X-ray tube

Abstract

To provide an X-ray tube capable of improving an effect of preventing corrosion of an output window by a protective film, and suppressing attenuation of an X-ray.SOLUTION: An X-ray tube 12 includes a protective film 33 provided on an outer surface side of an output window 28. The protective film 33 contains silicon in diamond-like carbon. The ratio of silicon in the diamond-like carbon is 5 to 6% in mass ratio. A film thickness in a peripheral region 28b of the output window 28 outside a central region 28a of the output window 28 facing an opening part 25 of a vacuum envelope 22 is thicker than a film thickness in the central region 28a of the output window 28, the film thickness in the central region 28a of the output window 28 is 0.3 to 0.6 μm, and the film thickness in the peripheral region 28b of the output window 28 is 0.6 to 1.2 μm, in a film thickness distribution.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an X-ray tube that outputs X-rays.

Background Art

[0002] Conventionally, for example, there is an X-ray tube used for material analysis. The vacuum envelope of this X-ray tube has a tip diameter that gradually narrows and a tip surface that is flat. An opening is formed in the flat tip surface, and an output window that closes this opening and transmits X-rays is provided. For example, beryllium is used as a material for the output window with little X-ray attenuation, and furthermore, the thickness of the beryllium of the output window is as thin as several tens to several hundreds of μm in order to reduce X-ray attenuation.

[0003] The peripheral edge of the opening of the vacuum envelope is composed of a stainless steel component with a thermal expansion coefficient close to that of beryllium, which is the material of the output window, and has good joinability. The output window is joined to this stainless steel component with a brazing material, and the structure maintains the vacuum tightness of the vacuum envelope. Since the stainless steel component has a large X-ray attenuation, the opening of the vacuum envelope is made as large as possible so that more X-rays can be extracted.

[0004] When using the X-ray tube, in order to bring the outer surface of the output window close to the sample, corrosive substances contained in the sample fly onto the outer surface of the output window, or the outer surface of the output window is exposed to corrosive gases. When the X-ray tube is used in such an environment, the outer surface of the output window corrodes, and if the output window is thin, holes will open early, and it will be impossible to maintain the vacuum tightness of the vacuum envelope. For this reason, a protective film is provided on the outer surface of the output window.

[0005] For the protective film, a low-element material such as diamond-like carbon is selected in order to suppress X-ray attenuation, and furthermore, it is desirable to suppress X-ray attenuation from the output window.

[0006] After the output window is joined to the output window mounting part of the vacuum enclosure by a brazing material, a compressive force acts on the output window in the central direction due to the difference in thermal expansion between the beryllium of the output window and the stainless steel of the output window mounting part. This thermal stress strongly exists in the peripheral part of the output window. When corrosive substances contained in the sample fly onto the output window or the output window is exposed to a corrosive gas, stress corrosion cracking is likely to occur in the peripheral part of the output window where the thermal stress remains. Therefore, it is desired to improve the corrosion prevention effect of the output window by a protective film.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] The problem to be solved by the present invention is to provide an X-ray tube capable of improving the corrosion prevention effect of the output window by a protective film and suppressing the attenuation of X-rays.

Means for Solving the Problems

[0009] The X-ray tube of this embodiment includes a vacuum envelope body provided with an opening and an output window mounting portion around the opening, a vacuum envelope having an X-ray output window with a peripheral portion attached to the output window mounting portion to close the opening, an anode target disposed at a position facing the output window within the vacuum envelope, a cathode filament disposed within the vacuum envelope to emit electrons toward the anode target, and a protective film provided on the outer surface side of the output window. The protective film contains silicon in diamond-like carbon, the ratio of silicon in the diamond-like carbon is 5 to 6% by mass ratio, the film thickness in the peripheral region of the output window, which is outside the central region of the output window facing the opening of the vacuum envelope, is thicker than the film thickness in the central region of the output window, and the film thickness in the central region of the output window is 0.3 to 0.6 μm, and the film thickness in the peripheral region of the output window is 0.6 to 1.2 μm, and it is provided with such a film thickness distribution.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] Hereinafter, one embodiment will be described with reference to the drawings.

[0012] FIG. 2 shows an X-ray tube device 10 used for material analysis and the like.

[0013] The X-ray tube device 10 includes a cylindrical tube container 11, an X-ray tube 12 provided at one end of the tube container 11, a high-voltage receptacle 13 provided at the other end of the tube container 11 to which a high-voltage cable is connected, a connection portion 14 that electrically connects the X-ray tube 12 and the high-voltage receptacle 13, a cooling pipe 15 disposed within the tube container 11 through which a coolant circulates, and the like.

[0014] FIG. 1 shows a part of the X-ray tube 12. Note that the X-ray tube 12 shown in FIG. 1 is illustrated with the top and bottom reversed with respect to the X-ray tube 12 shown in FIG. 2.

[0015] The X-ray tube 12 includes a vacuum envelope 22. The vacuum envelope 22 has a cylindrical portion 22a, and an inclined portion 23 with a gradually decreasing diameter is formed on the tip side of the cylindrical portion 22a, and a flat portion 24 is formed on the tip surface. A circular opening 25 is formed in the flat portion 24, and an annular output window mounting portion 26 is formed on the peripheral edge of the opening 25. An annular mounting groove 27 is provided on the outer surface side of the vacuum envelope 22 in the output window mounting portion 26. At least the output window mounting portion 26 of the vacuum envelope 22 is formed of, for example, stainless steel as the material.

[0016] An output window 28 for outputting X-rays is attached to the output window mounting portion 26 of the vacuum envelope 22 so as to close the opening 25. This output window 28 is made of, for example, beryllium, which is a material with little X-ray attenuation. Further, in order to reduce the attenuation of X-rays, the thickness of beryllium is as thin as several tens to several hundreds of μm.

[0017] The output window 28 is provided in a disk shape, and the peripheral portion is arranged in the mounting groove 27 from the outer surface side of the output window mounting portion 26 and joined by a brazing material, closing the opening 25 and maintaining the vacuum tightness of the vacuum envelope 22.

[0018] Also, inside the vacuum envelope 22, an anode target 29 is arranged facing the inner surface of the output window 28, a focusing electrode (not shown) is arranged on the outer surface of the anode target 29, and a cathode filament 30 is arranged outside the focusing electrode. Then, the electrons 31 emitted from the cathode filament 30 are irradiated onto the anode target 29, and the X-rays 32 emitted from the anode target 29 pass through the output window 28 and are output to the outside.

[0019] On the outer surface side of the output window 28 on the atmosphere side, a protective film 33 for protecting the output window 28 is formed by, for example, a vapor deposition method. The protective film 33 prevents corrosion of the output window 28 even when corrosive substances scatter on the outer surface of the output window 28 or the outer surface of the output window 28 is exposed to corrosive gases during analysis using the X-ray tube 12. The protective film 33 is formed from the output window 28 across the outer surface of the vacuum enclosure 22 around the output window 28.

[0020] The protective film 33 mainly uses diamond-like carbon and contains silicon in the diamond-like carbon for the purpose of improving heat resistance. By setting the ratio of silicon in the diamond-like carbon to 5 to 6% by weight, it is possible to have the function of improving heat resistance and suppressing the attenuation of the X-ray 32.

[0021] In the manufacturing process of the X-ray tube 12, there is a degassing process for increasing the degree of vacuum inside the vacuum enclosure 22. In this degassing process, the X-ray tube 12 is exposed to an atmosphere at a high temperature of, for example, about 500°C. In this high-temperature atmosphere, diamond-like carbon deteriorates by combining with oxygen, and there is a risk that the protective film 33 peels off from the output window 28. Therefore, in order to prevent deterioration of the protective film 33 in a high-temperature atmosphere, silicon (Si) is contained in the diamond-like carbon, and the heat resistance is improved.

[0022] If the content of this silicon is increased, the heat resistance of diamond-like carbon is improved. However, since silicon has a larger atomic number than beryllium or carbon, if the content of silicon is increased too much, the attenuation of the X-ray 32 becomes large, and impurity lines are likely to occur when the X-ray 32 passes through the protective film 33.

[0023] From these facts, by setting the ratio of silicon in the diamond-like carbon to 5 to 6% by mass, it is possible to optimize the balance between improving heat resistance and suppressing X-ray attenuation.

[0024] Furthermore, the protective film 33 includes a central protective film portion 33a provided for the central region 28a of the output window 28 facing the opening 25 of the vacuum vessel 22, and a peripheral protective film portion 33b provided for the peripheral region 28b of the output window 28 which is outside (peripheral side) of the central region 28a of the output window 28. The film thickness of the peripheral protective film portion 33b of the protective film 33 is thicker than the film thickness of the central protective film portion 33a of the protective film 33, and the film thickness of the central protective film portion 33a of the protective film 33 is 0.3 to 0.6 μm, and the film thickness of the peripheral protective film portion 33b of the protective film 33 is provided in a film thickness distribution of 0.6 to 1.2 μm. The central region 28a of the output window 28 where the central protective film portion 33a is provided is a non-bonding region inside the bonding region where the output window 28 and the vacuum vessel 22 are bonded and is an X-ray transmission region, and the peripheral region 28b of the output window 28 where the peripheral protective film portion 33b is provided is a bonding region where the output window 28 and the vacuum vessel 22 are bonded and is a non-X-ray transmission region.

[0025] If the film thickness of the central protective film portion 33a of the protective film 33 in the central region 28a of the output window 28 is less than 0.3 μm, the protective film 33 is likely to peel off from the output window 28 (for example, due to deterioration of the protective film 33 in a high-temperature atmosphere). On the other hand, if it is greater than 0.6 μm, the attenuation of the X-ray 32 increases.

[0026] If the film thickness of the peripheral protective film portion 33b of the protective film 33 in the peripheral region 28b of the output window 28 is less than 0.6 μm, the stress corrosion cracking prevention effect is small. Therefore, in order to enhance the stress corrosion cracking prevention effect, a thicker film is preferable. However, considering the productivity of the film formation process, etc., 1.2 μm, which is at most about twice the film thickness of the central protective film portion 33a of the protective film 33 in the central region 28a of the output window 28, is preferable.

[0027] When the output window 28 and the output window mounting portion 26 are joined by a brazing material during the manufacture of the vacuum enclosure 22, the temperatures of the output window 28 and the output window mounting portion 26 increase. At this time, due to the difference in thermal expansion between the beryllium of the output window 28 and the stainless steel of the output window mounting portion 26, the output window mounting portion 26 is joined in a state where it expands more than the output window 28. When the greatly expanded output window mounting portion 26 is cooled and shrinks after joining, a thermal stress that compresses in the central direction acts on the output window 28. This thermal stress strongly exists in the peripheral portion of the output window 28 fixed to the output window mounting portion 26.

[0028] When using the X-ray tube 12 without the protective film 33 in an environment where corrosive substances contained in the sample fly to the output window 28 or the output window 28 is exposed to a corrosive gas, stress corrosion cracking is highly likely to occur in the peripheral portion of the output window 28 outside the opening 25 where the thermal stress of the output window 28 remains, and it is known that the probability of stress corrosion cracking occurring in the central portion of the output window 28 inside the opening 25 where the thermal stress is negligible is small.

[0029] Therefore, by providing the protective film 33 on the outer surface side of the output window 28, the ratio of silicon in the diamond-like carbon of the protective film 33 being 5 to 6% by mass ratio, forming the film thickness of the peripheral protective film portion 33b of the protective film 33 in the peripheral region 28b of the output window 28 outside the opening 25 of the vacuum enclosure 22 thicker than the film thickness of the central protective film portion 33a of the protective film 33 in the central region 28a of the output window 28 facing the opening 25 of the vacuum enclosure 22, setting the film thickness of the central protective film portion 33a of the protective film 33 in the central region 28a of the output window 28 to be 0.3 to 0.6 μm, and the film thickness of the peripheral protective film portion 33b of the protective film 33 in the peripheral region 28b of the output window 28 to be 0.6 to 1.2 μm, the peripheral portion of the output window 28 where stress corrosion cracking is likely to occur and the joint portion with the output window mounting portion 26 are blocked from the corrosive atmosphere, the occurrence of stress corrosion cracking of the output window 28 can be prevented, and since the thickness of the central protective film portion 33a of the protective film 33 in the central region 28a of the output window 28 facing the opening 25 is thin, a decrease in the X-ray dose output can be suppressed.

[0030] Thus, according to the X-ray tube 12 of the present embodiment, it is possible to improve the corrosion prevention effect of the output window 28 by the protective film 33 and suppress the attenuation of the X-ray dose.

[0031] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0032] 12 X-ray tube 22 Vacuum enclosure 25 Opening 26 Output window mounting portion 28 Output window 28a Central region 28b Peripheral region 29 Anode target 30 Cathode filament 31 Electron 32 X-ray 33 Protective film

Claims

【Claim 1】 A vacuum envelope body provided with an opening and an output window mounting portion around the opening, and a vacuum envelope having an X-ray output window with a peripheral portion attached to the output window mounting portion to close the opening, An anode target disposed at a position facing the output window within the vacuum envelope, A cathode filament disposed within the vacuum envelope for emitting electrons to the anode target, A protective film provided on the outer surface side of the output window, Comprising, The protective film, Contains silicon in diamond-like carbon, and the ratio of the silicon in the diamond-like carbon is 5 to 6% by mass ratio, The film thickness in the peripheral region of the output window, which is outside the central region of the output window facing the opening of the vacuum envelope, is thicker than the film thickness in the central region of the output window, and the film thickness in the central region of the output window is 0.3 to 0.6 μm, and the film thickness in the peripheral region of the output window is 0.6 to 1.2 μm. It is provided with a film thickness distribution, An X-ray tube characterized by this.

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