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abstract | An ion source has an extraction system configured to produce ultra-short ion pulses, i.e. pulses with pulse width of about 1 μs or less, and a neutron source based on the ion source produces correspondingly ultra-short neutron pulses. To form a neutron source, a neutron generating target is positioned to receive an accelerated extracted ion beam from the ion source. To produce the ultra-short ion or neutron pulses, the apertures in the extraction system of the ion source are suitably sized to prevent ion leakage, the electrodes are suitably spaced, and the extraction voltage is controlled. The ion beam current leaving the source is regulated by applying ultra-short voltage pulses of a suitable voltage on the extraction electrode. |
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054935997 | summary | BACKGROUND OF THE INVENTION The present invention pertains to the art of reducing off-focal radiation and collimating in connection with x-ray generation. It finds particular application in conjunction with annular x-ray tubes for CT scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention will also find application in conjunction with the generation of radiation for other applications. Typically, a patient is positioned in a supine position on a horizontal couch through a central bore of a CT scanner. An x-ray tube is mounted on a rotatable gantry portion and rotated around the patient at a high rate of speed. For faster scans, the x-ray tube is rotated more rapidly. However, rotating the x-ray more rapidly decreases the net radiation per image. As CT scanners have become faster, larger x-ray tubes have been developed which generate more radiation per unit time to maintain the desired radiation dose at higher speeds. Larger tubes, of course, cause high inertial forces. High performance x-ray tubes for CT scanners and the like commonly include a stationary cathode and a rotating anode disk, both enclosed within an evacuated housing. As more intense x-ray beams are generated, there is more heating of the anode disk. In order to provide sufficient time for the anode disk to cool by radiating heat through the vacuum to surrounding fluids, x-ray tubes with progressively larger anode disks have been built. The larger anode disk requires a larger x-ray tube which does not readily fit in the small confined space of an existing CT scanner gantry. Particularly in a fourth generation scanner, incorporating a larger x-ray tube and heavier duty support structure requires moving the radiation detectors to a larger diameter. A longer radiation path between the x-ray tube and the detectors would require that the detectors be physically larger to subtend the required solid angle. Larger detectors would be more expensive. Not only is a larger x-ray tube required, larger heat exchange structures are required to remove the larger amount of heat which is generated. Rather than rotating a single x-ray tube around the subject, others have proposed using a switchable array of x-ray tubes, e.g. five or six x-ray tubes in a ring around the subject. See, for example, U.S. Pat. No. 4,274,005 to Yamamura. However, unless the tubes rotate, only limited data is generated and only limited image resolution is achieved. If multiple x-ray tubes are rotated, similar mechanical problems are encountered trying to move all the tubes quickly and remove all of the heat. Still others have proposed constructing an essentially bell-shaped, evacuated x-ray tube envelope with a mouth that is sufficiently large that the patient can be received a limited distance in the well of the tube. See, for example, U.S. Pat. No. 4,122,346 issued Oct. 24, 1978 to Enge or U.S. Pat. No. 4,135,095 issued Jan. 16, 1979 to Watanabe. An x-ray beam source is disposed at the apex of the bell to generate an electron beam which impinges on an anode ring at the mouth to the bell. Electronics are provided for scanning the x-ray beam around the evacuated bell-shaped envelope. One problem with this design is that it is only capable of scanning about 270.degree.. Still others have proposed open bore x-ray tubes. See, for example, U.S. Pat. No. 5,125,012 issued Jun. 23, 1992 to Schittenhelm and U.S. Pat. No. 5,179,583 issued Jan. 12, 1993 to Oikawa. These large diameter tubes are constructed analogous to conventional x-ray tubes with a glass housing and a sealed vacuum chamber. Such tubes are expensive to fabricate and are expensive to repair or rebuild in case of tube failure. Copending U.S. application Ser. No. 08/224,958 discloses a ring anode disposed in the housing. An annular rotor is rotatably received in the toroidal housing. At least one cathode is mounted on the rotor for generating an electron beam which strikes the anode target. The rotor and the cathode are rotated such that the electron beam is rotated around the ring anode. X-rays are emitted from a ring anode that is struck by energetic electrons from one of selected cathodes on the rotor. The more precisely the x-rays are collimated into a fan or other preselected shaped beam, the sharper and more artifact free the resultant CT images are. One consideration is the amount of off-focal radiation produced during generation of the x-ray beam. Off-focal radiation is produced primarily due to energetic backscattered electrons whose energy is comparable to x-rays in locations off of the focal spot. The backscattered electrons tend to cause x-rays to be generated from broad areas of the x-ray anode and any surrounding material that may be at a positive potential relative to the cathode. Off-focal radiation has a negative effect on the image quality of x-ray images, particularly the reconstructed CT images. The off-focal radiation is a broad source of radiation that tends to blur in CT images and to cause more pronounced artifacts in the region of the interface of high and low contrast objects. Moreover, a fixed collimator attached to the rotating frame within the vacuum enclosure is one method that can create the required fan beam of x-rays. This approach is most effective for fixed single or multiple slice applications in which each cathode assembly has an individual collimator. It is difficult and inconvenient to adjust collimators within a high vacuum. Mechanical adjustment mechanisms increase a risk of vacuum contamination. The present invention contemplates a new and improved toroidal x-ray tube and CT scanner which resolves the above referenced difficulties and others. SUMMARY OF THE INVENTION A large diameter toroidal housing is provided. An annular anode is mounted in the evacuated annular interior of the housing along with a rotating frame assembly. At least one cathode assembly is mounted to the rotating frame for rotation therewith. In accordance with another aspect of the present invention, a pre-collimator is supported in the interior of the housing. The pre-collimator has a slot for passage of the x-ray beam subsequent to generation thereof. In accordance with a more limited aspect of the present invention, the pre-collimator is mounted on the rotating frame in alignment with at least one cathode assembly. In accordance with a more limited aspect of the present invention, a second pre-collimator is supported by the anode. The second pre-collimator includes a second slot for passage of the x-ray beam. In accordance with another aspect of the present invention, a ring collimator is supported on the exterior of the housing inside the patient aperture for collimating the beam into a fan-shaped beam. The collimator comprises a first ring and a second ring. In accordance with a more limited aspect of the present invention, the x-ray tube is further provided with an arrangement for adjusting the distance between the first and second rings. In accordance with another aspect of the present invention, the toroidal x-ray tube is incorporated into a CT scanner. One advantage of the present invention is that it reduces off-focal radiation. Another advantage of the present invention is that it produces improved CT images with minimal blurring and artifacts particularly in the region of the interface of high and low contrast objects. Another advantage of the present invention is that it reduces x-ray bremsstrahlung, undesired deflected electrons, produced if backscattered electrons strike material in the solid angle viewed by the x-ray detection system. Yet another advantage of the present invention resides in improved collimation. Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. |
043607365 | summary | TECHNICAL FIELD This invention relates to radiation shields of the type comprising a container formed of thin flexible material filled with a radiation attenuating liquid. BACKGROUND OF THE PRIOR ART Radiation shields of the type comprising a container formed of thin flexible material filled with a radiation attenuating liquid were originally disclosed in my U.S. Pat. No. 4,090,087, issued May 14, 1978. Such radiation shields have come into widespread use. However, despite their popularity, their use has presented certain problems. Radiation shields of this type now in use are simply dunnage bags--that is, large rubber bags somewhat similar in appearance to water mattresses. Such shields are satisfactory for most purposes, but they have presented some problems where dimensional accuracy and dimensional stability are problems. That is because the surfaces of the shields tend to bulge in a non-uniform and somewhat unpredictable fashion when the shield is filled with a radiation attenuating liquid. OBJECTS OF THE INVENTION It is, therefore, a general object of the invention to provide a radiation shield which will obviate or minimize problems of the type previously described. It is a particular object of the invention to provide a radiation shield which maintains its dimensional accuracy and dimensional stability when the shield is filled with a radiation attenuating liquid. Other objects and advantages of the invention will become apparent from the detailed description of a preferred embodiment given hereinafter. BRIEF SUMMARY OF THE INVENTION The invention is a radiation shield for use in installations containing sources of radiation. The radiation shield comprises a container formed of thin flexible material and means connecting opposing walls of the container to maintain the distance therebetween when the container is filled with a radiation attenuating liquid. Preferably, the means are either drop stitches or wing tabs. |
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abstract | A method of creating writing data for writing a pattern on a target workpiece by using a writing apparatus provided with a plurality of columns that emit charged particle beams includes inputting information on distance between optical centers of the plurality of columns, inputting layout data and virtually dividing a writing region indicated by the layout data into a plurality of small regions, by a width of one integer-th of the distance indicated by the information on distance, converting, for each small region, the layout data to a format adaptable to the writing apparatus to create, for the each small region, the writing data whose writing region is divided into the small regions, and outputting the writing data. |
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description | This application is a 371 of PCT Application No. PCT/CA2018/050098, filed on Jul. 26, 2018, which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/450,935, filed on Jan. 26, 2017. The entirety of the contents of the referenced applications are hereby incorporated by reference. The invention relates to an exit window for an electron beam used for isotope production. Commercial radioisotopes, such as 99Mo/99mTc, which is used as a radiotracer in nuclear medicine diagnostic procedures, are produced using nuclear fission based processes. For instance, 99Mo can be derived from the fission of highly enriched 235U. Due to nuclear proliferation concerns and the shutdown of nuclear facilities used for producing commercial radioisotopes, alternative systems and methods are being used for producing commercial radioisotopes without the use of nuclear fission. One such method is the use of a high energy electron linear accelerator to produce nuclear reactions within a target material through one or more reaction processes. Use of this method to produce molybdenum-99 and the systems used to produce molybdenum-99 through this method are described in Patent Cooperation Treaty Application Nos. PCT/CA2014/050479 and PCT/CA2015/050473, the entirety of which are hereby incorporated by reference. High energy electron beams produced from an electron linear accelerator may be used for material processing (transformation or transmutation) at the nuclear level utilizing a variety of nuclear reactions. Isotopes of an element may be produced in this manner. As linear accelerators must operate in an evacuated atmosphere (i.e., under vacuum) and the processed material must be cooled to dissipate the heat caused by some of the nuclear reactions and interactions, a suitable electron beam exit window is required to separate the two environments. Some high power electron beam windows are thin metal foil designs with many variations in layers, coatings and support structures. Thin foils are used for a variety of reasons, such as to increase the size of the window to allow the electron beam to be swept across the window, to reduce the attenuation of the electron beam by the window, and to reduce the nuclear interactions with the window itself. As a linear accelerator produces a small axial pulsed electron beam, sweeping of the electron beam allows larger processing volumes and reduces hot spots on the window foil. Electron beam attenuation is detrimental to many electron processing technologies due to lost efficiency and the nuclear interactions with the window cause a downstream radiation shower, dynamic thermal stresses, and potential cooling challenges, all of which are proportional to the window thickness. While the foil designs evolved to meet the current lower energy, non-nuclear reaction producing, electron beam process requirement, they were not designed for high energy electron beam isotope production utilizing the Bremsstrahlung radiation shower. As the foil windows tend to be thin structures, they cannot withstand high pressure differentials across them. Most electron beam processing is done without forced or pressurized cooling of the target medium as the absorbed power density is much lower. The foils suffer fatigue failure due to high dynamic thermally induced stresses caused by the pulsed electron beam. Accordingly, a solution that addresses, at least in part, the above and other shortcomings is desired. According to one aspect of the invention, there is provided an exit window for an electron beam from a linear accelerator for use in producing radioisotopes. The exit window comprises a cylindrical channel operatively connectable at one end to a vacuum chamber configured for travel of the electron beam; a domed dished head at the other end of the channel, the dished head comprising a convex portion having a protruding crown configured for pass-through of the electron beam wherein the geometry of the domed dished head is proportioned to resist pressure stress created by cooling medium circulating around the protruding crown and the vacuum in the cylindrical channel and maintain the combined thermal and pressure stress below the fatigue limit of the material forming the exit window. In some embodiments, the domed dished head has an ellipsoidal profile. In some embodiments, the domed dished head has a torispherical profile. In some embodiments, the domed dished head has a recessed crown radii that is 125% to 80% of the cylindrical channel's diameter. In some embodiments, the domed dished head has an inner knuckle radii that is 20% to 40% of the cylindrical channel's diameter. In some embodiments, the domed dished head has a recessed crown radii of 12 mm. In some embodiments, the domed dished head has an inner knuckle radii of 2.7 mm. In some embodiments, the domed dished head has an inner knuckle radii that is 30% to 6% of the cylindrical channel's diameter. In some embodiments, the protruding crown has a circular or generally oval shape. In some embodiments, the protruding crown comprises a plurality of raised portions, each of the raised portions having a smaller diameter as the protruding crown extends outwards. In some embodiments, the exit window is a single integral piece. In some embodiments, the exit window comprises beryllium, copper, steel, stainless steel, titanium, alloys or any of the foregoing, or a combination of any of the foregoing. In some embodiments, the exit window comprises Ti-6Al-4V. In some embodiments, the cylindrical channel has a diameter of 6-10 mm. In some embodiments, the cylindrical channel has a diameter of 10-20 mm. In some embodiments, the linear accelerator is capable of producing an electron beam having an energy of at least 10 MeV to about 50 MeV. In some embodiments, the linear accelerator is capable of producing an electron beam having at least 5 kW of power to about 150 kW of power. In some embodiments, the electron beam passing through the protruding crown has an energy of a least 30 MeV. In some embodiments, the exit window is removably mountable to a window flange. In some embodiments, the combined pressure stress resulting from the cooling medium and thermal stress resulting from pulsed electron beam heating of the exit window is kept below the fatigue limit of the exit window. In some embodiments, compressive stresses from a pressure differential resulting from the cooling medium and the vacuum partially offset tensile stresses on the exit window caused by heating by the electron beam. In some embodiments, the protruded crown has a thickness of about 0.15 mm to about 0.75 mm. In some embodiments, the protruded crown has a thickness of about 0.35 mm. In some embodiments, the pressure differential created by the cooling medium and the vacuum is at least 690 kPa. In some embodiments, the pressure differential created by the cooling medium and the vacuum is between 100 kPa to 2000 kPa. In some embodiments, the linear accelerator is capable of pulsing the electron beam at 1-600 hertz. In some embodiments, the exit window is shaped to fit into a converter target holder. In some embodiments, the exit window is shaped to fit into a production target cooling tube. In some embodiments, the converter target holder holds Tantalum (Ta) target discs. In some embodiments, the radioisotope comprises molybdenum-99 (99Mo). In some embodiments, the exit window is mountable to a mating flange utilizing a Conflat™ style knife edge vacuum sealing method. In some embodiments, the exit window is mountable for utilizing welding or brazing techniques. In the description which follows, like parts are marked throughout the specification and the drawings with the same respective reference numerals. The description which follows and the embodiments described therein are provided by way of illustration of an example or examples of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation and not limitation of those principles and of the invention. In some instances, certain structures and techniques have not been described or shown in detail in order not to obscure the invention. The embodiments described herein relate to an exit window for an electron beam from a linear accelerator for use in producing radioisotopes. The exit window comprises a cylindrical channel operatively connectable at one end to a vacuum chamber configured for travel of the electron beam; and a domed dished head at the other end of the channel. The domed dished head comprises a convex portion having a protruding crown configured for pass-through of the electron beam wherein the geometry of domed dished head is proportioned to resist pressure stress created by cooling medium circulating around the protruding crown and the vacuum in the cylindrical channel and to maintain combined thermal and pressure stresses below the fatigue limit of the material of construction of the exit window. Isotopes of an element may be produced by ejecting a neutron from the nucleus of the atom by bombarding the atom with relativistic high energy photons, also referred to as gamma radiation. This process is known as the photoneutron or the gamma, neutron (γ, η) reaction. The energy of the incident photons exploits the giant resonance neutron peak of the atoms and is typically between 10 and 30 million electron volts (MeV). The incident photons are produced from the interaction of high energy electrons with a converter target or the production target matter. The high energy electrons originate from an electron linear accelerator. The linear accelerator produces bunched packets of electrons with a speed approaching that of the speed of light at a pulse rate up to the kilohertz (kHz) range. Once the electrons packets strike the target matter, a radiation shower develops. Of the various nuclear interactions that occur in this shower, high energy photon production is one of them. The electron beam passing through the exit window is produced by a linear accelerator. The linear accelerator is a linear particle accelerator that increases the velocity of charged subatomic particles by subjecting the particles to a series of oscillating electric potentials along a linear beamline. Generation of electron beams with a linear accelerator generally requires the following elements: (i) a source for generating electrons, typically a cathode device, (ii) a high-voltage source for initial injection of the electrons into, (iii) a hollow pipe vacuum chamber whose length will be dependent on the energy desired for the electron beam, (iv) a plurality of electrically isolated cylindrical electrodes placed along the length of the pipe, and (v) a source of radio frequency energy for energizing each of cylindrical electrodes. The high energy particles generated by the linear accelerator cause photonuclear reactions to occur within the targets. In some embodiments, the photonuclear reaction comprises a photoneutron reaction. In some embodiments, the photonuclear reaction comprises a photofission reaction. In some embodiments, the photonuclear reaction comprises a photodisintegration reaction. In some embodiments, the photonuclear reaction comprises one or more of photoneutron, photofission, and photodisintegration reactions. FIGS. 1A to 1C illustrate an embodiment of the exit window according to the present disclosure. Exit window 10 comprises a channel 40 leading to a domed dished head 14 on one side. The domed dished head 14 comprises convex portions 20 and 22 (corner knuckle) and concave portions 24 and 25 (inner knuckle). When installed onto the converter target holder, the convex portions 20 and 22 of exit window 10 faces the cooling medium that is used to cool the targets, such as Mo100 or Tantalum (Ta) targets, and the like, held in the converter target holder. The concave portions 24 and 25 face the vacuum in the channel 40 through which the electron beam 68 travels. In the illustrated embodiment, the convex portions 20 and 22 form a protruding crown 28 through which the electron beam 68 travels and corner knuckle 22 transitions from the protruding crown 28 to the outer channel portion 30. The concave portions 24 and 25 comprise a recessed crown 32 through which the electron beam 68 travels and an inner knuckle 25 that transitions from the recessed crown 32 to the inner channel portion 16. In this embodiment, exit window 10 has a cross-sectional shape that is externally torispherical (the crown radii and the corner knuckle radii). In some embodiments, exit window 10 has a cross-sectional shape that is externally generally hemispherical or ellipsoidal. In some embodiments, exit window 10 has a cross-sectional shape for fitting onto a converter target holder. Exit window 10 is removably couplable onto the converter target holder. In the illustrated embodiment, exit window 10 comprises fastener channels 12. Fasteners can be inserted through fastener channels 12 to mount exit window 10 within a converter target holder. In some embodiments, exit window 10 comprises fasteners for fastening it onto a converter target holder. In this embodiment, the fastener channels 12 are cylindrical channels having a circular cross-section. In other embodiments, the fastener channels 12 comprises channels having different cross-sectional shapes. In some embodiments, the exit window 10 could be fastened or welded directly into the production target cooling tube. In some embodiments, exit window 10 can be mounted within a converter target holder using any methods known to a person skilled in the art. In the illustrated embodiment, the domed dished head 14 has a torispherical profile having defined crown radii and knuckle radii. In some embodiments, the recessed crown 32 has a radii of 12 mm. In some embodiments, the inner knuckle 25 has a radii of 2.7 mm. In some embodiments the protruding crown 28 has a radii of 24 mm and the corner knuckle 22 has a radii of 5.4 mm. In some embodiments, the diameter of the cylindrical channel is at or between 6-10 mm. In some embodiments, the diameter of the cylindrical channel is at or between 10-20 mm. In some embodiments, the domed dished head 14 has an ellipsoidal profile. In some embodiments, the ellipsoidal profile has an inner minor diameter of 8 mm and an inner major diameter of 10 mm. In some embodiments, the domed dished head 14 has an inner knuckle radii of 30% to 6% of the diameter of the cylindrical channel. In the illustrated embodiment, the geometry of the domed dished head 14 is proportioned to resist pressure stress created by cooling medium circulating around the convex portions 20 and 22 and the vacuum in the channel 40 and to maintain the combined pressure and thermal stress below the fatigue limit of the material. The exit window 10 is proportioned so that the electron beam 68 passes through the recessed crown 32 and then protruding crown 28. When positioned within the converter target holder 60, the cooling medium flows around the outside of the convex portions 20 and 22 of the exit window 10 and the external major diameter of the exit window 10. The combined mechanical and thermal stress resulting from the pressure differential across the exit window 10 and the heat from the electron beam 68 passing through the exit window 10 are kept below the fatigue limit of the material. Positioning the exit window 10 so that the convex portions 20 and 22 are subject to the higher pressure may reduce the overall stress regime of exit window 10 during operation. The compressive stress from external pressure may also offset the tensile stress caused by electron beam 68 heating of the exit window 10. The exit window 10 also has to separate the linear accelerator vacuum from a pressurized cooling medium or liquid target medium (i.e., greater than atmospheric pressure) and withstand the pressure differential created by the cooling medium and the vacuum. In some embodiments, exit window 10 can withstand a pressure differential that is less than 690 kPa. In some embodiments, exit window 10 can withstand a pressure differential equal to or greater than 690 kPa. In some embodiments, exit window 10 can withstand a pressure differential that is at or between the range of 100 kPa to 2000 kPa. In the embodiment illustrated in FIGS. 1A-1C, exit window 10 comprises portions for effecting a vacuum seal across the back flange of the exit window 10. In this embodiment, exit window 10 comprises circular cut-outs 26a and 26b which are shaped to fit a gasket, which may be made of copper or other materials known to a person skilled in the art. In this embodiment, the vacuum seal is formed using a Conflat™ knife edge flange. The knife edge cuts into the copper gasket to effect the vacuum seal. In some embodiments, exit window 10 is mountable for utilizing welding or brazing techniques. In the illustrated embodiment, protruding crown 28 has a circular cross-sectional shape. In some embodiments, protruding crown 28 has a generally oval cross-sectional shape. In some embodiments, protruding crown 28 has an elliptical cross-sectional shape. In some embodiments, the convex portions 20 and 22 of exit window 10 are polished to reduce the likelihood of surface cracks developing in the exit window 10 due to high cycle fatigue. In some embodiments, the concave portions 24 and 25 of exit window 10 are polished to reduce the likelihood of surface cracks developing in the exit window 10 due to high cycle fatigue. The polishing may be done using steel wool and polishing compound and then polishing compound as applied to a buffing cloth. The exit window 10 is formed of a material that is of lower cost, has high machinability, is resistant to aggressive media, has high tensile strength at elevated temperatures, and has a predictable fatigue limit, or a combination of any or all of the foregoing. In one embodiment, the exit window is formed of Ti-6Al-4V. In some embodiments, the exit window 10 is formed of beryllium, copper, steel, stainless steel, titanium, alloys of any of the foregoing, or a combination of any of the foregoing. Other metal, metal alloys, or materials known to a person skilled in the art could be used provided the metal, metal alloy, or material is compatible with the cooling medium and the stress levels on the exit window 10 remain below the fatigue limit of the material at temperature. In the illustrated embodiment, the exit window 10 is located between an evacuated linear accelerator or a linear accelerator antechamber and a pressurized fluid cooled target. In the embodiments with a liquid target, the exit window 10 is configured to contain the liquid itself. In some embodiments, the exit window 10 can withstand cooling medium or liquid target medium that is aggressive. In some embodiments, the cooling medium or liquid target medium is oxidizing. In some embodiments, the cooling medium or liquid target medium is acidic. In some embodiments, the cooling medium or liquid target medium is de-ionized. In the illustrated embodiment, the electron beam 68 from the linear accelerator is stationary and not swept. In some embodiments, the electron beam 68 has an energy of at least 30 MeV, which is much higher than most commercial processing installations (e.g., less than 10 MeV). In some embodiments, the linear accelerator is capable of producing an electron beam having at least 5 kW of power to about 150 kW of power and to produce a flux of at least 10 MeV to about 50 MeV bremsstrahlung photons. In some embodiments, the linear accelerator is capable of producing an electron beam having about 150 kW of power. In some embodiments, the electron beam is a pulsed beam. In some embodiments, the linear accelerator is capable of pulsing the electron beam at 1 to 600 hertz. In the illustrated embodiment, exit window 10 can withstand the cyclic temperature fluctuations caused by the pulsed electron beam 68. The exit window 10 in the illustrated embodiment has a geometry which allows the structure of exit window 10 to flex outward from internal heating of the exit window 10 induced by the electron beam 68 and to flex inward from external pressure, such as the pressure from the pressurized cooling medium or liquid target medium. The geometry of exit window 10 as described in the illustrated embodiments allows the exit window 10 to withstand the pressure differential between 100 kPa to 2000 kPa. In some embodiments, the thickness of the portion of the protruding crown 28 through which the electron beam 68 passes is at least 0.35 mm. In some embodiments, the thickness of the portion of the protruding crown 28 has a varying thickness in the range of 0.15 mm to 0.75 mm. In some embodiments, the thickness of the outer channel portion 30 is 0.75 mm. Varying the thickness of the protruding crown 28 allows exit window 10 to flex under stress while maintaining the stress under the fatigue limit of the material of exit window 10. Different portions of exit window 10 may have different thicknesses depending on the pressure of the pressurized cooling medium or target medium and the temperature fluctuations due to heating induced by electron beam 68. FIG. 2 illustrates the exit window 10 fitted into the converter target holder 60. In one embodiment, the exit window 10 is mounted to a flange that utilizes a Conflat™ style knife edge vacuum sealing method. In some embodiments, there is a copper gasket in between the two knife edges. In some embodiments, other vacuum sealing methods known to a person skilled in the art may also be used. In some embodiments, the window flange is replaceable. In some embodiments, exit window 10 is fully welded onto converter target holder 60. In some embodiments, graphite ring seal may be used for connecting the exit window 10 to converter target holder 60. The converter target holder 60 is operatively connected to piping 62 that allows cooling medium to travel into the converter target holder 60. In this embodiment, the exit window 10 is fitted into the converter target holder 60 and electron beam 68 is directed through the exit window 10 and into converter target holder 60. Conflat™ flange 64 seals the converter target assembly into the vacuum chamber and fitting 66 connects the water supply to the converter target assembly. In the illustrated embodiment, the commercial radioisotope comprises molybdenum-99 (99Mo) and the targets comprise molybdenum-100 (100Mo) or Ta target discs. In some embodiments using the photo-neutron reaction, the commercial radioisotope comprises 47Sc, 67Cu, or 88Y and the corresponding targets comprise 48Ti, 68Zn, or 89Y. In some embodiments using the neutron capture reaction, the commercial radioisotope comprises 32P, 46Sc, 56Mn, 75Se, 90Y, 166Ho, 177Lu, 192Ir, 198Au and the corresponding targets comprises 31P, 45Sc, 55Mn, 74Se, 89Y, 165Ho, 176Lu, 191Ir, 197Au. In some embodiments, using the photo-fission reaction, the commercial radioisotope comprises 99Mo from photon induced fission of 238U or neutron induced fission of 235U from ejected neutrons. In some embodiments, converter target holder 60 comprises the bremsstrahlung converter station 70 as described in PCT Patent Application Nos. PCT/CA2014/050479 and PCT/CA2015/050473. Testing of an embodiment of the exit window 10 was conducted over multiple linear accelerator runs with varying power levels and run durations. All tests were conducted by confirming proper vacuum conditions in the vacuum chamber and establishing cooling water flow over the back of the exit window 10. The linear accelerator is turned on and beam power is increased from 1 kW to the target power level in 2 kW to 5 kW increments averaging two minutes between each increment. Initial testing was conducted at power levels ranging from 1 kW to 24 kW and durations of beam pulsing from under an hour to approximately ten hours. Further testing was done with 72 hour endurance runs conducted at 24 kW beam power and at 30 kW beam power. With these tests, an embodiment of the exit window 10 was subject to 370 million electron beam pulses, at beam power ranging from 1 kW to 30 kW, and exit window 10 did not suffer any cracks or damage to its structural integrity as a result of such electron beam pulsing and the high cycle stresses created by such pulsing. This embodiment of exit window 10 was subject to a further 90 million electron beam pulses, totalling 460 million electron beam pulses, at beam power ranging from 1 kW to 30 kW, and such embodiment did not suffer any cracks or damage to its structural integrity as a result of such electron beam pulsing and the high cycle stresses created by such pulsing. The methods and systems disclosed herein may provide some advantages: By employing a domed dished head profile, the exit window 10 can have a lower thickness which can lower thermal stress on the exit window 10 caused by the electron beam. While the illustrated embodiment has a cylindrical channel, the channel may have other shapes that allow pass-through of the electron beam. The geometry of the exit window 10 can provide flexibility to allow the exit window 10 to maintain lower stress levels as the exit window 10 contracts and expands as a result of the pressure differential and the temperature fluctuation caused by the pulsed electron beam, respectively. Exit window 10 lasts longer when compared to a chemical vapor deposition diamond exit window, resulting in increased production and reduced downtime. For example, a 600 Hz pulsed electron beam would cause a typical exit window (without the features of exit window 10) to fail in around 10,000,000 cycles, or 4.6 hours. For isotope production, this translates to less radioactive waste and less radiation dose to workers who have to replace or handle the activated components. Where a component is referred to above, unless otherwise indicated, reference to that component should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention. Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments. The embodiments of the invention described above are intended to be exemplary only. Those skilled in this art will understand that various modifications of detail may be made to these embodiments, all of which come within the scope of the invention. |
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055815928 | description | DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION FIG. 1 is a sectional side view of a radiographic imaging arrangement. A tube 1 generates and emits x-radiation 2 which travels toward a body 3. Some of the x-radiation 4 is absorbed by the body while some of the radiation penetrates and travels along paths 5 and 6 as primary radiation, and other radiation is deflected and travels along path 7 as scattered radiation. Radiation from paths 5, 6, and 7 travels toward a photosensitive film 8 where it will become absorbed by intensifying screens 9 which are coated with a photosensitive material that fluoresces at a wavelength of visible light and thus exposes photosensitive film 8 (the radiograph) with the latent image. When an anti-scatter grid 10 is interposed between body 3 and photosensitive film 8, radiation paths 5, 6, and 7 travel toward the anti-scatter grid 10 before film 8. Radiation path 6 travels through translucent material 11 of the grid, whereas both radiation paths 5 and 7 impinge upon absorbing material 12 and become absorbed. The absorption of radiation path 7 constitutes the elimination of the scattered radiation. The absorption of radiation path 5 constitutes the elimination of part of the primary radiation. Radiation path 6, the remainder of the primary radiation, travels toward the photosensitive film 8 and becomes absorbed by the intensifying photosensitive screens 9 that fluoresce at a wavelength of visible light and thus exposes photosensitive film 8 with the latent image. FIG. 2 is a sectional side view a portion of an anti-scatter x-ray grid 10. As discussed above, an important parameter in the design is the grid ratio r, which is defined as the ratio between the height h of the x-ray absorbing strips 12 and the distance d between them. For medical diagnostic radiography the ratios generally range from 2:1 to 16:1. Another interdependent variable in the design parameters is the line rate of strips per centimeter. An absorbing strip must be thin enough to permit the total combined thicknesses of the strips and the distances between them to fit within a given centimeter and provide the predetermined line rate. Typically, line rates vary from 30 to 80 lines per centimeter and the absorbing strips have a width w along the sectional side view on the order of 15 to 50 .mu.m. Using the present invention, higher line rates (up to about 300) can be achieved, and therefore image contrast can be improved. FIGS. 3 and 4 are front and sectional side views respectively of a cutting blade 21. FIG. 5 is a partial perspective view of a channel through a substantially non-absorbent substrate. According to an embodiment of the present invention, an anti-scatter x-ray grid is fabricated by cutting the surface of a solid sheet of non-absorbent substrate material 11 to form the desired plurality of linear absorber channels of the desired dimensions. The substrate may comprise any substantially non-absorbent material having appropriate structural and thermal properties to withstand further processing and use. The words "substantially non-absorbent" mean that the substrate thickness and material are sufficient to prevent substantial attenuation of x-radiation such that at least 85% (and preferably at least 95%) of the x-radiation will pass through the substrate. In one embodiment the substrate comprises a plastic such as Ultem.RTM. polyetherimide (Ultem is a trademark of General Electric Co.). Other examples of appropriate substrate material include substantially non-absorbent polyimides, polycarbonates, other polymers, ceramics, woods, graphite, glass, metals, or composites thereof. The substrate may further include filler material such as particles or fibers including carbon, glass, or ceramic, for example, which can be useful to provide proper mechanical characteristics. The substrate provides structural support for the grid, and plastic materials are particularly useful because they absorb less radiation than aluminum strips. The saw may comprise a blade adapted to cut appropriately thin and deep channels in substrate 11. Examples of such saws 21 include saws of the type used in the semiconductor industry for dicing silicon wafers such as manufactured by Tokyo Seimitsu of Japan and Semitec of Santa Clara, Calif., for example. A thin blade portion 20 extends from a thicker inner portion 22 which is rotated about an axis 24. Preferably, the blade thickness ranges from about 15 to 70 .mu.m SO that these saws can provide desired line rates. In one embodiment the blade comprises a diamond-coated resin. Other materials appropriate for the saw blades include, for example, materials such as metals or resins having hard carbide coatings such as silicon or tungsten carbide. Either a plurality of blades can be arranged side by side to cut the channels simultaneously or a single blade can cut each of the channels sequentially. If the blade is not of sufficient depth, then one fabrication technique is to turn the substrate over and cut on the opposite surface of the substrate to form a channel having two portions 26a and 26b such as shown in FIG. 5a. Preferably, for ease of later fabrication, channels do not extend completely through the substrate. The channel configuration may be one of several types. In one embodiment, the channels are each perpendicular to the surface of the substrate. In another embodiment, some of the channels are at a predetermined angle to the surface to form a focused grid. Commercially available cutting saws typically cut perpendicular to flat substrates. If an angle is desired, the angle can be obtained, for example, as shown in the embodiment of FIG. 6, which is a sectional side view of a substrate support surface which is rotatable for providing the desired angle of substrate channel. Even if angled channels are not desired, a movable support table for use under the substrate such as available from Anorad Corporation of Hauppaugue, N.Y., is useful because blades for cutting semiconductor wafers are not always large enough (or do not always have enough range of motion) to create the desired length of channels. The channels are not limited to the rectangular shapes obtainable with the above described cutting saw. The channels can alternatively be round or comprise other types of cavities and can be formed by any of a number of methods such as etching, molding, heat deforming and/or reforming, milling, drilling, or any combination thereof. After the channels are formed, absorbing material 12, which is substantially absorbent, is applied to the channels. The words "substantially absorbent" mean that the thickness and material density are sufficient to cause substantial attenuation of x-radiation such that at least 90% (and preferably at least 95%) of the x-radiation will be absorbed. In one embodiment of the present invention, the channels are filled under vacuum conditions with an absorbing material that can be readily melt-flowed into the channels. In a preferred embodiment the absorbing material comprises a lead-bismuth alloy. Other substantially absorbent materials can include metals such as lead, bismuth, gold, barium, tungsten, platinum, mercury, thallium, indium, palladium, silicon, antimony, tin, zinc, and alloys thereof. The substrate material and absorbing material must be chosen so that the substrate material is able to withstand the temperatures required for melting and flowing the absorbing material during the amount of time required for the fabrication process. FIG. 7 is a sectional side view of the channel 26 coated with an optional adhesion promoting material 34. To aid in the adhesion of the absorbing material, the adhesion promoting material can be formed on the channel surfaces. In one embodiment, copper is coated to a sufficient thickness to provide a substantially continuous coating on the channel surfaces. Other appropriate adhesion promoting materials include nickel and iron, for example. Any residual adhesion promoting material on an outer surface of the substrate can be removed either at this time or at a later time simultaneously with residual absorbing material. FIG. 8 is a view similar to that of FIG. 7 after the channel has been filled with the absorbing material. An alloy commercially available from Belmont Metals of Brooklyn, N.Y., has a eutectic at 44% lead-56% bismuth with a melting point of 125.degree. C. Ranges of 40% lead-60% bismuth through 50% lead-50% bismuth would also be advantageously close to the eutectic. This is the preferred filling material since it forms a low melting point eutectic and it has a mass absorption coefficient of 3.23 at 125 KeV, which is superior to that of pure lead (3.15 at 125 KeV). The use of a plastic non-absorbent substrate material with a lead-bismuth absorbing material is advantageous because the substrate remains stable at the low melting point of the absorbing material. Any residual adhesion promoting material and/or non-absorbing material remaining on the outer surfaces of the substrate can be removed by a technique such as polishing, milling, or planing, for example. Any of a variety of finishing techniques such as polishing, painting, laminating, chemical grafting, spraying, gluing, or the like, may be employed if desired to clean or encase the grid to provide overall protection or aesthetic appeal to the grid. FIG. 9 is a view similar to that of FIG. 8 after the surfaces of the substrate and absorbing material are coated with a protective layer 38. The protective layer may comprise similar materials as those described with respect to the substrate. In one embodiment, protective layer 38 comprises a plastic such as polyetherimide. The protective layer comprises substantially non-absorbent material and helps to protect the substrate and absorbing material surfaces from scratches. Furthermore, the protective layer is useful for safety concerns when the absorbing material includes a metal such as lead. EXAMPLE A grid prototype of a substrate comprising Ultem polyetherimide 1000 was made using a precision dicing saw where a 10.times.10.times.0.5 cm sample was cut on one face to produce channels in the surface that had a width w of 50 .mu.m, a height h of 600 .mu.m and a length 1 of 10 cm (w, h, and I shown in FIG. 5), and such that the line rate was 67 lines/cm, the lines being equally spaced to give a grid ratio of 6:1. The substrate was then vacuum filled with the 44% lead-56% bismuth alloy at 140.degree. C. by immersing the substrate into the molten metal and subjecting it to a pressure of less than 10 Torr. The substrate was removed and allowed to cool to ambient temperature and was then polished smooth to remove any excess or stray metal. The device was examined microscopically, and the channels were found to be completely and uniformly filled. The device of the present invention is reworkable in that the absorbing material which is not completely or properly flowed in the channels can be removed by heating the assembly and reflowing the absorbing material. Furthermore, this feature can be used to reclaim (remove) the absorbing material before later disposal of any grids. This removal capability is advantageous, especially in situations where lead may cause a safety-related concern and in situations where recycling of the substrate material is desired. While only certain preferred features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. |
abstract | A radiation exposure region to be irradiated with particle beams and a peripheral region thereof are respectively divided into pluralities of exposure regions, radiation treatment simulation for applying particle beams according to the shape of each divided exposure region is performed, and a radiation treatment condition is obtained for causing the flatness of the radiation exposure region to be in a desired range, and a dose of particle beams applied to the unit exposure region of the peripheral region to be minimum. Thus, the problem of low efficiency of radiation is solved. |
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description | This patent application claims the priority benefit under 35 U.S.C. § 120 of U.S. Utility patent application Ser. No. 15/404,477, filed on Jan. 12, 2017, and entitled, “FUEL ASSEMBLY WITH AN EXTERNAL DASHPOT DISPOSED AROUND A GUIDE TUBE PORTION” the contents of which are hereby incorporated herein by reference. The disclosed concept pertains generally to nuclear reactors and, more particularly, to nuclear assemblies that employ guide thimbles with enhanced stiffness in the dashpot region. In most water cooled nuclear reactors, the reactor core is comprised of a large number of elongated fuel assemblies. In pressurized water nuclear reactors (PWR), these fuel assemblies typically include a plurality of fuel rods held in an organized array by a plurality of grids spaced axially along the fuel assembly length and attached to a plurality of elongated thimble tubes of the fuel assembly. The thimble tubes typically receive control rods or instrumentation therein. Top and bottom nozzles are on opposite ends of the fuel assembly and are secure to the ends of the thimble tubes that extend above and below the ends of the fuel rods. When the control rods scram, they freefall and can impact the bottom nozzle at a high velocity, potentially causing damage to components of the nuclear reactor. In a standard fuel assembly design, approximately two feet before full insertion of the control rods into the fuel assembly, the tips of the control rods enter a small portion of the thimble tube called the dashpot. The diameter of the dashpot is approximately one millimeter larger than the control rods. Because the control rods are moving very fast at this point in the scram, there is a large volume of water which has to be accelerated up past the falling rods to make room for them in the dashpot. This process causes the control rods to decelerate rapidly, thus lessening the impact velocity of the falling control rod. Incomplete rod insertion (IRI) events are problematic in nuclear reactors. An IRI event occurs when the control rod cannot be completely inserted through the thimble tube. One of the primary causes of an IRI event is a distortion in the fuel assembly and the thimble tube. The distortion is most critical in the dashpot area of the thimble tube where the clearance between the control rod and the inner surface of the thimble tube is minimal. A lack of stiffness in the dashpot region of the thimble tube can cause the thimble tube to be susceptible to distortion and increase the chance of an IRI event occurring. There is a need to improve the stiffness of the dashpot region of thimble tubes. However, there is also a need to minimize the number of parts and assembly steps of fuel assemblies. In accordance with an embodiment of this concept, a nuclear fuel assembly comprises: a top nozzle; a bottom nozzle; a plurality of grids arranged in between the top nozzle and the bottom nozzle and supporting the guide tubes in the spaced parallel array at spaced axial elevations between the top nozzle and bottom nozzle, the plurality of grids including a bottom grid disposed closest to the bottom nozzle among the plurality of grids; and a plurality of control rod guide assemblies. At least one of the control rod guide assemblies includes: a guide tube having an axial dimension, the guide tube being supported by the plurality of grids and extending axially between the top nozzle and the bottom nozzle, the guide tube having an upper portion having a first radius and a lower portion having a second radius less than the first radius; and an external dashpot tube disposed around a portion of the lower portion in an area beginning at the bottom grid and extending toward the top nozzle. these and other objects are satisfied by a holding fixture for assisting in assembly of a support grid for nuclear fuel rods and including a plurality of straps each having a plurality of slots extending approximately half a height of the straps and tabs formed beside or between the slots. In accordance with another embodiment of the concept, a control rod guide assembly for use with a nuclear reactor fuel assembly including a top nozzle, a bottom nozzle, and a plurality of grids comprises: a guide tube having an axial dimension, the guide tube being supported by the plurality of grids and extending axially between the top nozzle and the bottom nozzle, the guide tube having an upper portion having a first radius and a lower portion having a second radius less than the first radius; and an external dashpot tubes disposed around a portion of the lower portion in an area beginning at the bottom grid and extending toward the top nozzle. In accordance with an embodiment of this concept, a nuclear fuel assembly comprises: a top nozzle; a bottom nozzle; a plurality of grids arranged in between the top nozzle and the bottom nozzle and supporting the guide tubes in the spaced parallel array at spaced axial elevations between the top nozzle and bottom nozzle, the plurality of grids including a bottom grid disposed closest to the bottom nozzle among the plurality of grids; and a plurality of control rod guide assemblies. At least one of the control rod guide assemblies includes: a guide tube having an axial dimension, the guide tube being supported by the plurality of grids and extending axially between the top nozzle and the bottom nozzle, the guide tube having an upper portion having a first radius and a lower portion having a second radius less than the first radius; and an external dashpot tube disposed around a portion of the lower portion in an area beginning at the bottom grid and extending toward the top nozzle. These and other objects are satisfied by a holding fixture for assisting in assembly of a support grid for nuclear fuel rods and including a plurality of straps each having a plurality of slots extending approximately half a height of the straps and tabs formed beside or between the slots. FIG. 1 illustrates a typical nuclear fuel assembly 10 for a pressurized water reactor that can employ control rod guide assemblies in accordance with embodiments of the disclosed concept to slow down the control rods when they are dropped into the reactor core under a scram condition. FIG. 1 shows a side sectional view of a nuclear reactor fuel assembly, represented in vertically shortened form and being generally designated by reference character 10. The fuel assembly 10 has a structural skeleton which, at its lower end includes a bottom nozzle 14. The bottom nozzle 14 supports the fuel assembly 10 on a lower core support plate 18 in the core region of the nuclear reactor (not shown). In addition to the bottom nozzle 14, the structural skeleton of the fuel assembly 10 also includes a top nozzle 12 at its upper end and a number of guide tubes or thimbles 20, which extend longitudinally between the bottom and top nozzles 14 and 12 and at the opposite ends are rigidly attached thereto. The structural skeleton of the fuel assembly 10 further includes a plurality of traverse grids 22 that are axially spaced along, and mounted to, the guide tubes 20. In the final assembly the grids function to maintain an organized array of elongated fuel rods 24 traversely spaced and supported by the grids 22. Also, the structural skeleton of the fuel assembly 10 includes an instrumentation tube 16 located in the center thereof, which extends and is captured between the bottom and top nozzles 14 and 12. With such an arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conveniently handled without damaging the assembled parts. The fuel rods 24 are not actually part of the structural skeleton of the fuel assembly 10, but are inserted, respectively, in the individual cells within the grids 22 before the top nozzle is finally affixed at the end of fuel assembly manufacture. As mentioned above, the fuel rods 24, as in the array shown in the fuel assembly 10, are held in space relationship with one another by the grids 22 spaced in tandem along the fuel assembly length. Each fuel rod 24 includes a stack of nuclear fuel pellets 26 and is closed at its opposite ends by upper and lower fuel rod end plugs 28 and 30. The pellets 26 are maintained in the stack by plenum spring 32 disposed between the upper end plug 28 and the top of the pellet stack. The fuel pellets 26, composed of fissile material, are responsible for creating the thermal power of the reactor. A liquid moderator/coolant such as water or water containing boron, is pumped upwardly through a plurality of flow openings in the lower core support plate 18 to the fuel assembly 10. The bottom nozzle 14 of the fuel assembly 10 passes the coolant upwardly through the guide tubes 20 and along the fuel rods 24 of the assembly 10 in order to extract heat generated therein for the production of useful work. For the purpose of illustration, FIG. 1 shows a 17×17 array of fuel rods 24 in a square configuration, it should be appreciated that other arrays of different designs and geometries are employed in various models of pressurized reactors. To control the fission process, a number of control rods 34 are reciprocally movable in the guide tubes 20 located at predetermined positions in the fuel assembly 10. A rod cluster control mechanism 36 positioned above the top nozzle 12 supports the control rod 34. The control mechanism has an internally threaded cylindrical member 38 which functions as a drive rod with a plurality of radial extending flukes or arms 44. Each arm 44 is interconnected to a control rod 34 such that the control rod mechanism 36 is operable to move the control rods vertically in the guide tubes 20 to thereby control the fission process in the fuel assembly 10, all in a well-known manner. The grids 22 are mechanically attached to the control rod guide thimbles 20 and the instrumentation tube 16 by welding, or preferably by bulging. Bulging is particularly desirable where welding dissimilar materials is difficult. FIG. 2 is a side sectional view in section of a typical control rod guide assembly including a TnT dashpot region, FIG. 3A is a side sectional view of a lower portion of the TnT dashpot region of the control rod guide assembly of FIG. 2, and FIG. 3B is a side sectional view in section of an upper portion of the TnT dashpot region of the control rod guide assembly of FIG. 2. The control rod guide thimble assembly includes a guide tube 100, an internal dashpot tube 102, and a bottom grid sleeve 104. The control rod guide assembly also includes an internal dashpot tube end plug 108 and a guide tube end plug 110. In the completed control rod guide assembly, the internal dashpot tube 102 is disposed inside the guide tube 100 and reduces the internal diameter of the guide tube 100 in the dashpot region in order to provide the dashpot functionality. Forming and installing the control rod guide assembly into a fuel assembly requires numerous steps. The bottom grid sleeve 104 is welded onto the bottom grid 106 of the fuel assembly. Then, two weld operations are performed to assemble guide tube 100 and the internal dashpot tube 102. Next, the guide tube 100 is inserted into the skeleton of the fuel assembly with tooling screws and bulged onto the bottom grid sleeve 104. Next, the internal dashpot tube 102 is inserted into the guide tube 100 using a second set of tooling screws and the internal dashpot tube 102 is bulged onto the guide tube 100. The insertions of the guide tube 100 and the internal dashpot tube 102 each require tooling screws to be inserted and then removed from the guide tube 100 and internal dashpot tube 102, respectively. Similarly, each bulging operation requires bulging tools to be inserted and then removed. Each step of the manufacturing process adds to the amount of time required to manufacture and install the control rod guide assembly. Additionally, each part of the control rod guide assembly adds to its cost. The TnT dashpot region of the control rod guide assembly enhances the stiffness of the dashpot region. However, as described above, there are numerous steps required to manufacture and install this type of control rod guide assembly in a fuel assembly. FIG. 4 is a side sectional view in section of a typical pushpoint type control rod guide assembly. The pushpoint control rod guide assembly includes an upper portion 200, a transitional portion 202, and a lower portion 204. The lower portion 204 has an internal radius that is less than the upper portion 200. The transitional portion 202 connects the upper portion 200 and the lower portion 204 and transitions in radius from the greater radius of the upper portion 200 to the lesser radius of the lower portion 204. The lower portion 204 is formed in a dashpot region of the control rod guide assembly that begins above a bottom grid 206 and extends below the bottom grid 206. The reduced radius of the lower portion 204 provides the dashpot functionality of the control rod guide assembly. The control rod guide assembly of FIG. 4 requires fewer manufacturing steps and parts compared to the control rod guide assembly of FIG. 2. However, the control rod guide assembly of FIG. 4 is more susceptible to a lack of stiffness in the dashpot region that the control rod guide assembly of FIG. 2. FIG. 5 is a side sectional view in section of a control rod guide assembly in accordance with an example embodiment of the disclosed concept. The control rod guide assembly of FIG. 5 provides enhanced stiffness in the dashpot region compared to the pushpoint type control rod guide assembly of FIG. 4 while requiring fewer manufacturing steps and parts compared to the control rod guide assembly with the TnT dashpot region of FIG. 2. The control rod guide assembly of FIG. 5 may be employed, for example, in conjunction with the fuel assembly 10 of FIG. 1 or with any other suitable type of fuel assembly for a nuclear reactor. The control rod guide thimble assembly includes guide tube having an upper portion 300, a transitional portion 302, and a lower portion 304. The lower portion 304 has a lesser radius than the upper portion 300 and the transitional portion 302 connects the upper and lower portions similar to the pushpoint type control rod guide assembly. The lower portion 304 is formed in a dashpot region of the control rod guide assembly that begins above a bottom grid 306 and extends below the bottom grid 306. The bottom grid 306 may be, for example, the lower most grid 22 of the fuel assembly 10 of FIG. 1. The reduced radius of the lower portion 304 provides the dashpot functionality of the control rod guide assembly. The guide tube of the control rod guide assembly of FIG. 5 is similar to the pushpoint type control rod guide assembly of FIG. 4. However, the control rod guide thimble assembly in accordance with example embodiments of the disclosed concept further includes an external tube 308. The external tube 308 is disposed around the bottom portion 304 of the guide tube. The external tube 308 is formed in the dashpot region above bottom grid 306. The external tube 308 provides enhanced stiffness to the dashpot region without affecting the internal diameter of the lower portion 304 of the guide tube. The external tube 308 also includes one or more weep holes 310 formed therein. The weep holes 310 help with potential thermal hydraulic concerns such as reducing the chance that boiling occurs in the annular region between the lower portion 304 of the guide tube and the external tube 308. The external tube 308 is attached to the lower portion 304 of the guide tube by bulging the guide tube onto the external tube 308. As a result of the bulging, bulges 312 are formed in the guide tube and the external tube 308. In some example embodiments of the disclosed concept one bulge is formed in an upper half of the external tube 308 and one bulge is formed in the lower half of the external tube 308. However, it will be appreciated that any number of bulges may be formed at any number of locations along the external tube 308 without departing from the scope of the disclosed concept. In some example embodiments of the disclosed concept, two weep holes 310 are formed in the external tube 308, one in an upper half of the external tube 308 and one in the lower half of the external tube 308. Additionally, in some example embodiments of the disclosed concept, the weep holes 310 are formed in the external tube 308 between the bulges 312. However, it will be appreciated by those having ordinary skill in the art that any number of weep holes 310 may be formed at any number of locations in the external tube 308 without departing from the scope of the disclosed concept. In some example embodiments of the disclosed concept, the lower portion 312 of the guide tube and the external tube 308 are substantially cylindrical. A substantially cylindrical object may have bulges and weep holes formed in it and still be considered substantially cylindrical. It will be appreciated by those having ordinary skill in the art that the lower portion 312 of the guide tube and the external tube 308 may have different shapes without departing from the scope of the disclosed concept. The control rod guide assembly of FIG. 5 with the external tube 308 provides enhanced stiffness compared to the control rod guide assemblies of FIGS. 2 and 4. Table 1 shows test results comparing the lateral stiffness in the dashpot region of the a control rod guide assembly with a TnT dashpot region (FIG. 2), a pushpoint type control rod guide assembly (FIG. 4), and a control rod guide assembly including an external tube (FIG. 5). TABLE 1Average LateralStiffness at .25 InchDeflection (lb/in)Description0 Deg90 DegBenefit17 OFA Pushpoint Type858670%Control Rod Guide Assembly17 OFA Control Rod Guide147144Assembly With External Tube17 RFA Pushpoint Type Control10210048%Rod Guide Assembly17 RFA Control Rod Guide150149Assembly With External Tube17 RFA Control Rod Guide12213025%Assembly With TnT DashpotRegion As shown in Table 1, the control rod guide assembly with the external tube 308 provides enhanced stiffness over the control rod guide assembly with the TnT dashpot region and the pushpoint type control rod guide assembly. Additionally, the control rod guide assembly with the external tube 308 uses less parts that the control rod guide assembly with the TnT dashpot region at least because it only has one guide tube end plug rather than the guide tube end plug 110 and the internal dashpot tube end plug 108. Moreover, the control rod guide assembly with the external tube 308 requires less operations to install than the control rod guide assembly with the TnT dashpot region. FIG. 6 is a flowchart of a method of installing the control rod guide assembly of FIG. 5 in accordance with an example embodiment of the disclosed concept. The process begins at 400 where the guide tube and the external tube 308 are provided. The guide tube and external tube 308 may be for example, the guide tube and external tube 308 shown in FIG. 4. At 402, the guide tube is inserted into the skeleton of a nuclear reactor assembly, such as the nuclear reactor assembly shown in FIG. 1, to the lower middle grid of the nuclear reactor fuel assembly. The lower middle grid is the second closest grid to the bottom nozzle of the nuclear reactor fuel assembly. Next, at 404 the external tube 308 is installed on the guide tube. The external tube 308 may be installed by sliding it over the guide tube. At 406, insertion of the guide tube is completed, for example, by continuing to insert the guide tube into the skeleton to the bottom nozzle. Then, at 408, the guide tube is attached to the skeleton. The guide tube may be attached to the skeleton in any suitable manner such as, without limitation, using a thimble screw to hold it in place. Finally, at 410, the guide tube is bulged onto the external tube 308. The process of installing the control rod guide assembly shown in FIG. 6 requires less steps than the process required to install the control rod guide assembly with the TnT dashpot region. For example, the process of FIG. 6 only requires one bulge operation. In contrast, the process to install the control rod guide assembly with the TnT dashpot region requires separate bulge operations that each require insertion and removal of bulging tools and adding to the time required to complete installation. Moreover, the resultant installed control rod guide assembly provides enhanced stiffness over the control rod guide assembly with the TnT dashpot region or the pushpoint type control rod guide assembly. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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054835607 | abstract | A method and an apparatus for testing, repairing or exchanging nozzles of the bottom of a reactor pressure vessel include inserting individual shielding containers into the reactor pressure vessel. Shafts pass through a shielding container and water-filled cartridges can be inserted into the shafts. Tubes for receiving probes of an in-core instrumentation are embedded into bottom plates of the remaining shielding containers and into bottoms of the cartridges. After removing a cartridge, a carrier for working tools can be introduced into the shaft. In this way the radioactive loading is considerably reduced by the probes inside or outside the reactor pressure vessel. |
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abstract | The present invention provides a system 10 for irradiating a breast 20 of a patient 22. The system 10 comprises a gantry 12 rotatable about a horizontal axis 14 and comprising a radiation source 16 for generating a radiation beam 18 and a detector 24 spaced from the radiation source 16, and a barrier 26 disposed between the patient 22 and the gantry 12. The barrier 26 is provided with an opening 30 adapted to allow a breast 20 passing therethrough to be exposed to the radiation beam 18. In some embodiments, the barrier 26 is provided with an opening 30 adapted to allow both the breast 20 and the tissue leading from the breast to axilla and the muscle tissue of the adjacent chest wall passing therethrough to be exposed to the radiation beam 18. |
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abstract | The invention relates to gratings for X-ray differential phase-contrast imaging, a focus detector arrangement and X-ray system for generating phase-contrast images of an object and a method of phase-contrast imaging for examining an object of interest. In order to provide gratings with a high aspect ratio but low costs, a grating for X-ray differential phase-contrast imaging is proposed, comprising a first sub-grating (112), and at least a second sub-grating (114; 116; 118), wherein the sub-gratings each comprise a body structure (120) with bars (122) and gaps (124) being arranged periodically with a pitch (a), wherein the sub-gratings (112; 114; 116; 118) are arranged consecutively in the direction of the X-ray beam, and wherein the sub-gratings (112; 114; 116; 118) are positioned displaced to each other perpendicularly to the X-ray beam. |
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048448621 | abstract | A hairpin spring for holding a fuel rod in a fuel assembly grid consists of a metal strip bent to form two mutually confronting legs arranged to be welded together locally. At least in a zone which bears on the other leg, one of the legs is U-shaped and straddles the other leg through a respective window of the grid. The legs of the U may be formed as appendices bent substantially at 90.degree.. The arms may also close up slightly so that the other leg can snap thereinto or flare for self-centering of the other arm. |
055704085 | description | BEST MODE FOR CARRYING OUT THE INVENTION Referring now to FIG. 1, the basic elements of a typical x-ray source are shown. Filament 10, is heated, by applying a voltage, to a temperature such that electrons 12, are thermally emitted. These emitted electrons are accelerated by an electric potential difference to anode 14, which is covered with target material 16, where they strike within a given surface area of the anode which is called the spot size 18. X-rays 20, are emitted from the anode as a result of the collision between the accelerated electrons and the atoms of the target. In order to control the spot size, electromagnetic focusing means 22, is positioned between electron emitting filament 10, and anode 14, so that the electron beam passes within its area of influence. X ray sources with spot sizes of 2 microns or less are available commercially. However, as the electron spot size decreases, so does the production of x rays. FIG. 2 shows how x ray power (production of x rays), and the power density (power/spot area) of a source varies with spot diameter. Noting that the linear vertical scale on the right of the graph is used for the total power, it can be seen from the lower tail 24, of total power curve 26, that power decreases nearly linearly with spot diameter for very small spot sizes. Turning our attention now to the power density curve 28, and noting that the vertical scale on the left of the graph, which applies to this curve is logarithmic, it can be seen that there is an inverse relationship between the power density and the spot diameter. The reason for this is that the total power varies linearly with spot diameter, while the area varies as the inverse of the square of the spot diameter. Thus it can be seen that even though total x-ray production is decreased, the power density increases with decreasing spot size. Monolithic capillary optics allow unprecedented possibilities for efficient use of the increased power density of small spot x-ray sources. The combination of the smaller spot source, and properly engineered monolithic capillary optic of the subject invention can thus lead to a substantial increase in intensity of small diameter output x-ray beams. Specific design parameters vary depending on the energy of x-rays used. Two types of systems are particularly pointed out. First, a system in which a very intense small diameter quasi-parallel beam is formed and second a system in which a very small, intense converging x-ray spot is formed. In all cases, systems of the type defined by the subject invention can be easily differentiated from other prior art systems based on a much reduced source to optic distance. FIG. 3 shows an x-ray source 30, and multi-fiber polycapillary optic 32. In order for the polycapillary fiber 33 to efficiently capture radiation from source 30, the collection angle 34 of the capillary must be less than the critical angle for total external reflection. This angle is dependent on the x-ray energy. For a typical example of an approximately 8 keV optic with polycapillary outer diameters of around 0.5 millimeters, simple geometric considerations lead to the conclusion that the optic must be placed at least 150 millimeters away from the source. The subject invention is defined by optics which are placed no more than half that distance from the source. The first embodiment of the subject invention is shown in FIG. 4. The system 40, for producing a high intensity, small diameter x-ray beam comprises two main components; a small spot x-ray source 42, and a monolithic capillary optic 44. The two components are separated by a distance f, known as the focal distance, measured along optical axis 46. The optic 44 comprises a plurality of hollow glass capillaries 48 which are fused together and plastically shaped into configurations which allow efficient capture of divergent x radiation 43 emerging from x-ray source 42. In this example the captured x-ray beam is shaped by the optic into a quasi-parallel beam 50. The output beam is not completely parallel because of divergence due to the finite critical angle of total external reflection. The channel openings 52 located at the optic input end 54 are roughly pointing at the x-ray source. The ability of each individual channel to essentially point at the source is of critical importance to the subject invention for several reasons: 1) It allows the input diameter of the optic to be sufficiently decreased, which in turn leads to the possibility of smaller optic output diameters; 2) it enables efficient capture of x-rays even when the source spot is decreased; 3) it makes efficient x-ray capture possible for short optic to source focal lengths. The diameters of the individual channel openings 52 at the input end of the optic 54, are smaller than the channel diameters at the output end of the optic 56. The class of optics used in the subject invention are monolithic. This means that the walls of the channels themselves 70, form the support structure which holds the optic together. For this case, the maximum capture angle is given by 2.psi., where .psi. is the maximum bend angle of a curved capillary. In a preferred embodiment the x-ray source 42 has a spot size of roughly 30 microns and is located approximately 1.0 millimeter from the input end 54 of capillary optic 44. The collection angle .psi. for this optic is around 0.2 radians. The optic produces an output beam 50 with a diameter of essentially 1.0 millimeter. The overall length of the optic is approximately 8.0 Millimeters. The increase in intensity is expected to be more than roughly 2 orders of magnitude brighter than currently available laboratory sources. FIG. 5 shows a second embodiment of the subject invention. Again the source/optic system 80, comprises small spot x-ray source 82, and monolithic capillary optic 84. The optic has channels formed by individual glass capillaries 89 which have been fused together. The channel openings 86 at the input end 88 are positioned to capture radiation from divergent source 82. In this particular embodiment, however, the optic output end 90 is shaped to form a very small spot converging beam. For this case, because the radiation is turned through twice the angle of the quasi-parallel output optic, so the maximum capture angle is just .psi., the maximum bend angle. A preferred embodiment of this system, designed for approximately 8 keV x-rays, can be specified as follows. Again referring to FIG. 5, the x-ray source 82, has an anode spot size of around 100 micrometers. The converging optic 84, is placed essentially 27 millimeters in front of the source. The acceptance angle of the optic 85 is roughly 0.13 radians, and the optic has an output focal length 87 of nearly 2 millimeters. The overall length of the optic is about 165 millimeters. The optic input diameter 88 is approximately 7 millimeters, with input channel diameters of essentially 14 micrometers. The output diameter 90 is roughly 0.6 millimeters. The maximum channel diameter is around 10 micrometers. This invention has been specified in part by specific embodiments. It is to be understood that it will be apparent to those skilled in the art that various modifications, substitutions, additions and the like can be made without departing from the spirit of the invention, the scope of which is defined by the claims which follow and their equivalents. |
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description | FIG. 1 shows the layout of a system in which the light sources are coupled together according to the addition method. The light sources 1.1, 1.2 in the present case have a small source diameter, in this case laser plasma sources are further investigated. Regarding the basic layout of EUV-illumination systems, we refer to the applicant""s pending applications EP 99 1 06348.8, submitted on Mar. 2, 1999, entitled xe2x80x9cIllumination system, especially for EUV-lithographyxe2x80x9d, U.S. Ser. No. 09/305,017, submitted on May 4, 1999, entitled xe2x80x9cIllumination system particularly for EUV-lithographyxe2x80x9d, now U.S. Pat. No. 6,198,793 B1, and PCT/EP 99/02999, submitted on May 4, 1999, entitled xe2x80x9cIllumination system, especially for EUV-lithographyxe2x80x9d, whose disclosure contents are incorporated in their entirety in the present application. Each system part 10.1, 10.2 is essentially identical in construction and comprises a light source 1.1, 1.2, a collector mirror 2.1, 2.2, and a field raster element plate 4.1, 4.2. The light of each source is collected by means of the collector mirror assigned to a particular source and transformed into a parallel or convergent light bundle. The field raster elements of the particular field raster element plate 4.1, 4.2 decompose the light bundle and create secondary light sources 6 in the diaphragm plane of the illumination system. These secondary light sources are imaged by the field lens (not shown) or field mirror in the exit pupil of the illumination system, which is the entrance pupil of the objective lens (not shown) The field raster elements of the field raster element plate are arranged on the plate and oriented so that the images of the field raster elements are superimposed in the reticle plane 9. The systems are brought together where the field raster element plates are located. The field raster element plates are located on a pyramid, the number of the sides of the pyramid corresponds to the number of coupled partial systems. The angle of inclination of the pyramid sides is chosen such that the illuminated fields of the partial systems in.the reticle plane 9 are superimposed. The partial systems parts 10.1, 10.2 are arranged such that their partial pupils fill the diaphragm plane of the illumination system optimally. In the embodiment shown in the drawings, the partial systems are oriented such that they possess a common system axis. The angular spacing of the partial system is then 360xc2x0/number of systems. For four partial systems, FIG. 2 shows the illumination of the pyramid, on each of the four lateral surfaces 20.1, 20.2. 20.3, 20.4 of the pyramid one field raster element plate of a partial system in the area of the illuminated surface 22.1, 22.2, 22.3, 22.4 is arranged. The field raster elements are arranged and oriented such that the images of the field raster elements overlap in the reticle plane 9. The angle of inclination of the pyramid surfaces 20.1, 20.2. 20.3, 20.4 is chosen such that the illuminated fields of the partial system superimpose in the reticle plane. The illumination in the diaphragm plane is provided by four circular partial pupils 30.1, 30.2. 30.3, 30.4, as shown in FIG. 3, which in turn are divided into individual secondary light sources 6, corresponding to the number of illuminated field raster elements of the field raster element plates. In FIG. 3, the aperture of the total system is NAObj=0.025 and the aperture of the system parts is NATeilsystem=0.0104. Depending on the number of coupled partial systems, one can imagine the arrangement and symmetries of the partial pupils 30.1, 30.2. 30.3, 30.4, 30.5, 30.6 as shown in FIGS. 4A through 4D with coupling of 3, 4, 5 and 6 sources. The maximum diaphragm diameters of the partial systems are derived from the total aperture NAObj of the objective lens in the diaphragm plane and the number of partial systems or subsystems. NA Teilsystem = NA obj 1 + 1 sin xe2x80x83 ( π Anzahl ) Whereby: Teilsystem=partial system; Anzahl=number of partial systems When the pupil of each subsystem is filled, the pupil can be illuminated to xcex7% of the maximum. η = Anzahl · 1 ( 1 + 1 sin xe2x80x83 ( π Anzahl ) ) 2 Whereby: Anzahl=number of partial systems The following table gives NAsystem part and the filling factor xcex7 for NAObj=0.025: Hence, the maximum attainable filling factor with the addition method using four subsystems and NAObj=0.025 is achieved with xcex7max≈0.69. As a boundary condition, the overall Etendu of the coupled sources may not exceed the system, Etendu LCill=xcex7maxxc2x7LCObj; thus, we must always have: xcexa3LCixe2x89xa6LCill all sources FIG. 5 shows a second form of embodiment of the invention, in which the light sources 50.1, 50.2 are pinch plasma sources, for example. The source diameter of the pinch plasma sources is not negligible. A partial illumination system with pinch plasma source comprises the light source 50.1, 50.2, a collector mirror 52.1, 52.2, which collects the light and illuminates the field raster element plate 54.1, 54.2. The field raster elements of the plate produce secondary light sources. At the location of the secondary light sources, the pupil raster elements are arranged on a pupil raster element plate. The field raster elements of the field raster element plate are used to shape the field and the pupil raster element of the pupil raster element plate correctly image the field raster element in the reticle plane. Preferably, each field raster element is assigned to a pupil raster element. The light is guided by reflection from the field raster elements of the field raster element plates to the pupil raster element of the pupil raster element plate 56.1, 56.2 and from there to the reticle, or object 58. The systems are brought together at the location of the pupil raster element plates. The pupil raster element plates are located on a pyramid. The number of sides of the pyramid corresponds to the number of coupled subsystems. The angle of inclination of the pyramid sides is chosen such that the illuminated fields of the partial systems or subsystems are brought together in the reticle plane. If the subsystems have a common system axis, then the angular spacing of the system parts is 360xc2x0/number of systems and the pupil raster element plates of the subsystem are preferably arranged on the lateral surfaces of a pyramid, as shown in FIG. 2. The advantage of the addition method of coupling is that identical or similar illumination systems can be coupled together. The raster element plates of the subsystems are separate and can thus be fabricated separately. In the addition method, it should be noted that intensity differences of the individual sources are directly passed on to the illumination of the pupils, and thus the intensity of the partial pupils is dictated by the source power. The intensity distribution in the diaphragm plane becomes independent of the intensities of the individual sources if one mixes the secondary light sources in the pupil plane. This technique is also hereafter designated as the mixing method. Whereas in the addition method the beam bundles of each source only penetrate after passing through the diaphragm plane, in the mixing method the beam bundles penetrate in front of the diaphragm plane and are mixed in the diaphragm plane. The maximum aperture for each subsystem is adapted to the desired angle of filling of the objective aperture. As in the addition method, systems of identical construction can be coupled together for the individual sources. They are uniformly arranged about a common system axis. The systems are coupled together in the plane of the secondary light sources. FIG. 6 shows an illumination system based on the mixing method for coupling of several light sources. The light sources once again are laser plasma sources. The same components as in FIG. 5 are designated with the same reference numbers. In contrast to FIG. 5, for example, there is a single pupil raster element plate 100, which includes a plurality of pyramids. The pupil raster element plate 100 is arranged at the location of the secondary light sources, which are produced by the field raster elements. A secondary light source is located on each flank, or lateral side, of the plurality of pyramids. The schematic representation of FIG. 7 shows a typical arrangement of the field raster elements 110 on the field raster element plate. Each field raster element plate produces a grid of secondary light sources in the diaphragm plane. The distribution of the secondary light sources in the diaphragm plane corresponds to the arrangement of the field raster elements. By shifting the subsystems, as depicted in FIG. 8, the grids of secondary light sources can be brought to be located next to each other, corresponding to the number of subsystems. If four sources are coupled together, the arrangement of secondary light sources 6 shown in the schematic representation of FIG. 8 is obtained. For the correct superimposing of the four subsystems, each set of secondary light sources is located on a mirrored pyramid. The flanks of the pyramid are inclined such that the images of the field raster elements are superimposed in the reticle plane. The schematic representation of FIG. 9 shows a segment of the pupil raster element plate. One clearly recognizes the individual pupil raster elements 104 that are formed by the flanks of an equilateral pyramid 106. If the Etendu (LC) of the individual sources is small, the pupil raster elements can be designed as plane mirrors, i.e., the flanks of the equilateral pyramids 106 are planar. When the source diameter is not negligible, such as with pinch plasma sources, the pupil raster elements 104 must image the field raster elements in the object plane, for example, the reticle plane. In this case, a concave mirror surface 108, as shown in FIG. 10, must be worked into the pyramid flanks. The schematic representation of FIG. 10 shows a system in which several pinch plasma sources are coupled with a pupil raster element plate comprising pupil raster elements with concave surfaces. The same components as in FIG. 6 are given the same reference numbers. The examples shown in FIGS. 5 through 10 are designed for four coupled sources. However, the same method can be used for three, five, six or more sources. The grids should then be shifted such that the secondary light sources are located on the side faces of pyramids. The degree of filling of the pupil is limited similar to the addition method. The advantages of the mixing method are that the individual sources are mixed in the pupil plane. Fluctuations in source intensity are not shown in the pupil as inhomogeneous pupil illumination. Furthermore, the system pupil can be filled more uniformly with secondary light sources. As a third method of coupling several light sources together, the segment method shall be described. The segment method works similar to the addition method. The coupled illumination systems are uniformly distributed about a common system axis. Each system has a corresponding segment to fill the diaphragm plane. Instead of filling this segment with a circle as in the addition method, one can uniformly fill up the segment by orienting the field raster elements on the field raster element plate. FIG. 11 shows the illumination of one of four segments 200 of the system pupil 202, when four sources are coupled together. In segment 200 secondary light sources 6 corresponding to the number of illuminated field raster elements are formed. In order for the individual light bundles to be correctly superimposed in the reticle plane, pupil raster elements must be arranged at the location of the secondary light sources, which deflect the light bundles so that the images of the field raster elements are superimposed in the reticle plane. Depending on the size of the source, the pupil raster elements have planar surfaces for point like sources or concave surfaces for extended sources. Accordingly, field and pupil raster elements are tilted individually and without symmetry. The advantage of the segment method is the optimal filling of the diaphragm plane with secondary light sources 6 by a pairwise tilting of field and pupil raster elements. Although no optical components have been depicted in the preceding examples of embodiments of the illumination systems after the lenses or mirrors with raster elements, it is obvious to the person skilled in the art that field lenses or field mirrors must be provided after the lenses or mirrors with raster elements in order to shape the annular field in the reticle plane and to image the diaphragm plane into the exit pupil of the illumination system, for example. This is shown in FIG. 12. The illumination system of the second embodiment, shown in FIG. 5 was adapted by introducing a field lens 300 between the pupil raster element plates 56.1 and 56.2. The field lens 300 represents an optical unit, which can also comprise two or more mirrors. The field lens 300 images the plurality of secondary light sources formed on the pupil raster element plates 56.1 and 56.2 into the exit pupil 310. In this regard, concerning the basic layout of EUV illumination systems, refer to the applicant""s pending applications EP 99 1 06348.8, submitted on Mar. 2, 1999, entitled xe2x80x9cIllumination system, especially for EUV-lithographyxe2x80x9d, U.S. Ser. No. 09/305,017, submitted on May 4, 1999 entitled xe2x80x9cIllumination system particularly for EUV-lithographyxe2x80x9d, and PCT/EP 99/02999, submitted on May 4, 1999, entitled xe2x80x9cIllumination system, especially for EUV-lithographyxe2x80x9d, whose disclosure contents are incorporated in their entirety in the present application. An EUV-projection exposure system is shown in FIG. 13. The illumination system is already shown in FIG. 12. The reticle 58 is imaged by the projection objective lens 320 onto the wafer 330. The EUV-projection exposure system can be realized as a stepper or scanning system. |
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claims | 1. A lithographic exposure device for fabricating a microporous filter membrane, said microporous filter membrane not supported by a solid substrate, comprising:means for exposing a membrane substrate to a beam comprising at least one energetic particle, wherein said energetic particle has an energy level greater than about 10 keV;means for applying a high emissivity coating to said membrane substrate prior to exposing said membrane substrate to said beam;means for conveying said membrane substrate; anda mask positioned between said membrane substrate and at least one source of said at least one energetic particle, said beam comprising at least one particle transmitted through said mask. 2. The lithographic exposure device of claim 1, wherein said device fabricates a filter membrane comprising at least one pore. 3. The lithographic exposure device of claim 1, wherein said mask is substantially stationary. 4. The lithographic exposure device of claim 1, wherein said means for conveying said membrane substrate further comprises a clamp for securing said membrane substrate. 5. The lithographic exposure device of claim 1, wherein said means for conveying said membrane substrate advances said membrane substrate in a stepwise fashion, and wherein said membrane substrate is advanced about a length of said mask for every step. 6. The lithographic exposure device of claim 1, further comprising an etchant exposure system. 7. The lithographic exposure device of claim 1, further comprising a means for removing said high emissivity coating from said filter membrane substrate after said exposure. 8. A filter membrane produced with a device according to claim 1. 9. The lithographic exposure device of claim 1, wherein said energetic particle is selected from at least one of an ion, a photon, an electron, a neutral energetic atom and an energetic molecule. 10. The lithographic exposure device of claim 1, wherein said energetic particle comprises at least one of hydrogen or helium ions. 11. A lithographic exposure device for fabricating a microporous filter membrane, said microporous filter membrane not supported by a solid substrate, comprising:a radiation source directed at least partially on a membrane substrate, wherein said radiation source's emitted radiation comprises a beam of at least one energetic particle, wherein said energetic particle has an energy level greater than about 10 keV;a device for applying a high emissivity coating to a membrane substrate prior to exposure to said radiation source;a device for conveying said membrane substrate comprising at least one supply reel and at least one take-up reel; anda mask positioned between said membrane substrate and at least one source of said at least one energetic particle, said beam comprising at least one particle transmitted through said mask. 12. The lithographic exposure device of claim 11, wherein said mask is substantially stationary. 13. The lithographic exposure device of claim 11, wherein said device for conveying said membrane substrate further comprises a clamp for securing said membrane substrate. 14. The lithographic exposure device of claim 13, wherein said clamp is electrostatic. 15. The lithographic exposure device of claim 11, further comprising an etchant exposure system. 16. The lithographic exposure device of claim 11, further comprising a device for removing a high emissivity coating from said filter membrane substrate after said lithographic exposure. 17. A filter membrane produced with the device according to claim 11. 18. The lithographic exposure device of claim 11, wherein said energetic particle comprises helium ions. 19. The lithographic exposure device of claim 11, wherein said energetic particle comprises hydrogen ions. 20. A process for fabricating a microporous filter membrane, said microporous filter membrane not supported by a solid substrate, said process comprising the steps of:conveying a membrane substrate in a stepwise fashion adjacent a mask;applying a high emissivity coating to said membrane substrate;damaging said membrane substrate with at least one beam comprising at least one energetic particle emitted from at least one radiation source directed at least partially through said mask, wherein said energetic particle has an energy level greater than about 10 keV, and wherein said damaging occurs after said application of said high emissivity coating to said membrane substrate; andremoving said damaged membrane substrate with an etchant. 21. The process of claim 20, wherein said step of conveying said membrane substrate in a stepwise fashion advances said membrane substrate about a length of said mask for every step. 22. The process of claim 20, wherein said membrane substrate is substantially stationary for at least a portion of each step. 23. A filter membrane produced according to the process of claim 20. 24. The process of claim 20, wherein said high thermal emissivity coating is applied only to one side of said membrane substrate. 25. The process of claim 20, further comprising the step of removing said high emissivity coating from said membrane substrate after said damaging. 26. The process of claim 20, wherein said energetic particle comprises at least one of hydrogen or helium ions. 27. A process for fabricating a microporous filter membrane, said process comprising the steps of:applying an intermediate mask layer and a resist coating to a membrane substrate;applying a high emissivity coating to said membrane substrate;conveying said membrane substrate in a stepwise fashion adjacent a mask;exposing said resist coating with at least one beam comprising at least one energetic particle emitted from at least one radiation source directed at least partially through said mask, wherein said energetic particle has an energy level greater than about 10 keV, and wherein said exposure occurs after said application of said high emissivity coating to said membrane substrate;developing said resist coating;etching said resist coating's pattern through said intermediate mask layer; andetching said intermediate mask layer's pattern into said membrane substrate. 28. The process of claim 27, wherein said high thermal emissivity coating is applied only to one side of said membrane substrate. 29. The process of claim 27, further comprising the step of removing said high emissivity coating from said membrane substrate after said exposure. 30. The process of claim 27, wherein said energetic particle comprises at least one of hydrogen or helium ions. |
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description | The present invention relates to a radiation-shielding glass and a method of manufacturing the same. Particularly, the present invention relates to a technology for providing a radiation-shielding glass with an effective property and allowing the radiation-shielding glass to be properly used in any application depending on a demand. In general, in order to block radiation, a metallic lead, iron, or concrete is used for the walls of facilities handling radiation, such as those of medical institutions. In this case, it is necessary to provide a room with a window when an equipment control room, an examination room, or the like is partitioned with concrete or the like. In addition, when an examination is performed by injection or inhalation of radiation-generating drug or the like into a subject, a protection screen is required for preventing the whole body of a doctor, a laboratory technician, a nurse, or the like from directly receiving radiation when observing the medical conditions of a subject close at hand, for example, by confirming the complexion and the pulse of the subject. For ensuring the safety of the human body by blocking radiation, the window and the protection screen require abilities of blocking radiation from a radiation source, so-called radiation-shielding ability. Besides, if the existence of the subject cannot be precisely confirmed with eyes, various kinds of adverse effects will be caused. In the medical field, in particular, the examination results of the subject can be adversely affected. Thus, the window and the protection screen should be provided with visibility. On the other hand, in recent years in the medical field, the execution of positron emission tomography (PET) examination, which can perform an early detection of cancer cells, has been promoted. Specifically, according to the following Non-patent Document 1, the PET examination represents the so-called “positron tomography”. It describes that the PET-CT device or the like is a new examination method to diagnose the cause of illness and the symptom by taking the activity of the heart, brain, or the like as a tomogram. As a diagnostic drug used for the PET examination, there is a compound in which a sugar component is labeled with a positron nuclide and the compound depending on the purpose of the examination is prepared in the form of an “injection” or an “inhalant”. Thus, the compound can be incorporated into the body by intravenous injection or breathing, so a tomogram can be taken by the PET-CT device. In this case, positrons are released from the labeled compound and then collide with an electron to generate radiation. In other words, 18F-FDG, for example, causes a gamma ray which is equivalent to energy of 0.511 MeV, so the detection of the gamma ray by the PET-CT device enables to specify the presence or absence of cancer cells, a focus size, and the like. Therefore, under the environment of the medical examination involving the PET examination, the subject given a diagnostic drug generates gamma rays in every direction, so an essential requirement is to prevent the body of an examiner such as a doctor from directly being exposed to the gamma rays. Further, representative examples of the radiation-shielding windows and radiation-shielding protection screens conventionally known in the art include a PbO-containing glass with high radiation-shielding property disclosed in Patent Document 1 described below. [Patent Document 1] JP 02-212331 A [Non-patent Document 1] General study business for medical technology assessment of Grant-in-Aid for Scientific Research funded from the Ministry of Health, Labor and Welfare, 2005, Study group for the security of the radiation safety in the PET examination institution, Ed., Guide line for the security in FDG-PET examination (2005) URL: http://www.jsnm.org/report/pet-anzen-gl.pdf The radiation-shielding glass disclosed in Patent Document 1 is the glass which is hard to cause a dielectric breakdown even it has high radiation-shielding property and contains a sufficient amount CeO2 for preventing the glass from coloring by radiation. Specifically, the glass, which contains a predetermined amount of PbO for enhancing the radiation-shielding property and a sufficient amount of CeO2 to inhibit coloring by radiation, further contains Na2O and K2O at a limited ratio to prevent the glass from a dielectric breakdown. However, the radiation-shielding glass disclosed in the document is a technology for preventing the glass from coloring by radiation but not for inhibiting the inherent coloring of the glass. Therefore, needles to say, even if the radiation-shielding glass is prevented from coloring attributed to radiation, the inherent coloring of the glass is not inhibited as far as the glass is already colored with its inherent color. Further, the PbO-containing glass conventionally used in medical facilities is excellent in radiation-shielding ability but has a disadvantage of poor visibility, because the PbO-containing glass is being colored to an extent that its transparency is inhibited inadversely. Therefore, as far as such glass is used as a radiation-shielding window or a radiation-shielding protection screen, a situation in which a subject cannot be precisely assessed with visual recognition will be caused. Particularly, in the medical field, it may result in an extremely serious problem such as a misdiagnosis. In spite of such a disadvantage, it is the actual condition that transparency, an important property with respect to visual recognition of the subject, is not considered at all. Therefore, a problem arises in that, with respect to the degree of transparency of such kind of glass, the level required for reasonable visibility is unknown. Therefore, the first object of the present invention is to provide a radiation-shielding glass capable of ensuring appropriate transparency to make sufficient visibility of the subject in addition to ensuring sufficient radiation-shielding ability. It is the actual condition that, as radiation-shielding means for the PET examination, any established effective material has not been found with respect to what kind of material is optimally used as a principal material among metallic lead, iron, glass, and the like even if a radiation-shielding window or a radiation-shielding protection screen is prepared. In other words, it is extremely important that the radiation-shielding means for the PET examination ensures sufficient radiation-shielding ability and sufficient visibility to prevent the body from directly being exposed to gamma rays while a doctor precisely confirm the complexion or the like of the subject. In that case, even if a shielding window or a shielding protection screen against gamma rays is fabricated using glass, it is the actual condition that a matter of how to optimize the basic composition of glass for properly shielding the gamma rays emitted from the subject and for properly recognizing the subject visually is not yet clarified in the PET examination. Therefore, in the field of the PET examination, an engineering development of improving the glass to impart an excellent property will not be performed with a proper directional guideline in the future unless the basic composition of glass for shielding gamma rays is found out first. Therefore, a second object of the present invention is to find out the basic composition of glass capable of ensuring good visibility of the subject in addition to ensuring sufficient shielding ability against gamma rays emitted from the subject when the PET examination is performed. A radiation-shielding glass according to the present invention is devised to solve the first object and includes a glass composition in % by mass of 10 to 35% SiO2, 55 to 80% PbO, 0 to 10% B2O3, 0 to 10% Al2O3, 0 to 10% SrO, 0 to 10% BaO, 0 to 10% Na2O, and 0 to 10% K2O. The radiation-shielding glass has a total light transmission at a wavelength of 400 nm at a thickness of 10 mm of 50% or more. Here, the term “at a thickness of 10 mm” described above means a case in which the radiation-shielding glass is assumed to be a plate glass with a plate thickness of 10 mm. In addition, the term “total light transmission” means an average total light transmission with respect to the plate glass (hereinafter, the same will apply). Note that, the term “percent (%)” represented in the following description indicates “% by mass”. The radiation-shielding glass constructed as described above contains 55% or more of PbO, so the radiation-shielding ability thereof can be substantially enhanced. In addition, the total light transmission of the radiation-shielding glass is 50% or more at a wavelength of 400 nm at a thickness of 10 mm. Thus, it becomes possible to ensure a suitable transparency to obtain sufficient visibility. Further, components other than PbO in the composition are limited in the predetermined ranges. Thus, a glass which is hard to be devitrified can be obtained with a result that the viscosity of the glass can be increased at the time of forming molten glass. Consequently, it becomes possible to obtain a glass with a large plate thickness. Therefore, the radiation-shielding glass, which can be provided with high transparency, radiation-shielding ability, and devitrification resistance at once, can be obtained. In particular, if the radiation-shielding glass has a large plate thickness, the radiation-shielding ability and the transparency can be maintained at very high levels. Consequently, the radiation-shielding glass having a very advantageous merit can be realized. In this case, it is preferable that the surface of the radiation-shielding glass be subjected to a low-reflection treatment with the formation of a thin film (e.g., antireflection film) having an appropriate refractive index and an appropriate thickness. The reflection loss of the radiation-shielding glass thus obtained is preferably 0.3 to 4.0, and the lower limit thereof may be 0.5, but the upper limit thereof is more preferably 3.5. In this way, like the above radiation-shielding glass, the visibility of the glass can be more improved while the total light transmission thereof at a wavelength of 400 nm at a thickness of 10 mm is 50% or more. Here, the reflection loss R of the glass is a value which can be calculated by R=((n−1)/(n+1))2, where n represents the refractive index of the glass. Further, a radiation-shielding glass according to the present invention is devised to solve the second object and includes a glass composition in % by mass of 10 to 35% SiO2, 55 to 80% PbO, 0 to 10% B2O3, 0 to 10% Al2O3, 0 to 10% SrO, 0 to 10% BaO, 0 to 10% Na2O, and 0 to 10% K2O. The radiation-shielding glass is used for a gamma-ray shielding material for a PET examination. In other words, the inventors of the present invention have found that the radiation-shielding glass having such a basic composition can be appropriately used as a gamma-ray shielding material for use in PET examination. Specifically, as already described, PbO amount is 55% or more, so the radiation-shielding ability can be extensively enhanced. Besides, components other than PbO in the composition is limited in the respective predetermined ranges, so the radiation-shielding glass, which can be provided with high transparency, radiation-shielding ability, and devitrification resistance at once, can be obtained. In particular, if the radiation-shielding glass has a large plate thickness, the radiation-shielding ability and the transparency can be maintained at very high levels. As far as the glass is provided with such properties, a desired base material having a sufficient gamma-ray shielding property and a sufficient visibility can be obtained as a gamma-ray shielding material for use in PET examination. Therefore, in the field of the PET examination, a novel and useful gamma-ray shielding glass, that is, the gamma-ray shielding glass which enables to prevent an examiner such as a doctor from directly being exposed to the gamma rays emitted from a subject due to the administration of a diagnostic drug and to prevent the doctor or the like from making a misdiagnosis on the subject (patient) at the time of checking a complexion thereof, can be obtained. The radiation-shielding glass preferably includes 200 ppm or less of Fe2O3 and 50 ppm or less of Cr2O3. When the radiation-shielding glass is constructed as above, the coloring of the glass due to Fe2O3 and Cr2O3 contained as impurities can be suppressed as far as possible. In other words, the inventors have found that factors having influence on the transparency of the radiation-shielding glass are glass impurities typified by Fe2O3 and Cr2O3 as those having significant influence thereon, and that a significant improvement in transparency of the radiation-shielding glass can be attained by limiting the content of Fe2O3 to 200 ppm or less and limiting the content of Cr2O3 to 50 ppm or less. Here, the reason why the radiation-shielding glass is colored with Fe2O3 and Cr2O3 contained as impurities is that PbO shows the absorption of light in an ultraviolet range and thus affects the coloring of the glass even if the contents of Fe2O3 and Cr2O3 as impurities are small. In particular, even if the contents thereof are very little, PbO has a property of coloring the glass when the melting temperature of the glass is high. It may be due to the oxidation-reduction reaction of Fe ion or a change in coordination number of Fe ion. Therefore, from a view point of suppressing coloring the glass, it is important to strictly control the impurities of Fe2O3 and Cr2O3. Thus, the coloring of the radiation-shielding glass can be suppressed as far as possible by limiting the contents of Fe2O3 and Cr2O3, which are contained as impurities in the glass, to 200 ppm or less and 50 ppm or less, respectively. The impurities of Fe2O3 and Cr2O3 are mixed in the glass from raw materials or from equipment used in the process of grinding or mixing the raw materials (e.g., equipment constructed of materials such as iron and stainless steel). Thus, the contents of Fe2O3 and Cr2O3 in the glass can be reduced by using a raw material with small contents of Fe2O3 and Cr2O3. In addition, the materials of the equipment used in the process of grinding or mixing the raw materials may be replaced with materials which can be hardly mixed with Fe2O3 and Cr2O3 or materials without mixing with Fe2O3 and Cr2O3, or the process of removing Fe2O3 and Cr2O3 may be introduced, thereby reducing the content of Fe2O3 and Cr2O3 in the glass. By taking the above measures, the content of Fe2O3 in the glass can be limited to 200 ppm or less and the content of Cr2O3 in the glass can be limited to 50 ppm or less. Radiation used in medical facilities include X-rays and gamma rays which have different strengths of radiation energies. In other words, the permeability of gamma-ray is higher than that of X-ray, so the radiation-shielding glass should have a large plate thickness for providing the radiation-shielding glass with a sufficient radiation-shielding property. In medical facilities dealing with gamma rays, the desired transparency of the radiation-shielding glass to be used in a radiation-shielding window and a radiation-shielding protection screen is an extremely important property in combination with a condition that the above plate thickness should be enlarged. On the other hand, it is necessary to examine many subjects in any of medical facilities dealing with the PET examination, so radiation is continuously emitted from the subjects injected with or inhaling drugs all around a facility for pharmaceutical synthesis, a facility for drug preparation, a drug infusion room, a waiting room for subjects, an examination room, and the like in any of medical facilities dealing with the PET examination. Therefore, a serious problem may occur that doctors, laboratory technicians, and nurses, who carry out the examination, will be cumulatively covered with and exposed to the radiation. According to the above Non-patent Document 1, a guideline about a decrease in exposure dose of a laboratory technician or about radiation protection is disclosed. Gamma rays generated from positron nuclide have an effective dose equivalent of 2.2 mm sievert. It is assumed that the laboratory technician is exposed to a large amount of radiation within a short time in consideration of each actual equivalent dose corresponding to 0.3 mm sievert per once in the chest X-ray examination. From the above point of view, the radiation exposure management for doctors and the like is important in the medical facilities dealing with the PET examination. Thus, it is required that the radiation-shielding glass have sufficient radiation-shielding ability, so the composition of the glass should necessarily contain a lot of PbO. Therefore, if the content of PbO is 55% or more, the glass can be provided with higher radiation-shielding ability than the conventional radiation-shielding glass in addition to the previously-explained advantages, thereby being applicable to those applications. In addition, the plate thickness of the radiation-shielding glass should be enlarged to shield radiation as far as possible. For stably forming a glass with a large plate thickness, however, the glass should be molded in a high viscosity state. Thus, there is a need of a glass without being devitrified at high viscosity, with high liquidus viscosity. In addition, for shielding against radiation as far as possible, there is a need of including a large amount of PbO in the glass composition of the radiation-shielding glass. In this case, however, the glass tends to become thermally unstable, so the glass which is more difficult to be devitirified can be required. The radiation-shielding glass includes components other than PbO in the glass composition which are limited in the predetermined ranges, so it can show extremely high thermal stability and the plate thickness of the glass can be easily enlarged even when the content of PbO is high. The radiation-shielding glass preferably includes 100 to 20,000 ppm of Sb2O3 as the glass composition, includes 0 to 20,000 ppm of Cl2 as the glass composition, or the glass composition is substantially free from As2O3. In this way, a clarifier used may be Sb2O3 or Cl2, and As2O3 harmful to the environment is not contained. Thus, there is no risk of polluting the environment at the time of performing the glass production process or waste glass disposition. Besides, Sb2O3 or Cl2 is a clarifier with a property of generating a large amount of clear gas when melting glass is in low temperature, so the following advantages may be also provided. That is, as already stated, from a viewpoint of suppressing the coloring of the glass, it is important to control impurities, Fe2O3 and Cr2O3, strictly. On the other hand, it may be also important to reduce the melting temperature of the glass in order to inhibit the reaction of Fe ion or the like. Simultaneously, it is also important to reduce the melting temperature of the glass from an energy standpoint. However, if the melting temperature of the glass is lowered, the viscosity of the glass at the time of melting becomes high, which makes it difficult to obtain a foamless glass. In order to obtain the foamless glass, it is important to use a clarifier which generates clear gas within a temperature, ranging from the temperature at the time of vitrification reaction to the temperature at the time of homogenization melting. In addition, the clarification of the glass is carried out such that gas generated in the vitrification reaction is purged out of the glass melt by clear gas and minute foam remained at the time of the homogenization melting is then floated and removed by enlarging the diameter of the foam with the clear gas which is generated again. However, if the viscosity of the glass at the time of melting is high, these effects are hard to obtain. The radiation-shielding glass of the present invention is defined based on the above findings and has a composition that allows the glass to be molten at low temperatures. Specifically, the content of PbO is 55% or more to make the glass capable of being molten at low temperatures while Sb2O3 or Cl2 which generates a large amount of clear gas at low temperature is used as a clarifier. Thus, it becomes possible to solve the above disadvantages of melting property at low temperatures, foam quality, and transparency at once. Further, the radiation-shielding glass preferably has a chromaticity for a C light source calculated from a total light transmission at 380 to 700 nm in a region surrounded by X and Y coordinates (X, Y)=(0.3101, 0.3160), (0.3250, 0.3160), (0.3250, 0.3400), and (0.3101, 0.3400). Here, the term “chromaticity” described above means a measured value of a plate glass with a plate thickness of 10 mm when the radiation-shielding glass is assumed to be a plate glass and the term “total light transmission” means an average total light transmission of the plate glass (hereinafter, the same will apply). In this way, the transparency of the glass can be secured more reliably. In other words, if the chromaticity of the glass is out of the above range, the coloring glass becomes remarkable and the transparency of the glass becomes worse, thereby making the visibility worse. Thus, those disadvantages can be avoided by placing the chromaticity within the above range. The radiation-shielding glass preferably has a liquidus viscosity of 103.5 dPa·s or more. Thus, a liquidus viscosity of 103.5 dPa·s or more allows the glass to be thermally stable without particles and devitrification even if the glass is formed at high viscosity. As a result, the forming of glass with large plate thickness can be attained. On the other hand, if the liquidus viscosity is less than 103.5 dPa·s, the glass is easily devitrified and its stable production becomes difficult. Thus, it becomes difficult to obtain the glass with large plate thickness. In particular, the glass with a large PbO content has a tendency of being devitrified easily, so the glass is preferably provided with a liquidus viscosity of 103.5 dPa·s or more. In this case, the glass may have a liquidus viscosity of 103.0 dPa·s or more. Note that the liquidus viscosity of the glass can be increased by raising the content of SiO2 while lowering the content of B2O3. Here, the term “liquidus viscosity” described above means the viscosity of the glass at liquidus temperature. Specifically, the liquidus temperature of the glass indicates a value obtained by placing a powdery sample with 300 to 500 μm in size, which is sufficiently washed, in a platinum boat, retaining it for 48 hours in an electric furnace with a temperature gradient of 800 to 500° C., cooling it in the air, and measuring a temperature when the deposition of a crystal is initiated in the glass. The liquidus viscosity of the glass represents a value obtained such that the viscosity thereof equivalent to liquidus temperature is calculated from a viscosity curve formed from viscosity obtained by the platinum pulling-up method. Note that it is preferable to grind the surface of the glass because the deposit position of a crystal deposited in the glass is easily distinguished. Further, the radiation-shielding glass as described above preferably has a density of 4.00 g/cm3 or more. In other words, when the glass has a density of less than 4.00 g/cm3, a disadvantage of difficulty in obtaining high radiation-shielding ability is caused. Thus, the density is favorably in the above numerical value range. From such a viewpoint, the density of the glass is more preferably 4.20 g/cm3 or more. Further, the density of the glass can be raised by an increase in content of each of PbO, SrO, and BaO. Further, the strain point of the above radiation-shielding glass is preferably 360° C. or more. In other words, if the strain point is lower than 360° C., a disadvantage in that the glass tends to be influenced by thermal deformation or thermal shrinkage in the thermal process is caused. Thus, the strain point is favorably in the above numerical value range. From such a viewpoint, the strain point is more preferably 380° C. or more. Note that the strain point can be raised by an increase in content of each of SiO2 and Al2O3. Further, the radiation-shielding glass has a plate-like body formed in a plate shape and the plate-like body preferably has a plate thickness of 10 mm or more. Thus, because the glass is a plate-like body in the form of a plate, radiation can be shielded over a large area. In addition, a sufficient radiation-shielding ability can be obtained by forming the plate-like body with a plate thickness of 10 mm or more. Thus, gamma rays with higher permeability than X rays can be effectively shielded. In particular, the glass effectively shields gamma rays generated from positron nuclide with a high effective dose. Thus, a doctor, a laboratory technician, a nurse, or the like who performs the PET examination can be effectively prevented from a situation of being cumulatively stand in radiation and exposed to the radiation. From such a viewpoint, the plate thickness of the plate-like body is 14 mm or more, preferably 18 mm or more, and more preferably 22 mm or more. Note that the upper limit of the plate thickness of the plate-like body is preferably 60 mm. In addition, the radiation-shielding glass described above has a gamma-ray attenuation coefficient of preferably 0.5 cm−1 or more, more preferably 0.55 cm−1 or more, still more preferably 0.6 cm−1 or more, and further preferably 0.65 cm−1 or more at a gamma-ray energy of 0.511 MeV. Here, the radiation attenuation coefficient (gamma-ray attenuation coefficient) is used as a parameter representing radiation-shielding ability, or a numeric value representing how much incident radiation is absorbed. The larger the value of the gamma-ray attenuation coefficient is, the more excellent the radiation-shielding ability is. In other words, if the gamma-ray attenuation coefficient is less than 0.5 cm−1 at a gamma-ray energy of 0.511 Mev, a sufficient radiation-shielding ability cannot be obtained. Thus, the gamma-rays having higher permeability than the X-rays cannot be effectively shielded. Further, the gamma-rays generated from positron nuclide with a high effective dose cannot be effectively shielded, so a doctor who performs the PET examination may be cumulatively stand in radiation and then resulted in a situation of being exposed to the radiation. Therefore, if the gamma-ray attenuation coefficient is in the above numerical value range, such a disadvantage will hardly occur. In this case, for attaining the above second object, the radiation-shielding glass having a characteristic feature of being used for a gamma-ray shielding material for the PET examination is preferably used in a gamma-ray shielding window or a gamma-ray shielding protection screen. Thus, the radiation-shielding glass can be used in a gamma-ray shielding window for the PET examination or a gamma-ray shielding protection screen for the PET examination, so the gamma rays generated from positron nuclide with high radiation permeability can be effectively shielded. Thus, a doctor, a laboratory technician, a nurse, or the like who performs the PET examination can be effectively prevented from a situation of being cumulatively stand in radiation and exposed to the radiation. In particular, if it is used as a gamma-ray shielding protection screen for the PET examination, a more preferable effect can be obtained, because the distance between a subject and a doctor or the like interrupted by the screen is short and there is a high necessity to avoid the radiation exposure. In addition, when a laboratory technician or a nurse observes the medical conditions of a subject close at hand, the medical conditions of the subject (e.g., the complexion or the like of the subject) can be properly determined visually. Therefore, problems such as a misdiagnosis by misobserving the medical conditions of the subject, are effectively avoided. On the other hand, for attaining the above first object, the radiation-shielding glass having a feature of having a total light transmission of 50% or more at a wavelength of 400 nm at a thickness of 10 mm is preferably used in a gamma-ray shielding window for medical purposes or a gamma-ray shielding protection screen for medical purposes. Thus, the radiation-shielding glass has a high radiation-shielding ability, excellent transparency without coloring, and high liquidus viscosity while being capable of increasing the plate thickness of the glass, so it can further enhance the gamma-ray shielding ability. In addition, when a laboratory technician or a nurse observes the medical conditions of a subject close at hand, the medical conditions of the subject can be properly determined visually. Further, the radiation-shielding glass is preferably used for a gamma-ray shielding window for a PET examination or a gamma-ray shielding protection screen for a PET examination. Thus, gamma rays generated from positron nuclide with high radiation permeability can be effectively shielded, so a doctor, a laboratory technician, a nurse, or the like who performs the PET examination can be effectively prevented from a situation of being cumulatively stand in radiation and exposed to the radiation. In particular, the window or the protection screen has excellent transparency. Thus, when a laboratory technician or a nurse observes the medical conditions of a subject close at hand, the medical conditions of the subject (e.g., the complexion or the like of the subject) can be more properly determined visually. Therefore, problems such as a misdiagnosis by misobserving the medical conditions of the subject, are more effectively avoided. The radiation-shielding glass is a glass plate formed in a plate shape, and it is preferable that an effective dose build-up factor for the radiation based on a glass composition and a density of a glass plate to be formed be calculated before the formation of the glass plate, an effective dose transmission of the glass plate to be formed for the radiation be calculated by multiplying the effective dose build-up factor by a transmission when the radiation is perpendicularly incident on the glass plate to be formed, and a theoretical plate thickness value of the glass plate to be formed be determined based on the effective dose transmission, and an actual plate thickness is set to be equal to or higher than the theoretical plate thickness value. Thus, the transmission (transmission without a consideration of an influence of scattered rays of radiation) when the radiation is perpendicularly incident on the glass plate to be molded is corrected by an effective dose build-up factor (hereinafter, simply referred to as build-up factor) that represents an increment of the dosage by the scattered rays. Based on the amended transmission (effective dose transmission), the plate thickness of the glass plate to be formed (i.e., theoretical plate thickness value) is determined. Therefore, the radiation-shielding glass plate is formed based on the theoretical plate thickness value in consideration of an influence of the scattered rays of the radiation. Consequently, the radiation including scattered rays can be properly shielded and the desired radiation-shielding ability can be ensured with an appropriate plate thickness. Thus, the plate thickness becomes unnecessarily large with respect to the desired radiation-shielding ability. Therefore, the situation where unrighteous soaring costs of the radiation-shielding glass plate can be avoided reliably. Here, the fact that radiation can be shielded means that the incident radiation is absorbed by the shield. The radiation is attenuated by the photoelectric effect or the Compton scattering in the shield. As shown in FIG. 1, when the energy of radiation incident on the substance is small, almost all of the radiation can be attenuated according to the photoelectric effect where the radiation collides with electrons in atoms and completely lose the energy thereof. In contrast, when the energy of radiation increases and enters the energy region of gamma-rays exceeding 200 KeV, the degree of attenuation of gamma-rays in the substance is almost equal to the degree due to the Rayleigh scattering or the Compton scattering. The Rayleigh scattering is a phenomenon in which the gamma rays only change the direction thereof without loss of energy by colliding with electrons in atoms. However, the Compton scattering is a phenomenon in which a part of the energy of the gamma-rays incident on the substance is given to electrons to change the energy state thereof and the direction thereof. As a result, the gamma rays are considered to be absorbed and scattered. In general, for the shielding performance, a plate thickness at which the transmission of the lead glass and the transmission of lead against a direct ray become equal is represented by a parameter of a lead equivalent. If the gamma ray (direct ray) of the lead glass of 10 mm in thickness has a gamma-ray attenuation rate of 50% and lead of 3 mm in thickness has a gamma-ray attenuation rate of 50%, then the glass of 10 mm in thickness has a shielding ability of 3 mm Pb (3 mm equivalent). Further, as shown in FIG. 2(A), when a radiation emitted from a radiation source is a narrow beam, the gamma-ray intensity entered into a shield (radiation-shielding glass plate) is defined as I0, the gamma-ray intensity exited the shield is defined as I, the linear attenuation coefficient of the shield corresponding to the energy of gamma-ray to be used is defined as μ (/cm), and the thickness of the shield is defined as t (cm), the relationship of I=I0×exp (−μt) can be established. However, when the radiation emitted from the radiation source are spreading beams, the relation of I=B×I0×exp (−μt) where the build-up factor of the shield is defined as B can be established. For example, in the case of the PET examination, the radiation source is a subject, radiation can be radiated in all angles as illustrated in FIG. 2(B). A part of the radiation is scattered when passing through the shield and the direction thereof is changed. Thus, with respect to the dose of the radiation passing through the shield, the dose of photons or the like being scattered is added to the dose of radiation rays directly passing through the shield. Therefore, for obtaining a dose rate after the radiation passing through the shield, the equation of I=B×I0×exp (−μt) should be used in consideration of the dose scattering on the shield. In the case of carrying out the shielding calculation for the radiation-shielding glass plate, a lead equivalent is generally used. In other words, first, the transmission of lead should be revealed. The data of transmission and build-up factor B of lead is described in “Shielding calculation business manual for radiation facilities, 2000” edited and published by the Nuclear Safety Technology Center (incorporated association) and widely used for the databases of the shielding calculation. At present, the influence of scattering is not considered when the lead glass commercially marketed for the X-ray shielding is diverted to a radiation-shielding glass plate for the PET examination. Thus, the risk is increasing because the amount of gamma-rays actually permeating the glass is increasing, and the amount of the radiation exposure also increases. In particular, when the radiation energy enters the energy region of gamma rays, which exceeds 200 KeV, the plate thickness of the shield should be designed, considering the influence of gamma rays scattered in the shield. Thus, the build-up factor B of the radiation-shielding glass plate is calculated by a computer simulation and the plate thickness thereof is then designed using the build-up factor B. As a result, a glass with higher safety with respect to gamma ray shielding can be designed and provided. In the radiation-shielding glass, it is preferable that the theoretical plate thickness value be obtained by further making a comparison between an effective dose transmission of lead obtained based on an effective dose build-up factor of lead with respect to the radiation and the effective dose transmission of the glass plate to be formed. Thus, the theoretical plate thickness value of the glass plate to be formed can be determined based on lead with a demonstrated radiation-shielding ability. Thus, when the radiation-shielding glass is actually formed based on the theoretical plate thickness value, the radiation-shielding ability required for the radiation-shielding glass can be ensured with a more appropriate plate thickness. Further, it is preferable that the theoretical plate thickness value be set to a value where the effective dose transmission of the glass plate to be formed is 60% or less with respect to a gamma ray at 0.511 MeV. Thus, for example, the radiation-shielding glass formed with a theoretical plate thickness value can be suitably utilized as a gamma-ray shielding window or a gamma-ray shielding protection screen used in the PET examination. In addition, the effective dose build-up factor of the glass plate to be formed is preferably calculated by Monte Carlo method. Thus, the build-up factor of a glass plate to be formed can be accurately calculated in a simple manner. Further, the radiation-shielding glass preferably has, when the theoretical plate thickness value is defined as t, the actual plate thickness in the range of t or more and 1.3 t or less. In other words, if the radiation-shielding glass plate has a plate thickness less than a theoretical plate thickness value t, the radiation containing scattered rays cannot be sufficiently shielded. In addition, if the plate thickness of a radiation-shielding glass plate for medical uses is more than 1.3 times higher than the theoretical plate thickness value t, the plate thickness is unnecessarily enlarged with respect to the desired radiation-shielding ability, resulting in unrighteous soaring costs. Therefore, if the radiation-shielding glass plate for medical uses has a plate thickness (t or more and 1.3 t or less) in the above-mentioned numerical value range, the radiation containing scattered rays can be appropriately shielded and the desired radiation-shielding ability can be satisfied with the optimal plate thickness. Further, a decrease in visibility due to an unnecessary increase in plate thickness of the radiation-shielding glass plate for medical uses can be favorably avoided. In other words, for example, the medical conditions of the subject can be favorably observed through the radiation-shielding glass plate for medical uses. Further, the radiation-shielding glass preferably has a density of 4.00 g/cm3 or more, and an effective dose transmission of 60% or less with respect to a gamma ray at 0.511 MeV. Those radiation-shielding glasses above preferably have a size of 800 mm×1,000 mm. Thus, when the radiation-shielding glass is used for a gamma-ray shielding window for medical uses and a gamma-ray shielding protection screen for medical uses, the visibility of the glass can be increased. Thus, the medial conditions of the subject can be easily observed by a doctor, a laboratory technician, a nurse, or the like who carrying out the PET examination. In addition, if the length and width of the shielding surface of the radiation-shielding glass for medical uses is 800 mm×1,000 mm or more, gamma rays generated from positron nuclide with higher radiation permeability than X-rays can be effectively shielded. Thus, a doctor, a laboratory technician, a nurse, or the like who performs the PET examination can be effectively prevented from a situation of being cumulatively exposed to radiation and suffered from the radiation more than a safety level. In particular, it is more preferable in the case of using a gamma-ray shielding protection screen for the PET examination, because there is a high demand for the use of the gamma-ray shielding protection screen in a state that the distance between a subject and a doctor or the like is short, with the protection screen interposed therebetween, while avoiding radiation exposure. As a radiation-shielding glass article including the above radiation-shielding glass, it is preferable to include a single plate glass formed of the radiation-shielding glass. Thus, there is no need of employing a method of enhancing the radiation-shielding ability of the glass by performing a lamination process or the like to attach a plurality of thin glass plates on top of one another. Thus, the production can be facilitated. Further, the steps are few and a problem in cost increasing or the like due to the soaring material costs is not caused. As a result, it becomes possible to greatly contribute to lower the costs of all the radiation-shielding glass articles. Note that depending on purposes, the surface of the glass plate may be provided with any of various functional films. On the other hand, a method of manufacturing the radiation-shielding glass described above includes a step of obtaining molten glass by melting a glass material in a melting furnace, where the molten glass has a melting temperature of 1,400° C. or less. In other words, when the melting temperature of molten glass is higher than 1,400° C. in a method for manufacturing such a kind of radiation-shielding glass, the glass tends to be colored even if the contents of impurities, Fe2O3 and Cr2O3, are small. Besides, an environmental load becomes large and leads to the soaring of energy costs, so a disadvantage of increased production costs occurs. However, if the molten glass has a melting temperature of 1,400° C. or lower, such a disadvantage can be effectively avoided. From this viewpoint, the melting temperature is more preferably 1,350° C. or lower or 1,300° C. or lower, still more preferably 1,250° C. or lower or 1,200° C. or lower. Further, as a method of forming radiation-shielding glass described above, various forming methods are known in the art, including a roll out method, a float method, a slot down draw method, an overflow down draw method, a redraw method, and the like. Any of them may be suitably selected. In particular, the radiation-shielding glass described above is preferably formed by the roll out method. The roll out method efficiently produces a plate glass with a large plate thickness and the molten glass can be formed quickly. Thus, the glass can hardly cause the devitrification at the time of formation, so the plate glass with a large plate thickness can be more efficiently obtained. As a method of manufacturing radiation-shielding glass, it is preferable to further include a step of setting a theoretical plate thickness value, including: calculating an effective dose build-up factor for the radiation based on a glass composition and a density of a glass plate to be formed before a step of forming a glass plate from a molten glass; calculating an effective dose transmission of the glass plate to be formed for the radiation by multiplying the effective dose build-up factor by a transmission when the radiation is perpendicularly incident on the glass plate to be formed; and setting the theoretical plate thickness value of the glass to be formed based on the effective dose transmission. Thus, an advantage of using an effective dose build-up factor to set the theoretical plate thickness value of a glass plate to be formed is already described, so the description thereof will be omitted herein. In this case, in the step of setting the theoretical plate thickness value, the theoretical plate thickness value is preferably set by making a comparison between an effective dose transmission of lead obtained based on an effective dose build-up factor of lead against the radiation and an effective dose transmission of the glass plate to be formed. Thus, an advantage by setting the theoretical plate thickness value of the glass plate to be formed based on lead whose shielding ability against radiation has been demonstrated is also already described, so the description thereof will be omitted herein. Note that the method of manufacturing a radiation-shielding glass for medical uses and the radiation-shielding glass for medical uses according to the present invention may have the following configuration as a basic feature. In other words, the method of manufacturing radiation-shielding glass for medical uses may have a basic feature of calculating an effective dose build-up factor for radiation based on the glass composition and the density of the glass plate to be formed before the step of forming a glass plate, calculating an effective dose transmission of the glass plate to be formed for the radiation by multiplying the effective dose build-up factor by a transmission when the radiation is perpendicularly incident on the glass plate to be formed, and setting the theoretical plate thickness value of the glass plate to be formed based on the effective dose transmission. The radiation-shielding glass for medical uses may have a basic feature where the glass is a glass plate having a plate thickness equal to or larger than the theoretical plate thickness value of the glass. As described above, according to the radiation-shielding glass of the present invention corresponding to the first object, the glass composition includes 55% or more of PbO, so the radiation-shielding ability of the glass can be considerably enhanced. Besides, the total light transmission at a wavelength of 400 nm at a thickness of 10 mm is 50% or more, so appropriate transparency can be ensured to attain sufficient visibility. In addition, according to the radiation-shielding glass of the present invention corresponding to the second object, a desired base material having sufficient gamma-ray shielding performance and sufficient visibility can be obtained as a gamma-ray shielding material for use in PET examination. Thus, in the field of the PET examination, it becomes possible to prevent an examiner such as a doctor from directly being exposed to gamma rays radiated from a subject with administration of a diagnostic drug, while effectively avoiding a misdiagnosis or the like when a doctor or the like confirms the complexion or the like of the subject. Hereinafter, the embodiments of the present invention will be described. The radiation-shielding glass according to the present embodiment includes a glass composition in % by mass of 10 to 35% SiO2, 55 to 80% PbO, 0 to 10% B2O3, 0 to 10% Al2O3, 0 to 10% SrO, 0 to 10% BaO, 0 to 10% Na2O, and 0 to 10% K2O. The radiation-shielding glass has a total light transmission at a wavelength of 400 nm at a thickness of 10 mm of 50% or more and is used for a gamma-ray shielding material for a PET examination. Further, the clarifier includes Sb2O3 or Cl2 but substantially does not contain As2O3 which is harmful to the environment. Further, the content of Fe2O3 and Cr2O3, which are impurities, are 200 ppm or less and 50 ppm or less, respectively. The reasons for limiting the basic composition of the glass as described above will be described below. SiO2 is a component forming the network of the glass. The content thereof is 10 to 35%, preferably 10 to 30%, more preferably 20 to 30%. If the content of SiO2 exceeds 35%, the high-temperature viscosity of the glass is increased. As a result, it becomes difficult to melt and form the glass and the radiation-shielding ability of the glass is decreased. In contrast, if the content of SiO2 is less than 10%, the amount of a component forming the skeleton of the glass becomes too small. As a result, the glass becomes thermally unstable and the water resistance of the glass is decreased. PbO is a component for shielding against radiation. The content of PbO is 55 to 80%, preferably 60 to 80%, more preferably 65 to 80%, and still more preferably 70% to 80%. If the content of PbO exceeds 80%, the contents of components other than PbO becomes relatively small and the glass is made thermally unstable. On the other hand, if the content of PbO is 50% or less, the radiation-shielding ability of the glass is decreased. B2O3 is a component that lowers the high-temperature viscosity of the glass to enhance melting property and formability and also heightens the thermal stability of the glass. The content of B2O3 is 0 to 10%, preferably 0.1 to 8%, and more preferably 0.1 to 5%. If the content of B2O3 exceeds 10%, the water resistance of the glass is decreased. Al2O3 is a component that enhances the thermal stability of the glass. The content of Al2O3 is 0 to 10%, preferably 0.1 to 8%, and more preferably 0.1 to 5%. If the content of Al2O3 exceeds 10%, the high-temperature viscosity of the glass is increased. As a result, it becomes difficult to melt and form the glass and the radiation-shielding ability of the glass is decreased. SrO and BaO are components for adjusting the viscosity and the devitrification of the glass and enhancing the radiation-shielding ability thereof. The content of each of SrO and BaO is 0 to 10%, preferably 0 to 8%, and more preferably 0 to 5%. If the content of SrO or BaO exceeds 10%, the glass becomes thermally unstable. Na2O and K2O are components that lower the high-temperature viscosity of the glass while enhancing the melting property and the formability of the glass. The content of each of Na2O and K2O is 0 to 10%, preferably 0 to 8%, and more preferably 1 to 5%. If the content of Na2O or K2O exceeds 10%, the radiation-shielding ability of the glass is decreased. Sb2O3 is a component that acts as a clarifier. The content of Sb2O3 is 100 to 20,000 ppm (preferably 200 to 20,000 ppm, 500 to 20,000 ppm, 1,000 to 20,000 ppm, more than 5,000 to 20,000 ppm, 5,500 to 20,000 ppm, 6,000 to 20,000 ppm). If the content of Sb2O3 is less than 100 ppm, clarification ability can be hardly obtained and foam in the glass can be hardly reduced. Further, if the content of Sb2O3 exceeds 20,000 ppm, an increase in raw material costs occurs because Sb2O3 is expensive. Cl2 is a component that acts as a clarifier. The content of Cl2 is 0 to 20,000 ppm, preferably 200 to 20,000 ppm, more preferably 500 to 20,000 ppm, and still more preferably 1,000 to 10,000 ppm. If the content of Cl2 exceeds 20,000 ppm, an excess volatilization volume of Cl2 facilitates deterioration of the glass. Note that the content of Cl2 indicates the remaining amount of Cl2 in the glass. Sb2O3 used as a clarifier in the present embodiment generates a significant amount of clear gas (oxygen gas) as a result of a chemical reaction due to a change in ionic valency in the temperature range of 900° C. or more. In particular, a significant amount of clear gas is generated at low temperature of 1,000 to 1,200° C. Further, Cl2 decomposes and then vaporizes at a temperature range of 900° C. or higher, thereby generating clear gas (e.g., chlorine gas). Therefore, a high clarification effect can be obtained when Sb2O3 or Cl2 is used as a clarifier even if a temperature ranging from the temperature at the time of vitrification reaction to the temperature at the time of homogenization melting is of low temperatures. Thus, a radiation-shielding glass without coloring and foam can be efficiently obtained. Note that any of other components can be added up to 10% as far as it does not impair the properties of the glass. When the radiation-shielding glass of the present embodiment is prepared, a plate glass is formed by the roll out method in the process of melting a glass material in a melting furnace to obtain a molten glass and then forming the molten glass into a plate glass. Here, the roll out method will be described in detail. As shown in FIG. 3, a molten glass 2 molten in a melting furnace 1 is passed through the gap between a pair of forming rolls 3 to form a strip-shaped glass ribbon 4. Then, the glass ribbon 4 is transferred by a plurality of transfer rolls 5 while being cooled, thereby forming a plate glass. Subsequently, the plate glass is finally provided as the radiation-shielding glass. As Examples 1 to 24 of the present invention, 24 kinds of glass compositions of radiation-shielding glasses (gamma-ray shielding glass) for medical uses, particularly for the PET examination, were subjected to the measurements of density, gamma-ray attenuation coefficient, strain point, liquidus temperature, liquidus viscosity, and transmission (total light transmission at a wavelength of 400 nm at a thickness of 10 mm). The results are shown in Table 1 below. TABLE 1Example123456789101112GlassSiO22627.12426.52524252427.624.627.620compositionPbO71.771.771.771.771.771.771.771.768686871.7(% by mass)B2O31.2—3.21.21.21.21.21.21.21.21.21.2Al2O3————12—————5SrO————————25——BaO——————12——2—Na2O———————————1K2O0.50.50.5—0.50.50.50.50.50.50.50.5Sb2O30.60.60.50.60.60.40.60.60.60.60.60.5Cl—0.10.1——0.2——0.10.10.10.1Density(g/cm3)5.245.235.265.235.255.265.315.395.055.265.065.33Gamma-ray attenuation0.670.660.670.660.670.670.680.69———0.67coefficient(cm−1)strain point(° C.)386401380393393399384381409412403398Liquidus temperature620645550700630690620615————(° C.)Liquidus viscosity5.45.56.34.35.34.55.25.1————(dPa · s)Transmission(%)707565707575757570707060Example131415161718192021222324GlassSiO22020.820.62025.321.321.320.320.821.320.820.8compositionPbO71.77069706868656565737575(% by mass)B2O31.24793321—211Al2O33430.5—2125111SrO1————12.521—1—BaO1————12.531.5——1Na2O1———222351——K2O0.50.5——1133110.50.5Sb2O30.50.60.30.40.60.60.60.60.60.60.60.6Cl0.10.10.10.10.10.10.10.10.10.10.10.1Density(g/cm3)5.475.135.035.015.135.145.085.045.005.405.635.64Gamma-ray attenuation0.690.640.630.630.640.640.630.620.610.690.720.72coefficient(cm−1)strain point(° C.)380396393360404364358352394355379376Liquidus temperature—————650———620640660(° C.)Liquidus viscosity—3.9———4.0———4.34.44.0(dPa · s)Transmission(%)606575807570756050606565 First, raw materials were prepared to obtain glass having a composition shown in Table 1 and a prepared batch was then placed in a quartz crucible, followed by melting at 1,150° C. for 1 hour as shown in Table 1. Subsequently, the molten glass was poured on a carbon plate to be formed into a plate shape. After gradually cooling, sample glass for each evaluation was prepared. The respective samples thus obtained were shown in Table 1 in terms of density, transmission, and the like with respect to 24 different glass compositions. It should be noted that in Table 1, the values of the density, transmission, and the like represented by the symbol “−” means unmeasured values. The density was determined by the well-known Archimedes method. The gamma-ray attenuation coefficient of gamma-ray energy (0.511 Mev) was calculated by calculation from the data of Photx. In addition, the strain point was measured based on ASTM C336-71. Note that the higher strain point is favorable and it can suppress thermal deformation and thermal shrinkage of a glass substrate in the heat process. The liquidus temperature was measured as follows. A well-washed powdery sample of 300 to 500 μm in size was placed in a platinum boat and then held in an electric furnace having a temperature gradient of 800 to 500° C. for 48 hours, followed by cooling in the air. Then, the temperature at which a crystal began to deposit in the glass was measured as the liquidus temperature of the glass. The liquidus viscosity was determined by creating a viscosity curve from viscosity obtained by the platinum pulling-up method and calculating the viscosity of glass which is equivalent to liquidus temperature from the viscosity curve. The measurement of transmission was performed using Spectrophotometer UV-2500 PC, manufactured by Shimadzu Corporation. A measured wavelength was 380 to 700 nm, a measurement speed (scan speed) was a low speed, a slit width was 5 nm, and a sampling pitch was 1 nm (that is, measurement was conducted at intervals of 1 nm). As is evident from Table 1, the transmission of the radiation-shielding glasses of Examples 1 to 24 were in the range of 50% to 80%. Most of those had transmission of 65% to 75%, having proper transparency. As Examples 25 to 30 of the present invention, 6 kinds of glass compositions of radiation-shielding glasses (gamma-ray shielding glass) for the PET examination were subjected to the measurements of density, thermal expansion coefficient α, strain point, liquidus temperature, liquidus viscosity, gamma-ray attenuation coefficient, chromaticity, and melting temperature. The results are shown in Table 2 below. In addition, the Comparative Examples 1 to 3 4-are shown in Table 3 below. TABLE 2Example252627282930GlassSiO226.027.124.026.525.024.0compositionPbO71.771.771.771.771.771.7(% by mass)B2O31.2—3.21.21.21.2Al2O3————1.02.0BaO——————K2O0.50.50.5—0.50.5Sb2O30.60.60.60.60.60.6ImpurityFe2O32012020202070(ppm)Cr2O30.20.210501.00.2Density(g/cm3)5.245.235.265.235.255.26α (×10−7/° C.)828384798180strain point(° C.)385400380395395400Liquidus temperature(° C.)620645550700630690Liquidus viscosity(dPa · s)5.45.56.34.35.34.5Gamma-ray attenuation0.670.660.670.660.670.67coefficient at 0.511 MeV(cm−1)ChromaticityX coordinate0.31140.32060.31240.31490.31200.3167Y coordinate0.31850.33660.32390.33480.31940.3270Evaluation of chromaticity◯◯◯◯◯◯Melting temperature115011501150115011501150 TABLE 3Comparative Example123GlassSiO226.026.026.0compositionPbO71.771.771.7(% by mass)B2O31.21.21.2Al2O3———BaO———K2O0.50.50.5Sb2O30.60.60.6ImpurityFe2O3250210210(ppm)Cr2O30.20.220Density(g/cm3)5.245.245.24α (×10−7/° C.)828282strain point(° C.)385385385Liquidus temperature(° C.)620620620Liquidus viscosity(dPa · s)5.45.45.4Gamma-ray attenuation0.670.670.67coefficient at 0.511 MeV(cm−1)ChromaticityX coordinate0.33000.32750.3290Y coordinate0.35600.35000.3570Evaluation of chromaticityXXXMelting temperature115011501150 First, raw materials were prepared to obtain glass having a composition shown in Tables 2 and 3 and a prepared batch was then placed in a quartz crucible, followed by melting at each temperature shown in Tables 2 and 3 for 1 hour. Subsequently, the molten glass was poured on a carbon plate to be formed into a plate shape. After gradually cooling, sample glass for each evaluation was prepared. The respective samples thus obtained were shown in Tables and 3 in terms of density, melting temperature, and the like with respect to 6 kinds of glass compositions. The density was determined by the well-known Archimedes method. For the thermal expansion coefficient α, a cylindrical sample of 5.0 mm in diameter and 20 mm in length was prepared and then an average thermal expansion coefficient at 30 to 380° C. was measured by a dilatometer. In addition, the strain point was measured based on ASTM C336-71. Note that the higher strain point is favorable and it can suppress thermal deformation and thermal shrinkage of a glass substrate in the heat process. The liquidus temperature was measured as follows. A well-washed powdery sample of 300 to 500 μm in size was placed in a platinum boat and then held in an electric furnace having a temperature gradient of 800 to 500° C. for 48 hours, followed by cooling in the air. Then, the temperature at which a crystal began to deposit in the glass was measured as the liquidus temperature of the glass. The liquidus viscosity was determined by creating a viscosity curve from viscosity obtained by the platinum pulling-up method and calculating the viscosity of glass which is equivalent to liquidus temperature from the viscosity curve. The gamma-ray attenuation coefficient of gamma-ray energy (0.511 Mev) was calculated by calculation from the data of Photx. The chromaticity was measured and evaluated as follows. A measurement sample was a mirror polished sample glass with dimensions of 20 mm×30 mm×10 mm thickness. The measurement sample was subjected to the measurement of transmission at intervals of 1 nm using Spectrophotometer UV-2500 PC, manufactured by Shimadzu Corporation. The chromaticity was determined under the conditions in which a measured wavelength was 380 to 700 nm, a measurement speed was a low speed, a slit width was 5 nm, and a radiation source was C. When the chromaticity for the C light source calculated from a total light transmission of 380 to 700 nm was in the region surrounded by X and Y coordinates (X, Y)=(0.3101, 0.3160), (0.3250, 0.3160), (0.3250, 0.3400), and (0.3101, 0.3400) was represented by “∘” and the chromaticity out of the region was represented by “×”. As is evident from Table 2, the radiation-shielding glass of the present invention showed a gamma-ray attenuation coefficient of 0.66 cm−1 or more at 0.511 MeV, thereby having a good radiation-shielding ability. In addition, it showed good color tone. On the other hand, as is evident from Table 3, the radiation-shielding glass of Comparative Example 1 resulted in poor glass transparency, because Fe2O3 content was 250 ppm and the chromaticity had coordinates of (X, Y)=(0.3300, 0.3560). The radiation-shielding glass of Comparative Example 2 resulted in poor glass transparency, because Fe2O3 content was 210 ppm and the chromaticity had coordinates of (X, Y)=(0.3275, 0.3550). The radiation-shielding glass of Comparative Example 3 resulted in poor glass transparency, because Fe2O3 content was 210 ppm, Cr2O3 content was 20 ppm, and the chromaticity had coordinates of (X, Y)=(0.329, 0.3570). The radiation-shielding glass of each of Comparative Examples 1 to 3 shown in Table 3 had a transmission of less than 50%. As Examples 31 to 38 of the present invention, 8 kinds of glass compositions of radiation-shielding glasses (gamma-ray shielding glass) for the PET examination were subjected to the measurements of density, thermal expansion coefficient a, strain point, liquidus temperature, liquidus viscosity, gamma-ray attenuation coefficient, chromaticity, foam, and melting temperature. The results are shown in Table 4 below. In addition, the Comparative Examples 4 to 6 are shown in Table 5 below. As Examples 31 to 38 of the present invention, 8 kinds of glass compositions of radiation-shielding glasses (gamma-ray shielding glass) for the PET examination were subjected to the measurements of density, thermal expansion coefficient α, strain point, liquidus temperature, liquidus viscosity, gamma-ray attenuation coefficient, chromaticity, foam, and melting temperature. The results are shown in Table 4 below. In addition, the Comparative Examples 5 to 7 are shown in Table 5 below. TABLE 4Example3132333435363738GlassSiO226.027.124.026.525.024.025.024.0compositionPbO71.771.771.771.771.771.771.771.7(% by mass)B2O31.2—3.21.21.21.21.21.2Al2O3————1.02.0——BaO——————1.02.0Na2O————————K2O0.50.50.5—0.50.50.50.5Sb2O30.60.60.50.60.60.40.60.6Cl2—0.10.1——0.2——Density(g/cm3)5.245.235.265.235.255.265.315.39α (×10−7/° C.)8283847981808587strain point(° C.)385400380395395400385380Liquidus temperature(° C.)620645550700630690620615Liquidus viscosity(dPa · s)5.45.56.34.35.34.55.25.1Gamma-ray attenuation0.670.660.670.660.670.670.680.69coefficient at 0.511 MeV(cm−1)Color tone◯◯◯◯◯◯◯◯Foam◯◯◯◯◯◯◯◯Melting temperature11501150115011501150115011501150 TABLE 5Comparative Example456GlassSiO226.027.152.0compo-PbO71.771.733.0sitionB2O31.2——(% byAl2O3——0.5mass)BaO———Na2O——7.0K2O0.50.57.0CeO2——0.5Sb2O3———Cl2—0.1—As2O3—0.6—SnO20.6——Density(g/cm3)5.245.233.24α (×10−7/° C.)8283100strain point (° C.)385400370Liquidus temperature(° C.)620645NotmeasurementLiquidus viscosity (dPa · s)5.45.5NotmeasurementGamma-ray attenuation0.670.660.34coefficient at 0.511 MeV(cm−1)Color tone◯X◯FoamX◯◯Melting temperature115014501150 First, raw materials were prepared to obtain glass having a composition shown in Tables 4 and 5 and a prepared batch was then placed in a quartz crucible, followed by melting at each temperature shown in Tables 4 and 5 for 1 hour. Subsequently, the molten glass was poured on a carbon plate to be formed into a plate shape. After gradually cooling, sample glass for each evaluation was prepared. For each of the samples thus obtained, density, thermal expansion coefficient, liquidus temperature, liquidus viscosity, gamma-ray attenuation coefficient at gamma-ray energy (0.511 Mev), color tone, foam, and melting temperature are shown in Tables 4 and 5. The density was determined by the well-known Archimedes method. For the thermal expansion coefficient α, a cylindrical sample of 5.0 mm in diameter and 20 mm in length was prepared and then an average thermal expansion coefficient at 30 to 380° C. was measured by a dilatometer. In addition, the strain point was measured based on ASTM C336-71. Note that the higher strain point is favorable and it can suppress thermal deformation and thermal shrinkage of a glass substrate in the heat process. The liquidus temperature was measured as follows. A well-washed powdery sample of 300 to 500 μm in size was placed in a platinum boat and then held in an electric furnace having a temperature gradient of 800 to 500° C. for 48 hours, followed by cooling in the air. Then, the temperature at which a crystal began to deposit in the glass was measured as the liquidus temperature of the glass. The liquidus viscosity was determined by creating a viscosity curve from viscosity obtained by the platinum pulling-up method and calculating the viscosity of glass which is equivalent to liquidus temperature from the viscosity curve. The gamma-ray attenuation coefficient of gamma-ray energy (0.511 MeV) was calculated by calculation from the data of Photx. For the color tone of the glass, formed glass was subjected to mirror polishing to have a thickness of 10 mm and the degree of coloring was then confirmed visually, followed by the measurement of transmission at 380 to 700 nm using Spectrophotometer UV-2500 PC, manufactured by Shimadzu Corporation. A transmission of 80% or more was represented by “∘” and a transmission of less than 80% was represented by “×”. The foam in the glass was evaluated using a stereoscopic microscope (×100). The foamless glass was represented by “∘” and the foam-detected glass was represented by “×”. As is evident from Table 4, the radiation-shielding glass of the present invention showed a gamma-ray attenuation coefficient of 0.66 cm−1 or more at 0.511 MeV, thereby having a good radiation-shielding ability. In addition, it showed good color tone and good foam quality. In contrast, as is evident from Table 5, the radiation-shielding glass of Comparative Example 4 showed poor foam quality. In addition, the radiation-shielding glass of Comparative Example 5 using As2O3 as a clarifier and showed a high melting temperature of 1,450° C., thereby resulting in colored glass. The radiation-shielding glass of Comparative Example 6 had a small PbO content of 33.0%, so it showed a small gamma-ray attenuation coefficient of 0.34 cm−1 at gamma-ray energy of 0.511 Mev, thereby resulting in poor radiation-shielding ability. As Examples 39 to 46 of the present invention, 8 kinds of glass compositions of radiation-shielding glasses (gamma-ray shielding glass) for the PET examination were subjected to the measurements of density, thermal expansion coefficient a, strain point, liquidus temperature, liquidus viscosity, and gamma-ray attenuation coefficient. The results are shown in Table 6 below. In addition, the Comparative Examples 7 and 8 are shown in Table 7 below. TABLE 6Example3940414243444546GlassSiO226.027.124.026.525.024.025.024.0compositionPbO71.771.771.771.771.771.771.771.7(% by mass)B2O31.2—3.21.21.21.21.21.2Al2O3————1.02.0——BaO——————1.02.0Na2O————————K2O0.50.50.5—0.50.50.50.5CeO2————————Sb2O30.60.60.60.60.60.60.60.6Cl2—0.1——————Density(g/cm3)5.245.235.265.235.255.265.315.39α (×10−7/° C.)8283847981808587strain point(° C.)385400380395395400385380Liquidus temperature(° C.)620645550700630690620615Liquidus viscosity(dPa · s)5.45.56.34.35.34.55.25.1Gamma-ray attenuation0.670.660.670.660.670.670.680.69coefficient at 0.511 MeV(cm−1) TABLE 7Comparative Example78GlassSiO248.052.0compo-PbO37.033.0sitionB2O3——(% byAl2O3—0.5mass)BaO——Na2O6.57.0K2O7.57.0CeO2—0.5Sb2O31.0—Cl2——Density(g/cm3)3.363.24α (×10−7/° C.)95100strain point (° C.)350370Liquidus temperature(° C.)NotNotmeasurementmeasurementLiquidus viscosity (dPa · s)NotNotmeasurementmeasurementGamma-ray attenuation0.360.34coefficient at 0.511 MeV(cm−1) First, raw materials were prepared to obtain glass having a composition shown in Tables 6 and 7 and a prepared batch was then placed in a quartz crucible, followed by melting at 1,150° C., as shown in Tables 6 and 7, for 1 hour. Subsequently, the molten glass was poured on a carbon plate to be formed into a plate shape. After gradually cooling, sample glass for each evaluation was prepared. For each of the samples thus obtained, density, thermal expansion coefficient, liquidus temperature, liquidus viscosity, and gamma-ray attenuation coefficient at gamma-ray energy (0.511 Mev) are shown in Tables 6 and 7. The density was determined by the well-known Archimedes method. For the thermal expansion coefficient α, a cylindrical sample of 5.0 mm in diameter and 20 mm in length was prepared and then an average thermal expansion coefficient at 30 to 380° C. was measured by a dilatometer. In addition, the strain point was measured based on ASTM C336-71. Note that the higher strain point is favorable and it can suppress thermal deformation and thermal shrinkage of a glass substrate in the heat process. The liquidus temperature was measured as follows. A well-washed powdery sample of 300 to 500 μm in size was placed in a platinum boat and then held in an electric furnace having a temperature gradient of 800 to 500° C. for 48 hours, followed by cooling in the air. Then, the temperature at which a crystal began to deposit in the glass was measured as the liquidus temperature of the glass. The liquidus viscosity was determined by creating a viscosity curve from viscosity obtained by the platinum pulling-up method and calculating the viscosity of glass which is equivalent to liquidus temperature from the viscosity curve. The gamma-ray attenuation coefficient of gamma-ray energy (0.511 MeV) was calculated by calculation from the data of Photx. As is evident from Table 6, the radiation-shielding glass for a PET examination of the present invention showed a gamma-ray attenuation coefficient of 0.66 cm−1 or more at 0.511 Mev, thereby having a good radiation-shielding ability. On the other hand, as is evident from Table 7, the gamma-ray shielding glass of Comparative Example 7 showed a small PbO content of 37% in the glass, so the gamma-ray attenuation coefficient was 0.36 cm−1, resulting in small gamma-ray shielding ability. Further, the gamma-ray shielding glass of Comparative Example 8 also showed a small PbO content of 33% in the glass, so the gamma-ray attenuation coefficient was 0.34 cm−, resulting in small gamma-ray shielding ability. Next, by using a build-up factor, an example of a method of designing the plate thickness of radiation-shielding glass for medical uses according to the present invention will be described. The composition of lead glass and the physical properties thereof are specifically shown in Tables 8 and 9. TABLE 8Composition (% by mass)SiO234B2O33PbO55BaO5Na2O1K2O2Density4.36 g/cm3Ray attenuation coefficient0.51/cmThermal expansion coefficient80 × 10−7/° C. TABLE 9Composition (% by mass)SiO227B2O3 1PbO71BaO—Na2O—K2O 1Density5.20 g/cm3Ray attenuation coefficient0.65/cmThermal expansion coefficient81 × 10−7/° C. First, raw materials were prepared to obtain a radiation-shielding glass plate for medical uses having a composition shown in Tables 8 and 9 and a prepared batch was then placed in a quartz crucible, followed by melting at 1,150° C., as shown in Tables 8 and 9, for 1 hour. Subsequently, the molten glass was poured on a carbon plate to be formed into a plate shape. After gradually cooling, sample glass for each evaluation was prepared. For each of the samples thus obtained, density, thermal expansion coefficient, and gamma-ray attenuation coefficient at gamma-ray energy (0.511 MeV) are shown in Tables 8 and 9. The density was determined by the well-known Archimedes method. For the thermal expansion coefficient α, a cylindrical sample of 5.0 mm in diameter and 20 mm in length was prepared and then an average thermal expansion coefficient at 30 to 380° C. was measured by a dilatometer. The ray attenuation coefficient of gamma-ray energy (0.511 MeV) was calculated by calculation from the data of Photx. The build-up factor B of gamma-ray energy (0.511 MeV) was calculated from the composition and the density of the glass. There are two methods for calculating the build-up factor B: one is a method of using a comparatively simple calculation formula; and the other is a method of making use of the behavior of the radiation in detail, such as absorption and scattering, in a medium between a radiation source and an evaluation point. The Monte Carlo method which is one of the latter was employed this time. Then, the build-up factor B was calculated by computer simulation for a case where lead glass is used for the shield. Calculation results of effective dose transmission for each of the case where the build-up factor B was used and the case where the build-up factor B was not used with respect to each plate thickness are shown in Tables 10 and 11. The Monte Carlo method simulates the behavior of actual radiation using a random number. TABLE 100.511 MeV gamma-ray effective dosetransmission (%)CompositionBuild-upBuild-upBuild-up1factorfactor usedfactor unusedμtt (cm)BB × exp (−μt)exp (−μt)001.001001001.02.01.4152373.05.91.991055.09.82.4920.77.013.72.940.30.09 TABLE 110.511 MeV gamma-ray effective dosetransmission (%)CompositionBuild-upBuild-upBuild-up2factorfactor usedfactor unusedμtt (cm)BB × exp (−μt)exp (−μt)001.001001001.01.51.3552373.04.61.83955.07.72.221.50.77.010.82.560.20.1 Next, the effective dose transmission of lead is shown in Table 12 which is cited from data of “Shielding calculation business manual for radiation facilities, 2000” published by the Nuclear Safety Technology Center. Note that the effective dose transmission of lead shown in Table 12 is also calculated in consideration of the build-up factor of lead against the gamma rays. TABLE 12Lead (business manual)PlateEffective dosethickness (cm)transmission (%)0.278.60.369.00.460.40.552.60.739.71.025.71.512.2 From the results shown in Tables 10, 11, and 12, a correlation calibration curve was drawn with the plate thickness and the transmission. The plate thickness of radiation-shielding glass plate for medical uses equivalent to the transmission of each lead thickness was read from the correlation calibration curve. The results thereof are shown in Table 13. TABLE 13Lead plateCorrespondingCorrespondingEffectiveplate thickness ofplate thickness ofdosecomposition 1 (mm)composition 2 (mm)Platetrans-Build-upBuild-upBuild-upBuild-upthicknessmissionfactorfactorfactorfactor(mm)(%)usedunusedusedunused278.68.24.85.93.7369.012.07.38.85.7552.619.212.614.29.91025.736.726.627.620.8 As is evident from Table 13, if the effective dose build-up factor is not used in designing plate thickness of radiation-shielding glass plate for medical uses, the transmission of a gamma ray becomes high and the design thereof is on the side of risk. If the examination is conducted under such a state, accumulative exposure of radiation of a person engaged in the examination is large and they are placed at risk. On the other hand, when a large build-up factor B for water, concrete, or the like is used for calculation because the build-up factor B is uncertain at the time of designing the plate thickness of radiation-shielding glass plate for medical uses, a thick shield more than needed may be required, although it is safe in terms of protection. For example, a situation, where the costs of the radiation-shielding glass plate for medical uses soar unrighteously, may be brought about when it is used for a wall or a window surrounding the PET examination equipment. On the other hand, the radiation-shielding glass plate for medical uses of the present invention uses an effective dose build-up factor calculated by the Monte Carlo method to design the plate thickness of the glass. Therefore, the above problems can be suitably avoided. Note that when the radiation-shielding glass plate for medical uses is actually formed, the theoretical plate thickness value is suitably selected according to the shielding ability (effective dose transmission) to be required by the glass plate. Then, the glass plate with a plate thickness of 1 to 1.3 times the selected theoretical plate thickness value is formed. Further, the reflection loss of the shielding glass plate for medical uses is preferably 3.5% or less at Na-D line. A decrease in reflection loss can be adjusted by forming a thin film on the surface of the glass plate. Industrial Applicability The radiation-shielding glass of the present invention is preferable for a gamma-ray shielding window for medical uses or a gamma-ray shielding protection screen for medical uses. In particular, it is preferable for a gamma-ray shielding window for a PET examination or a gamma-ray shielding protection screen for the PET examination. Further, the radiation-shielding glass of the present invention can be favorably used in peepholes of a gamma-ray irradiation room for an atomic reactor, a hot cape for fissionable material processing, and an accelerator (betatron, linac, etc.), a protection board for X-ray, a portable radiation protector, a lead glass block, radiation-shielding glasses, and the like. |
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abstract | A radiation generating apparatus includes a radiation generation tube including an electron emitting source having an electron emitting member, a transmission type target, a tubular backward shielding member having an electron passing hole facing the target layer at one end, located at the electron emitting source side of the transmission type target, and connected to the periphery of the base member. The radiation generating apparatus further includes a collimator having an opening for defining an angle for extracting the radiation at the opposite side of the electron emitting source side of the transmission type target, and an adjusting device connected to the collimator, and configured to vary an opening diameter of the opening, wherein the target layer has a portion separated from a connection portion of the base member and the backward shielding member at the periphery. |
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description | This invention pertains generally to direct current power supplies and more particularly to such power supplies that power the ex-core neutron detectors of a nuclear power plant. In a pressurized water reactor power generating system, heat is generated within the core of a pressure vessel by a fission chain reaction occurring in a plurality of fuel rods supported within the core. The fuel rods are maintained in a spaced relationship within fuel assemblies with the space between fuel rods forming coolant channels through which borated water flows. Hydrogen within the coolant water moderates the neutrons emitted from enriched uranium within the fuel to increase the number of nuclear reactions and thus increase the efficiency of the process. Control rod guide thimbles are interspersed within the fuel assemblies in place of fuel rod locations and serve to guide control rods which are operable to be inserted or withdrawn from the core. When inserted, the control rods absorb neutrons and thus reduce the number of nuclear reactions and the amount of heat generated within the core. Coolant flows through the assemblies out of the reactor to the tube side of steam generators where heat is transferred to water in the shell side of the steam generators at a lower pressure, which results in the generation of steam used to drive a turbine. The coolant exiting the tube side of the steam generator is driven by a main coolant pump back to the reactor in a closed loop cycle to renew the process. The power level of a nuclear reactor is generally divided into three ranges: the Source or Startup Range, the Intermediate Range, and the Power Range. The power level of the reactor is continuously monitored to assure safe operation. Such monitoring is typically conducted by means of neutron detectors placed outside and inside the reactor core for measuring the neutron flux of the reactor. Since the neutron flux in the reactor at any point is proportional to the fission rate, the neutron flux is also proportional to the power level. Fission and ionization chambers have been used to measure flux in the Source, Intermediate and Power Range of a reactor. Typical fission and ionization chambers are capable of operating at all normal power levels, however, they are generally not sensitive enough to accurately detect low level neutron flux emitted in the Source Range. Thus, separate low level Source Range detectors are typically used to monitor neutron flux when the power level of the reactor is in the Source Range. The high voltage supply is a component within the Nuclear Instrumentation System (NIS) which delivers bias voltages to the ex-core neutron detectors which convert the high voltage to charge pulses or current at rates or magnitudes dependent on the neutron flux. The pulse rates and currents are processed by the NIS for information on plant power and to provide signals for subsequent safety systems. There are two versions of the power supply whose output voltage range differs: One version covers 0 to 1500 VDC and the other covers 0 to 2500 volts of direct current (VDC). In each NIS there are typically three different types of detectors which require the high voltage bias for operation, two of which require up to 1500 VDC while a third requires up to 2500 VDC. A new high voltage power supply design is needed as a replacement for an existing design which was installed during the construction of the nuclear plant. The existing unit contains proprietary and outdated technology which is becoming difficult to repair and/or replace. Extended vendor lead times and reliability issues are becoming more common. Various aspects of the high voltage required for the detectors and the NIS overall dictate particular functional requirements of the high voltage supply. For instance, the system requires a high voltage that is very low in alternating current (AC) components (ripple) or impulsive noise, which could be translated by the detector into pulses that combine with the desired neutron generated pulses and interfere with the processed information or trip signals. Faults in the NIS cabling can lead to short circuits on the output of the supply or other degraded load conditions. The high voltage power supply must address these conditions while remaining intact once the faults are addressed. This invention provides a power supply including an alternating current input and a direct current output that is configured to be adjustable between substantially 0 and 2,500 VDC. A test point on the power supply is configured to provide an operator with information about any voltage ripple superimposed on the direct current output. In one embodiment, the power supply comprises two separate circuit modules, a first module of the two separate circuit modules comprises a line powered switcher for converting the alternating current input into a steady state direct current at the direct current output and a second module of the two separate circuit modules comprises a high voltage switcher constructed to raise the voltage level provided by the first module to a desired adjustable output voltage. In the foregoing embodiment the first module and the second module are respectively independent switched mode power supplies. Preferably, the first module includes a series arrangement of, an input current limiter, a first surge protector, an inrush limiter, a line filter, an EMI filter, a second surge protector, an input rectifier/filter, a transformer, an output rectifier and an output filter. One of the first surge protector and the second surge protector is preferably a Metal Oxide Varistor and another of the first surge protector and the second surge protector is a transient voltage suppressor. The foregoing embodiment further includes a feedback controller/switch optically coupled in series with a reference generator in parallel with series arrangement of the transformer, output rectifier and output filter. In another embodiment, the second module comprises a wire-wound potentiometer connected between a reference voltage and ground with the wiper configured to move along and in electrical contact with the resistive wire within the potentiometer, the wiper being connected in a series arrangement including a buffer amplifier, a controller, a driver/switches, a high voltage transformer, an output rectifier doubler and an output filter. Preferably, a feedback loop extends between an output of the output filter and an input to the controller. This embodiment, desirably, also includes an overvoltage sensing circuit connected between an output of the output filter and the controller in parallel with the series arrangement, the overvoltage sensing circuit being configured to identify an overvoltage condition and signal the controller when an overvoltage condition is detected to shut down the high voltage portion of the power supply. This embodiment also may include an overcurrent sensing circuit connected between the controller and the driver/switches, in parallel with the series arrangement, the overcurrent sensing circuit being configured to identify an overcurrent condition and signal the controller when an overcurrent condition is detected to shut down the power supply. Preferably, the power supply is at least partially enclosed within a housing including a plurality of lights visible from the housing which, when lit, respectively identify an overcurrent, overvoltage and ripple condition in the direct current output. This invention provides a replacement for currently in use ex-core nuclear detector power supplies that were originally available in two versions intended to be used in different NIS ranges. Specifically, the Source Range application requires a higher bias voltage and its supply generates up to 2500 VDC to the BF3 neutron detectors used in that range. The other version generates up to 1500 V and is used in the Power and Intermediate Range applications. Each version of the units of this invention is configured to provide the detector bias from an applicable drawer, with the unit mounted in the drawer bracket and connected to the detector with a dedicated triaxial cable. A terminal block connector on the unit provides connections to the drawer to interface to test points or a meter (depending on the version), the high voltage adjustment potentiometer, and AC power inputs. The unit is configurable using two jumpers located on the printed circuit board. Depending on the range selection jumper location the unit will either be the 1500 V version or the 2500 V version. A second jumper selects whether the unit metering circuit interfaces to a test point (1500V version) or a meter (2500 V version). The jumpers are for use during manufacture of the units and not for customer configuration. In general, the design structure of the replacement power supply (10) of this invention is shown in FIG. 1 and is comprised of two independent switched mode power supplies (SMPS) (12), (14); where one supply (12) creates the unit's internal power from the external AC source (16) and another supply (14) creates the high voltage, which is distributed at the output (18). The line powered switcher (12) provides the power for the entire unit when AC power is applied; it will also provide the required peak power for all output conditions of the high voltage power unit (10) with as much efficiency as reasonably possible to reduce overall power dissipation in the drawers and, therefore, the entire NIS. The line powered switcher (12) also provides abundant levels of input surge protection and electro-magnetic interference (EMI) filtering for greater reliability and low risk of signal emissions. A block diagram of the line powered switcher (12) is shown in FIG. 2. The AC input is fed through a current limiter (24), such as a fuse, to a surge protection device (26), such as a Metal Oxide Varistor. The output of the Varistor is inputted to an inrush limiter (28), which outputs through a line filter (30) to an electro-magnetic interference filter (32). The output of the electro-magnetic interference filter is conveyed through another surge protector (34), such as a transient voltage suppressor, to an input rectifier/filter (36), whose output is connected to the input of transformer (38). The output of the transformer (38) is conveyed through the output rectifier (40) and the output filter (42) to the input of the current limiter (44). A controller/switch (50) is serially connected though optical isolation (52) to a reference generator (54) with the series connection extending between the transformer (38) and the input of the output current limiter (44). The output of the output current limiter (44) is approximately 18 VDC at 2.5 A and the series connection of the shunt output voltage clamp (46) and the linear regulator (48) with the output of the output current limiter (44) provides a second DC output of approximately 15 volts to the high voltage generator (switcher) (14). A circuit schematic of the Line Power Supply (12) portion of the High Voltage Power Supply (10) is shown in FIG. 8. The high voltage portion employs another switched mode power supply (SMPS) (14) using a push-pull converter topology with voltage feedback. The push-pull converter has advantages of compact design and lower output ripple. A voltage doubler is used to double the output voltage of the transformer during the rectification. An output filter is used to reduce the ripple to required levels. The feedback mechanism is used to provide a stable regulated output based on a precision reference. FIG. 3 is a block diagram of the high voltage portion (14) of the High Voltage Power Supply (10) of this invention. The 15 VDC output from the Line Powered Switcher (12) provides the operating power for the controller integrated circuit as well as other active electronic components used in the High Voltage Switcher (14). The 18 VDC output from the Line Powered Switcher (12) is fed to an 18 VDC input (72) on the high voltage transformer (70) on the High Voltage Switcher (14). A precision reference input (56), of approximately 10 VDC in this exemplary embodiment, is provided at the high terminal (58) on the potentiometer (63) on the input side of the High Voltage Switcher (14). A variable output through the potentiometer wiper (62) controls the amount of the voltage that appears at the High Voltage Switcher output terminal (92). The low side (60) of the potentiometer (63) coil is grounded and the output of the potentiometer wiper (62) is fed through a buffer amplifier (64) to the negative side of controller error amplifier (66), which functions to serve as the target set-point voltage within the controller (66) whose output pulses are of a width based on the difference between the target voltage and the feedback voltage from the feedback circuit (80). The output of the controller (66) is fed through driver/switches (68) to an input on the high voltage transformer (70) whose alternating current output is further enhanced and converted to direct current by the output rectifier/doubler (74) and output filter (76). The output is then clamped by the output voltage clamp (78) and is available to be communicated to the ex-core radiation detectors at output terminal (92). A reduced magnitude sample of the output is also fed back by the feedback loop (80) to the positive input on the controller (66) to provide a stable output based on the precision reference supplied by the wiper (62). The output (92) is also fed back through an output scaler (84) to an overvoltage sensor (86) and a meter driver (88). The overvoltage sensor (86) identifies an abnormally high voltage condition and sends a shutdown signal to the controller (66) upon such an occurrence. The overvoltage sensor (86) also provides an indicator signal (94) that identifies an abnormally high voltage condition of the High Voltage Generator (10) on the casing of the High Voltage Generator. In the case of the Source Range drawer, the output of the meter drive (88) is available to drive a meter on the face of an instrumentation drawer in which the High Voltage Generator is maintained. For the Intermediate Range and Power Range drawers, the meter drive signal is used to drive a test point built into the drawers. This is configurable at the time of manufacture with a jumper setting within the meter drive circuitry (88) that corresponds to another jumper that sets the output voltage range. The output (92) is also conveyed to a ripple sensor (82) that conveys any ripple in the output signal and provides both an indicator signal in cases of excessive ripple voltage which is determined by comparison to a permanent set-point within the ripple sensor circuit (82). An overcurrent sensor (90) monitors the current from the driver/switches (68) and provides a shutdown signal to the controller (66) when an abnormal condition is monitored and provides an indicator signal which shows on the casing (96). Thus, the output voltage can be varied between 0 and 2500 VDC at 0 to 10 mA (depending on the load) by varying the position of the potentiometer wiper (62). One of the important objectives of the high voltage output of this invention is to maintain low output ripple (15 mV pk-pk) at all voltages and loads. Output ripple can be more precisely defined as Periodic and Random Deviations (PARD) which encompasses periodic ripple as well as periodic impulsive type noise caused by internal supply switching and non-periodic changes in the output due to various other circuit interactions. Specific printed circuit board layout and grounding techniques will help reduce PARD to the required level. The high voltage portion of the supply (14) will also source up to 10 mA of load current at all output voltages, provide adjustment down to 0 VDC, and provide interfaces to the drawer potentiometer (63) and meter for proper control and monitoring. Another important objective of the invention is to include various fault protection capabilities to limit the consequences of internal failures and external faults. For instance, through the current sensing circuit (90), the output will contain a current limit of approximately 13 mA regardless of output voltage. This prevents the supply from overload in an abnormally heavy load or a short circuit on the output. In the unlikely event of an internal fault in the high voltage feedback, a voltage sensing circuit (86) will shut down the high voltage if the output exceeds the programmed voltage by approximately 250 V. The Line Powered Switcher (12) contains an output voltage clamp (46) to prevent the output from exceeding 20 VDC. If the voltage exceeds 20 VDC excessive current through the clamp will cause a fuse to open to reduce the risk of unpredictable high voltage circuit behavior. This prevents overload in the Line Powered Switcher (12) and reduces risk of fire. The over-voltage and over-current conditions both contain LEDs (94), (98) on the top panel of the High Voltage Generator casing (96) to indicate entry into those modes of operation, as can be appreciated from FIGS. 4 and 5. An additional protection circuit also ensures the high voltage output is disengaged if the external programming potentiometer is faulty or is not connected properly. Redundant fault detection circuitry in the form of a clamp prevents the unit from significantly exceeding the output voltage range in the case of multiple point failures. AC ripple diagnostics can be performed on the replacement power supply with a Bayonet Neill-Concelman (BNC) Connector ripple test point (100) shown in FIG. 6. The test point will allow direct ripple measurement while in operation without affecting the output during normal operation. In situations where the ripple is extreme and may effect detector operation, an LED (102) on the top panel, as shown in FIGS. 4 and 5, will indicate excessive ripple beyond approximately 50 mV peak. The High Voltage Power Supply of this invention will offer more flexibility in adjustment than the current supplies which have a lower limit of approximately 300 VDC. The supply of this invention will be able to adjust to 0 VDC which will eliminate the need to switch in separate supplies during customer bias curve generation and other related service activities. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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06240153& | abstract | A reactor stud cleaning apparatus is presented for cleaning studs, nuts, and washers used to secure reactor heads on nuclear reactors. The cleaning apparatus is a self-contained unit having a housing that includes two independent sealable compartments allowing cleaning of two studs simultaneously. Each sealable compartment has a topside covering with a port that allows reactor studs to be lowered into the apparatus keeping the longitudinal axis of the reactor stud maintained in a substantially vertical position. Inside the sealable compartments is a turn table for vertically mounting a reactor stud and for rotating the stud about its longitudinal axis. Brushes, rotatably mounted inside the compartment, are used to clean the reactor stud. The apparatus also has a cleaning fluid circulation system for circulating solvents or other cleaning agents or fluids over the reactor stud during cleaning. |
description | This invention relates to the interchangeability of handling gloves with or without a rolled edge, with continuity of sealed confinement in the following industrial fields: pharmacy, animal keeping, chemicals, etc. More precisely, the invention relates to a device for changing a handling glove bidirectionally from the inside of a glove box to the outside or from the outside of the glove box to the inside, also called a confinement containment or isolator. Said device being designed to replace a used glove by a new glove, comprising a cuff with a sealed connection to a cuff sleeve and a glove made of a flexible material with a sealed connection to a glove sleeve. The assembly thus formed is also called a cuff port. The invention also relates to a method for replacing a used glove by a new glove using the device according to this invention. Highly volatile toxic products and chemicals are routinely handled in confined environments. Confined environments are also used to protect elements from external pollution when handling is required in a sterile medium, for example in the case of the pharmaceutical industry for packaging of injectable medicines, raising laboratory animals under aseptic conditions, anti-cancer products handled in hospital pharmacies, food processing, etc. These confined environments comprise a sealed containment. The containment is fitted with openings in which gloves are fixed, so that manipulations can be done from outside the containment. Thus, a person introducing a hand into a glove can manipulate objects contained inside the containment without a risk of polluting them and without a risk of being contaminated. These gloves can be fitted on the containment in different ways, for example by glove rings fixed to the containment, called shoulder ports for gloves fixed by a collar or containment ring for gloves fitted on interchangeable support ring using a ejection mechanism called an ejection gun, replacing the used glove ring by pushing it out with a new glove ring. Shoulder ports are used equally well for cells with negative pressure and for cells with positive pressure. Shoulder ports surround the operator's hand and arm, up to the shoulder. Ejectable ring systems are only used at the present time for cells under negative pressure because the ejection mechanism is large and its high volume and heavy weight make it impossible to use it inside the confinement. In particular in the animal raising and pharmaceutical environments in sterile confinement, the glove made in a single length is split into two elements, namely a high relatively strong part called a cuff. The cuff is connected at the containment to a shoulder port that can be circular or oval and is large to allow more clearance for the operator. Furthermore, the glove is separated into a lower part that is connected to a sleeve at the wrist and is used to fit a glove appropriate for each manipulation. This glove can be replaced by a new glove from inside the confinement using the other hand. However, the replacement procedure is very difficult. This method is acceptable in a research laboratory but certainly not in an industrial environment or in hospital pharmacies. Document FR 2 913 362 describes a method of replacing a glove previously installed on a glove ring that fits into the cuff ring fixed at its end. Interchangeability of the used glove is obtained by passing a sterile new glove inside the confinement. This glove is fitted in a tool called the “support”. A second tool called the “pusher” is fitted inside the cuff. The glove is engaged on the cuff ring on the inside of the isolator, the support containing the new glove fixed on its ring is brought into place to engage it on the used glove ring. The cuff ring is slid into place from the used glove ring onto the new glove ring by pushing the pusher in reaction from the support. This method requires dexterity on the part of the operator and remains complex. The special tools, the pusher and the support, one of which holds the used glove in a cavity and the other holds the new glove in a cavity with no risk of trapping, are thus tools with a non-negligible size inside the cell, particularly for the pusher. The adopted principle for glove rings to enable interchangeability uses two stages. Each ring is composed of a first sleeve for which the inside diameter fits inside the cuff ring and a second sleeve with a diameter smaller than the diameter of the first sleeve so that the glove and its attachment can be fitted by a collar with two diametrically opposite heads. The diameter of the heads must be less than the inside diameter of the first sleeve so that one can penetrate into the other as necessary for the adopted interchangeability principle. The major disadvantages of this principle are a reduction in the dexterity of the operator because the glove ring composed of two sleeves is thickened and because of the increase in length due to their superposition. The consequence of this state of affairs is to increase the weight and the size of the glove at the operator's wrist, which correspondingly reduces his dexterity and increases his fatigue. The axial stop of the glove ring in the cuff ring is obtained by the use of hard points. In the case of the sealing means described above, the interchangeability force becomes continuous and therefore the operator loses the feel of the click-fit means used as end of attachment indicators as they pass through the hard points. Subsequently, the operator is not sure that he has finished transferring the glove onto the cuff ring. There is a risk that he might withdraw the pusher with the used glove before the new glove has been placed on the ring. There are also the following secondary disadvantages of this principle: placement of the first glove requires a mask or a special tool; the tapered lid requires a longer movement distance of the piston from the support by a value equal to the height of the lid, which has the effect of increasing the size and weight of the tools; the orientation of the glove can be wrong. The glove can be placed with the thumb at the top which is the correct position, or with the thumb at the bottom which is an incorrect position. There is no foolproof device to be certain that that the thumb is in the right position at the top. Consequently, the purpose of this invention is to disclose a device to replace the glove on the cuff that overcomes the disadvantages listed above and that gives greater safety and ease of operation for operators in the confinement. A first purpose of the invention is a device to replace a handling glove from the inside to the outside of a glove box and from the outside to the inside under confinement, said device being designed to replace a used glove by a new glove comprising a cuff connected in a sealed manner to a shoulder port mounted in a sealed manner on the wall of a confinement containment connected in a sealed manner to a cuff sleeve, and a glove made of a flexible material connected in a sealed manner to a glove sleeve. According to the invention, the outside of the glove sleeve comprises a determining number of snap-fitting studs on the flexible sectors, and the cuff sleeve that has a cylindrical internal surface without any obstacles, comprises the same number of axial ramps on the inside to guide the snap-fitting studs into the anchor cavities, locking the glove sleeve in the cuff sleeve, forming a fully sealed assembly called a cuff port once assembled. The snap-fitting studs on the glove sleeve engage in the axial grooves of the cuff sleeve. The tabs fitted on the flexible sectors clip into small cavities locking the glove sleeve in the cuff sleeve, so that the sealed assembly forms an indissociable cuff port. No tools are necessary to replace the glove. Interchangeability by a new glove is achieved by introducing the studs on the glove sleeve body into the peripheral entries of the axial grooves of the cuff sleeve and synchronously, retraction pins retract the studs from the glove sleeve to be replaced, releasing them from the cuff sleeve by means of a thrust in the direction of translation. The new glove sleeve clips into place and is locked on the cuff sleeve, while releasing the old glove sleeve. A static and dynamic seal during the replacement is advantageously composed of at least one seal with one or two lips, either injected or embedded in a sealed manner in the groove of the glove sleeve provided on the glove sleeve body to give a permanent seal between the cuff sleeve and the glove sleeve. This seal is maintained at all times when the glove seal is being replaced. Slip of the elastomer of the seal between the cuff ring and the glove ring is improved by surface ionisation that has the advantage of hardening the elastomer only on the surface and reducing the coefficient of friction, increasing its durability and its resistance to sterilisation products. Bombardment of the elastomer during surface ionisation with Silver ions makes the surface active to neutralise bacteria, which has two very important advantages: slip and antibacterial action, the combined translation/rotation movement of the glove sleeve in contact with the internal wall of the cuff sleeve body therefore takes place effortlessly and reinforces the integrity of replacement of the glove by its antibacterial action. Preferably, the device to replace the glove comprises a seal with one or two elastomer lips on which surface ionisation has been done to improve its slip properties, facilitating placement of a new ring and ejection of the old ring. It comprises snap-fitting studs (49) and stud retraction pins (47) provided with a visual and mechanical foolproofing system, such that the glove will always be put in the right working position. The glove replacement device does not require any special tool for the interchangeability manipulation by the operator, visual marks are used to facilitate positioning during interchangeability actions consisting of a simple translation. Preferably, the glove replacement device comprises a locking system composed of snap-fitting studs inserted into appropriate cavities. These snap-fitting studs can only be unclipped after the retraction pins have entered the housings in the flexible sectors to retract inwards into the glove sleeve, this action unclipping these snap-fitting studs. Preferably, the glove replacement device comprises a glove sleeve composed of a glove sleeve body comprising devices to guide and lock this glove sleeve body in the cuff sleeve body. It comprises a ring for assembly of the glove in the glove sleeve body, the support being achieved by the glove assembly ring in the glove sleeve body. The seal between the glove sleeve body and the glove assembly ring is achieved by pressing the elastomer of the glove. Preferably, the device to replace the glove is composed of the cuff sleeve body and a cuff assembly ring. The assembly ring presses the cuff against the stop on the cuff sleeve body, this sealing the cuff sleeve, and the complete assembly is held in place by a mechanical assembly making them indissociable. Another main purpose of the invention is a method of replacing a used glove by a new glove using a device like that described above. It comprises the following phases: a new glove fitted with its glove sleeve is placed inside the confinement containment; the two cuff sleeve assembly and glove assembly rings are fixed together by force fitting them one into the other; the new glove sleeve is pushed into the used glove sleeve on the cuff sleeve until the new sleeve locks in the axial ramps in the cuff sleeve body until the visual mark is reached and a locking “click” is heard and the used glove sleeve is completely disengaged from inside the cuff. At least three female notches are formed on the edge of the used glove sleeve body into which three male notches fit to pull the new glove sleeve into the correct position, namely with the thumb upwards. Three housings are also provided in the flexible sectors into which the pins of the new glove sleeve fit to unclip the studs of the used glove sleeve. Interchangeability does not require any tools in the case of a work station with two gloves. It is sufficient to hold the new glove sleeve with the other hand through the glove, to place it on the cuff port respecting the marks made on the cuff and glove sleeves, engage the studs in the axial grooves holding the faces of the glove sleeves in contact with each other and pushing. The used glove sleeve moves out as the translation continues, the new glove sleeve clips into place and the used glove sleeve drops inside the cuff. Preferably, the end of cycle safety system locks the new glove sleeve in rotation relative to the cuff sleeve, and consists of studs snap-fitting into cavities provided for this purpose, preventing any radial or axial movement. The operator is assured that the glove sleeve is correctly locked by hearing a “click” sound and by a visual positioning indicator. These two signals prove that the glove is well locked and is in the right position. Advantageously, the elastomer seal contains a decontaminant that neutralises any bacteria originating from inside the cuff, advantageously the configuration of the seal will make the connection leak tight. According to the method of replacing a used glove sleeve by a new glove using a device according to the invention: if the system is used under negative pressure, the cuff is rolled up towards the outside of the cell, while if the system is used under positive pressure, the used glove is rolled up towards the outside of the cuff; if the system is used under negative pressure, the new glove is rolled up towards the inside of its own sleeve; a new glove fitted with its glove sleeve is placed inside the confinement cell (isolator) in the case of positive pressure and outside in the case of negative pressure; in both cases (positive and negative pressure), the new glove sleeve is placed on the used glove sleeve in position in the cuff sleeve body. The slopes at the entry to the housings enable precentring of the pins; the new glove sleeve is pushed into place on the old glove sleeve, which has the effect of engaging the male notches in the female notches of the old glove sleeve and in the same movement, engaging the retraction pins in the housings of the old glove sleeve. This has the effect of retracting the snap-fitting studs towards the inside of the previous glove sleeve; the block of the two glove sleeves is pushed in translation into the cuff sleeve body, thus locking the new glove sleeve into the cuff sleeve body under the effect of the snap-fitting studs in the axial ramps in the cuff sleeve body, aligned with the end of locking mark located on the cuff sleeve body, signalled by a “click”. The used glove sleeve is pushed clear into the inside of the cuff for a system used under positive pressure. The used glove sleeve is pushed clear into the inside of the glove box for a system used under negative pressure. Marks followed by the letter “a” refer to parts installed for operation in positive pressure. Marks followed by the letter “b” refer to parts installed for operation in negative pressure. The same parts can be used for an assembly for cells in positive pressure and for cells in negative pressure, simply by inverting the cuff sleeve body 21a (installation in positive pressure) or 21b (installation in negative pressure) and the glove sleeve body 40a, 40b. For assembly of a cell in negative pressure, the glove 60b is rolled up on its assembly ring 42a and 42b. FIG. 1 shows a device for replacing a handling glove in positive pressure. This device is fixed on a shoulder port 4 installed in a sealed manner on a wall 2 of a confinement containment in this case, the cuff 6 is fixed on the shoulder port by a collar 5. The cuff 6 can be fixed onto the shoulder port by any other appropriate method, for example by anchoring into a cavity by injection of silicone, by trapping the skin of the cuff 6 by a glued intermediate part, by gluing or by welding depending on the materials present. At its end opposite to the end fixed on the glove ring, the cuff 6 is fixed to a cuff sleeve 20 inside which a glove sleeve 40a is installed. A glove 60a is fixed to the glove sleeve 40a. The assembly compose of the cuff sleeve 20 and the glove sleeve 40a is called the cuff port 10. The glove 60a is installed on the glove sleeve 40a by any appropriate method, and in particular it can be installed by anchoring and trapping using an assembly ring in the glove sleeve. The internal volume of the cuff 7 corresponds to the atmosphere outside the glove box. FIG. 2 shows the assembly of the cuff port that enables interchangeability from inside to outside using the same parts, applicable for use in a glove box under positive pressure, used particularly for pharmaceutical applications. FIG. 3 shows the assembly of the cuff port that enables interchangeability using these same parts with no special tools, from outside to inside, applicable for use in a glove box under negative pressure. The cuff sleeve body 21 is inverted, the cuff 6 is fixed in exactly the same way as in FIG. 2. The glove sleeve 40b is presented inside the cuff which means that the glove 60b has to be installed by inverting it on its assembly ring 42b. The case of a cell in positive pressure (sterile) is considered in the following. Therefore the glove is replaced from the inside of the containment towards the outside. FIG. 4a shows the glove sleeve 40a composed of a glove sleeve body 41 on which a seal 43 is fitted in a groove. A glove 60 is fitted on its glove assembly ring 42b, the assembly is inserted into the glove sleeve body 41 in a sealed manner by pressing and gluing or welding, making it indissociable from the glove assembly ring 42b thus forming the glove sleeve 40. FIG. 4b shows the cuff sleeve 20 composed of a cuff sleeve body 21 on which the cuff 6 is installed above a stop 23, the assembly ring of the cuff sleeve 22 is inserted on the cuff sleeve 21 in exactly the same way as the glove assembly ring 42a. FIG. 4c shows the glove sleeve 40a put into place manually without any special tools into the cuff sleeve 20a thus forming the cuff port 10. FIG. 5 shows the cuff port cuff 10 and glove 60 assembly installed correctly, with the thumb in the vertical position facing upwards. FIG. 6 is a larger scale view showing details of the cuff port 10 with the cuff sleeve 20 and the glove sleeve 40 and the volume that they create. This volume enables good penetration of gases to fully sterilise this volume. It guarantees good decontamination of exposed surfaces. Depending on operations to be performed, for example in the animal raising business, this volume has to be protected to prevent the introduction of anything that could hinder interchangeability of the system. FIG. 6 helps to get a better understanding of the following figures. FIG. 7 shows the cuff sleeve body 21 alone. The inside includes a clearance reaming 28 in which there are at least three entrances 29 to ramps 30, preferably at intervals of 120°. These do not open up outside the cuff sleeve body 21. This clearance reaming 28 is slightly larger than the reaming 27 so that the seal is not damaged as it passes through the axial ramps 30 and makes it easier for the operator to introduce the glove sleeve 40. There is a non-return stud 31 with a rectangular shape in the circular direction these axial ramps 30, followed by a cavity 37 terminating the axial ramps 30, so that the snap-fitting studs 49 that fit into the cavities 37 can be snapped into place. The function of the non-return stud 31 is to prevent escape from the groove during the passage in the groove 58. The functions of the visual mark 37 are to keep the glove sleeve body 41 in the locked position on the cuff sleeve body 21 and to create a resonant “click” that the operator hears, to confirm locking. Moreover, one 36 of the visual marks is located on the cuff sleeve body 21, and the other 51 is located on the glove sleeve body 41, confirming this position by being aligned. Therefore the non-return studs 31 act as non-return devices preventing any relative axial and radial movement between the cuff sleeve 20 and the glove sleeve 40. The operator can use an engagement mark 38 to visually bring the glove sleeve 40 into position on the cuff sleeve 21, facilitating its engagement in the clearance reaming 28. The seal 43 fits into the reaming 27 maintaining dynamic continuity of the seal through the interchangeabiity phase and then a static seal. The outside of the cuff sleeve body 21 includes a first shoulder on which there are marks 36 and 38, and that comprise a groove 25 after these marks in which a glue deposit can be placed or in which material can be poured in the case of a welded assembly. This is followed by a second groove called the cuff end 24 preventing complex assembly of the cuff 6 on its sleeve body 21. This housing is followed by a shoulder called the sleeve retaining stop 23. Finally, the grooves 24 and 35 are symmetrical behind this stop 23 on the outside of the shell 26, with a cuff end groove 24′ and a groove 25′ enabling use of the system in the case of a glove box in negative pressure. FIG. 8 shows the assembly ring of the cuff sleeve 22 on the cuff sleeve body 21 alone, the inner centring reaming 32 centres the cuff sleeve body 21. The shoulder 33 comes into contact with the stop 23 holding the cuff in position by pressure while the glue is setting or during welding. Furthermore, this shoulder 33 has a second very important function of protecting the cuff against shocks, that increases its life. FIG. 9 shows the glove sleeve body 41 alone. This shell-shaped part performs the following functions: unclip, using the three stud retraction pins 47 located behind the glove sleeve body 41, when they engage in the three pairs of housings 52; drive the new glove sleeve 41, also located behind the glove sleeve body 41, by the stud retraction pins 47, so as to translate the used glove sleeve 41; snap fit by three snap-fitting studs 48 located on the tree flexible sectors 48 in front of the glove sleeve body 41; reception of the stud retraction pins of the new sleeve of the new glove by three housings 52, for which progressive penetration during placement of this new glove sleeve by the operator forces the pins 47 to retract the snap-fitting studs inwards in the radial direction into the glove sleeve body due to deformation of the flexible sectors 48. This flexibility is possible due to the three through slots 50; seal between the outside of the glove sleeve and the inside of the cuff sleeve body 21. To achieve this, a groove 44 holds the single-lip type seal 43 in the example shown, but it could be an O-ring, double-lip seal, quadrilobe seal, etc. This seal 43 must be composed of a food compatible material, rubber etc. (see FIG. 6). The seal is achieved by compression of the lip of the seal 43 in contact with the smooth internal wall of the reaming 27 of the cuff sleeve body 21. Slip of the elastomer is achieved by surface ionisation that has the advantage of hardening the elastomer on the surface and increasing slip, while reducing the coefficient of friction. Ionisation can be achieved using auto-bactericide silver ions to maintain sterility of the part of the seal 43 in contact with the inside of the cuff sleeve body 21; visual presentation of the glove sleeve 40 on the cuff sleeve, due to a mark 51 on the outside of the cylindrical part of the sleeve body 41 and on the front edge; leak tightness of the glove mounted on its assembly ring 42 (see FIG. 10) that bears on the inner shoulder 53 of the glove sleeve body 41; indissociably retaining the glove to the glove sleeve body 41 and the centring ring 57 of the glove assembly ring 42. FIG. 9a shows an enlarged detail of a flexible sector 48 with its snap-fitting stud 49, its reception housing 52 for the retraction pins 47, and the groove 47 and the slot 50A, to facilitate understanding. FIG. 10 shows only the glove assembly ring 42 composed of a collar 56 into which the glove 60 fits and that enables it to bear on the inner shoulder 53 of the glove sleeve body 41. This collar terminates by a centring shell 57 with the inner guide stop 54 of the glove sleeve body 41 (see FIGS. 6 and 9). One of the main advantages of the invention is placement of the glove that is achieved simply by the operator applying longitudinal pressure. This avoids the need for the operator to make uncomfortable rotation movements, particularly like those necessary with bayonette systems. PARTS LIST MarkItem 2Wall (of the confinement containment) 4Shoulder port 5Collar (holding the cuff on the shoulder port) 6Cuff 7Interior of the cuff10Cuff port: 10a assembly in positive pressure10b assembly in negative pressure20Cuff sleeve: 20a assembly in positive pressure20b assembly in negative pressure21Cuff sleeve body: 21a assembly in positive pressure21b assembly in negative pressure22Cuff sleeve assembly ring: 22a assembly in positive pressure 22b assembly in negative pressure23Stop (outside of the cuff retention)24Cuff end groove: assembly in positive pressure24′Cuff end groove: assembly in negative pressure25Groove: assembly in positive pressure25′Groove: assembly in negative pressure26Interchangeability shell27Reaming (of the shell to assure that the seal is maintained when the glove is replaced)28Clearance reaming (protection of the seal)29Entry (engagement of tabs in the axial ramps)30Axial ramps31Non-return stud32Inner reaming (centring of 22 on 21)33Shoulder (holding 6 on 23 by axial pressure and protection of the cuff 6 against shocks)36Visual mark (start and end of locking)37Cavity (for tabs after snap-fitting)38Glove sleeve engagement mark40a, 40bGlove sleeve: 40a for assembly in positive pressure40b for assembly in negative pressure41a, 41bGlove sleeve body: 41a for assembly in positive pressure41b for assembly in negative pressure42a, 42bAssembly ring (glove): 42a for assembly in positive pressure 42b for assembly in negative pressure43Seal44Groove (for seal)47Stud retraction pin48Flexible sectors supporting snap-fitting studs49Snap-fitting studs50Through slot (that increases the flexibility of flexible sectors)51Mark (visual for alignment with mark 36)52Housing (for retraction pins)53Inner shoulder (glove skin support)54Inner guide stop forming a natural groove 55 between the sleeve body 41 and the glove assembly ring 4255Space56Glove support collar57Shell (for centring on the glove sleeve body 41)58Groove60a, 60bGlove: 60a for assembly in positive pressure60b for assembly in negative pressure |
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claims | 1. A method for storing and cooling nuclear waste canisters comprising:providing a manifold storage system comprising a vertical air inlet downcomer, a piping network fluidly coupled to the downcomer, and a plurality of vertically oriented storage shells each fluidly coupled to the piping network, each storage shell forming a cavity configured for holding a nuclear waste canister;positioning a hermetically sealed nuclear waste canister containing high level nuclear waste into each cavity of the storage shells to form an annular gap between each canister and their respective shells, the nuclear waste generating heat;drawing cooling air from the ambient atmosphere into the downcomer;distributing the cooling air from the downcomer through the piping network to the storage shells;introducing the cooling air into the annular gaps of each storage shell;heating the cooling air via the nuclear waste in each storage shell thereby producing heated air; andventing the heated air from the storage shells back to the ambient atmosphere. |
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description | This application is a divisional application of U.S. patent application Ser. No. 13/696,690 filed on Jan. 21, 2013 which is a U.S. national stage of PCT international application no. PCT/GB2011/050889 filed on May 9, 2011 which claims priority to GB application no. 1007655.2 filed on May 7, 2011, the disclosure of all of these applications is incorporated herein by reference, in its entirety. This invention relates to methods and apparatuses for producing very high localized energies. It relates particularly, although not exclusively, to generating localized energies which potentially may be high enough to cause nuclear fusion. The development of fusion power has been an area of massive investment of time and money for many years. This investment has been largely centered on developing a large scale fusion reactor, at great cost. However, there are other theories that predict much simpler and cheaper mechanisms for creating fusion. Of interest here is the umbrella concept “inertial confinement fusion”, which uses mechanical forces (such as shock waves) to concentrate and focus energy into very small areas. Much of the confidence in the potential in alternative methods of inertial confinement fusion comes from observations of a phenomenon called sonoluminescence. This occurs when a liquid containing appropriately sized bubbles is driven with a particular frequency of ultrasound. The pressure wave causes bubbles to expand and then collapse very violently; a process usually referred to as inertial cavitation. The rapid collapse of the bubble leads to non-equilibrium compression that causes the contents to heat up to an extent that they emit light [Gaitan, D. F., Crum, L. A., Church, C. C., and Roy, R. A., Journal of the Acoustical Society of America, 91(6), 3166-3183 June (1992)]. There have been various efforts to intensify this process and one group has claimed to observe fusion [Taleyarkhan, R. P., West, C. D., Cho, J. S., Lahey, R. T., Nigmatulin, R. I., and Block, R. C., Science, 295(5561), 1868-1873 March (2002)]. However, the observed results have not yet been validated or replicated, in spite substantial effort [Shapira, D. and Saltmarsh, M., Physical Review Letters, 89(10), 104302 September (2002)]. This is not the only proposed mechanism that has led to luminescence from a collapsing bubble; however it is the most documented. Luminescence has also been observed from a bubble collapsed by a strong shock wave [Bourne, N. K. and Field, J. E., Philosophical Transactions of the Royal Society of London Series A—Mathematical Physical and Engineering Sciences, 357(1751), 295-311 February (1999)]. It is this second mechanism, i.e. the collapse of a bubble using a shockwave, to which this invention relates. It has been proposed in U.S. Pat. No. 7,445,319 to fire spherical drops of water moving at very high speed (˜1 km/s) into a rigid target to generate an intense shock wave. This shock wave can be used to collapse bubbles that have been nucleated and subsequently have expanded inside the droplet. It is inside the collapsed bubble that the above-mentioned patent expects fusion to take place. The mechanism of shockwave generation by high-speed droplet impact on a surface has been studied experimentally and numerically before and is well-documented (including work by one of the present patent inventors, [Haller, K. K., Ventikos, Y., Poulikakos, D., and Monkewitz, P., Journal of Applied Physics, 92(5), 2821-2828 September (2002)].) The present invention differs from U.S. Pat. No. 7,445,319, even though the fundamental physical mechanisms are similar, because it does not utilize a high speed droplet impact. The present invention aims to provide alternatives to the aforementioned techniques and may also have other applications. When viewed from a first aspect the invention provides a method of producing a localized concentration of energy comprising creating at least one shockwave propagating through a non-gaseous medium so as to be incident upon a pocket of gas within the medium wherein the pocket of gas is attached to a surface comprising a depression shaped so as partially to receive the gas pocket. The invention also extends to an apparatus for producing a localized concentration of energy comprising: a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is attached to a surface comprising a depression shaped so as partially to receive the gas pocket; and means for creating at least one shockwave propagating through said medium so as to be incident upon said pocket of gas. It is known to those skilled in the art that in general an interaction between a shockwave in a non-gaseous medium and a gas bubble in that medium can generate a high speed transverse jet of the non-gaseous medium that moves across the bubble, impacting the leeward bubble wall. This is one of the mechanisms which gives rise to the well-known problem of cavitation damage of surfaces when shockwaves are generated in the presence of micro-bubbles formed on the surface. In accordance with the present invention however, the inventors have appreciated that this naturally-occurring phenomenon can be appropriately adapted and harnessed to produce very high localized energy concentration which can be used, e.g. to potentially create nuclear fusion as will be explained later. In embodiments of the invention, the phenomenon of a jet being formed during bubble collapse is controlled to promote formation of this transverse jet and enhancement of its speed, and the surface depression is designed to receive the transverse jet impact whilst trapping a small volume of the original gas pocket between the impacting jet and itself. This leads to various physical mechanisms that cause very substantial energy focusing in this volume of trapped gas. More particularly by designing the surface depression explicitly to receive the high speed jetting formed by the interaction of the incident shockwave with the gas pocket, then as the incident shock interacts with the surface of the gas pocket it forms a transmitted shock and a reflected rarefaction. If the contact is the correct shape, i.e. curving away from the incident shockwave, then this rarefaction will act to focus the flow to a point. This then results in the formation of the high speed transverse jet which can, purely as an example, reach over 2000 ms−1 for a 1 GPa shockwave. When this jet strikes the surface of the depression a strong shockwave is generated within by the force of the impact in a manner analogous to the high speed droplet impact situation described in U.S. Pat. No. 7,445,319. The shape of the surface in the depression opposite where the shockwave is incident could be flat so that the jet contacts the surface at a point. In a preferred set of embodiments however the surface depression and gas pocket are arranged such that the initial contact region is a curve which forms a closed loop—e.g. a ring. This makes it possible to trap a portion of the gas pocket between the jet tip and the edge of the depression. To achieve this, a section of the target surface has a curvature greater than that of the tip of the jet and this part of the surface is placed such that the jet impacts into it. Upon impacting, a toroidal shockwave is generated whose inner edge propagates towards the base of the depression and towards the trapped portion of gas. Combining this with the ‘piston’ effect of the gas halting the motion of the impacting jet yields extremely strong heating of the trapped gas. For example, for a given strength of shockwave the peak temperatures can be increased by over an order of magnitude by these arrangements as compared to a bubble attached to a planar surface. The depression could take a number of shapes. In a set of embodiments it tapers in cross-section away from the mouth. The depression could resemble a dish—e.g. being continuously curved. The surface need not be continuously curved however. In a set of embodiments the surface more closely resembles a crack rather than a dish shape. This could be defined by stating that the depth is greater than the width or by the presence of a region of curvature at the tip of the crack greater than the curvature (or maximum curvature) of the portion of the gas pocket received in it. In one set of embodiments the surface comprises a plurality of discrete portions, e.g. with a gradient discontinuity between them. The portions could themselves be partial ellipses, parabolas, and so on, but equally could be straight. A particular set of embodiments of surfaces made from discrete portions could be described as piecewise polynomial. As above, the bubble could be small in comparison to the dimensions of the crack such that it is attached only to one side or it could be of similar size so as to close it off. It is not essential that there is only one depression which partly receives the gas pocket; a gas pocket could extend across, and be partially received by, a plurality of depressions. In a particular set of embodiments the high speed jet is arranged to strike an area of surface that has been prepared with a particular roughness or microscopic shape such that many small portions of the pocket of gas are trapped between the jet tip and the target surface, i.e. the many small depressions are small in comparison to the size of the transverse jet tip. When viewed from a second aspect the invention provides a method of producing a localized concentration of energy comprising creating at least one shockwave propagating through a non-gaseous medium so as to be incident upon a pocket of gas suspended within the medium, wherein the pocket of gas is spaced from a surface shaped so as at least partially to reflect said shockwave in such a way as to direct it onto said gas pocket. The invention also extends to an apparatus for producing a localized concentration of energy comprising: a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is spaced from a surface; and means for creating at least one shockwave propagating through said medium so as to be incident upon said pocket of gas,wherein said surface is shaped so as at least partially to reflect said shockwave in such a way as to direct it onto said gas pocket. Thus it will be seen that in accordance with this aspect of the invention the surface can be used to increase energy concentration in the gas by reflecting and/or focusing the shockwave onto it. The arrangement could be such that the shockwave impacts the surface before the gas pocket, but preferably the incident shock interacts with the gas pocket, causing it to collapse, and subsequently the incident shock and/or any of the numerous shocks generated by the cavity collapse (the existence of which will be known to those skilled in the art) interact with the target surface in such a way that they are reflected back towards the remains of the gas pocket, causing it to be collapsed a second or further times and thus enhancing the heating obtained. There are many shapes and configurations which the surface might take. The configuration of the surface will determine how the shockwave interacts with it and the shape of the surface relative to the placement and shape of the gas pocket will determine how the shockwave interacts with the gas pocket, which it may do so before, simultaneously or after it interacts with the surface. This in turn affects the dynamics of the collapse and hence can increase temperatures and densities that are achievable through compression of the gas by the shockwave. In some embodiments, the peak temperatures can be increased by over an order of magnitude, when compared with a similar shock interacting with an isolated bubble. The surface could be planar, but preferably it is non-planar—e.g. curved. The surface need not be continuously curved. For example, in one set of embodiments the concave surface comprises a plurality of discrete portions, e.g. with a gradient discontinuity between them. The portions could themselves be partial ellipses, parabolas, and so on, but equally could be straight. A particular set of embodiments of surfaces made from discrete portions could be described as piecewise polynomial. Preferably the surface is shaped in such a way that the reflected shocks are focused on the gas pocket. The spacing and geometry of the surface will determine (among other factors such as the speed of the shockwave through the medium) what interaction there is between the originally-incident and reflected shockwaves and the interaction of both of these with the gas pocket. In a preferred set of embodiments the surface is shaped to focus the reflected shock to a point. Thus, for example, in the case of an essentially planar incident shockwave the surface could be parabolic or elliptic with the gas pocket at its focal point. However other shapes could be used to account for curvature in the wavefronts of the shockwave. It will be appreciated that the considerations are somewhat analogous to those in the focusing of radio waves and other electromagnetic waves. The optimum spacing between the gas pocket and the surface will depend inter alia on the relative shapes of the reflecting surface and the gas pocket. In a particular set of embodiments of the invention the gas pocket is placed no more than three times the maximum radius of curvature of the closest section of surface away from the surface. In a particular example, the edge of the gas pocket closest to the surface is spaced from it by a distance of less than five times the dimension of the widest part of the bubble gas pocket, preferably less than three times the widest dimension, e.g. less than twice the widest dimension. In a set of embodiments of the second aspect of the invention the shockwave is first incident upon the pocket of gas, compressing the volume of the pocket, and then the shockwave is reflected from the reflecting surface and is incident again on the pocket of gas, compressing it further. The spacing could be arranged so that the reflected shockwave is incident upon the pocket of gas when the volume of the pocket is still contracting from the initial shockwave, when it has reached a point of minimum volume from being compressed by the initial shockwave, or while the volume of the pocket is expanding after compression by the initial shockwave. The collapse of the gas pocket by the incident shockwave produces several strong shockwaves as a result. In another set of embodiments in which the gas pocket is spaced from the surface, the target surface is optimized to reflect these generated shocks back towards the collapsed bubble. For example, the impact of the high speed transverse jet (described in the context of the first aspect of the invention) generates a shockwave that moves outwards from the point of impact dissipating as it travels. The surface could be shaped to conform to this shockwave and reflect it back towards the bubble, which would cause it to become a converging shockwave and to focus its energy back into the collapsed gas pocket. When viewed from a third aspect the invention provides a method of producing a localized concentration of energy comprising creating at least one shockwave propagating through a non-gaseous medium so as to be incident upon a pocket of gas within the medium wherein the pocket of gas is attached to a non-planar surface shaped to concentrate the intensity of the shockwave which is incident upon the pocket of gas. The invention also extends to an apparatus for producing a localized concentration of energy comprising: a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is attached to a surface; and means for creating at least one shockwave propagating through said medium so as to be incident upon said pocket of gas,wherein said surface is shaped to concentrate the intensity of the shockwave which is incident upon the pocket of gas. In accordance with this aspect of the invention the geometry of the surface can be used to control the reflections of the incident shockwave before it reaches the bubble such that the collapse of the bubble is intensified, for example such that the initially incident shockwave is more conforming to the bubble surface. As before, there are many shapes and configurations which the surface might take to provide suitable regions for attaching the pocket of gas to the surface and the configuration of the surface will determine how the shockwave interacts with it and the shape of the surface relative to the placement and shape of the bubble will determine how the shockwave interacts with the gas pocket, which it may do so before, simultaneously or after it interacts with the surface. This in turn affects the dynamics of the collapse and hence can increase temperatures and densities that are achievable through compression of the gas by the shockwave. In some embodiments, the peak temperatures can be increased by over an order of magnitude, when compared with a similar shock interacting with an isolated bubble. In a preferred set of embodiments, the surface is concave which has the effect of focusing the energy and intensifying the initial formation of the shockwave. In some non-limiting examples, the surface could have an ellipsoid or paraboloid shape. The surface need not be continuously curved. For example, in one set of embodiments the concave surface comprises a plurality of discrete portions, e.g. with a gradient discontinuity between them. The portions could themselves be partial ellipses, parabolas, and so on, but equally could be straight. A particular set of embodiments of surfaces made from discrete portions could be described as piecewise polynomial. The gas pocket could be attached to any part of the surface but is preferably attached to the bottom or center point. The dimensions of the gas pocket could be small in comparison to the width or depth of the concave surface—e.g. so as to be attached only to one side of the concavity, or it could of similar size—e.g. so as to attach to the surface in an annulus around the base of the depression. The concavity could resemble a bowl—e.g. being continuously curved. In a set of embodiments however the surface more closely resembles a crack rather than a bowl shape. This could be defined by stating that the depth is greater than the width or by the presence of a region of curvature at the tip of the crack greater than the curvature (or maximum curvature) of the bubble. As above, the gas pocket could be small in comparison to the dimensions of the crack such that it is attached only to one side or it could be of similar size so as to close it off. In one set of embodiments the shape of the surface is configured to trigger a transition from regular to Mach reflection of the incident shockwave, thus altering the shape of the shockwave that then reaches the gas pocket. In another set of embodiments the shape is controlled such that the reflections overlap and interact with one another, again acting to change the shape of the shockwave or interacting system of shockwaves when it contacts the gas pocket. By carefully controlling these factors an intensification of the peak temperatures can be obtained over the case where the surface is planar. In a particular set of embodiments the surface might have a plurality of concave portions. Additionally or alternatively the or each concave portion may have a plurality of gas pockets attached thereto. The aspects of the invention set out above are not mutually exclusive. Thus, for example, the surface might comprise a depression shaped so as partially to receive the gas pocket, thereby exploiting the jetting phenomenon and away from the depression the surface could be shaped to concentrate the intensity of the shockwave which is incident upon the pocket of gas. This could allow the properties of the jet—e.g. its speed—to be controlled to maximize the concentration of energy. Such combinations could be beneficial in providing the desired behavior of the shockwave within the depression in other ways. In any embodiments where the bubble is attached to the surface this could be over a single contact patch or, by appropriate design of the surface texture, at a plurality of discrete contact points/regions. As well as creating a particular shape for the target surface, in one set of embodiments the micro-structure or wetting characteristics of the surface can be optimized to control the speed of the shockwave near the surface, e.g. to increase the speed near the surface, thereby changing the shockwave's shape and hence the nature of the interaction between the shockwave and the gas pocket. As previously discussed, an appropriately shaped gas pocket can be used in this set of embodiments to match the shape of the shockwave to the shape of the gas pocket, thereby allowing the dynamics of the gas pocket's collapse to be controlled in order to maximize the temperature and density achieved on compression. The surface to which the gas pocket is attached is not limited to having a single depression (e.g. to exploit the jetting phenomenon described above) and thus in one set of embodiments, the target surface comprises a plurality of depressions. Each individual depression may be shaped to encourage energy focusing by causing the shockwave to converge on one or more bubbles. That is to say, the surface may be prepared with more than one site where the shockwave will interact with a shaped section of surface containing either an attached or nearby gas pocket, thus providing infinite scalability. An advantage of employing a plurality of depressions is that a greater proportion of the shockwave energy may be harnessed. For example, a large pocket of gas could be spread across a plurality of depressions, or smaller individual volumes of gas could be located within each individual depression. For the former case, depending upon the number of such depressions, the size of an individual depression will be significantly smaller than the size of the pocket of gas. For a larger volume of medium able to accommodate a large number of depressions, this points towards simplicity of manufacturing for an energy-producing fusion apparatus. Such pluralities of depressions could be formed in a number of ways. For example, a solid surface could be drilled or otherwise machined to produce depressions or pits. In one set of embodiments, however, the depressions are created by the surface texture of the surface. For example, the surface could be blasted with an abrasive material, etched or otherwise treated to give a desired degree of surface roughness which provides, at the microscopic level, a large number of pits or depressions. The surface could be constructed from a solid, as implied in many of the embodiments outlined above, but it could equally well be a liquid. In the case of a solid, any of the proposed materials in U.S. Pat. No. 7,445,319 could be suitable. In the case of a liquid the required surface shape could be achieved in a number of ways. For example, the surface of a volume of liquid could be excited with a suitable vibration (e.g. using ultrasound or another method) to generate a wave having the desired shape. Alternatively the desired shape could be achieved through the contact angle between a liquid and a solid surface with appropriately matched wetting properties. Of course, this latter example shows that the surface could comprise a combination of solid and liquid. Where the target surface comprises a liquid it will generally be denser than the non-gaseous medium. Of course, as has already been alluded to, some embodiments may comprise a plurality of pockets of gas within the medium. These pockets of gas may all be attached to the surface, may all be positioned near the target surface, or there may be a mixture. The aspects of the invention described herein provide alternatives to the technique described in U.S. Pat. No. 7,445,319 which may carry their own benefits. The present inventors have recognized that there are significant challenges in the nucleation of a bubble in a droplet fired at high speed into a target, as suggested in U.S. Pat. No. 7,445,319. The timing will have to be very precise for the bubble to be at a favorable moment of its expand-collapse cycle when the shock strikes. The method by which the high speed droplets are created as required by U.S. Pat. No. 7,445,319 and detailed in U.S. Pat. No. 7,380,918 is also complex and expensive. By contrast such complexity and associated expense can be avoided in accordance with at least preferred embodiments of the present invention. Thus, the various aspects of the present invention provide much simpler techniques for compressing a volume of gas entrapped in a gas pocket as a shockwave simply needs to be created within the medium in which the gas pocket is formed. Moreover the theoretical and computer modeling of both techniques carried out by the present inventors suggests that the method in accordance with the present invention can give pressure and temperature intensities which are an order of magnitude greater than the method detailed in U.S. Pat. No. 7,445,319. The more static framework that can be employed in accordance with the invention to compress a gas pocket using a shockwave allows much greater control (compared to a free bubble) over how the shockwave strikes and interacts with the pocket. The initial shockwave could be created in a number of different ways by a number of different devices depending on the pressure required. For example, an explosive plane wave generator could be used to provide high intensity shockwaves. In preferred embodiments such an explosive device can create a shockwave pressure of between 0.1 GPa and 50 GPa, and in another preferred embodiment a lithotripsy device could be used to generate shockwave pressures of 100 MPa to 1 GPa. The term “gas” as used herein should be understood generically and thus not as limited to pure atomic or molecular gases but also to include vapors, suspensions or micro-suspensions of liquids or solids in a gas or any mixture of these. The “non-gaseous medium” should be understood generically and thus could include liquids, non-Newtonian liquids, semi-solid gels, materials that are ostensibly solid until the passage of the shockwave changes their properties, suspensions or micro-suspensions and colloids. Examples include but are not limited to water, oils, solvents such as acetone, hydrogels and organogels. It should be understood that the liquid will have a greater density than the gas in the pocket. The non-gaseous medium could be any suitable substance for creating a shockwave in, such as a liquid or a semi-solid gel. The gas pocket can then be provided by a bubble suspended within the liquid or gel medium in the required location, either near to or attached to the target surface. Using a gel or a viscous liquid has the advantage that it is easier to control the location of the bubble within the medium, compared to a lower viscosity liquid in which the buoyancy of the bubble may overcome the viscosity of the liquid. As will be appreciated, being able to control the position of the bubble is particularly important in the set of embodiments in which the bubble is located near to the target surface rather than being attached to it. In the set of embodiments in which the bubble is attached to the target surface, the nature of the target surface, e.g. the material, or any indentations or depressions in it, could help to adhere the bubble to the target surface. Using a gel or viscous liquid also has the advantage that it will be easier to control the detailed shape of the bubble. Due to the more static nature of the setup of the device when compared to U.S. Pat. No. 7,445,319, much more control can be exercised over the shape of the bubble. In the set of embodiments where the bubble is attached to the surface, it may be spherical in shape apart from where it is truncated by its attachment to the target surface, for example it could be hemi-spherical. In some embodiments the bubble joins the target surface normal to it whereas in others a different angle is required. In a superset of these embodiments the bubble itself is not spherical in nature but takes a different shape that includes but is not limited to ellipsoids, cardioids, variations from spherical, cardioid or ellipsoid shape in which the surface has perturbations that could be described, for example, by a Fourier series and bubbles with other distinct shapes such as cones or trapezoids. It will be apparent that, for example, a conical bubble would be difficult to achieve in a true liquid medium but that in the case of a gel medium this set of embodiments becomes possible and could be advantageous. In the aspect of the invention in which the bubble is not attached to the surface, it is free from the constraints of the surface and is therefore able to take any shape required, such as ellipsoids, etc. In a set of such embodiments the shape of the bubble and the shape of the target surface can be appropriately matched, e.g. if the depression is hemispherical, the bubble would be spherical. The gas pocket itself must be formed in some manner. In a particular set of embodiments it is nucleated using a system similar to that described in U.S. Pat. No. 7,445,319, where a laser is used in conjunction with nano-particles in the liquid to nucleate a bubble. In a different set of embodiments a bubble could be nucleated using an unstable emulsion of different liquids. In another set the bubble is nucleated using an appropriately targeted pressure wave designed to induce cavitation in the liquid. In the set of embodiments where the gas pocket is attached to the wall, a specifically controlled volume of gas could be pumped in through a passage in the target surface in order to expand a bubble on the surface. This set of embodiments has the advantage of great control over the contents and size of the gas pocket generated. In the set of embodiments where the liquid medium is a gel the gas pocket can be pre-manufactured by punching or otherwise cutting out or molding the correct shape from the gel block to be used. In another set of embodiments the gas pocket is formed with the use of a pre-manufactured membrane that defines the boundary between the gas pocket and the medium and hence also defines the gas pocket's shape. The use of a thin membrane in this manner allows a decoupling of the liquid and gas materials, allowing any choice of combination of compositions to be made. It also allows the shape of the gas pocket to be controlled with a precision not available to other methods. The membrane could be formed from any suitable material, e.g. glass e.g. plastic e.g. rubber. Having a prefabricated membrane allows a liquid medium to be used more easily as the volume of gas is trapped against the target surface and therefore cannot float away or be otherwise disturbed. In a particular set of embodiments the membrane is frangible and is arranged to break upon impact from the shockwave such that it has no influence on the resulting dynamics. In one set of embodiments the prefabricated membrane includes a line or region of weakness, so that upon impact from the shockwave it breaks along the line or in the region of weakness. The line or region of weakness can be arranged so that the position of the breach has an influence on the ensuing flow patterns, for example this could help control the formation and dynamics of the transverse jetting. In another set of embodiments the membrane is designed to deform with the collapsing cavity. In the set of embodiments where the gas pocket is not attached to the surface, the concept of a gas pocket contained within a membrane is also useful. In a particular set of embodiments the gas pockets near the surface take the form of small glass beads filled with an appropriate gas. This has the same advantage of giving control over the shape of the gas pocket. In a preferred set of embodiments, the methods described herein are potentially may be employed to generate nuclear fusion reactions. The fuel for the reaction could be provided by the gas in the pocket, the medium, or the fuel could be provided by the target surface itself. Any of the fuels mentioned in U.S. Pat. No. 7,445,319 is suitable for use in the present invention. The device in the present invention is not as restricted, regarding size, as U.S. Pat. No. 7,445,319 where the size of the droplet constrains the maximum bubble size. It may be advantageous to have a larger apparatus where a larger volume of gas is heated. The volume of gas in each pocket may be chosen depending on the circumstances but in one set of preferred embodiments it is between 5×10−11 and 5×10−3 liters. The fusion reactions which it may potentially be possible to obtain in accordance with certain embodiments of the invention could be used for net energy production (the long term research aim in this field), but the inventors have appreciated that even if the efficiency of the fusion is below that required for net energy production, the reliable fusion which may potentially be obtainable in accordance with embodiments of the invention is advantageous for example in the production of tritium which can be used as fuel in other fusion projects and is very expensive to produce using currently existing technologies. The potential fusion may also be beneficial in giving a fast and safe neutron source which has many possible applications that will be apparent to those skilled in the art. Moreover, it is not essential in accordance with the invention to produce fusion at all. For example, in some embodiments the techniques and apparatus of the present invention may be advantageously employed as a sonochemistry reactor which can be used to access extreme and unusual conditions. The Applicant notes that the scope of the present invention does not extend usage of a shockwave or static pressure causing an ultrasound shockwave, nor to usage of a device that generates ultrasound shockwaves (e.g. a lithotripsy device). Nor does the scope of the claimed invention include a pocket of gas being collapsed through the process of sonoluminescence. Nor does the scope of the claimed invention include a nuclear fusion reaction. FIGS. 1a and 1b show schematically arrangements in accordance with two respective embodiments of one aspect of the invention. In each case a solid surface 6, for example made from high strength steel, is placed inside a non-gaseous medium 8 in the form of a hydrogel, for example a mixture of water and gelatine. Defined in the hydrogel medium 8 is a gas pocket 2 filled with vaporous fuel which is potentially suitable for taking part in a nuclear fusion reaction. In both cases the gas pocket 2 is attached to the target surface 6 inside a concave depression. In the case of the first embodiment in FIG. 1a, the depression 4 is parabolic and relatively large such that only one side of the gas pocket 2 is attached to the surface 6. The size of the apparatus is flexible but a typical dimension of this diagram could be between 0.1 and 1×10−5 m. In the case of the second embodiment in FIG. 1b, the gas pocket 2 is received in a much smaller, V-shaped tapering depression 5 which could be machined or formed as the result of a naturally occurring crack in the surface 6. In operation a shockwave 10 is created from an explosion, for instance with a pressure of 5 GPa, within the gel medium 8. This is represented in both FIGS. 1a and 1b as a line propagating in the direction of the arrow towards the pocket of gas 2. First the shockwave 10 strikes the upper parts of the target surface 6, causing the shockwave 10 to change shape as it advances towards the pocket of gas 2. In this manner the shape of the shockwave 10 that advances into the pocket of gas 2 can be explicitly controlled by shaping the surface 6 accordingly. The shaped shockwave 10 will then strike the pocket of gas 2, compressing it against the target surface 6 as the shockwave 10 propagates through the gas pocket 2. Reflections of the shockwave 10 from the surface 6 after it has propagated through the pocket 2 travel back through the pocket, reinforcing those propagating from the original direction and further compressing the gas pocket. The compression of the gaseous fuel inside the pocket causes intense local heating which potentially may be sufficient to generate a nuclear fusion reaction. FIGS. 2a, 2b and 2c show three successive stages of a shockwave interacting with a pocket of gas 12 spaced from a surface 16 in accordance with another aspect of the invention. In this embodiment the pocket of gas 12 is immobilized in the gel 18 in a concave depression 14 in the surface 16. FIG. 2a shows a shockwave 20 propagating through the gel medium 18, in the direction of the arrow, approaching the gas pocket 12. FIG. 2b shows the shockwave 20 as it is incident for the first time upon the gas pocket 12. The shockwave acts on the volume of gas 12 to compress it, in a similar manner to the embodiments shown in FIGS. 1a and 1 b. At the same time the shockwave 20 is reflected from the upper sides of the concave depression 14 in the surface 16. FIG. 2c shows the third snapshot in the sequence, by which time the shockwave 20 has passed through the volume of gas 12, compressing it significantly. Also by this time, the shockwave 20 has been reflected from the surface 16 and is travelling back towards the pocket of gas 12 in the direction indicated by the arrow. The reflected shockwave 20 now has a shape resembling the shape of the concave depression 14 and is focused towards the pocket of gas 12 upon which it is incident for a second time, compressing it further and therefore further increasing the temperature and pressure within it. FIGS. 3a and 3b show, in accordance with yet another aspect of the invention, two successive stages of a shockwave interaction with a pocket of gas 22 attached to a surface 26 so as to cover and fill a V-shaped tapering depression 24. Although the tapering depression 24 is of a similar shape to that in FIG. 1b, relative to the size of the tapering depression, the volume of gas in the pocket 22 is much greater than it is in FIG. 1b. For example the width of the bubble could be of the order of 1 cm. FIG. 3a shows the shockwave 30 propagating through the medium 28 (which could be the same material as in previous embodiments or a different material could be used), in the direction of the arrow, towards the gas pocket 22. FIG. 3b shows a later stage in the interaction, after the shockwave 30 has struck the gas pocket 22. The portion 27 of the shockwave 30 that has struck the edge of the pocket of gas 22 is reflected as a result of the large change in density from the medium 28 to the gas 22. This reflected portion 27 forms a rarefaction fan which propagates away from the gas pocket 22 and therefore creates a low pressure region between the reflected portion 27 and the gas pocket 22. The medium 28 flows into this low pressure region as a jet 29 which then traverses the gas pocket 22, trapping a fraction of the gas therein between the tip of the jet 29 and the tapering depression 24 in the surface 26, thereby causing compression and heating of the gas in the manner previously described. FIG. 1b shows a further configuration which is also suitable as an embodiment of this aspect of the invention. FIG. 4 shows a further embodiment of the previous aspect of the invention in which a pocket of gas 32 is attached to a target surface 36 in a tapering depression 34. This embodiment is different from those previously described in that the pocket of gas 32 is separated from the medium 38 by a prefabricated membrane 33. The prefabricated membrane 33 is frangible i.e. it is designed to break on the impact of the shockwave 40. Once the prefabricated membrane 33 has been broken by the impact of the shockwave 40, the shockwave 40 continues to propagate into the depression 34 compressing the pocket of gas 32 in the same manner as for the previous embodiments. FIG. 5 is a variant of the embodiment shown in FIG. 3a. In this embodiment there are multiple smaller depressions 42 at the bottom on a large depression 44. The pocket of gas 46 is partially received both by the large depression 44 and by the multiple smaller depressions 42. In operation of this embodiment the jet formed when the shockwave (not shown) hits the pocket of gas 46 will highly compress multiple small volumes of the gas by trapping them in the small depressions 42, in a similar manner to that described above with reference to FIGS. 3a and 3b. Although specific examples have been given, it will be appreciated that there are a large number of parameters that influence the actual results achieved, for example liquid or gel medium density, ambient pressure and temperature, composition of the gas and of the liquid or gel, impact angle of the shockwave, target surface shape and micro-structure of the target surface. In each of the embodiments described above, the diagrams shown are a vertical cross-section through a three-dimensional volume of gas and target surface and hence they depict embodiments that are rotationally symmetric. However, this is not essential to the invention. In particular the surface could comprise discrete surface portions in the rotational direction either instead of, or as well as in the vertical cross-section shown. In the latter case the target surface would be multi-facetted. Each facet could give rise to separate but converging shockwaves. In all of the embodiments described, the apparatus can be used by creating a shockwave in the medium which is incident upon a volume of gas containing deuterated water vapor. In numerical modeling of the experiment, the techniques described herein give rise to a peak pressure of ˜20 GPa which is sufficient to cause temperatures inside the collapsed volume of gas in excess of 1×106 Kelvin which potentially may be sufficient for a nuclear fusion reaction of the deuterium atoms. In some non-limiting examples the resulting neutrons could be used in other processes, or could be absorbed by a neutron absorber for conversion of the kinetic energy of the neutrons to thermal energy and thus conventional thermodynamic energy generation. |
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summary | ||
055374506 | claims | 1. An on-line method of detecting failed nuclear fuel elements in an operating water cooled nuclear reactor having a plurality of control cells which contain nuclear fuel bundles and into which damping rods can be reciprocated to start, stop and control the rate of nuclear chain reaction, the reactor producing an off-gas stream which, in the case of the existence of one or more failed nuclear fuel elements, includes O-19, N-13, N-16, Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides, comprising, while the reactor continues to operate: a) flowing the off-gas stream from the reactor to a detecting cell of a gamma spectrograph, the flowing being for a time sufficient to reduce gamma radiation produced by O-19 and N-16 nuclides and to reduce Compton scattering produced by O-19, N-13 and N-16 nuclides sufficiently so that the magnitudes of the gamma radiation from at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides can be determined in the gas cell, the spectrograph being of sufficiently high resolution to allow such determination; and b) determining the magnitude of the gamma radiation from the at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides in the off-gas stream; and further including, when the magnitude of the gamma radiation from one or more of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides is such as to indicate the existence of failed cladding among one or more of the fuel cells, the steps of, while the reactor continues to operate: c) reciprocating damping rods in a selected subset of the fuel cells sufficiently so as to change the rate of nuclear chain reaction of the selected subset; d) repeating the flowing and determining steps; e) designating other fuel cells as the selected subset and repeating steps c) and d) until the effect of the reciprocation of the damping rods in the selected subset on the magnitude of the gamma radiation from the at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides in the off-gas stream indicates that a member cell of the selected subset exhibits failed cladding. f) maintaining a damping rod of the member cell reciprocated into the member cell of the selected subset which exhibits failed cladding sufficiently to stop nuclear chain reaction of the member cell. a) flowing the off-gas stream from the reactor to a detecting cell of a gamma spectrograph, the flowing being for a time sufficient to reduce gamma radiation produced by O-19 and N-16 nuclides and to reduce Compton scattering produced by O-19, N-13 and N-16 nuclides sufficiently so that the magnitudes of the gamma radiation from at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides can be determined in the gas cell, the spectrograph being of sufficiently high resolution to allow such determination; b) determining the magnitude of the gamma radiation from the at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides in the off-gas stream; c) reciprocating damping rods in a selected subset of the fuel cells sufficiently so as to change the rate of nuclear chain reaction of the selected subset; d) repeating the flowing and determining steps; e) designating other fuel cells as the selected subset and repeating steps c) and d) until the effect of the reciprocation of the damping rods in the selected subset on the magnitude of the gamma radiation from the at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides in the off-gas stream indicates that a member cell of the selected subset exhibits failed cladding; f) reciprocating the appropriate rods into the leaking cell or cells sufficiently to alleviate the leak or leaks; and g) continuing operation of the reactor thereafter. increasing the degree of withdrawal of rods from non-leaking control cells to increase the amount of power being generated by the reactor. 2. A method as set forth in claim 1, further including, while the reactor continues to operate: 3. A method as set forth in claim 2, wherein in step b) the at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides comprises the Xe-133 nuclide. 4. A method as set forth in claim 3, wherein in step b) the magnitude of the Xe-138 nuclide is also determined and wherein a marked increase in the ratio of the magnitude of gamma radiation attributable to Xe-133 to that attributable to Xe-138 is used as an indicator of failed cladding. 5. A method as set forth in claim 1, wherein in step b) the at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides comprises the Xe-133 nuclide. 6. A method as set forth in claim 5, wherein in step b) the magnitude of the Xe-138 nuclide is also determined and wherein a marked increase in the ratio of the magnitude of gamma radiation attributable to Xe-133 to that attributable to Xe-138 is used as an indicator of failed cladding. 7. A method as set forth in claim 1, wherein in step b) the at least one of the Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides comprises the Xe-133 nuclide. 8. A method as set forth in claim 7, wherein in step b) the magnitude of the Xe-138 nuclide is also determined and wherein a marked increase the ratio of the magnitude of gamma radiation attributable to Xe-133 to that attributable to Xe-138 is used as an indicator of failed cladding. 9. A method as set forth in claim 1, wherein the time sufficient to reduce gamma radiation produced by O-19 and N-16 nuclides and to reduce Compton scattering produced by O-19, N-13 and N-16 nuclides sufficiently so that the magnitudes of the gamma radiation from Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides can be determined in the gas cell falls within a range from about 3 to about 30 minutes. 10. A method as set forth in claim 1 wherein the flowing of step a) is at a flowrate between about 1 and about 30 cubic feet per hour. 11. A method of continuing to operate an operating water cooled nuclear reactor having a plurality of control cells which contain nuclear fuel bundles and into which damping rods can be reciprocated to start, stop and control the rate of nuclear chain reaction, the reactor producing an off-gas stream which, in the case of the existence of one or more failed clad nuclear fuel elements, includes O-19, N-13, N-16, Kr-85m, Kr-87, Kr-88, Xe-133, Xe-135, Xe-135m and Xe-138 nuclides, the reactor exhibiting one or more leaks indicative of non-catastrophic cladding failure, comprising, while the reactor continues to operate: 12. A method as set forth in claim 11, further including: 13. A method as set forth in claim 12, wherein the increasing is sufficient so that the reactor is operating at substantially full power. 14. A method of detecting failed cladding in a nuclear reactor comprising determining the ratio, in an off-gas stream from the reactor, of the magnitude of gamma radiation attributable to Xe-133 to that attributable to Xe-138. |
claims | 1. A soft X-ray projection exposure apparatus having at least one metal mirror constituting at least one of an illumination optical system and a projection optical system, the at least one mirror comprising: a metal substrate having a front surface and a rear surface; a thin film of an amorphous substance formed on the front surface of the metal substrate, a front surface of the amorphous substance being polished to optical smoothness; and a multi-layer film formed on the front surface of the thin film, wherein the multi-layer film reflects X-rays of a specified wavelength, and wherein at least a principal component of the amorphous substance is one of nickel or a nickel alloy. 2. The soft X-ray projection exposure apparatus according to claim 1 , wherein the at least one mirror satisfies a condition of: claim 1 xcex1xc2x7Qxc2x7d 2 /(2xcex7)xe2x89xa610 xe2x88x929 where xcex7 is a thermal conductivity of the metal substrate, xcex1 is a coefficient of linear expansion, Q is a thermal flux applied to the metal mirror by electromagnetic radiation, and d is a mean thickness of the mirrors. 3. The soft X-ray projection exposure apparatus according to claim 1 , wherein the metal substrate includes an Invar alloy. claim 1 4. The soft X-ray projection exposure apparatus according to claim 1 , wherein the metal substrate includes at least one of aluminum, copper, beryllium, silver, gold, and an alloy containing at least one of aluminum, copper, beryllium, silver, gold. claim 1 5. The soft X-ray projection exposure apparatus according to claim 1 , wherein a front surface roughness of the amorphous substance is at most 0.5 nm. claim 1 6. The soft X-ray projection exposure apparatus according to claim 1 , wherein at least a principal component of the amorphous substance is selected from a set consisting of silicon oxide, silicon carbide, PSG (phospho-silicate glass), silicon nitride, silicon, and carbon. claim 1 7. The soft X-ray projection exposure apparatus according to claim 1 , wherein the back surface of the metal substrate is cooled so that the back surface is maintained at a constant temperature. claim 1 8. A mirror, for use when large amounts of heat from incident electromagnetic radiation is absorbed, comprising: a metal substrate having a front surface and a back surface; a thin film of an amorphous substance formed on the front surface of the substrate, and having a surface polished to optical smoothness, wherein at least a chief component of the amorphous substance is one of nickel or a nickel alloy. 9. The mirror according to claim 8 further comprising: claim 8 a multi-layer film formed on a surface of the thin film, wherein the multi-layer reflects X-rays of a specified wavelength. 10. The mirror according to claim 8 , wherein the surface roughness of the amorphous substance is at most 0.5 nm. claim 8 11. The mirror according to claim 8 , wherein the mirror satisfies a condition of: claim 8 xcex1xc2x7Qxc2x7d 2 /(2xcex7)xe2x89xa610 xe2x88x929 [m] where xcex7 is a thermal conductivity of the substrate, xcex1 is a coefficient of linear expansion, Q is a thermal flux on the mirror from electromagnetic radiation, and d is a mean thickness of the mirror. 12. The mirror according to claim 8 , wherein a thermal conductivity of the substrate is at least 200 [W/mxc2x7K]. claim 8 13. The mirror according to claim 8 , wherein a material of the metal substrate includes one of aluminum, an alloy containing aluminum, copper, an alloy containing copper, beryllium, an alloy containing beryllium, silver, an alloy containing silver, gold, and an alloy containing gold. claim 8 14. The mirror according to claim 8 , wherein the back surface of the substrate is cooled so that the back surface is maintained at a constant temperature. claim 8 15. A method for manufacturing a mirror comprising: preparing a metal substrate; forming an amorphous thin film containing a nickel alloy as a chief ingredient on a surface of the metal substrate; and working a surface of the amorphous thin film into an optically smooth surface. 16. The method according to claim 15 further comprising: claim 15 forming a multi-layer film that reflects X-rays of a specified wavelength on the surface of the amorphous thin film that has been worked into an optically smooth surface. 17. The method according to claim 15 wherein the step of forming an amorphous thin film includes a plating process. claim 15 |
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054815860 | summary | FIELD OF THE INVENTION The present invention relates to an automatic position control system for x-ray machines such as mammography machines. In particular, the present invention relates to a position control system which maintains the position of a scanning x-ray beam in coincidence with the center of an x-ray sensor that moves with the scanning x-ray beam. The present invention also relates to the x-ray sensor used in such a position control system. BACKGROUND OF THE INVENTION FIG. 1 is a schematic diagram illustrating a prior art mammography machine (100). The mammography machine (100) has an x-ray source (103), a beam limiting device (104) and a support platform (106) for positioning a part of the patient's body, which in this case is the breast (102). The mammography machine (100) also includes the x-ray sensor (101) and the CCD detector (105). The x-ray sensor (101) is attached to the CCD detector (105) and moves along the track (107). The x-ray sensor (101) is used to determine the quantity of energy passing through the breast (102). The CCD detector (105) is used to create an image for diagnostic purposes. In other mammography machines, the CCD sensor (105) is not utilized and the image is made on a film. The x-ray sensor (101) is also used in automatic exposure controls to control the time of exposure of an x-ray source (103) and, when film is used, to provide the proper optical density on the film. This type of sensor might include solid state devices, ionization chambers or photo-multiplier tubes. In several applications, a narrow x-ray beam (108) is scanned across the breast (102). A slot scanning x-ray procedure is one such application. In slot scanning applications, a beam limiting device (104) is swept to produce the narrow scanning x-ray beam (108). It is desirable to know the location of the scanning x-ray beam (108) as well as its intensity. To obtain an x-ray exposure, the beam limiting device (104), the x-ray sensor (101) and the CCD detector (102) traverse the breast (102) at a constant velocity. Thus the narrow x-ray beam (108) scans across the breast (102) from right to left as indicated by the arrow (121). During exposure of the breast (102), the CCD detector (105) and sensor (101) move along track (107) from right to left as indicated by the arrows (111). FIG. 2 is an enlargement of the lower portion of the x-ray machine shown in FIG. 1, detailing the x-ray sensor (101), the CCD detector (105) and the track (107) used for movement. FIG. 2 also shows arrows (111) which indicate the direction of movement along the track (107). The movement of the sensor (101) and detector (105) along track (107) is aligned with the scanning narrow x-ray beam (108). The x-ray beam (108) is scanned by a servo-positioning motor (110) which moves the beam limiting device (104). FIG. 3 is an enlargement of the upper portion of the x-ray machine shown in FIG 1, detailing the servo-positioning motor (110) and the beam limiting device (104). Slot scanning applications described in the current literature all rely on mechanical interfaces for moving the scanning x-ray beam (108), sensor (101) and the detector (105). These interfaces are complex and costly and are prone to alignment problems which reduce the quality of the produced image. In short, the quality of a slot scanning system is a function of the location of the scanning x-ray beam (108) as well as its intensity. It is a function of the accuracy of synchronously moving the beam limiting device (104), the sensor (101) and the detector (105) in the same direction (111) across the breast (102). In view of the foregoing, it is an object of the invention to provide an automatic position control system for an x-ray machine such as a mammography machine in which the x-ray beam and x-ray sensor synchronously scan across the breast or other part of the patient's body. It is a principal object of the invention to provide an x-ray machine especially for mammography which includes an automatic position control system for maintaining the position of an x-ray beam with respect to an x-ray sensor without cumbersome mechanical interfaces. It is also an object of the invention to provide an x-ray sensor for use in such a position control system, which sensor outputs a signal indicative of the position of a narrow x-ray beam. SUMMARY OF THE INVENTION This and other objects are achieved by the present invention which provides an automatic position control system for x-ray machines for use in mammography or other applications. The control system maintains alignment of a scanning narrow x-ray beam with a sensor. The present invention provides a servo-driven motion control system which automatically aligns the x-ray beam with the x-ray sensor. According to one embodiment of the invention, a narrow x-ray beam is produced. The narrow x-ray beam illuminates the breast (or other body part) of the patient. The x-ray beam, after passing through the breast, is sensed by an x-ray sensor. The narrow x-ray beam and sensor move synchronously to scan across the breast. The x-ray beam is scanned by a servo-positioning motor which controls the position of a beam limiting device. The sensor is moved by a sensor positioning motor. The feedback system operates as follows: The sensor senses the position of the narrow x-ray beam relative to the sensor and sends a signal representing the x-ray beam position to a feedback amplifier. The feedback amplifier compares the signal representing the position of the x-ray beam with a preset reference signal and sends the difference (i.e., error signal) to a servo-positioning motor controller. This motor controller controls the servo-positioning motor which moves the beam limiting device to center the narrow x-ray beam over the sensor. The sensor can be implemented by various technologies, including but not limited to an ionization chamber, a photodiode array, a CCD array or a photocell with phosphor. Illustratively, the sensor receiving the x-ray radiation is an ionization chamber which generates an ionization current. Such an ionization chamber comprises two elements (i.e., electrodes) separated by a gas or air. One of the element comprises a plurality of sensing strips separated by resistors. Furthermore, this element has two terminals each terminated by a terminating resistor. The voltage between the two terminals is a signal representing the position of the x-ray beam. According to another embodiment of the x-ray sensor, a plurality of photodiodes are connected in series and separated by resistors. The sensor has two terminals (at either end of the series connected photodiodes), with each terminal being terminated by a resistor. The voltage between the two terminals is a signal which represents the position of the x-ray beam. The present invention solves the problem of simultaneously correlating and achieving the correct alignment of the sensor and the beam limiting device without cumbersome mechanical interfaces. The x-ray positioning sensor of the present invention allows for an automatic alignment through its ability to sense the position of the scanning narrow x-ray beam. The mechanical mechanisms used in the prior art to move the sensor are replaced by a simple servo-driven motion control system. |
041347897 | summary | This invention relates to a method of refuelling of a nuclear reactor and to a device for carrying out said method. In more exact terms, the invention relates to an improvement in the refuelling of a nuclear reactor which permits more rapid handling operations. It is known that a nuclear reactor core which serves as an energy source is constituted by fuel assemblies which are in turn constituted by an array of fuel elements of fissile material. During reactor operation, the fraction of uranium-235 contained in said fuel decreases. It is therefore necessary at intervals to replace the partly spent fuel by fresh fuel. Refuelling of the reactor core therefore consists on the one hand in removing the spent fuel and on the other hand in introducing fresh fuel into the reactor or in displacing a fuel element from one region of the reactor core to another. In order to obtain a better understanding of the problems which arise at the moment of re-charging of a reactor with nuclear fuel, reference can be made to the accompanying FIG. 1 in which a pressurized water reactor (PWR) is shown diagrammatically in sectional elevation. The following description relates to the case of a PWR but it is readily apparent that the invention could apply just as readily to any type of reactor. The pressurized water reactor essentially comprises a pressure vessel 2 which is closed at the top by a closure head assembly 4. The pressure vessel is pierced by apertures such as the nozzle 6 which are connected to ducts for circulating the coolant liquid within the pressure vessel 2. Provision is made within the vessel for a lower structure consisting essentially of a core barrel 8, the top portion of which is applied against an internal annular shoulder or support ledge 16 of the pressure vessel 2. By means of the lower core support plate 10, the bottom portion of the core barrel 8 supports the fuel assemblies such as those designated by the reference 12. Provision is also made within the pressure vessel 2 for a top internal structure which is constituted by the upper support plate 14 and the upper core plate 18, said plates being connected by the spacer members formed by the control rod guide tubes 20, the complete assembly being positioned by the upper plate 14 which rests on the support ledge 16 of the pressure vessel. The upper core plate 18 is essentially intended to prevent "levitation" of the fuel assemblies 12 under the action of the coolant which flows upwards through the reactor core. To this end, the upper portion of each fuel assembly 12 can be provided with an elastic system compressed by the upper core plate 18. Reactivity control is accomplished by means of neutron absorbers or control rods. A control rod is constituted by a drive shaft 22 slidably fitted within the control rod guide tubes 20 and adapted to carry absorber rods such as the rod 24 which are inserted into hollow tubes formed within the fuel assemblies 12. The upper end of each control rod drive shaft 22 traverses the closure head assembly 4 of the reactor through leak-tight thermal sleeves 26 and is connected to a control rod drive mechanism 28. It is clear from this intentionally brief outline that, in order to refuel a nuclear reactor core or in other words to withdraw and replace the fuel assemblies in an unloading and reloading operation, it is necessary to remove the reactor closure head assembly 4, then the upper internal structure which is essentially constituted by the upper support plate 14 and the upper core plate 18 as well as the control rods and drive shafts. All these operations are complex and time-consuming and obviously entail the need for reactor shutdown. It is therefore essential to simplify refuelling operations and to reduce the time required. This becomes a particularly important consideration if refuelling is to be performed several times a year. French Pat. No. 71,24817 of July 7th, 1971 describes a method of refuelling a nuclear reactor which consists in removing in a single unit both the pressure vessel lid, the upper internal structure and the control rods, and in storing the complete assembly next to the reactor vessel. This system is attended by certain drawbacks in that means have to be provided for locking the control rod drive mechanisms in the top position and that both the upper internal structure and the control rod absorbers have to be stored with the reactor vessel lid or closure head. These two elements are radioactive, which does not facilitate inspection of the closure head assembly and control rod drive mechanisms. The present invention is precisely directed to a method for refuelling a nuclear reactor and to a device for carrying out said method which overcomes the disadvantages mentioned in the foregoing. In particular, the method according to the invention permits separate removal of the reactor vessel closure head and the upper internal structure as well as the control rods. The method of refuelling essentially comprises the following steps: the reactor closure head is removed after having disengaged this latter from the control rods which are left in the bottom position and said closure head is then stored; the control rods are brought to the top position and secured to the upper internal structure; the assembly constituted by the upper internal structure and the control rods is removed and stored; the spent fuel is replaced and the upper internal structure and the closure head are put back in position. In an alternative mode of execution, the method comprises the following steps: the control rods are brought to the top position and secured to the upper internal structure; the reactor closure head is removed; the assembly constituted by the control rods and the upper internal structure is removed and stored; the spent fuel is replaced and the upper internal structure and the closure head are put back in position. The invention further relates to an unloading device which essentially comprises a frame provided in the lower portion thereof with members for locking said frame on the upper internal structure and a moving platform which is capable of translational motion in a vertical direction with respect to said frame, said moving platform being provided with means for securing the upper extremities of the control rod drive shafts to said moving platform, said frame being provided with means for producing said movement of translation and guiding of said platform, the travel of the moving platform being substantially equal to the travel of the control rods within the reactor core. In a preferred form of construction, the frame is provided at the lower end with a circular flange having an internal diameter at least equal to that of the circle which is circumscribed about all the control rod position locations, vertical columns which serve to guide the moving platform and are attached to said flange at the lower ends, said columns being attached at their upper ends to a second flange comprising means for displacing said platform in translational motion, said platform being provided with an aperture opposite to each control rod drive shaft, the end of each shaft being capable of penetrating into the corresponding aperture, a member for locking each drive shaft being associated with each aperture. The invention is also concerned with a device for carrying out the alternative form of the method, said device being distinguished by the fact that the rigid structure comprises radial ribs fixed on an open-topped cylindrical canister, the wall of said canister being provided with bored recesses for accommodating a first series of balls which are capable of projecting from said canister and penetrating to a partial extent into notches formed in the so-called upper plate, that said drive shaft is hollow and provided at the lower end which penetrates into said canister with bored recesses for accommodating a second series of balls which are capable of projecting from said drive shaft so as to penetrate to a partial extent into notches formed in the internal wall of said canister, and that said device comprises movable means for causing alternate penetration of the balls of the first series into the corresponding notches so as to secure the absorber rods to said upper internal structure and the balls of the second series into the corresponding notches so as to secure said drive shaft to said canister. Said movable means are preferably constituted by a sleeve whose lower portion is capable of sliding within the interior of said canister and whose upper portion is capable of sliding within the interior of the lower end of the drive shaft, and means for displacing said sleeve in vertical motion, the external profile of the upper portion and the lower portion of said sleeve being such that said portions perform a cam function which permits the alternate motion of said balls. |
055704018 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 4, the preferred embodiment of the present invention comprises a wetwell airspace which has been divided into a multiplicity of chambers through the use of wetwell airspace divider partitions or equivalent structure. The number of chambers resulting from incorporation of airspace divider partitions would, in the preferred embodiment, be matched one-for-one to the number of PCC heat exchangers provided for the PCCS. A multiplicity of single-disk vacuum breakers of ordinary design (or of developed high-reliability design) - generally using a minimum of one vacuum breaker per chamber but using more than one per chamber if economically advantaged - are provided to give a pressure-relieving pathway between each respective chamber and the (common) drywell airspace, which is not compartmentalized. For ease of discussion, FIG. 4 depicts a partition 78 which divides the wetwell airspace into two chambers 26A and 26B, which can communicate individually with the drywell 20 via respective vacuum breakers 36A and 36B. However, it is understood that the present invention encompasses the use of one or more partitions to form two or more wetwell airspace chambers. Each wetwell airspace divider partition 78 is designed to provide leaktight structure (with, perhaps, steel plate bounding liners) spanning radially across the entire original SBWR wetwell airspace and extending from the diaphragm floor to partially (preferred embodiment) or fully (alternative embodiment) down into the suppression pool 24. The submergence into the pool by the airspace divider partition must be, as a minimum, the submergence designed for the PCC heat exchanger vent pipes 66A and 66B plus some margin. As can be seen from examination of FIG. 4, the compartmentalized wetwell airspace is thus made able to withstand the loss of any single chamber's driving .DELTA.P - and therefore the loss of driving pressure causing flow through the respective PCC heat exchanger - while enabling all other chambers and their respective PCC heat exchangers to continue passive throughflow operation nominally unaffected by the event, whether this be a single active failed-open vacuum breaker condition or a high drywell/wetwell bypass leakage condition in the impaired chamber. As seen in FIG. 4, a small portion of pool water inventory in the impaired chamber 26A will be displaced. This will cause a modest rise in the surface elevation of the pool in each of the other chambers (e.g., 26B). This will produce a sightly higher operating .DELTA.P across the PCC heat exchanger/vent pipe combination, as the vent pipe operational submergence has been increased (modestly). However, these conditions do not significantly affect the operations of the PCC heat exchanger 54B, as the higher .DELTA.P is offset by the slightly longer water column now being expelled from the PCC heat exchanger vent pipes 66B. Noncondensable gases originally in the impaired chamber's airspace will migrate (slowly) back to the drywell airspace once the vacuum breaker failure takes place. The noncondensable gases will then be swept up by the operating PCC heat exchangers and discharged into their respective connected chambers. Therefore a pro rata higher partial pressure for noncondensable gases will also develop in the unfaulted chambers. While containment peak pressure (at 72 hr post-LOCA) will thus be higher for the case of one vacuum breaker failed open, the containment/PCCS designer can minimize the extent of this incrementally increased pressure condition by utilizing either or both of the following means: (a) using more than three PCC heat exchangers (which is the number in the conventional SBWR) and therefore obtaining more than three wetwell airspace chambers; and (b) using individual PCC heat exchanger vent pipes, one per PCC heat exchanger lower drum (of which there are conventionally two such lower drums in each currently designed PCC heat exchanger), instead of using a combined PCC heat exchanger vent pipe (which, as now designed, accepts and merges noncondensable gases from both lower drums), and allocating an individual wetwell airspace chamber to each such PCC heat exchanger vent pipe. As should be apparent from the foregoing disclosure, the present invention provides a containment system design for plants of the SBWR type characterized by their use of passive decay heat rejection systems which can meet design-for-licensability goals given either the consequence of a vacuum breaker in the failed open state or the consequence of a high drywell/wetwell bypass leakage state being present. The foregoing disclosed preferred embodiment incorporating at least one wetwell airspace divider partitions is an example of a containment configuration which accomplishes this goal. Other variations and modifications will be apparent to persons skilled in the design of passive pressure systems for boiling water reactors. All such variations and modifications are intended to be encompassed by the claims set forth hereinafter. |
claims | 1. A vertical travel robotic tank cleaning system for cleaning tanks, comprising:a mast assembly that mounts to a riser structure, the mast assembly comprising a vertically adjustable mast that includes a telescopic assembly comprised of an outer circular tube section and an inner circular tube section that can slide past each other lengthwise with slide pads therebetween;a telescopic boom attached to the mast assembly;a turntable connected to the mast assembly that rotates the telescopic boom;a hose management system that accommodates axial and radial motion of the telescopic boom;a nozzle assembly on an end of the telescopic boom, the nozzle assembly includes a plurality of nozzles attached together as a rigid unit on a distal end of the telescopic boom with pan and tilt capability, the plurality of nozzles comprises one low pressure and high flow nozzle between a pair of orbital wash nozzles, each nozzle in the nozzle assembly includes a center line axis which are substantially parallel with each other, the one low pressure and high flow nozzle provides a spray up to approximately 500 psi (pounds per square inch) and up to approximately 500 gpm (gallons per minute), the orbital wash nozzles each provides a solid, zero-degree water fluid stream rotating in a conical pattern up to 5,000 psi (pounds per square inch) and up to approximately 50 gpm (gallons per minute); anda manifold system for supplying and returning working hydraulic fluid. 2. The vertical travel robotic tank cleaning system of claim 1, wherein the mast assembly includes a maximum body diameter that allows installation through a hole as small as 12 inches in diameter. 3. The vertical travel robotic tank cleaning system of claim 1, further comprising:a plurality of hydraulically actuated cylinders and motors allowing operation of the system in hazardous and explosive environments. 4. The vertical travel robotic tank cleaning system of claim 1, wherein the telescopic boom rotates approximately 180 degrees relative to a vertical axis in either direction. 5. The vertical travel robotic tank cleaning system of claim 1, wherein the telescopic boom pivots approximately 90 degrees from vertical to horizontal and extends and retracts approximately 30 feet to allow the nozzle assembly to maneuver around the perimeter of a tank. 6. The vertical travel robotic tank cleaning system of claim 1, further comprising:a nickel plating to counteract corrosive environments. 7. The vertical travel robotic tank cleaning system of claim 1, wherein the nozzle assembly at an outer end of the telescopic boom moves through two degrees of freedom for allowing twist over a longitudinal axis and rotation about a perpendicular axis. 8. The vertical travel robotic tank cleaning system of claim 1, wherein the telescopic boom is extendable and retractable to allow the nozzle assembly an extended reach to allow each nozzle to move closer to a work surface over a larger area. 9. The vertical travel robotic tank cleaning system of claim 1, wherein the telescopic boom pivots approximately 90 degrees from vertical to horizontal, and the boom extends and retracts to allow the nozzle assembly to maneuver around the perimeter of a tank, and the mast twists by the turntable causing the boom to rotate circumferentially about the perimeter of the tank. 10. The vertical travel robotic tank cleaning system of claim 9, wherein the nozzle assembly pivots and twists relative to the telescopic boom. 11. The vertical travel robotic tank cleaning system of claim 1, wherein the nozzle assembly pivots and twists relative to the telescopic boom. 12. A vertical travel robotic tank cleaning system for cleaning tanks, comprising:a mast assembly that mounts to a riser structure, the mast assembly comprising a vertically adjustable mast that includes a telescopic assembly comprised of an outer circular tube section and an inner circular tube section that can slide past each other lengthwise with slide pads therebetween;a telescopic boom attached the mast assembly;a turntable connected to the mast assembly that rotates the telescopic boom;a hose management system that accommodates axial and radial motion of the telescopic boom;a nozzle assembly on an end of the telescopic boom, the nozzle assembly includes a plurality of nozzles rigidly attached on a distal end of the telescopic boom with pan and tilt capability, the plurality of nozzles comprises one low pressure and high flow nozzle between a pair of orbital wash nozzles, each nozzle in the nozzle assembly includes a center line axis which are substantially parallel with each other; anda manifold system for supplying and returning working hydraulic fluid. 13. The system of claim 12, wherein the at least one low pressure and high flow nozzle provides a spray up to approximately 500 psi (pounds per square inch) and up to approximately 500 gpm (gallons per minute). 14. The system of claim 12, wherein each orbital wash nozzle provides a solid, zero-degree water fluid stream rotating in a conical pattern up to 5,000 psi (pounds per square inch) and up to approximately 50 gpm (gallons per minute). 15. The system of claim 12, wherein the telescopic boom pivots approximately 90 degrees from vertical to horizontal and extends and retracts approximately 30 feet to allow the nozzle assembly to maneuver around the perimeter of a tank. 16. The system of claim 12, wherein the nozzle assembly that includes the plurality of nozzles attached together as the rigid unit at an outer end of the telescopic boom moves through two degrees of freedom for allowing twist over a longitudinal axis and rotation about a perpendicular axis. 17. The vertical travel robotic tank cleaning system of claim 12, wherein the telescopic boom pivots approximately 90 degrees from vertical to horizontal and the boom extends and retracts to allow the nozzle assembly to maneuver around the perimeter of a tank, and the mast twists by the turntable causing the telescopic boom to rotate circumferentially about the perimeter of the tank. 18. The vertical travel robotic tank cleaning system of claim 17, wherein the nozzle assembly pivots and twists relative to the boom. 19. The vertical travel robotic tank cleaning system of claim 12, wherein the nozzle assembly pivots and twists relative to the telescopic boom. 20. A vertical travel robotic tank cleaning system for cleaning tanks, comprising:a mast assembly that mounts to a riser structure, the mast assembly comprising a vertically adjustable mast that includes a telescopic assembly comprised of telescopic tubes;a telescopic boom attached to the mast assembly by a pivot point, the telescoping boom pivots approximately 90 degrees from vertical to horizontal;a turntable connected to the mast assembly that rotates the telescopic boom, wherein the telescopic boom rotates and pivots relative to the riser structure; anda nozzle assembly attached by attach components to an outer end of the telescopic boom, the nozzle assembly includes a rigid unit comprising one low pressure and high flow nozzle between a pair of orbital wash nozzles, each nozzle in the nozzle assembly includes a center line axis which are substantially parallel with each other, the attach components allows the nozzle assembly move through two degrees of freedom to twist over a longitudinal axis and rotation about a perpendicular axis, relative to the outer end of the telescoping boom. |
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summary | ||
claims | 1. A radiation beam therapy system comprising:a plurality of treatment devices, including:a charged-particle accelerator that provides a beam of energetic charged particles;a treatment station that allows positioning of a patient to receive at least a portion of the beam of charged particles; anda beam delivery system that delivers the beam of charged particles to the patient positioned at the treatment station;a database component that stores parameters associated with respective treatment devices, wherein the parameters comprise instructional information that can be used to configure the respective treatment devices for operation;an interface component that allows an authorized user to modify at least one of the parameters associated with a respective treatment device; anda management component that,retrieves a subset of parameters from the database, the subset of parameters including at least one of the stored parameters and modified parameters,generates a data storage element comprising the subset of parameters in a format recognizable by the selected treatment device, wherein the data storage element permits configuration of the selected treatment device based, at least in part, on the subset of parameters, anddistributes the data storage element to the selected treatment device to thereby permit the selected treatment device to operate independently of the database component. 2. The system of claim 1, wherein the management component has no direct link to the plurality of treatment devices. 3. The system of claim 1, wherein the management component retrieves parameters upon receiving a request from the treatment devices inquiring whether parameter updates are available. 4. The system of claim 1, wherein the management component retrieves parameters, generates a data storage element, and distributes updated parameters to the treatment devices, after a parameter modification is requested by a user, on a periodic basis via a control file. 5. The system of claim 1, wherein the management component waits for administrator approval before retrieving the subset of parameters, generating the data storage elements, and distributing the data storage elements. 6. The system of claim 1, wherein administrator approval temporarily allows the at least one parameter modification. 7. The system of claim 1, wherein the parameters include one or more of treatment data, configuration parameters, operations parameters, and control settings. 8. The system of claim 1, wherein the interface component allows the user to temporarily modify the one or more parameters and temporarily modified parameters expire after a predetermined period of time and/or revert to previously stored values after the system control files are generated. 9. The system of claim 1, wherein the selected treatment device requires at least one of the parameters in the subset of parameters for operation. 10. A radiation beam management system configured to control a plurality of proton beam therapy systems that comprise treatment devices including a radiation beam source and a beam transport device, the radiation beam management system comprising:a database that stores a plurality of parameters associated with respective treatment devices, wherein a parameter comprises instructional information that can be used to control a treatment device;an interface that allows an authorized user to modify at least one parameter of the plurality of parameters, wherein the at least one parameter is associated with a respective treatment device; anda management component configured toretrieve a subset of parameters from the database, wherein the subset of parameters includes at least one of the stored parameters and modified parameters,generate a system control file comprising the retrieved subset of parameters, wherein the system control file is usable to control the respective treatment device based, at least in part, on the instructional information comprised therein, andtransmit the system control file to a proton beam therapy system associated with the respective treatment device, thereby permitting the respective treatment device to operate independently of the database. 11. The system of claim 10, wherein the management component has no direct link to the plurality of treatment devices. 12. The system of claim 10, wherein the management component retrieves parameters upon receiving a request from the treatment devices inquiring whether parameter updates are available. 13. The system of claim 10, wherein the management component retrieves parameters, generates a data storage element, and distributes updated parameters to the treatment devices, after a parameter modification is requested by a user, on a periodic basis via the control file. 14. The system of claim 10, wherein the proton beam therapy system comprises a control station, and wherein the management component transmits the system control file to the control station, and wherein the control station transmits the system control file to the respective treatment device. 15. The system of claim 14, wherein the respective treatment device is a proton energy source, an accelerator, a beam transport system, a switchyard, a gantry, or a treatment platform. 16. The system of claim 10, wherein the subset of parameters in the control file is arranged so as to enable the respective treatment device to recognize each of the parameters. 17. The system of claim 10, wherein the parameters include one or more of treatment data, configuration parameters, operations parameters, and control settings. 18. The system of claim 10, wherein the interface is configured to prevent the user from modifying parameters while a patient is being treated by the proton beam therapy system. 19. The system of claim 10, wherein the system control file is a flat file or a binary file. 20. The system of claim 10, wherein the management component is configured to transmit the system control file to a plurality of proton beam therapy systems. |
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abstract | A lower and upper end plugs of an annular fuel rod, into and out of which cooling water flows, comprises: a lower end plug including a filter for debris which has a plurality of pins intersecting each other at the proper position of an inner channel main inlet, through-holes into which the pins of the debris filter are fitted, and at least one inner channel auxiliary inlet through which the cooling water flows into a lower inner channel thereof when the inner channel main inlet is blocked by debris, and which has a through-hole shape; and an upper end plug including at least one upper handling groove and hole, into which a fuel rod handling tool is coupled, at a proper position of an inner circumference of the inner channel main outlet in a circumferential direction. |
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051732491 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred embodiment of the invention will now be described with reference to FIGS. 2-5, wherein like numerals represent like elements. As shown in FIGS. 2a, 4 and 5, a flux thimble removal tool in accordance with the present invention includes two basic units: a lower pulling unit 20 and a cutting/storage unit 22 that sits atop the lower pulling unit. Pulling unit 20 houses a gripper unit 30a, drive motor 68, gears 32, 66, helix drive shaft 40a (all of which are shown in FIG. 4), guide bar 26a, slide bar 24a, and guide tube 36, all of which are adapted to gradually extract neutron flux thimbles 38 one a time from the RV 74 (see FIG. 5) of a PWR, and to feed the thimble in segments to the cutting/storage unit 22. Cutting/storage unit 22 further extracts the thimble, then severs the further extracted portion. The operation is continued until the thimble is fully extracted from the RV and reduced to a quantity of easily-disposable segments. A video camera (not shown) may also be installed to facilitate surveillance of the operation. The walls of pulling unit 20 are fabricated from thin wall pipe. The respective lengths of units 20 and 22 are approximately 1 meter and 2 meters. Cutting/storage unit 22 is coupled via sockets 46 and pins 50 to pulling unit 20. Unit 22 houses a second gripper unit 30b; second drive shaft 40b, which is coupled via a stanchion 44 to drive shaft 40a and which has threads with an equal but opposite pitch to the threads of lower drive shaft 40a; second slide bar 24b and guide 26b and removable radiation shielding 48, all of which is shown in FIG. 2a. In addition, as shown in FIG. 3, unit 22 houses a cutting unit comprising blade 42, cutter block 54, pivot pin 56, tie rod 58, compression spring 60, and connection 62 to a portable hydraulic apparatus (not shown) for activating the blade. In operation, pulling unit 20 is mounted on the seal table 18 of the PWR, which normally serves as a pipe support (see FIG. 5); gripper 30a is then positioned to enable jaws 70 to grip the thimble; helix drive 40a is then rotated, thereby lifting the gripper and thimble upward from seal table 18. This lifting is continued until gripper 30a reaches the top of helix drive shaft 40a, at which time the top of the thimble protrudes into gripper 30b of cutting/storage unit 22. The motor 68 is then reversed, which causes lower gripper 30a to release the thimble and move downward and upper gripper 30b to take hold of the thimble and move upward, thereby pulling the thimble to the top of unit 22. Motor 68 is stopped when the thimble reaches the top of unit 22; the hydraulic apparatus (not shown) is activated to sever the thimble; and the motor is then again reversed, causing upper gripper 30b to release the severed segment and begin pulling up the next segment. Upper unit 22 is separated from lower unit 20 after one or more thimbles are removed and is thereafter transferred to a place where the spent thimbles can be stored permanently. Both the lower and upper units are provided with removable radiation shields 48. The flux thimble removal tool described above is unique in that it facilitates the removal, cutting and disposal of BMI flux thimbles through the seal table as opposed to through the RV; however the true scope of the invention is not limited to the specific, preferred embodiment described above. For example, the preferred embodiment may be adapted to remove thimbles inserted through the top head of the RV, and may also be adapted to remove detector thimbles other than neutron flux thimbles. Many other modifications and variations of the preferred embodiment will fall within the true scope of the invention, which is set forth in the following claims. |
description | This application is a continuation of International Application No. PCT/CN2017/092702, filed on Jul. 13, 2017, which claims priority to Chinese Patent Application No. 201610930008.7, filed on Oct. 31, 2016; Chinese Patent Application No. 201621154870.5, filed on Oct. 31, 2016, the disclosures of which are hereby incorporated by reference. The present disclosure relates generally to a radioactive ray irradiation therapy system, and, more particularly, to a neutron capture therapy system. As atomics moves ahead, such radiotherapy as Cobalt-60, linear accelerators and electron beams has been one of major means to cancer therapy. However, conventional photon or electron therapy has been undergone physical restrictions of radioactive rays; for example, many normal tissues on a beam path will be damaged as tumor cells are destroyed. On the other hand, sensitivity of tumor cells to the radioactive rays differs greatly, so in most cases, conventional radiotherapy falls short of treatment effectiveness on radioresistant malignant tumors (such as glioblastomamultiforme and melanoma). For the purpose of reducing radiation damage to the normal tissue surrounding a tumor site, target therapy in chemotherapy has been employed in the radiotherapy. While for high-radioresistant tumor cells, radiation sources with high RBE (relative biological effectiveness) including such as proton, heavy particle and neutron capture therapy have also developed. Among them, the neutron capture therapy combines the target therapy with the RBE, such as the boron neutron capture therapy (BNCT). By virtue of specific grouping of boronated pharmaceuticals in the tumor cells and precise neutron beam regulation, BNCT is provided as a better cancer therapy choice than conventional radiotherapy. BNCT takes advantage that the boron (10 B)-containing pharmaceuticals have high neutron capture cross section and produces 4He and 7Li heavy charged particles through 10B(n,α)7Li neutron capture and nuclear fission reaction. As illustrated in FIG. 1, a schematic view of boron neutron capture reaction are shown, the two charged particles, with average energy at about 2.33 MeV, are of linear energy transfer (LET) and short-range characteristics. LET and range of the alpha particle are 150 keV/micrometer and 8 micrometers respectively while those of the heavy charged particle 7Li are 175 keV/micrometer and 5 micrometers respectively, and the total range of the two particles approximately amounts to a cell size. Therefore, radiation damage to living organisms may be restricted at the cells' level. When the boronated pharmaceuticals are gathered in the tumor cells selectively, only the tumor cells will be destroyed locally with a proper neutron source on the premise of having no major normal tissue damage. BNCT is also well known for binary cancer therapy, for its effectiveness depending on the concentration of the boronated pharmaceuticals and the number of the thermal neutrons at the tumor site. Thus, besides development of the boronated pharmaceuticals, improvement of quality of the neutron source also plays a significant role in BNCT researches. Therefore, it is really necessary to provide a new technical solution so as to solve the foregoing problem. The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. In order to obtain neutron beams with various spectrums during neutron capture therapy to meet the requirements for the neutron beam energy spectrum during actual treatments, an aspect of the present disclosure provides a neutron capture therapy system, the neutron capture therapy system includes an accelerator, the accelerator generates a charged particle beam; a neutron generator, the neutron generator generates a neutron beam after being irradiated by charged particle beam; a vacuum tube, the vacuum tube transports the charged particles accelerated by the accelerator to the neutron generator; a beam shaping assembly, the beam shaping assembly includes a moderator and a reflector surrounding the moderator, the moderator moderates the neutrons generated by the neutron generator to a preset spectrum, and the reflector leads the deflected neutrons back to increase the neutron intensity within the preset spectrum; and a collimator, the collimator concentrates the neutrons generated by the neutron generator; the spectrum of the neutron beam is changed by changing the spectrum of the charged particle beam. The spectrum of the neutron beam indirectly changes by changing the spectrum of charged particle beam irradiates to the neutron generator primarily, thereby the depth dose distribution is changed. Further, in order to achieve different spectrum of charged particle beam, a microwave generator is used to provide different pulses to accelerate the particles source in the accelerator. The neutron capture therapy system includes a microwave generator capable of injecting microwaves into the accelerator, the spectrum of the charged particle beam output by the accelerator changes according to the microwaves injected at different frequencies, when the spectrum of the charged particle beam is at a first value, the charged particles react with the neutron generator and generates a spectrum of neutron beam at a first value, and when the spectrum of the charged particle beam is at a second value, the charged particles react with the neutron generator and generates a spectrum of neutron beam at a second value, wherein the spectrum of the first value of the charged particle beam is lower than that of the second value, and the spectrum of the first value of the neutron beam is lower than that of the second value. Further, the spectrum of the charged particle beam changes as the changing of electric field intensity of the accelerator (at the accelerator end). The structures before the charged particles and the neutron generator undergo a nuclear reaction are understood to be the accelerator end. More particularly, an electric field generating device is provided outside the vacuum tube and/or the neutron generator, the electric field generating device is capable of generating an electric field so as to accelerate or decelerate the charged particle beam before the charged particle beam irradiates to the neutron generator. The electric field generating device refers to devices capable of generating an electric field on the outer periphery of the vacuum tube or the neutron generator and capable of accelerating or decelerating the charged particles by the electric field before being irradiated to the neutron generator, for example, an energized electrode. Further, the neutron capture therapy system further includes a beam energy spectrum adjusting member capable of adjusting the spectrum of the charged particle beam, when the beam energy spectrum adjusting member is located in the vacuum tube and is in front of the neutron generator, the spectrum of the charged particle beam is adjusted after irradiating to the beam energy spectrum adjusting member, and the charged particle beam then irradiates to the neutron generator to generate the neutron beam. Further, the vacuum tube is provided with an accommodating portion, the beam energy spectrum adjusting member is accommodated in the accommodating portion and is connected with a driving mechanism capable of moving the beam energy spectrum adjusting member, when the driving mechanism controls the beam energy spectrum adjusting member to move to the front of the neutron generator, the spectrum of the charged particles changes after irradiating to the beam energy spectrum adjusting member and then irradiates to the neutron generator; when the driving mechanism controls the beam energy spectrum adjusting member to be accommodated in the accommodating portion but not in front of the neutron generator, the charged particle beam directly irradiates to the neutron generator. More particularly, the neutron capture therapy system includes a plurality of the beam energy spectrum adjusting members, and different numbers of the beam energy spectrum adjusting members have different spectrum adjustment effects on the charged particle beam, the driving mechanism drives each beam energy spectrum adjusting member to move up or down separately to adjust the spectrum of the charged particle beam. The neutron energy spectrum adjusting member may be made of materials capable of generating neutrons, such as beryllium or lithium. Each beam energy spectrum adjusting member is made of different materials, and the beam energy spectrum adjusting member made of different materials has different spectrum adjustment effects on the charged particle beam. Further, the neutron generator is connected to a power supply device and energized by the power supply device, and the beam spectrum of the charged particle beam changes after the charged particles irradiates to the energized neutron generator. In order to obtain neutron beams with various spectrums during neutron capture therapy to meet the requirements for the neutron beam energy spectrum during actual treatments, another aspect of the present disclosure provides a neutron capture therapy system, the neutron capture therapy system includes an accelerator, the accelerator generates a charged particle beam; a neutron generator, the neutron generator generates a neutron beam after being irradiated by charged particle beam; a vacuum tube, the vacuum tube transports the charged particles accelerated by the accelerator to the neutron generator; a beam shaping assembly, the beam shaping assembly includes a moderator and a reflector surrounding the moderator, the moderator moderates the neutrons generated by the neutron generator to a preset spectrum, and the reflector leads the deflected neutrons back to increase the neutron intensity within the preset spectrum; a collimator, the collimator concentrates the neutrons generated by the neutron generator; and at least a beam energy spectrum adjusting member, before the charged particle beam irradiates to the neutron generator, the charged particle beam irradiates to the beam energy spectrum adjusting member and achieves adjustment of the charged particle beam spectrum. Further, the beam energy spectrum adjusting member is located in the vacuum tube and is able to move from a first location to a second location, when the beam energy spectrum adjusting member is in the first location, the charged particle beam irradiates to the beam energy spectrum adjusting member before irradiating to the neutron generator; when the beam energy spectrum adjusting member is in the second location, the charged particle beam directly irradiates to the neutron generator. Further, a plurality of the beam energy spectrum adjusting members are located in the vacuum tube and move from a first location to a second location separately, different members of the beam energy spectrum adjusting members have different effects on the adjustment of the charged particle beam spectrum. More particularly, the vacuum tube is provided with an accommodating portion located below the neutron generator, the beam energy spectrum adjusting members are accommodated in the accommodating portion, and each beam energy spectrum adjusting member is able to move upward to the first location or downward to the second location separately. Further, the beam energy spectrum adjusting members are in the same structure but with different thickness, and each beam energy spectrum adjusting member has different effect on the adjustment of the charged particle beam spectrum. More particularly, the beam energy spectrum adjusting members are made of different materials. More particularly, at least one of the beam energy spectrum adjusting members is made of materials capable of generating a neutron beam. In order to obtain neutron beams with various spectrums during neutron capture therapy to meet the requirements for the neutron beam energy spectrum during actual treatments, another aspect of the present disclosure provides a neutron capture therapy system, the neutron capture therapy system includes an accelerator for generating a charged particle beam; a neutron generator for generating a neutron beam after being irradiated by charged particle beam; a vacuum tube for transporting the charged particles accelerated by the accelerator to the neutron generator; a beam shaping assembly including a moderator for moderating the neutrons generated by the neutron generator to a preset spectrum and a reflector surrounding the moderator for leading the deflected neutrons back to increase the neutron intensity within the preset spectrum; a collimator for concentrating the neutrons generated by the neutron generator; and means for changing the spectrum of the charged particle beam, whereby the spectrum of the neutron beam changes, for example, the neutron capture therapy further includes at least a beam energy spectrum adjusting member connected to a driving mechanism for changing the spectrum of the charged particle beam, the beam energy spectrum adjusting member is able to move from a first location to a second location under the controlling of the driving mechanism, when the beam energy spectrum adjusting member is in the first location, the charged particle beam irradiates to the beam energy spectrum adjusting member before irradiating to the neutron generator and achieves adjustment of the charged particle beam, whereby the spectrum of the neutron beam changes; when the beam energy spectrum adjusting member is in the second location, the charged particle beam directly irradiates to the neutron generator. Further, a plurality of the beam energy spectrum adjusting members are located in the vacuum tube, and move from the first location to the second location separately, different members of the beam energy spectrum adjusting members have different effects on the adjustment of the charged particle beam spectrum. Compared to the prior art, the neutron capture therapy system of the present disclosure indirectly changes the spectrum of the neutron beam by adjusting the spectrum of the charged particle beam to meet different requirements for the spectrum of the neutron beam under different treatment conditions, and has a simple structure and is easy to implement. Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. The above described drawing figures illustrate aspects of the disclosure in at least one of its exemplary embodiments, which are further defined in detail in the following description. Features, elements, and aspects of the disclosure that are referenced by the same numerals in different figures represent the same, equivalent, or similar features, elements, or aspects, in accordance with one or more embodiments. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Neutron capture therapy (NCT) has been increasingly practiced as an effective cancer curing means in recent years, and BNCT is the most common. Neutrons for NCT may be supplied by nuclear reactors or accelerators. Take AB-BNCT for example, its principal components include, in general, an accelerator for accelerating charged particles (such as protons and deuterons), a target, a heat removal system and a beam shaping assembly. The accelerated charged particles interact with the metal target to produce the neutrons, and suitable nuclear reactions are always determined according to such characteristics as desired neutron yield and energy, available accelerated charged particle energy and current and materialization of the metal target, among which the most discussed two are 7Li (p, n) 7Be and 9Be (p, n)9B and both are endothermic reaction. Their energy thresholds are 1.881 MeV and 2.055 MeV respectively. Epithermal neutrons at a keV energy level are considered ideal neutron sources for BNCT. Theoretically, bombardment with lithium target using protons with energy slightly higher than the thresholds may produce neutrons relatively low in energy, so the neutrons may be used clinically without many moderations. However, Li (lithium) and Be (beryllium) and protons of threshold energy exhibit not high action cross section. In order to produce sufficient neutron fluxes, high-energy protons are usually selected to trigger the nuclear reactions. No matter BNCT neutron sources are from the nuclear reactor or the nuclear reactions between the accelerator charged particles and the target, only mixed radiation fields are produced, that is, beams comprise neutrons and photons having energies from low to high. As for BNCT in the depth of tumors, except the epithermal neutrons, the more the residual quantity of radiation ray is, the higher the proportion of nonselective dose deposition in the normal tissue is. Therefore, radiation causing unnecessary dose should be lowered down as much as possible. Besides air beam quality factors, dose is calculated using a human head tissue prosthesis in order to understand dose distribution of the neutrons in the human body. The prosthesis beam quality factors are later used as design reference to the neutron beams, which is elaborated hereinafter. The International Atomic Energy Agency (IAEA) has given five suggestions on the air beam quality factors for the clinical BNCT neutron sources. The suggestions may be used for differentiating the neutron sources and as reference for selecting neutron production pathways and designing the beam shaping assembly, and are shown as follows: Epithermal neutron flux >1×109 n/cm2s Fast neutron contamination <2×10−13 Gy-cm2/n Photon contamination <2×10−13 Gy-cm2/n Thermal to epithermal neutron flux ratio <0.05 Epithermal neutron current to flux ratio >0.7 Note: the epithermal neutron energy range is between 0.5 eV and 40 keV, the thermal neutron energy range is lower than 0.5 eV, and the fast neutron energy range is higher than 40 keV. 1. Epithermal Neutron Flux The epithermal neutron flux and the concentration of the boronated pharmaceuticals at the tumor site codetermine clinical therapy time. If the boronated pharmaceuticals at the tumor site are high enough in concentration, the epithermal neutron flux may be reduced. On the contrary, if the concentration of the boronated pharmaceuticals in the tumors is at a low level, it is required that the epithermal neutrons in the high epithermal neutron flux should provide enough doses to the tumors. The given standard on the epithermal neutron flux from IAEA is more than 109 epithermal neutrons per square centimeter per second. In this flux of neutron beams, therapy time may be approximately controlled shorter than an hour with the boronated pharmaceuticals. Thus, except that patients are well positioned and feel more comfortable in shorter therapy time, and limited residence time of the boronated pharmaceuticals in the tumors may be effectively utilized. 2. Fast Neutron Contamination Unnecessary dose on the normal tissue produced by fast neutrons are considered as contamination. The dose exhibit positive correlation to neutron energy, hence, the quantity of the fast neutrons in the neutron beams should be reduced to the greatest extent. Dose of the fast neutrons per unit epithermal neutron flux is defined as the fast neutron contamination, and according to IAEA, it is supposed to be less than 2*10−13Gy-cm2/n. 3. Photon Contamination (Gamma-Ray Contamination) Gamma-ray long-range penetration radiation will selectively result in dose deposit of all tissues in beam paths, so that lowering the quantity of gamma-ray is also the exclusive requirement in neutron beam design. Gamma-ray dose accompanied per unit epithermal neutron flux is defined as gamma-ray contamination which is suggested being less than 2*10−13Gy-cm2/n according to IAEA. 4. Thermal to Epithermal Neutron Flux Ratio The thermal neutrons are so fast in rate of decay and poor in penetration that they leave most of energy in skin tissue after entering the body. Except for skin tumors like melanocytoma, the thermal neutrons serve as neutron sources of BNCT, in other cases like brain tumors, the quantity of the thermal neutrons has to be lowered. The thermal to epithermal neutron flux ratio is recommended at lower than 0.05 in accordance with IAEA. 5. Epithermal Neutron Current to Flux Ratio The epithermal neutron current to flux ratio stands for beam direction, the higher the ratio is, the better the forward direction of the neutron beams is, and the neutron beams in the better forward direction may reduce dose surrounding the normal tissue resulted from neutron scattering. In addition, treatable depth as well as positioning posture is improved. The epithermal neutron current to flux ratio is better of larger than 0.7 according to IAEA. The prosthesis beam quality factors are deduced by virtue of the dose distribution in the tissue obtained by the prosthesis according to a dose-depth curve of the normal tissue and the tumors. The three parameters as follows may be used for comparing different neutron beam therapy effects. 1. Advantage Depth Tumor dose is equal to the depth of the maximum dose of the normal tissue. Dose of the tumor cells at a position behind the depth is less than the maximum dose of the normal tissue, that is, boron neutron capture loses its advantages. The advantage depth indicates penetrability of neutron beams. Calculated in cm, the larger the advantage depth is, the larger the treatable tumor depth is. 2. Advantage Depth Dose Rate The advantage depth dose rate is the tumor dose rate of the advantage depth and also equal to the maximum dose rate of the normal tissue. It may have effects on length of the therapy time as the total dose on the normal tissue is a factor capable of influencing the total dose given to the tumors. The higher it is, the shorter the irradiation time for giving a certain dose on the tumors is, calculated by cGy/mA-min. 3. Advantage Ratio The average dose ratio received by the tumors and the normal tissue from the brain surface to the advantage depth is called as advantage ratio. The average ratio may be calculated using dose-depth curvilinear integral. The higher the advantage ratio is, the better the therapy effect of the neutron beams is. To provide comparison reference to design of the beam shaping assembly, we also provide the following parameters for evaluating expression advantages and disadvantages of the neutron beams in the embodiments of the present disclosure except the air beam quality factors of IAEA and the abovementioned parameters. 1. Irradiation time⇐30 min (proton current for accelerator is 10 mA) 2. 30.0RBE-Gy treatable depth>=7 cm 3. The maximum tumor dose>=60.0RBE-Gy 4. The maximum dose of normal brain tissue⇐12.5RBE-Gy 5. The maximum skin dose⇐11.0RBE-Gy Note: RBE stands for relative biological effectiveness. Since photons and neutrons express different biological effectiveness, the dose above should be multiplied with RBE of different tissues to obtain equivalent dose. In actual neutron capture therapy process, different patients and tumors often require different energies of neutrons, and how to get an appropriate spectrum of the neutron beam for treatment according to the specific situation is to be solved. Before the charged particle beam irradiates to the neutron generator, change its spectrum, so as to provide multiple spectrums of neutron beam. Since the spectrum of the charged particle beam is changed and the neutron beam is generated by the irradiation of the charged particle beam to neutron generator, the spectrum changing of the charged particle beam directly affects the spectrum of the neutron beam. The spectrum of the neutron beam is changed by changing the spectrum of the charged particle beam according to the present disclosure which includes but not limits to boron neutron capture therapy, and the neutron capture therapy system of the present disclosure is specifically described below. As shown in FIG. 2, the present disclosure provides a neutron capture therapy system 100. The neutron capture therapy system 100 includes an accelerator 200 for generating a charged particle beam P, a neutron generator 10 for generating a neutron beam after being irradiated by the charged particle beam P, a beam shaping assembly 11, and a collimator 12. The beam shaping assembly 11 includes a moderator 13 and a reflector 14 surrounding the moderator 13. The neutron generator 10 generates a neutron beam N after being irradiated by the charged particle beam P, the moderator 13 decelerates the neutron beam N generated by the neutron generator 10 to a preset spectrum, and the reflector 14 leads the deflected neutrons back to increase the neutron intensity within a preset spectrum, and the collimator 12 concentrates the neutrons generated by the neutron generator for irradiation. The spectrum of the charged particle beam can be varied, the neutron capture therapy system 100 indirectly changes the spectrum of the neutron beam generated by the neutron generator by changing the spectrum of the charged particle beam. Since the neutron beam N is generated by irradiating the neutron generator 10 with the charged particle beam P, the spectrum changing of the charged particle beam P affects the spectrum of the neutron beam N. That is, the present disclosure indirectly changes the spectrum of the neutron beam N by changing the spectrum of the charged particle beam P so as to provide a better neutron depth dose distribution. As a first embodiment, as shown in FIG. 3, the neutron capture therapy system 100a further includes a microwave generator 300 disposed at accelerator end. Accordingly, the similar features will be labeled with the same numerals, but with an “a” appended thereto. The microwave generator 300 is capable of generating microwaves of different frequencies, and the accelerator 200 accelerates the particle source in the accelerator according to different frequencies of the injected microwaves to change the spectrum of the charged particle beam output by the accelerator. The higher the frequency of the microwave injected into the accelerator 200 is, the faster the accelerator 200 accelerates the particle source, and the higher the spectrum of the charged particle beam P is, the higher the spectrum of the neutron beam N generated by the neutron generator 10 after being irradiated by the charged particle beam P is; the lower the frequency of the microwave injected into the accelerator 200 is, the slower the accelerator 200 accelerates the particle source, and the lower the spectrum of the charged particle beam P is, the lower the spectrum of the neutron beam N generated by the neutron generator 10 after being irradiated by the charged particle beam P is. When the spectrum of the charged particle beam is low (which is named the first value), the spectrum of the neutron beam generated by the reaction of the charged particle with the neutron generator is low (the spectrum value of the first neutron beam); when the spectrum of the charged particle beam is high (which is named the second value), the spectrum of the neutron beam generated by the reaction of the charged particle with the neutron generator is high (the spectrum value of the second neutron beam), wherein the first value is lower than the second value, the spectrum value of the first neutron beam is lower than the spectrum value of the second neutron beam. As shown in FIG. 4, as a second embodiment of the neutron capture therapy system 100b, the spectrum of the charged particle beam P is changed by changing the electric field intensity at the accelerator end. Accordingly, the similar features will be labeled with the same numerals, but with a “b” appended thereto. Since the electric field intensity at the accelerator end greatly affects the acceleration speed of the charged particle beam P, and the acceleration speed of the charged particle beam P directly affects the spectrum of the charged particle beam P, the spectrum of the neutron beam N generated by the charged particle beam P irradiates to the neutron generator 10 is affected. As a specific embodiment for changing the electric field intensity at the accelerator end, the present disclosure provides an electric field generating device 16 outside the vacuum tube 15 or outside the neutron generator 10 to generate an electric field capable of accelerating or decelerating the charged particle beam P before irradiating to the neutron generator 10. Preferably, the electric field generating device 16 refers to an energized electrode. The electric field intensity difference is adjusted by controlling the voltage difference at the energized electrode to accelerate or decelerate the charged particle beam P, and the details will not be described herein. Actually, the purpose of providing such an electric field generating device 16 outside the vacuum tube 15 or outside the neutron generator 10 is to provide a second adjustment of the spectrum of the charged particle beam P accelerated by the accelerator 200, so as to obtain a neutron beam N with a spectrum level that is required in accordance with the neutron capture therapy when the charged particle beam P irradiates to the neutron generator 10. That is, the spectrum of the charged particle beam P is changed by changing the electric field at the accelerator end so as to indirectly change the spectrum of the neutron beam N. Certainly, such an electric field generating device 16 may also be disposed outside the vacuum tube 15 and outside the neutron generator 10 respectively to adjust the spectrum of the charged particle beam P several times, thereby making it easier to achieve the spectrum adjustment, and finally obtaining the neutron beam N with a spectrum level required for the treatment. FIG. 5 is a third embodiment of the present disclosure of the neutron capture therapy system 100c for changing the spectrum of the charged particle beam P. Accordingly, the similar features will be labeled with the same numerals, but with a “c” appended thereto. In the present embodiment, a beam energy spectrum adjusting member 17 is located in the vacuum tube 15 and in front of the neutron generator 10, and the charged particle beam P irradiates to the beam energy spectrum adjusting member 17 to perform spectrum adjustment, and then irradiates to the neutron generator 10 to generate a neutron beam N, and finally achieves spectrum adjustment of the neutron beam N. The beam energy spectrum adjusting member 17 is disposed in the vacuum tube 15 and located below the neutron generator 10. The vacuum tube 15 is provided with an accommodating portion 151 under the neutron generator 10, and the beam energy spectrum adjusting member 17 is accommodated in the accommodating portion 151. Since different numbers of beam energy spectrum adjusting member 17 have different effects on the adjustment of the spectrum of the charged particle beam P, a plurality of beam energy spectrum adjusting members 17 are disposed in the vacuum tube 15, and each beam energy spectrum adjusting member 17 is respectively connected to a driving mechanism 18, and the driving mechanism 18 controls each of the beam energy spectrum adjusting member 17 to move upward or downward respectively, that is, the driving mechanism 18 can simultaneously move one or more of the beam energy spectrum adjusting member 17 upward or downward. During actual neutron capture therapy, the driving mechanism 18 is operated in accordance with the spectrum requirements of the neutron beam N, and the motion of each beam energy spectrum adjusting member 17 is controlled by the driving mechanism 18. When the driving mechanism 18 controls the beam energy spectrum adjusting member 17 to move upward, the beam energy spectrum adjusting member 17 moves in front of the neutron generator 10, and the charged particle beam P irradiates to the beam energy spectrum adjusting member 17 to perform spectrum adjustment, and then the charged particle beam P irradiates to the neutron generator 10; when the driving mechanism 18 controls the beam energy spectrum adjusting member 17 to move downward, the beam energy spectrum adjusting member 17 is accommodated in the accommodating portion 151, and the charged particle beam P directly irradiates to the neutron generator 10. The spectrum of the charged particle beam P is adjusted by the beam energy spectrum adjusting member 17, thereby indirectly adjusts the spectrum of the neutron beam N. Furthermore, the beam energy spectrum adjusting member may be disposed at other positions in the vacuum tube besides the position below the neutron generator, as long as it can be located in or not in front of the neutron generator when the spectrum of the charged particle beam needs or does not need to be adjusted. In order to facilitate the manufacture and installation of the beam energy spectrum adjusting member 17, each beam energy spectrum adjusting member 17 is designed to have the same structure and each beam energy spectrum adjusting member 17 is sequentially arranged in the accommodating portion 151. The cross sections of the beam energy spectrum adjusting member 17 and the neutron generator 10 perpendicular to the irradiation direction of the charged particle beam P are circular, and the radius of the beam energy spectrum adjusting member 17 is smaller than that of the neutron generator 10. In order to alleviate the heat of the beam energy spectrum adjusting member 17 after being irradiated by the charged particle beam P, a cooling device (not shown) is provided on the outer periphery of the beam energy spectrum adjusting member 17. The arrangement of the cooling device of the beam energy spectrum adjusting member 17 can refer to the cooling method of the neutron generator 10 in the prior art, which will not be specifically described herein. When the charged particle beam P irradiates to the beam energy spectrum adjusting member 17, the beam energy spectrum adjusting member 17 adjusts the spectrum of the charged particle beam P, and the cooling device cools the beam energy spectrum adjusting member 17. The thickness of each of the beam energy spectrum adjusting members 17 may be the same or different. In addition, the materials of the beam energy spectrum adjusting members 17 may be the same or different. When all the beam energy spectrum adjusting members 17 are made of the same materials, different requirements for the neutron beam N spectrum during neutron capture therapy can be achieved by controlling different numbers of the beam energy spectrum adjusting members 17 to move upward to be in front of the neutron generator 10. When the beam energy spectrum adjusting member 17 is made of different materials, different requirements for the neutron beam N spectrum during neutron capture therapy can be achieved by controlling different numbers of beam energy spectrum adjusting members 17 to move upward, or by the controlling one or several of the beam energy spectrum adjusting members 17 made of different materials to move upward. Alternatively, the beam energy spectrum adjusting member 17 may be made of materials capable of generating a neutron beam N, such as lithium or beryllium. It should be noted that when the beam energy spectrum adjusting member 17 is made of a material capable of generating the neutron beam N, the beam energy spectrum adjusting member 17 should be placed as close as possible to the neutron generator 10, so that both the neutron beam generated by the irradiation of the charged particle beam P to the beam energy spectrum adjusting member 17 and the neutron beam generated by the irradiation of the charged particle beam P to the neutron generator are effectively utilized. Certainly, even the materials of the beam energy spectrum adjusting member 17 can not generate a neutron beam, it also can be used as long as the beam energy spectrum adjusting member 17 is disposed in the vacuum tube 15 and is able to move upward under the control of the driving mechanism 18 to be in front of the neutron generator 10, and realize the spectrum adjustment on the charged particle beam P irradiates to the neutron generator 10. Referring to FIG. 6, as a fourth embodiment, the neutron generator 10 of the neutron capture therapy system 100d is connected to a power supply device 20. Accordingly, the similar features will be labeled with the same numerals, but with a “d” appended thereto. The neutron generator 10 is energized by the power supply device 20 to generate an electric field inside the neutron generator, and the beam spectrum of the charged particle beam P changes after the charged particle beam P irradiates to the neutron generator 10 being energized. Certainly, in order to obtain a neutron beam N with better quality, it is also implementable to provide a microwave generator, an electric field generating device, a beam energy spectrum adjusting member, and a neutron generator connected to a power supply device simultaneously, so as to realize multiple spectrum adjustments on the charged particle beam P during the neutron capture therapy, and make it easier to obtain the neutron beam of the required spectrum level, which will not be specifically described herein. The above illustrates and describes basic principles, main features and advantages of the present disclosure. Those skilled in the art should appreciate that the above embodiments do not limit the present disclosure in any form. Technical solutions obtained by equivalent substitution or equivalent variations all fall within the scope of the present disclosure. |
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summary | ||
050826034 | claims | 1. A method of treatment of a high-level radioactive waste containing platinum group elements comprising adding boron or a boron compound to a calcined material of the high-level radioactive waste in an amount of 0.5 to 10% by weight in terms of boron as a simple substance, heating the resultant mixture at a temperature of about 1000.degree. C. or above under a reduction condition to melt the mixture and to alloy the platinum group elements present in the calcined material with boron, recovering a layer of the resultant platinum group element alloys from a layer of residual oxides through sedimentation, and solidifying the layer of the residual oxides to form a volume-reduced high-level radioactive solidified waste. 2. The method according to claim 1, wherein the boron compound to be added is boron nitride, sodium boron hydride or boron carbide. 3. The method according to claim 1, wherein heating is carried out in an atmosphere of air having a reduced oxygen content, nitrogen or argon. 4. The method according to claim 1, wherein heating is carried out in the presence of a reducing agent. 5. The method according to claim 4, wherein the reducing agent is hydrogen, carbon monoxide, carbon, alkaline earth metals, rare earth elements or aluminum. 6. The method according to claim 1, wherein heating is carried out at a temperature ranging from about 1500.degree. to about 2000.degree. C. |
summary | ||
063079178 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view of an X-ray apparatus having a soller slit, according to an embodiment of the present invention. The X-ray apparatus comprises an X-ray generator 1, a monochromator unit 2, a divergence limiting slit 3 and a goniometer 4. A soller slit 18 is arranged within the monochromator unit 2, together with a monochromator 22. The X-ray generator 1 includes a casing 6, a rotary target 7 housed in the casing 6 and a filament 8 also housed in the casing 6. The filament 8 is heated by applying an electric current thereto to generate thermoelectron. The thermoelectron is accelerated by a voltage applied between the filament 8 and the target 7 and collides with an area of an outer peripheral surface of the target 7. X-rays are emitted from the area of the outer peripheral surface of the target 7, that is, an X-ray focal point F and diverges therefrom. The X-rays are derived externally through an X-ray deriving window 9 provided in an appropriate portion of the casing 6. In this embodiment, the so-called line focus having a length in a direction perpendicular to the drawing sheet of FIG. 1 is considered as the X-ray focal point F. The monochromator unit 2 has a structure, which is shown in FIG. 2. FIG. 3 is a cross section taken along a line X--X in FIG. 2 and FIG. 4 is a cross section taken along a line Y--Y in FIG. 2. As shown in FIGS. 2 to 4, the monochromator unit 2 includes a cylindrical housing 11 and a monochromator support table 12 housed in the housing 11. The housing 11 is formed in a bottom thereof with a through-hole 13, in which a rotary shaft 12a extending form the bottom of the monochromator support table 12 is rotatably fitted. Opposing X-ray transparent windows 37 each having an appropriate size are formed in a peripheral wall of the housing 11 to allow X-ray to pass through the housing 11. As shown in FIG. 3, a rotary drive bar 14 is connected to a portion of the rotary shaft 12a, which protrudes externally of the housing 11. A top end of a thumb screw 16 is in contact with a top portion of the rotary drive bar 14 as shown in FIG. 2, so that a rotation of the thumb screw 16 makes the monochromator support table 12 rotate about a center axis Xm thereof by a desired angle. A step `D` is formed on an upper surface of the monochromator support table 12 along a center line thereof as shown in FIG. 4. A monochromator assembly 17 is arranged on the lower side of the step `D` and the soller slit 18 is arranged on the upper side of the step `D` in an opposing relation to the monochromator assembly 17. As is clear from FIG. 4, the monochromator assembly 17, the soller slit 18 and the housing 11 are rotatable all together about the axis line Xm of the monochromator. That is, the soller slit 18 is rotated in unison with the monochromator assembly 17. The monochromator assembly 17 includes a support base 21 fixedly connected to a longitudinal side piece of a support member 19 having a `L`-shaped cross section and a multi-layered monochromator 22 formed on a surface of the support base 21 as films, as shown in FIG. 5. The support base 21 is formed from, for example, a single crystal silicon substrate or a stain-less steal, etc., and a surface thereof, on which the multi-layered monochromator 22 is formed, forms a parabolic line `B` such as shown in FIG. 6. The monochromator assembly 17 is located in a predetermined position defined by the multi-layered monochromator 22 in contact with the step `D`. The multi-layered monochromator 22 is formed by superimposing heavy element layers 31 and light element layers 32 alternately periodically by using a suitable film forming method such as sputtering, as shown in FIG. 11. Since the surface of the support base 21 is parabolic as shown in FIG. 6, the multi-layered monochromator 22 formed thereon takes in the form of parabolic as well. Interplaner spacing between lattice planes of the multi-layered monochromator 22 is varied dependently upon location such that X-rays incident thereon at different incident angles are reflected by the multi-layered monochromator 22 to form parallel X-rays. In detail, the interplanar spacing between lattice planes is small at the X-ray incident side where the incident angle of X-rays is large, while being large at the X-ray exit side where the incident angle is small, and besides, the interplanar spacing is continuously changed in an intermediate area. It should be noted that the configuration of the surface of the monochromator 22 is not always parabolic and a flat plane surface shown in FIG. 10 may be used in place of the parabolic surface shown in FIG. 11. As shown in FIG. 6, a slit member 23 is directly fixed to an X-ray incident side end surface of the support base 21. A monochromator slit 24 formed in the slit member 23 is arranged in a position in the X-ray incident side end surface. In this embodiment, the X-ray focal point `F` is positioned on a center line of the parabolic line `B`, a distance L1 between the X-ray focal point `F` and the slit 24 is set to 80 mm, X-ray take-in angle .theta.1 is set to 0.5.degree. and a length L2 of the monochromator 22 is set to 40 mm. With the above mentioned construction of the monochromator 22, X-ray diverging from the X-ray focal point `F` is incident on the monochromator 22 while a cross section of the X-rays is restricted by the monochromator slit 24. Subsequently, the X-rays are reflected, and thus, diffracted by the monochromator 22, and then, go out thereof as parallel X-ray beams. Since the multi-layered monochromator 22 having the parabolic shape changes a lot of incident X-rays into diffracted X-rays, it is possible to obtain diffracted X-rays which is much more intense compared with that obtainable by a single crystal monochromator, etc. In FIG. 2, the soller slit 18 arranged in opposing relation to the monochromator assembly 17 is constructed by alternately laminating the metal foils 27 and the spacers 28 on the base 26, as shown in FIG. 7. In more detail, the soller slit 18 is constructed by alternately laminating the metal foils 27 and the spacers 28 on the base 26, inserting screws 29 into the lamination, and then, screwing the screws 29 into threaded holes 33 formed in the base 26. The metal foil 27 is formed of any material such as stainless steal, which is impermeable for X-rays. The spacer 28 is formed of, for example, stainless steal or brass. Thickness of the spacer 28, that is, distance `T` between adjacent metal foils 27, and length L3 of the metal foil 27 are set such that divergence angle .theta.2 shown in FIG. 8 becomes in the order from 0.5.degree. to 5.degree.. Further, in FIG. 7, height `H` of the soller slit 18 is set to 10 mm to 20 mm and thickness of the metal foil 27 is set to in the order to 0.05 mm. The metal foils 27 are supported on one side by the spacers 28 with the other side being opened as free ends, which are in contact with the surface of the monochromator 22 as shown in FIG. 4. Since the surface of the monochromator 22 is parabolic in this embodiment, the free ends of the metal foils 27 are made parabolic correspondingly thereto. Incidentally, the aimed purpose of the metal foils 27 to collimate the diverging X-rays to parallel X-ray beams also be achieved when the free ends of the metal foils 27 are arranged in the vicinity of the surface of the monochromator 22. That is, the metal foils 27 functions well when a small gap existing between the free ends of the metal foils 27 and the surface of the monochromator 22. Further, as shown in FIG. 7, the spacer 28 has a delta configuration having a forwardly peaked center portion 28a of a front end and both end portions 28b thereof behind. In general, the metal foil is very thin and its rigidity is low, so that it is easily warped. However, when the spacers 28 having such delta configuration are used, it is possible to increase the rigidity of the metal foils 27. Further, since the delta configuration of the spacer 28 does not constitute any obstacle to propagation of X-rays `R` diffracted by the monochromator 22 after being emitted from the X-ray focal point `F`, the spacer 28 do not adversely influence on a result of X-ray measurement. In the X-ray diffraction measurement, it is usual to limit a width of X-rays by arranging slits before and after the specimen `S` or the monochromator 22. This width limitation is performed in order to remove X-ray components such as scattered X-rays and/or fluorescent X-rays, which degrade S/N ratio. In the strict meaning, however, if a slit is arranged in front of a monochromator, etc., scattered X-rays may be generated by the slit, which may degrade S/N ratio in the result of X-ray measurement. In this embodiment, the peaked center portion 28a of the spacer 28, that is, the apex of the delta configuration is positioned in the vicinity of the monochromator 22. Therefore, unnecessary X-rays which may cause noise are effectively removed by the center portion 28a to thereby make S/N ratio high, resulting in a reliable result of measurement. Returning to FIG. 1, the goniometer 4 includes a .theta. rotary table 41 rotatable about an axis line Xs of the specimen and a 2.theta. rotary table 42 rotatable about an axis line Xs of the specimen independently from the .theta. rotary table 41. The specimen `S` to be measured is mounted on the .theta. rotary table 41. A .theta. rotary drive device 43 is operatively connected to the .theta. rotary table 41 and a 2.theta. rotary drive device 44 is operatively connected to the 2.theta. rotary table 42. These rotary drive devices are constituted with, for example, driving power sources such as electric motors and power transmission mechanisms including, for example, worm gears and worm wheels. A counter arm 46 is mounted on an appropriate position on the 2.theta. rotary table 42. A scattered X-ray limiting slit 47, a light receiving slit 48 and an X-ray counter 49 are fixedly mounted in appropriate positions on the counter arm 46. The scattered X-ray limiting slit 47 functions to prevent scattered X-rays generated from various members arranged in the vicinity of the X-ray passage from taking in the X-ray counter 49. The light receiving slit 48 functions to determine the width of X-rays incident on the X-ray counter 49. An operation of the X-ray apparatus including the soller slit will now be described. Prior to an X-ray measurement with using the X-ray apparatus shown in FIG. 1, the various constitutional components of the X-ray apparatus are positioned in constant positions with respect to the X-ray optical axis. Thus, the optical axis regulation is carried out. For example, an angle 2.theta.c of the X-ray focal point `F` with respect to the monochromator 22 and an angle .theta.c of the monochromator 22 about the axis line Xm thereof are set to calculated angle positions, respectively. Subsequently, the angle .theta.c of the monochromator 22 is finely regulated by rotating the thumb screw 16 shown in FIG. 2. Further, the angle 2.theta.c of the X-ray focal point `F` is finely regulated. Then, the monochromator 22 is finely regulated in a direction Yc perpendicular to the X-ray optical axis. In finely regulating these angles and the monochromator, intensity of X-rays counted by the X-ray counter 49 is measured to find out the positions at which the intensity becomes maximum. The angle position of the monochromator 22 at which the X-ray intensity becomes maximum is the best position of the monochromator 22 with respect to the optical axis of the X-ray. Positional regulation of other constitutional components than the monochromator unit 2, for example, the divergence limiting slit 3, the scattered X-ray limiting slit 47 and the light receiving slit 48, etc., with respect to the optical axis of the X-ray is performed by using known methods. Depending upon an X-ray apparatus, the monochromator 53 and the monochromator slit 52 may be provided separately as shown in FIG. 12. In such X-ray apparatus, it is necessary to regulate positions thereof independently, while keeping them in a mutually related state. However, such work is complicated and time consuming. On the contrary, the monochromator slit 24 is always fixed in the constant position with respect to the monochromator 22 by mounting the monochromator 24 directly in the predetermined position on the X-ray incident side end surface of the monochromator 22 as shown in FIG. 1. Thus, in regulating the monochromator unit 2 in the predetermined position with respect to the optical axis of X-ray, it is enough to regulate only the monochromator 22, while there is no need of executing a specific position regulation work for the monochromator slit 24. As a result, the work for regulating the position of the monochromator unit 2 corresponding to the X-ray optical axis becomes very simple, so that the work is performed reliably and rapidly. After the regulation of the position of various constitutional components in the X-ray apparatus corresponding to the X-ray optical axis is completed in the manner mentioned above, the measurement using X-rays is performed. First, as shown in FIG. 2, the housing 11 is set around the monochromator assembly 17 and the soller slit 18 in such a way that intensity of X-rays passing through the monochromator unit 2 becomes high enough to perform the X-ray measurement. Then, as shown in FIG. 1, the specimen `S` is mounted in a predetermined position on the .theta. rotary table 41, and then, X-rays are generated from the X-ray focal point `F`. X-rays thus generated are introduced into the monochromator unit 2 to be incident on the monochromator 22, as shown in FIG. 2. At this moment, X-rays are diffracted by the monochromator 22 to be made monochromatic at a predetermined wavelength. Since, in this embodiment, the interplanar spacing between lattice planes of the monochromator 22 is regulated differently in the longitudinal direction thereof, that is, in the propagating direction of X-rays, X-rays incident on the monochromator 22 can be diffracted by the whole surface of the monochromator 22. Therefore, a highly intense X-rays can be obtained from the monochromator 22. Further, since the surface of the monochromator 22 is parabolic, X-rays emitted from the monochromator 22 are derived as parallel beams, particularly, parallel in a horizontal direction. That is, according to the monochromator 22 according to this embodiment, monochromator and highly intense X-ray beams parallel in the horizontal direction can be obtained. As shown in FIG. 2, the soller slit 18 is arranged in the facing relation to the monochromator 22 in such a manner that the top ends of the metal foils 27 come in contact with or in the vicinity of the surface of the monochromator 22. Therefore, X-ray beams to be made parallel to the horizontal direction by the monochromator 22 is made parallel to a vertical direction by the soller slit 18 as well. In the conventional X-ray apparatus shown in FIG. 12, the soller slit 54 is arranged in the position remote from the monochromator 53. Therefore, a space corresponding to the distance therebetween is required. On the contrary, in the X-ray apparatus of this embodiment shown in FIG. 1, the soller slit 18 is incorporated in the monochromator unit 2. Therefore, the space dedicated to only the soller slit 18 is unnecessary, so that the X-ray apparatus can be reduced in size or there is a space provided around the goniometer 4. In addition, intensity of the X-ray is increased. Parallel and monochromatic X-ray beams having a high intensity obtained by the monochromator unit 2 are incident on the specimen `S` as shown in FIG. 1. When the X-ray measurement is performed on the basis of the parallel beam method, parallel beams are incident on the specimen `S` by a low angle, that is, at a very small incident angle. A part of such incident X-rays are diffracted by the specimen `S` and detected by the X-ray counter 49 to calculate the intensity thereof. On demand, the .theta. rotary table 41 is rotated continuously or intermittently at a predetermined angular velocity and, simultaneously, the 2.theta. rotary table 42 is rotated in the same direction at an angular velocity which is twice the angular velocity of the .theta. rotary table 41, during a time for which X-rays are incident on the specimen `S`. Both the diffraction angle and the intensity of X-rays diffracted by the specimen `S` can be measured during such rotations of the tables. As mentioned, since the one sides of the metal foils 27 of the soller slit 18 are made the opened end in the X-ray apparatus according to this embodiment of the present invention, the open end portion can be arrange in facing relation to the surface of the monochromator 22. Therefore, there is no need of providing the space dedicated to only the soller slit 18 on the optical axis of X-rays. As a result, it is possible to reduce the size of the whole X-ray apparatus. Further, since the soller slit 18 is mounted directly on and preferably integrally with the monochromator 22, it is possible to automatically determine the relative positions thereof. As a result, there is no need of separately regulating the positions of the monochromator 22 and the soller slit 18 with respect to the optical axis of X-rays prior to the X-ray measurement. Therefore, the optical axis regulation work is very easily performed for the various constitutional components in the X-ray apparatus. Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the described embodiments and can be modified or changed within a true scope of the present invention which is defined by the appended claims. For example, the soller slit 18 is arranged in the opposing relation to the monochromator 22 arranged in between the X-ray focal point `F` and the specimen `S` in the embodiment shown in FIG. 1. However, in place of or in addition to the soller slit 18, a soller slit having an open end portion according to the present invention can be arranged in an opposing relation to the specimen `S`. There is an X-ray apparatus in which a monochromator is arranged between a specimen `S` and an X-ray counter 49. In such apparatus, the soller slit according to the present invention may be arranged in an opposing relation to the monochromator. Referring to FIG. 2, the monochromator unit has the monochromator having the parabolic X-ray diffraction plane such as shown in FIG. 6. However, it is, of course, possible to apply the present invention to a monochromator having a flat X-ray diffraction plane as well. Further, a single crystal monochromator or other usual monochromators can be used in place of the multi-layered monochromator. The X-ray apparatus shown in FIG. 1 is a mere example, so that the X-ray generator 1, the goniometer 4, etc. may have other structures than those shown in the drawings. |
summary | ||
044329334 | claims | 1. A nuclear fuel pellet which comprises a hollow sphere having a homogeneously integral and continuous wall consisting essentially of at least one of the group of glass, ceramic, metal and plastic materials, said wall having a permeability rate for hydrogen isotopes which decreases with decreasing temperature and is sufficiently low at room temperature and one atmosphere pressure to retain within said sphere hydrogen isotopes at pressures of at least ten atmospheres, said wall of said hollow sphere having a diameter not greater than two millimeters, and a quantity of a fuel including at least one isotope of hydrogen contained within the interior of said hollow sphere in an amount sufficient to possess a pressure of at least ten atmospheres at room temperature. 2. The fuel pellet set forth in claim 1 in which said fuel contained within said sphere is in an amount sufficient to possess a pressure of at least forty atmospheres at room temperature. 3. A fuel pellet as defined in claim 1 in which said hollow sphere has a wall thickness of at least one micron. 4. A fuel pellet as defined in claim 1 in which said fuel is in gaseous form. 5. A fuel pellet as defined in claim 1 in which said fuel is disposed as a solidified layer on the inner surface of said hollow sphere such that said fuel forms a solidified hollow spherical shell. 6. A fuel pellet as defined in claim 1 in which any gaseous impurities in said hollow sphere are disposed as a layer of solidified impurities on the inner surface of said hollow sphere and said fuel is disposed within said layer of solidified impurities. 7. A fuel pellet as defined in claim 6 in which said fuel is disposed as a soldified hollow spherical shell of fuel within said layer of solidified impurities disposed on the inner surface of said hollow sphere. 8. A fuel pellet as defined in claim 1 further comprising a continuous coating of glass or metal on the exterior of said hollow sphere. 9. A fuel pellet as defined in claim 8 wherein said coating consists essentially of at least one of the group of lead glass, bismuth glass, soda-lime glass, copper and aluminum. 10. The fuel pellet set forth in claim 5 which said fuel contained within said sphere is in an amount sufficient to possess a pressure of at least forty atmospheres at room temperature. 11. The fuel pellet set forth in claim 6 in which said fuel contained within said sphere is in an amount sufficient to possess a pressure of at least forty atmospheres at room temperature. 12. The fuel pellet set forth in claim 8 in which said fuel contained within said sphere is in an amount sufficient to possess a pressure of at least forty atmospheres at room temperature. |
summary | ||
description | This invention relates generally to radiation collimators, and more particularly, to leaf-type X-ray collimators for use in diagnostic medical imaging. X-ray collimators are used in medical imaging applications to limit the field of an X-ray beam to a shape and size just sufficient to expose the area requiring diagnosis in a patient's body, and prevent unnecessary exposure of the surrounding area to X-rays. In other terms, a collimator helps to minimize the X-ray exposure and maximize the efficiency of X-ray dosage, to obtain optimum amount of pictorial data for diagnosis. Generally, X-ray collimators provide a reduction in the field of an X-ray beam, by collimating the X-ray beam either to a substantial rectangular shape, a circular shape or a combination thereof, depending upon the configuration of the leaves or blades that block the X-rays for field reduction. A typical configuration of an X-ray collimator that provides a rectangular collimation, includes at least a pair of planar blade members constructed of an X-ray attenuating material and arranged along the path of X-rays, which when moved to closer proximity in mutually opposing directions, block the X-rays, and thereby reduce the field of X-ray to a substantially rectangular shape for focusing on the area of a patient's body requiring diagnosis. However, the rectangular field shape encompasses a fairly large area of X-ray exposure as against the useful area of image and therefore results in low dosage efficiency. The dosage efficiency “{acute over (η)}” is given by the relation:{acute over (η)}=Useful area of Image/Emitted area in same plane A typical configuration of an X-ray collimator that provides a circular collimation includes a discrete set of discs constructed of an X-ray attenuating material and arranged in a circular fashion, along the path of X-rays. On actuation, the discs limit the field size of X-ray beam to variable diameters, thereby providing a discrete circular collimation, for focusing on an area of a patient's body, requiring diagnosis. Although the discrete circular field shape encompasses comparatively lesser area of X-ray exposure than the rectangular field shape, the drive mechanism for the discs is complicated in structure, and also there is no significant increase in the dosage efficiency. Another known configuration of an X-ray collimator (also popularly used for collimating gamma radiation in nuclear medicine), that provides a circular collimation includes eight to sixteen leaves constructed of an X-ray attenuating material, and arranged in a “camera-iris” type configuration. On actuation, the leaves allow increase or decrease in diameter of the X-ray beam, thereby obtaining a fairly continuous circular collimation, for focusing on the area of a patient's body requiring diagnosis. Although this configuration provides an improved dosage efficiency and enables performing a nearly continuous circular (e.g. octagonal) collimation by limiting the field of X-rays to a substantially larger extent than the discrete collimation technique, the collimator is complicated in structure and also very expensive (although feasible for use in nuclear medicine due to high risks associated with gamma ray exposure) for use in an X-ray apparatus. Yet another configuration of a circular collimator is disclosed in the European Patent Document EP 1 026 698 A2, published Oct. 8, 2000, applicant “Ein-Gal, Moshe”, which provides a novel revolving collimator system that can shape a radiation beam emanating from a radiation source with a plurality of mutually alignable collimators and pre-collimators. The collimators and pre-collimators are mounted on a plurality of revolving plates preferably stacked along a common axis. A control system with servomotors selectively rotates any one of the collimator plates, thereby aligning a plurality of collimators to form a path for collimating a radiation beam. This collimator, collimates and pre-collimates radiation beams over a wide range of diameter apertures suitable for virtually any kind of radiotherapy treatment plan. Although this system enables collimating the radiation beam to circular shape with different diameters, the system is much more complex as it makes use of selective and independent control mechanisms for each one of the collimator plates. Yet another known configuration of a circular collimator includes a slidable leaf member having a collimating aperture therewithin, wherein the degree of sliding is proportional to the projected area of image exposure. Although this configuration adopts a simple mechanism, and allows continuous circular collimation, the dosage efficiency is not apparently significant. Although these known collimators provide either a circular collimation, rectangular collimation or a combination thereof, none of the collimators provide (i) a simple configuration (ii) improved dosage efficiency (iii) efficient collimation and (iv) a cost effective solution for collimating X-rays, in terms of risk associated with X-ray exposure vis a vis the effort of treatment. In an embodiment, a single-leaf X-ray collimator is provided. The single-leaf collimator comprises at least one collimating leaf member disposed along the path of X-rays. The collimating leaf member comprises at least one collimating aperture and is configured to rotate about at least one of a horizontal or a vertical plane, wherein leaf member collimates the X-ray beam to about an elliptical shape. Various embodiments of the present invention provide a single-leaf collimator for X-rays, especially for use in diagnostic medical imaging. However, the embodiments are not so limited, and may be implemented in connection with other systems such as, for example, for collimating gamma rays in nuclear devices, etc. In various embodiments, a single-leaf collimator for X-rays is provided, wherein the collimator comprises at least one collimating leaf member configured to rotate about at least one of a horizontal or vertical plane wherein said leaf member produces a collimated X-ray beam of about a continuous elliptical shape. FIG. 1 shows a schematic plan view of a single-leaf collimator according to one embodiment of the present invention. The collimator includes at least one collimating leaf member 11 constructed of an X-ray attenuating material and disposed in-between an X-ray tube head 12 and an imager 13 as a part of an X-ray equipment such as, for example, a CT scanner, etc. At least one collimating aperture 111 (shown in FIG. 2), is provided in the collimating leaf member 11 for allowing an X-ray beam 16 emanating from a focal plane 17 of an X-ray tube head 12 to pass through the collimating leaf member 11 for collimation and to focus on a patient's body (not shown) positioned in front of the imager 13. In an example, the collimating leaf member 11 is constructed of an X-ray attenuating material such as, copper, lead, tungsten, and an alloy thereof. In another example, the collimating leaf member 11 is constructed of a plastic material impregnated with tungsten. FIG. 2. In an embodiment, the collimating aperture 111 provided in the collimating leaf member comprises a substantial circular shape. The collimating leaf member 11 defines a plane and is configured to rotate (e.g. tilt) in at least one of a horizontal or vertical direction (e.g. along the directions indicated by arrows). Note that the rotation of the collimating leaf member 11 results in collimation of the X-ray beam 16 passing through the substantially circular aperture 111 to about continuous elliptical shape. It should be noted that the size of the collimating leaf member 11 is substantially large to cover the entire field of the X-ray beam, in the tilted position and allow passage of X-ray beam only through the collimating aperture 111. In an example, a drive means such as, for example, a DC Servo motor may be used to tilt the collimating leaf member 111 to a predetermined angle so as to produce an optimum collimated shape. In another example, the drive means used for tilting the collimating leaf member may be a hydraulic or pneumatic actuator. In an embodiment, the drive means and the collimating leaf member 11 are enclosed within a common housing (not shown). The housing is configured for securing detachedly to the tube head 12 using fasteners, or configured integral with the tube head 12. FIG. 3 shows another embodiment, wherein an auxiliary leaf member 15 (e.g, a dummy plate) constructed of an X-ray attenuating material is disposed in combination with the collimating leaf member 11. For example, the auxiliary leaf member 15 may be secured in close proximity to the collimating leaf member 11. The auxiliary leaf member 15 may include at least one auxiliary aperture 151 for passage of X-ray beam therethrough, to the collimating leaf member 11. The size of the auxiliary leaf member 15 is configured much larger than the collimating leaf member 11 to sufficiently block the X-rays at all tilted positions of the collimating leaf member 11. For example, in a tilted position of the collimating leaf member 11, the projected width of the collimating leaf member 11 may become less than the width of the X-ray beam at that corresponding position, which may cause the X-ray beam to pass around the edges of the collimating leaf member 11 towards the patient's body. The purpose of the auxiliary leaf member 15 is to allow passage of X-ray beam through the aperture 111 of the collimating leaf member 11 for collimation and prevent passing over of X-ray beam around the edges of the collimating leaf member 11 to the patient's body, by sufficiently blocking the X-ray beam at all sliding positions of the collimating leaf member 11. A sufficient space is configured for rotation (tilting) of the collimating leaf member 11 without interference with the auxiliary leaf member 15. It should be noted the auxiliary leaf member 15 is suitable for use in combination with the collimating leaf member 11 in equipments, in which mounting of a large tiltable collimating leaf member 11 sufficient enough to block the X-rays at all tilted positions is not possible or difficult. In an example, the auxiliary leaf member 15 is made of X-ray attenuating materials such as, for example, lead, tungsten, copper or an alloy thereof. In another example, the auxiliary leaf member is constructed of a plastic material impregnate with tungsten. In an embodiment, a drive means for operating the collimating leaf member 111 is mounted on the auxiliary leaf member 15. For example, a DC servomotor may be used for driving the collimating leaf member 11. In other examples, a hydraulic or a pneumatic actuator may be used for driving the collimating leaf member 11. FIG. 4 shows an X-ray image obtained using an iris type collimator having eight blades in accordance with the prior art. The image obtained includes eight edges (octagonal shape) representing wastage of X-ray dose at the edges. It should be noted that the dosage efficiency is a measure of the useful area of image against the area of X-ray exposure on the same plane. Accordingly, FIG. 4 shows an X-ray image obtained using single-leaf type collimator according to one embodiment of the present invention. The image obtained has an elliptical shape (without edges) encompassing a large useful area thereby resulting in an improved dosage and collimating efficiency. The dosage efficiency offered by the elliptical collimation is increased compared to a combination of rectangular and circular collimation as shown in FIG. 3. Thus, various embodiments of the present invention provide a single-leaf X-ray collimator for use in diagnostic medical imaging. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification for example, the collimator leaf member may be configured to slide in combination with tilting, provide various forms and methods of tilt and drive to the collimating leaf member. The collimating and auxiliary apertures may have various shapes for example, an elliptical shape, to obtain various shapes and sizes of collimated X-ray beam. However all such modifications are deemed to have been covered within the spirit and scope of the claims. |
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044938101 | claims | 1. A nondestructive, non-invasive method of determining at least one quantity selected from the group consisting of fissile content, reactivity, and burnup of a fissile material contained within a multiplying system bounded by an arbitrarily chosen physical boundary, wherein said multiplying system comprises (a) said fissile material which emits neutrons and has fissionable components and (b) a second material which comes in contact with said fissile material, said method using no external neutron-emitting interrogation source, said method comprising: (a) making a first measurement N.sub.A of emitted particle-count rate of at least one type of emitted particle selected from the group consisting of neutrons and gamma rays, wherein said at least one type of emitted particle is emitted by said fissile material, wherein said first measurement is made by using at least one suitable detector, and wherein a first reflector material is positioned adjacent to said multiplying system while said first measurement is made; (b) making a second measurement N.sub.B of emitted particle-count rate of said at least one type of emitted particle emitted by said fissile material, wherein said second measurement is made by using at least one suitable detector, wherein a second reflector material replaces said first reflector material and is reproducibly positioned adjacent to said multiplying system while said second measurement is made; and then (c) using the equation ##EQU4## wherein M.sub.B is the multiplication and .DELTA.k.sub.eff is the change in the effective multiplication constant k.sub.eff, determine the local multiplication or average multiplication, and wherein said multiplying system is not changed during the time period in which steps 1(a) and 1(b) are performed. (a) a support means for supporting said multiplying system in a fixed, reproducible position; (b) a detection system comprising at least one detector which detects at least one type of particle selected from the group consisting of neutrons and gamma rays, wherein said detection system is located in a fixed position spaced apart from said multiplying system and wherein said detection system can be operably connected to a means for operating said detection system; (c) a first reflector material (i) to be located in a reproducible first position such that at least a portion of said first reflector material is located adjacent to but not necessarily surrounding said multiplying system while a first measurement is made with said detection system, and then (ii) to be next removed from said first position; (d) a second reflector material to be located in substantially said first position when said first reflector material is removed from said first position and while a second measurement is made with said detection system; and (e) a means for alternately positioning said first reflector material and said second reflector material adjacent to said multiplying system. 2. A method according to claim 1, and including also the step of correlating either the multiplication or change in count rate to a quantity selected from the group consisting of burnup, reactivity, and fissile content with a functional relationship between the measured count rate of step 1(a) and the measured count rate of step 1(b), wherein said multiplying system is not changed during the time period in which steps 1(a) and 1(b) are performed. 3. A method according to claim 1 or claim 2, wherein multiple detectors are used to obtain a profile of a quantity selected from the group consisting of burnup, reactivity, and fissile content. 4. A method according to claim 3, wherein said first reflector material is water and wherein said second reflector material is cadmium. 5. A method according to claim 3, wherein said first reflector material is graphite and wherein said second reflector material is cadmium. 6. A method according to claim 3, wherein said fissile material being measured is a spent fuel assembly. 7. An apparatus for measuring at least one quantity selected from the group consisting of burnup, fissile content, and reactivity of a fissile material which emits neutrons, which has fissionable components, and which is located within a multiplying system, wherein said multiplying system is bounded by an arbitrarily chosen physical boundary and wherein said multiplying system comprises said fissile material and a second material which comes in contact with said fissile material, said apparatus comprising: 8. An apparatus according to claim 7, wherein said first reflector material is in the form of at least one removable rotating plate which can rotate toward and away from said multiplying system. 9. An apparatus according to claim 7, wherein said first reflector material is in the form of a slidable sheath which slides along said multiplying system. 10. An apparatus according to claim 8 or claim 9 wherein said first reflector material is cadmium and wherein said second reflector material is water. 11. An apparatus according to claim 8 or claim 9, wherein a multiplicity of detectors is used to obtain simultaneously a multiplicity of measurements of local multiplications. 12. An apparatus according to claim 9, wherein a motor drives said slidable sheath, thus providing a scanning system. 13. An apparatus according to claim 8 or claim 9 and including also said multiplying system. 14. An apparatus according to claim 13, wherein said fissile material is a spent fuel assembly. |
claims | 1. A method of layout decomposition, comprising:receiving layout design data;generating first intensity information by performing an optical simulation on the layout design data with a light source having a dipole oriented in a first direction;generating second intensity information by performing an optical simulation on the layout design data with a light source having a dipole orientated in a second direction, the second direction being perpendicular to the first direction; anddecomposing, using a computer, the layout design data into a first layout portion and a second layout portion based on one or both of the first intensity information and the second intensity information, the first layout portion being associated with the light source having the dipole oriented in the first direction and the second layout portion being associated with the light source having the dipole oriented in the second direction. 2. The method recited in claim 1, wherein decomposing the layout design data is further based on additional information. 3. The method recited in claim 2, wherein the additional information is user-provided. 4. The method recited in claim 2, wherein the additional information is geometric information. 5. The method recited in claim 1, further comprising:performing OPC (optical proximity correction) on one or both of the first layout portion and the second layout, and adjusting layout decomposition based on whether one or more conditions for adjusting layout decomposition are met. 6. The method recited in claim 5, wherein one of the one or more conditions is that a correction made by the OPC would exceed a threshold value. 7. The method recited in claim 5, wherein one of the one or more conditions is that a process-window simulation predicts a risk of bridging between a feature and a neighboring feature. 8. The method recited in claim 5, wherein adjusting layout decomposition includes changing a feature in the layout design data from being a single-exposure feature to being a double-exposure feature or from being a double-exposure feature to being a single-exposure feature. 9. The method recited in claim 5, wherein adjusting layout decomposition is further based on one or both of the first intensity information and the second intensity information. 10. The method recited in claim 5, wherein adjusting layout decomposition is further based on information provided by a user. 11. The method recited in claim 1, further comprising:grouping features in the layout design data into a plurality of categories based on one or both of the first intensity information and the second intensity information. 12. The method recited in claim 11, wherein the two or more categories include dipole-strong, dipole-weak, and dipole-neutral categories. 13. The method recited in claim 11, wherein adjusting layout decomposition is further based on which one of the two or more categories a feature data belongs to. 14. The method recited in claim 1, wherein the first intensity information and the second intensity information include partial intensity distribution information. 15. The method recited in claim 14, wherein the partial intensity distribution information includes image contrast information. 16. The method recited in claim 14, wherein the partial intensity distribution information includes image slope information. 17. A processor-readable device storing processor-executable instructions for causing one or more processors to perform a method of layout decomposition, the method comprising:receiving layout design data;generating first intensity information by performing an optical simulation on the layout design data with a light source having a dipole oriented in a first direction;generating second intensity information by performing an optical simulation on the layout design data with a light source having a dipole orientated in a second direction, the second direction being perpendicular to the first direction; anddecomposing the layout design data into a first layout portion and a second layout portion based on one or both of the first intensity information and the second intensity information, the first layout portion being associated with the light source having the dipole oriented in the first direction and the second layout portion being associated with the light source having the dipole oriented in the second direction. 18. The processor-readable device recited in claim 17, wherein decomposing the layout design data is further based on additional information. 19. The processor-readable device recited in claim 17, wherein the method further comprising:performing OPC (optical proximity correction) on one or both of the first layout portion and the second layout, and adjusting layout decomposition based on whether one or more conditions for adjusting layout decomposition are met. 20. The processor-readable device recited in claim 19, wherein adjusting layout decomposition is further based on one or both of the first intensity information and the second intensity information. 21. A system comprising one or more processors, the one or more processors programmed to perform a method of layout decomposition, the method comprising:receiving layout design data;generating first intensity information by performing an optical simulation on the layout design data with a light source having a dipole oriented in a first direction;generating second intensity information by performing an optical simulation on the layout design data with a light source having a dipole orientated in a second direction, the second direction being perpendicular to the first direction; anddecomposing the layout design data into a first layout portion and a second layout portion based on one or both of the first intensity information and the second intensity information, the first layout portion being associated with the light source having the dipole oriented in the first direction and the second layout portion being associated with the light source having the dipole oriented in the second direction. 22. The system recited in claim 21, wherein decomposing the layout design data is further based on additional information. 23. The system recited in claim 21, wherein the method further comprising:performing OPC (optical proximity correction) on one or both of the first layout portion and the second layout, and adjusting layout decomposition based on whether one or more conditions for adjusting layout decomposition are met. 24. The system recited in claim 23, wherein adjusting layout decomposition is further based on one or both of the first intensity information and the second intensity information. |
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abstract | A nuclear steam supply system utilizing gravity-driven natural circulation for primary coolant flow through a fluidly interconnected reactor vessel and a steam generating vessel. In one embodiment, the steam generating vessel includes a plurality of vertically stacked heat exchangers operable to convert a secondary coolant from a saturated liquid to superheated steam by utilizing heat gained by the primary coolant from a nuclear fuel core in the reactor vessel. The secondary coolant may be working fluid associated with a Rankine power cycle turbine-generator set in some embodiments. The steam generating vessel and reactor vessel may each be comprised of vertically elongated shells, which in one embodiment are arranged in lateral adjacent relationship. In one embodiment, the reactor vessel and steam generating vessel are physically discrete self-supporting structures which may be physically located in the same containment vessel. |
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046833790 | claims | 1. A lamp, comprising an envelope; a gas in said envelope discharge means and for effecting a discharge; and a mixture of substances in said envelope for emitting radiation in response to a discharge, said mixture including a first substance which emits radiation having energy maxima in the red, blue and green bands of the visible range, a second substance which emits radiation having an energy maximum in the long-wave Portion of the UVA band, and a third substance which emits radiation in a part of the UV range extending from the short-wave portion of the UVA band down to approximately 300 nm in the long-wave portion of the UVB band, the third substance's radiation having an energy maximum in the short-wave portion of the UVA band the energy maximum of radiation in the long-wave portion of the UVA band lying between 370 and 390 nm and being less pronounced than the energy maxima in the red, blue and green bands of the visible range, and the energy maximum of radiation in the short-wave portion of the UVA band being substantially less pronounced than the energy maximum in the long-wave portion of the UVA band. 2. The lamp of claim 1, wherein said third substance emits radiation from 300 to at least 320 nm. 3. The lamp of claim 1, wherein said second substance emits radiation between approximately 350 and 400 nm. 4. The lamp of claim 2, wherein said third substance emits radiation up to approximately and at least slightly above 350 nm. 5. The lamp of claim 1, wherein the percentage of said first substance is at least 80 percent of the sum of said first, second and third substances. 6. The lamp of claim 1, wherein the percentage of said second substance exceeds the percentage of said third substance. 7. The lamp of claim 1, wherein said second substance contains europium-activated strontium fluoroborate. 8. The lamp of claim 1, wherein said third substance contains cerium-strontium-magnesium aluminate. 9. The lamp of claim 1, wherein said second substance constitutes between 5 and 10 percent of the sum of said first, second and third substances. 10. The lamp of claim 1, wherein said third substance constitutes between 1 and 4 percent of the sum of said first, second and third substances. 11. The lamp of claim 1, wherein the energy maximum of radiation in the long-wave portion of the UVA band is at approximately 380 nm. 12. The lamp of claim 1, wherein said first substance emits radiation in a range extending from about 390 nm across at least the major part of the visible spectrum. 13. The lamp of claim 1, wherein said gas has a low pressure so as to effect a low-pressure discharge. 14. The lamp of claim 4, wherein said third substance emits radiation up to approximately 370 nm. 15. The lamp of claim 5, wherein the percentage of said first substance is between about 86 and about 94 percent of the sum of said first, second and third substance. |
abstract | An improved personal radiation protection system that substantially contours to an operator's body is suspended from a suspension means. The garment is operable to protect the operator from radiation. The suspension means is operable to provide constant force and allows the operator to move freely in the X, Y and Z planes simultaneously, such that the protective garment, face shield, illumination means or other attachments integrated the system are substantially weightless to the operator. A face shield and arm cover can also be incorporated with the system, such that the face shield and arm cover are substantially weightless to the operator. The suspension means may be mounted to the ceiling, a vertical wall, the floor, or on a mobile platform. |
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description | A number of commissioning tests were performed to ensure that the furnaces used, which are radio frequency (RF) furnaces, function correctly and there is compatibility between the Zircaloy cladding and the molten stainless steel. In addition commissioning tests also involved resistance measurements on lengths of cladding which had been oxidised in air to produce an oxide layer having a thickness of approximately 20 xcexcm. The tests showed that the stainless steel started to melt at approximately 1250xc2x0 C., that is to say, at a considerably lower temperature than its specified melting point range of 1400-1455xc2x0 C. The tests also demonstrated that the high resistance of the zirconium oxide ( greater than 2 Mxcexa9) is eliminated, the resistance dropping to 0.1xcexa9 before the stainless steel begins to melt. A test carried out in a graphite crucible without the presence of stainless steel revealed that zirconium oxide is reduced on heating in a pure argon/carbon monoxide atmosphere. In addition the tests demonstrated that Zircaloy reacts strongly with molten stainless steel at 1500xc2x0 C. resulting in penetration of the stainless steel melt inside the Zircaloy cladding and severe interaction between the two alloys. The microstructure of both the stainless steel and the Zircaloy cladding is altered. The steel structure consisted of austenite grains in a complex eutectic mixture with inclusions of graphite flakes. The Zircaloy structure had an xcex1-Zr layer in the outer surface and columnar grains at the remaining inside thickness. There was also a layer of intermetallic compounds at the Zircaloy/stainless steel interface. In some tests the cladding had cracked at the stainless steel miniscus region due to the complex interaction in molten stainless steel, that is to say, differential contraction between the two alloys on cooling and hoop stresses generated in the Zircaloy cladding as a result of oxygen diffusion to form an xcex1-Zr layer. The shape of the Zircaloy cladding within the solidified steel was no longer round but heavily convoluted and the cladding was reduced in thickness. Tests were carried out at 1255, 1310, 1358 and 1415xc2x0 C. to determine the optimum temperature for reduction of the zirconium dioxide and to develop a good fusion bond between the Zircaloy and the stainless steel. The results showed that, although the resistance had dropped to a minimum value (approximately 0.02xcexa9) in all cases, there was a lack of fusion bonding at temperatures of 1255 and 1310xc2x0 C. The tests performed at 1358 and 1415xc2x0 C. show both elimination of the oxide layer and good fusion bonding between the two alloys. Accordingly, the optimum temperature was selected to be about 1385xc2x0 C. (midway between 1358 and 1415xc2x0 C.) to ensure good fusion bonding and minimised embrittlement of the cladding. Further tests were performed on single cladding lengths with differing oxide thicknesses (15, 19, 36 and 42 xcexcm) at 1385xc2x0 C. In all cases the high resistance due to the zirconium dioxide layer dropped to 0.1xcexa9 before the stainless steel began to melt. Subsequent to the stainless steel melting, there was a very small further drop in resistance probably due to dissolution of the residual oxide layer on the Zircaloy clad surface. A minimum resistance of around 0.025xcexa9 was attained in all cases before the temperature was raised to 1385xc2x0 C. There was no systematic relationship between the oxide thickness and the temperature to achieve a minimum; even the cladding with the maximum oxide thickness (42 xcexcm) achieved the minimum resistance at a similar temperature. A visual metallographic examination of the samples after the tests indicated complete melting of the stainless steel and good fusion bonding between the Zircaloy and the stainless steel. In a further test a small model fuel assembly (comprising a 3xc3x973 matrix of Zircaloy cladding lengths) was heated to a melt temperature of about 1385xc2x0 C. Movement of the rod assembly (supporting the nine cladding lengths) to one side of the graphite crucible occurred at about 1300xc2x0 C. indicating the bulk melting of the stainless steel block. A rapid drop in resistance from above 2 Mxcexa9 to less than 0.1xcexa9 occurred in the temperature range between 1000 and 1260xc2x0 C. Subsequently the resistance continued to drop very slowly with temperature until a minimum value of 0.025xcexa9 was recorded at 1350xc2x0 C. There was no further drop in resistance during heating to the target temperature of 1385xc2x0 C. After the test, it was found that the steel had melted around all the Zircaloy lengths and there was good contact between the two alloys. One cladding length had broken near the meniscus region and two lengths showed two cracks in the same region, the rest remaining intact. In order to limit embrittlement of the cladding melt interface, the experimental technique was modified to hold the cladding partially immersed in the stainless steel block during the heating and melting process. Immediately before cooling begins the cladding is fully immersed into the melt. In this way the top length of the cladding with limited embrittlement is encased by the stainless steel cast, thus reducing the tendency to fracture at the gas/melt interface. The minimum resistance criterion is met by the lower part of the Zircaloy cladding, which is fully fused in the stainless steel. Two Tests were Carried Out: Test 1: Heating to 1370xc2x0 C. at 200xc2x0 minxe2x88x921, hold time 2 minutes and cooling at xcx9c200xc2x0 C. minxe2x88x921 ie furnace turned off. Test 2: Heating to 1370xc2x0 C. at 200xc2x0 C. minxe2x88x921, hold time 2 minutes and cooling at 50xc2x0 C. minxe2x88x921. In order to allow partial immersion of the cladding during the heating and melting process and subsequent full immersion at the target temperature, some alterations were made to the RF furnace components. The stainless steel block was redesigned ie a 38 mm deep bore was drilled in the top length to immerse the cladding partially during the heating and melting process and the bottom 12 mm length was a solid block to allow the full immersion (further immersion by 10 mm) after melting. The graphite cubicle was dished at the top part to accommodate the molten metal ejected during the full immersion. The top plate of the furnace was provided with double seal entry to allow the gas tight movement of the cladding during the full immersion of the cladding at the final stage. The experimental technique involved heating the Zircaloy tube having an oxide layer xcx9c30 xcexcm, and stainless steel contained in a graphite crucible using a R F furnace. As open-ended tubes were provided, a plugging devise (alumina pellet) is inserted in the bottom of the tubes to minimise entry of the stainless steel melt during the test. The conductivity across the cladding/melt interface is measured in each case. The melt temperature (graphite inside temperature) was monitored by a thermocouple located inside a closed end alumina tube, inserted into a bore drilled in the crucible wall thickness just next to the stainless steel surface. Another similar thermocouple was set up to measure the temperature near the bottom end of the stainless steel block (at a mid position of 12 mm long solid stainless steel end). The inside of the cladding is flushed with helium gas during each test in order to exclude any residual oxygen. For both tests the resistance had decreased to a lower value of 0.1xcexa9 before melting of the stainless steel had initiated. The decrease in resistance occurred very rapidly in the temperature range of 1150 to 1300xc2x0 C. Below this temperature range the ZrO2 resistance was out of the resistance measurement range ( greater than 2 Mxcexa9), and the system produced erratic resistance values. In both the tests gas, possibly CO/CO2, was observed sparging through the molten stainless steel, and this effect was more pronounced and lasted longer for test 2. There were no surface cracks at the gas/melt interfaces or failure of the Zircaloy cladding during post test handling. However, a longitudinal crack appeared after test 1, 20 mm below the gas/melt interface; and a circumferential crack after test 2, 10 mm below the gas/melt interfaces (at the sites of cavities in the stainless steel cast). No stainless steel was observed inside the Zircaloy tubes after the tests. In test 1, the resistance dropped to 0.1xcexa9 at 1275xc2x0 C. and continued to drop very slowly with temperature until a minimum value of 0.032xcexa9 was recorded at the target melt temperature (xcx9c1370xc2x0 C.). The resistance value stayed almost constant on cooling the sample to room temperature. After the test, it was found that the steel had melted around the Zircaloy cladding and there was good contact between the two materials. There was no sign of cracking in the region of the gas/melt interface. The ejection of molten metal onto the dished part of the graphite crucible during the full immersion of the cladding indicated that the stainless steel had been fully molten. In test 2, the resistance dropped to 0.1xcexa9 at 1290xc2x0 C. and continued to drop very slowly with temperature until a minimum value of 0.025xcexa9 was recorded at the target melt temperature. The resistance value increased slightly to 0.029xcexa9 on cooling the sample to room temperature. After the test, it was found that the steel had melted around the Zircaloy cladding and there was good contact between the two materials. There was no sign of cracking in the region of the gas/melt interface. The ejection of molten metal onto the dished part of the graphite crucible during the full immersion of the clad indicated that the stainless steel had been fully molten. The samples for metallographic examination from each test were selected from two different positions; a transverse section at a position on the tip of the inner thermocouple and a longitudinal section at the gas/melt interface. The results of transverse sections show that there was good fusion bonding between the Zircaloy cladding and stainless steel (in both cases); however, in some areas (especially in the case of test 2) the contact between the two was lost due to the cavities in the melt. The photomicrographs show that the microstructure of the solidified stainless steel consisted of light and dark phases in the form of acicular (both light and dark phases) and polygonal (usually dark phases) grains. Coarse graphite flakes were also found within the mixture of the light and dark phases. The graphite flake size depends on the cooling rate, the faster the cooling rate the smaller the size. The Zircaloy had recrystallised with single grains traversing the cladding wall. The recrystallised grains also seemed to have a eutectic phase between them. The micrographs show three distinctive layers across the stainless steel Zircaloy interface; a thin layer (xcx9c5 xcexcm thick) next to the stainless steel surface, an adjacent smooth layer (xcex1-Zr(O) (xcx9c90 xcexcm thick) grown into the Zircaloy matrix and an intermetallic layer (xcx9c15 xcexcm thick) at the xcex1-Zr(O)/Zircaloy interface. The results of longitudinal sections show that there was a lack of fusion bonding between the Zircaloy cladding and stainless steel (in both cases, in a small depth studied up to 3.5 mm) near the gas/melt interface due to the presence of unreduced ZrO2 at the stainless steel/Zircaloy interface. The presence of ZrO2 was patchy and to a lesser extent in test 2 (than in test 1) which seems to be due to the slow cooling rate and hence the longer reaction time. However, the resultant improvement in embrittlement was better in test 1 as evidenced by topography of tiny cracks; the cracks being wider and longer in the case of test 2 than in test 1 at the Zircaloy cladding surface around the gas/melt interface. As has been indicated above, the present invention has application to the electric chemical dissolution of any metallic object, in particular to metallic assemblies where it is difficult to ensure good electrical conduct to all the parts of the assembly. |
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051924919 | description | Referring now to the figures of the drawing in detail and first, particularly, to FIGS. 1 and 2 thereof, there is seen a cross-sectional view of a cross-shaped control element 1 of a boiling water reactor. The control element 1 receives tubes 2 containing absorber material that extend along the longitudinal axis of the control element. The control element, which is disposed in a water pond or pool 3, has a can be brought to various test positions with the aid of a non-illustrated hoist and which is kept free of water by means of a compressed air connection 5. A collimator system 6 is integrated into the hood 4 in such a way that two vanes of the control element 1 are always exposed to a divergent collimator 7, as shown by phantom lines in FIG. 2. The collimator 7 has an inlet opening with a neutron source 8. In each case, a film cassette 9 which contains an image recorder is situated opposite the collimator 7 in the same measurement plane. The film cassette 9 is disposed in a holding device 10 which has a construction and relationship to the hood 4 that is explained below in connection with FIG. 3. As can be seen from FIG. 3 which is on an enlarged scale, the hood 4 has a wall with an opening 11 therein adjacent the film cassette. The opening 11 is disposed in a common measurement plane of the neutron source 8, the collimator system 6 and the film cassette 9 and its cross section corresponds to the cross section of the image recorder used in the film cassette 9. The holding device 10 fits over the opening 11 and is joined to the wall of the hood 4 through a sheet-metal casing 12 in such a way that a housing is produced which only has an opening 27 in its lower surface 13. The sheet-metal casing 12 has side walls 28 extended perpendicular to the wall of the hood 4, with which the sheet-metal casing 12 forms a form-locking guide channel for the film cassette 9. A form-locking connection is one which connects two elements together due to the shape of the elements themselves, as opposed to a force-locking connection, which locks the elements together by force external to the elements. The holding device 10 is consequently in communication with the internal space of the hood 4 through the opening 11 and is a part of the hood which is also kept free of water through the compressed air connection 5. The sheet-metal casing 12 of the holding device 10 is drawn downwards to such an extent that it terminates at about one height measurement of the film cassette below the lower edge of the opening 11. Projecting from the film cassette 9 is a coupling piece 14 which extends downwards at an angle and which enters into a detachable coupling link 15 with a coupling rod 16 extended approximately parallel to the hood 4. The length of the coupling rod 16 is dimensioned in such a way that it can be moved from outside the water pond 3 by manual actuation. The film cassette can therefore be introduced through the opening 27 into the water-free space of the holding device 10 by remote control. In order to reliably reach the measuring position, the holding device 10 has a centering piece 17 with a guide surface 18 that adjoins a stop 19 for the film cassette 9. The stop 19 has a truncated conical construction and receives an upper part 20 of the film cassette 9, which is likewise constructed with regard to its shape, in such a way as to center it. In the limit position, the film cassette 9 is centered by its lower frame part 22 on a projection 23. The projection 23 is a component of a guide piece 24 which extends below the opening 27. The film cassette 9 is held in the measuring position by at least one locking device 21 which comes out of a recess 29 in the guide piece 24 in such a way as to rest against a stop pin 30 provided on the coupling piece 14 with the aid of a non-illustrated pneumatic cylinder. The guide piece 24 carries a skimmer 25 which is already disposed in the water-free space of the holding device 10 and removes water residues from the surface of the film cassette 9 adjacent the opening 11. The skimmer 25 consequently assists the action of an air current flowing in the direction of an arrow 26, which also contributes to the removal of residual water. In order to ensure that no water can penetrate into the internal space of the cassette during the transport of the film cassette 9 through the water pond 3 to the hood 4, the part of the coupling piece 14 which is of tubular construction has a non-illustrated compressed air connection, so that air can pass through a hole 31 in the cassette 9 into its internal space. |
claims | 1. In combination with a nuclear reactor pressure vessel, said nuclear reactor vessel being positioned in a pedestal, reactor pressure vessel drain piping being positioned on the bottom of said nuclear reactor pressure vessel, an inspection apparatus for piping, said inspection apparatus for piping comprising: a carriage set on a rail arranged under said reactor pressure vessel drain piping in parallel with a horizontal portion of said reactor or pressure vessel drain piping inside a said pedestal; a driving means for moving said carriage along said rail; a falling prevention mechanism for preventing said carriage from falling from said rail; a camera mounted on said carriage and monitoring a relative position between said camera and said reactor pressure vessel drain piping; and a thickness measuring means mounted on said carriage for measuring the thickness of said reactor pressure vessel drain piping. 2. An inspection apparatus for piping according to claim 1 , further comprising: claim 1 a control means for controlling said driving means; a displaying means for displaying an image monitored by said camera; and an outputting means for outputting a measurement result obtained by sa d thickness measuring means; and wherein said means each are installed outside said pedestal. 3. An inspection apparatus for piping according to claim 1 , wherein said rail is bendable, said carriage is supported by said rail, and said rail has end portions which are fixed. claim 1 4. An inspection apparatus for piping according to claim 3 , wherein said rail comprises a plurality of plate members and hinge mea s for flexibly connecting adjacent plate members. claim 3 5. An inspection apparatus for piping according to claim 3 , wherein said end portions of said rail are fixed to control rod drive housings adjacent to said end portions. claim 3 |
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claims | 1. An extreme ultraviolet light source in which a magnetically self-confined plasma is produced via a pulsed discharge and subsequently the plasma energy in a small region of the plasma is increased by absorption of laser light resulting in locally increased excitation of ionic species that radiate extreme ultraviolet light, wherein a direction of current flow is reversed on successive pulses. 2. A source as in claim 1, in which an axial static magnetic field is applied to guide a coaxial discharge between opposed open-ended heat pipes and the laser impinges radially onto the discharge plasma. 3. A source as in claim 2, in which ignition of the discharge is assisted by a potential applied to a disc electrode located symmetrically between the main discharge electrodes, with a central hole through which the discharge passes. 4. A source as in claim 3, in which lithium is confined within a buffer gas heat pipe formed by the electrodes and the central disc with wide angle vapor containment and reflux. 5. A source as in claim 1, in which each phase of the discharge comprises a quiescent low current period followed by a high current period of shorter duration that pinches the plasma and increases its density and temperature in preparation for laser heating. 6. A source as in claim 5, in which the low current ranges from 1 Amp to 100 Amp and the high current ranges from 100 Amp to 10 kAmp. 7. A source as in claim 5, in which the quiescent period has a duration between 5 μsec and 50 μsec and the high current period has a duration between 500 nsec and 5 μsec. 8. An extreme ultraviolet light source at 13.5 nm based on the emission of lithium ions in which a magnetically self-confined lithium plasma of electron density less than 1019 cm−3 is produced via a pulsed discharge and subsequently the plasma energy in a small region of the plasma is increased by absorption of laser light at the carbon dioxide laser wavelength, resulting in locally increased excitation of hydrogen-like lithium to its resonance level and increased radiation at 13.5 nm, wherein a direction of current flow is reversed on successive pulses. 9. A source as in claim 8, in which an axial static magnetic field is applied to guide a coaxial discharge between opposed open-ended lithium heat pipes and the carbon dioxide laser impinges radially onto the discharge plasma. 10. A source as in claim 8, in which the lithium is confined within a buffer gas heat pipe with wide angle vapor containment and reflux. 11. A source as in claim 8, in which a Z-pinch discharge provides the magnetically self-confined lithium volume for the purpose of increasing the lithium ion density and creating a plasma density greater than 1017 electrons per cm3 at an electron temperature exceeding five electron volts. 12. A source as in claim 8, in which a hypocycloidal pinch discharge geometry is applied to the production of a lithium plasma density greater than 1017 electrons per cm3 at an electron temperature exceeding five electron volts. |
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046997490 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates the nuclear steam supply system of a pressurized water reactor (PWR) nuclear power generating unit which embodies the present invention. The system comprises a nuclear reactor 1 which includes an upright, generally cylindrical reactor core 3 housed in a pressure vessel 5. The core 3 contains fissionable material in which sustained fission reactions occur to generate heat which is absorbed by reactor coolant in the form of light water passed through the core 3. The reactor coolant is circulated in a primary loop which includes a hot leg conduit 7 to convey the heated reactor coolant from the reactor core 3 to the primary side of a steam generator 9 where the heat is transferred to feed water on the secondary side to produce steam. This steam is utilized in a secondary loop (not shown) in a well-known manner to drive a turbine-generator set (also not shown) which produces electric power. The reactor coolant is returned to the reactor core 3 through a cold leg conduit 11 by a reactor coolant pump 13. While one primary loop is shown in FIG. 1 for illustration, in practice a typical PWR has two to four primary loops each serving its own steam generator. Long term adjustment of the reactivity of the reactor core 3 is controlled by disolving a neutron absorbing material such as boron in the reactor coolant which is circulated through the core. The reactor coolant also serves as a moderator to slow the fast neutrons released by the fission reactions down to the energy levels required for sustained fission reactions. A PWR possesses a negative temperature moderator coefficient in that as the water becomes cooler and hence denser, it slows down more fast neutrons to the critical level for fission and thus increases the reactivity of the core. The reactivity of the core 3 is also regulated by control rods 15 made of neutron absorbing material which are inserted into the core 3 vertically from above. The control rods 15 are positioned by a control rod drive system 17 under the direction of a control system 19. Since the control rods move in the axial direction within the core, they have an affect on the axial distribution of core power. Some of the control rods 15 are part length rods which in some installations are used to help control the axial distribution of power within the core. In all installations, the positioning of the control rods is managed by the control system 19 to maintain the axial distribution of power within prescribed limits. It has long been recognized that the power generated by the reactor 1 is proportional to the fast neutron flux escaping from the core 3. Hence, the power is typically measured by elongated neutron detectors 21 (one shown) extending vertically at spaced locations around the pressure vessel 5. These detectors have upper and lower sections 21a and 21b which provide separate indications of the power in the upper and lower portions of the core 3 respectively. The usual practice is to provide four such neutron detectors spaced evenly around the pressure vessel to generate four independent measurements of the neutron flux. The redundancy provided by the mulitple detectors assures the reliability required for protection and control purposes. The separate flux measurement made by the upper and lower halves 21a and 21b of the neutron detectors are transmitted to the control system 19 over lines 23 and 25 respectively. The control system 19 processes the neutron flux signals from the detectors 21a and 21b to calculate the axial offset in accordance with the formula: ##EQU1## This axial offset is a measurement of the skewing of power within the core in the axial direction. A typical scheme for operating a PWR is to maintain the axial offset at a preselected value, which changes through the fuel cycle, during normal operation of the reactor. A typical target value for the axial offset expressed as a percentage is +2 to 3% with an operating band which typically ranges upwards to 7%. If the axial offset drifts outside of this band, the power is reduced to bring it back within limits. As previously mentioned, skewing of the power can also be measured in terms of axial shape index which reverses the terms in the numerator in the above equation thereby referencing the index to the bottom of the core. Under normal operating conditions, radial power distribution within the core is not a concern because movement of the control rods is synchronized to provide symmetry about the longitudinal axis of the core. Provision is made, however, for the possibility that that symmetry could be broken for instance by a dropped rod. Due to the physics of a PWR, the dropped rod will cause an immediate decrease in the power generated in the vicinity of the dropped rod which will initially result in a reduction in the total power generated by the core. The reactor will then attempt to meet the load placed upon it by the demand for steam in the secondary loops by increasing power in the remainder of the core, which as mentioned previously, could lead to local overheating elsewhere in the core. The present invention addresses this problem by detecting the dropped rod condition but shutting the reactor down only when conditions warrant. Our analysis has shown that unprogrammed insertion of certain rods has more affect on other portions of the core than other dropped rods. The effects of the dropping of the various rods into the core were considered for the worst case condition which occurs when there is a large amount of reactivity, available through dilution of the boron in the reactor coolant, through a drop in reactor coolant temperature and through withdrawal of partially inserted control rods. The limiting factor is the departure from nucleate boiling ratio (DNBR) limits. We have determined that as long as the axial offset remains within identifiable limits, applicable to all dropped rod conditions, the DNBR limits for all other localities in the core will not be exceeded and it is not necessary therefore to shutdown the reactor. The situation is aided to some extent by the fact that the dropping of multiple control rods reduces the reactivity to the extent that the power is automatically reduced to a safe level even with the resultant radial peaking of power. In the present invention, a dropped rod condition is detected in a manner similar to that used in U.S. Pat. No. 4,399,095, i.e. by monitoring the negative rate of change of the fast neutron flux. Novel means are then used to determine whether the dropped rod condition warrants shutting down the reactor. FIG. 2 illustrates schematically a portion of the control system 19 of FIG. 1 for implementing the invention. A similar circuit is provided for each of the detector channels 21. The output of each half 21a and 21b of each fast neutron detector is applied to a neutron flux processor 27 which sums the two outputs to generate a power signal on line 29 and generates an axial offset signal which is calculated according to the formula set forth above and applied to line 31. The power signal is applied to a conventional dynamic rate-lag compensation circuit 33 which generates an output representative of the rate of change in the power. If the output of the dynamic rate-lag circuit is negative enough to exceed a preselected setpoint characteristic of a dropped rod, a negative rate bistable 35 will change state. The change of state of the bistable 35 is stored by a memory unit 37 which maintains the stored bistable output until manually reset. Thus, while the flux will subsequently rise as other portions of the core respond to meet the load demand, the indication of the dropped rod condition is preserved. The output of the memory unit 37 is applied to an AND circuit 39. The axial offset signal on lead 31 is compared with two axial offset setpoint signals X.sub.1 and X.sub.2 in bistables 41 and 43 respectively. The output of bistable 43 is applied to an AND gate 45 together with a signal from a part length rod out indicator 47. If the part length rods are out and the axial offset exceeds the set point value X.sub.2, a signal is applied by AND gate 45 to an OR gate 49. On the other hand, if the part length rods are in, and the axial offset exceeds the set point value X.sub.1, bistable 41 will apply a signal to OR gate 49. Either signal is applied by OR gate 49 to AND gate 39 together with the output of the memory circuit 37. If the memory 37 has been set to indicate a dropped rod condition, AND 39 gates either signal indicating that an axial offset limit has been exceeded to an OR gate 51 which, in turn, applies a signal to a two out of four voting logic circuit 53 together with similar signals from the other channels. If a signal is also applied to the two out of four voting logic circuit 53 by any other channel, a reactor trip signal is generated. The reactor trip signal is applied to the rod drive system 17 to insert all of the control rods into the core to shut the reactor down. The output of the rate lag circuit 33 is also compared with a second set point signal in a bistable 55. The value of the set point signal applied to the bistable 55 is selected to be indicative of a rate of decrease in reactor power so severe as to require immediate shutdown of the reactor. Thus, if this set point value is exceeded, the signal generated by the bistable 55 is stored in a memory unit 57 and is applied through the OR gate 51 to the two out of four logic circuit 53 until the memory is manually reset. Again, at least one other channel must also apply a signal to the two out of four voting logic circuit 53 in order to generate a reactor trip. This trip generated when the decrease in flux rate exceeds the set point applied to the bistable 55 is the conventional high flux rate trip signal currently provided in PWRs, and is shown here to illustrate how this trip interfaces with the invention. As mentioned, the set point value for the decrease in flux rate applied to bistable 35 is selected to indicate a dropped rod condition. An exemplary value for this set point corresponds to a value obtained when a 0.05 to 0.1% reactivity worth control rod is dropped into the core. Typical values for the axial offset set point signals applied to the bistables 41 and 43, respectively, which would cause a reactor to trip under a dropped rod condition are approximately +10% with the part length rods out and approximately 0% with the part length rods in. With the present invention, the reactor is only shutdown if axial offset limits indicative of unacceptable local power peaks are exceeded and the reactor can often be run at full power with a dropped control rod. Thus, the invention reduces the likelihood of interruption of reactor operation when a control rod is dropped and allows greater utilization of the reactor under these conditions. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teaching of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
051981823 | abstract | A method of forming a neutron-absorbing tube or a section of such tube, and the resulting tube. An elongate, generally rectangular metal ingot having a hollow interior is formed with at least one elongate metal divider in the interior forming chambers. The chambers are filled with a uniformly dispersed mixture of finely divided boron and particles of a finely divided metal, the ingot is then soaked to an elevated temperature and hot rolled to form a thin, rigid neutron-absorbing sheet having opposite metal edge portions and an elongated metal spacer portion at each metal divider. The sheet is then longitudinally bent at each spacer portion. A tube is formed by welding one or more bent sheet along the side edge portions. |
051990571 | claims | 1. An image formation-type soft X-ray microscopic apparatus comprising: a pulse X-ray source for applying X-rays; a single concave aspherical multilayer film condenser for reflecting the X-rays emitted from said pulse X-ray source so as to condense said X-rays on a sample; a two-dimensional X-ray imaging sensor; a phase zone plate objective optical system for forming an image of said sample on said two-dimensional X-ray imaging sensor by using said X-rays; image processing means connected to said two-dimensional X-ray imaging sensor; and output means connected to said image processing means for the purpose of outputting an image of said sample. .lambda.: wavelength of X-ray .DELTA..lambda.: spectral width. a pulse X-ray source capable of emitting X-rays; irradiation means having a concave reflecting surface for reflecting X-rays emitted from said pulse X-ray source so that the X-rays are condensed on a test piece; a zone plate objective for forming an image of the test piece; a two-dimensional X-ray imaging element for receiving the test piece image formed by said zone plate objective; image processing means connected to said two-dimensional X-ray imaging element; and output means connected to said image processing means to output the image of the test piece. an X-ray source capable of emitting X-rays; a light source for supplying illumination light for the optical microscope; irradiation means having a multilayer concave reflecting mirror for reflecting X-rays emitted from said X-ray source so that the X-rays are condensed on a test piece, said multilayer concave reflecting mirror having a reflection area for reflecting the illumination light for the optical microscope formed at least on its peripheral portion; a zone plate objective for forming an image of the test piece by condensing X-rays transmitted through the test piece; a two-dimensional X-ray imaging element for detecting the test piece image formed by said zone plate objective; and an optical microscope objective having an aperture formed along its optical axis to enable formation of an optical path for the zone plate objective, said zone plate objective is disposed so that the optical axes of said zone plate objective and said optical microscope objective coincide with each other in said aperture formed through said optical microscope objective. 2. An image formation-type of soft X-ray microscopic apparatus according to claim 1, wherein said concave aspherical multilayer film condenser is a rotary elliptical multilayer film reflecting mirror, said pulse X-ray source being disposed as the first focal point of said rotary elliptical multilayer film reflecting mirror, and said sample being disposed at the second focal point thereof. 3. An image formation type of soft X-ray microscopic apparatus according to claim 2, wherein said pulse X-ray source is a pulse laser excitation plasma X-ray source which condensing pulse lasers on a target to generate X-rays, said X-rays are monochromatized by said rotary elliptical multilayer film reflecting mirror, and photon counting imaging is performed by using the X-rays of one pulse emitted by excitation by said pulse laser. 4. An image formation-type of soft X-ray microscopic apparatus according to claim 3, wherein said pulse laser excitation X-ray source generates X-rays with intensity in terms of the maximum number n.sub.max of the photons per pixel incident on said two-dimensional X-ray imaging sensor, which is within the following range: EQU 25.ltoreq.n.sub.max <.lambda./.DELTA..lambda. 5. An image formation-type of soft X-ray microscopic apparatus according to claim 4, wherein said pulse laser excitation plasma X-ray source generates pulse X-rays which permits said two-dimensional X-ray imaging element to image by using one pulse having a pulse width of 1 .mu.s or less, the number of period Nc of the layer structure of said rotary elliptical multilayer film reflecting mirror is 50 to 400, and the X-rays emitted from said pulse laser X-ray source are monochromatized by said rotary elliptical multilayer film reflecting mirror so that .lambda./.DELTA..lambda.=50 to 400 and are condensed on a sample. 6. An image formation-type of soft X-ray microscopic apparatus according to claim 5, wherein the wavelength region of the X-rays applied to said sample from said rotary elliptical multilayer film reflecting mirror is 2.3 to 4.4 nm. 7. An image formation type soft X-ray microscopic apparatus comprising: 8. An image formation type soft X-ray microscopic apparatus according to claim 7, wherein said concave reflecting surface is an aspherical surface multilayer film mirror which separates X-rays in a predetermined wavelength range from the X-rays emitted from said pulse X-ray source and makes the separated X-rays travel to the test piece, and said zone plate objective is a phase zone plate objective. 9. An image formation type soft X-ray microscopic apparatus according to claim 7, wherein said irradiation means includes a diffraction grating which separates X-rays in a predetermined wavelength range from the X-rays emitted from said pulse X-ray source and condenses the X-rays in the predetermined wavelength range to the test piece in cooperation with said concave reflecting surface. 10. An image formation type soft X-ray microscopic apparatus according to claim 9, wherein said diffraction grating of said irradiation means comprises a reflection type diffraction grating formed on said concave reflecting surface to form a toroidal concave diffraction grating. 11. An image formation type soft X-ray microscopic apparatus according to claim 10, wherein said irradiation means further includes a light shielding plate disposed at a point to which light is condensed by said toroidal concave diffraction grating, said light shielding plate having an aperture, and a second concave reflecting mirror, X-rays passed through the aperture of said shielding plate being condensed on the test piece by said second concave reflecting mirror. 12. An image formation type soft X-ray microscopic apparatus according to claim 9, wherein said irradiation means includes two concave reflecting mirrors, and said diffraction grating is a reflection type flat-plane diffraction grating, one of said concave reflecting mirrors making X-rays from said pulse X-ray source travel to said flat-plane diffraction grating while making the same generally parallel, the other of said concave reflecting mirrors condensing, on the test piece, X-rays in the predetermined wavelength range from said flat-plane diffraction grating. 13. An image formation type soft X-ray microscopic apparatus according to claim 9, wherein the angle .alpha. at which X-rays from said pulse X-ray source are mainly incident upon said concave reflecting surface and said diffraction grating is within the range of 8.degree..ltoreq..alpha..ltoreq. 8.degree. . 14. An image formation type soft X-ray microscopic apparatus according to claim 13, wherein said pulse X-ray source comprises a pulse laser excitation plasma X-ray source which condenses pulse laser light on a target to generate X-rays, and said two-dimensional X-ray imaging element effects photon counting imaging with one-pulse X-rays excited and emitted by the pulse laser light. 15. An image formation type soft X-ray microscopic apparatus according to claim 14, wherein said pulse laser excitation X-ray source has an X-ray generation intensity such that the maximum number n.sub.max of photons incident upon said two-dimensional X-ray imaging element and detected per pixel is EQU 25.ltoreq.n.sub.max. 16. An image formation type soft X-ray microscopic apparatus according to claim 15, wherein said pulse laser excitation plasma X-ray source generates one-pulse X-rays having a pulse width of not more than 1 .mu.s and having an intensity such as to enable imaging with said two-dimensional X-ray imaging element, and wherein if the wavelength of the X-rays is .lambda. and the spectrum width is .DELTA..lambda., the X-rays from said pulse laser are condensed on the test piece after being monochromatized by said diffraction grating so that .lambda./.DELTA..lambda.=50 to 500. 17. An image formation type soft X-ray microscopic apparatus according to claim 16, wherein the wavelength range of X-rays condensed on the test piece by said diffraction grating is 2.3 to 4.4 nm. 18. An image formation type soft X-ray microscopic apparatus having an optical microscope, comprising: 19. An image formation type soft X-ray microscopic apparatus according to claim 18, wherein said optical microscope objective has a body tube member projecting to the test piece side, and said zone plate is mounted in said body tube member. 20. An image formation type soft X-ray microscopic apparatus according to claim 18, wherein said X-ray source includes a laser light source and a laser irradiation optical system for leading light from said laser light to the X-ray target, illumination light for said optical microscope being supplied through a light separating device disposed in said laser irradiation optical system. |
description | The disclosure relates to an improved beam deflection arrangement within a combined radiation therapy and magnetic resonance unit. Generally in radiation therapy the aim is to irradiate a target within the human body in order to combat diseases, in particular cancer. For this purpose a high dose of radiation is specifically generated in an irradiation center (isocentre) of an irradiation apparatus. During irradiation the problem often arises that the irradiation target in the body can move. For instance, a tumor in the abdomen can move during breathing. On the other hand, in the period between radiation treatment planning and actual radiation treatment a tumor may have grown or have already shrunk. It was therefore proposed to check the position of the irradiation target in the body during radiation treatment by imaging, in order to control the beam or if necessary discontinue the irradiation, and thus increase the success of the therapy. This is in particular relevant for irradiation targets in the upper and lower abdomen as well as in the pelvic area, for example the prostate. To minimize the dose of radiation outside the target volume and thus protect healthy tissue, the entire radiation generation is moved around the patient. This concentrates the radiation dose in the beam in the area of the rotational axis. Both X-ray and ultrasound systems were proposed as the imaging medium for monitoring the therapy. These, however, provide only a limited solution to the problem. In the case of ultrasound imaging the necessary penetration depth is lacking for many applications. In X-ray imaging the X-ray sensors can be disrupted or damaged by the gamma radiation of the accelerator. Furthermore, the quality of the tissue images is often unsatisfactory. For this reason, at present mainly positioning aids and fixing devices or markings made on the skin of the patient are used to ensure that the patient is in the same position in the irradiation apparatus as decided in the radiation treatment planning and that the irradiation center of the irradiation apparatus is actually consistent with the irradiation target. These positioning aids and fixing devices are, however, expensive and in most cases they are uncomfortable for the patient. In addition, they conceal the risk of irradiation errors because as a rule no further check of the actual position of the irradiation center is carried out during irradiation. Magnetic resonance is a known technique which permits both particularly good soft-tissue imaging as well as spectroscopic analysis of the area being examined. As a result this technique is fundamentally suitable for monitoring radiation therapy. In U.S. Pat. No. 6,366,798 a radiation therapy device is combined with various magnetic resonance imaging systems. In all the different versions mentioned here the magnet arrangement of the magnetic resonance imaging system is divided into two parts. In addition, in some versions key parts of the magnetic resonance imaging system rotate with the radiation source of the radiation therapy device. In each case the radiation source is outside the magnetic resonance imaging system and must be protected by means of shields from the stray field of the magnetic resonance imaging system. A division of the magnet, a rotatable magnet and shielding of the radiation source represent elaborate technical solutions and increase the cost. In GB 2 427 479 A, U.S. Pat. No. 6,925,319 B2, GB 2 247 478 A, US 2005/0197564 A1 and US 2006/0273795 A1 further devices are described in which a radiation therapy device or an X-ray imaging system are combined with a magnetic resonance imaging system. GB 2 393 373 A describes a linear accelerator with an integrated magnetic resonance imaging system. In one exemplary embodiment the magnetic resonance imaging system comprises means for compensation of a magnetic field in order to minimize the field strength of the magnetic field of the magnetic resonance imaging system at the location of the accelerator. In another exemplary embodiment a filter is used in order to compensate for possible heterogeneity caused in a therapy beam by the magnetic field of the magnetic resonance imaging system. US2008/0208036 describes a combined radiation therapy and magnetic resonance unit similar to that described below in relation to FIGS. 1-4 of the present application. FIG. 1 shows a schematic representation (not to scale) of a conventional combined radiation therapy and magnetic resonance unit 1 as described in US2008/0208036 with a magnetic resonance diagnosis part 3 and a radiation therapy part 5. The magnetic resonance diagnosis part 3 comprises a main magnet 10, a gradient coil system comprising two, in this case, symmetrical partial gradient coils 21A, 21B, high-frequency coils 14, for example two parts of a body coil 14A, 14B, and a patient bed 6. All these components of the magnetic resonance part are connected to a control unit 31 and an operating and display console 32. In the example presented, both the main magnet 10 and the partial gradient coils 21A, 21B are essentially shaped like a hollow cylinder and are arranged coaxially around the horizontal axis 15. The inner shell of the main magnet 10 limits in radial direction (facing away vertically from the axis 15) a cylinder-shaped interior 7, in which the radiation therapy part 5, the gradient system, high-frequency coils 14 and the patient bed 6 are arranged. More precisely the radiation therapy part 5 is located in the interior 7 between the outer side of the gradient coil system 21A and 21B and the inwardly facing shell surface of the main magnet 10. In addition to the magnet coils the main magnet 10 comprises further structural elements, such as supports, housing etc., and generates the homogenous main magnetic field necessary for the magnetic resonance examination. In the example shown the direction of the main magnetic field is parallel to the horizontal axis 15. High-frequency excitation pulses which are irradiated by means of high-frequency coils 14 are used to excite the nuclear spins of the patient. The signals emitted by the excited nuclear spins are also received by high-frequency coils 14. The axially distanced partial gradient coils 21A, 21B in each case comprise gradient coils 20, which are in each case completely enclosed by a shield 27. The gradient coil 20 comprises supports and individual gradient coils which irradiate magnetic gradient fields for selective layer excitation and for location-coding of the magnetic resonance signals in three spatial directions. The radiation therapy part 5 is arranged on a gantry 8 and comprises an electron accelerator 9, which here is configured as a linear accelerator, a beam deflection arrangement 17, a target anode 19, a homogenizing body 22 and a collimator 23. The gantry 8 can feature a recess (broken lines), by which access to the magnetic resonance diagnosis part remains possible also from this side. The electron accelerator 9 of the radiation therapy part 5 comprises an electron source 11, for example a tungsten cathode, which generates an electron beam 13, which is accelerated by the electron accelerator 9 preferably pulsed parallel to the main magnetic field of the main magnet 10. The electron accelerator 9 for example generates electron beam pulses with a length of 5□s every 5 ms. If the electron accelerator 9 generates pulsed electron beams 13, it can be built more compactly, e.g. with a length of about half a meter, and still withstand the impact of the high-energy electron beams 13. The electrons of the electron beam 13 are accelerated by electric alternating fields in cylinder-shaped hollow conductors of the electron accelerator 9. The electrons of the electron beam 13 are accelerated to energies up to a magnitude of several MeV. The electron accelerator 9 is connected to an accelerator control unit 12 to control the alternating fields and the electron source 11. The electron beam 13 leaves the electron accelerator 9 at the end opposite the electron source and is deflected by the beam deflection arrangement 17 through 90° radially inward in the direction of axis 15. For this purpose the beam deflection arrangement 17 comprises a magnet which generates a suitable magnetic field. The magnet is configured as an electromagnet made of non-ferromagnetic materials to prevent undesired interaction with the surrounding magnetic fields. As the beam deflection arrangement 17 has to work in a strong, outer magnetic field, it has been modified compared with other conventional beam deflection arrangements. To be able to deflect the pulsed electron beam 13 in a small space, the beam deflection arrangement 17 must generate strong magnetic fields. To reduce the power loss, the magnetic field of the beam deflection arrangement 17 is a pulsed magnetic field which is synchronized with the pulsed electron beam 13. For this purpose the beam deflection arrangement 17 is connected to a beam deflection control unit 18 which is also connected to the accelerator control unit 12. The deflected electron beam 13 hits the target anode 19 and generates an X-ray beam that emerges from the target anode in the beam elongation along an X-ray beam path. The X-ray beam is homogenized by the homogenizing body 22. The collimator 23 is arranged in an annular slot between the distanced partial gradient coils 21A, 21B in the X-ray beam after the target anode 19. The proximity to the irradiation target thus achieved improves the radiation luminance and the effectiveness of the collimator 23. The collimator 23 enables the direction of the X-ray beam and the cross-section of the X-ray beam to be influenced. For this purpose the collimator 23 incorporates moveable adjusters 24, which permit the X-ray beam to pass only in a certain direction, e.g. only parallel to the radial axis 26 or up to at most in one direction through an angle α away from the axis 26, and only with a certain cross-section. It is also possible to set the adjusters 24 of the collimator 23 in such a way that no X-ray beams can pass parallel to the axis 26 and only angled X-ray beams in one direction through certain angles away from the axis 26 can pass through. To control the adjusters 24 the collimator 23 is connected to a collimator control unit 25. Such collimators are adequately known. By way of example reference can be made to multi-leaf collimators. They make it possible to perform intensity modulated radiation therapy (IMRT), in which the size, shape and intensity of the X-ray beam can be optimally adapted to the irradiation target. In particular IMRT also enables the irradiation center to be positioned outside the rotational axis of the radiation therapy device. The X-ray beam penetrates the examination subject, in this case the patient P, and the X-ray beam path runs through a diagnosis volume D of the magnetic resonance diagnosis part 3. To minimize the local dose of radiation outside the irradiation target volume, the radiation therapy part rotates around the axis 15 of the main magnetic field. As a result, the full dose is applied only in the irradiation center B. The collimator 23 constantly adapts the cross-section of the X-ray beam to the actual outline of the irradiation target even during rotation. The gantry 8 is configured for rotation of the radiation therapy part. A gantry control unit 29 controls the movement of the radiation therapy part 5. As an example the radiation therapy part 5 is shown as radiation therapy part 5′ after rotation through 180°. The gantry control unit 29, the collimator control unit 25, the beam deflection control unit 18, the accelerator control unit 12 and the control unit 31 are connected to each other so that the diagnosis data collected by the magnetic resonance diagnosis part, for example the three-dimensional shape of the irradiation target, the rotational position of the radiation therapy part, as well as the collimator settings with regard to cross-section and direction of the X-ray beam and the generation of pulsed beams described above can be coordinated with each other. The patient bed 6 is preferably moveable in three spatial directions so that the target area of the irradiation can be positioned precisely in the irradiation center B. For this purpose the control unit 32 is expediently configured for controlling a movement of the patient bed. FIGS. 2 to 4 show segments of further exemplary conventional configurations of a combined radiation therapy and magnetic resonance unit as described in US2008/0208036 which may be improved by inclusion of a beam deflection arrangement. In the exemplary configurations shown in particular the arrangement of a respective radiation therapy part 5, 105, 205, 305 varies from the exemplary embodiment in FIG. 1. For the sake of clarity, therefore, only the upper section of a main magnet 110, 210, 310 of the combined radiation therapy and magnetic resonance unit up to about one high-frequency coil 114, 214, 314 of the combined radiation therapy and magnetic resonance unit is shown. The rest of the configuration and its mode of operation are, unless otherwise described, essentially the same as in the example shown in FIG. 1, to which reference is hereby made. FIG. 2 shows a main magnet 110 of the combined radiation therapy and magnetic resonance unit on whose side facing an interior 107 of the combined radiation therapy and magnetic resonance unit a gradient coil system 120 is arranged. The gradient coil system 120 comprises in particular primary coils 121 and secondary coils 122. Between primary coils 121 and secondary coils 122 a free space is located in which the radiation therapy part 105 of the combined radiation therapy and magnetic resonance unit is arranged. Such a distanced arrangement of the primary and secondary coils 121 and 122 increases the efficiency of the gradient coil system 120. In addition, high-frequency coils 114 are arranged on the side of the gradient coil system facing the interior 107. The gradient coil system 120 or at least the primary coils 121 as shown in the example in FIG. 1 can be divided into two partial gradient coils 121A, 121B and arranged in such a way that at least parts of the radiation therapy part 105 can move in an annular space between the parts in a rotation of the radiation therapy part 105 around the axis of the main magnetic field. In this case the high-frequency coils 114 are also advantageously divided correspondingly into two partial high-frequency coils 114A and 114B. Alternatively it is conceivable for the gradient coil system 120 to be configured in such a way that together with the radiation therapy part 105 it can rotate around the axis of the main magnetic field. In this case a division of the gradient coil system 120 or of the primary coils is not absolutely appropriate. It suffices to configure the primary coil 121 in such a way that it can let the radiation therapy part 105 penetrate into the interior 107 at one point in order to emit the therapy beams onto an irradiation center B. The same applies to the high-frequency coils 114. It may be necessary here to compensate for the mechanical turning of the gradient coil system 120 by suitable activation of the gradient currents. Such an electric rotation of gradient fields is, however, a usual capability of standard magnetic resonance systems. Nevertheless, high requirements should be imposed on the accuracy and reproducibility of the rotation. Thanks to its particularly compact design this exemplary embodiment gives the patient an exceptional amount of room in the interior 107. Advantageously, a collimator of the radiation therapy part 105 is incorporated in a particularly flat configuration in the exemplary embodiment shown in FIG. 2 in order to give the patient even more room in the interior 107 of the combined radiation therapy and magnetic resonance unit. FIG. 3 presents a segment of a further combined radiation therapy and magnetic resonance unit. A gradient coil system 220 is arranged on the side of a main magnet 210 facing an interior 207 of the combined radiation therapy and magnetic resonance unit. Standard components can be used for the main magnet 210 and the gradient system 220, which among other things reduces cost. Again on the side of the gradient system 220 facing the interior 207 high-frequency coils 214 are arranged. Between the gradient system 220 and the high-frequency coils 214, however, adequate space is left in order to arrange a radiation therapy part 205 of the combined radiation therapy and magnetic resonance unit between the gradient system 220 and the high-frequency coils 214. During irradiation of an irradiation center B the radiation therapy part 205 rotates around the main magnetic field axis of the combined radiation therapy and magnetic resonance unit. In a similar way as in the structure of FIG. 2 the high-frequency coils 214 can here too either be divided into two partial high-frequency coils 214A and 214B in such a way that at least parts of the radiation therapy part 205 can move in an annular gap between the partial high-frequency coils 214A and 214B. Alternatively, the high-frequency coils 214 can be rotated with the radiation therapy part 205. FIG. 4 shows schematically a segment of a further combined radiation therapy and magnetic resonance unit. In this case, high-frequency coils 314 are arranged within a gradient system 320 which itself is arranged within a main magnet 310. A radiation therapy part 305 is arranged on the side facing an interior 307 of the combined radiation therapy and magnetic resonance unit. As in the arrangements presented above the radiation therapy part 305 rotates during irradiation around the main magnetic field axis of the combined radiation therapy and magnetic resonance unit. In this exemplary embodiment no particular structural measures are necessary with regard to the gradient system 320 and the high-frequency coils 314 to make this rotational movement of the radiation therapy part possible. Advantageously the inner radius of the high-frequency coils 314 is as big as possible and the radiation therapy part is as flat as possible so that the patient is not cramped in the interior 307. The radiation therapy part 105, 205, 305 of the structures in FIGS. 2 to 4 in each case incorporates essentially the same construction as the radiotherapy part 5 shown in FIG. 1. For the sake of clarity the individual components are not shown again. The rotational movement of the radiation therapy parts 105, 205, 305 and/or the gradient coil system 120, 220, 320 and/or the high-frequency coils 114, 214 is indicated in each case by a broken-line arrow. If necessary, in the structures of FIGS. 2, 3 and 4 the radiation therapy part 105, 205, 305 and the magnetic resonance part, in particular the gradient system 120, 220, 320 and/or the high-frequency coils 114, 214, 314, are not operated at the same time but are alternated in order to exclude possible disruptive interaction, in particular between moving parts of the radiation therapy part 105, 205, 305 and electromagnetic alternating fields of the magnetic resonance part. It is an object to provide an improved beam deflection arrangement for a combined radiation therapy and magnetic resonance unit for example as described above. In a radiation therapy and magnetic resonance unit, a magnetic resonance diagnosis part is provided. A radiation therapy part is provided for irradiation of an irradiation area within an interior of the diagnosis part. The radiation therapy part comprises a beam deflection enclosure for deflecting an electron beam toward an axis of the diagnosis part from an initial trajectory parallel to the axis. The beam deflection enclosure comprises a first magnetic field in a region of the beam deflection enclosure but of opposite direction and effective to cancel a main magnet field of the diagnosis part. A second magnet field is directed perpendicular to a trajectory of the electron beam to cause the electron beam to be deflected inward towards the axis. Further advantages and details of the exemplary embodiment will emerge as described below and with reference to the drawing. The examples listed do not represent a restriction of the invention. For the purposes of promoting an understanding of the principles of the invention, reference will now be made to preferred exemplary embodiments/best mode illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and such alterations and further modifications in the illustrated embodiments and such further applications of the principles of the invention as illustrated as would normally occur to one skilled in the art to which the invention relates are included herein. FIGS. 5 to 8 show three examples of possible configurations of beam deflection arrangements 17 which can be used in a radiation therapy part of a combined radiation therapy and magnetic resonance unit, for example as described above. The present exemplary embodiments provide beam deflection arrangements in which the electron beam is not subjected to the magnetic field of the main magnet as its path is deflected. According to the present exemplary embodiments, this is achieved by applying a cancelling field, in the opposite direction to the main magnet field, so that the effective magnetic field in the region of the electron beam deflection is approximately zero, and further applying a deflecting magnetic field to cause the required deflection of the electron beam. A stream of electrons moving through a magnetic field is subjected to a force which will deflect the path of the electrons. US 2008/0208036 describes various arrangements of beam deflection arrangement in which the electron beam is exposed to the main magnet field as well as to a further magnetic field applied for the purpose of deflecting the electron beam. This causes the electron beam to be deflected in a complex path, akin to a conical spiral. Modelling of such a path is difficult, and construction of deflection arrangements to achieve such a path is also difficult. According to the preferred embodiments, by cancelling the main magnet background field in the region of the deflection path of the electron beam, the electron beam may follow a simpler deflection trajectory, in two-dimensions only. Such a deflection path is more easily modelled, and the arrangement to effect such a deflection is simpler to produce. FIG. 5 illustrates the concept of a first embodiment of the present invention. As shown, the electron beam 13 is initially travelling in a direction parallel to the main magnet field B0. As such, the path of the electron beam is not affected by the main magnet field. A magnetic arrangement 505 causes deflection of the path of the electron beam, such that it hits target anode 19 to cause emission of X-rays. According to this embodiment of the invention, magnetic arrangement or enclosure 505 encloses a volume 510 within which cancelling field Bc is generated. Cancelling field Bc is essentially of equal magnitude to the main magnet field B0 in the volume 510, but directed in the opposite direction. The overall effect is that fields B0 and Bc cancel each other out, leaving volume 510 essentially free of background field. Magnetic arrangement 505 also generates a deflection field Bd, directed perpendicular to the direction of travel of the electron beam. This deflection field has the effect of deflecting the electron beam 13 through an angle of 90°, in a plane, onto target 19. Magnetic arrangement 505 preferably extends to target 19, to prevent exposure of the electron beam 13 to the background field B0 while the electron beam is travelling perpendicular to the main magnet field. If the electron beam were exposed to the main magnet field in that region, the beam would be deflected away from the target. The deflection field Bd is represented in conventional notation as being directed away from the viewer in FIG. 5, and is preferably of constant intensity throughout the volume 510, leading the electron beam to follow an arc of radius ρ. The electron beam is deflected through 90°, and its momentum in the original direction of travel has become zero by the time it hits the target 19. FIG. 6 shows a wire-frame representation of the shape of magnetic arrangement 505 and the enclosed volume 510 in an example embodiment. FIG. 7 shows a possible electrical arrangement of conductors, on the surface of a magnetic arrangement 505 of the shape illustrated in FIG. 6. The conductors 515 as shown have been positioned as calculated by a computer simulation to produce a combined magnetic field equal to the sum of the cancellation field Bc and the deflection field Bd. As will be appreciated by those skilled in the art, the required arrangement of conductors 515 will vary according to several factors, including the required radius of deflection ρ, the energy of the incoming electron beam 13 and the strength of the main magnet field B0. FIG. 8 shows a deflection arrangement 17 according to another embodiment of the present invention. According to this invention, a separate field cancelling magnet 805 is provided. This may comprise an electromagnet, such as a pair of coils arranged to generate a magnetic field Bc of equal magnitude, but opposite direction, to the main magnet field B0 in the region of the deflection of the electron beam 13. However, it may be preferred to use a permanent magnet arrangement to generate Bc, provided that it does not cause loss of homogeneity in an imaging region of the main magnet. With the main magnet field B0 effectively cancelled in the region of the beam deflection, the magnetic arrangement 810 need only deflect the electron beam as if in a zero background magnetic field. In the arrangement of FIG. 8, a magnetic arrangement 810 of similar shape to the magnetic arrangement 505 of FIGS. 6-7 is provided, enclosing a volume 815. It only provides deflection field Bd. As with the arrangement of FIGS. 6-7, magnetic arrangement 810 generates a deflection field Bd, directed perpendicular to the direction of travel of the electron beam 13. This deflection field has the effect of deflecting the electron beam through an angle of 90°, in a plane, onto target 19. The electron beam's momentum in the original direction of travel has become zero by the time it hits the target 19. Magnetic arrangement 810 preferably extends to target 19, to prevent exposure of the electron beam 13 to the background field B0 while the electron beam is travelling perpendicular to the main magnet field. If the electron beam were exposed to the main magnet field in that region, the beam would be deflected way from the target. The deflection field Bd is represented in conventional notation as being directed away from the viewer in FIG. 8, and is preferably of constant intensity throughout the volume 815, leading the electron beam to follow an arc of radius ρ. Computer simulations, well within the capability of those skilled in the art, may be performed to determine an appropriate pattern of conductors, and an appropriate DC current, to apply to the magnetic arrangement 810. The magnetic arrangement must provide the required deviation for the electron beam, yet not provide a stray field so strong that it interferes with the homogeneity of the main magnet field. Depending on the chosen operation of the radiation therapy part, the magnetic arrangements 505, 810, 805 may be operated intermittently, as a pulsed magnet. Although preferred exemplary embodiments are shown and described in detail in the drawings and in the preceding specification, they should be viewed as purely exemplary and not as limiting the invention. It is noted that only preferred exemplary embodiments are shown and described, and all variations and modifications that presently or in the future lie within the protective scope of the invention should be protected. |
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abstract | A scattered ray absorption grid enhancing a scattered ray absorption property without increasing costs is provided. A grid portion of the scattered ray absorption grid is constituted by use of plate members obtained in such a manner that a powder containing tungsten 50% by weight or more is hardened with a binder so that the powder has a spatial filling rate of 40% or more. |
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055442048 | description | SPECIFIC DESCRIPTION FIG. 1 shows a nuclear reactor having a ring-shaped reactor core 10, a central column 11 and a main supply of coolant represented by the inlets 12 and 13 extending to a space 14 distributing the main coolant flow to passages 15 opening into the core 10. The main body of fissionable fuel is received in the core and the reactive zone is represented between the horizontal planes 16 and 17 and within the annular region represented by the generatrices 18 and 19. At the upper end of the reactor, passages 20 carry the heated coolant to an annular space 21 whence the coolant is lead away via the ducts 22 and 23 to the remainder of the main coolant circulation which can include an energy recovery system for producing electrical energy, heat-exchangers or the like for lowering the temperature of the coolant. According to the invention, a reactivity-controlling system is provided in the form of a vertical compartment 25 within the central column 11, an upper portion of which is in the reactive zone and a lower portion of which is outside the reactive zone and the neutron flux thereof. The compartment 25 is disposed above the annular space 26 which also forms a distributing space for a portion of the coolant which can be admitted into this space via an annular sieve structure 27 and axial-sieve structures 28. The coolant flow through the compartment 25 is branched from the main coolant stream as represented by the arrows 29. At the upper end of the chamber 25 is another sieve structure 30 which screens nuclear-fuel particles 31 in the compartment 25 from the branched coolant stream. The branched coolant stream which fluidizes masses of fuel particles 31 in the compartment 25 and forms an expanded bed thereof in the reactive zone, passes into a collecting chamber 32 from which the branched coolant returns at 33 to the main coolant flow. Within the compartment 25 gravity acts on the coated fuel particles 31 in the direction of arrow 34 and thus the flow of branched coolant through this compartment is in the direction of arrow 35. Arrows 36 represent the main coolant flow through the reactor. As can be seen from FIG. 1, moreover, the sieve-like structures 27, 28, 30 are so constructed that the fuel particles 31 cannot pass from the compartment 25 either upwardly or downwardly, but can be held suspended in the reaction region as long as the main coolant flow is sustained and, of course, as long as there is a branched fluidizing coolant flow. As can be seen from FIG. 2, however, should there be a failure of the coolant flow (note the lack of arrows 36 in the reactor), an accumulation S of the particles due to gravity in the space 26 removes the fuel particles from the reactive region and thus reduces the reactivity by the order of 0.5 to 1%, leading to hot shutdown of the reactor. In the embodiment of FIGS. 1 and 2, the branched flow passes through a region of the reactor which is free from nuclear fuel until fuel particles are entrained into it namely the upper part of column 11 above the particle-collecting space in arriving at and upon departing from the compartment 25, and in the case of a breeder reactor, can pass through the breed-blanket shell and in the case of a thermal reactor through the reflector as may be desired. The space 26 and the volume of the fuel particles S is such that the reduction in reactivity is the 0.5 to 1% indicated. |
abstract | Systems and methods for dispensing radioactive liquids using a liquid dispensing apparatus are described. The apparatus includes a support arm rotatable about a rotation axis, an actuator operatively connected to the support arm and configured to at least one of rotate the support arm about the rotation axis and displace the support arm in a direction parallel to the rotation axis, and a pipette assembly mounted to the support arm. The pipette assembly includes a pipette tip defining an opening through which liquids are aspirated and dispensed, a piston, and a stepper motor operatively connected to the piston to control linear displacement of the piston. |
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abstract | Image evaluation method capable of objectively evaluating the image resolution of a microscope image. An image resolution method is characterized in that resolution in partial regions of an image is obtained over an entire area of the image or a portion of the image, averaging is performed over the entire area of the image or the portion of the image, and the averaged value is established as the resolution evaluation value of the entire area of the image or the portion of the image. This method eliminates the subjective impressions of the evaluator from evaluation of microscope image resolution, so image resolution evaluation values of high accuracy and good repeatability can be obtained. |
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abstract | The invention relates to a method for checking an irradiation installation in which a dose distribution is deposited in a target object by means of a treatment beam, said method comprising the following steps: an irradiation planning data record optimized for the irradiation of a moving target volume is provided; a movement signal that reproduces a movement of the target volume is provided; a phantom is irradiated, said phantom being formed for detecting a dose distribution deposited in the phantom during or after the irradiation, using the control parameters stored at the irradiation planning data record and the movement signal; a dose distribution deposited in the phantom is determined; a dose distribution to be expected is calculated on the basis of parameters that are related to the control of the irradiation installation during the irradiation; and the determined dose distribution deposited in the phantom is compared to the calculated dose distribution to be expected. The invention also relates to a corresponding device and an irridation installation comprising such a device. |
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048270636 | summary | The invention relates to a nuclear reactor fuel assembly having mutually parallel fuel rods and guide tubes for control rods, two lattice-like spacers with mesh openings through each of which one fuel rod is guided and retained in a force-locking manner or one guide tube is guided and secured, an additional lattice secured at least to one of the guide tubes and disposed between the two spacers as seen in the longitudinal direction of the fuel rods and the guide tubes, the additional lattice having mesh openings, and turbulence-promoting vanes protruding beyond the sides of the mesh openings, one fuel rod being guided with play or one guide tube being guided through each of the mesh openings. A nuclear reactor fuel assembly of this type is known from European Patent Application No. 0 148 452, corresponding to U.S. Application Ser. No. 567,448, filed Dec. 30, 1983. The additional lattice of this prior art fuel assembly has square mesh openings formed therein and is made of inner sheet-metal ribs that pass through one another at right angles. On the outside of the fuel assembly, the additional lattice has four outer ribs that define a square periphery of the additional lattice and are secured on the inner sheet-metal ribs that are at right angles thereto. The surface of the additional lattice formed by the inner sheet-metal ribs has rigid bearing nubs thereon for the fuel rods in the mesh openings, and each trailing edge of the holes for the fuel rods formed by an inner sheet-metal rib is provided with a single turbulence-promoting vane thereon. The turbulence-promoting vanes serve to mix the coolant, such as water, that flows longitudinally through the nuclear reactor fuel assembly in a nuclear reactor, for example a pressurized water reactor. Mixing of the coolant is intended to prevent the coolant from being unevenly heated over the cross section of the fuel assembly and to prevent the particular fuel rods of the fuel assembly that are heated to the greatest extent and thus are undergoing the severest stress from being inadequately cooled. However, the mixing lattice leads to considerable pressure losses in the coolant. It is accordingly an object of the invention to provide a nuclear reactor fuel assembly, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which reduces the pressure losses. With the foregoing and other objects in view there is provided, in accordance with the invention, a nuclear reactor fuel assembly, comprising mutually parallel fuel rods and guide tubes for control rods, two lattice-like spacers having mesh openings formed therein, one of the fuel rods or one of the guide tubes being guided and secured in each of the mesh openings, an additional lattice secured at least to one of the guide tubes between the two spacers as seen in the longitudinal direction of the fuel rods and the guide tubes, the additional lattice having mesh openings formed therein defining sides of the mesh openings and a smooth and flat surface of the additional lattice in the mesh openings, turbulence-promoting vanes protruding beyond the sides of the mesh openings formed in the additional lattice, one of the fuel rods being guided with play or one of the guide tubes being guided through each of the mesh openings formed in the additional lattice, and brackets gripping the additional lattice between at least one of the fuel rods or the guide tubes at the outside of the fuel assembly. It has been demonstrated that in this way, uniform heating of the coolant in the nuclear reactor is attained even if the size and/or the number of turbulence-promoting vanes on the spacers is reduced. The spacers may even not have any turbulence-promoting vanes at all, which leads to particularly low pressure losses in the coolant. Spacers that do not have turbulence-promoting vanes can also be manufactured more economically. In accordance with another feature of the invention, the additional lattice has mutually parallel leading and/or trailing edges with zig-zag portions, each of the zig-zag portions being compactly disposed in the plane of one of the sides of one of the mesh openings formed in the additional lattice. In accordance with a further feature of the invention, the additional lattice has mutually parallel leading and/or trailing edges on which the turbulence-promoting vanes are disposed, each of the edges having ends and being associated with one of the sides of the additional lattice, each two adjacent turbulence-promoting vanes on one of the mutually parallel edges of the additional lattice being twisted in mutually opposite directions about the longitudinal direction of the fuel rods and the guide tubes, located on one of the edges of one of the mesh openings of the additional lattice for a fuel rod, and tapered to a point and protruding beyond the side of the mesh opening associated with the edge at one of the ends of the edge. This structure produces a more extensive evening out of the temperature of the coolant flowing through the fuel assembly in a nuclear reactor, while at the same time having low pressure losses for the coolant. In accordance with an added feature of the invention, the additional lattice is spaced apart from the two first-mentioned spacers by unequal distances. As a result, turbulence caused by spacers in the liquid coolant flowing through the fuel assembly in a nuclear reactor calms down, so that the coolant once again flows to the additional lattice in a uniform flow, and the turbulence-promoting vanes of the additional lattice can become optimally effective. A better transfer of heat to the coolant then takes place on the way to the next spacer. In accordance with a concomitant feature of the invention, the zig-zag portions of the leading and/or trailing edges are mutually staggered. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a nuclear reactor fuel assembly, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. |
abstract | Detecting diversion of spent fuel from Pressurized Water Reactors (PWR) by determining possible diversion including the steps of providing a detector cluster containing gamma ray and neutron detectors, inserting the detector cluster containing the gamma ray and neutron detectors into the spent fuel assembly through the guide tube holes in the spent fuel assembly, measuring gamma ray and neutron radiation responses of the gamma ray and neutron detectors in the guide tube holes, processing the gamma ray and neutron radiation responses at the guide tube locations by normalizing them to the maximum value among each set of responses and taking the ratio of the gamma ray and neutron responses at the guide tube locations and normalizing the ratios to the maximum value among them and producing three signatures, gamma, neutron, and gamma-neutron ratio, based on these normalized values, and producing an output that consists of these signatures that can indicate possible diversion of the pins from the spent fuel assembly. |
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summary | ||
claims | 1. A method for determining a material composition for a thin film layer in a test sample, the method comprising:applying an electron probe microanalysis (EPMA) operation to the thin film layer to generate a set of characteristic x-rays; andgenerating an output value for the material composition based on the set of characteristic x-rays and a measured thickness value for a test layer in the test sample,wherein the test layer is the thin film layer, wherein the material composition is material phase, and wherein generating the output value comprises:identifying a first one of a plurality of trial phases for the thin film layer defining an expected composition that is substantially consistent with a calculated composition, the expected composition being based on the first one of the plurality of trial phases, a density for the test layer defined by the first one of the plurality of trial phases, and the measured thickness value for the test layer, and the calculated composition being based on the set of characteristic x-rays, the measured thickness value for the thin film layer, and the density for the test layer; andproviding the first one of the plurality of trial phases as the output value. 2. The method of claim 1, wherein identifying the first one of the plurality of trial phases comprises:selecting a test one of the plurality of trial phases;determining a density for the test one of the plurality of trial phases;deriving an expected composition for the test one of the plurality of trial phases based on the density and the measured thickness value, and the test one of the plurality of trial phases;comparing the expected composition of the test one of the plurality of trial phases to a calculated composition of the test one of the plurality of trial phases, the calculated composition of the test one of the plurality of trial phases being derived from the set of characteristic x-rays, the measured thickness value, and the density;repeating the steps of selecting, determining, deriving, and comparing until the expected composition for the test one of the plurality of trial phases is consistent with the calculated composition of the test one of the plurality trial phases; andassigning the test one of the plurality of trial phases as the first one of the plurality of trial phases. 3. The method of claim 2, wherein identifying the first one of the plurality of trial phases further comprises updating the measured thickness value according to the test one of the plurality of trial phases. 4. The method of claim 1, wherein identifying the first one of the plurality of trial phases comprises:generating a set of expected compositions for the plurality of trial phases, each of the set of expected compositions being determined by one of the plurality trial phases, a density defined by the one of the plurality of trial phases and the measured thickness value;generating a set of calculated compositions for the plurality of trial phases, each of the set of calculated compositions being determined by the set of characteristic x-rays, the measured thickness value, and the density defined by the one of the plurality of trial phases;comparing each of the set of expected compositions for the plurality of trial phases to an associated one of the set of expected compositions for the plurality of trial phases to determine the first one of the plurality of trial phases. 5. The method of claim 4, wherein generating a set of expected compositions for the plurality of trial phases comprises adjusting the measured thickness value based on the one of the plurality of trial phases, andwherein generating a set of calculated compositions for the plurality of trial phases comprises adjusting the measured thickness value based on the one of the plurality of trial phases. 6. The method of claim 1, wherein the thin film layer comprises one of a silicide layer formed over a single crystalline silicon substrate, a phosphorous-doped polysilicon layer formed over the single crystalline silicon substrate, a silicon germanium boron layer formed over the single crystalline silicon substrate, and a silicon oxy-nitride layer formed over the single crystalline silicon substrate. 7. An electron probe microanalysis (EPMA) tool comprising:an e-beam generator for directing an e-beam at a test sample, the test sample comprising a thin film formed on a substrate;an x-ray detector for measuring a set of characteristic x-rays generated by the test sample in response to the e-beam; andmaterial composition determination logic for determining a material composition of the thin film, the material composition determination logic comprising:compilation logic for compiling measured thickness data for a test layer in the test sample and the set of characteristic x-rays; andanalysis logic for determining a material composition for the thin film based on the measured thickness data for the test layer and the set of characteristic x-rays,wherein the test layer is the thin film, and wherein the analysis logic comprises:logic for identifying a first one of a plurality of trial phases for the thin film, the first one of the plurality of trial phases defining an expected composition that is substantially consistent with a calculated composition for the first one of the plurality of trial phases; andlogic for providing the first one of the set of trial phases as the material phase of the thin film,wherein the expected composition is based on the first one of the plurality of trial phases, a density for the test layer defined by the first one of the plurality of trial phases, and the measured thickness data for the test layer, andwherein the calculated composition for the first one of the plurality of trial phases is based on the set of characteristic x-rays, the density, and the measured thickness data for the test layer. 8. The EPMA tool of claim 7, wherein the logic for identifying the first one of the plurality of trial phases comprises:logic for selecting a test one of the plurality of trial phases;logic determining a density for the test one of the plurality of trial phases;logic for generating an expected composition for the test one of the plurality of trial phases based on the density, the measured thickness data for the test layer, and the test one of the plurality of trial phases;logic for comparing the expected composition of the test one of the plurality of trial phases with a calculated composition of the test one of the plurality of trial phases, the calculated composition of the test one of the plurality of trial phases being derived from the set of characteristic x-rays, the measured thickness data for the test layer, and the density;logic for repeatedly applying the logic for selecting, the logic for determining, the logic for generating, and the logic for comparing until the expected composition of the test one of the plurality of trial phases is consistent with the calculated composition of the test one of the plurality of trial phases; andlogic for assigning the test one of the plurality of trial phases as the first one of the plurality of trial phases. 9. The EPMA tool of claim 7, further comprising a material phase database for providing the set of trial phases. 10. The EPMA tool of claim 7, further comprising a communications interface for receiving at least one of the set of trial phases and the thickness of the thin film. 11. The EPMA tool of claim 7, wherein the thin film comprises one of a silicide layer formed over a single crystalline silicon substrate and a phosphorous-doped polysilicon layer formed over the single crystalline silicon substrate. 12. A system for determining a material composition of a thin film in a test sample, the system comprising:means for compiling a set of characteristic material data generated by directing a probe beam at the thin film, the means for compiling the set of characteristic material data comprising an electron probe microanalysis module;means for compiling measured thickness data for a test layer in the test sample; andmeans for determining the material composition using the set of characteristic material data and the measured thickness data,wherein the test layer comprises the thin film, andwherein the means for determining the material composition comprises:means for identifying a first one of a plurality of trial phases for the thin film layer, the first one of the plurality of trial phases defining an expected composition that is substantially consistent with a calculated composition for the first one of the plurality of trial phases; andproviding the first one of the plurality of phases as the material composition,wherein the expected composition is based on the first one of the plurality of trial phases, a density for the test layer defined by the first one of the plurality of trial phases, and the measured thickness data for the test layer, andwherein the calculated composition for the first one of the plurality of trial phases is based on the set of characteristic material data, the density, and the measured thickness data for the test layer. 13. The system of claim 12, further comprising means for accessing a material phase database to compile the set of trial phases. 14. The system of claim 12,wherein the probe beam comprises an e-beam, andwherein the set of characteristic material data comprises a set of characteristic x-rays. 15. The system of claim 12, further comprising means for performing optical metrology on the test sample to generate the measured thickness data for the test layer. |
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claims | 1. An optical grating, comprising:a substrate having a surface with a periodic structure, wherein the structure is embodied to diffract incident radiation with a predetermined wavelength (λT) into a predetermined order of diffraction, anda coating applied onto the periodic structure, wherein the coating has at least one layer that is embodied to suppress the diffraction of the incident radiation into at least one higher order of diffraction than the predetermined order of diffraction,wherein at least one layer of the coating is embodied as a total reflection layer with a critical angle (αT), wherein the critical angle is smaller than an angle of incidence (α) of the incident radiation for the predetermined order of diffraction and is greater than the angle of incidence (α) of the incident radiation for at least one higher order of diffraction. 2. The optical grating as claimed in claim 1, wherein the structure is embodied to diffract extreme ultraviolet (EUV) radiation with the predetermined wavelength (λT) into the predetermined order of diffraction. 3. The optical grating as claimed in claim 1, wherein the structure is embodied to diffract the incident radiation with the predetermined wavelength (λT) into the first order of diffraction. 4. The optical grating as claimed in claim 1, wherein the total reflection layer is formed from a material that has an absorption length of more than 10 nm at the predetermined wavelength (λT). 5. The optical grating as claimed in claim 4, wherein the total reflection layer is formed from a material that has an absorption length of more than 50 nm at the predetermined wavelength (λT). 6. The optical grating as claimed in claim 4, wherein the material of the total reflection layer is selected from the group consisting of: Zr, Pd, C, Ru, Mo, Nb, Sn, Cd, or alloys, carbides, nitrides, oxides, borides or silicides thereof. 7. The optical grating as claimed in claim 1, wherein at least one layer of the coating is embodied as an absorber layer which has a greater absorption length for the predetermined order of diffraction than for at least one higher order of diffraction. 8. The optical grating as claimed in claim 7, wherein the absorber layer has a critical angle (αT) that is greater than an angle of incidence (α) of the incident radiation for the predetermined order of diffraction. 9. The optical grating as claimed in claim 7, wherein the material of the absorber layer is selected from the group consisting of: Si, Mo, or carbides, nitrides, oxides, or borides thereof, and MoSi2. 10. The optical grating as claimed in claim 7, wherein the absorber layer is applied onto the total reflection layer. 11. The optical grating as claimed in claim 1, wherein the coating has at least one layer that is embodied to diffract incident radiation with a first polarization state perpendicular to a plane of incidence onto the optical grating more strongly in the predetermined order of diffraction than incident radiation with a second polarization state that is perpendicular to the incident radiation with the first polarization state. 12. The optical grating as claimed in claim 1, wherein the coating has at least one layer a thickness (d2) and a material of which are selected such that constructive interference occurs for the incident radiation with the predetermined wavelength (λL) in the predetermined order of diffraction and destructive interference occurs for at least one higher order of diffraction. 13. The optical grating as claimed in claim 1, wherein the predetermined wavelength (λT) lies in a wavelength range between 13 nm and 16 nm. 14. The optical grating as claimed in claim 13, wherein the coating has a total reflection layer made of Ru, Zr, Pd, Nb, Mo, or alloys, carbides, nitrides, oxides, borides, or silicides thereof, or C, and an absorber layer, applied to the layer of total internal reflection, made of Si, SiC, Si3N4, SiO, or SiO2. 15. The optical grating as claimed in claim 1, wherein the predetermined wavelength (λT) lies in a wavelength range between 6 nm and 8 nm. 16. The optical grating as claimed in claim 15, wherein the coating has a total reflection layer made of Cd or Sn and an absorber layer made of Mo. 17. The optical grating as claimed in claim 1, wherein the periodic structure comprises a blaze structure. 18. The optical grating as claimed in claim 1, having a reflectivity of more than 50% for incident radiation with the predetermined wavelength (λT) in the predetermined order of diffraction. 19. An optical arrangement, comprising:a light source configured to produce radiation andat least one optical grating as claimed in claim 1 and arranged to diffract the radiation of the light source with the predetermined wavelength (λT) into the predetermined order of diffraction. 20. The optical arrangement as claimed in claim 19, configured as an EUV lithography system, wherein the light source is configured to produce EUV radiation. 21. The optical arrangement as claimed in claim 19, wherein the incident radiation is incident on the optical grating at at least one angle of incidence (α) in an angle of incidence range (Δα) between 70° and 90°. 22. An optical grating, comprising:a substrate having a surface with a periodic structure, wherein the structure is embodied to diffract incident radiation with a predetermined wavelength (λT) into a predetermined order of diffraction, anda coating applied onto the periodic structure, wherein the coating has at least one layer that is embodied to suppress the diffraction of the incident radiation into at least one higher order of diffraction than the predetermined order of diffraction,wherein the coating has at least one layer that is embodied to diffract incident radiation with a first polarization state perpendicular to a plane of incidence onto the optical grating more strongly in the predetermined order of diffraction than incident radiation with a second polarization state that is perpendicular to the incident radiation with the first polarization state. |
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abstract | A target unit for producing Cu67 radioisotope is described herein, and comprises a cage body releasably coupled to a screw-on cap; and a ceramic capsule containing a solid Zn68 target ingot and having one open end and one closed end and defining an interior chamber for the target ingot. The ceramic capsule is releasably contained between the cage body and the screw-on cap with a lid disposed on the open end of the capsule and a washer positioned between the lid and the screw-on cap. The screw-on cap and the washer provide a water-tight seal between the lid and the capsule. The interior of the capsule is in intimate physical contact with the target ingot; and the Zn68 of the target ingot is free of traces of residual oxygen that interfere with contact of the Zn68 to the capsule. |
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050358529 | claims | 1. An elongated guide tube support pin for removably mounting a lower flange of a control rod guide tube to a core plate having a bore, wherein a variable shear load is applied to said guide tube relative to said core plate, comprising: a first pin portion mountable on the lower flange of the guide tube; and a second pin portion receivable within the bore of the core plate and frictionally engageable therein, said second pin portion having a split leaf section including an upper portion and a lower portion whose outer diameter is substantially the same as the inner diameter of the bore, and a split intermediate section having a tapered outer diameter for causing stresses in said split leaf section to be substantially uniform wherever a shear load is applied to the support pin. a first pin portion mountable on the guide tube lower flange; and a second pin portion resiliently receivable within said upper core plate bore, said second pin portion including a solid body section adjacent said first pin portion and having an outer diameter which is accommodated by said bore by a close clearance fit, and a split leaf section including a split intermediate section extending from said solid body section and having an outer diameter less than the outer diameter of said solid body section and a split end section extending from said split intermediate section and having a portion that biasingly engages at least a portion of the wall of said bore, said split intermediate section being tapered from a maximum outer diameter adjacent said solid body section to a minimum outer diameter substantially adjacent said split end section such that said support pin is secured within said upper core plate by a fictional fit wherein loads applied transversely to said longitudinal axis of said support pin are reacted to substantially in pure shear by said second pin portion substantially through said solid body section, and wherein the tapered varying outer diameter of said split intermediate section causes the stress through said split leaf section to be substantially constant. at least one support pin comprising a first pin portion mountable on the first structural member, and a second pin portion receivable within the bore; locking means mounted on said support pin for retaining the first structural member against the second structural member; and stress reduction means including a washer disposed around said support pin between said locking means and the first structure member, wherein said washer and said locking means include mutually engaging, rounded surfaces for eliminating bending moments and stresses on said support pin during mounting of said locking means on said support pin. a support pin having a longitudinal axis and comprising a first pin portion mountable on the guide tube lower flange, and a second pin portion receivable within said upper core plate bore, said second pin portion including a solid body section adjacent said first pin portion and having an outer diameter which is accommodated by said bore by a close clearance fit, and a split leaf section including a split intermediate section extending from said solid body section and having a tapered outer diameter less than the outer diameter of said solid body section for reducing stress in said split leaf section, and a split end section extending from said split intermediate section and biasingly engaging at least a portion of the wall of said bore; locking means mounted on said first pin portion of said support pin for retaining the guide tube lower flange between said solid body section of said second pin portion and said locking means; and a washer disposed around said first pin portion between said locking means and the control rod guide tube flange, said washer and said locking means including mutually engaging rounded surfaces for eliminating bending moments and stresses on said support pin during mounting of said locking means on said first pin portion of said support pin. a first pin portion mountable on the first structural member; and a second pin portion receivable within the bore and frictionally engageable therein, said second pin portion having a split leaf section inclining an upper portion and a lower portion whose outer diameter is substantially the same as the inner diameter of the bore, and a split intermediate section having a tapered outer diameter for causing stresses in said split leaf section to be substantially uniform wherever a shear load is applied to the support pin, wherein said upper portion of said second pin portion includes a solid body section between said first pin portion and said split leaf section and having an outer diameter which is accommodated by the bore by a close clearance fit, said split intermediate section outer diameter is less than the outer diameter of said solid body section, and said lower portion of said split leaf section further includes a split end section extending from said split intermediate section and biasingly engaging at least a portion of the wall of the bore to secure said support pin therein by a frictional fit, and wherein shear loads applied transversely to said longitudinal axis of said support pin are secured to substantially in pure shear by said second pin portion substantially through said solid body section. 2. The support pin according to claim 1, wherein said split intermediate section has a maximum diameter at its end adjacent said upper portion and a minimum diameter at its opposite end adjacent to said lower portion. 3. The support pin according to claim 1, wherein said upper portion of said second pin portion includes a solid body section between said first pin portion and said split leaf section and having an outer diameter which is accommodated by the bore by a close clearance fit, said split intermediate section outer diameter is less than the outer diameter of said solid body section, and said lower portion of said split leaf section further includes a split end section extending from said split intermediate section and biasingly engaging at least a portion of the wall of the bore to secure said support pin therein by a frictional fit, and wherein shear loads applied transversely to said longitudinal axis of said support pin are reacted to substantially in pure shear by said second pin portion substantially through said solid body section. 4. A mounting system for removably mounting a lower flange of a control rod guide tube over an opening in an upper core plate of a nuclear reactor comprising at least one elongated support pin mountable on the guide tube lower flange and resiliently receivable in a bore formed in the upper core plate, wherein said support pin has a longitudinal axis and comprises: 5. The mounting system according to claim 4, wherein said mounting system further comprises a plurality of support pins for mounting the lower flange of a control rod guide tube over an opening in the upper core plate of a nuclear reactor. 6. The mounting system according to claim 4, wherein said lower flange of said control rod guide tube is formed with a through-bore and said first pin portion of said support pin is receivable within said through-bore. 7. The mounting system according to claim 4, further comprising locking means for retaining the guide tube lower flange between said solid body section of said second pin portion and said locking means. 8. The mounting system according to claim 7, wherein said first pin portion of said support pin includes and externally threaded section and wherein said locking means includes an internally threaded section which threadedly engages said externally threaded section of said first pin portion. 9. The mounting system according to claim 8, wherein said locking means further includes a locking nut having side walls and said locking nut comprises a crimpable cylindrical section integrally connected to said internally threaded section and extending from the outermost portion of said internally threaded portion. 10. The mounting system according to claim 9, wherein said first pin portion further includes an end section remotely positioned from said second pin portion adjacent said externally threaded section and having a plurality of recesses formed on the external surface, and wherein said crimpable cylindrical section of said locking nut is crimpingly engageable with at least one of said plurality of recesses of said support pin to prevent relative rotation between said locking nut and said support pin. 11. The mounting system according to claim 8, wherein said locking means includes a locking nut having side walls, said first pin portion further includes an end section remotely positioned from said second pin portion adjacent said externally threaded section and having a plurality of recesses formed on the external surface, and said mounting system further comprises crimping means for engaging at least one of said plurality of recesses of said support pin to prevent relative rotation between said locking nut and said support pin. 12. The mounting system according to claim 11, wherein said crimping means includes a crimp cap mounted on said end section of said support pin. 13. The mounting system according to claim 4, wherein said split intermediate section is uniformly tapered such that said split intermediate section is conical. 14. The mounting system according to claim 13, wherein said split intermediate section has a shape that maintains stresses in said support pin below the yield point of said support pin. 15. The mounting system according to claim 13, wherein said split intermediate section includes a plurality of leaves separated by a longitudinal gap, wherein said longitudinal gap extends into said solid body section to increase the flexibility of said support pin. 16. The mounting system according to claim 8, further comprising a washer disposed around said first pin portion between said locking means and the control rod guide tube flange. 17. The mounting system according to claim 16, wherein said washer includes stress reduction means for eliminating bending moments and stresses on said support pin during mounting of said locking means on said first pin portion of said support pin. 18. The mounting system according to claim 17, wherein said stress reduction means includes a concave spherical surface formed on the upper surface of said washer, said spherical surface being shiftable during mounting of said locking means to compensate for nonperpendicular alignment between said support pin and the control rod guide tube flange. 19. A support pin system for removably mounting a first structural member to a second structural member having a bore, said support pin system comprising: 20. The support pin system according to claim 19 wherein said support pin has a longitudinal axis and includes a first pin portion mounted to the first structural member and a second pin portion secured within the bore, said second pin portion having a solid body section adjacent said first pin portion and having an outer diameter which is accommodated by the bore by a close clearance fit and a split leaf section including a split intermediate section extending from said solid body section and having a tapered outer diameter less than the outer diameter of said solid body section and a split end section extending from said split intermediate section and biasingly engaging at least a portion of the wall of the bore, wherein said tapered shape of said split intermediate section lowers stresses in said split leaf section. 21. A mounting system for removably mounting the lower flange of a control rod guide tube over an opening in the upper core plate of a nuclear reactor comprising at least one elongated support pin mounted on the guide tube lower flange and resiliently receivable in a bore formed in the upper core plate, wherein said mounting system comprises: 22. An elongated support pin for removably mounting a first structural member to a second structural member having a bore, wherein a variable shear load is applied to said first structural member relative to said second structural member, comprising: |
claims | 1. A heel effect compensation filterwhich is configured to have a thickness distribution that uniforms an X-ray intensity angular distribution that is nonuniform in a body axis direction of a subject in an X-ray flux irradiated space,the space being formed by an X-ray flux diverging from an anode in a body width direction of the subject and diverging in a shape of an approximate sector in the body axis direction orthogonal to the body width direction due to the X-ray intensity angular distribution affected by a heel effect, when the X-ray flux generated on the anode by irradiating a thermoelectron beam flux from a cathode to the anode is irradiated on the subject through a wedge filter configured to have a cylindrical concave surface with a curve being formed in the body width direction of the subject, whereinthe thickness distribution is defined by Formula 1: ( y ′ z ′ ) = ( L ( θ ) cos θ FFD FCD ( FCD tan θ - L ( θ ) sin θ ) ) ( θ ≤ cone angle ) ( Formula 1 ) where, on a plane containing an irradiation axis of the X-ray flux and a beam irradiation axis of the thermoelectron beam flux, the irradiation axis of the X-ray flux is defined as a Y-axis, and an axis orthogonal to the Y-axis at a distance FCD along the Y-axis in a direction of X-ray flux irradiation is defined as a Z-axis; z′ and y′ represent positions in corresponding axial directions with the proviso that an intersection point of the Z-axis and the Y-axis is defined as an origin point; FFD is defined as a predetermined distance along the Y-axis from a position of the anode; θ is defined as a predetermined angle within a range of a cone angle symmetrically diverging from the position of the anode relative to the irradiation axis of the X-ray flux; and La(θ) is defined as a length in a y′ direction at the angle θ. 2. The heel effect compensation filter according to claim 1, wherein the heel effect compensation filter is separable into pieces and a distance in the heel effect compensation filter through which the X-ray flux transmits during usage is equal to the thickness distribution. 3. The heel effect compensation filter according to claim 1, wherein either of an X-ray flux-incoming side transmissive surface and an X-ray flux-outgoing side transmissive surface is configured as a cylindrical convex surface with a curve being formed in the body axis direction of the subject and the other is configured as a flat surface. 4. The heel effect compensation filter according to claim 1, wherein either of an X-ray flux-incoming side transmissive surface and an X-ray flux-outgoing side transmissive surface is configured as a cylindrical convex surface with a curve being formed in the body axis direction and the other is configured as a cylindrical concave surface with a curve being formed in the body width direction orthogonal to the body axis direction. 5. The heel effect compensation filter according to claim 1, which is employed in an X-ray CT scanner having 32 arrays or more of X-ray detectors. 6. An X-ray irradiator in which a thermoelectron beam flux is irradiated from a cathode to an anode and an X-ray flux generated on the anode is irradiated on a subject, whereinthe heel effect compensation filter according to claim 1 is disposed between the anode and the subject at a predetermined distance,the filter being configured to adjust the X-ray intensity angular distribution of the X-ray flux to become uniform that is nonuniform in a body axis direction of the subject in an X-ray flux irradiated space,the space being formed by the X-ray flux diverging from the anode in a body width direction of the subject and diverging in a shape of an approximate sector in the body axis direction orthogonal to the body width direction due to the heel effect. 7. An X-ray CT scanner in which the X-ray irradiator according to claim 6 is employed. 8. A method for X-ray CT imaging which reduces an artifact of image data obtained by an X-ray CT scanner by employing the heel effect compensation filter according to claim 1 in the X-ray CT scanner and reducing a difference in CT value of the image data obtained along a body axis direction. |
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claims | 1. A motor stand for a primary motor-driven pump unit of a pressurized water nuclear reactor comprising:an upper flange, anda fixing means configured to fix a transverse holding means of said primary motor-driven pump unit, said primary motor-driven pump unit comprising an electric motor having a lower flange configured to engage with said upper flange of said motor stand,wherein said fixing means comprises:an annular element arranged between said upper flange of said motor stand and said lower flange of said motor, said annular element comprising at least one radial excrescence formed by an appendage having a top face and a bottom face, said appendage being formed by two adjacent projecting bosses and a recessed zone formed between said two adjacent projecting bosses, wherein said appendage is formed integrally with said annular element and shares a common plane with said annular element;an upper plate and a lower plate fastened to the appendage and covering both faces of said appendage, said upper plate and lower plate each comprising a central bore opening into the recessed zone therein through which an axis is configured to be mounted; anda space delimited by said recessed zone and bordered by the upper plate and the lower plate, said space being configured to receive and to link said transverse holding means to said fixing means via said axis. 2. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 1, wherein said upper plate and said lower plate are each formed by an angle comprising two lateral branches and the central bore. 3. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 2, wherein the fixing means comprises the axis passing through the central bore of said angles and configured to pass through said transverse holding means so as to fix the fixing means to said transverse holding means. 4. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 2, wherein said angles comprise bores passing through said lateral branches configured to receive screwing means. 5. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 4, wherein at least one of the two angles comprises means for blocking the rotation of said screwing means. 6. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 5, wherein said means for blocking the rotation of said screwing means is formed by grooves located level with each of the lateral branches. 7. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 4, wherein at least one of the two angles is manufactured with said annular element. 8. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 1, wherein said annular element is rendered integral with said upper flange of said motor stand by screwing means. 9. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 1, wherein said motor stand comprises a plurality of pins passing through said annular element and said upper flange and configured to block the rotation of said annular element. 10. The motor stand of a primary motor-driven pump unit of a pressurized water nuclear reactor according to claim 1, wherein said upper flange comprises a tenon and said annular element comprises a complementary mortise, said tenon and said complementary mortise being configured to withstand radial stresses transmitted by said transverse holding means. 11. A primary motor-driven pump unit of a pressurized water nuclear reactor, comprising:an electric motor having a lower flange;a motor stand comprising:an upper flange configured to engage with said lower flange of said electric motor, anda fixing means configured to fix a transverse holding means of said primary motor-driven pump unit, wherein said fixing means comprises:an annular element arranged between said upper flange and said lower flange of said motor, said annular element comprising at least one radial excrescence formed by an appendage having a top face and a bottom face, said appendage being formed by two adjacent projecting bosses and a recessed zone formed between said two adjacent projecting bosses, wherein said appendage is formed integrally with said annular element and shares a common plane with said annular element;an upper plate and a lower plate fastened to the appendage and covering both faces of said appendage, said upper plate and lower plate each comprising a central bore opening into the recessed zone therein through which an axis is configured to be mounted; anda space delimited by said recessed zone and bordered by the upper plate and the lower plate, said space being configured to receive and to link said transverse holding means to said fixing means via said axis, andarticulated supports supporting said primary motor-driven pump unit,wherein the position of the at least one radial excrescence of said motor stand is modifiable as a function of the location of said articulated supports by angular modification of the position of the fixing means between the upper flange and the lower flange of said motor. |
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summary | ||
054815789 | summary | TECHNICAL FIELD The present invention relates to a lower tie plate assembly for a nuclear reactor fuel bundle, and particularly to a debris catcher incorporated within the lower tie plate assembly, the debris catcher formed by perforated tubes abutting the underside of the lower tie plate grid. The grid and the debris catcher are constructed to afford minimum pressure loss for coolant flow through the lower tie plate assembly and into the fuel bundle region downstream of the lower tie plate assembly. BACKGROUND Boiling water nuclear reactors have been in operation for many years. Commencing with their initial construction and throughout their service lives, these reactors have been known to accumulate debris in their closed circulation moderator (coolant) systems. This debris can become an operating hazard if allowed to enter into the fuel bundle core region containing the heat generating fuel rods. In fact, debris is a leading cause of fuel rod failure in boiling water nuclear reactors (BWR's). In order to understand this problem, a summary of reactor construction as it relates to the accumulation of debris in the core needs will be helpful. Thereafter, the fuel bundle construction will be described with emphasis on the need to preserve substantially unchanged the regions of pressure drop within the fuel bundles. The effects caused by debris entering into the fuel rod region of the fuel bundles will then be summarized. In boiling water nuclear reactor construction, the reactor is provided with a large, central core. Liquid water coolant/moderator flow enters the core from the bottom and exits the core as a water steam mixture from the top. The core includes many side-by-side fuel bundles, each containing a plurality of fuel rods. Water is introduced into each fuel bundle through a fuel bundle support casting from a high pressure plenum situated below the core. Water passes in a distributed flow through the individual fuel bundles and about the fuel rods where it is heated to generate steam, and then exits the upper portion of the core as a two-phase water steam mixture from which the steam is extracted for the generation of energy. The core support castings and fuel bundles are a source of pressure loss in the circulation of water through the core. By properly controlling such pressure losses, substantially even distribution of flow across the individual fuel bundles of the reactor core is achieved. When it is remembered that there are as many as 750 individual fuel bundles in a reactor core, it can be appreciated that assurance of the uniformity of flow distribution is important. To interfere with the existing pressure drop within the fuel bundles could negatively affect the overall distribution of coolant/moderator within the fuel bundles of the reactor core. The fuel bundles for a boiling water nuclear reactor are typically supported between lower and upper tie plate assemblies. The lower tie plate assembly is a one- or two-piece structure including a) an upper grid and 2) a lower inlet nozzle and associated structure providing a transition region from the inlet nozzle to the grid. The inlet nozzle provides for coolant entry to an enlarged flow volume within the flow transition region of the lower tie plate assembly. At the upper end of the flow volume, there is located a tie plate grid. The tie plate grid has two purposes. First, it provides a mechanical support connection for the weight of the individual fuel rods to be transmitted through the lower tie plate assembly to the fuel support casting. Secondly, the tie plate grid provides a path for liquid water moderator to flow into the fuel bundle region for passage between the side-by-side supported fuel rods. Above the lower tie plate grid, each fuel bundle includes a matrix of upstanding fuel rods, each containing fissionable material which, when undergoing nuclear reaction, transfers energy to the flowing water to produce the power generating steam. The matrix of upstanding fuel rods is engaged at its upper end by the upper tie plate assembly. Usually, water rods also extend (within the fuel rod matrix) between the upper and lower tie plate assemblies for improvement of the water moderator to fuel ratio, particularly in the upper region of the fuel bundle. Fuel bundles also include a number of fuel rod spacers at varying elevations along the length of each bundle. These spacers are required because the fuel rods are long (about 160 inches) and slender (about 0.4 to 0.5 inches in diameter), and would come into abrading contact under the dynamics of fluid flow and nuclear power generation. The spacers provide appropriate lateral restraints for each fuel rod at their respective elevations and thus prevent abrading contact between the fuel rods and maintain the fuel rods at uniform spacing relative to one another along the length of the fuel bundle for optimum performance. It will be appreciated that these spacers are sites where debris can be trapped and damage the fuel rods. Each fuel bundle is surrounded by an elongated channel. This channel confines water flowing between the upper and lower tie plate assemblies to a single bundle in an isolated flow path. The channel also serves to separate the steam generating flow path through the fuel bundles from the surrounding core bypass region used for the penetration of the control rods. The water in the bypass region also provides neutron moderation. In the operation of a boiling water nuclear reactor, maintenance of the originally designed flow distribution is very important. Specifically, from the core inlet to the core outlet, about 20 pounds per square inch (psi) of the pressure drop is encountered at typical flow operating conditions. About 7 to 8 psi of this pressure drop occurs through the inlet orifice and fuel support casting. This pressure drop is mainly to assure the uniform distribution of coolant/moderator flow through the many fuel bundles making up the core of the reactor, and is related to the prevention of operating instabilities within the reactor at certain power rates. At the lower tie plate assembly of each fuel bundle, from the inlet nozzle into the flow volume and through the tie plate grid, about 1 to 11/2 psi pressure drop occurs which contributes to uniform flow distribution between the individual fuel rods of each fuel bundle. Finally, through the fuel bundle itself--from the exit of the lower tie plate assembly to the exit at the upper tie plate assembly--about 11 psi of pressure drop usually occurs. When new fuel bundles are introduced into a reactor core, these flow resistances must be preserved. Otherwise, the coolant/moderator flow distribution could be compromised among the various types of fuel in the reactor core. With respect to the tie plate grid of the lower tie plate assembly, a matrix of cylindrical bosses and webs generally form the grid. The bosses are sized to receive the fuel rod end plugs. The flow area between the bosses and webs is the primary factor in controlling pressure drop resulting from water flow through the grid. In early grid constructions, the fuel rods had greater cross-sectional diameters and the bosses were large. In more recent grid constructions, however, the fuel rods have smaller cross-sectional diameters and the bosses are smaller. Also, in early constructions, fewer fuel rods formed a fuel bundle than in recent constructions. Even with all of these changes in grid and bundle construction, however, it is necessary to avoid significant changes in pressure drop. For example, a core may be composed of older (8.times.8) bundles and newer (10.times.10) bundles, and the flow through each bundle preferably is uniform. One challenge with new fuel bundle constructions, and particularly lower tie plate grid constructions, is to accommodate more fuel rods and to perform a debris catching function, yet maintain a flow rate substantially equivalent to the flow experienced in older bundle constructions. Typically, debris within boiling water nuclear reactors can include extraneous materials left over from reactor construction, and outage maintenance and repair activities. During the numerous outages and repairs, even further debris accumulates. Because nuclear reactors constitute closed circulation systems, it will be appreciated that debris will essentially accumulate with increasing age and use of the reactor. A particularly vexing but usual place for the accumulation of debris is in the fuel bundles between the fuel rods, and particularly in the vicinity of the fuel rod spacers. Debris particles tend to lodge between the spacer structure and the fuel rods and often dynamically vibrate with the coolant/moderator flow in abrading contact to the sealed cladding of the fuel rods. SUMMARY OF THE INVENTION The present invention relates to a lower tie plate assembly incorporating a unique debris catcher which results in little if any additional flow resistance and attendant pressure drop. The lower tie plate assembly includes the usual upper pad which forms the lower tie plate grid and a lower pad which forms the lower tie plate flow volume and lower inlet orifice or nozzle. The upper and lower parts may be secured together by suitable means, such as welding. Before describing the debris catcher in any detail, however, a further brief discussion of the grid construction will be helpful. As mentioned above, the lower tie plate grid supports the fuel rods in a manner enabling a smooth, substantially uniform expansion of coolant flow into the channeled fuel bundle. To accomplish the latter, a plurality of laterally spaced, generally cylindrical bosses defining through openings, extend between upper and lower surfaces of the lower tie plate grid and receive lower ends of the fuel rods. Webs also extend between those surfaces and interconnect the bosses. The bosses are arranged on vertical centerlines arranged at the corners of square matrices, with the webs extending linearly between the bosses along the sides of the square matrices. Convex portions of the cylindrical bosses extend between the right angularly related webs of each matrix. Thus, the webs and the convex portions of the bosses of the upper portion of the lower tie plate grid define coolant flow openings or flow areas between the bosses. In accordance with this invention, a debris catcher is provided immediately upstream of the lower tie plate grid, within the flow volume of the lower tie plate assembly. The debris catcher is formed by a plurality of perforated, cylindrical tubes, one for each boss in the grid. Each tube has an open lower end and, for those lower tie plate designs where the fuel rod end plugs rest on the bosses, a closed or capped upper end. For those lower tie plate designs where the fuel rod end plugs are threadably received within the grid bosses, the tubes may be open at their respective upper ends. In either case, the upper ends of the tubes may be secured to the grid bosses by a welded, slip fit, screw thread or other suitable connection. The cylindrical side wall of each tube is provided with perforations or apertures substantially uniformly distributed about the entire periphery of the side wall. In an exemplary embodiment, the tubes may be in the range of from about 0.50 to about 1.0 inch in length, and may have outside diameters substantially equal to the boss diameters. At the upstream ends of the perforated tubes (i.e., the lowermost ends, located remote from the grid), the tubes are attached by any suitable means (welding, screw thread, etc.) to a plate having chambered holes corresponding to a typical flow nozzle shape corresponding to the tubes but closing off all flow between the tubes. This plate is also secured about its periphery to the inside surface of the peripheral wall defining the lower tie plate flow volume, so that no significant size debris particles can flow between the inner wall of the flow volume and the plate. It will be appreciated that the tubes and plate may be preassembled and then secured within the flow volume of the lower tie plate assembly, such that the debris catcher tubes abut, but are not otherwise fixed to, the bosses on the underside of the grid. With the above described construction, it will be appreciated that substantially all coolant flow is forced to flow into the debris catcher tubes, change direction to flow out through the perforations in the tube sidewalls, and then resume upward flow through the coolant flow spaces between the bosses in the tie plate grid. Any debris in the coolant flow above a predetermined size will be caught in the debris catcher tubes and thus prevented from flowing upwardly into the channeled fuel rod bundle. In accordance with a broad aspect of the invention, therefore, there is provided a lower tie plate assembly for a nuclear reactor comprising an upper grid portion and a lower body portion, the upper grid portion having a plurality of fuel rod supporting bosses separated by flow openings, and the body portion including a bottom nozzle and a peripheral wall extending between the bottom nozzle and the upper grid portion to define a flow volume therein; and a debris catcher including a plurality of perforated tubes having open lower ends, one of said perforated tubes abutting a lowermost end of each of the plurality of fuel rod supporting bosses. In accordance with another aspect of the invention, there is provided a fuel bundle and lower tie plate assembly for a nuclear reactor comprising a plurality of fuel rods .supported between an upper tie plate and a lower tie plate assembly, the lower tie plate assembly comprising an upper grid portion and a lower body portion, the upper grid portion having a plurality of fuel rod supporting bosses interconnected by a plurality of webs thus forming flow openings between the bosses; the body portion including an inlet nozzle and a peripheral wall extending between the bottom nozzle and the upper grid portion to define a flow volume therein; and a debris catcher including a plurality of perforated tubes, one of the tubes engaging and extending downwardly from a lowermost end of each of the plurality of fuel rod supporting bosses. The invention as described combines low flow resistance with high debris catching capability in a relatively simple design. Other objects and advantages of the invention will become apparent from the description which follows. |
abstract | A fuel assembly attains high burnup and increases reactor shut-down margin when loaded into a reactor core wherein a water gap width on a control rod side and a water gap width on a side opposite to the control rod side are almost equal to each other. The fuel assembly has a plurality of fuel rods arranged in a square lattice pattern, each fuel rod being filled with nuclear fuel pellets and also has at least one neutron moderator rod shifted toward one corner where a control rod is inserted, away from a cross sectional center of the fuel assembly. |
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description | This application claims priority under 35 U.S.C. §119(e) from Provisional Application Ser. No. 61/561,966, entitled “Method and Apparatus to Volume Reduce Boiling Water Reactor Fuel Channels for Storage,” filed Nov. 21, 2011. 1. Field This invention relates generally to the disposal of highly radioactive components, and, more particularly, to a method for reducing the volume of radioactive rectangular tubular fuel channels for storage. 2. Related Art One type of commonly used boiling water nuclear reactor employs a nuclear fuel assembly comprised of fuel rods surrounded by a fuel channel. The fuel channel is a 5.3 inch (13.4 cm) square tube having rounded corners, approximately 14 feet long, with open ends. The channels are typically made of zircoloy and have a wall thickness of 0.08, 0.10 or 0.12 inch (0.2, 0.25 or 0.3 cm). There are a large number of fuel assemblies in a boiling water reactor, and approximately one-third of these assemblies are normally replaced each year. Even though the fuel channels are normally reused after the fuel rods are removed, for various reasons, they need to replaced from time to time, thereby requiring these highly radioactive fuel channels to be disposed of safely. Following functional service, irradiated fuel channels are difficult to store and dispose of because of their size, configuration, embrittled condition and radiological history. These used fuel channels are highly radioactive for two reasons. First, the zircoloy metal itself becomes radioactive during operation in the nuclear reactor. Secondly, a crust or crud forms on the outside of the fuel channels which is also radioactive. Heretofore, in the United States, the irradiated fuel channels have been stored in spent fuel pools at the nuclear plants in which they experienced service. This type of storage is extremely space inefficient, but dry-cask storage is not readily available. Accordingly, boiling water reactor operators would prefer to dispose of the fuel channels offsite as soon as reasonably practicable. Fuel channels and other irradiate hardware are typically classified as class C low level radioactive waste, as defined and determined pursuant to 10 CFR 61 and related regulatory guidance. Since Jul. 1, 2008 low level radioactive waste generators within the United States that are located outside of the Atlantic compact (i.e., Connecticut, New Jersey and South Carolina) have not had access to offsite class B or class C low level radioactive waste disposal capacity. A lack of offsite disposal capacity has caused boiling water reactor operators considerable spent fuel pool overcrowding. Though currently very uncertain and subject to numerous regulatory and commercial challenges, class B and C low level radioactive waste disposal capacity for the remainder of the United States low level radioactive waste generators is anticipated in the near future. In order for the fuel channels to be shipped for offsite storage an economical method of packaging the fuel channels will be required for such offsite storage to be efficient and cost effective. For that to practically occur, the volume of the fuel channels will have to be significantly reduced. One prior art method for the volume reduction of fuel channels that has been employed is the imprecise crushing and shearing of segments of the fuel channel directly above an open disposal liner placed in the bottom of the spent fuel pool into which the crushed and sheared sections fall. Other methods which have been suggested are described in U.S. Pat. Nos. 4,295,401, 4,507,840 and 5,055,236. For the general purposes of this description, the principal component of a boiling water reactor fuel channel is a metallic generally square, elongated tube the approximate length of a fuel assembly. Following the useful life of a fuel channel, its primary metal constituents are embrittled as a result of prolonged neutron exposure. Segmentation of the fuel channel causes the embrittled metal to shatter thereby exposing the spent fuel pool to unwanted and highly radioactive debris. Furthermore, packaging for disposal requires size reduction of the fuel channels to fit within commercially available, licensed shipping casks and/or to efficiently utilize disposal package space. Lateral segmentation of the fuel channels is generally a prerequisite in order to efficiently utilize the shipping casks, and has historically been technically problematic. Accordingly, a new method is desired that enables lateral segmentation and compaction of the fuel channel components without historic untoward consequences. More specifically, such a method is desired that will minimize the creation of any collateral radioactive debris. Further, such a method is desired that can be efficiently performed cost effectively. These and other objects are achieved by the method claimed hereafter for reducing the volume of an elongated boiling water reactor fuel assembly fuel channel for storage. The method includes the step of enclosing the fuel channel within an outer sleeve. The method then laterally compacts the fuel channel within the outer sleeve. Desirably, the step of enclosing the fuel channel in the outer sleeve includes the step of closing a top and bottom of the sleeve prior to the step of laterally compacting the fuel channel. In one embodiment, the step of closing the top and bottom of the sleeve includes the steps of inserting an inner sleeve within the fuel channel with the inner sleeve extending over the elongated dimension of the fuel channel and attaching the top of the outer sleeve to a top of the inner sleeve and the bottom of the outer sleeve to a bottom of the inner sleeve around an entire circumference of the fuel channel. Preferably, the outer sleeve is constructed from a malleable metal such as aluminum or copper. In still another embodiment, the sleeve is perforated to allow water to escape and, preferably, the perforations have traps to prevent debris from escaping with the water. Desirably, the laterally compacting step is performed with a full length compactor that extends a compacting surface of the compactor over the entire elongated dimension of the fuel channel. The method may further include the step of laterally segmenting the fuel channel in the outer sleeve into segmented pieces of a desired length, after the laterally compacting step. Preferably, the segmenting step includes the step of shearing the outer sleeve and the fuel channel. The method may then further include the step of packaging the segmented pieces for storage. In accordance with one embodiment of the invention claimed hereafter and as shown in FIG. 1, a fuel channel 10 is inserted into an outer sleeve 12 that is sealed on top by a cover 16 and a bottom cover 28. The sleeve 12, bottom cover 28 and top cover 16 completely seal the fuel channel 10 within the interior of the sleeve 12. Alternatively, the sleeve 12 and bottom cover 28 can be constructed as an integral can in which the fuel channel 10 can be loaded and sealed by the cover 16. The sleeve or can completely encompasses the channel's length and is preferably made from a malleable metal such as aluminum, copper or other relatively malleable, inexpensive metal. The sleeve, for example, may be on the order of one-eighth inch (0.32 cm) thick. The can or sleeve can have a prefabricated bottom 28 and a “lid” or “top” 16 that will be installed following insertion of the fuel channel 10. Portions of the sleeve or can 12 (i.e., sidewalls, top and/or bottom) will be perforated and screened or otherwise trapped with a trap such as shown at 26 in FIG. 1, to allow water to escape without permitting debris within the sleeve enclosure from escaping. Once the fuel channel is secured within the sleeve enclosure 12, the enclosure will be subjected to a full length hydraulic compactor 20 which will compact the sleeve enclosure in the lateral direction, i.e., a compacting force applied laterally to opposite sides of the sleeve enclosure, preferably over the entire length of its elongated dimension. The sleeve enclosure will then contain shattered fuel channel material which will be isolated by the sleeve from the spent fuel pool. Following compaction, the sleeve enclosure containing the fuel channel may be laterally segmented to a desired length by use of hydraulic shears 22. The physical limitations of the storage facility or transport casks and the radiation levels of the incremental sections of the sleeve containing the fuel channel will dictate the optimal location along the length of the fuel channel at which lateral segmentation is desired. The can or sleeve is intended to limit or eliminate fuel channel spring back and capture shattered metal that has been embrittled by neutron exposure. Similarly, the can or sleeve is intended to provide a seal at the lateral shearing locations which will continue to contain the shattered material after the segments are separated. The seal is formed from the shear blades forcing the opposite walls of the sleeve against each other as the blades penetrate the sleeve and fuel channel metal. Once sheared, the canned fuel channel sections may be handled and packaged in a cask 30 in a manner that optimizes physical and radiological efficiency. In an alternate embodiment an inner sleeve 14 that extends at least the length of the fuel channel 10 may be inserted inside the fuel channel and the top of the inner sleeve 14 may be drawn to the top of the outer sleeve 12 and the bottom of the inner sleeve 14 may be drawn to the bottom of the outer sleeve 12 in place of the top 16 and bottom 28 seals previously noted. Alternatively the tops and bottoms of the inner and outer sleeves 14 and 12 may be welded together to form the debris seal between the sleeves. The liner container enclosing the fuel channel may then be crushed and sheared as previously noted. Regardless of the method used, the entire process is carried out under water in the spent fuel pool 18. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the general concepts disclosed and any and all equivalents thereof. |
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summary | ||
claims | 1. A portable device for use in curing gel nail preparations on human hands and feet, said device comprising: a housing having a front wall, a back wall, two side walls, a top and a bottom, said front wall having three horizontal openings therethrough, an uppermost opening, a middle opening and a lowermost opening, three compartments situated within said housing, a first compartment accessed through said uppermost opening, a second compartment accessed through said middle opening and a third compartment accessed through said lowermost opening; three partitions disposed within said housing, a first partition defining the first compartment, a second partition defining the second compartment and a third partition defining the third compartment, each partition forming the walls of the compartment and including a floor and a ceiling; and three UV lamps, a first UV lamp affixed near the ceiling of the first compartment, a second UV lamp affixed near the floor of the second compartment, and a third UV lamp affixed near the ceiling of the third compartment, whereby when the index and three fingers of the hands are placed flat on the floor of the first compartment and the thumbs are placed flat against the ceiling of the second compartment, radiation from the first UV lamp is directed toward the floor of the first compartment and radiation from the second UV lamp is directed toward the ceiling of the second compartment so the fingernails receive direct radiation, and when the feet are placed flat on the floor of the third compartment, radiation from the third UV lamp is directed toward the floor of the third compartment and the toe nails receive direct radiation. 2. A device as in claim 1 wherein the floor of the first compartment, the ceiling of the second compartment and the floor of the third compartment are substantially flat. claim 1 3. A device as in claim 2 wherein the remainder of the partition in each compartment is curved to best concentrate the UV radiation toward the flat ceiling and floors. claim 2 4. A device as in claim 3 wherein the inner surfaces of the partitions are coated with a reflective material to reflect the UV light and assist in concentrating same toward the flat ceiling and floors. claim 3 5. A device as in claim 1 wherein the first, second and third UV lamps are tubular. claim 1 6. A device as in claim 1 wherein the first opening and the third opening are substantially the width of the front wall. claim 1 7. A device as in claim 1 wherein the second opening is horizontally centered. claim 1 8. A device as in claim 1 wherein the vertical extent of the second opening is greater than that of the first opening. claim 1 9. A device as in claim 1 wherein the vertical extent of the third opening is greater than that of the first opening. claim 1 10. A device as in claim 1 further comprising a hand rest disposed between the uppermost opening and the middle opening, said hand rest comprising a rounded member extending outwardly from said front wall and extending horizontally at least the length of the middle opening. claim 1 11. A device as in claim 1 wherein the first compartment is dimensioned to contain the index and three fingers of both hands. claim 1 12. A device as in claim 1 wherein the second compartment is dimensioned to contain the thumbs of both hands. claim 1 13. A device as in claim 1 wherein the third compartment is dimensioned to contain both feet. claim 1 14. A device as in claim 1 further comprising a power means for activating the UV lamps, said power means selected from the group consisting of line current and a rechargeable battery. claim 1 15. A device as in claim 14 wherein the power means comprises both line current and a rechargeable battery. claim 14 16. A device as in claim 15 wherein the line current is delivered by means of an electric cord. claim 15 17. A device as in claim 16 further comprising a retractable cord mechanism to contain the electric cord when not in use, said retractable cord mechanism being disposed within the housing. claim 16 18. A device as in claim 1 further comprising a control panel disposed in the front wall of the housing, said control panel containing timer means to preset the length of time required for curing the gel nail preparations, visible readout means to indicate the time remaining for the curing process, and lamp selection means to activate the desired UV lamps. claim 1 19. A portable device for use in curing gel nail preparations on human hands and feet, said device comprising: a housing having a front wall, a back wall, two side walls, a top and a bottom, said front wall having three horizontal openings therethrough, an uppermost opening, a middle opening and a lowermost opening; three compartments situated within said housing, a first compartment accessed through said uppermost opening, a second compartment accessed through said middle opening and a third compartment accessed through said lowermost opening; three partitions disposed within said housing, a first partition defining the first compartment, a second partition defining the second compartment and a third partition defining the third compartment, each partition forming the walls of the compartment and including a floor and a ceiling; three UV lamps, a first UV lamp affixed near the ceiling of the first compartment, a second UV lamp affixed near the floor of the second compartment, and a third UV lamp affixed near the ceiling of the third compartment; and power means for activating the UV lamps, said power means comprising both line current and a rechargeable battery, whereby the device operates by line current and when the line current is disconnected the device operates by means of the battery, and when the index and three fingers of the hands are placed flat on the floor of the first compartment and the thumbs are placed flat against the ceiling of the second compartment, radiation from the first UV lamp is directed toward the floor of the first compartment and radiation from the second UV lamp is directed toward the ceiling of the second compartment so the fingernails receive direct radiation, and when the feet are placed flat on the floor of the third compartment, radiation from the third UV lamp is directed toward the floor of the third compartment and the toe nails receive direct radiation. 20. A device as in claim 19 further comprising a hand rest disposed between the uppermost opening and the middle opening, said hand rest comprising a rounded member extending outwardly from said front wall and extending horizontally at least the length of the middle opening. claim 19 |
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051724030 | summary | FIELD OF THE INVENTION AND RELATED ART This invention relates to an X-ray exposure apparatus for lithographically transferring onto a semiconductor wafer a fine pattern of a semiconductor integrated circuit, by using soft X-rays. As a light source of such an X-ray exposure apparatus, known are a bulb type one which produces X-rays by electron beam excitation, one which uses X-rays produced from plasma, one that uses synchrotron orbit radiation, and the like. All of these X-ray sources produce X-rays in vacuum. Accordingly, an X-ray source is usually disposed in a vacuum and gas-tight X-ray source accommodating chamber, and produced X-rays are projected to a mask or wafer through a blocking window made of a material (usually, beryllium (Be)) having a high X-ray transmission factor. If in this case atmosphere is present in the path of X-ray transmission from the blocking window to a wafer, X-rays are absorbed by the atmosphere, resulting in an increase in exposure time and thus in a decrease of the throughput. Considering an X-ray exposure apparatus as an industrial productive machine, the decrease in throughput is a critical problem. In an attempt to solve this, a proposal has been made, in accordance with which an alignment mechanism for a mask and a wafer is disposed in a vacuum and gas-tight container chamber (hereinafter "stage accommodating chamber") and such stage accommodating chamber is filled with a particular gaseous fluid (usually, helium (He) gas) of reduced pressure, lower than the atmospheric pressure, having little X-ray absorbency (Japanese Patent Application No. 63-49849). In this type of X-ray exposure apparatus, however, the amount of X-ray transmission through the path from the blocking window to the wafer is greatly affected by the helium gas ambience within the stage accommodating chamber. If the purity or pressure of helium introduced into the stage accommodating chamber changes largely, the amount of X-ray exposure changes, which results in reduction in precision of an exposure apparatus. Additionally, it is necessary to retain the purity of helium at a high level and also to keep the variation thereof small. If it is desired to control the purity by using some purity detecting means, use of a very high precision detection and control means is necessary. In that respect, an X-ray exposure apparatus has been proposed in U.S. patent application Ser. No. 07/417,054 filed Oct. 4, 1989, now copending U.S. patent application Ser. No. 07/733,977, filed Jul. 22, 1991, assigned to the same assignee of the subject application, which apparatus is arranged so that, even after the inside gas of a stage accommodating chamber is replaced by helium, a constant amount of helium is continuously supplied into the chamber to compensate for the reduction in the purity due to introduction of an impure gas into the stage accommodating chamber. FIG. 6 shows this X-ray exposure apparatus. In FIG. 6, a barrel 5 is coupled to an X-ray source (not shown) and, to this barrel 5, a stage accommodating chamber 19 is coupled. The barrel 5 is equipped with a beryllium blocking window 6 and the X-rays passing therethrough are used. The stage accommodating chamber 19 accommodates therein a mask 13, a mask chuck 14, a wafer 15, a wafer chuck 16 and a wafer stage 18. To the stage accommodating chamber 19, a low vacuum pump 11 such as an oil rotation pump, for example, is coupled by way of a variable valve 10. The valve 10 is adapted to change the opening (conductance) thereof automatically in response to a signal from a controller 9. By means of a pressure sensor 8 and a pressure detecting port 7, the pressure within the stage accommodating chamber 19 can be detected and, on the basis of this detection, the controller 9 controls the opening of the variable valve 10. By this, the inside pressure of the stage accommodating chamber 19 is controlled and maintained constant. Denoted at 1 is a helium tank and denoted at 2 is a valve the opening of which can be adjusted manually. The He gas can be supplied through a He supply port 3. In this type of X-ray exposure apparatus, first the inside of the stage accommodating chamber 19 is vacuum evacuated to a predetermined pressure by using the low vacuum pump 11 and, thereafter, a helium gas is supplied to fill the stage accommodating chamber 19 with a reduced pressure helium ambience, and the exposure process is executed in this ambience. SUMMARY OF THE INVENTION In this example, the control of the helium ambience (purity and pressure) is conducted with respect to the entirety of helium gas in the stage accommodating chamber 19. However, since in the stage accommodating chamber 19, many elements such as the mask 13, the wafer 15, the mask chuck 14, the wafer chuck 16, the wafer stage 18 and the like are accommodated, it is not easy to correctly predict the flow of helium within the stage accommodating chamber 19. Also, when the wafer stage 18 moves, there is a possibility of the production of a regional flow. If this occurs, it is not possible to maintain the entire helium ambience in the stage accommodating chamber 19 uniform and, in the X-ray projection path from the beryllium blocking window 6 to the wafer 15 (to which the control is actually required), the purity of helium is liable to be degraded or the pressure thereof tends to change. It is accordingly a primary object of the present invention to provide an X-ray exposure apparatus by which in the X-ray projection path the helium ambience can be maintained at a predetermined purity and a predetermined pressure, whereby high-precision X-ray exposure is ensured. In accordance with an aspect of the present invention, a helium supplying port and a helium discharging port as well as a pressure detecting port are provided in the neighborhood of an X-ray projection path from a blocking window, to be passed by the X-rays, to the wafer. This makes it possible to execute weighted control of the helium ambience in the X-ray projection path in which the control is actually required. Additionally, a thin film may be provided between a mask and the blocking window to suppress vibration of the mask due to the gas flow of helium, to thereby ensure high precision exposure. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. |
048779695 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, a transport flask for radioactive material comprises a hollow cylindrical body 1 provided with cooling fins 2 and lifting trunnions 3. In use the open end of the body is closed by a lid (not shown) which can be bolted to the body. The interior of the body accommodates a plurality of substantially identical members 4 which cooperate to define channels 5 to receive radioactive waste containers. In the example of FIG. 1 the members 4 define seven such channels 5. With reference to FIGS. 2 and 3, each member 4 comprises an elongate aluminium body having concave longitudinally extending surfaces 6 and 7 which each define substantially a half of channel 5. Radially outer surface 8 of the member is curved to conform to the curvature of the interior of the body 1. Radially inner surface 9 of the member 4 is curved to define a portion of a central channel 5. A stepped groove 10, which extends the length of the member 4 is formed in the surface 8. A plurality of T-shaped keys 11 are fixedly secured to the flask body at regular intervals about the interior thereof, the keys 11 extending the length of the body. The keys 11 are dimensioned to slidably receive the stepped grooves in the members 4. A clamping bar 12 cooperates with each key 11 to clamp the member 4 in position, the clamping bar being secured to the T-piece by bolts 13, conveniently three in number, spaced at equal intervals along the length of the bar. During assembly, each member 4 slides along its locating T-shaped key 11 into its required position within the flask body. The member 4 is then clamped securely to the wall of the flask body by tightening the bolts 13 to a predetermined torque. The stepped groove opens into an enlarged passage 14 which can receive a tool for applying the required torque to the bolts. The member 4 is so shaped that initially contact is made against the flask wall at the longitudinal edges of the member. Upon tightening the bolts the member deforms elastically until contact is made along the full extent of the radially outer surface of the member. This ensures good thermal contact between the member and the flask body. The individual members 4 cooperate to define the channels 5 within the flask body. Containers containing radioactive material can be accommodated in the channels and the members 4 provide for the conduction of heat generated within the containers to the flask body. As the structure within the flask is formed from a plurality of individual and substantially indentical separate members 4, the cost of manufacture can be less than that of a single monolithic support. The build-up of stresses or distortion is minimised as a result of the separate members. A further advantage lies in the recovery of containers which might become jammed or stuck within the channels as it is possible to remotely release the members 4 to thereby free the containers. |
claims | 1. A method for preparing particles of an oxalate of one or more actinides, comprising:precipitating the actinide(s) in a form of actinide(s) oxalate particles in a fluidized bed reactor by bringing a first aqueous solution comprising the actinide(s) into contact with a second aqueous solution of oxalic acid or of an oxalic acid salt in the fluidized bed reactor, and forming the actinide(s) oxalate particles having a spherical or quasi-spherical shape, andcollecting the so precipitated actinide(s) oxalate particles. 2. The method of claim 1, in which the first aqueous solution has a total concentration of actinide(s) of 0.01 to 300 g/L. 3. The method of claim 1, in which the second aqueous solution has a concentration of oxalic acid or oxalic acid salt of 0.05 to 1 mole/L. 4. The method of claim 2, in which the volume ratio of the first aqueous solution to the second aqueous solution is such that the oxalic acid or the oxalic acid salt is in excess compared to an amount of oxalic acid or oxalic acid salt required for precipitating the actinide(s) in stoichiometric conditions, the excess being from 0.01 to 0.5 mole/L. 5. The method of claim 1, in which the actinide(s) is (are) present in the first aqueous solution in a form of nitrate(s). 6. The method of claim 1, in which the first aqueous solution is an acid solution. 7. The method of claim 6, in which the first aqueous solution is an aqueous solution comprising from 0.1 to 4 moles/L of nitric acid. 8. The method of claim 1, in which at least one of the first and second aqueous solutions further comprises a monocharged cation constituted of atoms of oxygen, carbon, nitrogen and hydrogen. 9. The method of claim 8, in which the monocharged cation is a hydrazinium ion and is present in the first aqueous solution in a form of hydrazinium nitrate. 10. The method of claim 1, in which precipitating the actinide(s) oxalate particles comprises fluidizing, decanting and sedimenting the actinide(s) oxalate particles and the fluidized bed reactor has a vertical main axis and comprises:an intermediate part in which the actinide(s) oxalate particles are fluidized;an upper part in which the actinide(s) oxalate particles are decanted; anda lower part in which the actinide(s) oxalate particles are sedimented. 11. The method of claim 10, in which precipitating the actinide(s) oxaloate particles comprises:fluidizing the actinide(s) oxalate particles by introducing the first and second solutions into the fluidized bed reactor, at least one of the first and second solutions being introduced into the lower part of the fluidized bed reactor to create an ascending current of liquid and thereby to form a fluidized bed of actinide(s) oxalate particles in the intermediate part of the fluidized bed reactor;decanting the actinide(s) oxalate particles in the upper part of the fluidized bed reactor to form two phases, a solid phase constituted of the actinide(s) oxalate particles and a liquid phase resulting from a mixing and a depletion into actinide(s) and into oxalic acid or oxalic acid salt of the first and second aqueous solutions;sedimenting the actinide(s) oxalate particles in the lower part of the fluidized bed reactor; andwithdrawing the actinide(s) oxalate particles measuring less than 10 μm which are in the upper part of the fluidized bed reactor and transferring said particles into the lower part of the fluidized bed reactor. 12. The method of claim 1, in which the actinide(s) is (are) chosen from uranium, plutonium, neptunium, thorium, americium and curium. 13. The method of claim 1, in which the actinide(s) oxalate is an oxalate of uranium(IV) and plutonium(III), an oxalate of uranium(IV) and americium(III), an oxalate of uranium(IV) and curium(III), an oxalate of uranium(IV), plutonium(III) and neptunium(IV), an oxalate of uranium(IV), plutonium(III) and americium(III), an oxalate of uranium(IV), americium(III) and curium(III), an oxalate of uranium(IV), plutonium(III), americium(III) and curium(III), or an oxalate of uranium(IV), plutonium(III), neptunium(IV), americium(III) and curium(III). 14. A method for preparing a compound chosen from oxides, carbides and nitrides of one or more actinides, which comprises:preparing particles of an oxalate of one or more actinides by a method according to claim 1; andcalcining the actinide(s) oxalate particles. 15. The method of claim 14, in which the actinide(s) oxalate is an oxalate of uranium(IV) and plutonium(III), an oxalate of uranium(IV) and americium(III), an oxalate of uranium(IV) and curium(III), an oxalate of uranium(IV), plutonium(III) and neptunium(IV), an oxalate of uranium(IV), plutonium(III) and americium(III), an oxalate of uranium(IV), americium(III) and curium(III), an oxalate of uranium(IV), plutonium(III), americium(III) and curium(III), or an oxalate of uranium(IV), plutonium(III), neptunium(V), americium(III) and curium(III). 16. The method of claim 14, in which the compound is an oxide of uranium and plutonium, an oxide of uranium and americium, an oxide of uranium(IV) and curium(III), an oxide of uranium, plutonium and neptunium, an oxide of uranium, plutonium and americium, an oxide of uranium, americium and curium, an oxide of uranium, plutonium, americium and curium, or an oxide of uranium, plutonium, neptunium, americium and curium. |
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062332988 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUT THE INVENTION) The present invention results from a novel combination of particle accelerator, reactor, and chemical separations technology which enables transmutation of spent commercial reactor nuclear fuel in a more simple, less costly, and more effective means than by implementation of existing reactor technology or other subcritical transmutation concepts. The present invention acts to nullify the weapons-usefulness of the commercial plutonium in the waste, reduce the long-term radioactivity of the waste, recover the nuclear energy in the waste and sell such energy into the commercial grid, and eliminate the possibility of recriticality of the remnant waste in permanent storage. These functions are accomplished without producing a pure stream of weapons- useful plutonium or implementation of fuel fabrication, reprocessing, fuel refabrication, or the technology of fast breeder reactors. The value of the power sold is expected to be sufficient to pay both capital and operations costs for waste destruction. The invention consists of a subcritical reactor-like process moderated by graphite through which flows a molten salt medium carrying plutonium and minor actinides ("PMA") and fission products in solution. Liquid fuel is continually fed into the subcritical system vessel and continually removed so that the total volume of liquid is approximately constant. The continuous insertion of fresh fissile fuel from the LWR waste and the continuous removal of fission product by removal of the carrier establishes an equilibrium subcritical reactivity which may be maintained indefinitely. The subcriticality is associated with fission chains of finite length as opposed to nearly infinitely long chain reaction as in an ordinary reactor. Subcriticality is maintained such that the average fission chain contains from approximately 10 to approximately 100 fission events and preferably from approximately 20 to approximately 40 fission events. The fission chains are started by a particle beam with sufficient energy to produce many neutrons per particle when the particle expends its energy by striking a liquid target within the vessel that contains lead or bismuth or both. The combination of particle beam current, beam energy, and average fission events per chain is sufficient to produce a fission power in the range of hundreds of megawatts. The fission heat is recovered from the molten salt by a heat exchanger internal to the vessel that allows for the removal of the heat and the generation of electric power in, for example, a steam cycle. The power consumed by the accelerator in accelerating this beam is small (about 10%) compared to the electric power generated. The large heat transfer metallic surface inside the heat exchanger serves, in addition to heat transfer, as a deposition site for several of the metallic fission products. The deposition of these fission products outside of the region of high neutron flux limits the loss of neutrons by non-useful absorption and makes more neutrons available for PMA transmutation. The heat exchangers are designed to be readily replaceable providing additional means for fission product removal besides being carried away in the removed molten salt. Some of the fission products are noble gases or form volatile fluoride species that are not confined by the carrier salt. These fission products are removed by the flow of helium gas, or similar inert gas, across a free turbulent surface of the molten salt. The isotopic composition of the feed PMA chemical elements is transmuted to a new isotopic composition by thermal neutron absorption. Not all neutron absorption events on isotopes which may be caused to fission by thermal neutrons result in fission events. Those that result in fission deplete the number of fissile nuclides; those that do not cause fission also decrease the number of fissile nuclides by transforming them to non-fissile species. The residence time of the PMA in the system in equilibrium is long enough for several neutron absorption events on the same nuclide. Therefore the equilibrium composition is significantly depleted in fissile species compared to the feed and is incapable of supporting a self-sustained continuous chain reaction and is not practical for use in nuclear weapons. The incoming fluid medium feed stream, which contains weapons-useful plutonium, is nearly immediately mixed with the equilibrium mixture in the transmuter and is therefore nearly immediately transformed into non-weapons useful material. Therefore, in contrast to other waste destruction schemes, weapons-useful material can never be recovered after feed into the transmuter. The feed for the transmuter is prepared by removal of the zirconium fuel cladding metal and separation of the uranium from the PMA and fission product by fluorination. The PMA and fission product may be fed into the transmuter together or the PMA may be further separated from the fission product and PMA only fed into the transmuter. In either case, a pure stream of weapons plutonium is never produced or stored. No separations chemistry or recycle is required for the process fluid medium exit stream. The effectiveness of transmutation depends to a large degree on the number of neutrons available for absorption into those species to be destroyed or transmuted. Neutrons absorbed into stable fission products provide no benefit and this process becomes a significant means for loss of neutrons. This means for neutron loss is reduced by the transmutation of the most absorptive fission product by thermal neutron capture to non-absorptive fission product. For the most troublesome nuclides this transmutation in a thermal spectrum occurs in a time much shorter than the residence time of the fission product in the transmuter. Therefore the neutron absorption probability of the fission product is decreased by the ratio of the transmutation time to the residence time. The nuclide .sup.242m Am, which has the largest fission cross section of any nuclide by far, might have nuclear weapons potential. It is produced in significant quantities in waste destruction systems based on a fast neutron spectrum, whether in reactors or accelerator-driven systems. Because of its very large thermal fission cross section, it is destroyed immediately after it is produced in the thermal spectrum so that useful amounts cannot be recovered from the exit stream. The benefits from the practice of this invention derive from the successful implementation and combination of a thermal neutron spectrum, liquid fuel, the continuous feed and removal of liquid fuel, and the accelerator, which makes possible safe operation with liquid fuel and allows enhancement of useful neutrons. The benefits are made available with reduced front-end processing, and without back-end separations, recycle, fuel fabrication or fuel refabrication, or the implementation of technology from breeder reactor development. The present invention incorporates an accelerator and other design features in such a way as to offset and eliminate several components and operations of high cost approaches to treatment of nuclear wastes; the present invention also allows for the use of less expensive structural materials. Furthermore, electric power generated by the present invention is saleable into the commercial grid at a price equal near that of conventional power plant LWRs thereby generating revenue to pay the present invention's capital and operational costs for transmutation. Thus, in a preferred operational mode of the present invention, the cost of transmutation is near zero. The present invention is not designed to destroy all of the radioactive constituents of the waste, so geologic storage of the remnant waste from the present invention is still necessary. However, present invention accomplishes the following: destroys essentially all of the weapons-useful material in commercial reactor spent fuel; recovers nearly all fission energy of plutonium and other fissioning nuclides; reduces long-term waste radioactivity; decouples nuclear power production from an associated large weapon-useful waste inventory; and recovers full costs by generation and sale of electric power. Part of the reason that the low capital and operating costs are possible compared to other transmutation technologies is that the present invention achieves its objectives while: replacing reprocessing with more modest front-end chemistry; eliminating separation of a pure stream of plutonium; eliminating back-end chemistry; eliminating fuel fabrication and refabrication; and reducing accelerator size by a factor of about two when compared to other transmutation concepts. The present invention's transmutation process also ameliorates problems of geologic storage. The sufficiency by which it allows geologic storage to proceed for the transmuted waste remnant in all likelihood will differ from one nation to another depending on many factors. However with a transmutation program eliminating the concerns for weapons-useful nuclear material, one nation need have no concern about how other nations dispose of transmutation remnant, in sharp contrast to the current status amongst nations. Therefore, deployment of the present invention will transform the character of the geologic storage debate while also producing other benefits. If radioactivity of the remnant remains a concern, the radioactivity can be reduced by an additional factor of 200 by extensions of the present invention's technology. Although the cost of this further reduction is not zero, the incremental cost is small because the extended technology is applied to only the remnant rather than the full amount of the waste. To achieve the foregoing objectives while keeping the cost sufficiently low for widespread deployment as mentioned above, one embodiment of the present invention for transmuting waste from commercial nuclear power plants includes a liquid heavy metal target that is struck by a proton beam of high current and intensity for the purpose of producing neutrons. These neutrons originate near the center of a tank having a volume defined by several meters in diameter and several meters in height. These neutrons, generated with energies in the million electron volts range, undergo scattering in graphite that fills most of the tank volume. The scattering reduces the neutron energies into or near to the thermal range that is the energy of about 0.07 electron volts corresponding approximately to the operating temperature of the graphite. Holes in the graphite filling the volume of the tank serve as flow paths for a liquid carrier salt mixture such as NaF--ZrF.sub.4. The waste actinides including primarily Pu, Np, Am and Cm and fission products to be transmuted, after being separated from the commercial reactor spent fuel, are converted to fluoride salts and dissolved into the liquid carrier salt. The neutrons produced by the accelerator interact with the waste by neutron capture in the fission products and by absorption in the actinides leading to fission or capture. Each fission releases several neutrons on average which slow down by scattering in the graphite. The concentration of the waste and other constituents and the geometry of the system is adjusted so that a continuous chain reaction is almost but actually not possible. Therefore, a continuous chain reaction such as that in a conventional reactor is impossible; however a self-terminating chain reaction having an average chain length in the neighborhood of approximately 10 to approximately 100, or more preferably approximately 20 to approximately 40, fission events in length is possible. Each neutron produced by the accelerator has the opportunity to start such a fission chain. The number of neutrons produced per second by the accelerator beam is large enough that the fission rate in the system, and therefore the fission power, is in the range of several hundreds of megawatts. In general, the present invention's destruction of actinide atoms by fission creates fission products that almost always are two in number for each atom destroyed. In a preferred embodiment of the present invention, actinide atoms are added to the system as fast as they are destroyed by fission by adding fresh actinide waste to the liquid fuel. Also fission products are removed from the fuel as fast as they are created by fission by draining away the salt which carries the actinide and the fission products. Therefore, an equilibrium is established with carrier salt being added and removed at the same volume rate, with actinide being added as fast as it is burned away, and with fission products being removed as fast as they are produced in the system. In this equilibrium condition the carrier salt level in the system remains relatively constant and the fission product and actinide concentrations remain relatively constant. The average chain length is therefore controlable, e.g., it can be maintained relatively constant at approximately 20-40 fission events or as otherwise desired. The residence time in the tank of the carrier salt and the other salts dissolved in the reactor vessel is several years during which time about 80% of the actinide atoms are caused to fission. An essential feature which enables high performance is fission product burn-out. In the thermal neutron flux of this system, high cross section fission products are transmuted to low cross section nuclides in a time much less than the residence time of the fission product nuclides in the system. The result is that the average capture cross section of the fission products is much smaller than in other transmutation systems. Non-beneficial capture of neutrons in fission products is reduced with corresponding significant enhancement in system waste burn-up performance. In a preferred embodiment of the present invention, the carrier salt is heated by the energy released in the fission process. The internal flow of the salt is therefore through the graphite, then to internal heat exchangers, and then back through the graphite. The salt therefore never leaves the tank in normal operation. The carrier salt, which may also be called the primary salt, is cooled in the heat exchangers inside the tank by heat transfer to a second salt with lower melting point which flows in an external loop referred to as the secondary loop. This loop contains a steam generator which cools the secondary salt by converting the heat to steam which is used to drive a steam turbine for electric power generation. The electric power generated is more than sufficient to power the accelerator which provides the proton beam used to produce the neutrons which start the fission chains. About 90% of the electric power generated is saleable into a commercial grid at a price which is likely to pay all of the capital and operations cost of the system. If all of these costs actually are paid by electric power sales, the cost of destruction of the waste is zero. The benefits of the present invention include the destruction of the nuclear weapons useful material in commercial spent fuel, the conversion of remnant actinide waste to a form highly unfavorable for nuclear weapons use, the conversion of the remnant waste to a form for which criticality is virtually impossible in permanent geologic storage or in any operations preceding geologic storage, and the extraction of about 80% of the fission energy potentially recoverable from the commercial spent fuel. In addition longer-lived fission product species such as .sup.129 I and .sup.99 Tc are reduced. The advantages of this method compared to other proposals is that it requires no back-end chemistry, no solid fuel fabrication, no solid fuel refabrication, no fuel cooling time prior to chemistry and no system down time for refueling. There also are no transportation requirements among the facilities required for the foregoing functions. In addition, because the fission chain length is maintainable steady with time, the accelerator required is smaller, and therefore the capital cost, operating cost, and electric power usage are smaller than that for competing systems. Virtually all of the world's nuclear power is produced from conventional light water reactors (LWRs) which produce in addition to nuclear power waste containing weapons-useful plutonium, americium and neptunium. Each of the approximately 400 LWRs in the world produces about 250 kg per year of plutonium and neptunium. By the end of an assumed lifetime of 40 years, these reactors will produce more than 4,000,000 kilograms of plutonium. Some nations wish to view this material as an asset and accordingly have devised mixed oxide (MOX) fuel fabrication for burning this material in light water reactors. However, this approach does not allow the burning of nearly all of the plutonium and, as seen in the upper part of FIG. 1, it requires a complex infrastructure. In the scenario presented in the upper part of FIG. 1, separation of a pure stream of plutonium in a reprocessing step occurs first. Subsequent to this required reprocessing step, solid MOX fuel assemblies are manufactured out of this highly radioactive material, which is considerably more difficult compared with the manufacture of ordinary LWR fuel assemblies because of the radioactivity. Such technology allows two cycles of MOX burning before going through the reprocessing step to produce pure plutonium for burning in fast reactors. In principle it can all be burned away in fast reactors with repeated recycle. Alternatively, bypass of MOX burning in the LWRs is possible followed by fast reactor burning. However, a fast reactor is considerably more expensive to build and operate than an LWR, thus significant burning of plutonium has only been done in LWRs, which is an incomplete process. In any case, geologic storage of the remnant waste is required. Other nations such as the U. S. and Sweden fear that the pure plutonium stream produced in reprocessing represents a high proliferation risk and, therefore, plan to bury the spent fuel directly into geologic storage facilities. This approach has an additional benefit that the total cost of nuclear power is reduced by avoiding the reprocessing and the subsequent plutonium burning steps. However, this approach also results in the accumulation of enormous amounts of weapons-useful material in repository storage as stated above. While it is no threat as long as it stays in storage, the International Atomic Energy Agency has argued that such waste must be guarded in perpetuity which probably is not practical. There is potentially great benefit from recovering plutonium from geologic storage for weapons use. It has been shown that a nation or subnational group wishing to develop nuclear weapons sometime in the future will find it ten times faster and ten times less expensive to recover plutonium from geologic storage than to develop reactors to produce plutonium or to produce highly enriched uranium by isotopic separation. Many would therefore argue that the U. S. policy of direct storage of spent fuel must change to one allowing burning sufficient to at least eliminate the weapons-useful material and thus make possible geologic storage safe at least from the proliferation perspective. Interest is rising world-wide in the use of fast reactors and accelerator-driven systems for the purpose of waste burning. Fast reactors alone appear not to be practical because of the high cost already mentioned and because, according to the U. S. National Academy of Sciences, the reduction of plutonium would require an impracticably long campaign. Accelerator-driven fast reactors are also under study, but an argument can be made that if fast reactors and associated facilities are already too expensive, how can one make these systems practical with the addition of an expensive accelerator? Proponents believe that the accelerator will reduce the cost of some of the facilities and thereby make the costs acceptable. The intent behind the present invention is to make plutonium burning practical by using an accelerator with a thermal spectrum system to eliminate associated elements completely as illustrated in the bottom part of FIG. 1. An embodiment of the present invention, as shown in the lower part of FIG. 1, uses a fluorination step for removal of zirconium and uranium which are the main constituents of the spent fuel. The actinides alone or the actinides plus the fission products are then fed into the thermal spectrum liquid fueled system labeled as Tier-1 accelerator driven system (ADS) in FIG. 1. Without any further steps and with only a single pass, the weapons-useful material is eliminated. The 20% of the non-weapons-useful actinide which remains from actinide-only burning is recycled to a system similar to embodiments of the present invention. In such a system nearly complete burn-up is possible of the actinide and long-lived fission product thereby eliminating most of the need for geologic storage. Alternatively, the 20% non-weapons remnant is converted to oxide and sent to geologic storage. Both the ADS technology and "established technology" of FIG. 1 eliminate weapons-useful material and require geologic storage of the remnant, so their functional performance reaches basically the same end result. However, the evident elimination of many functions by comparison of the top and bottom of FIG. 1 is the reason that the thermal spectrum system incorporating an accelerator is practical from a cost perspective in spite of the inclusion of an accelerator. The accelerator allows the elimination of several costly facilities and operations. FIG. 2 shows the various elements and functions of the apparatus. A conventional LWR 10 generates 1000 megawatts of electric power for distribution into the commercial grid and about 3000 megawatts of fission heat. In FIG. 2, a transmuter 16 is fed with approximately 300 kg per year of plutonium and minor actinide and outputs approximately 65 kg per year of plutonium and minor actinide and approximately 235 kg per year of fission product along with NaF--ZrF.sub.4 carrier salt. As shown in FIG. 2, approximately 240 MW of electric power is available for input to a commercial grid; sale of this power pays for most of the transmutation capital and operating cost. The transmuter 16 is practically placed either at the power plant site or at a central transmutation site. Overall, the system shown in FIG. 2 destroys weapons plutonium or other weapons material, eliminates the possibility of underground criticality in a repository, recovers 80% of fission energy before waste emplacement, and eliminates instantly and irreversibly the weapons potential of plutonium upon entry into the transmuter 16. The spent fuel assemblies which are removed from the reactor undergo a fluorination process 11 based on established non-aqueous chemistry which converts the constituents, except for noble gases, to fluoride chemical compounds. The fuel assemblies are dad with zirconium which is converted to ZrF.sub.4 salt. The uranium inside the fuel assemblies is converted to UF.sub.6 and stored in canisters 12 for possible reuse. Alternatively, the canisters are sent to geologic storage 13. The reactor produces 300 kg/year of higher actinide which consists mostly of plutonium and about 15% minor actinide. The reactor also produces 1200 kg/year of fission products. Both the higher actinides and fission products are sent to the transmuter 16, or, alternatively, only the higher actinides are sent. If the fission products are not sent to the transmuter, they are sent 14 to geologic storage. If fission products are not sent to the transmuter, the fluorination step 11 is supplemented by additional non-aqueous separations operations to remove the fission products. Some of the ZrF4 is sent to the transmuter along with the higher actinides and fission products. Before entering the transmuter, NaF or a material of similar neutronic, chemical, and physical character is added 15 to the actinide and fission product mixture in about equal amounts in molecules to the ZrF.sub.4. The NaF and ZrF.sub.4 make up about 90% of the total of the fluoride molecules being added into the transmuter. Together they form a molten salt with a melting point of about 550 degrees Celsius and this molten salt mixture becomes a carrier for the higher actinide and fission product fluorides which are dissolved into the carrier. If the transmuter processes waste as fast as it is produced in the LWR, a feed of 300 kg/year of plutonium and minor actinide (PMA) is required by the system. If all of the fission product produced in the LWR per year is fed into the system as fast as it is produced, about 1200 kg/year flows into the system. The transmuter 16 is a nuclear-reactor-like facility which however is subcritical and incapable of supporting a continuous chain reaction. However, fission chains of finite length of about 10 to 100, and preferably 20 to 40, fissions in the actinide material are started by neutrons produced by a beam of protons. In a preferred embodiment of the present invention, this beam enters the transmuter in a vertical or near vertical direction and strikes a liquid target that may consist of a heavy metal such as lead or a lead-bismuth mixture. For a beam energy of 1 GeV, one proton produces about thirty neutrons in expending its energy in the lead and about half of these neutrons start fission chains. Heat from the fission process Is converted to electric power 17 by steam-driven turbines and most of this electric power is saleable into the commercial grid 18. Roughly 10% of the electric power is used by the accelerator and therefore not sold into the grid. The fraction of the 300 kg/year of PMA fed into the transmuter which is destroyed depends on the amount of fission product from the commercial LWR which is fed into the transmuter. Any portion between almost all or almost none of the LWR fission product is sent into the system. If almost none is sent in, about 80% of the PMA is destroyed by fission and about 600 megawatts of fission thermal power is produced. In that case the amount of actinide fissioned is about 240 kg/year and the amount of fission product generated by this fission and removed from the transmuter is the same amount or about 250 kg/year. If almost all of the fission product from the LWR is sent in, the fraction of the PMA fissioned is less and is about 66%. Therefore about 200 kg/year of PMA is fissioned and the same amount of fission product or about 200 kg/year are created internally. The fission thermal power produced is also less and is about 500 megawatts. The fission product removed from the system is all of that sent in which is 1200 kg/year plus 200 kg/year generated in transmutation for a total of 1400 kg/year. The salt removed from the system containing the transmuted PMA and fission products is placed in steel canisters 19 for cooling and possible further transmutation for complete destruction of PMA and long-lived fission products. Alternatively, the removed salt is convertible from fluoride to oxide and sent to geologic storage after an appropriate cool-down period. FIG. 3 is a schematic representation showing the essential difference between recycle for fission product removal as commonly proposed in transmutation and a continuous flow embodiment of the present invention. The conventional approach to transmutation as shown in the upper part of FIG. 3, typically includes an accelerator 20, usually incorporates solid fuel, and involves closely coupled back-end chemistry. Waste is fed 21 Into the transmuter 22 by appropriate means and removed 23 after partial burning for the purpose of fission product removal 24. The removal process requires a high degree of efficiency In returning nearly all of the PMA to the transmuter for further transmutation. Returning some of the fission product, as well as PMA, is acceptable but less desirable. The extracted fission product typically goes to storage 25 with as little PMA mixed with the stored fission product as practical. One problem with this conventional approach is the cost, expense, and time required for the back-end fission product removal. At a minimum the chemistry operation is substantial, but there is also possibly the need for fuel destruction, fuel refabrication, fuel cooling and down time for fuel removal and insertion. The lower section of FIG. 3 illustrates the comparative simplicity of a continuous flow embodiment of the present invention which incorporates an accelerator 30. LWR waste is fed 26 into the transmuter 27 in the form of molten fluoride salt. The transmuter is considered a tank, or vessel, in which the waste entering as (PMA).sub.1 and (f. p.).sub.1 dissolved in NaF--ZrF.sub.4 is transmuted to other forms by neutron-induced reactions. After the system has reached equilibrium, molten salt consisting of the carrier NaF--ZrF.sub.4, the (PMA).sub.2 and (f. p.).sub.2 is removed 28 from the tank at the same rate that salt is fed into the tank. This removed salt is not returned to the tank but is stored in appropriate canisters 29. Therefore back-end chemistry as well as possible fuel destruction, fuel cooling, and fuel refabrication are eliminated. Capital and operating costs are reduced and the cost of down-time spent in removing and adding fuel also is eliminated. The removed salt has a different composition from the fed salt. Although the carrier salt is unchanged, the input (PMA), concentration is reduced by the fission process and the isotopic composition transformed to the output (PMA).sub.2. The input (f. p.).sub.1 concentration in the carrier salt is increased by the fission products produced by fission in the transmuter to the output (f. P.).sub.2 concentration. Note the seemingly trivial point that the removed salt has the same composition as the salt in the tank. This point is important because it means that the isotopic composition of the fed salt is changed immediately and irreversibly upon mixing with the salt in the tank. This is a valuable feature from the perspective on non-proliferation of nuclear weapons. For most transmutation concepts, the inventory of weapons-useful material is quite large and feeding it into a transmuter for destruction does not prevent its being removed before destruction is complete. This embodiment of the present invention, by contrast, has the feature that once the weapons-useful material is fed in, it immediately is rendered no longer useful for nuclear weapons use. The degree of the change between the input and internal composition of the actinide is illustrated in FIG. 4 where the input and output (or internal) isotopic compositions of the actinides are compared for the case of no feed of LWR fission products. The back bars show the isotopic abundance of the spent fuel plutonium and minor actinide which is the feed for the transmuter. The front bars show the major reduction in total actinide and the isotopic composition in the exit stream. Only about 20% of the LWR actinide feed remains in the exit stream, so nearly all of the fission energy from the plutonium and minor actinide is recovered. Clearly the exit isotopic composition is no longer dominated by the fissile species .sup.239 Pu and .sup.241 Pu and the weapons value and criticality potential are greatly reduced. If this material is sent to geologic storage, the actinide load is reduced overall by a factor of almost five, the plutonium content is reduced by seven, and the neptunium is reduced by ten. The Np reduction is significant because it is the most mobile of the actinides in a geologic repository and because it is the only isotopically pure weapons-useful material in LWR spent fuel. Data presented in FIG. 4 as a fractional abundance versus isotope for feed and output after a single pass through the system are as follow: Isotope Feed Output .sup.237 Np 0.045 0.0093 .sup.241 Am 0.051 0.0040 .sup.238 Pu 0.014 0.0052 .sup.239 Pu 0.515 0.0325 .sup.240 Pu 0.238 0.0197 .sup.241 Pu 0.079 0.0186 .sup.242 Pu 0.048 0.0536 .sup.243 Am 0.009 0.0223 .sup.244 Cm 0.000 0.0414 .sup.245 Cm 0.000 0.0012 .sup.246 Cm 0.000 0.0043 Total 1.000 0.2121 A key feature of the present invention that makes possible this degree of transmutation without back-end reprocessing is the reduction in the fission product effective capture cross section for neutrons (the term cross section is the apparent area of the atomic nucleus which would intercept neutrons flying in random directions through the medium and it is measured in a unit of area of 10.sup.-24 cm.sup.2 called the barn). The average cross section for the fission product material arising from the fission process might be about 30 barns if one averaged over all of the capture cross sections weighting them with the fission product abundances. However a few of the fission products have cross sections much larger than thirty barns. Naturally these fission products are more rapidly transmuted than those with smaller cross sections and in almost every case the capture cross section of the daughter fission product after neutron absorption is much lower than that of the parent. If the nuclides with the larger capture cross sections are transmuted to a nuclide with a smaller cross section in a time short compared to the average residence time of the fission product in the tank, the fission product with large cross sections are not present most of the time. For the embodiment of the present invention described here, the average fission product capture cross section undergoing irradiation in the tank 27 is found to be 6.00 barns instead of 30 barns. This reduced effective fission product capture cross section is of great importance to the degree of burn-up possible for PMA. Loss of neutrons by capture on fission products does not allow them to be used to destroy as much PMA. An important feature of the thermal spectrum as implemented in this invention is that the rate of burn-up of PMA or f. p. is fast enough to make practical this reduction in effective fission product cross section. The Target-Blanket An accelerator-driven system (ADS) for transmutation of commercial nuclear waste is shown in FIGS. 5 and 6. The system is driven by an accelerator in order to start many chains which run for a relatively short time in contrast to a reactor for which the chain runs continuously until the reactor is shut down. The effective multiplication factor k.sub.eff, which is 1.00 for a continuous chain reactor, is reduced to the range of 0.98-0.95 for which the corresponding chain length is about 50-20 fission events. One significant advantage of this mode is that the neutrons, which otherwise are required to maintain a continuous chain, are put to other uses, in particular, the destruction of nuclear waste. A second benefit is that constraints on reactor design required to keep k.sub.eff =1 are relaxed and a broader design parameter space is practical. For example, an accidental injection of reactivity which leads to a runaway chain reaction for a reactor with k.sub.eff =1 is hardly noticed with k.sub.eff =0.96. Neutrons are produced via the spallation process by the accelerator beam 31 as it moves through a vacuum 32 and strikes and penetrates a lead or lead-bismuth target 33. The lead is circulated to external heat exchangers 35, 36. Some of these protons strike neutrons or protons in the lead target nuclei and eject them in the forward direction with a lower energy than the incident proton. These second particles of neutrons, and sometimes protons, then strike other particles which are forward moving but with lower energy. This spallation cascade continues until the primary proton and other charged particles come to rest. The total cascade length is approximately one meter for 1-GeV beam energy. In any of these nuclear collisions, the struck nucleus is always excited to some degree and these "hot" nuclides get rid of this excess energy by "boiling off" neutrons. In fact about 90% of the neutrons are produced in boil-off reactions. The boil-off neutrons also are isotropic in contrast to the forward moving direct reaction neutrons. The lead length is longer by about one meter than the limit of primary and secondary proton penetration. The forward moving direct reaction neutrons continue to move downward exciting other nuclides and losing energy in the process. Altogether about 30 neutrons are produced by each 1 -GeV proton. Most of these neutrons are produced with energies between 0.5 MeV and 5 MeV and slow down by inelastic scattering at higher energies and by elastic scattering in the lead at lower energies. By the time that the neutrons reach the metallic container for the lead 53 (in FIG. 6), which has a larger radius than the radial limit of proton penetration, the neutrons' energy is sufficiently low that neutron damage to the metallic containment vessel for the lead is low enough for acceptable engineering practice. A small component of higher energy neutrons remain and sometimes strike the vessel wall, but the intensity of these neutrons is reduced sufficiently that damage by them to the lead container is acceptable. The radius and length of the lead canister is sufficiently larger than the limits of primary and secondary proton penetration that the neutron production is near the maximum possible and that the energy of the neutron flux striking the wall is reduced sufficiently to limit damage to the container wall to an acceptable level. The production of neutrons by the spallation process and the moderation of the neutrons into the thermal range is an essential feature of embodiments of the present invention described herein. Neutrons generated via beam-target interactions pass through the container into surrounding graphite 49 and moderate further eventually reaching a thermal temperature in which the neutron spectrum is nearly in equilibrium with the temperature of the graphite. The neutrons move further outward into a blanket made up of vertical hexagonal graphite logs 38, 52 with one or more channels carrying the salt 37, 39, 50 containing the fissile material. The graphite log may also have a removable graphite sleeve inside 51. The assemblies fit into a graphite or HASTELLOY.RTM.-N metal, or metal of similar properties, plenum 47 at the bottom. Solid hexagonal graphite assemblies providing a reflector thickness around the outside of about 50-cm are not shown. Between 35% and 60% of the accelerator-produced neutrons start fission chains depending on design details. These chains run for 20-50 fission events before stopping depending on the design details. Therefore if 50% of the accelerator-produced neutrons start a fission chain of length 50 fission events, one 1 GeV proton would generate 30.times.50.times.0.5=650 fission events which corresponds to an energy of 650.times.0.2 GeV=130 GeV. For a beam current of 6 mA, the fission power level would be 750 MWt. Heat is dissipated in the medium and is extracted and converted to electric power with a thermal-to-electric efficiency of about 42% made possible by the high (up to about 720 degrees Celsius) operating temperature of the molten salt. Some of this power is fed back to the accelerator, which generally operates with a buss bar efficiency of about 45%. For these numbers, the portion of the generated power required to drive the accelerator is 6/(600.times.0.42.times.0.45)=5.0%. In practice, fewer than 50% of the accelerator-produced neutrons might start fission chains and the fraction of generated power required by the accelerator is usually larger. Salt flows upward and out of the channels into a shallow pool on top of the graphite and then outward to a circumferential channel above an array of heat exchangers 41 which fill the 360-degree volume below the circumferential channel. Salt flows fast enough that salt fountains 48 form as the salt leaves the channels. The salt is pumped downward 40 through the heat exchangers to the bottom of the tank 46 and across the bottom of the tank before returning through the plenum 47 into the channels in the graphite. The heat is transferred to a second salt of lower melting point than the primary salt which flows into collecting piping 42 surrounding the top of the tank with the piping supported by an appropriate structure 43. A flow of helium gas across the top of the salt pool 45 collects volatile fission product species and carries them through a heated channel (not shown) away from the tank and to a condensation system for separation of different species as required. The overall dimension of the system is about five meters in diameter and about five meters in height. An embodiment of the present invention includes a fuse system to enhance safety by fail-safe interruption of nuclear power production. A wire with melting point at a temperature higher than that of the salt in normal operation, but lower than the temperature at the threshold for system damage, is placed in the salt trough or other appropriate place. The wire provides a key voltage or current for operating the injector of the accelerator. Melting of the wire by overheat in an accident would result in a short-circuiting of the electricity to the injector and therefore to an instantaneous removal of the proton beam current. A similar wire performing in the same way would be used to sense a malfunction in the liquid lead spallation target and thereby to interrupt automatically the accelerator beam and therefore the power generation. In order to limit corrosion by the molten salt to an inconsequential level, it is necessary to control the fluoride ion balance in the system. A procedure maybe employed similar to that used at the Oak Ridge National Laboratory in the Molten Salt Reactor Experiment, which incorporated a metal in the molten salt circuit which formed fluoride salt with the excess fluorine. Features of the present invention are open to modification and include, but are not limited to, fission energy production, removal, and conversion to electric power, processes for removal of volatiles using helium or other gas flow; techniques for fail-safe termination of electric power production using a fusing system for both the molten salt and the liquid lead as part of a safety system; implementation of means for maintaining ion fluoride balance; and halogenization of reactor spent fuel for preparation of the spent fuel for transmutation. Performance Features The particular design of the present invention's transmutation system was developed to enable performance in several respects which are not possible with alternative transmutation designs. These features and the comparison with the fast spectrum are discussed briefly below. Conversion to Non-Weapons Plutonium Part of the reason that the system described here yields a plutonium remnant which is not weapons-useful without implementation of reprocessing is the more favorable cross sections of the thermal spectrum for fissioning the odd isotopes, which are most desirable in weapons material, and for not destroying the even isotopes, which are not desirable in weapons material. By contrast, the fast spectrum incorporated in alternative designs destroys by fission both even and odd isotopes without significant discrimination. The plutonium remnant from transmutation in a fast spectrum is therefore necessarily much more weapons-useful than the remnant from thermal spectrum transmutation. Production of a New Type of Weapon-Useful Material during Transmutation The nucleus .sup.242m Am has a thermal cross section for fission ten times higher than that for .sup.239 Pu. It also releases more neutrons per fission than .sup.239 Pu and features a cross section dependence on neutron energy favorable for certain types of nuclear explosives. Because it has such a high thermal cross-section for fission, it is virtually non-existent in LWR spent fuel. It is destroyed soon after it is produced in the LWR because of its large thermal fission cross section. Any .sup.242m Am produced in the thermal spectrum transmuter is destroyed even more rapidly than in a LWR. In transmutation of LWR waste in fast spectrum systems, .sup.242m Am is created but it is not destroyed nearly as readily as in the thermal spectrum. In addition it is produced with about three times greater likelihood from neutron capture on .sup.242 Am in the fast spectrum than in the thermal spectrum. The result is that .sup.242m Am is produced in significant quantities in a fast spectrum transmuter but it is not produced in a thermal spectrum transmuter. Therefore, proliferation of nuclear weapons material may be a concern in regard to .sup.242m Am for the fast spectrum but not for the thermal spectrum. Inventory of Actinide Required for Transmutation Weapons-useful material is made inaccessible to a significant degree when it is in spent fuel assemblies prior to transmutation. It is confined in a case of metal cladding and removal from spent fuel assemblies system is further deterred by the gamma radioactivity of the spent fuel. Once the integrity of the spent fuel has been destroyed and transmutation begun, weapons material can in principle be recovered at any point in the transmutation process. The larger the concentration of plutonium and the greater the amount of plutonium carried in the system, the easier it is to recover. The high thermal cross section for fission makes it possible to transmute waste in a thermal spectrum with a minimum of weapons-useful inventory. For a fast spectrum the inventory required for transmutation is ten to thirty times higher. Of course there is no weapons-useful material in the present invention; it is only accessible potentially during the time interval between destruction of the spent fuel assemblies and entry into the transmuter. For the fast spectrum, weapons-useful plutonium is accessible before transmutation, during transmutation if the transmuter is stopped for removal of its inventory, and during the reprocessing and fuel refabrication steps. Reactivity Stability during Transmutation and Required Fission Power The system of the present invention maintains constant reactivity by the use of liquid fuel and the constant inflow and removal of actinide and/or fission product. The only fission energy produced is that from the fission of the LWR waste being destroyed. Solid fuel systems cannot maintain stability since fissile material is burned up and not replaced. To more nearly approach stability in solid fuel systems, fissile material is produced and partially burned by breeding from .sup.238 U or .sup.232 Th. While stability is improved, as much as half of the fission energy produced is from the bred fissile material (.sup.233 U or .sup.239 Pu). Therefore, the fission power per kilogram of commercial plutonium destroyed is twice as high as in a liquid fueled system. Consequentially, the capital investment in facilities is also twice as high as in a liquid fueled system to destroy the weapons useful material at the same rate. Reactivity Stability during Transmutation and Accelerator Power Some of the instability in reactivity of a solid fueled system still remains even when including breeding of fissile material from .sup.238 U or .sup.232 Th. The reactivity changes sufficiently in spite of the breeding to require a change in accelerator power by a factor of about two to maintain constant fission power. Therefore, the accelerator operates only about half of the time at its highest power level. The capital Investment in the accelerator Is only used half of the time. For the liquid fueled system, reactivity is constant and the accelerator operates at full power all of the time. In addition the power of the accelerator is proportional to the fission power which is twice as large per kilogram of plutonium destroyed for a solid fueled system as for a liquid fueled system. Taken together, the accelerator capital investment for destroying a given amount of plutonium is four times as large for a solid-fueled system as for a liquid-fueled system. Removal of Some of the Metallic Fission Products Many of the fission products combine with free fluorine in the salt and form fission product fluoride salt, which circulate with the carrier salt. However, several of the metallic fission products instead deposit on metallic surfaces. In a preferred embodiment of the present invention, virtually the entire metallic surface is in the heat exchangers. These fission products are, therefore, deposited where they do not parasitically absorb neutrons and spoil the neutron economy. After several years, the fission products accumulate sufficiently that the performance of the heat exchanger is compromised, at which point the heat exchanger is replaced. Therefore, the design of the present invention includes means for fast and easy replacement of the internal heat exchangers. System Application The application of the system to two scenarios is shown in FIGS. 7 and 8. These calculations assume that only PMA from LWR fuel is added to the transmuters. Nuclear Energy Growth through Transmutation; 100 LWR Deployment The impact of the deployment of the transmuters on the inventory of PMA from a 100-LWR fleet is shown in FIG. 7 where the arrest in the growth of these materials and the reduction to a minimum equilibrium quantity is presented. The figure assumes an indefinitely long deployment of one hundred 3000-MWt LWRs made partly possible by transmutation deployment. Without transmutation, the inventory of Pu and minor actinide waste would grow by 2050 to about 1800 tons total from these LWRS. For simplicity it is assumed that the LWRs were deployed at the rate of five per year for twenty years with deployment beginning in 1975. It is assumed also that the transmutation technology would be ready for deployment by 2015. If one 750-MWt transmuter were deployed for each LWR, it would only stop the growth in PMA waste or weapons-useful material at a national inventory of about 1000 tons. To eliminate the potential weapons from this material would require as shown in FIG. 7 a system twice as large using a 1500-MWt version of the Tier 1 technology (or two 750-MWt systems per LWR). The curves assume the deployment of the Tier 1 1500 MWt transmuters at the rate of 10 per year between 2015 and 2025. By the year 2050, the weapons material is brought under control. The reduction of the weapons material is therefore achieved in about one human generation. The only weapons material left is the untransmuted neptunium remaining in the transmuters and in the transmuted waste remnant. The deployment of these transmutation systems would increase the nuclear power by 50% during the 35-year burn-down period. After that point the 100 ADS deployment, if retained, would be twice as large as necessary. The ADS fleet could be maintained to accommodate the waste from an increase from the 100 LWR fleet to 200 LWRS. In this event the nuclear power output would grow by a factor of 2.5 without the presence of weapons-useful material in geologic storage. Nuclear Energy Close-Out Option; 100 LWR Fleet FIG. 8 presents the nuclear closeout option for nuclear power using transmutation. One hundred 750-MWt transmuters are deployed between 2015 and 2025, which would allow about 16 years for development and demonstration of the transmutation technology. The upper curve shows the production of nuclear waste without transmutation assuming that the LWR lifetime is 40 years. The curve below shows the build up of weapons useful material that is mostly plutonium but also includes the neptunium. The next curve shows the time dependence for the reduction of the weapons material that is reduced by a factor of about 50 in about 40 years. The lowest curve shows the accumulation of transmuted PMA which is free of weapons material and which is reduced by a factor of about 5 below that of the untransmuted waste stream. This material is either sent to geologic storage or to similar transmuters with backend separations where the actinide content is reduced by an additional factor of 200 for a total actinide reduction factor of 1000. Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference. |
description | This application claims, under 35 U.S.C. 119(e), priority to and the benefit of U.S. Provisional Application No. 61/329,425, filed Apr. 29, 2010. This application is, under 35 U.S.C. 120, a continuation-in-part application of U.S. application Ser. No. 12/434,888 (now U.S. Pat. No. 8,368,403), filed May 4, 2009 and U.S. application Ser. No. 13/030,780 (now U.S. Pat. No. 9,134,449), filed Feb. 18, 2011. Technical Field The present disclosure relates generally to the logging of subsurface formations surrounding a wellbore using a downhole logging tool, and particularly to obtaining gain-corrected measurements. Background Art Logging tools have long been used in wellbores to make, for example, formation evaluation measurements to infer properties of the formations surrounding the borehole and the fluids in the formations. Common logging tools include electromagnetic tools, nuclear tools, and nuclear magnetic resonance (NMR) tools, though various other tool types are also used. Early logging tools were run into a wellbore on a wireline cable, after the wellbore had been drilled. Modern versions of such wireline tools are still used extensively. However, the need for information while drilling the borehole gave rise to measurement-while-drilling (MWD) tools and logging-while-drilling (LWD) tools. MWD tools typically provide drilling parameter information such as weight on the bit, torque, temperature, pressure, direction, and inclination. LWD tools typically provide formation evaluation measurements such as resistivity, porosity, and NMR distributions. MWD and LWD tools often have components common to wireline tools (e.g., transmitting and receiving antennas), but MWD and LWD tools must be constructed to not only endure but to operate in the harsh environment of drilling. A method to obtain gain-corrected measurements. A measurement tool having one or more arrays is provided, wherein the arrays include two co-located triaxial transmitters and two co-located triaxial receivers. Measurements are obtained using the transmitters and the receivers. Impedance matrices are formed from the obtained measurements and the impedance matrices are combined to provide gain-corrected measurements. The apparatus may alternatively be a while-drilling logging tool having one or more arrays, wherein each array comprises a transmitter, a receiver, and a buck, and wherein the signal received by the receiver is subtracted from the signal received by the buck or vice versa. A slotted shield may be incorporated into either embodiment of the tool. The slots may form one or more island elements. A material is disposed in the slots. The islands and shield body have complementary tapered sides that confine the islands within the shield body. Other aspects and advantages will become apparent from the following description and the attached claims. Some embodiments will now be described with reference to the figures. Like elements in the various figures will be referenced with like numbers for consistency. In the following description, numerous details are set forth to provide an understanding of various embodiments and/or features. However, it will be understood by those skilled in the art that some embodiments may be practiced without many of these details and that numerous variations or modifications from the described embodiments are possible. As used here, the terms “above” and “below”, “up” and “down”, “upper” and “lower”, “upwardly” and “downwardly”, and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe certain embodiments. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or diagonal relationship as appropriate. FIG. 1 illustrates a well site system in which various embodiments can be employed. The well site can be onshore or offshore. In this exemplary system, a borehole 11 is formed in subsurface formations by rotary drilling in a manner that is well known. Some embodiments can also use directional drilling, as will be described hereinafter. A drill string 12 is suspended within the borehole 11 and has a bottom hole assembly 100 which includes a drill bit 105 at its lower end. The surface system includes platform and derrick assembly 10 positioned over the borehole 11, the assembly 10 including a rotary table 16, kelly 17, hook 18 and rotary swivel 19. The drill string 12 is rotated by the rotary table 16, energized by means not shown, which engages the kelly 17 at the upper end of the drill string. The drill string 12 is suspended from a hook 18, attached to a traveling block (also not shown), through the kelly 17 and a rotary swivel 19 which permits rotation of the drill string relative to the hook. As is well known, a top drive system could alternatively be used. In the example of this embodiment, the surface system further includes drilling fluid or mud 26 stored in a pit 27 formed at the well site. A pump 29 delivers the drilling fluid 26 to the interior of the drill string 12 via a port in the swivel 19, causing the drilling fluid to flow downwardly through the drill string 12 as indicated by the directional arrow 8. The drilling fluid exits the drill string 12 via ports in the drill bit 105, and then circulates upwardly through the annulus region between the outside of the drill string and the wall of the borehole, as indicated by the directional arrows 9. In this well known manner, the drilling fluid lubricates the drill bit 105 and carries formation cuttings up to the surface as it is returned to the pit 27 for recirculation. The bottom hole assembly 100 of the illustrated embodiment includes a logging-while-drilling (LWD) module 120, a measuring-while-drilling (MWD) module 130, a roto-steerable system and motor, and drill bit 105. The LWD module 120 is housed in a special type of drill collar, as is known in the art, and can contain one or a plurality of known types of logging tools. It will also be understood that more than one LWD and/or MWD module can be employed, e.g. as represented at 120A. (References, throughout, to a module at the position of 120 can alternatively mean a module at the position of 120A as well.) The LWD module includes capabilities for measuring, processing, and storing information, as well as for communicating with the surface equipment. In the present embodiment, the LWD module includes a resistivity measuring device. The MWD module 130 is also housed in a special type of drill collar, as is known in the art, and can contain one or more devices for measuring characteristics of the drill string and drill bit. The MWD tool further includes an apparatus (not shown) for generating electrical power to the downhole system. This may typically include a mud turbine generator powered by the flow of the drilling fluid, it being understood that other power and/or battery systems may be employed. In the present embodiment, the MWD module includes one or more of the following types of measuring devices: a weight-on-bit measuring device, a torque measuring device, a vibration measuring device, a shock measuring device, a stick/slip measuring device, a direction measuring device, and an inclination measuring device. An example of a tool which can be the LWD tool 120, or can be a part of an LWD tool suite 120A, is shown in FIG. 2. As seen in FIG. 2, upper and lower transmitting antennas, T1 and T2, have upper and lower receiving antennas, R1 and R2, therebetween. The antennas are formed in recesses in a modified drill collar and mounted in insulating material. The phase shift of electromagnetic energy as between the receivers provides an indication of formation resistivity at a relatively shallow depth of investigation, and the attenuation of electromagnetic energy as between the receivers provides an indication of formation resistivity at a relatively deep depth of investigation. U.S. Pat. No. 4,899,112 can be referred to for further details. In operation, attenuation-representative signals and phase-representative signals are coupled to a processor, an output of which is coupleable to a telemetry circuit. Recent electromagnetic logging tools use one or more tilted or transverse antennas, with or without axial antennas. Those antennas may be transmitters or receivers. A tilted antenna is one whose dipole moment is neither parallel nor perpendicular to the longitudinal axis of the tool. A transverse antenna is one whose dipole moment is substantially perpendicular to the longitudinal axis of the tool, and an axial antenna is one whose dipole moment is substantially parallel to the longitudinal axis of the tool. A triaxial antenna is one in which three antennas (i.e., antenna coils) are arranged to be mutually independent. That is, the dipole moment of any one of the antennas does not lie in the plane formed by the dipole moments of the other two antennas. Three orthogonal antennas, with one antenna axial and the other two transverse, is one example of a triaxial antenna. Two antennas are said to have equal angles if their dipole moment vectors intersect the tool's longitudinal axis at the same angle. For example, two tilted antennas have the same tilt angle if their dipole moment vectors, having their tails conceptually fixed to a point on the tool's longitudinal axis, lie on the surface of a right circular cone centered on the tool's longitudinal axis and having its vertex at that reference point. Transverse antennas obviously have equal angles of 90 degrees, and that is true regardless of their azimuthal orientations relative to the tool. One possible embodiment of antenna design includes multi-component coils. For example, a co-located triaxial tilted antenna used for downhole resistivity measurements may be provided. The tilted coils each comprise a portion of a closed circuit around the collar perimeter, and can be either embedded in a recess about the tool collar or in a nonconductive cylinder that slides over the collar. The design has at least one triaxial antenna that can be used as a transmitter (or a receiver) with at least one additional antenna displaced along the tool axis as a receiver (or a transmitter). Multiple antennas with different spacings and frequencies may be used to cover the desired conductivity ranges and depths of investigation. The effect of farther transmitter-receiver spacing and/or a more conductive formation is compensated by using a lower frequency signal. FIG. 3 shows a tool with a tilted transmitter and a triaxial orthogonal receiver (the three receivers could also be orthonormal to one another). FIG. 4 shows the magnetic dipole equivalent of a logging tool with a co-located triaxial tilted transmitter and a tilted receiver, and FIG. 5 shows another embodiment in which the transmitter and the receiver are both co-located triaxial tilted antennas. It can be shown that the square of the norm of raw measurements between a transmitter, T, and a receiver, R, is a function of the instantaneous tool face angle, and that it can be decomposed into a finite set of Fourier coefficients. Below is the general formula of the coupling between two magnetic dipoles with known orientations, as depicted in FIG. 6. FIG. 6 shows a T and an R antenna both tilted so that their equivalent magnetic dipole moments are at an angle β relative to the tool axis (45 degrees for FIG. 6). However, as shown, the antennas may have different azimuthal orientations. The azimuthal orientation of T relative to R is denoted by an angle α. That is, α is the angle between the projection of the receiver dipole moment onto the tool-fixed xy-plane and the projection of the transmitter dipole moment onto the same (or a parallel) plane. During drilling, if the tool rotates, for example, by a tool face angle ϕ, the T and R magnetic moments will rotate along with the tool while measurements are performed. The voltage measured at the receiver is then: V TR ( ϕ ) = 1 2 ( cos α , sin α , 1 ) · [ cos ϕ sin ϕ 0 - sin ϕ cos ϕ 0 0 0 1 ] · [ ( xx ) ( xy ) ( xz ) ( yx ) ( yy ) ( yz ) ( zx ) ( zy ) ( zz ) ] · [ cos ϕ - sin ϕ 0 sin ϕ cos ϕ 0 0 0 1 ] · ( 1 0 1 ) where the components of the coupling matrix (in the middle) (ij) are the elementary measurements in the absence of rotation when a transmitter in the i direction and a receiver in the j direction are used. The two matrices multiplying the coupling matrix are the rotation matrices that account for tool face angle. Finally, the vector on the right hand side is the orientation of the R dipole moment, while the one on the left hand side is that of the T antenna. The three matrixes in the middle can be re-written as M leading to:VTR(ϕ)=mTt·M(ϕ)·mR where M is given by: M ( ϕ ) = [ ( xx ) + ( yy ) 2 + ( xy ) + ( yx ) 2 sin ( 2 ϕ ) + ( xy ) - ( yx ) 2 + ( yy ) - ( xx ) 2 sin ( 2 ϕ ) + ( xz ) cos ( ϕ ) + ( yz ) sin ( ϕ ) ( xx ) - ( yy ) 2 cos ( 2 ϕ ) ( xy ) + ( yx ) 2 cos ( 2 ϕ ) ( yx ) - ( xy ) 2 + ( yy ) - ( xx ) 2 sin ( 2 ϕ ) + ( xx ) + ( yy ) 2 - ( xy ) + ( yx ) 2 sin ( 2 ϕ ) - ( yz ) cos ( ϕ ) - ( xz ) sin ( ϕ ) ( xy ) + ( yx ) 2 cos ( 2 ϕ ) ( xx ) - ( yy ) 2 cos ( 2 ϕ ) ( zx ) cos ( ϕ ) + ( zy ) sin ( ϕ ) ( zy ) cos ( ϕ ) - ( zx ) sin ( ϕ ) ( zz ) ] From the preceding equations, it is apparent that voltages measured at receivers will be periodic functions of the tool face angle ϕ and 2ϕ. The measured voltage can be represented as the second order Fourier expansion given by:VTR(ϕ)=a+b·cos(ϕ)+c·sin(ϕ)+d·cos(2ϕ)+e·sin(2ϕ)Those coefficients are simple linear combinations of individual terms of the coupling tensor. The relationships between the Fourier coefficients and the tensor coefficients are given by the next set of equations (after normalization by a factor of two): { DC Term = a = ( zz ) + cos ( α ) ( xx ) + ( yy ) 2 + sin ( α ) ( yx ) - ( xy ) 2 cos Term = b = ( zx ) + cos ( α ) ( xz ) + sin ( α ) ( yz ) sin Term = c = ( zy ) - sin ( α ) ( xz ) + cos ( α ) ( yz ) cos 2 Term = d = cos ( α ) ( xx ) - ( yy ) 2 + sin ( α ) ( xy ) + ( yx ) 2 sin 2 Term = e = - sin ( α ) ( xx ) - ( yy ) 2 + cos ( α ) ( xy ) + ( yx ) 2 ( 1 ) The extraction of Fourier coefficients is actually a linear problem, since the measured voltage at the receiver is a linear function of the unknown vector x=[a, b, c, d, e] with a known vector w expressed as:w=[1, cos(ϕ), sin(ϕ), cos(2ϕ), sin(2ϕ)]T Once at least five measurements are performed at different angles, the vector of Fourier coefficients can be computed by a Least-Square fit: V = [ V 1 ⋮ V N ] = [ 1 cos ( ϕ 1 ) sin ( ϕ 1 ) cos ( 2 ϕ 1 ) sin ( 2 ϕ 1 ) ⋮ ⋮ ⋮ ⋮ ⋮ 1 cos ( ϕ N ) sin ( ϕ N ) cos ( 2 ϕ N ) sin ( 2 ϕ N ) ] · [ a b c d e ] = K . u So u=MT(MT·M)−1V. It is also possible to have an on-line estimation of the same quantities by applying a Recursive Least-Square with the following goal function: J LS ( n ) = ∑ i = 1 n λ n - i ( V ( i ) - w ( i ) T . x ( i ) ) To reduce the effect of outliers that could appear in the data, we transform this problem goal function into: J M ( n ) = ∑ i = 1 n λ n - i ρ ( e ( i ) ) = ∑ i = 1 n λ n - i ρ ( y ( i ) - w T ( i ) x ( i ) ) with ρ ( e ) = { e 2 2 , 0 < e < ξ ξ 2 2 , otherwise which is the classic Huber function. The symbol ξ corresponds to a good estimate of noise standard deviation. To estimate ξ, the standard deviation of noise, we compute residuals on a sliding window of past points versus prediction based on computed Fourier coefficients by applying the following algorithm:{circumflex over (σ)}(n)=λσ{circumflex over (σ)}(n−1)+(1−λσ)c1med({e2(n),e2(n−1), . . . ,e2(n−Nw−1)})This estimate is robust through the usage of median filtering on a set of past observed values, and is made adaptive by the exponential weight used in the update formula. Once the Fourier coefficients are estimated, calibrated measurements can be constructed. The following shows how different kinds of measurements can be computed. The descriptions are split based on harmonics, because each harmonic leads to a measurement having a different azimuthal sensitivity. DC terms lead to measurements that do not depend on azimuth, first harmonic terms lead to measurements having a cos(ϕ) sensitivity, and second harmonic terms lead to measurements having a cos(2ϕ) sensitivity. Using equation set (1) with lines 1, 2 and 3, and defining M α = 1 rst H Cos D C & N α = 1 rst H Sin D C ,we have the first harmonic equations: { - M α cos ( α ) ( xx ) + ( yy ) 2 ( zz ) - M α sin ( α ) ( xy ) - ( yx ) 2 ( zz ) + ( xz ) ( zz ) + cos ( α ) ( zx ) ( zz ) + sin ( α ) ( zy ) ( zz ) = M α - N α cos ( α ) ( xx ) + ( yy ) 2 ( zz ) - N α sin ( α ) ( xy ) - ( yx ) 2 ( zz ) + ( yz ) ( zz ) - sin ( α ) ( zx ) ( zz ) + cos ( α ) ( zy ) ( zz ) + N α Since we have three transmitting antennas, we have a sufficient system of equations: { - M β 1 cos ( β 1 ) ( xx ) + ( yy ) 2 ( zz ) - M β 1 sin ( β 1 ) ( xy ) - ( yx ) 2 ( zz ) + ( xz ) ( zz ) + cos ( β 1 ) ( zx ) ( zz ) + sin ( β 1 ) ( zy ) ( zz ) = M β 1 - N β 1 cos ( β 1 ) ( xx ) + ( yy ) 2 ( zz ) - N β 1 sin ( β 1 ) ( xy ) - ( yx ) 2 ( zz ) + ( yz ) ( zz ) - sin ( β 1 ) ( zx ) ( zz ) + cos ( β 1 ) ( zy ) ( zz ) = N β 1 - M β 2 cos ( β 2 ) ( xx ) + ( yy ) 2 ( zz ) - M β sin ( β 2 ) ( xy ) - ( yx ) 2 ( zz ) + ( xz ) ( zz ) + cos ( β 2 ) ( zx ) ( zz ) + sin ( β 2 ) ( zy ) ( zz ) = M β 2 - N β2 cos ( β2 ) ( xx ) + ( yy ) 2 ( zz ) - N β sin ( β2 ) ( xy ) - ( yx ) 2 ( zz ) + ( yz ) ( zz ) - sin ( β2 ) ( zx ) ( zz ) + cos ( β 2 ) ( zy ) ( zz ) = N β 2 - M β 3 cos ( β 3 ) ( xx ) + ( yy ) 2 ( zz ) - M β sin ( β3 ) ( xy ) - ( yx ) 2 ( zz ) + ( xz ) ( zz ) + cos ( β 3 ) ( zx ) ( zz ) + sin ( β 3 ) ( zy ) ( zz ) = M β 3 - N β3 cos ( β3 ) ( xx ) + ( yy ) 2 ( zz ) - N β sin ( β3 ) ( xy ) - ( yx ) 2 ( zz ) + ( yz ) ( zz ) - sin ( β3 ) ( zx ) ( zz ) + cos ( β3 ) ( zy ) ( zz ) = N β3 Solving this system in the Least-Square sense yields: ( zx ) ( zz ) , ( zy ) ( zz ) , ( xz ) ( zz ) , ( yz ) ( zz ) and the following calibrated measurements are created: { SDA = - 20 * log 10 1 + ( zx ) ( zz ) 1 - ( zx ) ( zz ) · 1 - ( xz ) ( zz ) 1 + ( xz ) ( zz ) SDP = 180 * angle ( 1 + ( zx ) ( zz ) 1 - ( zx ) ( zz ) · 1 - ( xz ) ( zz ) 1 + ( xz ) ( zz ) ) / π Using equation set (1) with lines 1, 4 and 5 yields: { - O β cos ( β ) ( xx ) + ( yy ) 2 ( zz ) - O β sin ( β ) ( xy ) - ( yx ) 2 ( zz ) + cos ( β ) ( xx ) - ( yy ) 2 ( zz ) + sin ( β ) ( xy ) + ( yx ) 2 ( zz ) = O β - P β cos ( β ) ( xx ) + ( yy ) 2 ( zz ) - P β sin ( β ) ( xy ) - ( yx ) 2 ( zz ) - sin ( β ) ( xx ) - ( yy ) 2 ( zz ) + cos ( β ) ( xy ) + ( yx ) 2 ( zz ) = P β with O α = 2 nd H Cos D C & P α = 2 nd H Sin D C . Because we have three transmitting antennas, we have a sufficient system of equation: { - O β 1 cos ( β 1 ) ( xx ) + ( yy ) 2 ( zz ) - O β 1 sin ( β 1 ) ( xy ) - ( yx ) 2 ( zz ) + cos ( β 1 ) ( xx ) - ( yy ) 2 ( zz ) + sin ( β 1 ) ( xy ) + ( yx ) 2 ( zz ) = O β 1 - P β 1 cos ( β 1 ) ( xx ) + ( yy ) 2 ( zz ) - P β 1 sin ( β 1 ) ( xy ) - ( yx ) 2 ( zz ) - sin ( β 1 ) ( xx ) - ( yy ) 2 ( zz ) + cos ( β 1 ) ( xy ) + ( yx ) 2 ( zz ) = P β 1 - O β 2 cos ( β 2 ) ( xx ) + ( yy ) 2 ( zz ) - O β 2 sin ( β 2 ) ( xy ) - ( yx ) 2 ( zz ) + cos ( β 2 ) ( xx ) - ( yy ) 2 ( zz ) + sin ( β 2 ) ( xy ) + ( yx ) 2 ( zz ) = O β 2 - P β 2 cos ( β 2 ) ( xx ) + ( yy ) 2 ( zz ) - P β 2 sin ( β 2 ) ( xy ) - ( yx ) 2 ( zz ) - sin ( β 2 ) ( xx ) - ( yy ) 2 ( zz ) + cos ( β 2 ) ( xy ) + ( yz ) 2 ( zz ) = P β 2 - O β 3 cos ( β 3 ) ( xx ) + ( yy ) 2 ( zz ) - O β 3 sin ( β 3 ) ( xy ) - ( yx ) 2 ( zz ) + cos ( β 3 ) ( xx ) - ( yy ) 2 ( zz ) + sin ( β 3 ) ( xy ) + ( yx ) 2 ( zz ) = O β 3 - P β 3 cos ( β 3 ) ( xx ) + ( yy ) 2 ( zz ) - P β 3 sin ( β 3 ) ( xy ) - ( yx ) 2 ( zz ) - sin ( β3 ) ( xx ) - ( yy ) 2 ( zz ) + cos ( β 3 ) ( xy ) + ( yx ) 2 ( zz ) = P β 3 Solving this system in the Least-Square sense yields: ( xx ) - ( yy ) 2 ( zz ) , ( xx ) + ( yy ) 2 ( zz ) We can construct the calibrated measurements: { SHA = - 20 * log 10 ( xx ) ( yy ) SHP = 180 * angle ( ( xx ) ( yy ) ) / π . For the DC terms, assuming the knowledge of the currents, we have three impedances: L β i = D C Current i So the system of equations becomes: { L β 1 = ( zz ) + cos ( β 1 ) ( xx ) + ( yy ) 2 + sin ( β 1 ) ( xy ) - ( yx ) 2 L β 2 = ( zz ) + cos ( β 2 ) ( xx ) + ( yy ) 2 + sin ( β 2 ) ( xy ) - ( yx ) 2 L β 3 = ( zz ) + cos ( β3 ) ( xx ) + ( yy ) 2 + sin ( β 3 ) ( xy ) - ( yx ) 2 for which we solve for ( zz ) , ( xx ) + ( yy ) 2 , ( xy ) - ( yx ) 2 ,and the created calibrated measurements are: { HRA = 20 * log 10 ( xx ) + ( yy ) 2 ( zz ) SHP = 180 * angle ( ( xx ) + ( yy ) 2 ( zz ) ) / π . A triaxial co-located orthonormal antenna, where the magnetic moments shown in FIG. 8 are oriented about the axis of the metal collar, is suitable for LWD use. These moments can be skewed or non-orthogonal. The most convenient construction is where the magnetic moments m1, m2, and m3 are orthonormal, separated by 120 degrees about the z-axis, and tilted at an angle of arctan(sqrt(2)) (54.74 degrees). The coils are assumed to be imbedded in a non-conductor within a recess in the collar. This assembly of orthonormal co-located coils is then protected by a slotted metal shield. The coils can be recessed in the collar with a shield fixed over them, or the coils can be embedded in a non-conductive tube that is inserted into the shield itself. A method of designing such shield and antenna configurations is described below. For the purpose of these discussions, we will concentrate on the magnetic dipole equivalent of a tilted coil. For convenience, it we assume the windings of a tilted coil are in a plane, it can be characterized by two angles. In the description here, the tilt angle is defined as the angle between the normal to the plane and a transverse axis (x or y for example). As such the tilt angle relative to the z axis is 90−β, as shown in FIG. 7. Note that the normal to the antenna plane is the equivalent magnetic dipole of the antenna. The second angle is the standard azimuthal angle, φ, used in the polar coordinate system and is the angle between the x axis and the projection of the normal onto the xy-plane. With these definitions, the trajectory or equations of a tilted coil winding are:x=R·cos φy=R·sin φz=R·tan β·cos φ,where 90−β is the tilt angle of the coil with respect to the z axis, R is the radius of the coil, and φ is the azimuthal angle. The shield is a cylindrical structure that encompasses the tilted coil. It contains a series of cut outs or slots to allow electromagnetic radiation to pass through the metallic shield, as shown in FIG. 9. The location of the slots may be equally spaced along the trajectory of the coil. That would functionally make the arc length between any two slots equal to:si=·φiφ+1√{square root over (1+R2 tan2β sin2ω)}dω=Ccoil/Nslot,where β is the tilt angle, φi is the angle where the slot and coil intersect,Ccoil∫02π√{square root over (1+R2 tan2β sin2ω)}dωis the coil circumference, and Nslot is the number of slots. The slots are orthogonal to the coil trajectory so that: z i ( φ i ) = ∫ 0 φ i d φ - d z d φ + C = R tan β ln tan ( φ 2 ) + C , where C = z ( φ i ) - R tan β ln tan ( φ i 2 ) . The trajectory of the i-th slot is now given as: z ( φ ) = z i ( φ ) - z ( φ i ) = R tan β ln tan ( φ 2 ) / tan ( φ i 2 ) , where φ min = 2 tan - 1 ( tan ( φ i 2 ) e - h s · tan β / 2 R ) and φ max = 2 tan - 1 ( tan ( φ i 2 ) e h s · tan β / 2 R ) . Here the projection of the slot height or length along the tool axis is set equal to hs. As shown in the embodiment of FIG. 10, biaxial co-located antennas tilted 45 degrees with respect to the tool axis may be wrapped on a recessed metal collar. The two coils are azimuthally offset by 180 degrees from each other, but the azimuthal offset is not limited to 180 degrees. FIG. 11 shows triaxial co-located tilted antennas that are azimuthally offset by 120 degree from each other. The supporting metal collar is preferably recessed as shown in FIG. 11. To have a signal loss less than 2 dB, the recess width is preferably about 8 times greater than the recess height. FIG. 11 also shows a calibration coil. The calibration coil provides a simple way to calibrate the antennas simultaneously. A small current sent to the calibration coil generates a magnetic field. The co-located antennas receive this magnetic field and generate induced currents that are proportional to their efficiencies. Thus, the induced currents provide calibration factors for the tilted coils. As mentioned above, shields are cylindrical structures with slots. If the structure is conductive (metallic), then the slots are non-conductive and vice versa. For a metallic shield enclosing a coil, the slots are distributed around the circumference of the shield and they are cut to be perpendicular to the coil wire. The number of slots is a design variable. Increasing the number of slots reduces the attenuation of the radiation through the slots, but as the number of slots increases, the mechanical integrity of the shield is reduced and, above four or five slots, the gain in attenuation is not as great. FIGS. 12a-12c show the effect of varying the number of slots for three co-located coils that are tilted at 54.74 degrees relative to the tool axis (which gives a set of three orthogonally aligned antennas) and are distributed 120 degrees azimuthally. In FIGS. 12a-12c the three coils are shown as sinusoidal curves with their corresponding slots. With six slots (FIG. 12a), only two slots intersect and the shield has good mechanical integrity. When the number of slots is increased to ten, as in FIG. 12b, up to four slots can intersect and create a diamond shape that is not physically connected to the remainder of the metal structure. In FIG. 12b, there are six diamond shaped cut outs that we call “islands”. These cut out islands need to be kept in the shield structure for both electrical and mechanical reasons. A method of achieving this is to taper the edges of the island piece and the associated shield so that the island's outer surface dimensions are smaller than the shield opening while the island's inner surface dimensions are larger than the shield opening. FIG. 13 shows a cross sectional view of this arrangement. Since the slots are filled with non-conductive material such as epoxy, the pieces are held together. FIG. 12c shows twelve slots which not only create islands, but also a complete cut around the circumference of the shield, which can be detrimental to the mechanical structure of the shield. Another design parameter is the length of the slots. Increasing the length of the slots improves the efficiency of the antenna. However, above certain slot lengths the improvement is marginal at best. As with the higher number of slots, the longer slot length reduces the mechanical integrity of the shield and can lead to islands. FIGS. 14a-14c show the effect of varying the slot length for three co-located antennas with 54.74 degree tilt relative to the tool axis and 120 degree azimuthal offsets. As FIG. 14a shows, with slot lengths of 3 inches, some of the slots intersect, but only in pairs, so that there are no islands. When the slot length is increased to four inches, as in FIG. 14b, the structure comes very close to forming islands without actually doing so. However, the connections may not be strong enough for mechanical reasons and provisions such as that shown in FIG. 13 may be used to enhance the mechanical integrity of the shield. As the slot length increases to 6 inches, as in FIG. 14c, formation of islands is unavoidable. FIG. 15 is another example of a shield slot pattern. In this embodiment, each coil is tilted 45 degrees with respect to the tool axis. The three co-located antennas are azimuthally rotated by 120 degrees relative to each other although the offset angle is not limited to 120 degrees. Note that the vertical extent of this shield is less than that of FIG. 12a or 14a. This is due to the tilt angle. It was noted above that a preferred antenna configuration is one in which three co-located antenna coils are azimuthally rotated by 120 degrees and tilted at an angle of arctan √2 (which is approximately 54.74 degrees). In that case, the vector potential of the magnetic field of a tilted coil at a point sufficiently far away, i.e., at a distance r, from the magnetic source can be expanded into an infinite series involving inverse powers of that distance r. Higher power terms are generally neglected. If the first three terms of the expansion are kept, the third term is found to be zero at the particular angle arctan √2. Thus, dipole coils tilted at that angle can produce a cleaner dipole field. As alluded to above, alternative embodiments for measuring the LWD triaxial resistivity tool response are possible. Certain tool configurations allow for the generation of one or more combinations of tool responses that remove the gains of the receivers and the transmitters. One such tool, a triaxial propagation tool, preferably operates at multiple frequencies, in the MHz range, to cover the conductivity range from 0.1 ohm-m to 1000 ohm-m. However, such a tool potentially has a limited depth of investigation and limited conductivity range per frequency. This is not an ideal configuration for geo-steering, but may be adequate for formation evaluation near the tool. This response may be inverted for Rh, Rv, dip, azimuth, and bed thickness. This information may be used to build a formation model for inputs to the lower frequency, longer spacing tool described above. Each measurement spacing will involve two receiver antennas and two transmitters. An alternative tool configuration comprises a triaxial induction tool. The triaxial induction tool generally comprises multiple main (transmitters and receivers) coils and bucking coils, all spaced along the tool's longitudinal axis, and generally operates at a single frequency, typically around 25 kHz. The induction tool typically has one or more arrays, wherein each array comprises a transmitter, a receiver, and a buck, and wherein the signal received by the receiver is subtracted from the signal received by the buck or vice versa. In an LWD environment borehole corrections and invasion information are not needed to correct the raw measurements of the deeper measurements, thus one would need less spacing. The resistivity range of operation for an induction measurement is generally from 0.1 to 500 ohm-m, and the depth of investigation will be on the order of the spacing. This measurement is ideal for geo-steering, formation geology, and formation evaluation. Each measurement spacing will involve two receiver antennas and a single transmitter antenna. This yields a net decrease in the number of antennas compared to the propagation measurements since only one triaxial transmitter will be needed for all the triaxial receiver spacings. Various techniques exist for making measurements using magnetic dipole moment transmitters and receivers for a transverse anisotropic medium with plane-parallel layers that are transversely isotropic (TI anisotropy). Preferably, to make such measurements, the thickness of the bed is greater than the transmitter-receiver spacing for a given transmitter-receiver pair. For example, for a transmitter carrying a current I, the voltage V measured at the receiver can be expressed in terms of tensor-transfer impedance ZRT:V=IuR·ZRT·uT, Eq 2where uR and uT are a unit vectors along the receiver and transmitter coil axes, respectively. The transfer impedance ZRT has the following symmetry property:ZRT=ZTRT,where the superscript T denotes the transpose. Two sets of orthogonal unit vectors are introduced ux, uy, uz, for the formation, and uX, uY, uZ, for the tool coordinates, with uZ along the axis of symmetry of the tool. The z-axis is perpendicular to the layers, oriented upward. The tool axis is confined to the x-z plane (i.e., the formation azimuth is zero). The formation dip angle is denoted by α, so that the formation system with respect to the tool system is given by:uX=ux cos α+uz sin αuY=uy uZ=−ux sin α+uz cos α Eq. 3 The symmetrized measurement in the tool coordinates can be transformed or rotated to formation coordinates as follows: V XX = I X u X · Z _ _ RT · u X V XY = I X u X · Z _ _ RT · u Y V XZ = I X u X · Z _ _ RT · u Z Eq . 4 V YX = I Y u Y · Z _ _ RT · u X … V ZZ = I Z u Z · Z _ _ RT · u Z Eq . 5 Note that all the off-diagonal terms with the subscript Y are zero due to the tool being confined to the xz-plane. Now we can express the voltage in the formation coordinates for all nine terms of the tensor: V XX = I X ( u x cos α + u z sin α ) · Z _ _ RT · ( u x cos α + u z sin α ) V XY = I X ( u x cos α + u z sin α ) · Z _ _ RT · u y = 0 V XZ = I X ( u x cos α + u z sin α ) · Z _ _ RT · ( - u x sin α + u z cos α ) … V ZZ = I X ( - u x sin α + u z cos α ) · Z _ _ RT · ( - u x sin α + u z cos α ) Eq . 6 For the triaxial co-located tool configuration shown in FIG. 16, which has two transmitters and two receivers placed symmetrical about the tool origin and along its axis, we can express the transfer impedance for the uphole transmitter T1 and uphole receiver R1 as:z11=GT1Z11GR1, Eq. 7where GT1 and GR1 are the diagonal complex gain matrices for T1 and R1, respectively, and Z11 is the transfer impedance for T1 and R1, respectively. Similarly, we can express the transfer impedance for other possible combinations:z12=GT1Z12GR2,z21=GT2Z21GR1, andz22=GT2Z22GR2.Next, we can combine these measurements as the product of the near, inverse transfer impedance and the far transfer impedance for a downwardly propagating wave:Td=(z11)−1z12 and for an upwardly propagating wave:Tu=(z22)−1z21.To remove the sensor gains resulting from sensor geometry and electronic variation, we can combine Td and the transpose of Tu term by term:M1(α)=Td·*TuT=(z11)−1z12·*[(z22)−1z21]T Eq. 8For the special case of Eq. 8 when the relative dip is zero or where α=0 in Eq 6, we have: M 1 ( α = 0 ) = ( Z x 1 x 2 Z x 2 x 1 Z x 1 x 1 Z x 2 x 2 0 0 0 Z y 1 y 2 Z y 2 y 1 Z y 1 y 1 Z y 2 y 2 0 0 0 Z z 1 z 2 Z z 2 z 1 Z z 1 z 1 Z z 2 yz 2 ) . Note that the ZZ-term is just the usual axial response upon taking the logarithm. Likewise, the other diagonal terms could be handled in the same fashion to remove the undesired gains. For the special case of Eq. 8 when the relative dip is non-zero in Eq. 6, we have: ( ( Z x 1 x 2 Z z 1 z 1 - Z x 1 z 1 Z z 1 x 2 ) ( Z x 2 x 1 Z z 2 z 2 - Z x 2 z 2 Z z 2 x 1 ) ( Z x 1 x 1 Z z 1 z 1 - Z x 1 z 1 Z z 1 x 1 ) ( Z x 2 x 2 Z z 2 z 2 - Z x 2 z 2 Z z 2 x 2 ) 0 ( Z x 2 x 1 Z z 2 z 2 - Z x 2 x 2 Z z 2 x 1 ) ( Z x 1 z 1 Z z 1 z 2 - Z x 1 z 2 Z z 1 x 1 ) ( Z x 1 x 1 Z z 1 z 1 - Z x 1 z 1 Z z 1 x 1 ) ( Z x 2 x 2 Z z 2 z 2 - Z x 2 z 2 Z z 2 x 2 ) 0 Z y 1 y 2 Z y 2 y 1 Z y 1 y 1 Z y 2 y 2 0 ( Z x 1 x 1 Z z 1 z 2 - Z x 1 z 2 Z z 1 x 1 ) ( Z x 2 x 1 Z z 2 z 2 - Z x 2 z 2 Z z 2 x 1 ) ( Z x 1 x 1 Z z 1 z 1 - Z x 1 z 1 Z z 1 x 1 ) ( Z x 2 x 2 Z z 2 z 2 - Z x 2 z 2 Z z 2 x 2 ) 0 ( Z x 1 x 1 Z z 1 z 2 - Z x 1 z 2 Z z 1 x 1 ) ( Z x 2 x 2 Z z 2 z 1 - Z x 2 z 1 Z z 2 x 2 ) ( Z x 1 x 1 Z z 1 z 1 - Z x 1 z 1 Z z 1 x 1 ) ( Z x 2 x 2 Z z 2 z 2 - Z x 2 z 2 Z z 2 x 2 ) ) . In this case, the XX and ZZ terms are more complex, but the attenuation and phase responses of these terms are as expected. The XZ and ZX terms do not behave quite as expected since we multiplied by the transpose of the Tu term, however those terms do have large responses when approaching a horizontal bed at high dip. There are many ways to manipulate these tensors and another option is to matrix multiply Td and Tu:M2=Td*Tu=(z11)−1z12*(z22)−1z21 Eq. 9For the special case of Eq. 8 when the relative dip is non-zero in Eq. 6, we have: M 2 ( α ≠ 0 ) = ( A 0 D gz 1 gx 1 0 B 0 E gx 1 gz 1 0 C ) . There we see that the off-diagonal terms have a receiver gain ratio that can be measured using the fact that the tool rotates. Thus, every 90 degree rotation of the tool, the gain ratio of gx/gz is equal to gy/gz and so on. Alternatively, we can multiply the xz-term by the zx-term. We can calculate the attenuation and phase from the formulation: ln M 2 = ln ( z _ _ 1 , 2 ( z _ _ 11 ) - 1 * z _ _ 21 ( z _ _ 22 ) - 1 ) = ln [ ( z _ _ 11 ) - 1 z _ _ 12 ] 2 + ln [ ( z _ _ 22 ) - 1 z _ _ 21 ] 2 Eq . 10 This is obtained by taking the matrix natural log of the square root of Eq. 9 To do that, we first perform the element multiplication in Eq. 8. Then we take the element square root, and finally the matrix natural logarithm to determine a harmonic average for borehole compensation. We modeled the triaxial tool shown in FIG. 16. Plots of the elements of Eq. 10 and the tensor with azimuth set to zero with varying Rh, Rv, and dip were studied using a point dipole formulation for transfer impedance for a formation with dip, azimuth, Rh, and Rv. See FIGS. 17-24 for some characteristic responses of Td. The attenuation and phase of tensor Td was modeled for the case of azimuth=0 degrees. The tool was modeled for frequencies of 400 kHz and 2 MHz with transmitter-center receiver spacing of 30 (36) inches and a receiver to receiver spacing of 12 (6) inches. The attenuation and phase have good sensitivity versus anisotropy and dip, but these are shallow measurements due to the high frequencies in skin effect contribution to the voltage. The tool attenuation and phase shift response using ln√{square root over (M2)} while logging through a three-bed formation having varying dip and anisotropy can be modeled. A simple exemplary formation model is shown in FIG. 25. The resistivity attenuation and phase transformations are plotted for the tool operating at 400 kHz and 2 MHz in an infinite homogeneous formation in FIGS. 26-29. Note that the XX resistivity transforms are doubled valued, therefore we will only make the transforms from the low resistivity to the minimums. Next we plot the responses of the tool logging through three beds at a dip of 60 degrees and as a function of anisotropy ratios of 1, 2, 5, 10, and 20. The diagonal terms XX, YY, and ZZ are in units of resistivity or ohm-m, while the XZ and ZX terms are in units of dB. The resistivity responses are shown in FIGS. 30-33. Next we plot the responses of the tool logging through three beds as a function of dip for an anisotropy ratio of two. The diagonal terms XX, YY, and ZZ are in units of resistivity or ohm-m, while the XZ and ZX terms are in units of dB. The resistivity responses are shown in FIGS. 34-37. The tensor responses for the triaxial induction tool in wireline are well known. We can also measure the apparent conductivity tensor σappk for the k-th spacing and invert a 1D-dipping layered earth model for the Rh_k, Rv_k, dip_k, azi_k, and bed thickness: σ app k = ( σ xx σ xy σ xz σ yx σ yy σ yz σ zx σ zy σ zz ) → Inversion ( R h , R v , dip , azi , h ) The calibration of the triaxial or tensor resistivity tool on the LWD platform for i-th transmitter and the j-th receiver and the k-th spacing cab be functionally expressed as:σijkapp=gelec(Te)gijkTTL(σijkmeas−σijkSEC(Ta))where σijkapp is the calibrated complex apparent conductivity and gijkTTL is the gain correction defined for a modeled reference tilted test loop as: g ij TTL = σ ijk TTL Ref σ ijk TTL Meas . The modeled tilted test loop response is given by σijkTTLRef and the measured tilted test loop response is given by σijkTTLMeas. The tilted test loop is shown in FIG. 40 as it is logged over a triaxial induction LWD tool or put at specified axial and azimuthal positions.The phase correction is: Δ φ = atan ( Δ Im ( σ ij TTL Ref ) Δ Re ( σ ij TTL Ref ) ) - atan ( Δ Im ( σ ij TTL Meas ) Δ Re ( σ ij TTL Meas ) ) The raw measurement is scaled as: σ ijk meas = η jk K ijk V R jk I T i where ηjk is the electronics gain/phase correction, Kijk is a sensitivity factor, VRjk is the voltage on the receiver, and ITi is the transmitter current. The background correction, σijkSEC(T), is given by: σ ijk SEC ( T ) = η jk K ijk V jk SEC ( T ) I i ( T ) . A test loop is used to either transmit or receive a test signal for each transmitter, receiver, and bucking coil on an LWD induction tool. The gain can then be determined for each of those antennas. The temperature offset is acquired by slowly heating the tool and then fitting the tool response to a nth-order polynomial fit. The coefficients are then stored downhole, as are the gains, to correct or calibrate the tool's raw measurements. Thus, the gain-corrected receiver signal and the gain-corrected buck signal can be subtracted one from the other to provide an LWD induction measurement. The suggested LWD tenser resistivity tool with three spacings is shown below in FIG. 39. A typical tool response to a zero azimuth formation versus dip and anisotropy is shown in FIG. 38. Again, there is good sensitivity to anisotropy and dip. It should be appreciated that while the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. |
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claims | 1. A pressurizer for a pressurized water nuclear power plant, comprising:an upper cap equipped with a nozzle, the nozzle being covered, on an inner face of the nozzle, with a coating;an end piece connected to the nozzle through a first weld;a thermal protective sleeve;a support piece; anda fixing arrangement configured to fix the thermal protective sleeve to the support piece, the fixing arrangement being used to remove the thermal protective sleeve without cutting the first weld such that the first weld is maintained for inspection, the thermal protective sleeve being removed without cutting the end piece,wherein the support piece is fixed on the coating, the fixing arrangement including an external thread on the thermal protective sleeve and an internal thread on the support piece, the external thread being screwed on the internal thread, andwherein the thermal protective sleeve protects the first weld disposed inside the nozzle and is mounted in such a manner that the sleeve can be removed from inside the pressurizer using the fixing arrangement. 2. The pressurizer according to claim 1, wherein the sleeve includes, on an external surface of the sleeve, a plurality of antivibration pads, the pads being regularly distributed. 3. The pressurizer according to claim 1, wherein the support piece presents a further external thread, and wherein the pressurizer further comprising: a spray head screwed on the further external thread. 4. The pressurizer according to claim 3, wherein a lower end of the sleeve is such that, when the sleeve is in place, the lower end is positioned between the support piece and the spray head. 5. The pressurizer according to claim 3, further comprising: an arrangement locking in rotation the spray head. 6. The pressurizer according to claim 5, wherein the arrangement is fixed to the support piece through a second weld. 7. A method for removing a thermal protective sleeve of a pressurizer, comprising:removing a second weld between an arrangement of the pressurizer and a support piece of the pressurizer, the pressurizer further including an upper cap equipped with a nozzle, an end piece connected to the nozzle through a first weld, the thermal protective sleeve protecting the first weld disposed inside the nozzle, and a fixing arrangement configured to fix the thermal protective sleeve to the support piece, the fixing arrangement being used to remove the thermal protective sleeve without cutting the first weld such that the first weld is maintained for inspection, the thermal protective sleeve being removed without cutting the end piece, wherein the thermal protective sleeve is removed from inside the pressurizer using the fixing arrangement, the nozzle being covered, on an inner face of the nozzle, with a coating, the support piece being fixed on the coating, the fixing arrangement including an external thread on the thermal protective sleeve and an internal thread on the support piece, the external thread being screwed on the internal thread, the support piece presenting a further external thread, the pressurizer further including a spray head screwed on the further external thread, a lower end of the protective sleeve is such that, when the protective sleeve is in place, the lower end is positioned between the support piece and the spray head, the arrangement locking in rotation the spray head and being fixed to the support piece through the second weld;removing the arrangement;unscrewing the spray head; andunscrewing the thermal sleeve. |
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description | This application is a division of U.S. application Ser. No. 11/637,314, filed Dec. 12, 2006. Not applicable. Not applicable. The present invention relates to normalizing readings on testing machines, and more particular to normalizing photon count readings on testing machines having more than one photon counter. Testing of biological samples is often carried out using, for example, wet chemistry, in conjunction with automatic testing machines. In some such tests, samples are dispensed in reaction trays having a plurality of wells for handling a plurality of samples, with the analysis of the different samples often involving counting photons emitted from the samples. There is no known single photon counting standard, however, and, therefore, it is only possible to obtain relative relationships between single photon sources and photon detectors (photon counters). Further, there is an intrinsic variability among photomultiplier tubes used to count photons, which variability requires a normalization method to obtain similar count values among different photon counters, such as are typically encountered in testing machines (a plurality of photon counters facilitates higher volume testing). In such cases, for example with the ABBOTT PRISM™ System available from Abbott Laboratories, Inc. of 100 Abbott Park Road, Abbott Park, Ill. 60064, the testing machine may have a plurality of different tracks for different types of tests, with each track having two photon counters, which are used in conjunction with trays having a plurality of rows of wells, with each row having two wells (e.g., two columns of wells in eight rows). In use, a tray is advanced through the testing machine row by row, with one photon counter counting photons emitted from each well of one column of wells and the second photon counter counting photons emitted from each well of the other (adjacent) column of wells. Given the intrinsic variability and extremely sensitive nature of photon counters, however, it is essentially impossible to expect that each of the photon counters will be identical, or will obtain identical results even under identical conditions (which can never be achieved in any event). Therefore, it has been necessary to normalize the readings obtained by different photon counters, that is, to determine a factor of difference between the photon counters, which may be used to obtain comparable results among a plurality of photon counters. For example, in a simplified example, if a known source is read, and one photon counter is found to return readings that are 10% higher than the known source, and the other photon counter is found to return readings that match what would be expected from the known source, readings taken during testing by the former photon counter would be reduced to take into account the 10% overcount, thereby giving test results that are therefore more reliable. Of course, accurate test results are particularly critical in many such biological testing situations, because incorrect results are not merely testing failures, but may also result in a misdiagnosis of an individual's condition and subsequent improper treatment of a patient. In order to determine normalization values among photon counters of a testing machine, optic module verification tools (OMVT) have heretofore been used. Such devices are essentially duplicates of reaction trays, including at least one well in each column (i.e., associated with each photon counter) having a known photon emitter. The well of a tray 10 including such a prior art photon emitter in one of the wells of the tray is illustrated in FIG. 1. Specifically, the photon emitter 20 is disposed beneath a tray well 22, and includes an optic standard 26 contained within a capsule 28, both of which rest on a cap 30. Suitably secured over the optic standard 26 is a filter glass 34, and a foam support 36 is provided at the bottom of the tray 22 to assist in locating the filter glass 34 at the desired position adjacent the bottom of the tray well 22. The optic standard 26 is carbon-14 (C14) mixed with a suitable epoxy resin as a soup or slurry, which is then cast in the desired plug shape. For normalization, the photon emission of each photon emitter is first measured according to a standard. For example, normalization trays have been measured at a central location where such standardized measurements can take place, with each photon emitter assigned the measured photon count. Such normalization trays have then been distributed for use with testing machines, with one normalization tray provided at each geographic location where a testing machine is found. At each testing machine, the normalization tray is run through the machine one or more times in order to obtain a photon count by each photon counter from the photon emitter associated therewith. The photons counted at the test machine by each photon counter are then been compared to the assigned measured photon count as previously determined for each photon emitter, with those values used to normalize the results obtained by the different photon counters, when photons emitted from test specimens are subsequently counted. Unfortunately, while the photon emitter such as described above might be thought to be subject to little decay, because it is based on C14 having a long half-life (5568 years), experience has shown that the photons emitted by such emitters in fact may decay relatively quickly, so that the quantity of emitted photons may fall below a desired minimum level in as short a period of time as a few months. In that case, a new optic module verification device (normalization tray) can be obtained from the central location (or the old one must be essentially completely remanufactured with a new photon emitter) with normalization values obtained against the standard. Alternatively, the device can continue to be used after being re-measured according to the standard, but with photon emissions that are below the preferred minimum level for reliable normalization of the test machine. Neither option is preferred for both cost and operational reasons. The present invention is directed toward overcoming one or more of the problems set forth above. In one aspect of the present invention, an optic module verification device is provided for use for periodic normalization of a testing machine used to test samples in wells of reaction trays, where the testing machine includes X photon counters, which each count photons emitted from different tray wells, where X is an integer greater than 1. The verification device includes a verification tray defining at least X verification wells and a photon emitter in each verification well. The verification wells are located so as to each be associated with a different one of the photon counters when used in the testing machine. Each photon emitter includes a C14 source, a scintillator adjacent the C14 source, and a filter over the scintillator, wherein each photon emitter has a determined initial base value for emitted photons, and each photon emitter is positioned in its verification well to emit photons through the filter to the associated photon counter when used in the testing machine. In one embodiment of this aspect of the present invention, the filter is a neutral density glass filter. In another embodiment of this aspect of the present invention, the scintillator is a plastic element with opposite generally flat surfaces. In a further embodiment, one surface of the scintillator is abraded, e.g., roughened, to minimize internal reflectivity. In still another embodiment of this aspect of the present invention, the verification device includes an open bottom tray in each of the verification wells, and the photon emitters are positioned beneath the bottom of the tray with the filter adjacent the opening in the bottom of the tray. In a further embodiment, a capsule is removably securable to a cap to define a space therebetween for enclosing the photon emitter, the capsule including a shoulder surrounding an opening against which the filter is secured, and a spring is positioned between the cap and the C14 source to bias the C14 source and the scintillator against the filter. In still a further embodiment, the capsule shoulder is aligned with the opening in the bottom of the tray. In yet another embodiment of this aspect of the present invention, additional wells in the verification device are closed to prevent emission of photons, with the additional wells each being positioned so as to be associated with one of the photon counters. In another embodiment of this aspect of the present invention, the testing machine is adapted to count photons of a selected wavelength of light based on designed wet chemistry for a test specimen, and the scintillator mimics the selected wavelength of light. In still another embodiment of this aspect of the present invention, the C14 source comprises a steel disk having a surface adjacent the scintillator, the surface coated with C14 having about five (5) micro-curies of activity. In yet another embodiment of this aspect of the present invention, a Mylar coating overlies the C14 coating on the surface of the steel disk. In another aspect of the present invention, a modular photon emitter is provided, the emitter including a spring, a disk including a Beta source, a plastic scintillator disk adjacent the Beta source, a neutral density filter over the scintillator disk, and a bottom cap and a capsule securable together to define a cylindrical chamber with an opening at one end of the capsule. The spring, the disk including a Beta source, the plastic scintillator disk, and the filter are encapsulated in the cylindrical chamber with the filter adjacent the aforementioned opening at one end of the capsule and the spring biasing the disk including a Beta source and the plastic scintillator disk toward the opening. In one embodiment of this aspect of the present invention, the surface of the scintillator disk adjacent the Beta source disk is roughened. In another embodiment of this aspect of the present invention, the Beta source is C14. In still another embodiment of this aspect of the present invention, the capsule includes an annular face surrounding the opening, and the filter is secured against the annular face. In yet another embodiment of this aspect of the present invention, the bottom cap and the capsule include mating threads for releasably securing the bottom cap and the capsule together. In still another aspect of the present invention, a method is provided for periodically normalizing two photon counters of a testing machine used to test samples in wells of reaction trays by counting photons emitted from the wells of the reaction trays. The method includes the step of (a) initially providing a verification device having two photon emitters, each photon emitter including a C14 source, a scintillator adjacent the C14 source, and a filter over the scintillator. Then, in step (b) normalized reference values for each photon emitter are determined, in step (c) photons emitted from the photon emitters of the verification device are counted on the testing machine, wherein one of the photon counters counts the photons emitted from one of the photon emitters and the other photon counter counts the photons emitted from the other photon emitter, in step (d) normalization values for the photon counters are determined based on the normalized reference values and the photons emitted from the photon emitters counted by the photon counters, in step (e) samples are tested in wells of the reaction tray by counting photons using the two photon counters, and in step (f) the values of photons counted from the samples are normalized using the normalization values. Then, in step (g), steps (e) and (f) are repeated to test a plurality of reaction trays having wells with samples therein, and in step (h), steps (c) and (d) are periodically repeated. When the counted photons in step (c) fall below a predetermined value, the verification device is updated by replacing the scintillator of each photon emitter, and repeating steps (b) through (h). In one embodiment of this aspect of the present invention, the scintillators are chosen so that the photon emitters each have an initial reference value for emitted photons as determined in step (b) within a selected range, with the predetermined value being the lower end of the selected range. A normalization tray 100 with photon emitters 102 for use in normalizing readings on a testing machine or instrument 104 (see FIG. 6) is illustrated in FIGS. 2-5. The tray 100 includes a base 110 beneath a reaction tray 112 defining a plurality of wells 114, specifically sixteen wells 114 in two columns of wells having eight rows (see FIG. 3). It should be appreciated that not all of the wells are used with this normalization tray 100, but that such a configuration is advantageously used to match the configuration of trays used in testing so that the normalization tray 100 can be conveniently handled in the testing machine 104. Thus, screw plugs 120 can be advantageously secured in those wells 114 that are not actually used for normalization (e.g., by securing those plugs in threaded inserts 122 in the tray base 110 as shown in FIG. 4). A photon emitter 102 according to the present invention is illustrated in FIGS. 2 and 4. The photon emitter 102 includes a stainless steel knurled bottom cap 130 with a suitable spring member 132 (e.g., a wave spring such as illustrated) disposed therein. Supported above the spring member 132 is a C14 source 140, a plastic scintillator disk 146, and a suitable filter glass 150. The C14 source 140 can advantageously be a steel disk with a C14 plating on the top surface of the disk and a Mylar coating thereon, with sufficient C14 applied to provide about 5 micro-curies of activity. The scintillator disk 146 absorbs energy emitted by the C14 source 140 and, in response, fluoresces photons at a characteristic wavelength. The material of the plastic scintillator disk 146 can thus be selected so as to generate photons at the wavelength to be detected by the testing machine 104. For example, if the testing machine 104 operates to count photons in a blue wavelength (e.g., about 420 nanometers) to determine wet chemistry test results for biological samples, a plastic scintillator disk 146 that will emit photons at about 420 nanometers (such as a polyvinyl toluene disk) can advantageously be chosen for inclusion in the photon emitter 102. For example, an Eljen-212 plastic scintillator disk (having a polyvinyltoluene polymer base, and available from Eljen Technology, 300 Crane Street, Sweetwater, Tex. 79556) having a half inch diameter and 0.020 inch thickness can be used. Further, it has been found that abrading, e.g., roughening or sanding, at least one flat surface of the scintillator disk 146 (so as to not have the smoother surface generally produced by molding of such disks) will advantageously minimize internal reflectivity of the plastic scintillator disk 146. For example, sanding of the material of the plastic scintillator disk can be advantageously performed using a random-orbital sander and 400 grit sandpaper, with the sanding (wet or dry) performed to yield a uniform scoring/dullness of the cast sheet of scintillation material. The operation is done to yield a level of scoring/dullness involving only the briefest exposure to the sander, with the sanding removing less than 5% of the original thickness of the cast sheet of scintillation material. Glass-bead blasting is another method that has also been found to acceptably mar the plastic scintillator disk 146. Preferably, only the side of the plastic scintillator disk 146 that faces the Beta source (C14 source 140) is sanded, with the other side of the plastic scintillator disk 146 being left alone. The filter glass 150 serves to knock back some of the light, and thereby helps the photon counters (photodiscriminators) better count single photon events. For example, a Schott NG-5 neutral grey glass density filter can be advantageously used (e.g., a filter having a half inch diameter and thickness of about 0.079 inch). A cylindrical stainless steel capsule 160 is configured so as to encapsulate the spring 132, the C14 source 140, the plastic scintillator disk 146, and the filter glass 150. As best shown in FIG. 2, the capsule 160 includes an outer threaded portion 162 so that it can be secured to the bottom cap 130 by screwing into an inner thread 164 of the bottom cap 130. Further, the upper end of the capsule 160 is tapered so as to generally match the underside of the tapered well 114 of the reaction tray 112, and the upper end of the capsule 160 further includes a downwardly facing annular surface 168 adapted to be engaged against the upper face of the filter glass 150. The filter glass 150 can be suitably secured to the capsule 160, by means of gluing, by means of a low bloom “super glue” (e.g., cyanoacrylate glue that does not evaporate out onto the surrounding surfaces). A relief groove 170 around the capsule's annular surface 168 can be advantageously provided for excess glue from that attachment, helping to also ensure that glue does not disadvantageously leak onto the top of the filter glass 150, through which photons are intended to pass. It should be appreciated, therefore, that the photon emitters 102 will be reliably configured with the plastic scintillator disk 146 and the C14 source 140 pressed up against the underside of the filter glass 150 by the spring 132. Foam member(s) 180 or other suitable spring-like member(s) can also be advantageously provided beneath the photon emitter(s) 102 near the bottom of the tray base 110 to ensure that the photon emitter(s) 102 are positioned precisely as desired, with the filter glass 150 against the bottom of the well 114 defining portion of the reaction tray 112. As illustrated in FIG. 5, the tray 100 can include a row with two wells 114A, 114B with photon emitters 102A, 102B. Adjacent wells 114C, 114D can be provided with black pieces of foam material 184 to block the openings at the bottom of the wells 114C, 114D to provide wells where no photons will be present (and thereby provide a check when normalizing the photon counters). FIG. 6 illustrates how to use the tray 100 of the present invention to normalize the photon counters of a testing machine or analyzer 104, that is, as would occur when testing samples (in which test results can be determined by counting the photons generated by wet chemistry on, e.g., biological samples in different wells of a similar tray, with the wet chemistry of the sample generating light via chemical luminescence, wherein the quantity of light emitted is proportional to the chemical reactivity). The tray 100 is moved through a track 190 of the analyzer 104 so as to index the tray wells 114 beneath photodiscriminators or photon counters 200A, 200B of the analyzer 104. Photon counts are recorded for at least wells 114A, 114B, and preferably also wells 114C, 114D (to verify that essentially no photons are counted at wells 114C, 114D). (A suitable shroud surrounding the wells 114 and photon counters 200A, 200B can be provided to prevent environmental photons from affecting the count; however, that shroud has been omitted from the figures for the sake of simplification.) In this manner (as discussed below and essentially as previously accomplished), the readings determined by the photon counters 200A and 200B can be normalized so that readings taken during actual tests of samples can be relied upon as accurate. Specifically, the tray 100 according to the present invention, once manufactured, is first tested by a reference device to determine a normalized verification value for each photon emitter 102A, 102B, and those verification values are recorded on the tray 100 for each photon emitter 102A, 102B. For example, one of the photon emitters 102A may be determined to emit 12,000 photons in a given time frame whereas the other photon emitter 102B may emit only 11,500 photons in that time frame. The tray 100 is then sent to a facility for use in connection with that facility's testing machine 104, such as a PRISM® testing machine available from Abbott Laboratories, Inc. To use, the tray 100 is periodically run through the testing machine 104, with the recorded verification values of each photon emitter 102A, 102B checked against the readings taken by that machine's photon counters 200A, 200B. During such periodic testing (e.g., once a month or so), the tray 100 is run through the testing machine 104, with readings taken of a plurality of photon counts (e.g., ten counts) for each photon emitter 102A, 102B. Those readings can be evaluated for consistency (e.g., if the standard deviation divided by the mean of the readings for a photon emitter 102A or 102B is greater than 0.1, a problem with the photon counter 200A or 200B used to count photons from the emitter 102A or 102B is indicated). During such use of the tray 100 for normalizing readings in the photon counters 200A, 200B, it has been found that over time there will be some decay in the quantity of photons emitted, notwithstanding the long half-life of C14. However, for the normalization process, it is preferred that the photon counts not vary by more than about 10% of the verification values determined for the photon emitters 102A, 102B during manufacture. However, as illustrated in FIG. 7 for the prior art photon emitter 20 illustrated in FIG. 1, a tray 10 having an emitter with an initial photon count of 12,000 has been found to decay to the point of failure, with unacceptably low photon emissions relative to the initial verification values that it can essentially be considered to fail in less than 200 days. At that point, the tray 10 has heretofore been returned to the manufacturing facility (e.g., in Dallas, Tex. for the PRISM® testing machine, available from Abbott Laboratories) so that new verification values can be determined, although those values are at a much lower value than preferred (e.g., less than 10,000 photons in a given time frame), and will thereafter decay even further. While the tray 10 has then been used thereafter for a while, eventually, the photon count of the refurbished tray 10 will have fallen so low that it can no longer be used. At that point (e.g., about a year in total), the tray 10 is no longer suitable for use and a new tray must be manufactured and shipped to the testing facility to maintain the testing machine 104. By contrast, as illustrated in FIG. 8, the photon emitters 102 of the present invention have been found to decay much more slowly, such that unacceptably low photon emissions are not first encountered for nearly 1½ years (versus less than 200 days with the prior art). At that point, the tray 100 can be shipped back to the manufacturing facility, and the tray can be advantageously refurbished by merely replacing the plastic scintillator disks 146 in the photon emitters 102. In this case, the photon counts of the refurbished photon emitters 102 may actually turn out to be higher than in the original tray 100, and thus not only can the tray 100 be used nearly three times as long (about three years versus one year with the prior art tray 10), but after being refurbished the photon counts will be in the desirable range. It should thus be appreciated that the normalization tray 100 and photon emitters 102 according to the present invention are modular and portable. They are also customizable for different light spectra by changing the configurations and dimensions of the component parts. Moreover, the radioactive source, the plastic scintillator disk, the neutral density filter, and/or the spacing of components can variously be changed to provide portable stable normalization sources for a wide variety of instrument reader assemblies, photomultiplier tubes, and other photon counting devices. Further, the components of the present invention can be easily manufactured with reliable repeatability. Still other aspects, objects, and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. It should be understood, however, that the present invention could be used in alternate forms where less than all of the objects and advantages of the present invention and preferred embodiment as described above would be obtained. |
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claims | 1. A method, comprising:providing a gas field ion beam system, comprising:an external housing,an internal housing within the external housing,an electrically conductive tip within the internal housing,a gas supply configured to supply a gas to the internal housing, the gas supply comprising a tube terminating within the internal housing, andan extractor electrode having a hole configured to permit ions generated in the neighborhood of the tip to pass through the hole into the external housing, andregularly heating the external housing, the internal housing, the electrically conductive tip, the tube and the extractor electrode to a temperature above 100° C.,wherein, after heating the external housing, the internal housing, the electrically conductive tip, the tube and the extractor electrode, continuing to heat the electrically conductive tip while cooling the internal housing, the tube and the extractor electrode to a cryogenic temperature. 2. The method of claim 1, further comprising cooling the external housing to room temperature before cooling the internal housing, the tube and the extractor electrode to cryogenic temperature. 3. The method of claim 2, further comprising cooling the electrically conductive tip to the cryogenic temperature after cooling the internal housing, the tube and the extractor electrode to the cryogenic temperature. 4. The method of claim 1, further comprising opening a bye-pass valve of the gas supply to achieve a gas flow from the gas supply into a vacuum space outside the internal housing. 5. The method of claim 1, further comprising heating the electrically conductive tip while keeping the internal housing, the tube and the extractor electrode at the cryogenic temperature. 6. The method of claim 5, wherein the electrically conductive tip is heated to a temperature of 300° C. or more. 7. The method of claim 1, comprising heating the electrically conductive tip for one minute or more. 8. The method of claim 1, further comprising supplying light to the electrically conductive tip while keeping the internal housing, the tube and the extractor electrode at a cryogenic temperature, wherein a level of the light is at least 100 mW/mm2. 9. The method of claim 1, further comprising applying a voltage difference between the electrically conductive tip and the extraction electrode while heating the electrically conductive tip or supplying light to the electrically conductive tip, wherein the voltage difference causes an electrical field of at least 35 V/nm. 10. The method of claim 1, wherein the one or more gases comprise neon or a noble gas with atoms having a mass larger than neon. 11. The method of claim 10, further comprising cooling the external housing to room temperature before cooling the internal housing, the tube and the extractor electrode to cryogenic temperature. 12. The method of claim 11, further comprising cooling the electrically conductive tip to the cryogenic temperature after cooling the internal housing, the tube and the extractor electrode to the cryogenic temperature. 13. The method of claim 10, further comprising heating the electrically conductive tip while keeping the internal housing, the tube and the extractor electrode at the cryogenic temperature. 14. The method of claim 10, comprising heating the electrically conductive tip for one minute or more. 15. The method of claim 10, further comprising supplying light to the electrically conductive tip while keeping the internal housing, the tube and the extractor electrode at a cryogenic temperature, wherein a level of the light is at least 100 mW/mm2. 16. The method of a claim 1, wherein:the electrically conductive tip comprises a terminal shelf with a predefined number of atoms; andthe method further comprises:in a first mode of operation, operating the gas field ion beam system with a predefined voltage between the tip and the extractor electrode to generate an ion beam, and interacting the ion beam with a sample,in a second mode of operating, recording a field ion microscopic image of the terminal shelf of the tip in order to verify that the terminal shelf of the tip has the predefined number of atoms, andincreasing the voltage between the tip and the extractor electrode in the second mode of operation compared to the predefined voltage to provide an electrical field strength of at least of 35 V/nm at the terminal shelf of the tip. 17. The method of claim 16, wherein in the first mode of operation the electrical field strength at the terminal shelf of the tip is below 35 V/nm. 18. The method of claim 1, wherein:the electrically conductive tip comprises a terminal shelf with a predefined number of atoms; andthe method further comprises:in a first mode of operation, operating the gas field ion beam system with a predefined voltage between the tip and the extractor electrode to generate an ion beam, and interacting the ion beam with a sample, andin a second mode of operation, recording a field ion microscopic image of the terminal shelf of the tip in order to verify that the terminal shelf of the tip has the predefined number of atoms and irradiating light to the tip, wherein the light level is at least 100 mW/mm2. |
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description | The present invention relates to computer-assisted monitoring, processing, and reporting of the status and performance of machines. There are currently a variety of methods for monitoring and controlling the motion and status of machines in manufacturing, production, and processing environments, such as a factory. For example, processor-based controls, such as a computer numerical control (CNC), are used to control the motion of machines such as machine tools and robots that are used in a variety of manufacturing environments. A programmable logic control (PLC) may also be used to control the motion of a machine in a manufacturing, production or processing environment. Older equipment may be controlled by relays and relay logic. All of these types of controls focus primarily on machine operation and very little on the information that the machine can provide to others. Usually, a machine control is designed to communicate directly to an operator of the machine equipment. It provides the operator with the information necessary to run the machine and make changes to the machine as needed. If one wishes to collect and analyze machine productivity, maintenance, status, quality, signal, or alarm information in real-time or over an interval of time, this information is either not available or needs to be derived from raw signals. The usual way to collect such information is manually by the operator. This implies a number of disadvantages. Typically, an operator must be present at all times to monitor the machine and the information collected is either recorded manually on paper or manually entered into a computer on the factory floor. Thus, it is possible that only a fraction of the useful information will be captured. Further, due to the high-level of human interaction required, this method is also prone to inaccuracies. In addition, the necessity of human interaction introduces delays that make this approach unsuitable for real time-decision making. Other solutions for automated data collection and reporting involve a more complicated integration effort and rely on the machine data being stored in a database on a central server on a network. However, this signifies that machine data must constantly be sent to the central server for processing. Thus, such solutions may require additional network resources and may increase network congestion. Further, should the central server or network fail, valuable machine data will be lost and monitoring and some level of control will be jeopardized. In addition, the network, central server, and machine connections may all have to be configured separately through a variety of interfaces which may increase configuration time and complexity both during initial installation and recovery after failure of a system component. Accordingly, what is required is a system and method that automatically monitors machines and captures data which may then be processed and reported in a manner configurable by the user. The system and method should also provide for generation of output signals, in response to the results of processing the machine data and also configurable by the user, which may be used for pausing or stopping a machine or causing lights or buzzers to be activated. The system and method should allow for viewing of reports based on processed machine data. The system and method should further allow for simple configuration of all aspects of the system, also via a convenient and familiar interface mechanism. Users should be able to view and request reports, as well as effect system configuration, remotely from a client computing device on a network. To minimize reliability issues and network traffic, however, such a system should provide integrated data processing and storage management and storage of configuration information, output signal generation, report generation in a variety of formats, as well as the mechanism for generating the user interfaces, within one machine monitoring device. The machine monitoring device should also contain connectors that allow desired machines to be easily connected to the machine monitoring device and to connect the machine monitoring device to the network. Thus, the machine monitoring device should constitute a self-contained unit that acts as a server to provide all desired services to users on the client computing devices, which should act as clients of the machine monitoring device. The present invention addresses the various requirements identified above. The present invention relates to a computer-assisted machine monitoring system and method. The invention uses a compact machine monitoring device (MMD) connected to a machine. The MMD comprises a central processing unit (CPU) software modules, storage capabilities, a number of connectors for input and output for the machine to which the MMD is connected, serial ports, and ports for connection to a network. The input connectors accept a variety of types of inputs (digital, analog), allowing for simple connection to almost any machine. The output connectors, such as digital output connectors or the like of the MMD carry MMD output signals generated by the MMD, in response to data received from the input connectors and processed by the MMD, to any machine or device attached to the output connector. These output signals may be used for a variety of purposes, including, for example, pausing a machine, stopping a machine, and instructing a machine to continue operation, as well as activating or deactivating physical signals connected to the output connector such as lights, buzzers or the like. Serial ports, such as RS232 or RS485 or the like, allow for serial input and output between the MMD and the machine and other devices. The MMD software modules include an engine that transforms data input received from the machine connected to the MMD to capture information desired by the user for inclusion in reports. The engine also generates MMD output signals and automated e-mail notifications based on machine data input received and transformations effected. Data transformed by the engine for inclusion in the reports is stored in an on-board database system module resident on the MMD. Reports are created by two software modules. Reports requested specifically for viewing by users may be generated on user request by a server software module, such as a web server, on the MMD which generates the requested report and outputs the report via a user interface, such as a web page, also generated by the server software module. Reports may also be automatically generated and output, without user interfaces or user requests, to a client computing device (CD) on the network by a separate reporter module for archiving purposes or use by other applications. Report content, report format, data transformations by the engine, MMD inputs from machines, and MMD output signals are set out in configuration information which is stored and distributed to other software modules by a configuration interface module. Data is entered into this module via user interfaces generated by the server. The server that generates the user interfaces for reports and configuration may be a world wide web server (web server) that generates user interfaces in the form of world wide web pages (web pages) or the like. According to another aspect of the invention, a method for monitoring machines using an MMD comprises three steps. Beginning with the configuration step, the user determines which reports are desired and the information required, connects the MMD to the machine and to the network, and configures the MMD network connections, MMD inputs and MMD output signals, e-mail notifications, and reports. Once network connectivity is established, this configuration step is carried out using the user interfaces provided by the server module. Next, during the monitoring step, the engine monitors the machine for changes in input, operates desired transformations on the input changes to produce variable changes for inclusion in reports, forwards the reports to the database system for storage, and generates output signals in response to inputs from machines and the results of transformations effected. Finally, during the reporting step, modules that generate reports query the database system to generate reports that are output either to users for viewing in a user interface on the CD or for archiving and use by other applications on a CD. The present invention provides a computer-assisted system and method for remotely monitoring and controlling machines in a wide variety of environments. Specifically, the invention facilitates remote monitoring of machines via a self-contained machine monitoring device (MMD) which is connected to one or more client computing devices (CDs) on a network. The MMD is a compact device containing a processing engine, a server for generating displays and user interfaces, a database system, and machine and network connectivity capabilities. The MMD provides all machine and network connectivity, machine input and output, data storage and processing, reporting, user interface generation, and system configuration capabilities. As such, it furnishes a complete, self-contained, and compact system, readily attachable to almost any machine. Since the MMD provides self-contained data storage, processing, configuration and reporting services, it is not dependent on external computers for any of these functions, but remains capable of transmitting reports for archival storage on a CD if desired, thus increasing reliability and reducing network traffic. In fact, for all functions, the MMD constitutes a self contained unit that acts as a server to the CDs. The CDs, in turn, act as client mechanisms for remotely requesting, storing and viewing report data and remotely entering and viewing MMD configuration information. Reference is first made to FIG. 1, a block diagram of a system utilizing the present invention shown generally as 10. One or more machines 15 is connected to an MMD 20. A machine 15 may comprise a device of any type, as long as the device provides outputs and, if desired, inputs that may be attached to the MMD 20. These outputs and inputs may include, for example, digital inputs, digital outputs, analog inputs, analog outputs, serial communications, and network, such as Ethernet, communications. As such, machines 15 may include any devices having simple digital or analog outputs, Programmable Logic Controls (PLCs), Computer Numeric Controls (CNCs), Ethernet ports, or serial ports for RS232/RS485 connections, among others. The MMD 20 may generate MMD 20 output signals, such as digital output signals or the like, in response to data received from the machine 15 and processed by the MMD 20, which may be transmitted on the MMD 20 to any machine 15 attached to an MMD 20 output connector, MMD 20 serial ports, or MMD 20 network ports. These MMD 20 output signals may be used for a variety of purposes, including, for example, pausing a machine 15, stopping a machine 15, and instructing a machine 15 to continue operation, as well as activating or deactivating user notification devices such as lights, buzzers or the like. Other types of inputs to the MMD 20 and outputs from the MMD 20 are possible. It is not the intention of the inventors to limit input and output types and their possible uses to a given connection type, communication protocol, or specific type of machine 15. Each MMD 20 is attached to a network 25 and acts as a server for all machine 15 control and monitoring functions. The network 25 used may be a local area network, wide area network, an intranet, the internet, wireless network, or any combination of the aforementioned network types. However, the network types mentioned serve only as examples. It is not the intent of the inventors to restrict the use of the present invention to a specific network type or protocol. Data from the MMD 20 is transmitted over a data link 30 from the MMD 20 to the network 25 where it is transported to a client computing device (CD) 35 via a data link 30 from the network 25 to the CD 35. The CD 35 may be any type of computing device capable of receiving, transmitting, and displaying data in the format provided by the network 25 and the MMD 20. A CD 35 may comprise, among other devices, personal computers, handheld computers, personal data assistants (PDA), and cellular phones. The data links 30 between the MMD 20 and the network 25 and the CD 35 may be either wireless data links or wire line data links, provided they can carry data in the protocol used by the MMD 20 and the CD 35. The CD 35 is used for remotely configuring the MMD 20, for remotely requesting and viewing reports from the MMD 20, and for receiving copies and back-ups of report data in another format if desired. All configuration and report requesting and viewing transactions are carried out via user interfaces generated by the MMD 20. MMD 20 handles all of the instructions, processing, configuration requests, report generation, and data storage. The MMD 20 also generates all back-up report data that may eventually be sent to a CD 35 on the network 25, MMD 20 output signal generation, as well e-mail notifications in response to given machine 15 inputs, such as alarms, depending on the MMD 20 configuration. Reports and configuration information are requested by users and displayed via user interfaces generated by the MMD 20 and transmitted to a CD 35 where the user views reports and configuration. Configuration information and report request parameters are also entered via user interfaces generated by the MMD 20. Thus, the MMD 20 handles all data processing, configuration, monitoring, user interface generation, and reporting and constitutes a self-contained unit for all such services. As such, the MMD 20 acts as a server to the CDs 35. The CD 35 is only used for inputting requests, displaying results output by the MMD 20, and for archiving of MMD 20 reports on a CD 35 elsewhere on the network 25, if desired. In one embodiment of the invention, the user interfaces for entering report requests and configuration information and for viewing the reports and configuration information are comprised of web pages in world wide web format wherein configuration information and report requests are entered and configuration and reports requested are displayed in a web browser on a users CD 35. These web page user interfaces use Hypertext Markup Language (HTML) to control the overall layout of the user interfaces, Extensible Markup Language (XML) to define the data structures used for inputs and outputs to the user interfaces, and JAVA programming applets to display any requested reports in graphical format. Reports may also automatically output without user viewing, to a CD 35 on the network 25 in a format such as comma separated values (CSV) or in Microsoft Excel™ format for archiving purposes or use by other applications. In addition, a designated MMD 20 can monitor the running status of all of the other MMDs 20 and provide a web page user interface that facilitates access to reports on any MMD 20 connected to the network 25. Upon user request, the designated MMD 20 generates a web page user interface viewable on a CD 35, that contains a list, for example a hierarchal tree, of all the MMDs 20 within a frame on the web page. The user may then select the MMD 20 attached to the machine 15 that the user wishes to view from the list, which causes the selected MMD 20 to generate a web page to allow the user to view/select reports available on the MMD 20 chosen in another frame on the web page designated for report viewing. It is also possible for a designated MMD 20 to generate reports that compile data from reports output from multiple MMDs 20. The user interfaces, report formats, and language tools used to generate the user interfaces for the present embodiment are exemplary. The user interfaces used and generated by the MMD 20 for presenting reports to the user and for entering configuration and report requests may be of any type that may be readily displayed by the CD 35. It is not the intent of the inventors to restrict the use of the present invention to a given reporting type format, user interface mechanism, or language for developing and displaying reports or user interfaces. Thus, it is not the intent of the inventors to limit user interfaces to interfaces in the form of world wide web pages or to limit the type of server to a world wide web server that generates such interfaces in the form of world wide web pages. Referring now to FIG. 2, a block diagram of the hardware components of the MMD is shown generally as 40. The MMD 20 contains a variety of connectors and ports for inputs from, and outputs to, a machine 15. Input connectors 45 may include digital input connectors 50 which assure that the MMD 20 can receive digital inputs, i.e. inputs in digital format, from the connected machine 15. Similarly, the MMD 20 may possess one or more analog input connectors 55 which allow the MMD 20 to receive analog inputs, i.e. inputs in the form of analog signals. The MMD 20 may also include one or more serial ports 60, such as RS232 or RS485 (COM) ports 65 or the like, for serial communications, including serial input and serial output, with machines 15 capable of using such serial ports 60. These serial ports 60 are also used for handling serial protocol communications. This may include, for example, communication from manual input devices such as handheld terminals and barcode scanners as well as outputs to Light Emitting Diode (LED) display boards. The MMD 20 may also contain one or more output connectors 70, such as a digital output connector 75, for sending MMD 20 output signals instructions to a connected machine 15 or other connected device. Finally, one or more network ports 80, such as an Ethernet port 85 or the like, on the MMD 20 assure network 25 communications to CDs 35 or machines 15 capable of using network protocols. Machines 25 capable of using network protocols, such as Ethernet or the like, may be indirectly connected to the MMD 20 by communicating with the MMD 20 over the network 25. The MMD 20 also contains a number of elements that allow the MMD 20 to act as a self-contained computing device. Instructions and operations for MMD 20 are controlled by a Central Processing Unit (CPU) 90. Synchronization of activities and instructions are carried out by reference to a real time clock 95. MMD 20 and machine 15 data is stored in flash memory 100, read-only-memory (ROM) 105, random-access-memory (RAM) 110, on an internal disk 115, or other storage media, not shown, internal to the MMD 20. The MMD 20 may also have one or more LEDs 120 for indicating MMD 20 power status and the status of various MMD 20 input connectors 45, output connectors 70, serial ports 60 and network ports 80. In one embodiment, the MMD 20 comprises a plurality of digital input connectors 50, a plurality of analog input connectors 55, a plurality of serial RS232 ports 65, one software selectable serial RS232/RS485 port 65, and a plurality of digital output connectors 75. Configuration information is stored in the read/write flash memory 100, which allows for preservation of configuration information in the event of a power failure. A long-life battery 125 functions as a power back-up mechanism and ensures that the MMD 20 can continue functioning in the event of such a failure. The MMD 20 reads and stores other useful data via ROM 105 and RAM 110, or disk storage 115. Should connections to the network 25 cease to function, this data can be forwarded on to a CD 35 when network 25 connections are re-established. Thus, the MMD 20 may retain its configuration information and continue temporarily to monitor the machine 15, without data loss, even in the event of a power or network 25 failure. The MMD 20 also includes a plurality of MMD LEDs 120 for indicating the status of the input voltage, digital input connectors 50, digital output connectors 75, COMI serial (RS232/RS485 ) port 65, and network connectivity via the Ethernet port 85. The Ethernet port 85 may also be used to communicate with machines 15 capable of Ethernet communications. Other than a CD 35, machines 15 capable of Ethernet communications will often not be directly attached to the MMD 20. Rather, they will communicate with the MMD 20 over the network 25. As one skilled in the art will recognize, however, other combinations for use of memory, battery 125 backup capability, input connectors 45, output connectors 70, serial ports 60, network ports 80, and use of LEDs 120 are possible. Reference is now made to FIG. 3, a logical flow diagram of the software modules of the MMD 20, shown generally as 130. To aid the reader in understanding the logical flow of the modules of MMD 20, we will also be referring to features of FIG. 2. In brief, the software modules are comprised of the following: a configuration interlace module 135 for managing configuration information, an engine 140 for performing transformations on machine inputs and generating outputs based on the machine inputs, a database system 145 for storing report data, drivers 150 for translating machine inputs to a format useable by the engine and engine outputs for use by machines, a reports Common Gateway Interface (CGI) module 155 and reporter module 160 which generate reports, and a web server 165 or the like for generating user interfaces for requesting and viewing reports and for entering and viewing configuration information, as well as handling all input from the user interfaces. The reports CGI module 155 is comprised within the web server 165 and specifically handles all user requests for reports and outputs the reports in the form of web page user interfaces. The web server further comprises a configuration CGI module 170 which specifically handles generation of web page user interfaces for entering and viewing configuration information. The database system 145 is further comprised of a database manager 175 and a database 180. The database manager 175 reads and writes data to the database 180 which stores the actual information required for report generation. These modules are explained in greater detail below. The configuration interface module 135 stores and manages the MMD configuration information, which is stored in flash memory 100. The configuration information is determined primarily as a function of the reports that must be generated and includes variable names for inputs from machines and outputs required for reports, transformations to be performed by the engine, structure of the database 180 within the database system 145, report formats, and queries. The configuration interface module 135 is the only module that can read or write to the flash memory 100 that contains the configuration information. Thus, the configuration interface module 135 is used for reading and writing of configuration information for the MMD 20 to the flash memory 100 during the initial MMD 20 configuration and after configuration changes. As such, the configuration interface module 135 interacts with the configuration CGI module 170, which generates the web page interface through which the user enters and views configuration information on the CD 35. The configuration CGI module 170 transmits configuration information entered by the user to the configuration interface module 135, which then writes this information to the flash memory 100. In addition, the configuration interface module 135 also supplies all necessary configuration information, by reading from the flash memory 100, to all other modules after configuration changes or during MMD 20 initialization. The other modules receive this information during initialization and store it in memory for subsequent use. Thus, once the other modules have been initialized with the configuration information, the configuration interface module 135 does not need to provide this information again unless there is a change in configuration or system re-start, such as after a power failure, etc. By using the configuration interface module 135 as an intermediary between all other modules and the configuration information stored in the flash memory 100, the MMD 20 ensures that each module is furnished with the configuration information required for the module's tasks and that only one module accesses the configuration information in the flash memory 100 at any given moment. The configuration interface module 135 also maintains, as part of the configuration information, user names and passwords. Users may thus use these passwords, from web page user interfaces, to view and modify system configuration information as required for the daily use of the system. Different levels of access and modification permissions are accorded to users based on their classification as belonging to a group having certain access and modification rights. For example, there could be three groups of users, such as basic users, administrators, and integrators, with basic users having the least rights, administrators having additional rights, and integrators having the most rights. In this manner, the ability to effect necessary modifications to the configuration information is ensured while maintaining security. The engine 140 monitors machine inputs via the drivers 150 for changes to determine whether the value received for a given input is not the same as the previous value received for that input, in which case an input change is detected. More specifically, the drivers 150 receive the inputs from the digital input connectors 50, analog input connectors 55, and serial RS232/RS285 ports 65 and translate them into a format useable by the engine 140. For each input, there is a variable associated with the input's value. The engine 140 compares the last value received for each input, as contained in the variable associated with the input, with the current value of the input. If an input change is detected, the engine 140 applies transformations to the input value for which an input change has been detected. These transformations may include basic mathematical transformations such as multiplication or division, Boolean logic, comparison with other values, and transformation for measuring and comparing inputs or variables over a given period of time. An example of possible transformations is shown in Table 1. TABLE 1# ofOperationinputsResult Variable ValueCOPY1copy of the input variableInvert1Boolean inverse of the input variableBitwise Invert1bitwise invert of the input variableAbsolute Value1absolute value of the input variablePlus +2Input1 + Input2Minus −2Input1 − Input2Multiplied By * 2Input1 * Input2Divided By/2Input1/Input2Less Than <2TRUE if Input1 < Input2 otherwiseFALSEGreater Than >2TRUE if Input1 > Input2 otherwiseFALSELess Than2TRUE if Input1 <= Input2 otherwiseor Equal To <=FALSEGreater Than2TRUE if Input1 >= Input2 otherwiseor Equal To >=FALSEIs Equal To ==2TRUE if Input1 equals Input2 otherwiseFALSEIs Not Equal To !=2TRUE if Input1 is not equal to Input2otherwise FALSEAnd2TRUE if Input1 is TRUE and Input2 isTRUE otherwise FALSEOr2TRUE if Input1 is TRUE or Input2 isTRUE or both are TRUE otherwiseFALSEExclusive Or2TRUE if only Input1 is TRUE or onlyInput2 is TRUE otherwise FALSERound2Rounds Input1 to accuracy specified byInput2Value Sampling2Copies Input1 but only at fixed timeintervals which are specified by Input2Deadband2Copies Input1 but only if its value haschanged by the amount specified byInput2Timer (seconds)1# of seconds thatInput1 has been TRUE forCounter1# of times that Input1 has been TRUELimit Output Range3Copies Input1 but only if its value iswithin the specified Lower Limit andUpper LimitMax Over Time2maximum value that Input1 has had overthe time period specified by Input2Min Over Time2minimum value that Input1 has had overthe time period specified by Input2Spread Over Time2maximum value that Input1 has had overthe time period specified by Input2Count Over Time2# of times that Input1 has been TRUEover the time period specified by Input2Average Cycle Time2ratio of seconds to # of times that Input1has been TRUE over the time periodspecified by Input2 The result of each transformation is another variable designated to hold the value of the result of the transformation. As such, an input change may undergo a number of transformations, using a number of intermediate variables, until the result required for inclusion as a field in a report or for display as a graph in a report, referred to as a report variable, is calculated. Variables required for such displays are referred to as report variables. When the engine 140 is finished processing the input change, it forward the results, i.e. any resulting report variables, to the database manager 175. Only changes in the value of report variables, referred to as report variable changes, are transmitted by the engine 140 to the database manager 175 for storage in the database 180. By limiting any transformations on inputs with a view to transmission to the database manager 175 to those cases where an input change is detected, as opposed to using more traditional methods of processing and storing all inputs on a constant basis, the engine 140 consumes less resources. The fact that only report variable changes are sent by the engine to the database manager 175 and recorded in the database 180 further minimizes storage requirements and processing resources required. However, since the engine 140 is constantly monitoring all inputs received from the machine 15, input changes are detected and variable changes are calculated and stored almost instantly, thus ensuring precision of the MMD 20 reports is not compromised. The engine 140, may also generate engine outputs in the form of MMD 20 output signals and email notifications in response to inputs from machines 15, whether there has been an input change or not, or in response to the result of transformations undertaken by the engine 140 in response to an input change. For example, the engine 140 could generate instructions to activate or deactivate a PLC, relay, or LED that would be sent, via the drivers 150, over a digital output connector 75. E-mail notifications may be sent with a time delay, or to one or more recipients, the identity and quantity of recipients also being dependent on the results of the handling of the input. Such e-mails would be sent via the Ethernet port 85. Variable names and the exact transformations applied by the engine 140, are dependent on the reports which must be made available and instructions for handling inputs, both of which are set out in the configuration information. This information is transmitted to the engine 140 by the configuration interface module 135 when the engine 140 is initialized or after a configuration change. The engine 140 may also use thresholds provided in the configuration information during transformation of the input change to determine whether the resulting variable is significant enough to be handled/transformed further and transmitted to the database manager 175 or not. Engine outputs, namely digital outputs for MMD 20 output signals and e-mail notifications performed by the engine 140, are also governed by the configuration information. The database 180 is the repository for report variables required for generating the reports. It receives and outputs information via the database manager 175. The database manager 175 is the only module that has direct access to the database 180. All other modules that need read/write access to the database 180 must use the database manager 175. In this fashion, the database manager 175 ensures that only one module can access data from the database 180 at any given time, thus ensuring that data integrity is not compromised by one module writing to the database 180 while another module is reading from it. In particular, the database manager 175 executes Structured Query Language (SQL) queries received from the reports CGI module 155 and reporter module 160 and extracts and processes data from the database 180 as required by the queries. The database manager 175 then forwards the results of these queries, generally as collections of records, to the reports CGI module 155 and reporter module 160 which output them as required. The exact contents and structure of the database 180 are dependent on the data inputs from the machine 15, the transformations and report variable changes resulting from treatment by the engine 140, and the database 180 structure. The database structure is based on the report variables which must be stored so as to be entered as in fields or displayed as graphs in the desired reports as set out in the configuration information. The database manager 175 establishes the database 180 structure, in accordance with this configuration information, and reads and writes records and fields of the database 180 in accordance with this structure. The configuration information is transmitted to the database manager 175 by the configuration interface module 135 upon initialization of the database manager 175 after powering up the MMD 20 or after a configuration change. For each report specified in the configuration information, there is a corresponding table in the database 180. Each report variable, as established in the report configuration information, constitutes a field within each record of the table assigned to that report. Each record within a table captures all of the values for the report variables required for the record as well as the time at which these variables held that value. New records are input to a table in the database 180 only when there is a change in one or more report variables required for the record. In this manner, processing resources and storage space required for the database 180 are reduced. For example, suppose a report indicating whether a machine 15 is running or not is set out in the report configuration information. Upon initialization, the configuration interface module 135 will transmit the names of the report variable used to capture the running status to the machine 15 for display in the report and an identifier for the report to the database manager 175. The database manager 175 will then execute an SQL command to cause a table bearing the identifier's name to be created in the database 180. Each record in the table will include a field for the value of the report variable that represents the running status of the machine 15, as well as a field for the time at which the report variable for the running status of the machine 15 acquired that value. When the value for the report variable changes, after processing by the engine 140 and submission of the new value to the database manager 175, the database manager 175 causes a new record to be created in the table which captures the new value and the time at which the change in value occurred. Although the present embodiment makes use of a relational database, it is not the intention of the inventors to restrict the database 180 or database manager 175 to a relational format. A person skilled in the art will recognize that other formats for the database 180 and database manager 175 are possible. The drivers 150 are responsible for handling inputs from and outputs to machines 15 connected to the MMD via the digital input connectors 50, analog input connectors 55, digital output connectors 75, Ethernet port 85, and serial RS232/RS485 ports 65. As such, the drivers 150 can handle digital inputs, analog inputs, and serial communications and provide such inputs in a format useful to the engine 140. In turn, the engine 140 uses drivers 150 to forward the engine 140 outputs that the engine 140 generates to the appropriate output connectors 70, RS232/RS485 serial ports 65, or Ethernet port 85. For example, MMD 20 digital output signals could be transmitted to a machine 15 connected to a digital output connector 75 via drivers 150. The web server 165 generates all user interfaces and handles all input and output to them. The interfaces are displayed as web pages in a web browser on a CD 35, from which the user enters information into the web page and views results. More specifically, the web server 165 generates web page user interfaces for requesting reports and entering report parameters. This functionality is ensured by the reports CGI module 155 which is comprised within the web server 165. In addition, the web server 165 also ensures generation of web page user interfaces for entering and viewing the configuration information via the configuration CGI module 170, also comprised within the web server 165. It should be noted that the configuration CGI module 170 and reports CGI module 155 do not necessarily have to be implemented within the web server 165 and could instead be implemented as external modules to the web server 165, yet resident on the MMD 20, that would provide data from which the web server 165 would generate and transmit the required web page user interfaces. It is not the intention of the inventors to restrict the exact placement within the MMD 20 of the reports CGI module 155 or configuration CGI module 170 with regard to the web server 165. The reports CGI module 155 is a module that generates reports and which is comprised within the web server 165. The reports CGI module 155 provides a user friendly, web page interface for generating MMD 20 reports on the connected machine's 15 status. When a user requests to view the reports available for a machine 15, the reports CGI module 155 generates a web page containing a menu of reports to view. The user may then select a report and enter the desired report parameters into the web page interface provided by the reports CGI module 155 to the CD 35 for the report selected. The parameters typically involve time intervals, referred to as shifts, for monitoring the machine 15 between a scheduled start and end time for workers or machines 15. The reports CGI module 155 then uses the parameters input by the user to generate an SQL query which is sent to the database manager 175. The database manager 175 executes the query to obtain the desired information from the database 180 and transmits the results to the reports CGI module 155. The reports CGI module 155 uses this information to generate a web page containing the selected report which is transmitted to the user's CD 35. The contents and structure of the reports, which dictate the SQL queries, are output to the reports CGI module 155 by the configuration interface module 135 during initialization. The reports CGI module 155 is capable of modifying reports in real-time in response to changes in inputs, as handled by the engine 140 and database manager 175 and set out during configuration, to allow a user to see changes as they occur. Using templates that set out each basic type of report, the reports CGI module 155 generates HTML files to control the appearance of the web pages, java applets to generate graphs, and XML files to contain and describe data structures used by the reports. The reporter module also generates reports. However, reports generated by the reporter module 160 are not requested and displayed via user interfaces generated by the reports CGI module 155 of the web server 165. Rather, if so configured, the reporter module 160 automatically generates and writes backups of all MMD 20 reports to a CD 35 on the network 25 at pre-determined time intervals. The time intervals, contents of the reports, and format of the reports are output to the reporter module 160 by the configuration interface module 135 during initialization. The reporter module 160 uses this information to generate an SQL query at the pre-configured time intervals and transmits the query to the database manager 175. The database manager 175 executes the query to obtain the desired information from the database 180 and transmits the results to the reporter module 160. The reporter module 160 then uses this information to generate a report which it transmits to the designated CD 35 on the network. The report may be output in a format such as Microsoft Excel or CSV format, depending on the configuration information. Reports can be stored on the designated CD 35 either as a single continuous file for all reports or as a separate file for each period of time, which may represent a work shift within the production environment, defined in the configuration information. The configuration CGI module 170 provides an easy to use, user-friendly web page user interface for configuring all of the MMD 20 settings. It is comprised within the web server 165. More specifically, the configuration CGI module 170 generates HTML web pages into which configuration information may be entered or viewed. These web pages are created based on templates which contain the basic web page structure for each type of configuration information to be entered or displayed. Using the templates, the configuration CGI module 170 generates HTML files to control the overall appearance of the configuration web pages while storing data structure information required for the web pages in XML files. The user enters configuration information in the web page interface transmitted to the CD 35 via the configuration CGI module 170. In addition, the configuration CGI module 170 also allows a user to upload or download existing configurations to/from a networked CD 35. Once the configuration information is entered, the configuration CGI module 170 reads/writes the information to the configuration interface module 135, which in turn reads/writes the data to the flash memory 100. Although the present embodiment makes use of HTML, XML, and JAVA to define web page interfaces and/or reports, it is not the intention of the inventors to restrict such interfaces and/or reports to a web base format or to use a particular language to generate the web pages. A person skilled in the art will recognize that other formats for the reports are possible and that other languages or tools may be used to generate them. It should be apparent to one skilled in the art that the placing of the input connectors 45 and/or output connectors 70, serial ports 60, network ports 80, engine 140, drivers 150, database system 145, reporter module 160, configuration interface module 135, and web server 165 has a positive cumulative effect on reliability and use of network 25 resources. All user configuration entries and displays, as well as report generation, are handled on-board via the web server 165, including the reports CGI module 155 and configuration CGI module 170, and reporter module 160. On-board storage of machine 15 report data is assured by the database system 145, comprised of the database manager 175 and database 180. All required hardware capabilities for processing for machine 15 inputs and engine 140 outputs, as well as serial and network communications are also located within the MMD 20. For all of these functions, the MMD 20 constitutes a self-contained unit and acts as a server to the CDs 35 over the network 25 for, thereby eliminating the need for a central server elsewhere and increasing reliability. Since almost all MMD 20 data processing and interface generation is also handled within the MMD 20, network 25 traffic is also reduced. FIG. 4 is flowchart of a method for using the present invention, shown generally as 185. It demonstrates the overall method for use of the invention. Beginning at the configuration step 190, the MMD 20 is configured by the user. This includes connecting the machine 15 to the MMD 20 and configuring reports, variables, network ports 80 and connections, serial communications via serial ports 60, machine 15 inputs via input connectors 45 and MMD 20 output signals via output connectors 70. At the end of this step 165, required configuration information is transmitted to the software modules. The MMD 20 software modules are then initialized with the configuration information. Next, at the monitoring step 195, the MMD 20 monitors the machine 15. During this step 195, the engine 140 monitors and transforms the machine's 15 inputs, provides engine 140 outputs as configured, and sends necessary information as report variable changes to the database system 145. Next, at the reporting step 200, the MMD 20 generates reports as requested by the user and transmits them to the user via a user interface generated by the web server 165 and displayed on the user's CD 35. The MMD 20 also generates reports automatically, via the reporter module 160, at given intervals and formats, as configured, and sends the reports to a CD 35 via the network 25 for archiving or processing by other applications. It should be noted that the monitoring step 195 is ongoing and is constantly repeated, even while reports are being generated automatically and requested by the user during the reporting step 200. Thus the monitoring step 195 and reporting step 200 constitute an ongoing cycle that continues until the MMD 20 is disabled, not shown, or there is a change in MMD 20 configuration, not shown. Reference is now made to FIG. 5, a flowchart of the MMD configuration step 190 of FIG. 4, shown generally as 205. Beginning with the report determination step 210, the user determines what type of reports the user desires and the information required for such reports. Examples of reports include: machine status reports, signal reports, maintenance reports, product count reports, and alarms. Machine status reports monitor the time the machine 15 is in a given state. For example, the report might show the relative times that the machine 15 has been running, cutting, undergoing maintenance, idle, off, etc. Machine status reports can be cumulative or chronological. A cumulative machine status report may provide a pie chart that shows the proportions of the time interval during which the machine 10 was in each state. For a chronological machine status report, a bar chart may be used to illustrate which states the machine 10 was in at each moment over a given interval of time. Machine status reports require that the user determine which states that the user wants to monitor. Signal reports plot information over time, such as temperature, vibration, spindle load, and cabinet humidity. These reports thus allow users to see trends in the signal but also what is occurring in real time. The user can also define limits which can be displayed on the chart and the user can choose to have the engine 140 generate alarms and/or send e-mails as the limits are approached or surpassed. This report requires that the user determine the information to be monitored, applicable limits, and actions to be taken as limits are approached or surpassed. Maintenance reports determine whether fault information is available from the machine 15 (via the RS232/RS485 serial ports 65) and to track fault information. Faults can be recorded with a start and end time along with their duration. The reports can be cumulative maintenance reports, which display bar charts for the length of each fault. The reports can also be chronological maintenance reports which show the status of each fault type over a given period of time. Finally, maintenance reports can also be preventative maintenance meter type reports. These reports allow a user to work with an input like a car does with its odometer. The user can reset the meter at any time and let it keep track of the input for a predefined time interval. Maintenance reports require that a user identify the type of fault to be monitored as well as the desired time intervals. A product count report displays a bar chart that shows production count, such as number of units produced by a machine 15, over the course of a shift or number of shifts. Usually a digital signal is used to determine a completed cycle and a factor is used by the engine to determine how many parts were produced from that cycle. However, with serially input data using a serial RS232/RS485 port 65, a user can gather batch and part numbers to reference identification information with the part count data. The user must identify the desired information and the intervals required for this report. Alarms can be based on any signal, real or derived. Alarms can be emails generated by the engine 140 and sent to a CD 35. The engine 140 can also allow for a delay so that the same alert can be escalated to multiple people within an organization. The user must identify the events for which they wish to have an e-mail notification generated, to which e-mail address the notification should be directed and what the time delay should be applied before sending the e-mail (time delay relative to when the alarm occurred). Multiple email notifications can be configured with different time delays and different recipients for the same alarm. Thus, an e-mail notification can be sent, as an e-mail notification escalation, to increasing numbers of people at increasing levels of authority as time goes on if the condition that has caused the e-mail notification for an alarm to be generated is not corrected. Next, at the input/output identification step 215, the user must identify the inputs required to capture the information required for the reports. Thus, for each report desired, the user must determine which inputs and outputs are necessary to generate or provide the information required for the report and the signals required to provide such inputs and outputs. These will determine which combinations of digital input connectors 50, analog input connectors 55, digital output connectors 75, and serial RS232/RS485 ports 65 are necessary. The signals available will vary by type of machine 15. From an input perspective, a combination of digital signals may be used to derive the desired information or machine state. Analog inputs also may be combined with digital inputs to provide additional information. For example, an analog voltage input may be used to indicate when the machine 15 is cutting versus whether the machine 15 is simply running or not, as might be indicated by a digital input. As for outputs, the user will have to decide which output connectors 70 to a machine 15, or serial RS232/RS248 ports 65, or Ethernet port 85 may be used to provide the required MMD output signals. Next, at the machine connection step 220, the user connects the appropriate outputs from the machine 15 to the corresponding digital input connectors 50, analog input connectors 55, and serial RS232/RS485 ports 65 on the MMD 20 to provide the inputs required. For example, digital outputs from the machine are connected to digital input connectors 50 on the MMD 20, analog outputs are connected to analog input connectors 55 on the MMD 20. Serial connections from the machine are connected to the serial RS232/RS485 ports 65 to provide serial inputs and outputs. As well, any additional digital, analog or serial inputs can be added to bring data into the MMD 20. Digital outputs to the machine 15 are ensured by connecting digital output connectors 75 from the MMD 20 to digital inputs on the machine 15 or machine lights such as LEDs. The user may also connect an Ethernet-enabled machine 15 to the Ethernet port 85 to provide inputs at this time. However, preferably, such a machine will be connected to the network 25, over which the machine 25 will communicate with the MMD 20. Moving now to the network configuration step 225, the user may connect a CD 35 directly to the MMD 20 to configure the Internet Protocol (IP) settings by which the MMD 20 will communicate with the network 25. A network configuration utility allows the user to set parameters for the IP address, the domain name server (DNS) address, the gateway address, the subnet address information, and whether Dynamic Host Configuration Protocol (DHCP) services are available. After the IP configuration information has been entered, the user may connect the MMD 20 to the network 25 via the Ethernet port 85 which will allow the user to continue configuration via a web page user interface from any CD 35 on the network 25 or from a CD 35 directly connected to the MMD 20. To do so, the user enters the IP address of the MMD 20 device from any web browser enabled CD 35. The web server 165 then generates an initial web page interface containing a menu of configuration and reports options and transmits it to the CD 35. From this web page interface, the user selects the configuration option. This causes a configuration web page user interface to be generated by the configuration CGI module 170. From the configuration web page interface, the user then selects the desired configuration items, which causes the configuration CGI module 170 to generate additional pages for entering or viewing the appropriate configuration information. For example, if a user wishes to configure inputs, the user first selects configuration from the initial web page user interface menu, which causes the configuration CGI module 170 to generate the configuration web page user interface containing the configuration options. From this page, the user then selects the option for configuration of inputs. This causes the configuration CGI module 170 to generate another web page containing the necessary fields into which the user may enter the information necessary for configuring the input. This information is transmitted back to the configuration CGI module 170 which processes the configuration information entered and transmits it the configuration interface module 135 which, in turn, stores it in the flash memory 100 and transmits it to the appropriate modules. Proceeding now to the machine information step 230, the user enters basic machine 15 and MMD 20 information via one or more web page user interfaces generated for this purpose by the configuration CGI module 170. This information includes, among other things: a device name to associate the MMD 20 with the machine 15 to which it is connected, system user names and corresponding passwords, whether the user desires that digital signals for alarms be inverted, IP address information if not already provided, and the IP address of a time server for providing time information. If desired, the user may also choose to import or export configuration information to/or from a file on the user's CD 35. Moving next to the shift configuration step 235, the user defines the shifts that are used in the reports generated by the reports CGI module 155 and reporter module 160. The shifts are used to determine default time intervals for reporting purposes and refer to the period between a scheduled start and end time for workers or machines 15. Relevant shift information is eventually forwarded to the reports CGI module 155 and reporter module 160. To configure shifts, the user selects the shift configuration option from the configuration web page user interface. This causes a shift configuration web page user interface to be generated by the configuration CGI module 170. The user then enters information into the shift configuration web page user interface to assign a name to each shift, define the time intervals applicable to the shift, and assign a color to be used to represent the shift in reports that display graphical representations of machine data for the shift. Moving now to the input configuration step 240, the user enters the configuration information for the inputs identified during the input and output identification step 215. For each input from the machine 15, the user enters a variable name and any transformations to be performed by the engine 140. For each input, the user also enters the associated MMD 20 digital input connector 50, MMD 20 analog input connector 55, IP address for machines 15 providing Ethernet inputs, or MMD serial RS232/R285 port 65. For example, for digital inputs, users may choose to flatten or invert the digital signal. For analog inputs, it is often desirable to specify a scaling method for the analog signal. For serial inputs, such as data received from bar code readers, it may be desirable to specify a bit mask. The variable names and the operations to be effected are eventually forwarded to the engine 140 for use in handling the inputs. This information is entered and viewed via web page user interfaces created by the configuration CGI module 170. Next, during the output configuration step 245, MMD outputs and output variables are configured. These may include the generation of MMD 20 output signals which are transmitted by the engine 140 via the output connectors 70. During this step, the user selects an output configuration option from the menu item on the configuration web page user interface. This causes the configuration CGI module 170 to generate an output configuration web page user interface. Using this interface, the user defines additional transformations which are to be effected by the engine 140 on the variables assigned to inputs in the input configuration step 240. The result of such a definition is a new variable which can, if desired, be used as an input for another transformation defined during this phase of configuration. Thus, the user continually adds transformations and creates new variables until the user has defined variables that represent the information necessary for report variables. All of the variables and operations are eventually forwarded to the engine 140 which, once the MMD 20 is configured and operating, carries out the desired transformations on the variables and sends the resulting report variable to the database manager 175. Once the variables are established, the user may also choose to have any or all of them, including report variables, forwarded on to an Object Link Embedding for Process Control (OPC) server automatically for another application to access. For example, if a user desired that a digital input, input A, be inverted and compared for logical equivalence with another digital input, input B, the user would first define the variable names for each input during the input configuration step 240 and would also specify that the value of input A was to be inverted. Then, during the output configuration step 245, the user would specify that the value of input A is to be compared to the value of input B for logical equivalence and that the result be stored in another variable. The user could then define another transformation using the variable containing the result of the logical equivalence comparison. The result of this last transformation would be stored in still another variable defined by the user and associated with this last transformation. It is during the output configuration step 245 that the IP address of any MMD 20 designated to monitor the status of other MMDs 20 is entered. If such an address is entered and the user activates this monitoring feature, then, during initialization, the MMD 20 will send machine status information (such as whether the machine is running or not) and the MMDs 20 IP address to the designated MMD 20. Monitored MMDs 20 will only transmit new machine status information to the designated MMD 20 if there is a change in status. This information is used by the web server 165 of the designated MMD 20 node to allow the user to navigate from MMD 20 to MMD 20 in a list, such as a hierarchal tree, and view the reports and basic machine 15 running status of each MMD 20. Proceeding now to the reports configuration step 250, the user defines and configures the reports. From the configuration web page user interface, the user selects the reports configuration option. This causes the configuration CGI module 170 to generate a web page menu of all the different report types. From this menu, the user selects the desired report type and the configuration CGI module 170 generates a web page user interface for entering and viewing the configuration information for a report of the selected type. The user then enters the required information for generating the report. This information includes the variable names to be used as the values displayed in the report. These are the variables that are stored in the database 180. Additional information, such as color information for graphs displayed in reports and labels for fields may also be entered. The user repeats this process for all reports desired. For certain reports and values, the user may specify whether the engine 140 should send e-mail notifications, as well as the recipients, frequency, and delays of such notifications. The user may also choose to have all reports automatically forwarded by the reporter module 160 to a CD 35 on the network 25 for archiving or use by another application. The report variable names, report types, and structures to be stored in the database are eventually forwarded, via the configuration interface module 135, to the database manager 175 which creates a table for each report. Variables names to be monitored for e-mail notifications, as well as notification parameters, are forwarded to the engine 140. Report types and required information, such as variable names required and shift, time interval or color information, are forwarded to the reports CGI module 155 and, if the user has opted to have the reporter module 160 automatically forward reports in CSV or Microsoft Excel format to a CD 35 on the network 25 at given intervals, to the reporter module 160 as well. Moving now to the save configuration step 255, the user may elect to save configuration information to the flash memory 100. If the user so chooses, the configuration CGI module 170 transmits the configuration information to the configuration interface module 135 which writes the information to the flash memory 100. The configuration interface module 135 may then access the configuration information in the flash memory 100 and forward the appropriate configuration information to the other modules. The user may subsequently alter the configuration by again choosing the configuration option from the initial web page generated when the MMDs 20 IP address is entered on the user's CD 35. The above configuration procedure is provided as an example. It is not the intention of the inventors to limit the configuration procedure to the order specified above. It will be apparent to one skilled in the art that the order and content of some steps may be modified. Reference is now made to FIG. 6, a flowchart, shown generally as 260, of the monitoring step 195 of FIG. 4. Beginning with the input change detection step 265, the engine 140 automatically monitors the machine 15 for input changes via the drivers 150. The engine 140 may also issue MMD 20 output signals and e-mail notifications during this step 265. For example, the engine 140 may be configured to issue an MMD 20 output signal or e-mail notification after the machine 15 has been in a certain state for 15 seconds. Thus, the state of the input will not have changed when MMD 20 output signal or e-mail notification is triggered. Next, at the change processing step 270, the engine 140 processes any detected input change by effecting transformations on the input change, which may result in changes to the values of report variables, and issues any MMD 20 output signals or e-mail notifications required as a result of the transformations. The transformations undertaken are based on the configuration information. Finally, at the storage step 275, changes in the values of report variables are forwarded to the database manager 175 which stores them in the appropriate format and table of the database 180, based on the MMD 15 configuration information. Reference is now made to FIG. 7, a flowchart of the reporting step 200 of FIG. 4 for automated reports. This flowchart is shown generally as 280. The MMD 20 may automatically generate reports at certain time intervals, depending on whether this option is chosen during the configuration step 190. Beginning with the query generation step 285, the reporter module 160 generates an SQL query and transmits it to the database manager 175. Next, at the query processing step 290, the database manager 175 executes the query by interrogating the database 180 and transmits the result back to the reporter module 160. Finally, at the report output step 295, the reporter module 160 receives the query results, transforms them into one or more reports in the format specified in the configuration information, and transmits the report over the network 25 to a CD 35. The report may be stored on the CD 35 for archival purposes and/or used by the user or other applications, such as factory/plant automation software. FIG. 8 is a flowchart of the reporting step 200 of FIG. 4 for user requested web page reports, shown generally as 300. Beginning with the web report request step 305, the user enters the IP address of the MMD 20 attached to the machine 15 the user wishes to view. The web server 165 then generates an initial web page user interface menu from which the user may choose to view reports or enter or view configuration information. The user selects the option to view reports and the reports CGI module 155 generates a report selection web page user interface from which the user may choose a report to view. Next, at the web report selection step 310, the user selects a report from the web page report selection user interface menu. If the report selected requires that the user enter parameters for generating the report, the reports CGI module 155 generates a web page user interface for the desired report from which the user enters the required parameters. If, however, the report does not require a user to enter parameters, or if default values for the report were specified during configuration, the parameter entry web page user interface will not be displayed and the reporting step will automatically to the next step. These scenarios are not shown in FIG. 8. Next, at the web query generation step 315, the reports CGI module 155 generates an SQL query which is sent to the database manager 175. This query incorporates any parameters entered by the user during the web report selection step 310. Next, at the web query processing step 320 the database manager 175 executes the query to obtain the desired information from the database 180 and transmits the results to the reports CGI module 155. Finally, at the web report output step 325, the reports COt module 155 uses the information returned by the database manager 175 to generate a web page containing the report which is transmitted to the user's CD 35. The reports CGI module 155 can constantly repeat the web query generation step 315, the web query processing step 320, and the web report output step 325 to capture and report changes in inputs and variables, as handled by the engine 140 and database manager 175. This allows the user to see the changes as they occur in real time. Also, as mentioned above, the user may specify during configuration that the reports CGI module 155 generate a series of default reports, using default parameters, that will appear as soon as the user types in the IP address of the MMD 20. In this scenario, not shown in FIG. 8, the web query generation step 315, the web query processing step 320, and the web report output step 325 are automatically undertaken for the default reports and parameters as soon as the MMDs 20 IP address is entered. The result is that the initial web page user interface menu generated by the web server 165 will display the default reports, generated by the reports CGI module 155 with default parameters, along with the menu of available reports and configuration options. Any reports subsequently chosen from the reports menu which also have default parameters specified will also be automatically generated by the reports CGI module 155 with these parameters when selected. The user then has only to enter specific parameters for reports where there are no default parameters or when the user wishes to use different parameters. If the MMD 20 for which the IP address is entered during the web report request step 320 is designated to monitor other MMD devices, the web server 165 of that MMD 16 node will generate an initial web page user interface menu having a frame containing a list, for example a hierarchal tree, from which a user may select different MMDs 20 accessible from the designated MMD 20 for report viewing. Each entry in the list will be associated with IP address of the associated MMD and the MMDs machine status information. Actual reports will be displayed in another frame allocated to that effect. If the user desires, the machine status of each machine 15 attached to an MMD 20 can be obtained by moving a mouse pointer device over the name of the MMD 20 attached to the device on the list of MMDs. When a user selects a MMD 20, a reports request is sent to the MMD 20 selected as if the user had entered the IP address of the selected MMD 20. Subsequently, the request is handled by the selected MMDs 20 web server 165 and reports CGI module 155 as described above and shown in FIG. 8, except that all of the web report pages and menus generated are shown within the frame allocated for report viewing. The user may then navigate to another MMD 20 to view its reports by clicking on the node within the frame containing the list of MMDs. In this fashion, the user may view the reports available from a variety of MMDs 20 in succession without being obligated to type in the IP address of each successive MMD 20. It will be apparent to one skilled in the art that various modifications to the invention and embodiment described herein are possible without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation. |
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claims | 1. A method for fabricating a collimator assembly, said method comprising:forming a first collimator grid having a first surface and an opposing second surface from a plurality of adjacent layers of radiation-absorbing material, the first collimator grid defining a plurality of first cells, each first cell of the plurality of first cells aligned in a first direction and extending between the first surface and the second surface and through the plurality of adjacent layers of radiation-absorbing material;coupling a reinforcing layer to the formed first collimator grid such that the reinforcing layer extends across the plurality of first cells substantially perpendicular to the first direction; andcoupling a second collimator grid to the reinforcing layer, the second collimator grid having a first surface and an opposing second surface, the second collimator grid defining a plurality of second cells extending between the first surface and the second surface, each second cell of the plurality of second cells substantially aligned with a respective first cell of the plurality of first cells of the first collimator grid. 2. A method in accordance with claim 1, wherein coupling a second collimator grid to the reinforcing layer further comprising coupling the second collimator grid to the reinforcing layer using an adhesive material. 3. A method in accordance with claim 1, further comprising coupling at least one attachment wing to the collimator assembly at least an end surface of the collimator assembly. 4. A method in accordance with claim 3, wherein the at least one attachment wing is coupled to the collimator assembly using an adhesive material. 5. A method in accordance with claim 1, further comprising coupling the collimator assembly to a gantry within a detection system using at least one mechanical fastener. 6. A method in accordance with claim 1, wherein the reinforcing layer is coupled to the first collimator grid using an adhesive material. 7. A collimator assembly, comprising:a first collimator grid comprising a first surface and a second surface, said first collimator grid comprising a plurality of adjacent layers of radiation-absorbing material defining a plurality of first cells, each said first cell of the said plurality of first cells aligned in a first direction and extending between said first surface and said second surface and through said plurality of adjacent layers of radiation-absorbing material;a reinforcing layer coupled to said first collimator grid such that said reinforcing layer extends across said plurality of first cells substantially perpendicular to said first direction, said reinforcing layer comprising a substantially X-ray transparent material; anda second collimator grid coupled to said reinforcing layer, said second collimator grid comprising a first surface and an opposing second surface, said second collimator grid defining a plurality of second cells that extend between said first surface of said second collimator grid and said second surface of said second collimator grid, each said second cell substantially aligned with a respective first cell of said plurality of first cells. 8. A collimator assembly in accordance with claim 7, wherein said reinforcing layer extends through each said first cell and each said second cell. 9. A collimator assembly in accordance with claim 7, wherein said reinforcing layer comprises a carbon fiber material. 10. A collimator assembly in accordance with claim 7, wherein said first collimator grid comprises a tungsten-loaded epoxy. 11. A collimator assembly in accordance with claim 7, further comprising at least one attachment wing coupled to said collimator assembly, said at least one attachment wing comprises a material having a higher tensile strength than a tungsten-loaded epoxy. 12. A detection system, comprising:an X-ray source for generating an X-ray beam;a multi-row detector;an examination zone defined between said X-ray source and said multi-row detector; anda collimator assembly coupled between said multi-row detector and said examination zone, said collimator assembly comprising:a first collimator grid comprising a first surface and a second surface, said first collimator grid comprising a plurality of adjacent layers of radiation-absorbing material defining a plurality of first cells, each said first cell of said plurality of first cells aligned in a first direction and extending between said first surface and said second surface and through said plurality of adjacent layers of radiation-absorbing material;a reinforcing layer coupled to said first collimator grid such that said reinforcing layer extends across said plurality of first cells substantially perpendicular to said first direction, said reinforcing layer comprising a substantially X-ray transparent material; anda second collimator grid coupled to said reinforcing layer, said second collimator grid comprising a first surface and an opposing second surface, said second collimator grid comprising a plurality of adjacent layers of radiation-absorbing material defining a plurality of second cells that extend between said first surface of said second collimator grid and said second surface of said second collimator grid, each said second cell of said plurality of second cells substantially aligned with a respective first cell of said plurality of first cells. 13. A detection system in accordance with claim 12, wherein said reinforcing layer comprises a carbon fiber material. 14. A detection system in accordance with claim 12, wherein said first collimator grid comprises a tungsten-loaded epoxy. 15. A detection system in accordance with claim 12 further comprising at least one attachment wing coupled to said collimator assembly. 16. A detection system in accordance with claim 15, further comprising a gantry coupled to said X-ray source and said detector, wherein said at least one attachment wing is coupled to said gantry. 17. A detection system in accordance with claim 12, wherein said first collimator grid comprises a grid of first cells, wherein a number of first cells within said grid is equal to a number of elements of said multi-row detector. |
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abstract | A method and apparatus for extending the period a nuclear steam supply system spent fuel pool can be safely passively cooled by storing the spent fuel offloaded from the reactor, in the containment for one reactor operating cycle. During a refueling the spent fuel that is not to be returned to the reactor and the spent fuel that will be returned to the reactor are stored separately in shielded locations within the containment. After one operating cycle, the spent fuel stored within the containment that was not returned to the reactor just prior to the last operating cycle, is offloaded to the spent fuel pool and replaced by the newly offloaded spent fuel that is being retired. |
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abstract | Systems and methods are described for an electron holography microscopy. Changing a size of an electron object image includes maintaining rotation of the electron object image with respect to a final image plane and/or maintaining an aspect ratio defined by an astigmatic object illumination with respect to the final image plane constant by adjusting a condenser electron lens set |
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description | 1. Field of the Invention This invention relates generally to systems and methods for image acquisition and, more specifically, to systems and methods for collecting computed tomography (CT) image data. 2. Background of the Invention Computed tomography is an imaging technique that has been widely used in the medical field. In a procedure for computed tomography, an x-ray source and a detector apparatus are positioned on opposite sides of a portion of a patient under examination. The x-ray source generates and directs a x-ray beam towards the patient, while the detector apparatus measures the x-ray absorption at a plurality of transmission paths defined by the x-ray beam during the process. The detector apparatus produces a voltage proportional to the intensity of incident x-rays, and the voltage is read and digitized for subsequent processing in a computer. By taking thousands of readings from multiple angles around the patient, relatively massive amounts of data are thus accumulated. The accumulated data are then analyzed and processed for reconstruction of a matrix (visual or otherwise), which constitutes a depiction of a density function of the bodily section being examined. By considering one or more of such sections, a skilled diagnostician can often diagnose various bodily ailments such as tumors, blood clots, etc. A problem associated with existing CT imaging systems is that a patient may not feel comfortable confined within a gantry opening, especially when the image data collection procedure takes too long. Mechanical configuration and/or regulatory rules may limit the rotation rate of a gantry on which the x-ray source and the image detector are mounted. Some of the existing CT imaging devices have gantry speed that is limited to one rotation per minute. Although some of the existing CT scanners can be configured to rotate about a patient faster, the volumetric data set generated from such scanners may have motion artifacts between slices. Another problem associated with existing CT imaging systems is that a slice thickness is generally larger than a resolution of a pixel within a slice. For example, an existing CT imaging system may generate a slice every 1 centimeter, while a resolution of a pixel within a slice is 0.5 millimeter. In order to create better resolution between slices, scanners have been developed that has an increased number of detectors in the Z-axis (axis of rotation) direction. However, increasing the number of detectors in the Z-axis increases the manufacturing cost of the detector, which is already quite expensive as it is based on traditional single crystal silicon electronics coupled to x-ray converters. For the foregoing, improved apparatus and method for collecting CT image data and generating CT images would be desirable. In accordance with some embodiments of the invention, a radiation projection detector for generating signals in response to a radiation beam is provided. The detector has a first imager that includes a conversion layer configured to generate light photons in response to a radiation, a photo detector array aligned with the conversion panel, the photo detector array having a plurality of lines of detector elements, and an access circuit coupled to the photo detector array and configured to collect signals from two or more of the lines of detector elements simultaneously. By collecting signals from two or more lines of detector elements simultaneously or in parallel, the time it takes to readout signals from all lines of the detector elements in the detector can be reduced. This in turn, improves a frame rate of the detector. In some embodiments, the radiation projection detector includes a second imager. In such cases, the access circuit is configured to collect signals from the first imager and the second imager simultaneously. The plurality of the imagers provides another level of multiplexing in that signals from one or more lines of detector elements in the first imager can be read simultaneously with signals from one or more lines of detector elements in the second imager. In accordance with other embodiments of the invention, a radiation projection detector for generating signals in response to a radiation beam is provided. The detector has a first imager that includes a photoconductor layer configured to generate a charge in response to a radiation, a detector array aligned with the photoconductor layer, the detector array having a plurality of lines of detector elements, and an access circuit coupled to the detector array and configured to collect signals from two or more of the lines of detector elements simultaneously. By collecting signals from two or more lines of detector elements simultaneously or in parallel, the time it takes to readout signals from all lines of the detector elements in the detector can be reduced. This in turn, improves a frame rate of the detector. In some embodiments, the radiation projection detector includes a second imager. In such cases, the access circuit is configured to collect signals from the first imager and the second imager simultaneously. The plurality of the imagers provides another level of multiplexing in that signals from one or more lines of detector elements in the first imager can be read simultaneously with signals from one or more lines of detector elements in the second imager. Other aspects and features of the invention will be evident from reading the following detailed description of the preferred embodiments, which are intended to illustrate, not limit, the invention. Various embodiments of the present invention are described hereinafter with reference to the figures. It should be noted that the figures are not drawn to scale and elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of specific embodiments of the invention. They are not intended as an exhaustive description of the invention or as a limitation on the scope of the invention. In addition, an aspect described in conjunction with a particular embodiment of the present invention is not necessarily limited to that embodiment and can be practiced in any other embodiments of the present invention. Referring now to the drawings, in which similar or corresponding parts are identified with the same reference numeral, FIG. 1 illustrates a computed tomography (CT) image acquisition system 10, which includes a detector 24 constructed in accordance with an embodiment of the present invention. The system 10 includes a gantry 12, and a panel 14 for supporting a patient 16. The gantry 12 includes an x-ray source 20 that projects a beam of x-rays, such as a fan beam or a cone beam, towards the detector 24 on an opposite side of the gantry 12 while the patient 16 is positioned at least partially between the x-ray source 20 and the detector 24. The x-ray source 20 may include a collimator 21 for adjusting a shape of the x-ray beam. The detector 24 has a plurality of sensor elements configured for sensing a x-ray that passes through the patient 16. Each sensor element generates an electrical signal representative of an intensity of the x-ray beam as it passes through the patient 16. In the illustrated embodiment, the CT image acquisition system 10 also includes a processor 54, a monitor 56 for displaying data, and an input device 58, such as a keyboard or a mouse, for inputting data. The processor 54 is coupled to a gantry rotation control 40. The rotation of the gantry 12 and the operation of the x-ray source 20 are controlled by the gantry rotation control 40, which provides power and timing signals to the x-ray source 20 and controls a rotational speed and position of the gantry 12 based on signals received from the processor 54. Although the control 40 is shown as a separate component from the gantry 12 and the processor 54, in alternative embodiments, the control 40 can be a part of the gantry 12 or the processor 54. During a scan to acquire x-ray projection data (i.e., CT image data), the x-ray source 20 projects a beam of x-rays towards the detector 24 on an opposite side of the gantry 12, while the gantry 12 rotates about the patient 16. In one embodiment, the gantry 12 makes a 360° rotation around the patient 16 during image data acquisition. Alternatively, if a full cone detector is used, the system 10 may acquire data while the gantry 12 rotates 180° plus the angle of the beam pattern. Other angles of rotation may also be used, depending on the particular system being employed. In one embodiment, the detector 24 is configured to generate at least 900 frames of images in less than 1 second. In such case, the gantry 12 only needs to rotate around the patient 16 once in order to collect sufficient amount of image data for reconstruction of computed tomography images. In other embodiments, the detector 24 may be configured to generate frames at other speeds. FIG. 2 shows a detector 24 constructed in accordance with an embodiment of the present invention. As shown in FIG. 2, the detector 24 comprises an imager 100 that includes a x-ray conversion layer 60 made from a scintillator element, such as Cesium Iodide (CsI), and a photo detector array 62 (e.g., a photodiode layer) coupled to the x-ray conversion layer 60. The x-ray conversion layer 60 generates light photons in response to x-ray radiation, and the photo detector array 62, which includes a plurality of detector elements 64, is configured to generate electrical signal in response to the light photons from the x-ray conversion layer 60. In the illustrated embodiment, both the x-ray conversion layer 60 and the photo detector array 62 are pixilated, thereby forming a plurality of imaging elements 104. However, the x-ray conversion layer 60 may be non-pixilated in an alternative embodiment. As shown in FIG. 2, the imager 100 has a curvilinear surface (e.g., a partial circular arc). Such configuration is beneficial in that each of the imaging elements 104 of the imager 100 is located substantially the same distance from the x-ray source 20. In an alternative embodiment, the imager 100 may have a rectilinear surface or a surface having other profiles. In the illustrated embodiment, each image element 104 (or pixel) has a cross sectional dimension that is approximately 200 microns or more, and more preferably, approximately 300 microns or more. However, image elements having other dimensions may also be used. The imager 100 can be made from amorphous silicon, crystal and silicon wafers, crystal and silicon substrate, or flexible substrate (e.g., plastic), and may be constructed using flat panel technologies or other techniques known in the art of making imaging device. FIG. 3 depicts one configuration of electrical components for the imager 100 in accordance with an embodiment of the present invention. The imager 100 includes a plurality of the image elements 104, each of which comprises a photodiode 106 (forming part of the detector element 64) that generates an electrical signal in response to a light input. The photodiode 106 receives light input from the x-ray conversion layer 60 that generates light in response to x-rays. The photodiodes 106 are connected to an array bias voltage 122 to supply a reverse bias voltage for the image elements. A transistor 108 (such as a thin-film N-type FET) functions as a switching element for the image element 104. When it is desired to capture image data from the image elements 104, control signals 114 are sent to a gate driver 112 to “select” the gate(s) of transistors 108. The gate driver 112 is connected to a low gate voltage 127 that drives the gate control lines. Electrical signals from the photodiodes 106 are passed through lines 116 to corresponding charge amplifiers 110. The output of the charge amplifiers 110 is sent to a “sample and hold” stage for further image processing/display. In one embodiment, the gate driver 112 is a part of an access circuit, which may be secured to an edge of the imager 100. The access circuit may also include the charge amplifiers 110. While FIG. 3 only shows four image elements 104a–104d, those skilled in the art understands that the imager 100 may include many such image elements 104, depending upon the size and resolution of the imaging device. In addition, although only two lines 126a and 126b of image elements 104 are shown, the imager 100 may include more than two lines 126 of image elements 104. The imager 100 performs simultaneous sampling of image data from image elements 104 in a correlated manner. In the illustrated embodiment, the imager 100 includes corresponding amplifiers 110 for each of the image elements 104 on the two lines 126a and 126b, thereby allowing image data from the two lines 126a and 126b of image elements 104 to be collected or read simultaneously (i.e., at substantially the same time). All the switching transistors 108a–108d for image elements 104a–104d on the two lines 126a and 126b are tied to the same control line 202 extending from gate driver 112. When the image data for the two lines 126a and 126b of image elements 104 are desired, control signals 114 are sent to the gate driver 112 to select the transistor gates for the desired lines (e.g., 126a and 126b) of image elements. The electrical signals from the entire lines 126a and 126b of image elements are passed to their corresponding charge amplifiers 110, which output signal data to the subsequent sampling stage. If the imager 100 has more than two lines 126 of image elements 104, to form an entire image frame, image data are collected two lines at a time until all lines 126 of image elements 104 on the imager 100 have been sampled. For a given configuration of the imager 100, a signal readout time for each line 126 of image elements 104 depends on the time it takes to turn on a pixel and discharge a corresponding signal, and is generally fixed (e.g., approximately 40 microseconds per second). As such, by configuring the imager 100 to allow signals from two or more lines of image elements 104 to be read simultaneously or in parallel, the time it takes to readout signals from all the lines 126 of the imager can be reduced. This in turn, improves a frame rate (i.e., number of frames that can be generated by the imager 100 per second) of the imager 100. Although the above embodiment of the imager 100 has been described as having a two-line readout configuration, in alternative embodiments, the imager 100 may have a configuration that allows signals be collected from more than two lines of image elements 104 at a time. FIG. 4 shows a variation of the imager 100 which has a four-line readout configuration. As shown in FIG. 4, image elements 104 on every four lines (e.g., 126a–126d or 126e–126h) are connected to corresponding devices, such as amplifiers 110a–110p (not shown) through connecting lines 126a–116p and connecting pads 410a–410p, respectively. In the illustrated embodiment, all the switching transistors for image elements 104 on the four lines 126a–126d are tied to the same control line 202a extending from the gate driver 112, and all the switching transistors for image elements 104 on the four lines 126e–126h are tied to the same control line 202b extending from the gate driver 112. When the image data for the four lines 126a–d of image elements 104 are desired, control signals 114 are sent to the gate driver 112 to select (via the control line 202a) the transistor gates for the four lines 126a–126d of image elements 104. The electrical signals from the image elements 104 on the four lines 126a–d are passed to their corresponding charge amplifiers 110a–p, which output signal data to the subsequent sampling stage. To collect signals from the next four lines 126e–126h of image elements 104, control signals 114 are sent to the gate driver 112 to select (via the control line 202b) the transistor gates for the four lines 126e–126h of image elements 104. To form an entire image frame, image data are collected four lines at a time until all lines of image elements 104 on the imager 100 have been sampled. As shown in FIG. 4, the number of connecting pads 410 or interconnects can be accommodated within a given length is limited by the size of the connecting pads 410 and a spacing between the connecting pads 410. The number of connecting pads 410 that can be fitted within a given length may limit the number of lines 126 of image elements 104 that can be connected to corresponding devices, such as the amplifiers 110. In one embodiment, to increase the interconnects of the imager 100, each image element 104 may be made larger, or alternatively, the number of image elements 104 along each line 126 may be reduced. For example, in one embodiment, each image element 104 may have a cross sectional dimension that is larger than approximately 300 microns, or more preferably, more than approximately 400 microns. However, image elements having other dimensions may also be used. Those skilled in the art understand that the larger the image element 104, and/or the fewer the number of the image elements 104 along each line 126, the higher the interconnects, and the higher the frame rate that can be achieved. Although the imager 100 has been described as having the x-ray conversion layer 60, in alternative embodiments, the imager 100 may use different detection schemes. For example, in alternative embodiments, instead of having the x-ray conversion layer 60, the imager 100 may include a photoconductor, which generates electron-hole-pairs or charges in response to x-ray. FIG. 5 schematically shows an imager 500 constructed in accordance with alternative embodiments of the present invention. The flat panel imager 500 includes an x-ray conversion panel 510 aligned with a detector array 520. The x-ray conversion panel 510 includes a first electrode 502, a second electrode 504, and a photoconductor 506 secured between the first electrode 502 and the second electrode 504. The electrodes 502 and 504 may be made from a wide variety of materials, such as silver, chromium, aluminum, gold, nickel, vanadium, zinc, palladium, platinum, carbon, etc., and alloys of these materials. The photoconductor 506 can be made from a variety of materials, such as mercuric Iodide (HgI2), Lead Iodide (PbI2), Bismuth Iodide (BiI3), Cesium Iodide (CsI), Cadmium Zinc Telluride (CdZnTe), Amorphous Selenium (a-Se), or equivalent thereof. Other materials known in the art may also be used. The photoconductor 506 may be a single or poly-crystalline layer. The photoconductor 506 is preferably deposited by physical vapor deposition (PVD) or particle in binder process (PIB). Alternatively, if the photoconductor 506 is deposited on a separate substrate (such as those made from Cadmium Zinc Telluride (Cd(1-x)ZnxTe) semiconductor crystals or ZnTe materials), then it may be secured to the first and second electrodes 502 and 504 by indium bump(s). Alternatively, the photoconductor 506 may also be secured to the first and second electrodes 502 and 504 by a suitable adhesive, depending on the materials from which the photoconductor 506 and the first and second electrodes 502 and 504 are made. Other techniques known in the art may also be used to secure the photoconductor 506 to the first and second electrodes 502 and 504. Photoconductors and imagers made therefrom are well known in the art, and therefore would not be described in further details herein. When using the flat panel imager 500, the first and second electrodes 502 and 504 are biased by a voltage source to create a potential difference or a bias between the first and second electrodes 502 and 504. The biased electrodes 502 and 504 create an electric field across the region between the first and second electrodes 502 and 504. When the photoconductor 506 is irradiated by x-ray, a response, such as electron hole pairs (EHPs) or charges, are generated and drift apart under the influence of the electric field across the region between the first and second electrodes 502 and 504. The charges are collected by the detector array 520, which includes a plurality of detector elements 522 arranged in a two-dimensional array. The detector elements 522 are configured to generate electric signals in response to the charges collected on the first electrode 502. In one embodiment, the detector elements 522 are amorphous silicon (a-Si:H) charge detectors. Each detector element 522 may have a storage capacitor to store the charge generated by the X-rays and collected by the first electrode 502. Each detector element 522 may also include a switching element, such as a thin film transistor (TFT), a switching diode, or the like, to access the collected charge by readout electoronics. Optionally the detector elements 522 can contain further components for signal or charge buffering and amplification. The detector elements 522 may also include polycrystalline silicon or organic active elements. Each of the detector elements 522 forms a pixel of the X-ray image generated using the detector array 520. The detector array 520 also includes a pixel access circuit (not shown) coupled to detector elements 522. The pixel access circuit accesses the detector elements 522 and reads the electric signals from the detectors elements 522. The process of accessing detector elements 522 and reading electric signals there from is similarly discussed previously with reference to FIG. 3. In one embodiment, pixel access circuit includes a gate driver that generates row access signals to sequentially access detector elements 522 by rows and reads electric signals out of detector elements 522 by columns. Each row access signal can access either a single row or multiple rows of detectors elements 522. Likewise, each read action can read electric signals from either a single column or a plurality of columns of the detectors elements 522. FIG. 6 shows another embodiment of the detector 24 that includes a plurality of imagers 600. In one embodiment, each imager 600 has a panel width 602 that is between 2 to 10 centimeters (cm), and a panel depth 604 that is between 20 to 60 cm, and more preferably, between 30 to 40 cm. However, each imager 600 may also have other dimensions in alternative embodiments. In the illustrated embodiment, each of the imagers 600 is stacked against an edge of a neighboring imager 600. This configuration is beneficial in that the imagers 600 provide a non-discontinuous surface to capture image signals, thereby preventing a gap in the collected image data. Alternatively, the imagers 600 may be positioned next to each other such that a substantially continuous surface can be formed. Although eight imagers 600 are shown, in alternative embodiments, the detector 24 may include one or other numbers of imagers 600, depending on a particular specification of the detector 24. In addition, although the imagers 600 collectively form a curvilinear profile of the detector 24, in alternative embodiments, the imagers 600 may collectively form an approximately straight surface or other profiles for the detector 24. Constructing the detector 24 using a plurality of the imagers 600 has several advantages. First, the manufacturing cost of the detector 24 is reduced since it is easier and less expensive to manufacture a number of smaller imagers 600 than to manufacture a single imager of sufficient size that can meet the specification of the detector 24. In addition, the plurality of the imagers 600 provides another level of multiplexing in that signals from one or more lines of image elements 104 in one of the imagers 600 can be read simultaneously with signals from one or more lines of image elements 104 in another of the imagers 600 by the gate driver 112. In one embodiment, the gate driver 112 can be configured to read signals from the first two rows of all of the imagers 600 simultaneously, and then from the next two rows, etc., until signals from all the rows of the imagers 600 have been read. Such configuration provides a much higher frame rate for the detector 24, thereby allowing more image data to be collected in a given period. For example, assuming that the detector 24 has fourteen imagers 600, each of which has fifty rows of image elements 104. In such case, if an average readout rate for a row is 40 microseconds, it will take 2000 microseconds (=40 microseconds×50 rows) to read signals from the entire detector 24, thereby providing 500 frame rate per second ( 1/2000 microseconds). If multiple rows readout scheme is used, e.g., assuming signals are read from every two rows simultaneously, it will take 1000 microseconds to read signals from the entire detector 24, thereby providing 1000 frame rate per second. Both of these configurations provide much better frame rate than conventional detectors that use a single row readout scheme for the entire detector. For example, using a conventional readout scheme, it will take 24000 microseconds (=40 microseconds×600 rows) to read signals from-a detector that has the same number of rows (i.e., 600 rows) of image elements, providing only 41 frame rate per second. Those skilled in the art understand that the more the number of the flat panel imagers 600 used, the higher the frame rate that can be achieved. Constructing the detector 24 using a plurality of the imagers 600 can also provide better resolution for images. For example, for a given prescribed frame rate, the detector 24 can be configured to provide better resolution by using more number of the imagers 600 that are smaller, but have lower pixel pitch. In one embodiment, the detector 24 includes twenty-four imagers 600, each of which has a panel width of approximately 2.5 centimeters and has a pixel pitch of approximately 380 um. Such configuration provides approximately the same frame rate, but a much higher resolution, as compared to a detector that includes fourteen imagers 600, with each imager 600 having a panel width of approximately 4.5 centimeters and a pixel pitch of approximately 500 um. It should be noted that in the illustrated embodiment in which a plurality of the imagers 600 is used, the reading of signals is not limited to two or more rows at a time, and that the gate driver 112 can be configured to access one row of image elements 104 at a time. For example, in alternative embodiments, the gate driver 112 can be configured to read signals from the first rows of all of the imagers 600 simultaneously, and then from the second rows, etc., until signals from all the rows of the imagers 600 have been read. FIG. 7 shows a multiplex multi-row readout unit 650 that may be implemented in any of the above-described embodiments of imagers or in conventional imagers. The readout unit 650 includes a plurality of switches 652 connected to a common pad 654. Each of the switches 652 has a low resistance, thereby allowing signals from the image elements 104 to be read quickly. During use, the switches 652 switch consecutively to transmit signals to the common pad 654. The common pad 654 may be coupled to a device, such as an amplifier, a storage device, or a processor, which receives the signals. In the illustrated embodiment, the readout unit 650 includes four switches 652. However, the readout unit 650 may also include other numbers of switches 652 in alternative embodiments. Computer System Architecture FIG. 8 is a block diagram that illustrates an embodiment of a computer system 700 upon which an embodiment of the invention may be implemented. Computer system 700 includes a bus 702 or other communication mechanism for communicating information, and a processor 704 coupled with the bus 702 for processing information. The processor 704 may be an example of the processor 54, or alternatively, an example of a component of the processor 54, of FIG. 1. The computer system 700 also includes a main memory 706, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus 702 for storing information and instructions to be executed by the processor 704. The main memory 706 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor 704. The computer system 700 further includes a read only memory (ROM) 708 or other static storage device coupled to the bus 702 for storing static information and instructions for the processor 704. A data storage device 710, such as a magnetic disk or optical disk, is provided and coupled to the bus 702 for storing information and instructions. The computer system 700 may be coupled via the bus 702 to a display 77, such as a cathode ray tube (CRT), for displaying information to a user. An input device 714, including alphanumeric and other keys, is coupled to the bus 702 for communicating information and command selections to processor 704. Another type of user input device is cursor control 716, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor 704 and for controlling cursor movement on display 77. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane. The invention is related to the use of computer system 700 for collecting and processing image data. According to one embodiment of the invention, such use is provided by computer system 700 in response to processor 704 executing one or more sequences of one or more instructions contained in the main memory 706. Such instructions may be read into the main memory 706 from another computer-readable medium, such as storage device 710. Execution of the sequences of instructions contained in the main memory 706 causes the processor 704 to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in the main memory 706. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software. The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to the processor 704 for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as the storage device 710. Volatile media includes dynamic memory, such as the main memory 706. Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise the bus 702. Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read. Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to the processor 704 for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to the computer system 700 can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to the bus 702 can receive the data carried in the infrared signal and place the data on the bus 702. The bus 702 carries the data to the main memory 706, from which the processor 704 retrieves and executes the instructions. The instructions received by the main memory 706 may optionally be stored on the storage device 710 either before or after execution by the processor 704. The computer system 700 also includes a communication interface 718 coupled to the bus 702. The communication interface 718 provides a two-way data communication coupling to a network link 720 that is connected to a local network 722. For example, the communication interface 718 may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, the communication interface 718 may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, the communication interface 718 sends and receives electrical, electromagnetic or optical signals that carry data streams representing various types of information. The network link 720 typically provides data communication through one or more networks to other devices. For example, the network link 720 may provide a connection through local network 722 to a host computer 724 or to a medical equipment 726. The data streams transported over the network link 720 can comprise electrical, electromagnetic or optical signals. The signals through the various networks and the signals on the network link 720 and through the communication interface 718, which carry data to and from the computer system 700, are exemplary forms of carrier waves transporting the information. The computer system 700 can send messages and receive data, including program code, through the network(s), the network link 720, and the communication interface 718. Although particular embodiments of the present inventions have been shown and described, it will be understood that it is not intended to limit the present inventions to the preferred embodiments, and it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present inventions. For example, the operations performed by the processor 54 can be performed by any combination of hardware and software within the scope of the invention, and should not be limited to particular embodiments comprising a particular definition of “processor”. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense. The present inventions are intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the present inventions as defined by the claims. |
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