JP3869319B2 - X-ray tube target and method of manufacturing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray tube target (also referred to as an anti-cathode or an anode) for generating characteristic X-rays of lanthanoids, and to a manufacturing method thereof.
[0002]
[Prior art]
In X-ray transmission devices and X-ray interferometers, it may be preferable to set the wavelength of X-rays used (that is, X-ray energy) within a specific numerical range. In this case, when radiation light is used as an X-ray source, X-rays having an arbitrary wavelength can be extracted with sufficient intensity, so that a desired wavelength can be used. However, in an laboratory or the like, if an X-ray tube is used to extract X-rays with practical intensity, only characteristic X-rays determined by the material of the target of the X-ray tube can be used, and the wavelength is limited. In order to use X-rays having a desired wavelength, it is necessary to select a target material having such characteristic X-rays.
[0003]
In an X-ray transmission device or an X-ray interferometer for medical use or living organisms (for example, fossils), a clear image may be obtained if X-ray energy in the range of 25 to 50 keV is used. It is difficult to obtain X-rays in such an energy range with practical intensity using an X-ray tube. For example, when copper is used as the target material, the energy of the characteristic X-ray (Kα ray) is 8.0 keV. The energy of the characteristic X-ray depends on the atomic number of the target material. If the atomic number increases, the energy of the characteristic X-ray increases. Therefore, when trying to extract X-rays having energy larger than that of copper, it is necessary to use a target material having an atomic number larger than that of copper. For example, the characteristic X-ray energy of molybdenum is 17.5 keV, silver is 22.2 keV, and tungsten is 59.0 keV. As described above, the characteristic X-ray of the target material that is normally used is either smaller or larger than the above-mentioned range of 25 to 50 keV. Lanthanoids are elements having atomic numbers of 57 to 71, and the energy of characteristic X-rays (Kα rays) of these elements is in the range of 33.4 to 54.1 keV. Therefore, if a lanthanide can be used as a target material for an X-ray tube, X-rays having an energy in the range of 25 to 50 keV can be obtained at a laboratory level.
[0004]
The use of rare earth elements as a target material is known, and there are the following known examples. Japanese Patent Application Laid-Open No. 2001-202910 discloses an X-ray tube using a rare earth target. This X-ray tube is for generating characteristic X-rays of rare earth elements. Specifically, the surface layer of gadolinium (Gd) or dysprosium (Dy) is anoded via an intermediate layer (Ti or Mo). It is formed on the body (Cu or Ag).
[0005]
[Problems to be solved by the invention]
As described above, there exist some that use rare earth elements as target materials as they are, but it is difficult to obtain practically sufficient X-ray intensity using lanthanoids as target materials as they are. Lanthanoids, for example, have a much lower thermal conductivity and a lower melting point than copper. For example, when an electron beam hits a lanthanoid, the generated heat does not escape well, and the electron beam irradiation region dissolves. Resulting in. Therefore, a sufficient load cannot be applied to the X-ray tube (a sufficient power can be input). The X-ray tube disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2001-202910 is also considered difficult to extract X-rays with sufficient intensity.
[0006]
When lanthanoids are borides, the melting point is very high and the thermal conductivity is better than that of a single substance. Therefore, borides are considered to be more suitable for the target material. By using boride, the allowable load increases about three times. It is also known to use a lanthanoid boride as a target material, and there are the following known examples. U.S. Pat. No. 3,934,164 discloses a target made of a rare earth element boride for an X-ray tube of an X-ray diagnostic imaging apparatus. Thereby, characteristic X-rays of rare earth elements are generated. Specifically, a rod-shaped cerium hexaboride (CeB ₆ ) chip is embedded in the groove of the anode disk, and a large number of these chips are arranged side by side to be a target. The above-mentioned Japanese Patent Application Laid-Open No. 2001-202910 also mentions that lanthanum hexaboride (LaB ₆ ) is used as the material of the secondary X-ray target.
[0007]
However, even if a lanthanoid is a boride, its thermal conductivity is an order of magnitude smaller than that of copper, and a sufficient X-ray intensity cannot be obtained. This point has been confirmed by the inventors through experiments, and will be described below. Lanthanum hexaboride (LaB ₆ ) was formed on the target surface by vapor deposition and sputtering to obtain a lanthanum hexaboride thin film having a thickness of 10 μm. This was irradiated with an electron beam and subjected to a load test. However, X-rays with sufficient intensity could not be obtained stably. As another method, a lanthanum hexaboride sintered compact (with a density of 85%) is bonded (brazed) to a copper target surface and irradiated with an electron beam to perform a load test. It was. The thickness of the flakes was successively reduced from 1 mm to 0.1 mm, and a load test was performed. However, X-rays with sufficient intensity could not be obtained stably. That is, when the tube voltage / tube current is about 30 kV-10 mA, the surface becomes so rough that a high load cannot be applied. The cause is that the heat conductivity of lanthanum hexaboride is small, so that the heat escape does not go well, and the electron beam irradiation surface becomes rough or discharge occurs.
[0008]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a practical X-ray tube target capable of generating characteristic X-rays of lanthanoids with sufficient strength and a method for manufacturing the target. It is to provide.
[0009]
[Means for Solving the Problems]
The target of the X-ray tube of the present invention is characterized in that a lanthanoid boride or carbide sintered body infiltrated with copper is used as an X-ray generating material. By making the lanthanoid boride or carbide, the melting point is remarkably higher than that of the lanthanoid alone, so that the X-ray generating material does not dissolve when irradiated with an electron beam. Furthermore, heat conductivity can be improved by making such a boride or carbide into a sintered body and infiltrating copper into the voids. As a result, heat easily escapes from the X-ray generating material, and surface roughening and melting due to overheating can be prevented.
[0010]
Lanthanoid is a general term for elements of the lanthanum series, and 15 types of elements having atomic numbers 57 to 71, that is, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are pointed out. The energy of characteristic X-rays (Kα rays) of these lanthanoids is 33.4 to 54.1 keV. Therefore, X-rays generated from an X-ray generating material containing a lanthanoid include characteristic X-rays in such an energy range, and can be used, for example, as a target for medical or biological X-ray tubes. When the target of the present invention is used, substances other than lanthanoids (boron, carbon, copper) are also present in the electron beam irradiation region, and characteristic X-rays are also generated from these substances. It can be removed using a monochromator or filter.
[0011]
The following are known as lanthanoid borides, and in principle, any of these can be used in the present invention. _{LaB 4, LaB 6, CeB 4} , CeB 6, PrB 4, PrB 6, NdB 4, NdB 6, NdB 66, SmB 2, SmB 4, SmB 6, SmB 66, EuB 6, GdB 2, GdB 4, GdB 6 _{, GdB 12, GdB 66, TbB} 2, TbB 4, TbB 6, TbB 12, TbB 66, DyB 2, DyB 4, DyB 6, DyB 12, DyB 66, HoB 2, HoB 4, HoB 6, HoB 12, HoB _{66, ErB 2, ErB 4,} ErB 12, ErB 66, TmB 2, TmB 4, TmB 12, TmB 66, YbB 2, YbB 4, YbB 6, YbB 12, YbB 66, LuB 2, LuB 4, LuB 12, LuB ₆₆ .
[0012]
Further, the following are known as lanthanoid carbides, and in principle, any of these can be used in the present invention. LaC ₂ , La ₂ C ₃ , La ₂ C, La ₃ C, La ₁₅ C ₁₉ , CeC ₂ , Ce ₂ C ₃ , PrC ₂ , Pr ₂ C ₃ , NdC ₂ , Nd ₂ C ₃ , Sm ₂ C ₃ , _{EuC 2, EuC 6, GdC 2} , DyC 2, HoC 2, Ho 2 C 3, ErC 2, YbC 6, LuC 2.
[0013]
And lanthanum hexaboride (LaB ₆ ) and cerium hexaboride (CeB ₆ ) are the most suitable because they are easily available and easy to handle.
[0014]
If a sintered body of a lanthanoid boride or carbide is infiltrated into the void with a metal having a higher thermal conductivity than the sintered body, the overall thermal conductivity is improved. Therefore, any metal having such a thermal conductivity is effective as it is infiltrated. However, in consideration of thermal conductivity, melting point, price, etc., it is optimal to infiltrate copper practically. If the metal has a low melting point, it will be melted by the heat when it is irradiated with an electron beam. If the melting point is too high, it will be necessary to heat the sintered body to a considerably high temperature. This makes it difficult to select the capsule material to be described later. Considering these points, copper is optimal.
[0015]
The target of the present invention can be manufactured using the following steps. (A) A step of forming a void in the copper block. (B) A step of disposing a lanthanoid boride or carbide sintered body in the space. (C) The process of accommodating the said copper block inside the capsule which consists of material with melting | fusing point higher than copper. (D) A step of infiltrating copper into the sintered body by heating the capsule to a temperature equal to or higher than the melting point of copper in a pressurized atmosphere to dissolve the copper block. (E) A step of cutting out a thin piece from the sintered body infiltrated with copper. (F) A step of bonding the thin piece to a target of an X-ray tube.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 to FIG. 5 are diagrams illustrating each process for manufacturing one embodiment of the target of the present invention. This embodiment is an example in which a lanthanum hexaboride sintered body infiltrated with copper is used as an X-ray generating material.
[0017]
FIG. 1 is a perspective view showing a state in which a sintered body of lanthanum hexaboride is inserted into a copper block. First, the sintered body 10 of lanthanum hexaboride is formed in a cylindrical shape having a diameter of 6 mm and a length of 12 mm. This sintered body 10 is obtained by pressing lanthanum hexaboride powder to a density of 60% and sintering in vacuum at 1600 ° C. Here, the density of the sintered body is a percentage of the density of the sintered body relative to the density of the lanthanum hexaboride crystal (mass per unit volume). Next, a cylindrical space 14 is formed in the copper cylindrical block 12. The inner diameter of the void 14 is slightly larger than the diameter of the sintered body 10. The sintered body 10 is inserted into the void 14, and a copper plug 16 is filled on the sintered body 10 to cover it. As a result, the sintered body 10 is completely surrounded by the copper block 12.
[0018]
FIG. 2 is a front sectional view showing a state in which the copper block is accommodated in the capsule. Capsule 18 is made of stainless steel, which has a higher melting point than copper. The capsule 18 includes a circular lower plate 20 and an upper plate 22 and a cylindrical side wall 24. First, the lower plate 20 and the side wall 24 are welded at the outer peripheral portion 21 of the lower plate 20 to make a capsule with the upper end opened. Next, the copper block 12 containing the sintered body 10 is accommodated therein. Next, the upper plate 22 is welded to the upper end of the side wall 24 at the outer peripheral portion 23. As a result, the copper block 12 is sealed in the capsule 18. An exhaust port 26 is provided in the upper plate 22 of the capsule 18. The inside of the capsule 18 is evacuated by exhausting from the exhaust port 26 in the direction of the arrow 28, and air is expelled from the minute voids inside the sintered body 10. When exhausting is completed, the exhaust port 26 is sealed off at the cutting point 30. This completes the capsule 18 containing the copper block 12.
[0019]
FIG. 3 is a front sectional view showing a state in which the capsule 18 is heated by a HIP (Hot Isostatic Pressing) apparatus. The internal space of the HIP device is surrounded by an upper lid 32, a lower lid 34, and a high-pressure cylinder 36. The high pressure cylinder 36 is cooled by cooling water 37. On the lower lid 34, there is a processing object table 38 on which the above-described capsule 18 is placed. A heater 40 and a heat insulating layer 42 are disposed around the capsule 18. Argon gas 45 is supplied from the gas inlet / outlet 44 of the upper lid 32 to pressurize the interior of the HIP apparatus to about 900 atm. The upper lid 32 and the lower lid 34 are supported by press frames from above and below, and can withstand such high pressure. The capsule 18 is heated to 1100 ° C. using the heater 40. At this temperature, the copper in the capsule 18 is completely dissolved (the melting point of copper is 1083 ° C.). And since the high pressure is acting on the capsule 18, the melt | dissolved copper is pushed in in the space | gap of a sintered compact. Then, it cools to room temperature and takes out the capsule 18 from a HIP apparatus.
[0020]
FIG. 4 is a cross-sectional view of the capsule 18 that has been HIP processed by the HIP apparatus as described above, cut along a cross section perpendicular to the axial direction thereof. Inside the capsule 18 is solidified copper 44, and inside is a lanthanum hexaboride sintered body 10 infiltrated with copper. The sintered body 10 is cut out by cutting lines 46 and 48 to form thin pieces having a thickness of 0.1 to 0.5 mm. Thus, when it cuts out by the cutting lines 46 and 48 near the center, and it processes to the size of 12 mm x 6 mm, the whole is the thin piece 50 which consists of "the lanthanum hexaboride sintered compact in which copper was infiltrated" (FIG. 5). Is obtained). Further, in FIG. 4, after cutting along the cutting lines 52 and 54 close to the outer periphery of the cylindrical sintered body 10 and processing this into a size of 12 mm × 6 mm, as shown in FIG. A thin piece 60 composed of the infiltrated lanthanum hexaboride sintered body 56 and copper 58 on both sides is obtained. The thin piece 60 made of copper 58 on both sides is superior to the thin piece 50 made entirely of sintered body in terms of heat escape. When the focal spot size on the target is, for example, 10 mm × 1 mm, an electron beam is applied only to the sintered body 56 even in the thin piece 60 in which only the central width, for example, 2 to 3 mm is a sintered body. it can.
[0021]
By the way, even if copper is infiltrated, the lanthanum hexaboride sintered body is inferior in thermal conductivity to the copper block. Therefore, it is preferable to make the thin piece 50 as thin as possible from the viewpoint of thermal conduction. However, in consideration of the accuracy of the cutting operation of the thin piece 50 and the life as the X-ray generating material, the thickness of the thin piece 50 is limited to about 0.1 mm. Practically, it is preferably about 0.1 to 0.5 mm as described above. If it is thicker than this, the heat will not escape well and the surface of the lanthanum hexaboride will become rough.
[0022]
FIG. 5 is a perspective view showing a process of joining the thin piece 50 to the target 62 of the X-ray tube. A recess 63 having a depth of 0.1 to 0.5 mm and a size of 12 mm × 6 mm is formed on the surface of the target 62. In this, the thin piece 50 produced as mentioned above is joined using a metal brazing material. This thin piece 50 becomes the X-ray generating material on the target 62. Further, when the thin piece 60 whose center is a sintered body is joined, the central portion of the lanthanum hexaboride sintered body 56 in the thin piece 60 becomes the X-ray generating material.
[0023]
FIG. 6 is a cross-sectional view of the vicinity of the target of the X-ray tube 65 including the target 62 to which the thin piece 50 is bonded. A separator 64 is provided inside the target 62, and cooling water 66 flows through a flow path partitioned by the separator 64, so that the target portion on the back side of the thin piece 50 is efficiently cooled. The electron beam 68 hits the thin piece 50, and X-rays 70 are generated therefrom, pass through the window 72, and come out of the X-ray tube 65. By using the target of this embodiment, it was possible to stably supply power up to a tube voltage / tube current of 58 kV-10 mA. The extracted X-ray 70 was spectrally separated by a monochromator, and a characteristic X-ray of lanthanum with sufficient intensity (Kα ray is 33.4 keV energy) was obtained. When cerium hexaboride is used instead of lanthanum hexaboride, characteristic X-rays (energy is 34.7 keV) of cerium can be obtained.
[0024]
The example of FIG. 6 is an example of a fixed target (stationary target), but the present invention can also be applied to a rotor target (rotating anti-cathode). In that case, a sintered body infiltrated with copper is disposed so as to form a band on the circumferential locus irradiated with the electron beam.
[0025]
In the above-described embodiment, copper is infiltrated into a lanthanum hexaboride sintered body having a density of 60%, but the density of the rattan hexaboride sintered body is preferably about 60 to 80%.
[0026]
【The invention's effect】
The target of the X-ray tube of the present invention uses a lanthanoid boride or carbide sintered body infiltrated with copper as an X-ray generating material, and therefore can generate characteristic X-rays of lanthanoids. In addition, a practical target having a high melting point and easy heat release can be obtained.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a state in which a sintered body of lanthanum hexaboride is inserted into a copper block.
FIG. 2 is a front sectional view showing a state in which a copper block is accommodated in a capsule.
FIG. 3 is a front sectional view showing a state in which the capsule is heated by the HIP device.
FIG. 4 is a cross-sectional view of a capsule that has been HIP-processed by an HIP device, cut along a cross section perpendicular to the axial direction thereof.
FIG. 5 is a perspective view showing a process of joining an X-ray generating material to a target of an X-ray tube.
FIG. 6 is a cross-sectional view of the vicinity of a target of an X-ray tube.
[Explanation of symbols]
10 Sintered body 12 Copper block 14 Void 18 Capsule 50 Sintered flake 62 Target 63 Recess 65 X-ray tube 68 Electron beam 70 X-ray 72 Window

Claims (4)

A target for an X-ray tube, wherein a lanthanoid boride or carbide sintered body infiltrated with copper is used as an X-ray generating material. 2. The X-ray tube target according to claim 1, wherein the sintered body is lanthanum hexaboride. The X-ray tube target according to claim 1, wherein the sintered body is cerium hexaboride. An X-ray tube target manufacturing method comprising the following steps.
(A) A step of forming a void in the copper block.
(B) A step of disposing a lanthanoid boride or carbide sintered body in the space.
(C) The process of accommodating the said copper block inside the capsule which consists of material with melting | fusing point higher than copper.
(D) A step of infiltrating copper into the sintered body by heating the capsule to a temperature equal to or higher than the melting point of copper in a pressurized atmosphere to dissolve the copper block.
(E) A step of cutting out a thin piece from the sintered body infiltrated with copper.
(F) A step of bonding the thin piece to a target of an X-ray tube.

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