JP2000314800A - Pulse-like high luminance gamma-ray generating method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate γ rays of short wavelength and high luminance by irradiating laser beams of specific irradiation intensity to target material to generate γrays. SOLUTION: A laser source 1 is formed as a glass laser of wavelength 1053 nm, for instance, to generate laser beams in a pulse state at about 1-10 Hz. The laser beams are converged by a concave mirror 7 in a vacuum chamber 3 to irradiate an irradiated part 8 on the surface of target material 4. The laser beams at the irradiated part 8 are to have an intensity of about 1018-1022 W/cm2, and the outer diameter is about 1-50 μmϕ, for instance. The target material 4 is suitably selected from the atomic numbers 1-100, and the target material 4 is moved into a vacuum chamber 5 by a moving means 9 to prevent the target material 4 from being consumed at the irradiated part 8 by the laser beams. Gamma rays of about 0.1 MeV-1 GeV with directivity of short wavelength are generated in a radiating direction 11a extended from a laser irradiating direction 11, by braking radiation in the target material 4 of electrons accelerated by the light pressure of laser beams, and the energy thereof is controlled by changing converging intensity and the kind of material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a method and an apparatus capable of generating a line and performing diagnosis or the like of a test object.

[0002]

2. Description of the Related Art Conventionally, radiographic apparatuses have been used in fields such as medical radiography and industrial nondestructive radiography. In these imaging apparatuses, a braking X-ray or a characteristic X-ray generated by irradiating a metal target with electrons is used as an X-ray light source. The brightness of these X-rays is low,
A long exposure time of about 10 minutes to 1 hour is required for observing the inside of a metal part having a thickness of 1 cm. For this reason, for example, it is impossible to perform an exposure within several seconds to one time or an inspection within several times in an automobile production line or an electric appliance production line. X-rays generated from a conventional X-ray tube are wavelengths at which the internal structure of a metal can be observed. However, since the luminance is low, an exposure time of several tens minutes or more is required to observe a substance having a thickness of several cm. . This is not practical.

There is synchrotron radiation as a high-brightness X-ray light source. This device is a large-scale facility, and the building itself is regulated, so that it cannot be used in a factory line. The X-ray light source has a large light source size and poor spatial resolution of an obtained image.

As another prior art, an X-ray microscope apparatus or an evaluation apparatus using laser plasma soft X-rays has been proposed (JP-A-7-128500, JP-A-8-3800).
04311). These prior art devices is, 10 ⁸ W /
Soft X-rays of less than 10 to 20 keV generated at an irradiation intensity of laser light from cm ² to 10 ¹³ W / cm ² are used, the wavelength is relatively long, and the luminance is insufficient. In such prior art, when a target material is irradiated with laser light, plasma is generated, and electrons move thermally, thereby generating X-rays. Such X-rays do not have directivity, and therefore cannot increase the intensity of X-rays per unit area, and have insufficient luminance as described above. In laser plasma soft X-rays, soft X-rays having a wavelength of 1 nm or more are mainly used. Therefore, X-ray penetration power is weak,
Since only thin polymer materials of less than submillimeters and living bodies can be observed, the range of use is small.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to generate so-called hard γ-rays having a high luminance and a short wavelength, thereby observing various test objects with high spatial resolution and high throughput. Pulsed high-brightness γ-ray generation method and apparatus for enabling diagnosis
Another object of the present invention is to provide a gamma-ray diagnostic device.

[0006]

Means for Solving the Problems The present invention, ^1018
This is a pulsed high-brightness γ-ray generation method characterized in that γ-rays are generated by irradiating a target material with a pulsed laser beam of ²² W / cm ² .

Further, the present invention relates to 10 ¹⁸ to 10 ²² W / cm ^2.
A pulsed high-brightness γ-ray generation method characterized in that γ-rays having directivity of about 0.1 MeV to about 1 GeV are generated by irradiating the target material with the pulsed laser light of (1).

[0008] The present invention also provides a container having a γ-ray transmission window made of a material having a small γ-ray attenuation rate and forming a vacuum chamber;
A laser source that is provided in the container and generates pulsed laser light of 10 ¹⁸ to 10 ²² W / cm ² ,
A pulsed high-brightness γ-ray generator characterized in that a laser beam from a laser source is irradiated and a generated γ-ray includes a target material that transmits through a γ-ray transmission window of the container to the outside of the container.

According to the present invention, high strength of 10 ¹⁸ W /
A target material is irradiated with a laser beam of cm ² or more.
Since such high-intensity laser light has a high light pressure, the pressure of the laser light accelerates electrons of the target material, causing a phenomenon in the region of relativity. When the electrons are accelerated, the orbit of the electrons is changed, whereby hard γ rays having directivity are generated from the target material. The laser beam has an intensity of 10 as described above.
^Although it is more preferable to be larger than ¹⁸ W / cm ² , it may be, for example, less than 10 ²² W / cm ² . When the intensity of the laser light is less than 10 ¹⁸ W / cm ² , the pressure of the laser light is small, and the acceleration of electrons becomes insufficient.
Therefore, hard gamma rays having directivity cannot be generated. Thus, hard γ-rays having directivity are generated from the target material.

The generated γ-rays have a wavelength of about 0.1 MeV
It has an energy of about 1 GeV. As a result, a test object such as a knife or an automobile part made of a metal material such as iron or stainless steel has a thickness of about 2 to 7 cm and can transmit γ-rays, which has been impossible in the past. Observation of the inspected object becomes possible for the first time. The laser light is pulsed, so that it is relatively easy to generate high intensity laser light. Such pulsed laser light is emitted from a laser source, for example, at about 0.0003 (= 1/3).
600) at a repetition rate of -10 Hz or higher.

Exposure time of once or several times is several cm
In order to observe a substance having a thickness, it is necessary to generate γ-rays having high brightness at a short wavelength of 1 nm or less. To achieve this, a laser beam from a high-intensity laser device whose pulse width is from femtoseconds to picoseconds and whose energy is from subjoules to several hundred kjoules is converted into a target material,
Condensed irradiation is performed so as to have an irradiation intensity of 10 ¹⁸ W / cm ² or more to generate high-density and high-temperature plasma. The diameter of the focused spot is 1 to 50 μm, and this spot diameter determines the spatial resolution of the obtained image. As a result, γ-rays having high brightness at a short wavelength of 1 ° or less are generated. By using this as a light source, exposure of several cm
Observing a thick material is realized.

According to the present invention, as an object to be inspected, metals, synthetic resins, ceramics, polymers, internal structures and internal tissues of a living body having a thickness of several μm to several cm can be measured in a short time from femtosecond to nanosecond. Thus, an apparatus that can be used for material analysis, defect inspection, medical diagnosis, and the like in a wide range of fields that can be observed with a computer can be realized.

The space where the laser light from the laser source irradiates the target material is a vacuum chamber in the container. Therefore, the laser light is irradiated on a gas or other substance to attenuate the intensity of the laser light, Problems such as generation of undesired γ-rays do not occur.

The γ-ray transmission window is made of a material having a small γ-ray attenuation rate, and may be made of a metal material such as aluminum or beryllium, or may be made of other materials.

According to the present invention, the laser source has a wavelength of 1053.
nm glass laser.

According to the present invention, a laser beam having a wavelength of 1053 nm and its harmonics can be generated with high intensity by using a glass laser.

Further, the present invention is characterized in that the laser source generates a laser beam having a pulse width of about 0.1 × 10 ⁻¹² to 10 × 10 ⁻¹² sec.

According to the present invention, the pulse width of the laser light generated from the laser source can be selected in a short time, thereby obtaining a high-intensity laser light. When the pulse width is about 0.
When the intensity is less than 1 × 10 ^-12 sec, the intensity of the laser light is likely to be insufficient. In the range exceeding about 10 × 10 ^-12 sec, high intensity laser light is continuously generated temporally. Becomes difficult.

Further, according to the present invention, the target material is a metal,
It is a synthetic resin or a substance which is a liquid or gas at room temperature and solidifies at a low temperature lower than room temperature.

According to the present invention, any material can be used as the target material. For example, each material having an atomic number of 1 to 100 can be used. Thus, gamma rays having directivity can be obtained. The target material may be a metal, a synthetic resin, or the like. In addition, the target material
It may be a liquid or gas at room temperature, a substance solidified at a low temperature lower than room temperature, and may be a solid at an extremely low temperature state such as hydrogen H or deuterium D, for example, a temperature lower than 18K. .

Further, the present invention is characterized in that it includes a moving means provided in the container for moving the target material.

According to the present invention, the target material is irradiated with the laser beam by moving the target material in the vacuum chamber of the container by the means for moving the laser beam from the laser source. Partial wear can be prevented and gamma rays can be generated reliably.

According to the present invention, there is also provided the above-described pulsed high-brightness γ-ray generator, wherein an object to be inspected to be irradiated with γ-rays from a γ-ray transmission window is arranged outside the container, and A gamma-ray diagnostic apparatus characterized in that detection means for detecting a gamma-ray transmission image of an object to be inspected on a two-dimensional detection surface is disposed on a side of the body opposite to the gamma-ray transmission window.

According to the present invention, the γ-rays generated from the target material in the vacuum chamber of the container are radiated to the object to be inspected through the γ-ray transmission window, and the γ-ray transmission image is obtained by the detection means.
It is detected on the dimension detection surface. Thus, the object to be inspected can be observed.

According to the present invention, there is further provided a transporting means for sequentially transporting the object to be inspected at a position irradiated with γ-rays from a γ-ray transmitting window, and the laser source emits the pulsed laser light. It occurs at a predetermined number of times at the γ-ray irradiation position.

According to the present invention, the test object is sequentially conveyed to the γ-ray irradiation position by the conveying means,
For example, a mass-produced test object can be inspected efficiently. The laser beam has a pulse shape, and diagnosis can be performed by irradiating the object to be inspected moved by the moving means one or more times with γ-rays. Thus, a large number of test objects can be nondestructively inspected in a short time.

[0027]

FIG. 1 is a simplified system diagram showing the overall configuration of a gamma ray diagnostic apparatus 24 according to an embodiment of the present invention. This γ-ray diagnostic device 24 basically has a pulsed γ
X-ray generator 25 and subject 1 to be subjected to γ-ray diagnosis
And a detecting unit 17 for detecting a γ-ray transmission image of the test object 14 conveyed by the conveying unit 13. In the pulsed γ-ray generator 25, the pulsed laser light from the laser source 1 is guided into the vacuum chamber 3 via the vacuum path forming means 2 for propagating the laser light, and is irradiated on the target material 4. The path forming means 2 and the vacuum chamber 3 constitute a container 6 forming a vacuum chamber 5. The laser source 1 is provided in the path forming means 2.

The laser source 1 has a wavelength of, for example, 1053 nm.
And intermittently generates a laser beam at a pulse rate of 1 to 10 Hz, for example. This laser light is condensed by a concave mirror 7 provided in the vacuum chamber 3 and irradiates an irradiation portion 8 on the surface of the target material 4. The laser beam in the irradiated portion 8 is 10 ¹⁸ to 10
^It has an intensity of ²² W / cm ² , and the outer diameter of the laser beam at the irradiated portion 8 is, for example, 1 to 50 μmφ. Concave mirror 7
Is a so-called off-axis parabolic mirror or a condensing mirror instead. The wavelength of the laser beam may be 0.1 to 10 μm, and particularly preferably 0.1 to 2.0 μm.

The target material 4 has an atomic number of 1 to 100.
A suitable one is selected from the group consisting of, for example, a metal and a synthetic resin, or a substance which is a liquid or a gas at room temperature and solidifies at a low temperature lower than room temperature. The moving means 9
The target material 4 is moved in the vacuum chamber 5, and thereby, the irradiated portion 8 of the target material 4 by the laser beam changes, so that consumption of the target material 4 can be prevented. The target material 4 withstands irradiation of a high repetition laser (for example, a repetition rate of about 0.0003 (= 1/3600) Hz or more).

By irradiating the target material 4 with the converged laser light at the irradiation part 8, the laser irradiation direction 11 is generated by the braking radiation in the target material 4 of the electrons accelerated by the pressure of the laser light. 0.1Me having a short-wavelength directivity in the radiation direction 11a on the extension of
Hard gamma rays of V to about 1 GeV are generated. Generated γ
The energy of the line is controlled by controlling the condensing intensity of the concave mirror 7 or the like which is the intensity per unit area of the laser beam.
The adjustment can be made by changing the type of the target material 4.

The γ-ray generated from the target material 4 is γ-ray
The γ-ray irradiation region 1 is applied to each of the plurality of inspected objects 14 that are transmitted through the window 12 and sequentially conveyed by the conveying unit 13.
Irradiation at 5. The test object 14 is sequentially conveyed by the conveying means 13 in the direction of the arrow 16.

FIG. 2 shows the γ-ray transmission window 12 of the vacuum chamber 3.
It is sectional drawing of a vicinity. The base end of the cylinder 21 is fixed to a through hole 19 formed in the outer peripheral wall 18 of the vacuum chamber 3. An outward flange 22 is formed at the free end of the cylindrical body 21. The γ-ray transmission window 12 is flange-joined by a flange 22.

The γ-ray transmission window 12 forms a part of the outer peripheral wall 18 of the vacuum chamber 3. The γ-ray transmission window 12 is made of a material having a small γ-ray attenuation rate, and may be made of a metal material such as aluminum or beryllium. When the γ-ray transmission window 12 is made of the aforementioned aluminum, its thickness may be, for example, 12 mm. Vacuum chamber 3
Is made of a metal material such as iron, for example.
Its thickness may be, for example, 80 mm.

The detecting means 17 for detecting the γ-ray transmission image of the inspection object 14 is disposed on the opposite side of the inspection object 14 from the γ-ray transmission window 12 (upper part in FIG. 1). This detecting means 17
Is configured by arranging a large number of pixels in a matrix in order to detect a γ-ray transmission image of the inspection object 14 on a two-dimensional detection surface. Each pixel derives a signal level corresponding to the intensity of the γ-ray. The γ-ray indicated by the arrow 11a passes through the inspection object 14, and the γ-ray transmission image is captured by the detection unit 17 and converted into an electric signal.

In another embodiment of the present invention, the detecting means 1
Reference numeral 7 may be a photographic film or an imaging plate that is sensitive to γ-rays. The detecting unit 17 also receives a light-emitting plate that emits light at an emission intensity corresponding to the intensity of the γ-rays based on the γ-ray transmission image transmitted through the inspection object 14, and receives light from the light-emitting plate, and the two-dimensional detection surface An imaging unit for detecting a luminescent image may be included, and the imaging unit may have a large number of pixels in the same matrix as described above, or may be a photosensitive photographic film or the like.

In the embodiment shown in FIGS. 1 and 2 described above, the object to be inspected 14 is arranged so as to be almost in contact with the detecting means 17 having the two-dimensional detecting surface. In another embodiment, in order to enlarge the γ-ray transmission image of the inspection object 14 so that it can be detected by the detection unit 17, the inspection object 14 and the detection unit 1
7 are set apart from each other by a predetermined distance a. The distance between the target material 4 that generates γ-rays and the inspection object 14 is b
, The magnification M of the γ-ray transmission image of the test object 14
Is M = (a + b) / b. The spatial resolution at that time is determined by the spot size of 1 to 50 μm of γ-rays.

The experimental results of the present inventor will be described. In the embodiment of the present invention shown in FIGS. 1 and 2, the target material 4 is polystyrene containing deuterium. The laser source 1 is a glass laser, and the laser light has a wavelength λ = 1 μm.
m, the pulse width is 0.6 × 10 ⁻¹² sec, and the ^focused intensity of the laser beam in the laser beam irradiated portion 8 of the target material 4 is 10 ¹⁹ W / c as shown by the reference numeral 27 in FIG.
m ² . As shown in FIG. 2, the test object 14 is
Stainless steel knife, from thin 2mm to thick 20
with each part up to mm. By irradiating the target material 4 with a single pulsed laser beam, a γ-ray transmission image was obtained by the detection means 17. The detecting means 17 is an imaging plate manufactured by Fuji Film Co., and has a high intensity dynamic range of about 105. Thus, the inspection object 14
It was confirmed that the γ-ray transmission image attains a spatial resolution within 0.1 mm.

Reference numeral 27 in FIG. 3 indicates the characteristics of the generated γ-rays indicating the experimental results by the present inventors, as described above. Reference numerals 28 and 29 in FIG. 3 are comparative examples, and 1 × 10 ¹⁶ to 2 × 10
The characteristics of γ-rays obtained when irradiating a laser beam of × 10 ¹⁶ W / cm ² are shown. With such characteristics 28 and 29,
The energy of the generated γ-rays is clearly low, and there is no directivity, and therefore the penetrating power is weak, so that a desired thick test object cannot be inspected.

[0039]

According to the first, second and third aspects of the present invention, it is possible to generate high-brightness, short-wavelength hard γ-rays, and thus have a large γ-ray transmission power, and Γ-ray transmission image can be obtained, and the nondestructive inspection can be easily performed. Since the γ-rays generated here have directivity, the intensity per unit area is increased, and this can also increase the penetrating power of the test object.

According to the fourth aspect of the present invention, by using a glass laser, the high-intensity pulsed laser light of the present invention can be obtained relatively easily.

According to the fifth aspect of the present invention, the pulse width of the laser beam generated from the laser source is selected in a short time.
High-intensity laser light can be obtained, and thereby pulsed high-brightness γ-rays can be generated.

According to the sixth aspect of the present invention, the target material may be a metal, a synthetic resin, or the like, and may be a substance that is a liquid or a gas at normal temperature and solidifies at a low temperature. By using any of such target materials, various desired short-wavelength γ-rays can be obtained.

According to the seventh aspect of the present invention, by moving the target material in the container, the laser beam irradiated portion of the target material is always kept fresh, thereby preventing the laser beam irradiated portion from being consumed. , Γ-rays can be reliably generated.

According to the eighth aspect of the present invention, various types of γ-rays are emitted from the γ-ray transmission window to the object to be inspected, and the γ-ray transmission image is detected by the two-dimensional detection surface of the detection means. A non-destructive inspection of the inspection object can be performed.

According to the ninth aspect of the present invention, the test object is sequentially conveyed to the position where the γ-ray is irradiated from the γ-ray transmission window of the container by the conveying means. Thus, for example, non-destructive inspection can be performed on mass-produced test objects sequentially by transmitting γ-rays. The test object transported to the position, in response to irradiation of the target material with pulsed laser light, pulsed γ-ray, single or multiple times,
Flash irradiation can be performed. When the object to be inspected has a thick shape with a large attenuation rate of γ-rays, a γ-ray transmission image can be clearly obtained by the detecting means by a plurality of irradiations of γ-rays. Thus, the present invention can be implemented in a wide range of fields such as material analysis, defect inspection, and medical diagnosis.

[Brief description of the drawings]

FIG. 1 is a simplified system diagram showing the overall configuration of a γ-ray diagnostic apparatus 24 according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the vicinity of a γ-ray transmission window 12 of the vacuum chamber 3.

FIG. 3 is a graph showing experimental results of the present inventor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser source 2 Path forming means 3 Vacuum chamber 4 Target material 5 Vacuum chamber 6 Container 7 Concave mirror 8 Laser light irradiation part 9 Moving means 11 Laser irradiation direction 12 γ-ray transmission window 13 Transport means 14 Inspection object 15 γ-ray irradiation area 17 Detecting means 24 γ-ray diagnostic device 25 Pulsed γ-ray generator

Claims (9)

[Claims] 1. A target material is irradiated with a pulsed laser beam of 10 ¹⁸ to 10 ²² W / cm ² to obtain γ.
A method for generating a pulsed high-brightness γ-ray, comprising generating a line. 2. A gamma ray having a directivity of about 0.1 MeV to about 1 GeV is generated by irradiating a pulsed laser beam of 10 ¹⁸ to 10 ²² W / cm ² to a target material. High-brightness γ-ray generation method. 3. A container having a γ-ray transmission window made of a material having a small γ-ray attenuation rate and forming a vacuum chamber, and a pulsed laser provided in the container and having a dose of 10 ¹⁸ to 10 ²² W / cm ^2. A laser source that generates light, and a target material that is provided in the container, is irradiated with laser light from the laser source, and the generated γ-ray passes through the γ-ray transmission window of the container to the outside of the container. Pulsed high-brightness gamma-ray generator. 4. The pulsed high-brightness γ-ray generator according to claim 3, wherein the laser source is a glass laser having a wavelength of 1053 nm. 5. The laser source has a pulse width of about 0.1 × 10
^5. The pulsed high-brightness γ-ray generator according to claim 3, wherein the pulsed high-brightness γ-ray generator generates a laser beam of ^-12 to 10 × 10 ^-12 sec. 6. The method according to claim 3, wherein the target material is a metal, a synthetic resin, or a substance that is liquid or gas at room temperature and solidified at a low temperature lower than room temperature. The high-brightness γ-ray generator according to the above. 7. The pulsed high-brightness γ-ray generator according to claim 3, further comprising a moving means provided in the container for moving the target material. 8. An inspected object provided with the pulsed high-brightness γ-ray generator according to any one of claims 3 to 6, wherein γ-rays are emitted from a γ-ray transmission window outside the container. A gamma ray diagnosis, wherein a detection means for detecting a gamma ray transmission image of the inspected object on a two-dimensional detection surface is arranged on a side opposite to the gamma ray transmission window with respect to the inspected object. apparatus. 9. A transfer means for sequentially transferring an object to be inspected at a position where γ-rays are transmitted from a γ-ray transmitting window, wherein a laser source emits a pulsed laser beam to the γ-ray irradiation. 9. The γ-ray diagnostic apparatus according to claim 8, wherein the γ-ray diagnostic apparatus is generated a plurality of times at a position.