X-ray tube and x-ray generator

Abstract

The present invention provides an X-ray tube and an X-ray generator in which impure rays included among X-rays radiated from the X-ray tube can be reduced. The 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) that is electrically connected to the target electrode (2) and applies a voltage to the target electrode (2); a glass tube (4) containing 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) provided in the emission direction of the X-rays generated from the target electrode (2). A conductive film (4b) is formed on at least a part of the inner wall of the glass tube (4) on the side where the window part (4a) is provided, and the conductive film (4b) is electrically connected to the window frame (5).

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 that applies 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. A conductive film is formed on at least a portion of the inner wall of the glass tube on the side where the window portion is provided, and the conductive film is electrically connected to the window frame.

[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 conductive film is formed on at least a portion of the inner wall of the glass tube on the side where the window portion is provided, and by electrically connecting the conductive film to the window frame, it is possible to 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 generator according to an embodiment; 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 equipotential lines of an X-ray tube; Fig. 5 is a diagram for explaining the destination of reflected electrons reflected by a target electrode; Fig. 6 is a diagram showing the trajectories of electrons depending on whether or not an electric charge is charged on the inner wall of a glass tube; Fig. 7 is a schematic diagram of an X-ray generator according to a modified example;

[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] [X-ray Generator] In this embodiment, the configuration of an X-ray tube and an X-ray generator used in an X-ray fluorescence apparatus 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 an X-ray fluorescence apparatus 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 an apparatus that requires the reduction of impurity rays. Fig. 1 is a schematic diagram of an X-ray generator 10 according to this embodiment.

[0012] X-ray generator 10 includes an X-ray tube including a filament electrode 1, a target electrode 2, a rod electrode 3, a glass tube 4, and a window frame 5, 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 from the glass tube 4 to the outside. 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 copper, for example. A cooling fin 3a with excellent thermal conductivity and voltage resistance is attached to the end of the rod electrode 3 extending to the outside.

[0013] In the X-ray tube, a filament electrode 1, a target electrode 2, and a rod electrode 3 are arranged in a straight line, and a window 4a is provided in the glass tube 4 at a position perpendicular to the straight line. 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 and extracted through the window 4a. An X-ray tube that extracts X-rays through the window 4a provided on the side of the glass tube 4 in this way is called a side window type X-ray tube.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 3 is a schematic diagram for explaining the generation of impurity rays contained in X-rays. As shown in FIG. 3, electrons emitted from a filament electrode 1 collide with a target electrode 2 along a trajectory A, are reflected by the target electrode 2, and collide with a point C on the side of a rod electrode 3 along a trajectory B. When the electrons collide with the side of the rod electrode 3, characteristic X-rays D due to the material of the rod electrode 3 are generated at point C. Because copper (Cu) is used as the material of the rod electrode 3, the impurity characteristic X-rays of copper (Cu) shown in FIG. 2 are generated as a result. Note that the target electrode 2 has a sufficient thickness (for example, a thickness of about 100 μm), so that electrons do not pass through the target electrode 2 and reach the rod electrode 3.

[0019] Therefore, in order to suppress the generation of impurity rays contained in X-rays, it is possible to either reduce the reflected electrons that reach the side surfaces of the rod electrode 3 or prevent the generation of impurity rays due to the reflected electrons that reach the side surfaces of the rod electrode 3. In order to prevent the generation of impurity rays due to the reflected electrons that reach the side surfaces of the rod electrode 3, it is necessary 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 on the side surfaces of the rod electrode 3.

[0020] However, if the material of the target electrode 2 is rhodium (Rh), which is a hard and difficult-to-machine material with a Vickers hardness of 1000 or more, it is necessary to plate the side surface of the rod electrode 3 with expensive rhodium (Rh) or to provide a cover member. In particular, when rhodium plating is applied to the side surface of the rod electrode 3, the rhodium plating that is widely used to protect white precious metals such as silver, platinum, and white gold has a plating thickness of 0.1 μm or less, making it difficult to achieve a plating thickness (e.g., 1.5 to 2 μm) that is sufficient to prevent reflected electrons from reaching the rod electrode 3. Furthermore, because rhodium (Rh) is a difficult-to-machine and expensive material, it is not practical to fabricate the cover member provided on the side surface of the rod electrode 3 by lathe processing or the like.

[0021] Therefore, in the X-ray tube according to this embodiment, the reflected electrons reaching the side surface of the rod electrode 3 are reduced to suppress the generation of impurity rays contained in X-rays. First, the X-ray tube is modeled. For example, the filament electrode 1 has an outer diameter of 12 mm, and a 4 mm x 0.8 mm slot is provided in its center. The target electrode 2 is positioned 5 mm away from the tip of the filament electrode 1, tilted 70 degrees from the vertical direction. The X-ray tube is modeled with the target electrode 2 having an outer diameter of 10 mm, the glass tube 4 having an outer diameter of 30 mm, a length of 39 mm, and the window portion 4a having an inner diameter of 10 mm.

[0022] Furthermore, Fig. 4 is a diagram showing equipotential lines of an X-ray tube. As shown in Fig. 1, when the filament electrode 1 is connected to the GND electrode to a potential of 0 kV, the target electrode 2 is set to a potential of 25 kV by the voltage generation circuit 6, and the window frame 5 is connected to the GND electrode to a potential of 0 kV, the potential inside the glass tube 4 becomes the equipotential lines shown in Fig. 4. A voltage was applied to the modeled X-ray tube so as to create the equipotential lines shown in Fig. 4, and a simulation was performed to see how the reflected electrons reflected by the target electrode 2 travel when electrons are irradiated from the filament electrode 1 to the target electrode 2.

[0023] FIG. 5 is a diagram illustrating the destinations of the reflected electrons reflected by the target electrode 2. When a potential of 25 kV is applied to the target electrode 2, 49% of the reflected electrons return to the target electrode 2, and 51% of the reflected electrons leave the target electrode 2. Of the reflected electrons that return to the target electrode 2, approximately 70% reach the target electrode 2 and generate X-rays, similar to the irradiated electrons, and the remaining approximately 30% become reflected electrons again. In the present disclosure, the behavior of the second reflected electrons is not considered. Of the reflected electrons that leave the target electrode 2, 8% (approximately 15.7% of the reflected electrons that leave the target electrode 2) reach the side surface of the rod electrode 3 directly, while 43% (approximately 84.3% of the reflected electrons that leave the target electrode 2) reach the inner wall of the glass tube 4, which has an inner diameter of 30 mm.

[0024] When a potential of 50 kV is applied to the target electrode 2, 46% of the reflected electrons return to the target electrode 2, and 54% of the reflected electrons leave the target electrode 2. Of the reflected electrons that leave the target electrode 2, 8% (approximately 14.8% of the reflected electrons that leave the target electrode 2) reach the side surface of the rod electrode 3 directly, while 46% (approximately 85.2% of the reflected electrons that leave the target electrode 2) reach the inner wall of the glass tube 4, which has an inner diameter of 30 mm.

[0025] When a potential of 75 kV is applied to the target electrode 2, 44% of the reflected electrons return to the target electrode 2, and 56% of the reflected electrons leave the target electrode 2. Of the reflected electrons that leave the target electrode 2, 8% (approximately 14.3% of the reflected electrons that leave the target electrode 2) reach the side surface of the rod electrode 3 directly, while 48% (approximately 85.7% of the reflected electrons that leave the target electrode 2) reach the inner wall of the glass tube 4, which has an inner diameter of 30 mm.

[0026] 5, regardless of the potential applied to the target electrode 2, 8% of the reflected electrons that miss the target electrode 2 reach directly the side surface of the rod electrode 3. On the other hand, as the potential applied to the target electrode 2 increases, the proportion of the reflected electrons that reach the inner wall of the glass tube 4 increases.

[0027] Electrons that reach the inner wall of the glass tube 4 remain there, causing the inner wall of the glass tube 4 to become electrically charged. A simulation was performed to determine how reflected electrons would travel if they were to fly toward the inner wall of the glass tube 4, which is already electrically charged. Figure 6 shows the trajectories of electrons on the inner wall of the glass tube depending on whether or not the inner wall is electrically charged. Figure 6(a) shows the trajectories of electrons when there is no charge on the inner wall of the glass tube, and Figure 6(b) shows the trajectories of electrons when there is a charge on the inner wall of the glass tube. The areas indicated by the white circles and dashed lines in Figure 6(b) are charged with reflected electrons.

[0028] 6(b), when the inner wall of the glass tube is charged, most of the reflected electrons that fly toward the charged inner wall of the glass tube 4 are changed in direction by the repulsive force of the charged charge and fly toward the side of the positively charged rod electrode 3. As a result, of the reflected electrons that fly toward the inner wall of the glass tube 4, most of the reflected electrons, excluding the reflected electrons that charge the inner wall of the glass tube 4, reach the side of the rod electrode 3, and the number of reflected electrons that reach the side of the rod electrode 3 increases. The increase in the reflected electrons that reach the side of the rod electrode 3 also increases the generation of X-rays (impurity rays) generated from the side of the rod electrode 3.

[0029] Therefore, in the X-ray generator 10 according to this embodiment, as shown in FIG. 1, a conductive film 4b is formed on the portion of the inner wall of the glass tube 4 that is charged by the reflected electrons. That is, the conductive film 4b is formed on at least a portion of the inner wall of the glass tube 4 on the side where the window portion 4a is provided. Furthermore, the conductive film 4b is electrically connected to the window frame 5. The window frame 5 is electrically connected to the GND electrode. Therefore, the reflected electrons that hit the inner wall of the glass tube 4 flow through the window frame 5 to the GND electrode, preventing the inner wall of the glass tube 4 from becoming charged with an electric charge.

[0030] If the inner wall of the glass tube 4 can be prevented from being charged with an electric charge, it is possible to prevent the reflected electrons that reach the inner wall of the glass tube 4 from changing their flight direction toward the side surface of the rod electrode 3, as shown in Figure 6(a). Specifically, when a potential of 25 kV is applied to the target electrode 2, 43% of the reflected electrons that reach the inner wall of the glass tube 4 can be prevented from being directed toward the side surface of the rod electrode 3. When a potential of 50 kV is applied to the target electrode 2, 46% of the reflected electrons that reach the inner wall of the glass tube 4 can be prevented from being directed toward the side surface of the rod electrode 3. When a potential of 75 kV is applied to the target electrode 2, 48% of the reflected electrons that reach the inner wall of the glass tube 4 can be prevented from being directed toward the side surface of the rod electrode 3.

[0031] In this way, the reflected electrons that hit the inner wall of the glass tube 4 flow through the window frame 5 to the GND electrode, preventing the inner wall of the glass tube 4 from becoming electrically charged. This allows the X-ray generator 10 to reduce the generation of impurity rays that would otherwise be generated by the reflected electrons reaching the inner wall of the glass tube 4. Specifically, when a potential of 25 kV is applied to the target electrode 2, the impurity rays generated at the side of the rod electrode 3 can be reduced by 84.3%. When a potential of 50 kV is applied to the target electrode 2, the impurity rays generated at the side of the rod electrode 3 can be reduced by 85.2%. When a potential of 75 kV is applied to the target electrode 2, the impurity rays generated at the side of the rod electrode 3 can be reduced by 85.7%.

[0032] In an actual X-ray generator 10, the effects of second, third, etc. reflected electrons must be taken into consideration, but these effects are thought to be small. Therefore, the X-ray generator 10 can reduce about 80% of the impurity rays generated on the side surfaces of the rod electrode 3 by forming a conductive film 4b on at least a part of the inner wall of the glass tube 4.

[0033] Although it has been explained that the window frame 5 is electrically connected to the GND electrode, it is sufficient that the potential be lower than that of the target electrode 2. Furthermore, it has been explained that the conductive film 4b is provided on at least a portion of the inner wall of the glass tube 4 (particularly the portion that is charged by reflected electrons), but the conductive film 4b may also be formed in a ring shape on the inner wall of the glass tube 4.

[0034] Furthermore, the conductive film 4b used must not undergo brittle fracture even when continuously exposed to X-rays for a long period of time. Furthermore, X-rays may be generated when reflected electrons collide with the conductive film 4b, potentially creating new impurity rays. Therefore, it is preferable that the material for the conductive film 4b formed on the inner wall of the glass tube 4, where the reflected electrons reach, does not contain any elements that would create impurity rays that would interfere with analytical evaluation.

[0035] Specifically, it is preferable to use an ITO film (indium tin oxide doped film), a DLC film (diamond-like carbon film), or the like for the conductive film 4b. Since the ITO film contains elements such as tin (Sn) and indium (In), there is a risk that these characteristic X-rays may be generated as impurity rays, but it is easy to form a film on the glass tube 4. The DLC film is resistant to X-rays and has little effect on impurity rays because it is composed only of carbon (C).

[0036] 1 , the filament electrode 1 and window frame 5 are at GND potential, and the target electrode 2 and rod electrode 3 are at positive potential. The window frame 5 and rod electrode 3 are connected by the glass tube 4, which is an insulator, so no discharge occurs between the window frame 5 and the rod electrode 3. However, if a conductive film 4b is formed on the inner wall of the glass tube 4 and electrically connected to the window frame 5 to set it to GND potential, the distance along the inner wall of the glass tube 4 between the end of the conductive film 4b and the rod electrode 3 becomes shorter, and there is a possibility that creeping discharge may occur on the inner wall of the glass tube 4.

[0037] Therefore, in the X-ray generator according to the modified example, the glass tube 4 is made longer so as to ensure a distance along the inner wall of the glass tube 4 between the end of the conductive film 4b and the rod electrode 3. Fig. 7 is a schematic diagram of an X-ray generator 10a according to the modified example. In the X-ray generator 10a shown in Fig. 7, the same components as those in the X-ray generator 10 shown in Fig. 1 are designated by the same reference numerals, and detailed description thereof will not be repeated.

[0038] In the X-ray generator 10a, the glass tube 40 has a length that ensures a predetermined creepage distance L between the conductive film 4b and the rod electrode 3. If 1 mm provides insulation up to 1 kV, and a potential of 50 kV is applied to the target electrode 2, the length of the glass tube 40 is designed so that the creepage distance L is 50 mm or more.

[0039] In the X-ray generators 10 and 10a described above, a method of reducing reflected electrons reaching the side surfaces of the rod electrode 3 is employed as a method for suppressing the generation of impurity rays contained in X-rays. However, this method may be used in combination with a method for preventing the generation of impurity rays due to reflected electrons reaching the side surfaces of the rod electrode 3. Specifically, in the X-ray generators 10 and 10a, the side surfaces of the rod electrode 3 may be plated with the same material (e.g., rhodium (Rh)) as the target electrode 2. Even if it is currently not possible to plate the side surfaces of the rod electrode 3 with a thin rhodium plating thickness of 0.1 μm or less, the generation of impurity rays contained in X-rays can be further reduced by using this method in combination with a configuration in which a conductive film 4b is formed on the inner wall of the glass tube 40.

[0040] Aspects It will be understood by those skilled in the art that the above-described embodiments are specific examples of the following aspects.

[0041] (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 frame that is 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, wherein a conductive film is formed on at least a portion of the inner wall of the glass tube on the side where the window portion is provided, and the conductive film is electrically connected to the window frame.

[0042] According to the X-ray tube described in paragraph 1, by forming a conductive film on at least a part of the inner wall of the glass tube on the side where the window portion is provided and electrically connecting the conductive film to the window frame, it is possible to reduce impurity rays contained in the X-rays emitted from the X-ray tube.

[0043] (Item 2) In the X-ray tube according to item 1, the window frame is electrically connected to a GND electrode.

[0044] (Item 3) In the X-ray tube according to item 1 or 2, the conductive film is formed on the inner wall of the glass tube facing the rod electrode.

[0045] (4) In the X-ray tube according to any one of the above items 1 to 3, the glass tube has a length that ensures a predetermined creepage distance between the conductive film and the rod electrode.

[0046] (Item 5) In the X-ray tube according to any one of items 1 to 4, the target electrode is made of rhodium and the rod electrode is made of copper.

[0047] (Item 6) The X-ray tube according to any one of items 1 to 5, wherein the film is an ITO film or a diamond-like carbon film.

[0048] (Item 7) An X-ray tube according to any one of items 1 to 6, wherein the filament electrode, the target electrode, and the rod electrode are arranged on a straight line, and a window portion is provided in the glass tube at a position perpendicular to the straight line.

[0049] (Item 8) An X-ray generator according to one aspect includes the X-ray tube according to any one of items 1 to 7, and a voltage generation circuit for generating a high voltage to be applied to the X-ray tube.

[0050] 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.

[0051] REFERENCE SIGNS LIST 1 Filament electrode, 2 Target electrode, 3 Rod electrode, 3a Cooling fin, 4, 40 Glass tube, 4a Window portion, 4b Conductive film, 5 Window frame, 6, 7 Voltage generating circuit, 10, 10a X-ray generator.

Claims

1. An X-ray tube for generating X-rays, comprising: 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 frame that is 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, wherein a conductive film is formed on at least a portion of the inner wall of the glass tube on the side where the window portion is provided, and the conductive film is electrically connected to the window frame.

2. The X-ray tube according to claim 1, wherein the window frame is electrically connected to a GND electrode.

3. The X-ray tube according to claim 1, wherein the conductive film is formed on the inner wall of the glass tube facing the rod electrode.

4. The X-ray tube according to claim 1, wherein said glass tube has a length that ensures a predetermined creepage distance between said conductive film and said rod electrode.

5. The x-ray tube of claim 1, wherein said target electrode is made of rhodium and said rod electrode is made of copper.

6. The X-ray tube according to claim 1, wherein the conductive film is an ITO film or a diamond-like carbon film.

7. The X-ray tube according to claim 1, wherein said filament electrode, said target electrode, and said rod electrode are arranged on a straight line, and said window portion is provided in said glass tube at a position perpendicular to said straight line.

8. 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 the X-ray tube.

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