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039363490	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown a fast neutron nuclear reactor comprising a central zone 1 having plutonium enriched fuel elements, an intermediate zone 2 having more highly enriched fuel elements and a zone 3 of breeder fuel elements. In addition to fuel elements the central and intermediate zone include some control rod guide tubes (only two being indicated and designated `C`) and the inner zone also includes some shut down rod guide tubes (only one being indicated and designated `S`). Except at the periphery of the breader zone 3, the components are generally arranged in modules each comprising a cluster of four components of which at least three are fuel elements. One of the fuel elements of each module is rigidly supported in upright position whilst the remaining fuel elements are tilted towards the rigidly supported fuel element. Where one of the components of the module is a central rod guide tube it may be free standing or may lean on the fuel elements but does not have interlocking bearing pads. FIG. 2 shows a module of four components comprising types X, Y and Z wherein the component type Z is rigidly supported whilst components type X and Y are tilted towards the centre of the cluster as indicated by arrows designated 4. The rigidly supported components are indicated by cross-hatching in FIG. 1 and the four associated components of each module are indicated by broken lines. The arrows 4a in FIG. 1 indicate the loading direction of the components which are not in regular module. Either of components type `X` can be a control rod or shut down rod guide tube but neither type `Y` or type `Z` can be so used; type Y is excluded because stability of the module depends on the interlocking afforded by this component during refuelling of type `Z`, and type Z is excluded because it defines the position of the module with respect to the remainder of the core. The fuel elements, control rod guide tubes and shut down rod guide tubes are generally similar in outward form except that the guide tubes do not have the interlocking bearing pads. A fuel element is shown in FIGS. 3, 4 and 5. Each fuel element comprises a cluster of fuel pins (not shown) enclosed by a wrapper of hexagonal cross-section and designated 5 in FIG. 3. The fuel element has a lower spike 6 which is engageable with a socket associated with a diagrid, for example, as in the manner described in U.S. Pat. No. 3,383,287 whereby the fuel elements are disposed generally upright. The elements types X Y which are arranged to tilt have resilient spikes 6 and the tilt is achieved in conventional manner as disclosed in U.S. Pat. No. 3,383,287 by eccentrically in the diagrid sockets. The rigidly supported element type Z, of course, has a substantially rigid spike 6. The upper end region of the element has a cylindrical portion 7 and the transition from circular section to hexagonal section is effected by a hexagonal taper 8. The transition from hexagonal section to circular section at the lower end region of the element is effected by a circular taper 9. Immediately above the circular taper there is a group of rib like extended corner features or splines 10 projecting outwardly as shown in FIG. 4. Intermediate the ends of the element there are bearing pads 11 in the form of spline like ribs 11a on each side of the wrapper 5. Each pad 11 comprises one full width and one half width ribs 11a which can interlock with co-operating ribs and half width ribs 11a on adjacent fuel elements as shown in FIG. 2. A single bearing pad 11 is shown in FIG. 6 the ribs 11a having taper lead in surfaces 11b and 11c at each end. When a fuel element is being loaded into a reactor core in the presence of installed fuel elements, the fuel element is suspended and lowered to enter the spike 6 alongside the upper cylindrical portion 7 of an installed adjacent element. Further lowering brings the circular taper 9 in contact with a side of the hexagonal taper 8 of the adjacent element so that the fuel element is displaced sideways generally into its correct azimuthal position relative to the centre of the cluster of components. By further lowering of the fuel element the extended corner features 10 abut the sloping hexagonal tapers 8 of the adjacent element and the reaction between the corner features and the adjacent element causes rotation of the element to a position such that the bearing pads 11 will pass between adjacent fuel element wrappers 5, and the wrapper 5 of the suspended element will pass between the pads 11 on adjacent elements. When the fuel element is lowered sufficiently to engage the lower ends of the ribs 11a with the upper ends of the ribs 11a of adjacent elements, the taper lead in surfaces 11b of the ribs assist in radial and fine rotational adjustment of the fuel element, and the taper surfaces 11a assist in radial alignment, to engage the ribs accurately so that the fuel element can be fully lowered and spiked into the diagrid. The interlocking ribs 11a of the bearing pads 11 accurately locate all the components of the cluster and lateral slip of the components is reduced to very small limits. The second construction of nuclear reactor shown in FIGS. 7 and 8 is generally similar to the first construction except that fuel elements only are arranged generally in clusters of six, each resiliently tilted towards a central void to form a circular arch. The central void can be occupied by a free standing control rod or shut down rod guide tube. In FIG. 7 some of the control rod and shut down rod guides tubes are shown and again designated `C` and `S` respectively, but in the breeder zone some of the voids are left vacant some examples being designated `O`. A basic module 12 of six fuel element is enlarged in some regions, for example, the module designated 13 has an additional fuel element appended to it and the module designated 14 has two additional fuel elements appended to it. The appended fuel elements are arranged to tilt towards the centre of the basic cluster.
	claims	1. A radiographic apparatus for acquiring radiological images, comprising:a radiation source for emitting radiation;a radiation detector having a detecting plane with radiation detecting elements arranged in a matrix form thereon for detecting the radiation;an image generating device for generating images based on detection signals outputted from the radiation detector;a radiation grid placed to cover the detecting plane of the radiation detector, and having absorbing foil strips extending longitudinally and arranged transversely;a grid image storage device for storing a plurality of grid images picked up while varying positions in a transverse direction of the radiation source and the radiation detector, without an object under examination interposed between the radiation source and the radiation detector, the grid images having shadows of the radiation grid reflected thereon;an original image storage device for storing an original image picked up with the object under examination interposed between the radiation source and the radiation detector, the original image having a fluoroscopic image of the object under examination and the shadows of the absorbing foil strips of the radiation grid reflected thereon;a selecting device for selecting one grid image having a pattern most similar to a pattern of the shadows of the radiation grid reflected on the original image, from the plurality of grid images stored in the grid image storage device; andan eliminating device for eliminating the shadows of the absorbing foil strips from the original image based on the grid image selected by the selecting device;wherein the positions of the radiation grid and the radiation detector are determined such that, when the radiation source and the radiation detector are in a standard position, an arrangement pitch of the shadows of the absorbing foil strips appearing on the detecting plane of the radiation detector as a result of a radiation beam being emitted from the radiation source and blocked by the radiation grid is an integral multiple of an arrangement pitch in a transverse direction of the radiation detecting elements, and the shadows of the absorbing foil strips appear without covering transversely adjacent pairs of the detecting elements. 2. The radiographic apparatus according to claim 1, wherein the grid images stored in the grid image storage device have been picked up while shifting the position of the radiation detector relative to the radiation source in the transverse direction. 3. The radiographic apparatus according to claim 1, wherein the grid images stored in the grid image storage device have been picked up without anything placed between the radiation source and the radiation grid. 4. The radiographic apparatus according to claim 1, wherein the grid images stored in the grid image storage device have been picked up with a phantom, which generates scattered rays, placed between the radiation source and the radiation grid. 5. The radiographic apparatus according to claim 1, further comprising:a profile generating device for generating profiles each having pixel values arranged in a row in the transverse direction of the radiation grid, based on images each having pixel values arranged in two dimensions;wherein the selecting device is arranged to select the one grid image using an original image profile generated from the original image, and grid profiles generated from the grid images. 6. The radiographic apparatus according to claim 5, wherein the profile generating device is arranged to generate an estimated profile from the original image profile when the radiation grid is not reflected on the original image, and generate a profile for comparison by subtracting the estimated profile from the original image profile, and wherein the selecting device is arranged to select the one grid image by selecting a grid profile most similar to the profile for comparison. 7. The radiographic apparatus according to claim 6, wherein the selecting device is arranged to determine similarity between the profile for comparison and the grid profiles by a correlational method. 8. The radiographic apparatus according to claim 1, further comprising a C-arm for supporting the radiation source and the radiation detector. 9. The radiographic apparatus according to claim 2, further comprising a C-arm for supporting the radiation source and the radiation detector. 10. The radiographic apparatus according to claim 3, further comprising a C-arm for supporting the radiation source and the radiation detector. 11. The radiographic apparatus according to claim 4, further comprising a C-arm for supporting the radiation source and the radiation detector. 12. The radiographic apparatus according to claim 5, further comprising a C-arm for supporting the radiation source and the radiation detector. 13. The radiographic apparatus according to claim 6, further comprising a C-arm for supporting the radiation source and the radiation detector. 14. The radiographic apparatus according to claim 7, further comprising a C-arm for supporting the radiation source and the radiation detector. 15. The radiographic apparatus according to claim 1, wherein the radiation grid is a synchronous grid with an arrangement of the absorbing foil strips synchronized with an arrangement of the detecting elements of the radiation detector. 16. The radiographic apparatus according to claim 2, wherein the radiation grid is a synchronous grid with an arrangement of the absorbing foil strips synchronized with an arrangement of the detecting elements of the radiation detector. 17. The radiographic apparatus according to claim 3, wherein the radiation grid is a synchronous grid with an arrangement of the absorbing foil strips synchronized with an arrangement of the detecting elements of the radiation detector. 18. The radiographic apparatus according to claim 4, wherein the radiation grid is a synchronous grid with an arrangement of the absorbing foil strips synchronized with an arrangement of the detecting elements of the radiation detector. 19. The radiographic apparatus according to claim 5, wherein the radiation grid is a synchronous grid with an arrangement of the absorbing foil strips synchronized with an arrangement of the detecting elements of the radiation detector. 20. The radiographic apparatus according to claim 6, wherein the radiation grid is a synchronous grid with an arrangement of the absorbing foil strips synchronized with an arrangement of the detecting elements of the radiation detector.
	abstract	An inspecting apparatus for reducing a time loss associated with a work for changing a detector is characterized by comprising a plurality of detectors 11, 12 for receiving an electron beam emitted from a sample W to capture image data representative of the sample W, and a switching mechanism M for causing the electron beam to be incident on one of the plurality of detectors 11, 12, where the plurality of detectors 11, 12 are disposed in the same chamber MC. The plurality of detectors 11, 12 can be an arbitrary combination of a detector comprising an electron sensor for converting an electron beam into an electric signal with a detector comprising an optical sensor for converting an electron beam into light and converting the light into an electric signal. The switching mechanism M may be a mechanical moving mechanism or an electron beam deflector.
051805480	summary	FIELD OF THE INVENTION The present invention relates to a grid having mixing fins for a nuclear fuel assembly, the grid having the particular function of improving the mixing of streams of coolant flowing upwards through the assembly and of making the temperature within the assembly more uniform. BACKGROUND OF THE INVENTION The invention relates more particularly to mixing grids of the type comprising at least two sets of crossed plates fixed together at their crossover points, delimiting cells some of which are for receiving fuel rods and the other are for receiving guide tubes, the grids being provided with coolant-stirring fins extending the plates downstream and disposed to deflect the coolant transversely to its general flow direction, each plate being provided with abutment means projecting inwards from each of the faces of the cells for receiving fuel rods. The invention is particularly applicable to fuel assemblies in which the support structure includes guide tubes interconnected two end fittings and, in addition to mixing grids of the above kind that do not participate in supporting the rods (i.e. to supporting them vertically), at least one additional grid for carrying the rods. For this purpose, the grid is provided with springs cut out from the plates or fixed to the plates and designed to urge the rods against abutment means constituted by bosses situated opposite. Development in reactor characteristics, in particular towards higher thermohydraulic performance and combustion rates gives rise to the use of grids other than supporting grids having abutment means delimiting passages that are larger in size than the rods, thereby facilitating coolant flow and avoiding damage to the rod sheaths during insertion. This clearance is small enough to limit rod vibration to an amplitude smaller than that which could give rise to the sheath being damaged and to the stirring fins being hammered by the rods. The present invention seeks in particular to provide a grid of the above type in which the abutment means participate in making the temperature within an assembly more uniform, without giving rise to excessive headloss. SUMMARY OF THE INVENTION To this end, the present invention provides a mixing grid in which the abutment means comprise, in each wall separating two internal cells occupied by fuel rods, two portions of plate that are cut out and deformed into a scoop-shape, and that are offset relative to each other in the coolant flow direction, with the scoops projecting in opposite directions and tending to cause coolant to pass from one cell to another. The term "internal" designates a cell surrounded on all of its sides by plates, consequently it applies to all of the cells of a belted grid, but it excludes the outermost cells of a grid that does not have a belt. Such a structure can be used both for structural grids that provide mechanical strength to the assembly as a whole and are provided with an outer belt that may possibly extend further in the flow direction than the other plates, and also for grids hat have a thermodynamic function only and do not have a belt. The scoop-shaped abutment means are constituted by deforming approximately semicircular zones of the plates, opening either to an edge of the plate or else to a slot formed through the plate transversely to the flow direction. The two scoops may be in the general form of half a truncated cone. The scoops offset in the coolant flow direction may occupy a fraction only of the width of the plate (i.e., they may optionally extend up the entire height of the grid). In an advantageous embodiment, each of the fins engages only one of the cells in the grid (i.e., extends to one side only of the line of intersection with another plate), and each plate includes no more than one half-fin at each cell corner. It may then be advantageous either to place the scoops on a line parallel to the general flow direction through the assembly but offset from the middle of the cell wall, or else to dispose them on a line that slopes relative to the general flow direction. For example, the fins may be disposed as described in French Pat. No. 84 16803 (published under No. 2 572 837).
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	description	This application claims the benefit of priority to U.S. Provisional Application No. 61/807,218, filed Apr. 1, 2013, which is herein incorporated by reference in its entirety. The present disclosure relates generally to devices and methods for synthesizing radionuclides, and more particularly, to the use of a quasi-neutral plasma jet for the synthesis of radionuclides. Positron emission tomography (PET) is a method of imaging that uses radiolabeled probe molecules to target, detect, and quantify biological processes in vivo. PET techniques are used to study disease mechanisms, to develop new diagnostic and therapeutic methods, to detect early stage disease, and to monitor responses to therapies. The equipment, infrastructure, and personnel currently required to produce PET probes severely constrain the availability and diversity of probes, hindering advances in disease diagnosis, therapy, and medical research that requires this imaging method. The approach to synthesis of biochemical compounds with radioactive nuclei generally starts with a charged particle accelerator. Particle accelerators have the following attributes: an ion source, electrostatic extraction optics that select a single polarity of ion for acceleration, electromagnetic fields to accelerate and focus the ions, a vacuum chamber to prevent elastic and inelastic scattering of the ion beam, collimation apertures, and external shielding to protect operators and electronics from neutron and ionizing radiation produced in the accelerator. Referring to FIG. 1, positive or negative ions are formed in an ion source (101), typically by electron impact, then separated by polarity (anions from cations) and mass (atomic ions from molecular ions and electrons) and accelerated in a linear or cyclotron accelerator (102) with electromagnetic fields to increase their kinetic energy. The charged beam is then extracted from the accelerator (103), collimated, and shaped using electrostatic lenses. Approximately 20% of the beam current is lost in the cyclotron, contaminating the housing with heavy radioactive nuclei and neutron radiation. Extraction of negative ions such as 1H− is also accomplished with electrostatic fields. These anions must then be converted to protons by passing them through a carbon foil to strip two electrons with almost 100% efficiency. Since energetic negative ions do not undergo nuclear reactions with the metallic accelerator components and the reactive positive ion beam has a short path, activation of the housing is reduced. However, the acceleration of negative ions requires ultra high vacuum (<10−10 atmospheres) to mitigate charge neutralization. The acceleration of all charged species also produces electromagnetic radiation; at the energies required for subsequent formation of radionuclides, this is ionizing radiation that requires heavy, bulky shielding (104) for safe operation. Effective formation and acceleration of ions by electromagnetic fields requires operation in vacuum chamber (105), so the next step impinges the energetic ion flux through a window material (105) and onto a solid, liquid, or gas precursor material (106). The energetic ions convert some of the precursor (106) to radionuclides (107) by nuclear reactions. The mixture of precursor and radionuclides (106, 107) are transferred (108) to a separately shielded (109) hot cell or microfluidic reactor where chemical reactions (110) and purifications (111) convert the radionuclide into an injectable radiochemical reagent. The collision of the accelerated ions with the precursor material occasionally results in a nuclear reaction whose probability is quantified as the integral of the product of a cross-section Q(E), the energy distribution of the ion flux (f(E)), and the relative velocity of the ion and precursor nuclei (v(E)). The rate of radionuclide (RN) production from a concentration of precursor is given by ⅆ [ RN ] ⅆ t = [ Precursor ] * ∫ Q ⁡ ( E ) * f ⁡ ( E ) * v ⁡ ( E ) ⁢ ⅆ E ( Eq ⁢ ⁢ 1 ) These nuclear reactions yield an unstable material that decays by releasing a positron, which in turn collides with an ambient electron to produce two counter-propagating gamma rays. The gamma rays are then recorded by coincidence detection in a toroidal sensor. Following tomographic inversion the location of the decaying radionuclide can be determined to within fractions of a millimeter. PET imaging has been applied to the diagnosis of vascular function (Laking et al., The British Journal of Radiology, 76 (2003), S50-S59 E), arthritis (Bruijnen et al., Arthritis Care & Research Vol. 66, No. 1, January 2014, pp 120-130), and tumerogenesis (Aluaddin, Am J Nucl Med Mol Imaging 2012;2(1):55-76), among many others. The specific activity (SA) of a radioactive tracer is an important figure of merit for a PET reagent. It is defined as the intensity of radiation divided by the mass or number of moles of material, and it decreases with time (t) according to the expression exp(−t/τ) where the decay rate (1/τ) is a fundamental property of the specific radionuclide. This decay begins the moment a radionuclide is formed, and extensive research has been devoted to methods of swiftly and efficiently inserting the radionuclide into a biological probe through chemical reactions and purifications to produce a PET reagent in the shortest possible times. Representative values of τ are listed in table I. Small values of τ imply rapid decay, which is advantageous because it produces more decay events per second and therefore greater signal to noise ratios when collecting image data. However, for these same values of τ any factor that increases t leads to a faster loss of potency of the reagent. TABLE IProperties of four representative medical isotopes that are produced by proton bombardment.MedicalDecay time (τ)NuclearEnergyYieldIsotopeminutesReaction(MeV)(milliCi @ sat)11C29.311B (p, n)8-20 40/μA11C29.314N (p, α)12100/μA13N14.413C (p, n)5-10115/μA13N14.416O (p, α)8-18 65/μA15O2.9415N (p, n)4-10 47/μA15O2.9416O (p, pn)>26 25/μA18F15818O (p, n)8-17180/μA One problem with the current methods is their requirement for an accelerator or cyclotron to produce the ion beam from which radionuclides are formed. Cyclotrons require heavy and expensive magnets, high voltages, substantial electric power, and extensive radiation shielding. For example, Bhaskar Mukherjee has summarized the shielding requirements in Optimisation of the Radiation Shielding of Medical Cyclotrons using a Genetic Algorithm, which is incorporated herein by reference in its entirety. According to Mukherjee, “[t]he important radioisotopes produced by Medical Cyclotrons for present day diagnostic nuclear medicine include 201T1 (T1/2=73.06 h) and 67Ga (T1/2=78.26 h). These radioisotopes are generated by bombarding the thick copper substrates electroplated with enriched parent target materials with 30 MeV protons at ˜400 μA beam current. The target bombardments result in the production of intense fields of high-energy neutrons and gamma rays.” A summary of medical cyclotron characteristics abstracted from a presentation by Jean-Marie Le Goff, [A very low energy cyclotron for PET isotope Production, European Physical Society Technology and Innovation Workshop Erice, 22-24 Oct. 2012] is reproduced in Table II. As can be seen with reference to Table II, the average weight of a medical cyclotron is 36 tons, the average weight required for shielding is 47 tons, and the average power requirement is 101 kilowatts. The smallest device in Table II has a total weight of ten tons and requires 10 kW of power. In other words, the size, weight, and power of a cyclotron require that it be placed in a fixed installation. TABLE IIParameters including size, weight, and power of some commercial cyclotrons thatare used for medical isotope production.BeamCycltronShieldCompanyCyclotronEao:rgyCurrentIonRF Frequ.WeightWeightPowerNameModelParticles(MeV)(μA)Source(MHz)(tons)(tons)(kW)ACSITR14H−14>100 Cusp74224060ACSITR19(9)H−(D−)19, 9 >300 (100)Cusp74 (37)2265ACSITR24H−24>300 Cusp83.58480ACSITR30(15)H−, (D−)30, 151500 (400)Cusp56150ABTTabletopH+ 7.5 5PIG723.27.610BestBSCI 14pH•14100PIG731460BestBSCI 35pH−15-351500 Cusp7055280BestBSCI 70pH−70800Cusp58195400CIAECYCCIAE14H−14400CuspCIAECYCCJAE70H−70750CuspNIIEFACC-18/9H−, (D−)18, 9 100 (50)Cusp38.220Feb-00EUROMEVIsotraceH•12100Cusp1083.840GEMINItraceH− 9.6>50PIG10194035GEPETtraceH−, (D−)16.5, 18.6 >100 (6.5)PIG27224770IBACyclone 3D+ 3.8 60PIG14514IBACyclone10/5H−, (D−)10, 5 >100 (35) PIG42124035IBACyclone11H+11120PIG42135235IBACyclone18/9H−, (D−)18, 9 150 (40)PIG422550IBACyclone30H−, (D−)30, 151500 Cusp50180H−, (D−)350 (50)(50)IBACyclone70H2+, He++30-70, 15-5 (35)66 (30)125350KIRAMSKIRAMS-30H•15-30500Cusp64KIRAMSKotrun-13H+40100PIG77.32080187SiemensEclipseRDH−112 × 40PIG113935SiemensEclipseHI/STH−112 × 40PIG7235SumitomoHM-7H−, (D−)7.5, 3.830SumitomoHM-10H−, (D−)9.6, 4.852SumitomoHM-12/5H−, (D−)12, 6 60 (30)PIG45115645SumitomoHM-18H−, (D−)18, 10 90 (50)PIG45248655Average3647101 A second problem with PET isotope synthesis stems from the fact that materials prepared at the fixed cyclotron site lose specific activity during transport to the site where patients are scanned. This problem is particularly acute when the transport time t_transport is long compared to the decay time τ, because the specific activity drops by exp(−ttransport/τ). A third problem results from the economics of producing the reagents at a central site. In order to spread the capital and operating costs of the facility many doses must be made at once, and these must be distributed in a timely manner to patients at dispersed locations. This complicates the logistics of patient care because scanning facilities must be choreographed with the production schedule of the cyclotron while accounting for material degradation in transit. Yet another problem is that isotopes with very short lifetimes (small values of τ) cannot be used except in very close proximity to the accelerator because their specific activity degrades too rapidly to permit detection with useful signal to noise ratios in a PET scanner. For example, the half-life of H215O, a PET tracer used to measure perfusion in cardiac imaging, is only 2 minutes. Another problem is that production of multiple doses at once requires higher beam currents, which in turn demand windows between the vacuum and precursor regions that can manage thermo-mechanical stresses without significantly degrading the energy or current of the ion beam. A second problem with higher beam currents is collateral radiation damage to the chemical composition of the precursor. The irradiation of a large protein molecule containing nitrogen with large currents of 2H+ ions from a cyclotron to synthesize 15O radiolabels, for example, may degrade or denature the protein. This collateral damage limits the range of precursor materials to those that resist radiation damage, such as H218O, one precursor for production of 18F by proton beams. Once a radionuclide is formed it can be chemically bound into a molecule that serves to mark specific molecular or biological activity. For example, 18F is produced from H218O as aqueous 18F− anions that are converted through one or more chemical reactions to 18F-fluoro-deoxyglucose. This injectable reagent is taken up in vivo by cells and accumulates in their mitochondria, providing an indication of cellular metabolism rates. These chemical reactions and purifications are performed in heavily shielded enclosures or ‘hot cells’, named so due to the large amount of shielding required to prevent radiation exposure to the operators. The typical reaction volume of “hot cells” is of the order of 1 milliliter (mL) though the amount of radioactive atoms or molecules present is extremely small, typically 6×1011 atoms or molecules. A typical processing time processing (tprocess) is 40-50 minutes, that with the exception of 18F, exceeding by far the decay time of most interesting RN. The time and care required for this manual conversion contributes significantly to loss of specific activity in the final product. Van Dam et al. disclosed a significant improvement in U.S. Pat. No. 7,829,032, entitled Fully Automated Microfluidic System for the Synthesis of Radiolabeled Biomarkers for Positron Emission Tomography, which is incorporated herein by reference in its entirety. Incorporating small-volume, automated processing substantially reduced the time required to convert radioactive precursors to injectable reagents, enabling higher specific activity and safer production than prior methods. However, a limitation of this approach is that it separates production of the radioisotope from chemical conversion, so the time to transfer radionuclides between a cyclotron and the microfluidic system (ttransfer), indicated schematically by (108) in FIG. 1, contributes to loss of specific activity according to equation (1). U.S. Pat. No. 8,080,815 discloses use of microfluidic systems to synthesize radioactive tracers, which is incorporated herein by reference in its entirety. This reference discloses use of commercial micro-fluidic technology to process radionuclides created by a small cyclotron accelerator that separately produces radionuclide for one dose for human image needs, for example approximately 10 milliCurie (mCi) for 18F-fluoro-deoxyglucose. This method suffers from all of the shielding and auxiliary deficiencies of electromagnetic accelerators, and also from the need to convey radionuclides from the cyclotron to the microfluidic reactor as indicated by (108) in FIG. 1. Referring to FIGS. 3 and 4, charged particle accelerators have the following attributes: (1) an ion source system, (2) magnetic and/or electric fields that form and accelerate beams of single polarity charged particles with energy sufficient to undergo nuclear reactions, (3) a target for irradiation by the charged particle beams, and (4) a shielding system. Cyclotron accelerators were introduced in 1932 by E. O. Lawrence, who received the 1939 Nobel Prize for “the invention and development of the cyclotron and for results obtained with it, especially with regard to artificial radioactive elements.” Cyclotrons and linear accelerators require a stream of particles of only one polarity because they use a combination of fixed and oscillatory electromagnetic fields that produce opposite forces on charges of different polarity. These beams are streams of particles whose center of mass moves with high velocity while its spread in energy, ΔE, is smaller than its energy E (ΔE/E<<1). Note that as ΔE approaches E the divergence of the beam increases, obviating further acceleration and directing toward targets. Cyclotrons have been widely used for production of radioisotopes and are commercially available, as summarized in Table II. However, the acceleration of the charged particles generates electromagnetic radiation that can damage electronics and is hazardous to human operators. These large, complex machines require kilowatts of electric power and many tons of radiation shielding. Moreover, the use of high voltages in vacuum requires careful shielding and insulation, contributing to the complexity and expense of conventional accelerators. Efficient generation of radionuclides requires maximizing the integrated product of the velocity-weighted energy distribution f(E)*v(E) with the cross section Q(E) in equation 1 above. Another problem with accelerator-based radionuclide synthesis is that the resulting ion beams generally have energies well above that for which the radionuclide precursor has its maximum cross section. This in turn requires larger currents to increase the production rate, concurrently increasing collateral radiation damage to the precursor materials. Accordingly, there exists a need for additional devices and methods for production of radioactive reagents, and in particular, devices and methods that avoid the aforementioned limitations. Such devices and methods would be particularly useful in nuclear medicine, including positron emission tomography. Disclosed herein are methods and apparatus for portable production of radiolabeled chemical compounds for use in nuclear medicine, radiology, and medical imaging. The methods use a directed jet of quasi-neutral plasma to activate precursor materials that undergo nuclear reactions and produce radionuclides. The radionuclides can be subsequently converted to radiolabeled compounds (e.g., radionuclides can be converted by microfluidic reactions and purifications to an injectable radioactive reagent). The plasma jet can be produced by firing a sub-picosecond laser pulse with peak power greater than about one terawatt and less than about thirty terawatts at a solid, liquid, or gaseous target in vacuum. The jet can be directed by target normal sheath acceleration through a window onto a solid, liquid, or gaseous precursor that undergoes nuclear reactions to produce radionuclides. The irradiated precursor can be contained in a disposable reusable cartridge that converts the radiolabeled precursor into injectable reagent using standard microfluidic chemical reactions and purifications. The wavelength, pulse duration, focus, and energy of the laser, as well as the density gradients, composition, and orientation of the target can be selected to produce a plasma jet whose ion energy distribution substantially overlaps the cross-section for nuclear transformation of the precursor to a desired radionuclide. The apparatus can have dramatically smaller size, weight, power, shielding requirements, and operating costs than prior systems, thereby allowing portable devices that can be located proximate to the patient and imaging scanner. The disclosed methods and apparatus moreover can relieve the logistical burden of transporting radioactive materials and scheduling patients, and provide radioactive probes with higher specific activity and shorter half-lives to be used in nuclear medicine and medical imaging. These and other advantages of the method and apparatus will be apparent from the detailed description below. The present disclosure relates to methods and devices for synthesizing radiochemical compounds. The methods include generating a quasi-neutral plasma jet, and directing the plasma jet onto a radionuclide precursor to provide one or more radionuclides. The radionuclides can be used to prepare radiolabeled compounds, such as radiolabeled biomarkers. The methods and devices can use a quasi-neutral plasma jet impinging through a window onto a precursor in a microfluidic reactor for subsequent chemical reactions and purifications. The plasma jet can be produced by target normal sheath acceleration created by a light pulse interacting with a dense solid, liquid, or gaseous target. This can eliminate the need for conventional accelerators, reducing the size, weight, power, and shielding requirements, and enabling portable production of and access to short-lived radioisotopes for biomedical imaging and radiology. Definition of Terms Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting. The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of” and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not. The conjunctive term “or” includes any and all combinations of one or more listed elements associated by the conjunctive term. For example, the phrase “an apparatus comprising A or B” may refer to an apparatus including A where B is not present, an apparatus including B where A is not present, or an apparatus where both A and B are present. The phrases “at least one of A, B, . . . and N” or “at least one of A, B, . . . N, or combinations thereof” are defined in the broadest sense to mean one or more elements selected from the group comprising A, B, . . . and N, that is to say, any combination of one or more of the elements A, B, . . . or N including any one element alone or in combination with one or more of the other elements which may also include, in combination, additional elements not listed. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (for example, it includes at least the degree of error associated with the measurement of the particular quantity). The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4.” The term “about” may refer to plus or minus 10% of the indicated number. For example, “about 10%” may indicate a range of 9% to 11%, and “about 1” may mean from 0.9-1.1. Other meanings of “about” may be apparent from the context, such as rounding off, so, for example “about 1” may also mean from 0.5 to 1.4. The term “pre-pulse light,” as used herein, may refer to light that arises from amplified spontaneous emission whose intensity is less than about 10−4 times that of the main pulse. The energy in the pre-pulse can be spread out over much longer times and may cause ionization of target material that interferes with TNSA. There are two types of pre-pulses: (1) pedestal—duration of a few to tens of picoseconds—since this is long compared to the light pulse its intensity is comparatively small; and (2) leakage from a regenerative amplifier whose duration is slightly longer than the light pulse so its relative intensity is 10−6 to 10−8. Methods and Apparatus Radionuclides can be created by bombardment of a precursor with a quasi-neutral plasma jet, and in particular, a quasi-neutral plasma jet that contains a significant flux of positive ions with an energy distribution f(E) that spans the cross section Q(E) of the relevant nuclear reaction. Referring to FIG. 2, the plasma jet can be produced by irradiating a solid, liquid, or gaseous target (201) with a sub-picosecond light pulse from a light source (202) whose energy, wavelength, pulse-shape, and focus are selected to control f(E) for ions in the resulting plasma. In certain embodiments, only the target (201) is contained in a vacuum chamber (203). The plasma can be directed through a thin foil or window (204) directly into a microfluidic cartridge (205) that contains radionuclide precursor (206). The resulting radionuclide (207) can be subjected to microfluidic reactions (208) and purifications (209) to produce an injectable PET reagent. In certain embodiments, no transfer of radionuclide to a separate reactor is required, as indicated for previous approaches by the arrow (108) in FIG. 1. Only one lightweight shield (211) for the radioactive decay products of the radionuclide may be required. No heavy shielding may be required, and in particular, no heavy shielding (103) that protects from radiation produced in the accelerator. In certain embodiments, the microfluidic cartridge (205) is disposable and produces a single dose of reagent. The disclosed methods do not require isolation of charged particles with one polarity. The absence of an electromagnetic accelerator can reduce the size, weight, power, and shielding requirements for the system to the point that it can be portable. Since the synthesis of the PET reagent can occur proximate to the patient, the contribution of ttransport to the decay of specific activity is reduced or eliminated. Referring to FIG. 3, quasi-neutral plasma jets (304,306) may be generated on either or both sides of an illuminated target. The light pulse may enter through optical window (301) on the left side of the vacuum chamber (302) and strike the left face of the targets (303, 305). If the target (303) is thicker than about 1 millimeter, the primary direction of the plasma jet (304) is to the left in FIG. 3. If the target (305) is thinner than about 100 microns, then the primary direction of the plasma get (306) is to the right. Accordingly, one or more foils or windows (307, 308) that are transparent to these plasma jets can be placed between the targets, held under vacuum, and the radionuclide precursor, which is held at pressures greater than about 100 kPa. FIG. 4 shows details of an exemplary pulsed light source. The pulsed light source (400) produces a primary pulse (401) that is preceded by one or more lower energy pre-pulses (402). In order to prevent light with energy of more than about 10−10 times that of the light pulse, sacrificial thin foils (403) or plasma mirrors (404) that absorb this pre-pulse energy may be configured between the light source and the target. Plasma mirrors (404) may be shaped to focus the primary light pulse, as indicated by the arrows labeled (401) and (405) in FIG. 4. Plasma lenses (406), created by pulsed irradiation of a region through which the main light pulse subsequently passes, may also be arranged to further focus the light onto the target, as indicated by the arrows labeled (406) and (407). These plasma lenses have the advantage that they are not damaged by the high intensity of the light pulse; in contrast to conventional solid refractive or reflective optics. Properties of plasma lenses are described in A plasma microlens for ultrashort high power lasers, by Yiftach Katzir, Shmuel Eisenmann, Yair Ferber, Arie Zigler, and Richard F. Hubbard, Applied Physics Letters 95, 031101 (2009), which is incorporated herein by reference in its entirety. The plasma lens selectively refocuses lower intensity or pre-pulse light to further reduce its intensity at the target while retaining the focus of the (α>1) light pulse at the target. The light pulse with minimal (<10−10) contributions from pre-pulses (407) is focused onto the target to produce the quasi-neutral plasma jet. One example of optimizing production according to equation 1 refers to FIG. 5. The cross section for the reaction 14N+1H→11C+4He (501) refers to the left, linear abscissa, while the narrow energy distributions f(E) at 10 MeV (502) and 17 MeV (503) that are produced by an linear or cyclotron accelerator and the broader f(E) produced by the quasi-neutral plasma (504) are shown with the logarithmic abscissa on the right side of the graph. Manipulation of the distribution function ƒ(E) by judicious choice of the light source and plasma target parameters provides flexibility in optimizing the integrand of Equation 1 that is not possible for accelerator produced beams, whose only adjustable parameter is the charged particle beam energy. A first step may include converting the energy of short, high power pulses of light to energetic plasma jets by bombarding thin material targets. Coherent light sources that generate ultra-short (0.03-2 picoseconds), high power (>1018 Watts/cm2) pulses in the wavelength range of 0.5-10 nm and experiments using them to bombard targets revealed that judicious choice of the laser and target parameters converts photon energy to quasi-neutral energetic jets of plasmas with controlled ionic content. The fundamental physical process, known as Target Normal Sheath Acceleration (TNSA), converts pulses of light to energetic, quasi-neutral plasma jets with hot electrons (temperature of several Mega-Electron Volts (MeV)) and protons with energy up to 30 MeV. These plasma jets have high brightness (>5×1010 protons per pulse), small virtual source size (<1 μm), low emittance (0.005π mm·mrad) and conversion efficiency of light energy to multi-MeV protons between 1-10%. Machi, in Superintense Laser-Plasma Interaction Theory Primer, Springer Briefs in Physics, (New York:Springer Verlag, 2013), summarizes the experimental and theoretical developments of converting light to quasi-neutral plasma jets, the disclosure of which is incorporated herein by reference in its entirety. TNSA can include two steps. A first step comprises the almost instantaneous ionization and formation of quasi-neutral plasma with electrons whose temperature substantially exceeds that of the heavier positive ions. An important parameter for TNSA is the ratio of the maximum plasma density n to the critical density of the plasma nc, defined on the basis of the laser parameters as nc=1.1×1021λ−2 cm−3, where λ is the laser wavelength in microns (μm). The critical density is the plasma density at which the laser frequency equals the electron plasma frequency. Experiments and theory have established that, for subcritical interactions, when n<nc, the target is transparent to radiation and very little laser energy is transferred to the plasma. Optimal coupling occurs for values equal to or slightly above nc. Another important parameter that controls the conversion of light energy to energetic plasma jets is the value of the dimensionless vector potential, α0, =0.6λ √I, where I is the laser intensity in units of 1018 W/cm2 and λ is the laser wavelength in μm. The parameter α0 represents the ratio of the oscillatory momentum of the plasma electrons in the presence of the laser field to moc. The electron temperature Te is of the order of the cycled averaged oscillation energy in the electric field of the laser light in vacuum and is given by T e = m o ⁢ c 2 ( 1 + 1 2 ⁢ a o 2 - 1 ) Values of αo larger than unity imply that the temperature of the electrons Te exceeds one MeV. Computer simulations and experiments indicate that the distribution function of the hot electrons fe has the form: f e ⁡ ( E ) ∼ ⅇ - ( E - T e 0.6 ⁢ T e ) 2 The second step involves expansion of the hot electrons into the vacuum surrounding the thin target, producing a transient electrostatic sheath. Quasi-neutrality is quickly restored by transferring energy from the hot electrons to the ions. Self-similar solutions confirmed by experiments indicate formation of a quasi-neutral energetic plasma jet containing ions with energy up to 10 Te follows charge neutralization. FIG. 6 shows the experimental proton flux measured by Snavely et al. [Phys. Rev. Lett., 85, 2945, 2000] from a flat, 100 μm thick, hydrocarbon polymer target irradiated with a 1 μm laser whose peak intensity was 3×1020 W/cm2, corresponding to a value of αo≈10. The interaction created proton-dominated plasma jets on both sides of the target with energy up to 60 MeV and conversion efficiency of light to fast plasma jets of 10%. This flux was directed normal to the target with angular width close to 10 degrees. This and other experiments and theory gave proton energy spectra f(E)˜e−E/Te. In certain embodiments, a short laser pulse can be impinged onto solid targets to produce a quasi-neutral plasma jet with an ion energy distribution falling between about 1 and about 15 MeV. Examples of a solid target include polymeric or metallic foils with adsorbed moisture, hydrogen, deuterium, or molecules containing hydrogen, thin metallic targets upon which one or more, less dense “foam” layers are deposited [Sgattoni et al., Physical Review E85,036405, 2012] and “limited mass targets” [Buffechoux et al, Physical Review Letters 105, 015005, 2010] with surface area smaller than 104 μm2 and thickness less than 10 μm. In certain embodiments, a short laser pulse can be focused onto a liquid film or liquid droplet to produce a quasi-neutral plasma jet. The liquid composition and optical thickness are chosen so as to maximize the plasma density gradient following irradiation, which in turn produces optimal target normal sheath interactions. In certain embodiments, a short laser pulse can be impinged onto a pulsed gas jet. This composition of the gas jet is chosen to produce specific ions of, for example, H+, D+, or He+. A second requirement for the gas jet is that it have sufficient optical and mass density to produce plasmas with n>nc and sharp gradients in the plasma density following the first few femtoseconds of the irradiation. In order to achieve these conditions, the backing pressure behind the pulsed valve from which the jet is formed preferably exceeds 100 kPa, and more preferably is greater than 10 MPa. A sub millimeter diameter pulsed gas jet device described by Sylla et al. [Review of Scientific Instruments, 83, 033507,2012] produces pressures of 30-40 MPa, enabling TNSA under overcritical or critical conditions and facilitating control of the plasma density gradients. Many pulsed light sources produce optical radiation that precedes the light pulse. This ‘pre-pulse’ radiation can interact with the target and interfere with TNSA. In certain embodiments, one or more plasma mirrors [Monot et al., Optics Letters, 29, 8093,2004; Buffechoux et al. Physical Review Letters 105, 015005, 2010] can be utilized to preferentially absorb this radiation and to thereby increase the ratio of energy in the light pulse to that preceding the light pulse, also known as pre-pulse contrast, above 1010. In certain embodiments, plasma microlenses [Kazir et al., Applied Physics Letters, 95,031101, 2009; Nakatsutsumi et al., Optics Letters 35, 2314, 2010] can be used to increase the light intensity on the target by about a factor of 10 and to achieve extremely low focal f-numbers. This can increase the conversion efficiency of light to plasma jets and can reduce the diameter of the plasma target chamber to less than about 15 cm, enabling the system size and weight to be substantially less than prior art cyclotrons and linear accelerators. Recognizing that ions produced by TNSA are emitted in the direction normal to the target surface, whether the target is flat or has curvature, the quasi-neutral plasma jet can be focused by appropriately shaping the target surface, for example by the use of a concave or spherical target. Ion beams produced by traditional accelerators are strongly defocused by the Coulomb force between ions, requiring strong electrostatic and magnetic fields to collimate and direct the ions. The disclosed plasma jets are quasi-neutral and can be focused with relative ease. Focusing from a curved target was demonstrated experimentally, where the plasma jet intensity increased by an order of magnitude when spherical, rather than flat, thin foil targets were used. [Kaluza et al., Phys. Rev. Lett., 93, 045003-1-4 (2004)]. The same logic applies to liquid and gas jet targets, where the geometric shape of the target density profile can be chosen to focus the quasi-neutral plasma jet. The light pulse may be generated by commercial Ti:sapphire laser systems with appropriate optics, such as the Amplitude Technologies TT-Mobile system. [http://www.amplitude-technologies.com]. Alternative methods for producing sub-picosecond optical pulses with minimal pre-pulse energy including fiber amplifiers, Nd:YAG amplifiers, optical parametric chirped-pulse amplifiers, and the like are familiar to those practiced in the art of laser physics and may be used so long as the value of α0 is greater or equal to 1. The laser pulse energy, duration, and wavelength are chosen to produce a quasi-neutral plasma whose energy distribution f(E) maximizes the production rate of radionuclide from the specific solid, liquid, or gaseous target based on their cross-sections Q(E) in accordance with equation 1. Examples of controlling f(E) and the efficiency of TNSA by combinations of laser energy, pulse shape, transient plasma lenses and mirrors, and various target compositions with pulsed light sources are shown in FIGS. 6 through 10. FIG. 6 shows the flux and energy of protons produced from a 100 μm thick hydrocarbon film by TNSA with αo≈10. The flux and energy emerging from the illuminated side of the target (squares) was about a factor of twenty larger than the plasma jet emerging from the target's other side (triangles). [Snavely et al. Phys. Rev. Lett., 85, 2945, 2000]. The proton flux induced by the hydrocarbon target was five times larger than for the gold target. Analysis and simulations indicate that the ionic component of the energetic plasma jets has three different origination channels: from the rear side to the forward direction, from the front side to the forward direction, and from the front side to the backward direction. The efficiency and energy of the plasma jet depend strongly on the sharpness of the density gradient [Mackinnon et al. Physical Review Letters 86,1769, 2001]. In most of the early experiments the sharpest density gradient occurred on the illuminated side of the target thereby generating a dominant plasma jet in the backward direction. The influence of target thickness on TNSA has been elucidated. Referring to FIG. 7, experiments by Fuchs et al., [Nature Physics, 2, 48 2006] show that thin targets are more efficient convertors of light to energetic plasma jets than thick targets. [Borghesi et al. Phys Rev Lett., 92, 055003, (2004)] demonstrated, as shown in FIG. 8, that the value of f(E) can be significantly controlled by the target thickness. These plasma jets whose proton energy distribution function ƒ(E) is shown in FIG. 8, have low emittance (0.1 π mm·mrad at 15 MeV). This obviates the need for collimation of the plasma beam by electrostatic lenses, as previously necessary. FIG. 7 also shows the scaling of the maximum proton energy and efficiency with target thickness that favors thinner targets down to 20 μm thickness. The laser pre-pulse destroyed the sharpness of the density gradient at the back surface for channels thinner than 10 μm. The understanding of the role of the laser pulse shape led to the development of additional scaling laws. First, experiments [Ceccotti et al., Physical Review Letters, 99, 185002, 2007] discovered that the maximum energy and the conversion efficiency continue to increase for target thickness smaller than 10 μm, as long as the contrast between laser pulse and its pre-pulse is very large. These results are shown in FIG. 9. More than three-fold increase in maximum energy with half the laser intensity has been demonstrated by using targets as thin as 0.1 μm. In these very thin targets the forward and backward plasma jet are symmetric. As shown in FIG. 10, [Buffechoux et al, Physical Review Letters 105, 015005, 2010] demonstrated that decreasing the surface target area dramatically increases both the conversion efficiency and the maximum proton energy. For example, reducing the surface area from 107 to 2×103 μm2 increases the efficiency by a factor of 30, to 4%, while increasing the maximum proton energy by a factor of 3 to 14 MeV, for a 2 μm thick target and I≈2×1019 W/cm2. The fundamental reason for the efficiency increase is confinement of the hot electrons by reflection from the edges of the target that increases both the number density and temperature of the hot electrons. These and other considerations provide control of f(E) and light to plasma jet conversion efficiency through changes in the geometry, phase (solid, liquid, or gas), and dimensions of the target as well as the focus, energy, pulse shape, and wavelength of the light source. The precursor material, a non-limiting example being H218O, can be exposed to the plasma jet through a suitable window material. Since the plasma is formed in a vacuum and the precursor is a condensed or gaseous phase with non-zero pressure, a material that is transparent to and undamaged by the quasi-neutral plasma and that does not leak or fail from the pressure difference between the precursor and the vacuum chamber is preferred. Transparent materials preferably have average atomic numbers less than about 12, for example poly-p-phenylene-benzo-bis-oxazole (PBO), or an aramid such as Kevlar™ which contain only C, H, O, and N. PBO and Kevlar are non-limiting examples of materials with large elastic moduli (315 GPa and 125 GPa, respectively) and tensile strengths, as well as low gas permeabilities. A thin film or foil of these and similar materials can provide an impermeable barrier between the precursor at high pressures and the plasma jet in the vacuum chamber while being transparent to the MeV ions and electrons that comprise the plasma jet. In certain embodiments, radionuclides are formed directly in the microfluidic reactor that subsequently transforms the radionuclide into an injectable reagent through chemical reactions and purifications. This can eliminate the time required to transfer (ttransfer) radionuclides formed in cyclotrons to hot cells or microreactor systems, thereby increasing the specific activity of the product. In certain embodiments, a reusable or, preferably, a disposable sterile microfluidic cartridge is provided that contains the window, precursor, and other chemical materials to complete transformation of a quasi-neutral plasma flux into an injectable reagent. Individual doses of various nuclear probe molecules can be conveniently prepared from the same system without requirements for cleaning, radioactive decontamination, or sterilization. The ability to prepare useful quantities of short-lived radioisotopes incorporated into arbitrary molecular compositions gives rise to further embodiments in non-destructive testing of materials and systems, tagging, tracking, and locating, and other non-medical applications. It is understood that the foregoing detailed description and accompanying examples are merely illustrative and are not to be taken as limitations upon the scope of the invention, which is defined solely by the appended claims and their equivalents. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art.
	claims	1. An x-ray optical system comprising:a multiple corner optic assembly including a plurality of single corner Kirkpatrick-Baez side-by-side optics positioned about an optical axis, each single corner optic including a first reflective surface and a second reflective surface orthogonal to the first reflective surface, the first and second reflective surfaces extending from an optic entrance zone to an optic exit zone, the single corner optics being positioned about the optical axis such that the first and second reflective surfaces of each single corner optic face the optical axis and the optic entrance and exit zones of each single corner optic are respectively aligned defining an assembly entrance zone and an assembly exit zone, each single corner optic being configured to condition an x-ray beam having an x-ray wavelength, wherein the plurality of single corner optics includes a first single corner optic configured to condition a first x-ray beam having a first x-ray wavelength; andan adjustable aperture assembly positioned at one of the assembly entrance and exit zones, the adjustable aperture assembly including at least one movable body portion having an aperture formed therethrough, wherein a first movable body portion is movable relative to the first single corner optic to adjust a size or shape of the first x-ray beam to at least one of adjust optic focal spot size, adjust convergence of the first x-ray beam, and occlude the first x-ray beam having the first x-ray wavelength. 2. The x-ray optical system of claim 1, wherein the first movable body portion is movable relative to the first single corner optic to define an open beam state, a closed beam state, and a partially open beam state, wherein the open beam state is defined when the first movable body portion is positioned relative to the first single corner optic such that the aperture of the first movable body portion is aligned with respect to the first x-ray beam so as to maximize the size of the first x-ray beam, wherein the closed beam state is defined when the first movable body portion is positioned relative to the first single corner optic such that the aperture of the first movable body portion is aligned with respect to the first x-ray beam so as to block the first x-ray beam, wherein the partially open beam state is defined when the first movable body portion is positioned relative to the first single corner optic in between the open beam state and the closed beam state. 3. The x-ray optical system of claim 2, wherein the first movable body portion is movable from the open beam state to the closed beam state in a first direction toward the optical axis and in a second direction away from the optical axis. 4. The x-ray optical system of claim 3, wherein the adjustable aperture assembly is positioned at the assembly entrance zone, wherein the first movable body portion adjusts optic focal spot size when moved in the first direction, and wherein the first movable body portion adjusts convergence of the first x-ray beam when moved in the second direction. 5. The x-ray optical system of claim 3, wherein the adjustable aperture assembly is positioned at the assembly exit zone, wherein the first movable body portion adjusts convergence of the first x-ray beam when moved in the first direction, and wherein the first movable body portion adjusts optic focal spot size when moved in the second direction. 6. The x-ray optical system of claim 1, wherein the first movable body portion is movable relative to more than one single corner optic to adjust the shape or size of more than one x-ray beam. 7. The x-ray optical system of claim 1, wherein the first movable body portion includes more than one aperture formed therethrough. 8. The x-ray optical system of claim 1, further comprising a fixed aperture assembly positioned at least one of the entrance and exit zones, the fixed aperture assembly including a fixed body portion and an aperture formed therethrough, the fixed body portion coupled to at least one of the single corner optics of the multiple corner optic assembly, the fixed body portion configured to block a portion of the x-rays entering the x-ray optical system. 9. The x-ray optical system of claim 8, wherein the fixed aperture assembly is positioned between the multiple corner optic assembly and the adjustable aperture assembly. 10. The x-ray optical system of claim 1, wherein the multiple corner optic assembly is non-symmetric. 11. The x-ray optical system of claim 1, wherein the multiple corner optic assembly is symmetric. 12. The x-ray optical system of claim 1, wherein the reflective surfaces are multi-layer Bragg surfaces, wherein the first single corner optic includes multilayer Bragg surfaces configured to reflect the first x-ray beam having the first wavelength, wherein a second single corner optic of the plurality of single corner optics includes multilayer Bragg surfaces configured to reflect a second x-ray beam having a second wavelength different from the first wavelength. 13. The x-ray optical system of claim 2, wherein the plurality of single corner optics includes a second single corner optic configured to condition a second x-ray beam having a second x-ray wavelength, wherein the adjustable aperture assembly includes a second movable body portion having a second aperture formed therethough, wherein the second movable body portion is movable relative to the second single corner optic to adjust the size or shape of the second x-ray beam to at least one of adjust optic focal spot size, adjust convergence of the second x-ray beam, and occlude the x-ray beam having the second x-ray wavelength. 14. The x-ray optical system of claim 13, wherein the second movable body portion is movable relative to the second single corner optic between an open beam, a closed beam state, and a partially open beam state, wherein the open beam state is defined when the second movable body portion is positioned relative to the second single corner optic such that the aperture of the second movable body portion is aligned with respect to the second x-ray beam so as to maximize the size of the second x-ray beam, wherein the closed beam state is defined when the second movable body portion is positioned relative to the second single corner optic such that the aperture of the second movable body portion is aligned with respect to the second x-ray beam so as to block the second x-ray beam, wherein the partially open beam state is defined when the second movable body portion is positioned relative to the second single corner optic in between the open beam state and the closed beam state. 15. The x-ray optical system of claim 14, wherein the first movable body portion is positioned relative to the first single corner optic in the closed beam state when the second movable body portion is positioned relative to the second single corner optic in one of the open beam state and the partially open beam state, and wherein the second movable body portion is positioned relative to the second single corner optic in the closed beam state when the first movable body portion is positioned relative to the first single corner optic in one of the open beam state and the partially open beam state such that the optical system is capable of conditioning x-ray beams of one wavelength at a time. 16. The x-ray optical system of claim 1, wherein the plurality of single corner optics includes at least four single corner optics. 17. The x-ray optical system of claim 1, wherein the plurality of single corner optics are coupled together to form a substantially enclosed multiple corner optic assembly, the reflective surfaces of the single corner optics forming an inner surface of the optic assembly.
	abstract	An extreme ultraviolet light generation system may include a laser device configured to emit pulse laser light, an EUV light concentrating mirror configured to reflect and concentrate extreme ultraviolet light generated by irradiating a target with the pulse laser light, and a processor configured to receive a first energy parameter of the extreme ultraviolet light and control an irradiation frequency of the pulse laser light with which the target is irradiated so that change in a second energy parameter related to energy per unit time of the extreme ultraviolet light reflected by the EUV light concentrating mirror is suppressed.
	summary
	claims	1. A method for producing a reaction product containing 99mTc, comprising:providing a100Mo-metal target to be irradiated,accelerating protons with only a single acceleration unit to form a proton beam having an energy suitable for inducing a 100Mo(p, 2n)99mTc nuclear reaction,irradiating the 100Mo-metal target with the proton beam having the energy suitable for inducing the 100Mo(p, 2n)99mTc nuclear reaction,heating the 100Mo-metal target to a temperature of over 300° C., andobtaining the 99mTc made in the 100Mo-metal target in a sublimation-extraction process with the aid of oxygen gas, which is routed over the 100Mo-metal target forming 99mTc-technetium oxide in the process. 2. The method of claim 1, additionally comprising feeding the obtained 99mTc-technetium oxide to an alkaline solution to form 99mTc-pertechnetate. 3. The method of claim 1, wherein the 100Mo-metal target is in the form of a film, in the form of a powder, in the form of tubules, in the form of a grid structure, in the form of spheres, or in the form of metal foam. 4. The method of claim 1, wherein the 100Mo-metal target is held by a thermally insulating mount. 5. The method of claim 1, wherein heating of the 100Mo-metal target is achieved by the irradiation by the proton beam. 6. The method of claim 1, wherein the heating is achieved by conducting current through the 100Mo-metal target. 7. The method of claim 1, wherein the heating is achieved by heating a chamber in which the 100Mo-metal target is arranged. 8. A device for producing a reaction product containing 99mTc, comprising:a 100Mo-metal target,a single accelerator unit for accelerating protons, with only the single acceleration unit, to form a proton beam directed at the 100Mo-metal target to thereby irradiate the 100Mo-metal target, the proton beam having an energy which is suitable for inducing a 100Mo(p, 2n)99mTc nuclear reaction when the 100Mo-metal target is irradiated by the proton beam,wherein the device is configured to heat the 100Mo-metal target to a temperature of over 300° C., anda sublimation-extraction system for extracting 99mTc, including:a gas supply line for routing oxygen gas onto the irradiated and heated 100Mo-metal target forming 99mTc-technetium oxide by sublimation, anda gas discharge line for extracting the sublimated 99mTc-technetium oxide. 9. The device of claim 8, further comprising a liquid chamber with an alkaline solution into which the 99mTc-technetium oxide is routed for the formation of 99mTc-pertechnetate. 10. The device of claim 8, wherein the 100Mo-metal target is available in the form of a film, in the form of a powder, in the form of tubules, in the form of a grid structure, in the form of spheres or in the form of metal foam. 11. The device of claim 8, wherein the 100Mo-metal target is held by a thermally insulating mount. 12. The device of claim 8, comprising a circuit for conducting current through the 100Mo-metal target to heat the 100Mo-metal target to the temperature of over 300° C. 13. The device of claim 8, wherein the 100Mo-metal target is arranged in a heatable chamber to heat the 100Mo-metal target to the temperature of over 300° C. 14. The method of claim 1, additionally comprising feeding the obtained 99mTc-technetium oxide to a sodium hydroxide solution. 15. The device of claim 8, further comprising a liquid chamber with a sodium hydroxide solution into which the 99mTc-technetium oxide is routed for the formation of 99mTc-pertechnetate. 16. The method of claim 1, additionally comprising feeding the obtained 99mTc-technetium oxide to a salt solution to form 99mTc-pertechnetate. 17. The device of claim 8, further comprising a liquid chamber with a salt solution into which the 99mTc-technetium oxide is routed for the formation of 99mTc-pertechnetate. 18. A method for producing a reaction product containing 99mTc, comprising:providing a 100Mo-metal target to be irradiated,accelerating protons in an acceleration unit to form a proton beam,irradiating the 100Mo-metal target with the proton beam having an energy suitable for inducing a 100Mo(p, 2n)99mTc nuclear reaction,heating the 100Mo-metal target, by the irradiation by the proton beam, to a temperature of over 300° C., andobtaining the 99mTc made in the 100Mo-metal target in a sublimation-extraction process with the aid of oxygen gas, which is routed over the 100Mo-metal target, heated to the temperature over 300° C., forming 99mTc-technetium oxide in the process. 19. The method of claim 18, comprising forming the proton beam with a single acceleration unit. 20. The method of claim 18, further comprising feeding the formed 99mTc-technetium oxide to an alkaline solution to form 99mTc-pertechnetate. 21. The method of claim 18, further comprising feeding the formed 99mTc-technetium oxide to a salt solution to form 99mTc-pertechnetate. 22. The method of claim 18, wherein the 100Mo-metal target comprises a film in the form of: a powder, tubules, a grid structure, spheres, or a metal foam. 23. The method of claim 18, comprising holding the 100Mo-metal target with a thermally insulating mount. 24. The device of claim 8, wherein the 100Mo-metal target is heated to the temperature over 300° C. by the irradiation of the proton beam from the single accelerator unit.
056446080	summary	This invention relates to the cooling of spent fuel assemblies used in nuclear power plants. BACKGROUND OF THE INVENTION In nuclear power plants, it is customary to provide a pool of water for the purpose of cooling spent fuel assemblies, which are immersed in the pool of water. It is necessary to circulate and cool the water of the pool, and in most installations, a water-water heat exchanger is used to cool both the water from the spent fuel pool and the water that is used to cool components of the reactor. The component cooling water is circulated through the water-water heat exchanger through which the water from the pool is also circulated. Such water-water heal exchangers are relatively large and expensive, and the ultimate cooling therefor is obtained from a service water system, such as a river, lake or other source. If there is a loss of supply of water from the service water system, or if the water-water heal exchanger becomes inoperative, the spent fuel cooling system is inoperative. Also, with the present systems, the time allotted for repair of the component cooling system and the service water system is usually limited to the reactor refueling time during which all of the fuel assemblies from the reactor core are also in the spent fuel pool. Such time is on the order of twelve hours and can be inadequate. There exists a need to provide a redundant cooling system in order to permit repair of the main cooling system or to act as a standby system. To provide a redundant water-water heat exchanger to handle the cooling load in the event of such a failure or problem or during refueling is considered to be prohibitive not only because of cost and space limitations, but also because a redundant water-water system would not provide protection against loss of service water or component cooling water systems. The use of a conventional air cooled heat exchanger as a redundant cooler is also impractical because such an exchanger is relatively inefficient, and to provide the same cooling capacity as the water-water heat exchanger would require a large installation. It is known in the art that heat exchangers which employ pipe coils through which the liquid to be cooled is to circulate and which are subjected to a flow of air, such as ambient air, into which a spray of water is directed, are more efficient in cooling than heat exchangers which use only ambient air without a water spray for cooling. Compact plate-fin heat exchangers have been used, for example in aircraft. Such heat exchangers provide greater heat transfer surface per unit volume by the use of fins of very small cross section brazed or otherwise attached in good thermal contact with the primary heat transfer surface. The two principal arrangements employing extended surfaces are the plate-fin exchanger, which has no pipe coils, and the tube-fin exchanger. The primary heat transfer surface of the plate-fin design consists of multiple parallel plates connected by fins; the space between each pair of plates comprises a fluid passage. Alternate fluid passages are connected in parallel by suitable headers to form the two "sides" of the heat exchanger. In the strip-fin type of plate-fin exchanger, metal strips arranged either staggered or in-line serve as the fins. Tube-fin heat exchangers have fins on only one side of the primary surface, and tubes (either round or flattened) placed through holes in thin metal plates and to which the tubes are brazed. The preferred heat exchanger of the present invention has fins on both sides of the heat transfer surface and employs no tubes. U.S. Pat. No. 4,969,507 describes a falling film air-cooled surface condenser in which droplets of coolant liquid are detached from the falling film of water and entrained by a flow of coolant air, enhancing heat exchange. It has now been found that a heat exchanger of reasonable size and cost and which uses, as the coolant, ambient air into which a spray of water is directed concurrently with the flow of cooling air, can be used not only to substitute for the conventional water-water heat exchanger in the event the latter becomes inoperative, but also to provide component and spent fuel cooling in the event of failure of the water supply to the component cooling system, and hence, to the spent fuel water-water heat exchanger. BRIEF SUMMARY OF THE INVENTION In accordance with the invention, a plate-fin or tube-fin heat exchanger through which the water to be cooled is circulated and which employs a flow of air such as ambient air into which water from an auxiliary source, such as a storage tank, public water mains, river or lake, is sprayed, can, by means of appropriate valves and pipes, be employed, at least temporarily, as a substitute for the conventional water-water heat exchanger, as a supplemental cooler or as a heat exchanger for component cooling water and the spent fuel pool water in the event that the normal supply of water for such latter purposes fails. Accordingly, a heat exchanger or heat exchanger assembly with a set of individual plate-fin or tube-fin cooling surfaces, employing as the coolant an air-water spray and having a cooling capacity at least equal to the cooling capacity of the conventional water-water heat exchanger, is connected by valves and pipes to the conventional system so that: (1) The water-water heat exchanger is isolated from the spent fuel pool cooling loop and cooling is done by the air-water spray coolant heat exchanger; or (2) The air-water spray coolant heat exchanger is connected and operated in parallel with the water-water heat exchanger to provide supplemental cooling, in such situations as when there is a discharge of the reactor core or when the service water temperature is abnormally high; or (3) The air-water spray coolant heat exchanger provides cooling of the spent fuel pool water and the component cooling water system which cools the reactor components in such situations as when there is a failure of service water supply. The preferred air-water spray coolant heat exchanger of the invention achieves a significantly higher effectiveness than heat exchangers previously known. The term effectiveness as used in this description means the ratio of the actual temperature decrease of the fluid being cooled to the maximum theoretical temperature decrease which can be achieved with a coolant medium of a given temperature. To accomplish this effectiveness it is necessary to employ spray nozzles which produce very finely "atomized" water droplets which form a mist uniformly distributed within the heat exchanger. The effectiveness of the cooling can be greatly increased by using a mist of fine water droplets entrained in cooling air passed through the heat exchanger. Effectiveness can be increased as much as eight times as compared to cooling with air as the sole cooling medium. The mean diameter of the individual water droplets should be no greater than 240 microns, preferably less than 100 microns. The particularly preferred average water droplet diameter is about 50 microns. The spray of water is not directed through any slots or openings. The water spray in the form of very fine mist is injected into the air stream entering the heat exchanger as a result of the suction produced by a fan. The spray droplets are driven by small scale turbulence within the heat exchanger to collect on the fin and plate surfaces, providing a thin film of liquid which evaporates, transferring heat. When the temperature of the air stream as it enters the heat exchanger goes down slightly as a result of the presence of the water mist, the evaporative heat transfer from the air to the mist droplets significantly enhances the overall heat transfer from the water to be cooled by the heat exchanger. The heat exchanger can be of either the tube-fin or the plate-fin type. Preferably, the plate-fin type of heat exchange surface with either strip fins or louvered fins is used. Such surfaces are described in the reference textbook Compact Heat Exchangers by Kays and London, McGraw Hill, second edition, 1954 in Chapter 9 and illustrated in FIGS. 9-3, 9-5 and 9-6 of that text, which sections and figures are herein incorporated by reference.
	description	This application claims priority from U.S. provisional patent application Ser. No. 61/683,992, filed Aug. 16, 2012, the content of which is incorporated herein in its entirety. This invention was made with government support under Grant No. DE-AC07-05ID14517, awarded by the Department of Energy. The government has certain rights in the invention. The present invention relates generally to thermoacoustic devices used in combination with high temperature processes. Thermoacoustic devices are structures that are configured to produce acoustic waves in the presence of a temperature differential or, conversely, to produce a temperature differential in the presence of acoustic waves. The earliest recorded instance of the conversion of heat to sound is the Kibitsunokama, an instrument used in historical Japanese shrine rituals. This instrument was mentioned in a Buddhist monk's diary written in 1568, and was described in a story published in 1776. The first record in the scientific literature of the thermoacoustic generation of sound was an experiment by Byron Higgins, in 1777, in which acoustic oscillations in a large pipe were excited by suitable placement of a hydrogen flame inside the pipe. The Rijke tube, an early extension of Higgins' work, is well known to modern acousticians as a dramatic lecture demonstration. Higgins' research eventually evolved into the modern science of pulse combustion, whose applications included the German V-1 rocket (the “buzz bomb”) used in World War II and the residential pulse-combustion furnace introduced by Lennox, Inc. in 1982. The Sondhauss tube is the earliest thermoacoustic engine that is a direct antecedent of a thermoacoustic engine of the type used in the present invention. Nearly two hundred years ago, glassblowers noticed that when a hot glass bulb was attached to a cool glass tubular stem, the stem tip sometimes emitted sound. Sondhauss quantitatively investigated the relation between the pitch of the sound and the dimensions of the apparatus. John W. Strutt (Lord Rayleigh) was the first to provide a qualitative explanation of the process that converted heat to sound in the Sondhauss tube in 1896: “If heat be given to the air at the moment of greatest condensation, or be taken from it at the moment of greatest rarefaction, the vibration is encouraged.” Although Rayleigh's qualitative understanding was correct, it was not until nearly a century later that Nikolas Rott published a series of papers which created a detailed theoretical framework that could produce a unified quantitative description of thermoacoustic phenomena and explicitly calculate the behavior of the Sondhauss tube or Taconis tube. The efficient production of standing sound waves in sealed resonators by thermoacoustic processes started development at the Los Alamos National Laboratory in the early 1980s. By 1988, the field of thermoacoustic energy conversion had advanced to the point where experimentalists were contemplating thermoacoustic engine designs that could be competitive with other traditional heat engine technologies. One of the best-documented standing-wave thermoacoustic engines was described by G. W. Swift. A standing-wave thermoacoustic engine of the type fabricated and analyzed by G. W. Swift in 1992 includes a porous medium, known as the “stack”, along which the heat flows from a electrically-heated hot heat exchanger to a water-cooled (exhaust) cold heat exchanger. The “thermal core” (i.e., the stack and the two heat exchangers) is contained within a rigid-walled cylindrical pressure vessel that acts as the standing-wave acoustic resonator oscillating in its fundamental plane-wave mode (i.e., the resonator's length is approximately one-half of the acoustic wavelength). The hot end of the resonator is surrounded by thermal insulation and the ambient-temperature end is connected to a variable flow resistor (i.e., needle valve) and a tank that forms an adjustable acoustic load on the engine. The present invention provides various embodiments of thermoacoustic devices for use with high temperature processes, such as self-powered monitoring of a nuclear fuel-rod. A thermoacoustic device may be integral with a nuclear fuel-rod or a separate device with a nuclear heat source, such as a fuel pellet or an absorber of high energy particles or electromagnetic radiation (i.e. a gamma absorber). Further embodiments of the present invention are well suited to use in high temperature industrial processes such as the melt-processing of glass or metal and other processes or systems in which high temperatures are used. A first embodiment of the present invention provides a system for high temperature materials, including a thermoacoustic sensing device. The system includes a high temperature container for holding a high temperature material, with the container having a containment wall. A thermoacoustic device is responsive to a temperature in the container. The device includes a housing defining an interior chamber. The housing has a high temperature end and a low temperature end. The housing is at least partially disposed in the high temperature container such that the high temperature end is in thermal communication with the high temperature material. The housing is configured such that an acoustic standing wave is produced in the interior chamber of the housing when there is at least a sufficient temperature differential between the high and low temperature ends of the housing. The frequency of the acoustic standing wave depends on an effective temperature in the interior chamber. In certain embodiments, the system further includes a stack having a hot end and a cold end. The stack is disposed in the interior chamber between the high and low temperature ends of the housing and is positioned such that the acoustic wave is produced in the interior chamber when there is at least a critical temperature gradient in the stack. In certain embodiments, the high temperature container is a nuclear container and the high temperature material is nuclear fuel disposed in fuel rods. A coolant is disposed in the nuclear container and surrounds the fuel rods. The thermoacoustic device has a nuclear heat source disposed in the interior chamber at the high temperature end of the housing and spaced from the hot end of the stack. In some versions, the nuclear heat source is a portion of nuclear fuel. In other versions, the nuclear heat source is a high energy absorber operable to absorb high energy radiation from the nuclear fuel and the fuel rods. In some versions, the housing of the thermoacoustic device is completely disposed in the coolant in the nuclear container. In certain embodiments, the high temperature container is a nuclear container and the system further includes fuel rod housings disposed in the nuclear container. The high temperature material is nuclear fuel disposed in the fuel rod housings and a coolant is disposed in the nuclear container and surrounds the fuel rod housings. One of the nuclear fuel rod housings further defines the housing of the thermoacoustic device and at least a portion of the nuclear fuel in the nuclear fuel rod is spaced from the hot end of the stack. Some versions include a second thermoacoustic device and one of the nuclear fuel rod housings further defines the housing for the second thermoacoustic device. The housing has an interior chamber. The second thermoacoustic device has a stack disposed in the interior chamber and a nuclear heat source spaced from the stack of the second thermoacoustic device. The nuclear heat source of the second thermoacoustic device may be a further portion of nuclear fuel in one of the nuclear fuel rod housings or, alternatively, the nuclear heat source of the second thermoacoustic device may be a high energy absorber. Certain embodiments of a system in accordance with the present invention may further include a second thermoacoustic device responsive to a temperature in the container, with this device including a housing defining an interior chamber, the housing being at least partially disposed in the nuclear container such that the high temperature end is in thermal communication with the nuclear fuel. The second thermoacoustic device has a stack with a hot end and a cold end, and the stack is disposed in the interior chamber between the high and low temperature ends of the housing and positioned such that an acoustic wave is produced in the interior chamber when there is at least a critical temperature gradient in the stack. A nuclear heat source is disposed in the interior chamber at the high temperature end of the housing and is spaced from the hot end of the stack. The nuclear heat source in one of the thermoacoustic devices is a portion of the nuclear fuel and the nuclear heat source of the other of the thermoacoustic devices is a high energy absorber. In certain embodiments of the present invention, the high temperature material is an at least partially liquefied material, and this material may be metal or glass. In certain embodiments in the present invention, the housing of the thermoacoustic device is at least partially disposed in the containment wall such that the high temperature end is in thermal communication with the high temperature material and the low temperature end is in thermal communication with an environment external to the container. In some version of the present invention, the housing of the thermoacoustic device is closed on the high temperature end and open to the environment on the low temperature end. In certain embodiments of the present invention, the thermoacoustic device lacks heat exchangers. In accordance with a further aspect of the present invention, a method is provided for monitoring the temperature of high temperature process. The method comprises providing a thermoacoustic device, wherein the device includes a housing defining an interior chamber. The housing has a high temperature end and a low temperature end. The housing is configured such that an acoustic wave is produced in the interior chamber of the housing when there is at least a sufficient temperature differential between the high and low temperature ends of the housing. A frequency of the acoustic standing wave depends on an effective temperature in the interior chamber. The housing of the thermoacoustic device is at least partially disposed in a high temperature container in which the high temperature process occurs. The high temperature end of the housing is in thermal communication with the high temperature process. The frequency of the acoustic standing wave is monitored. In certain embodiments of the method, the thermoacoustic device further includes a stack having a hot end and a cold end. The stack is disposed in the interior chamber between the high and low temperature ends of the housing and positioned such that the acoustic wave is produced in the interior chamber when there is at least a critical temperature gradient in the stack. A nuclear heat source is disposed in the interior chamber at the high temperature end of the housing and is spaced from the hot end of the stack. In accordance with a further embodiment of the present invention, a nuclear thermoacoustic device includes a housing defining an interior chamber and a portion of nuclear fuel disposed in the interior chamber of the housing. A stack has a hot end and a cold end and is disposed in the interior chamber of the housing and spaced from the portion of nuclear fuel with the hot end directed toward the portion of nuclear fuel. The stack and portion of nuclear fuel are positioned such that an acoustic standing wave is produced in the interior chamber when there is at least a critical temperature gradient in the stack. A frequency of the acoustic standing wave depends on an effective temperature in the interior chamber. The device may be a fuel rod and the housing may be a fuel rod housing. The frequency of the acoustic standing wave may further depend on the molecular mass of the gas mixture in the interior chamber, with the gas mixture changing as the fission products of the nuclear fuel are evolved. The stack may be a ceramic element with an array of parallel channels. In some embodiments, the thermoacoustic device lacks heat exchangers. In accordance with yet a further embodiment of the present invention, a nuclear fuel rod with the thermoacoustic device includes a housing having a resonance chamber defined therein and a nuclear heat source disposed in the housing. The device is configured such that an acoustic standing wave is produced in the interior chamber when there is at least a sufficient temperature differential between the high and low temperature ends of the housing. In some versions, a thermoacoustic stack is disposed in the housing. The nuclear heat source may be a portion of the nuclear fuel disposed in the housing. In some versions, the thermoacoustic device lacks heat exchangers. The present invention provides various embodiments of thermoacoustic devices for use with high temperature processes, such as self-powered monitoring of a nuclear fuel-rod, system or process. A thermoacoustic device may be integral with a nuclear fuel-rod or a separate device with a nuclear heat source, such as a fuel pellet or an absorber of high energy radiation (i.e. a gamma absorber). Various non-limiting examples of devices in accordance with the present invention will be discussed herein. FIG. 1 provides a schematic view of a generic nuclear power system, to assist in explaining how certain embodiments of the present invention may be utilized. The system 10 includes a reactor core 12 housed in a nuclear container 14. The core includes a plurality of nuclear fuel rods 16 and control rods 18. A coolant of some type fills the inside 20 of the nuclear container 14 for extracting heat from the nuclear fuel rods 16. In some reactors, the coolant is liquid water, typically under high pressure, while in other reactors coolants such as liquid sodium are used. The coolant circulates through a primary loop 22 into a heat exchanger 24. In this example, water fills the heat exchanger 24 and the heat from the primary loop 22 turns the water to steam, which is guided through a secondary loop 26. The steam drives a steam turbine and electric generator 28, thereby producing electrical power. In this example, the secondary loop continues into a secondary heat exchanger 30 where heat is extracted from the steam, returning it to the liquid state. As known to those of skill in the art, nuclear power systems may take a wide variety of forms. The version discussed above is not limiting on the present invention. The nuclear fuel in a nuclear power system typically is housed in nuclear fuel rods, which are supported in a fuel rod cluster. FIG. 2 is a perspective view of an exemplary nuclear fuel rod cluster that may be used with or form part of certain embodiments of the present invention. The fuel rod cluster 40 includes a support structure 42, which in this example includes multiple support grids 44, each with multiple openings for receiving fuel rods 46. The support grids 44 support the rods 46 in a generally parallel arrangement, with the rods spaced apart to allow coolant to circulate around the rods. The number of fuel rods 46 in the support structure 42 may be changed depending on the desired performance of the nuclear power system. The cluster 40 is merely an example of an approach to supporting nuclear fuel rods. Referring now to FIG. 3, an embodiment of a thermoacoustic device is shown at 50. The device 50 includes a housing 52 defining an interior chamber 54, which acts as an acoustic resonator. In this version, the housing 52 is generally cylindrical with a cylindrical side wall 56 extending between two end walls 58 and 60. A nuclear heat source 62 is disposed in the interior chamber adjacent the end wall 58. A stack 64 is disposed in the interior chamber and is spaced from the nuclear heat source 62. The nuclear heat source heats the proximal end of the stack, which may be referred to as a hot end 66. The distal end 68 of the stack 64 may be referred to as a cold end, though the terms “hot” and “cold” are merely intended to reflect the relative temperatures of the two ends of the stack. The “cold” end may be at a temperature well above ambient, but lower than the “hot” end during operation of the thermoacoustic device. The housing 52 may be said to have a high temperature end 70 and a low temperature end 72, with the nuclear heat source 62 being disposed in the interior chamber at the high temperature end. The nuclear heat source 62 heats the hot end 68 of the stack as well as the surrounding portions of the housing 52. In operation, the housing 52 is immersed in a coolant such that heat is removed from the outer surface of the housing 52. Both the high temperature end 70 and low temperature end 72 are exposed to the coolant, but the high temperature end of the housing will be at a higher temperature than the low temperature end due to the heating from the nuclear heat source 62. If desired, the high temperature end 70 may be at least partially insulated from the surrounding coolant, to further increase the temperature of the high temperature end 70. The cold end 68 of the stack 64 will be at a lower temperature than the hot end 66 as heat flows out of the low temperature end 72 of the housing 52. Because of the temperature gradient across the stack 64, heat flows through the stack from the hot end to the cold end. The stack 64 is a porous thermoacoustic element that converts a portion of this heat flow or temperature gradient into an acoustic standing wave within the resonator defined by the interior chamber 54. The stack may take a variety forms. In the illustrated embodiment, the stack is a ceramic element that has a regular array of parallel channels. The channels may have a round or square cross-section, or other shapes. Other stack types include a metal spiral, metal foam, metal felt, ceramic or carbon foam, or honeycomb structure. The temperature gradient developed across the stack will convert some of the heat flow to a high-amplitude standing wave within the resonator. As known to those of skill in the art, the conversion of the heat flow to an acoustic standing wave occurs when there is a temperature gradient along the stack that exceeds the critical temperature gradient in the stack. Put another way, the acoustic standing wave is created when there is at least a critical temperature gradient in the stack. This may also be expressed as a sufficient temperature differential between the hot and cold ends of the stack. A sufficient temperature differential is one that is sufficient to cause the conversion of at least a portion of the heat flow to an acoustic standing wave. In typical thermoacoustic devices or engines, a heat exchanger is provided at each end of the stack. As shown, the thermoacoustic device 50 does not have a heat exchanger at either end. Further explanation of this will be provided below. Alternative embodiments could be provided with one or more heat exchangers, but preferred embodiments lack such exchangers. In some versions, the nuclear heat source 62 is a fuel pellet that provides heat by radioactive decay or nuclear fission. This version is a nuclear fuel rod, though the amount of fuel in the illustrated embodiment is significantly less than in a typical fuel rod. The stack converts a small fraction of the heat flux into a high-amplitude acoustic standing wave. Electromagnetic radiation from the fuel pellet 62 is represented by waves at 74. The electromagnetic radiation 74 heats the hot end 66 of the stack 64, and a portion of the resulting heat flux through the stack is converted to an acoustic standing wave. As will be explained in more detail below, the frequency of the acoustic standing wave will depend on a number of factors. First, the frequency will change with the temperature inside the chamber 54. This is because the speed of sound varies with temperature. However, the temperature in the chamber is not uniform, with some areas being much hotter than others. As such, the speed of sound is also not uniform. For simplicity, the temperature in the chamber will be referred to as an effective temperature, with the effective temperature being the temperature at which a same-sized idealized resonator would produce the same frequency. As will be clear to those of skill in the art, the effective temperature may be calculated as an integrated or weighted average of the temperature in the chamber. Calculations and experimental results show that the frequency of the acoustic standing wave increases with the effective temperature in the chamber, allowing the frequency to be used to determine the temperature. The frequency of the standing acoustic wave will also depend on the mean molecular mass of the gas mixture in the interior chamber 54, as will be explained in more detail below. As the nuclear fuel pellet 62 decays, fission products are evolved and these fission products will alter the gas mixture and the resulting mean molecular mass of the gas mixture. Experiments show that the frequency of the acoustic standing wave is directly correlated to the ration of the square root of the polytropic coefficient, γ=cP/cV, to the mean molecular mass, M, of the gas. As such, the frequency may be used to provide information about the gas mixture. The high-amplitude acoustic standing wave in the chamber 54 produces a gas pumping effect, referred to as acoustic streaming, generally represented by the gas circulation streamlines 76. This acoustic streaming provides convective heat transfer from the cold end 68 of the stack 64 to the walls of the housing 52, which are cooled by the coolant surrounding the housing. Unlike with a typical thermoacoustic engine, an ambient-temperature (exhaust) heat exchanger is not required at the cold end of the stack. The acoustic streaming actually increases the heat transfer from the nuclear fuel to the surrounding coolant, as compared to a fuel rod without the thermoacoustic elements. This embodiment of the present invention exploits the standing sound wave to both enhance the heat transfer through the fuel-rod to the surrounding coolant or heat transfer fluid and to provide information about the physical status of the fuel-rod's interior that may include the temperature of the gas contained within the fuel-rod, the condition of the fuel pellets (e.g., the extent of crack formation), and the rate of production of radioactive decay products (e.g., krypton or xenon gas). Since this information is “encoded” by the frequency and/or amplitude of the sound produced within the fuel-rod by the thermoacoustic heat engine, that information can be transmitted by sound radiated from the fuel-rod and transmitted through the surrounding heat transfer fluid. Such “acoustic telemetry” can be particularly useful when there is a reactor incident or accident that is accompanied by the interruption of electrical service required to power a conventional sensor (e.g., thermocouple, thermistor) or provide the electronic telemetry link to the reactor's operators. Information about the fuel-rod's status (e.g., temperature) could be obtained by reception of the sound, therefore being entirely independent of electrical service, since the sound is generated directly from the heat produced by the nuclear fuel. The acoustic signal may be picked up by a remote microphone or hydrophone, or by an operator listening to the signal from within the coolant, or by a geophone or accelerometer attached to an exterior surface of the containment vessel 14. In an alternative embodiment of the present invention, the nuclear heat source 62 is a high energy radiation absorber, such as a gamma absorber. FIG. 3 may also represent this embodiment, with the high energy radiation absorber being represented at 62. In this embodiment, the thermoacoustic device 50 is disposed in a nuclear system close enough to nuclear fuel to be exposed to high energy radiation. The radiation is absorbed by the absorber 62, causing the temperature of the absorber to rise. The hot absorber then heats the hot end 66 of the stack by radiant, convective and/or conductive heating. The device 50 otherwise operates as previously described. However, unlike in the embodiment with nuclear fuel as the heat source, the high energy radiation absorber does not evolve fission gases, and therefore the mean molecular mass of the gas mixture in the chamber does not change. As such, changes in frequency of the acoustic standing wave are attributable to changes in temperature and not to changes in molecular mass of the gas mixture or changes in the nuclear fuel. In one embodiment of the present invention, two or more thermoacoustic devices are disposed in a nuclear system with some of the devices having a portion of nuclear fuel (such as a fuel pellet) as the nuclear heat source and some having a high energy absorber as the heat source. The two types of thermoacoustic devices will react differently over time. The temperature of the high energy absorber will depend on the quantity of high energy radiation emitted by the nuclear fuel in proximity to the absorber, which will be the fuel in surrounding fuel rods. The acoustic frequency of this device will depend on the absorber temperature and the temperature of the coolant around the housing. The device with nuclear fuel as a heat source will produce an acoustic wave whose frequency depends on the condition of the nuclear fuel contained therein, including the mean molecular mass of the gas mixture and the cracking of the fuel, and the temperature in the chamber, which is a product of the radiative heating of the stack and the temperature of the coolant. Referring again to FIG. 2, a first thermoacoustic device is shown at 78 and a second thermoacoustic device is shown at 80. These devices may have different types of nuclear heat sources so as to provide different types of information. Referring now to FIG. 4, a further embodiment of a fuel rod is shown at 82. As shown in FIG. 2, a typical fuel rod is an elongated cylinder. Some may have a length of approximately twelve feet, though other lengths are used. As known to those of skill in the art, such rods include portions of nuclear fuel and space for fission gas products. They may also include structures for positioning or applying force to the fuel. FIG. 4 illustrates the end portions of a rod 82, each of which includes a thermoacoustic device as discussed previously. As shown, a portion of nuclear fuel 84 is present in the end portions and stacks 86 are disposed outboard of the fuel 84. Alternatively, thermoacoustic devices may be provided in other locations in a fuel rod. As a further alternative, one end of the fuel rod may be sealed off from the fuel and a thermoacoustic device may be provided in this area with a high energy radiation absorber as the heat source. This provides a fuel rod with both types of thermoacoustic device discussed above, one with nuclear fuel as the heat source and one with a high energy absorber as the heat source. Embodiments of the present invention are also useful in various high temperature processes and systems. For example, glass and metal are processed at high temperatures, and the temperatures often require careful and accurate monitoring. Embodiments of the present invention include high temperature systems and processes with a thermoacoustic device responsive to temperature in the system or process. Exemplary systems will be described, but other systems will be clear to those of skill in the art. FIG. 5 is a schematic of a portion of a glass melt system including thermoacoustic devices. The glass melt system 90 includes a high temperature container 92 for containing the melted or melting glass. The container 92 has a containment wall 94 defining the bottom, sides and top of the container 92. Glass, as the high temperature material, is shown in the bottom of the container 92. As known to those of skill in the art, the glass may go through different areas of the melt system and may be circulated in various ways. In FIG. 5, an inlet is shown at 96, with raw materials being added through this inlet. The glass may be heated in various ways, such as heating of the container, heating elements within the glass, combustion of gas above the glass and other methods known to those of skill in the art. Typically, thermocouples are used for monitoring the temperature in the container, but the thermocouples require electrical leads that penetrate the wall 94 of the container 92 and may become unreliable. The effort of replacing a thermocouple or fixing the electrical leads is expensive and is impossible to do while the melter is operating. In accordance with the present invention, one or more thermoacoustic devices are provided and are responsive to a temperature in the container 92. A plurality of such thermoacoustic devices are indicated at 98. FIG. 6 provides a cross sectional schematic of one thermoacoustic device 98, installed such that it extends through the wall 94. The thermoacoustic device includes a housing 100 having a high temperature end 102 and a low temperature end 104. The housing is at least partially disposed in thermal communication with the high temperature material, which is molten glass in this example. In this embodiment, the housing 100 penetrates the containment wall 94 so that the high temperature end 102 is in the glass melt, thereby providing direct thermal contact. The housing 100 has an interior chamber 106 defined therein. A stack 108 is disposed in the interior chamber 106 and is spaced from the high temperature end 102 of the housing 100. The stack has a hot end 110 directed toward the high temperature end 102 of the housing 100 and a cold end 112 directed toward the low temperature end 104. The stack may take a variety of forms, as discussed before. In the illustrated embodiment, the low temperature end 104 of the housing 102 is open to the ambient environment outside the high temperature container 92. The housing may be generally cylindrical. Alternatively, other shapes may be used, and the low temperature end may be closed rather than open. In the embodiment with the open low temperature end 104, the housing 100 is disposed in the containment wall such that approximately two-thirds of the housing is in thermal contact with the glass and approximately one-third is external to the container 92. As discussed with earlier embodiments, the temperature gradient across the stack 108 is partially converted to a high amplitude standing acoustic wave. In this version, the housing has a length equal to three-quarters of a wavelength of the acoustic wave, and the stack is positioned just outboard of the containment wall 94. In operation, the thermoacoustic device 98 produces an acoustic standing wave when there is a sufficient temperature differential between the hot and colds ends of the stack, creating at least a critical temperature gradient in the stack. The frequency of the standing wave varies with the integrated average temperature in the chamber 106. This acoustic wave may be heard in the open air around the container and may be picked up by a microphone 114 near the device 98, such as positioned in the side of the housing 100 near the low temperature end 104 or at a remote location, as shown in phantom lines representing alternative locations. In this way, no electrical wiring need penetrate the container 92. As with the earlier embodiment, the thermoacoustic device 98 does not have a heat exchanger at either end. Alternative embodiments could be provided with one or more heat exchangers, but preferred embodiments lack such exchangers. FIG. 7 shows an alternative “stackless” thermoacoustic device 116. It is similar to the device 98 in FIG. 6, but operates without a stack. As known to those of skill in the art, such a stackless thermoacoustic device may be known as a Sondhauss tube or Taconis device. Such a thermoacoustic device will create a standing acoustic wave when there is a sufficient temperature differential between the ends of the housing. Such a stackless thermoacoustic device may be used in any embodiment of the present invention, though versions with stacks are generally preferred as having improved efficiency. FIG. 8 shows a further alternative thermoacoustic device 118, which is similar to the device 98 in FIG. 6, but has a closed end 119 at the low temperature end of the housing. For some embodiments of the present invention, an open low temperature end is preferred, as it allows increased exposure to the temperature in the surrounding environment. However, a close ended housing may be substituted for a open ended housing in any embodiment herein, and vice versa. It should also be noted that, while the thermoacoustic devices are illustrated herein as generally cylindrical, the housings may be any shape. FIG. 9 provides a schematic of a portion of a metal processing system 120 including thermoacoustic devices in accordance with a further embodiment of the present invention. The illustrated system represents a continuous casting process, though the present invention may be part of other metal processing systems, or other high temperature processes. FIG. 9 illustrates a ladle 122 filled with liquefied metal 124. The metal flows into a tundish 126 and then into a mold 128. A plurality of thermoacoustic devices 130 are provided in various locations, for monitoring the temperatures in these locations. Each thermoacoustic device may be as described in FIG. 6 or may take other forms. Referring back to FIG. 1, the nuclear power system 10 also may be considered a system for high temperature materials. In this case, the high temperature material is the nuclear fuel and the thermoacoustic devices are disposed inside the vessel 14. FIG. 10 provides a diagram of a generic high temperature process or system 150 having a high temperature container 152 with a containment wall 154. The container may be open or closed. A high temperature material 156 may be disposed in the container 152. A thermoacoustic device is shown at 160 and another at 162. The devices 160 and 162 are at least partially disposed in the container so as to be in thermal communication with the process or material 156 therein. The device 160 penetrates the containment wall 154 so that the high temperature end is in thermal communication with the material 156 and the low temperature end is in thermal communication with the environment outside of the container. The device 162 is entirely disposed in the container 152. In this version, the two ends must have different temperature environments in order to have a sufficient temperature differential in the interior chamber. In the nuclear example discussed above, the high temperature end has a nuclear heat source, though other approaches may be used to create a sufficient temperature differential. For example, a process my have different temperature zones within a common container, and the two ends may be in different zones. Alternatively, one or more heat exchangers may be used to exhaust heat from the cold end of a stack or the low temperature end of the housing. The diagram of FIG. 10 may represent the nuclear system or metal or glass melt systems discussed above, as well as other high temperature processes or systems. Additional examples include chemical processes such as cracking and gasification. We turn now to a more detailed explanation of some of the science behind certain embodiments of the present invention, with particular emphasis on the versions for use with nuclear systems, having a portion of nuclear fuel in the thermoacoustic device or engine. Simple explanations of the operation of thermoacoustic standing-wave heat engines are readily available. This section will focus on the aspects of the fuel-rod thermoacoustic engine that are new and particular to this implementation. At the most basic level, there are two significant differences between a fuel-rod engine such as shown schematically in FIG. 3 and a generic standing-wave thermoacoustic engine. Both engines have a “stack” where the thermoacoustic effect converts heat flow into sound production. The difference is that the fuel-rod engine lacks both a hot and ambient-temperature (exhaust) heat exchanger. The lack of a physical hot heat exchanger structure in the fuel-rod thermoacoustic engine is possible due to the high temperatures produced by the fuel or other heat source generated by another industrial process. The transfer of heat from the fuel pellets to the hot end of the stack can be accomplished efficiently by electromagnetic (thermal) radiation. At the simplest level, radiative heat transfer from the fuel pellets to the hot end of the stack is governed by the Stefan-Boltzmann Law:Eb=σT4 (1)The total radiant energy emitted by a “black body”, Eb, is proportional to the fourth-power of the absolute (Kelvin) temperature T of the radiating surface where σ≡[π2kB4/60h3c2]=5.67×10−8 W/m2−oK4. The actual expression for the heat transfer is more complicated than Eq. (1), since it involves the area of both the hot end of the stack Ast and its absolute temperature Tst, as well as the effective radiating area Ahot of the heat source (e.g., fuel pellet) and its temperature Thot. It is also necessary to introduce the electromagnetic emissivities εst of the hot end of the stack, the heat source, and the hot end of the resonator, to account for the deviation in the radiative properties of the hot surfaces from the ideal black-body behavior (i.e., complete emission and absorption at all wavelengths). The net rate of heat transfer to the hot end of the stack Qhot is determined by the difference in the stack hot-end temperature, Tst, which determines the steady-state re-radiation of heat back to the heat source, and the temperature of the heat source, Thot.Qhot=σ[εhotAhotThot4−εstAstTst4] (2) Again, Eq. (2) is a simplification that creates an effective hot surface emissivity εhot, which averages over the various surfaces and their conditions (e.g., polished, oxidized, rough, etc.) and the range of electromagnetic wavelengths, and an effective hot radiating area Ahot. That effective area averages over all propagation angles of the electromagnetic radiation. Similar approximations have been made to characterize the effective emissivity of the stack's hot end εst, and the area Ast, which is related to the cross-sectional area of the stack. The significant result of the simplified expression for the heat transfer rate Qhot in Eq. (2) is that the heat transfer from the fuel to the hot end of the stack is proportional to the absolute temperatures raised to the fourth power. At the high temperatures created by the radioactive decay of the fuel pellets, electromagnetic radiative heat transfer is a very efficient way to heat the hot-end of the stack. For that reason, no separate hot heat exchanger is required, unlike a typical system described by Swift in 1992. To validate the operation and effectiveness of the present invention, an experimental prototype of a thermoacoustic device was constructed. A high temperature end of the thermoacoustic device was heated with a heating element, to simulate the heat that would otherwise be provided by the nuclear heat source. The stack was a Celcor (an extruded cordierite ceramic product produced by Corning Environmental Technologies) ceramic stack with 1,100 cells/in2, and was indirectly heated by the heating element. The resonator contained air at a mean pressure pm=125 kPa. The air temperature at the ambient end of the resonator was controlled by a water bath surrounding the resonator and remained at 24° C. throughout an experimental run. Once a sufficient temperature differential was established across the stack, there was an onset of thermoacoustic oscillations. After onset, the temperature difference became fairly stable at ΔT=326±14° C. The average frequency of the thermoacoustically-generated standing wave was f=885±9 Hz. Another feature of the fuel-rod thermoacoustic engine is the absence of an ambient-temperature heat exchanger, such as a water-cooled version that may be used in a typical thermoacoustic engine described by Swift in 1992. The purpose of the ambient-temperature (cold) heat exchanger is to exhaust waste heat from the end of the stack so that the temperature gradient across the stack is maintained. Maintenance of that temperature gradient across the stack is required for the conversion of heat to sound produced by the thermoacoustic processes within the stack. The fuel-rod thermoacoustic resonator is able to eliminate the ambient-temperature heat exchanger because the high-amplitude acoustic standing wave generates a streaming flow of gas. The pattern of this acoustically-induced steady flow is a collection of streaming cells that drives gas flow in one direction near the center of the resonator's axis and in the opposite direction along the walls of the resonator. This is illustrated by the arrows 76 in FIG. 3. The acoustically-generated streaming flow carries heat away from the ambient-temperature end of the stack and transports the gas along the resonator wall to efficiently transfer the heat to the wall that is in excellent thermal contact with the surrounding heat conduction fluid, usually water. Acoustical streaming also takes place within the pores of the stack. Although this streaming has a small influence on the temperature distribution along the stack, it is not important in this context. This acoustically-induced streaming in a Kundt's tube that supported a standing-wave was first observed and reported by Dvo{hacek over (r)}ák in 1876. It was explained by J. W. Strutt (Lord Rayleigh) in 1883. The time-averaged, second-order steady flow in the axial direction <u2> and in the transverse (radial) direction <v2> were calculated by Rayleigh from the amplitude of the first-order acoustical velocity u1 for a standing wave of wavelength λ in a gas with sound speed c, where x is the position along the axis of the resonator and r is the radial distance from the axis in a toroidal streaming cell of length L. 〈 u 2 〉 = 3 8 ⁢ u 1 2 c ⁢ ( 1 - 2 ⁢ ⁢ r 2 R 2 ) ⁢ sin ⁡ ( π ⁢ ⁢ x L ) ( 3 ) 〈 v 2 〉 = 3 8 ⁢ u 1 2 c ⁢ 2 ⁢ ⁢ π ⁢ ⁢ r λ ⁢ ( 1 - r 2 R 2 ) ⁢ cos ⁡ ( π ⁢ ⁢ x L ) ( 4 ) Rayleigh's theory was extended by Nikolas Rott to include (i) the acoustic temperature fluctuations T1 caused by the acoustic pressure, p1, (T1/Tm)=[(γ−1)/γ](p1/pm); (ii) the thermal boundary layer with thickness δκ=(2κ/ρcPω)½, where κ is the thermal conductivity of the gas, ρ is the gas density, cP is the gas specific heat at constant pressure, the polytropic coefficient γ=cP/cV, and ω=2πf; (iii) the variation of mean temperature Tm with respect to the axial coordinate x; and (iv) the dependence of viscosity μ and thermal conductivity κ on temperature, assuming the form for the viscosity of μ (T)∝Tβ, where β is a constant (typically about 0.7) that depends on the properties of the fluid. These considerations modify the axial component of the time-averaged streaming velocity from the Rayleigh result of Eq. (3). 〈 u 2 〉 = ( 1 + α 1 ) ⁢ 3 8 ⁢ u 1 2 c ⁢ ( 1 - 2 ⁢ ⁢ r 2 R 2 ) ⁢ sin ⁡ ( π ⁢ ⁢ x L ) ( 5 ) α 1 = 2 3 ⁢ ( 1 - β ) ⁢ ( 1 - γ ) ⁢ P r 1 + P r ( 6 ) The Prandtl number, Pr=μcP/κ=(δv/δκ)2, is the dimensionless ratio of the fluid's ability to transmit viscous shear to its ability to transfer heat by thermal conduction (e.g., for molasses Pr is very large and for mercury Pr is very small). Thompson and Atchley used laser Doppler anemometry to measure the time-averaged acoustically-driven streaming flow outside the viscous boundary layer as a function of a dimensionless parameter that they designated as the nonlinear Reynolds number, Re. R e = 2 ⁢ ( u 1 c ) 2 ⁢ ( R δ v ) 2 ( 7 ) They identified two cases corresponding to slow streaming (Re<<1) that is described by Rott in Eqs. (5) and (6) and others and “nonlinear streaming” characterized by Re>˜1. A relevant result for heat transfer enhancement by thermoacoustically-driven streaming in the fuel-rod thermoacoustic engine can be deduced. The classical theory for the time-averaged streaming velocity works quite well up to relatively high amplitudes, but even where the classical theory breaks down, the velocity profile near the resonator's walls is still well-represented by the classical results of Eq. (5). Since it is the streaming velocity near the resonator's walls that controls the heat transfer (i.e., the Nusselt number) from the gas to the heat transfer fluid surrounding the resonator, the classical theory should be adequate for sound pressure levels expected to be generated thermoacoustically within the fuel-rod resonator. If one measures the normalized time-averaged axial streaming velocity <u2>/M2co=<u2>co/u12 as a function of radial position in the tube using laser Doppler anemometry in a tube with radius R=23 mm at f=310 Hz, in air with the thermodynamic sound speed co, the profile is generally parabolic. At this amplitude, Re=5.7, the classical theory of Eqs. (5) and (6) provides an accurate description of the parabolic flow profile. For this measurement, the peak acoustic p1=ρcou1=900 Pa, hence p1/pm=0.9%. The normalized time-averaged axial streaming velocity <u2>/M2co=<u2>co/u12 as a function of radial position in a tube measured using laser Doppler anemometry at f=310 Hz, in air with the thermodynamic sound speed co has a profile that is less parabolic. At this amplitude, Re=19, there is substantial deviation from the classical theory of Eqs. (5) and (6). Although this deviation is substantial near the tube's axis, the behavior of the velocity in the region closest to the resonator's walls, r/R≲±1, the flow field is rather close to the classical prediction. For this measurement, the peak acoustic p1=?ρcou1=1.64 kPa, hence pl/pm=1.7%. The measured root-mean-square acoustic pressures ranged from 400 to 750 Parms so the range of peak acoustic pressure is 1.1 kPa>p1>570 Pa, corresponding to 1.1%>p1/pm>0.6%, which is within the range of measurements for streaming velocity discussed above. Heat can be transferred from higher temperatures to lower temperatures by three mechanisms: conduction, convection, or radiation. Radiation has already been treated in the discussion of the transfer of heat from the fuel pellets to the hot-end of the thermoacoustic stack. In general, heat transfer by convection of a moving fluid is always more efficient than by conduction by the same stagnant fluid. The influence of sound on heat transfer is a problem that has generated considerable experimental and theoretical interest. An early estimate of acoustical effects that enhance heat transfer was made by Westervelt in 1960. His treatment was based on earlier experiments for acoustical flow around a cylinder. Mozurkewich studied the effect of sound on heat transfer specifically related to thermoacoustics, but also focused on cylindrical objects in the sound field. All of these investigations, as well as others, attribute enhanced heat transfer to the presence of streaming. Westervelt proposed a critical Reynolds number Rc for the onset of acoustically-enhanced heat transfer arguing that when the acoustical particle displacement x1=v1/ω exceeded the thickness of the viscous boundary layer δv=(2μ/ρω)1/2=(2v/ω))1/2, then streaming brings fresh fluid to the heat transfer surface and sweeps away the previous fluid parcel, along with the heat it had collected. R c = v 1 2 ω ⁢ ⁢ v = ( x 1 δ v ) 2 ( 8 ) It is expected that the presence of a standing wave will enhance heat transfer because (i) the sound wave will cause the gas in the acoustically-driven resonator to exhibit steady flow (streaming) and because (ii) the heat that drives the thermoacoustic resonance will be transported along the “stack” and part of that heat will be converted to (acoustic) work. That work will also be dissipated at the resonator walls due to thermoviscous losses and will be transmitted out of the resonator through the resonator walls that are presumed to be in thermal contact with a surrounding pool of water. Preliminary measurements were made with an earlier thermoacoustic engine prototype known as the “Submersible Thermoacoustic Resonator” (Submersible). Those measurements indicated that the heat transfer from the inside of the resonator to the surrounding water was enhanced by the presence of the thermoacoustically-generated standing wave. Subsequently, more careful measurements were made that allowed the standing wave sound field to be suppressed without changing any other experimental parameters and was thus able to quantify both thermoacoustically-mediated heat transfer enhancement mechanisms (i.e., increased heat transfer through the stack and increased heat transfer from the gas to the resonator walls and into the surrounding heat transfer fluid). The speed of sound c in an ideal gas is a function of the gas properties and the absolute (Kelvin) temperature. c = γ ⁢ ⁢ ⁢ ⁢ T M ( 9 ) The polytropic coefficient, γ=cP/cV, and the mean molecular mass, M, depend upon the gas. For a binary gas mixture with species of molecular mass M1 and concentration x1 and mass M2, with concentration x2=(1−x1), the mean molecular mass is M=x1M1+(1−x1)M2. In a standing-wave resonator that does not have a uniform temperature, like the fuel-rod resonator (e.g., hot gas near the fuel behind the stack but close to ambient temperature gas ahead of the stack), then the effective sound speed, ceff, defined in terms of the frequency f1 for the fundamental (i.e., approximately one-half wavelength within the full length of the resonator, L) depends upon the temperature distribution.ceff=2Lf1 (10) Substitution of Eq. (10) into Eq. (9) suggests that the frequency of the sound generated by the thermoacoustic engine divided by the square-root of the absolute temperature T should be an invariant since the dimensions of the resonator do not depend on temperature: f1/√T=constant. Experimental data demonstrated that f1/√T remains constant when T is based on the absolute gas temperature on the ambient-temperature side of the resonator. It is easier to understand the relationship between sound speed, frequency, and temperature if the standing-wave resonator is conceptualized as consisting of three sections: two gas springs representing the gas trapped at the ends against the rigid ends and an inertial “gas mass” in the center section that is experiencing simple-harmonic-motion that is restored by the stiffness of the two gas springs at the ends. The effective stiffness of the gas spring is related to the inverse of the compliance C of the gas in the two end portions. C = V γ ⁢ ⁢ p m ( 11 ) In Eq. (11), V is the volume each of the two sections of the resonator acting as the gas springs. In this approximation V=AL/3, where L is the overall length of the resonator and A is the resonator's cross-sectional area, presumed in this case to be independent of position. γpm is the product of the ratio of specific heats (i.e., the polytropic coefficient of the gas) times the mean gas pressure. An equivalent circuit approximation to a standing-wave resonator consists of two “gas springs” represented by the two capacitors and a “gas mass” represented by the inductor between the springs. In this approximation, the acoustic pressure amplitudes in the springs are constants of opposite sign represented by Re[p1], where Re[ ] indicates the real value of a complex quantity. The gas volume-velocity amplitude is constant and −90° out-of-phase and decreases linearly to zero as it must when the gas approaches the rigid ends of the resonator. The effective inertance L of the gas mass in the center of the model can be expressed in terms of the length of the “gas mass”0 section Δx=L/3 in this approximation and the cross-sectional area of the resonator, A. L = ρ m ⁢ Δ ⁢ ⁢ x A ( 12 ) If one recognizes that the stiffness (k∝C−1) of the two equivalent gas springs depends only upon the mean pressure pm of the gas in the resonator and the equivalent mass (m∝L) is proportional to the density of the gas ?ρm, but only in the center section. Since the pressure pm is constant throughout the resonator, the resonance frequency f1∝(k/m)1/2, will depend upon the gas density in the center section, hence the temperature in the center. Although a lumped-element approximation is not precise, it is possible to use computer modeling software to calculate the resonance frequency precisely, since the software actually integrates the wave equation throughout the entire thermoacoustic resonator. Such a computer model was applied to a fuel-rod thermoacoustic sensor (engine) and it allowed the calculation of the entire behavior of the resonator, including the resonance frequency and the temperatures in all segments of the resonator. Based on the results of this model, the sound speed in the hot end of the resonator is c(780° K)=560 m/sec. In the ambient-temperature duct, the sound speed is c(340° K)=370 m/sec. The model calculates the effective length L of the resonator by calculating the entire gas-filled volume of the resonator and dividing by the cross-sectional area of the resonator A=2.4×10−4m2 to produce L=0.195 m. Based on the resonance frequency f1=965 Hz and Eq. (10), the effective sound speed ceff=377 m/sec. As claimed in the approximate lumped-element model, the frequency of the resonance f1 is indicative of an effective sound speed of 377 m/sec which is much closer to the sound speed in the ambient duct (370 m/sec) than that in the hot end of the resonator (560 m/sec). In addition to the frequency of the thermoacoustically-generated standing wave, there is also information about the fuel-rod that can be inferred from changes in amplitude of the radiated sound. The fuel pellets in a fuel-rod are known to degrade over time in a way that produces cracks. Those cracks can have two effects on the standing wave: Since the cracks provide additional volume for the gas, the effective length of the resonator increases and the resonance frequency decreases. In addition, the cracks provide additional dissipative surface area that reduces the amplitude of the sound. By observation of those two changing characteristics of the sound radiated by the thermoacoustic fuel-rod resonator, it might be possible to track the degradation of the fuel pellets over time. Also, it might be possible to excite more than one resonance in a thermoacoustic fuel-rod resonator. Because different modes have different pressure and velocity distributions within the resonator, it might be possible to use the multiplicity of sound frequencies and amplitudes to detect other properties of the gas within the fuel-rod resonator, such as the concentration of radioactive decay products (e.g., krypton or xenon gas). Finally, combinations of resonators, in good thermal contact with each other, could produce different frequencies but one of the resonators would not have any fuel pellets included. The difference in the frequencies of two such resonators could simultaneously provide information about the temperature of both and the presence of decay products in the resonator that contains the fuel pellets. Certain embodiments of the present invention require only the simple addition of a single component (i.e., a thermoacoustic stack) to a nuclear fuel-rod. Unlike other thermoacoustic engines, this embodiment does not require either a hot heat exchanger to deliver heat to the stack or an ambient-temperature heat exchanger to remove the exhaust heat from the stack. Due to the high temperatures produced by the nuclear fuel pellets within the fuel-rod thermoacoustic engine, electromagnetic (thermal) radiation can transport the required heat to the hot end of the stack. The thermoacoustically-induced standing wave that is produced is of sufficient amplitude (see Eqs. (7) and (8)) to create streaming of the gas which efficiently removes the exhaust heat from the ambient-temperature end of the stack and delivers it convectively to the walls of the resonator and thereby to the surrounding heat transfer medium, typically water in a pressurized water reactor or a spent fuel pond. This streaming flow is an acoustic gas circulation pump that requires no moving parts or auxiliary plumbing. As discussed herein, the acoustically-pumped gas circulation significantly enhances the heat transfer efficiency of the fuel-rod resonator over the heat transfer rate of an identical structure that does not support an acoustic standing wave. Since the sound wave can radiate from the fuel-rod resonator to the surrounding fluid, it is possible to detect the amplitude and frequency of the standing sound wave within the fuel-rod resonator remotely without the necessity of providing electrical power either for sensing or for telemetry. As shown, both theoretically and experimentally, knowledge of the frequency of the standing-wave resonance is indicative of the temperature of the fuel-rod and the surrounding heat transfer fluid. There are other parameters of fuel-rod performance and fuel pellet degradation that may be sensed remotely by a thermoacoustic oscillation in a nuclear fuel-rod. Such additional information might involve monitoring of the amplitude, as well as frequency, of the fundamental resonance mode or simultaneous excitation of more than one standing-wave resonance mode in a single resonator. Further information might be remotely accessible by combinations of multiple fuel-rod resonators. Referring now to FIG. 11, a further alternative embodiment of a thermoacoustic device is shown generally at 170. This device 170 may be described as U-shaped, having a housing 172 with two end portions 174 and 176 joined by a connection portion 178. This embodiment acts like two interconnected thermoacoustic devices. In the illustrated version, the two end portions 174 are disposed in thermal communication with a hot material, such as by penetrating the containment wall 180 of the crucible. These end portions each become high temperature ends of the housing and the connecting portion 178 is the corresponding low temperature portion of both thermoacoustic devices. In a version with a stack, stacks 182 and 184 are disposed in the housing 172 between the connecting portion 178 and each end portion 174 and 176. Each stack has a hot end directed toward the high temperature end of the housing and a cold end directed toward the connecting portion. In the illustrated embodiment, the end portions 174 and 176 are each approximately a half wavelength long. A microphone or other sensor, not shown, may be added to the housing, inside or out to pick up the acoustic waves. It is preferred that such a sensor not be positioned at the midpoint of the connection portion 178, since this would be a pressure node. While the device 170 is illustrated as a symmetrical U-shaped housing, other shapes are possible, and the device may be non-symmetrical. For example, one end portion may be a different length than the other. As a further alternative, the orientation of the thermoacoustic device may be flipped such that the connecting portion is the high temperature “end” and the two end portions are outside the credible and are the low temperature ends. The positions of the stacks, if present, would need to be adjusted, as will be clear to those of skill in the art As will be clear to those of skill in the art, the herein described embodiments of the present invention may be altered in various ways without departing from the scope or teaching of the present invention. It is the following claims, including all equivalents, that define the scope of the present invention.
	description	This application is a division of U.S. patent application Ser. No. 13/282,217, filed Oct. 26, 2011, the entire disclosure of which is incorporated by reference herein. The following relates to the nuclear reactor arts, electrical power generation arts, nuclear reactor control arts, nuclear electrical power generation control arts, thermal management arts, and related arts. In nuclear reactor designs for steam generation, such as boiling water reactor (BWR) and pressurized water reactor (PWR) designs, a radioactive reactor core is immersed in primary coolant water at or near the bottom of a pressure vessel. In BWR designs heat generated by the reactor core boils the primary coolant water creating steam that is extracted by components (e.g., steam separators, steam dryer, or so forth) located at or near the top of the pressure vessel. In PWR designs the primary coolant is maintained in a compressed or subcooled liquid phase and is either flowed out of the pressure vessel into an external steam generator, or a steam generator is located within the pressure vessel (sometimes called an “integral PWR” design). In either design, heated primary coolant water heats secondary coolant water in the steam generator to generate steam. An advantage of the PWR design is that the steam comprises secondary coolant water that is not exposed to the radioactive reactor core. In either a BWR design or a PWR design, the primary coolant flows through a closed circulation path. Primary coolant water flowing upward through the reactor core is heated and rises through a central region to the top of the reactor, where it reverses direction and flows downward back to the reactor core through a downcomer annulus defined between the pressure vessel and a concentric riser structure. This is a natural convection flow circuit for such a reactor configuration. However, for higher power reactors it is advantageous or necessary to supplement or supplant the natural convection with motive force provided by electromechanical reactor coolant pumps. In a conventional approach, glandless pumps are used, in which a unitary drive shaft/impeller subassembly is rotated by a pump motor. This design has the advantage of not including any seals at the drive shaft/impeller connection (hence the name “glandless”). For nuclear reactors, a common implementation is to provide a unitary reactor coolant pump comprising the sealless drive shaft/impeller subassembly, the motor (including the stator, a rotor magnet or windings, and suitable bearings or other drive shaft couplings), and a supporting flange that supports the motor and includes a graphalloy seal through which the drive shaft passes to connect the pump motor with the impeller. The reactor coolant pump is installed by inserting the impeller through an opening in the reactor pressure vessel and securing the flange over the opening. When installed, the impeller is located inside the pressure vessel and the pump motor is located outside of the pressure vessel (and preferably outside of any insulating material disposed around the pressure vessel). Although the motor is outside of the pressure vessel, sufficient heat still transfers to the pump motor so that dedicated motor cooling is typically provided in the form of a heat exchanger or the like. External placement of the pump motor simplifies electrical power connection and enables the pump motor to be designed for a rated temperature substantially lower than that of the primary coolant water inside the pressure vessel. Only the impeller and the impeller end of the drive shaft penetrate inside the pressure vessel. Disclosed herein are improvements that provide various benefits that will become apparent to the skilled artisan upon reading the following. In one aspect of the disclosure, an apparatus comprises a pressurized water reactor (PWR) including: a cylindrical pressure vessel with its cylinder axis oriented vertically; a nuclear reactor core disposed in the cylindrical pressure vessel; a separator plate disposed in the cylindrical pressure vessel that separates the pressure vessel to define an integral pressurizer containing a pressurizer volume disposed above the separator plate and a reactor vessel portion defining a reactor volume disposed below the separator plate and containing the nuclear reactor core, wherein the separator plate restricts but does not completely cut off fluid communication between the pressurizer volume and the reactor volume; and a reactor coolant pump including (i) an impeller disposed inside the pressure vessel in the reactor volume, (ii) a pump motor disposed outside of the pressure vessel, and (iii) a drive shaft operatively connecting the pump motor with the impeller, wherein (1) at least a portion of the pump motor is disposed above the separator plate, (2) no portion of the reactor coolant pump is disposed in the pressurizer volume, and (3) the drive shaft passes through an opening in the pressure vessel that is at least large enough to pass the impeller. In another aspect of the disclosure, a method comprises installing a reactor coolant pump comprising a pump motor, a driveshaft, an impeller, and a mounting flange on a pressurized water reactor (PWR) comprising a pressure vessel and a nuclear reactor core disposed in the pressure vessel, the installing including: pre-assembling the pump motor, the driveshaft, the impeller, and the mounting flange outside of the pressure vessel to form a pump assembly as a unit disposed outside of the pressure vessel in which the pump motor is connected with the impeller by the driveshaft; inserting the impeller and the driveshaft of the pump assembly through an opening of the pressure vessel while the pump motor remains outside of the pressure vessel; and securing the flange of the pump assembly to an outside of the pressure vessel to mount the pump assembly on the pressure vessel; wherein the inserting and securing mounts the pump assembly on the pressure vessel with the drive shaft of the pump assembly oriented vertically. In another aspect of the disclosure, the reactor coolant pump of the immediately preceding paragraph further comprises a pump diffuser that is not a component of the unitary pump assembly formed by the pre-assembling, and the installing of the immediately preceding paragraph further comprises disposing the pump diffuser inside the pressure vessel in an operation other than the inserting and the securing operations. In another aspect of the disclosure, an apparatus comprises a reactor coolant pump including a pump assembly and a pump diffuser. The pump assembly includes a pump motor, an impeller, and a driveshaft that operatively connects the pump motor and the impeller as said pump assembly. The pump diffuser is configured to receive the impeller. The pump diffuser is not secured with the pump assembly. In another aspect of the disclosure, an apparatus comprises a reactor coolant pump as set forth in the immediately preceding paragraph, and a pressurized water reactor (PWR) including a cylindrical pressure vessel with its cylinder axis oriented vertically, a nuclear reactor core disposed in the cylindrical pressure vessel, and a separator plate disposed in the cylindrical pressure vessel that separates the pressure vessel to define an integral pressurizer volume disposed above the separator plate and a reactor vessel portion containing the nuclear reactor core disposed below the separator plate. The reactor coolant pump is mounted on the cylindrical pressure vessel of the PWR with the impeller disposed in the pump diffuser and with at least a portion of the pump motor being disposed above the separator plate. No portion of the reactor coolant pump passes through the integral pressurizer volume. In another aspect of the disclosure, an apparatus comprises a reactor coolant pump and a pressurized water reactor (PWR). The reactor coolant pump includes a pump motor, an impeller, a driveshaft that operatively connects the pump motor and the impeller, and a pump diffuser. The pump motor, the impeller, the driveshaft, and the pump diffuser are secured together as a unitary pump assembly with the impeller disposed in the pump diffuser. The PWR includes a cylindrical pressure vessel with its cylinder axis oriented vertically, a nuclear reactor core disposed in the cylindrical pressure vessel, and a separator plate disposed in the cylindrical pressure vessel that separates the pressure vessel to define an integral pressurizer volume disposed above the separator plate and a reactor vessel portion containing the nuclear reactor core disposed below the separator plate. The unitary pump assembly is mounted on the cylindrical pressure vessel of the PWR with at least a portion of the pump motor disposed above the separator plate and with no portion of the reactor coolant pump passing through the integral pressurizer volume. With reference to FIGS. 1-4, a pressurized water reactor (PWR) includes a cylindrical pressure vessel 10. As used herein, the phrase “cylindrical pressure vessel” indicates that the pressure vessel has a generally cylindrical shape, but may in some embodiments deviate from a mathematically perfect cylinder. For example, the illustrative cylindrical pressure vessel 10 has a circular cross-section of varying diameter along the length of the cylinder, and has rounded ends, and includes various vessel penetrations, vessel section flange connections, and so forth. The cylindrical pressure vessel 10 is mounted in an upright position having an upper end 12 and a lower end 14. However, it is contemplated for the upright position to deviate from exact vertical orientation of the cylinder axis. For example, if the PWR is disposed in a maritime vessel then it may be upright but with some tilt, which may vary with time, due to movement of the maritime vessel on or beneath the water. The PWR further includes a diagrammatically indicated radioactive nuclear reactor core 16 comprising a mass of fissile material, such as a material containing uranium oxide (UO2) that is enriched in the fissile 235U isotope, arranged fuel rod bundles or so forth disposed in a fuel basket or other support assembly configured to mount in suitable mounting brackets or retention structures of the pressure vessel 10 (core mounting features not shown). Reactivity control is provided by a diagrammatically indicated control rod system 18, typically comprises assemblies of control rods that are mounted on connecting rods, spiders, or other support elements. The control rods comprise a neutron absorbing material and the control rod assemblies (CRA's) are operatively connected with control rod drive mechanism (CRDM) units that controllably insert or withdraw the control rods into or out of the reactor core 16 to control or stop the chain reaction. As with the reactor core 16, the control rod system 18 is shown diagrammatically and individual components such as individual control rods, connecting rods, spiders, and CRDM units are not shown. The diagrammatically illustrated control rod system is an internal system in which the CRDM units are disposed inside the pressure vessel 10. Some illustrative examples of internal control rod system designs include: Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, U.S. Pub. No. 2010/0316177 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety; and Stambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”, Int'l Pub. WO 2010/144563 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. Alternatively, external CRDM units may be used—however, external CRDM units require mechanical penetrations through the top or bottom of the pressure vessel 10 to connect with the control rods. In its operating state, the pressure vessel 10 of the PWR contains primary coolant water that serves as primary coolant and as a moderator material that thermalizes neutrons. The illustrative PWR includes an integral pressurizer as follows. A separator plate 20 is disposed in the cylindrical pressure vessel 10. The separator plate 20 separates the pressure vessel 10 to define: (1) an integral pressurizer 22 containing a pressurizer volume disposed above the separator plate 20; and (2) a reactor vessel portion 24 defining a reactor volume disposed below the separator plate 20. The nuclear reactor core 16 and the control rod system 18 is disposed in the reactor volume. The separator plate 20 restricts but does not completely cut off fluid communication between the pressurizer volume and the reactor volume. As a result, pressure in the pressurizer volume communicates to the reactor volume, so that the operating pressure of the reactor volume can be adjusted by adjusting pressure in the pressurizer volume. Toward this end, a steam bubble is maintained in the upper portion of the pressurizer volume, and the integral pressurizer 22 includes heater elements 26 for applying heat to increase the temperature (and hence increase pressure) in the integral pressurizer 22. Although not shown, spargers may also be provided to inject cooler steam or water to lower the temperature (and hence pressure) in the integral pressurizer 22. In a PWR the primary coolant water is maintained in a subcooled state. By way of illustrative example, in some contemplated embodiments the primary coolant pressure in the sealed volume of the pressure vessel 10 is at a pressure of about 2000 psia and at a temperature of about 300-320° C. Again, this is merely an illustrative example, and a diverse range of other subcooled PWR operating pressures and temperatures are also contemplated. The reactor core 16 is disposed in the reactor volume, typically near the lower end 14 of the pressure vessel 10, and is immersed in the primary coolant water which fills the pressure vessel 10 except for the steam bubble of the integral pressurizer 22. (The steam bubble also comprises primary coolant, but in a steam phase). The primary coolant water is heated by the radioactive chain reaction occurring in the nuclear reactor core 16. A primary coolant flow circuit is defined by a cylindrical central riser 30 disposed concentrically with and inside the cylindrical pressure vessel 10, and more particularly in the reactor volume. Heated primary coolant water rises upward through the central riser 30 until it reaches the top of the riser, at which point it reverses flow and falls through a downcomer annulus 32 defined between the cylindrical central riser 30 and the cylindrical pressure vessel 10. At the bottom of the downcomer annulus 32 the primary coolant water flow again reverses and flows back upward through the nuclear reactor core 16 to complete the circuit. In some embodiments, an annular internal steam generator 36 is disposed in the downcomer annulus 32. Secondary coolant water flows into a feedwater inlet 40 (optionally after buffering in a feedwater plenum), through the internal steam generator 36 where it is heated by proximate primary coolant in the downcomer annulus 32 and converted to steam, and the steam flows out a steam outlet 42 (again, optionally after buffering in a steam plenum). The output steam may be used for driving a turbine to generate electricity or for some other use (external plant features not shown). A PWR with an internal steam generator is sometimes referred to as an integral PWR, an illustrative example of which is shown in Thome et al., “Integral Helical Coil Pressurized Water Nuclear Reactor”, U.S. Pub. No. 2010/0316181 A1 published Dec. 16, 2010 which is incorporated herein by reference in its entirety. While this publication discloses a steam generator employing helical steam generator tubes, other tube geometries including straight (e.g., vertical) once-through steam generator tubes, or recirculating steam generators, or U-Tube steam generators, or so forth are also contemplated. In embodiments disclosed herein, circulation of the primary coolant water is assisted or driven by reactor coolant pumps (RCPs) 50. With particular reference to FIG. 4, each reactor coolant pump (RCP) 50 includes: an impeller 52 disposed inside the pressure vessel 10 (and more particularly in the reactor volume); a pump motor 54 disposed outside of the pressure vessel 10; and a drive shaft 56 operatively connecting the pump motor 54 with the impeller 52. At least a portion of the pump motor 54 is disposed above the separator plate 20, and no portion of the reactor coolant pump 50 is disposed in the pressurizer volume of the integral pressurizer 22. Each RCP 50 of the embodiment of FIGS. 1-4 further includes an annular pump casing or diffuser 58 containing the impeller 52. Locating the RCPs 50 proximate to the integral pressurizer 22 places the openings in the pressure vessel 10 for passage of the drive shafts 56 at elevated positions. This elevated placement reduces the likelihood of substantial primary coolant loss in the event of a loss of coolant accident (LOCA) involving the RCPs 50. Moreover, the impellers 52 operate at the “turnaround” point of the primary coolant flow circuit, that is, at the point where the primary coolant water reverses flow direction from the upward flow through the central riser 30 to the downward flow through the downcomer annulus 32. Since this flow reversal already introduces some flow turbulence, any additional turbulence introduced by operation of the RCPs 50 is likely to be negligible. The RCPs 50 also do not impede natural circulation, which facilitates the implementation of various passive emergency cooling systems that rely upon natural circulation in the event of a loss of electrical power for driving the RCPs 50. Still further, the RCPs 50 are also far away from the reactor core 16 and hence are unlikely to introduce flow turbulence in the core 16 (with its potential for consequent temperature variability). On the other hand, the placement of the RCPs 50 at the elevated position has the potential to introduce turbulence in the primary coolant water flow into the internal steam generator 36. To reduce any such effect, in the embodiment of FIGS. 1-4 the RCPs 50 are buffered by an inlet plenum 60 and an outlet plenum 62. Primary coolant water flowing out of the top of the cylindrical central riser 30 flows into the inlet plenum 60 where the flow reverses direction, aided by the RCPs 50 which impel the primary coolant water to flow downward into the downcomer annulus 32. Said another way, the RCPs 50 discharge primary coolant into the outlet plenum 62 which separates the RCPs 50 from the internal steam generator 36. Optionally, a flow diverter element or structure may be provided at or proximate to the top of the central riser 30 to assist in the flow reversal. In the illustrative embodiment, a flow diverter screen 63 serves this purpose; however, in other embodiments other diverter elements or structures may be used. By way of additional illustrative examples, the flow diverter or structure may be embodied by side openings near the top of the central riser, or by shaping the separator plate to serve as a flow diverter. Alternatively, a flow diverter structure may be on the outlet plenum 62. The RCPs 50 output impelled primary coolant water into the output plenum 62 which buffers flow from the pumps into the annular steam generator 36. The primary coolant flows from the outlet plenum 62 either into the steam generator tubes (in embodiments in which the higher pressure primary coolant flows inside the steam generator tubes) or into a volume surrounding the steam generator tubes (in embodiments in which the higher pressure primary coolant flows outside the steam generator tubes). In either case, the primary coolant flow from the RCPs 50 into the steam generator 36 is buffered so as to reduce flow inhomogeneity. Additionally, because each RCP 50 outputs into the outlet plenum 62 and is not mechanically connected with an inlet of the internal steam generator 36, the failure of one RCP 50 is less problematic. (By comparison, if the RCPs are mechanically coupled into specific inlets of the steam generator, for example by constructing the pump casing so that its outlet is coupled with an inlet of the steam generator, then the failure of one RCP completely removes the coupled portion of the steam generator from use). The illustrative RCPs 50 of FIGS. 1-5 are mounted using relatively small openings in the pressure vessel 10. In particular, in some embodiments the opening through which the driveshaft 56 passes is too small for the pump casing 58 to pass through. With reference to FIG. 5, to enable the disclosed approach in which the opening is too small for the pump casing 58 to pass through, the pressure vessel 10 includes a closure at or below the separator plate 20 and (in the illustrative example) at or above the top of the internal steam generator 36. The closure includes mating flanges 64A, 64B that seal together in mating fashion with suitable fasteners such as a combination of cooperating tension nuts and tension studs. In this way, a head 10H of the pressure vessel 10 can be removed from the remainder of the pressure vessel 10 by opening the closure 64 (e.g., by removing the fasteners) and lifting off the vessel head via lifting lugs 69 thus separating the flanges 64A, 64B (see FIG. 5, but note that FIG. 5 diagrammatically shows the head 10H and vessel remainder each tilted to reveal internal components; whereas, typically the head 10H is removed by lifting it straight up, i.e. vertically, using a crane or the like and then optionally moving the lifted head 10H laterally to a docking location). The vessel head 10H defines the integral pressurizer 22 and also includes the portion of the pressure vessel 10 that supports the RCPs 50. Therefore, removing the head 10H of the pressure vessel 10 simultaneously removes the integral pressurizer 22 and the RCPs 50. Removal of the vessel head 10H exposes the upper and lower surfaces of the outlet plenum 62 and provides access from below to the pump casings 58. Thus, during a maintenance period during which the pressure vessel 10 is depressurized and the vessel head 10H removed, the pump casings 58 could be installed or replaced if needed. The RCP 50 can be installed as follows. The pump casings 58 are typically installed first. This can be done during manufacture of the vessel head 10H or at any time prior to installation of the vessel head 10H to form the complete pressure vessel 10. The pump motor 54, impeller 52, and connecting drive shaft 56 are pre-assembled as a unit, and in some embodiments may be a commercially available pump such as a glandless pump of the type used in boil water reactor (BWR) systems. The pump assembly 52, 54, 56 is mounted as a unit at an opening of the pressure vessel 10 by inserting the impeller 52 and drive shaft 56 into the opening and bolting a mounting flange 70 of the pump assembly to the pressure vessel 10 with the mounted pump motor 54 located outside of the pressure vessel 10 and supported on the pressure vessel 10 by the mounting flange 70. In an alternative assembly sequence, it is contemplated to mount the pump assembly 52, 54, 56 as a unit onto the pressure vessel 10 prior to installation of the vessel head 10H to form the complete pressure vessel 10 and either before or after installation of the pump casings 58. By employing the illustrative embodiment in which the opening for the RCP 50 is too small for the pump casing 58 to pass, these openings are made small so as to minimize the likelihood and extent of a loss of coolant accident (LOCA) at these openings. However, the approach still enables use of a commercially available unitary pump assembly including the pump motor 54, impeller 52, and drive shaft 56 secured together as said unitary pump assembly. The pump casing 58, on the other hand, is not secured with the unitary pump assembly 52, 54, 56. The number of RCPs 50 is selected to provide sufficient motive force for maintaining the desired primary coolant flow through the primary coolant circuit. Additional RCPs 50 may be provided to ensure redundancy in the event of failure of one or two RCPs. If there are N reactor coolant pumps (where N is an integer greater than or equal to 2, for example N=12 in some embodiments) then they are preferably spaced apart evenly, e.g. at 360°/N intervals around the cylinder axis of the cylindrical pressure vessel 10 (e.g., intervals of 30° for N=12). The externally mounted pump motors 54 are advantageously spaced apart from the high temperature environment inside the pressure vessel 10. Nonetheless, substantial heat is still expected to flow into the pump motors 54 by conduction through the flanges 70 and by radiation/convection from the exterior of the pressure vessel 10. Accordingly, in the illustrative embodiment the RCPs 50 further include heat exchangers 74 for removing heat from the pump motors 54. Alternative thermal control mechanisms can be provided, such as an open-loop coolant flow circuit carrying water, air, or another coolant fluid. Moreover, it is contemplated to omit such thermal control mechanisms entirely if the pump motors 54 are rated for sufficiently high temperature operation. Another advantage of the illustrative configuration is that the pump motor 54 of the RCP 50 is mounted vertically, with the drive shaft 56 vertically oriented and parallel with the cylinder axis of the cylindrical pressure vessel 10. This vertical arrangement eliminates sideways forces on the rotating motor 54 and rotating drive shaft 56, which in turn reduces wear on the pump motor 54 and other pump components. Yet another advantage of the illustrative configuration is that no portion of the RCP 50 passes through the integral pressurizer volume. This simplifies design of the integral pressurizer 22 and shortens the length of the drive shaft 56. However, since conventionally the pressurizer is located at the top of the pressure vessel, achieving this arrangement in combination with vertically oriented pump motors 54 and vertically oriented drive shafts 56 entails reconfiguring the pressurizer. In the embodiment of FIGS. 1-5, the cross-section of the vessel head of the cylindrical pressure vessel 10 includes a narrowed portion defining a recess 76 of the integral pressurizer 22. The recess 76 allows the pump motors 54 to be disposed at least partially in the recess 76 so as to provide sufficient room for the vertically mounted pump motors 54. The recess 76 should be large enough to accommodate the pump motor 54 during installation. Still yet another advantage of placing the RCPs 50 at the head of the pressure vessel is that this arrangement does not occupy space lower down in the pressure vessel, thus leaving that space available for accommodating internal CRDM units, a larger steam generator, or so forth. The embodiment of FIG. 1-5 is illustrative, and it is contemplated that the various components such as the integral pressurizer 22, the RCPs 50, and so forth may be modified in various ways. With reference to FIGS. 6-9, some additional illustrative embodiments are set forth. With reference to FIGS. 6 and 7, an alternative embodiment of the upper vessel section is shown. The alternative embodiment of FIGS. 6 and 7 differs from the embodiment of FIGS. 1-5 in that it has a modified pressure vessel 110 in which (1) the closure 64 for removing the vessel head is omitted and (2) a differently shaped integral pressurizer 122 is provided. Unlike the integral pressurizer 22 of the embodiment of FIGS. 1-5 which included the recess 76 for accommodating the RCPs 50, the integral pressurizer 122 is instead narrowed (that is, of smaller cross-section diameter) over its entire height to accommodate the RCPs 50. This approach has the advantage of providing more vertical space for mounting the pump motors 54 (which can be especially advantageous if a long drive shaft is inserted when the motor is installed). A disadvantage of the integral pressurizer 122 as compared with the pressurizer 22 is that the former has reduced a reduced pressurizer volume due to its being narrowed over its entire height rather than over only the recess 76. The embodiment of FIGS. 6 and 7 can employ the same RCP mounting arrangement as is used in the embodiment of FIGS. 1-5, including mounting the RCP 50 at an opening of the pressure vessel that is too small for the pump casing or diffuser 58 to pass through. Since the vessel head is not removable to allow insertion of the diffuser 58, another access pathway such as an illustrative manway 130 is suitably provided for inserting the diffuser 58 into the pressure vessel. The manway 130 is typically already required to provide access for performing steam generator tube plugging or other maintenance operations—accordingly, no additional vessel penetration is required to enable the use of the disclosed pumps installed at small vessel openings. With particular reference to FIG. 7, installation of the RCPs 50 is shown. FIG. 7 shows the vessel head before installation of the RCPs 50, and with one RCP 50 positioned above an opening 132 that is sized to be too small to pass the diffuser 58 but is large enough to pass the impeller 52. In illustrative FIG. 7 the corresponding diffuser 58 is already mounted inside the pressure vessel 110 on a support plate 134 below the pressurizer separator plate 20. The support plate 134 also serves as the pressure divider separating the suction and discharge sides of the diffuser 58. In FIG. 7 the manways 130 are shown as capped. (Note that in FIG. 7 only two diffusers 58 are shown, with one that corresponds to the one RCP 50; more typically, all diffusers 58 will be installed via the open manways 130 into their respective openings of the support plate 134 before capping the manways 130.) To install the illustrative RCP 50 shown in FIG. 7, the impeller 52 and drive shaft 56 are inserted through the opening 132 so as to position the impeller 52 at its designed position inside the diffuser 58, and the flange 70 is bolted onto the opening 132 to form a seal (typically assisted by a gasket, o-ring, or other sealing element at the flange 70. With reference to FIG. 8, another embodiment is shown. This embodiment differs from the embodiment of FIGS. 6-7 in that (i) the openings 132 are replaced by larger openings 142 that are sufficiently large to pass the entire assembly inclusive of the diffuser 58, and (ii) in the embodiment of FIG. 8 the RCP 50 is installed as a unitary pump assembly including the motor 54, impeller 52, drive shaft 56, and diffuser 58. In this embodiment the unitary pump assembly includes the motor 54, impeller 52, drive shaft 56, and diffuser 58 secured together as said unitary pump assembly 52, 54, 56, 58 with the impeller 52 disposed in the diffuser 58 in the unitary pump assembly. FIG. 8 diagrammatically indicates the installation by showing the unitary pump assembly 52, 54, 56, 58 (note, the impeller 52 is inside the diffuser 58 and hence not visible in FIG. 8) arranged above a corresponding one of the openings 142 preparatory to inserting the diffuser 58 into the opening 142. This embodiment has the advantage of enabling use of commercially available pumps that may include the pump casing, and also enables removal/replacement of the diffuser 58 via the opening 142. Additionally, this embodiment facilitates pre-alignment of the impeller 52 inside the diffuser 58 prior to installing the RCP 50 at the reactor. The embodiment of FIG. 8 includes the manways 130. In the embodiment of FIG. 8 the manways 130 are not used for installation/replacement of diffusers 58, but are typically used for performing steam generator tube plugging or other maintenance operations (possibly including inspection of the diffusers 58). The illustrative embodiments are examples of contemplated variations and variant embodiments; additional variations and variant embodiments that are not illustrated are also contemplated. For example, while the illustrative PWR is an integral PWR including the internal steam generator 36, in some contemplated alternative embodiments an external steam generator is instead employed, in which case the feedwater inlet 40 and steam outlet 42 are replaced by a primary coolant outlet port to the steam generator and a primary coolant inlet port returning primary coolant from the steam generator (alternative embodiment not shown). Moreover, while advantages are identified herein to not mechanically coupling the RCPs 50 to the internal steam generator, it is alternatively contemplated to couple the RCPs to the steam generator inlet, for example by replacing the outlet plenum 62 and illustrative diffusers 58 with pump casings having outlets directly connected with primary coolant inlets of the steam generator. The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
	summary
	description	This application claims priority to U.S. Provisional Patent Application Ser. No. 60/925,916, filed Apr. 23, 2007, and which is herein incorporated by reference. The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC for the operation of Lawrence Livermore National Laboratory. The present invention relates to nuclear fuel, and more particularly, this invention relates to a nuclear fuel that resists swelling, and methods for making the same. For use as nuclear fuel, enriched uranium hexafluoride is converted into uranium dioxide (UO2) powder that is then processed into pellet form. The pellets are then fired in a high temperature sintering furnace to create hard, ceramic pellets of enriched uranium. The cylindrical pellets then undergo a grinding process to achieve a uniform pellet size. The pellets are stacked, according to each nuclear reactor core's design specifications, into tubes of corrosion-resistant metal alloy, called cladding. The tubes are sealed to contain the fuel pellets; these tubes are called fuel rods. Nuclear fuel swelling of Uranium Dioxide-based fuels (and possibly other nuclear fuels) is a life limiting phenomenon controlling the residence of nuclear fuel assemblies in the core of current Light Water Reactors (LWRs). Current strategies for prolonging the residence time of nuclear fuel assemblies reactor cores consist of leaving a gap between the fuel pellet and the surrounding cladding that the nuclear fuel can expand into, and modifying the oxygen content away from stoichometric ratios to help control the rate of swelling. A nuclear fuel according to one embodiment comprises an assembly of nuclear fuel particles; and continuous open channels defined between at least some of the nuclear fuel particles, wherein the channels are characterized as allowing fission gasses produced in an interior of the assembly to escape from the interior of the assembly to an exterior thereof without causing significant swelling of the assembly. A nuclear fuel according to another embodiment comprises an assembly of nuclear fuel particles having a periphery defining an overall volume of the assembly, the assembly characterized as allowing fission gasses produced in an interior of the assembly to escape from the interior of the assembly to an exterior thereof, wherein the assembly maintains about the same overall volume during a nuclear fission chain reaction involving the nuclear fuel particles thereof. A method for fabricating a nuclear fuel according to one embodiment comprises consolidating a precursor of a nuclear fuel to produce an open nanoscale porosity material having a density of at least about 68% of a theoretical maximum density of the material. A method for fabricating a fuel assembly according to one embodiment comprises consolidating nuclear fuel particles under conditions that produce a material in which the fuel particles form nano-scale ligaments and continuous open channels are defined between at least some of the ligaments, wherein the channels are characterized as allowing fission gasses produced in an interior of the assembly to escape from the interior of the material to an exterior thereof without causing significant swelling of the material. Other aspects, advantages and embodiments of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention. The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations. Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified. The following description discloses several preferred embodiments of nuclear fuels and methods for making the same. In one general embodiment, a nuclear fuel comprises an assembly of nuclear fuel particles, and continuous open channels defined between at least some of the nuclear fuel particles. The channels are characterized as allowing fission gasses produced in an interior of the assembly to escape from the interior of the assembly to an exterior thereof without causing significant swelling of the assembly. In another general embodiment, a nuclear fuel comprises an assembly of nuclear fuel particles having a periphery defining an overall volume of the assembly (i.e., the volume of the assembly as measured along its periphery (outer side(s)), without taking into account any internal porosity of the assembly), the assembly characterized as allowing fission gasses produced in an interior of the assembly to escape from the interior of the assembly to an exterior thereof, where the assembly maintains about the same overall volume during a nuclear fission chain reaction involving the nuclear fuel particles thereof. In one general embodiment, a method for fabricating a nuclear fuel comprises consolidating a precursor of a nuclear fuel to produce an open nanoscale porosity material having a density of at least about 68% of a theoretical maximum density of the material. In another general embodiment, a method for fabricating a fuel assembly comprises consolidating nuclear fuel particles under conditions that produce a material in which the fuel particles form nano-scale ligaments and continuous open channels are defined between at least some of the ligaments, where the channels are characterized as allowing fission gasses produced in an interior of the assembly to escape from the interior of the material to an exterior thereof without causing significant swelling of the material. Particularly preferred embodiments address the problem of fuel swelling by controlling the material microstructure at the nano-scale so as to make a nuclear fuel material that does not significantly swell during fission and requires little or no gap between the fuel and the cladding to allow for expansion. Particularly preferred embodiments exhibit no swelling, and therefore require no gap between the fuel and the cladding to allow for expansion. Nuclear fuels according to some embodiments described herein may be used in current LWR power reactors and future nuclear reactors as fuel that does not swell and impart mechanical loading on the cladding materials. The fuel form has the potential of significantly increasing the residence time of nuclear fuel in reactor cores and increasing their operating efficiency. Nuclear fuel is any material that can be consumed to derive nuclear energy. One type of nuclear fuel comprises heavy fissile elements that can be made to undergo nuclear fission chain reactions in a nuclear fission reactor; nuclear fuel can refer to the material or to physical objects (for example fuel bundles composed of fuel rods) composed of the fuel material, perhaps mixed with structural, neutron moderating, or neutron reflecting materials. Illustrative fissile nuclear fuels include 235U, 239Pu, thorium, etc. One particularly preferred nuclear fuel comprises uranium dioxide, which is a black semiconductor solid. It can be made by reacting uranyl nitrate with a base (ammonia) to form a solid (ammonium uranate). It is heated (calcined) to form U3O8 that can than be converted by heating in an argon/hydrogen mixture (700° C.) to form UO2. The chemical properties of the fuel or precursor may be similar to those of current fuels used in LWR reactors. However, many embodiments of the fuels and materials processing described herein have or form a different microstructure that is superior to current nuclear fuels, particularly in terms of its swelling characteristics. In particularly preferred embodiments, the microstructure includes interconnected nano-scale ligaments with interconnected nanopores that allow the fission gasses, which otherwise would build up, to escape into the plenum region of the fuel pin and not lead to any swelling. In some processes described herein, a continuous open nanoscale porosity and nanoscale ligament structure is maintained throughout the synthesis and consolidation (and, if necessary, reduction). One approach to forming a nuclear fuel can be summarized as consolidation of precursor (e.g. UO3 or U3O8) or final fuel (e.g. UO2) materials to produce a continuous open nanoscale porosity material at about 68% or more of its Theoretical Maximum Density (TMD), preferably with nanoscale ligaments coupling the building blocks together. The nanoscale ligaments may be formed, at least in part, of nuclear fuel particles. Accordingly, the ligaments may include a series of linked particles, or struts, etc. that make up the structural network. The length of the nanoscale ligaments are preferably selected to form a nuclear fuel material in which fission gasses are allowed to escape from an interior thereof without causing significant swelling of the material. Without wishing to be bound by any theory, the inventors believe that the coupling by nanoscale ligaments creates mean free paths for fission gasses to escape in such a manner that a probability of a fission gas atom encountering another fission gas atom and forming a bubble (which could cause the material to swell) is less than the probability of the atom escaping from the interior of the material. Nano-scale ligaments may be in the range of about 0.1 nanometer to about 1000 microns, more preferably in the range of about 1 nanometer to about 10 nanometers, even more preferably in the range of about 5±2 nanometers to about 10±2 nanometers. Pore diameters may be in about the same ranges, or higher or lower. It should be noted that the closer the nuclear fuel is to its TMD, the less enrichment it needs to be a good fuel for typical reactors. Conversely, the more enriched the nuclear fuel raw material is, the lower the percent of TMD is required. That said, about 68% of TMD is based on typical nuclear fuel raw materials, and the actual percentage of TMD selected may be higher or lower than about 68%. A pictorial representation of potential processing and approaches are depicted in FIGS. 1A-4C, described immediately below, and followed by a description of potential synthesis and consolidation methods. FIGS. 1A-1C describe how loose powders are consolidated in one approach. As shown in FIG. 1A, a loose nanoscale powder, e.g., comprising particles 100 of fuel or precursor, is collected. As depicted in FIG. 1B, the nanoscale powder is optionally partially consolidated. As depicted in FIG. 1C, the nanoscale powder is consolidated by compression to about the desired density under conditions that minimize grain/ligament growth of the particles. Note that some grain/ligament growth may be allowed to form a nanoporous solid. Methods for consolidation by compression are described below. Referring next to FIGS. 2A-2C, there is shown an approach for consolidating a monolith. As shown in FIG. 2A, a gel network is formed, the gel network comprising particles 100 of nuclear fuel and/or a precursor thereof. Any suitable method for forming a gel network may be used. For example, the gel network may be formed by sol-gel processing, an example of which is described below. Whichever approach of forming the monolith is ultimately selected, it may be desirable to control the ligament size. Sol-gel processing provides good control over ligament length. As depicted in FIG. 2B, the monolith is optionally partially consolidated. As depicted in FIG. 2C, the monolith is consolidated by compaction to about the desired density. For example, the monolith may be compacted by compression to form a nanoporous solid. Methods for consolidation by compression are described below. Referring next to FIGS. 3A-3C, there is shown an approach for compacting coated powders. As shown in FIG. 3A, a coated powder 300 is gathered, and optionally partially consolidated as shown in FIG. 3B. The coated powder comprises the nuclear fuel particles and/or a precursor thereof, along with a sacrificial coating. As depicted in FIG. 3C, the monolith is consolidated by compaction to about the desired density. For example, the monolith may be compacted by compression. Methods for consolidation by compression are described below. Then the coating is at least partially removed, thereby leaving an assembly of uncoated particles 302. In a similar approach to that shown in FIGS. 3A-3C, a powder/porogen mixture may be formed and compacted. The porogen is then removed, thereby creating pores in the material. Referring next to FIGS. 4A-4C, there is shown an approach using an interpenetrating network (IPN). FIG. 4A depicts a first network 400 comprising nuclear fuel and/or a precursor thereof. FIG. 4B depicts a second network 402, which acts as a porogen. FIG. 4C depicts an IPN formed of the first and second networks 400, 402. Examples of IPN synthesis are presented below. The IPN may or may not be further consolidated, depending on its density. In many instances, the IPN is compacted. Then, the second network is removed using any appropriate process to generate final porosity. Differences between this approach and that described with reference to FIGS. 3A-3C is that this approach permits greater determination of distribution of the second phase, composition, and relative proportions of porogen/network. The IPN approach may also provide improved continuity of the pores. In any of the approaches herein, where a precursor is used, further chemical processing may be performed to convert the precursor to a nuclear fuel. This can be accomplished at elevated temperatures and reduced oxygen levels in the presence of a reductant (e.g. hydrogen). For example, as mentioned above a precursor such as U3O8 may be reduced to the fuel, UO2 by heating the U3O8 in an argon/hydrogen mixture at 700° C. The conditions are preferably chosen to minimize unwanted structural evolution. Reduction may be performed after synthesis and/or consolidation. Synthesis Following are several methods of synthesizing the starting materials used in the creation of nuclear fuels. It should be noted that the following description is presented by way of example and is in no way meant to be limiting. Further, the various methods set forth below may be used in conjunction with the processes described above with reference to FIGS. 1A-4C, as well as any other embodiment or permutation described in or derived from the teachings herein. Of course, other methods of consolidation may also be used. There are a number of ways to generate nanoscale building blocks of nuclear fuels, for example, oxide based fuels. Nonlimiting examples of methods of synthesis include attrition of larger particles (e.g., high energy ball milling and sieving), nanoscale powders produced by flame spray pyrolysis, plasma spraying or related techniques, wet chemical or sol-gel processes, etc. In order to address the problem of fuel swelling, however the starting materials are produced, they are preferably able to be consolidated to densities of about 68% of the TMD or greater (e.g., 66%, 70%, 72%, 75%, 80%, 90%, etc.), while maintaining continuous open nanoscale porosity and minimizing structural evolution and grain growth to the initial nanoscale ligament structure throughout the synthesis and consolidation (and, if necessary, reduction) processes. Examples of approaches to produce materials using sol-gel synthesis will be described below. However, one may readily substitute starting materials generated by different techniques into the process at the appropriate stage. Various consolidation approaches are also described later, and some of their advantages are noted. The production of materials meeting defined criteria may involve any or all of the steps described, or variations thereof comprising at least some different steps. In further approaches, even lower densities may be employed, e.g., about 60% of the TMD or greater (e.g., 58%, 62%, 64%, 66%, 70%, 72%, 75%, 80%, 90%, etc.). Sol-gel chemistry involves the reversible reactions of chemicals in solution to produce nanometer-sized primary particles, called “sols”. The “sols” can be linked to form a three-dimensional solid network, called a “gel”, with the remaining solution residing within the continuous open porosity of the resulting network. In one approach, reactive monomers are mixed into a solution of nuclear fuel particles. Polymerization then occurs leading to a highly cross-linked three- dimensional solid network resulting in a gel. Solution chemistry determines the nanostructure morphology and composition, which in turn determine the material properties such as pore and primary particles sizes, gel time, surface areas, and density. When using sol-gel process one can readily achieve 1-100 nm ligaments by choice of the initial chemistry, aging, and processing (drying) conditions. Other ligament lengths are also achievable, Controlled evaporation of the liquid phase results in a moderately dense porous solid, often referred to as a “xerogel”. Since these reactions are reversible, xerogel processing may be advantageous (along with aging) to evolve the primary or initial structure to afford larger length scale ligaments if necessary. Supercritical extraction (SCE) eliminates the surface tension and in so doing the capillary forces of the retreating liquid phase that collapse the pores. The results of SCE are highly porous, (less dense than xerogel) solids known as “aerogels”. We have already demonstrated the feasibility of this technique to prepare uranium oxide aerogels with nanometer length scale ligaments. [See Satcher et al., J. Non-Cryst Solids 319, 241-246 (2003)] An alternative to the use of supercritical drying is the use of low surface tension solvents can also be used to retain this dimensionality on drying to produce a material typically know as an ambigel. [See Mansour et al., J. Electrochem. Soc., 150, 4, A403-A413, 2003] These three techniques are generally used to produce materials that are monolithic in nature, and ensure that a continuous open porosity has been maintained throughout the bulk of the material. Stress may be applied during the extraction phase to increase the density of the resulting materials. A typical gel structure is characteristically very uniform because the particles and the pores between them are on the nanometer size scale. Such homogeneity provides a uniformity of the material properties, which may be beneficial for present purposes. By use of the sol-gel processing, materials can be made, for example, by solution addition, solution exchange, powder/particle addition, functionalized solid network, and functionalized particle network. The methodologies of the above sol-gel manufacturing techniques are briefly described as follows: Solution Addition: The nuclear fuel constituent is dissolved in a solvent which is compatible with the reactive monomer and mixed into the pre-gel solution prior to gelation. Upon gelation, the nuclear fuel constituent is uniformly distributed within the pores of the solid network formed by the polymerization of the reactive monomer. Solution Exchange. After gelation, the liquid phase is exchanged with another liquid which contains a nuclear fuel constituent, thus allowing deposition of the nuclear fuel constituent within the gel. Powder/Particle Addition: The nuclear fuel constituent, in particulate form, is either mixed with the pre-gel solution or added to a premade gel, resulting in a composite of gel and suspended particles. Functionalized Solid Network: Use of reactive monomers which have functionalized sites dangling throughout the solid network after gelation. Dissolution of the nuclear fuel constituent in mutually compatible solvents and diffusing into the gel allows the nuclear fuel constituent to react and bind to the functionalized site. Thus, the amount of nuclear fuel constituent may be controlled by the number of functionalized sites while ensuring homogeneity at the molecular level. Functionalized Particle Network: Functionalizing the nuclear fuel constituent molecules so that they can be reacted in solution to directly form a three dimensional solid (gel) which incorporates the nuclear fuel molecules at the finest scale. In this embodiment, the solid network is the nuclear fuel material and, if desired, the concentration can be controlled by co-reacting with other inert reactive monomers. The use of composites to introduce sacrificial porogens or produce an interpenetrating network (IPN) may also be used to define pore size, distribution, and interconnectivity in the final material. Techniques such as freeze-drying, spray-drying, or distillation may be used to remove the initial solvent in a fashion that avoids nanoparticle agglomeration. Thus, powders with dimensions representative of the primary particle dimensions, composition, or distribution of phases (e.g. IPNs) of bulk materials from the sol-gel process can be produced for consolidation. The use of sacrificial porogens to assist in retaining porosity and facilitate consolidation, e.g. carbon or polyethyleneglycol (PEG) is known. While this methodology has potential, the likelihood of closed porosity formation is high. Therefore, more preferred is the preparation of an IPN of ceramic, nuclear fuel or precursor thereof, and organic polymer. Methodology for creating such IPN is found in U.S. Pat. No. 6,712,917 to Gash et al., which is herein incorporated by reference. The IPN is then consolidated at low temperatures, followed by removal of one of the phases, in this case the organic polymer (organic/inorganic). In another approach, one may also produce an IPN, consolidate the composite, then oxidatively remove/burn out the organic phase below the sintering temperature. Plasma etching may also be used to remove the organic phase (e.g., in an IPN) to generate final porosity. In addition to occupying physical space, the polymer acts as a lubricant to assist consolidation. In yet another approach, the use of an epoxide method to generate oligimers as IPN/scaffold coating may afford the simplest approach to IPN formation. [See, e.g., Cash et al., Chem. Mater. V13, 2001, p 999] Inorganic/inorganic systems may also be used in some approaches. In the case of an inorganic/inorganic system one may chemically etch one phase selectively as in the example of using an HCl etch to selectively remove TiO2 from a SiO2/TiO2 mix to create gradient index materials. In embodiments which use a fluid component during the synthesis phase, where present, the fluid may be removed in a fashion that avoids agglomeration. Consolidation Following are several methods of consolidating materials used during the creation of nuclear fuels. It should be noted that the following description is presented by way of example and is in no way meant to be limiting. Further, the various methods set forth below may be used in conjunction with the processes described above with reference to FIGS. 1A-4C, as well as any other embodiment or permutation described in or derived from the teachings herein. Of course, other methods of consolidation may also be used. Consolidation to about the desired density can be achieved by various techniques or a combination of techniques. One approach to consolidation includes the direct compression of a monolithic material produced as described above. Alternatively nanoscale powders produced may be directly consolidated or slip cast then consolidated to intermediate density porous materials. One illustrative approach would utilize isostatic pressing as a first step. Isostatic pressing is used for compressing powdered and other materials into shaped pre-forms or general products. There are two main types of isostatic presses: cold isostatic presses (CIP) that function at room temperature and hot isostatic presses (HIP) that function at elevated temperatures. Cold isostatic pressing applies pressure from multiple directions for achieving greater uniformity of compaction (high-quality parts) and increased shape capability, compared to uniaxial pressing. For example, cold isostatic pressing comprises compacting a material into a predetermined shape by the application of pressure via a fluid through a flexible mold. This technique has many advantages over uniaxial pressing e.g., high green density and strength, fabrication of complicated parts, green machinery, etc. This method is widely used for advanced ceramics, generally for high-performance applications and can typically consolidate to densities of approximately 40-50% of TMD, making it particularly useful for partial consolidation. To get to about 68% or more of the TMD, conventional hot pressing at well below sintering temp may be used. Compression may also be performed using a relatively new sintering technique known as Spark Plasma Sintering (SPS). SPS is also known as Field Assisted Sintering Technique (FAST) or Pulsed Electric Current Sintering (PECS). A main characteristic of the SPS process in one approach is that the pulsed DC current directly passes through a graphite die, as well as the powder compact (comprising nuclear fuel particles or precursor thereof), in the case of conductive samples. Therefore, the heat is generated internally, in contrast to the conventional hot pressing, where the heat is provided by external heating elements. This facilitates a very high heating or cooling rate (up to 600K/min), hence the entire process generally is very fast, possibly being completed within a few minutes. The general speed of the process ensures it has the potential of densifying powders with nanosize or nanostructure while avoiding coarsening that accompanies standard densification routes. Whether plasma is generated has not been confirmed yet, especially when non-conductive powders are compacted. It has been reported that densification is enhanced by the use of a pulsed DC current or field. One could effectively use the current or plasma assist to “weld” particles together to enhance mechanical properties of the final piece. The feasibility of sintering nanoscale powders without significant grain growth has been successfully demonstrated. For example, SPS has been shown to produce nanocrystalline ZrO2 materials while maintaining nanogram size. [See Munir: J. Mat. Res. V19, N11, 2004, p 3255.] At least one of the inventors has also observed compaction of sol-gel derived amorphous tungsten oxide materials starting at temperatures as low as 200° C. (at 300 MPa), well below the melting point of the oxide. An additional advantage of SPS over conventional hot pressing is the rapidity of heating so that materials need not dwell at elevated temperatures for prolonged periods, thus minimizing viscous flow and grain growth. The SPS process is generally operated at low O2 partial pressure, and by using graphite dies, a reducing environment is maintained. This is particularly advantageous in this application when used with a precursor of an oxide-based nuclear fuel, since it can contribute to the reduction of the precursor (e.g., UO3 or U3O8 to UO2 or at minimum, preclude oxidation during consolidation. If material other than the nuclear fuel, e.g., UO2, is used for consolidation, a subsequent reduction may be required. Again, this can be accomplished at elevated temperatures and reduced oxygen levels in the presence of a reductant (e.g. hydrogen). The conditions are preferably chosen to minimize unwanted structural evolution. In Use The nuclear fuel may be encased in cladding, thereby forming a fuel rod. Aluminum, stainless steel, and zirconium alloys are illustrative cladding materials. As noted above, the porosity of the material minimizes or eliminates expansion of the nuclear fuel, thereby allowing the material to abut the inner surface of the cladding. The finished fuel rods may be grouped in special fuel assemblies that may then be used to build up the nuclear fuel core of a power reactor. For the most common types of reactors, the tubes may be assembled into bundles with the tubes spaced precise distances apart. These bundles may also be given a unique identification number, which enables them to be tracked from manufacture through use and into disposal. As alluded to above, the nuclear fuel may be used in a nuclear reactor such as a LWR or other type. Those skilled in the art will have an understanding of the chemistry and physics of the various types of nuclear reactors and how nuclear fuel is used therewith, and therefore only a brief description is provided below. A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate. The most significant use of nuclear reactors is as an energy source for the generation of electrical power and for the power in some ships (e.g., nuclear marine propulsion). This is usually accomplished by methods that involve using heat from the nuclear reaction to power steam turbines. For a nuclear power plant, the heat is provided by nuclear fission inside the nuclear reactor. When a relatively large fissile atomic nucleus (e.g., 235U or 239Pu) is struck by a neutron it forms two or more smaller nuclei as fission products, releasing energy and neutrons in a process called nuclear fission. The neutrons then trigger further fission. When this nuclear chain reaction is controlled, the energy released can be used to heat water, produce steam and drive a turbine that generates electricity. A light water reactor or LWR is a thermal nuclear reactor that uses ordinary water, also called light water, as its neutron moderator. This differentiates it from a heavy water reactor, which uses heavy water as a neutron moderator. In practice all LWRs are also water cooled. While ordinary water has some heavy water molecules in it, their concentration is not enough to be important in most applications. The most common LWRs are pressurized water reactors and boiling water reactors. Many other reactors are also (light) water cooled, notably the RBMK and some military plutonium production reactors. These are not regarded as LWRs, as they are moderated by graphite, and as a result their nuclear characteristics are very different. Most light-water reactors use uranium 235 as a fuel, enriched to approximately 3 percent. Although this is its major fuel, the uranium 238 atoms also contribute to the fission process by converting to plutonium 239—about one-half of which is consumed in the reactor. Light-water reactors are generally refueled every 12 to 18 months, at which time, about 25 percent of the fuel is replaced. Light water reactors tend to be simpler and cheaper to build than heavy water reactors. Power-generating capabilities are comparable. Light water reactors are the type used by the U.S. military in its Naval nuclear powered vessels. This is so due to the inherent safety of these type reactors. Since light water is used as both a coolant and a moderator in these reactors, if one of these reactors suffers damage due to attack, and thereby compromise of the reactor core's integrity, the ensuing release of this light water acts to shut down the reactor. Moderators help to encourage the nuclear mass to achieve fission by lowering the average speed of the neutrons to a level which augments the probability of occurrence of neutron-Uranium collisions susceptible to lead to a Uranium nucleus fission. When the moderator is removed, the average energy of the neutrons becomes too high for the chain reaction to sustain itself. Currently-offered LWRs include the ABWR, AP1000, ESBWR, European Pressurized Reactor, VVER and SWR-1000. While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
	claims	1. A container for a gas-tight encapsulation of a fuel rod or of a fuel rod section, the container comprising:unipartite closure plugs each having a duct formed therein; anda hollow cylindrical container part having two free ends closed off in a fluid-tight manner by said unipartite closure plugs, said hollow cylindrical container part having a scavenging chamber fluidly connected to an exterior via said duct exclusively in an intermediate position assumed during an assembly process before an end position is reached and in the intermediate position said unipartite closure plugs projecting out of said hollow cylindrical container part by an axial projecting length in relation to an end position of said unipartite closure plugs. 2. The container according to claim 1, wherein said duct has a first duct section which runs parallel to a longitudinal central axis of said unipartite closure plug from an inner face side of said unipartite closure plug and issues into a second duct section, said second duct section running transversely with respect to said longitudinal central axis and extending from a shell surface of said unipartite closure plug. 3. The container according to claim 1, wherein said unipartite closure plugs and/or said hollow cylindrical container part are equipped, on an outer circumference and/or on an inner circumference, respectively, with detent devices which serve for detachably fixing said unipartite closure plug in the intermediate position. 4. The container according to claim 3, wherein each of said unipartite closure plugs has an annularly encircling flange, and in a fully assembled position, each of said unipartite closure plugs is seated by way of said annularly encircling flange on a face surface of said hollow cylindrical container part. 5. The container according to claim 4, further comprising an annularly encircling seam selected from the group consisting for weld seams and brazed seams, said annularly encircling flange and said face surface are connected to one another in a cohesive manner by said annularly encircling seam. 6. The container according to claim 3, wherein said unipartite closure plugs are fixed in a fluid-tight fashion in said hollow cylindrical container part by means of a shrink-fit connection. 7. A device for a gas-tight encapsulation of a fuel rod or a fuel rod section in a container, the device comprising:a first processing chamber having a first opening formed therein;a second processing chamber having a second opening formed therein;said first and second processing chambers disposed spaced apart from one another and on a common system axis;said first and second openings each receiving a respective free end of the container issuing into said first and second processing chambers, such that said first and second processing chambers, when the container is disposed between them, can be fluidically connected to one another exclusively via the container itself;said first processing chamber having an inlet and said second processing chamber having an outlet for a scavenging gas; andeach of said first and second processing chambers having means for closing the container in a gas-tight manner. 8. The device according to claim 7, wherein said first and second processing chambers are disposed so as to be displaceable along the common system axis. 9. The device according to claim 7,further comprising sealing rings for sealing said first and second openings; andwherein each of said first and second processing chambers has a pressure ram which annularly surrounds said first or second opening and which can be advanced in a direction of the common system axis toward said first or second opening and by means of which, by way of an advancing movement in the direction of the common system axis, a force with a component acting transversely with respect thereto is exerted on said sealing rings disposed on said first or second opening and which surrounds said first or second opening. 10. The device according to claim 7, further comprising a connecting pipe for rigidly connecting said first and second processing chambers to one another along the common system axis, said connecting pipe having face-side ends and projecting by way of said face-side ends into said first and second processing chambers and into which the container can be inserted such that the container projects by way of free ends beyond said connecting pipe. 11. The device according to claim 10,wherein said inlet is formed by an inlet pipe;wherein said outlet is formed by an outlet pipe, said inlet pipe and said outlet pipe issue into said first and second processing chambers respectively and a central axes of said inlet pipe and said outlet pipe coincide with the common system axis and between said inlet pipe and said outlet pipe, said connecting pipe is disposed in each case with an axial spacing, such that, between face sides facing toward one another, there remain a first and a second free space respectively; andfurther comprising first and second sleeves, said connecting pipe connected in fluid-tight fashion to said inlet pipe and to said outlet pipe by means of said first and second sleeves, respectively, which is disposed so as to be axially displaceable into a first position, and wherein said first and second sleeves are displaceable into a second position in which the first and second free spaces are open to said first and second processing chambers respectively. 12. The device according to claim 11, further comprising at least one sealing element disposed between the container and said connecting pipe, said at least one sealing element can be set such that said first and second processing chambers are fluidically connected to one another exclusively via the container. 13. The device according to claim 7, further comprising:a pump;a heating device; anda bypass line connecting said inlet to said outlet, said bypass line running outside said first and second processing chambers, in such a way that a closed gas circuit is formed, wherein, in said closed gas circuit, there are disposed said pump and said heating device for respectively circulating and heating a heating gas situated in said closed gas circuit. 14. The device according to claim 7, wherein each of said first and second processing chambers has a pressure ram for exerting a pressure force that acts in the direction of the common system axis. 15. The device according to claim 11, wherein each of said first and second processing chambers has a welding head which is mounted such that said welding head can be rotated about, and advanced toward, the common system axis. 16. The device according to claim 15, further comprising a cleaning brush disposed in each of said first and second processing chambers, said cleaning brush mounted so as to be rotatable about, and advanced toward, the common system axis. 17. The device according to claim 16, further comprising a common rotary ring, said welding head and said cleaning brush disposed on said common rotary ring. 18. The device according to claim 17, wherein said common rotary ring is formed by an annularly encircling flange disposed on each of said first and second sleeves. 19. A method for gas-tight encapsulation of a fuel rod or a fuel rod section in a container by means of a device, the container including unipartite closure plugs each having a duct, and a hollow cylindrical container part having two free ends closed off in a fluid-tight manner by said unipartite closure plugs, the hollow cylindrical container part having a scavenging chamber fluidly connected to an exterior via the duct exclusively in an intermediate position assumed during an assembly process before an end position is reached and in the intermediate position the unipartite closure plugs projecting out of the container part by an axial projecting length in relation to an end position of the unipartite closure plugs, the device containing:a first processing chamber having a first opening formed therein;a second processing chamber having a second opening formed therein;the first and second processing chambers disposed spaced apart from one another and on a common system axis;the first and second openings each receiving a free end of the container issuing into the first and second processing chambers, such that the first and second processing chambers, when the container is disposed between them, can be fluidically connected to one another exclusively via the container itself;the first processing chamber having an inlet and said second processing chamber having an outlet for a scavenging gas; andeach of the first and second processing chambers having means for closing the container in gas-tight fashion, which method comprises the steps of:introducing a free end of the container part, equipped with a unipartite closure plug in the intermediate position and which contains the fuel rod or the fuel rod section, through the first opening into the first processing chamber;introducing an opposite free end through the second opening into the second processing chamber, such that the first and second processing chambers are fluidically connected to one another exclusively via the container part itself; andinjecting the scavenging gas into the container part and expelling water situated in the container part through a build-up of a positive pressure. 20. The method according to claim 19, wherein after an expulsion of the water, pumping a heating gas through the container part. 21. The method according to claim 19, which further comprises:subsequently, pressing the unipartite closure plug into the container part as far as an end position; andconnecting the unipartite closure plug in a fluid-tight manner to the container part. 22. The method according to claim 19, which further comprises cohesively connecting the unipartite closure plug to the container part by means of an annularly encircling weld seam or brazed seam. 23. The method according to claim 19, which further comprises fixing the unipartite closure plug in a fluid-tight manner in the hollow cylindrical container part by means of a shrink-fit connection.
	abstract	The present disclosure relates to a method of consolidating a calcine comprising radioactive material, the method comprising mixing 60-80% (by weight) of a radionuclide containing calcine with at least one non-radioactive additive, such as an oxide, and hot isostatic pressing the mixture to form a stable monolith of glass/ceramic. In one embodiment, the ratio of radionuclide containing calcine to additives is about 80:20 by weight, wherein the non-radioactive additive comprises oxides such as BaO, CaO, Al2O3, TiO2, SiO2 and others, that combine with the waste elements and compounds to form a ceramic mineral or glass/ceramic material, after hot isostatic pressing. Non-limiting examples of mineral phases that may be formed are: hollandite (BaAl2Ti6O16), zirconolite (CaZrThO7), and perovskite (CaTiO3).
	description	Hereinbelow, an evacuation use sample chamber and a circuit pattern forming apparatus representing one embodiment of the present invention will be explained, while taking an electron beam pattern drawing apparatus as an example, with reference to the drawings. An electron beam pattern drawing apparatus is one in which through generation of electron beam under a super high vacuum environment and scanning therewith LSI patterns are formed on a semiconductor substrate or a glass substrate called as a mask which is used for an exposure apparatus such as a stepper. At first, a first embodiment will be explained with reference to FIGS. 1 through 5. FIG. 1 shows a constitution of an electron beam pattern drawing apparatus representing the first embodiment of the present invention. As shown in FIG. 1, a column 1 is mounted on a sample chamber cover 11, and inside a sample chamber (also called as a work chamber) 10 a sample stage (also called a sample displacement stand or a displacement table device) which is movable in XYZ directions in the drawing, namely an XYZ stage 20 is disposed. The sample chamber cover 11 is designed to be driven by a motor 40 and a friction drive mechanism 41 and is attached with an open and close cover 42 which maintains vacuum inside the column 1. In the XYZ stage 20, Z stage 23 movable in Z direction is mounted on an XY stage 9 movable in XY directions and a top table 21 which holds a sample 8 is coupled to the Z stage 23 by an expandable actuator 22. Further, a bar mirror 13 is attached to the top table 21 and through measurement by laser distance variation to a laser interference meter 12 management of sample position can be performed. The top table 21 will be explained with reference to FIGS. 2 and 3. FIG. 2 shows a perspective view of the top table 21 and FIG. 3 shows a cross sectional view taken along line Axe2x80x94A in FIG. 2. On the top table 21, a sample use recessed portion 21F having depth of about the thickness of the sample 8 and an evacuation use groove portion 21E surrounding the same are formed, and pin Z mechanisms 21A which are used during sample transportation are attached below respective holes. Further, at the time of transportation a pin 21D passes through the hole 21B and acts on the pin Z mechanism to lift up the top table and to facilitate the sample transportation. Further, in order to perform differential evacuation stably, it is necessary to keep flow rate of gas to be evacuated at constant. When it is designed in such a manner that distance AD between the sample use recessed portion 21F and the evacuation use groove portion 21E as illustrated in the drawing is determined more than the radius of an electron beam passage use hole formed in the bottom face of the sample chamber cover 11 and even when the edge of the sample is shifted in XY directions with reference to the center of column the electron beam passage use hole covers inside the evacuation use groove portion, a circuit pattern can be stably drawn over the entire surface of the sample. Now, a series of flow from carrying in the sample into the sample chamber 10 to carrying out the same after completing a circuit pattern drawing will be explained. At a predetermined position of the XYZ stage 20 the sample 8 carried in is held on the top table 21 and the sample 8 is displaced immediately below the column 1. Thereafter, the top table 21 is displaced upward by the Z stage 23 into a detectable range of a Z sensor 19 which can detects position in height direction and inclination of the sample 8. Subsequently, the distance between the upper face of the sample 8 and the bottom face of the sample chamber cover 11 and parallelism of the sample 8 with respect to the bottom face of the sample chamber cover 11 are detected by means of the Z sensor 19 and the actuator 22 is caused to expand or contract so as to assume a distance and parallelism which permit differential evacuation. While keeping a predetermined distance (a few xcexcm-10 and a few xcexcm) and parallelism, vacuum evacuation is performed through the evacuation use tube 21C so as to depressurize a region surrounded by the evacuation use groove portion 21E, the bottom face of the sample chamber cover 11 and the open and close cover 42, and the degree of vacuum in the region is measured by a pressure gauge 50 attached on the sample chamber cover 11. After the region reaches to the degree of vacuum in the column 1, the open and close cover 42 is opened to start a pattern drawing. After completing the pattern drawing, the open and close cover 42 is closed to shield the inside of the column 1, and after terminating the evacuation from the top table 21, the sample 8 is lowered by driving the Z stage 23, then the sample 8 is carried out at the sample transportation position by displacing the XY stage 9. Now, the differential evacuation around a wafer will be explained with reference to FIG. 4. Since the distance between the upper face of the top table 21 and the bottom face of the sample chamber cover 11 is narrow as from a few xcexcm to 10 and few xcexcm, when a flow rate of evacuated gas from the upper face of the top table 21 is sufficiently large with respect to a flow rate flowing into the evacuation use groove portion 21E from inside the sample chamber 10 being in low vacuum, depressurization rapidly advances after the start of evacuation because of small volume of the region surrounded by the evacuation use groove portion 21E, the bottom face of the sample chamber cover 11 and the open and close cover 42. Further, the smaller the distance G1 between the upper face of the top table 21 and the bottom face of the sample chamber cover 11, the less is the flow rate from the region in low vacuum. Accordingly, when it is designed to evacuate the environment around the sample 8 into high vacuum in the shortest time, it is sufficient as illustrated in FIG. 5 to provide a step in the top table 21 and to determine the distance G1 between the upper face of the top table 21 at the outer portion from the evacuation use groove portion 21E and the bottom face of the sample chamber cover 11 smaller than the distance G2 between the upper face of the top table 21 and the bottom face of the sample chamber cover 11. Now, a second embodiment will be explained with reference to FIGS. 6 through 11. FIG. 6 shows a constitution of an electron beam pattern drawing apparatus representing the second embodiment of the present invention. As illustrated in FIG. 6, the XYZ stage 20 is guided by an air bearing and is movable in XYZ direction like the first embodiment, and in place of the sample chamber which maintains vacuum, the sample chamber cover 11, on which the column 1 is mounted, is supported by a framework 31 provided with a variation eliminating mechanism 32. A region surrounded by the framework 31, a base disk 33 and the sample chamber cover 11 (which corresponds to the inside of the sample chamber in the first embodiment) is in the atmospheric state, therefore, such preliminary evacuation installation as the load chamber is unneeded for the sample transportation. Further, because of the use of the air bearing no lubricants such as lubricant oil are needed, therefore, possible contamination such as inside the column and parts around the sample can be greatly reduced. The structure of the top table 21 and the differential evacuation of the second embodiment will be explained with reference to FIGS. 7 through 9. FIG. 7 shows a perspective view of the top table 21 of the second embodiment, FIG. 8 shows a cross sectional view taken along line Bxe2x80x94B in FIG. 7, and FIG. 9 is a diagram showing the differential evacuation action. The top table 21 is provided with, in addition to the mechanism as explained in connection with the first embodiment, an air pad 21I of a porous material such as ceramics which permits passing of gas and a gas supply use tube 21J which permits supply of compressed gas. In the present embodiment, through blowing out gas fed from the gas supply use tube 21J from the upper face of the air pad 21I, the top table 21 can be supported through the air bearing with respect to the bottom face of the sample chamber cover 11. In the structure of the top table 21 as explained in connection with the first embodiment, when the environment around the top table 21 is in atmospheric pressure and the environment around the sample 8 is in high vacuum, a high pressure caused by the pressure difference will act onto the bottom face of the top table 21, thereby, the top table 21 possibly contacts to the bottom face of the sample chamber cover 11. According to the second embodiment through the gas supply pressure from the air pad 21I the distance G3 between the top table 21 and the bottom face of the sample chamber cover 11 is kept constant and the above possible contact can be avoided. Further, through managing the profile irregularity of the bottom face of the sample chamber cover 11, the top table 21 moves following the bottom face of the sample chamber cover 11, thereby, variation amount in the height direction of the top table 21 can be reduced. Further, FIG. 10 is an example where a step xcex94Z is provided between the upper face of the air pad 21I and the upper face of the top table 21 at the outer circumferential side in order to reduce air flow rate flown in into the evacuation use groove portion 21E from the air pad 21I. In the present structure, since the distance G3 between the bottom face of the sample chamber cover 11 and the air pad 21I is selected larger than the distance G1 between the bottom face of the sample chamber cover 11 and the upper face of the top table 21, the air fed from the air pad 21I can be easily flown out from the top table 21, thereby, the environment around the sample can be kept in further higher vacuum. Further, as shown in FIG. 11 through provision of the evacuation use groove portion in two or more steps, it is possible to evacuate around the sample more rapidly into a high degree of vacuum. Hereinabove, the circuit pattern forming apparatuses have been explained by taking the electron beam pattern drawing apparatuses as examples, the circuit pattern forming apparatus of the present invention can be used as a circuit pattern inspection apparatus for inspecting circuit patterns for samples on which circuit patterns are already formed. According to the present invention, through the stable gas evacuation the environment around the sample can be kept in high degree of vacuum constantly, thereby, an evacuation use sample chamber which can realize always stable vacuum is provided. Further, through use of the evacuation use sample chamber a circuit pattern forming apparatus can be provided which permits a pattern drawing (exposure, inspection) over the entire face of a sample under environment condition of the sample chamber in low degree of vacuum or in atmospheric pressure while keeping the electron beam passage in high vacuum and without deteriorating the attitude accuracy of the top table.
051503921	abstract	An X-ray mask membrane 12 is discussed wherein a cantilever and tip portion such as used on an atomic force or scanning tunneling microscope are fabricated directly as part of the mask. The mask is located over a wafer and the vertical (z) motion of the tip with respect to the wafer is achieved with a piezoelectric device which is mounted on a movable support above the cantilever. Piezoelectric device may be a tube having an electrode divided into quadrants so that the end of the tube could be positioned in three dimensions to allow for alignment of the end of the tube to the cantilever tip. X and Y motion of the tip and the mask membrane relative to the wafer is achieved by mounting the wafer on an x-y stage driven by piezoelectric or other transducers. The wafer includes a raised alignment mask on its upper surface. The wafer, mask membrane, and z piezoelectric tube are held rigidly but adjustably with respect to each other by a mechanical fixture. The z piezoelectric tube is lowered until it touches the cantilever; it is then lowered further by the designed gap spacing, deflecting the cantilever downward. The wafer is then raised until it is detected by the tip on the cantilever, either by sensing a tunneling current (STM) or a force (AFM). The wafer is now at the correct z gap setting, and is scanned back and forth in the x and y directions until the location of the alignment mark is determined by the cantilever tip following the contours of the alignment mark, thus setting the proper alignment between the wafer and the mask in the x, y direction.
	claims	1. An electrolytic method of loading hydrogen into a cathode comprising:placing the cathode and an anode in an electrochemical reaction vessel filled with a solvent;mixing a DC component and an AC component to produce an electrolytic current such that the electrolytic current comprises a DC biased waveform wherein an AC waveform is superimposed onto a DC waveform;applying the electrolytic current to the cathode, wherein a first voltage and a second voltage applied to the cathode relative to the anode that load hydrogen onto the cathode are negative,wherein the DC component includes cycling between:the first voltage applied to the cathode for a first period of time;the second voltage applied to the cathode for a second period time;wherein the first voltage is more negative than the second voltage, andwherein the second period of time is shorter than the first period of time; andwherein the AC component has a frequency between about 1 Hz and about 100 kHz; andwherein the peak sum of the voltages supplied by the DC component and AC component is higher than the dissociation voltage of the solvent. 2. The method of claim 1, further comprising:performing an initial loading comprising:mixing an initial DC component and an initial AC component to produce an initial electrolytic current such that the initial electrolytic current comprises a DC biased waveform wherein an AC waveform is superimposed onto a DC waveform;applying the initial electrolytic current to the cathode, wherein a third voltage and a fourth voltage applied to the cathode relative to the anode that load hydrogen onto the cathode are negative,wherein the initial DC component includes cycling between:the third voltage applied to the cathode for a third period of time;the fourth voltage applied to the cathode for a fourth period time;wherein the fourth voltage is higher than the third voltage;wherein the third period of time and the fourth period of time are approximately the same; andwherein the third voltage is lower than the first voltage and the fourth voltage is lower than the second voltage; andwherein the initial AC component has a frequency between about 1 Hz and about 100 kHz. 3. The method of claim 1, further comprising sealing the electrochemical reaction vessel. 4. The method of claim 3, further comprising flushing the electrochemical reaction vessel with a reductive gas prior to sealing the electrochemical vessel. 5. The method of claim 1, further comprising applying a magnetic field to the electrochemical reaction vessel. 6. The method of claim 1, wherein the frequency of the AC component is dynamically adjusted. 7. The method of claim 1, wherein the DC component and AC component of the electrolytic current is mixed with a DC bias. 8. The method of claim 1, wherein the cathode is comprised of at least one of palladium or a palladium alloy. 9. The method of claim 1, wherein the cathode has a hydrogen diffusion rate greater than about 0.1 cm3/cm2/s. 10. The method of claim 1, wherein the cathode has a hydrogen diffusion rate greater than about 1.4 cm3/cm2/s. 11. The method of claim 1, wherein the solvent is a solution containing LiOH. 12. The method of claim 1, wherein the solvent is a solution containing LiOD. 13. A system for electrolytic loading of hydrogen into a cathode comprising:an electrochemical reaction vessel filled with a solvent;a cathode and an anode disposed within the electrochemical reaction vessel;an electrolytic current source connected to the cathode, wherein the electrolytic current source is programmed to apply an electrolytic current to the cathode, wherein a first voltage and a second voltage applied to the cathode relative to the anode that load hydrogen onto the cathode are negative, and wherein the electrolytic current comprises:a DC component, wherein the DC component cycles between:the first voltage applied to the cathode for a first period of time;the second voltage applied to the cathode for a second period time;wherein the first voltage is more negative than the second voltage, andwherein the second period of time is shorter than the first period of time; anda AC component with a frequency between about 1 Hz and about 100 kHz;wherein the peak sum of the voltages supplied by the DC component and AC component is higher than the dissociation voltage of the solvent andwherein the DC component and the AC component are mixed such that the electrolytic current comprises a DC biased waveform wherein an AC waveform is superimposed onto a DC waveform. 14. The system of claim 13, wherein the electrochemical reaction vessel is sealed. 15. The system of claim 14, wherein the electrochemical reaction vessel is flushed with a reductive gas prior to sealing. 16. The system of claim 13, further comprising a magnetic field applied to the electro chemical reaction vessel. 17. The system of claim 13, wherein the frequency of the AC component is dynamically adjusted. 18. The system of claim 13, further comprising a mixer, wherein the mixer mixes the DC component and AC component of the electrolytic current with a DC bias. 19. The system of claim 13, wherein the cathode is comprised of at least one of palladium or a palladium alloy. 20. The system of claim 13, wherein the cathode has a hydrogen diffusion rate greater than about 0.1 cm3/cm2/s. 21. The system of claim 13, wherein the cathode has a hydrogen diffusion rate greater than about 1.4 cm3/cm2/s. 22. The system of claim 13, wherein the solvent is a solution containing LiOH. 23. The system of claim 13, wherein the solvent is a solution containing LiOD.
	description	This application claims the benefit of Korean Patent Application No. 10-2012-0074862, filed on Jul. 10, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 1. Field of the Invention The present invention relates to an apparatus and method for safely controlling a control rod of a nuclear reactor for a nuclear power plant. 2. Description of the Related Art Generally, an apparatus for controlling a control rod of a nuclear reactor may control a position and a speed of the control rod, and the like, using an automated algorithm in order to converge an output of heat or neutrons generated by the nuclear reactor to a power demand desired by a user. The apparatus is disclosed in Korean Patent Application No. 10-2002-0047040, and Japanese Patent Laid-Open Publication No. JP 2004150928. In a nuclear reactor for a nuclear power plant, an output of the nuclear reactor may be controlled by controlling a speed of the control rod formed by a neutron absorber. However, during the controlling process, software or hardware errors may occur and controlling of the control apparatus may be performed in an inverse order. In addition, despite the control apparatus being operated in a normal state, the control rod or a control rod assembly may be withdrawn instantaneously by an external mechanical force resulting from damage to the nuclear reactor, or a rapid change in a flow speed in the nuclear reactor. When the control rod assembly is withdrawn contrary to an intended control, a neutron absorbing function of the control rod may be partially lost, and the output of the nuclear reactor may increase. Such an increase in the output of the nuclear reactor may result in critical safety problems. Accordingly, accident prevention based on a concept of safety design in nuclear power industries may be needed. In this vein, there is a need for an apparatus for sensing such an accident, and preventing a withdrawal of the control rod mechanically in order to prevent a secondary accident when an accident occurs. An aspect of the present invention provides an apparatus and method for controlling a control rod of a nuclear reactor for a nuclear power plant, the apparatus and method that may control the nuclear reactor more safely by stopping a withdrawal of the control rod mechanically because an output of the nuclear reactor may increase when the control rod is withdrawn irrespective of an intended control of the control rod. According to an aspect of the present invention, there is provided an apparatus for controlling a control rod of a nuclear reactor for a nuclear power plant, the control rod to be inserted into or withdrawn from the nuclear reactor, the apparatus including a first controller to output a signal to insert or withdraw the control rod, a mechanical portion to perform insertion or withdrawal of the control rod in response to the signal output by the first controller, the mechanical portion including a movement process portion disposed at an upper end of the control rod, a stop latch to restrain the control rod by an electromagnetic interaction with the movement process portion, a moving latch to move the control rod by restraining the control rod by an electromagnetic interaction with the movement process portion, and a lift coil to insert or withdraw the control rod by lifting or lowering the moving latch fixed to the moving process portion, a detector to detect a position or a speed of the control rod when the control rod is inserted or withdrawn by the mechanical portion, and a brake to stop the control rod by force when the control rod is withdrawn irrespective of an intended control of the control rod. According to another aspect of the present invention, there is also provided a method of controlling a control rod of a nuclear reactor for a nuclear power plant, the method including, when the control rod is withdrawn irrespective of an intended control of the control rod, due to a malfunction of an apparatus for controlling the control rod of the nuclear reactor for the nuclear power plant, detecting, by a detector, a data value corresponding to a position or a speed of the control rod, transmitting the detected value to a second controller, transmitting a command to operate a brake based on the value transmitted to the second controller, and quickly stopping, by the brake, the abnormal withdrawal of the control rod by force, based on the transmitted command. In controlling a control rod of a nuclear reactor for a nuclear power plant using the configuration and method described above, since an output of the nuclear reactor may be increased when the control rod is withdrawn irrespective of an intended control, the nuclear reactor may be controlled more safely by stopping the withdrawal of the control rod mechanically. Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. Exemplary embodiments are described below to explain the present invention by referring to the figures. Hereinafter, a system for controlling an output of a nuclear reactor according to an embodiment of the present invention will be described in detail with reference to FIG. 1. FIG. 1 is a diagram illustrating a configuration of a system 100 for controlling an output of a nuclear reactor provided to describe an apparatus for controlling a control rod of a nuclear reactor for a nuclear power plant according to an embodiment of the present invention. Referring to FIG. 1, the system 100 may include a sensor 110 to sense an output of heat or neutrons generated by the nuclear reactor, a calculator 120 to calculate an error of the sensed output of the heat or the neutrons with respect to a predetermined power demand, and to calculate a control pressure based on the error, and an output controller 130 to control a position of a control rod 10 based on the control pressure. The system 100 may be configured to control an output of the nuclear reactor by controlling the position of the control rod 10. The output of the nuclear reactor may correspond to the output of the heat or the neutrons. A nuclear power plant using the system 100 may increase the output of the heat or the neutron when the control rod 10 is withdrawn from the nuclear reactor, for example, when the control rod 10 rises from the nuclear reactor. The sensor 110 may sense the output of the heat or the neutrons generated by the nuclear reactor, and may output the sensed output of the heat or the neutrons to the calculator 120. The calculator 120 may calculate an error of the output of the heat or the neutrons with respect to the predetermined power demand, calculate a control pressure based on the error, and output the calculated control pressure to the output controller 130. The control pressure may correspond to a speed of movement of the control rod 10. The output controller 130 may control the position of the control rod 10 based on the control pressure. The calculator 120 may be configured to detect the control pressure, using a predetermined output controlling algorithm. The predetermined output controlling algorithm may employ a method of increasing the output by withdrawing, for example, raising, the control rod 10 when a current output is lower than the predetermined power demand, and decreasing the output by inserting, for example, lowering, the control rod 10 when the current output is higher than the predetermined power demand. Hereinafter, an apparatus for controlling a control rod of a nuclear reactor for a nuclear power plant according to an embodiment of the present invention will be described in detail with reference to FIGS. 2 through 4. FIG. 2 is a diagram illustrating a configuration of an apparatus for controlling a control rod of a nuclear reactor for a nuclear power plant according to an embodiment of the present invention. Referring to FIG. 2, the apparatus, by which a control rod 10 may be inserted into or withdrawn from the nuclear reactor, may include a first controller 200 to output a signal to insert or withdraw the control rod 10, a mechanical portion 300 to perform insertion or withdrawal of the control rod 10 in response to the signal output by the first controller 200, a detector 400 to detect a position or a speed of the control rod 10 when the control rod 10 is inserted or withdrawn by the mechanical portion 300, and a brake 500 to stop the control rod 10 by force when the control rod 10 is withdrawn irrespective of an intended control of the control rod 10. Here, the mechanical portion 300 may include a movement process portion 20 disposed at an upper end of the control rod 10, a stop latch 310 to restrain the control rod 10 by an electromagnetic interaction with the movement process portion 20, a moving latch 320 to move the control rod 10 by restraining the control rod 10 by an electromagnetic interaction with the movement process portion 20, and a lift coil 330 to insert or withdraw the control rod 10 by lifting or lowering the moving latch 320 fixed to the moving process portion 20. The apparatus may further include a second controller 600 to operate the brake 500 in response to a brake signal being received from the detector 400. The first controller 200 may control a position or a speed of the control rod 10, based on data associated with the insertion or the withdrawal of the control rod 10, and may obtain a desired output of the nuclear reactor by controlling the control rod 10. In addition, a control value output by the first controller 200 may be transferred to the mechanical portion 300. The mechanical portion 300 may be operated based on the control value. The control rod 10 may be inserted or withdrawn by the mechanism portion 300. As an example, the first controller 200 may control the insertion or the withdrawal of the control rod 10 in the nuclear reactor, using a data output value. The mechanical portion 300 may include the movement process portion 20, the stop latch 310, the moving latch 320, and the lift coil 330. At least three pairs of latches and coils may be operated by sequential movement and dissolution. The stop latch 310 may be inserted into a recess of the movement process portion 20 disposed in an upper portion of the control rod 10 to stop the control rod 10. For example, the stop latch 310 of the mechanical portion 300 may be inserted into or withdrawn from the recess of the movement process portion 20 disposed in the upper portion of the control rod 10 by an electromagnetic interaction, like an electromagnet, using a control algorithm of the first controller 200. The stop latch 310 may stop the control rod 10 according to an intended control. The moving latch 320 may be inserted in the recess of the moving process portion 20 disposed in the upper portion of the control rod 10 to control a movement of the control rod 10. For example, the moving latch 320 of the mechanical portion 300 may be inserted into or withdrawn from the recess of the moving process portion 20 disposed in the upper portion of the control rod 10 by an electromagnetic interaction, like an electromagnet, using the control algorithm of the first controller 200. The moving latch 320 may move the control rod 10 according to an intended control. In addition, the moving latch 320 may be connected to the lift coil 300, and may be lifted or lowered by the lift coil 330. The lift coil 330 may lift or lower the moving latch 320, and may correspond to a main power source for inserting or withdrawing the control rod 10. In addition, the lift coil 330 may control a position or a speed at which the control rod 10 is to be inserted or withdrawn. That is, the lift coil 330 may control the position or the speed at which the control rod 10 is to be inserted or withdrawn, based on a control signal of the first controller 200. The detector 400 may correspond to a linear encoder. The detector 400 may detect linear position information of the control rod 10, and may calculate a speed of the control rod 10 based on the detected linear position information. When the calculated speed is greater than or equal to a predetermined reference value, the detector 400 may transfer an output signal to the first controller 200 or the second controller 600. For example, the detector 400 corresponding to the linear encoder may recognize an insertion or a withdrawal of the control rod 10 by recognizing the position of the control rod 10, and may control the control rod 10 according to an intended control, by extracting speed information of the control rod 10 from the position information. In addition, the detector 400 may apply a blocking signal to a blocking portion (not shown) connected to the mechanical portion 300, thereby blocking a power to be applied to the mechanical portion 300. The brake 500 may stop the control rod 10 mechanically when the control rod 10 is withdrawn contrary to an intended control, due to an electrical or mechanical malfunction of the nuclear reactor. For example, the control rod 10 may be withdrawn irrespective of an intended control due to an error in a control circuit of the first controller 200. Also, the control rod 10 may be withdrawn when a coupling between the control rod 10 and the control apparatus is damaged due to unexpected factors, for example, damage to the nuclear reactor, a change in a flow speed, and the like. In this instance, the brake 500 may stop the control rod 10 mechanically to prevent a further withdrawal of the control rod 10, thereby preventing an increase in the output of the nuclear reactor. The second controller 600 may control the brake 500, by outputting an electrical signal to the brake 500 based on a resulting value detected by the detector 400. For example, the second controller 600 may compare a data value detected with respect to the position or the speed of the control rod 10 by the detector 400 to a predetermined control value. When the detected data value differs from the predetermined control value, the second controller 600 may determine that an accident happens, and may output a braking command to the brake 500, thereby stopping the control rod 10 by force. FIG. 3 is a cross-sectional view illustrating a brake 500 included in an apparatus for controlling a control rod 10 of a nuclear reactor for a nuclear power plant according to an embodiment of the present invention. Referring to FIG. 3, the brake 500 in the apparatus for controlling the control rod 10 of the nuclear reactor for the nuclear power plant may include a first recess 510 disposed on a side of the control rod 10, a second recess disposed on an external wall corresponding to the first recess 510, and a stopper 530 disposed in an internal portion of the second recess, and configured to be inserted into the first recess 510 to stop a withdrawal of the control rod 10 by force. The first recess 510 may be formed by a first wall 511, a second wall 512, and a third wall 513. A plurality of first recesses 510 may be disposed on the external surface of the control rod 10 at regular intervals. In addition, a shape and a size of the first recess 510 are not limited to the embodiment of FIG. 3, and may vary depending on a structure of the control rod 10. The second recess 520 may be formed by a first wall 521, a second wall 522, and a third wall 523. The second recess 520 may be disposed on the external wall corresponding to the control rod 10, and may form a space sufficient for installing the stopper 530. In addition, a shape and a size of the second recess 520 are not limited to the embodiment of FIG. 3, and may vary depending on a structure of the control rod 10 A spring 532 or a hydraulic device 532 may be disposed at an end of the stopper 530, and a roller 531 may be disposed at another end. In addition, when the control rod 10 operates normally, the stopper 530 may be fixed in the second recess 520 while the spring 532 or the hydraulic device 532 is compressed. When the control rod 10 is withdrawn due to a malfunction, a pressure of the spring 532 or the hydraulic device 532 may be released. In this instance, the stopper 530 may rotate perpendicularly such that a side surface of the stopper 530 may be in contact with the first wall 521 of the second recess 520, and another side surface of the stopper 530 may be in contact with the first wall 511 of the first recess 510. In particular, when the control rod 10 operates normally, the stopper 530 may be stopped in an internal portion of the second recess 520 while being compressed by a device, for example, the spring 532 or the hydraulic device 532. When the control rod 10 is withdrawn due to a malfunction, the second controller 600 may transmit a brake signal to the brake 500. The pressure of the spring 532 or the hydraulic device 532 may be released, the stopper 530 may rotate perpendicularly such that a side surface of the stopper 530 may be in contact with the first wall 521 of the second recess 520, and another side surface of the stopper 530 may be in contact with the first wall 511 of the first recess 510. Accordingly, the withdrawal of the control rod 10 caused by the malfunction may be prevented. FIG. 4 is a cross-sectional view illustrating a stopper according to an embodiment of the present invention. Referring to FIG. 4, a brake 500 may include a first recess 510 disposed on a side of a control rod 10, a second recess 520 disposed on an external wall corresponding to the first recess 510, and a stopper 530 disposed in an internal portion of the second recess 520, and configured to be inserted into the first recess 510 to stop a withdrawal of the control rod 10 by force. In this instance, a plurality of first recesses 510 may be disposed on an external surface of the control rod 10 at regular intervals. In addition, a roller 531 may be disposed in the stopper 530. Here, the first recess 510 may be formed by a first wall 511, a second wall 512, and a third wall 513, and the second recess 520 may be formed by a first wall 521, a second wall 522, and a third wall 523. In a case in which the stopper 530 is in contact with a projection (not shown), as opposed to the first recess 510 of the control rod 10 when the stopper 530 rotates due to a malfunction of the control rod 10, the roller 531 of the stopper 530 may slide along a surface of the projection, thereby preventing the stopper 530 from being damaged by an external force or friction. In addition, since the roller 531 may slide along the surface of the projection to be in contact with the first wall 511 of the first recess 510, the control rod 10 may be stopped by force. In addition, when the control rod 10 is inserted, for example, lowers, the roller 531 of the stopper 530 may be pushed down by the control rod 10 in an inserting direction of the control rod 10, and the stopper 530 may be fixed in the second recess 520 by an electromagnetic interaction. For example, when the control rod 10 is inserted, the roller 531 of the stopper 530 may be pushed down in a lower direction by the projection of the control rod 10, and may be pushed into the second recess 520 such that the stopper 530 may be fixed in the second recess 520 by an electromagnetic interaction. Accordingly, since the stopper 530 may be pushed by the projection of the control rod 10 to be fixed in the second recess 520 when the control rod 10 is inserted, the stopper 530 may not act as a brake and thus, a safety of the nuclear reactor may be secured. Here, the roller 531 of the stopper 530 may correspond to a compression roller. Hereinafter, an apparatus for controlling a control rod of a nuclear reactor for a nuclear power plant according to another embodiment of the present invention will be described in detail with reference to FIGS. 5A and 5B. FIGS. 5A and 5B are cross-sectional views illustrating a stopper according to another embodiment of the present invention. Referring to FIGS. 5A and 5B, a brake 500 may include a first recess 510 disposed on a side of a control rod 10, a second recess 520 disposed on an external wall corresponding to the first recess 510, and a stopper 530 disposed in an internal portion of the second recess 520, and configured to be inserted into the first recess 510 to stop a withdrawal of the control rod 10 by force. Here, the first recess 510 may be formed by a first wall 511, a second wall 512, and a third wall 513, and the second recess 520 may be formed by a first wall 521, a second wall 522, and a third wall 523. In addition, a plurality of first recesses 510 may be disposed on an external surface of the control rod 10 at regular intervals. FIG. 5A illustrates the stopper 530 of the brake 500 being fixed in the internal portion of the second recess 520 when the control rod 10 operates normally, and 5B illustrates the stopper 530 of the brake 500 being inserted into an internal portion of the first recess 510 when the control rod 10 is withdrawn due to a malfunction. The stopper may 530 include an inclined surface disposed at a position corresponding to the first recess 510. A surface of the stopper 530 may be fixed to the second recess 520 by a spring 532 or a hydraulic device 532, and a roller 531 may be disposed on a bottom surface of the stopper 530. In addition, when the control rod 10 operates normally, the stopper 530 may be fixed in the second recess 520 while the spring 532 or the hydraulic device 532 is compressed. When the control rod 10 is withdrawn due to a malfunction, a pressure of the spring 532 or the hydraulic device 532 may be released. In this instance, the stopper 530 may protrude in a direction of the control rod 10 such that a portion of the bottom surface of the stopper 530 may be in contact with the first wall 511 of the first recess 510, and a portion of the stopper 530 may be fixed in the second recess 520. Accordingly, when the portion of the stopper 530 is inserted into the first recess 510, the withdrawal of the control rod 10 caused by the malfunction may be prevented. Here, the roller 531 of the stopper 530 may correspond to a compression roller. In a case in which the stopper 530 is in contact with a projection (not shown), as opposed to the first recess 510 of the control rod 10 when the stopper 530 protrudes in the direction of the control rod 10 due to a malfunction of the control rod 10, the roller 531 of the stopper 530 may slide along a surface of the projection, thereby preventing the stopper 530 from being damaged by an external force or friction. In addition, since the roller 531 may slide along the surface of the projection to be in contact with the first wall 511 of the first recess 510, the control rod 10 may be stopped by force. In addition, when the control rod 10 is inserted to be in contact with the inclined surface of the stopper 530, the stopper 530 may be pushed in a direction of the second recess 520 by the control rod 10, and may be fixed in the second recess 520 by an electromagnetic interaction. Accordingly, since the control rod 10 may be inserted in a lower direction while sliding along the inclined surface of the stopper 530 when the control rod 10 is inserted, the stopper 530 may not act as a brake and thus, a safety of the nuclear reactor may be secured. A braking time of the control rod 10 may be determined based on a withdrawing speed of the control rod 10, a density of the first recess 510, a distance from the control rod 10 to the external wall, and the like. Accordingly, the braking time of the control rod 10 may be extended or shortened by adjusting the foregoing factors. Hereinafter, a method of controlling a control rod of a nuclear reactor for a nuclear power plant according to an embodiment of the present invention will be described in detail. The method may include, when the control rod is withdrawn due to an error in an apparatus for controlling the control rod of the nuclear reactor for the nuclear power plant, detecting, by a detector, a data value corresponding to a position or a speed of the control rod, transmitting the detected value to a second controller, operating, by the second controller, a brake based on the transmitted signal, and stopping, by a stopper of the brake being inserted in a first recess, the abnormal withdrawal of the control rod mechanically. Here, the method may further include determining, by the second controller, a malfunction of the control rod, by comparing the value detected by the detector to a predetermined control value. In addition, the method may further include controlling the stopper to be fixed in an internal portion of a second recess, or to be inoperative when the control rod is inserted. Accordingly, the apparatus and method for controlling the control rod of the nuclear reactor for the nuclear power plant may stop the control rod mechanically when a safety accident occurs due to a malfunction or an excessive speed of the control rod, thereby minimizing an over-inserting time of the control rod and preventing an increase in an output of the nuclear reactor. According to exemplary embodiments of the present invention, there is provided an apparatus and method for controlling a control rod of a nuclear reactor for a nuclear power plant, the apparatus and method that may control the nuclear reactor more safely by stopping a withdrawal of the control rod mechanically because an output of the nuclear reactor may increase when the control rod is withdrawn irrespective of an intended control of the control rod. Although a few exemplary embodiments of the present invention have been shown and described, the present invention is not limited to the described exemplary embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
	description	An example of a device and additional supporting structures are described in FIG. 5. FIG. 5 illustrates three parts: a source 100, mounted to a coaxial mounting bus 102 which in turn is connected to an impulse circuit 104. The source is the device which forms a compound plasma configuration (PMK). The coaxial mounting bus is a convenient way to attach the source to the impulse circuit and allow for linking of the axial flux produced in the source through the forming PMK. The impulse circuit is one way to drive the source in order to form a compound plasma configuration. The compound plasma configuration is produced at the formation end 106 of the source 100. An end on view of this formation end is shown in FIG. 6. The outermost ring is an optional insulating support cylinder 108. Moving toward the center the next ring in represents an annular electrode 111. Continuing inward, the next ring represents insulation 112, which is strong, rigid, and completely fills the volume within the conducting cylinder 110 and within which is embedded a helical conductor 114, both of which are shown in FIG. 7. Protruding from the helical conductor 114 through the insulation 112 are a plurality of pins 116. Also protruding through the insulation is the annular electrode 111 which is electrically connected to the conducting cylinder 110. FIG. 7 is a cut away side view of the source 100. The generally cylindrical helical conductor 114 is composed of a plurality of equally spaced wires 118, each wire forming a similar helical path. Preferably, the helical conductor is composed of at least three wires, most preferably at least 5 wires. These individual wires 118 may have an insulating coating which may be different from the insulation 112 within which the helical conductor 114 is embedded. The wires 118 together each traverse the full length of the helical conductor 114 in the heliform manner described, and then constrict into a straight axial bundle 113, illustrated in FIG. 8, in the region beyond the termination of conducting cylinder 110 at the attached conducting support disk 120. The axial bundle 113 is within and coaxial with insulating tube 124, thus allowing axial magnetic flux produced by the helical conductor 114 during operation to link together around the conducting cylinder. The conducting cylinder 110 is electrically connected to a conducting support disk 120, which may optionally have a slit 122 cut through it to help suppress currents induced by axial magnetic flux. Conducting support disk 120 has fastening holes 228 for fastening the coaxial mounting bus 102 to the source 100. Extending through the conducting cylinder 110, through the support disk 120, and out, is an insulating tube 124 within which an extension of the axial bundle 113 attach to connector rod 126. The insulating tube may form part of the insulation 112 within which the helical conductor 114 is embedded. Extending out from the insulating tube 124 is a connector rod 126. The connector rod 126 is electrically connected to the axial bundle 113, and therefore electrically coupled to the helical conductor 114. FIG. 8 is a magnified illustration of a helical conductor 114. As illustrated, the wires 118 form one or more revolutions around the axis 130 of the helical conductor 114, and a tangent 128 to the wires forms an angle a 132 with the axis 130 of the helical conductor 114. The angle describes what is known in the art as helicity. Generally, helicity is low so that this angle would normally be below 30 degrees, preferably 10-30 degrees. This allows for PMKs to be formed with less residual velocity and better energy efficiency. However, this may sacrifice source life; the magnetic stress can be quite high since the helical conductor will suffer net strong radial compression. By setting the helicity to 45 degrees, the source currents will tend to be more force-free, relieving radial stress, and generally leading to a longer useful life and the capacity for higher loadings, i.e., high power. With this choice of helicity, push-off velocities can be on the order of ten kilometers per second in STP air, leaving the PMK with less total internal energy. For forming a PMK with more kinetic energy, the angle is preferably 30-80 degrees. As the helical conductor is lengthened, the greater the magnetic field and the more energy is transfered into the growing PMK. However, this increases the inductance and slows down the current pulse. By considering the speed of the current pulse, and these two competing factors, a length suitable to the circuit which drives the source can be selected. The outward radial stress of high loadings on conducting cylinder 110 generally is well tolerated with a choice of conducting materials and the support of support cylinder 108. FIG. 8 also illustrates a cylinder of the insulation 112 which would be inside the helical conductor 114 and the axial bundle 113. The insulation 112 inside of the source may completely fill the interior of the conducting cylinder 110 and encase the helical conductor 114. For materials used for a more expensive version of this source, the insulation 112 inside of the source may be filled with a strong, high temperature non-porous ceramic with resistance to mechanical shock and plasma flux, which fills the interior of a refractory conducting cylinder 110 and embeds a refractory helical conductor 114. One suitable candidate for such conducting medium is pure boron metal. For highly loaded fusion applications the refractory conducting media may be composed of the purified isotope, boron 11 (11B). The choice of material used in the annular electrode 111 includes using the same conducting material as the conducting cylinder 110. Likewise, the pins 116 may be made of the same material as the helical conductor 114 by extending the wires 118, with any insulation removed, for a short distance beyond the insulator 112. For materials used for a less expensive version of this source, see the Example. FIG. 18 shows an alternative embodiment of the source 100. A pinching coil 280 may be placed coaxially in the plane of the electrodes or just above the source 100, and can be used to pinch off and separate the compound plasma configuration as formation has finished, in the region where plasma sheath 192, illustrated in FIG. 12H, would be attached to the annular electrode 111. This may allow for the reduction of contaminants from the pins 116 or annular electrode 111 from entering the forming PMK. Furthermore, this pinching coil may also be bowl shaped, in which case it can add additional momentum to the compound plasma configuration translating away from the source. A section of the support cylinder 108 which would normally be present has been cut away (dotted line) in FIG. 18 in order to illustrate flux slots 282 and conducting cylinder 110. The flux slots 282 may be formed in the conducting cylinder 110 to provide flux produced by the helical conductor 114 an alternate opening to more freely link by reentering above the conducting disk 134. A perspective of the coaxial mounting bus 102 is illustrated in FIG. 9. The coaxial mounting bus functions to electrically couple the source 100 and the impulse circuit 104, without interfering with magnetic fields produced by the source 100 during operation. The ends of the coaxial mounting bus 102 may be a front conducting disk 134 with a front hole 136 in the center, and a rear conducting disk 135 with rear hole 137. These conducting disks 134 and 135 are connected together by a plurality of conducting support rods 138. The support rods 138 electrically and mechanically couple the conducting disks 134 and 135, without inhibiting the linking of magnetic flux produced by the source 100 during operation. The source 100 may be attached to the coaxial mounting bus 102 and axial center pin 147 by fastening the support disk 120 to the front conducting disks 134, as illustrated in FIG. 5. This electrically couples the conducting cylinder 110 to the coaxial mounting bus 102. The rear conducting disk 135 is electrically coupled to the impulse circuit 104. The insulating tube 124 and connector rod 126 of the back end of the source 140 passes through the front hole 136 in the front conducting disk 134 and within the axial center insulator tube 149. As also illustrated in FIG. 5, the connector rod 126 can be electrically coupled to the impulse circuit 104 via the axial center pin 147, for example, using a swage connector 151. The electrical coupling of the axial center pin 147 can pass through the hole 137 in the rear conducting disk 135 and electrically connect to the impulse circuit 104. The front conducting disk 134 may also have a plurality of holes 142 for attachment of the support rods 138, as well as a plurality of fastening holes 144 for attachment to the support disk 120. For electrical coupling to the impulse circuit 104, the rear conducting disk 135 may have fastening holes 145 for attachments to electrically couple to the impulse circuit 104. The rear conducting disk may also have holes 143 for attachment of support rods 138. In FIG. 5 axial insulator tube 149 has been omitted in order to make visible those elements which would otherwise be hidden, such as the axial center pin 147, the hole in the rear conducting disk 137, and the swage connector 151. The impulse circuit 104 is schematically illustrated in FIG. 10. The impulse circuit 104 contains circuit elements connected through a parallel plate transmission line, which is composed of a ground plate 288, a capacitor plate 290 and a source plate 292. A parallel plate transmission line is suitable for high power applications, or alternatively, a bundle of coaxial cables could be substituted for the parallel plate transmission line. The ground plate 288 is continuous and connects all circuit elements and ground 298. The high voltage plate consists of two pieces, a capacitor plate 290 and a source plate 292. The capacitor plate 290 and source plate 292 may be electrically connected through a fast-rise high current firing switch 150. The impulse circuit 104 has a power supply 146, which is connected across the capacitor plate 290 and the ground plate 288. The capacitor plate 290 is connected to the high side of capacitor bank 148 and the high side of the firing switch 150. The ground plate 288 is connected to the ground side of the capacitor bank 148 and each of the elements connected to the source plate 292. The source plate 292 connects the low voltage side of the firing switch 150 to the high voltage side of the crowbar switch 152, and is electrically coupled to the source 100 through the coaxial mounting bus 102. The low side of the crowbar switch 152 and the conducting cylinder 110 are electrically coupled coaxially to the ground plate 288, the latter via axial center pin 147. Optionally, along the electrical coupling between the high voltage side of capacitor bank 148 and the capacitor plate 290 may be a fuse 156. FIG. 10 also includes plasma 158 produced during operation. The impulse circuit is principally a modified LC circuit, for the purpose of achieving a rectified current waveform. This may be achieved through the use of crowbar switches or by balancing the inductance and capacitance of the circuit against the inductive load of the forming plasma. The capacitor bank supplies stored energy in the form of charge at a high potential to drive high current levels to the source and developing compound plasma configuration. The low inductance parallel plate transmission line, and low inductance circuit elements, including the high current switch, allow the total stored charge to drive a fast rising current pulse through the source and developing compound plasma configuration. At peak current, the circuit energy is stored magnetically in proportion to the distributed inductance of the circuit elements. More of the circuit inductance may be concentrated in the forming PMK during its maturing stages of development. This will have the effect of retarding the current of the circuit, producing a waveform in which the current is depleted more quickly, as shown in FIG. 11. Although the current may be dropping with time, the effective energy stored within the increasing inductive load of the maturing PMK continues to increase. Near the peak of the current pulse, the crowbar (shorting) switch, or bank of such switches, is used to shunt the current across a transmission line between the capacitor bank and the remaining circuit components. The crowbar switch 152 can be activated using for example, trigger 160. This procedure traps or locks the circuit energy in the magnetic (high current) mode, thus thwarting the loss of magnetic energy from the maturing compound plasma configuration. Shunting the current across the transmission line between the capacitor bank and the remaining circuit components hinders circuit current reversal, or ringing, by inhibiting the circulating current from recharging the capacitors, in conjunction with the increasing inductance of the forming PMK, significantly extending the lifetimes of the capacitors. The current wave form is almost lightning-like with a very fast rise time or leading edge and followed by a monotonically decreasing decay time, where the rate of drop decreases due to the rising inductance load of the maturing compound plasma configuration. FIG. 11 is a graphical diagram illustrating current generated by the impulse circuit versus time. As used in this application, bactrian-shape means exactly the shape of the current versus time curve of FIG. 11. The letters on the time axis correspond to the formation stages of the compound plasma configuration illustrated in FIGS. 12A through 12H. Once the capacitor bank has been charged, the firing switch is closed, allowing current to flow through the impulse circuit, and the source, breaking down the fluid and forming a plasma annulus between the annular electrode and the pins. This drives current through the helical conductor, through the pins, through the conducting cylinder, as well as through the plasma present between the pins and the annular electrode. The current which passes through the helical conductor also generates and partitions magnetic fields, both an axial or solenoidal field in the z direction along the axis and within the volume of the helical conductor, and an azimuthal field within the volume between the helical conductor and the conducting cylinder. The axial field generated within the helical conductor extends outwardly from both ends of the helical conductor, and links externally to the conducting cylinder. At one end, this magnetic flux passes through coaxial mounting bus and at the other end it passes outward through a hole defined by the pins and the inner rim of the plasma annulus. Essentially, this flux does not cut the surface of the plasma annulus or the conducting cylinder. The azimuthal magnetic field exerts pressure on the conducting cylinder, the helical conductor and the plasma annulus and its radial current, inflating the plasma to initiate formation of a series of stages of PMK formation, to produce a compound plasma configuration, and illustrated in FIGS. 12A through 12H. The impulse circuit described here lies at a low level of energy and peak power in comparison with the far higher range of energy and peak power currently used in the field. Furthermore, there are Marx generators, and inductively driven pulse generator, for example, technology which may be used to drive a suitably scaled source. For very high energy cases, conventional fuses or delayed inductive opening switches may optionally be employed to extinguish the remaining current and isolate the source from the newly formed PMK late in the discharge, as indicated in FIG. 11. Such a device may also be employed with a resistive bypass. This will have the effect of reducing the current after energy transfer into the forming compound plasma configuration. Consequently, there may be a reduction in the amount of blow off plasma and therefore less wear on the source. The compound plasma configuration of the present invention comprises a kernel 36, a vacuum field region 26, and a mantle 28, as mentioned above, and may be established in the same type of gaseous environments as described in the earlier referenced patents of the same inventor. However, the unique formation method and apparatus of the present invention provide the resulting PMK with different structural characteristics than that of the previously. disclosed PMKs. The present invention has a rather small volume between the pins and the annular electrode, so the energy of the circuit is deposited initially in a small volume. Consequently the present invention has very high power density. In contrast, the previous devices deposited their energy across a large volume, resulting in low power density. The PMKs formed by the present invention gain higher conductivity faster, as well as more energy quickly, because the power density is so concentrated. A detailed cross section of the mantle 28 is shown in FIGS. 13A-B. The cross section of the mantle can be viewed as having two principal sections, when surrounded by fluid 10, rather than a plasma. The innermost section is the ionized region 166 and the outer section is the weakly ionized region 168. When formed in air, each region of the mantle has layered plasma regimes which form a radial gradient in the mantle plasma, and is arranged in descending order from highest energy (innermost layer) to lowest energy (outermost layer). When formed in an inert gas which does not form molecules, layer differentiation is simpler. The ionized region has a sharp edge 170 which is itself composed of a wider outer (vacuum region side) predominately ion layer 172 and a thinner inner (plasma side) predominately electron layer 174, as shown in the magnified view of FIG. 13B. This sharp edge has a boundary which is nearly a perfect step function from mantle 28 to a vacuum field region 26. It acts as a close approximation to the results anticipated under the ideal of a step function. This boundary may be slightly diffuse, in a degraded PMK, due to the presence of impurities such as dust, poor formation or nearness to the end of the lifetime of the PMK. Continuing outward from the electron layer 174 is a hot layer 176, a photo ionized plasma 178 and finally a divergence layer 180. The divergence layer 180 is the layer farthest from the kernel 36, into which the majority of the fully ionizing radiation from the kernel can penetrate. The bulk of the ionizing radiation from the kernel plasma is absorbed in the divergence layer 180 due to the influx through the weakly ionized region 168 by diffusion of the excited high capture cross section neutrals. The weakly ionized region 168 has an innermost photo excited layer 182, and a mixed plasma fluid edge 184. This layer may contain ionized molecules and is enclosed by the fluid 10, such as a gaseous atmosphere. FIGS. 12A through 12H illustrate the inflation sequence of a plasma to form a compound plasma configuration (PMK). The formation sequence, once properly triggered and set under the proper conditions, as taught by the invention, proceeds automatically. FIG. 12A illustrates the triggering stage of PMK formation, showing an initial plasma annulus 186, with diverging solenoid field 188 protruding through a central hole 190 in the plasma annulus 186. The plasma annulus forms between the pins 116 and the annular electrode 111, neither of which are shown in FIGS. 12A through 12H, for clarity. The plasma annulus is formed when an impulse current is initially fed to the source 100. FIG. 12B illustrates the plasma ballooning stage of PMK formation, formed by the forces of the azimuthal field 198 upon the plasma annulus 186. This ballooning stage is similar to the, plasma focus, which is well known by artisans skilled in the art of plasma physics, except that the axial magnetic field 196 is trapped within the newly formed central channel 194, which prevents pinch-off of channel 194 by compression due to the surrounding azimuthal field 198. Therefore, in the plasma ballooning stage, a plasma sheath 192 and central channel 194 are formed from the plasma annulus 186. The current passing through the source 100 and the plasma annulus 186 generate an axial magnetic field 196 which threads through a central channel 194. An internal azimuthal field 198 is formed which fills the plasma cavity 199 and impinges upon the facing surfaces of the plasma channel 194 and plasma sheath 192. Both fields produce pressure against the surface of the central plasma channel 194. In the region of pins 116 at the terminus 195 of the central channel 194, the plasma remains resistive and turbulent during the formation, allowing some mixing of the azimuthal 198 and axial fields 196. This mixing drives powerful vortex flows in the plasma, which can erode the pins 116. By making the pins 116 blade-like with their edges aligned with the flow of the vortex, a reduction in drag and ablation may occur. FIG. 12C illustrates the linear Z-pinch stage of PMK formation. In this stage, the plasma sheath 192 continues to inflate, and the central channel 194 elongates. The elongation of the central channel 194 with its attendant high current and azimuthal field 198 and trapped axial field 196 resembles the stabilized classical linear Z-pinch. The plasma cavity 199 continues to expand rapidly, mostly by growing in length, as long as magnetic energy is pumped into it. This stage may occur when the circuit current has reached its maximum value, approximately at 162 in FIG. 11. FIG. 12D illustrates the helical stage of PMK formation. As the central channel 194 continues to lengthen, a second instability (M=1) comes into play, which triggers slowed kinking of the central channel 194 due to the embedded axial field 196. A nearly uniform helical winding of the growing central channel 194 produces plasma channel helix 200. As this process continues, the growing helix 200 increases the circuit inductance, reducing the circuit current level while increasing the energy of the forming PMK. A poloidal field component, illustrated by flux lines 202, which links the helix 200 together, becomes dominant. Dominance of the poloidal field 202 is associated with the tilting of the azimuthal field 198 and the increase in helicity of the central channel 194 in the region of the helix 200. The winding process, driven by magnetohydrodynamic (MHD) forces, i.e., the interaction of the conducting fluid (the plasma) with magnetic and electric fields, twists the central channel 194 into a helix 200. The lengthening and formation of this helical geometry increases the inductance and increases the local magnetic energy and pressure, which acts upon the plasma, producing a plasma sheath 192 with a more plumped profile in the neighborhood of helix 200, as illustrated at 203. FIG. 12E illustrates the coalescent stage of PMK formation. Once multiple loops 205 of the helix 200 exist they begin to contract into the mid-plane of the helix 200. This action is driven by the MHD forces of the poloidal magnetic field 202 on the loops 205 of the helix 200 which forces the helix 200 to form a tighter coil with increased helicity. The growing helix 200 continues to contract into the mid-plane of the helix 200 and also expand outward. The vertical contraction and radial expansion forces are strongest at the mid-plane of the helix 200 due to the increased mutual flux density. Finally the loops 205 within the mid-plane begin coalescence in to an initially resistive plasma ring 204, thus forming a closed current circuit within the plasma ring 204, which is driven by the poloidal field 202 of the coalescing helix 200, as illustrated in FIG. 12F. Once the plasma ring 204 is first formed, all of its flux, including that of the linked uncoalesced loops 205 of the helix 200, is xe2x80x9ctrappedxe2x80x9d within the plasma ring 204 and is no longer available to drive current in the external circuit. The contraction of the helix 200 increases the magnetic coupling in the plasma ring 204, driving an EMF that accelerates the electron current of the plasma ring (azimuthal current 208 and poloidal current 211) to energetic or relativistic values, illustrated in FIG. 12G. The increase in intensity of the flux 210 results from substantial loss of the azimuthal field 198 component within the plasma ring 204. This effect also provides an EMF which drives runaway azimuthal currents 208 at the inner surface of the forming mantle, to relativistic values. These processes generate EMFs on the order of tens of kilovolts per loop. Since the closing time is on the order of many microseconds, which allows many revolutions to multiply the per loop EMF, high gamma runaway currents of many million electron volts are produced. The resulting energetic electron currents 208 and 211, on the order of ten gamma, are associated with conductivities, known as hyperconductivity, of at least about five or six orders of magnitude greater than either copper or thermal plasma conductivities. In the present invention the conductivity is preferably at least 1010 (ohmxe2x88x92cm)xe2x88x921, more preferably at least 1011 (ohmxe2x88x92cm)xe2x88x921, most preferably at least 1012 (ohmxe2x88x92cm)xe2x88x921. With the collapsed azimuthal field 198 and plasma of the straight section of the central channel 194, the neighboring plasma sheath 192, closes inward driven by the fluid 10. The portion of the central channel that does not coalesce into the ring current, dissipates rapidly, as indicated at 209. This completes the formation of the stable and distinctive compound plasma configuration, or PMK, 42, illustrated in FIG. 12H. FIG. 12H illustrates the compound plasma configuration of the present invention. Both the kernel 36 and the mantle 28 have hyperconducting currents. In addition to the parts already described, the PMK 42 has two axi-symmetric polar magnetic cusps 296. These magnetic cusps 296 eject remnant central channel plasma, as well as divergence layer generated plasma, which act as polar end plugs 294. The compound plasma configuration of the present invention is distinct from those described in U.S. Pat. Nos. 4,023,065; 4,891,180; 5,015,432; and 5,041,760 as well as those partially described by Wells et al. The distinct PMK of the present invention has a lifetime and stability orders of magnitude greater, because the currents have a dramatically higher conductivity, also termed hyperconductivity. Distinguishing features between the previous compound plasma configuration and that of the present invention include a sharp edge between the plasma and the vacuum field region 26, both between the mantle 28 and the vacuum field region 26, as well as between the kernel 36 and the vacuum field region 26. Other differences include: the ability to produce high pressure confinement fields using much higher current densities, but without excessive destabilization due to the magneto-plasma heating rates; the ability to use mantle plasma formed over its non-polar regions to capture and conserve the energy of ionizing radiation from the plasma kernel 36 to provide plasma mass, which may also act as end plugging eject a 294 to block the incursion of incoming diffusive neutrals into the polar magnetic cusps 296; and the ability to preferentially eject higher atomic number elements and thus lessen the radiation cooling rate of the mantle 28 in a sort of natural diverter action. The energy used to form the previously made compound plasma configuration, having a very short lifetime and a similar size, as demonstrated by Wells et al, exceeds by more than 100 times that used to generate the PMK of the present invention. Furthermore, compound plasma configurations of the present invention have stable lifetimes about 1000 times longer. Another distinguishing feature of the compound plasma configurations of the present invention are the occurrence of knock-on beams. These beams may appear to emanate from nodes on the equatorial belt of the mantle, and may be visible when they excite the surrounding fluid under certain conditions. Localized low pressure at the mantle surface may attract the nodes. For example, for a compound plasma configuration with a net drift through the surrounding fluid, the beam emissions may occur on a low pressure or xe2x80x9cdown windxe2x80x9d side. These emission points may also be controlled by manipulating the localized plasma pressure along the boundary in the mantle, such as by gas puffing, magnetic impulses, etc. The trajectory of these knock-on beams, once they exit the mantle, can be controlled or shaped with the application of electric or magnetic fields. The beam currents may be measured, which is a reflection of the collisionality of hyperconducting currents of the compound plasma configuration. Furthermore, the strength and direction of the beams may be affected by the geometry of the mantle, the size and age of mantle, and the amount and type of the impurities incorporated into the compound plasma configuration. A dense powerful pulse of hyperconducting electrons may also be derived from the deliberate mechanical breaking, or occasionally from the catastrophic natural termination, of a compound plasma configuration. This releases the hyperconducting currents as a highly compact, tangentially (to their confined orbit) escaping beam. These beams can be directed to produce powerful bursts of high intensity X-rays when they impact densely high atomic number elements, such as lead or tungsten. These high gamma electrons may also be used to transmute elements. The boundary between the mantle 28 and the vacuum field region 26, as well as the kernel 36 and the vacuum field region 26, has a sharp edge. FIGS. 17A-17D provide graphical diagrams explaining the nature of the sharp edge at the boundary of plasma and the vacuum field. FIG. 17A shows a thermal conducting mode profile having a diffuse edge, where T0 260 is electron temperature, np 258 is plasma density, R0 262 is the position of the peak plasma density near the boundary with the vacuum field region and R0+xcex94R 266 is the width of the diffuse Larmor radii (overlapping) vacuum field region boundary at the extreme of the vacuum field region. This diffuse edge is associated with higher energy transport and deeper radial electron thermal gradients that are more typical of a PMK made by the prior art methods, such as partially described in Wells et al. A compound plasma configuration of the present invention, however, has a sharp edge graphically depicted in the hyperconducting mode shown in FIG. 17B. The PMK has reduced density and electron temperature gradients as well as a much narrower Larmor edge at the extreme vacuum field region, which is associated with clamped diffusion due to a hyperconducting boundary current. The relativistic currents in the compound plasma configuration of the present invention, with their hyperconductivity, lead to the sharp edge. FIGS. 17C and 17D provide graphical diagrams explaining the nature of the sharp edge, and refocusing of the boundary sheet current and maintenance of its relativistic (hyperconducting) currents. FIG. 17C shows the peak magnetic energy density B2/2xcexc0 268 at the plasma edge at r0 264 which monotonically decays into the peak plasma density edge at r0+xcex94r0 266 (electron Larmor radii). The ion Larmor radii extend from the plasma edge r0+xcex94r 266 to r0 264 in the vacuum field. The net electric field energy density xcex50E2/2 272 results from the cumulative field generated by the populations of the ions and the electrons in this region. The electric potentials are shown, in FIG. 17D and include a magnetic accelerating EMF ∂B("PHgr")/∂t 274 which accelerates the current whose distribution is shown as jr 276 which is centered in the notch between the peak magnetic energy density B2/2xcexc0 268 and the peak electric energy density xcex50E2/2 272. The electric field distribution E(r) 278 is also illustrated in FIG. 17D for completeness. The dynamics for keeping the currents centered in this notch are as follows. For an electron flowing in the region of net higher magnetic energy density, the accelerating force provided by the magnetic accelerating EMF ∂B("PHgr")/∂t 274 exceeds the drag due to the lower particle density in that region. Thus the electron experiences a net acceleration, producing a higher Bxc3x97v force as the electron experiences a nudge into the region of higher electric energy density. However, the accelerating magnetic EMF ∂B("PHgr")/∂t 274 is partially neutralized and reduced in this region by the current, and its net acceleration is diminished. Consequently, since the current drag is increased due to the higher particle density hr 270 the electron experiences a net deceleration in this region, which decreases the magnetic component of the Lorenz force and allows the electric component to predominate. Thus, the electron is nudged into the region of higher magnetic energy and lower particle density. Balance between acceleration and drag and the reduction of the net Lorenz force occurs in the mid region which is represented by the surface of the peak current density jr 276 as well as radial balance between the magnetic and electric pressure, allowing for fantastic dynamic confinement. Since knock-on electrons are driven quite directly forward when struck by high gamma current electrons, and provided with shared kinetic energy, these too maybe confined within the current sheet. If the number of knock-on electrons together with the current electrons exceed the confinement capacity of its associated confining field, then the excess knock-on electrons will be expelled. In other words, these electrons or others will be sacrificed to maintain equilibrium and will fly outward, penetrating the boundary, and provide the energetic particles present in the beams, which protrude at various nodes, as discussed above. Of course, the exit of such beams could be more diffuse, and in certain blanket fluids generate a glowing ring about the plasma mantle. Even hyperconducting electrons have collisions, but these are predominantly confined to small angle scattering, which will produce ionizing radiation. This may excite nitrogen gas, causing florescence, when embedded in a blanket fluid containing this gas. The radiation can trigger the production of ozone and various nitrous oxides, including even nitrogen pentoxide, when blanketed by atmospheric air. Therefore, the distinct compound plasma configuration could be used by the chemical and electronics industries for lithography or chemical synthesis. A PMK has a variety of uses. Clean fusion, for the generation of energy compactly and with exceptionally high average power densities, which will both extend and enable additional energy applications, is more fully described in the four above-mentioned patents. For fusion, the source may be scaled up to a larger size, and a gas blanket of fusion fuel may be used as the initial blanket fluid during formation. Furthermore, the pins and annular electrode may be selected from a material, such as boron 11 (11B), which does not interfere with the fusion process. For fusion, the PMK may be formed with much more energy, for example one megajoule, using a capacitor bank charged up to 65 KV or more, and using the appropriate capacitance to meet the desired level of energy of the PMK. The PMK may be precompressed using high pressure gas with a pressure of approximately 2000-6000 atmospheres. Leveraged piston compression may then be used to reach higher pressures, such as 20 kilobars for a p-boron 11 ignition. Even higher pressures may be useful for studying stellar processes; pressures as high as 90 megabars have been achieved using explosively driven inductive discharges at the MTF project at Los Alamos/Aremis. A PMK burner is illustrated in FIG. 19. PMK burners have been described in the above cited patents. To accomplish the requirement for pressures higher than described in previous patents, a dual piston 308 apparatus and compression cylinder 306 may be used. The volume of the burn chamber at ignition is essentially that of the combined volume of the scoops 310 when the compression heads 304 are essentially closed at peak compression. Furthermore, the massive piston rod 312 will act to inertially confine the volume of the scoops 310 for a period of time on the order of ten milliseconds, allowing an efficient burn. Due to the small combined volume of the scoops 310, as the heads 304 withdraw, two magnetically constricted aperture outlets 314 on opposing sides are exposed. This will allow for the quick escape of the fluid in the chamber 340, now a plasma, including the remnant PMK plasma, which can be directly or indirectly used in various applications. In FIG. 16 inductive MHD convertors 238, described below, are present at the exit of the aperture outlets 314. A strong solenoidal field coil 318 lining each aperture will force the plasma to divert along the axis and avoid the wall surfaces. To avoid the erosion of the piston heads 304 and compression cylinder 306 surfaces, they can be coated with an ablatable material which will protect, and cool by sublimation, the wall surfaces of the compression heads and chamber. As the piston rod 312 and head 304 continue to withdraw, latching mechanisms can be triggered to release the compression head 304 from the piston rod 312 in the chamber 316 and disengage from the cylinder 306, allowing for their continuous or intermittent replacement. Variable pressure source 326 can be used to precompress the PMK before inertial confinement, or in conjunction with the action of the pistons 308. The PMK formation chamber 232 is where the PMKs are initially formed in the fusion fuel, prior to delivery to the chamber 340. Furthermore, the PMKs may be precompressed prior to delivery to the chamber 304. The actual dimensions of a PMK burner may vary based on the power output, and therefore the apparatus illustrated in FIG. 19 may vary widely in both size and load capacity. In the PMK burner pressures on the order of 20,000 atmospheres can be obtained using inertial confinement. When pressure is applied through adiabatic compression, the energy concentration of the kernel of the PMK will increase dramatically, increasing the pressure, plasma density, and decreasing the volume, resulting in an increase in temperature above critical fusion ignition temperatures. If the initial size of the PMK is large, then a sufficient quantity of fusion fuel will be present to drive a robust burn. Fusion will occur within the burner and substantial fusion energy will be released. Once fusion occurs, the fusion energy released will supply additional energy to the PMK, and the surrounding fluid, increasing the temperature and pressure of the fluid, thereby continuing the compression heating of the kernel and assuring continued burning to efficiently consume the fuel. This will assure an efficient output even in the case of non-neutron yielding fuel, such as protium boron 11 (p-11B). To maintain a three phase operation at 60 HZ, a battery of devices of the type illustrated in FIG. 19 may be constructed and energized sequentially. Thus, each device will provide energy output as its PMK burns, and as the PMK burns out and the fluid, now a plasma, is released, subsequent ignition and burner apparatus are started to continue generating power. Also, the rapid exchange of compression heads can be handled in the same manner as the exchange of barrels in a Gattling gun. Thus, these elements can be taken out of the duty cycle and replaced during continuous operation. The exchanged heads can be annealed, reconditioned or even replaced, allowing for long-term continuous operation. A compound plasma configuration can be used with PMK burner to generate a highly pressurized, hot, dense, and conducting plasma which can be used to directly generate electricity in an inductive MHD process, schematically illustrated in FIG. 16. FIG. 16 is an idealized inductive MHD convertor 238 and power take-off transformer 218. A superconducting circuit 342 contains a solenoid 214 coupled to a superconducting primary coil 344 of a power take-off transformer 218. The circuit also includes a bypass switch 346 and an opening switch 348 which allows for external charging by a charger 350 of a substantial current in the superconducting circuit 342 and the charging of a substantial field in the superconducting solenoid 214. Since this current is in a steady-state when the inductive MHD convertor 238 is not operating, the output bus 220 is off. Also present is a secondary coil 352 of the transformer. Hot plasma 212 from a PMK burner for example, is coaxially fed into a magnetically energized solenoid 214. As the plasma enters the cusp of the solenoidal field of solenoid 214, it displaces the local magnetic field laterally, compressing it against the solenoidal 214, increasing the energy of the field. This produces a driving EMF of the current of circuit 342, and effectively reduces the inductance of the solenoid 214. The current surge in the superconducting circuit 342 produces an increase in the field of the flux circuit of transformer 218, thus causing an EMF and transient pulse to form in the secondary coil 352, which is seen at the output bus 220. The energy is extracted from the hot plasma 212 by its adiabatic expansion against the magnetic field of the solenoid 214. The resulting expansion cooled plasma exits the solenoid as warm plasma 216, which can then be used to drive pulsed direct currents in a cogenerator consisting of a conducting MHD convertor, which is well known to artisans in the field of MHD technology. The inductive MHD convertor 238 has electric conversion efficiencies from 70-95%, depending on the fuel burned in the fusion process, and use of co-generation. The inductive MHD convertor may be used as part of a system for electric power generation. FIG. 14 is a block diagram for an electric power generation system. Fusion fuel 230, such as boron and hydrogen, is fed into a PMK formation chamber 232. The PMK is then fed first to a precompressor 234 and then a fusion compressor/burn chamber 236, which may be, for example, the PMK burner 300 described above. The hot plasma thus formed is fed into an inductive MHD convertor 238. The thermal fusion energy is converted into electricity, as well as warm plasma 216, which may be split between a conductive MHD generation 244 and a dialable (passing through magnetic choke 240) plasma jet/torch 242 for applications requiring direct thermalization. The residual deionized plasma/gas emanating from the conductive MHD generator 244 can be fed into a Sterling cycle electric convertor as represented by the steam electric convertor 246. The residual gas emanating from the steam electric convertor 246 may be recycled through the fusion compression and burn chamber 236. The residual heat collected from the generator and convertor elements of this system may be removed through a radiator 248. The direct current produced in the conductive MHD generator 244 is fed in along a separate path from the alternating current produced by the inductive MHD convertor 238 and the steam generator 246, to output bus 220. In a similar fashion a high thrust propulsive thermal rocket engine can be made. FIG. 15 is a block diagram of such a thermal engine. Fusion fuel 230 is fed into a PMK formation chamber 232. Atmospheric gas may be used to resupply the compression blanket for both the precompressor 234 and the fusion compressor/burner 236. Simultaneously, the PMK is then fed into a precompressor 234, and then to a fusion compressor/burner 236. This allows the precompression and fusion compression burn to be carried out with air from atmospheric air intake 250, so that air will make up the bulk of the reaction mass 252 eventually expelled through the magnetic inductive solenoid/nozzle 254, which acts both as a directive thrust nozzle and inductive MHD convertor, in order to recover operating energy to drive the system. The nozzle 254 may have a superconducting solenoid similar to the superconducting solenoid 214 of an inductive MHD convertor 238, except the shape may be parabolic in order to recover some of the energy of the plasma as electricity, while allowing a substantial amount of the energy to remain in the plasma (reaction mass 252) to provide thrust. PMKs can be accelerated with an electric or magnetic accelerator, for example, a powerfully pulsed coaxial oscillating coil. Accelerators can be used in tandem and sequentially fired or phased to coincide with the position of the PMK as it moves, further accelerating the PMK. The distinct compound plasma configuration of the present invention can also be used for cutting and welding, with the scale of the device appropriate for the welding task. For example, a rapid firing (60 HZ) PMK generator and accelerator may be used to form an energetic plasma beam for cutting or slicing. Similarly, a PHASER (Phased Hyperkinetic Acceleration for Shock EMP Radiation) gun can be produced, by using a phased accelerator to launch hyperkinetic PMKs through the atmosphere or exoatmosphere. A hyperkinetic PMK is a PMK which is moving at a speed greater than that of a bullet fired from a gun, but slower than {fraction (1/100)} the speed of light. Such PMKs would act like encapsulated magnetoplasmoid bullets which could deliver EMP impulses to remote targets through the atmosphere. Preferably, a hyperkinetic PMK has a velocity of at least 1 km/sec, more preferably at least 5 km/sec, most preferably at least 10 km/sec. These PMKs would be held in a compressed and energetic state during transit to the target by the reaction pressure of the bow shock and ram compression due to deceleration. The bow shock would act as an extension of the plasma mantle and therefore become an integral part of a modified mantle of the flying PMK The hyperconducting currents in the kernel and modified mantle (the bow shock plasma-vacuum field boundary) would clamp the diffusion of both particle and field flux through the inner surface of the bow shock. The kernel plasma would remain magnetically insulated until catastrophic impact with the target occurred. The EMP impulse delivered by such a device could be used for defensive or safety applications, such as the interruption of the computer control of a runaway vehicle. A high specific thrust rocket engine, a PMK hyperdrive, can also be made as shown in block diagram form in FIG. 20. The PMK hyperdrive 338 is similar to the thermal engine 356 previously described, except the design has been hanged because of the unavailability of the atmosphere as unlimited reaction mass. Fusion fuel 230 is fed into a PMK formation chamber 232, and the PMK formed is transferred to a precompressor 234, and then to a fusion compressor/burn chamber 236 to burn the fusion fuel. The hot plasma produced may then be fed into an electric power generator 354, to produce electricity. The electric power generator 354 may have any number of stages describe for electric power generation in FIG. 14, such as an inductive MID convertor 238 and a conductive MHD generator 246. Preferably the electric power generator would remove as much heat from the fusion burn as possible. The electric power 336 produced by the electric power generator 354 can be distributed as needed. Parallel to the electric power generation, the reaction mass 330 is converted into plasma 252. The reaction mass is fed into a PMK formation chamber, along with spent fuel from the electric power generator 354. The PMK formed in the PMK formation chamber 232 may then be fed to a precompressor 234 and then accelerated in the PMK accelerator 332. The PMK may then be sent out the nozzle 334. The nozzle 334 may have a superconducting solenoid similar to the superconducting solenoid 214 of an inductive MHD convertor 238, except it would have a parabolic shape. The PMK could be electrically disrupted, such as by turbulence, to recover some of the electrical energy of the plasma as electricity, while allowing a substantial amount of the kinetic energy to remain in the plasma reaction mass 252 to provide thrust. The PMK hyperdrive uses a combination of power from a closed cycle electric PMK power generator and then uses that power to produce powerful continuous acceleration of PMKs for thrust. The magnetic energy may be recovered inductively as the accelerated PMKs are vectored into a thrust producing beam. Such a high specific thrust or (hyper thrust rocket engine) could be used for transportation between planets and to and from planetary surfaces which contain little or no atmosphere. Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified. The following is an example of an inexpensive working device. The conducting cylinder is composed of ⅝xe2x80x3 copper tubing while the helical conductor is composed of lengths of single strand 12-gauge copper electrical wire. A half-inch insulating fiberglass reinforced thin-walled plastic tube #124 which extend the full length of the distance between the annular electrode plane and the connecting rod acts as an insulating spacer between conducting cylinder and helical conductor. A vacuum potable epoxy fills the space within insulating tube and thus embeds the helical conductor. The insulating material on the 12-gauge electrical wires is excellent as a spacer between the multiple elements in the helical conductor, while the wires in the axial bundle are stripped over the length which is inserted and brazed into the connector rod. The connector rod s composed of a xe2x85x9cxe2x80x3 brass plumbing stud. The insulating stress support cylinder which fits snugly over the conducting cylinder is a thick-walled fiberglass reinforced epoxy tube. Five to eight pins are used, and the pins are simply the ends of the wires which form the helical conductor, stripped of any insulation. The pins are pointed in a direction which is a continuation of the helical path of the wires in the helical conductor. At the formation end of the source the epoxy is white for intense pulse tolerance, while away from the formation end of the source the protrusion of the thin walled fiberglass reinforced epoxy tube is green. The annular electrode is the end of the cylindrical conductor, protruding from the insulation. The helix formed by each wire has approximately a single turn across the length of the helical conductor. The angle between the tangent of the wires and the axis of the helical coil is 10-45 degrees. The length of the helical conductor is a few inches. The pins each are 1-3 mm long. The parallel plates connecting the circuit elements are composed of xe2x85x9 inch thick copper sheets 18 inches wide, with an intervening larger insulating sheet, and are of suitable lengths to accommodate the circuit elements. The plates may have the dimensions of a foot and a half by 6 or 8 feet. Six 25 to 50 microfarad 20 KV rectangular parallel piped capacitors are attached from their cases to the ground plate and from their flat pancake insulated center pins to the capacitor plate, so that the parallel inductance of the bank can be maintained. The capacitor plate and source plate are connected to a coaxial spark gap or rail gap switch of low inductance which for atmospheric work is set for air breakdown between 7 and 12 kilovolts. Likewise, an array of 6 or 8 class A ignitrons in grounded coaxial housings are attached to the source plate by their axial bolts. The ignitrons are 50 to 100 kiloampere, 20-25 kilovolt crowbar ignitrons. These can be equally spaced along a circular perimeter which is centered on the connecting coaxial mounting bus. The pulse trigger for the crowbar switch should be delayed from the firing of the switch to occur just before peak bank current is achieved. This timing may be adjusted to optimize performance, reliability and efficiency. A series fuse may be used to prevent capacitor failure from an otherwise catastrophic short circuit. These may be made in the form of fusible wire which links each center pin of the capacitors to the plate gap or alternately a disk composed of foil connected in the manner of a washer from the center pin to the capacitor plate. The volume of the PMK produced with this version of the main circuit is about 75 cm3, about the size of a chicken egg. Just prior to firing the source, a small prepulse may be sent through the source. In some cases when the main circuit does not fire, the prepulse appears to have created a small airborne PMK the size of a ping-pong ball, but likely with a kernel plasma of 2-3 mm diameter, judging by their approximate 10 millisecond lifetime. The prepulse is produced by a separate circuit which is identical to the impulse circuit, except the capacitance is a small fraction (1 xcexcF) of the main bank, and there is no crowbar switch. Operation of the Invention First, a prepulse may be sent through the source to ionize the region between the pins and the end of the conducting cylinder. Tens of microseconds later, the firing switch is closed, sending the main pulse through the source. At peak current, on the order of one microsecond later, the trigger of the crowbar switch may be fired, crowbarring the circuit. The PMK is allowed to form and detach, where it is free to move within the air. Optionally, the fuse may be broken to interrupt and smother any residual current. The PMK so formed may have some kinetic energy, outward along the axis of the source. Provisional Application Ser. No. 60/080,580 filed on Apr. 3, 1998, Provisional Application Ser. Nos. 60/004,287, 60/004,255 and No. 60/004,256, all filed on Sep. 25, 1995, as well as international application PCT/US96/15474, filed Sep. 24, 1996, are all hereby incorporated by reference. Having now fully described the invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.
042232244	description	DETAILED DESCRIPTION Referring now to the drawings, FIG. 1 shows a cross-section through an electron microscope perpendicular to the beam direction in the plane of the specimen holder. The housing, which can be evacuated, is identified by reference numeral 1. In this housing is located a specimen stage 2. This specimen stage is moved by two drive plungers 3 and 4 which pass through the wall of the housing in a vacuum-tight manner, in the plane defined by plungers 3 and 4. Between specimen stage 2 and plungers 3 and 4 is a positive force transmission which is maintained by a tension spring 5. Plunger 3 has a point 3a which engages a wedge-shaped depression provided in specimen stage 2. Plunger 4 is equipped with a roller 4a which rolls on a plane counter-surface of specimen stage 2. It should be noted, however, that any other cross feed can be used instead of this specimen stage drive. Specimen stage 2 has a conical opening 2a into which rod-shaped specimen holder 6 is inserted. For inserting and removing specimen holder 6, the wall of housing 1 is equipped at the proper point with a lock (not shown for the purpose of simplification). At its forward end, specimen holder 6 has an opening for a specimen. Reference numeral 8 identifies the bending line of the fundamental vibration of this rod-shaped, unilaterally supported specimen holder. The vibration antinode of this fundamental vibration is located at the free end of the specimen holder. However, since opening 7 for the specimen itself is located at this point, supplemental oscillator 10 cannot be mounted directly at the location of the vibration antinode. However, it is fastened in a holder 11 as close as possible to the specimen and therefore still in the region of large vibration amplitudes. FIG. 1a shows a cross-section through specimen holder 6 and supplemental oscillator 10 perpendicular to the plane of the drawing. As can be seen from this figure, specimen holder 6 has a rectangular-shaped cross-section. The two circular lines around holder 6 are projections of the inner and outer areas of the conical part of the holder seated in specimen stage 2. Specimen holder 6 includes a holder 11 for receiving the supplemental oscillator. In accordance with the shape of the cross-section of holder 6, supplemental oscillator 10 is also rectangular-shaped with the same sides ratio as specimen holder 6. This assures that the resonance frequencies of specimen holder 6 and supplemental oscillator 10 are approximately equal in the two preferred directions, i.e., along the two rectangle sides. FIG. 2 shows a cross-section through another embodiment of an electron microscope in the plane of the specimen holder. This microscope includes an annular-shaped adjustable specimen stage 2 including an aperture 2a for permitting the passage of a specimen holder 1 therethrough. The specimen holder 15 is rod-shaped, but contrary to the embodiment of the apparatus illustrated in FIG. 1, passes through the wall of housing 1 and is secured in this wall in a first support 16, shown simply as a sphere for the purpose of simplification. Besides support action, this sphere also has a sealing effect. The other end of specimen holder 15 has a point 15a which engages a correspondingly shaped conical depression in specimen stage 2. In the vicinity of first support 16, housing 1 is provided with a cylinder 17 which accommodates a compression spring 18. Due to this compression spring 18, positive force transmission always exists between point 15a of specimen holder 15 and the specimen stage. Cylinder 17 leads to a lock (not shown). Specimen holder 15 has a bore hole 19 at the point of the electron beam for receiving the specimen. Reference numeral 20 identifies the bending line of the fundamental vibration of the specimen holder in the plane of the section and perpendicular to the axis of the specimen holder. The base of a supplemental oscillator 21 is located at the point of the vibration antinode and consists of a block 22 screwed to the specimen holder 15 which receives supplemental oscillator 21. To receive block 22 and supplemental oscillator 21, specimen holder 15 is provided with a slot 23 in this region. FIG. 2a shows a cross-section through specimen holder 15 and supplemental oscillator 21 perpendicular to the plane of the drawing. The cross-section of holder 15 is circular in this embodiment and only the region of the slot deviates somewhat from this shape. Supplemental oscillator 21 mounted in block 22 also has a circular cross-section and consists of a bronze wire onto which a tube of polytetrafluoroethylene is shrunk. If specimen holder 15 is excited to resonance vibration, for example, by soil vibrations, then supplemental oscillator 21 also starts to vibrate. The polytetrafluoroethylene tube applied to the bronze wire is then deformed inelastically, i.e., energy is consumed, and supplemental oscillator 21 is damped thereby. The mass of supplemental oscillator 21 can be very small compared to the mass of specimen holder 15. With a fixed mass ratio .mu.=m.sub.Z /m.sub.S, optimum suppression of the interfering specimen holder vibration is obtained if the damping .phi.=(.mu./2(1+.mu.)).sup.1/2 and if at the same time the frequency ratio .alpha.=f.sub.Z /f.sub.S =1/(1+.mu.), where f.sub.Z represents the resonance frequency of the supplemental oscillator and f.sub.S the resonance frequency of the specimen holder. If, for example, .mu.=10.sup.-3 is set as the mass ratio, then an optimum damping .phi..sub.opt .apprxeq.0.02 and an optimum frequency ratio .alpha..sub.opt .apprxeq.0.999. The resonance frequency of the supplemental oscillator is therefore only 0.1% higher than that of the specimen holder. In the embodiments of the apparatus shown in FIGS. 1 and 2, two rod-shaped specimen holders 6 and 15, respectively, for laterally inserting a specimen into an electron microscope were shown. FIG. 3 shows an embodiment in which a specimen holder 25 is inserted into the specimen stage in the direction of the electron beam. Coupled by means of a slide ring, specimen stage 2 rests on the upper part of an objective pole piece 27. By means of plungers 3 and 4, of which only plunger 4 is visible in FIG. 3, as well as spring 5, the specimen stage is movable in the plane perpendicular to the electron beam. In this embodiment, a specimen cartridge with a conical upper part 25a and a tube 25b which extends to the point of maximum field strength in the pole piece gap serves as the specimen holder. Specimen 28 is fastened at that point. Conical part 25a of specimen holder 25 is connected to specimen stage 2 by friction and can therefore vibrate with the latter only in synchronism. Tube 25b, however, can be excited to vibrations which can lead to a change of position relative to the specimen stage and the objective pole piece 27. Reference numeral 29 identifies the flexing line of the first resonance frequency. The base of a bi-axial supplemental oscillator 30, which is connected to specimen holder 25 by means of a housing 31, is located approximately at the point of the vibration antinode, which means in this case, however, also at the point of specimen 28. FIG. 4 shows a section of a specimen holder which is of tubular design, at least in the portion shown. In the interior of tube 36 is disposed a tri-axial supplemental oscillator 37 which in this embodiment consists of a disc-shaped rubber mass 38, in the center of which a mass 39 is disposed so that it can vibrate. The latter mass may comprise brass or alloy steel. This tubular section of the specimen holder could be, for example, part of specimen holder 6 or part of specimen holder 15. The bi-axial vibration damper used in the embodiments shown in the drawings could then be eliminated. The reason it may be necessary under some conditions to employ a tri-axial vibration damper with such rod-shaped specimen holders although it can be assumed that the rod-shaped specimen holder itself is rigid in the rod direction, is that in the apparatus shown in FIG. 1, specimen stage 2 can vibrate in the direction of the rod-shaped specimen holder in such a manner that the ring diameter changes periodically in this direction, and in the embodiment shown in FIG. 2 rod 15 vibrates against rod point 15a, which can be considered as a spring. FIG. 5 shows an enlarged view of a rod-shaped supplemental oscillator 21 which consists of a spring wire 41 surrounded by a jacket of elastomer, for example, of polytetrafluoroethylene or synthetic rubber. FIG. 6 shows another embodiment of supplemental oscillator 21, which consists again of spring wire 41. In this embodiment, wire 41 is surrounded not only by a jacket 42 of elastomer, but also by a metal cylinder 43. A deformation of the elastomer between wire 41 and metal cylinder 43 occurs and thereby, vibration damping, when wire 41 vibrates. FIG. 7 shows a supplemental oscillator 50 which is fastened at one end to a holder 54. Supplemental oscillator 50 can be attached to a specimen holder by this holder and consists of a spring wire 51 which is surrounded over the larger part of its length by a jacket of any desired elastomer. The forward part of spring wire 51, which is not surrounded by jacket 52, has a thread onto which a nut 53 can be screwed. Nut 53 represents an additional weight which can be moved back and forth over a certain range along the length of supplemental oscillator 50. The resonance frequency of oscillator 50 can thereby be varied within certain limits and adapted to the resonance frequencies of the specimen holder more easily. The present invention is applicable not only to electron microscopes such as these described previously herein, but also to ion microscopes or to electron or ion diffraction apparatus. In addition to the different specimen holders shown in the various embodiments of the invention, the vibration damper of the invention can also be attached to the vibrating parts of a mechanical goniometer, such as is used, for example, in scanning surface microscopes as a specimen holder. The vibration damper of the invention can also be used for all parts in the interior of a charged-particle beam optical apparatus which are not frictionally coupled to the apparatus and can therefore be excited to vibrations of their own. By using additional supplemental oscillators, resonant vibrations of higher order can also be suppressed. In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. What is claimed is:
	description	This invention is related to U.S. patent application Ser. No. 11/314,375 or U.S. Pat. No. 7,228,255 entitled “ADJUDICATION MEANS IN METHOD AND SYSTEM FOR MANAGING SERVICE LEVELS PROVIDED BY SERVICE PROVIDERS”, filed on even date herewith, and U.S. patent application Ser. No. 11/314,301 or U.S. Patent publication USPN 2006-0133296A1 entitled “QUALIFYING MEANS IN METHOD AND SYSTEM FOR MANAGING SERVICE LEVELS PROVIDED BY SERVICE PROVIDERS”, filed on even date herewith. 1. Technical Field The invention relates to service management and service presentation systems, wherein measurement data regarding services delivered by Service Providers to customers are gathered and handled to compute and communicate service indicators defined in service level agreements and, in particular, relates to a method for managing the service levels provided by Service Providers. 2. Related Art A Service Provider (SP) provides, hosts, or manages resources for its customers. A resource can be a server, a particular application on a server, a networking device, people in a help desk to answer users, people to fix problems, people to manage and change systems configuration and location, . . . etc. . . . or a complex solution made of multiple elements to accomplish or support a customer business process. The Service Provider and the customer can be different firms, or different departments in a large global enterprise where departments are organized as support services for other departments, e.g. Marketing, Research, Sales, Production. Normally, a Service Level Agreement (SLA) is executed (i.e., signed) between a provider and a customer to define the role of each party and to remove any ambiguity from the business relationship. Such a SLA: Identifies the parties involved in the agreement. Describes the service to be provided, and identifies in a measurable and quantifiable manner indicators of the quality of the service on which obligations will be set, with a possible series of exceptions and stipulations in the way to calculate these indicators. Defines the obligations, called Service Levels (SLs), to be met on the identified indicators, so that the expected quality of the delivered services is set in an un-ambiguous manner. Defines the agreement period for which these obligations are set forward. Pre-defines penalties to be paid/executed by the SP if the commitment(s) is (are) not met. If a commitment is exceeded, a reward can also be predefined, to be paid by the customer. Also defines reporting policies, corrective actions, dispute resolution procedures, termination criteria, intellectual property. A SLA is encountered when considering utilities to be trusted “always-on” services such as providing water, electricity, gas, telephone, e-service (e.g., e-Business On Demand), etc. In fact, a SLA exists when a specific service offer including commitments is engaged with a customer. By itself, a SLA does not bring any change in the level of service delivered. The Service Provider and/or the customer need to implement a Service Level Management (SLM) program that will actually result in higher levels of services. Indeed, a SLA only specifies the agreed criteria for determining whether or not a set of agreed service quality levels are met. When not met, the issue is to determine what caused the violation, maybe how to improve the service, or change the SLA or the provider. The Service Level Management begins with the development of new service levels for a new contract and continues throughout the life of the contract to ensure Service Level commitments are met and maintained. The Service Level Management is commonly identified as the activities of: negotiating, identifying and agreeing the measurable services that support the Business Process of a customer, and defining the SLA articulation in an offering for service with Service Level Objectives (SLO) also known as Service Level Targets (SLT), monitoring resources used to deliver a service and capturing data on how well these resources perform from monitors or from logs, calculating intermediate and high level Service Levels results or scores using the predefined service parameters formulae (called metrics) and taking into account all kinds of exceptions that can occur, assessing attainment versus commitments and possible penalties or rewards, assessing impact of operational outages or degradations in terms of SLAs (services) and financial impacts, alerting in real-time of possible or effected outages, diagnosing problems for resolution, enforcing corrective actions wherever possible to regulate the delivery system and therefore try to proactively guarantee the achievement of obligations, reporting to the provider and the customer on real numbers versus contractual numbers, and sealing final numbers to be used for rebates or rewards, rebating to customers when commitments are not achieved, or rewarding the provider when commitments are exceeded, and refining, improving and reviewing SLA definitions, service levels and services that support the customer's Business Process. Today, there are SLA Management Systems which are automated for managing SLAs such as IBM Tivoli Service Level Advisor, Computer Associates SLM, Digital Fuel or InfoVista. They are built to accomplish, at least, a minimum set of tasks such as capturing data from monitoring systems, and they participate or supply information to other service management activities such as alerting, enforcing or reporting. However, these systems provide no complete answer to the service level management problem. Indeed, very often a piece of the solution used to support the customer business process which is managed by the Service Provider is coming from the customer, or is under the customer's responsibility (shared or not with the Service Provider). The means used by these systems do not automatically take such situations into account where an SLA is violated due to Customer's responsibility. In such cases, the result must be revised to reflect the true responsibility of the SP only after calculation by these systems. In addition, when a SLA is violated, or when the SP is attempting to improve its delivered service, a lot of investigation can be done on monitoring data, and it has to take into account the problem expressed above. These SLA Management Systems do not provide any help on these tasks which can then be time consuming and not very efficient, or require the use of other complex and costly means to implement external tools for correlation between data and results. The present invention provides a method for managing at least one service level of a service provided by a service provider to a customer of the service provider under a service level agreement, said service level agreement being a contract between the service provider and the customer, said method comprising: adjudicating measurement data to correct the measurement data in accordance with at least one adjudication element that provides information relating to how to correct the measurement data, said information in each adjudication element identifying which data of the measurement data is to be changed by said each adjudication element; transforming the adjudicated measurement data into operational data by reorganizing the adjudicated measurement data into one or more groups of data; evaluating the operational data by applying a formula to the operational data, resulting in the operational data being configured for being subsequently qualified; and qualifying the operational data after said evaluating, said qualifying comparing the evaluated operational data with specified service level targets for at least one service level period during which the service has been performed, said qualifying identifying from said comparing data points selected from the group consisting of good data points of the operational data meeting the specified service level targets, bad data points of the operational data not meeting the specified service level targets, and combinations thereof, wherein said adjudicating, transforming, evaluating, and qualifying are performed by software modules of an execution engine. The present invention provides a system for managing at least one service level of a service provided by a service provider to a customer of the service provider under a service level agreement, said service level agreement being a contract between the service provider and the customer, said system comprising an execution engine for performing a method, said method comprising: adjudicating measurement data to correct the measurement data in accordance with at least one adjudication element that provides information relating to how to correct the measurement data, said information in each adjudication element identifying which data of the measurement data is to be changed by said each adjudication element; transforming the adjudicated measurement data into operational data by reorganizing the adjudicated measurement data into one or more groups of data; evaluating the operational data by applying a formula to the operational data, resulting in the operational data being configured for being subsequently qualified; and qualifying the operational data after said evaluating, said qualifying comparing the evaluated operational data with specified service level targets for at least one service level period during which the service has been performed, said qualifying identifying from said comparing data points selected from the group consisting of good data points of the operational data meeting the specified service level targets, bad data points of the operational data not meeting the specified service level targets, and combinations thereof, wherein said adjudicating, transforming, evaluating, and qualifying are performed by software modules of an execution engine. The present invention provides a method and system for managing the Service Levels provided by Service Providers to a customer by introducing a step of modification of input data (adjudication) taking into consideration external information elements related to input data (adjudication elements) such as the SLA contract clauses, or such as input from the service manager or other enterprise management systems, in order to produce new modified input data for Service Level calculations and then to qualify the resulting detailed calculation data (operational data) with regards to their participation in achieving or not Service Level Targets. The invention relates to a system for managing a service level provided by a Service Provider to a customer comprising a processing engine for transforming measurement data into operational data using service time profiles and Services Level business logics, and evaluating the operational data in order to produce Service Level results and qualified operational data. The processing engine comprises means for adjudicating the actual measurement data before transforming them into operational data, this adjudication being made by using a set of adjudication elements describing the modifications to bring, means for evaluating the operational data by applying SLA specified service level evaluation formula, and means for qualifying operational data after they have been evaluated, this qualification being made by comparing operational data with qualification values determined with regard to Service Level targets for each business period (i.e., service level period). A system according to the invention comprises a repository of the descriptions of the Service Level Agreement (SLA) corresponding to each Service Level (SL), a first datastore for the actual measurement data, a second datastore for adjudication elements, a third datastore for SL results, operational data, adjudicated data and a processing engine for processing an evaluation cycle for each Service Level. The processing engine 10, illustrated in FIG. 1, includes software modules of a computer system to process the measurement data received as input and to provide qualified operational data as output. As described hereafter, the process performed by the processing engine 10 comprises essentially four main steps: a step of adjudicating the input measurement data (step 12); a step of transforming the adjudicated data into operational data (step 14); a step of evaluating these operational data (step 16); and a step of qualifying the operational data (step 18). In other words, as illustrated in FIG. 2, the process is implemented for each Service Level (SL) 20. First, the measurement data for the service level is retrieved (step 22), such measurement data being related to the evaluated SL period (i.e., business period). Then, all the adjudication elements related to the evaluated SL period are retrieved (step 24) from the second datastore for the adjudication elements and the SL evaluation cycle can be executed (step 26) as per SLA descriptions. Finally, the adjudicated data, the qualified operational data, and the SL results are stored (step 28) into the third datastore. Referring again to FIG. 1, the step 12 of adjudicating is used to correct the actual measurement data to reflect the real domain of responsibility of the Service Provider, or to reflect reality because, for some reason, the monitors provide incorrect data. A new set of adjudicated data is produced by this step. Although the actual measurement data are different from the adjudicated ones, reference data to the actual measurement data are still available to be used by other systems requiring the original observed data, or so that changes can be audited in support of legal purposes. Adjudication elements 30 provide information relating to how to correct the measurement data. The adjudication elements 30 may be sourced from the contract clauses 32 created at contract signing time and are valid for the whole Service Level life (exclusion cases, special conditions, limits on resources, etc.). The adjudication elements 30 may also be created, from the adjudication console 34, at any time during the Service Level life by Service Managers when executing their Service Level Management tasks. Finally, the adjudication elements 30 may be created automatically from other Enterprise Management systems 36 like Problem and Change Management, using responsibility fields and other information. The adjudication elements 30 hold a reason for the modifications they bring, which will be shown to the end customer and must be agreed by the customer, and information about the creator who/which is first authenticated and goes through processes of authorization. Each “modified” (i.e., adjudicated) data point contains a list of references to applied adjudication elements and clauses in their specific order of appliance, for auditing, detailed reporting/explanation, customer relationship, legal justification and later billing exploitation (rebate or reward). Each adjudication element 30 is persistently saved/locked into an unchangeable state as soon as it is used so that no more modification can happen to the locked adjudicated element, for guaranteeing that proper information is available for auditing controls. This step also supports a parallel information management process whereby the adjudication can be sealed so that no more modification can be made to the Service Level result and other produced data for a given Service Level period; i.e. no more adjudication element can be created for this Service Level period. This corresponds to a process of finalization just before result data is sent to billing systems or used for other legal purposes, and after they have been reviewed and agreed upon with the customer. Each time an SL is requested to be evaluated, the process illustrated in FIG. 3 is executed. First, all measurements are copied as adjudicated measurements with an empty modification history chain (step 38), thus enabling to store a history of modifications to each measurement. Then, the process checks whether there is still an adjudication element to apply (step 40) to the set of adjudicated measurements. If it is the case, the adjudication element is locked as mentioned above (step 42) and the identification of the measurement data to be changed from the adjudication element is got (step 44). Then, it is checked whether it corresponds to an existing adjudicated element identification (step 46). If so, the adjudicated measurement contents are replaced by the contents specified in the adjudication elements and the adjudication element identification is added to the modification history chain (step 48). If it is not the case, a new adjudicated measurement is created with this identification and filled with the contents specified in the adjudication element and this adjudication element is added to the modification history chain (step 50). In both cases, the process is looped back to the step of checking whether there is still an adjudication element to apply (step 40). Returning to FIG. 1, the second step 14 performed by the processing engine 10 is to transform the adjudicated measurement data into operational data by using a service time profile 52 describing the Service Level time logic (also commonly referred to as a service calendar and defining different periods of service with possibly different SLT's) and the specific business logic defined in the Service Level. The second step 14 organizes/merges the adjudicated measurement data into a more appropriate form for evaluating attained service levels and producing summary service level results. In addition, each produced operational data point refers back to the original adjudicated measurement data point(s) it comes from, for tracing and auditing purposes. For example, a Service Level time logic can contain critical periods and off-peak hours in a month where different targets are to be achieved, or periods of no service (i.e., the service level targets may be a function of time or time-varying during the business period(s) in which the measurement data was obtained). Monitoring devices and data collection systems have no knowledge of this information which is contract specific, and a measurement data point can cover multiple such periods. Appropriate sets of data points need to be produced for generation of service level results and comparison with different service level targets. And to continue the example, if measurements are coming from different probes monitoring the same resource, they need to be merged using a logic 54 specified in the Service Level before they can be used for Service Level calculations when evaluating and producing summary service level results. The adjudicated data may be transformed into operational data by being reorganized into one or more groups of data. As an example, the step of transforming the adjudicated data into operational data may be decomposed in two sub-steps. This example illustrates how adjudicated data are propagated to the next steps of the evaluation process. 1. Merging of several measurement data (i.e., a plurality of sets of measurement data) on the same monitored resource, independently from the SL Service Time Profile (or business schedule), into a single set of data. This part defines precisely the format of initial and transformed data, and since they are precisely identified and defined, the description of the SL business logic to merge data can be itself a program, supplied by the people who have defined the Service Level with the customer, or by the customer himself. The merging step gathers adjudicated measurements per measurement type id, and at the same time it creates a pre-operational data point (i.e. an operational data point with no business schedule state) for each adjudicated data point, keeping the adjudicated values as they are and a reference to the original adjudicated data point. Then, it selects for each group the corresponding business logic from the SL information, and for each group, it applies the merge logic to produce a new set of pre-operational data points per group. How the merge logic is executed on the data points is implementation dependent: this can be an interpreter, a dynamic call to a compiled form of the logic, etc. As an example, 3 probes are monitoring a URL, and it is defined in the SL that an outage is declared when all 3 probes agree to see an outage, and that this outage lasts from the first probe measurement detecting it to the first probe measurement returning to normal. In this case, only one measurement type is seen, i.e. observed URL state, so there will be only one group, based on a common feature of the 3 groups wherein the common feature is the only one measurement type. 3 measurements feeds come in, identified by their different monitoring resource ids. To further simplify, each data point can only mention an outage time and duration for the given resource id/probe. There is no need to show records of observed normal state, since by default, what is not an outage means is available. After being adjudicated, these measurement data are put in one group of measurement, and then merged using the supplied logic. In this case, the formal logic supplied can be: build one data set of pre-operational points sorted by measurement timestamp filed, from the group of data sets, go through each non excluded point in sorted order, and see if the time interval it describes (timestamp, timestamp+duration) overlaps with the time interval of two following or simultaneous points with different resource ids. if yes, create a new operational data point from these 3 points using the operational data point creation tool, and set the timestamp to the one of the current point, and the duration to the minimum of (timestamp+duration) of the 3 points minus this point timestamp, discard the 3 operational data points used to create this one, and insert this one in the sorted list instead, retaining in it the list of original adjudicated data points. if not, discard the data point. 2. Split of measurement data against service Time Profile periods (Service Level time logic) to create separate sets for each period. This step allows applying the same process in parallel to each set of data without caring anymore about the Service Time Profile before getting to the SL result comparison stage. The split step takes as input the output of the previous step, that is pre-operational data points with no business schedule state set yet. The external input of this step is a calendar showing the active business state for each time in the processed Service Level. The logic of this step is: a—for each pre-operational data point, get the business state for the data point timestamp from the calendar, and set it for the new operational data point, b—if the point is a summary point (i.e. not a unique point in time, but covers a time range), look at the calendar to check if the business state changes before the end time of the interval covered by the summary point, c—if yes, create a new operational data point from this point. Set the timestamp of this new point to the time of change of the business state, set its business period state to this new state, and set its end time or duration to match with the end of the current point. Set the end time or duration of the current point to the time of change of the business state. Then, restart sub-step c—using the new operational data point. As an example, if an outage lasts from 3 pm to 11 pm and the Service Time Profile states that in a day, 8 am to 8 pm is normal hours, and outside of 8 am to 8 pm is off peak hours with a different target, then the outage needs to be split in two pieces, one from 3 pm to 8 pm with business period state as “normal hours”, and one from 8 pm to 11 pm with business period state as “off peak hours”. The preceding example illustrates splitting the single set of data (resulting from the preceding merging step) into a plurality of groups of data corresponding to a plurality of sub-periods (3 pm to 8 pm and 8 pm to 11 pm in the preceding example) of the business period(s) during which the measurement data was gathered. Then, the operational data are evaluated (step 16) through a Service Level evaluation using a formula 56, specifying which data are to be fed as input, what is the form of data (response time, availability, counts, states), and how the input data should be processed to produce summary intermediate and top Service Level attainment results. There is one set of data produced per business period in the Service Time Profile. The data produced by this step are to be used directly for Service Level attainment comparison, for reporting on service levels, and for input to other Enterprise Management systems. It is matched against what is contractually committed by the provider and represents a negotiated value and quality of the delivered service. The operational data resulting from the evaluation step 16 are configured for being qualified. The operational data resulting from adjudicated data are qualified (step 18) with regards to their participation in achieving or not achieving the Service Level targets 58 for each business period during which the service(s) provided by the Service Provider has been performed. The qualifying step identifies good operational data points with labels like “In Profile” (=contributes to good SL result) or bad operational data points with labels like “Out Of Profile” (=contributes to degrading SL result). The qualifying step also determines deltas to breaking limit (i.e., differentials by which the identified data points differ from the specified service level targets). The deltas to breaking limit (i.e., differentials) are used to determine a margin by which the identified good and/or bad data points contribute to the high level SL results; i.e., contribute to meeting or not meeting the specified service level targets (for example, time remaining before “Out Of Profile” or violation for problem resolution times). The deltas to breaking limit (i.e., differentials) and the margin may be stored in the third datastore. This enriching of operational data is to be used by the Service Provider Managed Operations people and by their automated systems to continuously track the detailed contribution to the end to end final service level, to understand their impact on it, and to help them prioritize work and actions in order to guarantee the end to end service level. As an example of the latter, the time remaining before violation for problems resolution is an information to be used to understand which problems to solve first in the list of currently open problems. As an example of the former, showing which detailed metrics contribute to SL result degradation helps to pinpoint quickly in the input data set what are the points to improve, and to control the effect of corrective actions. This is possible because each operational data point points back to adjudicated data, which in turn has in its history the list of modifications made to the initial data points. In addition, the delta to breaking limit information gives an idea of the amount of effort to spend to improve the service level, and of where to concentrate to yield best benefits. The qualification implementation process requires the creation of a rule for each type of operational data which is used to qualify them. This results in a set of qualification rules specific to each Service Level. Each operational data produced by the previous steps in the Service Level evaluation cycle has a data code associated with it that is used to retrieve the qualification rule to apply for this service level and for the business period it is in. These rules can be in executable code and they are executed on each operational data at qualification time, or they can be description of tests to be done and conditions to be met and they are interpreted at qualification time also. Each rule is dependent on the service level evaluation formula and target. There can be some commonality between multiple service levels or not, and in case of commonality, the rules can be shared. The process for creating a rule is illustrated in FIG. 4, for each operational data, a rule identification is got 62 in a table of rules using the operational data type id, the service level id and the business period id. The rule is then executed or interpreted 64 in comparison with the operational data. Then, it is checked 66 whether the result is positive. If it is the case, the operational data are qualified as “In Profile” 68 and, if not, the operational data are “Out Of Profile” 70. The result is stored as delta (i.e., differential) to target, to be used as explained above. For example, the SLA defines that 95% of URL response time measurements should be less than 2 seconds. Operational data produced by this SL evaluation is a list of response time measurements spread over the evaluation period and the 95th percentile value of the measurement list. In this case, it is possible to use one qualification rule only common to both types of operational data set. This rule is to compare the response time operational data value with 2 seconds and to answer positively (In Profile) if less than or equal or else negatively (Out Of Profile), and to store the delta in the operational data point.
	summary
	claims	1. A fuel assembly for use in a nuclear reactor, the fuel assembly comprising:at least one fuel rod; andan outer channel surrounding the at least one fuel rod, the outer channel including a first side wall, a second side wall, a third side wall, and a fourth side wall, the first side wall being opposite the third side wall, the second side wall being opposite the fourth side wall, the first and second side walls being select side walls, the third and fourth side walls being other side walls, an entirety of the select side walls as a whole being thicker than an entirety of the other side walls as a whole. 2. The fuel assembly of claim 1, wherein the select side walls of the outer channel face a control blade in the nuclear reactor. 3. A fuel assembly for use in a nuclear reactor, the fuel assembly comprising:at least one fuel rod; andan outer channel surrounding the at least one fuel rod, the outer channel including a first side wall, a second side wall, a third side wall, and a fourth side wall, the first side wall being opposite the third side wall, the second side wall being opposite the fourth side wall, the first and second side walls being select side walls, the third and fourth side walls being other side walls, an entirety of the select side walls as a whole being fabricated of a zirconium alloy that is more resistant to radiation-induced deformation than Zircaloy-2, an entirety of the other side walls as a whole being fabricated of a zirconium alloy that is equally or less resistant to radiation-induced deformation than Zircaloy-2. 4. The fuel assembly of claim 1, wherein the other side walls are approximately 20 mil or more thinner on average than the select side walls. 5. The fuel assembly of claim 3, wherein the select side walls include only at least one of Zircaloy-4, NSF, and VB. 6. The fuel assembly of claim 1, wherein the select side walls are approximately 20 mils or more thicker on average than the other side walls. 7. The fuel assembly of claim 2, wherein the select side walls are directly adjacent to the control blade.
	summary
	abstract	A method of producing a Fresnel zone plate (15) comprising: making available a substrate (1, 4, 7) which is rotationally symmetrical with respect to its center axis (1a, 4a, 7a); applying layers (2a-d; 5a-d; 8a-d; 11) following in succession by means of an atomic layer deposition (ALD) method to faces (1b-c; 4b-c; 7b-c) of the substrate (1, 4, 7) without rotation of the substrate (1, 4, 7) in order to form a coated substrate, and severing (3a, b; 6a, b; 9a, b) at least one slice (13) from the coated substrate (1, 4, 7), by the coated substrate (1, 4, 7) being divided at least once at a right angle to the center axis (1a, 4a, 7a).
051732521	summary	BACKGROUND OF THE INVENTION This invention relates to spacers for use in nuclear fuel bundles, the spacers maintaining individual fuel rods or tubes containing fissionable materials in their designed spaced apart relation. More particularly, a spacer is disclosed which has a spring that can be placed within and removed from the previously assembled spacer. Further, provision is made for the insertion of fuel rods through the spacers of a fuel bundle with the spring of the spacer in the compressed, partially inserted state for avoiding scratching of inserted fuel rods on fuel bundle assembly. SUMMARY OF THE PRIOR ART Modern boiling water nuclear reactors include a core composed of many discrete fuel bundles. Water circulates from the bottom of each fuel bundle, is heated in passing upward through each fuel bundle, and passes out the top of each fuel bundle in the form of heated water and steam. The fuel bundles are composed of discrete groups of fuel rods--sealed tubes which contain nuclear fuel. Typically, the fuel rods are supported upon a lower tie plate and held in side-by-side vertical relation by an upper tie plate. Water flow is confined within a fuel bundle channel extending from the lower tie plate to the upper tie plate. In addition to supporting the fuel rods, the lower tie plate admits water into the interior of the fuel bundle. The upper tie plate--in addition to maintaining the fuel rods upright--permits the heated water and generated steam to exit the fuel bundle. The fuel bundles are typically about 160 inches in length. Consequently, the individual fuel rods within the fuel bundles are flexible along the length of the fuel bundle. If unsupported, the individual fuel rods could easily move out of their intended side-by-side spacing responsive to the forces of flow induced vibration and metallic creep. The reader will understand that metallic creep is a well known phenomenon resulting from both pressure and radiation within the reactor. Preservation of the intended side-by-side spacing of fuel rods within a fuel bundle is important. Specifically, if the fuel rods are not maintained within their desired side-by-side spacing, the designed nuclear reaction and concurrent heat generation with steam production does not occur efficiently. To maintain the required spacing between the individual fuel rods and to prevent unwanted vibration, it has long been the practice of the nuclear industry to incorporate spacers along the length of the fuel bundles. Typically, anywhere from five to ten spacers--usually seven--are placed within the each fuel bundle. The spacers are preferably placed at varying elevations along the length of the fuel bundle to brace the contained fuel rods in their designed location. Design considerations of such fuel rod spacers are well known. They include retention of rod-to-rod spacing; retention of fuel assembly shape; allowance for fuel rod thermal expansion; restriction of fuel rod vibration; ease of fuel bundle assembly; minimization of contact areas between the spacer and fuel rods; maintenance of structural integrity of the spacer under normal and abnormal (such as seismic) loads; minimization of reactor coolant flow distortion and restriction; maximization of thermal limits; minimization of parasitic neutron absorption; and minimization of manufacturing costs including adaption to automated production. Spacer construction is easily understood. Each spacer has the task of maintaining the precise designed spacing of the particular matrix of fuel rods at the spacer's elevation within a fuel bundle. It has been a common practice to provide each spacer with a matrix of ferrules for surrounding each fuel rod of the matrix of fuel rods. Each ferrule is provided with at least one stop. The fuel rods when biased into the stop(s) of their ferrules have their precise designed side-by-side spacing preserved. The necessary biasing of the fuel rods within the spacers has been accomplished by individual springs. In the prior art it has been a common practice to have two side-by-side ferrules share the same spring at a common aperture defined between the ferrules. Typically the shared spring is of the loop configuration having two spring legs joined together at the top and at the bottom to form a continuous and elongated loop spring. One spring leg protrudes through the common aperture into a first ferrule of a ferrule pair and biases the fuel rod in the ferrule against the stops of the first ferrule of the ferrule pair. The other spring leg protrudes through the common aperture into the other ferrule of the ferrule pair and biases the other fuel rod in the second ferrule against the stops of the second ferrule of the ferrule pair. Maintaining the loop springs of the prior art within the side-by-side ferrule pairs has been difficult. The common aperture between adjacent ferrules has been defined by configuring an aperture in each ferrule and confronting the ferrules at these defined apertures. The confronted apertures define the common aperture. These confronted apertures have been configured with irregular shapes having protruding internal surfaces--for example apertures of the "E" variety have been used. By the expedient of either overlapping or confronting protruding portions of the confronted apertures between the loops of the prior art springs, capture of the springs into the common aperture between the spacers has resulted. With the loop springs confined in the common aperture between the metal walls of a ferrule pair, the required spring biasing in two ferrules requires only a single confined loop spring. Unfortunately, modern fuel bundle design has complicated the design of spacers and spacer springs. Fuel bundles are now more densely packed with smaller diameter fuel rods. As a consequence, the space available for both spring movement and capture of the spring to the spacer is vastly reduced. As fuel bundles become more dense, the number of springs required across a spacer has increased. Unfortunately, the required movement of the springs in either maintaining the fuel rods in alignment or permitting assembly of the fuel bundle in the first instance has remained unchanged. The practical effect of having denser fuel bundles is the need to redesign the springs within fuel bundle spacers. The assembly of fuel bundles has further complicated this problem. Specifically, the biasing springs of individual spacers have a tendency to scratch fuel rods when fuel rods are inserted into the spacers. These scratches can be the location where corrosion of the fuel rods starts during their in-service life. This being the case, it has been desirable to encase fuel rods in protective plastic sheaths during their insertion into the spacers. Once insertion is complete, the plastic sheaths are removed. The use of the plastic sheaths can prevent scratches. Unfortunately, the same plastic sheaths require additional spring flexure during fuel bundle assembly. This additional flexure is necessary to permit the plastic protective coating to be temporarily inserted along with the fuel rods into the fuel bundle. In some fuel bundles requiring the use of these plastic sheaths, the existing spring flexure is not within design tolerance when two plastic covered fuel rods are placed simultaneously within the ferrules of a ferrule pair. As a consequence, construction of some fuel bundles requires a complex procedure for inserting the fuel rod. Given a ferrule pair and spring, a first fuel rod with a plastic sheath is inserted into one ferrule of the pair, and the sheath is removed. Then a second fuel rod with a plastic sheath is inserted into the remaining ferrule and its sheath is removed. This procedure is required because the prior art springs cannot deflect far enough to accommodate both fuel rods and both plastic sheaths simultaneously. If this alternating insertion procedure must be followed over a 9 by 9, 10 by 10, 11 by 11 or 12 by 12 matrix in a carefully controlled sequence, it can be understood that a spring design which permits the elimination of these plastic sheaths without increasing the risk of undesirable scratches is desirable. The springs of the prior art are also difficult to replace if they become damaged. Replacing known springs requires that the ferrule pair be cut apart, along with the damaged spring. Then a new ferrule pair with a spring must be inserted and the ferrules rewelded. A spring design which could be more easily replaced would be a substantial improvement. Finally, those familiar with mechanical design and mechanical design tolerances will realize that exact dimensions and perfect alignment are never achieved. Instead, a tolerance range is specified. The cost of manufacture increases as the tolerance range is narrowed. In prior art spacers, and to a greater degree in new designs, a very tight tolerance range is required for the springs and ferrules. If a spring can be designed with greater flexibility, and a mounting method which allows more spring deflection, the tolerances can be less restrictive. Because of at least the given design considerations, designing springs having improved flexibility for use in spacers has become a high priority. A standard method for providing increased flexibility is to vary the width of the spring, using a lesser width in regions of low stress. Unfortunately, the width of the current loop spring is not easily varied. The loop spring starts out as a continuous circular loop of constant width and is then bent into its final shape. The circular loop, or the final spring could be machined to a varying width, but the cost would be high. COPENDING PATENT APPLICATION Not Prior Art In my copending patent application Ser. No. 07/623,828 filed Dec. 6, 1990 entitled Self Locating Springs for Ferrule Spacer, now U.S. Pat. No. 5,078,961 issued Jan. 7, 1992, I set forth an improved spring construction which is self centering with respect to confronted ferrules. In this invention, a ferrule spacer is disclosed with each of the discrete ferrules surrounding a fuel rod within the fuel rod matrix. Ferrule pairs are used for capturing a spring between the ferrules. Each ferrule defines an aperture for confrontation with the corresponding aperture in the adjacent ferrule of the ferrule pair. The ferrules at their respective ferrules define two types of apertures. A common aperture opening to the center of each of the ferrules is defined for the capture of the spring between the ferrules. Paired side apertures opening to the outside of each of the ferrules are defined. It is into these paired side areas that portions of the springs protrude to cause the self centering feature of this disclosure. Loop springs are used in this disclosure. One portion of the loop protrudes into one ferrule for biasing one fuel rod passing through that ferrule. Another portion of the loop protrudes into the other ferrule for biasing another fuel rod passing though that ferrule. The loops springs have tabs. These tabs protrude out of the paired side apertures. These tabs in combination with the side apertures cause the centering feature of the springs. SUMMARY OF THE INVENTION In the present disclosure, the prior art practice of having two side-by-side ferrules share the same biasing spring for two adjacent fuel rods is followed. Consequently, paired ferrules are each provided with apertures for capturing a single spring between the ferrules. The springs are provided with a continuously looping main body having protruding tabs on opposite sides of the springs. The paired ferrules are confronted at their respective apertures for the capture of the springs at their main body and to provide defined side apertures between the confronted apertures for permitting protrusion of spring tabs for holding and centering the springs within the confronted apertures. Modification of the confronted apertures occurs to permit insertion of the spring in a compressed disposition from the side of the ferrules. Once the spring is inserted fully between the ferrules it expands. And once the spring expands, it is captured. As a consequence, spacer construction can be substantially completed prior to the insertion of the springs. In the construction of the disclosed spacer, at least two ferrules are welded together to form the confronted apertures and side apertures between the ferrule pair. After the ferrules have been welded together, a spring is compressed with a tool, such as a needle-nosed pliers, inserted vertically into the interstitial space formed by the two ferrules, and then moved horizontally into the central aperture between two ferrules. After the spring is fully inserted it springs open and is captured in the slots between the two ferrules. The spring herein consists of two identical halves which are welded together. The manufacture of the spring begins with flat strip material. A punching operation provides the variation in width required for optimum spring design and provides the locating tabs. The tab portions are included at either end of the spring, are used for entrapping the springs within their respective ferrule apertures, and are incorporated into the spring legs to produce a spring having longer spring legs with a resulting lesser range of spring force over the designed range of spring deflection. OTHER OBJECTS, FEATURES AND ADVANTAGES An object of this invention is to mount a loop type spring between a ferrule pair in a spacer assembly without having the material of the ferrules intrude within the loop of the spring. According to this aspect of the invention, paired ferrules are provided with confronting apertures. These apertures when confronted provide two functions. First, they trap between the ferrules the main body of the loop type spring. Second, they provide confining slots defined between the respective ferrule pairs. To mate with these confining slots, tabs protrude from the main body of the loop springs on either side of the loop springs. The tabs extend from the trapped main body of the loop spring within the confronted apertures into the confining slots. As a result, the loop springs are held to the confronted apertures of the ferrule pair by the tabs. An advantage of the disclosed spring is that it is self centering with respect to the ferrule pair. Under the forces of compression exerted on the fuel rods, the spring seeks and maintains its designed position with respect to the ferrule pair. An additional advantage of the disclosed spring design is that the material of the ferrules is no longer required to penetrate in between the discrete legs of the loop springs. This being the case, the spring legs are permitted a relatively greater movement--this compression permitting movement of each leg toward the remaining leg until contact of one spring leg with its opposed spring leg occurs. No longer is spring leg movement limited by the structure of portions of the ferrules invading the interstitial space between the discrete spring legs of the loop spring. A further advantage of the disclosed spring and ferrule construction is that assembly of the spacers is simplified. In the past the loop springs have had to be individually threaded to portions of the ferrules and thereafter trapped in place by manipulation of the confronting ferrules. With the design here disclosed, simple trapping of the spring between confronted ferrules is all that is required. An additional advantage of the spring construction here disclosed is that the spring can be partially inserted into the ferrule apertures, allowing fuel rods to be inserted through the ferrules without contacting the springs. This eliminates the need to use plastic sheaths to protect fuel rods as they are inserted. An additional object of this invention is that the spring can be inserted into and removed from the ferrules after the ferrules and their bands are welded together to form the spacer unit. As no disassembly of the spacer unit is necessary to remove a defective or failed spring, repair and replacement of springs and/or fuel rods is greatly simplified.
048470430	abstract	An improved liquid jet pump for water is described in which the water issuing from the jet pump drive nozzle passes into a nozzle mixing chamber where steam is introduced to nozzle outflow. This steam, traveling in the same direction as and converging upon the liquid driving stream, is raised to high velocities. These uncommonly high velocities of steam are attained both as a result of passage through a converging/diverging nozzle and the action of condensation upon the passing liquid stream. The liquid driving stream is supplied at a temperature which promotes immediate condensation of the steam molecules of the high speed steam jet. A process of momentum exchange immediately occurs within the drive nozzle mixing chamber between the high-velocity steam and the parallel-moving slower liquid stream with momentum being transferred from the steam to the liquid driving stream. The liquid driving stream with its enhanced momentum is thereafter exhausted from the nozzle mixing chamber and used conventionally to drive the jet pump. Improved jet pump recirculation system is described for use with current and advanced boiling water nuclear reactors.
047160080	summary	BACKGROUND OF THE INVENTION The invention relates to a device for control of the core of a nuclear reactor by means of clusters with diverse functions. such as control clusters and spectral shift clusters. A method which provides for better utilization of nuclear fuel and reduced uranium fuel costs involves shifting the neutron energy spectrum in the core of the reactor from "soft" to "hard" during the early phase of the operating cycle or core life. For this purpose, it has been proposed, for example, during the first part of the reactor operating cycle, to introduce into the core the rod clusters of material which preferentially absorbs slow neutrons (typically fertile material which can be converted into fissile material under the action of the slow neutrons, such as depleted uranium). A hardening of the neutron spectrum is thus produced both by the reduction in the volume of the moderator in the core and by absorption of low-energy neutrons. In a second part of the reactor operating cycle, the rod clusters which exhibit non-fission slow neutron absorption are withdrawn from the reactor core and the fissile material in the nuclear fuel contained in the assemblies during the first phase is consumed. Reference may be made, for example, to European Patent Application Nos. 108,019 and 108,020. In such reactors, joint use is then made of clusters of neutron-absorbing rods, which may be inserted to a greater or lesser extent into the assemblies forming the reactor core to control the latter, and of spectral shift clusters which are completely inserted into the fuel assemblies forming the reactor core during the first part of the operating cycle. In particular, the control clusters and the spectral shift clusters may be associated with the same reactor core assemblies, with a common motorized drive. European Patent Application No. 111,435 describes a device incorporating control clusters and spectral shift clusters which are coaxial, each with a rotational symmetry of distribution of the rods in the fuel assembly with which they are associated. Movement of the clusters is produced by two coaxial control shafts rectilinearly moveable along a fluid-tight enclosure and equipped with means for locking the shafts in a plurality of positions. Each shaft connected to a control cluster is actuated by conventional means comprising electromagnetic coils and pawls. On the other hand, each shaft for controlling a spectral shift cluster, which is mounted coaxially inside the shaft of the control cluster, comprises a piston slidably accomodated in the control shaft and upwardly moved upon opening of a valve for pressure/release in the upper part of the fluid tight enclosure along which the control shafts are movable. In its uppermost position, the spectral shift shaft can be coupled to the control cluster shaft by fingers which engage in a groove in the spectral shift shaft. While such a fine-control device is generally satisfactory, it nevertheless has the disadvantage that the motions of the shafts are not entirely independent, since the spectral shift shaft is subject to the motions of the control shaft. The spectral shift clusters are consequently partly inserted even when insertion is not desirable. French Pat. No. 2,168,564 discloses fuel assemblies associated with guide/tubes along which a plurality of cluster control shafts slide individually. The rods of these clusters are distributed with a rotational symmetry in relation to the rod distribution pattern in the fuel assembly. While such a device provides complete uncoupling in guidance and movement of the various control shafts, as well as a uniform distribution of the rods in the fuel assembly, it has the disadvantage of being very bulky due in particular to the requirement for control and guidance means situated inside and outside the vessel and associated with each of the control shafts. For a description of hydraulic and electromechanical drive means for such shafts, reference may be had to French Pat. No. 2,232,820. SUMMARY OF THE INVENTION It is an object of the invention to overcome the above-mentioned disadvantage, and it is a more specific object to provide a device for fine control of the core of a nuclear reactor by means of clusters with diverse functions, which device is of reduced bulk and in which the shafts for controlling the clusters and the associated guiding means are completely independent of each other. For that purpose, a device for fine control of the core of a nuclear reactor having a vessel containing pressurized fluid (typically pressurized water) and a core immersed in the fluid and incorporating a plurality of vertically arranged fuel assemblies comprises a first set of clusters arranged to be guided and inserted more or less deeply into some of said fuel assemblies and a second set of clusters arranged to be guided and inserted completely into some of said fuel assemblies during part only of the core operating cycle. Each of the clusters consists of a group of rods arranged parallel to each other, arranged for being movable vertically along the assemblies and inside a guide structure for guiding the rods. Each cluster has an upper carrier movable inside and along a guide tube positioned inside the guide structure. The carrier is fast with a vertically movable drive shaft. Means for moving the shafts controlling the clusters of the first set may be conventional and comprise electromagnetic coils and pawls. The means for moving the drive shafts of the clusters of the second set are hydraulic. Such drive shafts each move in a fluid-tight enclosure communicating with the vessel and which may be partially depressurized at the upper end thereof. Means are provided for individually locking the shafts driving the clusters of the second set in a higher position and for unlocking them. According to one aspect of the invention, one fuel assembly out of every two is associated with two unsymmetrical clusters, namely a cluster of the first set and a cluster of the second set. The guide tubes of the two clusters are arranged symmetrically relative to the axis of a same guide structure associated with the fuel assembly. The means for guiding and moving the cluster carriers are independent of each other. The guide structures associated with fuel assemblies are typically polygonal in shape. According to a particular feature of the invention, the assembly formed by the carrier and the drive shaft of each cluster is equipped with slide blocks for guiding the said assembly inside the guide tube in which it moves. According to another feature of the invention, the guide tubes are held in position inside the guide structure by guide plates or partitions which are perpendicular to the axis of the guide structure and equipped with at least one vertical spacer rod extending along the axis of the guide structure. In a particular embodiment of the invention, the means for locking each drive shaft associated with a cluster of the second set in a "high" position and for unlocking the shaft comprises: two pawls pivotably connected to a casing fixed inside the enclosure and capable of engaging in a groove in the control shaft. a rotatable bush formed with two cams, one for opening the pawls and the other for closing the pawls, and means for rotating the rotatable bush responsive to axial movement of the drive shaft. Preferably, the means for turning the rotatable bush when the control shaft moves axially comprises a thimble movable axially, equipped with two studs cooperating with inclined abutting surfaces on the rotatable bush and a shoulder which a chamfer of the control shaft abuts when the latter moves upwards.
	abstract	Systems and methods are provided to perform efficient, automatic cyclotron initialization, calibration, and beam adjustment. A process is provided that allows the automation of the initialization of a cyclotron after overnight or maintenance imposed shutdown. In one embodiment, five independent cyclotron system states are defined and the transition between one state to another may be automated, e.g., by the control system of the cyclotron. According to these embodiments, it is thereby possible to achieve beam operation after shutdown with minimal manual input. By applying an automatic procedure, all active devices of the cyclotron (e.g., RF system, extraction deflectors, ion source) are respectively ramped to predefined parameters.
	claims	1. A method of detecting a presence of a material comprising an actinide in a container, comprising:a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;d) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron; ande) based upon the determined energy of a statistically significant number of said detected energetic prompt neutrons exceeding a predetermined value, identifying the material comprising the actinide as present in the container. 2. The method of claim 1, wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 3. The method of claim 2, wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 4. The method of claim 2, wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 5. The method of claim 2, wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 6. The method of claim 2, wherein the lower energy is determined based upon materials potentially present in the container. 7. The method of claim 2, wherein the lower energy is determined based upon materials present in the container. 8. The method of claim 1, wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 9. The method of claim 1, wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 10. The method of claim 1, wherein determining the energy of the said detected neutron comprises measuring a time of flight of the said detected neutron. 11. The method of claim 1, wherein determining the energy of the said detected neutron comprises analyzing an energy deposited in at least one of said at least one neutron detector. 12. The method of claim 1, wherein the container is located such that at least two neutron detectors capable of distinguishing between photons and neutrons view the said container, the said neutron detectors viewing the container from different viewing angles relative to the photon beam, and neutrons are detected in at least two of said at least two neutron detectors; further comprisingf) determining a total neutron yield in at least two of said at least two neutron detectors in a predetermined neutron energy range; andg) based upon comparing the said total neutron yields from the said at least two neutron detectors viewing the container from different viewing angles relative to the photon beam, determining that the present actinide is an odd-even isotope if the total yields disclose an isotropic distribution of neutrons as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the total yields disclose an anisotropic distribution of neutrons as a function of angle relative to the photon beam. 13. The method of claim 1, further comprising:f) for at least one new viewing angle different from said first viewing angle relative to the photon beam,i) moving at least one of said at least one neutron detector such that at least one of said at least one moved neutron detector views the said container from the said new viewing angle relative to the photon beam;ii) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy;iii) detecting in at least one of said at least one moved neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container; andiv) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron;g) for at least two of said first and said at least one new viewing angles relative to the photon beam, determining a total neutron yield in at least one of said at least one neutron detector and at least one o east one moved neutron detector in a predetermined neutron energy range at the said viewing angle relative to the photon beam; andh) based upon comparing the said total neutron yields, determining that the present actinide is an odd-even isotope if the total yields disclose an isotropic distribution of neutrons as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the total yields disclose an anisotropic distribution of neutrons as a function of angle relative to the photon beam. 14. The method of claim 1, wherein the container is located such that at least two neutron detectors capable of distinguishing between photons and neutrons view the said container, at least two of the said at least two detectors viewing the container from different viewing angles relative to the photon beam, and neutrons are detected in at least two of said at least two neutron detectors; further comprising:f) determining a neutron energy distribution in at least two of said at least two neutron detectors; andg) based upon comparing the said neutron energy distributions from the said at least two neutron detectors viewing the container from different viewing angles relative to the photon beam, determining that the present actinide is an odd-even isotope if the energy distributions do not change by more than a predetermined amount as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the energy distributions change by more than a predetermined amount as a function of angle relative to the photon beam. 15. The method of claim 1, further comprising:f) for at least one new viewing angle different from said first viewing angle relative to the photon beam,i) moving at least one of said neutron detectors such that the said moved neutron detector views the said container from the said new viewing angle relative to the photon beam;ii) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy;iii) detecting in said at least one moved neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container; andiv) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron;g) for at least two of said first and said at least one new viewing angles relative to the photon beam, determining a neutron energy distribution in at least one of said at least one neutron detector and at least one of said at least one moved neutron detector in a predetermined neutron energy range at the said viewing angle relative to the photon beam; andh) based upon comparing the said neutron energy distributions, determining that the present actinide is an odd-even isotope if the energy distributions do not change by more than a predetermined amount as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the energy distributions change by more than a predetermined amount as a function of angle relative to the photon beam. 16. The method of claim 1, further comprising:f) illuminating at least a portion of the said container with at least one additional photon beam each having a new different predetermined cutoff photon energy, each new different predetermined cutoff photon energy also being different from said first predetermined cutoff energy such as to comprise only photons of energies no greater than said new different predetermined cutoff energy;g) detecting in at east one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of at least one of said at least one additional photon beam with at least a portion of the said container;h) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron;i) choosing a higher neutron energy region where neutrons from a (γ, n) process are not energetically permitted for any of said predetermined cutoff photon energies, and a lower energy region where neutrons from a (γ, n) process are energetically permitted for all of said predetermined cutoff photon energies;j) for each said predetermined cutoff photon energy, determining a neutron yield in at least one of said at least one neutron detector in at least two predetermined neutron energy ranges, wherein at least one predetermined neutron energy range encompasses the higher energy region where neutrons from a (γ, n) process are not energetically permitted; and wherein at least one other predetermined neutron energy range encompasses the lower energy region where neutrons from a (γ, n) process are energetically permitted; andk) based upon comparing the said determined neutron yields in at least one of said at least one neutron detector, resulting respectively from said photon beam and said at least one additional photon beam comprising photons of energies no greater than said first and new different predetermined cutoff energies, respectively, confirming that the material comprising the present actinide is present in the container if an increase in the said neutron yield between a lower predetermined cutoff photon energy and a higher predetermined cutoff photon energy, in the higher predetermined neutron energy range where neutrons from a (γ, n) process are not energetically permitted, is not substantial in comparison to an increase in neutron yield in the lower predetermined neutron energy range, where neutrons from a (γ, n) process are energetically permitted. 17. The method of claim 1, further comprising:f) illuminating at least a portion of the said container with at least one additional photon beam each having a new different predetermined cutoff photon energy, each new different predetermined cutoff photon energy also being different from said first predetermined cutoff energy such as to comprise only photons of energies no greater than said new different predetermined cutoff energy;g) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of at least one of said at least one additional photon beam with at least a portion of the said container;h) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron;i) for at least two of said predetermined cutoff photon energies, determining a neutron energy distribution in at least one of said at least one neutron detector; andj) based upon comparing the said determined neutron energy distributions in at least one of said at least one neutron detector, resulting respectively from said photon beam and said at least one additional photon beam comprising photons of energies no greater than said first and new different predetermined cutoff energies, respectively, confirming that the material comprising the present actinide is present in the container if the said neutron energy distributions change by no more than a predetermined amount as a function of cutoff photon energy. 18. The method of claim 1, further comprising:f) illuminating at least a portion of the said container with at east one additional photon beam each having a new different predetermined cutoff photon energy, each new different predetermined cutoff photon energy also being different from said first predetermined cutoff energy such as to comprise only photons of energies no greater than said new different predetermined cutoff energy;g) detecting in at east one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of at least one of said at least one additional photon beam with at least a portion of the said container;h) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron;i) for each said predetermined cutoff photon energy, determining a neutron yield in at least one of said at least one neutron detector in a plurality of predetermined neutron energy ranges;j) for each said predetermined neutron energy range; determining a neutron yield curve as a function of photon cutoff energy; andk) based upon comparing the said determined neutron yield curves in at least one of said at least one neutron detector for the said predetermined neutron energy ranges, confirming that the material comprising the present actinide is present in the container if the said neutron yield curves change by no more than a predetermined amount as a function of neutron energy. 19. A method of detecting a presence of a material comprising an actinide in a container, comprising:a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;d) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron; ande) based upon the determined minimum energy of a statistically significant number of said detected energetic prompt neutrons exceeding a predetermined value, identifying the material comprising the actinide as present in the container. 20. The method of claim 19, wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 21. The method of claim 20, wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 22. The method of claim 20, wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 23. The method of claim 20, wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 24. The method of claim 20, wherein the lower energy is determined based upon materials potentially present in the container. 25. The method of claim 20, wherein the lower energy is determined based upon materials present in the container. 26. The method of claim 19, wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 27. The method of claim 19, wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 28. The method of claim 19, wherein determining the minimum energy of the said detected neutron comprises analyzing an energy deposited in at least one of said at least one neutron detector. 29. The method of claim 19, wherein the container is located such that at least two neutron detectors capable of distinguishing between photons and neutrons view the said container, the said neutron detectors viewing the container from different viewing angles relative to the photon beam, and neutrons are detected in at least two of said at least two neutron detectors; further comprisingf) determining a total neutron yield in at least two of said at least two neutron detectors in a predetermined neutron minimum energy range; andg) based upon comparing the said total neutron yields from the said at least two neutron detectors viewing the container from different viewing angles relative to the photon beam, determining that the present actinide is an odd-even isotope if the total yields disclose an isotropic distribution of neutrons as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the total yields disclose an anisotropic distribution of neutrons as a function of angle relative to the photon beam. 30. The method of claim 19, further comprising:f) for at least one new viewing angle different from said first viewing angle relative to the photon beam,i) moving at least one of said at least one neutron detector such that at least one of said moved at least one neutron detector views the said container from the said new viewing angle relative to the photon beam;ii) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy;iii) detecting in at least one of said at least one moved neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container; andiv) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron;g) for at least two of said first and said at least one new viewing angle relative to the photon beam, determining a total neutron yield in at least one of said at least one neutron detector and at least one of said at least one moved neutron detector in a predetermined neutron minimum energy range at the said viewing angle relative to the photon beam; andh) based upon comparing the said total neutron yields, determining that the present actinide is an odd-even isotope if the total yields disclose an isotropic distribution of neutrons as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the total yields disclose an anisotropic distribution of neutrons as a function of angle relative to the photon beam. 31. The method of claim 19, wherein the container is located such that at least two neutron detectors capable of distinguishing between photons and neutrons view the said container, at least two of the said at least two detectors viewing the container from different viewing angles relative to the photon beam, and neutrons are detected in at least two of said at least two neutron detectors; further comprising:f) determining a neutron minimum energy distribution in at least two of said at least two neutron detectors; andg) based upon comparing the said neutron minimum energy distributions from the said at least two neutron detectors viewing the container front different viewing angles relative to the photon beam, determining that the present actinide is an odd-even isotope if the minimum energy distributions do not change by more than a predetermined amount as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the minimum energy distributions change by more than a predetermined amount as a function of angle relative to the photon beam. 32. The method of claim 19, further comprising:f) for at least one new viewing angle different from said first viewing angle relative to the photon beam,i) moving at least one of said neutron detectors such that the said moved neutron detector views the said container from the said new viewing angle relative to the photon beam;ii) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy;iii) detecting in said at least one moved neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container; andiv) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron;g) for at least two of said first and said at least one new viewing angles relative to the photon beam, determining a neutron minimum energy distribution in at least one of said at least one neutron detector and at least one of said at least one moved neutron detector in a predetermined neutron minimum energy range at the said viewing angle relative to the photon beam; andh) based upon comparing the said neutron minimum energy distributions determining that the present actinide is an odd-even isotope if the minimum energy distributions do not change by more than a predetermined amount as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the minimum energy distributions change by more than a predetermined amount as a function of angle relative to the photon beam. 33. The method of claim 19, further comprising:f) illuminating at least a portion of the said container with at least one additional photon beam each having a new different predetermined cutoff photon energy, each new different predetermined cutoff photon energy also being different from said first predetermined cutoff energy such as to comprise only photons of energies no greater than said new different predetermined cutoff energy;g) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of at least one of said at least one additional photon beam with at least a portion of the said container;h) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron;i) choosing a higher neutron energy region where neutrons from a (γ, n) process are not energetically permitted for any of said predetermined cutoff photon energies, and a lower energy region where neutrons from a (γ, n) process are energetically permitted for all of said predetermined cutoff photon energies;j) for each said predetermined cutoff photon energy, determining a neutron yield in at least one of said at least one neutron detector in at least two predetermined neutron minimum energy ranges, wherein at least one predetermined neutron minimum energy range encompasses the higher energy region where neutrons from a (γ, n) process are not energetically permitted; and wherein at least one other predetermined neutron minimum energy range encompasses the lower energy region where neutrons from a (γ, n) process are energetically permitted; andk) based upon comparing the said determined neutron yields in at least one of said at least one neutron detector, resulting respectively from said photon beams and said at least one additional photon beam comprising photons of energies no greater than said first and new different predetermined cutoff energies, respectively, confirming that the material comprising the present actinide is present in the container if an increase in the said neutron yield between a lower predetermined cutoff photon energy and a higher predetermined cutoff photon energy, in the higher predetermined neutron minimum energy range where neutrons from a (γ, n) process are not energetically permitted, is not substantial in comparison to an increase in neutron yield in the lower predetermined neutron minimum energy range, where neutrons from a (γ, n process are energetically permitted. 34. The method of claim 19, further comprising:f) illuminating at least a portion of the said container with at least one additional photon beam each having a new different predetermined cutoff photon energy, each new different predetermined cutoff photon energy also being different from said first predetermined cutoff energy such as to comprise only photons of energies no greater than said new different predetermined cutoff energy;g) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of at least one of said at least one additional photon beam with at least a portion of the said container;h) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron;i) for at least two of said predetermined cutoff photon energies, determining a neutron minimum energy distribution in at least one of said at least one neutron detector; andj) based upon comparing the said determined neutron minimum energy distributions in at least one of said at least one neutron detector, resulting respectively from said photon beams and said at least one additional photon beam comprising photons of energies no greater than said first and new different predetermined cutoff energies, respectively, confirming that the material comprising the present actinide is present in the container if the said neutron minimum energy distributions change by no more than a predetermined amount as a function of cutoff photon energy. 35. The method of claim 19, further comprising:f) illuminating at least a portion of the said container with at least one additional photon beam each having a new different predetermined cutoff photon energy, each new different predetermined cutoff photon energy also being different from said first predetermined cutoff energy such as to comprise only photons of energies no greater than said new different predetermined cutoff energy;g) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of at least one of said at least one additional photon beam with at least a portion of the said container;h) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron;i) for each said predetermined cutoff photon energy, determining a neutron yield in at least one of said at least one neutron detector in a plurality of predetermined neutron minimum energy ranges;j) for each said predetermined neutron minimum energy range; determining a neutron yield curve as a function of photon cutoff energy; andk) based upon comparing the said determined neutron yield curves in at least one of said at least one neutron detector for the said predetermined neutron minimum energy ranges, confirming that the material comprising the present actinide is present in the container if the said neutron yield curves change by no more than a predetermined amount as a function of neutron energy. 36. A method of detecting a presence of a material comprising an actinide in a container, comprising:a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;d) determining that an energy of a statistically significant number of said detected energetic prompt neutrons exceeds a predetermined value; ande) based upon the determination that the energy of the statistically significant number of said detected energetic prompt neutrons exceeds the predetermined value, identifying the material comprising the actinide as present in the container. 37. The method of claim 36, wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 38. The method of claim 37, wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 39. The method of claim 37, wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 40. The method of claim 37, wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 41. The method of claim 37, wherein the lower energy is determined based upon materials potentially present in the container. 42. The method of claim 37, wherein the lower energy is determined based upon materials present in the container. 43. The method of claim 36, wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 44. The method of claim 36, wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 45. The method of claim 36, wherein determining that the energy of the statistically significant number of said detected energetic prompt neutrons exceeds a predetermined value comprises analyzing an energy deposited in at least one of said at least one neutron detector. 46. The method of claim 36, wherein the container is located such that at least two neutron detectors capable of distinguishing between photons and neutrons view the said container, the said neutron detectors viewing the container from different viewing angles relative to the photon beam, and neutrons are detected in at least two of said at least two neutron detectors; further comprisingf) determining a total neutron yield in at least two of said at least two neutron detectors in a predetermined neutron energy range; andg) based upon comparing the said total neutron yields from the said at least two neutron detectors viewing the container from different viewing angles relative to the photon beam, determining that the present actinide is an odd-even isotope if the total yields disclose an isotropic distribution of neutrons as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the total yields disclose an anisotropic distribution of neutrons as a function of angle relative to the photon beam. 47. The method of claim 36, further comprising:f) for at least one new viewing angle different from said first viewing angle relative to the photon beam,i) moving at least one of said at least one neutron detector such that at least one of said at least one moved neutron detector views the said container from the said new viewing angle relative to the photon beam;ii) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy;iii) detecting in at least one of said at least one moved neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container; andiv) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron;g) for at least two of said first and said at least one new viewing angles relative to the photon beam, determining a total neutron yield in at least one of said at least one neutron detector and at least one of said at least one moved neutron detector in a predetermined neutron energy range at the said viewing angle relative to the photon beam; andh) based upon comparing the said total neutron yields, determining that the present actinide is an odd-even isotope if the total yields disclose an isotropic distribution of neutrons as a function of angle relative to the photon beam, and determining that the present actinide is an even-even isotope if the total yields disclose an anisotropic distribution of neutrons as a function of angle relative to the photon beam. 48. A method of detecting a presence of a material comprising an actinide in a container, comprising:a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;d) determining that more than a predetermined number of energetic prompt neutrons with energies above a first predetermined value have been detected;e) selecting a second predetermined value of energy greater than said first predetermined value;f) illuminating at least a portion of the said container with a photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy;g) detecting in at least one of said at least one neutron detector some additional energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;h) based upon a determined energy of a statistically significant number of said additional energetic prompt neutrons exceeding the second predetermined value, identifying the material comprising the actinide as present in the container.
	description	The present invention relates to a silicotitanate molded body, a production method thereof, and the use thereof. In particular, the present invention relates to a silicotitanate molded body usable as an adsorbent for removing radioactive cesium and/or radioactive strontium in a waste solution that is generated within a nuclear power plant and that also contains competing ions originated from seawater and so forth as well as relates to a production method thereof, an adsorbent comprising the silicotitanate molded body, and a decontamination method by using the adsorbent. The Fukushima Daiichi Nuclear Power Plant Accident caused by the Great East Japan Earthquake on Mar. 11, 2011 has been generating huge amount of radioactive waste solutions containing radionuclides. Such radioactive waste solutions include: contaminated water generated from cooling water that has been poured into the reactor pressure vessels, reactor containment vessels, and spent fuel pools; trench water accumulated inside trenches; subdrain water pumped up from wells called subdrain installed around the reactor buildings; groundwater; and seawater (hereinafter, referred to as “radioactive waste solutions”). From these radioactive waste solutions, radioactive substances are removed at treatment facilities, called SARRY (Simplified Active Water Retrieve and Recovery System, for cesium removal), ALPS (Advanced Liquid Processing System, for multi-nuclide removal), and so forth, and treated water is collected in tanks. Examples of substances that are capable of selectively adsorbing and removing radioactive cesium include ferrocyanide compounds, such as Prussian blue; mordenite, which is a type of zeolites; aluminosilicates, and titanium silicate (CST). To remove radioactive cesium, for example, SARRY uses IE-96 from UOP LLC, which is an aluminosilicate, and IE-911 from UOP LLC, which is CST. Meanwhile, examples of substances that are capable of selectively adsorbing and removing radioactive strontium include natural zeolites, synthetic zeolite A and X, titanates, and CST. To remove radioactive strontium, for example, ALPS uses a titanate adsorbent. According to “Basic Data on Contaminated Liquid Water Treatment for Fukushima Daiichi NPS (CLWT)” (Non Patent Literature (NPL) 1) published by the Division of Nuclear Fuel Cycle and Environment of the Atomic Energy Society of Japan, it is reported concerning the cesium and strontium adsorption performance of IE-910 from UOP LLC, which is powder CST, and IE-911 from UOP LLC, which is bead CST, that the powder CST exhibits adsorption capacity for radioactive cesium and strontium whereas the bead CST exhibits high adsorption performance for cesium but low adsorption performance for strontium. Moreover, it is also reported that a modified CST obtained through surface treatment of a titanium silicate compound by bringing into contact with an aqueous sodium hydroxide solution having a sodium hydroxide concentration within a range of 0.5 mol/L or more to 2.0 mol/L achieves cesium removal efficiency of 99% or higher and strontium removal efficiency of 95% or higher (Patent Literature (PTL) 1). Powder CST can be used for a treatment method by coagulation and sedimentation, for example, but is unsuitable for a method adopted by SARRY and ALPS of passing water to be treated through a column packed with an adsorbent. To improve strontium adsorption performance of granular CST, the treatment and operation disclosed in PTL 1 and NPL 2 have been investigated. However, such treatment and operation pose a problem in which increased costs result due to a large amount of chemicals needed. For this reason, there is a need for a treatment method of a radioactive waste solution that eliminates cumbersome treatment or operation, that exhibits high adsorption performance for both cesium and strontium, and that uses granular CST suitable for flow treatment in an adsorption column. Meanwhile, CST is heat sensitive and thus undergoes the compositional change upon strong heating. Consequently, the cesium and strontium adsorption capacity deteriorates. In the case of a zeolite molded body, the strength of the molded body is enhanced by using a binder, such as clay minerals, and firing at 500° C. or higher and 800° C. or lower. As mentioned above, however, CST cannot be fired since the adsorption capacity deteriorates upon strong heating. Accordingly, CST needs to be formed without strong heating. Further, it has been reported that sodium ions tend to suppress ion-exchange reactions between radioactive cesium and CST (NPL 2). Accordingly, there is a problem of low removal performance of radioactive cesium and radioactive strontium from seawater, which has a high sodium ion concentration. To enhance adsorption performance for cesium and strontium from seawater containing sodium ions, the present inventors have proposed an adsorbent for cesium and strontium, comprising: at least one selected from crystalline silicotitanates represented by the general formulae: Na4Ti4Si3O16.nH2O, (NaxK(1-x))4Ti4Si3O16.nH2O and K4Ti4Si3O16.nH2O wherein x represents a number of more than 0 and less than 1 and n represents a number of 0 to 8; and at least one selected from titanate salts represented by the general formulae: Na4Ti9O20.mH2O, (NayK(1-y))4Ti9O20.mH2O and K4Ti9O20.mH2O wherein y represents a number of more than 0 and less than 1 and m represents a number of 0 to 10 as well as a production method thereof (PTL 2). Despite high adsorption capacity for cesium or strontium, this adsorbent has low strength as a molded body and is brittle, thereby generating a lot of fine powder under wet conditions. Accordingly, washing with a large amount of water is required before use. Moreover, there was a concern that the adsorbent could be crushed under external loads, such as friction and flow pressure. Further, a silicotitanate molded body useful for adsorption and removal treatment of cesium or strontium in seawater and in groundwater has been proposed. The silicotitanate molded body is obtained by drying powder containing one or more oxides selected from the group consisting of silica, alumina, zirconia, and tungsten oxide as inorganic binders as well as silicotitanate having the sitinakite structure, followed by forming (PTL 3). As described hereinafter as a Comparative Example, however, there is a problem in which the molded body obtained by this method generates a lot of fine powder. PTL 1: Japanese Patent No. 5285183 PTL 2: Japanese Patent No. 5696244 PTL 3: Japanese Unexamined Patent Application Publication No. 2016-102053 NPL 1: “Basic Data on Contaminated Liquid Water Treatment for Fukushima Daiichi NPS (CLWT)” http://www.nuce-aesj.org/projects:clwt:start NPL 2: JAEA—Research 2011—037 An object of the present invention is to provide a silicotitanate molded body having high strength and reduced generation of fine powder, a production method thereof, an adsorbent for radioactive cesium and/or radioactive strontium comprising the silicotitanate molded body, and a decontamination method of radioactive cesium and/or radioactive strontium by using the adsorbent. According to the present invention, a silicotitanate molded body having high strength and reduced generation of fine powder; a production method thereof; an adsorbent for radioactive cesium and/or radioactive strontium comprising the silicotitanate molded body; and a decontamination method of radioactive cesium and/or radioactive strontium by using the adsorbent are provided. Specific embodiments are as follows. [1] A silicotitanate molded body comprising: crystalline silicotitanate particles that have a particle size distribution in which 90% or more, on volume basis, of the particles have a particle size within a range of 1 μm or more and 10 μm or less and that are represented by a general formula of A2Ti2O3(SiO4).nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2; and an oxide of one or more elements selected from the group consisting of aluminum, zirconium, iron, and cerium. [2] The silicotitanate molded body according to [1], further comprising niobium. [3] The silicotitanate molded body according to [1] or [2], wherein the silicotitanate molded body has a compressive strength at failure of 5.0 N or more. [4] The silicotitanate molded body according to any one of [1] to [3], wherein a content of the oxide of one or more elements selected from the group of aluminum, zirconium, iron, and cerium is 20 wt % or less. [5] The silicotitanate molded body according to any one of [1] to [4], wherein the molded body has a cylindrical shape having an average diameter within a range of 300 μm or more and 3,000 μm or less. [6] An adsorbent for cesium and/or strontium, comprising the silicotitanate molded body according to any one of [1] to [5]. [7] A decontamination method of a radioactive waste solution, comprising bringing the adsorbent for cesium and/or strontium according to [6] into contact with a waste solution containing radioactive cesium and/or radioactive strontium. [8] The decontamination method of a radioactive waste solution according to [7], comprising bringing the radioactive waste solution into contact with the adsorbent in a column flow mode at a linear velocity LV of 2 m/h or more and 40 m/h or less and a space velocity SV of 10 h−1 or more and 300 h−1 or less. [9] A production method of the silicotitanate molded body according to any one of [1] to [5], comprising: extruding a mixture containing crystalline silicotitanate that has a particle size distribution in which 90% or more, on volume basis, of particles have a particle size within a range of 1 μm or more and 10 μm or less and that is represented by a general formula of A2Ti2O3(SiO4).nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2 and an oxide of one or more elements selected from the group consisting of aluminum, zirconium, iron, and cerium to form a molded body; and subsequently drying the molded body. According to the present invention, a silicotitanate molded body having high strength and reduced generation of fine powder is provided. Due to high compressive strength at failure and reduced generation of fine powder, the silicotitanate molded body of the present invention is useful for an adsorbent to be packed in columns. The silicotitanate molded body of the present invention exhibits particularly excellent adsorption capacity for cesium and/or strontium and is thus suitable for decontamination of a radioactive waste solution containing radioactive cesium and/or radioactive strontium, especially for decontamination using columns. The present invention provides a silicotitanate molded body comprising: crystalline silicotitanate particles that have a particle size distribution in which 90% or more, on volume basis, of the particles have a particle size within a range of 1 μm or more and 10 μm or less and that are represented by a general formula of A2Ti2O3(SiO4).nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2; and an oxide of one or more elements selected from the group consisting of aluminum, zirconium, iron, and cerium. The term “crystalline silicotitanate” according to the present invention indicates that the main peak is detected in the 2θ range of 10° or more and 13° or less in X-ray diffraction analysis with a Cu—Kα source. Preferably, a peak is also detected in any one or more 2θ ranges of 14° or more and 16° or less, 25° or more and 28° or less, 26° or more and 29° or less, and 33° or more and 36° or less. In the silicotitanate molded body of the present invention, the content of the crystalline silicotitanate is preferably 80 wt % or more, more preferably 85 wt % or more and 99.9 wt % or less, and particularly preferably 90 wt % or more and 99.9 wt % or less. The silicotitanate molded body of the present invention reduces particles released therefrom since the crystalline silicotitanate before extrusion forming has an extremely narrow particle size distribution in which 90% or more, on volume basis, of the particles have a particle size in the range of 1 μm or more and 10 μm or less and preferably 95% or more of the particles have a particle size in the range of 1 μm or more and 10 μm or less; or 90% or more, on volume basis, of the particles have a particle size in the range of 2 μm or more and 10 μm or less and preferably 95% or more of the particles have a particle size in the range of 2 μm or more and 10 μm or less, and consequently, such crystalline silicotitanate can yield a dense molded body. The silicotitanate molded body of the present invention preferably further comprises niobium. Niobium (Nb) is basically and preferably contained in the form of partial substitution of titanium (Ti) in the crystalline silicotitanate. The oxide of one or more elements selected from the group consisting of aluminum, zirconium, iron, and cerium are contained in an amount of preferably 20 wt % or less and more preferably 0.1 wt % or more and 10 wt % or less relative to the silicotitanate molded body. The oxide of one or more elements selected from the group consisting of aluminum, zirconium, iron, and cerium, which is contained in the silicotitanate molded body of the present invention, can be confirmed by detecting the characteristic peak of each oxide in X-ray diffraction analysis with a Cu—Kα source. When niobium is further contained, the content of niobium as Nb2O5 is 2 wt % or more, preferably 5 wt % or more and 20 wt % or less, and particularly preferably 10 wt % or more and 20 wt % or less relative to the crystalline silicotitanate. The silicotitanate molded body of the present invention preferably has a compressive strength at failure of 5.0 N or more, preferably 8.0 N or more, and more preferably 10 N or more; and 25 N or less, preferably 20 N or less, and more preferably 15 N or less. Within the above ranges, the silicotitanate molded body is neither broken during column packing nor crushed under liquid pressure during column flow treatment and is thus particularly suitably used as an adsorbent for flow treatment of huge amount of liquids. The silicotitanate molded body of the present invention preferably has a cylindrical shape having an average diameter in the range of 300 μm or more and 3,000 μm or less. The average diameter is more preferably in the range of 400 μm or more and 2,000 μm or less and particularly preferably in the range of 500 μm or more and 1,000 μm or less. Within the above ranges, it is possible to realize the packing pressure and packing density during column packing within preferable ranges that are required to maintain a good balance between adsorption performance and pressure drop. Moreover, the silicotitanate molded body is easily produced. According to the present invention, an adsorbent for radioactive cesium and/or radioactive strontium comprising the above-described silicotitanate molded body is also provided. The adsorbent of the present invention may further comprise one or more other components selected from ion-exchange resins, ion-exchange fibers, chelating resins, chelating fibers, calcium alginate, chitosan, iron oxide, iron hydroxide, activated carbon, silver zeolite, silver compounds, hydrotalcite, geopolymers, silicates, titanium oxide, silica gel, amorphous aluminum silicate, zeolites, titanates, amorphous silicotitanate, manganese oxide, manganates, ferrocyanide compounds, hydroxyapatite, magnesium oxide, magnesium hydroxide, cerium oxide, cerium hydroxide, zirconium oxide, and zirconium hydroxide. According to the present invention, a decontamination method of a radioactive waste solution, comprising bringing the above-described adsorbent for radioactive cesium and/or radioactive strontium into contact with a radioactive waste solution containing radioactive cesium and/or radioactive strontium is also provided. As the decontamination method of a radioactive waste solution of the present invention, also provided is a decontamination method of a radioactive waste solution, comprising bringing the radioactive waste solution into contact with the adsorbent in a column flow mode at a linear velocity LV of 2 m/h or more and 40 m/h or less, preferably LV of 5 m/h or more and 30 m/h or less, and more preferably LV of 10 m/h or more and 20 m/h or less; and a space velocity SV of 10 h−1 or more and 300 h−1 or less, preferably SV of 15 h−1 or more and 200 h−1 or less, and more preferably 20 h−1 or more and 50 h−1 or less. The adsorbent of the present invention exhibits high compressive strength in addition to high adsorption capacity for cesium and strontium. Accordingly, the adsorbent can perform stable decontamination for a long period of time without easily adsorption breakthrough in treatment of a large amount of radioactive waste solutions at high linear velocity and space velocity. Further, according to the present invention, also provided is a production method of the silicotitanate molded body, comprising: extruding a mixture containing crystalline silicotitanate particles that have a particle size distribution in which 90% or more, on volume basis, of the particles have a particle size in the range of 1 μm or more and 10 μm or less and preferably 95% or more of the particles have a particle size in the range of 1 μm or more and 10 μm or less; or 90% or more, on volume basis, of the particles have a particle size in the range of 2 μm or more and 10 μm or less and preferably 95% or more of the particles have a particle size in the range of 2 μm or more and 10 μm or less and that are represented by a general formula of A2Ti2O3(SiO4).nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2 as well as an oxide of one or more elements selected from the group consisting of aluminum, zirconium, iron, and cerium to form a molded body; and subsequently drying the molded body. The preparation method of the crystalline silicotitanate is not particularly limited, but the crystalline silicotitanate is preferably obtained by mixing a silicic acid source, an alkali metal compound, a niobium source, titanium tetrachloride, and water to yield a niobium-containing mixed gel and subjecting the resulting niobium-containing mixed gel to hydrothermal reactions under pressurized conditions in an autoclave at 120° C. or higher and 200° C. or lower and preferably 140° C. or higher and 200° C. or lower for 6 hours or more and 100 hours or less and preferably 12 hours or more and 80 hours or less. Before the hydrothermal reactions, the niobium-containing mixed gel is more preferably aged at 20° C. or higher and 100° C. or lower and preferably 20° C. or higher and 70° C. or lower for 0.5 hour or more and 2 hours or less under atmospheric pressure. Hereinafter, the present invention will be further specifically described by means of Examples and Comparative Examples. [Preparation of Silicotitanate Formed Bodies] (1) First Step A mixed aqueous solution was obtained by mixing and stirring 115 g of Sodium Silicate 3 (from Nippon Chemical Industrial Co., Ltd., SiO2: 28.96%, Na2O: 9.37%, H2O: 61.67%, SiO2/Na2O=3.1), 670.9 g of 25% caustic soda aqueous solution (industrial 25% sodium hydroxide, NaOH: 25%, H2O: 75%), and 359.1 g of deionized water. To the mixed aqueous solution, 25.5 g of niobium hydroxide (Nb2O5: 76.5% by mass) was added and mixed with stirring, and subsequently, 412.3 g of titanium tetrachloride aqueous solution (from Osaka Titanium technologies Co., Ltd., 36.48% aqueous solution) was continuously added by a Perista pump over 0.5 hour, thereby producing a niobium-containing mixed gel. The gel was aged after addition of the titanium tetrachloride aqueous solution by sitting still at room temperature (25° C.) for 1 hour. (2) Second Step The niobium-containing mixed gel obtained in the first step was placed in an autoclave, heated to 160° C. over 1 hour, and reacted under stirring with this temperature maintained for 18 hours. The slurry after reaction was filtered. The filtration residue was dried, subjected to X-ray diffraction analysis, and confirmed to be the crystalline silicotitanate represented by the general formula of A2Ti2O3(SiO4).nH2O where A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2 (FIG. 1). A wet cake (in Examples 2 to 8 and Comparative Examples 1 to 4 hereinafter, simply referred to as “wet cake after filtration”) that was obtained after filtration and before drying in the above-described second step and that contained the crystalline silicotitanate represented by the general formula of A2Ti2O3(SiO4).nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2 was added with 1.0 wt % of aluminum oxide relative to the crystalline silicotitanate, extrusion-molded into 0.8 mm-diameter cylindrical shapes; subsequently dried; and classified into a range of 425 μm or more and 840 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. In addition, the particle size distribution of the silicotitanate particles in the wet cake is shown in FIG. 3. A wet cake after filtration obtained in the above-described second step was added with 1.0 wt % of aluminum oxide relative to the crystalline silicotitanate, extrusion-molded into 0.6 mm-diameter cylindrical shapes; subsequently dried; and classified into a range of 300 μm or more and 710 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was added with 1.0 wt % of aluminum oxide relative to the crystalline silicotitanate, extrusion-molded into 1.0 mm-diameter cylindrical shapes; subsequently dried; and classified into a range of 500 μm or more and 1,000 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was added with 1.0 wt % of aluminum oxide relative to the crystalline silicotitanate, extrusion-molded into 1.2 mm-diameter cylindrical shapes; subsequently dried; and classified into a range of 840 μm or more and 1,400 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was added with 0.5 wt % of aluminum oxide and 10.0 wt % of zirconium oxide relative to the crystalline silicotitanate, extrusion-molded into 0.5 mm-diameter cylindrical shapes; subsequently dried; and classified into a range of 300 μm or more and 600 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was added with aluminum oxide and a binder (silica sol), extrusion-molded into 1.0 mm-diameter cylindrical shapes; subsequently dried; and classified into a range of 500 μm or more and 1,000 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was added with 1.0 wt % of aluminum oxide relative to the crystalline silicotitanate, extrusion-molded into 0.8 mm-diameter cylindrical shapes; subsequently dried; pulverized; and classified into a range of 425 μm or more and 840 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was added with 1.0 wt % of aluminum oxide relative to the crystalline silicotitanate, extrusion-molded into 0.6 mm-diameter cylindrical shapes; subsequently dried; pulverized; and classified into a range of 425 μm or more and 840 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was extrusion-molded into 0.8 mm-diameter cylindrical shapes without being added with aluminum oxide and the like; subsequently dried; and classified into a range of 425 μm or more and 840 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was extrusion-molded into 0.6 mm-diameter cylindrical shapes without being added with aluminum oxide and the like; subsequently dried; and classified into a range of 300 μm or more and 710 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. A wet cake after filtration obtained in the above-described second step was dried and pulverized. The resulting powder was mixed with water and a binder (silica sol); extrusion-molded into 1.0 mm-diameter cylindrical shapes; dried; and classified into a range of 500 μm or more and 2,000 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. In addition, the particle size distribution of the powder obtained by drying and pulverizing the wet cake after filtration is shown in FIG. 3. The silicotitanate molded bodies prepared in Comparative Example 3 were further pulverized and classified into a range of 600 μm or more and 1,400 μm or less. The resulting silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. (1) First Step A mixed aqueous solution was obtained by mixing and stirring 60 g of Sodium Silicate 3 (from Nippon Chemical Industrial Co., Ltd., SiO2: 28.96%, Na2O: 9.37%, H2O: 61.67%, SiO2/Na2O=3.1), 224.3 g of 25% caustic soda aqueous solution (industrial 25% sodium hydroxide, NaOH: 25%, H2O: 75%), 34.6 g of 85% caustic potash (solid reagent potassium hydroxide, KOH: 85%), and 82.5 g of pure water. To the mixed aqueous solution, 203.3 g of titanium tetrachloride aqueous solution (from Osaka Titanium technologies Co., Ltd., 36.48% aqueous solution) was continuously added by a Perista pump over 0.5 hour, thereby producing a mixed gel. The mixed gel was aged after addition of the titanium tetrachloride aqueous solution by sitting still at room temperature (25° C.) for 1 hour. (2) Second Step The mixed gel obtained in the first step was placed in an autoclave, heated to 170° C. over 1 hour, and reacted under stirring with this temperature maintained for 96 hours. The slurry after reaction was filtered, thereby obtaining a wet cake containing crystalline silicotitanate (general formula: A4Ti4Si3O16.nH2O). The wet cake was extrusion-molded into 0.6 mm-diameter cylindrical shapes and classified into a range of 300 μm or more and 710 μm or less, thereby yielding silicotitanate molded bodies. The obtained silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. The wet cake obtained in Comparative Example 5 was extrusion-molded into 0.6 mm-diameter cylindrical shapes; dried; subsequently pulverized; and classified into a range of 300 μm or more and 710 μm or less. The resulting silicotitanate molded bodies were measured for the compressive strength at failure and the amount of generated fine powder. [X-Ray Diffraction] X-ray diffraction: D8 Advance S from Bruker Corporation was used. A Cu—Kα source was used. The measurement conditions were set to tube voltage of 40 kV, tube current of 40 mA, and scanning rate of 0.1°/sec. [Measurement of Particle Size Distribution] The particle size distribution was measured as volume distribution by using a laser diffraction/scattering-type particle size distribution analyzer (Microtrac MT 3300EXII from MicrotracBEL Corp.). A measurement sample was prepared as pretreatment by dispersing a sample in water, adding sodium hexametaphosphate into the resulting dispersion, and treating with ultrasonic waves for 2 minutes. The measurement conditions were set to particle refractive index of 1.81 and solvent refractive index of 1.333. [Measurement of Compressive Strength at Failure] One of the prepared silicotitanate molded bodies was measured for the compressive strength at failure by using a compression tester TCD 200 (DFGS 10) from John Chatillon & Sons Inc. In the same operation, twenty silicotitanate molded bodies were measured for the compressive strength at failure, and an average was calculated. [Measurement of the Amount of Generated Fine Powder] A glass column with an inner diameter of 30 mm was filled with 350 mL of the prepared silicotitanate molded bodies at the layer height of 50 cm. Through this column, pure water was passed upward at a flow rate of 0.3 L/min to spread out the silicotitanate molded body layer. Water was each collected at the column outlet when water in an amount of 10 times (3.5 L), 20 times (7.0 L), or 30 times (10.5 L), respectively, the amount of the silicotitanate molded bodies was passed through and measured, with a turbidimeter, for turbidity as the amount of generated fine powder. [Measurement of the Amount of Adsorbed Cesium and Strontium] Quantitative analysis of cesium-133 and strontium-88 was performed by using an inductively coupled plasma mass spectrometer (ICP-MS), Agilent 7700x model from Agilent Technologies. Each sample was diluted 1,000 times with dilute nitric acid and analyzed as a 0.1% nitric acid matrix. As standard samples, aqueous solutions each containing 0.05 ppb, 0.5 ppb, 1.0 ppb, 5.0 ppb, and 10.0 ppb of strontium, as well as aqueous solutions each containing 0.005 ppb, 0.05 ppb, 0.1 ppb, 0.5 ppb, and 1.0 ppb of cesium were used. TABLE 1Measurement ResultTurbidity as amountof generated fineAmountAmountpowder [—]ofofCompressiveAmount of wateradsorbedadsorbedAddedstrength at102030CsSroxideShapefailure [N]timestimestimes[mg/mL][mg/mL]Ex. 1Al2O3Cylindrically13.5117<1>17.03.0moldedEx. 2Al2O3Cylindrically8.61265>18.43.2moldedEx. 3Al2O3Cylindrically11.215127>17.22.3moldedEx. 4Al2O3Cylindrically7.517105>17.11.5moldedEx. 5Al2O3,Cylindrically8.1136<1>14.33.2ZrO2moldedEx. 6Al2O3Cylindrically6.26<1<1>20.24.0moldedEx. 7Al2O3Pulverized10.8117<1>21.03.7after extrusionEx. 8Al2O3Pulverized9.4175<1>19.73.7after extrusionComp. Ex. 1—Cylindrically1.369<1<1>19.73.5moldedComp. Ex. 2—Cylindrically0.96175<1>15.52.6moldedComp. Ex. 3—Cylindrically13.6603021>18.11.8moldedComp. Ex. 4—Pulverized13.1603126>16.42.1Comp. Ex. 5—Cylindrically2.5502718>18.11.3moldedComp. Ex. 6—Pulverized1.62063714>18.11.3 As shown in Examples 1 to 6 of Table 1, the silicotitanate molded bodies exhibit a high compressive strength at failure and a reduced amount of generated fine powder, where the silicotitanate molded bodies are obtained by: incorporating aluminum oxide and/or zirconium oxide into a wet cake of the crystalline silicotitanate represented by the general formula of A2Ti2O3(SiO4).nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2: extrusion-molding the wet cake; followed by drying. Moreover, as shown in Examples 7 and 8, it is revealed that a high compressive strength at failure and a reduced amount of generated fine powder are achieved even when a wet cake of the crystalline silicotitanate is added with aluminum oxide and/or zirconium oxide, extrusion-molded into cylindrical shapes, subsequently dried, and further pulverized. In contrast, as shown in Comparative Examples 1 and 2, the silicotitanate molded bodies exhibit a reduced amount of generated fine powder but a low compressive strength at failure, where the silicotitanate molded bodies are obtained by: extrusion-molding a wet cake of the crystalline silicotitanate represented by the general formula of A2Ti2O3(SiO4).nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2 without incorporating aluminum oxide or zirconium oxide; followed by drying. Moreover, as shown in Comparative Examples 3 and 4, it is revealed that the silicotitanate molded bodies exhibit a high compressive strength at failure but a large amount of generated fine powder, where the silicotitanate molded bodies are obtained by: drying a wet cake of the crystalline silicotitanate represented by the general formula of A2Ti2O3(SiO4).nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2 without incorporating aluminum oxide or zirconium oxide; subsequently pulverizing; and further extrusion-molding. Further, as shown in Comparative Examples 5 and 6, the silicotitanate molded bodies exhibit a low compressive strength at failure and a large amount of generated fine powder, where the silicotitanate molded bodies are obtained by: extrusion-molding a wet cake of the crystalline silicotitanate represented by the general formula of A4Ti4Si3O16.nH2O wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number of 0 to 2 without incorporating aluminum oxide or zirconium oxide; followed by drying. [Preparation of Simulated Contaminated Seawater 1] An aqueous solution with a salt concentration of 0.03 wt % was prepared by using a chemical for artificial seawater production, MARINE ART SF-1 from Osaka Yakken Co., Ltd. (sodium chloride: 22.1 g/L, magnesium chloride hexahydrate: 9.9 g/L, calcium chloride dihydrate: 1.5 g/L, anhydrous sodium sulfate: 3.9 g/L, potassium chloride: 0.61 g/L, sodium hydrogen carbonate: 0.19 g/L, potassium bromide: 96 mg/L, borax: 78 mg/L, anhydrous strontium chloride: 13 mg/L, sodium fluoride: 3 mg/L, lithium chloride: 1 mg/L, potassium iodide: 81 μg/L, manganese chloride tetrahydrate: 0.6 μg/L, cobalt chloride hexahydrate: 2 μg/L, aluminum chloride hexahydrate: 8 μg/L, ferric chloride hexahydrate: 5 μg/L, sodium tungstate dihydrate: 2 μg/L, ammonium molybdate tetrahydrate: 18 μg/L). A simulated contaminated seawater 1 was prepared by adding, as cesium concentration, 0.5 mg/L of cesium chloride into the aqueous solution. [Passing of Simulated Contaminated Seawater 1 Through Columns] Each glass column with an inner diameter of 30 mm was filled with 10 mL of the silicotitanate molded bodies prepared in Example 2 as an adsorbent at the layer height of 1.4 cm, and the simulated contaminated seawater 1 was passed through the glass column downward at a flow rate of 11.5 mL/min (linear velocity LV=1.6 m/h, space velocity SV=70 h−1), 23.5 mL/min (linear velocity LV=3.4 m/h, space velocity SV=140 h−1), or 47.0 mL/min (linear velocity LV=6.7 m/h, space velocity SV=280 h−1). The treated water was regularly collected at each column outlet and measured for cesium and strontium concentrations by ICP-MS. Decontamination was considered to be completed when a value of cesium and strontium concentrations (C) in the treated water at the column outlet divided by the respective initial cesium and strontium concentrations (C0) in the simulated contaminated seawater 1 reaches 0.1. The cesium removal performance is shown in FIG. 4, and the strontium removal performance is shown in FIG. 5. In FIGS. 4 and 5, the horizontal axis is B.V. indicating that the simulated contaminated seawater in what times the volume of the adsorbent is passed through, whereas the vertical axis is a value of the cesium and strontium concentration (C) at the column outlet divided by the cesium and strontium concentration (C0) at the column inlet, respectively. FIGS. 4 and 5 reveal that the silicotitanate molded bodies of the present invention exhibit remarkably excellent adsorption capacity despite the space velocity SV in an extremely high range of 70 h−1 or more and 280 h−1 or less as a column flow rate of the simulated contaminated seawater 1. [Preparation of Simulated Contaminated Seawater 2] An aqueous solution with a salt concentration of 0.17 wt % was prepared by using a chemical for artificial seawater production, MARINE ART SF-1 from Osaka Yakken Co., Ltd. (sodium chloride: 22.1 g/L, magnesium chloride hexahydrate: 9.9 g/L, calcium chloride dihydrate: 1.5 g/L, anhydrous sodium sulfate: 3.9 g/L, potassium chloride: 0.61 g/L, sodium hydrogen carbonate: 0.19 g/L, potassium bromide: 96 mg/L, borax: 78 mg/L, anhydrous strontium chloride: 13 mg/L, sodium fluoride: 3 mg/L, lithium chloride: 1 mg/L, potassium iodide: 81 μg/L, manganese chloride tetrahydrate: 0.6 μg/L, cobalt chloride hexahydrate: 2 μg/L, aluminum chloride hexahydrate: 8 μg/L, ferric chloride hexahydrate: 5 μg/L, sodium tungstate dihydrate: 2 μg/L, ammonium molybdate tetrahydrate: 18 μg/L). A simulated contaminated seawater 2 was prepared by adding, as cesium concentration, 1.0 mg/L of cesium chloride into the aqueous solution. [Passing of Simulated Contaminated Seawater 2 Through Columns] Each glass column with an inner diameter of 16 mm was filled with 200 mL of the silicotitanate molded bodies prepared in Example 3 as an adsorbent at the layer height of 100 cm, and the simulated contaminated seawater 2 was passed through the glass column downward at a flow rate of 66.5 mL/min (linear velocity LV=20 m/h, space velocity SV=20 h−1). The treated water was regularly collected at the column outlet and measured for cesium and strontium concentrations by ICP-MS. Decontamination was considered to be completed when a value of cesium and strontium concentrations (C) in the treated water at the column outlet divided by the respective initial cesium and strontium concentrations (C0) in the simulated contaminated seawater 2 reaches 0.1. The cesium removal performance is shown in FIG. 6, and the strontium removal performance is shown in FIG. 7. In FIGS. 6 and 7, the horizontal axis is B.V. indicating that the simulated contaminated seawater in what times the volume of the adsorbent is passed through, whereas the vertical axis is a value of the cesium and strontium concentrations (C) at the column outlet divided by the cesium and strontium concentrations (C0) at the column inlet, respectively. FIGS. 6 and 7 reveal that the silicotitanate molded bodies of the present invention exhibit excellent adsorption performance for cesium and strontium even in a waste solution with a high salt concentration.
	abstract	A system (1) for point of care diagnosis and/or analysis of a body fluid of a patient, includes at least one cartridge (2), at least one handheld diagnosis and/or analysis device (3) and at least one data processing device (4). Each cartridge (2) comprises a sample receiving room (5) for receiving a sample of the body fluid to be diagnosed and/or analyzed, a diagnosing and/or analyzing arrangement (6) for measuring at least one physiological parameter of the sample, and a first interface (7) for connecting the cartridge (2) to the handheld device (3). Each handheld device (3) comprises one second interface (8) for connecting one of said cartridges (2) to the handheld device (3), a measurement arrangement (9) co-operating with the connected cartridge (2) for measuring the parameter and generating measurement data thereof, and one third interface (13) for connecting the handheld device (3) to the data processing device (4). Each data processing device (4) comprises one fourth interface (14) for connecting one of said handheld devices (3) to the data processing device (3), and a data processing unit (15) co-operating with the connected handheld device (3) for further processing the measurement data.
	description	This application is a national phase application under 35 U.S.C. § 371 of International Application No. PCT/US2017/050066, filed Sep. 5, 2017, which claims priority to U.S. Provisional Patent Application Ser. No. 62/385,346 filed Sep. 9, 2016 and entitled “APPARATUS AND METHODS FOR MAGNETIC CONTROL OF RADIATION ELECTRON BEAM”, the entire contents of each of which are incorporated herein by reference. Electron beam radiation therapy utilizes ionizing radiation, typically as part of cancer treatment to destroy malignant cells. Radiation therapy may be curative in a number of types of cancer if they are localized to one area of the body. It may also be used as part of adjuvant therapy to prevent tumor recurrence after surgery to remove a primary malignant tumor. For example, electron beam radiation therapy may be used as part of adjuvant therapy in the early stages of certain types of cancer such as breast cancer. Radiation therapy is commonly applied to the cancerous tumor due to its ability to control cell growth. Ionizing radiation works by damaging the DNA of cancerous tissue leading to cellular death. To reduce exposure of healthy tissues (e.g. tissues which radiation must pass through to treat the tumor), radiation beams can be aimed from different angles to intersect at the tumor. Electron beam radiation therapy is currently used to direct radiation to a target region (e.g. a region containing the tumor) to destroy cells within the target region. Typical electron systems are limited in the depth that a target region can be successfully treated. In addition, typical systems do not provide dynamic control of the radiation depth and can direct unwanted radiation to healthy tissues surrounding the target region. For example, with existing systems the beam energy is manually selected to control the depth of radiation penetration up to a peak dose depth of approximately 3 cm (determined by currently commercially available maximum clinical electron beams energy of 20 MeV). In such systems the beam energy is increased in order to increase the depth of radiation penetration. This provides for higher radiation levels for tissue at or near the surface, and can lead to unwanted excessive radiation exposure to surrounding healthy tissue. Accordingly, a need exists for new radiation therapy apparatus and methods that provide greater control of radiation dosage levels at varying depths and minimize radiation exposure to surrounding healthy tissues. As explained in more detail below, exemplary embodiments of the present disclosure enable improvements in many aspects of electron beam radiation therapy as compared to current apparatus and methods. Exemplary embodiments of the present disclosure include an electron beam delivery and control system using very high energy electrons (VHEE) to produce a localized focal spot of high radiation dosage within the target volume. Exemplary embodiments are able to control the location of the focal spot through a technique referred to herein as magnetically optimized very high energy electron treatment (MOVHEET). Apparatus incorporating MOVHEET techniques can be dynamically controlled to produce a distribution of radiation dosage within a target region (e.g. a tumor volume) that is higher than surrounding normal tissue. This ability can result in greater normal tissue sparing and a larger degree of radiation control around the tumor volume. Exemplary embodiments include the ability to dynamically focus an electron beam of 50-250 megaelectron volts (MeV) to a focal spot at a desired target depth. As used herein, the term “depth” when used in reference to the focal spot refers to a dimension measured parallel to the electron beam (e.g. parallel to the primary axis of the beam prior to entering the magnetic control apparatus). The desired target depth can be determined by a radiation treatment plan dose distribution, where the output of the focusing system is a beam with optimized symmetry and a focusing angle that results in a low beam density at the target surface producing low entrance dose. Methods for dynamically controlling the focal spot depth of the electron focusing system can include the use of magnetic fields outside the target volume to alter the electron trajectories to produce the desired beam behavior. One embodiment of the focusing system utilizes quadrupole magnetic fields which are produced by a magnet having four inwardly directed poles such that each adjacent pole carries a magnetic field of opposite polarity. Current-carrying coils can be arranged in such a way to produce a magnetic field inside the ferromagnetic magnet material, where the strength of the magnetic quadrupole field may be adjusted by varying the coil current. This type of magnet design is referred to as iron-dominated. Another embodiment of a quadrupole magnet is based on a coil-dominated design where the current-carrying coils are designed in such a way such that the magnetic multipole field experienced by the charged particle beam is produced directly by the coils themselves without the use of a ferromagnetic core. Varying the current in the coils adjust strength of the magnetic field. A quadrupole magnetic field has the effect of defocusing a charged particle beam in one plane while focusing the beam in the orthogonal plane. This can allow for overall focusing in both planes being accomplished with a combination of quadrupole magnets whose currents, positions, and other magnet parameters have been chosen to produce the desired beam. A variety of exit beam shapes may be used, and certain configurations of quadrupoles may be used to generate symmetric beams. In one such configuration, a combination of three collinear quadrupole magnets can produce symmetrically focused beams for parallel incoming electron beams. Such systems can also provide for stigmatic focusing of a diverging beam where the beam focal spot may be adjusted by varying the quadrupole magnet strengths (alone or in conjunction with other parameter alterations). In another such configuration, a combination of two collinear quadrupole magnets can be use to produce output beams with an oblong shape that may be ideal for certain dose distributions that have strict spatial tolerances due to surrounding critical structures. The use of quadrupole systems with two or three quadrupoles allows for the user to choose the appropriate focusing distribution based on the target area. For example, in order to attain the desired depth dose distribution for the range of depths typically used for clinical treatment (e.g. 0-35 centimeters), the quadrupole separation distances and triplet position can be varied to achieve the optimal treatment beam. During operation, a quadrupole magnet system can produce a focused beam when the quadrupoles are operated under a specific set of conditions determined by the solution to a system of differential equations that govern the trajectories of the electrons within the field regions. In exemplary embodiments, a control system for the magnet parameters takes the dose distribution from the treatment planning software and uses an algorithm to calculate the necessary focusing system parameters to produce the desired beam trajectories. The beam can also be scanned laterally by means of orthogonal dipole fields which produce a uniform offset to the beam in their respective directions to produce a three-dimensional dose distribution. Other embodiments may mechanically move the focusing system to produce a three-dimensional dose distribution. The lateral scanning parameters can be included in the beam control system and determined by the treatment planning software. For focusing systems using diverging input beams, the beam divergence and origination point are also variables that can be determined by the control system algorithm. As an example, a pencil beam may be made divergent by the use of a scattering foil designed to produce a unique divergence pattern, where the divergent beam is then passed through a collimator in order to restrict the divergence angle for input into the quadrupole focusing system. The relative locations between the scattering foil, collimator, and quadrupole entrance are unique for a particular exit beam and can be determined along with the quadrupole settings. It should be noted that magnetic fields can have inherent inconsistencies or errors that can translate into nonuniformities in the focused electron beam. Careful consideration for such inconsistencies may be taken into account with the use of sextupole and octupole configurations, for example, to compensate for various geometrical and chromatic inconsistencies. One embodiment of the focusing system may use a quadruplet of quadrupole magnets coincident with three interspersed octupole magnets to produce a focused beam with geometrical aberration correction. In certain embodiments, an algorithm may be used to solve for the magnet parameters that produce a symmetrically focused beam where inconsistencies introduced by the quadrupoles have been compensated for by the octupole magnets producing a higher quality dose distribution in the target volume. The control system can dynamically adjust the parameters to optimize the beam determined by the treatment planning system. It is understood that the magnet configurations disclosed herein are merely exemplary, and that other combinations of magnets may be used to correct for other magnet-induced inconsistencies. Certain embodiments may dynamically control beam depth by utilizing a posterior solenoidal magnet to produce a magnetic field gradient within the target volume such that the electrons reverse direction at a depth determined by the magnetic field strength. An anterior solenoidal magnet may be used in conjunction with the posterior magnet to modify the magnetic field in the target volume and enhance the dose deposition. The localized high dose region depth may be controlled with a control system designed to adjust the solenoid currents based on the desired dose distribution. Exemplary embodiments include an apparatus for controlling a radiotherapy electron beam, where the apparatus comprises: an electron beam generator configured to generate an electron beam; a plurality of magnets producing a plurality of magnetic fields configured to focus the electron beam to a focal spot; and a control system configured to alter one or more parameters of the plurality of magnets to move the focal spot from a first location to a second location, where the first location is located at a first depth within a target region and the second location is located at a second depth within the target region. In certain embodiments, the target region is below an epidermal surface of a subject; the first location or the second location is at a depth between 0 and 50 centimeters from the epidermal surface. In particular embodiments, the electron beam has a energy of between 50 and 250 megaelectron volts (MeV). In some embodiments, the energy of the beam is not modulated when the focal spot is moved from the first location to the second location. In specific embodiments, the plurality of magnets comprise a plurality of collinear multipole magnets. In certain embodiments, the plurality of collinear multipole magnets comprises at least two collinear quadrupole magnets. In particular embodiments, the one or more parameters of the plurality of magnets comprises a separation distance between the plurality of collinear multipole magnets; and the control system is configured to alter the separation distance between the plurality of collinear multipole magnets. In some embodiments, the plurality of magnets comprise an anterior lens magnet, a posterior reflective magnet, and a plurality of radial focal magnets. In specific embodiments, the plurality of magnets comprise electromagnets; the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and the control system is configured to alter the electrical current through the electromagnets. In certain embodiments, the electromagnets are iron-dominated or coil dominated superconducting electromagnets. In particular embodiments, the plurality of magnetic fields are configured to focus the electron beam at a convergence angle of between 50 and 500 mrad. In some embodiments, the plurality of magnetic fields are configured to focus the electron beam at a convergence angle of between 200 and 400 mrad. In specific embodiments, the control system comprises an algorithm to calculate the one or more parameters of the plurality of magnets. In certain embodiments, the control system receives input from a treatment planning software program configured to calculate a dose distribution. In particular embodiments, the focal spot comprises a maximum electron dose concentration. Exemplary embodiments include a method of controlling a radiotherapy electron beam, where the method comprises: generating an electron beam; directing the electron beam through a plurality of magnetic fields produced by a plurality of magnets; focusing the electron beam to a focal spot with the plurality of magnetic fields; and altering one or more parameters of the plurality of magnets to move the focal spot from a first location to a second location where the first location is located at a first depth within a target region and the second location is located at a second depth within the target region. In certain embodiments, the target region is below an epidermal surface of a subject; and the first location or the second location is at a depth between 0 and 50 centimeters from the epidermal surface. In particular embodiments, the electron beam has a power of between 50 megaelectron volts and 250 megaelectron volts. In some embodiments, the power of the beam is not modulated when the focal spot is moved from the first location to the second location. In specific embodiments, the plurality of magnets comprise a plurality of collinear multipole magnets. In certain embodiments, the plurality of collinear multipole magnets comprises at least three collinear quadrupole magnets. In particular embodiments, the one or more parameters of the plurality of magnets comprises a separation distance between the plurality of collinear multipole magnets; and the control system is configured to alter the separation distance between the plurality of collinear multipole magnets. In some embodiments, the plurality of magnets comprise an anterior lens magnet, a posterior reflective magnet, and a plurality of radial focal magnets. In specific embodiments, the plurality of magnets comprise electromagnets; the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and the control system is configured to alter the electrical current through the electromagnets. In certain embodiments, the plurality of magnetic fields are configured to focus the electron beam at a convergence angle of between 100 and 500 mrad. In particular embodiments, the plurality of magnetic fields are configured to focus the electron beam at a convergence angle of between 200 and 400 mrad. In some embodiments, the control system comprises an algorithm to calculate the one or more parameters of the plurality of magnets. In specific embodiments, the control system receives input from a treatment planning software program configured to calculate a dose distribution. In certain embodiments, the focal spot comprises a maximum electron dose concentration. Exemplary embodiments include an apparatus for controlling a radiotherapy electron beam, where the apparatus comprises: an electron beam generator configured to generate an electron beam with a power between 50 megaelectron volts and 250 megaelectron volts; a plurality of magnets configured to focus the electron beam at a focal spot; and a control system configured move the focal spot from a first location at a first depth to a second location at a second depth, wherein the power of the electron beam is maintained at a consistent level when the focal spot is moved from the first location to the second location. In certain embodiments, the first location and the second location are located within a target region. In particular embodiments, the target region is below an epidermal surface of a subject; and the first location or the second location is at a depth between 10 and 20 centimeters from the epidermal surface. In some embodiments, the control system is configured to alter one or more parameters of the plurality of magnets to move the focal spot from the first location to the second location. In specific embodiments, the control system comprises an algorithm to calculate the one or more parameters of the plurality of magnets. In certain embodiments, the control system receives input from a treatment planning software program configured to calculate a dose distribution. In particular embodiments, the plurality of magnets comprise a plurality of collinear multipole magnets. In some embodiments, the plurality of collinear multipole magnets comprises at least three collinear quadrupole magnets. In specific embodiments, the one or more parameters of the plurality of magnets comprises a separation distance between the plurality of collinear multipole magnets; and the control system is configured to alter the separation distance between the plurality of collinear multipole magnets. In certain embodiments, the plurality of magnets comprise an anterior lens magnet, a posterior reflective magnet, and a plurality of radial focal magnets. In particular embodiments, the plurality of magnets comprise electromagnets; the control system is configured to alter one or more parameters of the plurality of magnets to move the focal spot from the first location to the second location; the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and the control system is configured to alter the electrical current through the electromagnets. In particular embodiments, the plurality of magnets are configured to focus the electron beam at a convergence angle of between 100 and 500 mrad. In some embodiments, the plurality of magnets are configured to focus the electron beam at a convergence angle of between 200 and 400 mrad. In specific embodiments, the focal spot comprises a maximum electron dose concentration. Certain embodiments include a method of controlling a radiotherapy electron beam, where the method comprises: generating an electron beam having a power between 50 megaelectron volts and 250 megaelectron volts; focusing the electron beam to a focal spot with a plurality of magnets; and moving the focal spot from a first location at a first depth to a second location at a second depth while maintaining the power of the electron beam at a consistent level. In particular embodiments, the first location and the second location are located within a target region. In certain embodiments, the target region is below an epidermal surface of a subject; the first location or the second location is at a depth between 10 and 20 centimeters from the epidermal surface. In some embodiments, moving the focal spot from a first location at a first depth to a second location at a second depth comprises altering one or more parameters of the plurality of magnets. In specific embodiments, the control system comprises an algorithm to calculate the one or more parameters of the plurality of magnets. In particular embodiments, the control system receives input from a treatment planning software program configured to calculate a dose distribution. In certain embodiments, the plurality of magnets comprise a plurality of collinear multipole magnets. In some embodiments, the plurality of collinear multipole magnets comprises at least three collinear quadrupole magnets. In specific embodiments, the one or more parameters of the plurality of magnets comprises a separation distance between the plurality of collinear multipole magnets; and altering one or more parameters of the plurality of magnets comprises altering the separation distance between the plurality of collinear multipole magnets. In certain embodiments, the plurality of magnets comprise an anterior lens magnet, a posterior reflective magnet, and a plurality of radial focal magnets. In particular embodiments, the plurality of magnets comprise electromagnets; and moving the focal spot from a first location at a first depth to a second location at a second depth comprises altering an electrical current through the electromagnets. In certain embodiments, the plurality of magnets are configured to focus the electron beam at a convergence angle of between 100 and 500 mrad. In particular embodiments, the plurality of magnets are configured to focus the electron beam at a convergence angle of between 200 and 400 mrad. In some embodiments, the focal spot comprises a maximum electron dose concentration. In the following, the term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically. The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more” or “at least one.” The terms “about”, “substantially” and “approximately” mean, in general, the stated value plus or minus 5%. The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternative are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements, possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features, possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description. Referring initially to FIG. 1, an apparatus 100 for controlling a radiotherapy electron beam is shown. In this embodiment, apparatus 100 comprises an electron beam generator 150 configured to generate an electron beam 155. Apparatus 100 further comprises a plurality of magnets 105 that includes collinear multipole magnets. In this embodiment, magnets 105 include a first quadrupole magnet 101, a second quadrupole magnet 102 and a third quadrupole magnet 103. First quadrupole magnet 101 comprises first pole 111, second pole 112, third pole 113 and fourth pole 114. It is understood that second quadrupole magnet 102 and third quadrupole magnet 103 also comprise four poles (not labeled in the figures for purposes of clarity). A top perspective view of magnets 105 is shown in FIG. 2. During operation of apparatus 100, magnets 105 produce a plurality of magnetic fields configured to focus electron beam 155 and provide a maximum electron dose concentration at a focal spot in a target region. Referring specifically to FIGS. 3 and 4, simulated dose distribution plots are shown for apparatus 100 in the X-Z plane (FIG. 3) and Y-Z plane (FIG. 4). Dose distributions where calculated using the Monte Carlo calculation code FLUKA© which is a general purpose code for simulating the interactions of energetic particles in matter. See “The FLUKA Code: Developments and Challenges for High Energy and Medical Applications” T. T. Böhlen, F. Cerutti, M. P. W. Chin, A. Fassò, A. Ferrari, P. G. Ortega, A. Mairani, P. R. Sala, G. Smirnov and V. Vlachoudis, Nuclear Data Sheets 120, 211-214 (2014); see also “FLUKA: a multi-particle transport code” A. Ferrari, P. R. Sala, A. Fassò, and J. Ranft, CERN-2005-10 (2005), INFN/TC_05/11, SLAC-R-773. FIGS. 3 and 4 were produced by tracking 2.5×105 with a minimum step size of 0.05 cm, charged particle cutoff energy of 10 keV, and dose binning grid size of 1 mm. In this example, electron beam 155 is a 100 megaelectron volt (MeV), 5 centimeter radius electron beam. Electron beam 155 is shown passing through 100 centimeters of air and incident on a water phantom (at Z dimension 0 centimeters, corresponding to an epidermal surface of a subject). In the illustrated embodiment, magnets 105 are configured as a quadrupole triplet and function as a symmetric uniform focusing lens. As shown in FIG. 3, first quadrupole magnet 101 focuses electron beam 155 in the X-Z plane, while second quadrupole magnet 102 defocuses electron beam 155, and third quadrupole magnet 103 focuses electron beam 155. As shown in FIG. 4, magnets 101, 102 and 103 perform the inverse operations on electron beam 155 in the Y-Z plane. In particular, first quadrupole magnet 101 defocuses beam 155 in the Y-Z plane, while second quadrupole magnet 102 focuses electron beam 155, and third quadrupole magnet 103 defocuses electron beam 155. As shown in FIGS. 3 and 4, magnets 105 may be configured to focus electron beam 155 and provide a maximum electron dose concentration at a focal point 125. As explained further below, during operation control system 190 (shown in FIG. 1) can alter one or more parameters of magnets 105 to move focal spot 125 to different depths within a target region in the Z-plane. In exemplary embodiments, the power of electron beam 155 is not modulated when focal spot 125 is moved to different depths within a target region. For example, control system 190 may control the position of individual magnets in the group of magnets 105 in order to alter the separation distance between the magnets. In particular, control system 190 may alter the separation distance between first quadrupole magnet 101 and second quadrupole magnet 102. Control system 190 may also alter the separation distance between second quadrupole magnet 102 and third quadrupole magnet 103. The separation distance between magnets 101, 102 and 103 may be altered by any one of suitable mechanisms, including for example, one or more linear actuators. For example, as shown in FIG. 1, control system 190 can control the position of magnets 101, 102 and 103 via linear actuators 131, 132 and 133 respectively. By adjusting the position of each magnet 101, 102 and 103, the separation distances between the magnets can be altered. The alteration of the separation distances between magnets in the group of magnets 105 affects the focusing of electron beam 155 and convergence angle A, shown in FIG. 4. As convergence angle A is increased, focal spot 125 is moved closer to magnets 105. Conversely, as the separation distance between magnets 105 is controlled to decrease convergence angle A, focal spot 125 is moved farther from magnets 105. In certain embodiments, apparatus 100 can increase convergence angle A up to values of approximately 400 milliradians. This can allow focal spot 125 to be moved within the target region, which is typically between 0 and 35 centimeters from the surface. It is understood that a similar convergence angle is present in the X-Z plane of FIG. 3. The convergence angle present in FIG. 3 is not labeled for purposes of clarity. In other embodiments, control system 190 may control different parameters in order to control electron beam 155 and focal spot 125. For example, in certain embodiments magnets 105 may comprise electromagnets and control system 190 can be configured to alter the electrical current through the electromagnets. Similar to the magnet separation distance, altering the electrical current through each of magnets 101, 102 and 103 can also affect convergence angle A and the position of focal spot 125. Accordingly, the alteration of magnet parameters (e.g. magnet separation distance or electrical current) can change the depth of focal spot 125 by allowing focal spot 125 to be moved closer to and farther from magnets 105 in an axial direction (e.g. collinear with electron beam 155). The ability to control convergence angle A and the location of focal spot 125 via magnetic parameters can provide numerous advantages. For example, the radiation dose can be reduced in regions outside of the target region. In particular, the ability to create a higher convergence angle can provide a larger cross section of beam 155 at the skin surface as compared to the cross section at focal spot 125. Particular embodiments may be capable of producing surface entrance doses as low as fifteen percent of the maximum dose at the focal spot 125, as opposed to typical current technologies that provide surface doses of approximately eighty or ninety percent of the maximum dosage. The ability to control the axial depth location of the focal spot and minimize radiation dosage levels to healthy tissues outside the target region can improve patient outcomes and reduce recovery times. Furthermore, exemplary embodiments also provide the ability to control the depth of the radiation dose peak at focal point 125 within a target region without modulating the energy of beam 155. Current electron therapy technology typically varies the energy of the electron beam to adjust the depth of penetration, which is done manually and is not suited for dynamic control of the dosage level. For example, changing the energy of the beam to adjust the depth of penetration does not allow for independent control of focal spot depth and radiation levels. In contrast, exemplary embodiments of the present disclosure are configured to penetrate the full clinical range of patient thicknesses and then use the magnetic system parameters to produce a high dose focal region in the target which may be moved throughout the target depth. The target depth can be controlled by parameters (e.g. magnet current and/or positions) other than electron beam energy levels. As a result of dose peak depth control as disclosed herein, beams of varying dose peak depths may be superimposed to produce a region of constant dose over a region of depth within the patient corresponding to a tumor or treatment site. FIG. 5 illustrates a graph of a simulated percent dose distributions for 140 MeV electron beams on water for a 5 centimeter radius circular beam. In one plot of FIG. 5, the electron beam is not focused, while in the other plot the same beam is focused with a collinear quadrupole magnet configuration as shown in FIGS. 1 and 2. As shown in FIG. 5, the percent dose at the surface (e.g. depth of 0 cm) is substantially reduced for the focused beam as compared to the unfocused beam. The focused beam provides a dose at the surface of between 20 and 30 percent of the maximum dose, while the unfocused beam provides a surface dose of between 70 and 80 percent of the maximum. FIG. 5 also illustrates the focused beam provided a maximum dose at slightly less than 15 cm depth. Other embodiments may comprise a different configuration of magnets than those previously shown and described. For example, referring now to FIG. 6, an apparatus 200 comprises a plurality of magnets 205 that are not collinear and are configured to control an electron beam 255. In this embodiment, magnets 205 are configured as solenoidal electromagnets and comprise an anterior lens magnet 201, a posterior reflective magnet 202, and a plurality of radial focal magnets 203, 204, 206 and 207. During operation of apparatus 200, a control system 290 can control parameters of magnets 205 to focus beam 255 at different depths, in a manner similar to the previously-described embodiments. For example, control system 290 can control an electrical current through each of magnets 201-204 and 206-207. Control system may also be configured to control the position of magnets 201-204 and 206-207 so that the separation distance between each of the magnets is altered to change the focal spot (not shown in FIG. 6 for purposes of clarity) of beam 255. In the configuration shown in FIG. 6, anterior lens magnet 201 is the primary source of focusing. Radial focal magnets 203, 204, 206 and 207 produce a magnetic field within the target that modifies the anterior lens magnet 201 field and provides additional focusing. The plane of radial focal magnets 203, 204, 206 and 207 can be adjusted based on the treatment depth. Posterior reflective magnet 202 produces a magnetic field gradient such that electrons are reflected at a depth dependent on the magnetic field strength of magnet 202, resulting in a radiation dose confined to a desired depth. FIG. 7 illustrates a graph of simulated percent depth dose curves for 100 MeV, 5 cm radius electron beams incident on a water phantom, where the beam has been focused using the FIG. 6 configuration with different depths of the magnetic plane as defined by the in-plane magnets 203, 204, 206, and 207. As shown in FIG. 7, the different depths magnetic planes corresponds to a shift in the dose peak to different depths. The 40 cm magnetic plane has a maximum dose peak at approximately 16 cm, the 35 cm magnetic plane has a maximum dose peak at approximately 13.5 cm, the 30 cm magnetic plane has a maximum dose peak at approximately 11.5 cm, and the 25 cm magnetic plane has a maximum dose peak at approximately 8.5 cm. For comparison, the percent depth dose curve for a 5 cm radius circular beam of 20 MeV electrons without any focusing magnetic fields is shown. As shown in FIG. 7, the surface dose of the unfocused 20 MeV beam is between 80 and 90 percent, while the focused beams have a surface dose between 10 and 20 percent. FIG. 8 illustrates a Monte Carlo calculation of a composite dose distribution from five focused electron beams of varying energies on a prostate CT (computed tomography) image using the magnet configuration shown in FIG. 6. FIG. 9 illustrates a Monte Carlo calculation of a composite dose distribution from 10 focused electron beams of varying energies utilizing a form of “dose painting” (e.g. altering the depth of a focal spot for each of the beams). This technique can be been used to increase the high dose coverage throughout the prostate using the magnet configuration shown in FIG. 6. FIG. 10 illustrates a graph of the percent dose versus depth for different configurations of the embodiment shown in FIG. 6 utilizing radial focal magnets with an anterior lens magnet and a posterior reflective magnet. The graphs include a 25 centimeter magnetic plane configuration, a 40 centimeter magnetic plane configuration with the intensities of each distribution optimized to produce a simulated spread out Bragg peak (“pseudo SOBP”) configuration. The graphs illustrated in FIG. 10 included simulated data for a 100 MeV electron beam with a 5 centimeter radius. All of the devices, apparatus, systems and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the devices, apparatus, systems and methods of this invention have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the devices, apparatus, systems and/or methods in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims. The contents of the following references are incorporated by reference herein: U.S. Pat. No. 4,806,766 U.S. Pat. No. 5,113,162 U.S. Pat. No. 5,161,546 U.S. Pat. No. 6,292,538 U.S. Pat. No. 8,436,326 U.S. Pat. No. 8,350,226 U.S. Pat. No. 8,933,651 U.S. Pat. No. 9,095,705 U.S. Pat. No. 9,153,409 U.S. Pat. No. 9,283,407 U.S. Pat. No. 9,289,624 U.S. Pat. Pub. 2011/0180731 U.S. Pat. Pub. 2015/0187538 PCT Pat. Pub. WO2015/102680 PCT Pat. Pub. WO2012/070054 Korean Pat. Pub. 101416559B1 “An Adjustable, Short-Focal Length Permanent-Magnet Quadrupole Based Electron Beam Final Focus System”, Kim et al., Mar. 11, 2005 available at http://pbpl.physics.ucla.edu/Research/Experiments/Beam_Radiation_Interaction/Thomson_Scattering/_references/PMQ_final_print.pdf “Laser-Driven Very High Energy Electron/Photon Beam Radiation Therapy in Conjunction with a Robotic System”, Nakajima et al., Appl. Sci. 2015, 5, 1-20. “The FLUKA Code: Developments and Challenges for High Energy and Medical Applications” T. T. Böhlen, F. Cerutti, M. P. W. Chin, A. Fassò, A. Ferrari, P. G. Ortega, A. Mairani, P. R. Sala, G. Smirnov and V. Vlachoudis, Nuclear Data Sheets 120, 211-214 (2014). “FLUKA: a multi-particle transport code” A. Ferrari, P. R. Sala, A. Fassò, and J. Ranft, CERN-2005-10 (2005), INFN/TC_05/11, SLAC-R-773.
060884177	abstract	An apparatus and a method for detecting and locating leaks in a nuclear plant, in particular a pipeline in a nuclear plant, include a collection line which is permeable to a substance to be detected and which communicates with a pump and with a sensor for the substance. The sensor has a detector for detecting the radioactivity of the substance or a branch line which communicates with a detector for detecting radioactivity branches off upstream of the sensor. If a radioactive substance reaches the collection line and penetrates it, then the location of the leak can be determined from the instant at which the radioactive substance reaches the detector.
	description	The invention relates to method and a device for removing particles, such as atoms, molecules, clusters, ions, and the like, generated by means of a radiation source during generation of short-wave radiation having a wavelength of up to approximately 20 nm, by means of a first gas guided at high mass throughput between the radiation source and a particle trap arranged in a wall of a mirror chamber. The method according to the invention and the device according to the invention can be used in connection with generating radiation in a wavelength range of approximately 2 nm up to approximately 20 nm in lithography or microscopy. WO-A-00/28384 discloses such a method for a lithography device in which soft x-ray radiation and extreme ultraviolet radiation are used. In this device, a chamber containing a wafer is separated by means of a wall from optical devices. In the wall, an opening is provided that allows passage of a noble gas and of short-wave radiation. When irradiating the wafer with short-wave radiation, contaminants are released that can reach through the opening the optical devices. By means of a curtain of noble gas that is positioned in the vicinity of the wafer, it is possible to prevent the contaminant particles from reaching the optical devices because they collide with the particles of the noble gas. In particular, when irradiating the wafer with short-wave radiation, contaminants of a high molecular weight will result. Such particles can be slowed only insufficiently. When such molecules deposit on the optical device, for example, a mirror, its reflective properties drop drastically as a result of absorption phenomena. Also, so-called “thermal” particles with a high kinetic energy can be only minimally deflected despite their relatively minimal mass. Typically, particles are also generated when operating a radiation source for short-wave radiation in the wavelength range of up to approximately 20 nm. The short-wave radiation of a modern high-performance source is generated within a plasma that is made available either by electric discharge or a focused laser pulse. In the case of electric discharge, particles that can absorb the short-wave radiation are inevitably produced as a result of the employed working gas and electrode erosion. In the case of laser-induced plasma, a so-called target is heated and evaporated within a short period of time by laser radiation. In the vapor phase, atoms and ions are produced within the plasma. As a result of the very high temperature of the plasma in the order of several 10 eV, such particles of the plasma have a high kinetic energy. They can have a relatively great average free length of path within a vacuum chamber that is required, of course, for a loss-free transfer of the radiation produced within the plasma into a mirror chamber. In this way, it is possible that such particles can deposit on an optical device or an article to be irradiated. In particular, damage of the surfaces of a beam-guiding device, such as a collector mirror, by so-called sputtering is observed. WO-A-02/054153 discloses an exposure system with a vacuum chamber wall in which a particle trap is arranged. This particle trap has a lamella-like structure that defines several neighboring narrow sectors. These sectors extend essentially parallel to the direction of propagation of the radiation. The sectors are provided with varying width and length. A wall configured in this way and arranged between the radiation source and a mirror chamber enables an almost loss-free transfer of the short-wave radiation, wherein the particles accelerated in the direction toward the mirror chamber are retained by the lamella-like structure. Particularly particles having a relatively great mass that can be produced by plasma-chemical processes or upon erosion of an electrode material are not reliably retained by such a particle trap alone. The invention has therefore the object to provide a method of the aforementioned kind which protects with simple measures optical devices and/or articles to be irradiated against contamination. This object is solved for a method of the aforementioned kind in that a second gas is introduced into the mirror chamber and its pressure is adjusted such that it is at least as high as the pressure of the first gas. In this connection, the realization that, as a result of the introduced second gas, passage of the first gas through the particle trap into the mirror chamber can be almost completely prevented, is especially important for the present invention. The slowed contaminant particles are therefore no longer transported by the particles of the first gas that otherwise would enter the mirror chamber. Entrainment of the contaminant particles by means of the employed first gas through the particle trap into the mirror chamber is prevented. The particle trap is practically made impenetrable for the first gas and/or the contaminant particles. By means of the wall and the particle trap that is essentially transparent for the short-wave radiation, a sufficient spatial separation between the mirror chamber and the radiation source is achieved. The slowed or decelerated contaminant particles can be finally removed by vacuum. By means of the afore described particle trap, it is, for example, possible to guide different gases with different spatial orientation during operation of the radiation source by adjusting the width and/or the length of the sectors while simultaneously providing high permeability for the short-wave radiation. The method can be improved in that the pressure of the second gas is adjusted such that it is higher than the pressure of the first gas. Of course, the second gas introduced at a higher pressure into the mirror chamber flows through the sectors of the particle trap in the direction toward the radiation source. The contaminant particles that are generated by the radiation source in the opposite direction can be slowed or deflected by collision with the particles of the first gas. Of course, since the short-wave radiation can be absorbed well by almost any material, the method according to the invention is usually carried out such that the high pressure of a gas is to be understood as a partial pressure of up to several 10 pascal. Typically, the partial pressure of a working gas of a radiation source operating by electrical discharge is approximately 10 pascal. In an advantageous embodiment of the method, it is provided that the first gas is guided transversely to the propagation direction of the radiation within a channel that is at least partially laterally bounded. The first gas can be guided between the particle trap and the radiation source, for example, such that the contaminant particles are transported away relatively quickly from the beam path of the short-wave radiation. The flow of the first gas, by means of the channel, removes the contaminant particles generated by the radiation source as well as, optionally, the particles of the second gas flowing through the particle trap. The particle-containing flow can be removed finally by means of a pump connected to the channel. According to another advantageous embodiment of the method, it can be provided that the first gas is a noble gas with an atomic weight of at least 39 g/mol, for example, argon or krypton. Without intending to limit the invention to a certain theory, collision between contaminant particles and particles of the first gas can achieve effective entrainment effects. In particular, clusters of a relatively high molecular weight can be transported away particularly efficiently by means of particles of the first gas having relatively great mass, velocity, and/or collision cross-section. Particularly by means of the high mass throughput of the first gas, the quantity of gas particles of the first gas can be adjusted in the area of the beam path of the short-wave radiation such that only a small fraction of the short-wave radiation will be absorbed thereby. For example, with a nozzle-shaped or jet-shaped channel that opens near the particle trap, a gas curtain can be generated that is maintained by a noble gas flow through the channel. Advantageously, the method is carried out such that a substance that is essentially transparent for the radiation, for example, helium or hydrogen, is introduced as the second gas. The short-wave radiation guided through the particle trap can be guided within the mirror chamber across relatively large travel distances to different optical devices, for example, a mirror, a mask, or grating. In order to minimize the absorption of the short-wave radiation by means of the second gas introduced into the mirror chamber, a gas with a relatively high transmission for short-wave radiation is employed. For a partial pressure of 20 pascal, the transmission of hydrogen is approximately 97.6% per meter traveled. Under the same conditions, the transmission for helium is approximately 78% per meter traveled. In another advantageous embodiment of the method, it is proposed that a flow velocity of the first gas and/or of the second gas is adjusted by means of appropriate devices. Such devices can be, for example, pumps or valves. These devices are used, for example, for introducing, preferably at a constant flow velocity, the first gas and/or the second gas for generating a high mass throughput. The first gas and the second gas are provided in separate storage containers, for example, a gas cylinder. When using vacuum pumps, for example, turbo pumps or turbo-molecular pumps, it is possible to quickly replace a second gas that is contaminated by diffusion effects with particles of the first gas with a new, pure second gas. In order to prevent contamination of the pump when removing the gas mixture contaminated with contaminant particles, appropriate filters can be employed. The filter can be a cold trap, for example. The invention has furthermore the object to provide a device of the aforementioned kind that protects with simple features optical devices and/or articles to be irradiated against contamination. This object is solved according to the invention for a device of the aforementioned kind in that a second gas can be introduced into the mirror chamber whose pressure is adjustable with appropriate devices to be at least as high as the pressure of the first gas. Since the advantages of the further embodiments of the device disclosed in the dependent claims correspond essentially to those of the method according to the invention, a detailed description of these dependent claims is not provided here. The method according to the invention and the device according to the invention can be used advantageously in connection with the generation of radiation in a wavelength range of approximately 2 nm up to approximately 20 nm for a lithography device or for a microscope. If not indicated otherwise, identical reference numerals indicate always the same technical features and refer to FIGS. 1 through 3. FIG. 1 shows a first embodiment of a device according to the invention for removing contaminant particles 14 generated by means of a radiation source 10 during generation of short-wave radiation 12 having a wavelength of up to 20 nm. The contaminant particles 14 include atoms, molecules, clusters, ions, and the like that are generated in the radiation source 10, for example, by means of a plasma emitting the short-wave radiation 12. Particles of a target evaporated by a pulsed focused laser beam are also to be considered as a further source of the contaminant particles 14. Alternatively, the contaminant particles 14 originate from a working gas that is introduced into an electrode gap of a triggered, electrically operated discharge device, not illustrated. In this connection, a typically occurring cathode spot causes erosion of electrode material upon transmission of electrical energy. The electrically conducting high-melting electrode material, for example, molybdenum or tungsten, has the tendency to form clusters. Also, substances that are used as working gas, for example, iodine and tin that enable an especially-efficient generation of short-wave radiation 12, can be converted into clusters with relatively high molecular weight. A first gas 22 is introduced at high mass throughput between the radiation source 10 and particle trap 20, also referred to as foil trap, that is arranged within the wall 16 of the mirror chamber 18. The first gas 22 that flows at high velocity can transport away in the flow direction of the first gas 22 by entrainment effects particularly the contaminant particles 14 that migrate from the radiation source 10 in the direction of the particle trap 20. Passing of the contaminant particles 14 through a particle trap 20 can be prevented in this way. Moreover, for example, deposition of contaminant particles 14 or damage to, for example, the reflective components of the particle trap 20 by colliding contaminant particles 14 can be reduced. In order to prevent penetration of the first gas 22 into the mirror chamber 18, a second gas 24 is introduced into the mirror chamber 18 whose pressure is at least as high as the pressure of the first gas 22. The second gas 24 in the mirror chamber 18 provides essentially a counter pressure. Therefore, the first gas 22 does not flow through the particle trap 20. Entrainment effects between the contaminant particles 14 and first gas 22 in the direction of the mirror chamber 18 are reduced to a minimum. A valve 28 is provided for adjusting the pressure of the second gas 24. The resulting mixture of particles of the first gas 22 and of contaminant particles 14 is removed by a pump P. The pump P ensures moreover a high mass throughput of the first gas 22. The first embodiment of the device according to the invention illustrated in FIG. 1 can be used for generating radiation 12 in a wavelength range of approximately 2 nm up to approximately 20 nm for a lithography device (not illustrated). An optical device, arranged in the mirror chamber 18, for example, a mirror, a mask or a wafer can be protected against soiling with the contaminant particles 14. As illustrated in FIG. 2, the second embodiment of the device according to the invention has a radiation source 10 that generates short-wave radiation 12 and contaminant particles 14. Particularly the contaminant particles 14 having a momentum that is directed in the direction toward the particle trap 20 can be slowed or deflected by means of the first gas 22. In this connection, the pressure of the second gas 24 is adjusted to be higher than the pressure of the first gas 22 by means of the valve 28. The second gas 24 flows through the particle trap 20 and enters the flow of the first gas 22 that transports mainly the contaminant particles 14 toward the pump P. The first gas 22 is guided transversely to the propagation direction of radiation 12 within a channel 26 that is at least partially laterally bounded. In this way, a preferred direction and a layer thickness can be preset for the first gas 22 wherein the layer thickness can be configured within the area of the particle trap 20 in the form of a continuously maintained gas curtain. Similar to a waterfall, the particles of the first gas 22 entrain the contaminant particles 14. When the first gas 22 is a noble gas having an atomic weight of at least 39 g/mol, for example, argon or krypton, particularly contaminant particles 14 having a relatively high molecular weight can be removed in the direction of the pump P, for example, by collision. By means of a defined arrangement of the walls 16 of the channel 26, the width of the gas curtain can be adjusted such that the radiation 12 penetrating it is absorbed only minimally. In this way, it is possible to introduce also substances as the first gas 22 that have only minimal transmission with regard to the short-wave radiation 12. The second embodiment of the device illustrated in FIG. 2 can be used, for example, for generating radiation 12 in the wavelength range of approximately 2 nm up to approximately 20 nm for a microscope. In the third embodiment illustrated in FIG. 3, the radiation 12 is guided onto an optical device, a mirror 30 in the illustrated embodiment, arranged in the mirror chamber 18. For preventing additional absorption by means of the contaminant particles 14 or the first gas 22, a substance that is essentially transparent for the radiation 12, for example, helium or hydrogen, is introduced into the mirror chamber 18 as a second gas 24. LIST OF REFERENCE NUMERALS10radiation source12radiation14contaminant particles16wall18mirror chamber20particle trap22first gas24second gas26channel28, 28′valve30mirrorP, P′pump
042809223	summary	The invention relates to a method and device for removing radiant, pulverulent synthetic wastes and, more particularly such wastes which are mixed dry with a thermoplastic mass in a kneader and then delivered from a discharge opening of the kneader into a container capable of providing a final storage therefor, while gases and/or vapors are withdrawn from degassing domes of the kneader. Such synthetic wastes are, especially, filter materials which are introduced into nuclear facilities or installations for purifying radioactive liquids or gases and which can contain a varying fraction or portion of organic substance. According to the heretofore known method of the German Published Non-Prosecuted Application DE-OS 25 31 584, an effort is made to prevent decomposition of the synthetic wastes when intermixed in bitumin by keeping the bitumin temperature as low as possible. Limits are set, in this case, however, because the viscosity of the bitumin sharply increases with reducing temperature so that the embedding and mixing operations are rendered more difficult. The gases produced during decomposition of the synthetic wastes can be withdrawn, in fact, by means of the degassing domes, which lie between the end of the kneader at which the latter is supplied or charged and the discharge opening, and are connected to a degassing device. They create an impermissible danger there, however, due to their explosibility and concentration. It is accordingly an object of the invention to provide a method and device for removing radiant, pulverulent synthetic wastes wherein danger of decomposition and gas formation of the synthetic wastes is reduced without requiring the temperature of the bitumin to become undesirably low. Simultaneously, it is an object of the invention to provide such a method and device wherein a dangerous concentration of partly explosive gas in the degassing dome is prevented. In this regard, the dried filter residues are to be metered to the bitumin so that no blockages or obstructions occur. With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of removing radiant, pulverulent synthetic wastes which are mixed dry with a thermoplastic mass in a kneader and then delivered from a discharge opening of the kneader into a container capable of providing a final storage therefor, while gases and/or vapors are withdrawn from degassing domes of the kneader, which comprises delivering fluidic dried wastes by mechanical movement through a metering tube into a degassing dome in the kneader disposed next to the discharge opening, and admitting scavenging gas into the metering tube at least temporarily in direction toward the kneader. Through this invention, the mixing time is considerably shortened and, accordingly, the thermal loading or stressing of the material being embedded is reduced because the transit time of the synthetic wastes is not provided any more by the movement of the wastes. through the entire kneader but rather only by the movement thereof through the short distance between the "last" degassing dome and the discharge opening of the kneader. In this manner, the mixing time can be shortened to one-third or even less. thus, the decomposition, which indeed, does not occur abruptly, is accordingly reduced. In this regard, due to the mechanical movement in the metering tube, the accuracy of the metering operation is improved so that it is actually possible to manage with such brief mixing times. Furthermore, due to the scavenging gas, the metering tube is kept free of contaminating vapors so that the removal of gases or vapors limited in essence to this degassing dome can effect no obstruction or blockage. In accordance with another feature of the invention, the method comprises applying vibratory motion to the metering tube as the mechanical movement, and in accordance with further features of the invention, the vibratory motion is applied transversely to the longitudinal axis of the metering tube. In accordance with an additional feature of the invention, the method comprises continuously admitting the scavenging gas into the metering tube in order to avoid the formation of clumps by the wastes. If necessary, by varying the amount of scavenging gas, obstructions in the metering tube can be removed. Besides, ordinary air as well as other gases can be introduced which, if need be, due to the content of inert components therein, can avoid danger of explosion even when disruptions occur in the feed of the scavenging air. In accordance with yet another feature of the invention, the method includes periodically heating the metering tube which preferably projects vertically into the degassing dome, with steam. Thereby, all at once, a given heating of the tube is achieved which facilitates expulsion of condensation products and possible bitumin splashes or spray along the short path to the discharge opening. In accordance with yet a further feature, the steam is passed through the metering tube, and is admitted from the metering tube into the degassing dome for scavenging synthetic powders adhering therein. For this purpose, a steam-conducting jacket disposed around the metering tube is provided with suitable discharge or exhaust openings. In accordance with yet an added feature of the invention, the method comprises mixing the wastes in a ratio of about 60:40 with bitumin which is at a temperature of from 110.degree. to 150.degree. C. and which is preferably distillation bitumin (B 15 or B 25). In accordance with the device of the invention, there is provided a kneader for embedding radiant synthetic wastes in bitumin comprising a plurality of degassing domes and formed with a discharge opening, one of the degassing domes being located adjacent the discharge opening and having a metering tube displaceable with respect to the one degassing dome. In accordance with another feature of the invention, the metering tube has a heating steam jacket. In accordance with a further feature of the invention, the kneader includes nozzles disposed on the metering tube and extending from the steam jacket into the one degassing dome. In accordance with an added feature of the invention, the kneader includes a vibrator disposed on the one degassing dome, the metering tube being connected to the vibrator. In accordance with a concomitant feature of the invention, the kneader includes a scavenging-gas union provided on the metering tube. 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 method and device for removing radiant, pulverulent synthetic wastes, 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.
052788830	claims	1. A low pressure drop spacer for positioning and retaining the fuel rods of a nuclear fuel assembly, said fuel assembly being formed of a plurality of parallel elongated fuel rods, comprising: a perimeter strip which circumscribes a region within the assembly through which the fuel rods extend, the strip having an upstream edge and a downstream edge, the strip being adapted to form a plurality of first apertures positioned toward the upstream edge and a plurality of second apertures positioned toward the downstream edge; a plurality of grid members extending within the region and arranged within the region to divide the region into a plurality of subregions, the grid members being secured to the perimeter strips; each one of the plurality of grid members having a grid upstream edge and a grid downstream edge, the grid members being adapted to form a plurality of first apertures positioned toward the upstream edge of the perimeter strip and a plurality of second apertures positioned toward the downstream edge of the perimeter strip; a first spring fork comprising a first end strip and a plurality of parallel pairs of first spring strips secured to the first end strip, each one of the parallel pairs of first spring strips extending into the region and through a corresponding one of the plurality of first apertures in the perimeter strip and further extending through a corresponding one of the plurality of the first apertures in the grid members, the first fork positioned in a first plane extending in a first direction defined by the plurality of pairs of first spring strips; a second spring fork comprising a second end strip and a plurality of parallel pairs of second spring strips secured to the second end strip, each one of the parallel pairs of second spring strips extending into the region and through a corresponding one of the plurality of second apertures in the perimeter strip and further extending through a corresponding one of the plurality of the second apertures in the grid members, the second fork positioned in a second plane substantially parallel to said first plane, said second plane extending in a second direction defined by said plurality of pairs of second spring strips such that the second spring fork is superposed on the first spring fork so as to form fuel rod passageways through which the fuel rods extend. an outer channel surrounding the plurality of fuel rods for conducting coolant/moderator about the fuel rods from the bottom of the assembly toward the top of assembly; an inner channel having at least one wall for conducting coolant/moderator through the inner channel from the bottom of the assembly toward the top of the assembly; and at least one low pressure drop spacer for positioning and retaining the fuel rods, the spacer comprising: a perimeter strip which circumscribes a region within the assembly through which the fuel rods extend, the strip having an upstream edge and a downstream edge, the strip being adapted to form a plurality of first apertures positioned toward the upstream edge and a plurality of second apertures positioned toward the downstream edge; a plurality of grid members extending within the region and arranged within the region to divide the region into a plurality of subregions, the grid members being secured to the perimeter strips; each one of the plurality of grid members having a grid upstream edge and a grid downstream edge, the grid members being adapted to form a plurality of first apertures positioned toward the upstream edge of the perimeter strip and a plurality of second apertures positioned toward the downstream edge of the perimeter strip; a first spring fork comprising a first end strip and a plurality of parallel pairs of first spring strips secured to the first end strip, each one of the parallel pairs of first spring strips extending into the region and through a corresponding one of the plurality of first apertures in the perimeter strip and further extending through a corresponding one of the plurality of the first apertures in the grid members, the first fork positioned in a first plane extending in a first direction defined by the plurality of pairs of first spring strips; a second spring fork comprising a second end strip and a plurality of parallel pairs of second spring strips secured to the second end strip, each one of the parallel pairs of second spring strips extending into the region and through a corresponding one of the plurality of second apertures in the perimeter strip and further extending through a corresponding one of the plurality of the second apertures in the grid members, the second fork positioned in a second plane substantially parallel to said first plane, said second plane extending in a second direction defined by said plurality of pairs of second spring strips such that the second spring fork is superposed on the first spring fork so as to form fuel rod passageways through which the fuel rods extend. 2. The spacer as in claim 1 wherein the parallel pairs of first strips are provided with first spring members which act against said fuel rods within the fuel rod passageways. 3. The spacer as in claim 2 wherein the parallel pairs of second spring strips are provided with second spring members which act against said fuel rods within the fuel rod passageways. 4. The spacer as in claim 3 wherein the perimeter strip has a plurality of perimeter strip dimple pairs comprising a first perimeter dimple and a second perimeter dimple, the first perimeter dimple being positioned toward the upstream edge of the perimeter strip, and the second perimeter dimple being positioned toward the downstream edge of the perimeter strip. 5. The spacer as in claim 4 wherein the grid members have a plurality of grid member dimple pairs comprising a first grid dimple and a second grid dimple, the first grid dimple being positioned toward the upstream edge of the grid member, and the second grid dimple being positioned toward the downstream edge of the grid member. 6. The spacer as in claim 5 wherein at least one of the first perimeter dimples and second perimeter dimples and the first grid dimples and the second grid dimples is adapted to form an opening for the passage of coolant. 7. The spacer as in claim 6 having two first spring forks. 8. The spacer as in claim 6 having two second spring forks. 9. The spacer as in claim 6 having two first spring forks and two second spring forks. 10. The spacer as in claim 9 wherein each of the first spring forks has six pairs of spring strips. 11. The spacer as in claim 10 wherein each of the second spring forks has six pairs of spring strips. 12. The spacer as in claim 11 wherein each pair of spring strips is attached to the end strip at a right angle. 13. The spacer as in claim 12 wherein at least one of the first spring members and the second spring members further have convolutions which alternate in abutting and in opposite directions and which extend to form a hexagonal channel for the unobstructed flow of coolant. 14. The spacer as in claim 13 wherein each one of the parallel pairs of the first spring strips and each one of the parallel pairs of the second spring strips are secured together at alternating abutting convolutions. 15. The spacer as in claim 14 wherein the spring strips are made of a springy material. 16. The spacer as in claim 15 wherein the spring strips have cutouts. 17. The spacer as in claim 16 wherein the first end strip of the first spring fork further includes a seal means to direct coolant from outside the region through which the fuel rods extend into the region. 18. The spacer as in claim 17 wherein the second end strip of the second spring fork further includes a seal means to direct coolant from outside the region through which the fuel rods extend into the region. 19. The spacer as in claim 18 wherein the means for sealing is the first end strip which is adapted to have a contoured seal surface. 20. The spacer as in claim 19 wherein the means for sealing further includes the second end strip which is adapted to have a contoured seal surface. 21. The spacer of claim 20 wherein the perimeter strip is made of zircaloy. 22. The spacer of claim 21 wherein the grid members are made of zircaloy. 23. The spacer of claim 22 wherein the spring forks are made of Inconel. 24. A nuclear fuel assembly for boiling water reactors, the assembly having a plurality of elongated fuel rods supported between a lower tie plate positioned toward the bottom of the assembly and an upper tie plate positioned toward the top of the assembly; 25. The fuel assembly as in claim 24 wherein the parallel pairs of first strips are provided with first spring members which act against said fuel rods within the fuel rod passageways. 26. The fuel assembly as in claim 25 wherein the parallel pairs of second spring strips are provided with second spring members which act against said fuel rods within the fuel rod passageways. 27. The fuel assembly as in claim 26 wherein the perimeter strip has a plurality of perimeter strip dimple pairs comprising a first perimeter dimple and a second perimeter dimple, the first perimeter dimple being positioned toward the upstream edge of the perimeter strip, and the second perimeter dimple being positioned toward the downstream edge of the perimeter strip. 28. The fuel assembly as in claim 27 wherein the grid members have a plurality of grid member dimple pairs comprising a first grid dimple and a second grid dimple, the first grid dimple being positioned toward the upstream edge of the grid member, and the second grid dimple being positioned toward the downstream edge of the grid member. 29. The fuel assembly as in claim 28 wherein at least one of the first perimeter dimples and second perimeter dimples and the first grid dimples and the second grid dimples is adapted to form an opening for the passage of coolant. 30. The fuel assembly as in claim 29 having two first spring forks. 31. The fuel assembly as in claim 29 having two second spring forks. 32. The fuel assembly as in claim 29 having two first spring forks and two second spring forks. 33. The fuel assembly as in claim 32 wherein each of the first spring forks has six pairs of spring strips. 34. The fuel assembly as in claim 33 wherein each of the second spring forks has six pairs of spring strips. 35. The fuel assembly as in claim 34 wherein each pair of spring strips is attached to the end strip at a right angle. 36. The fuel assembly as in claim 35 wherein at least one of the first spring members and the second spring members further have convolutions which alternate in abutting and in opposite directions and which extend to form a hexagonal channel for the unobstructed flow of coolant. 37. The fuel assembly as in claim 36 wherein each one of the parallel pairs of the first spring strips and each one of the parallel pairs of the second spring strips are secured together at alternating abutting convolutions. 38. The spacer as in claim 37 wherein the spring strips are made of a springy material. 39. The spacer as in claim 38 wherein the spring strips have cutouts. 40. The fuel assembly as in claim 39 wherein the first end strip of the first spring fork further includes a first seal means to seal a flow space existing between the outer channel and the perimeter strip. 41. The fuel assembly as in claim 40 wherein the second end strip of the second spring fork further includes a second seal means to seal a flow space existing between the outer channel and the perimeter strip. 42. The fuel assembly as in claim 41 wherein the first means for sealing is a contoured surface formed from the first end strip. 43. The fuel assembly as in claim 42 wherein the second means for sealing is a contoured surface formed from the second end strip. 44. The spacer of claim 43 wherein the perimeter strip is made of zircaloy. 45. The fuel assembly of claim 44 wherein the grid members are made of zircaloy. 46. The fuel assembly of claim 45 wherein the spring forks are made of Inconel. 47. The fuel assembly as in claim 45 further including a retainer strip means for securing the at least one low pressure drop spacer to the inner channel. 48. The fuel assembly as in claim 47 wherein the retainer strip means further includes inner channel wall flow tab means extending into the region to direct liquid condensing on the inner channel walls toward the fuel rods.
	claims	1. A scanning interference electron microscope, comprising:a specimen stage;an electron optical system for illuminating an electron beam on a specimen placed and held on the specimen stage; andan imaging system for detecting electrons generated from the specimen by the scanning,wherein the electron optical system hasan electron gun,means for splitting an electron beam generated by the electron gun into two optical paths,means for scanning one of the electron beams whose optical paths were splitted onto the specimen, andthe imaging system has one pair of asymmetric two-dimensional detectors with integration capability for detecting interference fringes of the electron beam having transmitted through the specimen by the electron beam scanning and the electron beam having passed through other electron optical axis, andone of the asymmetric two-dimensional detectors is a detector for phase detection and the other asymmetric two-dimensional detector is a detector for amplitude detection. 2. A scanning interference microscope, comprising:a specimen stage;means for scanning an electron beam on a specimen placed and held on the top of the specimen stage;means for generating interference fringes for an electron beam having transmitted through the specimen; andone pair of asymmetric two-dimensional detectors with integration capability for detecting the interference fringes,wherein one of the asymmetric two-dimensional detectors is a detector for phase detection and the other asymmetric two-dimensional detector is a detector for amplitude detection. 3. The scanning interference electron microscope according to claim 1,wherein the asymmetric two-dimensional detector with integration capability is comprised of a plurality of electron beam sensing elements and outputs a one-dimensional interference-fringe image signal whose each pixel has a value equal to a value obtained by integrating the interference fringes in a direction parallel to the interference fringes. 4. The scanning interference electron microscope according to claim 2,wherein the asymmetric two-dimensional detector with integration capability is comprised of a plurality of electron beam sensing elements and outputs a one-dimensional interference-fringe image signal whose each pixel has a value equal to a value obtained by integrating the interference fringes in a direction parallel to the interference fringes. 5. The scanning interference electron microscope according to claim 1, comprising:driving means for driving a specimen stage and control means for controlling the stage driving means,wherein the control means controls the specimen stage driving means so that an optical path of one electron beam which is different from the other electron beam being scanned onto the specimen passes through a position which does not give rise to transmission through the specimen. 6. The scanning interference electron microscope according to claim 2, comprisingdriving means for driving a specimen stage and control means for controlling the stage driving means,wherein the control means controls the specimen stage driving means so that an optical path of one electron beam which is different from the other electron beam being scanned onto the specimen passes through a position which does not give rise to transmission through the specimen. 7. The scanning interference electron microscope according to claim 1,Wherein the asymmetric two-dimensional detector with integration capability is rotationable in a two-dimensional plane. 8. The scanning interference electron microscope according to claim 7, comprisingmeans for adjusting conditions of forming the interference fringes on the detector. 9. The scanning interference electron microscope according to claim 3, comprising:storage means which maintains a first one-dimensional interference-fringe image signal obtained when both of the two splitted electron beams pass through a vacuum region and a second one-dimensional interference-fringe image signal obtained when one of the two splitted electron beams transmits through the specimen and the other electron beam passes through a vacuum region; anda signal processor which calculates the amount of phase shift generated when the electron beam transmits through the specimen and the amount of amplitude of the electron beam having transmitted through the specimen from the first one-dimensional interference-fringe image signal and the second one-dimensional interference-fringe image signal. 10. The scanning interference electron microscope according to claim 9,wherein the signal processor calculates the amount of amplitude of the electron beam having transmitted through the specimen by performing calculation which adds the first one-dimensional interference-fringe image signal and the second one-dimensional interference-fringe image signal for each pixel of the asymmetric two-dimensional detector with integration capability. 11. The scanning interference electron microscope according to claim 9,wherein the signal processor performs a calculation which compares the second one-dimensional interference-fringe image signal with the first one-dimensional interference-fringe image signal for each pixel of the asymmetric two-dimensional detector with integration capability, retains values of pixels each having a value equal to or more than a fixed threshold, and sets values of other pixels to zero,performs a calculation which integrates the second one-dimensional interference-fringe image signals subjected to the above-mentioned calculation over the entire pixels of the asymmetric two-dimensional detector with integration capability,normalizes a value obtained by the above-mentioned calculation with a predetermined value, and obtains the amount of phase shift from an arc cosine of the normalized value. 12. The scanning interference electron microscope according to claim 9,wherein the signal processor performs a calculation which brings signals corresponding to cosines of the phases or signals obtained by converting the cosines of the phases into phase values, ranging from a minimum to a maximum, into correspondence with Hue values of the HLS color model ranging from zero to unity, and a calculation which brings the amplitude data ranging from a minimum to a maximum into correspondence with Lightness values in the HLS color model ranging from zero to unity, andthe display means displays the phase data and amplitude data so processed, overlaying one signal on the other. 13. The scanning interference electron microscope according to claim 4, comprising:storage means which maintains a first 1-dimensional interference-fringe image signal obtained when both of the two splitted electron beams pass through a vacuum region and a second one-dimensional interference-fringe image signal obtained when one of the two splitted electron beams transmits through the specimen and the other electron beam passes through a vacuum region; anda signal processor which calculates the amount of phase shift generated when the electron beam transmits through the specimen and the amount of amplitude of the electron beam having transmitted through the specimen from the first 1-dimensional interference-fringe image signal and the second one-dimensional interference-fringe image signal. 14. The scanning interference electron microscope according to claim 13,wherein the signal processor calculates the amount of amplitude of the electron beam having transmitted through the specimen by performing calculation which adds the first one-dimensional interference-fringe image signal and the second one-dimensional interference-fringe image signal for each pixel of the asymmetric two-dimensional detector with integration capability. 15. The scanning interference electron microscope according to claim 13,wherein the signal processor performs a calculation which compares the second 1-dimensional interference-fringe image signal with the first one-dimensional interference-fringe image signal for each pixel of the asymmetric two-dimensional detector with integration capability, retains values of pixels each having a value equal to or more than a fixed threshold, and sets values of other pixels to zero,performs a calculation which integrates the second one-dimensional interference-fringe image signals subjected to the above-mentioned calculation over the entire pixels of the asymmetric two-dimensional detector with integration capability,normalizes a value obtained by the above-mentioned calculation with a predetermined value, and obtains the amount of phase shift from an arc cosine of the normalized value. 16. The scanning interference electron microscope according to claim 13,wherein the signal processor performs a calculation which brings signals corresponding to cosines of the phases or signals obtained by converting the cosines of the phases into phase values, ranging from a minimum to a maximum, into correspondence with Hue values of the HLS color model ranging from zero to unity, and a calculation which brings the amplitude data ranging from a minimum to a maximum into correspondence with Lightness values in the HLS color model ranging from zero to unity, andthe display means displays the phase data and amplitude data so processed, overlaying one signal on the other.
	summary
051715180	claims	1. A method of determining differences in the rate of heat transfer through first and second tube walls, comprising: (a) obtaining a tubing segment having a first wall, the first wall including an inner surface defining an inner side of the tubing segment and a radially spaced outer surface defining an outer side of the tubing segment, (b) supporting a quantity of thermally conductive material on one of the inner side and the outer side of the tubing segment having a first wall, the thermally conductive material being in thermal contact with the first wall, (c) placing one of a heating medium and a cooling medium having an initial temperature T.sub.a on the other of the inner side and the outer side of the tubing segment in thermal contact with the first wall, and determining the time required for the temperature of a portion of the thermally conductive material in thermal contact with the first wall to change from a first temperature T.sub.1 to a second temperature T.sub.2, T.sub.1 and T.sub.2 being outside the melting range and vaporization range of the thermally conductive material, (d) obtaining a tubing segment having a second wall, the second wall including an inner surface defining an inner side of the tubing segment and a radially spaced outer surface defining an outer side of the tubing segment, (e) supporting a quantity of thermally conductive material on one of the inner side and outer side of the tubing segment having a second wall, the thermally conductive material being in thermal contact with the second wall, (f) placing one of a heating medium and a cooling medium having an initial temperature T.sub.b on the other of the inner side and outer side of the tubing segment in thermal contact with the second wall, and determining the time required for the temperature of a predetermined portion of the thermally conductive material in thermal contact with the second wall to change from a third temperature T.sub.3 to a fourth temperature T.sub.4, T.sub.3 and T.sub.4 being outside the melting range and vaporization range of the thermally conductive material, T.sub.3 being greater than T.sub.4 when T.sub.1 >T.sub.2 and T.sub.3 being less than T.sub.4 when T.sub.1 <T.sub.2, and (g) comparing the times obtained in steps (b) and (f). (h) after step (c), removing the medium having an initial temperature T.sub.a from thermal contact with the first wall, placing one of a heating medium and a cooling medium having an initial temperature T.sub.c on the other of the inner side and the outer side of the tubing segment in thermal contact with the first wall, and determining the time required for the temperature of the portion of the thermally conductive material in thermal contact with the first wall to change from a fifth temperature T.sub.5 to a sixth temperature T.sub.6, T.sub.5 being greater than T.sub.6 when T.sub.1 <T.sub.2 and T.sub.5 being less than T.sub.6 when T.sub.1 >T.sub.2, (i) after step (f), removing the medium having an initial temperature T.sub.b from thermal contact with the second wall, placing one of a heating medium and a cooling medium having an initial temperature T.sub.d on the other of the inner side and the outer side of the tubing segment in contact with the second wall, and determining the time required for the temperature of the portion of the thermally conductive material in thermal contact with the second wall to change from a seventh temperature T.sub.7 to an eighth temperature T.sub.8, T.sub.7 being greater than T.sub.8 when T.sub.3 <T.sub.4, and T.sub.7 being less than T.sub.8 when T.sub.3 >T.sub.4, and (j) comparing the times obtained in steps (h) and (i). (a) removing a segment of fouled tubing from a heat exchanger, the tubing segment having a first wall including an inner surface and a radially spaced outer surface, (b) supporting a quantity of a thermally conductive material in contact with one of the inner surface and the outer surface of the first wall, (c) placing one of a heating medium and a cooling medium having a constant temperature T.sub.a in contact with the other of the inner surface and the outer surface of the first wall, and subsequently determining the time required for the temperature of a predetermined portion of the thermally conductive material to change from a first temperature T.sub.1 to a second temperature T.sub.2, T.sub.1 and T.sub.2 being outside the melting range and vaporization range of the thermally conductive material, (d) obtaining a substantially clean segment of heat exchanger tubing having a second wall including an inner surface and an outer surface, (e) supporting a quantity of the thermally conductive material in contact with one of the inner surface and the outer surface of the second wall, (f) placing the medium used in step (c) in contact with the other of the inner wall and the outer wall of the tubing segment and determining the time required for the temperature of the thermally conductive material to change from T.sub.1 to T.sub.2, and (g) comparing the times obtained in steps (c) and (f). 2. The method of claim 1, wherein the tubing segment having a second wall is obtained by altering the physical characteristics of the tubing segment having a first wall. 3. The method of claim 2, wherein altering the physical characteristics of the tubing segment having a first wall includes cleaning at least one of the inner surface and outer surface of the tubing segment having a first wall. 4. The method of claim 1, wherein the tubing segment having a first wall is obtained from a heat exchanger after use. 5. The method of claim 1, wherein T.sub.1 =T.sub.3 and T.sub.2 =T.sub.4. 6. The method of claim 1, wherein T.sub.a =T.sub.b. 7. The method of claim 1, wherein the medium having a temperature T.sub.a and the medium having a temperature T.sub.b are kept at constant temperatures when time measurements are made. 8. The method of claim 7, wherein T.sub.1 =T.sub.3, T.sub.2 =T.sub.4 and T.sub.a =T.sub.b. 9. The method of claim 1, wherein the mediums having temperatures T.sub.a and T.sub.b are baths containing water. 10. The method of claim 1, wherein steps (c) and (f) are conducted repeatedly and average values of time are calculated for each step. 11. The method of claim 1, wherein the quantity of thermally conductive material in thermal contact with the first wall has the same conductivity and composition as the quantity of thermally conductive material in contact with the second wall. 12. The method of claim 11, wherein the thermally conductive material has a higher thermal conductivity than the first and second walls. 13. The method of claim Il, wherein the thermally conductive material is an alloy comprising lead and bismuth. 14. A method according to claim 1, wherein at least one of the inner surface and outer surface of the tubing segment having a first wall is radioactive. 15. A method according to claim 1, further comprising the step of determining the percent difference in the rate of heat transfer through the tubing segment having a first wall and the tubing segment having a second wall, taking into account any differences between T.sub.1 and T.sub.3, T.sub.2 and T.sub.4, and the mediums having the temperatures T.sub.a and T.sub.b, and taking into account any changes in T.sub.a and T.sub.b during the measurement process. 16. The method of claim 1, further comprising: 17. The method of claim 16, wherein T.sub.a =T.sub.b, T.sub.c =T.sub.d, T.sub.1 =T.sub.3, T.sub.2 =T.sub.4, T.sub.5 =T.sub.7 and T.sub.6 =T.sub.8 18. The method of claim 16, wherein steps (c), (f), (h) and (i) are conducted repeatedly and average values of time are calculated. 19. A method of determining a change in the rate of heat transfer through the wall of a heat exchanger tube due to fouling of the surface of the tube, comprising the steps of:
	description	Priority is hereby claimed to U.S. Provisional Application No. 61/883,631, filed on Sep. 27, 2013. The contents of U.S. Provisional Application No. 61/883,631 are incorporated herein by reference. This disclosure relates generally to features for use in a particle beam scanning system. Particle therapy systems use an accelerator to generate a particle beam for treating afflictions, such as tumors. In operation, particles are accelerated in orbits inside a cavity in the presence of a magnetic field, and removed from the cavity through an extraction channel. A magnetic field regenerator generates a magnetic field bump near the outside of the cavity to distort the pitch and angle of some orbits so that they precess towards, and eventually into, the extraction channel. A beam, comprised of the particles, exits the extraction channel. A scanning system is down-beam of the extraction channel. In this context, “down-beam” means closer to an irradiation target (here, relative to the extraction channel). The scanning system moves the beam across at least part of the irradiation target to expose various parts of the irradiation target to the beam. For example, to treat a tumor, the particle beam may be “scanned” over different cross-sections of the tumor. An example proton therapy system may comprise a particle accelerator, a scanning system, and a gantry on which the particle accelerator and at least part of the scanning system are mounted. The gantry is rotatable relative to a patient position. Protons are output essentially directly from the particle accelerator and through the scanning system to the position of an irradiation target, such as a patient. The particle accelerator may be a synchrocyclotron. An example particle therapy system comprises a synchrocyclotron to output a particle beam; a magnet to affect a direction of the particle beam to scan the particle beam across at least part of an irradiation target; and scattering material that is configurable to change a spot size of the particle beam prior to output of the particle beam to the irradiation target. The example particle therapy system may include one or more of the following features, either alone or in combination. The example particle therapy system may include a degrader to change an energy of the beam prior to output of the particle beam to the irradiation target. The degrader may be down-beam of the scattering material relative to the synchrocyclotron, and may be computer-controlled. The synchrocyclotron may comprise: a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles from a plasma column, where the cavity has a magnetic field causing particles accelerated from the plasma column to move orbitally within the cavity; an extraction channel to receive the particles accelerated from the plasma column and to output the received particles from the cavity; and a regenerator to provide a magnetic field bump within the cavity to thereby change successive orbits of the particles accelerated from the plasma column so that, eventually, particles are output to the extraction channel. The magnetic field may be between 4 Tesla (T) and 20 T and the magnetic field bump may be at most 2 Tesla. The scattering material may comprise multiple scatterers, each of which may be movable into, or out of, a path of the particle beam. In some examples, only one of the multiple scatterers at a time may be movable into the path of the particle beam. The scattering material may include piezoelectric material that is responsive to an applied voltage to increase or decrease in thickness. The scattering material may be configurable to change a spot size of the particle beam during a course of treatment of the irradiation target or in between times of treatment of the irradiation target (e.g., not during the course of treatment). The scanning performed by the particle therapy system may be spot scanning. The spot size may be changeable from scan-location to scan-location. The spot size may be changeable on a time scale on the order of tenths of a second, on the order of tens of milliseconds, or on the order of some other time scale. An example particle therapy system may comprise: a synchrocyclotron to output a particle beam; a scanning system to receive the particle beam from the synchrocyclotron and to perform spot scanning of at least part of an irradiation target with the particle beam, where the scanning system is controllable to change a spot size of the particle beam; and a gantry on which the synchrocyclotron and at least part of the scanning system are mounted, where the gantry is configured to move the synchrocyclotron and at least part of the scanning system around the irradiation target. The example particle therapy system may include one or more of the following features, either alone or in combination. The scanning system may comprise: structures to move the particle beam output from the synchrocyclotron in three-dimensions relative to the irradiation target; and scattering material, among the structures, that is configurable to change the spot size of the particle beam. The scattering material may comprise multiple scatterers, each of which may be movable into, or out of, a path of the particle beam. In some examples, only one of the multiple scatterers at a time is movable into the path of the particle beam. The scattering material may comprise piezoelectric material that is responsive to an applied voltage to increase or decrease in thickness. The scattering material may be configurable to change a spot size of the particle beam during a course of treatment of the irradiation target. The scattering material may be configurable to change a spot size of the particle beam in between times of treatment of the irradiation target (e.g., not during the course of treatment). The scanning performed by the scanning system may be spot scanning. The spot size may be changeable from scan-location to scan-location. The spot size may be changeable on a time scale on the order of tenths of a second, on the order of tens of milliseconds, or on some other time scale. An example particle therapy system may comprise: a synchrocyclotron to output a particle beam; a scanning system to receive the particle beam from the synchrocyclotron and to perform spot scanning of at least part of an irradiation target with the particle beam; and one or more processing devices to control the scanning system to scan a cross-section of the irradiation target according to an irregular grid pattern. The example particle therapy system may include one or more of the following features, either alone or in combination. In an example, in the irregular grid pattern, spacing between spots to be scanned varies. The irregular grid pattern may have a perimeter that corresponds to a perimeter of the cross-section of the irradiation target. A scanning speed of the particle beam between different spots on the cross-section of the irradiation target may be substantially the same or it may be different. For example, a scanning speed of the particle beam may be different between at least two different pairs of spots on the cross-section of the irradiation target. The example particle therapy system may include memory to store a treatment plan. The treatment plan may comprise information to define the irregular grid pattern for the cross-section of the irradiation target, and also to define irregular grid patterns for other cross-sections of the irradiation target. Different irregular grid patterns for different cross sections of the irradiation target may have at least one of: different numbers of spots to be irradiated, different locations of spots to be irradiated, different spacing between spots to be irradiated, or different pattern perimeters. The scanning system may comprise: a magnet to affect a direction of the particle beam to scan the particle beam across at least part of an irradiation target; and scattering material that is configurable to change a spot size of the particle beam prior to output of the particle beam to the irradiation target. The scattering material may be down-beam of the magnet relative to the synchrocyclotron. The scanning system may also comprise a degrader to change an energy of the beam prior to output of the particle beam to the irradiation target. The degrader may be down-beam of the scattering material relative to the synchrocyclotron. The synchrocyclotron may comprise: a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles from a plasma column, where the cavity has a magnetic field causing particles accelerated from the plasma column to move orbitally within the cavity; an extraction channel to receive the particles accelerated from the plasma column and to output the received particles from the cavity as part of the particle beam; and a regenerator to provide a magnetic field bump within the cavity to thereby change successive orbits of the particles accelerated from the plasma column so that, eventually, particles output to the extraction channel. The magnetic field may be between 4 Tesla (T) and 20 T and the magnetic field bump may be at most 2 Tesla. The particle therapy system may comprise a gantry on which the synchrocyclotron and the scanning system are mounted. The gantry may be configured to move the synchrocyclotron and at least part of the scanning system around the irradiation target. The one or more processing devices may be programmed to effect control to interrupt the particle beam between scanning of different cross-sections of the irradiation target. An example particle therapy system may comprise: a synchrocyclotron to output a particle beam; a magnet to affect a direction of the particle beam to scan the particle beam across a cross-section of an irradiation target; and one or more processing devices to control the magnet to scan the cross-section of the irradiation target according to an irregular grid pattern, and to control an energy of the particle beam between scanning of different cross-sections of the irradiation target. The example particle therapy system may include one or more of the following features, either alone or in combination. The example particle therapy system may comprise a degrader to change an energy of the particle beam prior to scanning the cross-section of the irradiation target. The degrader may be down-beam of the magnet relative to the synchrocyclotron. The one or more processing devices may be configured to control movement of one or more parts of the degrader to control the energy of the particle beam between scanning of different cross-sections of the irradiation target. In an example, in the irregular grid pattern, spacing between spots to be scanned varies. The irregular grid pattern may have a perimeter that corresponds to a perimeter of the cross-section of the irradiation target. A scanning speed of the particle beam between different spots on the cross-section of the irradiation target may be substantially the same or different. The example particle therapy system may comprise memory to store a treatment plan. The treatment plan may comprise information to define the irregular grid pattern for the cross-section of the irradiation target, and also to define irregular grid patterns for different cross-sections of the irradiation target. Different irregular grid patterns for different cross sections of the irradiation target may have at least one of: different numbers of spots to be irradiated, different locations of spots to be irradiated, different spacing between spots to be irradiated, or different pattern perimeters. The synchrocyclotron may comprise: a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles from a plasma column, where the cavity has a magnetic field causing particles accelerated from the plasma column to move orbitally within the cavity; an extraction channel to receive the particles accelerated from the plasma column and to output the received particles from the cavity as part of the particle beam; and a regenerator to provide a magnetic field bump within the cavity to thereby change successive orbits of the particles accelerated from the plasma column so that, eventually, particles output to the extraction channel. The magnetic field may be between 4 Tesla (T) and 20 T and the magnetic field bump may be at most 2 Tesla. The example particle therapy system may comprise a gantry on which the synchrocyclotron and the scanning system are mounted. The gantry may be configured to move the synchrocyclotron and at least part of the scanning system around the irradiation target. The one or more processing devices may be programmed to effect control to interrupt the particle beam between scanning of different cross-sections of the irradiation target. The scanning may be raster scanning, spot scanning, or a combination thereof. The synchrocyclotron may be a variable-energy machine. The one or more processing devices may be programmed to control the energy of the particle beam produced by the variable-energy synchrocyclotron between scanning of different cross-sections of the irradiation target by controlling the synchrocyclotron to output the particle beam at a specified energy level. Two or more of the features described in this disclosure, including those described in this summary section, may be combined to form implementations not specifically described herein. Control of the various systems described herein, or portions thereof, may be implemented via a computer program product that includes instructions that are stored on one or more non-transitory machine-readable storage media, and that are executable on one or more processing devices. The systems described herein, or portions thereof, may be implemented as an apparatus, method, or electronic system that may include one or more processing devices and memory to store executable instructions to implement control of the stated functions. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. Like reference symbols in the various drawings indicate like elements. Described herein is an example of a particle accelerator for use in an example system, such as a proton or ion therapy system. The example system includes a particle accelerator—in this example, a synchrocyclotron—mounted on a gantry. The gantry enables the accelerator to be rotated around a patient position, as explained in more detail below. In some implementations, the gantry is steel and has two legs mounted for rotation on two respective bearings that lie on opposite sides of a patient. The particle accelerator is supported by a steel truss that is long enough to span a treatment area in which the patient lies and that is attached at both ends to the rotating legs of the gantry. As a result of rotation of the gantry around the patient, the particle accelerator also rotates. In an example implementation, the particle accelerator (e.g., the synchrocyclotron) includes a cryostat that holds a superconducting coil for conducting a current that generates a magnetic field (B). In this example, the cryostat uses liquid helium (He) to maintain the coil at superconducting temperatures, e.g., 4° Kelvin (K). Magnetic pole pieces or yokes are located inside the cryostat, and define a cavity in which particles are accelerated. In an example implementation, the particle accelerator includes a particle source (e.g., a Penning Ion Gauge—PIG source) to provide a plasma column to the cavity. Hydrogen gas is ionized to produce the plasma column. A voltage source provides a radio frequency (RF) voltage to the cavity to accelerate particles from the plasma column. As noted, in this example, the particle accelerator is a synchrocyclotron. Accordingly, the RF voltage is swept across a range of frequencies to account for relativistic effects on the particles (e.g., increasing particle mass) when accelerating particles from the column. The magnetic field produced by running current through the superconducting coil causes particles accelerated from the plasma column to accelerate orbitally within the cavity. A magnetic field regenerator (“regenerator”) is positioned near the outside of the cavity (e.g., at an interior edge thereof) to adjust the existing magnetic field inside the cavity to thereby change locations (e.g., the pitch and angle) of successive orbits of the particles accelerated from the plasma column so that, eventually, the particles output to an extraction channel that passes through the cryostat. The regenerator may increase the magnetic field at a point in the cavity (e.g., it may produce a magnetic field “bump” at an area of the cavity), thereby causing each successive orbit of particles at that point to precess outwardly toward the entry point of the extraction channel until it reaches the extraction channel. The extraction channel receives particles accelerated from the plasma column and outputs the received particles from the cavity as a particle beam. The superconducting (“main”) coils can produce relatively high magnetic fields. The magnetic field generated by a main coil may be within a range of 4 T to 20 T or more. For example, a main coil may be used to generate magnetic fields at, or that exceed, one or more of the following magnitudes: 4.0 T, 4.1 T, 4.2 T, 4.3 T, 4.4 T, 4.5 T, 4.6 T, 4.7 T, 4.8 T, 4.9 T, 5.0 T, 5.1 T, 5.2 T, 5.3 T, 5.4 T, 5.5 T, 5.6 T, 5.7 T, 5.8 T, 5.9 T, 6.0 T, 6.1 T, 6.2 T, 6.3 T, 6.4 T, 6.5 T, 6.6 T, 6.7 T, 6.8 T, 6.9 T, 7.0 T, 7.1 T, 7.2 T, 7.3 T, 7.4 T, 7.5 T, 7.6 T, 7.7 T, 7.8 T, 7.9 T, 8.0 T, 8.1 T, 8.2 T, 8.3 T, 8.4 T, 8.5 T, 8.6 T, 8.7 T, 8.8 T, 8.9 T, 9.0 T, 9.1 T, 9.2 T, 9.3 T, 9.4 T, 9.5 T, 9.6 T, 9.7 T, 9.8 T, 9.9 T, 10.0 T, 10.1 T, 10.2 T, 10.3 T, 10.4 T, 10.5 T, 10.6 T, 10.7 T, 10.8 T, 10.9 T, 11.0 T, 11.1 T, 11.2 T, 11.3 T, 11.4 T, 11.5 T, 11.6 T, 11.7 T, 11.8 T, 11.9 T, 12.0 T, 12.1 T, 12.2 T, 12.3 T, 12.4 T, 12.5 T, 12.6 T, 12.7 T, 12.8 T, 12.9 T, 13.0 T, 13.1 T, 13.2 T, 13.3 T, 13.4 T, 13.5 T, 13.6 T, 13.7 T, 13.8 T, 13.9 T, 14.0 T, 14.1 T, 14.2 T, 14.3 T, 14.4 T, 14.5 T, 14.6 T, 14.7 T, 14.8 T, 14.9 T, 15.0 T, 15.1 T, 15.2 T, 15.3 T, 15.4 T, 15.5 T, 15.6 T, 15.7 T, 15.8 T, 15.9 T, 16.0 T, 16.1 T, 16.2 T, 16.3 T, 16.4 T, 16.5 T, 16.6 T, 16.7 T, 16.8 T, 16.9 T, 17.0 T, 17.1 T, 17.2 T, 17.3 T, 17.4 T, 17.5 T, 17.6 T, 17.7 T, 17.8 T, 17.9 T, 18.0 T, 18.1 T, 18.2 T, 18.3 T, 18.4 T, 18.5 T, 18.6 T, 18.7 T, 18.8 T, 18.9 T, 19.0 T, 19.1 T, 19.2 T, 19.3 T, 19.4 T, 19.5 T, 19.6 T, 19.7 T, 19.8 T, 19.9 T, 20.0 T, 20.1 T, 20.2 T, 20.3 T, 20.4 T, 20.5 T, 20.6 T, 20.7 T, 20.8 T, 20.9 T, or more. Furthermore, a main coil may be used to generate magnetic fields that are within the range of 4 T to 20 T (or more) that are not specifically listed above. In some implementations, such as the implementation shown in FIGS. 1 and 2, large ferromagnetic magnetic yokes act as a return for stray magnetic field produced by the superconducting coils. For example, in some implementations, the superconducting magnet can generate a relatively high magnetic field of, e.g., 4 T or more, resulting in considerable stray magnetic fields. In some systems, such as that shown in FIGS. 1 and 2, a relatively large ferromagnetic return yoke 82 is used as a return for the magnetic field generated by superconducting coils. A magnetic shield surrounds the yoke. The return yoke and the shield together dissipated stray magnetic field, thereby reducing the possibility that stray magnetic fields will adversely affect the operation of the accelerator. In some implementations, the return yoke and shield may be replaced by, or augmented by, an active return system. An example active return system includes one or more active return coils that conduct current in a direction opposite to current through the main superconducting coils. In some example implementations, there is an active return coil for each superconducting coil, e.g., two active return coils—one for each superconducting coil (referred to as a “main” coil). Each active return coil may also be a superconducting coil that surrounds the outside of a corresponding main superconducting coil. Current passes through the active return coils in a direction that is opposite to the direction of current passing through the main coils. The current passing through the active return coils thus generates a magnetic field that is opposite in polarity to the magnetic field generated by the main coils. As a result, the magnetic field generated by an active return coil is able to dissipate at least some of the relatively strong stray magnetic field resulting from the corresponding main coil. In some implementations, each active return may be used to generate a magnetic field of between 2.5 T and 12 T or more. An example of an active return system that may be used is described in U.S. patent application Ser. No. 13/907,601, filed on May 31, 2013, the contents of which are incorporated herein by reference. Referring to FIG. 3, at the output of extraction channel 102 of particle accelerator 105 (which may have the configuration shown in FIGS. 1 and 2) is an example scanning system 106 that may be used to scan the particle beam across at least part of an irradiation target. FIG. 4 shows examples of the components of the scanning system include a scanning magnet 108, an ion chamber 109, and an energy degrader 110. Other components of the scanning system are not shown in FIG. 4, including scatterers for changing beam spot size. These components are shown in other figures and described below. In an example operation, scanning magnet 108 is controllable in two dimensions (e.g., Cartesian XY dimensions) to direct the particle beam across a part (e.g., a cross-section) of an irradiation target. Ion chamber 109 detects the dosage of the beam and feeds-back that information to a control system. Energy degrader 110 is controllable (e.g., by one or more computer programs executable on one or more processing devices) to move material into, and out of, the path of the particle beam to change the energy of the particle beam and therefore the depth to which the particle beam will penetrate the irradiation target. FIGS. 5 and 6 show views of an example scanning magnet 108. Scanning magnet 108 includes two coils 111, which control particle beam movement in the X direction, and two coils 112, which control particle beam movement in the Y direction. Control is achieved, in some implementations, by varying current through one or both sets of coils to thereby vary the magnetic field(s) produced thereby. By varying the magnetic field(s) appropriately, the particle beam can be moved in the X and/or Y direction across the irradiation target. In some implementations, the scanning magnet is not movable physically relative to the particle accelerator. In other implementations, the scanning magnet may be movable relative to the accelerator (e.g., in addition to the movement provided by the gantry). In this example, ion chamber 109 detects dosage applied by the particle beam by detecting the numbers of ion pairs created within a gas caused by incident radiation. The numbers of ion pairs correspond to the dosage provided by the particle beam. That information is fed-back to a computer system that controls operation of the particle therapy system. The computer system (not shown), which may include memory and one or more processing devices, determines if the dosage detected by ion chamber is the intended dose. If the dosage is not as intended, the computer system may control the accelerator to interrupt production and/or output of the particle beam, and/or control the scanning magnet to prevent output of the particle beam to the irradiation target. FIG. 7 shows a range modulator 115, which is an example implementation of energy degrader 110. In some implementations, such as that shown in FIG. 7, range modulator includes a series of plates 116. The plates may be made of one or more of the following example materials: carbon, beryllium or other material of low atomic number. Other materials, however, may be used in place of, or in addition to, these example materials. One or more of the plates is movable into, or out of, the beam path to thereby affect the energy of the particle beam and, thus, the depth of penetration of the particle beam within the irradiation target. For example, the more plates that are moved into the path of the particle beam, the more energy that will be absorbed by the plates, and the less energy the particle beam will have. Conversely, the fewer plates that are moved into the path of the particle beam, the less energy that will be absorbed by the plates, and the more energy the particle beam will have. Higher energy particle beams penetrate deeper into the irradiation target than do lower energy particle beams. In this context, “higher” and “lower” are meant as relative terms, and do not have any specific numeric connotations. Plates are moved physically into, and out of, the path of the particle beam. For example, as shown in FIG. 8, a plate 116a moves along the direction of arrow 117 between positions in the path of the particle beam and outside the path of the particle beam. The plates are computer-controlled. Generally, the number of plates that are moved into the path of the particle beam corresponds to the depth at which scanning of an irradiation target is to take place. For example, the irradiation target can be divided into cross-sections, each of which corresponds to an irradiation depth. One or more plates of the range modulator can be moved into, or out of, the beam path to the irradiation target in order to achieve the appropriate energy to irradiate each of these cross-sections of the irradiation target. In some implementations, the range modulator does not rotate with the accelerator, but rather remains in place and move plates into, and out of, the beam path. In some implementations, a treatment plan is established prior to treating the irradiation target. The treatment plan may specify how scanning is to be performed for a particular irradiation target. In some implementations, the treatment plan specifies the following information: a type of scanning (e.g., spot scanning or raster scanning); scan locations (e.g., locations of spots to be scanned); magnet current per scan location; dosage-per-spot, spot size; locations (e.g., depths) of irradiation target cross-sections; particle beam energy per cross-section; plates to move into the beam path for each particle beam energy; and so forth. Generally, spot scanning involves applying irradiation at discrete spots on an irradiation target and raster scanning involves moving a radiation spot across the radiation target. The concept of spot size therefore applies for both raster and spot scanning. In some implementations, the overall treatment plan of an irradiation target includes different treatment plans for different cross-sections of the irradiation target. The treatment plans for different cross-sections may contain the same information or different information, such as that provided above. One or more scatterers may be inserted at one or more points in the particle beam path to change the size of the scanning spot prior to output to the irradiation target. For example, in some implementations, one or more scatterers may be movable into, or out of, the beam path down-beam of the scanning magnet but before (up-beam of) the energy degrader. Referring to FIG. 9, for example, a scatterer 120 may be moved into, or out of the beam path at location 122 or at location 123. In other implementations, scatterers may be positioned at different or multiple locations between magnet 108 and energy degrader 110. For example, there may be one or more scatterers placed immediately down-beam of the magnet and one or more scatterers placed immediately up-beam of the energy degrader. In still other implementations, one or more scatterers may be placed in the beam path either up-beam of the magnet or down-beam of the degrader. The one or more scatterers placed in the beam path up-beam of the magnet or down-beam of the degrader may be alone, in combination, or in combination with one or more scatterers in the beam path between the magnet and the energy degrader. Example scatterers may be made of one or more of the following example scattering materials: lead, brass or similar materials. Other materials, however, may be used in place of, or in addition to, these example scattering materials. In some implementations, the scatterers may be plates having the same or varying thickness, and may be similar in construction the plates of the energy degrader shown in FIG. 7. Each such plate may introduce an amount of scattering into the particle beam, thereby increasing the spot size of the particle beam relative to the spots size of the beam that emerged from the extraction channel. In some implementations, the more plates that are introduced into the particle beam, the larger the spot of the particle beam will be. In some implementations, such as the plate-based implementations described above, the scatterers may supplant the energy degraders. For example, in addition to performing scattering, the scatterers may also absorb beam energy, thereby affecting the eventual energy output of the beam without use of energy degraders down-beam of, or up-beam of, the scatterers. In such example implementations, the scatterers may be computer-controlled in the same manner as the energy degraders described above to provide both an appropriate level of beam scattering and an appropriate amount of beam energy degradation. Accordingly, in some implementations, separate energy degraders are not used. In some implementations, both the scatterers and one or more energy degraders are used to affect the output energy of the particle beam. For example, in an implementation, the scatterers may be used to reduce the energy of the beam to a certain level, and the energy degrader may be used to provide further beam energy reduction, or vice versa. Such implementations may enable reduction in the size of the energy degrader. In some implementations, the scatterers may provide a finer level of energy degradation than the energy degrader, or vice versa, thereby enabling either one or the other of the scatterers or the energy degrader to provide fine beam level energy adjustment and the other of the scatterers or the energy degrader to provide coarse beam level energy adjustment (where coarse and fine are relative terms, and do not have any particular numerical connotations). In some implementations, each scatterer may be a wheel or other rotatable structure, which is either disposed within the beam path or moveable into, or out of, the beam path. The structure may have variable thickness ranging from a maximum thickness to a minimum thickness, which produce different amounts of scattering and, thus, different beam spot sizes. The structure may be movable relative to the beam to place one of the multiple thicknesses in the beam path. Typically, if a wheel, the structure is offset, so that edges of the wheel, having different thicknesses, impact the particle beam during rotation. Such example scatterers may be made of one or more of the following example materials: lead, brass or similar materials. Other materials, however, may be used in place of, or in addition to, these example scattering materials. In an example implementation, the structure may be a rotatable variable-thickness wedge having a wheel-like shape. The structure scatters the particle beam, thereby varying the spot size of the beam during scanning. The thicker portions of the structure provide more scattering (and thus increase the spots size more) than the thinner portions of the structure. In some implementations, the structure may contain no material at a point where the particle beam is meant to pass without any scattering (e.g., spot size increase). In some implementations, the structure may be movable out of the beam path. Referring to FIG. 10, in some implementations, structure 124 may have continuously varying thickness to thereby enable scattering along a variable continuum and thereby enabling a continuous range of spots sizes. In the example of FIG. 10, the thickness varies continuously from a minimum thickness 126 to a maximum thickness 125. Referring to FIG. 11, in some implementations, the thicknesses of the structure may vary step-wise, to enable discrete amounts of scattering. In the example of FIG. 11, the thickness varies in steps from a minimum thickness 129 to a maximum thickness 128. Any of the example scatterers described herein including, but not limited to, the example wheel-based implementations described above, may also be used to affect beam energy, thereby reducing the need for, or eliminating the need for, a separate energy degrader. As was also the case above, any scatterer may be used in conjunction with the energy degrader to provide different energy level reductions and/or coarse/fine energy reduction. In some implementations, example spot sizes may range between 4 mm and 30 mm sigma or between 6 mm and 15 mm sigma. Other spot sizes, however, may be implemented in place of, or in addition to, these example spot sizes. In some implementations, a single one or more scatterers of the type shown in FIG. 9, of the type shown in FIG. 10, or of the type shown in FIG. 11 may be positioned up-beam of the magnet, down-beam of the magnet and up-beam of the energy degrader, and/or down-beam of the energy degrader. In some implementations, any combinations of scatterers of the type shown in FIG. 9, of the type shown in FIG. 10, and of the type shown in FIG. 11 may be positioned up-beam of the magnet, down-beam of the magnet and up-beam of the energy degrader, and/or down-beam of the energy degrader. Generally, mechanical scatterers, which move scattering material into, or out of, the path of the particle beam, have a response time on the order of tenths of a second (s), e.g., 0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.6 s, 0.7 s, 0.8 s, 0.9 s or longer. That is, such scatterers may be computer-controlled, and the amount of time to physically move scattering material into, or out of the particle beam, may be on the time scale of tenths of a second, and sometimes longer. In some implementations, the example scatterers of FIGS. 9, 10 and 11 have a response time on the order of tenths of a second, e.g., 0.1 s, 0.2 s, 0.3 s, 0.4 s, 0.5 s, 0.6 s, 0.7 s, 0.8 s, 0.9 s or longer. Notably, however, in some implementations, the examples scatterers of FIGS. 9, 10 and 11 may have a response time of less than 0.1 s. In some implementations, piezoelectric scatterers may be used instead of, or in addition to, the mechanical scatterers described above. A piezoelectric scatterer may be made of a piezoelectric scattering material, which is disposed in the beam path such that application of applied voltage to the piezoelectric scatterer causes the piezoelectric scatterer to increase in thickness in the longitudinal direction of the particle beam. Conversely, application of a different voltage causes the piezoelectric scatterer to decrease in thickness in the longitudinal direction of the particle beam. In this way, the thickness of the scattering material, and thus the amount of scattering produced thereby, can be varied. As above, variations in the amount of scattering result in variations in the scan spot size (e.g., the more scattering, the bigger the spot). As was also the case above, a piezoelectric scatterer may be computer controlled. In some implementations, a piezoelectric scatterer may have a response time on the order of tens of milliseconds, e.g., 10 ms, 20 ms, 30 ms, 40 ms, 50 ms, 60 ms, 70 ms, 80 ms, 90 ms or longer in some implementations. In some implementations, one or more piezoelectric scatterers may be positioned either up-beam of the magnet, down-beam of the magnet and up-beam of the energy degrader, and/or down-beam of the energy degrader. In some implementations, combinations of one or more piezoelectric scatterers may be used with one or more scatterers of the type shown in FIG. 9, of the type shown in FIG. 10, and/or of the type shown in FIG. 11 positioned either up-beam of the magnet, down-beam of the magnet and up-beam of the energy degrader, and/or down-beam of the energy degrader. Accordingly, in some implementations, one or more piezoelectric scatterers may be located, either alone, or with one or more scatterers of the type shown in FIG. 9, of the type shown in FIG. 10, and/or of the type shown in FIG. 11 up-beam of the magnet, down-beam of the magnet and up-beam of the energy degrader, and/or down-beam of the energy degrader. In some implementations, spot size may be changed during treatment of an irradiation target cross-section, or in between treatment of different irradiation target cross-sections. For example, in some implementations, spot size may be changed between irradiation of different areas on the same cross-section of an irradiation target, e.g., the spot size may be changed between adjacent spots. Thus, in some implementations, changes in spot size may be made from spot-to-spot. In some implementations, spot size remains constant for a cross-section of the irradiation target, and is changed in between different cross-sections. In some implementations, spot size remains constant for a cross-section of the irradiation target, and is changed only in between different cross-sections. In some implementations, spot size may differ in different areas of the same cross-section. Generally, changes in spot size may be specified in the treatment plan for the irradiation target and/or the treatment plans for cross-sections of the irradiation target. In some implementations, the scanning system may include a collimator 127 (FIG. 3) to collimate the particle bean, and an aperture (not shown) that is placeable relative to the irradiation target to limit the extent of the particle beam and thereby the shape of the spot applied to the irradiation target. In some implementations, spot size is controllable based on whether the particle therapy system includes one or more of those features. For example, an aperture may be placed in the beam path down-beam of the energy degrader and before the particle beam hits the irradiation target. The aperture, such as aperture 129 of FIG. 12, may contain an area (e.g., a hole 130) through which the particle beam passes and other material 131 defining the hole that prevents passage of the particle beam. In some implementations, therefore, the aperture defines the spot size. In such implementations, in the presence of an aperture and depending on the size and type of the aperture, the computer that implements the treatment plan may determine not to control spot size, at least part of the time (e.g., when the spot from the particle accelerator—the native spot size—is larger than the aperture hole). In some implementations, the treatment plan for an irradiation target may be non-uniform (e.g., irregular). In this regard, traditionally and particularly in spot scanning systems, treatment plans define regular (e.g., rectangular) grids for an irradiation target. The regular grid includes a regular pattern of evenly-spaced target locations to which spots of irradiation are to be applied. In most cases, however, the portion (e.g., cross-section) of the irradiation target to be treated does not have a shape that corresponds to that of the regular grid. Accordingly, at locations of the regular grid that are off of the irradiation target, the particle beam is interrupted or directed so that the particle beam is not applied at those locations. In the example particle therapy system described herein, a treatment plan may specify scanning according to a non-uniform grid. Various features of the particle therapy system may be controlled by computer (e.g., one or more processing devices) to implement scanning along a non-uniform grid. A non-uniform grid may have an irregular grid pattern that corresponds to (e.g., substantially tracks) the perimeter of an irradiation target. For example, the non-uniform grid may have spots arranged within a perimeter that substantially tracks the perimeter of a cross-section of the target to be irradiated using a particular treatment plan. An example of an irregular perimeter 132 for a non-uniform grid is shown in FIG. 13. The perimeter is typically of an irregular (e.g., non-polygonal, non-circular, non-oval, and so forth) shape to track the typically irregular shape of the cross-section of the irradiation target. However, in some instances, the non-uniform grid may have a regular (e.g., polygonal, circular, oval, and so forth) perimeter, e.g., if that perimeter corresponds to the perimeter of the irradiation target. The non-uniform grid may include spot locations (e.g., locations to be irradiated) that are at regular intervals or locations within the perimeter or that are at irregular intervals or locations within the perimeter. In this context, an “interval” refers to a space between spots and a “location” refers to a place on the target where a spot is applied. So, for example, spots may be scanned in lines, which are regular locations, but at irregular intervals. Also, for example, spots may be scanned so that they have the same spacing, which are regular intervals, but that are at irregular locations. Examples are shown in the figures. For example, FIG. 14 shows an example non-uniform grid having an irregular perimeter 133 and having spot locations 134 that are at regular intervals and regular locations. FIG. 15 shows an example non-uniform grid 135 having an irregular perimeter and having spot locations 136 that are at regular intervals and irregular locations. FIG. 16 shows an example non-uniform grid 137 having an irregular perimeter and having spot locations 138 that are at irregular intervals and regular locations. FIG. 17 shows an example non-uniform grid having a regular perimeter 139 (e.g., a rectangle) and having spot locations 140 that are at regular intervals and irregular locations. FIG. 18 shows an example non-uniform grid having a regular perimeter 141 and having spot locations 142 that are at irregular intervals and regular locations. A computer system that controls the particle therapy system may also control scanning magnet 108 or other elements of the scanning system according to the treatment plan to produce non-uniform grid scanning. Other types of non-uniform grids may also be used for scanning. By implementing non-uniform grid scanning, the example particle therapy system described herein reduces the need to interrupt or redirect the particle beam during scanning. For example, in some implementations, the particle beam is interrupted between scanning different depth cross-sections of an irradiation target. In some in some implementations, the particle beam is only interrupted between scanning different depth cross-sections of an irradiation target. So, for example, during irradiation of a particular depth cross-section of the irradiation target, the particle beam need not be interrupted or redirected so as not to hit the target. A treatment plan may specify, for an irradiation target or cross-section thereof, a non-uniform grid to be scanned and spot sizes at each scan location of the non-uniform grid. Elements of the particle therapy system, including the scanning system, may then be computer-controlled to scan the cross-section according to the non-uniform grid and variable spot size. For example, as shown in FIG. 19, scanning may be performed so, at a perimeter 144 of an irregular cross-section, smaller spots 145 are deposited at a relatively high density. In an interior region of the irregular cross-section, larger spots 146 may be deposited at a density that is lower than the density of spots deposited at the perimeter. As a result, the cross-section of the irradiation target may be more accurately scanned with or without the use of apertures and without interrupting or redirecting the particle beam. In some implementations, the scanning is performed at a same speed from spot-to-spot. In some implementations, raster scanning may be performed using a variable spot size and non-uniform scanning grid. Control over the various components of the particle therapy system are similar to the control performed to implement spot scanning using these features. Different cross-sections of the irradiation target may be scanned according to different treatment plans. As described above, in some examples, the energy degrader is used to control the scanning depth. In some implementations, the particle beam may be interrupted or redirected during configuration of the energy degrader. In other implementations, this need not be the case. Described herein are examples of treating cross-sections of an irradiation target. These are generally cross-sections that are perpendicular to the direction of the particle beam. However, the concepts described herein are equally applicable to treating other portions of an irradiation target that are not cross-sections perpendicular to the direction of the particle beam. For example, an irradiation target may be segmented into spherical, cubical or other shaped volumes, and those volumes treated according to the concepts described herein. The processes described herein may be used with a single particle accelerator, and any two or more of the features thereof described herein may be used with the single particle accelerator. The particle accelerator may be used in any type of medical or non-medical application. An example of a particle therapy system that may be used is provided below. Notably, the concepts described herein may be used in other systems not specifically described. Referring to FIG. 20, an example implementation of a charged particle radiation therapy system 500 includes a beam-producing particle accelerator 502 having a weight and size small enough to permit it to be mounted on a rotating gantry 504 with its output directed straight (that is, essentially directly) from the accelerator housing toward a patient 506. Particle accelerator 502 also includes a scanning system of a type described herein (e.g., FIGS. 3 to 19). In some implementations, the steel gantry has two legs 508, 510 mounted for rotation on two respective bearings 512, 514 that lie on opposite sides of the patient. The accelerator is supported by a steel truss 516 that is long enough to span a treatment area 518 in which the patient lies (e.g., twice as long as a tall person, to permit the person to be rotated fully within the space with any desired target area of the patient remaining in the line of the beam) and is attached stably at both ends to the rotating legs of the gantry. In some examples, the rotation of the gantry is limited to a range 520 of less than 360 degrees, e.g., about 180 degrees, to permit a floor 522 to extend from a wall of the vault 524 that houses the therapy system into the patient treatment area. The limited rotation range of the gantry also reduces the required thickness of some of the walls (which are not directly aligned with the beam, e.g., wall 530), which provide radiation shielding of people outside the treatment area. A range of 180 degrees of gantry rotation is enough to cover all treatment approach angles, but providing a larger range of travel can be useful. For example the range of rotation may be between 180 and 330 degrees and still provide clearance for the therapy floor space. The horizontal rotational axis 532 of the gantry is located nominally one meter above the floor where the patient and therapist interact with the therapy system. This floor is positioned about 3 meters above the bottom floor of the therapy system shielded vault. The accelerator can swing under the raised floor for delivery of treatment beams from below the rotational axis. The patient couch moves and rotates in a substantially horizontal plane parallel to the rotational axis of the gantry. The couch can rotate through a range 534 of about 270 degrees in the horizontal plane with this configuration. This combination of gantry and patient rotational ranges and degrees of freedom allow the therapist to select virtually any approach angle for the beam. If needed, the patient can be placed on the couch in the opposite orientation and then all possible angles can be used. In some implementations, the accelerator uses a synchrocyclotron configuration having a very high magnetic field superconducting electromagnetic structure. Because the bend radius of a charged particle of a given kinetic energy is reduced in direct proportion to an increase in the magnetic field applied to it, the very high magnetic field superconducting magnetic structure permits the accelerator to be made smaller and lighter. The synchrocyclotron uses a magnetic field that is uniform in rotation angle and falls off in strength with increasing radius. Such a field shape can be achieved regardless of the magnitude of the magnetic field, so in theory there is no upper limit to the magnetic field strength (and therefore the resulting particle energy at a fixed radius) that can be used in a synchrocyclotron. The synchrocyclotron is supported on the gantry so that the beam is generated directly in line with the patient. The gantry permits rotation of the cyclotron about a horizontal rotational axis that contains a point (isocenter 540) within, or near, the patient. The split truss that is parallel to the rotational axis, supports the cyclotron on both sides. Because the rotational range of the gantry is limited, a patient support area can be accommodated in a wide area around the isocenter. Because the floor can be extended broadly around the isocenter, a patient support table can be positioned to move relative to and to rotate about a vertical axis 542 through the isocenter so that, by a combination of gantry rotation and table motion and rotation, any angle of beam direction into any part of the patient can be achieved. The two gantry arms are separated by more than twice the height of a tall patient, allowing the couch with patient to rotate and translate in a horizontal plane above the raised floor. Limiting the gantry rotation angle allows for a reduction in the thickness of at least one of the walls surrounding the treatment room. Thick walls, typically constructed of concrete, provide radiation protection to individuals outside the treatment room. A wall downstream of a stopping proton beam may be about twice as thick as a wall at the opposite end of the room to provide an equivalent level of protection. Limiting the range of gantry rotation enables the treatment room to be sited below earth grade on three sides, while allowing an occupied area adjacent to the thinnest wall reducing the cost of constructing the treatment room. In the example implementation shown in FIG. 20, the superconducting synchrocyclotron 502 operates with a peak magnetic field in a pole gap of the synchrocyclotron of 8.8 Tesla. The synchrocyclotron produces a beam of protons having an energy of 250 MeV. In other implementations the field strength could be in the range of 4 T to 20 T and the proton energy could be in the range of 150 to 300 MeV; however, field strength and energy are not limited to these ranges. The radiation therapy system described in this example is used for proton radiation therapy, but the same principles and details can be applied in analogous systems for use in heavy ion (ion) treatment systems. As shown in FIGS. 1, 2, 21, 22, and 23, an example synchrocyclotron 10 (e.g., 502 in FIG. 1) includes a magnet system 12 that contains an particle source 90, a radiofrequency drive system 91, and a beam extraction system 38. The magnetic field established by the magnet system has a shape appropriate to maintain focus of a contained proton beam using a combination of a split pair of annular superconducting coils 40, 42 and a pair of shaped ferromagnetic (e.g., low carbon steel) pole faces 44, 46. The two superconducting magnet coils are centered on a common axis 47 and are spaced apart along the axis. As shown in FIGS. 24 and 25, the coils are formed by of Nb3Sn-based superconducting 0.8 mm diameter strands 48 (that initially comprise a niobium-tin core surrounded by a copper sheath) deployed in a twisted cable-in-channel conductor geometry. After seven individual strands are cabled together, they are heated to cause a reaction that forms the final (brittle) superconducting material of the wire. After the material has been reacted, the wires are soldered into the copper channel (outer dimensions 3.18×2.54 mm and inner dimensions 2.08×2.08 mm) and covered with insulation 52 (in this example, a woven fiberglass material). The copper channel containing the wires 53 is then wound in a coil having a rectangular cross-section. The wound coil is then vacuum impregnated with an epoxy compound. The finished coils are mounted on an annular stainless steel reverse bobbin 56. Heater blankets 55 are placed at intervals in the layers of the windings to protect the assembly in the event of a magnet quench. The entire coil can then be covered with copper sheets to provide thermal conductivity and mechanical stability and then contained in an additional layer of epoxy. The precompression of the coil can be provided by heating the stainless steel reverse bobbin and fitting the coils within the reverse bobbin. The reverse bobbin inner diameter is chosen so that when the entire mass is cooled to 4 K, the reverse bobbin stays in contact with the coil and provides some compression. Heating the stainless steel reverse bobbin to approximately 50 degrees C. and fitting coils at a temperature of 100 degrees Kelvin can achieve this. The geometry of the coil is maintained by mounting the coils in a reverse rectangular bobbin 56 to exert a restorative force 60 that works against the distorting force produced when the coils are energized. As shown in FIG. 22, the coil position is maintained relative to the magnet yoke and cryostat using a set of warm-to-cold support straps 402, 404, 406. Supporting the cold mass with thin straps reduces the heat leakage imparted to the cold mass by the rigid support system. The straps are arranged to withstand the varying gravitational force on the coil as the magnet rotates on board the gantry. They withstand the combined effects of gravity and the large de-centering force realized by the coil when it is perturbed from a perfectly symmetric position relative to the magnet yoke. Additionally the links act to reduce dynamic forces imparted on the coil as the gantry accelerates and decelerates when its position is changed. Each warm-to-cold support includes one S2 fiberglass link and one carbon fiber link. The carbon fiber link is supported across pins between the warm yoke and an intermediate temperature (50-70 K), and the S2 fiberglass link 408 is supported across the intermediate temperature pin and a pin attached to the cold mass. Each pin may be made of high strength stainless steel. Referring to FIG. 1, the field strength profile as a function of radius is determined largely by choice of coil geometry and pole face shape; the pole faces 44, 46 of the permeable yoke material can be contoured to fine tune the shape of the magnetic field to ensure that the particle beam remains focused during acceleration. The superconducting coils are maintained at temperatures near absolute zero (e.g., about 4 degrees Kelvin) by enclosing the coil assembly (the coils and the bobbin) inside an evacuated annular aluminum or stainless steel cryostatic chamber 70 that provides a free space around the coil structure, except at a limited set of support points 71, 73. In an alternate version (e.g., FIG. 2) the outer wall of the cryostat may be made of low carbon steel to provide an additional return flux path for the magnetic field. In some implementations, the temperature near absolute zero is achieved and maintained using one single-stage Gifford-McMahon cryo-cooler and three two-stage Gifford McMahon cryo-coolers. Each two stage cryo-cooler has a second stage cold end attached to a condenser that recondenses Helium vapor into liquid Helium. In some implementations, the temperature near absolute zero is achieved and maintained using a cooling channel (not shown) containing the liquid helium, which is formed inside a superconducting coil support structure (e.g., the reverse bobbin), and which contains a thermal connection between the liquid helium in the channel and the corresponding superconducting coil. An example of a liquid helium cooling system of the type described above, and that may be used is described in U.S. patent application Ser. No. 13/148,000 (Begg et al.). The coil assembly and cryostatic chambers are mounted within and fully enclosed by two halves 81, 83 of a pillbox-shaped magnet yoke 82. The iron yoke 82 provides a path for the return magnetic field flux 84 and magnetically shields the volume 86 between the pole faces 44, 46 to prevent external magnetic influences from perturbing the shape of the magnetic field within that volume. The yoke also serves to decrease the stray magnetic field in the vicinity of the accelerator. As shown in FIGS. 1 and 26, the synchrocyclotron includes a particle source 90 of a Penning ion gauge geometry located near the geometric center 92 of the magnet structure 82. The particle source may be as described below, or the particle source may be of the type described in U.S. patent application Ser. No. 11/948,662 incorporated herein by reference. Particle source 90 is fed from a supply 99 of hydrogen through a gas line 201 and tube 194 that delivers gaseous hydrogen. Electric cables 94 carry an electric current from a current source 95 to stimulate electron discharge from cathodes 192, 190 that are aligned with the magnetic field 199. In some implementations, the gas in gas tube 101 may include a mixture of hydrogen and one or more other gases. For example, the mixture may contain hydrogen and one or more of the noble gases, e.g., helium, neon, argon, krypton, xenon and/or radon (although the mixture is not limited to use with the noble gases). In some implementations, the mixture may be a mixture of hydrogen and helium. For example, the mixture may contain about 75% or more of hydrogen and about 25% or less of helium (with possible trace gases included). In another example, the mixture may contain about 90% or more of hydrogen and about 10% or less of helium (with possible trace gases included). In examples, the hydrogen/helium mixture may be any of the following: >95%/<5%, >90%/<10%, >85%/<15%, >80%/<20%, >75%/<20%, and so forth. Possible advantages of using a noble (or other) gas in combination with hydrogen in the particle source may include: increased beam intensity, increased cathode longevity, and increased consistency of beam output. In this example, the discharged electrons ionize the gas exiting through a small hole from tube 194 to create a supply of positive ions (protons) for acceleration by one semicircular (dee-shaped) radio-frequency plate that spans half of the space enclosed by the magnet structure and one dummy dee plate 102. In the case of an interrupted particle source (an example of which is described in U.S. patent application Ser. No. 11/948,662), all (or a substantial part) of the tube containing plasma is removed at the acceleration region. As shown in FIG. 27, the dee plate 200 is a hollow metal structure that has two semicircular surfaces 203, 205 that enclose a space 207 in which the protons are accelerated during half of their rotation around the space enclosed by the magnet structure. A duct 209 opening into the space 207 extends through the yoke to an external location from which a vacuum pump can be attached to evacuate the space 207 and the rest of the space within a vacuum chamber 219 in which the acceleration takes place. The dummy dee 202 comprises a rectangular metal ring that is spaced near to the exposed rim of the dee plate. The dummy dee is grounded to the vacuum chamber and magnet yoke. The dee plate 200 is driven by a radio-frequency signal that is applied at the end of a radio-frequency transmission line to impart an electric field in the space 207. The radio frequency electric field is made to vary in time as the accelerated particle beam increases in distance from the geometric center. The radio frequency electric field may be controlled in the manner described in U.S. patent application Ser. No. 11/948,359, entitled “Matching A Resonant Frequency Of A Resonant Cavity To A Frequency Of An Input Voltage”, the contents of which are incorporated herein by reference. For the beam emerging from the centrally located particle source to clear the particle source structure as it begins to spiral outward, a large voltage difference is required across the radio frequency plates. 20,000 Volts is applied across the radio frequency plates. In some versions from 8,000 to 20,000 Volts may be applied across the radio frequency plates. To reduce the power required to drive this large voltage, the magnet structure is arranged to reduce the capacitance between the radio frequency plates and ground. This is done by forming holes with sufficient clearance from the radio frequency structures through the outer yoke and the cryostat housing and making sufficient space between the magnet pole faces. The high voltage alternating potential that drives the dee plate has a frequency that is swept downward during the accelerating cycle to account for the increasing relativistic mass of the protons and the decreasing magnetic field. The dummy dee does not require a hollow semi-cylindrical structure as it is at ground potential along with the vacuum chamber walls. Other plate arrangements could be used such as more than one pair of accelerating electrodes driven with different electrical phases or multiples of the fundamental frequency. The RF structure can be tuned to keep the Q high during the required frequency sweep by using, for example, a rotating capacitor having intermeshing rotating and stationary blades. During each meshing of the blades, the capacitance increases, thus lowering the resonant frequency of the RF structure. The blades can be shaped to create a precise frequency sweep required. A drive motor for the rotating condenser can be phase locked to the RF generator for precise control. One bunch of particles is accelerated during each meshing of the blades of the rotating condenser. The vacuum chamber in which the acceleration occurs is a generally cylindrical container that is thinner in the center and thicker at the rim. The vacuum chamber encloses the RF plates and the particle source and is evacuated by the vacuum pump 211. Maintaining a high vacuum insures that accelerating ions are not lost to collisions with gas molecules and enables the RF voltage to be kept at a higher level without arcing to ground. Protons traverse a generally spiral orbital path beginning at the particle source. In half of each loop of the spiral path, the protons gain energy as they pass through the RF electric field in space 107. As the ions gain energy, the radius of the central orbit of each successive loop of their spiral path is larger than the prior loop until the loop radius reaches the maximum radius of the pole face. At that location a magnetic and electric field perturbation directs ions into an area where the magnetic field rapidly decreases, and the ions depart the area of the high magnetic field and are directed through an evacuated tube 38, referred to herein as the extraction channel, to exit the yoke of the cyclotron. A magnetic regenerator may be used to change the magnetic field perturbation to direct the ions. The ions exiting the cyclotron will tend to disperse as they enter the area of markedly decreased magnetic field that exists in the room around the cyclotron. Beam shaping elements 407, 409 in the extraction channel 38 redirect the ions so that they stay in a straight beam of limited spatial extent. As the beam exits the extraction channel it is passed through a beam formation system 225 (FIG. 22) comprised of a scanning system of the type described herein. Beam formation system 125 may be used in conjunction with an inner gantry that controls application of the beam. Stray magnetic fields exiting from the cyclotron may be limited by both the pillbox magnet yoke (which also serves as a shield) and a separate magnetic shield 214. The separate magnetic shield includes of a layer 217 of ferromagnetic material (e.g., steel or iron) that encloses the pillbox yoke, separated by a space 216. This configuration that includes a sandwich of a yoke, a space, and a shield achieves adequate shielding for a given leakage magnetic field at lower weight. As described above, in some implementations, an active return system may be used in place of, or to augment, the operation of the magnetic yoke and shield. As mentioned, the gantry allows the synchrocyclotron to be rotated about the horizontal rotational axis 532. The truss structure 516 has two generally parallel spans 580, 582. The synchrocyclotron is cradled between the spans about midway between the legs. The gantry is balanced for rotation about the bearings using counterweights 222, 224 mounted on ends of the legs opposite the truss. The gantry is driven to rotate by an electric motor mounted to one or both of the gantry legs and connected to the bearing housings by drive gears. The rotational position of the gantry is derived from signals provided by shaft angle encoders incorporated into the gantry drive motors and the drive gears. At the location at which the ion beam exits the cyclotron, the beam formation system 225 acts on the ion beam to give it properties suitable for patient treatment. For example, the beam may be spread and its depth of penetration varied to provide uniform radiation across a given target volume. The beam formation system includes active scanning elements as described herein. All of the active systems of the synchrocyclotron (the current driven superconducting coils, the RF-driven plates, the vacuum pumps for the vacuum acceleration chamber and for the superconducting coil cooling chamber, the current driven particle source, the hydrogen gas source, and the RF plate coolers, for example), may be controlled by appropriate synchrocyclotron control electronics (not shown), which may include, e.g., one or more computers programmed with appropriate programs to effect control. The control of the gantry, the patient support, the active beam shaping elements, and the synchrocyclotron to perform a therapy session is achieved by appropriate therapy control electronics (not shown). As shown in FIGS. 20, 28, and 29, the gantry bearings are supported by the walls of a cyclotron vault 524. The gantry enables the cyclotron to be swung through a range 520 of 180 degrees (or more) including positions above, to the side of, and below the patient. The vault is tall enough to clear the gantry at the top and bottom extremes of its motion. A maze 246 sided by walls 248, 150 provides an entry and exit route for therapists and patients. Because at least one wall 152 is not in line with the proton beam directly from the cyclotron, it can be made relatively thin and still perform its shielding function. The other three side walls 154, 156, 150/248 of the room, which may need to be more heavily shielded, can be buried within an earthen hill (not shown). The required thickness of walls 154, 156, and 158 can be reduced, because the earth can itself provide some of the needed shielding. Referring to FIGS. 28, 29 and 30, for safety and aesthetic reasons, a therapy room 160 may be constructed within the vault. The therapy room is cantilevered from walls 154, 156, 150 and the base 162 of the containing room into the space between the gantry legs in a manner that clears the swinging gantry and also maximizes the extent of the floor space 164 of the therapy room. Periodic servicing of the accelerator can be accomplished in the space below the raised floor. When the accelerator is rotated to the down position on the gantry, full access to the accelerator is possible in a space separate from the treatment area. Power supplies, cooling equipment, vacuum pumps and other support equipment can be located under the raised floor in this separate space. Within the treatment room, the patient support 170 can be mounted in a variety of ways that permit the support to be raised and lowered and the patient to be rotated and moved to a variety of positions and orientations. In system 602 of FIG. 31, a beam-producing particle accelerator of the type described herein, in this case synchrocyclotron 604, is mounted on rotating gantry 605. Rotating gantry 605 is of the type described herein, and can angularly rotate around patient support 606. This feature enables synchrocyclotron 604 to provide a particle beam directly to the patient from various angles. For example, as in FIG. 31, if synchrocyclotron 604 is above patient support 606, the particle beam may be directed downwards toward the patient. Alternatively, if synchrocyclotron 604 is below patient support 606, the particle beam may be directed upwards toward the patient. The particle beam is applied directly to the patient in the sense that an intermediary beam routing mechanism is not required. A routing mechanism, in this context, is different from a shaping or sizing mechanism in that a shaping or sizing mechanism does not re-route the beam, but rather sizes and/or shapes the beam while maintaining the same general trajectory of the beam. Further details regarding an example implementation of the foregoing system may be found in U.S. Pat. No. 7,728,311, filed on Nov. 16, 2006 and entitled “Charged Particle Radiation Therapy”, and in U.S. patent application Ser. No. 12/275,103, filed on Nov. 20, 2008 and entitled “Inner Gantry”. The contents of U.S. Pat. No. 7,728,311 and in U.S. patent application Ser. No. 12/275,103 are hereby incorporated by reference into this disclosure. In some implementations, the synchrocyclotron may be a variable-energy device, such as that described in U.S. patent application Ser. No. 13/916,401, filed on Jun. 12, 2013, the contents of which are incorporated herein by reference. The particle accelerator used in the example particle therapy systems and example scanning systems described herein may be a variable-energy particle accelerator. Different spot-size scatterers may be configured for use with different energies produced by a variable-energy particle accelerator. Likewise, different energy degraders, if used (and, in some cases, they may not be), may be configured for use with different energies produced by a variable-energy particle accelerator. The energy of the extracted particle beam (the particle beam output from the accelerator) can affect the use of the particle beam during treatment. In some machines, the energy of the particle beam (or particles in the particle beam) does not increase after extraction. However, the energy may be reduced based on treatment needs after the extraction and before the treatment. Referring to FIG. 32, an example treatment system 910 includes an accelerator 912, e.g., a synchrocyclotron, from which a particle (e.g., proton) beam 914 having a variable energy is extracted to irradiate a target volume 924 of a body 922. Optionally, one or more additional devices, such as a scanning unit 916 or a scattering unit 916, one or more monitoring units 918, and an energy degrader 920, are placed along the irradiation direction 928. The devices intercept the cross-section of the extracted beam 914 and alter one or more properties of the extracted beam for the treatment. A target volume to be irradiated (an irradiation target) by a particle beam for treatment typically has a three-dimensional configuration. In some examples, to carry-out the treatment, the target volume is divided into layers along the irradiation direction of the particle beam so that the irradiation can be done on a layer-by-layer basis. For certain types of particles, such as protons, the penetration depth (or which layer the beam reaches) within the target volume is largely determined by the energy of the particle beam. A particle beam of a given energy does not reach substantially beyond a corresponding penetration depth for that energy. To move the beam irradiation from one layer to another layer of the target volume, the energy of the particle beam is changed. In the example shown in FIG. 32, the target volume 924 is divided into nine layers 926a-926i along the irradiation direction 928. In an example process, the irradiation starts from the deepest layer 926i, one layer at a time, gradually to the shallower layers and finishes with the shallowest layer 926a. Before application to the body 922, the energy of the particle beam 914 is controlled to be at a level to allow the particle beam to stop at a desired layer, e.g., the layer 926d, without substantially penetrating further into the body or the target volume, e.g., the layers 926e-926i or deeper into the body. In some examples, the desired energy of the particle beam 914 decreases as the treatment layer becomes shallower relative to the particle acceleration. In some examples, the beam energy difference for treating adjacent layers of the target volume 924 is about 3 MeV to about 100 MeV, e.g., about 10 MeV to about 80 MeV, although other differences may also be possible, depending on, e.g., the thickness of the layers and the properties of the beam. The energy variation for treating different layers of the target volume 924 can be performed at the accelerator 912 (e.g., the accelerator can vary the energy) so that, in some implementations, no additional energy variation is required after the particle beam is extracted from the accelerator 912. So, the optional energy degrader 920 in the treatment system 10 may be eliminated from the system. In some implementations, the accelerator 912 can output particle beams having an energy that varies between about 100 MeV and about 300 MeV, e.g., between about 115 MeV and about 250 MeV. The variation can be continuous or non-continuous, e.g., one step at a time. In some implementations, the variation, continuous or non-continuous, can take place at a relatively high rate, e.g., up to about 50 MeV per second or up to about 20 MeV per second. Non-continuous variation can take place one step at a time with a step size of about 10 MeV to about 90 MeV. When irradiation is complete in one layer, the accelerator 912 can vary the energy of the particle beam for irradiating a next layer, e.g., within several seconds or within less than one second. In some implementations, the treatment of the target volume 924 can be continued without substantial interruption or even without any interruption. In some situations, the step size of the non-continuous energy variation is selected to correspond to the energy difference needed for irradiating two adjacent layers of the target volume 924. For example, the step size can be the same as, or a fraction of, the energy difference. In some implementations, the accelerator 912 and the degrader 920 collectively vary the energy of the beam 914. For example, the accelerator 912 provides a coarse adjustment and the degrader 920 provides a fine adjustment or vice versa. In this example, the accelerator 912 can output the particle beam that varies energy with a variation step of about 10-80 MeV, and the degrader 920 adjusts (e.g., reduces) the energy of the beam at a variation step of about 2-10 MeV. The reduced use (or absence) of the energy degrader, which can include range shifters, helps to maintain properties and quality of the output beam from the accelerator, e.g., beam intensity. The control of the particle beam can be performed at the accelerator. Side effects, e.g., from neutrons generated when the particle beam passes the degrader 920, can be reduced or eliminated. The energy of the particle beam 914 may be adjusted to treat another target volume 930 in another body or body part 922′ after completing treatment in target volume 924. The target volumes 924, 930 may be in the same body (or patient), or may belong to different patients. It is possible that the depth D of the target volume 930 from a surface of body 922′ is different from that of the target volume 924. Although some energy adjustment may be performed by the degrader 920, the degrader 912 may only reduce the beam energy and not increase the beam energy. In this regard, in some cases, the beam energy required for treating target volume 930 is greater than the beam energy required to treat target volume 924. In such cases, the accelerator 912 may increase the output beam energy after treating the target volume 924 and before treating the target volume 930. In other cases, the beam energy required for treating target volume 930 is less than the beam energy required to treat target volume 924. Although the degrader 920 can reduce the energy, the accelerator 912 can be adjusted to output a lower beam energy to reduce or eliminate the use of the degrader 920. The division of the target volumes 924, 930 into layers can be different or the same. And the target volume 930 can be treated similarly on a layer by layer basis to the treatment of the target volume 924. The treatment of the different target volumes 924, 930 on the same patient may be substantially continuous, e.g., with the stop time between the two volumes being no longer than about 30 minutes or less, e.g., 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 5 minutes or less, or 1 minute or less. As is explained herein, the accelerator 912 can be mounted on a movable gantry and the movement of the gantry can move the accelerator to aim at different target volumes. In some situations, the accelerator 912 can complete the energy adjustment of the output beam 914 during the time the treatment system makes adjustment (such as moving the gantry) after completing the treatment of the target volume 924 and before starting treating the target volume 930. After the alignment of the accelerator and the target volume 930 is done, the treatment can begin with the adjusted, desired beam energy. Beam energy adjustment for different patients can also be completed relatively efficiently. In some examples, all adjustments, including increasing/reducing beam energy and/or moving the gantry are done within about 30 minutes, e.g., within about 25 minutes, within about 20 minutes, within about 15 minutes, within about 10 minutes or within about 5 minutes. In the same layer of a target volume, an irradiation dose is applied by moving the beam across the two-dimensional surface of the layer (which is sometimes called scanning beam) using a scanning unit 916. Alternatively, the layer can be irradiated by passing the extracted beam through one or more scatterers of the scattering unit 16 (which is sometimes called scattering beam). Beam properties, such as energy and intensity, can be selected before a treatment or can be adjusted during the treatment by controlling the accelerator 912 and/or other devices, such as the scanning unit/scatterer(s) 916, the degrader 920, and others not shown in the figures. In this example implementation, as in the example implementations described above, system 910 includes a controller 932, such as a computer, in communication with one or more devices in the system. Control can be based on results of the monitoring performed by the one or more monitors 918, e.g., monitoring of the beam intensity, dose, beam location in the target volume, etc. Although the monitors 918 are shown to be between the device 916 and the degrader 920, one or more monitors can be placed at other appropriate locations along the beam irradiation path. Controller 932 can also store a treatment plan for one or more target volumes (for the same patient and/or different patients). The treatment plan can be determined before the treatment starts and can include parameters, such as the shape of the target volume, the number of irradiation layers, the irradiation dose for each layer, the number of times each layer is irradiated, etc. The adjustment of a beam property within the system 910 can be performed based on the treatment plan. Additional adjustment can be made during the treatment, e.g., when deviation from the treatment plan is detected. In some implementations, the accelerator 912 is configured to vary the energy of the output particle beam by varying the magnetic field in which the particle beam is accelerated. In an example implementation, one or more sets of coils receives variable electrical current to produce a variable magnetic field in the cavity. In some examples, one set of coils receives a fixed electrical current, while one or more other sets of coils receives a variable current so that the total current received by the coil sets varies. In some implementations, all sets of coils are superconducting. In other implementations, some sets of coils, such as the set for the fixed electrical current, are superconducting, while other sets of coils, such as the one or more sets for the variable current, are non-superconducting. In some examples, all sets of coils are non-superconducting. Generally, the magnitude of the magnetic field is scalable with the magnitude of the electrical current. Adjusting the total electric current of the coils in a predetermined range can generate a magnetic field that varies in a corresponding, predetermined range. In some examples, a continuous adjustment of the electrical current can lead to a continuous variation of the magnetic field and a continuous variation of the output beam energy. Alternatively, when the electrical current applied to the coils is adjusted in a non-continuous, step-wise manner, the magnetic field and the output beam energy also varies accordingly in a non-continuous (step-wise) manner. The scaling of the magnetic field to the current can allow the variation of the beam energy to be carried out relatively precisely, although sometimes minor adjustment other than the input current may be performed. In some implementations, to output particle beams having a variable energy, the accelerator 912 is configured to apply RF voltages that sweep over different ranges of frequencies, with each range corresponding to a different output beam energy. For example, if the accelerator 912 is configured to produce three different output beam energies, the RF voltage is capable of sweeping over three different ranges of frequencies. In another example, corresponding to continuous beam energy variations, the RF voltage sweeps over frequency ranges that continuously change. The different frequency ranges may have different lower frequency and/or upper frequency boundaries. The extraction channel may be configured to accommodate the range of different energies produced by the variable-energy particle accelerator. Particle beams having different energies can be extracted from the accelerator 912 without altering the features of the regenerator that is used for extracting particle beams having a single energy. In other implementations, to accommodate the variable particle energy, the regenerator can be moved to disturb (e.g., change) different particle orbits in the manner described above and/or iron rods (magnetic shims) can be added or removed to change the magnetic field bump provided by the regenerator. More specifically, different particle energies will typically be at different particle orbits within the cavity. By moving the regenerator in the manner described herein, it is possible to intercept a particle orbit at a specified energy and thereby provide the correct perturbation of that orbit so that particles at the specified energy reach the extraction channel. In some implementations, movement of the regenerator (and/or addition/removal of magnetic shims) is performed in real-time to match real-time changes in the particle beam energy output by the accelerator. In other implementations, particle energy is adjusted on a per-treatment basis, and movement of the regenerator (and/or addition/removal of magnetic shims) is performed in advance of the treatment. In either case, movement of the regenerator (and/or addition/removal of magnetic shims) may be computer controlled. For example, a computer may control one or more motors that effect movement of the regenerator and/or magnetic shims. In some implementations, iron rods (magnetic shims) can be moved into and out of any appropriate part of magnetic yoke 82 to alter and control the magnetic field produced in the acceleration cavity. In some implementations, the regenerator is implemented using one or more magnetic shims that are controllable to move to the appropriate location(s). In some implementations, a structure (not shown) is at the entrance to the extraction channel is controlled to accommodate the different energies produced by the particle accelerator. For example, the structure may be rotated so that an appropriate thickness intercepts a particle beam having a particular energy. The structure thus absorbs at least some of the energy in the particle beam, enabling the particle beam to traverse the extraction channel, as described above. As an example, table 1 shows three example energy levels at which example accelerator 912 can output particle beams. The corresponding parameters for producing the three energy levels are also listed. In this regard, the magnet current refers to the total electrical current applied to the one or more coil sets in the accelerator 912; the maximum and minimum frequencies define the ranges in which the RF voltage sweeps; and “r” is the radial distance of a location to a center of the cavity in which the particles are accelerated. TABLE 1Examples of beam energies and respective parameters.BeamMagnetMaximumMinimumMagnetic FieldMagnetic FieldEnergyCurrentFrequencyFrequencyat r = 0 mmat r = 298 mm(MeV)(Amps)(MHz)(MHz)(Tesla)(Tesla)2501990132998.78.22351920128978.48.02111760120937.97.5 Details that may be included in an example particle accelerator that produces charged particles having variable energies are described below. The accelerator can be a synchrocyclotron and the particles may be protons. The particles may be output as pulsed beams. The energy of the beam output from the particle accelerator can be varied during the treatment of one target volume in a patient, or between treatments of different target volumes of the same patient or different patients. In some implementations, settings of the accelerator are changed to vary the beam energy when no beam (or particles) is output from the accelerator. The energy variation can be continuous or non-continuous over a desired range. Referring to the example shown in FIG. 1, the particle accelerator (synchrocyclotron 502), which may be a variable-energy particle accelerator like accelerator 912 described above, may be configured to particle beams that have a variable energy. The range of the variable energy can have an upper boundary that is about 200 MeV to about 300 MeV or higher, e.g., 200 MeV, about 205 MeV, about 210 MeV, about 215 MeV, about 220 MeV, about 225 MeV, about 230 MeV, about 235 MeV, about 240 MeV, about 245 MeV, about 250 MeV, about 255 MeV, about 260 MeV, about 265 MeV, about 270 MeV, about 275 MeV, about 280 MeV, about 285 MeV, about 290 MeV, about 295 MeV, or about 300 MeV or higher. The range can also have a lower boundary that is about 100 MeV or lower to about 200 MeV, e.g., about 100 MeV or lower, about 105 MeV, about 110 MeV, about 115 MeV, about 120 MeV, about 125 MeV, about 130 MeV, about 135 MeV, about 140 MeV, about 145 MeV, about 150 MeV, about 155 MeV, about 160 MeV, about 165 MeV, about 170 MeV, about 175 MeV, about 180 MeV, about 185 MeV, about 190 MeV, about 195 MeV, about 200 MeV. In some examples, the variation is non-continuous and the variation step can have a size of about 10 MeV or lower, about 15 MeV, about 20 MeV, about 25 MeV, about 30 MeV, about 35 MeV, about 40 MeV, about 45 MeV, about 50 MeV, about 55 MeV, about 60 MeV, about 65 MeV, about 70 MeV, about 75 MeV, or about 80 MeV or higher. Varying the energy by one step size can take no more than 30 minutes, e.g., about 25 minutes or less, about 20 minutes or less, about 15 minutes or less, about 10 minutes or less, about 5 minutes or less, about 1 minute or less, or about 30 seconds or less. In other examples, the variation is continuous and the accelerator can adjust the energy of the particle beam at a relatively high rate, e.g., up to about 50 MeV per second, up to about 45 MeV per second, up to about 40 MeV per second, up to about 35 MeV per second, up to about 30 MeV per second, up to about 25 MeV per second, up to about 20 MeV per second, up to about 15 MeV per second, or up to about 10 MeV per second. The accelerator can be configured to adjust the particle energy both continuously and non-continuously. For example, a combination of the continuous and non-continuous variation can be used in a treatment of one target volume or in treatments of different target volumes. Flexible treatment planning and flexible treatment can be achieved. A particle accelerator that outputs a particle beam having a variable energy can provide accuracy in irradiation treatment and reduce the number of additional devices (other than the accelerator) used for the treatment. For example, the use of degraders for changing the energy of an output particle beam may be reduced or eliminated. The properties of the particle beam, such as intensity, focus, etc. can be controlled at the particle accelerator and the particle beam can reach the target volume without substantial disturbance from the additional devices. The relatively high variation rate of the beam energy can reduce treatment time and allow for efficient use of the treatment system. In some implementations, the accelerator, such as the synchrocyclotron 502 of FIG. 1, accelerates particles or particle beams to variable energy levels by varying the magnetic field in the accelerator, which can be achieved by varying the electrical current applied to coils for generating the magnetic field. As shown in FIGS. 3, 4, 5, 6, and 7, example synchrocyclotron 10 (502 in FIG. 1) includes a magnet system that contains a particle source 90, a radiofrequency drive system 91, and a beam extraction system 38. FIG. 35 shows an example of a magnet system that may be used in a variable-energy accelerator. In this example implementation, the magnetic field established by the magnet system 1012 can vary by about 5% to about 35% of a maximum value of the magnetic field that two sets of coils 40a and 40b, and 42a and 42b are capable of generating. The magnetic field established by the magnet system has a shape appropriate to maintain focus of a contained proton beam using a combination of the two sets of coils and a pair of shaped ferromagnetic (e.g., low carbon steel) structures, examples of which are provided above. Each set of coils may be a split pair of annular coils to receive electrical current. In some situations, both sets of coils are superconducting. In other situations, only one set of the coils is superconducting and the other set is non-superconducting or normal conducting (also discussed further below). It is also possible that both sets of coils are non-superconducting. Suitable superconducting materials for use in the coils include niobium-3 tin (Nb3Sn) and/or niobium-titanium. Other normal conducting materials can include copper. Examples of the coil set constructions are described further below. The two sets of coils can be electrically connected serially or in parallel. In some implementations, the total electrical current received by the two sets of coils can include about 2 million ampere turns to about 10 million ampere turns, e.g., about 2.5 to about 7.5 million ampere turns or about 3.75 million ampere turns to about 5 million ampere turns. In some examples, one set of coils is configured to receive a fixed (or constant) portion of the total variable electrical current, while the other set of coils is configured to receive a variable portion of the total electrical current. The total electrical current of the two coil sets varies with the variation of the current in one coil set. In other situations, the electrical current applied to both sets of coils can vary. The variable total current in the two sets of coils can generate a magnetic field having a variable magnitude, which in turn varies the acceleration pathways of the particles and produces particles having variable energies. Generally, the magnitude of the magnetic field generated by the coil(s) is scalable to the magnitude of the total electrical current applied to the coil(s). Based on the scalability, in some implementations, linear variation of the magnetic field strength can be achieved by linearly changing the total current of the coil sets. The total current can be adjusted at a relatively high rate that leads to a relatively high-rate adjustment of the magnetic field and the beam energy. In the example reflected in Table 1 above, the ratio between values of the current and the magnetic field at the geometric center of the coil rings is: 1990:8.7 (approximately 228.7:1); 1920:8.4 (approximately 228.6:1); 1760:7.9 (approximately 222.8:1). Accordingly, adjusting the magnitude of the total current applied to a superconducting coil(s) can proportionally (based on the ratio) adjust the magnitude of the magnetic field. The scalability of the magnetic field to the total electrical current in the example of Table 1 is also shown in the plot of FIG. 33, where BZ is the magnetic field along the Z direction; and R is the radial distance measured from a geometric center of the coil rings along a direction perpendicular to the Z direction. The magnetic field has the highest value at the geometric center, and decreases as the distance R increases. The curves 1035, 1037 represent the magnetic field generated by the same coil sets receiving different total electrical current: 1760 Amperes and 1990 Amperes, respectively. The corresponding energies of the extracted particles are 211 MeV and 250 MeV, respectively. The two curves 1035, 1037 have substantially the same shape and the different parts of the curves 1035, 1037 are substantially parallel. As a result, either the curve 1035 or the curve 1037 can be linearly shifted to substantially match the other curve, indicating that the magnetic field is scalable to the total electrical current applied to the coil sets. In some implementations, the scalability of the magnetic field to the total electrical current may not be perfect. For example, the ratio between the magnetic field and the current calculated based on the example shown in table 1 is not constant. Also, as shown in FIG. 33, the linear shift of one curve may not perfectly match the other curve. In some implementations, the total current is applied to the coil sets under the assumption of perfect scalability. The target magnetic field (under the assumption of perfect scalability) can be generated by additionally altering the features, e.g., geometry, of the coils to counteract the imperfection in the scalability. As one example, ferromagnetic (e.g., iron) rods (magnetic shims) can be inserted or removed from one or both of the magnetic structures. The features of the coils can be altered at a relatively high rate so that the rate of the magnetic field adjustment is not substantially affected as compared to the situation in which the scalability is perfect and only the electrical current needs to be adjusted. In the example of iron rods, the rods can be added or removed at the time scale of seconds or minutes, e.g., within 5 minutes, within 1 minute, less than 30 seconds, or less than 1 second. In some implementations, settings of the accelerator, such as the current applied to the coil sets, can be chosen based on the substantial scalability of the magnetic field to the total electrical current in the coil sets. Generally, to produce the total current that varies within a desired range, any combination of current applied to the two coil sets can be used. In an example, the coil set 42a, 42b can be configured to receive a fixed electrical current corresponding to a lower boundary of a desired range of the magnetic field. In the example shown in table 1, the fixed electrical current is 1760 Amperes. In addition, the coil set 40a, 40b can be configured to receive a variable electrical current having an upper boundary corresponding to a difference between an upper boundary and a lower boundary of the desired range of the magnetic field. In the example shown in table 1, the coil set 40a, 40b is configured to receive electrical current that varies between 0 Ampere and 230 Amperes. In another example, the coil set 42a, 42b can be configured to receive a fixed electrical current corresponding to an upper boundary of a desired range of the magnetic field. In the example shown in table 1, the fixed current is 1990 Amperes. In addition, the coil set 40a, 40b can be configured to receive a variable electrical current having an upper boundary corresponding to a difference between a lower boundary and an upper boundary of the desired range of the magnetic field. In the example shown in table 1, the coil set 40a, 40b is configured to receive electrical current that varies between −230 Ampere and 0 Ampere. The total variable magnetic field generated by the variable total current for accelerating the particles can have a maximum magnitude greater than 4 Tesla, e.g., greater than 5 Tesla, greater than 6 Tesla, greater than 7 Tesla, greater than 8 Tesla, greater than 9 Tesla, or greater than 10 Tesla, and up to about 20 Tesla or higher, e.g., up to about 18 Tesla, up to about 15 Tesla, or up to about 12 Tesla. In some implementations, variation of the total current in the coil sets can vary the magnetic field by about 0.2 Tesla to about 4.2 Tesla or more, e.g., about 0.2 Tesla to about 1.4 Tesla or about 0.6 Tesla to about 4.2 Tesla. In some situations, the amount of variation of the magnetic field can be proportional to the maximum magnitude. FIG. 34 shows an example RF structure for sweeping the voltage on the dee plate 100 over an RF frequency range for each energy level of the particle beam, and for varying the frequency range when the particle beam energy is varied. The semicircular surfaces 103, 105 of the dee plate 100 are connected to an inner conductor 1300 and housed in an outer conductor 1302. The high voltage is applied to the dee plate 100 from a power source (not shown, e.g., an oscillating voltage input) through a power coupling device 1304 that couples the power source to the inner conductor. In some implementations, the coupling device 1304 is positioned on the inner conductor 1300 to provide power transfer from the power source to the dee plate 100. In addition, the dee plate 100 is coupled to variable reactive elements 1306, 1308 to perform the RF frequency sweep for each particle energy level, and to change the RF frequency range for different particle energy levels. The variable reactive element 1306 can be a rotating capacitor that has multiple blades 1310 rotatable by a motor (not shown). By meshing or unmeshing the blades 1310 during each cycle of RF sweeping, the capacitance of the RF structure changes, which in turn changes the resonant frequency of the RF structure. In some implementations, during each quarter cycle of the motor, the blades 1310 mesh with the each other. The capacitance of the RF structure increases and the resonant frequency decreases. The process reverses as the blades 1310 unmesh. As a result, the power required to generate the high voltage applied to the dee plate 103 and necessary to accelerate the beam can be reduced by a large factor. In some implementations, the shape of the blades 1310 is machined to form the required dependence of resonant frequency on time. The RF frequency generation is synchronized with the blade rotation by sensing the phase of the RF voltage in the resonator, keeping the alternating voltage on the dee plates close to the resonant frequency of the RF cavity. (The dummy dee is grounded and is not shown in FIG. 34). The variable reactive element 1308 can be a capacitor formed by a plate 1312 and a surface 1316 of the inner conductor 1300. The plate 1312 is movable along a direction 1314 towards or away from the surface 1316. The capacitance of the capacitor changes as the distance D between the plate 1312 and the surface 1316 changes. For each frequency range to be swept for one particle energy, the distance D is at a set value, and to change the frequency range, the plate 1312 is moved corresponding to the change in the energy of the output beam. In some implementations, the inner and outer conductors 1300, 1302 are formed of a metallic material, such as copper, aluminum, or silver. The blades 1310 and the plate 1312 can also be formed of the same or different metallic materials as the conductors 1300, 1302. The coupling device 1304 can be an electrical conductor. The variable reactive elements 1306, 1308 can have other forms and can couple to the dee plate 100 in other ways to perform the RF frequency sweep and the frequency range alteration. In some implementations, a single variable reactive element can be configured to perform the functions of both the variable reactive elements 1306, 1308. In other implementations, more than two variable reactive elements can be used. Control of the particle therapy system described herein and its various features may be implemented using hardware or a combination of hardware and software. For example, a system like the ones described herein may include various controllers and/or processing devices located at various points. A central computer may coordinate operation among the various controllers or processing devices. The central computer, controllers, and processing devices may execute various software routines to effect control and coordination of testing and calibration. System operation can be controlled, at least in part, using one or more computer program products, e.g., one or more computer program tangibly embodied in one or more information carriers, such as one or more non-transitory machine-readable media, for execution by, or to control the operation of, one or more data processing apparatus, e.g., a programmable processor, a computer, multiple computers, and/or programmable logic components. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a network. Actions associated with implementing all or part of the operations of the particle therapy system described herein can be performed by one or more programmable processors executing one or more computer programs to perform the functions described herein. All or part of the operations can be implemented using special purpose logic circuitry, e.g., an FPGA (field programmable gate array) and/or an ASIC (application-specific integrated circuit). Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only storage area or a random access storage area or both. Elements of a computer (including a server) include one or more processors for executing instructions and one or more storage area devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from, or transfer data to, or both, one or more machine-readable storage media, such as mass PCBs for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Non-transitory machine-readable storage media suitable for embodying computer program instructions and data include all forms of non-volatile storage area, including by way of example, semiconductor storage area devices, e.g., EPROM, EEPROM, and flash storage area devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Any “electrical connection” as used herein may imply a direct physical connection or a connection that includes intervening components but that nevertheless allows electrical signals, including wireless signals, to flow between connected components. Any “connection” involving electrical circuitry mentioned herein, unless stated otherwise, is an electrical connection and not necessarily a direct physical connection regardless of whether the word “electrical” is used to modify “connection”. Any two more of the foregoing implementations may be used in an appropriate combination in an appropriate particle accelerator (e.g., a synchrocyclotron). Likewise, individual features of any two more of the foregoing implementations may be used in an appropriate combination. Elements of different implementations described herein may be combined to form other implementations not specifically set forth above. Elements may be left out of the processes, systems, apparatus, etc., described herein without adversely affecting their operation. Various separate elements may be combined into one or more individual elements to perform the functions described herein. The example implementations described herein are not limited to use with a particle therapy system or to use with the example particle therapy systems described herein. Rather, the example implementations can be used in any appropriate system that directs accelerated particles to an output. Additional information concerning the design of an example implementation of a particle accelerator that may be used in a system as described herein can be found in U.S. Provisional Application No. 60/760,788, entitled “High-Field Superconducting Synchrocyclotron” and filed Jan. 20, 2006; U.S. patent application Ser. No. 11/463,402, entitled “Magnet Structure For Particle Acceleration” and filed Aug. 9, 2006; and U.S. Provisional Application No. 60/850,565, entitled “Cryogenic Vacuum Break Pneumatic Thermal Coupler” and filed Oct. 10, 2006, all of which are incorporated herein by reference. The following applications are incorporated by reference into the subject application: the U.S. Provisional Application entitled “CONTROLLING INTENSITY OF A PARTICLE BEAM” (Application No. 61/707,466), the U.S. Provisional Application entitled “ADJUSTING ENERGY OF A PARTICLE BEAM” (Application No. 61/707,515), the U.S. Provisional Application entitled “ADJUSTING COIL POSITION” (Application No. 61/707,548), the U.S. Provisional Application entitled “FOCUSING A PARTICLE BEAM USING MAGNETIC FIELD FLUTTER” (Application No. 61/707,572), the U.S. Provisional Application entitled “MAGNETIC FIELD REGENERATOR” (Application No. 61/707,590), the U.S. Provisional Application entitled “FOCUSING A PARTICLE BEAM” (Application No. 61/707,704), the U.S. Provisional Application entitled “CONTROLLING PARTICLE THERAPY (Application No. 61/707,624), and the U.S. Provisional Application entitled “CONTROL SYSTEM FOR A PARTICLE ACCELERATOR” (Application No. 61/707,645). The following are also incorporated by reference into the subject application: U.S. Pat. No. 7,728,311 which issued on Jun. 1, 2010, U.S. patent application Ser. No. 11/948,359 which was filed on Nov. 30, 2007, U.S. patent application Ser. No. 12/275,103 which was filed on Nov. 20, 2008, U.S. patent application Ser. No. 11/948,662 which was filed on Nov. 30, 2007, U.S. Provisional Application No. 60/991,454 which was filed on Nov. 30, 2007, U.S. Pat. No. 8,003,964 which issued on Aug. 23, 2011, U.S. Pat. No. 7,208,748 which issued on Apr. 24, 2007, U.S. Pat. No. 7,402,963 which issued on Jul. 22, 2008, U.S. patent application Ser. No. 13/148,000 filed Feb. 9, 2010, U.S. patent application Ser. No. 11/937,573 filed on Nov. 9, 2007, U.S. patent application Ser. No. 11/187,633, titled “A Programmable Radio Frequency Waveform Generator for a Synchrocyclotron,” filed Jul. 21, 2005, U.S. Provisional Application No. 60/590,089, filed on Jul. 21, 2004, U.S. patent application Ser. No. 10/949,734, titled “A Programmable Particle Scatterer for Radiation Therapy Beam Formation”, filed Sep. 24, 2004, and U.S. Provisional Application No. 60/590,088, filed Jul. 21, 2005. Any features of the subject application may be combined with one or more appropriate features of the following: the U.S. Provisional Application entitled “CONTROLLING INTENSITY OF A PARTICLE BEAM” (Application No. 61/707,466), the U.S. Provisional Application entitled “ADJUSTING ENERGY OF A PARTICLE BEAM” (Application No. 61/707,515), the U.S. Provisional Application entitled “ADJUSTING COIL POSITION” (Application No. 61/707,548), the U.S. Provisional Application entitled “FOCUSING A PARTICLE BEAM USING MAGNETIC FIELD FLUTTER” (Application No. 61/707,572), the U.S. Provisional Application entitled “MAGNETIC FIELD REGENERATOR” (Application No. 61/707,590), the U.S. Provisional Application entitled “FOCUSING A PARTICLE BEAM” (Application No. 61/707,704), the U.S. Provisional Application entitled “CONTROLLING PARTICLE THERAPY (Application No. 61/707,624), and the U.S. Provisional Application entitled “CONTROL SYSTEM FOR A PARTICLE ACCELERATOR” (Application No. 61/707,645), U.S. Pat. No. 7,728,311 which issued on Jun. 1, 2010, U.S. patent application Ser. No. 11/948,359 which was filed on Nov. 30, 2007, U.S. patent application Ser. No. 12/275,103 which was filed on Nov. 20, 2008, U.S. patent application Ser. No. 11/948,662 which was filed on Nov. 30, 2007, U.S. Provisional Application No. 60/991,454 which was filed on Nov. 30, 2007, U.S. patent application Ser. No. 13/907,601, which was filed on May 31, 2013, U.S. patent application Ser. No. 13/916,401, filed on Jun. 12, 2013, U.S. Pat. No. 8,003,964 which issued on Aug. 23, 2011, U.S. Pat. No. 7,208,748 which issued on Apr. 24, 2007, U.S. Pat. No. 7,402,963 which issued on Jul. 22, 2008, U.S. patent application Ser. No. 13/148,000 filed Feb. 9, 2010, U.S. patent application Ser. No. 11/937,573 filed on Nov. 9, 2007, U.S. patent application Ser. No. 11/187,633, titled “A Programmable Radio Frequency Waveform Generator for a Synchrocyclotron,” filed Jul. 21, 2005, U.S. Provisional Application No. 60/590,089, filed on Jul. 21, 2004, U.S. patent application Ser. No. 10/949,734, titled “A Programmable Particle Scatterer for Radiation Therapy Beam Formation”, filed Sep. 24, 2004, and U.S. Provisional Application No. 60/590,088, filed Jul. 21, 2005. Other implementations not specifically described herein are also within the scope of the following claims.
054715130	summary	TECHNICAL FIELD The present invention relates generally to nuclear reactors, and, more specifically, to an improved boiling water reactor. BACKGROUND ART A conventional boiling water reactor (BWR) includes a pressure vessel containing a nuclear reactor core above which are disposed in turn conventional steam separators and dryers. The vessel is filled with a cooling and moderating fluid such as water to a predetermined normal water level located generally near the middle of the steam separators. The core boils the water for generating a steam-water mixture which rises upwardly into the steam separators, which remove some of the water therefrom, with additional water being further removed therefrom from the steam dryers positioned above the steam separators. The dried steam is conventionally discharged from the vessel to a conventional steam turbine, for example, which powers an electrical generator for generating electrical power provided to an electrical utility grid. A typical BWR is controlled by a plurality of control rods which extend downwardly from the core through conventional guide tubes extending from the bottom of the core to the lower head of the pressure vessel which defines therebetween a lower plenum. Extending downwardly from the lower head are a plurality of conventional control rod drives (CRDs) which are effective for selectively inserting the control rods upwardly into the core for reducing reactivity therein, and for selectively withdrawing the control rod downwardly from the core for increasing reactivity therein. Accurate intermediate positions of the control rods may be obtained by using a conventional drive screw which is selectively rotated in opposite directions by a conventional stepper motor to selectively translate upwardly and downwardly a ball nut threadingly engaged therewith. An elongate piston rests on the ball nut and is coupled to a respective control rod for raising and lowering the control rod as the ball nut is correspondingly translated. In order to obtain relatively instantaneous insertion of the control rods during a SCRAM operation, a pressurized fluid such as water is conventionally channeled through the CRD for lifting the piston and in turn lifting the control rod independently of the ball nut. In order to fully withdraw the control rods from below the core, the guide tubes extending between the core and the vessel lower head must have a vertical height approximately equal to the length of the control rods. The height of the core also has a vertical height approximately equal to the length of the control rods so that the control rods may be fully inserted therein. The conventional steam separators additionally require a suitable vertical height for effectively separating water from the steam-water mixture. And additional vertical height is required for the steam dryer disposed above the steam separators. Accordingly, the overall height of the pressure vessel must be suitable for containing these several components and for allowing the effective functioning thereof. A typical pressure vessel for a BWR sized for generating steam to power a turbine-generator for providing electrical power to the electrical utility grid is about 21 meters tall, with the reactor generating on the order of about 1,000 megawatts electric (MWe) and higher. Such a large pressure vessel, which is typically made from steel has a correspondingly high weight requiring large cranes for the assembly thereof into a power plant. A conventional BWR typically includes conventional recirculation pumps which operate for channeling downwardly the water within the pressure vessel in a conventional annular downcomer surrounding the core, which recirculated water enters the lower plenum and flows upwardly through the core. Since the water used to generate the reactor steam also cools the reactor, systems are typically provided to ensure that adequate water is always contained within the pressure vessel and above the core during all modes of operation of the reactor, including abnormal modes such as that occurring in a conventional loss of coolant accident (LOCA) wherein the coolant water leaks from the reactor system and must be suitably replaced for maintaining an adequate level of water within the pressure vessel above the core. In one type of advanced BWR, a gravity-driven cooling system (GDCS) includes a pool of water located outside the pressure vessel at an elevation above the reactor core to provide makeup water in a LOCA situation for example. In order to use the GDCS makeup water, the reactor pressure vessel must be first depressurized in a conventional manner to sufficiently reduce the pressure therein so that the pressure head of the elevated GDCS makeup water is sufficient to force the makeup water into the vessel to supplant the lost reactor water for maintaining the reactor water level above the core. Since depressurization of the pressure vessel takes several minutes, the vessel continues to lose its coolant water either as a liquid or from the steam being generated and discharged therefrom, which loss of water must be suitably made up to ensure an adequate water level within the vessel. One arrangement for ensuring adequate water level within the vessel is to provide a greater initial amount of water in the pressure vessel above the core by suitably increasing the normal elevation of the water level within the vessel. By initially providing more water within the vessel, adequate reserves of the water therein may be maintained during a LOCA situation until the vessel may be suitably depressurized and makeup water provided thereto from the GDCS pool. The increased normal water level within the vessel, however, requires a corresponding increase in the height of the pressure vessel, which correspondingly increases its manufacturing complexity and weight. Furthermore, in another abnormal situation involving an accidental trip of all the recirculation pumps, recirculation of the coolant water within the vessel will occur solely by natural recirculation flow of the water therein with the core-heated rising, and the relatively cooler water within the downcomer falling. By increasing the normal water level as described above, the natural recirculation flow of the coolant water within the vessel is also increased, which is effective for providing additional margin against conventionally known nuclear-thermal-hydraulic instability of the coolant water following an all-pump trip. Furthermore, the increased normal water level is also effective for improving conventional thermal margins and peak pressures for other types of plant operating transient conditions. Analysis indicates that an increase in the normal water level within the pressure vessel of about 7 meters is required both to apply an effective gravity driven cooling system in a LOCA situation, and to achieve suitably stable operation following an all recirculation pump trip situation for a reactor sized for generating about 1350 MWe. However, in order to provide the additional 7 meters of water above the reactor core, the entire pressure vessel must be extended 7 meters above the core which would increase the normal length thereof from about 21 meters to at least 28 meters. Such a large pressure vessel is near the current fabrication limits, and near the current crane capacity limits for assembling the vessel in the power plant. The relatively large pressure vessel increases the complexity and cost of its use within the power plant. OBJECTS OF THE INVENTION Accordingly, one object of the present invention is to provide a new and improved boiling water reactor (BWR). Another object of the present invention is to provide an improved BWR having an increased normal water level above a reactor core therein without correspondingly increasing the length of the pressure vessel. Another object of the present invention is to provide an improved BWR having an increased normal water level therein with bottom-mounted control rod drives having gravity-aided SCRAM capability. Another object of the present invention is to provide an improved BWR having an increased normal water level above the core thereof which concurrently provides space for withdrawal of the control rods from the core and for providing guidance thereof. DISCLOSURE OF INVENTION A boiling water reactor includes a pressure vessel containing a reactor core, chimney, steam separator assembly, and steam dryer assembly therein, with the vessel being filled with reactor water to a normal water level through the steam separator assembly. A plurality of control rod drives extend downwardly from the bottom of the pressure vessel and are operatively joined to control rods extending upwardly into the reactor core. The chimney includes a plurality of channels disposed above the core and laterally spaced apart to define guide slots for receiving the control rods as they are selectively translated upwardly out of the core by the control rod drives. The chimney has a vertical height for increasing the normal water level above the reactor core and for providing a space for the control rods withdrawn from the reactor core by the bottom-mounted control rod drives. In a preferred embodiment, the control rods are selectively withdrawn upwardly from the core and inserted downwardly into the core by the control rod drives, which also are effective for selectively releasing the control rods for allowing gravity to insert the control rods into the core.
	claims	1. A supercritical-pressure water cooled reactor comprising: a reactor vessel including: first and second end parts dimensioned to contain supercritical-pressure coolant and a shell part disposed between the first and the second end parts dimensioned to contain sub-critical-pressure coolant; first and second core-support plates each having a plurality of through-holes, the first and the second core-support plates being disposed in and fixed to the reactor vessel so that the core-support plates divide space inside the reactor vessel into first and second supercritical-pressure portions in the first and the second end parts, respectively, and a sub-critical pressure portion in the shell part; a plurality of fuel tubes each having an interior volume, an outer surface and first and second open ends fixed to one of the through-holes in the first core-support plate and one of the through-holes in the second core-support plate, respectively, so that the interior volumes of the fuel tubes are in fluidic communication with the supercritical-pressure portions, the outer surfaces of the fuel tubes can be exposed to the sub-critical pressure coolant, and the supercritical-pressure coolant and the sub-critical pressure coolant cannot be mixed together in the reactor vessel; a plurality of nuclear fuel assemblies disposed in the fuel tubes; a supercritical-pressure water inlet disposed in the reactor vessel for introducing supercritical-pressure water into one of the supercritical-pressure portions; a supercritical-pressure steam outlet disposed in the reactor vessel for extracting supercritical-pressure steam generated in the fuel tubes out of one of the supercritical-pressure portions; a sub-critical pressure coolant inlet disposed in the reactor vessel for introducing sub-critical pressure coolant into the sub-critical pressure portion; a sub-critical pressure coolant outlet disposed in the reactor vessel for extracting sub-critical pressure coolant out of the sub-critical pressure portion; a plurality of control rods which are arranged so that the control rods can be inserted into the sub-critical pressure portion adjacent to the fuel tubes through the shell part; and a control rod drive for driving the control rods from outside of the reactor vessel. 2. A supercritical-pressure water cooled reactor according to claim 1 , wherein the supercritical-pressure water inlet and the supercritical-pressure steam outlet are disposed in the first and the second end parts, respectively. claim 1 3. A supercritical-pressure water cooled reactor according to claim 1 , wherein: claim 1 the reactor vessel is arranged so that an axis of the shell part lies horizontally; and the control rods are arranged substantially vertically. 4. A supercritical-pressure water cooled reactor according to claim 1 , wherein: claim 1 the open ends of the fuel tubes penetrate and are fixed to the through-holes with adapters inserted between the fuel tubes and the through-holes. 5. A supercritical-pressure water cooled reactor according to claim 1 , further comprising: claim 1 a dividing plate for dividing the first supercritical-pressure portion into inlet and outlet chambers; wherein the first core-support plate has inlet and outlet portions facing the inlet and the outlet chambers, respectively, wherein some of the through-holes are disposed in the inlet portion and the rest of the through-holes are disposed in the outlet portion; and wherein the supercritical-pressure water inlet and the supercritical-pressure steam outlet are disposed in the inlet and the outlet chambers, respectively. 6. A supercritical-pressure water cooled reactor comprising: a reactor vessel including a shell part having two ends with an inlet header on one end and an outlet header on the other end; first and second core-support plates each having a plurality of through-holes, the first core-support plate being fixed to the inlet header, the second core-support plate being fixed to the outlet header, so that an inlet header portion for containing supercritical-pressure coolant, an outlet header portion for containing supercritical-pressure coolant and a shell portion between them for containing sub-critical-pressure coolant are formed in the reactor vessel; a plurality of fuel tubes each having an outer surface and first and second open ends fixed to one of the through-holes of the first and the second core-support plates, respectively, for forming sealed passages of the supercritical-pressure coolant from the inlet header portion to the outlet header portion via the fuel tubes so that the supercritical-pressure coolant and the sub-critical pressure coolant cannot be mixed together in the reactor vessel, wherein the outer surfaces of the fuel tubes are exposed to the sub-critical pressure coolant; a plurality of nuclear fuel assemblies disposed in the fuel tubes; a feed water inlet disposed in the reactor vessel for introducing supercritical-pressure water into the inlet header portion; a main steam outlet disposed in the reactor vessel for extracting supercritical-pressure steam out of the outlet header portion; a coolant inlet disposed in the reactor vessel for introducing sub-critical pressure coolant into the shell portion outside of the fuel tubes; a coolant outlet disposed in the reactor vessel for extracting sub-critical pressure coolant out of the shell portion outside of the fuel tubes; a plurality of control rod guide tubes inserted into the shell portion outside of the fuel tubes; a plurality of control rods which are arranged so that the control rods can be inserted into the control rod guide tubes; and a control rod drive for driving the control rods from outside of the reactor vessel. 7. A supercritical-pressure water cooled reactor comprising: a reactor vessel having a first end and a second end and including a shell part with an inlet-outlet header on the first end and an intermediate header on the second end; first and second core-support plates each having a plurality of through-holes, the first and the second core-support plates being fixed to the inlet-outlet header and the intermediate header, respectively, so that an inlet-outlet header portion, an intermediate header portion and a shell portion between them are formed in the reactor vessel; a dividing plate for dividing the inlet-outlet header portion into inlet and outlet chambers, so that the first core-support plate is divided into inlet and outlet portions each having a plurality of the through-holes; a first group of fuel tubes, each having first and second open ends, the first open end being fixed to one of the through-holes of the inlet portion of the first core-support plate, and the second open end being fixed to one of the through-holes of the second core-support plate for forming sealed passages of the supercritical-pressure coolant from the inlet chamber to the intermediate header portion; a second group of fuel tubes, each having third and fourth open ends, the third open end being fixed to one of the through-holes of the second core-support plate, and the fourth open end being fixed to one of the through-holes of the outlet portion of the first core-support plate for forming sealed passages of the supercritical-pressure coolant from the intermediate header portion to the outlet chamber, wherein the supercritical-pressure coolant and the sub-critical pressure coolant cannot be mixed together in the reactor vessel, and outer surfaces of the fuel tubes are exposed to the sub-critical pressure coolant; a plurality of nuclear fuel assemblies disposed in the fuel tubes; a feed water inlet disposed in the reactor vessel for introducing supercritical-pressure water into the inlet chamber; a main steam outlet disposed in the reactor vessel for extracting supercritical-pressure steam out of the outlet chamber; a coolant inlet disposed in the reactor vessel for introducing sub-critical pressure coolant into the shell portion outside of the fuel tubes; a coolant outlet disposed in the reactor vessel for extracting sub-critical pressure coolant out of the shell portion outside of the fuel tubes; a plurality of control rod guide tubes inserted into the shell portion outside of the fuel tubes; a plurality of control rods which are arranged so that the control rods can be inserted into the control rod guide tubes; and a control rod drive for driving the control rods from outside of the reactor vessel. 8. A supercritical-pressure water cooled reactor comprising: a reactor vessel including a shell part with an inlet-outlet header on an end; a core-support plate with a plurality of through-holes fixed to the inlet-outlet header, so that an inlet-outlet header portion and a shell portion are formed in the reactor vessel; a dividing plate for dividing the inlet-outlet header portion into inlet and outlet chambers so that the core-support plate is divided into inlet and outlet portions each having a fraction of the plurality of through-holes; a plurality of curved fuel tubes, each having first and second open ends fixed to one of the through-holes of the inlet and outlet portions of the core-support plate, respectively, for forming sealed passages of the supercritical-pressure coolant from the inlet chamber to the outlet chamber via the fuel tubes, wherein the supercritical-pressure coolant and the sub-critical pressure coolant cannot be mixed together in the reactor vessel, and outer surfaces of the fuel tubes are exposed to the sub-critical pressure coolant; a plurality of nuclear fuel assemblies disposed in the fuel tubes; a feed water inlet disposed in the reactor vessel for introducing supercritical-pressure water into the inlet chamber; a main steam outlet disposed in the reactor vessel for extracting supercritical-pressure steam out of the outlet chamber; a coolant inlet disposed in the reactor vessel for introducing sub-critical pressure coolant into the shell portion outside of the fuel tubes; a coolant outlet disposed in the reactor vessel for extracting sub-critical pressure coolant out of the shell portion outside of the fuel tubes; a plurality of control rod guide tubes inserted into the shell portion outside of the fuel tubes; a plurality of control rods which are arranged so that the control rods can be inserted into the control rod guide tubes; and a control rod drive for driving the control rods from outside of the reactor vessel. 9. An electric power generation plant having: (a) a supercritical-pressure water cooled reactor comprising: a reactor vessel including: first and second end parts for containing supercritical-pressure coolant and a shell part disposed between the first and the second end parts for containing sub-critical pressure coolant which is separated from the supercritical-pressure coolant in the reactor vessel; first and second core-support plates each having a plurality of through-holes, the first and the second core-support plates being disposed in and fixed to the reactor vessel so that the core-support plates divide space inside the reactor vessel into first and second supercritical-pressure portions in the first and the second end parts, respectively, and a sub-critical pressure portion in the shell part; a plurality of fuel tubes each having an inner volume, an outer surface, and first and second open ends fixed to one of the through-holes in the first core-support plate and one of the through-holes in the second core-support plate, respectively, so that the inner volumes of the fuel tubes are in fluidic communication with the supercritical-pressure portions, the outer surfaces of the fuel tubes can be exposed to the sub-critical pressure coolant, and the supercritical-pressure coolant and the sub-critical pressure coolant cannot be mixed together in the reactor vessel; a plurality of nuclear fuel assemblies disposed in the fuel tubes; a supercritical-pressure water inlet disposed in the reactor vessel for introducing supercritical-pressure water into one of the supercritical-pressure portions; a supercritical-pressure steam outlet disposed in the reactor vessel for extracting supercritical-pressure steam generated in the fuel tubes out of one of the supercritical-pressure portions; a sub-critical pressure coolant inlet disposed in the reactor vessel for introducing sub-critical pressure coolant into the sub-critical pressure portion; a sub-critical pressure coolant outlet disposed in the reactor vessel for extracting sub-critical pressure coolant out of the sub-critical pressure portion; a plurality of control rods which are arranged so that the control rods can be inserted into the sub-critical pressure portion adjacent to the fuel tubes through the shell part; and a control rod drive for driving the control rods from outside of the reactor vessel; (b) a higher pressure turbine receiving the supercritical-pressure steam extracted from the supercritical-pressure portion of the reactor; (c) means for extracting part of output steam of the higher pressure turbine to introduce the output steam to the sub-critical pressure portion of the reactor; (d) a lower pressure turbine receiving the sub-critical pressure coolant extracted from the sub-critical pressure portion of the reactor; and (e) an electric generator driven by at least one of the higher and lower pressure turbines. 10. A supercritical-pressure water cooled reactor according to claim 8 , wherein: claim 8 the reactor vessel is arranged so that an axis of the shell part lies substantially horizontally; and the control rod guide tubes are arranged substantially vertically.
052176819	abstract	A prestressed pressure vessel safety enclosure is used as a pressure safety enclosure for a nuclear reactor pressure vessel or other primary system vessel containing fluid or gaseous material under high pressure, such as, steam generators, pressurizers and pumps. The special pressure vessel enclosure comprises a first pressure vessel containment assembly surrounding the primary pressure vessel. A pair of first upper and lower pressure vessel jackets are adapted to enclose and be spaced apart, respectively, from the upper and lower portions of the first pressure vessel containment assembly with the rims of the jackets adapted to be slidable and sealed with respect to the first pressure vessel containment assembly. The spaces between the jackets and pressure vessel containment assembly are filled with a high boiling point, low melting point metal. Upper and lower ring girders, connected to each other by tension tendon members, in conjunction with upper and lower jacket bearing plates and skirts are used to apply a force to the respective upper and lower jackets for moving the jackets toward or away from each other This application of force achieves continuously adjustable compression in the pressure vessel safety enclosure walls in order to compensate for creep and relaxation of tendon members and of the enclosure walls.
	description	This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-201443 on Aug. 5, 2008 in Japan, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to a writing apparatus and a writing method, and more particularly to an apparatus and a method for writing complementary patterns used for double patterning or double exposure. 2. Description of Related Art The lithography technology which promotes micro-miniaturization of semiconductor devices is extremely important as being the only process whereby patterns are formed in the semiconductor manufacturing. In recent years, with the high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. Then, in order to form a desired circuit pattern on such semiconductor devices, there is a need for a highly accurate master or “original” pattern (also called a mask or a reticle). Therefore, with the miniaturization of the circuit critical dimension, an exposure light source having a shorter wavelength is required. As a method for extending the life of an ArF laser, which is an example of the exposure light source, a double exposure technique and a double patterning technique attract attention in recent years. The double exposure is a method of continuously exposing the same region on a resist coated wafer while exchanging two masks. (For example, refer to Patent Literature 1.) Then, through developing and etching processes, a desired pattern is formed on the wafer. On the other hand, the double patterning is a method of exposing a resist coated wafer by using the first mask, and after developing and etching processes, the wafer is coated with resist again so that the same region thereof may be exposed using the second mask. These techniques have an advantage in that they can be performed as an extension of the current technique. In these techniques, two masks are necessary for obtaining a desired pattern on the wafer. FIG. 8 is a schematic diagram showing masks used for the double patterning. In order to expose a desired pattern 302 onto the wafer, since sufficient resolution cannot be obtained by using a photomask 300, the mask needs to be divided into two as shown in FIG. 8. That is, a pattern 312 being a part of the pattern 302 is formed on a photomask 310, and a pattern 314 being the residual part of the pattern 302 is formed on a photomask 320. Then, the two photomasks 310 and 320 are set in order in an exposure apparatus, such as a stepper and a scanner, to be exposed respectively. These photomasks are manufactured using an electron beam writing apparatus. Since the electron beam writing technique intrinsically has excellent resolution, it is used for producing highly precise master patterns. FIG. 9 is a schematic diagram showing operations of a variable-shaped type electron beam (EB) writing apparatus. The variable-shaped type electron beam writing apparatus operates as follows: A first aperture plate 410 has a quadrangular, such as a rectangular opening or “hole” 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 that has passed through the opening 411 into a desired rectangular shape. The electron beam 330, emitted from a charged particle source 430 and having passed through the opening 411, is deflected by a deflector so as to pass through a part of the variable-shaped opening 421 and thereby to irradiate a target workpiece or “sample” mounted on a stage. The stage continuously moves in one predetermined direction (e.g. X direction) during writing or “drawing”. In other words, a rectangular shape as a result of passing through both the opening 411 and the variable-shaped opening 421 is written in the writing region of a target workpiece 340 on the stage. This method of forming a given shape by letting beams pass through both the opening 411 and the variable-shaped opening 421 is referred to as a variable shaped method. As described above, through the operations of the electron beam writing apparatus, a plurality of photomasks for the double exposure or for the double patterning exposure is manufactured. Then, when writing using the electron beam pattern writing apparatus, drift of the electron beam occurs as a temporal change. As a result, there is a problem that a positional deviation occurs between positions in writing the first mask and the second mask which are complementarily related, even when writing at a desired position. In the case of the positional deviation, consequently, a superposition error (overlay error) of the patterns occurs. For example, there is a problem that adjacent patterns which are to be separated from each other keeping a predetermined distance therebetween contact each other to cause a short circuit. In the mask manufacturing process, as mentioned above, there is a problem that an error caused by drift of electron beams occurs between writing positions of complementary mask patterns. Therefore, there exists a problem in that a superposition error between patterns is induced when exposing using these two masks. It is an object of the present invention to provide a writing apparatus and a writing method that can reduce superposition errors between patterns. In accordance with one aspect of the present invention, a writing apparatus includes a writing unit configured to write a first pattern onto a first mask substrate and a second pattern being complementary to the first pattern onto a second mask substrate using a charged particle beam, and an addition unit configured to add a positional deviation amount of the first pattern having been written on the first mask substrate to a writing position of the second pattern, wherein the writing unit writes the second pattern at the writing position on the second mask substrate, where the positional deviation amount of the first pattern has been added. In accordance with another aspect of the present invention, a writing method includes writing a first pattern onto a first mask substrate using a charged particle beam, measuring a position of the first pattern having been written on the first mask substrate, and writing a second pattern being complementary to the first pattern onto a second mask substrate by shifting a position by a positional deviation amount of the first pattern obtained as a result of the measuring. In the following Embodiments, there will be described a structure using an electron beam as an example of a charged particle beam. However, the charged particle beam is not limited to the electron beam. Another charged particle beam, such as an ion beam, may also be used. FIG. 1 is a schematic diagram showing a structure of a writing apparatus according to Embodiment 1. In FIG. 1, a writing apparatus 100 or “lithography apparatus 100” includes a writing unit 150 and a control unit 160. The writing apparatus 100 is an example of a charged particle beam writing apparatus. The writing unit 150 includes an electron lens barrel 102 and a writing chamber 103. The writing apparatus 100 writes one of two complementary patterns onto one of two mask substrates 10 and 20, and writes the other of the two complementary patterns onto the other of the mask substrates 10 and 20. The control unit 160 includes a writing data processing unit 110, a deflection control circuit 120, a digital-to-analog converter (DAC) 130, an amplifier 132, and magnetic disk drives 109 and 140. In the electron lens barrel 102, there are arranged an electron gun assembly 201, an illumination lens 202, a first aperture plate 203, a projection lens 204, a deflector 205, a second aperture plate 206, an objective lens 207, and a deflector 208. In the writing chamber 103, there is movably arranged an XY stage 105, on which the two mask substrates 10 and 20 are placed. As a typical example of the two mask substrates 10 and 20, a photomask substrate for double exposure or double patterning exposure can be cited. Such a mask substrate may be a mask blank in which no patterns are formed yet, for example. The deflection control circuit 120 includes a deflection position calculation unit 122, a grid matching correction (GMC) unit 124, a complementary mask residual error correction unit 126, a deflection voltage calculation unit 128, and a memory 129. In the deflection control circuit 120, processing of each function, such as the deflection position calculation unit 122, the grid matching correction unit 124, the complementary mask residual error correction unit 126, and the deflection voltage calculation unit 128, may be implemented by software. Alternatively, the deflection position calculation unit 122, the grid matching correction unit 124, the complementary mask residual error correction unit 126, and the deflection voltage calculation unit 128 may be configured by hardware such as an electric circuit. Alternatively, they may be executed by a combination of hardware and software, or a combination of hardware and firmware. When implemented by software or a combination of software and hardware etc., data to be input into the deflection control circuit 120 or data being processed or having been processed is stored in the memory 129 each time. In the magnetic disk drive 109, there are stored a writing data file in which one of the complementary patterns is defined and another writing data file in which the other of the complementary patterns is defined. In the magnetic disk drive 140 (storage unit), a GMC map 142 is stored, and after writing one of the complementary patterns, a residual error map 144 is to be stored. While only the structure elements necessary for explaining Embodiment 1 are shown in FIG. 1, it should be understood that other structure elements generally necessary for the writing apparatus 100 may also be included. FIG. 2 is a flowchart showing main steps of a method for writing complementary patterns according to Embodiment 1. As shown in FIG. 2, the writing method of the complementary pattern in Embodiment 1 executes each of the steps: a first mask deflection position calculation step (S102), a first mask grid matching correction (GMC) step (S104), a first mask writing step (S106), a first mask residual error measurement step (S108), a residual error map creation step (S110), a second mask deflection position calculation step (S112), a second mask grid matching correction (GMC) step (S114), a second mask residual error correction step (S116), and a second mask writing step (S118). First, in the writing data processing unit 110, writing data in which one of the complementary patterns is defined is read from the magnetic disk drive 109, and converted into shot data of the format used in the apparatus. The shot data is output to the deflection control circuit 120. The shape and the writing position of a pattern will be controlled based on this shot data. Now, the writing position will be explained. On the XY stage 105, the mask substrate 10 (first mask substrate) which is to be written first as one of the complementary masks is placed. In step S102, as a deflection position calculation step of the first mask, the deflection position calculation unit 122 calculates a deflection position of each shot that forms the complementary pattern to be written on the mask substrate 10. For example, it is preferable to perform the calculation by using polynomials as shown in the following equations (1-1) and (1-2). The case of calculating deflection position coordinates (Xi, Yi) of design coordinates (xi, yi) will be described as an example.Xi=a0+a1·x+a2·y+a3·x2+a4·xy+a5y2+a6·x3+a7·x2y+a8·xy2+a9·y3 (1-1)Yi=b0+b1·x+b2·y+b3·x2+b4·xy+b5y2+b6·x3+b7·x2y+b8·xy2+b9·y3 (1-2) The coefficients a0 to a9 and b0 to b9 may be obtained by approximating position data, which was measured prior to the writing, and be set in the deflection control circuit 120. For example, the coordinate system of the writing apparatus is corrected based on an error between a measured position and a design position by performing calibration, etc. of the electron beam 200. While the third order polynomial is used in this case, it is not limited thereto, and the n-th order polynomial may also be used. This polynomial can correct a positional deviation between the design coordinate and the position actually written. However, such correction may not be sufficient. Then, it is preferable to further perform GMC in the writing apparatus 100. In step S104, as a grid matching correction (GMC) step of the first mask, the grid matching correction unit 124 reads the GMC map 142 from the magnetic disk drive 140, and corrects the deflection position (Xi, Yi) which has already been calculated. When the correction was not completely performed by the third order polynomial mentioned above, it is effective to correct herein by using the map. The GMC map 142 is created prior to the writing. In the writing apparatus 100, for correcting the coordinate system of the writing apparatus 100 to be an ideal one, the whole surface of the mask to be written is divided into grids having predetermined dimensions, in a mesh-like state, and the position of the apex of each mesh is measured. Then, based on the error between the measured position and the design position, the coordinate system of the writing apparatus is corrected. This function is called the “grid matching correction (GMC). Specifically, a pattern for GMC measurement is written at the position corresponding to the apex of each mesh on the mask blank coated with resist. Then, after performing processing such as developing and etching for the mask, the position accuracy is measured from the pattern written. Based on measured results, the GMC map 142 for correcting positions is created. FIG. 3 shows as an example of a data file of the GMC map according to Embodiment 1. The correction amount (x′i, y′i) for correcting the dimension error at the design coordinates (xi, yi) is defined as data of the GMC map 142 as shown in FIG. 3. In this case, x′1=50 nm and y′1=−20 nm are shown as an example. Using this GMC map 142, the coordinate system of the writing apparatus is corrected. The coordinates (X′i, Y′i) after the grid matching correction (GMC) can be obtained by the following equations (2-1) and (2-2), for example.X′i=Xi+x′i (2-1)Y′i=Yi+y′i (2-2) In this case, there is shown correction is performed by reading the correction amount (x′i, y′i) for correcting the dimension error at the design coordinates (x0, y0) from the GMC map 142, and adding it to the already calculated deflection position coordinates (Xi, Yi). Then, the deflection voltage calculation unit 128 calculates a deflection voltage (Ex, Ey) to be used as a deflection amount for deflecting the electron beam 200 by the deflector 208, using the deflection position coordinates (X′i, Y′i) obtained after the correction as arguments. The deflection voltage can be calculated by the following equations (3-1) and (3-2).Ex=F(X′i) (3-1)Ey=G(Y′i) (3-2) In step S106, as a writing step of the first mask, the writing unit 150 writes one (first pattern) of the complementary patterns onto the first mask substrate 10, using the electron beam 200. Specifically, first, a deflection voltage (Ex, Ey) signal being a digital signal is output from the deflection control circuit 120 to the DAC 130. Then, the signal is converted into an analog deflection voltage in the DAC 130, and amplified by the amplifier 132 to be applied to the deflector 208. Operations of the writing unit 150 will now be described below. The electron beam 200 emitted from the electron gun assembly 201, which is an example of an irradiation unit, irradiates the entire first aperture plate 203 having a quadrangular, such as a rectangular opening, by the illumination lens 202. At this point, the electron beam 200 is shaped to be a quadrangle such as a rectangle. Then, after having passed through the first aperture plate 203, the electron beam 200 of a first aperture image is projected onto the second aperture plate 206 by the projection lens 204. The position of the first aperture image on the second aperture plate 206 is deflection-controlled by the deflector 205 so as to change the shape and size of the beam. Thereby, the electron beam 200 has been shaped. After having passed through the second aperture plate 206, the electron beam 200 of a second aperture image is focused by the objective lens 207 and deflected by the deflector 208. As a result, the shaped electron beam 200 reaches a desired position on the mask substrate 10 placed on the XY stage 105. Since the XY stage 105 moves continuously, the writing apparatus 100 performs writing while the XY stage 105 is continuously moving. Alternatively, the stage may move in a step and repeat manner. In that case, the writing apparatus 100 performs writing while the XY stage 105 is stopping during the step and repeat movement. As mentioned above, one (first pattern) of the complementary patterns is written onto the mask substrate 10 used as the first mask substrate. It is preferable for the first pattern to include a plurality of patterns for measurement. FIG. 4 shows an example of the pattern written priorly to the other of the two complementary patterns according to Embodiment 1. As shown in FIG. 4, a plurality of patterns 16 for measurement is also written on the mask substrate 10 in addition to the original pattern 12. These patterns 16 for measurement will be used to measure a dimension error of the first pattern mentioned later. Therefore, it is preferable to write the patterns 16 such that they are arranged all over the mask surface. While the shape of the pattern 16 is not particularly limited, it is preferable to have the shape of a cross, for example. Next, the other (second pattern) of the complementary patterns is to be written on the mask substrate 20 used as the second mask substrate. However, if the other pattern is written as it is, there is a possibility that a short circuit may occur as mentioned above because, with the temporal change of the beam drift, the first pattern contacts the second pattern when the first and second patterns are exposed onto the semiconductor substrate etc. Therefore, in Embodiment 1, a dimension error of the first pattern which has already been written on the mask substrate 10 is measured and then the second pattern is written onto the mask substrate 20 in view of the error. In step S108, as a residual error measurement step of the first mask, the written mask substrate 10 is moved out of the writing apparatus 100 in order to measure a positional deviation amount of the pattern having been written on the mask substrate 10. In this case, since a plurality of patterns 16 for measurement are written, positional deviations of them are measured. Thus, the amount of the positional deviation of the first pattern is measured at a plurality of positions on the substrate surface of the first mask substrate 10. In step S110, as a residual error map creation step, the residual error map 144, where the positional deviation of the pattern written on the mask substrate 10 is defined at each position, is created based on the measurement result. At this point, not a correction amount for correcting the positional deviation but a positional deviation amount itself is defined. The positional deviation amount at each coordinate of the first pattern may be defined as an approximated value at each corresponding coordinate on the map, obtained or “calculated” from the approximate equation of the positional deviation acquired from patterns 16 for measurement measured at a plurality of positions. The created residual error map 144 is stored in the magnetic disk drive 140. It is preferable to generate the format of the data file of the residual error map 144 to be in the form that can also be used in other writing apparatus. The reason for this is that such format can respond even when the mask substrate 10 and the mask substrate 20 are written by different writing apparatuses. FIG. 5 shows an example of the data file of the residual error map of the pattern priorly written in Embodiment 1. In FIG. 5, the positional deviation amount (x″i, y″i) of the pattern 16 for measurement at design coordinates (xi, yi) is defined as data of the residual error map 144. In this case, x″1=10 nm and y″1=−10 nm are shown as an example. It may be difficult to arrange the pattern 16 for measurement on the mask substrate 10 depending on the layout of the pattern 12 to be actually arranged. In such a case, it is acceptable to measure a positional deviation of the writing position of the pattern 12 being an actual pattern. In that case, the residual error map 144 may be created based on the positional deviation of the actual pattern. Then, the mask substrate 20 (second mask substrate) being the other of the complementary masks will be written. First, in the writing data processing unit 110, writing data in which the other (second pattern) of the complementary patterns is defined is read from the magnetic disk drive 109, and converted into shot data of the format used in the apparatus. Then, the shot data is output to the deflection control circuit 120. Based on this shot data, the shape and writing position of the pattern is to be controlled. The writing position will also be particularly described. Then, the mask substrate 20 being the other of the complementary masks to be written later is arranged on the XY stage 105. Now, the steps will be explained in order. In step S112, as a deflection position calculation step of the second mask, the deflection position calculation unit 122 calculates a deflection position of each shot that forms the complementary pattern to be written on the mask substrate 20. It is preferable to perform the calculation by also using polynomials as shown in the equations (1-1) and (1-2) whose coefficients had already been set beforehand. In step S114, as a grid matching correction (GMC) step of the second mask, the GMC unit 124 reads the GMC map 142 previously prepared from the magnetic disk drive 140, and corrects the deflection position (Xi, Yi) of the shot for the second pattern which has already been calculated. The method of correction is the same as that for the deflection position of the shot for the first pattern. That is, the coordinates (X′i, Y′i) after the grid matching correction can be obtained by the equations (2-1) and (2-2). If the deflection voltage is calculated as it is, it cannot respond to the temporal change of the writing position produced during from writing the first pattern to writing this second pattern. Then, in Embodiment 1, the writing position is corrected using the residual error map 144 as described below. In step S116, as a residual error correction step of the second mask, the complementary mask residual error correction unit 126 reads the residual error map 144 from the magnetic disk drive 140, and corrects the position of the second pattern to be shifted by the amount of the positional deviation of the first pattern written on the mask substrate 10. For example, the coordinates (X″i, Y″i) of after the residual error correction can be obtained by the following equations (4-1) and (4-2).X″i=X′i+x″i (4-1)Y″i=Y′i+y″i (4-2) In this case, there is shown correction is performed by acquiring the positional deviation (x″i, y″i) of the first pattern at the design coordinates (x0, y0) from the read residual error map 144, and adding it to the already calculated deflection position coordinates (X′i, Y′i) of after the GMC corresponding to the design coordinates (x0, y0). The complementary mask residual error correction unit 126 serves as an example of an addition unit. Thus, it is preferable that the complementary mask residual error correction unit 126 adds a value at a position of the first pattern acquired from the approximate equation acquired using positional deviations of the first pattern, measured at a plurality of positions, as a positional deviation amount at the position of the first pattern, to the writing position of the second pattern corresponding to the position of the first pattern. Then, the deflection voltage calculation unit 128 calculates a deflection voltage (Ex, Ey) to be used as an amount of deflecting the electron beam 200 by the deflector 208, while using the deflection position coordinates (X″i, Y″i) of after the correction, obtained as mentioned above, as arguments. The deflection voltage can be obtained by substituting X″i for X′i and Y″i for Y′i in the equations (3-1) and (3-2). In step S118, as a writing step of the second mask, the writing unit 150 writes the other (second pattern) of the complementary patterns onto the second mask substrate 20 using the electron beam 200. Specifically, first, a deflection voltage (Ex, Ey) signal for the second pattern, being a digital signal, is output to the DAC 130 from the deflection control circuit 120. Then, the signal is converted into an analog deflection voltage in the DAC 130, amplified by the amplifier 132, and applied to the deflector 208. Then, it is written by the writing unit 150. Operations of the writing unit 150 have already been described above. Thus, the other (second pattern) of the complementary patterns is written onto the mask substrate 20 serving as the second mask substrate. FIG. 6 is a schematic diagram for explaining the change of the writing position according to Embodiment 1. In FIG. 6, first, the deflection position P0 is obtained by performing a deflection position calculation. Then, the position P0 is corrected to the position denoted by P1, based on the GMC map 142. However, if nothing is done, it cannot respond to the temporal change of the writing position. Then, the position P1 is corrected to the position denoted by P2 by shifting by the positional deviation of the first pattern, based on the residual error map 144. Thus, deviation of the positional relation between the first pattern and the second pattern can be reduced by correcting the second pattern at the time of its being written while regarding the positional deviation of the first pattern as a writing position temporal change produced during from the first pattern writing to the second pattern writing. As a result, contact between the first pattern and the second pattern can be avoided. FIG. 7 shows an example of patterns on the two mask substrates and a pattern of after the double patterning according to Embodiment 1. As shown in FIG. 7, when the pattern 12 of the mask substrate 10 previously written deviates from the position shown by the solid line to the one shown by the dotted line, the pattern 14 of the mask substrate 20 is also written shiftedly from the solid line position to the dotted line position. Therefore, the pattern 32 finally exposed onto the wafer 30 using the two mask substrates 10 and 20 can maintain the positional relationship between the patterns 12 and 14, thereby reducing the deviation of the positional relation. According to Embodiment 1, as described above, since the position of one pattern (second pattern) is shifted by the positional deviation of the other pattern (first pattern), the superposition error of the two patterns can be reduced. Therefore, contact of the adjacent patterns can be avoided. While the embodiment has been described with reference to specific examples, the present invention is not limited thereto. The method mentioned above can be similarly applied to a photomask for double exposure which exposes a plurality of complementary patterns in a superimposed manner. Moreover, while the grid matching correction (GMC) step (S114) of the second mask is performed in the example mentioned above, it is not limited thereto. It is acceptable even to omit the GMC step (S114) of the second mask, and to perform the residual error correction step (S116) of the second mask following the deflection position calculation step (S112) of the second mask. Moreover, it is also acceptable even to omit the GMC step (S104) of the first mask. While description of the apparatus structure, control method, etc. not directly required for explaining the present invention is omitted, some or all of them may be suitably selected and used when needed. In addition, any other writing apparatus and writing method that include elements of the present invention and that can be appropriately modified by those skilled in the art are included within the scope of the present invention. Additional advantages and modification will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
	description	The present application is a continuation-in-part of U.S. patent application Ser. No. 13/280,941, filed Oct. 25, 2011, and, like that application, claims the priority of U.S. Provisional Application Ser. No. 61/407,113, filed Oct. 27, 2010, and of U.S. Provisional Application Ser. No. 61/533,407, filed Sep. 12, 2011, all three of which prior applications are incorporated herein by reference. The present invention relates to methods and apparatus for interrupting, steering and/or varying the spatial sweep and resolution of a beam of radiation, and, more particularly, a beam used for x-ray inspection. One application of x-ray backscatter technology is that of x-ray inspection, as employed, for example, in a portal through which a vehicle passes, or in a system mounted inside a vehicle for inspecting targets outside the vehicle. In such a system, an x-ray beam scans the target and detectors measure the intensity of backscattered radiation as the inspection vehicle and target pass each other. During inspection that images backscattered x-rays, it would be desirable for the operator to be able to control the x-ray beam's viewing angle, viewing direction, beam resolution and filtration. In accordance with embodiments of the invention, methods and apparatus are provided for scanning a beam of radiation with respect to a target. In certain embodiments, a scanning apparatus is provided for scanning a beam in a single dimensional scan. The apparatus has a source of radiation for generating a fan beam of radiation effectively emanating from a source axis and characterized by a width. The source also has an angle selector, stationary during the course of scanning, for limiting the angular extent of the scan, and a multi-aperture unit rotatable about a central axis in such a manner that beam fluence incident on a target is conserved for different fields of view of the beam on the target. In some embodiments, there may also be an inner or an outer width collimator for collimating the width of the fan beam. In accordance with alternate embodiments of the present invention, the multi-aperture unit may include rings of apertures spaced laterally along the central axis in such a manner that relative axial motion of the multi-aperture unit relative to the x-ray beam plane places a ring of apertures in the beam that is collimated by a corresponding opening angle in the angle selector. In accordance with other embodiments of the invention, the angle selector may include a slot of continuously variable opening. The central axis may be substantially coincident with the source axis, or either forward-offset of rearward-offset relative to the central axis. The multi-aperture unit may include rectangular slots. In accordance with yet other embodiments of the invention, the scanning apparatus may also have a collimator, which may either be an “inner collimator” or an “outer collimator,” each of which is defined below. The collimator may limit one or both of the width of the beam or the angular extent of the scan. In the former case, the collimator is referred to as a width collimator. An inner width collimator may include two or more slots of different widths. The width collimator, in some embodiments, may be fixed in width during the course of scanning the beam. In accordance with further embodiments of the present invention, the angle selector may include a plurality of discrete slots, and also a shutter position. In accordance with more embodiments of the present invention, the source of radiation may be an x-ray tube, and may be a source of radiation of a type generating a fan beam exceeding 60° in opening angle. The scanning apparatus may also be coupled to a platform, and may have an enclosing conveyance for conveying the scanning apparatus past an inspection target. The scanning apparatus may be coupled to a platform in conjunction with at least one further scanning apparatus. In accordance with alternate embodiments of the invention, the scanning apparatus may have a filter disposed within the beam for changing the energy distribution of the beam and/or for governing a dose of radiation incident on a target or portion of a target. The filter may be disposed on a filter tube, which may be adapted for selecting insertion of a plurality of filters and may include a beam shutter. The multi-aperture unit may include two nested, multi-aperture collimators, and may include an inner multi-aperture hoop made of material opaque to the beam. The multi-aperture unit may additionally include rings of apertures spaced laterally along the tube axis in such a manner that relative axial motion of the inner multi-aperture hoop relative to the beam plane places a ring of apertures in the beam that is collimated by a corresponding opening angle in the angle selector. The multi-aperture unit may also include an outer multi-aperture hoop rotatable in registration with the inner multi-aperture hoop. The outer multi-aperture hoop may include a plurality of apertures configured as horizontal slots in such a manner as to define a minimum size of emitted pencil beams along a sweep direct of the beams. Where there are two multi-aperture hoops, the inner and outer multi-aperture hoops may be mechanically integral. There may be an outer variable width collimator for defining a width of the beam that enters or exits the outer multi-aperture hoop. In other embodiments of the scanning apparatus, radiation may be emitted through a plurality of apertures at different angles with respect to the target, such that pencil beams of penetrating radiation sweep in alternation through the target in such a manner as to provide a stereoscopic view of an interior volume of the target. The scanning apparatus may have a rotation assembly adapted to provide for rotation of the source of radiation about the source axis, such as to reduce absorption of emitted radiation in the source anode, an effect referred to as the “heel” effect. The multi-aperture unit may include substantially rectangular through-holes. In accordance with alternate embodiments of the invention, a chopper is provided for interrupting a beam of particles, wherein the chopper has an obscuring element substantially opaque to passage of the particles in the propagation direction, and at least one through-hole in the obscuring element adapted for passage through the obscuring element of particles in the propagation direction, where the through-hole is characterized by a tapered dimension in a plane transverse to the propagation direction. Finally, the chopper has an actuator for moving the obscuring element in such a manner as to cause at least a portion of the beam of particles to traverse the at least one through hole on a periodic basis. The through-hole of the chopper maybe substantially conical or substantially biconical. The particles in the chopped beam may be massless, including electromagnetic radiation over a specified range of wavelengths. In other alternate embodiments, a chopper is provided for interrupting a beam of particles that has an obscuring element substantially opaque to passage of the particles in the propagation direction and at least one through-hole in the obscuring element adapted for passage through the obscuring element of particles in the propagation direction, the through-hole characterized by a rectangular cross section in a plane transverse to the propagation direction. In yet other alternate embodiments, a collimator is provided for narrowing a beam of particles, where the collimator has an obscuring element substantially opaque to passage of the particles in the propagation direction, and a gap in the obscuring element where the width of the gap varies as a function of distance along the long dimension relative to an edge of the gap. The gap may be fixed or adapted to be varied in at least one of the long and narrow dimensions. In accordance with another embodiment of the invention, a beam chopping assembly is provided that has a rotating element including at least one through-hole of rectangular cross-section. In yet other embodiments of the present invention, a method is provided for inspecting an object based on the transmission of x-rays through an object. The method has steps of: a. generating a fan beam of radiation; b. collimating the width of the fan beam with a collimator that is stationary during the course of a scan of the object, the scan characterized by an extent; c. limiting the extent of the scan with an angle selector; and d. varying a field of view of the beam on the object by means of a multi-aperture unit rotatable about a central axis in such a manner that beam fluence incident on a target is the same per revolution for all selected scan angles. The method may also include varying a direction of the scan, and the step of varying a field of view may include varying from a primary rapid scan to a secondary high-resolution scan of a suspect area. Definitions. As used herein, and in any appended claims, the following terms shall have the meanings indicated unless the context requires otherwise. “Beam resolution,” as used herein, shall refer to the product of a vertical resolution and a horizontal resolution. “Vertical” refers to the plane containing the swept pencil beam described herein, i.e., a plane perpendicular to the axis of rotation of the hoop described herein. The terms “horizontal” and “width” refer herein to the “axial” direction, which is to say, a direction parallel to the axis of rotation of the hoop(s) described herein. “Resolution,” in either of the foregoing vertical or horizontal cases, refers to the height (for instance, in angular measure, such as degrees, or minutes of arc, etc.) of the pencil beam when stationary on a stationary target, and the term assumes a point-like origin of the x-ray beam. Similarly, the areal beam resolution has units of square degrees or steradians, etc. Alternatively, resolution may be quoted in terms of a point spread function (PSF) at a specified distance from a defining aperture. The “zoom angle” is the angular extent of the scanning x-ray beam in the vertical direction, designated by numeral 15 in FIG. 1. The term “commensurate,” as applied to angular intervals, refers to intervals related by whole number ratios, such that rotational cycles of distinct components repeat after a complete revolution of one component. The term “fluence,” unless otherwise noted, is used herein, and in the appended claims, to mean the total integrated x-ray intensity in the chosen scan angle, for each revolution of the chopper wheel. Fluence is sometimes referred to as “flux,” although “flux” may sometimes have other meanings. The term “areal density” as applied to an x-ray beam, shall refer to instantaneous x-ray intensity per unit area delivered to a region of the target. As used herein and in any appended claims, a collimator shall be referred to as “inner” if it lies closer to a source of radiation than any hoop of apertures rotating about an axis coinciding with, or parallel to, the axis of the source of radiation. A collimator shall be referred to as “outer” if it is disposed further from a source of radiation than a hoop of apertures rotating about an axis coinciding with, or parallel to, the axis of the source of radiation. Preferred embodiments of the present invention provide a versatile beam scanner (VBS) (or, “flexible beam former” (FBF)), which may, particularly, refer to a mechanism in which the intensity of x-rays on a target increases inversely with the angular field of view on the target. While embodiments of the invention are described, herein, with reference to x-rays derived from an x-ray source, it is to be understood that various embodiments of the invention may advantageously be employed in the context of other radiation, whether electromagnetic or relating to beams of particles, and that all such embodiments are within the scope of the present invention. It should also be understood that embodiments of the present invention may be applied to the formation of images of x-rays transmitted through a target as well as to the formation of images of x-rays scattered from the target, or for any application where steering and focusing a beam subject to conservation of beam fluence might be advantageous. In particular, in various embodiments of the present invention, a versatile beam scanner may advantageously be mounted on a vehicle or conveyance of any sort, or on a portal inspecting moving objects. Moreover, multiple versatile beam scanners may be mounted on a single portal or other platform, with beams temporally or spatially interleaved to preclude or reduce crosstalk. The resolution of a beam on a target, where the beam is formed through a collimating hoop, is determined by the target's distance, the height of the collimation slots in the outermost hoop, and the width of the variable width collimator that is adjacent, either directly inside or directly outside the outermost hoop. Methods, in accordance with embodiments of the present invention, provide for improving an image by improving the vertical resolution of the scanning pencil beam, and providing independent views with different vertical resolutions. These are discussed in detail, below. In accordance with preferred embodiments of the present invention, the axial (width) resolution is controlled with a variable collimator 180 (shown in FIG. 7, and referred to herein as an outer width collimator). The angular (height resolution) is controlled by the integration time, and by two other parameters: the combination of wheel speed and scan angle, and a time constant associated with x-ray detection, namely the decay time of a scintillation phosphor. Typically, the integration time is set between 1 μs and 12 μs, with the number of resolved pixels in a vertical scan determined by the scan angle and rotational speed. For purposes of example, a hoop rotation rate of 3600 rpm, with 6 scans/revolution (as explained in detail below), and 500 pixels per scan, corresponds to ˜6 μs integration, and a beam resolution of approximately 0.1° per pixel. Basic elements of a VBS may be separated into a first part—an inner scanner, described with reference to FIG. 1, and designated generally by numeral 2, that is common to many embodiments, and a second part—an outer scanner 200 (shown in FIG. 7), that may be omitted for some applications. In particular, for low-energy applications, preferred embodiments employ a single scanner, and, more particularly, a single aperture ring, as discussed in detail, below. Also, for close objects, use of a single aperture ring, as described below, is preferred. While, for purposes of explanation herein, the elements of a VBS are summarized as a series of elements with increasing radii, it is to be understood that the order of the elements in the inner scanner can be varied. Elements of the VBS may include: a source 4 of penetrating radiation, such as an x-ray tube, that emits a fan beam 8 of x-rays over a wide angle, preferably greater than 60°, such as 120°, and in a plane (referred to, herein, as the “vertical” plane) that is typically perpendicular to the direction of vehicle and target passage; a selectable filter 155, mounted in filter tube 150 (shown in FIG. 7), for changing the energy distribution of the x-ray beam or for adjusting the radiation dose delivered to a target or to a portion of the target; an inner width, or slot, collimator 14 and angle selector 34 in the plane of the x-ray beam, made of material that is opaque to the x-ray beam, that control the scan angle and scan direction; a multi-aperture tube 50, made of material opaque to the x-rays, which rotates through the fan beam created by the slot-collimator to create a sweeping pencil beam; an outer widthcollimator 180 (shown in FIG. 7), stationary during scanning, having an adjustable jaw width 185 that controls the horizontal width of the x-ray beam that inspects the target; and an outer multi-aperture hoop 170 (shown in FIG. 7) that rotates in registration with the inner multi-aperture unit. It is to be understood that the versatile beam scanner described herein may operate with a solitary hoop or ring of apertures. In that case it may be advantageous to place a variable width collimator outside the hoop or ring. In the case where both an outer hoop and an inner ring are employed, the beam-forming requirements of the outer hoop are advantageously reduced, since the beam incident on the outer hoop is already collimated to a pencil beam. Thus, x-ray opaque material need only be provided around the apertures of the outer hoop 170. One application of a versatile beam scanner, designated generally by numeral 3, is depicted in FIG. 18, solely by way of example, and without limitation. X-ray source 4 is mounted on an x-ray inspection vehicle 180, providing transverse motion relative to a target of inspection 181. By operation of source 4 and scanner 3, x-ray beam 182 is scanned across target 181, and backscattered radiation 184 is detected by detector modules 100, with one or more detector signals generated by detector modules 100 subsequently converted by a processor 180 into an image of contents of target 181. Referring to FIG. 1, the selectable widths of slot 22 (and 24) of slot collimator 14 defines the width of fan beam 8, which is emitted from x-ray tube 4 and effectively emanates at, or near, a source axis 6. The maximum opening angle of fan beam 8 is the x-ray tube's beam angle; it defines the maximum angular sweep 15 of the pencil beam. The opening angle for inspecting target (shown in FIG. 18) can be changed, either by the operator, or by operation of processor 188 (shown in FIG. 18). The opening angle may be changed in fixed steps commensurate with 360°, with the maximum angle, as stated, limited by the x-ray tube's beam angle. The angle selector 34 can be rotated to change the direction of the sweep. Angle selector 34 typically remains fixed during the course of scanning. Angle selector 34 has rings of apertures 40 (best seen in FIG. 3A) that define the angular extent of the scan of the pencil beam 70. The combination of the slot collimator 14 and the apertures 56 in the aperture ring 50 defines the cross-section of pencil beam 70 (shown in FIG. 4). Each lateral ring of apertures 40 corresponds to one of the quantized opening angles of variable-slot collimator 14. When one of the opening angles of slot collimator 14 is chosen, angle selector 34 is moved laterally to place the appropriate ring of apertures in the beam. The number of apertures in each ring is commensurate with 360°. Alternatively, angle selector 34 may provide for continuous variation of opening angle from closure (as shown in FIG. 3B) to an opening of 120° (as shown in FIG. 3E), with other opening angles shown by way of example. The zoom angle, i.e., the angular extent of the scanning x-ray beam, may be determined by the lateral position of the spinning inner multi-aperture unit 50 and outer hoop 170. “Lateral,” as used herein, refers to a position along an axis parallel to the axis 6 about which components 50 and 170 rotate. In order to change that lateral position (and, thereby, the zoom angle), the offset of the plane of the fan beam is varied (in a step-wise fashion) with respect to the plane of apertures that define the zoom angle. (The offset is relative; either the beam or the aperture plane may be moved.) In a preferred embodiment of the invention, the aperture devices, which are rotating at high speed, are not be translated, but, rather, the rest of the beam forming system is translated with respect to rotating aperture devices, however, it is to be understood that either configuration falls within the scope of the present invention. When the target (not shown) is distant from the inner scanner 2, the outer unit 200 may preferably be used to further define the cross-section of the pencil beam at the target. Referring now to FIG. 7, the outer unit 200 consists of a slot-collimator 180 (shown in FIG. 7) to refine the width of the scanning beam, and a rotating hoop 170 with apertures 175 to refine the height of the pencil beam 70. The apertures 175 in the outer hoop 170 are equally-spaced, and their number is equal to the maximum number of apertures in a ring of the inner multi-aperture tube 50. The number is also commensurate with the number of apertures in each of the rings of the inner beam-forming unit. The outer hoop is light-weight, thereby advantageously reducing its rotational moment of inertia. The beam defining apertures are typically tungsten inserts. The slotted outer width collimator 180 (shown in FIG. 7), with adjustable jaw width, controls the horizontal width of the x-ray beam that inspects the target, and is stationary during scanning. The slot collimator, 180, shown interior to the aperture ring 170, may also be exterior to it, within the scope of the present invention. One novel and advantageous feature of embodiments of the present invention is the focusing feature. The decrease of the scan angle—in order to focus on a portion of the target—results in a corresponding increase in the beam intensity, since the number of slots illuminated by the source per revolution of the hoop increases as the scan angle decreases. Thus, the resulting beam fluence on the target is the same per revolution for all selected scan angles. This means that the areal density (defined above) of x-rays in a 15° view is six times greater than in a 90° view of the target. A further novel feature is the operator's ability to change the cross-section of the scanning pencil beam by moving the jaws of the fixed collimator 14, or the variable collimator 180, to change the width of the image pixel, or changing the integration time of the detected signal to change the height of the image pixel. Yet another novel feature is the operator control of the viewing direction of the x-ray scan. In accordance with certain embodiments of the present invention, angle selector 34 and/or aperture ring 50, and/or variable collimator 180 may be selected automatically by processor 188 on the basis of the proximity of inspected target 181 (shown in FIG. 18), and the height or relative speed of the inspection system and inspected target. One or more sensors 186 (shown in FIG. 18) may be used to determine one or more of the foregoing parameters. Imaging data may also be used for that purpose. Similarly, filter 155 and collimator 180 may also be adjusted on the fly, such as to control a radiation dose on the basis of human occupancy of the inspected target, for example. The flexible beam former, in accordance with the various embodiments taught herein, may be advantageously applied to the formation of images of x-rays transmitted through a target or to the formation of images of x-rays scattered from the target. It can be applied to a scan taken by rotating the scanning system. It can be implemented by manual changes carried out when the scanner is turned off, though the preferred embodiment is for changes carried out during the scan and even automatically in response to programmed instructions. The versatility of the x-ray scanners taught herein allows the operator to obtain the most effective inspection for targets at distances and relative traversal speeds that can each vary over more than an order of magnitude. Without loss of generality, the apparatus and methods described herein may be applied here to image formation of x-rays backscattered from a target that moves perpendicularly at constant speed through the plane of the scanning pencil beam. Embodiments of the invention, in several variants, are now described with reference to FIGS. 1 to 8. In a preferred embodiment, described with particular reference to FIGS. 1-7, a single beam of x-rays is produced, under operator or automatic control, that scans the target through selected field-of-view angles of 90°, 45°, 30°, or 15°, with a chosen cross-section, at the target. The 90° opening is the normal position; the three other openings provide 2×, 3× and 6× zooming. Of course, it will be understood that the basic concepts described herein may readily be applied to applications that may involve a different number of different scanning angles as well as different x-ray energies. The concepts can also be applied to the creation of beams that scan at different inclination angles through the target. Referring to FIG. 1, a scanning apparatus is designated generally by numeral 2. An x-ray tube 4 produces a fan beam of x-rays 8 that is emitted perpendicular to the x-ray tube axis 6. An angle-defining unit 10, which is stationary during a beam scan, intercepts the beam 8. The angle-defining unit 10 defines the width and angle of the fan beam, either through operator control or automatically according to external criteria. In a preferred embodiment, the angle-defining unit 10 is a variable slot shown in a simplified version in FIGS. 3B-3E. Angle-defining unit 10 is opaque to the x-ray beam 8 except for the continuously-variable slot 41 (shown in FIG. 3C, by way of example), whose opening angle and pointing direction may be controlled by servo motors. FIG. 3B shows the slot closed, while FIGS. 3C-3E show opening angles of 15°, 60° and 120°, respectively. It should be noted that alternate methods for obtaining the versatility provided by tubes 14 and 34 are within the scope of the present invention. Further versatility can be provided by rotating the entire x-ray producing unit including the x-ray tube itself, as further described below. Angle-defining tubes 14 and 34 can be rotated so that opaque sections of both tubes intercept the exiting beam without shutting down the x-ray tube or the beam-forming wheels. Rotation of the unit 10 allows the sweeping beam to point in any directions inside the maximum fan beam 8 from the x-ray tube. Further versatility in aiming the fan beam can be obtained by rotations of the entire x-ray generator. Angle selector 34, or another element, may serve as an x-ray shutter, whose power-off position is closed, to shutter the x-ray beam to comply with safety regulations. The shutter can be combined with other features such as the filter changer. More particularly, filter tube 150 (shown in FIG. 7) may have multiple angular positions, one of which (such as its “parked” position) may include an x-ray-opaque element serving as a beam shutter. Sweeping pencil beams 70 are formed by a tube 50 with apertures 56 (best seen in FIG. 4) that rotates through the fan beam created by the inner collimators collectively labeled 10. Tube 50 is made of material opaque to the x-rays. The height of apertures 56 together with the width of slot 22 or 24 define the cross-section of pencil beam 70 that exits from the scanner 2. In the preferred embodiment of tube 50, the apertures are slots 56 rather than the traditional holes. The apertures of tube 50 and hoop 170 may be slots in both cases. Slots 56 are arranged in a pattern that is determined by the maximum scan angle and the number of smaller scan angles in the design. The total number of slot apertures is commensurate with 360°. The scan angles are also commensurate with 360°. FIG. 6 shows the pattern in a depiction in which the multi-aperture tube 50 is stretched out as a flat ribbon 80. The aperture slots 84 are dark gray horizontal bars, while the beam position is a light gray ribbon. The slots are arranged in the 4-choice example above: 90°, 45°, 30°, and 15°. Ribbon 80 has a four-fold repeat pattern of 6 slots, making a total of 24 slots along the circumference. The slots are arranged so that each of the 4 angular openings, 90°, 45°, 30° or 15°, can be placed in the beam 70 by moving the tube 50 laterally. Variable Beam Scanner for distant targets. The basic unit 2 (shown in FIG. 1) has applications for inspecting targets that are close enough to the beam-forming aperture for the scanning x-ray pencil beam to create a useful image. An x-ray inspection system, mounted inside a vehicle, and used, for example, to image targets outside the vehicle, requires, in practice, an additional beam forming aperture to usefully inspect targets outside the vehicle. As a rule of thumb, with many exceptions, the beam-forming aperture 175 (in FIG. 7) should not be much further from the target than five times the distance from the x-ray tube's focal spot to the beam-forming aperture; the closer the better. The basic unit 2, shown in FIG. 1, can, in principle, be used for distant objects by making the diameter of the multi-aperture tube 50 as large as necessary. This approach can be useful for low-energy x-ray beams that can be effectively shielded by relatively light-weight hoops. For x-ray energies in the hundreds of keV, which require thick shields of high-Z material, a large radius results in a large rotational moment of inertia, which in turn limits the rotational speed of the beam scanner, and that in turn limits the speed with which the inspection unit can scan the target. The solution to the aforementioned difficulty is to use the multi-aperture tube 50, constructed of x-ray-opaque material, as an initial collimator and add a light-weight, rotating large-diameter outer hoop 170, and another stationary outer width collimator 180 to refine the cross section of the pencil beam. This concept is illustrated in FIGS. 7 and 8. Before describing these figures, the importance of this approach is further elaborated. The rotational moment of inertia of a hoop is proportional to MR2, where M is the mass of the hoop and R is its radius. The mass M required to effectively absorb an x-ray beam of a given energy is itself approximately proportional to the radius R since the thickness of the needed absorber is approximately independent of radius. Thus the rotational moment of inertia of the multi-aperture hoop is approximately proportional to the cube of the hoop's radius. Example: An 8″ OD tube made of ½″ thick tungsten has a rotational moment of inertia that is 25 times smaller that of a 24″ OD tube made of ½″ thick tungsten. (The thicknesses correspond to 20 mean free paths (mfp) of absorption at 180 keV, i.e. an attenuation of ˜109.) Combining the smaller radius tungsten tube with an outer hoop made almost entirely of light-weight material results in a significantly lower moment of inertia of the system, hence a higher maximum rotational speed. FIG. 7 is an exploded view showing the elements of a preferred embodiment for distant targets. Each element is considered in turn. Basic unit 2 is the same as that shown in FIG. 1 except for the addition of an x-ray filter 150 in the form of a thin tube that surrounds x-ray tube 4. An empty slot in one quadrant of the filter tube 150 allows the full x-ray fan beam 8 to emerge. Filter tube 150 can be rotated so that different filters can intercept the fan beam to change the energy distribution or the deposited dose at the target, or to block any emergent beam entirely. For example, a truck may be scanned with an automatically inserted filter 155 to reduce the dose when the passenger compartment is being scanned. The variable filter tube may be omitted if the application does not require changing the energy distribution of the x-ray beam. The maximum opening angle of the scanning beam is defined by the slot collimator 14 with its discrete set of slots or the continuously variable slot 41 shown in FIGS. 3B-3E, whose angular extent is controllable. As above, an inner aperture ring coarsely generates a square flying spot by passing a slot (up to 24 slots per revolution in the examples herein) across the fan-beam slit. After the beam passes out of the inner aperture ring 58, it travels until it encounters a pair of jaws 180 that has an adjustable gap 185. These jaws (which may also be referred to as the “outer width collimator,” or as a “clamshell collimator”) redefine the width of the beam and enable the final spot width to be adjusted if necessary or desired. A hoop 170 rotates in registration with the inner multi-aperture tube 58. The number of the equally-spaced apertures 175 in hoop 170 is equal to the largest number of apertures in the rings 58 of tube 50; in this example, there are 24 slots 175 spaced 15° apart. The length of the slots 175 is larger than the zero-degree slot width of tube 50; that is, the length is greater than any of the slots in the inner multi-aperture tube 50. The outer hoop 170 is preferably supported by duplex bearings on the far side. Various elements of the embodiment depicted in FIG. 7 are shown schematically in FIG. 10, for further clarity. One of various alternate embodiments of the present invention is now described with reference to FIG. 10A. In what might be referred to as a “bundt aperture system, designated generally by numeral 900, multi-aperture tube 280 and the multi-aperture hoop 290 (of FIG. 9) are a single unit 90. Inner apertures 92 and outer apertures 94 co-rotate about x-ray source 4. Adjustable jaws 16 may be disposed between the co-rotating sets of apertures. The bundt configuration, shown in an assembly view, may not have the versatility of the embodiment depicted in FIG. 7, and it may have a larger rotational moment of inertia, but it does have the mechanical advantage of simplicity in changing the sweeping angle, from say 90° to 15°, by step-wise translation of the bundt 90 and its drive motor, which is coupled to shaft 300 (shown in FIG. 7). Different scan angles are selected by translating the bundt scanner so as to register a selected plane of bundt slots with the plane of the fan beam. In accordance with yet another embodiment of the present invention, the bundt and drive motor may remain fixed while the rest of the unit is translated. The embodiments described above are but a few of the permutations that embody the basic concept of an operator-controlled, multi-slot collimation coupled with a multi-aperture pencil-beam creator. For example, the three basic components—width collimator 14, angle collimator 34 and multi-aperture unit 50—can be permuted in any of the six possible configurations, the choice being made on the basis of application and mechanical design considerations. One alternate configuration would have the x-ray beam traversing unit 34 first, then unit 14 and finally unit 50. Another has the x-ray beam traverse the unit 50 first, then unit 14 and then unit 34. Similarly, the beam may traverse the aperture ring 170 and then the variable collimator 180. It should be noted that among the variations that retain the fundamental concepts of zooming with variable beam resolution is the reliance of the variable angle collimator 34 to act also as the first width collimator, thus eliminating the separate width collimator 14. This simplification comes at a cost of some versatility (e.g. the number of opening angles are more restrictive) but may be useful for some applications, in particular when using the outer tube configurations of FIG. 7 or FIG. 10B in which the width of the beam at the target is controlled by the variable gap 180 in FIG. 7 or 16 in FIG. 10B. Filter wheel 150 may provide a variable filter to change the radiation dose delivered to the target or to modify the energy distribution of the x-ray beam. Filters may also be incorporated in the slots of the variable angle tube 34 to place filters in the 45°, 30° and 15° slots that progressively increase the filtration of the lower energy components of the x-ray beam, to reduce the dose without significantly affecting the higher energy components of the x-ray beam. It should also be noted that filter wheel 150 may be omitted, for example, for applications in which the inspection is always carried out on inanimate objects. Additionally, filters may be incorporated into a subset of the slots, such as into alternating slots, for example. In still another configuration, hoop 50 has a larger number of apertures such that multiple apertures are illuminated by fan beam 8, producing two pencil beams 70 that sweep in alternation through the target at different angles to obtain a stereoscopic view of the interior. This application uses a wide fan beam and an appropriate multi-aperture unit and slot collimators. Improving an image by improving the vertical resolution of the scanning pencil beam. In the discussion, supra, with reference to FIG. 7, slots 175 of rotating outer hoop 170 are all the same height, h, as depicted in FIG. 11A for one set of slots for the four different scan angles, 90°, 45°, 30° and 15°, in the example of a preferred embodiment. However, to change the height resolution, in accordance with alternate embodiments of the present invention, the slot heights in the outermost rotating aperture hoop must be changed, as illustrated by the following three examples. FIG. 11B shows an additional ring 102 of half-height slots added to the 15° ring of apertures. The operator can select either the 15° or the 15s° lateral position; the latter reducing the height of the beam at the target by a factor of two. The width the slots in the aperture hoop has been increased by about 3 mm to accommodate the extra ring of apertures. In a preferred embodiment, 4 rings of apertures are maintained, but the heights of all the slots in the 15° ring are halved. This mode uses half of the six-fold gain in areal intensity of x-rays on the target, compared to the 90° view, to improve the vertical resolution by a factor of 2. In another embodiment of the invention, rings of apertures of different heights are added to the 90° viewing angle. That allows automated changes in height resolution as a function of the target distance. A target passing at a distance of 5 ft. might be most appropriately scanned with the aperture ring that has 1-mm slot heights, while a target passing at 3 feet might be more appropriately scanned with a 0.5-mm resolution. It should be clear that, within the practical constraints of weight and size, more than one of the above examples can be accommodated on a single rotating hoop. Two Independent Views with different vertical resolutions. Embodiments of the present invention may also be used to simultaneously obtain two (or more) images each with its own vertical resolution. FIG. 11C shows a slot pattern for obtaining two separate 15° views. Alternate 15° sweeps form one image with a vertical resolution h, and another image with a vertical resolution h/2, or smaller. Improved spatial resolution can be essential for resolving issues of interpretation in the image. Dual Energy. In other embodiments of the present invention, filters may be placed in all, or in a subset of, the slots of one of the arrays of slots, with either the same or different vertical heights, to change the x-ray energy distribution impinging on the target. In the slot configuration of FIG. 11C, a filter in the alternate slots of the 15° scan can produce a separate view that minimizes the lower-energies that inspect the target and thus enhances the image of deeper penetrating radiation. If all the slots in the 15° scan have the same height, a filter placed in alternate slots may yield new information, including material identification, when the filtered image is compared with the unfiltered energy image. The two-view or dual-energy modes are achieved to particular advantage in accordance with the present invention. The aperture hoop 170, rotating at the nominal speed of 3600 rpm, makes a 15° scan every 680 microseconds. A target vehicle, moving at the nominal speed of 5 kph, travels ˜1 mm during that scan, which is much smaller than the beam size at the nominal target distance of 5 feet. As a consequence, the two views will be within 10% of overlap registration. The above calculation indicates that even when no provision is made to change the height of the pencil beam, the slots in the beam-resolution defining hoop should not have the same heights. The correct heights will depend on the application. Horizontal resolution. For distant targets, where two concentric rotating hoops (50 and 170) of apertures are employed, the horizontal resolution is determined by the slit width 185 of the outer slot collimator 180. The plates that form the width collimator are controlled by servo-motors. In a preferred embodiment, the width collimator is in the form of a clamshell whose jaw opening is controlled by a single motor near the clamshell's hinge. The width may be controlled by the operator or may be automatically changed as a function, for example, of the relative speed of the inspection vehicle and the target. For inspection of close targets it may not be useful or desirable to use the outer hoop 170 and the outer slit 125. In that case the horizontal resolution would normally be controlled by changing the width of the 90° slot 24 of the inner tube 14, though other methods will be apparent to those familiar with mechanical design. The width of slot 24 for the preferred embodiments is nominally 2 mm wide or less, though any slot width falls within the scope of the present invention. The variable width collimator may also be designed to minimize the non-uniform intensity of the fan beam across the angular range of the fan. The fan beam from an x-ray tube typically exhibits a roll-off in intensity away from the central axis. For a wide-angle fan beam, with angular extent of 90° or more, the roll-off in intensity from the central ray can be 30% or more. In FIGS. 8A and 8B, the variable width collimator 180 has a non-uniform gap 185. The gap width increases away from the midpoint. For clarity the gap is exaggerated in the depiction. The shape of the opening can be tailored to the angular distribution of the x-rays from the x-ray tube; such data is generally supplied by the tube manufacturer. Dwell Control. Prior discussion has concentrated on the aspect of the zoom feature, taught herein, which allows for changing the viewing angle while preserving the fluence incident on the inspected target. A concomitant aspect of the zoom feature is that the variation with zoom of the number of scans per unit time has its own advantages and applications. When used without changing the collimation, but especially when combined with the variable collimator, the inspecting beam can be made to spread evenly over the target so as to minimize undersampling and oversampling. Undersampling occurs when the beam moves too quickly to allow resolution of a pixel as defined by the beam cross section, thereby resulting in missing information. The combination of variable viewing angle and variable scans per unit time (or, equivalently, dwell time per pixel) is a powerful way to obtain higher throughput with minimum undersampling. In preferred embodiments of the invention, the highest number of scans per revolution for the desired angle of scan is used, and the collimator is opened to the largest acceptable spatial resolution. Oversampling, which is not so serious a problem as under-sampling, can be traded for better resolution. When transverse motion of the source relative to the target is slow, the collimator slot may be narrowed and the integration time diminished to provide even sampling with improved resolution. Offset Hoop. U.S. Provisional Application Ser. No. 61/533,407 introduces the concept of backscatter x-ray inspection (BX) by a scanning pencil beam of x-rays produced by an electron beam whose the axis is offset from the axis of rotation of a rotating ring of apertures that forms the scanning beam. Offsetting a source behind the axis of rotation of an aperture hoop had been known. The novel forward-offset concept has inherent advantages, as in the application of x-ray inspection portals, where its effectiveness for faster scanning at close geometries allows a greater throughput of inspected vehicles. In accordance with embodiments of the present invention, components of angle selection and variable-beam resolution are added to forward offset scanning to significantly increase the system's versatility. In one embodiment of the present invention, a forward-offset portal system that inspects vehicles from both sides and the top, can, on the fly, change the angle rate of scan per revolution, as well as the scan resolution and the radiation exposure, to optimally inspect either trucks or cars. An effective portal inspection system of cars and trucks may use the x-ray backscatter technique (BX) to scan from both sides and from the top, as the vehicles pass through. The x-ray beams from the three BX systems are interleaved to prevent cross talk. That requirement places a severe limitation on the speed of the inspected vehicles. For example, a standard one-sided BX system that uses a 3-spoke aperture hoop, when applied to a three-sided inspection, limits the truck speed to less than 4 kph. To overcome this limitation, U.S. Provisional Application 61/533,407 teaches offsetting the x-ray tube axis forward of the axis of the aperture hoop that forms the pencil beams. The forward offset concept allows wide-angle scans of trucks with a six-aperture hoop, and a nine- or even a 12-aperture hoop for scanning smaller vehicles. To increase the versatility of the forward offset concept, embodiments of the present invention in which the axes of the x-ray tube 4 and of the hoop 114 of rotating apertures coincide, as now described with reference to FIG. 12. The scan angle of fan beam 110 is defined by an angle selecting ring 111 that may be a variable slot or a ring with two or more fixed slots. The outer hoop 114 contains the beam-forming rings of apertures 115, each ring of apertures matches a given selected scan angle. A wide-angle collimator 113 confines the beam from the angle selector 111 to a single ring 115 of apertures. To co-plane the beam 110 from the angle selector with the appropriate ring of apertures, the x-ray tube 4 plus angle selector 111 plus collimator 113 are on a movable positioning platform (not shown), which serves to move those elements in a direction into the plane depicted in the cross-sectional view. The system may include the following components: a. an x-ray tube 4, well-shielded by a tube shield 112, where the x-ray tube is offset from the center of a rotating hoop, and produces a fan beam 110 of x-rays that emanates approximately perpendicular to the x-ray tube's beam axis. b. a rotatable angle-selector ring 111, with a variable angular slot or with selectable angular slots, is coaxial with x-ray tube 4. The ring 111, typically made predominately of lead, is impenetrable to the x-rays except for the slots that define the scan angles available for inspection. To optimize the scanning of both trucks and cars, there may be two or more slots to accommodate the different heights of trucks, SUVs and cars. The closed position of the angle-selector ring, which is the default position when the power is off, is the x-ray shutter for the system. c. an outer hoop 114, made of material that effectively blocks all x-rays except for those that pass through equally-spaced apertures 116, forms the pencil beams 70 of x-rays. The rotational axis of the hoop 117 is offset from the axis of the x-ray tube 4 by a distance D (shown in FIG. 13). The apertures may be arranged in separate rings. The number of apertures in a given ring must be commensurate with 360°; e.g. six apertures spaced 60° apart. Each ring of apertures corresponds to one of the opening angles in the angle-selector ring. d. a collimator (typically, a clamshell collimator) 180 (shown in FIGS. 7 and 8A-8B) between the collimator ring and the outer hoop co-planes the fan beam to the appropriate ring of apertures for the selected angular scan. The azimuthal opening of the collimator is fixed to accommodate the widest scan angle. The axial opening angle of the collimator controls the x-ray beam's axial resolution as well as the radiation dose on the target. A separate filter ring 150, coaxial with the x-ray tube, with angular segments of different absorbers to filter the x-ray beam either to control the radiation dose on the target and/or to control the energy spectrum of the x-rays on the target. X-ray tube 4, angle selector 111 and clamshell collimator 180 are mounted on a platform that moves, under motor control, to place the fan beam plane in the plane of the aperture ring appropriate for the selected angle. It should be noted that in some applications the rotating outer hoop translates, the other components are stationary. One of the innovations in this invention is the use of rectangular slots instead of round or oval holes for purposes of chopping a beam. As used herein, the terms “slot,” “aperture,” and “through-hole” may be used interchangeably. The chopped beam may be a beam of particles having mass or of massless particles, including electromagnetic radiation over a specified wavelength range. In accordance with various embodiments of the present invention, a chopper, such as aperture wheel 170 (shown in FIG. 10B), interrupts a beam of particles 70 characterized by a propagation direction. The chopper has a solid portion, which is an obscuring element substantially opaque to passage of the particles in the propagation direction. Aperture wheel 170 has one or more through-holes 175 (shown in FIG. 10B) in the obscuring element adapted for passage through the obscuring element of particles in the propagation direction. Aperture wheel 170 is spun by an actuator (not shown to interpose the through-holes 175 in the beam on a periodic basis. The innovation of rectangular chopper apertures has two independent advantages over traditional round or oval apertures. First, is its usefulness in a single ring of apertures. The size of the pencil beam determines its spatial resolution or point spread function. Oval or circular apertures result in fixed resolutions that are difficult to change precisely. Slot apertures have fixed angular widths but variable axial lengths (dimension parallel to the beam axis) controlled by the clamshell collimator opening. The size of the beam spot can be precisely controlled by the collimator opening and the integration time of the pixel. The second advantage is evident when the outer aperture hoop has two or more rings of apertures, i.e., zooming ability, each ring with a different number of apertures. Round or oval apertures strongly limit the ability to vary the size of the pencil beams. The use of slots, as exemplified in FIGS. 11A-11C, has both advantages of manufacturability and greater range of the axial width for a given length of slot. The azimuthal widths of the slots are typically the same across all the slots, although they need not be equal, within the scope of the present invention. The slot lengths (parallel to the x-ray tube axis) preferably have a pattern that is determined by the opening angles of angle-selector ring 111. In a 3-angle selector ring, for example, one ring has 3 apertures spaced 120° apart; an adjacent ring has 6 apertures spaced 60° apart; a third adjacent ring has 9 apertures spaced 40° apart. The pattern of slots is: 3 long slots at 0°, 120°, and 240° for the scan angles that are common to the 3 modes, and 12 short slots for scan angles that are unique to their mode. The slotted pattern has the significant advantage over round or oval apertures that the axial extent of the beams can be quantitatively adjusted by the clamshell collimator to change the beam resolution and/or adjust the radiation dose. In addition to rectangular through-holes, a chopper in accordance with embodiments of the present invention may also have biconical (“hourglass”) or conical through-holes, as shown, respectively, in FIGS. 17A-17B, and 17C-17D, respectively. Such shapes advantageously serve to maximize beam throughput in the face of lateral beam offset. In embodiments employing more than one ring of apertures, each ring of apertures should have its own unique conical angles. Slotted apertures preferably have different slopes along the slots. The offset scanner concept described herein may be applied advantageously to both forward and backward offsets. For heuristic reasons, the offset scanner is describe herein primarily in terms of an offset in the forward direction (i.e., toward the target, as might be employed in portal systems for inspecting large and small vehicles, however it is to be understood that the relative position of the tube axis and hoop axis does not limit the scope of the invention as claimed. FIG. 13 is a schematic drawing depicting the geometry of the system. The tube is forward-offset by a distance D from the axis of the hoop of radius R. The fan beam exits to the right; the center of the fan is at 0°. Apertures 116 along the rim are equally spaced, i.e., commensurate with 360°. Six apertures, spaced 60° apart are shown in FIG. 13. Aperture 1 is at an angle θ with respect to the hoop axis, and an angle φ with respect to the tube axis; φ>θ. The relationship between φ, θ, R and D is given by: tan ⁢ ⁢ ϕ = sin ⁢ ⁢ θ cos ⁢ ⁢ θ - D R . ( 1 ) In the case of a backward offset, D/R is added to cos θ in the denominator rather than subtracted. FIG. 14 is a graph of the scan angle (or, equivalently, opening angle, 2φ), as a function of the ratio of the forward offset D to the radius R, for 3, 4, 6, 8, 9, and 12 scans per revolution (s/r) of the aperture tube. The number of scans per revolution (or, s/r values) is determined by the angular spacings, 20, between apertures, which are 120°, 90°, 60°, 45°, 40° and 30° respectively. For large values of D/R, φ can become negative, i.e., unphysical. (There are no unphysical values of D/R for backward offsets.) Within obvious constraints, the offset of the axis of x-ray tube with respect to the axis of the rotating outer hoop can be any direction and can have a wide range of values, including zero. FIG. 14 shows the scan angles obtainable for aperture rings of 3, 4, 6, 9 and 12 apertures. A single revolution of the wheel allows the beam to scan 12 times over an angular range of 90 degrees (D/R=0.7), for example. That spreads the beam intensity over 1080 degrees of scan in one revolution of the aperture hoop. At 6 times per revolution of 120 degrees spreads the beam intensity over 720 degrees of scan in one revolution. This feature, by itself, is a potent tool for reducing undersampling. Undersampling is an inevitable bottleneck to increasing maximum vehicle speeds to increase throughput. Until now, higher rotational speeds have been sought in order to achieve higher throughput, however the present invention advantageously provides requisite additional fluence without resorting to higher rotational speeds. Different D/R values can be used in a single scanning system. In the most general case, the x-ray tube plus a continuously variable angular selector can be moved both radially and axially to produce a continuously variable anglular scan. In practice, however, the D/R value is typically fixed. That still gives the system considerable flexibility to optimize the x-ray beam flux on the target; i.e., to obtain maximum utilization of the fluence. The following examples illustrate. The fan beam from the x-ray tube is collimated to have an azimuthal extent of 120° and an axial width of ˜2°. The x-ray tube is forward offset 24 cm from the center of a 60 cm diameter hoop (D/R=0.4). When trucks are inspected, the 4-aperture ring is selected and the beam opening angle selector is set at 120°. (A 120° beam is presently the practical limit for available x-ray tubes.) When cars/SUVs are inspected, the 8-aperture ring, and 72° slot are selected. The interleaving requirement results in 2 scans per revolution from each side of a truck and 4 scans per revolution from each side of a car. The x-ray tube is forward offset 36 cm from the center of a 60 cm diameter hoop (D/R=0.6). FIG. 14 shows that a 124° scan can be obtained 6 times per revolution and a 70° scan can be obtained 12 times per revolution of the aperture ring. The 124° is effective for scanning sides of trucks while the 70° scan is sufficient for scanning through the top of trucks, and sufficient for use from every side of cars and SUVs. Cars can be scanned 4 times per revolution from all three sides. Trucks can be scanned 2 times per revolution from the sides and 4 times per revolution from the top. An aperture hoop rotating at 3,000 rpm makes one revolution in 0.02 seconds. During that time, a vehicle traveling at 12 kph moves 66 mm The resulting under-sampling with one scan per revolution at an acceptable beam resolution results in unacceptable inspections at 12 kph. As a consequence, speeds through present three-side portal inspections are limited to ˜4 kph because there is only one sweep per revolution from each side, Examples 1 and 2 above show that forward offset allows trucks to be scanned twice as rapidly from the sides and 4 times as rapidly from the top. Cars can be scanned 4 times per revolution from every side. These additional scans per revolution of the beam-forming wheel, together with an adjustable beam width by means of the clamshell collimator, allows trucks to be effectively inspected at 12 kph, and cars inspected at still higher speeds. In accordance with various embodiments of the invention, rings of individual round or oval apertures may be used. Slots, however, when used with the clamshell collimator, are preferable, especially when multiple rings are used. FIG. 6 shows the pattern of 12 slots for Example 2 above. 6 of the slots, as 0°, 60°, 120, 180°, 240 and 300° are double width slots, while 6 slots at 30°, 90°, 150°, and 210°, 270° and 330° are single width slots. Either the 6-aperture ring or the 12 aperture ring can be selected; the 12 aperture ring is depicted in the figure. The clamshell collimator can change the aperture width from fully closed to 5 mm wide in that example, to cover a wide range of beam sizes and delivered dose. Rotation of the X-ray Tube. In accordance with further embodiments of the present invention, provision is made for rotation of x-ray tube 4 about its axis 6 (shown in FIG. 1). Rotatability of the x-ray tube may advantageously increase the angular volume subject to inspection by the system, and may additionally be used to improve the beam resolution, as now described with reference to FIGS. 15A-15C, and 16. As shown in the perspective view of FIG. 16, x-ray tube 4 together with the angle selector 113, filter ring 150, and clamshell collimator 180 are rotatably mounted on a platform 5 that moves linearly to co-plane the selected fan beam with the appropriate ring of apertures. The fan beam 8 with an angular extent 15, typically provided by the tube's manufacturer, constrains the ability to change the usable direction and extent of that beam. For example, in the standard configuration in which the 120° fan beam from the x-ray tube is emitted horizontally, the basic scanning apparatus 2 can only manipulate the x-ray beam within that space. Advantages of a rotatable platform to versatile scanning systems in accordance with the present invention are now described. An important application of the rotatable platform is to increase the angular range of backscatter inspection. For example, the maximum height that can be inspected in conventional portal systems using a 120° fan beams is about 14 feet. Higher vehicles cannot be fully inspected. The addition of a rotatable platform corrects that problem, allowing a second inspection of the top portion of a vehicle or targets that are 20 feet high or more. Another important application is to improve the spatial resolution of a secondary inspection of a small area of a vehicle. For example, a suspect area, found in a 120° scan, can be closely inspected by zooming into the suspect area with a 15° scan. The nine-fold gain in flux density will significantly improve the image of a suspect area. If, however, the suspect region is in the outer reaches of the 120° fan beam from the x-ray tube, the spatial resolution of the beam will be far from optimum and the full advantage of the zoom will not be realized. The resolution can be improved substantially by rotating the platform so that the axial ray of the scanning beam is centered on the suspect region. The sequence of steps is shown schematically in FIG. 15A to 15C, for a suspect region at the extreme of a 120° scan. In FIG. 15A, the 15° scan, defined by the scan-angle selector 113, is centered on the beam axis of the 120° fan beam 7 from the tube. The pencil beam emanates from a small, symmetric focal spot and the quality of the pencil beam is the best it can be for that x-ray tube. Without a rotatable platform, the suspect area is inspected with a 15° scan by rotating the two arms of the scan-angle selector 113 counter-clockwise 52.5°, using actuators 9, to the configuration shown in FIG. 15B. The quality of the pencil beams, however, has worsened because the effective focal spot has grown substantially. FIG. 15C shows the same geometry for a 15° scan of the suspect area, now formed by rotating the platform counter-clockwise 52.5° the beam axis from the x-ray tube is along the center of the 15° scan, and the beam quality has been optimized. Improvement in resolution due to centering the inspected object in the x-ray tube emission beam can be further understood as follows. The spatial resolution of the backscatter image is determined by the cross-section of the x-ray beam, and that size is constrained by the focal spot size of the electrons on the anode. The typical x-ray tube (operated in a reflection configuration) focuses a line source of electrons (from a coil filament) as a line onto the anode, which is tilted with respect to the electron beam. The effective size of the focal spot depends on the viewing angle. For example, a line source of x-rays from an anode, tilted 15° with respect to the electron beam, is 1 mm high by 4 mm. The line source of electrons spreads the heat load on the anode, allowing for higher power dissipation and hence higher x-ray flux. The focal spot size of commercial x-ray tubes is specified only for the axial ray direction; in this example, the width of the focal spot is 1 mm and the effective height is also ˜1 mm. The focal spot size at the extreme of a 120° fan beam, however, is a line source 1 mm wide by 4×sin 60°=3.5 mm long. Moreover, the beam quality is further diminished by the increased absorption of the x-rays in the anode itself, the so-called heel effect. Rotating the axial ray from the x-ray tube into the center of the zoom angle effectively eliminates both these effects. Degradation of resolution with angular displacement from the center of the scan constrains the acceptable angular spread of the scanning pencil beam. Given that constraint, it is nonetheless often important to obtain the best spatial resolution for inspecting a specific target area that is not close to the central axis. To solve this problem the x-ray tube may be rotated together with the beam collimation so that the central axis of the x-ray beam is pointing in the direction of the desired target area. Operator and Automated Features. It is to be understood that the focusing operation may be performed by an operator, on the basis of an indicated suspect area that constitutes a portion of the inspected object. The angular opening of the scan, the direction of the scan, the beam's spatial resolution, and the number of scans per revolution can each or in combination be changed by the operator or by automation on the basis of the target height, and target distance from the beam chopper assembly, and relative speed of the target with respect to the assembly. The identical apparatus may thus advantageously be employed for performing a primary rapid scan, followed by a secondary, high-resolution, small-area scan of a suspect area found in a first, rapid scan. For illustration, the operator may focus on a small, suspect area of a target that has first been scanned with a broad beam. A 3-aperture ring may produce a 120° wide scan of a large vehicle. The collimators of the angle selector may then be closed to form a horizontal 15° fan beam, with good resolution since its source is 1 mm×1 mm, in this example. The collimators may be rotated together through 52.5° to center the 15° fan beam onto a specified portion of the inspection target. The x-ray beam is now more concentrated by a factor of 6 compared to the 120° beam, but the effective source size is now close to 1 mm×3.5 mm and much of the concentration gain has been lost. The tube/collimator may be rotated so that the central axis of the beam points along the center of the 15° sweep. The inspection is now carried out with optimum resolution. The rotation of the x-ray tube reduces the degradation of beam resolution at angles far from the axial direction. In some applications it may be advantageous to accept the degradation in resolution and increase the beam width to obtain as much fluence as possible with that resolution. One method for doing so is to make the gap 185 of clamshell collimator 180 in an hour-glass shape, as shown in FIGS. 8A-8B, with the minimum opening of, for example, 3 mm in the center (for the central rays), increasing as a function of angle to either side of center. It should be borne in mind that maximizing the throughput does not equalize the flux across the scan angle. When the finite size of the focal spot is taken into account, the intensity of the x-ray beam may vary by as much as a factor of 2 between its center and the extremes of +−55 degrees. The shaped collimator gap serves to equalize flux across the scan angle. The embodiments of the invention described herein are intended to be merely exemplary; variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in any appended claims. In particular, single device features may fulfill the requirements of separately recited elements of a claim.
039473180	description	Referring now to FIG. 1, the inventive liquid-metal-cooled reactor 1 comprises two rotatable plugs 2 and 3, one of them /plug 2/ being arranged in the other /plug 3/ and having a hole 4. The plug 2 may be provided with additional holes. The reactor 1 also comprises a housing 5, a cover /not shown/, a core with fuel element stacks 6 washed by a coolant 7, and a recharging mechanism 8 with a guide tube 10 adapted to move through the hole 4 of the rotating plug 2 with the aid of a plug 9. The guide tube 10 accommodates a rod 11 with a gripper 12 for gripping the stack 6 and removing it from the core into the guide tube 10. The reactor 1 further comprises a device for detecting stacks 6 with leaky fuel elements. The guide tube 10 serves as a sampler in the detecting device, which makes for consecutive sampling of the coolant from each stack 6. Provided in the wall of the guide tube 10 is a duct 13 for feeding an inert carrier gas into the sampler which duct communicates with the inner space of the guide tube 10 through a hole 14 made in the wall of the tube 10 level with the bottom end 15 of the stack 6 transferred from the core of the reactor 1 into the tube 10. The duct 13 for feeding the inert carrier gas also communicates with a doser 16 of a known design through a pipe 17. A duct 18 for evacuating the inert carrier gas together with the gases evolved from a coolant sample from the sampler is provided in the wall of the guide tube 10 and communicates with the inner space thereof through a hole 19 made in the wall of the tube 10 above level B of the coolant 7 in the tube 10 /C is the coolant level in the vessel of the reactor 1/. The other outlet of the duct communicates through a pipe 20 with means 21 for measuring the radioactivity of the outgoing gases, preferably in the form of a conventional instrument for measuring the concentration of a radioactive gas. Turning now to FIG. 2, the modified inventive reactor 22, as compared to the reactor 1 of FIG. 1, comprises a duct 23 for feeding the inert carrier gas provided in the wall of the rod 11 and communicating with the inner space thereof through a hole 24 made in proximity to the end face of the rod 11. Fitted on the bottom end of the latter is a sealing member 25 shutting off the coolant flow from the stack 6. Made above the coolant level B in the tube 10, in the wall of the rod 11, are a plurality of holes 26 through which the inner space of the rod 11 communicates with the hole 19 in the guide tube 10 to direct the inert carrier gas together with the accumulated gas through the duct 18 and the pipe 20 to the means 21 for measuring the radioactivity of the gas. The liquid-metal-cooled reactor provided with a device for detecting stacks with leaky fuel elements operates as follows. The detection of stacks with leaky fuel elements during the recharging of fuel element stacks is ensured by the structure of the liquid-metal-cooled reactor 1 shown in FIG. 1. The tube 10 of the recharging mechanism 8 is positioned, by means of the rotatable plugs 2 and 3, above the fuel element stack 6, then lowered by means of the drive 9 towards the cap of the stack 6. The gripper 12 grips the cap and, as the rod 11 is moved up, the stack 6 is introduced into the tube 10. The inert carrier gas is fed under a pressure exceeding that of the coolant 7 from the doser 16 through the pipe 17 and duct 13 into the inner space of the tube 10 containing the coolant 7. The inert carrier gas makes the coolant 7 bubble in the space, thus degassing it and entraining the radioactive gases from leaky fuel elements of the stack 6. Then, the gas mixture passes through the hole 19, duct 18 and pipe 20 to the measuring means 21. To avoid introducing the stack 6 into the tube 10, use should preferably be made of a reactor embodied as shown in FIG. 2. The tube 10 is positioned, by means of the plugs 2 and 3, above the stack 6 being controlled, and the rod 11 is lowered, by means of the drive /not shown/ until the rod is tightly fitted on the stack 6 by means of the sealing member 25. The inert carrier gas is fed under a pressure exceeding that of the coolant 7 from the doser 16 through the pipe 17 and duct 23 into the inner space of the guide tube 10, the pressure of the inert carrier gas being sufficient to maintain the level B of the coolant 7 in the tube 10. After the accumulation of gases in the inner space of the tube, the pressure of the inert carrier gas is brought down, the coolant is bubbled and the accumulated radioactive gas is evacuated. Then, the inert carrier gas together with the radioactive gases evolved from the sample of the coolant 7 are also delivered to the measuring means 21 through the inner space of the rod 11, holes 26 and 19, duct 18 and pipe 20. If the measuring means 21 indicates that the concentration of radioactivity has reached a critical level, the stack 6 is removed from the core of the reactor 22. To do this, the rod 11 is lifted by means of its drive, the tip 25 is detached from the stack 6, the gripper 12 is made to grip the cap of the stack 6, and the rod 11 together with the griper 12 and the stack 6 are directed into the guide tube 10 to be extracted from the reactor 22. The inventive reactor with a device for detecting stacks with leaky fuel elements permits of consecutive checks, upon stopping the reactor, of all stacks with the ultimate aim of locating stacks with leaky fuel elements without removing them from the reactor core, as well as easy extraction (with the aid of conventional means and devices) of the faulty stacks from the reactor. If necessary, the stacks may be checked at the same time with their recharging, both when the coolant is stationary and when circulated by force. Thus, the time required to shut down the reactor to locate stacks with leaky fuel elements is minimized, thereby allowing considerable savings to be made. By applying the present invention to a reactor known as the type BR-5, it has become possible to reduce the shut-down time required to check a fuel element stack to one hour /from six hours with the old construction/, and in the case of another reactor, known under the designation BOR-60, to half an hour. Moreover, this method of detecting faulty stacks has proved highly reliable /in the case of the latter reactor type, not a single faulty stack was missed even though a single measurement was taken/. The present invention assures total reactor and personnel safety.
	claims	1. A method, comprising the steps of:positioning a solid mixture including copper-67 and zinc-68 in a sublimation apparatus, the sublimation apparatus including:a heating element,a sublimation vessel comprising quartz disposed adjacent the heating element such that the heating element heats a portion thereof,a collection vessel removably disposed within the sublimation vessel, anda crucible containing the solid mixture therein and being configured to position the solid mixture in fluid communication with the collection vessel; andheating the solid mixture and thereby forming a metal vapor having greater than 90% by weight zinc-68,wherein the metal vapor flows to and condenses within the collection vessel and a solid residue comprising at least a portion of the copper-67 remains in the crucible. 2. The method of claim 1, wherein the zinc-68 of the heated solid mixture has a greater vapor pressure that that of the copper-67 of the heated solid mixture. 3. The method of claim 1, further comprising placing and maintaining the sublimation apparatus under a vacuum during the step of heating the solid mixture. 4. The method of claim 1, further comprising, after the step of heating the solid mixture, backfilling the sublimation vessel with an inert gas and raising a pressure of the sublimation apparatus. 5. The method of claim 4, further comprising, after the step of backfilling the sublimation vessel with an inert gas, mixing the solid residue remaining in the crucible with an aqueous organic acid to form an acidic solution comprising metal ions including copper-67. 6. The method of claim 5, further comprising purifying the copper-67 of the acidic solution. 7. The method of claim 1, further comprising recycling zinc-68 of the metal vapor as a metal target for production of additional copper-67. 8. The method of claim 1, the collection vessel comprising graphite.
	summary
058964320	summary	BACKGROUND OF THE INVENTION The present invention relates generally to nuclear reactors, and, more specifically, to electrochemical corrosion potential sensors. A nuclear power plant includes a nuclear reactor for heating water to generate steam which is routed to a steam turbine which extracts energy therefrom for powering an electrical generator to produce electrical power. The nuclear reactor is typically in the form of a boiling water reactor having suitable nuclear fuel disposed in a reactor pressure vessel in which water is heated. The water and steam are carried through various components and piping which are typically formed of stainless steel, with other materials such as alloy 182 weld metal and alloy 600 being used for various components directly inside the reactor pressure vessel. It has been found that these materials tend to undergo intergranular stress corrosion cracking depending on the chemistry of the material, degree of sensitization, the presence of tensile stress, and the chemistry of the reactor water. By controlling any one or more of these critical factors, it is possible to control the propensity of a material to undergo intergranular stress corrosion cracking. However, it is known that intergranular stress corrosion cracking may be controlled or mitigated by controlling a single critical parameter called the electrochemical corrosion potential of the material of interest. Thus, considerable efforts have been made in the past decade to measure the electrochemical corrosion potential of the materials of interest during the power operation of the reactor. This, however, is not a trivial task because the electrochemical corrosion potential of the material varies depending on the location of the material in the reactor circuit. For example, a material in the reactor core region is likely to be more susceptible to irradiation assisted stress corrosion cracking than the same material exposed to an out-of-core region. This is because the material in the core region is exposed to the highly oxidizing species generated by the radiolysis of water by both gamma and neutron radiation under normal water chemistry conditions, in addition to the effect of direct radiation assisted stress corrosion cracking. The oxidizing species increases the electrochemical corrosion potential of the material which in turn increases its propensity to undergo intergranular stress corrosion cracking or irradiation assisted stress corrosion cracking. Thus, a suppression of the oxidizing species is desirable in controlling intergranular stress corrosion cracking. An effective method of suppressing the oxidizing species coming into contact with the material is to inject hydrogen into the reactor water via the feedwater system so that recombination of the oxidants with hydrogen occurs within the reactor circuit. This results in an overall reduction in the oxidant concentration present in the reactor which in turn mitigates intergranular stress corrosion cracking of the materials, if the oxidant concentration is suppressed to very low levels. This method is called hydrogen water chemistry and is widely practiced for mitigating intergranular stress corrosion cracking of materials in boiling water reactors. When hydrogen water chemistry is practiced in a boiling water reactor, the electrochemical corrosion potential of the stainless steel material decreases from a positive value generally in the range of 0.050 to 0.200 V(SHE) under normal water chemistry to a value less than -0.230 V (SHE), where SHE stands for the Standard Hydrogen Electrode potential. There is considerable evidence that when the electrochemical corrosion potential is below this negative value, intergranular stress corrosion cracking of stainless steel can be mitigated and the intergranular stress corrosion cracking initiation can be prevented. Considerable efforts have been made in the past decade to develop reliable electrochemical corrosion potential sensors to be used as reference electrodes which can be used to determine the electrochemical corrosion potential of operating surfaces of components. These sensors have been used in more than a dozen boiling water reactors worldwide, with a high degree of success, which has enabled the determination of the minimum feedwater hydrogen injection rate required to achieve electrochemical corrosion potentials of reactor internal surfaces and piping below the desired negative value. However, the drawback of these sensors is that they have a limited lifetime in that some have failed after only three months of use while a few have shown evidence of operation for approximately six to nine months. Recent experience with two boiling water reactors in the United States has shown that the two major modes of failure have been the cracking and corrosive attack in the ceramic-to-metal braze used at the sensing tip, and the dissolution of the sapphire insulating ceramic material used to electrically isolate the sensing tip from the metal conductor cable for platinum and stainless steel type sensors. The electrochemical corrosion potential sensors may be mounted either directly in the reactor core region for directly monitoring electrochemical corrosion potential of in-core surfaces, or may be mounted outside the reactor core to monitor out-of-core surfaces. However, the typical electrochemical corrosion potential sensor nevertheless experiences a severe operating environment in view of the temperature of the water well exceeding 88.degree. C.; relatively high flowrates of the water up to and exceeding several m/s; and the high nuclear radiation in the core region. This complicates the design of the sensor since suitable materials are required for this hostile environment, and must be suitably configured for providing a watertight assembly for a useful life. As indicated above, experience with the typical platinum electrochemical corrosion potential sensor has uncovered shortcomings that lead to premature failure before expiration of a typical fuel cycle. Accordingly, it is desired to improve the design of electrochemical corrosion potential sensors for improving its useful life. SUMMARY OF THE INVENTION An electrochemical corrosion potential sensor is fabricated by initially joining an electrical conductor to a sensor tip. An electrical cable is joined to the tip conductor. Ceramic powder is fused under heat around the tip conductor to form an integral annular electrically insulating band therearound to insulate the tip from the cable. The insulating band may be formed by plasma spraying, or it may be molded and sintered to seal it to the tip and conductor without brazing. In the preferred embodiment, the band is formed of a chemically-stabilized-zirconia, such as yttria-stabilized-zirconia or magnesia-stabilized-zirconia. The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is more particularly described in the following detailed description taken in conjunction with the accompanying drawings.
	claims	1. A nuclear fuel assembly, comprising:a plurality of nuclear fuel pins;a fuel duct configured for insertion into a nuclear reactor vessel, including:a first hollow structure having a first cross-sectional geometry configured to expand in at least one dimension under stress, the first hollow structure configured to receive the plurality of nuclear fuel pins, anda second hollow structure disposed around the first hollow structure having a second cross-sectional geometry being different from the first cross-sectional geometry, the second hollow structure configured to distribute therethrough at least a portion of the stress of the first hollow structure,wherein under the stress, the first hollow structure and the second hollow structure define an interior space between the first hollow structure and the second hollow structure with at least a portion of the first hollow structure in physical contact with the second hollow structure, andwherein the first hollow structure permits fluid communication between the interior space and a region inside the first hollow structure. 2. The fuel assembly of claim 1, wherein the first cross-sectional geometry includes a polygon having more sides than the second cross-sectional geometry. 3. The fuel assembly of claim 1, wherein the first cross-sectional geometry includes a polygon having fewer sides than the second cross-sectional geometry. 4. The fuel assembly of claim 1, wherein the first cross-sectional geometry includes a dodecagon. 5. The fuel assembly of claim 1, wherein the second cross-sectional geometry includes a hexagon. 6. The fuel assembly of claim 1, wherein the first cross-sectional geometry includes a dodecagon and the second cross-sectional geometry includes a hexagon. 7. The fuel assembly of claim 1, wherein at least one of the first hollow structure and the second hollow structure has a wall thickness of between about 0.2 mm and about 5 mm. 8. The fuel assembly of claim 1, wherein at least one of the first hollow structure and the second hollow structure has a wall thickness varying along at least a portion of a respective circumference of the first cross-sectional geometry and the second cross-sectional geometry. 9. The fuel assembly of claim 1, wherein at least one of the first hollow structure and the second hollow structure includes at least one steel chosen from ferritic steel, martensitic steel, and non-ferritic steel. 10. The fuel assembly of claim 1, wherein at least one of the first hollow structure and the second hollow structure includes at least one material chosen from a Zr-based alloy, a Fe-based alloy, a ceramic, a refractory metal, a refractory alloy, and a composite material. 11. The fuel assembly of claim 1, wherein the first hollow structure is spaced apart from the second hollow structure. 12. The fuel assembly of claim 1, wherein at least a portion of the first hollow structure is coupled to at least a portion of the second hollow structure by at least one structural member. 13. The fuel assembly of claim 1, further including a coolant disposed in an interior of the first hollow structure. 14. The fuel assembly of claim 1, further including at least one instrument disposed interior the first hollow structure, the at least one instrument being configured to perform at least one function chosen from test, observe, and provide feedback regarding operational conditions. 15. The fuel assembly of claim 1, wherein at least a portion of the first hollow structure is in direct physical contact with a portion of the second hollow structure. 16. The fuel assembly of claim 15, wherein the first hollow structure has a periphery that is in direct physical contact with the second hollow structure. 17. The fuel assembly of claim 15, wherein the first hollow structure has at least one side that is in direct physical contact with the second hollow structure. 18. A nuclear fuel assembly, comprisinga nuclear fuel,a plurality of nuclear fuel elements, anda plurality of fuel ducts having the plurality of nuclear fuel elements disposed therein, at least one of the plurality of the fuel ducts including:a first hollow structure having a first cross-sectional geometry, the first hollow structure containing more than one of the plurality of nuclear fuel elements, the first hollow structure configured to expand radially outward under stress, anda second hollow structure disposed around the first hollow structure, and having a second cross-sectional geometry different from the first cross-sectional geometry, the second hollow structure configured to distribute therethrough at least a portion of the stress from the first hollow structure, with the first hollow structure in contact with the second hollow structure,wherein the first hollow structure and the second hollow structure define an interior space between the first hollow structure and the second hollow structure, andwherein the first hollow structure permits fluid communication between the interior space and a region inside the first hollow structure. 19. The fuel assembly of claim 18, wherein the at least one of the plurality of fuel ducts further includes at least one structure member that connects a point on a side of the first cross-sectional geometry of the first hollow structure to a corner of the second cross-sectional geometry of the second hollow structure. 20. The fuel assembly of claim 18, wherein the plurality of nuclear fuel elements are disposed in an interior of the first hollow structure. 21. The fuel assembly of claim 18, wherein the plurality of the fuel ducts define interstitial spaces therebetween, at least one of a coolant, inert gas, fuel material, and a monitoring device, being disposed in the interstitial spaces.
046559957	abstract	A fuel assembly, particularly advantageous for use with a BWR, wherein the fuel bundle is adapted to be inserted into an envelope formed from a flow channel and a lower nozzle assembly. The fuel bundle is essentially axially symmetrical having identical top and bottom tie plates. Within the fuel bundle, alternate fission gas plenums are disposed at the top and bottom of the bundle respectively.. During the refueling operation, the fuel bundle is removed from the reactor core, axially inverted and reinserted into the core for continued burn up. The invention takes advantage of the reactivity increase possible in a BWR when a partially burned fuel bundle is inverted.
054913454	claims	1. A vacuum canister for picking up and containing at least one of a fluid and a particulate material, comprising: a housing with a sealed vacuum chamber having a predetermined vacuum pressure therein; and a valve having a first port operable to be placed in fluid communication with said vacuum chamber and a second port for receiving at least one of a fluid and a particulate material, said valve being operable between a first position to seal said vacuum chamber and retain said predetermined vacuum within said vacuum chamber, and a second position to permit fluid flow through said valve from said second port into said vacuum chamber; whereby operation of said valve, in said second position when said second port is located adjacent at least one of a fluid and a particulate material, is effective to displace through said valve the at least one of a fluid and a particulate material into said housing. a housing for forming therein a sealed vacuum chamber; vacuum means for establishing a predetermined vacuum pressure within said vacuum chamber; and a valve having a first port for fluid communication with said vacuum chamber and a second port for receiving at least one of a fluid and a particulate material, said valve being operable between a first position to seal said vacuum chamber and retain a vacuum pressure within said vacuum chamber, and a second position to permit fluid flow through said valve from said second port to said first port; whereby operation of said valve, in said second position when said second port is located adjacent at least one of a fluid and a particulate material, is effective to displace through said valve the at least one of a fluid and a particulate material into said housing. providing a housing having therein a sealed vacuum chamber; providing a valve having a first port selectively operable to place it in fluid communication with said vacuum chamber and a second port for receiving at least one of a fluid and a particulate material, said valve being operable between a first position to seal said vacuum chamber and retain a vacuum within said vacuum chamber, and a second position to permit fluid flow through said valve from said second port to said first port; establishing a predetermined vacuum pressure within said vacuum chamber; locating at least one of a fluid and a particulate material adjacent said second port; and placing said valve in said second position to displace along with fluid flow through said valve the at least one of a fluid and a particulate material into said vacuum chamber. 2. The vacuum canister according to claim 1, wherein the at least one of a fluid and a particulate material is a hazardous material. 3. The vacuum canister according to claim 2, wherein said housing includes a protective layer having a predetermined thickness that is effective to contain the hazardous material within said housing, said protective layer being disposed in substantially covering relationship to said vacuum chamber. 4. The vacuum canister according to claim 3, wherein said hazardous material is a corrosive agent material. 5. The vacuum canister according to claim 4, wherein said protective layer is formed of glass. 6. The vacuum canister according to claim 3, wherein said hazardous material is a radioactive material. 7. The vacuum canister according to claim 6, wherein said protective layer is a predetermined thickness that is effective to shield radiation from the radioactive material contained within said housing. 8. The vacuum canister according to claim 7, wherein said protective layer is formed of lead. 9. The vacuum canister according to claim 1, further including a conduit disposed to the exterior of said valve and in fluid communication with said second port of said valve. 10. The vacuum canister according to claim 1, wherein said housing is sized and configured to be held by a person's hand. 11. The vacuum canister according to claim 10, wherein said valve is sized and configured to be operable by a finger of a person's hand. 12. The vacuum canister according to claim 1, wherein said valve includes biasing means for biasing said valve toward said first position to seal said vacuum chamber, said valve being operable to be selectively and repetitively moved to said second position to permit fluid flow through said valve. 13. A vacuum canister for picking up and containing at least one of a fluid and a particulate material, comprising: 14. The vacuum canister according to claim 13, wherein the at least one of a fluid and a particulate material is a hazardous material. 15. The vacuum canister according to claim 14, wherein said housing includes a protective layer having a predetermined thickness that is effective to contain the hazardous material within said housing, said protective layer being disposed in substantially covering relationship to said vacuum chamber. 16. The vacuum canister according to claim 13, wherein said valve includes biasing means for biasing said valve toward said first position to seal said vacuum chamber, said valve operable to be selectively or repetitively moved to said second position to permit fluid flow through said valve. 17. The vacuum canister according to claim 13, wherein said vacuum means for creating a vacuum within said vacuum chamber includes a preselected substance disposed in communication with said vacuum chamber for causing a vacuum-forming reaction with a gas within said vacuum chamber. 18. The vacuum canister according to claim 13, wherein said vacuum means for creating a vacuum within said vacuum chamber includes a slidable housing member for expanding the volume of said vacuum chamber. 19. The vacuum canister according to claim 13, wherein said housing is sized and configured to be held by a person's hand. 20. The vacuum canister according to claim 19, wherein said valve is sized and configured to be operable by a finger of a person's hand. 21. A method for picking up and containing at least one of a fluid and a particulate material, comprising the steps of: 22. The method according to claim 21, wherein said at least one of a fluid and a particulate material is a hazardous material. 23. The method according to claim 22, wherein said step of providing a housing includes the step of providing a protective layer having a predetermined thickness that is effective to contain the hazardous material within said housing, said protective layer being disposed in substantially covering relationship to said vacuum chamber. 24. The vacuum canister according to claim 21, wherein said step of providing a valve includes the step of providing biasing means for biasing said valve toward said first position to seal said vacuum chamber, said valve being operable to be selectively or repetitively moved to said second position to permit fluid flow through said valve.
	summary
	claims	1. A product irradiator comprising: a radiation source, an adjustable collimator, a turntable, a control system and a detection system, wherein said collimator comprises one or more radiation opaque shielding elements, and said detection system measures at least one the following parameters: transmitted radiation, instantaneous angular velocity of said turntable, angular orientation of said turntable, power of a radiation beam produced by said radiation source, energy of said radiation beam, width of said radiation beam, collimator aperture, position of an auxiliary shield, offset of said radiation beam from the axis of rotation of said turntable, distance of said turntable from collimator, distance of said collimator from said radiation source. 2. The product irradiator of claim 1 wherein said detection system is operatively linked with said control system. claim 1 3. A method of radiation processing a product comprising: i) placing said product onto a turntable and establishing at least one of the following properties: length, width, height, density, and density distribution of said product; ii) determining width for a collimated radiation beam required to produce a Dose Uniformity Ratio of from about 1 to about 2, within said product; iii) adjusting at least one of the following parameters in phase with turntable rotation: collimator aperture, distance between said turntable and collimator, and turntable offset, to obtain said width of a collimated radiation beam determined in step ii), wherein said width of said collimator aperture is adjusted as a function of angular orientation of said turntable; iv) producing a collimated radiation beam using a collimator comprising one or more radiation opaque shielding elements; and v) rotating said product within said collimated radiation beam for a period of time sufficient to achieve a minimum required radiation dose within said product. 4. A method of radiation processing a product comprising: i) placing said product onto a turntable and establishing at least one of the following properties: length, width, height, density, and density distribution of said product; ii) determining width for a collimated radiation beam required to produce a Dose Uniformity Ratio of from about 1 to about 2, within said product; iii) adjusting at least one of the following parameters in phase with turntable rotation: collimator aperture, distance between said turntable and collimator, and turntable offset, to obtain said width of a collimated radiation beam determined in step ii), wherein an angular velocity of said turntable is a parameter that may be adjusted, and wherein said collimated radiation beam is a collimated X-ray beam produced from high energy electrons generated by an electron accelerator, and power of said high energy electrons is adjusted; iv) producing a collimated radiation beam using a collimator comprising one or more radiation opaque shielding elements; v) rotating said product within said collimated radiation beam for a period of time sufficient to achieve a minimum required radiation dose within said product; and vi) detecting X-rays transmitted through said product. 5. The method of claim 4 , wherein during or following said step of detecting, is: claim 4 i) processing information obtained in said detecting step by a control system and altering, if required, of any of the following parameters: collimator aperture, distance between said turntable and collimator, turntable offset, position of auxiliary shield, angular velocity of said turntable, power of said high energy electrons. 6. A product irradiator comprising: i) an X-ray radiation source essentially consisting of an electron accelerator for producing high energy electrons, a scanning horn by directing said high energy electrons towards a convertor, said converter for converting said high energy electrons into X-rays to produce an X-ray beam, said X-ray beam directed towards a product requiring irradiation; ii) an adjustable collimator comprising one or more radiation opaque shielding element for shaping said X-ray beam; iii) a turntable upon which said product is placed, wherein said turntable may be movable towards or away from said adjustable collimator, or said turntable may be movable laterally, so that an axis of rotation of said product on said turntable is offset from axis of said X-ray beam; v) a detection system in operative association with said control system. 7. The product irradiator of claim 6 , further comprising an auxiliary shield. claim 6 8. The product irradiator of claim 7 , wherein said detection system measures at least one of the following parameters: transmitted X-ray radiation, instantaneous angular velocity of said turntable, angular orientation of said turntable, power of said high energy electrons, width of high energy electron beam, energy of said X-ray beam, aperture of said adjustable collimator, position of said auxiliary shield, offset of said radiation beam from axis of rotation of said turntable, distance of said turntable from collimator, and distance of said collimator from said radiation source. claim 7
054266777	description	DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also, in the following description, it is to be understood that such terms as "forward," "left," "right," "upwardly," "downwardly," and the like are words of convenience and are not to be construed as limiting terms. Referring now to the drawings, and more particularly to FIG. 1, there is illustrated a pressurizer vessel, generally referred to as 10, for use in a nuclear power plant as is well known in the art. The pressurizer vessel 10 includes a protective shell 20 having an upper head 30 and a lower head 40 both defining an interior portion 50 for containing any water and steam therein. The upper head 30 includes a manway 60 for allowing maintenance personnel and the like to enter the pressurizer vessel 10, and further includes a relief nozzle 70 for venting steam outside the pressurizer vessel 10 if the design pressure capability of the pressurizer vessel 10 is exceeded. The relief nozzle 70 is automatically opened above system design pressure, and can also be opened manually from a control console in a control room (both of which are not shown) if necessary. If system pressure continues to rise, a self-actuating safety nozzle 80, connected by piping to the relief nozzle 70, will open. Steam from the safety nozzle 80 or relief nozzle 70 is piped to a pressure relief tank (not shown) which contains sufficient water to condense the steam. A spray nozzle 90 is positioned atop the pressurizer vessel 10 and extends into the shell interior portion 50 for spraying water into the pressurizer vessel 10 which condenses the steam to water. Two lifting trunnions 100 both extend radially and outwardly from the protective shell 20 for lifting the pressurizer vessel 10 during installation and the like. A tiered, circular shaped heater support assembly 110 is located in the interior portion 50 of the lower head 40 and is attached to the shell 20 for structural support. The heater support assembly 110 is operable to matingly receive a plurality of electrical heaters 120. The heater support assembly 110 includes two horizontally oriented, spaced apart plates, top plate 130a and bottom plate 130b, each having a plurality of holes 140 which are respectively in registry with each other. Each pair of aligned holes 140 receives an electrical heater 120, typically a total of seventy eight, for heating the water. The electrical heaters 120 are tubular shaped elements and are either partially or totally submerged in the water during operation. This is because the water level varies up and down along an elevation (h) in the vessel interior 50 during operation due to the electrical power demand of the power plant and the like. A surge nozzle 150 attaches to the bottom of the pressurizer vessel 10 and extends up into the vessel interior 50 for allowing water from the primary loop (not shown) to flow into and out of the vessel interior 50 for maintaining proper pressurization of the primary loop. A support skirt 160 extends axially downwardly and radially outwardly from the lower head 40 and includes a plurality of holes 170 for attaching the pressurizer vessel 10 to its support structure, typically a floor (not shown). The preferred embodiment of the present invention includes replacing a presently existing electrical heater 120 with a temperature measuring device 180 of the present invention. Although in the preferred embodiment only one heater 120 is replaced, any number may be replaced as long as the heating function of the electrical heaters 120 is not impaired. The temperature detector 180 is installed extending through plate 130b for structural support. As will be discussed in detail below, the temperature measuring device 180 includes a plurality of thermocouples (not shown in FIG. 1) which enable the temperature detector 180 to detect temperature gradients in the water. Referring to FIG. 2, the temperature measuring device 180 of the present invention is illustrated in detail. The device 180 includes a housing 190 defining an interior portion 200. The housing 190 includes a generally cylindrical shaped side 210 terminating at one end with a rounded shaped tip 220 and with an opening 230 at its other end. The tip 220 is welded via a weldment 240 to the side 210 for providing a pressure boundary, and includes a hollowed-out portion 250 which provides access to the housing interior 200 during manufacturing for pressurizing the housing interior. The hollowed-out portion 250 is welded via a weldment 260 after pressurization for providing a pressure boundary. The temperature measuring device 180 is disposed in the holes 140 of the support plate 130a (both not shown in FIG. 2) so that the tip 220 points upwardly toward the upper head 30 (not shown in FIG. 2). A plurality of thermocouples 270 are disposed in the housing interior 200 and each extend through the side 210 for exposing a welded end 280 of each thermocouple to the environment surrounding the housing 190. This penetration allows each thermocouple 270 to measure the temperature of the surrounding environment. In this embodiment, the environment is typically water. By including a plurality of thermocouples 270 in the housing 190, a plurality of temperature readings is available from the respective thermocouples 270 for detecting temperature gradients. Thermocouples are well known in the art and are disclosed in U.S. Pat. Nos. 2,957,037, 2,924,976, and 2,946,835 all of which are hereby incorporated by reference. An enclosure 290 is matingly attached by a weldment 300 to the open end 230 of the housing 190 for forming a sealed enclosure. A counterbore 310 is provided in an interior portion of the enclosure 290 for purposes of fabrication. An air gap 320 is typically located between the housing 190 and the counterbore 310 for providing space for thermal expansion of the enclosure 290 and housing 190 during operation. A plurality of bores 330 extend through a bottom of the enclosure 290 for allowing the thermocouples 270 to exit the enclosure 290 and to be connected to process instrumentation (not shown), which is well known in the art, for processing the plurality of temperature readings. It can be appreciated that the number of bores 330 correspond to the number of thermocouples 270. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described merely a preferred or exemplary embodiment thereof.
058754075	abstract	A method for immobilizing waste chlorides salts containing radionuclides and hazardous nuclear material for permanent disposal, and in particular, a method for immobilizing waste chloride salts containing cesium, in a synthetic form of pollucite. The method for synthesizing pollucite from chabazite and cesium chloride includes mixing dry, non-aqueous cesium chloride with chabazite and heating the mixture to a temperature greater than the melting temperature of the cesium chloride, or above about 700.degree. C. The method further comprises significantly improving the rate of retention of cesium in ceramic products comprised of a salt-loaded zeolite by adding about 10% chabazite by weight to the salt-loaded zeolite prior to conversion at elevated temperatures and pressures to the ceramic composite.
046541861	claims	1. A device for rapid and precise determination of the power of a pressurized water nuclear reactor in steady state operation and during periods of transient operation, said reactor having a core and cooling loops having a cold branch and a hot branch, said device comprising, for each cooling loop (a) means for measuring, on the one hand, the neutron power (15) and, on the other hand, the temperature of the primary fluid at a single point in said cold branch and at a single point in said hot branch; (b) means for computing the enthalphy of the primary fluid in said cold branch and in said hot branch from said temperature measurements; (c) a register (6) which computes an enthalpy increase (7) of said primary fluid as it flows through said core, from the difference between the enthalpy (3') in said hot branch and the enthalpy (3) in said cold branch, delayed by a time shift operator (4) expressing the average time of transit .tau.0 of a molecule of primary fluid between said two points of temperature measurement; (d) a multiplier (8) of said increase in the enthalpy (7) by the flow rate of said primary fluid (9); (e) a comparator (14) of a thermal power signal which is obtained (11) and of a neutron power signal which is measured (15) and made dynamically equivalent to said thermal power signal (11); and (f) a corrector of the neutron power measurement signal (15) depending on the signal (21) produced by said comparator (14). 2. The device as claimed in claim 1, wherein said neutron power measurement signal (15) is made dynamically equivalent to said thermal power signal (11) by means of a point model (17) of heat transfer between the nuclear flux (15) and the thermal flux to said primary fluid, of a point model (18) of heat transfer of said primary fluid in the core, corresponding to the time of transit .tau..sub.i /2 of a molecule of primary fluid from the center of said core to the outlet of said core, and by means of a time shift operator (19) expressing the time of transit .tau..sub.5 of a molecule of primary fluid from the core outlet to the point of temperature measurement in said hot branch. 3. The device as claimed in claim 1 or 2, wherein the corrector (22) of said neutron power measurement signal (15) is an integrator. 4. The device as claimed in claim 1 or 2, comprising means for correcting, before its comparison to said thermal power signal (11), the neutron power measurement signal (15) for the temperature variations in the cold branch said, means comprising a correction coefficient (K.sub.1). 5. The device as claimed in claim 4, comprising means for delaying the cold branch temperature signal employed to correct said neutron power measurement signal (15), said means comprising a time shift operator expressing the time of transit .tau..sub.15 of a molecule of primary fluid between the point of temperature measurement in said cold branch and the core inlet. 6. The device as claimed in claim 5, comprising means for filtering said cold branch temperature signal to take account of the response time of said neutron power measurement signal (15) to a variation of the cold branch temperature. 7. The device according to claim 1 or 2, further comprising a device for fast and precise determination of the secondary power of said reactor, comprising for each cooling loop, in addition to said means for measuring temperature and computing the enthalpy in said cold branch and in said hot branch, imprecise but rapid means (25) for determining the thermal power produced by a steam generator associated with said reactor, a register (6') computing the reduction in the enthalpy of said primary fluid as it flows through said steam generator, from the difference between the enthalpy in said hot branch (3'), and in said cold branch (3), the enthalpy in said hot branch (3') being delayed by a time shift operator (4') expressing the time of transit .tau..sub.o of a molecule of primary fluid between the two temperature measurement points, a multiplier (8') of the decrease of enthalpy (7') by the flow rate (9) of said primary fluid, a comparator (14') of a signal (11') which is obtained at a multiplier output (8'), of the thermal power absorbed by the steam generator, to a signal (16') of the thermal power produced by said steam generator and determined by the said thermal power determining means (25), this signal (16') being made dynamically equivalent to the signal (11') of thermal power absorbed by the steam generator and a corrector (22') of the signal (16') of the thermal power produced by the steam generator depending on the signal (21') produced by said comparator (14'). 8. The device as claimed in claim 7, comprising means for making the measurement signal (16') of the thermal power produced by said steam generator dynamically equivalent to the signal (11') of thermal power absorbed by said steam generator, said means comprising a point model (17') of heat transfer between the secondary fluid and said primary fluid passing through the steam generator, of a point model (18') of heat transfer of said primary fluid in said steam generator, corresponding to the time of transit .tau..sub.10 /2 of a molecule of primary fluid from the center of said steam generator to the outlet of said steam generator and by means of a time shift operator (19') expressing the time of transit .tau..sub.11 of a molecule of primary fluid form the outlet of said steam generator to the point of measurement of the cold branch temperature. 9. The device as claimed in claim 7, wherein the corrector (22') of said measurement signal (16') of the thermal power absorbed by said steam generator is an integrator. 10. The device as claimed in claim 7, comprising means for compensating the dynamics of the measurements of the temperature of said primary fluid in said cold branch and said hot branch, said means comprising a phase lead corrector (12, 12') placed at the output of the multiplier (8, 8') of the change in enthalpy (7, 7') of the primary fluid by the flow rate (9) of the primary fluid. 11. The device as claimed in claim 7, comprising means for filtering the signal (9) of the primary flow rate before being entered into said multipliers (8, 8') in order to take account of the variation of the average time of transit .tau..sub.1 of a molecule of primary fluid passing through said core.
053176090	description	DESCRIPTION OF PREFERRED EMBODIMENTS The apparatus described below is applicable, in particular, to installing fuel rods in a nuclear fuel assembly of the kind described in French Patent No. 88 06860, to which reference may be made. Only a few indications on the structure of the assembly are therefore given. The assembly 20 comprises a skeleton made up of guide tubes 12, spacing grids 14 carried by the guide tubes 12, and terminal end nozzles 16. The grids are constituted by two mutually crossed sets of plates that are welded together at their crosspoints, thereby defining cells for receiving rods 18, distributed at the nodal points of a square array. The guide tubes 12 replace the fuel rods at some of the nodes of the array. To make up such a fuel assembly, the skeleton has its end nozzles removed. The rods are then pulled along the assembly, generally layer by layer, although it would also be possible to pull them through in other groups. The rod-installing apparatus shown in FIG. 2 serves to load rods into a skeleton 20 that is without its end nozzles. The apparatus comprises a stand 21 which carries means 22 for receiving the skeleton 20, which means are constituted by a bench that can tilt on the stand about an axis 23 between a horizontal position as shown in FIG. 2 and a vertical position from which the fuel assembly is taken up for handling purposes. When horizontal, the bench lies between a rod storage magazine 24 in which the rods are stored in an array that corresponds to the array that the rods are to occupy in the skeleton, and a displacement mechanism 26 for displacing pull bars horizontally. The mechanism is frequently carried by a carriage which enables the pull bars to be displaced longitudinally between a position in which an end clamp on each pull bar lies beyond the bench 22 and a position in which the clamps reach the plugs of the rods 18 that project from the magazine 24. When, as is usually the case, the mechanism 26 is designed to load an entire layer of rods at a time, it includes the same number of pull bars as the maximum number of rods that may exist in a layer, and it enables the pull bars to be displaced vertically so as to bring them into line with each of the layers in succession. Camera means are generally provided to enable the operation of the apparatus to be monitored remotely. FIG. 2 shows such means constituted by a camera 28 placed above the end of the magazine and making it possible to verify that the caps have been removed and that the rods have been grasped properly, and a second camera 29 which makes it possible to monitor that the caps have been engaged and the pull bars have been inserted. The apparatus of the invention also includes a cap-placing assembly 30 interposed between the skeleton-receiving means and the displacement mechanism 26. In the embodiment as shown, this cap-placing assembly is carried by a beam 32 belonging to the tilting bench 22. The apparatus also includes a cap-removing assembly 34 also fixed to the beam 32. Cap-Placing Assembly The cap-placing assembly shown in FIGS. 3 to 6 comprises a fixed support 36 and a removable receptacle 42. The fixed support 36 is in of a base having a reinforcing bracket and a sole plate fixed to the beam 32. A transverse groove 38 is formed in the base for temporarily fixing to a lug 40 belonging to a removable receptacle 42. Two wheels 44 placed at the two ends of the groove 38 hold the lug 40 laterally (FIG. 3). The removable receptacle 42 comprises a perforated body 46 provided with the lug 40, and in which passages 48 are provided that are distributed over the same array as the rods. The perforated body has countersunk holes and fixing flanges for a closure plate 50 that is held in place by screws 52, for example. The body 46 and the closure plate hold captive a grid 54 formed with housings 55 for receiving caps 56 (only one of which is shown in FIG. 6). A backing plate 58, likewise perforated, is fixed to the front of the body 46 and cooperates with the body to define a passage for receiving a moving plate 60. The grid 54, which is advantageously made of plastic material, is formed with the parallel housings 55. The diameter of the housings and the plastic material are chosen so that the grid is capable of retaining the caps 56 by friction. The length of the caps is less than the total thickness of the body 46 and of the grid 54. The leading ends of the caps are tapered. A clamp-receiving blind hole is formed in each cap. The purpose of the moving plate 60 is to prevent the caps 56 being expelled by the clamps of the pull bars when the latter penetrate into the caps 56, and to allow the caps to pass when the pull bars are to be inserted in the frame through the receptacle. For this purpose, the moving plate 60 is formed with holes distributed in an array identical to that of the rods in the skeleton and it is displaceable, in a direction at 45.degree. to the layers, between a locking position as shown in FIGS. 3, 4, and 5 (where each hole through the grid is situated halfway between two passages 48 through the body), and a position where the caps are free to pass. The passage in the perforated body 46 provides sufficient clearance for the grid to perform this displacement, as shown in FIG. 3. The displacements of the movable plate 60 are guided and controlled by means which may be those shown in FIGS. 3 and 5. In this embodiment, two of the corners of the moving plate 60 are extended by tabs 62. FIG. 3 uses solid lines to show the position of the moving plate in which it retains the caps and chain-dotted lines to show the position of the bottom tab when the moving plate is in its position where it allows the caps to pass through. The two tabs are guided in passages provided in the perforated body. A proximity detector 64 fixed to the base 36 serves to detect the position of the moving plate. The means shown in FIGS. 3 and 5 for displacing the movable plate comprise a double-acting actuator 66 whose cylinder is connected by a sleeve 68 to the perforated body 46 and whose rod 69 is coupled to the tab 62 via a hinged coupling 70. An end-of-stroke detector 72 may be provided to check proper operation of the actuator. It can be seen that the removable receptacle 42 constitutes a unit that is capable of being handled and transported by means of handles 74 (FIG. 3), in particular for reloading it at a distance from the apparatus. To install it, the tongue 40 is inserted in the groove 38. The perforated body 46 is locked in place by means of pins 76 provided with handles 78 and threaded through aligned bores in the perforated body 46 and in the tongue 40. Cap-Removing Assembly The cap-removing assembly includes a portion fixed to the beam 32 of the tilting bench and an extractor 100 that is vertically displaceable between an active cap-removing position and a retracted position in which it releases the removed caps and allows the pull bars to pass. The fixed portion comprises a lower bracket 82 securely fixed to the bottom face of the beam 32, e.g., by screws 84, and extended upwards by a vertical plate 86. It also includes an upper bracket 88 fixed to the beam and bearing against the plate 86. The upper bracket 88 shown in FIG. 7 is centered laterally on the beam by slidable keying means including a key fixed to the beam and a groove in the bracket 88. It is forced against the plate 86 by an eccentric 92 that rotates on the beam 32 and that is actuated by a lever 94. It is held vertically by bolts 96 pivoting on the upper bracket 88 and engaged in quick-tightening internally threaded knobs 98 for bearing against a plate secured to the beam (FIG. 8). The extractor 100 is shown in FIGS. 7 and 9 in the position it occupies while removing caps. The extractor comprises a frame made up of a plurality of parts assembled together. The frame is guided laterally by the lower and upper brackets 82 and 88. It may be regarded as comprising a vertical motion-transmitting bracket 102, an extender 104, and a jaw support 106. For example, it may be guided on the upper bracket 88 by wheels 116 that are carried by lateral tabs of the support and bear against the vertical face of the bracket and by slidable friction pads (FIG. 10). The upper and lower jaws 108 and 110 that are vertically movable on the support are designed to engage and hold the caps of an entire layer of pull bars. They are carried by respective levers 112 each rotating about an axis 114 fixed to the support 106. The jaws are provided with respective jaw plates. They bear against the support 106 via guide skids. Their back stroke is limited by studs 115 engaged in the support 106. A mechanism for vertically displacing the extractor 100 comprises an electric motor 118 carried by the lower bracket 82 and having a outlet shaft carrying a gear wheel 120 (FIG. 7). By means of a toothed belt 122, the gear wheel drives a toothed pulley wheel 124 fixed to a drive screw 126 secured against longitudinal movement on the lower bracket 82 by two bearings 128. Under the protection of a bellows 130, the screw 126 carries a nut 132 which is fixed to the motion-transmitting bracket 102 and which is thus prevented from rotating. The level of the extractor is given by a measurement system which, in the example shown in FIG. 7, includes a sensor 134 fixed to the motion-transmitting bracket 102 and provided with a reference fork 133 that moves relative to a graduated scale 136 fixed to the lower bracket 82. Advantageously, the position of the fork is adjustable, e.g., by means of an adjustment screw 138. The cap-removing assembly further comprises pneumatic ejection means for ejecting the caps removed by the jaws. In the example shown in FIG. 7, these means are constituted by a row of nozzles 140 fed by a manifold 142 fixed to the upper bearing 128. The mechanism for opening and closing the jaws 108 and 110 is shown in FIGS. 8 and 9. It comprises a linear actuator 143 whose rod has a terminal fork coupled by a pin 144 to two arms 146. These arms are connected to the levers 112 by means of respective pins 148. Two proximity sensors 150 fixed on the support 106 serve to determine the position of a tab 152 which is fixed to the terminal fork of the actuator rod, thereby indicating the closed or open state of the jaws. In FIG. 8, the tab 152 is shown facing the proximity detector that indicates that the jaws are opened. Finally, the extender 104 carries a cap-receiving tank 154 provided with a downwards feed hopper 105 situated facing the opening between the jaws. The tank is removable to enable ejected caps to be recovered. It is normally held in place by locks 156. The method of installing rods by means of apparatus of the kind described above is as follows, once an empty skeleton 20 without its end-fittings has been placed on the bench 22 facing a magazine 24 which contains rods in alignment with each of the rod-receiving places in the skeleton. When the apparatus is in its initial state, the pull bars of the mechanism 26 are fully retracted. The extractor 00 is in its higher position with its jaws open. Its level is adjusted so that the gap between the jaws faces the first layer of cells to be loaded. The level of the extractor can be adjusted automatically by energizing the motor 118 in an upward direction, starting from the bottom position of the extractor, until the level sensor 134 reaches a predetermined graduation on the scale 136. The mechanism 26 is adjusted in such a manner that the pull bars it carries are in alignment with the layer of rods to be inserted. A receptacle 42 whose grid has been filled with caps is placed on the fixed support 36, the actuator 66 being controlled so that the moving plate 60 remains in the position where it prevents the caps from moving out of the receptacle. The pull bars are then advanced with their clamps closed until the clamps (chain-dotted lines in FIG. 6) are pushed fully home inside the caps 56, whose conical ends are retained by the moving plate 60. The actuator 66 is then energized to displace the moving plate diagonally through half a pitch size, thereby allowing the caps 56 to pass through. To facilitate displacement of the moving plate 60, the pull bars may previously be slightly moved back to prevent the cap from rubbing. After the moving plate has been moved, the pull bars are advanced through the grids of the skeleton. The caps flex away the springs of the grids in the skeleton and avoid any danger of catching and of permanent deformation. The pull bars are thus advanced until the caps have passed through all of the grids, and have come out of the skeleton, after passing through guide holes (not shown) formed through the vertical wall of the upper bracket 88, so that the caps come between the jaws 108 and 110. Forward motion is then stopped. The actuator 142 is powered to clamp the caps between the jaws and to hold them. The pull bars are then moved back until they are disengaged from the jaws and from the upper bracket 88. The motor 118 is actuated to lower the extractor to the position shown in chain-dotted lines in FIG. 7, where the caps face the nozzles 140. The jaws are opened, e.g., by de-energizing the actuator 143, and the nozzles are fed with compressed air to eject the caps into the recovery tank 104 via the hopper 105. As soon as the extractor has moved down far enough to clear the path of the pull bars, the end clamps can be opened and the pull bars can be moved forwardly until the clamps engage the terminal plugs of the fuel rods. The clamps are then closed again. The pull bars can then be moved backwards so as to draw a layer of fuel rods through the grids. Once the fuel rods are in place, the clamps are opened. The mechanism moves the pull bars further back until they have cleared the cap-placing assembly. A new sequence of loading a layer of fuel rods can then be started, once the clamps of the pull bars have been closed again, the moving plate 60 returned to the position in which it holds the caps, and the extractor 100 and the pull bars moved through one step vertically so as to load another layer. When a layer includes locations for guide tubes, the corresponding pull bars are disconnected from the longitudinal displacement mechanism. Finally, when all of the rods are in place, the assembly is completed by securing the lower end nozzle and the upper end nozzle.
	claims	1. An elution system comprising:a radioisotope generator configured to release a daughter radioisotope during elution with an eluant thereby producing an eluate containing the daughter radioisotope, the daughter radioisotope being produced from radioactive decay of a parent radioisotope contained within the radioisotope generator;an eluate line configured to receive and convey eluate eluted from the radioisotope generator;an accumulator structure positioned downstream from the radioisotope generator and in fluid communication with the eluate line, the accumulator structure being configured to capture a larger amount of parent radioisotope than daughter radioisotope. 2. The system of claim 1, wherein the radioisotope generator comprises a generator column loaded with the parent radioisotope and the accumulator structure comprises a second column devoid of the parent radioisotope. 3. The system of claim 2, wherein the generator column and the second column are fabricated from a same material. 4. The system of claim 3, wherein the same material from which the generator column and the second column are fabricated is selected from the group consisting of stannic oxide, tin oxide, an organic matrix, and combinations thereof. 5. The system of claim 1, wherein the accumulator structure is configured to capture the larger amount of parent radioisotope than daughter radioisotope by preferentially binding any parent radioisotope present in the eluate received via the eluate line. 6. The system of claim 1, wherein the radioisotope generator comprises one of a 99Mo/99mTc generator, a 68Ge/68Ga generator, and a 82Sr/82Rb generator. 7. The system of claim 1, wherein the radioisotope generator is a 82Sr/82Rb generator. 8. The system of claim 1, further comprising a base frame with wheels, wherein the radioisotope generator, eluate line, and accumulator structure are mounted on the base frame so as to be movable. 9. The system of claim 1, further comprising an eluant line configured to supply the eluant to the radioisotope generator. 10. The system of claim 1, wherein the accumulator structure is configured to receive eluate from the eluate line so that the eluate flows at least one of through and over the accumulator structure.
	abstract	In one embodiment, a fusion reactor includes two internal magnetic coils suspended within an enclosure, a center magnetic coil coaxial with the two internal magnetic coils and located proximate to a midpoint of the enclosure, a plurality of encapsulating magnetic coils coaxial with the internal magnetic coils, and two mirror magnetic coil coaxial with the internal magnetic coils. The encapsulating magnetic coils preserve the magnetohydrodynamic (MHD) stability of the fusion reactor by maintaining a magnetic wall that prevents plasma within the enclosure from expanding.
055662170	claims	1. A subassembly for a spacer useful in a nuclear fuel bundle for maintaining a matrix of a plurality of nuclear fuel rods passing through the spacer in spaced-apart relation, comprising: first and second ferrules lying adjacent one another for receiving respective nuclear fuel rods, each ferrule having a pair of fuel rod contacting points along one side of the ferrule for abutting a fuel rod within the ferrule and a central opening along a side of the ferrule opposite said one side; a spring including a spring body lying in a plane, said body including opposite sides spaced from one another in said plane and having opposite end portions projecting to one side of said plane, a central portion lying between and spaced from said end portions, said central portion projecting to the opposite side of said plane, said body including openings on opposite sides of said central portion between said central portion and said end portions and between said spring body sides; said spring being disposed between said ferrules with said central portion in said central opening of said first ferrule and bearing against said second ferrule between said contacting points along said one side of said second ferrule, portions of said first ferrule on opposite sides of said central opening therethrough extending in respective openings of said spring, said end portions of said spring extending beyond opposite upper and lower edges of said first ferrule for bearing directly against a fuel rod passing through the first ferrule and biasing the fuel rod against the contacting points along said one side of said first ferrule, the opposite sides of said spring body lying between and externally of said first and second ferrules. a matrix of adjacent ferrules for receiving the fuel rods in said spacer; each ferrule having a pair of fuel rod contacting points along one side thereof for abutting a fuel rod within the ferrule and having an opening along a side of the ferrule opposite said one side; a plurality of springs, each spring including a spring body lying in a plane, said body including opposite sides spaced from one another in said plane and having opposite end portions projecting to one side of said plane, a central portion between and spaced from said end portions, said central portion projecting to the opposite side of said plane, said body including openings on opposite sides of said central portion and between said central portion and said end portions and between said spring body sides; each said spring being disposed between an adjacent pair of said ferrules with said central portion in said central opening of one of said adjacent ferrules and portions of said one ferrule on opposite sides of said opening therethrough extending in respective openings of said spring, the opposite sides of said spring body lying between and externally of said adjacent pair of said ferrules. 2. A subassembly according to claim 1 wherein said spring includes a pair of locating protuberances for engaging along an outer wall of said first ferrule to maintain said spring in position between said first and second ferrules. 3. A subassembly according to claim 1 wherein the opposite edges of said first and second ferrules define an axial dimension less than a dimension between said end portions of said spring. 4. A subassembly according to claim 1 wherein said first ferrule has a H/D ratio within a range of 0.8-0.4 wherein H is the height of the ferrule between said upper and lower edges thereof and D is the diameter of the first ferrule. 5. A subassembly according to claim 4 wherein the H/D ratio is about 0.6. 6. A subassembly according to claim 1 wherein said first and second ferrules have a H/D ratio within a range of 0.8-0.4 wherein H is the height of the ferrules between upper and lower edges thereof and D is the diameter of the ferrules. 7. A subassembly according to claim 6 wherein the H/D ratio for each said first and second ferrules is about 0.6. 8. A subassembly according to claim 1 wherein said contacting points comprise indentations along the sides of the ferrules extending the full axial length of the ferrules between the opposite edges. 9. A spacer for maintaining a matrix of nuclear fuel rods in spaced-apart relation between upper and lower tie plates, said spacer assembly comprising: 10. A spacer according to claim 9 wherein said end portions of each said spring extend above upper and lower edges of said ferrules for engaging the fuel rods at locations above and below the ferrules, respectively. 11. A spacer according to claim 9 wherein each ferrule has a H/D ratio within a range of 0.8-0.4 wherein H is the height of the ferrule between upper and lower edges thereof and D is the diameter of the ferrule. 12. A spacer according to claim 11 wherein the H/D ratio is about 0.6. 13. A spacer according to claim 9 wherein said sides of said springs include protuberances for engaging along outer sides of said ferrules to maintain said springs in position between said ferrules. 14. A spacer according to claim 9 wherein the opposite edges of said ferrules define an axial dimension less than said dimension between said end portions of said springs.
	summary
	claims	1. A zirconium-base alloy for nuclear reactors, comprising: 0.5-2 wt. % Sn, 0.07-0.6 wt. % Fe, 0.03-0.2 wt. % Ni, 0.05-0.2 wt. % Cr, the balance being zirconium and unavoidable impurities, wherein the zirconium-base alloy has an Fe content X, in weight percent, and precipitates having a mean size Y, in nanometers, and further wherein the Fe content of the zirconium-base alloy and the mean size of the precipitates in the zirconium-base alloy simultaneously satisfy each of the following relationships: i) Yxe2x89xa7xe2x88x92444xc3x97X+154; ii) Yxe2x89xa6910xc3x97Xxe2x88x9246; iii) Yxe2x89xa70; iv) Yxe2x89xa6300; and v) Xxe2x89xa60.6. 2. The zirconium-base alloy for nuclear reactors according to claim 1 , wherein: claim 1 the relationship i) is Yxe2x89xa7xe2x88x92989xc3x97X+362. 3. A zirconium-base alloy for nuclear reactors, comprising: 0.5-2 wt. % Sn, 0.07-0.6 wt. % Fe, 0.03-0.2 wt. % Ni, 0.05-0.2 wt. % Cr, with the balance being zirconium and unavoidable impurities, wherein the zirconium-base alloy has an Fe content X, in weight percent, and an annealing parameter Y (xcexa3Ai); and further wherein the Fe content and the annealing parameter of the zirconium-base alloy simultaneously satisfy each of the following relationships: i) 30+1.6xc3x9710 7 exp (0.7xc3x97log (Y))xe2x89xa7xe2x88x92444xc3x97X+154; ii) 30+1.6xc3x9710 7 xc3x97exp (0.7xc3x97log (Y))xe2x89xa6910xc3x97Xxe2x88x9246; iii) Yxe2x89xa71xc3x9710 xe2x88x9221 iv) Yxe2x89xa61xc3x9710 xe2x88x9215 ; and v) Xxe2x89xa60.6. 4. The zirconium-base alloy for nuclear reactors according to claim 3 , wherein relationship i) is claim 3 30+1.6xc3x9710 7 xc3x97exp(0.7xc3x97log (Y))xe2x89xa7xe2x88x92989xc3x97X+362. 5. A nuclear reactor component comprising a zirconium-base alloy as claimed in claim 1 . claim 1 6. The nuclear reactor component according to claim 5 , which is a fuel cladding tube for use in a fuel assembly, a spacer band, spacer cells, or a water rod. claim 5
039390381	description	DESCRIPTION OF THE PREFERRED EMBODIMENT The pressurized-water coolant nuclear reactor 1 shown by FIG. 1, includes a substantially cylindrical side wall 2 and a hemispherical bottom wall 3, the two walls being integral with each other, the side wall having pressurized water coolant connections 4 and a detachable cover 6 normally clamped firmly against the upper end of the side wall 2. The cover 6 carries various tubular connections 7 for the control rod drives. The core 5 may be conventional and consists of various individual fuel elements enclosed by the core vessel 10. These fuel elements are supported via a core frame 11 which rests on a flange 12 of the core vessel 10 (see FIG. 2), while the core vessel itself is suspended by its upper end via an annular flange 13, shown in FIG. 1, which rests on an internal shoulder 14 provided by the pressure vessel at its upper end. It can be appreciated that the core vessel, including its associated parts, is of substantial weight. It is the function of the core vessel intercept arrangement 17 to prevent this core vessel from accidentally falling through the entire distance beneath it and above the pressure vessel's bottom wall 3. The construction 17, as shown in FIG. 1, does not include all of the features of the present invention, its illustration in this figure being only to indicate in a general manner the location where the core vessel's intercept device is required. Referring now to FIGS. 2 and 3, which do show the details of the present invention, the detailed construction is as follows: The entire construction is made of metal having adequate ductility to avoid rupture when stressed beyond its elastic limit by the performance of its intended functions. The various parts may be interconnected, where required, by welding. The central column 18 comprises eight radially arranged, vertically elongated plates 18 inwardly interconnected by three vertically-interspaced short tubes 20, 20' and 20". Eight tubes in each instance form upper and lower strut systems, these being shown at 22 and 23, respectively, with each set of upper and lower tubes welded to one of the plates 19 at vertically interspaced locations. The annular series of columns are formed by plates 25 which are also radially arranged with respect to the center line of the construction and which are registered in each instance with one of the plates 19, the upper and lower strut members 22 and 23 converging and being welded at relatively closely interspaced upper and lower locations to the plates forming the annular series of vertical columns. The bottoms of the plates or columns 25 rest on the hemispherical bottom 3 near its periphery and close to its vertical side wall 2. The vertical columns 25 are aligned with the periphery of the core vessel 10 and they are connected with each other by a ring 26 arranged in a horizontal plane between the upper and lower tubular struts 22 and 23 of the strut sets. The tops of the columns or plates 25 carry a centering ring 27 which extends into the flange 12 of the core vessel 10, in interspaced but closely adjacent peripheral relationship with the flange 12. The plates 19 and 25 and upper portions 30 and 31 are reduced in cross-sectional areas by cutting the plates so they taper upwardly. The reduction in cross-sectional area is designed relative to the elastic limit of the plate metal and the anticipated falling force of the core vessel, so that these upper portions are deformed beyond their elastic limit by the falling core vessel to provide a shock-absorbing effect by the gradual dissipation of the falling energy of the core vessel as the parts plastically deform in a ductile manner. The spherical bottom 3 has an upwardly extending sleeve 33 welded to it with a cover 34 in which a slot is formed and in which is inserted the head 35 of a long tension bolt 36 which extends upwardly and through the intermediate tube 20' to which the blades 19 are welded, where the tension rod is provided with a screw-threaded engagement with a nut 37 engaging the top of this tube 20' and which pulls downwardly on the central column so that via the struts 22 and 23 the annular series of plates 25 are pulled downwardly against the arcuate sides of the bottom of the hemispherical vessel. The arrangement is such that between the bottom of the central column construction and the upper surface of the pressure vessel's bottom wall 3 a small space remains such as in the area of 20 mm space. This spacing is between the lower edge 40 of the central column, which comprises an annular ring to which the bottom edges of the plate 19 are welded. It is also to be noted that there is a slight space between the top level of the intercept framework and the bottom of the core vessel. Such spacing provides for thermal expansion and contraction but, incidentally, provides room for the core vessel to fall and gain momentum or kinetic energy, which is however absorbed gradually by the ductile deformation of the parts. All of the parts are symmetrically distributed about the vertical centerline of the pressure vessel's hemispherical bottom and the pressure vessel itself. Therefore, with all of the parts symmetrical as the framework deforms, there is little tendency for the core vessel to move laterally or angularly in its short descent. Lateral shifting is prevented by the ring 27 which is peripherally interspaced from the core vessel's flange 11 for only a distance required for thermal expansion and contraction movements.
	description	The present invention relates to a fault detector and method of detecting faults. More particularly, the present invention relates to the detection of valve movement of a valve in a fuel injector of an engine system via detection and analysis of discontinuities (“faults”) in the current through a control actuator of the valve. In electronically-controlled fuel injection systems, actuator controlled valves (e.g. solenoid valves) are used to control the flow of fuel within the injector, and hence, timing, pressure and quantity of fuel injected into the engine cylinders. For single-valve injection systems, such as Electronic Unit Injectors (EUIs) and Electronic Unit Pumps (EUPs) a single solenoid valve—known as the “Spill Valve”—is used to control the point, or set of conditions, at which fuel pressure within the injector volume begins to increase. If the valve is open, fuel will be allowed to “spill” to low pressure (the fuel tank). Alternatively, if the valve is closed, the mass of fuel within the injector will undergo pressurization due to the advancing cam-driven plunger reducing the injector volume. Injection of fuel into the engine's cylinder occurs once the fuel pressure within the injector becomes greater than the spring pressure that holds the injector needle closed against its seat, resulting in “injector needle lift”. Fuel injection will continue until the Spill Valve re-opens, spilling fuel to low pressure, resulting in the spring forcing the injector needle to return to its closed position. In this situation, the fuel pressure necessary to lift the needle at the start of injection (known as Nozzle Opening Pressure, or NOP) is related to the force within the needle spring (i.e. spring NOP). In the case of twin-valve injection systems, a secondary solenoid valve is used to regulate the control pressure applied to the back of the injector needle and, hence, NOP can exceed the needle spring pressure (i.e. variable NOP). This solenoid valve is known as the “Needle Control Valve”. It is a “three-way” valve, in that it exposes the port, whose pressure is to be controlled, to either a high control pressure (when de-energized) or a drain pressure (when energized). Similar actuator controlled valves are used in common rail fuel injection systems too. This invention refers to the control of both single and twin valve injection systems. Valve movement is facilitated by means of an actuator that comprises an electromagnetic stator (a series of coil windings wound around a stator core), through which a current is passed to activate an armature. A valve pin is directly attached to the armature, and subsequent movement of the armature/valve assembly is used to control flow of fuel within the injector. The valve pin is held in the open position by a return spring, therefore any electromagnetic force induced by the solenoid coil is working against the spring to close the valve. The control of the solenoid valve is divided into two general categories, a so called “pull-in” phase and a “hold phase”. During the pull-in phase, the armature of the solenoid-controlled valve is caused to close by the application of a first current level through the solenoid coil. During the hold phase a second, lower current level is supplied to the solenoid coil to keep the valve closed. The driving current provided during the pull-in phase is supplied by a capacitor. The capacitor and associated circuitry provide a further voltage supply means (in addition to the battery) and are hereinafter collectively referred to as the “boost circuit”. The driving current provided during the hold phase is supplied by applying the standard battery voltage across the solenoid coil in order to provide the second current level. A so-called “chopping circuit” controls the application of the battery voltage so that the required drive current supplied to the actuator throughout the injection is between defined upper and lower hold thresholds. As the battery voltage decreases, the chopping circuit may constantly apply the battery voltage to the solenoid coil during the entire hold phase of injection in order to maintain the driving current to the solenoid between the desired threshold levels. In order to maintain precise fuelling using fuel injection engines it is required that either the performance of an individual injector is known or the tolerance band of a group of injectors is well known within tight limits. As a consequence this means that factory limits during production must be tight and engine testing must be sensitive enough to pick up the performance of the injector(s). However, no matter how good the initial set up, there will be a drift in performance over the life of the injector as components bed in or wear out. In order to address the problem of component performance drift the FIE has to have internal control systems to compensate and such control systems need to be able to detect changes in injector performance. For electromagnetically controlled valves as described above, the control system may detect changes in valve performance through the detection of changes in the current profile of the coil used to drive valve motion. The current seen on a coil has a characteristic profile due to the induction effect of a decaying magnetic field and a valve moving through that field affects the current profile (this effect is generally termed back EMF). In particular, when the valve reaches the end of its travel, it will stop moving or bounce off of its seat/stop and this change can be detected as a discontinuity, or “fault”, in the current profile. Since the change in current profile corresponds to the valve meeting its stop and the valve at this point in its actuated state, it follows that what is being detected correlates with the physical events triggered by the actuated valve. Therefore, the change in the characteristic profile of the current provides an effective way to measure the start of injection or pressure rise without reference to external sensors. A fault detection system that is able to reliably and efficiently detect the changes in the current profile can then relate the change in the current profile to physical events such as the start/end of pressure and start/end of injection (delivery). This gives initial performance benefits as well as allowing the system to self correct if there are changes in valve response. It follows that one of the main disadvantages of the system without fault is that there is no way to control the injector timing to compensate for any changes that occur over the life of the system. It is known that the injector components can undergo two significant changes after installation, namely the bedding in period and wear caused during normal operation. These two conditions mean that the injector performance deviates from the factory set values over its service lifetime. There is currently no method to track changes in the valve movement characteristics in situ. Presently the only way to compare the valve performance is by removal from the application and testing in a controlled environment with reference to initial factory data (a ‘before and after’ type test). Existing fault detection relies on sampling either the voltage or current through the coil during a sampling window and then examining the measurements to determine when the valve has stopped moving. This method of fault detection has a number of shortcomings and performance limitations. One of these limitations is that the fault/sampling window actually adds energy to the system (since a voltage is artificially applied so as to drive additional current into the system) and as such is influencing the system performance. More specifically, the extra energy can extend the time the valve is actuated by adding enough energy to effectively re-actuate the valve or lead to erratic valve timing where the force/energy balance is close to sensitive limits. Fault windows may also have the problem that the window position has an influence on the position of the current discontinuity that is recorded. The closer the fault (“the discontinuity”) is to the end of the fault window, the more energy has entered the coil windings and as such this will tend to retard the natural progress of the valve (partial re-energization). This means the greater the window length before the fault, the greater the magnitude of the imposed error. As a result of the effects of window position, any detection routine must be able to rapidly and efficiently evaluate the available data and make a fault decision in the shortest possible time. This means that the detection criteria must be mathematically as simple as possible and be paired with a sufficiently powerful CPU to reduce the negative impacts of having the fault window in the wrong position. Ideally, a decision on the fault status should be decided on a shot to shot basis for the best performance benefits. Due to the operating environment of the injectors, there is typically a degree of electrical noise (typically high frequency RF) present in the engine system. Appropriate sampling methods and hardware acquisition can reduce this noise to a minimum but a successful fault strategy must also incorporate some form of noise filtering or rejection. Existing methods for fault detection that include digital signal processing are either too slow (mathematically intensive) to avoid the error due to window position or they are insufficiently effective at eliminating noise induced errors. Since the fault window is a deviation from the natural current decay by forced voltage application, there will always be a measured (i.e. non zero) current associated with it. A key difficulty in prior art fault detection systems is discriminating between a valid fault and a non valid event. In other words, the detection routine must be able to distinguish the difference between a natural current decay profile and a profile with the effects of a change in motion by the armature. The difference between these two profiles can be subtle and traditionally has been difficult to determine mathematically for the wide range of different possible valve motions. This is further complicated by the range of possible coil response profiles that all give slightly different current decay shapes. It is therefore an object of the present invention to provide a fault detector and an associated method of detecting valve movements that substantially overcomes or mitigates the above mentioned problems. According to a first aspect of the invention, there is provided a fault detector for detecting valve movement of a valve in a fuel injector of an engine system, the valve comprising an electromagnetic actuator that is arranged to move the valve between first and second valve positions during a valve cycle and the engine system comprising a sensor for sensing a current through the actuator. The detector comprises a controller arranged to control the sensor; inputs for receiving from the sensing means data related to the current through the actuator; a processor arranged to analyze the received data for current discontinuities; outputs for outputting a valve movement signal (e.g. fault detect signal) in dependence upon the current discontinuities determined by the processor. The controller is arranged to enable the sensor during a finite sampling window and is further arranged (i) to move the sampling window from a first window position for a first injection event to a progressively later window position for one or more subsequent injection events, (ii) to determine a new sampling window position on the basis of a valve movement signal output for at least two of the preceding window positions, and (iii) to feedback the new sampling window position for a subsequent injection event. The present invention provides a fault detector wherein the current through the actuator of a valve in an engine is received from a sensing means and then analyzed for discontinuities in the current profile, from which the presence of a fault can be deduced. In order to reduce the effects of the fault/sampling window adding energy to the system a control means is arranged to enable the sensing means only during a finite sampling window. Once a current discontinuity has been identified the detector can output a fault detect signal that may be a timing signal indicating the end of valve movement. If the detector is able to compare the discrete timing signal to known/expected valve operation then the detector may be able to determine unexpected valve operation. In such instances the detector may output an error signal that the vehicle's engine control unit (ECU) records or an error signal for display on the dashboard of the vehicle. If the detector is linked to or part of a valve control system then the output signal may be a control signal for adapting the firing characteristics of the injector. Subsequent injection events, for which the position of the window position is moved, may be either (i) successive injection events or (ii) one of pilot, main or post injection events within successive injection cycles. In one embodiment, the new sampling window position is determined as a median position of at least two of the preceding window positions, for which a fault detect signal is output. For example, the new sampling window position may be determined as a median position of three of the preceding window positions. The processor is arranged to analyze the current through the actuator during the sampling window and to look for and identify discontinuities in the current flow. Such discontinuities can be linked to, for example, the valve reaching its stop and so the processor is effectively able to determine valve movements in dependence upon measured current discontinuities. It is noted that the sensor may not directly sense the current through the actuator and may instead sense a parameter that is related to the current through the actuator. For example, the drive circuit may comprise a resistor in series with the actuator and the sensor may measure the voltage across the resistor. In order to reduce processing requirements, the sensor may be arranged to sample the current parameter at a plurality of sample points during the sampling window. Conveniently, the sensor may measure the current through a sensing resistor. Alternatively, the sensor may be arranged to sense the current through the actuator. Conveniently, the sensor may comprise a sensing resistor and the data received at the inputs may be related to the current through the sensing resistor or the voltage across the sensing resistor. The valve cycle may comprise a pull-in region during, a first voltage potential is applied across the actuator so that the valve is caused to move from a first state to a second state and a hold region, during which a second voltage potential or series of pulses at a second voltage potential is applied across the actuator. Conveniently, in such a “pull-in”/“hold” arrangement, the controller may be arranged to enable the sensor between the pull-in and hold regions of the valve cycle. The controller may also be arranged to enable the sensor after the hold region of the valve cycle. It is noted that these two enablement positions correspond to the points within the valve cycle when the valves within the engine are expected to reach one of their two operating positions. In order to allow the detection of faults, the controller may conveniently be arranged to output a control signal to one or more control switches in order to isolate the actuator from a power supply and to open a current path comprising the actuator and the sensor. It is noted that at the back end of the valve cycle, i.e. after the hold phase, the current through the actuator will fall towards zero. In order to detect the movement of the valve the control means may open a current path that is inactive during the pull-in and hold phases such that a current that includes the effects from the back EMF in the system flows through the sensor/drive circuit. Conveniently, the controller may be arranged to progressively move the sampling window away from the end of the hold region in successive injection events. Effective fault detection must include as small as possible a processing overhead for noise control. Using a method that relies solely on maxima detection in the current profile is ineffective since every sample will have a maximum that may or may not correspond to a valid fault. Using a threshold on the maxima is similarly ineffective since this does not allow for the range of possible valve/coil response patterns. Therefore, in order to identify current discontinuities in the current profile, the detector (processor within the detector) may be arranged to analyze the received data by determining the second derivative of the current through the actuator with respect to time. Conveniently, the processor may be arranged to determine the presence of a current discontinuity if a maxima or minima is detected in the second derivative of the current through the actuator. The second derivative may be determined based on a differential process, for which input data points are non-consecutive. This provides a processing advantage because a mathematical implementation based on a differential implementation is numerically one of the fastest operations that can be performed by a CPU. The received data may be input to an analysis routine of the processor in the form of integer values having no units, thereby to minimize data handling and manipulation requirements. Alternatively, the processor may be arranged to determine the presence of a current discontinuity if the second derivative of the current through the actuator exceeds a threshold value. This enables the detector to “filter out” transient effects within the current profile. For example, the second derivative of the current through the actuator should also exceed the threshold value for a set period of time in order for the detector to determine the presence of a current discontinuity. This also helps filter out transient spikes in the profile. Conveniently, the processor may be arranged to determine the location of the current discontinuity by determining the third derivative of the current, I, with respect to time, the location of the discontinuity being equal to the time when d3I/dt3=0. According to a second aspect of the present invention, there is provided a method of detecting valve movement of a valve in a fuel injector of an engine system, the valve comprising an electromagnetic actuator that is arranged to move the valve between first and second positions during a valve cycle, the method comprising sampling the current through the actuator during a finite sampling window, analyzing the sampled current for current discontinuities, and determining valve movements in dependence upon the current discontinuities. The method further comprises moving the sampling window from a first window position for a first injection event to a progressively later window position for one or more subsequent injection events, calculating a new sampling window position on the basis of a valve movement signal (e.g. fault detect signal) output for at least two of the preceding window positions, and feeding back the new sampling window position for a subsequent injection event. According to a third aspect of the present invention, there is provided a fault detector for detecting valve movement of a valve in a fuel injector of an engine system, the valve comprising an electromagnetic actuator that is arranged to move the valve between first and second positions during a valve cycle, the detector comprising: inputs for receiving data related to the current through the actuator; a processor arranged to analyze the received data for current discontinuities and outputs for outputting a valve movement signal (e.g. a fault detect signal) in dependence upon the current discontinuities determined by the processor. The processor is arranged to analyze the received data by determining the second derivative with respect to time of the current through the actuator. The processor may be further arranged to determine the second derivative based on a differential process, for which input data points are non-consecutive. According to a fourth aspect of the present invention, there is provided a method of detecting valve movement of a valve in a fuel injector of an engine system, the valve comprising an electromagnetic actuator that is arranged to move the valve between first and second positions during a valve cycle, the method comprising: sampling the current through the actuator in order to determine current data; analyzing the sampled current data for current discontinuities and outputting a valve movement signal in dependence upon the current discontinuities. The current data is analyzed by determining the second derivative with respect to time of the current through the actuator. The second derivative may determined based on a differential process wherein input data points are non-consecutive. The present invention extends to a computer program on a computer readable memory or storage device for execution by a computer, the computer program comprising a computer program software portion that, when executed, is operable to implement a method of the second or fourth aspects of the invention. The invention also extends to an engine control unit for a vehicle comprising a detector according to the first or third aspects of the invention. This process of differentiation provides a substantially more efficient method than the prior art, in terms of processing and memory resources. The method may be further improved by using non-unit delimited input data in the differential process. It is noted that optional features of the first aspect of the present invention may apply to the second, third and fourth aspects of the invention also. Another aspect of the invention provides a fault detector for detecting valve movement of a valve in a fuel injector of an engine system, the valve comprising an electromagnetic actuator that is arranged to move the valve between first and second positions during an engine operating cycle, the engine system comprising sensing means for sensing a current through the actuator, the detector comprising: control means arranged to control the sensing means; inputs for receiving from the sensing means data related to the current through the actuator; a processor arranged to analyze the received data for current discontinuities and outputs for outputting a valve movement signal in dependence upon the current discontinuities determined by the processor wherein the control means is arranged to enable the sensing means during a finite sampling window and is arranged to move the sampling window from a first position in the engine operating cycle to a second position in the engine operating cycle. FIG. 1 is a simple representative sketch showing a voltage waveform V that is applied across an actuator and two current profiles I1 and I2. The first current profile I1 shows the current that flows through the actuator coils as a result of back EMF when there are no sudden changes in the motion of the valve. It can be seen that the current profile is smooth. By contrast, in the second current profile I2 there is a discontinuity. This corresponds to a sudden change in the motion of the valve, e.g. when it reaches its stop. The present invention is concerned with the identification of these types of fault in the current through the actuator and with the minimization of the problems associated with known fault detection methods. FIG. 2 is a representation of a simple drive circuit 2 for a coil-based actuator 4, i.e. an electromagnetically controlled coil and a fault detector 6 in accordance with an embodiment of the present invention. The circuit comprises a power supply 8 (in this case 50V), a solenoid actuator 4 and a sensing means 10 that comprises a sensing resistor 12. Two controllable switches (switch 14 and switch 16) connect the power supply 8 to the sensing resistor 12 and actuator 4. Cross circuit connections 18, 20 are provided, each comprising a diode 22, 24 to restrict the direction of allowable current flow. The fault detector 6 comprises inputs 26 for receiving data related to the current through the actuator 4, processing means 28, control means 30 for controlling switches 14 and 16 and output means 32 for outputting a valve movement signal. The voltage across the sensing resistor can be measured and therefore the current through the solenoid determined. The power supply and controllable switches 14 and 16 may be controlled by, for example, an engine control unit (ECU) (not shown in FIG. 2). A typical current profile 40 representing the current through the actuator 4 during a single combustion cycle is shown in FIG. 3a. FIG. 3b shows the corresponding valve movement 42 as the current varies. The operation of the valve and drive circuit will now be described with reference to FIGS. 2 and 3. In order to initiate injection, both switches, 14 and 16, are closed. The current through the actuator 4 then rises from zero up to a maximum peak value 44. This phase of the injection cycle is referred to as the “pull-in” phase (or alternatively as the “front end”). Once the current has reached its maximum value, switch 14 is opened and the current begins to decay naturally. During this current decay the valve moves such that injection commences. As the current falls to a certain level, switch 14 is repeatedly opened and closed (or “chopped”) in order to maintain injection through the activated valve. This chopping is shown by a number of smaller peak values 46, 48, 50 in the current profile. This phase of the injection cycle is known as the “hold” phase. To terminate injection both switches 14 and 16 are opened and the current falls to zero. After a short time lag and as the current falls, the valve moves to its un-activated state. In order to detect when the valve reaches its stop, switch 16 may be re-opened such that a current path is formed. Due to the effects of the valve moving through the magnetic field created by the actuator coil, a back EMF is set up that either re-enforces the current or partially cancels the current (depending on the direction of motion of the valve). This period of EMF-related current and normal current superposition is shown in FIG. 3a (between 52 and 54). FIG. 3b shows the corresponding valve lift during the current events. When the valve reaches its stop there will be a discontinuity or fault 56 in the current profile that corresponds to feature 58 in FIGS. 3a/3b. (It is noted that the valve depicted in FIG. 3b undergoes a “bounce” event 59. This type of event can occur in cases of rapid valve timing changes where the valve may effectively bounce). This “fault detection” phase of FIGS. 3a and 3b is also known as the “back end” of the combustion cycle/engine operating cycle of the engine. It is also noted that there will be a further “fault” 60 that is produced as the valve first reaches its activated state (i.e. between the pull-in and hold phases). In any given combustion cycle there will be two faults 58, 60. To reduce processor loading the current profile is usually sampled within a defined period, herein termed as the “sampling window”. FIG. 3a has been marked to show the location of two sampling windows 62, 64 around the expected positions of the two faults. It is also noted that to reduce processor loading further the current through the actuator would normally be sampled at a number of defined sample points rather than continuously through the sampling window. This is illustrated in FIG. 3c wherein the sampling window 62 between the pull-in and hold phases is shown in more detail, and individual sampling points 66 are highlighted. FIG. 4 shows the effect the fault window may potentially have on the movement of the valve. It is noted that FIG. 4 shows a sample window 80 that is too early relative to the movement of the valve. The current profile at the end of the hold phase is shown in more detail in FIG. 4. A sampling window is also shown, during which a current that includes the effects from the back EMF in the system flows through the drive circuit. The current profile 70 during the sampling window has a characteristic shape. The movement of the valve as the current varies is also shown in the Figure. A first valve lift line 72 is shown that indicates that the valve should reach its stop position shortly after the end of the sampling window. A second valve movement trace 74 depicting the actual valve movement is also shown. This second trace 74 illustrates the effects of the current in reenergizing the drive circuit of the valve. It can be seen that the sampling window has the effect of delaying the valve. To reliably detect a fault in such circumstances is difficult. A prior art solution is to extend the duration of the sampling window (i.e. in this “back end” example of FIG. 4 this would be activated by keeping switch 2 closed for longer). This solution however would have the effect of delaying the valve movement even further since keeping switch 2 open for longer means that the current input and hence magnetic field strength affecting the valve would be greater, retarding its natural motion. A sampling window and method of fault detection in accordance with a first embodiment of the present invention is shown in FIG. 5. In this embodiment of the invention the sampling window is not fixed at a certain point in the combustion cycle of the engine but is instead capable of being swept in time between different cycles. In FIG. 5, five different sampling window locations are depicted relating to a specific injection event (e.g. pre-injection, main injection or post injection) within subsequent injection cycles. It is also noted that the five sampling window locations are arranged to be progressively moved away from the end of the hold region in successive injection cycles. This is done in order to ensure that the first fault is detected and to mitigate against the possibility of a secondary fault (caused by valve bounce as described) above being misclassified as the primary fault. The window 80 starts in an initial position (Position 1) that may be a fixed period of time after the end of the hold period. In this position the current profile 82 resembles the profile of FIG. 4, wherein the current slowly builds to a maximum at the end of the sampling window before falling away to zero. From the valve movement trace 84 shown in FIG. 5 it can be seen that the sampling window's initial position is too early and has missed the “fault point” 86 (i.e. the valve stop). In the next injection cycle the sampling window 80 has been advanced to a later time (Position 2). The profile 88 has now changed and the maximum 90 in the current profile is now seen to be located part way through the sampling window 80 (as opposed to at the end of the sampling window as in the first position). It is clear that the sampling window has “found” the fault 86. In Position 3, for the next injection cycle, the sampling window 80 has been moved even further forward in time. The current profile 92 is similar to that of Position 2 but the current discontinuity 94 now appears in a slightly earlier part of the current profile. In Positions 4 and 5, for subsequent injection cycles, the sampling window 80 has been moved past the first fault 86. The current profile 96 in Position 4 shows no evidence of a current discontinuity but the current profile 98 in Position 5 shows a further discontinuity 100 that represents a secondary valve stop event 102 (it is noted that in cases of rapid valve timing changes the valve may effectively bounce and so there will be a secondary fault). A few observations relating to the above discussion of the first embodiment of the invention are noted. Firstly, in Positions 2 and 3 it is noted that the position of the fault 86 is actually a constant time after the end of the hold period. It is only the sampling window 80 (and therefore current profile 88, 92) that has moved to a later time between Positions 2 and 3. Secondly, any prior art method of fault detection that relies on jumping to a last known location of the fault runs the risk that the secondary bounce event is detected and not the main event. The method according to the first embodiment of the present invention avoids any such issues and in fact has the advantage that both faults may be detected. The fault that is detected corresponds to a discrete timing point (i.e. the sharp/discontinuous end of valve movement). Therefore, once the fault has been detected, the detector may output a valve movement signal to, for example, the vehicle's ECU that comprises this discrete timing point. FIG. 5 describes the use of an adaptive sampling window 80 at the back end of the injection cycle. It is however noted that the same principle may be applied to a sampling window at the front end of the injection cycle. An example of such a sampling window is depicted in FIG. 3c and is discussed in more detail below. It is noted that in this case the sampling window 80/sample points 66 may be moved in time until the front end fault is detected. Further advantages of the adaptive sampling window according to the present embodiment of the invention are as follows: An adaptive window sweep allows detection of the fault when the individual valve characteristics are unknown. This means that the individual valve timings required for accurate and precise adjustment of waveforms can be found while the injector is running, instead of relying on factory testing. It also means that rapid valve timing changes (for example if the valve seat is damaged by debris) can be picked up and compensated for. The effect of energy input to the system can be minimized by moving the sampling/fault window as far as possible from sensitive areas. For example, if the sampling window is too close to the end of the hold region, the valve may not open and the valve actuation period may be extended. Similarly, if the sampling window is too far from the end of the hold region, there is a risk of unwanted detection of secondary bounces or other artifacts. As the window moves past the fault, less energy will be returned to the magnetic flux and hence there will be a smaller imposed error due to window position. A moving sampling window means that the fault can be searched for by a series of steps from the sampling window initial position (Position 1) to the sampling window end position (Position 5). Typically the start position is offset from the end of the hold region. The moving sampling window allows for detection of the fault under transient conditions without changing the major search parameters. The sampling window position is adapted to the different positions required for detection due to changed engine running conditions (e.g. speed/load changes). FIG. 5 gives an example of a back end sampling window sampled from a typical running condition. The minimum and maximum window positions are also adapted according to the current running conditions. This means that the effective search area can be maximized for each condition as well as avoid any problem areas. Where the fault position can be estimated (or is known) from a previous detection at a given condition, the adaptive window is able to jump directly to this location and begin fine tuning the position as below. After finding a fault, the adaptive window is able to centre itself on the fault position and fine tune the detection by small movements around the known fault point. This allows for higher precision as the fault value can then be an amalgam of several real time values. As described in relation to a further embodiment of the invention below, a suitable processing algorithm may be used to identify the presence of a fault. Advantageously, by moving the sampling window 80 at the front end of the injection cycle allows the same algorithm to be used for both types of detection since ultimately the algorithm will only see a limited number of samples. This improves both the memory usage and data handling requirements. The following further benefits are also noted with respect to a front end sampling window: The fact that a moving sampling window is used means that a reduced number of samples are required so as to reduce CPU and memory load for the sampling algorithm at both the front end and the back end. Using adaptive front end sampling means that there is better response to transient or rapidly changing engine conditions. Adaptive front end sampling also reduces the possibility of noise or spikes triggering a false detection since at any time only a fraction of the total current profile is being examined. The adaptive front end sampling window moves the region of sampled points in the current data away from the point of peak current in the same manner that the fault window is moved away from its minimum position. The delay between the peak current in the pull-in phase and the start of sampled region is increased in an analogous way to moving the window position for the back end. A key difference is that the start of the chop region is linked to the end of the sampling window by a set delay. This means that the start of the chop region relative to the sampling window is fixed but moves away from the peak position at the same time the sampling window is moved up until the maximum sampling position is reached. Thus if a fault is detected, the start of the chop region will occur at a set time after the fault in order to minimize the energy loss of the coil by reducing the time when the magnetic field is in the free decay state. FIGS. 6 to 8 show further, more detailed examples of an adaptive sampling window 80 in accordance with the first embodiment of the present invention and are considered in conjunction with FIG. 4 described above. FIG. 4 represents the initial position of the adaptive sampling window. As shown in FIG. 4 the window extends from approximately 0.25 milliseconds from the end of the hold phase to 0.75 milliseconds after the end of the hold phase. In FIG. 6 the start of the sampling window 80 has moved to approximately 0.3 milliseconds after the end of the hold phase. The end of the sampling window is now located at approximately 0.8 milliseconds. For comparison the location 108 of the maximum current from FIG. 4 is marked on FIG. 6 and it can clearly be seen that the maximum position has moved relative to FIG. 4. Valve movement (both normal motion 72 and window affected valve motion 74) is again marked on FIG. 6 and it can be seen that the window 80 ends just as the valve would (if the sampling window were not affecting valve motion) be approaching its stop position. However, because of the re-energizing effect of the window drive circuit the valve movement is again delayed. In FIG. 7 the sampling window 80 has again moved position and it now extends from approximately 0.4 milliseconds to 0.9 milliseconds after the end of the hold phase. In this Figure it can be seen that both of the valve movement traces reach zero within the confines of the sampling window thereby indicating that the sampling window is now overlapping the stop position of the valve. The current maximum positions 108, 110 from FIGS. 4 and 6 are marked on FIG. 7. The current profile now shows a discontinuity (fault) 112 at around 0.8 milliseconds after the end of the hold phase. In FIG. 8 the current maximum 114 is now clearly located within the window. For comparison the maximum from FIG. 4 is indicated on the current profile. The above description of the first embodiment of the invention relates to “sweeping” the fault window for successive injections within an engine operating cycle (e.g. speed/load condition). In practice, and as shown in FIG. 9, an injection cycle may include more than one injection event, in which case a fault window “sweep” takes place for each of the like-injection events over consecutive injection cycles. Referring to FIG. 9, an example injection cycle includes a pilot injection (or pre-injection), a main injection and a post injection. The current profile for three injection cycles is shown, together with the position of the moving fault window for each event. For injection cycle 1, the pre-injection has a fault window position A1, the main injection has a fault window position A2 and the post injection has a fault window position A3. Likewise, for injection cycle 2 the pre-injection has a fault window position B1, the main injection has a fault window position B2 and the post injection has a fault window position B3 and for injection cycle 3 the pre-injection has a fault window position C1, the main injection has a fault window position C2 and the post injection has a fault window position C3. A single valve cycle (i.e. where the valve moves from an initial position to an activated position and then returns to its initial position), corresponding to the pre-injection event of injection cycle 1, is indicated by the box X. FIG. 10 illustrates a flow diagram of the fault window sweep algorithm that is carried out for each injection event type of an injection cycle. The routine includes the following steps: An initial window position A1 is set for the pre-injection and, if a fault is detected, the fault position is input to a data buffer. For the next pre-injection event, the window position is moved through a window step to position B1 (as shown in FIG. 9) and, if a fault is detected, that position is stored in the data buffer. When three consecutive fault detection events have been detected, this is taken as an indication that a genuine valve stop event has been detected and these three fault detection times are transferred to the first three elements of a median data array. This sequence of events continues for the pre-injection events of consecutive injection cycles (third, fourth, fifth injection cycles . . . ), incrementing the window position by the window step for each cycle. The sequence of events is continued until such time as the fault window has moved to a maximum window position or until the median array has become full. If the maximum window position has been reached, this signifies that the sweep has completed but without the required number of consecutive faults having been detected (referred to as “a result”). When the median array becomes full, a valid fault timing point is determined as the median of the values in the median array. Where the sweep of window position completes without a result, the value of the maximum window position can be set in software to any convenient value, although for speed of operation (iterations of the sweep process) it is best to keep this value to the minimum required. Where a valid fault window position is determined from the median of the values in the median array, this window position may then be used to adjust the main waveform parameters. Thus, a given valve may perform at any opening speed and the main control waveform for the valve may be adjusted such that the corresponding physical event occurs at the required time. Since changing the main control waveform constitutes a change in operating conditions, the sweep process may also need to be re-iterated. In practice it may be useful to have programmatic damping on the number and size of adjustments to the main waveform to avoid unnecessary iteration of the sweep process. With the window in this optimum position for subsequent injection events the impact of the window position on the fault time is minimized and the accuracy of any further fault times are maximized. If the fault stops being detected at this centered position (for example if engine operating conditions change), the sweep process is restarted. The centered window position value may be stored in memory and used as the starting point for any subsequent sweep iterations to speed up the detection process. In this way the fault window position is adapted based on preceding fault detection events, the key feature being that feedback from the fault detection process is needed to determine the next window position. The same method steps are also followed for the main- and post-injection events of the injection cycles, with the fault positions for each being stored in a designated data buffer for that particular injection event type. A median value of fault position is determined once the median array is full and this value is used for subsequent injection events of that type. In practice it may be preferable to use more than three fault detection events to determine the median value. For example, the detection of three consecutive fault detection events may be taken as an indication that a genuine valve stop event has been detected, but subsequent fault detection events may be added to the median data buffer before the median value calculation is carried out. It can be seen from FIG. 11 and FIG. 12 that the greatest influence of window position on detected fault time occurs for the first few detections, so it is beneficial to add as many further detection events as possible to the median array. In this way the median value determined will have the least bias due to early window positions. A drawback to having a large median array size is the potential to sweep past the fault position before filling the median array. In this way the choice of median array size becomes a compromise between accuracy and robustness for any given application. For example, it may be preferable for the median value to be determined from three consecutive faults and a further three faults (not necessarily consecutive) within the sweep (i.e. before the maximum window position is reached). By way of example, FIGS. 11 and 12 show the result of the median fault position calculation for a series of six faults for transient and steady state engine operating conditions, respectively. By continually adapting the fault window position based on several preceding fault detection events (e.g. by calculating the median value), a more accurate selection of fault window position is selected that has the least impact the fault detect measurement. This feature is particularly useful for dealing with a wide range of operating conditions (both static and transient) that need not be known beforehand, as well as coping with a variety of valve configurations including pressure driven valves operating at high speeds (i.e. valves for which the basic timing parameters are affected by operating conditions). The first embodiment of the present invention relates to an adaptive window that may be used to detect faults in the operation of an electromagnetically controlled valve. In the second embodiment of the present invention an analysis technique for determining the presence of a discontinuity in the sampled current profile is disclosed. It can be seen from FIGS. 4, 6-8 that the position of the maximum in the current profile moves with the sampling window 80 until a fault 112 is uncovered, at which point the current maximum remains fixed. One method of analysis for determining the location of a fault is to record and plot the position (in time) of the current maximum. The location of a fault is determined by looking for “bunching” in the position of the current maximum, for example as the window is moved between successive positions (in different engine operating cycles) the temporal location of the current maximum is expected to change by a known amount. As the fault is approached the maximum will move relatively less (compared to readings taken before the sampling window reached the fault point) and so the measured current maximum positions will get closer to one another. The presence of the fault can then be inferred. The above analysis technique is potentially susceptible to mis-detection of the fault due to noise and other anomalies in the measured current profile. The signal processing required to implement the above technique may also place significant processing loading on the processor used to manipulate the sampled data. The second embodiment of the present invention therefore provides an analysis implementation that reduces calculation overhead and reduces the need for signal processing. The second embodiment of the present invention takes the sampled raw current data and determines the first and second derivatives of the current values with respect to time. The reason behind going to the second differential is that looking for a maximum by examination of the raw data alone leads to mis-detection, as every sample will have a maximum and using a threshold, above which the maximum is defined, implies that samples close to the fault points would still falsely trigger. The second differential method ensures that the sample has passed through a genuine maximum. In one aspect of this embodiment of the present invention the third differential of the current values may be determined and analyzed to determine where the third differential crosses zero. This further differential is used to avoid false detection caused by brief spikes or noise over the threshold limits. The method of using differentials in the detection routine gives a good detection response over a range of possible valve current signatures. Using differentials of the form outlined below also has the advantage of adding some filtering to the raw data and in this way increases the tolerance of the algorithm to sources of outside electrical noise as would be expected in the application environment. This method of differential implementation also has the benefit of faster calculation because it is based on the mathematical difference between values, which is numerically one of the fastest operations that can be performed by a CPU. This reduces the calculation overhead and eliminates the need for further signal processing. The second embodiment of the present invention will be described in detail with reference to FIGS. 14 to 20. In FIG. 13, however, a comparison of the analysis technique according to the second embodiment of the present invention is illustrated with respect to (i)-(iii) an idealized current profile (no fault) and (iv)-(vii) an idealized current profile exhibiting a fault. The left hand side of FIG. 13 shows (from top to bottom): graph (i)—the sampled current data for the current profile without a fault; graph (ii)—the first derivative of the current profile; graph—(iii) the second derivative of the current profile. The right hand side of FIG. 13 shows (from top to bottom): graph (iv)—the sampled current data for the current profile with a fault; graph (v)—the first derivative of the current profile; graph (vi)—the second derivative of the current profile; graph (vii)—the third derivative of the current profile. In graph (i) it can be seen that the current profile is a smooth curve. The derivative of this current profile is shown in graph (ii) and is seen to be a straight line of negative gradient. The second derivative of the current profile is therefore a straight line. By contrast, it can be seen that the current profile in graph (iv) has a discontinuity at the marked location. The first derivative of the current profile is shown in graph (v) and due to the discontinuity it is noted that the first derivative is not a straight line as was the case in graph (ii). In graph (vi) the second derivative of the current profile has been taken for the fault current profile and it can be seen that there is a minimum in the trace (and the minimum is centred on the position of the fault). The presence of the fault can therefore be conveniently be determined by calculating the second derivative and analyzing the second derivative for regions that exceed a threshold value. It is noted that the position of the minimum (or maximum in the case of a fault analysis performed on the front end of the injection cycle) equates to the location of the fault. The third derivative of the current profile may be determined to confirm the location of the fault (see graph (vii)), the fault being located at the zero crossing point of the third derivative. The rules and criteria for successful detection according to the second embodiment of the present invention are designed to be simple and robust on the basis of the values of the differential arrays. The second differential must be greater than a given threshold (the d2 threshold) and the third differential (d3) must cross zero in the same range of points that are above the d2 threshold. There is an added feature that there must be a minimum number of points to be a valid range for detection of the d3 zero crossing to avoid false triggering due to spikes/noise. Using the d3 zero crossing method means that even in areas of high d2 values (i.e. over the d2 threshold) only actual maxima will be detected. This benefit of the d3 system means that the broadest possible range of values is tested for possible fault characteristics. It also means that relatively low values of d2 threshold can be used so as to ensure the largest range of different valve responses can be analyzed at the same settings (i.e. it maximizes the variation that can be handled between units). Using the above method of detection also has the benefit of being able to discriminate between different valve motion events. Since the window moves linearly and the d2 threshold can be changed easily, the control of these parameters allows detection of first bounce (the initial impact of the valve upon its stop), second bounce (after the first bounce, the valve motion returns to its original course and again impacts the stop but with reduced force and speed) and other bounce events. The ability to detect the various bounce events has benefits for development and analysis in the motion of the valve can be studied in a more detailed way. A second major benefit to being able to collect bounce data is using this as an alternative to first bounce fault for timing control purposes. For example if the valve hitting its stop is rapid enough then there can be insufficient time for the corresponding fluid event to occur (such as pressurization due to restricted flow around the valve seat). In this instance, the second bounce may be a better predictor for the physical event as the valve is moving slower as it approaches its stop. The method of differential calculation is described below in conjunction with FIGS. 14 to 20. In FIG. 14, a current profile 120 is shown. During the sampling window the current is sampled m times at equal time intervals, x (in this example m=25), as indicated by sample points 122. FIG. 15 shows the sampled data points 122 only with the magnitude of the current sample marked for each data point. Each data point has also been numbered as 1 through 25. The parameter of differential spacing (ds) may be used to control the amount of filtering or ‘smoothing’ that is imposed on the data. ds is defined as the number of spaces between sampled points that is used in the differential process. FIG. 16 shows the data samples of FIG. 15 with a differential spacing of 5. As the gradient between any two points on the current sample is equivalent to the differential at a point halfway between the two, taking the gradient between points spaced ds apart gives the slope at a point halfway between the two. It follows that ds is therefore limited between ds=1 (consecutive points, no filtering) and ds = m 2 (half the sample size). The gradient between consecutive points would be Δ ⁢ ⁢ y Δ ⁢ ⁢ x ,which is y n + 1 - y n x n + 1 - x n (using n as the individual point number from n=1 to n=m.) Using derivative spacing ds, this becomes y ds + n - y n x ds + n - x n .With a fixed time interval, over which the samples are taken, which is equivalent to ss (sample spacing), this further reduces the measure of gradient to y ds + n - y n ds × ss (for the purposes of illustration, the gradient position can be thought of as ds 2 + nalthough this is not used in the actual detection process). Since ds and ss are controlled parameters and fixed during each iteration of the detection loop, they can be ignored. The reason they can be ignored is that the detection process does not need to know the absolute position in time and when ds and ss are fixed, they act effectively as a redundant multiplier of the form 1 ds × ss (Note that any thresholds applied for detection rules must take this into account). Thus the measure of gradient reduces to yds+n−yn. This means that in terms of processing, the derivative calculation becomes a difference of 2 numbers extracted from an array for the y and the x component becomes a constant. In this way both the calculation complexity and the memory requirements for differential generation are reduced. The derivative calculation for the first two data points in FIG. 16 is shown on the Figure. The derivative calculation can be carried out for all the data points shown in FIG. 16 and the results plotted on a further graph (see FIG. 17). As noted above FIG. 17 shows a graph of the first derivative values determined from the sampled current values of FIG. 16. In order to obtain the second derivative of the sampled current the derivative calculation described above can be repeated for the data points of FIG. 17. The second derivative calculation for the first two data points in FIG. 17 is shown once again on the figure and it is noted that the calculation can be carried out for all the first derivative data points in FIG. 13 to produce a further graph, shown in FIG. 18, which represents the second derivative with respect to time. The derivative calculation can be repeated once again on the data points of FIG. 19 in order to derive the third differential of the current profile. This calculation is once again shown for the first two data points on FIG. 18 and the third differential graph that results from this further calculation is shown in FIG. 19. FIG. 20 is a combined graph showing the current sampled during the fault window and the first, second and third derivatives (i.e. a combination of FIGS. 14 to 19). It is noted that the form of the derivative calculation described above will reduce the number of data points at each successive iteration of the process because the calculation relies on taking the difference between two data points and therefore the last five data points will, in the above example where ds=5, not have a corresponding data point to determine a difference value from. It is noted that the presence of a fault can be determined from FIG. 14 by the presence of a minimum in the second differential. The position of this minimum provides the position of the fault in the injection cycle and this position may be confirmed by analyzing the third differential graph of FIG. 19 for the zero crossing point. FIGS. 14 to 20 are a visual illustration of the analysis process according to the second embodiment of the present invention using data extracted from the typical waveform given in FIG. 14. Real units of time and current are shown as an aid only. In practice this data may be uncalibrated, having no units and be represented as integer values stored in memory. The integer values may be passed directly from the sampling routine, which minimizes the data handling and manipulation requirements. The invention utilizes a process of differentiation that includes inherent noise filtering properties that sets it apart from known differentiation methods. The differentiation process is substantially more efficient than previous methods in terms of processing and memory resources and is achieved through the use of non-unit delimited representations of the data and the difference between values being determined using an offset and subtraction technique (effectively a sliding binary mask). The binary mask aspect means that the method is particularly well suited to embedded hardware applications that may not have access to or need floating point capabilities. Instead of looking at the difference between successive data points, the difference between data points that may be several units in time spaced from one another are examined, and it is this feature that introduces the filtering benefit As also noted above, the fault that is detected corresponds to a discrete timing point (i.e. the sharp/discontinuous change to, or of, end of valve movement). Therefore, once the fault has been detected, the detector may output a valve movement signal to, for example, the vehicle's ECU that comprises this discrete timing point. It will be understood that the embodiments described above are given by way of example only and are not intended to limit the invention, the scope of which is defined in the appended claims. It will also be understood that the embodiments described may be used individually or in combination.
	claims	1. A deposition substrate comprising a support and a reflective layer disposed on the support,wherein the reflective layer includes light-scattering particles and a binder resin with a glass transition temperature of −100° C. to 60° C.,the thickness of the reflective layer is 5 to 300 μm, andthe volatile content in the reflective layer is not more than 0.5 mg/m2. 2. The deposition substrate according to claim 1, wherein the light-scattering particles include at least one selected from alumina, yttrium oxide, zirconium oxide, titanium dioxide, barium sulfate, silica, zinc oxide, calcium carbonate, glasses and resins. 3. The deposition substrate according to claim 1, wherein the light-scattering particles include at least one type of particles selected from hollow particles having a hollow portion within the particle, multi-hollow particles having a number of hollow portions within the particle, and porous particles. 4. The deposition substrate according to claim 1, wherein the light-scattering particles include at least titanium dioxide. 5. The deposition substrate according to claim 1, wherein the support includes a resin as a main component and the reflective layer is disposed on the support. 6. The deposition substrate according to claim 5, wherein the resin is polyimide. 7. The deposition substrate according to claim 1, further comprising a light-absorbing layer on the side opposite to a scintillator layer formation scheduled surface of the reflective layer. 8. A deposition substrate production method comprising forming a reflective layer including a binder resin on a support, and cutting the deposition substrate after the formation of the reflective layer. 9. The deposition substrate production method according to claim 8, wherein the glass transition temperature of the binder resin is −100 to 60° C., andthe thickness of the reflective layer is 5 to 300 μm. 10. A scintillator panel obtained by forming a scintillator layer by deposition on a scintillator layer formation scheduled surface of the deposition substrate described in claim 1. 11. The scintillator panel according to claim 10, wherein the light-scattering particles include at least one selected from alumina, yttrium oxide, zirconium oxide, titanium dioxide, barium sulfate, silica, zinc oxide, calcium carbonate, glasses and resins. 12. The scintillator panel according to claim 10, wherein the light-scattering particles include at least one type of particles selected from hollow particles having a hollow portion within the particle, multi-hollow particles having a number of hollow portions within the particle, and porous particles. 13. The scintillator panel according to claim 10, wherein the light-scattering particles include at least titanium dioxide. 14. The scintillator panel according to claim 10, wherein the support includes a resin as a main component and the reflective layer is disposed on the support. 15. The scintillator panel according to claim 14, wherein the resin is polyimide. 16. The scintillator panel according to claim 10, further comprising a light-absorbing layer on the side opposite to the surface of the reflective layer on which the scintillator layer is disposed. 17. The scintillator panel according to claim 10, wherein the scintillator layer has a columnar crystal structure formed by depositing raw materials including cesium iodide and one or more activators including at least thallium. 18. The scintillator panel according to claim 10, wherein the surface of the scintillator layer is covered with a protective film. 19. The scintillator panel according to claim 18, wherein the protective film is a polyparaxylylene film. 20. The scintillator panel according to claim 10, wherein the scintillator layer includes columnar crystals grown from an interface between the reflective layer and the scintillator layer. 21. The scintillator panel according to claim 10, wherein the scintillator panel is supported on a support plate having higher rigidity than the deposition substrate. 22. A scintillator panel manufacturing method comprising forming a reflective layer including a binder resin on a support, and forming a scintillator layer on the reflective layer by deposition, wherein the heights of columnar crystals forming the scintillator layer are aligned by applying a pressure of 1,000 to 10,000,000 Pa to the surface of the scintillator panel at a temperature not less than the glass transition temperature of the binder resin. 23. The scintillator panel manufacturing method according to claim 22, wherein the glass transition temperature of the binder resin is −100 to 60° C. and the thickness of the reflective layer is 5 to 300 μm.
	description	This application is a divisional application of U.S. patent application Ser. No. 10/988,514, filed on Nov. 16, 2004. This invention relates generally to an exposure apparatus for projecting a pattern of a mask onto a photosensitive substrate through a projection optical system and, more particularly, to an exposure apparatus that uses ultraviolet light as exposure light. The procedure of the production of semiconductor devices comprising a very fine pattern, such as LSIs or VLSIs, uses a reduction type projection exposure apparatus arranged to project, in a reduced scale, a circuit pattern formed on a mask onto a substrate having a coating of a photosensitive material, thereby to print the pattern on the latter. Since the packaging density of semiconductor devices has increased considerably, a reduction in size and width of a printed pattern has been required more and more. Thus, development of a resist process has been strengthened on one hand, and improvement of the exposure apparatus to meet the device miniaturization has been promoted on the other hand. As regards deep ultraviolet light, particularly, an ArF excimer laser having an emission wavelength of about 193 nm or a fluorine (F2) excimer laser having an emission wavelength of about 157 nm, it is known that there is an oxygen (O2) or moisture (H2O) absorbing band in the bandwidth region near these emission wavelengths. This means that, regarding the light path of an exposure optical system of a projection exposure apparatus in which deep ultraviolet light, such as an ArF excimer laser or a fluorine (F2) excimer laser is used as a light source, the concentration of a disturbing substance (hereinafter, this will be referred to also as an “impurity concentration”), such as oxygen or moisture, should be maintained at a low level, of a ppm order. To this end, the light path of exposure light in exposure apparatuses is partially purged by the use of an inactive or inert gas. FIGS. 16, 17 and 18 are sectional views, respectively, each showing a known exposure apparatus having purge means for partially purging the space near a wafer. More specifically, FIG. 16 shows a sectional structure, near a wafer, of an exposure apparatus, as disclosed in Japanese Laid-Open Patent Application, Publication No. 2001-358056. This apparatus is provided with a cover 9 that covers the exposure light path from the wafer-side lower end portion of a projection optical system 5 near a wafer stage 10, and a supply port 6 for blowing a purge gas, consisting of an inactive gas, into the inside of the cover 9. By supplying a purge gas into the cover 9 inside, gas purging is carried out. Here, in order to prevent the outside atmosphere from entering into the inside of the cover 9 from the outside thereof, the inside pressure of the cover 9 is made higher than the outside pressure, and also, the purge gas supplied into the inside of the cover 9 from the supply port 6 is caused to flow outwardly from the cover 9 through the clearance between the cover 9 and the wafer 11. In FIG. 16, denoted at 8 is the flow of purge gas. Denoted at 27 is a base table of the projection optical system, and denoted at 28 is a base table of a wafer stage. FIG. 17 shows an exposure apparatus as disclosed in Japanese Laid-Open Patent Application, Publication No. 2002-513856. In this apparatus, a stage member 203 includes a gas bearing 215 formed to surround the wafer supporting surface 213 of the stage member 203. The gas bearing 215 includes lands 216, 217, 218 and 219 formed on the stage member 203. A supply channel 220 is defined between the lands 216 and 217, while a supply channel 222 is defined between the lands 218 and 219. Inactive gases are supplied through these channels. Additionally, an exhausting channel 221 is defined between the lands 217 and 218, to exhaust the gas. The attraction produced by this gas bearing 215 is sufficient to apply a load to or urge the stage member 203 relative to a reference member 202, such that the stage member 203 tends to be attracted to the reference member 203 actually without contacting thereto. Thus, this enables the structure that the stage member 203 and the reference member 202 are disposed close to each other, with a clearance maintained therebetween. With the provision of this clearance, the flow upon the land can be a relatively high speed flow, and it prevents surrounding air from flowing into a chamber 204. Hence, a substrate W can be sealed inside the chamber 204. FIG. 18 shows an exposure apparatus as disclosed in Japanese Laid-Open Patent Application, Publication No. 2001-210587, and it illustrates a horizontal sectional view of a washing box 500 for a substrate stage, which comprises covers 510 and 520 that surround a central region 501 placed beneath a final element of a projection lens PL. In the exposure apparatus of FIG. 18, there are orifices 517 and 527 formed at the bottom faces of supply channels 511 and 523. Purge gases are supplied through these orifices whereby, as in the exposure apparatus of FIG. 17, gas bearings 518 and 528 for separate protection of covers 510 and 520 from a substrate W are provided. Outside the supply channels 511 and 523, there are exhaust channels 512 and 524 as well as a series of larger-size orifices 519 and 529 formed at the bottom faces of the channels. The purge gases from the gas bearings 518 and 528 are exhausted by this, whereby any atmospheric gas leaked to below the covers 510 and 520 is prevented from reaching the central region 501. Denoted at 521 is a purge gas supply channel, and denoted at 516 is an orifice 15 for supplying a purge gas to the central region 501 from the supply channel 521. Denoted at 540 is a skirt for restricting the flow of air leaking from under the covers 510 and 520 toward the central region 501. Both of FIGS. 17 and 18 are examples of purge means wherein a gas bearing is formed. In the exposure apparatus of FIG. 17, a gas bearing is defined by forming a channel at the stage side, whereas, in the exposure apparatus of FIG. 18, a gas bearing is defined by forming a channel at the projection lens side. On the other hand, in the trend of improvements in exposure apparatuses for dealing with device miniaturization, a strict precision of not greater than 10 nm is required for an X-Y positioning system for carrying a wafer thereon and positioning the same in place. To meet this requirement, a laser interferometer is used for the position measurement. In the distance measurement based on a laser interferometer, a change in gas concentration (variation of refractive index thereof) along the measurement light path is a factor of an error. The gas concentration (density) is variable with temperature and humidity. Thus, in order to reduce such variation, conventionally, this type of X-Y positioning system is provided with air conditioning means so that a temperature and humidity controlled gas is blown from a side face (or in the x or y direction) to thereby reduce a variation in temperature and humidity of the gas along the measurement light path. FIG. 19 is a schematic and plan view, showing a known example of an X-Y positioning system, which is usable in the exposure apparatus of FIG. 16. In FIG. 19, denoted at 10 is a wafer stage, and denoted at 11 is a wafer. Denoted at 14 is an X-axis laser interferometer, and denoted at 15 is an X-axis measurement light path. Denoted at 16 is an X-axis measurement mirror. Denoted at 17 is a Y-axis laser interferometer, and denoted at 18 is a Y-axis measurement light path. Denoted at 19 is a Y-axis measurement mirror. Denoted at 20 is an air conditioning system, and denoted at 21 is a blown gas. In the structure described above, by means of the air conditioning system 20, temperature and humidity controlled gas 21 is blown, by which the temperature and humidity around the wafer stage or along the X-axis measurement light path 15 and Y-axis measurement light path 16 are stabilized. In an exposure apparatus using deep ultraviolet light, as described above, a cover is provided at a wafer-side lower end portion of a projection optical system, while a supply port for blowing a purge gas into the inside of the cover is provided, by which the purge gas is supplied into the inside of the cover for purging of the same (FIG. 16). However, it has been found by the investigation made by the inventor of the subject application that, since the purge gas supplied into the inside of the cover flows outwardly from the inside of the cover and disperses around the wafer stage, there occurs non-uniformness of purge gas concentration around the wafer stage, which causes a measurement error of the laser interferometer. Such a measurement error directly causes defects of semiconductor devices produced, and a considerable decrease of productivity of the apparatus. Now, referring to FIGS. 20A, 20B, 21A and 21B, an uneven purge gas concentration around the wafer stage, caused by the purge gas flowing outwardly from the inside of the cover, will be explained. FIGS. 20A, 20B, 21A and 21B are plan views, respectively, around the wafer stage 10, and they are schematic contour-line illustrations of a purge gas concentration distribution produced when the purge gas flows outwardly from the inside of the cover 9. In the contour-line illustrations of FIGS. 20A-21B, the darker the color is, the higher the purge gas concentration is, and the lighter the color is, the lower the purge gas concentration is. A white color area depicts a zone where no purge gas is present. FIGS. 20A and 20B illustrate purge gas concentration distributions in a case wherein no air conditioning system is used. Referring to FIGS. 20A and 20B, a case wherein no air conditioning system is used will be explained first. FIG. 20A illustrates a purge gas concentration distribution as the wafer stage 10 has moved closest to the X-axis laser interferometer 14 and the Y-axis laser interferometer 17, in the exposure operation. FIG. 20B illustrates a purge gas concentration distribution as the wafer stage 10 has moved most remote from the X-axis laser interferometer 14 and the Y-axis laser interferometer 17, in the exposure operation. It is seen that, between when the wafer stage 10 is closest to the laser interferometers 14 and 17 and when it is most remote from them, the purge gas concentration distribution along the X-axis measurement light path 15 and the Y-axis measurement light path 18 is different, and that, depending on the position of the wafer stage, there is a difference in non-uniformness of purge gas concentration in the X-axis measurement light path 15 and the Y-axis measurement light path 18. The refractive index of the atmosphere and the refractive index of the purge gas are different. Therefore, the phenomenon of uneven purge gas concentration in the X-axis measurement light path 15 and the Y-axis measurement light path 18, with the wafer stage 10 position, means that, depending on the position of the wafer stage 10, the refractive index of the gas in the X-axis measurement light path 15 and the Y-axis measurement light path 18 is varying. This leads to a measurement error of the laser interferometer, causing many defects of product semiconductor devices and a considerable decrease of productivity of the apparatus. FIGS. 21A and 21B are schematic contour-line illustrations of a purge gas concentration distribution, in a case wherein an air conditioning system 20 is provided to blow a gas toward a position opposed to a reflection surface 19a of the Y-axis measurement mirror, such that an air-conditioned gas is blown from the air conditioning system 20. FIG. 21A is a schematic contour-line illustration of a purge gas concentration distribution as the wafer stage 10 has moved closest to the X-axis laser interferometer 14 and the Y-axis laser interferometer 17, in the exposure operation. FIG. 21B is a schematic contour-line illustration of a purge gas concentration distribution as the wafer stage 10 has moved most remote from the X-axis laser interferometer 14 and the Y-axis laser interferometer 17, in the exposure operation. As the air conditioning system 20 is provided, the purge gas flowing outwardly from the cover 9 is driven toward the downstream of the flow, by the flow of a blown gas 21. As a result of this, when the wafer stage 10 becomes closest to the laser interferometers 14 and 17 (FIG. 21A), the purge gas does not flow outwardly into the Y-axis measurement light path 18, such that uneven purge gas concentration does not occur. However, it is seen that uneven purge gas concentration is produced in the X-axis measurement light path 15. When the wafer stage 10 is most away from the laser interferometers 14 and 17 (FIG. 21B), it is seen that uneven purge gas concentration is produced both in the X-axis measurement light path 15 and the Y-axis measurement light path 18. It is seen from the above that, even if the air conditioning system is provided, there occurs a difference in non-uniformness of purge gas concentration in the X-axis measurement light path 15 and the Y-axis measurement light path 18, between when the wafer stage 10 is closest to the laser interferometers 14 and 17 and when it is most remote from them. This means that, even if the air conditioning system 20 is provided, depending on the position of the wafer stage 10, the refractive index of gas inside the X-axis measurement light path 15 and the Y-axis measurement light path 18 varies. This leads to a measurement error of the laser interferometer, and it causes many defects of produced semiconductor devices and a considerable decrease of productivity of the apparatus. In order to reduce such a measurement error, as described above, it is necessary to make small the unevenness of the purge gas concentration produced in the X-axis measurement light path 15 and the Y-axis measurement light path 18 and, to attain it, it is necessary to prevent the purge gas from flowing outwardly from the inside of the cover 9 or to reduce the amount of purge gas flow, flowing outwardly from the inside of the cover 9. While FIGS. 20A-21B have been described with reference to examples wherein the cover 9 has a rectangular shape, what has been described above substantially applies to a case wherein the cover has a cylindrical shape or the like. FIG. 17 described hereinbefore with reference to Japanese Laid-Open Patent Application, Publication No. 2002-513856, is an example wherein gas bearing 215 is produced as purge means. In order that the stage member 203 and the reference member 202 are disposed close to each other with a clearance maintained therebetween, and the 25 substrate W is sealingly placed inside the chamber 204, the gas bearing 215 must be produced to surround the substrate W. This requires a very complicated structure. Thus, a very strict machining precision is required for making the stage member 203, causing difficulty of machine production significantly, and raising the cost. The exposure apparatus of FIG. 18 described with reference to Japanese Laid-Open Patent Application, Publication No. 2001-210587, is an example wherein, as with the example of FIG. 17, gas bearings 518 and 528 are produced as purge means. In the structure of FIG. 18, purge gases are supplied through orifices 517 and 527 formed at the bottom of the supply channels 511 and 523, whereby gas bearings 518 and 528 are produced. On the other hand, through orifices 519 and 529 formed at the bottom of the exhaust channels 512 and 524, provided outside the supply channels 511 and 523, the purge gases from the gas bearings 518 and 528 are exhausted, by which the atmosphere leaked to below the covers 510 and 520 is prevented from reaching the central region 501. The invention disclosed in this patent document is focused on the provision of gas bearings 518 and 528 to prevent air from reaching the central region 501 from outside of the covers 510 and 520, and the purge gas flowing outwardly from the inside of the covers 510 and 520 is not at all considered. Furthermore, in the structure of FIG. 18, for purging the inside of the cover, the supply channels 511 and 523 have to be provided to approximately surround the central region 501 and, in addition thereto, the exhausted channels 512 and 524 should be provided outside the supply channels. Thus, as with the exposure apparatus of FIG. 17, the structure is very complicated. As a result, a very strict machining precision is required for making the supply channels 511 and 523 and the exhaust channels 512 and 524, significantly increasing the difficulty of machine production, and raising the cost. It is, therefore, desirable to develop purge means that enables, with a simple structure, prevention of purge gas from flowing outwardly from the inside of the cover, or a reduction of the amount of purge gas flowing outwardly from the inside of the cover. In the meantime, as described hereinbefore, the impurity concentration inside the cover should be maintained at a level of the ppm order. A simplest structure for purging the inside of the cover would be, as shown in FIG. 16, that a purge gas supply port is provided inside the cover 9 to supply the purge gas therefrom, and that, by blowing the purge gas into the interior of the cover 9, the inside pressure of the cover 9 is made higher than the outside pressure of the cover 9. The higher is the flow rate of purge gas flowing outwardly from the inside of the cover 9, the higher is the inside pressure of the cover 9, and the inside of the cover 9 can be purged more stably. However, if the amount of purge gas flowing outwardly from the inside of the cover 9 is large, the non-uniformness of purge gas concentration caused in the X-axis measurement light path 15 and the Y-axis measurement light path 18 becomes larger, making the measurement error larger. In order to reduce the measurement error, the purge gas flowing outwardly from the inside of the cover 9 should be prevented or, alternatively, the amount of purge gas flowing outwardly from the inside of the cover 9 should be decreased. Purging the inside of the cover 9 and reducing the measurement error are contradictory to each other, and satisfying both (purging the inside of the cover 9 and reducing the measurement error) simultaneously is not easy to accomplish. It is accordingly an object of the present invention to provide an exposure apparatus by which at least one of the problems described above can be solved. It is another object of the present invention to provide an exposure apparatus by which disturbing substances in a space between a projection optical system and a substrate can be purged while suppressing the outflow of a purge gas from that space. In accordance with an aspect of the present invention, to achieve the above objects, there is provided an exposure apparatus, comprising a projection optical system for projecting a pattern of an original onto a substrate, a stage for holding the substrate, a cover for substantially surrounding an exposure light path, from an end portion of the projection optical system, at a side facing said stage, to the stage, a first supply port provided inside the cover, for supplying a purge gas into a space surrounded by the cover, and a first exhaust port provided in an end portion of the cover at a side facing the stage, for exhausting the gas. Briefly, in accordance with the present invention, an exposure apparatus, by which disturbing substances in a space between a projection optical system and a substrate can be purged while suppressing the outflow of a purge gas from that space, is accomplished. 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. Preferred embodiments of the present invention will now be described with reference to the attached drawings. FIG. 1 illustrates the structure of a main portion of a step-and-scan type projection exposure apparatus according to an embodiment of the present invention. In FIG. 1, ultraviolet light directed from an unshown ultraviolet light source to an illumination system 1 inside the exposure apparatus illuminates a reticle 3, which is placed on a reticle stage 4. The pattern of the reticle 3 illuminated with light is imaged, in a reduced scale and by a projection optical system 5, upon a photosensitive material having been applied to a wafer 11 placed on a wafer stage 10, whereby the pattern is transferred to the photosensitive pattern. A cover 9 surrounds the light path of the ultraviolet light, from the wafer side lower end portion of the projection optical system 5 toward the wafer stage 10. Inside the cover 9 is a pair of first supply ports 6 disposed opposed to each other, for blowing a purge gas therethrough. Additionally, at the lower end of the cover 9, there is a first collection port 13 for sucking the purge gas and/or the atmospheric gas, wherein the collection port extends to surround the outer periphery of an exposure area. Here, as regards the purge gas, an inactive (inert) gas such as nitrogen, helium, argon, and so on, may be used. Depending on the amount of collection at the first collection port 13, it is possible that the atmosphere outside the cover 9 is collected through the first collection port 13. In this sense, the first collection port 13 may be described as having a function for sucking the purge gas and/or the atmospheric gas, as has just been described above. In the following description, for simplicity, the first collection port 13 will be described as collecting the purge gas. However, the “purge gas” to be mentioned may include the atmosphere outside the cover 9, not only the purge gas supplied from the first supply port 6. In the structure of FIG. 1, a purge gas is supplied from a purge gas supplying device 30 and through a pipe 60, into the inside of the cover 9 from the first supply port 6. There is a flow rate controller 40, which is provided between the purge gas supplying device 30 and the first supply port 6, such that the purge gas can be supplied into the inside of the cover 9 at a flow rate corresponding to control data from a main control system (not shown). There is a vacuum pump 33 provided in association with the first collection port 13, for collecting the purge gas through a pipe 63. A flow rate controller 43 is provided between the first collection port 13 and the vacuum pump 33, such that the purge gas can be collected through the first collection port 13 at a flow rate corresponding to control data from the main control system. Here, the flow rate controllers 40 and 43 control valves 50 and 53, respectively, to open and close them at a predetermined timing on the basis of control data from the main control system. In FIG. 1, denoted at 17 is a Y-axis laser interferometer, and denoted at 18 is a Y-axis measurement light path. Denoted at 19 is a Y-axis measurement mirror fixedly mounted on the wafer stage 10. While not shown in FIG. 1, there are similar elements provided with respect to the X direction, such as shown in FIG. 19, that is, X-axis laser interferometer 14, X-axis measurement light path 15 and X-axis measurement mirror 16 fixedly mounted on the wafer stage 10, for measuring the position with respect to the X direction. In FIG. 1, denoted at 2 is a sheet glass, and denoted at 8 is the flow of purge gas. Denoted at 27 is a base table for the projection optical system, and denoted at 28 is a base table for the wafer stage. In the exposure apparatus of FIG. 1, light emitted from a laser interferometer light source (not shown) is introduced into the Y-axis laser interferometer 17. The light introduced into the Y-axis interferometer 17 is divided by a beam splitter (not shown) provided inside the Y-axis interferometer 17, into light which is directed to a fixed mirror (not shown) inside the interferometer and light which is directed to the Y-axis measurement mirror 19. The light directed toward the mirror 19 goes along the Y-axis measurement light path 18 and it impinges on the Y-axis measurement mirror 19 fixedly mounted on the wafer stage 10, and the light is reflected by the reflection surface 19a of the mirror. Here, the reflected light again goes back along the Y-axis measurement light path 18 and returns to the beam splitter inside the Y-axis interferometer 17, such that it is superposed with the light reflected by the fixed mirror. Here, by detecting a change in interference of the light, the movement distance in the Y direction can be measured. The movement distance in the X direction can be measured similarly to the Y-axis measurement. The information on the movement distance detected in this manner is fed back to an X-Y driving system (not shown), and the positioning control of the wafer stage 10 is carried out on the basis of it. In the exposure apparatus of FIG. 1, for purging the inside of the cover 9, first, the main control system (not shown) applies a control signal to the flow rate controller 40 to open the valve 50, whereby a purge gas is supplied into the inside of the cover 9 through the first supply port 6, at a predetermined flow rate. Subsequently, a control signal is applied to the flow rate controller 43 to open the valve 53, whereby the purge gas is collected through the first collection port 13, at a predetermined flow rate. Here, the purge gas is supplied into the inside of the cover 9 through the first supply port 6 at a predetermined flow rate, so as to assure that in the exposure operation the impurity concentration inside the cover 9 is made lower than a desired level, that is, the inside of the cover 9 is purged. Although the flow rate of purge gas necessary for purging the inside of the cover 9 is different in dependence upon the shape of the cover 9 or the magnitude of the clearance between the cover 9 and the wafer 11, if the cover 9 has a rectangular shape and the clearance between the cover 9 and the wafer 11 is 1.5 mm, the inside of the cover 9 can be purged by supplying a purge gas from the first supply port at a flow rate not greater than 1 smlm (standard liter/min). As regards the flow rate necessary for purging the inside of the cover 9, it may be determined beforehand in the manner that: in a state in which the purge gas is not collected through the first collection port 13, the impurity concentration inside the cover 9 is measured while changing the supply flow rate from the first supply port, and the flow rate as a desired impurity concentration (or lower) is reached is chosen. Alternatively, it may be determined on the basis of simulations. Next, in the exposure apparatus of FIG. 1, wherein the first collection port 13 is provide so as to surround the outer periphery of the exposure area, the pressure inside the cover 9 and the pressure outside the cover 9, as well as the purge gas concentration distribution near the wafer stage 10, will be explained. Initially, referring to FIGS. 2A, 2B, 3A and 3B, a description will be made of a case wherein the flow rate control is made so that the flow rate of the purge gas to be supplied through the first supply port 6 becomes larger than the flow rate of the purge gas collected through the first collection port 13. FIG. 2A is a schematic illustration, showing the flow inside the cover 9 along a central sectional plane. FIG. 2B is a schematic isobaric illustration for the pressure distribution in the same plane as that of FIG. 2A. In the isobaric illustration of FIG. 2B, the darker the color is, the higher the pressure is, and the lighter the color is, the lower the pressure is. If the flow rate of the purge gas supplied through the first supply port 6 is greater than the flow rate of purge gas collected through the first collection port 13, as shown in FIG. 2A, a portion of the purge gas supplied from the first supply port 6 is collected by the first collection port, while the remainder flows outwardly of the cover 9. As a result, as shown in FIG. 2B, the pressure P1 inside the cover 9 becomes higher than the pressure P2 outside the cover 9, such that the inside of the cover 9 can be purged. FIG. 3A is a schematic isosbesticline chart of a purge gas concentration distribution as the wafer stage has moved closest to the X-axis laser interferometer 14 and the Y-axis laser interferometer 17 in the exposure operation. FIG. 3B is a schematic isosbestic-line chart of the purge gas concentration distribution as the wafer stage 10 has moved most remote from the X-axis laser interferometer 14 and the Y-axis laser interferometer 17 in the exposure operation. In these isosbestic-line charts, the darker the color is, the higher the purge gas concentration is, and the lighter the color is, the lower the purge gas concentration is. Since a portion of the purge gas supplied through the first supply port 6 is collected by the first collection port 13, the flow rate of purge gas flowing outwardly of the cover 9 can be reduced. Thus, it is seen that, in both of the case (FIG. 3A) wherein the wafer stage 10 comes closest to the interferometers 14 and 17 and the case (FIG. 3B) wherein the stage has moved most remote from the interferometers, the non-uniformness of purge gas concentration in the X-axis measurement light path 15 and the Y-axis measurement light path 18 is reduced significantly as compared with a case (FIG. 20) wherein the first collection port 13 is not provided. Hence, the measurement error to be produced in the laser interferometer can be reduced significantly. As described above, if the flow rate of purge gas supplied through the first supply port 6 is greater than the flow rate of purge gas collected by the first collection port 13, the pressure P1 inside the cover 9 becomes higher than the pressure P2 outside the cover 9, and as a result, the inside of the cover 9 can be purged. Moreover, the flow rate of purge gas flowing outwardly from the cover 9 can be reduced and, thus, the measurement error of the laser interferometer can be reduced. Next, referring to FIGS. 4A, 4B, 5A and 5B, a description will be made of a case wherein the flow rate control is made so that the flow rate of purge gas to be collected by the first collection port 13 becomes larger than the flow rate of purge gas to be supplied through the first supply port 6. In this case, depending on the collecting flow rate of the purge gas collected by the first collection port 13, it is possible that the pressure P1 inside the cover 9 becomes lower than the pressure P2 outside the cover 9. Here, a case wherein the pressure P1 inside the cover 9 is lower than the pressure P2 outside the cover 9 will be explained. FIG. 4A is a schematic view of the flow inside the cover 9 along a central sectional plane. FIG. 4B is a schematic isobaric illustration of a pressure distribution in the same plane as that of FIG. 4A. In the isobaric illustration of FIG. 4B, the darker the color is, the higher the pressure is, and the lighter the color is, the lower the pressure is. If the flow rate of purge gas collected by the first collection port 13 is larger than the flow rate of purge gas supplied through the first supply port 6, as shown in FIG. 4A, a flow of purge gas flowing from the inside of the cover 9 toward the first collection port 13 and a flow of atmosphere flowing from outside the cover 9 toward the first collection port 13 are produced. If the flow rate of atmosphere flowing from the outside of the cover 9 to the collection port 13 is large, as shown in FIG. 4B, the pressure P1 inside the cover 9 becomes lower than the pressure P2 outside the cover 9. However, it should be noted here that, in the region around the cover 9, the portion having a lowest pressure is an area near the first collection port 13. For this reason, even if the pressure P1 inside the cover 9 is lower than the pressure P2 outside the cover 9, there still is a flow of purge gas flowing from inside the cover 9 toward the collection port 13. As a result, inflow of atmosphere into the cover 9 from outside the cover, flowing across the collection port 13, can be avoided and, thus, the inside of the cover 9 can be purged. FIG. 5A is a schematic isosbesticline chart of a purge gas concentration distribution as the wafer stage 10 has moved closest to the X-axis laser interferometer 14 and the Y-axis laser interferometer 17 in the exposure operation. FIG. 5B is a schematic isosbestic-line chart of the purge gas concentration distribution as the wafer stage 10 has moved most remote from the X-axis laser interferometer 14 and the Y-axis laser interferometer 17 in the exposure operation. In these isosbestic-line charts, the darker the color is, the higher the purge gas concentration is, and the lighter the color is, the lower the purge gas concentration is. A white color depicts a zone where no purge gas is present. The purge gas supplied through the first supply port 6 is all collected by the first collection port 13. Therefore, the purge gas does not flow outwardly of the cover 9. Thus, it is seen that, in both of the case (FIG. 5A) wherein the wafer stage 10 comes closest to the interferometers 14 and 17 and the case (FIG. 5B) wherein the stage has moved most remote from the interferometers, there is no uneven purge gas concentration in the X-axis measurement light path 15 and the Y-axis measurement light path 18. Hence, the measurement error of the laser interferometer can be prevented. As described above, in the exposure apparatus of FIG. 1, wherein a first collection port 13 is provided so as to surround the outer periphery of the exposure area, since the purge gas supplied through the first supply port 16 is collected by the first collection port 13, the flow rate of purge gas flowing outwardly of the cover 9 from the inside of the cover can be reduced. Therefore, an uneven purge gas concentration produced in the X-axis measurement light path 15 and the Y-axis measurement light path 18 can be made small, and the measurement error of the laser interferometer can be reduced significantly. Furthermore, in order to avoid non-uniformness of a purge gas concentration in the X-axis measurement light path 15 and the Y-axis measurement light path 18 to thereby prevent measurement error of the laser interferometer, the flow rate control should desirably be made so that the flow rate of purge gas to be collected by the first collection port 13 becomes larger than the flow rate of purge gas to be supplied through the first supply port 6. Here, depending on the flow rate of purge gas collected by the collection port 13, it is possible that the pressure P1 inside the cover 9 becomes lower than the pressure P2 outside the cover 9. However, as described hereinbefore, even in such a case, the inside of the cover 9 can be purged. Furthermore, if, in this case, the collecting flow rate through the collection port 13 is too large, it may be possible that the flow velocity of atmosphere flowing toward the first collection port 13 from outside the cover 9 becomes fast and the atmosphere flows into the inside of the cover 9. Although the collecting flow rate through the first collection port in the case wherein the atmosphere flows into the cover 9 is different in dependence upon the shape of the cover 9 or the size of clearance between the cover 9 and the wafer 11, if, for example, the cover 9 has a rectangular shape and the clearance between the cover 9 and the wafer 11 is 1.5 mm, the atmosphere will not flow into the cover 9 as long as the collecting flow rate through the first collection port 13 is not greater than five times the supplying flow rate through the first supply port 6. As regards the upper limit of the collecting flow rate through the collection port 13, it may be determined beforehand in the manner that: the impurity concentration inside the cover 9 is measured while changing the collection flow rate through the collection port 13, and the flow rate as a desired impurity concentration (or lower) is reached is chosen. Alternatively, it may be determined on the basis of simulations. Then, the collection flow rate through the collection port 13 may be controlled so that the collection flow rate through the collection port is maintained to be not greater than the upper limit so determined beforehand. In the exposure apparatus of FIG. 1, as described above, with a very simple structure that a first supply port 6 is provided inside the cover 9 and a first collection port 13 is provided at a lower end portion of the cover 9 so as to surround the outer periphery of the exposure area, it is assured to purge the inside of the cover 9, such that a measurement error of the laser interferometer can be prevented effectively. In the exposure apparatus of the first embodiment, a single first collection port 13 is provided at the lower end of the cover 9 so as to surround the outer periphery of the exposure area. However, a couple of collection ports may be provided. With such a dual structure, the influence applied from outside the cover 9 to inside the cover 9 can be reduced more. FIG. 6 is a schematic view of an exposure apparatus, and it shows an example wherein a second collection port 13′ is provided outside the first collection port 13. Since the FIG. 6 embodiment is a modified form of the first embodiment, only the structural portion around the cover 9 is illustrated there. In FIG. 6, like numerals as those of FIG. 1 are assigned to corresponding components. In FIG. 6, there is a vacuum pump 33′ provided in association with the second collection port 13′, for collecting the purge gas through a pipe 63′. A flow rate controller 43′ is provided between the second collection port 13′ and the vacuum pump 33′, such that the purge gas can be collected through the second collection port 13′ at a flow rate corresponding to control data from a main control system (not shown). Here, the flow rate controller 43′ controls a valve 53′ to open and close it at a predetermined timing on the basis of control data from the main control system. In the exposure apparatus of the first embodiment (FIG. 1), in order to prevent outflow of the purge gas from the cover 9, the flow rate of purge gas collected by the first collection port 13 should be made larger than the flow rate of purge gas supplied through the first supply port 6. In the modified embodiment of FIG. 6, on the other hand, it is sufficient that the total flow rate of purge gas as collected by the first collection port 13 and the second collection port 13′ is larger than the flow rate of purge gas supplied through the first collection port 6. Here, referring to FIG. 7, a description will be made of the flow of gas near the cover 9 in a case wherein the flow rate of purge gas collected by the first collection port 13 is smaller than the flow rate of purge gas supplied through the first supply port 6, while the total flow rate of purge gas collected by the first and second collection ports 13 and 13′ is larger than the flow rate of purge gas supplied through the first supply port 6. FIG. 7 is a schematic view of the flow of gas inside the cover 9 and along a central sectional plane. As shown in FIG. 7, since the flow rate of purge gas collected by the first collection port 13 is smaller than the flow rate of purge gas supplied through the first supply port 6, a portion of the purge gas supplied by the first supply port 6 is not collected by the first collection port 13, and it forms a flow directed outwardly of the cover 9. Due to this flow, the pressure P1 inside the cover 9 is increased to a similar level as the pressure P1 inside the cover 9, as illustrated in FIG. 2B. The purge gas not collected by the first collection port 13 is collected by means of the second collection port 13′. Thus, there occurs no uneven purge gas concentration around the wafer stage and, therefore, a measurement error of the laser interferometer can be avoided. In the structure of FIG. 6, the structure of the cover 9 is somewhat complicated. However, with the provision of dual collection ports described above, the pressure P1 inside the cover 9 can be maintained at a high level and, furthermore, the measurement error of the laser interferometer can be prevented. These advantageous results are obtainable at once, in this structure. In the exposure apparatus of the first embodiment, the first collection port 13 is provided at the lower end of the cover 9 so as to 25 surround the outer periphery of the exposure area. However, depending on the disposition of various units constituting the exposure apparatus, there may be cases wherein the first collection port 13 cannot be provided to surround the outer periphery of the exposure area. For example, if a focus sensor of an oblique light incidence type is provided to detect the height (level) of the wafer surface, measurement light will be projected from one direction inside the cover 9, while a position sensor such as a CCD or PSD will be used at the other side to detect reflection light. In such a case, it is difficult to provide the first collection port 13 across the light path of the measurement light. Therefore, the collection port will have to be provided in a portion of the lower end of the cover 9. Even on such an occasion, however, since the purge gas can be collected by the first collection port 13, the flow rate of purge gas flowing outwardly of the cover 9 can be reduced, and thus, non-uniformness of purge gas concentration to be produced around the wafer stage 10 can be reduced significantly. If the first collection port 13 is provided in a portion of the lower end of the cover 9, in order to purge the inside of the cover 9, the pressure P1 inside the cover 9 should be made higher than the pressure P2 outside the cover 9. To this end, the flow rate control is made so that the flow rate of purge gas supplied through the first supply port 6 becomes larger than the flow rate of purge gas collected by the first collection port 13. In the flow rate control described above, a first pressure sensor 81 for measuring the pressure inside the cover 9 and a second pressure sensor 82 for measuring the pressure outside the cover 9 may be provided. The flow rate of purge gas to be supplied through the first supply port 6 and/or the flow rate of purge gas to be collected through the first collection port 13 may be controlled on the basis of the measurements made by the sensors 81 and 82, so that the pressure P1 inside the cover 9 becomes higher than the pressure P2 outside the cover 9. For example, when an oblique light incidence type focus sensor is provided with respect to the X direction, the first collection port 13 may be provided before and after the exposure area with respect to the X direction. On that occasion, a single pressure sensor may be provided inside the cover 9 as the first pressure sensor 81 for measuring the pressure P1 inside the cover 9, while a single pressure sensor may be provided outside the cover 9 as the second pressure sensor 82 for measuring the pressure outside the cover 9. Then, the flow rate of purge gas to be supplied through the first supply port 6 may be controlled on the basis of the measurements made by the sensors 81 and 82, so that the pressure P1 inside the cover 9 becomes higher than the pressure P2 outside the cover 9. If, for example, the pressure P2 outside the cover 9 becomes higher than the inside pressure P1 thereof due to a transitional pressure change resulting from a large change in atmospheric pressure outside the exposure apparatus, the main control system operates to increase the flow rate of purge gas supplied through the first supply port 6. In response, the pressure P1 inside the cover 9 rises and it becomes higher than the outside pressure P2, and thus, the inside of the cover 9 can be purged. Here, as a matter of course, a plurality of pressure sensors may be provided inside and outside the cover 9 to measure the pressure at a plurality of points with these pressure sensors and, on the basis of the measurement results, the flow rate of purge gas supplied through the first supply port 6 and/or the flow rate of purge gas collected by the first collection port 13 may be controlled. With the measurements at plural points, the inside of the cover 9 can be purged more stably. When a first collection port 13 is provided at a lower end of a cover 9 so as to surround the outer periphery of the exposure area as in the exposure apparatus of the first embodiment, as a matter of course, such pressure sensor means may be provided adjacent to the first collection port 13 so that the supply flow rate through the supply port 16 and/or the collection flow rate through the collection port 13 may be controlled to ensure that the pressure adjacent to the collection port 13 becomes higher than the inside pressure of the cover 9. Use of such pressure sensor means and the flow rate control method described above will be applicable also to exposure apparatuses according to Embodiments 2-5 to be described later. In the exposure apparatus of the first embodiment, the outside of the cover 9 is at the atmosphere. There may be cases wherein the outside of the cover 9 is purged by use of a purge gas having a higher impurity concentration as compared with the purge gas supplied into the cover 9, thereby to reduce the impurity concentration outside the cover 9. On such an occasion, as well, unevenness of purge gas concentration will occur in the X-axis measurement light path 15 and the Y-axis measurement light path 18, causing a measurement error of the laser interferometer. The exposure apparatus according to the first embodiment is obviously applicable even to such a case. This is also the case with exposure apparatuses to be described later with reference to Embodiments 2, 4 and 5. FIGS. 8A and 8B show the structure around a wafer stage of an exposure apparatus according to a second embodiment of the present invention. In the first embodiment, the first collection port 13 is provided at the lower end of the cover 9 so as to surround the four sides of the outer periphery of the exposure area. On the other hand, the second embodiment is an example wherein a collection port 13 is provided only at two sides of the lower end of the cover, adjacent to an X-axis measurement mirror 16 and a Y-axis measurement mirror 19, respectively. In FIG. 8A, which is a sectional view and FIG. 8B, which is a plan view, like numerals as those of FIG. 1 are assigned to corresponding components. The flow rate control method and the wafer stage 10 positioning method are similar to those described with reference to the first embodiment, and a duplicate description of them will be omitted here. In the exposure apparatus of the second embodiment, for purging the inside of the cover 9, first, a main control system (not shown) applies a control signal to a flow rate controller 40 to open a valve 50, whereby a purge gas is supplied into the inside of the cover 9 through the first supply port 6, at a predetermined flow rate. Subsequently, a control signal is applied to a flow rate controller 43 to open a valve 53, whereby the purge gas is collected through the first collection port 13, at a predetermined flow rate. Here, the flow rate control is made so that the flow rate of purge gas supplied through the first supply port 6 becomes larger than the flow rate of purge gas collected by the first collection port. In the exposure apparatus of the second embodiment, the first collection port 13 is provide only at the two sides at the lower end of the cover, facing the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, respectively. Therefore, as shown in FIGS. 9A and 9B, the flow rate of purge gas flowing out into the X-axis measurement light path 15 and the Y-axis measurement light path 18 can be reduced and, thus, the measurement error of the laser interferometer can be reduced significantly. In the exposure apparatus of the second embodiment, as described above, with a very simple structure that a first collection port 13 is provided at a lower end portion of the cover 9, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, it is assured to purge the inside of the cover 9, such that a measurement error of the laser interferometer can be prevented effectively. FIGS. 10A and 10B are schematic views, respectively, of the structure of a main portion of an exposure apparatus according to a third embodiment of the present invention. In the second embodiment, a collection port 13 is provided in the lower end portion of the cover, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19. The third embodiment is an example wherein an air conditioning system 20, as well, is provided to blow a gas toward a position opposed to the reflection surface 19a of a Y-axis measurement mirror 19, such that, by means of this air conditioning unit 20, a temperature controlled blow gas 21 is blown around the wafer stage. Here, the blown gas 21 may be air or a purge gas having an impurity concentration higher than that of the purge gas supplied through into the cover 9. With this arrangement, the total flow rate of inactive gas used in the exposure apparatus can be made smaller, such that the cost for operating the apparatus can be made cheaper. In FIG. 10A, which is a sectional view and FIG. 10B, which is a plan view, like numerals as those of FIG. 8 are assigned to corresponding components. The flow rate control method and the cover 9 inside purging method, as well as the wafer stage 10 positioning method are similar to those described with reference to the first and second embodiments, and a duplicate description of them will be omitted here. In the exposure apparatus of the third embodiment, the air conditioning system 20 is provided at a position opposed to the reflection surface 19a of the Y-axis measurement mirror 19. However, the air conditioning system 20 may be provided at a position facing the reflection surface 16a of the X-axis measurement mirror 16. Similar advantageous results as those in the third embodiment are obtainable even with such a structure. In the exposure apparatus of the third embodiment as described above, with a very simple structure that an air conditioning system 20 is provided at a position opposed to the reflection surface 19a of the Y-axis measurement mirror 19 or the reflection surface 16a of the X-axis measurement mirror 16, in addition to the structure of the second embodiment, it is assured to purge the inside of the cover 9 and a measurement error of the laser interferometer can be prevented effectively. The first to third embodiments have been described with reference to a purging method for purging the inside of the cover 9, in which a first supply port 6 is provided oppositely to supply a purge gas into the cover 9. However, there are many known methods usable to purge the inside of the cover 9, and this embodiment is applicable to any of these methods. For example, the assignee of the subject application has proposed various methods in Japanese Patent Application No. 2003-53892, in relation to purging the inside of a cover by causing a purge gas to flow in one direction inside the cover. The purging methods disclosed in Japanese Patent Application No. 2003-53892 are all applicable to the exposure apparatuses of the first to third embodiments. For example, FIG. 12 shows an example wherein one purging method disclosed in Japanese Patent Application No. 2003-53892 is applied to the exposure apparatus of the first embodiment described above. Except for a change in the purging method for purging the inside of the cover 9, this example is essentially the same as that of the first embodiment, and only the structural portion around the cover 9 is illustrated schematically in FIG. 12. Also, in FIG. 12, like numerals as those of FIG. 1 are assigned to corresponding components. Since the flow rate control has been described with reference to the first embodiment, a duplicate explanation will be omitted here. In FIG. 12, there is a vacuum pump 31 provided in association with a third collection port 7, for collecting the purge gas inside the cover 9 through a pipe 61. A flow rate controller 41 is provided between the third collection port 7 and the vacuum pump 31, such that the purge gas can be collected through the third collection port 7 at a flow rate corresponding to control data from a main control system, not shown. Here, the flow rate controller 41 controls a valve 51 to open and close it at a predetermined timing on the basis of control data supplied from the main control system. In the structure of FIG. 12, the first supply port 16 for supplying a purge gas is provided at one side of the interior of the cover 9 while the third collection port 7 for collecting the purge gas is provided at the other side, and this corresponds to the structure disclosed in Japanese Patent Application No. 2003-53892. With this structure, it is assured that, inside the cover 9, the purge gas flows in one direction. Therefore, even if various products (degassing) are generated during the exposure process due to a photosensitive material applied to the wafer surface, they can be collected efficiently and, thus, contamination of the surface of optical elements can be avoided effectively. In accordance with Japanese Patent Application No. 2003-53892, the flow rate of purge gas collected by the third collection port 7 is made smaller than the flow rate of purge gas supplied by the first supply port 6, by which the purge gas is caused to flow outwardly from the inside of the cover 9 and the pressure P1 inside the cover 9 is made larger than the pressure P2 outside the cover 9, and by which the inside of the cover 9 is purged. In the exposure apparatus of the first embodiment, the collection flow rate of purge gas collected by the first collection port 13 is made larger than the supply flow rate of purge gas supplied through the first supply port 6, by which outflow of the purge gas outwardly of the cover 9 is prevented and uneven purge gas concentration around the wafer stage 10 is avoided, and by which a measurement error of the laser interferometer is prevented. In consideration of this, in the exposure apparatus of the fourth embodiment, the flow rate control is carried out so that the flow rate of purge gas collected by the third collection port 7 becomes smaller than the flow rate of purge gas supplied through the first supply port 6 and also that the total flow rate of purge gas collected by the first collection port 13 and the third collection port 7 becomes larger than the flow rate of purge gas supplied through the first supply port 6. As described, the flow rate of purge gas collected by the third collection port 7 is made smaller than the flow rate of purge gas supplied through the first supply port 6, and, by doing so, a flow of purge gas directed from the inside of the cover 9 to the first collection port 13, which is provided to surround the outer periphery of the exposure area, is created. As a result, inflow of atmosphere into the cover 9 from outside the cover, flowing across the first collection port 13, can be avoided. Therefore, the inside of the cover 9 can be purged with a much simpler structure, without the necessity of orifices 517 and 527 provided at the bottom of the supply channels 511 and 523 in the conventional structure shown in FIG. 18. Furthermore, the total flow rate of purge gas collected by the first collection port 13 and the third collection port 7 is made larger than the flow rate of purge gas supplied through the first supply port 6. By doing so, outflow of the purge gas outwardly from the inside of the cover 9 can be prevented. As a result, uneven purge gas concentration around the wafer stage can be avoided and thus a measurement error of the laser interferometer can be prevented effectively. The fourth embodiment described above is an example wherein one purging method disclosed in Japanese Patent Application No. 2003-53892 is applied to the exposure apparatus of the first embodiment. However, it may be applied to the exposure apparatus according to the second embodiment or the third embodiment. On that occasion, since the first collection port 13 is provided at the lower end of the cover, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, for purging the inside of the cover 9, the flow rate control should be made so that the pressure P1 inside the cover 9 becomes higher than the pressure P2 outside the cover 9. To this end, for purging the inside of the cover 9, the total flow rate of purge gas to be collected by the first and third collection ports 13 and 7 should be controlled to be lower than the flow rate of purge gas supplied by the first supply port 16. A fifth embodiment of the present invention is an example (FIG. 13) in which another purging method as disclosed in Japanese Patent Application No. 2003-53892, different from the one applied to the fourth embodiment, is applied to an exposure apparatus according to the first embodiment. In FIG. 13, like numerals as those of FIGS. 1 and 12 are assigned to corresponding components. The flow rate control is essentially 25 the same as that made in the first or fourth embodiment, and a duplicate explanation will be omitted here. In FIG. 13, there is a second supply port 12 which is provided at a lower end of the cover adjacent to the first supply port 6, and inside the first collection port 13. A purge gas supplying system 32 is provided in association with the second supply port 12, through a pipe 62, such that a purge gas can be supplied from the second supply port 12 toward a wafer at a predetermined flow rate. There is a flow rate controller 42 between the second supply port 12 and the purge gas supplying system 32, and a purge gas can be supplied from the second supply port 12 toward the wafer at a flow rate corresponding to control data from a main control system, not shown. The flow rate controller 42 controls a valve 52 to open and close the same at a predetermined timing on the basis of a control signal from the main control system. In the structure of FIG. 13, the first supply port 6 for supplying a purge gas is provided at one side of the interior of the cover 9, while the third collection port 7 for collecting the purge gas is provided at the other side, and additionally, the second supply port 12 is provided at the lower end of the cover adjacent to the first supply port 6 (the first collection port 13 is not provided). This corresponds to the structure disclosed in Japanese Patent Application No. 2003-53892. As compared with the structure of the fourth embodiment (FIG. 12), the second supply port 12 is provided at the lower end of the cover, adjacent to the first supply port 6. This effectively prevents production of whirls near the area below the first supply port 6. Thus, as compared with the structure without the second supply port 12, the inside of the cover 9 can be purged more stably. In accordance with Japanese Patent Application No. 2003-53892, the flow rate of purge gas collected by the third collection port 7 is made smaller than the total flow rate of purge gas supplied by the first and second supply ports 6 and 12, by which the purge gas is caused to flow outwardly from the inside of the cover 9 and the pressure P1 inside the cover 9 is made larger than the pressure P2 outside the cover 9, and by which the inside of the cover 9 is purged. In the exposure apparatus of the first embodiment, the collection flow rate of purge gas collected by the first collection port 13 is made larger than the supply flow rate of purge gas supplied through the first supply port 6, by which outflow of the purge gas outwardly of the cover 9 is prevented, and uneven purge gas concentration around the wafer stage 10 is avoided, and by which a measurement error of the laser interferometer is prevented. In consideration of this, in the exposure apparatus of the fifth embodiment, the flow rate control is carried out so that the flow rate of purge gas collected by the third collection port 7 becomes smaller than the total flow rate of purge gas supplied through the first and second supply ports 6 and 12, and also that the total flow rate of purge gas collected by the first collection port 13 and the third collection port 7 becomes larger than the total flow rate of purge gas supplied through the first and second supply ports 6 and 12. As described, the flow rate of purge gas collected by the third collection port 7 is made smaller than the total flow rate of purge gas supplied through the first and second supply ports 6 and 12, and, by doing so, a flow of purge gas directed from the inside of the cover 9 to the first collection port 13, which is provided to surround the outer periphery of the exposure area, is created. As a result, inflow of atmosphere into the cover 9 from outside the cover, flowing across the first collection port 13, can be avoided. Furthermore, the second supply port 12 is provided so as to prevent formation of whirls near the area below the first supply port 6. Therefore, the inside of the cover 9 can be purged with a much simpler structure, without the necessity of orifices 517 and 527 provided at the bottom of the supply channels 511 and 523 in the conventional structure shown in FIG. 18. Moreover, the total flow rate of purge gas collected by the first collection port 13 and the third collection port 7 is made larger than the total flow rate of purge gas supplied through the first and second supply ports 6 and 12. By doing so, outflow of the purge gas outwardly from the inside of the cover 9 can be prevented. As a result, uneven purge gas concentration around the wafer stage can be avoided and thus, a measurement error of the laser interferometer can be prevented effectively. The fifth embodiment described above is an example wherein one purging method disclosed in Japanese Patent Application No. 2003-53892 is applied to the exposure apparatus of the first embodiment. However, it may be applied to the exposure apparatus according to the second embodiment or the third embodiment. On that occasion, since the first collection port 13 is provided at the lower end of the cover, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, for purging the inside of the cover 9, the flow rate control should be made so that the pressure P1 inside the cover 9 becomes higher than the pressure P2 outside the cover 9. To this end, for purging the inside of the cover 9, the total flow rate of purge gas to be collected by the first and third collection ports 13 and 7 should be controlled to be lower than the total flow rate of purge gas supplied by the first and second supply ports 6 and 12. The fourth and fifth embodiments of the present invention described above are examples in which two purging methods, as disclosed in Japanese Patent Application No. 2003-53892, are applied to an exposure apparatus according to the first, second and third embodiments. Japanese Patent Application No. 2003-53892 mentions further purging methods which are usable to purge the inside of the cover 9, and they may be applied to the exposure apparatus of the first to third embodiments of the present invention. The first to fifth embodiments described above use a vacuum pump for collecting the purge gas or atmospheric gas through the first or third collection port. It should be noted here that, regarding such a vacuum pump, a vacuum pump of the type without pulsation (pressure variation) may desirably be used in the sense that it applies no adverse influence to the purging performance. For example, a vacuum pump of a scroll type or a vacuum ejector that produces a vacuum by use of a pressurized gas will be preferable. Alternatively, a reservoir may be used to suppress the pulsation. In accordance with the embodiments of the present invention described hereinbefore, in an exposure apparatus using ultraviolet light, particularly, ArF excimer laser light or fluorine (F2) excimer laser light, the inside of the exposure light path near a wafer can be purged stably without being influenced externally and, additionally, non-uniformness of purge gas concentration around the wafer stage can be reduced effectively. As a result, the manufacturing cost of the exposure apparatus can be reduced, yet sufficient transmissivity as well as uniformness and stability of the ArF excimer laser light or fluorine (F2) excimer laser light are accomplished. Furthermore, the positioning of the wafer stage can be carried out very precisely. Therefore, projection exposure can be done very precisely and, thus, a fine circuit pattern can be projected satisfactorily. The present invention is not limited to the exposure apparatuses of the foregoing embodiments. The present invention is applicable also to any exposure apparatuses arranged to project a pattern of a mask onto a photosensitive substrate through a projection optical system, particularly, one that uses ultraviolet light as exposure light. There is no restriction in regard to the ultraviolet light which is suitably usable in the exposure apparatus as exposure light. However, as described in the introductory portion of this specification, the present invention is particularly effective when used with deep ultraviolet light, more specifically, ArF excimer laser light having an emission wavelength of about 193 nm or a fluorine (F2) excimer laser having an emission wavelength of about 157 nm. Next, an embodiment of a device manufacturing method, which uses an exposure apparatus described above, will be explained. FIG. 14 is a flow chart for explaining the procedure of manufacturing various microdevices such as semiconductor chips, (e.g., ICs or LSIs), liquid crystal panels, CCDs, thin film magnetic heads or micro-machines, for example. Step 1 is a design process for designing a circuit of a semiconductor device. Step 2 is a process for making a mask on the basis of the circuit pattern design. Step 3 is a process for preparing a wafer by using a material such as silicon. Step 4 is a wafer process, which is called a pre-process, wherein, by using the thus prepared mask and wafer, a circuit is formed on the wafer in practice, in accordance with lithography. Step 5 subsequent to this is an assembling step, which is called a post-process, wherein the wafer having been processed at step 4 is formed into semiconductor chips. This step includes an assembling (dicing and bonding) process and a packaging (chip sealing) process. Step 6 is an inspection step wherein an operation check, a durability check and so on, for the semiconductor devices produced by step 5, are carried out. With these processes, semiconductor devices are produced, and they are shipped (step 7). FIG. 15 is a flow chart for explaining details of the wafer process. Step 11 is an oxidation process for oxidizing the surface of a wafer. Step 12 is a CVD process for forming an insulating film on the wafer surface. Step 13 is an electrode forming process for forming electrodes upon the wafer by vapor deposition. Step 14 is an ion implanting process for implanting ions to the wafer. Step 15 is a resist process for applying a resist (photosensitive material) to the wafer. Step 16 is an exposure process for printing, by exposure, the circuit pattern of the mask on the wafer through the exposure apparatus described above. Step 17 is a developing process for developing the exposed wafer. Step 18 is an etching process for removing portions other than the developed resist image. Step 19 is a resist separation process for separating the resist material remaining on the wafer after being subjected to the etching process. By repeating these processes, circuit patterns are formed on the wafer. With these processes, high density microdevices can be manufactured at a lower cost. The present invention can be embodied in various forms, examples of which are as follows. (1) An exposure apparatus for projecting a pattern of a mask onto a photosensitive substrate through a projection optical system, characterized by a cover for surrounding an exposure light path from a wafer side lower end of the projection optical system to near a wafer stage, a first supply port provided in the cover, for blowing at least a purge gas, and a first collection port at the lower end of the cover, for sucking at least one of a purge gas, a purge gas having an impurity concentration higher than that of the first-mentioned purge gas and atmosphere. The first supply port is provided inside the cover to supply a purge gas into the inside of the cover. By this, a flow of purge gas flowing from the inside of the cover to the outside of the cover is created, and the pressure inside the cover becomes higher than the pressure outside the cover, whereby the inside of the cover can be purged. The first collection port is provided at the lower end of the cover, by which the purge gas can be collected through the first collection port. This effectively reduces the flow rate of purge gas flowing outwardly from the inside of the cover. Thus, non-uniformness of purge gas concentration produced around the wafer stage can be reduced, and a measurement error of a laser interferometer can be reduced effectively. With the structure described above, by providing a single first supply port inside the cover, the inside of the cover can be purged. Also, by providing only the first collection port at the lower end of the cover, the measurement error of the laser interferometer can be reduced. In an exposure apparatus having the structure described above, the positions where the first supply port and the first collection port are to be provided are not limited. With a very simple structure that the first supply port is provided inside the cover while the first collection port is provided at the lower end of the cover, it is assured to purge the inside of the cover and to reduce the measurement error of the laser interferometer. Further, with the structure described above, a flow of purge gas flowing from the inside of the cover to the outside of the cover is produced, and the pressure inside the cover is higher than the pressure outside the cover. Therefore, it is not necessary to make the clearance between the cover and the wafer or between the cover and the wafer stage very small. A sufficiently wide spacing can be held to avoid interference between the cover and the wafer or between the cover and the wafer stage. With the above-described structure, therefore, without provision of gas bearings, such as adopted in the exposure apparatus of FIG. 17 or 18, interference between the cover and the wafer or between the cover and the wafer stage can be avoided, and the manufacturing cost of the apparatus can be made lower. (2) An exposure apparatus according to Item (1), characterized by a wafer stage being able to be driven in mutually orthogonal X and Y directions, and laser interferometers for measuring the position with respect to the X and Y directions, wherein an X-axis measurement mirror and a Y-axis measurement mirror are provided on the wafer stage so that their reflection surfaces are disposed perpendicularly to an X-axis measurement light path and a Y-axis measurement light path, respectively, and wherein the first collection port is provided at the lower end of the cover, adjacent to the X-axis measurement mirror and the Y-axis measurement mirror. Referring to FIGS. 9A, 9B, 20A and 20B, advantageous effects obtainable with the structure that the first collection port 13 is provided at the lower end of the cover, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, will be explained. FIGS. 9A and 9B are plan views, respectively, of a portion around the wafer stage 10 in a case wherein the first collection port 13 is provided at the lower end of the cover, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, and these drawings are schematic contour-line illustrations regarding the purge gas concentration distribution. In the contour-line illustrations of FIGS. 9A and 9B, the darker the color is, the higher the purge gas concentration is, and the lighter the color is, the lower the purge gas concentration is. FIG. 9A is a schematic contour-line chart of a purge gas concentration distribution as the wafer stage 10 has moved closest to the X-axis laser interferometer 14 and the Y-axis laser interferometer 17, in the exposure operation. FIG. 9B is a schematic contour-line chart of a purge gas concentration distribution as the wafer stage 10 has moved most remote from the X-axis laser interferometer 14 and the Y-axis laser interferometer 17, in the exposure operation. Comparing FIGS. 9A and 9B with the conventional example shown in FIGS. 20A and 20B, it is seen that, in accordance with this form of the invention, with the provision of the collection port 13 at the lower end of the cover, adjacent to the X-axis measurement mirror and the Y-axis measurement mirror, the flow rate of purge gas flowing outwardly into the X-axis measurement light path 15 and the Y-axis measurement light path 18 is reduced in both the case (FIG. 9A or 20A) wherein the wafer stage 10 is closest to the laser interferometers 14 and 17 and the case (FIG. 9B or 20B) wherein it is most remote from them, and the unevenness of purge gas concentration in the X-axis measurement light path 15 and the Y-axis measurement light path 18 is reduced. With the provision of the first collection port 13 at the lower end of the cover, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, the flow rate of purge gas flowing outwardly into the X-axis measurement light path 15 and the Y-axis measurement light path 18 can be reduced. Thus, the unevenness the of purge gas concentration to be produced in the X-axis measurement light path 15 and the Y-axis measurement light path 18 can be reduced, and the measurement error of the laser interferometer can be reduced effectively. Therefore, with a very simple structure that a first supply port 6 is provided inside the cover 9 and a first collection port 13 is provided at a lower end portion of the cover 9, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, it is assured to purge the inside of the cover 9, and a measurement error of the laser interferometer can be prevented effectively. (3) An exposure apparatus according to Item (2), characterized by including temperature controlling means for blowing a gas toward a position opposed to a reflection surface of the X-axis measurement mirror or a reflection surface of the Y-axis measurement mirror. (4) An exposure apparatus according to Item (3), wherein the gas blown by the temperature adjusting means is an atmospheric gas or an inactive gas having an impurity concentration higher than that of the purge gas. Now, referring to FIGS. 11A and 11B, advantageous effects of the provision of temperature adjusting means for blowing a gas to a position opposed to the mirror reflection surface, will be explained. FIGS. 11A and 11B are schematic contour-line illustrations of a purge gas concentration distribution inside and around the cover 9, in a case wherein the first collection port 13 is provided at the lower end of the cover 9, adjacent to the X-axis measurement mirror 16 and the Y-axis measurement mirror 19, and wherein an air conditioning system 20 is provided to blow a gas toward a position opposed to a reflection surface 19a of the Y-axis measurement mirror 19, such that a gas is blown from the air conditioning system 20 toward the area around the wafer stage 10. In the schematic contour-line illustrations of FIGS. 11A and 11B, the darker the color is, the higher the purge gas concentration is, and the lighter the color is, the lower the purge gas concentration is. A white color area depicts a zone where no purge gas is present. FIG. 11A is a schematic contour-line illustration of a purge gas concentration distribution as the wafer stage 10 has moved closest to the X-axis laser interferometer 14 and the Y-axis laser interferometer 17, in the exposure operation. FIG. 11B is a schematic contour-line illustration of a purge gas concentration distribution as the wafer stage 10 has moved most remote from the X-axis laser interferometer 14 and the Y-axis laser interferometer 14 and the Y-axis laser interferometer 17, in the exposure operation. From FIGS. 11A and 11B, it is seen that, in both of the case (FIG. 11A) wherein the wafer stage 10 is closest to the interferometers 14 and 17 and the case (FIG. 11B) wherein it is most remote from them, there is approximately no purge gas present in the X-axis measurement light path 15 and the Y-axis measurement light path 18 and, therefore, there is no purge gas concentration distribution there. As described above, in the structure that a first collection port 13 is provided at the lower end of the cover, adjacent to the X-axis measurement mirror 15 and the Y-axis measurement mirror 19, while on the other hand, an air conditioning system 20 for blowing a gas toward the position opposed to the reflection surface 19a of the Y-axis measurement mirror 19 is provided so that a gas 21 is blown by the air conditioning system 20 toward the area around the wafer stage, regardless of the wafer stage position, it is possible to prevent production of an uneven purge gas concentration in the X-axis measurement light path 15 and the Y-axis measurement light path 18. As a result, a measurement error of the laser interferometer can be avoided effectively. In FIGS. 11A and 11B, the air conditioning system 20 is provided at a position opposed to the reflection surface 19a of the Y-axis measurement mirror 19. However, the air conditioning system 20 may be provided at a position facing the reflection surface 16a of the X-axis measurement mirror 16. Similar advantageous results as those in the third embodiment are obtainable even with such a structure. In accordance with this form of the present invention, with a very simple structure that, in addition to the structure mentioned in Item (2), an air conditioning system 20 is provided at a position opposed to the reflection surface 16a of the X-axis measurement mirror 16 or the reflection surface 19a of the Y-axis measurement mirror 19, it is assured to purge the inside of the cover 9, and a measurement error of the laser interferometer can be prevented effectively. (5) An exposure apparatus according to Item (1), wherein the first collection port is provided 10 so as to surround the outer periphery of an exposure area. (6) An exposure apparatus according to Item (5), wherein the collection flow rate through the first collection port is greater than the supply 15 flow rate through the first supply port. (7) An exposure apparatus according to Item (5), wherein a second collection port is provided outside the first collection port, so as to surround the outer periphery of the exposure area. (8) An exposure apparatus according to Item (7), wherein the collection flow rate through the first collection port is less than the supply flow rate through the first supply port, and wherein the total amount of the collection flow rate through the first and second collection ports is greater than the supply amount through the first supply port. (9) An exposure apparatus according to any one of Items (1)-(5) and (7), wherein a third collection port for sucking the purge gas is provided inside the cover and at a position opposed to the first supply port, so that the purge gas is caused to flow in one direction inside the cover. (10) An exposure apparatus according to Item (5), wherein a third collection port for sucking the purge gas is provided inside the cover and at a position opposed to the first supply port, so that the purge gas is caused to flow in one direction inside the cover, and wherein the collection flow rate through the third collection port is less than the supply flow rate through the first supply port, while the total collection flow rate through the first and third collection ports is greater than the supply flow rate through the first supply port. (11) An exposure apparatus according to any one of Items (1)-(5) and (7), wherein a third collection port for sucking the purge gas is provided inside the cover and at a position opposed to the first supply port, so that the purge gas is caused to flow in one direction inside the cover, and wherein a second supply port is provided inside the first collection port and at the lower end of the cover at least adjacent to the first supply port. (12) An exposure apparatus according to Item (5), wherein a third collection port for sucking the purge gas is provided inside the cover and at a position opposed to the first supply port, so that the purge gas is caused to flow in one direction inside the cover, wherein a second supply port is provided inside the first collection port and at the lower end of the cover at least adjacent to the first supply port, and wherein the collection flow rate through the third collection port is less than the total supply flow rate through the first and second supply ports, while the total collection flow rate through the first and third collection ports is greater than the total supply flow rate through the first and second supply ports. (13) An exposure apparatus according to any one of Items (1)-(12), wherein means for collecting the purge gas and/or atmosphere from the first or third collection port comprises a scroll type vacuum pump or a vacuum ejector. (14) An exposure apparatus according to any one of Items (1)-(13), wherein a reservoir is provided in a portion of a pipe for collecting the purge gas and/or atmosphere from the first or third collection port. (15) An exposure apparatus according to any one of Items (1)-(14), wherein one or more first pressure sensors for measuring the pressure inside the cover are provided inside the cover, wherein one or more second pressure sensors for measuring the pressure outside the cover are provided outside the cover, wherein one or more third pressure sensors for measuring the pressure near the fist collection port are provided at the lower end of the cover, adjacent to the first collection port, and wherein, on the basis of the measurement made through at least one of the first to third pressure sensors, at least one of the supply flow rate through the first supply port, the collection flow rate through the first collection port, the supply flow rate through the second supply port, and the collection flow rate through the third collection port is controlled so as to ensure that the pressure inside the cover becomes higher than the pressure outside the cover and/or that the pressure inside the cover becomes higher than the pressure around the first collection port. In accordance with these forms of the present invention described above, in an exposure apparatus using ultraviolet light, particularly, ArF excimer laser light or fluorine (F2) excimer laser light, the inside of the exposure light path near a photosensitive substrate can be purged stably without being influenced externally and, additionally, non-uniformness of purge gas concentration around the substrate stage can be reduced effectively. As a result, the manufacturing cost of the exposure apparatus can be reduced, yet sufficient transmissivity as well as uniformness and stability of the ArF excimer laser light or fluorine (F2) excimer laser light are accomplished. Furthermore, the positioning of the wafer substrate stage can be carried out very precisely. Therefore, projection exposure can be done very precisely and, thus, a fine circuit pattern can be projected satisfactorily. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. This application claims priority from Japanese Patent Application No. 2003-388198, filed Nov. 18, 2003, which is hereby incorporated by reference.
	claims	1. A radiation-shielding container for storing a syringe, the radiation-shielding container comprising:a body assembly for housing a portion of the syringe, the body assembly including a body shield formed of radiation shielding material, a body shell that defines a first cavity having an open end for receiving the body shield and defines a first chamber portion for receiving a portion of the syringe, wherein an inner wall of the body shell separates the first cavity and the first chamber portion, and a body plug secured to the body shell to cover the open end of the first cavity and retain the body shield within the first cavity; anda cap assembly for housing a portion of the syringe, the cap assembly including a cap shield formed of radiation shielding material, a cap shell that defines a second cavity having an open end for receiving the cap shield and defines a second chamber portion for receiving a portion of the syringe, wherein an inner wall of the cap shell separates the second cavity and the second chamber portion, and a cap plug secured to the cap shell to cover the open end of the second cavity and retain the cap shield within the second cavity,wherein the cap assembly is securable to the body assembly such that the first and second chamber portions define a chamber for storing the syringe. 2. The radiation-shielding container of claim 1 wherein the body shield is formed of lead. 3. The radiation-shielding container of claim 1 wherein the cap shield is formed of lead. 4. The radiation-shielding container of claim 1, and further comprising:a cap-securing structure including at least one radially outwardly and circumferentially extending rib defined by the shell of the body assembly; anda body-securing structure including at least one radially inwardly extending projection defined by the shell of the cap assembly for engagement with the cap-securing structure of the body assembly. 5. The radiation-shielding container of claim 1 wherein an inner surface of the body shield is positioned adjacent the inner wall of the body shell and extends substantially the length of the inner wall. 6. The radiation-shielding container of claim 5 wherein there is a clearance fit between the inner surface of the body shield and the inner wall of the body shell. 7. The radiation-shielding container of claim 1 wherein an inner surface of the cap shield is positioned adjacent the inner wall of the cap shell and extends substantially the length of the inner wall. 8. The radiation-shielding container of claim 7 wherein there is a clearance fit between the inner surface of the cap shield and the inner wall of the cap shell. 9. The radiation-shielding container of claim 1 wherein the body plug presses against the body shield to prevent movement of the body shield within the first cavity. 10. The radiation-shielding container of claim 1 wherein the cap plug presses against the cap shield to prevent movement of the cap shield within the second cavity. 11. The radiation-shielding container of claim 1, and further comprising a bio-liner received by the first chamber portion of the body assembly. 12. The radiation-shielding container of claim 1 wherein an open end of the cap shield substantially surrounds an open end of the body shield. 13. A radiation-shielding container for storing a syringe, the radiation-shielding container comprising:a body assembly for housing a portion of the syringe, the body assembly includinga body shell having an outer wall, an inner wall spaced apart from the outer wall, an end wall connecting the outer wall to the inner wall, and an open end, wherein the inner wall defines a first chamber portion for receiving the syringe, and the outer wall, the inner wall and the end wall define a first cavity,a body shield formed of radiation shielding material and having a substantially cylindrical shape, the body shield disposed within the first cavity of the body shell wherein an inner surface of the body shield lies adjacent the inner wall of the body shell, anda body plug configured and adapted for receipt by the open end of the body outer shell to cover the open end, wherein the body plug retains the body shield within the first cavity; anda cap assembly for housing a portion of the syringe, wherein the cap assembly is securable to the body assembly, the cap assembly includinga cap shell having an outer wall, an inner wall spaced apart from the outer wall, an end wall connecting the outer wall to the inner wall, and an open end, wherein the inner wall defines a second chamber portion for receiving the syringe, and the outer wall, the inner wall and the end wall define a second cavity,a cap shield formed of radiation shielding material and having a substantially cylindrical shape, the cap shield disposed within the second cavity of the cap shell wherein an inner surface of the cap shield lies adjacent the inner wall of the cap shell, anda cap plug configured and adapted for receipt by the open end of the cap shell to cover the open end, wherein the cap plug retains the shield within the second cavity. 14. The radiation-shielding container of claim 13 wherein the body shield is formed of lead. 15. The radiation-shielding container of claim 13 wherein the cap shield is formed of lead. 16. The radiation-shielding container of claim 13, and further comprising:a cap-securing structure including at least one radially outwardly and circumferentially extending rib defined by the shell of the body assembly; anda body-securing structure including at least one radially inwardly extending projection defined by the shell of the cap assembly for engagement with the cap-securing structure of the body assembly. 17. The radiation-shielding container of claim 13 wherein the outer wall of the body shell includes an annular groove, the radiation-shielding container further comprising a resilient O-ring positioned in the annular groove to provide a seal between the body and cap shells. 18. The radiation-shielding container of claim 13 wherein there is a clearance fit between the inner surface of the body shield and the inner wall of the body shell. 19. The radiation-shielding container of claim 13 wherein there is a clearance fit between the inner surface of the cap shield and the inner wall of the cap shell. 20. The radiation-shielding container of claim 13 wherein the body plug presses against the body shield to prevent movement of the body shield within the first cavity. 21. The radiation-shielding container of claim 13 wherein the cap plug presses against the cap shield to prevent movement of the cap shield within the second cavity. 22. The radiation-shielding container of claim 13 wherein the body plug is secured to the body shell. 23. The radiation-shielding container of claim 13 wherein the cap plug is secured to the cap shell. 24. The radiation-shielding container of claim 13, and further comprising a bio-liner received by the first chamber portion of the body shell. 25. The radiation-shielding container of claim 13 wherein an open end of the cap shield substantially surrounds an open end of the body shield. 26. A radiation-shielding container for storing a syringe, the radiation-shielding container comprising:a first assembly for housing a portion of the syringe, the first assembly including a shield formed of radiation shielding material, a shell that defines a first cavity having an open end for receiving the shield and defines a first chamber portion for receiving a portion of the syringe, wherein an inner wall of the shell separates the first cavity and the first chamber portion, and a plug secured to the shell to cover the open end of the first cavity and retain the shield within the first cavity; anda second assembly for housing a portion of the syringe, the second assembly including a shield formed of radiation shielding material and defining a second chamber portion,wherein the first and second assemblies are securable together such that the first and second chamber portions define a chamber for storing the syringe. 27. The radiation-shielding container of claim 26 wherein the second assembly comprises:a shell that defines a cavity having an open end for receiving the shield of the second assembly and defines the second chamber portion for receiving a portion of the syringe, wherein an inner wall of the shell separates the cavity and the second chamber portion; anda plug secured to the shell to cover the open end of the cavity and retain the shield within the cavity. 28. The radiation-shielding container of claim 26 wherein the second assembly includes a protective coating that substantially surrounds and encases the shield. 29. The radiation-shielding container of claim 28 wherein an open portion is formed in the protective coating, the second assembly including a plug fitted within the open portion to cover the shield. 30. A method of forming a radiation-shielding container for a syringe, the radiation-shielding container including a first shell and a second shell, each shell having an outer wall, an inner wall spaced apart from the outer wall, an end wall connecting the outer wall to the inner wall, and an open end, wherein the inner wall defines a chamber portion, and the outer wall, the inner wall and the end wall define a cavity, the method comprising:placing a first shield in the cavity of the first shell, the first shield formed of radiation shielding material, wherein an inner surface of the first shield is positioned adjacent the inner wall of the first shell;covering the open end of the first shell to retain the first shield within the cavity of the first shell;placing a second shield in the cavity of the second shell, the second shield formed of radiation shielding material, wherein an inner surface of the second shield is positioned adjacent the inner wall of the second shell;covering the open end of the second shell to retain the second shield within the cavity of the second shell;placing a syringe within the chamber portion of the first shell; andsecuring the second shell to the first shell wherein the syringe is confined within the chamber portions of the first and second shells. 31. The method of claim 30 wherein covering the open end of the first shell comprises securing a plug to the outer wall of the first shell. 32. The method of claim 31 wherein the plug prevents movement of the first shield within the first shell. 33. The method of claim 30 wherein covering the open end of the second shell comprises securing a plug to the outer wall of the second shell. 34. The method of claim 33 wherein the plug prevents movement of the second shield within the second shell.
	claims	1. A device for generating terahertz (THz) radiation having a short pulse laser with mode locking to which a pump beam is supplied, and a semiconductor component including a resonator-mirror, which semiconductor component simultaneously is designed for generating the THz radiation on the basis of impacting laser pulses, characterized in that the resonator mirror (M4) is provided with a semiconductor layer (8) which is partially permeable for the laser radiation of the short pulse laser (1), the absorption edge of the semiconductor layer being below the energy of the laser radiation of the short pulse laser (1), and electrodes (9, 10) connectable to a bias voltage source being mounted thereon so as to generate the THz radiation in the electric field and radiate it. 2. A device according to claim 1, characterized in that the resonator mirror (M4) is a resonator end mirror. 3. A device according to claim 1, characterized in that the resonator mirror (M4) is a saturable Bragg reflector (5). 4. A device according to claim 1, characterized in that the semiconductor layer (8) is made of a semiconductor material with short recombination time for free electrons. 5. A device according to claim 1, characterized in that the semiconductor layer (8) is a gallium-arsenide(GaAs) layer. 6. A device according to claim 5, characterized in that the semiconductor layer (8) is a low temperature gallium-arsenide (LT-GaAs) layer. 7. A device according to claim 1, characterised in that the semiconductor layer (8) is an aluminum-gallium-arsenide (AlGaAs) layer. 8. A device according to claim 7, characterised in that the semiconductor layer (8) is a low temperature aluminum-gallium-arsenide (LT-AlGaAs) layer. 9. A device according to claim 1, characterised in that a dielectric lens (13) for the emitted THz radiation is mounted on the side of the resonator mirror (M4) that faces away from the electrodes (9, 10). 10. A device according to claim 9, characterised in that the dielectric lens (13) is made of a material selected from the group consisting of silicon, gallium-arsenide (GaAs) or the like. 11. A device according to claim 1, characterised in that the strip-shaped, parallel electrodes (9, 10) are spaced at a distance (D) of from 30 μm up to a few mm from each other. 12. A device according to claim 1, characterised in that the strip-shaped electrodes (9, 10) have a width (B) of from 5 μm up to a few 10 μm. 13. A device according to claim 1, characterised in that the electrodes (9, 10) are made of metal. 14. A device according to claim 13, characterised in that the electrodes (9, 10) are made of a metal selected from the group comprising gold, aluminum, chromium, platinum-gold-or titanium-gold-layer systems. 15. A device according to claim 1, characterised in that the electrodes (9, 10) are formed by doped semiconductor material electrodes connected with metallic contacts. 16. A device according to claim 1, characterised in that at least the intensity centre of gravity of the beam cross-section (7′) of the laser beam (7) is located between the electrodes (9, 10). 17. A device according to claim 1, characterised in that the bias voltage source (16) is adapted to deliver variable bias voltages. 18. A semiconductor component including a resonator mirror to be used in a laser, which resonator mirror is adapted to enable mode-locked operation of the laser, wherein the semiconductor component simultaneously is designed to generate terahertz(THz) radiation on the basis of impacting laser pulses, characterised in that on the resonator mirror (M4), a semiconductor layer (8) partially permeable for the laser radiation (7) is provided, the absorption edge of the semiconductor layer being below the energy of the laser radiation (7) and electrodes (9, 10) connectable to a bias voltage source being mounted thereon in a manner known per se so as to generate the THz radiation in the electric field and radiate it. 19. A semiconductor component according to claim 18, characterised in that the resonator mirror (M4) is a resonator end mirror. 20. A semiconductor component according to claim 18 characterised in that the resonator mirror (M4) is a saturable Bragg reflector (5) known per se. 21. A semiconductor component according to claim 18, characterised in that the semiconductor layer (8) is made of a semiconductor material with short recombination time for free electrons. 22. A semiconductor component according to claim 18, characterised in that the semiconductor layer (8) is a gallium-arsenide(GaAs) layer. 23. A semiconductor component according to claim 22, characterised in that the semiconductor layer (8) is a low temperature gallium-arsenide (LT-GaAs) layer. 24. A semiconductor component according to claim 18, characterised in that the semiconductor layer (8) is an aluminum-gallium-arsenide (AlGaAs) layer. 25. A semiconductor component according to claim 24, characterised in that the semiconductor layer (8) is a low temperature aluminum-gallium-arsenide (LT-AlGaAs) layer. 26. A semiconductor component according to claim 18, characterised in that a dielectric lens (13) e.g. made of silicon, gallium-arsenide (GaAs) or the like, for the emitted THz radiation is mounted on the side of the resonator mirror (M4) that faces away from the electrodes (9, 10). 27. A semiconductor component according to claim 26, characterised in that the dielectric lens (13) is made of a material selected from the group consisting of silicon, gallium-arsenide (GaAs) or the like. 28. A semiconductor component according to claim 18, characterised in that the strip-shaped, parallel electrodes (9, 10) are spaced at a distance of from 30 μm up to a few mm from each other. 29. A semiconductor component according to claim 18, characterised in that the strip-shaped electrodes (9, 10) have a width of from 5 μm up to a few 10 μm. 30. A semiconductor component according to claim 18, characterised in that the electrodes (9, 10) are made of metal, e.g. gold, aluminum, chromium, platinum-gold- or titanium-gold-layer systems. 31. A semiconductor component according to claim 30, characterised in that the electrodes (9, 10) are made of metal selected from the group comprising gold, aluminum, chromium, platinum-gold- or titanium-gold-layer systems. 32. A semiconductor component according to claim 18, characterised in that the electrodes (9, 10) are formed by doped semiconductor material electrodes connected by metallic contacts. 33. A semiconductor component according to claim 18, characterised in that at least the intensity centre of gravity of the beam cross-section (7′) of the laser beam (7) is located between the electrodes (9, 10).
	description	Not Applicable Not Applicable 1. Technical Field of the Invention The present invention relates generally to strainer devices and, more particularly, to a suction strainer of modular construction which is adapted to remove entrained solids or debris from the cooling liquid in a nuclear reactor, and to reduce head loss across the strainer in the presence of liquids with such entrained solids or debris. 2. Description of the Related Art A nuclear power plant typically includes an emergency core cooling system that circulates large quantities of cooling water to critical reactor areas in the event of accidents. A boiling water reactor or BWR commonly draws water from one or more reservoirs, known as suppression pools, in the event of a loss of coolant accident. More particularly, water is pumped from the suppression pool to the reactor core and then circulated back to the suppression pool in a closed loop. A loss of coolant accident can involve the failure of reactor components that introduce large quantities of solid matter into the cooling water, which entrains the solids and carries them back to the suppression pool. For example, if a loss of coolant accident results from the rupture of a high pressure pipe, quantities of thermal insulation, concrete, paint chips and other debris can be entrained in the cooling water. In contrast to a BWR, a pressurized water reactor or PWR, after a loss of coolant accident, typically draws cooling water from a reactor water storage tank and, after a signal, shuts off the flow from the storage tank and recirculates this water through the reactor. In this regard, the pressurized water reactor has a containment area that is dry until it is flooded by the occurrence of an accident, with the emergency core cooling system using a pump connected to a sump in the containment area to circulate the water through the reactor. Nevertheless, the water that is pumped in the event of an accident will also usually contain entrained solids that typically include insulation, paint chips, and particulates. Thus, in both types of reactors (i.e., boiling water reactors and pressurized water reactors), cooling water is drawn from a reservoir and pumped to the reactor core, with entrained solids or debris potentially impairing cooling and damaging the emergency core cooling system pumps if permitted to circulate with the water. In recognition of the potential problems which can occur as a result of the presence of entrained solids or debris in the coolant water of the emergency core cooling system, it is known in the prior art to place strainers in the coolant flow path upstream of the pumps, usually by immersing them in the cooling water reservoir. It is critical that these strainers be able to remove unacceptably large solids without unduly retarding the flow of coolant. In this regard, the pressure (head) loss across the strainer must be kept to a minimum. Strainers are commonly mounted to pipes that are part of the emergency core cooling system and that extend into the suppression pool or sump, with the emergency core cooling system pumps drawing water through the strainers and introducing the water to the reactor core. There has been considerable effort expended in the prior art in relation to the design of strainers to decrease head loss across the strainer for the desired coolant flow. Existing strainers often include a series of stacked perforated hollow discs or flat perforated plates and a central core through which water is drawn by the emergency core cooling system pump. The perforated discs or plates prevent debris larger than a given size from passing the strainer perforations and reaching the pumps. As is apparent from the foregoing, large amounts of fibrous material can enter the circulating coolant water in the event of a reactor accident. This fibrous material, which often originates with reactor pipe or component insulation that is damaged and enters the emergency core cooling system coolant stream in the event of a loss of coolant accidents indicated above, typically accumulates on the strainer surfaces and captures fine particulate matter in the flow. The resulting fibrous debris bed on the strainer surfaces can quickly block the flow through the strainer, even though the trapped particulates may be small enough to pass through the strainer perforations. More particularly, the debris accumulates in a fluffy density in and on the strainer until the strainer becomes completely covered with a fiber and particulate debris bed. Once this occurs, the strainer loses its complex geometric surface advantages and becomes a simple strainer. Hours to days later, some debris typically dissolves into solution and interacts with chemicals present in the containment. At the same time, containment temperatures are trending down. This phenomenon causes certain chemical precipitates to form which eventually make their way to the strainer. Once they reach the strainer surface, the pressure drop across the strainer typically dramatically increases. The prior art has attempted to address the above-described flow blockage effect by making the strainer larger, the goal being to distribute the trapped debris over more area, reducing the velocity through the debris bed, and further reducing the head loss across the strainer as a whole. This solution, however, is often undesirable since the available space in a reactor for a suction strainer is usually limited, and further because larger strainers are typically more costly. As a result, the situation sometimes arises wherein the expected debris load after a loss of coolant accident can dictate a need for strainers that are too large for the space allotted for them in the containment area. Moreover, large strainers are often more difficult work with and thus more costly to install. In addition, prior art emergency core cooling system strainers have been constructed in ways that make them somewhat expensive to fabricate. The present invention addresses the aforementioned needs and overcomes many of the deficiencies associated with existing nuclear power plant strainer designs providing a strainer design which is specifically suited to reduce the differential pressure experienced across the strainer in nuclear power plants with medium to high fiber loads after chemical precipitate formation. Various features and advantages of the present invention will be described in more detail below. In accordance with the present invention, there is provided an increased efficiency strainer system which is particularly suited for use in the emergency core cooling system of a nuclear power plant. In certain embodiments of the present invention, the strainer system includes one or more strainer cassettes or cartridges, with each such cassette or cartridge including a plurality of strainer pockets disposed in side-by-side relation to each other. Multiple cassettes or cartridges may be assembled together to form a strainer module of the strainer system. More particularly, in one embodiment of the present invention, each cartridge has a generally quadrangular configuration, as do the individual strainer pockets included therein. In this particular embodiment, the strainer pockets of the cartridge each define an inflow end, with the inflow ends of the strainer pockets of the cartridge facing in a common direction. Within the cartridge, or the module including multiple cartridges, the inflow ends of one or more of the strainer pockets may be enclosed by an elastic metal membrane. When in a closed position, the membrane prevents liquid flow into the corresponding strainer pocket via the inflow end thereof. The membrane remains closed when only a low pressure load is exerted thereon, but is deflected or deformed into an open position when a high pressure load is exerted thereon. The movement of the membrane to its open position effectively opens the corresponding strainer pocket, thus allowing for the flow of liquid into the interior of the strainer pocket via the inflow end thereof. In accordance with another aspect of the present invention, it is contemplated that the above-described strainer cartridge(s) included in a strainer module of the strainer system may include flat, non-perforated face plates which extend from a surface of the cartridge(s) adjacent the inflow ends of the strainer pockets thereof. The non-perforated extended face plates cause the edges of a fiber and particulate debris bed forming at the inflow ends of the strainer pockets to compress and slowly curl in from an originally flush relationship to the face plates, which results in the creation of small flow paths between the face plates and debris bed as differential pressure continues to rise, thus allowing flow into the strainer and reducing head loss. As the strainer area affected by the flow receives more debris, fiber, particulate and chemical precipitate, the head loss increases until another flow path is opened into another area of the strainer. The creation of the flow paths, as caused by the optional inclusion of the extended face plates with the strainer cartridge(s), effectively reduces the maximum differential pressure experienced across the strainer and provides a way to potentially reduce required strainer surface area necessary to satisfy a particular containment recirculation net positive suction head requirement. In accordance with another embodiment of the present invention, the strainer cassette or cartridge has a generally circular configuration, with the strainer pockets thereof being arranged in side-by-side relation to each other in a generally circular pattern. In this particular embodiment, one or more of the strainer pockets of the strainer cartridge may be outfitted with the aforementioned elastic metal membrane. Additionally, if a strainer module is constructed including multiple circularly configured strainer cartridges disposed in stacked relation to each other, it is contemplated that all of the strainer pockets of one or more of the strainer cartridges included in the module may be outfitted with an elastic metal membrane. In accordance with another embodiment of the present invention, the strainer system comprises a plurality of cylindrically configured, tubular primary strainer elements. Each of the primary strainer elements defines an inflow end, and comprises concentrically positioned inner and outer walls which are each fabricated from a perforated metal material. The inflow end is typically defined solely by the inner wall of the primary strainer element. The inflow end of one or more of the primary strainer elements included in the strainer system may be covered by a rupture disc or segmented membrane which mirrors the functionality of the above-described elastic metal membrane. In this regard, the rupture disc or segmented membrane covering the inflow end of one or more of the primary strainer elements is operative to move from a normally closed position to an open position allowing direct liquid flow into the interior of the inner wall of the primary strainer element via the inflow end defined thereby when such rupture disc or segmented membrane is subjected to a high pressure load. In this particular embodiment of the strainer system, it is also contemplated that one or more of the primary strainer elements may include a secondary strainer element concentrically positioned within the inner wall of the primary strainer element, thus creating a double cylinder strainer construction as opposed to the single cylinder strainer construction provided by a primary strainer element standing alone. The secondary strainer element, if included with a primary strainer element, has a construction mirroring that of the surrounding primary strainer element, with the inflow end defined by the inner wall of the secondary strainer element optionally being covered by the above-described rupture disc or segmented membrane. In the double cylinder strainer construction, no rupture disc or segmented membrane is provided on the inflow end defined by the inner wall of the primary strainer element due to the concentric positioning of the secondary strainer element therein. The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. Common reference numerals throughout the drawings and detailed description to indicate like elements. Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same, FIGS. 1 and 2 illustrate an existing, prior art strainer cassette or cartridge 10. The cartridge 10 has a generally quadrangular configuration. When viewed from the perspective shown in FIGS. 1 and 2, the cartridge 10 includes an opposed pair of side walls 12 extending in spaced, generally parallel relation to each other, a top wall 14 extending between the top edges of the side walls 12, a bottom wall 16 extending in spaced, generally parallel relation to the top wall 14 between the bottom edges of the side walls 12, and a back wall 18 which extends between the back edges of the side walls 12 and between the back edges of the top and bottom walls 14, 16. In the strainer cartridge 10, the side, top, bottom and back walls 12, 14, 16, 18 are each fabricated from a perforated metal material. The strainer cartridge 10 further comprises a plurality of separator plates 20 which, when viewed from the perspective shown in FIGS. 1 and 2, are horizontally and vertically oriented between the side, top, bottom and back walls 12, 14, 16, 18 in a prescribed arrangement. More particularly, the separator plates 20 are arranged such that they, along with the side, top, bottom and back walls 12, 14, 16, 18, collectively define a plurality of strainer pockets 22 within the strainer cartridge 10. In the exemplary strainer cartridge 10 shown in FIGS. 1 and 2, a total of eight (8) strainer pockets 22 are included in the strainer cartridge 10, with the strainer pockets 22 being arranged in two side-by-side vertical columns of four (4) strainer pockets 22 each. Like the side, top, bottom and back walls 12, 14, 16, 18, each of the separator plates 20 is fabricated from a perforated metal material. As is most apparent from FIGS. 4 and 5, the horizontally oriented separator plates 20 included in the strainer cartridge 10 are preferably formed in a manner which imparts a generally parabolic configuration to each of the strainer pockets 22. In this regard, each of the strainer pockets 22 includes an open inflow end 24 at the front edges of the side, top, bottom and back walls 12, 14, 16, 18 and the front edges of the separator plates 20. In addition to the inflow end 24, each strainer pocket 22 includes an arcuate, concave back end 26 which is disposed proximate the back wall 18 of the strainer cartridge 10. As will be discussed in more detail below, in accordance with the present invention, the strainer cartridge 10 is provided with additional structural features which enhance the functionality thereof, and hence the functionality of a strainer module assembled to include one or more enhanced strainer cartridges. FIG. 3 depicts an exemplary strainer module 28 assembled by placing multiple strainer cartridges in side-by-side relation to each other. In the exemplary strainer module 28 shown in FIG. 3, a total of seven (7) strainer cartridges are included therein, with three (3) of the strainer cartridges being “enhanced.” For purposes of clarity, the “enhanced” strainer cartridges constructed in accordance with the present invention are labeled with the reference number “10a” in FIGS. 3 and 4 to differentiate the same from the prior art strainer cartridges 10. The remaining four (4) strainer cartridges included in the strainer module 28 are the prior art, non-enhanced strainer cartridges 10 described above. Those of ordinary skill in the art will recognize that the strainer module 28 may be assembled to include one or more enhanced strainer cartridges 10a and one or more standard strainer cartridges 10 in any combination, the aforementioned arrangement of three strainer cartridges 10a and four strainer cartridges 10 being exemplary only. When assembled to form the strainer module 28 shown in FIG. 3, the strainer cartridges 10, 10a are arranged such that the inflow ends 24 defined by the strainer pockets 22 thereof face in a common direction. When the strainer module 28 is integrated into a strainer system, a suction plenum is defined between the back wall of the strainer module 28 collectively defined by the back walls 18 of the strainer cartridges 10, 10a thereof. The suction plenum is fluidly coupled to a pump which, when activated, creates suction in the suction plenum as results in a differential pressure condition which causes liquid to be drawn into the inflow ends 24 of the strainer pockets 22 of the strainer cartridges 10, 10a, and thereafter through the strainer pockets 22 of the strainer cartridges 10, 10a into the suction plenum. As will be recognized, flow through the strainer cartridges 10, 10a of the strainer module 28 is achieved as a result of the fabrication of the strainer cartridges 10, 10a from the perforated metal material described above. FIG. 4 depicts an exemplary strainer system 30 which includes the strainer module 28 shown in FIG. 3 as paired with a second strainer module 29. The strainer module 29 is virtually identical to the strainer module 28, with the sole distinction being that is assembled with only the standard strainer cartridges 10 (i.e., a total of seven (7) of the cartridges 10 in side-by-side relation to each other). In the exemplary strainer system 30, the strainer modules 28, 29 are oriented in spaced, back-to-back relation to each other, with a suction plenum 32 being defined between the back walls of the strainer modules 28, 29. As will be recognized, in the exemplary strainer system 30, the activation of a pump fluidly coupled to the suction plenum 32 effectively draws liquid into the inflow ends 24 of the strainer pockets 22 of the strainer cartridges 10, 10a within each of the opposed strainer modules 28, 29, such liquid ultimately passing through the strainer cartridges 10, 10a and into the suction plenum 32. Again, the configuration of the strainer module 28 shown in FIG. 3 and the configuration of the strainer system 30 shown in FIG. 4 are intended to be exemplary only, with the present invention being directed in large measure toward the structural features added to the strainer cartridge 10 which facilitate the creation of the enhanced strainer cartridge 10a. These structural features or enhancements will now be described with particular regard to FIGS. 4 and 5. Referring now to FIGS. 4 and 5, in accordance with the present invention, it is contemplated that one or more of the strainer pockets 22 of each of the strainer cartridges 10a included in the exemplary strainer module 28 may be outfitted with a membrane 34 which is selectively moveable between a closed position and an open position. In the exemplary strainer system 30 shown in FIG. 4, a prescribed number of the strainer pockets 22 of the strainer module 28 included in the strainer system 30 are each outfitted with a membrane 34. Each membrane 34 is preferably fabricated from an elastic metal material and is pivotally connected to a corresponding strainer pocket 32 at a joint 36. Each membrane 34 is positioned at the inflow end 24 of the corresponding strainer pocket 22, and is sized so as to substantially cover such inflow end 24. Additionally, as is seen in FIG. 5, each strainer pocket 22 outfitted with a membrane 34 further preferably includes a membrane stopper 38 mounted thereto in opposed relation to the joint 36. In this regard, that edge of the membrane 34 disposed furthest from the joint 36 is normally abutted against the corresponding membrane stopper 38 when the membrane 34 is in its closed position. As indicated above, within one or more of the strainer cartridges 10a of the strainer module 28, the inflow end(s) 24 of one or more of the strainer pockets 22 may be enclosed by an elastic metal membrane 34. When in the closed position shown in FIGS. 4 and 5, the membrane 34 substantially prevents liquid flow into the corresponding strainer pocket 22 via the inflow end 24 thereof. The membrane 34 is normally maintained in its closed position by the abutment of one edge thereof against the corresponding membrane stopper 38, and remains in such closed position when only a low pressure load is exerted thereon. However, the exertion of a high pressure load on the membrane 34 effectively facilitates the deflection of deformation thereof into the open position in the manner shown by the phantom lines included in FIG. 5. As is apparent from FIG. 5, the level of flexion or deformation of the membrane 34 must be sufficient to cause the same to move beyond and thus be effectively disengaged from corresponding membrane stopper 38. Once the membrane 34 disengages the corresponding membrane stopper 38, such membrane 34 is free to rotate or pivot about the joint 36 to its fully open position. The movement of the membrane 34 to its open position effectively opens the corresponding strainer pocket 22, thus allowing for the flow of liquid into the interior of such strainer pocket 22 via the now unobstructed inflow end 24 thereof. Those strainer pockets 22 outfitted with the membranes 34 may be referred to as pressure controlled pockets or PCP's. Within the exemplary strainer module 28 including the strainer cartridges 10a, it is contemplated that approximately five percent (5%) of the strainer pockets 22 included in the strainer cartridges 10a will each be outfitted with a membrane 34 and thus function as a PCP. As a result, approximately ninety-five percent (95%) of the strainer pockets 22 included in the strainer cartridges 10a of the strainer module 28 will be open without membranes 34. With regard to the distribution of those strainer pockets 22 including membranes 34, it is also contemplated that such PCP's should be kept “clean” during the phase of debris coming on the strainer module 28 in the case of an accident. Accordingly, it is desirable that the strainer pockets 22 outfitted with membranes 34 be installed or located in a dead water zone of the strainer module 28 within the overall strainer system. Typically, this dead water zone may be in the middle of the strainer module 28 and/or at the opposite location of where debris typically enters into the containment. When the strainer module 28 is in use upon the occurrence of an accident, it is contemplated that the strainer pockets 22 outfitted with the membranes 34 will not open simultaneously, but rather will open sequentially as needed to cope with chemical effects in the debris laden water circulating through the strainer module 28. The sequential opening of the PCP's, as will usually occur when the pressure load exerted thereagainst by the debris field forming on the strainer module 28 exceeds the above-described high pressure threshold, facilitates an effective, controlled reduction in head loss, and further avoids any head loss “jump” due to clogging. As is further shown in FIGS. 3 and 4, the functional advantages to the exemplary strainer module 28 as a result of the inclusion of one or more PCP's in each of the strainer cartridges 10a may be further enhanced by additionally outfitting the strainer module 28 with flat, non-perforated face plates 40 which extend from prescribed surfaces of the strainer module 28 adjacent the inflow ends 24 of the strainer pockets 22 defined by the strainer cartridges 10, 10a thereof. More particularly, as is best seen in FIG. 3, the exemplary strainer module 28 includes a multiplicity of the extended face plates 40 which are attached to the front edges of corresponding ones of the top and bottom walls 14, 16 and separator plates 20 of the strainer cartridges 10, 10a included in the strainer module 28. The face plates 40 are arranged so as to define two generally quadrangular (e.g., rectangular) frames. As is seen in FIG. 3, the two quadrangular frames defined by the face plates 40 extend in spaced, generally parallel relation to each other. Since the face plates 40 are attached to the front edges of the top and bottom walls 14, 16 and separator plates 20, the frames defined thereby effectively circumvent the inflow ends 24 of a prescribed number of the strainer pockets 22, one or more of which may be outfitted with a membrane 34 so as to function as an above-described PCP. Those of ordinary skill in the art will recognize that the particular arrangement of the face plates 40 as shown in FIG. 3 is exemplary only, and that the number, size and arrangement of the face plates 40 may be selectively varied as needed to provide the functionality enhancements described below based on the particular environment or configuration of the strainer system in which the strainer module 28 outfitted with the face plates 40 is to be integrated. As indicated above, the face plates 40 extend forwardly from the strainer module 28 such that the two quadrangular frames defined by the face plates 40 effectively circumvent the inflow ends 24 of a prescribed number of the strainer pockets 22. As shown in FIG. 4, in the exemplary strainer system 30, though the strainer module 29 is not assembled to include the enhanced strainer cartridges 10a, such strainer module 29 is still outfitted with the above-described face plates 40 which are arranged on the strainer module 29 in the same pattern described above in relation to the strainer module 28. In this regard, the functional advantages attributable to the inclusion of the face plates 40 on the strainer module 28 are equally applicable to the strainer module 29, despite the absence therein of any of the PCP's. When included with the strainer module 29, the face plates 40 protrude forwardly from the strainer module 29 such that the spaced, generally parallel pair of quadrangular frames defined thereby circumvent the inflow ends 24 of a prescribed number of the strainer pockets 22 of the strainer module 29. As is further apparent from FIG. 4, the face plates 40 included with the strainer modules 28, 29 cause the edges of a fiber and particulate debris bed 42 which may form at the inflow ends of the strainer pockets 22 to compress and slowly curl in from an originally flush relationship to the inner surfaces of the face plates 40. This curling in of the debris bed 42 results in the creation of small flow paths between the inner surfaces of the face plates 40 and the debris bed 42 as differential pressure continues to rise, thus promoting liquid flow through the strainer modules 28, 29 and reducing head loss. The creation of these flow paths, as caused by the inclusion of the face plates 40 with the strainer modules 28, 29, effectively reduces the maximum differential pressure experienced across the strainer modules 28, 29. Those of ordinary skill in the art will recognize that the face plates 40 may be included on one, both or neither of the face plates 40. In this regard, the inclusion of the face plates 40 with one or both of the strainer modules 28, 29 is purely optional. Referring now to FIGS. 6-8, there is shown a strainer module 100 constructed in accordance with a second embodiment of the present invention. The strainer module 100 comprises a generally cylindrical, tubular main body section 102 which defines a section plenum 104 extending axially therethrough. Extending radially from the outer surface of the main body section 102 in spaced, generally parallel relation to each other are a plurality of circularly configured separator plates 106. Though not shown in FIG. 6, the main body section 102 includes openings formed therein which allow liquid flowing between the separator plates 106 to be drawn into the suction plenum 104 via such openings upon the creation of a pressure differential condition attributable to the activation of a pump fluidly coupled to the suction plenum 104. The strainer module 100 further comprises at least one circularly configured strainer cartridge 108 which is positioned between a prescribed adjacent pair of the separator plates 106. The strainer cartridge 108 comprises a multiplicity of wall members 110 which are arranged and attached to each other so as to collectively define a plurality of strainer pockets 112 of the strainer cartridge 108. In the strainer cartridge 108 shown in FIGS. 6 and 7, a total of ten (10) strainer pockets 112 are included in the strainer cartridge 108, with the strainer pockets 112 being arranged in a circularly configured array. The wall members 110 of the strainer cartridge 108 are each preferably fabricated from a perforated metal material. In the strainer cartridge 108 included in the strainer module 100, each of the strainer pockets 112 includes an open inflow end 114 which is defined by the peripheral edges of corresponding wall members 110. Thus, as seen in FIGS. 6 and 7, the inflow ends 114 of the strainer pockets 112 are directed or face radially outwardly relative to the suction plenum 104 defined by the main body section 102. In the strainer cartridge 108, each of the strainer pockets 112 is preferably outfitted with a membrane 116 which mimics the functionality of the above-described membrane 34. In this regard, each membrane 116 is preferably fabricated from an elastic metal material and is pivotally connected to a corresponding strainer pocket 112 at a joint 118. Each membrane 116 is positioned at the inflow end 114 of the corresponding strainer pocket 112, and is sized so as to substantially cover such inflow end 114. As is best seen in FIG. 7, each strainer pocket 112 is further outfitted with a membrane stopper 120 which is mounted thereto in opposed relation to the joint 118. In this regard, that edge of the membrane 116 disposed furthest from the joint 118 is normally abutted against the corresponding membrane stopper 120 when the membrane 116 is in its closed position. In the strainer cartridge 108, each membrane 116, when in its closed position, substantially prevents liquid flow into the corresponding strainer pocket 112 via the inflow end 114 thereof. Each membrane 116 is normally maintained in its closed position by the abutment of one edge thereof against the corresponding membrane stopper 120, and remains in such closed position when only a low pressure load is exerted thereon. However, the exertion of a high pressure load on the membrane 116 effectively facilitates the flexion or deformation thereof into the open position in the manner shown by the phantom lines included in FIG. 8. As is apparent from FIG. 8, the level of flexion or deformation of the membrane 116 must be sufficient to cause the same to move beyond and thus be effectively disengaged from the corresponding membrane stopper 120. Once the membrane 116 disengages the corresponding membrane stopper 120, such membrane 116 is free to rotate or pivot about the joint 118 to its fully open position. The movement of the membrane 116 to its open position effectively opens the corresponding strainer pocket 112, thus allowing for the flow of liquid into the interior of such strainer pocket 112 via the now unobstructed inflow end 114 thereof. Though, in FIG. 7, each of the strainer pockets 112 included in the strainer cartridge 108 is shown as being outfitted with a membrane 116, those of ordinary skill in the art will recognize that any number of the strainer pockets 112 less than the entire number thereof may be outfitted with a membrane 116 in any distribution or arrangement. Further, the strainer cartridge 108 may be assembled to include greater or fewer than ten strainer pockets 112 without departing from the spirit and scope of the present invention. Additionally, though the strainer module 100 is shown as including only one strainer cartridge 108 between one adjacent pair of the separator plates 106, those of ordinary skill in the art will also recognize that one or more additional strainer cartridges 108 may be included in the strainer module 100 between one or more other adjacent pairs of the separator plates 106. Within the strainer cartridge 108, it is contemplated that the strainer pockets 112 outfitted with the membranes 116 will not open simultaneously, but rather will open sequentially as needed to cope with chemical effects in debris laden water circulating through the strainer module 100. The sequential opening of the membranes 116 will usually occur when the pressure load exerted thereagainst by the debris field forming on the strainer module 100 exceeds a prescribed high pressure threshold as described above in relation to the strainer module 28. Referring now to FIG. 9, there is shown a strainer module 200 constructed in accordance with a third embodiment of the present invention. The sole distinction between the strainer modules 100, 200 lies in the separator plates 206 included in the strainer module 200 each having a generally quadrangular (e.g. square) configuration, as opposed to the circular configuration of the above-described separator plates 106 included in the strainer module 100. Referring now to FIGS. 10 and 11, there is shown a strainer module 300 constructed in accordance with a fourth embodiment of the present invention. The strainer module 400 comprises a main body section 402 which has a generally quadrangular cross-sectional configuration and defines a suction plenum 404. Attached to a common wall of the main body section 402 and protruding therefrom in spaced, generally parallel relation to each other are a plurality of (e.g., four) cylindrically configured, tubular primary strainer elements 406 which each fluidly communicate with the suction plenum 404. Each of the primary strainer elements 406 defines an inflow end 408, and comprises concentrically positioned outer and inner walls 410, 412. The outer and inner walls 410, 412 are each fabricated from a perforated metal, mesh-like material. The inflow end 408 is typically defined solely by the inner wall 412 of the primary strainer element 406. In the exemplary strainer module 400, the inflow end 408 of one of the primary strainer elements 406 is covered by a rupture disk or segmented membrane 414 which mirrors the functionality of the above-described membranes 34, 116. In this regard, the segmented membrane 414 is operative to move from a normally closed position (as shown in FIGS. 10 and 11) to an open position allowing direct liquid flow into the interior of the inner wall 412 of the corresponding primary strainer element 406 via the inflow end 408 defined thereby when such segmented membrane 414 is subjected to a high pressure load beyond a prescribed threshold. The segmented membrane 414 has a generally circular configuration and defines four (4) membrane quadrants which are individually movable relative to each other. In the strainer module 400 shown in FIGS. 10 and 11, it is also contemplated that one or more of the primary strainer elements 406 may include a secondary strainer element 416 concentrically positioned within the inner wall 412 of the primary strainer element 406, thus creating a double cylinder strainer construction as opposed to the single cylinder strainer construction provided by any primary strainer element 406 standing alone. The secondary strainer elements 416 defines an inflow end 418, and comprises concentrically positioned outer and inner walls 420, 422. The outer and inner walls 420, 422 are each fabricated from a perforated metal, mesh-like material. The inflow end 418 is typically defined solely by the inner wall 420 of the secondary strainer element 416. In the secondary strainer module 416, the inflow end 418 is covered by a rupture disk or segmented membrane 424 which mirrors the functionality of the above-described segmented membrane 414. In this regard, the segmented membrane 424 is operative to move from a normally closed position (as shown in FIGS. 10 and 11) to an open position allowing direct liquid flow into the interior of the inner wall 422 of the secondary strainer element 416 via the inflow end 418 defined thereby when such segmented membrane 424 is subjected to a high pressure load beyond a prescribed threshold. The segmented membrane 424 also has a generally circular configuration and defines four (4) membrane quadrants which are individually movable relative to each other. When the exemplary strainer module 400 is integrated into a strainer system, the creation of a pressure differential condition attributable to the activation of a pump fluidly coupled to the suction plenum 404 causes liquid to be drawn through the primary strainer elements 406 and the sole secondary strainer element 416 into the suction plenum 404. Within the strainer module 400, it is contemplated that the segmented membranes 414, 424 will not open simultaneously, but rather will open sequentially as needed to cope with chemical effects in debris laden water circulating through the strainer module 400. As described above in relation to the strainer module 28, the sequential opening of the segmented membranes 414, 424 will usually occur when the pressure load exerted thereagainst by a debris field forming of the strainer module 400 exceeds a prescribed high pressure threshold. Those of ordinary skill in the art will recognize that greater or fewer than four primary strainer elements 406 may be included in the strainer module 400 without departing from the spirit and scope of the present invention. Along these lines, more than one primary strainer element 406 may be outfitted with a segmented membrane 414, or with the above-described secondary strainer element 416 including its own segmented membrane 424. Further, no primary strainer module 406 need necessarily be outfitted with a secondary strainer element 416. This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.
	summary
040381374	abstract	A nuclear power reactor fuel bundle having a plurality of fuel rods disposed between two end plates positioned by tie rods extending therebetween. The assembled bundle is secured by one or more locking forks which pass through slots in the tie rod ends. Springs mounted on the fuel rods and tie rods are compressed by assembling the bundle and forcing one end plate against the locking fork to maintain the fuel rods and tie rods in position between the end plates. Downward pressure on the end plate permits removal of the locking fork so that the end plates may be removed, thus giving access to the fuel rods. This construction facilitates disassembly of an irradiated fuel bundle under water.
	description	This application is a divisional of prior application Ser. No. 10/244,187, filed on Sep. 16, 2002, now granted as U.S. Pat. No. 6,877,309, which claims the benefit of U.S. provisional application No. 60/323,506, filed Sep. 19, 2001, each of which is incorporated herein by reference in its entirety. This invention relates to the production of electricity through the use of nuclear energy, in particular nuclear fueled jets. For almost fifty years, electricity has been generated by large-scale power plants utilizing nuclear reactors as the energy source to heat the coolant in the reactor that, directly or indirectly, drives a turbine that generates electricity. Fuel assemblies containing fissile material are placed within the reactor core in precise patterns. The coolant is pumped through the reactor core, where the heat generated by the individual fuel assemblies is transferred to the coolant. In one common commercial power generation system—known as a pressurized water reactor system—the heated coolant is directed through at least one heat transfer apparatus (e.g., a heat exchanger) in which the thermal energy of the heated coolant is transferred to a secondary coolant which is then used to drive the turbine while the reactor coolant, now cooled, is pumped back to the reactor core in a closed loop coolant system. In another common commercial power generation system—known as the boiling water reactor system—the heated coolant is used to drive the turbine without the secondary transfer of thermal energy. Both power generation systems include thermal energy losses which reduces the overall electrical generation efficiency. While no serious threats to public health or the environment have occurred in the United States due to the operation of nuclear reactors in electrical power generation systems, the public perception of nuclear reactors includes numerous safety concerns. Although many of these concerns are exaggerated, they have resulted in multiple barriers to the continued operation of existing nuclear reactors as well as the design, placement and construction of newer reactors. Additionally, the safety concerns requires any operational nuclear reactor to adhere to a myriad of precautions and restrictions that are not found in other power generation systems such as coal which increases the cost of operating nuclear power generation stations. Due to the size of the conventional commercial nuclear power generation stations as well as the design and inherent operational characteristics of the nuclear reactor, nuclear power generation stations must, to the extent possible, be operated continuously. Also, locations suitable for such large power generation facilities are extremely limited. This is especially the case in densely populated areas with large electricity demands or in sparsely populated areas with electricity demands that are relatively small compared to the electricity supplied by a conventional commercial nuclear power generating station. Finally, many existing nuclear reactors are reaching the end of their originally licensed operational periods. Another power generation system that converts mechanical, rotational motion to electrical energy uses jets to create the rotational motion. For example, Blomquist, U.S. Pat. No. 4,208,590, discloses an electrical generating apparatus that uses at least two conventional internal combustion jet engines mounted on the ends of diametrically opposed rotatable blades that are attached to a central shaft. A circular-shaped rotor is affixed to the blades at a location between the central shaft and the jets. A stationary stator is attached to a base such that the rotor is in communication with the stator. When operating, the jets rotate the blades, causing the rotor to rotate relative to the stator, thereby generating electricity. The blades rest on wheels that are attached to the blades and travel within a track affixed to the base. The blades have ailerons for controlling the elevation of the blades as they are rotated by the jet engines. The system relies on the elevation of the blades being controlled by the ailerons for reducing the friction between the wheels and the track and between the hub to which the blades are attached and the central shaft upon which it rests. Internal combustion jet engines require a constant supply of extremely flammable jet fuel. Additionally, the exhaust from conventional jet engines contain many substances that are harmful to the environment and contribute to air pollution. Further, conventional jet engines are relatively inefficient in converting jet fuel to thrust energy. Therefore, the use of such a power generating system for any period of time increases the demand on hydrocarbon fuels and results in an increase in air pollution. Additionally, the power generating system has substantial energy losses due to the significant friction between the wheels and the track and between the hub and the shaft as well as the drag created by the ailerons moving through the air during operation. A similar power generation system is disclosed in Mount, U.S. Pat. No. 2,709,895. Mount uses ram jets or rocket motors that are attached to a rotatable plate that is connected to one end of a rotatable shaft. An electrical generator is attached to the opposite end of the shaft. Thrust created by the ram jets or the rocket motors causes the plate to rotate, which causes the shaft and generator to spin. Blomquist includes a secondary power generation system which uses the heat from the jet or rocket exhaust to heat water that surrounds a fire chamber into which the exhaust is directed. The heated water is used to create steam which drives a turbine. It is believed that the use of ram jets or rocket motors provides a more efficient fuel-to-thrust ratio than conventional internal combustion jet engines. However, it appears that additional external energy is required to create an initial rotational speed sufficient to allow the ram jets to operate. Further, a fan is required to provide sufficient air to the ram jets during operation. Liquid fueled rocket motors may be used instead of the ram jets, which reduces the size of the propulsion unit necessary to generate the same amount of thrust. However, using volatile liquid fuel introduces an additional danger. While the exhaust heat is used as a source for a secondary generator, the added equipment required to pump the water through the coolant jacket surrounding the fire chamber, into an associated coolant ring and through the turbine increases the losses experienced by the overall power generation system. Therefore, it is desired to design an electrical power generating system that takes advantage of the large energy-to-mass ratio and the long useful life of fissile material, which are singular characteristics of fissile material, and couple them with the relative energy conversion efficiency of an apparatus that converts rotational motion to electrical energy while eliminating or at least lessening the disadvantages associated with the current commercial nuclear power generating stations. Briefly summarized, the present invention is an apparatus for generating electricity that uses at least one jet engine fueled with fissile material. The nuclear fueled jet engine is affixed to an arm that projects from a central, rotatable shaft. The shaft is also attached to a device that converts rotational motion to electricity. The jet engine is positioned so that the thrust produced by the jet engine causes the engine and arm to travel in a radial direction around the longitudinal axis of the central shaft, rotating the central shaft. As the central shaft rotates, the rotational motion is converted to electricity. In a preferred embodiment, at least two jet engines are each affixed to an arm that is attached at diametrically opposed positions to the central shaft. In this configuration, the two diametrically opposed arms are considered a cross-beam. The thrust from the two jet engines rotate the central shaft and, ultimately, the device that converts the central shaft rotation to electricity. In a preferred embodiment, the device used to convert rotational energy to electricity is a generator having a rotor in communication with a stator. In another preferred embodiment, the device for converting rotational energy to electricity may be connected to the cross beam intermediate the jet engine and the rotatable central shaft. In another preferred embodiment, the central shaft has a stationary continuous inner trunk and a partial, rotatable, outer surface upon which the crossbeam is connected. A feature of the present invention is the use of fissile material to fuel the jet engines. Fissile material is material that undergoes the fission—splitting apart—process and in doing so creates at least two lighter elements and a known amount of energy. Such fissile materials include uranium, plutonium, thorium, and combinations thereof, called mixed-oxides (MOX). Another feature of the present invention is the use of a gas, for example hydrogen, helium or nitrogen, as both the propellant for the jet engine and the coolant for the fissile material located within the jet engines. One possible safety feature of the gas may be the ability to add a neutron poison to the gas in order to effectuate a rapid and complete shutdown of the jet engines. A preferred embodiment includes an enclosure surrounding the jet engines, the crossbeams, and at least a portion of the central shaft. This enclosure contains the gas used as the propellant and coolant as well as the fissile material within the jet engines. Another embodiment of the present invention may include locating the device for converting rotational motion to electricity along an inner surface of an enclosure in a position such that the exhaust of the jet engines engages the device. A power generating system 5, in accordance with a preferred embodiment of the present invention as shown in FIGS. 1 and 2, has two nuclear fueled jet turbine engines 10, attaching members 28, a rotatable central shaft 12, an apparatus for converting rotational motion to electricity 22, and a containment structure 16. Each of the jet turbine engines 10 is attached to one end of each of the connecting members 28. A second end of each of the attaching members 28, opposite the engines 10, is attached to the central shaft at a first position on the central shaft 12 such that the connecting members 28 are aligned and diametrically opposed thereto. The engines 10 and the attaching members 28 are oriented such that thrust generated by the engines 10 is perpendicular to a longitudinal axis of the central shaft 12 thereby causing the central shaft 12 to rotate about the longitudinal axis of the central shaft 12 when the engines 10 are operating. The central shaft 12 and the connecting members 28 may be used as conduits through which operational, control and safety systems and other equipment may be connected to the engines 10. The conversion apparatus 22 is disposed at a second position on the central shaft 12, thereby communicating the rotational motion of the central shaft 12 to the conversion apparatus 22. In a preferred embodiment, shown in FIGS. 1 and 2, the conversion apparatus 22 is a combination of a rotor 24 and a stationary stator 26, whereby the rotor 24 is affixed to the second position on the central shaft 12 and the stator 26 encloses the rotor 24 such that rotation of the central shaft 12 results in electricity being generated by the rotation of the rotor 24 within the confines of the stator 26. The containment structure 16 is filled with an operating gas (not shown) which serves as both the propellant for the jet engines 10 and the coolant for the nuclear fuel and other components within the engines 10. The operating gas may be, for example, hydrogen, helium, air, or a mixture thereof. In a preferred embodiment, shown in FIGS. 1 and 2, the containment structure 16 encloses the engines 10, the connecting members 28, and a portion of the central shaft 12. A seal is disposed between the central shaft 12 and the wall of the containment structure 16 where the two components intersect. The seal prevents leakage of the operating gas out of the containment structure 16. The temperature of the operating gas is regulated by a gas refrigeration apparatus (not shown). The containment structure 16 is designed to comply with current nuclear regulatory, safety, and security requirements. The containment structure may have any shape the complies with the above mentioned requirements and that fulfills its purpose with regard to the configuration of equipment therein. For example, the containment structure may be spherical, as shown in FIGS. 1 and 2, a vertical cylindrical as in FIG. 3, a horizontal cylinder as in FIGS. 4 and 5, or a toroidal shape as shown in FIGS. 6 and 7. Referring to FIGS. 1 and 2, a feature of the present invention may include guide members 18 that are affixable to the exterior of the engines 10 intermediate the engines 10 and the wall of the containment structure 16. A corresponding guide track 20 is affixable to the circumference of the wall of the containment structure 16 in alignment with the guide members 18 and the engines 10. The guide members 18 engage the guide track 20, thereby providing additional support to the engines 10 and may assist in maintaining the engines 10 in a fixed position relative to the longitudinal axis of the central shaft 12 when the engines 10 are operating and producing thrust. Another feature includes at least one circulation fan 30 attachable to the central shaft 12. The circulation fan 30 facilitates the circulation of the operating gas within the containment structure 16. A further feature is stabilizers 32 attachable to the connecting members 28 intermediate the engines 10 and the central shaft 12. The stabilizers 32 are aligned parallel to the longitudinal axis of the central shaft to provide additional aerodynamic balancing of the engines 10 during operation. Preferably, the stabilizers are airfoils. As discussed earlier and shown in FIGS. 1 and 2, the conversion apparatus 22 comprises a rotor 24 affixed to the central shaft 12 and a stationary stator 26 affixed to a base and surrounding the rotor 24. As the central shaft 12 rotates, the affixed rotor 24 rotates within the stationary stator 26, generating electricity which is then transmitted to a distribution system (not shown). Another preferred embodiment, as shown in FIG. 3, has multiple engines 110, each connected to the central shaft 112 by a corresponding connecting member 128. The engines 110 may be on a single plane or may be spaced longitudinally along the axis of the central shaft 112. In a preferred embodiment, shown in FIGS. 4 and 5, a rotor module 224 is affixed to the exterior of each engine 210 between the engines 210 and the wall of the containment structure 216. The rotor modules 224 are oriented toward the wall of the containment structure 216 where a stator belt 226 is affixed to the circumference of the containment structure 216 in alignment with the rotor modules 224. During operation, the engines 210 produce thrust, which causes the engines 210 and the affixed rotor modules 224 to rotate about the central shaft 212. As the engines 210 rotate, the rotor modules 224 rotatably communicate with the stator belt 226, thereby generating electricity. A further preferred embodiment of the present invention, shown in FIGS. 6 and 7, has the engines 310 enclosed within a toroidal-shaped containment structure 316. The containment structure 316 has an interior surface and an exterior surface. At least one stator belt 326 is affixed to the interior surface of the containment structure 316 at positions diametrically opposed to each other. At least one rotor module 324 is affixed to the exterior of each engine 310 and oriented toward the stator belt 326, such that the rotor module 324 is in a spaced apart juxtaposition with the stator belt 326. If multiple stator belts 326 and rotor modules 324 are used, then the stator belts are preferably spaced evenly about the interior surface of the containment structure 316 and a corresponding rotor module 324 is affixed to the exterior of each engine 310. As the engines 310 travel about the circular track within the containment structure 316, the rotor modules 324 rotate along the stator belts 326 and produce electricity. At least one guide member 318 is affixed to the exterior of each engine 310. The guide member 318 connects each of the engines 310 to a corresponding guide track 320 affixed to an area of the containment structure 316 such that the guide member 318 and track 320 do not interfere with the stator belts 326. The guide member 318 and track 320 maintains the engines 310 in alignment within the containment structure 316. The guide members 318 and track 320 may also be used as a conduit to each engine 310 for the placement of control, operation, and communication equipment (not shown) necessary to operate each engine 310. A feature of this embodiment may include an apparatus for maintaining the proper spacing between engines 310. Another feature of this embodiment may include an apparatus for initiating the operation of the engines 310 and the rotational motion of the apparatus. Additionally, a monorail type unit may be used for the guide member 318 and the track 320. One feature of the present invention is the engines (collectively identified by reference numeral 10) which may be jet turbine engines similar to conventional internal combustion jet turbine engines. The engines 10 are modified to use nuclear fuel, in particular any suitable fissile material such as uranium, plutonium, thorium, or a mixture thereof, as the primary fuel source. The engines 10 may also use conventional jet fuel as a secondary fuel source. The engines 10 are constructed to withstand the operating temperatures, the use of the operating gas, the forces exerted upon the engines due to the rotational motion experienced by the engines 10 during operation, and the effects of any radiation emitted by the nuclear fuel enclosed within the engines 10. Referring to FIG. 8, the jet turbine engine includes an inlet 50, a compressor 52, a burner section 56, a turbine 62, a shaft 54 that connects the compressor 52 and the turbine 62, and an outlet nozzle 64. A shroud 60 comprised of radiation shielding material surrounds the exterior of the burner section 56. An exterior housing 66 encloses the components. The burner section 56 includes a fuel core 70 comprised of fuel elements 72 containing fissile material assembled in a fuel element lattice (i.e., fuel elements arrayed in a geometric matrix) designed to optimize the operating parameters desired for the power generating apparatus 5. Coolant channels 74, which are part of the fuel element lattice, extend through the fuel core 70. The coolant channels 74 allow the operating gas to flow through the fuel core 70, removing the heat generated by the fuel elements 72 during operation, thus maintaining the fuel core 70 within the desired operating temperature range. Control elements 78 that contain a material that stops the chain reaction of the fissile material by absorbing neutrons (i.e., a “neutron poison”) are located within control channels formed within the fuel core 70. The control elements 78 are manipulated so that they, in tandem with the array of the fuel element lattice, regulate the chain reaction within the fuel core 70, thereby consequently regulating the energy produced by the power generation apparatus 5. During operation, the control elements 78 are manipulated to begin a nuclear fissioning process within the fuel elements 72 in the fuel core 70. Operating gas is drawn into the jet turbine engine through the inlet area 50 and passes through the compressor 52. The compressed operating gas enters the burner section 56 and flows through the coolant channels 74 in the fuel core 70, whereby the heat generated by the fuel elements 72 is transferred to the operating gas. The heated operating gas 44 exits the burner section and flows through the turbine 62, driving the turbine 62 as the operating gas expands. The operating gas then exhausts through the outlet nozzle. The thrust generated by the operating gas exiting the outlet nozzle pushes the jet turbine engine in the opposite direction to that of the exhaust flow. The flow of operating gas through the turbine 62 also drives the compressor 52 which is rotatably connected to the turbine 62 by the rotatable shaft 54. An alternative configuration of the jet turbine engine is the use of a turbofan engine. A turbofan engine may provide efficiencies greater than those provided by a jet turbine engine. Further, the turbofan engine allows a portion of the operating gas to bypass the fuel core, thereby providing cooling to the exterior of the fuel core in addition to the flow through the coolant channels 74. A nuclear-fueled ramjet engine may be used in the present invention instead of a jet turbine engine. The ramjet engine, shown in FIG. 9, is similar to the current designs of conventional ramjet engines except for the utilization of a nuclear fuel core in the burner (replacing the fuel injector of a conventional ramjet engine). The gas would enter the inlet 150 and be compressed. The gas would then be heated or ignited in the burner 156 from the heat of the nuclear fuel core 170, cooling the nuclear fuel core and providing thrust to the engine as it exited the nozzle 164. The design of the nuclear fuel core for the ramjet engine would be based on principles similar for the nuclear-fueled turbine engine plus the need to reflect the different flow characteristics of a ramjet engine as well as the specific requirements envisioned for the ramjet engine in a particular design. As with the nuclear-fueled turbine engine, some graphite or other shielding 160 around the nuclear fuel core would be considered. The ramjet engines may be used alone or in a configuration that includes the jet turbine engines. For example, the engines in the present invention should be capable of producing enough thrust to attain a high rotational speed. Thus, the additional efficiencies from using a nuclear-fueled ramjet at high speeds could be obtainable. If used as a supplement to the jet turbine or turbofan engines, the thrust from the ramjet engine would augment the thrust from the turbine engines or be used as the primary thrust for the system at times when it may be desirable to “power down” the nuclear-fueled turbine engines. To protect the conversion apparatus from excessive rotational speed, conventional gear reducing equipment (not shown) may be disposed between the central shaft and the conversion apparatus. The nuclear-fueled turbine engines and ramjets may be adapted to use a secondary fuel, e.g. jet fuel, to initially facilitate the operation of the engines and the production of threshold rotational motion. The designs of both a nuclear-fueled turbine engine and a nuclear-fueled ramjet engine should generally be able to incorporate advances currently being made and to be made in the future regarding jet engine design and thermal nuclear propulsion. The invention is intended to couple the superior qualities of nuclear fuel (its remarkable energy per mass and its long-life) with the efficiencies of jet propulsion to create an electric generating system taking better advantage of the nuclear fuel qualities and providing a simpler design that eliminates some of the significant energy losses from current nuclear reactor designs. These qualities also allow for substantially greater design flexibility as well as the capability to optimize the expected electricity production through the adjustment of various design features, including the type and configurations of the jet engines, the arrangement of nuclear fuel element lattice and other components in the fuel core, the type of the operating gas, the configuration of the containment vessel, and the type and configuration of other related components such as the refrigeration equipment and the apparatus for converting rotational motion to electricity. It is believed that applying current technologies and methodologies through computer modeling and other analyses, substantially enhanced design specifications can be achieved in a cost-effective manner and that these processes can be easily adapted to provide alternative designs for different, specific operational uses intended for this invention. The structure of the invention also is an inherently safer design than that of many current nuclear reactors because it should have a lower nuclear core power density, would use an inert gas as the coolant and have no heat exchanger. Additionally, the more efficient and simpler design of the invention should result in the use of a smaller quantity of nuclear fuel, and for a longer period of time, thus enhancing its safety features and providing advantages over other nuclear reactor designs as far as nuclear waste disposal. The invention's structure also minimizes the siting or location considerations for nuclear reactors. The invention could be used for general power production (including clustering units together) or for special purposes, such as localized use or meeting peak demands. This invention would utilize, with adaptions understood by those persons skilled in the art, current state-of-the-art materials and designs for jet engines and thermal nuclear propulsion. This invention also generally permits advances made in jet engine designs and thermal nuclear propulsion to be incorporated either through the designs of future systems or by minor retrofitting of then existing reactors that use this invention. It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.
053696751	claims	1. An apparatus for pressurizing a hollow expandable device installed inside a reactor pressure vessel or piping of a nuclear reactor, said reactor pressure vessel being surrounded by a drywell having a port for electrical lines, said hollow expandable device having an inlet, comprising: an outlet in fluid communication with said inlet of said hollow expandable device; means for containing a compressible fluid, said containing means being in fluid communication with said outlet; means for changing the pressure of said compressible fluid by a predetermined amount in response to electrical control signals, said pressure changing means being located within the confines of said drywell; and a first electrical line passing through said port in said drywell, said first electrical line being connected to said pressure changing means for conducting said electrical control signals thereto from outside the confines of said drywell. a double-cantilever beam crack growth sensor comprising first and second cantilever beams and a crack formation zone, each of said first and second cantilever beams having one end joined to said crack formation zone; a hollow expandable device mechanically coupled at respective ends thereof to the other ends of said first and second cantilever beams, said hollow expandable device being expandable in response to fluid pressure therein, said expanded hollow expandable device exerting a load that urges the other ends of said first and second cantilever beams mutually apart, the magnitude of said load being dependent on the pressure inside said hollow expandable device; electrically controllable pressurizing means for supplying fluid having a predetermined pressure to said hollow expandable means, said pressurizing means being located within the confines of said drywell; and electrical conducting means for transmitting electrical signals from outside the confines of said drywell to said pressurizing means. mechanically coupling one end of a hollow expandable device to one end of a first cantilever beam of said crack growth sensor; mechanically coupling the other end of said hollow expandable device to one end of a second cantilever beam of said crack growth sensor; installing said coupled hollow expandable device/crack growth sensor inside said reactor pressure vessel or inside piping of said nuclear reactor; installing an electrically controllable pressure source inside the confines of said drywell in fluid communication with said hollow expandable device; connecting said hollow expandable device and said electrically controllable pressure source to be in fluid communication; and establishing an electrical connection between said electrically controllable pressure source and an external source of electrical signals located outside the confines of said drywell. 2. The apparatus as defined in claim 1, wherein said containing means comprises a bellows in fluid communication with said outlet, and said pressure changing means comprises a piston connected to a movable end of said bellows and an electric motor coupled to said piston in a manner such that said piston is linearly displaced by operation of said electric motor, the pressure in said hollow expandable device being dependent on the position of said piston. 3. The apparatus as defined in claim 2, wherein said pressure changing means further comprises a threaded shaft connected to said piston, said electric motor comprising gears for engaging the threads on said threaded shaft. 4. The apparatus as defined in claim 3, wherein said electric motor is powered by an electrical power supply carried by a second electrical line which passes through said port in said drywell. 5. The apparatus as defined in claim 3, wherein said electric motor is controlled by said electrical control signals carried by said first electrical line. 6. The apparatus as defined in claim 1, wherein said containing means comprises a gas-filled chamber in fluid communication with said outlet, and said pressure changing means comprises an electric heater for heating the gas in said chamber, the pressure in said hollow expandable device being dependent on the temperature of said gas. 7. The apparatus as defined in claim 6, further comprising means for detecting the temperature of said gas-filled chamber. 8. The apparatus as defined in claim 1, wherein said containing means comprises a storage tank for liquid, and said pressure changing means comprises an electric pump/compressor in fluid communication with said outlet for pumping liquid from said storage tank to said hollow expandable device. 9. The apparatus as defined in claim 8, wherein said pressure changing means further comprises an accumulator in fluid communication with said outlet and with said pump/compressor. 10. The apparatus as defined in claim 9, further comprising valve means for preventing decompression of said hollow expandable device when said electric pump/compressor is off, said valve means being located along the path of fluid communication between said accumulator and said pump/compressor. 11. An apparatus for monitoring crack growth in a reactor pressure vessel or piping of a nuclear reactor, said reactor pressure vessel being surrounded by a drywell having a port for electrical lines, comprising: 12. The crack growth monitoring apparatus as defined in claim 11, wherein said hollow expandable means comprises a bellows. 13. The crack growth monitoring apparatus as defined in claim 11, wherein said pressurizing means comprises a bellows in fluid communication with said hollow expandable means, a piston connected to a movable end of said second bellows, and an electric motor connected to said electrical conducting means and coupled to said piston in a manner such that said piston is linearly displaced by operation of said electric motor, the pressure in said hollow expandable means being dependent on the position of said piston. 14. The crack growth monitoring apparatus as defined in claim 13, further comprising a threaded shaft connected to said piston, said electric motor comprising gears for engaging the threads on said threaded shaft. 15. The crack growth monitoring apparatus as defined in claim 11, wherein said pressurizing means comprises a gas-filled chamber in fluid communication with said hollow expandable means, an electric heater connected to said electrical conducting means for heating the gas in said chamber and means for detecting the temperature of said gas-filled chamber, the pressure in said hollow expandable means being dependent on the temperature of said gas. 16. The crack growth monitoring apparatus as defined in claim 11, wherein said pressurizing means comprises an electric pump/compressor connected to said electrical conducting means and in fluid communication with said hollow expandable means for pumping fluid therein, and valve means for preventing decompression of said bellows when said electric pump/compressor is off. 17. The crack growth monitoring apparatus as defined in claim 16, further comprising an accumulator in fluid communication with said hollow expandable means and with said pump/compressor, said valve means being located along the path of fluid communication between said accumulator and said pump/compressor. 18. A method for monitoring crack growth in a component of a nuclear reactor using a double-cantilever beam crack growth sensor, said nuclear reactor comprising a reactor pressure vessel surrounded by a drywell, comprising the following steps: 19. The method as defined in claim 18, further comprising the step of expanding said hollow expandable device using pressurized fluid from said pressure source, said hollow expandable device being expanded by a predetermined amount in dependence on the control signal received by said pressure source from said external source of electrical signals, whereby a predetermined load is applied to said crack growth sensor. 20. The method as defined in claim 18, wherein said electrical connection passes through a sealed port in said drywell.
	summary
	description	1. Field of the Invention The present invention relates to a charged particle beam apparatus for observing and inspecting the surface of a sample, such as semiconductor wafer or photomask, which is liable to be contaminated by irradiation with a charged particle beam and to have the image observation spoilt, and a contamination removal method therefor. 2. Description of the Related Art Heretofore, in an electron beam apparatus such as scanning electron microscope (SEM), it has been well known that image observation is hampered by the contamination of a sample attendant upon irradiation with an electron beam (refer to Non-patent Document 1). The contamination is said to be ascribable to the fact that the electron beam will impinge against hydrocarbons floating or adsorbed in the surface of the sample, to turn the hydrocarbons into carbon and to deposit the carbon on the sample. It is considered that much of the hydrocarbons will, not only be produced by gases emitted from the inside components of the apparatus, but also be brought into the SEM by the sample having already been contaminated. It is therefore often observed that the production rate of the contamination becomes much higher than usual. As countermeasures against the contamination in the electron beam apparatus, there are the following examples: (1) Low-temperature Contamination Prevention Apparatus: A metal plate held at a low temperature (for example, liquid nitrogen temperature) is disposed around a sample which is irradiated with an electron beam, so as to adsorb hydrocarbons into the metal plate and to diminish the contamination of the sample. (2) Purification and Degassing of Components: Components inside a sample chamber are subjected to ultrasonic cleaning with a solvent and are further degassed at high temperatures, and they are thereafter assembled into an electron beam apparatus, whereby hydrocarbons to be emitted are decreased, and the contamination of a sample is diminished. Even after the above countermeasures (1) and (2), the diminution of the contamination of the sample is sometimes unsatisfactory. Especially in the observation of the surface of a semiconductor wafer or photomask or a pattern length measurement on the surface, an identical place is measured a plurality of times. On this occasion, a pattern size is often changed by the contamination attendant upon the electron beam irradiation, and even when the magnitude of the change is slight, unallowable lowering in the reproduction precision of length measurement values is sometimes incurred. (3) Down-flow type Asher: Active oxygen is produced by radio-frequency discharge from a mixture gas consisting of O2 and CF4 and is reacted with hydrocarbons, thereby to remove contamination (refer to Non-patent Document 2). With this technique, an optimization control is difficult, and rather the lowering of the reproduction precision of length measurement values attributed to etching will be incurred in the observation of the surface of a semiconductor wafer or photomask or a pattern length measurement on the surface. As stated above, it cannot be said that the related-art countermeasures against the contamination in the electron beam irradiation apparatus are satisfactory. Meanwhile, in semiconductor manufacture, a dry cleaning method wherein organic substances on the surface of an Si substrate are removed by irradiation with ultraviolet rays has been well known. The principles of this method are as stated below. Oxygen O2 is dissociated into active oxygen O by the ultraviolet rays. Owing to the active oxygen, the organic substances undergo oxidation decompositions, thereby to be volatilized and removed. In particular, it has been known that a method of cleaning the Si substrate by irradiation with ultraviolet rays (vacuum ultraviolet rays at a wavelength of 172 nm) from an excimer lamp is effective (refer to Non-patent Document 3). This document indicates that, in the atmospheric air, when the density of the active oxygen at the sample surface is heightened by setting several mm or less as the distance between the sample and the window plane of the excimer lamp, a cleaning effect increases, whereas when the distance is made longer, the cleaning effect decreases because an ultraviolet dose to fall on the sample surface lessens due to the absorption of the ultraviolet rays by the atmospheric air, so the quantity of the active oxygen to appear in the vicinity of the surface lessens. It is to be noted, however, that the ultraviolet irradiation has never been employed for the removal or prevention of the contamination in the charged particle beam apparatus. [Non-patent Document 1] Electron Microscope (1981), Vol. 16, No. 1, p. 2, published by the Japanese Society of Microscopy [Non-patent Document 2] Materials of the 117th Study Meeting (1991), p. 137, 132nd Committee, published by Japan Society for the Promotion of Science [Non-patent Document 3] Paper Issue (1999), Vol. 83, No. 5, published by the Illuminating Engineering Institute of Japan An object of the present invention is to provide a charged particle beam apparatus such as length measurement apparatus and a contamination removal method therefor, in which a sample is irradiated with ultraviolet rays under the atmospheric pressure or a reduced pressure or in the gaseous atmosphere of oxygen or the like, so as to prevent, remove or diminish the contamination of the sample attributed to the irradiation of this sample with a charged particle beam, whereby the length measurement reproducibility of the pattern of a semiconductor wafer or a photomask, and so forth are enhanced without incurring the lowering of an operability or a throughput in the length measurement apparatus or the like. In order to accomplish the object, according to the invention, in a charged particle beam apparatus wherein an image is generated by irradiating a sample with a charged particle beam and detecting secondary electrons or the likes emitted from the sample, the sample is irradiated with ultraviolet rays for a predetermined time period before or after the automatic conveyance of the sample into a sample chamber, within a chamber the interior of which is held in the atmospheric air or at a reduced pressure, within a gas introduction chamber into which a gas such as oxygen is introduced, or within the sample chamber the interior of which is held at a reduced pressure or into which a gas such as oxygen is introduced, thereby to attain the prevention, removal or diminution of the contamination of the sample. Thus, in the charged particle beam apparatus, the contamination of the sample is removed or diminished without etching, before or after the observation of the sample based on the charged particle beam, whereby the reproduction precision of the length measurement of a pattern, and so forth can be enhanced, and an operability or a throughput can be enhanced in interlocking with the automatic conveyance of the sample. By way of example, an excimer lamp was applied to a length measurement SEM for photomasks. When the photomask contaminated by SEM observation was irradiated with ultraviolet rays based on the excimer lamp, the contamination was diminished or prevented, and the reproduction precision of length measurements was enhanced. Now, the present invention will be successively described in detail by taking an electron beam as an example of a charged particle beam. FIGS. 1A and 1B show the configurational views of embodiments of the invention, respectively. The illustrated configurational views are the partial plan views of a length measurement SEM for photomasks. In the embodiment shown in FIG. 1A, a sample (mask) 12 is irradiated with ultraviolet rays in a preparatory evacuation chamber 15 or/and a sample chamber 16 for a predetermined time period, thereby to remove the contamination of the sample 12. Referring to FIG. 1A, a SMIF (Standard Mechanical Interface) pod 11 is a box for accommodating and conveying a plurality of samples 12, here, masks (photomasks) in a clean state (a state where no dust is adherent). The sample (mask) 12 is a sample (mask) to-be-handled whose surface is irradiated with the ultraviolet rays for the predetermined time period so as to remove the contamination (the expression “removal” shall include both the removal of the contamination ascribable to electron beam irradiation or the like and the removal of hydrocarbons originating the contamination, and the same shall hold true hereinbelow). A conveyance robot 13 is a robot which opens the door of the SMIF pod 11, fetches a predetermined one of the samples (masks) 12 and conveys the fetched sample to a conveyance stage 14 here in this case, and which conversely conveys the sample 12 put on the conveyance stage 14, to the SMIF pod 11 and shuts the door. The conveyance stage 14 is a stage (a fixation bed or fixation case for conveying the sample 12) to which the sample (mask) 12 is fixed and which conveys this sample into the preparatory evacuation chamber 15 or the sample chamber 16 at a succeeding step, and in the reverse direction. The preparatory evacuation chamber 15 is a chamber which preparatorily evacuates air from the atmospheric air or leaks air into a vacuum up to the atmospheric air in order to convey the sample 12 into or out of the sample chamber 16 of high vacuum. Here in the preparatory evacuation chamber 15, an ultraviolet irradiation unit 21 is disposed so as to automatically irradiate the sample 12 with ultraviolet rays for a predetermined time period during the conveyance of this sample and to thus remove the contamination. The ultraviolet irradiation unit 21 which is disposed in the preparatory evacuation chamber 15 subjects the sample 12 conveyed into the preparatory evacuation chamber 15, to the ultraviolet irradiation for the predetermined time period, thereby to remove the contamination. Incidentally, although the ultraviolet irradiation unit 21 is shown by the side of the mask 12 within the preparatory evacuation chamber 15 in FIG. 1A, it is actually arranged over the mask 12 (anyway, the ultraviolet irradiation unit 21 may be capable of irradiating the whole surface of the mask 12). The sample chamber 16 is a chamber in which the sample (mask) 12 is scanned (as linear scan or planar scan) while being irradiated with the finely focused electron beam, so as to detect secondary electrons emitted from the sample 12 and to display an image. Here, the sample chamber 16 includes a body tube 17, an ultraviolet irradiation unit 22, etc. The body tube 17 focuses the electron beam finely so as to irradiate the surface of the sample 12 with the focused electron beam. In this state, the sample surface is scanned (as linear scan or planar scan), and the image is generated (refer to FIG. 3). The ultraviolet irradiation unit 22 which is disposed in the sample chamber 16 irradiates the sample 12 conveyed into the sample chamber 16, with ultraviolet rays for a predetermined time period, thereby to remove the contamination. Incidentally, although the ultraviolet irradiation unit 22 is shown by the side of the mask 12 within the sample chamber 16, it is actually arranged over the mask 12 (anyway, the ultraviolet irradiation unit 22 may be capable of irradiating the whole surface of the mask 12). Besides, the ultraviolet irradiation unit 22 may be mounted at any position of the upper plate of the sample chamber 16 as viewed in FIG. 1A. It is also allowed that an ultraviolet irradiation unit 25 which is disposed by the side of the body tube 17 is constructed of a compact deuterium lamp, so as to project ultraviolet rays onto the vicinity of an electron beam irradiation point on the surface of the mask 12. Owing to the above configuration, the surface of the sample 12 is irradiated with the ultraviolet rays for the predetermined time period by the ultraviolet irradiation unit 21, 22 or 25 within at least one of the preparatory evacuation chamber 15 and the sample chamber 16, whereby the contamination of the surface of the sample 12 can be removed by active oxygen or the like produced. In the embodiment shown in FIG. 1B, a sample 12 is irradiated with ultraviolet rays in an intermediate chamber 24 for a predetermined time period, thereby to remove the contamination of the sample 12. Since a SMIF pod 11, the sample (mask) 12, a conveyance stage 14, a preparatory evacuation chamber 15′, a sample chamber 16 and a body tube 17 are respectively identical to the constituents of the same reference numerals in FIG. 1A, they shall be omitted from description. Referring to FIG. 1B, a conveyance robot 13 is a robot which opens the door of the SMIF pod 11, fetches a predetermined one of the samples (masks) 12 and conveys the fetched sample to the conveyance stage 14 or the intermediate chamber 24 here in this case, which conveys the sample 12 between the intermediate chamber 24 and the conveyance stage 14, and which conveys the sample 12 put on the conveyance stage 14 or in the intermediate chamber 24, to the SMIF pod 11 and shuts the door. The intermediate chamber 24 is a chamber in which the sample 12 is put, so as to irradiate this sample with ultraviolet rays for a predetermined time period by an ultraviolet irradiation unit 23. Here, the intermediate chamber 24 includes the ultraviolet irradiation unit 23, etc. The ultraviolet irradiation unit 23 which is disposed in the intermediate chamber 24 subjects the sample 12 conveyed into the intermediate chamber 24, to the ultraviolet irradiation for the predetermined time period, thereby to remove the contamination. Owing to the above configuration, the surface of the sample 12 is irradiated with the ultraviolet rays for the predetermined time period by the ultraviolet irradiation unit 23 within the intermediate chamber 24, whereby the contamination of the surface of the sample 12 can be removed by active oxygen or the like produced. FIG. 2 shows a flow chart for explaining the operation of the invention (in correspondence with FIG. 1A). Steps S1 through S10 in FIG. 2 correspond to reference numerals 1 through 10 indicated in FIG. 1A, respectively. Referring to FIG. 2, the step S1 brings the sample 12 out of the SMIF pod 11. The step S2 puts the sample 12 on the conveyance stage 14. At the steps S1 and S2, the conveyance robot 13 in FIG. 1A turns the SMIF pod 11 into the open state, it fetches and conveys the predetermined sample (mask) 12, and it puts the fetched sample on the conveyance stage 14. The step S3 puts the sample 12 in the preparatory evacuation chamber 15. At this step, the sample 12 put on the conveyance stage 14 at the step S2 is automatically conveyed into the preparatory evacuation chamber 15 by a conveyance mechanism not shown, together with this conveyance stage 14. The step S4 irradiates the sample 12 with the ultraviolet rays. At this step, the whole surface of the sample 12 put in the preparatory evacuation chamber 15 at the step S3 (the sample 12 put on the conveyance stage 14) is irradiated with the ultraviolet rays for the predetermined time period by the ultraviolet irradiation unit 21 disposed in this preparatory evacuation chamber 15, thereby to remove the contamination. The step S5 puts the sample 12 in the sample chamber 16. At this step, the sample 12 subjected to the ultraviolet irradiation and contamination removal at the step S4 (the sample 12 put on the conveyance stage 14) is put in the sample chamber 16, and it is moved to the predetermined position of the body tube 17 (a position for measuring the length and photographing the image). The step S6 measures the length. At this step, the dimension of a designated pattern is measured as to the sample 12 set at the predetermined position of the body tube 17 at the step S5 (as will be described with reference to FIG. 5A or 5B). The step S7 puts the sample 12 out of the sample chamber 16. The step S8 puts the sample 12 out of the preparatory evacuation chamber 15. The step S9 puts the sample 12 out of the conveyance stage 14. The step S10 puts the sample 12 in the SMIF pod 11. At the steps S7, S8, S9 and S10, the sample 12 is conveyed from the sample chamber 16 into the SMIF pod 11 in a procedure reverse to that of the conveyance of this sample from the SMIF pod 11 into the sample chamber 16. Here, regarding the sample (mask) 12 put on the conveyance stage 14 within the preparatory evacuation chamber 15, the excimer lamp which emits the ultraviolet rays at the wavelength of 172 nm is disposed at the upper part of this preparatory evacuation chamber 15. The surroundings of the excimer lamp are held in a nitrogen atmosphere in order to prevent the ultraviolet rays from being absorbed by oxygen in the atmospheric air, and the excimer lamp is constructed so as to irradiate the mask (sample) 12 with the ultraviolet rays through its quartz window (refer to FIG. 4A). The preparatory evacuation chamber 15 is preliminarily evacuated by a low-vacuum pump such as dry pump, and the ultraviolet rays are projected onto the whole surface of the mask (sample) 12 (steps S3 and S4). Since the ultraviolet rays are projected during the preliminary evacuation, the contamination ascribable to the hydrocarbons, etc. can be removed without spoiling a throughput. The active oxygen is produced in the vicinity of the surface of the mask (sample) 12 by the ultraviolet rays, and organic substances on the surface of the mask (sample) 12 are turned into CO2 and H2O, which are volatilized and drawn off, so that the mask (sample) 12 is cleaned. In an example, a cleaning effect increased when the preparatory evacuation chamber 15 was evacuated to a pressure which was about 0.1 Torr lower than the atmospheric pressure. In this regard, since the distance between the surface of the mask (sample) 12 and the quartz window was about 1 cm, the ultraviolet rays were absorbed much in the atmospheric air, so that the active oxygen in the vicinity of the surface of the mask (sample) 12 decreased conspicuously. In contrast, owing to the reduced pressure of the interior of the preparatory evacuation chamber 15, the absorption of the ultraviolet rays will have decreased to effectively produce the active oxygen in the vicinity of the surface of the mask (sample) 12. Further, in order to increase the cleaning effect, oxygen O2, ozone O3 or the like gas in a suitable quantity may well be introduced into the preparatory evacuation chamber 15 in the reduced pressure state. After the cleaning and preliminary evacuation, the preparatory evacuation chamber 15 is regularly evacuated by a high-vacuum pump such as turbo molecular pump (oilless vacuum pump). Besides, a valve located between the preparatory evacuation chamber 15 and the sample chamber 16 is opened, and the mask (sample) 12 is conveyed to a sample stage not shown, disposed within the sample chamber 16 (step S5). As shown in FIG. 5A, the vicinity of a preset measurement point M on the surface of the mask (sample) 12 is moved directly under the body tube 17, and the line width L of a line, for example, has its image observed and is measured. The set place is repeatedly measured a plurality of times (step S6). After the image observation and the length measurement are ended, the mask (sample) 12 is put out of the sample chamber 16 into the preparatory evacuation chamber 15 (step S7). After the vacuum leakage of the preparatory evacuation chamber 15, the mask (sample) 12 is put out of the preparatory evacuation chamber 15 (step S8). Thereafter, the mask (sample) 12 is returned into the SMIF pod 12 (steps S9 and S10). Then, the series of operations for the image observation and length measurement are ended. In the embodiment of FIG. 2, the contamination is removed by irradiating the whole surface of the mask (sample) 12 with the ultraviolet rays before the length measurement, that is, before the electron beam irradiation. The reason therefor is as stated below. It is considered that the contamination ascribable to the hydrocarbons, etc. will have already adhered onto the surface of the photomask being the mask (sample) 12, at any step other than the SEM observation as precedes the process of FIG. 2, and that it will be brought into the apparatus shown in FIG. 1A. Therefore, the contamination should be removed from the whole region of the surface of the mask (sample) 12 before the electron beam irradiation. Of course, even in a case where the surface of the mask (sample) 12 has suffered from the contamination attendant upon the electron beam irradiation, on account of the SEM observation and length measurement at the preceding step, the embodiment of FIG. 2 brings forth the remarkable advantage that, owing to the ultraviolet irradiation, the contamination ascribable to the electron beam irradiation and also adherent substances such as hydrocarbons originating the contamination can be turned into the volatile gases (for example, CO2 and H2O) by the active oxygen, thereby to be removed (evacuated and removed). Besides, in a case where the mask (sample) 12 has not been contaminated by the electron beam irradiation and where the hydrocarbons or the likes are not adherent on the surface of this mask (sample) 12, the ultraviolet irradiation before the length measurement may well be omitted so as to perform only ultraviolet irradiation after the length measurement (unlike in FIG. 2, the ultraviolet irradiation is not performed before the length measurement, but it is performed after the length measurement, and this aspect will be described later with reference to FIG. 6A). In this case, the whole area of the surface of the mask (sample) 12 is irradiated with the ultraviolet rays during the vacuum leakage of the preparatory evacuation chamber 15, whereby the contamination attendant upon the image observation and length measurement is removed or diminished without spoiling a throughput. Besides, in a case where, in the process of FIG. 2, the contamination has not been satisfactorily removed by the ultraviolet irradiation of the mask (sample) 12, the average of length measurement values L sometimes increases gradually after the N times of length measuring operations (refer to FIG. 5B). In a case where an increment ΔL (=LN−L1) after the length measurement exceeds a preset reference value ΔLs, a process as shown in FIG. 6B is performed in which the mask (sample) 12 is conveyed out from the sample chamber 16 into the preparatory evacuation chamber 15, it is subjected to ultraviolet irradiation and cleaning again after vacuum leakage, and it is thereafter conveyed into the sample chamber 16 and subjected to a length measurement again, whereby a length measurement reproducibility can be enhanced. Moreover, since the series of processing operations shown in FIG. 2 or in FIG. 6A or 6B are automatically performed by a preset recipe, an operability is not spoilt. It is also possible that the vacuum pressure value of the preparatory evacuation chamber 15 during the ultraviolet irradiation is controlled so as to enhance the cleaning effect based on the ultraviolet irradiation. By way of example, oxygen is conducted from a nozzle onto the surface of the mask (sample) 12 for a predetermined time period so that the measurement value of a vacuum gauge may be held at 1 Torr. Further, optimum values may well be set in such a way that the irradiation time period of the ultraviolet rays and the number of times of the ultraviolet irradiations are experimentally found beforehand in accordance with the number of times of length measuring operations, a beam current and the like irradiation conditions for irradiating the mask (sample) 12 with the electron beam, the sort of the mask (sample) 12, and so forth. FIG. 3 shows a view for explaining the invention. This figure shows a configurational example of the body tube 17 as well as the sample chamber 16 in FIG. 1A or 1B. Referring to FIG. 3, an electron beam 51 is formed in such a way that electron rays are emitted from an electron gun 52 and are converged by a converging lens 63, and that the converged electron rays are fined by an objective lens 62 so as to be focused on the surface of the sample 12. Here, the sample 12 is scanned with the electron beam 51 by a deflection system not shown (scanned in either an X-direction or a Y-direction as a linear scan, or scanned in both the X-direction and the Y-direction as a planar scan). Besides, secondary electrons 44 emitted by scanning the sample 12 with the electron beam 51 are detected by a secondary electron detector 45 so as to display a so-called “line profile image” or secondary electron image on a display device not shown. The converging lens 63 converges the electron rays emitted from the electron gun 52. The objective lens 62 projects the electron beam 51 onto the sample 12 in the finely focused state. The finely focused electron beam 51 is deflected as a linear scan or a planar scan by the deflection system not shown. The sample 12 is a sample to be observed or to have a length measured, and it is, for example, a wafer or a photomask. The electron gun 52 is an electron gun of, for example, field emission type, and electrons are extracted, accelerated and emitted by applying a high electric field to a tip cathode at the distal end of this electron gun. An electron gun chamber 53 is a chamber in which the electron gun 52 is accommodated, and which is evacuated to a high vacuum by an ion pump 55. An orifice 54 is a small aperture, through which the electron beam 51 emitted from the electron gun 52 is passed, and which serves to hold the pressure difference (for example, 10−2 to 10−3 Torr) between the electron gun chamber 53 and a first intermediate chamber 56. The first intermediate chamber 56 is a chamber which is disposed between the electron gun chamber 53 and a second intermediate chamber 59, and which is evacuated to a vacuum by an ion pump 58. This first intermediate chamber 56 serves to hold the vacuum pressure of the electron gun chamber 53 low in cooperation with an orifice 57 which is a small aperture provided below. The second intermediate chamber 59 is a chamber which is provided over the objective lens 62, and in which the secondary electron detector 45 is disposed here in this case. An evacuation pipe 60 is connected to an unshown evacuation system (such as turbo molecular pump) which evacuates the second intermediate chamber 59 into a vacuum. The secondary electron detector 45 detects the secondary electrons 44 at a high efficiency in such a way that a positive high electric field is applied to the secondary electrons 44 emitted during the irradiation of the sample 12 with the electron beam 51, so as to move these electrons upwards while swirling them in the vicinity of the center axis of the objective lens 62 (swirling them by the electric field of the objective lens 62). The sample chamber 16 is a chamber which accommodates the sample 12, etc. therein and hold them in a vacuum. An ambient space 50 is a space around that region of the sample 12 which is linearly scanned or planarly scanned with the electron beam 51. In the ambient space 50, the surface of the sample 12 is irradiated with the ultraviolet rays by the ultraviolet irradiation unit 22 (shown in FIG. 1A), thereby to remove or diminish the contamination on the sample 12. On this occasion, although no illustration is made, oxygen (or air) is injected from a nozzle onto the surface of the sample 12, and the active oxygen is produced by the ultraviolet irradiation so as to turn the contamination of the surface of the sample 12 into the volatile gases (for example, CO2 and H2O), whereby the contamination is removed or diminished. When the sample chamber 16 has its internal pressure raised by introducing a gas thereinto, an orifice 61 serves to suppress the flow of the gas into the second intermediate chamber 59 as far as possible (usually, it serves to hold the pressure difference between the sample chamber 16 and the second intermediate chamber 59 (for example, 10−2 to 10−3 Torr). The body tube 17 having the above configuration is used as the body tube 17 of the identical reference numeral in FIG. 1A or 1B. FIGS. 4A and 4B show examples of the ultraviolet irradiation units in the invention (as side views), respectively. FIG. 4A exemplifies the ultraviolet irradiation unit 21 which is disposed in the preparatory evacuation chamber 15. Referring to FIG. 4A, an ultraviolet lamp 71 is a lamp which emits ultraviolet rays, and which is, for example, an excimer lamp. A quartz window 72 is a window through which the ultraviolet rays emitted from the ultraviolet lamp 71 disposed in the atmospheric air are introduced into the vacuum without loss, and which is made of quartz and induces little loss (transmission loss) for the ultraviolet rays. An O-ring 72 is an O-ring for vacuum sealing as seals the vacuum side of the mask 12 from the nitrogen atmosphere side of the ultraviolet lamp 71. The mask 12 is an example of the sample 12. A mask holder 74 is a holder which holds the mask 12. The ultraviolet irradiation unit 21 of the above configuration is disposed in the preparatory evacuation chamber 15 in FIG. 1A already referred to. Besides, the ultraviolet lamp 71 is lit up, and the generated ultraviolet rays are transmitted through the quartz window 72 and irradiate the whole surface of the mask (sample) 12 for the predetermined time period, automatically in accordance with the recipe during the preliminary evacuation of the preparatory evacuation chamber 15. Thus, it is permitted to remove or diminish the contamination as already described. FIG. 4B exemplifies the ultraviolet irradiation unit 23 which is disposed in the intermediate chamber 24. Referring to FIG. 4B, an ultraviolet lamp 81 is a lamp which emits ultraviolet rays, and which is, for example, an excimer lamp. A quartz window 82 is a window through which the ultraviolet rays emitted from the ultraviolet lamp 81 disposed in a nitrogen atmosphere are introduced into the intermediate chamber 24 without loss, and which is made of quartz and induces little loss (transmission loss) for the ultraviolet rays. A window frame 83 is interposed between the ultraviolet lamp 81 and the interspace of the intermediate chamber 24. The mask 12 is an example of the sample 12. A mask holder 84 is a holder which holds the mask 12. The ultraviolet irradiation unit 23 having the above configuration is disposed in the intermediate chamber 24 in FIG. 1B already referred to. Besides, in the state where the mask 12 is put in the intermediate chamber 24, the ultraviolet lamp 81 is lit up, and the generated ultraviolet rays are transmitted through the quartz window 82 and irradiate the whole surface of the mask (sample) 12 for the predetermined time period, automatically in accordance with the recipe. Thus, it is permitted to remove or diminish the contamination as already described. Here, in the case where the ultraviolet irradiation unit 23 is disposed in the intermediate chamber 24, the distance d between the surface of the mask (sample) 12 and the plane of the quartz window 82 as spaces the ultraviolet lamp 81 is set at a short distance of 1-2 mm in order to enhance a cleaning effect for this mask (sample), for example, a photomask disposed in the atmospheric air, by preventing the absorption of the ultraviolet rays attributed to oxygen in the atmospheric air. After having been set on the mask holder 84 within the intermediate chamber 24 by the conveyance robot 13 shown in FIG. 1B, the mask 12 is raised by an ascent/descent mechanism not shown, and the mask holder 84 is caused to abut on the window frame 83 at its part A, thereby to stipulate the distance d between the plane of the mask 12 and that of the quartz window 82 (FIG. 4B). After the distance d has been set, the whole area of the surface of the mask 12 is irradiated with the ultraviolet rays for, for example, 30 seconds. In order to increase the cleaning effect, a gas such as oxygen O2 or ozone O3 may well be introduced into the intermediate chamber 24. Here, although the function of an exhaust duct or the like for exhausting a gas, such as CO2, produced by the reaction between the ozone or active oxygen and the hydrocarbons on the surface of the mask 12 is not illustrated, the mechanism thereof is disposed. FIG. 4C shows examples of the transmission factor of the mask. More specifically, this figure exemplifies the variations of the transmission factor of transmitted light through the mask (sample) 12, versus the wavelength of the light. The curve of quartz glass as indicated by a solid line in the figure shows the transmission factor of a part which was subjected to the cleaning process based on the ultraviolet irradiation in the invention. On the other hand, the curve of quartz glass R as indicated by a broken line in the figure shows the transmission factor of a part which was not subjected to the cleaning process based on the ultraviolet irradiation. It is understood that both the curves overlap each other without a substantial difference, and that they are indistinguishable concerning exposure to, for example, an ArF excimer laser (at a wavelength of 193 nm). Thus, it has been revealed that, even when the contamination removal based on the ultraviolet irradiation is performed for the mask (sample) 12 made of the quartz glass, the transmission factor of this mask (sample) 12 does not change. FIGS. 5A and 5B show diagrams for explaining the invention (length measurement), respectively. FIG. 5A shows an example in which the line width or the like of a pattern on a mask (6″×6″) is measured. Referring to FIG. 5A, the mask 12 is in the shape of a plate of 6 inches×6 inches, and its surface is formed with microscopic patterns. Regarding the pattern which is designated for the length measurement on the mask 12, an enlarged pattern is shown at a lower part. The line width L designated on the pattern is measured. In the line measurement, the mask shown in FIG. 5A is fixed to the position of the sample 12 which underlies the body tube 17 constituting the SEM scanning side electron microscope as shown in FIG. 3 already referred to, this mask is planarly scanned with the spot of the finely focused electron beam 1 by moving the electron beam spot through and near the designated place M, the secondary electrons emitted on this occasion are detected by the secondary electron detector 45, and a brilliance is modulated with the detection signal of the secondary electron detector 24 in synchronism with the scan on the screen of the display device, so as to display a so-called “SEM image” (secondary electron image), whereby any defect or the like of the pattern is observed. Besides, in the length measurement, the mask is linearly scanned about the designated position M so as to display a line profile on the screen. Here, the brilliance becomes higher at the right and left edges of a line to-be-measured. It is therefore possible to perform the known precise length measurement of the microscopic pattern with the SEM, for example, the measurement of the distance between the edges as the width of the line. In the length measurement, the length measuring operations are repeated a plurality of times for the designated position M of the pattern. On this occasion, the number of times of the length measuring operations and the measured values of the line width L are plotted as shown in FIG. 5B. FIG. 5B shows an example of the plots of measurement results. In this figure, the axis of abscissas represents the number of times N of the length measuring operations, while the axis of ordinates represents the measured line width L. More specifically, the graph of FIG. 5B has been obtained by repeatedly measuring the line width L at the designated position M in FIG. 5A, and plotting the number of times N of the length measuring operations and the measured values of the line width L. With increase in the number of times N of the length measuring operations, the contamination of the mask 12 attributed to the electron beam irradiation appears, and the line width L enlarges gradually. Accordingly, letting L1 denote the first measurement value of the line width L and LN denote the Nth measurement value thereof, the difference ΔL=(LN−L1) in the repeated length measuring operations is calculated. When the calculated difference ΔL is not greater than a value corresponding to a precision experimentally obtained beforehand, it is decided that the contamination is less than a prescribed value, and that the length measurement values of the line width are correct. In contrast, when the calculated difference ΔL is greater than the value corresponding to the precision, the length measurement values are decided to be inaccurate and are disused, whereupon the mask 12 is irradiated with the ultraviolet rays as already described, thereby to remove the contamination of the surface of the mask 12. When the contamination removal by one time of ultraviolet irradiation is unsatisfactory, the ultraviolet irradiations are repeated a predetermined number of times. FIGS. 6A and 6B are flow charts for explaining the other operations of the invention, respectively. The flow chart of FIG. 6A shows an example in which, after the length measurement of the sample (mask) 12, this sample is irradiated with ultraviolet rays, thereby to remove or diminish the contamination. Here, steps S21 through S26 and S29 through S31 are respectively identical to the steps S1 through S6 and S8 through S10 in FIG. 2 already referred to, and they shall therefore be omitted from description. Referring to FIG. 6A, a step S27 puts the mask (sample) 12 in the preparatory evacuation chamber 15. At this step, the mask (sample) 12 which has been irradiated with the electron beam and has had the length of its pattern measured is put in the preparatory evacuation chamber 15. A step S28 irradiates the mask (sample) 12 with the ultraviolet rays. At this step, the mask (sample) 12 put in the preparatory evacuation chamber 15 at the step S27 has its whole surface irradiated with the ultraviolet rays for the predetermined time period by the ultraviolet irradiation unit 21 disposed in the preparatory evacuation chamber 15, thereby to remove the contamination. Subsequently, the mask (sample) 12 is conveyed into the SMIF pod 11 at the steps S29 through S31. As thus far described, after the length measurement of the mask (sample) 12, this mask (sample) 12 is irradiated with the ultraviolet rays in the preparatory evacuation chamber 15, so as to remove or diminish the contamination ascribable to the electron beam irradiation during the length measurement, whereby the clean mask (sample) 12 can be delivered to the next step. The flow chart of FIG. 6B shows an example in the case where the contamination is decided as being much when the difference ΔL obtained in the length measurement of the sample (mask) 12 is not smaller than the prescribed value ΔLs in FIG. 5B already referred to, where the mask (sample) 12 is returned into the preparatory evacuation chamber 15 and is irradiated with the ultraviolet rays so as to remove or diminish the contamination, and where the length measurement is repeated again. Here, steps S41, S42, S44, S46, S47, and S49 through S52 are respectively identical to the steps S1, S2, S4, S5, S6, and S7 through S10 in FIG. 2 already referred to, and they shall therefore be omitted from description. Referring to FIG. 6B, a step S43 preliminarily evacuates the preparatory evacuation chamber 15. This step is performed as the preliminary evacuation of the preparatory evacuation chamber 15 from the atmospheric pressure at the first time. At the second time, et seq., the step S43 is performed on condition that the decision of a step S48 is “NO”, in other words, that the difference ΔL in FIG. 5B as obtained by measuring the width of the pattern the plurality of times is not smaller than the prescribed value ΔLs, so the contamination is much. More specifically, at the second time, et seq., the mask (sample) 12 is conveyed into the preparatory evacuation chamber 15 at a step S53 (it is put out of the sample chamber 16), the preparatory evacuation chamber 15 is leaked at a step S54 so as to introduce the atmospheric air into this chamber 15, and the preparatory evacuation chamber 15 is preliminarily evacuated again at the step S43. Besides, as already stated, during the preliminary evacuation, the whole surface of the mask (sample) 12 is irradiated with the ultraviolet rays for the predetermined time period at the step S44, thereby to remove or diminish the contamination. The preparatory evacuation chamber 15 is regularly evacuated at a step S45, and the mask (sample) 12 is thereafter conveyed to the predetermined position of the sample chamber 16 at the step S46, whereupon the length measuring operations are repeated at the step S47. Here, at the steps S54 and S43, the preliminary evacuation is started after the preparatory evacuation chamber 15 has been leaked to establish the atmospheric pressure. However, the mere air (air containing oxygen, or oxygen) in the preparatory evacuation chamber 15 may well be leaked out in a small amount to the extent of satisfying the removal or diminution of the contamination based on the irradiation of the mask (sample) 12 with the ultraviolet rays (by way of example, the air or the like is leaked out to 1 Torr), whereby a time period for the preliminary evacuation is shortened. On the other hand, in a case where the decision of the step S48 is “YES” (in other words, where the difference ΔL is smaller than the prescribed value ΔLs in FIG. 5B), the results obtained by measuring the length of the pattern repeatedly the plurality of times are favorable, and the mask (sample) 12 is returned into the SMIF pod 11 at the steps S49 through S52 as already stated. By the way, in the case where the contamination is removed or diminished by the ultraviolet irradiation inside the sample chamber 16, oxygen is introduced so as to locally blow this oxygen against the surface of the mask (sample) 12 from a nozzle, after the SEM observation (SEM length measurement) by way of example, and that region of the mask (sample) 12 which includes a place irradiated with the electron beam is irradiated with the ultraviolet rays by the ultraviolet irradiation unit 22, whereby the contamination is removed or diminished by active oxygen produced. The place irradiated with the electron beam is stored in a memory. In a case where there is no spatial room for mounting an excimer lamp which is the ultraviolet irradiation unit 22, a compact deuterium lamp is used so as to project the ultraviolet rays onto the region irradiated with the electron beam and having a diameter of several mm. As described above, the invention pertains to charged particle beam apparatuses, especially length measurement apparatuses, which diminish the contaminations of samples, and it consists in a charged particle beam apparatus and a contamination removal method therefor, in which the contamination is diminished without etching, before or after the observation of the sample based on a charged particle beam, which enhance the reproduction precision of the length measurement of a pattern, and so forth, and which enhance an operability and a throughput in interlocking with the automatic conveyance of the sample.
062917366	abstract	A process for chemical fixation of radionuclides and radioactive compounds present in soils, solid materials, sludges and liquids. Radionuclides and other radioactive compounds are converted to low-temperature Apatite-Group structural isomorphs (general composition: (AB).sub.5 (XO.sub.4).sub.3 Z), usually phosphatic, that are insoluble, non-leachable, non-zeolitic, and pH stable by contacting with a sulfate, hydroxide, chloride, fluoride and/or silicate source and with a phosphate anion in either a one or two step process. The Apatitic-structure end product is chemically altered from the initial material and reduced in volume and mass. The end product can be void of free liquids and exhibits sufficiently high levels of thermal stability to be effective in the presence of heat generating nuclear reactions. The process occurs at ambient temperature and pressure.
	summary
	abstract	The present invention relates to an apparatus for forming a nano pattern capable of fabricating the uniform nano pattern at a low cost including a laser for generating a beam; a beam splitter for splitting the beam from the laser into two beams with the same intensity; variable mirrors for reflecting the two beams split by the beam splitter to a substrate; beam expansion units for expanding diameters of the beams by being positioned on paths of the two beams traveling toward the substrate; and a beam blocking unit, installed on an upper part of the substrate, transmitting only a specific region expanded through the beam expansion unit and blocking regions a remaining region, and a method for forming the nano pattern using the same.
048636738	claims	1. In a hydraulically actuated control rod drive of the type including: a reactor vessel having a pressurized interior; a core in said reactor vessel containing fissionable materials; a control rod for movement into and out of said core for the control of fission in said fissionable material of said nuclear reactor, said control rod moveable against ambient pressure interior of said reactor; a hydraulic fluid pressure source; means for moving said control rod into and out of said core in said nuclear reactor, said means including a hydraulic actuator for urging said control rod into insertion within said core of said reactor, said hydraulic actuator communicated to said hydraulic fluid pressure source through a hydraulic circuit; a check valve in said hydraulic circuit between said hydraulic actuator and said hydraulic fluid pressure source for preventing reverse flow of said hydraulic circuit responsive to the ejection of said control rod by ambient pressure within said reactor vessel, the improvement to said hydraulic circuit comprising a hydraulic conduit between said check valve and said hydraulic fluid pressure source; an isolation valve for isolating said conduit; a positive displacement piston and cylinder having a beginning piston stroke and an ending position stroke with a known positive displacement of fluid between said beginning and ending stroke position corresponding to insignificant ejection of said control rod from said reactor vessel; means for timing movement of said piston between said respective stroke positions for determining the rate of displacement of hydraulic fluid through said check valve; and means for connecting said piston through said isolation valve to said check valve whereby fluid passing through said check valve causes movement of said piston to indicate closure and integrity of said check valve without appreciable control rod ejection from said reactor. means for actuating said first microswitch upon admitting fluid to said piston and cylinder; means for actuating said second microswitch upon end of stroke of said piston within said piston and cylinder. providing a connected test conduit between said check valve and said fluid pressure source for enabling said check valve to seat upon flow through said conduit; providing a constant displacement hydraulic piston and cylinder, said piston having a stroke excursion within said cylinder for providing positive and known displacement, said displacement of said piston and cylinder corresponding to minimal ejection of said control rod from said core of said reactor; connecting said piston to said test conduit; permitting flow through said test conduit to said piston; timing the stroke of said piston in said piston cylinder whereby the integrity of said check valve is indicated as a function of the stroke of said piston with respect to time with short stroke indicating lack of check valve integrity and long stroke indicating check valve seating and sealing. 2. The invention of claim 1 and including a first and second microswitch; 3. The invention of claim 2 and wherein a timer is started by said first microswitch and stopped by said second microswitch. 4. The invention of claim 1 and including a quick disconnect between said positive displacement piston and said isolation valve for isolating said conduit. 5. A process for testing a check valve in a control rod drive in a nuclear reactor wherein a reactor vessel contains a core in a pressurized fluid environment and a control rod movable by a hydraulic piston by force through and from a hydraulic circuit into and out of the pressurized environment of said reactor vessel against the pressure of said pressurized environment, said hydraulic circuit including a fluid pressure source for insertion of said control rod and a conduit from said fluid pressure source to said hydraulic piston for inserting of said control rod and a check valve in said conduit between said pressure source and actuator for preventing reactor pressure ejection of said control rod from said reactor, the process for testing of the operation and integrity of said check valve comprising the steps of:
060382791	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to X-ray apparatuses, suitable for use in exposure systems, as well as in semiconductor device production. 2. Description of the Related Art A method known as an X-ray demagnification (reduced magnification) projection exposure method has been suitably used in the production of devices having fine patterns, such as semiconductor circuit elements. According to this method, a mask carrying a circuit pattern formed thereon is illuminated with X-rays so that the mask image, i.e., the circuit pattern, is projected at a prescribed demagnification onto a wafer surface so that a resist on the wafer surface is exposed, whereby the circuit pattern is transferred to the resist in a reduced scale. FIG. 10 shows an example of a conventional X-ray demagnification projecting exposure apparatus. This apparatus has, as its major components, an X-ray source 109, 110, 101, 111, an illuminating optical system 103, a reflective mask 104, a projection optical system 105, a stage 108 carrying a wafer 106, an alignment mechanism (not shown) for precisely aligning the positions of the mask 104 and the wafer 106, and a vacuum vessel and evacuating system (not shown) which cooperate with each other in maintaining a vacuum atmosphere around the entire optical system so as to prevent attenuation of t he X-rays. Laser-excited plasma, for example, is used as the X-ray source. A laser source 109 emits laser beam in the form of pulses, which hit a target 111 so that laser plasma is generated. X-rays emitted from a luminescent point 101 of the laser plasma are collected on the reflective mask 104 through a collecting lens (not shown). The luminescent point 101 of the laser plasma has a size on the order of several hundreds of .mu.m and, hence, can be regarded as being a point source. The X-rays 102 emitted from the luminescent point 101 pass through filter 112 and are collimated by a parabolic mirror 103 having a focal point located on the luminescent point 101. The projection optical system 105 includes a plurality of multi-layered reflective mirrors which demagnify (reduce the magnification of) the pattern on the mask 104 so as to project the pattern image of a reduced size on the surface of the wafer 106. The projection optical system 105 is usually constituted by a telecentric system. Conventional X-ray demagnifying projection exposure apparatuses, however, have suffered from the following problems. Namely, these conventional apparatuses could not provide resolution and focal depth which would be sufficient for projecting extremely delicate and fine patterns on masks onto wafers, thus failing to transfer such patterns with a desired high degree of precision. In order to obviate this problem, it has been proposed to improve the image forming performance by using a phase shift effect offered by a phase shift mask. However, it has been impossible to fully enjoy the effects of such a phase shift mask. These problems encountered with conventional devices are attributable to the following reasons. One of the characteristic parameters of an illuminating system is a coherence factor .sigma.. The coherence factor .sigma. is expressed as follows, representing the mask-side numerical aperture of the projection optical system by NA.sub.p1 and that of the illuminating optical system by NAi: EQU .sigma.=NAi/NA.sub.p1. The optimum value of the coherence factor .sigma. is determined based on the levels of resolution and contrast required in the transfer of the pattern. In general, a too small value of the coherence factor .sigma. allows an interference pattern to appear at edges of the fine pattern image projected on the wafer, while a too large coherence factor .sigma. reduces the contrast of the projected image. An illumination system having a coherence factor .sigma. of 0 (zero) is referred to as a "coherent illumination system". Such a coherent illumination system exhibits a constant optical system transfer factor (OTF) when the spatial frequency does not exceed a value given by NA.sub.p2 /.lambda. where NA.sub.p2 and .lambda. respectively indicate the wafer-side numerical aperture of the projection optical system and the wavelength of the X-rays. However, at higher spatial frequencies, the transfer factor OTF is zero, so that resolution of the image is impossible. In contrast, an illumination system having a coherence factor of 1 is referred to as an "incoherent illumination system". In this type of an illumination system, the transfer factor OTF decreases in accordance with an increase in the spatial frequency, but is not reduced to zero until the spatial frequency reaches a value which is given as 2.times.NA.sub.p2 /.lambda.. Thus, resolution is possible to a greater degree of fineness as compared with the coherent illuminating system. The conventional X-ray demagnifying projection exposure apparatuses, however, are designed such that the coherence factor .sigma. approximates 0 and, hence, operate under substantially coherent illuminating conditions. These apparatuses, therefore, have limited resolution and cannot transfer patterns having a high degree of fineness. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an X-ray generating apparatus and method capable of providing improved image forming performance over conventional devices, as well as a high-performance exposure apparatus and an improved device production method which make use of such an X-ray generating apparatus and method. To this end, according to a preferred form of the present invention, a light source is provided in the form of an aggregate of a plurality of luminescent points and X-rays emitted from these luminescent points are collected through an illuminating optical system so as to effect Kohler's-illumination on an object such as a mask. X-rays emitted from different luminescent points of the source impinge upon the mask at different incident angles. Therefore, when the entire light source composed of an aggregate of luminescent points has a finite size, the X-rays illuminating the mask also have a finite angular divergence. Furthermore, when the source has a non-uniform luminescent intensity distribution, the X-rays illuminating the mask also have a correspondingly non-uniform angular distribution, thus realizing modified illumination. The X-ray source composed of a plurality of luminescent points can be realized by applying a plurality of laser beams onto a plurality of points on a target. Alternatively, a laser beam from a single laser source is deflected so as to impinge upon a plurality of points on the target in a time-series manner. The detail of the methods of creating such an X-ray source will be described later in connection with the description of the preferred embodiments. Thus, the use of an aggregate of a plurality of luminescent points as the source of the X-rays makes it possible to widen the angular distribution of the X-rays illuminating a mask so as to provide a greater value of the coherence factor .sigma., and to achieve modified illumination such as ring illumination, oblique illumination and so forth. It is therefore possible to improve the image forming performance in terms of resolution and focal depth. When a phase shift mask is used, it is possible to make full use of the effect to improve the image forming performance offered by such a mask. In another preferred form of the present invention, an area X-ray source of finite size is used as the X-ray source. The X-rays emitted from this area source are collected on an object such as a mask through an illuminating optical system, thus effecting Kohler's-illumination on such an object. X-rays emitted from different points on the planar source irradiate the mask at different angles. Since the area X-ray source has a finite size, the X-rays illuminating the mask also have a correspondingly finite angle of divergence value. It is possible to vary the coherence factor by varying the form of the X-ray generating section, i.e., the configuration, size and position of the source. The planar X-ray source may have a non-uniform luminescent intensity distribution. In such a case, the X-rays illuminating the mask have a non-uniform angular distribution, thus realizing a modified illumination. It is thus possible to optimize the coherence factor .sigma. of the illumination system and to achieve modified illumination such as ring illumination or oblique illumination, by controlling the angular distribution of the X-rays illuminating the mask, by suitably setting the form of the X-ray source. Consequently, illuminating conditions can be optimized in accordance with the conditions of the exposure to be performed, contributing to improvement in the image forming performance in terms of resolution and focal depth. In one aspect, the present invention provides an X-ray generating device comprising a laser source for generating a laser beam and a plurality of points on a target for receiving the laser beam and for generating X-rays from portions of high temperature plasma on the target. In another aspect, the present invention provides an X-ray generating device comprising a laser source for generating a laser beam, an aperture, having a variable shape, for receiving the laser beam and for defining a secondary laser beam and a target for receiving the secondary laser beam and for generating X-rays from portions of high temperature plasma on the target. In yet another aspect, the present invention provides an X-ray irradiating apparatus comprising (i) an X-ray generating device comprising a laser source for generating a laser beam and a plurality of points on a target for receiving the laser beam and for generating X-rays from high temperature plasma on the target, and (ii) irradiating means for irradiating an object with the X-rays generated by the X-ray generating device. In yet another aspect, the present invention provides an X-ray irradiating apparatus comprising (i) an X-ray generating device comprising a laser source for generating a laser beam, an aperture, having a variable shape, for receiving the laser beam and for defining a secondary laser beam and a target for receiving the secondary laser beam and for generating X-rays from portions of high temperature plasma on the target, and (ii) irradiating means for irradiating an object with the X-rays generated by the X-ray generating device. In still another aspect, the present invention provides an X-ray generating method including generating at least one laser beam from at least one laser source, providing a plurality of points on a target for receiving the at least one laser beam and generating X-rays from portions of high temperature plasma on the target. In still another aspect, the present invention provides an X-ray generating method comprising generating a laser beam from a laser source, providing an aperture, having a variable shape, for receiving the laser beam and for defining a secondary laser beam, providing a target for receiving the secondary laser beam and generating X-rays from portions of high temperature plasma on the target. In yet another aspect, the present invention provides a method of producing a semiconductor device, and includes steps of generating at least one laser beam from at least one laser source, providing a plurality of points of high temperature plasma on a target for receiving the at least one laser beam, generating X-rays from the points on the target, irradiating a mask with the X-rays from the portions and projecting an image of the pattern carried by the irradiated mask onto a wafer. In still another aspect, the present invention provides a method of producing a semiconductor device, and includes steps of generating a laser beam from a laser source, providing an aperture, having a variable shape, for receiving the laser beam and for defining a secondary laser beam, providing a target for receiving the secondary laser beam, generating X-rays from portions of high temperature plasma on the target, irradiating a mask with X-rays from the portions and projecting an image of a pattern carried by the irradiated mask onto a wafer. The present invention can be applied to a wide variety of apparatuses which need illumination or irradiation with X-rays, such as, for example, an X-ray exposure apparatus, X-ray microscopes, X-ray examination apparatus, X-ray processing apparatus, and clinical X-ray apparatuses. The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.
046719199	claims	1. A method of monitoring reactor power levels in a nuclear reactor, comprising the steps of: (a) producing a sample signal indicating radiation detected during a sampling period having a predetermined length; (b) converting the sample signal into a converted signal; (c) multiplying the converted signal by a first constant to produce a first multiplied signal; (d) multiplying the converted signal by a second constant divided by the length of the sampling period to produce a second multiplied signal; (e) converting the first and second multiplied signals into current power level and rate of power level change signals, respectively; (f) summing a prior rate of power level change signal produced during an immediately previous sampling period with the second multiplied signal to produce the current rate of power level change signal in step (e); (g) summing a prior power level signal produced during the immediately previous sampling period with the length of the sampling period multiplied by the prior rate of power level change signal produced during the immediately previous sampling period to produce a predicted power level signal; (h) subtracting the predicted power level signal from the sample signal to produce the converted signal in step (b); (i) summing the first multiplied and predicted power level signals to produce the current power level signal in step (e); and (j) outputting the current power level, rate of power level change and predicted power level signals. radiation sensing means for sensing radiation emitted from the nuclear reactor and outputting a sample signal indicative of the radiation sensed during a sampling period having a predetermined length; and microprocessing means for converting the sample signal into reactor power level, rate of reactor power level change and predicted reactor power level signals. neutron sensing means for sensing neutrons emitted from the pressurized light water nuclear reactor and outputting a current indicative of the neutrons sensed during the sampling period; current-to-voltage converting means for converting the current output by said neutron sensing means into an analog voltage; and analog/digital converting means for converting the analog voltage output by said current-to-voltage converting means into the sample signal. means for converting the sample signal into a converted signal; means for multiplying the converted signal by a first constant to produce a first multiplied signal; means for multiplying the converted signal by a second constant divided by the length of the sampling period to produce a second multiplied signal; means for summing a prior rate of reactor power level change signal for an immediately previous sampling period with the second multiplied signal to produce the rate of reactor power level change signal for the sampling period; means for summing a prior reactor power level signal for the immediately previous sampling period with the length of the sampling period multiplied by the prior rate of reactor level change signal to produce the predicted reactor power level signal; means for subtracting the predicted reactor power level signal from the sample signal to produce the converted signal; and means for summing the first multiplied and predicted reactor power level signals to produce the reactor power level signal for the sampling period. (a) producing a sample signal f(k) indicating neutrons detected during a sampling period k having a predetermined length T; (b) producing a rate of power level change signal p(k) in accordance with ##EQU7## where p(k-1) is the rate of power level change during an immediately previous sampling period, .beta. is a constant with a value between zero and one, inclusive, and p.sub.p (k) is a predicted power level for a next sampling period; (c) producing a reactor power level signal p(k) in accordance with EQU p(k)=p.sub.p (k)-.alpha.[f(k)-p.sub.p (k)], where .alpha. is a constant equal to 2.sqroot..beta.-.beta.; and (d) producing the predicted power level p.sub.p (k) in accordance with EQU p.sub.p (k)=p(k-1)+T p(k-1), where p(k-1) is the power level of the immediately previous sampling period. neutron detecting means for detecting neutrons emitted from the pressurized light water nuclear reactor and outputting a sample signal f(k) indicative of the neutrons detected during a sampling period k having a predetermined length T; rate means for converting the sample signal k into a rate of power level change signal p(k) in accordance with ##EQU8## where p(k-1) is the rate of power level change for an immediately previous sampling period k-1, .beta. is a constant with a value between zero and one, inclusive, and p.sub.p (k) is a predicted power level for a next sampling period; power signal means for converting the sample signal into a reactor power level signal p(k) in accordance with EQU p(k)-p.sub.p (k)-.alpha.[f(k)-p.sub.p (k)], where .alpha. is equal to 2.sqroot..beta.-.beta.; and predicted power signal means for converting the sample signal into a predicted reactor power level signal p.sub.p (k) in accordance with EQU p.sub.p (k)=p(k-1)+T p(k-1), 2. A reactor power level monitor for a nuclear reactor, comprising: 3. A reactor power level monitor as recited in claim 2, wherein the sample signal contains noise and said microprocessor means comprises noise reduction means for reducing the noise in said sample signal. 4. A reactor power level monitor as recited in claim 2, wherein said radiation sensing means comprises: 5. A reactor power level monitor as recited in claim 2, wherein said microprocessor means comprises: 6. A method of monitoring reactor power levels in a pressurized light water nuclear reactor, comprising the steps of: 7. A reactor power level monitor for a pressurized light water nuclear reactor, comprising:
	summary
	summary
	abstract	A magnetic field coil arrangement for a magneto-optical trap comprises a first transparent substrate having a first surface, a second transparent substrate having a second surface opposite from the first surface, one or more side walls coupled between the first and second transparent substrates, a first set of magnetic field coils on the first surface of the first transparent substrate, and a second set of magnetic field coils on the second surface of the second transparent substrate. The second set of magnetic field coils in an offset alignment with the first set of magnetic field coils. The first and second sets of magnetic field coils are configured to produce a magnetic field distribution that mimics a quadrupole magnetic field distribution in a central location between the first and second transparent substrates.
	claims	1. A dual-energy ray scanning system, characterized in that said system comprises:a ray source for alternately emitting a high energy ray and a low energy ray;a filter comprising a low energy filtering element and a low energy transmitting element; anda control device for controlling said ray source and said filter to make said low energy filtering element of said filter be aligned with a beam exit direction of said ray source when said ray source emits a high energy ray so as to filter low energy portion of said high energy ray out and transmit high energy portion of said high energy ray out, and for controlling said ray source and said filter to make said low energy transmitting element of said filter be aligned with said beam exit direction of said ray source when said ray source emits the low energy ray so as to transmit said low energy ray out;wherein said low energy filtering element comprises a plurality of filter sheets;said low energy transmitting element comprises a plurality of transmission sheets;said filter sheets and said transmission sheets are arranged alternately and surround said ray source to form a cavity; andsaid ray source is located on a central axis of said cavity. 2. The dual-energy ray scanning system according to claim 1, characterized in that:said filter is a hollow cylinder shape; andsaid filter sheets and said transmission sheets are arranged parallel to said central axis of said cavity. 3. The dual-energy ray scanning system according to claim 1, characterized in that said filter sheets are equally sized and are arranged with equal distance each other. 4. The dual-energy ray scanning system according to claim 2, characterized in that said filter sheets are equally sized and are arranged with equal distance each other. 5. The dual-energy ray scanning system according to claim 1, characterized in that:said low energy filtering element is made of a high Z material; andsaid low energy transmitting element is a void or made of a low Z material,wherein Z represents an atomic number. 6. The dual-energy ray scanning system according to claim 1, characterized in that said ray source is an accelerator comprising a target and an electron gun for alternately emitting a high energy electron beam or a low energy electron beam, wherein said high energy electron beam bombards said target to generate a high energy ray and said low energy electron beam bombards said target to generate a low energy ray. 7. The dual-energy ray scanning system according to claim 1, characterized in that said ray source is an accelerator comprising an electron gun for emitting an electron beam and a target comprising a first part made of a first material and a second part made of a second material, wherein said electron beam emitted by said electron gun alternately bombard said first part or said second part of said target to respectively generate a high energy ray or a low energy ray. 8. A dual-energy ray inspecting system, characterized in that said dual-energy ray inspecting system comprises a dual-energy ray scanning system according to claim 1. 9. The dual-energy ray inspecting system according to claim 8, characterized in that said dual-energy ray inspecting system is a fix-mounted type dual-energy ray inspecting system, a movable type dual-energy ray inspecting system, or a vehicle-mounted type dual-energy ray inspecting system. 10. A dual-energy ray scanning method, characterized in that said method comprises:alternately arranging a plurality of filter sheets of a low energy filtering element of a filter and a plurality of transmission sheets of a low energy transmitting element of the filter to form a cavity;alternately emitting a high energy ray and a low energy ray by a ray source located on a central axis of the cavity; andcontrolling said ray source and a filter to make a low energy filtering element of said filter be aligned with a beam exit direction of said ray source when said ray source emits a high energy ray so as to filter low energy portion of said high energy ray out and transmit high energy portion of said high energy ray out, and to make a low energy transmitting element of said filter be aligned with said beam exit direction of said ray source when said ray source emits a low energy ray so as to transmit said low energy ray out. 11. The dual-energy ray scanning method according to claim 10, characterized in that said low energy filtering element is made of a high Z material, said low energy transmitting element is a void or made of a low Z material, wherein Z represents an atomic number. 12. A computer readable storage medium which stores a computer program, characterized in that said program is executed by a processor to implement said a dual-energy ray scanning method according to claim 10. 13. A computer device which comprises a memory, a processor, and a computer program which is stored in said memory and can be run by said processor, said computer device is characterized in that said processor executed said a dual-energy ray scanning method according to claim 10 by running said program.
	summary
	claims	1. An ion implanter, comprising:an ion source capable of generating an ion beam;a mass analyzer capable of analyzing said ion beam;a substrate holder capable of holding a workpiece to be implanted by said ion beam; anda control assembly capable of adjusting said ion beam in an adjustment space between said mass analyzer and said substrate holder, said control assembly comprising:a first bended bar magnet having a first bended support rod and one or more first coils dispensed on said first bended support rod with one or more first currents flowing through said first coils; anda second bended bar magnet having a second bended support rod and one or more second coils dispensed on said second bended support rod with one or more second currents flowing through said second coils;wherein said control assembly is configured according to at least one of the following:a first curvature of said first bended bar magnet being adjustable;a second curvature of said second bended bar magnet being adjustable;said first bended bar magnet having an adjustable shape; andsaid second bended bar magnet having an adjustable shape;wherein said first bended bar magnet is at a gap from said second bended bar magnet to form said adjustment space between said bended bar magnets. 2. The ion implanter as set forth in claim 1, wherein a width of said gap is adjustable. 3. The ion implanter as set forth in claim 1, wherein at least one of said first current and said second current is adjustable. 4. The ion implanter as set forth in claim 1, said control assembly being configured, according to one of the following:said first bended bar magnet and said second bended bar magnet being symmetrical around a centerline of said gap; andsaid first bended bar magnet and said second bended bar magnet being asymmetrical around said centerline of said gap. 5. The ion implanter as set forth in claim 1, said control assembly being configured according to at least one of the following:said first bended bar magnet being concave so that a midpoint of said first bended bar magnet is farther from a centerline of said gap than the two ends of said first bended bar magnet; andsaid second bended bar magnet being concave so that a midpoint of said second bended bar magnet is farther from said centerline of said gap than the two ends of said second bended bar magnet;said first bended bar magnet being convex so that a midpoint of said first bended bar magnet is closer to said centerline of said gap than said two ends of said first bended bar magnet; andsaid second bended bar magnet being convex so that a midpoint of said second bended bar magnet is closer to said centerline of said gap than said two ends of said second bended bar magnet. 6. The ion implanter as set forth in claim 1, said control assembly being configured according to at least one of the following:said first bended bar magnet having an arc shape;said second bended bar magnet having an arc shape;said first bended bar magnet having a curved shape;said second bended bar magnet having a curved shape;said first bended bar magnet having a zigzag shape; andsaid second bended bar magnet having a zigzag shape. 7. The ion implanter as set forth in claim 1, said control assembly being configured according to at least one of the following:said first coils being uniformly dispensed on said first bended support rod;said first coils being non-uniformly dispensed on said first bended support rod;said second coils being uniformly dispensed on said second bended support rod; andsaid second coils being non-uniformly dispensed on said second bended support rod. 8. The ion implanter as set forth in claim 1, said control assembly being configured according to at least one of the following:said first coils being electrically coupled with a first power source;said first coils being electrically coupled with two or more said first power sources;said second coils being electrically coupled with a second power source; andsaid second coils being electrically coupled with two or more said second power sources. 9. The ion implanter as set forth in claim 8, said control assembly being configured according to at least one of the following:different said first power sources being separately operated;different said second power sources being separately operated;said first power sources and said second power sources being separately operated;said first power sources behaving as one and only one power source;said second power sources behaving as one and only one power source; andsaid first power sources and said second power sources behaving as one and only one power source.
	claims	1. A filter system for filtering debris particles out of radiation emitted by a radiation source, and usable for lithography, the filter system comprising:a plurality of foils configured to trap the debris particles,at least one foil of the plurality of foils including at least two parts that have a mutually different orientation and that are connected to each other along a substantially straight connection line,each of the at least two parts substantially coinciding with a respective virtual plane, wherein each of the virtual planes extends through a predetermined position that substantially coincides with the radiation source,the substantially straight connection line coinciding with a virtual straight line that also extends through the predetermined position. 2. A filter system according to claim 1, wherein the filter system includes a support to which a first part of the at least two parts is connected at a first position of the support and to which a second part of the at least two parts is connected at a second position of the support. 3. A filter system according to claim 2, wherein a distance between the first and second position is fixed. 4. A filter system according to claim 2, wherein the support comprises an inner ring and an outer ring. 5. A filter system according to claim 4, wherein the inner ring and the outer ring are coaxial. 6. A filter system according to claim 2, wherein at least a part of the filter system is arranged to cool the support. 7. A filter system according to claim 2, wherein the filter system further includes a cooling system having a surface that is arranged to be cooled, the cooling system and the support being positioned with respect to each other such that a gap is formed between the surface of the cooling system and the support, and wherein the cooling system further is arranged to inject gas into the gap. 8. A filter system according to claim 7, wherein a path between an entrance position at which the gas enters the gap and an exit position from which the gas exits the gap forms a meandering path. 9. A filter system according to claim 7, wherein the gap is such that a smallest distance between the surface of the cooling system and the support is in a range from about 20 micrometers to about 200 micrometers. 10. A filter system according to claim 9, wherein the gap is such that a smallest distance between the surface of the cooling system and the support is in a range from about 40 micrometers to about 100 micrometers. 11. A filter system according to claim 7, wherein the support is rotatable with respect to the surface of the cooling system. 12. A filter system according to claim 7, wherein the surface of the cooling system is arranged to be stationary with respect to the support. 13. A filter system according to claim 7, wherein the surface of the cooling system is arranged to be cooled with a fluid. 14. A filter system according to claim 13, wherein the fluid is water. 15. A filter system according to claim 7, wherein the gas is argon. 16. A filter system according to claim 7, wherein the support is provided with a recess for holding the cooled gas before the cooled gas flows through the gap. 17. A filter system according to claim 1, wherein at least one of the at least two parts coincides with a virtual plane that is a straight plane. 18. A filter system according to claim 1, wherein the cooling system is arranged to cool the gas before injecting the gas in the gap. 19. A filter system according to claim 1, wherein each virtual plane is a straight plane. 20. A filter system according to claim 1, wherein at least one of the at least two foil parts includes a curvature. 21. A filter system according to claim 1, wherein the at least two foil parts are configured to accommodate thermal expansion by a substantially sideways movement of the connection line with respect to the overall orientation of the foil.
	abstract	An electron beam emitter includes an electron generator for generating electrons. The electron generator can have a housing containing at least one electron source for generating the electrons. The at least one electron source has a width. The electron generator housing can have an electron permeable region spaced from the at least one electron source for allowing extraction of the electrons from the electron generator housing. The electron permeable region can include a series of narrow elongate slots and ribs formed in the electron generator housing and extending laterally beyond the width of the at least one electron source. The electron permeable region can be configured and positioned relative to the at least one electron source for laterally spreading the electrons that are generated by the at least one electron source.
	claims	1. A nuclear reactor, comprising:a reactor driving system including a reactor vessel accommodating a reactor core and a steam generator to which a steam pipe and a water supply pipe are connected; anda reactor safety system including:a releasing isolation vessel accommodating gas and the reactor driving system,an absorbing isolation vessel formed at lower side of the releasing isolation vessel, having a passage formed as a double barrier comprised of a releasing isolation vessel barrier formed at the releasing isolation vessel and having a lower portion opened and an absorbing isolation vessel barrier formed at the absorbing isolation vessel and having an upper portion opened, communicating with the releasing isolation vessel through the passage and accommodating coolant,a transferring isolation vessel formed at upper side of the releasing isolation vessel and on the top of the absorbing isolation vessel and accommodating the gas and coolant,a releasing heat exchanger and an absorbing heat exchanger adjacently disposed to each other within the transferring isolation vessel to exchange heat with each other,a coolant spray pipe having one end in the absorbing isolation vessel and the other end having nozzle in the transferring isolation vessel, spraying coolant to the releasing heat exchanger and the absorbing heat exchanger adjacently disposed to each other,a condensing heat exchanger disposed outside the isolation vessels,a releasing heat exchange channel connected to the reactor vessel and the releasing heat exchanger to circularly distribute coolant,an absorbing heat exchange channel connected to the absorbing heat exchanger and the condensing heat exchanger to circularly distribute coolant, anda releasing isolation vessel communicating pipe formed to connect fluidly an upper portion of the releasing isolation vessel and an upper portion of the transferring isolation vessel,wherein coolant within the reactor safety system is selectively distributed in response to thermal-hydraulic conditions changed depending on a change in pressure within the reactor driving system and whether coolant is leaked to cool the reactor driving system. 2. The nuclear reactor of claim 1, wherein in the reactor safety system, coolant sprayed from the coolant spray pipe absorbs heat from coolant distributed within the releasing heat exchanger to be evaporated,coolant distributed within the absorbing heat exchanger absorbs heat of steam generated by the evaporation to condense the steam and is accommodated into the transferring isolation vessel,a heat transfer is made by a two-phase heat transfer mechanism for transferring heat from coolant within the releasing heat exchanger to coolant within the absorbing heat exchanger by evaporating and condensing coolant sprayed by the coolant spray pipe. 3. The nuclear reactor of claim 1, wherein the coolant spray pipe has one end communicating with the absorbing isolation vessel to be supplied with coolant and the other end provided with a nozzle to spray supplied coolant to the releasing heat exchanger and the absorbing heat exchanger and is provided with a coolant spray valve, andthe reactor safety system further includes:a coolant injection pipe having one end communicating with the transferring isolation vessel and the other end communicating with the releasing isolation vessel to inject coolant accommodated in the transferring isolation vessel into the releasing isolation vessel; anda coolant injection valve provided on the coolant injection pipe. 4. The nuclear reactor of claim 1, wherein the transferring isolation vessel has an accommodating barrier enclosing an area in which the releasing heat exchanger and the absorbing heat exchanger are disposed to accommodate the cold water within the transferring isolation vessel. 5. The nuclear reactor of claim 1, wherein the reactor safety system further includes:a releasing isolation vessel communicating valve provided on the releasing isolation vessel communicating pipe. 6. The nuclear reactor of claim 1, wherein the reactor safety system further includes:a releasing isolation vessel pressure reducing pipe formed to connect fluidly a lower portion of the releasing isolation vessel and a lower portion of the absorbing isolation vessel; anda releasing isolation vessel pressure reducing valve provided on the releasing isolation vessel pressure reducing pipe. 7. The nuclear reactor of claim 1, wherein the reactor safety system further includes:a steam bypass pipe having one end communicating with the steam pipe and the other end communicating with the releasing heat exchange channel to distribute the steam generated by the evaporation of coolant within the steam generator to the releasing heat exchange channel; anda steam bypass valve provided on the steam bypass pipe. 8. The nuclear reactor of claim 1, wherein the reactor safety system further includes:a steam release pipe having one end communicating with the steam pipe and the other end communicating with a space within the releasing isolation vessel to release steam generated by evaporation of coolant within the reactor vessel to the space within the releasing isolation vessel; anda steam release valve provided on the steam release pipe. 9. The nuclear reactor of claim 1, wherein the reactor safety system further includes:a coolant supplement pipe having one end communicating with the releasing heat exchange channel and the other end communicating with a space under a surface of coolant within the absorbing isolation vessel or the transferring isolation vessel to supplement coolant to the releasing heat exchange channel; anda coolant supplement valve provided on the coolant supplement pipe.
	summary
	summary
	summary
	description	The present invention relates to a photolithographic mask for patterning a photosensitive material, in particular on a wafer, having at least one structure region for imaging a structure on the photosensitive material, and an absorber structure for absorbing incident radiation. Furthermore, the invention relates to various methods for fabricating a photolithographic mask of this type. Photolithographic masks of this type serve for patterning a photosensitive material, in particular on a wafer. The masks have at least one structure region for imaging a structure on the photosensitive material and an absorber structure for absorbing incident radiation. In order to image the structure regions of the mask onto the plane of a wafer coated with photoresist, the mask is irradiated with light. The smaller the structures to be imaged are, the shorter, too, the wavelength of the irradiation light has to be in order that the resolution, limited by diffraction, can be increased. Wavelengths in the deep ultraviolet (DUV), e.g. 248 nm and 193 nm, are used nowadays for chip fabrication. Lithography in the vacuum ultraviolet (VUV) region (e.g. 157 nm) and in the extreme ultraviolet (EUV) region (e.g. 13–14 nm) will be used in the future. In chip production, a photolithographic mask has to be available for the exposure of thousands of wafers with sufficient quality. This poses the problem that the patterned surface of the mask has to be protected from contamination in particular by particles. For exposures in the DUV, use is made of transparent and stable membranes—so-called pellicles—that are clamped over the mask and thereby protect the structures to be imaged from particle deposition during exposure, transport and storage. The distance between the pellicles and the mask surface additionally has the effect that particles deposited thereon lie outside the depth of the focus range and are not imaged on the wafer. As the wavelength of the exposure light decreases, it is becoming increasingly difficult to find materials that have a high transparency and at the same time exhibit sufficient long-term stability. For so-called 157 nm lithography, no suitable membranes have been found hitherto; therefore, hard pellicles made of e.g. CaF2 with a thickness of about 800 μm are necessary, but these have to be taken into account as an optical element in the configuration of the optical beam path. For EUV lithography (EUVL) in the wavelength range of 13–14 nm, there are practically no materials that are optically transparent and at the same time mechanically stable enough to be suitable as a membrane material for a pellicle. Moreover, in EUVL, transmission masks can no longer be used, rather reflection masks are necessary. In this case, the light used for imaging would have to pass through a membrane not just once but twice. On account of the smaller structures of EUVL in relation to 157 nm or 197 nm lithography, the requirements with regard to the mask surface being free of particles are very much more stringent. Since there are no suitable membranes available, the surfaces of such masks have to be cleaned of particles that would be imaged on the wafers. Each cleaning operation may entail damage to the structure regions and the absorber structures. This leads to undesirable and unacceptable deviations of the imaged structures from the desired structures. It is accordingly an object of the invention to provide a photolithographic mask and methods for the fabrication of the mask that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type. With the foregoing and other objects in view there is provided, in accordance with the invention, a photolithographic mask for patterning a photosensitive material. The mask contains at least one structure region for imaging a structure on the photosensitive material, at least one protective layer made of a chemically and mechanically resistive material disposed on the structure region, and an absorber structure for absorbing incident radiation disposed next to the structure region. The invention provides for at least one structure region of the photomask to have at least one protective layer made of a chemically and mechanically resistive material. In this way, the photolithographic mask can be cleaned chemically and/or mechanically, without the structure regions being attacked and damaged by the chemical and/or mechanical cleaning media. Suitable liquid etchants or reactive gases are usually used during chemical cleaning. In mechanical cleaning methods, the patterned surface of the photomask is exposed to mechanical forces or impulses by gaseous, liquid or solid media. These include, by way of example, rinsing operations in a neutral liquid with or without ultrasonic assistance, brush methods, jet and plasma methods in which the surface is exposed to a liquid jet or bombardment with solid particles, e.g. chemically inert ions. Therefore, in the case of photomasks whose surfaces have hitherto been protected by pellicles, the solution according to the invention allows such pellicles to be dispensed with. The number of wafers that can be exposed by photomasks configured according to the invention for reflection exposure is similar to that using known photomasks whose surfaces are protected by a pellicle. At least one protective layer can preferably be fabricated by a method for atomic layer deposition. Such methods enable the deposition of layers that are very thin, i.e. have just a few atomic layers. Moreover, these layers can be deposited highly conformally onto arbitrary surface topographies, and they have no holes (pinholes) whatsoever despite their small layer thickness. The deposition of such thin protective layers either constitutes a negligible alteration of the desired nominal dimensions (the so-called critical dimensions (CD)) of the surface topographies particularly in the case of EUVL photomasks or can be compensated for through corresponding modifications of the absorber structure dimensions before the deposition of the thin protective layers. Moreover, the additional absorption and reflection losses are likewise negligibly low. Such a protective layer having a thickness of a few atomic layers enables multiple chemical and/or mechanical cleaning of photomasks that are provided for EUV lithography. The so-called atomic layer chemical vapor deposition (ALCVD) method has proved to be a particularly suitable method for atomic layer deposition. It has the above-mentioned properties during the layer deposition and enables very precise control of the deposition process. A preferred embodiment of the photomask is characterized in that the protective layer additionally extends over the surfaces of an absorber structure. Consequently, the protective layer completely seals the surface topography of the photomask. In addition to the structure regions, the surfaces of the three-dimensional absorber structure are also protected from an interaction with the respective cleaning media during chemical and/or mechanical cleaning. The protective layer is formed of at least one material being Al2O3, Ta2O5, ZrO2 and/or HfO2. Deviations from the specified stoichiometric compositions are also possible in this case. These materials afford the desired resistance to chemical and/or mechanical cleaning media and can be deposited as a thin film by atomic deposition methods described above. For the transmission exposure of photosensitive materials, in particular on wafers, the structure regions and the absorber structure of the photolithographic mask are disposed on a carrier element suitable for a transmission exposure. With the use of ultraviolet radiation having wavelengths in the region above 100 nm, quartz glass is usually appropriate as material for the carrier element. For the reflection exposure of photosensitive materials, in particular on wafers, the structure regions and the absorber structure of the photolithographic mask are preferably disposed on a carrier element that has a reflection device for reflecting the exposure radiation during the reflection exposure. Particularly with the use of an exposure radiation having a wavelength of less than 20 nm, it is advantageous for the reflection device to be configured as a Bragg reflector. The Bragg reflector contains, for example, an alternating sequence of two thin films having a defined layer thickness and refractive index. For EUVL, molybdenum and silicon, for example, are suitable as materials for the two thin films. The thin films of the Bragg reflector are usually deposited on a substrate having a low thermal expansion coefficient. In a preferred embodiment, the absorber structure is disposed on a buffer layer. The buffer layer serves as an etching stop during the anisotropic patterning of the absorber layer and protects the structure regions during defect repairs of the absorber structure. After the operation for repairing the absorber layer, the buffer layer is removed from the structure regions. Silicon oxide, in particular, is suitable as material for a repair buffer layer of this type. The absorber structure of the photolithographic mask preferably contains at least one of the following materials: Al, Cu, Ti, TiN, Ta, TaN, Ni and Cr. A first method for fabricating a photolithographic mask according to the invention for patterning a photosensitive material, in particular on a wafer, contains the following steps: provision of a carrier element, deposition of at least one protective layer made of a chemically and mechanically resistive material using a method of atomic layer deposition on a surface of the carrier element, and fabrication of an absorber structure on the surface of the protective layer by deposition and patterning of an absorber layer. The method provides a fabrication method for a photomask according to the invention whose structure regions are protected from an interaction and damage with chemical and/or mechanical cleaning media by a protective layer. A second method for fabricating a photolithographic mask according to the invention for patterning a photosensitive material, in particular on a wafer, contains the following steps: provision of a carrier element, deposition of at least one protective layer made of a chemically and mechanically resistive material using a method for atomic layer deposition on a surface of the carrier element, deposition of a buffer layer on the surface of the protective layer, fabrication of an absorber structure on the surface of the buffer layer by deposition and patterning of an absorber layer, repair of the absorber structure if necessary, and removal of the buffer layer in structure regions that are not covered by the absorber structure, by anisotropic etching, the protective layer serving as an etching stop. In this method, the absorber structure of the photomask has an additional buffer layer. During the fabrication process, the buffer layer preserves the structure regions together with the thin protective layer disposed thereon from damage during the patterning and repair operation for the absorber layer. In the sections of the structure regions the buffer layer can be completely removed in a simple manner by an anisotropic etching process because the underlying protective layer acts as an etching stop. An advantageous development of the first or second fabrication method provides for an additional protective layer made of a chemically and mechanically resistive material to be deposited by atomic layer deposition on the surfaces of the absorber structure and on the surfaces of the first protective layer in the structure regions. A complete sealing of the surface topography is achieved as a result. A third method for fabricating a photolithographic mask for patterning a photosensitive material, in particular on a wafer, contains the following steps: provision of a carrier element, fabrication of an absorber structure by deposition and patterning of an absorber layer on the surface of the carrier element, and deposition of at least one protective layer made of a chemically and mechanically resistive material by atomic layer deposition on the surface of the absorber structure and on the surface of the carrier element in the structure regions. In this method, as the last method step, the protective layer seals the entire surface topography of the photolithographic mask. A fourth method for fabricating a photolithographic mask for patterning a photosensitive material, in particular on a wafer, contains the following steps: provision of a carrier element, deposition of a buffer layer on a surface of the carrier element, fabrication of an absorber structure on the surface of the buffer layer by deposition and patterning of an absorber layer, repair of the absorber structure, removal of the buffer layer in structure regions that are not covered by the absorber structure, by anisotropic etching, and deposition of at least one protective layer made of a chemically and mechanically resistive material by atomic layer deposition on the surface of the absorber structure and on the surface of the carrier element in the structure regions. In a manner similar to that in the case of the second fabrication method, the absorber structure has an additional buffer layer disposed on the carrier element. The buffer layer fulfils the protective function already explained during the repair of the absorber structure and is subsequently removed in the sections of the structure regions by anisotropic etching. In all four fabrication methods, at least one protective layer is preferably deposited by an ALCVD method. In all the above-described methods for fabricating the photomask according to the invention, it is possible to provide both a carrier element made of a material suitable for a transmission exposure and a carrier element with a reflection device for a reflection exposure. 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 photolithographic mask and methods for the fabrication of the mask, 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. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a planar carrier element 1 of a mask, also called a mask blank. The planar carrier element 1 has a substrate 10 and a reflection device 11 that is disposed thereon and is configured as a Bragg reflector 11 in a known manner. The Bragg reflector 11 has a multilayer reflector layer with a multiplicity of alternating thin films, for which molybdenum and silicon, in particular, are suitable as materials in the application for EUVL. An absorber structure 20 is disposed in the form of a regular rib structure on a surface of the Bragg reflector 11. In this case, those regions of the carrier element 1 which are not covered by the absorber structure form the structure regions 30, which can be imaged onto a photosensitive material, for example onto a wafer coated with photoresist, by the photomask. The periodic rib structure shown is chosen here only by way of example; it is clear that the absorber structure 20 can be formed in a multiplicity of different topographies. A buffer layer 21 is situated in each case between the surface of the Bragg reflector 11 and the individual absorber structures 20. The buffer layer 21 was deposited during the fabrication process initially on the entire surface of the Bragg reflector 11. After the fabrication of the absorber structure 20 on the buffer layer 21, it ensures that the surface of the Bragg reflector 11 is not damaged during a mechanical or laser-optical repair operation for the absorber structure 20. After the repair of the absorber structure 20, the buffer layer 21 is removed by an anisotropic etching process in the sections of the structure regions 30. In the case of the photomask illustrated in FIG. 1A, the surfaces of the absorber structure 20 and of the structure regions 30 have a common protective layer 40. The protective layer 40 seals the entire surface topography of the photomask and protects the absorber structure 20 and the structure regions 30 from contact with and damage due to chemical and/or mechanical cleaning media. The protective layer 40 can preferably be deposited by an atomic layer deposition method, in particular ALCVD method, on the surface topography. These methods have the advantage that the surface topography is sealed with a highly conformal, etching and sputtering-resistant protective layer having a thickness of only a few atomic layers. The sputtering resistance is of importance primarily in the case of EUVL photomasks, since the light having the wavelengths used gives rise, by way of secondary-electron-induced processes, to highly excited particles that, through interaction with the unsealed surface of the photomask, can lead to damage thereto. With regard to the illustration in all the figures, it must be emphasized that the dimensions of the individual layers with respect to one another are not illustrated true to scale. The illustrations are diagrammatic, therefore, in order to be able to clearly illustrate the construction of the photomasks. The photomask illustrated in FIG. 1B has the same construction as described in connection with FIG. 1A with regard to the absorber structure 20 and the structure regions 30. In contrast to FIG. 1A, the carrier element 1 of the photomask does not have a reflection device. The photomask is configured for a transmission exposure of photosensitive material. Therefore, the carrier element 1 is composed of a material that has sufficient transmission for light having the wavelength used for the exposure. FIG. 2A shows a second embodiment of the photomask according to the invention. Identical elements are provided with identical reference symbols. In contrast to the first embodiment, the protective layer 40 is disposed on the surface of the Bragg reflector 11. During the fabrication of the photomask of this embodiment, the buffer layer 21 and the absorber structure 30 were deposited successively on the surface of the protective layer 40. The buffer layer 21, as described in connection with FIG. 1A, was subsequently removed in the structure regions 30 by an anisotropic etching step. The protective layer 40 serves as an etching stop in this case. FIG. 2B shows the photomask with a construction as in FIG. 2A, the carrier element 1 not having a reflection device and being composed of a material suitable for the transmission exposure. FIG. 3A shows a third embodiment of the photomask according to the invention. With regard to its construction and its fabrication, this embodiment corresponds to the photomask shown in FIG. 2A, the photomask having an additional second protective layer 40′ on the surfaces of the absorber structure 20 and on the surfaces of the first protective layer 40 in the structure regions 30. The additional second protective layer 40′ can be formed from the same material as the first protective layer 40 or from a different material. It is again fabricated by a method for atomic layer deposition, in particular by ALCVD. FIG. 3B shows the photomask with the same construction as in FIG. 3A, the carrier element 1 not having a reflection device and being composed of a material suitable for the transmission exposure.

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