X-ray tube

Abstract

The X-ray tube includes: a housing; the electron gun emits electron beams in the box body; and a target that generates X-rays by the incidence of the electron beam within the housing. The electron gun includes: a cathode emitting electrons; and a focusing electrode that focuses the electrons as electron beams on the target. The focusing electrode has a cylindrical shape having an inner surface and an outer surface. The inner surface has a first region and a second region located on the target side with respect to the first region. The average roughness of the second region is smaller than the average roughness of the first region.

Description

Technical Field

[0001] The present invention relates to X-ray tubes. Background Art

[0002] An X-ray tube is known, which includes: a housing; an electron gun that emits an electron beam in the housing; and a target that generates X-rays in the housing by the incidence of the electron beam, wherein the electron gun has a cathode that emits electrons and a focusing electrode that focuses the electrons as an electron beam on the target (for example, refer to Patent Document 1). Prior art literature Patent Literature

[0003] Patent Document 1: Japanese Patent No. 6619916 Summary of the invention Problems to be solved by the invention

[0004] In the above-mentioned X-ray tube, a negative high voltage may be applied to the cathode and the focusing electrode respectively with reference to the target. In such a case, it is extremely important to ensure sufficient withstand voltage characteristics in the X-ray tube in order to achieve stability in the operation of the X-ray tube.

[0005] An object of the present invention is to provide an X-ray tube capable of ensuring sufficient withstand voltage characteristics. Methods used to solve problems

[0006] An X-ray tube according to one aspect of the present invention is [1] "an X-ray tube comprising: a housing; an electron gun for emitting an electron beam in the housing; and a target for generating X-rays in the housing by the incidence of the electron beam, the electron gun comprising: a cathode for emitting electrons; and a focusing electrode for focusing the electrons as the electron beam on the target, the focusing electrode being in the shape of a tube having an inner surface and an outer surface, the inner surface having a first region and a second region located on the target side relative to the first region, the average roughness of the second region being smaller than the average roughness of the first region."

[0007] In the X-ray tube described in [1] above, the average roughness of the second region located on the target side relative to the first region on the inner surface of the cylindrical focusing electrode is smaller than the average roughness of the first region located on the opposite side of the target relative to the second region. Therefore, even when a negative high voltage is applied to the cathode and the focusing electrode with respect to the target as a reference, leakage current generated at the inner surface of the focusing electrode is unlikely to occur. In addition, the average roughness of the first region located on the cathode side relative to the second region on the inner surface of the cylindrical focusing electrode is larger than the average roughness of the second region located on the opposite side of the cathode relative to the first region. Therefore, even when cathode material is emitted from the cathode, the cathode material is easily captured in the first region, so leakage current generated at the cathode material attached to the inner surface of the housing is unlikely to occur. According to the above description, the X-ray tube described in [1] above can ensure sufficient withstand voltage characteristics.

[0008] The X-ray tube according to one aspect of the present invention may also be [2] "the X-ray tube described in [1], wherein the inner surface has an inner bottom surface facing the target side, and the inner bottom surface is the first region". With the X-ray tube described in [2], the cathode material is easily captured on the inner bottom surface, so that the generation of leakage current generated by the cathode material attached to the inner surface of the housing can be reliably suppressed.

[0009] An X-ray tube according to one aspect of the present invention may be [3] "the X-ray tube described in [2], wherein the inner surface further comprises an inner side surface, the first side surface of the inner side surface including the end portion on the cathode side is the first region, and the second side surface of the inner side surface including the end portion on the target side is the second region". By adopting the X-ray tube described in [3], it is possible to more reliably suppress the generation of leakage current generated at the inner surface of the focusing electrode and the generation of leakage current generated at the cathode material attached to the inner surface of the housing, etc.

[0010] The X-ray tube according to one aspect of the present invention may also be [4] "the X-ray tube described in [3], wherein the average roughness of the second side surface is greater than or equal to 0.4 μm and less than or equal to 1.0 μm, and the average roughness of the inner bottom surface is greater than or equal to 1.0 μm and less than or equal to 3.2 μm". By using the X-ray tube described in [4], it is possible to appropriately realize the second side surface that is less likely to generate leakage current and the inner bottom surface on which the cathode material is easily captured.

[0011] The X-ray tube according to one aspect of the present invention may be [5] "the X-ray tube described in [4], wherein the average roughness of the first side surface is greater than or equal to 1.0 μm and less than or equal to 1.6 μm". By using the X-ray tube described in [5], it is possible to appropriately realize the first side surface on which the cathode material can be easily captured.

[0012] The X-ray tube according to one aspect of the present invention may be [6] "the X-ray tube described in any one of [3] to [5], wherein the average roughness of the outer surface is smaller than the average roughness of the second side surface". By using the X-ray tube described in [6], leakage current is less likely to be generated at the outer surface of the focusing electrode, so that sufficient withstand voltage characteristics can be more reliably ensured.

[0013] The X-ray tube according to one aspect of the present invention may be [7] "the X-ray tube described in [6], wherein the average roughness of the outer surface is greater than or equal to 0.05 μm and less than or equal to 0.4 μm". By adopting the X-ray tube described in [7], it is possible to appropriately realize an outer surface that is less likely to generate leakage current.

[0014] The X-ray tube according to one aspect of the present invention may also be [8] "the X-ray tube described in [6] or [7], wherein the outer surface has a third region and a fourth region located on the target side relative to the third region, and the average roughness of the fourth region is smaller than the average roughness of the third region". By using the X-ray tube described in [8], the generation of leakage current at the outer surface of the focusing electrode as the generation location can be reliably suppressed.

[0015] The X-ray tube according to one aspect of the present invention may also be [9] "the X-ray tube described in [8], wherein the fourth region is a circular region including the end of the outer surface on the target side". By adopting the X-ray tube described in [9], the generation of leakage current at the outer surface of the focusing electrode as the generation location can be more reliably suppressed.

[0016] The X-ray tube according to one aspect of the present invention may be

[10] "the X-ray tube described in [8] or [9], wherein the focusing electrode further comprises an outer bottom surface facing the opposite side of the target, and the average roughness of the outer bottom surface is greater than the average roughness of the fourth region". By adopting the X-ray tube described in

[10] , the cathode material can also be easily captured on the outer bottom surface, so that the generation of leakage current generated by the cathode material attached to the inner surface of the housing can be more reliably suppressed. Effects of the Invention

[0017] According to the present invention, it is possible to provide an X-ray tube capable of ensuring sufficient withstand voltage characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a cross-sectional view of an X-ray generating device including an X-ray tube according to an embodiment. Figure 2 yes Figure 1 A cross-sectional view of an X-ray tube is shown. Figure 3 yes Figure 2 A cross-sectional view of the second gate electrode shown. Figure 4 is a cross-sectional view of a gate electrode according to a modification example. DETAILED DESCRIPTION

[0019] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same reference numerals are given to the same or corresponding parts in each figure, and repeated description is omitted. [Structure of X-ray generator]

[0020] like Figure 1 As shown, the X-ray generating device 10 includes an X-ray tube 1, a holding portion 11, a power supply portion 12, and a power supply portion 13. The X-ray generating device 10 is, for example, a micro-focus X-ray source used for X-ray non-destructive inspection.

[0021] The holding part 11 holds the X-ray tube 1. The holding part 11 is formed into a cylindrical shape by metal. The X-ray tube 1 is installed in a liquid-tight manner at one end 111 of the holding part 11. More specifically, the head 21 in the housing 2 of the X-ray tube 1 is installed in a liquid-tight manner at one end 111 in a state where the head 21 in the housing 2 of the X-ray tube 1 is arranged inside the opening 111a of the one end 111 and the tube body 22 in the housing 2 of the X-ray tube 1 is arranged inside the holding part 11. The power supply part 12 is installed in a liquid-tight manner at the other end 112 of the holding part 11. Insulating oil is sealed inside the holding part 11.

[0022] The power supply unit 12 generates a high voltage for applying to the X-ray tube 1. The power supply unit 12 includes a power supply box 121, an insulating block 122, and a booster unit 123. The power supply box 121 accommodates the insulating block 122 and the booster unit 123. The power supply box 121 is formed into a box shape by metal. The booster unit 123 is buried in the insulating block 122. The insulating block 122 is formed into a block shape by an insulating material such as epoxy resin. The booster unit 123 boosts the voltage introduced from the outside of the X-ray generating device 10 to generate a high voltage.

[0023] The power supply unit 13 supplies power from the power supply unit 12 to the X-ray tube 1. The power supply unit 13 has a plurality of wirings. The power supply unit 13 extends from the voltage booster 123 to the X-ray tube 1 via the opening 121a of the power supply box 121 and the opening 112a of the other end 112 of the holding unit 11. One end 13a of the power supply unit 13 is electrically connected to the X-ray tube 1. The other end 13b of the power supply unit 13 is electrically connected to the voltage booster 123. [Structure of X-ray tube]

[0024] like Figure 2As shown, the X-ray tube 1 includes a housing 2, an electron gun 3, and a target 4. In the present embodiment, the X-ray tube 1 is configured as a sealed transmission type X-ray tube that does not require replacement of parts.

[0025] The housing 2 accommodates the electron gun 3 and the target 4. The space inside the housing 2 is a space after vacuuming. The housing 2 includes a head 21, a tube 22, and a window member 23. The head 21 is formed of a metal (such as stainless steel, copper, copper alloy, iron alloy, etc.) into a cylindrical shape with the tube axis A as the center line. The tube 22 is formed of an insulating material (such as glass, ceramic, etc.) into a cylindrical shape with the tube axis A as the center line. The window member 23 is formed of an X-ray transmitting material (such as beryllium, aluminum, diamond, etc.) into a plate shape with the tube axis A as the center line.

[0026] The window member 23 is airtightly mounted on one end 211 of the head 21 in a state where the opening 211a of the one end 211 of the head 21 is blocked. One end 221 of the tube body 22 is airtightly mounted on the head 21 via a tube body flange 24 formed of a metal such as Kovar, in a state where the opening 212a of the other end 212 of the head 21 is arranged inside the tube body 22. The other end of the tube body 22 is folded inward to form an inner tube portion 222. A tube seat 27 is airtightly mounted on the end of the inner tube portion 222 via a tube body flange 25 formed of a metal such as Kovar and a tube seat flange 26. The tube seat 27 is formed of an insulating material (e.g., glass, ceramic, etc.) in a plate shape with the tube axis A as the center line.

[0027] The stem 27 is provided with a plurality of stem pins 28. The stem pins 28 penetrate the stem 27 in a state of being electrically insulated from each other and maintaining an airtight state. Figure 1 ) is electrically connected to a plurality of stem pins 28 on the inner side of the inner tube portion 222 .

[0028] The electron gun 3 emits an electron beam B in the housing 2. The electron gun 3 is disposed on a stem 27 in the housing 2. The electron gun 3 includes a heater 31, a cathode 32, a first grid electrode 33, a second grid electrode (focusing electrode) 34, and a support 35.

[0029] The heater 31 is composed of a filament that generates heat when energized. The cathode 32 emits electrons when heated by the heater 31. The first grid electrode 33 adjusts the amount of electrons emitted from the cathode 32. The heater 31, the cathode 32, and the first grid electrode 33 are electrically connected to corresponding stem pins 28, respectively.

[0030] The second grid electrode 34 focuses the electrons emitted from the cathode 32 and passing through the first grid electrode 33 on the target 4 as an electron beam B. The second grid electrode 34 also functions as an extraction electrode for forming an electric field for attracting the electrons constituting the electron beam B.

[0031] The support portion 35 is fixed to the stem flange 26 by welding, for example. The support portion 35 is formed of a conductive material (such as stainless steel) into a cylindrical shape with the stem axis A as the center line. The heater 31, the cathode 32, and the first grid electrode 33 are arranged inside the support portion 35. The second grid electrode 34 is mounted on the end of the support portion 35 on the opposite side of the stem 27. The support portion 35 is electrically connected to the corresponding stem pin 28 via the stem flange 26, and also functions as a power supply path for the second grid electrode 34.

[0032] The target 4 generates X-rays R in the housing 2 by the incidence of the electron beam B. The target 4 is arranged on the inner surface of the window member 23 on the tube axis A. In the present embodiment, the target 4 is a film formed on the inner surface of the window member 23. The target 4 is formed into a film shape by, for example, tungsten, molybdenum, copper, etc. The target 4 is electrically connected to the head 21. As an example, the target 4 and the head 21 are at ground potential.

[0033] In the X-ray tube 1 constructed as described above, the power supply unit 12 applies a negative high voltage to the electron gun 3 based on the potential of the target 4 and the head 21. As an example, the power supply unit 12 applies a negative high voltage (for example, -10 kV to -500 kV) to each part of the electron gun 3 via the power supply unit 13 and each tube base pin 28 when the target 4 and the head 21 are at ground potential. The electron beam B emitted from the electron gun 3 is focused on the target 4 along the tube axis A. The X-ray R generated in the irradiation area of ​​the electron beam B of the target 4 is transmitted through the target 4 and the window member 23 with the irradiation area as the focus and emitted to the outside. [Structure of the Second Gate Electrode]

[0034] like Figure 3 As shown, the second grid electrode 34 is formed into a cylindrical shape by a metal (such as tungsten, molybdenum, tantalum, stainless steel, etc.). In the present embodiment, the second grid electrode 34 has a side wall 37 and a bottom wall 38. The side wall 37 is formed into a cylindrical shape with the tube axis A as the center line. The bottom wall 38 is formed integrally with the side wall 37 at the end of the side wall 37 on the cathode 32 side. A recess 38a and a through hole 38b are formed in the bottom wall 38. The recess 38a opens on the target 4 side and has a cylindrical shape with the tube axis A as the center line. On the bottom surface of the recess 38a, the through hole 38b opens on the target 4 side and the cathode 32 side and has a cylindrical shape with the tube axis A as the center line. The second grid electrode 34 is configured in a manner that at least a portion of the target 4 side of the second grid electrode 34 is accommodated inside the head 21. In other words, the second grid electrode 34 is configured in a manner that at least a portion of the outer surface 52 described later is opposite to the inner surface of the head 21. Alternatively, the side wall 37 and the bottom wall 38 may be formed separately and joined to each other.

[0035] The second gate electrode 34 is in a cylindrical shape having an inner surface 51 and an outer surface 52. The inner surface 51 is a surface of the second gate electrode 34 that extends between the plane P1 and the plane P2 on the side of the center line L of the second gate electrode 34 (i.e., the inner side). The outer surface 52 is a surface of the second gate electrode 34 that extends between the plane P1 and the plane P2 on the side opposite to the center line L of the second gate electrode 34 (i.e., the outer side). The plane P1 is a plane passing through the end of the second gate electrode 34 on the target 4 side. In other words, the plane P1 is a plane including the opening on the target 4 side of the second gate electrode 34 (in this embodiment, the opening on the target 4 side of the cylindrical side wall 37). The plane P2 is a plane passing through the end of the second gate electrode 34 on the cathode 32 side. In other words, the plane P2 is a plane including the opening on the cathode 32 side of the second gate electrode 34 (in this embodiment, the opening on the cathode 32 side of the through hole 38b). In addition, in the present embodiment, the center line L of the second grid electrode 34 coincides with the tube axis A.

[0036] The inner surface 51 has an inner side surface 53. The inner side surface 53 is a surface extending along the center line L in the inner surface 51. The inner side surface 53 may also have an inclination relative to the center line L, in which case the inclination is less than 45 degrees (i.e., the taper is less than 90 degrees). In the present embodiment, the inner side surface 53 is the inner side surface of the side wall 37, and the inclination of the inner side surface is 0 degrees. The inner surface 51 further has an inner bottom surface 54 facing the target 4 side. The inner bottom surface 54 is the bottom surface of the inner surface 51 that faces the target 4, and is the bottom surface farthest from the target 4 (in other words, the bottom surface closest to the cathode 32). In the present embodiment, the inner bottom surface 54 is the bottom surface of the recess 38a.

[0037] The inner surface 51 has a first region R1 and a second region R2 located on the target 4 side relative to the first region R1. The first region R1 is a first side surface 531 including an end 53a on the cathode 32 side in the inner bottom surface 54 and the inner side surface 53. The second region R2 is a second side surface 532 including an end 53b on the target 4 side in the inner side surface 53. The outer surface 52 has a third region R3 and a fourth region R4 located on the target 4 side relative to the third region R3. The third region R3 is a surface of the outer surface 52 whose inclination relative to the center line L is less than 45 degrees (i.e., the taper is less than 90 degrees). In the present embodiment, the third region R3 is a tapered surface extending toward the target 4 side. The fourth region R4 is a circular region including the end 52a on the target 4 side of the outer surface 52. More specifically, the fourth region R4 is a circular chamfered surface extending outward from the annular end 52a to the cathode 32 side in a state of convex outward. The second gate electrode 34 further includes an outer bottom surface 55 facing the side opposite to the target 4. In the present embodiment, the outer bottom surface 55 is a surface of the bottom wall 38 of the second gate electrode 34 on the side opposite to the inner bottom surface 54.

[0038] The average roughness of the second region R2 is smaller than the average roughness of the first region R1. The average roughness of the first region R1 is greater than 1.0 μm and less than 3.2 μm. The average roughness of the second region R2 is greater than 0.4 μm and less than 1.0 μm. In more detail, the average roughness of the inner bottom surface 54 as the first region R1 is greater than 1.0 μm and less than 3.2 μm. The average roughness of the first side surface 531 as the first region R1 is greater than 1.0 μm and less than 1.6 μm. The average roughness of the second side surface 532 as the second region R2 is greater than 0.4 μm and less than 1.0 μm. The average roughness of the outer surface 52 is smaller than the average roughness of the second side surface 532. The average roughness of the outer surface 52 is greater than 0.05 μm and less than 0.4 μm. The average roughness of the fourth region R4 is smaller than the average roughness of the third region R3. The average roughness of the outer bottom surface 55 is greater than the average roughness of the fourth region R4. In addition, the average roughness refers to the arithmetic mean roughness Ra. A contact surface roughness meter, a laser microscope, a white interferometer, etc. can be used in the measurement of Ra. As an example, a contact surface roughness meter is preferably used in the measurement of Ra of the inner surface 51, and a white interferometer or a laser microscope is preferably used in the measurement of Ra of the outer surface 52. Here, the average roughness of region α is less than the average roughness of region β, which means that region α has an average roughness less than a specified value and region β has an average roughness greater than the specified value. In this case, in region α, if the value of the average roughness is less than the specified value, it can be either variable or constant. Similarly, in region β, if the value of the average roughness is greater than the specified value, it can be either variable or constant. In addition, the average roughness of region α is greater than the average roughness of region β, which means that region α has an average roughness greater than a specified value and region β has an average roughness less than the specified value. In this case, in region α, if the value of the average roughness is greater than the specified value, it can be either variable or constant. Similarly, within the region β, the average roughness value may be variable or constant as long as it is less than a predetermined value. In the present embodiment, the average roughness value of the inner surface 51 changes so as to gradually increase from the end 53b to the end 53a.

[0039] The second grid electrode 34 having the above-mentioned average roughness is manufactured as follows as an example. First, in an electrolyte, the surface of the cup-shaped cathode is placed in a state facing the outer surface 52 of the second grid electrode 34 electrically connected to the anode. On the other hand, the inner surface 51 of the second grid electrode 34 is not placed in a state facing the cathode. By performing electrolytic polishing in this state, the second grid electrode 34 having the above-mentioned average roughness is manufactured. In addition, mechanical polishing such as polishing may be performed on the outer surface 52 of the second grid electrode 34 before performing electrolytic polishing. [Function and Effect]

[0040] In the X-ray tube 1, the average roughness of the second region R2 located on the target 4 side with respect to the first region R1 is smaller than the average roughness of the first region R1 located on the opposite side of the target 4 with respect to the second region R2 on the inner side surface 51 of the second grid electrode 34. Therefore, even when a negative high voltage is applied to the cathode 32 and the second grid electrode 34 with respect to the target 4, leakage current generated at the inner side surface 51 of the second grid electrode 34 is unlikely to occur. In addition, the average roughness of the first region R1 located on the cathode 32 side with respect to the second region R2 on the inner side surface 51 of the second grid electrode 34 is larger than the average roughness of the second region R2 located on the opposite side of the cathode 32 with respect to the first region R1 on the inner side surface 51 of the second grid electrode 34. Therefore, even when cathode material is emitted from the cathode 32, the cathode material is easily captured in the first region R1, so that the cathode material is suppressed from reaching and adhering to the inner side surface of the housing 2, etc., and leakage current generated at the cathode material adhering to the inner side surface of the housing 2 is unlikely to occur. As described above, according to the X-ray tube 1, sufficient withstand voltage characteristics can be ensured.

[0041] In addition, when the target material is emitted from the target 4, the target material is also easily captured in the first region R1. By capturing the cathode material and / or the target material in the first region R1, it is possible to prevent the cathode material and / or the target material from falling into the housing 2 and becoming foreign matter. Therefore, leakage current generated at the foreign matter is not likely to occur. According to the above description, the X-ray tube 1 can ensure sufficient withstand voltage characteristics.

[0042] In the X-ray tube 1, the inner bottom surface 54 on the inner surface 51 facing the target 4 is formed as the first region R1. Thus, the cathode material is easily captured on the inner bottom surface 54, so the generation of leakage current generated by the cathode material attached to the inner surface of the housing 2 can be more reliably suppressed.

[0043] In the X-ray tube 1, the first side surface 531 including the end 53a on the cathode 32 side of the inner side surface 53 is configured as the first region R1, and the second side surface 532 including the end 53b on the target 4 side of the inner side surface 53 is configured as the second region R2. Thus, the generation of leakage current generated at the inner surface 51 of the second gate electrode 34 and the generation of leakage current generated at the cathode material attached to the inner surface of the housing 2 and the like can be suppressed more reliably at the same time.

[0044] In the X-ray tube 1, the average roughness of the second side surface 532 is 0.4 μm to 1.0 μm, and the average roughness of the inner bottom surface 54 is 1.0 μm to 3.2 μm. Thus, the second side surface 532 that is less likely to generate leakage current and the inner bottom surface 54 that is easy to capture the cathode material can be appropriately realized.

[0045] In the X-ray tube 1 , the average roughness of the first side surface 531 is 1.0 μm or more and 1.6 μm or less. This makes it possible to appropriately realize the first side surface 531 that can easily capture the cathode material.

[0046] In the X-ray tube 1, the average roughness of the outer surface 52 is smaller than that of the second side surface 532. This makes it difficult for leakage current to occur at the outer surface 52 of the second gate electrode 34, thereby more reliably ensuring sufficient withstand voltage characteristics.

[0047] In the X-ray tube 1, the average roughness of the outer surface 52 is 0.05 μm or more and 0.4 μm or less. This makes it possible to appropriately realize the outer surface 52 in which leakage current is less likely to occur.

[0048] In the X-ray tube 1, the average roughness of the fourth region R4 located on the target 4 side relative to the third region R3 on the outer surface 52 is smaller than the average roughness of the third region R3 located on the cathode 32 side relative to the fourth region R4. Thus, the generation of leakage current at the outer surface 52 of the second gate electrode 34 can be reliably suppressed.

[0049] In the X-ray tube 1, the fourth region R4 is a circular region including the end 52a of the outer surface 52 on the target 4 side. This can more reliably suppress the generation of leakage current generated at the outer surface 52 of the second gate electrode 34.

[0050] In the X-ray tube 1, the average roughness of the outer bottom surface 55 facing the opposite side of the target 4 is greater than the average roughness of the fourth region R4. As a result, the cathode material is also easily captured on the outer bottom surface 55, so the generation of leakage current generated by the cathode material attached to the inner surface of the housing 2 can be more reliably suppressed.

[0051] Here, the reasons why the average roughness of the inner surface 51 is set to be 0.4 μm or more and 3.2 μm or less and the average roughness of the outer surface 52 is set to be 0.05 μm or more and 0.4 μm or less will be described in detail.

[0052] As described above, in the X-ray tube 1, a negative high voltage is applied to the cathode 32 and the second grid electrode 34 respectively with reference to the target 4. When the value (absolute value) of the high voltage increases, the leakage current flowing to the part other than the cathode 32 in the electron gun 3 and the target 4 increases. Examples of the leakage current include leakage current caused by discharge generated between the part other than the cathode 32 in the electron gun 3 (mainly the second grid electrode 34) and the target 4 and the head 21 as the anode, leakage current caused by discharge generated between the foreign matter and the target 4 and the head 21 as the anode, and leakage current caused by discharge generated between the foreign matter and the electron gun 3. When the leakage current increases, the anode current increases even if the tube current is controlled to be constant. The tube current is a current flowing between the cathode 32 and the target 4, for example, a current calculated based on the voltage applied to the first grid electrode 33. The anode current is a current flowing between the electron gun 3 and “the target 4 and the head 21 as the anode” (ie, the sum of the tube current and the leakage current), and is a current measured by, for example, an ammeter electrically connected to the head 21 .

[0053] In the X-ray tube 1, when the anode current exceeds a predetermined threshold value, the operation of the X-ray tube 1 is stopped as a discharge occurs. Therefore, when the leakage current increases, the anode current easily exceeds the threshold value due to fluctuations in the tube current, and as a result, there is a problem that the operation of the X-ray tube 1 is easily stopped even if no discharge occurs.

[0054] Furthermore, when the leakage current increases, X-rays are emitted from the target 4 and / or the head 21 due to the incidence of electrons caused by the leakage current. Therefore, there is a problem that the focus of the X-rays R irradiated to the inspection object becomes multiple, resulting in a blurred X-ray image of the inspection object. In addition, there is a problem that the background noise increases in the X-rays R irradiated to the inspection object, resulting in a decrease in the contrast of the X-ray image of the inspection object.

[0055] Therefore, it is important that the leakage current does not become a value that causes the above-mentioned problem in the X-ray tube 1. By setting the average roughness of the inner surface 51 to 3.2 μm or less and the average roughness of the outer surface 52 to 0.4 μm or less, the leakage current can be prevented from increasing to a level that causes the above-mentioned problem.

[0056] On the other hand, when the value of the leakage current is too small, it is difficult to obtain the effect of releasing gas from the inner surface of the head 21 by the collision of electrons caused by the leakage current with the inner surface of the head 21. By setting the average roughness of the inner surface 51 to be 0.4 μm or more and the average roughness of the outer surface 52 to be 0.05 μm or more, it is possible to suppress the value of the leakage current from being reduced to a level where the effect of gas release cannot be obtained. In addition, the released gas can be removed by a getter arranged in the X-ray tube in a sealed X-ray tube such as the present embodiment, and can be removed by a pump arranged outside the X-ray tube in an open X-ray tube. [Modifications]

[0057] The present invention is not limited to the above-mentioned embodiments. Figure 4 As shown in (a), the bottom wall 38 of the second gate electrode 34 does not have a recess 38a (see Figure 3 In this case, the inner bottom surface 54 of the first region R1 is the surface of the bottom wall 38 on the target 4 side. Figure 4 As shown in (b) of FIG. 3 , the second gate electrode 34 has a side wall 37 but does not have a bottom wall 38. In any second gate electrode 34, on the inner surface 51 of the second cylindrical gate electrode 34, the average roughness of the second region R2 located on the target 4 side relative to the first region R1 is smaller than the average roughness of the first region R1 located on the opposite side of the target 4 relative to the second region R2. In other words, on the inner surface 51 of the second cylindrical gate electrode 34, the average roughness of the first region R1 located on the cathode 32 side relative to the second region R2 is larger than the average roughness of the second region R2 located on the opposite side of the cathode 32 relative to the first region R1.

[0058] Furthermore, on the inner surface 51 of the second cylindrical gate electrode 34, if the second region R2 is located on the target 4 side relative to the first region R1, the first region R1 may not be a region including the end 53a on the cathode 32 side of the inner side surface 53, and further, the second region R2 may not be a region including the end 53b on the target 4 side of the inner side surface 53. Furthermore, on the outer surface 52 of the second cylindrical gate electrode 34, if the fourth region R4 is located on the target 4 side relative to the third region R3, the fourth region R4 may not be a circular region including the end 52a on the target 4 side of the outer surface 52. Furthermore, the first region R1 and the second region R2 may be spaced apart from each other. Similarly, the third region R3 and the fourth region R4 may be spaced apart from each other.

[0059] The X-ray tube 1 may be configured as a sealed reflection type X-ray tube. Alternatively, the X-ray tube 1 may be configured as an open transmission type X-ray tube or an open reflection type X-ray tube. An open transmission type or open reflection type X-ray tube is an X-ray tube whose casing is openable, and components (such as window components and various parts of an electron gun) can be exchanged. In an X-ray generating device having an open transmission type or open reflection type X-ray tube, a vacuum pump is used to evacuate the space in the casing. Description of Reference Numerals

[0060] 1X-ray tube 2 Cabinet 3Electron Gun 4 targets 32 cathode 34 second grid electrode (focusing electrode) 51Inside surface 52 Outer surface 52a end 53 medial side 53a, 53b end 54 inner bottom 55 outer bottom surface 531 Side 1 532 Side 2 R1 Area 1 R2 Area 2 R3 Area 3 R4, Region 4.

Claims

1. An X-ray tube, characterized in that: include: Box; An electron gun for emitting an electron beam in the box; and A target for generating X-rays in the housing by the incidence of the electron beam, The electron gun comprises: a cathode that emits electrons; and a focusing electrode for focusing the electrons as the electron beam on the target, The focusing electrode is in a cylindrical shape having an inner surface and an outer surface. The inner surface has a first region and a second region located on the target side relative to the first region. The average roughness of the second region is smaller than the average roughness of the first region.

2. The X-ray tube according to claim 1, characterized in that: The inner surface has an inner bottom surface facing the target side, The inner bottom surface is the first area.

3. The X-ray tube according to claim 2, characterized in that: The inner surface also has an inner side surface, The first side surface of the inner side surface including the end portion on the cathode side is the first region. A second side surface including an end portion on the target side of the inner side surface is the second region.

4. The X-ray tube according to claim 3, characterized in that: The average roughness of the second side surface is not less than 0.4 μm and not more than 1.0 μm, The average roughness of the inner bottom surface is 1.0 μm or more and 3.2 μm or less.

5. The X-ray tube according to claim 4, characterized in that: The first side surface has an average roughness of 1.0 μm or more and 1.6 μm or less.

6. The X-ray tube according to any one of claims 3 to 5, characterized in that: The average roughness of the outer surface is smaller than the average roughness of the second side surface.

7. The X-ray tube according to claim 6, characterized in that: The average roughness of the outer surface is greater than or equal to 0.05 μm and less than or equal to 0.4 μm.

8. The X-ray tube according to claim 6 or 7, characterized in that: The outer surface has a third region and a fourth region located on the target side relative to the third region. The average roughness of the fourth region is smaller than the average roughness of the third region.

9. The X-ray tube according to claim 8, characterized in that: The fourth region is a circular region including an end portion on the target side of the outer surface.

10. The X-ray tube according to claim 8 or 9, characterized in that: The focusing electrode further has an outer bottom surface facing the opposite side to the target. The average roughness of the outer bottom surface is greater than the average roughness of the fourth region.

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