JP2001155897A - Short pulse hard x-ray generating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short pulse hard x-ray generating apparatus that can be used in fields of radiography, medical diagnosis, x-ray fluorescence analysis, and material surface reforming technology requiring high brightness of pulse x-ray, and application industry and medical diagnosis technology field such as non-destruction inspection, permeation image measurement requiring high speed phenomenon. SOLUTION: An photoelectrons are generated on a negative pole by the photoelectronic for short time as a short time width of pulse laser beam is in irradiated to one electrode between electrodes applied with high voltage within a vacuum container, and they are collided against a positive pole to generate short pulse x-ray.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The pulse X-ray generator according to the present invention is required to capture radiography, medical diagnosis, X-ray tendency analysis, material surface modification technology and high-speed phenomena which require pulsed X-rays of high luminance. It can be used in certain non-destructive inspection, industrial technology of X-ray application such as transmission image measurement, and medical diagnostic technology.

[0002]

2. Description of the Related Art It is impossible to generate pulsed X-rays having a pulse width of ns (10 ^-9 seconds) or a pulse width of ps (10 ^-12 seconds) using a conventional X-ray tube or the like. It is.

In such a case, in the prior art, there is a method of obtaining a pulse X-ray by injecting a pulse train of a pulsed electron beam from an electron source into a target using an accelerator. Alternatively, there is a method in which a very high-temperature plasma is generated by using a short-pulse laser having a large output to generate X-rays for inner-shell excitation or pulses for bremsstrahlung.

[0004]

In order to generate high-brightness pulsed X-rays by the conventional method, an expensive and large-scale apparatus such as an accelerator and a high-output short-pulse laser is required. Further, there is a problem that maintenance costs and expenses are high in operation. When performing an applied test in which pulsed X-rays are generated in such a state, a long preparation time until operation,
A plurality of dedicated personnel for each device is required, and there is a problem that the operation, testing, and electric energy efficiency are poor as a whole.

[0005]

In order to easily generate pulsed X-rays, the present invention utilizes soft X-rays from laser light and laser plasma, fluorescent light in the ultraviolet region, or either one of them. This is a pulse X-ray generator that efficiently generates pulse X-rays by generating photoelectrons between electrodes to which a high voltage is applied and colliding the photoelectrons with an anode.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) The present invention will be described with reference to FIG. 1. A short-pulse hard X-ray generator embodying the present invention is a high-voltage pulse generator, a Marx generator 1,
Synchronous control system 1 for synchronizing a metal vacuum vessel 2 for generating X-ray pulses including evacuation, a YAG laser device 13 and a Marx generator with a YAG laser device
1

[0007] The process of X-ray pulse generation starts with YA.
Pulse laser light 12 of fourth harmonic from G laser device 13
Is irradiated to the tip of the anode 6 inside the vacuum vessel 2 through the YAG laser light incident window 14 by the YAG laser light reflecting mirror 9. The reflected laser light 8 or the fluorescent light 8 from the laser plasma is generated from the place irradiated with the laser light, and when reaching the tip of the cathode 7 and the inner surface of the vacuum vessel 2 at the same potential as the cathode, photoelectrons 5 are generated by the photoelectric effect. I do.

The Marx generator 1 applies a high-voltage pulse to the anode 6 by the synchronization control trigger 10 from the synchronization control system 11 almost simultaneously with the irradiation of the anode 6 with the YAG laser beam 12. When a high voltage pulse is applied between the anode and the cathode, the photoelectrons 5 generated on the cathode 7 and the inner surface of the vacuum vessel 2
Are accelerated toward the anode 6 to obtain high kinetic energy and collide with the anode to emit pulsed X-rays 3 by bremsstrahlung. The pulse X-ray 3 is extracted from the pulse X-ray extraction window 4 and is used for application tests, measurement, and the like.

(2) Typical X-ray pulses generated by the short pulse hard X-ray generator of the present invention, accompanying laser pulses, applied high voltage pulses, and current pulse waveforms will be described with reference to FIG. Then, when the discharge voltage pulse 4 is applied to the anode simultaneously with the incidence of the laser pulse 3 on the anode surface in the vacuum vessel of the short pulse hard X-ray generator of the present invention, the X-ray pulse 1 is observed from the anode surface. . X-ray pulse 1 in FIG. 2 is measured by a scintillator having a fast rise time.

The observed X-ray pulse 1 is composed of a sharply rising peak first, followed by a long pulse. When the X-ray pulse 1 is passed through an iron plate of about 20 mm, only the hard X-ray pulse 2 having a sharp peak remains. This X-ray
Since this pulse width corresponds to the width of the laser pulse 3, it is generated based on photoelectrons due to the reflected light of the laser light from the anode surface.

Almost simultaneously with the generation of the photoelectrons, a high discharge voltage pulse 4 is applied to the anode, and the photoelectrons are accelerated and incident on the anode. Therefore, the sharp peak X-rays have high energy close to the charging voltage of the Marx generator. Consists of components.

The longer X-ray pulse in the latter half is a photoelectron generated by soft X-rays from the plasma generated by laser irradiation on the anode surface and fluorescent light in the ultraviolet region etc. incident on the cathode surface due to the pulse width. Is an X-ray pulse generated based on. In the X-ray pulse, the discharge current 5 starts to flow between the negative and positive electrodes through the laser plasma, and the discharge voltage 4 applied to the anode starts to decrease. The X-ray pulse has lower energy than the X-ray pulse.

(3) The effective energy of the X-ray pulse generated by the short-pulse hard X-ray generator of the present invention will be described with reference to FIG. 3. The effective energy of the X-ray pulse can be determined from the relationship between the intensity of the X-ray and the thickness thereof. The effective energy is derived from the slope of the attenuation curve obtained from the intensity of the attenuated X-ray and the thickness of the iron plate. A small inclination means that the attenuation is small, indicating that the X-ray has a high effective energy. When the X-ray pulse generated in the apparatus embodying the present invention is passed through iron plates having different thicknesses, the attenuation of the intensity is shown in FIG. From this attenuation curve, it can be seen that there are two types of slopes. There are two types of slopes, a slope that greatly attenuates in a region where the thickness of the iron plate is small, and a slope that attenuates in a region where the thickness of the iron plate is large.

By applying the attenuation coefficient of the iron plate to X-rays to these slopes, it can be seen that the first slope has an effective energy of about 80 keV and the other slope has an effective energy of about 150 keV. Thus, the X-ray pulse generated by the apparatus of the present invention is about 80 keV and about 150 keV.
It can be seen that it is composed of two component X-rays having an effective energy of

(4) As can be seen from the above description, when one of the metal electrodes disposed at very short intervals in the vacuum vessel is irradiated with the laser beam, the laser beam is irradiated from the cathode surface mainly through one of three routes. Photoelectrons are generated. Photoelectrons generated by direct incidence of laser light on the metal surface, photoelectrons generated by reflected laser light from the metal surface, and fluorescence such as soft X-rays and ultraviolet light from laser plasma generated by laser irradiation on the metal surface There are three types of photoelectrons.

At this time, the photoelectrons are generated in a pulsed manner within the pulse time width of the laser beam or within the fluorescence lifetime of the ionized excited atoms in the laser-produced plasma. When a high voltage is applied between the electrodes almost simultaneously with the generation of these photoelectrons, the photoelectrons enter the anode with kinetic energy corresponding to the potential energy applied between the electrodes. Photoelectrons incident on the anode are
X-rays are generated by bremsstrahlung. The photoelectrons are accelerated a short distance toward the anode by the high electric field between the electrodes at the same time as the generation thereof, so that the generated photoelectrons enter the anode without extending the time width. Therefore, a pulse X-ray having a pulse width corresponding to the time width of the laser beam or the lifetime of the fluorescence from the laser-produced plasma is generated from the anode.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
FIG. 1 shows a schematic diagram of the short pulse hard X-ray generator used. The apparatus includes a Marx generator 1 for generating a high-voltage pulse, a vacuum vessel 2 for X-ray generation in which a pin-shaped counter electrode is installed, a vacuum pump, a fourth harmonic (laser wavelength: 266 nm), and a laser energy of about It comprises a pulse YAG laser device 13 for generating 70 mJ and a pulse synchronization system 11 for adjusting the synchronization between the high voltage pulse and the pulse laser.

When the laser beam 12 is focused on the anode 6 in the vacuum vessel evacuated to a high vacuum, the reflected light 8 of the laser beam,
Soft X-rays and ultraviolet light of the laser plasma generated on the anode are incident on the surface of the cathode 7 (including the inner surface of the vacuum vessel) to generate photoelectrons 5. As shown in FIG. 2, a pulse voltage of 150 kV or more is applied to the anode in synchronization with the laser beam.

The photoelectrons generated on the cathode surface are accelerated by the potential energy applied between the anode and the cathode, are incident on the anode, and are irradiated with the X-ray pulse 3 shown in FIG.
From the anode surface. The pulsed X-ray consists of a first sharp peak pulse and a second half long pulse, and the total pulse width is about 400 ns. When the effective energy of the emitted pulse X-ray is measured by an attenuation method, as shown in FIG. 3, the pulse of the latter half has an effective energy of about 80 keV, and the pulse X-ray of the first half has a sharp peak of about 150 keV.
It was found to have an energy of keV.

The hard X-ray pulse shown in FIG.
X-ray pulse of about 150 keV that passed through the iron plate of FIG. Since this pulse width is equivalent to the pulse width of the laser light of 50 ns, it is understood that the first half of the pulse X-ray is due to photoelectrons generated by the reflection of the laser light incident on the cathode. The latter pulse X-ray is due to photoelectrons generated by the fluorescence 8 from the laser plasma generated on the anode incident on the cathode.

[0021]

According to the present invention, it is possible to generate pulsed hard X-rays more efficiently than in the conventional method. For this reason, it is possible to contribute to downsizing and high output of the pulse X-ray apparatus. X using a pulse X-ray generator
In the technology development field of wire application, it is more compact and easier to operate than the conventional equipment, so it has the effect of improving the test progress in the field.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a short-pulse hard X-ray generator embodying the present invention.

FIG. 2 is a diagram showing typical waveforms of an X-ray pulse, a laser pulse, an applied high-voltage pulse, and a current pulse in a short-pulse hard X-ray generator according to the present invention.

FIG. 3 shows a short pulse hard X by an attenuation method in the present invention.
FIG. 4 is a diagram illustrating an attenuation curve of an X-ray pulse generated by the line generator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Marx generator 2 Vacuum container (cathode) 3 Pulse X-ray 4 Pulse X-ray extraction window 5 Photoelectron 6 Anode 7 Cathode 8 Fluorescence from reflected laser light or laser plasma 9 YAG laser light reflection mirror 10 Synchronous control trigger 11 Synchronous control system 12 YAG laser beam 13 YAG laser device 14 YAG laser beam entrance window

Claims (9)

[Claims] 1. A method according to claim 1, wherein one of the electrodes between the electrodes to which a high voltage is applied in the vacuum vessel is irradiated with a pulse laser beam having a short time width to generate photoelectrons by a photoelectric effect on the cathode in a short time.
A pulse X-ray generator capable of generating short pulse X-rays by colliding this with an anode. 2. The generated photoelectrons are those which are emitted by directly or indirectly irradiating a cathode with a laser beam, or soft X-rays from a laser plasma generated by irradiating a laser beam on a metal surface. 2. The pulse X-ray generator according to claim 1, wherein fluorescent light such as ultraviolet rays is irradiated to the cathode in a short time and comes out. 3. The pulse X-ray generator according to claim 1, wherein the pulse X-rays generated from the anode surface are characteristic X-rays and X-rays caused by bremsstrahlung. 4. The method according to claim 1, wherein the intensity of the generated pulse X-rays depends on the intensity of incident laser light or the intensity of fluorescent light such as soft X-rays and ultraviolet rays emitted from laser-produced plasma. Pulse X-ray generator. 5. The pulse time width of the generated pulse X-ray is:
2. The pulse X-ray generator according to claim 1, wherein the pulse X-ray generator depends on a pulse time width of fluorescence from laser light or laser plasma. 6. The pulse X-ray generator according to claim 1, wherein the average effective energy or spectrum width of the generated X-rays depends on the voltage applied between the electrodes. 7. The pulse X-ray generator according to claim 1, wherein the pulse repetition number of the generated pulse X-ray depends on the pulse laser light repetition number. 8. The pulse X-ray generator according to claim 1, wherein the X-ray is generated at an anode in a vacuum vessel, and the cathode generates photoelectrons. 9. The pulse X-ray generator according to claim 1, wherein the voltage applied between the electrodes is synchronized with the irradiation of the pulsed laser beam and applied in a pulsed manner.