JP4619176B2 - Microfocus X-ray tube - Google Patents

Description

  The present invention relates to a cathode structure of a microfocus X-ray tube, and more particularly to a technique for improving the focusing efficiency of an electron beam.

  X-ray equipment that measures the dose of X-rays that have passed through the subject, creates an image based on the measured value of the dose, and inspects or diagnoses the subject is a foreign product inspection for various products. It is widely applied to X-ray fluoroscopy equipment, X-ray imaging equipment, etc. 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 micro focus with a focus size of 10 μm has begun to spread.

  On the other hand, in order to obtain a high-quality X-ray image in X-ray fluoroscopy, the electron beam current that generates X-rays (hereinafter referred to as X-ray tube current) is required to be as large as possible. For example, an X-ray apparatus for inspecting foreign matters in foods using a low-sensitivity line sensor, or an image intensifier (I.I. 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 uses both 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.

In general, when an electron beam is focused on a minute beam like a microfocus X-ray tube, the grid electrode of the cathode is formed in an axially symmetric shape, whereby the cross-sectional shape of the electron beam becomes substantially circular. The configuration of the electrode system that focuses the electron beam like an optical lens system is called an electron optical system. As a configuration of a microfocus X-ray tube that forms a micro focus using this electron optical system, there are those disclosed in Patent Document 1, Patent Document 2, Patent Document 3, and the like.
Japanese Patent Laid-Open No. 2003-7236 JP2003-317996A JP 2005-38825 A

  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 hinders the 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. In a microfocus X-ray tube, since the lens action of an electric field or a magnetic field is usually used to focus an electron beam, the above-mentioned space charge effect increases the current of the X-ray tube and makes it a micro focus. This is contrary to the reduction of the electron beam diameter. That is, when the beam current (X-ray tube current) of the electron beam is small, the lens action of the electric field or magnetic field can overcome the repulsion between electrons due to the space charge effect, so that the electron beam is sufficiently focused. However, when the beam current of the electron beam increases, the repulsive action between electrons due to the space charge effect increases and the above lens action becomes difficult to function, and the electron beam cannot be sufficiently focused. There is a problem that it ends up.

  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, a plurality of grid electrodes as disclosed in Patent Document 2 and Patent Document 3 are used. There is a method of forming an electric field lens by using. A typical example of this method is shown in FIG. FIG. 13 is a schematic configuration diagram of an electron gun for a microfocus X-ray tube. This electron gun is hereinafter abbreviated as a microfocus electron gun. Hereinafter, the structure and operation of the microfocus electron gun will be briefly described with reference to FIG. In FIG. 13, the microfocus electron gun 200 includes a cathode 202, a first grid electrode (hereinafter referred to as G1 electrode) 204, a second grid electrode (hereinafter referred to as G2 electrode) 206, and a third grid electrode (hereinafter referred to as G3 electrode). 208). The electron beam 210 emitted from the electron emission surface 202a of the cathode 202 is focused by an electron lens formed by the cathode 202 and the G1 electrode 204, the G2 electrode 206, and the G3 electrode 208, and collides with the anode target 212. And generate X-rays.

  The cathode 202 of the microfocus electron gun 200 is a hot cathode such as an oxide cathode or an impregnated cathode, and is used in a space charge limited region at a high temperature. A positive potential that is several tens of volts higher than the cathode potential is applied to the G1 electrode 204, and a positive potential that is several hundred to several thousand volts higher than the cathode potential is applied to the G2 electrode 206. These voltage values are determined in accordance with a desired beam current value and a focal dimension value. Electrons emitted from the electron emission surface 202a of the cathode 202 are extracted as an electron beam 210 by the positive potential voltage of the G1 electrode 204. The electron beam 210 passing through the opening (electron beam passage hole) 204a of the G1 electrode 204 while being accelerated is further accelerated by the G2 electrode 206. Here, an electron lens (cathode lens) that focuses the electron beam 210 by the potential difference between the G2 electrode 206 and the G1 electrode 204 is formed. The electron beam 210 is focused by the lens action of the cathode lens. By this focusing action, the electron beam 210 forms a virtual focus called a crossover 214 in the vicinity of the opening (electron beam passage hole) 206a of the G2 electrode 206.

  A voltage having a positive potential of about several thousand volts with respect to the cathode potential is applied to the G3 electrode 208. The G3 electrode 208 forms an electron lens (main lens) that projects the image point of the crossover 214 onto the target 212 in cooperation with other electrodes by this voltage. The electron beam 210 emitted from the crossover 214 is focused by the main lens formed by the G3 electrode 208 to form an image point 216 of a minute spot on the target 212. That is, the electron beam 210 that has passed through the crossover 214 is incident on the G3 electrode 208 while diverging, and is focused by the main lens formed in the vicinity thereof in the G3 electrode 208 and is focused after passing through the G3 electrode 208. The vehicle travels to the target 212 and forms an image point 216 on the target 212. This image point 216 becomes a focal point.

  Next, an example of the structure of the electron focusing system of a conventional microfocus electron gun will be described. FIG. 14 is a diagram schematically showing an electrode shape and an arrangement of an example of an electron focusing system of a conventional microfocus electron gun disclosed in Patent Document 3. In the configuration of FIG. 14, the diameter of the opening 206a of the G2 electrode 206 constituting the microfocus electron gun 200 is made smaller than the diameter of the opening 204a of the G1 electrode 204. Out of the electron beam 210 emitted from the electron emission surface 202a of the cathode 202, electrons outside the central axis 218 first collide with the vicinity of the opening 204a of the G1 electrode 204 and are then removed, and then the G2 electrode 206. It collides with the vicinity of the opening 206a and is removed. In this way, the openings 204a and 206a of the G1 electrode 204 and the G2 electrode 206 serve as a diaphragm for the electron beam 210. For this reason, most of the electron beam 210 that has passed through the opening 206a of the G2 electrode 206 is composed of electrons that travel on an orbit close to the central axis 218. As a result, in the subsequent focusing by the electron lens (main lens) formed by the G3 electrode 208, almost no spherical aberration is focused, so that a very small focal point 216 can be formed on the anode target 212. it can.

  As described above, a microfocus X-ray tube and an X-ray apparatus using the microfocus X-ray tube can obtain a large X-ray tube current together with a micro focus for the purpose of obtaining a high-quality fluoroscopic image and shortening an imaging time. An electron focusing system is required. In the microfocus electron gun 200, the size of the focal point 216 on the target 212 is the diameter of the crossover 214, the divergence angle of the electron beam 210 (the spread angle when the electron beam 210 travels from the crossover 214 toward the G3 electrode 208) ), A function such as a term due to the space charge effect. By reducing the diameter of the crossover 214 formed in the vicinity of the opening 206a of the G2 electrode 206, the size (diameter) of the focal point 216 on the target 212 can be reduced. In the microfocus electron gun 200, the diameter of the aperture 206a of the G2 electrode 206 is also reduced to serve as a diaphragm for the electron beam 210, and the electron beam 210 in the orbit far from the central axis 218 is removed to cross-over. The size (diameter) of 214 is miniaturized. Therefore, many high-energy electrons collide near the opening 206a of the G2 electrode 206, and the colliding part becomes high temperature, the change of the grid electrode interval occurs due to thermal expansion, worsening the focusing of the electron beam, and discharging. It can also be a cause. These phenomena become more prominent as the current amount of the electron beam 210 (X-ray tube current) increases.

  Further, in the above-described conventional microfocus electron gun 200, a means for preventing the reflected electrons from the anode target 212 is not sufficiently provided. The microfocus X-ray tube is used at an X-ray tube voltage of about 40 kV to 150 kV. In use, it is known that some electrons of the electron beam 210 that have collided with the focal point 216 of the target 212 are reflected from the focal point 216. This reflected electron has the same energy as that accelerated by the X-ray tube voltage, and thus reaches the periphery of the microfocus electron gun 200. In the microfocus electron gun 200, grid voltages having different potentials are applied to a plurality of grid electrodes, so that the grid electrodes are insulated from each other, and the plurality of grid electrodes are supported by an insulator 220. When reflected electrons are incident on the insulator 220, charges are accumulated in the insulator 220 and are charged. When the charge amount of the insulator 220 increases, a discharge between the insulator 220 and surrounding electrodes or a discharge between grid electrodes occurs. Furthermore, the electric potential of the grid electrode deviates from the applied voltage value due to the charging of the insulator 220, which adversely affects the focusing characteristics of the electron beam in the microfocus electron gun.

  In view of the above, the present invention improves the focusing efficiency of the electron beam in the electron focusing system, prevents charging of the insulator by the reflected electrons, and uses a microfocus X-ray tube having a micro focus and a large current and the same. An object is to provide an X-ray apparatus.

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 arranged in an electron beam path for focusing the electron beam into a thin linear beam. A cathode having an electron focusing system, an anode having a target that generates X-rays when the electron beam collides, an envelope that insulates and supports the cathode and the anode, and is sealed in a vacuum-tight manner, The plurality of grid electrodes of the electron focusing system of the cathode each have an opening for allowing the electron beam to pass therethrough, and an electron lens for focusing the electron beam by applying a potential based on the cathode to each grid electrode. In the microfocus X-ray tube having a grid electrode insulation support portion for insulatingly supporting the grid electrode, the electron focusing system is composed of at least three grid electrodes, Grid electrode (hereinafter, G1 referred electrode) that is closest to the cathode of the grid electrode inner circumferential surface of the opening of the smallest diameter thereof on the cathode side, have highest magnitude at the target side. Further, for example, in its middle increases as going to the target side, or that it is formed so as not to at least reduce.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G1 electrode is formed by one tapered surface, and the diameter thereof is the smallest on the cathode side.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G1 electrode is formed by connecting two or more tapered surfaces, and the diameter is the smallest on the cathode side.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G1 electrode is formed as a curved surface, and its diameter is the smallest on the cathode side.

  In the microfocus X-ray tube of the present invention, the diameter of the grid electrode (hereinafter referred to as the G2 electrode) that is second closest to the cathode among the grid electrodes is 1/2 of the minimum diameter of the G1 electrode. 2 or more.

In the microfocus X-ray tube of the present invention, the inner peripheral surface of the grid electrode (hereinafter referred to as G3 electrode) that is the third closest to the cathode among the grid electrodes has the largest diameter on the cathode side, smallest target side, and decreases as in the middle go to the target or that have been formed so as not to at least increase.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G3 electrode has a diameter that is the smallest on the cathode side, the largest on the target side, and increases in the middle toward the target side, or It is formed so as not to decrease at least.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G3 electrode is formed by a single tapered surface.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G3 electrode is formed by connecting two or more tapered surfaces.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G3 electrode is formed by connecting one or more tapered surfaces and one or more cylindrical surfaces.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G3 electrode is formed as a curved surface.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G3 electrode is formed by connecting one or more curved surfaces and one or more tapered surfaces.

Further, the microfocus X-ray tube of the present invention has a substantially cylindrical shape with a bottom and is provided with a cathode cover made of a metal material, the cathode cover covers the electron focusing system and the grid electrode insulating support, and the bottomed cylinder. It is disposed so as the bottom surface of the faces to the target, that has an opening is provided for passing the electron beam to the bottom surface of the bottomed cylinder.

  In the microfocus X-ray tube of the present invention, the opening of the cathode cover is coaxial with the central axis of the electron focusing system, and the size of the opening is a focal point formed by the collision of the electron beam on the target. The size is such that the insulator of the grid electrode insulating support portion can be hidden from (X-ray source) so that it cannot be seen directly.

  In the microfocus X-ray tube of the present invention, the cathode cover is grounded.

  In the microfocus X-ray tube of the present invention, a ground potential is applied to the cathode of the cathode.

  In the microfocus X-ray tube of the present invention, the anode is a rotating anode.

  The X-ray generator of the present invention includes a microfocus X-ray tube of the present invention, a high-voltage power supply unit that supplies a high voltage to the X-ray tube, and a plurality of grid electrodes that are cathodes of the X-ray tube. A grid power supply for supplying a grid voltage, an X-ray tube support for supporting an electrode and / or envelope of the X-ray tube, the X-ray tube, the high-voltage power supply, the grid power supply, and the X A container that contains and supports the tube support portion, an insulating oil that is filled in the container and insulates and insulates the X-ray tube and other components, and for buffering expansion and contraction of the insulating oil And a bellows attached to the container.

  The X-ray apparatus of the present invention includes the X-ray generation apparatus of the present invention, an X-ray detection apparatus that detects X-rays emitted from the X-ray generation apparatus and transmitted through the subject, and the X-ray detection apparatus. An image forming apparatus for generating an X-ray image of a subject by inputting a signal corresponding to a detected X-ray dose, and a control apparatus for controlling the X-ray generation apparatus, the X-ray detection apparatus, and the image forming apparatus. Have.

  The microfocus X-ray tube of the present invention is such that the inner peripheral surface of the opening of the G1 electrode among a plurality of grid electrodes constituting the electron focusing system of the cathode expands from the cathode side to the target side. Therefore, the potential distribution in the vicinity of the opening of the G1 electrode spreads outward from the conventional product, and with respect to an electron beam traveling on the outer orbit away from the central axis of the electron focusing system (hereinafter referred to as the outer electron beam). The crossover formed by the outer electron beam is formed at a position farther from the cathode than the conventional product. In contrast, an electron beam traveling on the inner orbit near the central axis of the electron focusing system (hereinafter referred to as the inner electron beam) is hardly affected by the above-described change in potential distribution, and the inner electron beam. The crossover by is formed at almost the same position as the conventional product. In the conventional product, there was a slight difference in position between the crossover by the outer electron beam and the crossover by the inner electron beam, and the former was formed at a position closer to the cathode than the latter, so the diameter of the crossover as a whole Was a big one. In the present invention, the position of the crossover of the outer electron beam and the position of the crossover of the inner electron beam can be substantially matched by improving the electron focusing system, and the diameter of the entire crossover can be made smaller than the conventional product. Became. By reducing the diameter of the crossover, the focal point on the target can be reduced.

  Further, in the microfocus X-ray tube of the present invention, the inner peripheral surface of the G1 electrode is formed by a single tapered surface, and the diameter increases toward the target side, so in the vicinity of the opening of the G1 electrode. The potential distribution spreads outside the conventional product. As a result, the trajectory of the outer electron beam expands, the crossover is formed at a position farther from the cathode, and approaches the crossover of the inner electron beam, so that the diameter of the entire crossover can be reduced. . In addition, by changing the taper angle of the taper surface, the potential distribution in the vicinity can be changed, so it is possible to easily correct the outer electron beam trajectory in the vicinity of the G1 electrode by simply changing the structure of the G1 electrode. it can.

  Further, in the microfocus X-ray tube of the present invention, since the inner peripheral surface of the opening of the G1 electrode is formed by connecting two or more tapered surfaces, the taper surface of each tapered surface can be changed or the tapered surface can be changed. The potential distribution in the vicinity of the opening of the G1 electrode can be changed in a considerably wide range by changing the length of.

  In addition, in the microfocus X-ray tube of the present invention, the inner peripheral surface of the G1 electrode opening is formed with a curved surface whose diameter increases as it goes to the target side. The potential distribution in the vicinity spreads outward from the conventional product, and the outer electron beam trajectory can be widened to reduce the diameter of the entire crossover.

  In the microfocus X-ray tube of the present invention, the diameter of the opening of the G2 electrode is set to 1/2 or more of the minimum diameter of the G1 electrode and is approximately the same as that of the G1 electrode. The electron beam that has passed through the aperture hardly collides with the G2 electrode, and a large electron beam current (X-ray tube current) is secured. In addition, since the electron beam no longer collides with the G2 electrode, the vicinity of the opening of the G2 electrode is not overheated, so there is no discharge phenomenon caused by it, and the X-ray tube can maintain a stable operation. .

In the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G3 electrode is made narrower as the diameter goes from the cathode side to the target side. Crossover formed near the target by the outer electron beam (hereinafter referred to as the target side). Crossover) is formed at a position closer to the cathode than the conventional product. On the other hand, the inner electron beam is hardly affected by the change in potential distribution, and the target side crossover by the inner electron beam is formed at substantially the same position as the conventional product. The outer electron beam has a crossover on the side close to the cathode (hereinafter referred to as the “cathode side crossover”) at a position away from the cathode by correcting the potential distribution by the G1 electrode. Although it is formed at a position farther from the cathode, the electron trajectory is corrected by correcting the potential distribution using the G3 electrode as described above, and the appropriate position, that is, almost the same position as the target side crossover by the inner electron beam. are formed on, Ru obtained small diameter target side crossover overall electron beam.

  Further, in the microfocus X-ray tube of the present invention, since the diameter of the inner peripheral surface of the G3 electrode opening becomes wider as it goes from the cathode side to the target side, the potential distribution in the vicinity of the G3 electrode opening is conventional. It will spread outward from the product, and it will act on the outside electron beam so that it will go further outward. The target side crossover of the outside electron beam will be farther from the cathode than the conventional product. It is formed. For this reason, the electron focusing system equipped with the G3 electrode having such a configuration is arranged so that the outer side of the cathode crossover of the outer electron beam is formed closer to the cathode by correcting the potential distribution by the G1 electrode. It is suitable for correcting electron trajectories of electron beams.

  In the microfocus X-ray tube of the present invention, the inner peripheral surface of the G3 electrode opening is formed by a single tapered surface, so the diameter of the inner peripheral surface can be increased by changing the taper angle of the tapered surface. Can be reduced or reduced. In addition, by changing the taper angle of the tapered surface, various types of potential distributions can be easily created near the opening of the G3 electrode.

  Further, in the microfocus X-ray tube of the present invention, the inner peripheral surface of the G3 electrode opening is formed by connecting two or more tapered surfaces, so that the taper angle of each tapered surface can be changed or the tapered surface can be changed. The potential distribution in the vicinity of the opening of the G3 electrode can be changed in a considerably wide range by changing the length of.

  Further, in the microfocus X-ray tube of the present invention, the inner peripheral surface of the G3 electrode opening is formed by connecting one or more tapered surfaces and one or more cylindrical surfaces. By changing the angle or changing the length of each surface, the potential distribution near the opening of the G3 electrode can be changed in a fairly wide range.

  Further, in the microfocus X-ray tube of the present invention, since the inner peripheral surface of the opening of the G3 electrode is formed with a curved surface, the diameter of the inner peripheral surface can be changed by changing the shape of the curved surface as in the case of the tapered surface. Can be increased or decreased. In addition, by changing the shape of the curved surface, various types of potential distributions can be easily created near the opening of the G3 electrode.

  Further, in the microfocus X-ray tube of the present invention, the inner peripheral surface of the opening of the G3 electrode is formed by connecting one or more curved surfaces and one or more tapered surfaces. By changing the taper angle of the surface or changing the length of each surface, the potential distribution in the vicinity of the opening of the G3 electrode can be changed in a considerably wide range.

  Further, in the microfocus X-ray tube of the present invention, the electron focusing system and the grid electrode insulating support portion are covered with a cathode cover made of a metal material with a bottomed cylindrical shape. The collision with the conductive cathode cover and the direct collision with the electron focusing system, the grid electrode insulating support, and the like are reduced. As a result, it is possible to prevent the reflected electrons from being charged on the insulator of the grid electrode insulating support part and other insulators, and causing an electrical failure to the electron focusing system due to the potential due to the charging.

  Further, in the microfocus X-ray tube of the present invention, the size of the opening of the cathode cover is such that the insulator of the grid electrode insulating support portion can be hidden from the focal point on the target so that it cannot be directly viewed. Since the reflected electrons from the focal point do not directly collide with the insulator, the reflected electrons are not charged to the insulator to cause a discharge or change in the potential of the grid electrode. The operation of the system is stable.

  In the microfocus X-ray tube of the present invention, since the cathode cover is grounded, even if reflected electrons from the target focus collide with the cathode cover, those reflected electrons are not charged on the cathode cover, Since the electric current flows to the ground, the electric disturbance due to the charged charged electrons is removed.

  In the microfocus X-ray tube of the present invention, since the ground potential is applied to the cathode of the cathode, the grid voltage applied to the grid electrode of the electron focusing system of the cathode is also lower than the X-ray tube voltage, The entire cathode of the X-ray tube and the insulation of the grid voltage generation circuit do not require special consideration. As a result, the electrical control of the cathode is simplified.

  Moreover, in the microfocus X-ray tube of the present invention, since the anode is a rotating anode, it is possible to apply a large electric load regardless of the micro focus, and by emitting a large dose of X-rays, A high-definition X-ray image can be obtained.

  In addition, since the X-ray generator of the present invention includes the microfocus X-ray tube of the present invention, taking advantage of the microfocus of the X-ray tube and the large X-ray tube current, high-definition X-rays An image can be obtained, and stable operation can be maintained by preventing charging of the insulator by reflected electrons from the focal point of the X-ray tube.

  Further, in the X-ray apparatus of the present invention, the X-ray generator which is a component of the X-ray apparatus includes the microfocus X-ray tube of the present invention. Taking advantage of this, high-definition X-ray images can be obtained and stable operation can be maintained for a long time.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the structure and operation of an embodiment of a microfocus X-ray tube according to the present invention will be described with reference to FIGS. FIG. 1 is an overall structural diagram of an 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. 1, and FIG. 3 is an electron focusing system which is a main part of FIG. 4 is a schematic configuration diagram of an electron focusing system of a conventional microfocus X-ray tube, and FIG. 5 is a calculation example of electron trajectories near the G1 electrode and G2 electrode of the electron focusing system of this embodiment. Figures 6 and 6 show calculation examples of electron trajectories near the G1 and G2 electrodes in the electron focusing system of the conventional microfocus X-ray tube. Fig. 7 shows the electrons in the electron focusing system of the conventional microfocus X-ray tube. FIG. 8 is a diagram for explaining the focusing state of the line, FIG. 8 is a diagram for explaining the focusing state of the electron beam in the electron focusing system of this embodiment, and FIG. 9 is formed on the target of this embodiment and the conventional product. It is the figure which showed the comparison of the current density distribution of a focus.

  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 that can obtain a microfocus (micro focus) and can be operated with a large X-ray tube current. The configuration and operation of the cathode 12 will be described in detail later with reference to FIGS. Prior to that, the entire structure excluding the cathode 12 will be described with reference to FIG.

  In FIG. 1, the anode 14 adopts a rotating anode type structure in order to increase the allowable load as an X-ray tube. The anode (hereinafter also referred to as a rotating anode) 14 is not limited to this and may be a fixed anode type. The rotating anode 14 is a disk-shaped target 18 that is an X-ray generation source, a rotor 20 that supports the target 18, a rotating shaft 22 that supports the rotor 20, a bearing 24 that rotatably supports the rotating shaft 22, and a bearing. It is composed of a fixing portion 26 that supports 24 and the like. The rotary anode 14 as a whole has almost the same structure as that of a general-purpose medical rotary anode X-ray tube. The target 18 has an umbrella shape and a disk shape, and is made of a metal material having a high atomic number and a high melting point such as tungsten or an alloy thereof. A thin beam-like electron beam 50 from the cathode 12 collides with the inclined surface of the target 18 to form a focal point 28.

  Next, the envelope 16 surrounds the target 18 of the rotating anode 14 and the tip of the cathode 12 and is coupled to a large diameter portion 30 that is maintained at a ground (ground) potential and a fixed portion 26 of the rotating anode 14. The anode insulating part 32 that insulates and supports the cathode 12 and the cathode insulating part 34 that insulates and supports the cathode 12 are constituted. The large-diameter portion 30 is a combination of a generally disc-shaped disc portion 36 and a large-diameter and thick-cylindrical cylindrical portion 38. The disc portion 36 and the cylindrical portion 38 are made of copper or stainless steel. It consists of metal materials such as. An X-ray emission window 40 is attached to an opening 36a provided in a portion of the disc portion 36 close to the focal point 28 on the target 18 of the rotating anode 14. The shape of the opening 36a of the disc portion 36 is processed according to the shape of the X-ray radiation window 40, and there are a circular shape and a rectangular shape, but it is usually a circular shape. The X-ray radiation window 40 is made of beryllium or the like having good X-ray transparency, and is coupled to the opening 36a of the disc portion 36 by welding or brazing via a window frame or the like. The anode insulating portion 32 includes a cylindrical portion 42 that is slightly thicker than the outer diameter of the rotor 20 of the rotating anode 14, a flare portion 44 that is widened in a cone shape so as to be coupled to the cylindrical portion 38 of the large diameter portion 30, and the rotating anode 14 An anode connection part 46 for coupling with the fixing part 26 is formed. The anode insulating part 32 is mostly made of an insulating material such as heat-resistant glass or ceramic, and the connecting part between the cylindrical part 38 of the large-diameter part 30 and the fixed part 26 of the rotating anode 14 at both ends is familiar with the insulating material. Metal materials are used. A cathode insulating portion 34 is coupled to the side surface of the cylindrical portion 38 of the large diameter portion 30 in a direction substantially perpendicular to the central axis 48 of the rotating anode 14. The cathode insulating portion 34 has a cylindrical shape with a thin outer diameter. One end of the cathode insulating portion 34 is coupled to the side surface of the cylindrical portion 38 of the large diameter portion 30 and the other end is coupled to the stem 70 of the cathode 12. Most of the cathode insulating portion 34 is made of an insulating material such as heat-resistant glass or ceramic.

  In FIG. 1, the central axis of the cylindrical portion 38 of the large-diameter portion 30 of the envelope 16 and the central axis 48 of the rotating anode 14 substantially coincide with each other, and the target 18 of the rotating anode 14 is positioned approximately at the center of the large-diameter portion 30. It will be. The anode insulating portion 32 is coupled to the side surface of the cylindrical portion 38 of the large diameter portion 30 so that the central axis of the cathode 12 substantially coincides with the focal point 28 on the target 18 of the rotating anode 14. As a result, the electron beam 50 from the cathode 12 collides with the focal point 28 on the target 18, and the X-ray 52 generated at the focal point 28 is externally transmitted through the X-ray emission window 40 attached to the disk portion 36 of the large-diameter portion 30. (Upward in the figure).

  Next, the configuration and operation of the cathode 12, which is the 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. In FIG. 2, FIG. 2 (a) is an overall structural view of the cathode, and FIG. 2 (b) is an enlarged view of the electron focusing system of the cathode. In FIG. 2, the cathode 12 includes a cathode 54 for generating an electron beam 50, an electron focusing system 56 for focusing the electron beam 50, a cathode support 58 for supporting the cathode 54, and three pieces constituting the electron focusing system 56. An electron focusing system insulator 66 that insulates and supports the grid electrodes 60, 62, and 64, a cathode cover 68 that covers the electron focusing system insulator 66, a stem 70 that supports the cathode 54, the electron focusing system 56, and the like. .

  The cathode 54 is an oxide or impregnated cathode and includes a heater for heating. The cathode 54 operates at a high temperature of 1000 K or more by heating the heater and emits thermoelectrons. The cathode 54 has a cylindrical shape with a bottom. A heater is insulated inside the cylinder, and thermal electrons are radiated from an outer surface (hereinafter referred to as an electron emission surface) 54a of the bottom of the cylinder. The cathode 54 is supported by a cathode support 58 and further supported by an electron focusing system insulator 66 via an electron focusing system 56. In this embodiment, the electron focusing system 56 includes three grid electrodes 60, 62, and 64. That is, a first grid electrode (hereinafter abbreviated as G1 electrode) 60 closest to the cathode 54, a second grid electrode (hereinafter abbreviated as G2 electrode) 62 closest to the cathode 54, and a third grid electrode closest to the third 64 (hereinafter abbreviated as G3 electrode). The number of grid electrodes constituting the electron focusing system 56 is not limited to three, and may be four or more. The three grid electrodes 60, 62, 64 each have openings 60a, 62a, 64a through which the electron beam 50 passes in the center, and between the cathode 54 and the target 18 of the rotating anode 14, G1 from the cathode 54 side. The electrode 60, the G2 electrode 62, and the G3 electrode 64 are arranged coaxially at appropriate intervals.

  In the electron focusing system 56, the G1 electrode 60 and the G2 electrode 62 are plate-like bodies, and openings 60a and 62a with small diameters are provided in the center thereof, and the whole is shaped like a cup in consideration of mounting and the like. Is formed. The G3 electrode 64 is provided with a large opening 64a in the center, and has a shape close to a cylindrical shape as a whole. In this embodiment, the inner peripheral surface of the opening 60a of the G1 electrode 60 is processed into a surface 74 that is tapered with respect to the central axis 72 of the electron focusing system 56, and the inner diameter thereof is the smallest on the cathode 54 side. . The tapered surface 74 improves the focusing efficiency of the cathode lens formed between the G1 electrode 60 and the G2 electrode 62, as will be described later. The taper angle of the taper surface 74 is about 27 ° in the illustrated example, but this taper angle can be appropriately changed according to the configuration of the electron focusing system. The inner peripheral surface of the opening 62a of the G2 electrode 62 is a cylindrical surface parallel to the central axis 72 of the electron focusing system 56 as in the conventional product. The inner peripheral surface of the opening 64a of the G3 electrode 64 is also processed into a surface 76 that is tapered with respect to the central axis 72 of the electron focusing system 56, and the inner diameter thereof is the largest on the cathode 54 side. The taper surface 76 is approximately 15 ° in the illustrated example, but this taper angle can also be appropriately changed according to the configuration of the electron focusing system. Further, the inner diameter of the opening 62a of the G2 electrode 62 is set to 1/2 or more of the minimum inner diameter of the opening 60a of the G1 electrode 60. This is to prevent electrons traveling in a position away from the central axis 72 of the electron beam 50 from colliding with the vicinity of the opening 62a of the G2 electrode 62, and the inner diameter of the opening 62a of the G2 electrode 62 is usually the G1 electrode. The size is set to be approximately the same as the minimum inner diameter of the 60 openings 60a. The shapes and dimensions of the openings 60a, 62a and 64a of the G1 electrode 60, G2 electrode 62 and G3 electrode 64 and the distance between them are related to the desired focal dimensions and the voltage applied to the respective grid electrodes 60, 62 and 64. To be determined. The voltage applied to the grid electrode (hereinafter referred to as grid voltage) is specified with reference to the potential applied to the cathode 54 (hereinafter referred to as cathode potential or cathode potential). In addition, although a heat-resistant metal material is used as the material of the grid electrodes 60, 62, 64, in the present invention, the high energy electron beam incident on the grid electrodes 60, 62, 64 is less than that of the conventional product. Stainless steel and the like can be used, and it is not necessary to use a refractory metal material such as molybdenum as in the conventional product. This can be expected to reduce material costs and processing costs.

  The three grid electrodes 60, 62, 64 of the electron focusing system 56 are supported by an electron focusing system insulator 66 composed of two rod-shaped insulators 66a in order to maintain insulation between the grid electrodes. The rod-like insulator 66a is made of heat-resistant glass or the like, and the insulator 66a and the grid electrodes 60, 62, 64 are bonded to the mounting bracket 66b attached to the outer periphery of each grid electrode by welding or the like. This is done by welding 66a. In some cases, ceramic may be used as the insulator 66a in addition to the heat-resistant glass. In this case, the insulator 66a and the mounting bracket 66b are coupled by brazing or the like. The electron focusing insulator 66 is supported on the stem 70 via a ring-shaped support 78. The stem 70 includes a support plate 70a made of a disk-shaped insulator, a plurality of lead wires 80 penetrating the support plate 70a, a ring-shaped connecting tube 70b coupled to the outer periphery of the support plate 70a, and a support body. A cylindrical electron focusing system support portion 70c for supporting 78 is formed. The support plate 70a is made of a heat-resistant insulator such as ceramic, and the support plate 70a, the lead wire 80, the connection tube 70b, and the electron focusing system support portion 70c are coupled by brazing. The lead wire 80 is for supplying a heater heating voltage, a cathode potential, a grid voltage, and the like. The connection tube 70b is made of a metal material that is compatible with the material of the support plate 70a, and is connected to the cylindrical connection fitting 34a provided at the end of the cathode insulating portion 34 of the envelope 16 by welding or the like. By this coupling, the entire cathode 12 is supported by the envelope 16. In addition, the distance between the target 18 of the rotating anode 14 and the tip of the cathode 12 is adjusted during the coupling. The electron focusing system support part 70c is a thin-walled cylinder and is disposed so as to surround the lead wire 80. One end of the electron focusing system support part 70c is coupled to the support plate 70a, and the other end is coupled to the support 78 supporting the electron focusing system insulator 66. ing. A plurality of openings are provided in the side surface of the electron focusing system support 70c, and the lead wire 80 and each electrode of the cathode 12 are electrically connected using the openings.

  In order to prevent the reflected electrons from the target 18 from reaching the electron focusing system 56 of the cathode 12 and other parts between the electron focusing system 56 and the target 18 of the rotating anode 14, a heat resistant metal such as stainless steel is used. A cathode cover 68 made of material is arranged. The cathode cover 68 has a cylindrical shape with a bottom, and the cylindrical portion 68 is directly connected to the large diameter portion 30 of the envelope 16. The cathode cover 68 and the large-diameter portion 30 may be directly connected, or may be connected via a medium made of a metal material or the like therebetween. A surface (bottom surface) 68b of the cathode cover 68 facing the target 18 is provided with an opening 84 through which the electron beam 50 passes. The cathode cover 68 covers the electron focusing system 56 and the electron focusing system insulator 66. Is arranged. The diameter of the opening 84 of the cathode cover 68 is larger than the diameter of the opening 64a of the G3 electrode 64 of the electron focusing system 56, but the two insulators of the electron focusing system insulator 66 that insulately support the grid electrodes 60, 62, 64 The interval is smaller than 66a. That is, the size of the opening 84 of the cathode cover 68 is set such that the insulator 66a is hidden from the focal point 28 on the target 18 so that the insulator 66a cannot be directly viewed. This prevents the reflected electrons from the focal point 28 of the target 18 from reaching the insulator 66a. The cathode cover 68 is disposed so that its opening 84 is coaxial with the central axis 72 of the electron focusing system 56 and close to the opening 64a of the G3 electrode 64. Further, the cathode cover 68 is connected to the large-diameter portion 30 of the envelope 16, so that it has the same potential as the large-diameter portion 30 and is held at the ground potential. In this way, the electron focusing system 56 of the cathode 12 and its peripheral portion are covered with the cathode cover 68 of the ground potential, and the opening 84 through which the electron beam 50 on the bottom surface 68b facing the target 18 passes has a minimum area. By making the hole, the reflected electrons from the focal point 28 of the target 18 are directed to the cathode cover 68 and the large-diameter portion 30 and then flow to the ground, so that the insulator 66a of the electron focusing insulator 66 is charged. Can be prevented.

  Next, the electron beam focusing state in the electron focusing system of the X-ray tube of the present embodiment will be described using FIGS. 3 to 9 in comparison with the conventional electron focusing system. 3 and 4 show the schematic configuration of the electron focusing system of this embodiment and the conventional product and the schematic shape of the electron beam. 5 and 6 show calculation examples of the electron trajectory in the vicinity of the G1 electrode and the G2 electrode in the electron focusing system of this embodiment and the conventional product. 3 and 4, when comparing the electron focusing system 56 of the present embodiment and the conventional electron focusing system 86, the shape of the inner peripheral surface of the opening of the G1 electrode and the G3 electrode and the diameter of the opening of the G2 electrode are different. . That is, while the inner peripheral surfaces of the openings 88a and 92a of the conventional G1 electrode 88 and G3 electrode 92 are parallel to the central axis 72 of the electron focusing system, the G1 electrode 60 and G3 electrode 64 of the present embodiment The inner peripheral surfaces of the openings 60a and 64a are tapered surfaces 74 and 76, and the tapered surface 74 of the G1 electrode 60 has a taper angle of about 27 °, and the diameter of the inner peripheral surface increases toward the target 18 side. The taper surface 76 of the G3 electrode 64 has a taper angle of about 15 °, and the diameter of the inner peripheral surface becomes smaller toward the target 18 side. Further, the diameter of the opening 62a of the G2 electrode 62 of the present embodiment is much larger than the diameter of the opening 90a of the conventional G2 electrode 90, and is almost the same as the minimum diameter of the opening 60a of the G1 electrode 60. The grid voltage applied to each grid electrode of the electron focusing system is almost the same voltage applied to both X-ray tubes, the positive potential of several tens of volts is applied to the G1 electrodes 60 and 88, and the G2 electrodes 62 and 90 are applied to the G2 electrodes 62 and 90. A positive potential of several hundred to several thousand V is applied, and a positive potential of several thousand V is applied to the G3 electrodes 64 and 92, respectively. These grid voltages are all based on the cathode potential. An X-ray tube voltage is applied between the cathode (cathode) and the anode (target) of the X-ray tube. As a result, in the focusing of the electron beam 50, the crossover 94 formed in the vicinity of the G2 electrode (cathode side crossover) is located farther from the G2 electrode than the conventional crossover 96. In the present embodiment, the size of the focal point 28 on the target 18 is slightly smaller than that of the conventional product. Further, as can be seen by comparing FIG. 5 and FIG. 6, in the G2 electrode 62 of the present embodiment, a part of the electron beam 50 collides in the vicinity of the opening 90a of the conventional G2 electrode 90. There is no danger of the electron beam 50 colliding near the opening 62a.

  Next, the focusing state of the electron beam in the electron focusing system of the conventional product and the present embodiment will be described with reference to FIGS. For the sake of simplicity in both figures, the electron beam 50 is typically selected from the inner electron beam traveling near the central axis 72 of the electron focusing system and the outer electron beam traveling away from the central axis 72 as representatives. We also approximated the travel of the above by a straight line and explained the focusing state of each electron beam. In FIG. 7, the inner peripheral surfaces of the openings 88a, 90a, and 92a of the G1 electrode 88, G2 electrode 90, and G3 electrode 92 of the conventional electron focusing system 86 are parallel to the central axis 72 as described above, and the opening of the G2 electrode 90 The diameter of 90a is smaller. In the electron focusing system 86 having such a configuration, the inner electron beam 98 is located at a position slightly closer to the G3 electrode 92 side from the opening 90a of the G2 electrode 90 (hereinafter referred to as an inner beam cathode side crossover) 100. Further, a target side crossover (hereinafter referred to as an inner beam target side crossover) 101 is formed on the target 18. On the other hand, the outer electron beam 102 forms a cathode side crossover (hereinafter referred to as an outer beam cathode side crossover) 104 in the opening 90a of the G2 electrode 90, and further, a target side crossover slightly before the target 18. (Hereinafter referred to as an outer beam target side crossover) 105 is formed. As a result, a slightly larger micro focus is formed on the target 18 in the conventional electron focusing system 86. Further, in the conventional electron focusing system 86, since the diameter of the opening 90a of the G2 electrode 90 is small, as shown in FIG. 6, a part of the outer electron beam 102, the outer one is the G2 electrode 90. It collided near the opening 90a, causing the temperature of the G2 electrode 90 to rise.

  In FIG. 8, in the electron focusing system 56 of the present embodiment, tapered surfaces 74 and 76 are provided on the inner peripheral surfaces of the openings 60a and 64a of the G1 electrode 60 and the G3 electrode 64, and the diameter of the opening 62a of the G2 electrode 62 is set to the G1 electrode. It is about the same as the minimum diameter of 60 openings 60a. In the electron focusing system 56 having such a configuration, as shown in FIG. 5, the potential distribution between the G1 electrode 60 and the G2 electrode 62 is improved, and the electron beam 50 by the cathode lens formed in this part by both electrodes is provided. Focusing is gentle, especially focusing on the outer electron beam 110 is gentle. Further, the focusing of the electron beam 50 by the main lens formed by the G3 electrode 64 is tight, and in particular, focusing on the outside electron beam 110 is tight. The inner electron beam 106 emitted from the electron emission surface 54a of the cathode 54 is focused by the cathode lens formed by the G1 electrode 60 and the G2 electrode 62, and almost the same as in the conventional electron focusing system 86, G2 An inner beam cathode side crossover 108 is formed at a position slightly closer to the G3 electrode 64 from the opening of the electrode 62, and is further focused by the main lens formed by the G3 electrode 64 to be focused on the target 18 on the inner beam target side crossover 109. Form. In addition, the outer electron beam 110 is gently focused by the improved cathode lens, and the outer electron beam 110 is located at the same position as the inner beam cathode side crossover 108, farther from the cathode 54 than in the conventional electron focusing system 86. A beam cathode side crossover 112 is formed. As a result, since the position of the inner beam cathode side crossover 108 and the position of the outer beam cathode side crossover 112 substantially coincide with each other, a small-diameter cathode side crossover 94 is obtained. Further, the outer electron beam 110 starts from the outer beam cathode side crossover 112 which is located farther from the cathode 54 than the conventional product, but is tightly focused by the improved main lens formed on the G3 electrode 64 and the target. An outer beam target side crossover 113 is formed on 18. As a result, a small focal point corresponding to the small-diameter crossover 94 in which the inner beam target side crossover 109 and the outer beam target side crossover 113 are combined on the target 18 is obtained.

  Further, in this embodiment, the inner peripheral surface of the opening 64 of the G3 electrode 64 of the electron focusing system 56 is a tapered surface 76 whose diameter decreases as it goes to the target 18 side, but this tapered surface 76 is limited to this. There may be a case of reverse inclination. That is, when focusing the outer electron beam 110 tightly, the tapered surface 76 is formed with an inclination as shown in FIG. 8, and conversely, when focusing the outer electron beam 110 loosely, the tapered surface 76 is The diameter is formed so as to increase toward the target 18 side. Further, the taper angle of the tapered surface 76 can be changed according to the tightness and looseness when the outer electron beam 110 is focused by the main lens.

  In FIG. 8, in the electron focusing system 56 of the present embodiment, the diameter of the opening 62a of the G2 electrode 62 is much larger than that of the conventional G2 electrode, so as shown in FIG. 110 is also focused without colliding with the G2 electrode 62. As a result, the G2 electrode 62 is not heated to the high temperature by the electron beam 50, so that there is no problem of discharging between the grid electrodes.

  FIG. 9 shows a comparison of the current density distributions of the focal points formed on the target of this example and the conventional product. In FIG. 9, the horizontal axis represents the position coordinates on the target, and the vertical axis represents the current density of the electron beam. In the figure, curve A is that of this embodiment, and curve B is that of a conventional product. In the case of the present embodiment, the current density of the electron beam is greatly increased and the focal spot size is reduced as compared with the conventional product with the same X-ray tube current. As the focal spot size on the target, the present embodiment has a size about 20% smaller than that of the conventional product. In the electron focusing system of this embodiment, even if the X-ray tube current is increased, the focusing state of the electron beam hardly changes, so that the micro focus can be maintained.

  FIG. 10 shows another example of the shape of the inner peripheral surface of the openings of the G1 electrode and the G3 electrode of the microfocus X tube according to the present invention. In the X-ray tube 10 of the present embodiment, the tapered surfaces 74 and 76 are shown as the shapes of the inner peripheral surfaces of the openings 60a and 64a of the G1 electrode 60 and the G3 electrode 64 of the electron focusing system 56, but the inner periphery of the openings 60a and 64a The shape of the surface is not limited to this, and may be other shapes as shown in FIG. Each drawing in FIG. 10 shows an upper cross section of the central axis 72 of the G1 electrode or the G3 electrode (hereinafter represented by the grid electrode). In the first other example of FIG. 10 (a), the inner peripheral surface of the opening 114a of the grid electrode 114 is formed by connecting the first tapered surface 116 and the second tapered surface 118. The inclination angle of the first tapered surface 116 is larger. In the second other example of FIG. 10B, the inner peripheral surface of the opening 114a of the grid electrode 114 is formed by connecting the first tapered surface 116, the cylindrical surface 120, and the second tapered surface 118. . In the third other example of FIG. 10 (c), the inner peripheral surface of the opening 114a of the grid electrode 114 has three tapered surfaces, that is, a first tapered surface 116, a second tapered surface 118, and a third tapered surface. It is formed by connecting the surfaces 121. All of the above tapered surfaces become smaller as the diameter of the inner peripheral surface of the opening 114a goes to the right, that is, as the distance from the cathode 54 increases. In the fourth other example of FIG. 10D, the inner peripheral surface of the opening 114a of the grid electrode 114 is formed by a curved surface 122. In the fifth other example of FIG. 10 (e), the inner peripheral surface of the opening 114a of the grid electrode 114 is formed by connecting the curved surface 122 and the tapered surface 116. In the curved surface 122, the diameter of the inner peripheral surface of the opening 114a also decreases as it goes to the right. The other examples of the sixth to tenth examples of FIGS. 10 (f) to 10 (g) are reversed from the left and right of the structural diagrams of the first to fifth other examples of FIGS. 10 (a) to 10 (e). The diameter of the inner peripheral surface of each grid electrode opening is formed so as to increase or at least not decrease toward the right side (target side). Conversely, the diameter of the inner peripheral surface of each grid electrode opening in the first to fifth other examples of FIGS. 10 (a) to 10 (e) decreases toward the right side (target side), Or at least it does not increase.

  As the G1 electrode, the shape of the inner peripheral surface of this opening makes it necessary to create a potential distribution in the vicinity of the G1 electrode so as to focus the outer electron beam loosely. Therefore, the G1 electrode of the first embodiment and FIG. f) The diameter of the inner peripheral surface of the opening, such as FIG. 10 (i), is formed so that it does not increase or at least does not decrease as it goes to the target side (the right side in the figure). Things are suitable. On the other hand, as for the G3 electrode, as in the first embodiment, it is necessary to create a potential distribution in the vicinity of the G3 electrode so as to focus the outer electron beam tightly. Since there is a case where it is necessary to create a potential distribution that converges in the vicinity of the G3 electrode, the diameter of the G3 electrode 64 of this embodiment in FIG. 2 and the apertures of FIGS. 10 (a) to 10 (e) It is formed so that it decreases or at least does not increase as it goes to the target side, and the G3 electrode 64 of this embodiment of FIG. 2 is reversed left and right, and FIGS. 10 (f) to 10 (g). Both those that are formed such that the diameter of the opening increases or at least does not decrease as it goes to the target are suitable.

  Next, an embodiment of the X-ray generator according to the present invention will be described with reference to FIG. FIG. 11 is a configuration diagram of the X-ray generator of the present embodiment. In FIG. 11, the X-ray generator 130 of the present embodiment includes a microfocus X-ray tube 10 according to the present invention, a container 132 containing the X-ray tube 10, the rotating anode 14 and the cathode 12 of the X-ray tube 10. A high voltage generating circuit 134 for supplying a high voltage, a grid voltage generating circuit 136 for supplying a grid voltage to a grid electrode constituting an electron focusing system of the cathode 12 of the X-ray tube 10, and a rotating anode 14 of the X-ray tube 10 It is composed of a stator 138 that rotates, an insulating oil 140 that insulates the X-ray tube 10, the high voltage generation circuit 134, the grid voltage generation circuit 136, and the like, a control circuit 142, and the like.

  The container 132 is usually a casing made of a metal plate or the like, and the shape is often a rectangular parallelepiped. In addition to the X-ray tube 10, the container 132 includes a high voltage generation circuit 134, a grid voltage generation circuit 136, and the like, and is filled with an insulating oil 140. A part of the inner wall of the container 132 and a portion near the target 18 of the rotary anode 14 of the X-ray tube 10 are covered with a lead plate or the like for X-ray prevention. The rotating anode 14, the high voltage generating circuit 134, and the grid voltage generating circuit 136 of the X-ray tube 10 are supported on the inner wall of the container 132 through a support made of an insulator or the like. The large-diameter portion 30 of the envelope 16 of the X-ray tube 10 is directly supported by the inner wall of the container 132, and the X-ray is extracted to the outside at a portion of the inner wall facing the X-ray emission window 40 of the X-ray tube 10. Aperture (X-ray radiation port) 144 is provided. The stator 138 is disposed around the rotor of the rotary anode 14 of the X-ray tube 10 and is supported on the inner wall of the container 132 via an insulator.

  The high voltage generation circuit 134 is composed of a high voltage transformer, a rectifier circuit, etc., and an AC voltage of commercial frequency is supplied from the control circuit 142 via the low voltage lead wire 146, and this is exchanged with the high voltage transformer. The voltage is boosted to a high voltage and then rectified by a rectifier circuit. As the high voltage generation circuit 134, a neutral grounding method is usually used, and a positive high voltage and a negative high voltage are generated. A positive high voltage passes through the high voltage lead wire 148 to the rotating anode 14 of the X-ray tube 10, and a negative high voltage passes through the high voltage lead wire 148 and the grid voltage generation circuit 136 to the cathode of the X-ray tube 10. Supplied to 12. The grid voltage generation circuit 136 includes a voltage regulator, an insulation transformer, a rectifier circuit, and the like. In this embodiment, since the grid voltage is different for each grid electrode, three sets of voltage regulators and the like are used to generate three grid voltages. In the grid voltage generation circuit 136, the AC voltage of the commercial frequency supplied from the control circuit 142 is adjusted to an appropriate voltage value by a voltage regulator to obtain a high potential AC voltage insulated by an insulation transformer, and then a rectifier circuit. To rectify the grid voltage. The grid voltage is supplied from the grid voltage generation circuit 136 to the G1, G2, and G3 electrodes of the electron focusing system 56 via the grid lead wire 150 and the lead wire of the stem 70 of the X-ray tube 10. The grid voltage generation circuit 136 also includes a heater power supply circuit for heating the cathode 54 of the cathode 12. The heater power supply circuit is composed of a voltage regulator and an insulation transformer, etc., and after adjusting the commercial frequency AC voltage supplied from the control circuit 142 to an appropriate voltage value by the voltage regulator, the heater power supply is insulated by the insulation transformer. A potential heater heating voltage is used. The heater heating voltage is supplied from the grid voltage generation circuit 136 to the heater of the cathode 54 via the heater lead wire 152 and the stem 70 lead wire.

  The control circuit 142 includes a power supply unit 154 for operating the X-ray tube 10, a control unit 156 for controlling the operation of the X-ray tube 10, and the like. The power supply unit 154 includes a primary power supply for the high voltage generation circuit 134, a primary power supply for the grid voltage generation circuit (including the heater heating circuit) 136, a stator drive power supply, and the like. The control unit 156 includes a computer (CPU) for controlling the load of the X-ray tube 10 and the like. Although the control circuit 142 may be incorporated in the X-ray generator 130 as described above, in many cases, it is included in the controller of the X-ray apparatus, and the X-ray generator is controlled by this controller. .

  Next, an embodiment of the X-ray apparatus according to the present invention will be described with reference to FIG. FIG. 12 is a schematic configuration diagram of an embodiment of an X-ray apparatus according to the present invention. In FIG. 12, an X-ray apparatus 160 of the present embodiment includes an X-ray generation apparatus 130 that generates X-rays, an X-ray detection apparatus 164 that detects an X-ray dose that has passed through a subject 162, and an X-ray detection apparatus 164. The image forming apparatus 166 forms an X-ray image of the subject 162 based on the output signal of the X-ray, the X-ray generation apparatus 130, the X-ray detection apparatus 164, the control apparatus 168 that controls the operation of the image forming apparatus 166, and the like. The Here, the X-ray generator 130 is an X-ray generator according to the present invention as shown in FIG. 11, and includes the microfocus X-ray tube 10 according to the present invention.

  The X-ray detection device 164 includes X-ray detection elements arranged in a line like a line sensor, and X-ray detection elements arranged in a plane like an image intensifier (II). Things are used. Since the X-ray detection device 164 outputs an electric signal having an intensity corresponding to the X-ray dose received from the normal X-ray element, the image forming device 166 uses the electric power distributed linearly or in a plane form from the X-ray detection device 164. Based on the signal, 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 164, and the film developing device corresponds to the image forming device 166. The control device 168 controls conditions for driving the microfocus X-ray tube 10, controls the X-ray detection operation of the X-ray detection device 164, controls the image creation operation of the image forming device 166, and the like. The control device 168 also supplies power supply voltage to other devices such as the X-ray generator 130.

  Since the X-ray generator and X-ray apparatus according to the present invention include the microfocus X-ray tube according to the present invention, a microfocus and a large X-ray tube current can be obtained, and X-ray magnified imaging with a microfocus is performed. High-definition X-ray images can be obtained in diagnosis and non-destructive inspection of fine internal structures, and stable operation can be maintained for a long time.

1 is an overall structural diagram of an 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 schematic configuration diagram of an electron focusing system as a main part of FIG. Schematic configuration diagram of an electron focusing system of a conventional microfocus X-ray tube. The figure which shows the example of a calculation of the electron trajectory in the vicinity of G1 electrode and G2 electrode of the electron focusing system of a present Example. The figure which shows the example of calculation of the electron trajectory in the vicinity of G1 electrode and G2 electrode of the electron focusing system of the conventional micro focus X-ray tube. The figure for demonstrating the focusing condition of the electron beam in the electron focusing system of the conventional micro focus X-ray tube. The figure for demonstrating the focusing condition of the electron beam in the electron focusing system of a present Example. Comparison of the current density distribution of the focal point formed on the target of this example and the conventional product. 6 shows another example of the shape of the inner peripheral surface of the opening of the G1 electrode and the G3 electrode of the microfocus X-ray tube according to the present invention. The block diagram of one Example of the X-ray generator which concerns on this invention. 1 is a schematic configuration diagram of an embodiment of an X-ray apparatus according to the present invention. 1 is a schematic configuration diagram of an electron gun for a microfocus X-ray tube. Schematic configuration diagram of an electron focusing system of a conventional microfocus X-ray tube.

Explanation of symbols

10 ... Microfocus X-ray tube (X-ray tube)
12 ... Cathode
14 ... Anode (rotary anode)
16 ... Envelope
18 ... Target
26 ・ ・ ・ Fixing part
28: Focus
30 ... Large diameter part
32 ... Anode insulation
34 ・ ・ ・ Cathode insulation
36 ... disk part
38 ... Cylindrical part
40 ... X-ray radiation window
48, 72 ... Center axis
50 ... electron beam
52 ... X-ray
54 ・ ・ ・ Cathode
54a ・ ・ ・ Electron emitting surface
56, 86 ... Electronic focusing system
58 ... Cathode support
60, 88 ... 1st grid electrode (G1 electrode)
60a, 62a, 64a, 84, 114a ... opening
62, 90 ... Second grid electrode (G2 electrode)
64, 92 ... Third grid electrode (G3 electrode)
66 ・ ・ ・ Electronic focusing insulator
66a ・ ・ ・ Insulator
68 ・ ・ ・ Cathode cover
68a ・ ・ ・ Cylindrical part
68b ・ ・ ・ Bottom
70 ... Stem
74, 76 ... Tapered surface
94, 96 ... crossover (cathode side crossover)
98, 106 ... Inner electron beam
100, 108 ... Inner beam cathode side crossover
101, 109 ... Inner beam target side crossover
102, 110 ... Outside electron beam
104, 112 ... Outer beam cathode side crossover
105, 113 ... Crossover on the outer beam target side
114 ・ ・ ・ Grid electrode
116, 123 ... 1st taper surface (taper surface)
118, 124 ... second tapered surface
120 ... Cylindrical surface
121, 125 ... Third taper surface (taper surface)
122, 126 ... curved surface
130 ... X-ray generator
132 ・ ・ ・ Container
134 ・ ・ ・ High voltage generator
136 ... Grid voltage generator
140 ・ ・ ・ Insulating oil
142 ... Control circuit
160 ... X-ray equipment
162 ... Subject
164 ... X-ray detector
166 ... Image forming apparatus
168 ... Control device

Claims (4)

The electron beam collides with a cathode having an electron beam generating cathode and an electron focusing system composed of a plurality of grid electrodes arranged in the electron beam path for focusing the electron beam into a thin linear beam. An anode having a target for generating X-rays, and an envelope that insulates and supports the cathode and the anode, and is sealed in a vacuum-tight manner, and each of the plurality of grid electrodes of the cathode electron focusing system passes through the electron beam. An electron lens for focusing an electron beam by applying a potential with respect to the cathode to each grid electrode, and having a grid electrode insulating support portion for insulating and supporting the grid electrode In microfocus X-ray tube,
The electron focusing system comprises at least three grid electrodes;
The inner peripheral surface of the opening of the grid electrode (G1 electrode) which is closest to said cathode of said grid electrode has a diameter smallest at the cathode side, rather most size at the target side, close to the third to the cathode A microfocus X-ray tube characterized in that the inner peripheral surface of the opening of the grid electrode (G3 electrode) has the largest diameter on the cathode side and the smallest on the target side .   2. The microfocus X-ray tube according to claim 1, wherein an inner peripheral surface of the opening of the grid electrode (G1 electrode) is formed so as to increase or at least not decrease toward the target side in the middle thereof. A featured microfocus X-ray tube.   2. The microfocus X-ray tube according to claim 1, wherein an inner peripheral surface of an opening of the grid electrode (G3 electrode) is formed so as to decrease or at least not increase toward the target side in the middle thereof. A featured microfocus X-ray tube.   The microfocus X-ray tube according to any one of claims 1 to 3, comprising a cathode cover made of a metal material and having a substantially cylindrical shape with a bottom, the cathode cover comprising the electron focusing system and the grid electrode insulating support. And a bottom surface of the bottomed cylinder is disposed to face the target, and an opening through which an electron beam passes is provided on the bottom surface of the bottomed cylinder. .

Images