X-ray tube and x-ray generator

Abstract

This X-ray tube comprises: a filament electrode (1); a target electrode (2) with which an electron beam emitted from the filament electrode (1) collides to generate X-rays; a rod electrode (3) which is electrically connected to the target electrode (2) and applies a voltage to the target electrode (2); a glass tube (4) which encloses the filament electrode (1), the target electrode (2), and the rod electrode (3); and a window frame (5) that is attached to a window part (4a) of the glass tube (4), the window part being provided in the emission direction of the X-rays generated from the target electrode (2). The rod electrode (3) has a columnar shape having a side surface. This X-ray tube is additionally provided with a coating member (8) which is affixed so as to cover a vicinity of the target electrode (2) and a portion of the side surface of the tip of the rod electrode (3).

Description

X-ray tubes and X-ray generators

[0001] The present disclosure relates to x-ray tubes and x-ray generating devices.

[0002] X-ray tubes are used as X-ray generating means for various applications, such as medical care, non-destructive testing, analytical evaluation, etc. As disclosed in Japanese Patent Laid-Open No. 2009-164038 (Patent Document 1), an X-ray tube is an electron tube in which an electron beam emitted from a cathode side under high vacuum and accelerated is caused to collide with an anode target electrode arranged on an anode side, causing X-rays to be emitted from the target electrode.

[0003] JP 2009-164038 A

[0004] Since X-ray tubes emit characteristic X-rays that correspond to the material of the target electrode, when used in an X-ray fluorescence device for analytical evaluation, the material of the target electrode is selected so that the X-rays do not overlap with the characteristic X-rays of the sample to be analyzed. However, even if the material of the target electrode is selected so that the X-rays do not overlap with the characteristic X-rays of the sample to be analyzed, the X-rays emitted from the X-ray tube contain impurity rays that are different from the characteristic X-rays corresponding to the target electrode material. When an X-ray tube containing such impurity rays is used to analyze or evaluate a sample, there is a risk that the impurity rays will hinder accurate analysis or evaluation.

[0005] The present disclosure has been made to solve such problems, and aims to provide an X-ray tube and an X-ray generator that can reduce impurity rays contained in X-rays emitted from the X-ray tube.

[0006] The X-ray tube disclosed herein is an X-ray tube that generates X-rays. The X-ray tube includes a filament electrode, a target electrode that generates X-rays when struck by an electron beam emitted from the filament electrode, a rod electrode electrically connected to the target electrode and applying a voltage to the target electrode, a glass tube that houses the filament electrode, the target electrode, and the rod electrode, and a window frame attached to a window portion of the glass tube that is provided in the direction of emission of X-rays generated from the target electrode. The rod electrode is columnar and has a side surface. The X-ray tube further includes a coating member attached near the target electrode and covering a portion of the side surface of the tip of the rod electrode.

[0007] The X-ray generator of the present disclosure includes the above-described X-ray tube and a voltage generation circuit for generating a high voltage to be applied to the X-ray tube.

[0008] In the present disclosure, a coating member is attached near the target electrode and covering a portion of the side surface of the tip of the rod electrode, so that the coating member can reduce impurity rays contained in the X-rays emitted from the X-ray tube.

[0009] Fig. 1 is a schematic diagram of an X-ray generating device according to an embodiment 1. Fig. 2 is a graph showing the spectrum of X-rays emitted from an X-ray tube. Fig. 3 is a schematic diagram for explaining the generation of impurity rays contained in X-rays. Fig. 4 is a diagram showing the relationship between incident energy and penetration depth. Fig. 5 is a diagram for explaining the attachment position of a coating member. Fig. 6 is a schematic diagram of an X-ray generating device according to an embodiment 2.

[0010] Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and description thereof will not be repeated.

[0011] First Embodiment [X-ray Generator] In this embodiment, the configuration of an X-ray tube and an X-ray generator used in a fluorescent X-ray device for analytical evaluation, etc. will be described. Note that the X-ray tube and X-ray generator according to this embodiment are not limited to use in fluorescent X-ray devices for analytical evaluation, etc., and may be used in medical or non-destructive testing as long as the X-ray tube and X-ray generator are used in a device that requires the reduction of impurity rays. Fig. 1 is a schematic diagram of an X-ray generator 10 according to the first embodiment.

[0012] X-ray generator 10 comprises an X-ray tube including a filament electrode 1, a target electrode 2, a rod electrode 3, a glass tube 4, a window frame 5, and a coating member 8, and voltage generation circuits 6 and 7 for generating a high voltage to be applied to the X-ray tube. Specifically, the X-ray tube is arranged in a vacuum envelope such as a glass tube 4, with the filament electrode 1 on the cathode side and the target electrode 2 on the anode side. The target electrode 2 is electrically connected to the rod electrode 3 and extends outside from the glass tube 4. Here, the target electrode 2 is made of a high-melting-point metal such as rhodium (Rh), and the rod electrode 3 is made of, for example, copper.

[0013] The coating member 8 is preferably made of the same material as the target electrode 2, for example, rhodium (Rh). The rod electrode 3 has a substantially cylindrical shape. The coating member 8 is attached so as to cover a portion of the side surface of the tip of the substantially cylindrical rod electrode 3 near the target electrode 2. The tip of the rod electrode 3 is a position on the negative side of the z-axis facing the filament electrode 1, as shown in FIG. 1 . The shape of the rod electrode 3 is not limited to a substantially cylindrical shape, and may be any other shape, such as a substantially polygonal pillar, as long as it is a long rod shape.

[0014] The coating member 8 is attached to the rod electrode 3 by brazing. For brazing, for example, silver solder with a melting point of approximately 840°C is used. The coating member 8 preferably has a thickness of 10 μm or more, and a commonly available rhodium foil with a thickness of approximately 10 μm may be used. In addition, a cooling fin 3a with excellent thermal conductivity and voltage resistance is attached to the end of the rod electrode 3 extending outward.

[0015] In the X-ray tube, the filament electrode 1, target electrode 2, and rod electrode 3 are arranged in a straight line (in the same axial direction), and a window 4a is provided in the glass tube 4 at a position perpendicular to (intersecting) this straight line (in the same axial direction). In the X-ray tube, electrons emitted from the cathode filament electrode 1 collide with the anode target electrode 2 to which a high voltage is applied, and X-rays are generated through the window 4a. An X-ray tube that extracts X-rays from the window 4a provided on the side of the glass tube 4 in this way is called a side window type X-ray tube. The coating member 8 is attached at a position opposite the window 4a in the y-axis direction.

[0016] Typically, a side window type X-ray tube is configured with an electron optical system in which the filament electrode 1 (cathode side) is at GND potential and the target electrode 2 (anode side) is at positive potential. The filament electrode 1 is set to GND potential and a current is passed through a voltage generation circuit 7 to generate thermoelectrons. The generated thermoelectrons fly toward the target electrode 2, which is at positive potential, and are aligned in direction by an electrostatic lens or the like (not shown) before colliding with the target electrode. X-rays generated by this collision are extracted to the outside of the X-ray tube through the window 4a.

[0017] Here, we will explain the X-ray spectrum when rhodium (Rh) is used as the material for the target electrode 2. Figure 2 is a graph showing the spectrum of X-rays emitted from an X-ray tube. Many types of target electrodes are used in X-ray fluorescence analyzers, but the characteristic X-rays of rhodium (Rh) are Kα rays (RhKaC) at 20.16 KeV and Lα rays at 2.7 KeV, which hardly overlap with the characteristic X-rays of the sample to be analyzed. For this reason, rhodium (Rh) target electrodes 2 are widely used in X-ray tubes used in X-ray fluorescence analyzers because of their versatility that allows them to be used with any sample.

[0018] However, even when rhodium (Rh) is used for the target electrode 2, a peak of Kα rays (CuKa), which are characteristic X-rays of copper (Cu), appears at approximately 8 KeV, as in the X-ray spectrum shown in Fig. 2. This peak is an impurity ray that is different from the characteristic X-rays of rhodium (Rh) of the target electrode 2. Since the impurity ray may interfere with highly accurate analytical evaluation in an X-ray fluorescence analyzer for analytical evaluation, it is desirable to minimize the impurity ray as much as possible.

[0019] Let us consider the mechanism by which copper (Cu) characteristic impurity X-rays are generated, even though rhodium (Rh) is used as the material for the target electrode 2. First, of the electrons (electron beam) that collide with the target electrode 2, approximately 60 to 70% of the electrons travel through the target electrode 2, and approximately 30 to 40% of the electrons are reflected by the target electrode 2 and become backscattered electrons. The target electrode 2 is usually connected to the rod electrode 3 by brazing, and both the target electrode 2 and the rod electrode 3 are at a positive potential. Therefore, among the backscattered electrons reflected by the target electrode 2, in addition to the backscattered electrons that return to the target electrode 2, there are also backscattered electrons that escape the target electrode 2 and reach the side of the rod electrode 3.

[0020] Figure 3 is a schematic diagram for explaining the generation of impurity rays contained in X-rays. As shown in Figure 3, electrons emitted from the filament electrode 1 collide with the target electrode 2 along trajectory A, are reflected by the target electrode 2, and collide with point C on the side surface of the rod electrode 3 along trajectory B. When the electrons collide with the side surface of the rod electrode 3, characteristic X-rays D due to the material of the rod electrode 3 are generated from point C. Since copper (Cu) is used as the material of the rod electrode 3, impurity rays of the characteristic X-rays of copper (Cu) shown in Figure 2 are generated as a result. Point C is a position on the side surface of the tip of the rod electrode 3 on the positive side in the y-axis direction.

[0021] Therefore, one possible method for suppressing the generation of impurity rays contained in X-rays is to prevent the generation of impurity rays due to reflected electrons that reach the side surfaces of the rod electrode 3. For example, in order to prevent the generation of impurity rays due to reflected electrons that reach the side surfaces of the rod electrode 3, it is possible to plate the side surfaces of the rod electrode 3 with the same material (for example, rhodium (Rh)) as the target electrode 2, or to provide a cover member (for example, Collar) made of the same material (for example, rhodium (Rh)) as the target electrode 2 around the entire periphery of the side surfaces of the rod electrode 3.

[0022] Here, the results of a simulation of the relationship between incident energy and penetration depth will be described. FIG. 4 is a diagram showing the relationship between incident energy and penetration depth. As shown in FIG. 4, the penetration depth increases as the incident energy of the electron beam from the filament electrode 1 increases. The penetration depth is the depth to which incident electrons penetrate before losing energy and being absorbed. For example, as shown in FIG. 4, when the incident energy is 25 keV, the penetration depth is approximately 1.6 μm, and when the incident energy is 50 keV, the penetration depth is approximately 5.0 μm.

[0023] Typically, the maximum incident energy of electron beams used in X-ray tubes is approximately 50 KeV. When rhodium plating is applied to the side surface of the rod electrode 3, the rhodium plating commonly used to protect white precious metals such as silver, platinum, and white gold has a thickness of less than 0.1 μm, making it difficult to achieve a plating thickness (e.g., 1.5 to 2 μm) sufficient to prevent reflected electrons from reaching the rod electrode 3. For this reason, as shown in FIG. 4 , the coating member 8 is preferably 10 μm or thicker, taking into account the penetration depth. Furthermore, since the target electrode 2 has a sufficient thickness (e.g., approximately 100 μm), electrons do not penetrate the target electrode 2 and reach the rod electrode 3.

[0024] Furthermore, rhodium (Rh) is a hard, difficult-to-machine material with a Vickers hardness of 1000 or more, and is also very expensive. Because rhodium (Rh) is a difficult-to-machine and expensive material, it is not practical to fabricate the cover member that is provided around the entire side surface of the rod electrode 3 by lathe processing or the like.

[0025] Therefore, in the X-ray tube according to the first embodiment, the side surfaces of the rod electrode 3 are not rhodium-plated, and a cover member (for example, a collar) is not provided to cover the entire periphery of the rod electrode 3. In the X-ray tube according to the first embodiment, a coating member 8 is attached to cover part of the side surfaces of the rod electrode 3, thereby preventing the generation of impurity rays due to reflected electrons that reach the side surfaces of the rod electrode 3.

[0026] Specifically, rhodium (Rh) foil having a thickness of 10 μm is used for the coating member 8. Rhodium (Rh) foil having a thickness of 10 μm is readily available on the market. Furthermore, since the coating member 8 is attached so as to cover a portion of the side surface of the rod electrode 3, lathe processing is not required as is the case with a cover member that covers the entire periphery, and since the rhodium (Rh) foil is 10 μm thick, it can be easily bent.

[0027] The attachment position of the coating member 8 will now be described. Fig. 5 is a diagram for explaining the attachment position of the coating member 8. Fig. 5 shows a perspective view of the rod electrode 3. The tip of the substantially cylindrical rod electrode 3 is inclined at an angle of approximately 45° from the positive y-axis direction to the negative z-axis direction with respect to the xy plane. The target electrode 2 is attached to the tip of the rod electrode 3 by brazing.

[0028] 3, reflected electrons that miss the target electrode 2 and reach the side surface of the rod electrode 3 collide with the rod electrode 3 on the positive side in the y-axis direction of the side surface of the tip of the rod electrode 3. Conversely, reflected electrons hardly reach the negative side in the y-axis direction of the side surface of the tip of the rod electrode 3. Therefore, if the attachment position of the coating member 8 is set to a position on the positive side in the y-axis direction that is less than half of the entire circumference of the side surface of the tip of the rod electrode 3, it is possible to reduce the generation of impurity characteristic X-rays due to reflected electrons.

[0029] In this way, the coating member 8 is attached by brazing near the target electrode 2 and so as to cover part of the side surface of the tip of the rod electrode 3. In other words, the coating member 8 is attached at a position where the inclination angle of the tip of the rod electrode 3 is closer to the obtuse angle side rather than the acute angle side when viewed from the yz plane. Furthermore, because the thickness of the coating member 8 is 10 μm, even though it is made of rhodium, which has high hardness, it can be easily bent along the curvature of the side surface of the rod electrode 3, as shown in FIG.

[0030] As described above, the coating member 8 is attached by brazing near the target electrode 2 and so as to cover part of the side surface of the tip of the rod electrode 3. This makes it possible to reduce impurity rays contained in X-rays emitted from the X-ray tube by the coating member 8. In particular, in the X-ray tube of embodiment 1, the coating member 8 is attached not along the entire circumference of the rod electrode 3 but along a position that is half or less of the entire circumference of the side surface of the tip of the rod electrode 3. Therefore, when rhodium, which is an expensive material that is difficult to process, is used, impurity rays can be effectively reduced with a small amount of rhodium.

[0031] <Embodiment 2> [X-ray Generator] In this embodiment, a case where a coating member 8 is applied to an end-window type X-ray tube will be described. Fig. 6 is a schematic diagram of an X-ray generator 30 according to embodiment 2. X-ray generator 30 of embodiment 2 includes an X-ray tube including a filament electrode 1, a target electrode 2, a rod electrode 3, a glass tube 4, a window frame 5, and a coating member 8, and voltage generation circuits 6 and 7 for generating a high voltage to be applied to the X-ray tube. The configuration of each part of X-ray generator 30 is the same as the configuration of each part of X-ray generator 10 of embodiment 1, and therefore detailed description thereof will be omitted.

[0032] The X-ray tube of embodiment 2 is an end-window X-ray tube in which the axial direction of the filament electrode 1 intersects with the axial direction of the rod electrode 3, and the window 4a is located on the side (positive side of the z-axis) where the axial direction of the filament electrode 1 intersects with the axial direction of the rod electrode 3. In an end-window X-ray tube, electrons emitted from the filament electrode 1, which is the cathode, collide with the target electrode 2, which is the anode to which a high voltage is applied, and the generated X-rays are extracted from the window 4a located on the positive side of the z-axis.

[0033] The coating member 8 is attached to a position on the opposite side of the filament electrode 1 (negative side of the y-axis) in the axial direction (z-axis) of the rod electrode 3. This is because reflected electrons that miss the target electrode 2 and reach the side surface of the rod electrode 3 collide with the rod electrode 3 on the negative side of the y-axis in the side surface of the tip of the rod electrode 3. Conversely, reflected electrons hardly reach the positive side of the y-axis in the side surface of the tip of the rod electrode 3. Therefore, if the coating member 8 is attached at a position on the negative side of the y-axis that is less than half of the entire circumference of the side surface of the tip of the rod electrode 3, it is possible to reduce the generation of impurity rays of characteristic X-rays due to reflected electrons.

[0034] 6, the coating member 8 is attached by brazing so as to cover a position on the negative side in the y-axis direction, which is near the target electrode 2 and which is equal to or less than half of the entire circumference of the side surface of the tip of the rod electrode 3. In this way, the position where the coating member 8 is attached is a position where it can prevent the generation of impurity rays due to reflected electrons that reach the side surface of the rod electrode 3. This allows the coating member 8 to reduce impurity rays contained in the X-rays emitted from the X-ray tube.

[0035] In an X-ray tube having multiple combinations of filament electrode 1 and target electrode 2, the coating member 8 may be attached to multiple positions where reflected electrons that leave the target electrode 2 and reach the side of the rod electrode 3 reach.

[0036] Aspects It will be understood by those skilled in the art that the above-described embodiments are specific examples of the following aspects.

[0037] (Item 1) An X-ray tube according to one aspect is an X-ray tube that generates X-rays and includes: a filament electrode; a target electrode that generates X-rays when struck by an electron beam emitted from the filament electrode; a rod electrode that is electrically connected to the target electrode and applies a voltage to the target electrode; a glass tube that contains the filament electrode, the target electrode, and the rod electrode; and a window portion provided in the glass tube for extracting X-rays generated from the target electrode, wherein the rod electrode is columnar and has a side surface, and further includes a coating member that is attached so as to cover a portion of the side surface of the tip of the rod electrode and in the vicinity of the target electrode.

[0038] According to the X-ray tube described in paragraph 1, a coating member is attached in the vicinity of the target electrode and so as to cover part of the side surface of the tip of the rod electrode, so that the coating member can reduce impurity rays contained in the X-rays emitted from the X-ray tube.

[0039] (2) In the X-ray tube according to the first aspect, the coating member is attached to a position that occupies half or less of the entire circumference of the side surface.

[0040] According to the X-ray tube described in the second aspect, the number of positions where the coating member is attached can be reduced compared to when the coating member is attached over the entire periphery of the side surface.

[0041] (Item 3) In the X-ray tube according to item 1 or 2, the coating member has a thickness of 10 μm or more.

[0042] According to the X-ray tube described in the third aspect, the coating member can be made thick enough to reliably reduce impurity rays.

[0043] (4) The X-ray tube according to any one of paragraphs 1 to 3, wherein the X-ray tube is a side window type in which the axial directions of the filament electrode and the rod electrode are coaxial, the window portion is disposed in a direction intersecting the axial direction of the rod electrode, and the coating member is attached in a position opposite the window portion.

[0044] According to the X-ray tube described in item 4, the coating member can be applied to a side window type X-ray tube.

[0045] (Item 5) An X-ray tube according to any one of items 1 to 3, wherein the X-ray tube is an end window type in which the axial direction of the filament electrode intersects with the axial direction of the rod electrode, the window portion is disposed on the side where the axial direction of the filament electrode intersects with the axial direction of the rod electrode, and the coating member is attached to a position on the opposite side of the rod electrode from the filament electrode in the axial direction.

[0046] According to the X-ray tube described in item 5, the coating member can be applied to an end-window type X-ray tube.

[0047] (Item 6) In the X-ray tube according to any one of items 1 to 5, the coating member is made of the same material as the target electrode.

[0048] According to the X-ray tube described in item 6, the generation of impurity rays can be reduced by using the same material for the coating member as for the target electrode.

[0049] (7) In the X-ray tube according to any one of the first to sixth aspects, the coating member is made of rhodium.

[0050] According to the X-ray tube described in item 7, the generation of impurity rays contained in X-rays can be appropriately reduced by the rhodium coating member.

[0051] (Item 8) In the X-ray tube according to any one of items 1 to 7, the coating member is a foil.

[0052] According to the X-ray tube described in item 8, by using a foil for the coating member, bending can be easily performed.

[0053] (Item 9) An X-ray generator according to one aspect includes the X-ray tube according to any one of items 1 to 8, and a voltage generation circuit for generating a high voltage to be applied to the X-ray tube.

[0054] According to the X-ray generating device described in Item 9, impurity rays contained in the X-rays emitted from the X-ray tube can be reduced by the coating member.

[0055] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0056] REFERENCE SIGNS LIST 1 Filament electrode, 2 Target electrode, 3 Rod electrode, 3a Cooling fin, 4 Glass tube, 4a Window portion, 5 Window frame, 6, 7 Voltage generating circuit, 8 Coating member, 10, 30 X-ray generating device

Claims

1. An X-ray tube for generating X-rays, comprising: a filament electrode; a target electrode with which an electron beam emitted from the filament electrode collides to generate X-rays; a rod electrode electrically connected to the target electrode and applying a voltage to the target electrode; a glass tube containing the filament electrode, the target electrode, and the rod electrode; and a window provided in the glass tube for extracting X-rays generated from the target electrode, wherein the rod electrode is columnar and has a side surface, and further comprising a coating member affixed to the vicinity of the target electrode and to cover a portion of the side surface of the tip of the rod electrode.

2. The X-ray tube according to claim 1, wherein the coating member is attached at a position that occupies less than half of the entire circumference of the side surface.

3. The X-ray tube according to claim 1, wherein the thickness of said coating member is 10 μm or more.

4. The X-ray tube according to claim 1, wherein the axial directions of the filament electrode and the rod electrode are coaxial, the window portion is a side window type disposed in a direction intersecting the axial direction of the rod electrode, and the coating member is affixed in a position opposite to the window portion.

5. The X-ray tube according to claim 1, wherein the X-ray tube is an end window type in which the axial direction of the filament electrode intersects with the axial direction of the rod electrode, the window portion is located on the side where the axial direction of the filament electrode intersects with the axial direction of the rod electrode, and the coating member is affixed to a position on the opposite side of the rod electrode from the filament electrode in the axial direction.

6. The X-ray tube of claim 1, wherein said coating member is made of the same material as said target electrode.

7. The X-ray tube of claim 6, wherein said coating member is rhodium.

8. The x-ray tube of claim 6, wherein the coating member is a foil.

9. An X-ray generating device comprising: the X-ray tube according to claim 1; and a voltage generating circuit for generating a high voltage to be applied to said X-ray tube.

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