JP2005172771A - Alpha/beta ray detection device and alpha/beta ray detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detection device and radiation detection method capable of simultaneously, rapidly and precisely detecting alpha-ray and beta-ray contaminating the surface of an object contaminated with radioactive materials, for example, an article carried out from a nuclear fuel processing facility. <P>SOLUTION: This radiation detection device comprises a vacuum vessel capable of storing the object contaminated with radioactive materials, the pressure of which can be reduced; and an alpha-ray detector and a beta-ray detector arranged within the vacuum vessel. In this detection device, the pressure in the vacuum vessel storing the object contaminated with radioactive materials is reduced, and alpha-ray and/or beta-ray generated from the object are detected by a pair of alpha-ray detector and beta-ray detector arranged each in at least three axial directions of x-axial direction, y-axial direction and z-axial direction within the vacuum vessel. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an α / β-ray detection apparatus and an α / β-ray detection method, and more specifically, for example, α-rays and β-rays from a radioactively contaminated object such as an article transported from a nuclear fuel processing facility. The present invention relates to an α / β-ray detection apparatus and an α / β-ray detection method that can simultaneously detect.

  For example, the measurement of the density of radioactive materials on the surface of nuclear fuel processing facilities, especially the articles carried out of their radiation control areas, is required by radiation-related laws such as the Reactor Regulation Act and the Industrial Safety and Health Act.

  The nuclides handled in the nuclear fuel processing facility are uranium (U), thorium (Th), and their daughter nuclides. Since these nuclides emit alpha and beta rays, alpha and beta rays are detected and various doses are measured for various items carried out from the radiation control area of the nuclear fuel processing facility. Safety must be confirmed.

  However, since the range distance of α rays in air is as short as about 3 cm, α rays and β rays could not be detected simultaneously. Therefore, the α ray and the β ray are individually detected, and each dose is measured. Also, since the range of α rays in air is short, the distance between the article and the α ray detector is an important factor in detecting the α ray, and as a result, the article and the α ray detector are almost in close contact with each other. In this state, α rays were detected.

  Thus, conventionally, it has been necessary to individually detect α rays and β rays and to measure each dose, so that the work is inferior in speed, and the time and labor required for the worker are extremely low. It was great.

  In view of such a current situation, the present invention simultaneously detects α-rays and β-rays radiated from an object contaminated with a radioactive substance, for example, an article carried out of a nuclear fuel processing facility, quickly and accurately. It is an object of the present invention to provide an α / β ray detection apparatus and an α / β ray detection method that can be performed.

  The present inventor has made various studies in order to solve the above problems, and as a result, the range of α rays can be increased by setting the detection environment in a reduced pressure state. The present inventors have found that it is possible to detect a line and a β-ray simultaneously and quickly and accurately, and based on this knowledge, the present invention has been completed.

That is, the first means for solving the problems of the present invention is as follows:
(1) It is possible to contain a target object contaminated with a radioactive substance and to have a decompression container capable of decompressing, and an α-ray detector and a β-ray detector disposed in the decompression container. This is a featured α / β ray detector.

As a preferable aspect in the first means,
The at least one set of the α-ray detector and the β-ray detector for each axial direction in the decompression container in at least three axial directions of the target object in the x-axis direction, the y-axis direction and the z-axis direction. And an α / β ray detection device in which each of the α ray detector and the β ray detector includes a light shielding film on the surface of the detector.

The second means for solving the above-mentioned problem of the present invention is as follows:
(2) A pair of α rays disposed in at least three axial directions of the x-axis direction, the y-axis direction, and the z-axis direction in the decompression container, wherein the decompression container containing the object contaminated with the radioactive substance is decompressed. An alpha / beta ray detection method, wherein alpha and / or beta rays generated from the object are detected by a detector and a beta ray detector.

As a preferable aspect in the second means,
After accommodating the object contaminated with the radioactive substance in the decompression vessel, the α-ray detector and the β-ray detector are used to reduce the pressure in the decompression vessel from normal pressure to reduced pressure. An α / β ray detection method for detecting α rays and / or β rays generated from an object can be mentioned.

  According to the present invention, it is possible to quickly and accurately detect an object contaminated with a radioactive substance, for example, alpha rays and beta rays contaminating the surface of an article carried out of a nuclear fuel processing facility at the same time. An α / β-ray detection device and an α / β-ray detection method that can be used are provided, which contributes greatly to environmental conservation in the field of handling nuclear fuel.

  (1) An α / β ray detection apparatus of the present invention is capable of containing an object contaminated with a radioactive substance and can be depressurized, an α ray detector and a β arranged in the depressurization vessel And a line detector.

  (2) Further, in the α / β ray detection method of the present invention, the inside of the decompression container containing the object contaminated with the radioactive substance is decompressed, and the x-axis direction, the y-axis direction and the z-axis direction are placed in the decompression container. The α ray and / or β ray generated from the object is detected by a pair of α ray detector and β ray detector arranged in at least three axial directions.

  Hereinafter, an α / β ray detection apparatus and an α / β ray detection method of the present invention will be described with reference to the drawings.

  FIG. 1 is a front view showing an α / β-ray detection apparatus as an example of the present invention.

  FIG. 2 is a system diagram showing a detection mechanism of α rays and β rays in an α / β ray detection apparatus which is an example of the present invention.

  FIG. 3 is an explanatory view showing a detector used in the α / β-ray detection apparatus as an example of the present invention.

  As shown in FIGS. 1 and 2, the α / β-ray detection device 1 includes a decompression vessel 3, a detector 2 disposed therein, an intake / exhaust device 4, a measurement display device 5, and a printer 6. And a preamplifier unit 7.

  The decompression container 3 is supported by a hinge or the like on the left side of the front so that the front can be opened and closed, and can be turned by a hinge or the like on the left side of the back toward the back. A back opening / closing door (not shown) that is supported and formed to be able to open and close the back, and when the front opening / closing door 13 and the back opening / closing door are closed, a sealed space is formed inside, and the intake / exhaust device 4 described later And a container body 14 configured to be able to reduce the pressure in the sealed space. The internal dimensions of the sealed space formed by the front open / close door 13, the back open / close door, and the container body 14 are 20 cm at the maximum, 40 cm at the maximum, and 40 cm at the maximum. Is preferred. With the decompression vessel 3 having the sealed space having such dimensions, the α-rays and β-rays can be detected by at least the detectors 2 arranged above and below. In the present invention, the internal dimensions of the sealed space are not limited to the above dimensions. For example, the internal space may be an internal space having a height of more than 20 cm, for example, 40 cm or 60 cm. Good. In the case of having such a large internal space, a mounting table for mounting the object to be measured may be disposed in this internal space. In addition, as long as this mounting base has the mounting function mentioned above, it may be called variously, such as a basket and a rack.

  The decompression vessel 3 is installed on a base 15 as shown in FIG. The base 15 can be moved by a caster 16 or the like, and can be fixed at a predetermined position so as not to move by a pin 17 whose vertical height can be adjusted.

  As shown in FIG. 3, the detector 2 includes two α / β-ray detectors 2A capable of performing α-ray detection and β-ray detection at the same time so that their detection front faces are the same. It is arranged side by side.

  Each α / β-ray detector 2A is a scintillator type detector in which a scintillator as a light emitter and a photomultiplier tube are combined. Specifically, as shown in FIG. 3, a flat α-ray detector 18, a flat β-ray detector 19 superimposed on the back surface of the α-ray detector 18, and a reinforcing member made of a transparent member that reinforces the laminate composed of the α-ray detector 18 and the β-ray detector 19. 20, a condensing unit 21 that condenses the light transmitted through the reinforcing member 20, and a photomultiplier tube 22 that amplifies the light collected by the condensing unit 21, and is detected from the photomultiplier tube 22. A signal is output.

  One light shielding film 23 is attached to the front surface of the two α-ray detectors 18 arranged in the same plane of the two α / β-ray detectors 2A. The light shielding film 23 has a function of blocking visible light and protecting the surface of the α-ray detector 18 from contamination, and is formed of various materials as long as the function is realized. A partition plate 24 is interposed between the parallel α / β ray detector 2A and the other α / β ray detector 2A.

  In the α / β-ray detector 2A having such a structure, as a material for forming the α-ray detector 18 that is a scintillator, an appropriate substance that emits light by incident α-rays is appropriately adopted. For example, organic compounds such as anthracene and trans-stilbene, NaI (TL), LiI (Eu), CsI (Tl), ZnS (Ag) and the like can be mentioned. Among these, ZnS (Ag) is suitable as an alpha ray scintillator. As a material for forming the β-ray detector 19, an appropriate substance that emits light by incident β-rays is appropriately used, but a plastic scintillator in which a phosphor is dispersed in plastic is preferable.

  As a scintillator for detecting α-rays and β-rays, in addition to the above, a fluorescent substance such as p-terphenyl or diphenyloxazole in an organic solvent such as toluene or xylene and a wavelength converter such as 1,4-di- [2 A liquid scintillator obtained by adding-(5-phenyloxazyl)]-benzene or the like to form a liquid cocktail can also be used.

  In the present invention, the detector is arranged so as to be able to detect α-rays and β-rays radiated from an article accommodated in the decompression vessel 3, and preferably in the x-axis direction in the decompression vessel. , Arranged in at least three axial directions of the y-axis direction and the z-axis direction. In the α / β ray detection apparatus shown in FIG. 1, two detectors 2-1 and 2-2 are provided on the inner surface of the front opening / closing door 13, and four detectors 2-3 are provided on the bottom surface of the decompression vessel 3. , 2-4, 2-5, 2-6, four detectors 2-7, 2-8, 2-9, 2-10 on the ceiling surface in the decompression vessel 3, one side in the decompression vessel 3 That is, two detectors 2-11 and 12-12 on the right side when viewed from the front, and two detectors 2-13 and 2-14 on the other side in the decompression vessel 3, that is, the left side when viewed from the front, And two detectors 2-15 and 2-16 are disposed on the inner surface of the rear opening / closing door, and a total of 16 detectors 2-1 to 2-16 are connected to the X axis, Y axis, and It will be arranged in the Z-axis direction.

  As described above, the arrangement of a plurality of detectors on the bottom surface and the ceiling surface in the decompression vessel 3 reliably detects α-rays and β-rays radiated from the article disposed in the central portion of the decompression vessel 3. It is to do.

  In order to depressurize the inside of the decompression vessel 3, the intake / exhaust device 4 is installed on the base 15. As long as the intake / exhaust device 4 has an ability to depressurize the sealed space of the decompression vessel 3 to -820 hPa, various devices can be combined and employed. In the α / β-ray detection device 1 shown in FIG. 1, the intake / exhaust device 4 is interposed in the dry pump 11, a pipe 25 for leading the air in the sealed space in the decompression vessel 3, and the pipe 25. The first filter 26 that cuts dust in the sealed space when the air in the sealed space is exhausted, the pressure gauge 27 that detects the pressure in the sealed space, and the air flow in the pipe 25 is cut off and opened. For example, a first electromagnetic valve 28 and an exhaust device 4A including a silencer 29 that shuts off noise generated by the dry pump 11, a pipe 30 communicating with the sealed space of the decompression vessel 3, and a pipe 30 An intake device 4B including a valve device to be interposed, for example, a second electromagnetic valve 31, and a second filter 32 that blocks dust in the air when air is introduced into the sealed space.

  In the preamplifier unit 7, preamplifiers 7-1 to 8 are connected to each detector 2 for each detector 2. Each preamplifier unit 7 receives the detection signal output from the detector 2, amplifies the input signal, and separates the detection signal into an α-ray detection signal based on α rays and a β-ray detection signal based on β rays. Then, the separated α-ray detection signal and β-ray detection signal are output to the measurement display device 5. That is, the preamplifier unit 7 is an αβ type preamplifier unit (hereinafter, the preamplifier unit 7 may be referred to as an αβ type preamplifier unit 7).

  As shown in FIG. 5, the αβ preamplifier unit 7 includes an amplifier 7A that amplifies the detection signal output from the photomultiplier tube 22, a differentiation circuit 7C that differentiates the detection signal through a buffer gate 7B, A reshaping circuit 7D for shaping the output signal output from the differentiating circuit 7C, an integrating circuit 7E for outputting the output signal from the amplifier 7A and integrating the detection signal via the buffer gate 7B, and an output from the integrating circuit 7E. The disc reshaping circuit 7F for shaping the output signal to be generated, and the adding circuit 7G for adding the output signal from the disc reshaping circuit 7D and the output signal from the disc reshaping circuit 7F to cancel the signal due to β rays And have.

  For example, as shown in FIG. 6, the output signal from the detector 2 appears as a small signal waveform appearing in a short time as shown by 19A, and the α-ray detector. The detection signal output from 18 appears as a signal waveform having a long amplitude and cycle as indicated by 18A, and the α-ray detection signal and the β-ray detection signal are greatly different. In the αβ preamplifier section 7, as shown in FIG. 7, the signal output from the detector 2 is simultaneously input to the differentiating circuit 7C and the integrating circuit 7E, and output from the differentiating circuit 7C by the disc reshaping circuit 7D. A signal smaller than a predetermined threshold is cut out and shaped to be a β-ray detection signal, and a signal smaller than the predetermined threshold is output from the integration circuit 7E in the disc reshaping circuit 7F. The α-ray detection signal is output by cutting and shaping, and subtracting the signal output from the disc shaping circuit 7F and the signal output from the disc shaping circuit 7D.

  The measurement display device 5 calculates the intensity of the α-ray and the intensity of the β-ray from the α-ray detection signal and the β-ray detection signal input from the preamplifier unit 7 and displays them on a display unit including a CRT screen or a liquid crystal display screen. Display the results.

  The printer unit 6 is configured to print the α ray intensity and β ray intensity calculated in the measurement display device 5.

  In FIG. 2, reference numeral 33 denotes a control power supply unit, which supplies power necessary for driving or operating the α / β-ray detection device to each unit and controls each unit.

  The α / β ray detection apparatus having the above configuration has the following effects.

  As shown in FIG. 1, first, an object contaminated with radiation is accommodated in a vacuum container 3. Here, examples of the object that can be measured by the α / β-ray detection apparatus according to the present invention include, for example, nuclear fuel processing facilities that handle uranium (U), thorium (Th), and their daughter nuclides, particularly their radiation control areas. For example, articles such as machines, instruments, devices, clothing, and miscellaneous goods that are carried out can be cited.

  The article is accommodated in the container main body 14, the front opening / closing door 13 and the back opening / closing door (not shown) are closed to form a sealed space, then the power is turned on by the control / power supply unit 33, and the first electromagnetic valve 28 is turned on. Open. The dry pump 12 in the intake / exhaust device 4 is driven to reduce the pressure in the sealed space in the decompression vessel 3 to, for example, -820 hPa (144.8 mmHg) Pa. At this time, radioactive fine particles that are detached from the articles in the decompression container 3 are trapped in the first filter 26. Therefore, radioactive fine powder is released outside the α / β-ray detection device 1 and does not diffuse into the atmosphere. In this respect, the α / β-ray detection device 1 can be said to be a safe device free from air pollution due to radioactive fine powder by its driving. When the first gauge 27 confirms that the inside of the decompression vessel 3 has reached a predetermined degree of decompression, the first electromagnetic valve 28 is closed.

  Next, the detector 2 detects α rays and β rays radiated from the article charged in the decompression vessel 3. In each α / β ray detector 2 </ b> A in the detector 2, when the α ray emitted from the article reaches the α ray detector 18, the α ray detector 18 emits light. The emitted light is collected by the light collector 21 and photoelectrically converted by the photomultiplier tube 22, and the converted electrical signal is amplified and output as a detection signal. In the α / β-ray detector 2 </ b> A, when the β-ray emitted from the article reaches the β-ray detector 19, the β-ray detector 19 emits light. As in the case of the α rays, the emitted light is condensed by the light collector 21, photoelectrically converted by the photomultiplier tube 22, and the converted electric signal is amplified and output as a detection signal. As the photomultiplier tube 22, an electrical signal in which an electrical signal based on α rays and an electrical signal based on β rays are superimposed is output to the preamplifier unit 7.

  In the α / β ray detector 1 shown in FIG. 1, the detector 2 is disposed in each of the X direction, the Y direction, and the Z direction in the decompression vessel 3, so that the articles accommodated in the decompression vessel 3 Can be measured in all directions. Therefore, α rays and β rays can be detected in a certain direction, but the detectors arranged in other directions cannot detect the radiation with the detectors arranged in the other directions. Such a detection omission does not occur in the α / β ray detection apparatus 1. In other words, the α / β ray detection apparatus 1 can reliably detect the radiation without causing a detection omission.

Further, since the preamplifier unit 7 used at this time adopts an α ray / β ray separation method,
In each preamplifier 7-1 to 8, the input detection signal is separated and the α-ray detection signal and the β-ray detection signal are output to the measurement / display device 5.

  The α rays and β rays measured by the measurement / display device 5 are displayed on, for example, a liquid crystal display unit in the measurement / display device 5 and printed out by the printer 6. When the detection and measurement of α-rays and β-rays are completed, the second electromagnetic valve 31 that has been closed until then is opened in order to return the reduced-pressure state in the reduced-pressure vessel 3 to the normal pressure state. Since the second filter 32 is interposed in the pipe 30, articles in the decompression vessel 3 are not contaminated by radon and / or tron existing in the atmosphere. When the inside of the decompression container 30 is returned to normal pressure, the article stored in the decompression container 3 is taken out.

  In addition, the α / β-ray detection device 1 of the present invention preferably has a failure diagnosis function and is a device that can constantly monitor a count value abnormality, a low / high voltage power supply abnormality, a detector abnormality, and the like. Furthermore, it is preferable that the apparatus has a power failure guarantee function and can be backed up for one week or longer.

FIG. 1 is a front view showing an α / β-ray detection apparatus as an example of the present invention. FIG. 2 is a system diagram showing a detection mechanism of α rays and β rays in an α / β ray detection apparatus which is an example of the present invention. It is a figure which shows the detector used for the alpha * beta-ray detection apparatus which is an example of this invention. FIG. 4 is an explanatory view showing the arrangement positions and the number of detectors arranged in the sealed space formed inside the container main body in the α / β-ray detection apparatus which is an example of the present invention. FIG. 5 is an explanatory diagram showing a preamplifier unit in an α / β-ray detection apparatus which is an example of the present invention. FIG. 6 is an explanatory diagram showing signal waveforms output from the detector in the α / β-ray detection apparatus as an example of the present invention. FIG. 7 is an explanatory diagram showing signal processing in the preamplifier section in the α / β-ray detection apparatus as an example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... alpha / beta ray detection apparatus, 2 ... detector, 2A ... alpha / beta ray detector, 3 ... decompression container, 4 ... intake / exhaust device, 4A ... exhaust device 4B..Intake device, 5 ... Measurement display device, 6 ... Printer, 7 ... Preamplifier unit, 7-1 to 7-8 ... Preamplifier, 11 ... Dry pump, 13 .... Front door, 14 ... Container body, 15 ... Base, 16 ... Caster, 17 ... Pin, 18 ... α-ray detector, 19 ... β-ray detector, 20 ... Reinforcing material, 21 ... Condensing part, 22 ... Photomultiplier tube, 23 ... Light shielding film, 24 ... Partition plate, 25 ... Pipe, 26 ... First filter, 27 ... Pressure gauge, 28 ... First electromagnetic valve, 29 ... Silencer, 30 ... Pipe, 31 ... Second filter, 32 ... Second electromagnetic valve, 33 ... Control the power supply unit

Claims (5)

  A vacuum container capable of containing an object contaminated with a radioactive substance and capable of reducing the pressure, and an α-ray detector and a β-ray detector disposed in the vacuum container. α ・ β ray detector. The at least one set of the α-ray detector and the β-ray detector for each axial direction in the decompression container in at least three axial directions of the target object in the x-axis direction, the y-axis direction, and the z-axis direction. The α / β ray detection apparatus according to claim 1, comprising: The α / β-ray detection device according to claim 1, wherein each of the α-ray detector and the β-ray detector includes a light-shielding film on a surface of the detector. A pair of α-ray detectors arranged in at least three axial directions of x-axis direction, y-axis direction, and z-axis direction in the reduced-pressure container in which a reduced-pressure container containing an object contaminated with a radioactive substance is decompressed; An α / β-ray detection method, wherein an α-ray and a β-ray generated from the object are detected by a β-ray detector. After accommodating the object contaminated with the radioactive substance in the decompression vessel, the α-ray detector and the β-ray detector are used to reduce the pressure in the decompression vessel from normal pressure to reduced pressure. The α / β ray detection method according to claim 4, wherein α ray and β ray generated from the object are detected.

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