JP3734019B2 - Plasma X-ray tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma X-ray tube of a plasma X-ray generator that generates X-rays from plasma generated by evaporating an anti-cathode material by high voltage discharge.
[0002]
[Prior art]
In recent years, flash X-ray photography has been used for observing an object that moves at high speed inside the object. For example, the dynamic function of the heart can be diagnosed by mixing an X-ray contrast agent into the blood and taking a radiograph of the heart's morphology at a particular moment. An X-ray source for such an application requires a high-energy, high-intensity monochromatic X-ray source.
As described above, high-intensity monochromatic X-rays are expected in various medical application fields, but there are only X-ray lasers and synchrotron radiation sources, and no X-ray source can be easily used anywhere. .
[0003]
Laser means amplification of light by stimulated emission light. In order to obtain X-rays by the principle of laser, a method using linear irradiation of a high energy pulse laser is generally used, but it is theoretically difficult to output a laser having a photon energy of 10 keV or more.
Further, although different from the laser, high-intensity monochromatic X-rays are obtained by synchrotrons. However, it is difficult to obtain a monochromatic X-ray having a photon energy of about 100 keV, and a sufficient machine time cannot be obtained. For this reason, the synchrotron is a very useful radiation source in basic research in the fields of medicine and engineering, but it is difficult to easily use it as a general-purpose medical radiation source.
[0004]
Under such circumstances, the present inventors have already proposed an X-ray generation method using a plasma X-ray generation source that can easily generate high-energy, high-intensity, and monochromatic X-rays (SPIE). Conf (44th) '99 .7.19). This method evaporates the counter-cathode (target) material by high-voltage discharge or the like to generate a plasma composed of the counter-cathode material, and absorbs the bremsstrahlung X-rays generated by colliding with the plasma to the counter-cathode material in the plasma. Thus, characteristic X-rays are generated.
[0005]
According to this method, since the bremsstrahlung X-rays generated by the electrons emitted from the cold cathode colliding with the plasma are used for generating characteristic X-rays, the bremsstrahlung is increased by increasing the discharge voltage of the high-voltage discharge. X-rays can be increased to the energy required to generate characteristic X-rays. 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, X-rays extracted in the long axis direction of the plasma have a long stimulated emission effect due to a long propagation distance in the plasma, increase the intensity of the characteristic X-ray, increase the absorption effect, and reduce the bremsstrahlung X-ray. Therefore, high-intensity characteristic X-rays can be extracted without a monochromatic filter.
The plasma X-ray generator having such a configuration is expected to be put to practical use as a quasi-monochromatic X-ray source with high energy and high intensity that has a simple configuration and can be used easily.
[0006]
The plasma X-ray generator having the above configuration will be described below 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 source 51, a high voltage capacitor 52 having a capacity of about 200 nF, a vacuum pump 53, a trigger pulse power source 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 charge accumulated in the high-voltage capacitor 52 causes discharge at the cathode, it is discharged to the plasma X-ray tube 55 and X-rays 62 are generated in the plasma X-ray tube 55.
The plasma X-ray tube 55 has a rod-like cathode 56 provided with a trigger electrode, and a counter cathode (target) 57 made of a specific material such as a rod or plate, and the counter cathode 57 is made of stainless steel via an insulating member 58. The vacuum vessel 59 is fixed. 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, and is kept at a vacuum level of about 1 mPa when connected to a vacuum pump during operation.
[0007]
In order to operate the X-ray generator 50, the high voltage capacitor 52 is charged to a predetermined high voltage V by the high voltage power source 51, and a trigger pulse is applied to the trigger electrode by the trigger pulse power source 54 to cause discharge. When the discharge starts, electrons are extracted from the cathode 56 and accelerated, and collide with the counter cathode 57 with kinetic energy of eV. At this time, since the current density and energy of the electrons are extremely high, the counter-cathode material is instantly evaporated, and a high magnetic field is generated around the current. Therefore, an extremely high-density plasma 62 composed of ions and electrons of the counter-cathode material. Is formed. The electrons that continue to hit the high-density plasma 62 emit bremsstrahlung X-rays. The high voltage V is sufficiently increased to give sufficient energy to the electrons, and braking X-rays having energy higher than the K absorption edge of the counter cathode material are generated. The bremsstrahlung X-rays are absorbed by exciting the K-shell electrons of the countercathode material. Electrons are transferred from other shells to vacant seats generated in the K shell, and characteristic X-rays such as Kα and Kβ are generated.
[0008]
The characteristic X-rays propagating in the plasma 62 gradually increase in intensity by stimulated emission. In addition, since the bremsstrahlung X-ray propagating through the plasma 62 and having an energy equal to or lower than the K absorption edge is absorbed by the transition between electron levels of the ionized target material in the plasma, the intensity is gradually weakened.
[0009]
FIG. 6 shows the actual measurement of X-ray spectra in the axial direction (longitudinal direction) and the transverse direction (short direction) of the shape of plasma generated when a plate-like counter-cathode is used in this plasma X-ray generator. The values are shown schematically.
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 axes of (a) and (b) indicate the energy of X-ray photons, the vertical axis indicates the X-ray intensity, and the two line spectra are characteristic X-rays Kα and Kβ.
As shown in FIG. 6, the X-ray spectrum in the axial direction 71 has a higher characteristic X-ray intensity and less braking X-ray components having a continuous spectral distribution than the transverse direction 72. From this, it can be seen that if an X-ray emitted in the axial direction 71 is used, it can be used as a monochromatic X-ray source without using a monochromatic filter.
[0010]
FIG. 7 is an example of an X-ray photograph using X-rays of a plasma X-ray generator using nickel as a rod-shaped counter-cathode material.
Nickel was used as the rod-shaped counter-cathode material, the high-voltage capacitor 52 was charged with a voltage of 50 kV, and a subject made of polymethyl methacrylate was photographed at a distance of 1.2 m from the plasma X-ray tube 55. A subject made of polymethyl methacrylate is a concentric stack of a plurality of discs having the same thickness (5 mm) whose diameter increases by a certain length. Polymethyl methacrylate absorbs nickel Kα and Kβ characteristic X-rays and transmits X-rays of other wavelengths.
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. 7 (a) and 7 (b), a contrast image depending on the thickness of polymethyl methacrylate is obtained, and it can be seen that X-ray images with monochromatic X-rays can be obtained without using a monochromatic filter. .
That is, it can be seen that X-rays generated by this plasma X-ray generator are sufficiently monochromatic.
[0011]
FIG. 8 is an X-ray photograph obtained by photographing the same subject as in FIG. 7 using nickel as the plate-like counter cathode material.
As is apparent from FIGS. 8A and 8B, the X-ray generated by the plasma X-ray generator is sufficiently monochromatic even when a plate-like counter cathode is used.
[0012]
FIG. 9 is an example of an X-ray photograph using a conventional solid target X-ray tube.
A conventional solid target X-ray tube has a filament at 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.
As is apparent from FIGS. 9A and 9B, a contrast image depending on the thickness of polymethyl methacrylate cannot be obtained without a monochromatic filter, and the X-rays produced by the conventional solid target X-ray tube are characteristic X-rays. In addition, it can be seen that a large amount of bremsstrahlung having a continuous spectral distribution is emitted.
Thus, since the plasma X-ray generator can easily generate extremely high intensity quasi-characteristic X-rays, it is expected as a general-purpose X-ray source of high-intensity quasicharacteristic X-rays.
[0013]
[Problems to be solved by the invention]
However, there is a problem to be improved for use as a general-purpose radiation source in the medical field.
First, the shade varies depending on the position on the X-ray photograph of FIGS. That is, the X-rays generated by the plasma X-ray generator have spatially uneven dose. It is necessary to eliminate dose unevenness for medical applications.
Second, in order to further expand the application field, a plasma X-ray generator with higher intensity is desirable.
Thirdly, it is desirable to easily cause discharge and to reduce the safety and cost of the apparatus.
Fourth, a cathode made of metal or the like is deformed when used repeatedly and has a short life.
[0014]
In view of the above problems, an object of the present invention is to provide a plasma X-ray tube that is used in a plasma X-ray generator and has high dose, is easy to cause discharge, and can be used repeatedly.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the plasma X-ray tube of the present invention generates a plasma composed of an anti-cathode material by evaporating the anti-cathode material by high voltage discharge, and generates a bremsstrahlung X-ray generated by colliding with the plasma. In a plasma X-ray tube used in a plasma X-ray generator for generating characteristic X-rays by being absorbed by an anti-cathode material in plasma,
A rod-shaped counter cathode and an annular cathode having an inner diameter larger than the outer diameter of the rod-shaped counter cathode;
The annular cathode is a plurality of annular cathode members having different outer diameters, inner diameters, and materials, which are fitted to each other so that the inner diameter sequentially increases from the side facing the counter cathode toward the side not facing the counter cathode, And the outer diameter of the annular cathode member has a shape that continuously increases from the side facing the counter cathode toward the side not facing the counter cathode,
To match the axes of the anticathode and said annular cathode of said rod-like and disposed apart a predetermined distance, and wherein the retrieving the X-ray from the opening of said annular cathode.
According to this configuration, since there is no cathode that extinguishes plasma in the X-ray extraction direction, the length of the plasma in the cathode direction is longer than when discharging using a rod-like cathode. Accordingly, the propagation distance of the extracted X-ray in the plasma is increased, the stimulated emission effect is increased, the intensity of the quasi-monochromatic X-ray is increased, and the absorption effect of the bremsstrahlung X-ray is increased. Sex increases.
Furthermore, since the inner diameter is larger than the outer diameter of the counter cathode, the stability of the plasma is increased and the variation in the spatial dose of the extracted X-ray is reduced. In addition, the cost of the plasma X-ray tube can be reduced.
[0016]
The annular cathode member facing the counter cathode is made of carbon / graphite, and the annular cathode member other than the annular cathode member made of carbon / graphite is made of metal. According to this configuration, the cost of the plasma X-ray tube can be reduced.
[0017]
Further, the discharge trigger electrode is disposed along the inner wall of the annular cathode and inside the annular cathode.
Further, the discharge trigger electrode, characterized in that disposed in the pores which are provided through the side wall of the annular cathode member facing said anticathode.
According to this configuration, the discharge trigger electrodes, without interrupting the X-ray is taken out, rather variations occur spatial dose of X-rays, characteristic X-rays of high strength can be obtained.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail based on 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 an annular cathode 3 having an inner diameter larger than the outer diameter of the rod-shaped counter-cathode 2. The rod-shaped counter-cathode 2 and the annular cathode 3 are arranged such that the axes 4 and 4 ′ thereof coincide with each other and are separated from each other by a predetermined distance d. It comes out in the direction.
Cyclic negative electrode 3 has an inner diameter a and an outer diameter b is a continuously toward the side not facing the anticathode 2 from the side facing the anticathode 2 larger shape.
Discharge trigger electrode 7 in close proximity to the inner wall 8 of the annular shade electrode 3, and along the inner wall 8, which is disposed within the annular shade electrode 3, the other discharge trigger electrode 9 is an annular shade pole 3 It is connected to one end.
The material of the annular shade electrode 3 is a carbon graphite. If carbon / graphite is used as the material of the annular cathode 3, the carbon / graphite is a high-melting-point, high-conductivity crystal, so that the annular cathode 3 is not deformed by a high-density current during discharge and is used repeatedly. can do.
Since other members constituting the plasma X-ray tube such as a vacuum vessel, an X-ray window, and a vacuum drawing pipe are the same as those in FIG.
[0019]
The plasma X-ray tube having the above configuration operates as follows.
The application of a trigger voltage between the trigger electrodes 7,9, the discharge trigger high electric field between the electrode 7 and the inner wall 8 of the annular shade electrode 3 occurs, the inner wall 8 near the gas is ionized. Ionizing a total gas plasma X-ray tube is triggered is ionized, electrons from the annular shade electrode 3 are accelerated by a voltage V applied to the high voltage capacitor, it strikes the anticathode 2. Since the energy and current density of the electrons are sufficiently high, atoms constituting the counter cathode 2 are instantly evaporated, and a plasma 10 composed of ions of atoms constituting the counter cathode 2 and ionized electrons is formed.
As shown in FIG. 1, the cathode of the present invention is a cyclic anionic pole 3, since the low-temperature heat source to extinguish the plasma 10 in the X-ray extraction direction 4 is not, compared to the conventional plasma using cathode rod-like 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, the current component in the vicinity of the annular cathode 3 also includes a component perpendicular to the axis 4. A Lorentz force in the direction is generated, and the plasma 10 becomes longer in the direction of the axis 4.
[0020]
Since the plasma 10 extends in the direction of the axis 4 in this way, the propagation distance of the extracted X-ray 5 in the plasma 10 is increased, the stimulated emission effect is increased, the intensity of the quasi-monochromatic X-ray is increased, and the bremsstrahlung. Since the X-ray absorption effect increases, the monochromaticity of the extracted X-rays increases.
Furthermore, since the inner diameter a of the annular cathode 3 is larger than the outer diameter of the rod-shaped anticathode 2 and toward the side where the outer diameter b of the annular shade electrode 3 is not facing the anticathode 2 from the side facing the anticathode 2 Therefore, the stability of the plasma 10 is increased, and the spatial dose variation of the extracted X-ray is reduced.
The discharge trigger electrode 7 in close proximity to the inner wall 8 of the annular shade electrode 3, and from along the inner wall 8 is arranged inside the annular shade electrode 3, the electric field strength is more increased, lower applied Discharge can be induced by voltage. Further, since the discharge trigger electrode 7 does not block the X-ray 5 to be taken out, the spatial dose variation is reduced.
[0021]
Next, a first embodiment will be described.
FIG. 2 is a diagram comparing the X-ray intensity, dose unevenness, and trigger easiness of the plasma X-ray tube of the present invention with a conventional plasma X-ray tube.
In FIG. 2, (a) is a conventional plasma X-ray tube composed of a plate-shaped counter cathode and a rod-shaped metal cathode, and (b) is a conventional plasma X-ray tube composed of a rod-shaped counter cathode 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 of 50 kV. All the counter-cathode materials used nickel.
The trigger electrode of the conventional plasma X-ray tube is formed by inserting a conductor through an insulating tube and inserting the insulating tube through a fine hole drilled in the center of the rod-shaped cathode, thereby exposing the conductor. Are arranged in a plane facing the counter-cathode of the rod-like cathode.
As shown in the figure, the X-ray intensity of the plasma X-ray tube (c) of the present invention is 6 times that of the conventional plasma X-ray tube (a) comprising a plate-like counter-cathode and a rod-like cathode. In addition, the X-ray intensity is twice that of the conventional plasma X-ray tube (b) made of a rod-like cathode.
In addition, the trigger voltage causing discharge is reduced to less than half compared to the conventional example using the metal cathodes (a) and (b).
[0022]
FIG. 3 is an X-ray photograph showing the uniformity of the spatial dose of the plasma X-ray tube of the present invention.
In the X-ray photography, similarly to the description in FIG. 7, nickel is used as the material of the rod-shaped counter-cathode 2 of the plasma X-ray tube of the present invention, and a high voltage capacitor is charged at a voltage of 50 kV. A subject made of polymethyl methacrylate was photographed at a distance of 2 m. A subject made of polymethyl methacrylate is a concentric stack of a plurality of discs having the same thickness (5 mm) whose diameter increases by a certain length. Polymethyl methacrylate absorbs nickel Kα and Kβ characteristic X-rays and transmits X-rays of other wavelengths.
As is apparent from FIG. 3, there is almost no dose variation in the plasma X-ray tube of the present invention, and it can be seen that the spatial uniformity of the dose is remarkably higher than that of the conventional example shown in FIGS.
[0023]
Next, a second embodiment will be described.
FIG. 4 is a cross-sectional view showing the configuration of the second embodiment.
4, the annular shade electrode 3, first, second annular cathode a first annular cathode member 11 made of carbon graphite, and fitted into the second annular cathode member 12 made of brass, fitted The member is formed by fitting to a third annular cathode member 13 made of stainless steel.
Further, the outer diameter of the first annular cathode member 11 and the second annular cathode member 12 made of brass is formed so that the diameters are gradually increased from the side facing the counter cathode 2 toward the side not facing the counter cathode. Has been.
Further, the discharge trigger electrode 7 is disposed through a ceramic tube 14 in a pore provided through the side wall of the annular cathode member 11 facing the counter cathode.
Carbon graphite can be easily processed by cutting, but cannot be fused with other substances. For this reason, it is difficult to fix a single annular electrode made of carbon graphite to a vacuum vessel made of stainless steel, resulting in an increase in cost.
According to this configuration, the annular cathode member 11 made of carbon graphite can be fitted and fixed to the second annular cathode member 12 made of brass, and the second annular cathode member 12 is made of the third stainless steel. The annular cathode member 13 can be fitted and fixed, and the third annular cathode member 13 made of stainless steel can be easily fused and fixed to a vacuum vessel made of stainless steel. Therefore, the cost can be reduced.
[0024]
In the above description, the counter cathode made of nickel has been described as an example, but other substances can of course be used as the counter cathode material. In particular, a material having a large atomic number is used as the counter cathode material, and an appropriate high pressure is used. It is clear that a characteristic X-ray source with higher energy can be obtained by discharging at.
[0025]
【The invention's effect】
As can be understood from the above description, according to the present invention, it is possible to provide a high-intensity, discharge-prone plasma X-ray tube that does not have uneven dose and can be used repeatedly.
Therefore, it can be used as a plasma X-ray tube of a plasma X-ray generator that generates quasi-monochromatic X-rays with high energy and high intensity that can be easily used. Thus, according to the present invention, it is extremely useful when used in the medical field that requires high-intensity monochromatic X-rays.
[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 trigger easiness of the plasma X-ray tube of the present invention with a conventional plasma X-ray tube.
FIG. 3 is an X-ray photograph showing the spatial dose uniformity of the plasma X-ray tube of the present invention.
FIG. 4 is a cross-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 shows an actual measurement of X-ray spectra in the axial direction (longitudinal direction) and transverse direction (short direction) of the shape of plasma generated when a plate-like counter-cathode 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 rod-shaped counter-cathode material.
FIG. 8 is an example of an X-ray photograph using X-rays of a plasma X-ray generator using nickel as a plate-like counter-cathode material.
FIG. 9 is an example of an X-ray photograph using a conventional solid target X-ray tube.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Plasma X-ray tube 2 Rod-shaped counter-cathode 3 Ring-shaped cathode 4 Rod-shaped counter-cathode axis 4 'Ring-shaped cathode axis 5 Extraction X-ray 6 Ring-shaped cathode opening 7 Trigger electrode 8 Ring-shaped cathode inner wall 9 Trigger electrode 10 Plasma 11 1st Annular cathode member 12 Second annular cathode member 13 Third annular cathode member 14 Ceramic tube 50 Plasma X-ray generator 51 High voltage power source 52 High voltage capacitor 53 Vacuum pump 54 Trigger pulse power source 55 Plasma X-ray tube 56 Rod cathode 57 Rod shape Counter cathode 58 Insulating member 59 Vacuum vessel 60 X-ray window 61 Vacuum drawing pipe 62 Plasma 63 Extraction X-ray 71 Axial extraction X-ray 72 Transverse extraction X-ray 73 Plate-shaped counter cathode

Claims (4)

Due to the high voltage discharge, the counter-cathode material is evaporated to generate a plasma made of the counter-cathode material, and the bremsstrahlung X-rays generated by colliding with the plasma are absorbed by the counter-cathode material in the plasma to generate characteristic X-rays. In a plasma X-ray tube used in a plasma X-ray generator,
A rod-shaped counter cathode and an annular cathode having an inner diameter larger than the outer diameter of the rod-shaped counter cathode;
The annular cathode is a plurality of annular cathode members having different outer diameters, inner diameters, and materials, which are fitted to each other so that the inner diameter sequentially increases from the side facing the counter cathode toward the side not facing the counter cathode, And the outer diameter of the annular cathode member has a shape that continuously increases from the side facing the counter cathode toward the side not facing the counter cathode,
A plasma X-ray tube characterized in that the rod-shaped counter-cathode and the annular cathode are aligned with a predetermined distance from each other, and an X-ray is taken out from an opening of the annular cathode. Said annular cathode member facing the anticathode is composed of carbon-graphite, annular cathode member other than annular cathode member made of the carbon graphite is characterized in that it consists of metal, the plasma X-ray tube according to claim 1. Discharge trigger electrode, along the inner wall of the annular shade electrode, and, characterized in that disposed within the annular shade electrode, plasma X-ray tube according to claim 1 or 2. 3. The plasma X-ray tube according to claim 1, wherein the discharge trigger electrode is disposed in a pore provided through a side wall of the annular cathode member facing the counter cathode.

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