X-ray tube

Abstract

To provide an X-ray tube capable of suppressing adhesion of metal atoms separated from a filament to an output window.SOLUTION: The X-ray tube according to the embodiment includes an envelope, an output window having a plate shape and provided at an end portion of the envelope, a target provided inside the envelope and facing the output window, a focusing electrode provided inside the envelope, having a tubular shape, and surrounding the target, and a filament provided inside the envelope and surrounding the focusing electrode. When a first line passing through a center of a surface of the output window on the target side and being in contact with an end portion of the focusing electrode on the output window side is defined, a center of the filament is located on a side where the focusing electrode is provided with respect to the first line.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to an X-ray tube. [Background technology]

[0002] One type of X-ray tube is a fixed anode X-ray tube. This type of X-ray tube includes, for example, an envelope and an output window provided at one end of the envelope. Inside the envelope, there are provided an anode assembly facing the output window, a cathode assembly provided near the end of the anode assembly on the output window side, and a focusing electrode provided between the anode assembly and the cathode assembly.

[0003] In such an X-ray tube, when a negative voltage is applied to the cathode assembly, thermions are generated in the filament attached to the cathode assembly. The generated thermions are accelerated by the potential difference between the anode assembly, to which a positive voltage is applied, and the cathode assembly, and their trajectories are bent by the electric field formed by the envelope and the focusing electrode, until they collide with the target attached to the anode assembly. X-rays generated by the thermions colliding with the target are irradiated outside the X-ray tube through the output window.

[0004] When thermal electrons are generated in the filament, metal atoms (e.g., tungsten atoms) contained in the filament evaporate and detach from the filament. In this case, some of the metal atoms detached from the filament may diffuse inside the envelope and attach to the output window. If the amount of metal atoms attached to the output window increases, the transmittance of X-rays may decrease, resulting in a decrease in the characteristic X-ray intensity, or the attached metal atoms may be excited by X-rays, resulting in the generation of unintended impure X-rays.

[0005] Therefore, there has been a demand for the development of an X-ray tube that can prevent metal atoms detached from the filament from adhering to the output window. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-91969 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide an X-ray tube that can prevent metal atoms detached from the filament from adhering to the output window. [Means for solving the problem]

[0008] An X-ray tube according to an embodiment includes an envelope, a plate-shaped output window provided at an end of the envelope, a target provided inside the envelope and facing the output window, a cylindrical focusing electrode provided inside the envelope and surrounding the target, and a filament provided inside the envelope and surrounding the focusing electrode. When a first line is defined that passes through the center of the surface of the output window facing the target and is tangent to the end of the focusing electrode facing the output window, the center of the filament is located on the side of the first line where the focusing electrode is provided. [Effects of the Invention]

[0009] According to the embodiments of the present invention, it is possible to provide an X-ray tube that can prevent metal atoms detached from the filament from adhering to the output window. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic partial cross-sectional view illustrating an X-ray tube according to an embodiment of the present invention. [Figure 2] FIG. 10 is a schematic cross-sectional view illustrating the positional relationship between an output window, a focusing electrode, and a filament according to a comparative example. [Figure 3] 3 is a schematic diagram illustrating the state of adhesion of metal atoms in the positional relationship shown in FIG. 2. FIG. [Figure 4]3 is a schematic cross-sectional view illustrating the positional relationship between an output window, a focusing electrode, and a filament according to the embodiment. FIG. [Figure 5] 5 is a schematic diagram illustrating the state of adhesion of metal atoms in the positional relationship shown in FIG. 4. FIG. [Figure 6] 10A and 10B are schematic cross-sectional views illustrating the positional relationship between an output window, a focusing electrode, and a filament according to another embodiment. [Figure 7] 7 is a schematic diagram illustrating the state of adhesion of metal atoms in the positional relationship shown in FIG. 6. FIG. [Figure 8] 10 is a graph illustrating the relationship between the positional relationship between the output window, the focusing electrode, and the filament, and the area ratio of a region to which metal atoms are unlikely to adhere. [Figure 9] 1 is a graph illustrating the relationship between the usage time of the X-ray tube and the characteristic X-ray intensity. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments will be illustrated with reference to the drawings. In the drawings, like components are designated by like reference numerals and detailed descriptions thereof will be omitted where appropriate.

[0012] The X-ray tube 1 according to this embodiment can be used in, for example, an X-ray fluorescence analyzer, although the use of the X-ray tube 1 is not limited to an X-ray fluorescence analyzer. In this specification, a pressure state lower than atmospheric pressure is referred to as a vacuum state.

[0013] FIG. 1 is a schematic partial cross-sectional view illustrating an X-ray tube 1 according to the present embodiment. As shown in FIG. 1, the X-ray tube 1 includes, for example, an X-ray generating unit 2, a tube container 3, a high-voltage receptacle 4, a cooling pipe 5, a joint 6, a water guide pipe 7, a conductive spring 8, an insulating cylinder 9, an empty tray 10, and a bellows 11.

[0014] There is no particular limitation on the installation direction of the X-ray tube 1. For example, the X-ray tube 1 can be installed so that the tube axis TA extends in the vertical direction, or so that the tube axis TA extends in a direction intersecting the vertical direction. Also, for example, the X-ray generating unit 2 side of the X-ray tube 1 can be oriented downward in the direction of gravity, upward in the direction of gravity, or horizontally.

[0015] The tube vessel 3 accommodates the X-ray generating unit 2, high-voltage receptacle 4, cooling pipe 5, joint 6, water-guiding pipe 7, conductor spring 8, insulating cylinder 9, empty tray 10, and bellows 11. The tube vessel 3 has, for example, a substantially cylindrical shape. The central axis of the tube vessel 3 can be, for example, substantially coaxial with the tube axis TA of the X-ray tube 1. The tube vessel 3 is formed, for example, from metal, and has a lead plate 3a attached to its inner wall. The internal space 3b of the tube vessel 3 is filled with insulating oil. The internal space 3b is, for example, the space between the inner wall of the lead plate 3a and the outer surfaces of the X-ray generating unit 2 and high-voltage receptacle 4, and is the space excluding the empty tray 10.

[0016] The high-voltage receptacle 4 has, for example, a generally cylindrical shape with one end open and the other end closed. A high-voltage cable is connected inside the high-voltage receptacle 4. The high-voltage receptacle 4 is provided liquid-tight at the end of the tube vessel 3 opposite the X-ray generating unit 2 side. A pair of connection terminals 4a are provided at the closed end of the high-voltage receptacle 4. The connection terminals 4a include a bushing of an external electrical circuit inserted into the high-voltage receptacle 4 and a terminal.

[0017] The cooling pipe 5 is a conduit for flowing a cooling liquid (e.g., pure water). The cooling pipe 5 has a spiral shape and is provided between the high-voltage receptacle 4 and the insulating cylinder 9. However, the cooling pipe 5 does not have to be provided in a spiral shape. The cooling pipe 5 has a cooling pipe 5b with a water inlet 5a through which a coolant is supplied, and a cooling pipe 5c with a water outlet 5b through which the coolant is discharged. The water inlet 5a of the cooling pipe 5b is connected to a circulating cooling device or the like that is a coolant supply source provided outside the X-ray tube 1. The end of the cooling pipe 5b opposite the water inlet 5a side is connected to a joint 6. The water outlet 5b of the cooling pipe 5c is connected to a circulating cooling device or the like. The end of the cooling pipe 5c opposite the water outlet 5b side is connected to the joint 6.

[0018] The joint 6 is provided near the center of the X-ray tube 1 and connects the cooling pipe 5 and the water guide pipe 7 .

[0019] The water guide pipe 7 has a substantially cylindrical outer pipe 7a and a substantially cylindrical inner pipe 7b provided inside the outer pipe 7a. The water guide pipe 7 extends, for example, along the pipe axis TA. The water guide pipe 7 is connected to the joint 6.

[0020] The outer pipe 7a is connected to the joint 6 and a support portion 23a of the anode assembly 23, which will be described later, in a liquid-tight manner. The inner pipe 7b has an outer diameter smaller than the inner diameter of the outer pipe 7a, and extends along the pipe axis TA.

[0021] The conductive spring 8 is provided between the connection terminal 4a and the joint 6. The conductive spring 8 electrically connects the connection terminal 4a and the joint 6.

[0022] The insulating cylinder 9 has a substantially cylindrical shape and is made of an insulating material. The insulating cylinder 9 has a structure that allows, for example, insulating oil to flow through it. One end of the insulating cylinder 9 is fixed to the inside of the tubular container 3, for example.

[0023] The empty tray 10 is a space isolated from the internal space 3b of the tube vessel 3 by a bellows 11. The empty tray 10 is provided to absorb volume changes that occur when the insulating oil filled in the internal space 3b of the tube vessel 3 expands or contracts. The empty tray 10 is in communication with the outside of the X-ray tube 1.

[0024] The bellows 11 is provided inside the tubular vessel 3 and separates the internal space 3b of the tubular vessel 3 from the empty tray 10. The bellows 11 can be made of an elastic material such as rubber. The bellows 11 can be a flexible elastic member. For example, the bellows 11 can be a so-called rubber bellows (rubber membrane). If the bellows 11 is a flexible elastic member, when the insulating oil expands or contracts, the empty tray 10, which communicates with the outside of the X-ray tube 1, can contract or expand via the bellows 11. In other words, the bellows 11 is provided so that the expansion or contraction of the insulating oil can be absorbed by the empty tray 10.

[0025] The X-ray generating unit 2 includes, for example, an envelope 21, an output window 22, an anode assembly 23, a cathode assembly 24, and a focusing electrode 25.

[0026] The envelope 21 has, for example, a cylindrical shape. The central axis of the envelope 21 can be, for example, approximately coaxial with the tube axis TA of the X-ray tube 1. One end of the envelope 21 (the end on the tube container 3 side) is open. The other end 21a of the envelope 21 has an approximately flat surface. A hole 21a1 is provided in the central region of the end 21a of the envelope 21.

[0027] The side of the envelope 21 near the end 21a forms an inclined portion 21b. The inclined portion 21b is inclined in a direction approaching the tube axis TA of the X-ray tube 1 as it approaches the end 21a. For example, the inner diameter (the inner wall dimension in a direction intersecting the tube axis TA) of the envelope 21 gradually decreases as it approaches the tip. The electric field formed by the inclined portion 21b and the focusing electrode 25 can control the trajectory of thermoelectrons traveling from the filament 24a toward the target 23b. For example, by changing the angle between the inner wall of the inclined portion 21b and the tube axis TA of the X-ray tube 1, the area (focus) where thermoelectrons enter the target 23b can be adjusted to an appropriate size. If the area (focus) where thermoelectrons enter the target 23b is adjusted to an appropriate size, melting of the target 23b due to overheating can be suppressed. The enclosure 21 can be made of a metal such as stainless steel.

[0028] The output window 22 has a disk shape and is provided at the end 21a of the envelope 21. The output window 22 is provided so that the hole 21a1 of the end 21a of the envelope 21 is airtight. For example, the periphery of the output window 22 is joined to the vicinity of the periphery of the hole 21a1 by brazing or the like. The output window 22 maintains the vacuum state inside the envelope 21 and transmits X-rays generated inside the envelope 21. For this reason, the output window 22 is made of a material that attenuates X-rays little. The output window 22 is made of, for example, beryllium. Furthermore, in order to reduce attenuation of X-rays, the thickness of the output window 22 can be, for example, about several tens of μm to several hundreds of μm.

[0029] Furthermore, depending on the application of the X-ray tube 1, the atmosphere in which the X-ray tube 1 is installed may contain scattered corrosive substances or corrosive gases. In such cases, a protective film may be provided to cover the surface of the output window 22 opposite to the target 23b side. The protective film may contain, for example, diamond-like carbon as its main material. The protective film may be formed by depositing a film so as to cover the output window 22 using a film-forming method such as vapor deposition. The thickness of the protective film may be, for example, approximately 0.5 μm to 1 μm.

[0030] The target 23b side of the anode assembly 23 is provided inside the envelope 21. The opposite side of the anode assembly 23 to the target 23b side is provided inside the tubular vessel 3. The anode assembly 23 includes, for example, a support portion 23a, a target 23b, and a sealing portion 23c.

[0031] The support portion 23a has a substantially cylindrical shape and extends along the tube axis TA of the X-ray tube 1. One end of the support portion 23a is provided inside the envelope 21 and faces the output window 22. The other end of the support portion 23a is provided inside the tube vessel 3 and is electrically connected to the high-voltage receptacle 4 via the joint 6, the conductor spring 8, and the connection terminal 4a. The support portion 23a is formed from a conductive material such as copper.

[0032] When a high voltage is applied to the high voltage receptacle 4 via a high voltage cable electrically connected to the high voltage receptacle 4, a high voltage (tube voltage) is applied between the target 23b electrically connected to the support portion 23a and the filament 24a.

[0033] The target 23b has, for example, a disk shape and is provided inside the envelope 21. The central axis of the target 23b can be, for example, approximately coaxial with the tube axis TA of the X-ray tube 1. The target 23b faces the output window 22. The target 23b can be provided, for example, at the end of the support part 23a that faces the output window 22. The target 23b contains a material that generates X-rays when collided with by thermal electrons. The target 23b contains, for example, at least one of Rh (rhodium), W (tungsten), molybdenum (Mo), chromium (Cr), palladium (Pd), platinum (Pt), and copper (Cu).

[0034] The sealing part 23c is provided inside the tubular vessel 3. The sealing part 23c airtightly seals the end of the X-ray generating part 2 opposite to the envelope 21 side. That is, the sealing part 23c is provided to maintain a vacuum state in the space inside the envelope 21. The sealing part 23c can be made of, for example, a glass material or ceramics.

[0035] The cathode assembly 24 is provided inside the envelope 2 . The cathode assembly 24 includes, for example, a filament 24a and a support 24b.

[0036] The filament 24a surrounds the focusing electrode 25 and the target 23b. The filament 24a is linear and has a substantially circular or C-shaped shape when viewed in a direction along the tube axis TA of the X-ray tube 1. The filament 24a can be formed, for example, from a wire containing tungsten as a main component.

[0037] One end of the support part 24b is electrically connected to the filament 24a. The other end of the support part 24b is electrically connected to a cable or the like provided outside the X-ray tube 1. For example, the filament 24a is electrically connected to the negative pole of a power supply provided outside the X-ray tube 1 via the support part 24b and the cable or the like.

[0038] The focusing electrode 25 has, for example, a substantially cylindrical shape. The central axis of the focusing electrode 25 can be, for example, substantially coaxial with the tube axis TA of the X-ray tube 1. The focusing electrode 25 surrounds the target 23b. When viewed from a direction along the tube axis TA of the X-ray tube 1, the focusing electrode 25 is provided between the target 23b and the filament 24a. The focusing electrode 25 can be made of, for example, a conductive material such as iron (Fe) or stainless steel.

[0039] Focusing electrode 25 and envelope 21 can be grounded. Focusing electrode 25 and envelope 21 can also be electrically connected to a power supply provided outside X-ray tube 1. When focusing electrode 25 and envelope 21 are connected to a power supply, the voltage applied to focusing electrode 25 and envelope 21 can be higher than the voltage applied to filament 24a and lower than the voltage applied to support portion 41.

[0040] When a negative voltage is applied to the filament 24a from a power supply provided outside the X-ray tube 1, the filament 24a is heated and thermoelectrons 200 are generated, as shown in FIGS. 4 and 6, which will be described later. Furthermore, a positive voltage is applied to the target 23b from a power source provided outside the X-ray tube 1 via a high-voltage cable, a high-voltage receptacle 4, and the support portion 23a.

[0041] The generated thermoelectrons 200 are accelerated by the potential difference between the target 23b, to which a positive voltage is applied, and the filament 24a, and their trajectories are bent by the electric field formed by the envelope 21 and the focusing electrode 25, causing them to collide with the target 23b. X-rays are generated when the thermoelectrons 200 collide with the target 23b. The generated X-rays pass through the output window 22 and are irradiated onto, for example, the surface of a sample for X-ray fluorescence analysis.

[0042] When thermoelectrons 200 are generated in the filament 24a, metal atoms (e.g., tungsten atoms) 24a1 contained in the filament 24a evaporate and are detached from the filament 24a. The metal atoms 24a1 detached from the filament 24a are electrically neutral and therefore move linearly inside the envelope 21 without being affected by the electric field formed inside the envelope 21. Therefore, some of the metal atoms 24a1 detached from the filament 24a may diffuse inside the envelope 21 and adhere to the surface of the output window 22 facing the target 23b. In this case, as the X-ray tube 1 is used for a long time, the metal atoms 24a1 may continue to adhere, and the amount of metal atoms 24a1 attached to the output window 22 may increase.

[0043] Since X-rays have difficulty passing through metal atoms 24a1 such as tungsten atoms, an increase in the amount of metal atoms 24a1 attached to output window 22 may reduce the transmittance of X-rays and lead to a decrease in the intensity of characteristic X-rays. Furthermore, the metal atoms 24a1 attached to output window 22 may be excited by X-rays, generating unintended impure X-rays, which may degrade the functionality of X-ray tube 1.

[0044] As a result of investigation, the inventor has found that if the positional relationship between the output window 22, the focusing electrode 25, and the filament 24a is appropriate, it is possible to prevent the metal atoms 24a1 from adhering to the output window 22. FIG. 2 is a schematic cross-sectional view illustrating the positional relationship between the output window 22, the focusing electrode 25, and the filament 24a according to a comparative example. FIG. 3 is a schematic diagram illustrating the state of attachment of the metal atoms 24a1 in the positional relationship shown in FIG.

[0045] 2, line 100 (corresponding to an example of a first line) passes through the center of the surface of output window 22 facing the target 23b and contacts the end of focusing electrode 25 facing the output window 22. In the positional relationship shown in FIG. 2, filament 24a is located on the opposite side of line 100 from the side on which focusing electrode 25 is provided. In such a case, as shown in FIG. 2, metal atoms 24a1 that have been detached from filament 24a and are moving linearly directly reach the entire surface of output window 22 facing the target 23b.

[0046] Therefore, as shown in FIG. 3, metal atoms 24a1 are attached to the entire surface of output window 22 on the target 23b side.

[0047] For example, as the X-ray tube 1 is used for a long time, the entire surface of the output window 22 facing the target 23b becomes covered with metal atoms 24a1, reducing the X-ray transmittance. This reduction in X-ray transmittance leads to a reduction in the characteristic X-ray intensity. Furthermore, the metal atoms 24a1 attached to the output window 22 may be excited by X-rays, generating unintended impure X-rays, potentially reducing the functionality of the X-ray tube 1.

[0048] FIG. 4 is a schematic cross-sectional view illustrating the positional relationship between output window 22, focusing electrode 25, and filament 24a according to the present embodiment. FIG. 5 is a schematic diagram illustrating the state of attachment of the metal atoms 24a1 in the positional relationship shown in FIG.

[0049] 4, the center of filament 24a is located on the side of line 100 where focusing electrode 25 is provided. In this case, as shown in FIG. 4, metal atoms 24a1 that have been detached from filament 24a and are moving linearly are blocked by focusing electrode 25, making it difficult for them to directly reach the central region of the surface of output window 22 facing target 23b.

[0050] Therefore, as shown in FIG. 5, metal atoms 24a1 adhere to the peripheral region of the surface of output window 22 facing target 23b, but are less likely to adhere to the central region of the surface of output window 22 facing target 23b.

[0051] In this case, as shown in Figure 4, if the center of the filament 24a is located on the side of the wire 100 where the focusing electrode 25 is provided, and the filament 24a is in contact with the wire 100, the ratio of the area of ​​the central region, to which metal atoms 24a1 are less likely to adhere, to the area of ​​the entire region of the output window 22 can be made 40% or more.

[0052] Here, metal atoms 24a1 adhere to the peripheral region of the surface of output window 22 facing target 23b, which can result in the aforementioned decrease in characteristic X-ray intensity and generation of impure X-rays. However, because the characteristic X-ray intensity and generation of impure X-rays in the central region of output window 22 are important for the function of X-ray tube 1, the effect of the decrease in characteristic X-ray intensity and generation of impure X-rays in the peripheral region of output window 22 on practical function is often small.

[0053] For example, when metal atoms 24a1 adhere to the entire area of ​​output window 22, the decrease in characteristic X-ray intensity is approximately 5% in annual terms (after 8760 hours of use). In contrast, when the ratio of the area of ​​the central region, to which metal atoms 24a1 are less likely to adhere, to the area of ​​the entire area of ​​output window 22 is approximately 40%, the decrease in characteristic X-ray intensity can be kept to approximately 2% or less in annual terms (after 8760 hours of use). In other words, the decrease in characteristic X-ray intensity can be kept to a practically acceptable level.

[0054] FIG. 6 is a schematic cross-sectional view illustrating the positional relationship between an output window 22, a focusing electrode 25, and a filament 24a according to another embodiment. FIG. 7 is a schematic diagram illustrating the state of attachment of the metal atoms 24a1 in the positional relationship shown in FIG.

[0055] 6, line 101 (corresponding to an example of the second line) passes along the periphery of the surface of output window 22 facing the target 23b and contacts the end of focusing electrode 25 facing the output window 22. In the positional relationship shown in FIG. 6, the center of filament 24a overlaps with line 101. In such a case, as shown in FIG. 6, metal atoms 24a1 that have been detached from filament 24a and are moving linearly are blocked by focusing electrode 25, making it difficult for them to directly reach the entire area of ​​the surface of output window 22 facing the target 23b.

[0056] 7, metal atoms 24a1 are unlikely to adhere to the entire surface of output window 22 facing target 23b. In this case, if the ratio of the area of ​​the central region, to which metal atoms 24a1 are unlikely to adhere, to the area of ​​the entire region of output window 22 is set to 90% or more, the decrease in characteristic X-ray intensity can be kept to approximately 1% or less on an annualized basis (after 8,760 hours of use). In other words, it is possible to almost completely eliminate the decrease in characteristic X-ray intensity and the generation of impure X-rays.

[0057] Furthermore, the center of the filament 24a may be positioned on the side of the wire 101 where the focusing electrode 25 is provided. In this way, the metal atoms 24a1 that have been detached from the filament 24a and are moving linearly are more likely to be blocked by the focusing electrode 25. This makes it possible to more reliably prevent the metal atoms 24a1 from adhering to the entire surface of the output window 22 facing the target 23b.

[0058] Here, if the distance between the center of the filament 24a and the wires 100 and 101 is increased, the area where the metal atoms 24a1 are blocked by the focusing electrode 25 increases, and therefore the area where the metal atoms 24a1 are difficult to adhere can be increased. However, if the distance between the center of the filament 24a and the wires 100 and 101 is increased, the area (focus) where the thermoelectrons 200 are incident on the target 23b becomes too small, which may cause the target 23b to melt due to overheating. As described above, the trajectory of the thermoelectrons 200 traveling from the filament 24a toward the target 23b can be controlled by, for example, the angle between the inner wall of the inclined portion 21b and the tube axis TA of the X-ray tube 1.

[0059] 4 and 6, the longer the distance between the center of the filament 24a and the wires 100 and 101, the larger the angle θ between the inner wall of the inclined portion 21b and the tube axis TA of the X-ray tube 1. In other words, by appropriately setting the angle θ according to the distance between the center of the filament 24a and the wires 100 and 101, it is possible to prevent the target 23b from melting due to overheating.

[0060] The appropriate range of the angle θ can be determined appropriately by conducting experiments or simulations depending on the distance between the center of the filament 24 a and the lines 100 and 101 .

[0061] FIG. 8 is a graph illustrating the relationship between the positional relationship between the output window 22, the focusing electrode 25, and the filament 24a, and the area ratio of the region to which the metal atoms 24a1 are difficult to attach. 8, A on the horizontal axis corresponds to the positional relationship in FIG. 4. B corresponds to the positional relationship in FIG.

[0062] 8A, if the positional relationship shown in Fig. 4 is used, the ratio of the area of ​​the central region, to which metal atoms 24a1 are less likely to adhere, to the area of ​​the entire region of output window 22 can be set to 40% or more. Therefore, the decrease in the characteristic X-ray intensity can be reduced to a practically acceptable level.

[0063] 8B, if the positional relationship shown in Fig. 6 is adopted, the ratio of the area of ​​the central region, to which metal atoms 24a1 are less likely to adhere, to the area of ​​the entire region of output window 22 can be set to 90% or more. As a result, it is possible to almost completely eliminate the decrease in the intensity of characteristic X-rays and the generation of impure X-rays.

[0064] FIG. 9 is a graph illustrating the relationship between the usage time of the X-ray tube 1 and the characteristic X-ray intensity. The 8760 hours on the horizontal axis of FIG. 9 corresponds to one year of continuous use of the X-ray tube 1. 9. C in FIG. 9 is the case of the positional relationship according to the comparative example shown in FIG. D in FIG. 9 is the case of the positional relationship according to the embodiment shown in FIG.

[0065] 9, in the case of the positional relationship according to the comparative example, the characteristic X-ray intensity significantly decreases as the usage time increases. The characteristic X-ray intensity after 8,760 hours is approximately 5% lower than the characteristic X-ray intensity after 0 hours of usage.

[0066] In contrast, in the case of the positional relationship according to the embodiment, the characteristic X-ray intensity does not decrease significantly even if the usage time is long. For example, the decrease in the characteristic X-ray intensity after 8760 hours can be kept within 1% of the characteristic X-ray intensity at 0 hours of usage.

[0067] That is, with the X-ray tube 1 according to this embodiment, it is possible to suppress the decrease in the characteristic X-ray intensity that occurs with long-term use. Therefore, even after long-term use, correction of the characteristic X-ray intensity is not necessary. Furthermore, even if correction of the characteristic X-ray intensity becomes necessary, the frequency of correction can be reduced. Therefore, it is possible to provide an X-ray tube 1 that is resistant to performance degradation and has a long life.

[0068] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples and are not intended to limit the scope of the invention. Design modifications to the above-described embodiments made by a person skilled in the art are also encompassed within the scope of the present invention as long as they incorporate the features of the present invention. For example, the shape, size, material, arrangement, etc. of each element included in the X-ray tube 1 are not limited to those exemplified, and can be changed as appropriate.

[0069] Furthermore, the elements of each of the above-described embodiments can be combined to the greatest extent possible, and such combinations are also included within the scope of the present invention as long as they include the features of the present invention. [Explanation of symbols]

[0070] 1 X-ray tube, 2 X-ray generating section, 21 envelope, 21b tilting section, 22 output window, 23 anode assembly, 23b target, 24 cathode assembly, 24a filament, 24a1 metal atoms, 25 focusing electrode, 100 wire, 101 wire, 200 thermal electrons

Claims

1. An enclosure; an output window having a plate shape and provided at an end of the envelope; a target provided inside the envelope and facing the output window; a focusing electrode provided inside the envelope, having a cylindrical shape, and surrounding the target; a filament provided inside the envelope and surrounding the focusing electrode; Equipped with An X-ray tube in which, when a first line is defined that passes through the center of the surface of the output window facing the target and is tangent to the end of the focusing electrode facing the output window, the center of the filament is located on the side of the first line on which the focusing electrode is provided.

2. 2. The x-ray tube of claim 1, wherein said filament is tangent to said first wire.

3. 2. The X-ray tube according to claim 1, wherein, when a second line is defined that passes through the periphery of the surface of the output window facing the target and is tangent to the end of the focusing electrode facing the output window, the center of the filament overlaps the second line or is located on the side of the second line on which the focusing electrode is provided.

4. 4. The X-ray tube according to claim 1, wherein the filament is linear and has a substantially circular or C-shaped shape when viewed in a direction along the central axis of the X-ray tube.

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