step S2) without estimating the amount of film thickness reduction in steps S3 and S4, so that only information regarding the film thickness reduction index value is output (in step S6). A method for calculating the film thickness reduction index value from the SEM image in this embodiment (in step S2) is the same as that described in the first embodiment. GUI screens of the input and output section of this embodiment are basically the same as those described in FIGS. 5 and 6 except that the column for the amount of film thickness reduction provided in the data list 506 shown in FIG. 5 is not provided, and that the columns for the estimation result of the film thickness reduction amount and for the estimated error provided in the data list 609 shown in FIG. 6 are not provided. FIG. 7B shows other examples of outputs in this embodiment. According to this embodiment, the index value represents a relative change in amount of film thickness reduction. As shown in FIG. 7B, the trend of the index value is monitored, whereby the process variation can be monitored. (Third Embodiment) A third embodiment of the invention is shown in FIG. 8. Although the first and second embodiments have described the method for measuring the resist pattern formed on the wafer, this embodiment has an object to detect a decrease in line width of a circuit pattern formed on a wafer together with the film thickness reduction of a resist pattern in the case of etching using the resist pattern as a mask. This embodiment employs a database 30 which registers a relationship between a resist line width and an etching bias, that is, between a line width of a resist pattern and a line width of the pattern etched, instead of the database for registering the relationship between the amount of film thickness reduction and the film thickness reduction index value in the first embodiment thereby to estimate an etching bias from the result of measurement of the film thickness reduction index value (in steps S23 and S24). Now, a method for making the database 30, and an SEM system employing the method will be described below. [SEM System] FIG. 8A shows the configuration of a length-measuring SEM system including a function of measuring the film thickness reduction in this embodiment. The length-measuring SEM system of this embodiment includes an SEM main unit 80, an image processing and whole controller 81, an arithmetic processor 82, and a database section 83. The SEM system is connected to a data server 84 via a network. The configurations of the SEM main unit 80 and the image processing and whole controller 81 are the same as those of the first embodiment described with reference to FIG. 1A. In this embodiment, the SEM image output from the image processing and whole controller 81 is processed in use by the arithmetic processor 82 with reference to information stored in the database section 83, and information regarding an etch bias is extracted. The result is fed to and stored in the data server 116 via a communication line. The arithmetic processor 82 includes a film thickness reduction index value measuring section 821, a database verification section 822, an etch bias estimation section 823, and an input and output section 824 having a display screen. [Entire Flow] FIG. 8B shows an entire flowchart of estimation of an etch bias performed by the arithmetic processor 82. (Step S21): A resist pattern is imaged by the SEM 80, and a signal obtained by the imaging is processed by the image processing and whole controller 81 to obtain an SEM image of a specimen. (Step S22): A film thickness reduction index value is calculated from the obtained image in the same way as that in step S2 of the first embodiment. (Step S23): The calculated index value is verified against the database 30 stored in the database section 83 for registering the relationship between the line width of the resist pattern and the line width of the pattern etched. A method for making the database 30 will be described later using FIG. 8C.(Step S24): An etch bias is estimated based on the result of verification.(Step S25): The estimated result is displayed on the display screen of the input and output section 824, and is then fed to and stored in the data server 84 via a communication line. The entire flow of estimation of the etch bias in this embodiment has been described above. The details of the main flow will be described below. [Method for Making Database] FIG. 8C shows the flow for making the database 30 for registering the relationship between the line width of the resist pattern and the line width of the pattern etched in this embodiment. (Step S31): Samples with resist patterns formed under various exposure conditions are prepared in the same way as that described in step S11 of the first embodiment. (Step S32): The film thickness reduction index value is calculated, and the line width of the pattern is measured in the same way as that in step S12 of the first embodiment. (Step S33): The height of the resist pattern is measured in the same way as that described in step S13 of the first embodiment thereby to determine the amount of film thickness reduction of the resist. (Step S34): A wafer with the resist pattern formed thereon is subjected to etching. (Step S35): The line width of the pattern formed on the wafer by the etching is measured. The wafer used in this step may be the same as that used in steps S32 and S33, or alternatively, may be another wafer obtained by the same process. Data about the measured line width of the pattern formed on the wafer etched is stored in relation to data about the dimension of the resist pattern measured in step S32, and the height of the resist pattern measured in step S33.(Step S36): A relationship between the amount of film thickness reduction of the resist determined in step S33 and an etching bias which is a difference between the line width of the resist pattern determined in step S32 and the line width of the etched pattern determined in step S35 is determined. One example of the relationship determined is represented in a graph 31. Based on the result, an approximate function is calculated, and the relationship between the etching bias and the film thickness reduction index value is determined(Step S37): A relationship between the etching bias determined and the film thickness reduction index value is stored in the database 30. At the same time, the film thickness reduction index value at which the etching bias increases is stored as a threshold, and further, variations in etching bias with respect to the film thickness reduction index value is calculated and then stored in the database 30.[Estimation of Etching Bias] In step S24 of estimating an etching bias as shown in FIG. 8B, the film thickness reduction index value calculated in step S22 is substituted into the approximate function on the database 30 calculated by the above step S36 thereby to estimate an etching bias. Alternatively, it is determined whether or not the etching bias exceeds the threshold. [GUI] FIG. 9 shows an example of the GUI screen 900 as one example of the input and output screen of the input and output section 84 of the SEM system according to this embodiment. The GUI screen is the same as one obtained by replacing the amount of film thickness reduction by the etch bias on the GUI screen shown in FIG. 5 of the first embodiment. More specifically, the GUI screen 900 includes an input portion 901 for inputting a name of the database 30 to be newly registered or updated. The GUI screen 900 displays information selected from the database 30 according to the name input in the form of a data list 906 and a graph 907. The data list 906 of this embodiment displays an etching bias value in addition to the film thickness reduction index value of the resist pattern, in place of the column for the film thickness reduction amount at the data list 506 of the first embodiment shown in FIG. 5. The etching bias value is a difference between a resist CD value (a dimension value of the resist pattern determined from the SEM image) and an etch CD value (a dimension value of the pattern formed on the wafer after etching which value is determined from the SEM image), and between a line width of the resist pattern (resist CD value) and a line width of the pattern etched (etch CD value). The graph 907 displayed in this embodiment differs from the case of the first embodiment shown in FIG. 5 in that the relationship between the etch bias and the film thickness reduction index value is displayed. On the other hand, the screen 900 includes a portion 902 for selecting a measurement recipe for obtaining a film thickness reduction index value for registration, an image display area 904 for displaying an image 903 registered in the selected recipe, and a portion 905 for selecting an area on the SEM image for use in calculation of the film thickness reduction index value on the displayed image 903. The screen 900 also includes a button 908 for executing the recipe after inputting these items, and a data list 906 adapted to be corrected by calculating the film thickness reduction index value based on the above set conditions, and automatically updating data, like the first embodiment. Further, data about the amount of film thickness reduction obtained by another device or means can be input to the data list 906 displayed on the screen 900. The storage of the input data in the database 30 only requires clicking of an updating button 909. This operation makes the relationship between the amount of film thickness reduction and the film thickness reduction index value in the form of function, which is registered in the database 30. The input and output section 824 of the SEM system displays a GUI screen 1000 including a setting section for estimating the amount of film thickness reduction by verification against the information of the database 30, and an output section for displaying the result. The GUI screen 1000 has a similar structure to that of the GUI screen 600 shown in FIG. 6 as described in the first embodiment. Like the first embodiment described above, in setting a measurement condition, the GUI screen 1000 includes a portion 1001 for selecting the database 30 for calculation of the film thickness reduction amount for reference, and a portion 1002 for displaying an area for use in the film thickness reduction index value on the SEM image automatically obtained by the selection based on the information of the database. Further, the GUI screen 1000 also includes a portion (film thickness reduction evaluation image selector) 1003 for selecting an image for evaluating the amount of film thickness reduction from the sets of images obtained, and an exertion button 1004 for instructing calculation of the film thickness reduction index value and for estimation of the amount of film thickness reduction for the selected image. The GUI screen 1000 further includes a portion 1006 for displaying an image 1005 selected. The GUI screen 1000 further includes a portion (recipe selector for evaluation of film thickness reduction) 1007 for selecting a measurement recipe, and an execution button 1008 for calculation of the film thickness reduction index value and for estimation of the amount of film thickness reduction based on the recipe selected. The cursor (not shown) is moved to the execution button 1008 on the screen 1000 and then the mouse (not shown) is clicked thereby to perform calculation of a film thickness reduction index value and of an etch bias, estimation of an error of the amount of film thickness reduction, and determination of NG, based on the set conditions. The results are displayed in the data list 1009, and the relationship between the etch bias and the film thickness reduction index value is displayed as the graph 1010. According to this embodiment, as shown in the graph 31 of FIG. 8, the relationship between the amount of film thickness reduction and the dimension of the pattern etched is not linear. When the amount of film thickness reduction exceeds a certain value, the etch bias quickly increases. This embodiment can determine whether or not the film thickness reduction caused is at a problematic level from a viewpoint of device characteristics. The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. |
|
051981858 | description | DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 shows a portion of an existing type of reactor 10. The portion shown is interior to a reactor vessel, namely, a portion of a reactor 10 having a plenum 12 and a shield 14. Coolant, as indicated by the arrows, flows into plenum and circulates among a plurality of penetrations 16. There is one penetration 16 for each fuel element 18. Only three penetrations 16 are shown although a greater number exists, perhaps 600. The left side of FIG. 1 represents a typical penetration 16 near the center of the reactor core; the right side, the reactor periphery; the center, an intermediate penetration 16. The purpose of penetrations 16 is to provide a path for coolant to flow down through shield 14 and into each element 18 to remove the heat of fission and radioactive decay. Penetration 16 comprises a slotted tube 24 having a plurality of vertical slots 26, a universal sleeve housing 28 within slotted tube 24 that extends from just above plenum 12 downward, surrounding fuel element 18. Universal sleeve housing 28 has an upper portion 30 and a lower portion 32 defined essentially by plenum 12 so that lower portion 32 is generally below plenum 12 and upper portion 30 is even with plenum 12. Universal sleeve housing 28 has a plurality of holes 38 in upper portion 30 arranged in rows and columns to allow the passage of coolant from plenum 12 through slots 26 and thence into interior 40 of sleeve 28. In lower portion 32 are orifice plates 44, 46, 48 which have holes 50. Orifice plates 44, 46, 48 are to restrict flow to fuel elements 18. Plates 44, 46, 48 will restrict more for peripheral positions than core interior positions, as suggested by the relative number of holes 50 in FIG. 1, which number is illustrative only. The number of holes 50 in orifice plates 44, 46, 48 varies from sleeve to sleeve. Slots 26 are lined up with holes 38 by a conventional keying arrangement between slotted tube 24 and housing 28. Toward the center of the core, orifice plates will have more holes than toward the periphery; for example, orifice plate 44 will have more holes 50 than orifice plate 46, which is at an intermediate position, and orifice plate 48, near the periphery of the core, will have the fewest holes 50. The number of holes 50 determines the amount of restriction in the flow of coolant to fuel elements 18. The fewer the number of holes 50, the lower the flow of coolant through orifice plates, 44, 46, 48. FIG. 2 shows a portion of a reactor 56 corresponding to that shown in FIG. 1. Reactor 56, however, incorporates the present invention. Reactor 56 has a plenum 58 and a shield 60. As with reactor 10 of FIG. 1, reactor 56 has penetrations 62 for its fuel elements 64. Penetrations 62 also have a slotted tube 70 with slots 72. However, each fuel element 64 is not surrounded with a universal sleeve housing as in reactor 10 of FIG. 1. Reactor 56 has a set of housings, generally similar to universal sleeve housing 28, but each different with respect to each other. FIG. 2 shows three housings 74, 76, 78, with housing 74 located toward the center of the reactor core, housing 76 located farther from the core center and housing 78 located near the core periphery. Housings 74, 76, 78 have holes 84 that allow coolant from plenum 58 to flow into the interiors 86, 88, 90, of housings 74, 76, 78, respectively, through slots 72 of slotted tube 70. Each housing 74, 76, 78, will have an upper portion 80 and a lower portion 82. Upper portion 80 is defined by plenum 58; that is, lower portion 82 is the part of housings 74, 76, 78 below plenum 58. Although holes 84 are shown in FIG. 2 to be of the same diameter and arranged in rows and columns, it is not necessary that the holes be of the same size or so arranged, although it is preferable to do so. It is important, however, to vary (and to control) the amount of coolant admitted to interiors 86, 88, 90, admitting more coolant to those interiors of penetrations near the center of the core and less to those near the periphery of the core. The amount may be varied by changing the total area of the holes of the housings through which coolant flows by varying the diameter of holes 84, by changing the number of holes 84, or, in fact, by changing the shape of the holes, to slots or ovals for example. The amount of coolant flowing to fuel elements 64 should be greatest toward the center of the reactor core and less farther out, least to the peripheral fuel elements 64. Although three housings (74, 76, 78) are shown in FIG. 2, a reactor core can be divided into an arbitrary number of zones (housings 74, 76, 78 representing three different zones) in the form of rings from the center of the core outward, with the amount of coolant entering the interior of the housings of fuel elements in each zone being equal and each outwardly laying zone receiving less coolant than those located in the immediately adjacent, inward zone. There are two design parameters that affect the amount of flow of coolant into fuel elements 64: the flow area of holes 84 and the elevation of that area relative to the coolant level in plenum 58. Therefore, in addition to holes 84 being all the same diameter and arranged in rows and columns, all housings 74, 76, 78 will preferably have rows beginning at the bottom of upper portion 80 and continuing up toward the top of upper portion 80. The number of rows of holes 84 will then be fewest in housing 78 and greatest for housing 74. There are no orifice plates in reactor 56. Although orifice plates also serve to restrict flow as does a reduction in the number of holes 84, the impact on the flow of fewer rows of holes in housings 76 and 78 than in 74 results in greater coolant flow to housings 74 under accident conditions. In reactor 56, the peripheral fuel elements 64 receive less coolant during normal operation than the interior fuel elements 64. FIGS. 3 and 4 illustrate the effect on flow to fuel elements 64 graphically. FIG. 3 is in particular a graph of several series of data points, each series corresponding to a number of zones. The graph shows the minimum flow of coolant to fuel elements during a LOCA versus the height of holes 84 beginning with a row on the bottom of upper portion 80. If the top rows of holes in the outermost zones are eliminated, the minimum flow of coolant increases. If the number of rows eliminated is five from the housings in the outer three zones of a particular reactor, minimum flow increases from 10.3 to 12.6 gallons per minute, a 22% increase. Greater increases are seen as more zones are revised to have five fewer rows. For five zones, the increase is 56% more coolant. In FIG. 4 the minimum coolant flow is graphed versus the number of zones having fewer holes. The different curves illustrate the change in flow versus the number of affected zones when different numbers of rows are eliminated. It will be seen that the larger the number of rows eliminated and the more zones that are affected, the greater will be the increase in the minimum flow of coolant during a LOCA. At some point, however, normal operation becomes affected by restricted flow. The precise number of holes or flow area in each zone depends on a great many reactor parameters including the power rating of the reactor, its coolant flow rate, its power density, average burnup of the fuel, accident assumptions, other measures taken to mitigate a LOCA, and so forth. However, restriction of flow to the peripheral assemblies by reduction of the flow area to the interiors of the fuel elements housings and lowering the elevation of the flow area relative to the plenum liquid level will generally result in a significant improvement in the flow of coolant to the core during LOCA without reducing flow during nominal conditions. It will be apparent to those skilled in the art that many changes and substitutions can be made to the preferred embodiment herein described without departing from the spirit and scope of the present invention which is defined by the appended claims. |
description | This application claims the benefit of PCT/EP2007/002109, filed Mar. 9, 2007, which application is incorporated herein by reference in its entirety. 1. Field of the Invention The invention relates to a micro-gripper for accommodating and holding micrometer-scale or sub-micrometer-scale objects and to a method for the production thereof. 2. Description of the Prior Art Micro-grippers are currently used in numerous fields in the context of microsystem technology. Thus, micro-grippers are used, for example, in microtechnology and nanotechnology for manipulation and mounting or for joining extremely small objects. Further areas of application for micro-grippers are found in physics, biology, chemistry, and medicine, micro-grippers being used, for example, in the context of the analysis and assaying of samples for accommodating, gripping, and holding the samples. The micro-grippers typically comprise a base body, which is connected to two or more movable and/or elastic gripping elements, which are used to accommodate and hold an object. At least one actuator provided on the micro-gripper is typically provided for the active actuation of the gripping elements, which moves the gripping elements, which act toward one another. In micro-grippers of this type, the gripping forces acting on the object may be partially set or regulated by a corresponding activation of the actuators. Micro-grippers without actuators are also known, in which the accommodation and holding of an object does not occur actively, but rather passively with exploitation of elastic material properties. Micro-grippers of this type have at least two opposing gripping elements spaced apart from one another, between which an object may be clamped. The gripping elements are elastically deformed by the clamping of an object between them, and thus generate elastic retention forces reacting onto the object. It is to be noted here that for the following statements, the term micro-gripper is restricted to the versions having only two gripping elements. Thus, an embodiment of a micro-gripper for micro-mounting is disclosed in the publication DE 195 23 229 A1, which comprises a base body, a piezotranslator fastened to the base body as a linear actuator, and a microstructure body connected to the base body and the piezotranslator. Two opposing gripping elements acting toward one another and a mechanical lever transmission having bending joints for the enlarging transmission of a linear movement of the piezotranslator onto the gripping elements are constructively unified in one component in the microstructure body. Upon a length change of the piezotranslator, the elastic bending elements deform and thus initiate a targeted movement of the gripping elements away from or toward one another. The production of the microstructure body is performed from a (100) silicon wafer polished on both sides having a thickness of 240 μm using the known structuring processes, lithography, and anisotropic etching. The microstructure body is subsequently fastened on the base body, a silicon substrate, using adhesive in such a way that only selected small contact areas between the microstructure body and the base body are glued, the bending elements and the gripping elements being axially displaceable along the contact faces. The production of the microstructure body from silicon, especially its good ability to be micro-structured and the lack of plastic deformation of silicon, is especially emphasized as the essential advantage of the described micro-gripper. In addition, the possibility exists of attaching piezoelectric, for example, piezoresistive layers to the gripping elements, in particular to their particular gripping faces, to convert the gripping force into an electrical signal and thus to adapt the gripping force to the object to be gripped. Further embodiments of micro-grippers which use piezosystems as actuators may be inferred, for example, from the publications DE 196 48 165 A1 and DE 101 14 551 C1. In addition to piezo systems, other elements or principles are also used to move the gripping elements. Thus, a micro-gripper may be inferred from the publication DE 197 15 083 A1, in which flat coils or permanent magnets of an electromagnetic drive are integrated in a yielding gripping mechanism. The closing of the gripping elements is caused by applying an external magnetic field. The publications US 2004/0004364 A1, US 2002/0061662 A1, and U.S. Pat. No. 5,149,673 A, in contrast, describe micro-grippers whose gripping elements may be moved using electrostatic attractive or repulsive forces. Finally, a nanogripper is disclosed in the publication US 2005/0029827 A1, in which the gripping elements may be moved by exploiting electro-thermal material properties. The gripping elements are connected via a jointed mechanism to elements which heat as a result of a current flux, expand, and cause a movement of the gripping elements via the jointed mechanism. The grippers cited up to this point all have the disadvantage that it is necessary to feed electrical or magnetic energy to the actuator to grip and hold objects. If this is interrupted or disturbed, a failure of the gripper occurs, that is, the object may detach from the micro-gripper in an undesired way. In addition, the necessary electrical adaptation of the micro-gripper in the required dimensions in the micrometer range is complex and costly. In particular, any contamination of the sample by the micro-gripper, for example, by a material transfer from a preceding sample to the next sample, is to be prevented for applications of micro-grippers in the scope of material analysis of micrometer-scale or sub-micrometer-scale samples. Therefore, for example, to grip and hold samples in the context of study, in particular using electron microscopes, such as transmission electron microscopes (TEM) or scanning electron microscopes (SEM), new micro-grippers are used for each sample. Because micro-grippers are only intended for a single use for purposes of this type, they are to be producible cost-effectively as mass produced products. Nonetheless, they must fulfill all the requirements to ensure reliable gripping and holding in such applications. The micro-grippers described above are not or are not optimally suitable for this purpose for the cited reasons, however. In addition to the micro-grippers having actuators described above, a micro-gripper is described in the publication US 2002/0166976 A1, which is particularly also suitable for use for gripping and holding a sample in the context of studies using TEM. The micro-gripper described therein comprises a rod-shaped or cylindrical elongate body, which has one or more receptacle slots open on three sides on one end in such a way that a sample may be clamped in the receptacle slot. The accommodation and holding of the sample is based, as described above, on the elastic deformation of the material surrounding the receptacle slot and the restoring force thus caused, which acts on the clamped sample. The following method may be inferred from the cited document for producing the micro-ripper. A piece of linear tungsten wire having a wire diameter of 50 μm is used as the starting material. In a first method step, an end area of the tungsten wire is initially processed using electropolishing or an etching method in such a way that the tungsten wire tapers in this end area toward the wire end to a diameter of a few micrometers. In a second work step, a receptacle slot open on three sides toward the end of the tapered area is worked out of the now conically tapering end area of the tungsten wire using an ion beam incident perpendicularly to the longitudinal axis of the tungsten wire. In a third method step, in addition to the first receptacle slot, for example, a second receptacle slot rotated by 90° thereto may be worked out by a further application of the ion beam. At least two or four gripping elements, between which an object may be clamped, thus arise in the tapered end area of the tungsten wire. The receptacle slot has a width of 2 μm and a depth of 30 μm according to one exemplary embodiment. The micro-gripper disclosed in US 2002/0166976A1 has the disadvantage that it is not technically possible by the specified production method to produce the faces adjoining the receptacle slot, that is, the internal clamping faces on the gripping elements, exactly parallel to one another. Rather, by applying the ion beam to produce a receptacle slot, the receptacle slot is wider on the side facing toward the ion beam than on the side facing away from the ion beam. The clamping faces defining the slot which are thus generated are therefore not oriented parallel to one another. This finally results in an uneven distribution of clamping forces on the object to be held and has the danger that objects clamped between the clamping faces may shift in relation to the micro-gripper. Furthermore, the described method is only suitable in a limited way, and/or not at all for mass production, because exact fixing and positioning of the tungsten wire is required individually for each micro-gripper, before the processing using the ion beam may be performed, which makes the production method time-consuming and costly. A production method of partially movable microstructures based on a dry-chemical etched sacrificial layer may be inferred from DE 195 22 004, the sacrificial layer, which typically comprises polyimide, being applied directly to a substrate layer, on which, completely spaced apart from the substrate layer by the sacrificial layer, a later partially movable micro-structured material layer is applied, for example, in further implementation as a cantilever with or without additional tip. For the purposes of the partial movement capability, the sacrificial layer located between the cantilever layer and the substrate layer is only partially removed in the course of a dry-chemical etching method, so that a residue of sacrificial layer remains in existence as a type of spacer. Proceeding from the described prior art, it is the object of the present invention to specify a method for producing a micro-gripper as well as a micro-gripper, in which the disadvantages described above are avoided. The micro-gripper is particularly to be cost-effectively producible as a mass-produced product, have opposing clamping faces which are oriented parallel to one another on the gripping elements in the idle state, and be suitable for accommodating, transporting, and holding material samples in the context of their study in a TEM or SEM. The invention specifies a method for producing a micro-gripper, which comprises a base body and a gripping body connected integrally to the base body, which projects beyond the base body and provides a receptacle slot on a free end area in such a way that a micrometer-scale or sub-micrometer-scale object may be clamped in the receptacle slot for gripping and holding. The method is essentially distinguished in that the base body and the gripping body are produced using a material deposition method with implementation of at least one shared first material layer and one shared second material layer, and the material layers are implemented as essentially flat and are bonded to one another. The invention further is a micro-gripper which is distinguished in that the base body and the gripping body are implemented as a uniform planar body, which is defined by two essentially flat overlapping planar body surfaces oriented parallel to one another. Features advantageously of the invention may be inferred from the description, in particular with reference to the exemplary embodiments. An essential concept of the invention is the production of a micro-gripper using a material deposition method with implementation of at least two flatly implemented material layers which are bonded to one another. Methods for depositing material are known in manifold forms to those skilled in the art. For the production according to the invention of a micro-gripper, methods from thin-film technology are especially suitable, by which the materials may be applied in thin layers, having layer thicknesses to below 1 μm, to a substrate. In particular, physical vapor deposition methods (PVD), that is, vapor deposition or sputtering, chemical vapor deposition methods (CVD), and methods derived therefrom, such as low-pressure CVD (LPCVD) or plasma-enhanced CVD (PECVD), or galvanic methods come into consideration for the deposition of the layers on the substrate. The layers thus deposited may be subsequently structured by masking or lithography methods having subsequent material abrasion by applying wet-chemical etching, reactive ion etching (RIE), sputter etching, ion beam etching, or plasma etching. Alternatively to the subsequent structuring of a layer already applied, the structuring of an applied layer may also be achieved by targeted local material deposition. Furthermore, by depositing a so-called sacrificial layer between two material layers and later removing the sacrificial layer, for example, by wet-etching methods, a nearly arbitrary three-dimensional structuring may be achieved on the material layers applied to the substrate. One skilled in the art is familiar with these technologies and their application. If a method described or known in the context of thin-film technology is used for the production according to the invention of a micro-gripper, the production method for the micro-gripper comprises the following method steps in a simple case. In a first method step, a flat substrate surface is provided. A silicon substrate is preferably suitable for this purpose because of its good surface planarity. In a second method step, a first sacrificial layer is applied to the substrate surface. In the third method step, the first material layer is applied to the first sacrificial layer. In the fourth method step, the application (and possibly the structuring) of the second sacrificial layer on the first material layer is performed, at least on a local area of the first material layer. The predominant part of the first material layer is typically not covered by the second sacrificial layer. The second sacrificial layer corresponds in its external dimensions in its application to the one local area to the receptacle slot to be produced on the gripping body, so that the receptacle slot is exposed after a removal of the second sacrificial layer in this area. In the fifth method step, the second material layer is applied to the second sacrificial layer and the areas of the first material layer not covered by the second sacrificial layer. In the simplest case, the first and the second material layers are bonded to one another directly with the exception of the one local area. In the sixth method step, the first and second sacrificial layers are removed. The removal of the second sacrificial layer implements the receptacle slot, the removal of the first sacrificial layer detaches the now completely produced micro-gripper from the substrate. Wet-chemical etching methods are suitable in particular for removing the sacrificial layers. As a result of method steps 1-6, a micro-gripper is obtained, which is distinguished in that the base body and the gripping body of the micro-gripper are implemented as a uniform planar body, which is defined by two essentially flat planar body surfaces oriented parallel to one another and overlapping. The external free surfaces of the first and second material layers correspond to the planar body surfaces. The receptacle slot on the gripping body preferably has two internal clamping faces situated parallel to one another, spaced apart from one another, and overlapping. The clamping faces preferably have a distance of 10 nm to 10 μm, in particular 50 nm to 1 μm to one another. The lateral dimensioning of the planar body surfaces, and thus the lateral shaping of the base body, the gripping body, and finally also the clamping faces in the receptacle slot, are performed by a corresponding structuring of the layers arising in the context of the material deposition method described. As described above, the desired structuring of a layer may be performed by a local, that is, laterally appropriately defined deposition of the layer or by an appropriate lateral structuring of an already deposited layer. Corresponding structuring methods are known to those skilled in the art. By such a structuring of the layers, it is possible in particular to predefine the lateral dimensioning of the micro-gripper to be produced nearly arbitrarily and thus adapt the shape of the base body, the gripping body, and the clamping faces to the desired requirements. By a corresponding structuring of the layers during the production method, micro-grippers, whose planar body surfaces completely overlap one another, are preferably produced. Furthermore, micro-grippers are preferably produced using the method according to the invention which are dimensioned and designed in such a way that they may accommodate and hold samples, which are to be studied using a TEM or SEM, for example, and which may be inserted directly into a commercially available sample retainer of a TEM or SEM. Micro-grippers in which the planar body surfaces correspond to a circular sector having a centerpoint angle α≦180° and the gripping body is situated projecting beyond a circular sector tip of the circular sector or whose planar body surfaces correspond to a circular segment having a centerpoint angle α≦180° and the gripping body is situated on the circular segment chord, in particular in the center of the circular segment chord, projecting beyond the circular segment, and the circular segment or the circular sector has a circle radius which is adapted to the radius of a sample retainer of a microscope, in particular an SEM or TEM, are particularly suitable for TEM/SCM applications of this type. For SEM or TEM, the radius of the sample retainer is typically 1.5 mm. In addition, the planar body surfaces may correspond to a polygon, the gripping body being situated projecting beyond a peripheral edge of the polygon, or may have further arbitrary shapes. The shape and relative position of the clamping faces on the receptacle slot is also determined by the structuring of the first and second material layers. The clamping faces preferably correspond to a polygon, in particular a rectangle or square, and completely overlap one another. For special applications, clamping faces which taper in the direction of the opening of the receptacle slot are also suitable in particular. Depending on the desired application, arbitrary further clamping face shapes are also possible by a corresponding structuring of the first and second material layers. Several further advantageous embodiments are now to be specified for the production method described up to this point. Thus, the following materials may be used for the sacrificial layers: plastic, metal, or in particular silicon oxide. The following materials may be used for the material layers: plastics, ceramic, metal, semimetal, or in particular polysilicon. The use of the specified materials for the sacrificial layers or the material layers is not arbitrary, however. Appropriate material combinations which are suitable for described material deposition and sacrificial layer technologies are known to one skilled in the art. The pairing of sacrificial layers made of silicon oxide and material layers made of polysilicon has proven especially suitable. However, the first and the second material layers may also comprise different materials and thus provide the micro-gripper according to the invention with special mechanical, electrical, magnetic, or chemical properties because of the different material properties of the first and the second material layers. Furthermore, it may be advantageous for reasons of method technology to apply one or more intermediate layers to the substrate surface before the application of the first sacrificial layer to the substrate surface. For stabilization and protection, the possibility additionally exists of applying one or more stabilization or protective layers to the second material layer. The simultaneous production of a plurality of micro-grippers on one or more planar substrates is possible in particular using the method according to the invention. Not only may manufacturing costs thus be reduced, but rather achievements of the object may also be implemented which, with high manufacturing precision, allow nearly arbitrary shaping of the flatly implemented micro-grippers, with shaping which is easy to change. The micro-grippers according to the invention are suitable in particular for accommodating, transporting, and holding material samples in the context of their study in a TEM or SEM. FIG. 1 shows a perspective view of a micro-gripper 8 produced according to the invention, which is implemented as a planar body. The planar body 8 comprises a first material layer 3 and a second material layer 4, which is bonded to the first material layer 3. The planar body 8 may be divided into a base body area having the associated planar body surface part 7 and a gripping body area having the gripping elements 1 and 2, between which the receptacle slot 6 is located. Furthermore, a continuous gap 6a running transversely to the gripping elements 1, 2 is provided in the connection area between base body and gripping body in the micro-gripper 8 shown. This gap is used for improved introduction of forces which arise by an elastic deformation of the gripping elements 1, 2 into the material layers 3 and 4. Thin webs 5 are provided on the right side of the micro-gripper 8 shown for fastening the micro-gripper on the substrate 9. The background for this is that during the etching process, in which the sacrificial layers are removed, the danger exists that the micro-gripper 8 may detach in an uncontrolled way from the substrate 9 and be lost. This is prevented by the thin webs 5, via which the micro-gripper still remains connected to the substrate after the etching of the sacrificial layers, as explained in greater detail hereafter. The planar body surface 7 is used as an adapter face, for example, for receiving the micro-gripper in a handling system (transport manipulator), or for inserting it into the receptacle unit of an analysis device (SEM, TEM). In the present case, it has the form of a polygon. The planar body surface may, however, be dimensioned optimally in accordance with the specified requirements in the context of the production method. FIGS. 2a and 2b show the mode of operation of the micro-gripper 8. The gripping body area of the micro-gripper 8 having the gripping elements 1, 2 and the receptacle slot 6 lying between the gripping elements 1, 2, as well as a material sample 10 on which a bevel 11 is provided, are shown. To accommodate the material sample 10 using the micro-gripper 8, according to FIG. 2a, the micro-gripper 8 having the gripping elements 1, 2 is guided from above to the bevel 11 of the material sample 10. The bevel 11 is used for an optimum friction lock between the gripping elements 1, 2 and the material sample 10. Fundamentally, such a bevel is not necessary, however. FIG. 2b shows that the gripping elements 1, 2 are pushed over the bevel 11 of the material sample and thus spread apart. An elastic deformation of the gripping elements 1, 2 is caused by the spreading, which generates a retention force on the bevel by reaction. Because of this retention force and the friction forces acting between the clamping faces of the gripping elements 1, 2 and the bevel 11, holding of the material sample is achieved. The micro-gripper from FIG. 1 is shown in the production phase after the sacrificial layers have been removed in FIGS. 3a and 3b. FIG. 3a first shows a view of the micro-gripper 8. The micro-gripper 8 is connected via the webs 5 to a retention area 20. Because the retention area 20 is connected fixed to the substrate 9 (not shown) even after the removal of the sacrificial layers, the micro-gripper 8 completely detached from the substrate 9 is still held by the retention area 20 via the webs 5. Unintended detachment or loss of the micro-gripper 8 after the removal of the sacrificial layers may thus be prevented. The webs 5 only have to be cut through to isolate the micro-gripper. The number, configuration, and cross-section (width and height) of the webs 5 are essentially directed according to the retention force, which is to be absorbed by the webs. FIG. 3b shows a section through the layer buildup along section line A-A′. It may be seen clearly that the substrate 9 is still connected fixed to the retention area 20 even after removal of the sacrificial layers. The micro-gripper 8 comprises the first material layer 3 and the second material layer 4, which are connected to one another. The removed sacrificial layers have exposed the receptacle slot 6 and the gap 6a. The micro-gripper 8 is connected to the retention area 20 via the webs 5, which are formed on the first material layer. FIGS. 4a-4g explain the method for producing the micro-gripper shown in FIGS. 3a and 3b on the basis of the step-by-step layer buildup in a cross-sectional illustration along section line A-A′ of FIG. 3a. FIG. 4a In a first method step, an intermediate layer 12a and 12b is applied to a flat substrate 9 made of silicon. This intermediate layer 12a comprises silicon nitride and is used as an electrical insulator, the intermediate layer 12b comprises polysilicon and is used as a starting layer. A first sacrificial layer 13 made of silicon oxide is now deposited on this intermediate layer 12. The first sacrificial layer 13 is subsequently masked. This is performed by applying a photoresist layer or a similar mask. The masking shape may be worked out by exposure using an electron beam or using UV light, for example. FIG. 4b After the masking has been finished, the first sacrificial layer 13 is removed at the exposed points using reactive ion etching (RIE). FIG. 4b shows that the sacrificial layer 13 is removed at least in the area on which the later retention area 20 is to be produced. FIG. 4c The first material layer 3 made of polysilicon is then deposited on the first sacrificial layer 13. The first material layer 3 is also, as described above, provided with a mask in the desired form and etched by RIE, for example. FIG. 4d A second sacrificial layer 14 is applied to the first material layer 3. This is also provided with a mask and etched in the desired form. The second sacrificial layer 14 remaining on the first material layer 3 corresponds in its geometric shapes 14a, 14b, 14c to the receptacle slot 6, the gap 6a, and the interruption of the second material layer 4 at the web 5 (compare FIG. 4e). If a larger cross-section of the web 5 is desired, the shape 14c may also be dispensed with. FIG. 4e The second material layer 4 made of polysilicon is deposited, masked, and correspondingly etched on the second sacrificial layer 14. As recognizable in FIG. 4e, the second material layer 4 is interrupted at the web 5 by the structuring of the second material layer 4. This is the case if an excessively large aspect ratio is expected, that is, the height of the web is greater than the width of the web. In the event of a desired larger cross-section of the web 5, the shape 14c is dispensed with, and the second material layer is applied directly to the web. In this case, the width of the web is not to be less than the height of the two layers, however. FIG. 4f A metal layer 15 is deposited on the second material layer 4 for stabilization. The metal layer 15 is also structured accordingly. This deposited metal layer 15 may also be used as a starting layer for further galvanic depositions. Instead of a metal layer 15, other materials, such as plastics or semimetals, may also be used for this purpose. FIG. 4g The last method step for producing the micro-gripper 8 comprises removing the first and second sacrificial layers 13, 14 by an etching solution. The selection for removing the sacrificial layers 13, 14 is directed according to the material which the sacrificial layers 13, 14 comprise, of course. The micro-grippers 8 produced according to the method according to FIGS. 4a-g may be used for accommodating and holding objects in the micrometer-range and sub-micrometer-range. A special application of the micro-gripper is the accommodation of electron-transparent samples for their subsequent study in a TEM or SEM. Samples of this type are prepared out of a material to be studied using the so-called focused ion beam technology (FIB technology) known to those skilled in the art. The typical methods for accommodating a TEM sample 40 of this type shown in FIG. 5 use a needle 41, which is fastened to the TEM sample 40 using material deposition. The micro-gripper 8 produced according to the invention, in contrast, allows an electron-transparent sample 40 produced using FIB technology to be accommodated using the gripping elements 1, 2 in an FIB preparation facility corresponding to FIGS. 2a and 2b. FIG. 6 shows the micro-gripper 8 and the TEM sample 40 clamped between the gripping elements 1, 2. The TEM sample 40 may be transferred directly into the TEM and is immediately available in the correct position for study using the electron beam 53. The essential advantage of this procedure is that the complicated so-called lift out process used up to this point is replaced by the one-time gripping of the TEM sample 40 by the micro-gripper. After the accommodation of the TEM sample 40, it may be studied together with the micro-gripper in the TEM. If necessary, after the TEM sample is accommodated by the micro-gripper, postprocessing of the TEM sample in the FIB preparation facility is possible. Because the width of the receptacle slot 6 of the micro-gripper 8 may only be varied within a specific range, the TEM sample 40 is dimensioned using the FIB technology in such a way that the sample thickness required for holding is achieved on the later contact face to the micro-gripper 8. The remaining area of the TEM sample is prepared to the electron transparency required for the TEM study. FIGS. 7a and 7b show a further advantageous embodiment of the micro-gripper 8 according to the invention. In this example, the micro-gripper 8 is used in connection with a half ring 70, which has an internal radius and an external radius. The micro-gripper 8 has a planar base body in the form of a circular sector, the gripping body having the TEM sample 40 being situated on the circular sector tip projecting beyond the circular sector. The radius of the circular sector of the base body shape is greater than the internal radius of the half ring 70. The external radius of the happening 70 and the radius of the circular sector of the base body are ideally equal. The micro-gripper 8 is accommodated with the aid of a device, such as a vacuum pipette, and fastened as shown to the half ring 70 using an adhesive. This half ring 70 may comprise different materials which are used in TEM analysis. The gripping elements 1, 2 project beyond the half ring, so that this configuration is suitable for accommodating TEM samples 40 from a substrate. FIG. 7b shows a detail enlargement of the acceptance of such a TEM sample 40 from an appropriately prepared substrate. Of course, micro-grippers having other shapes may also be fastened to the half ring 70. The external shape of the base body therefore does not necessarily have to be similar to a circular section. FIG. 8 shows an embodiment of the micro-gripper 8 according to the invention in which the base body is implemented having a semicircular planar body surface 7. The radius R of this semicircle is dimensioned in such a way that the micro-gripper 8 may subsequently be directly transferred into the sample retainer of the TEM. The micro-gripper 8 is first held by a receptacle device 31 and the acceptance of the TEM sample 40 is thus performed. This configuration allows the direct transfer of the micro-gripper 8 into the sample retainer of the TEM, without an additional adaptation to a semicircular ring having to be performed. If circular sectors having centerpoint angles <180° are used instead of the semicircular shape, the retention of the micro-gripper in the sample retainer of the TE microscope proves difficult, because the micro-gripper may slip laterally and is thus not engaged correctly by the clamping nut of the sample carrier. 1, 2 gripping elements 3 first material layer 4 second material layer 5 web 6, 6a receptacle slot, gap 7 planar body surface in the area of the base body 8 micro-gripper, flat body 9 substrate 10 material sample 11 bevel 12 intermediate layer 13 first sacrificial layer 14, 14a-c second sacrificial layer 15 metal layer, stabilization layer 20 retention area 31 receptacle device 40 TEM sample 53 electron beam 70 half ring |
|
050230468 | abstract | A drive unit for gripping and rotating a fuel rod during inspection of the fuel rod. A housing has a drive motor mounted at its first end with a spindle rotatably mounted in the housing and directly coupled to the drive motor. A recess at one end of the spindle adjacent the second end of the housing receives a substantially donut shaped rubber bladder. A flanged port that extends radially from the bladder and is in fluid communication with the interior of the bladder provides a means for pressurizing the bladder. This causes radial inward expansion of the bladder for gripping a fuel rod to be inspected. |
abstract | A shielded packaging system is formed by a top panel and a bottom panel that are connected to one another along a preselected extent of their respective peripheral edges. An opening is formed along the unconnected extent and provides access to the space between the panels that holds radioactive items. Each panel includes at least two layers of lead foil so that if a pinhole is formed in either layer, the probability of two pinholes lining up and enabling radiation to escape from the space is minimal. The layers of lead foil have at least one ridge formed in them at their respective peripheral edges so that radiation traveling in a straight path parallel to the top and bottom panels encounters the ridges and cannot escape through the edges of the package. |
|
051246104 | description | DESCRIPTTION OF THE PREFERRED EMBODIMENTS The present invention is directed to a safe and practical, long-life, electrical energy source made by the combination of a light emitting polymer,activated by a radioisotope source, with a photovoltaic cell, to produce electrical energy. As will be appreciated, the potential variations of such a combination are numerous. The practical feasibility of an electrical energy source in accordance with the present invention depends upon a number of consideration, including: (a) the choice of a suitable long-lived radioisotope, (b) the efficiency of the scintillation process in the polymer, (c) the efficiency of the photovoltaic cell, (d) radiation damage to the polymer and the photovoltaic cell, (e) the optical mating of the polymer and the photovoltaic cell, and (f) the geometry of the polymer and the photovoltaic cell. Each of these considerations will be discussed in describing the preferred embodiment of the present invention. It will be observed that the use of a light emitting polymer provides an opportunity to effectively design a safe and practical, long-life electrical energy source in response to these considerations. Referring now to FIG. 1, a cut-away pictorial representation of the preferred embodiment of the present invention is shown. The electrical energy source 10 is comprised of a planar sheet of light emitting polymer ("LEP") material 12 that is interposed between a pair of photovoltaic cells 14 and 16 having planar dimensions similar to the LEP material 12. The photovoltaic cells 14 and 16 and the LEP material 12 are encased in a sealed case 18, preferably a laser-welded, stainless steel case, having a pair of electrical contacts 20 and 22 exposed on one end of the case 18. The contacts 20 and 22 are disposed in a pair of ceramic insulators 24 and 26 and are connected to the photovoltaic cells 14 and 16 in such a manner that one of the contacts will provide a positve voltage potential and the other contact will provide a negative voltage potential. The LEP material 12 comprises a mixture of a polymer labelled with a tritium and an organic compound which emits light energy when subjected to radiation generated by the tritium. The organic compound is at least partly bonded to the polymer and the mixture is translucent at the specified frequency bandwidth of the light energy. Such an LEP material was obtained from Amersham International plc, Amersham Place, little Chalfont, Buckinghamshire, England, and pending NRC regulatory approval, may be available from Amersham International plc. Such an LEP material is described in the United Kingdom patent application, Ser. No. 90/08,268.6 by C. D. Bell and J. H. C. Howes, entitled TRITIATED LIGHT EMITTING POLYMER COMPOSITIONS, filed in the British Patent Office on Apr. 11, 1990, the disclosure of which is hereby incorporated by reference herein. Those aspects of the LEP material 12 that allow it to be used effectively in the present invention are discussed below in connection with the various design considerations set forth above. In the preferred embodiment, the photovoltaic cells 14 and 16 are amorphous thin-film silicon solar cells, Model No. 035-01581-01, available from ARCO Solar, Inc., Chatsworth, Calif., or their equivalent. These cells have their highest efficiency conversion (greater than 20%) in the blue range of the spectrum of visible light to match the frequency bandwidth of the emitted light of LEP material incorporting a phosphor that emits in the blue range. While the particular photovoltaic cells 14 and 16 in the preferred embodiment have been selected to match the blue range of the spectrum of visible light, it should be apparent that other photovoltaic cells may be selected to match the bandwidth of light emitted at other frequencies. In particular, as discussed below, it is known that a new solar cell, known as the Sunceram II (trademark), available from Panasonic's Industrial Battery Sales Div., is claimed to more efficient than conventional amorphous silicon solar cells, especially in the red range of the spectrum of visible light. To maximize the optical transfer between the LEP material 12 and the photovoltaic cells 14 and 16, the surfaces of the photovoltaic cells 14 and 16 not in contact with the LEP material 12 are coated with a reflective material, preferably an aluminum paint or equivalent. The edges of the LEP material 12 not in contact with the photovoltaic cells 14 and 16 are clad with a similar reflective material. The surfaces of the LEP material 12 and the photovoltaic cells 14 and 16 that abut one another are coated with a contact gel, Rheogel 210 C., available from Synthetic Technology Corp., McLain, Va., or its equivalent, as a means for optically coupling the surfaces to increase the amount of light that is transmitted from the LEP material 12 to the photovoltaic cells 14 and 16. SELECTION OF THE RADIOISOTOPE The radioisotope that is used in the LEP material 12 must produce sufficient scintillations in the LEP material to insure an adequate production of light for absorption by the photovoltaic cells 14 and 16. For safety purposes, it is desirable that the selected radioisotope be chemically bonded to the polymer. By chemically bonding the radioisotope to the polymer, any undesirable build-up of the radioisotope is prevented and the concentration levels of the radioisotope will remain constant no matter what environmental factors the LEP material 12 is subjected to. Unlike radioisotopes in a liquid or gaseous state, the bonding of the radioisotope to the polymer in the LEP material 12 of the present invention prevents the free release of radiation if the material or container is ever broken. The bonding of the radioisotope to the organic polymer is expected to result in NRC approval for the use of higher allowable levels of radioactive material for radioisotopes in this format. The radioisotope should have a half-life comparable to the desired useful lifetime of the electrical energy source 10. Because the power is directly proportional to the rate of decay of the radioisotope in the LEP material 12, for a given desired power output the rate of decay should ideally correspond to the power requirements of the electrical energy source 10. If the half-life is too long with respect to the useful life of the electrical energy source 10, then the amount of radioisotope required to produce the same rate of decay is increased, thus presenting increased safety and shielding problems. If the half-life is too short with respect to the useful life of the electrical energy source 10, then the amount of radioisotope required to produce the desired rate of decay at the end of the useful life of the electrical energy source requires that the LEP material 12 be overloaded initially, thus generating wasted energy at the beginning of the life of the device. Obviously, if a decaying power source is desired or acceptable this consideration is not important. To minimize the radiation hazards associated with use of a radioisotope, the radiation emitted by the selected radioisotope should not be very penetrating. Preferably, a high percentage of the radiation emitted by the radioisotope should be absorbed by the photovoltaic cells 14 and 16 or by the sealed case 18. Therefore, radioisotopes emitting gamma radiation or high-energy x-rays are not preferred; beta radiation emitters are preferred. In addition, the radioisotope must be selected so that it may be chemically bonded to the organic polymer to achieve the desired solid, captured state for the LEP material 12. A further consideration in selecting the radioisotope is the economic cost of the radioisotope. The cost of producing various radioisotopes varies by orders of magnitude. For example, the cost per curie of .sup.14 C. is more than two orders of magnitude greater than for .sup.3 H. Table I provides data on several radioisotopes, among others, that may be used with the electrical energy source 10 of the present invention. TABLE I ______________________________________ Radio- isotope .sup.3 H .sup.14 C .sup.10 Be .sup.32 Si .sup.32 P ______________________________________ Half- 12.3 5730 2.7 .times. 10.sup.6 650 .039 life (years) Max. 0.186 .156 .555 .22 1.71 beta Energy (MeV) Ave. .0056 .049 .194 .065 .68 beta Energy (MeV) Mass of 1.0 .times. 10.sup.-4 .22 75 .058 NA 1 curie (grams) Absorber .72 24 180 30 790 to stop betas (mg/cm.sup.2) Power 320 1.3 .015 76 Density (mW/g) ______________________________________ For the safety reasons mentioned above, beta-active radioisotopes are especially preferred in practicing the present invention. The decay of beta-active isotopes results in a continuum of beta energies being emitted from the radioisotope. This continuum extends from zero up to a maximum value as shown in Table I. The average beta energy is computed using the equation: EQU <E>=0.099E(1-Z.sup.0.5)(3+E.sup.0.6) where <E> is the average energy in MeV, E is the maximum energy in MeV, and Z is the atomic number of the daughter nucleus that results after the decay. The first three radioisotopes in Table I decay to stable elements, but .sup.32 Si decays to .sup.32 P, which in turn decays to stable sulphur. Therefore, the decay for each .sup.32 Si atom produces the combined beta energy of the decay of both the silicon and the phosphorous. One curie is defined to be 3.7.times.10.sup.10 decays/second. The mass of the radioisotope required to produce this activity is obtained from the following equation: EQU m=2.8.times.10.sup.-6 (T.sub.1/2)M where T.sub.1/2 is the half-life of the radioisotope expressed in years and M is the atomic mass. Because the radioisotope is an internal component of the polymer, a given thickness of shielding must be provided around the radioisotope-activated polymer to completely absorb all of the beta radiation. The following range relation was used to compute the required absorber thickness in Table I: EQU R=(540E-130(1-e.sup.-4E)) where R is in mg/cm.sup.2 and E, the maximum beta energy, is in MeV. In order to obtain the linear thickness required by the absorber to shield all beta radiation, one would divide R by the density of the absorber. For example, if a polymer of 2 g/cm.sup.3 is used as the absorber surrounding the LEP material 12, then the required thickness for .sup.3 H would be 0.0036 mm. Based upon the consideration set forth above and especially for safety reasons, the preferred radioisotope for the present invention is tritium. With a half-life of 12.36 years and a beta decay with an 0.0186 MeV maximum energy, tritium has been considered one of the most innocuous of fission produced radioisotopes. Because of the low energy and penetration power of the beta particle associated with its decay, tritium does not pose a significant external radiation hazard. The beta particles emitted by tritium are not even capable of penetrating the epidermis. In addition, the chemical bonding of the tritium in the solid polymer form prevents escape of the tritium in its gaseous state, thereby decreasing the chance that tritium may be absorbed into the body by skin penetration in the form of a gas or vapor. Another method to compare the various radioisotopes is to compare their relative power densities, the decay power produced per gram of material. With the greatest power density/gram and the least amount of absorbent material necessary to stop all beta particles from being emitted, tritium is the best choice for an electrical energy source that provides a low power, long-life electrical energy source when the requirements of a single electrical energy source are less than 5 to 10 milliwatts-hours for the desired lifetime of the electrical energy source, approximately 20 years or less. SCINTILLATION EFFICIENCIES As a beta particle generated by the selected radioisotope moves through the organic polymer, energy is released by several mechanisms: (a) excitation of .pi.-electrons to excited states, (b) .pi.-electron ionization, (c) excitation of other electrons to excited states, and (d) ionization of other electrons. All but the first of these mechanisms ultimately only result in an increased thermal energy within the LEP material 12. Only the first results in scintillation, the release of a photon from the organic phosphor or scintillant upon decay from the excited state. For many organic materials, this occurs with a probability of about 10%. Therefore, only about 10-20% of the energy deposited by a beta particle is available for light production. Because it may be necessary to shift the light produced by such scintillations into the portion of the spectrum to which the photovoltaic cells 14 and 16 are more sensitive, secondary and tertiary phosphors may also need to be added to the LEP material 12. This may result in further degradation of the scintillation efficiency of the LEP material 12. For a more detailed explanation of the operation of scintillators in response to beta radiation, reference is made to E. Schrafm, Organic Scintillator Detectors, 1973, pp. 67-74, which is hereby incorporated by reference herein. In the LEP material 12 of the preferred embodiment, the scintillation efficiency is increased by bringing the primary organic phosphor into a weak bonding with the tritiated organic polymer. Because the beta particle emitted by the tritium is of such low energy, the closer the tritium is located to the phosphor, the greater the probability that the beta particle will be able to interact with the phosphor. Because the average mean distance of the path of an emitted beta particle is less than 1 micron, the probabilities of interaction between the beta particle and the phosphor decrease dramatically unless the phosphor is located within that range. In the preferred embodiment, the LEP material 12 utilizes both a primary and a secondary phosphor. The primary organic phosphor may be any phosphor or scintillant in the groups PPO, PBD, or POPOP that operates to capture the beta particle and emit a photon in the ultraviolet frequency. The secondary phosphor may either be bonded to or admixed with the organic polymer and performs a Stokes shift on the emitted photon to shift its frequency to the desired frequency of the light to be emitted by the LEP material 12. The various techniques for performing a Stokes shift are well known in the art. Unlike the prior art techniques of admixing the tritium with the phosphor or encapsulating gaseous tritium in a glass vessel, the LEP material 12 utilized by the present invention maximizes the scintillation efficiency of the beta particle and the organic phosphor by positing the tritium relatively near the primary phosphor and by arranging the LEP material 12 such that it is generally optically transparent at the desired frequency of the emitted light. In addition, to minimize any optical blockage of photons emitted by the LEP material 12, it desirable that the catalysts for bonding both the radioisotope and the phosphor or scintillant be completely removed or disappear after the polymerization process. Referring now to FIG. 2, the spectral emissions of a blue phosphor and a yellow-green phosphor used as the secondary phosphor in the LEP material 12 are shown. FIG. 3 shows the relative scintillation efficiencies as a function of output voltages over various curie levels in the LEP material 12 utilizing each of these phosphors. As can be seen, the relative efficiency of the yellow-green phosphor decreases with increasing levels of the radioisotope. This effect, known as bleaching, is well known in the field of scintillation. Obviously, it is desirable that the phosphor(s) selected for use with the LEP material 12 should not be subject to bleaching or other types of deterioration as a result of activation by the particular radioisotope selected for use in the LEP material 12. It should be noted that although the preferred embodiments are described in terms of scintillants that emit energy in the visible spectrum, it is also possible to use a scintillant that emits electromagnetic energy in the ultraviolet, infrared, or other frequency bands of the electromagnetic spectrum. Accordingly, the term "light" as used in this application is intended to encompass all frequencies of electromagnetic radiation produced by scintillation activity. For example, if the average mean path of a photon emitted in the ultraviolet spectrum by the primary phosphor is sufficiently great to escape the polymer, and if a photovoltaic cell capable of absorbing energy having a wavelength of 400 nm or less were available, the LEP material 12 might not need a secondary phosphor and the energy emitted by the primary phosphor could be used directly to power the photovoltaic cells 14 and 16. In addition, the bandwidth of the emitted light from the LEP material 12 need not be limited to monochromatic light. Various combinations of primary and/or secondary phosphors in the LEP material could be used to broaden the bandwidth of either or both the intermediary or emitted energy from the LEP material 12. Again, the polymer structure of the LEP material allows the LEP material 12 to be designed to achieve these objectives. PHOTOVOLTAIC CELL EFFICIENCIES Presently, most of the work, both theoretical and practical, on the design of semiconductor photovoltaic cells relates to their use as solar cells that are designed to absorb all of the spectral energy available from the sun, either at AM0 conditions outside the earth's atmosphere, or at AM1 conditions at sea level. It is well known that there are both theoretical and practical efficiency limits for such solar cells. In theory, there are only two parameters that will determine the efficiency of a solar cell, the band gap energy of the solar cell material and the temperature of the cell. For an amorphous silicon solar cell, the bandgap energy of 1.1 eV means that only those photons of wavelengths less than about 1,100 nm are capable of producing electron-hole pairs in the photovoltaic cells that will result in the generation of electrical energy; the remaining energy is lost, usually in the form of heat. Referring now to FIG. 4, the maximum theoretical conversion efficiencies for a variety of photovoltaic cell materials are shown as a function of temperature and energy gap. In practice, there are a number of other factors that limit the conversion efficiency of solar cells, including the excess energy loss for photons that are within the band gap energy, the fill factor loss and the voltage loss as a result of the mismatch of the impedance of the load and the source. The net result is that typical solar cell efficiencies of only 20% are generally achievable to date. Recently, greater efficiencies have been achieved for a printed compound thin-film photovoltaic cell utilizing the group II-VI compound semiconductors CdS/CdTe. These solar cells, known as the Sunceram II, are available from Panasonic's Industrial Battery Sales Div., Secaucus, N.J., and utilize an n-layer (CdS) and a p-layer (CdTe) semiconductor films created by a film-fabrications process that entails paste application by screen printing and sintering in a belt-type furnace. The Sunceram II solar cells have an output five times higher than conventional amorphous silicon solar cells when illuminated by tungsten light. In the present invention, the design parameters of the photovoltaic cell do not have to be matched to the entire bandwidth of visible light to optimize absorption of the entire solar spectrum. Rather, the design of the photovoltaic cells 14 and 16 may be tailored to the particular bandwidth and wavelengths of emitted light from the LEP material 12. It is well known that different semiconductor materials have different bandgap energies and, hence, will absorb photons of different wavelengths (e.g., Si absorbs photons with .lambda.<1.1 .mu.m and GaAs absorbs photons with 1<0.9 .mu.m). However, the wavelength of the photon also determines where in the p-n junction the photons will be converted into electron-hole pairs. For short wavelengths (.lambda.=0.55 .mu.m), most photons will be converted into electron-hole pairs in a narrow region near the surface of the p-layer of the p-n junction. Whereas, at longer wavelengths (.lambda.=0.9 .mu.m), the absorption coefficient for the semiconductor is small and absorption takes place mostly in the n-layer of the p-n junction. FIG. 5 shows the collection efficiency for both the p-layer and the n-layer of a photovoltaic cell as a function of the wavelength of the incident light. The collection efficiency of the photovoltaic cell will be influenced by the minority-carrier diffusion length of the semiconductor material and by the absorption coefficient. A large absorption coefficient leads to heavy absorption near the surface of the p-n junction, resulting in strong collection in the skin layer. A small absorption coefficient allows deep penetration of photons so the base layer of the p-n junction becomes more important in carrier collection. A typical GaAs photovoltaic cell produces more of the skin layer effect, and a typical Si photovoltaic cell produces more of the base layer effect. For a more detailed discussion as to the effect of wavelength and semiconductor selection on the conversion efficiencies of the photovoltaic cell, reference is made to Edward S. Yang, Fundamentals of Semiconductor Devices, pp. 147-162 (1978). In the present invention, the selection of the primary and secondary phosphors of the LEP material 12 can be made to generate a monochromatic or a narrow bandwidth of emitted light, the frequency of which can be matched to the particular type of photovoltaic cell 14 and 16 desired. This matching depends upon the type of conversion desired (base vs. skin effect), the efficiency of the semiconductor material in the bandwidth, and other considerations relating to the design of the electrical energy source 10, including the curie loading, safety factors, the cost, and the environment in which the device will be operated. Although such a device is not currently available, it may be possible to provide a double-sided, monochromatic, bandwidth-matched photovoltaic cell for use with light emitting polymer in the present invention that could achieve conversion efficiencies of 60-70% or higher. POLYMER AND PHOTOVOLTAIC CELL RADIATION DAMAGE The long term performance of a polymer scintillator can be affected by the accumulated radiation dose deposited in the polymer. In addition, a variety of other factors can affect the aging of the polymer. The major variable in pure polymer aging are: (a) radiation intensity and wavelength distribution; (b) ambient temperature; (c) monomer content; (d) level of other impurities; and (e) oxygen concentration in the surrounding atmosphere. To increase the life of the polymer, the last four factors should all be minimized. For the LEP material 12, four additional factors affect the stability and aging of the polymer: (f) radiation resistance and purity of the scintillators used; (g) wavelength of the emitted light (the higher the better); (h) presence of multiple tritium labelled molecules (the lower the better), and (i) radioactive concentration level of the polymer. The basic polymer of the LEP material 12 of the preferred embodiment is known to have one of the lowest coefficients of radiation damage of any polymer. As for the photovoltaic cells, it is well known that radiation energies in excess of 4 KeV can damage the p-n junction in the semiconductor material. If the single conversion process taught by the prior art were used to produce electrical energy, the damage to one cm.sup.2 of a p-n junction caused by the beta particles emitted by a one curie of tritium would effectively destroy the p-n junction in a relatively short amount of time. In addition, if a single conversion process were used, the polymer containing the tritium could be no more than 1 micron thick, otherwise the polymer itself would prevent the beta particles from reaching the p-n junction. The present invention allows a double conversion process to be used with a low-level light source and still achieve a conversion efficiency that is equal to or greater than the conversion efficiencies achieved by single conversion processes. By efficiently converting the beta particles to photons in the LEP material 12, the present invention simultaneously solves the problems of radiation damage and the distance that the p-n junction can be located from the energy source. An additional advantage of utilizing the LEP material 12 of the present invention is that the LEP material 12 itself shields the p-n junction of the semiconductor material of the photovoltaic cells 14 and 16 from radiation damage, thereby increasing the useful life of the electrical energy source 10. OPTICAL MATING CONSIDERATIONS To maximize the transfer of light emitted by the LEP material 12, the LEP material 12 must be efficiently coupled to the photovoltaic cells 14 and 16. This is achieved by the use of a means for optically coupling the LEP material 12 with the photovoltaic cells 14 and 16 and by creating smooth surfaces on both the LEP material 12 and the photovoltaic cells 14 and 16. The primary purpose of the means for optically coupling the LEP material 12 and the photovoltaic cells 14 and 16 is to insure that as much of the light that is emitted by the LEP material 12 will be allowed to pass through to the light collecting surface of the photovoltaic cells 14 and 16. Unlike prior art devices, the means for optically coupling the two materials is not required to also serve as a means for isolating the two materials. In one embodiment, an anti-reflective coating matched to the frequency of the emitted light and the indices of refraction of the two materials is used as the means for optically coupling the two materials. Where the index of refraction of the polymer is n.sub.p and the index of refraction of the photovoltaic cell is n.sub.c, then the index of refraction of the anti-reflective coating should be the: EQU n.sub.r= (n.sub.p n.sub.c)0.5. The index of refraction of silicon is about 3.5 and the index of refraction for most polymers is around 1.5. Thus, the anti-reflective coating should have an index of refraction of about 2.3. The thickness of the anti-reflective coating should be 1/4 wavelength of the frequency of the emitted light. A similar effect may also be achieved by the use of an optical coupling gel, such as Rheogel 210C or its equivalent. As with the geometrical considerations to be discussed below, the effect on efficiency of the means for optically coupling the two materials may vary depending upon the materials selected and the manner of their construction. The light emitting surface of the LEP material 12 and the light collecting surfaces of the photovoltaic cells 14 and 16 should be as smooth as possible to aid in the transmission of light between the two. The existence of a rough interface between the two surfaces will alter the angles of incidence of the various light rays emitted by the LEP material 12 and could allow some of the light rays to be reflected back into the polymer, thereby lengthening their optical path and reducing the probability that they will be re-reflected back into the photovoltaic cells 14 and 16. It should also be noted that the use of optical concentrators in the optical mating between the LEP material 12 and the photovoltaic cells 14 and 16 could also be used to increase the optical efficiency of the conversion process. GEOMETRICAL CONSIDERATIONS The preferred method of constructing the LEP material 12 and the photovoltaic cells 14 and 16 is in the planar format shown in FIG. 1. In terms of optical efficiency, the geometrical shape of the LEP material 12 and the photovoltaic cells 14 and 16 will determine, to a certain extent, how much of the emitted light is actually received by the photovoltaic cells 14 and 16. In the planar embodiment shown in FIG. 1, there is a loss of emitted light from the edges of the LEP material 12 not in contact with the photovoltaic cells 14 and 16. For a sheet of LEP material 12 having dimensions of 42 mm.times.13 mm.times.0.5 mm, there would be a loss of emitted light of approximately 5% due to the optical aperture of .phi..sub.critical along the edges of the LEP material 12. This can be demonstrated by calculating the optimum numerical aperture based upon the indices of refraction for each material using Snell's law. This loss can be minimized by cladding the edges of the LEP material with a reflective coating in a manner similar to that known in the fiber optic field; however, the cladding will not achieve the optimum total internal reflection and some of the energy may be still absorbed or lost through the edges of the LEP material 12. Another advantage of the planar embodiment of the present invention is in maximizing the relative amount of surface area available between the LEP material 12 and the photovoltaic cells 14 and 16. The amount of power output available from the photovoltaic cells 14 and 16 is a direct function of the total surface area available for the light collecting surface. In addition, if the thickness of the LEP material is kept small, 0.5 mm, the average mean path of the photons emitted is not consumed by the thickness of the LEP material itself. In an alternative embodiment shown in FIG. 6, the LEP material 32 is arranged with a double-sided photovoltaic cell 34 in a multiple-layered configuration. In this embodiment the efficiency of the electrical energy source 30 is increased because the emitted light may be absorbed by more than a single photovoltaic cell. In addition, the photovoltaic cell 34 is capable of receiving light from both sides, as well as any light that may have passed through adjacent photovoltaic cells. The photovoltaic cell 34 could be a photovoltaic laminate, for example, constructed of a first semiconductor layer, a first conductive substrate layer, a dielectric isolation layer, a second conductive substrate layer, and a second semiconductor layer. Using the screening technique referred to above for the Sunceram II, the photovoltaic cell 34 might also be constructed as a three-part photovoltaic laminate comprising: semiconductor, dielectric, and semiconductor, with the conductive layer being overlayed by a screening process. In another embodiment shown in FIG. 7, the LEP material 42 is arranged with a double-sided photovoltaic cell 44 in a jelly-roll spiral configuration. In this embodiment the efficiency of the electrical energy source 40 is increased because of the minimum amount of edge surface relative to the light emitting and light absorbing surfaces of the LEP material 42 and the photovoltaic cell 44. One possible photovoltaic cell for this embodiment may be a new flexible photoelectric material developed by 3M, Minneapolis, Minn., in connection with the center for Amorphous Semiconductors at Iowa State University, Ames, Iowa. The top and bottom of the electrical energy source 40 may also be provided with circular photovoltaic cells (not shown) to further increase the efficiency by capturing any emitted light from the edges of the LEP material 42. In still another embodiment shown in FIG. 8, the LEP material 52 acts both as the light source for the photovoltaic cell 54 and the structural support for the electrical energy source 50. In this embodiment, the LEP material 52 is cast in the form of a sphere surrounding the photovoltaic cell 54. The photovoltaic cell 54 would also preferably be in the form of a sphere having a screened conductor around the periphery of the sphere. The LEP material 52 could be coated with a reflective material, such as aluminum, thereby insuring total internal reflection of all of the emitted light from the LEP material 52. Each of these spherical cells could be encased in an inactive polymer structure that would serve as the shielding and support for multiple cells for the electrical energy source 50. It will be apparent that the use of the LEP material 12 as the carrier for the selected radioisotope provides the present invention with numerous advantages in terms of the geometrical and design considerations for constructing the electrical energy source 10. Although only a limited number of possible design combinations of the LEP material 12 and the photovoltaic cells 14 and 16 (or single photovoltaic cell or double-sided photovoltaic cell) have been presented, it should be appreciated that many other designs will be possible because of the nature of the LEP material 12. OPTICAL CONTROL MEANS In still another embodiment of the present invention shown in FIGS. 9 and 10, the LEP material 60 is optically separated from the photovoltaic cells 62 by an optical control means 64 for controlling the amount of light that may be absorbed by the photovoltaic cells 62. The optical control means 64 may be a liquid crystal display (LCD) or lead lantium zirconium titinate (PZLT) or similar material that is either transparent or opaque, depending upon the voltage or current applied to the material. By controlling the amount of light that may be absorbed by the photovoltaic cells 62, the optical control means 64 also controls the output of the photovoltaic cells 62 and, hence, operates as either a voltage or current regulator depending upon the particular circuit that utilizes the electrical energy source of the present invention. The inclusion of the optical control means 64 allows the electrical energy source of the present invention to simulate an alternating current source from a direct current source without the need for any electrical circuitry external to the electrical energy source. It will be readily apparent that other circuit elements may be incorporated with the electrical energy source 10 of the present invention to optimize the electrical energy source for a particular application. As shown in FIG. 10, a zener diode 76 has been added to establish a fixed voltage level for the output of the electrical energy source 70 having LEP material 72 emitting light energy to be absorbed by the photovoltaic cells 74. A capacitor 78 has also been added to act as an internal electrical storage device that would be charged up to a predetermined voltage level over a given time period and then utilized to power the desired circuit for a relatively shorter time period, after which the electrical energy source 70 would recharge the capacitor 74 for the next demand period. In this way, the large amp-hour power of the electrical energy source 70 may be realized in applications where an intermittent power demand is required, but the demand is higher than the steady state power (either current or voltage) supplied by the electrical energy source 70. For example, if the electrical energy source 70 were used to power a telemetry detection/transmission circuit, such a circuit could be designed to have the detection portion run off the steady state power of the electrical energy source, with the transmission portion of the circuit powered for short durations by the capacitor 74. ELECTRICAL CONSIDERATIONS Not only is the electrical energy source 10 of the present invention unique as a battery because of its relatively long-life, other electrical characteristics of the electrical energy source 10 of the present invention make it particularly well-suited for certain applications. Based upon the test data reported in Tables II and III below, the internal impedance of the electrical energy sources in accordance with the present invention is calculated at approximately 5M Ohms. This high impedance is particularly desirable for low-power applications, such as CMOS and NMOS devices. Because the impedance of the load is easily matched to the impedance of the source, it is easier to achieve the maximum output from the electrical energy source of the present invention. The nature of the source of the electrical energy of the present invention, namely a generally constant rate of radioactive decay, allows the electrical energy source 10 to be short circuited without causing any damage to the device and, more importantly, without affecting the power available in the device at some time in the future. Unlike low-power chemical batteries, the electrical energy source of the present invention does not release all of its "stored" energy when it is short circuited. This means that there is no risk of explosion or damage to the device as a result of the short circuit. Also, when the short circuit is removed from the electrical energy source 10, the output of the device is immediately restored to its pre-short state. This allows the electrical energy source 10 to easily act as an ideal constant voltage source, even after the source has been short circuited. SAMPLE RESULTS The following tables set forth the measured voltage output of the circuit shown in FIG. 10 having a single electrical energy source in accordance with the present invention and utilizing both the blue and yellow-green phosphors for various curie levels. The LEP material was placed in intimate physical and optical contact with a single specially calibrated photovoltaic cell Model No. 035-015817-01, available from ARCO Solar, Inc., having dimensions of 38.times.17 mm. The measured voltages are measured in millivolts in parallel with a 10 Mohm input impedence of the volt meter used to take the measurements: TABLE II ______________________________________ Blue Phosphor 1 5 25 50 Ci/g Ci/g Ci/g Ci/g 45 .times. 41 .times. 47 .times. 48 .times. Dimensions (mm) 15 .times. 1 15 .times. 1 15 .times. 1 15 .times. 1 Total curies 0.62 2.7 15 34 ______________________________________ Output Voltages (millivolts) Load (ohms) 1K 0.00 0.05 0.15 0.3 4.7K 0.1 0.1 0.7 1.3 10K 0.1 0.2 1.3 2.6 22K 0.2 0.6 3.0 6.1 47K 0.3 1.1 5.8 2.0 68K 0.5 1.6 8.8 18.1 100K 0.75 2.4 13.1 27.1 150K 1.05 3.5 18.7 38.6 220K 1.5 4.9 26.6 54.7 330K 2.3 7.9 42.7 88.3 470K 3.0 10.1 54.7 112.7 680K 4.6 15.4 83.4 171.6 1M 5.9 19.8 107.1 220 2.2M 11.4 38.3 206 421 4.7M 20.4 68.3 365 727 10M 29.4 97.9 516 984 ______________________________________ TABLE III ______________________________________ Yellow-Green Phosphor 1 5 25 50 Ci/g Ci/g Ci/g Ci/g 35 .times. 47 .times. 55 .times. 49 .times. Dimensions (mm) 15 .times. 1 15 .times. 1 15 .times. 1 15 .times. 1 Total curies 0.46 2.83 13.7 31.6 ______________________________________ Output Voltages (millivolts) Load (ohms) 1K 0.00 0.0 0.1 0.1 4.7K 0.00 0.1 0.3 0.4 10K 0.0 0.2 0.7 0.8 22K 0.1 0.5 1.6 1.9 47K 0.2 0.8 3.1 3.8 68K 0.2 1.3 4.6 5.7 100K 0.3 1.9 6.9 8.4 150K 0.45 2.7 9.9 12.1 220K 0.65 3.8 14.0 17.1 330K 1.05 6.1 22.5 27.6 470K 1.25 7.9 28.7 35.2 680K 2.0 12.1 43.8 53.7 1M 2.5 15.5 56.3 68.9 2.2M 4.9 29.9 108.4 132.5 4.7M 8.7 52.9 190.7 233 10M 12.4 75.9 271.0 330 ______________________________________ Although the description of the preferred embodiment has been presented, it is contemplated that various changes could be made without deviating from the spirit of the present invention. Accordingly, it is intended that the scope of the present invention be dictated by the appended claims rather than by the description of the preferred embodiment. |
description | This application is a Continuation of U.S. National Stage Application Ser. No. 13/201,428, filed Aug. 12, 2011, published as U.S. Publication No. 2011/0293056, which was filed under 35 U.S.C. § 371 of International Patent Application PCT/US2010/024172, accorded an international filing date of Feb. 12, 2010, which claims benefit under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No. 61/152,221, filed Feb. 12. 2009, and incorporates by reference the contents of these applications in their entirety. This disclosure generally relates to the field of plasma physics, and, more particularly, to methods and apparatus for heating and/or compression of plasmoids. There is no question that the world's demand for energy will only increase. The advancement of virtually every modem society parallels the availability of copious, low-cost energy. The tremendous change that has been made to the Earth's atmosphere, and the potential looming climate catastrophe, are a consequence of the fact that energy was obtained by the consumption of staggering quantities of fossil fuels. The attractiveness of fusion as an energy source is well known and has been pursued as an energy source worldwide for many years. However, the entry of fusion as a viable, competitive source of power has been stymied by the challenge of finding an economical way to heat and confine the plasma fuel. The main challenges to plasma heating and confinement are the complexity and large physical scale of the plasma confinement systems and associated heating systems. The more massive the system required to confine and heat the fusion plasma, the higher the cost to develop and operate it. One decision by the majority fusion research community that drives the scale higher is the community's selection of the tokamak embodiment for plasma fuel confinement. The tokamak embodiment leads to large reactor sizes due to the low ratio of the plasma energy to magnetic energy and the need to operate at steady state (low power density). The research community has also expended great effort at the other end of the energy density spectrum, pursuing fusion at extremely high energy densities. Here, minute fuel pellets are compressed to fusion conditions by a large array of high power lasers. In this embodiment, the efficiency and complexity of the fast laser energy delivery systems become the problem, particularly the ability to rapidly and repetitively pulse these lasers to achieve reasonable levels of power efficiency. For magnetic systems, the threshold size of a steady state fusion reactor required to achieve ignition and offer a safe protective shielding will always be quite large. Unlike fission, where the first commercial reactor was 50 MW, a demonstration fusion reactor must start operation at multi-gigawatt powers. There is a relatively unexplored region in reactor size and plasma energy density that lies between these two energy density extremes. The fusion plasmoid envisioned here results in a fusion reactor that falls into this unexplored size and energy density range. A plasmoid is a coherent structure of plasma and magnetic fields, an example of which is the plasmoid commonly referred to as the Field Reversed Configuration (FRC). A quasi-steady fusion reactor based on plasmoids provides for a method to operate at an optimal power density. The methods and apparatus described herein provide a range of other desirable features as a source of neutrons including production of rare isotopes, diagnostic instruments and energy generation. For the generation of energy, many methods incorporate, but are not limited to, i) the generation of energy from fusion using a range of fuel (e.g., deuterium and lithium); ii) the conversion of Thorium to a fissile fuel; and the transmutation of the radioactive waste to energy. These present many possible advantages. For example, the unique ability of the plasmoid to be translated over distances of several meters allows for the formation and kinetic energy input to be added incrementally outside of the interaction chamber and breeding blanket. This avoids the numerous challenges confronting other approaches where the sophisticated devices needed to create, heat, and sustain the plasma must be co-located along with the reactor blanket and power processing systems. Also for example, such may allow plasma exhaust (divertor) region to be well removed from the reactor, eliminating critical power loading issues. The entire high field reactor vacuum magnetic flux is external to plasmoid flux and is therefore divertor flux. In a transient burn, the particle loss from the plasmoid will be overwhelmingly directed to the divertor regions as the axial flow time is many orders of magnitude smaller than the perpendicular particle diffusion time in the open flux region. As another example of the possible advantages, by virtue of the cyclic nature of the burn, virtually all of the fuel can be introduced during the initial formation of the plasmoid with no need for refueling. As yet another example, the ability to locate the divertor remotely in an essentially neutron-free environment makes tasks such as fuel recovery and divertor maintenance much easier to perform. As still another possible advantage, both reactor and divertor wall loading may be easily regulated by the pulse duty cycle. As yet still another possible advantage, due to the linear, cylindrical reactor geometry there can be a high conversion efficiency of the fast fusion neutrons. As even still another possible advantage, the simply connected, linear geometry of the reactor vessel is amenable to a liquid metal wall interface. This would allow for operation at the highest power density, and solve several plasma-material wall issues. The FRC has the highest β (the ratio of plasma energy density to confining magnetic field energy density) of all fusion plasmas, and the simple cylindrical nature of the confining field coils allows for the highest magnetic fields. Thus, a further possible advantage, is that the small ratio of the plasmoid volume to the neutron absorbing blanket volume provides for an optimal power density to be obtained without exceeding thermal limitations in the blanket. A yet further possible advantage, is that the small footprint allows for easy integration into existing power plant infrastructure. An even further possible advantage, is that the smaller reactor scale also means much faster and far less expensive iterations during the development phase which will be essential to the integration of improvements and new technologies. A even still further possible advantage, is that with eventual fusion power output in the 50 to 200 MW range, these devices can be modularized. Another unique possible advantage to a quasi-steady reactor is the possibility of direct energy conversion into electricity at high efficiency. The initially large volume, relatively cool plasmoid is accelerated to high velocity and then compressed into the fusion burn chamber much like fuel into an engine cylinder, however the compression ratio attained here is vastly greater (˜400) resulting in near unity thermal efficiency. The fusion reaction greatly intensifies as peak compression is reached, and the fusion burn rapidly expands the plasmoid. This expansion is powered directly by the high energy ions magnetically trapped within the plasmoid, for example the alpha particles when tritium and deuterium are employed as fuels. With expansion driven by the fusion products, the magnetic energy is returned hack into the circuit restoring the electrical energy expended in compressing the plasmoid initially. In this way energy can be directly converted to electricity avoiding the inefficient processes entailed in thermal conversion. The ability to make use of the plasma, fusion and electrical energy in a very efficient manner is unique to the concept described here, and enables the commercial application of fusion to be realized without resorting to larger scale, higher fusion gain systems. With the repetitive and efficient generation of plasmoids, brought to high temperature and density as they are injected into the interaction chamber, a compact, low-cost fusion reactor can be realized. The unique geometry and simplicity of the device provides for other applications for the surplus neutrons that would normally be absorbed in the blanket. These neutrons can he employed in a transformational manner where their ability to produce rare isotopes, or initiate the process of the conversion of one element into another can be exploited. Alternatively other gases can be heated and compressed using the methods described to produce other products. The methods and devices described herein allow the generation of high temperature plasma in a novel and unique manner that can operate in a power density that is distinct and advantageous compared to current devices, contains unique features that will speed and reduce the costs of development and minimize the energy required to heat the plasma. The plasmids that were generated employing at least one of the methods described herein, share several traits common to that of the FRC plasmoid. The FRC is a plasmoid with a symmetric toroidal geometry in which the confining magnetic field is provided primarily by toroidal plasma currents. The plasma pressure is contained by the encompassing magnetic pressure and magnetic tension with the result that the plasma energy dwarfs the FRC plasmoid magnetic field energy, and for this reason make the FRC the geometrically simplest, most compact, and highest of all magnetic confinement concepts. Although the method of rapid magnetic field reversal is employed in forming the plasmoid considered here, it differs from past methods of FRC formation in that the field is reversed incrementally in stages imparting a rapid axial motion to the plasmoid during formation. It is quite possible that this method generates distinctly different internal plasma flows and currents, and therefore magnetic fields, from that of the symmetric, in situ formation of the FRC. The primary features of the plasmoid generated here appear to be similar to the FRC plasmoid in general. The use of the descriptor FRC is therefore used to indicate the method of plasmoid formation rather than any specific internal magnetic configuration and other plasmoids can be accelerated and compressed using the methods described herein. The simply connected nature of the magnetic field of the FRC plasmoid with regard to the containment vessel and the linear confinement geometry, allow for the translation of the FRC plasmoid over large distances. These attributes make the FRC plasmoid especially attractive as a means to contain thermonuclear plasmas. These unique qualities, however, are realized at a cost. The topological simplicity makes the generation and sustainment of the large diamagnetic currents challenging. The configuration has net bad magnetic curvature and is susceptible to magnetohydrodynamic (MHD) interchange and kink modes. When isolated from the vessel wall by an external axial magnetic field, as is typically the case, the FRC plasmoid poloidal field represents essentially an anti-aligned dipole with regard to the external field and is therefore disposed to tilt instability. Despite these daunting issues, stable high-temperature FRC plasmoids have been readily formed where the requisite plasma heating and current generation was produced by rapid reversal of the axial magnetic field in cylindrical coil geometry. Once formed, the FRC is observed to he stable and the plasma well confined as long as the plasma remains in a kinetic regime. This regime is characterized by S*, the ratio of the FRC separatrix radius, rs and the ion collisionless skin depth c/ωpi. Both stability and transport are observed to rapidly deteriorate when S*/ε>5, where ε is the FRC separatrix elongation ε(=1s/2rs). The FRC plasmoid decays on a resistive time scale that is anomalous. The observed particle confinement, stated in terms of directly measured quantities that can be accurately measured across all experiments, yields the following scaling:τN=3.2×10−15 ε0.5xs0.8rs2.1n0.6 (1)where xs is the ratio of the FRC separatrix radius rs, to coil radius rc. With reasonable assumptions for the FRC relative size and shape (ε˜15 and xs=0.6), this scaling, together with kinetic condition, determine the plasma radius and density required to satisfy the Lawson criteria for fusion gain, i.e., n≥1.5×1023 m−3 and rs≤0.07 m. The high plasma energy density implied by these constraints prescribes a small, pulsed fusion regime for the FRC. However, these FRC plasmoid parameters have not been achieved by any methodologies previously employed in past experiments. A method of heating plasmoids may be summarized as including increasing a kinetic energy of at least one of at least two plasmoids initially separated from one another by a distance, each of the plasmoids having a respective initial thermal energy; and at least temporarily confining an interaction of the plasmoids in an interaction chamber in a higher energy density state at a thermal energy greater than a sum of the initial thermal energies of the plasmoids. Increasing a kinetic energy of at least one of the plasmoids may include accelerating at least one of the plasmoids relatively towards at least one of the other ones of the plasmoids. Increasing a kinetic energy of at least one of the plasmoids may include magnetically accelerating each of the plasmoids relatively towards one of the other ones of the plasmoids over at least a portion of the distance. Increasing a kinetic energy of at least one of the plasmoids may include accelerating at least one of the plasmoids relatively towards at least one of the other ones of the plasmoids, and may further include compressing at least one of the plasmoids while accelerating the at least one of the plasmoids. The method may further include causing the two plasmoids to produce a resultant plasmoid in the interaction chamber to convert the kinetic energy of the at least one of the plasmoids into thermal energy. The method may further include compressing at least one of the plasmoids with a magnetic field. The method may further include forming the at least two plasmoids. The method may further include forming each of at least two field reversed configuration (FRC) plasmoids outside of the reaction. Forming each of at least two field reversed configuration (FRC) plasmoids outside of the interaction chamber may include concurrently forming and accelerating at least one of the plasmoids. Forming each of at least two field reversed configuration (FRC) plasmoids outside of the interaction chamber may include concurrently forming, accelerating and compressing at least one of the plasmoids. Dynamically forming each of the two plasmoids by activating a series of magnetic coils in sequence may include forming an initial plasmoid by using a respective annular array of plasma sources for each of the two plasmoids and activating the series of magnetic coils in sequence. Forming each of the two plasmoids by activating a series of magnetic coils in sequence may include forming each of the two plasmoids by activating a respective series of independently-triggered magnetic coils in sequence. The method may further include sequentially reversing a plurality of coils to dynamically form the plasmoids. Increasing a kinetic energy of at least one of the plasmoids may include activating a series of magnetic coils in sequence to accelerate each of the plasmoids, the thermal energy of the resultant plasmoid including components of the conversion of a respective kinetic energy from the acceleration of each of the plasmoids, increasing a kinetic energy of at least one of the plasmoids may include simultaneously compressing and accelerating each of the plasmoids by activating a series of magnetic coils in sequence. Simultaneously compressing and accelerating each of the plasmoids by activating the series of magnetic coils in sequence may include each of the magnetic coils having a smaller radius than a preceding one of the magnetic coils in the series. The method may further include heating and compressing the plasmoids by self compression into a radially converging magnetic field. The method may further include collecting at least one of heat, tritium, helium 3, fissile fuel, medical isotopes or other products resulting from interaction of neutrons produced by reaction of the plasmoids with a blanket of material at least proximate the interaction chamber. An apparatus for heating plasmoids may be summarized as including a interaction chamber having a generally cylindrical shape with a first end and a second end, the interaction section; a first acceleration section that provides a first plasmoid coupling path to the interaction chamber; a second acceleration section that provides a second plasmoid coupling path to the interaction chamber; a first plurality of magnetic coils successively arranged along a least a portion of a length of the first acceleration section, the first plurality of magnetic coils configured to accelerate a first initial plasmid toward the interaction chamber with increasing kinetic energy; and a second plurality of magnetic coils successively arranged along a least a portion of a length of the second acceleration section, the second plurality of magnetic coils configured to accelerate a second initial plasmid toward the interaction chamber with increasing kinetic energy. The apparatus may further include a third plurality of magnetic coils successively arranged along at least a portion of an interaction chamber and surrounding an outer perimeter of interaction chamber configured to at least temporarily confine a resultant plasmoid in the interaction section. The apparatus may further include a first formation section to temporarily retain the first initial plasmoid, the first acceleration section located between the first formation section and the interaction chamber, the first plasmoid coupling path being linear; and a second formation section to temporarily retain the second initial plasmoid, the second formation section located between the second formation section and the interaction chamber, the second plasmoid coupling path being linear. The apparatus may further include a first plasma source configured to form a first initial plasmoid in the first formation section; and a second plasma source configured to form a second initial plasmoid in the second formation section. The apparatus may further include a first annular array of plasma sources to produce the first initial plasmoid in the first formation section; and a second annular array of plasma sources to produce the second initial plasmoid in the second formation section. The apparatus may further include a fourth plurality of magnetic coil successively arranged along at least a portion of the first formation section and surrounding an outer perimeter of the first formation section; and a fifth plurality of magnetic coils successively arranged along at least a portion of the second formation section and surrounding an outer perimeter of the second formation section. Each of the first and the second pluralities of magnetic coils may surround an outer perimeter of the first and the second acceleration sections respectively and may include a series of magnetic coils configured to be activated in sequence to accelerate the first and the second initial plasmoids, respectively. The apparatus may further include a blanket at least partially surrounding providing the interaction chamber; a quantity of lithium at least temporarily contained proximate the interaction chamber by the blanket; and an extraction system to extract tritium resulting from interaction of neutrons produced by interaction of the plasmas with the lithium proximate the interaction chamber. The apparatus may further include a blanket at least partially surrounding providing the interaction chamber; a quantity of lithium at least temporarily contained proximate the interaction chamber by the blanket; and an extraction system to extract heat resulting from interaction of neutrons produced by reaction of the plasmas with the lithium. A method of direct energy conversion of any or all parts of the input energy or product fusion energy may be summarized as including successively supplying electrical energy to a first series of magnets along at least a first acceleration section to accelerate a first plasmoid toward an interaction section of a interaction chamber; successively supplying electrical energy to a second series of magnets along at least a second acceleration section to accelerate a second plasmoid toward the interaction chamber; and recovering electrical energy from at least some of at least one of the first or the second series of magnets after the first and the second plasmoids begin interacting in the interaction chamber. Recovering electrical energy from at least some of the magnets may include recovering electrical energy from at least one of the magnets of both the first and the second series of magnets. The method of fusion generation may further include recovering thermal energy from a blanket of a material at least proximate the interaction chamber generated by the interaction of the first and the second plasmoids in the interaction chamber. The method of fusion generation may further include recovering a fuel from a blanket including a quantity of lithium at least proximate the interaction chamber generated by the interaction of the first and the second plasmoids in the interaction chamber. A fusion generation system may be summarized as including an interaction chamber in which at least two plasmoids may interact a first acceleration section that leads to the interaction chamber; a first series of magnets spaced longitudinally along at least a portion of the first acceleration section to accelerate a first plasmoid toward the interaction chamber; at least one circuit operable to successively supply electrical power to the magnets of at least the first series of magnets to accelerate at least a first one of the plasmoids toward the interaction chamber and to recover electrical energy from the magnetic circuits. The fusion generation system may further include a second acceleration section that leads to the interaction chamber; a second series of magnets spaced longitudinally along at least a portion of the second acceleration section to accelerate a second plasmoid toward the interaction chamber. The at least one circuit may be operable to successively supply electrical power to the magnets of at least the second series of magnets to accelerate at least a second one of the plasmoids toward the interaction chamber and to recover electrical energy from at least some of the magnets of at least the second series of magnets after the plasmoids interact in the interaction chamber. The fusion generation system may further include a thermal extraction subsystem thermally coupled to the blanket and operable to recover thermal energy produced by the interaction of the plasmoids in the interaction chamber. The thermal extraction subsystem may include a steam powered electrical generator or other heat engine. A method of plasmoids may be summarized as including forming at least a first plasmoid in a formation section; and accelerating at least the first plasmoid concurrently with forming the first plasmoid. The method may further include compressing at least the first plasmoid concurrently with forming and accelerating the first plasmoid. The method may further include sequentially reversing a plurality of coils to dynamically form at least the first plasmoid. Accelerating at least the first plasmoid may include accelerating at least the first plasmoids relatively towards at least one other plasmoid. Accelerating at least the first plasmoid may include magnetically accelerating at least the first plasmoids relatively towards at least one other plasmoid over at least a portion of a distance. Compressing at least the first plasmoid concurrently with forming and accelerating the first plasmoid may include compressing at least one of the plasmoids with a magnetic field. The plasmoid based fusion reactor includes a interaction chamber, a plurality of magnetic coils, and two sets of annular arrays of plasma sources. The interaction chamber has a generally cylindrical shape with a first end and a second end. The interaction chamber includes an interaction section in the middle of the interaction chamber. Two formation sections are positioned at respective ends of the interaction chamber. Two acceleration sections are positioned between respective formation and interaction sections. Each series of magnetic coils surround an outer perimeter of a respective section. Each set of the annular array of plasma sources is located at a respective end of the formation chamber and configured to form an initial plasmoid. Each of the series of magnetic coils surrounding the outer perimeter of the formation sections and the acceleration sections includes a series of independently-triggered magnetic coils configured to be activated in sequence to accelerate a plasmoid. The plasmoid may be a plasma magnetically confined within a magnetic ‘bottle’ and generated by currents that flow in the plasma itself, rather than in external coils. The equilibrium size and shape of the plasmoid may, for example, be approximately equivalent to that of an elongated football. The reactor may have scale consistent with the size and energy density required for fusion. The reactor may advantageously employ a simple linear geometry. The reactor may advantageously realize a high plasma-to-magnetic energy ratio and closed-field confinement. Each of these advantages contributes to low reactor cost. Another advantage is the capability to move the plasmoid over relatively large distances. Yet another possible advantage of the approach is avoidance of the complications that plague other more conventional approaches, which include sophisticated devices to create, heat, and sustain the plasma and must be co-located with a reactor blanket and power processing systems. The plasmoids may be accelerated to high velocity and injected into a fusion interaction chamber much like fuel into an engine cylinder. The confining magnetic field continues to compress the plasmoids toward fusion conditions, intensifying the fusion reaction as peak compression is reached. In a method analogous to the operation of a conventional diesel engine, the fusion “burn” rapidly expands the plasmoid. Plasmoid expansion is powered directly by the high energy alpha particle that is created along with the neutron in the fusion reaction. In a further embodiment, the alpha particle is magnetically trapped in the resultant plasmoid. With alpha particle-driven expansion, magnetic energy is returned back to an original source circuit, thereby restoring the electrical energy initially expended in compressing the plasmoids. In this way a self-perpetuating compression cycle that forms a fusion engine (FE) is established. One advantage of these embodiments is that fusion, plasma and electrical energy are all used efficiently. In yet another embodiment, these advantages are used in a commercial application to provide power at a low cost. Using certain fusion reactions, for example between deuterium and tritium, the fusion reaction produces neutrons that can interact with lithium containing materials in a blanket surrounding a interaction chamber such that the energetic neutrons are absorbed by the lithium and converted into tritium fuel and heat. The heat may be advantageously used to generate electricity, either in a way conventional to a power plant operating on a steam cycle, or in alternative ways. One advantage of this embodiment is that the device produces heat for conventional power generation and at the same time produces more tritium fuel than it consumes. In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with the field reversed configuration have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments. Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.” Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments. As a proof-of-principle experiment (demonstration) of the plasmoid heating apparatus, an embodiment referred to as the prototype experimental device (PED) is constructed and demonstrated. The PED comprises two magnetically driven coil systems for the formation, acceleration, and compression of a field reversed configuration (FRC) plasmoid to high velocity with respect to the other (up to 800 km/s). The motional energy of the accelerated FRC plasmoid provides a significant fraction of the energy needed to heat the plasma to fusion temperatures, as well as provides a means to further compress the plasmoid into higher magnetic fields and smaller chambers. The motional energy becomes rapidly converted to thermal energy when the two FRC plasmoids merge. In the experiment, the FRC plasmoids are observed to interact/merge with one another, forming a resultant, hot (5 million ° K.) plasmoid that is further compressed and heated (up to 20 million ° K.) by an axial magnetic field. FIG. 1 illustrates a fusion reactor 5 according to one non-limiting embodiment. In one embodiment, the fusion reactor 5 may include an interaction chamber 10 in the center, a formation, accelerator and compression section 36 on each end of the interaction chamber 10, and a FRC plasmoid formation section 34 next to each accelerator/compression section 36. The fusion reactor 5 may additionally include a divertor 14 on the outer end of each formation section 34. The fusion reactor 5 may also include interaction chamber coils 30, 32 around the outer perimeter of the interaction chamber 10, accelerator coils 22 around the outer perimeter of the acceleration/compression section 36, formation coils 18 around the outer perimeter of the formation section 34, and end coils 28 around the outer perimeter of the fusion reactor 5 between the extreme end of each formation section 34 and the respective divertor 14. The fusion reactor 5 may further include an annular array of small plasmoid sources 38 located near a dielectric vacuum tube wall under the first formation/acceleration coil 18 nearest the end coils 28. The chamber wall 16 of the fusion reactor 5 may act as a vacuum boundary. FIGS. 2 through 7 depict cross sections taken in a plane passing through the axis of symmetry of the fusion reactor 5 to show the magnetic configuration. Only the magnetic coils of the fusion reactor 5 are shown for clarity. The dashed lines delineate magnetic field contours, and the arrows indicate the polarity of the magnetic field. The sequence of FIGS. 2 through 7 illustrates the temporal changes in magnetic field structure. In particular, the sequence from FIG. 2 through FIG. 7 illustrates the magnetic field contours at various key times in the operation of the FRC fusion reactor 5. The field contours reflect results from a resistive, two-dimensional MHD numerical calculation. The changes in the magnetic field contours shown in FIGS. 2 through 7 were produced by energizing the axial array of coils in a properly sequenced manner. The magnetic waveforms for the coils 18, 22, and 28 are preferably produced with a rise time and magnitude that maintains the maximum axial field gradient across the FRC plasmoid consistent with maintaining FRC plasmoid stability and isolation from the vacuum boundary 16. The number of coils employed, as well as the field magnitude and timing used in this process is determined by the desire to maintain, in the frame of the FRC plasmoid, a quasi-stationary magnetic geometry that increases in magnitude and decreases in scale as the FRC plasmoid moves through the acceleration/compression section 36 into the interaction chamber 10. To minimize the FRC plasmoid formation time, as well as maximize acceleration, the PED device is constructed so that a new formation methodology could be employed, which is referred to as dynamic formation, and is described in greater detail below. In virtually all previous FRC experiments a monolithic field reversed theta pinch (FRTP) coil was employed. W dynamic formation the FRTP is replaced with a set of electrically isolated and independently triggered formation coils 18. In one embodiment, all the formation coils 18 are supplied with an initial reverse bias field 26 indicated by arrows pointing to the left (see FIG. 2). A forward bias (arrows to the right) is applied to the end coils 28 and the accelerator coils 22, as well as the interaction chamber coils 30 and 32. In one embodiment, the FRC plasmoid formation section 34 is increased in radius to provide for greater initial FRC plasmoid flux and energy. This is followed at smaller radius by a set of accelerator/compression coils 22 with forward bias increasing as the radius decreases moving towards the interaction chamber 10, in one embodiment, a gradual reduction in radius and increase in compression result as an FRC plasmoid travels down the acceleration/compression section 36. In one embodiment, the interaction chamber 10 is matched to the smaller radius of the acceleration/compression section 36. Alternatively, a smaller or larger interaction/compression chamber may be employed depending on the manner in which the fusion burn process is to be sustained, as well as the optimum blanket geometry for neutron irradiation. In the experiments, the formation coils 18 are energized sequentially to both form, accelerate, and compress the FRC plasmoids simultaneously. The process is illustrated in FIG. 3 where magnetic field contours reflect the magnetic configuration at the midpoint of the FRC plasmoid formation in time, By executing field reversal in this sequenced fashion the FRC plasmoid internal flux 72 can be maintained throughout the entire process. The FRC plasmoid formation is completed with field line closure as depicted in FIG. 4. At this point the FRC plasmoid 20 is now magnetically isolated from the vacuum wall 16. The FRC plasmoid 20 continues to be accelerated by the gradient magnetic field produced by the sequenced formation coils 18 now acting as accelerator coils. In one embodiment, the initial, low energy plasma is generated by the annular array of small plasma sources 38. The plurality of these sources is dictated by the need to achieve an azimuthally uniform initial plasma. The annular plasma formed by these sources must be free of azimuthal non-uniformities in order to not seed instability as the plasma is radially compressed during FRC plasmoid formation. The plasma at this time is susceptible to flute-like instabilities. These modes are stabilized by finite ion gyro-orbit effects once the ions are heated with the completion of FRC plasmoid formation (see FIG. 4). The radial proximity of the plasma near the wall assures good flux retention through field reversal. The pulse length and magnitude of the plasma flow are important in that these parameters determine the inventory and initial length of the FRC plasmoid. The use of plasma sources in this manner also provides for a means to keep the interaction chamber 10 and the acceleration/compression sections 36 at high vacuum. This is important as a significant neutral density dramatically affects FRC plasmoid behavior during acceleration and compression. In demonstration experiments, a significant neutral gas density prevented both FRC plasmoid merging and equilibrium. As important as obtaining the proper density and temperature of the plasmoid for fusion, is the amount of internal poloidal flux of the FRC plasmoid as the FRC plasmoid lifetime scales directly with this quantity. A characteristic of all past FRC experiments formed in a FTP is that there are two distinct phases of FRC formation where this flux is lost. The first is the flux that is lost in the reversal process itself. This flux loss is characterized by the fraction of the initial reverse bias flux that still remains after the external axial field as been reversed to a level where the radial magnetic pressure exceeds the pressure of the bias flux and plasma, and the plasma has moved radially away from the vacuum wall. The remaining flux is referred to as the “lift-off” flux. As the field is reversed, a conductive plasma sheath is formed at the vacuum tube wall that inhibits further loss of reverse flux. The sheath however is resistive enough that a significant fraction of the reverse flux is lost. The second period of flux loss occurs as this plasma sheath moves radially inward with the rise of the forward field. To reach equilibrium the plasma must broaden onto the outer forward field. The flux loss at this time is due to the turbulent transport that occurs during relaxation of the FRC plasmoid into equilibrium. A new formation technique is realized that maximizes lift-off flux and minimizes subsequent flux loss. It also provides for a method to simultaneously accelerate, rapidly translate and compress the FRC plasmoid into a much smaller, higher field coil without diminishing the plasmoid axial motion. The entire process is referred to as dynamic formation. Dynamic formation describes the complete, continuous process employed to form, accelerate and compress the FRC plasmoid into the compression chamber where it is merged with its mirror image to form the ultimate plasmoid to be compressed to thermonuclear conditions. The dynamic formation method was incorporated into the design and construction of the PED in FIG. 8 as well as the device depicted in FIGS. 2 thru 7. A more detailed description of dynamic formation and its advantages follows. Standard FRTP formation employs a long cylindrical pinch coil that is reversed with the simultaneous formation of a reversed field throughout the entire coil. The FRC is generated by the following sequence of events: (1) A weakly ionized gas is produced in an axial magnetic field. This field is usually referred to as the bias field. (2) Voltage is applied to the coil reversing the direction of the axial magnetic field. The induced azimuthal electric field generates a strong ionizing current that prohibits the loss of the initial axial field now referred to as the trapped reversed field. (3) Increasing (forward) axial field now provides for the formation of the FRC. Forward flux equal to the trapped reversed flux forms closed field lines inside the vacuum chamber. Plasma can now flow on these field lines from the inner (reversed) field to the outer field and relax to form a proper radial and axial equilibrium distribution. (4) Increasing the magnetic field further radially compresses and heats the FRC. This additional field is now external to the FRC insulating it from the vacuum boundary. The closed field line IRC contracts axially into a high β equilibrium to balance the compressional effect of the external axial field. In this manner a magnetically isolated plasmoid is formed that is neutrally stable to translation if the external guide field is uniform. The entire time from the lift-off of the plasma sheath to the relaxation into equilibrium is characterized by anomalous flux and energy loss. If translation of the FRC is also desired, even more time is lost while the FRC is subsequently accelerated. After being formed, the FRC can be caused to translate out of the FRTP coil by either activating a separate trigger coil that was not employed for formation, or by having constructed the FRTP coil with a slight radial taper where the small axial field gradient eventually causes the FRC to drift to the end of the coil where it feels the strong magnetic gradient at the end of the coil and is ejected. This method for producing the FRC and its directed motion is undesirable for several reasons. First, it takes considerable time for the FRC to relax to an equilibrium all the while losing both inventory (mass) and flux. Second, it provides essentially for only the thermal energy of the FRC to be converted into directed energy. The expanding radius of the conical coil also reduces the magnetic field B, and plasmoid azimuthal current J, and therefore significantly diminishes the accelerating J×B body force acting on the FRC as it translates out of the coil. These are serious drawbacks that would limit the efficiency of the FRC acceleration, compression and heating. All of these disadvantages are avoided in the dynamic formation method. The sequential excitation of the formation coils provides for several advancements over the traditional triggered field reversed theta pinch or conical pinch. Specifically: (1) sequential excitation creates a very strong axial gradient in the axial magnetic field which produces a powerful axial body force with the initiation of every coil. (2) The FRC plasmoid formation occurs simultaneously with acceleration providing for the most rapid FRC plasmoid formation and translation possible. (3) The FRC plasmoid flux is preserved during the entire formation/acceleration process, as the reverse bias flux is undiminished until the last coil is reversed. In the traditional FRTP method flux loss occurs simultaneously all along the coil so that the “clock” on internal flux loss begins once the reversal is initiated. In the sequential method this reversal is reenacted with each coil excitation and reversal flux is maintained at the initial value up to last coil to be reversed. This process can be carried out all the way up to insertion of the FRC plasmoid into the compression chamber if desired, and was demonstrated on the PED although it was not found to be the optimal method. A coil is designated as a formation coil if it initiated with a reverse bias field. It is designated an accelerator coil if it has a forward bias field initially. Employing this nomenclature, only the first four coils are operated as formation coils for the device operation depicted in FIGS. 2 thru 7. The prototype experimental device was operated with as few as four and as many as eight formation coils. The employment of four or five formation coils was found to be optimum. (4) The coil prior to the coil about to be energized naturally injects some plasma forward inside the next coil near the vacuum wall as it is activated. This process provides for a more rapid sheath formation under the next reversing coil. This minimizes flux loss during reversal and maximizes the amount of internal flux that can be realized. (5) With no need for a conical coil, combined with the maximum possible internal flux, the largest axial and radial Lorentz (J×B) force acting on the FRC is achieved. It is therefore possible to perform magnetic compression into smaller coils at the same time the FRC is being accelerated or translated. Great advantage of this last point is taken in the design and operation of the device as described by FIGS. 1 through 7. The FRC plasmoid velocity is maintained or even increased while it is simultaneously being compressed into smaller and smaller coils at higher field. Dynamic formation therefore provides for the staged compression of the FRC plasmoid all the way into the reactor compression chamber. It is made possible by the proper sequencing of the axial array of short cylindrical coils while employing the correct magnetic field rise time and strength to first form the FRC plasmoid, and then to maintain the FRC plasmoid in a quasi-equilibrium during the remainder of the process. The desired final goal with dynamic formation is the insertion of a well formed plasmoid at high velocity, density and temperature into the compression chamber where it is merged with an identical plasmoid moving in the opposite direction. Once merged the dynamic formation phase of the FRC plasmoid ends and the final compression phase begins. The ability to operate with a coil system that can perform the proper dynamic formation is critical in obtaining this goal. The proper sequencing is illustrated in FIGS. 3 thru 7. After the FRC plasmoid 20 is formed and injected into the acceleration/compression sections 36 (see FIG. 5), the FRC plasmoid 20 is further accelerated by sequentially energizing the accelerator coils 22, producing a magnetic field of increasing strength as the radius is reduced. The FRC plasmoid 20 is compressed into an ever increasing magnetic field until it reaches its terminal velocity (see FIG. 6). At this point the FRC plasmoid penetrates the high magnetic field 70 generated by the interaction chamber coils 30 and 32 due to the large axial momentum attained through the acceleration and compression process prior to this point. This manner of FRC plasmoid compression is referred to as self compression as it occurs without application of any external forces, for example, the energizing of any external coils. The compression into the higher magnetic field region is manifested by a momentum reduction of the FRC plasmoid. The FRC plasmoid 20 as shown in FIG. 6 preferably still has a significant axial velocity after it enters the interaction chamber 10 to overcome the axial magnetic forces of the interaction chamber field that tend to eject the FRC plasmoid until it is fully within the chamber coils 30 and 32. This remnant velocity is rapidly converted into ion thermal energy on collision with the oppositely directed FRC plasmoid 20 (see FIG. 7). The collision and stagnation of the two FRC plasmoids is all that is needed to provide for this energy conversion. The merging of the two FRC plasmoids into a resultant FRC plasmoid as depicted in FIG. 7 is not critical, but is believed to occur in all the experiments that were performed on the PED. The rapid increase in FRC plasmoid thermal energy from this conversion is accompanied by a rapid increase in FRC plasmoid length. This expansion can be redirected into a radial expansion by employing a separate magnetic coil 32 to create a magnetic field at the end of the main interaction chamber coils 30 that is at least as large as the field external to the FRC plasmoid at the midplane. A larger-radius FRC plasmoid confined by a mirror field is preferable, as the confinement is observed to be several times better than the scaling predicted by equation (1) above. To demonstrate the conceived embodiment, a prototype experimental device 80 was constructed, shown schematically in FIG. 8. The PED 80 is similar in design to the embodiment of the FRC fusion reactor 5 illustrated in FIG. 1, differing primarily in that the accelerator coils 22 and chamber wall 16 are reduced in radius in a stepwise fashion rather than as a continuous taper. The manner of reduction is not critical, but is preferably made as gradual as possible to avoid inducing plasma turbulence as the FRC plasmoid is accelerated and compressed. In the embodiment the device described in FIG. 8 two oppositely directed FRC plasmoids each having a mass of 0.1-0.2 mg at velocities ranging from 200 to 300 km/s are merged. It is constructed in manner such that the resultant plasmoid may be compressed by an axial magnetic field to thermonuclear temperatures. The device is 3 meters in length and consists of two, 1 meter long FRC plasmoid formation, acceleration, pre-compression regions, referred to as Dynamic Formation Sections (DFS), which are positioned axially at each end and a one meter central compression section. The vacuum boundary for the device consists of two 28 cm diameter clear quartz cylindrical tube sections, roughly 50 cm in length that are mated to each end of a smaller 20 cm diameter, 2 meter long quartz cylinder that also serves as the vacuum boundary inside the compression section. This smaller cylinder extends equally out each end of the compression section roughly 50 cm to form part of the DFS vacuum boundary. Vacuum forces are supported through the two 6-way crosses at each end of the device. These crosses also contain a turbomolecular vacuum pump, vacuum measurement devices, and observation windows for fast framing cameras and other spectroscopic equipment. The central compression section consists of four identical 3-turn magnets that are energized by capacitor energy storage modules with sufficient energy to produce a central compression magnetic field of 1.2 T. The two outer coils and two inner coils of the compression bank are each powered by ten and five 14.6 μF capacitors respectively, and all are charged to a voltage of 15 kV. The end coils, having significantly more energy, form a mirror magnetic field axially with a mirror ratio of roughly 1.25. The rise time of the central compression bank magnetic field is roughly 18 μs. The compression field coils are energized one to two microseconds prior to the arrival of the two FRC plasmoids. After the peak field is reached, the magnetic field is sustained by activating a “crowbar” switch that routed the magnet current so as to circulate the current only through the compression coil. The use of the crowbar on this device allows for more detailed measurements of the plasma confinement as well as fusion neutron production. For energy recovery this current would normally be allowed to flow back into the capacitor to recover both the magnetic and plasma energy not lost during compression. The second method for preionization is the application of an azimuthal array of coaxial plasma discharge sources located radially at the periphery of the quartz wall, and axially at the upstream end of each DFS as shown in FIG. 8. Deuterium gas is introduced via an array of matched fast puff valves mounted to the breach end of the coaxial plasma sources. The timing of the gas puff is made to provide for breakdown and ionization of the neutral gas during the rise of the reverse bias field with negligible neutral gas inside either DFS or compression chamber. Each plasma source is inductively isolated from the others, and each array is energized with a common 54 μF capacitor charged up to 7 kV, which results in a discharge current of up to 10 kA through each plasma source for a duration of 20 to 30 μs. The array of plasma discharges ionize essentially all of the neutral gas introduced to form the FRC plasmoids. The magnitude and flow speed of the ionized deuterium out of the plasma sources is adjusted to provide the desired plasma density under the formation coils at the desired time for initiating the FRC plasmoid formation sequence. Both dynamic formation sections consist of an end bias coil, and eight independently triggered formation/acceleration/pre-compression coils with a spacing of 10 cm. The employment of these coils in a sequential manner, with the appropriate magnetic field coil rise time and timing comprise what is referred to as dynamic formation (to be described in detail below). Typically the first four coils are initialized with a reverse bias field of 0.06 to 0.08 T. A forward bias is applied to the end bias coils, the remaining dynamic formation coils, as well as the four coils of the compression section. In this way two magnetic cusp fields are introduced axially within the dynamic formation section. The plasmoid separatrix is thus established inside the vacuum prior to field reversal. Each formation and acceleration coil is constructed of a band of copper wrapped around the quartz tube and insulated with shrink tubing and polyethylene sheet. Each single turn coil is 7.5 cm wide and spaced at 10 cm intervals along the axial length of each DFS. Each coil is connected to the energy storage capacitors and switches with sixteen parallel runs of high voltage coaxial cable. This results in a power delivery system that is well coupled with minimal stray inductance. These coils are energized sequentially (magnetic field rise time 1.6 μs) over an interval roughly 5 μs for forming, accelerating and compressing the FRC plasmoid. The magnetic field swing produced in each coil is 0.8 T at a charging voltage of 30 kV. The coil to coal coupling is found to be 25% in vacuum and less with a plasmoid present. For optimal dynamic formation a typical timing delay from coil to coil is 0.4 μs for the formation coils, and somewhat less for the acceleration coils. Each coil is independently energized, initiated by a single, high voltage, high current thyratron switch. The thyratron is of a special manufacture often referred to as a pseudo-spark switch. The switch can be reliably operated at DC holding voltages 35 kV, delivering a maximum current of 100 kA with a jitter of 30 ns or less, which more than meets the timing and power transfer requirements for proper sequencing of the coils during the discharge. Precise control of the apparatus is accomplished by using computer controlled timing and data acquisition equipment. Initial design parameters (physical dimensions, plasma parameters, applied magnetic field, timing sequence, etc.) are determined by employing a two dimensional (r and z in cylindrical coordinates), resistive, magnetohydrodynamic (MUD) computer code. The MHD code is initialized with the appropriate initial experimental conditions: device radius, length and coil spacing, plasma density, temperature, and spatial distribution. Calculations are performed where coil voltages, magnetic waveforms, and in particular, the timing of all coils are varied in order to arrive at the optimum dynamic formation sequence. Based on these numerical calculations, hardware (including but not limited to: capacitors, coils, high current switches, and fast gas puff valves are specified, designed and/or purchased to provide for operation of the apparatus in a manner similar to that employed in the MHD code calculations. The electrical circuit design is based on obtaining the desired current waveforms. This effort was aided with circuit design software such as SPICE, which is used to model the coupling and performance of the various high-voltage coils used to generate the magnetic fields. After the individual hardware components are built, they are tested and modified until the hardware performance closely matches the required design parameters. FIG. 10 shows a charge control subsystem 100, according to one illustrated embodiment. The charge control subsystem 100 includes a charge control unit 102, voltage monitor 104, charge supply 106 and charge storage such as one or more capacitors 108. The capacitor(s) 108 may, for example, take the form of one or more super- or ultra-capacitors. Control of capacitor voltage VC across the capacitor 108 is accomplished by the application of a charge control unit 102. The charge control unit is responsive to the voltage monitor 104 which monitors the voltage VC across the capacitor 108. The charge control unit 102 compares that voltage VC to a voltage set-point or threshold, for example, using solid state logic, and sends appropriate signal(s) to the charging power supply 106 to continue or discontinue charging the capacitor 108. FIG. 11 shows a control subsystem 120, according to one illustrated embodiment. The control subsystem 120 may include timing hardware 122, switch hardware 124 and one or more capacitors 126. The timing hardware 122 may generate a trigger signal Which can then be sent to the switch hardware 124 to initiate discharge of the capacitor 126. The trigger signal may be generated by conventional timing hardware, such as provided by National Instruments using PXI timing cards such as the National Instruments 6602 in a PXI chassis, such as the PXI-1045, or Jorway 221A Timing Module powered by a CAMAC crate. Both were deployed in IPA. Timing resolution is limited by the frequency of the timing clock. In the case of the Jorway 221A, the timing clock runs at 10 MHz resulting in a timing resolution of 0.1 microseconds. The timing hardware 122 may be computer controlled using National instruments Labview application program executing on a processor based computer system 128 such as personal computer (PC) or any other processor based device. In the software instructions stored on one or more computer-readable media 130 (e.g., optical disk, magnetic disk, RAM, ROM) and executed by one or more processors. The desired timing sequence may be programmed in a manner that will enable the timing hardware 122 to approximately replicate the timing of the transient magnetic fields that were used in the MHD code design. The software outputs commands 121 to control the timing cards, such as the Jorway 221A or a National Instruments 6602 which output a TTL level signal or similar bipolar logic signal. This logic signal can be used to directly trigger the switch hardware 124 on the appropriate capacitor. Alternatively, as is more usual, the logic signal may be used to trigger a light emitting diode (LED) which is then coupled to the switch hardware 124 through an optical fiber and a photodiode (PD) receiver, in this manner, many individual trigger signals may be sent to every switch on the apparatus, and can be controlled with 0.1 microsecond precision (or better if a faster timing clock is used). The trigger signals also control the timing of fast puff valves 132, arc discharge timing on the plasma source, as well as initiation of high speed camera 134 photography and data acquisition electronics 136. Confirmation that the processes described above are obtained in the experiments is found in a detailed comparison between experimental data and the numerical MHD code results. An array of external lux and axial magnetic field probes are installed under each coil set (28, 18, 22, 32, and 30 from FIG. 1). From this array the excluded flux due to the presence of the FRC plasmoid is obtained, and the FRC plasmoid velocity, radius, length, and energy is determined. The same dynamic behavior of the FRC plasmoid formation, acceleration and velocity observed in the experiments is reproduced in the numerical calculations producing results similar to those shown in FIGS. 2 through 7. A Helium-Neon laser based interferometer measured the cross tube line density at the axial mid-plane, i.e., center of the interaction chamber coil 30, From this diagnostic and the magnetic measurements, the plasma density and pressure balance temperature is obtained. Deuterium plasmas are employed and calibrated neutron detectors are positioned radially outside the magnets at the chamber center to measure the D-D fusion neutron flux. The merging and conversion of the supersonic FRC plasmoid (as determined from the ratio of the plasmoid motional energy to thermal energy), is observed to take place on the Alfvenic timescale. The two FRC plasmoids do not rebound and separate. Instead they merge sufficiently to form a plasmoid that functionally behaves as a single entity as indicated by the peak excluded flux appearing and remaining at the axial mid-plane. The basic equilibrium parameters observed during compression indicate a well-confined plasmoid with up to three times the confinement predicted by in-situ scaling (Equation (1)), proving evidence that adequate confinement for fusion can be obtained by this method. Total temperature is calculated based on radial pressure balance. During compression, evidence indicates that this results in total temperatures of 10 million ° K. or more. The overwhelmingly larger ion mass compared to the electron dictates that the ions receive virtually all of the FRC plasmoid kinetic energy upon merging. A strong neutron signal is detected during magnetic compression from two shielded, scintillator-based neutron detectors. When corrected for FRC geometry, attenuation and scattering in intervening material, a much higher ion temperature (Ti ˜20 million ° K.) was inferred compared with magnetic compression from radial pressure balance with external axial magnetic field. The anomalously large signal is well beyond what can be attributed to measurement error of the plasma density and volume. The high temperature is most likely the result of a non-thermal ion population, but the mechanism for maintaining this over the FRC plasmoid lifetime is not known. The magneto-kinetic acceleration, translation and compression of the FRC plasmoid provide a unique path to achieve the necessary high efficiency and simplicity. The singular ability of the FRC plasmoid to be translated over distances of several meters allows for the FRC formation and kinetic energy input for fusion burn to be accomplished outside of the interaction chamber 10 and breeding blanket 12 (see FIG. 5). In one embodiment, the divertor 14 may be removed from the FRC fusion reactor 5, eliminating the critical power loading issues faced in other fusion embodiments such as the tokamak. Tritium flow is expected to be significantly improved in the embodiment of the fusion reactor 5 as shown in FIG. 1. The entire high field reactor vacuum flux 70 is external to FRC plasmoid flux 72 and is thus effectively diverted flux (see FIGS. 6 and 7), in a transient burn, the particle loss from the plasmoid is overwhelmingly directed to the divertor region in the divertors 14 as the axial flow time is many orders of magnitude smaller than the perpendicular particle diffusion time in the open flux region. By virtue of the cyclic nature of the burn, virtually all of the tritium can be introduced during the initial formation of the FRC plasmoids with no need for refueling. All tritium introduced can be conveniently recovered in the divertors 14 with each pulse. The ability to access the divertors 14 remotely in an essentially neutron free environment makes prospects for near unity tritium recovery much more feasible. The ability of the FRC plasmoids 20 to be translated over distances of several meters allows for the FRC plasmoid formation and addition of kinetic energy for heating to be realized outside of the interaction chamber 10 and breeding blanket 12. The high energy density state is obtained through both compression and the rapid conversion of the FRC plasmoid axial kinetic energy. Compression occurs during acceleration by increasing the magnetic field 52 (see FIG. 5), and reducing the radius of accelerator coils 22, Compression also occurs through self compression converting FRC plasmoid axial motion as the FRC plasmoids are injected into a convergent magnetic field 24 (see FIG. 2), and finally by magnetic compression from the interaction chamber axial magnetic field 72 (see FIG. 7). Employing magnetic fields in this way provides for a means to achieve high electrical efficiency in heating and compression the plasmoid. By having the compression be reversible, it is also the key to directly recovering the magnetic and plasmoid energy that was used to create the fusion condition initially. Most importantly, this energy recovery occurs in a manner that restores the energy back into the same form that it was initially, i.e, it is electrical in nature and does not suffer from the unavoidable energy losses associated with thermal conversion. Devices that can operate in this way are referred to as direct energy converters. The energy recovery is a natural consequence of operating the magnets in an oscillatory mode. Energy introduced in compressing and heating the plasmoid is recovered back into the energy storage system (e.g. capacitors). Once the energy has been returned, the circuit is opened to prevent the energy from flowing back into the coils at an inappropriate time. Although there are other electronic means that could be used to achieve this, the current interruption is most readily accomplished in a low loss manner by the inclusion of a high power diode array in the circuit. This cyclic process could ideally be done in a manner that entailed no losses, with the result being no net energy consumed in creating the fusion energy. The energy gain of such a system would be essentially infinite. In reality there are always some Ohmic losses in the circuits as well as plasma loss during the process. The energy loss from the plasmoid can be more than compensated for by the production of high energy fusion alpha particles within the plasmoid. The push back on the magnetic circuit from this additional component of pressure produced by the alpha particles energizes the circuit by doing work on the magnetic compression fields. The fusion alpha energy can be directly converted into stored electrical energy in this way. The plasma loss during the fusion burn can also be extracted in the divertor regions at each end of the device. This can be accomplished by having this directed stream of plasma do work on a magnetic field introduced into this region for this purpose. TO make a significant impact on world energy needs, the energy yield must be substantially increased from the scale of the proof-of-principle experiments conducted using the embodiments described above. In another embodiment of the PED, the scale increases by roughly a factor of three, increasing the plasma temperature by roughly a factor of four. In this embodiment, the plasma temperature required for optimum operation as a fusion reactor is approximately 80 million ° K. A significant advantage of this method is that due to its simplicity and the ease with which it can be scaled. The method also reduces the time and cost to develop specific embodiments. By one development path, the final device is approached incrementally by scaling up previously built devices. Due to the unique geometry and simplicity of the concept, there are immediate applications for the device even at the level of development attained in the prototype. The fusion reaction creates a copious supply of high energy neutrons, and the unique device geometry makes these neutrons very available for conversion in the blanket 94 surrounding the device (see FIG. 9). As previously discussed, in one embodiment these neutrons are used for the production of more fuel (tritium) for continued operation of the reactor as well as the startup of new, future reactors, Due to the high conversion efficiency of the reactor configuration, surplus neutrons absorbed in the blanket with the generation of heat can be converted to electricity through a conventional steam cycle or other heat engines. However, these energetic neutrons have potentially more valuable uses than heat generation. These neutrons can be employed in a transformational manner, for example to produce rare isotopes or initiate the process of the conversion of one element into another. These roles for the fusion neutrons, particularly for applications that enable alternate forms of energy generation, are the focus of an alternative embodiment of the prototype. In fact, in one embodiment the prototype device meets the requirements of an efficient and high fluence neutron source demanded for alternate methods of energy generation. With the device prototype employed for its neutron production capabilities, the energy yield is determined by the energy that can be released from the by-products created by the fusion neutrons, rather than from fusion energy alone. In this manner the prototype performs as an energy amplifier; the fusion energy gain is no longer critical because the fuel the prototype creates has the potential for creating far more energy. In this embodiment, the device need not be developed beyond the near breakeven conditions sought in the prototype to have a major impact on energy generation. A compact neutron source in the form of the devices described herein, as one application, may facilitate the transitioning of the current nuclear industry away from fission of uranium to a different cleaner and safer fuel. The alternate fuel cycle may be based on thorium. With a thorium-based nuclear fuel, fission-based nuclear power delivers what the current uranium fission-based reactor cannot: abundant, safe, and clean energy with no long-lived high-level radioactive waste, and essentially no chance for proliferation. These benefits are achievable with little or no modification to existing reactors. Thus, embodiments of a ground-breaking method and means for heating and compressing plasmas to thermonuclear temperatures and densities have been disclosed. The implementation according to the various embodiments disclosed herein provides several advantages over other known plasma implementations. For instance, the disclosed embodiments provide methods for forming and heating plasma to thermonuclear conditions and for efficiently forming and repetitively heating and compressing the FRC plasmoid. Moreover, it is believed that an apparatus according to the various embodiments will permit the construction of power generating thermonuclear reactors that are significantly smaller and less expensive than currently planned devices according to other known plasma implementations. The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Although specific embodiments and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. The teachings provided herein of the various embodiments can be applied to other context, not necessarily the disclosed context of fusion generally described above. It will be understood by those skilled in the art that, although the embodiments described above and shown in the figures are generally directed to the context of fusion, applications related to a thorium fuel generator or a waste burner, for example, may also benefit from the concepts described herein. While many aspects of the methods and apparatus are set out in the summary and the claims as discrete sub-acts or subcomponents (e.g., dependent claims), one of skill in the art will appreciate that any one or more of these sub-acts or sub-components (e.g., limitations of the dependent claims) may be combined with the overall method or components (e.g., limitations of the independent claims), and that the remaining sub-acts or subcomponents (e.g., limitations of remaining dependent claims) may include those other sub-acts or components. Thus, any of the limitations of the dependent claims may be incorporated into the respective independent claim, and the remaining dependent claims that depend from that amended independent claim would include such limitations. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. |
|
abstract | A jet pump for a nuclear reactor includes a riser and an inlet mixer having a set of nozzles and a mixing section for receiving coolant flow from the nozzles and suction flow from an annular space between the reactor vessel and the shroud core. To minimize or eliminate electrostatic deposition of charged particulates carried by the coolant on interior wall surface of the inlet-mixer of the jet pump, and also to inhibit stress corrosion cracking, the interior wall surfaces of the nozzles and mixing section are coated with a ceramic oxide such as TiO2 and Ta2O5 to thicknesses of about 0.5-1.5 microns. |
|
abstract | An ion beam current uniformity monitor, ion implanter and related method are disclosed. In one embodiment, the ion beam current uniformity monitor includes an ion beam current measurer including a plurality of measuring devices for measuring a current of an ion beam at a plurality of locations; and a controller for maintaining ion beam current uniformity based on the ion beam current measurements by the ion beam current measurer. |
|
claims | 1. A system for separating and coupling a nuclear fuel assembly having guide thimbles from/to a top nozzle including a flow channel plate for flow of coolant having guide holes, the system comprises:a lock insert comprising a body in a hollow shape coupled with the guide thimble; and an insertion part provided on a top portion of the body and configured to be inserted into the guide hole, the circumference of the insertion part being variable in size, thereby being capable of being inserted into the guide hole, to support the nuclear fuel assembly to the top nozzle by being coupled to the guide hole provided in a flow channel plate of the top nozzle; anda separation member configured to separate the lock insert from the guide hole,wherein,the insertion part comprises:a first latching member having a step with which a top surface of the flow channel plate is brought into contact; anda second latching member having a step with which a bottom surface of the flow channel plate is brought into contact,wherein the first latching member comprises a latching groove, and the top surface of the flow channel plate is provided a protruding member protruded from the top surface, the protruding member being of the same shape as the latching groove to be inserted into the latching groove, andthe separation part is configured to provide a space accommodating an outer circumferential surface of the first latching member protrudingly provided on the top surface of the flow channel plate, to apply external force to the outer circumferential surface of the first latching member while accommodating the outer circumferential surface of the first latching member, thereby the size of the circumference of the insertion part being varied to release the coupling between the lock insert and the flow channel plate. 2. The system of claim 1, wherein the insertion part is provided with at least one predetermined slot along a longitudinal direction of the insertion part, thereby the circumference of the insertion part is variable in size. |
|
description | 1. Field of the Invention This invention pertains generally to a nuclear reactor fuel assembly and more particularly to a nuclear fuel assembly that employs a spacer grid that applies pressure to the cladding of the fuel rods after the fuel rods are loaded in the fuel assembly. 2. Description of the Prior Art The primary side of nuclear reactor power generating systems which are cooled with water under pressure comprises a closed circuit which is isolated and in heat exchange relationship with a secondary side for the production of useful energy. The primary side comprises the reactor vessel enclosing a core internal structure that supports a plurality of fuel assemblies containing fissile material, the primary circuit within heat exchange steam generators, the inner volume of a pressurizer, pumps and pipes for circulating pressurized water; the pipes connecting each of the steam generators and pumps to the reactor vessel independently. Each of the parts of the primary side comprising a steam generator, a pump and a system of pipes which are connected to the vessel form a loop of the primary side. For the purpose of illustration, FIG. 1 shows a simplified nuclear reactor primary system, including a generally cylindrical reactor pressure vessel 10 having a closure head 12 enclosing a nuclear core 14. A liquid reactor coolant, such as water is pumped into the vessel 10 by pump 16 through the core 14 where heat energy is absorbed and is discharged to a heat exchanger 18, typically referred to as a steam generator in which heat is transferred to a utilization circuit (not shown), such as a steam driven turbine generator. The reactor coolant is then returned to the pump 16, completing the primary loop. Typically, a plurality of the above described loops are connected to a single reactor vessel 10 by reactor coolant piping 20. An exemplary reactor design is shown in more detail in FIG. 2. In addition to the core 14 comprised of a plurality of parallel, vertical, co-extending fuel assemblies 22, for purposes of this description, the other vessel internal structures can be divided into the lower internals 24 and the upper internals 26. In conventional designs, the lower internals function is to support, align and guide core components and instrumentation as well as direct flow within the vessel. The upper internals restrain or provide a secondary restraint for the fuel assemblies 22 (only two of which are shown for simplicity in this figure), and support and guide instrumentation and components, such as control rods 28. In the exemplary reactor shown in FIG. 2, coolant enters the reactor vessel 10 through one or more inlet nozzles 30, flows down through an annulus between the vessel and the core barrel 32, is turned 180° in a lower plenum 34, passes upwardly through a lower support plate 37 and a lower core plate 36 upon which the fuel assemblies 22 are seated and through and about the assemblies. In some designs, the lower support plate 37 and the lower core plate 36 are replaced by a single structure, the lower core support plate, at the same elevation as 37. The coolant flow through the core and surrounding area 38 is typically large on the order of 400,000 gallons per minute at a velocity of approximately 20 feet per second. The resulting pressure drop and frictional forces tend to cause the fuel assemblies to rise, which movement is restrained by the upper internals, including a circular upper core plate 40. Coolant exiting the core 14 flows along the underside of the upper core plate 40 and upwardly through a plurality of perforations 42. The coolant then flows upwardly and radially to one or more outlet nozzles 44. The upper internals 26 can be supported from the vessel or the vessel head and include an upper support assembly 46. Loads are transmitted between the upper support assembly 46 and the upper core plate 40, primarily by a plurality of support columns 48. A support column is aligned above a selected fuel assembly 22 and perforations 42 in the upper core plate 40. The rectilinearly moveable control rods 28 typically include a drive shaft 50 and a spider assembly 52 of neutron poison rods that are guided through the upper internals 26 and into aligned fuel assemblies 22 by control rod guide tubes 54. The guide tubes are fixedly joined to the upper support assembly 46 and connected by a split pin 56 force fit into the top of the upper core plate 40. The pin configuration provides for ease of guide tube assembly and replacement if ever necessary and assures that the core loads, particularly under seismic or other high loading accident conditions are taken primarily by the support columns 48 and not the guide tubes 54. This support column arrangement assists in retarding guide tube deformation under accident conditions which could detrimentally affect control rod insertion capability. FIG. 3 is an elevational view, represented in vertically shortened form, of a fuel assembly being generally designated by reference character 22. The fuel assembly 22 is the type used in a pressurized water reactor and has a structural skeleton which, at its lower end includes a bottom nozzle 58. The bottom nozzle 58 supports the fuel assembly 22 on a lower core support plate 60 in the core region of the nuclear reactor (the lower core support plate 60 is represented by reference character 36 in FIG. 2). In addition to the bottom nozzle 58, the structural skeleton of the fuel assembly 22 also includes a top nozzle 62 at its upper end and a number of guide tubes or thimbles 54, which extend longitudinally between the bottom and top nozzles 58 and 62 and at opposite ends are rigidly attached thereto. The fuel assembly 22 further includes a plurality of transverse grids 64 axially spaced along and mounted to the guide thimbles 54 (also referred to as guide tubes) and an organized array of elongated fuel rods 66 transversely spaced and supported by the grids 64. Although it cannot be seen in FIG. 3 the grids 64 are conventionally formed from orthogonal straps that are interleafed in an egg crate pattern with the adjacent interface of four straps defining approximately square support cells through which the fuel rods 66 are supported in transversely spaced relationship with each other. In many conventional designs springs and dimples are stamped into the opposing walls of the straps that form the support cells. The springs and dimples extend radially into the support cells and capture the fuel rods therebetween; exerting pressure on the fuel rod cladding to hold the rods in position. Also, the assembly 22 has an instrumentation tube 68 located in the center thereof that extends between and is mounted to the bottom and top nozzles 58 and 62. With such an arrangement of parts, fuel assembly 22 forms an integral unit capable of being conveniently handled without damaging the assembly of parts. As mentioned above, the fuel rods 66 in the array thereof in the assembly 22 are held in spaced relationship with one another by the grids 64 spaced along the fuel assembly length. Each fuel rod 66 includes a plurality of nuclear fuel pellets 70 and is closed at its opposite ends by upper and lower end plugs 72 and 74. The pellets 70 are maintained in a stack by a plenum spring 76 disposed between the upper end plug 72 and the top of the pellet stack. The fuel pellets 70, composed of fissile material, are responsible for creating the reactive power of the reactor. The cladding which surrounds the pellets functions as a barrier to prevent the fission by-products from entering the coolant and further contaminating the reactor system. To control the fission process, a number of control rods 78 are reciprocally moveable in the guide thimbles 54 located at predetermined positions in the fuel assembly 22. Specifically, a rod cluster control mechanism 80 positioned above the top nozzle 62 supports the control rods 78. The control mechanism has an internally threaded cylindrical hub member 82 with a plurality of radially extending flukes or arms 52. Each arm 52 is interconnected to the control rods 78 such that the control rod mechanism 80 is operable to move the control rods vertically in the guide thimbles 54 to thereby control the fission process in the fuel assembly 22, under the motive power of control rod drive shafts 50 which are coupled to the control rod hubs 82, all in a well-known manner. As previously mentioned, the fuel assemblies are subject to hydraulic forces that exceed the weight of the fuel rods and thereby exert significant forces on the fuel rods and the fuel assemblies. In addition, there is significant turbulence in the coolant in the core caused by mixing vanes on the upper surfaces of the straps of many grids, which promote the transfer of heat from the fuel rod cladding to the coolant. The substantial flow forces and turbulence can result in severe fretting of the fuel rod cladding if motion of the fuel rods is not restrained. Fretting of the fuel rod cladding can lead to a breach and expose the coolant to the radioactive byproducts within the fuel rods. Furthermore, when the fuel rods are first loaded within the fuel assemblies and are inserted through the support cells and by the springs and dimples the surface of the cladding can become marred which can promote corrosion which can also lead to fuel cladding failure. Thus, an improved means of supporting the fuel rods within a fuel assembly grid is desired that will better restrain the rods without scarring the cladding during fuel assembly manufacturer. This invention achieves the foregoing objectives by providing an improved nuclear fuel assembly for supporting a parallel array of a plurality of elongated nuclear fuel rods between a lower nozzle and an upper nozzle having an axial length along the elongated dimension of the nuclear fuel rods. A plurality of spaced, improved support grids are arranged in tandem along the axial length of the fuel rods between the upper nozzle and the lower nozzle, at least partially enclosing an axial portion of the circumference of each fuel rod within a support cell of the support grids to maintain the lateral spacing between fuel rods. The improved support grid is made up essentially of an egg-crate base grid having a plurality of orthogonal intersecting straps that define the support cells at the intersection of each of the four adjacent straps that surround the nuclear fuel rods. A length of each strap between the intersections of the four adjacent straps forms a wall of the corresponding support cell. A lock-support sleeve fits within at least one of the support cells and preferably all of the support cells that support fuel rods and is adapted to have a first orientation that loosely receives a corresponding nuclear fuel rod therethrough and a second orientation that places a transverse pressure on the fuel rod to restrain the fuel rod axially and radially; the lock-support sleeve being rotatable between the first orientation and the second orientation. In one embodiment, at least one wall of the base grid cooperates with a wall on the lock sleeve to restrain rotation of the lock-support sleeve when the lock-support sleeve is rotated to the second orientation. The means for restraining rotation of the lock-support sleeve may be one of a male or female lock member on at least one wall of the support cell and another of the male or female lock member on at least one wall of the lock-support sleeve. The male and female member may respectively be a protrusion and a hole, wherein the protrusion is sized to fit within the hole when aligned. Preferably, the means for restraining rotation of the lock-support sleeve when the lock-support sleeve is rotated in the second orientation also restrains the axial movement of the lock-support sleeve relative to the support cell when the lock-support sleeve is in the second orientation. Desirably, the means for restraining the axial movement of the lock-support sleeve relative to the support cell does not restrain thermal growth or growth as a result of irradiation, in the axial direction. In one embodiment, the lock-support sleeve is a quasi four-sided sleeve having generally rounded corners that are bulged out radially with walls of the lock-support sleeve extending between the bulged out corners. The circumferential contour of the lock-support sleeve is so configured that when the lock-support sleeve is rotated from the first orientation where the corners are substantially aligned with the intersection between straps, to the second orientation wherein the corners are substantially aligned with a mid-section in the walls of the support cell between the intersections between the adjacent straps, at least two walls of the lock-support sleeve move radially inward to place a lateral force on the corresponding fuel rod and restrain the fuel rod axially. Preferably when the lock-support sleeve is rotated to the second orientation all four walls of the lock-support sleeve bend radially inward to place a lateral force on the corresponding fuel rod and restrain the fuel rod axially. Desirably, when at least one wall of the lock-support sleeve bends radially inward it makes contact with the fuel rod over the entire height of the lock-support sleeve. In still another embodiment the height of a wall of the support cells that support fuel rods is longer in the axial direction than the corresponding height of a wall of the lock-support sleeve. Preferably, the additional height of the support cells accommodates a removable stop that is appended to a lower portion of at least one wall of the lock-support sleeve outside of the path of the fuel rod that extends through the lock-support sleeve. The removable stop supports the lock-support sleeve in the axial direction when the lock-support sleeve is in the first orientation. Preferably the removable stop is a positioning bar that passes through and is supported by openings in the lower portion of two walls of the lock-support sleeve; desirably, two opposing walls of the lock-support sleeve. In one preferred embodiment the removable stop comprises at least two positioning bars, one on either side of the fuel rod path. This invention further includes a method of loading a fuel rod into an elongated nuclear fuel assembly skeleton having an axial direction along the longitudinal dimension of the fuel assembly. The fuel assembly skeleton includes a bottom nozzle, a plurality of transversely spaced thimble tubes attached at one end to the bottom nozzle and extending up axially towards a top nozzle that will be attached at the other end of the thimble tubes once an array of fuel rods are inserted into the fuel assembly skeleton. A plurality of spaced support grids are arranged in tandem along the axial length of the thimble tubes and attached to at least some of the thimble tubes. The support grids are designed to at least partially enclose an axial portion of the circumference of each fuel rod within a support cell of the support grids to maintain lateral spacing between fuel rods. At least one of the support grids is made up, at least in part, of an egg-crate base grid having a plurality of orthogonal intersecting straps that define the support cells at the intersection of each four adjacent straps that surround the nuclear fuel rods. A length of each strap between the intersections of the four adjacent straps forms a wall of the corresponding support cell. A lock-support sleeve fits within at least some of the support cells and is configured to loosely receive a corresponding nuclear fuel rod therethrough in a first orientation and in a second orientation place transverse pressure on the fuel rod to load and restrain the fuel rod axially; the lock-support sleeve being rotatable between the first orientation and the second orientation. Generally the method of this invention includes the steps of: maintaining all of the lock-support sleeves that are in axial alignment, in the first orientation; completely inserting a fuel rod into the fuel assembly through each of the lock-support sleeves in the axially transverse position in the fuel assembly skeleton in which the fuel rod is inserted; and loading the fuel rod to place a transverse pressure on the fuel rod after the fuel rod is completely inserted into the fuel assembly skeleton by moving the lock-support sleeves surrounding the fuel rod to the second orientation. Preferably, the loading step includes the step of rotating the lock-support sleeve 45° around the support cell. In one embodiment the lock-support sleeve is a quasi four-sided sleeve having generally rounded corners that are bulged out radially. In such case the rotating step includes the steps of capturing at least two adjacent corners of the lock-support sleeve with a tool having fingers which extend within the corresponding bulges and a leverage arm and rotating the leverage arm to rotate the lock-support sleeve within the support cell. Desirably, the rotating step also includes accessing the lock-support sleeve with the tool from an underside of the support grid. In another embodiment, the method of this invention includes the step of locking the lock-support sleeve in the second orientation. Desirably, prior to the step of completely inserting the fuel rod, the method further includes the steps of inserting a removable positioning bar in a lower portion of the support cell out of the path the fuel rod will occupy when inserted and inserting the lock-support sleeve into the support cell in the first orientation. In this last embodiment the method of this invention further includes the step of removing the positioning bar from the support cell after the lock-support sleeve is moved to the second orientation; preferably after it is locked in that position. This invention provides a new fuel assembly for a nuclear reactor and more particularly an improved spacer grid design for a nuclear fuel assembly. The improved grid is generally formed from an egg-crate base support grid, illustrated in FIG. 4, formed from two orthogonally positioned sets of parallel spaced straps 84 and 86 that are interleafed in a conventional manner and surrounded by an outer strap 88 to form the base support grid 90. The orthogonal straps 84 and 86, and in the case of the outer rows, the outer strap 88 define the support cells 94 at the intersection of each four adjacent straps that surround the nuclear fuel rods. With a length of each strap, along the straps elongated dimension, between the intersections of the four adjacent straps, forming a wall 96 of the support cells 94. Preferably, each base grid support cell 94 that supports a fuel rod has a fuel rod lock-support sleeve the preferred embodiment of which is illustrated in FIG. 5 and represented by reference character 92. Basically, the lock-support sleeve 92 is adapted to fit within at least some of the support cells 94 that support fuel rods and in a first orientation of the sleeve 92 within the support cell 94 the sleeve 92 loosely receives the nuclear fuel rod therethrough. In this orientation the support sleeve has a small clearance with the fuel rod so that the fuel rod may be loaded therethrough without scratches, gall balls or any other damage that is normally encountered when the fuel rods are loaded into conventional spring grids. After a fuel rod is completely inserted through each of its grids and finally positioned within the fuel assembly skeleton the lock-support sleeve 92 may be rotated within the support cells 94 to a second orientation that pressures at least one side wall 98 radially inward to bear a lateral force against the fuel rod and prevent the fuel rod from moving both axially and radially. The sleeves 92 will not be welded to the base grid 90 thus permitting the sleeves 92 to be manufactured from different materials or alloys that can exhibit different axial thermal growth and growth due to irradiation. In the preferred embodiment the lock-support sleeve is a quasi four-sided sleeve having generally rounded corners 100 that are bulged out radially with the side walls 98 of the lock-support sleeves 92 extending between the bulged out corners 100. As shown, the lock-support sleeve 92 is configured so that when the lock-support sleeve is rotated from a first orientation where the corners 100 are substantially aligned with the intersection between straps 84 and 86, to a second orientation wherein the corners 100 are substantially aligned with a mid-section in the walls 96 of the support cells 94 between the intersection between the orthogonal straps 84 and 86, at least two of the walls 98 of the lock-support sleeve 92 bend radially inward to place a lateral force on the corresponding fuel rod and retain the fuel rod in the axial position in which it was loaded. As can be seen from FIG. 5 the lock-support sleeve 92 has protrusions 102 which extend radially outward from the corners 100. The protrusions can be readily observed in FIGS. 5, 6a and 6b. FIG. 6a shows a perspective view of a support cell 94 of the base grid 90 viewed from the top of the cell with a lock-support sleeve 92 centered in the cell 94 and engaged with a tool 106 that is employed by this invention to rotate the lock-support sleeve 92 within the support cell 94. The lock-support sleeve 92 is shown in the first orientation with the bulged corners 100 substantially aligned with the intersection between straps 84 and 86, which provides a loose fitting clearance between the side walls 98 of the lock-support sleeve 92 and the fuel rod which is not shown. FIGS. 6a and 6b show the lock-support sleeve 92 engaged by the tool 106 of this invention used to rotate the lock-support sleeve within the support cell 94. The tool 106 has a leverage arm 108 which is attached to a laterally extending wing 110 that has two fingers 112 which, at their distal end are shaped to engage the bulged portion of the corners 100 from the inside of the bulge. The tool can have a flexible handle to facilitate 45° rotation at some difficult to maneuver locations, e.g., around thimble tubes 54. With the tool 106 engaged in the corners 100 the leverage arm 108 can be employed to rotate the lock-support sleeve 92 within the support cell 94. When the lock-support sleeve 92 is rotated 45° to the second orientation wherein the corners 100 are substantially aligned with a mid-section in the walls 96 of the support cells 94 between the intersection between the adjacent straps 84 and 86, the protrusions 102 engage the openings 104 in the support cell walls 96 to lock the lock-support sleeve from further rotation under normal operating conditions. It should be appreciated though, that the lock-support sleeve 92 can be rotated by the tool 106 to unlock the engagement of the protrusions 102 with the openings 104 should it be necessary to unlock the fuel rods for any reason. Accordingly, the protrusions 102 in the openings 104 lock the support sleeve in position in a second orientation to restrain both the axial movement as well as further rotation while permitting differential axial growth between the lock-support sleeve 92 and the support cell 94. It should also be appreciated that other means of locking the lock-support sleeve 92 to the support cell 94 could be employed to accomplish the same purpose. For example, though not as desirable, the protrusions can be extended in a radial inward direction from the walls 96 of the support cell 94 and corresponding openings can be provided in the corners 100 of the lock-support sleeve 92. FIG. 7a shows a plan view of a lock-support sleeve 94 rotated to the second orientation within the support cell 94 capturing a fuel element 114 against the side walls 98 of the lock-support sleeve 92. The bulged corners 100 have a generally rounded circumference in that they have a central flat section 116 with a slightly angled periphery portion 118 that curves into a radially inward connecting strap 120 that connects to the side wall 98. As the bulged corners are rotated from the first orientation, where they loosely fit within the corners of the support cell 94 (as shown in FIGS. 6a and 6b), to the mid-section of the side wall 96 of the support cell 94, the side walls 96 of the support cells 94 first engage the slightly angled portion 118 of the bulged corners 100, which urges the sides of the lock-support sleeve 98 to move radially inward applying pressure against the cladding of the fuel rod 114. As the lock-support sleeve continues to rotate towards the mid-section of the side wall 96 of the support cell 94 the flat sections of the bulged corners 116 snap into engagement with the side walls 96 and engage the protrusions 102 within the openings 104 to lock the lock-support sleeve 92 in the second orientation. Thus the side walls 98 are brought to bear against the cladding of the fuel rod 114 over the entire length of the side walls 98 securing the fuel rod both axially and radially within the fuel assembly. In the preferred embodiment all four side walls 98 engage the cladding of the fuel rod 114, though it should be appreciated that the concepts of this invention can be employed with two opposing sides 98 of the lock-support sleeve 92 being forced into engagement with the fuel rod 114. When the lock-support sleeve 92 is positioned within the support cell 94 in the first orientation it is loosely seated in the center of the support cell and a support means has to be provided to prevent the lock-support sleeve from dropping out of the support cell 94. FIGS. 8 and 9 show one such arrangement which can be used for this purpose. FIG. 8 shows a perspective view with the support cell 94 turned on its side with the tool 106 supporting the lock-support sleeve 92 in place within the center of the interior of the support cell 94. FIG. 9 shows the arrangement of FIG. 8, providing a perspective from the bottom side of the support cell 94. From FIG. 9 it can be appreciated that in the arrangement shown in FIGS. 8 and 9 the height of the lock-support sleeve 92 in the axial direction is slightly shorter than the height of the corresponding walls of the support cell 94. This permits positioning bars 122 to be inserted through openings 124 in opposing side walls 96 of the support cell 94 at lateral positions in the lower portions of the support cells 94 out of the path of the fuel rods. The positioning bars 122 thus support the lock-support sleeves 92 axially when the lock-support sleeves 92 are in the first orientation. It should be appreciated that other means for supporting the lock-support sleeve 92 within the support cells 94 can be employed. For example, a portion of the side walls 96 at the lower end of the support cell 94 can be bent inward to serve as such a support. However, the positioning bars 122 are preferred because after the lock-support sleeve is rotated to the second orientation and locked into position, by aligning the protrusions 102 with the mating openings 104, the positioning bars 122 are preferrably removed thus reducing the amount of metal that could affect neutron economy and obstructions to coolant flow. The invention also includes a method of loading a fuel rod into an elongated nuclear fuel assembly skeleton having an axial direction along the longitudinal dimension of a fuel assembly, a bottom nozzle, a plurality of transversely spaced thimble tubes attached at one end to the bottom nozzle and extending up axially toward a top nozzle that will be attached at the other end of the thimble tubes once the array of fuel rods are inserted into the fuel assembly skeleton, and a plurality of spaced support grids arranged in tandem along the axial length of the thimble tubes and attached to at least some of the thimble tubes. The support grids are designed to at least partially enclose an axial portion of the circumference of each fuel rod within a support cell of the support grids to maintain a lateral spacing between fuel rods. At least one of the support grids includes an egg-crate base grid having a plurality of orthogonal intersecting straps that define the support cells at the intersection of each four adjacent straps that surround the fuel rods; a length of each strap between the intersections of the four adjacent straps forming a wall of the corresponding support cell. A lock-support sleeve is adapted to fit within preferably each of the support cells that support fuel elements or rods and in the first orientation loosely receive the fuel rod therethrough. In a second orientation with respect to the base grid, the lock-support sleeve places a transverse pressure on the fuel rod to load and restrain the fuel rod axially, the lock-support sleeve being rotatable between the first orientation and the second orientation. The method including the steps of: maintaining all the lock-support sleeves that are in axial alignment, in the first orientation; completely inserting a fuel rod into the fuel assembly through each of the lock-support sleeves in the axially transverse position in the fuel assembly skeleton in which the fuel rod is inserted; and loading the fuel rod to place a transverse pressure on the fuel rod after the fuel rod is completely inserted into the fuel assembly skeleton, by moving the lock-support sleeve surrounding the fuel rod to the second orientation. Preferably the loading step includes the step of rotating the lock-support sleeve 92 45° around the support cell 94. In one preferred embodiment the lock-support sleeve 92 is a quasi four-sided sleeve having generally rounded corners that are bulged out radially and the rotating step includes the steps of capturing at least two adjacent corners of the lock-support sleeve 92 with a tool 106 having fingers 112 which extend within the corresponding bulges 100 and a leverage arm 108. The rotating step rotates the leverage arm to rotate the lock-support sleeve 92 within the support cell 94. Preferably the lock-support sleeve 92 is accessed with the tool 106 from the underside of the support cell 94 to avoid damaging any of the coolant swirl vanes extending above the upper side of the support cell 94. The method of this invention further preferably includes the step of locking the lock-support sleeve in the second orientation. In one embodiment, the method of this invention includes the steps of inserting a removable positioning bar in a lower portion of the support cell 94 out of the path of the fuel rod 114 prior to the step of completely inserting the fuel rod, and inserting the lock-support sleeve 92 into the support cell 94 in the first orientation. Additionally, the latter embodiment includes the step of removing the positioning bar 122 from the support cell 94 after lock-support sleeve 92 is moved to the second orientation. Because there are four or eight dimples or protrusions 102 on each lock-support sleeve 92 and four or eight cutouts 104 on each support cell 94 of the base grid 90, the lock-support sleeves are locked axially and radially after being rotated. Also, the preload is added between the support sleeve 92 and fuel rod 114 after the rotation step due to the designed shape of the lock-support sleeve 92 and especially the bulged corners 100. The fuel rods can be loaded and the sleeves can be locked row by row. Specific pattern loading of the fuel rods during assembly is not needed since there is no transverse loading force, which could bow the assembly for row-by-row loading. A single rod can be loaded in any special location first. The material and texture (such as transverse) for the base grid 90 will be selected to have less growth radially than the lock-support sleeves 92, therefore, positive contact will be maintained between the fuel rods 114 and the lock-support sleeves 92 even after the fuel assembly is irradiated. The material and shape of the lock-support sleeve 92 are selected to allow more growth in a direction toward the fuel rod 114 to further increase the load between the fuel rod and the lock-support sleeves 92 under irradiation. The sleeve 92 could be made of Inconel to provide the appropriate characteristics under irradiation. To limit the neutron penalty of this material, a hole or notches could be punched into the sleeve if it is made of Inconel. Thus the support grid of this invention enables loading of the fuel rods while avoiding scratches, gall balls and other surface damage that typically occur during fuel rod loading. Positive preload will be maintained even after the end of the fuel cycle. The lock-support sleeve has four full-length line contacts with the fuel rod that maximizes the contact area and reduces wear due to fretting. None of the support features lift off the rod during reactor operation and the rod will return to the center even under extreme lateral shipping loads. Furthermore, the grid of this invention reduces manufacturing costs because of the reduced number and complexity of stamped features on the grid parts. Mixing vanes can also be added to the top of the base grid straps as in conventional grids to enhance coolant mixing. While specific embodiments of the invention have been described in detail, it will 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. |
|
054024544 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the figures of the drawing, in which the same reference numerals are used for components corresponding to one another, and first, particularly, to FIG. 1 thereof, there is seen a reactor safety vessel 1 of a nuclear power station (which is not further shown) that includes a reinforced concrete structure 2 (shown in sections) and at least one non-illustrated reactor pressure vessel of a nuclear reactor. The reinforced concrete structure 2 carries a sample-taking container 3 in a manner which is not illustrated in greater detail. The container is connected to an injector 8 by means of a filling and emptying line 5 which starts from the immediate vicinity of a bottom 4 of the container, and by means of a gas line 7 starting from its dome 6. The injector 8 is in turn connected by a line 10 to a sample sorting and suction device 11. The line 10 has a bushing 9 which penetrates the wall of the reactor safety vessel 1. The sample sorting device 11 serves at the same time to control the sample-taking container 3 and to control a sample draw-off and dilution device 12. The difference in pressure between the atmosphere in the vessel and the interior of the sample-taking container amounts to up to 5000 hPa. An inlet channel 26, the sample-taking container 3 with all of its built-in fittings, the filling and emptying line 5, the gas line 7, the injector 8 and the line 10 starting from the injector 8, are made essentially of radiation-resistant material, for example special steel. Two serially connected controllable valves 13 and 14 are installed in the line 10 between the bushing 9 and the sample sorting and suction device 11. In addition, a non-illustrated throttle may be provided, which restricts the flow through the line 10, and a sorption filter for organoiodine may be inserted into the line. The sample draw-off and dilution device 12 is connected through a feed line 15 and a return line 16 to the sample sorting device 11 and contains a sample feed pump 17, a distributor 18 and connection fittings 19 for a plurality of sample transport containers 20. The samples are taken in the sample transport containers 20 to an examination laboratory for accurate assessment. Before their assessment, the samples are separated into gaseous constituents and washing liquid 25 which contains other parts of the samples, after the samples have been drawn off by suction through a throttle 34 working in the laval velocity range and through a water separator 36 into a vacuum vessel 32. The containment atmosphere radioactivity is detected and/or the composition thereof is detected there by gas chromatography and .gamma./.beta. measurement. Radioactivity can also be continuously measured in the partial flow of outgoing gas and in the washing liquid circuit. The return of the gas and liquid activities into the vessel 1 is effected in a manner which is not shown, but is advantageously carried out through the sample-taking container 3. In the sample sorting and suction device 11 a separator 31, for example in the form of a centrifugal separator and collector for separating the washing liquid, and a quick-opening valve 30, are accommodated. In the vacuum or storage and suction vessel 32 a vacuum of less than 500 hPa, which is necessary for drawing off by suction, is produced by means of a pump 33, and the washing liquid 25 being drawn off by suction is stored. During sample taking operation, the throttle 34 is operated predominantly with critical stress relief, so that a constant volume flow is taken out over the entire operating range of the sample taking device, from a maximum of about 10000 hPa down to normal atmospheric pressure, and additional throughput regulating means are not necessary. Through the use of a secondary pipe heating system 35, any condensate formed upstream of the throttle 34 is vaporized again and passed in vapor form through the throttle 34. Level adjustment and system temperature control are effected through non-illustrated media connections for deionized water, steam and nitrogen. In a modified variant, the system has its own non-illustrated integrated evaporator. The washing liquid 25 in the sample-taking container 3 is varied, for example with respect to pH value from acid to alkaline, so that elementary iodine and organoiodine are selectively retained. The retention of organoiodine is therefore possible even in an externally disposed sorption filter 36. Through pH value variation followed by measurement, it is also possible to measure the composition of the gas with respect to CO.sub.2, CO, etc., as well as, with or without washing liquid, the H.sub.2 concentration. The sample-taking container 3 is electropolished or teflon-coated on its surface and is constructed in such a way that depositions are largely avoided. Measuring time intervals can be flexibly adapted to a fault sequence and other events in the vessel 1. After being drawn off by suction from the sample-taking container 3, the washing liquid 25 is diluted until the radioactivity of the sample is lower than 10.sup.9 Bq/m.sup.2. In the case of embodiments in the form of a two-line system, the filling and emptying line 5 of the sample-taking container 3 can be led separately into the separator 31 in the sorting device 11, so that continuous measurement operation is achieved and/or minimization of the washing liquid 25 in the gas line 7 is achieved. The previously mentioned functional principle can also be applied to the configuration of a sample-taking container 3 directly downstream of the valves 13 and 14, including the back-washing action in an inlet line, while largely retaining the advantages of the process, and can also be used as a sample taking and measuring system in exhaust air systems. In configurations including a plurality of sample taking devices, gas can be taken out through one sample taking device and continuous pumping-back can be effected through another sample taking device. Through the use of a non-illustrated accompanying supply system which, for example, is battery-fed, for the electrical and instrumentation control of the sample taking system, operation is ensured even in the event of current failure. FIGS. 2 and 3 show a sample-taking container 3 having a conical, downwardly tapering lower part 21. In the exemplary embodiment shown in FIG. 2 the lower part 21 surrounds a venturi nozzle 22 and in the exemplary embodiment shown in FIG. 3 the lower part 21 surrounds a filling body, which serves as a flow distributor 23, and a plurality of nozzles 24 in the bottom 4. The lower part 21 is filled with a transport or conveying fluid which at the same time serves as the washing liquid 25. The filling and emptying line 5 leads into the lower part 21 at the bottom 4. The dome 6 is filled with gas. The velocity of a flow of the sample in the venturi nozzle 22, in the venturi nozzles 24 and in a venturi nozzle 40 shown in FIG. 4, is slightly, and preferably 10% to 30%, below a critical nozzle velocity, as long as no condensation of the sample occurs in the washing liquid 25. The velocity of flow is increased to the critical nozzle velocity as soon as the sample condenses, at least partially, in the washing liquid 25, with the sample-taking container 3 being operated under the conditions of pressure and temperature prevailing in the vessel 1. Gaseous constituents of the sample and of the transport fluid can then react chemically with one another. In the exemplary embodiments shown in FIGS. 2 and 3, the part 21 is surrounded by the inlet channel 26 which has a bottom end that feeds the venturi nozzle 22 or the nozzles 24. The inlet channel 26 has a top end which is situated approximately at the height of a transition from the part 21 to a cylindrical part of the sample-taking container 3. The top end of the inlet channel 26 is gas-tightly closed by a bursting disk 27 during normal operation of the reactor safety vessel 1. In the exemplary embodiment shown in FIG. 4, the gas line 7 passes through the sample-taking container 3 over its entire height, down to the bottom 4 and is open at the bottom end. In this type of embodiment, slot-like openings 29 are provided just above the bottom 4 in the gas line 7, so that the bottom end of the gas line 7 in the sample-taking container itself acts as a venturi nozzle 40. An inlet channel leading into the lower part of the sample-taking container 3 is dispensed with in this embodiment. Instead, however, the bursting disk 27 is disposed directly on the upper part of the sample-taking container 3, for the ventilation and pressure relief of the latter. In each case a venturi nozzle 22, 24, 40 dipping into a washing liquid 25 is provided in the sample-taking container 3, above the bottom 4 of the latter. The volume of the washing liquid 25 is at most approximately equal to half the volume of the sample-taking container 3, that is to say about 2 to 3 liters, and the inlet channel 26 or the gas line 7 leads into the sample-taking container 3 below the venturi nozzle 22, 24, 40. The process for obtaining samples from the atmosphere in the reactor safety vessel 1 is initiated by filling the sample-taking container 3 with the transport fluid 25 through the line 10 and the filling and emptying line 5. The temperature of the washing liquid 25 at the beginning of a sample taking process is slightly lower than that of the atmosphere in the vessel 1. At the end of the filling operation the bursting disk 27 is caused to react and the transport fluid has reached a level 28. The pressure in the line 10 is thereupon lowered, so that a sample of the atmosphere from the reactor safety vessel 1 flows into the sample-taking container 3. The velocity of flow of the sample is kept constant by throttling taking place in the venturi nozzle 22, 24, 40 and/or in the throttle 34 disposed outside the vessel 1. In this case the sample is mixed in the venturi nozzle 22 shown in FIG. 2, in the flow distributor 23 shown in FIG. 3 or in the venturi nozzle 40 from the gas line 7 and the openings 29 shown in FIG. 4, with the transport fluid acting as the washing liquid 25. In order to initiate obtaining a sample, the sample-taking container 3 may also be subjected to superatmospheric pressure, for example by introducing nitrogen, until the bursting disk 27 at the free end of the inlet channel 26 breaks. During the mixing of the sample with the transport fluid 25 a part of the sample is dissolved, a part is condensed in the transport fluid 25 and the rest remains in gas form and collects in the dome 6, or remains in the form of small bubbles distributed in the transport fluid 25. Through inactive iodine additions and a variation of the pH value of the washing liquid 25, elementary organic iodine, CO, CO.sub.2 and other gas from the sample are also retained in the washing liquid 25. When sample-taking containers 3 according to FIGS. 2 and 3 are used, the inlet channel 26 is flushed with the transport fluid 25 before the latter is drawn off, with the fluid being forced one or more times to the height of the bursting disk 27 through pressure variations in the line 10 and the sample-taking container 3. The level height 28 of the washing liquid 25, preferably in the inlet channel 26, is thus varied by pressure changes in the transport fluid, with the washing liquid 25 being raised, after the sample has flowed in, at least once to the height of an inlet opening at the free end of the inlet channel 26 for the sample. After adequate flushing of the inlet channel 26, the transport fluid 25 containing a part of the sample, together with the gas mixture contained in the dome 6, is conveyed outwards into the sample sorting device 11 by a sudden pressure reduction in the line 10. The above-described flushing is unnecessary in the embodiment of the sample-taking container 3 according to FIG. 4, so that in this embodiment the sudden pressure reduction for conveying the sample to the sample sorting device 11 is effected immediately after the bottom end of the gas line 7 comes into action as a venturi nozzle. In each case a mixture of carrier gas, gaseous constituents of the sample and the transport fluid, which likewise contains constituents of the sample, is conveyed into the sample sorting device 11 through the line 10. This mixture is prepared, as far as is necessary, in the sample sorting device 11 and thereupon is filled into the sample transport containers 20 by means of the sample draw-off device 12. In the application of the process according to the invention it is ensured, because of the very short, back-washed inlet channel 26 or because of the absence of an inlet channel, that practically all of the constituents of a sample are contained in the aforesaid mixture and consequently are detectable in the assessment of the samples. |
abstract | A cryogenically cooled radiation shield device and method are provided to shield an area, such as the capsule of a space vehicle, from radiation. A cryogenically cooled radiation shield device may include at least one first coil comprised of a superconducting material extending about an area to be shielded from radiation. The cryogenically cooled radiation shield device also includes a first conduit extending about the area to be shielded from radiation. The at least one first coil is disposed within the first conduit. The cryogenically cooled radiation shield device also includes a second conduit extending about the area to be shielded from radiation. The first conduit is disposed within the second conduit. The cryogenically cooled radiation shield device also includes a first cryogen liquid disposed within the first conduit and a second cryogen liquid, different than the first cryogen liquid, disposed within the second conduit exterior of the first conduit. |
|
abstract | An ion generator (10) generally includes: a shielding shell (11), a cathode device (16), and an annular anode (14). The shielding shell has a first end (113), an opposite second end (115) and a main body (111) therebetween. The first end has an electron-input hole (13). The second end has an ion-output hole (15). The main body has a gas inlet (170) for introducing an ionizable gas (170). The cathode device faces the electron-input hole for emitting electrons to enter the shielding shell so as to ionize the ionizable gas thereby generating ions. The cathode device includes a conductive base (160) and at least one field emitter (161) thereon. The annular anode is arranged in the shielding shell. The anode is aligned with the ion-output hole. |
|
claims | 1. A charged particle accelerator system comprising:a dielectric wall accelerator (DWA) including:a high gradient lens section that transports a charged particle beam and controls a beam spot size of the charged particle beam;a main DWA section that accelerates the charged particle beam, wherein the high gradient lens section and the main DWA section comprise a series of alternating layers of insulators and conductors with a hollow center, the series of alternating layers stacked together to form a single high gradient insulator (HGI) tube to allow propagation of the charged particle beam through the hollow center of the HGI tube;a plurality of transmission lines connected to the high gradient lens section;a plurality of transmission lines connected to the main DWA section; andone or more voltage sources configured to supply an adjustable voltage value to each transmission line of the plurality of transmission lines connected to the high gradient lens section and the main DWA section to establish an adjustable electric field profile. 2. The charged particle accelerator system of claim 1, further comprising:a charged particle source configured to produce the charged particle beam, and the DWA configured to receive, dynamically shape and accelerate the charged particle beam from the charged particle source; anda timing and control component configured to produce timing and control signals to the charged particle source and the DWA via the transmission lines. 3. The charged particle accelerator system of claim 1, wherein the one or more voltage sources are configured to establish a substantially linear longitudinal electric field within the high gradient lens section. 4. The charged particle accelerator system of claim 3, wherein the substantially linear longitudinal electric field increases monotonically as a function of distance from entrance of the high gradient lens section. 5. The charged particle accelerator system of claim 3, wherein the substantially linear longitudinal electric field decreases monotonically as a function of distance from an entrance of the high gradient lens section. 6. The charged particle accelerator system of claim 1, wherein the one or more voltage sources are configured to establish a radial electric field at one or more subsections within the high gradient lens section and to thereby focus or defocus the charged particle beam propagating through the HGI tube. 7. The charged particle accelerator system of claim 6, wherein the one or more voltage sources are configured to establish at least one of:a positive valued radial electric field to focus a positively charged particle beam;a positive valued radial electric field to defocus a negatively charged particle beam;a negative valued radial electric field to focus a negatively charged particle beam; ora negative valued radial electric field to defocus a positively charged particle beam. 8. The charged particle accelerator system of claim 1, wherein the one or more voltage sources are configured to supply a first set of voltage values to the high gradient lens section and the main DWA section to produce an output charged particle beam with a particular set of baseline characteristics. 9. The charged particle accelerator system of claim 8, wherein producing an output charged particle beam with a set of baseline characteristics includes producing a minimum output beam spot size at a target location. 10. The charged particle accelerator system of claim 8, wherein the baseline characteristics comprises a beam radius, a beam spot size, a beam energy, a beam emittance, a beam uniformity, a beam intensity, and a beam slope. 11. The charged particle accelerator system of claim 8, wherein the one or more voltage sources are configured to supply a second voltage value to at least one subsection of the main DWA section such that the second voltage value is different from a first voltage value supplied to the at least one subsection to produce the particular set of baseline characteristics. 12. The charged particle accelerator system of claim 11, wherein the second voltage value is zero. 13. The charged particle accelerator system of claim 8, wherein the one or more voltage sources are configured to supply a second voltage value to at least one subsection of the high gradient lens section such that the second voltage value is different from a first voltage value supplied to the at least one subsection to produce the particular set of baseline characteristics. 14. The charged particle accelerator system of claim 1, wherein the DWA further comprises:an end section comprise a series of alternating layers of insulators and conductors with a hollow center, the series of alternating layers stacked together with the alternating layers of insulators and conductors associated with the high gradient lens section and the main DWA section to form the single high gradient insulator (HGI) tube; anda plurality of transmission lines connected to the end section, wherein the one or more voltage sources are configured to supply an adjustable voltage value to each transmission line of the plurality of transmission lines connected to the end section. 15. The charged particle accelerator system of claim 14, wherein the one or more voltage sources are configured to supply a voltage value to at least one subsection of the end section and to thereby increase the charged particle beam energy. 16. The charged particle accelerator system of claim 14, wherein the plurality of transmission lines connected to each of the high gradient lens section, the main DWA section and the end section are configured to be independently adjusted. 17. A method of shaping a charged particle beam, comprising:establishing a desired electric field across a plurality of sections of a dielectric wall accelerator (DWA), wherein the DWA comprises:a high gradient lens section,a main DWA section, wherein the high gradient lens section and the main DWA section comprise a series of alternating layers of insulators and conductors with a hollow center, the series of alternating layers stacked together to form a single high gradient insulator (HGI) tube to allow propagation of a charged particle beam through the hollow center of the HGI tube,a plurality of transmission lines connected to the high gradient lens section,a plurality of transmission lines connected to the main DWA section, andone or more voltage sources configured to supply an adjustable voltage value to each transmission line of the plurality of transmission lines connected to the high gradient lens section and the main dielectric wall section to establish an adjustable electric field profile; anddirecting the charged particle beam through the DWA. 18. The method of claim 17, wherein establishing the desired electric field comprises adjusting the one or more voltage sources to establish a substantially linear longitudinal electric field within the high gradient lens section. 19. The method of claim 18, wherein the substantially linear longitudinal electric field increases monotonically as a function of distance from entrance of the high gradient lens section. 20. The method of claim 18, wherein the substantially linear longitudinal electric field decreases monotonically as a function of distance from entrance of the high gradient lens section. 21. The method of claim 17, wherein establishing the desired electric field comprises adjusting the one or more voltage sources to establish a radial electric field at one or more subsections within the high gradient lens section and to thereby focus or defocus the charged particle beam propagating through the HGI tube. 22. The method of claim 21, wherein adjusting the one or more voltage sources establishes at least one of:a positive valued radial electric field to focus a positively charged particle beam;a positive valued radial electric field to defocus a negatively charged particle beam;a negative valued radial electric field to focus a negatively charged particle beam; ora negative valued radial electric field to defocus a positively charged particle beam. 23. The method of claim 17, wherein establishing the desired electric field comprises adjusting the one or more voltage sources to supply a first set of voltage values to the high gradient lens section and the main DWA section to produce an output charged particle beam with a particular set of baseline characteristics. 24. The method of claim 23, wherein producing the output charged particle beam with the particular set of baseline characteristics includes producing a minimum output beam spot size at a target location. 25. The method of claim 23, wherein the baseline characteristics comprises a beam radius, a beam spot size, a beam energy, a beam emittance, a beam uniformity, a beam intensity, and a beam slope. 26. The method of claim 23, further comprising adjusting the one or more voltage sources to supply a second voltage value to at least one subsection of the main DWA section such that the second voltage value is different from a first voltage value supplied to the at least one subsection to produce the particular set of baseline characteristics. 27. The method of claim 26, wherein the second voltage value is zero. 28. The method of claim 23, further comprising adjusting the one or more voltage sources to supply a second voltage value to at least one subsection of the high gradient lens section such that the second voltage value is different from a first voltage value supplied to the at least one subsection to produce the particular set of baseline characteristics. 29. The method of claim 23, further comprising adjusting the one or more voltage sources to supply a second set of voltage values to the high gradient lens section or the main DWA section to produce an output charged particle beam with a set of characteristics different from the baseline characteristics. 30. The method of claim 29, wherein the second set of voltage values produces an output charged particle beam that is different from the output charged particle beam with the particular set of baseline characteristics in at least one of: a beam radius, a beam spot size, a beam energy, a beam emittance, a beam uniformity, a beam intensity, and a beam slope. 31. The method of claim 17, further comprising adjusting the one or more voltage sources to supply a voltage value to at least one subsection of an end section of the DWA to increase the charged particle beam energy, whereinthe end section comprises a series of alternating layers of insulators and conductors with a hollow center, the series of alternating layers stacked together with the alternating layers of insulators and conductors associated with the high gradient lens section and the main DWA section to form the single high gradient insulator (HGI) tube; and whereina plurality of transmission lines are connected to the end section; and whereinthe one or more voltage sources are configured to supply an adjustable voltage value to each transmission line of the plurality of transmission lines connected to the end section. 32. The method of claim 17, further comprising introducing a timing offset to de-synchronize the charged particle beam that enters the HGI tube and sequence of voltage values applied to the main DWA section to produce an output charged particle beam with a set of characteristics different from the baseline characteristics. 33. The method of claim 17, further comprising introducing, at entrance to the DWA, a mismatch between the charged particle beam characteristics and the DWA to produce an output charged particle beam with a set of characteristics different from the baseline characteristics. 34. A method for treatment of a patient using a charged particle accelerator system, the method comprising:irradiating one or more target areas within the patient's body with a charged particle beam that is output from the charged particle beam accelerator system, the charged particle accelerator system comprising:a charged particle source;a dielectric wall accelerator (DWA), wherein the DWA comprises:a high gradient lens section,a main DWA section, wherein the high gradient lens section and the main DWA section comprise a series of alternating layers of insulators and conductors with a hollow center, the series of alternating layers stacked together to form a single high gradient insulator (HGI) tube to allow propagation of a charged particle beam through the hollow center of the HGI tube,a plurality of transmission lines connected to the high gradient lens section,a plurality of transmission lines connected to the main DWA section, andone or more voltage sources configured to supply an adjustable voltage value to each transmission line of the plurality of transmission lines connected to the high gradient lens section and the main dielectric wall section to establish an adjustable electric fieldthe charged particle accelerator system further comprising a timing and control component configured to produce timing and control signals to the charged particle source, the high gradient lens and the dielectric wall accelerator; andadjusting the one or more voltage sources to supply a first set of voltage values to the high gradient lens section and the main DWA section to produce an output charged particle beam with a particular set of baseline characteristics. 35. The method of claim 34, wherein producing the output charged particle beam with the particular set of baseline characteristics includes producing a minimum output beam spot size at a target location. 36. The method of claim 34, wherein the baseline characteristics comprises a beam radius, a beam spot size, a beam energy, a beam emittance, a beam uniformity, a beam intensity, and a beam slope. 37. The method of claim 34, further comprising irradiating the one or more target areas within the patient's body with a modified charged particle beam with a set of characteristics different from the baseline characteristics. 38. The method of claim 37, wherein the modified charged particle beam is produced by adjusting the one or more voltage sources to supply a second set of voltage values to the high gradient lens section or the main DWA section. 39. The method of claim 37, wherein the modified charged particle beam is produced by introducing a timing offset to de-synchronize the charged particle beam that enters the HGI tube and sequence of voltage values applied to the main DWA section. 40. The method of claim 37, wherein the modified charged particle beam is produced by introducing, at entrance to the DWA, a mismatch between the charged particle beam characteristics and the DWA. |
|
claims | 1. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor comprising: a plurality of nuclear fuel rods arranged in a matrix in a channel box and means to allow flowing light water acting as both a moderator and a coolant in spaces between said nuclear fuel rods, said mixed oxide nuclear fuel assembly being positionable in a reactor core, wherein: 20 through 40% of the quantity of said nuclear fuel rods are mixed oxide nuclear fuel rods, each of which contains fissionable plutoniums having only one kind of enrichment grade selected from a range of 5 through 15 weight %, and 80 through 60% of the quantity of said nuclear fuel rods are UO 2 fuel rods containing U isotopes at least including U 235 . 2. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 1 , wherein: claim 1 20 through 25% of the quantity of said nuclear fuel rods are mixed oxide nuclear fuel rods. 3. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 2 , further comprising: claim 2 a plurality of gadolinium rods containing U isotopes at least including U 235 and gadolinium, said gadolinium rods being positionable at an area where the effects of said moderator are strong. 4. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 2 , wherein: claim 2 the enrichment grade of said U 235 is selected from a range of 1 through 5 weight %. 5. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 2 , wherein: claim 2 said mixed oxide nuclear fuel rods are positionable at an area where the effects of said moderator are weak. 6. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 2 , further comprising: claim 2 a water rod arranged in an area where effects of said moderator are weak. 7. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 1 , wherein: claim 1 each of said mixed oxide nuclear fuel rods contains fissionable plutoniums having only one kind of enrichment grade selected from a range of 10 through 15 weight %. 8. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 7 , further comprising: claim 7 a plurality of gadolinium rods containing U isotopes at least including U 235 and gadolinium, said gadolinium rods being positionable at an area where the effects of said moderator are strong. 9. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 7 , wherein: claim 7 the enrichment grade of said U 235 is selected from a range of 1 through 5 weight %. 10. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 7 , wherein: claim 7 said mixed oxide nuclear fuel rods are positionable at an area where the effects of said moderator are weak. 11. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 7 , further comprising: claim 7 a water rod arranged in an area where effects of said moderator are weak. 12. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 1 , wherein: claim 1 the enrichment grade of said U 235 is selected from a range of 1 through 5 weight %. 13. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 12 , further comprising: claim 12 a plurality of gadolinium rods containing U isotopes at least including U 235 and gadolinium, said gadolinium rods being positionable at an area where the effects of said moderator are strong. 14. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 12 , further comprising: claim 12 a water rod arranged in an area where effects of said moderator are weak. 15. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 1 , wherein: claim 1 said mixed oxide nuclear fuel rods are positionable at an area where the effects of said moderator are weak. 16. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 15 , further comprising: claim 15 a plurality of gadolinium rods containing U isotopes at least including U 235 and gadolinium, said gadolinium rods being positionable at an area where the effects of said moderator are strong. 17. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 15 , wherein: claim 15 the enrichment grade of said U 235 is selected from a range of 1 through 5 weight %. 18. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 15 , further comprising: claim 15 a water rod arranged in an area where effects of said moderator are weak. 19. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 1 , further comprising: claim 1 a plurality of gadolinium rods containing U isotopes at least including U 235 and gadolinium, said gadolinium rods being positionable at an area where the effects of said moderator are strong. 20. A mixed oxide nuclear fuel assembly employable for a thermal neutron/light water reactor in accordance with claim 1 , further comprising: claim 1 a water rod arranged in an area where effects of said moderator are weak. |
|
049960199 | summary | The invention relates to a storage container for receiving low or medium activity radioactive waste embedded in a filling material. Radioactive waste storage containers generally comprise a drum and a cover able to seal said drum. When the radioactive waste has been placed in the drum, the cover is put into place and joined to the drum, e.g. by means of a joint ensuring the confinement of the container. The filling material is then injected into the container by an injection tube or passage provided for this purpose. In the present state of the art, the storage containers are made from concrete, combined with metal fittings generally made from iron-reinforced concrete with a thickness of at least 6 mm. In a structure of this type, the rods constituting the fitting are located at a minimum distance, generally at least equal to 25 mm, from the surface of the drum or cover. The connecting zone between the drum and the cover, which has a joint which can e.g. be made from cement or resin, consequently forms a fitting-free zone, whose thickness is at least equal to 50 mm. This zone has a modulus of elasticity different from that of the other parts of the container constituted by concrete and fittings and a reduced strenght. Therefore cracks and fractures may occur in this zone, particularly under the effect of differential expansions or handling shocks. Very dense concrete types exist, whose use would make it possible to solve these problems. However, such concrete types are too expensive for their use to be envisaged in this case. In addition, e.g. EP-A-0 248 693 discloses concretes incorporating metal fibers. As illustrated by GB-A-2 023 056, an irradiated nuclear fuel rod can be coated with a metal fiber-reinforced concrete. However, this is a coating produced in a single operation, which does not solve the problem of the connection between the drum and the cover, when the latter has to be fixed to the drum following the introduction of the radioactive waste into it. The invention specifically relates to a container for the storage of radioactive waste designed in such a way as to have a homogeneous structure, even in the connection zone between the drum and the cover, so that it is resistant to shocks and corrosion, while still having a satisfactory seal with respect to air and water and having a relatively low cost. According to the invention, this result is obtained by means of a radioactive waste storage container comprising a drum having a waste introduction opening and a cover for the tight sealing of said opening, said container being characterized in that it is completely made from concrete reinforced by metal fibers, including in the junction zone between the cover and the drum, said junction zone having, around said opening, at least one keying groove. The metal fibers used for reinforcing the concrete are, for example, steel, cast iron, stainless steel or galvanized steel fibers. It is advantageous to use a filling material formed by metal fiber-reinforced concrete, so that the container filled with waste and said material constitute a monolithic block. In a first embodiment of the invention, the container comprises at least one keying joint, which is also made from metal fiber-reinforced concrete and which simultaneously penetrates the keying grooves formed in the drum and on the cover. In a second embodiment of the invention, the cover is directly cast on the drum and penetrates a keying groove formed in the drum. In a third embodiment of the invention, in the junction zone between the cover and the drum, there is a metal fiber-reinforced concrete keying joint, cast into a dovetail space formed between an outer peripheral edge of the cover and an inner peripheral edge of the drum surrounding the opening of the latter. The latter embodiment simplifies the procedure of sealing the drum, because sealing can be carried out without it being necessary to produce a formwork. Advantageously, the cover has at least one filling passage internally provided with a keying groove and by which the metal fiber-reinforced concrete can be injected around the waste previously placed in the container. |
summary | ||
047449381 | summary | BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for producing fissionable deposits and, more particularly, to a method for producing fissionable deposits of ultralow-mass for reactor neutron dosimetry on a substrate by recoil ion-implantation, and an apparatus related thereto. Ultralow-mass fissionable deposits have proved useful as fissioning sources for solid state track recorder fission rate measurements in high intensity neutron fields. These fission rate measurements are used to derive information for neutron dosimetry purposes. A solid state track recorder placed adjacent to a thin fissionable deposit records tracks from the recoiling fission fragments which result from the fission in the deposit. If the fissionable deposit is sufficiently thin, the effects of self-absorption can be ignored. The number of these tracks observed with an optical microscope after chemical etching of the solid state track recorder is proportional to the number of fissions that has occurred in the fissionable deposit. Thus, the number of fission fragment tracks per square centimeter, i.e., the track density, in the solid state track recorder can be used to calculate the fission rate per unit area in the fissionable deposit. For typical high neutron fluence applications, such as reactor core dosimetry or reactor component dosimetry, it has been found that a limitation is placed on using solid state track recorders due to the maximum track density that can be used without excessive track overlap, usually about 10.sup.6 tracks/cm.sup.2. In order to avoid excessively high track densities, low-mass fissionable deposits can be used to reduce the number of fissions that will occur at a given neutron fluence. For example, in dosimetry applications for light water reactor pressure vessel surveillance, .sup.235 U deposits with masses as low as 1.5.times.10.sup.-13 grams are required to produce a usable solid state track recorder track density. Similarly, low masses of other isotopes, such as .sup.237 Np, .sup.238 U, .sup.239 Pu, are required for dosimetry in light water reactor pressure vessel surveillance. It has been found that the technical problems associated with the manufacture of such low-mass deposits can be overcome through the use of isotopic spiking/electroplating techniques to characterize the masses of these ultralow-mass fissionable deposits. For example, ultralow-mass deposits can be produced by an electroplating technique using, e.g., .sup.237 U (7 day half-life) as an isotopic spike for .sup.235 U and .sup.238 U, .sup.239 Np (2.4 day half-life) as a spike for .sup.237 Np, and .sup.236 Pu (2.85y half-life) as a spike for .sup.239 Pu. The shorter half-life isotopic spike is used as a chemical tracer to overcome the fact that the radioactivity of the principal isotope of the respective fissionable deposit renders the principal isotope undetectable when present in such low masses as can be employed according to the present invention. However, it has also been found that the amount of the isotopic spike that can be added to a fissionable deposit is limited by the nuclear properties of the isotopic spike. For example, .sup.237 U decays to .sup.237 Np, which is itself fissionable. As as result, the amount of the isotope to which the spike eventually decays must be kept small enough (by limiting the amount of spike added) to keep the fission rate of the isotope to which the spike decays small relative to the decay rate of the isotope of interest in the deposit. Also, in order to ensure that the added .sup.237 U is a valid radiochemical tracer for .sup.235 U, a series of chemical steps or chemical equilibration procedures must be carried out. After the addition of .sup.237 U to .sup.235 U, the mixture must be subjected to an alternating series of chemical oxidations and reductions to drive the .sup.237 U and .sup.235 U into an identical mixture of oxidation states. These chemical procedures typically take 1-2 days. In particular regard to .sup.239 Pu deposits, the .sup.236 Pu isotopic spike itself is fissionable and must therefore be used in limited amounts. In addition, for .sup.239 U deposits spiked with .sup.236 Pu, several experimental problems arise. For example, in the case of .sup.239 Pu fission rates in a solid state track recorder measured at the mid-plane location in the reactor cavity in the annular gap of an operating commercial power reactor during a typical operating cycle, .sup.239 Pu fissionable deposits with masses on the order of 10.sup.-13 gram are required to produce an optimum number of fission tracks. Namely, due to the previously explained limitations, the maximum allowable .sup.236 Pu/.sup.239 Pu spike ratio results in a count rate of only about 0.3 disintegrations per minute (dpm) for such a .sup.239 Pu deposit of 10.sup.-13 gram. In order to desirably characterize the decay rate of this deposit to better than 2% for mass calibration purposes, a counting time of about twelve days may be required. In practice, higher masses (e.g., 6.times.10.sup.-13 gram) are produced resulting in higher count rates (e.g., 1 dpm) and shorter count times (e.g., 2 days). The resulting track densities are higher and are more difficult to count. Also, due to the low sample count rate, counters with very low background count rates of about 0.1 dpm must be used. However, the decay properties of the isotopic spike make maintenance of the low backgrounds difficult. For example, .sup.236 Pu decays as follows: ##STR1## Thus, many radioactive decay products accumulate from the decay of .sup.236 Pu, and these decay products must be periodically removed from the counters by cleaning to maintain low counter backgrounds. In light of the above, a simpler and more reliable method is needed for producing fissionable deposits of ultralow-mass for nuclear reactor dosimetry. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and apparatus for producing ultralow-mass fissionable deposits for reactor neutron dosimetry by recoil ion-implantation capable of eliminating the need for isotopic spiking procedures. It is another object of the present invention to provide a method and apparatus for producing ultralow-mass fissionable deposits for reactor neutron dosimetry by recoil ion-implantation capable of eliminating the need for electroplating techniques and the related high purity chemical requirements. It is another object of the present invention to provide a method and apparatus for producing ultralow-mass fissionable deposits for reactor neutron dosimetry by recoil ion-implantation capable of producing highly uniform deposits previously unavailable through electroplating methods. It is another object of the present invention to provide a method and apparatus for producing ultralow-mass fissionable deposits for reactor neutron dosimetry by recoil ion-implantation wherein only the apparatus need be calibrated. It is another object of the present invention to provide a method and apparatus for producing ultralow-mass fissionable deposits for reactor neutron dosimetry by recoil ion-implantation capable of using a variety of substrates for ion implantation. It is another object of the present invention to provide a method and apparatus for producing ultralow-mass fissionable deposits for reactor neutron dosimetry by recoil ion-implantation, wherein the masses of the fissionable deposits produced can be controlled precisely. It is another object of the present invention to provide a method and apparatus for producing ultralow-mass fissionable deposits for reactor neutron dosimetry by recoil ion-implantation, wherein the resulting material in the fissionable deposit is isotopically pure. Finally, it is an object of the present invention to provide a method and apparatus for producing ultralow-mass fissionable deposits for reactor neutron dosimetry by recoil ion-implantation capable of producing fissionable deposits of extremely low masses on solid state track recorders. To achieve the foregoing and other objects of the present invention, and in accordance with the purposes of the invention, there is provided an alpha recoil ion-implantation method and related apparatus which use an alpha emitting source that is a radioactive parent of the daughter isotope of interest to implant into a substrate the recoil ions of the daughter resulting from the alpha decay. For example, a .sup.241 Am source in thin layer form can be placed next to a substrate such as a solid state track recorder in a vacuum which houses an assembly for rotating opposing disks receiving the alpha emitting source and the solid state track recorder, respectively. Each alpha decay of .sup.241 Am results in a .sup.237 Np ion with enough recoil energy to be implanted into the solid state track recorder. Fissionable deposits of .sup.239 Pu, .sup.235 U, and .sup.238 U can also be made by using this method and apparatus. Fissionable deposits with masses appropriate for high neutron fluence dosimetry are thusly prepared. |
summary | ||
039492320 | abstract | A well-logging sonde employes a neutron generator. It has a high-voltage supply for the target of the neutron generator tube. The sonde includes an insulated high-voltage conductor for connecting the supply to target, and there is a metallic ring supported on the insulation surrounding the conductor. The ring and conductor form a capacitor that is connected to a circuit for controlling the deenergization of the high-voltage supply if an arc occurs. |
052951693 | claims | 1. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said reactor pressure vessel is arranged; a containment vessel housing said dry well; means defining a suppression chamber holding a suppression-pool water and forming above the suppression-pool water a first wet well; and passage means allowing said dry well to communicate with said suppression-pool water; wherein said facility further comprises: (a) means for defining a second wet well communicating with said first wet well; and (b) cooling means for keeping said second wet well at a temperature lower than that of said first wet well at the time of a loss-of-coolant accident. (c) a steel wall which surrounds at least said suppression-pool water in contact therewith to provide said containment vessel; and (d) an outer peripheral pool containing a cooling water in contact with the outer peripheral surface of said steel wall. (a) means for defining a second wet well communicating with said first wet well; and (b) means for separating a mixture fluid consisting of a noncondensing gas in said suppression chamber and a steam from said suppression-pool water in the noncondensing gas and the steam and for causing the stem after the separation to remain in said first wet well and the noncondensing gas to be collected in said second wet well. (c) a steel wall which surrounds at least said suppression-pool water in contact therewith to provide said containment vessel; and (d) cooling means for cooling the outer peripheral surface of said steel wall. (a) dividing means for dividing the wet well of said suppression chamber into a first space which is in contact with the water surface of said suppression-pool water and a second space which is not in contact therewith; (b) first passage means which allows said first space to communicate with said second space and which has an area smaller than that of said dividing means; and (c) cooling means for keeping said second space at a temperature lower than that of said first space. (d) second passage means allowing a lower section of said second space to communicate with said suppression-pool water. (e) at least one convection promoting pipe which is arranged in said outer peripheral pool and which has at least one upper opening situated below the water surface of said suppression-pool water at a position above outlets of said vent pipes and at least one lower opening situated in the suppression-pool water at a position below the outlets of said vent pipes, with said upper and lower openings communicating with each other to allow said pool water to pass therethrough. (f) a convection promoting plate which is arranged in said suppression-pool water along said steel wall and which has an upper end positioned higher than outlets of said vent pipes and a lower end positioned lower than the outlets of said vent pipes, with the difference in height between said upper end and the outlets of said vent pipes being larger than the difference in height between the outlets of said vent pipes and said lower end. (a) means arranged on the water surface of the suppression-pool water of said suppression chamber for serving to restrain evaporation of the suppression-pool water. (b) a steel wall surrounding at least said suppression-pool water in contact therewith to provide said containment vessel; and (c) cooling means for cooling the outer peripheral surface of said steel wall. (a) a hydrophobic-material layer which is formed on the water surface of said suppression-pool water and which has a saturation vapor pressure and a density that are lower than those of the suppression-pool water. (a) circulation passage means which has an intake opening situated in said suppression-pool water at a position higher that the suppression-pool water side outlet of the passage means and a discharge opening situated in said suppression-pool water at a position lower than the same, with at least a part of said circulation passage means being situated outside said suppression chamber. (b) cooling means provided in that portion of said circulation passage means which is situated outside said suppression chamber. (a) circulation passage means at least a part of which is situated outside said suppression chamber for causing the suppression-pool water to be circulated from a position higher than the suppression-pool water side outlet of the passage means to a position lower than the same. (b) cooling means provided in that portion of said circulation passage means which is situated outside said suppression chamber. (a) at least one convection promoting pipe which is arranged in said outer peripheral pool and which has at least one upper opening situated below the water surface of said suppression-pool water at a position above outlets of said vent pipes and at least one lower opening situated in the suppression-pool water at a position below the outlets of said vent pipes, with said upper and lower openings communicating with each other to allow said suppression-pool water to pass therethrough. wherein the height of the dry-well-side openings of said first vent pipes is so determined that when the water level in the dry well, in which water overflowing from said reactor pressure vessel accumulates at the time of a loss-of-coolant accident, has attained a core submerging level which allows submergence cooling of said core, the water in the dry well starts to flow into said first suppression chamber through said first vent pipes. (a) a second suppression chamber situated above said first suppression chamber and including a suppression pool and a wet well, said suppression pool communicating with said dry well through a plurality of second vent pipes; and (b) a line equipped with a valve and connecting said second suppression chamber with said reactor pressure vessel to provide an emergency core cooling system. (a) equalizing means which, for a long period of time after a loss-of-coolant accident, cools the core by supplying water into said pressure vessel, utilizing said suppression-pool water and the drawdown water accumulated in said dry well as a water source. (b) first detection means for detecting a pressure in said pressure vessel; (c) second detection means for detecting a water level in said pressure vessel; (d) third detection means for detecting a pressure in said dry well; (e) a pressure reducing valve connected with said pressure vessel and adapted to allow the steam in said pressure vessel to escape to said dry well; and (f) control means which is adapted to open said pressure reducing valve, in response to a low-water-level signal indicative of low water level in said pressure vessel and supplied from said second detection means and to a high-pressure signal indicative of high pressure in said dry well and supplied from said third detection means, so as to allow the steam in said pressure vessel to escape therefrom, and which, afterwards, opens said isolation valve to operate said equalizing means, in response to a low-pressure signal indicative of low pressure in said pressure vessel. 2. A reactor containment facility as claimed in claim 1, wherein said suppression chamber is divided into a first chamber containing said suppression-pool water and a second chamber, said second wet well being defined by said second chamber. 3. A reactor containment facility as claimed in claim 1, further comprising: 4. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said rector pressure vessel is arranged; a containment vessel housing said dry well; means defining a suppression chamber holding a suppression-pool water and forming above the suppression-pool water a first wet well; and a passage means allowing said dry well to communicate with said suppression-pool water; wherein said facility further comprises: 5. A reactor containment facility as claimed in claim 4, further comprising: 6. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said reactor pressure vessel is arranged; means defining a suppression chamber holding a suppression-pool water and forming, in the space above the suppression-pool water, a wet well; a plurality of vent pipes allowing said dry well to communicate with said suppression-pool water of said suppression chamber in contact therewith to provide a containment vessel which houses said drywell and said suppression chamber; and an outer peripheral pool containing a cooling water in contact with the outer peripheral surface of said steel wall; wherein said facility further comprises: 7. A reactor containment facility as claimed in claim 6, further comprising: 8. A reactor containment facility as claimed in claim 6, wherein said steel wall further surrounds said first and second spaces, said cooling means including an air passage formed outside said steel wall. 9. A reactor containment facility as claimed in claim 6, wherein said cooling means includes a recess region formed by extending downwards the outer peripheral section of said second space to be in thermal contact with the cooling water of said outer peripheral pool. 10. A reactor containment facility as claimed in claim 6, further comprising: 11. A reactor containment facility as claimed in claim 6, further comprising: 12. A reactor containment facility comprising: a reactor pressure vessel containing a core; a drywell in which said reactor pressure vessel is arranged; a containment vessel housing said dry well; means defining a suppression chamber holding a suppression-pool water and forming, in the space above the suppression-pool water, a wet well; and passage means allowing said dry well to communicate with said suppression-pool water; wherein said facility further comprises: 13. A reactor containment facility as claimed in 12, further comprising: 14. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said reactor pressure vessel is arranged; means defining a suppression chamber holding a suppression-pool water and forming, in the space above the suppression-pool water, a wet well; a plurality of vent pipes allowing said dry well to communicate with said suppression-pool water; a steel wall which surrounds at least the suppression-pool water of said suppression chamber in contact therewith to provide a containment vessel which houses said dry well and said suppression chamber; and an outer peripheral pool containing a cooling water in contact with the outer peripheral surface of said steel wall; wherein said facility further comprises: 15. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said reactor pressure vessel is arranged; a containment vessel housing said dry well; means defining a suppression chamber holding a suppression-pool water and forming, in the space above the suppression-pool water a wet well; and passage means allowing said dry well to communicate with said suppression-pool water; wherein said facility further comprises: 16. A reactor containment facility as claimed in claim 15, further comprising: 17. A reactor containment facility comprising: a reactor pressure vessel containing a core; a drywell in which said reactor pressure vessel is arranged; a containment vessel housing said dry well; means defining a suppression chamber holding a suppression-pool water and forming, in the space above the suppression-pool water, a wet well; and passage means allowing said dry well to communicate with said suppression-pool water; wherein said facility further comprises: 18. A reactor containment facility as claimed in claim 17, further comprising: 19. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said reactor pressure vessel is arranged; means defining a suppression chamber holding a suppression-pool water and forming, in the space above the suppression-pool water, a wet well; a plurality of vent pipes allowing said dry well to communicate with said suppression-pool water; a steel wall which surrounds at least the suppression-pool water of said suppression chamber in contact therewith to provide a containment vessel which houses said dry well and said suppression chamber; and an outer peripheral pool containing a cooling water in contact with the outer peripheral surface of said steel wall; wherein said facility further comprises: 20. A reactor containment facility as claimed in claim 19, wherein the difference in height between said upper opening and the outlets of said vent pipes is larger than the difference in height between the outlets of said vent pipes and said lower opening. 21. A reactor containment facility as claimed in claim 19, wherein said convection promoting pipe includes upper and lower header pipes respectively arranged at upper and lower positions in said outer peripheral pool and a plurality of heat transfer pipes allowing said upper and lower header pipes to communicate with each other. 22. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said reactor pressure vessel is arranged; means defining a first suppression chamber holding a suppression-pool water and forming, in the space above the same, a wet well; a plurality of first vent pipes allowing said dry well to communicate with said suppression-pool water; a steel wall which surrounds at least the suppression-pool water of said suppression chamber contact therewith to provide a containment vessel which houses said dry well and said first suppression chamber; an outer peripheral pool containing a cooling water in contact with the outer peripheral surface of said steel wall; and an emergency core cooling system adapted to cool the core by supplying a water into said pressure vessel at the time of a loss-of-coolant accident; 23. A reactor containment facility as claimed in claim 22, wherein the amount of coolant stored in a water source of said emergency core cooling system is set such as to be substantially equal to the sum of the amount of coolant needed for raising the water level in the dry well up to said core submerging level and the amount of coolant required for making the water level of said suppression-pool water equal to said core submerging level. 24. A reactor containment facility as claimed in claim 22, wherein a structure for reducing the amount of coolant when the water level in said dry well has been raised to said core submerging level is provided in that portion of the space in said dry well which is below said core submerging level. 25. A reactor containment facility as claimed in claim 22, further comprising means defining a second suppression chamber situated above said first suppression chamber and including a suppression pool containing pool water, said suppression pool communicating with said dry well through a plurality of second vent pipes, said second suppression chamber being connected with said reactor pressure vessel through a line equipped with a valve for allowing the pool water of the second suppression chamber to be used as a water source for said emergency core cooling system. 26. A reactor containment facility as claimed in claim 25, wherein the amount of coolant of said second suppression chamber is set such as to be substantially equal to the sum of the amount of coolant needed for raising the water level in the dry well up to said core submerging level and the amount of coolant required for making the water level of said suppression-pool water equal to said core submerging level. 27. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said reactor pressure vessel is arranged; a first suppression chamber holding a suppression-pool water and forming, in the space above the suppression-pool water, a wet well; a plurality of first vent pipes allowing said dry well to communicate with said pool water; a steel wall which surrounds at least the suppression-pool water of said suppression chamber in contact therewith to provide a containment vessel which houses said dry well and said first suppression chamber; and an outer peripheral pool containing cooling water in contact with the outer peripheral surface of said steel wall; wherein said facility further comprises: 28. A reactor containment facility as claimed in claim 27, wherein the height of the dry-well-side openings of said first vent pipes is set at a level substantially equal to a core submerging level which is that water-level in the dry well at which submergence cooling of said core can be effected with the water in the dry well, having overflowed from said reactor pressure vessel and accumulated in the dry well at the time of a loss-of-coolant accident. 29. A reactor containment facility as claimed in claim 28, wherein the amount of coolant of said second suppression chamber is set such as to be substantially equal to the sum of the amount of coolant needed for raising the water level in the dry well up to said core submerging level and the amount of coolant required for making the water level of said suppression-pool water equal to said core submerging level. 30. A reactor containment facility comprising: a reactor pressure vessel containing a core; a dry well in which said reactor pressure vessel is arranged; mean defining a suppression chamber holding a suppression-pool water and forming, in the space above the suppression-pool water, a wet well; a plurality of vent pipes allowing said dry well to communicate with said suppression-pool water; a steel wall which surrounds at least the suppression-pool water of said suppression chamber in contact therewith to provide a containment vessel which houses said dry well and said suppression chamber; an outer peripheral pool containing cooling water in contact with the outer peripheral surface of said steel wall; and an emergency core cooling system adapted to cool the core by supplying water into said pressure vessel at the time of a loss-of-coolant accident; wherein said facility further comprises: 31. A reactor containment facility as claimed in claim 30, wherein the opening in said suppression-pool water of said equalizing means is near the water surface of the pool water. 32. A reactor containment facility as claimed in claim 30, wherein said equalizing means includes: a first equalizing line connecting said suppression-pool water with said pressure vessel; a second equalizing line branching off from said first equalizing line and opening at a position below said dry well; an isolation valve provided between a point at which said first equalizing line is connected with said pressure vessel and a branching point at which said second equalizing line branches off; and check valves respectively provided in said first and second equalizing lines, said check valve in the first equalizing line being positioned between said branching point and the point at which the first equalizing line is connected with said suppression-pool water. 33. A reactor containment facility as claimed in claim 32, wherein the opening in said suppression-pool water of said first equalizing line is near the water surface of the suppression-pool water. 34. A reactor containment facility as claimed in claim 32, further comprising: 35. A reactor containment facility as claimed in claim 32, wherein said isolation valve comprises a blasting valve or an electrically operated valve. 36. A reactor containment facility as claimed in claim 32, wherein said first and second equalizing lines are respectively equipped with each two of said isolation valves and check valves arranged in parallel. |
description | The present invention relates to a positioning apparatus and an atmosphere substituting method applicable to a semiconductor exposure apparatus and the like, and an exposure apparatus and a device manufacturing method capable of using the positioning method and atmosphere substituting method. In recent years, an exposure technique using a synchrotron radiation beam is under development to cope with the shrinkage in feature size of semiconductor device. When a synchrotron radiation beam is used, attenuation of X-rays in air becomes a problem. In order to prevent this problem, for example, according to a method proposed in Japanese Patent Laid-Open No. 2-156625, an exposure positioning mechanism is set in a chamber having an He atmosphere with less X-ray attenuation, and He is used also as the working fluid for a static pressure type bearing used in the exposure positioning mechanism. Conventionally, in an exposure apparatus having such a positioning mechanism, if the apparatus is not to be operated for a long period of time, the exposure apparatus is turned off with the chamber being filled with nitrogen at an atmospheric pressure, so impure air will not enter the chamber from the outside. Also, when maintenance for machines in the chamber is to be performed, the chamber is filled with nitrogen, and then the chamber is partly opened to perform maintenance. In this manner, when the operation check of the wafer stage is to be performed with the chamber being filled with nitrogen or open to the atmosphere, nitrogen or dry air is used for a static pressure type bearing since exposure is not performed and in order to avoid consumption of expensive He. With this prior art, after the operation of the wafer stage is checked, when exhausting nitrogen in the chamber to vacuum and substituting He for nitrogen to turn on the exposure apparatus, nitrogen or dry air left in the static pressure type bearing of the positioning mechanism gradually leaks into the chamber. Accordingly, it takes a long period of time for the He impurity in the exposure atmosphere in the chamber to reach a level at which exposure is possible. The present invention has been made in view of the problem of the prior art, and has as its object to shorten a time required for the gas purity to reach a level at which exposure is possible in a positioning apparatus, atmosphere substituting method, exposure apparatus, and device manufacturing method using such a chamber, when substituting a gas in the chamber. In order to achieve the above object, according to the present invention, a first positioning apparatus used in a chamber and using a static pressure gas bearing is characterized by comprising second gas supply means for supplying a second gas to the static pressure gas bearing when substituting a gas in the chamber from a first gas to the second gas. In this arrangement, when substituting the gas in the chamber from the first gas to the second gas, if the second gas is supplied to the static pressure gas bearing, the first gas remaining in the static pressure gas bearing is eliminated. Hence, unlike in the prior art, the first gas remaining in the static pressure gas bearing does not leak over a long period of time. As a result, the second gas can reach a necessary purity at which, e.g., exposure is possible, faster, and substitution to the second gas is performed quickly. According to the present invention, an atmosphere substituting method of substituting a gas in a chamber incorporating a positioning apparatus using a static pressure gas bearing from a first gas to a second gas is characterized by comprising the second gas supply step of supplying the second gas to the static pressure gas bearing in substituting the air in the chamber. With this arrangement, substitution to the second gas is similarly performed quickly. According to the present invention, a second positioning apparatus including substituting means for substituting a gas in a chamber by exhausting a first gas from the chamber and introducing a second gas thereto and positioning means used in the chamber and using a static pressure gas bearing is characterized by comprising bearing exhaust means for exhausting the gas from the static pressure gas bearing through a pipe connected to the static pressure gas bearing. In this arrangement, when exhausting the first gas in the chamber and introducing the second gas, if the first gas is exhausted through the pipe connected to the static pressure gas bearing, the first gas remaining in the static pressure gas bearing is exhausted. Hence, unlike in the prior art, the first gas remaining in the static pressure gas bearing does not leak over a long period of time. As a result, the second gas can reach a necessary purity at which, e.g., exposure is possible, faster, and substitution to the second gas is performed quickly. If exhaust of the first gas and exhaust of the static pressure gas bearing are performed simultaneously, a time required for exhausting the first gas is shortened, and substitution to the second gas is performed more quickly. According to the present invention, an exposure apparatus including exposure means for exposing a target exposure substrate placed in a chamber and positioning means for positioning the target exposure substrate, the positioning means using a static pressure gas bearing and using as a working fluid the same type of gas as that of an atmosphere in the chamber, is characterized in that the positioning means comprises the above first and second positioning apparatuses arranged in the chamber. In this arrangement, after the operation check of the positioning means is performed in the first gas atmosphere, when substituting the second gas for the first gas in order to start actual exposure, the second gas can quickly reach a purity, at which exposure is possible, with the first or second positioning apparatus of the present invention. According to the present invention, a first device manufacturing method including the atmosphere substituting step of substituting a gas in a chamber incorporating a positioning apparatus using a static pressure gas bearing from a first gas to a second gas and the exposure step of positioning a target exposure substrate with the positioning apparatus and exposing a predetermined pattern after the atmosphere substituting step is characterized by comprising the second gas supply step of supplying the second gas to the static pressure gas bearing in substituting the gas in the atmosphere substituting step. Also, in this case, when substituting the second gas for the first gas, the second gas can quickly reach a purity at which exposure is possible. As a result, devices can be efficiently manufactured. According to the present invention, a second device manufacturing step including the atmosphere substituting step of substituting a gas in a chamber by exhausting a first gas from a chamber incorporating a positioning apparatus using a static pressure gas bearing and introducing a second gas thereto and the exposure step of positioning a target exposure substrate with the positioning apparatus and exposing a predetermined pattern after the atmosphere substituting step is characterized by comprising the bearing exhaust step of exhausting the gas of the static pressure gas bearing through a pipe connected thereto simultaneously with exhausting the gas in the substituting step. In this case as well, the second gas can quickly reach a purity at which exposure is possible, and devices can be efficiently manufactured. Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. In preferred embodiments of the present invention, when substituting the gas in the chamber from the first gas to the second gas, the gas in the chamber is substituted. The second gas is supplied to a static pressure gas bearing before a start of, simultaneously with, or after a start of substituting the gas. Note that the second gas is He, that the chamber is of an exposure apparatus, and that the exposure apparatus is an X-ray exposure apparatus employing a synchrotron radiation beam as an exposure beam. Further, the exposure apparatus is an exposure apparatus employing an F2 laser beam as an exposure beam. Sometimes, substitution from the static pressure gas bearing is performed after the second gas is supplied to the static pressure gas bearing. The embodiments of the present invention will be described in more detail. FIG. 1 is a view showing the arrangement of an exposure apparatus according to the first embodiment of the present invention. Referring to FIG. 1, reference numeral 1 denotes a mask; 2, a mask surface plate for supporting the mask 1; 3, a wafer; 4a, a wafer chuck; and 4b, a fine movement stage. The wafer 3 is drawn by vacuum suction and held with the mask 1, mask surface plate 2, wafer chuck 4a, and fine movement stage 4b. Reference numeral 5 denotes a coarse movement stage on which the fine movement stage 4b is set. The fine movement stage 4b is movable finely on the coarse movement stage 5. The coarse movement stage is movable in a long stroke. Reference numeral 6 schematically shows a gas bearing which supports and guides the coarse movement stage 5. The gas bearing 6 will be called an LHB hereinafter, which is an acronym for a linear He bearing. Referring to FIG. 1, LHB 6 is mounted on the side of a stage surface plate 7. However, the invention is not limited to this. For example, LHB 6 may be mounted on the coarse movement stage to be opposed against a stage surface plate 7 discussed below. Reference numeral 7 denotes a stage surface plate for supporting a wafer stage comprised of the fine movement stage 4b, coarse movement stage 5, and LHB 6 within a vertical plane. Referring to FIG. 1, the stage surface plate 7 supports the wafer stage within the vertical plane. However, the invention is not limited to this. For example, the stage surface plate 7 may support the wafer stage within the horizontal plane. Reference numeral 8 denotes a frame for supporting the mask surface plate 2 and stage surface plate 7; 9, support members 9 for supporting the frame 8 on a clean room floor 10; 11, support members for supporting the clean room floor 10 on a factory building floor 12; 13, a chamber for accommodating the exposure apparatus; and 14, a beryllium window for dividing a beam line 15, which is set at high vacuum during exposure from the chamber 13, and transmitting a synchrotron radiation beam through it. Reference numeral 16 denotes a bypass line of the beryllium window 14 having a bypass valve 17; 18, a gate valve for disconnecting the beam line 15 from a beam line 19, which is connected to a synchrotron located upstream and always set at a high vacuum; 20, a high vacuum gauge; 21, a differential pressure sensor; 22, an absolute pressure sensor; and 24 and 25, vacuum exhaust pumps for evacuating the beam line 15 through a vacuum exhaust valve 23 to maintain it at a high vacuum. Reference numeral 26 denotes an He supply unit for introducing He into the chamber 13 through an He supply valve 27; 28, a nitrogen supply unit for introducing nitrogen into the chamber 13 through a nitrogen supply valve 29; and 30, an He circulating unit 30 for compressing and purifying He in the chamber 13, which is recovered by an He recovering line 33 through an He recovering valve 34, adjusting it to a predetermined temperature and pressure, and returning it to the chamber 13 through a low-pressure He supply line 31 including a low-pressure He supply valve 32. Reference numeral 35 denotes a high-pressure He supply line; for supplying high-pressure He generated by the He circulating unit 30 to the LHB 6 through a high-pressure He supply valve 36; 37, a nitrogen supply unit for supplying nitrogen, in place of He, to the LHB 6 through a nitrogen supply valve 38 when operating the wafer stage in an atmosphere; 39, a vacuum exhaust pump 39 for evacuating the chamber 13 through a vacuum exhaust valve 40. The vacuum exhaust pump 39 is set in the chamber 13 having an exhausted atmosphere. Reference numeral 41 denotes a valve for releasing the pressure in the chamber 13 to the atmosphere. FIG. 2 is a flow chart showing a process used when checking, in the exposure apparatus described above, the operation of the wafer stage in an He atmosphere set at an atmospheric pressure. In this process, the respective portions of the apparatus are operated by a controller 50. The controller 50 controls the wafer stage, the vacuum exhaust pumps 24 and 25, the He supply unit 26, the nitrogen supply unit 28, the He circulating unit 30, the nitrogen supply unit 37, the vacuum exhaust pump 39 and valve controller 51. Further, the controller 50 may control the above units on the basis of outputs from the sensors 21 and 22. The valve controller 51 controls an operation of opening and shutting the above valves, an amount of throttle of the valve when the valve is a variable valve, and the like. As shown in FIG. 2, when this process is started, nitrogen supply to the LHB 6 is stopped by closing the nitrogen supply valve 38 (step S1). The high-pressure He supply valve 36 is opened to start He supply to the LHB 6 (step S2). The low-pressure He supply valve 32 and He recovering valve 34 are opened, and the operation of the He circulating unit 30 is started, to start He circulation in the chamber 13 (step S3). Hence, impurity gases remaining in the LHB 6 and high-pressure He supply line 35 are cleared away, and nitrogen in the chamber 13 can be substituted by He quickly. The process of step S3 can be performed simultaneously with step S2. FIG. 3 is a flow chart showing a process in an exposure apparatus according to the second embodiment of the present invention, which is performed when the exposure apparatus is to be turned on again after maintenance for machines in the chamber is ended or after long-term operation is stopped. The arrangement of this exposure apparatus is identical to that shown in FIG. 1. When the process is started, as shown in FIG. 3, if the wafer stage is used, a nitrogen supply valve 38 is closed to stop nitrogen supply to an LHB 6 (step S11). At this point in time, all the valves are close except a bypass valve 17 of a beryllium window 14 (and an atmosphere release valve 41 when a chamber 13 is opened to the atmosphere). A high-pressure He supply valve 36 is open for a predetermined period of time to supply He to the LHB 6 (step S12). Then, (if the atmosphere release valve 41 is open, after it is closed, and) a vacuum exhaust valve 40 is opened to start evacuating the chamber 13. Since the bypass valve 17 is open, the chamber 13 and a beam line 15 communicate with each other, so that they are evacuated simultaneously. When an absolute pressure sensor 22 confirms that the chamber 13 is evacuated to a predetermined pressure, the vacuum exhaust valve 40 is closed (step S13). Subsequently, the bypass valve 17 is closed (step S14). An exhaust valve 23 for the beam line 15 is opened, the beam line 15 is set at a higher vacuum by two vacuum exhaust pumps 24 and 25 (e.g., a turbo molecular pump and a dry pump) (step S15). Along with this, an He supply valve 27 is opened to introduce He into the chamber 13. He is filled into the chamber 13 until the pressure in the chamber 13 indicated by the absolute pressure sensor 22 reaches a predetermined pressure. After that, the He supply valve 27 is closed (step S16). A low-pressure He supply valve 32 and He recovering valve 34 are opened to start operation of an He circulating unit 30 (step S17). At this time point, the wafer stage can be driven. Thus, the high-pressure He supply valve 36 is opened to start He supply to the LHB 6 (step S18), and the wafer stage is initialized in accordance with a predetermined procedure. Simultaneously, a wafer transfer system and mask transfer system (not shown) are also initialized. When a high vacuum gauge 20 confirms that the beam line 15 is evacuated to the same vacuum degree as that of a beam line 19, a gate valve 18 can be opened to perform exposure. FIG. 9 shows a process similar to that of the prior art arrangement. In FIG. 9, steps where the same processes as those of the embodiment of FIG. 3 are performed are denoted by the same step numbers as in FIG. 3. As is seen from FIGS. 3 and 9, the second embodiment is different from that of the prior art in that step S12 is added to it. According to this embodiment, in step S12, the high-pressure He supply valve 36 is open for a predetermined period of time to supply He to the LHB 6. Therefore, impurity gases remaining in the LHB 6 and high-pressure He supply line 35 can be cleared away and exhausted outside the chamber 13 in the following step S13. As a result, an He impurity degree at which exposure is possible can be reached quickly. FIG. 4 is a flow chart showing a process in an exposure apparatus according to the third embodiment of the present invention. The process of FIG. 4 is different from that of FIG. 3 in that, while steps S12 and S13 are performed separately in FIG. 3, they are performed simultaneously in the third embodiment. More specifically, after nitrogen supply to an LHB 6 is stopped (step S11), as shown in FIG. 4, a vacuum exhaust valve 40 is opened to start evacuating a chamber 13 (step S13-1), and He is supplied to the LHB 6 for a predetermined period of time (step S12). After the interior of the chamber 13 reaches a predetermined vacuum degree, the vacuum exhaust valve 40 is closed, and evacuation of the chamber 13 is ended (step S13-2). The operations from step S14 are identical to those of FIG. 3. According to this embodiment, He is supplied to a high-pressure He supply line 35 and the LHB 6 while the chamber 13 is being evacuated. Therefore, the high-pressure He supply line 35 and LHB 6 can be rinsed to exhaust residual nitrogen. FIG. 5 is a view showing the arrangement of an exposure apparatus according to the fourth embodiment of the present invention. Referring to FIG. 5, reference numeral 42 denotes an exhaust pump for evacuating a high-pressure He supply line 35 through a high-pressure He supply line exhaust valve 43. Except for this, the arrangement of FIG. 5 is the same as that of FIG. 1, and elements having the same functions as those shown in FIG. 1 are denoted by the same reference numerals as in FIG. 1. FIG. 6 is a flow chart showing a process of this exposure apparatus. In FIG. 6, the same process steps having the same contents as those of FIG. 3 are denoted by the same step numbers as in FIG. 3. In this process, steps S11 to S17 are the same as steps S11 to S17 of FIG. 3 except for step S12. When a chamber 13 is completely filled with He (step S16) and the operation of an He circulating unit 30 is started (step S17), a high-pressure He supply valve 36 is opened to supply high-pressure He to an LHB 6 for a predetermined period of time, and the high-pressure He supply valve 36 is closed (step S12). A high-pressure He supply line exhaust valve 43 is opened, the LHB 6 and high-pressure He supply line 35 are evacuated by the exhaust pump 42 for a predetermined period of time, and thereafter the valve 43 is closed (step S19). Hence, nitrogen remaining in the LHB 6 and high-pressure He supply line 35 is exhausted. Then, the high-pressure He supply valve 36 is opened again to start He supply to the LHB 6 (step S18). With the above process, remaining nitrogen does not leak from the LHB 6, and a time required for setting He in the chamber 13 to a predetermined purity is shortened greatly. FIG. 7 is a flow chart showing a process in an exposure apparatus according to the fifth embodiment of the present invention. The arrangement of this exposure apparatus is identical to that shown in FIG. 5. In FIG. 7, the processing steps having the same contents as those of FIG. 6 are denoted by the same step numbers as in FIG. 6. In this process, after nitrogen supply to an LHB 6 is stopped (step S11), in step S13a, chamber evacuation (step S13) and LHB evacuation (step S19) of FIG. 6 are performed simultaneously. More specifically, a vacuum exhaust valve 40 and high-pressure He supply line exhaust valve 43 are opened simultaneously, and the chamber 13 is evacuated by two vacuum exhaust pumps 39 and 42. According to this embodiment, since removal of impurity gas remaining in the LHB 6 and in a high-pressure He supply line 35, and evacuation of a chamber 13 are performed simultaneously, and since the exhaust capability is increased by the two pumps, a time required for setting the interior in the chamber 13 to an He atmosphere can be shortened greatly. FIG. 8 is a flow chart showing a process in an exposure apparatus according to the sixth embodiment of the present invention. The arrangement of this exposure apparatus is identical to that shown in FIG. 5. In FIG. 8, the processing steps having the same contents as those of FIG. 7 are denoted by the same step numbers as in FIG. 7. As shown in FIG. 8, after nitrogen supply to an LHB 6 is stopped (step S11), a high-pressure He supply valve 36 is open for a predetermined period of time to supply He to the LHB 6 (step 12). Then, two vacuum exhaust valves 40 and 43 are opened simultaneously to evacuate a chamber 13 with corresponding two vacuum exhaust pumps 39 and 42 (step S13a). The operations from steps S14 are identical to those of FIG. 3. According to this embodiment, because of the process of step S13a, a time required for evacuating the chamber 13 can be shortened. As a time required for He to reach a predetermined purity, after the chamber 13 is filled with He, is also shortened, a time required after the apparatus is turned on until exposure becomes possible can be shortened greatly. An embodiment of a device manufacturing method utilizing the exposure apparatus described above will be described. FIG. 10 shows the flow of the manufacture of a microdevice (e.g., a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin film magnetic head, a micromachine, or the like). In step 1 (circuit design), pattern design of the device is performed. In step 2 (mask fabrication), a mask formed with the designed pattern is fabricated. In step 3 (wafer manufacture), a wafer is manufactured by using a material such as silicon or glass. Step 4 (wafer process) is called a pre-process where the mask and wafer prepared in the above manner are used to form an actual circuit on the wafer in accordance with lithography. Step 5 (assembly) is called a post-process where the wafer fabricated in step 4 is formed into semiconductor chips. Step 5 includes an assembly step (dicing, bonding), a packaging step (chip encapsulation), and the like. In step 6 (inspection), inspection such as an operation confirmation test, a durability test, and the like of the semiconductor device manufactured in step 5 is performed. The semiconductor device is completed through these steps, and is shipped (step 7). FIG. 11 shows a detailed flow of the above wafer process (step 4). In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the wafer surface. In step 13 (electrode formation), electrodes are formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted in the wafer. In step 15 (resist process), a resist is applied to the wafer. In step 16 (exposure), the circuit pattern of the mask is printed on each of a plurality of shot regions of the wafer in alignment, and exposed by the exposure apparatus or exposure method described above. In step 17 (development), the exposed wafer is developed. In step 18 (etching), a portion of the wafer other than the developed resist image is removed. In step 19 (resist removal), the resist which has become unnecessary after etching is removed. These steps are repeatedly performed to form circuit patterns on the wafer in a multiple manner. When the production method of this embodiment is used, a large-size device, which is conventionally difficult to manufactures can be manufactured at a low cost. As has been described above, according to the present invention, when substituting the gas in the chamber from the first gas to the second gas, for example, the second gas is supplied to a static pressure gas bearing before a start of, simultaneously with, or after a start of exhausting the gas from the chamber. Therefore, the first gas remaining in the static pressure gas bearing can be exhausted easily, so that a time required for the second gas to reach a predetermined impurity can be shortened. Since evacuation of the static pressure gas bearing is performed simultaneously with vacuum exhaust of the chamber, a time required since the first gas remaining in the static pressure gas bearing is exhausted until the second gas reaches a predetermined impurity can be shortened, and a time required for evacuating the chamber can also be shortened. As a result, a time required for substituting the second gas for the first gas can be further shortened. As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims. |
|
claims | 1. A fuel assembly, comprising:a fuel element case for a boiling water reactor;a spacer for laterally holding a bundle of fuel rods, said fuel element case surrounding said spacer, said spacer including two inner edge webs and two outer edge webs, said two inner edge webs being adjacent an interspace for a control element;an inner gap formed between said two inner web edges and said fuel element case, said inner gap extending substantially along said two inner web edges;an outer gap formed between said two outer web edges and said fuel element case, said outer gap extending substantially along said outer web edges;spring elements extending away from said two inner edge webs and into said inner gap, said spring elements supported against said fuel element case, said spring elements holding said spacer held in an off-center position such that said outer gap is narrower than said inner gap; andstuds projecting from said outer edge webs and into said outer gap, said studs ensuring that said outer gap maintains a minimum dimension. 2. The fuel assembly according to claim 1 wherein said spring elements include a first spring element and a second spring element, and said inner gap extends at least from said first spring element to said second spring element. 3. The fuel assembly according to claim 1, wherein said spacer has a corner, and at least one of said spring elements is disposed adjacent said corner of said spacer. 4. The fuel assembly according to claim 1, wherein said fuel element case has inner sides, and said spring elements press said spacer away from said inner sides of said fuel element case with a force extending transversely with respect to a corresponding one of said inner edge webs. 5. The fuel assembly according to claim 1, further comprising a control element disposed in the interspace. 6. The fuel assembly according to claim 1, wherein each of said inner web edges has a total length, and said inner gap extends along said total length of said inner web edges. 7. A core cell for a boiling water reactor, the core cell having four fuel elements, and a control element disposed between said four fuel elements, each one of said four fuel elements comprising:a fuel element case for a boiling water reactor;a spacer for laterally holding a bundle of fuel rods, said fuel element case surrounding said spacer, said spacer including two inner edge webs and two outer edge webs, said two inner edge webs being adjacent the control element, said two outer edge webs being remote from the control element;an inner gap formed between said two inner web edges and said fuel element case, said inner gap extending substantially along said two inner web edges;an outer gap formed between said two outer web edges and said fuel element case, said outer gap extending substantially along said outer web edges;spring elements extending away from said two inner edge webs and into said inner gap, said spring elements supported against said fuel element case, said spring elements holding said spacer held in an off-center position such that said outer gap is narrower than said inner gap; andstuds projecting from said outer edge webs and into said outer gap, said studs ensuring that said outer gap maintains a minimum dimension. |
|
claims | 1. A beam tracking system for a scanning-probe type atomic force microscope, comprising:a base to carry a sample to be scanned;a cantilevered probe to scan said sample in order to obtain topographic information representing a surface of said sample;a laser source to generate a laser beam;an optical module to align and introduce said laser beam to said probe;a feedback module, comprising a photo sensing device, to receive a reflected laser beam reflected from said probe and to introduce said reflected laser beam to said photo sensing device;a probe driving device to drive said probe to scan three-dimensionally;an approach mechanism to drive said probe and to adjust the relative position of said probe and said sample; andan information processing module to pick up signals contained in said reflected laser beam as sensed by said photo sensing device and to convert said signals into topographic signals representing the surface of said sample;wherein said optical module comprises an objective lens to focus said laser beam;said probe is located approximately at the focal point of said objective lens;and said laser source, said optical module, said feedback module and said probe are driven by said approach mechanism to move in synchronization. 2. The beam tracking system for a scanning-probe type atomic force microscope according to claim 1, further comprising a correction lens positioned above said photo sensing device to linearly compensate said reflected laser beam. 3. The beam tracking system for a scanning-probe type atomic force microscope according to claim 2, wherein said information processing module further comprises a false deflection calculation means to calculate false deflection (Δνρ) of said probe according to the to the following equation: Δ υ P = L 3 f Δ X B ( 3 ) wherein L is length of cantilever of said probe, f is focal length of said objective lens and ΔνB is shift distance of probe during scanning. 4. The beam tracking system for a scanning-probe type atomic force microscope according to claim 3, wherein said probe driving device comprises a vertical scanning driver and a horizontal scanning driver. 5. The beam tracking system for a scanning-probe type atomic force microscope according to claim 3, wherein the relative position between said probe and said objective lens is maintained constant by a lens holder. 6. The beam tracking system for a scanning-probe type atomic force microscope according to claim 2, wherein said correction lens locates above said photo sensing device at a distance of fc/C, wherein fc is the focal length of said correction lens and C is a constant. 7. The beam tracking system for a scanning-probe type atomic force microscope according to claim 1, wherein said information processing module further comprises a false deflection calculation means to calculate false deflection (Δνρ) of said probe according to the following equation: Δ υ P = L 3 f Δ X B ( 3 ) wherein L is length of cantilever of said probe, f is focal length of said objective lens and ΔXB is shift distance of probe during scanning. 8. The beam tracking system for a scanning-probe type atomic force microscope according to claim 7, wherein said probe driving device comprises a vertical scanning driver and a horizontal scanning driver. 9. The beam tracking system for a scanning-probe type atomic force microscope according to claim 7, wherein the relative position between said probe and said objective lens is maintained constant by a lens holder. |
|
claims | 1. Lead substitute material for radiation protection purposes in the energy range of an X-ray tube with a voltage of 60–125 kV, characterised in that the lead substitute material comprises Sn, Bi and optionally W, or compounds of these metals, and the composition of the lead substitute material is a function of the nominal lead equivalent value. 2. Lead substitute material according to claim 1, characterised in that it comprises10–20% by weight of a matrix material,50–75% by weight of Sn, or Sn compounds, and20–35% by weight of Bi, or Bi compounds,for nominal lead equivalent values of up to 0.15 mm, and40–60% by weight of Sn, or Sn compounds,15–30% by weight of Bi, or Bi compounds, and0–30% by weight of W, or W, compoundsfor nominal lead equivalent values of 0.15–0.60 mm. 3. Lead substitute material according to claim 2, characterised in that it comprises10–20% by weight of a matrix material,52–70% by weight of Sn, or Sn compounds, and21–32% by weight of Bi, or Bi compounds,for nominal lead equivalent values of up to 0.15 mm, and42–57% by weight of Sn, or Sn compounds,15–30% by weight of Bi, or Bi compounds, and5–27% by weight of W, or W compounds,for nominal lead equivalent values of 0.15–0.60 mm. 4. Lead substitute material according to any one of the preceding claims, characterised in that it comprises a structure made up of layers with differing composition. 5. Lead substitute material according to claim 4, characterised in that it comprises a structure made up of at least two layers with differing composition, which are separate or connected together, the layer further away from the body comprising predominantly Sn and the layer(s) near the body comprising predominantly Bi and optionally W. |
|
041522044 | abstract | A device for controlling the power output of a core reactor and for turning ff the same, in which that portion of the device which contains absorber material comprises a first component in the form of absorber rods for turning off the core reactor which absorber rods are movable into the filling provided in the reflector of the reactor. That portion of the device which contains absorber material furthermore comprises a second component in the form of plates which serve for controlling the output of the core reactor and are displaceable in that chamber portion of the reflector which is defined by the top surface of the filling and by the reflector wall above the filling. |
description | This is a Continuation-in-Part of Application No. PCT/IL2015/050135 filed Feb. 5, 2015, which claims the benefit of U.S. Provisional Application No. 61/936,402 filed Feb. 6, 2014. The disclosure of the prior applications is hereby incorporated by reference herein in its entirety. This invention was made with government support under W911NF-13-1-0485 awarded by US Army RDECOM. The US government has certain rights in the invention. The invention is in the field of radiation imaging and relates to imaging techniques utilizing pinhole arrays. References considered to be relevant as background to the presently disclosed subject matter are listed below: [1] R. A. Vogel, D. Kirch, M. Lefree, and P. Steele, “A New Method of Multiplanar Emission Tomography Using a Seven Pinhole Collimator and an Auger Scintillation Camera,” J. Nucl. Med. 19 (6), 648-654 (1978). [2] N. U. Schramm, G. Ebel, U. Engeland, T. Schurrat, M. Bèhè and T. M. Behr, “High-Resolution SPECT Using Multipinhole Collimation,” IEEE Trans. Nucl. Sci. 50 (3), 315-320 (2003). [3] R. H. Dicke, “Scatter-hole cameras for x-rays and gamma rays,” Astrophys. J. 153, L101-L106 (1968). [4] L. T. Chang, B. Macdonald, V. Perez-Mendez, L. Shiraishi, “Coded Aperture Imaging of Gamma-Rays Using Multiple Pinhole Arrays and Multiwire Proportional Chamber Detector,” IEEE Trans. Nucl. Sci. NS-22, 374-378 (1975). [5] E. E. Fenimore and T. M. Cannon, “Coded aperture imaging: predicted performance of uniformly redundant arrays,” Appl. Opt. 17 (2), 3562-3570 (1978). [6] Mu Z, Hong B, Li S Liu Y H, “A noval three-dimensional image reconstruction method for near-field coded aperture single photon emission computerized tomography”. Med Phys. 2009:36; 1533-1542. [7] Chen Y W, Yamanaka M, Miyanaga N, Yamanaka T, Nakai S, Yamanaka C, “Three-dimensional reconstructions of laser-irradiated targets using URA coded aperture cameras”. Opt Commun 1989: 71; 249-255. [8] Koral K F, Rogers W L, Knoll G F, “Digital tomographic imaging with time-modulated pseudorandom coded aperture and anger camera”. J Nucl Med. 1974: 16; 402-413 Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter. It is known for many years to use pinhole optics in imaging techniques. Light rays propagating from a region of interest on one side of a mask and passing through a small pinhole of the mask expanding on the other side of the mask and may be used to generate an image of the region of interest. Pinhole optics may provide various advantages over the common use of lens systems, such as reducing linear distortion, providing virtually infinite depth of focus and wide angular field of view. Additionally, pinhole imaging is useful for non-optical radiation frequencies, such as X-rays, Gamma radiation and basically any wave- or particle-like phenomena. Imaging characteristics of a pinhole generally depend inter alia on the cross-sectional dimension (diameter) of the pinhole. For a large pinhole, the resulting image is typically in the form of a uniform disc being a geometrical shadow of the pinhole. For a very small pinhole, the resulting image is a Fresnel or Fraunhofer diffraction pattern. Intermediate pinhole sizes can provide imaging of a scene. An optimal pinhole diameter can be determined as a compromise between the large spot image of the large pinhole and the wide diffraction pattern of the small pinhole size. Within the image generating range of pinhole sizes there is a tradeoff between image resolution and light intensity. A larger pinhole transmits relatively higher radiation intensity, i.e. higher number of photons per time, but results in lower image resolution. On the other hand, the smaller pinholes provide high resolution image but with lower radiation intensity. This may result in darker image and/or may require longer exposure times. Thus, the pinhole size affects image resolution, contrast, brightness, exposure times, and signal to noise ratio. Several techniques are known, aimed at improving imaging techniques utilizing a plurality of pinholes to improve brightness and/or resolution. WO 2010/119,447 describes an optical system for use with a predetermined light detection surface comprising a multitude of light sensitive pixels. The optical system comprises an optical window defining a predetermined light transmission pattern formed by a multiple spaced apart light transmissive regions, configured in accordance with said multitude of light sensitive pixels. The configuration of said multiple spaced apart light transmissive regions define an irregular arrangement of said regions with respect to said multitude of light sensitive pixels. Said optical window with said irregular arrangement is configured for collecting light beams from different directions from a scenery to be imaged and for directing, on each of said light sensitive pixels, the light component formed by a distinct set of light intensities, corresponding to said light beams collected from different directions, thereby providing spatially distinct light intensity patterns overlapped on said light detection surface and corresponding to said light beams collected from different directions. U.S. Pat. No. 6,545,265B describes a method for mixing pairs of confocal images and different arrangements for fast generation of parallel confocal images and the combination thereof in real time. The method is used for improving contrast and resolution in confocal images. The suggested arrangements point to some possibilities for a meaningful application of the method for image mixing in parallel confocal single-beam or double-beam methods for the generation of highly resolved images in real time for a wide variety of different applications, especially also for material inspection. By combining at least two confocal images, a resolution of the fine structure of the object is achieved in the mixed image. Contrast, lateral resolution and depth resolution are improved in the mixed image of the object to be examined, which can also be a phase object. Further, the method permits the generation of very highly resolved three-dimensional digital images of optical objects to be examined. US 2006/279,845 describes an optical system comprised of a monolithic microlens array assembly that consists of two groups of microlenses sub-assemblies having different pitches between the adjacent lenses. A ratio between the pitches of sub-assemblies is determined by a predetermined relationship between the parameters of the optical system so that the microlenses of the first sub-assembly create a plurality of individual intermediate images arranged side-by-side in a common intermediate plane that are transferred by the microlenses of the second sub-assembly to the final image plane in the form of a plurality of identical and accurately registered images interposed onto each other. This is achieved due to the aforementioned ratio between the pitches. Microlenslet arrays are currently used in three-dimensional integral imaging for optical reconstruction. In integral imaging, lenses have been preferred over pinholes for a number of reasons. Low resolution, low light level image reconstruction, and long exposure time to capture enough photons are the disadvantages of pinhole arrays for imaging. However, the advantages of pinhole optics, besides simplicity, are almost complete freedom from linear distortion, virtually infinite depth of focus and a very wide angular field, as well as the ability to provide imaging of non-optical electromagnetic radiation such as X-ray, gamma radiation etc. There is a need in the art for a novel technique enabling high resolution imaging utilizing one or more pinhole arrays. The technique of the present invention allows for producing high quality image data of a region of interest utilizing two or more arrays of pinholes, each array having a predetermined different arrangement of pinholes. The arrangements of pinholes in the two or more arrays are selected to provide desired total effective transmission function of radiation collection during two or more image acquisition steps through respectively said two or more pinhole arrays. Generally, pinhole based imaging requires selection between image resolution (optical resolution) and intensity (energy), and according to the convention approach the improvement of one of this factor is unavoidably on the cost of the other. However, the technique of the present invention allows utilizing the benefits of pinhole imaging, for imaging with optical as well as non-optical radiation, while providing greater input intensity without reducing the resolution achieved. This is achieved in the technique of the present invention by utilizing the concept of pinhole imaging in combination with spatial and temporal image multiplexing to provide efficient imaging and enabling high quality reconstruction of the image data. According to the technique of the invention, input radiation (optical or non-optical) propagating from a region of interest is collected by an imaging system for a predetermined total exposure time. The input radiation is being sequentially imaged through a set of two or more pinhole (aperture) arrays for corresponding time periods. Each pinhole array is a mask formed by a radiation blocking surface having a preselected arrangement of one or more pinholes of predetermined dimensions and shape allowing transmission of radiation. The set of pinhole arrays comprises two or more pinhole arrays (e.g. masks having predetermined number of pinholes), each comprising an arrangement of predetermined number of pinholes of selected desired dimension(s) and geometry/shape(s). For each array, radiation collected by the pinholes results in multiple overlapping images on an imaging plane (of a detector). According to the present technique, the multiplicity of such overlapping images is collected for predetermined exposure time. Thus, a sequence of two or more input image data pieces are produced via collection of input radiation by the two or more pinhole arrays, respectively, each image data piece corresponding to a selected pinhole array and a selected collection (exposure) time. The image data pieces are then processed based on the arrangement of the pinholes in each array and exposure time(s) defining together the total effective transmission function, to determine a restored image data indicative of the region of interest. Generally, radiation transmission through an array of two or more pinholes generates loss of information due to interference of radiation portions passing through the different pinholes. This can be seen in a spectrum of spatial frequency transmission associated with the pinhole array and having one or more spatial frequencies with zero transmission. The technique of the present invention utilizes a set of two or more pinhole arrays selected such that if one of the arrays has zero or low transmission for a certain spatial frequency within desired resolution limits, one or more other arrays of the set is/are configured to have higher transmission at said spatial frequency, such that the total effective transmission function provides non-null transmission for all spatial frequencies within desired resolution limits Thus, the proper selection of aperture arrays such that cumulative transmission of the set forms an effective transmission function with non-null values within the desired resolution limits. This selection of the set of aperture arrays also provides for relatively simple and efficient post processing of the input image data to generate restored image of the region of interest. The processing just utilizes data about the total effective transmission function and its inverse operator for image reconstruction. In some embodiments of the invention, it provides for full 3-D imaging for far field or near field cases with improved depth resolution by presenting the multi variable coded aperture (MVCA) design. The MVCA is composed of several variable coded apertures (so-called “variable pinhole cameras”), as described above, operable in a non-overlapped fashion. In multi pinhole array and coded aperture imaging a higher number of pinholes is used in order to obtain light intensity and SNR improvements. The unique variable coded aperture (VCA) design is based on both variable and time multiplexed pinholes array. The advantage of time modulated coded aperture over a stationary design is to preserve the image frequency contents more efficiently. This multi variable coded aperture system (MVCA) is able to achieve higher resolution imaging due to higher SNR and light intensity enhancements, and also by overcoming the loss of spectral information. Also, the multi-pinhole non-overlapped matrix design is able to provide increased depth of field for 3D imaging. This MVCA technique allows a wide range of design options for many applications that determine the characteristics of the optical imaging system. Thus, according to one broad aspect of the present invention, there is provided a method for use in three-dimensional imaging of a region of interest. The method comprises: (a) collecting input radiation from the region of interest using at least first and second collection paths with different at least first and second angular orientations, respectively, with respect to the region of interest, wherein said collecting of the input radiation for each collection paths comprising collecting the input radiation through a selected set of a plurality of a predetermined number of aperture arrays, each array having a predetermined arrangement of apertures and collecting the input radiation during a collection time period, wherein said selected set of the aperture arrays and the corresponding collection time periods defining a total effective transmission function of the radiation collection for said collection path, (b) generating first and second image data pieces corresponding to the collected input radiation through the first and second collection paths, respectively, each of said image data comprising the predetermined number of image data pieces corresponding to the input radiation collected through the aperture arrays respectively, (c) processing the first and second image data pieces utilizing total effective transmission function of the radiation collection through the first and second collection paths, and determining a restored three-dimensional image of the region of interest. The set of aperture arrays in each collection path is preferably selected such that said total effective transmission function provides non-null transmission for spatial frequencies being lower than a predetermined maximal spatial frequency. Generally, this maximal spatial frequency may be defined by a minimal aperture size. The minimal aperture size defining the maximal spatial frequency may be selected in accordance with geometrical resolution of image detection. According to one other broad aspect, the present invention provides an imaging system comprising: an optical unit comprising a radiation collection unit and a detection unit for detecting radiation collected by the radiation collection unit, the collection unit comprising at least two mask arrangements defining at least two radiation collection regions respectively, each of the mask arrangements being configured and operable to sequentially apply a plurality of a predetermined number of spatial filtering patterns applied on radiation incident thereon (collected thereby) from a region of interest, each filtering pattern being formed by a predetermined arrangement of apertures in the corresponding collection region, the detected radiation thereby comprising at least two elemental image data pieces corresponding to the collected radiation from said at least two collection regions; a control unit comprising: a mask controller module; and an image processing module; wherein the mask controller module is configured for operating each of said at least two mask arrangements to selectively apply said different filtering patterns during selected exposure time periods, each of said at least two elemental image data pieces thereby corresponding to the radiation collected during the selected exposure time period; and the image processing module is configured for receiving and processing said at least two elemental image data pieces, said processing comprising utilizing predetermined data indicative of a total effective transmission function of each the said at least two mask arrangements, and determining a plurality of at least two restored elemental images respectively being together indicative of a three dimensional arrangement of the region of interest from which the input radiation is being collected. The selected plurality of the predetermined number of spatial filtering patterns of each of said at least two mask arrangements may be preselected to provide said effective transmission function which provides non-null transmission for spatial frequencies lower than a desired predetermined maximal spatial frequency for each of said at least two collection regions. According to some embodiment, the detection unit may comprise at least two detection regions corresponding with said at least two collection regions such that detection of the collected input radiation from said at least two collection regions is non overlapping. The at least two detection regions may be regions of a common radiation sensitive surface, or regions of at least two separate radiation sensitive surfaces respectively. In some embodiments of the invention, at least one of said at least two mask arrangements may be configured as a replaceable mask arrangement comprising the plurality of the predetermined number of masks defining the spatial filtering patterns, said control unit being configured to selectively place one of the masks in the respective one of said at least two collection regions. For example, at least one of said at least two mask arrangements may comprise an array of replaceable mask units carrying said predetermined number of the spatial filtering patterns and being mechanically replaceable in the corresponding radiation collection region. More specifically, the replaceable mask arrangement may be configured as a mechanical wheel comprising said predetermined number of the aperture arrangements each defining the corresponding filtering pattern. Alternatively or additionally, at least one of said at least two mask arrangements may be configured as an electronic mask arrangement configured and operable for varying the aperture arrangement defining the spatial filtering pattern, said control unit being configured to operate said mask arrangement to vary the aperture arrangement selectively provide one of the spatial filtering patterns in the respective one of said at least two collection regions. For example, the electronic mask arrangement may be configured as a radiation transmission modulator. Additionally, in some embodiments of the invention, at least one of said at least two mask arrangements may comprise a multiplexed arrangement of apertures corresponding to said predetermined number of spatial filtering patterns, said multiplexed arrangement of apertures comprising groups of apertures corresponding to different filtering patterns, each group of apertures comprises a wavelength selective filter configured for transmission of a predetermined wavelength range being a part of a total wavelength range for imaging. Generally, the collection unit may comprise two mask arrangements defining at least two radiation collection regions respectively, or an arrangement of more than two mask arrangement. In some embodiments the optical unit may comprise an array of more than two of the collection regions. Such array may be configured with at least one of the following arrangements of the collection regions: 2×2, 2×3, 2×4, 2×5, 3×3, 3×4, 3×5, 4×4, 4×5 and 5×5, or generally N×M where N and M are integers. Typically additional array arrangements may be used. The control unit may further comprise a 3D image processing module configured and operable for receiving and processing said plurality of the restored elemental images to thereby determine data about the three dimensional arrangement of the region of interest. Additionally, the control unit may further comprise a set selection module configured to be responsive to input data comprising data about desired resolution and brightness and to determine a corresponding set of the filtering patterns having non-null effective transmission function. It should be generally noted that the system may be configured for imaging with input radiation of at least one of the following wavelength ranges: IR radiation, visible light radiation, UV radiation, X-ray radiation, Gamma radiation. According to yet another broad aspect, the present invention provides a method for imaging a region of interest comprising: (a) collecting input radiation from the region of interest through at least two collection regions, said collecting comprising applying at each of said at least two collection regions a selected sequence of at least two different filtering patterns during predetermined collection time periods, wherein said selected sequence of the at least two different filtering patterns and the corresponding collection time periods defining a total effective transmission function of the radiation collection which provides non-null transmission for spatial frequencies lower than a desired predetermined maximal spatial frequency for each of said at least two collection regions, (b) generating at least two elemental image data pieces, each corresponding to the collected input radiation with said sequence of the at least two filtering patterns, (c) processing the at least two elemental image data pieces utilizing said total effective transmission function of each of the radiation collection regions, and determining at least two restored elemental images of the region of interest respectively being together indicative of a three-dimensional arrangement of the region of interest. In some embodiments, each of said at least two different filtering patterns may be in the form of an aperture array comprising a predetermined number and arrangement of pinholes. Generally, the predetermined collection time periods of the selected at least two different filtering patterns may be selected for optimizing transmission intensities for selected spatial frequencies. It should be noted that typically the maximal spatial frequency may be defined by a minimal aperture size. The minimal aperture size defining the maximal spatial frequency may be selected in accordance with geometrical resolution of image detection. According to some embodiments of the invention, the method may further comprise detecting image data pieces corresponding to each of said at least two collection regions using a single readout mode for all of said collection time periods of the aperture arrays, thereby integrating said image data pieces to form the corresponding elemental image data pieces in one scan time while selectively using the different filtering patterns. The processing of the at least two elemental image data pieces for generating the restored elemental images of the region of interest may comprise: determining a sum of intensity maps of said image data pieces and utilizing inverting the distortion effect caused by the total effective transmission function, to thereby generate said restored image data. Said processing may comprise utilizing a Weiner deconvolution of the effective transmission function. Generally, the restored elemental images may be determined in spatial frequency domain. According to yet some embodiments of the invention, the selected sequence of at least two different filtering patterns comprising a plurality of a predetermined number of aperture arrays and is selected in accordance of a desired Radiation Intensity Improvement (RII) factor to provide imaging of the region of interest with improved image brightness and/or image quality. The selection of said selected sequence of at least two different filtering patterns may comprise: determining desired resolution for imaging and a corresponding minimal aperture dimension; determining the shape and angle of each aperture, determining a number of aperture to provide desired brightness of imaging; determining said predetermined number of arrays; determining aperture arrangement in each array to provide non-null total effective transmission function of the set of aperture arrays. The determining of aperture arrangement may comprise: determining aperture arrangement of a first array; determining a corresponding effective transmission function; identifying spatial frequencies for which said effective transmission function provides transmission lower than a predetermined threshold; and determining one or more additional aperture arrangement such that transmission of said one or more of the additional aperture arrangement at said identified spatial frequencies is above a predetermined threshold. According to some embodiments of the invention, the collection of input radiation through said at least two collection regions may comprise, arranging said at least two collection regions for collecting input radiation from said region of interest along at least two different optical axes, said at least two different optical axes being parallel to each other. According to one other broad aspect of the invention, there is provided an imaging system comprising: (a) a mask defining a radiation collection surface for spatial filtering of input radiation being collected, the mask comprising a plurality of apertures and being configured and operable to selectively provide a plurality of a predetermined number of spatial filtering patterns of the mask, each filtering pattern being formed by a predetermined arrangement of apertures in said collection surface; (b) a control unit comprising: a filtering controller module; an image acquisition module and an image processing module; wherein the filtering/module is configured for operating said mask to selectively collect the input radiation by different filtering patterns during selected exposure time periods; the image acquisition module is configured for receiving image data pieces corresponding to the collection of the input radiation through said filtering patterns respectively during said selected exposure time periods; and the image processing module is configured for receiving and processing the image data pieces and utilizing data indicative of a total effective transmission function of the radiation collection through said mask, and determining a restored image data of a region of interest from which the input radiation is being collected. The selected plurality of a predetermined number of spatial filtering patterns of the mask may be preselected to provide said effective transmission function with non-null transmission for spatial frequencies lower than a desired predetermined maximal spatial frequency. Generally, the mask may be configured as a replaceable mask comprising plurality of a predetermined number of spatial filtering patterns such that the mask may be configured to selectively place a selected spatial filtering pattern on the radiation collection surface of the mask. For example, the mask may be configured as a mechanical wheel comprising said two or more aperture arrays each defining a corresponding filtering pattern. Additionally or alternatively, the mask may be configured as a radiation transmission modulator and configured to electronically vary filtering pattern thereof. According to some embodiments, the mask may comprise a multiplexed arrangement of apertures corresponding to said predetermined number of spatial filtering patterns, said multiplexed arrangement of apertures may comprise groups of apertures corresponding to different filtering patterns, each group of apertures comprises a wavelength selective filter configured for transmission of a predetermined wavelength range being a part of a total wavelength range for imaging. The processor unit may further comprise a set selection module configured to be responsive to input data comprising data about desired resolution and brightness and to determine a corresponding set of filtering patterns having non-null effective transmission function. According to yet some embodiments, the processor unit may further comprise a depth resolution pre-processing module configured to determine depth resolved effective transmission function in accordance with aperture arrangement of the set of filtering patterns. The image processing module may be configured and operable to determine a plurality of restored depth resolved image data pieces, each of the depth resolved restored image data pieces corresponds to a selected object plane in accordance with a corresponding depth resolved effective transmission function, thereby providing three-dimensional information about the region of interest. According to some embodiments, the system may be configured for imaging with input radiation of at least one of the following wavelength ranges: IR radiation, visible light radiation, UV radiation, X-ray radiation, Gamma radiation. According to yet one other broad aspect of the invention, there is provided a method for use in pinhole based imaging, the method comprising: determining a pinhole dimension based on data about: locations of object plane, location of image plane and desired maximal resolution; determining a desired number of apertures based on desired image brightness per time unit; selecting a first aperture array comprising one or more apertures of the desired dimension; determining a first set of spatial frequency values for which transmission of said first aperture array is below a predetermined threshold; determining at least one additional aperture array having aperture arrangement providing that transmission at said first set of spatial frequencies is above a corresponding predetermined threshold; wherein a total number of apertures divided by a total number of arrays provides a factor for said desired brightness per time unit. Reference is made to FIGS. 1A and 1B, there schematically shown the principles of pinhole based imaging of an object 2 in a region of interest using single- and multi-pinhole imaging system. As shown in FIG. 1A, input radiation coming from the object 2 (e.g. emitted or reflected from the object) is collected by a radiation collection surface of a pinhole based imaging system to form an image 8 on an image plane. In this example, the radiation collection surface is defined by a mask 10 in the form of radiation blocking surface having an aperture 5 of a predetermined dimension and shape. As generally known in the art, radiation transmission through the aperture 5 provides an inverted image 8 of the object 2 in the image plane, which can be viewed on a screen or collected by a detector. As indicated above, such pinhole based imaging system can provide imaging with effectively infinite depth of focus. Additionally, the imaging system provides magnification based on a ratio between the distance Z of the object plane 2 to the aperture mask 10 and the distance U of the image plane (screen, detector) and the mask 10 (i.e. radiation collecting surface). Thus, the imaging system provides magnification of:M=U/Z (equation 1)Additional parameters, such as image resolution and brightness, are determined by dimension (e.g. diameter) of the pinhole in relation to the wavelength of radiation used and the distance to the image plane U. Generally, in order to achieve high resolution imaging, the angular separation (minimal difference in angular orientation if two features visible as separated on the image plane) is selected to be as small as possible. However, for apertures having large radius R in the geometric limit, R2>>λU, the angular separation θgeometric is reduced, while for smaller apertures, the angular separation θdiffraction is proportional to the inverse of the radius: θ geometric ≈ 2 R Z + U ZU θ diffraction ≈ 0.61 λ R ( equation 2 ) It can be estimated that using a pinhole having a radius R=√{square root over (0.61λU)} for imaging of a region of interest located in far field distance and a pinhole having a radius R≈√{square root over (0.61λU/(1+M))} for imaging of an object located in near field distance, will provide high resolution imaging. Such resolution may be diffraction limited, and the smallest features seen separated at the image plane (screen) have a size of ρ = 0.61 λ U R when imaging objects in large distances from the mask; or about the diameter of the pinhole (i.e. 1 R-1.5 R) for imaging objects in relatively close proximity or near field. These resolution limits are based on Rayleigh condition. In this connection, for the purposes of the present application, the terms near- and far-filed distances should be interpreted differently than is generally known in optics. In pinhole based imaging, far-field distance is defined as a distance between the object plane and the radiation collecting surface being large enough such that a phase difference between the radiation components collected at the opposite ends of an aperture is much less than the wavelength, i.e. the wavefront of the radiation from the object plane arriving at the radiation collection surface is substantially planar. In such distance individual contributions of radiation components interacting with the pinholes can be treated as though they are substantially parallel. Generally far-field distance is significantly greater than W2/λ, where λ is the wavelength and W is the largest dimension of the aperture. The Fraunhofer equations can be used to model the diffraction effects of the radiation passage through the pinhole in such far-field distances. Thus, generally far-field is defined when the distance from the object plane to the pinhole mask is larger than the area of the apertures in the mask divided by the wavelength of radiation used. Similarly, near-field condition exists when the distance from the object plane to the mask is smaller than the ratio of the largest aperture's area and the wavelength. As also noted above, the larger the aperture size, the higher the image brightness, as more input radiation may pass through the larger aperture and reach the image plane. This also reduces the signal to noise ratio of the detection. Therefore, pinhole imaging according to the conventional approach has an inherent tradeoff between image resolution and brightness limiting the uses thereof. In this connection, FIG. 1B illustrates imaging of an object 2 through a mask 10 having two apertures 5a and 5b. In general, such imaging system may provide similar image resolution while twice the collected intensity. However, if the two apertures are not separated enough, the two images 8a and 8b are overlapping. This reduces the ability to differentiate between spatial features in the collected image. The present invention provides a novel approach for use in pinhole based imaging, while enabling to increase image brightness without the need to sacrifice resolution. In this connection, reference is made to FIG. 2 illustrating a system 100 for pinhole based imaging of a region of interest. The system 100 includes a mask unit 120 formed by at least one physical mask defining a radiation collection surface for input radiation arriving from the region of interest, and a processor unit 160. According to the invention, the radiation collection is performed by sequentially or selectively collecting radiation with different arrays of pinholes (i.e. different spatial filtering patterns). This may generally be implemented by replacing a mask (pattern) in the radiation collection path. Preferably, however, the mask 120 may include a single mask configured and operable to define two or more different spatial filtering patterns and selectively collect input radiation with one selected spatial filtering pattern at a time (i.e. during a collection session). The mask has radiation transmitting regions (pinholes, apertures, windows) arranged in spaced-apart relationship within the radiation collecting surface. It should be noted that such radiation transmitting regions spaced by blocking regions may be implemented as a passive mask or electronic mask (spatial radiation modulator). It should also be noted, and will be described more specifically further below, that the light collecting surface may be planar, i.e. all the radiation transmitting regions are located in substantially the same plane, or may not be planar such that different radiation transmitting regions are located in different planes. The latter may be implemented by providing a certain surface relief of the mask or by making the radiation transmitting regions at different depths of the mask. To facilitate understanding, in the description below, such radiation transmitting regions are referred to as apertures or pinholes. Thus, each of the spatial filtering patterns is formed by a predetermined arrangement of spatially separated apertures in the collection surface. Generally, the mask 120 may include (or operated to define in case of electronic mask) two or more pinhole arrays (three arrays 10a-10c are shown in the figure), each defining a different spatial filtering pattern, and may be associated with a suitable mechanism for selectively utilizing each of the different pinhole arrays for collection of input radiation. The mask 120 may for example be configured as a rotating plate, as will be described further below, made with apertures such that displacement of the plate results in that one of the two or more patterns is involved in the radiation collection, i.e. is in the active region of the mask with respect to the radiation propagation. Alternatively, a spatial radiation modulator (such as spatial light modulator SLM that may include suitable polarizers on each aperture thereof) may be used and operable to electronically vary transmission of regions therein. In some embodiments, the mask 120 may be in the form of single plate having plurality of apertures of two or more groups (arrays); each group of apertures defines a spatial filtering pattern. For example, each of the aperture groups may include a wavelength selective filter allowing transmission of input radiation of a wavelength range being part of the spectrum used for imaging, thus providing multiplexed selective filtering of input radiation. It should be noted that, generally, any appropriate technique for applying selective spatial filtering to input radiation with the set of aperture arrays may be used such that imaging is provided through two or more selected aperture arrays. Specifically, the mask 120 includes two or more pinhole arrays, e.g. 10a and 10b, each configured with a selected predetermined number and arrangement of pinholes of predetermined dimensions and shapes. Thus, input radiation from the region of interest is collected through a selected set of a plurality of a predetermined number of aperture arrays, where each array has a predetermined arrangement of apertures and is operated to collect the input radiation during a collection time period. The selected set of the aperture arrays defines a predetermined total effective transmission function of the radiation collection. Preferably, also the corresponding collection time periods for the aperture arrays are selected to further optimize the image quality. For each radiation collection session implemented using the selected aperture array, image data piece is created, to thereby generate image data of the cumulative radiation collection sessions through the set of aperture arrays. The image data is processed utilizing the data about the total effective transmission function of the radiation collection, and a restored image of the region of interest is determined. Preferably, the set of aperture arrays is selected such that the total effective transmission function provides non-null transmission for spatial frequencies lower than a predetermined maximal spatial frequency. The maximal spatial frequency is typically defined by a minimal aperture size, which may in turn be selected in accordance with geometrical resolution of image detection. The collection time periods of the selected aperture arrays are selected for optimizing transmission intensities for selected spatial frequencies. As shown in FIG. 2, the processor unit 160 may be connected to the mask assembly 120 for controlling its operation for selectively utilizing the different aperture/pinhole arrays for collection of input radiation (e.g. shifting/rotating the mask to place a different aperture array in the radiation collection path). Additionally, the processor unit 160 may be connectable to a detector 140 which may be a constructional part of the system or not, for receiving detector output indicative of the image data pieces generated from input radiation impinging on the radiation sensing surface of the detector 140. The processor unit 160 may thus include a filtering controller module 165 configured to operate the mask assembly 120 to sequentially select a spatial filtering pattern to be used for light collection session (e.g. select a pinhole/aperture array such as 10a, 10b or 10c in FIG. 2). Further provided in the processor is an image acquisition module 170 configured for receiving image data pieces generated by the detector 140 in response to collected input radiation for a selected collection time period. The processor unit 160 further includes an image processing module 180 configured for receiving the image data pieces from the image acquisition module 170 and processing the image data pieces to determine a restored image data of the region of interest. The system may be configured for determining data indicative of a set (e.g. sequence) of spatial filtering patterns to be used in the radiation collection sessions, using a set selection module 190 being part of the processor unit 160 or a separate control unit. The set selection module 190 is configured to select and determine the set of aperture arrays, as will be described further below. Alternatively, such data about the set of aperture array and their corresponding collection time periods may be previously determined and provided as input data to the system. The processor unit may also include a depth resolving pre-processor 195 configured for determining a so-called depth resolved total effective transmission functions corresponding to radiation collection through the above-described set of aperture arrays from different locations respectively of the object plane. This will also be described more specifically further below. Reference is made to FIG. 3, FIGS. 4A-4C and FIG. 5 exemplifying three mask assembly configurations providing three filtering patterns each formed by an aperture array. FIG. 3 shows a mask assembly formed by a single rotating mask 120 having three (generally two or more) regions 10a, 10b and 10c each including a different array of apertures, i.e. different apertures' arrangement providing a different spatial filtering pattern for the radiation being collected. The mask is, selectively rotatable about a rotation axis 12 to selectively place one of the regions 10a, 10b and 10c in radiation collection path. The number of the regions and the arrangement of apertures therein (including size(s) of the apertures and their relative accommodation) are selected to provide the desired total effective transmission function as described above. FIGS. 4A-4C show a filtering mask assembly 120 which define a plurality of spaced-apart apertures, generally at 5. In this example, the mask assembly defines a single mask which is formed by two plates, P1 and P2 as shown in FIG. 4B, configured such that at least one plate is rotatable with respect to the other about an axis RA. Each plate is formed with multiple apertures. Relative rotation of the plates results in that each respective orientation of the plates creates a different active apertures' array (spatial filtering pattern) for use in radiation collection. In the present not limiting example, one of the plates, e.g. plate P2, is configured such that it includes all the apertures required to create the desired set of the selected aperture arrays, while the other plate P1 has the same apertures' arrangement but with at least one of the arrays having a different angular orientation as compared to the at least one other array in the same plate. More specifically, the mask assembly is configured such that when the two plates P1 and P2 are aligned at angular orientation Φ=0 the apertures 5 relating to aperture array 10a in plate P1 overlap the corresponding apertures in plate P2 and thus allow transmission of radiation there through (FIG. 4A). As at least one of the two plates is rotated with respect to the other plate, the angular orientation between the plates is different resulting in a different overlapping between the apertures providing a different active set of apertures. FIGS. 4B and 4C exemplify the arrays resulting from the angular orientations between the plates of respectively 30° and 60° resulting in different active apertures arrays 10b and 10b. FIG. 5 exemplifies a different configuration of a mask assembly 120. Here the mask assembly includes a mask with multiple apertures and a spectral filter aligned with and located close to the mask. The spectral filter is operable to have different spectral transmissions (illustrated here for simplicity by primary colors R, G, B) in different radiation collection sessions. The spectral transmissions may be such that the entire aperture provides transmission of one or more spectral bands. The number of the apertures and their arrangement (including size(s) of the apertures, their relative accommodation, and groups of spectral band associated with the apertures due to controlled variation of the spectral transmission of the spectral filter) are selected to provide the desired total effective transmission function as described above. Reference is made to FIGS. 6A to 6F illustrating the principles of a somewhat different embodiment of the invention. In this example, the set of aperture arrays is arranged such that apertures are spaced also along an optical axis, i.e. are located in different planes of the radiation collection surface. In other words, the apertures are located such as to define pre-determined radiation collection plane, including a so-called primary collection plane U1, and at least one other plane located closer or further to the image plane as compared to the primary plane. In this example, three such collection planes are shows. In this configuration, local effective transmission functions of the radiation collection by the apertures of the closer plane U2 and the apertures of the further plane U3 are respectively stretched and condensed in the spatial domain with respect to that of the apertures of the primary plane U1. The stretch/condensing factors are a priori known. Then, the image data pieces corresponding to radiation collection by apertures of the collection planes U2 and U3 are processed by applying the a priori known stretch/condensing factors to the respective local effective transmission functions, and the results for the collection planes U1,U2,U3 are summed to get the total effective transmission function. As indicated above, the number of the apertures and their arrangement are selected to provide the desired total effective transmission function as described above. The following is the description of the operational principles of the above-described imaging technique of the invention. To this end, a single image piece formed at the detector 140 by input radiation collected through an aperture array having N pinholes is: S array ( x , y ) = ∑ n = 1 N ∑ m = 1 N s ( x + d n ( x ) , y + d m ( y ) ) ( equation 3 ) where dn(x), dm(y) are the (x,y) coordinated of the locations of the pinholes within the array relative to the center of the array, S(x,y) is the image generated by a single pinhole and Sarray(x,y) is the image generated by radiation collection through the array. Generally, the processor unit 160 and the image processing module 180 thereof utilize the image data pieces in the spatial frequency domain. To this end the image processing module 180 may include a Fourier module configured to determine the 2-dimensional Fourier transform (typically a discrete Fourier transform) of the collected image data pieces, providing:Sarray(u,v)=∫∫Sarray(x,y)e−2πi(ux±vy)dxdy (equation 4)This Fourier transformed image data piece can be represented as a product of a single pinhole image and the array configuration:Sarray(u,v)=S(u,v)·F(u,v) (equation 5)where S(u,v) is the Fourier transform of the image generated by a single pinhole and F defines an effective transmission function of a pinhole array having plurality of N pinholes: F ( u , v ) = ∑ n = 1 N ∑ m = 1 N ⅇ - 2 π i ( ud n ( x ) + vd m ( y ) ) ( equation 6 ) It should be noted that a radiation transmission through a single array of pinholes may generally cause interference between radiation components passing through different pinholes of the array. Thus, the effective transmission function F(u,v) of a single pinhole array, having more than a single pinhole, typically has zero transmission for certain spatial frequencies. To avoid reducing of sensitivity to spatial frequencies, the technique of the present invention utilizes a predetermined number of two or more aperture arrays. Generally, the filtering controller module 165 selects first aperture array and the image acquisition module 170 generates image data piece corresponding to radiation collection within exposure time t1, a second aperture array is used for collection of radiation from the same region of interest for exposure time of t2, and similarly for additional aperture arrays if used. For a plurality of L arrays, each used for exposure time period of t1 the resulting Fourier transformed image data is: ∑ l = 1 L S array ( l ) ( u , v ) · t l = S ( u , v ) ∑ l = 1 L F ( l ) ( u , v ) · t l ( equation 7 ) In this connection it should be noted that summation of the image data pieces may be done by the detector 140 collecting input radiation for the entire exposure time (i.e. exposed to input radiation during collection through all of the aperture arrays) and providing a “combined” readout of exposure, or by the image processing module 180 determining a sum of the image data piece provided by the detector 140. The sum of individual effective transmission function of all the aperture arrays, together with corresponding exposure times provides a total effective transmission function (TETF): G ( u , v ) = ∑ l = 1 L F ( l ) ( u , v ) · t l ( equation 8 ) Thus, according to the present invention, the set of aperture arrays is selected such that the total effective transmission function G (u,v) provides non-null transmission for spatial frequencies up to a predetermined limit Such predetermined limit is determined by the maximal resolution obtained by radiation collection with a single pinhole of corresponding diameter. More specifically, the aperture arrays/masks and corresponding exposure times are selected to provide:G(u,v)≠0∀(u,v)ε{|u|<umax|v|<vmax} (equation 9) Therefore, the total effective transmission function is determined in accordance with the aperture arrays used by the imaging system 100 and corresponding exposure times. Thus, the image processing module 180 can determine restored image data indicative of the region of interest in accordance with: S ( u , v ) = [ ∑ l = 1 L S array ( l ) ( u , v ) · t l ] · G ( u , v ) - 1 ( equation 10 ) To determine the image data in spatial coordinates system the image processing module can determine an inverse Fourier transform. It should be noted that G(u,v)−1 may be determined by any suitable algorithm Generally linear matrices may be used for image reconstruction. To this end Weiner deconvolution algorithms may also be used to determine G(u,v)−1. Generally speaking, the sum of intensity maps of the image data pieces is determined, and then a distortion effect, caused by the total effective transmission function, is inverted to thereby generate the restored image data Wiener deconvolution is used for correction of noise addition to a convolution based problem. Generally, given a system y(r)=h(r)*x(r)+n(r), where * is convolution operator, x(r) is the input signal (generally image data of the region of interest), h(r) is the impulse response of the system, n(r) is an unknown signal such as noise and y(r) is the observed/measured signal. It should be noted that as the present technique related to spatial domain, the Wiener algorithm is described herein using spatial coordinates defined by r. The Wiener deconvolution is generally used to identify an operator g−1 (r) providing an estimation {circumflex over (x)}(r)=g−1(r)*y(r) such that {circumflex over (x)}(r) is an estimation of x(r) minimizing the mean square error. In the frequency domain the Wiener deconvolution algorithm provides: G - 1 ( f ) = H * ( f ) S ( f ) H ( f ) 2 S ( f ) + N ( f ) ( equation 11 ) where G−1 and H are Fourier transform of g−1 and h in the frequency domain ƒ (spatial frequency), S(ƒ) is the mean power spectral density of x(r) and N(ƒ) is the mean power spectral density of the noise n(r). In this connection it should be noted that G−1 as describe herein in equation 11 refers to the inverse effective transmission function according to the present technique and thus the (−1) superscript is used herein, differently than the general terms of wiener algorithm. Also, as indicated above, the set of aperture arrays is selected to satisfy the condition that total effective transmission function is non-null for spatial frequencies within the desired resolution limits. As known from various de-convolution algorithms, zero (or close to zero) values of the effective transmission function may cause amplification of noise in the restored image data and reduce the signal to noise ratio. Reference is made to FIG. 7 exemplifying a method for selection of the set of aperture arrays for use in the imaging system 100. Initially the desired parameters of the system need to be determined. The resulting image resolution is determined (step 1010) in accordance with a diameter of the apertures, together with distance from mask to the detector F, from the objects to the mask Z and the wavelength of radiation used as described above with reference to equation 2. In some configurations, a minimal aperture diameter may be selected to define the desired resolution and one or more additional, larger diameters may be selected to further increase image brightness. At a next design step (1020), a desired energy transmission is determined. The energy transmission may be determined as a factor of improvement with respect to a single pinhole system, or with respect to a standard optical imaging system. The energy transmission can be presented as Radiation Intensity Improvement (RII) factor which is used to determine the number of apertures in the arrays and the number of arrays used. The maximal RII can be determined for equal accumulation time by the ratio: RII = N L · π R 1 2 π R single 2 ( equation 12 ) where N is the total number of apertures used, L is the number of arrays, R1 is the radius of the apertures in the arrays and Rsingle is the radius of a corresponding single pinhole system used in comparison. The energy transmission is determined in accordance with detector sensitivity and appropriate accumulated exposure time. At this stage a general decision about number of aperture arrays and arrangement of the apertures in each array is to be made (1030). For example, for desired RII of 2, two aperture arrays may be used each having two apertures along an axis. Generally the number of aperture arrays is selected to be as low as possible while providing the desired condition of equation 9. Additionally, the aperture arrangement in each array may be 1-dimensional, i.e. apertures arranged along an axis, or 2-dimensional. In step 1040 an aperture arrangement for the first array is determined. It should be noted that the order of selection of the arrays is of no importance at the imaging session. Generally the aperture arrangement of the first array may be determined arbitrarily, however generally a simple arrangement of one aperture at the center of the radiation collection surface and one aperture at certain distance therefrom along a selected axis may be preferred. Generalization to two dimensional arrangements may be done by copying 1-dimensional arrangement along a second axis and/or rotation of such 1-dimensional arrangement. Once a first aperture array is selected, the corresponding effective transmission function is determined and the “problematic” spatial frequencies are marked (1050). As indicated above, the effective transmission function is determined in accordance with equation 6 and the marked “problematic” spatial frequencies satisfy F(l)(u1, v1)=0 or under a predetermined threshold (e.g. below 0.1). It should be noted that such spatial frequencies are marked only within the resolution limits defined by the aperture diameter. At this stage, additional aperture arrays may be determined (1060), the number and diameter of apertures is selected in accordance with desired resolution and energy transmission, while the arrangement of the apertures is determined to provide finite values of the corresponding effective transmission function for the spatial frequencies marked for the previous array(s) (1070). This process may be performed for two, three or more aperture arrays until an appropriate set of aperture arrays is selected (1080). It should be noted that the set of aperture arrays may be pre-selected for design and assembly of the imaging system. Alternatively, the processor unit 160 of imaging system 100 may further include a set selection unit (190 in FIG. 2) configured to determine an appropriate set of aperture arrays in accordance with input parameters about desired resolution and energy transmission. Generally, the former method is suitable for use with pinholes punctured into a radiation blocking mask, while the later is more suitable of use with electronically controlled varying patterned mask 120. Additionally, the selection of an appropriate set of aperture array is configured to optimize the transmission of the aperture arrays for different spatial frequencies. To this end, the selection process may also include determining an estimated total effective transmission function, assuming equal exposure times for all aperture arrays. The estimated effective transmission function may then be compared to a Pinhole Transmission Function (PTF). Generally the set of aperture arrays is selected to optimize transmission of spatial frequencies with the resolution limits to thereby optimize imaging of the region of interest. To this end the aperture arrays, as well as corresponding exposure times are selected such that for at least some spatial frequencies within the desired resolution limits, the total effective transmission function provides transmission that is greater than that of the PTF. The above described technique can also be utilized for acquiring 3-dimensional image data. More specifically, the technique allows obtaining of image data pieces from a region of interest and to determine depth information from the acquired image data pieces. Reference is made to FIG. 8A illustrating imaging of objects located at different distances from the imaging system 100 and determining of depth information. As shown in the figure, objects located at different distances from the imaging system 100, or from the patterned mask 120 thereof, generate different images on the detector. This is due to the multiplicity of apertures in each aperture arrays. Generally, if the distance Z between the object and the patterned mask is of the order of the distance between the apertures of the two or more apertures arrays used for imaging, images thereof taken through two or more separate pinholes provide a stereoscopic like image data pieces. More specifically, as shown in FIG. 8A objects 2a and 2b, located respectively at distances Z1 and Z2 from the imaging system actually see the different apertures of the array in different angular directions. Thus, radiation propagating from object 2a and passing through the topmost pinhole 5b reach the detector 140 to generate an image 8a1. This is while radiation propagating from object 2b and passing through the same pinhole 5b generates an image 8a2 at a slightly different location on the detector 140. This effect may be considered as a result of varying magnification M for different objects in accordance with equation 1 above. To this end, the processor unit 160 of the imaging system 100 may utilize predetermined information about expected distances of objects within the region of interest as well as desired depth resolution to determine different effective transmission functions in accordance with the different distances. Such 3-dimensional information is typically more effective in near-field imaging as described above, however it should be noted that depth information may be determined based on image data pieces acquired by the system of the present invention even in the far-field. The processor unit 160 may thus include a depth resolving pre-processor 195 (in FIG. 2) configured to determine variation of the effective transmission function in accordance with desired depth resolution to be extracted from the image data pieces. However, effective transmission function data corresponding to depth resolving of the imaging system may be pre-configured and provided to the system, e.g. stored in a corresponding storage unit. Generally, to provide depth information, the effective transmission function may be determined for different locations of an object with respect to the patterned mask 120. If the actual locations of the apertures in an aperture array are described by dn-actual, defined for a pre-selected magnification factor M=0 as defined in equation 1 (i.e. reference object plane at infinity), for objects located at different Z distances from the mask and having magnification M=M1 the effective locations of apertures in the array are viewed asdn′=(1+M1)dn (equation 13)Thus, a new effective depth transmission function F(l)Z(u,v) can be defined for each array and each distance Z, as well as a new total effective depth transmission function GZ′(u,v). After collection of image data pieces onto the detector 140, the image processing module 180 may utilize the depth resolved effective transmission functions provided by the depth resolution pre-processor 195 to determined plurality of restored image data sets, each indicative to object distance Z in connection with the corresponding effective transmission function GZ′(u,v) for the distance. Thus, the image processing module generates plurality of restored image data elements as follows: S Z - min = [ ∑ l = 1 L S array ( l ) ( u , v ) · t l ] · G Z - min ′ ( u , v ) - 1 ⋮ S Z - max = [ ∑ l = 1 L S array ( l ) ( u , v ) · t l ] · G Z - max ′ ( u , v ) - 1 ( equation 14 ) It should be noted that the number of Z planes obtained by corresponding effective depth transmission functions GZ′(u,v) determine the depth resolution. Additionally, the maximal possible depth resolution is determined by rules of triangulation and in accordance with geometrical resolution of the detector unit 140. In this connection, variation of the distance of an object from the mask can be detected if an image generated by radiation transmission through at least one of the apertures in at least one aperture array shifts by at least one pixel with respect to a distance of a reference object plane. This condition provides that d n ( Z - max ) ′ = Z max + U Z max · d n ( actual ) ≥ 1 pixel x , y ( equation 15 ) More specifically, the variation in relative location of the apertures as seen from different (in this case maximal) depth locations is larger than the spacing between pixels of the detector. Additionally, a similar condition may be provided for differentiating between depth locations yielding: Δ d n ( Z - planes ) ′ = d n ( Z 1 - planes ) ′ - d n ( Z 2 - plane ) ′ = Z 2 - Z 1 Z 1 · Z 2 · U · d n ( actual ) ≥ 1 pixel x , y ( equation 16 ) It should be noted that, in the case of depth information, the image processing unit 180 is configured to reconstruct image data for each of the Z-planes. For each reconstructed data only objects located in the corresponding Z-plane will be accurately reconstructed providing in-focus image data. Objects located in other Z-planes will provide blurry reconstructed image data similar to ‘out-of-focus’ image data. Reference is now made to FIGS. 8B to 8D illustrating yet another embodiment of the invention enabling full 3-D imaging of a region of interest, being far field or near field as describe above. As indicated above, the use of multiple pinhole arrays provides the system ability for imaging with improved depth resolution. This is done by presenting the multi variable coded aperture (MVCA) design that is composed of several variable coded apertures in a non-overlapped structure. FIG. 8B illustrates schematically, by way of a block diagram, an imaging system 200 configured for use in pinhole based 3-D imaging of a region of interest. The system 200 includes an optical unit 202 and a control unit 204. The optical unit 202 includes multiple (generally at least two) imaging units such that each imaging unit is configured generally similar to the above-described system 100 exemplified in FIG. 2. More specifically, each of the imaging units, e.g. 202a and 202b, includes a light collection surface defined by a mask unit 120 and configured to collect input radiation and direct the input radiation to generate an image on a predetermined image plane; and a detector unit 140, e.g. a sensor array, configured for collecting image data generated at the image plane. Generally, the different imaging units (202a and 202b) may utilize common detector unit, however the image data collection is preferably non-overlapping, i.e. such that each imaging unit generates an image data piece (elemental image) associated thereto. The optical unit 202 is connectable to the control unit 204, which is configured for processing the elemental images from the plurality of imaging units 202a, 202b etc. The control unit includes a processing arrangement configured to separately process the elemental images to generate corresponding set of reconstructed elemental images of the region of interest. The set of reconstructed elemental image data pieces correspond to images of the region of interest from plurality of different points of view and thus include information about three-dimensional arrangement of the region of interest. In some configurations, the control unit 204 may also include a 3-D image processing module 206. The 3-D image processing module 206 may typically be configured for processing the plurality of reconstructed elemental image data pieces in accordance with data about the arrangement of the plurality of imaging units (e.g. 202a, 202b) of the optical unit 202, to provide reconstructed data about 3D arrangement of the region of interest. In this connection it should be noted that the output data indicative of three-dimensional arrangement of the region of interest may be in the form of raw set of plurality of elemental image data pieces stored and transmitted for further processing or direct view. In some other configurations, the 3D image processing module 206 may be configured to extract the 3D arrangement to provide data about arrangement that can be used without additional processing. An example of image data collection and generating of resulting 3D data is shown in FIGS. 8C and 8D. FIG. 8C illustrates radiation collection and arrangement of a multi-pinhole imaging system 200 and a 3D object being imaged 300. In this example the system includes nine imaging units arranged in an array and configured for generating nine separate elemental image pieces corresponding to the scene/object being imaged. Input radiation (electromagnetic radiation of one or more selected wavelength ranges being optical or not) arriving from the region of interest. Each imaging unit is configured to collect input radiation sequentially through a set of pinhole arrays as described above and collect the generated image data on a detector (being a separate detector or a region of sensing pixels on a common detector providing non-overlapping collection regions) providing a set of a plurality of captured elemental images. Each image data piece of the set of captured elemental images includes image data captured through the set of pinhole arrays and thus generally includes overlapping image data of the region of interest. The control unit is configured for receiving the captured elemental image data pieces from the plurality of imaging units and for processing each of the captured elemental image data pieces to generate a set of a plurality of reconstructed elemental images. In this connection, FIG. 8D illustrates extraction of scene arrangement data from the set of reconstructed elemental images of the scene. It should be noted that in some embodiments, the set of elemental images may be stored, transmitted for further processing and/or presented as is. However, according to some embodiments of the invention, the control unit 204 of the imaging system 200 as shown in FIG. 8B, include a 3D image processor 206 configured and operable to extract data about three dimensional arrangement of the scene from the set of elemental image pieces. The three dimensional arrangement data may be extracted by any suitable processing type and is based on determining small variations in the elemental images resulting from variations in point of view thereof. The 3D image processing may be configured to utilize one or more algorithms such as back propagation algorithms for determining the three dimensional arrangement of the scene, or any other suitable algorithm. An example of the mask configurations and operation of such 3D imaging system will be described below with reference to FIGS. 16A to 16D and FIGS. 17A to 17L. The following exemplify the use of the technique and system of the present invention in imaging. FIGS. 9A-9K show three aperture arrays, corresponding effective transmission functions and images of a test object. FIG. 9A-9C show aperture configuration of three aperture arrays having pinholes of diameter 170 μm; FIG. 9D illustrates the locations and numbering of the apertures. The set of aperture arrays is selected to provide 5.66 brighter imaging relative to a single pinhole of similar diameter. The locations of the apertures in the three arrays of FIGS. 9A-9C are shown in table 1 in relative units determined in accordance with pixel size of the detector and distances in the system (i.e. U and Z). TABLE 1Location (x, y)[relative units]Location #Hole #(0, 0)11, 5, 9(1, 0)2 2(1, 1)3 3(0, 1)4 4(3, 0)56, 10(3, 3)67, 11(0, 3)78, 12(−6, 3) 813(−6, 0) 914(−6, −6)1015 (0, −6)1116 (3, −6)1217 As shown, apertures 1, 5 and 9 are located at the center of the mask and the rest of the apertures are arranged around to provide non-null effective transmission function. FIGS. 9E and 9F illustrate the absolute values of the effective transmission functions for each aperture array and the total effecting transmission function based on selected exposure time weights. As shown in FIGS. 9E and 9F, graph line G0 shows the transmission function of a single pinhole located at the center of the mask and having similar dimension. Graphs F1, F2 and F3 show the effective transmission function of aperture arrays of FIGS. 9A-9C respectively. As can be seen from the figures, the effective transmission function of a single pinhole is in the form of sinc(ƒ) function having a main lobe defining the resolution limits Aperture array of FIG. 9A has several zero points while aperture arrays of FIGS. 9B and 9C are designed to have zero values at different spatial frequencies in order to provide the total effective transmission function Gtotal with non-null values for spatial resolutions within the resolution limits. It should be noted that the aperture arrays shown here are actually configured as replications of a one-dimensional array and thus the effective transmission function can be fully described in a 1D graph. FIGS. 9G to 9K show experimental results illustrating the efficiency of the above described technique. FIG. 9G shows image of a test object taken with visible light through a single pinhole of diameter of 170 μm; FIG. 9H shows an image of the same object through a pinhole of diameter of 250 μm; FIG. 9I shows an image of the object through a pinhole of diameter of 350 μm; FIG. 9J shows raw image data generated after sequential exposure through the three aperture arrays of FIGS. 9A-9C without post-processing; and FIG. 9K shows reconstructed image after post-processing. As shown, increasing the pinhole diameter increases the image brightness but decreases resolution. This is while the reconstructed image generated in accordance with the above described technique provides higher image brightness with no reduction of resolution and thus provides greater signal to noise ratio. FIGS. 10A-10E show image data of simulation results using one-dimensional and two-dimensional aperture arrays configured as exemplified in FIGS. 9A-9C. The one-dimensional aperture arrays were configured with aperture locations including apertures 1, 2; 5, 6; and 14, 9, 10 as exemplified in FIG. 9D and provide image brightness increase of 2.33. FIG. 10A shows an image taken through a single pinhole of similar diameter; FIG. 10B shows a similar image taken through a pinhole diameter bigger by 150%; FIG. 10C shows reconstructed image taken in accordance with the above described technique utilizing one-dimensional aperture arrays; and FIGS. 10D and 10E show respectively raw image data and reconstructed image taken in accordance with the multi aperture technique utilizing two-dimensional aperture arrays. As shown, increasing the aperture diameter increases image brightness at cost of resolution. This is while the reconstructed images according to the present invention provide increased brightness with no reduction in resolution. Additionally, this technique allows for use of smaller apertures thereby increasing the resolution for similar or greater image brightness. FIGS. 11A-11J illustrates simulation of Gamma imaging using the technique of the present invention. FIG. 11A shows the structure of arrays 1-3 and corresponding aperture dimensions; FIGS. 11B-11G show graphs of the arrays and corresponding effective transmission functions; FIG. 11H shows a single pinhole transmission as well the separate and total effective transmission functions of the arrays; and FIGS. 11I-11J show simulated images for imaging using a single pinhole (FIG. 11I) and reconstructed image (FIG. 11J) utilizing the technique of the invention with the pinhole arrays shown in FIG. 11A with conventional simulation techniques emulating bone scan for osteomyelitis transverse slice image (negative colors) using Gallium 67 radiation. Both FIGS. 11I and 11J illustrated a region of the figure in magnification, and as shown, the reconstructed image provides higher resolution and signal to noise ratio and thus provides information on features (marked with an arrow) that cannot be resolved in the image generated by a single pinhole. The aperture arrays provide brightness increase of 2.33 with respect to a single pinhole system of similar diameter. As shown the aperture arrays are selected such that the total effective transmission function (Gtotal in FIG. 11H) in non-null for spatial frequencies within the resolution limits of the single pinhole dimensions. Table 2 below provides the resulting signal and noise measurements: TABLE 2Object tobackgroundSingle pinhole systemMulti pinhole arraysratioAccumulation time = 180 secTotal accumulation time = 180 sec1:1.2SignalNoiseSNRSignalNoiseSNRObject13.568378063.88248863.4947633631.579604585.629208825.60995436Background11.167943903.341762483.3419322826.1246000005.160685505.06223447 As shown in Table 2, the signal to noise ratio (SNR) provided by the technique of the invention is significantly higher with respect to a single pinhole system. The improvement is greater than √{square root over (2.33)}, and is higher than √{square root over (2.5)} within similar exposure time and providing similar resolution limits. FIGS. 12A-12C show experimental results of Gamma imaging of a resolution test object having a plurality of lead lines with different density on a surface. FIG. 12A shows image of the test object through a single pinhole of diameter of 4.45 mm; FIG. 12B shows imaging of the test object using a single pinhole of diameter of 2 mm; and FIG. 12C shows reconstructed image of the test object utilizing the technique of the invention with a set of aperture arrays as shows in FIG. 12A with pinhole diameter of 2 mm. As shown the image of FIG. 12A is relatively bright but does not provide sufficient resolution to differentiate between the fine lines in two of the regions of the object. Utilizing a smaller pinhole, in FIG. 12B, increases the resolution, however it limits the image brightness and thus for one of the regions, the brightness of the image is not sufficient in order to recognize the fine lines. This is while the use of the technique of the invention allows to increase the resolution as well as provide sufficient image brightness to identify the fine lines in all in all of the regions of the test object as can be seen in FIG. 12C. FIGS. 13A-13F show experimental depth resolved imaging based on the above described technique utilizing the aperture arrays of FIG. 11A. FIG. 13A shows a case having four radiation sources of different power located at different distances from the front surface of the case. The distance between the close sources and the further ones is 60 mm FIG. 12B illustrates an imaging scheme and a side view of the sources' locations in the case to illustrate the different locations of the sources. FIG. 12C shows an image of the object as generated by imaging through a single pinhole of 2 mm in diameter. In this image all four radiation sources can be seen with limited resolution and brightness. Additionally this image cannot provide data about distance of the sources with respect to the mask; this is partially due to the high depth of focus (effectively infinite) of pinhole based imaging. FIG. 13D shows a raw image resulting of collecting radiation through three aperture arrays as shown in FIG. 11A. This image is blurry and requires reconstruction to provide meaningful information. Such information is provides in FIGS. 13E and 13F showing image reconstruction results for Zmax and Zmin distances respectively. The distances are defined in accordance of existing knowledge of thickness of the object being image and desired depth resolution. As shown, in each restored image there are two sources marked clearly and a multiplicity of points resulting from input radiation from the sources of the other location. This technique allows the use of X-ray and Gamma imaging for localizing of tumors or other radiation sources without the need to collect plurality of images from different locations. And in general to reduce radiation collection time thus allowing the use of faster decaying radiation sources and reduce the damage to the subjects. FIGS. 14A-14C as well as FIGS. 15A-15D show alternative aperture array arrangement suitable for use with the technique of the present invention. As described above, the arrangement of apertures in the aperture arrays is selected to provide non-null transmission in all spatial frequencies within the desired resolution limits. FIGS. 14A and 14B show a set of two aperture arrays, each having 25 apertures in a predetermined arrangement providing together an effective transmission function with finite transmission in all spatial frequencies within the resolution of a single pinhole of the corresponding diameter as well as beyond that resolution. The absolute value of the total effective transmission function is shown in FIG. 14C. This graph shows the total effective transmission function Gtotal with respect to transmission of a single pinhole of a similar diameter Gσ. Such set of aperture arrays provide RII of 25 and thus increases brightness of imaging 25 times with respect to imaging through a single pinhole. Alternatively, this technique can be used to provide similar brightness with reduces exposure time. Additionally, FIGS. 15A-15D exemplify the use of aperture arrays having different pinhole diameters. FIG. 15A shows three sets of aperture arrays of similar arrangement. Set I is similar to the aperture arrangement described in FIGS. 9A-9D and Table 1. Sets II is configured with additional apertures and set III provides apertures of different diameters to allow higher brightness. FIGS. 15B to 15D show respective total effective transmission functions with respect to transmission of a single pinhole. Specifically, FIG. 15B is the total effective transmission of set I; FIG. 15C shows the total effective transmission function of set II; and FIG. 15D shows the total effective transmission function of set III. As shown the use of additional apertures provides the total effective transmission to be greater in modulus with respect to the transmission of a single pinhole for more spatial frequencies. Thus providing higher imaging efficiency with respect to both brightness and contrast while does not require and loss in resolution and/or exposure time. FIGS. 16A to 16D and 17A to 17L show experimental data of three dimensional imaging of a region of interest utilizing the technique as described with reference to FIGS. 8B to 8D. FIG. 16A show the experimental setup for 3D image capturing, the region of interest includes two different objects located at different distances from the imaging system. The imaging system includes an array of mask arrangement including an array of 3×3 collection regions, each configured for sequential collection through a set of three aperture arrays shown in FIG. 16B. The elemental image data pieces collection through the different collection regions are detected in non-overlapping regions of the CCD based detector. FIG. 16B shows an array of 3×3 collection regions, three aperture arrays are sequentially used in each collection region for collection marked as Array1, Array2 and Array3. It should be noted, although not specifically exemplified here, that the imaging system may use two or more collection regions, collecting radiation from the region of interest along two or more different (parallel or not) optical axes. Typically, the collection regions may be arranged in an array having at least one of the following configurations: 1×2, 1×3, 1×4, 1×5, 2×2, 2×3, 2×4, 2×5, 3×3, 3×4, 3×5, 4×4, 4×5, 5×5 and any other configurations or a rotated array configuration. FIGS. 16C and 16D show an elemental image (FIG. 16C) and reconstructed elemental image (FIG. 16D) as collection by one of the collection regions of the system. As shown, the raw image is blurred as it includes image data collected through a plurality of pinholes and detected by overlapping region of the detector. The reconstructed elemental image shown in FIG. 16D provides large depth of focus due to the use of pinhole based imaging and shows both objects clearly. To illustrate the three dimensional arrangement of the objects in the region of interest, the set of nine elemental reconstructed images were further processed by back propagation processing to provide images corresponding to limited depth of focus and being focused onto different distances along a general optical axis of the system. FIGS. 17A to 17L show integral image reconstruction utilizing back propagation technique based on the set of reconstructed elemental images provided by the imaging system of the invention. The images present the region of interest in focusing z-planes at slice ranges between 120 mm to 174 mm from the collection surface. FIG. 17A shows focusing plane at 120 mm; FIG. 17B shows focusing plane at 126 mm; FIG. 17C shows focusing plane at 132 mm; FIG. 17D shows focusing plane at 136 mm; FIG. 17E shows focusing plane at 138 mm; FIG. 17F shows focusing plane at 140 mm; FIG. 17G shows focusing plane at 146 mm; FIG. 17H shows focusing plane at 152 mm; FIG. 17I shows focusing plane at 160 mm; FIG. 17J shows focusing plane at 162 mm; FIG. 17K shows focusing plane at 166 mm and FIG. 17L shows focusing plane at 174 mm. As shown, one of the objects, marked by four dots has a sharp image for focusing plane around 136-138 mm corresponding with its location closer to the imaging system (shown in FIG. 16A). This is while the object marked as “D” is seen sharply at focusing plane around 162-166 mm corresponding with its further location from the imaging system. It should be noted, that the extraction of three dimensional data about the arrangement may be done by various different techniques. Moreover, the plurality of reconstructed elemental images may be presented in a way that allows a user to visualize the 3D arrangement of the region of interest (e.g. by presenting one elemental image to the right eye and another to the left eye of the user). Thus the present invention provide a technique and system for imaging a region of interest through two or more aperture arrays and for reconstruction of the acquired image data to provide reconstructed images of the region of interest. The technique can be used with any wavelength of electromagnetic radiation including, but not limited to, infra-red radiation, visible light radiation, ultra violet radiation, X-ray radiation, Gamma radiation or any other wavelength where a blocking material can be used. The technique may also be used to provide depth information based on image data without the need to move the imaging system or the object. |
|
041585984 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1 of the drawings, a container 16 is mounted for rotation on a bearing 23 that also supports the weight of the rotating system. For example, the device of FIG. 1 will be rotated on a turntable like that used to support rotating restaurants, etc. The bearing 23 rests on a base 15. Rotation of the container 16 is achieved by a shaft 26 attached thereto and extending through the base 15 and driven at low speed (about 45 rpm) by a motor 27. The container 16 contains a body of molten lithium 17 such that when the motor 27 is energized, the lithium 17 and container 16 will then rotate as a rigid body with the free surface of the liquid lithium forming a paraboloid of revolution 14. Since lithium is a good electrical conductor, its reflectivity will be high. Accordingly, the parabolic shape of the rotating lithium surface 14 is utilized in the present invention as a laser mirror. A parabolic mirror has the property of directing light rays which are parallel to the axis of the symmetry to a point at the focus as illustrated in FIG. 2. Only a few of the light rays are shown in FIG. 2 for the sake of clarity. Furthermore, light rays forming a plane wave front initially perpendicular to a mirror symmetry axis will reach the focus at the same time. The rotating container 16 of FIG. 1 is enclosed by means of an outer container 25 affixed to the base 15, and bearings 24 are coupled between the respective containers 16 and 25 to provide rotational stability to the rotating container 16. The container 25 also contains molten lithium 22, for example, which flows therethrough by means of flow lines 32 and 31 and suitable control valves to a heat exchanger in the same manner as described in the above-mentioned U.S. Pat. No. 3,624,239, to Arthur P. Fraas. Heat which is produced in the lithium 17 by the reactions within the container 16, is transferred through the walls of the rotating container 16 to the flowing lithium 22 within the container 25. Thus, the lithium 22 is the actual heat exchange fluid. Separate sets of radial fins 20 and 21 are arrayed on the inner and outer vertical walls, respectively, of the rotating container 16 such that these fins aid in the transfer of heat between the two liquids 17 and 22. It should be noted that the opening in the upper portion of the container 16 is coupled by any suitable means to vacuum pumps and a tritium recovery unit, not shown, in a conventional manner. In the uppermost portion of the container 16 defining a partially recessed chamber, there are mounted a plurality of pulsed neodymium glass lasers 19, for example, having the respective outputs therefrom directed through respective optical filters 29. The maximum energy density of the individual laser beams from each of the lasers 19 is held to 10J/cm.sup.2 or less. This makes it possible to utilize mirrors with the lasers since presently available mirrors will withstand this kind of energy density. Accordingly, a plurality of respective plane-surface mirrors 30 are used at the top of the paraboloid in order to remove the lasers 19 from the direct path of reaction-produced neutrons, x-rays and charged particles. These mirrors 30 reflect the laser beams from the filters 29 into respective paths that are parallel with the axis of symmetry of the paraboloid, such that after further reflection from the surface 14 of the liquid lithium, all of the laser beams will end up at the focal point 18 of the paraboloid. It should be understood that the respective filters 29 and mirrors 30 may be mounted by respective brackets, not shown, to the inside wall of the upper part of housing 16, with the brackets extending from the filters and mirrors at right angles to the plane of the paper. A frozen D-T fuel pellet is either dropped or fired down the axis of symmetry from an injection station 28 in order to reach the focal point simultaneously with the light from the pulsed lasers 19. By calculation, it has been determined that a parabolic mirror does in fact meet the illumination uniformity requirement of 96%. It should be understood during normal operation that a plurality of fuel pellets are sequentially dropped or fired in timed sequence into the device of FIG. 1 and each pellet is ignited by the light from the pulsed lasers 19 as it reaches the focal point 18. In other calculations, it has been determined that the lasers will have to produce at the circumference of the mirror surface 14 an energy density of about 5.4 mJ/cm.sup.2 collimated to within a half angle of 43 .mu.rad and near the center a density of 10J/cm.sup.2 collimated within 1.8 .mu.rad. As mentioned above, such requirements fortunately compare favorably with the capabilities of presently available neodymium glass lasers. It has been estimated that 60 kJ of laser light is sufficient to produce 1800 kJ of energy. For a pellet 0.4 mm in radius with 60 kJ of 1.06 .mu.m light, the paraboloid mirror rotating at a frequency of 0.75 Hz would need to be 2.8 m in radius and 9.2 m in height. Although the requirement on the half angle of beam divergence is most severe for lasers whose rays follow paths closest to the periphery of the paraboloid mirror, the lasers located near the axis of the paraboloid, and which must produce the most power, need to be collimated to within a half angle of only 1.8 .mu.rad. The opening in the chamber 16 just above the paraboloid is about 5.5 m in diameter, and the opening above the lasers is about 1.5 m in diameter, for example. Exemplary parameters for each of the lasers 19 are as follows: 1) wavelength (frequency) is of a selected value in the range from 2000A.degree.-10,000A.degree.; 2) the pulse shape and power are the same as illustrated on page 141, FIG. 1a, of the above-mentioned publication in Nature 239 (1972) 139; 3) the pulse length is about 25 ns; and 4) the intensity (fluence) is 10J/cm.sup.2. Each of the injected pellets, for example, is a sphere with a radius of 0.4 mm and comprising 1/2 D.sub.2, 1/2T.sub.2, equimolar. The pellets are injected at a rate of about 1 sec..sup.-1. The lasers in the chamber 16 are caused to operate in a manner as described in an article by T. J. Burgess, published in IEEE Trans. on Plasma Science PS-1 No. 2, pp. 26-29 (1973). The present invention is not limited to the device of FIG. 1, as described hereinabove. Another preferred embodiment of the present invention is illustrated in FIG. 3 of the drawings which operates upon the same basic principle as the device of FIG. 1. In the device of FIG. 3, a liner 36 is provided with a plurality of apertures, as shown and is shaped to conform to the parabolic geometry required of the lithium mirror surface formed thereof in the operation of the device to be described hereinbelow. An inner structural wall 38 is provided with a plurality of apertures, as shown, and is separated from the liner 36 to define a plenum 37 therebetween. A main pressure vessel wall 40 is also provided with a plurality of apertures, as shown, and is separated from the wall 38 to define a main blanket chamber region 39 therebetween. An outer wall 42 is separated from the vessel wall 40 to define a chamber 41 therebetween. The liner 36 is provided with a lip portion 36' and the blanket region 39 and the chamber 41 are closed off by means of a closure member 53, such that the lip portion 36' and the member 53 define an opening 44 therebetween through which hot liquid lithium is arranged to flow from a heat exchanger, not shown, by means of conventional feed means, not shown. The outer wall 42 is provided with an exit hole 43 by means of a hollow extension 54 which is coupled by any suitable and conventional means back to the heat exchanger. The liquid lithium when flowing through the inlet 44, then flows into the plenum 37 where a smaller portion then flows through the apertures in the liner 36, and a larger portion flows through the larger apertures in the wall 38 to fill the chamber 39, and all the excess lithium then flows through the still larger holes in the vessel wall 40 into the chamber 41. The lithium then flows from the chamber 41 back to the heat exchanger through the opening 43 as discussed above. It should be understood that suitable pumps, not shown, are utilized to pump the lithium from the heat exchanger to the device of FIG. 3 and thence back to the heat exchanger. The mass flow rate of the lithium is about 10.sup.5 g/sec. The inlet temperature of the liquid lithium into the plenum 37 is about 673.degree. K., and the outlet temperature of the lithium exiting from the outlet 43 is about 1050.degree. K., for example. It should be noted that, when the device of FIG. 3 is being rotated during the operation thereof, the liquid lithium that flows through the apertured liner 36 will form a parabolic mirror surface 46. A member 48 which is supported in any desired and conventional manner is provided with an opening which is in axial alignment with the axis of rotation of the device. Mounted on the underside of the member 48 is an inverted conical mirror 45 with a half-angle of 45.degree. which is utilized to direct the laser light from a plurality of lasers, as represented by the plurality of laser beams 51 and 51', into the parabolic cavity as defined by the lithium mirror 46 on the liner 36. It should be noted that the plurality of lasers, not shown, for providing the laser beams 51 and 51' are stationary and are mounted by any suitable means external to the device of FIG. 3, and have the same exemplary parameters as the lasers utilized in the device of FIG. 1, and are caused to operate in the same manner as in FIG. 1. The laser beams must pass through windows in the rotating chamber, not shown, housing the device of FIG. 3, and the beams continue on to strike the rotating mirror 45. The window material can be the same as in the lasers themselves. The mirror 45 has a machined metal surface, for example, with a height of 6.86 m and a radius of 6.86 m, for example. The mirror 45 is provided with a hole at its tip through which frozen pellets like those of FIG. 1 are adapted to be sequentially injected from a source, not shown, and through the axial hole in the support member 48. The pellets are injected into the paraboloid cavity, for example, by means of a gas gun similar to that described by Hovingh et al. in the report UCRL-75368, May 3, 1973, of the Lawrence Livermore Laboratory. Each pellet would have to travel at a speed at least 20 m/sec to reach the focus 47 of the paraboloid in a time of the order of 1 sec or less. The gun described by Hovingh et al. would have a barrel length of 0.5 cm and would be energized by helium gas at a temperature of 20.degree. K. and a pressure of 7.3 torr. It should be understood that a similar gas gun is utilized in the device of FIG. 1 for pellet injection. Tracking of a pellet can be accomplished by a tracking laser beam 52 and an optical detector, not shown, as illustrated in FIG. 3. When the pellet reaches the focus 47 of the paraboloid, it would cut the laser beam 52, and the resulting reduction in signal at the optical detector can then be used to fire the high power lasers used to implode the pellet. It should be noted that the device of FIG. 3 is mounted on a turntable, not shown, and is adapted to be rotated in a manner similar to that for rotating restaurants, etc. The angular velocity of such a turntable for rotating the device of FIG. 3 is about 0.42 sec.sup.-1 = 25.2 rpm, for example. The parabolic mirror 46 has a height of 16.8 m and a top radius of 6.86 m, for example. The liquid lithium mirror has a thickness of 0.05 cm; the liner 36 of Nb, for example, has a thickness of 1.0 cm; the plenum 37 has a thickness of 10.0 cm; the wall 38 has a thickness of 5.0 cm; the main blanket region 39 has a thickness of 70.0 cm; the pressure vessel wall 40 has a thickness of 10.0 cm; and the outer vessel wall 42 has a thickness of 10.0 cm, for example. The mirror support member 48 is provided with an opening 50 which is coupled to a supersonic spray condenser(s), not shown, such as disclosed by L. A. Booth, Nuc. Eng. Des. 24 263 (1973), for the purpose to be discussed hereinbelow. The main purpose of the conical mirror 45 is to isolate the lasers from the pellet radiations. Since the conical mirror subtends a fractional solid angle of about 0.02, it will intercept only a few megawatts of particle flux emanating from the pellet. Thus, the mirror can be cooled, when such may be necessary, by passing a heat transport fluid through it in a conventional manner. The device of FIG. 3 operates in substantially the same manner as the device of FIG. 1, and both devices will produce a copious quantity of neutrons and x-rays. Also, the neutrons are utilized to breed tritium in the respective lithium blankets which trititum may be recovered in an external recovery system, not shown, in a conventional manner. The frequency at which pellet ignitions can be accommodated by the device of FIG. 3 will depend upon the time for the various structures to return to the state necessary to implode the next pellet. Necessary conditions which are readily apparent are: (1) vacuum should be re-established in the parabolic cavity; (2) solid structures supporting the parabolic surface should quit oscillating; (3) and waves launched on the parabolic lithium surface should damp out. A discussion of the times required to achieve these various conditions will now be given below. The absorption of x-rays and charged particles generated by the pellet will ablate the surface of the parabolic lithium cavity. If the pressure of this ablated material in the cavity is not reduced below 1 torr, the light on the next laser pulse may be refracted into such a direction as to miss hitting the next pellet. The work of Booth, as described in Nuc. Eng. Des, Vol. 24, p. 263, 1973, has shown that sufficient pumping speed can be developed by a supersonic spray condenser to reduce the pressure in a wetted-wall cavity below 1 torr in a time of the order of 1 sec. When the ablated material is completely removed, the equilibrium cavity pressure will be about 4 .times. 10.sup.-2 torr, which is the vapor pressure of lithium at 867.7.degree. K., the steady-state temperature of the parabolic mirror surface. The mechanical reaction of the ablated lithium as it leaves the liquid surface will launch waves in the bulk of the liquid. Other waves will be launched in the lithium by the sudden deposition of energy in the blanket by absorption of the neutron pulses. The combination of these disturbances will set the solid structures in the device into oscillation. The oscillations, however, will be a minor problem, since Booth has shown that they damp out in times of the order of milliseconds. The waves on the parabolic lithium surface, however, damp out more slowly. The damping time .tau. for waves of wavelengths l in an incompressible fluid is given by: EQU .tau. = l.sup.2 /4.pi..sup.2 v, where v is the kinematic viscosity of the fluid. The value of v is about 6.4 .times. 10.sup.-3 cm.sup.2 sec.sup.-2 at the temperature of the lithium at the parabolic surface. If the damping time is to be of the order of 1 sec, then the lithium surface must not propagate waves with wavelengths much longer than 0.5 cm. To assure a wavelength no longer than 0.5 cm, the lithium surface is divided into regions of approximately equal area having no side longer than 0.5 cm. This is accomplished by using solid partitions which just barely reach the free liquid surface of the paraboloid, as illustrated in FIG. 4 of the drawings. It should be noted that the height of the partitions in FIG. 4 has been exaggerated in comparison with the thickness of the liner 36 for the sake of clarity. Between microexplosions, the level of the liquid surface should be below the top of the partitions for points on the parabolic surface lying below the focal plane, this is guaranteed, inasmuch as the charged-particle flux from the pellet will vaporize the surface down to about 20 .mu.. For points lying above the focal plane, the liquid level can be lowered by pumping. After waves have died out in either case, the level can be restored by pumping lithium from the plenum through the liner 36. Consequently, the damping time for waves will be about 1 sec, and the free liquid surface will return to a parabolic figure in a like time. This invention has been described by way of illustration rather than by limitations and it should be apparent that it is equally applicable in fields other than those described. |
abstract | A method including providing a nuclear reactor neutron source that includes an enclosure delimiting a chamber, a nuclear reactor core arranged inside the chamber and configured to produce neutrons from a nuclear fuel element inside the nuclear reactor core; installing a beam generator arranged to generate a beam directed into the chamber; and installing, inside the chamber, a target arranged to eject neutrons upon impact of the beam such that neutrons are ejected from the target and emitted from the chamber. |
|
summary | ||
050733346 | claims | 1. In a nuclear system having a core of a plurality of wrapper tubes, and a fuel assembly disposed within each of the tubes, a self-actuated nuclear shutdown system comprising: a control rod guide tube surrounded by the wrapper tubes of the core of the nuclear system with a space defined directly above the guide tube being surrounded by upper ends of the wrapper tubes, a control rod disposed coaxially with said control rod guide tube; an electromagnet disposed above said control rod in the nuclear system; drive shaft means connected to said electromagnet for moving said electromagnet axially of said control rod guide tube over a predetermined distance; temperature-sensitive magnetic material forming the upper end of each of the wrapper tubes, the temperature-sensitive magnetic material of the wrapper tubes disposed entirely above the level at which the upper end of said control rod guide tube is located in the nuclear system, said upper ends of the wrapper tubes formed of the temperature-sensitive magnetic material each having an axial length equal to said predetermined distance over which said drive shaft means moves said electromagnet, and the temperature-sensitive magnetic material having a characteristic by which the saturation magnetic flux density thereof is reduced when the temperature thereof is raised above its Curie-point; said temperature-sensitive material and said electromagnet operable to establish a magnetic circuit which latches said control rod to said electromagnet, when the electromagnet is positioned in said space surrounded by the upper ends of the wrapper tubes and the temperature thereof is below its Curie-point, the magnetic circuit being broken when coolant flowing in the nuclear system through the wrapper tubes reaches a temperature sufficient to raise the temperature of the temperature-sensitive magnetic material above its Curie-point, whereupon said control rod will become unlatched from said electromagnet so as to drop into said control rod guide tube. a control rod guide tube surrounded by the wrapper tubes of the core of the nuclear system, a control rod disposed coaxially with said control rod guide tube; an electromagnet disposed above said control rod in the nuclear system; drive shaft means connected to said electromagnet for moving said electromagnet axially of said control rod guide tube over a predetermined distance; a respective extension tube of temperature-sensitive magnetic material extending coaxially from an upper end of each of the wrapper tubes, and the extension tubes surrounding a space directly above said control rod guide tube in the nuclear system, each said extension tube disposed entirely above the level at which the upper end of said control rod guide tube is located in the nuclear system, and having an axial length equal to said predetermined distance over which said drive shaft means moves said electromagnet, and the temperature-sensitive magnetic material having a characteristic by which the saturation magnetic flux density thereof is reduced when the temperature thereof is raised above its Curie-point; said temperature-sensitive material nd said electromagnet operable to establish a magnetic circuit which latches said control rod to said electromagnet, when the electromagnet is positioned within said space surround by the extension tubes and the temperature thereof is below its Curie-point, the magnetic circuit being broken when coolant flowing the nuclear system through the wrapper tubes reaches a temperature sufficient to raise the temperature of the temperature-sensitive magnetic material above its Curie-point, whereupon said control rod will become unlatched from said electromagnet so as to drop into said control rod guide tube. a control rod guide tube surrounded by the wrapper tubes of the core of the nuclear system with a space defined directly above the guide tube being surrounded by upper ends of the wrapper tubes, a control rod disposed coaxially with said control rod guide tube; an electromagnet disposed above said control rod in the nuclear system; drive shaft means connected to said electromagnet for setting said electromagnet at a predetermined position during normal operation of the nuclear system and for moving said electromagnet axially of said control rod guide tube over a predetermined distance; ferromagnetic material forming the upper end of each of the wrapper tubes, the ferromagnetic material of the wrapper tubes disposed entirely above the level at which the upper end of said control rod guide is located in the nuclear system, and said upper ends of the wrapper tubes formed of the ferromagnetic material each having an axial length equal to said predetermined distance over which said drive shaft means moves said electromagnet; a respective extension tube of temperature-sensitive magnetic material extending coaxially from the upper end of each of the wrapper tubes with a space defined directly above said guide rod control tube being surrounding by the extension tubes, each said extension tube disposed adjacent said predetermined position, and the temperature-sensitive magnetic material having a characteristic by which the saturation magnetic flux density thereof is reduced when the temperature thereof is raised above its Curie-point; said temperature-sensitive material and said electromagnet operable to establish a magnetic circuit which latches said control rod to said electromagnet, when the electromagnet is positioned in said space surrounded by said extension tubes and the temperature thereof is below its Curie-point, the magnetic circuit being broken when coolant flowing in the reactor system through the wrapper tubes reaches a temperature sufficient to raise the temperature of the temperature-sensitive magnetic material above its Curie-point, whereupon said control rod will become unlatched from said electromagnet so as to drop into said control rod guide tube. 2. In a nuclear system having a core of a plurality of wrapper tubes, and a fuel assembly disposed within each of the tubes, a self-actuated nuclear shutdown system comprising: 3. In a nuclear system having a core of a plurality of wrapper tubes, and a fuel assembly disposed within each of the tubes, a self-actuated nuclear shutdown system comprising: |
description | The present invention relates generally to a detector system for x-ray imaging and more particular to a detector system provided with edge-on detector modules. Among the semi-conductor material that may be used a detector materials silicon has many advantages such as high purity and low energy required for creation of charge carriers and also high mobility of charge carriers, all of which makes silicon predominating in the available semiconductor materials used primarily for radiation detectors. By implanting heavily doped layers as electrical contacts on top of low doping silicon and by applying a reverse bias to the junction to make the detector fully depleted, the radiation created charge carriers electron-hole pairs can be collected by the corresponding charge collecting electrodes. There has been a considerable interest in silicon as the material for photon-counting detectors in particular for medical imaging. By far most detectors operate in an integrating mode in the sense that they integrate the signal from a multitude of x-rays and this signal is only later digitized to retrieve a best guess for the number of incident x-rays in a pixel. The last years so called photon counting detectors have emerged as a feasible alternative in some applications and commercially available mainly in mammography. The photon counting detectors have an advantage since in principal the energy of each interacting x-ray can be measured which yields additional information about the composition of the object, leading to improved image quality and/or a decrease in radiation dose. Silicon has been used successfully in applications with lower energy as is for example outlined by M. Danielsson, et al., “Dose-efficient system for digital mammography”, Proc. SPIE, Physics of Medical Imaging, vol. 3977, pp. 239-249 San Diego, 2000. The main challenge with silicon is its low atomic number and low density which means it has to be made very thick for higher energies to be an efficient absorber. The low atomic number also means the fraction of Compton scattered x-ray photons in the detector will dominate over the Photo absorbed photons which will create problem with the scattered photons since they may induce signals in other pixels in the detector which will be equivalent to noise in those pixels. There has been a continuous effort on evaluating the feasibility of employing silicon for high energy applications, such as computed tomography, as described in U.S. Pat. No. 8,183,535 B2 Mats Danielsson et al. “Silicon detector assembly for x-ray imaging”, Cheng Xu et al.: “Energy resolution of a segmented silicon strip detector for photon-counting spectral CT” Nuclear Instruments and Methods in Physics Research 715201311-17 and Xuejin Liu et al.: “Spectral response model for a multibin photon-counting spectral computed tomography detector and its applications” Journal of Medical Imaging 23 2015 033502. An edge-on configuration of the silicon detector is described, with which the detection efficiency of silicon is increased significantly. Thin anti-scatter foil of a high Z element is attached to substrate to stop the scattered photons as a result of Compton scattering from reaching other silicon substrates. Detectors having detector modules provided with collimators are illustrated in US2004/0251419 A1, Nelson et al. There it is shown how each detector in a strip detector is provide with a collimator. Adjacent strip detectors are separated by an air-gap. Performance degradation from radiation-induced damages is a problem for any semi-conductor detectors. The relevant study on silicon has been carried out for decades. Particles traversing a silicon detector may interact with the material leading to ionizing or non-ionizing energy deposition. In both cases damage to silicon detector is possible. There are two types of radiation damages in silicon detectors, bulk damage and surface damage. The bulk damage due to the non-ionizing energy loss of incident particles is hard to happen for energy less than around 300 keV, whereas the surface damage causes most of the problems for silicon detectors used in the energy range of x-ray imaging from 40 keV to 250 keV. The surface damage is mainly introduced by the ionizing energy loss of charged particles or x-ray photons, which leads to the build-up of positive charges and traps in silicon dioxide and at the interface between silicon and silicon dioxide. The success of silicon detectors using the planar processes relies strongly on the possibility to passivate the front-side surface with an oxide layer. Most often a silicon dioxide layer is grown thermally on silicon substrate by exposing silicon to an oxidizing ambient at elevated temperatures. When an x-ray interacts with a silicon detector, a cloud of charge carriers is released. The charge carriers created within silicon can be collected by charge collecting electrodes under an applied electric field, but those created within the silicon dioxide layer are trapped at the interface between silicon and silicon dioxide. Within several nanometer from the interface between silicon and silicon dioxide, the region is highly disordered, where the deep level defects are located. The deep level defects in silicon dioxide can trap holes and form fixed and positive oxide charges, which would cause some problems of the detector. There are some other kinds of defects in silicon dioxide and at the interface between silicon and silicon dioxide, discussed by Jiaguo Zhang: X-ray radiation damage studies and design of a silicon pixel sensor for science at the XFEL, and Jörn Schwandt: Design of a radiation hard silicon pixel sensor for x-ray science. The defects induced by radiation impact electrical properties and mainly cause the following performance degradation of silicon detectors: increase of leakage current, increase of depletion voltage, increase of capacitance, formation of electron accumulation layer, decrease of breakdown voltage and charge loss near the interface between silicon and silicon dioxide. The electron-accumulation layer is relevant to the change of electrical properties of silicon detectors, and prevents the full depletion of a detector at the surface. The charge collection efficiency would also be affected by the electron-accumulation layer in the volume near the front-side surface of a detector. Consequently, there is a need in the art for semi-conducting detectors, in particular silicon detectors, which are less sensitive when exposed to x-ray radiation. An object of the present disclosure is to provide a detector system having detectors with improved robustness with regard to x-ray sensitivity. A more particular object is to provide a detector system with edge-on detector modules with improved robustness with regard to x-ray sensitivity. According to an aspect of the proposed technology there is provided a detector system for x-ray imaging. The detector system comprises a detector having a plurality of edge-on detector modules. Each of the edge-on detector modules comprises a first edge that is adapted to be oriented towards an x-ray source and a front-side running essentially parallel to the direction of incoming x-rays. The front-side comprises at least one charge collecting electrode. At least a subset of the plurality of edge-on detector modules being pairwise arranged, front-side to front-side, whereby a front-side to front-side gap is defined between the front-sides of the pairwise arranged edge-on detector modules. The pairwise arranged edge-on detector modules are associated with an anti-scatter collimator arranged in the x-ray path between the x-ray source and the edge-on detector modules and overlapping the front-side to front-side gap. Embodiments of the proposed technology provide a detector system where the sensitive insulating layer provided on the detector module front-side is protected from damaging and deteriorating inflicted by direct impact from x-ray radiation. Particular embodiments of the proposed technology also provides a detector system which is insensitive to misalignment of detector modules and thus keeps a steady geometrical efficiency. Particular embodiments of the proposed technology also provides a mechanism to prevent artifacts from direct illumination on backsides or shadowing effects. The proposed technology also provides various detector system designs that enable improved charge collection. FIG. 8 is a schematic diagram of an x-ray detector system according to an exemplary embodiment. In this example there is shown a schematic view of an X-ray detector with x-ray source B emitting x-rays C. The detector comprises a number of detector modules stacked side by side. The detector modules comprises an edge D pointing back towards the source, and they are preferably arranged in a slightly curved overall configuration. Two possible scanning motions (E, F) of the detector are indicated. In each scanning motion the source may be stationary or moving, in the scanning motion indicated by E the x-ray source and detector may be rotated around an object positioned in between. In the scanning motion indicated with F the detector and the source may be translated relative to the object, or the object may be moving. Also in scan motion E the object may be translated during the rotation, so called spiral scanning. By way of example, for CT implementations, the x-ray source and detector may be mounted in a gantry that rotates around the object or subject to be imaged. FIG. 7 provides an illustration of a particular edge-on detector in larger detail. It is illustrated how a front-side of a detector comprises a number of detector strips wherein each strip comprises a number of depth segments formed by charge collecting electrodes running in the direction of the incoming x-rays, in this particular geometry in the negative y-direction. FIG. 1 is a schematic diagram illustrating an example cross section of a semi-conductor substrate, e.g. a silicon substrate 101 with surface radiation damage. The metal contacts 102 of the charge collecting electrodes are deposited on top of P-plus implantation 103 of the corresponding electrodes. The oxide layer 104 on the front-side of a silicon detector is most sensitive to x-ray radiation, with fixed positive charge formed at the interface between silicon and silicon dioxide after long term x-ray radiation. Ideally, charge carriers released by each interacting photon will move along the field lines and then be collected by the corresponding charge collecting electrodes under the effect of an applied electric field by feeding a reverse bias to the backside metal contact 105 of the detector. However, an electron accumulation layer 106 formed below the interface between silicon and silicon dioxide prevents the full depletion of the sensor at the front-side surface, which results in weak electric field in this region and thus loss of charge carriers. A high electric field is also a consequence near the edge of charge collecting electrodes indicated by 107, leading to a reduction of break down voltage. The detector modules illustrated in FIG. 8 comprises a semi-conducting material, such as silicon, that have a front-side and a back-side. The front-side, of which FIG. 1 provides an illustration, carries the electronic features of the detector. In particular embodiments routing traces connects the charge collecting electrodes with front-end electronics, and there are also embodiments that may also comprise optional features such as doped and un-doped regions as well as insulating regions. The insulating regions are highly sensitive to x-ray radiation and will be affected negatively if x-rays impinge directly on the front-sides. It is an object of the proposed technology to provide a detector with improved robustness in so far that the front-side of the detector modules making up the detector are protected from the possibly deteriorating effects of impinging x-rays. That is, the proposed technology aims to provide a mechanism whereby x-ray sensitive front-sides of the detector modules are protected from damaging x-rays. The protective features of the proposed technology also provides for a detector system that enables improved charge collection. A basic mechanism is to protect the front-side of edge-on detectors, such as silicon edge-on detectors by using an anti-scatter collimator which prevents high intensity direct x-ray beam from reaching the front-side volume of the detectors, thereby correspondingly reducing the risk of radiation damage. The anti-scatter collimator is needed for most x-ray medical imaging applications to reduce the amount of object scatter in order to e.g. increase the image quality. Furthermore, the present invention can help to keep a steady geometrical efficiency in case of misalignment of detector modules, which is another benefit. In what follows the detector system will be described by using a particular detector material in the form of silicon. This is however not an essential feature since the various embodiments to be described work equally well with any semi-conducting material. That is, the detector system according to the proposed technology may comprise detector modules of any suitable semi-conducting material. To this end there is provided a detector system for x-ray imaging. Reference is made to FIG. 2 which illustrates schematically a detector system that comprises a detector having a plurality of edge-on detector modules 201. Each of the edge-on detector modules 201 comprises a first edge that is adapted to be oriented towards an x-ray source and a front-side 202 running essentially parallel to the direction of incoming x-rays. The front-sides 202 of the detector modules comprises at least one charge collecting electrode. At least a subset of the plurality of edge-on detector modules 201 making up the detector are pairwise arranged, front-side to front-side, whereby a front-side to front-side gap is defined between the front-sides of the pairwise arranged edge-on detector modules 201. The pairwise arranged edge-on detector modules 201 are associated with an anti-scatter collimator 203 arranged in the x-ray path between said x-ray source and said edge-on detector modules 201 and overlapping said front-side to front-side gap. FIG. 2 provides a simplified diagram illustrating how a collimator 203 is arranged over the front-side to front-side gap defined by two adjacent detector modules 201. This particular arrangement provides protection to the front-sides 202 of the detectors. The fact that the collimator overlaps the gap also provides protection from x-rays that impinges on the detector at an angle. In greater detail there is shown a pair of detector modules 201 with front-side surfaces 202 facing each other and an anti-scatter collimator 203 positioned or arranged on top of the front-side surfaces of both detector modules. The anti-scatter collimator is made of high Z material which can efficiently absorb the direct x-ray beam and x-ray photons scattered by the object. The detector modules are arranged in edge-on configuration by orienting an edge of the detector modules towards incoming x-rays. In the present embodiment, the front-sides of the detector modules face each other, thus the anti-scatter collimator covers the front-side surface of both detector modules, which prevents the direct x-ray beam from reaching the front-side surfaces of the detector modules, and thus less surface damage. As can be seen in e.g. FIG. 8, a detector according to the proposed technology may comprise a number of detector modules stacked side-by-side. The stacking of the modules should, according to the proposed technology, comprise at least a subset of detector modules that are pairwise arranged in such a manner that the front-side of a particular detector module faces the front-side of another detector module. It is preferable if the anti-scatter collimator 203 comprises a collimator of a high Z material. Since the collimator is intended to absorb the impinging radiation the fact that there is a high Z material will ensure an efficient absorption and hence a reduced risk that high energy radiation impinges on the sensitive parts of the detector modules. That is, the sensitive parts arranged on the front-side of the detector modules. A particular embodiment of the proposed technology provides a detector system wherein the front-side to front-side gap between adjacent detector modules comprises an anti-scatter foil. This optional feature will provide still further protection to the front-sides since the anti-scatter foil will provide a counter measure to possible residual radiation emanating from, e.g. the anti-scatter collimator 203. The anti-scatter foil may in a particular embodiment comprise a high Z material, such as tungsten. FIG. 3 is a schematic diagram illustrating how a pair of detector modules 201 is provided with an anti-scatter foil 201 that is attached in between the front-sides of the detector modules. Also shown is an anti-scatter collimator 203 provided on top of the anti-scatter foil. The front-side surfaces of both detector modules are attached to the anti-scatter foil, thus the anti-scatter collimator covers both the anti-scatter foil and the front-side surfaces of the detector modules, which protects the front-side surfaces of the detector modules. FIG. 4 is in turn a schematic diagram illustrating how the silicon detector pairs as illustrated in FIG. 3 are positioned next to each other to form an array of detector modules. In order to have the detector modules suffering from less radiation damage, the front-side surfaces should be covered by the anti-scatter collimator to prevent the direct x-ray beam from reaching the x-ray sensitive volume. One should avoid the cases illustrated in FIG. 5, with the front-side edge 202 of the silicon detector module either aligned with the edge of the anti-scatter collimator 203 or out of the coverage of the anti-scatter collimator. In both cases, the direct x-ray beam may impinge on the front-side surfaces of the detector modules, resulting in radiation damage. Therefore, the covered volume at the front-side surface should exceed 1% of the total detector volume to avoid the above two cases. FIG. 6 is a schematic diagram illustrating how the above arrangement of anti-scatter collimator can help to keep a steady geometrical efficiency in case of geometrical misalignment of the detector modules. This example illustrates an edge-on configuration of the detector modules 201 with the anti-scatter collimator 203 covering both the front-sides of the detector modules and the anti-scatter foil 204. A volume of detector modules on the front-side becomes shadowed 206. Mechanical alignment may be a challenge for long detectors and geometrical misalignment may cause artifacts in images. As indicated in FIG. 6 of the present embodiment, there is almost no loss of geometrical efficiency caused by the geometrical misalignment of the detector modules. Reference is now made to FIG. 4 which provides a schematic illustration of an array of detector modules where a number of detector modules are pairwise arranged so that their front-sides face each other. Each of the pairs is provided with an anti-scatter collimator arranged so as to overlap the gap between the front-sides of adjacent detector modules. In the drawing it is also illustrated an optional anti-scatter foil arranged in the space between the detector modules. The backside of a detector module arranged in the pairwise configuration shown will face the backside of another neighboring detector module. This will lead to a back-side to back-side gap 205 between adjacent detector modules. According to a particular embodiment of the proposed technology there is thus provided a detector system wherein the backside of at least one edge-on detector module 201 of the pairwise arranged edge-on detector modules 201 is arranged to face the backside of a corresponding edge-on detector module 201 in such a way that a back-side to back-side gap is formed between said edge-on detector module 201 and said corresponding edge-on detector module 201. The back-side to back-side gap defined by adjacent detector modules may according to a particular embodiment be provide with an attenuating material that is arranged to prevent direct x-ray irradiation on the backside of said edge-on detector modules 201 or shadowing effects. A particular purpose with the attenuating material provided in the gap is to make the detected number of x-ray counts less sensitive to geometrical misalignment. The narrow gap may to this end be filled with an attenuator, such as silicone, which holds a similar attenuation characteristic as silicon. In case of misalignment, the attenuator provided between the detector modules will prohibit direct illumination on the detector side and make the detected spectrum close to that which has travelled through the silicon bulk. Another beneficial feature achieved is that the attenuating material may reduce the amount of x-ray radiation that penetrates the backside of the edge-on detector modules 201. To this end a high Z material such as tungsten could be used, those materials may however lead to shadowing which will negatively affect the efficiency of the detector, a mere air-filled gap would in turn result in direct illumination on the backsides which will also lead to a negative impact on the detector system. To this end the inventors have realized that a preferred material should have similar attenuation characteristics as the semi-conductor material used in the detector, e.g. silicon. A particular example that may be used in the case the detector modules comprises silicon is silicone, which contains silicon. Silicone has similar attenuating features as silicon and this combination forms a particular suitable embodiment. Many other combinations or detector materials and attenuating materials are however possible. The main purpose being that the attenuating material have similar attenuation characteristics as the material used as the detector material. The embodiments described above are merely given as examples, and it should be understood that the proposed technology is not limited thereto. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the present scope as defined by the appended claims. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. M. Danielsson, et al., “Dose-efficient system for digital mammography”, Proc. SPIE, Physics of Medical Imaging, vol. 3977, pp. 239-249 San Diego, 2000 U.S. Pat. No. 8,183,535 B2 Mats Danielsson et al. “Silicon detector assembly for x-ray imaging” Cheng Xu et al.: “Energy resolution of a segmented silicon strip detector for photon-counting spectral CT” Nuclear Instruments and Methods in Physics Research 715201311-17 Xuejin Liu et al.: “Spectral response model for a multibin photon-counting spectral computed tomography detector and its applications” Journal of Medical Imaging 23 2015 033502 US2004/0251419 A1 Nelson et al. “Device and system for enhanced SPECT, PET, and Compton scatter imaging in nuclear medicine” J. Zhang, “X-Ray Radiation Damage Studies and Design of a Silicon Pixel Sensor for Science at the XFEL”, Doctoral Thesis, University of Hamburg, DESY-THESIS-2013-018 2013. J. Schwandt, “Design of a Radiation Hard Silicon Pixel Sensor for X-ray Science”, Doctoral Thesis, Hamburg University, DESY-THESIS-2014-029 2014. |
|
056299710 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of nuclear medicine. Particularly, the present invention relates to the field of transmission scanning to provide nonuniform attenuation correction within a gamma camera system. 2. Background of the Invention Non-uniform photon attenuation is an important factor that affects the quantitative accuracy of images collected using Single Photon Emission Computerized Tomography (SPECT) camera systems and can decrease the sensitivity of these systems for lesion detection. Nonuniform photon attenuation distorts images by interfering with and partially absorbing the radiation emitted from an organ containing a radio-pharmaceutical. Photon attenuation within SPECT systems tends to degrade images by also introducing image artifacts and other distortions that can result in false positive detection or the undetection of lesions. The effects of photon attenuation are especially complex in cardiac studies as a result of nonuniform attenuation attributed to the thorax. In transmission scanning, the source of radiation is directed toward the associated scintillation detector through the object of interest or patient. If the radiation field is significantly larger than the patient, the radiation source is allowed to directly radiate the detector, causing a high count rate in the scintillation detector. Those parts of the detector that become directly radiated are called unobstructed portions of the detector. It is not advantageous to allow large unobstructed detector areas because the resultant increase in count rate can lead to image degradation and in some cases the event detection electronics and processes can become overloaded (e.g., due to pulse pile-up) and temporarily terminate operation. These high count rates tend to reduce the imaging performance of the imaging system by loading down the signal detection and processing circuitry of the gamma camera. Transmission computed tomography (TCT) can be used as a method for generating a nonuniform attenuation correction distribution. The transmission image data is gathered using a known source (e.g., line, sheet, or flood) of radiation. If performed separately from the SPECT emission study, the collection of the transmission data requires additional data acquisition time and the collection of the transmission and emission data is susceptible to misregistration effects due to patient (e.g., "object") movement between the data gathering sessions. However, whether the transmission data is collected simultaneously with the collection of the emission data or not, the patient is generally exposed to additional radiation in order to collect the transmission data. Depending on the size and shape of the patient, different amounts of transmission radiation are required in order to collect the minimum required amounts of transmission data. Systems overexpose the patient with transmission radiation in order to obtain the minimum required amount without regard to the shape or size of the patient. What is needed is a system that can effectively minimize the exposure period of the patient to radiation utilized in collection of the transmission data by considering the particular size and shape contributions of the patient. The present invention offers such advantageous solutions. Accordingly, it is an object of the present invention to provide improvements within gamma camera systems utilizing nonuniform attenuation correction techniques for improved image quality generation. It is an object of the present invention to determine the minimum exposure time required for the most attenuating portion of a scanned object during a transmission study. It is an object of the present invention to provide the above while considering the size and shape contributions of a particular patient. It is another object of the present invention to provide a reduced radiation exposure period for generation of transmission data used in creating a nonuniform attenuation correction distribution. These and other objects of the present invention not specifically mentioned above will become clear upon discussions of the present invention herein. SUMMARY OF THE INVENTION A scan speed procedure and method is described wherein a minimum radiation exposure period is determined on an object by object basis for a transmission study. Two transmission scan phases are performed including a prescan followed by a second transmission scan phase. The first scan consists of a transmission prescan performed using a radiation source over the object. This prescan is of a rapid and predetermined duration (Tp). A resultant count density associated with the object is then generated and examined. The portion having the smallest count density (Cm) is determined and a value (Co) representing the minimum required number of counts for transmission study is given. From the above, a transmission period (Ts) is determined by the system and the second transmission phase (a multi-pass scan phase) is performed for the duration Ts. The computed duration Ts represents the minimum exposure duration required to collect transmission data to ensure that the count density distribution associated with the object will contain at least Cm count density over each portion of the object. Specifically, embodiments of the present invention include an mechanism for collecting transmission data associated with an object, the mechanism including: a scintillation detector for receiving radiation and reporting image information; a line source of radiation for emitting transmission radiation through the object to the scintillation detector; a processor coupled to receive information from the scintillation detector and coupled to control the line source of radiation, the processor for controlling the line source of radiation to perform a first transmission prescan phase over the object for a first duration and generating in response thereto a first count density information; the processor for computing a second duration for a second transmission scan phase based on the first count density information; the processor for controlling the line source of radiation to perform the second transmission scan phase over the object for the second duration and generating in response thereto a second count density information, the second duration representing a minimum duration of exposure of the object required for generating the second count density information; the processor for generating a set of attenuation correction factors based on the second count density information, the set of attenuation correction factors for use in correcting image data gathered by the scintillation detector during emission scanning; and a memory unit coupled to store and provide access to the first and the second count density information. Embodiments of the present invention include the above and wherein the second count density information is a distribution over different portions of the object and wherein the processor is for receiving, as input, a minimum count density wherein the distribution contains at least the minimum count density for each portion of the object, wherein the processor is for analyzing the first count density information and determining a minimum observed count density in response thereto wherein the minimum observed count density corresponds to a portion of the object that exhibits maximum attenuation and wherein the processor determines the second duration according to the procedure: ##EQU1## wherein Ts is the second duration, Co is the minimum observed count density, Tp is the first duration, and Cm is the minimum count density. Embodiments of the present invention include in a nuclear camera system having a pair of scintillation detectors for receiving radiation and reporting image information; a pair of radiation line sources each for emitting transmission radiation through an object to an associated scintillation detector; and a computer system, a computer implemented method of collecting transmission data associated with the object, the method including the steps of: obtaining a minimum count density value desired for each portion of a resultant count density distribution; controlling the pair of radiation line sources to perform a first transmission prescan phase over the object for a first predetermined duration and generating in response thereto a first count density distribution; computing a second duration for a second transmission scan based on the first count density distribution; controlling the pair of radiation line sources to perform the second transmission scan phase over the object for the second duration and generating in response thereto the resultant count density distribution, the second duration representing a minimum duration of exposure of the object required to generate the second count density distribution; and generating a set of attenuation correction factors based on the second count density information, the set of attenuation correction factors for use in correcting image data acquired during emission scanning. |
047598999 | abstract | A nuclear reactor includes a core submerged in a pool of liquid. Under normal conditions, coolant flows through the core without intermixing with the liquid in the pool. In the event of failure of the primary coolant circulation system, liquid from the pool flows through openings in the primary circulation system so as to cool the core by natural convection. Flow through the openings during normal operating conditions may be controlled regardless of the flow rate. |
summary | ||
description | This application is a national phase of International Application No. PCT/EP2008/068172, entitled “METHOD OF PROCESSING FISSION CHAMBER MEASUREMENT SIGNALS”, which was filed on Dec. 22, 2008, and which claims priority of French Patent Application No. 07 60331, filed Dec. 24, 2007. The present invention relates to the area of non-destructive measuring techniques. More precisely, the invention concerns a method to process measurement signals delivered by a fission chamber and obtained by active neutron interrogation. The processing method of the invention is particularly well adapted to the processing of raw signals delivered by a fission chamber calibration device such as a device subject of a patent application filed on this same day by the Applicant and titled “Device to measure count rates and associated fission chamber calibration device”, these devices being recalled in the present application. Fission chambers are used to detect neutrons. A fission chamber contains fissile matter and a gas able to be ionized. Under the action of neutrons, the fissile matter emits particles which ionize the gas. The quantity of ionized gas translates the quantity of neutrons received in the fission chamber. Only part of the fissile matter, called the “effective mass” takes part in the emission of particles which ionize the gas. In practice, precise knowledge of the effective mass is necessary to determine absolute physical magnitudes i.e. the neutron flux or spectral indices. The processing method of the invention can be used to calculate the effective mass of the fissile isotope from measurements delivered by a calibration device such as the device mentioned above. Up to date, the calibration of fission chambers is conducted in a nuclear reactor either in a thermal spectrum (or thermal column) or a fission spectrum. Numerous calibration methods have been developed in this respect. These methods all require the use and availability of a research reactor. For safety reasons, these methods require the setting up of cumbersome experimental procedures and are therefore costly. In addition, research reactors provided with calibration devices are becoming increasingly less numerous worldwide, hence the need to travel if it is desired to calibrate a fission chamber. The processing method of the invention allows the reliable, precise, controlled determination of the effective masses of fission chambers, without the above-mentioned disadvantages. The invention concerns a method to determine the effective masses of N deposits of fissile matter respectively placed in N measurement fission chambers, N being an integer of 1 or higher, characterized in that it comprises: A) a first measuring step in which the count rate is measured of N deposits of fissile matter of known effective masses respectively placed in N calibration fission chambers that are respectively identical regarding their outer dimensions to the N measurement fission chambers, to form a matrix [C]0 of count rates of known fissile matter deposits, B) a second measuring step during which the count rate is measured of N deposits of fissile matter placed in the N measurement fission chambers, to form a matrix [C] of count rates of the fissile matter deposits, the second measuring step being conducted under identical measuring conditions to the measuring conditions under which the first measuring step is conducted, and C) a computing step to calculate a column matrix [m] such that:[m]=[C]·I([a]×([a]0−1×[m]0−1×[C]0)), the coefficients of the matrix [m] being the effective masses to be determined, the symbols “·I” and “x” respectively being the “matrix division” operator and the “matrix product” operator, and the matrices [a], [a]0−1 and [m]0−1 respectively being: matrix [a], a known matrix of the isotopic analyses associated with the N deposits of fissile matter whose effective masses are to be determined, matrix [a]0−1, an inverse matrix of a known matrix [a]0 of the isotopic analyses associated with the N deposits of fissile matter of known effective masses, matrix [m]0−1, an inverse matrix of a known matrix [m]0 whose coefficients are the known effective masses of the N known deposits of fissile matter. According to an additional characteristic of the method of the invention, a variance matrix var[m] of matrix [m] is calculated, such that:var[m]={var[C]+[mij2]×(var[a]×[Xij2]+[aij2×var[X])}·I{([a]×[X])ij2]}, in which: var[C] is the variance matrix of matrix C, var[a] is the variance matrix of matrix [a], var[X] is the variance matrix of matrix [X] such that:[X]=[a]0−1×[m]0−1×[C]0, [mij2] is the matrix consisting of the terms mij to the power of 2, the terms mij being the coefficients of matrix [m], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix, [aij2] is the matrix consisting of the terms aij to the power of 2, the terms aij being the coefficients of matrix [a], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix, [Xij2] is the matrix consisting of the terms Xij to the power of 2, the terms Xij being the coefficients of matrix [X], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix, [([a]×[X]ij2] is the matrix consisting of the terms ([a]×[X])ij to the power of 2, the terms ([a]×[X])ij being the coefficients of the product matrix [a]×[X], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix. In substance, the invention comprises three parts: a) Equating the problem which, via a matrix equation system, allows the count rate recorded for the fission chambers to be expressed in relation to the effective masses, to the isotopic compositions of the chambers, and to the effective macroscopic fission cross-sections per unit of mass of the isotopes in the neutron spectrum with respect to the considered configuration of the calibration device, b) Primary calibration intended to determine the effective macroscopic cross-sections per unit of mass of the different isotopes of interest in a given configuration of the calibration device (this step requires the use of primary standard fission chambers whose effective mass and isotope compositions are accurately known, these primary standards then possibly being derived from specific fabrication or having been previously calibrated in another calibration device (e.g. a reactor), c) A secondary calibration which, with knowledge of the isotope compositions and count rates obtained in the calibration device by active neutron interrogation, allows determination of the effective mass of the main isotope contained in the fission chambers. The processing method of the invention, for all actinides and using a calibration device in fast neutron configuration, allows calibration accuracies to be obtained that are equivalent to those obtained in a reactor. For a calibration device in thermal neutron configuration, the processing method of the invention allows accuracies to be obtained which are equivalent to those obtained in a reactor for fissile isotopes with thermal neutrons. In all the figures, the same references designate the same parts. FIGS. 1-4, as a non-limiting example, show a fission chamber count rate measuring device, which delivers count rate measurements able to be processed using the method of the invention. FIG. 1 illustrates a measurement cell which takes part in the count rate measuring device. The measurement cell 1 consists of an enclosure 2 which contains a material 3 in which a cavity 4 is formed, and of a neutron counter K. The material forming the enclosure 2 is polyethylene for example, and the material 3 is graphite for example. A longitudinal cavity 5 able to receive a fission chamber is formed inside the material 3. A neutron generator 6 is placed in the material 3 in the vicinity of the cavity 5. The cylindrical cavity 5 opens into cavity 4 via an opening O. In the embodiment shown in FIG. 1, the neutron counter K is placed next to the enclosure 2. The invention also concerns the case in which the neutron counter is located inside the enclosure 2. FIG. 2 is a partial cross-sectional view of a first exemplary structure which takes part in the count rate measuring device. The structure shown in FIG. 2 is intended to obtain a fast neutron spectrum. The cavity 5 contains two coaxial cylindrical housings 8, 9, housing 8 surrounding housing 9. The housings 8 and 9 are in stainless steel, for example, and 1 mm thick. A foil of material 13 e.g. a cadmium foil 1 mm thick, covers the outer face of the cylinder 9. The function of the foil material 13 is to capture the thermal neutrons i.e. the neutrons whose energy is less than 0.625 eV. A block of material 10 is placed in the space which separates the foil of material 13 from the housing 8. The material 10 e.g. borolene (i.e. boron and polyethylene) has a thickness of 16 mm for example. Two alignment bushings 15 and 16 hold in place and align the cylindrical housings 8 and 9 inside the cavity 5. An abutment B closes the cavity on the side of the alignment bushing 16. The fission chamber CH is placed inside the cylindrical housing 9. A first end of the fission chamber is connected to a connection element 12 which collects the electrons created by ionization of the gas contained in the chamber. This first end of the fission chamber is placed at a distance D from the opening O, the other end of the chamber being placed at a distance d from the abutment B. The connection element 12 is connected to a rigid coaxial cable 11. A cylindrical tube 17 for example a tube in stainless steel 1 mm thick aligned with the cylindrical housing 9 is placed in cavity 4. An alignment bushing 14 holds the rigid coaxial cable 11 in the cylindrical tube 17. A connector connects the rigid coaxial cable 11 to a flexible measuring cable 7 which transmits the signal towards processing circuits (not shown in FIG. 2; see FIG. 3). The guide and positioning system consisting of elements 14, 15 and 16 advantageously guarantees good reproducibility of the axial position and radial alignment of the chamber CH. The accuracy obtained for this position can be in the order of 1 mm for example, even less. Also the fission chamber CH, the connection element 12 and the coaxial cable 11 are capable of moving longitudinally inside the cylindrical tube 9. The longitudinal movement of the fission chamber advantageously allows an optimal position of the chamber to be sought, namely the position in which measurement results correspond to maximum flux. The materials and dimensions of the structure of the invention illustrated in FIG. 2 are preferably obtained using the Monte-Carlo N-Particle calculation code. It is precisely with this calculation code that the materials and dimensions mentioned above were obtained. However, other materials having equivalent characteristics could also be chosen to form this structure. The choice of these other materials would then entail different sizing to obtain substantially equivalent performance levels. The materials mentioned above allow a calibration device to be formed which has “acceptable” dimensions i.e. a device that is neither too voluminous nor too cumbersome. The choice of stainless steel for the cylindrical housings 8, 9 and 17 is able to impart excellent rigidity to the entire device and to guarantee resistance to wear. The choice of borolene is warranted through the good resistance of this material to ageing, through its efficacy in terms of thermal neutron capture and its low cost. The alignment device 14, 15, 16 of the fission chamber is specific for each chamber diameter considered. The alignment bushings 14, 15 16 and the abutment B are in stainless steel for example. The diameters of the alignment bushings and the machining of the abutment B are adapted to the diameter of the rigid coaxial cable 11. In the structure described above, only those neutrons which are not slowed down/thermalized in the graphite of the cell and in the borolene enter inside the fission chamber. Therefore the fission chamber only sees the fast neutrons emitted by the generator 6, i.e. those neutrons which have not undergone any interaction. FIG. 3 is a partial cross-sectional view of a second exemplary structure which takes part in the count rate measuring device. The structure in FIG. 3 is adapted to obtaining a thermal neutron spectrum. The cavity 5 comprises all the constituent elements already described with reference to FIG. 2, with the exception of the block of material 10 and the cadmium foil 13. The space between the housings 8 and 9 here is filled with air. As previously, the position of the fission chamber can be adjusted longitudinally using sliding means as mentioned previously for example. The neutrons derived from the generator 6 here are able to enter the fission chamber irrespective of their energies. However, these neutrons beforehand pass through a thickness of graphite of between 0 cm and about 40 cm for example, depending on the position taken up by the fission chamber in the housing 9, making it possible to discriminate between their energy in relation to their time of arrival at the fission chamber i.e. in relation to the graphite thickness through which they have passed. As a non-limiting example, the calculations made using the Monte-Carlo MCNP4C2 code have shown that more than 99.9% of the neutrons emitted by a neutron generator with a firing frequency of 125 Hz, after each firing, are thermal neutrons over a time range ranging from between 700 μs as and 3,500 μs, irrespective of the axial position of the chamber in the calibration device. FIG. 4 is a block diagram of the fission chamber count rate measuring device. The measuring device comprises: a measurement cell 1 such as described above, in which a fission chamber CH, a neutron generator 6 and a neutron counter K are integrated, a processing system ST to process signals delivered by the fission chamber CH and by the counter K, and which delivers firstly a signal representing a signal delivered by the fission chamber and secondly a signal representing the signal delivered by the counter K, and a computing circuit 34 which calculates the count rate C of the fission chamber standardized, with respect to the signal delivered by the counter K, using signals delivered by the processing system ST. The processing system ST comprises: a preamplifier 18 which amplifies the signal delivered via the measuring cable 7 by the fission chamber CH, an amplifier 20 connected to the preamplifier 18 by a multi-conductor cable 19 which transmits a high voltage HT and low voltage BT towards the fission chamber CH, an electronic circuit 21 connected via a cable 27 to the neutron generator 6, an acquisition circuit 32 which comprises an amplifier 22, an acquisition board 23 and a high voltage circuit 24, the amplifier 22 via a cable 26 receiving the signal delivered by the counter K and via an electric connection 33 receiving the high voltage delivered by circuit 24, the cable 26 supplying high voltage HT0 to the counter K, the acquisition board 23 via an electric connection 29 receiving the signal delivered by the amplifier 20 and via an electric connection 28 receiving the signal delivered by the electronic circuit 21, the amplifier 22 delivering the signal representing the signal delivered by the counter K, and the acquisition board 23 delivering the signal representing the signal delivered by the fission chamber. As a non-limiting example, the count rate measuring device illustrated in FIG. 4 only contains a single fission chamber. More generally, a count rate measuring device contains N fission chambers, N being an integer of 1 or more. FIG. 5 gives a block diagram of the method to determine effective mass conforming to the invention. The method is described for the general case in which N effective masses of N fissile deposits contained in N measurement fission chambers are calculated simultaneously. Each fissile deposit contains a main isotope and impurities. The method of the invention firstly comprises two measuring steps E1 and E2. Step E1 is a step to measure the count rates of N deposits of fissile matter of known effective masses placed in N calibration fission chambers respectively identical to the N measuring fission chambers, and step E2 is a step to measure the count rates of N deposits of fissile matter whose effective masses are to be determined. By “identical” fission chamber is meant fission chambers whose outer dimensional characteristics (chamber diameter and length) are identical to the nearest manufacturing tolerances, the other characteristics not necessarily being identical. Step E1 leads to the formation of a matrix [C]0 which is the matrix of the measured count rates of N deposits of fissile matter of known effective masses, and step E2 leads to the formation of a matrix [C] which is the matrix of the measured count rates of the N deposits of fissile matter whose effective masses are to be determined. The matrices [C]0 and [C] are formed for example from standardized count rate measurements delivered by a device conforming to the device shown in FIG. 4. During steps E1 and E2, the measured count rates are obtained under identical measuring conditions. By “identical measuring conditions” is meant that, in both cases, the fission chamber occupies an identical position in the measuring cell, that the configuration of measurements is identical (fast neutrons or thermal neutrons) and the time range over which the measurements are made is identical. Steps E1 and E2 are followed by a step E3 to calculate a matrix [m] such that:[m]=[C]·I([a]×([a]0−1×[m]−1×[C]0)) (1),in which the symbols “·I” and “x” respectively represent the “matrix division” operator and the “matrix multiplication” operator. Matrix [m] is a column matrix whose coefficients are the effective masses it is sought to determine. Matrices [a], [a]0−1 and [m]0−1 are known matrices: matrix [a] is the matrix of the isotopic analyses of the N deposits of fissile matter contained in the N fission chambers, standardized with respect to the main isotopes, matrix [a]0−1 is the inverse matrix of matrix [a]0 of the isotopic analyses of the N known deposits of fissile matter, and matrix [m]0−1 is the inverse matrix of the column matrix [m]0 formed from the N known effective masses associated with the N known deposits of fissile matter. Using the known matrices [a], [a]0−1 and [m]0− and using the matrices [C] and [C]0 constructed from the measurements indicated above, it then becomes possible to calculate matrix [m] (cf. equation (1)). In addition to matrix [m], the computing step E3 also calculates the matrix of variances [var(m)], in which var(m) represents the variance of the effective mass m. The equation of the variance matrix is explained below. Assuming the independence of the coefficients of matrices [a]0−1, [m]0−1 and [C]0, the variance matrix of matrix m is written:var[m]={var[C]+[mij2]×(var[a]×[Xij2]+[aij2]×var[X])}·I{[([a]×[X]ij2]} (2),in which: var[C] is the variance matrix of matrix C, var[a] is the variance matrix of matrix [a], var[X] is the variance matrix of matrix [X] such that:[X]=[a]0−1×[m]0−1×[C]0 (3), [mij2] is the matrix consisting of the terms mij to the power of 2, the terms mij being the terms of matrix [m], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix, [aij2] is the matrix consisting of the terms aij to the power of 2, the terms aij being the terms of matrix [a], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix, [Xij2] is the matrix consisting of the terms Xij to the power of 2, the terms Xij being the terms of matrix [X], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix, [([a]×[X])ij2] is the matrix consisting of the terms ([a]×[X])ij to the power of 2, the terms ([a]×[X])ij being the terms of the product matrix [a]×[X], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix. In general, a fission chamber with main isotope i contains impurities. In practice, U-234 and U-236 impurities are often present in negligible quantity in Uranium U-233, U-235 or U-238 chambers and therefore do not give rise to any problem. With regard to Pu-238 chambers for example, the U-234 impurity is a product of the radioactive decay of Pu-238 with a period of 87.7 years. With a sufficiently recent Pu-238 chamber therefore the quantity of U-234 will be negligible. In cases in which it is not possible to neglect impurities, the method of the invention advantageously takes their influence into account. The calculated coefficients of matrix [m] are then equivalent effective masses which, in addition to the effective masses of the main isotopes, take into consideration the effective masses of the impurities present in the fission chamber. As an indicative example, the expression of an equivalent effective mass of a main isotope Pu-238 containing U-234 impurities will now be given. The equivalent number Neq of nuclei of the Pu-238 isotope contained in a fission chamber is calculated using the following equation: N eq = ( N 4 × σ 4 , c σ 8 , c + N 8 ) in which: N4 is the number of U-234 nuclei contained in the chamber and known from analysis, N8 is the number of Pu-238 nuclei contained in the chamber and known from analysis, σ4,c is the effective microscopic fission cross-section of the impurity U-234, calculated using the MCNP4C2 code for example, under the measurement conditions (counting time interval and fast or thermal neutron spectrum under consideration), σ8,c is the effective microscopic fission cross-section of Pu-238, calculated using the MCNP4C2 code for example, under the measurement conditions (counting time interval and fast or thermal type of the neutron spectrum under consideration). The equivalent effective mass meq of Pu-238 which is taken into account as coefficient of the matrix [m] is then given by the following formula: m eq = m 4 × 238 234 × σ m 4 c σ m 8 c + m 8 in which: m4 is the effective mass of U-234 in the chamber, 238 is the mass number of Pu-238, 234 is the mass number of U-234, σm4c is the effective microscopic fission cross-section per unit of mass of U-234, calculated using the MCNP4C2 code for example, under the measurement conditions (counting time interval and fast or thermal type of the neutron spectrum under consideration), σm8c is the effective microscopic fission cross-section per unit of mass of Pu-238, calculated using the MCNP4C2 code for example, under the measurement conditions (counting time interval and fast or thermal type of the neutron spectrum under consideration), m8 is the effective mass of Pu-238 in the chamber. FIG. 6 gives a block diagram of the fission chamber calibration device which uses the method of the invention. In addition to the elements mentioned with reference to FIG. 4, the calibration device comprises a computing circuit 35. The computing circuit 35 e.g. a computer, applies the calculation method of the invention described with reference to FIG. 5. The effective mass m and associated variance (m) are calculated using the measured count rate C (generally matrix [C]), the measured count rate C0 (generally matrix [C]0) and the known data a, a0−1 and m0−1 (respectively matrices [a], [a]0−1 and [m]0−1 in general). By way of illustration and validation of the method of the invention, the calibration results are given below which were obtained for fission chambers with the main isotopes: Th-232, U-235, U-238, Np-237, Pu-239, Pu-240, Pu-241, Pu-242 and Am-241. These results were obtained for both configurations (thermal and fast) of the calibration device according to the invention, via active neutron interrogation. They are validated relative to calibrations performed in a reactor. The results obtained in the thermal and fast configurations were also compared and validated with respect to each other. The results are given in Tables 1-11 at the end of the description. Obtaining Reference Data Table 1 summarizes all the isotopic compositions of the fission chambers considered. The isotope percentages are standardized relative to that of the main isotope. The coefficient of variation (i.e. relative uncertainty) on isotope percentage is obtained by feedback from experience on isotope analyses and therefore depends on laboratory and analysis means. For information, the correlation used to determine the coefficient of variation y as a % in relation to isotope percentage x is:y=0.002406 x−0.609 The known effective masses of the main isotopes are obtained by reactor calibration for example (see Table 2) allowing determination of the number of nuclei represented by matrix [n] such that:[n][m]×[a]. Results of Primary Calibration In the fast configuration of the calibration device, the count rates obtained from the primary standard chambers are given in Table 3. They are standardized with respect to the count rate of the Helium3 monitor. It is to be noted that the Unat n° 3 and Pu-239 n° 6 chambers were not taken into account in the primary standards. They will be used further on to verify the validity of the results obtained with respect to their mass calibrated in a reactor. Having regard to the above data, it is easy to solve equation (3), hence the result in Table 4 expressed relative to a unit of mass chosen to be 1 μg. It is ascertained that the relative uncertainty regarding the effective macroscopic cross-sections per unit of mass of all the isotopes is excellent, in the order of 1% to 4%, of which less than 1% derived from measurement reproducibility and about 2% to 3% derived from uncertainties on the masses of the primary standards. In the thermal configuration of the calibration device, the count rates obtained from the primary standard chambers are given in Table 5. They are standardized relative to the count rate of the Helium3 monitor. Having regard to the above data, it is easy to solve equation (3), giving the results in Table 6 expressed relative to a unit of mass chosen to be 1 μg. It is ascertained that the relative uncertainty on the effective macroscopic cross-sections per unit of mass of the fissile isotopes with thermal neutrons is excellent, in the order of 2% to 3%, of which less than 1% derived from measurement reproducibility and about 2% to 3% derived from uncertainties on the masses of the primary standards. On the other hand, the uncertainty related to the effective macroscopic cross-sections per unit of mass of the non-fissile isotopes with thermal neutrons is high (˜10% for Pu-242, ˜20% for Pu-240), since the cross-sections of these isotopes are very small, in the order of 100 times smaller than those of Pu-239, Pu-241 and U-235. It is also noted that a zero effective cross-section is found mathematically for U-238. By way of indication, all these elements indeed prove that the interrogation neutron spectrum of the fission chambers in the thermal configuration of the calibration device is purely thermal. Secondary Effective Mass Calibration of the Fission Chambers Table 7 gives the list of fission chambers calibrated for effective mass in the calibration device with fast configuration, and the associated counts and uncertainties. Table 8 gives the list of fission chambers calibrated for effective mass in the calibration device with thermal configuration, and the associated counts and uncertainties. Calibration Results with Fast Configuration The matrix of the isotope compositions and their associated uncertainties being known from Table 1, the effective masses are obtained through equation (1) (see Table 9). It is ascertained that the uncertainties for calibrated effective masses are in the order of 2% to 3% for the actinides examined (5% for Am-241), and are therefore comparable with those obtained by reactor calibrations. For the 6 chambers calibrated both in the device with fast configuration (“Dispo”) and in a reactor (“Reactor”), a difference Dispo - Reactor Reactoris obtained which is less than the experimental uncertainty (CV (%)). It can therefore be concluded that the results are coherent, which validates the measurements made in the calibration device with fast configuration.Results of Thermal Configuration Calibrations The matrix of isotope compositions and their associated uncertainties being known from Table 1, the effective masses are obtained from equation (1) (see Table 10). It is ascertained that the uncertainties on calibrated effective masses are in the order of 2% to 3% for fissile isotopes with thermal neutrons (U-235, Pu-239), and are therefore comparable with those obtained with reactor calibrations. For non-fissile isotopes with thermal neutrons (Pu-240 and U-238 in this case) higher uncertainties (of between 5% and 80% depending on the quantity of fissile impurities contained in these deposits of non-fissile main isotopes with thermal neutrons) are observed. These uncertainties are distinctly greater than those observed with calibrations under fast configuration of the calibration device by active neutron interrogation, or with reactor calibrations. In terms of quality, it is to be noted that the thermal configuration calibrations only allow correct performance levels to be obtained, in terms of accuracy, for the fissile isotopes with thermal neutrons. Nonetheless, for the 6 chambers calibrated both in the device with thermal configuration (“Dispo”) and in a reactor (“Reactor”), a difference Dispo - Reactor Reactoris ascertained that is less than the experimental uncertainty (CV (%)). It can therefore be concluded that the results are coherent, which validates the measurements made in the calibration device with thermal configuration.Comparison Between Fast and Thermal Configuration Calibrations Table 11 gives the comparison between the results obtained with the calibration device with thermal and fast configurations. Excellent agreement is found between the results, the difference at all times being distinctly less than one standard deviation from experimental uncertainty. TABLE 1Isotope composition of the fission chambers, as a % of the main isotopeMainchamberIsotopenoTh232U235U238Np237Pu239Pu240Pu241Pu242Am241Th2321100.00%0.00%0.00%0.00%0.00%0.00%0.00%0.00%0.00%primary standardsU23520.00%100.00%1.03%0.00%0.00%0.00%0.00%0.00%0.00%Unat30.00%0.73%100.00%0.00%0.00%0.00%0.00%0.00%0.00%Unat40.00%0.73%100.00%0.00%0.00%0.00%0.00%0.00%0.00%Np23750.00%0.00%0.00%100.00%0.00%0.00%0.00%0.00%0.00%Pu23960.00%0.00%0.00%0.00%100.00%0.88%0.00%0.01%0.00%Pu23970.00%0.00%0.00%0.00%100.00%1.42%0.01%0.00%0.05%Pu24080.00%0.00%0.00%0.00%0.79%100.00%0.14%0.17%0.56%Pu24190.00%0.00%0.00%0.00%1.91%8.54%100.00%6.85%146.58Pu242100.00%0.00%0.00%0.00%1.04%3.14%0.34%100.00%0.34%Am241110.00%0.00%0.00%2.76%2.10%0.00%0.00%0.00%100.00%chambers to beU235120.00%100.00%1.03%0.00%0.00%0.00%0.00%0.00%0.00%calibratedU235130.00%100.00%6.35%0.00%0.00%0.00%0.00%0.00%0.00%U235140.00%100.00%1.43%0.00%0.00%0.00%0.00%0.00%0.00%U235150.00%100.00%1.43%0.00%0.00%0.00%0.00%0.00%0.00%U-238160.00%0.04%100.00%0.00%0.00%0.00%0.00%0.00%0.00%U-238170.00%0.24%100.00%0.00%0.00%0.00%0.00%0.00%0.00%Np237180.00%0.00%0.00%100.00%0.00%0.00%0.00%0.00%0.00%Np237190.00%0.00%0.00%100.00%0.00%0.00%0.00%0.00%0.00%Pu239200.00%0.00%0.00%0.00%100.00%1.42%0.01%0.00%0.05%Pu239210.00%0.00%0.00%0.00%100.00%0.89%0.00%0.01%0.00%Pu239220.00%0.00%0.00%0.00%100.00%0.89%0.00%0.01%0.00%Pu240230.00%0.00%0.00%0.00%0.79%100.00%0.14%0.17%0.56%Pu240240.00%0.00%0.00%0.00%0.79%100.00%0.14%0.17%0.56%Am241250.00%0.00%0.00%2.70%0.21%0.06%0.00%0.00%100.00% TABLE 2Masses of primary standard chamberschambermain isotopenoMass of main isotope (μg)Th23211009.51U2352226.22Unat3545.05Unat4401.77Np2375367.73Pu2396161.73Pu239732.95Pu2408291.46Pu241971.30Pu2421085.19Am2411126.58 TABLE 3Counts and associated uncertainties of the primary standardchambers, with fast configuration of the calibration device.chamberMain isotopenointegral/monitorCV (%)Th23210.000959620.96%U23520.0120856610.80%Unat40.0015304970.97%Np23750.0031526410.92%Pu23970.0019754050.95%Pu24080.0026781120.95%Pu24190.0022826910.95%Pu242100.0007426261.15%Am241110.0002986852.83% TABLE 4Column vector [X] of the effective macroscopic integral fissioncross-sections per unit of mass (unit of mass of 1 μg) standardizedto the monitor, in the fast configuration of the calibration device.Xuncertainty on XCV (%) on XTh2329.51E−072.73275E−082.87%U2355.34E−05 1.2567E−062.35%U2383.42E−061.19067E−073.48%Np2378.57E−06 2.4552E−072.86%Pu2395.98E−051.44212E−062.41%Pu2408.63E−063.43628E−073.98%Pu2411.53E−05 1.1934E−070.78%Pu2427.74E−063.19593E−074.13%Am2419.74E−064.92311E−075.05% TABLE 5Counts and associated uncertainties of the primary standardchambers, with thermal configuration of the calibration device.chambermain isotopenointegral/monitorCV (%)U23521.4262E−020.42%Unat41.8436E−041.01%Pu23972.7746E−030.75%Pu24082.5193E−040.97%Pu24192.0253E−030.61%Pu242101.1311E−041.29%Am241118.0131E−051.62% TABLE 6Column vector [X] of the effective macroscopic integral fissioncross-sections per unit of mass (unit of mass of 1 μg) standardizedto the monitor, with thermal configuration of the calibration device.XCV (%) over XU2356.3032E−052.31%U2380—Pu2398.4161E−052.39%Pu2401.5047E−0721.41% Pu2412.4924E−053.11%Pu2423.7305E−0710.78% Am2411.2487E−066.38% TABLE 7Counts and associated uncertainties of the chambers to becalibrated, with fast configuration of the calibration device.main isotopechamber nointegral/monitorCV (%)U235120.0077966680.74%U235130.0062724350.89%U235150.0011033721.35%Unat30.0019858920.97%U-238160.0107859620.72%U-238170.0085686590.94%Np237180.002417720.92%Np237190.0007837531.11%Pu239200.0018725430.98%Pu23960.0098595990.89%Pu239210.0017399921.02%Pu239220.0056824720.98%Pu240230.0012892460.98%Pu240240.001291880.97%Am241250.0004246612.12% TABLE 8counts and associated uncertainties of the chambers to be calibrated,with thermal configuration of the calibration device.main isotopechamber nointegral/monitorCV (%)U235129.2204E−030.52%U235148.7994E−020.18%U235151.2893E−030.85%Unat52.4655E−040.87%U-238168.2559E−051.14%U-238173.7104E−040.92%Pu239202.5886E−030.85%Pu23961.3617E−020.43%Pu239212.3803E−030.63%Pu239228.0689E−030.48%Pu240231.1742E−041.03%Pu240241.1558E−041.04% TABLE 9Effective masses of the fission chambers in fast configuration.Effectivemass in dispo.reactor-calibratedDispo − Reactorisotopechamber no(μg)CV (%)mass (μg)CV (%)ReactorCV (%)U23512145.942.48%140.962.53%3.53%3.54%U23513117.012.52%////U2351520.652.72%////Unat3521.323.32%545.052.60%−4.35% 4.22%U-238163134.193.55%////Np23718282.013.02%////Np2371991.423.08%////Pu2392031.232.61% 30.472.47%2.51%3.60%Pu2396164.612.58%161.732.20%1.78%3.39%Pu2392129.052.62%////Pu2392294.872.61%////Pu24023140.303.88%137.013.78%2.40%5.42%Pu24024140.603.88%133.333.78%5.45%5.42%Am2412542.035.32%//// TABLE 10Effective masses of the fission chambers in thermal configuration.Effectivemass in dispo.reactor-calibratedDispo − Reactorisotopechamber no(μg)CV (%)mass (μg)CV (%)ReactorCV (%)U235141396.252.33%////U23512146.302.38%140.962.53%3.79%3.47%U2351520.462.45%////U-238162772.0778.01%////Unat3537.477.36%545.052.60%−1.39% 7.80%Pu2396161.782.44%161.732.20%0.03%3.29%Pu2392030.742.54% 30.472.47%0.89%3.54%Pu2392128.272.46%////Pu2392295.862.45%////Pu24024133.746.42%133.333.78%0.31%7.45%Pu24023135.905.22%137.013.78%−0.81% 6.45% TABLE 11comparison between the effective masses obtained in thermal and fast configurations.Effective mass (μg)Effective massin thermal(μg) in fastthermal − fastisotopechamber noconfigurationCV (%)config.CV (%)fastCV (%U23512146.302.38%145.942.48%0.25%3.44%U2351520.462.45%20.652.72%−0.92%3.66%U-238162772.0778.01%3134.193.55%−11.55%78.09%Unat3537.477.36%521.323.32%3.10%8.07%Pu2396161.782.44%164.612.58%−1.72%3.55%Pu2392030.742.54%31.232.61%−1.57%3.64%Pu2392128.272.46%29.052.62%−2.69%3.59%Pu2392295.862.45%94.872.61%1.04%3.58%Pu24023133.746.42%140.303.88%−4.68%7.50%Pu24024135.905.22%140.603.88%−3.34%6.50% |
|
claims | 1. A pulsed generator of a pinch plasma comprising:two opposed coaxially aligned electrodes with convex profiles;a steady magnetic field applied parallel to the common axis of the electrodes;a limiter disc located between the electrodes with a hole centered on the axis, and a fill of low pressure gas, wherein:a pulsed voltage between the electrodes drives a current initially in a cylindrical sheet of diameter defined by the said hole, the current sheet being collapsed by the plasma pinch effect onto the convex surfaces of the electrodes, compressing the static magnetic field into a protective sheath over each surface, and forming a dense, high temperature plasma pinch on the axis between the electrodes. 2. A generator as in claim 1, driven by an alternating pulsed voltage. 3. A generator as in claim 1, in which the pulse frequency is sufficiently high for partial gas ionization to persist between pulses. 4. A generator as in claim 1, in which an ignition voltage pulse is applied to the limiter disc prior to the application of the main current pulse. 5. A generator as in claim 1, in which the convex electrode profiles are substantially conical. 6. An extreme ultraviolet source system comprising at a minimum the plasma pinch generator of claim 1, a collector reflective optical element, and means to reduce the working gas pressure along the path from the plasma to the point of use. 7. A generator as in claim 1, with a plurality of limiter discs distributed between the electrodes. 8. A generator as in claim 7, in which the working gas is a metal vapor contained by helium gas in a wide angle heat pipe, the limiter discs having conical shapes and comprising the metal vapor condensation and return surfaces of the heat pipe. 9. An extreme ultraviolet source based on the 13.5 nm emission of doubly-ionized lithium energized by a plasma pinch formed in the plasma generator of claim 8. 10. An extreme ultraviolet source based on the emission of a metal ion energized in the plasma pinch generator of claim 8 with the plasma further heated in a small volume by a pulsed laser to enhance EUV emission from the heated region. 11. An extreme ultraviolet source based on the 13.5 nm emission of doubly-ionized lithium energized in the plasma pinch generator of claim 8 with the plasma further heated in a small volume by a pulsed carbon dioxide laser to enhance 13.5 nm emission from the heated region. 12. A generator as in claim 8, in which metal vapor is charged and replenished by evaporation from a chamber internal to an electrode via a small hole on the axis of an electrode. |
|
description | This application claims priority benefit of Great Britain Patent Application Number 0619518.4, filed Oct. 3, 2006. The invention relates to an X-ray photoelectron spectroscopy (XPS) analysis system suitable for analysing an insulating sample, and an XPS analysis method. Surface analysis for materials characterisation involves directing a beam of primary particles (photons, electrons, ions etc.) to the surface of a sample and measuring the energy or mass of the secondary particles (photons, electrons, ions etc.) emitted from the surface as a result. Control of the electric potential of the sample surface is important, to ensure accurate measurements can be taken. In monochromated XPS analysis, a primary beam of monochromatic X-ray photons causes the emission of secondary electrons from the sample surface. For an insulating sample (such as an insulator, an electrically isolated conductive sample, a conductive sample with an insulating surface, or a sample including one or more electrically isolated regions), the emission of secondary electrons leaves the analysis region positively charged. It is known to use an electron flood gun to provide charge compensation for the electrons emitted from the sample surface. The purpose of the flood gun is to charge the surface to a negative potential, approximately equivalent to the energy of the incident electrons in the flood, so that a dynamic steady state is set up, in which flood electrons reach the sample surface at the same rate as the secondary electrons leaving the surface and any excess flood electrons are reflected from the surface. In practice, however, a uniform surface potential is not provided. Any areas of the sample surface which are not irradiated by X-rays, but receive incident electrons, become charged to the potential of the most energetic incident electrons. These areas then act to repel flood electrons which are needed to replace the photoemitted electrons from the analysis region which is irradiated by X-rays. The net negative charge developed around the irradiated, analysis region also acts to defocus the electron beam from the flood gun. These effects are particularly severe when the sample is much larger than the analysis region. It is known to use a beam of low-energy, positive ions to neutralise this build-up of negative charge. Larson and Kelly, “Surface charge neutralisation of insulating samples in X-ray photoemission spectroscopy”, Journal of Vacuum Science and Technology A, 16(6), November/December 1998, pp 3483-3489, indicate that the principal cause of the negative potential in the region surrounding the analysis region is the energy spread of the flood electrons from the electron flood gun, which includes a high-energy tail. Larson and Kelly use a neutralising system in which a high current density flood gun with a narrow energy spread is used in combination with a source of low-energy, positive ions. GB-A-2,411,763 provides a background discussion of the above problem and discloses a combined flood gun, which provides a source of electrons and a source of positively charged particles and is capable of focusing the electron flood beam and the positive particle beam independently towards the sample surface. Although the combined flood gun of GB-A-2,411,763 provides an effective instrument for neutralising the unwanted electrons at the sample surface, facilitating further the control of the potential of the sample surface would be desirable. The invention aims to address the above and other objectives by providing an improved XPS analysis system for surface analysis. According to one aspect of the invention, there is provided an X-ray photoelectron spectroscopy analysis system for analysing an insulating sample, the system comprising: an X-ray generating means having an exit opening and being arranged to generate primary X-rays which pass out of the exit opening in a sample direction towards a sample surface for irradiation thereof, the X-ray generating means in use additionally generating unwanted electrons which would pass out of the exit opening substantially in the sample direction; and an electron deflection field generating means arranged to generate a deflection field upstream of the sample surface, the deflection field being configured to deflect the unwanted electrons away from the sample direction, such that the unwanted electrons are prevented from reaching the sample surface. The present inventor has established that a significantly more troublesome source of energetic incident electrons is the X-ray monochromator itself. That is, the electrons from the X-ray monochromator have a more significant effect on the negative potential on the sample surface than the flood electrons in the high-energy tail of the energy distribution from the electron flood gun. Careful measurements have demonstrated that, even though there is no direct line of sight from the X-ray source in the X-ray monochromator to the sample surface, there is a sufficient number of electrons generated in the X-ray monochromator to cause significant charging of the sample surface. It is understood that these electrons result from a) scattering from the walls of the monochromator chamber and from the monochromator crystal by high-energy electrons from the electron gun used to generate X-rays at the X-ray source; b) X-ray photoelectron emission from the walls of the monochromator chamber and from the monochromator crystal and its mount, excited by both the Al (aluminium) K-alpha X-rays and the Bremsstrahlung radiation from the X-ray source; and c) secondary and higher-order electrons generated by both of the processes (a) and (b) and by electron bombardment of the target anode in the X-ray source. It has been established that, while the electron currents of the above incident electrons may be relatively small—perhaps in the region of a few hundred picoamps reaching the sample surface—the electrons may nevertheless cover a wide energy range. In principle, the energy of such an electron may be up to the energy of the X-ray source electron beam from the electron gun, which is typically 15 kV, but the electron energy is normally up to a few tens of electron volts. So, despite being a comparatively small current, the electrons from the X-ray generating means can have a much higher energy than flood electrons from a flood gun and, by charging the surface of the sample over a large area to a large negative potential, can prevent the flood electrons from ever reaching the analysis area. Initial attempts by the inventor to remove the unwanted electrons from the X-ray monochromator involved the use of an X-ray window at the exit port of the X-ray monochromator. The window was made from ultra-thin aluminium or polymer, with a high transmission of around 90% at the aluminium K-alpha X-ray wavelength, to achieve effective blocking of unwanted electrons from the X-ray source. However, the inventor found that, because typically 10% of the X-rays passing from the monochromator to the source were absorbed by the window, further unwanted electrons were generated by this process and could reach the sample with high energy, so that the net unwanted electron current at the sample surface was not significantly reduced through use of the window. As a result of further investigations, the inventor has established that an effective technique for addressing the problem of energetic incident electrons is to apply a deflection field across the pathway of the unwanted electrons upstream of the sample surface. The deflection field is arranged to deflect the unwanted electrons away from their trajectory to the sample surface, such that the unwanted electrons are prevented from reaching the surface. As a result of the deflection field applied to the unwanted electrons, the unwanted electrons are diverted away from their path and allowed to hit other components in the analysis system, such as the analysis chamber sidewall. The deflection field is arranged to be of sufficient strength to deflect high-energy, as well as low-energy, unwanted electrons away from the sample surface. The deflection field has no effect on the desired primary X-rays travelling towards the sample surface, so that primary beam irradiation of the surface may continue as normal. In this way, embodiments of the invention are able to provide a reduction by more than a factor of ten in the unwanted electron current reaching the sample surface. Consequently, where a charge neutralisation system is employed (as described in GB-A-2,411,763 or by any other means), the positive ion beam generated by the charge neutralisation system to compensate for the arrival of energetic incident electrons at the sample surface may be reduced in current, in correspondence with the reduction of the unwanted electron current. This results in a reduction in sample damage caused by the positive ion beam. Furthermore, with a reduction in the positive ion beam current required by the charge neutralisation system, the amount of gas which is to be ionised for providing the ion beam may be significantly reduced. A reduction in the amount of gas, which is typically argon, which needs to be admitted to the charge neutralisation system and the analysis chamber leads to a reduction in contamination in the system. Overall, the performance of the charge neutralisation system may be enhanced by improved ease of use, in view of the above benefits, especially for large samples where the ion beam techniques above have limited efficacy. The invention relates to an X-ray photoelectron spectroscopy apparatus and method, which aim to address in particular the undesirable surface-charging problem encountered when analysing the surface of an insulating sample. A significant cause of the problem was identified by the inventor as being electrons generated in the X-ray generator. The inventor addressed this problem by applying a deflection field across the pathway of the unwanted electrons upstream of the sample surface. X-ray generators are known from many different technical fields. It is to be noted that many prior art X-ray generators would not be suitable for XPS surface analysis of a sample, in view of their operational or structural configurations. X-ray generators for XPS analysis of samples are generally low-power, typically of a few hundred watts; low-energy, typically electron energies up to 15 kV; produce very soft X-rays, typically with an energy of 1.5 kV (expressed in the same terms as electron energies); and are generally designed for continuous operation, without a vacuum window between the X-ray source and the sample. X-ray generators used in medical applications, for example, are generally high-power, typically several kilowatts; very high-energy, typically electron energies above 50 kV; produce hard X-rays, typically above 10 kV; and operate for only short periods. Other X-ray generators, which are set for such high-energy operation, find application in X-ray diffraction or X-ray imaging. As indicated above, such high-energy X-ray generators are unsuitable for XPS sample surface analysis, since the hard X-rays generated would not interact with atoms at the sample surface, but would penetrate deep within the sample. A number of prior art X-ray generators are configured as a sealed tube, with an X-ray-transmissive vacuum window, which is arranged to withstand atmospheric pressure. The soft (aluminium K-alpha) X-rays generally used for XPS surface analysis are of such low energy that sealed tubes with X-ray windows which are thick enough to support atmospheric pressure are not suitable, since they will effectively not transmit such X-rays. Indeed, some X-ray generators specifically take advantage of this effect; in particular in X-ray diffraction arrangements, where it is desirable to have only a single, characteristic, hard X-ray irradiating beam (so it is beneficial to filter out any characteristic, soft X-rays). It may be possible to employ a very thin window (typically of aluminium) with a soft X-ray source for sample surface analysis, but such a window could not be made thick enough to sustain an atmospheric pressure difference. Indeed, as mentioned above, the use of such a window can itself generate secondary electrons, which has a detrimental effect on the surface-charging problem identified in the application. A number of high-energy X-ray generators suffer from the problems of the X-ray window becoming hot or patient tissue becoming damaged, from very high-energy electrons produced in the X-ray generators. Neither of these problems is relevant for X-ray generators suitable for XPS sample surface analysis. Furthermore, such problems in a high-energy X-ray generator may be dealt with by reducing the electron beam in the X-ray generator down to the milliamp or microamp level. Electrons with energies below a few hundred volts would be of little interest, since they would cause no significant patient tissue damage or window heating (indeed, their path length in air would generally be too short to reach the patient). In XPS sample surface analysis, it is desirable to reduce the electron beam reaching the sample surface down to below the nanoamp level. In addition, it has been recognised by the inventor that it is precisely those electrons of energies in the range of a few volts to a hundred volts which cause most of the surface-charging effects. In high-energy X-ray generators, high-energy electrons may be deflected away from the window or the patient, but eventually they must hit the wall of the chamber somewhere, at which point they will typically produce a large quantity of lower-energy, secondary electrons. If the X-ray generator has a sealed window, these secondary electrons may or may not escape, depending on their energy, but in any case they will have lost enough energy no longer to be a problem in medical applications, say. They would, however, still have enough energy to cause surface charging in an XPS system. If the X-ray generator does not have a window, as would be the case generally for XPS, using soft X-rays, then a large fraction of these lower-energy, secondary electrons would certainly escape and cause surface-charging effects. This invention lies in the field of XPS analysis. Prior art X-ray generators used in XPS analysis are configured specifically to this field. The surface-charging problem caused by the unwanted electrons generated in XPS X-ray generators was not recognised in the prior art. The recognition by the inventor of this problem has led to the modification of an X-ray generator as used for XPS analysis. Preferably, the deflection field generating means is located near to, at, or upstream of the exit opening. That is, the deflection field generating means may be located outside of the X-ray generating means, but near to its exit opening; or it may be around or adjacent the exit opening; or it may be located on the X-ray generating means side of the exit opening. It is preferable for the electron deflection field to be generated in the region of the exit opening, in this way, since the unwanted electrons may then be dealt with before, or as, they pass out of the exit opening. This provides a relatively large distance over which the deflected unwanted electrons may travel so as to avoid the sample surface. Preferably, the unwanted electrons are deflected so that they are received by the sidewalls of an analysis chamber holding the sample. Preferably, the deflection field is transverse to the sample direction. This has the benefit of providing the largest deflecting force on the unwanted electrons for a given field strength. Preferably, the X-ray generating means has a housing portion terminating in the exit opening. The deflection field generating means may be located internally of the housing portion; that is, within the arm, or flight tube, heading towards the exit opening of the X-ray generating means. This provides a reasonable separation between the deflection field generating means and the sample, so that any field at the sample surface is acceptably low. Alternatively, the deflection field generating means may be located externally of the housing portion; that is, on the outside of the arm, or flight tube, of the X-ray generating means heading towards the exit opening. This facilitates access to the deflection field generating means for repair or removal, for example, during bake-out of the system. In addition, this facilitates the configuration and operation of the deflection field generating means if this is provided by an electromagnet. Preferably, the system comprises an analysis chamber for holding the sample. The chamber comprises a sidewall having an entrance port therethrough in communication with the exit opening of the X-ray generating means, to allow X-rays to pass from the generating means to the sample surface. In a preferred embodiment, the deflection field generating means is located in this port. This ensures that the deflection field acts on all of the unwanted electrons which have been generated in the X-ray generating means and which have passed out of the exit opening. The inventor has found that best results are achieved when the deflection field generating means is positioned outside or within this chamber sidewall, since this helps to ensure that the deflecting field inside the chamber is acceptably low. The currently preferred position is near to the port where the X-rays pass through the chamber sidewall, as the beam is generally narrow here and the volume through which the deflection field is required to act is relatively small. The electron deflection field may be magnetic and may be provided using an electromagnet. This provides the possibility of controlling the magnetic field strength during operation. Preferably, however, the deflection field generator comprises a permanent magnet. This provides a simple and effective mechanism for deflecting the unwanted electrons, since once the permanent magnet is positioned in place no further configuration or control of it is required. The deflection field generator may be arranged to produce a local magnetic field of between 1 mT and 100 mT. Preferably, the local magnetic field is between 10 mT and 50 mT. The inventor has found that such a magnetic field is effective to stop all high-energy unwanted electrons. Preferably, at least the part of the chamber sidewall comprising the entrance port is made of a magnetic material, such as soft iron or preferably a nickel-iron alloy. In this way, it may be configured to act as a flux return path for the magnetic field. Furthermore, the chamber sidewall made of such a magnetic material may be used to provide magnetic shielding of the sample surface from the deflection field. Preferably, the chamber sidewall is sufficiently thick that the magnetic field applied by the deflection field generator does not saturate the sidewall material and the shielding factor remains high. The inventor has in this way been able to achieve a low field at the sample, of less than 10−6 T. Alternatively, the deflection field generator may comprise an electrostatic field generator. This is preferably achieved by providing a transverse electrostatic field in the region of the exit opening/entrance port. A number of electrode configurations could be selected to provide such a field, but most simply a pair of electrically isolated parallel plates, preferably with equal and opposite potentials applied thereto, could be mounted respectively above and below the opening/port. As before, the sample still needs to be shielded from the deflection field and techniques known in the art can be used to achieve this. Preferably, however, the electron deflection field is provided magnetically. Preferably, the X-ray generating means is arranged to produce monochromated primary X-rays. It is thereby possible to provide a highly focused beam of primary X-rays. Advantageously, the analysis system may comprise a second electron deflection field generating means. The first and second electron deflection field generating means may then be placed at different locations within the system, selected from 1) in the entrance port of the side wall of the analysis chamber; 2) internally of the housing portion of the X-ray generating means; and 3) externally of the housing portion of the X-ray generating means. This may be advantageous where the chamber sidewall is relatively thin, so that the strength of a deflection field generating means located in the port would have to be correspondingly reduced. By providing a further electron deflection field generating means upstream of the port, for example, deflection of the unwanted electrons away from the sample surface may be more certain. According to a further aspect of the invention, there is provided a method of X-ray photoelectron spectroscopy analysis by primary beam irradiation of a sample surface, the method comprising the steps of: generating at an X-ray generating means primary X-rays in a sample direction towards a sample surface; additionally generating at the X-ray generating means unwanted electrons which would travel in the sample direction towards the sample surface; and providing an electron deflection field upstream of the sample surface to deflect the unwanted electrons away from the sample direction, such that the unwanted electrons are prevented from reaching the sample surface. Preferably the system(s) of the invention form part of a spectroscopic system for secondary particle emission surface analysis of a sample, also comprising an analysis chamber, a flood gun, and a secondary particle analyser. According to a still further aspect of the invention, there is provided an X-ray photoelectron spectroscopy analysis system for surface analysis of an insulating sample, the system comprising: an analysis chamber for holding the sample, the chamber comprising a sidewall having a port therethrough; and an X-ray generation means arranged to supply X-rays through the port in the chamber for primary beam irradiation of the sample surface, wherein, in use, unwanted electrons are generated in the X-ray generation means and travel from the X-ray generation means towards the sample surface, the system further comprising and electron deflection field generating device located at, near to, or upstream of the port and arranged to deflect the unwanted electrons such that the unwanted electrons do not reach the sample surface. Other preferred features and advantages of the invention are set out in the description and in the dependent claims which are appended hereto. Referring to FIG. 1, a schematic spectroscopic system for secondary particle emission surface analysis of a sample is shown. The system includes an analysis chamber 10, which is typically a vacuum chamber capable of sustaining an ultra-high vacuum. The chamber 10 holds a sample 20, whose surface 22 is to be investigated for materials characterisation. In the embodiment shown, the system is set up for X-ray photoelectron spectroscopy. As such, the primary particle generator is an X-ray generator 30, which in this case is configured to produce monochromatic X-rays. The primary particle generator 30 comprises an X-ray source 40 and an X-ray monochromator 50. The X-ray source 40 is provided by a high-energy electron gun 42, which is arranged to accelerate electrons towards a target anode 44. The target anode 44 includes aluminium, so that electron bombardment of the target generates X-rays at the aluminium K-alpha wavelength. The resulting X-rays 46 travel from the X-ray source 40 towards a monochromator crystal 52. When the X-rays 46 strike the monochromator crystal 52, they are Bragg reflected as a monochromated beam of X-rays 56 and focused towards the sample surface 22. The monochromated X-rays 56 pass out of the primary particle generator 30 through an exit opening 32, into the analysis chamber 10. As discussed above, for insulating samples, a flood gun 60 is employed to provide charge neutralisation at the sample surface 22, during analysis. The flood gun may be of any suitable type, but is preferably that disclosed in GB-A-2,411,763. The monochromated X-ray photons cause the emission of secondary, photoelectrons from the sample surface 22. The photoelectrons are collected in the analysis chamber 10 and focused towards an analyser entrance opening 72, for energy analysis in a spectroscopic analyser/detector 70. FIG. 2 shows a sectional view of a part of such a spectroscopic system. The part shown includes parts of a primary particle generator 230 and an analysis chamber 210. This figure illustrates the generation of unwanted electrons 248, 258. FIG. 2 shows an electron gun 242 and target anode 244 in communication with an entrance arm or flight tube 255 to the monochromator 250. The entrance arm 255 leads to the monochromator crystal 252, which is held in place on a crystal mount 251. Downstream of the crystal 252 is an exit arm or flight tube 257 from the monochromator 250. The exit arm 257 terminates in an exit opening 232 to the primary particle generator 230. The entrance and exit arms 255, 257 are provided within entrance and exit housing portions 253, 254, respectively. The monochromator housing portion 254 is fixed to a sidewall 212 of an analysis chamber 210. The sidewall 212 has an entrance port 214, which is in communication with the exit opening 232 of the primary particle generator 230. The entrance port 214 acts as an extension of the exit arm 257 of the primary particle generator 230 and is directed towards the sample surface 222 of a sample 220 held in the analysis chamber 210. In this way, primary X-rays generated by the primary particle generator 230 may pass out of the generator through the exit arm 257 and entrance port 214 and are focused towards an analysis region of the sample surface 222. As well as producing primary X-rays at the target anode 244, the electron bombardment of the anode also results in the emission of high-energy secondary electrons from the anode. The emission of such secondary electrons is illustrated schematically by broken arrow 248. The high-energy electrons originating from the X-ray source 240 are scattered from the walls of the monochromator chamber (entrance and exit arms 255, 257), from the monochromator crystal 252 and from its mount 251. Stimulation of such surfaces by X-rays, either aluminium K-alpha X-rays or Bremsstrahlung X-rays, can lead to photoelectron emission. Direct electron bombardment of such surfaces by these electrons and by electrons originating from the X-ray source 240 can also result in the emission of secondary or higher-order electrons. The production of such unwanted electrons within the primary particle generator 230 is illustrated by exemplary arrows 258. At least a proportion of the unwanted electrons would pass out of the primary particle generator 230, through the exit opening 232 and entrance port 214, towards the sample surface 222, resulting in a build-up of undesirable negative charge on the sample surface. FIG. 3 shows a similar sectional view to that of FIG. 2, but without the arrows showing the unwanted electron production. Accordingly, like features are referred to with like reference numerals (the initial digit corresponding to the number of the figure). The embodiment of FIG. 3 incorporates an electron deflection field generator, in the form of a permanent magnet 380. The magnet 380 is positioned within the sidewall 312 of the analysis chamber 310, on an internal surface of the entrance port 314. The magnet 380 is positioned in a vertically upper region of the entrance port 314, adjacent an interface between the entrance port and the exit opening 332 of the primary particle generator 330. The location of the magnet 380 in FIG. 3 is the currently preferred position for the electron deflection field generator. The chamber sidewall 312—at least that part surrounding the entrance port 314—is made of a magnetic material, such as soft iron or, preferably, a nickel-iron alloy. This serves a number of purposes. Firstly, the chamber sidewall 312 can be used to shield the sample surface magnetically from the magnetic field produced by the magnet 380. If the chamber sidewall 312 is sufficiently thick that the magnetic field produced by the magnet 380 does not saturate the material forming the sidewall and its shielding factor remains high, it is possible to achieve a magnetic field at the sample surface of less than 10−6 T, which is sufficiently low as to have a negligible effect on photoelectrons emitted from the sample surface. Secondly, the magnetic part of the sidewall 312 surrounding the entrance port 314 forms part of the magnetic circuit for the magnetic flux from the magnet 380. Where the sidewall 312 is not required to have magnetic properties (i.e., away from the entrance port 314), the sidewall may be made of other material, including non-magnetic materials. For example, such other parts of the sidewall 312 may be made of stainless steel or an aluminium alloy. With a magnetic material surrounding the entrance port 314, the magnet 380 may be positioned within the entrance port and held in place by magnetic attraction to the surface of the entrance port. If desired, additional mechanical mounting (which may include a machined recess in the surface of the entrance port) and fixings may be provided to hold the magnet 380 in place. Once the magnet is fitted in place within the entrance port 314, there is no further set-up required for its operation. In this way, the magnet 380 is arranged in the entrance port 314 to provide a magnetic field which is essentially transverse to the direction of the unwanted electrons travelling towards the sample surface 322. The force on the unwanted electrons may accordingly be towards a maximum value for a given strength of magnetic field and speed of the unwanted electrons. The force on the unwanted electrons acts to deflect them to one side or the other, preferably into the surface of the entrance port 314 or other parts of the chamber sidewall 312 of the analysis chamber 310. The magnetic field should be of sufficient strength to deflect the highest-energy unwanted electrons, such that they are prevented from reaching the sample surface 322 and instead hit the sidewall 312 of the chamber 310. Any low-energy unwanted electrons are forced to circulate in the magnetic field, until they also hit the surface of the entrance port 314 or other parts of the sidewall 312. The inventor has found that a magnetic field across the entrance port 314 of a few to tens of millitesla is sufficient to prevent the high-energy unwanted electrons from arriving at the sample surface 322. Accordingly, a magnetic flux density of between 1 mT and 100 mT is desirable. Preferably, however, the value is between 10 mT and 50 mT. Thus, although the charge neutralisation technique disclosed in GB-A-2,411,763 provides an effective way of neutralising the unwanted electrons at the sample surface, the inventor has found that even better results may be obtained by removing the majority of the unwanted electrons before they reach the sample surface. Indeed, the unwanted electron current reaching the sample surface can be reduced by more than a factor of ten, using the above embodiment. A first benefit of this is that the positive ion beam generated by a charge neutralisation system employed with the analysis system (either as described by GB-A-2,411,763 or any other suitable means) can be correspondingly reduced in ion current, thereby reducing damage caused to the sample during analysis. A second benefit is that, because the positive ion beam current may be reduced, the amount of gas which is to be ionised to provide the ion beam (typically argon gas) which needs to be admitted to the charge neutralisation system and the analysis chamber may be significantly reduced. Accordingly, contamination of the analysis system may be reduced. A further benefit is that the performance of the charge neutralisation system may be enhanced by the improvement in ease of use, especially for large samples where the ion beam neutralisation techniques above have limited efficacy. In particular, the set-up of the flood gun is much easier. Once the flood gun has been initially aligned with the analysis region on the sample surface, it has been found that no further alignment is necessary to accommodate samples of varying size, shape, electrical properties, or surface texture. Furthermore, no adjustments have been found to be required when the spot size of the monochromated X-ray beam is varied. FIG. 4 shows, schematically, a sectional view of an entrance port 414 to an analysis chamber (not shown). As discussed above, a part 413 of the sidewall of the chamber near the entrance port 414 is made of a magnetic material, in the preferred embodiment. A permanent magnet 480 is held in place to an inside surface of the entrance port 414, by magnetic attraction. The north pole of the magnet 480 faces the inside surface of the entrance port 414, to which the magnet is held. Magnetic flux lines 482 leave the north pole of the magnet 480 and are returned towards the south pole by the flux return path provided by the magnetic part 413 of the chamber sidewall. In this way, magnetic flux lines 482 run generally transversely across the entrance port 414. It will be appreciated that the polarity of the magnet is not important, since this will merely affect whether the unwanted electrons are deflected to one side or the other. In the currently preferred embodiment, the entrance port in the chamber sidewall is rectangular, with dimensions of approximately 20 mm by 100 mm. Also, the magnet preferably has dimensions (length, width, depth) of 60 mm by 12 mm by 2.5 mm, with the direction of magnetisation substantially normal to the large faces of the magnet. The chamber sidewall forming the flux return path preferably has a thickness of about 40 mm at this point. However, although these dimensions are currently preferred, they are not critical to the operation of the invention and other suitable configurations are envisaged. The magnet used in this embodiment is a permanent magnet. Preferably, the permanent magnet used is bakeable without losing its magnetisation. Generally, surface analysis systems operate in ultra-high vacuum conditions. Such UHV systems are routinely baked to temperatures of 100° C. or greater, in order to achieve pressures below around 10−8 torr. If the magnet cannot be baked to such temperatures without demagnetising, then it would need to be removed for bake-out. This is clearly not possible if the magnet is to be located inside the vacuum region and still extremely inconvenient even if the magnet is mounted outside of the vacuum region. A high-temperature grade of neodymium iron boron or of samarium cobalt has been found to be suitable. FIG. 5 shows a sectional view of part of an X-ray generator and an analysis chamber, illustrating an embodiment with the electron deflection field generating means in an alternative position. In the embodiment shown, the electron deflection field generator is a permanent magnet 580. The magnet 580 is located outside of the analysis chamber 510 and is fixed to an inside surface of the exit arm 557 to the X-ray monochromator 550. The monochromator housing portions 553, 554 are not made from a magnetic material, to avoid interfering with the electrons generated by the electron gun of the X-ray source. Accordingly, the magnet 580 is held in place using mechanical fixings, which may include a machined recess, spring clips, screws etc., as will be readily understood. The magnet 580 is configured to provide a magnetic field substantially transverse to the direction of the unwanted electrons heading towards the exit opening 532 of the primary particle generator 530. Thus, in the same way as before, the electrons are deflected by the magnetic field to one side or the other. Preferably, the deflected unwanted electrons are absorbed by the surfaces of the exit arm 557 and entrance port 514 but, in any case, are prevented from reaching the sample surface 522. In the embodiment shown, with the magnet 580 external to the chamber sidewall, no dedicated flux return path has been employed. While not essential, it would nevertheless be beneficial to use a flux return path, machined as a separate magnetic component and disposed around the exit arm 557 at the location of the magnet 580. The alternative position for the magnet 580, shown in FIG. 5, may be beneficial where the chamber sidewall 512 of the analysis chamber 510 is not thick enough to provide adequate magnetic shielding to the sample 520 with the magnet 580 being positioned closer to, or within, the sidewall. In an alternative embodiment, the magnet is positioned outside of the vacuum region (i.e. not within the exit arm 557 or the entrance port 514). The magnet could be located outside of the monochromator housing portion 554, or in a suitable recess within the housing portion (but not inside the exit arm 557 itself), such that its magnetic field penetrates through the non-magnetic housing portion and into the exit arm 557 and/or part of the entrance port 514, to deflect the unwanted electrons. In general, this embodiment would result in a lower field strength within the exit arm 557 or entrance port 514, for a given magnet, but might be advantageous if the magnet is provided by an electromagnet, or if a high bake-out temperature for the system necessitates the removal of a permanent magnet during bake-out. As will be understood from the above embodiments, the electron deflection field generator is arranged to deflect unwanted electrons away from their path towards a sample surface upstream of the sample. The inventor has found it is preferable for a magnet to be positioned within the chamber sidewall or outside of the chamber sidewall (for example, internally of the entrance port, internally of the exit arm to the X-ray generator, or externally of the exit arm to the X-ray generator), so as to reduce or minimise the introduction of any magnetic field inside the analysis chamber. The inventor has found that an effective location for the magnet is just outside the chamber sidewall, either internally or externally of the exit arm of the X-ray monochromator. However, the inventor has established that the optimum position for the magnet is within the chamber sidewall, on the surface of the entrance port, using the chamber sidewall itself as a magnetic flux return path. Placing the magnet near to the entrance port in this way has the benefit that the beam passing through the entrance port (the beam containing unwanted electrons) is relatively narrow, so that the volume through which the magnetic field needs to act is relatively small. In the above embodiments, the magnet used to provide the electron deflection field is a permanent magnet. However, in some embodiments, it may be desirable to employ an electromagnet to provide the electron deflection field. In this case, the configuration and function of the electromagnet would be the same as for the embodiments using a permanent magnet. However, when an electromagnet is used, it is preferable for the electromagnet to be mounted externally of the analysis chamber and externally of the exit arm to the X-ray monochromator. The use of a magnetic field to deflect charged particles, by means of either a permanent magnet or an electromagnet, is known. For example, U.S. Pat. No. 5,204,530 discloses a noise reduction technique for negative-ion quadrupole mass spectrometry. A weak magnetic field is supplied between a quadrupole mass spectrometer and an ion collector/detector. A beam passes through the quadrupole and enters the magnetic field, where electrons are deflected away from the beam path to an electron collector and the negative ions pass undeflected to the ion collector where they are detected and recorded as a mass spectrum. However, to the knowledge of the inventor, the surface-charging problem in XPS, caused by relatively high-energy unwanted electrons from an X-ray monochromator has not previously been recognised. The inventor believes that the technique of the present invention is considered to be a significant improvement in the field of XPS. Although the above embodiments employ a magnet as the electron deflection field generator, an electrostatic field generator could alternatively be used. Such an arrangement could employ an electrostatic field of sufficient strength to deflect the electrons away from their path towards the sample surface, so that they impinge upon the walls of the analysis chamber, its entrance port, or the exit arm of the monochromator. Alternatively, the electrostatic field could be employed to repel the unwanted electrons completely, so that they do not pass further downstream of the electrostatic field. In order to deflect the unwanted electrons, preferably a transverse electrostatic field is created in the region of the exit opening of the primary X-ray generator or the entrance port to the analysis chamber. A number of electrode configurations may be chosen to provide this electrostatic field, as will be understood readily, but most simply a pair of electrically isolated parallel plates could be mounted above and below the opening/port. Preferably the plates would be arranged to have equal and opposite potentials applied to them, for providing the transverse electrostatic field. The electrostatic field required to deflect or stop the high-energy electrons from the X-ray generator is relatively large and is reasonably difficult to generate in a way which does not physically obstruct the X-ray beam passing towards the sample, or produce stray electrostatic fields which interfere with the secondary particle analysis. Given such mechanical design considerations, the preferred embodiment of the invention involves the use of a permanent magnet, as described above. In the embodiments described above, a single electron deflection field generator has been employed. However, in some embodiments, it may be advantageous to provide a second electron deflection field generator. This may be so, for example, if the strength of a single electron deflection field is required to be below a certain level, so as not to interfere with the analysis of secondary particles in the analysis chamber. Providing two electron deflection fields at separate locations may provide greater certainty of unwanted electron deflection. The first magnetic or electrostatic field may be applied 1) in the entrance port of the sidewall of the analysis chamber; 2) internally of the housing portion of the X-ray generator; or 3) externally of the housing portion of the X-ray generator. The second electron deflection field may then be applied at another of the above regions. |
|
summary | ||
claims | 1. A reflective optical element, comprising:a substrate;a dielectric layer system; anda metallic coating between the substrate and the dielectric layer system,wherein the dielectric layer system is configured to reflect radiation at an operating wavelength greater than or equal to 150 nm and comprises at least one four-layer sequence of layers, the at least one four-layer sequence of layers comprising:a layer composed of material having a lower refractive index n1 at the operating wavelength,a layer composed of material having a higher refractive index n2 at the operating wavelength,a first layer composed of material having a medium refractive index n3 at the operating wavelength, where n1<n3<n2, anda second layer composed of the material having the medium refractive index n3,wherein the four-layer sequence is (LM1HM2)m or (HM1LM2)m, where L designates the layer composed of material having the lower refractive index n1 at the operating wavelength, H designates the layer composed of material having the higher refractive index n2 at the operating wavelength, M1 designates the first layer composed of material having a refractive index n3 at the operating wavelength, and M2 designates the second layer composed of material having a refractive index n3 at the operating wavelength, and where m designates a number of the four-layer sequences in the dielectric layer system, andwherein the layer (L) composed of material having the lower refractive index n1 is composed of at least one of: aluminum fluoride, cryolite, chiolite, lithium fluoride and magnesium fluoride, the layer (H) composed of material having the higher refractive index n2 is composed of at least one of: neodymium fluoride, gadolinium fluoride, dysprosium fluoride, lanthanum fluoride and aluminum oxide, and the layers (M1, M2) composed of material having the medium refractive index n3 are composed of at least one of: magnesium fluoride, yttrium fluoride and silicon dioxide. 2. The reflective optical element as claimed in claim 1, wherein the layer of the dielectric layer system which is furthest away from the substrate is a layer composed of material having the medium refractive index n3. 3. The reflective optical element as claimed in claim 1, wherein the layer of the dielectric layer system which is second closest to the substrate is composed of material having the medium refractive index n3. 4. The reflective optical element as claimed in claim 1, wherein the metallic coating comprises at least one of: aluminum, an aluminum-silicon alloy, an aluminum-manganese alloy, an aluminum-silicon-manganese alloy, and rhodium. 5. An optical system for a lithography device or a microscopy device comprising a reflective optical element as claimed in claim 1. 6. The reflective optical element as claimed in claim 1, configured for an operating wavelength in a deep ultraviolet (DUV) or vacuum ultraviolet (VUV) wavelength range. 7. A lithography device for an operating wavelength in a DUV or VUV wavelength range comprising a reflective optical element as claimed in claim 1. 8. A microscope device for an operating wavelength in a DUV or VUV wavelength range comprising a reflective optical element as claimed in claim 1. 9. A reflective optical element, comprising:a substrate;a dielectric layer system configured to reflect radiation at an operating wavelength between 240 nm and 300 nm; anda metallic coating between the substrate and the dielectric layer system,wherein the dielectric layer system comprises at least one four-layer sequence of layers, the at least one four-layer sequence of layers comprising:a layer composed of material having a lower refractive index n1 at the operating wavelength,a layer composed of material having a higher refractive index n2 at the operating wavelength,a first layer composed of material having a medium refractive index n3 at the operating wavelength, where n1<n3<n2, anda second layer composed of the material having the medium refractive index n3,wherein the four-layer sequence is (LM1HM2)m or (HM1LM2)m, where L designates the layer composed of material having the lower refractive index n1 at the operating wavelength, H designates the layer composed of material having the higher refractive index n2 at the operating wavelength, M1 designates the first layer composed of material having a refractive index n3 at the operating wavelength, and M2 designates the second layer composed of material having a refractive index n3 at the operating wavelength, and where m designates a number of the four-layer sequences in the dielectric layer system, andwherein the layer (L) composed of material having the lower refractive index n1 is composed of at least one of: aluminum fluoride, cryolite, chiolite, lithium fluoride and magnesium fluoride, the layer (H) composed of material having the higher refractive index n2 is composed of at least one of: yttrium oxide, hafnium oxide, scandium oxide, zirconium oxide, aluminum nitride and synthetic diamond, and the layers (M1, M2) composed of material having the medium refractive index n3 is composed of at least one of: barium fluoride, gadolinium fluoride, lanthanum fluoride, neodymium fluoride, dysprosium fluoride, aluminum oxide, yttrium fluoride, ytterbium fluoride and silicon dioxide. 10. The reflective optical element as claimed in claim 9, wherein the layer of the dielectric layer system which is furthest away from the substrate is a layer composed of material having the medium refractive index n3. 11. The reflective optical element as claimed in claim 9, wherein the layer of the dielectric layer system which is second closest to the substrate is composed of material having the medium refractive index n3. 12. The reflective optical element as claimed in claim 9, wherein the metallic coating comprises at least one of: aluminum, an aluminum-silicon alloy, an aluminum-manganese alloy, an aluminum-silicon-manganese alloy, and rhodium. 13. A lithography device for operating within the 240 nm to 300 nm wavelength range comprising a reflective optical element as claimed in claim 9. 14. A microscope device for operating within the 240 nm to 300 nm wavelength range comprising a reflective optical element as claimed in claim 9. 15. A reflective optical elementa substrate;a dielectric layer system configured to reflect radiation an operating wavelength between 150 nm and 240 nm; anda metallic coating between the substrate and the dielectric layer system,wherein the dielectric layer system comprises at least one four-layer sequence of layers, the at least one four-layer sequence of layers comprising:a layer composed of material having a lower refractive index n1 at the operating wavelength,a layer composed of material having a higher refractive index n2 at the operating wavelength, anda first layer composed of material having a medium refractive index n3 at the operating wavelength, where n1<n3<n2, anda second layer composed of the material having the medium refractive index n3,wherein the four-layer sequence is (LM1HM2)m or (HM1LM2)m, where L designates the layer composed of material having the lower refractive index n1 at the operating wavelength, H designates the layer composed of material having the higher refractive index n2 at the operating wavelength, M1 designates the first layer composed of material having a refractive index n3 at the operating wavelength, M2 designates the second layer composed of material having a refractive index n3 at the operating wavelength, and where m designates a number of the four-layer sequences in the dielectric layer system, andwherein the layer (L) composed of material having the lower refractive index n1 is composed of at least one of: aluminum fluoride, cryolite, chiolite, lithium fluoride and magnesium fluoride, the layer (H) composed of material having the higher refractive index n2 is composed of at least one of: neodymium fluoride, gadolinium fluoride, dysprosium fluoride, lanthanum fluoride and aluminum oxide, and the layers (M1, M2) composed of material having the medium refractive index n3 are composed of at least one of: magnesium fluoride, yttrium fluoride and silicon dioxide. 16. The reflective optical element as claimed in claim 15, wherein the layer of the dielectric layer system which is second closest to the substrate is composed of material having the medium refractive index n3. 17. The reflective optical element as claimed in claim 15, wherein the metallic coating comprises at least one of: aluminum, an aluminum-silicon alloy, an aluminum-manganese alloy, an aluminum-silicon-manganese alloy, and rhodium. 18. A lithography device for operating within the 150 nm and 240 nm wavelength range comprising a reflective optical element as claimed in claim 15. 19. A microscope device for operating within the 150 nm and 240 nm wavelength range comprising a reflective optical element as claimed in claim 15. |
|
summary | ||
054886422 | description | DETAILED DESCRIPTION OF THE INVENTION Although the principles of the invention are applicable to other cooling systems, the invention will be described in connection with a known type of spent fuel and reactor component cooling system. Such a system is illustrated in the accompanying drawings along with the added apparatus of the invention. As shown in FIG. 1, the known system comprises a spent fuel pool 1 filled with water 2 which can contain additives of a known type. Spent radioactive fuel assemblies 3 which have been removed from a reactor, not shown, are immersed in the pool of water 2. The water 2 must be kept at a temperature well below its boiling temperature, and the water 2 is cooled by pumping it out of the pool 1 by means of a pump 4 and sending it through pipes and valves 5 and 6 to a water conduit assembly 7, which can be a plurality of tubes, from which it returns to the pool 1 by way of a pipe 8. In a conventional cooling system, the assembly 7 through which the water 2 from the spent fuel pool is circulated is contained in a water-tight housing 9 of a heat exchanger 10 which receives and returns cooling water from and to another heat exchanger 11 of known construction which forms part of a cooling system for reactor components, e.g. reactor coolant pumps. Cooling water from a suitable source, e.g. a river, is supplied by a line 12 to the heat exchanger 11 and then dumped back to the source via line 11a. In the arrangement of the invention, the water from the spent fuel pool can be passed through the conventional heat exchanger 9, or the conventional heat exchanger can be bypassed, or the conventional heat exchanger and the heat exchanger of the invention can both be used. As examples of the spent fuel pool water cooling which can be required, it can be necessary to remove 13 million BTU/hour, 131 hours after a third of the reactor fuel assemblies are immersed in the water 2 and 12 million BTU/hour, 174 hours after such immersion of the assemblies. In a full core discharge case, i.e. when all of the reactor fuel assemblies are immersed in the water 2, the heat removal rate can be as much as 26 million STU/hour, 360 hours after immersion of the assemblies in the water 2. When the reactor is shut down for maintenance and refueling, all of the assemblies are transferred from the reactor to the spent fuel pool. The procedure can take about twelve hours, which provides only a relatively short time for the maintenance or repair of the service water/component cooling system. Also, if there is a failure of the component cooling system 11 or the supply of water by way of the line 12, the reactor operation must be discontinued, and there would be a loss of spent fuel pool water cooling. In accordance with the invention, these problems can be overcome by the addition of the apparatus described hereinafter without a substantial modification of the known system, and with equipment of relatively small size and cost as compared to the size and cost of a conventional water-water heat exchanger such as the heat exchanger 10. The heat exchanger which is added in accordance with the present invention also is more reliable than a water-water heat exchanger. In the preferred embodiment of the invention, the added apparatus comprises a pump 13, valves 14, 15, 16 and 17, a heat exchanger 18 which uses air and water spray for the coolant and the interconnecting pipes shown in the drawing. The heat exchanger unit 18 comprises a spray water conduit W, a duct 22, one bank 20 of water spray heads or nozzles 20a and a fan 25. Air is supplied to the duct 22 from any convenient source, which can be the known spent fuel ventilation system normally used in the known cooling system, and water is supplied through the conduit W to the nozzles or spray heads 20a of the bank 20 from any convenient source thereof, e.g. public water mains, but preferably, the water is supplied thereto from a storage tank so that the spray water is always available and is independent of other sources which can more readily fail. When valves 14 and 17 are open and valves 5 and 6 are closed, water 2 of the spent fuel pool is circulated by the pump 13 and is returned to the pool 1 by way of the interconnecting pipe lines 30, 31, 32, as shown by the arrows in FIG. 1. As the water 2 passes through the heat exchange unit 18, a stream of air driven by the fan 25 impinges on the heat exchange surfaces, and water is sprayed into the flow of air and onto the unit 18 from the spray head nozzles 20a of bank 20 to thereby remove heat from the water 2. With the temperature of the water 2 at 150.degree. F., with the temperature of the ambient air entering the duct 22 at 75.degree. F., the heat exchanger 18 can remove heat from the water 2 in an amount equal to about 22 million BTU/hour. For this result, the operating conditions of the heat exchanger are as follows: ______________________________________ Air flow rate 72,000 cfm through duct 22 Total water flow 2,250 g./min. through unit 18 Air flow area 180 sq. ft. Air flow velocity 900 ft./min. Spray water flow 120 g./min. ______________________________________ About one-third of the water sprayed into the air stream is being evaporated to achieve the above result. If a larger fraction of the sprayed water is evaporated, the cooling effect will be enhanced. If the temperature of the air entering the duct 22 is lower, the amount of heat removed under the same conditions is greater. Let it be assumed that the heat exchanger 10 for the spent fuel water 2 is not available for cooling the water 2 or that the component cooling heat exchanger 11 or cooling water supplied from a river or other source by the line 12 is not available (first case), and that the heat removal requirements are 22 million BTU/hour. With the heat exchanger 18 and the operating conditions thereof described hereinbefore, the added equipment of the invention can assume the entire cooling load under the following conditions: ______________________________________ Component Condition ______________________________________ Pump 13 Operating Valve 14 Open Valve 5 Closed Valve 16 Closed Valve 17 Open Valve 6 Closed Valve 15 Open or closed ______________________________________ Let it be assumed that the heat exchanger 10 is operative but that supplemental cooling is required (second case), such as in the full discharge case previously described. With the heat exchanger 18 and the described operating conditions thereof, the added equipment can provide supplemental cooling with the components in the following conditions: ______________________________________ Component Condition ______________________________________ Pumps 4 and 13 Operating Valve 14 Open Valve 5 Open Valve 16 Closed Valve 17 Open Valve 6 Open Valve 15 Closed ______________________________________ Let it be assumed that the supply of water by the line 12 is lost and that it is desired to continue cooling of the water 2 and the reactor components, e.g. pump seals, etc. (third case). With the heat exchanger 18 and the described operating conditions thereof, the added equipment of the invention can provide such cooling with the components set as follows: ______________________________________ Component Condition ______________________________________ Pump 13 Operating Valve 14 Open Valve 5 Closed Valve 16 Open Valve 17 Closed Valve 6 Open Valve 15 Open or closed ______________________________________ Although not preferred, the added apparatus can be simplified by the elimination of the pump 13 and the valve 15, the valve 14 being connected directly to the pump 4 and the valve 5. For that modified apparatus, in the first case assumed hereinbefore, the heat exchanger 18 can assume the entire cooling load with the components set as follows: ______________________________________ Component Condition ______________________________________ Pump 4 Operating Valve 14 Open Valve 5 Closed Valve 16 Open or closed Valve 17 Open Valve 6 Closed ______________________________________ In the second case assumed hereinbefore, the modified apparatus can supply supplemental cooling with the components set as follows: ______________________________________ Component Condition ______________________________________ Pump 4 Operating Valve 14 Open Valve 5 Open Valve 16 Open or closed Valve 17 Open Valve 6 Open ______________________________________ In the third case assumed hereinbefore, the modified apparatus can continue cooling of the water 2 and the reactor components with the components set as follows: ______________________________________ Component Condition ______________________________________ Pump 4 Operating Valve 14 Open Valve 5 Closed Valve 16 Open Valve 17 Closed Valve 6 Open ______________________________________ The heat exchanger unit 18, which uses air entraining a sprayed mist of water as the coolant medium, is shown to be of known cross-flow plate-fin construction as illustrated in FIGS. 2 and 3, wherein the liquid to be cooled flows in channels between pairs of parallel sheets (the water side) while the coolant medium comprising air carrying a mist of fine droplets flows in channels arranged alternately with the water channels between the parallel sheets (the air side). That is, flows of mist-carrying air and of water being cooled flow past opposite sides of the parallel sheets for indirect heat exchange through the sheets. By cross-flow, it is meant that the flows of water and air are essentially directed at right angles to each other in a well known mode of operation, illustrated for example in FIG. 9-3 of Kays and London, Compact Heat Exchangers, second edition, 1954 and in the accompanying FIG. 3. Strip-fins can be employed only on the side of the heat exchange surfaces over which air carrying the water spray passes, or on both sides of the heat exchange surfaces. The strip-fins are preferably formed of copper. When strip-fins are employed on both sides of the heat exchange surfaces, a lower water spray rate can be used to produce a given cooling rate. Although the heat exchange unit of the type described is illustrated in FIG. 1, in many applications more than one heat exchange unit can provide the higher cooling rates as shown in FIG. 4. The number of heat exchange units to be arranged in tandem can be determined in accordance with the cooling capacity requirements of any given application. In certain cases, the first of a plurality of heat exchange units can be operated without any water spray, in which case, a downstream unit (or units) that is sprayed with water droplets, is more effective. Such an arrangement is shown in FIG. 4. FIG. 4 shows an alternate form of sprayed water heat exchanger according to the invention. In the embodiment of FIG. 4 three heat exchangers in tandem are employed, rather than the single heat exchanger unit 18 shown in FIG. 1. Each of the heat exchanger units 19, 20 and 21 can have the same structure as the single unit 18 that constitutes the heat exchanger of FIG. 1, and therefore the units 19, 20 and 21 are not described in detail. The heat exchanger units 20 and 21 are shown in FIG. 4 to have their own, individually operable banks 23 and 24 of water headers and respective spray nozzles 23a, 24a. The arrangement of FIG. 4 can provide greater cooling and more flexibility than that of FIG. 1. Experimental tests have been performed to compare the performance of similarly dimensioned tube-fin and plate-fin heat exchangers, both provided with means for spraying finely atomized droplets of water into the flow of coolant air through the heat exchangers. The results for the tube-fin heat exchanger demonstrated that the cooling capacity could be increased by a factor of four times that of the same heat exchanger with no water spray. Test results for the plate-fin heat exchanger demonstrated that the cooling capacity of the exchanger with sprayed water droplets exceeded by a factor of eight times that of the same heat exchanger with no water spray. The test heat exchangers represented approximately one-thirtieth of full scale air side frontal area of the heat exchanger which would actually be employed in an alternate spent fuel cooling system for a nuclear power generating plant, but the results are believed to demonstrate that either tube-fin or plate-fin air cooling heat exchangers augmented by spraying atomized water droplets having a mean diameter of 250 microns or less into the cooling air can be used for the purpose of the invention. The water spray can be produced by use of suitable high inlet pressure, hydraulic or air atomizing spray nozzles such as those available from suppliers such as Spraying Systems Co. of Wheaton, Ill. The nozzles can be arranged on headers that are opened and closed by solenoid valves for control of the amount of water sprayed. That is, one or more of a plurality of spray headers can be activated to provide the desired spray flow. Preferably the nozzles have built-in strainers. When the air flow through the heat exchanger is directed horizontally, the nozzles are arranged to spray water droplets concurrently with the air flow while the flow of water to be cooled on the water side of the plates is in a direction perpendicular to the direction of the flow of cooling air. Other arrangements will suggest themselves to those acquainted with the art of heat transfer. |
abstract | A radiation therapy apparatus has a multi-leaf collimator device having a pair of collimator components which respectively comprise a plurality of leaves arranged close to one another such that the leaves face one another across an irradiation axis, and configured to set a desired irradiation field by individually moving the leaves. One of the collimator components is arranged with an offset with respect to the other collimator component, within a range of a leaf-width. |
|
summary | ||
abstract | Systems and methods for generating a coherent matterwave beam are provided. In some aspects, a system includes a plurality of beam generating units. Each of the plurality of beam generating units is configured to generate a stream of charged particles. The system also includes a magnetic field generator configured to expose the plurality of streams to a magnetic field such that (i) the charged particles of the plurality of streams undergo phase synchronization with one another in response to a vector potential associated with the magnetic field and (ii) the plurality of streams is directed along one or more channels to combine with one another and produce a coherent matterwave beam. |
|
claims | 1. An ElectroMagnetic Mechanical Pulser (“EMMP”) comprising:an input configured to accept a continuous input electron beam;a Traveling Wave Metallic Comb Stripline kicker (“TWMCS” kicker) located downstream of the input and having an internal passage through which the electron beam passes, the TWMCS kicker being configured to impose an oscillatory transverse deflection on the electron beam according to at least one of a transverse time-varying electric field and a transverse time-varying magnetic field generated within the TWMCS kicker by a first RF traveling wave propagated through the TWMCS kicker;a Chopping Collimating Aperture (“CCA”) located downstream of the TWMCS kicker and configured to block the electron beam when its deflection exceeds a threshold maximum or minimum, thereby chopping the electron beam into a chopped stream of electron pulses having an electron pulse repetition rate and duty cycle;an output configured to allow electron pulses to emerge from the EMMP as an output stream of electron pulses having a pulse repetition rate and a pulse duty cycle; anda vacuum chamber surrounding all elements of the EMMP and configured to provide a vacuum that is sufficient to allow the electron beam to pass through the EMMP without significant attenuation thereof by residual gasses, wherein:the TWMCS kicker includes at least one pair of opposing combs;each of said opposing combs of said pair of combs comprises a strip from which a plurality of substantially identical, equally spaced-apart blocks extend as teeth;the combs of the pair of combs are spaced apart with teeth facing inward such that the internal passage through which the electron beam passes is between the teeth of the pair of combs;the pair of combs includes an RF energy input proximal to a first end thereof and an RF energy output proximal to an opposite, second end thereof;the teeth of the pair of combs are configured to control a phase velocity of a traveling RF wave propagating from the first end to the second end so that it is matched to an electron velocity of the electron beam; andall exposed surfaces of the pair of combs are electrically conductive. 2. The EMMP of claim 1, further comprising a dispersion suppressing section downstream of the CCA, the dispersion suppressing section being configured to suppress a residual dispersion of the stream of electron pulses arising from the deflection imposed by the TWMCS kicker. 3. The EMMP of claim 2, wherein the dispersion suppressing section includes a demodulating mirror TWMCS having an internal passage through which the electron beam passes downstream of the CCA the mirror TWMCS having a physical configuration that causes a phase velocity of a second RF traveling wave propagated through the mirror TWMCS to be matched to a velocity of the electron beam, the mirror TWMCS being configured to demodulate the oscillatory transverse deflection imposed on the electron beam by the TWMCS kicker. 4. The EMMP of claim 2, wherein the dispersion suppressing section includes at least one magnetic quadrupole. 5. The EMMP of claim 1, wherein the pulse repetition rate of the electron pulses in the output stream is tunable from 0.1 GHz to 20 GHz. 6. The EMMP of claim 1, wherein a pulse length of the electron pulses in the output stream is tunable from 100 fs to 10 ps. 7. The EMMP of claim 1, wherein the duty cycle of the electron pulses in the output stream is tunable from 1% to 10%. 8. The EMMP of claim 1, wherein the pulse repetition rate and the duty cycle of the electron pulses in the output stream are independently tunable. 9. The EMMP of claim 1, wherein the EMMP is configured to accept input electron beams having a kinetic energy between 100 and 500 keV. 10. The EMMP of claim 1, wherein the TWMCS kicker includes two pair of opposing combs through which the electron beam simultaneously passes, the two pair of opposing combs being arranged such that a first pair thereof deflects the electron beam in a first deflection plane and a second pair thereof deflects the electrons in a second deflection plane that is orthogonal to the first deflection plane, wherein a line of intersection between the first and second deflection planes lies along the internal passage through which the electron beam passes. 11. The EMMP of claim 1, wherein the EMMP further comprises a down-selecting TWMCS positioned downstream of the CCA and configured to reduce the pulse repetition rate of the output stream by deflecting some pulses out from the chopped stream of electron pulses that emerges from the CCA. 12. The EMMP of claim 11, wherein the EMMP further includes a down-selecting aperture located downstream of the down-selecting TWMCS. 13. The EMMP of claim 1, wherein at least one of the combs of the pair of combs can be laterally shifted toward and away from the other of the combs of the pair of combs. 14. The EMMP of claim 1, wherein the RF energy output is connected to a terminating impedance. 15. The EMMP of claim 14, wherein the terminating impedance is a 50 Ohm impedance. 16. The EMMP of claim 1, wherein an orientation of at least one of the combs of the pair of combs can be varied in orientation so as to adjust an angle between the pair of combs. 17. The EMMP of claim 1, wherein an aperture size of the CCA is mechanically adjustable. 18. The EMMP of claim 1, wherein the CCA includes an aperture that is not circular. 19. The EMMP of claim 18, wherein the CCA includes an elongated aperture having a height thereof that is at least twice as large as a width thereof. 20. The EMMP of claim 1, wherein the EMMP includes an aperture having electrically isolated elements that enable the aperture to function as at least one of a beam position monitor and a beam current monitor. 21. The EMMP of claim 1, further comprising at least one magnetic or electrostatic beam deflecting element that is configured to adjust a propagating direction of the electron beam. 22. A method of generating electron pulses, the method comprising:providing an EMMP according to claim 1;causing a continuous electron beam to pass through the TWMCS kicker while applying RF energy to the RF energy input of the TWMCS kicker, said RF energy causing a traveling RF wave to propagate through the TWMCS kicker, said traveling RF wave having a phase velocity that is substantially equal to an electron velocity of the electron beam, thereby imposing a spatial oscillation on the continuous electron beam;causing the spatially oscillating electron beam to impact the CCA, so that the CCA blocks the electron beam when its deflection exceeds a threshold maximum or minimum, thereby chopping the electron beam into a stream of electron pulses having a desired electron pulse repetition rate;adjusting an amplitude of the applied RF energy so as to adjust widths of the electron pulses to be equal to a desired electron pulse width; andadjusting a frequency of the applied RF energy so that it is equal to one half of a desired electron pulse repetition rate. 23. The method of claim 22, wherein the desired electron pulse repetition rate is between 100 MHz and 50 GHz, and the desired electron pulse width is in a range 100 fs to 10 ps. 24. The method of claim 22, wherein the specified electron pulse energy is between 100 keV and 500 keV. 25. The method of claim 22, wherein the TWMCS kicker includes two orthogonal pairs of combs, and wherein the method further comprises applying RF energy to a first of the pairs of combs at a first frequency and applying RF energy to a second of the pairs of combs at a second frequency. 26. The method of claim 22, wherein:the TWMCS kicker includes two orthogonal pairs of combs;the CCA includes an aperture opening having a non-circular shape: andthe method further comprises applying RF energy to a first of the pairs of combs at a first RF amplitude and applying RF energy to a second of the pairs of combs at a second RF amplitude, and varying the electron pulse width by varying a difference between the first and second RF amplitudes. 27. The method of claim 22, wherein the EMMP further comprises a down-selecting TWMCS positioned downstream of the CCA, and the method further comprises applying RF energy at a first RF frequency F1 to the TWMCS kicker and applying RF energy to the down-selecting TWMCS at a second RF frequency F2, wherein either F1/F2 or F2/F1 is an integer. 28. The method of claim 27, wherein the EMMP further comprises a down-selecting aperture downstream of the down-selecting TWMCS. 29. The method of claim 28, wherein the down selecting aperture includes an opening having a height thereof that is at least twice as large as a width thereof. |
|
claims | 1. A method for improving the energy generating output of a nuclear reactor while satisfying a maximum subcritical banked withdrawal position (MSBWP) reactivity limit, comprising:ranking enrichments of individual fuel rods by evaluating an uranium enrichment of fuel rods at a two top-most nodes of each fuel rod of a fuel bundle, a highest ranked fuel rod being a fuel rod with the lowest enrichment of uranium at said two top-most nodes, the evaluation of the two top-most nodes being performed by discounting existence of any natural uranium blanket,replacing a highest ranked fuel rod with a fuel rod containing natural uranium in either the top node, or the two top-most nodes,performing a core simulation to determine whether there is any margin to a MSBWP reactivity limit,repeating the replacing and performing function for each lower ranked fuel rod until no fuel rods violate the MSBWP reactivity limit, so as to achieve a desired lattice design for the top of the fuel bundle, andoperating the core of the reactor having fuel bundles configured with the desired lattice design at the top of the fuel bundle. 2. The method of claim 1, wherein the top node of each fuel rod in the fuel bundle is natural uranium, thereby providing the fuel bundle with a 6-inch natural uranium blanket at the top of the fuel bundle. 3. The method of claim 1, wherein the two top-most nodes of the fuel rods of the fuel bundle are between 138 and 150 inches from the bottom of the fuel bundle, and the top-most node between 144 and 150 inches from the bottom of the fuel bundle is natural uranium. 4. The method of claim 1, wherein the top-most node is located between 144 and 150 inches from the bottom of the fuel bundle, and a lower of the two top-most nodes is located between 138 and 144 inches from the bottom of the fuel bundle. |
|
044434022 | abstract | Method and apparatus for detecting defective fuel elements in a nuclear reactor assembly. The assembly (20) is kept entirely immersed in a liquid such as water, ultrasonic waves are propagated successively in each of the fuel elements of the assembly or rods (21), an ultrasonic sensor (25) is disposed near the assembly (20) and the waves which may be scattered into the protective liquid by the defects in the fuel rod are picked up to determine the presence of a defective assembly and locate the defective rod in the assembly. The invention is particularly applicable to fuel assemblies of a pressurized water nuclear reactor. |
description | A product irradiation device according to the present invention is illustrated at 10 in FIG. 1. The product irradiation device 10 includes a transportable or mobile enclosure 12 and an irradiator shell 14, illustrated in FIG. 2, disposed in enclosure 12. The enclosure 12 includes a top wall or roof 15, a bottom wall or floor 16, opposing side walls 17 and 17xe2x80x2, a forward wall 18 and a rearward wall 19. In the case of enclosure 12, the walls 15, 16, 17, 17xe2x80x2, 18 and 19 are flat or planar with top wall 15 parallel to bottom wall 16, side walls 17 and 17xe2x80x2 parallel to one another and forward wall 18 parallel to rearward wall 19. A plurality of doors 20 are provided on enclosure 12, the doors 20 being selectively closeable to close the enclosure 12 and being selectively openable to present access openings communicating with the interior of enclosure 12. As shown in FIG. 1, two pairs of doors 20 are hingedly mounted on side wall 17 with the doors 20 of each pair disposed next to one another or in side by side relation. Accordingly, each pair of doors 20, when open, presents an access opening on the side wall 17 corresponding or substantially corresponding in size to the height and the combined widths of the doors 20. The pairs of doors 20 are disposed at spaced locations along side wall 17 such that the access openings presented thereby are also spaced from one another. Another pair of doors 20 defines the rearward wall 19, the doors of the another pair being hingedly mounted to side walls 17 and 17xe2x80x2, respectively, at a rearward end of the enclosure 12 as shown in FIG. 1. When the another pair of doors 20 defining rearward wall 19 are open, an access opening circumscribed by the top, bottom and side walls is presented at the rearward end of the enclosure 12. At least one additional pair of doors 20 (not visible in FIG. 1) is provided on side wall 17xe2x80x2, the at least one additional pair of doors 20 being aligned with one of the pairs of doors 20 on side wall 17. In the case of enclosure 12, the rearwardmost pair of doors 20 on side wall 17 is aligned, in a direction transverse or perpendicular to a longitudinal axis of enclosure 12, with the at least one additional pair of doors 20 on side wall 17xe2x80x2. The access opening presented when the rearwardmost pair of doors 20 on side wall 17xe2x80x2 are open serves as an exit or discharge opening for exit or discharge of irradiated products from the product irradiation device 10. The access opening presented when the at least one additional pair of doors on side wall 17 are open serves as an entry opening for introduction or entry of non-irradiated products into the product irradiation device 10. The doors 20 may be mounted on the enclosure 12 singly or in pairs depending on the sizes of the doors and the sizes desired for the access openings. Preferably, at least some of the access openings are of a size to permit human access and the introduction of necessary equipment into the interior of the enclosure. Doors 20, arranged singly or in pairs, may be provided on any or all walls of the enclosure. The doors 20 may be provided with latches or locks for locking the doors in a closed position, and such latches or locks may be conventional. Although the doors are disclosed herein as being hingedly mounted on the enclosure, it should be appreciated that the doors can be mounted on the enclosure in various other ways, such as being slidably mounted on the enclosure. The enclosure 12 is mounted or supported on a plurality of wheels 22 by which the enclosure 12 can be transported along the ground or other surface. The enclosure 12 is mounted on six sets of wheels 22 as shown in FIG. 1. Three sets of wheels 22 are disposed adjacent or proximate the rearward end of the enclosure 12 while another three sets of wheels 22 are disposed intermediate the rearward end and a forward end of the enclosure 12. The three sets of wheels 22 disposed adjacent or proximate the rearward end are rearwardly spaced from the three sets of wheels 22 disposed intermediate the forward and rearward ends. No wheels 22 are provided at, adjacent or proximate the forward end since the forward end of enclosure 12 is adapted to be removably coupled to a powered wheeled vehicle (not shown) by which the enclosure 12 is transported along the ground or other surface. Apparatus and/or structure for coupling the enclosure 12 to a powered wheeled vehicle may be conventional in nature, such as that employed in conventional truck trailer design whereby the forward end of the enclosure 12 is supported upon one or more sets of wheels of the powered wheeled vehicle. The enclosure 12 is provided with a selectively extendable, selectively retractable rigid brace or support 24 for supporting the forward end of the enclosure when the enclosure is not coupled to the powered wheeled vehicle. FIG. 1 shows the support 24, which is located at, adjacent or proximate the forward end of enclosure 12, extended beneath the bottom wall 16 in a direction perpendicular thereto. When the support 24 is thusly extended, a pair of feet 25 of the support 24 engage the ground or other surface upon which the wheels 22 are disposed, only one foot 25 being visible in FIG. 1. The support 24 supports the forward end of the enclosure 12 so that the enclosure 12 is in a level, horizontal position and prevents movement of the enclosure 12 upon the ground or other surface. Of course, the enclosure 12 may also be provided with a suitable brake for preventing movement of the enclosure 12 upon the ground or other surfaces. When the support 24 is retracted, the feet 25 do not engage the ground or other surface and movement of the enclosure 12 thereupon via the wheels 22 is permitted. Preferably, the enclosure 12 is a standard truck trailer, as shown in FIG. 1, capable of being coupled to a truck by which the truck trailer is transported. It should be appreciated, however, that other standard enclosures, such as a rail car or a transportable container, may be used for enclosure 12. The enclosure 12 is capable of being transported or delivered to a loading dock or other suitable location at a manufacturing or processing facility or other source of products to be irradiated with the product irradiation device 10. Once delivered to the desired location, the enclosure 12 is detached from the truck and is parked, as shown in FIG. 1, without requiring any foundation work or other onsite construction or fabrication. The enclosure 12 can be provided with a plurality of braces 24 at various locations along the floor 16 thereof. Accordingly, once the enclosure 12 has been delivered to the desired location, the wheels 22 can be removed therefrom and the enclosure can be supported entirely by the plurality of braces 24. Of course, the braces 24 should be considered illustrative in that various support structure can be used to support the enclosure, with or without removal of the wheels 22. The product irradiation device 10 is entirely self-contained in that all systems needed to operate the product irradiation device, as well as auxiliary equipment therefor, and to accomplish irradiation of products therewith are provided in or on the product irradiation device and do not require any integration with or supply of power from the manufacturing or processing facility or other source of the products to be irradiated. Equipment for various purposes, such as electricity generation, refrigeration, heating, ventilation and/or cooling (HVAC) and any other necessary or optional service, and the systems for operating such equipment, are provided in or on the enclosure 12. FIG. 1 illustrates enclosure 12 provided with a generator module 26 and an HVAC module 28, both of which are mounted or supported on the top wall 15 of the enclosure 12. The generator module 26 is used to generate electricity for various purposes, while the HVAC module 28 is used for heating, ventilation and/or cooling of the shell 14 and/or the enclosure 12 as well as for removing heat from an irradiation source disposed in shell 14 as explained further below. The HVAC module 28 can include a suitable compressor or other equipment capable of refrigerating the interior of the shell 14 and/or the interior of enclosure 12 where the products to be irradiated require refrigeration, as in the case of frozen products. The irradiator shell 14 is disposed entirely within the interior of enclosure 12. The external size of irradiator shell 14 is smaller in size than the interior of enclosure 12, and the portion of the interior of enclosure 12 not occupied by irradiator shell 14 is used to accommodate equipment necessary or useful for operation of the product irradiation device 10. In the case of product irradiation device 10, the irradiator shell 14 has an external configuration and size to fit within the interior of a standard truck trailer, i.e. enclosure 12. The irradiator shell 14 is shielded to minimize or prevent exposure of operating personnel, the public and the environment to ionizing radiation. Accordingly, it is preferred that the irradiator shell 14 be at least partly made of radiation impenetrable or absorbable material, such as steel or lead, forming a wall or walls enclosing an irradiation source and a product transport channel circumscribed or defined by an interior surface or surfaces of the wall or walls of the irradiator shell. The interior surface or surfaces defining the product transport channel are preferably made of stainless steel, as are exterior or visible surfaces of the shell 14, while the bulk of the shell 14 is made of less costly carbon steel or lead. The irradiator shell 14 has a generally T-shaped external configuration with a longitudinal shell section 30 and a transverse shell section 32 joined to and extending perpendicularly to the longitudinal shell section 30. Preferably, the longitudinal and transverse shell sections each have a square or rectangular external cross-sectional configuration, although other external cross-sectional configurations are possible. As shown in FIG. 2, the longitudinal shell section 30 has a square external cross-sectional configuration, and the transverse shell section has a rectangular external cross-sectional configuration. The longitudinal shell section 30 is defined by a planar upperwall 34, a planar lower wall 35 parallel to upper wall 34, a pair of planar, parallel side walls 36 and 36xe2x80x2 extending between upper wall 34 and lower wall 35 and a planar end wall 37. The transverse shell section 32 is defined by the planar upper wall 34, the planar lower wall 35, a planar side wall 38 extending between upper wall 34 and lower wall 35, a pair of planar side wall segments 39 and 39xe2x80x2 parallel to side wall 38 and a pair of planar end walls 40 and 40xe2x80x2. The side wall segments 39 and 39xe2x80x2, one of which is disposed on each side of the longitudinal shell section 30, extend between upper wall 34 and lower wall 35 and also extend between side walls 36 and 36xe2x80x2 and end walls 40 and 40xe2x80x2, respectively. The end wall 37 is parallel to the side wall 38 and the side wall segments 39 and 39xe2x80x2. The side walls 36 and 36xe2x80x2 are parallel to the end walls 40 and 40xe2x80x2. As best shown in FIG. 3, a product transport passage or channel 41 is defined within the irradiator shell 14 and is made up of inner longitudinal channel sections 42 and 42xe2x80x2, outer transverse channel sections 43 and 43xe2x80x2 disposed at first ends of the inner longitudinal channel sections 42 and 42xe2x80x2, respectively, an inner transverse channel section 44 disposed at opposite or second ends of the inner longitudinal channel sections 42 and 42xe2x80x2, respectively, and outer longitudinal channel sections 45 and 45xe2x80x2 disposed at outer ends of the outer transverse channel sections 43 and 43xe2x80x2, respectively. The outer longitudinal channel sections 45 and 45xe2x80x2 extend from the outer ends of the outer transverse channel sections 43 and 43xe2x80x2, respectively, to openings or ports 46 and 46xe2x80x2, respectively, in the transverse shell section 32. The openings or ports 46 and 46xe2x80x2 are disposed on planar exterior surfaces of side wall segments 39 and 39xe2x80x2, respectively, and establish communication with the product transport channel 41 from externally of the shell 14. The openings or ports 46 and 46xe2x80x2 are disposed adjacent planar exterior surfaces of the side walls 36 and 36xe2x80x2, respectively. The inner longitudinal channel sections 42 and 42xe2x80x2 are parallel to one another and extend longitudinally in the longitudinal shell section 30 and part way into the transverse shell section 32. The outer transverse channel sections 43 and 43xe2x80x2, which are disposed within the transverse shell section 32, are perpendicular to the inner longitudinal channel sections 42 and 42xe2x80x2 and the outer longitudinal channel sections 45 and 45xe2x80x2. The outer transverse channel sections 43 and 43xe2x80x2 have inner ends communicating with the first ends of the inner longitudinal channel sections 42 and 42xe2x80x2, respectively, and have the outer ends thereof communicating with the outer longitudinal channel sections 45 and 45xe2x80x2, respectively. The inner transverse channel section 44 is perpendicular to the inner longitudinal channel sections 42 and 42xe2x80x2. The inner transverse channel section 44 is disposed in the longitudinal shell section 30 and extends between the opposite or second ends of the inner longitudinal channel sections 42 and 42xe2x80x2, respectively. The outer longitudinal channel sections 45 and 45xe2x80x2 are disposed in the transverse shell section 32 and are parallel to the inner longitudinal channel sections 42 and 42xe2x80x2. The outer longitudinal channel sections 45 and 45xe2x80x2 extend between the outer ends of the outer transverse channel sections 43 and 43xe2x80x2, respectively, and the openings or ports 46 and 46xe2x80x2, respectively. The product transport channel 41 and the ports 46 and 46xe2x80x2 have a cross-sectional configuration and size large enough to accommodate and facilitate the passage therethrough of products, such as products 47 shown in FIGS. 2 and 3. Preferably, the cross-section of the product transport channel 41 and the ports 46 and 46xe2x80x2 corresponds as close as possible in size and configuration to the external cross-section of the individual products 47, or to containers such as bins or baskets holding one or more products, while allowing the products 47 or the containers for the products to freely pass therethrough. The products 47 are moved in a longitudinal direction through the inner and outer longitudinal channel sections 42, 42xe2x80x2, 45 and 45xe2x80x2 and are moved in a transverse direction, perpendicular to the longitudinal direction, through the inner and outer transverse channel sections 43, 43xe2x80x2 and 44. Although the direction of movement for the products 47 through the channel 41 thusly changes, the orientation or position of the products 47 does not change as the products are introduced in, moved through and discharged from channel 41. When the products 47 are moved in channel 41 in the longitudinal direction, an external dimension D1 of the products 47 is aligned with the longitudinal direction of movement. When the products 47 are moved in channel 41 in the transverse direction, an external dimension D2 of the products 47 is aligned with the transverse direction of movement. In the instance of products 47, the external dimension D1 is a major or maximum external dimension defining a major axis of the products while the external dimension D2 is a minor external dimension defining a minor axis of the products. Where the external dimensions D1 and D2 are equal or the same, the channel 41 may be of uniform or constant cross-section from port 46 to port 46xe2x80x2. Where external dimensions D1 and D2 are not the same, as shown for products 47, the channel 41 can be of non-uniform or non-constant cross-section from port 46 to port 46xe2x80x2. In particular, longitudinal channel sections 42, 42xe2x80x2, 45 and 45xe2x80x2 can have a cross-section corresponding in size and shape to the cross-section of external dimension D2 while the transverse channel sections 43, 43xe2x80x2 and 44 can have a cross-section corresponding in size and shape to the cross-section of external dimension D1. It should be appreciated, therefore, that the cross-section of channel 41 may be uniform and constant or non-uniform and non-constant depending on the cross-sectional dimensions of the products and the direction of movement of the products in the channel 41. The cross-section of the channel 41 and the ports 46 and 46xe2x80x2 is defined or circumscribed by a planar interior surface or surfaces of the wall or walls of the irradiator shell 14, such interior surface or surfaces preferably being made of stainless steel as described above. The planar interior surface 48 of lower wall 35 is a transport surface 48 upon which the products 47 are directly supported and are moved through the irradiator shell 14. The transport surface 48, which is non-moving, may be finished, such as by polishing or other treatment, to minimize friction when the products are moved thereupon. Any or all of the other interior surfaces of the walls of the irradiator shell 14 defining the channel 41 may be finished, such as by polishing or other treatment, to minimize friction and promote passage of the products through the channel 41. The walls of irradiator shell 14 are of sufficient thickness to prevent the emission of unsafe levels of radiation externally of shell 14 from an irradiation source disposed within the shell 14. An irradiation source 49, shown in FIG. 3, is disposed in shell 14 and includes an array of elongate rods 50 made of radioactive material, such as Cobalt 60. Rods 50 extend vertically in shell 14 with their central longitudinal axes, respectively, disposed in a plane P1 perpendicular to upper and lower walls 34 and 35. A shield plug 51 is provided above the upper end of each rod 50, and each rod 50 is disposed in an outer tube or jacket 52 to form a rod assembly as shown in FIG. 4. Tubes 52 containing rods 50 are disposed close to one another in parallel, side by side relation to be arranged in shell 14 linearly or in series with the central longitudinal axes of rods 50 disposed in the plane P1, which contains the central longitudinal axis of longitudinal shell section 30 and is perpendicular to the transport surface 48 and parallel to the side walls 36 and 36xe2x80x2 and the end walls 40 and 40xe2x80x2. Rods 50, with their outer tubes 52, are disposed in a shell insert 53 disposed between inner longitudinal channel section 42 and inner longitudinal channel section 42xe2x80x2. The shell insert 53 has spaced, planar, parallel side faces 54 and 54xe2x80x2 between which the tubes 52 containing rods 50 are disposed, the side faces 54 and 54xe2x80x2 being parallel to plane P1. The side faces 54 and 54xe2x80x2 extend vertically in the shell 14 between a planar interior surface of the upper wall 34 and the planar interior surface of the lower wall 35, i.e. the transport surface 48. The side faces 54 and 54xe2x80x2 extend longitudinally in the shell 14 from a planar interior surface of side wall 38 up to the inner transverse channel section 44, whereat the side faces 54 and 54xe2x80x2 are joined to one another by a transverse end face 55. The rods 50 are serially or linearly arranged between the side faces 54 and 54xe2x80x2 to extend therebetween a linear distance corresponding or substantially corresponding to the linear distance between the end face 55 and a plane P2 containing planar exterior surfaces of side wall segments 39 and 39xe2x80x2 as shown in FIGS. 2 and 3. The linear distance that the rods 50 occupy within the shell 14 defines an active length for the irradiation source 49. The number of and spacing for the rods in shell 14 may vary depending on the radiation strength or intensity of the individual rods 50, the total or cumulative radiation strength or intensity desired for the source 49 and/or the desired active length. The radiation strength or intensity of the individual rods 50 can vary depending on the number of and spacing for the rods 50, the total radiation strength or intensity desired for the irradiation source and/or the desired active length. The rods 50 have diameters concentrically received within the tubes 52, respectively. The perpendicular distance between side faces 54 and 54xe2x80x2 is sufficient to accommodate the tubes 52 therebetween. The rods 50 and tubes 52 have a length extending perpendicularly between the upperwall 34 and the lower wall 35, such length being at least as great as the perpendicular distance between the interior surface of upper wall 34 and the interior surface of lower wall 35, i.e. the transport surface 48. The shield plugs 51 have a stepped configuration for reception in correspondingly configured openings or holes, respectively, in the upper wall 34 as shown in FIGS. 2 and 4. The shield plugs 51 are removably disposed in the upper wall 34 allowing the rods 50 to be removed and/or replaced via withdrawal through the openings or holes in upper wall 34. In particular, the rods 50 can be individually installed and/or removed at the same time that product irradiation is taking place. The irradiation source, i.e. rods 50, is not transported with the enclosure 12 or shell 14. Rather, the enclosure 12 and shell 14 are transported and delivered to the source of the products separately from the irradiation source. It is contemplated that the irradiation source would be purchased from suppliers equipped with licensed transport casks and from whom disposal services would also be obtained. The shell insert 53 partitions or divides the shell 14 into an inlet or entry side disposed on one side of insert 53 and, therefore, plane P1, and an outlet or exit side disposed on the other or opposite side of insert 53 and, therefore, plane P1. The side wall segment 39 is disposed on the one side of plane P1 while the side wall segment 39xe2x80x2 is disposed on the opposite side of plane P1. Accordingly, the port 46 constitutes an inlet or entry port, disposed on the one side of plane P1, while the port 46xe2x80x2 constitutes an outlet or exit port, disposed on the opposite side of plane P1, the inlet and outlet ports being disposed in plane P2, which is perpendicular to plane P1. A prescribed path is defined in shell 14 between the inlet port 46 and the outlet port 46xe2x80x2 and along which the products 47 are moved through the shell 14. The prescribed path, which corresponds to the transport channel 41, begins at the inlet port 46 and includes, in sequence, the outer longitudinal channel section 45, the outer transverse channel section 43, the inner longitudinal channel section 42, the inner transverse channel section 44, by which the inlet side and the outlet side are in communication, the inner longitudinal channel section 42xe2x80x2, the outer transverse channel section 43xe2x80x2 and the outer longitudinal channel section 45xe2x80x2, the prescribed path terminating at the outlet port 46xe2x80x2. Hence, the transport surface 48 extends from the inlet port to the outlet port, which is spaced or remote from or disposed at a different location than the inlet port. A portion of the prescribed path is in a high radiation zone of the transport channel 41, the high radiation zone corresponding to the active length of the irradiation source 49. Accordingly, the high radiation zone is defined between plane P2 and the inner transverse channel section 44 and thusly includes the inner longitudinal channel sections 42 and 42xe2x80x2. The shell 14 can be introduced in the interior of enclosure 12 via the access opening presented when the doors 20 forming rearward wall 19 are open. The lower wall 35 of shell 14 is supported upon the bottom wall or floor 16 of enclosure 12. The shell 14 is positioned in the interior of enclosure 12 so that the inlet port 46 and the outlet port 46xe2x80x2 are aligned with the entry and exit openings, respectively, of the enclosure, the entry and exit openings being presented when the rearwardmost doors 20 on side walls 17 and 17xe2x80x2, respectively, are open. Subsequent to introduction and proper positioning of shell 14 in the interior of enclosure 12, the doors 20 forming rearward wall 19 will normally remain closed and locked. The doors 20 defining the entry and exit openings, respectively, will be open during operation of the product irradiation device 10 and will normally be closed and locked when the product irradiation device 10 is not in operation. Products 47, prior to being irradiated, are presented at the inlet port 46 via a delivery member 60 extending through the entry opening of enclosure 12 and establishing communication between the inlet port 46 and the source of the products 47. The delivery member 60 may be supplied as part of the product irradiation device 10 or as a separate component provided by the user of the product irradiation device, in which case the product irradiation device may be supplied without a delivery member. In the case of product irradiation device 10, the delivery member 60 is supplied as part of the product irradiation device and includes a roller ramp 61 extending through the entry opening of enclosure 12 and having a first end positioned in front of the inlet port 46, adjacent or in abutment with the planar exterior surface of the side wall 36, and a second end disposed at or proximate the source of the products 47. The first end of the roller ramp 61 is located directly in front of the inlet port 46 so that a product 47 supported on the first end is aligned with the inlet port 46 and is ready to be passed therethrough into the transport channel 41. The second end of the roller ramp 61 is disposed, externally of enclosure 12, at a convenient location at the source of the products 47. For example, the second end of the roller ramp 61 may be disposed at a loading dock or other location of the manufacturing or processing facility for the products 47. The second end of roller ramp 61 is elevated or disposed higher than the first end thereof so that the products 47 are conveyed by gravity from the second end to the first end. Accordingly, the roller ramp 61 will be disposed at an obtuse angle to the ground or other surface upon which the enclosure 12 is supported. As shown in FIG. 2, the first end of the roller ramp 61 may be angled relative to the remainder thereof so that the first end of the roller ramp 61 is disposed in the same or substantially the same plane as the transport surface 48. Products 47 positioned upon the second end of the roller ramp 61 are automatically conveyed by gravity from the second end to the first end of the roller ramp 61, as facilitated by rollers of the roller ramp, the products 47 being guided or directed by upstanding, parallel side rails 62 of the roller ramp 61. As shown in FIGS. 2 and 3, the perpendicular distance between side rails 62 corresponds to the external dimension D1 of the products 47. The products 47 are conveyed along the delivery member 60 in a transverse direction perpendicular to plane P1 with the minor axis or external dimension D2 of the products 47 longitudinally or axially aligned with the transverse direction of conveyance of the products along the delivery member and with the major axis or external dimension D1 of the products parallel with plane P1. Accordingly, products are presented at the first end of the delivery member with the major axis longitudinally or axially aligned with inlet port 46 and outer longitudinal channel section 45. The exterior surface of side wall 36 serves as a stop or abutment for the products 47 at the first end of the delivery member 60 and facilitates alignment of the products 47 with the inlet port 46 and with the outer longitudinal channel section 45. Products 47, subsequent to being irradiated, exit the shell 14 through the outlet port 46xe2x80x2 and are discharged onto a discharge member 64 extending through the exit opening of enclosure 12. The discharge member 64 may be supplied as part of the product irradiation device 10 or as a separate component provided by the user, in which case the product irradiation device can be supplied without a discharge member. In the case of product irradiation device 10, the discharge member 64 is supplied as part of the product irradiation device and includes a roller ramp 65, similar to the roller ramp 61. The roller ramp 65 extends through the exit opening of enclosure 12 and has a first end positioned in front of the outlet port 46xe2x80x2, adjacent or in abutment with a planar exterior surface of the side wall 36xe2x80x2, and a second end disposed at or proximate the source of the products 47. As shown in FIGS. 2 and 3, the first end of the roller ramp 65 is located directly in front of the outlet port 46xe2x80x2 so that a product 47 discharged through the outlet port 46xe2x80x2 is delivered onto the first end of the roller ramp 65. The second end of the roller ramp 65 is disposed, externally of enclosure 12, at a convenient location at the source of the products 47. For example, the second end of the roller ramp 65 may be disposed at another loading dock or location of the manufacturing or processing facility for the products 47. The second end of roller ramp 65 is disposed lower than the first end thereof so that the products 47 are conveyed by gravity from the first end to the second thereof. Accordingly, the roller ramp 65 will be disposed at an acute angle to the ground or surface upon which the enclosure 12 is supported. As shown in FIG. 2, the first end of the roller ramp 65 may be angled relative to the remainder thereof so that the first end of the roller ramp 65 is disposed in the same or substantially the same plane as the transport surface 48. Products 47 discharged through the outlet port 46xe2x80x2 onto the first end of roller ramp 65 are automatically conveyed from the first end to the second end thereof as facilitated by rollers of the roller ramp 65, and the products 47 are guided by upstanding, parallel side rails 62 of the roller ramp 65. The products 47 are discharged from the outlet port 46xe2x80x2 with their major axis or external dimension D1 parallel to plane P1. The products 47 are conveyed along the discharge member 64 in a transverse direction perpendicular to plane P1 with the minor axis or external dimension D2 of the products 47 longitudinally or axially aligned with the transverse direction of conveyance of the products along the discharge member and with the major axis or external dimension D1 parallel with plane P1. It should be appreciated that the delivery member, the discharge member, the shell and/or the enclosure may be provided with a mechanism or mechanisms for securing the first ends of the delivery member and the discharge member, respectively, adjacent the inlet port and the outlet port, respectively. It should be further appreciated that the mechanism or mechanisms used to secure the first ends of the delivery member and/or the discharge member, respectively, adjacent the inlet port and outlet port, respectively, can be designed to allow the delivery member and/or discharge member to be detached or released from the shell and/or the enclosure. Accordingly, the delivery member and/or the discharge member can be detached or removed from the enclosure and/or the shell when the product irradiation device is not in use. The delivery member and/or the discharge member can be designed for movement between a deployed position, wherein the delivery member and/or the discharge member extends externally from the enclosure, and a nondeployed position, wherein the delivery member and/or the discharge member is disposed within the enclosure. For example, the delivery member and/or the discharge member may be pivotably, hingedly or rotatably mounted to the enclosure and/or the shell so that the delivery member and/or the discharge member may be pivotably, rotatably or hingedly moved into the enclosure to assume the non-deployed position and may be pivotably, hingedly or rotatably moved out from the enclosure to assume the deployed position. It should also be appreciated that the angular orientations of the delivery member and the discharge member, respectively, including the first ends thereof, can be selected, adjusted or varied in accordance with the conveying speed desired for the products therealong. A plurality of hydraulic or pneumatic actuators 66 are provided in or on the product irradiation device 10 for moving or advancing the products 47 incrementally into, through and out of the shell 14 in the prescribed path. The actuators 66 serve to push and/or pull the products 47, in fixed increments, into, through and out of the shell 14, and each includes a hydraulic or pneumatic cylinder 68 and a piston 70 slidably disposed in the cylinder 68. Seven actuators 66a, 66b, 66c, 66d, 66e, 66f and 66g are provided for product irradiation device 10 as best shown in FIG.3. The actuator 66a serves to push a product 47 disposed at the first end of the delivery member 60 through the inlet port 46 and into the outer longitudinal channel section 45. The actuator 66a is disposed externally of shell 14 in its entirety with its cylinder 68a and piston 70a longitudinally or axially aligned with the inlet port 46 and the outer longitudinal channel section 45. As shown in FIGS. 2 and 3, the cylinder 68a is secured to or mounted on the exterior surface of side wall 36 via a mounting block secured to the side wall 36. The piston 70a, which has a longitudinal axis parallel with plane P1 and perpendicular to plane P2, is longitudinally, slidably movable within the cylinder 68a in response to variation in fluidic pressure within the cylinder 68a. The piston 70a is slidably movable relative to cylinder 68a between a retracted position wherein a product engaging end 74a of the piston 68a is disposed adjacent, close to or in abutment with the cylinder 68a and an extended position wherein the product engaging end 74a is disposed further away from the cylinder 68a and, in particular, is adjacent or aligned with the plane P2 and, therefore, with the inlet port 46 as shown in dotted lines in FIG. 3. In the retracted position for piston 70a, the product engaging end 74a is spaced from the plane P2, and the distance that the end 74a is spaced from plane P2, i.e. the stroke of piston 70a, is at least as large as the external dimension D1 of the products 47. A product 47, when disposed at the first end of the delivery member 60, thusly has its external dimension D1 disposed between the inlet port 46 and the product engaging end 74a when the piston 70a is in the retracted position. In this manner, the major or maximum external dimension D1 will be disposed parallel to plane P1 and perpendicular to plane P2 when the product 47 is disposed at the first end of the delivery member 60 between the inlet port 46 and the product engaging end 74a. The product engaging end 74a engages the product 47 disposed at the first end of the delivery member 60 as the piston 70a is moved from the retracted position to the extended position. The product engaging end 74a engages the product from behind, such that a pushing force is applied to a rearward end 80xe2x80x2 of the product in the direction of its major axis. The product engaging end 74a can be formed as or provided with structure or a surface having a size and configuration to facilitate application of the pushing force on the product 47 as the piston 70a is moved toward the extended position. In the case of piston 70a, the product engaging end 74a is formed as a plate having a flat or planar surface for contacting or engaging a flat or planar surface of the product 47. When the piston 70a is in the extended position, as shown in dotted lines in FIG. 3, the product 47 pushed thereby will have passed through the inlet port 46 and will be disposed in the outer longitudinal channel section 45. When the piston 70a is thereafter moved from the extended position to the retracted position, a next subsequent product 47 is automatically presented, due to gravity, at the first end of the delivery member 60 and is ready to be pushed by the piston 70a through the inlet port 46 and into the outer longitudinal channel section 45 in response to movement of the piston 70a from the retracted position to the extended position. Movement of the next subsequent product 47 through the inlet port 46 and into the outer longitudinal channel section 45 by the piston 70a causes the next subsequent product to engage, in end to end relation, the next preceding product, i.e. the product 47 previously moved into the outer longitudinal channel section 45 by the piston 70a. Accordingly, each time the piston 70a is moved from the retracted position to the extended position, a product 47 disposed at the first end of the delivery member 60 is moved through the inlet port 46 into the outer longitudinal channel section 45, causing corresponding movement of all preceding products in the outer longitudinal channel section 45 due to end to end contact or abutment between the products. In this manner, the product at the first end of the delivery member and preceding products in the outer longitudinal channel section 45 are each moved or advanced a single position or increment corresponding to external dimension D1. The products 47 moved by actuator 66a are moved in a longitudinal direction parallel to plane P1 with the major axis or external dimension D1 disposed parallel to plane P1 and in longitudinal or axial alignment with the longitudinal direction of movement. Each time the piston 70a is moved from the extended position to the retracted position, another product is presented at the first end of the delivery member 60 in alignment with the actuator 66a and the inlet port 46. In the case of product irradiation device 10, the outer longitudinal channel section 45 has a length, parallel to plane P1, corresponding to external dimension D1. Accordingly, only one product 47 can be disposed entirely within the outer longitudinal channel section 45 at a time. A product 47 disposed entirely in the outer longitudinal channel section 45 will be pushed, moved or advanced by a next subsequent product, acted upon by the piston 70a, into the outer end of the outer transverse channel section 43, which is aligned and continuous with the outer longitudinal channel section 45. As shown in dotted lines in FIG. 3, a product moved into the outer end of the outer transverse channel section 43 is in end to end contact or abutment with the next subsequent product disposed in the outer longitudinal channel section 45. It should be appreciated that the length of the outer longitudinal channel section can be increased to accommodate more than one product. The actuator 66b serves to push a product located at the outer end of the outer transverse channel section 43 such that the product and all preceding products disposed in the outer transverse channel section 43 is/are advanced or moved a single position or increment. The actuator 66b is similar to actuator 66a and has its cylinder 68b and piston 70b longitudinally or axially aligned with the outer transverse channel section 43. As shown in FIG. 3, the cylinder 68b is secured within, on or to the end wall 40 externally of channel 41, with a longitudinal axis of piston 70b perpendicular to plane P1 and parallel to plane P2. When the piston 70b of actuator 66b is in the retracted position, the product engaging end 74b thereof is aligned or flush with or is disposed within a recess of the interior surface of end wall 40. Accordingly, a product 47 is capable of being moved, in response to actuation of actuator 66a, from the outer longitudinal channel section 45 into the outer end of the outer transverse channel section 43 as described above. The thusly moved product 47 will have its major axis or external dimension D1 longitudinally aligned with the outer longitudinal channel section 45 and will also have its minor axis or external dimension D2 longitudinally or axially aligned with the outer transverse channel section 43. When the piston 70b is thereafter moved from the retracted position to the extended position, the product disposed at the outer end of the outer transverse channel section 43 is engaged, from behind, by the product engaging end 74b, such that a pushing force is applied to an outer side 78 of the product in the direction of its minor axis. The product 47 disposed at the outer end of the outer transverse channel section 43 is thusly pushed, moved or advanced one position or increment, the product being moved in a transverse direction perpendicular to plane P1 while its major axis or external dimension D1 remains parallel to plane P1. When the piston 70b is thereafter moved from the extended position to the retracted position, a next subsequent product 47 is able to be moved into the outer end of the outer transverse channel section 43 in response to actuation of actuator 66a. When the piston 70b is moved to the extended position after a subsequent product 47 has been moved into the outer end of the outer transverse channel section 43, the piston 70b moves the subsequent product 47, which engages the outer side 78 of the next preceding product 47, in the transverse direction. Accordingly, the product at the outer end of the outer transverse channel section 43 as well as preceding products in the outer transverse channel section 43 are each advanced a single position or increment. In the case of product irradiation device 10, the outer transverse channel section 43 has a length, between the planar interior surface of end wall 40 and the side face 54, slightly greater than three times the external dimension D2. Accordingly, there is a gap or space 76 between a product at the outer end of the outer transverse channel section 43 and a next preceding product within the outer transverse channel section 43. The distance that the product engaging end 74b is extended perpendicularly beyond the interior surface of end wall 40 when the piston 70b is in the extended position defines the stroke for piston 70b and corresponds to the external dimension D2 plus the width of the gap or space 76. In this manner, a product at the outer end of outer transverse channel section 43 is advanced by piston 70b a single position or increment corresponding to the external dimension D2 plus the width of gap 76 while the next preceding product within the outer transverse channel section 43 is advanced, due to side to side contact or abutment between the products, a single position or increment corresponding to the external dimension D2. Subsequent to being so advanced, the next preceding product is disposed at an inner end of the outer transverse channel section 43, as shown in dotted lines in FIG. 3, with its major axis or external dimension D1 longitudinally or axially aligned with the inner longitudinal channel section 42, the inner end of the outer transverse channel section 43 being longitudinally aligned and continuous with the inner longitudinal channel section 42. The products 47 are moved, via actuation of actuator 66b, in the transverse direction perpendicular to plane P1 with the minor axis or external dimension D2 longitudinally or axially aligned with the transverse direction of movement. The actuator 66c serves to push a product 47 at the inner end of the outer transverse channel section 43 into the inner longitudinal channel section 42. The actuator 66c is similar to actuators 66a and 66b and has its cylinder 68c and piston 70c longitudinally or axially aligned with the inner longitudinal channel section 42. The cylinder 68c is secured within, on or to the side wall 38 externally of channel 41 with a longitudinal axis of piston 70c parallel to plane P1. When the piston 70c is in the retracted position, the product engaging end 74c thereof is aligned or flush with or disposed within a recess in the interior surface of side wall 38 such that a product 47 is capable of being moved, in response to actuation of actuator 66b, into the inner end of outer transverse channel section 43 as described above. When the piston 70c is thereafter moved from the retracted position to the extended position, the product 47 disposed at the inner end of the outer transverse channel section 43 is engaged, from behind, by the product engaging end 74c, which applies a pushing force against a forward end 80 of the product in the direction of its major axis, and is moved in a longitudinal direction parallel to plane P1 into the inner longitudinal channel section 42 as shown in dotted lines in FIG. 3. The product 47 at the inner end of the transverse channel section 42 is thusly moved or advanced a single position or increment while its major axis or external dimension D1 remains parallel to plane P1. Thereafter, when the piston 70c is moved from the extended position to the retracted position, a next subsequent product 47 is able to be moved into the inner end of the outer transverse channel section 43. When the piston 70c is moved from the retracted position to the extended position after a subsequent product 47 has been moved into the inner end of the outer transverse channel section 43, the subsequent product as well as preceding products in the inner longitudinal channel section 42 are each advanced, due to end to end contact or abutment of the products, a single position or increment corresponding to the external dimension D1. When a sufficient number of products 47 are disposed in the inner longitudinal channel section 42, operation of actuator 66c causes a most preceding product 47 in the inner longitudinal channel section 42 to be moved into an outer end of the inner transverse channel section 44 as shown in dotted lines in FIG. 3, the outer end of the inner transverse channel section 44 being longitudinally aligned and continuous with the inner, longitudinal channel section 42. The products 47 are moved, via actuation of actuator 66c, in the longitudinal direction with the major axis or external dimension D l thereof longitudinally or axially aligned with the longitudinal direction of movement. Since the pushing force of piston 70c is applied to forward ends 80 of the products while the pushing force of piston 70a is applied to rearward ends 80xe2x80x2 of the products, the longitudinal direction of movement for products advanced by actuator 66a is opposite the longitudinal direction of movement for products advanced by actuator 66c. In the case of product irradiation device 10, the distance that product engaging end 74c is extended perpendicularly beyond the interior surface of side wall 38 when the piston 70c is in the extended position defines the stroke for piston 70c and corresponds to the external dimension D1. Accordingly, when piston 70c moves a product at the inner end of outer transverse channel section 43, the product and all preceding products disposed in the inner longitudinal channel section 42 are each advanced a single position or increment corresponding to the external dimension D1. The inner longitudinal channel section 42 has a length between the inner end of outer transverse channel section 43 and the outer end of inner transverse channel section 44 corresponding to the combined external dimensions D1 of six products 47. Therefore, six products 47 are disposed in the inner longitudinal channel section 42 during normal operation of the product irradiation device 10 with such products in contact or abutment with one another in end to end relation. In addition, the most preceding product in inner longitudinal channel section 42 contacts or abuts the product, shown in dotted lines in FIG. 3, at the outer end of the inner transverse channel section 44 in end to end relation, and the most subsequent product in the inner longitudinal channel section 42 contacts or abuts the product, shown in dotted lines in FIG. 3, at the inner end of the outer transverse channel section 43 in end to end relation. Of course, the length of inner longitudinal channel section 42 can be increased or decreased to accommodate more or fewer products therein. The actuator 66d serves to push a product at the outer end of the inner transverse channel section 44 so as to advance the product in the inner transverse channel section 44 a single position or increment. The actuator 66d is similar to actuators 66a, 66b and 66c. Actuator 66d has its cylinder 68d and piston 70d longitudinally or axially aligned with the inner transverse channel section 43. The cylinder 68d is secured within, on or to the side wall 36, externally of channel 41, with a longitudinal axis of piston 70d perpendicular to plane P1. When the piston 70d is in the retracted position, the product engaging end 74d thereof is aligned or flush with or is disposed within a recess in the interior surface of side wall 36. Accordingly, a product 47 is capable of being moved, in response to actuation of actuator 66c, from the inner longitudinal channel section 42 into the outer end of the inner transverse channel section 44 as described above. The thusly moved product will have its major axis or external dimension longitudinally or axially aligned with the inner longitudinal channel section 42 and will have its minor axis or external dimension D2 longitudinally or axially aligned with the inner transverse channel section 44, with its major axis or external dimension D1 remaining parallel to plane P1. When the piston 70d is thereafter moved from the retracted position to the extended position, the product 47 disposed at the outer end of inner transverse channel section 44 is engaged, from behind, by product engaging end 74d such that a pushing force is applied to the outer side 78 of the product in the direction of its minor axis. The product disposed at the outer end of inner transverse channel section 44 is thusly moved or advanced a single position or increment in the transverse direction perpendicular to plane P1. When the piston 70d is moved back to the retracted position, a next subsequent product 47 is able to be moved from the inner longitudinal channel section 42 into the outer end of transverse channel section 44 in response to actuation of actuator 66c. When the piston 70d is moved to the extended position after a subsequent product has been moved into the outer end of the inner transverse channel section 44, the subsequent product is advanced in the inner transverse channel section 44. Products 47 are moved, via actuation of actuator 66d, in the transverse direction perpendicular to plane P1 with the minor axis or external dimension D2 longitudinally or axially aligned with the transverse direction of movement and the major axis or external dimension D1 parallel to plane P1. The transverse direction of movement for products advanced by actuator 66d is in the same direction as the transverse direction of movement for products advanced by actuator 66b. In the case of product irradiation device 10, the inner transverse channel section 44 has a length defined between interior surfaces of side walls 36 and 36xe2x80x2, respectively, and the length of inner transverse channel section 44 is greater than the combined external dimensions D2 of two products 47. Accordingly, the distance that the product engaging end 74d of piston 70d is extended perpendicularly beyond the interior surface of side wall 36, when the piston 70d is in the extended position, defines the stroke of piston 70d and is greater than the external dimension D2. In particular, the stroke of piston 70d is equal to the length of the inner transverse channel section 44 minus the external dimension D2. In this manner, a product 47 is moved by piston 70d from the outer end of inner transverse channel section 44 to the opposite, outer end of inner transverse channel section 44 in a single stroke, the opposite, outer end of the inner transverse channel section 44 being longitudinally aligned and continuous with the inner longitudinal channel section 42xe2x80x2. Accordingly, the product 47 moved by piston 70d does not advance any preceding products in the inner transverse channel section 44 since no preceding products can be accommodated in inner transverse channel section 44. Since the product moved by piston 70d, in a single stroke, is moved from the outer end of the inner transverse channel section 44 to the opposite, outer end of the inner transverse channel section 44, such product is moved from the inlet side to the outlet side of the shell 14. The actuator 66e serves to push the product 47 disposed at the opposite, outer end of the inner transverse channel section 44 into the inner longitudinal channel section 42xe2x80x2 such that it and preceding products disposed in the inner longitudinal channel section 42xe2x80x2 is/are advanced a single position. The actuator 66e is similar to actuators 66a, 66b, 66c and 66d and has its cylinder 68e and piston 70e longitudinally or axially aligned with the inner longitudinal channel section 42xe2x80x2. The cylinder 68e is secured in, on or to the end wall 37, externally of channel 41, with a longitudinal axis of piston 70e parallel to plane P1. When the piston 70e is in the retracted position, the product engaging end 74e thereof is aligned or flush with or disposed within a recess in the interior surface of end wall 37 such that a product 47 is capable of being moved, in response to actuation of actuator 66d, from the outer end of inner transverse channel section 44 to the opposite, outer end of the inner transverse channel section 44 as described above. The thusly moved product 47 will have its major axis or external dimension D1 longitudinally or axially aligned with the inner longitudinal channel section 42xe2x80x2 and, therefore, parallel to plane P1. When the piston 70e is thereafter moved from the retracted position to the extended position, the product 47 disposed at the opposite, outer end of inner transverse channel section 44 is engaged, from behind, by the product engaging end 74e, which applies a pushing force against the rearward end 80xe2x80x2 of the product in the direction of its major axis. As shown in dotted lines in FIG. 3, the product disposed at the outer end of inner transverse channel section 44 is moved in the longitudinal direction, parallel to plane P1, into the inner longitudinal channel section 42xe2x80x2 and is advanced a single position or increment while its major axis or external dimension D1 remains parallel to plane P1. Thereafter, when the piston 70e is moved back to the retracted position, a subsequent product 47 is able to be moved into the opposite, outer end of the inner transverse channel section 44 via actuator 66d. When the piston 70e is moved from the retracted position to the extended position after a subsequent product has been moved into the opposite, outer end of inner transverse channel section 44, the subsequent product as well as preceding products in the inner longitudinal channel section 42xe2x80x2 are each advanced a single position or increment, corresponding to the external dimension D l, due to end to end abutment or contact between the products in the inner longitudinal channel section 42xe2x80x2. When a sufficient number of products are disposed in the inner longitudinal channel section 42xe2x80x2, operation of actuator 66e causes a most preceding product in the inner longitudinal channel section 42xe2x80x2 to be moved into an inner end of the outer transverse channel section 43xe2x80x2, the inner end of the outer transverse channel section 43xe2x80x2 being longitudinally aligned and continuous with the inner longitudinal channel section 42xe2x80x2. Products 47 are moved, via actuation of actuator 66e, in the longitudinal direction with the major axis or external dimension D1 longitudinally or axially aligned with the longitudinal direction of movement. The longitudinal direction of movement for products advanced by actuator 66e is in the same direction as the longitudinal direction of movement for products advanced by actuator 66a, which is opposite the longitudinal direction of movement for products advanced by actuator 66c. In the case of product irradiation device 10, the distance that the product engaging end 74e is disposed beyond the interior surface of end wall 37 when the piston 70e is in the extended position defines the stroke for piston 70e and is equal to external dimension D1. The length of inner longitudinal channel section 42xe2x80x2 is the same as the length of inner longitudinal channel section 42 such that six products 47 are accommodated in the inner longitudinal channel section 42xe2x80x2 in end to end contact or abutment. The most subsequent product in the inner longitudinal channel section 42xe2x80x2 is in end to end contact or abutment with the product at the opposite, outer end of inner transverse channel section 44 as shown in dotted lines in FIG. 3. The most preceding product in the inner longitudinal channel section 42xe2x80x2 is in end to end contact or abutment with the product at the inner end of the outer transverse channel section 43xe2x80x2. Of course, the length of the inner longitudinal channel section 42xe2x80x2 can be modified in order to accommodate a greater or fewer number of products therein, and the length of the inner longitudinal channel section 42xe2x80x2 does not have to be the same as the length of inner longitudinal channel section 42 so that different numbers of products can be accommodated therein. The actuator 66f serves to pull a product 47 at the inner end of outer transverse channel section 43xe2x80x2 to advance the product a single position or increment in the outer transverse channel section 43xe2x80x2. The actuator 66f has a cylinder 68f mounted in, on or to the end wall 40xe2x80x2, externally of channel 41, and a piston 70f slidably disposed in the cylinder 68f for movement between extended and retracted positions in response to variation in fluidic pressure in the cylinder 68f. The cylinder 68f and piston 70f are aligned with the outer transverse channel section 43xe2x80x2 with a longitudinal axis of piston 70f perpendicular to plane P1 such that the piston 70f is slidable within a space between an upper side of the product or products 47 in outer transverse channel section 43xe2x80x2 and the top wall 34 of shell 14 or within a recess formed in the top wall 34 of shell 14. The piston 70f has a product engaging end 74f depending therefrom and disposed in abutment with the side face 54xe2x80x2 or within a recess of side face 54xe2x80x2 in the extended position so as not to block or obstruct movement of a product, in response to actuation of actuator 66e, from the inner longitudinal channel section 42xe2x80x2 into the inner end of the outer transverse channel section 43xe2x80x2. The product engaging end 74f is formed as a flat plate or is otherwise configured to engage the product disposed at the inner end of outer transverse channel section 43xe2x80x2. In the extended position for piston 70f, the product engaging end 74f is in a position to engage the outer side 78 of the product at the inner end of the outer transverse channel section 43xe2x80x2, and such product will be disposed between the end 74f and the interior surface of end wall 40xe2x80x2. The product engaging end 74f engages the outer side 78 of the product at the inner end of outer transverse channel section 43xe2x80x2 such that a pushing force is applied to the outer side 78 of the product in the direction of its minor axis when the piston 70f is moved to the retracted position. The product at the inner end of outer transverse channel section 43xe2x80x2 is moved by piston 70f in a transverse direction, perpendicular to plane P1, toward the outer end of the outer transverse channel section 43xe2x80x2. As the product at the inner end of outer transverse channel section 43xe2x80x2 is moved by piston 70f, a preceding product or products 47 in outer transverse channel section 43xe2x80x2 is/are moved or advanced in the outer transverse channel section 43xe2x80x2 due to side to side contact or abutment between the products. The products 47 are moved, in response to actuation of actuator 66f, in the transverse direction with the minor axis or external dimension D2 longitudinally or axially aligned with the transverse direction of movement and with the major axis or external dimension D1 parallel to plane P1. The transverse direction of movement for the products advanced by actuator 66f is in the same direction as the transverse direction of movement for products advanced by actuators 66b and 66d. In the case of product irradiation device 10, the outer transverse channel section 43xe2x80x2 has a length between side face 54xe2x80x2 and the interior surface of end wall 40xe2x80x2, and the length of the outer transverse channel section 43xe2x80x2 is the same or substantially the same as the length of outer transverse channel section 43. When the product 47 at the inner end of outer transverse channel section 43xe2x80x2 is pulled by piston 70f, a single next preceding product is moved, in response thereto, into the outer end of the outer transverse channel section 44xe2x80x2 as shown in dotted lines in FIG. 3, the outer end of the outer transverse channel section 43xe2x80x2 being longitudinally aligned and continuous with the outer longitudinal channel section 42xe2x80x2. There is a gap or space 77 between the product 47 disposed at the inner end of the transverse channel section 43xe2x80x2 and the next preceding product in the outer transverse channel section 43xe2x80x2. Depending on the design of actuator 66f, the stroke of piston 70f, i.e. the distance that the piston 70f moves between the extended and retracted positions, may correspond or substantially correspond to the external dimension D2 plus the width of the gap or space 77, which is the case for actuator 66f. Accordingly, in the retracted position, the product engaging end 74f will have moved from the extended position a distance equivalent or substantially equivalent to the dimension D2 plus the width of gap 77. It should be appreciated that the piston 70f does not have to extend into the outer transverse channel section 43xe2x80x2 in the extended position or in the retracted position such as, for example, when the piston 70f is slidably disposed in a passageway or recess formed in the interior surface of upper wall 34 with only the end 74f protruding into the outer transverse channel section 43xe2x80x2. When the piston 70f is moved from the extended position to the retracted position, the product at the inner end of the outer transverse channel section 43xe2x80x2 is pulled thereby. The next preceding product in the outer transverse channel section has its outer side 78 spaced, by the width of gap 77, from the inner side 78xe2x80x2 of the product disposed at the inner end of the outer transverse channel section 43xe2x80x2. As the product at the inner end of the outer transverse channel section 43xe2x80x2 is pulled by piston 70f, the inner side 78xe2x80x2 thereof engages the outer side 78 of the next preceding product such that the next preceding product is advanced therewith. Accordingly, products in outer transverse channel section 43xe2x80x2 are moved or advanced by actuator 66f a single position or increment corresponding or substantially corresponding to the external dimension D2 plus the width of gap 77. The next preceding product is thusly moved into the outer end of the outer transverse channel section 43xe2x80x2 as shown in dotted lines in FIG. 3, and the product pulled by end 74f becomes a next preceding product for the next product to be moved from the inner longitudinal channel section 42xe2x80x2 into the inner end of the outer transverse channel section 43xe2x80x2 following return of piston 70f to the extended position. It should be appreciated that, depending on the length of the outer transverse channel section 43xe2x80x2, no gap need be present between the products therein, in which case the stroke of piston 70f can be equivalent to the dimension D2 so that the product or products is/are pulled or moved by piston 7Of an increment equivalent to one product width. Actuator 66g serves to push a product 47 at the outer end of the outer transverse channel section 43xe2x80x2 into the outer longitudinal channel section 45xe2x80x2. The actuator 66g is similar to actuators 66a, 66b, 66c, 66d and 66e and includes cylinder 68g mounted within, on or to the side wall 38, externally of channel 41, with its piston 70g longitudinally or axially aligned with the outer longitudinal channel section 45xe2x80x2. The longitudinal axis of piston 70g is parallel to plane P1; and, when the piston 70g is in the retracted position, the product engaging end 74g thereof is aligned or flush with or is disposed within a recess in the interior surface of side wall 38. Accordingly, a product 47 is capable of being moved into the outer end of outer transverse channel section 43xe2x80x2 in response to actuation of actuator 66f as described above. The thusly moved product 47 will have its major axis or external dimension D1 longitudinally or axially aligned with the outer longitudinal channel section 45xe2x80x2 and will have its minor axis or external dimension D2 longitudinally or axially aligned with the outer transverse channel section 43xe2x80x2, the outer transverse channel section 43xe2x80x2 being longitudinally aligned and continuous with the outer longitudinal channel section 45xe2x80x2. When the piston 70g is thereafter moved from the retracted position to the extended position, the product 47 disposed at the outer end of the outer transverse channel section 43xe2x80x2 is engaged, from behind, by product engaging end 74g such that a pushing force is applied to the forward end 80 of the product in the direction of its major axis. The product disposed at the outer transverse channel section 43xe2x80x2 is thusly moved or advanced a single position or increment in the longitudinal direction parallel to plane P1 as shown in FIG. 3. Accordingly, the product disposed at the outer end of the outer transverse channel section 43xe2x80x2 is moved into the outer longitudinal channel section 45xe2x80x2 causing products 47 in the outer longitudinal channel 45xe2x80x2 to be correspondingly moved or advanced a single position or increment. The products 47 moved by actuator 66g are moved in the longitudinal direction, parallel to plane P1, with the major axis or external dimension D1 longitudinally or axially aligned with the longitudinal direction of movement. The longitudinal direction of movement for products advanced by actuator 66g is in the same direction as the longitudinal direction of movement for products 47 advanced by actuator 66c. The major axis or external dimension D1 of the products moved by actuator 66g remains parallel to plane P1. When the piston 70g is moved back to the retracted position, a next subsequent product 47 is able to be moved into the outer end of the outer transverse channel section 43xe2x80x2 in response to actuation of actuator 66f. When the piston 70g is moved to the extended position after a subsequent product has been moved into the outer end of the outer transverse channel section 43xe2x80x2, the subsequent product and preceding products are advanced a single position due to end to end contact or abutment between the products. In the case of product irradiation device 10, the outer longitudinal channel section 45xe2x80x2 has a length that is the same as the length of the outer longitudinal channel section 45, and the stroke for piston 70g is the same as that for piston 70a. When a product at the outer end of the outer transverse channel section 43xe2x80x2 is pushed by actuator 66g, a single next preceding product in outer longitudinal channel section 45xe2x80x2 is thereby pushed through the outlet port 46xe2x80x2 and is discharged onto the first end of the discharge member 64. The product 47 that is discharged onto the first end of the discharge member 64 is automatically conveyed, by gravity, toward the second end of the discharge member allowing a next subsequent product 47 to be discharged onto the first end thereof the next time that piston 70g is moved to the extended position. Products 47 are conveyed along the discharge member 64 in a transverse direction perpendicular to plane P1 while the major axis or external dimension D1 of the products remains parallel to plane P1. The transverse direction of movement for products 47 along the discharge member 64 is in the same direction as the transverse direction of movement for products 47 along the delivery member 60 and within the outer transverse channel sections 43 and 43xe2x80x2 and the inner transverse channel section 44. The fluid used to operate the actuators may comprise a liquid or a gas, such as compressed air. A fluid supply system (not shown) including a fluid source, conduits for supplying fluid to the cylinders from the fluid source and valves for controlling the pressure of fluid in the cylinders is disposed externally of the shell 14 and, preferably, is disposed within the interior of enclosure 12. A control system (not shown) for effecting automatic, timed extension and retraction of the pistons, individually or in selective unison, is also disposed externally of shell 14 and, preferably, within the interior of enclosure 12. In particular, the control system is adapted, via an appropriate software program, to effect automatic, simultaneous extension and retraction of pistons 70a, 70c, 70e and 70g in alternating sequence with simultaneous extension and retraction of pistons 70b, 70d and 70f. The control system preferably includes computer software and a control panel by which extension and retraction of particular pistons can be selected and by which the timing for extension and retraction of the pistons can be selected and adjusted as desired to control the speed with which the products 47 are moved through the transport channel 41. The excess space in enclosure 12 may be used to store additional rods 50 as well as machinery for removing and inserting the rods 50 in transport containers and for removing and replacing rods 50 within the shell 14. In particular, the enclosure 12 will have a storage container therein, capable of storing the rods 50 after receipt from the supplier. The delivery and discharge members 60 and 64 may also be stored in the interior of enclosure 12 when the product irradiation device 10 is not in use. Preferably, the control system is adapted to provide verification of piston movement and, therefore, proper operation or actuation of the actuators. The control system can include an indicator, such as an alarm, to provide an indication of malfunction of the actuators. For example, the indicator can be responsive to failure of one or more of the pistons to properly extend and/or retract. The control system can also be adapted to identify the location or locations of a malfunction or malfunctions, such as identification of a particular piston or pistons that does/do not properly extend and/or retract. According to a preferred embodiment of the product irradiation device 10, the enclosure 12 has an interior length of approximately 52.5 feet, an interior width of approximately 99 inches and an interior height of approximately 110 inches. The shell 14 has an overall length, between exterior surfaces of end wall 37 and side wall 38, of approximately 5 feet, 4xc2xc inches, a major width, between exterior surfaces of end walls 40 and 40xe2x80x2, of approximately 7 feet, 4xc2xd inches, a minor width, between exterior surfaces of side walls 36 and 36xe2x80x2, of approximately 3 feet, 10xc2xd inches and a height, between exterior surfaces of upper and lower walls 34 and 35, of approximately 45 inches. The active length for irradiation source 49 is approximately 8 feet, 3 inches. An interior width of shell 14, between interior surfaces of side walls 36 and 36xe2x80x2 is approximately 22xc2xd inches. Rods 50 may be conventional, such as the Cobalt 60 rods supplied by MDS Nordian of Canada and Reviss/Puridec of the United Kingdom. Typical rods have a diameter of 0.380 inch and an active length of 16.0 inches. In the preferred embodiment, each rod 50 has a radiation strength or intensity of 10,000 curies, and one hundred twenty rods 50 are linearly arranged in the shell insert. The tubes 51 are preferably made of stainless steel and have an outer diameter of 0.5 inch. The faces of shell insert 53 are made of stainless steel, and the shell insert has an inner width, defined between interior surfaces of side faces 54 and 54xe2x80x2 of 0.5 inch. The shield plugs 55 are preferably made of stainless steel. It should be appreciated that the specific dimensions of the enclosure, the shell, the irradiation source, the tubes and the shell insert can vary and that the specific dimensions described herein for a preferred embodiment should be considered exemplary. Similarly, the various dimensions of the transport channel can vary, and greater or fewer numbers of products can be accommodated in the various transport channel sections than those illustrated herein by way of example. Furthermore, corresponding sections of the transport channel do not have to accommodate the same number of products. The products 47 are illustrated in FIGS. 2 and 3 as boxed products, each comprising a box made of a radiation penetrable material and a product, object, substance or material, such as food, to be irradiated disposed within the box. As an example, each product 47 may comprise a plurality of preformed hamburgers enclosed in a sealed box. The boxes of products 47 have a rectangular configuration including a pair of planar, parallel, outer and inner sides 78 and 78xe2x80x2, respectively, a pair of planar, parallel, upper and lower sides 79 and 79xe2x80x2, respectively, and a pair of planar, parallel, forward and rearward ends 80 and 80xe2x80x2, respectively, connecting sides 78, 78xe2x80x2, 79 and 79xe2x80x2 as shown in FIG. 2. However, it should be appreciated that the product irradiation device 10 can be used to irradiate various types of naturally and artificially produced or created products including boxed products and non-boxed products as well as products having different sizes and configurations. As a further example, the products to be irradiated may comprise flowers or other plant material, the irradiation of which results in relatively longer shelf/vase life and increased freshness. In the case of products 47, the boxes thereof are irradiated in order to enhance the quality of the products, substances or materials disposed within the boxes. However, it should be appreciated that products, substances or materials to be irradiated can be irradiated using the product irradiation device 10 without being disposed or enclosed in boxes or other containers. FIG. 5 illustrates a modification of products to be irradiated in accordance with the present invention. FIG. 5 illustrates a basket 147 containing a plurality of smaller, individual packages or objects 157 to be irradiated. A plurality of baskets 147 can be supplied for use with the product irradiation device, and the packages or objects 157 are placed in the baskets 147 prior to passage of the baskets 147 through the product irradiation device. Each basket has a bottom 181 to be disposed upon and in contact with the transport surface when the baskets 147 are moved through the transport channel. The baskets 147 are continuously moved into, through and out of the product irradiation device in the same manner as described herein for boxes 47. The objects 157 can be of variable sizes or can be the same size. In FIG. 5, the objects 157 are shown as packages of different, variable sizes. As shown in dotted lines in FIG. 2, the products 47 can be provided with a radiation monitoring or indicating device 82. The radiation monitoring or indicating device 82 is disposed on an outer surface of the box of a product 47, such as being disposed on the outer surface of inner side 78xe2x80x2. The radiation monitoring or indicating device 82 is capable of providing a visual indication, for example a color change, of exposure of product 47 to the proper dose of radiation. In the case of products 47, the products, substances or materials to be irradiated are normally placed and sealed in the boxes as part of their manufacturing or processing procedures. Accordingly, the products 47 may be irradiated subsequent to manufacture or processing without any additional handling, exposure to the environment or other interference with the products, materials or substances disposed inside the boxes. The length of sides 78, 78xe2x80x2, 79 and 79xe2x80x2 between ends 80 and 80xe2x80x2 corresponds to the external dimension D1 of the products 47. The distance between outer and inner sides 78 and 78xe2x80x2 corresponds to the external dimension D2 of the products 47. The external dimensions D1 and D2 correspond to the length and width, respectively, of products 47. The distance between upper and lower sides 79 and 79xe2x80x2 corresponds to the height of products 47, which is smaller than D1 but larger than D2. In a method of irradiating products, such as products 47, according to the present invention, the pair of doors 20 defining the entry and discharge openings, respectively, of enclosure 12 are opened. The delivery member 60 is positioned to extend through the entry opening with the first end of the delivery member positioned directly in front of the inlet port 46 and the second end of the delivery member positioned at a location at or proximate the source, such as a manufacturing or processing facility, of the products 47. Similarly, the discharge member 64 is positioned to extend through the discharge opening with the first end of the discharge member positioned directly in front of the outlet port 46 xe2x80x2 and the second end of the discharge member positioned at a different location at or proximate the source. The products 47 are supplied sequentially to the second end of the delivery member 60 manually or mechanically via suitable machinery. Each product 47 is positioned on the delivery member with one of its lower sides 79xe2x80x2 disposed upon and in contact with the rollers of the delivery member 60. The products 47 are automatically conveyed or moved, due to gravity, in sequence along the delivery member 60 such that the most preceding product 47 on the delivery member 60 arrives at the first end thereof, the products being guided along the delivery member by the side rails 62. The products 47 are positioned on and conveyed along the delivery member 60 with the major axis or external dimension D1 parallel to plane P1. The products 47 are moved along the delivery member 60 in the transverse direction perpendicular to plane P1, and the exterior surface of the side wall 36 serves as a stop or abutment for a product when it arrives at the first end of the delivery member, whereby a product disposed at the first end of the delivery member 60 is longitudinally or axially aligned with the inlet port 46 and the outer longitudinal channel section 45. When operation of the product irradiation device 10 is initially commenced or started up, the most preceding product 47 on the delivery member will be a lead product. The actuator 66a is operated as described above, individually or simultaneously with actuators 66c, 66e and 66g, to push the product 47 disposed at the first end of the delivery member 60 through the inlet port 46 into the outer longitudinal channel section 45 such that the product is advanced a single increment or position. Where the product 47 at the first end of the delivery member 60 is the lead product, as during initial start up, no preceding products 47 are disposed in channel 41 to be moved by the lead product or by the actuators 66c, 66e and 66g. It should be appreciated, therefore, that actuator 66a can be actuated individually during start up without actuation of actuators 66c, 66e and 66g. When the actuators 66b, 66d and 66f are actuated subsequent to actuation of actuators 66a, 66c, 66e and 66g, i.e, following retraction of pistons 70a, 70c, 70e and 70g, no preceding products are disposed in channel 41 to be moved or advanced thereby where the product previously moved into the channel 41 through the inlet port 46 is the lead product. It should be appreciated, therefore, that the actuator 66a can be actuated individually or simultaneously with actuators 66c, 66e and 66g in sequential repetition during initial start up, without actuation of actuators 66b, 66d and 66f, until the lead product has arrived at the outer end of outer transverse channel section 43. Once the lead product 47 has been pushed through the inlet port 46 into the outer longitudinal channel section 45, the next successive or subsequent product 47 arrives at the first end of the delivery member 60 and is longitudinally or axially aligned with the inlet port 46. When the actuator 66a is thereafter actuated, individually or simultaneously with actuators 66c, 66e and 66g, the next subsequent product 47 now disposed on the first end of the delivery member 60 is pushed through the inlet port 46 into the outer longitudinal channel section 45, correspondingly moving the next preceding product, i.e. the lead product 47, into the outer end of the outer transverse channel section 43. Accordingly, each time a product 47 is pushed by piston 70a through the inlet port 46 from the first end of the delivery member, the next subsequent product 47 on the delivery member is automatically conveyed to the first end thereof, following retraction of the piston 70a, and is ready to be moved through the inlet port into the shell 14. Similarly, each time a product 47 is pushed by piston 70a through the inlet port 46 into the outer longitudinal channel section 45, the forward end 80 of that product engages, abuts or contacts the rearward end 80xe2x80x2 of the next preceding product and thereby pushes the next preceding product into the outer end of the outer transverse channel section 43. Once the lead product 47 has arrived at the outer end of the outer transverse channel section 43, the actuator 66b is actuated, individually or simultaneously with actuators 66d and 66f, to push the lead product toward the inner end of the outer transverse channel section 43 whereby the lead product is advanced to the next position in channel 41. The next time that the actuator 66a is actuated following retraction of piston 70b, the product that is next subsequent to the lead product is moved from the outer longitudinal channel section 45 into the outer end of the outer transverse channel section 43. When the actuator 66b is thereafter actuated individually or simultaneously with actuators 66d and 66f, following retraction of piston 70a and piston 70c (if previously extended), the next subsequent product disposed at the outer end of outer transverse channel section 43 is pushed by piston 70b. The inner side 78xe2x80x2 of the next subsequent product engages, abuts or contacts the outer side 78 of the lead product and moves the lead product into the inner end of the outer transverse channel section 43. Following retraction of piston 70b, the actuators 66a and 66c are actuated simultaneously, with or without simultaneous actuation of actuators 66e and 66g, to push another subsequent product from the first end of the delivery member 60 through the inlet port 46 into the outer longitudinal channel section 45 and to simultaneously push the lead product disposed at the inner end of outer transverse channel section 43 into the first end of the inner longitudinal channel section 42. As the another subsequent product is moved through the inlet port into the outer longitudinal channel section 45, the product next preceding thereto is moved from the outer longitudinal channel section 45 into the outer end of outer transverse channel section 43 via abutment of the forward end of the another subsequent product with the rearward end of the product next preceding thereto. The actuator 66b is actuated, individually or simultaneously with actuators 66d and 66f, following retraction of pistons 70a and 70c. As a result thereof, the product disposed at the outer end of the outer transverse channel section 43 is pushed by piston 70b and is advanced a single increment. As the product disposed at the outer end of the outer transverse channel section 43 is advanced by piston 70b, its inner side 78xe2x80x2 engages, contacts or abuts the outer side 78 of the next preceding product, which is next subsequent to the lead product. Accordingly, the product that is next subsequent to the lead product is moved into the inner end of the outer transverse channel section 43. The actuators 66a and 66c continue to be actuated simultaneously, with or without simultaneous actuation of actuators 66e and 66g, in alternating sequence with actuation of actuator 66b, with or without simultaneous actuation of actuators 66d and 66f. In this manner, products 47 continue to be advanced a single position or increment in channel 41. Once six products 47 are disposed in inner longitudinal channel section 42, the lead product disposed at the second end thereof is moved into the outer end of inner transverse channel section 44 the next time the actuators 66a and 66c are simultaneously actuated, with or without simultaneous actuation of actuators 66e and 66g. Once the lead product has been moved from the second end of the inner longitudinal channel section 42 into the outer end of inner transverse channel section 44, actuator 66d is actuated simultaneously with actuator 66b, with or without simultaneous actuation of actuator 66f, following retraction of pistons 70a and 70c. Actuation of actuator 66d causes the product at the outer end of inner transverse channel section 44, i.e. the lead product, to be moved into the opposite, outer end of the inner transverse channel section 44. Simultaneous actuation of actuator 66b therewith causes a most preceding product in the outer transverse channel section 43 to be moved into the inner end thereof. Following return of pistons 70b and 70d to the retracted position, actuator 66e is actuated simultaneously with actuators 66a and 66c, with or without simultaneous actuation of actuator 66g. The lead product is moved by actuator 66e from the opposite, outer end of inner transverse channel section 44 into the second end of the inner longitudinal channel section 42xe2x80x2. Simultaneously therewith, a new subsequent product is pushed by actuator 66a through the inlet port 46 into the outer longitudinal channel section 45 causing the product next preceding thereto to be moved into the outer end of the outer transverse channel section 43. In addition, a product disposed at the inner end of the outer transverse channel section 43 is simultaneously pushed by actuator 66c into the first end of inner longitudinal channel section 42 causing a product disposed at the second end of the inner longitudinal channel section, i.e. the product next subsequent to the lead product, to be moved into the outer end of the inner transverse channel section 44. The actuators 66b and 66d are actuated simultaneously, with or without actuation of actuator 66f, in alternating sequence with simultaneous actuation of actuators 66a, 66c and 66e, with or without actuation of actuator 66g, such that six products will be disposed in inner longitudinal channel section 42xe2x80x2 in end to end relation, with the lead product 47 disposed at the first end of the inner longitudinal channel section 42xe2x80x2. The next time actuators 66a, 66c and 66e are simultaneously actuated, the lead product 47 is moved into the inner end of the outer transverse channel section 43xe2x80x2. Once the lead product 47 has been moved from the inner longitudinal channel section 42xe2x80x2 into the inner end of outer transverse channel section 43xe2x80x2, the actuator 66f is actuated simultaneously or in unison with actuators 66b and 66d. The lead product 47 disposed at the inner end of outer transverse channel section 43xe2x80x2 is pulled by piston 70f toward the outer end of outer transverse channel section 43xe2x80x2. Simultaneously therewith, the product at the outer end of outer transverse channel section 43 is advanced a single increment by piston 70b and the product at the outer end of inner transverse channel section 44 is moved to the opposite, outer end thereof by piston 70d. When the actuators 66a, 66c and 66e are thereafter actuated simultaneously, the product that is next subsequent to the lead product is moved from the inner longitudinal channel section 42xe2x80x2 into the inner end of outer transverse channel section 43xe2x80x2, the product at the second end of inner longitudinal channel section 42 is moved into the outer end of inner transverse channel section 44 and the product in the outer longitudinal channel section 45 is moved into the outer end of outer transverse channel section 43. The next time actuators 66b, 66d and 66f are simultaneously actuated, the lead product 47 disposed in outer transverse channel section 43xe2x80x2 is moved into the outer end of outer transverse channel section 43, the product next subsequent to the lead product is pulled by piston 70f a single increment, the product at the outer end of inner transverse channel section 44 is pushed by piston 70d to the opposite, outer end thereof, the product at the outer end of outer transverse channel section 43 is pushed by piston 70d a single increment and the product next preceding thereto is moved into the inner end of outer transverse channel section 43. The actuators 66a, 66c, 66e and 66g are thereafter actuated simultaneously or in unison. As a result thereof, the lead product 47 at the outer end of outer transverse channel section 43xe2x80x2 is pushed by piston 70g into the outer longitudinal channel section 45xe2x80x2. In addition, the products in outer longitudinal channel section 45 and inner longitudinal channel sections 42 and 42xe2x80x2 are each advanced a single position or increment as previously described. The actuators 66b, 66d and 66f are thereafter simultaneously actuated to advance the products in the outer transverse channel sections 43 and 43xe2x80x2 and the inner transverse channel section 44 as described above. The next time actuators 66a, 66c, 66e and 66g are actuated simultaneously, the product that is disposed in the outer end of the outer transverse channel section 43xe2x80x2 is moved therefrom into the outer longitudinal channel section 45xe2x80x2 causing movement of the next preceding product, i.e. the lead product 47, through the outlet port 46xe2x80x2 for discharge onto the first end of the discharge member 64. Simultaneously therewith, the products within the outer longitudinal channel section 45 and the inner longitudinal channel sections 42 and 42xe2x80x2 are incrementally advanced as described above. The lead product 47 discharged onto the first end of the discharge member 64 is automatically conveyed, by gravity, toward the second end of the discharge member 64 for removal therefrom. As a result of continuous supply of products to the delivery member and continuous actuation or operation of actuators 66a, 66c, 66e and 66g in alternation with actuators 66b, 66d and 66f, the products 47 are continuously introduced in, advanced through and discharged from the product irradiation device 10. Once the lead product has been discharged from the product irradiation device, initial start up will be completed. The transport channel will be filled to capacity with products to be irradiated, and normal operation of the product irradiation device will ensue. When the product irradiation device is to be shut down following establishment of normal operation, dummy products, similar in size and shape to the actual products 47, are sequentially introduced and advanced in the transport channel in place of the actual products 47 until the last actual product 47 has been discharged therefrom. The transport channel will then be filled to capacity with dummy products, such as empty boxes, and the product irradiation device will be ready for shut down, which would typically occur during the third daily operating shift. When the product irradiation device is thereafter restarted, typically at the beginning of the first daily operating shift, actual products 47 are introduced in and advanced through the transport channel, and the dummy products discharged from the device are retrieved. The retrieved dummy products can be saved for reuse. Once the last dummy product has been discharged from the product irradiation device, normal operation of the product irradiation device will ensue. As the products 47 are moved through the transport channel 41, they are moved past the irradiation source 49. In particular, the products 47 are moved past the irradiation source 49 as they are moved through inner longitudinal channel sections 42 and 42xe2x80x2, i.e. the high radiation zone. The products 47 have their external dimension D1 disposed parallel to plane P1 and, therefore, the irradiation source 49, as they enter, move through and are discharged from the shell 14. The inner side 78xe2x80x2 of the products 47 faces the irradiation source 49 as the products move through the inner longitudinal channel section 42, and the outer side 78 of the products faces the irradiation source 49 as the products move through the inner longitudinal channel section 42xe2x80x2. The outer and inner sides 78 and 78xe2x80x2 that face the irradiation source 49 during movement of the products 47 through the shell 14 constitute the major external dimension for the products 47 such that a major or maximum area or part of the products is exposed to the maximum radiation. Each product 47 has its lower side 79xe2x80x2 in direct contact with the transport surface 48, i.e. the interior surface of lower wall 35. As the products 47 enter, move through and are discharged from the transport channel 41, the lower sides 79xe2x80x2 remain in contact with the transport surface 48. The parallel orientation of the major axis or external dimension D1 with the plane P1 as the products enter, move through and are discharged from the shell 14 is maintained by the close correspondence of the cross-sectional size and configuration of the transport channel 41 to the external cross-sectional sizes and configurations of the products. Accordingly, as the products are moved through the shell, opposite sides of the products are irradiated without requiring rotation of the products or other undesired displacement of the products from their parallel orientation with plane P1. The products 47 enter the shell 14 on one side of the enclosure 12 and are discharged from the shell 14 on an opposite side of the enclosure 12. In particular, the products 47 enter the enclosure 12 at a location disposed on side wall 17 and exit the enclosure 12 at a location disposed on the side wall 17xe2x80x2. Accordingly, the products 47 enter and exit the product irradiation device 10 at different, remote locations such that nonirradiated products entering the product irradiation device 10 should not become confused or intermingled with irradiated products exiting the product irradiation device 10. In the preferred method of irradiating products, the actuators 66a, 66c, 66e and 66g are actuated simultaneously in alternating sequence with simultaneous actuation of actuators 66b, 66d and 66f in ten second intervals. Accordingly, ten seconds after the pistons 70a, 70c, 70e and 70g are simultaneously extended, the pistons 70b and 70d are simultaneously extended and the piston 70f is retracted simultaneously with extension of pistons 70b and 70d. The pistons 70a, 70c, 70e and 70g are again simultaneously extended ten seconds after simultaneous extension of pistons 70b and 70d and retraction of piston 70f, and so on. A new product 47 will enter the shell 14 every ten seconds, and each product will spend approximately three minutes in the shell 14 passing through the transport channel 41. It should be appreciated, however, that the speed of movement of the products through the transport channel can be adjusted by adjusting the intervals at which new products are introduced in the transport channel and by adjusting the timing for extension and retraction of the pistons. For example, it may be desirable to decrease the speed of the products through the transport channel to increase the dosage of radiation imparted to the products. The speed of the products may also be adjusted to account for decay of the irradiation source. For example, the speed of products through the shell may be decreased to offset radioactive decay of rods 50. In an alternative embodiment, the shell 14 can be rotated, as shown by the arrow 84 in FIG. 2, 90 degrees from the position shown in FIG. 2. The upper and lower walls 34 and 35, respectively, will then define side walls for the shell 4, the side wall 36, side wall segment 39 and end wall 40 will define an upper wall for the shell 14, and the side wall 36xe2x80x2, side wall segment 39xe2x80x2 and end wall 40xe2x80x2 will define a lower wall for the shell 14. In this orientation, the inlet port 46 will be disposed along a top of the shell 14, and the outlet port 46xe2x80x2 will be disposed along a bottom of the shell 14. Of course, the delivery and discharge members can be modified, as necessary, to permit gravity conveyance of products to the inlet port 46 and gravity conveyance of products away from the outlet port 46xe2x80x2. Where the shell 14 is rotated 90 degrees, a suitable enclosure for the shell can be provided, the enclosure having entry and exit openings establishing communication with the inlet and outlet ports, respectively, from externally of the enclosure. By rotating the shell 90xc2x0, the plane P1 of the irradiation source will be oriented horizontally rather than vertically as in the case of shell 14. In this manner, products will pass above and below the irradiation source rather than passing the irradiation source on opposite sides thereof as in the case of product irradiation device 10. In order to illustrate this arrangement, FIG. 3 can be considered representative of a side view of a modified shell that has been rotated 90xc2x0 and, in particular, a side view of shell 14 rotated 90xc2x0. When thusly rotated, the shell 14 can be modified so that the inlet port 46 and the outlet port 46xe2x80x2 are not located at the top and bottom, respectively, of the shell. For example, it may be desirable for the inlet and outlet ports 46 and 46xe2x80x2 to be disposed on opposite sides of or on the same side of the shell. Accordingly, as an example, the outer longitudinal channel section 45 and the outer transverse channel section 43 can be disposed in the same plane or at the same elevation as the inner longitudinal channel section 42 so that the transport surfaces of the outer longitudinal channel section 45, the outer transverse channel section 43 and the inner longitudinal channel section 42 are all disposed in the same plane, such plane being parallel to the plane P1 of the irradiation source. Similarly, the outer longitudinal channel section 45xe2x80x2 and the outer transverse channel section 43xe2x80x2 can be disposed in the same plane or at the same elevation as the inner longitudinal channel section 42xe2x80x2 so that the transport surfaces of the outer longitudinal channel section 45xe2x80x2, the outer transverse channel section 43xe2x80x2 and the inner longitudinal channel section 42xe2x80x2 are all disposed in the same plane, such plane being parallel to the plane P1 of the irradiation source and the plane containing the transport surfaces of channel sections 42, 43 and 45. With this approach, vertical lowering of the products is needed at only one location in that the products would only need to be vertically lowered from the outer end to the inner end of the inner transverse channel section 44, the outer and inner ends of channel section 44 now being upper and lower ends thereof since the channel section 44 is oriented vertically due to rotation of the shell 14 by 90xc2x0. The modified shell design discussed above is particularly amenable to irradiating relatively small objects or packages contained in baskets. The modified shell design allows products to be transported through the shell with bottoms, rather than sides, of the products, such as bottoms of the baskets, disposed and supported on the transport surface, thusly minimizing concerns with product shifting within containers, boxes or baskets as could occur when the containers, boxes or baskets are supported or placed on their sides when passing through the transport channel. In the modified shell design, the inlet and outlet ports may be located on the same side of the shell in order to minimize total width of the device. No moving mechanical parts are disposed in the high radiation zone of the shell 14 which would require access to the interior of the shell 14 in order to perform maintenance and/or repair. The pistons 70 are disposed outside of or beyond the high radiation zone. Each of the cylinders 68 is mounted externally of the transport channel 41, either on, to or within the walls of the shell, allowing the actuators to be accessed externally of the shell interior in order to perform maintenance and/or repair. The actuators are simple linear devices that are easily removable and replaceable for maintenance without removing the irradiation source from the device. The transport surface 48, upon and along which the products are moved, is formed by an interior surface or surfaces of the shell 14 without requiring any moving support surfaces or parts. The products are irradiated at the processing or manufacturing facility or other source thereof and are ready for transport or distribution immediately upon discharge from the irradiation device. The prescribed path for the products through the shell is uncomplicated and eliminates or reduces the risk of malfunction and/or damage to the products being irradiated. Human operation or intervention is greatly minimized in that irradiation is accomplished automatically once the control system has been set to select a desired automatic, timed operation for the actuators. Various natural or artificially created products can be irradiated with the product irradiation device. The irradiator shell 14 and the arrangement of the prescribed path therethrough allow the size of the irradiator shell to be minimized for reduced cost and material needs. The actuators are simple and uncomplicated and are compatible for use with various types of products to be irradiated. The strokes or extensions of the pistons can vary in accordance with the dimensions of the products and the distance that the products must be moved in the transport channel. The size and configuration of the inlet and outlet ports may closely correspond to the size and configuration of the products to minimize excess space or gaps at the inlet and outlet ports. The size and configuration of the inlet and outlet ports as well as the cross-sectional size and configuration of the transport channel are preferably no larger than necessary to accommodate the products therein so as to eliminate or greatly reduce the risk of inadvertent human access to the interior of the shell. Accordingly, the inlet and outlet ports are sized to prevent or preclude human access passively, without any interlocks and/or opening/closing mechanisms. The product engaging ends of the actuators can have various configurations in accordance with the characteristics of the products to be engaged thereby, and the product engaging ends may have planar or non-planar surfaces. Depending on the cross-sectional size of the transport channel, the product engaging ends do not have to be aligned or flush with or disposed within the walls of the shell in the retracted position but, rather, can protrude into the transport channel. The pistons of the actuators can be mounted for movement within the wall or walls of the shell with only the product engaging ends thereof protruding into the transport channel in the extended position to engage the products to be moved thereby. The product irradiation device is intended to be fabricated offsite and can be assembled and tested prior to shipment to the site at which product irradiation is to take place. The product irradiation device can be shipped as two or more subassemblies, which are reassembled on site. It should be appreciated that the subject invention is subject to various modifications, variations and changes in detail. Accordingly, the foregoing description of the preferred embodiments should be considered illustrative only and should not be taken in a limiting sense. |
|
summary | ||
abstract | An operation method and apparatus in a pressure vessel of a nuclear reactor is provided. The operation apparatus including a body and a guide inserted from the upper side of the nuclear reactor to an interior of the jet pump. The operation apparatus circulate water inside the pressure vessel. The guide is positioned at the end of a body of the operation apparatus, and is inclined with respect to the center axis of the body so as to be inserted into a side opening of the jet pump. |
|
description | This application claims the benefit of U.S. Provisional Patent Application No. 61/525,973, which was filed Aug. 22, 2011. The entire disclosure of U.S. Provisional Patent Application No. 61/525,973, which was filed Aug. 22, 2011, is incorporated herein by reference. This disclosure relates to shields for inhibiting the propagation of radiation and, more specifically, to panels that may be used for inhibiting the propagation of alpha, beta and/or gamma radiation. At nuclear power plants and some other types of facilities, provisions are made to protect people from propagating radiation, such as alpha, beta and/or gamma radiation. Whereas this disclosure primarily refers to protecting people from the propagating radiation, it should be understood throughout this disclosure that it may be desirable to protect other objects, such as certain types of equipment, from radiation. It is known to protect one or more people from propagating radiation by positioning one or more shields between the source of the radiation and people. Examples of known shields include portable panels formed by encasing lead in a steel shell, flexible blankets comprising silicone impregnated with tungsten, and flexible blankets comprising lead. Notwithstanding, there is a desire for radiation shields that provide a new balance of properties. One aspect if this disclosure is the provision of a panel for functioning as a barrier to radiation, wherein the panel includes at least one layer for restricting the passage of radiation, and the layer for restricting the passage of radiation may be, but is not limited to, a layer of silicone impregnated with metal (e.g., tungsten and/or iron). The impregnated silicone layer may be mounted to and supported by at least one other structure of the panel. For example, the impregnated silicone layer may be positioned between, and laminated to, other layers of the panel. In one embodiment, the impregnated silicone layer is positioned between foam layers of the panel to form a core, and the core is positioned between exterior layers of the panel. One or more of the exterior layers of the panel may be in the form of sheet metal, such as a sheet of steel, or any other suitable structure. In one example, for each side of the panel, the foam and steel may be together characterized as a composite that substantially provides strength to the panel, whereas the silicone impregnated with metal substantially provides the radiation attention of the panel. One or more of the layers of the panel may be secured together with adhesive material interposed therebetween and/or the panel may be held together by at least one channel member. In one example, each of the layers of the panel extend to top, bottom, and side edges of the panel, grooves of generally C or U-shaped shaped channel members are respectively in receipt of the edges of the panel, and the channel members are respectively joined end-to-end with one another so that the panel is enclosed in a frame. The frame may be characterized as being part of the panel. The channel members of the frame may be lengths of metal, or they may be formed by durable, strong tape or any other suitable structure. In an alternative embodiment, one or more layers of the panel may be secured together with mechanical fasteners such as, but not limited to, clips, screws, nuts and bolts, or any other suitable fasteners. In one embodiment, each of the panels, with or without a frame, is strong enough to support at least its own weight without deforming substantially, and may be referred to as a structural insulated panel. The panels may be installed permanently, or they may be portable and be repeatably moved do different locations. For example, the panels may be equipped with one or more features, such as handles for being gripped, eyelets for lifting, wheels for rolling, and/or any other suitable features. In accordance with one aspect of this disclosure, a panel for attenuating radiation may include a layered structure comprising a laminate secured between layers of metal, wherein the laminate may comprise a flexible layer comprising polymeric material and metal for attenuating radiation, and a layer of foam secured to the layer of silicone containing metal, wherein the flexible layer is more flexible than the layer of foam. In accordance with another aspect of this disclosure, a panel for attenuating radiation, may include a layered structure having a plurality of layers that are secured together, wherein the plurality of layers may include a layer comprising polymeric material and metal for attenuating radiation, a layer of foam, and an exterior layer, wherein the exterior layer is harder than each of the layer of foam and the layer of silicone containing metal, and an exterior surface of the exterior layer is substantially nonporous. According to another aspect of this disclosure, a panel for attenuating radiation includes a layered structure and a channel member. The layered structure comprises a first exterior layer at least partially defining a first side of the panel, a second exterior layer at least partially defining a second side of the panel, wherein the second side of the panel is opposite the first side of the panel, and an interior layer comprising polymeric material and metal, wherein the metal is for attenuating radiation, and the interior layer is positioned between the first and second exterior layers. A compound edge of the layered structure comprises an edge of the first exterior layer and an edge of the second exterior layer. The channel member is mounted to the compound edge of the layered structure. The channel member defines a groove, and the groove is in receipt of the compound edge of the layered structure, so that the groove is in receipt of both the edge of the first exterior layer and the edge of the second exterior layer. The foregoing presents a simplified summary of some aspects of this disclosure in order to provide a basic understanding. The foregoing summary is not an extensive summary of the disclosure and is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. The purpose of the foregoing summary is to present some concepts of this disclosure in a simplified form as a prelude to the more detailed description that is presented later. For example, other aspects of this disclosure will become apparent from the following. Exemplary embodiments of this disclosure are described below and selected features are illustrated in the accompanying figures, in which like numerals refer to like parts throughout the several views. The following description provides examples and should not be interpreted as limiting the scope of the invention. A panel 10 of a first embodiment of this disclosure is described in the following with reference to FIGS. 1-5. The panel 10 may be used, for example, as a barrier to radiation, and it may also be used as a structural panel or a structural insulated panel. Referring to FIGS. 1 and 2, the panel 10 includes a layered structure 12 and one or more edge covers 13 for at least partially covering one or more edges of the layered structure. The edge covers 13 may cooperatively form a frame 14 that extends at least partially around, or more specifically extends all the way around and encloses, the layered structure 12, as will be discussed in greater detail below. Referring to FIGS. 2 and 3, the layered structure 12 includes in interior layer 16 positioned between exterior layers 20, and the layered structure may optionally further include intermediate layers 18 respectively positioned between the interior and exterior layers. The layers 16, 18, 20 of the layered structure 12 may be secured together by the edge cover(s) 13, frame 14 and/or one or more bonding layers 22, 23 (FIG. 3). Any suitable adhesive materials may be used for the bonding layers 22, 23, and one or more of the bonding layers may be omitted. The adhesive materials and other components of the panel 10 will typically be selected to be durable in the environments in which the panel may be used. For example, the components of the panel 10 may be selected so that panel will perform satisfactorily for an extended period of time as a barrier to radiation, a structural panel and/or a structural insulated panel. As a specific example, when the panel 10 is to be used as a barrier to radiation, the components selected for use in the panel will typically be those types of components that will not degrade, or not degrade too much, when exposed to radiation for an extended period of time. More generally, the components of the panel 10 may be tailored to the intended usage of the panel. For example, the exterior layers 20 and frame 14 may be made of metal, such as steel, or stainless steel, for purposes of cleanliness and durability. In accordance with the first embodiment, the interior layer 16 is operative for functioning as a barrier to radiation, such as by attenuating propagating radiation (e.g., alpha, beta and gamma radiation). Whereas the interior layer 16 may be any suitable material, the interior layer of the first embodiment is a flexible layer comprising polymeric material and metal, wherein the metal is for attenuating radiation. More specifically, the polymeric material comprises silicone and the metal comprises tungsten and/or iron, and the silicone at least partially contains the tungsten and/or iron. Even more specifically, the tungsten and/or iron may be impregnated in the silicone. Even more specifically, the flexible interior layer may consist essentially of silicone impregnated with tungsten and/or iron. The silicone may also or alternatively be impregnated with any other suitable materials. For example, the interior layer 16 may be a flexible layer of Silflex brand radiation shielding material available from, for example, MarShield (Mars Metal Company division of Marswell Metal Industries Ltd.) or American Ceramic Technology, Inc. Alternatively, the interior layer may comprise any other suitable material(s) for attenuating radiation. That is, this disclosure is not limited to the Silflex brand radiation shielding material available from MarShield or American Ceramic Technology, Inc. For example, any suitable source for the interior layer 16 may be used. As will be discussed in greater detail below, the interior layer 16 may be mounted to each of the intermediate layers 18 so that the intermediate layers at least partially support the interior layer and/or the combination of the intermediate and exterior layers 18, 20 support the interior layer, and the exterior layers 20 may form a protective cover or shield of the layered structure 12/panel 10. Referring to FIG. 3 and as a more specific example, the interior layer 16 may be a 0.5 inch thick layer of silicone impregnated with tungsten and/or iron (e.g., Silflex brand shielding material), each of the intermediate layers 18 may be a 2.0 inch thick layer of expanded polystyrene foam secured to the opposite sides of the interior layer by respective inner bonding layers 22, and each of the exterior layers 20 may be a piece of sheet metal respectively secured to the intermediate layers by respective outer bonding layers 23. The sheet metal may be coated, such as with paint. The exterior layers 20 may be twenty six gauge steel sheet metal, and typically the exterior layers will be ferromagnetic, as will be discussed in greater detail below. The exterior layers 20 may also be stainless steel sheet metal. The panel 10 may have an overall width of forty-six inches, and a height of eighty inches. Each of the above-mentioned dimensions may be approximate, and may vary by plus or minus any suitable percentage, such as five, ten, fifteen, twenty, twenty-five and/or any other suitable percentage. More generally, a wide variety of dimensions and/or other variations are within the scope of this disclosure. For example and as alluded to above, one or more of the layers 16, 18, 20, 22, 23, edge covers 13 and/or the frame 14 may be omitted, although the interior layer 16 will typically be included when it is desired to attenuate radiation (e.g., gamma radiation). As another example, radiation attenuation can be increased or decreased by changing the thickness of the interior layer 16 and/or the characteristics of the interior layer (e.g., changing the amount and/or type of the metal in the interior layer). Dimensions and other features of the panel 10 may vary depending upon any space constraints, cost constraints, amount of radiation attenuation desired, preferences and/or any other relevant factors. Referring to FIG. 2, the layered structure 12 includes a top edge that may be referred to as a compound top edge 24 because preferably (e.g., optionally) the top edge of each of the layers 16, 18, 20 extends substantially all the way to and is substantially coextensive with the compound top edge. Similarly, typically the other edges of each of the layers 16, 18, 20 respectively extend substantially all the way to and are substantially coextensive with right, left and bottom compound edges 26, 28, 30 of the layered structure 12. At least partially reiterating from above and in accordance with the first embodiment, the interior layer 16 in isolation may be a flexible sheet of material for restricting the propagation of radiation therethrough, and the edges of the interior layer respectively extend substantially all the way to and are substantially coextensive with the compound edges 24, 26, 28, 30 in an effort to maximize the breadth of the shielding provided by the interior layer. For securing the interior layer 16 in its broadly spread configuration, the interior layer 16 is secured between, and to both of, the intermediate layers 18 by the respective inner bonding layers 22, and the edges of the inner bonding layers respectively extend substantially all the way to and are substantially coextensive with the compound edges 24, 26, 28, 30. The intermediate layers 18 and/or the intermediate layers 18 in combination with the exterior layers 20 are typically more rigid than the interior layer 16. In one embodiment, the combinations of the intermediate and exterior layers 18, 20 (e.g., outer laminates comprising the intermediate and exterior layers), optionally further in combination with the inner bonding layers 22, are cooperative to support the intermediate layer in its broad configuration in which the edges of the intermediate layer respectively extend substantially all the way to and are substantially coextensive with the compound edges 24, 26, 28, 30 of the layered structure 12. In one aspect of this disclosure, the layered structure 12 may be characterized as including a core or central laminate 32 (FIG. 3) that comprises the interior and intermediate layers 16, 18 with the respective inner bonding layers 22 therebetween. As one example of a method of forming the central laminate 32, a first of the intermediate layers 16 of the central laminate may be laid out horizontally, the upper surface first intermediate layer may be substantially completely covered with a first layer of adhesive material (for forming a first of the bonding layers 22), the interior layer 16 of the central laminate may be laid out over/onto the first layer of adhesive material in a substantially superposed relationship with the first intermediate layer, the second of the intermediate layers of the central laminate may be laid out horizontally, the upper surface second intermediate layer may be substantially completely covered with a second layer of adhesive material (for forming the second of the bonding layers), and the laminate of first intermediate layer, first bonding layer and interior layer may be laid out over/onto the second layer of adhesive material so that the interior layer and the first and second intermediate layers are all substantially superposed with one another, and the opposite sides of the interior layer are respectively in opposing face-to-face contact with the bonding layers. The exterior layers 20 may be mounted to the opposite sides of the central laminate 32 in a similar manner. Alternatively, the central laminate 32 and/or the layered structure 12 may be formed in any other suitable manner. For example, in the central laminate 32, the bonding layers 22 may be omitted, so that the intermediate layers 18 are in direct opposing face-to-face contact with/are directly bonded to the interior layer 16. That is, the materials of the interior and intermediate layers 16, 18 may be selected so that the bonding layers 22 of adhesive material may be omitted. For example, the interior layer 16 may be formed and cured integrally with the intermediate layers 18 so that the intermediate layers are directly bonded to the interior layer without the bonding layers 22. For example, the intermediate layers 18 may be extruded onto the interior layer 16 and/or the intermediate and interior layers may be coextruded so that the intermediate layers are directly bonded to the interior layer without the bonding layers 22. Alternatively, any suitable materials (e.g., the bonding layers 22 of adhesive material) may be interposed between the interior and intermediate layers 16, 18. As another example, one or both of the intermediate layers 18 and bonding layers 22 may be omitted, in which case the interior layer 16 may be secured to one or more of the exterior layers 20, such as by way of one or more of the outer bonding layers 23. Reiterating from above and as will be discussed in greater detail below, the layered structure 12 may be used without the edge covers 13/frame 14; therefore, the layered structure 12 in isolation may be referred to as the panel. When the layered structure 12 is used without the edge covers 13/frame 14, the exterior layers 20 may be secured to the central laminate 32 in any suitable manner, such as by way of the respective outer bonding layers 23. More specifically and in accordance with the first embodiment, the exterior layers 20 are respectively bonded to the intermediate layers 18, such as by way of the outer bonding layers 23, so that the exterior and intermediate layers are cooperative for together supporting the interior layer 16. Accordingly, the layered structure 12 as a whole may be a laminate. One or more of the layers 16, 18, 20 of the layered structure 12 may alternatively and/or additionally be secured together by way of one or more of the edge covers 13, the frame 14, one or more suitable mechanical fasteners and/or in any other suitable way. In accordance with one acceptable method of the first embodiment, the panel 10 may be used as a portable shield for functioning as a barrier to radiation, such as alpha, beta and/or gamma radiation, as will be discussed in greater detail below. Accordingly, for purposes of durability and ease of any needed decontamination, the compound edges 24, 26, 28, 30 of the layered structure 12 may be fully and securely enclosed in the frame 14. The frame 14 may be characterized as being part of the panel 10, or the frame may be characterized as being a feature that may optionally be mounted to the panel/layered structure 12. Referring to FIGS. 1 and 2, each of the edge covers 13 may be referred to as a part or member of the frame 14 (e.g., a frame member). In the first embodiment, the frame members or edge covers 13 are respectively mounted to the compound edges 24, 26, 28, 30 of the layered structure 12, such as for protecting the compound edges and/or holding the layers 16, 18, 20 together. As shown in FIG. 2, each edge cover 13 is a generally C or U-shaped structural channel member having a web 40 and flanges 42 extending from the web. For each edge cover 13, the flanges 42 are substantially parallel to one another and extend substantially perpendicularly away from opposite edges of a web 40, so that a groove 44 is defined by the edge cover. Each edge cover 13 may be constructed of metal, steel, or any other suitable material. In the first embodiment, the grooves 44 of the edge covers 13 are respectively in receipt of marginal portions of the layered structure 12, so that, for each edge cover: the web 40 is in opposing face-to-face configuration with the respective compound edge 24, 26, 28, 30 of the layer structure; the front flange 42 of the edge cover is in opposing face-to-face relation with the respective marginal portion of the front exterior layer 20 of the layered structure; and the rear flange 42 of the edge cover is in opposing face-to-face relation with the respective marginal portion of the rear exterior layer 20 of the layered structure. In addition, adjacent ends of the edge covers 13 are mounted to one another, such as by welding, or through the use of any other suitable fastening techniques or fasteners. More specifically, the ends of the edge covers 13 may be oblique, as shown in FIGS. 1 and 2, so that the adjacent ends of the edge covers are connected to one another at miter joints held together by welds or other suitable fastening techniques or fasteners. Adjacent ends of the edge covers 13 may be mounted to one another in any other suitable manner. For example, each end of the edge covers 13 may have a shape other than the oblique shape of a miter joint, and adjacent ends of the edge covers may be in an overlapping configuration with respect to one another. The edge covers 13, and thus the frame 14, may be sized so that one or more of, such as each of, the opposing face-to-face configurations mentioned above may simultaneously be opposing face-to-face contacts, so that the margin of the layered structure 12 is securely held in the frame in an interference or friction fit. Not only may such a tight fit hold, or at least partially hold, the layered structure 12 together, it may also seek to minimize any open areas that may receive and harbor any contaminants to which the panel may be exposed. Alternatively, one or more of, such as each of, the opposing face-to-face configurations mentioned above may be a configuration in which the subject pair of surfaces are facing toward one another with one or more features positioned therebetween. For example, for each of the subject pair of surfaces that are facing toward one another, a bonding layer may be positioned therebetween, and any suitable adhesive materials may be used for the bonding layers. As a more specific example, each of the edge covers 13 may be formed of one or more strips of adhesive-backed tape, such as durable, strong tape or any other suitable structure. For example and not limitation, such a tape be an adhesive-backed strip of metal foil. Whereas the tape from which the edge covers 13 may be formed may be any suitable material, the tape may more specifically comprise a flexible strip that comprises polymeric material and metal for attenuating radiation, a flexible strip of silicone impregnated with metal, a flexible strip that comprises silicone impregnated with tungsten and/or iron, or more specifically the edge covers 13 may consist essentially of adhesive-backed silicone impregnated with tungsten and/or iron. As a more specific example, the edge covers 13 may be formed from, or at least partially formed from, Silflex brand shielding material, or any other suitable silicone tungsten/iron attenuation product, that is in the form of tape. Alternatively, one or more layers or edges of layered structure 12 may be secured together and/or covered with mechanical fasteners such as, but not limited to, clips. As indicated previously, this disclosure is not limited to the Silflex brand radiation shielding material available from MarShield or American Ceramic Technology, Inc. For example, any suitable source for the interior layer 16 may be used. In the first embodiment, the panel 10, with or without the frame 14, is strong enough to support at least its own weight without deforming substantially. As mentioned above, the panel 10 may be used as a portable barrier shield. Referring to FIG. 4 for example, the panel 10 may be equipped with one or more features, such as handles for being gripped, eyelets 46 for use in lifting the panel, wheels 48 for use in rolling the panel, and/or any other suitable features. For example, the eyelets 46 or any other suitable features for facilitating lifting of the panel, such as with a chain and overhead crane, may be attached to the upper portion of the frame 14, or in any other suitable location, such as by welding, or through the use of any other suitable fastening techniques or fasteners. In the first embodiment, the wheels 48 support stabilizers, or legs 50, which in turn support the panel 10. The legs 50 are respectively mounted by hinges 52 to the front and rear flanges 42 of the right and left edge covers 13. Each leg 50 includes an upright plate 54 mounted to, and extending upwardly from, a base plate 56 of the leg. The 52 hinges are respectively connected between the upright plates 54 and the front and rear flanges 42 of the right and left edge covers 13. The wheels 48 are positioned beneath, and rotatably mounted to, the base plates 56. More specifically, the wheels 48 may be components of conventional leveling castors that are mounted to the base plates 56. In additional to including one or more of the wheels 48 for rolling across a supporting surface, such as a floor, each leveling castor may include a vertically adjustable member for engaging the floor. The vertically adjustable members of the leveling castors may be operated in a concerted manner that seeks to cause each of the vertically adjustable members to simultaneously be in contact with the floor, which seeks to avoid wobbling of the panel relative to the floor. Alternatively, the wheels 48/castors may be omitted and the lower surfaces of the base plates 56 and optionally also the web 40 of the bottom edge cover 13 may engage the floor. The hinges 52 allow the legs 50 to be pivoted between a wide range of configurations, such as between an extended configuration for relatively greater stabilization, and a retracted configuration for relatively less stabilization/storage. A fixing or locking mechanism may be associated with each of the legs 50 for releasably securing the legs 50 relative to the panel 10 in the desired configuration. In FIG. 4 for example, the front right and left legs 50 are shown locked in extended and retracted configurations, respectively. The locking mechanism associated with each pivotable leg 50 may include a bar 60 with downwardly bent opposite ends for being removably received in receptacles 62 of the frame 14 and receptacles 64 of the legs 50. For example, the frame's receptacles 62 may be in the form of pieces of pipe mounted (e.g., welded) to the flanges 42 of the bottom edge cover 13, and the leg's receptacles 50 may be in the form holes in the base plates 56. Alternatively, any other suitable features may be used for releasably securing the pivotable legs 50 relative to the panel 10, or the legs 50 may be permanently fixedly mounted (i.e., nonpivotably mounted) to the panel. The panel 10 together with the frame 14 and other features mounted thereto may be referred to as a panel assembly 66. Each of the exterior components of the panel 10 or panel assembly 66, or at least the exterior layers 20, may be made of metal, or more specifically steel, for purposes of cleanliness and durability. In addition, each of the exterior components of the panel 10 or panel assembly 66 may be made of a ferromagnetic metal, so that the ability of the panel 10 to shield radiation may be supplemented by magnetically attaching one or more radiation shielding blankets (not shown), or the like, to the exterior of the panel. For example, magnets may be built into or otherwise mounted to the radiation shielding blankets or other accessories, so that the blankets or other accessories can be attached to one or more exterior surfaces of the panel 10, such as the front or rear exterior layers 20, by way of the magnets. Alternatively, one or more of the exterior components of the panel 10 or panel assembly 66 may be made of a material other than metal, such as a material having a strong, substantially smooth and non-porous surface that is both durable and easy to clean (e.g., decontaminate, if exposed to radioactive contamination). For example, one or more of the exterior components of the panel 10 or panel assembly 66 may be made of suitable polymeric materials. The layered structure 12, a portion of the layered structure 12, the panel 10, the and the panel assembly 66 may each be put to a variety of uses, such as, but not limited to, inhibiting the propagation of radiation. For example, FIG. 5 illustrates a series of panel assemblies 66 arranged edge-to-edge, and positioned adjacent to a radiological hot zone 68 so that the series of panel assemblies 66 define a shielded area that is very generally designated by the numeral 70. The radiological hot zone 68 is shown in FIG. 5, for example and not limitation, as being in the form of a section of piping that may be part of a nuclear reactor coolant system, and may be emitting alpha, beta and/or gamma radiation. The series of panel assemblies 66 is positioned between the shielded area 70 and radiological hot zone 68. For example and assuming no other sources of radiation, humans would receive less of a radiation dose per time in the shielded area 70 as compared to the radiological hot zone 68. Therefore, when possible, a computer work station or other support services will be arranged in the shielded area 70 rather than the radiological hot zone 68. When manual work must be done in the radiological hot zone 68, the humans doing the manual work may do preparatory work, take breaks or otherwise rest, or the like, in the shielded area 70. Each of the layered structure 12, a portion of the layered structure 12, panel 10, and panel assembly 66 may be used as a barrier, or as part of a barrier, for attenuating radiation emitted from a wide variety of sources. For example, the panel assembly 66 may be moved, such as using the eyelets 46 and/or wheels 48, between a variety of radiological hot zones 68 in one or more nuclear power plants or in any other facilities where radiological hot zones may be present. Alternatively or in addition, each of the layered structure 12, a portion of the layered structure 12, and/or the panel 10 may be used as a structural panel or a structural insulated panel. Directional references (e.g., top, upper, lower, bottom, front, back, rear, left, right, top, bottom, above, below, crosswise and the like) may have been used in this disclosure for ease of understanding and not for the purpose of limiting the scope of this disclosure. Accordingly, while the present disclosure has generally been provided in terms of certain illustrated configurations, directional references related thereto are provided only for example. The above examples are in no way intended to limit the scope of the present invention. It will be understood by those skilled in the art that while the present disclosure has been discussed above with reference to exemplary embodiments, various additions, modifications and changes can be made thereto without departing from the spirit and scope of the invention as set forth in the claims. |
|
046541705 | summary | CROSS-REFERENCE TO-RELATED APPLICATION This application is related to application Ser. No. 501,980, filed June 7, 1983 by A. P. Murray et al., titled "Decontamination of Metal Surfaces in Nuclear Power Reactors," now U.S. Pat. No. 4,587,043. BACKGROUND OF THE INVENTION Water or various gases are used in many types of unclear reactors to remove heat from the reactor core, which is then directly or indirectly used to generate electricity. In a pressurized water reactor (PWR) water circulates between the reactor core and a steam generator in a primary loop. In the steam generator the heat is transferred to a secondary loop of water which forms steam which then runs turbine electric generators. In a boiling water reactor (BWR) the water in the primary loop is under less pressure so that, after heating in the nuclear core, it is in a gaseous form. In other types of nuclear reactors, such as high temperature gas reactors (HTGR), a gas such as carbon dioxide or helium transfers heat from the reactor core to the steam generator. Regardless of whether the heat transfer medium is water or a gas, however, it picks up contaminants and corrosion products from the metals with which it is in contact. The contaminants are radioactivated in the nuclear core, and then deposit on metal surfaces in the cooling system. These contaminants include chromium which enters the coolant when base metals such as stainless steel or Inconel corrode. Chromium (+6) is soluble (e.g., as dichromate, Cr.sub.2 O.sub.7.sup.--) but chromium (+3) forms an oxide with a spinel structure, which is very difficult to remove from the metal surfaces. Such spinel-like oxides include chromium substituted nickel ferrites, such as Cr.sub.0.2 Ni.sub.0.6 Fe.sub.2.2 O.sub.4, which tend to form under the reducing conditions found in pressurized water reactors. The deposits can also contain nickel ferrite, hematite, magnetite, and various radionuclides. Hematite, Fe.sub.3 O.sub.4, and, to a lesser extent, nickel ferrite, NiFe.sub.2 O.sub.4, tend to form under the oxidizing conditions found in boiling water reactors, but these are easier to remove than chromium substituted ferrites. Radionuclides in the deposits can come from non-radioactive ions that enter the coolant and are made radioactive by neutron bombardment in the core. For example, cobalt from hard facing alloys, which are used in seals and valve facings, can go from non-radioactive cobalt 59 to highly hazardous and radioactive cobalt 60 when bombarded by neutrons. Also, stable nickel 58, from high nickel alloys (e.g., Inconel), can be irradiated to produce radioactive cobalt 58. These deposits can form on the inside surfaces (primary surfaces) of the primary loop of a pressurized water reactor, or in the steam generator, or in the piping in between. The deposits could also form on the steam generating side (secondary surfaces) of the steam generator, but there the problem is much less severe because the radioactivity is lower and the deposits are more easily dissolved. In a boiling water reactor the deposits can form on turbine blades or in any part of the cooling loop. In a high temperature gas reactor, the deposits can form on the primary cooling loop. Generally, the deposits formed in pressurized water reactors are the most difficult to remove, so if a process and composition can remove those deposits, it can also remove deposits formed in other types of reactors. While the deposits are usually too thin to plug any of the tubing, they represent a safety hazard to personnel because of their high radioactivity. Thus, in order to inspect the cooling system and perform maintenance on it, it is necessary to decontaminate it first so that the hazard to humans is reduced or eliminated. In addition to the radiation hazard the deposits present, they also prevent the formation of a good seal when tubing must be repaired. This is done by "sleeving," inserting a new, smaller tube into the old tube and swaging the tubes together. In a steam generator it is necessary to hone a tube with an abrasive to remove the oxide layer down to clean metal in order to obtain a good seal by swaging or brazing. Because this is a time-consuming task, it increases the radiation exposure to the technician. In spite of their thinness, (usually only about 2 to 5 microns), radioactive deposits in the cooling systems of nuclear reactors are very tenacious and difficult to remove. Many techniques have been tried to eliminate these deposits. Inhibitors have been added to the coolant system, but most inhibitors break down under the extreme conditions of temperature and radiation, and, in doing so, may form corrosive products. Continuous precipitation of the ions forming the deposits has been found to be ineffective. Many decontamination solutions which have been tried may themselves corrode the metals in the cooling system or may work too slowly to be economical. This is particularly true of concentrated reagents, which may require shutting down the power plant for several months. Speed in decontaminating is important because a generator which is shut down can cost a utility a million dollars a day in lost electricity. SUMMARY OF THE INVENTION We have discovered that metal surfaces coated with compounds containing radioactive substances can be effectively decontaminated by contact with an aqueous solution of an alkali metal hypohalite at a pH of at least 12 followed by contact with a decontamination solution. Unlike the alkali metal permanganate oxidizing solutions previously used, the oxidizing solution of this invention is transparent and dilute. Transparency is an advantage because it enables the operator to observe the effectiveness of the oxidation of the coating and alter process parameters accordingly to increase the effectiveness. Because the oxidizing solutions of this invention are dilute they result in a much smaller quantity of radioactive waste which must be disposed of. While the alkali permanganate oxidizing solutions tended to deposit manganese on the coating, which had to be redissolved prior to dissolution of the coating, the oxidizing solution of this invention does not form precipitates when in use. Finally, the oxidizing solution of this invention is at least as effective as alkali permanganate in decontaminating the metal surfaces of nuclear reactors. |
058870458 | abstract | A tube of zirconium-based alloy for constituting all or a portion of a cladding or guide tube for a nuclear fuel assembly. The tube is made of an alloy containing, by weight, 1.0-1.7% of tin, 0.55-0.80% of iron, 0.20-0.60% total of chromium and/or vanadium, and 0.10-0.18% of oxygen, with 50-200 ppm of carbon and 50-120 ppm of silicon. The alloy further contains only zirconium and unavoidable impurities, and it is completely recrystallized. |
claims | 1. A nuclear reactor system, comprising:a support plate that includes a flange that extends beyond a perimeter of the support plate, wherein the flange includes an aperture with a longitudinal aperture axis; anda latch assembly that includes a latch housing with a longitudinal latch axis and is disposed above the flange, wherein the latch housing is configured and arranged for at least a first and a second rotational orientation; anda core barrel that includes a support block that extends beyond a perimeter of the core barrel, wherein the flange of the support plate is disposed vertically intermediate the support block and the latch housing, and the support block is configured to restrain a downward displacement of the support plate such that when the latch housing is in the first rotational orientation, the support plate is locked to the core barrel,wherein when the latch housing is in the first rotational orientation, the longitudinal latch axis is substantially aligned with the longitudinal aperture axis of the flange and the latch housing is receivable through the aperture of the flange such that the latch housing does not restrain an upward displacement of the support plate, andwhen the latch housing is in the second rotational orientation, the longitudinal latch axis is substantially transverse to the longitudinal aperture axis and the latch housing is not receivable through the flange such that the latch housing restrains the upward displacement of the support plate. 2. The nuclear reactor system of claim 1, wherein the latch assembly further includes an elongate member that extends through the flange and a main bore of the latch housing, wherein the latch housing is configured and arranged to rotate about the elongate member between the first and the second rotational orientations. 3. The nuclear reactor system of claim 1, wherein a relative angular difference between the first and the second rotational orientations of the latch housing is 90 degrees. 4. The nuclear reactor system of claim 1, wherein an upper surface of the flange includes an indent, and when the latch housing is in the second rotational orientation, the indent receives at least a portion of the latch housing that projects from a lower surface of the latch housing, and when received by the indent, the portion of the latch housing that projects from the lower surface of the latch housing is configured to resist a rotation of the latch housing away from the second rotational orientation. 5. The nuclear reactor system of claim 1 further comprising:a latch mechanism that is at least partially housed within the latch housing and includes at least a spheroidal member, a biasing member that provides a biasing force on the spheroidal member, and a setscrew to adjust a magnitude of the biasing force. 6. The nuclear reactor system of claim 1 further comprising:a nut disposed above the latch housing that restrains an upward displacement of the latch housing. 7. The nuclear reactor system of claim 4, wherein the portion of the latch housing that projects from the lower surface of the latch housing comprises a spheroidal member. 8. The nuclear reactor system of claim 2, wherein a relative angular difference between the first and the second rotational orientations of the latch housing is 90 degrees. 9. The nuclear reactor system of claim 8, wherein an upper surface of the flange includes an indent, and when the latch housing is in the second rotational orientation, the indent receives at least a portion of the latch housing that projects from a lower surface of the latch housing, and when received by the indent, the portion of the latch housing that projects from the lower surface of the latch housing is configured to resist a rotation of the latch housing away from the second rotational orientation. 10. The nuclear reactor system of claim 9, further comprising a nut disposed above the latch housing that restrains an upward displacement of the latch housing. 11. A nuclear reactor system, comprising:a support plate that includes a flange that extends beyond a perimeter of the support plate, wherein the flange includes an aperture with a longitudinal aperture axis; anda latch assembly that includes a latch housing with a longitudinal latch axis and is disposed above the flange, wherein the latch housing is configured and arranged for at least a first and a second rotational orientation,wherein when the latch housing is in the first rotational orientation, the longitudinal latch axis is aligned with the longitudinal aperture axis of the flange and the latch housing is receivable through the aperture of the flange such that the latch housing does not restrain an upward displacement of the support plate, andwhen the latch housing is in the second rotational orientation, the longitudinal latch axis is transverse to the longitudinal aperture axis and the latch housing is not receivable through the flange such that the latch housing restrains the upward displacement of the support plate, andan upper surface of the flange includes an indent, and when the latch housing is in the second rotational orientation, the indent receives at least a portion of the latch housing that projects from a lower surface of the latch housing, and when received by the indent, the portion of the latch housing that projects from the bottom surface of the latch housing resists a rotation of the latch housing away from the second rotational orientation. 12. The nuclear reactor system of claim 11, further comprising a core barrel that includes a support block that extends beyond a perimeter of the core barrel, wherein the flange of the support plate is disposed vertically intermediate the support block and the latch housing, and the support block is configured to restrain a downward displacement of the support plate such that when the latch housing is in the first rotational orientation, the support plate is locked to the core barrel. 13. The nuclear reactor system of claim 11, wherein the latch assembly further includes an elongate member that extends through the flange and a main bore of the latch housing, wherein the latch housing is configured and arranged to rotate about the elongate member between the first and the second rotational orientations. 14. The nuclear reactor system of claim 11, wherein a relative angular difference between the first and the second rotational orientations of the latch housing is 90 degrees. 15. The nuclear reactor system of claim 11, further comprising:a latch mechanism that is at least partially housed within the latch housing and includes at least a spheroidal member, a biasing member that provides a biasing force on the spheroidal member, and a setscrew to adjust a magnitude of the biasing force. 16. The nuclear reactor system of claim 11, further comprising a nut disposed above the latch housing that restrains an upward displacement of the latch housing. 17. The nuclear reactor system of claim 12, wherein the latch assembly further includes an elongate member that extends through the flange and a main bore of the latch housing, wherein the latch housing is configured and arranged to rotate about the elongate member between the first and the second rotational orientations. 18. The nuclear reactor system of claim 17, wherein a relative angular difference between the first and the second rotational orientations of the latch housing is 90 degrees. 19. The nuclear reactor system of claim 18, further comprising:a latch mechanism that is at least partially housed within the latch housing and includes at least a spheroidal member, a biasing member that provides a biasing force on the spheroidal member, and a setscrew to adjust a magnitude of the biasing force. 20. The nuclear reactor system of claim 19, further comprising a nut disposed above the latch housing that restrains an upward displacement of the latch housing. |
|
description | The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. For a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. In describing the present invention, a variety of terms are used in the description. As used herein unless otherwise specified, the term electron beam as used throughout this specification is meant to include any beam comprising charged particles as is known to those skilled in the art. Atomic scale point source electron beams have many potential advantages for scanning electron microscopy, including higher resolution at lower voltages in much more compact configurations; these electron beam sources also are advantageously used in vacuum microelectronic devices. The primary disadvantage is the requirement for operation at ultra-high vacuum when used as electron field emitters to avoid damage by ion bombardment. By using a miniature ultra-high vacuum chamber to permanently enclose the field emission part, the vacuum requirements for the rest of a scanning electron microscope can be greatly relaxed, leading to major operational and economic advantages, and a much wider range of practical application of this uniquely advantageous point source of coherent electron beams. In one embodiment, the invention of this patent application comprises the structure and utilization of a mono-atomic tip in place of conventional field emission sources, providing a far superior initial electron beam in terms of narrow beam divergence and narrow energy spread and greatly reducing the requirements for high beam voltages and expensive electron optical systems needed for very high resolution imaging. The enclosed point source electron beam generator described in this specification may operate with a miniature ultra-high vacuum enclosure with an electron-transparent window. This enables the rest of the system to be operated under more conventional vacuum conditions. The rest of the system may comprise conventional or, due to the very narrow electron beam sources produced at relatively low voltages, greatly miniaturized versions of conventional scanning electron microscopes, scanning transmission microscopes, point projection Fresnel microscopes, electron beam lithography systems, and vacuum microelectronic devices. An alternative means of generating very fine electron beams at low voltages (about 50 to 500 volts) from a conventional electron beam and coupling it to a superconducting nano-channel is also disclosed. Such beams can be used for the microscopy systems and vacuum microelectronic devices. Very fine electron beams from any of the above sources may be guided and/or manipulated by superconducting nano-channels. As is known to those in the field of electron beam technology, suitably oriented magnetic fields may be used to confine electron beams for some distance once they have been suitably created and formed. The small size of the electron beam source of this invention and the ability to position it close to the ultimate target makes it feasible to wholly immerse the entire source-to-target system in the bore of a powerful magnetic field generating system whose internal magnetic field is oriented parallel to the main electron beam axis. The magnetic field system, depending on system size and performance requirements, may employ permanent magnets or conventional electromagnets or superconducting electromagnets, optionally augmented with magnetic pole pieces, following common practices well known to those in the art. Immersing the entire system in this magnetic field has the net effect of causing electrons that would normally radially diverge from the main beam axis to instead spiral around it. For scanning electron microscopy or scanning electron beam surface modification applications, either the source or target would need to be mechanically scanned relative to the other. Such scanning may for instance be implemented by any of the lateral electro-mechanical scanning techniques that are used for scanning tunneling microscopes or atomic force microscopes, following common practices well known to those in the field. In the remainder of this specification reference will be made to the use of single walled superconducting carbon nanotubes. However, it is to be understood that multi-walled superconducting carbon nanotubes may be utilized as well, as may be any other essentially atomically perfect nanotube structure, which, if not naturally superconducting, may be optionally externally coated with a thin film of superconducting material. In the preferred embodiment illustrated in FIG. 1, there is illustrated a tip assembly 10 comprised of a high quality electron-transparent thin wall 12 positioned at the distal end 14 of an ultra-high vacuum chamber 16. The thin wall 12 is electron-transparent, i.e., electron beams may be passed through it without significant dispersion or attenuation, relative to the intended application. Electron transparency is a function of electron energy and the type and thickness of the thin wall material. Using means well known to those skilled in the art, the initial electron beam energy would be set for attaining an acceptable level of electron transparency for a particular thin wall material, and then, if needed, the electron beam energy would subsequently be raised or lowered as appropriate for the intended application. Electron-transparent thin-walls and structures and materials comprising them are well known to those skilled in the art. Reference may be had, e.g., to U.S. Pat. Nos. 6,300,631 (Method of thinning an electron transparent thin film membrane on a TEM grid using a focused ion beam), 6,194,720 (Preparation of transmission electron microscope samples), 6,188,068, 6,140,652, 6,100,639, 6,060,839, 5,986,264, 5,940,678 (electronic transparent samples), 5,633,502, 4,680,467, 3,780,334 (Vacuum tube for generating a wide beam of fast electrons), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification. Referring again to FIG. 1, and in the embodiment depicted, wall 12 is preferably a film that preferably has a thickness of from about 1 to about 50 nanometers. In one preferred embodiment, film 12 consists essentially of silicon nitride, boron nitride, or diamond. The wall 12, in combination with wall 18, defines a chamber 16. The vacuum within chamber 16 is preferably greater than about 10xe2x88x927 Torr. In one aspect of this embodiment, the vacuum within chamber 16 is from about 10xe2x88x927 to about 10xe2x88x9210 Torr. The vacuum within chamber 16 may be created by conventional means. In one embodiment, (not shown) the tip assembly 10 is placed within an ultra high vacuum chamber (not shown) during its manufacturing assembly process and chamber 16 is vacuum sealed to the electron transparent wall 12 thus enclosing an ultra high vacuum within chamber 16. The chamber 16 has a relatively small volume, of preferably less than about 1 cubic millimeter. In one embodiment, the chamber 16 has a volume of less than about 0.1 cubic millimeters. Referring again to FIG. 1, it will be seen that the tip assembly 10 is utilized within a sample vacuum chamber 20 whose volume may be at least about 1,000 times as great as the volume of chamber 16. However, the vacuum in chamber 20 may be substantially lower than the vacuum in chamber 16. The pressure in chamber 20 is typically at least about 10 to 1,000 times as great as the pressure within chamber 16. Referring again to FIG. 1, and in the preferred embodiment depicted therein, the tip assembly 10 is disposed above sample 22 and can be moved, by means described elsewhere in this specification, so that it is closer to or further away from sample 22. Referring again to FIG. 1, and in the preferred embodiment depicted therein, an extraction electrode assembly 24 is preferably disposed around chamber 16. Electrode assembly 24 is electrically connected to external voltage supply 26 by means of conductors 28 and 30. In another embodiment, not shown, the extraction electrode assembly 24 is disposed within chamber 24. In one embodiment, the extraction electrode assembly 24 is electrically charged to an electrical potential typically in the range 50 to 500 volts with respect to the field emission tip 32 (which is the mono-atomic point source of electron beam 34). In the embodiment depicted in FIG. 1, tip assembly 10 may comprise either a single or multi walled carbon nanotube 32 or a tungsten mono-atomic point emitter (not shown). Reference may be had to U.S. Pat. Nos. 6,159,742 (Nanometer-scale microscopy probes), 4,939,363 (Scanning tunneling microscope), and the like. The entire disclosure of each of these United States patents is hereby incorporated by reference into this specification. The extraction electrode assembly 24 may optionally be fashioned from a superconducting material to take advantage of the Meissner effect for narrowing the emission cone of electrons from the emitter due to the superconducting material""s expulsion and thus confinement of the magnetic fields of the emerging electrons. The Meissner effect is the ability of a material in a superconducting state to expel all magnetic fields therefrom (i.e., such a superconductor is perfectly diamagnetic and exhibits a permeability of zero). Reference may be had, e.g., to U.S. Pat. No. 4,975,669 (Magnetic bottle employing Meissner effect). The entire disclosure of this United States patent is hereby incorporated by reference into this specification. Referring again to FIG. 1, and in the preferred embodiment depicted therein, the emission tip 32 is attached to an electrically insulating tip enclosure 36 to isolate the tip 32 from electrode 24. An electrical connection is made from the voltage source 26 to the electrode 24 by means of conductor 28. An electrical connection is made from the voltage source 26 to the tip 32 by means of conductor 30. The entire assemblage is attached to an electrically insulating supporting mount 40. In this preferred embodiment, the beam extraction voltage preferably is selected according to the type of ultra thin film material used for the electron window 12, since, as is known to those skilled in the arts, transparency is energy dependent. After passage through the electron window 12, the beam 34 can subsequently be accelerated or decelerated as needed to a target-relative voltage in the range of about 20 to 1,000 volts. FIG. 2 illustrates another configuration of a tip assembly 50 in which tip 32 is in the shape of a carbon nanotube. In this embodiment, tip 32 has a relatively small diameter, in the range of 0.3 to 10 nanometers. In this embodiment, the carbon nanotube may be composed of single or multi-walled metallic-type carbon nanotube; alternatively, it may be composed of tungsten mono-atomic point emitter or other suitable material. Referring again to FIG. 2, the tip 32 is preferably embedded in a support structure 42, which also serves as a thermal sink and ultra-high vacuum seal to a superconducting single walled metallic-type carbon nanotube 44 of relatively larger diameter (in the range, e.g., of approximately 5 to 200 nanometers), which also serves as a field emission extraction electrode and as a miniature ultra-high vacuum chamber. Electrical lead 43 passes through the support structure 42 to provide a means for creating an electrical potential difference between tip 32 and wall 44. In this embodiment, the electron beam 34 emerges from the field emitter 32 and is confined and focused by the superconducting nanotube 44. Since the momentum of the electrons in beam 34 is largely parallel to the wall 44, relatively little force is required to confine it within wall 44. This beam penetrates and emerges from the semispherical end cap 46. This end cap is less strongly superconducting, or may not be superconducting at all, than the rest of the carbon nanotube 44. Since the momentum of the electron beam 34 is perpendicular to the middle of end cap 46, the middle of end cap 46 serves as an electron window for certain material-dependent electron beam energies. An optional coating of material 48, which may optionally be superconducting, may be used for purposes of vacuum sealing, enhanced mechanical strength, or enhanced superconducting focusing of electron beam 34. In another embodiment (not shown), coating 48 may be connected to the electrical lead 43 and is then used as an electron extraction electrode, instead of nanotube 44. FIG. 3 illustrates another preferred embodiment of this invention. In this configuration, a fixed or dynamic emitter tip positioning system 60 is enclosed in a miniature ultra high vacuum chamber 62 and support structure 64. The tip 32 preferably has a relatively small diameter, e.g. in the range of approximately 0.3 to 10 nanometers; single walled metallic-type carbon nanotube 32 serves as an atomic point source field emitter of electrons 34. Alternatively, the atomic point source field emitter 32 may be a multi-walled carbon nanotube or a tungsten mono-atomic point emitter or other suitable material. This electron emitter 32 is embedded in a positioning system 60. The support structure 64 also serves as a thermal sink and ultra-high vacuum seal to a superconducting single walled metallic-type carbon nanotube 66 of relatively larger diameter, e.g. in the range of approximately 5 to 200 nanometers, which serves both as a field emission extraction electrode and as a miniature ultra-high vacuum chamber. The electron beam 34 emerges from the field emitter 32 and is confined and focused by the superconducting nanotube 66. The electron beam 34 penetrates the semispherical end cap 46 and emerges from the end of it. This end cap is less strongly superconducting or may not be superconducting at all. Since the momentum of the electron beam is perpendicular to the end cap 46 it serves as an electron window. An optional coating of material 48, optionally superconducting, may be used for purposes of vacuum sealing, enhanced mechanical strength, or enhanced superconducting focusing of the electron beam. In the embodiment depicted in FIG. 3, electrical leads 67, 68 are connected to a voltage supply (not shown) which provides the electrical potential difference between the tip 32 and the field emission extraction electrode 66. Alternatively, an optional electrical lead 69 may be connected to a voltage supply (not shown) when the optional coating of material 48 is to be utilized as the field emission extraction electrode. The relatively larger single walled carbon nanotubes in FIGS. 2 and 3 may be quite long compared to their diameter, e.g. on the order of a micron or more; in general, such nanotubes have aspect ratios of at least about 1:10 to 1:1000. The material properties (such as toughness and springiness of such nanotubes) may be adapted to allow the nanotubes to optionally be subjected to mechanical bending involving various high frequency resonant motion patterns, in the kilohertz through megahertz range, depending on specific geometry for purposes of directing, diverting, modulating, or scanning the emergent electron beam. There are several forms of carbon nanotubes. In general, the most commonly studied forms of carbon nanotubes have physical properties such that they conduct electricity better than copper, they have a tensile strengths over 100 times that of steel, they become superconductors when cooled to extremely low temperatures, and they are exceptionally tough and resilient when subjected to mechanical bending. The electron transparent structures illustrated in the Figures can be formed by the carbon nanotube end caps 46 shown in FIGS. 2 and 3. Alternatively, or additionally, these electron transparent structures may be replaced, in part or in whole, by mechanically attaching some other ultra thin film of suitably electron transparent material to the end of an uncapped carbon nanotube. The micro-enclosed point source electron beam generators 10 of FIG. 1 and 32 of FIGS. 2 and 3 may be mechanically scanned near the target to be imaged or incorporated into the tip of an atomic force microscope for the purpose of very high resolution electron microscopy and spectroscopy; or such point source electron beam generators 10 of FIG. 1 and 32 of FIGS. 2 and 3 can be incorporated into an electron beam micro-column, such as described in xe2x80x9cFabrication of electron-beam microcolumn aligned by scanning tunneling microscopexe2x80x9d, Jeong-Young Park, et al, Journal of Vacuum Science and Technology A, Volume 15, Number 3, May/Jun 1997, 1499-1502. FIG. 4 illustrates the use of a micro-enclosed point source of electrons 70, (which may consist of any of the systems shown in FIGS. 1, 2, and 3) to substantially improve on other devices, such as, e.g., the device disclosed in Thomas George""s xe2x80x9cMiniature Electron Microscopes Without Vacuum Pumpsxe2x80x9d, NASA Technical Brief, Vol. 22, No. 8. (JPL NEW TECHNOLOGY REPORT NPO-20335). A low-to-medium vacuum enclosure 72 contains the whole system; in general, the pressure within enclosure 72 is from about 10xe2x88x923 to 10xe2x88x926 Torr. An optional superconducting cylinder 74 can be used for narrowing the conical emerging electron beam. An optional beam extraction electrode and/or beam acceleration or deceleration electrodes 76 may be used. Electrode pair 78 and electrode 80 are used for scan deflection and focus. Backscattered electron detectors 82 are placed above the observation and manipulation stage 84. Secondary and backscattered electrons may be detected either by a micro channel plate, or a channeltron, or by other conventional means. The use of superconducting channels for manipulating electron beams has been described in xe2x80x9cHigh Tc bulk superconductor wigglersxe2x80x9d, Hidenori Matsuzawa, et al, Applied Physics Letters, Volume 59, Number 2, Jul. 8, 1991, 141-142. FIG. 5 shows how a relatively large (in the range of approximately 0.1 to 100 micron diameter) beam of electrons or positive ions 90 may be narrowed into a beam 100 by means of a superconducting channel assembly 88. Beam 90 passes through superconducting material 92 with a converging funnel channel 94 to a channel 96 of dimensions in the range of approximately 1 to 100 nanometer diameter, and through a connected single walled superconducting carbon nanotube 98. The superconducting structure 92 may optionally be split in planes perpendicular to the funnel axis into several mutually insulating segments that are mutually electrified so as to facilitate the attraction of electrons into each successive segment. FIG. 6 illustrates the use of superconducting carbon nanotubes 110, 112 in the range of about 0.3 to 100 nanometers in diameter constructed into a Y-junction 114. Because superconductivity is likely substantially reduced in the junction region itself, this region would normally be externally coated with a thin film of superconducting material 116. The more general use of high temperature superconductors for such coatings and the coating of all channels removes the requirement that the carbon nanotubes be superconducting or be used at the temperature at which they are superconducting. This system can be used to couple an electron beam 120 with an ion beam 122 or with another source of electrons at a different energy level, from inlets 110, 112 into the Y-junction 114 and to the single coaxial outlet 118. One of several means of using such a system is to use the electron beam for target illumination and positioning purposes, and using the ion beam for transient milling or ion deposition purposes. Alternatively, the Y-junction assembly 130 shown in FIG. 7 can be used to split an electron beam 132 entering inlet 134 into 2 beams 136, 138 exiting at outlets 140, 142. Additional thin film coating 144 of a superconducting material may optionally be employed to enhance the superconducting property at the junction 148. Such junctions need not be symmetric in branching angles or in terms of nanotube diameters. Multiple such splitting and merging junctions may be combined in practice, and may be structured so as to implement nano-scale electron beam analogs of fluidic technology, including feedback loops. Modulation mechanisms may be provided by external pulsed magnetic fields above the local superconducting shielding level, induction of trapped magnetic fields inside and along the axis of nano-channel loops, locally induced transient thermal excursions above the superconducting threshold temperature, mechanical bending, and the use of electrically insulated superconducting channel segments at differing potentials. These can be used in vacuum electronic device systems that dispense with individual solid state cathodes and individual solid state anodes. Such systems can also be realized without using carbon nanotubes, by exploiting the fabrication techniques that are used for micro-electro-mechanical systems. Such device systems can implement analog and digital types of transducer, signal processing, and computing functions. The highly modulated electron beam output of such systems can be used for subsequently miniaturized electron microscopy implementation, and for corollary use in spatially resolved electrochemistry processes. FIG. 8 illustrates one preferred use of the electron beam emitter assembly 50 of FIG. 2 together with the superconducting channel assemble 88 of FIG. 5. A material 160 is used to attach assembly 50 to the assembly 88. In one embodiment, material 160 is a non-conducting material, e.g. Nylon-6, Nylon-66, Teflon or the like, and electrically isolates assembly 50 from assembly 88. In another embodiment, material 160 is a superconducting material. The ability to generate, guide and manipulate electron beams or other charged particle is an essential feature of microscopy devices, such as e.g., Scanning Tunneling Microscopes (STM) and Atomic Force Microscopes (AFM). The superconducting nano-channel structures of this invention, comprising carbon-based nanotubes, may be used with microscopy probes. They may also operate with a miniature ultra-high vacuum enclosure with an electron-transparent widow. Free standing flexible superconducting nanometer scale tubes and fixed superconducting nanometer scale channels formed on supporting substrates, manufactured by means well known to those skilled in the art of micro-lithography and related micro-fabrication techniques, may be further used for conveying coherent electron beams with energies corresponding to wavelengths of a similar order of magnitude (e.g. a few electron volts) and provides a nanometer scale electron beam analog of micron scale fiber optical systems. FIG. 9 is a schematic representation of one embodiment of a device for guiding charged particle beams comprising a superconducting nano-channel. Referring to FIG. 9, device 170 comprises a superconducting channel 171 consisting essentially of a superconducting material 178 in the form of a tube, for guiding electron beam or other charged particle beam 180. In the embodiment depicted in FIG. 9, beam 180 passes through an approximately 90 degree bend 176 in the channel 171 and exits at the channel distal end 174. In other embodiments, bend 176 may be constructed with a structure having an arc of other than 90 degrees. Bend 176 is preferably greater than zero degrees, and as much as 180 degrees in an embodiment wherein the direction of the particle beam 180 is to be substantially reversed. In a further embodiment, charged particle beam guiding device 170 is an apparatus for generating and guiding a charged particle beam. Referring again to FIG. 9, apparatus 170 comprises a point source particle beam generator coupled to a superconducting nano-channel, the end thereof being sealed with an electron beam transparent membrane. FIG. 9 illustrates a preferred embodiment in which electron beam emitter assembly 50 is coupled to superconducting channel 171 for conveyance of coherent electron beam 180. At the proximal end 172 of channel 171 is attached electron source 50. An electron transparent window 173 is sealed to channel end 174 to form an ultra-high vacuum region 175 through which electron beam 180 travels. Because of the nano-scale dimensions of superconducting channel 171, ultra-high vacuum conditions may be achieved within region 175. It will be apparent that any of the enclosed point source electron beam generators previously described and shown in FIGS. 1, 2, or 3 will be suitable for electron source 50. It will be further apparent that electron transparent membrane or window 173 may be either substantially planar, or a semi-spherical cap, and of the materials previously described in this specification and shown in FIGS. 1, 2, and 3. FIG. 10A is a schematic representation of a side view of a superconducting nano-channel network, and FIG. 10B is a top view of the representation of FIG. 10A taken along line 10Bxe2x80x9410B of FIG. 10A. FIGS. 10A and 10B illustrate a preferred embodiment in which 2-D, xe2x80x9c2.5-Dxe2x80x9d, and 3-D superconducting nano-channels may be fabricated on a substrate using lithographic or stereo-lithographic means. Referring to FIGS. 10A and 10B, assembly 300 comprises substrate 302 onto which superconducting material 304 is deposited by means known in the art. Superconducting nano-channels 306 and 308 may be formed using lithography or stereo-lithography, or other suitable micro-fabrication means, wherein areas 303, 305, and 307 of material 304 have edges substantially parallel to each other, thereby forming channels 306 and 308. In one embodiment, additional layers of superconducting material (not shown) may be deposited on top of superconducting material 304 to completely enclose channels 306 and 308, and to provide additional channels (not shown), thus forming a complex network of superconducting channels. Electron beams or other charged particles may be guided and manipulated through the network of superconducting channels taking advantage of the Meissner effect of superconductors (repulsion forces). Layers of insulating material (not shown) may be deposited so that the complex network of superconducting nano-channels may be segmented into sections held at different electrical potentials by one or more power sources (not shown). Superconducting material 304 may comprise C60 hybrids or boron nitride. Superconducting nano-channel networks may be combined with conventional integrated circuit technology to fabricate integrated (nano and pico-beam) vacuum nano-electronic devices (both digital and analog). These devices may be used to generate and modulate nano and pico-electron beams for high-resolution imaging, or for gathering and processing information obtained from detectors and transducers. It will be apparent that although a two dimensional embodiment is depicted in FIGS. 10A and 10B, three dimensional embodiments may be readily fabricated wherein the substrate 302 has a three dimensional topography. FIGS. 11A, 11B, and 11C are schematic representations of embodiments of superconducting nano-channels having nano-scale superconducting rods. FIGS. 11A, 11B, and 11C illustrate preferred embodiments in which a superconducting nano-channel suitable for guiding and manipulating nano-electron beams and other charged particles may be formed by geometrically arranging nano-scale superconducting rods or wires around a central region. Referring to FIG. 11A, and in the embodiment depicted therein, rods 352 are provided with a substantially circular cross section. Rods 352 are arranged in physical contact with one another, around center rod 354. Referring to FIG. 11B, central rod 354 is removed to form a central superconducting nano-channel 356 bounded by superconducting rods 352. Electron beams or other charged particles may flow through channel 356. Referring to FIG. 11C, in an alternate embodiment comprising four rods 352, superconducting rods 352 arranged around central superconducting nano-channel 358, through which electron beams or other charged particles may flow. In the embodiment depicted in FIG. 11C, superconducting rods 352 are not in physical contact with one another. It is to be understood, that superconducting rods 352 may have cross sections other than a circular one. It is also to be understood that superconducting rods 352 may not be continuously straight along their length, they may or may not be solid in cross section, and may or may not be held at the same electrical potential by one or more power source (not shown) unless they are in electrical contact. Superconducting rods 352 may be coated with conductive material (not shown). Any suitable scaffold or similar device, many of which are known to those skilled in the art, may be used to hold superconducting rods 352 together. FIG. 12 is a schematic representation of a superconducting nano-channel having multiple layers. FIG. 12 illustrates a preferred embodiment in which a layer of superconducting material 404 is deposited on substrate 402. Referring to FIG. 12, a layer of non-conducting material 406 is deposited on top of superconducting layer 404. Another layer of superconducting material 408 is then deposited on top of non-conducting layer 406. Superconducting channels 410, 412, and 414 may be formed using conventional lithographic techniques. The relative degree of confinement of each superconducting nano-channels 410, 412, and 414 may be geometrically modulated to suit any particular application. For example, superconducting nano-channels 410 and 414 would be more strongly confining than superconducting nano-channel 412, due to the greater relative enclosure of superconducting material. On the other hand, charged particles 416 traveling through superconducting channel 412 will experience Meissner effect repulsion originating from the four quadrants 420, 422, 424, and 426. The structures described in this and other embodiments of this invention may be combined with conventional integrated circuits and micro electro-mechanical fabrication techniques to produce, but not limited to, imaging and detecting devices. FIGS. 13A and 13B are schematic representations of embodiments of a superconducting nano-channel split in the axial direction, i.e. parallel to the central axis of the nano-channel. FIGS. 13A and 13B illustrate a preferred embodiment in which the superconducting nano-channel is a superconducting nano-cylinder. Referring to FIG. 13A, superconducting nano-cylinder 450 is axially split into two half-cylinders 452 and 454 separated by a small gap 451. A layer of conductive material 456 and 458 may be applied to the inner surfaces of half-cylinders 452 and 454. Referring to FIG. 13B, a layer of insulating material 462 and 464 separates the inner surface of half-cylinders 452 and 454 and the layer of conductive material 456 and 458. A very small voltage provided by a power source (not shown) may be applied across conductive material 456 and 458. This arrangement would force charged particles traveling through superconducting channel 460 to orient with the electric field within superconducting channel 460 if the charge distribution of said traveling charged particles is in the least asymmetric. In another embodiment (not shown) superconducting nano-cylinder 450 may be twisted into other shapes, including a double helical slit, so as to impart a torque on particles traveling through superconducting channel 460. Alternatively, superconducting nano-cylinder 450 could be split in several places, creating a plurality of superconducting segments that could be driven by a polyphase AC signal to impart a torque on particles traveling through superconducting channel 460, but in a readily variable and electronically controlled fashion. An axial cylindrical split into ⅓ and ⅔ radial segments (with an optional helical twist) would xe2x80x9creflect backxe2x80x9d a non-uniform repulsive magnetic field. FIG. 14 is a schematic representation of a superconducting nano-channel connected to a support system. Referring to FIG. 14, there is depicted assembly 750, in which superconducting nano-wires are used to make superconducting loops 754, 756, and 758, which are connected to a support system 760. Superconducting loops 754, 756, and 758 constitute an approximation to a whole superconducting tube. Dividing a superconducting tube into a plurality of superconducting loops offers the same properties of a whole tube while providing additional means for shaping and modulating the charged particle beam. Charged particles 752 traveling through superconducting loops 754, 756, and 758 will experience Meissner effect (repulsion forces). Many other (not shown) wire-like and/or ribbon-like shapes, e.g., ellipses, semicircles, baseball seam curves, U-shaped loops, etc., may be configured as superconducting nano-channels approximations through which charged particles may travel. These shapes may additionally be electrically charged or magnetized (by running electrical currents through them), thereby affording a multiplicity of characteristic particle optical effects. Depending on the relative size and position of such shape superconducting elements relative to charged nano or picobeam trajectories, such shapes may be subject to electrostatic charging, which would alter their particle optical effects. Likewise, depending on the type of support structure used, such shapes may have predetermined discharge rates, and may be cross-coupled to other shapes. Furthermore, the anode currents of electrically split anodes in the path of deflectable charged picobeams may be used to differentially drive various electric or magnetic superconducting shapes, thus influencing the trajectory of the same or other charged nano or picobeams. The use of flexible shapes or flexible mounts adds another dimension of possibilities, both for simple deflection and for multiple mechanical resonance modes, especially since even very small motions can have a geometrically magnified leverage effect on charged nano or picobeams, or an exponentially magnified leverage effect on tunnel currents across small gaps. FIGS. 15A, 15B, and 15C are schematic representations of embodiments of superconducting nano-channels split into unequal portions. FIGS. 15A and 15B illustrate a preferred embodiments in which a superconducting cylinder 900, e.g., a superconducting nano-tube which is split into unequal portions along its length by straight split lines 906 and 908, which are parallel to central axis 901 of cylinder 900. FIG. 15B is a perspective view of the embodiment depicted in FIG. 15A. Referring to FIGS. 15A and 15B, superconducting cylinder 900 is split into a major superconducting segment 902 and a minor superconducting segment 904, which have different arc displacements but are of the same radius of curvature. Non-superconducting material in gaps 906 and 908 may be used to hold superconducting segments 902 and 904 together. FIG. 15C illustrates another embodiments in which a superconducting cylinder 950 is split into a major superconducting segment 902 and a minor superconducting segment 904 by non-straight split lines 910 and 912. Superconducting segment 952 and a minor superconducting segment 954 have different sizes and different shapes. Non-superconducting material may be used to hold superconducting segments 952 and 954 together as described previously. FIGS. 16A-16D are schematic representations of embodiments of merging superconducting nano-channels. In like manner, superconducting nano-channel approximations as described in the embodiment depicted in FIG. 14 may also be merged together. Merged superconducting nano-channels may be used to mix injected charged particles. They may also be used as transport assemblies for charged particles, or to modulate one charged particle beam with another. They may also be used to dynamically switch the trajectory of charged particles from one nano-channel to another. Referring to FIG. 16A, superconducting assembly 1000 is shown in which superconducting nano-channels 1002 and 1004, into which charged particle beams 1014 and 1016 are injected and mixed, are first merged together and then separated, forming exit superconducting nano-channels 1006 and 1008, from which charged particle beams 1018 and 1020 emerge. Electrical leads 1010 and 1012 may be used to provide electrical power supplied by a power source (not shown). FIG. 16B shows a sectional view of the merged superconducting nano-channels through line 16Bxe2x80x9416B of FIG. 16A. In the embodiment depicted in FIG. 16B, electrical conductors 1030 and 1032 located on the inner surface of superconducting assembly 1000 are provided. Referring to FIGS. 16A and 16B, by applying a potential difference to electrically isolated electrical conductors 1030 and 1032, charged particle beams 1014 and/or 1016 may have their exit trajectories switched between superconducting nano-channels 1006 and 1008 to emerge as charged particle beams 1018 or 1020. The walls of superconducting assembly 1000 as shown in FIG. 16A may be partitioned into nearly contiguous but electrically isolated segments, thus negating to need to have separate electrical conductors 1030 and 1032. FIG. 16C illustrates a preferred embodiment in which superconducting rods made of superconducting nano-wires are used to form an approximation to a superconducting nanotube, as previously described in the embodiments shown in FIGS. 11A-11C. Referring to FIG. 16C, superconducting nano-channel 1002 (see FIG. 16A) is approximated by superconducting rods 1042, 1044, 1046, and 1048, to define superconducting nano-channel 1050. Likewise, superconducting nano-channel 1004 (see FIG. 16A) is approximated by superconducting nano-rods 1052, 1054, 1056, and 1058 to define superconducting nano-channel 1060. Electron beams or other charged particles traveling through superconducting nano-channels 1050 and 1060 may be guided and manipulated, taking advantage of the Meissner effect (repulsion forces). Referring to FIG. 16D, cross sectional view of a superconducting nano-channel created by the merging of superconducting nano-channels 1002 and 1004 at a plane defined by line 16Bxe2x80x9416B (as shown in FIG. 16A) is replaced by the approximation defined by superconducting nano-channel 1062, which is created by superconducting rods 1042, 1044, 1046, 1048, 1052, 1054, 1056, and 1058, which in turn are positioned at the corner points of an octagon. An electrical voltage provided by a power source (not shown) may be applied to electrical conductors 1064 and 1068 to guide and manipulate electron beams or other charged particles traveling through superconducting nano-channel 1062. Superconducting nano-channel 1062 thus becomes a switching region where electron beams or other charged particles may be guided to the desired exit channels as described in the embodiment shown in FIG. 16A. FIG. 17 is a schematic representation of a superconducting nano-channel Y-junction. FIG. 17 illustrates a preferred embodiment in which superconducting glass capillaries may be used to guide and manipulate electron beams and other charge particles. Superconducting glass capillaries, with exit ports as small as about 10 nanometers, have an advantageously amorphous and anatomically smooth surface. They may be used for merging, for example, x-rays (both hard x-rays and soft x-rays) and electron beams (both nano and pico beams) or other charged particles. Superconducting glass capillaries may be able to produce geometric beam energy concentration gains on the order of 1000 or more. Referring to FIG. 17, there is shown a Y-shaped glass capillary 1100 having its inner surface coated with a glass layer 1114, and having its outer surface coated with a layer of superconducting material 1112. Superconducting glass capillary 1100 comprises entry ports 1104 and 1108, and a very narrow exit port 1116. A controllably, intermittent x-ray beam 1102 is introduced into port 1104 and is guided by glass layer 1114, while a controllably, intermittent electron beam or other charged particle beam 1106 is introduced into port 1108 by a side branch coupler (not shown) and is guided by superconducting material layer 1112. Charged particle beam 1106 is introduced at a suitable angle relative to x-ray beam 1102 in order to minimally impact and minimally intercept the x-ray beam 1102. After reaching the intersection area 1110 (i.e. shared space), both beams 1102 and 1106 begin to narrow their spread, before exiting the superconducting glass capillary 1100 through narrow exit port 1116. Both beams 1102 and 1106 are controllably turned ON and OFF by suitable means (not shown) to select which beam (mode) is in operation. These hybrid superconducting nano-channels, so described because of their ability to guide and manipulate a plurality of beams, may be used for multi-mode imaging, microanalysis, lithography and stereolitography. An application of how this mode switching may be used to perform two distinct functions almost simultaneously will be described as follows: in a first mode, charged particles might be guided and manipulated for imaging and identifying the topography or other feature of a substrate for subsequent x-ray irradiation by a second mode. In another application, electronic beams or other charged particle beams may be modulated over the shared space with intensely concentrated x-rays (or vice versa, with suitable adjustments of electron energy and nano-channel diameter). Additional interactions involving other types of charged particles or nano-particle beams, including transient electron states and ionization is to be considered within the scope of this invention. FIG. 18 is a schematic representation of a superconducting nano-channel with internal superconducting wires. FIG. 18 illustrates a preferred embodiment in which superconducting nano-channels have different diameters at their respective ends. In the case of unidirectional propagation, the beam input end has a larger diameter than the beam exit end. The larger diameter allows the superconducting nano-channels to internally accommodate a plurality of superconducting wires defining coaxial structures, which may be arranged in a straight, helical, or other suitable configurations. An electrical potential provided by a power source (not shown) may be applied to the coaxial structures to modulate the axial and radial velocity components of electron beams or other charged particles traveling through the superconducting nano-channel. Referring to FIG. 18, superconducting nano-channel 550 is shown having a beam input end 552 and a beam exit end 554. The diameter of beam input end 552 is larger than the diameter of beam output end 554. Beam input end 552 accommodates a coaxial structure comprising superconducting nano-wires 560. An electrical potential provided by an electrical source (not shown) and applied to superconducting nano-wires 560 may be used to modulate the axial and radial velocity components of electron beam or other charged particle beam 558 traveling through central channel 556. FIG. 19 is a schematic representation of a superconducting nano-channel as a field ionizer. FIG. 19 illustrates a preferred embodiment in which superconducting nano-channels are used as volcano field ionizers for magnetic nano-particles. Volcano field ionizers make use of a relatively small diameter hollow cathode tube for injecting materials into a region with a very high electric field gradient, which subsequently ionizes the injected materials. Referring to FIG. 19, superconducting nano-channel 606 is shown having an optional bend region 614. Superconducting nano-channel 606 comprises beam input end 610 and beam exit end (nozzle) 612. A beam of magnetic nano-particles 608 is injected into the superconducting nano-channel 606 through beam input end 610 and exits through nozzle 612. Electrodes 602 and 604 provide a large electrical potential difference between electrodes 602, 604 and nozzle 612. Said large electrical potential difference ionizes magnetic particles 608 in the vicinity of the high electric field region 616 of nozzle 612. Electrodes 602 and 604 may optionally be part of another follow-on superconducting-nano-channel segment. In another embodiment (not shown), superconducting nano-channels may be used to focus and guide traveling antiprotons for medical applications, such as killing tumors. A suitable liquid nitrogen capillary micro-transport system using a suitable aerogel-based super-insulation may be used for chilling the superconducting nano-channel. Thus, rather than having to use a high energy beam to hit the tumor from multiple angles (which damages other healthy tissue along each such pathxe2x80x94i.e. overshoot and undershoot), a single lower velocity beam could be delivered directly to the ultimate target by a thin superconducting nano- or micro-channel probe of the types described elsewhere in this specification. A low velocity beam could be more readily deflected (steered to target) at the tumor site by micro-deflection coils or micro-deflection electrodes than high velocity beams. Since the matter/anti-matter interaction region would thereby be highly localized, so too would the relative density and distribution of (e.g., gamma-ray) radiation of the anti-proton/proton annihilation. FIGS. 20A-20C are schematic representations of a superconducting nano-channel as a component of an acoustic wave detector system. FIGS. 20A-20C illustrate a preferred embodiment in which superconducting nano-channels may be used as integral components of an acoustic wave detector. If coherent (i.e. highly monochromatic and well collimated) electron beams or other charged particle beams or magnetic nano or pico-beams are injected into superconducting nano-channels that are deformable by acoustic waves, the acoustic waves produce pronounced perturbations in the electron beams or other charged particle beams or magnetic nano or pico beams as they travel through the superconducting nano-channel. The charged particles exit the superconducting nano-channel in a perturbed state. Referring to FIG. 20A, charged particle beam 1254 is injected and travels through superconducting nano-channel 1252, which is attached to support 1256. An end cap 1266 is used to cap superconducting nano-channel 1252 and to keep vacuum within region 1268 of superconducting nano-channel 1252. In the absence of acoustic waves, superconducting nano-channel 1252 remains motionless. Referring to FIGS. 20B and 20C, acoustic wave 1258 propagating in the direction shown by arrow 1260 will cause superconducting nano-channel 1252 to oscillate back and forth, thus deflecting the charged particle beams 1262 and 1264 as they exit superconducting nano-channel 1252. Position sensitive beam detectors (not shown) may be used to detect deflected beams 1262 and 1264 as they exit superconducting nano-channel 1252. These superconducting nano-channel configurations, which take advantage of deflected charged particles, may be used in analog signal processing devices, high-sensitivity and high-bandwidth nano-vibration sensors, pico-beam scanning and chopping operations, and the like. Furthermore, systems comprising superconducting nano-channels, in which deflected charged particles may be modulated, may be suitably mechanically loaded and mechanically driven for generating charged particle scanning patterns. The superconducting nano-channel structures of this invention, comprising carbon-based nanotubes or other types of nanotubes, may be used with microscopy probes. They may also operate with a miniature ultra-high vacuum enclosure with an electron-transparent widow. Furthermore, these structures may be combined with conventional integrated circuits and micro electro-mechanical fabrication techniques to produce, but not limited to, imaging and detecting devices. It is, therefore, apparent that there has been provided, in accordance with the present invention, a method and apparatus for guiding and manipulating electron beams or other charged particles. While this invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. |
|
abstract | An X-ray shield device according to one embodiment of the present invention comprises an X-ray shielding plate positioned between an X-ray source and a support member for a subject; a shielding plate driving mechanism including a supporting portion for supporting the X-ray shielding plate, the shielding plate driving mechanism being operable to move the shield plate supported by the supporting portion in a movement plane of the shielding plate perpendicular to a path of X-ray irradiation; and an X-ray shielding plate exchanging means for exchanging the X-ray shielding plate supported by the supporting portion for another X-ray shielding plate of different size. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.