X-ray tube

Abstract

To provide an X-ray tube capable of suppressing the generation of air gaps in an insulated valve during operation.SOLUTION: An X-ray tube includes: a vacuum enclosure including an insulating valve having a first end and a second end, and a metal member joined to the first end; an electron gun held at the first end via the metal member within the vacuum enclosure for emitting electrons; and a target held at the second end, for receiving the electrons emitted from the electron gun to generate X-rays. At the first end, a ratio C defined by the following formula (1) is 55% or more. C=100×([K]+[R1]+[R2]) / [Na] ...(1) (In formula (1), [Na] represents the content (atom%) of Na, [K] represents the content (atom%) of K, [R1] represents the content (atom%) of alkali metal elements having a larger atomic number than K, and [R2] represents the content (atom%) of alkaline earth metal elements.)SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As an X-ray tube used for a microfocus X-ray source or the like, there is known an X-ray tube including a vacuum envelope having a cylindrical insulating bulb, an electron gun provided in the vacuum envelope for emitting electrons emitted from a cathode, a target for generating X-rays by receiving the electrons emitted from the electron gun, and a metal target holder for holding the target.

[0003] In the X-ray tube described in Patent Document 1 below, a glass container which is an insulating bulb has two ends, a target holder is fixed to one end, and an X-ray transmission assembly is fixed to the other end.

[0004] In the X-ray tube described in Patent Document 2 below, the insulating bulb has two ends, a target holder is fixed to one end, and a metal body housing the electron gun is fixed to the other end.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, both of the X-ray tubes described in Patent Documents 1 and 2 above had room for improvement in terms of suppressing the generation of voids in the insulating bulb during operation.

[0007] Therefore, an object of the present invention is to provide an X-ray tube capable of suppressing the generation of voids in an insulating valve during operation.

Means for Solving the Problems

[0008] To solve the above problems, the inventors first prepared a structure in which a first metal member and a second metal member were fusion-connected to both ends of a glass valve, which is a cylindrical insulating valve, and placed this structure in a furnace at 400 °C, which is extremely higher than the temperature of the insulating valve during normal operation, in an atmospheric pressure atmosphere. In the structure, an experiment was conducted in which the second metal member was connected to the positive electrode side of the power supply, the first metal member was connected to the negative electrode side of the power supply, and a DC high voltage was applied between the first metal member and the second metal member. Then, when observing the vicinity of the interface between the first metal member and the glass valve and the interface between the second metal member and the glass valve with a microscope, it was found that voids were formed due to cracks or peeling in a certain structure. Moreover, the voids were formed in the vicinity of the interface between the first metal member and the glass valve. On the other hand, as a result of performing SEM analysis and elemental mapping analysis on the elements in the vicinity of the locations where voids were observed inside or on the surface of the glass valve due to cracks or peeling in the structure, a finding was obtained that sodium was aggregated around the voids. Sodium is common as an element constituting glass, but in particular, in an X-ray tube to which a high voltage is applied, a glass with a high sodium content may be used in order to improve the withstand voltage characteristics. From this, the inventors considered that at least at the end of the glass valve joined to the first metal member, by making the sodium content relatively small with respect to the total content of potassium, alkali metal elements having an atomic number larger than that, and alkaline earth metal elements, it might be possible to suppress the deterioration of the physical properties (adhesion and mechanical strength) of the end portion. Therefore, as a result of further intensive studies by the inventors, it was found that the above problems can be solved by making the ratio of the total content of potassium, alkali metal elements having an atomic number larger than that, and alkaline earth metal elements to the sodium content equal to or more than a predetermined value, and the present invention has been achieved.

[0009] That is, the X-ray tube of the present invention is "[1] an X-ray tube including a vacuum envelope including an insulating bulb having a first end portion and a second end portion, and a metal portion joined to the first end portion, an electron gun held at the first end portion via the metal portion in the vacuum envelope and emitting electrons, and a target held at the second end portion and generating X-rays by receiving the electrons emitted from the electron gun, wherein at the first end portion, the ratio C defined by the following formula (1) is 55% or more." C = 100×([K] + [R1] + [R2]) / [Na] ··· (1) (In the formula (1), [Na] represents the content ratio (atom%) of sodium, [K] represents the content ratio (atom%) of potassium, [R1] represents the content ratio (atom%) of an alkali metal element having an atomic number larger than that of potassium, and [R2] represents the content ratio (atom%) of an alkaline earth metal element.) According to the X-ray tube described in the above [1], since the target is held at the second end portion and the electron gun is held at the first end portion via the metal portion, when a high voltage is applied between the electron gun (metal portion) and the target to cause electrons from the electron gun to enter the target with a desired energy, a high voltage is applied between the first end portion and the second end portion of the insulating bulb. Even in this case, according to the X-ray tube of the present invention, by relatively reducing the content ratio ([Na]) of sodium with respect to the total content ratio ([K] + [R1] + [R2]) of potassium, an alkali metal element having an atomic number larger than that thereof, and an alkaline earth metal element, deterioration of the physical properties (adhesion and mechanical strength) of the first end portion can be suppressed, generation of voids at the first end portion can be suppressed, and thus generation of voids in the insulating bulb can be suppressed.

[0010] The X-ray tube of the present invention may also be "[2] the X-ray tube described in the above [1], wherein at the second end portion, the ratio C defined by the formula (1) is 55% or more." According to the X-ray tube described in [2] above, even at the second end portion, by making the sodium content rate ([Na]) relatively small with respect to the total content rate ([K] + [R1] + [R2]) of potassium, alkali metal elements having an atomic number larger than that, and alkaline earth metal elements, deterioration of the physical properties (adhesiveness and mechanical strength) of the second end portion can be suppressed, generation of voids at the second end portion can be suppressed, and thus generation of voids in the insulating valve can be more effectively suppressed.

[0011] The X-ray tube of the present invention may be the X-ray tube described in [3] above, "wherein the insulating valve further has a valve main body portion between the first end portion and the second end portion, and in the valve main body portion, the ratio C is 55% or more". According to the X-ray tube described in [3] above, not only at the first end portion and the second end portion but also in the valve main body portion, by making the sodium content rate ([Na]) relatively small with respect to the total content rate ([K] + [R1] + [R2]) of potassium, alkali metal elements having an atomic number larger than that, and alkaline earth metal elements, deterioration of the physical properties (adhesiveness and mechanical strength) of the entire insulating valve can be suppressed, and thus generation of voids in the insulating valve 10 can be more effectively suppressed.

[0012] The X-ray tube of the present invention may be the X-ray tube described in any one of [1] to [3] above, "wherein at the first end portion, the ratio C is 63% or more". According to the X-ray tube described in [4] above, by applying a high voltage between the electron gun and the target in order to make electrons from the electron gun enter the target with a desired energy, even when a higher voltage is applied between the metal portion and the joint portion made of metal, generation of voids at the first end portion of the insulating valve can be suppressed, and generation of voids in the insulating valve can be suppressed.

[0013] The X-ray tube of the present invention may be the X-ray tube described in any one of [1] to [4] above, "wherein at the first end portion, the ratio C is 1000% or less".

[0014] The X-ray tube of the present invention may be the "X-ray tube according to any one of [1] to [5] above, wherein the sodium content in the first end portion is 2.20 atom% or less." According to the X-ray tube described in [6] above, since the sodium content in the first end portion is 2.20 atom% or less, a high voltage is applied between the electron gun and the target in order to cause electrons from the electron gun to enter the target with a desired energy. Even when a high voltage is applied between the metal portion and the metal joint portion, the generation of voids at the first end portion of the insulating valve can be effectively suppressed, and the generation of voids in the insulating valve can be effectively suppressed.

Advantages of the Invention

[0015] According to the present invention, there is provided an X-ray tube capable of suppressing the generation of voids in an operating insulating valve.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and duplicate explanations are omitted.

[0018] The X-ray tube 1 shown in FIG. 1 is a so-called reflection type X-ray tube, and includes a vacuum envelope 2, an electron gun 20, a target T, and a target holder 30. The electron gun 20 emits electrons toward the target T. The target T generates X-rays by receiving electrons emitted from the electron gun 20. The target holder 30 is a metal member that holds the target T.

[0019] The vacuum enclosure 2 includes an insulating valve 10 having a first end portion 11 and a second end portion 12, and a metal portion 40A joined to the first end portion 11 of the insulating valve 10. The metal portion 40A includes a metal housing 40 having a cylindrical internal space S1, and a first joining portion 50 made of metal that joins the first end portion 11 of the insulating valve 10 and the metal housing 40. The X-ray tube 1 also includes a second joining portion 60 made of metal that joins the second end portion 12 of the insulating valve 10 and the target holder 30. Here, the first joining portion 50 and the second joining portion 60 only need to be made of metal and do not have to be configured as independent members. For example, the first joining portion 50 may be configured as a part of the metal housing 40, or the second joining portion 60 may be configured as a part of the target holder 30.

[0020] The insulating valve 10 is formed in a substantially cylindrical shape and has an internal space S2 that communicates with the internal space S1 of the metal housing 40. The internal spaces S1 and S2 are in a vacuum state. The insulating valve 10 includes a valve body portion 13 between the first end portion 11 and the second end portion 12. The valve body portion 13 is composed of a cylindrical portion 13a and a tapered portion 13b that connects the cylindrical portion 13a and the second end portion 12 and tapers from the cylindrical portion 13a toward the second end portion 12.

[0021] The metal housing 40 includes a cylindrical portion 41, a flange portion 42 protruding outward from the cylindrical portion 41, an extending portion 43 extending along the tube axis AX from the end face on the first joint portion 50 side of the cylindrical portion 41, a bottom portion 44 closing the opening on the side opposite to the insulating valve 10 of the cylindrical portion 41, and an electron gun housing portion 46 for housing the electron gun 20. The material of the metal housing 40 is composed of a metal material such as stainless steel or kovar metal, for example. An opening is formed in the bottom portion 44, and an X-ray emission window 45 for emitting X-rays generated by the target T is fixed to the opening. The material of the X-ray emission window 45 is an X-ray transmissive material and is composed of, for example, beryllium or aluminum. The flange portion 42 is provided on the outer periphery of the cylindrical portion 41 and is a portion for supporting the X-ray tube 1 in an X-ray generating apparatus (not shown). The tip of the extending portion 43 is inserted into the internal space S2 of the insulating valve 10 and is interposed between the first end portion 11 of the insulating valve 10 and the target holder 30. Thereby, the discharge between the first end portion 11 of the insulating valve 10 and the target holder 30 is suppressed.

[0022] The first joint portion 50 joins the first end portion 11 of the insulating valve 10 and the metal housing 40. The first joint portion 50 includes an annular support portion 51 provided outside the extending portion 43 on the surface of the cylindrical portion 41 of the metal housing 40 on the insulating valve 10 side, and a ring portion 52 extending along the extending direction of the extending portion 43 from the outer peripheral edge portion of the support portion 51. The first joint portion 50 (ring portion 52) and the insulating valve 10 (first end portion 11) are hermetically joined by fusion. The first joint portion 50 (support portion 51) and the metal housing 40 are hermetically joined by welding. The material of the first joint portion 50 (support portion 51 and ring portion 52) is, for example, kovar metal, and a material having a coefficient of thermal expansion close to that of the material constituting the insulating valve 10 (first end portion 11) is preferably adopted. The tip of the ring portion 52 is embedded in the first end portion 11 of the insulating valve 10. Therefore, the insulating valve 10 is firmly fixed to the metal housing 40 via the first joint portion 50.

[0023] The second joint portion 60 is composed of a cylindrical fixing portion 61 fixed to the target holder 30, a ring portion 62 joined to the second end portion 12 of the insulating valve 10, and a tapered intermediate portion 63 connecting the fixing portion 61 and the ring portion 62. The second joint portion 60 (fixing portion 61) and the target holder 30 are hermetically joined by welding. The second joint portion 60 (ring portion 62) and the insulating valve 10 (second end portion 12) are hermetically joined by fusion bonding. The material of the second joint portion 60 (fixing portion 61 and ring portion 62) is, for example, Kovar metal, and a material having a thermal expansion coefficient close to that of the material constituting the insulating valve 10 (second end portion 12) is preferably employed. The second joint portion 60 is fixed to the target holder 30 by the fixing portion 61 of the second joint portion 60 being joined to the connecting portion 32 of the target holder 30.

[0024] The electron gun 20 is held at the first end portion 11 of the insulating valve 10 via the cylindrical portion 41 of the metal part 40A and the first joint portion 50 within the vacuum enclosure 2, and includes a cathode C that emits electrons, a heater 21, a grid electrode 22, a power supply pin 23, and an insulating stem 24. The cathode C, the heater 21, and the grid electrode 22 are attached to the stem 24 via a plurality of power supply pins 23 that extend in parallel respectively. The cathode C, the heater 21, and the grid electrode 22 are supplied with power from the outside via the corresponding power supply pins 23. A predetermined potential is applied to the cathode C, the heater 21, and the grid electrode 22 by the power supply pins 23, and the cathode C is heated by the heater 21, whereby electrons are emitted from the cathode C. The emitted electrons pass through the opening 46a of the electron gun housing portion 46 while being focused by the grid electrode 22, and are emitted toward the target. The electron gun housing portion 46 is formed in a cylindrical shape, is fixed to the metal housing 40, and the electron gun housing portion 46 and the metal housing 40 are electrically connected. The internal space of the electron gun housing portion 46 communicates with the internal spaces S1 and S2 via the opening 46a. Therefore, the electron gun housing portion 46 constitutes a part of the metal housing 40 that forms the vacuum enclosure 2.

[0025] The target T is disposed on the first end 11 side of the insulating valve 10 inside the vacuum enclosure 2 and is held at the second end 12 via the second joint 60. The target T is a plate-shaped member serving as an anode and is made of a high melting point metal material such as tungsten or molybdenum, for example. The target T is located on the tube axis AX (central axis of the cylindrical portion 13a of the insulating valve 10) of the X-ray tube 1. The target T is accommodated inside the metal housing 40 (internal space S1).

[0026] The target holder 30 is inserted into the vacuum enclosure 2. The target holder 30 includes a cylindrical main body portion 31 extending along the tube axis AX, a cylindrical connecting portion 32 supported by the second joint 60 in the main body portion 31, a rod-shaped portion 33 extending along the tube axis AX from the end of the main body portion 31 on the housing 40 side, and a protruding portion 34 protruding outward from the main body portion 31. The tip surface of the rod-shaped portion 33 is an inclined surface 33a inclined with respect to the tube axis AX, and the target T is disposed on the inclined surface 33a and is electrically connected to the target holder 30.

[0027] At the first end 11 of the insulating valve 10, the ratio C defined by the following formula (1) is 55% or more. C = 100×([K] + [R1] + [R2]) / [Na] ··· (1) In the above formula (1), [Na] represents the content rate (atom%) of sodium, [K] represents the content rate (atom%) of potassium, [R1] represents the content rate (atom%) of an alkali metal atom having an atomic number larger than that of potassium, and [R2] represents the content rate (atom%) of an alkaline earth metal element. Here, the content rate (atom%) is the atomic percentage.

[0028] According to the above X-ray tube 1, since the target T is held at the second end portion 12 via the second joint portion 60 and the electron gun 20 is held at the first end portion 11 via the metal portion 40A, when a high voltage is applied between the electron gun 20 (metal portion 40A) and the target T to cause electrons from the electron gun 20 to enter the target T with a desired energy, a high voltage is applied between the first end portion 11 and the second end portion 12 of the insulating valve 10. More specifically, in the present embodiment, a positive high voltage is applied to the target T via the target holder 30 to obtain a desired energy. In this case, since the target T, the target holder 30, and the second joint portion 60 are at the same potential, all are in a state where a high voltage is applied. On the other hand, the metal housing 40, the electron gun housing portion 46, and the first joint portion 50 are at the same potential in a state of being relatively lower in potential than the target T, for example, the ground potential. That is, since a high voltage is also applied between the first joint portion 50 and the second joint portion 60, a high voltage is also applied between the first end portion 11 and the second end portion 12 of the insulating valve 10. Even in this case, according to the X-ray tube 1, by making the sodium content ([Na]) relatively small with respect to the total content ([K]+[R1]+[R2]) of potassium, an alkali metal element having an atomic number larger than that, and an alkaline earth metal element, deterioration of the physical properties (adhesiveness and mechanical strength) of the first end portion 11 can be suppressed, generation of voids at the first end portion 11 can be suppressed, and thus generation of voids in the insulating valve 10 can be suppressed.

[0029] Here, the insulating valve 10 will be described in more detail. As shown in FIG. 2, the first end portion 11 of the insulating valve 10 refers to a portion from the end face on the housing 40 side to the position of the total length of the length L along the extending direction of the ring portion 52 and the length t in the direction along the outer peripheral surface of the first end portion 11. Here, L is the length of the portion of the ring portion 52 embedded in the first end portion 11 (hereinafter also referred to as the "embedded portion"), and t is the length along the outer peripheral surface of the first end portion 11, and is the length calculated by the arithmetic mean of the thickness t1 from the outer peripheral surface of the embedded portion to the outer peripheral surface of the first end portion 11 and the thickness t2 from the inner peripheral surface of the embedded portion to the inner peripheral surface of the first end portion 11. The second end portion 12 refers to the portion up to the position of the total length of the length along the extending direction of the embedded portion embedded in the second end portion 12 among the ring portions 62 and the length in the direction along the outer peripheral surface of the second end portion 12 from the end surface on the side opposite to the valve main body portion 13. Here, the length in the direction along the outer peripheral surface of the second end portion 12 refers to the length calculated by the arithmetic mean of the thickness from the outer peripheral surface of the embedded portion of the ring portion 62 to the outer peripheral surface of the second end portion 12 and the thickness from the inner peripheral surface of the embedded portion to the inner peripheral surface of the second end portion 12.

[0030] The insulating valve 10 is formed of an insulating material. As the insulating material, for example, glass or ceramics is used. In the above formula (1), examples of the alkali metal element represented by R1 include cesium and rubidium. Examples of the alkaline earth metal element represented by R2 include calcium, magnesium, strontium, and barium.

[0031] In the first end portion 11, the ratio C may be 55% or more, and may be 60% or more, 63% or more, or 70% or more. However, when the ratio C is 63% or more, even if a higher voltage is applied between the first joint portion 50 and the second joint portion 60, the generation of voids in the first end portion 11 can be suppressed, and the generation of voids in the insulating valve 10 can be suppressed.

[0032] When the ratio C is 55% or more, the ratio C may be 1000% or less, 900% or less, or 800% or less.

[0033] The content rate of sodium in the first end portion 11 is not particularly limited and may be 2.20 atom% or less. In this case, since the content rate of sodium in the first end portion 11 is 2.20 atom% or less, even if a high voltage is applied between the first joint portion 50 and the second joint portion 60, the generation of voids in the first end portion 11 can be effectively suppressed, and the generation of voids in the insulating valve 10 can be effectively suppressed. The sodium content in the first end portion 11 may be 2.0 atom% or less, 1.0 atom% or less, or 0.5 atom% or less.

[0034] In the insulating valve 10, the ratio C may be 55% or more at the first end portion 11, and in the second end portion 12 and the valve body portion 13, the ratio C may be 55% or more or less than 55%. For example, the ratio C may be 55% or more at the first end portion 11 and the second end portion 12, and less than 55% at the valve body portion 13. In this case, also in the second end portion 12, by making the sodium content ([Na]) relatively small with respect to the total content ([K]+[R1]+[R2]) of potassium, an alkali metal element having an atomic number larger than that, and an alkaline earth metal element, deterioration of the physical properties (adhesion and mechanical strength) of the second end portion 12 can be suppressed, generation of voids in the second end portion 12 can be suppressed, and thus generation of voids in the insulating valve 10 can be further suppressed. Further, by making the ratio C in the valve body portion 13 less than 55% (that is, increasing the sodium content), the withstand voltage characteristics of the insulating valve 10 are improved. Therefore, it is possible to achieve both suppression of generation of voids and improvement of withstand voltage characteristics in the insulating valve 10.

[0035] Also, the ratio C may be 55% or more at the first end portion 11, the valve body portion 13, and the second end portion 12 (that is, for the entire insulating valve 10). In this case, not only at the first end portion 11 and the second end portion 12 but also in the valve body portion 13, by making the sodium content ([Na]) relatively small with respect to the total content ([K]+[R1]+[R2]) of potassium, an alkali metal element having an atomic number larger than that, and an alkaline earth metal element, deterioration of the physical properties (adhesion and mechanical strength) of the entire insulating valve 10 can be suppressed, and generation of voids in the entire insulating valve 10 can be further suppressed.

[0036] The ratio C may be 55% or more at the first end portion 11, and less than 55% at the valve body portion 13 and the second end portion 12.

[0037] Incidentally, the value of the above ratio C can be increased by decreasing [Na] or increasing [K]+[R1]+[R2]. Conversely, it can be decreased by increasing [Na] or decreasing [K]+[R1]+[R2]. The increase or decrease of [Na] can be achieved, for example, by increasing or decreasing the addition amount of sodium oxide as a raw material during the production of the insulating valve 10 such as glass. The increase or decrease of [K]+[R1]+[R2] can be achieved, for example, by increasing or decreasing the addition amounts of potassium oxide, alkali metal oxides containing an alkali metal element having an atomic number larger than potassium, and alkaline earth metal oxides as raw materials during the production of the insulating valve 10 such as glass.

[0038] [Na], [K], [R1], and [R2] refer to the values measured by the fluorescent X-ray analysis (XRF) method. Specifically, [Na], [K], [R1], and [R2] refer to the values measured using the following apparatus under the following measurement conditions. (Apparatus) ZSX Primus (manufactured by Rigaku Corporation) (Measurement Conditions) Analysis mode: Qualitative analysis mode Tube voltage: 30 - 50 kV Tube current: 60 - 100 mA X-ray irradiation range: φ10 - 20 mm

[0039] As described above, the embodiments of the present invention have been explained, but the present invention is not limited to the above embodiments.

[0040] For example, the X-ray tube 1 of the above embodiment is a so-called reflection type X-ray tube, but the present invention is also applicable to a transmission type X-ray tube. FIG. 3 is an end view showing a transmission type X-ray tube as another embodiment of the X-ray tube of the present invention. In the transmission type X-ray tube 1A shown in FIG. 3, an insulating valve 10, a target holder 30, and an X-ray emission window 45 constitute a vacuum envelope. Here, the target holder 30 is a metal housing. A target T is provided on the vacuum side surface (electron gun 20A side) of the X-ray emission window 45. In the X-ray tube 1A, the material of the X-ray emission window 45 is, for example, diamond, the target T is a thin film made of a high melting point metal material such as tungsten or molybdenum, and the target holder 30, the X-ray emission window 45, the target T, and the second joint 60 are electrically connected. In the X-ray tube 1A, a potential (for example, ground potential in this embodiment) is applied to the X-ray emission window 45 and the target T via the target holder 30. On the other hand, the electron gun 20A has a metal cylindrical support member 70 and a second grid electrode 71 supported by the support member 70, and a relatively negative high potential is applied to the target T. The electron gun 20A is held at the first end 50 of the insulating valve 10 via the first joint 50. The first joint 50 is electrically connected to the second grid electrode 71 via the support member 70 and has the same potential as the second grid electrode 71 and the support member 70. In this embodiment, the first joint 50 is a metal part. When a high voltage is applied between the target T and the electron gun 20A, a high voltage is also applied between the first joint 50 and the second joint 60, so a high voltage is also applied between the first end 11 and the second end 12 of the insulating valve 10. The first joint 50 and the second joint 60 only need to be made of metal and do not have to be configured as independent members. For example, although the first joint 50 is an independent member from the support member 70, it may be configured as a part of the support member 70. Also, although the second joint 60 is an independent member from the target holder 30, it may be configured as a part of the target holder 30. In this case, the target T will be joined to the second end 12 via the target holder 30.

[0041] In addition, in this embodiment, the electron gun 20A is held at the first end portion 11 of the insulating valve 10 via the first joint portion 50. However, electrode members (for example, the second grid electrode 71 and the support member 70) constituting the electron gun 20A may be directly held at the first end portion 11 of the insulating valve 10. In this case, the electrode member becomes a metal part.

[0042] In the above embodiment, a part of the electron gun 20 is disposed in the internal space S1 of the metal housing 40A. However, the electron gun 20 may be disposed in the vacuum envelope 2. For example, the whole of the electron gun 20 may be disposed in the internal space S2 of the insulating valve 10.

[0043] [Experimental Example] Hereinafter, the effects of the present invention will be verified using experimental examples.

[0044] <Experimental Example 1> First, a structure including a glass valve as the insulating valve 10, a first joint portion 50, and a second joint portion 60 in the X-ray tube 1 shown in FIG. 1 was prepared. Specifically, the first end portion 11 of the insulating valve 10 was melted by heating the ring portion 52 of the first joint portion 50, and fused (sealed) with the ring portion 52 so that a part thereof was embedded in the first end portion 11. On the other hand, the second end portion 12 of the insulating valve 10 was melted by heating the ring portion 62 of the second joint portion 60, and fused (sealed) with the ring portion 62 so that a part thereof was embedded in the second end portion 12. Thus, the structure was prepared.

[0045] The insulating valve 10, the first joint portion 50, and the second joint portion 60 were configured as follows. (Insulating Valve 10) As the glass, a glass containing 67.46 atom% of oxygen, 19.52 atom% of silicon, 6.18 atom% of boron, and having the content rates of sodium ([Na]), potassium ([K]), R1 ([R1]), and R2 ([R2]) and the ratio C shown in Table 1 was used. In Table 1, "-" indicates that R1 was not observed.

[0046] (First Joint Portion 50) Material: Kovar metal

[0047] (Second joint 60) Material: Kovar metal

[0048] <Experimental Example 2> As the glass, a glass containing 68.18 atom% oxygen, 18.70 atom% silicon, and 8.45 atom% boron, and having the content rates of sodium ([Na]), potassium ([K]), R1 ([R1]), and R2 ([R2]) and the ratio C as shown in Table 1 was used, and a structure was fabricated in the same manner as in Experimental Example 1 except for this.

[0049] <Experimental Example 3> As the glass, a glass containing 67.23 atom% oxygen, 19.82 atom% silicon, and 8.61 atom% boron, and having the content rates of sodium ([Na]), potassium ([K]), R1 ([R1]), and R2 ([R2]) and the ratio C as shown in Table 1 was used, and a structure was fabricated in the same manner as in Experimental Example 1 except for this.

[0050] <Experimental Example 4> As the glass, a glass containing 66.51 atom% oxygen, 16.79 atom% silicon, and 8.16 atom% boron, and having the content rates of sodium ([Na]), potassium ([K]), R1 ([R1]), and R2 ([R2]) and the ratio C as shown in Table 1 was used, and a structure was fabricated in the same manner as in Experimental Example 1 except for this.

[0051] <Evaluation> (Test 1) The structures of Experimental Examples 1 to 4 were placed in a furnace set at 400 °C, left for 3600 seconds in an air atmosphere, and then Test 1 was conducted in which a voltage of 1 kV (DC voltage) was applied. The holding time of the structure after being placed in the furnace was 1 hour. Also, the voltage was connected such that the first end was on the negative electrode side of the power supply and the second end was on the positive electrode side of the power supply. (Test 2) Test 2 was conducted in the same manner as Test 1, except that the applied voltage was set to 3 kV. However, since voids were confirmed to have occurred in the structure of Experimental Example 4 during Test 1, Test 2 was not performed on it. Therefore, in Table 1, “-” is indicated for Test 2. (Observation of voids) After Test 1 was completed, the vicinity of the interface between the ring portion 52 and the first end portion 11 of the first end portion 11 in the structure was observed with a microscope to examine whether voids such as cracks or delamination had occurred. After Test 2 was completed, in the same manner as above, it was examined whether voids such as cracks or delamination had occurred. The results are shown in Table 1.

[0052]

Table 1

[0053] From the results shown in Table 1, in Test 1 where the applied voltage was 1 kV, in Experimental Examples 1 to 3 where the ratio C was 55% or more, no voids were observed in the vicinity of the interface between the ring portion 52 and the first end portion 11 of the first end portion 11 in the structure. On the other hand, in Test 1 where the applied voltage was 1 kV, in Experimental Example 4 where the ratio C was less than 55%, voids were observed in the vicinity of the interface between the ring portion 52 and the first end portion 11 of the first end portion 11 in the structure.

[0054] From the above, it is considered that even in an X-ray tube during operation, by setting the ratio C to 55% or more, the generation of voids in the insulating valve can be suppressed.

Explanation of reference numerals

[0055] 1, 1A…X-ray tube, 2…Vacuum enclosure, 10…Insulating valve, 11…First end portion, 12…Second end portion, 13…Valve main body portion, 20, 20A…Electron gun, 30…Target holder, 40A…Metal portion, 50…First joint portion, 60…Second joint portion, C…Cathode, T…Target.

Claims

1. A vacuum envelope including an insulating valve having a first end portion and a second end portion, and a metal portion joined to the first end portion; An electron gun held at the first end portion via the metal portion within the vacuum envelope and emitting electrons; And a target held at the second end portion and generating X-rays by receiving electrons emitted from the electron gun. An X-ray tube in which, at the first end portion, a ratio C defined by the following formula (1) is 55% or more. C = 100×([K] + [R １ ] + [R ２ ]) / [Na]... (1) (In the formula (1), [Na] is the content rate (atom%) of sodium, [K] is the content rate (atom%) of potassium, [R １ ] is the content rate (atom%) of an alkali metal element having an atomic number larger than that of potassium, and [R ２ ] represents the content rate (atom%) of an alkaline earth metal element.)

2. The X-ray tube according to claim 1, wherein, at the second end portion, the ratio C is 55% or more.

3. The insulating valve further has a valve main body portion between the first end portion and the second end portion, The X-ray tube according to claim 2, wherein, in the valve main body portion, the ratio C is 55% or more.

4. The X-ray tube according to claim 1, wherein, at the first end portion, the ratio C is 63% or more.

5. The X-ray tube according to claim 1, wherein, at the first end portion, the ratio C is 1000% or less.

6. The X-ray tube according to claim 1, wherein the content rate of sodium in the first end portion is 2.20 atom% or less.

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