X-ray tube

Abstract

An X-ray tube comprises a case, an electron gun that emits an electron beam within the case, and a target that generates X-rays upon incidence of the electron beam within the case. The electron gun has a cathode that emits electrons and a focusing electrode that focuses electrons as an electron beam onto the target. The focusing electrode has a tubular 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. The average illuminance of the second region is lower than the average illuminance of the first region.

Description

Technology Field

[0001] The present disclosure relates to an X-ray tube. Background Technology

[0002] It is known that in an X-ray tube comprising a case, an electron gun that emits an electron beam within the case, and a target that generates X-rays by the incidence of an electron beam within the case, the electron gun comprises a cathode that emits electrons and a focusing electrode that focuses electrons as an electron beam onto the target (see, for example, Patent Document 1). Prior art literature

[0003] [Patent Document 1] : Japanese Patent Publication No. 6619916 The problem to be solved

[0004] In an X-ray tube as 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 withstand voltage characteristics in the X-ray tube is extremely important for realizing operational stability of the X-ray tube.

[0005] The present disclosure aims to provide an X-ray tube capable of securing sufficient withstand voltage characteristics. means of solving the problem

[0006] One aspect of the present disclosure is an X-ray tube [1] “a case, an electron gun that emits an electron beam within the case, and a target that generates X-rays by the incidence of the electron beam within the case, 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, and the focusing electrode has a tubular shape having an inner surface and an outer surface, wherein the inner surface includes a first region and a second region located on the target side with respect to the first region, and the average roughness of the second region is smaller than the average roughness of the first region.”

[0007] In the X-ray tube described in [1] above, on the inner surface of the focusing electrode which has a tubular shape, the average roughness of the second region located on the target side relative to the first region is smaller than the average roughness of the first region located on the opposite side of the target relative to the second region. As a result, even when a negative high voltage is applied to the cathode and the focusing electrode respectively relative to the target, it is difficult for a leakage current to occur with the inner surface of the focusing electrode as the source. Also, on the inner surface of the focusing electrode which has a tubular shape, the average roughness of the first region located on the cathode side relative to the second region is larger than the average roughness of the second region located on the opposite side of the cathode relative to the first region. As a result, even when the cathode material is emitted from the cathode, the cathode material is easily captured in the first region, so it is difficult for a leakage current to occur with the cathode material attached to the inner surface of the case, etc. as the source. According to the above, the X-ray tube described in [1] can secure sufficient withstand voltage characteristics.

[0008] The X-ray tube of one aspect of the present disclosure may be [2] an X-ray tube described in [1], in which “the inner surface has an inner bottom surface facing the target side, and the inner bottom surface is the first region.” According to the X-ray tube described in [2], the cathode material is easily captured on the inner bottom surface, so the generation of leakage current at the source of the cathode material attached to the inner surface of the case, etc., can be more reliably suppressed.

[0009] The X-ray tube of one aspect of the present disclosure may be [3] an X-ray tube described in [2], wherein the inner surface further has an inner side, and the first side including the end of the cathode side among the inner side is the first region, and the second side including the end of the target side among the inner side is the second region. According to the X-ray tube described in [3], the generation of leakage current at the inner surface of the focusing electrode and the generation of leakage current at the cathode material attached to the inner surface of the case, etc., can be more reliably suppressed.

[0010] The X-ray tube of one aspect of the present disclosure may be [4] the X-ray tube described in [3], in which the average roughness of the second side 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. According to the X-ray tube described in [4], a second side in which leakage current is unlikely to occur and an inner bottom surface in which cathode material is likely to be captured can be very suitably realized.

[0011] The X-ray tube of one aspect of the present disclosure may be [5] the X-ray tube described in [4], in which the average roughness of the first aspect is 1.0 μm or more and 1.6 μm or less. According to the X-ray tube described in [5], the first aspect in which the cathode material is easily captured can be very suitably realized.

[0012] The X-ray tube of one aspect of the present disclosure may be [6] an 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 aspect. According to the X-ray tube described in [6], it is difficult for leakage current to occur at the outer surface of the focusing electrode, so sufficient withstand voltage characteristics can be more reliably secured.

[0013] The X-ray tube of one aspect of the present disclosure may be [7] the X-ray tube described in [6], in which the average roughness of the outer surface is 0.05 μm or more and 0.4 μm or less. According to the X-ray tube described in [7], an outer surface that is unlikely to generate leakage current can be very suitably realized.

[0014] The X-ray tube of one aspect of the present disclosure may be [8] an X-ray tube described in [6] or [7], wherein the outer surface comprises a third region and a fourth region located on the target side relative to the third region, and the average illuminance of the fourth region is smaller than the average illuminance of the third region. According to the X-ray tube described in [8], the generation of leakage current at the outer surface of the focusing electrode can be reliably suppressed.

[0015] The X-ray tube of one aspect of the present disclosure may be [9] the X-ray tube described in [8], in which the fourth region is a round region including the end of the target side on the outer surface. According to the X-ray tube described in [9], the generation of leakage current at the outer surface of the focusing electrode can be more reliably suppressed.

[0016] The X-ray tube of one aspect of the present disclosure may be

[10] an X-ray tube described in [8] or [9], in which the focusing electrode further has an outer bottom surface facing the opposite side of the target, and the average illuminance of the outer bottom surface is greater than the average illuminance of the fourth region. According to the X-ray tube described in

[10] , the cathode material is easily captured even on the outer bottom surface, so the generation of leakage current at the source of the cathode material attached to the inner surface of the case, etc., can be more reliably suppressed. Effects of the invention

[0017] According to the present disclosure, it is possible to provide an X-ray tube capable of securing sufficient withstand voltage characteristics. Brief explanation of the drawing

[0018] [Fig. 1] Fig. 1 is a cross-sectional view of an X-ray generating device having an X-ray tube of one embodiment. [Fig. 2] Fig. 2 is a cross-sectional view of the X-ray tube shown in Fig. 1. [Fig. 3] Fig. 3 is a cross-sectional view of the second grid electrode shown in Fig. 2. [Fig. 4] Fig. 4 is a cross-sectional view of a grid electrode of a modified example. Specific details for implementing the invention

[0019] Hereinafter, the embodiments disclosed in this invention will be described in detail with reference to the drawings. In addition, in each drawing, the same or substantial parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0020] [Configuration of X-ray generator]

[0021] As shown in FIG. 1, the X-ray generating device (10) is equipped with an X-ray tube (1), a storage and holding unit (11), a power supply unit (12), and a power supply unit (13). The X-ray generating device (10) is, for example, a microfocus X-ray source used for X-ray non-destructive inspection.

[0022] The storage and holding section (11) stores and holds the X-ray tube (1). The storage and holding section (11) is formed in a tubular shape using metal. The X-ray tube (1) is liquid-sealed and mounted on one end (111) of the storage and holding section (11). More specifically, the head (21) of the case (2) of the X-ray tube (1) is positioned inside the opening (111a) of the one end (111), and the valve (22) of the case (2) of the X-ray tube (1) is positioned inside the storage and holding section (11), so that the head (21) is liquid-sealed and mounted on the one end (111). The power supply section (12) is liquid-sealed and mounted on the other end (112) of the storage and holding section (11). Insulating oil is sealed inside the storage and holding section (11).

[0023] 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 case (121), an insulating block (122), and a boost unit (123). The power case (121) accommodates the insulating block (122) and the boost unit (123). The power case (121) is formed in a box shape by metal. The boost unit (123) is embedded in the insulating block (122). The insulating block (122) is formed in a block shape by an insulating material such as epoxy resin. The boost unit (123) boosts the voltage introduced from outside the X-ray generator (10) and generates a high voltage.

[0024] The power supply unit (13) supplies power to the X-ray tube (1) from the power supply unit (12). The power supply unit (13) has multiple wires. The power supply unit (13) is extended to the X-ray tube (1) from the booster unit (123) through the opening (121a) of the power supply case (121) and the opening (112a) of the other end (112) of the storage and maintenance 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 booster unit (123).

[0025] [Composition of X-ray Tubes]

[0026] As shown in FIG. 2, the X-ray tube (1) is equipped with a case (2), an electron gun (3), and a target (4). In this embodiment, the X-ray tube (1) is configured as a sealed, transparent X-ray tube that does not require replacement of parts.

[0027] The case (2) accommodates the electron gun (3) and the target (4). The space within the case (2) is a space where vacuum drawing is performed. The case (2) has a head (21), a valve (22), and a window member (23). The head (21) is formed in a tubular shape with the tube axis (A) as the centerline by a metal (e.g., stainless steel, copper, copper alloy, iron alloy, etc.). The valve (22) is formed in a tubular shape with the tube axis (A) as the centerline by an insulating material (e.g., glass, ceramic, etc.). The window member (23) is formed in a plate shape with the tube axis (A) as the centerline by an X-ray transmitting material (e.g., beryllium, aluminum, diamond, etc.).

[0028] The window member (23) is hermetically mounted to the end portion (211) of the head (21) while blocking the opening (211a) of the end portion (211) of the head (21). The end portion (221) of the valve (22) is hermetically mounted to the head (21) through a valve flange (24) made of metal such as Kovar, while the opening (212a) of the other end portion (212) of the head (21) is positioned inside the valve (22). The other end portion of the valve (22) forms an inner tube portion (222) by being folded inward. A stem (27) is hermetically mounted to the end portion of the inner tube portion (222) through a valve flange (25) and a stem flange (26) made of metal such as Kovar. The stem (27) is formed in a plate shape with the tube axis (A) as the centerline by means of an insulating material (e.g., glass, ceramic, etc.).

[0029] A plurality of stem pins (28) are installed in the stem (27). Each stem pin (28) penetrates the stem (27) while being electrically insulated from one another and maintaining a tight seal. In the X-ray generator (10), one end (13a) of the feed section (13) (see FIG. 1) is electrically connected to a plurality of stem pins (28) inside the inner tube (222).

[0030] The electron gun (3) emits an electron beam (B) inside the case (2). The electron gun (3) is positioned on a stem (27) inside the case (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 member (35).

[0031] The heater (31) is composed of a filament that generates heat when current is applied. The cathode (32) emits electrons by being heated by the heater (31). The first grid electrode (33) regulates the amount of electrons emitted from the cathode (32). Each of the heater (31), the cathode (32), and the first grid electrode (33) is electrically connected to a corresponding stem pin (28).

[0032] The second grid electrode (34) focuses electrons emitted from the cathode (32) and passed 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 to extract electrons constituting the electron beam (B).

[0033] The support member (35) is fixed to the stem flange (26), for example, by welding. The support member (35) is formed in a tubular shape with the tube axis (A) as the centerline by a conductive material (e.g., stainless steel). The heater (31), cathode (32), and first grid electrode (33) are arranged inside the support member (35). The second grid electrode (34) is mounted on the end opposite to the stem (27) in the support member (35). The support member (35) is electrically connected to the corresponding stem pin (28) through the stem flange (26) and also functions as a power supply path for the second grid electrode (34).

[0034] The target (4) generates X-rays (R) by the incidence of an electron beam (B) within the case (2). The target (4) is positioned on the inner surface of the window member (23) along 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 a film shape, for example, by 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.

[0035] 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) based on the potential of the target (4) and the head (21). For example, the power supply unit (12) applies a negative high voltage (e.g., -10 kV to -500 kV) to each part of the electron gun (3) through the feed unit (13) and each stem pin (28) while the target (4) and the head (21) are at ground potential. The electron beam (B) emitted from the electron gun (3) is focused onto the target (4) along the tube axis (A). The X-ray (R) generated in the irradiation area of ​​the electron beam (B) at the target (4) passes through the target (4) and the window member (23) with the irradiation area as the focus and is emitted to the outside.

[0036] [Composition of the 2nd Grid Electrode]

[0037] As shown in FIG. 3, the second grid electrode (34) is formed in a tubular shape using 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 in a cylindrical shape with the tube axis (A) as the centerline. 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 concave portion (38a) and a through hole (38b) are formed in the bottom wall (38). The concave portion (38a) opens toward the target (4) and has a cylindrical shape with the tube axis (A) as the centerline. The through hole (38b) is open toward the target (4) side and the cathode (32) side on the bottom surface of the concave portion (38a) and has a circular outer shape with the tube axis (A) as the centerline. The second grid electrode (34) is positioned so that at least a portion of the target (4) side of the second grid electrode (34) is received inside the head (21). In other words, the second grid electrode (34) is positioned so that at least a portion of the outer surface (52) described later faces the inner surface of the head (21). Additionally, the side wall (37) and the bottom wall (38) may be formed as separate bodies and joined together.

[0038] The second grid electrode (34) has a tubular shape having an inner surface (51) and an outer surface (52). The inner surface (51) is a surface that extends between plane P1 and plane P2 on the side opposite to the centerline (L) of the second grid electrode (34) (i.e., the inner side) of the second grid electrode (34). The outer surface (52) is a surface that extends between plane P1 and plane P2 on the side opposite to the centerline (L) of the second grid electrode (34) (i.e., the outer side) of the second grid electrode (34). Plane P1 is a plane that passes through the end of the second grid electrode (34) on the target (4) side. In other words, plane P1 is a plane that includes the opening on the target (4) side of the second grid electrode (34) (in this embodiment, the opening on the target (4) side of the cylindrical side wall (37)). Plane P2 is a plane that passes through the end of the cathode (32) side of the second grid electrode (34). In other words, Plane P2 is a plane that includes the opening on the cathode (32) side of the second grid electrode (34) (in this embodiment, the opening on the cathode (32) side of the through hole (38b)). Also, in this embodiment, the centerline (L) of the second grid electrode (34) coincides with the tube axis (A).

[0039] The inner surface (51) has an inner side (53). The inner side (53) is a surface that runs along the centerline (L) among the inner surface (51). The inner side (53) may have a slope with respect to the centerline (L), and in that case, the slope is 45 degrees or less (i.e., the taper is 90 degrees or less). In this embodiment, the inner side (53) is the inner side of the side wall (37), and the slope of the inner side is 0 degrees. The inner surface (51) further has an inner bottom surface (54) facing the target (4). The inner bottom surface (54) is a bottom surface among the inner surface (51) that faces the target (4), and is the bottom surface furthest from the target (4) (in other words, closest to the cathode (32)). In this embodiment, the inner bottom surface (54) is the bottom surface of the concave portion (38a).

[0040] The inner surface (51) includes a first area (R1) and a second area (R2) located on the target (4) side with respect to the first area (R1). The first area (R1) is a first side (531) including an inner bottom surface (54) and an end (53a) on the cathode (32) side of the inner side (53). The second area (R2) is a second side (532) including an end (53b) on the target (4) side of the inner side (53). The outer surface (52) includes a third area (R3) and a fourth area (R4) located on the target (4) side with respect to the third area (R3). The third area (R3) is a surface of the outer surface (52) with a gradient of 45 degrees or less with respect to the centerline (L) (i.e., a taper of 90 degrees or less). In this embodiment, the third region (R3) is a tapered surface extending toward the target (4). The fourth region (R4) is a rounded area including the end (52a) toward the target (4) on the outer surface (52). More specifically, the fourth region (R4) is a rounded chamfered surface extending outwardly toward the cathode (32) side from the annular end (52a) in a convex state toward the outside. The second grid electrode (34) further has an outer bottom surface (55) facing toward the opposite side of the target (4). In this embodiment, the outer bottom surface (55) is a surface opposite to the inner bottom surface (54) at the bottom wall (38) of the second grid electrode (34).

[0041] The average illuminance of the second region (R2) is smaller than the average illuminance of the first region (R1). The average illuminance of the first region (R1) is 1.0 μm or more and 3.2 μm or less. The average illuminance of the second region (R2) is 0.4 μm or more and 1.0 μm or less. More specifically, the average illuminance 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 illuminance 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 illuminance 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 illuminance of the outer surface (52) is smaller than the average illuminance 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 the average roughness of the third region (R3). The average roughness of the outer bottom surface (55) is larger than the average roughness of the fourth region (R4). Additionally, the average roughness refers to the arithmetic mean roughness Ra. For measuring Ra, a contact surface roughness meter, a laser microscope, a white interferometer, etc., may be used. For example, a contact surface roughness meter is preferred for measuring Ra of the inner surface (51), and a white interferometer or a laser microscope is preferred for measuring Ra of the outer surface (52). Here, the fact that the average roughness of region (α) is smaller than the average roughness of region (β) means that region (α) has an average roughness less than a predetermined value, and region (β) has an average roughness greater than the predetermined value. In this case, within region (α), if the value of the average illuminance is less than a predetermined value, it may vary or remain constant. Likewise, within region (β), if the value of the average illuminance is greater than or equal to a predetermined value, it may vary or remain constant. Furthermore, the statement that the average illuminance of region (α) is greater than the average illuminance of region (β) means that region (α) has an average illuminance greater than or equal to a predetermined value, and region (β) has an average illuminance less than the aforementioned predetermined value.In this case, within region (α), the value of the average roughness may vary or remain constant as long as it is greater than or equal to a predetermined value. Likewise, within region (β), the value of the average roughness may vary or remain constant as long as it is less than or equal to a predetermined value. In this embodiment, the value of the average roughness of the inner surface (51) changes so that it gradually increases from the end (53b) to the end (53a).

[0042] A second grid electrode (34) having an average roughness as described above is manufactured as follows, as an example. First, in the electrolytic solution, the surface of a cup-shaped cathode is positioned to face the outer surface (52) of the second grid electrode (34) which is electrically connected to the anode. Meanwhile, the inner surface (51) of the second grid electrode (34) is positioned so that the cathodes are not facing each other. By performing electrolytic polishing in this state, a second grid electrode (34) having an average roughness as described above is manufactured. Additionally, before electrolytic polishing is performed, mechanical polishing such as buff polishing may be performed on the outer surface (52) of the second grid electrode (34).

[0043] [Mechanisms and Effects]

[0044] In the X-ray tube (1), on the inner surface (51) of the second grid electrode (34) which has a tubular shape, 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). As a result, even when a negative high voltage is applied to the cathode (32) and the second grid electrode (34) respectively with respect to the target (4), it becomes difficult for a leak current to occur at the inner surface (51) of the second grid electrode (34). In addition, on the inner surface (51) of the second grid electrode (34) which has a tubular shape, the average roughness of the first region (R1) located on the cathode (32) side with respect to the second region (R2) is greater than the average roughness of the second region (R2) located on the opposite side from the cathode (32) with respect to the first region (R1). As a result, even when cathode material is emitted from the cathode (32), the cathode material is easily captured in the first region (R1), so the cathode material reaching and adhering to the inner surface of the case (2) is suppressed, and it becomes difficult for a leak current to occur at the point where the cathode material attached to the inner surface of the case (2) is generated. By the above, sufficient withstand voltage characteristics can be secured in the X-ray tube (1).

[0045] In addition, even when the target material is emitted from the target (4), the target material becomes easier to capture in the first region (R1). By capturing the cathode material and / or the target material in the first region (R1), the cathode material and / or the target material can be prevented from falling out of the case (2) and becoming foreign matter. Therefore, it becomes difficult for a leakage current to occur at the source of the foreign matter. As a result of the above, sufficient withstand voltage characteristics can be secured with the X-ray tube (1).

[0046] In the X-ray tube (1), on the inner surface (51), the inner bottom surface (54) facing the target (4) is configured as a first region (R1). By doing so, the cathode material is easily captured on the inner bottom surface (54), and thus the generation of leakage current originating from the cathode material attached to the inner surface of the case (2) can be more reliably suppressed.

[0047] In the X-ray tube (1), a first side (531) including the end (53a) on the cathode (32) side of the inner side (53) is configured as a first region (R1), and a second side (532) including the end (53b) on the target (4) side of the inner side (53) is configured as a second region (R2). By doing so, both the generation of leakage current at the inner surface (51) of the second grid electrode (34) and the generation of leakage current at the cathode material attached to the inner surface of the case (2) can be more reliably suppressed.

[0048] In the X-ray tube (1), the average roughness of the second side (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. By this, the second side (532), where leakage current is unlikely to occur, and the inner bottom surface (54), where cathode material is likely to be captured, can be very suitably realized.

[0049] In the X-ray tube (1), the average roughness of the first side (531) is 1.0 μm or more and 1.6 μm or less. By this, the first side (531) where the cathode material is easily captured can be very appropriately realized.

[0050] In the X-ray tube (1), the average roughness of the outer surface (52) is smaller than the average roughness of the second side (532). Because of this, it becomes difficult for a leak current to occur at the outer surface (52) of the second grid electrode (34), so sufficient withstand voltage characteristics can be more reliably secured.

[0051] 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. By this, the outer surface (52) where leakage current is unlikely to occur can be very appropriately realized.

[0052] In the X-ray tube (1), on the outer surface (52), the average illuminance of the fourth region (R4) located on the target (4) side relative to the third region (R3) is smaller than the average illuminance of the third region (R3) located on the cathode (32) side relative to the fourth region (R4). By doing so, the occurrence of leakage current at the outer surface (52) of the second grid electrode (34) can be reliably suppressed.

[0053] In the X-ray tube (1), the fourth region (R4) is a round-shaped region including the end (52a) on the target (4) side of the outer surface (52). By doing so, the generation of leak current at the outer surface (52) of the second grid electrode (34) can be suppressed more reliably.

[0054] In the X-ray tube (1), the average roughness of the outer bottom surface (55) facing the opposite side from the target (4) is greater than the average roughness of the fourth region (R4). Because of this, the cathode material is more easily captured even on the outer bottom surface (55), so the generation of leakage current originating from the cathode material attached to the inner surface of the case (2) can be suppressed more reliably.

[0055] Here, the reason for setting the average roughness of the inner surface (51) to 0.4 μm or more and 3.2 μm or less, and the average roughness of the outer surface (52) to 0.05 μm or more and 0.4 μm or less, is explained in detail.

[0056] 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 respect to the target (4). When the value (absolute value) of this high voltage increases, the leakage current flowing between the "cathode (32) in the electron gun (3)" and the "target (4)" increases. Examples of leakage currents include, for instance, leakage current caused by a discharge between the "part other than the cathode (32) in the electron gun (3) (mainly the second grid electrode (34))" and the "anode target (4) and head (21)," leakage current caused by a discharge between the "foreign object" and the "anode target (4) and head (21)," and leakage current caused by a discharge between the "foreign object" and the "electron gun (3)." If this leakage current increases, the anode current increases even if the tube current is controlled to be constant. The tube current is the current flowing between the cathode (32) and the target (4), and is, for example, the current calculated based on the voltage applied to the first grid electrode (33). 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).

[0057] In the X-ray tube (1), when the anode current exceeds a predetermined threshold, the operation of the X-ray tube (1) can be stopped as a discharge has occurred. Therefore, if the leakage current increases, the anode current is likely to exceed the threshold due to fluctuations in the tube current, and as a result, there is a risk that the operation of the X-ray tube (1) may be stopped even though no discharge has occurred.

[0058] Additionally, if the leakage current increases, X-rays are emitted from the target (4) and / or head (21) by the incidence of electrons caused by the leakage current. Consequently, the focal points of the X-rays (R) irradiated onto the inspection target become multiple, and as a result, there is a risk that the X-ray image of the inspection target will become faint. Furthermore, background noise increases in the X-rays (R) irradiated onto the inspection target, and as a result, there is a risk that the contrast in the X-ray image of the inspection target will decrease.

[0059] Therefore, in the X-ray tube (1), it is important to ensure that the value of the leakage current does not become large enough to lead to the aforementioned problem. By making the average roughness of the inner surface (51) 3.2 μm or less and the average roughness of the outer surface (52) 0.4 μm or less, the leakage current value can be suppressed from becoming large enough to lead to the aforementioned problem.

[0060] Meanwhile, if the value of the leak current becomes too small, it becomes difficult to obtain the effect of gas being emitted from the inner surface of the head (21) by electrons caused by the leak current colliding with the inner surface of the head (21). By making the average roughness of the inner surface (51) 0.4 μm or more and the average roughness of the outer surface (52) 0.05 μm or more, it is possible to suppress the leak current value from becoming so small that the gas emission effect cannot be obtained. In addition, the emitted gas can be removed by a getter placed inside the X-ray tube in a sealed type X-ray tube such as the present embodiment, and by a pump placed outside the X-ray tube in an open type X-ray tube.

[0061] [Variation Example]

[0062] The present disclosure is not limited to the above embodiments. For example, as shown in FIG. 4(a), the bottom wall (38) of the second grid electrode (34) may not have a concave portion (38a) (see FIG. 3) formed therein. In this case, the inner bottom surface (54), which is the first region (R1), is the surface on the target (4) side of the bottom wall (38). Also, as shown in FIG. 4(b), the second grid electrode (34) may have a side wall (37) and may not have a bottom wall (38). In any second grid electrode (34), on the inner surface (51) of the second grid electrode (34) which has a tubular shape, 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). In other words, on the inner surface (51) of the second grid electrode (34) which has a tubular shape, the average roughness of the first region (R1) located on the cathode (32) side with respect 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) with respect to the first region (R1).

[0063] Additionally, regarding the inner surface (51) of the second grid electrode (34) having a tubular shape, if the second region (R2) is located on the target (4) side with respect to the first region (R1), the first region (R1) does not need to be an area including the end (53a) on the cathode (32) side of the inner side (53), and the second region (R2) does not need to be an area including the end (53b) on the target (4) side of the inner side (53). Additionally, regarding the outer surface (52) of the second grid electrode (34) having a tubular shape, if the fourth region (R4) is located on the target (4) side with respect to the third region (R3), the fourth region (R4) does not need to be a round-shaped area including the end (52a) on the target (4) side of the outer surface (52). Additionally, the first region (R1) and the second region (R2) may be separated from each other. Likewise, the third region (R3) and the fourth region (R4) may be separated from each other.

[0064] The X-ray tube (1) may be configured as a sealed reflective X-ray tube. Alternatively, the X-ray tube (1) may be configured as an open-transmitting X-ray tube or an open reflective X-ray tube. An open-transmitting or open reflective X-ray tube is an X-ray tube in which the case is configured to be openable and parts (e.g., window members, parts of the electron gun) can be replaced. In an X-ray generating device equipped with an open-transmitting or open reflective X-ray tube, vacuum evacuation of the space inside the case is performed by a vacuum pump. Explanation of the symbols

[0065] 1… X-ray tube, 2… case, 3… electron gun, 4… target, 32… cathode, 34… second grid electrode (focusing electrode), 51… inner surface, 52… outer surface, 52a… end, 53… inner side, 53a, 53b… end, 54… inner bottom, 55… outer bottom, 531… first side, 532… second side, R1… first region, R2… second region, R3… third region, R4… fourth region.

Claims

Claim 1 An X-ray tube comprising a case, an electron gun that emits an electron beam within the case, and a target that generates X-rays by the incidence of the electron beam within the case, 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, and wherein the focusing electrode is formed in a tubular shape having an inner surface and an outer surface by a single member, and wherein the inner surface includes a first region and a second region located on the target side with respect to the first region, and wherein the average illuminance of the second region is smaller than the average illuminance of the first region. Claim 2 In claim 1, the inner surface has an inner bottom surface facing the target side, and the inner bottom surface is the first region, an X-ray tube. Claim 3 In paragraph 2, the inner surface further has inner sides, and among the inner sides, a first side including the end on the cathode side is the first region, and among the inner sides, a second side including the end on the target side is the second region, X-ray tube. Claim 4 An X-ray tube according to paragraph 3, wherein the average roughness of the second side 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. Claim 5 In paragraph 4, the X-ray tube wherein the average roughness of the first side is 1.0 μm or more and 1.6 μm or less. Claim 6 An X-ray tube according to any one of paragraphs 3 to 5, wherein the average roughness of the outer surface is smaller than the average roughness of the second side. Claim 7 In claim 6, the X-ray tube wherein the average roughness of the outer surface is 0.05 μm or more and 0.4 μm or less. Claim 8 In claim 6, the outer surface comprises a third region and a fourth region located on the target side with respect to the third region, and the average illuminance of the fourth region is smaller than the average illuminance of the third region, X-ray tube. Claim 9 In claim 8, the fourth region is a round-shaped region including the end of the target side on the outer surface, in an X-ray tube. Claim 10 In claim 8, the focusing electrode further has an outer bottom surface facing the opposite side to the target, and the average illuminance of the outer bottom surface is greater than the average illuminance of the fourth region, X-ray tube.

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