JP2001116897A - X-ray source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray source allowing for better controllability of the waveforms of pulsed X-rays. SOLUTION: The X-ray source 1 includes a cathode 3 and an anode 4 disposed in a spaced relationship inside a vacuum container and to which high voltages are applied, and a positive ion generating means 70 for generating positive ions 7 inside an electric field 5 formed between the cathode 3 and the anode 4. The anode 3 is bombarded with secondary electrons 8 produced by bombardment of the cathode 4 with the positive ions 7, to generate an X-ray 9 from the anode 3. Generation of the positive ions 7 is controlled to control the waveform of the X-ray.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse X-ray generation technique, and more particularly to an X-ray source applicable to a nondestructive inspection apparatus and an analyzer.

[0002]

2. Description of the Related Art In nondestructive measurement using X-rays, pulsed X-rays may be used due to required measurement characteristics. For example, when imaging a dynamic phenomenon by a radiography method, if the movement of the subject is not so fast, a normal X
It can be measured by a fluoroscopic technique using X-rays obtained from a source. However, when imaging a phenomenon that changes at a very high speed by radiography, the X-rays to be used also need to be pulsed. Such a pulsed X
As an X-ray source for generating X-rays, there is known an X-ray generation technique using dielectric breakdown caused by a high voltage (for example, see “X-ray Handbook”, pages 234 and 235 (see the Electronic Science Laboratory). In this method, a high voltage is instantaneously applied between a cathode and an anode to cause dielectric breakdown, and electrons extracted from the cathode collide with the anode to generate X-rays.

Further, a gas X-ray tube using a cold cathode and a high vacuum X-ray tube using a heating cathode are also known. In a gas X-ray tube, positive ions existing in a tube maintained at a constant gas pressure are injected into a cathode, and electrons that fly out of the cathode collide with a counter-cathode such as glass or metal, thereby generating X-rays. Things. This gas X-ray tube has a problem that it is difficult to operate and unstable in operation due to the nature of the gas itself and the nature of positive ion implantation during operation. on the other hand,
There is also known a high vacuum X-ray tube whose operation is stabilized by using a high temperature tungsten-filament as a cathode and a metal such as solid tungsten as a counter cathode, but this type of X-ray source is a continuous X-ray X-ray tube. Although suitable as a radiation source, it is not suitable as an X-ray source that generates pulsed X-rays.

[0004]

A conventional X-ray source that generates pulsed X-rays has a problem that it is difficult to control the waveform (crest value and pulse width) and wavelength of the X-ray such as the peak value and pulse width. There is. This is because X using dielectric breakdown by high voltage
In the source, electrons are generated by dielectric breakdown, which has unstable reproducibility, so the current controllability is poor and it is difficult to control the peak value and pulse width that characterize the waveform shape of the generated pulsed X-ray. This is because Also, the generated X
The pulse width of the line is also limited to several nanoseconds (s), and it is difficult to obtain X-rays having a pulse width longer than several nanoseconds. This is because a large amount of electrons instantaneously collide with the anode to generate plasma, which prevents the electrons from colliding with the anode and limits the generated X-rays to the initial current pulse. .

[0005] Energy (wavelength) generated by X-rays
Can be controlled by a voltage applied to the cathode and the anode, but a high voltage must be applied to cause dielectric breakdown, so that a low voltage cannot be applied. Therefore, it is not possible to obtain long-wavelength X-rays having low energy, and there is a problem that the generated energy (wavelength) of the generated X-rays is limited. Therefore, the present invention solves the above-mentioned problems of the conventional X-ray source for generating pulsed X-rays,
An object of the present invention is to provide an X-ray source having good controllability of an X-ray waveform of a pulsed X-ray.

[0006]

According to the present invention, positive ions are accelerated by an electric field in a vacuum to collide with a cathode, and secondary electrons generated at that time are used as an electron source, and the generated electrons are accelerated by the electric field. Then, X-rays are generated by colliding with the anode. By controlling the generation of positive ions, the generation of secondary electrons is controlled, and the waveform of X-rays is controlled.

Therefore, the X-ray source of the present invention generates positive ions in a cathode and an anode which are arranged at an interval in a vacuum vessel and to which a high voltage is applied, and an electric field formed between the cathode and the anode. And a positive ion generating means for generating the positive ions. FIG. 1 is a schematic diagram for explaining the configuration of the X-ray source of the present invention. X-rays are generated from the anode by colliding secondary electrons formed by the collision between positive ions and the cathode with the anode, and the X-ray waveform is controlled by controlling the generation of positive ions. In FIG. 1, an anode 3 and a cathode 4 are arranged in a vacuum 2 at an interval, and an electric field 5 is formed by applying a high voltage between the electrodes. Positive ion generating means 70 generates positive ions 7 in the electric field 5. Positive ions 7 generated in the electric field 5 move toward the cathode 4 by the electric field and collide with the cathode 4. Secondary electrons 8 generated by collision between positive ions 7 and cathode 4 move toward anode 3 by electric field 5. When the secondary electrons 8 collide with the anode 3, X-rays 9 are generated.

The X-ray source of the present invention controls the generation of X-rays by controlling the generation of positive ions, and includes a positive ion generation control means as the mechanism. The positive ion generation control means generates positive ions in an electric field formed between the cathode and the anode, and controls the amount and position of the generated positive ions in the electric field to generate X-rays. The X-ray waveform is controlled by controlling the peak value and / or pulse width of the X-ray.

A first form of the positive ion generation control means has a positive ion generation mechanism by laser irradiation. The mechanism of generating positive ions by laser irradiation is to irradiate the residual gas in the vacuum vessel with a laser to ionize the residual gas and generate positive ions.By irradiating the laser in the electric field, the positive ion is generated in the electric field. Generate ions. In the first form of the positive ion generation control means, the first control method for controlling the peak value of the X-ray changes the amount of positive ions generated at the initial stage of laser incidence by controlling the intensity of the incident laser light. The peak value of the generated X-rays can be increased by increasing the intensity of the incident laser light to increase the amount of generated positive ions.

In the first form of the positive ion generation control means, the second control method for controlling the peak value of the X-rays is to control the residual gas density by controlling the pressure in the vacuum vessel to thereby control the initial stage of laser incidence. The amount of generated positive ions is changed, and the peak value of the generated X-rays can be increased by increasing the amount of generated positive ions by increasing the residual gas density. In the first mode of the positive ion generation control means, a third control method for controlling the peak value of the X-rays includes:
By controlling the irradiation position of the incident laser light within the electric field, the energy when the positive ions collide with the cathode is changed, and the energy obtained by the positive ions from the electric field is changed depending on the irradiation position of the laser light. By bombarding positive ions with high energy on the cathode,
By increasing the amount of secondary electrons generated, the peak value of the generated X-rays can be increased.

In the first mode of the positive ion generation control means, the first control method for controlling the pulse width of X-rays is such that positive ions are generated between an anode and a cathode in an electric field to generate positive ions. Stagger the time to reach the cathode,
The pulse width of the generated X-rays is controlled by controlling the width at the time when the positive ions reach the cathode. In the first form of the positive ion generation control means, the second control method for controlling the pulse width of X-rays generates positive ions along the distance between the anode and the cathode in the electric field and shifts the generation position of the positive ions. This shifts the time and position at which the positive ions reach the cathode, prevents scattering of secondary electrons by the positive ions, controls the pulse width of the generated X-rays, and increases the X-ray generation efficiency.

A second form of the positive ion generation control means includes an ion source and a mechanism for introducing positive ions generated by the ion source. The mechanism for introducing positive ions generates positive ions in the electric field by discharging the positive ions generated by an ion source such as an ion gun into the electric field. By controlling the amount of positive ions introduced into the electric field and the position of generation,
The peak value and / or pulse width of the generated X-rays are controlled. In the second embodiment of the positive ion generation control means, the first control method for controlling the peak value of the X-ray changes the amount of generated positive ions by controlling the amount of introduced positive ions, The peak value of the generated X-rays can be increased by increasing the amount of generated positive ions.

In the second embodiment of the positive ion generation control means, the second control method for controlling the peak value of the X-rays is to control the pressure in the vacuum vessel to reduce the residual gas density, as in the first embodiment. By controlling, the amount of generated positive ions at the initial stage of laser incidence can be changed, and the peak value of X-rays can be increased. In the second form of the positive ion generation control means, the third control method for controlling the peak value of the X-rays is to control the position of introducing the positive ions in the electric field.
Changes the energy at which positive ions strike the cathode.

In the second embodiment of the positive ion generation control means, the first and second control methods for controlling the pulse width of X-rays can be the same as those of the first embodiment, and the method for controlling the pulse width between the anode and the cathode in an electric field is performed. The time at which the positive ions arrive at the cathode is shifted by introducing positive ions along the axis, and the pulse width of the generated X-rays is controlled by controlling the width during the time at which the positive ions arrive at the cathode. In addition, by shifting the generation position of the positive ions, the scattering of the secondary electrons due to the positive ions is prevented, and the generation efficiency of the X-ray is increased. In the second embodiment of the positive ion generation control means, the change of the introduction position of the positive ions is as follows.
This can be performed using an electric field lens or the like.

[0015] In the first embodiment of the positive ion generation control means using an irradiation laser, the irradiation point of the irradiation laser may be an anode or a target provided in the vacuum vessel in addition to the space in the vacuum vessel. it can. The wavelength of the generated X-rays can be controlled by changing the voltage applied between the anode and the cathode, and the wavelength of the generated X-rays can be shortened by increasing the voltage. Conversely, the wavelength of X-rays generated by lowering the voltage value can be lengthened.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a schematic diagram for explaining a configuration example of the X-ray source of the present invention. In FIG. 2, an X-ray source 11 has an anode 3 and a cathode 4 opposed to each other in a vacuum vessel 12, and applies a high voltage by a power supply 15.
An electric field 5 is formed between the anode 3 and the cathode 4. Vacuum container 1
An exhaust pump 13 and a gas source 14 are connected to 2, and the pressure in the vacuum vessel 12 can be controlled by controlling the exhaust by the exhaust pump 13 and the supply of gas from the gas source 14. The pressure in the vacuum chamber 12 depends on the generation efficiency of X-rays, such as the generation efficiency of positive ions due to the ionization of the residual gas and the degree to which secondary electrons are diffused by positive ions and hindered from moving to the anode when moving to the anode. Affect the factors that contribute to.

The pressure in the container is, for example, 1/75 × 1
0 ^-1 Pascal (Pa)-1/75 × 10 ^-2 Pascal (P
a) It is set to about (10 ⁻⁵ Torr to 10 ⁻⁶ Torr).
Further, a high vacuum of about ^1/75 × 10 ⁻⁴ Pascal (Pa) can be used. Here, 1 Pascal (P
a) is set to 7.5 × 10 ⁻³ Torr.
The high voltage applied by the power supply 15 is, for example, about 30 kilovolts (kV) to about 40 kilovolts kV. Note that X-rays having a short wavelength can be obtained by applying a higher voltage. Note that the anode 3 is attached to the vacuum vessel 3 via an insulating material.

A positive ion generation mechanism 71 by laser irradiation is provided as positive ion generation control means. The positive ion generating mechanism 71 focuses a laser beam 71a having a high intensity from a laser light source (not shown, for example, a Q-switch laser light source) on the region of the electric field 5 in the vacuum chamber 12 by the optical system 71b. The vacuum chamber 12 is provided with a window 16 for introducing a laser beam 71a from outside.

Condensed laser light 7 in vacuum vessel 12
1a ionizes the residual gas in the vacuum vessel 12. A region 19 shown in FIG. 2 schematically shows an ionization region. Positive ions 7 are generated in the ionization region 19 by ionization. The positive ions 7 move toward the cathode 4 by the electric field 5 and collide with the cathode 4 to generate secondary electrons 8.
The secondary electrons 8 move toward the anode 3 by the electric field 5 and collide with the anode 3 to generate X-rays 9. The X-ray 9 is taken out of the vacuum vessel 12 through a window 17 provided in the vacuum vessel 12.

FIG. 3 is a time chart for explaining the operation of the X-ray source according to the present invention. FIG. 3 (a) shows the state of laser beam irradiation, and FIG. 3 (b) shows the state of X-ray generation. Is shown. X-rays are generated after a lapse of time t after irradiation with laser light. The elapsed time t depends on the arrangement interval between the anode and the cathode, the electric field strength, and the like, and is determined mainly by the time until the positive ions reach the cathode. In a normal configuration, it is about several nanoseconds (ns) to about 1 microsecond (μs). X-rays are generated every time a laser beam is irradiated, and the X-rays can be interrupted by irradiating the laser beam from a laser light source at a predetermined interval T. The X-ray generation interval is determined by the laser light generation interval T. For example, when a 10 kilohertz (kHz) laser light source is used, X-rays can be generated at 100 microsecond (μs) intervals.

Next, in the X-ray source having the configuration shown in FIG.
The X-ray waveform control will be described. As X-ray waveform control, control of wavelength, control of peak value, and control of pulse width will be described. The length of the X-ray wavelength indicates the intensity of energy provided by the X-ray. The wavelength of this X-ray can be controlled by the voltage applied between the anode and the cathode. Since the X-ray source of the present invention is configured to generate X-rays using positive ions generated by a positive ion generating mechanism, the X-ray source is 30 to 40 kilovolts (kV).
A wide voltage range from a relatively low voltage to a high voltage can be obtained, whereby X-rays having a long wavelength to a short wavelength can be generated. In a configuration in which X-rays are generated using a conventional discharge, it is necessary to apply a high voltage in order to generate a discharge, which limits the wavelength of the generated X-rays. Since there is no restriction on the applied voltage, the width of the wavelength of the generated X-ray can be widened.

Next, the control of the X-ray peak value of the X-ray source of the present invention will be described with reference to FIG. The peak value of the X-ray depends on the amount of secondary electrons colliding with the anode, and the amount of secondary electrons depends on the amount of generated positive ions. Therefore, the peak value of X-rays can be controlled by the amount of secondary electrons generated or the amount of positive ions generated. In the first method of controlling the peak value of the X-ray, the intensity of the incident laser light is controlled to change the generation amount of positive ions generated at the initial stage of laser incidence, thereby controlling the peak value of the X-ray. The intensity of the incident laser light is controlled by controlling a laser light source (not shown). When the intensity of the incident laser light is increased, the generation amount of positive ions increases, the generation amount of secondary electrons increases, and the peak value of X-rays increases.

The second method of controlling the peak value of X-rays is to control the pressure in the vacuum vessel to control the residual gas density, thereby changing the amount of positive ions generated at the initial stage of laser irradiation. Control the peak value of. X of the present invention
The radiation source controls the amount of secondary electrons by controlling the amount of positive ions by controlling the residual gas density, thereby controlling the peak value of X-rays. When the density of the residual gas in the vacuum vessel increases, the amount of generated positive ions increases, the amount of secondary electrons increases, and the peak value of X-rays increases. Conversely, when the density of the residual gas decreases, the positive The amount of ions generated decreases, the amount of secondary electrons generated decreases, and the peak value of X-rays decreases.

The third of the peak value control of the X-ray is to control the irradiation position of the incident laser light within the electric field,
The energy at which the positive ions strike the cathode is changed, thereby controlling the peak value of the X-ray. The X-ray source of the present invention controls the amount of secondary electrons generated by changing the energy that positive ions obtain from the electric field depending on the irradiation position of the laser light,
Controls the peak value of X-rays. When positive ions collide with the cathode with high energy, the amount of secondary electrons generated increases, and the peak value of the generated X-rays increases.

In FIG. 4, the irradiation position of the laser beam is different between FIGS. 4 (a) and 4 (b). FIG. 4 (a)
Irradiates a laser beam 73P to an irradiation position P near the anode 3 with respect to an electric field 5 formed between the anode 3 and the cathode 4, and FIG. Q is irradiated with a laser beam 73Q. The positive ions 7 generated at the irradiation position P obtain higher energy than the positive ions 7 generated at the irradiation position Q before colliding with the cathode 4 by the electric field 5 and collide with the cathode 4 with high energy. As the energy colliding with the cathode 4 increases, the amount of generated secondary electrons increases, and the peak value of the generated X-rays increases. FIG. 4C schematically shows the difference between the peak values of X-rays generated when the irradiation positions are P and Q.

Next, the pulse width control of the X-ray of the X-ray source of the present invention will be described with reference to FIGS. The pulse width of X-rays depends on the time width of secondary electrons hitting the anode, and the time width of secondary electrons depends on the time width of positive ions hitting the cathode. Therefore, the pulse width of the X-ray is adjusted by distributing the generation of the positive ions along the space between the anode and the cathode in the electric field, thereby shifting the time at which the positive ions reach the cathode and the time width at which the positive ions reach the cathode. Control by controlling.

The first type of X-ray pulse width control is to distribute positive ions along the space between the anode 3 and the cathode 4 in the electric field 5 as shown in FIG. This positive ion distribution is
It can be formed by irradiating a laser beam 73 deformed into a band shape by an optical system. 5A and 5B, positive ions are distributed between an irradiation position 7R near the anode 3 and an irradiation position 7S near the cathode 4 side. When positive ions are generated at the irradiation position 7R and the irradiation position 7S at the same time, between the time tr at which the positive ions generated at the irradiation position 7R reach the cathode 4 and the time ts at which the positive ions generated at the irradiation position 7S reach the cathode 4 Has a time difference of (tr-ts). Due to this time difference, the cathode 4 has (tr−ts)
Positive ions arrive during the time width of, and during this time, secondary electrons are generated and X-rays are generated. Thus, the pulse width of X-rays is controlled by controlling the distribution of the generation of positive ions. Note that, as described with reference to the peak value of the X-ray, the positive ions generated at the irradiation position 7R have higher energy than the positive ions generated at the irradiation position 7S.
The peak value of the line changes with time, and the initial peak value decreases.

By irradiating the laser beam 73 in parallel with the direction of the electric field, a positive ion distribution can be formed. FIG. 6A shows a case where the laser beam 73 is irradiated in parallel to the direction of the electric field. Positive ions formed by irradiation with the laser beam 73 become distribution regions 19 parallel to the electric field direction. In this distribution region 19, between the positive ions generated at the irradiation position 7R on the anode 3 side and the positive ions generated at the irradiation position S on the cathode 4 side, as shown in FIG. The width is given to control the pulse width of the generated X-ray.

The second of the X-ray pulse width control is that positive ions reach the cathode by distributing the positive ions along the anode 3 and the cathode 4 in the electric field 5 and displacing the generation positions of the positive ions. It shifts the time and position,
X generated by preventing scattering of secondary electrons by positive ions
It controls the pulse width of the line and increases the X-ray generation efficiency. As shown in FIG. 6B, the positive ion distribution is formed by irradiating the laser beam 73 at an angle with respect to the direction of the electric field to shift the position where the positive ions are generated.
By irradiating the laser beam 73, the positive ion distribution region 19 formed is distributed obliquely in the direction of the electric field. In the distribution region 19, the irradiation position 7R on the anode 3 side and the irradiation position S on the cathode 4 side are shifted in the generation position of the positive ions. When the generation position is shifted, when the secondary electrons generated at the cathode 4 move to the anode 3, the rate at which the secondary electrons collide with the positive ions decreases, and the scattering by the positive ions decreases. Thereby, the energy lost by the scattering of the secondary electrons with the positive ions can be reduced, and the X-ray generation efficiency can be increased.

Next, another configuration example of the positive ion generating mechanism by laser irradiation of the X-ray source of the present invention will be described with reference to FIG. The positive ion generating mechanisms 71 ′ and 71 ″ shown in FIG.
Positive ions are generated by irradiating a laser beam to the anode or a target in a vacuum vessel. FIG. 7 (a)
The positive ion generating mechanism 71 ′ shown in FIG. 7 is configured to irradiate the anode 3 with a laser beam 71a, and the positive ion generating mechanism 71 ″ shown in FIG. 71a is irradiated. In this configuration example, the peak value of the X-ray can be controlled by changing the intensity of the laser light to be irradiated. In the configuration using the target 6, the peak value of the X-ray can be controlled by changing the position of the target 6 or the position of the target 6 irradiated with the laser light.

Another configuration example for controlling the pulse width of the X-ray source of the present invention will be described with reference to FIG. The configuration example shown in FIG.
The shape of the cathode 4 ′ is deformed to change the distance between the anode 3 and the facing surface.
The pulse width is controlled by making the moving distance of the positive ions located along the distance different.

Another example of the positive ion generation control means of the present invention will be described with reference to FIG. The positive ion generation control means 72 of this configuration example includes an ion source 72a and a mechanism for introducing positive ions generated by the ion source. The mechanism for introducing the positive ions generates the positive ions in the electric field by discharging the positive ions generated by the ion source 72a such as an ion gun into the electric field. The introduction mechanism is an electric field lens 72b.
The position of the positive ions in the electric field can be controlled.

As in the above-described configuration using laser light, it is possible to control the peak value and / or pulse width of the generated X-rays by controlling the amount of positive ions introduced into the electric field and the generation position. it can.

[0034]

As described above, according to the X-ray source of the present invention, the controllability of the X-ray waveform of the pulsed X-ray can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a configuration of an X-ray source according to the present invention.

FIG. 2 is a schematic diagram for explaining a configuration example of an X-ray source according to the present invention.

FIG. 3 is a time chart for explaining the operation of the X-ray source of the present invention.

FIG. 4 is a diagram for explaining the control of the X-ray peak value of the X-ray source of the present invention.

FIG. 5 is a diagram for explaining X-ray pulse width control of the X-ray source of the present invention.

FIG. 6 is a diagram for explaining X-ray pulse width control of the X-ray source according to the present invention.

FIG. 7 is a view for explaining another configuration example of a positive ion generating mechanism by laser irradiation of the X-ray source of the present invention.

FIG. 8 is a diagram for explaining another configuration example for controlling the pulse width of the X-ray source according to the present invention.

FIG. 9 is a diagram for explaining another configuration example of the positive ion generation control means of the present invention.

[Explanation of symbols]

1,11 ... X-ray source, 2 ... Vacuum, 3 ... Anode, 4,4 ',
4 '' ... cathode, 5,25 ... electric field, 6 ... target, 7 ...
Positive ions, 7R, 7S: irradiation position, 8: secondary electrons, 9:
X-ray, 12: vacuum vessel, 13: exhaust pump, 14: gas source, 15: power supply, 16, 17 ... window, 19 ... ionization area, 71, 72 ... positive ion generation mechanism, 71a, 73, 7
3P, 73Q: laser beam, 71b: optical system, 72a:
Ion source, 72b ... electric field lens.

Claims (2)

[Claims] 1. A cathode and an anode which are spaced apart from each other in a vacuum vessel and to which a high voltage is applied, and a positive ion generating means for generating positive ions in an electric field formed between the cathode and the anode. An X-ray source, comprising: generating X-rays from an anode by colliding secondary electrons formed by collision between positive ions and a cathode with an anode; and controlling X-ray waveform by controlling generation of positive ions. 2. The method according to claim 1, wherein said positive ion generating means generates positive ions by ionizing a residual gas in a vacuum vessel by condensing a laser, and controls an X-ray waveform by controlling a laser irradiation state. X described in item 1
Source.