JP2005038825A - Microfocus x-ray tube and x-ray apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microfocus X-ray tube which reconciles the miniaturization of dimensions at its focus point and an increase in an X-ray tube current. <P>SOLUTION: An electron focusing system 42 of a cathode in an X-ray tube comprises a cathode 40 for emitting an electron beam 64, three grid electrodes (G1 electrode 50, G2 electrode 52, and G3 electrode 54), and a target 18 of an anode 14. The diameter of the aperture 52a of the G2 electrode 52 is smaller than that of the aperture 50a of the G1 electrode 50, and positive potential with respect to the potential of the cathode 40 is applied to the G1 electrode 50, the G2 electrode 52, and the G3 electrode 54. The electron beam 64 emitted from the cathode 40 is increased in current by enhancing an acceleration electric field generated by the G1 electrode 50, and since electrons in the peripheral area of the electron beam 64 are eliminated not only by the G1 electrode 50 but also by the G2 electrode 52 as a result, focusing with a main lens 67 is conducted effectively without spherical aberrations, and a microfocus electron beam is obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an X-ray generator suitable for an industrial or medical X-ray fluoroscopy device, and more particularly to an X-ray generator capable of generating X-rays with extremely high luminance and an X-ray device using the X-ray generator. About.

  X-ray equipment that measures the dose of X-rays that have passed through the subject, creates an image based on that dose, and inspects or diagnoses the subject is a foreign product inspection and defect inspection for various products. For medical purposes, it is widely applied to X-ray fluoroscopy devices and X-ray imaging devices.

  In such an X-ray apparatus, it is desirable to obtain an enlarged image of the object as much as possible in order to perform a good examination or diagnosis when the object in the subject is very small. For this purpose, in the X-ray generator or the X-ray tube used therefor, it is necessary to make the size of an X-ray source (hereinafter referred to as a focal point) that is an X-ray generation region as small as possible. In response to such a request, in recent years, a microfocus X-ray tube having a focus size of 10 μm has begun to spread (for example, Patent Document 1).

  On the other hand, in order to obtain a high-quality fluoroscopic image, it is required that an electron beam current for generating X-rays (hereinafter referred to as an X-ray tube current) be as large as possible. For example, image intensifiers (I / I) for X-ray equipment that uses a low-sensitivity line sensor to inspect foreign substances in foods, and images of specimens (subjects) flowing on the production line In an in-line automatic inspection X-ray apparatus that obtains an instantaneous still image using the shutter function of the camera, an improvement in sensitivity is required by increasing the X-ray tube current. Also in the medical X-ray apparatus, in an apparatus that combines X-ray film imaging and X-ray fluoroscopy, it is necessary to improve sensitivity by increasing the X-ray tube current in order to shorten the imaging time.

  However, in the microfocus X-ray tube, there is a space charge effect due to the charge of the electron beam itself as a factor that prevents an increase in the X-ray tube current. This is an effect that electrons are repelled by charges of electrons and the beam diameter of the electron beam is increased. Since the microfocus X-ray tube which is the subject of the present invention normally uses a lens action of an electric field or a magnetic field to focus an electron beam, the space charge effect makes it possible to increase and decrease the X-ray tube current. This is contrary to the reduction of the beam diameter of the electron beam for focusing. That is, when the electron beam current (X-ray tube current) is small, the lens action of the electric field or magnetic field can overcome the repulsive action of electrons due to the space charge effect, so that the electron beam can be sufficiently focused. However, when the beam current of the electron beam is increased, the above lens action does not function, and there is a problem that the electron beam cannot be sufficiently focused.

  As an electron focusing method for obtaining an extremely small focus as in the case of the microfocus X-ray tube which is the subject of the present invention, there is a method of forming an electric field lens using a plurality of electrodes. A typical example of this type of prior art is an electron gun for a cathode ray tube (CRT). The structure and operation of the CRT electron gun will be briefly described below. FIG. 12 shows a schematic configuration of the most basic in-line type electron gun for a CRT electron gun. In FIG. 12, the electron gun 200 includes a cathode 202 and four grid electrodes 204, 206, 208 and 210. The electron beam 212 radiated from the electron emission surface 202a of the cathode 202 is focused by an electron lens formed by the cathode 202 and the four grids 204, 206, 208, 210 to form a thin beam, and collides with the phosphor screen 222. The phosphor on the phosphor screen 222 is caused to emit light.

  In FIG. 12, four grid electrodes 204, 206, 208, and 210 are a first grid electrode (hereinafter abbreviated as G 1) 204, a second grid electrode (hereinafter abbreviated as G 2) 206 in order from the cathode 202. It is called a third grid electrode (hereinafter abbreviated as G3) 208 and a fourth grid electrode (hereinafter abbreviated as G4) 210, and the openings 204a, 206a, 208a, 210a are formed along the central axis of the electron gun 200, respectively. Have. Of the five electrodes of the electron gun 200, a portion constituted by the three electrodes of the cathode 202, G1204, and G2206 is called a tripolar portion, and a cathode lens 214 is formed in this portion. A prefocus lens 216 is formed between G2206 and G3208, and a main lens 218 is formed between G3208 and G4210.

  Cathode 202 is a hot cathode such as an oxide or impregnated cathode and is used in the space charge limited region at a high temperature of 1000K or higher. The amount of electron beam current from the cathode 202 is controlled by applying a voltage obtained by amplifying the video signal to the cathode 202. This amount of current increases as the cathode voltage decreases. G1204 is always given a voltage lower than that of the cathode 202, and G2206 is given an acceleration voltage about 400 to 1000V higher than the potential of the cathode 202. The current from the cathode 202 is applied to the beam through the opening 204a of the G1204. It is pulled out to the G2206 side. The electron beam is once focused by the cathode lens 214, forms a crossover 220 in the vicinity of G2206, and then enters the main lens 218 while diverging. Before being incident on the main lens 218, the prefocus lens 216 receives a slight focusing action. The tripolar portion and the prefocus lens 216 may be collectively referred to as a beam forming region.

The main lens 218 is a lens that projects a crossover 220, which is an object point, onto the phosphor screen 222 as an image point 224. That is, the main lens 218 has a role of focusing the incident electron beam 212 while diverging from the crossover 220 to form an image point 224 of a minute spot on the phosphor screen 222. A voltage (focus voltage) of 5 to 10 kV is applied to G3208, and a final acceleration voltage of 20 to 30 kV is applied to G4210, and the main lens 218 is formed by this potential difference. After passing through G4210, the electron beam 212 travels through the non-electric field space to the phosphor screen 222, and forms an image point 224 on the phosphor screen 222.
JP 2001-273860 A

  In the conventional CRT electron gun 200 described above, since it is assumed that the beam diameter of the electron beam 212 is normally focused to about 100 μm at the image point 224, a microfocus X-ray that requires a focal size of 10 μm or less. It cannot be applied directly to the tube. The cause of the increase in the beam diameter of the electron beam 212 is mainly due to the space charge effect and the spherical aberration of the lens. The space charge effect is a repulsive action of the electrons constituting the electron beam 212, but the repulsive action becomes larger as the beam diameter is made smaller and focusing becomes difficult. . The space charge effect increases as the current of the electron beam 212 increases, and the two characteristics required for the microfocus X-ray tube are contradictory to the large current.

  On the other hand, the spherical aberration of the lens occurs when the electron trajectory constituting the electron beam 212 is away from the central axis of the electron focusing system composed of the cathode 202 and the four grid electrodes 204, 206, 208, 210. This is unavoidable when the electron beam 212 is focused by the electron optical system. In order to minimize the spherical aberration, the beam diameter when the electron beam 212 enters the lens region is made as small as possible so that each electron can draw an electron trajectory that is as far as possible from the central axis of the electron optical system. I think it would be good.

  In view of the above, the present invention solves the problem of micro focus and large current, which are contradictory characteristics of the micro focus X-ray tube, and provides a micro focus X having an electron focusing system that obtains micro focus and large current. An object is to provide a tube and an X-ray apparatus using the same.

  In order to achieve the above object, a microfocus X-ray tube according to the present invention includes a cathode for generating an electron beam, and a plurality of grid electrodes disposed in a path of the electron beam to focus the electron beam into a narrow beam. An electron focusing system comprising: an anode that generates X-rays when the electron beam collides; and a cathode, the electron focusing system, and an envelope that encloses the anode in a vacuum-tight manner. Each of the plurality of grid electrodes has an opening for allowing the electron beam to pass therethrough, and an electron lens for focusing the electron beam is formed by applying a potential to each grid electrode with respect to the cathode. In the microfocus X-ray tube, the electron focusing system includes at least three grid electrodes, and is second closest to the cathode of the grid electrodes. Grid electrode (hereinafter, referred to as a second grid electrode) the opening diameter of the closest grid electrode to the cathode (hereinafter referred to as the first grid electrode) is obtained by less than the opening diameter of (claim 1).

  In the microfocus X-ray tube of the present invention, the aperture diameter of the second grid electrode is further set to be 1/2 or less of the aperture diameter of the first grid electrode.

  In the microfocus X-ray tube of the present invention, a positive potential is applied to the first grid electrode with respect to the potential of the cathode (claim 2).

  In the microfocus X-ray tube of the present invention, the potential applied to the first grid electrode (hereinafter referred to as the first grid electrode potential) and the potential applied to the second grid electrode (hereinafter referred to as the second grid electrode potential). And the potential applied to the grid electrode (hereinafter referred to as the third grid electrode) that is the third closest to the cathode (hereinafter referred to as the third grid electrode potential) is a positive potential with respect to the cathode potential. Is.

  In the microfocus X-ray tube of the present invention, at least the first grid electrode and the second grid electrode among the plurality of grid electrodes of the electron focusing system are made of a refractory metal material having a melting point of 2000 ° C. or higher or an alloy thereof. (Claim 3).

  In the microfocus X-ray tube of the present invention, the refractory metal material is one of molybdenum, tungsten, or tantalum.

  In the microfocus X-ray tube of the present invention, at least the surfaces of the first grid electrode and the second grid electrode among the plurality of grid electrodes are subjected to heat dissipation treatment (claim 4).

In the microfocus X-ray tube of the present invention, the heat dissipation process is one of a blackening process or a roughening process.

  Further, in the microfocus X-ray tube of the present invention, heat radiation fins are further attached to at least the first grid electrode and the second grid electrode among the plurality of grid electrodes (claim 5).

  Further, in the microfocus X-ray tube of the present invention, the surface heat radiation treatment and the radiation fins are attached to at least the first grid electrode and the second grid electrode among the plurality of grid electrodes.

  In the microfocus X-ray tube of the present invention, an X-ray tube voltage applied to the anode is used as a final acceleration voltage for focusing the electron beam in the electron focusing system.

  Further, in the microfocus X-ray tube of the present invention, the anode further has a rotating anode structure.

  The X-ray generator of the present invention includes a microfocus X-ray tube according to the present invention having a micro focus, a high-voltage power supply unit that supplies a high voltage to the microfocus X-ray tube, and the microfocus X-ray tube A grid power supply for supplying a grid voltage to a plurality of grid electrodes of the cathode of the electrode, an electrode insulation support for insulatingly supporting the electrodes of the microfocus X-ray tube, the microfocus X-ray tube and the high voltage power supply A casing that encloses and supports the grid power supply unit and the electrode insulating support unit, an insulating oil that is filled in the casing and that immerses and insulates the microfocus X-ray tube and other components, and expansion of the insulating oil And a bellows attached to the housing for buffering the contraction (Claim 6).

  Further, in the X-ray generator of the present invention, the anode of the microfocus X-ray tube has a rotating anode structure, a stator for rotationally driving the anode of the microfocus X-ray tube in the housing, and the stator A stator power supply for supplying a voltage to be applied to is included.

  An X-ray apparatus of the present invention includes an X-ray generation apparatus according to the present invention that generates X-rays, an X-ray detection apparatus that detects X-rays generated from the X-ray generation apparatus and transmitted through the subject, An image forming apparatus for generating an X-ray image of the specimen by inputting a signal corresponding to a detected X-ray dose output from the X-ray detection apparatus, the X-ray generation apparatus, the X-ray detection apparatus, and the image formation And a control device for controlling the device (claim 7).

  In the microfocus X-ray tube of the present invention, since the aperture diameter of the second grid electrode constituting the electron focusing system of the cathode is made smaller than the aperture diameter of the first grid electrode, it is emitted from the electron emission surface of the cathode. Out of the electron beam, electrons outside the central axis are first removed by colliding with the vicinity of the opening of the first grid electrode, and then by colliding with the vicinity of the opening of the second grid electrode. Thus, most of the electron beam that has passed through the opening of the second grid electrode is made up of electrons that travel on an orbit close to the central axis. As a result, in the focusing by the electron lens (main lens) formed thereafter, the spherical aberration is almost completely focused, so that a very small focal point can be formed on the anode target (claim 1). ).

  Further, in the microfocus X-ray tube of the present invention, the opening diameter of the second grid electrode is set to 1/2 or less of the opening diameter of the first grid electrode. The electron removal action works effectively in this range. In the range where the opening diameter of the second grid electrode is larger than 1/2 of the opening diameter of the first grid electrode, the collision of the electron beam to the vicinity of the opening is small and smaller than 1/2 of the opening diameter of the first grid electrode. As the electron beam collides, the number of collisions of electron beams increases rapidly, and the action of removing electrons from the outer periphery of the electron beam is significantly improved.

  In the microfocus X-ray tube of the present invention, the aperture diameter of the cathode second grid electrode is made smaller than the aperture diameter of the first grid electrode, and a positive potential is applied to the first grid electrode with respect to the cathode potential. Therefore, the potential of the first grid electrode accelerates the electron beam emitted from the electron emission surface of the cathode toward the first grid electrode to increase the X-ray tube current, and the first grid electrode and the second grid electrode The grid electrode can efficiently remove the electrons traveling on the outer orbit away from the central axis of the electron beam in the vicinity of the opening, thereby miniaturizing the focal dimension (claim 2).

  Further, in the microfocus X-ray tube of the present invention, the first grid electrode potential, the second grid electrode potential, and the third grid electrode potential are set to the cathode potential in the voltage application to the grid electrode of the electron focusing system of the cathode. Since the positive potential is increased, the X-ray tube current is increased by the positive first grid electrode potential and the second grid electrode potential, and the second and third grid electrodes are increased by the positive third grid electrode potential. And overfocusing of the electron beam by the main lens formed by the anode target can be prevented. That is, since the anode potential is very high in the X-ray tube, if the third grid electrode potential is negative, the focusing of the electron beam by the main lens becomes overfocusing, and the focal size becomes large. By setting the grid electrode potential to a positive potential, an appropriate main lens is formed, and the electron beam is properly focused.

  In the microfocus X-ray tube of the present invention, the first grid electrode and the second grid electrode of the electron focusing system of the cathode are made of a refractory metal material having a melting point of 2000 ° C. or higher or an alloy thereof. Even if the vicinity of the electrode opening is heated by the collision of some electron beams emitted from the cathode and the temperature rises, thermal deformation and secondary electron emission do not occur. Characteristics such as tube current can show stable operation (claim 3).

  In the microfocus X-ray tube of the present invention, one of molybdenum, tungsten, or tantalum is used as the refractory metal material constituting the first grid electrode and the second grid electrode. Even if a part of the electron beam collides with the vicinity of the opening of the electrode, stable operation can be maintained without causing thermal deformation or secondary electron emission.

  Further, in the microfocus X-ray tube of the present invention, since heat treatment is performed on the surfaces of at least the first grid electrode and the second grid electrode among the plurality of grid electrodes, the heat radiation of both grid electrodes is sufficiently performed. This suppresses the temperature rise, prevents thermal deformation and secondary electron emission even if part of the electron beam collides with both grid electrodes, and prevents overheating of the insulator supporting both grid electrodes. The X-ray tube can maintain stable operation.

  Further, in the microfocus X-ray tube of the present invention, the blackening process or the roughening process is performed as the heat dissipation process on the surfaces of at least the first grid electrode and the second grid electrode among the plurality of grid electrodes. Sufficient heat dissipation of the grid electrode suppresses temperature rise, does not cause thermal deformation or secondary electron emission, and prevents overheating of the insulator that supports both grid electrodes, so stable operation Can be maintained.

  Further, in the microfocus X-ray tube of the present invention, since the heat radiation fins are attached to at least the first grid electrode and the second grid electrode among the plurality of grid electrodes, the heat radiation of both grid electrodes is sufficiently performed, X-rays are used to prevent temperature rise, prevent thermal deformation and secondary electron emission even if part of the electron beam collides with both grid electrodes, and prevent overheating of the insulator that supports both grid electrodes. The tube can maintain stable operation (claim 5).

  In the microfocus X-ray tube of the present invention, the X-ray tube voltage applied to the anode is used as the final acceleration voltage for focusing the electron beam in the cathode electron focusing system. In order to form the main lens, it is not necessary to provide a special additional grid electrode or a power source for the grid voltage applied to the main lens, simplifying the X-ray tube and the X-ray generator and reducing the cost. Reduction can be achieved.

  Further, in the microfocus X-ray tube of the present invention, since the anode has a rotating anode structure, the focal position where the electron beam collides with the target rotates, so that the effective focal area is larger than that of the fixed anode structure. The load resistance can be greatly improved.

  Further, in the X-ray generator of the present invention, together with the microfocus X-ray tube according to the present invention having a micro focus, a high voltage power supply unit, a grid power supply unit, and the like are accommodated in one casing and integrated together. Therefore, the microfocus X-ray tube can be driven only by connecting a power cord for supplying a low voltage AC voltage. As a result, the X-ray generator is very compact and easy to handle (claim 6).

  In the X-ray generator of the present invention, since the anode of the microfocus X-ray tube has a rotating anode structure, the effective focal size of the X-ray tube can be significantly increased compared to that of the fixed anode structure. And the load resistance can be greatly improved.

  In addition, since the X-ray apparatus of the present invention uses the X-ray generator including the microfocus X-ray tube according to the present invention, a focal dimension of 10 μm or less and a practical value of the X-ray tube current can be obtained. Using this X-ray apparatus, it is possible to effectively carry out precision diagnosis by X-ray magnified photography with a micro focus and non-destructive inspection of minute internal structures of industrial products (Claim 7).

Embodiments of the present invention will be described below with reference to the accompanying drawings.
First, the structure and operation of the first embodiment of the microfocus X-ray tube according to the present invention will be described with reference to FIGS. FIG. 1 is an overall structural view of a first embodiment of a microfocus X-ray tube according to the present invention, FIG. 2 is an enlarged cross-sectional view of a cathode part which is a main part of FIG. 1, and FIG. 3 is a main part of FIG. It is a figure for demonstrating the structure of an electron focusing system.

  In FIG. 1, a microfocus X-ray tube (hereinafter abbreviated as an X-ray tube) 10 of the present embodiment includes a cathode 12 that generates an electron beam, an anode 14 that generates an X-ray when the electron beam collides, It comprises an envelope 16 that encloses the cathode 12 and the anode 14 in a vacuum-tight manner and supports them in an insulating manner. The X-ray tube 10 of this embodiment is characterized by the configuration of the cathode 12 for forming the microfocus, and the configuration and operation will be described in detail later with reference to FIGS. Prior to that, the structure of other parts will be described with reference to FIG.

  In FIG. 1, the anode 14 adopts a rotary anode type structure. The anode (hereinafter also referred to as a rotating anode) 14 is not limited to this and may be a fixed anode type. However, in order to effectively utilize the characteristics of the small focal point and the large current, which are the characteristics of the X-ray tube of the present invention, the rotating anode type in which the effective focal area increases by rotation is much more advantageous. The rotary anode 14 supports an X-ray generation target 18, a rotor 20 that supports the target 18, a rotary shaft 22 that supports the rotor 20, a bearing 24 that rotatably supports the rotary shaft 22, and a bearing 24. It comprises a fixed part 26 and the like. The rotary anode 14 as a whole has substantially the same structure as the rotary anode of a general-purpose medical rotary anode X-ray tube. The target 18 is an umbrella-shaped disk and is made of a metal material having a high atomic number such as tungsten and having a high melting point. A beam-shaped electron beam collides with the inclined surface of the target 18 from the cathode 12 to form a focal point 28. The rotor 20 has a large-diameter portion 20b that constitutes a motor by combining a small-diameter portion 20a that supports the target 18 and a stator that is disposed on the outer periphery of the rotor 10. The small diameter portion 20a is made of a high melting point and high strength metal material such as molybdenum. The large-diameter portion 20b has a bottomed cylindrical shape. The cylindrical portion is mainly made of a highly conductive metal material such as copper, and the bottom portion is made of a high-strength material such as molybdenum or stainless steel. The large diameter portion 20b is coupled to the small diameter portion 20a at the bottom. The rotating shaft 22 has a disk-shaped portion that is coupled to the bottom of the large-diameter portion 20b of the rotor 20 and a thin-diameter rod-shaped portion that is coupled to the inner ring of the bearing 24, and is made of a high-strength steel material or the like. The bearing 24 is composed of an inner ring, a ball, an outer ring and the like, and the material thereof is composed of a high strength steel material or the like. Since the bearing 24 is used in a vacuum, it is lubricated with silver, lead, molybdenum disulfide, or the like. Two bearings 24 are used, and the rotating shaft 22 is supported at two locations. The fixed portion 26 is composed of a cylindrical portion 26a for fixing the outer rings of the two bearings 24, and an anode end 26b that is coupled to the envelope 16 and to which an anode potential is applied. The fixing portion 26 is mainly made of a metal material having good thermal conductivity such as copper.

  Next, the envelope 16 surrounds the target 18 of the rotating anode 14 and the tip of the cathode 12, and is coupled to the large-diameter portion 30 held at the ground potential and the fixed portion 26 of the rotating anode 14 to insulate them. It comprises an anode insulating part 32 for supporting and a cathode insulating part 34 for insulatingly supporting the cathode 12. The large-diameter portion 30 is a combination of a large-diameter disk 30a and a large-diameter thick cylinder 30b, and the disk 30a and the cylinder 30b are made of a metal material such as copper or stainless steel. An X-ray radiation window 36 is attached to a circular opening provided in a portion of the disk 30a close to the focal point 28 on the target 18. The X-ray radiation window 36 is made of beryllium or the like having good X-ray transparency, and is coupled to the opening of the disk 30a by welding or brazing via a window frame or the like. A plurality of (for example, 3 to 6) holes used for supporting the X-ray tube 10 are formed in the thick portion of the cylinder 30b along the central axis direction. An anode insulating portion 32 is coaxially coupled to the cylinder 30b on the opening side of the cylinder 30b (the side opposite to the disk 30a). The anode insulating part 32 is connected to a cylindrical part 32 a slightly thicker than the outer diameter of the rotor 20 and a flare part 32 b which is widened in a cone shape so as to be connected to the cylinder 30 b of the large diameter part 30, and a fixed part 26 of the rotating anode 14. And an anode connecting portion 32c for the purpose. Most of the anode insulation part 32 is made of an insulating material such as heat-resistant glass or ceramic, and a metal material that is compatible with the insulation is used for the connecting part with the large-diameter part 30 on both ends and the fixed part 26 of the rotating anode 14 Has been. A cathode insulating portion 34 is coupled to the side surface of the cylinder 30b of the large diameter portion 30 in a direction substantially perpendicular to the central axis of the rotating anode 14. The cathode insulating portion 34 has a cylindrical shape with a thin outer diameter, and is coupled to the side surface of the cylinder 30b of the large diameter portion 30 in the vicinity of one end thereof and to the stem 48 of the cathode 12 at the other end. The cathode insulating portion 34 is mostly made of an insulating material such as heat resistant glass or ceramic. Further, an exhaust pipe 38 used for evacuating the X-ray tube 10 is attached to a portion of the side surface of the cylinder 30b of the large diameter portion 30 facing the cathode insulating part 34.

  Next, the configuration and operation of the cathode 12, which is a main part of the X-ray tube 10 of this embodiment, will be described with reference to FIGS. First, the structure of the cathode 12 of the X-ray tube 10 will be described with reference to FIG. 2A in FIG. 2 is a structural diagram of the entire cathode 12, and FIG. 2B is an enlarged view of the electron focusing system. In FIG. 2, the cathode 12 includes a cathode 40 that generates an electron beam, an electron focusing system 42 that focuses the electron beam, an electric field relaxation shield 43 that relaxes the electric field of the electron focusing system 42, and a cathode that supports the cathode 40. A support body 44, an electron focusing system insulator 46 that insulates and supports the three grid electrodes constituting the electron focusing system 42, a stem 48 that supports the cathode 40, the electron focusing system 42, and the like are included.

  The cathode 40 is an oxide or impregnated cathode and includes a heater 41 for heating, and emits thermoelectrons at a high temperature of 1000K or higher. The cathode 40 has a bottomed cylindrical shape, and a heater 41 for heating is insulated and disposed inside the cylinder, and thermal electrons are emitted from an outer surface (hereinafter referred to as an electron emission surface) 40a of the bottom. . The cathode 40 is supported by a cathode support 44 made of a refractory metal material or an insulating material, and further supported by an electron focusing system insulator 46 via an electron focusing system 42. The electron focusing system 42 includes three grid electrodes, that is, a first grid electrode (hereinafter abbreviated as G1 electrode) 50, a second grid electrode (hereinafter abbreviated as G2 electrode) 52, and a third grid electrode (hereinafter abbreviated as G1 electrode). , Abbreviated as G3 electrode) 54. Each of the three grid electrodes 50, 52, 54 has openings 50a, 52a, 54a through which electron beams pass in the center, and between the cathode 40 and the target 18 of the anode 14, the G1 electrode 50 is formed from the cathode 40 side. The G2 electrode 52 and the G3 electrode 54 are arranged coaxially at an appropriate interval. The G1 electrode 50 and the G2 electrode 52 are plate-like bodies and are provided with small openings 50a and 52a at the center thereof, and are formed in a cup shape as a whole in consideration of mounting and the like. The G3 electrode 54 is provided with a large opening 54a in the center, and has a shape close to a cylindrical shape as a whole. As will be described later, the opening diameters of the G1 electrode 50, the G2 electrode 52, and the G3 electrode 54 and the distance between them are determined in relation to the desired focal size and the voltage applied to each grid electrode. As the material of the grid electrodes 50, 52, 54, a heat resistant metal material is used.

    Between the electron focusing system 42 and the target 18, an electric field relaxation shield 43 made of an insulating material such as ceramic is disposed in order to relax the electric field of the electron focusing system 42. The electric field relaxation shield 43 has a disk shape, and its outer periphery is directly coupled to one end of the cathode insulating portion 34 of the envelope 16. The combined body of the electric field relaxation shield 43 and the cathode insulating part 34 is disposed so as to cover the entire electron focusing system 42. An opening 43a having a diameter larger than the opening 54a of the G3 electrode 54 is provided at the center of the electric field relaxation shield 43. The opening 43a of the electric field relaxation shield 43 is coaxial with the central axis of the electron focusing system 42, and the G3 electrode It arrange | positions so that it may adjoin to 54 opening 54a.

  The three grid electrodes 50, 52, and 54 of the electron focusing system 42 are insulated and supported by an electron focusing system insulator 46 disposed on the outside thereof. The electron focusing insulator 46 is a cylinder or a plurality of (for example, 3 to 6) rod-like bodies arranged in a ring shape (here, four rod-like bodies are arranged), and is mainly made of glass or Made of an insulator such as ceramic. The grid electrodes 50, 52, 54 are supported by brazing or embedding (heating and welding) the support fittings coupled to the outer periphery of the grid electrodes 50, 52, 54 to the electron focusing system insulator 46. Is done. The cathode support 44 is insulated and supported by the G1 electrode 50, and is supported by the electron focusing system insulator 46 via the G1 electrode 50. A connection fitting 47 for connecting to the stem 48 is coupled to the end of the electron focusing insulator 46 on the stem 48 side. The connection fitting 47 is a cylindrical fitting and is coupled to the electron focusing insulator 46 via a support fitting in the same manner as other grid electrodes.

  The stem 48 includes a disk-shaped support plate 58, a plurality of lead wires 60 that pass through the support plate 58 and guided into the X-ray tube, and an electron focusing system support 62 coupled to the support plate 58. Consists of The support plate 58 is made of an insulating material such as ceramic or glass, and the lead-in lead wire 60 is made of a metal wire that is thermally compatible with the support plate 58. There are 1 lead wire 60 for the cathode, 2 for the heater, 3 for the grid electrode, and 1 or more for the other (getter evaporating, etc.). 6 or more are required. The introduction lead wire 60 is coupled and supported to the support plate 58 by brazing or welding. Further, in this embodiment, a cylindrical electron focusing system support 62 is provided to support the electron focusing system insulator 46, and a connection fitting 47 of the electron focusing system insulator 46 is coupled to this end by welding or the like. ing. The connection between the electrode constituting the cathode 12 and the lead-in lead 60 is made inside the electron focusing system support 62 or the electron focusing system insulator 46. The stem 48 is coupled to the cathode insulating portion 34 by welding, brazing or welding. In the illustrated example, a metal ring is attached to the outer periphery of the support body 58 of the stem 48 by brazing, and is joined to the ring attached to the end of the cathode insulating portion 34 by welding.

  Next, the details and operation of the configuration of the electron focusing system of the present embodiment will be described with reference to FIG. FIG. 3 schematically shows a configuration of an electron focusing system which is a main part of the present embodiment. In FIG. 3, the G1 electrode 50, the G2 electrode 52, and the G3 electrode 54 of the electron focusing system 42 are sequentially arranged coaxially between the electron emission surface 40a of the cathode 40 and the target 18. The centers of the openings 50a, 52a, 54a of the grid electrodes 50, 52, 54 through which the electron beam 64 passes are aligned with the central axis of the electron focusing system 42. As can be seen from FIG. 3, the diameter of the opening 52a of the G2 electrode 52 is smaller than the diameter of the opening 50a of the G1 electrode 50. The diameter of the opening 54a of the G3 electrode 54 is significantly larger than that of the G1 electrode 50, for example, several times or more. The G1 electrode 50 and the G2 electrode 52 use thin plates having a thickness of 0.2 mm or more, whereas the G3 electrode 54 has a thickness (the length in the central axis direction of the electron focusing system) of several millimeters. 50 and G2 electrode 52 are much thicker. Further, the electrode interval of the electron focusing system 42 is the interval between the cathode 40 and the G1 electrode 50 (hereinafter referred to as K-G1 interval) and the interval between the G1 electrode 50 and the G2 electrode 52 (hereinafter referred to as G1). -G2 interval) is approximately the same as the thickness of the G1 electrode 50 and G2 electrode 52 (0.1 to 0.5 mm), whereas the interval between the G2 electrode 52 and the G3 electrode 54 (hereinafter referred to as "G2 interval"). The distance between the G3 electrode 54 and the target 18 of the anode 14 (hereinafter abbreviated as G3-A distance) is 10 mm or more. Yes.

  As for the voltage applied to each electrode of the electron focusing system 42, the G1 electrode 50 has a positive potential (hereinafter referred to as G1 potential) of about several volts relative to the potential of the cathode 40 (hereinafter referred to as cathode potential). The G2 electrode 52 has a positive potential of about several hundred volts with respect to the cathode potential (hereinafter referred to as G2 potential), and the G3 electrode 54 has a positive potential of about several hundred volts with respect to the cathode potential (hereinafter referred to as G3 potential). Are applied respectively. Further, an X-ray tube operating voltage (in this embodiment, about +10 to +150 kV with respect to the cathode potential, hereinafter referred to as an X-ray tube voltage) is applied to the target 18. By thus applying voltages to the grid electrodes 50, 52, 54 and the target 18, the cathode lens 65 is located near the G1 electrode 50, the prefocus lens 66 is located near the G2 electrode 52, and the G3 electrode 54 is located nearby. Main lenses 67 are formed to focus the electron beam 64. The value of the voltage applied to the grid electrodes 50, 52 and 54 is controlled in accordance with the desired focal size and electron beam current (hereinafter also referred to as X-ray tube current).

  In the electron focusing system 42 of the X-ray tube 10 of this embodiment, in order to obtain a micro focus, (1) the opening diameter of the opening 52a of the G2 electrode 52 is made smaller than the opening diameter of the opening 50a of the G1 electrode 50; 2) The potential of the G1 electrode 50, that is, the G1 potential is made higher than the potential of the cathode 40, and (3) the G1 electrode 50 and the G2 electrode 52 are made of a refractory metal. Hereinafter, the contents and effects will be described in detail.

  In FIG. 3, the cathode 40 is heated by the heater 41 and raised to its operating temperature, whereby thermoelectrons are emitted from the electron emission surface 40a of the cathode 40, and these thermoelectrons are drawn out by the positive potential of the G1 electrode 50. And accelerated to form an electron beam 64. The amount of current of the electron beam 64 is proportional to the third power of the electric field strength of the front surface of the electron emission surface 40a of the cathode 40 if the cathode 40 is sufficiently heated to reach the operating temperature. Therefore, in order to obtain more X-ray tube current, it is an effective means to apply a positive potential to the G1 electrode 50 to increase the electric field strength on the front surface of the electron emission surface 40a. In this embodiment, as described above, since a positive potential of about several + V is applied to the G1 electrode 50 with respect to the cathode 40, an accelerating electric field is formed in front of the electron emission surface 40a of the cathode 40, and X-rays are generated. The tube current increases. On the other hand, in the example of the electron gun for CRT shown in the conventional example, a negative potential is applied to the G1 electrode, and the effective emission area of electron emission on the electron emission surface of the cathode is adjusted to obtain an electron beam. The amount of current that is generated is controlled.

  In this embodiment, the electron beam 64 passing through the opening 50a of the G1 electrode 50 while being accelerated is further accelerated by the G2 electrode 52. In other words, since a positive potential higher than the positive potential of the G1 electrode 50 is applied to the G2 electrode 52, another acceleration is performed by the G2 electrode 52. A cathode lens 65 that focuses the electron beam 64 is formed between the G1 electrode 50 and the G2 electrode 52 by the potential difference between the G2 electrode 52 and the G1 electrode 50. The electron beam 64 is focused by the electron focusing action of the cathode lens 65. By this focusing action, the electron beam 64 goes to the opening 54a of the G2 electrode 54 and forms a crossover 68 as an object point.

  Since a positive potential is applied to the G1 electrode 50 and the G2 electrode 52 in this way, it is unavoidable that the electron beam 64 from the cathode 40 collides around the openings 50a and 52a of the G1 electrode 50 and the G2 electrode 52. Absent. Due to the collision of the electron beam 64, the temperature of the G1 electrode 50 and the G2 electrode 52, particularly around the openings 50a and 52a, rises. As a result, thermal deformation of the G1 electrode 50 and G2 electrode 52 and changes in the focusing action of the electron lens occur. In order to prevent these, in this embodiment, the G1 electrode 50 and G2 electrode 52 are made to have a high melting point, for example 2000 It is composed of a high-strength metal material with a melting point of ℃ or higher. As these metal materials, for example, molybdenum, tungsten, tantalum, etc., or alloys thereof are selected and used. Among these, molybdenum is most suitable because it has good workability and is easily available.

  Due to the temperature rise of the G1 electrode 50 described above, thermal electrons are generated slightly from the high temperature portion around the opening 50a of the G1 electrode 50, and are added to the electron beam 64 from the cathode 40. Such secondary stray electrons increase the radius of the electron trajectory of the electron beam 64 in the radial direction, which adversely affects the focal spot size. Further, even in the electron beam 64 normally emitted from the cathode 40, in order to obtain a small focal size, it is preferable that the radial expansion of the electron trajectory of the electron beam 64 is as small as possible. Considering these, in the present invention, the opening diameter of the G2 electrode 52 is made smaller than the opening diameter of the G1 electrode 50. When only the focal size is considered, the smaller the aperture diameter of the G2 electrode 52 is, the better. However, since there is a problem that the X-ray tube current cannot be sufficiently obtained, the aperture diameter of the G2 electrode 52 is practically set to the G1 electrode. A suitable value is about 1/2 to 1/10 of the 50 opening diameter. In the calculation example of FIG. 4 shown below, the aperture diameter of the G2 electrode 52 is set to 1/5 of the aperture diameter of the G1 electrode 50, and a focal size of about 5 μm is obtained.

  By making the opening diameter of the G2 electrode 52 smaller than the opening diameter of the G1 electrode 50, stray electrons generated from the G1 electrode 50 and the G2 electrode 52 can be prevented from proceeding beyond the G2 electrode 52. it can. At the same time, since the electron beam 64 enters the prefocus lens 67 formed by the G2 electrode 52, the G3 electrode 54, and the target 18 of the anode 14, the radial expansion of the electron trajectory is reduced. The spherical aberration of 42 can be reduced, and the electron beam 64 can be focused on a small focal point.

  Further, by applying a positive G1 voltage to the G1 electrode 50 and accelerating the electron beam 64, the incident direction of the electron beam 64 toward the opening 52a of the G2 electrode 52 is parallel to the central axis of the electron focusing system 42. Since the expansion in the radial direction of the electron trajectory becomes smaller and closer to the direction, the spherical aberration due to the main lens 67 can be reduced.

  The electron beam 64 that has passed through the opening 52a of the G2 electrode 52 is focused to a desired focal size by the main lens 67 formed by the electron focusing system. Here, the main lens 67 is formed by a potential difference among the G2 electrode 52, the G3 electrode 54, and the anode 14. For example, when 150 kV is applied to the anode 14, a positive potential of about 30 V is applied to the G 1 electrode 50, a positive potential of about 500 V is applied to the G 2 electrode 52, and a positive potential of about 300 V is applied to the G 3 electrode 54. A focal point of 10 μm or less can be formed on the target 18.

  The G1, G2, and G3 potentials applied to the three grid electrodes 50, 52, and 54 constituting the electron focusing system 42 are examined in relation to the focal dimension and the X-ray tube current. In order to make it smaller, it is effective that the G1, G2, and G3 potentials are positive with respect to the cathode 40 potential. Although the effectiveness of setting the G1 potential to the positive potential has been described above, the focusing action of the electron lens formed by the electron focusing system 42 works more effectively when the G2 potential and the G3 potential are also set to the positive potential. According to the inventor's calculations and examinations, it has been found that when at least one of the G2 potential and the G3 potential is a negative potential, the focal spot size becomes large. This is because the potential of the target 18 of the anode 14 is a high positive potential of 100 kV or more, so that a potential difference between the G2 potential or the G3 potential and the potential of the target 18 becomes excessive, resulting in overfocusing and a large focal size. It is judged that it will become.

  In the electron focusing system 42 of the X-ray tube 10 of the present embodiment, in order to make the focal size 10 μm or less, the G1 potential of the G1 electrode 50 is about +30 to +150 V, the G2 potential of the G2 electrode 52 is about +500 to +1500 V, It is appropriate to set the G3 potential of the G3 electrode 54 to about 0 to + 3000V. In this embodiment, by appropriately combining these grid potentials, a focal size of 10 μm or less is obtained, and since the G1 potential is held at a positive potential, a practical X-ray tube current is also obtained. .

  An example of the potential distribution and the electron trajectory in the electron focusing system of the microfocus X-ray tube of the present embodiment will be described with reference to FIGS. FIG. 4 shows an example of calculation examples of potential distribution and electron trajectory in the electron focusing system of the microfocus X-ray tube of this embodiment. FIG. 5 is an enlarged view of a range from the cathode of FIG. 4 to the G2 electrode. The electron focusing system 42 of the X-ray tube 10 is composed of an impregnated cathode, a G1 electrode 50 having a thickness of 0.2 to 0.3 mm, an opening diameter of 0.5 mm, and a G2 electrode 52 having a thickness of 0.2 to 0.3 mm. The diameter is 0.1mm, the G3 electrode 54 is 3mm thick (or the total length), the opening diameter is 4mm, the K-G1 and G1-G2 intervals are 0.2mm, the G2-G3 intervals are about 1.5mm, and the G3-A intervals are about 15mm. It is. In addition, with respect to the potential applied to each electrode, with reference to the potential of the cathode 40, the G1 potential is + 30V, the G2 potential is + 525V, the G3 potential is + 1900V, and the anode potential is + 150kV. As the grid electrode material, molybdenum is used for the G1 electrode 50 and the G2 electrode 52, and stainless steel is used for the G3 electrode 54.

  In this calculation example, the focal size on the target 18 is 5 μm, and the X-ray tube current is 0.4 mA. In FIG. 4, the electron beam 64 forms a crossover 68 in the vicinity of the G2 electrode 52, becomes the maximum beam diameter in the opening 52a of the G3 electrode 54, and then is focused by the main lens 67, and the minimum beam on the target 18 A focal point 28 is formed as a diameter image point. Further, according to the enlarged view of FIG. 5, the electron beam 64 radiated from the electron emission surface 40a of the cathode 40 collides with the vicinity of the opening 50a of the G1 electrode 50 and is removed. Further, it can be seen that the beam diameter of the electron beam 64 that has passed through the opening 50a of the G1 electrode 50 is sharply reduced between the G1 electrode 50 and the G2 electrode 52. This is considered to be the effect of applying a positive potential to the G1 electrode 50 and the focusing action of the cathode lens 65 formed between the G1 electrode 50 and the G2 electrode 52. Further, a slight amount of the electron beam 64 on the outer periphery of the electron beam 64 that has passed through the opening 50a of the G1 electrode 50 collides with the vicinity of the opening 52a of the G2 electrode 52 and is removed. The crossover 68 is formed at a position where the electron beam 64 exits the opening 52a of the G2 electrode 52 and advances slightly toward the G3 electrode 54. The electron beam 64 that has reached the crossover 68 is composed of only electrons closer to the central axis because electrons at positions away from the central axis are removed in two stages by the G1 electrode 50 and the G2 electrode 52. It will be. As a result, when the electron beam 64 is focused by the main lens 67 formed by the G2 electrode 52, the G3 electrode 54, and the target 18 of the anode 14, the beam can be focused with almost no spherical aberration. Here, a focal point 28 of 5 μm) can be formed on the target 18. In this embodiment, the electron focusing system 42 is composed of three grid electrodes, but the number of grid electrodes is not limited to this, and it goes without saying that it may be four or more as required.

  In FIG. 5, as described above, a part of the electron beam 64 from the cathode 40 collides with the vicinity of the opening 50a of the G1 electrode 50 and the vicinity of the opening 52a of the G2 electrode 52. Becomes larger. However, in this embodiment, since the G1 electrode 50 and the G2 electrode 52 are made of a refractory metal material (here, molybdenum), thermal deformation and secondary electron emission can be suppressed.

  Next, the structures of the second and third embodiments of the microfocus X-ray tube according to the present invention will be described with reference to FIGS. In each of these embodiments, the heat dissipation of the cathode electron focusing system, particularly the first grid electrode and the second grid electrode, is improved, and the temperature rise is suppressed. First, the structure of the second embodiment of the microfocus X-ray tube according to the present invention will be described with reference to FIG. FIG. 6 is an enlarged view of the cathode part of this embodiment, FIG. 6 (a) is a structural diagram of the entire cathode, and FIG. 6 (b) is an enlarged view of the electron focusing system. FIG. 6 (a) has almost the same structure as FIG. 2 (a) except for the electron focusing system 42a.

  In this embodiment, in FIG. 6B, the blackening process 55 is applied to the surfaces of the first grid electrode 50, the second grid electrode 52, and the third grid electrode 54 of the electron focusing system 42a. As the blackening treatment 55, black chrome plating or the like is performed. By this blackening process 55, the thermal radiation rate of the surface of each grid electrode increases from about 0.2 to 0.8. In the drawing, the blackening process 55 is performed on the outer surface of each grid electrode (indicated by a thick black line). However, the present invention is not limited to this and may be performed on another surface such as the inner surface. In this embodiment, the blackening process 55 is performed on all grid electrodes. However, the range of the blackening process 55 is the first in which the amount of incident electron beams from the cathode 40 is large and the temperature rises greatly. Only the grid electrode 50 and the second grid electrode 52 are limited, and the third grid electrode 54 with a small amount of incident electron beams and a small temperature rise may be excluded. In the present embodiment, the heat radiation effect from the grid electrode surface is greatly improved and the temperature rise of the grid electrode is suppressed by improving the thermal emissivity of the grid electrode surface.

  In the microfocus X-ray tube of the present invention, a heat-resistant metal such as molybdenum is used for the grid electrode of the electron focusing system, and a structure capable of withstanding an increase in collisions of electron beams caused by applying a positive potential to the grid electrode is used. In order to further improve the X-ray output, it is necessary to consider the heat resistance limit of the insulator (such as the electron focusing insulator 46) that supports these grid electrodes. When trying to obtain a large amount of X-ray tube current (electron dose) that reaches the heat resistance limit of this insulator, in order to prevent overheating of this insulator, it is intended to enhance the heat dissipation effect of the grid electrode. This is the main purpose of the blackening process 55 on the surface of the grid electrode of this embodiment. As a result of the above blackening treatment 55, the thermal emissivity of the grid electrode surface increases from about 0.2 to 0.8, so the heat dissipation from the grid electrode surface also increases, the temperature rise of the grid electrode is suppressed, and the cooling effect is improved. can get.

ここで、Qは伝熱量、σはステファンーボルツマンの定数、εは熱輻射率、T1はグリッド電極の温度、T2は周囲の物体の温度である。数１を用いて、黒化処理前後のグリッド電極の温度の差を概算してみることにする。黒化処理前のグリッド電極の温度をT10、熱輻射率をε10、黒化処理後のグリッド電極の温度をT11、熱輻射率をε11とする。周囲の物体は通常グリッド電極に比べて熱容量が大きいため、グリッド電極の黒化処理にかかわらず温度（T2）は変わらないと考え、簡単のため、T2＝0とおく。グリッド電極の黒化処理の前後で入力熱量が同じで、かつ周囲の物体の温度（T2）が変わらないということから、グリッド電極からの放熱量（Q）も黒化処理の前後で等しい。従って、数１から数2が成り立つ。

黒化処理によりグリッド電極の熱輻射率εがε10＝0.2からε11＝0.8に向上するので、数２の変形により数３が得られる。

As the grid electrode cooling effect by the blackening treatment 55 on the grid electrode surface, the following is roughly obtained. In the present embodiment, the electron focusing system 42a is in a vacuum, and the heat conduction element among the heat transfer elements is only the lead lead 60 that applies a voltage, and since this is a thin line, the heat dissipation effect is small, and the electron focusing The thermal radiation elements from the system 42a to the surrounding cathode insulating part 34 and the electric field relaxation shield 43 are dominant. The heat transfer between two objects due to heat radiation is expressed by Equation 1.

Here, Q is the amount of heat transfer, σ is the Stefan-Boltzmann constant, ε is the thermal emissivity, T1 is the temperature of the grid electrode, and T2 is the temperature of the surrounding object. Using Equation 1, the temperature difference between the grid electrodes before and after the blackening process is approximated. It is assumed that the temperature of the grid electrode before blackening treatment is T10, the thermal radiation rate is ε10, the temperature of the grid electrode after blackening treatment is T11, and the thermal radiation rate is ε11. Since the surrounding object usually has a larger heat capacity than the grid electrode, it is assumed that the temperature (T2) does not change regardless of the blackening process of the grid electrode. For simplicity, T2 = 0 is set. Since the amount of input heat is the same before and after the blackening process of the grid electrode and the temperature (T2) of the surrounding object does not change, the amount of heat released from the grid electrode (Q) is also the same before and after the blackening process. Therefore, Equation 1 to Equation 2 hold.

Since the heat emissivity ε of the grid electrode is improved from ε10 = 0.2 to ε11 = 0.8 by the blackening process, Equation 3 is obtained by the transformation of Equation 2.

  Since the temperature of the grid electrode when the blackening treatment was not performed was around 500 ° C., applying Equation 3 would reduce the temperature of the grid electrode to around 270 ° C., thereby obtaining a significant cooling effect. For example, when glass is used as the insulator supporting the grid electrode, softening starts at around 700 ° C. However, since the temperature of the grid electrode is greatly reduced by this embodiment, the thermal problem is solved. As a result, it is possible to increase the X-ray tube current value that has been limited so far by the temperature of the grid electrode.

  In this embodiment, the surface of the grid electrode is blackened to enhance the heat dissipation effect. However, similar heat dissipation can be achieved by using other heat dissipation treatment and roughening the surface of the grid electrode. An effect is obtained. As the surface roughening treatment, a sandblast treatment or the like is performed on the surface of the grid electrode. The range of the roughening process is the same as that of the blackening process. The heat dissipation effect is slightly inferior to the blackening treatment, but the operation is simple.

  Next, the structure of the third embodiment of the microfocus X-ray tube according to the present invention will be described with reference to FIG. FIG. 7 is an enlarged view of the electron focusing system of the cathode of this example. Since this embodiment is the same as the structure of the first embodiment and the second embodiment of the microfocus X-ray tube according to the present invention except for the electron focusing system 42b of the cathode, the other parts are shown in FIG. Omitted. In the present embodiment, in FIG. 7, radiating fins 56 are attached to the outer peripheral surfaces of the first grid electrode 50 and the second grid electrode 52 of the electron focusing system 42b. The radiating fins 56 are formed by processing a plate-like body into a T-shape, L-shape as shown, or a plate-like body as it is, and a plurality of, for example, three or six radiating fins 56 are provided on each grid. Attached to the outer peripheral surface of the electrode with a gap. As a material of the heat radiation fin 56, a metal material having high thermal conductivity is suitable, and the same material as that of the grid electrode or copper or copper alloy is used. The coupling between the radiation fin 56 and the grid electrode is performed by brazing or welding. In the case of the present embodiment, since the radiating fin 56 protrudes from the outer peripheral surface of the grid electrode, the electron focusing system insulator 46 is preferably an annular arrangement of a plurality of rod-shaped bodies, and the radiating fin 56 is It arranges so that it may enter between rods.

  In the present embodiment, by dissipating the heat radiation fins 56 on the outer peripheral surfaces of the first grid electrode 50 and the second grid electrode 52, the heat radiation action of both grid electrodes is improved, and both grid electrodes are the same as in the second embodiment. The temperature of is suppressed. As a result, overheating of insulators such as the electron focusing insulator 46 can be prevented, and the X-ray tube current can be increased.

  In this embodiment, the radiation fin 56 is attached to the first grid electrode 50 and the second grid electrode 52, but the radiation fin 56 may be attached to the third grid electrode 54. In this case, the third grid electrode 54 also improves the heat dissipation action, and an effect of suppressing the temperature rise is obtained. In the present embodiment, the fins 56 may be attached to the outer peripheral surfaces of the first grid electrode 50 and the second grid electrode 52, and the electrode surface may be blackened 55. At this time, the blackening process 55 may be performed on the surface of the heat radiation fin 56. In this case, the heat radiation effect of the grid electrode is improved as compared with the second embodiment, which is effective when it is desired to further increase the X-ray tube current.

  Next, the configuration of an embodiment of the X-ray apparatus according to the present invention will be described with reference to FIGS. FIG. 8 is a schematic configuration diagram of an embodiment of the X-ray apparatus according to the present invention. In FIG. 8, the X-ray apparatus 70 of this embodiment includes an X-ray generation apparatus 72 that generates X-rays, an X-ray detection apparatus 76 that detects an X-ray dose that has passed through a subject 74, and an X-ray detection apparatus 76. An image forming apparatus 78 that forms an X-ray image of the subject 74 based on the output signal, an X-ray generator 72, an X-ray detector 76, a controller 80 that controls the operation of the image forming apparatus 78, and the like. The Here, the X-ray generator 72 includes the microfocus X-ray tube 10 according to the present invention.

  The X-ray generator 72 includes a high-voltage power source, a grid power source and the like in addition to the microfocus X-ray tube 10 according to the present invention, and details thereof will be described later with reference to FIGS. Examples of the X-ray detection device 76 include those in which X-ray detection elements are arranged in a line like a line sensor, and those in which X-ray detection elements are arranged in a plane like an image intensifier (II), etc. Used. Since the X-ray detection device 76 outputs an electrical signal having an intensity corresponding to the normally received X-ray dose, the image forming device 78 uses the linear distribution or planar distribution electrical signal from the X-ray detection device 76. Thus, an X-ray image that is a planar image is formed. When an X-ray film is used as the X-ray detection means, the X-ray film corresponds to the X-ray detection device 76, and the film developing device corresponds to the image forming device 78. The control device 80 performs control of conditions for driving the microfocus X-ray tube 10, control of the X-ray detection operation of the X-ray detection device 76, control of the image creation operation of the image forming device 78, and the like. The control device 80 also supplies power supply voltage to other devices such as the X-ray generator 72.

  9 to 11 show the configuration of an embodiment of the X-ray generator according to the present invention. FIG. 9 is a cross-sectional view of the X-ray generator when viewed from the X-ray emission window. 10 is a cross-sectional view of the X-ray generator cut along the central axis of the anode and cathode of the X-ray tube, and FIG. 11 is a cross-sectional view seen from the direction orthogonal to FIGS. In FIG. 9, the X-ray generator 72 is collected as a single rectangular parallelepiped device, and a microfocus X-ray tube 10, a high voltage power supply 84, a grid power supply 86, a stator power supply 88, etc. are contained in a rectangular parallelepiped case 82. It is immersed in the insulating oil 90 and stored. The case 82 is made of a metal plate such as a steel plate, and is assembled into a substantially rectangular parallelepiped casing as a whole by welding or screwing. The case 82 is provided with a low-voltage power plug 92 for introducing a low-voltage current, an X-ray window 94 for taking out X-rays to the outside, an oil inlet 96 for injecting insulating oil 90 into the inside, and the like.

  9 to 11, the X-ray tube 10 is supported by coupling the large-diameter portion 30 of the envelope 16 to the upper inner wall of the case 82 and the fixing portion 26 of the anode 14 to the anode support 98. Yes. A stator 100 for rotationally driving the rotor 20 is disposed on the outer periphery of the rotor 20 of the anode 14 of the X-ray tube 10. In FIG. 11, the large-diameter portion 30 of the envelope 16 of the X-ray tube 10 is a disk to which the X-ray radiation window 36 is attached by a plurality of, for example, three screws 102 provided on the upper inner wall of the case 82. The portion 30a is fixed so as to be in close contact with the inner wall of the upper surface of the case 82. At this time, oil tightness between the disk portion 30a of the large diameter portion 30 and the case 82 is performed by the 0 ring 104 or the like. The X-ray emission window 36 of the X-ray tube 10 and the X-ray window 94 of the case 82 are also aligned.

  A cylindrical X-ray tube shield 106 with a bottom is disposed at a position surrounding most of the anode 14 of the X-ray tube 10 and the stator 100. The anode 14 of the X-ray tube 10 is supported by the side inner wall of the case 82 through the X-ray tube shield 106. The X-ray tube shield 106 includes a cylindrical portion 108 and a bottom plate portion 110. The cylindrical portion 108 is made of a metal material or an insulator, and the bottom plate portion 110 is made of a high-strength metal material. A shield plate 112 made of a lead plate or the like is attached to the inner wall of the cylindrical portion 108 to shield X-rays. The upper end portion of the cylindrical portion 108 extends to the vicinity of the cathode insulating portion 34 and the large diameter portion 30 of the envelope 16 of the X-ray tube 10, and the lower end portion has a high-voltage lead wire (hereinafter referred to as an anode) on the anode side. An anode lead introduction port 116 for introducing 149 (referred to as a lead wire) is attached. The anode lead introduction port 116 has a pipe shape and is made of an insulating material such as an epoxy resin. The anode lead introduction port 116 is disposed through the wall surface of the cylindrical portion 108. The bottom plate portion 110 has a bottom portion 110a that indirectly supports the anode 14 of the X-ray tube 10, and a fixing portion 110b for fixing the entire X-ray shield 106 to the side wall of the case 82. The fixing portion 110b is a screw. It is fixed to the side wall of the case 82 by 111 or the like.

  The anode support 98 that supports the anode 14 of the X-ray tube 10 is made of a metal material having good conductivity, and is bonded to and supported by the anode insulating support 118. Further, the anode insulating support 118 is coupled to and supported by the bottom plate part 110 of the X-ray tube shield 106. The anode support 98 has a small-diameter cylindrical portion 98a that is coupled to the fixed portion 26 of the anode 14, and a circular flange portion 98b that is coupled to the anode insulating support 118, and an anode lead wire 149 is provided on the circular flange portion 98b. It is connected. The anode insulating support 118 has a cylindrical portion 118a that is coupled to the circular flange portion 98b of the anode support 98, and a thick circular flange portion 118b that is coupled to the bottom plate portion 110 of the X-ray tube shield 106. Made of high-strength insulating material such as epoxy resin. The anode support 98 and the anode insulating support 118 are joined by tightening and fixing the circular flange portion 98b of the anode support 98 with a large diameter screw. In some cases, the circular flange portion 98b of the anode support 98 is embedded in the anode insulating support 118 by molding. The anode insulating support 118 and the bottom plate portion 110 of the X-ray tube shield 106 are coupled by screw fixing or adhesion.

  A stator insulating cylinder 120 is disposed between the stator 100 and the anode insulating portion 32 of the envelope 16 of the X-ray tube 10. The stator insulating cylinder 120 has a thin cylindrical portion 120a and a flange portion 120b spreading outward, and is made of an insulating material such as epoxy resin. The stator 100 is supported by a stator support 122 arranged on the outer periphery. The stator support 122 is coupled to and supported by the anode insulating support 118. The stator support 122 includes a cylindrical ring portion 122a that holds the stator 100 on its outer periphery, and an insulating support portion 122b that connects the ring portion 122a and the anode insulating support 118. The ring portion 122a is made of a metal material or an insulating material, and is coupled to the stator 100 with screws or the like. The insulating support part 122b has a plurality of, for example, three pillars and a support part that supports these pillars collectively, and both ends of the pillar are coupled to the ring part 122a and the support part with screws or the like, The support portion is fastened to the inner periphery of the upper portion of the cylindrical portion 118a of the anode insulating support 118 with screws. The whole or most of the insulating support 122b is made of an insulating material such as an epoxy resin.

  In FIG. 10, a bellows 124 for buffering expansion and contraction of the insulating oil 90 due to heat is attached to the inner wall of the lower surface of the case 82. The bellows 124 has an axisymmetric bag shape as a whole, and an 0-ring portion 124a for maintaining oil tightness is provided at the opening. The bellows 124 is made of oil-resistant rubber or the like, and the bag-like portion 124b excluding the 0-ring portion 124a is processed to be thin and deforms in response to the expansion and contraction of the insulating oil 90. The bellows 124 is fixed using a ring portion 126, a pressing plate 128, a screw 130, and the like provided on the inner wall of the lower surface of the case 82. An air vent opening 132 is provided on the surface of the lower wall of the case 82 on which the bellows 124 is fixed.

  Next, the high voltage power supply 84 will be described with reference to FIGS. The high voltage power source 84 is a neutral point grounding type cockcroft-Wallton circuit, and includes an anode high voltage generator 140 and a cathode high voltage generator 142. Each of the high voltage generators 140 and 142 includes a transformer 144, a capacitor 146, and a resistor 147. After the low-voltage AC voltage introduced from the low-voltage power plug 92 is boosted by the transformer 144, a plurality of stages of capacitors 146 and resistors 147 are provided. The voltage is further boosted to a DC high voltage. The number of capacitors 146 and resistors 147 in the high voltage generators 140 and 142 is determined according to the value of the output voltage of the high voltage power supply 84. In this embodiment, since the rated voltage of the X-ray tube 10 is 150 kV, each high voltage generator 140, 142 generates 75 kV. For example, the boosting is performed by a combination of the capacitor 146 and the resistor 147 in five stages. In this case, a voltage of 15 kV is shared by one capacitor 146. Elements such as the transformer 144, the capacitor 146, and the resistor 147 constituting the high voltage power supply 84 are arranged on the high voltage power supply board 148, and the high voltage power supply board 148 is insulated and supported on the inner wall of the case 82.

  Regarding the connection between the high voltage power source 84 and the X-ray tube 10, first, the anode lead wire 149 drawn from the high voltage side terminal of the anode high voltage generating unit 140 is introduced into the X-ray tube shield 106. Through the opening 116, it is led to the circular flange portion 98b of the anode support 98, and this is coupled to the circular flange portion 98b by a screw or the like. Next, a cathode-side high-voltage lead wire (hereinafter referred to as a cathode lead wire) 150 drawn from the high-voltage side terminal of the cathode high-voltage generator 142 is led to the stem 48 of the cathode 12 of the X-ray tube 10, and the stem Connected to cathode lead 60a among 48 lead wires 60.

  Next, the grid power supply 86 will be described with reference to FIGS. The grid power supply 86 applies a grid voltage based on the potential of the cathode 40 of the cathode 12 to the three grid electrodes 50, 52, 54 of the cathode 12 of the X-ray tube 10. Since the potential of the cathode 40 of the cathode 12 is at a negative high potential, the grid voltage output from the grid power supply 86 is also at a negative high potential. For this reason, the grid power supply 86 is arranged on a grid power supply substrate 152 made of an insulating material, like the high voltage power supply 84. The grid power supply 86 is usually composed of an insulation transformer 154 and a rectifying element 156, etc., and a low-voltage AC voltage introduced from the low-voltage power plug 92 is input, boosted by the insulation transformer 154, and rectified by the rectifying element 156. The DC voltage is divided by the voltage divider 155 to generate the G1, G2, and G3 voltages. As for the grid voltage, the G1, G2, and G3 voltages may be generated separately and independently. In this case, three sets of insulating transformer 154 and rectifying element 156 are required. The latter case is advantageous when it is necessary to adjust each grid voltage separately. A heater voltage for heating the cathode 40 is also generated here as part of the grid power supply 86. The heater voltage is generated from the low-voltage AC voltage using the insulation transformer 153.

  In the connection between the grid power supply 86 and the X-ray tube 10, all the voltages of the grid power supply 86 are supplied to the cathode 12 of the X-ray tube 10, so all the leads 157 from the grid power supply 86 are connected to the X-ray tube. Connected to the lead lead 60 of the stem 48 of the ten cathodes 12. Of the output terminals of the grid power supply 86, the lead wire 157a from the 0V terminal (cathode potential terminal) is the lead 60a of the cathode 40, the lead wire 157b from the G1 voltage terminal is the lead 60b of the G1 electrode 50, The lead wire 157c from the G2 voltage terminal is connected to the lead 60c of the G2 electrode 52, and the lead wire 157d from the G3 voltage terminal is connected to the lead 60d of the G3 electrode 54, respectively. Furthermore, lead wires 157e and 157f from a heater voltage terminal for heating the heater 41 are connected to the two leads 60e and 60f of the heater 41.

  Next, the stator power supply 88 will be described with reference to FIGS. A low voltage AC voltage is used for the stator power supply 88. The stator 100 is usually a single-phase capacitor-run type (some are three-phase type) and is composed of a main coil and a phase advance auxiliary coil. An AC voltage and an AC voltage obtained by advancing this with a capacitor are used. In the present embodiment, since the two-phase AC voltage is generated inside the case 82, the phase advance capacitor 160 is disposed on the stator power supply board 158, and the phase advance capacitor 160 is connected to the low voltage power plug 92. Low voltage AC voltage is supplied via When a low voltage AC voltage is input to the phase advance capacitor 160, a phase advance AC voltage is output, so that both the input voltage and the output voltage are connected to the coil terminal of the stator 100. The two-phase AC voltage can be generated outside the case 82. In that case, these voltages are introduced into the case 82 from the low voltage power plug 92 and connected to the coil terminal of the stator 100. The In this case, the stator power supply board 158 and the like are provided not in the case 92 but in the control device 80.

  In the above embodiment, the anode 14 of the X-ray tube 10 is a rotary anode type. However, the present invention is not limited to this, and the present invention can also be applied to a case where the anode of the X-ray tube is a fixed anode type. In this case, the stator 100 disposed on the outer periphery of the anode of the X-ray tube is unnecessary, and accordingly, the stator power supply 88 for driving the stator 100 is also unnecessary. Further, as the anode of the X-ray tube becomes a fixed anode shape, the shape of the X-ray tube can be made into a thin columnar shape and simplified, so that the X-ray generator as a whole is made compact.

1 is an overall structural diagram of a first embodiment of a microfocus X-ray tube according to the present invention. FIG. 2 is an enlarged view of a cathode part which is a main part of FIG. FIG. 2 is a diagram for explaining a configuration of an electron focusing system which is a main part of FIG. FIG. 2 is a diagram showing an example of calculation examples of potential distribution and electron trajectory in the electron focusing system of FIG. FIG. 5 is an enlarged view of a range from the cathode of FIG. 4 to the G2 electrode. The enlarged view of the cathode part of the 2nd Example of the microfocus X-ray tube which concerns on this invention. FIG. 6 is an enlarged view of a cathode portion of a third embodiment of the microfocus X-ray tube according to the present invention. 1 is a schematic configuration diagram of an embodiment of an X-ray apparatus according to the present invention. Sectional drawing when it sees from the direction of the X-ray radiation window of one Example of the X-ray generator which concerns on this invention. Sectional drawing which cut | disconnected the X-ray generator of FIG. 9 along the central axis of the anode and cathode of an X-ray tube. Sectional drawing which looked at the X-ray generator of FIG. 9 from the direction orthogonal to FIG. 9, FIG. The schematic block diagram of the In-line type | mold electron gun of an example of the electron gun for CTR.

Explanation of symbols

10 ... Microfocus X-ray tube (X-ray tube)
12 ... Cathode
14 ... Anode (rotary anode)
16 ... Envelope
18 ... Target
20 ... Rotor
26 ・ ・ ・ Fixing part
28 ... Focus (X-ray source)
30 ... Large diameter part
32 ... Anode insulation
34 ・ ・ ・ Cathode insulation
36 ... X-ray radiation window
40 ... Cathode
41 ... Heater
42 ... Electron focusing system
46 ... Electronic focusing insulator
48 ... Stem
50 ・ ・ ・ First grid electrode (G1 electrode)
50a, 52a, 54a ... opening
52 ・ ・ ・ Second grid electrode (G2 electrode)
54 ... Third grid electrode (G3 electrode)
55 ・ ・ ・ Blackening treatment
56 ... Heat radiation fin
60 ... Lead wire
62 ... Electronic focusing system support
64 ... electron beam
65 ... Cathode lens
67 ... Main lens
68 ... Crossover
70 ・ ・ ・ X-ray equipment
72 ・ ・ ・ X-ray generator
76 ... X-ray detector
78 ... Image forming apparatus
80 ... Control device
82 ・ ・ ・ Case
84 ・ ・ ・ High voltage power supply
86 ・ ・ ・ Grid power supply
88 ... Stator power supply
90 ・ ・ ・ Insulating oil
92 ... Low-voltage power plug
98 ... Anode support
100 ... stator
106 ... X-ray tube shield
118 ・ ・ ・ Anode insulation support
124 ... Bellows
140 ... Anode voltage generator
142 ... Cathode voltage generator
144 ... Transformer
146: Capacitor
147 ... resistance
148 ... High voltage power supply board
152 ... Grid power supply board
153,154 ... Insulation transformer
156 ... Rectifying element
158 ... Stator power supply board
160 ... Phase advance capacitor

Claims (7)

  The electron beam collides with the cathode that generates the electron beam, the electron focusing system including a plurality of grid electrodes arranged in the path of the electron beam to focus the electron beam into a narrow beam, and the X-ray An anode for generating the cathode, the cathode, the electron focusing system, and an envelope for sealing the anode in a vacuum-tight manner, and a plurality of grid electrodes of the electron focusing system each have an opening for allowing the electron beam to pass therethrough. A microfocus X-ray tube that forms an electron lens for focusing the electron beam by applying a potential to each grid electrode with reference to the cathode, and the electron focusing system includes at least three electron focusing systems. An opening diameter of a grid electrode (hereinafter referred to as a second grid electrode) that is composed of a grid electrode and is second closest to the cathode among the grid electrodes Grid electrode (hereinafter referred to as the first grid electrode) which is closest to the cathode microfocus X-ray tube, characterized in that it has less than the opening diameter of.   2. The microfocus X-ray tube according to claim 1, wherein a positive potential is applied to the first grid electrode with respect to the potential of the cathode.   3. The microfocus X-ray tube according to claim 1, wherein at least the first grid electrode and the second grid electrode among the plurality of grid electrodes of the electron focusing system are made of a refractory metal material having a melting point of 2000 ° C. or higher or an alloy thereof. A microfocus X-ray tube that is constructed. 4. The microfocus X-ray tube according to claim 1, wherein a heat dissipation process is performed on at least surfaces of the first grid electrode and the second grid electrode among the plurality of grid electrodes. .   4. The microfocus X-ray tube according to claim 1, wherein a radiation fin is attached to at least the first grid electrode and the second grid electrode among the plurality of grid electrodes.   A microfocus X-ray tube having a micro focus, a high voltage power supply unit for supplying a high voltage to the microfocus X-ray tube, and a grid for supplying a grid voltage to a plurality of grid electrodes of the cathode of the microfocus X-ray tube A power supply, an electrode insulation support that insulates and supports the electrodes of the microfocus X-ray tube, the microfocus X-ray tube, the high-voltage power supply, the grid power supply, and the electrode insulation support are included and supported. A housing, an insulating oil filled in the housing and dipping and insulating the microfocus X-ray tube and other components, and a bellows attached to the housing to buffer expansion and contraction of the insulating oil An X-ray generator including the microfocus X-ray tube according to claim 1 as the microfocus X-ray tube. X-ray generator for. Corresponding to the X-ray generator that generates X-rays, the X-ray detector that detects X-rays generated from the X-ray generator and transmitted through the subject, and the detected X-ray dose output from the X-ray detector In an X-ray apparatus having an image forming apparatus that inputs a signal to generate an X-ray image of the specimen, and a control device that controls the X-ray generation apparatus, the X-ray detection apparatus, and the image forming apparatus, An X-ray apparatus using the X-ray generator according to claim 6 as the X-ray generator.

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