X-ray tube

Abstract

To provide an X-ray tube that can ensure sufficient withstand voltage characteristics.SOLUTION: An x-ray tube comprises: a housing; an electron gun that emits an electron beam inside the housing; and a target that generates x-rays in response to receiving the electron beam inside the housing. The electron gun has: a cathode 32 that discharges electrons; and a second grid electrode 34 that focuses the electrons on the target 4 as the electron beam. The second grid electrode 34 is a cylinder that has an inside surface 51 and an outside surface 52. The inside surface 51 includes a first area R1, and a second area R2 that is positioned on the target side 4 with respect to the first area R1. An average roughness of the second area R2 is less than an average roughness of the first area R1.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an X-ray tube. [Background technology]

[0002] An X-ray tube is known that includes a housing, an electron gun that emits an electron beam within the housing, and a target that generates X-rays within the housing when the electron beam is incident on it, in which the electron gun has a cathode that emits electrons and a focusing electrode that focuses the electrons onto the target as an electron beam (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6619916 Summary of the Invention [Problem to be solved by the invention]

[0004] In the X-ray tube described above, a negative high voltage may be applied to each of the cathode and the focusing electrode relative to the target. In such cases, ensuring sufficient voltage resistance characteristics in the X-ray tube is extremely important for achieving stable operation of the X-ray tube.

[0005] An object of the present invention is to provide an X-ray tube that can ensure sufficient voltage resistance characteristics. [Means for solving the problem]

[0006] The X-ray tube of the present invention is [1] "an X-ray tube comprising: a housing; an electron gun that emits an electron beam within the housing; and a target that generates X-rays within the housing when the electron beam is incident on it, wherein the electron gun has a cathode that emits electrons and a focusing electrode that focuses the electrons as the electron beam onto the target, the focusing electrode having a cylindrical shape with an inner surface and an outer surface, the inner surface including a first region and a second region located on the target side relative to the first region, and 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 of 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 from the second region. This reduces the likelihood of leakage current originating from the inner surface of the focusing electrode, even when a negative high voltage is applied to the cathode and the focusing electrode relative to the target. Furthermore, the average roughness of the first region located on the cathode side of the second region on the inner surface of the cylindrical focusing electrode is greater than the average roughness of the second region located on the opposite side of the cathode from the first region. This reduces the likelihood of leakage current originating from cathode material attached to the inner surface of the housing, etc., even when the cathode material is released from the cathode, as the cathode material is more likely to be captured in the first region. As a result, the X-ray tube described in [1] above can ensure sufficient voltage resistance characteristics.

[0008] The X-ray tube of the present invention may be [2] "the X-ray tube according to [1], wherein the inner surface has an inner bottom surface facing the target, and the inner bottom surface is the first region." According to the X-ray tube according to [2], the cathode material is more likely to be captured on the inner bottom surface, so that it is possible to more reliably suppress the occurrence of leakage current originating from the cathode material adhering to the inner surface of the housing, etc.

[0009] The X-ray tube of the present invention may be [3] "the X-ray tube according to [2], wherein the inner surface further has an inner side surface, a first side surface of the inner side surface including an end portion on the cathode side being the first region, and a second side surface of the inner side surface including an end portion on the target side being the second region." The X-ray tube according to [3] can more reliably suppress both the occurrence of leakage current originating from the inner surface of the focusing electrode and the occurrence of leakage current originating from cathode material adhered to the inner surface of the housing, etc.

[0010] The X-ray tube of the present invention may be [4] "the X-ray tube according to [3], wherein the average roughness of the second side surface is 0.4 μm or more and 1.0 μm or less, and the average roughness of the inner bottom surface is 1.0 μm or more and 3.2 μm or less." The X-ray tube according to [4] can preferably achieve a second side surface that is less likely to generate leakage current and an inner bottom surface that is more likely to capture cathode material.

[0011] The X-ray tube of the present invention may be [5] "the X-ray tube according to [4], wherein the average roughness of the first side surface is 1.0 μm or more and 1.6 μm or less." The X-ray tube according to [5] can preferably realize a first side surface that is easy to capture cathode material.

[0012] The X-ray tube of the present invention may be [6] "the X-ray tube according to 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." According to the X-ray tube according to [6], leakage current originating from the outer surface of the focusing electrode is less likely to occur, so that sufficient voltage resistance characteristics can be more reliably ensured.

[0013] The X-ray tube of the present invention may be [7] "the X-ray tube according to [6], wherein the average roughness of the outer surface is 0.05 μm or more and 0.4 μm or less." The X-ray tube according to [7] can preferably achieve an outer surface that is less likely to generate leakage current.

[0014] The X-ray tube of the present invention may be [8] "the X-ray tube according to [6] or [7], wherein the outer surface includes a third region and a fourth region located on the target side of the third region, and the average roughness of the fourth region is smaller than the average roughness of the third region." According to the X-ray tube according to [8], it is possible to reliably suppress the occurrence of leakage current originating from the outer surface of the focusing electrode.

[0015] The X-ray tube of the present invention may be [9] "the X-ray tube according to [8], wherein the fourth region is a rounded region including the end of the outer surface on the target side." According to the X-ray tube according to [9], it is possible to more reliably suppress the occurrence of leakage current originating from the outer surface of the focusing electrode.

[0016] The X-ray tube of the present invention may be

[10] "the X-ray tube according to [8] or [9], wherein the focusing electrode further has an outer bottom surface facing away from the target, and the average roughness of the outer bottom surface is greater than the average roughness of the fourth region." According to the X-ray tube according to

[10] , the cathode material is also more likely to be captured on the outer bottom surface, so that it is possible to more reliably suppress the occurrence of leakage current originating from the cathode material adhering to the inner surface of the housing, etc. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an X-ray tube that can ensure sufficient voltage resistance characteristics. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view of an X-ray generating device including an X-ray tube according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the X-ray tube shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the second grid electrode shown in FIG. 2. [Figure 4] FIG. 10 is a cross-sectional view of a grid electrode according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted. [Configuration of X-ray generator]

[0020] 1, the X-ray generator 10 includes an X-ray tube 1, a holder 11, a power supply 12, and a power supply 13. The X-ray generator 10 is a microfocus X-ray source used, for example, in X-ray nondestructive testing.

[0021] The holding part 11 holds the X-ray tube 1. The holding part 11 is formed into a cylindrical shape from metal. The X-ray tube 1 is attached liquid-tight to one end part 111 of the holding part 11. More specifically, the head 21 of the housing 2 of the X-ray tube 1 is attached liquid-tight to the one end part 111 with the head 21 being disposed inside the opening 111a of the one end part 111 and the bulb 22 of the housing 2 of the X-ray tube 1 being disposed inside the holding part 11. The power supply part 12 is attached liquid-tight to the other end part 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 to be applied to the X-ray tube 1. The power supply unit 12 has a power supply case 121, an insulating block 122, and a booster unit 123. The power supply case 121 houses the insulating block 122 and the booster unit 123. The power supply case 121 is formed in a box shape from metal. The booster unit 123 is embedded in the insulating block 122. The insulating block 122 is formed in a block shape from an insulating material such as epoxy resin. The booster unit 123 boosts a voltage introduced from outside the X-ray generator 10 to generate a high voltage.

[0023] Power supply unit 13 supplies power from power supply unit 12 to X-ray tube 1. Power supply unit 13 has a plurality of wires. Power supply unit 13 extends from booster unit 123 to X-ray tube 1 through opening 121a of power supply case 121 and opening 112a of the other end 112 of holder 11. One end 13a of power supply unit 13 is electrically connected to X-ray tube 1. The other end 13b of power supply unit 13 is electrically connected to booster unit 123. [X-ray tube configuration]

[0024] 2, the X-ray tube 1 includes a housing 2, an electron gun 3, and a target 4. In this 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 vacuum space. The housing 2 has a head 21, a bulb 22, and a window member 23. The head 21 is made of metal (e.g., stainless steel, copper, copper alloy, iron alloy, etc.) and is formed into a cylindrical shape with the tube axis A as its center line. The bulb 22 is made of an insulating material (e.g., glass, ceramic, etc.) and is formed into a cylindrical shape with the tube axis A as its center line. The window member 23 is made of an X-ray transparent material (e.g., beryllium, aluminum, diamond, etc.) and is formed into a plate shape with the tube axis A as its center line.

[0026] The window member 23 is airtightly attached to one end 211 of the head 21, closing the opening 211a of the one end 211 of the head 21. One end 221 of the bulb 22 is airtightly attached to the head 21 via a valve flange 24 made of a metal such as Kovar, with the opening 212a of the other end 212 of the head 21 positioned inside the bulb 22. The other end of the bulb 22 is folded inward to form an inner cylindrical portion 222. A stem 27 is airtightly attached to the end of the inner cylindrical portion 222 via a valve flange 25 and a stem flange 26, both made of a metal such as Kovar. The stem 27 is formed from an insulating material (e.g., glass, ceramic, etc.) in a plate shape with the tube axis A as its centerline.

[0027] A plurality of stem pins 28 are provided on the stem 27. The stem pins 28 penetrate the stem 27 while being electrically insulated from one another and maintaining airtightness. In the X-ray generator 10, one end 13a of the power supply unit 13 (see FIG. 1) is electrically connected to the plurality of stem pins 28 inside the inner cylindrical portion 222.

[0028] The electron gun 3 emits an electron beam B within the housing 2. The electron gun 3 is disposed on a stem 27 within the housing 2. The electron gun 3 has 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 each electrically connected to a corresponding stem pin 28.

[0030] The second grid electrode 34 focuses the electrons emitted from the cathode 32 and passing through the first grid electrode 33 onto the target 4 as an electron beam B. The second grid electrode 34 also functions as an extraction electrode that forms an electric field for extracting the electrons that make up the electron beam B.

[0031] The support part 35 is fixed to the stem flange 26, for example, by welding. The support part 35 is formed of a conductive material (for example, stainless steel) into a cylindrical shape with the tube axis A as its center line. The heater 31, the cathode 32, and the first grid electrode 33 are arranged inside the support part 35. The second grid electrode 34 is attached to the end of the support part 35 opposite to the stem 27. The support part 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 when the electron beam B is incident on it within the housing 2. The target 4 is arranged on the inner surface of the window member 23 on the tube axis A. In this embodiment, the target 4 is a film formed on the inner surface of the window member 23. The target 4 is formed in the form of a film made of, for example, tungsten, molybdenum, copper, or the like. 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 configured as described above, a negative high voltage is applied to the electron gun 3 by the power supply unit 12, with the potentials of the target 4 and head 21 as reference. As an example, the power supply unit 12 applies a negative high voltage (for example, −10 kV to −500 kV) to each component of the electron gun 3 via the power supply unit 13 and each stem pin 28, with the target 4 and head 21 at ground potential. The electron beam B emitted from the electron gun 3 is focused on the target 4 along the tube axis A. X-rays R generated in the region of the target 4 irradiated with the electron beam B are focused at the irradiated region and transmitted through the target 4 and window member 23 before being emitted to the outside. [Configuration of the second grid electrode]

[0034] As shown in FIG. 3 , the second grid electrode 34 is formed into a cylindrical shape from a metal (e.g., tungsten, molybdenum, tantalum, stainless steel, etc.). In this 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 its center line. The bottom wall 38 is formed integrally with the side wall 37 at an end of the side wall 37 on the cathode 32 side. A recess 38 a and a through hole 38 b are formed in the bottom wall 38. The recess 38 a opens toward the target 4 and has a cylindrical outer shape with the tube axis A as its center line. The through hole 38 b opens toward the target 4 and the cathode 32 at the bottom surface of the recess 38 a and has a cylindrical outer shape with the tube axis A as its center line. The second grid electrode 34 is disposed so that at least a portion of the second grid electrode 34 on the target 4 side is accommodated inside the head 21. In other words, the second grid electrode 34 is disposed so that at least a portion of an outer surface 52 (described later) faces the inner surface of the head 21. The side wall 37 and the bottom wall 38 may be formed as separate bodies and joined together.

[0035] The second grid electrode 34 has a cylindrical shape having an inner surface 51 and an outer surface 52. The inner surface 51 is a surface of the second grid electrode 34 that extends between planes P1 and P2 on the side of the center line L of the second grid electrode 34 (i.e., the inner side). The outer surface 52 is a surface of the second grid electrode 34 that extends between planes P1 and P2 on the side opposite the center line L of the second grid electrode 34 (i.e., the outer side). The plane P1 is a plane that passes through the end of the second grid electrode 34 on the target 4 side. In other words, the plane P1 is a plane that includes the opening of the second grid electrode 34 on the target 4 side (in this embodiment, the opening of the cylindrical side wall 37 on the target 4 side). The plane P2 is a plane that passes through the end of the second grid electrode 34 on the cathode 32 side. In other words, the plane P2 is a plane that includes the opening of the second grid electrode 34 on the cathode 32 side (in this embodiment, the opening of the through-hole 38b on the cathode 32 side). In this 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 of the inner surface 51 that extends along the center line L. The inner side surface 53 may have a slope with respect to the center line L, in which case the slope is 45 degrees or less (i.e., the taper is 90 degrees or less). In the present embodiment, the inner side surface 53 is an inner side surface of the side wall 37, and the slope of the inner side surface is 0 degrees. The inner surface 51 further has an inner bottom surface 54 facing the target 4. The inner bottom surface 54 is the bottom surface of the inner surface 51 that faces the target 4 and is the 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 includes a first region R1 and a second region R2 located closer to the target 4 than the first region R1. The first region R1 is the inner bottom surface 54 and a first side surface 531 including an end 53a of the inner side surface 53 on the cathode 32 side. The second region R2 is a second side surface 532 including an end 53b of the inner side surface 53 on the target 4 side. The outer surface 52 includes a third region R3 and a fourth region R4 located closer to the target 4 than the third region R3. The third region R3 is a surface of the outer surface 52 whose slope with respect to the center line L is 45 degrees or less (i.e., the taper is 90 degrees or less). In this embodiment, the third region R3 is a tapered surface widening toward the target 4. The fourth region R4 is a rounded region including an end 52a of the outer surface 52 on the target 4 side. More specifically, the fourth region R4 is a rounded, chamfered surface that protrudes outward from the annular end 52a and extends outward toward the cathode 32. The second grid electrode 34 further has an outer bottom surface 55 that faces away from the target 4. In this embodiment, the outer bottom surface 55 is the surface of the bottom wall 38 of the second grid electrode 34 that is opposite to the inner bottom surface 54.

[0038] The average roughness of the second region R2 is smaller than that of the first region R1. The average roughness of the first region R1 is 1.0 μm or more and 3.2 μm or less. The average roughness of the second region R2 is 0.4 μm or more and 1.0 μm or less. More specifically, the average roughness of the inner bottom surface 54, which is the first region R1, is 1.0 μm or more and 3.2 μm or less. The average roughness of the first side surface 531, which is the first region R1, is 1.0 μm or more and 1.6 μm or less. The average roughness of the second side surface 532, which is the second region R2, is 0.4 μm or more and 1.0 μm or less. The average roughness of the outer surface 52 is smaller than that of the second side surface 532. The average roughness of the outer surface 52 is 0.05 μm or more and 0.4 μm or less. The average roughness of the fourth region R4 is smaller than that of the third region R3. The average roughness of the outer bottom surface 55 is greater than that of the fourth region R4. The average roughness refers to the arithmetic mean roughness Ra. Ra can be measured using a contact surface roughness meter, a laser microscope, a white light interferometer, or the like. For example, a contact surface roughness meter is preferred for measuring Ra of the inner surface 51, and a white light interferometer or a laser microscope is preferred for measuring Ra of the outer surface 52. Here, the expression "the average roughness of region α is smaller than that of region β" means that region α has an average roughness less than a predetermined value and region β has an average roughness equal to or greater than the predetermined value. In this case, within region α, the average roughness value may be either variable or constant as long as it is less than the predetermined value. Similarly, within region β, the average roughness value may be either variable or constant as long as it is equal to or greater than the predetermined value. Furthermore, the expression "the average roughness of region α is greater than that of region β" means that region α has an average roughness equal to or greater than a predetermined value and region β has an average roughness less than the predetermined value. In this case, the average roughness value within region α may vary or be constant as long as it is equal to or greater than a predetermined value. Similarly, the average roughness value within region β may vary or be constant as long as it is less than a predetermined value. In this embodiment, the average roughness value of inner surface 51 varies so as to gradually increase from end 53b to end 53a.

[0039] The second grid electrode 34 having the average roughness described above is manufactured, for example, as follows. First, in an electrolyte, the surface of a cup-shaped cathode is placed in a state where it faces the outer surface 52 of the second grid electrode 34, which is electrically connected to the anode. On the other hand, the inner surface 51 of the second grid electrode 34 is placed in a state where it does not face the cathode. Electrolytic polishing is performed in this state, thereby manufacturing the second grid electrode 34 having the average roughness described above. Note that before electrolytic polishing, the outer surface 52 of the second grid electrode 34 may be mechanically polished, such as by buffing. [Action and effect]

[0040] In the X-ray tube 1, on the inner surface 51 of the cylindrical second grid electrode 34, the average roughness of the second region R2 located on the target 4 side of the first region R1 is smaller than the average roughness of the first region R1 located on the opposite side of the target 4 from the second region R2. This makes it difficult for a leak current to occur from the inner surface 51 of the second grid electrode 34, even when a negative high voltage is applied to each of the cathode 32 and the second grid electrode 34 with respect to the target 4. Furthermore, on the inner surface 51 of the cylindrical second grid electrode 34, the average roughness of the first region R1 located on the cathode 32 side of the second region R2 is larger than the average roughness of the second region R2 located on the opposite side of the cathode 32 from the first region R1. As a result, even when cathode material is emitted from the cathode 32, the cathode material is more likely to be captured in the first region R1, which prevents the cathode material from reaching and adhering to the inner surface of the housing 2, making it less likely that a leak current will occur from the cathode material adhering to the inner surface of the housing 2. As a result, the X-ray tube 1 can ensure sufficient voltage resistance characteristics.

[0041] Furthermore, even when target material is emitted from the target 4, the target material is more likely to be captured in the first region R1. Capturing the cathode material and / or target material in the first region R1 can prevent the cathode material and / or target material from falling into the housing 2 and becoming foreign matter. This makes it less likely that a leak current will occur at the location where the foreign matter is generated. As a result, the X-ray tube 1 can ensure sufficient voltage resistance characteristics.

[0042] In the X-ray tube 1, the inner bottom surface 54 facing the target 4 side of the inner surface 51 is configured as the first region R1. This makes it easier for the cathode material to be captured on the inner bottom surface 54, so that the occurrence of leakage current originating from the cathode material adhering to the inner surface of the housing 2 or the like can be more reliably suppressed.

[0043] In the X-ray tube 1, a first side surface 531 including an end 53a of the inner side surface 53 on the cathode 32 side is configured as a first region R1, and a second side surface 532 including an end 53b of the inner side surface 53 on the target 4 side is configured as a second region R2. This makes it possible to more reliably suppress both the occurrence of leakage current originating from the inner surface 51 of the second grid electrode 34 and the occurrence of leakage current originating from cathode material attached to the inner surface of the housing 2, etc.

[0044] In the X-ray tube 1, the average roughness of the second side surface 532 is 0.4 μm or more and 1.0 μm or less, and the average roughness of the inner bottom surface 54 is 1.0 μm or more and 3.2 μm or less. This makes it possible to preferably realize the second side surface 532 in which leakage current is less likely to occur, and the inner bottom surface 54 in which cathode material is more likely to be captured.

[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, which makes it possible to suitably realize the first side surface 531 on which the cathode material is easily captured.

[0046] In the X-ray tube 1, the average roughness of the outer surface 52 is smaller than the average roughness of the second side surface 532. This makes it difficult for a leak current to occur from the outer surface 52 of the second grid electrode 34, thereby more reliably ensuring sufficient voltage resistance 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, which makes it possible to preferably 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, which is located closer to the target 4 than the third region R3, is smaller than the average roughness of the third region R3, which is located closer to the cathode 32 than the fourth region R4, on the outer surface 52. This makes it possible to reliably suppress the occurrence of leakage current originating from the outer surface 52 of the second grid electrode 34.

[0049] In the X-ray tube 1, the fourth region R4 is a rounded region that includes the end 52a of the outer surface 52 on the target 4 side. This makes it possible to more reliably suppress the occurrence of leakage current originating from the outer surface 52 of the second grid electrode 34.

[0050] In the X-ray tube 1, the average roughness of the outer bottom surface 55 facing away from the target 4 is greater than the average roughness of the fourth region R4. This makes it easier for the cathode material to be captured also on the outer bottom surface 55, so that the occurrence of leakage current originating from the cathode material adhering to the inner surface of the housing 2, etc., can be more reliably suppressed.

[0051] Here, the reason why the average roughness of the inner surface 51 is set to 0.4 μm or more and 3.2 μm or less, and the average roughness of the outer surface 52 is set to 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 each of the cathode 32 and the second grid electrode 34 relative to the target 4. As the value (absolute value) of this high voltage increases, the leakage current flowing in areas other than between the cathode 32 of the electron gun 3 and the target 4 increases. Examples of leakage current include leakage current caused by discharge between parts of the electron gun 3 other than the cathode 32 (mainly the second grid electrode 34) and the target 4 (which serves as an anode) and the head 21, leakage current caused by discharge between a foreign object and the target 4 (which serves as an anode) and the head 21, and leakage current caused by discharge between a foreign object and the electron gun 3. When this 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, and is calculated based on the voltage applied to the first grid electrode 33, for example. The anode current is the current flowing between the electron gun 3 and the "anode target 4 and head 21" (i.e., the sum of the tube current and the leakage current), and is, for example, the current measured by an ammeter electrically connected to the head 21.

[0053] In the X-ray tube 1, when the anode current exceeds a predetermined threshold, it is determined that a discharge has occurred, and the operation of the X-ray tube 1 is stopped. Therefore, if the leakage current becomes large, the anode current is more likely to exceed the threshold due to fluctuations in the tube current, etc., and as a result, the operation of the X-ray tube 1 may be more likely to be stopped even though a discharge has not occurred.

[0054] Furthermore, when the leakage current increases, electrons caused by the leakage current enter the target 4 and / or the head 21, causing X-rays to be emitted from the target 4 and / or the head 21. This causes the X-rays R irradiated onto the inspection object to have multiple focal points, which may result in a blurred X-ray image of the inspection object. Furthermore, background noise may increase in the X-rays R irradiated onto the inspection object, which may result in a decrease in contrast in the X-ray image of the inspection object.

[0055] Therefore, it is important to prevent the leakage current value from becoming large enough to cause the above-mentioned problems 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, it is possible to prevent the leakage current value from becoming large enough to cause the above-mentioned problems.

[0056] On the other hand, if the value of the leakage current becomes too small, it becomes difficult to obtain the effect of electrons caused by the leakage current colliding with the inner surface of head 21 to release gas from the inner surface of head 21. By setting the average roughness of inner surface 51 to 0.4 μm or more and the average roughness of outer surface 52 to 0.05 μm or more, it is possible to prevent the value of the leakage current from becoming so small that the gas release effect cannot be obtained. In a sealed X-ray tube such as that of this embodiment, the released gas can be removed by a getter placed inside the X-ray tube, and in an open X-ray tube, it can be removed by a pump placed outside the X-ray tube. [Variations]

[0057] The present invention is not limited to the above-described embodiment. For example, as shown in FIG. 4A, the bottom wall 38 of the second grid electrode 34 may not have the recess 38a (see FIG. 3). In this case, the inner bottom surface 54, which is the first region R1, is the surface of the bottom wall 38 facing the target 4. Also, as shown in FIG. 4B, the second grid electrode 34 may have a side wall 37 but not a bottom wall 38. In any of the second grid electrodes 34, the average roughness of the second region R2 located on the target 4 side of the first region R1 on the inner surface 51 of the cylindrical second grid electrode 34 is smaller than the average roughness of the first region R1 located on the opposite side of the target 4 from the second region R2. In other words, on the inner surface 51 of the cylindrical second grid electrode 34, the average roughness of the first region R1 located on the cathode 32 side relative to the second region R2 is greater than the average roughness of the second region R2 located on the opposite side of the first region R1 from the cathode 32.

[0058] Furthermore, as long as the second region R2 is located closer to the target 4 than the first region R1 on the inner surface 51 of the cylindrical second grid electrode 34, the first region R1 does not have to be a region including the end 53a of the inner side surface 53 facing the cathode 32, and the second region R2 does not have to be a region including the end 53b of the inner side surface 53 facing the target 4. As long as the fourth region R4 is located closer to the target 4 than the third region R3 on the outer surface 52 of the cylindrical second grid electrode 34, the fourth region R4 does not have to be a rounded region including the end 52a of the outer surface 52 facing the target 4. The first region R1 and the second region R2 may be separated from each other. Similarly, the third region R3 and the fourth region R4 may be separated 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 housing is configured to be openable, allowing parts (for example, window members and parts of the electron gun) to be replaced. In an X-ray generator equipped with an open transmission type or open reflection type X-ray tube, the space inside the housing is evacuated by a vacuum pump. [Explanation of symbols]

[0060] 1... X-ray tube, 2... Housing, 3... Electron gun, 4... Target, 32... Cathode, 34... Second grid electrode (focusing electrode), 51... Inner surface, 52... Outer surface, 52a... End, 53... Inner side Side surface, 53a, 53b... end, 54... inner bottom surface, 55... outer bottom surface, 531... first side surface, 532... second side surface, R1... first region, R2... second region, R3... third region, R4... fourth region.

Claims

1. The housing and an electron gun that emits an electron beam within the housing; a target that generates X-rays in response to the electron beam being incident thereon, The electron gun comprises: a cathode that emits electrons; a focusing electrode that focuses the electrons onto the target as the electron beam; the focusing electrode is formed of a single member into a cylindrical shape having an inner surface and an outer surface; the inner surface includes a first region and a second region located on the target side relative to the first region; An X-ray tube, wherein the average roughness of the second region is smaller than the average roughness of the first region.

2. the inner surface has an inner bottom surface facing the target; The X-ray tube of claim 1 , wherein the inner bottom surface is the first region.

3. the inner surface further comprises an inner side; a first side surface including an end portion of the inner side surface on the cathode side is the first region; The X-ray tube according to claim 2 , wherein a second side surface of the inner side surface including an end portion on the target side is the second region.

4. the average roughness of the second side surface is 0.4 μm or more and 1.0 μm or less; 4. The X-ray tube according to claim 3, wherein 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 , wherein the average roughness of the first side surface is not less than 1.0 μm and not more than 1.6 μm.

6. The x-ray tube of claim 3 , wherein the average roughness of the outer surface is less than the average roughness of the second side surface.

7. 7. The X-ray tube of claim 6, wherein the average roughness of the outer surface is 0.05 μm or more and 0.4 μm or less.

8. the outer surface includes a third region and a fourth region located on the target side relative to the third region; The X-ray tube according to claim 6 , wherein the average roughness of the fourth region is smaller than the average roughness of the third region.

9. 9. The X-ray tube according to claim 8, wherein the fourth region is a rounded region that includes an end of the outer surface on the target side.

10. the focusing electrode further has an outer bottom surface facing away from the target; The X-ray tube of claim 8 , wherein the average roughness of the outer bottom surface is greater than the average roughness of the fourth region.

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