JP2006164819A - Microfocus x-ray tube and x-ray device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microfocus X-ray tube having an effective focal spot without bias in resolution in an X-ray extraction direction and having a large allowable load. <P>SOLUTION: An electron focusing system 14 of the negative electrode of the X-ray tube is composed of a cathode electrode 12, four grid electrodes such as a G1 electrode 20, a G2 electrode 22, a G3 electrode 24 and a G4 electrode 24; and the respective grid electrodes include openings 20a, 22a, 24a and 26a for passing an electron beam emitted from an electron emission surface 12a of the cathode electrode 12 therethrough. Only the opening 26a of the G4 electrode 26 is formed into an elliptical shape. By applying a positive grid potential and a negative grid potential, with respect to the potential of the cathode electrode 12, to the G1 electrode 20 through the G3 electrode 24 and to the G4 electrode 26, respectively, the electron beam is focused into a thin beam by the G1 electrode 20 through the G3 electrode 24, and the cross-sectional shape of the electron beam is formed into an elliptical shape by the G4 electrode 26. By hitting the electron beam against an inclined surface of a target of the positive electrode, a nearly circular effective focal spot can be provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray tube having a micro focus used for industrial use or medical use, and an X-ray apparatus using the X-ray tube, and more particularly to a technique for improving the focus resolution of the X-ray tube.

  X-ray devices that measure the dose of X-rays that have passed through a subject, create an image based on that dose, and inspect or diagnose the subject are used for industrial inspection of defects and foreign matter. For medical purposes, it is widely used for diagnosis by fluoroscopy or radiography. 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 a good 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.

  In order to obtain a high-quality fluoroscopic image, it is desirable to increase the X-ray dose. For this purpose, the value of the electron beam current (hereinafter referred to as the X-ray tube current) that generates X-rays is as large as possible. Is required. For example, an X-ray device that uses a line sensor with low X-ray sensitivity to inspect foreign substances in foods, etc., or an image intensifier (II) ) In-line automatic X-ray equipment for automatic inspection that uses the camera's shutter function to obtain a still image for a moment, an improvement in sensitivity is required by increasing the X-ray tube current. Also, in medical X-ray equipment, 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 problem of thermal shock due to the power of the electron beam colliding with the anode target as a factor that hinders the increase of the X-ray tube current. That is, in the case of a microfocus X-ray tube, the electron beam is extremely narrowed and made incident on the anode target, so that the heat input density is extremely large, and if the current of the electron beam is simply increased further, the focal plane of the target May melt thermally. Therefore, in the conventional microfocus X-ray tube, the electron beam power allowed by the manufacturer, that is, the allowable load, is set to an extremely small value as compared with a normal medical X-ray tube.

  On the other hand, 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 focusing by forming an electric field lens using a plurality of electrodes. A representative example of this type of prior art is an electron gun for a cathode ray tube (hereinafter abbreviated as CRT). The structure and operation of the CRT electron gun will be briefly described below. FIG. 11 shows a schematic configuration of the most basic in-line type electron gun for a CRT electron gun. In FIG. 11, the CRT 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 the electron lens formed by the cathode 202 and the four grid electrodes 204, 206, 208, and 210 to form a thin electron beam 212. Colliding and causing the phosphor on the phosphor screen 222 to emit light.

  In FIG. 11, four grid electrodes 204, 206, 208, and 210 are a first grid electrode (hereinafter abbreviated as G1 electrode) 204, a second grid electrode (hereinafter abbreviated as G2 electrode) 206, and a third grid electrode in order from the cathode 202. Called 208 (hereinafter abbreviated as G3 electrode) 208 and fourth grid electrode (hereinafter abbreviated as G4 electrode) 210, each has openings 204a, 206a, 208a, 210a along the central axis of electron gun 200. Of the five electrodes of the electron gun 200, a portion constituted by the three electrodes of the cathode 202, the G1 electrode 204, and the G2 electrode 206 is called a tripolar portion, and the cathode lens 214 is formed in this portion. A prefocus lens 216 is formed between the G2 electrode 206 and the G3 electrode 208, and a main lens 218 is formed between the G3 electrode 208 and the G4 electrode 210, respectively.

  The cathode 202 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 of 1000K or higher. The amount of current of the electron beam 212 from the cathode 202 is controlled by applying a signal obtained by amplifying the video signal to the cathode 202. This amount of current increases as the cathode voltage decreases. A voltage lower than that of the cathode 202 is always applied to the G1 electrode 204, and an acceleration voltage higher by about 400 to 1000V than the potential of the cathode 202 is applied to the G2 electrode 206. The current from the cathode 202 passes through the opening 204a of the G1 electrode 204, becomes an electron beam 212, and is drawn out to the G2 electrode 206 side. The electron beam 212 is once focused by the cathode lens 214, forms a crossover 220 in the vicinity of the G2 electrode 206, 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 an electron 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 the G3 electrode 208, and a final acceleration pressure of 20 to 30 KV is applied to the G4 electrode 210, and the main lens 218 is formed by this potential difference. After passing through the G4 electrode 210, 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.

In general, when an electron beam is focused on a minute beam (beam), the grid electrodes are arranged in an axially symmetric arrangement as described above, and the cross-sectional shape of the electron beam in the direction perpendicular to the traveling direction is substantially circular. It becomes. 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 example of a microfocus X-ray tube that forms a micro focus using this electron optical system, Patent Document 1, Patent Document 2, and the like are disclosed.
JP 2003-317996 A JP 2003-7236 A

  The microfocus X-ray tube disclosed in Patent Document 1 employs a cathode structure as shown in FIG. The configuration of the cathode of this microfocus X-ray tube is basically the same as that of the electron gun for CRT shown in FIG. 11, and the electron focusing system 230 includes a cathode electrode 232, a G1 electrode 234, a G2 electrode 236, and a G3 electrode. 238 and anode target. The G1 electrode 234 and the G2 electrode 236 have small-diameter openings, the G3 electrode 238 has a large opening, and the centers of the respective openings are arranged along the central axis of the electron focusing system. The G1 electrode 234 has a positive potential (for example, OV to +100 V) with respect to the potential of the cathode electrode 232 (cathode potential), and the G2 electrode 236 has a positive potential (for example, from OV) higher than the potential of the G1 electrode 234. +2000 V), and a positive or negative potential (for example, −500 V to +500 V) lower than the potential of the G2 electrode 236 is applied to the G3 electrode 238, respectively. Further, a positive potential of +10 kV to +150 kV with respect to the cathode potential is applied to the anode target. As a result, the thermoelectrons radiated from the cathode electrode 232 are focused on a thin beam-like electron beam to form a microfocus on the anode target. At this time, the electron beam is focused to a substantially circular beam having an outer diameter of about 10 μm.

  Since the conventional microfocus X-ray tube disclosed in Patent Document 1 and Patent Document 2 described above employs an axially symmetric electron optical system, the cross-sectional shape in the direction orthogonal to the traveling direction of the electron beam is It is almost circular. For this reason, a reflective X-ray output method (a method that uses X-rays that are reflected and radiated to the space where the electron beam is incident on the target surface when the target where the electron beam collides is thick. In the case of an X-ray tube with a partial X-ray tube), the shape of the focal point (hereinafter referred to as the effective focal point) viewed from the X-ray extraction direction (X-ray detector side) is usually an elliptical shape. . The shape of the effective focal point is an ellipse. When the subject is viewed and imaged, the direction parallel to the incident direction of the electron beam (hereinafter sometimes referred to as the longitudinal direction) and the direction orthogonal thereto (hereinafter referred to as the vertical direction) , Sometimes referred to as the lateral direction), and the effective focal spot size is different. Hereinafter, the dimension of the effective focus in the direction parallel to the incident direction of the electron beam will be referred to as the effective focus length dimension, and the dimension orthogonal to the dimension will be referred to as the effective focus width dimension. This effective focal size determines the resolution of the image obtained at the X-ray inspection. The difference in effective focal size between the vertical and horizontal directions of the X-ray emission area means that the vertical and horizontal resolutions are different. As a result, an inspection accuracy is deteriorated.

  In order to prevent this, an X-ray output method called a transmission type, that is, a method of outputting X-rays to the space on the side where the target is transmitted in the traveling direction of the electron beam may be used. Since the X-rays cannot be extracted to the outside unless the thickness of the target is fixed and the target is extremely thin, the allowable load is remarkably reduced, and as a result, the X-ray output is also reduced. In general, the rotary anode method is adopted to increase the allowable load of the X-ray tube, but in this case, it is difficult to realize the structure unless it is a reflection type. Therefore, the reflection type microfocus X-ray tube using the conventional electron optical system has a problem that the effective focal point has an elliptical shape and the resolution is biased.

  However, if the angle formed by the X-ray extraction direction and the target inclined surface (hereinafter referred to as the target angle) is 45 degrees, the effective focal point shape is almost the same as the electron beam shape. The shape of the focal point is almost circular, and the width and length dimensions of the effective focal point are the same, so there is no bias in resolution. However, the target angle defines the X-ray emission range of the X-ray tube, and it cannot be practically 45 degrees.

  In order to solve this problem, the cross-sectional shape of the electron beam incident on the target may be shaped into an appropriate ellipse so that the shape of the effective focus is substantially circular corresponding to the target angle. That is, when the target angle is larger than 45 degrees, the cross-sectional shape of the electron beam is an ellipse whose dimension in the width direction is larger than the dimension in the length direction, and when the target angle is smaller than 45 degrees, the dimension in the length direction is The shape of the effective focus viewed from the X-ray extraction direction may be substantially circular as an ellipse that is larger than the dimension in the width direction.

  Furthermore, in the microfocus X-ray tube, the input load of the electron beam input to the focal plane of the anode target is extremely high, so the allowable load is remarkably limited. Conventionally, the rotating anode method has been adopted. However, the rotational speed is limited due to the bearing structure. In addition to improving the rotation speed of the anode, it is effective to make the cross-sectional shape of the electron beam elliptical as a means for improving the allowable load.

  In view of the above, an object of the present invention is to provide a microfocus X-ray tube having an effective focus with no bias in resolution in the X-ray extraction direction and a large allowable load, and an X-ray apparatus using the microfocus X-ray tube. .

  In order to achieve the above object, a microfocus X-ray tube according to the present invention includes a cathode electrode that emits an electron beam, and a plurality of grid electrodes that are arranged in a path of the electron beam to focus the electron beam into a narrow beam. A cathode having a cathode, an anode having a target that generates X-rays by collision of an electron beam, and the cathode and the anode are sealed in a vacuum-tight manner, and has an X-ray emission window that emits X-rays generated by the target to the outside. A plurality of grid electrodes each having an opening for passing an electron beam, and applying a grid potential based on the cathode electrode to each grid electrode to obtain a micro focus In the focus X-ray tube, the shape of the opening of at least one of the grid electrodes is an ellipse or a shape that approximates an ellipse, and the electron beam It is obtained by a generally elliptical beam cross-section (claim 1).

  Further, in the X-ray tube of the present invention, at least four grid electrodes are further arranged, and the shape of the grid electrode opening closest to the anode target of the grid electrodes is an ellipse or an ellipse-like shape. It is what.

  In the X-ray tube of the present invention, a negative potential with respect to the potential of the cathode electrode is further applied to the grid electrode having an opening having an elliptical shape or a shape approximated to an elliptical shape.

  Further, in the X-ray tube of the present invention, the aperture diameter of the grid electrode having an opening having an elliptical shape or a shape approximated to an elliptical shape is longer in the central axis direction of the anode and shorter in a direction perpendicular thereto. Yes.

  In the X-ray tube of the present invention, the anode is a rotary anode type.

  In the X-ray tube of the present invention, the portion of the envelope to which the X-ray emission window is attached is made of a metal material.

  The X-ray generator of the present invention includes an X-ray tube having a micro focus, a high voltage generating circuit for supplying a high voltage between the cathode and the anode of the X-ray tube, and a plurality of cathodes of the X-ray tube. Includes a grid voltage generation circuit for supplying a grid voltage to the grid electrode, an electrode insulation support for insulating and supporting the electrode of the X-ray tube, an X-ray tube, a high voltage generation circuit, a grid voltage generation circuit, and an electrode insulation support And a supporting housing, an insulating medium filled in the housing, dipping and insulating the X-ray tube and other components, and a buffer attached to the housing for buffering expansion and contraction of the insulating medium In the X-ray generator including the mechanism, the X-ray tube is the microfocus X-ray tube of the present invention (claim 2).

  In the X-ray generator of the present invention, the high voltage generation circuit is further of a neutral point grounding system.

  The X-ray apparatus of the present invention includes an X-ray generator that generates X-rays, an X-ray detector that detects X-rays generated from the X-ray generator and transmitted through the subject, and an X-ray detector. An X-ray apparatus having an image forming apparatus that creates an X-ray image of a subject based on a signal corresponding to the detected X-ray dose, and an X-ray generation apparatus, an X-ray detection apparatus, and a control device that controls the image forming apparatus The X-ray generator is the X-ray generator according to claim 2 (Claim 3).

  In the microfocus X-ray tube of the present invention, the shape of the opening of at least one of the grid electrodes constituting the electron focusing system of the cathode is an ellipse or a shape approximated to an ellipse. Since the cross-sectional shape of the beam of the electron beam passing through the aperture is substantially elliptical, a substantially circular effective focal point can be obtained by colliding the electron beam with a target having a target angle corresponding to the cross-sectional shape of the beam. It becomes possible. As a result, a microfocus X-ray tube with an effective focus with no bias in resolution in the X-ray extraction direction can be obtained, so high-definition X with almost the same resolution in the vertical and horizontal directions can be used for magnified imaging of the subject. A line image can be obtained, and the inspection accuracy of a fine object can be improved.

  Further, in the X-ray tube of the present invention, at least four grid electrodes are arranged, and the shape of the grid electrode opening closest to the anode target among the grid electrodes is an ellipse or an ellipse-like shape. Therefore, after the electron beam is focused on a thin beam capable of obtaining microfocus by another preceding grid electrode, the electron beam can be narrowed down to an elliptical cross-sectional beam by the grid electrode closest to the target. As a result, an electron beam having a minute and elliptical cross-sectional shape can be easily obtained without adding a complicated electron focusing system.

  Further, in the X-ray tube of the present invention, a negative potential with respect to the potential of the cathode electrode is applied to the grid electrode having an elliptical shape or an opening approximate to an elliptical shape. By adjusting both the dimensions and the grid potential, the cross-sectional shape (elliptical shape) of the electron beam can be controlled according to the target angle.

  Further, in the X-ray tube of the present invention, the aperture of the grid electrode having an elliptical shape or an elliptical shaped opening is longer in the electron beam beam length direction and shorter in the electron beam beam width direction. Therefore, the length dimension of the actual focal point formed on the target by this electron beam is much larger than the actual focal width dimension. As a result, since the focal area on the target is increased, the X-ray tube load that can be input to the X-ray tube can be increased, and the X-ray dose that can be emitted from the X-ray tube can be increased.

  In the X-ray tube of the present invention, since the anode is a rotating anode type, the effective focal area on the anode target is greatly increased, and the X-ray tube load that can be input to the X-ray tube is greatly increased. The X-ray dose that can be emitted from the X-ray tube can be significantly increased.

  In the X-ray tube of the present invention, the portion of the envelope to which the X-ray emission window is attached is made of a metal material and has a ground potential. Therefore, when the X-ray emission window is mounted on an X-ray apparatus or the like, It can be attached directly or very close to the outer wall of the X-ray tube storage container, and the distance between the focal point of the X-ray tube and the subject can be reduced during X-ray imaging. As a result, the enlargement ratio at the time of X-ray imaging can be increased, and a high-definition X-ray image can be obtained.

  In addition, the X-ray generator of the present invention has a micro focus X-ray tube having a fine and substantially circular effective focal point and a large allowable load. High-definition X-ray images with no deviation in the vertical and horizontal directions can be obtained, and inspection accuracy of minute objects can be improved, and high-magnification imaging is also possible. Become.

  In the X-ray generator of the present invention, since the high voltage generating circuit is a neutral point grounding system, the high voltage insulation in the X-ray generating device is facilitated, and the size of the X-ray generator casing is reduced. Can be small. In addition, an X-ray emission window attached to the envelope of the X-ray tube can be attached directly or very close to the housing, so that the X-ray tube focus and the subject can be located during X-ray imaging. The distance can be reduced, and high-magnification shooting is possible.

  In addition, the X-ray apparatus of the present invention has an X-ray generator that incorporates a microfocus X-ray tube having a microscopic and substantially circular effective focus. A high-definition X-ray image without deviation in the horizontal direction can be obtained, the inspection accuracy of a minute object can be improved, and high-magnification imaging can be performed.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
First, the structure and operation 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 a diagram showing the structure of the main part of the cathode, which is the main part of FIG. 1, and FIG. 3 is an operation of the cathode of FIG. FIG. 4 is a diagram for explaining the relationship between the cross-sectional shape of the electron beam and the shape of the effective focus, and FIG. 5 is an example of the electron beam trajectory calculation in the X-ray tube of this embodiment.

  In FIG. 1, a microfocus X-ray tube (hereinafter abbreviated as an X-ray tube) 1 of the present embodiment includes a cathode 2 that generates an electron beam, an anode 3 that generates an X-ray when the electron beam collides, The cathode 2 and the anode 3 are opposed to each other, and the envelope 4 is enclosed in a vacuum-tight manner and is insulated and supported. The X-ray tube 1 of this embodiment is characterized by the configuration of the cathode 2 for forming a micro focus (micro focus), 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.

  In FIG. 1, the anode 3 adopts a rotary anode type structure. This anode (hereinafter also referred to as a rotating anode) 3 is not limited to this, and may be of a fixed anode type. However, in the rotating anode type, since the effective focal area on the target is remarkably increased by rotating, the X-ray tube load can be increased and it is effective for increasing the generated X-ray dose. . The rotary anode 3 includes a target 30 serving as an X-ray generation source, a rotor 32 that supports the target 30, a rotating shaft (not shown) that supports the rotor 32, and a bearing (not shown) that rotatably supports the rotating shaft. ) And a fixing portion 34 for supporting the bearing. An anode end 35 is provided at the end of the fixed portion 34. The anode end 35 supports the anode side of the X-ray tube 1 and feeds the anode potential. The rotary anode 3 as a whole has substantially the same structure as the rotary anode of a general-purpose medical rotary anode X-ray tube. The target 30 has an umbrella shape and a disk shape, and is made of a metal material having a high atomic number such as tungsten and having a high melting point. An electron beam 28 from the cathode 2 collides with the inclined surface 36 of the target 30 to form a focal point 38 that becomes an X-ray generation source. The rotating anode 3 rotates around its central axis 48.

  Next, the envelope 4 surrounds the target 30 portion of the rotating anode 3 and the tip portion of the cathode 2, and is coupled to the large diameter portion 40 held at the ground potential and the fixed portion 34 of the rotating anode 3, It comprises an anode insulating part 42 that insulates and supports this, and a cathode insulating part 44 that insulates and supports the cathode 2. The large-diameter portion 40 has a shape in which a large-diameter disk 40a and a large-diameter thick cylinder 40b are joined. The circular plate 40a and the cylinder 40b are made of a metal material such as copper or stainless steel. An X-ray radiation window 46 is attached to a circular opening provided in a portion of the disc 40a close to the focal point 38 of the target 30. The X-ray radiation window 46 is made of beryllium or the like having good X-ray transparency, and is coupled to the opening of the disk 40a by welding or brazing via a window frame or the like. The X-ray 5 is extracted through the X-ray emission window 46 in a direction parallel to the central axis 48 of the rotating anode 3 (upward direction in the drawing). The anode insulating portion 42 includes a cylindrical portion 42a having a diameter slightly larger than the outer diameter of the rotor 32, a flare portion 42b widened in a cone shape so as to be coupled to the cylinder 40b of the large diameter portion 40, and a fixing portion 34 of the rotating anode 3. And an anode connection portion 42c for coupling with the. Most of the anode insulating portion 42 is made of an insulating material such as heat-resistant glass or ceramic, and a metal material that is compatible with the insulating material is used for the flare portion 42b and the anode connecting portion 42c at both ends. A cathode insulating portion 44 is coupled to the side surface of the cylinder 40b of the large diameter portion 40 in a direction substantially perpendicular to the central axis 48 of the rotating anode 3. The cathode insulating portion 44 has a cylindrical shape with a thin outer diameter, and is mostly made of an insulating material such as heat resistant glass or ceramic. One end of the cathode insulating portion 44 is coupled to the side surface of the cylinder 40b of the large diameter portion 40, and the other end is coupled to the stem 19 serving as the support portion of the cathode 2. Due to this coupling, the electron focusing system of the cathode 2 and the target 30 of the rotary anode 3 are arranged to face each other.

  Next, the configuration and operation of the cathode 2, which is the main part of the X-ray tube 1 of this embodiment, will be described with reference to FIGS. FIG. 2 shows the structure of the main part of the cathode 2, and FIG. 3 is a diagram for explaining the operation of the cathode 2. First, the structure of the cathode 2 of the X-ray tube 1 will be described with reference to FIG. 2, FIG. 2 (a) is a cross-sectional view of the main part of the cathode 2, and FIG. 2 (b) is a view of the main part of the cathode 2 as viewed from the target 30 side of the anode 3. In FIG. 2 (a), the cathode 2 includes a cathode electrode 12 that generates an electron beam, an electron focusing system 14 that focuses the electron beam into a thin beam, and an electron focusing system insulator 18 that supports and insulates the electron focusing system 14. A stem 19 (not shown, see FIG. 1) for insulatingly supporting the entire cathode 2 is formed. The cathode electrode 12 is supported by a cathode support 16, and the cathode support 16 is insulated and supported by an electron focusing system insulator 18 through an electron focusing system 14. The electron focusing system 14 is composed of four grid electrodes 20, 22, 24, 26. Of these, the three grid electrodes 20, 22, 24 share the role of focusing the electron beam into a thin beam, and the fourth The grid electrode 26 shares the role of making the cross-sectional shape of the electron beam beam elliptical. In the present embodiment, the case where the number of grid electrodes constituting the electron focusing system 14 is four will be described, but this number is not limited to this and may be five or more.

  In FIG. 2, a cathode electrode 12 is an oxide or impregnated cathode, and includes a heater for heating, and emits thermoelectrons at a high temperature of 1000 K or more by heating of the heater. A voltage of several volts is applied to the heater from a heater heating power source described later. The cathode electrode 12 has a cylindrical shape with a bottom, a heater for heating is disposed inside the cylinder, and thermal electrons are emitted from an outer surface (hereinafter referred to as an electron emission surface) 12a of the bottom. The cathode electrode 12 is made of a heat-resistant metal material or an insulating material. The thermoelectrons emitted from the electron emission surface 12 of the cathode electrode 12 are focused by an electron lens formed by an electron focusing system 14 disposed on the left side of the electron emission surface 12 to form a thin beam of electron beams 28.

  The electron focusing system 14 includes four grid electrodes, that is, a first grid electrode (hereinafter abbreviated as G1 electrode) 20, a second grid electrode (hereinafter abbreviated as G2 electrode) 22, and a third grid electrode ( Hereinafter, it is composed of a fourth grid electrode (hereinafter abbreviated as G4 electrode) 26 and a fourth grid electrode (abbreviated as G3 electrode) 24. Each of the four grid electrodes 20, 22, 24, 26 has openings 20a, 22a, 24a, 26a through which the electron beam 28 passes in the center, and between the cathode electrode 12 and the target 30 of the rotating anode 3, the cathode From the electrode 12 side, the G1 electrode 20, the G2 electrode 22, the G3 electrode 24, and the G4 electrode 26 are arranged coaxially at appropriate intervals. The G1 electrode 20 and the G2 electrode 22 are plate-like bodies, and openings 20a and 22a having a small diameter are provided at the center thereof, and the whole is formed in a cup shape in consideration of mounting and the like. The G3 electrode 24 is provided with an opening 24a having a large diameter at the center thereof, and has a shape close to a cylindrical shape as a whole. As shown in FIG. 2 (b), the G4 electrode 26 is provided with an elliptical opening 26a at the center thereof, and has a generally cylindrical shape as a whole. The dimensions of the openings 20a, 22a, 24a, 26a of the G1 electrode 20, G2 electrode 22, G3 electrode 24, and G4 electrode 26 and the distance between them are the desired focal size and the voltage applied to each grid electrode, as will be described later. Determined in relation to As the material of the grid electrodes 20, 22, 24, 26, a heat resistant metal material is used.

  The four grid electrodes 20, 22, 24, and 26 of the electron focusing system 14 are insulated and supported by an electron focusing system insulator 18 disposed on the outside thereof. The electron focusing system insulator 18 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 20, 22, 24, 26 are supported by brazing or embedding the support fittings bonded to the outer periphery of the grid electrodes 20, 22, 24, 26 to the electron focusing insulator 18 (heating and welding). ) And combining. The cathode support 16 is insulated and supported by the G1 electrode 20, and is supported by the electron focusing insulator 18 via the G1 electrode 20. A connection fitting for connecting to the stem 19 is coupled to the end of the electron focusing insulator 18 on the stem 19 side. This connection fitting is a cylindrical fitting and is coupled to the electron focusing insulator 18 via the support fitting in the same manner as the grid electrodes 20, 22, 24, and 26.

  Next, details of the configuration and operation of the electron focusing system 14 of the present embodiment will be described with reference to FIGS. FIG. 3 schematically shows the configuration of the electron focusing system 14, which is the main part of the present embodiment. 2 and 3, the G1 electrode 20, the G2 electrode 22, the G3 electrode 24, and the G4 electrode 26 of the electron focusing system 14 are provided between the electron emission surface 12a of the cathode electrode 12 of the cathode 2 and the target 30 of the rotary anode 3. They are arranged sequentially on the same axis. The centers of the openings 20a, 22a, 24a, 26a of the grid electrodes 20, 22, 24, 26 through which the electron beam radiated from the cathode electrode 12 passes are made to coincide with the central axis of the electron focusing system 14. The openings 20a, 22a, 24a of the G1 electrode 20, G2 electrode 22, and G3 electrode 24 are circular, but the opening 26a of the G4 electrode 26 is elliptical. In addition, in order to narrow the electron beam 28 into a narrow beam near the cathode electrode 12, the apertures 20a and 22a of the G1 electrode 20 and the G2 electrode 22 have a small diameter of 1 mm or less, but the G3 electrode 24 and the G4 electrode 26 The apertures 24a and 26a have a large diameter of several millimeters because the emphasis is on electric field focusing.

  Further, as a voltage applied to each grid electrode 20, 22, 24, 26 of the electron focusing system 14, a voltage based on the potential of the cathode electrode 12 (hereinafter referred to as a cathode potential) is applied. The G1 electrode 20 has a positive potential of about several tens of volts with respect to the cathode potential (from 0 V to +100 V, hereinafter referred to as G1 potential), and the G2 electrode 22 has a positive potential of about several hundred volts with respect to the cathode potential (from 0 V). + 2,000V, hereinafter referred to as G2 potential), the G3 electrode 24 has a positive potential of about several hundred volts relative to the cathode potential (0V to + 500V, hereinafter referred to as G3 potential), and the G4 electrode 26 has a cathode potential. On the other hand, a negative potential of about several tens of volts (−10 V to −100 V, hereinafter referred to as G4 potential) is applied. Furthermore, an X-ray tube operating voltage (in this embodiment, about +10 kV to +150 kV with respect to the cathode potential, hereinafter referred to as an X-ray tube voltage) is applied to the target 30. Thus, by applying the grid voltage and the X-ray tube voltage to the grid electrodes 20, 22, 24, 26 and the target 30, the cathode lens 50 is located near the G1 electrode 20, and the prefocus lens 52 is located near the G2 electrode 22. However, the main lens 54 is formed near the G3 electrode 24, and the electron beam 28 emitted from the electron emission surface 12a of the cathode electrode 12 is focused. Further, the cross-sectional shape of the electron beam 28 is focused into an elliptical shape by the electric field generated in the elliptical opening 26a of the G4 electrode 26. That is, the electron beam 28 is focused into an elliptical cross-sectional shape by receiving a diverging action in the major axis direction of the ellipse of the elliptical opening 26a of the G4 electrode 26 and a focusing action in the minor axis direction. The value of the voltage applied to the grid electrodes 20, 22, 24, and 26 is controlled according to the desired focal size and the value of the current of the electron beam 28 (hereinafter also referred to as X-ray tube current).

  The electron focusing system of the X-ray tube according to the present invention is characterized in that an electron beam 28 having a beam cross-sectional shape of an ellipse is formed in order to obtain a microfocus having a substantially circular effective focus. Therefore, in this embodiment, a G4 electrode 26 having an elliptical opening 26a is added between the G3 electrode 24 and the target 30 of the rotating anode 3, and the G4 electrode 26 has a negative potential with respect to the cathode potential. By applying the G4 potential, the cross-sectional shape of the electron beam 28 is made elliptical. The contents and effects will be described below.

  FIG. 4 is a diagram for explaining the relationship between the cross-sectional shape of the beam of the electron beam 28 and the shape of the effective focus. In FIG. 4, an electron beam 28 having an elliptical beam cross-sectional shape 28a collides with the inclined surface 36 of the target 30 from the left direction indicated by arrow 28 to generate X-ray 5, but X-ray 5 is generated by arrow 6 It is taken out in the upward direction indicated by. An actual focal point 38 is formed on the inclined surface 36 of the target 30 with which the electron beam 28 has collided.The actual focal point 38 is taken out in the direction of taking out the X-ray 5 (the direction indicated by the arrow 6, hereinafter referred to as the X-ray main radiation direction). The effective focus 56 is seen from 6). Hereinafter, for the cross-sectional shape of the beam of the electron beam 28, the direction (vertical direction in the drawing) of the central axis 48 of the rotating anode 2 is referred to as the electron beam beam length direction, and the direction orthogonal thereto is referred to as the electron beam beam width direction For the effective focal point 56, the radial direction of the target 30 is referred to as the effective focal length direction, and the direction orthogonal thereto is referred to as the effective focal length direction, and for the real focal point 38, the direction along the inclined surface 36 of the target 30 is the actual focal length. The direction perpendicular to this direction is called the actual focal width direction. An angle 58 formed between the inclined surface 36 of the target 30 and the X-ray main radiation direction 6 is referred to as a target angle.

  The relationship between the cross-sectional shape of the beam of the electron beam 28 and the shape of the effective focal point 56 changes depending on the target angle 58. Similarly, the relationship between the cross-sectional shape of the beam of the electron beam 28 and the shape of the actual focal point 38 also changes depending on the target angle 58. In the example shown in the figure, the target angle 58 is 45 degrees or less and the shape of the effective focal point 56 is almost circular. In this case, the cross-sectional shape of the electron beam 28 is the electron beam beam length. The dimension in the direction (hereinafter referred to as the electron beam beam length dimension) is an ellipse that is larger than the dimension in the electron beam beam width direction (hereinafter referred to as the electron beam beam width dimension). At this time, the shape of the actual focal point 38 is also elliptical, but the actual focal width direction dimension, that is, the actual focal width dimension is substantially the same as the electron beam beam width dimension, whereas the actual focal length direction dimension, that is, the actual focal length dimension. The focal length dimension is larger than the electron beam beam length dimension. When the target angle 58 is 45 degrees, the cross-sectional shape of the beam of the electron beam 28 and the shape of the effective focal point 56 are substantially the same, but are different for other target angles 58. The electron beam width dimension and the effective focal width dimension are almost the same at any target angle 58, but the target angle 58 is less than 45 degrees between the electron beam beam length dimension and the effective focal length dimension. In this case, the electron beam beam length dimension is larger than the effective focal length dimension, and when the target angle 58 exceeds 45 degrees, the electron beam beam length dimension becomes smaller than the effective focal length dimension.

  In the case of a microfocus X-ray tube, an increase in the X-ray dose is required as the focal spot size is reduced, and this requires an increase in the X-ray tube load, that is, the X-ray tube current. In order to achieve the object, the target angle 58 is made smaller than 45 degrees so that the actual focal spot size is as large as possible even in the present embodiment even if the effective focal spot size is the same. As the target angle 58, an angle of about 10 to 30 degrees is usually selected. In order to increase the X-ray dose, the target angle 58 should be as small as possible. However, if the target angle 58 is too small, the X-ray irradiation range will be narrowed, causing problems in X-ray photography. Angle 58 is preferred. In consideration of the resolution of the X-ray image to be taken, it is desirable that the effective focal point 56 has a circular shape. Therefore, in the X-ray tube 1 of this embodiment, the shape of the actual focal point 38 and the beam of the electron beam 28 are used. The cross-sectional shape is an ellipse or a shape close thereto. Considering that the target angle 58 is 45 degrees or less, the cross-sectional shape of the beam of the electron beam 28 is preferably an ellipse whose electron beam beam length dimension is larger than the electron beam beam width dimension. In the X-ray tube 1 of the present embodiment, in order to make the cross-sectional shape of the beam of the electron beam 28 elliptical, a G4 electrode 26 is added to the electron focusing system 14 of the cathode 2, and the shape of the opening 26a of the G4 electrode 26 is changed. It is oval.

  In the X-ray tube of the present embodiment, the electron beam 28 is focused using the G1 electrode 20, the G2 electrode 22, and the G3 electrode 24 in the electron focusing system 14 of the cathode 2, and the cross-sectional shape of the beam is substantially circular. It is made minute. Further, in the G4 electrode 26, in consideration of the target angle 58, an elliptical aperture 26a is arranged to form an electron beam 28 having an elliptical cross-sectional shape suitable for the target angle 58, and the G4 electrode By applying a negative G4 potential with respect to the cathode potential to 26, the cross-sectional shape of the beam of the electron beam 28 is made elliptical.

  FIG. 5 shows an example of trajectory calculation of the electron beam 28 in the X-ray tube 1 of the present embodiment. In this example, a G4 potential of −20 V or less with respect to the cathode potential is applied to the G4 electrode 26. FIG. 5 shows an example of electron trajectory calculation in three planes including the central axis of the electron focusing system 14. This is because the aperture 26a of the G4 electrode 26 has an elliptical shape, and the electron focusing system 14 becomes non-axisymmetric as a whole, making it difficult to calculate the trajectory of the electron beam. The electron beam trajectory calculation is performed on the assumption that the dimensions of each part of the electron focusing system 14 are axisymmetrically distributed within the plane in each plane divided into three planes with different aperture sizes of 26a. It was. FIG. 5 (a) shows the relationship between the three planes A, B, C and the G4 electrode 26. The plane A is a cross section in the direction in which the diameter of the elliptical aperture 26a is long (electron beam beam length direction), The plane C is a cross section in the direction in which the diameter of the elliptical opening 26a is short (electron beam beam width direction), and the plane B is a cross section in the direction of an angle (45 degrees) between the plane A and the plane C. 5 (b) to 5 (d) illustrate examples of electron trajectory calculation results in three planes. FIG. 5 (b) corresponds to plane A, and FIG. 5 (c) corresponds to plane B. FIG. 5 (d) corresponds to the plane C. In each of FIGS. 5 (b) to 5 (d), the cathode electrode 12, the G1 electrode 20, the G2 electrode 22, the G3 electrode 24, the G4 electrode 26, and the target 30 are arranged in this order from the left side of the drawing. Other than that, it has the same structure and dimensions. As shown in FIG. 5 (a), only the G4 electrode 26 has a different diameter of the opening 26a. In FIG. 5 (b), the diameter of the opening 26a is large, and the openings are in the order of FIG. 5 (c) and FIG. 5 (d). The aperture of 26a is small. 5 (b) to 5 (d), the vertical thin line indicates the electron beam 28 and the thick line running in the horizontal direction on the equipotential line.

  5 (b) to (d), the beam width of the electron beam 28 on the inclined surface 36 of the target 30 corresponds to the size of the aperture 26a of the G4 electrode 26, and the aperture 26a has a large aperture. In the case of FIG. 5 (b), the beam width of the electron beam 28 is large, and in the case of FIG. 5 (d) where the aperture 26a is small, the beam width of the electron beam 28 is small. In the illustrated example, the diameter of the opening 26a of the G4 electrode 26 is changed within a range of about 5 mm to about 10 mm, whereas the beam width of the electron beam 28 is changed within a range of about 10 μm to about 100 μm, The rate of change is very large. From this result, the aperture 26a of the G4 electrode 26 corresponds to the target angle 58, the aperture in the electron beam beam width direction is made smaller, and the ellipse with the larger aperture in the electron beam beam length direction is made into an elliptical shape. The cross-sectional shape of the beam is focused into an appropriate ellipse, and the effective focal point 56 can be made substantially circular.

  In the above, in order to make the cross-sectional shape of the beam of the electron beam 28 elliptical, the shape of the opening 26 of the G4 electrode 26 is elliptical, but the shape of the opening 26 of the G4 electrode 26 is not limited to this, It may have another shape that approximates an ellipse. For example, by making the opening of the G4 electrode 26 the rectangular opening 26b shown in FIG. 6 or the elongated octagonal opening 26c, a potential distribution close to the potential distribution in the case of the elliptical opening 26a is formed in the vicinity of the G4 electrode 26. In these cases, the cross-sectional shape of the beam of the electron beam 28 can be substantially elliptical, and the object of the present invention can be achieved. At this time, the short diameter of the rectangular opening 26b or the octagonal opening 26c corresponds to the electron beam beam width direction, and each long diameter corresponds to the electron beam beam length direction.

  FIG. 7 shows a schematic configuration of an embodiment of the X-ray generator according to the present invention. This figure shows an example of the arrangement of main components of the X-ray generator 70 of the present embodiment. In FIG. 7, the microfocus X-ray tube 1 according to the present invention is stored in a storage container 72 of an X-ray generator 70. The storage container 72 is a rectangular parallelepiped casing made of a metal plate-like body, and a lead plate for X-ray prevention or the like is attached to a necessary portion of the inner surface. The shape of the housing may be another shape such as a cylindrical body. The X-ray tube 1 is fixed to the central portion of the storage container 72. Since the large-diameter portion 40 of the envelope 4 of the X-ray tube 1 is made of a metal material and has a ground potential, it is directly fixed to the upper wall surface of the storage container 72, and the anode end 35 of the rotary anode 3 is mainly made of an insulator. It is supported by a fixing member 74 and is fixed to the lower wall surface of the storage container 72. At this time, the X-ray emission window 46 of the X-ray tube 1 is sized and adjusted so as to be disposed directly or close to the upper wall surface of the storage container 72. It is located near the outer surface, and it becomes possible to increase the enlargement ratio at the time of enlargement photography. Further, the power feeding portion 76 of the cathode 2 of the X-ray tube 1 is disposed toward the left wall surface of the storage container 72.

A high voltage generating circuit 78 is insulated and supported on the right wall surface of the storage container 72, and a heater power supply circuit 82 for heating the grid voltage generating circuit 80 and the cathode electrode 12 is insulated and supported on the left wall surface. A stator 84 for rotating the rotating anode is disposed on the outer periphery of the X-ray tube 1 on the anode side. The inside of the storage container 72 is filled with insulating oil 86 to insulate each component. For this insulation, in addition to the insulating oil 86, other liquid insulators or gaseous insulators such as sulfur hexafluoride (SF ₆ ) may be used. Further, since the insulating oil 86 is heated by the X-ray tube 1 or the like, a buffer mechanism (not shown) such as a bellows is attached to the storage container 72 in order to buffer expansion and contraction of the insulating oil 86. .

  A negative high voltage potential and a positive high voltage potential are fed from a high voltage generation circuit 78 to a power feeding portion 76 of the cathode 2 of the X-ray tube 1 and an anode end 35 of the rotary anode 3 through lead wires (not shown). ing. In addition, four grid potentials, that is, G1, G2, G3, and G4 potentials, and heater heating voltage are supplied from the grid voltage generation circuit 80 and the heater power supply circuit 82 to the power feeding unit 76 of the cathode 2 of the X-ray tube 1. Power is supplied through the lead wire. These voltages are led to the electron focusing system 14 of the cathode 2 of the X-ray tube 1 through the introduction line of the stem 19 of the cathode 2, and the G1 electrode 20, G2 electrode 22, G3 electrode 24, G4 electrode 26 and Supplied to the cathode electrode 12.

  Next, a high voltage generation circuit, a grid voltage generation circuit, and a heater power supply circuit will be described with reference to FIGS. FIG. 8 shows an example of a high voltage generation circuit. The illustrated high voltage generation circuit 78 includes a high voltage control unit 88 and a high voltage generation unit 90. The high voltage control unit 88 includes an input power supply, a high voltage setting unit, a high voltage detection unit, a high voltage comparison determination unit, and the like. The high voltage generator 90 includes a transformer 92, a booster circuit 94, and the like.

  In the high voltage control unit 88, the value of the high voltage (X-ray tube voltage) applied to the X-ray tube 1 is set by the high voltage setting unit, and the transformation of the high voltage generation circuit 78 is performed based on this X-ray tube voltage setting value. The input voltage to the device 92 is controlled. As shown in FIG. 8, the input voltage to the transformer 92 is generated by an input power supply unit 102 including an AC power supply 96, a rectifier circuit 98, and an inverter circuit 100. The input power supply unit 102 is controlled by the control circuit 104. The high voltage control unit 88 divides and measures the high voltage generated by the high voltage generation circuit 78 in the high voltage detection unit with a resistance voltage divider, and outputs the result as an actual measurement value to the high voltage comparison determination unit. Compare the high voltage set value with the actual high voltage value to determine the presence or absence of a difference. If there is a difference, one of the transformers 92 is connected via the high voltage setting unit so that the two match. The voltage applied to the next side (the output voltage of the input power supply unit 102) is controlled.

The input power supply unit 102 of the high voltage control unit 88 generates an input voltage to the primary side of the transformer 92. This input voltage is an inverter circuit after the output AC voltage of the AC power supply 96 is rectified by the rectifier circuit 98. 100 is converted to a pulse voltage of high frequency (for example, about 25 kHz). Here, the inverter circuit 100 is subjected to pulse width modulation (PWM) control (hereinafter abbreviated as PWM control) by the control circuit 104. Hereinafter, the control circuit 104 is also referred to as a PWM circuit. When increasing the secondary side voltage (E ₂ ) of the transformer 92, the PWM circuit 104 increases the pulse width of the inverter circuit 100 to increase the average current flowing in the primary side coil of the transformer 92. Increase the secondary voltage (E ₁ ). On the contrary, when the secondary side voltage (E ₂ ) is lowered, the PWM circuit 104 reduces the pulse width of the inverter circuit 100 to reduce the average current flowing in the primary side coil of the transformer 92, thereby reducing the primary side voltage. Reduce the voltage (E ₁ ).

  As the booster circuit 94 of the high voltage generator 90, a Cockcroft-Walton circuit type voltage doubler circuit (hereinafter abbreviated as "cockcroft circuit") 94 composed of a combination of a capacitor and a diode is employed. Various values can be taken as the value of the high voltage generated by the high voltage generating circuit 78, but in the present embodiment, the maximum value of the X-ray tube voltage applied to the X-ray tube 1 is set to 150 kV, and the value on the anode side It uses a medieval point grounding system that applies a voltage of + 75kV and -75kV to the cathode side.

  In the illustrated example, the cock croft circuit 94 includes an anode side cock croft circuit 94a and a cathode side cock croft circuit 94b, both of which are configured by a combination of four capacitors and four diodes. The maximum voltage generated by a pair of capacitors and diodes is approximately 18.75 kV. It goes without saying that the number of sets of capacitors and diodes in the cockcroft circuit 94 is not limited to the above, but may be increased or decreased.

  In the cockcroft circuit 94, when the output voltage on the secondary side of the transformer 92 is Vm, the voltage values at the nodes of the anode side cockcroft circuit 94a and the cathode side cockcroft circuit 94a of the cockcroft circuit 94 are Vm, 2Vm, 3Vm, ... and increase. However, the negative sign is negative in the cathode side cockcroft circuit 94b. Here, the maximum voltage value is +4 Vm on the anode side, whereas it is −4 Vm on the cathode side, so that the X-ray tube voltage is +8 Vm.

As the transformer 92 of the high voltage generator 90, a transformer having a large turn ratio is usually used. When the turns ratio of the primary side and the secondary side of the transformer 92 is set to 1: 100, for example, when the maximum value of the X-ray tube voltage output from the cockcroft circuit 94 is 150 kV, the secondary side voltage (E _Since the maximum value of ₂ ) is 18.75 kV as described above, it is necessary to generate only 187.5 V as the maximum value of the primary side voltage (E ₁ ).

  FIG. 9 shows an example of a grid voltage generation circuit 80 and a heater power supply circuit 82 that constitute the X-ray generation device 70 of the present embodiment. In FIG. 9, the grid voltage generation circuit 80 generates four grid potentials to be supplied to the four grid electrodes of the electron focusing system 14 of the cathode 2, and the heater power supply circuit 82 raises the cathode electrode 12 of the cathode 2. A heater heating voltage for heating the heater 110 used for temperature is generated. The grid voltage generation circuit 80 is supplied to the G1 potential generation circuit 112 that generates the G1 potential supplied to the G1 electrode 20, the G2 potential generation circuit 114 that generates the G2 potential supplied to the G2 electrode 22, and the G3 electrode 24 A G3 potential generation circuit 116 that generates the G3 potential and a G4 potential generation circuit 118 that generates the G4 potential supplied to the G4 electrode 26 are included.

  In FIG. 9, the heater power supply circuit 82, the G1 potential generation circuit 112, the G2 potential generation circuit 114, the G3 potential generation circuit 116, and the G4 potential generation circuit 118 are composed of substantially the same components. The heater power supply circuit 82 will be taken up and its configuration will be described. The heater power supply circuit 82 includes an AC power supply 120, a voltage regulator 122, an insulation transformer 124, a rectifier 126, a capacitor 128, and the like. In the heater power supply circuit 82, the AC voltage from the AC power supply 120 is adjusted to the required input voltage value as the heater heating voltage by the voltage regulator 122, and the high voltage is insulated from the low potential primary side by the isolation transformer 124. The voltage is output as a secondary voltage, and is a heater heating voltage rectified by the rectifier 126 and the capacitor 128. In general, a voltage of several volts is used as the heater heating voltage in this embodiment. In the G1 potential generation circuit 112, the G2 potential generation circuit 114, the G3 potential generation circuit 116, and the G4 potential generation circuit 118, the G1 potential, the G2, the G3 potential, and the G4 potential are generated as in the case of the heater heating power supply 82. The The grid potential differs from the heater heating voltage in that the voltage value is higher than the heater heating voltage and the polarity is also negative. For these points, it is sufficient to change the specifications of the constituent elements or change the polarity of the wiring.

  In the example of FIG. 9, the case where the number of grid electrodes of the cathode 2 is four has been described. However, when the number of grid electrodes of the cathode 2 is five or more or three or less, the grid voltage of FIG. In the generation circuit, the number of grid potential generation circuits may be increased or decreased corresponding to the number of grid electrodes.

  The X-ray apparatus according to the present invention includes an X-ray generator 70 that includes the microfocus X-ray tube 1 according to the present invention, a support plate on which the subject is placed, and an X-ray that detects X-rays that have passed through the subject. X-ray detector, X-ray generator 70, housing for subject, X-ray detector, etc., controller for controlling the position of X-ray generator 70, support plate and X-ray detector, etc. Consists of Since this X-ray apparatus includes the microfocus X-ray tube 1 as an internal X-ray tube, when used for nondestructive inspection, it is suitable for precise inspection of a subject by magnified imaging. FIG. 10 shows an example of a layout diagram in enlarged photographing by the X-ray apparatus of the present embodiment. In FIG. 10, the X-ray tube 1, the subject 140, and the X-ray detector 142 housed in the X-ray generator 70 are arranged in the X-ray main radiation direction (vertical direction in the drawing) 6. The subject 140 is supported by a support plate 144 made of a material having good X-ray transparency. X-rays 5 radiated from the focal point 38 formed on the target 30 of the X-ray tube 1 are transmitted through the subject 140 and then received by the light receiving surface 146 of the X-ray detector 142. On the light receiving surface 146, the X-ray 5 is converted into an image signal, and an enlarged photographed image of the subject 140 is obtained.

  When the distance from the focal point 38 of the X-ray tube 1 to the subject 140 is A, and the distance from the subject 140 to the light receiving surface 146 of the X-ray detector 142 is B, the geometric enlargement of the captured image of the subject 140 The rate M is (A + B) / A. In the present invention, as described above, since the X-ray tube 1 is of the neutral point grounding system, the distance between the focal point 38 of the X-ray tube 1 and the X-ray radiation window 46 of the envelope 4 is significantly shortened. Therefore, the distance between the focal point 38 and the subject 140 can be significantly reduced as compared with the conventional case. As a result, the geometric magnification ratio M of the photographed image can be increased as compared with the prior art, and a fine inspection of the subject 140 can be performed accurately.

  Also, in the microfocus X-ray tube 1 of the present invention, the cross-sectional shape of the electron beam beam is made almost elliptical, so that a substantially circular effective focus can be obtained and the length of the actual focus is increased. As a result, an effective focus with an unbiased resolution was obtained in all directions of the captured image, and the X-ray dose could be increased. As a result, in the above-described magnified photographing, a photographed image with no bias in resolution depending on the direction can be obtained, and magnified photographing with a higher magnification ratio can be performed.

1 is an overall structural diagram of an embodiment of a microfocus X-ray tube according to the present invention. FIG. 2 is a diagram showing the structure of the main part of the cathode in FIG. FIG. 2 is a diagram for explaining the operation of the cathode of FIG. The figure for demonstrating the relationship between the cross-sectional shape of an electron beam, and the shape of an effective focus. An example of electron beam trajectory calculation in the X-ray tube of the present embodiment. Another example of G4 electrode opening. The example of arrangement | positioning of the main components of the X-ray generator which concerns on this invention. An example of a high voltage generation circuit. An example of a grid voltage generation circuit and a heater power supply circuit. An example of the layout in the expansion imaging | photography with the X-ray apparatus which concerns on this invention. The figure which shows schematic structure of the most basic in-line type electron gun in the electron gun for CRT. An example of a cathode structure of a conventional microfocus X-ray tube.

Explanation of symbols

1 ... Microfocus X-ray tube (X-ray tube)
2 ... Cathode
3 ... Anode (rotary anode)
4 ... Envelope
5 ... X-ray
12 ... Cathode electrode
12a ・ ・ ・ Electron beam emitting surface
14 ... Electron focusing system
16 ... Cathode support
18 ... Electronic focusing insulator
19 ... Stem
20 ... 1st grid electrode (G1 electrode)
20a ・ ・ ・ G1 electrode opening
22 ・ ・ ・ Second grid electrode (G2 electrode)
22a ・ ・ ・ G2 electrode opening
24 ・ ・ ・ 3rd grid electrode (G3 electrode)
24a ・ ・ ・ G3 electrode opening
26 ・ ・ ・ 4th grid electrode (G4 electrode)
26a, 26b, 26c ・ ・ ・ G4 electrode opening
28 ... Electron beam
30 ・ ・ ・ Target
36 ... Inclined surface
38 ・ ・ ・ Focus (actual focus)
40 ... large diameter part
42 ... Anode insulation
44 ・ ・ ・ Cathode insulation
46 ・ ・ ・ X-ray emission window
48 ・ ・ ・ Center axis of rotating anode
50 ... Cathode lens
52 ・ ・ ・ Prefocus lens
54 ... Main lens
56: Effective focus
58 ・ ・ ・ Target angle
70 ・ ・ ・ X-ray generator
72 ・ ・ ・ Storage container
78 ・ ・ ・ High voltage generator
80 ・ ・ ・ Grid voltage generator
82 ... Heater power circuit
88 ・ ・ ・ High voltage controller
90 ・ ・ ・ High voltage generator
92 ... Transformer
94 ... Booster circuit (cockcroft circuit)
94a ・ ・ ・ Anode-side cockcroft circuit
94b: Cathode side cockcroft circuit
96 ・ ・ ・ AC power supply
98 ... Rectifier circuit
100 ・ ・ ・ Inverter circuit
102 ... Input power supply
104 ... Control circuit (PWM circuit)

Claims (3)

  A cathode having a cathode electrode that emits an electron beam, a plurality of grid electrodes arranged in the path of the electron beam to focus the electron beam into a narrow beam, and a target that generates X-rays by collision of the electron beam And an envelope having an X-ray emission window that seals the cathode and the anode in a vacuum-tight manner and radiates X-rays generated at the target to the outside. In a microfocus X-ray tube that has an aperture for passing light and obtains a micro focus by applying a grid potential based on a cathode electrode to each grid electrode, at least one grid of the grid electrodes The shape of the opening of the electrode is an ellipse or a shape that approximates an ellipse, and the cross-sectional shape of the beam of the electron beam is approximately an ellipse. Carcass X-ray tube.   A microfocus X-ray tube having a micro focus (hereinafter abbreviated as X-ray tube), a high voltage generating circuit for supplying a high voltage between the cathode and anode of the X-ray tube, and a plurality of cathodes of the X-ray tube A grid voltage generation circuit for supplying a grid voltage to each grid electrode, an electrode insulation support for insulating and supporting the electrodes of the X-ray tube, an X-ray tube, a high voltage generation circuit, a grid voltage generation circuit, and an electrode insulation support Enclosed and supporting housing, filled in the housing, immersed in the X-ray tube and other components, insulated, and attached to the housing to buffer the expansion and contraction of the insulating medium 2. An X-ray generator including a buffer mechanism, wherein the X-ray tube is the microfocus X-ray tube according to claim 1.   An X-ray generator that generates X-rays, an X-ray detector that detects X-rays generated from the X-ray generator and transmitted through the subject, and a signal corresponding to the detected X-ray dose output from the X-ray detector An X-ray apparatus having an image forming apparatus that creates an X-ray image of a subject based on the above, and an X-ray generation apparatus, an X-ray detection apparatus, and a control device that controls the image forming apparatus. An X-ray apparatus according to 2, wherein the X-ray generator is described above.

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