WO2013118593A1 - Target structure and radiation generator - Google Patents
Target structure and radiation generator Download PDFInfo
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- WO2013118593A1 WO2013118593A1 PCT/JP2013/051683 JP2013051683W WO2013118593A1 WO 2013118593 A1 WO2013118593 A1 WO 2013118593A1 JP 2013051683 W JP2013051683 W JP 2013051683W WO 2013118593 A1 WO2013118593 A1 WO 2013118593A1
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- Prior art keywords
- radiation
- target
- target structure
- diamond substrate
- plane
- Prior art date
Links
- 230000005855 radiation Effects 0.000 title claims abstract description 76
- 239000000758 substrate Substances 0.000 claims abstract description 87
- 229910003460 diamond Inorganic materials 0.000 claims abstract description 68
- 239000010432 diamond Substances 0.000 claims abstract description 68
- 239000013078 crystal Substances 0.000 claims abstract description 20
- 239000010410 layer Substances 0.000 claims description 46
- 229910045601 alloy Inorganic materials 0.000 claims description 10
- 239000000956 alloy Substances 0.000 claims description 10
- 239000011229 interlayer Substances 0.000 claims description 8
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 8
- 229910052721 tungsten Inorganic materials 0.000 claims description 8
- 239000010937 tungsten Substances 0.000 claims description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 6
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 claims description 6
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 4
- 239000010936 titanium Substances 0.000 claims description 4
- 229910052719 titanium Inorganic materials 0.000 claims description 4
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 3
- 239000011651 chromium Substances 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 3
- 239000011733 molybdenum Substances 0.000 claims description 3
- 229910052758 niobium Inorganic materials 0.000 claims description 3
- 239000010955 niobium Substances 0.000 claims description 3
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 3
- 229910052763 palladium Inorganic materials 0.000 claims description 3
- 238000002601 radiography Methods 0.000 claims description 3
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 2
- 229910052804 chromium Inorganic materials 0.000 claims description 2
- 229910017052 cobalt Inorganic materials 0.000 claims description 2
- 239000010941 cobalt Substances 0.000 claims description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 2
- 239000010949 copper Substances 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 230000004044 response Effects 0.000 claims description 2
- 229910052702 rhenium Inorganic materials 0.000 claims description 2
- WUAPFZMCVAUBPE-UHFFFAOYSA-N rhenium atom Chemical compound [Re] WUAPFZMCVAUBPE-UHFFFAOYSA-N 0.000 claims description 2
- 229910052703 rhodium Inorganic materials 0.000 claims description 2
- 239000010948 rhodium Substances 0.000 claims description 2
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 claims description 2
- 230000002035 prolonged effect Effects 0.000 abstract description 3
- 230000000052 comparative effect Effects 0.000 description 13
- 238000000034 method Methods 0.000 description 13
- 238000000151 deposition Methods 0.000 description 12
- 230000008021 deposition Effects 0.000 description 12
- 239000000463 material Substances 0.000 description 11
- 238000010894 electron beam technology Methods 0.000 description 10
- 238000005498 polishing Methods 0.000 description 9
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 8
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 230000005540 biological transmission Effects 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 230000003746 surface roughness Effects 0.000 description 5
- 238000005219 brazing Methods 0.000 description 4
- 230000017525 heat dissipation Effects 0.000 description 4
- 229910000679 solder Inorganic materials 0.000 description 4
- 239000010409 thin film Substances 0.000 description 4
- 239000007769 metal material Substances 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- 238000004544 sputter deposition Methods 0.000 description 3
- 229910001369 Brass Inorganic materials 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000010951 brass Substances 0.000 description 2
- 239000012159 carrier gas Substances 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
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- 235000008390 olive oil Nutrition 0.000 description 2
- 238000001308 synthesis method Methods 0.000 description 2
- 239000004925 Acrylic resin Substances 0.000 description 1
- 229920000178 Acrylic resin Polymers 0.000 description 1
- 229910002708 Au–Cu Inorganic materials 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910019582 Cr V Inorganic materials 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- 239000006061 abrasive grain Substances 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 238000004380 ashing Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 229910052790 beryllium Inorganic materials 0.000 description 1
- ATBAMAFKBVZNFJ-UHFFFAOYSA-N beryllium atom Chemical compound [Be] ATBAMAFKBVZNFJ-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 229910052759 nickel Inorganic materials 0.000 description 1
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- 239000004033 plastic Substances 0.000 description 1
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- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- 238000013519 translation Methods 0.000 description 1
- 238000007740 vapor deposition Methods 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
- H01J35/08—Anodes; Anti cathodes
- H01J35/112—Non-rotating anodes
- H01J35/116—Transmissive anodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2235/00—X-ray tubes
- H01J2235/08—Targets (anodes) and X-ray converters
- H01J2235/081—Target material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/16—Vessels; Containers; Shields associated therewith
- H01J35/18—Windows
- H01J35/186—Windows used as targets or X-ray converters
Abstract
A target structure according to the present invention includes a target layer 8b that is formed on a diamond substrate 8a and emits radiation when irradiated with electrons. In at least a portion of a surface of the diamond substrate 8a on which the target layer 8b is formed, a dominant crystal plane is a (100) plane. The target structure according to the present invention can rapidly dissipate heat generated in the target layer. Thus, a radiation generator including the target structure according to the present invention can stably emit radiation over a prolonged period.
Description
DESCRIPTION
TARGET STRUCTURE AND RADIATION GENERATOR
Technical Field
[0001] The present invention relates to a target structure that includes a target formed on a substrate and a radiation generator that includes the target structure.
Background Art
[0002] A radiation generator generates radiation by emitting electrons from an electron source and colliding the electrons with a target. When the electrons emitted from the electron source enter the target, most of their incident energy is converted into heat. Thus, the target generates heat. If the heat generated in the target fails to be sufficiently dissipated, the heat damages the target, which results in failure to obtain a stable amount of radiation.
[0003] PTL 1 discloses an X-ray anode that includes a target thin film disposed on a surface of a diamond
substrate and that rapidly dissipates heat generated in the target thin film from the diamond substrate.
Citation List
Patent Literature
[0004] PTL 1 PCT Japanese Translation Patent Publication No. 2003-505845
Summary of Invention
Technical Problem
[0005] The use of a diamond substrate enhances a heat dissipation effect. Thus, a stable amount of radiation can be obtained in cases of radiation output in a relatively short time.
[0006] However, targets in medical applications often require radiation output with a stable amount of radiation over a prolonged period. A long period of electron
irradiation of a target causes poor adhesion between a diamond substrate and a target thin film, which results in degradation of heat dissipation characteristics. Even in cases where an interlayer is interposed between the diamond substrate and the target thin film so as to improve the initial adhesion therebetween, a long period of electron irradiation causes poor adhesion between the diamond substrate and the interlayer, which results in degradation of heat dissipation characteristics.
[0007] The present invention provides a target structure that allows heat generated in a target to be rapidly dissipated due to a target being disposed on a specific surface of a diamond substrate, and a radiation generator that includes the target structure.
Solution to Problem
[0008] A target structure according to the present
invention includes a target layer that is formed on a diamond substrate and emits radiation in response to irradiation with electrons. In at least a portion of a surface of the diamond substrate on which the target layer is formed, a dominant crystal plane is a (100) plane.
Advantageous Effects of Invention
[0009] The target structure according to the present invention has a structure that facilitates a bond between the diamond substrate and the target layer, thereby
improving adhesion therebetween. This allows heat generated in the target layer to be rapidly dissipated to the diamond substrate. Thus, the use of the target structure according to the present invention can produce a stable amount of radiation over a prolonged period.
Brief Description of Drawings
[0010] Fig. 1 is a cross-sectional view illustrating a configuration of an example of a radiation generator that includes a target structure according to the present invention;
Figs. 2A to 2D are cross-sectional views illustrating four exemplary target structures according to the present invention;
Fig. 3 is a cross-sectional view illustrating a
configuration of an example of a radiation source that includes a target structure according to the present
invention; and
Fig. 4 is a drawing illustrating a configuration of a radiography system that includes a radiation generator according to the present invention.
Description of Embodiments
First Embodiment
[0011] Referring to Fig. 1, a radiation generator 13 that includes a target structure according to the present
invention will be described.
[0012] The radiation generator 13 includes a radiation source 1 and a driving circuit 14, which are disposed inside an envelope 11 having an emission window 10. The remaining space of the envelope 11 is filled with an insulating liquid 17 such as an insulating oil. The envelope 11 has a
grounding terminal 16.
[0013] The envelope 11 can be composed of a high-strength material, such as iron, stainless steel, or brass. The emission window 10 allows radiation 15 emitted from the radiation source 1 to exit to the outside of the radiation generator 13 therethrough. The emission window 10 can be composed of a plastic that contains no heavy elements, such as an acrylic resin or a polymethyl methacrylate resin.
[0014] The radiation source 1 is constituted by a vacuum vessel 6 that includes a transmission window 9, an electron source 3 disposed inside the vacuum vessel 6, and a target
structure 8 held by a shield 7.
[0015] The electron source 3 includes an electron emission unit 2 that emits electrons. The electron source 3 can have any electron emission mechanism as long as the amount of electrons emitted by the electron source is controllable from the outside of the vacuum vessel 6. Examples of the electron source include a hot-cathode electron source and a cold-cathode electron source. The electron source 3 is electrically connected to the driving circuit 14 disposed outside the vacuum vessel 6 via a terminal 4 that penetrates through the vacuum vessel 6. This allows control of the amount of electron emission and the ON/OFF state of electron emission. Electrons emitted by the electron emission unit 2 are accelerated by applying an accelerating voltage to form an electron beam 5 having an energy of about 10 to 200 keV. Then, the electron beam 5 enters a target layer, which is disposed in the target structure 8 so as to face the
electron emission unit 2. The accelerating voltage is applied between the electron source 3 and the shield 7.
[0016] The target structure 8 includes a diamond substrate (hereafter, may be referred to as simply "substrate") and the target layer formed on the substrate. The target layer faces the electron emission unit 2. The diamond substrate is prepared so that the (100) plane is the dominant crystal plane in at least a portion of the surface of the substrate
on which the target layer is formed. The term "(100) plane" refers to a plane represented by a Miller index of (100) . The target structure 8 is clamped with the shield 7 that includes a rear shield 7a and a front shield 7b, thereby being maintained in position.
[0017] The rear shield 7a includes an electron beam passing hole that guides the electron beam 5 to an electron beam irradiation region (radiation generation region) of the target layer. The rear shield 7a also serves as a shield against radiation emitted backward from among radiation emitted from the electron beam irradiation region in all directions. The front shield 7b has an aperture through which desired radiation emitted forward exits from among radiation emitted from the electron beam irradiation region in all directions. The front shield 7b also serves as a shield against unwanted radiation. The shield 7 can be composed of any material having electric conductivity and thermal conductivity. Specifically, the shield 7 can be composed of a material that intercepts radiation generated at 30 to 150 kV. Examples of such a material include tungsten, tantalum, molybdenum, zirconium, niobium, and alloys thereof.
[0018] The shield 7 and the target structure 8 can be joined with each other by brazing (not shown) . A brazing material is suitably selected depending on the material of
the shield 7, the allowable temperature limit of the shield 7, and the like. For example, in cases where the
temperature of a target structure 8 is greatly increased, a Cr-V-based alloy, a Ti-Ta-Mo-based alloy, a Ti-V-Cr-Al-based alloy, a Ti-Cr-based alloy, a Ti-Zr-Be-based alloy, a Zr-Nb- Be-based alloy, or the like can be used as a brazing metal for a high-melting-point metal. In addition, a brazing material containing a Au-Cu alloy as a main component, a nickel solder, a brass solder, a silver solder, or a
palladium solder can be used.
[0019] The vacuum vessel 6 can be composed of glass, a ceramic, or the like. The vacuum vessel 6 has an internal space 12 that has been evacuated (depressurized) . The vacuum vessel 6 includes the transmission window 9 that allows the radiation 15 generated in the target layer of the target structure 8 to pass therethrough and exit to the outside through the emission window 10. Accordingly, the transmission window 9 can be composed of a material that can maintain an adequate degree of vacuum in the vacuum vessel 6 and that minimizes attenuation of the radiation 15 that passes therethrough. Examples of such a material include beryllium, carbon, diamond, and glass. Desirably, the material contains no heavy elements. The internal space 12 can be maintained at a degree of vacuum such that the mean free path of electrons is maintained, in other words,
electrons can fly between the electron source 3 and the target layer that emits radiation. The degree of vacuum can be 1 x 10~4 Pa or less. The degree of vacuum can be suitably selected in consideration of the electron source used, the operational temperature, and the like. In the case of a cold-cathode electron source or the like, the degree of vacuum can be 1 x 1CT6 Pa or less.
[0020] Now referring to Figs. 2A to 2D, the target
structure 8 according to the present invention will be described.
[0021] Fig. 2A illustrates a target structure 8 including a single-crystal diamond substrate 8a and a target layer 8b formed on a (100) plane of the single-crystal diamond
substrate 8a. The (100) plane of diamond has a surface energy of σ = 9.2 J/m2, which is greater than σ = 5.3 J/m2 of a (111) plane and σ = 6.5 J/m2 of a (110) plane. Therefore, the (100) plane bonds with the target layer 8b more easily than other crystal planes. The present invention employs these characteristics to enhance adhesion between the
substrate 8a and the target layer 8b. The (100) plane of the diamond substrate 8a need not necessarily be exposed over the entirety of the surface of the diamond substrate 8a. However, the dominant crystal plane needs to be the (100) plane in at least a portion of the surface of the substrate on which target layer 8b is formed. Preferably, the ratio
of surface occupied by the (100) plane is 50% or more of a portion of the surface of the substrate on which the target layer 8b is formed. The same applies to the below-mentioned diamond substrates shown in Figs. 2B to 2D.
[0022] The (100) plane may be obtained during manufacture of the single-crystal diamond by promoting the growth of the
(100) plane, or alternatively, after the manufacture of the single-crystal diamond by cutting it so that the (100) plane is exposed at the surface of the single-crystal diamond.
[0023] The target layer 8b can be generally composed of a metal material having an atomic number of 26 or more. Metal materials having a higher thermal conductivity and a higher melting point are more suitable. Specifically, metal materials such as tungsten, molybdenum, chromium, copper, cobalt, iron, rhodium, palladium, rhenium and alloy
materials thereof can be suitably used. The thickness of the target layer 8b is 1 to 15 microns. However, the optimal thickness of the target layer 8b varies because the penetration depth of the electron beam into the target layer 8b, that is, the radiation generation region also varies depending on the accelerating voltage.
[0024] The target layer 8b is formed on the diamond substrate 8a by sputtering or vapor deposition.
Alternatively, the target layer 8b having a predetermined thickness can be formed by rolling or polishing and then
diffusion-bonded to the diamond substrate 8a at a high temperature and pressure.
[0025] Fig. 2B illustrates a target structure 8 including a single-crystal diamond substrate 8a having asperities on the (100) plane of the substrate and a target layer 8b formed on the single-crystal diamond substrate 8a. Although not only the (100) plane but also other crystal planes, such as the (111) and (110) planes, of the single-crystal diamond substrate 8a are exposed since the asperities include edges and tapers in a microscopic view, it is considered that the (100) plane of the single-crystal diamond substrate 8a is mainly exposed. Particularly, in cases where a single- crystal diamond substrate 8a has asperities of about 0.01 to 0.2 microns, the (100) plane is dominant and the size of the asperities is appropriate, which produces a synergistic effect of chemical bonding and physical adhesion. The term "size of asperities" refers to a height difference between the peaks and the valleys in the surface of the substrate.
[0026] The asperities on the surface of the substrate can be formed by physically polishing the surface with a metal bonded abrasive, a scaife, or the like. In this case, the size of asperities varies depending on the type of metal bonded abrasive or the type of diamond abrasive grain used for scaife polishing. Generally, polishing with a metal bonded abrasive produces asperities having a size of about
0.1 to 2.0 microns. Scaife polishing produces asperities having a size of about 0.05 to 0.2 microns.
[0027] Alternatively, other than polishing, the asperities may be formed by heating a diamond substrate at about 750°C to 850°C to cause the surface of the substrate to be
slightly graphitized or amorphized, and then removing the graphitized or amorphized product from the surface with hydrofluoric acid or the like. The heating may also be performed using a laser beam. According to this method, the asperities can be arranged regularly at intervals of a few microns to several tens of microns. The asperities, which are formed by heating a diamond substrate by the above heating method and then removing the product with
hydrofluoric acid or the like, generally have a size of about 0.01 to 0.1 microns, which varies depending on the heating temperature.
[0028] In cases where the asperities of the surface of the substrate are small (for example, 0.01 to 0.2 microns) as shown in Fig. 2B, the surface of the target layer 8b formed on the substrate becomes substantially uniform.
[0029] In cases where the asperities of the surface of the substrate are large (for example, 1 micron or more) as shown in Fig. 2C, asperities occur on the surface of the target layer 8b so as to be aligned with the asperities of the surface of the substrate. However, a diameter of a region
irradiated with an electron beam, that is, a focal diameter of the electron beam is generally about 0.1 to 1.5 mm, which is sufficiently large compared with the asperities of about a few microns. Thus, it is considered to be substantially uniform.
[0030] As described above, preferably, the surface of the substrate has asperities having a size of 0.01 microns or more and 2.0 microns or less.
[0031] Fig. 2D illustrates a target structure 8 including an interlayer 8c that is composed of titanium, niobium, or the like and formed on a surface of a substrate, and a target layer 8b formed on the interlayer 8c. Formation of the interlayer 8c on the (100) plane further enhances
adhesion. It is needless to say that, in this case, the diamond substrate shown in Fig. 2D may have asperities on the surface of the substrate as in Figs. 2B and 2C.
[0032] The target structure according to the present invention can be applied to both a reflection-type target and a transmission-type target. In a reflection-type target, the sizes of a target and a diamond substrate can be
increased in order to enhance the heat dissipation capacity. On the other hand, a transmission-type target is required to have a thin target and a thin diamond substrate, and thus it is difficult to increase the sizes of a target and a diamond substrate. Thus, the target structure according to the
present invention is more suitably applied to a
transmission-type target.
Second Embodiment
[0033] Referring to Fig. 3, a radiation generator
including the target structure according to another
embodiment of the present invention will be described. This embodiment is similar to the first embodiment, except that the radiation source 1 has a different configuration.
[0034] In this embodiment, a target structure 8 also serves as a vacuum seal. A vacuum chamber 18 defines an enclosed space maintained at a vacuum by means of a flange 19 and a shield 7 which holds the target structure 8. The target structure 8 also serves as the transmission window 9 of the first embodiment. Therefore, a member corresponding to the transmission window 9 in the first embodiment can be omitted, which contributes to a reduction in attenuation of radiation emitted to the outside.
Third Embodiment
[0035] Referring to Fig. 4, a radiography system that includes the radiation generator according to the first or second embodiment will be described.
[0036] A radiation generator 13 is disposed so as to face a panel sensor 22 (radiation detector) , and a radiographic object 21 is interposed therebetween. While the radiation generator 13 emits radiation 15, a controller 23 controls
the radiation generator 13 and the panel sensor 22 in a cooperative manner to allow the radiation 15 that has passed through the radiographic object 21 to be detected by the panel sensor 22. Image data output from the panel sensor 22 are analyzed by a personal computer 24 and displayed as an image. The radiographic object 21 may be a human body, an animal, an electronic circuit, or the like.
Examples
Formation of Asperities
[0037] The (100) plane of the diamond substrate was grown by a super-high pressure synthesis method, and the resulting diamond substrate was used as a diamond substrate for
deposition. The diamond substrate had a disk shape
(cylindrical shape) with a diameter of 5 mm and a thickness of 1 mm. Asperities were formed on a surface of the diamond substrate by one of the following methods of Examples 1 to 5. Example 1
[0038] The (100) plane of the diamond substrate for
deposition was polished with a metal bonded polishing plate that used diamond abrasive powder with a grain size of #200. Example 2
[0039] Diamond abrasive paste with a grain size of #1000 was diluted with olive oil and dropped onto a scaife. The (100) plane of the diamond substrate for deposition was polished using the scaife rotating at 1500 rpm.
Example 3
[0040] The (100) plane of the diamond substrate for deposition was polished by the same polishing method under the same polishing conditions as in Example 2.
Example 4
[0041] The diamond substrate for deposition was maintained at 800°C for 10 minutes so that the surface of the substrate was graphitized. Then, the graphitized portion was removed by chemical etching with hydrofluoric acid.
Example 5
[0042] The (100) plane of the diamond substrate for deposition was irradiated with a laser beam at an output power of 100 W for an irradiation time of 0.2 msec so that the surface of the substrate was graphitized. Then, the graphitized portion was removed by chemical etching with hydrofluoric acid.
Deposition of Target Layer
[0043] Each of the diamond substrates obtained in Examples 1, 2, 4, and 5 was previously subjected to UV-ozone ashing so that organic matters on the (100) plane of the substrate was removed. Then, a tungsten layer having a thickness of 7 microns was formed as a target layer on each substrate by sputtering using Ar as a carrier gas. Thus, target
structures 8 were formed.
[0044] The diamond substrate obtained in Example 3 was
also cleaned by the same method as described above so that organic matters on the surface of the substrate was removed. Then, a titanium layer having a thickness of 0.1 microns was formed as an interlayer on the substrate by sputtering using Ar as a carrier gas, and a tungsten layer having a thickness of 7 microns was formed as a target layer on the titanium layer. Thus, a target structure 8 was formed.
Preparation of Radiation Source
[0045] The target structure 8 manufactured by the above method was integrally attached to a shield 7 composed of tungsten. Next, as shown in Fig. 1, the target structure 8 was disposed so as to face an electron source 3 that was an impregnated thermionic-emission gun and then sealed in a vacuum to form a radiation source 1. In the same manner as above, five radiation sources were prepared.
Comparative Example 1
[0046] In Comparative Example 1, the (111) plane of the diamond substrate was grown by a super-high pressure
synthesis method, and the resulting diamond substrate was used as a diamond substrate for deposition. Diamond
abrasive paste with a grain size of #1000 was diluted with olive oil and dropped onto a scaife. The (100) plane of the diamond substrate for deposition was polished using the scaife rotating at 1500 rpm. The diamond substrate was cleaned so that organic matters on the surface of the
substrate was removed. Then, a tungsten layer having a thickness of 7 microns was formed as a target layer on the substrate. Thus, a target structure 8 was formed. The method for removing the organic matters and the conditions and method for deposition of the target layer were the same as in Examples. Then, a radiation source including the target structure 8 was prepared by the same method as the preparation of the radiation sources of Examples.
Comparative Example 2
[0047] In Comparative Example 2, a polycrystalline diamond substrate produced by CVD was used as a diamond substrate for deposition. Then, a tungsten layer having a thickness of 7 microns was formed as a target layer on the substrate. Thus, a target structure 8 was formed. The conditions and method for deposition of the target layer were the same as in Comparative Example 1. Then, a radiation source
including the target structure 8 was prepared by the same method as the preparation of the radiation source of
Comparative Example 1.
Measurement of Orientation and Asperities of (100) Plane
[0048] The crystal planes of the diamond substrate were measured by the X-ray diffraction method. The ratio of
(100) plane is a ratio of diffracted intensity corresponding to the (100) plane relative to a total of 100 for all
crystal planes. The size of asperities (surface roughness) of the crystal plane on the surface of the substrate was measured with a surface roughness tester.
Generation of Radiation and Method for Measuring
Radiation
[0049] The amount of radiation emitted from each of the radiation sources in Examples and Comparative Examples was measured with a semiconductor-type dosimeter. The operating conditions of the radiation sources were as follows:
acceleration voltage of 100 kV, current of 2 mA, irradiation time of 10 msec, and rest time of 90 msec.
Evaluation Result
[0050] Table 1 shows the surface roughness and the ratio of (100) plane of each of target structures in Examples and Comparative Examples. The surface roughness in Example is a maximum value of 1.2 microns in Example 1 and a minimum value of 0.01 microns in Example 5. Values in the other
Examples are in the middle range therebetween. The ratio of (100) plane is a minimum value of 50 in Example 1 and 90 or 95 in the other Examples. The surface roughnesses in
Comparative Examples 1 and 2 are 0.1 microns and 0.2 microns, respectively. The ratio of (100) plane in Comparative
Examples 1 and 2 are 5 and 20, respectively.
[0051] Table 2 shows a change in amount of radiation emitted from each of the radiation sources in Examples and
Comparative Examples. During an operating time of 100 hours, the radiation sources in Examples 1 to 5 and Comparative Examples 1 and 2 show no decrease in the amount of radiation with time of pulse-generation. However, after 300 hours of operation, difference in amount of radiation gradually began to increase. After 700 hours, the amounts of radiation in Comparative Examples 1 and 2 are decreased to 50% of the respective initial values, whereas the amounts of radiation in Examples 1 to 5 are maintained at 75% to 80% of the respective initial values. Thus, it was confirmed that the present invention is effective.
[0052 ]
[Table 1]
[0053]
[Table 2]
Other Embodiments
[0054] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
[0055] This application claims the benefit of Japanese Patent Application No. 2012-022976, filed February 06, 2012, which is hereby incorporated by reference herein in its entirety.
Reference Signs List
[0056] 8 target structure
8a diamond substrate
8b target layer
Claims
[1] A target structure comprising a target layer that is formed on a diamond substrate and emits radiation in
response to irradiation with electrons, wherein, in at least a portion of a surface of the diamond substrate on which the target layer is formed, a dominant crystal plane is a (100) plane .
[2] The target structure according to Claim 1, wherein the portion of the surface of the diamond substrate on which the target layer is formed has asperities having a size of 0.01 microns or more and 2.0 microns or less.
[3] The target structure according to Claim 1 or 2, wherein the ratio of surface occupied by the (100) plane is 50% or more of the portion of the surface of the diamond substrate on which the target layer is formed.
[4] The target structure according to any one of Claims 1 to 3, wherein the target layer is composed of tungsten, molybdenum, chromium, copper, cobalt, iron, rhodium,
palladium, rhenium, or an alloy thereof.
[5] The target structure according to any one of Claims 1 to 4, wherein an interlayer is formed between the diamond substrate and the target layer.
[6] The target structure according to Claim 5, wherein the interlayer is composed of titanium or niobium.
[7] A radiation generator comprising:
a radiation source that includes the target structure according to any one of Claims 1 to 6 and an electron source that emits electrons with which the target structure is irradiated; and
a driving unit that controls the radiation source.
[8] A radiography system comprising:
the radiation generator according to Claim 7;
a radiation detector that detects radiation that has been emitted by the radiation generator and has passed through a radiographic object; and
a controller that controls the radiation generator and the radiation detector in a cooperative manner.
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JP2012022976A JP5911323B2 (en) | 2012-02-06 | 2012-02-06 | Target structure, radiation generating apparatus including the target structure, and radiation imaging system |
JP2012-022976 | 2012-02-06 |
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WO2013118593A1 true WO2013118593A1 (en) | 2013-08-15 |
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