X-ray tube

Abstract

To provide an X-ray tube capable of preventing significant change of an X-ray amount discharged.SOLUTION: An X-ray tube comprises: a positive electrode that includes a target layer discharging an X-ray by injecting an electron beam; and a negative electrode in which three electron guns are arranged in parallel, including a filament discharging an electron, a housing groove housing the filament, and a convergence groove converging the electron discharged from the filament as an electron beam to a target layer. The three electron guns are a center electron gun opposite to the positive electrode and both side electron guns positioned with the center electron gun sandwiched therebetween. In the center electron gun, a filament center shaft along a long direction at a width direction center of the filament and a housing groove center shaft along the long direction at the width direction center of the housing groove are matched. The convergence groove center shaft along the long direction is deviated from the filament center shaft at the width direction center of the convergence groove.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] The electron beam emitted from the filament is focused by a storage groove and a focusing groove arranged around the filament, and forms a focal point on the target. When electron beams emitted from multiple electron guns are imaged on a target, deviation from the focus on the target will result in deviation from the image, so it is desirable that each focal position be approximately the same on the anode. For example, in the case of three electron guns, the electron beam emitted from the central electron gun will have an approximately straight trajectory and will hit the anode, but the electron beams emitted from the side electron guns will have a curved trajectory and will head towards the anode.

[0003] Meanwhile, there is desorbed gas inside the X-ray tube, and adsorbed gas exists on the surface of the components. The adsorbed gas on the component surface is desorbed by heat or electron impact, causing an increase in pressure inside the tube. When the electron beam is emitted for the first time after the X-ray tube has not been operated for a long time, the adsorbed gas on the anode surface is desorbed, and some of it is ionized by the electron beam. The electrons generated by this are directed toward the anode, and the positive ions are directed toward the electron gun. Because positive ions have a large mass, they head toward the filament of the central electron gun without bending their trajectory. When positive ions collide with the filament of the central electron gun, the temperature of the filament rises, which can cause the electron beam emitted from the electron gun to increase.

[0004] At the time of the next exposure, there is less gas adsorbed on the anode surface, so this phenomenon is less likely to occur. In other words, if the electron beam fluctuates between the first and second exposures, the amount of X-rays emitted from the X-ray tube will change significantly, which can cause problems when processing images. Furthermore, since ionized positive ions hardly bend, this type of problem is less likely to occur with a double-sided electron gun. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-135265 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of this embodiment is to provide an X-ray tube that can prevent the amount of X-rays emitted from the X-ray tube from changing significantly. [Means for solving the problem]

[0007] This embodiment is an X-ray tube comprising: an anode having a target layer that emits X-rays when an electron beam is incident thereon; a cathode having three electron guns arranged in parallel, each having a filament that emits electrons, a storage groove that stores the filament, and a focusing groove that focuses the electrons emitted from the filament as an electron beam toward the target layer; and the three electron guns are a central electron gun that faces the anode and side electron guns that are located on either side of the central electron gun, and the central axis of the central electron gun extending along the longitudinal direction at the center of the width of the filament coincides with the central axis of the storage groove extending along the longitudinal direction at the center of the width of the storage groove, and the central axis of the focusing groove extending along the longitudinal direction at the center of the width of the focusing groove is offset from the central axis of the filament. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of an X-ray tube assembly according to an embodiment. [Figure 2] FIG. 2(a) is a cross-sectional view showing the cathode and anode according to the first embodiment, and FIG. 2(b) is a plan view of the cathode. [Figure 3] FIG. 3 is a cross-sectional view showing a cathode and an anode according to the second embodiment. [Figure 4]FIG. 4(a) is a cross-sectional view showing a cathode and an anode according to a comparative example, and FIG. 4(b) is a plan view of the cathode. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present embodiment will be described below with reference to the drawings. The disclosure is merely an example, and appropriate modifications that a person skilled in the art can easily make while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part compared to the actual embodiment for clarity of explanation, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, components that perform the same or similar functions as those described above with reference to the previous drawings are designated by the same reference numerals, and redundant detailed descriptions may be omitted as appropriate.

[0010] FIG. 1 is a cross-sectional view of an X-ray tube assembly according to an embodiment. As shown in Fig. 1, the X-ray tube assembly includes an X-ray tube 1, a housing 20, and insulating oil 9. In this embodiment, the X-ray tube 1 is a rotating anode X-ray tube.

[0011] The X-ray tube 1 includes a cathode 10 , an anode 11 , a rotor 5 , a fixed body 6 , a vacuum envelope 19 , and a stem portion 2 . The rotor 5 is formed in a cylindrical shape with one end closed. The rotor 5 extends along a rotation axis R, which is the central axis of rotation of the rotor. The rotor 5 is rotatable around the rotation axis R. The rotor 5 is made of a material such as Fe (iron) or Mo (molybdenum).

[0012] The fixed body 6 is formed in a columnar shape. The diameter of the fixed body 6 is smaller than the inner diameter of the rotor 5. The fixed body 6 is provided coaxially with the rotor 5 and extends along the rotation axis R. The fixed body 6 is made of a material such as Fe or Mo. The fixed body 6 is fitted into the rotor 5 and fixed to the vacuum envelope 19. Although not shown, the gap between the rotor 5 and the fixed body 6 is filled with a metal lubricant such as a gallium-indium-tin alloy (GaInSn). For this reason, the X-ray tube 1 uses a sliding bearing.

[0013] The anode 11 is disposed opposite one end of the fixed body 6 in the direction along the rotation axis R. The anode 11 has a target layer 11a located on the outer surface of the anode. The anode 11 is fixed to the rotating body 5 via a connecting member 7. The anode 11 is formed of a material such as a heavy metal, for example, Mo. The target layer 11a is formed of a metal having a higher melting point than the material used for the anode 11. For example, it is formed of a tungsten alloy. The anode 11 is provided coaxially with the rotating body 5 and the fixed body 6. The anode 11 is rotatable around the rotation axis R. The anode 11 emits X-rays when electrons emitted from the cathode 10 collide with the target layer 11a. The anode 11 is electrically connected to the terminal 4 via the rotating body 5, the fixed body 6, etc.

[0014] The cathode 10 has a plurality of electron guns, three electron guns 12, 13, and 13 (described later) in this embodiment. The cathode 10 is disposed opposite the target layer 11a of the anode 11 with a gap therebetween.

[0015] The vacuum envelope 19 houses the anode 11 and the cathode 10. The vacuum envelope 19 is made of an insulating material such as glass or ceramic, or a combination of an insulating material and a conductive material such as metal. The vacuum envelope 19 is sealed, and the interior is maintained in a vacuum state. The vacuum envelope 19 has an X-ray transmission window 19a that allows X-rays to pass through to the vicinity of the target layer 11a facing the cathode 10. The stem portion 2 is connected to the vacuum envelope 19, and has a plurality of pins 3 attached thereto.

[0016] The housing 20 houses the X-ray tube 1. The housing 20 has an X-ray transmission window 20a that allows X-rays to pass through near the target layer 11a facing the cathode 10. The housing 20 houses the X-ray tube 1 and other components, and is filled with insulating oil 9 as a coolant. Although not shown, the housing 20 also houses a stator coil that rotates the rotor 5.

[0017] Next, the cathode 10 according to the first embodiment will be described in detail with reference to FIG. FIG. 2(a) is a cross-sectional view showing the cathode and anode according to the first embodiment, and FIG. 2(b) is a plan view of the cathode shown in (a), shown at a position corresponding to the cross section of the cathode shown in (a). The cathode 10 has a total of three electron guns 12, 13, 13: a central electron gun 12 and two side electron guns 13, 13 positioned on either side of the central electron gun. The three electron guns 13, 12, 13 are arranged at intervals in the rotation direction of the target layer 11a. Each of the electron guns 12, 13, 13 has a filament 14 that emits electrons e, a storage groove 15 that stores the filament 14, and a focusing groove 16 that focuses the electrons e emitted from the filament 14 as an electron beam toward the target layer 11a. Each filament 14 is formed into a coil shape from a material whose main component is tungsten. The filament 14 and the cathode 10 are each connected to a pin 3 shown in FIG.

[0018] As shown in (a) of Figure 2, the central electron gun 12 is positioned facing the focal point F of the target layer 11a, and the openings of the storage groove 15 and the focusing groove 16 also face the focal point F of the target layer 11a, and the groove wall 15a of the storage groove 15 and the groove wall 16a of the focusing groove 16 are formed approximately perpendicular to the target layer 11a. On the other hand, the openings of the storage groove 15 and the focusing groove 16 of the electron guns 13, 13 are inclined toward the focal point F of the target layer 11a, and the groove wall 15a of the storage groove 15 and the groove wall 16a of the focusing groove 16 are formed inclined relative to the target layer 11a.

[0019] Next, the relationship between the filament 14, the storage groove 15, and the focusing groove 16 of the central electron gun 12 will be described. The filament 14 is long and has a filament central axis 14b extending along the longitudinal direction at the center in the width direction (or the center of the coil), and the storage groove 15 is long like the filament 14 and has a storage groove central axis 15b extending along the longitudinal direction at the center in the width direction. The focusing groove 16 has a focusing groove central axis 16b that is parallel to the filament central axis 14a and extends along the longitudinal direction at the center in the width direction. As shown in FIG. 2(a), the filament central axis 14b and the storage groove central axis 15b are aligned and coaxial, and the focusing groove central axis 16b is offset from the filament central axis 14b. The deviation between the focusing groove central axis 16b and the filament central axis 14b is at least half the width (or at least the radius) of the filament 14, and the larger this deviation, the better; for example, it is preferable that the deviation be at least the width (or at least the diameter) of the filament 14. The cathode 10 is provided to surround the orbit of the electrons e traveling from the filament 14 toward the anode 11, and functions as a focusing electrode.

[0020] Next, the operation and effects of the first embodiment will be described. A relatively negative voltage is applied to each filament 14 and cathode 10. A relatively positive voltage is applied to the anode 11. An X-ray tube voltage (hereinafter referred to as "tube voltage") is applied between the anode 11 and the cathode 10, so that electrons emitted from the filament 14 are accelerated and incident on the target layer 11a as an electron beam. As an example, the tube voltage is 50 kV or more and 160 kV or less.

[0021] Electrons e emitted from the filaments 14 of the central electron gun 12 and the side electron guns 13, 13 are each focused by the electric field near the opening of the focusing groove 16, and become bent electron beams that are incident on the focal point F on the target layer 11a. At this time, the electron beams from the side electron guns 13, 13 are significantly bent before they are incident on the focal point F.

[0022] On the other hand, when there are escaping gas particles M between the cathode 10 and the anode 11, the escaping gas particles M are ionized to generate negative ions and positive ions, of which the positive ions, which have a larger mass, head toward the central electron gun 12 without bending at all. However, in this embodiment, in the central electron gun 12, although the filament central axis 14b and the storage groove central axis 15b are aligned, the focusing groove central axis 16b is deviated from the filament central axis 14b, and therefore, as shown by arrow N, the positive ions collide at a position deviated from the filament central axis 14b, thereby suppressing the impact of the positive ions and suppressing an increase in the electron beam due to a rise in temperature of the filament 14. This reduces the variation in the electron beam between the first exposure, in which there is a large amount of escaping gas particles M, and the second exposure, in which there is almost no escaping gas particles M, and prevents a large change in the amount of X-rays emitted from the X-ray tube 1. Furthermore, the deviation between the focusing groove central axis 16b and the filament central axis 14b is simply a deviation parallel to the filament central axis 14b and the storage groove central axis 15b and in the direction in which the three electron guns 12, 13, 13 are arranged, so that the cathode 10 can be easily designed. In this embodiment, direct collision with the filament 14 can be almost completely eliminated by shifting the focusing groove central axis 16b from the filament central axis 14b by more than the radius of the filament 14 (more than half the width).

[0023] A comparative example is shown in Fig. 4. In the comparative example in Fig. 4, in the central electron gun 12 formed on the cathode 10, the filament central axis 14b, the storage groove central axis 15b, and the focusing groove central axis 16b are aligned. As is clear from the comparative example shown in Fig. 4, when the focal groove central axis 16b coincides with the filament central axis 14b, the positive ions N ionized from the escaping gas particles M move directly toward the filament central axis 14b and collide with the filament 14. For this reason, in the comparative example shown in Fig. 4, the temperature of the filament 14 rises due to the collision of the positive ions N, causing an increase in the electron beam emitted from the central electron gun 12, which may result in a large change in the amount of X-rays emitted from the X-ray tube 1 depending on whether or not there are escaping gas particles M. In contrast to this, according to this embodiment, as described above, the focus groove central axis 16b is shifted from the filament central axis 14b, so that when departing gas particles M are present, it is possible to reduce the collision of positive ions with the filament 14 and suppress an increase in the electron beam due to a rise in the temperature of the filament 14. This makes it possible to prevent a large change in the amount of X-rays emitted from the X-ray tube depending on whether or not departing gas particles M are present.

[0024] Other embodiments will be described below. In the embodiments described below, parts that have the same effects as the first embodiment described above will be given the same symbols, and detailed descriptions of those parts will be omitted. A second embodiment will be described with reference to FIG. In the second embodiment, the central electron gun 12 is inclined at an angle P, and the filament central axis 14b and the storage groove central axis 15b are inclined at an angle P. The central axis 16b of the focusing groove Matching do. According to the second embodiment, the same effects as those of the first embodiment can be obtained, and by providing both the storage groove 15 and the focusing groove 16 at an angle P, the filament central axis 14b and the focusing groove central axis 16b can be aligned. Because it can be matched It is easy to design a trajectory that focuses electrons e to the focal point F. That is, in the second embodiment, since there is little bias between the left and right in the trajectory of the electrons e emitted from the filament 14 of the central electron gun 12, the left and right groove walls 16a of the focusing groove 16 can be formed approximately symmetrically, which also simplifies the design of the cathode 10.

[0025] Although an embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. This novel embodiment can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment and its modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as defined in the claims.

[0026] The filament 14 serving as the electron emission source is not limited to a coil-shaped one, and various types of filaments can be used. For example, the cathode 10 may have a flat filament instead of a coil-shaped filament. In this case, the same effects as those of the above-described embodiment can be obtained. A flat filament is a filament having a flat upper surface (electron emission surface) and a flat lower surface.

[0027] For example, the embodiments of the present invention are not limited to the rotating anode X-ray tube 1 described above, but are applicable to various rotating anode X-ray tubes, various fixed anode X-ray tubes, and other X-ray tubes. [Explanation of symbols]

[0028] 1...X-ray tube 10...cathode 11...anode 11a...target layer 12...Central electron gun 13...Both side electron guns 14...filament 14b...central axis of filament 15...storage groove 15b...storage groove central axis 16…Focusing groove 16b…Focusing groove center axis

Claims

[Claim 1] an anode having a target layer that emits X-rays when an electron beam is incident thereon; a cathode in which three electron guns are arranged in parallel, each having a filament that emits electrons, a storage groove that stores the filament, and a focusing groove that focuses the electrons emitted from the filament as an electron beam toward the target layer; the three electron guns are a central electron gun facing the anode and two side electron guns positioned on either side of the central electron gun, The central electron gun is an X-ray tube in which a central axis of the filament extending along the longitudinal direction at the center of the width direction of the filament coincides with a central axis of the storage groove extending along the longitudinal direction at the center of the width direction of the storage groove, and the central axis of the focusing groove extending along the longitudinal direction at the center of the width direction of the focusing groove is separated from the central axis of the filament by more than half the width of the filament, and further, there is no conductor between the filament and the target layer, and positive ions generated when electrons emitted from the filament collide with detached gas particles present between the filament and the target layer are prevented from colliding with the filament.

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