JP2002313267A - Plasma x-ray tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma X-ray tube that is used for a plasma X-ray generating device and that has no unevenness of dosage, has high strength and good excitation of discharge, and can be used repeatedly. SOLUTION: The plasma X-ray tube has a pair of cathodes of a bar-shape 2 and a ring-shape cathode 3 having an inside diameter larger than the outside diameter of the pair of cathodes of bar-shape 2, and by making the axis of the pair of cathodes of bar-shape 2 and the ring shape cathode 3 coincide, and arranging them at a prescribed interval, X-rays are extracted from the opening part 6 of the ring-shape cathode 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma X-ray tube of a plasma X-ray generator for generating X-rays from plasma formed by evaporating an anti-cathode material by high voltage discharge.

[0002]

2. Description of the Related Art In recent years, flash X-ray photography has been used for observing a fast moving object inside the object. For example, the dynamic function of the heart is to mix X-ray contrast agents into the blood,
The morphology of the heart at a particular moment can be diagnosed by radiography. An X-ray source for such an application requires a high-energy, high-intensity monochromatic X-ray source. Thus, high-intensity monochromatic X-rays are expected in various medical applications, but there are only sources such as X-ray lasers and synchrotron radiation, and there is no X-ray source that can be used easily anywhere. .

[0003] Laser means amplification of light by stimulated emission light. To obtain X-rays based on the principle of laser, a method using linear irradiation of a high-energy pulse laser is generally used. However, it is difficult in principle to output a laser having a photon energy of 10 keV or more. Although different from a laser, high-intensity monochromatic X-rays are obtained by a synchrotron. However, it is difficult to obtain monochromatic X-rays having a photon energy of about 100 keV, and a sufficient machine time cannot be obtained. Thus, the synchrotron is a very useful source in basic research in the fields of medicine and engineering, but it is difficult to easily use it as a general-purpose source in medicine.

In such a situation, the present inventors have already proposed an X-ray generation method using a plasma X-ray generation source capable of easily generating high-energy, high-intensity, and monochromatic X-rays. (SPIE Conf (44t
h) '99 .7.19). According to this method, a target cathode material is evaporated by high-voltage discharge or the like to generate plasma composed of the cathode material, and bremsstrahlung X-rays generated by collision with the plasma are absorbed by the cathode material in the plasma. Thus, characteristic X-rays are generated.

According to this method, bremsstrahlung X-rays generated by the collision of electrons emitted from the cold cathode with the plasma are used for generating characteristic X-rays. Therefore, the discharge voltage of the high-voltage discharge is increased. , The bremsstrahlung X-ray has the characteristic X
The energy required to produce the lines can be increased. Therefore, characteristic X-rays that are quasi-monochromatic X-rays can be easily generated. Further, since the plasma density is high due to the high magnetic field generated by the high-density current, characteristic X-rays can be generated with high efficiency.
In addition, the X-rays extracted in the major axis direction of the plasma have a large stimulated emission effect due to a long propagation distance in the plasma, and the intensity of the characteristic X-rays increases. Therefore, high-intensity characteristic X-rays can be extracted without using a monochromatic filter. The plasma X-ray generator having such a configuration is expected to be put to practical use as a high-energy, high-intensity quasi-monochromatic X-ray source that has a simple configuration and can be used easily.

Hereinafter, a plasma X-ray generator having the above-described configuration will be described with reference to FIG. FIG. 5 is a diagram showing the principle of the plasma X-ray generator. The X-ray generator 50 includes a high-voltage power supply 51 and a high-voltage condenser 52 having a capacity of about 200 nF.
, A vacuum pump 53, a trigger pulse power supply 54 for starting discharge, and a plasma X-ray tube 55.
The current path of the X-ray generator 50 is designed as a low impedance coaxial transmission path in order to increase the current density. The high-voltage capacitor 52 can be charged up to about 100 kV. When the electric charge accumulated in the high-voltage capacitor 52 causes discharge at the cathode, it is discharged to the plasma X-ray tube 55,
X-rays 62 are generated by the plasma X-ray tube 55. Plasma X
The wire tube 55 includes a rod-shaped cathode 56 having a trigger electrode,
And a bar or plate-shaped counter electrode (target) 57 made of a specific substance. The counter cathode 57 is fixed to a stainless steel vacuum vessel 59 via an insulating member 58. The vacuum vessel 59 is provided with an X-ray window 60 made of polyethylene terephthalate, and a piping 61 for evacuation on the side wall. During operation, the vacuum vessel 59 is connected to a vacuum pump to maintain a degree of vacuum of about 1 mPa.

To operate the X-ray generator 50,
A high-voltage power supply 51 causes a high-voltage capacitor 52 to have a predetermined high-voltage V
And the trigger pulse power supply 54 applies a trigger pulse to the trigger electrode to cause discharge. When the discharge starts, electrons are extracted from the cathode 56 and accelerated,
It collides with the anti-cathode 57 with kinetic energy of eV. At this time, since the electron current density and energy are extremely high,
Since the anti-cathode material evaporates instantaneously and a high magnetic field is generated around the current, a very high density plasma 62 composed of ions and electrons of the anti-cathode material is formed. The subsequently arriving electrons collide with the high-density plasma 62 and emit braking X-rays. The high voltage V is made sufficiently high to give sufficient energy to the electrons to generate a braking X-ray having energy equal to or higher than the K absorption edge of the anti-cathode material. The braking X-rays are the K
It excites shell electrons and is absorbed. Electrons from other shells transit to the vacant space created in the K shell to generate characteristic X-rays such as Kα and Kβ.

The intensity of characteristic X-rays propagating in the plasma 62 gradually increases due to stimulated emission. In addition, the damping X-rays having energy equal to or lower than the K absorption edge propagating in the plasma 62 are absorbed by the transition between the electron levels of the ionized target material in the plasma, so that the intensity thereof is gradually reduced.

FIG. 6 shows the X-rays in the axial direction (longitudinal direction) and the transverse direction (transverse direction) of the plasma generated when a plate-shaped negative electrode is used in this plasma X-ray generator. FIG. 3 schematically shows actual measured values of a spectrum. FIG. In FIG. 6, (a) is an X-ray spectrum taken in the axial direction and (b) is an X-ray spectrum taken in the transverse direction. The horizontal axis of (a) and (b) shows the energy of the X-ray photon, the vertical axis shows the X-ray intensity, and the two line spectra show the characteristic X-ray K
α and Kβ. As shown in FIG. 6, the X-ray spectrum in the axial direction 71 has a larger characteristic X-ray intensity than the transverse direction 72 and has a continuous spectrum distribution.
There are few line components. From this, it is understood that if X-rays emitted in the axial direction 71 are used, it can be used as a monochromatic X-ray source without using a monochromatic filter.

FIG. 7 is an example of an X-ray photograph using X-rays of a plasma X-ray generator using nickel as a material for a bar-shaped anti-cathode. Nickel is used as a rod-shaped cathode material, and the high-voltage capacitor 52 is charged at a voltage of 50 kV.
A subject composed of methacrylate was photographed. The subject made of polymethyl methacrylate is formed by concentrically stacking a plurality of five disks of the same thickness (5 mm) whose diameter increases by a constant length. Polymethyl methacrylate absorbs the Kα and Kβ characteristic X-rays of nickel,
X-rays of other wavelengths are transmitted. FIG. 7A is a photograph taken without using a monochromatic filter, and FIG. 7B is an X-ray photograph taken through a nickel monochromatic filter. As is clear from FIGS. 7A and 7B, a contrast image depending on the thickness of polymethyl methacrylate is obtained, and it is understood that a radiograph by monochromatic X-rays can be obtained without using a monochromatic filter. . That is, X generated by the plasma X-ray generator
It can be seen that the line is sufficiently monochromatic.

FIG. 8 is an X-ray photograph of the same subject as in FIG. 7 using nickel as a plate-shaped anti-cathode material. As is clear from FIGS. 8A and 8B, it is understood that the X-rays generated by the plasma X-ray generator are sufficiently monochromatic even when a plate-shaped counter cathode is used.

FIG. 9 is an example of a radiograph by a conventional solid target X-ray tube. Conventional solid target X
The wire tube has a filament on a cathode, emits thermoelectrons by heating the filament, and collides the thermoelectrons with a cooled solid target to generate X-rays. A voltage of 50 kV was continuously applied to the nickel target, and irradiation was performed for a long time to take an image. As is clear from FIGS. 9A and 9B, a contrast image depending on the thickness of the polymethyl methacrylate cannot be obtained without the monochromatic filter, and the X-rays from the conventional solid target X-ray tube have the characteristic X.
It can be seen that a large amount of braking X-rays having a continuous spectral distribution are emitted in addition to the lines. Thus, the plasma X
Since the X-ray generator can easily generate extremely high-intensity quasi-characteristic X-rays, it is expected as a general-purpose X-ray source for high-intensity quasi-characteristic X-rays.

[0013]

However, there is a problem to be solved for use as a general-purpose radiation source in the medical field. First, the shading differs depending on the position on the radiographs of FIGS. 7 and 8. That is, this plasma X
X-rays generated by the X-ray generator have a spatially uneven dose.
For medical applications, it is necessary to eliminate dose unevenness. Secondly, a plasma X-ray generator having a higher intensity is desirable in order to further expand the field of application. Third, it is desirable to make it easier to cause discharge and to reduce the safety and cost of the device. Fourth, a cathode made of metal or the like is deformed when used repeatedly, and has a short life.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a plasma X-ray tube which is used in a plasma X-ray generator, has a uniform dose, is high in intensity, easily causes discharge, and can be used repeatedly. And

[0015]

In order to solve the above-mentioned problems, a plasma X-ray tube according to the present invention generates a plasma made of an anti-cathode material by evaporating an anti-cathode by high voltage discharge.
In a plasma X-ray tube used in a plasma X-ray generator that generates characteristic X-rays by absorbing bremsstrahlung X-rays generated by colliding with the plasma by an anti-cathode substance in the plasma,
A bar-shaped counter-cathode and an annular cathode having an inner diameter larger than the outer diameter of the bar-shaped counter-cathode, wherein the rod-shaped counter-cathode and the annular cathode are arranged so that their axes coincide with each other and are separated by a predetermined distance; X-rays are extracted from the openings. According to this configuration, since there is no cathode for extinguishing the plasma in the X-ray extraction direction, the length of the plasma in the cathode direction is longer than in the case where discharge is performed using a rod-shaped cathode. Therefore, the propagation distance of the extracted X-rays in the plasma becomes longer,
Since the stimulated emission effect is increased, the intensity of the quasi-monochromatic X-ray is increased, and the monochromaticity of the extracted X-ray is increased because the absorption effect of the bremsstrahlung X-ray is increased. Furthermore, since the inner diameter is larger than the outer diameter of the counter electrode, the stability of the plasma is increased, and the variation in the spatial dose of the extracted X-rays is reduced.

The annular electrode has a shape in which the inner and outer diameters of the annular electrode continuously increase from the side facing the negative electrode to the side not facing the negative electrode. Further, the invention is characterized in that the trigger electrode is arranged inside the annular electrode close to the inner wall of the annular electrode and along the inner wall of the annular electrode. The material of the annular electrode is carbon graphite. According to this configuration, since the outer diameter has a shape that continuously increases from the side facing the negative electrode to the side not facing the negative electrode, the plasma is further stabilized, and the spatial dose of the extracted X-rays varies. Is reduced. In addition, the trigger electrode does not block the X-rays to be extracted, so that the spatial dose of the X-rays does not vary. If carbon graphite is used for the material of the ring electrode, since carbon graphite is a high melting point and highly conductive crystal,
The annular electrode can be used repeatedly without being deformed by the high-density current at the time of discharge.

Further, the annular electrode is formed by fitting a plurality of annular electrodes having different diameters and materials so that the diameter increases in order from the side facing the negative electrode to the side not facing the negative electrode, and The outer shape of the annular electrode is characterized by a shape that continuously increases from the side facing the negative electrode to the side not facing the negative electrode. Further, the material of the annular electrode facing the counter electrode is carbon graphite. Further, the inner diameter of the annular electrode made of carbon graphite facing the opposite electrode is characterized in that the inner diameter increases from the side facing the opposite electrode to the side not facing the opposite electrode. Further, the trigger electrode is provided in a pore provided through the side wall of the annular electrode facing the counter electrode. According to this configuration, the spatial dose variation is small,
High-intensity characteristic X-rays can be obtained, and the cost of the plasma X-ray tube can be reduced.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram schematically showing a configuration of a plasma X-ray tube of the present invention. In the figure, a plasma X-ray tube 1 has a rod-shaped counter cathode 2 and a rod-shaped counter cathode 2.
And an annular cathode 3 having an inner diameter larger than the outer diameter of the rod-shaped counter-cathode 2 and the annular cathode 3, the axes 4, 4 'of the rod-shaped counter-cathode 2 and the annular cathode 3 are aligned, and The X-rays 5 are arranged apart from each other by a predetermined distance d, and are taken out of the opening 6 of the annular cathode 3 in the direction of the axis 4. The annular electrode 3 has a shape in which the inner diameter a and the outer diameter b continuously increase from the side facing the negative electrode 2 toward the side not facing the negative electrode 2. The discharge trigger electrode 7 is disposed inside the annular electrode 3 close to and along the inner wall 8 of the annular electrode 3, and the other discharge trigger electrode 9 is provided at one end of the annular electrode 3. It is connected. Also,
The material of the annular electrode 3 is carbon graphite.
Other members constituting the plasma X-ray tube, such as a vacuum vessel, an X-ray window, and a vacuum pipe, are the same as those in FIG.

The plasma X-ray tube having the above configuration operates as follows. When a trigger voltage is applied between the trigger electrodes 7 and 9, a high electric field is generated between the trigger electrode 7 and the inner wall 8 of the annular electrode 3, and the gas near the trigger electrode 8 is ionized. Triggered by the ionization, all the gas in the plasma X-ray tube is ionized, and electrons from the annular electrode 3 are accelerated by the voltage V applied to the high-voltage capacitor, and collide with the counter electrode 2. Since the energy and current density of the electrons are sufficiently high, the atoms forming the counter cathode 2 are instantaneously evaporated, and the plasma 10 is formed from the ions of the atoms forming the counter cathode 2 and the ionized electrons. As shown in FIG. 1, since the cathode of the present invention is an annular electrode 3, there is no low-temperature heat source for extinguishing the plasma 10 in the X-ray extraction direction 4, and therefore, compared to a conventional plasma using a rod-shaped cathode, The plasma 10 becomes longer in the direction of the axis 4. Further, since the inner diameter a of the annular cathode 3 is larger than the outer diameter of the rod-shaped counter-cathode 2, a current component near the annular cathode 3 includes a component perpendicular to the axis 4, and the magnetic field generated by this current component causes Directional Lorentz force is generated, and the plasma 10 becomes longer in the direction of the axis 4.

Since the plasma 10 extends in the direction of the axis 4 in this manner, the propagation distance of the extracted X-rays 5 in the plasma 10 is increased, and the stimulated emission effect is increased.
The monochromaticity of the extracted X-rays increases because the intensity of the rays increases and the effect of absorbing the bremsstrahlung X-rays increases. Furthermore, since the inner diameter a of the annular cathode 3 is larger than the outer diameter of the bar-shaped anti-cathode 2, the outer diameter b of the annular electrode 3 moves from the side facing the anti-cathode 2 to the side not facing the anti-cathode 2. Since it has a shape that increases continuously, the stability of the plasma 10 increases, and the spatial dose variation of the extracted X-rays decreases. In addition, since the discharge trigger electrode 7 is disposed inside the annular electrode 3 in the vicinity of the inner wall 8 of the annular electrode 3 and along the inner wall 8, the electric field strength is further increased, and the discharge trigger electrode 7 is provided at a lower applied voltage. Discharge can be caused. Trigger electrode 7
However, since the X-rays 5 to be extracted are not blocked, the spatial dose variation is reduced.

Next, a first embodiment will be described. FIG.
FIG. 2 is a diagram comparing the X-ray intensity, dose unevenness, and ease of trigger of the plasma X-ray tube of the present invention with those of a conventional plasma X-ray tube.
In FIG. 2, (a) is a conventional plasma X-ray tube comprising a plate-shaped negative electrode and a rod-shaped metal cathode, and (b) is a conventional plasma X-ray tube comprising a rod-shaped negative electrode and a rod-shaped metal cathode. (C) is a plasma X-ray tube of the present invention. The measurement was performed using the same plasma X-ray apparatus and the same charging voltage 5.
The test was performed at 0 kV. Nickel was used as the anti-cathode material. The trigger electrode of the conventional plasma X-ray tube is
The conductor is inserted through an insulating tube, and the insulating tube is inserted through a hole drilled at the center of the rod-shaped cathode. The conductor-exposed portion for inducing discharge is arranged in the plane of the rod-shaped cathode facing the opposite cathode. Has been established. As shown in the figure, the plasma X-ray tube (c) of the present invention
The X-ray intensity of the conventional plasma X-ray tube (b) consisting of a bar-shaped negative electrode and a rod-shaped cathode is 6 times that of the conventional plasma X-ray tube (a) consisting of a plate-shaped negative electrode and a rod-shaped cathode. It has twice the intensity of X-rays as compared. Further, the trigger voltage for inducing the discharge is reduced to less than half as compared with the conventional example using the metal cathode of (a) and (b).

FIG. 3 is a radiograph showing the uniformity of the spatial dose of the plasma X-ray tube of the present invention. In the radiography, nickel is used as the material of the bar-shaped counter cathode 2 of the plasma X-ray tube according to the present invention, similarly to the description in FIG.
The high voltage capacitor is charged with a voltage of 50 kV, and the plasma X
A subject made of polymethyl methacrylate was photographed at a distance of 1.2 m from the tube. The subject made of polymethyl methacrylate is formed by concentrically stacking a plurality of five disks of the same thickness (5 mm) whose diameter increases by a constant length. Polymethyl methacrylate is
Absorbs the Kα and Kβ characteristic X-rays of nickel, and
Lines are transparent. As is clear from FIG. 3, the dose variation of the plasma X-ray tube of the present invention was hardly recognized, and FIG.
It can be seen that the spatial uniformity of the dose is significantly higher than that of the conventional example shown in FIG.

Next, a second embodiment will be described. FIG. 4 is a sectional view showing the configuration of the second embodiment. In FIG.
The annular electrode 3 is formed by fitting a first annular electrode 11 made of carbon graphite to a second annular electrode 12 made of brass, and connecting the fitted first and second annular electrodes to a third ring made of stainless steel. It is formed by fitting to the annular electrode 13. Further, the outer diameter of the first annular electrode 11 and the second annular electrode 12 made of brass is formed so that the diameter increases sequentially from the side facing the negative electrode 2 to the side not facing the negative electrode. I have. Further, the trigger electrode 7 is disposed via a ceramic tube 14 in a fine hole provided through the side wall of the annular electrode 3 facing the counter electrode. Carbon graphite can be easily processed by cutting, but cannot be fused with other substances. For this reason, it is difficult to fix the ring electrode made of carbon graphite alone to a vacuum vessel made of stainless steel, and the cost increases. According to this configuration, the annular electrode 11 made of carbon graphite can be fitted and fixed to the second annular electrode 12 made of brass,
The second annular electrode 12 can be fitted and fixed to the third annular electrode 13 made of stainless steel, and the third annular electrode 13 made of stainless steel is easily fused and fixed to a vacuum container made of stainless steel. it can. Therefore, the cost can be reduced.

In the above description, the counter electrode made of nickel has been described as an example. However, it is of course possible to use another substance as the counter electrode material. In particular, a material having a large atomic number is used as the counter electrode material. It is clear that a discharge at an appropriate high pressure results in a higher energy characteristic X-ray source.

[0025]

As can be understood from the above description, according to the present invention, it is possible to provide a plasma X-ray tube which is free from unevenness in dose, has a high intensity, easily causes discharge, and can be used repeatedly. . Therefore, it can be used as a plasma X-ray tube of a plasma X-ray generator that can easily be used and generates high-energy, high-intensity quasi-monochromatic X-rays. Thus, the present invention is extremely useful when used in the medical field where high intensity monochromatic X-rays are required.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a plasma X-ray tube of the present invention.

FIG. 2 is a diagram comparing the X-ray intensity, dose unevenness, and ease of triggering of the plasma X-ray tube of the present invention with those of a conventional plasma X-ray tube.

FIG. 3 is an X-ray photograph showing spatial dose uniformity of the plasma X-ray tube of the present invention.

FIG. 4 is a sectional view showing a configuration of a second embodiment.

FIG. 5 is a diagram showing the principle of a plasma X-ray generator.

FIG. 6 is a graph showing an actual measurement of an X-ray spectrum in an axial direction (longitudinal direction) and a transverse direction (transverse direction) of a plasma shape generated when a plate-shaped negative electrode is used in a plasma X-ray generator. The values are shown schematically.

FIG. 7 is an example of an X-ray photograph using X-rays of a plasma X-ray generator using nickel as a material for a bar-shaped counter cathode.

FIG. 8 is an example of an X-ray photograph using X-rays of a plasma X-ray generator using nickel as a plate-shaped anti-cathode material.

FIG. 9 is an example of a radiograph by a conventional solid target X-ray tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma X-ray tube 2 Bar-shaped cathode 3 Ring cathode 4 Rod-shaped cathode axis 4 'Annular cathode axis 5 Extraction X-ray 6 Annular cathode opening 7 Trigger electrode 8 Inner wall of annular cathode 9 Trigger electrode 10 Plasma 11 First Annular cathode 12 second annular cathode 13 third annular cathode 14 ceramic tube 50 plasma X-ray generator 51 high-voltage power supply 52 high-voltage condenser 53 vacuum pump 54 trigger pulse power supply 55 plasma X-ray tube 56 rod-shaped cathode 57 rod-shaped cathode 52 Insulating member 59 Vacuum container 60 X-ray window 61 Vacuum piping 62 Plasma 63 Extraction X-ray 71 Axial extraction X-ray 72 Transverse extraction X-ray 73 Plate-shaped negative electrode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05H 1/24 H05G 1/00 K

Claims (7)

[Claims] 1. A high voltage discharge evaporates an anti-cathode material to generate plasma composed of the anti-cathode material, and absorbs bremsstrahlung X-rays generated by collision with the plasma to the anti-cathode material in the plasma. A plasma X-ray tube used for a plasma X-ray generator for generating X-rays, comprising: a rod-shaped counter cathode; and an annular cathode having an inner diameter larger than the outer diameter of the rod-shaped counter cathode. Align the axis of the annular cathode, and disposed at a predetermined distance,
A plasma X-ray tube, wherein X-rays are extracted from the opening of the annular cathode. 2. The annular electrode according to claim 1, wherein the annular electrode has a shape in which an inner diameter and an outer shape increase continuously from a side facing the negative electrode to a side not facing the negative electrode. Plasma X-ray tube. 3. The plasma X-ray tube according to claim 1, wherein a discharge trigger electrode is provided along an inner wall of the annular electrode and inside the annular electrode. 4. The plasma X-ray tube according to claim 1, wherein the material of the annular electrode is carbon graphite. 5. A plurality of annular electrodes having different outer diameters, inner diameters, and materials are fitted to each other such that the inner diameters are sequentially increased from a side facing the negative electrode to a side not facing the negative electrode. 2. The plasma X according to claim 1, wherein the annular electrode has a shape in which the outer diameter of the annular electrode continuously increases from the side facing the negative electrode to the side not facing the negative electrode. Wire tube. 6. The plasma X-ray according to claim 5, wherein the annular electrode facing the opposite cathode is made of carbon graphite, and the annular electrodes other than the annular electrode facing the opposite cathode are made of metal. tube. 7. The plasma X-ray tube according to claim 5, wherein the discharge trigger electrode is disposed in a pore provided through a side wall of the annular electrode facing the counter electrode.